WO2018051830A1 - Silver paste for flexible substrate - Google Patents

Silver paste for flexible substrate Download PDF

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Publication number
WO2018051830A1
WO2018051830A1 PCT/JP2017/031811 JP2017031811W WO2018051830A1 WO 2018051830 A1 WO2018051830 A1 WO 2018051830A1 JP 2017031811 W JP2017031811 W JP 2017031811W WO 2018051830 A1 WO2018051830 A1 WO 2018051830A1
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WO
WIPO (PCT)
Prior art keywords
silver
conductive film
silver paste
substrate
flexible
Prior art date
Application number
PCT/JP2017/031811
Other languages
French (fr)
Japanese (ja)
Inventor
中山　和尊
章宏 酒井
佐保子 隅田
Original Assignee
株式会社ノリタケカンパニーリミテド
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社ノリタケカンパニーリミテド filed Critical 株式会社ノリタケカンパニーリミテド
Priority to JP2018539636A priority Critical patent/JP6734925B2/en
Priority to CN201780056367.7A priority patent/CN109690698A/en
Priority to KR1020197009714A priority patent/KR20190054095A/en
Publication of WO2018051830A1 publication Critical patent/WO2018051830A1/en

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
    • H05K1/095—Dispersed materials, e.g. conductive pastes or inks for polymer thick films, i.e. having a permanent organic polymeric binder
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B5/00—Non-insulated conductors or conductive bodies characterised by their form
    • H01B5/14—Non-insulated conductors or conductive bodies characterised by their form comprising conductive layers or films on insulating-supports
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
    • H05K1/097—Inks comprising nanoparticles and specially adapted for being sintered at low temperature
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/0806—Silver
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/011—Nanostructured additives

Definitions

  • the present invention relates to a silver paste capable of forming a conductive film on a substrate having low heat resistance such as a resin.
  • Patent Documents 1 and 2 disclose, for example, a silver powder excellent in low-temperature sinterability for suitably forming a film at a low temperature, and a silver paste containing this silver powder.
  • Patent Document 3 discloses a silver paste containing silver powder and a thermoplastic resin that cures at a low temperature.
  • the conductive film obtained from this thermosetting silver paste has a problem that it easily peels from the substrate when the polymer film substrate is repeatedly bent.
  • the polymer film substrate is required to be formed at a lower temperature (for example, 140 ° C. or lower) than conventional because the thermal sensitivity is increased by thinning the layer.
  • This invention is made
  • thermosetting silver paste has a thickness of about 10 to 30 ⁇ m. According to the study by the present inventors, it has been found that when a polymer film substrate including a conductive film formed from a thermosetting silver paste is repeatedly curved, the conductive film is easily peeled due to its hardness and thickness. did.
  • this type of thermosetting silver paste uses an insulating thermosetting resin as a binder for silver particles. Therefore, in order to ensure the conductivity of the conductive film to be formed, it is difficult to use fine silver nanoparticles having a large specific surface area because it leads to an increase in the binder, and the average particle diameter is approximately 2 to 5 ⁇ m or more. It was necessary to use flaky silver powder.
  • the conductive film formed from the particles having the average particle diameter is stably formed when the thickness is approximately 10 ⁇ m or more, and the conductivity of the conductive film, the film strength, the adhesiveness, etc. In consideration of the compatibility with the physical properties, it was difficult to reduce the thickness of the conductive film.
  • a silver paste for a flexible substrate (hereinafter sometimes simply referred to as “silver paste”, “paste”, etc.) provided by the present invention to solve the above-mentioned problems is used for forming a conductive film on a flexible film substrate.
  • silver paste This silver paste for flexible substrates contains (A) silver powder, (B) a thermoplastic polyester resin as a binder, and (C) a solvent for dissolving the thermoplastic polyester resin.
  • the thermoplastic polyester resin (B) has a glass transition point of 60 ° C. or more and 90 ° C. or less, and is contained in a proportion of 5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the silver powder. It is said.
  • the solvent (C) has a boiling point of 180 ° C. or higher and 250 ° C. or lower, and includes a phenyl group in the molecular structure.
  • a flexible conductive film having a thickness of, for example, 3 ⁇ m or less can be suitably formed on the flexible substrate at a low temperature of 140 ° C. or less with good adhesion. Accordingly, it is difficult to peel off from the substrate, and for example, a conductive film in which peeling is suppressed can be formed even when the substrate is repeatedly bent. In addition, for example, even when the substrate is bent or stretched at 90 ° (stretched straight), a conductive film in which peeling is suppressed can be formed.
  • the average particle diameter of silver powder means the cumulative 50% particle diameter in the number-based particle size distribution measured based on observation with an electron microscope.
  • the particle size distribution is determined by, for example, using a scanning electron microscope (SEM) or the like, observing silver powder at an appropriate magnification (eg, 50,000 times), and 100 or more (eg, 100 to 1000) silver particles. It can be created based on the equivalent-circle diameter determined for the particles.
  • SEM scanning electron microscope
  • the glass transition point of the thermoplastic polyester resin can be measured according to the glass transition point measurement method specified in JIS K7121: 1987 “Method for measuring plastic transition temperature”. Specifically, the glass transition point of the thermoplastic polyester resin is obtained by, for example, using a differential thermal analysis (DTA) apparatus or a differential scanning calorimetry (DSC) apparatus to heat a measurement sample and a standard substance at a constant speed. The glass transition point of the sample can be grasped by measuring the difference in the amount of heat between the sample and the standard material based on the change in the heat capacity in the sample. In heating, for example, it is preferable that the sample is heated to a temperature at least about 30 ° C.
  • DTA differential thermal analysis
  • DSC differential scanning calorimetry
  • the glass transition point described in the data sheet etc. of the said product can be employ
  • the (A) silver powder comprises spherical silver fine particles having an aspect ratio of 1.5 or less and nonspherical silver fine particles having an aspect ratio exceeding 1.5. It is characterized by including.
  • a protective agent made of an organic amine having 5 or less carbon atoms is attached to the surface of the silver powder. This enhances the dispersion stability of the silver powder in the paste, and the silver particles are placed in a suitable position from the paste storage state to the paste being applied to the substrate and baked to provide a dense and homogeneous conductive. A film can be formed.
  • the technology disclosed herein provides an electronic device.
  • the electronic element includes a flexible film substrate and a conductive film provided on the flexible film substrate.
  • the electrically conductive film is characterized by being the hardened
  • the silver paste can form a conductive film having good followability and adhesion with respect to the bending and bending of the flexible substrate. Therefore, even when the substrate is bent or bent, an electronic element in which floating or peeling of the conductive film is suppressed is realized.
  • the conductive film has an average thickness of 0.2 ⁇ m or more and 3 ⁇ m or less.
  • the sheet resistance of the conductive film is a value when the thickness of the conductive film is converted to 10 ⁇ m and is characterized by 100 m ⁇ / ⁇ or less.
  • the technology disclosed herein provides a method for manufacturing an electronic device.
  • the manufacturing method includes preparing a flexible film substrate, preparing any one of the above-mentioned silver pastes for a flexible substrate, supplying the silver paste for a flexible substrate on the flexible film substrate, and for the flexible substrate Drying the flexible film substrate supplied with the silver paste, and heat-treating the flexible film substrate supplied with the dried silver paste for flexible substrate to form a conductive film.
  • supply of the said silver paste for flexible substrates is implemented so that the average thickness of the said electrically conductive film formed may be 3 micrometers or less, and the temperature for the said drying is the said heat
  • the temperature is lower than the glass transition point of the plastic polyester resin, and the temperature of the heat treatment is 20 ° C. or more higher than the glass transition point.
  • the silver paste for a flexible substrate disclosed herein is essentially a conductive film that can form a cured product by heat treatment at a low temperature (for example, 140 ° C. or less), and the cured product exhibits electrical conductivity (conductivity). It is. Prior to the heat treatment, the silver paste may be dried. Characteristically, the conductive film itself has flexibility and adhesion to the substrate, and is realized, for example, as exhibiting good substrate followability even for a flexible substrate.
  • Such a silver paste for flexible substrates contains (A) silver powder, (B) a thermoplastic polyester resin as a binder, and (C) a solvent for dissolving the thermoplastic polyester resin as main components.
  • each structural component of the silver paste for flexible substrates disclosed here is demonstrated.
  • Silver powder is a material for mainly forming a film body (conductive film) having high electrical conductivity (hereinafter simply referred to as “conductive”) such as electrodes, conductive wires and conductive films in electronic devices and the like. is there.
  • conductive electrical conductivity
  • Silver (Ag) is preferable as a conductor material because it is not as expensive as gold (Au), is hardly oxidized, and is excellent in conductivity.
  • the composition of the silver powder is not particularly limited as long as it is a powder (aggregation of particles) containing silver as a main component, and a silver powder having desired conductivity and other physical properties can be used.
  • the main component means that it is the maximum component among the components constituting the silver powder.
  • Examples of the silver particles constituting the silver powder include particles composed of silver, a silver alloy, a mixture or a composite thereof, and the like.
  • Preferred examples of the silver alloy include a silver-palladium (Ag—Pd) alloy, a silver-platinum (Ag—Pt) alloy, and a silver-copper (Ag—Cu) alloy.
  • core-shell particles in which the core is made of metal other than silver, such as copper or silver alloy, and the shell covering the core is made of silver can also be used.
  • the silver powder tends to have higher conductivity as the purity (silver (Ag) content) is higher, it is preferable to use a silver powder having higher purity.
  • the silver powder preferably has a purity of 95% or more, more preferably 97% or more, and particularly preferably 99% or more.
  • the average particle size as silver powder is such that sintering by heat treatment at a relatively low temperature (eg, 140 ° C. or lower, typically about 110 ° C. to 135 ° C.) is suitably realized.
  • a relatively low temperature eg, 140 ° C. or lower, typically about 110 ° C. to 135 ° C.
  • a diameter of 40 nm or more and 100 nm or less is used.
  • finer particles for example, fine particles of several nm to several tens of nm
  • the sintered body of binderless silver particles forms a dense sintered body, and the bulk characteristics are strongly expressed, and cracking occurs when the conductive film is curved. That is, flexibility (flexibility) cannot be exhibited.
  • the average particle diameter of the silver powder is preferably 40 nm or more (exceeding 40 nm), more preferably 45 nm or more, and particularly preferably 50 nm or more.
  • the average particle size of the silver powder is preferably 100 nm or less (less than 100 nm), more preferably 95 nm or less, and particularly preferably 90 nm or less. For example, 55 nm or more and 85 nm or less are suitable.
  • a silver powder does not contain the particle
  • the minimum value (Dmin) of the particle size is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more.
  • the maximum value (Dmax) of the particle size is preferably 300 nm or less, more preferably 250 nm or less, and particularly preferably 200 nm or less. In other words, it is preferred that it does not substantially contain coarse particles exceeding 300 nm, preferably exceeding 250 nm, for example exceeding 200 nm.
  • the silver powder disclosed here has an appropriate spread in the particle size distribution.
  • the value (D90-D10) obtained by subtracting the cumulative 10% particle size (D10) from the cumulative 90% particle size (D90) in the number-based particle size distribution is 70 nm or more, typically 75 nm or more. It is preferable that it is approximately 220 nm or less, for example, 210 nm or less.
  • the silver particles having a relatively small particle diameter are arranged so as to fill the gaps between the silver particles having a relatively large particle diameter when the silver powder is sintered. Can be sintered. As a result, it is possible to realize a conductive film that is sintered in a state in which the silver powder is more densely packed and has excellent conductivity.
  • the ratio (D10 / D90) is approximately 0.3 or more between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10). More preferably, it is 0.33 or more.
  • the ratio (D10 / D90) is preferably 0.6 or less, and more preferably 0.55 or less.
  • the shape of the silver particles constituting the above silver powder is not particularly limited. For example, it may be spherical, elliptical, crushed, flaky, flat, fibrous or the like. From the viewpoint of forming a thinner and more uniform film by printing, the shape of the silver particles is preferably spherical or nearly spherical.
  • One index representing the sphericity of silver particles is the aspect ratio when the shape of silver particles is evaluated in two dimensions.
  • the aspect ratio is, for example, that when 100 or more (for example, 100 to 1000) silver particles are observed with an electron microscope or the like and a rectangle circumscribing the outer shape of the silver particles in the observed image is drawn, It can be calculated as the ratio of the length of the long side to the length (major axis / minor axis).
  • the arithmetic average value of the aspect ratio for each silver particle is adopted as the aspect ratio of the silver powder. Incidentally, the closer the aspect ratio is to 1, the better the isotropic property, and the three-dimensional shape of the silver particles becomes nearly spherical.
  • silver particles having an aspect ratio of 1.5 or less are referred to as “spherical particles”, and silver particles having an aspect ratio of less than 1.5 are referred to as “non-spherical particles”.
  • the silver powder disclosed here may contain spherical silver particles and non-spherical silver particles.
  • spherical particles may enter into gaps where non-spherical particles are arranged, or non-spherical particles may enter into gaps where spherical particles are arranged.
  • a highly sintered body can be obtained. Thereby, the contact area of silver particles increases and the conductor film excellent in electroconductivity can be formed.
  • the ratio of the spherical silver particle of aspect ratio 1.5 or less is 60 number% or more of the whole silver powder.
  • the nonspherical silver particles having an aspect ratio of less than 1.5 are preferably 40% by number or less of the silver particles constituting the silver powder.
  • the spherical silver particles are more preferably 70% by number or more of the total silver powder, particularly preferably 80% by number or more, for example, 85% by number or more, or 90% by number or more. Since the silver powder is composed of particles having such a shape, the stability, surface smoothness, homogeneity, filling properties, etc. of the silver particles from when the silver paste is supplied to the base material until it is heat-treated are effective. Enhanced. Thereby, the filling property of silver particles, the surface smoothness of the conductive film to be formed, and the like are improved, and a conductive film having higher conductivity can be obtained.
  • the average particle size of the silver powder disclosed herein is on the order of nanometers and is relatively fine. Therefore, since silver powder of this size is generally easy to aggregate, a protective agent that suppresses aggregation can be provided on the surface of the silver particles.
  • the surface of silver powder (silver particles) is coated with a protective agent. Thereby, the surface stability of silver particles can be maintained, and aggregation of silver particles can be efficiently suppressed.
  • the silver paste disclosed herein can be stably stored with good dispersibility over a long period of time because aggregation of silver particles in the solvent is suppressed.
  • the fluidity of silver particles can be improved and the printability can be improved.
  • the type of the surface protective agent is not particularly limited, but the protective agent is detached from the surface of the silver particles during the heat treatment from the viewpoint that it can be burned off from the surface of the silver particles by heat treatment (firing) in a short time at a low temperature. It is preferable that it is easy.
  • the protective agent preferably has a low sublimation point, boiling point and decomposition temperature at atmospheric pressure, and forms a relatively weak bond (for example, coordination bond) with silver.
  • the protective agent is preferably an organic amine having 5 or less carbon atoms.
  • the organic amine having 5 or less carbon atoms include methylamine, ethylamine, n-propylamine, isopropylamine, butylamine, pentylamine, 2-methoxyethylamine, 2-ethoxyethylamine, 3-methoxypropylamine, 3-ethoxy Primary aliphatic amines such as propylamine; Secondary aliphatic amines such as dimethylamine, diethylamine, methylbutylamine, ethylpropylamine, and ethylisopropylamine; Tertiary aliphatics such as trimethylamine, dimethylethylamine, and diethylmethylamine An amine;
  • the number of carbon atoms of the organic amine is preferably 3 or more, and more preferably 4 or more.
  • the organic amine may contain an alkoxy group such as a methoxy group or an ethoxy group in the structure. Any one of these organic amines may be used alone or in combination of two or more. Thereby, said dispersion stability can be more suitably realized.
  • the ratio of the protective agent can be 1.2 parts by mass or less. In other words, 98.8 parts by mass or more of the silver powder can be composed of silver particles.
  • the proportion of the protective agent is preferably 1.1 parts by mass or less, for example, 1 part by mass or less.
  • the silver paste disclosed herein does not substantially contain a component (corrosive component) that can generate an erosion gas during firing. That is, for example, it is permissible for a corrosive component to be inevitably mixed due to a manufacturing process or a manufacturing facility of silver powder, but it is preferable that such a corrosive component is not intentionally included.
  • corrosive components include halogen components such as fluorine (F) and chlorine (Cl), sulfur (S) components, and the like. These components are preferably not contained in the silver powder itself, and are preferably not contained in the protective agent.
  • the silver paste does not substantially contain such a corrosive component because corrosion deterioration of the semiconductor manufacturing apparatus, contamination of foreign matter into the semiconductor element, and alteration of the electrodes and substrate of the semiconductor element can be suppressed. Furthermore, it is preferable not to include components that may adversely affect the human body and the environment, such as lead (Pb) components and arsenic (As) components.
  • these corrosive components such as fluorine (F), chlorine (Cl), sulfur (S), lead (Pb), and arsenic (As) are 0.1 parts by mass when the silver powder is 100 parts by mass. It is preferable to be suppressed to (1000 ppm) or less. These corrosive components are preferably suppressed to 0.1 parts by mass (1000 ppm) or less in total when the silver powder is 100 parts by mass.
  • thermoplastic polyester (polyester: PEs) resin functions as a binder component in the silver paste disclosed herein. Due to the inclusion of this thermoplastic polyester resin, the silver paste disclosed here softens the binder by heating, and the binder is cured by subsequent heat dissipation (cooling), thereby supporting the bonding between the silver particles and the adhesion to the substrate. Is done. Typically, it is considered that it contributes to the bonding between the sintered silver powder and the substrate. In addition, there exist a thermosetting thing and a thermoplastic thing in a polyester resin, The thermosetting polyester resin etc. were used as a binder in the conventional silver paste of this kind. On the other hand, in the technique disclosed herein, the binder function is realized by utilizing reversible plasticity expression by heating of the thermoplastic polyester resin as described above.
  • thermoplastic polyester resin As described above, the behavior of the thermoplastic polyester resin as the binder is softened by heat treatment and hardened by subsequent cooling.
  • the thermoplastic polyester resin is preferably softened before the sintering of the silver powder and hardened after the sintering from the viewpoint of improving the adhesion to the substrate.
  • Tg glass transition point
  • thermoplastic polyester resin undergoes a large volume change due to heat treatment or temperature change. Furthermore, since the thermoplastic polyester resin is in a cured state at normal temperature, it is preferable that the thermoplastic polyester resin is soluble in a solvent described later.
  • a thermoplastic polyester resin that preferably satisfies such requirements, an amorphous (non-crystalline) resin can be preferably used.
  • An amorphous resin can be understood as a resin having a structure in which molecular chains are not randomly mixed in a cured state and molecular chains are randomly mixed.
  • Amorphous thermoplastic polyester resin is, for example, soluble in a solvent and has a glass transition point, but can be understood as a compound having no clear crystalline melting point.
  • the glass transition point of the thermoplastic polyester resin depends on the heat resistance temperature of the material constituting the substrate, it cannot be generally stated.
  • a heat treatment temperature for sintering silver powder for example, 140 ° C. or lower, typically Is preferably a temperature sufficiently lower than about 110 ° C. to 135 ° C.
  • the temperature is 20 ° C. or more (for example, about 20 ° C. to 50 ° C.) lower than the heat treatment temperature.
  • the glass transition point is preferably 90 ° C. or lower, more preferably 85 ° C. or lower, and particularly preferably 80 ° C. or lower.
  • the glass transition point of the thermoplastic polyester resin is preferably higher than the temperature at which the solvent in the silver paste is almost volatilized, for example, the drying temperature of the silver paste.
  • the glass transition point is preferably about 20 ° C. higher than the drying temperature.
  • the glass transition point is preferably 60 ° C. or higher (over 60 ° C.), more preferably 63 ° C. or higher, and particularly preferably 65 ° C. or higher.
  • Such a glass transition point belongs to a relatively high class among commonly used thermoplastic polyester resins.
  • the temperature is extremely high as a binder for resin substrates such as PET.
  • thermoplastic polyester resin various compounds containing, as a main component or a main monomer, a polyester-based structure obtained by polycondensation of a polycarboxylic acid and a polyalcohol can be used as a repeating unit constituting the resin.
  • the “main component” means a monomer component corresponding to the repeating unit that is contained most on a mass basis among the repeating units constituting the main skeleton of the thermoplastic polyester resin. This main component may preferably be a monomer component contained in the thermoplastic polyester resin in an amount exceeding 50 mass%.
  • the monomer component corresponding to the polycarboxylic acid constituting the polyester structure is not particularly limited.
  • a polycarboxylic acid may be an acyclic polycarboxylic acid or a saturated or unsaturated alicyclic polycarboxylic acid.
  • aliphatic dibasic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, glutamic acid, sebacic acid, dodecanedioic acid, brassylic acid, dimer acid; furandicarboxylic acid, diphenyldicarboxylic acid, 1
  • Preferred examples include alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; dibasic acids such as aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Of these, an aromatic dibasic acid is preferable.
  • the monomer component corresponding to the polyalcohol which comprises a polyester-type structure.
  • the polyalcohol include aliphatic polyalcohol, alicyclic polyalcohol, and aromatic polyalcohol.
  • an aliphatic or alicyclic diol is preferable.
  • Specific examples of the monomer component corresponding to the polyalcohol include ethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-cyclohexanedimethanol and the like. Diols are preferred. These may have an alicyclic skeleton in the side chain, or may not have such an alicyclic skeleton in the side chain.
  • the thermoplastic polyester resin may be, for example, a polymer of a monomer raw material that includes a polyester-based structure as a main monomer and can further include a submonomer that is copolymerizable with the main monomer.
  • the main monomer means a component occupying more than 50% by weight of the monomer composition in the monomer raw material.
  • the main monomer can be, for example, an ester of a polycarboxylic acid typified by the dibasic acid exemplified above and a polyol typified by a diol.
  • the main monomer is a polycondensation reaction product of terephthalic acid and ethylene glycol (PET main monomer), a polycondensation reaction product of terephthalic acid and butanediol (PBT main monomer), naphthalene dicarboxylic acid, It may be a polycondensation reaction product (PEN main monomer) with ethylene glycol or a polycondensation reaction product (PBN main monomer) of naphthalenedicarboxylic acid and butanediol. Any one of these main monomers may be contained alone or in combination of two or more.
  • the secondary monomer a component capable of introducing a crosslinking point into the polyester structure or enhancing the adhesive force of the polyester structure is preferable.
  • a carboxy group-containing monomer typified by monocarboxylic acid, dicarboxylic acid and its anhydride, etc .; typified by hydroxyalkyl (meth) acrylate compound, alcohol compound, ether compound, polyether compound, etc.
  • Hydroxyl group-containing monomers amide group-containing monomers represented by (meth) acrylamide; isocyanate group-containing monomers represented by (meth) acryloyl isocyanate; phenyl group-containing monomers represented by styrene compounds, phenyl ether compounds, etc. Can be mentioned. These submonomers may be contained alone or in combination of two or more.
  • thermoplastic polyester resin has appropriate flexibility after curing. Therefore, components such as a crosslinking agent and a crosslinking aid may be included for the purpose of improving the flexibility and adhesiveness after curing.
  • crosslinking agents and crosslinking aids may include isocyanate compounds, polyfunctional melamine compounds, polyfunctional epoxy compounds, polyhydroxy compounds, and the like. Specific examples include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, araliphatic polyisocyanates, polyhydroxy compounds, and the like.
  • a crosslinking agent and a crosslinking aid can be used individually by 1 type or in combination of 2 or more types.
  • the secondary monomer, the crosslinking agent, the crosslinking auxiliary agent, and the like have a chemical structure that does not introduce an unsaturated group into the thermoplastic polyester resin. That is, the thermoplastic polyester resin is preferably a saturated copolymer polyester. Thereby, since the adhesiveness to the PET film board
  • the number average molecular weight (Mn) is not particularly limited. However, when the number average molecular weight is less than 2000, it is difficult to express adhesiveness and / or tackiness required as a binder. Since there are cases, it is not preferable. From this viewpoint, the number average molecular weight is preferably 2000 or more, more preferably 5000 or more, and still more preferably 10,000 or more. On the other hand, when the number average molecular weight of the thermoplastic polyester resin exceeds 100,000, there may be a problem that the solubility in a solvent is extremely lowered and the printability is poor.
  • the number average molecular weight is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 10,000 or more and 30,000 or less.
  • Such a number average molecular weight belongs to a relatively high class among the amorphous thermoplastic polyester resins generally used.
  • thermoplastic polyester resin can be obtained by those skilled in the art who have touched the disclosure of the present specification, depending on the film substrate used. Can be appropriately designed and blended through adjustment of the combination and the blending amount thereof, and the adjustment of the glass transition point and molecular weight. Moreover, such a thermoplastic polyester resin can also be obtained by using a commercially available product.
  • Examples of such commercially available products include, for example, Elitel (registered trademark) UE3200, UE9200, UE3201, UE3203, UE3600, UE9600, UE3660, UE3690 manufactured by Unitika Ltd., and Polyester (registered by Nippon Synthetic Chemical Industry Co., Ltd.). Trademarks) TP236, TP220, TP235, Dynapol (registered trademark) L205, L206, L208, L952, L907 manufactured by Evonik Industries AG, VITEL (registered trademark) 2100, 2200 manufactured by Bostik, and the like.
  • thermoplastic polyester resin is 5 mass parts or more with respect to 100 mass parts of said silver powder. It is important to be included in the ratio.
  • the thermoplastic polyester resin is more preferably 5.3 parts by mass or more, and particularly preferably 5.5 parts by mass or more.
  • the thermoplastic polyester resin exhibits insulating properties, it is preferable to suppress the content in the silver paste as much as possible. From this viewpoint, the content of the thermoplastic polyester resin is preferably 8 parts by mass or less, more preferably 7.8 parts by mass or less, and particularly preferably 7.5 parts by mass or less with respect to 100 parts by mass of the silver powder. .
  • (C) Solvent As the solvent, various solvents capable of dissolving the above-mentioned (B) thermoplastic polyester resin can be used. Moreover, it has the function to disperse
  • the solvent is a high boiling point solvent having a boiling point of 180 ° C. or higher.
  • the solvent volatilizes and the property of the silver paste changes. Can be suppressed.
  • the volatilization of the solvent before the supply of the silver paste to the base material increases the viscosity of the silver paste to make the printing conditions unstable, or the conductive film formed by increasing the silver powder content in the silver paste. This is not preferable because it causes variations in the film thickness.
  • the boiling point of the solvent is 250 ° C. or lower, the solvent can be volatilized quickly in a short time at a temperature sufficiently lower than the heat treatment temperature for sintering the silver powder.
  • the boiling point of the solvent exceeds 250 ° C., the solvent component tends to remain in the coating film obtained by drying the silver paste, making it difficult to form a suitable film.
  • the solvent contains a phenyl group in the molecular structure, since the solubility of the thermoplastic polyester resin is increased and the paste properties suitable for printing can be easily adjusted. That is, when the solvent contains a phenyl group, the affinity for the non-aqueous thermoplastic polyester resin is increased, and the solvent is thermodynamically stable and hardly oxidized or reduced. Further, due to the presence of the phenyl ring exhibiting rigidity, an appropriate viscosity can be stably and suitably imparted to the silver paste. As a result, when the silver paste is supplied to the base material, it is possible to prepare a silver paste with high workability and printing stability. As a result, a homogeneous coating film (including a conductive film) can be stably formed.
  • the number of phenyl groups in the molecular structure may be one.
  • the silver paste can be supplied to the substrate by a printing method while keeping the properties of the silver paste stable.
  • This can be a very advantageous characteristic in the future production of electronic devices, for example, when a roll-to-roll process is fully employed.
  • the boiling point and volatility of the solvent are not exactly the same, considering the use of the silver paste disclosed here and the characteristics of the solvent used, the volatility is determined based on the boiling point of the solvent. It can be said that there is no problem.
  • a non-aqueous solvent that satisfies the above boiling point and contains a phenyl group
  • solvents include, for example, oxyalkylene monophenyl ethers typified by ethylene glycol monophenyl ether (245 ° C.), propylene glycol monophenyl ether (243 ° C.), etc .; methyl phenyl ether (154 ° C.), ethyl phenyl ether ( 184 ° C.), butyl phenyl ether (210 ° C.), alkylphenyl ether represented by methyl phenyl ethyl ether (184 ° C.), etc .; benzyl alcohol (205 ° C.), isophorone (215 ° C.), benzaldehyde (179 ° C.), benzyl acetate Benzenes represented by (212 ° C.) and the like.
  • oxyalkylene monophenyl ethers typified
  • a non-aqueous dispersion medium In a non-aqueous dispersion medium, hydrophobic interaction, interfacial adsorption by ions, electrostatic repulsion effect, and the like are suppressed.
  • the use of a highly polar solvent is not preferable because the protective agent is eroded. Therefore, it is also preferable to select a solvent having a dispersibility suitable for the surface characteristics of the silver powder as the dispersoid. For example, since the size of the silver powder used here is a sub-nanometer size as described above, it is expected that the effect of improving the dispersibility using the dispersant cannot be expected or becomes difficult.
  • a solvent capable of suitably dispersing the silver powder without using a dispersant can be preferably used as the solvent. From this point of view, it is particularly preferable to use the above oxyalkylene monophenyl ether as the solvent.
  • the ratio of the (C) solvent in the silver paste is not particularly limited as long as it is an amount capable of dissolving the thermoplastic polyester resin.
  • it can be appropriately adjusted according to the supply method so that the workability and supply performance when supplying the silver paste to the substrate are good.
  • the ratio of the silver powder can be about 50% by mass or more of the entire silver paste, preferably 60% by mass or more. It may be 70% by mass or more.
  • the ratio of a silver powder can be 90 mass% or less of the whole silver paste, 85 mass% or less is preferable, for example, preparing so that it may become 80 mass% or less is illustrated.
  • a ratio of a solvent it can be set as about 10 mass% or more of the whole silver paste, 15 mass% or more is preferable, for example, it may be 20 mass% or more.
  • the ratio of a solvent can be 50 mass% or less of the whole silver paste, 40 mass% or less is preferable, for example, it may be 30 mass% or less.
  • the silver paste disclosed here does not need to contain components other than said (A) silver powder, (B) thermoplastic polyester resin, and (C) solvent essentially. However, in the range which does not deviate from the purpose of the present application, the inclusion of various components in addition to the above-mentioned (A) silver powder, (B) thermoplastic polyester resin, and (C) solvent is allowed. As these components, an additive added for the purpose of improving the properties of the silver paste for a flexible substrate, an additive added for the purpose of improving the properties of the conductive film as a cured product, and the like can be considered. .
  • Examples include surfactants, dispersants, fillers (organic fillers, inorganic fillers), viscosity modifiers, antifoaming agents, plasticizers, stabilizers, antioxidants, preservatives, and the like.
  • One of these additives may be contained alone, or two or more thereof may be contained in combination. However, it is not preferable to contain components that inhibit (A) sintering of silver powder and (B) binder performance by the thermoplastic polyester resin, and additives in amounts that inhibit these components. From such a viewpoint, for example, an inappropriate silver particle protective agent or inorganic filler is not preferable.
  • the total content of these components is preferably about 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 1% by mass or less based on the total silver paste.
  • the silver paste for flexible substrates can be prepared by blending the above components in a predetermined ratio, and uniformly mixing and kneading. In mixing, each constituent material may be mixed at the same time. For example, after (B) a thermoplastic polyester resin and (C) solvent are mixed to prepare a vehicle, (A) silver powder is added to the vehicle. You may make it mix. When other additives are added, there is no particular limitation on the timing of the addition. For mixing, for example, a three-roll mill can be used.
  • the silver paste for a flexible substrate thus prepared can be cured at a lower temperature (typically 140 ° C. or lower, for example, 110 to 135 ° C.), for example. And after supplying the silver paste for flexible substrates with a desired pattern on arbitrary board
  • a lower temperature typically 140 ° C. or lower, for example, 110 to 135 ° C.
  • this electrically conductive film uses said thermoplastic epoxy resin as a binder, electrically conductive film itself is provided with flexibility.
  • the average thickness of the conductive film is not strictly limited. However, in order to improve the adhesion of the conductive film and the substrate followability when the substrate is bent, the thickness of the conductive film is 3 ⁇ m or less. It is preferable to do. By controlling the thickness of the conductive film in this manner, excellent adhesion to the base material can be maintained not only when the substrate is repeatedly bent but also when the substrate is repeatedly bent.
  • the thickness of the conductive film is preferably 0.2 ⁇ m or more.
  • silver powder can be laminated
  • the conductivity of such a conductive film depends on the shape and thickness of the conductive film, it cannot be generally stated.
  • the sheet resistance when the thickness of the conductive film is converted to 10 ⁇ m is 100 m ⁇ / ⁇ or less. Obtainable.
  • the sheet resistance can be, for example, 80 m ⁇ / ⁇ or less, and preferably 60 m ⁇ / ⁇ or less.
  • the material to which the silver paste for flexible substrate disclosed herein is applied is not strictly limited.
  • the target is a flexible substrate made of polymer (plastic), paper, cloth, etc.
  • the excellent characteristics of the silver paste disclosed here are remarkably exhibited.
  • polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polypropylene and ethylene-propylene copolymers, polyimide resins, polychlorinated resins are generally used.
  • a polymer film made of a thermoplastic resin such as vinyl is preferably used.
  • These base materials may have any form of a single layer or a multilayer.
  • Such a flexible substrate may constitute a flex portion of a rigid flexible substrate including a rigid portion for mounting components and the like and a flex portion for bending.
  • “flexible” means that it is flexible and can be bent or bent. Usually, it means that it can be bent or bent with a relatively weak force without damaging the object itself at room temperature.
  • the flexible substrate is a term for a hard substrate that does not bend without temperature change or the presence of a coating layer.
  • the deflection amount when a load is applied to the tip of the cantilevered substrate at room temperature for example, is 0.001 or more (typically 0.1 or more, for example, 1 or more) can be grasped as a substrate that can be deformed.
  • the silver paste disclosed here can be applied to a flexible substrate with extremely high flexibility.
  • a substrate may be a film base material having a curvature that can be wound around a winding core (core) having a cross-sectional diameter of 20 mm or less.
  • the base material may be a film that can be wound around a core with a diameter of preferably 10 mm or less, particularly preferably 6 mm or less.
  • the silver paste disclosed here can be applied to a flexible substrate having extremely excellent flexibility.
  • Such a substrate can be, for example, a substrate that is not damaged by repeated folding at a folding angle of 90 ° to 120 °.
  • the thickness of the flexible substrate is not particularly limited.
  • a substrate having a thickness of about 3 to 200 ⁇ m for example, 5 to 100 ⁇ m, typically 10 to 50 ⁇ m is widely used from the viewpoint of flexibility.
  • the flexible substrate preferably has a predetermined rigidity (strength) because it can be repeatedly bent and bent.
  • a polyester film can be preferably used as the flexible substrate, and a PET film substrate can be particularly preferably used among them.
  • the PET film substrate is also preferable in that it is frequently used as a flexible printed circuit board (FPC) or a flexible cable substrate. Therefore, a method for suitably manufacturing an electronic device by forming a conductive film on a PET film substrate using the silver paste for flexible substrate disclosed herein will be described below.
  • the electronic device manufacturing method disclosed herein essentially includes the following steps (1) to (5).
  • a flexible substrate is prepared.
  • a silver paste is supplied on the flexible substrate.
  • the flexible substrate supplied with the dried silver paste is heat-treated to form a conductive film.
  • Steps (1) and (2) can be understood from the description of the silver paste and the substrate described above, and thus the description thereof is omitted here.
  • the silver paste disclosed here is supplied onto the prepared flexible substrate.
  • the method for supplying the silver paste is not particularly limited.
  • various printing methods such as ink jet printing, gravure printing, screen printing, flexographic printing, offset printing, spin coating, and aerosol / jet printing can be employed. These printings may be performed by a step (intermittent) method or a continuous method such as roll-to-roll.
  • the silver paste is prepared in a property suitable for each printing method.
  • the silver paste disclosed here can be preferably used for the purpose of forming a conductive film having an arbitrary pattern over a relatively wide area on a flexible substrate by, for example, screen printing.
  • the thickness of the conductive film obtained after the heat treatment is 3 ⁇ m or less (for example, less than 3 ⁇ m). It is preferable to control the supply amount of the paste.
  • the thickness of the conductive film exceeds 3 ⁇ m, it is preferable from the viewpoint of conductivity.
  • the thickness of the conductive film is more preferably 2.7 ⁇ m or less, and particularly preferably 2.5 ⁇ m or less. Moreover, it is not preferable that the thickness of the conductive film obtained after the heat treatment is less than 0.2 ⁇ m because sufficient adhesion between the conductive film and the flexible substrate is difficult to be realized. Moreover, it is not preferable also in the point that the electroconductivity of an electrically conductive film may fall.
  • the thickness of the conductive film is preferably 0.2 ⁇ m or more, more preferably 0.5 ⁇ m or more, and particularly preferably 0.7 ⁇ m or more.
  • the thickness of the conductive film can be obtained as an arithmetic average value (that is, average thickness) when the dimension in the direction perpendicular to the substrate surface is measured at 10 points or more.
  • each component contained in the silver paste volatilizes the solvent, softens the resin and then hardens, and the silver powder sinters.
  • a conductive film is formed by the sintered silver powder and the cured resin.
  • the volatilization of the solvent, the softening and hardening of the resin, and the sintering of the silver powder proceed simultaneously.
  • the silver powder sinters in a state where the solvent is completely volatilized and only the solid content of the silver paste remains densely on the substrate. It is preferable because a conductive film can be obtained.
  • an appropriate binder function can be expressed with a smaller amount of resin. This is preferable.
  • the resin is preferable because the silver powder is cured after the sintering is completely completed, so that the sintered silver can be bonded to the substrate while suppressing the inhibition of the sintering of the silver powder.
  • the “drying” in the step (4) is a step mainly performed for the purpose of leaving only the solid content of the silver paste on the substrate by volatilizing the solvent contained in the silver paste.
  • the “heat treatment” in the step (5) is a step performed mainly for the purpose of sintering the silver powder on the substrate. Then, after the step (4), the resin is softened on the way to the step (5), and the resin is cured while the heating in the step (5) is finished and cooled. Therefore, when manufacturing the electronic device disclosed herein, it is important to appropriately control the temperatures of the drying in the step (4) and the heat treatment in the step (5) according to the silver paste.
  • the drying in the step (4) may be natural drying, or may utilize means such as blow drying, heat drying, vacuum drying, freeze drying and the like. Heating and drying are preferable because drying can be easily performed in a shorter time.
  • the heating means in the heat drying is not particularly limited, and it can be dried using various known dryers.
  • This drying step is performed at a temperature lower than the glass transition point (Tg) of the thermoplastic epoxy resin used for the silver paste.
  • the drying step is preferably performed by heating to a temperature lower by about 2 ° C. to 30 ° C. than the glass transition point.
  • the drying temperature is lower than the glass transition point, and is preferably set to a range of about 60 ° C. ⁇ 10 ° C., for example.
  • the heat treatment in step (5) is performed at a temperature at which the silver powder can be sintered and higher than the glass transition point of the thermoplastic epoxy resin.
  • the conductive film is formed by a heat treatment at a lower temperature, and thus the heat treatment can be performed in a temperature range of 140 ° C. or lower.
  • a thermoplastic epoxy resin having a glass transition point of 60 ° C. or higher and 90 ° C. or lower is used, so that the heat treatment temperature is the thermoplastic epoxy resin contained in the silver paste. It can be set according to the glass transition point.
  • the heat processing temperature is preferably about 100 ° C. to 135 ° C., more preferably 100 ° C. to 130 ° C., and particularly preferably 100 ° C. to 120 ° C. This heat treatment can be carried out using various known heating devices and drying devices.
  • the silver powder which is a solid component of the silver paste is sintered, and the silver particles form a good electrical contact.
  • the cooling after the heat treatment cures the thermoplastic epoxy resin to support the joining of the sintered bodies of the silver powder more reliably, and the flexible and strong bonding between the sintered body and the PET substrate. Realize adhesion.
  • a conductive film having high conductivity and good adhesiveness can be easily formed at a low temperature even on a flexible substrate. Since this conductive film is formed using a printing technique, it is realized as a film having a uniform thickness with an arbitrary pattern.
  • the flexible substrate on which such a conductive film is formed can maintain extremely good adhesion between the substrate and the conductive film even after being deformed.
  • the conductive film can maintain conductivity even after deformation. Specifically, even when the substrate is repeatedly bent greatly, peeling and cracking of the conductive film are highly suppressed. In addition, as shown in Examples described later, even when the substrate is repeatedly bent, peeling and cracking of the conductive film are highly suppressed. Therefore, according to the technology disclosed herein, for example, a conductive film such as movable part wiring can be suitably formed by printing on a flexible substrate that bends repeatedly at a hinge part or the like.
  • an electronic element for example, FPC
  • FPC field-convex portion
  • a flexible cable that is excellent in repeated bendability and can be wired in a space-saving manner in the drive unit or the like is realized.
  • Such a flexible substrate with a conductive film can be suitably used as an electronic element used in various fields such as electric devices, semiconductor devices, solar cells, displays, sensors, and biomedical devices.
  • Embodiment 1 Preparation of silver powder
  • Three types of silver powders A to C having different average particle diameters were prepared. Specifically, butylamine as a surface modifier and butanol as a solvent and particle size control agent are mixed at a predetermined molar ratio at room temperature (25 ° C.), and after adding silver oxalate, the mixture is stirred. While heating to about 100 ° C., substantially spherical silver powders B and C having surfaces stabilized with organic amines were obtained. The average particle size of the silver powder was controlled by adjusting the addition amount of the particle size control agent (molar ratio of the organic amine and the particle size control agent) and further classifying.
  • the particle size control agent molar ratio of the organic amine and the particle size control agent
  • the silver powder A is a commercially available flaky silver powder, and since the average particle diameter in a plan view is relatively large at 2000 nm, no surface modifier is used.
  • the average particle diameters (D50) and shapes of the silver powders A to C thus prepared were calculated by SEM observation and are shown in Table 1 below.
  • a vehicle for dispersing the silver powder was prepared. Specifically, first, two types of resins, a crystalline epoxy resin (EP) and an amorphous polyester resin (PEs), were prepared as binder resins.
  • the epoxy resin a resin having a softening point of 65 ° C. and a number average molecular weight (Mn) of 1 ⁇ 10 3 , which is widely used as a binder for a thermosetting conductive paste, was used.
  • the polyester resin a thermoplastic resin having a number average molecular weight (Mn) of 23 ⁇ 10 3 and a glass transition point (Tg) of 65 ° was used.
  • propylene glycol monophenyl ether having a phenyl group in the molecular structure and capable of suitably dissolving the binder resin was prepared.
  • the boiling point (Tb) of propylene glycol monophenyl ether is 243 ° C.
  • a predetermined amount of each resin and solvent was weighed into a glass bottle container, stirred manually, and then heated in a steam oven at about 100 ° C. for about 10 to 20 hours. During the heating, hand stirring was performed as necessary. This gave two vehicles.
  • the prepared silver powders A to C and a vehicle were mixed at a predetermined ratio, and mixed and kneaded using a three-roll mill to prepare silver pastes of Examples 1 to 5.
  • the silver powder and the vehicle were set to a ratio in which the resin in the vehicle was 10 parts by mass or 6 parts by mass with respect to the mass of the silver powder (100 parts by mass).
  • the silver paste was adjusted to have a viscosity of 50 to 150 Pa ⁇ s at 25 ° C.-20 rpm by adding a solvent.
  • the silver pastes of Examples 1 to 5 prepared in this way were applied to the surface of a PET resin film substrate (thickness 100 ⁇ m) by screen printing.
  • a calendered # 640 stainless mesh was used and printed in a thin layer so that the film thickness after heat treatment (firing) was approximately 1 ⁇ m.
  • the printing pattern was arranged by arranging one rectangular solid coating pattern of 3 cm ⁇ 1.5 cm and a sheet resistance measurement pattern described later side by side.
  • the sheet resistance measurement pattern was a linear pattern in which the dimensions after firing were adjusted so that the total length was 10 cm or more and the width was 0.5 mm.
  • Example 4 The silver paste of Example 4 was printed by changing the stainless steel mesh so that the thickness after the heat treatment was 10 ⁇ m (this is Example 4 * ).
  • the printed substrate was dried in a dryer at 60 ° C. for 10 minutes and then heat-treated at 120 ° C. for 20 minutes to form the conductive films of Examples 1 to 5.
  • the film thickness of the obtained conductive film was measured and shown in the column of “Firing thickness” in Table 1 below.
  • each characteristic of sheet resistance, adhesiveness, and bending adhesiveness was evaluated with the following method, and the result was shown in the said column of the following Table 1.
  • substrate of a electrically conductive film was evaluated by performing the adhesive test using a double-sided tape. Specifically, a double-sided tape (manufactured by Nichiban Co., Ltd., NW-10 for general use, width 1 cm ⁇ length 1.5 cm) was attached on the test stand. And the electrically conductive film part formed on the PET board
  • a double-sided tape manufactured by Nichiban Co., Ltd., NW-10 for general use, width 1 cm ⁇ length 1.5 cm
  • the edge of the PET substrate is pinched with a finger, and the direction along the longitudinal direction of the double-sided tape is 120 ° to 150 ° from the initial attachment position of the PET substrate (ie, the angle formed by the PET substrate is 60 ° to The film substrate was peeled from the double-sided tape by pulling it diagonally upward and rearward at 30 °.
  • ⁇ when the area ratio of the part remaining on the film substrate after peeling is 95% or more, the area ratio of the remaining part is The case of less than 95% and 80% or more is indicated by “ ⁇ ”, and the case where the remaining area ratio is less than 80% is indicated by “X”.
  • the durability of the conductive film when the substrate was bent was evaluated. Specifically, first, the sheet resistance (initial sheet resistance) of the conductive film formed on the PET substrate was measured as described above. Next, the PET substrate provided with the conductive film was bent along the surface of the test table having a right angle (90 °) corner, and the PET substrate was bent at a right angle at the conductive film portion. Thereafter, the bent PET substrate was straightened, and the PET substrate and the conductive film were again bent at a right angle at the same folding position. This operation was repeated until the total number of bendings was six.
  • the silver paste of Example 1 is an example of a widely used thermosetting silver paste using a flake-type silver powder A having an average particle diameter of 2000 nm and an epoxy resin.
  • a conductive film having a thickness of about 10 ⁇ m can be suitably formed.
  • the silver paste of Example 1 it is not possible to print a conductive film as thin as 1 ⁇ m even under the same printing conditions, and the film thickness of the conductive film becomes thicker based on the particle size of the silver particles. I was able to confirm. In this example, it was found that a conductive film having a thickness approximately equal to the average particle diameter of the silver particles and having a thickness of about 2 ⁇ m can be formed.
  • the conductive film of Example 1 has a low film strength due to the fact that the silver particles are not sintered with each other and has a small thickness with respect to the size of the silver particles. Was found to peel off. Furthermore, since the thermosetting resin is crystalline, the hardness after curing is high. Therefore, although the thickness of the conductive film was relatively thin, formation of cracks in the conductive film and peeling from the substrate were confirmed by one-time bending, and it was found that the bending resistance was poor. In other words, according to the silver paste of Example 1, it was found that it was difficult to form a conductive thin film having a low sheet resistance and good adhesion on a flexible substrate having low heat resistance.
  • the silver pastes of Examples 2 and 4 are low-temperature curable silver pastes using a polyester resin having a glass transition point of 65 ° C., and the average particle diameter of the silver powder used is (Example 2) Silver Powder B: It is different between 500 nm and (Example 4) silver powder C: 70 nm.
  • silver pastes were used, it was confirmed that a target conductive film having a thickness of 1 ⁇ m could be formed.
  • the glass transition point of the binder resin is 65 ° C.
  • the binder resin is sufficiently softened by heat treatment at 120 ° C. and then hardened, and the silver particles and the silver particles and the substrate are well bonded to each other. It was confirmed that a good conductive film could be formed.
  • the polyester resin used as the binder is non-crystalline, so the conductive film has flexibility and substrate followability and high bending resistance. Even when the base material is repeatedly bent, the sheet resistance of the conductive film is significantly increased. It was confirmed that there was no. From this, it was found that by using a thermoplastic resin having an appropriate glass transition point as the binder resin, a conductive thin film having low heat resistance and good adhesion to a flexible substrate can be formed.
  • the conductive film of Example 4 using fine silver powder C is partly sintered by heat treatment and is higher than the conductive film of Example 2. It showed adhesiveness.
  • the sheet resistance of the conductive film of Example 4 was as low as 50 m ⁇ / ⁇ , whereas the sheet resistance of the conductive film of Example 2 using silver powder B having an average particle diameter of 500 nm still exceeded 1000 m ⁇ / ⁇ . . It can be considered that this is because, in the conductive film of Example 4, since the average particle diameter is sufficiently small, the silver particles are sintered to form a good contact in the conductive film.
  • the silver particles B used in Example 2 are not sintered by heat treatment at a low temperature, the silver particles cannot form a good contact in a film having a limited thickness of about 1 ⁇ m, for example. From this, it was found that the average particle diameter of the silver powder is preferably about 100 ⁇ m or less, for example.
  • the silver paste of Examples 3, 4, and 5 uses silver powder C, and the amount of the polyester resin having a glass transition point of 65 ° C. is (Example 3) 0 part by mass (not used), (Example 4) 6 parts by mass, (Example 5) It is changed at 10 parts by mass.
  • Example 3 0 part by mass (not used)
  • Example 4 6 parts by mass
  • Example 5 It is changed at 10 parts by mass.
  • the sheet resistance of the conductive film was extremely low at 10 m ⁇ / ⁇ for the conductive film of Example 3 in which the amount of binder resin used was zero, and it was found that the sheet resistance increased as the binder resin increased.
  • the sheet resistance of the conductive film of Example 4 having a binder resin amount of 6 parts by mass is sufficiently low as 50 m ⁇ / ⁇
  • the conductive film of Example 5 having a binder resin amount of 10 parts by mass is the same as the conductive film of Example 1.
  • the sheet resistance was found to be extremely high, exceeding 1000 m ⁇ / ⁇ . From this, it was found that the binder resin is preferably less than 10 parts by mass, for example, 8 parts by mass or less with respect to the silver powder.
  • a thermoplastic binder resin with an appropriate glass transition point it is possible to form a film with good adhesion by low-temperature firing while reducing the amount of resin, and to achieve low sheet resistance and adhesiveness. It turns out that they can be compatible at a high level.
  • Example 4 As described above, it was found that by using the silver paste of Example 4, it is possible to form a conductive film having extremely good adhesion to a flexible PET substrate with low heat resistance. Therefore, using the silver paste of Example 4, a conductive film of Example 4 * having a thickness of 10 ⁇ m was formed in the same manner as when a conventional thermosetting silver paste was used. As a result, like the conductive film of Example 4, the conductive film of Example 4 * had low sheet resistance and excellent adhesiveness while being fired at a low temperature. However, since the film thickness was as thick as 10 ⁇ m, the conductive film was floated or cracked by bending, and in this example, satisfactory results were not obtained with respect to bending resistance.
  • the silver paste of Example 4 can be particularly suitably used to form a thin film having a thickness of less than 10 ⁇ m, for example, a film thickness of 3 ⁇ m or less in order to have flexibility. It was.
  • Embodiment 2 [Preparation of silver paste]
  • a substantially spherical silver powder C having an average particle diameter of 70 nm using butylamine as a surface modifier was prepared.
  • the silver powder C prepared here was almost spherical in shape, non-spherical silver fine particles having an aspect ratio exceeding 1.5 were present at a ratio of about 10% by mass or less. It could be confirmed.
  • binder resins as shown in Table 2, five types of amorphous polyester resins (PEs) A to E having different glass transition points (Tg) of 7 to 84 were prepared.
  • the solvent as shown below, in addition to propylene glycol monophenyl ether, three kinds of organic solvents having different boiling points (Tb) were prepared.
  • the prepared silver powder and vehicle are blended at a ratio of silver powder: resin of 75: 4 (that is, 100 parts by mass: 5.3 parts by mass), and mixed and kneaded using a three-roll mill.
  • the silver pastes of Examples 6 to 13 were prepared.
  • the silver paste was prepared by adding a solvent so that the viscosity at 25 ° C.-20 rpm was 50 to 150 Pa ⁇ s.
  • the film thickness of the obtained conductive film was measured, and the average value was shown in the column of “Firing thickness” in Table 2 below. Further, the obtained conductive film was evaluated for sheet resistance and adhesiveness in the same manner as in Embodiment 1, and the results are shown in the corresponding column of Table 2 below.
  • Examples 6 to 10 in Table 2 are silver pastes prepared under the same conditions except that polyester resins A to E having different glass transition points were used.
  • the sheet resistance of the conductive film formed from these silver pastes was small in Examples 6 and 7, where the glass transition point of the binder resin was lower than the drying temperature. From this point alone, it seems that the glass transition point of the binder resin is preferably a low value of, for example, 50 ° C. or less.
  • the conductive films of Examples 6 and 7 having a low sheet resistance have extremely low adhesion to the base material despite the same resin amount. This is considered to be because, for example, when the silver paste is dried at 60 ° C., volatilization of the solvent and softening of the binder occur at the same time, and stable film formation cannot be performed.
  • the drying and firing of the silver paste are performed in separate steps (in two steps), and the solvent is sufficient. Firing can be performed on the volatilized application body. From this, it was found that the conductive films of Examples 8 to 10 have a slightly high sheet resistance, but have high adhesion to the substrate, and can achieve both low sheet resistance and substrate adhesion. In particular, for the silver pastes of Examples 8 and 9, it was found that a conductive film having excellent sheet resistance characteristics and adhesiveness can be stably formed without being greatly affected by the firing temperature.
  • the glass transition point of the binder resin tends to be preferably lower than the heat treatment temperature in order to form a conductive film on a film-like substrate having low heat resistance. For example, it is preferably about 30 ° C. lower than the heat treatment temperature.
  • Examples 11 to 13 are examples in which silver paste was prepared by changing the type of solvent.
  • (b) 2- (2-butoxyethoxy) ethyl acetate was used as the solvent.
  • 2- (2-butoxyethoxy) ethyl acetate was used as the solvent, the binder resin was dissolved to produce a silver paste, but the resulting silver paste was too viscous to perform printing. could not. This is thought to be because 2- (2-butoxyethoxy) ethyl acetate does not have a phenyl group.
  • a thickener is added to such a low-viscosity silver paste, the properties of the resulting conductive film are significantly deteriorated, which is not practical.
  • Example 12 (c) ethylene glycol monophenyl ether was used as a solvent.
  • the silver paste could be adjusted to a viscosity suitable for printing.
  • a conductive film having excellent sheet resistance and adhesiveness can be formed by setting the temperature of the heat treatment to a range of 105 ° C. to 125 ° C. Note that by reducing the temperature of the heat treatment to 105 ° C. to 115 ° C., the adhesiveness can be further improved, and a conductive film with a better balance between sheet resistance and adhesiveness can be obtained. It was also confirmed that a conductive film having a lower sheet resistance can be formed by increasing the temperature to 0C.
  • Example 13 diethylene glycol monophenyl ether was used as a solvent. When diethylene glycol monophenyl ether was used as the solvent, the binder resin could not be dissolved in the solvent, and the silver paste itself could not be prepared.
  • Diethylene glycol monophenyl ether is an alkylene glycol similar to (c) ethylene glycol monophenyl ether, but its boiling point greatly exceeds 250 ° C. Since the boiling point may reflect the molecular structure and its characteristics, diethylene glycol monophenyl ether having a boiling point exceeding 250 ° C. is considered to be inappropriate as a solvent for the silver paste for flexible substrates disclosed herein.

Abstract

Provided is a silver paste for a flexible substrate for which an electrically conductive film having good adhesiveness can be formed on a flexible substrate having low heat resistance. The silver paste for a flexible substrate contains: (A) a silver powder; (B) a thermoplastic polyester resin as a binder; and (C) a solvent by which to dissolve the thermoplastic polyester resin. The silver powder (A) has a mean particle diameter of 40-100 nm. The thermoplastic polyester resin (B) has a glass transition point of 60-90°C, and is contained at a ratio of 5-8 parts by mass to 100 parts by mass of silver powder. The solvent (C) has a boiling point of 180-250°C, and contains a phenyl group in the molecular structure.

Description

フレキシブル基板用銀ペーストSilver paste for flexible substrates
　本発明は、樹脂等の耐熱性の低い基板に導電膜を形成することができる銀ペーストに関する。
　本出願は、２０１６年９月１６日に出願された日本国特許出願２０１６－１８２２９１号に基づく優先権を主張している。その出願の全内容は本明細書中に参照として組み入れられている。 The present invention relates to a silver paste capable of forming a conductive film on a substrate having low heat resistance such as a resin.
This application claims priority based on Japanese Patent Application No. 2016-182291 filed on Sep. 16, 2016. The entire contents of that application are incorporated herein by reference.
　電子部品を搭載する回路基板については、小型化、薄型化、軽量化および高機能化に伴い、無機基板に代えて、ポリマー基板上に導電膜を印刷することが行われてきている。ポリマー基板は無機基板に比較して耐熱性に劣ることから、導電膜を形成するための導電性ペーストに対しても低温（例えば４００℃以下）で製膜が可能なことが求められる。特許文献１～２には、例えば、低温での製膜を好適に行うための低温焼結性に優れた銀粉末と、この銀粉末を含む銀ペーストが開示されている。また特許文献３には、銀粉末と低温で硬化する熱可塑性樹脂とを含む銀ペーストが開示されている。 With regard to circuit boards on which electronic components are mounted, conductive films have been printed on polymer substrates instead of inorganic substrates in accordance with miniaturization, thinning, weight reduction, and high functionality. Since the polymer substrate is inferior in heat resistance as compared with the inorganic substrate, it is required that the polymer substrate can be formed at a low temperature (for example, 400 ° C. or lower) even for the conductive paste for forming the conductive film. Patent Documents 1 and 2 disclose, for example, a silver powder excellent in low-temperature sinterability for suitably forming a film at a low temperature, and a silver paste containing this silver powder. Patent Document 3 discloses a silver paste containing silver powder and a thermoplastic resin that cures at a low temperature.
国際公開第２０１４／０８４２７５号公報International Publication No. 2014/084275 日本国特許出願公開第２０１３－３６０５７号公報Japanese Patent Application Publication No. 2013-36057 国際公開第２０１３／０８１６６４号公報International Publication No. 2013/081664
　ところで、近年、薄くフレキシブルなポリマーフィルムを基板とし、銀ペーストに代表される導電性ペーストを印刷することで、フレキシブルプリント配線基板（Flexible printed circuits：ＦＰＣ）をハイスループットかつ低コストで大量生産することが行われている。この種の基板に用いられる銀ペーストとしては、製膜された導電膜自体にも柔軟性が求められることから、基材の耐熱温度以下の温度で硬化する熱硬化性樹脂をバインダとして含む熱硬化型銀ペーストが汎用されている。しかしながら、この熱硬化型銀ペーストから得られる導電膜は、ポリマーフィルム基板を繰り返し湾曲させた場合に基板から剥離しやすいという問題があった。また、ポリマーフィルム基板は、薄層化により熱感受性が高まることから、従来よりも更に低温（例えば１４０℃以下）で製膜することが求められてもいる。 By the way, in recent years, flexible printed circuit boards (FPC) are mass-produced with high throughput and low cost by printing a conductive paste typified by silver paste using a thin and flexible polymer film as a substrate. Has been done. As the silver paste used for this type of substrate, since the formed conductive film itself is required to have flexibility, thermosetting containing a thermosetting resin that cures at a temperature lower than the heat resistant temperature of the base material as a binder. Mold silver paste is widely used. However, the conductive film obtained from this thermosetting silver paste has a problem that it easily peels from the substrate when the polymer film substrate is repeatedly bent. In addition, the polymer film substrate is required to be formed at a lower temperature (for example, 140 ° C. or lower) than conventional because the thermal sensitivity is increased by thinning the layer.
　本発明はかかる点に鑑みてなされたものであり、その目的は、耐熱性の低いフレキシブルな基板に低温で接着性の良い導電膜を形成することができるフレキシブル基板用銀ペーストを提供することにある。 This invention is made | formed in view of this point, The objective is to provide the silver paste for flexible substrates which can form a conductive film with favorable adhesiveness at low temperature on a flexible substrate with low heat resistance. is there.
　従来のこの種の熱硬化型銀ペーストから得られる導電膜は、厚みが概ね１０～３０μｍ程度である。本発明者らの検討によると、熱硬化型銀ペーストから形成された導電膜を備えるポリマーフィルム基板を繰り返し湾曲させると、導電膜はその硬さと厚みとに起因して剥離し易くなることを知見した。ここで、この種の熱硬化型銀ペーストは、絶縁性の熱硬化型樹脂を銀粒子のバインダとして用いている。そのため、形成される導電膜の導電性を確保するためには、微細で比表面積の大きい銀ナノ粒子を用いることはバインダの増大に繋がるため困難であり、平均粒子径がおおよそ２～５μｍ以上のフレーク形状の銀粉末を用いることが必要であった。その結果、かかる平均粒子径の粒子から形成される導電膜が安定して形成されるのは、厚みがおおよそ１０μｍ以上の場合となってしまい、導電膜の導電性と、膜強度や接着性等の物理特性との両立を考慮した場合、導電膜の厚みを薄くすることは困難であった。 A conductive film obtained from such a conventional thermosetting silver paste has a thickness of about 10 to 30 μm. According to the study by the present inventors, it has been found that when a polymer film substrate including a conductive film formed from a thermosetting silver paste is repeatedly curved, the conductive film is easily peeled due to its hardness and thickness. did. Here, this type of thermosetting silver paste uses an insulating thermosetting resin as a binder for silver particles. Therefore, in order to ensure the conductivity of the conductive film to be formed, it is difficult to use fine silver nanoparticles having a large specific surface area because it leads to an increase in the binder, and the average particle diameter is approximately 2 to 5 μm or more. It was necessary to use flaky silver powder. As a result, the conductive film formed from the particles having the average particle diameter is stably formed when the thickness is approximately 10 μm or more, and the conductivity of the conductive film, the film strength, the adhesiveness, etc. In consideration of the compatibility with the physical properties, it was difficult to reduce the thickness of the conductive film.
　そこで本発明者らは、フレキシブルな基板にフレキシブルな導電膜を形成するには、ナノメートルオーダーの銀粉末の使用が欠かせない、との視点から鋭意研究した結果、本発明を完成するに至った。すなわち、上記課題を解決すべく本発明が提供するフレキシブル基板用銀ペースト（以下、単に「銀ペースト」、「ペースト」等という場合がある。）は、フレキシブルフィルム基板に導電膜を形成するための銀ペーストである。このフレキシブル基板用銀ペーストは、（Ａ）銀粉末と、（Ｂ）バインダとしての熱可塑性ポリエステル樹脂と、（Ｃ）上記熱可塑性ポリエステル樹脂を溶解させる溶剤と、を含んでいる。そして（Ａ）銀粉末は、平均粒子径が４０ｎｍ以上１００ｎｍ以下であることを特徴としている。また、（Ｂ）熱可塑性ポリエステル樹脂は、ガラス転移点が６０℃以上９０℃以下であって、銀粉末１００質量部に対して、５質量部以上８質量部以下の割合で含まれることを特徴としている。そして（Ｃ）溶剤は、沸点が１８０℃以上２５０℃以下であって、分子構造にフェニル基を含むことを特徴としている。 Therefore, the present inventors have intensively studied from the viewpoint that the use of silver powder of nanometer order is indispensable for forming a flexible conductive film on a flexible substrate, and as a result, the present invention has been completed. It was. That is, a silver paste for a flexible substrate (hereinafter sometimes simply referred to as “silver paste”, “paste”, etc.) provided by the present invention to solve the above-mentioned problems is used for forming a conductive film on a flexible film substrate. Silver paste. This silver paste for flexible substrates contains (A) silver powder, (B) a thermoplastic polyester resin as a binder, and (C) a solvent for dissolving the thermoplastic polyester resin. And (A) silver powder has an average particle diameter of 40 nm or more and 100 nm or less. The thermoplastic polyester resin (B) has a glass transition point of 60 ° C. or more and 90 ° C. or less, and is contained in a proportion of 5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the silver powder. It is said. The solvent (C) has a boiling point of 180 ° C. or higher and 250 ° C. or lower, and includes a phenyl group in the molecular structure.
　このようなフレキシブル基板用銀ペーストを用いることで、フレキシブル基板に、１４０℃以下の低温で、例えば３μｍ以下の厚みのフレキシブルな導電膜を密着性良く好適に形成することができる。このことにより、基板から剥がれ難く、例えば基板を繰り返し湾曲させた場合であっても剥離の抑制された導電膜を形成することができる。また例えば、基板を９０°に折り曲げたり、伸ばしたり（真っ直ぐに広げたり）した場合であっても、剥離の抑制された導電膜を形成することができる。 By using such a silver paste for a flexible substrate, a flexible conductive film having a thickness of, for example, 3 μm or less can be suitably formed on the flexible substrate at a low temperature of 140 ° C. or less with good adhesion. Accordingly, it is difficult to peel off from the substrate, and for example, a conductive film in which peeling is suppressed can be formed even when the substrate is repeatedly bent. In addition, for example, even when the substrate is bent or stretched at 90 ° (stretched straight), a conductive film in which peeling is suppressed can be formed.
　なお、銀粉末の平均粒子径は、電子顕微鏡観察に基づき測定された個数基準の粒度分布における、累積５０％粒子径を意味する。粒度分布は、具体的には、例えば、走査型電子顕微鏡（ＳＥＭ）等を用い、適切な倍率（例えば５万倍）で銀粉末を観察し、１００個以上（例えば１００～１０００個）の銀粒子について求めた円相当径を基に作成することができる。 In addition, the average particle diameter of silver powder means the cumulative 50% particle diameter in the number-based particle size distribution measured based on observation with an electron microscope. Specifically, the particle size distribution is determined by, for example, using a scanning electron microscope (SEM) or the like, observing silver powder at an appropriate magnification (eg, 50,000 times), and 100 or more (eg, 100 to 1000) silver particles. It can be created based on the equivalent-circle diameter determined for the particles.
　また、熱可塑性ポリエステル樹脂のガラス転移点は、ＪＩＳ Ｋ７１２１：１９８７「プラスチックの転移温度測定方法」に規定されるガラス転移点の測定方法に準じて測定することができる。熱可塑性ポリエステル樹脂のガラス転移点は、具体的には、例えば、示差熱分析（ＤＴＡ）装置または示差走査熱量測定（ＤＳＣ）装置を用い、測定試料と標準物質とを一定の速さで加熱し、試料中の熱容量の変化に基づく試料と標準物質との間の熱量の差を計測することで、試料のガラス転移点を把握することができる。加熱に際しては、例えば、試料のガラス転移終了時より少なくとも約３０℃高い温度まで加熱し、当該温度に１０分間程度保持したのちに、ガラス転移点よりも約５０℃低い温度まで急冷することが好ましい。なお、市販の熱可塑性ポリエステル樹脂を用いる場合は、当該製品のデータシート等に記載されたガラス転移点を採用することができる。 Further, the glass transition point of the thermoplastic polyester resin can be measured according to the glass transition point measurement method specified in JIS K7121: 1987 “Method for measuring plastic transition temperature”. Specifically, the glass transition point of the thermoplastic polyester resin is obtained by, for example, using a differential thermal analysis (DTA) apparatus or a differential scanning calorimetry (DSC) apparatus to heat a measurement sample and a standard substance at a constant speed. The glass transition point of the sample can be grasped by measuring the difference in the amount of heat between the sample and the standard material based on the change in the heat capacity in the sample. In heating, for example, it is preferable that the sample is heated to a temperature at least about 30 ° C. higher than that at the end of the glass transition of the sample, held at that temperature for about 10 minutes, and then rapidly cooled to a temperature about 50 ° C. lower than the glass transition point. . In addition, when using a commercially available thermoplastic polyester resin, the glass transition point described in the data sheet etc. of the said product can be employ | adopted.
　ここに開示されるフレキシブル基板用銀ペーストの好ましい一態様において、（Ａ）銀粉末は、アスペクト比が１．５以下の球形銀微粒子と、アスペクト比が１．５超過の非球形銀微粒子とを含むことを特徴としている。このことにより、銀粉末の焼結が好適に促進されて、よりシート抵抗の低い導電膜を形成することができる。 In a preferred embodiment of the silver paste for a flexible substrate disclosed herein, the (A) silver powder comprises spherical silver fine particles having an aspect ratio of 1.5 or less and nonspherical silver fine particles having an aspect ratio exceeding 1.5. It is characterized by including. By this, sintering of silver powder is accelerated | stimulated suitably and the electrically conductive film with lower sheet resistance can be formed.
　ここに開示されるフレキシブル基板用銀ペーストの好ましい一態様において、（Ａ）銀粉末の表面には、炭素数５以下の有機アミンからなる保護剤が付着していることを特徴としている。このことにより、ペースト中での銀粉末の分散安定性が高まり、ペースト保存状態から、ペーストを基板に塗布し焼成する間にわたり、銀粒子同士が互いに好適なポジションに配置され、緻密で均質な導電膜を形成することができる。 In a preferred embodiment of the silver paste for flexible substrates disclosed herein, (A) a protective agent made of an organic amine having 5 or less carbon atoms is attached to the surface of the silver powder. This enhances the dispersion stability of the silver powder in the paste, and the silver particles are placed in a suitable position from the paste storage state to the paste being applied to the substrate and baked to provide a dense and homogeneous conductive. A film can be formed.
　他の側面において、ここに開示される技術は電子素子を提供する。この電子素子は、フレキシブルフィルム基板と、フレキシブルフィルム基板上に備えられた導電膜と、を含む。そして導電膜は、上記のいずれかに記載のフレキシブル基板用銀ペーストの硬化物であることにより特徴づけられる。上記の銀ペーストは、フレキシブル基板の湾曲および折れ曲がりに対して追随性および接着性の良好な導電膜を形成することができる。したがって、基板を湾曲させたり折り曲げたりした場合であっても、導電膜の浮きや剥離等が抑制された電子素子が実現される。 In another aspect, the technology disclosed herein provides an electronic device. The electronic element includes a flexible film substrate and a conductive film provided on the flexible film substrate. And the electrically conductive film is characterized by being the hardened | cured material of the silver paste for flexible substrates in any one of said. The silver paste can form a conductive film having good followability and adhesion with respect to the bending and bending of the flexible substrate. Therefore, even when the substrate is bent or bent, an electronic element in which floating or peeling of the conductive film is suppressed is realized.
　ここに開示される電子素子の好ましい一態様において、上記導電膜の平均厚みは、０．２μｍ以上３μｍ以下である。例えば、上記導電膜のシート抵抗は、導電膜の厚みを１０μｍに換算したときの値で、１００ｍΩ／□以下であることにより特徴づけられる。これにより、シート抵抗とフレキシブル性のバランスがより良好な導電膜を備える電子素子が実現される。 In a preferred embodiment of the electronic element disclosed herein, the conductive film has an average thickness of 0.2 μm or more and 3 μm or less. For example, the sheet resistance of the conductive film is a value when the thickness of the conductive film is converted to 10 μm and is characterized by 100 mΩ / □ or less. Thereby, an electronic device including a conductive film with a better balance between sheet resistance and flexibility is realized.
　さらに他の側面において、ここに開示される技術は、電子素子の製造方法を提供する。この製造方法は、フレキシブルフィルム基板を用意すること、上記のいずれかのフレキシブル基板用銀ペーストを用意すること、上記フレキシブルフィルム基板上に、上記フレキシブル基板用銀ペーストを供給すること、上記フレキシブル基板用銀ペーストが供給された上記フレキシブルフィルム基板を、乾燥させること、上記乾燥された上記フレキシブル基板用銀ペーストが供給された上記フレキシブルフィルム基板を、熱処理して導電膜を形成すること、を含む。そして、上記フレキシブル基板用銀ペーストの供給は、形成される上記導電膜の平均厚みが３μｍ以下となるように実施し、上記乾燥のための温度は、上記フレキシブル基板用銀ペーストに含まれる上記熱可塑性ポリエステル樹脂のガラス転移点よりも低い温度であり、上記熱処理の温度は、上記ガラス転移点よりも２０℃以上高い温度であることを特徴とする。これにより、ここに開示されるフレキシブル基板用銀ペーストを用いて、フレキシブル基板上に、接着性および導電性が良好な導電膜を備える電子素子を好適に製造することができる。 In still another aspect, the technology disclosed herein provides a method for manufacturing an electronic device. The manufacturing method includes preparing a flexible film substrate, preparing any one of the above-mentioned silver pastes for a flexible substrate, supplying the silver paste for a flexible substrate on the flexible film substrate, and for the flexible substrate Drying the flexible film substrate supplied with the silver paste, and heat-treating the flexible film substrate supplied with the dried silver paste for flexible substrate to form a conductive film. And supply of the said silver paste for flexible substrates is implemented so that the average thickness of the said electrically conductive film formed may be 3 micrometers or less, and the temperature for the said drying is the said heat | fever contained in the said silver paste for flexible substrates. The temperature is lower than the glass transition point of the plastic polyester resin, and the temperature of the heat treatment is 20 ° C. or more higher than the glass transition point. Thereby, the electronic element provided with the electrically conductive film with favorable adhesiveness and electroconductivity on a flexible substrate can be suitably manufactured using the silver paste for flexible substrates disclosed here.
　以下、本発明の好適な実施形態を説明する。なお、本明細書において特に言及している事項（例えば、フレキシブル基板用銀ペーストの構成やその性状）以外の事柄であって、本発明の実施に必要な事柄（例えば、当該ペーストの基材への適用するための詳細な手法等）は、本明細書により教示されている技術内容と、当該分野における当業者の一般的な技術常識とに基づいて実施することができる。なお、本明細書において数値範囲を示す「Ａ～Ｂ」との表記は、Ａ以上Ｂ以下を意味する。 Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification (for example, the structure and properties of the silver paste for flexible substrates) and matters necessary for the implementation of the present invention (for example, to the base material of the paste) The detailed technique for applying the above can be implemented based on the technical contents taught by the present specification and general technical common knowledge of those skilled in the art. In this specification, the notation “A to B” indicating a numerical range means A or more and B or less.
［フレキシブル基板用銀ペースト］
　ここで開示されるフレキシブル基板用銀ペーストは、本質的に、低温（例えば１４０℃以下）での熱処理により硬化物を形成し得るとともに、その硬化物が電気伝導性（導電性）を示す導電膜である。なお、熱処理に先行して、銀ペーストは乾燥されていてもよい。ここで特徴的なことに、この導電膜は、それ自体が基板に対する柔軟性と接着性とを備えており、例えばフレキシブルな基板に対しても良好な基板追随性を示すものとして実現される。このようなフレキシブル基板用銀ペーストは、主たる構成成分として、（Ａ）銀粉末と、（Ｂ）バインダとしての熱可塑性ポリエステル樹脂と、（Ｃ）熱可塑性ポリエステル樹脂を溶解させる溶剤と、を含む。以下、ここに開示されるフレキシブル基板用銀ペーストの各構成成分について説明する。 [Silver paste for flexible substrates]
The silver paste for a flexible substrate disclosed herein is essentially a conductive film that can form a cured product by heat treatment at a low temperature (for example, 140 ° C. or less), and the cured product exhibits electrical conductivity (conductivity). It is. Prior to the heat treatment, the silver paste may be dried. Characteristically, the conductive film itself has flexibility and adhesion to the substrate, and is realized, for example, as exhibiting good substrate followability even for a flexible substrate. Such a silver paste for flexible substrates contains (A) silver powder, (B) a thermoplastic polyester resin as a binder, and (C) a solvent for dissolving the thermoplastic polyester resin as main components. Hereinafter, each structural component of the silver paste for flexible substrates disclosed here is demonstrated.
　（Ａ）銀粉末
　銀粉末は、電子素子等における電極、導線や電導膜等の電気伝導性（以下、単に「導電性」という。）の高い膜体（導電膜）を主として形成するため材料である。銀（Ａｇ）は、金（Ａｕ）ほど高価ではなく、酸化され難くかつ導電性に優れることから導体材料として好ましい。銀粉末は、銀を主成分とする粉末（粒子の集合）であればその組成は特に制限されず、所望の導電性やその他の物性を備える銀粉末を用いることができる。ここで主成分とは、銀粉末を構成する成分のうちの最大成分であることを意味する。銀粉末を構成する銀粒子としては、例えば、銀および銀合金ならびにそれらの混合物または複合体等から構成された粒子が一例として挙げられる。銀合金としては、例えば、銀－パラジウム（Ａｇ－Ｐｄ）合金、銀－白金（Ａｇ－Ｐｔ）合金、銀－銅（Ａｇ－Ｃｕ）合金等が好ましい例として挙げられる。例えば、コアが銀以外の銅や銀合金等の金属から構成され、コアを覆うシェルが銀からなるコアシェル粒子等を用いることもできる。 (A) Silver powder Silver powder is a material for mainly forming a film body (conductive film) having high electrical conductivity (hereinafter simply referred to as “conductive”) such as electrodes, conductive wires and conductive films in electronic devices and the like. is there. Silver (Ag) is preferable as a conductor material because it is not as expensive as gold (Au), is hardly oxidized, and is excellent in conductivity. The composition of the silver powder is not particularly limited as long as it is a powder (aggregation of particles) containing silver as a main component, and a silver powder having desired conductivity and other physical properties can be used. Here, the main component means that it is the maximum component among the components constituting the silver powder. Examples of the silver particles constituting the silver powder include particles composed of silver, a silver alloy, a mixture or a composite thereof, and the like. Preferred examples of the silver alloy include a silver-palladium (Ag—Pd) alloy, a silver-platinum (Ag—Pt) alloy, and a silver-copper (Ag—Cu) alloy. For example, core-shell particles in which the core is made of metal other than silver, such as copper or silver alloy, and the shell covering the core is made of silver can also be used.
　銀粉末は、純度（銀（Ａｇ）の含有量）が高いほど導電性が高くなる傾向があることから、純度の高いものを使用することが好ましい。銀粉末は、純度９５％以上が好ましく、９７％以上がより好ましく、９９％以上が特に好ましい。例えば、純度が９９．５％程度以上（例えば９９．８％程度以上）の銀粉末を使用することで、極めて低抵抗の導電膜を形成できるためにより好ましい。 Since the silver powder tends to have higher conductivity as the purity (silver (Ag) content) is higher, it is preferable to use a silver powder having higher purity. The silver powder preferably has a purity of 95% or more, more preferably 97% or more, and particularly preferably 99% or more. For example, it is more preferable to use a silver powder having a purity of about 99.5% or more (for example, about 99.8% or more) because an extremely low resistance conductive film can be formed.
　また、ここに開示される技術では、比較的低温（例えば１４０℃以下、典型的には、１１０℃～１３５℃程度）の熱処理による焼結が好適に実現されるように、銀粉末として平均粒子径が４０ｎｍ以上１００ｎｍ以下のものを用いるようにしている。一般に、粒径の微小な粒子（例えば数ｎｍ～数１０ｎｍの微細粒子）ほど低温での焼結性が高まるため、バインダの使用量を低減できる点において好ましいと言える。しかしながら、バインダレスの銀粒子の焼結体は緻密な焼結体を形成し、バルク特性が強く発現されて、導電膜を湾曲させた場合に割れが発生してしまう。すなわち、フレキシブル性（柔軟性）を発揮し得ない。また、平均粒子径が４０ｎｍよりも小さいと、熱処理よりも低い温度（例えば銀ペーストの基材への供給時や、乾燥時といったより低温環境；例えば２０℃～１００℃程度）においても銀粒子が焼結（自己焼結を含む。）を起こし易く、安定した成膜が不可能となるために好ましくない。かかる観点から、銀粉末の平均粒子径は４０ｎｍ以上（４０ｎｍ超過）が好ましく、４５ｎｍ以上がより好ましく、５０ｎｍ以上が特に好ましい。 Further, in the technique disclosed herein, the average particle size as silver powder is such that sintering by heat treatment at a relatively low temperature (eg, 140 ° C. or lower, typically about 110 ° C. to 135 ° C.) is suitably realized. A diameter of 40 nm or more and 100 nm or less is used. In general, finer particles (for example, fine particles of several nm to several tens of nm) have higher sinterability at low temperatures, which is preferable in that the amount of binder used can be reduced. However, the sintered body of binderless silver particles forms a dense sintered body, and the bulk characteristics are strongly expressed, and cracking occurs when the conductive film is curved. That is, flexibility (flexibility) cannot be exhibited. Further, when the average particle diameter is smaller than 40 nm, the silver particles are not produced even at a temperature lower than that of the heat treatment (for example, in a lower temperature environment such as when the silver paste is supplied to the substrate or during drying; for example, about 20 to 100 ° C.). Sintering (including self-sintering) is likely to occur and stable film formation is impossible, which is not preferable. From this viewpoint, the average particle diameter of the silver powder is preferably 40 nm or more (exceeding 40 nm), more preferably 45 nm or more, and particularly preferably 50 nm or more.
　その一方で、銀粒子の平均粒子径が大きすぎると、低温での焼結が困難となり、導電性の良好な導電膜を得ることが困難となり得る。また、低温での焼結が可能であっても、低抵抗に安定して成膜できる導電膜の最低厚みが大きくなり、その結果、導電膜の厚みにより十分な柔軟性を発現し難くなる。かかる観点から、銀粉末の平均粒子径は１００ｎｍ以下（１００ｎｍ未満）が好ましく、９５ｎｍ以下がより好ましく、９０ｎｍ以下が特に好ましい。例えば、５５ｎｍ以上８５ｎｍ以下が好適である。 On the other hand, if the average particle diameter of the silver particles is too large, sintering at a low temperature becomes difficult, and it may be difficult to obtain a conductive film having good conductivity. Further, even if sintering at a low temperature is possible, the minimum thickness of the conductive film that can be stably formed with low resistance is increased, and as a result, sufficient flexibility is hardly exhibited due to the thickness of the conductive film. From this viewpoint, the average particle size of the silver powder is preferably 100 nm or less (less than 100 nm), more preferably 95 nm or less, and particularly preferably 90 nm or less. For example, 55 nm or more and 85 nm or less are suitable.
　なお、銀粉末は品質安定性の観点から、粒径の細かすぎる粒子や粒径の粗大すぎる粒子を含まないことが好ましい。例えば、好ましくは、銀粉末の個数基準の粒度分布において、粒径の最小値（Ｄｍｉｎ）は１０ｎｍ以上が好ましく、２０ｎｍ以上がより好ましく、例えば３０ｎｍ以上が特に好ましい。換言すれば、１０ｎｍ未満、好ましくは２０ｎｍ未満、例えば３０ｎｍ未満の超微粒子を実質的に含有しないことが好ましい。また例えば、個数基準の粒度分布において、粒径の最大値（Ｄｍａｘ）は３００ｎｍ以下が好ましく、２５０ｎｍ以下がより好ましく、例えば２００ｎｍ以下が特に好ましい。換言すれば、３００ｎｍ超過、好ましくは２５０ｎｍ超過、例えば２００ｎｍ超過の粗大な粒子を実質的に含有しないことが好ましい。 In addition, it is preferable that a silver powder does not contain the particle | grains with a too small particle diameter or a particle | grain with a too large particle diameter from a viewpoint of quality stability. For example, preferably, in the number-based particle size distribution of silver powder, the minimum value (Dmin) of the particle size is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more. In other words, it is preferable to contain substantially no ultrafine particles of less than 10 nm, preferably less than 20 nm, for example less than 30 nm. For example, in the number-based particle size distribution, the maximum value (Dmax) of the particle size is preferably 300 nm or less, more preferably 250 nm or less, and particularly preferably 200 nm or less. In other words, it is preferred that it does not substantially contain coarse particles exceeding 300 nm, preferably exceeding 250 nm, for example exceeding 200 nm.
　ここに開示される銀粉末は、粒度分布に適度な広がりを有することが好ましい。例えば、具体的には、個数基準の粒度分布における累積９０％粒径（Ｄ９０）から累積１０％粒径（Ｄ１０）を差し引いた値（Ｄ９０－Ｄ１０）が７０ｎｍ以上、典型的には７５ｎｍ以上であることが好ましく、また、概ね２２０ｎｍ以下、例えば２１０ｎｍ以下であることが好ましい。このように粒度分布に適度な広がりを持たせることにより、銀粉末の焼結時に、相対的に粒径の小さな銀粒子が、相対的に粒径の大きな銀粒子の隙間を埋めるように配置されて焼結し得る。その結果、銀粉末がより高密度に充填した状態で焼結され、導電性に優れた導電膜を実現することができる。 It is preferable that the silver powder disclosed here has an appropriate spread in the particle size distribution. For example, specifically, the value (D90-D10) obtained by subtracting the cumulative 10% particle size (D10) from the cumulative 90% particle size (D90) in the number-based particle size distribution is 70 nm or more, typically 75 nm or more. It is preferable that it is approximately 220 nm or less, for example, 210 nm or less. Thus, by giving the particle size distribution an appropriate spread, the silver particles having a relatively small particle diameter are arranged so as to fill the gaps between the silver particles having a relatively large particle diameter when the silver powder is sintered. Can be sintered. As a result, it is possible to realize a conductive film that is sintered in a state in which the silver powder is more densely packed and has excellent conductivity.
　また、上記の累積９０％粒径（Ｄ９０）と累積１０％粒径（Ｄ１０）との間には、これらの比（Ｄ１０／Ｄ９０）が概ね０．３以上の関係があることが好ましく、例えば０．３３以上であることがより好ましい。また、比（Ｄ１０／Ｄ９０）は、０．６以下が好ましく、０．５５以下がより好ましい。 In addition, it is preferable that the ratio (D10 / D90) is approximately 0.3 or more between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10). More preferably, it is 0.33 or more. The ratio (D10 / D90) is preferably 0.6 or less, and more preferably 0.55 or less.
　以上の銀粉末を構成する銀粒子の形状は特に制限されない。例えば、球状、楕円状、破砕状、鱗片状、平板状、繊維状等であってよい。より薄く均質な膜を印刷により形成するとの観点からは、銀粒子の形状は球形もしくは球形に近いことが好ましい。銀粒子の球形度を表す一つの指標として、銀粒子の形状を二次元で評価したときのアスペクト比が挙げられる。このアスペクト比は、例えば、１００個以上（例えば、１００～１０００個）の銀粒子を電子顕微鏡等により観察し、当該観察像における銀粒子の外形に外接する矩形を描いたときの、短辺の長さに対する長辺の長さの比（長径／短径）として算出することができる。ここでは、各銀粒子に関するアスペクト比の算術平均値を、銀粉末のアスペクト比として採用している。なお、アスペクト比は、１に近いほど等方性に優れ、銀粒子の３次元での形状が球状に近くなる。一方、アスペクト比が大きくなるほど異方性が高くなり、銀粒子の形状は非球状、例えば平板状や繊維状などの形状に近くなる。ここでは、アスペクト比１．５以下の銀粒子を「球状粒子」と呼び、アスペクト比１．５未満の銀粒子を「非球状粒子」と呼ぶ。 The shape of the silver particles constituting the above silver powder is not particularly limited. For example, it may be spherical, elliptical, crushed, flaky, flat, fibrous or the like. From the viewpoint of forming a thinner and more uniform film by printing, the shape of the silver particles is preferably spherical or nearly spherical. One index representing the sphericity of silver particles is the aspect ratio when the shape of silver particles is evaluated in two dimensions. The aspect ratio is, for example, that when 100 or more (for example, 100 to 1000) silver particles are observed with an electron microscope or the like and a rectangle circumscribing the outer shape of the silver particles in the observed image is drawn, It can be calculated as the ratio of the length of the long side to the length (major axis / minor axis). Here, the arithmetic average value of the aspect ratio for each silver particle is adopted as the aspect ratio of the silver powder. Incidentally, the closer the aspect ratio is to 1, the better the isotropic property, and the three-dimensional shape of the silver particles becomes nearly spherical. On the other hand, the larger the aspect ratio, the higher the anisotropy, and the shape of the silver particles is close to a non-spherical shape such as a flat plate shape or a fiber shape. Here, silver particles having an aspect ratio of 1.5 or less are referred to as “spherical particles”, and silver particles having an aspect ratio of less than 1.5 are referred to as “non-spherical particles”.
　また、ここに開示される銀粉末は、球形銀粒子と非球形銀粒子とを含んでいてもよい。球形銀粒子と非球形銀粒子との混合体においては、例えば非球状粒子が配列した隙間に球状粒子が入り込んだり、球状粒子が配列した隙間に非球状粒子が入り込んだりして、全体としての充填性の高い焼結体を得ることができる。これにより、銀粒子同士の接触面積が増加して、導電性に優れた導体膜を形成することができる。
　なお、ここに開示される銀粉末については、アスペクト比１．５以下の球形銀粒子の割合が、銀粉末全体の６０個数％以上であることが好ましい。換言すると、アスペクト比１．５未満の非球形銀粒子が、銀粉末を構成する銀粒子のうち４０個数％以下であることが好ましい。球形銀粒子は、銀粉末全体の７０個数％以上であることがより好ましく、例えば８０個数％以上であることが特に好ましく、例えば８５個数％以上としたり、９０個数％以上であってよい。銀粉末がこのような形状の粒子により構成されることで、銀ペーストが基材に供給されてから熱処理されるまでの銀粒子の安定性や表面平滑性、均質性、充填性等が効果的に高められる。これにより、銀粒子の充填性や形成される導電膜の表面平滑性等が向上されて、より導電性の高い導電膜を得ることができる。 Moreover, the silver powder disclosed here may contain spherical silver particles and non-spherical silver particles. In a mixture of spherical silver particles and non-spherical silver particles, for example, spherical particles may enter into gaps where non-spherical particles are arranged, or non-spherical particles may enter into gaps where spherical particles are arranged. A highly sintered body can be obtained. Thereby, the contact area of silver particles increases and the conductor film excellent in electroconductivity can be formed.
In addition, about the silver powder disclosed here, it is preferable that the ratio of the spherical silver particle of aspect ratio 1.5 or less is 60 number% or more of the whole silver powder. In other words, the nonspherical silver particles having an aspect ratio of less than 1.5 are preferably 40% by number or less of the silver particles constituting the silver powder. The spherical silver particles are more preferably 70% by number or more of the total silver powder, particularly preferably 80% by number or more, for example, 85% by number or more, or 90% by number or more. Since the silver powder is composed of particles having such a shape, the stability, surface smoothness, homogeneity, filling properties, etc. of the silver particles from when the silver paste is supplied to the base material until it is heat-treated are effective. Enhanced. Thereby, the filling property of silver particles, the surface smoothness of the conductive film to be formed, and the like are improved, and a conductive film having higher conductivity can be obtained.
　なお、上記のとおり、ここに開示される銀粉末の平均粒径は、ナノメートルオーダーであり比較的微細である。したがって、この程度の寸法の銀粉末は一般に凝集しやすいことから、銀粒子の表面に凝集を抑制する保護剤を備えることができる。典型的には、銀粉末（銀粒子）の表面は保護剤によって被覆されている。これにより、銀粒子の表面安定性を維持することができ、銀粒子同士の凝集を効率的に抑制することができる。その結果、ここに開示される銀ペーストは、溶剤中での銀粒子の凝集が抑制されて、長期間に亘って分散性良く安定して保存することができる。また、例えば銀ペーストを各種の印刷法により基材に供給する際にも、銀粒子の流動性が高められ、印刷性が良好になり得る。延いては、均質でムラの抑制された塗膜を形成することができる。 Note that, as described above, the average particle size of the silver powder disclosed herein is on the order of nanometers and is relatively fine. Therefore, since silver powder of this size is generally easy to aggregate, a protective agent that suppresses aggregation can be provided on the surface of the silver particles. Typically, the surface of silver powder (silver particles) is coated with a protective agent. Thereby, the surface stability of silver particles can be maintained, and aggregation of silver particles can be efficiently suppressed. As a result, the silver paste disclosed herein can be stably stored with good dispersibility over a long period of time because aggregation of silver particles in the solvent is suppressed. Further, for example, when silver paste is supplied to a substrate by various printing methods, the fluidity of silver particles can be improved and the printability can be improved. As a result, it is possible to form a coating film that is homogeneous and suppressed in unevenness.
　この表面保護剤の種類に特に制限はないが、低温で短時間での熱処理（焼成）により銀粒子の表面から焼失し得るとの観点から、保護剤は加熱処理に際して銀粒子の表面から脱離しやすいものであることが好ましい。保護剤は、例えば、大気圧での昇華点や沸点、分解温度が低く、銀と比較的弱い結合（例えば配位結合）を形成するものであることが好ましい。 The type of the surface protective agent is not particularly limited, but the protective agent is detached from the surface of the silver particles during the heat treatment from the viewpoint that it can be burned off from the surface of the silver particles by heat treatment (firing) in a short time at a low temperature. It is preferable that it is easy. For example, the protective agent preferably has a low sublimation point, boiling point and decomposition temperature at atmospheric pressure, and forms a relatively weak bond (for example, coordination bond) with silver.
　そこで、ここに開示される技術においては、保護剤が、炭素数５以下の有機アミンであることが好ましい。炭素数５以下の有機アミンの具体例としては、メチルアミン、エチルアミン、ｎ－プロピルアミン、イソプロピルアミン、ブチルアミン、ペンチルアミン、２－メトキシエチルアミン、２－エトキシエチルアミン、３－メトキシプロピルアミン、３－エトキシプロピルアミン等の第１級脂肪族アミン；ジメチルアミン、ジエチルアミン、メチルブチルアミン、エチルプロピルアミン、エチルイソプロピルアミン等の第２級脂肪族アミン；トリメチルアミン、ジメチルエチルアミン、ジエチルメチルアミン等の第３級脂肪族アミン；が例示される。有機アミンの炭素数は、３以上であることが好ましく、４以上であることがより好ましい。また、この有機アミンは、例えばメトキシ基やエトキシ基等のアルコキシ基を構造内に含んでいてもよい。これらの有機アミンは、いずれか１種が単独で用いられてもよいし、あるいは２種以上の組み合わせとして用いられていてもよい。これにより、上記の分散安定性をより好適に実現することができる。 Therefore, in the technique disclosed herein, the protective agent is preferably an organic amine having 5 or less carbon atoms. Specific examples of the organic amine having 5 or less carbon atoms include methylamine, ethylamine, n-propylamine, isopropylamine, butylamine, pentylamine, 2-methoxyethylamine, 2-ethoxyethylamine, 3-methoxypropylamine, 3-ethoxy Primary aliphatic amines such as propylamine; Secondary aliphatic amines such as dimethylamine, diethylamine, methylbutylamine, ethylpropylamine, and ethylisopropylamine; Tertiary aliphatics such as trimethylamine, dimethylethylamine, and diethylmethylamine An amine; The number of carbon atoms of the organic amine is preferably 3 or more, and more preferably 4 or more. The organic amine may contain an alkoxy group such as a methoxy group or an ethoxy group in the structure. Any one of these organic amines may be used alone or in combination of two or more. Thereby, said dispersion stability can be more suitably realized.
　なお、後述するが、基板に供給され乾燥された銀ペースト（塗膜）に対し低温で短時間の熱処理（焼成）を施すとき、焼成後の導電膜に高い導電性を発現させるためには、保護剤の残存量と銀粒子の熱収縮量とを小さく抑えることが重要である。そして保護剤の残存や銀粒子の熱収縮を低く抑えるためには、銀粉末における保護剤の割合を出来る限り少なくすることが有効であり得る。ここに開示される技術では、銀粒子の平均粒子径を上記範囲とすることで、従来に比べて顕著に低い保護剤の含有割合を実現している。具体的には、銀粉末（銀粒子部分）を１００質量部としたときに、保護剤の割合は１．２質量部以下とすることができる。換言すれば、銀粉末の９８．８質量部以上を銀粒子により構成することができる。保護剤の割合は、好ましくは１．１質量部以下であり、例えば１質量部以下であるとよい。これにより、低温で短時間の焼成であっても保護剤の残留と銀粒子の熱収縮とを効果的に抑制することができ、導電性に優れた塗膜を形成することができる。 As will be described later, when a short heat treatment (firing) is performed at a low temperature on the silver paste (coating film) supplied to the substrate and dried, in order to express high conductivity in the conductive film after firing, It is important to keep the remaining amount of the protective agent and the heat shrinkage amount of the silver particles small. In order to keep the remaining of the protective agent and the thermal shrinkage of the silver particles low, it can be effective to reduce the proportion of the protective agent in the silver powder as much as possible. In the technique disclosed herein, the content ratio of the protective agent is significantly reduced as compared with the prior art by setting the average particle diameter of the silver particles in the above range. Specifically, when the silver powder (silver particle part) is 100 parts by mass, the ratio of the protective agent can be 1.2 parts by mass or less. In other words, 98.8 parts by mass or more of the silver powder can be composed of silver particles. The proportion of the protective agent is preferably 1.1 parts by mass or less, for example, 1 part by mass or less. Thereby, even if it is baking for a short time at low temperature, the residual of a protective agent and the thermal contraction of silver particle can be suppressed effectively, and the coating film excellent in electroconductivity can be formed.
　また、ここに開示される銀ペーストについては、焼成の際にエロージョンガスを発生し得るような成分（腐食成分）を実質的に含まないことが好ましい。つまり、例えば銀粉末の製造工程や製造設備などに起因して、腐食成分が不可避的に混入することは許容し得るが、そのような腐食成分は意図して含まないことが好ましい。このような腐食成分としては、例えば、フッ素（Ｆ）や塩素（Ｃｌ）などのハロゲン成分、硫黄（Ｓ）成分などが挙げられる。これらの成分は、銀粉末自体に含まれないことが好ましく、また、保護剤に含まれないことも好ましい。銀ペーストがこのような腐食成分を実質的に含まないことで、半導体製造装置の腐食劣化や、半導体素子への異物混入、半導体素子の電極や基板等の変質を抑制できるために好ましい。また、さらに、鉛（Ｐｂ）成分やヒ素（Ａｓ）成分など、人体や環境に対して悪影響となり得る成分も含まないことが好ましい。例えば、これらフッ素（Ｆ），塩素（Ｃｌ），硫黄（Ｓ），鉛（Ｐｂ），ヒ素（Ａｓ）等の各腐食成分は、銀粉末を１００質量部としたときに、０．１質量部（１０００ｐｐｍ）以下に抑えられていることが好ましい。これらの腐食成分は、銀粉末を１００質量部としたときに、合計で０．１質量部（１０００ｐｐｍ）以下に抑えられていることが好ましい。 Moreover, it is preferable that the silver paste disclosed herein does not substantially contain a component (corrosive component) that can generate an erosion gas during firing. That is, for example, it is permissible for a corrosive component to be inevitably mixed due to a manufacturing process or a manufacturing facility of silver powder, but it is preferable that such a corrosive component is not intentionally included. Examples of such corrosive components include halogen components such as fluorine (F) and chlorine (Cl), sulfur (S) components, and the like. These components are preferably not contained in the silver powder itself, and are preferably not contained in the protective agent. It is preferable that the silver paste does not substantially contain such a corrosive component because corrosion deterioration of the semiconductor manufacturing apparatus, contamination of foreign matter into the semiconductor element, and alteration of the electrodes and substrate of the semiconductor element can be suppressed. Furthermore, it is preferable not to include components that may adversely affect the human body and the environment, such as lead (Pb) components and arsenic (As) components. For example, these corrosive components such as fluorine (F), chlorine (Cl), sulfur (S), lead (Pb), and arsenic (As) are 0.1 parts by mass when the silver powder is 100 parts by mass. It is preferable to be suppressed to (1000 ppm) or less. These corrosive components are preferably suppressed to 0.1 parts by mass (1000 ppm) or less in total when the silver powder is 100 parts by mass.
　（Ｂ）熱可塑性ポリエステル樹脂
　熱可塑性ポリエステル（polyester：ＰＥｓ）樹脂は、ここに開示される銀ペーストにおけるバインダ成分として機能する。この熱可塑性ポリエステル樹脂の含有により、ここに開示される銀ペーストは、加熱によりバインダが軟化し、その後の放熱（冷却）によりバインダが硬化して、銀粒子同士の結合と基板との接着がサポートされる。典型的には、焼結した銀粉末と基板との接合に寄与するものと考えられる。なお、ポリエステル樹脂には、熱硬化性のものと熱可塑性のものとが存在し、従来のこの種の銀ペーストでは、熱硬化性のポリエステル樹脂等がバインダとして使用されていた。これに対して、ここに開示される技術においては、上述のように熱可塑性のポリエステル樹脂の加熱による可逆的な可塑性の発現を利用して、バインダ機能を実現するようにしている。 (B) Thermoplastic polyester resin The thermoplastic polyester (polyester: PEs) resin functions as a binder component in the silver paste disclosed herein. Due to the inclusion of this thermoplastic polyester resin, the silver paste disclosed here softens the binder by heating, and the binder is cured by subsequent heat dissipation (cooling), thereby supporting the bonding between the silver particles and the adhesion to the substrate. Is done. Typically, it is considered that it contributes to the bonding between the sintered silver powder and the substrate. In addition, there exist a thermosetting thing and a thermoplastic thing in a polyester resin, The thermosetting polyester resin etc. were used as a binder in the conventional silver paste of this kind. On the other hand, in the technique disclosed herein, the binder function is realized by utilizing reversible plasticity expression by heating of the thermoplastic polyester resin as described above.
　なお上記のように、バインダとしての熱可塑性ポリエステル樹脂の挙動は、熱処理によって軟化し、その後の冷却により硬化する。
　ここで、（１）熱可塑性ポリエステル樹脂は、上記の銀粉末の焼結よりも前に軟化し、焼結よりも後に硬化することが、基材への密着性を高める観点で好ましい。換言すると、熱可塑性のポリエステル樹脂としては、銀粉末の焼結のための熱処理温度に対応して、相対的に低い適切なガラス転移点（Ｔｇ）を有するものを好ましく用いることができる。詳細は明らかではないが、このことにより、熱処理中に熱可塑性ポリエステル樹脂の殆どが軟化して銀粉末と基板との界面に到達し、銀粉末の焼結を阻害することなく、銀粉末と基板との結着に好適に寄与すると考えられる。 As described above, the behavior of the thermoplastic polyester resin as the binder is softened by heat treatment and hardened by subsequent cooling.
Here, (1) The thermoplastic polyester resin is preferably softened before the sintering of the silver powder and hardened after the sintering from the viewpoint of improving the adhesion to the substrate. In other words, as the thermoplastic polyester resin, those having a relatively low appropriate glass transition point (Tg) corresponding to the heat treatment temperature for sintering the silver powder can be preferably used. Although details are not clear, this allows most of the thermoplastic polyester resin to soften during the heat treatment and reach the interface between the silver powder and the substrate, without inhibiting the sintering of the silver powder and the substrate. It is thought that it contributes suitably to binding with.
　また、（２）熱可塑性ポリエステル樹脂は、銀粉末と同様に、熱処理や温度変化によって大きな体積変化が生じることは好ましくない。さらに、熱可塑性ポリエステル樹脂は、常温では硬化状態にあることから、後述の溶剤に可溶であることが好ましい。このような要求を好適に満たすものとして、熱可塑性ポリエステル樹脂としては、非晶性（非結晶性）のものを好ましく用いることができる。非晶性樹脂とは、硬化状態において、分子鎖に規則的な配列が見られず、分子鎖がランダムに混ざりあった構造を有する樹脂として理解することができる。非晶性の熱可塑性ポリエステル樹脂は、例えば、溶剤に可溶であり、ガラス転移点は有するが、明確な結晶融点を有さない化合物として把握することができる。 (2) As with the silver powder, it is not preferable that the thermoplastic polyester resin undergoes a large volume change due to heat treatment or temperature change. Furthermore, since the thermoplastic polyester resin is in a cured state at normal temperature, it is preferable that the thermoplastic polyester resin is soluble in a solvent described later. As a thermoplastic polyester resin that preferably satisfies such requirements, an amorphous (non-crystalline) resin can be preferably used. An amorphous resin can be understood as a resin having a structure in which molecular chains are not randomly mixed in a cured state and molecular chains are randomly mixed. Amorphous thermoplastic polyester resin is, for example, soluble in a solvent and has a glass transition point, but can be understood as a compound having no clear crystalline melting point.
　熱可塑性ポリエステル樹脂のガラス転移点は、基板を構成する材料の耐熱温度にもよるため一概には言えないが、例えば、銀粉末の焼結のための熱処理温度（例えば１４０℃以下、典型的には、１１０℃～１３５℃程度）よりも十分に低い温度であることが好ましい。好適な一例として、例えば、熱処理温度よりも２０℃以上（例えば２０℃～５０℃程度）低い温度であることが好ましい。かかる観点から、ガラス転移点は、９０℃以下が好ましく、８５℃以下がより好ましく、８０℃以下が特に好ましい。その一方で、熱可塑性ポリエステル樹脂のガラス転移点は、銀ペースト中の溶剤がほぼ揮発する温度、例えば、銀ペーストの乾燥温度よりも高いことが好ましい。例えば、乾燥温度よりも２０℃程度高いことが好ましい。かかる観点から、ガラス転移点は、６０℃以上（６０℃超過）が好ましく、６３℃以上がより好ましく、６５℃以上が特に好ましい。このようなガラス転移点は、一般に使用されている熱可塑性ポリエステル樹脂の中では比較的高い部類に属するものである。例えば、ＰＥＴ等の樹脂基板用のバインダ類としては極めて高い温度であるといえる。 Although the glass transition point of the thermoplastic polyester resin depends on the heat resistance temperature of the material constituting the substrate, it cannot be generally stated. For example, a heat treatment temperature for sintering silver powder (for example, 140 ° C. or lower, typically Is preferably a temperature sufficiently lower than about 110 ° C. to 135 ° C.). As a suitable example, it is preferable that the temperature is 20 ° C. or more (for example, about 20 ° C. to 50 ° C.) lower than the heat treatment temperature. From this viewpoint, the glass transition point is preferably 90 ° C. or lower, more preferably 85 ° C. or lower, and particularly preferably 80 ° C. or lower. On the other hand, the glass transition point of the thermoplastic polyester resin is preferably higher than the temperature at which the solvent in the silver paste is almost volatilized, for example, the drying temperature of the silver paste. For example, it is preferably about 20 ° C. higher than the drying temperature. From this viewpoint, the glass transition point is preferably 60 ° C. or higher (over 60 ° C.), more preferably 63 ° C. or higher, and particularly preferably 65 ° C. or higher. Such a glass transition point belongs to a relatively high class among commonly used thermoplastic polyester resins. For example, it can be said that the temperature is extremely high as a binder for resin substrates such as PET.
　このような熱可塑性ポリエステル樹脂としては、当該樹脂を構成する繰返し単位として、ポリカルボン酸とポリアルコールとが縮重合したポリエステル系構造を主成分または主モノマーとして含む各種の化合物を用いることができる。
　なお、「主成分」とは、熱可塑性ポリエステル樹脂の主たる骨格を構成する繰返し単位のうち、質量基準で最も多く含まれる繰返し単位に対応するモノマー成分を意味する。この主成分は、好ましくは、熱可塑性ポリエステル樹脂に５０質量％を超えて含まれるモノマー成分であり得る。 As such a thermoplastic polyester resin, various compounds containing, as a main component or a main monomer, a polyester-based structure obtained by polycondensation of a polycarboxylic acid and a polyalcohol can be used as a repeating unit constituting the resin.
The “main component” means a monomer component corresponding to the repeating unit that is contained most on a mass basis among the repeating units constituting the main skeleton of the thermoplastic polyester resin. This main component may preferably be a monomer component contained in the thermoplastic polyester resin in an amount exceeding 50 mass%.
　ポリエステル系構造を構成するポリカルボン酸に対応するモノマー成分は特に限定されない。かかるポリカルボン酸としては、非環式ポリカルボン酸であってもよいし、飽和または不飽和の脂環式ポリカルボン酸であってもよい。例えば、シュウ酸、マロン酸、コハク酸、グルタル酸、アジピン酸、酒石酸、グルタミン酸、セバシン酸、ドデカン二酸、ブラシル酸、ダイマー酸などの脂肪族二塩基酸；フランジカルボン酸、ジフェニルジカルボン酸、１，４－シクロヘキサンジカルボン酸などの脂環式ジカルボン酸；フタル酸、イソフタル酸、テレフタル酸、ナフタレンジカルボン酸などの芳香族二塩基酸等の二塩基酸等が好適例として挙げられる。なかでも、芳香族二塩基酸であることが好ましい。また、ポリエステル系構造を構成するポリアルコールに対応するモノマー成分についても特に限定されない。ポリアルコールとしては、例えば、脂肪族ポリアルコール、脂環式ポリアルコール、芳香族ポリアルコール等が挙げられる。高い接着性が得られるとの観点において、脂肪族または脂環式ジオールが好ましい。ポリアルコールに対応するモノマー成分としては、具体的には、例えば、エチレングリコール、プロピレングリコール、トリメチレングリコール、１，２－ブタンジオール、１，３－ブタンジオール、１，４－シクロヘキサンジメタノール等のジオール類であることが好ましい。これらは側鎖に脂環骨格を有するものであってもよいし、かかる脂環骨格を側鎖に有さないものであってもよい。 The monomer component corresponding to the polycarboxylic acid constituting the polyester structure is not particularly limited. Such a polycarboxylic acid may be an acyclic polycarboxylic acid or a saturated or unsaturated alicyclic polycarboxylic acid. For example, aliphatic dibasic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, glutamic acid, sebacic acid, dodecanedioic acid, brassylic acid, dimer acid; furandicarboxylic acid, diphenyldicarboxylic acid, 1 Preferred examples include alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; dibasic acids such as aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Of these, an aromatic dibasic acid is preferable. Moreover, it does not specifically limit about the monomer component corresponding to the polyalcohol which comprises a polyester-type structure. Examples of the polyalcohol include aliphatic polyalcohol, alicyclic polyalcohol, and aromatic polyalcohol. In view of obtaining high adhesiveness, an aliphatic or alicyclic diol is preferable. Specific examples of the monomer component corresponding to the polyalcohol include ethylene glycol, propylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-cyclohexanedimethanol and the like. Diols are preferred. These may have an alicyclic skeleton in the side chain, or may not have such an alicyclic skeleton in the side chain.
　また、上記熱可塑性ポリエステル樹脂としては、例えば、ポリエステル系構造を主モノマーとして含み、この主モノマーと共重合性を有する副モノマーをさらに含み得るモノマー原料の重合物であってもよい。ここで主モノマーとは、上記モノマー原料におけるモノマー組成の５０重量％超を占める成分をいう。主モノマーは、例えば、上記に例示した二塩基酸に代表されるポリカルボン酸と、ジオール類に代表されるポリオールとのエステルであり得る。また他の一例として、主モノマーは、テレフタル酸とエチレングリコールとの重縮合反応物（ＰＥＴ系主モノマー）、テレフタル酸とブタンジオールとの重縮合反応物（ＰＢＴ系主モノマー）、ナフタレンジカルボン酸とエチレングリコールとの重縮合反応物（ＰＥＮ系主モノマー）、ナフタレンジカルボン酸とブタンジオールとの重縮合反応物（ＰＢＮ系主モノマー）であり得る。これらの主モノマーは、いずれか１種のみが単独でまたは２種以上が組み合わされて含まれていてもよい。 The thermoplastic polyester resin may be, for example, a polymer of a monomer raw material that includes a polyester-based structure as a main monomer and can further include a submonomer that is copolymerizable with the main monomer. Here, the main monomer means a component occupying more than 50% by weight of the monomer composition in the monomer raw material. The main monomer can be, for example, an ester of a polycarboxylic acid typified by the dibasic acid exemplified above and a polyol typified by a diol. As another example, the main monomer is a polycondensation reaction product of terephthalic acid and ethylene glycol (PET main monomer), a polycondensation reaction product of terephthalic acid and butanediol (PBT main monomer), naphthalene dicarboxylic acid, It may be a polycondensation reaction product (PEN main monomer) with ethylene glycol or a polycondensation reaction product (PBN main monomer) of naphthalenedicarboxylic acid and butanediol. Any one of these main monomers may be contained alone or in combination of two or more.
　副モノマーとしては、ポリエステル系構造に架橋点を導入したり、ポリエステル系構造の接着力を高めたりし得る成分が好ましい。副モノマーとしては、例えば、モノカルボン酸，ジカルボン酸およびその無水物等に代表されるカルボキシ基含有モノマー；ヒドロキシアルキル（メタ）アクリレート化合物，アルコール化合物，エーテル系化合物，ポリエーテル系化合物等に代表される水酸基含有モノマー；（メタ）アクリルアミド等に代表されるアミド基含有モノマー；（メタ）アクリロイルイソシアネートに代表されるイソシアネート基含有モノマー；スチレン化合物、フェニルエーテル化合物等に代表されるフェニル基含有モノマー等が挙げられる。これらの副モノマーは、１種のみが単独でまたは２種以上が組み合わされて含まれていてもよい。 As the secondary monomer, a component capable of introducing a crosslinking point into the polyester structure or enhancing the adhesive force of the polyester structure is preferable. As the secondary monomer, for example, a carboxy group-containing monomer typified by monocarboxylic acid, dicarboxylic acid and its anhydride, etc .; typified by hydroxyalkyl (meth) acrylate compound, alcohol compound, ether compound, polyether compound, etc. Hydroxyl group-containing monomers; amide group-containing monomers represented by (meth) acrylamide; isocyanate group-containing monomers represented by (meth) acryloyl isocyanate; phenyl group-containing monomers represented by styrene compounds, phenyl ether compounds, etc. Can be mentioned. These submonomers may be contained alone or in combination of two or more.
　また、熱可塑性ポリエステル樹脂は、硬化後に適度な柔軟性を備えることが好ましい。したがって、硬化後の柔軟性や接着性などを向上させる等の目的で、架橋剤や架橋助剤等の成分を含んでいてもよい。このような架橋剤、架橋助剤としては、例えば、イソシアネート化合物、多官能性メラミン化合物、多官能性エポキシ化合物、ポリヒドロキシ化合物等であってよい。具体的には、例えば、脂肪族ポリイソシアネート類、脂環族ポリイソシアネート類、芳香族ポリイソシアネート類、芳香脂肪族ポリイソシアネート類、ポリヒドロキシ化合物類などが挙げられる。架橋剤および架橋助剤は、１種を単独でまたは２種以上を組み合わせて使用することができる。 Further, it is preferable that the thermoplastic polyester resin has appropriate flexibility after curing. Therefore, components such as a crosslinking agent and a crosslinking aid may be included for the purpose of improving the flexibility and adhesiveness after curing. Examples of such crosslinking agents and crosslinking aids may include isocyanate compounds, polyfunctional melamine compounds, polyfunctional epoxy compounds, polyhydroxy compounds, and the like. Specific examples include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, araliphatic polyisocyanates, polyhydroxy compounds, and the like. A crosslinking agent and a crosslinking aid can be used individually by 1 type or in combination of 2 or more types.
　なお、導電膜の化学的および光化学的安定性を高めるために、副モノマーや架橋剤および架橋助剤等は、熱可塑性ポリエステル樹脂に不飽和基を導入しない化学構造のものであることが好ましい。すなわち、熱可塑性ポリエステル樹脂は、飽和共重合ポリエステルであることが好ましい。これにより、フレキシブルフィルム基板として汎用されているＰＥＴフィルム基板への接着性が特に高められるために好ましい。 In addition, in order to improve the chemical and photochemical stability of the conductive film, it is preferable that the secondary monomer, the crosslinking agent, the crosslinking auxiliary agent, and the like have a chemical structure that does not introduce an unsaturated group into the thermoplastic polyester resin. That is, the thermoplastic polyester resin is preferably a saturated copolymer polyester. Thereby, since the adhesiveness to the PET film board | substrate currently used widely as a flexible film board | substrate is improved especially, it is preferable.
　上記の熱可塑性ポリエステル樹脂を用いる場合、数平均分子量（Ｍｎ）は特に限定されないが、数平均分子量が２０００未満であると、バインダとして必要な接着性および／または粘着性を発現することが困難な場合があるため好ましくない。かかる観点から、数平均分子量は、２０００以上が好ましく、５０００以上がより好ましく、１万以上がさらに好ましい。一方で、熱可塑性ポリエステル樹脂の数平均分子量が１０万を超えると、溶剤への溶解性が極端に低下して印刷性に劣るなどの問題が生じる場合がある。かかる観点から、数平均分子量は１０万以下が好ましく、５万以下が、さらに好ましくは１万以上３万以下であってよい。このような数平均分子量は、一般に使用されている非晶性の熱可塑性ポリエステル樹脂の中では比較的高い部類に属する。 When the above thermoplastic polyester resin is used, the number average molecular weight (Mn) is not particularly limited. However, when the number average molecular weight is less than 2000, it is difficult to express adhesiveness and / or tackiness required as a binder. Since there are cases, it is not preferable. From this viewpoint, the number average molecular weight is preferably 2000 or more, more preferably 5000 or more, and still more preferably 10,000 or more. On the other hand, when the number average molecular weight of the thermoplastic polyester resin exceeds 100,000, there may be a problem that the solubility in a solvent is extremely lowered and the printability is poor. From this viewpoint, the number average molecular weight is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 10,000 or more and 30,000 or less. Such a number average molecular weight belongs to a relatively high class among the amorphous thermoplastic polyester resins generally used.
　なお、熱可塑性ポリエステル樹脂における上記の柔軟性および接着性並びに溶剤可溶性等の特性は、本明細書の開示に触れた当業者であれば、使用するフィルム基材に応じて、主モノマーと副モノマーとの組み合わせやその配合量、ならびに、ガラス転移点および分子量等の調整を通じて、適宜に設計し調合することができる。
　また、このような熱可塑性ポリエステル樹脂は、市販品を入手して利用することもできる。かかる市販品の一例としては、例えば、ユニチカ（株）製のエリーテル（登録商標）ＵＥ３２００，ＵＥ９２００，ＵＥ３２０１，ＵＥ３２０３，ＵＥ３６００，ＵＥ９６００，ＵＥ３６６０，ＵＥ３６９０、日本合成化学工業（株）製のポリエスター（登録商標）ＴＰ２３６，ＴＰ２２０，ＴＰ２３５、Ｅｖｏｎｉｋ Ｉｎｄｕｓｔｒｉｅｓ ＡＧ社製のＤｙｎａｐｏｌ（登録商標）Ｌ２０５，Ｌ２０６，Ｌ２０８，Ｌ９５２，Ｌ９０７、Ｂｏｓｔｉｋ社製のＶＩＴＥＬ（登録商標）２１００，２２００等が挙げられる。 In addition, the above-mentioned properties such as flexibility and adhesiveness and solvent solubility in the thermoplastic polyester resin can be obtained by those skilled in the art who have touched the disclosure of the present specification, depending on the film substrate used. Can be appropriately designed and blended through adjustment of the combination and the blending amount thereof, and the adjustment of the glass transition point and molecular weight.
Moreover, such a thermoplastic polyester resin can also be obtained by using a commercially available product. Examples of such commercially available products include, for example, Elitel (registered trademark) UE3200, UE9200, UE3201, UE3203, UE3600, UE9600, UE3660, UE3690 manufactured by Unitika Ltd., and Polyester (registered by Nippon Synthetic Chemical Industry Co., Ltd.). Trademarks) TP236, TP220, TP235, Dynapol (registered trademark) L205, L206, L208, L952, L907 manufactured by Evonik Industries AG, VITEL (registered trademark) 2100, 2200 manufactured by Bostik, and the like.
　なお、上記の熱可塑性ポリエステル樹脂は、銀粉末の焼結体を含む導電膜に十分な柔軟性と接着性とを付与するために、上記の銀粉末１００質量部に対して、５質量部以上の割合で含まれることが肝要である。熱可塑性ポリエステル樹脂は、５．３質量部以上であることがより好ましく、５．５質量部以上であることが特に好ましい。
　一方で、熱可塑性ポリエステル樹脂は絶縁性を示すことから、銀ペースト中での含有量はできる限り少なく抑えることが好ましい。かかる観点から、熱可塑性ポリエステル樹脂の含有量は、銀粉末１００質量部に対して、８質量部以下であることが好ましく７．８質量部以下がより好ましく、７．５質量部以下が特に好ましい。 In addition, in order to provide sufficient softness | flexibility and adhesiveness to the electrically conductive film containing the sintered compact of silver powder, said thermoplastic polyester resin is 5 mass parts or more with respect to 100 mass parts of said silver powder. It is important to be included in the ratio. The thermoplastic polyester resin is more preferably 5.3 parts by mass or more, and particularly preferably 5.5 parts by mass or more.
On the other hand, since the thermoplastic polyester resin exhibits insulating properties, it is preferable to suppress the content in the silver paste as much as possible. From this viewpoint, the content of the thermoplastic polyester resin is preferably 8 parts by mass or less, more preferably 7.8 parts by mass or less, and particularly preferably 7.5 parts by mass or less with respect to 100 parts by mass of the silver powder. .
　（Ｃ）溶剤
　溶剤としては、上記の（Ｂ）熱可塑性ポリエステル樹脂を溶解させ得る各種の溶剤を用いることができる。また、銀ペーストの固形分たる上記銀粉末を分散させる機能をも有する。この溶剤については特に制限はないが、例えば、上記の（Ａ）銀粉末および（Ｂ）熱可塑性ポリエステル樹脂を組み合わせて使用する銀ペーストの焼成を好適に実現し、導電性に優れた導電膜を作製し得る、との観点から、沸点が１８０℃以上２５０℃以下の溶剤であることが好ましい。また、分子構造にフェニル基を含むことが好ましい。 (C) Solvent As the solvent, various solvents capable of dissolving the above-mentioned (B) thermoplastic polyester resin can be used. Moreover, it has the function to disperse | distribute the said silver powder which is solid content of a silver paste. Although there is no restriction | limiting in particular about this solvent, For example, baking of the silver paste used combining said (A) silver powder and (B) thermoplastic polyester resin suitably implement | achieves, and the electrically conductive film excellent in electroconductivity is obtained. From the viewpoint that it can be produced, a solvent having a boiling point of 180 ° C. or higher and 250 ° C. or lower is preferable. Moreover, it is preferable that a phenyl group is included in molecular structure.
　溶剤は、沸点が１８０℃以上の高沸点溶剤であることで、例えば、任意の基材に印刷法により連続的に銀ペーストを供給する際に、溶剤が揮発して銀ペーストの性状が変化してしまうことを抑制することができる。銀ペーストの基材への供給前の溶剤の揮発は、銀ペーストの粘度を上昇させて印刷条件を不安定にさせたり、銀ペースト中の銀粉末の含有率を上昇させて形成される導電膜の膜厚にばらつきをもたらしたりするために好ましくない。また、溶剤の沸点が２５０℃以下であることで、銀粉末の焼結のための熱処理温度よりも十分に低い温度で、溶剤を短時間で速やかに揮発させることができる。また、この溶剤の沸点が２５０℃を超過すると、銀ペーストを乾燥して得られる塗膜に溶剤成分が残留しがちとなり、好適な成膜が行い難くなるために好ましくない。 The solvent is a high boiling point solvent having a boiling point of 180 ° C. or higher. For example, when the silver paste is continuously supplied to an arbitrary substrate by a printing method, the solvent volatilizes and the property of the silver paste changes. Can be suppressed. The volatilization of the solvent before the supply of the silver paste to the base material increases the viscosity of the silver paste to make the printing conditions unstable, or the conductive film formed by increasing the silver powder content in the silver paste. This is not preferable because it causes variations in the film thickness. Further, when the boiling point of the solvent is 250 ° C. or lower, the solvent can be volatilized quickly in a short time at a temperature sufficiently lower than the heat treatment temperature for sintering the silver powder. On the other hand, if the boiling point of the solvent exceeds 250 ° C., the solvent component tends to remain in the coating film obtained by drying the silver paste, making it difficult to form a suitable film.
　また、溶剤が分子構造にフェニル基を含むことで、上記の熱可塑性ポリエステル樹脂の溶解性が高まるとともに、印刷に適したペースト性状を調整しやすいために好ましい。すなわち、溶剤がフェニル基を含むことで、非水性である熱可塑性ポリエステル樹脂に対する親和性が高まり、熱力学的に安定して酸化・還元を受けにくい。また、剛性を示すフェニル環の存在により、銀ペーストに対して適度な粘性を安定して好適に付与することができる。その結果、銀ペーストを基材に供給する際に、作業性や印刷安定性の高い銀ペーストの調製を可能としている。延いては、均質な塗膜（導電膜をも含む。）を安定的に形成することができる。分子構造におけるフェニル基の数は１つであってよい。 Further, it is preferable that the solvent contains a phenyl group in the molecular structure, since the solubility of the thermoplastic polyester resin is increased and the paste properties suitable for printing can be easily adjusted. That is, when the solvent contains a phenyl group, the affinity for the non-aqueous thermoplastic polyester resin is increased, and the solvent is thermodynamically stable and hardly oxidized or reduced. Further, due to the presence of the phenyl ring exhibiting rigidity, an appropriate viscosity can be stably and suitably imparted to the silver paste. As a result, when the silver paste is supplied to the base material, it is possible to prepare a silver paste with high workability and printing stability. As a result, a homogeneous coating film (including a conductive film) can be stably formed. The number of phenyl groups in the molecular structure may be one.
　このように、適切な溶剤を用いて銀ペーストを調整することにより、銀ペーストの性状を安定に保ちながら、該銀ペーストを印刷法により基材に供給することができる。このことは、今後の電子素子の製造において、例えば、ロールｔｏロールプロセスが全面的に採用された際に極めて有利な特性となり得る。なお、溶剤の沸点と揮発性とは厳密には一致しないものの、ここに開示される銀ペーストの用途と使用する溶剤の特性とを考慮すると、溶剤の沸点を基にして揮発性を把握しても差し支えないと言える。 Thus, by adjusting the silver paste using an appropriate solvent, the silver paste can be supplied to the substrate by a printing method while keeping the properties of the silver paste stable. This can be a very advantageous characteristic in the future production of electronic devices, for example, when a roll-to-roll process is fully employed. Although the boiling point and volatility of the solvent are not exactly the same, considering the use of the silver paste disclosed here and the characteristics of the solvent used, the volatility is determined based on the boiling point of the solvent. It can be said that there is no problem.
　このような溶剤としては、上記の沸点を満足し、フェニル基を含む非水性の溶剤を特に制限なく用いることができる。かかる溶剤の一例として、例えば、エチレングリコールモノフェニルエーテル（２４５℃），プロピレングリコールモノフェニルエーテル（２４３℃）等に代表されるオキシアルキレンモノフェニルエーテル；メチルフェニルエーテル（１５４℃），エチルフェニルエーテル（１８４℃），ブチルフェニルエーテル（２１０℃），メチルフェニルエチルエーテル（１８４℃）等に代表されるアルキルフェニルエーテル；ベンジルアルコール（２０５℃），イソホロン（２１５℃），ベンズアルデヒド（１７９℃），酢酸ベンジル（２１２℃）等に代表されるベンゼン類；等が挙げられる。なお、上記バインダの溶解性を考慮すると、分子構造におけるアルキル基の鎖長は短いことが好ましい。例えば、溶剤の分子構造において、アルキル基の直鎖の炭素数は３以下が好ましい。 As such a solvent, a non-aqueous solvent that satisfies the above boiling point and contains a phenyl group can be used without particular limitation. Examples of such solvents include, for example, oxyalkylene monophenyl ethers typified by ethylene glycol monophenyl ether (245 ° C.), propylene glycol monophenyl ether (243 ° C.), etc .; methyl phenyl ether (154 ° C.), ethyl phenyl ether ( 184 ° C.), butyl phenyl ether (210 ° C.), alkylphenyl ether represented by methyl phenyl ethyl ether (184 ° C.), etc .; benzyl alcohol (205 ° C.), isophorone (215 ° C.), benzaldehyde (179 ° C.), benzyl acetate Benzenes represented by (212 ° C.) and the like. In consideration of the solubility of the binder, the chain length of the alkyl group in the molecular structure is preferably short. For example, in the molecular structure of the solvent, the linear carbon number of the alkyl group is preferably 3 or less.
　なお、非水性の分散媒においては、疎水性相互作用やイオンによる界面吸着、静電反発効果等が抑制される。その一方で、分散質としての銀粉末に使用される保護剤の種類によっては、極性の高い溶媒の使用は保護剤を浸食してしまうために好ましくない。したがって、溶剤としては、分散質としての銀粉末の表面特性に適した分散能を有する溶剤を選択することも好適である。また、例えば、ここで使用する銀粉末の大きさが上記のとおりサブナノメートルサイズであることから、分散剤を用いての分散性の向上効果は期待できないか困難となることが予想される。したがって、銀粉末の分散安定化の観点から、溶剤としては、分散剤の使用なく銀粉末を好適に分散し得る溶剤を好ましく用いることができる。かかる観点から、溶剤としては、上記のオキシアルキレンモノフェニルエーテルの使用が特に好適である。 In a non-aqueous dispersion medium, hydrophobic interaction, interfacial adsorption by ions, electrostatic repulsion effect, and the like are suppressed. On the other hand, depending on the type of the protective agent used for the silver powder as the dispersoid, the use of a highly polar solvent is not preferable because the protective agent is eroded. Therefore, it is also preferable to select a solvent having a dispersibility suitable for the surface characteristics of the silver powder as the dispersoid. For example, since the size of the silver powder used here is a sub-nanometer size as described above, it is expected that the effect of improving the dispersibility using the dispersant cannot be expected or becomes difficult. Therefore, from the viewpoint of stabilizing the dispersion of the silver powder, a solvent capable of suitably dispersing the silver powder without using a dispersant can be preferably used as the solvent. From this point of view, it is particularly preferable to use the above oxyalkylene monophenyl ether as the solvent.
　銀ペーストにおける（Ｃ）溶剤の割合は、熱可塑性ポリエステル樹脂を溶解し得る量であれば、その他は特に制限されない。例えば、銀ペーストを基材に供給する際の作業性、供給性が良好となるよう、供給手法に応じて適宜調整することができる。例えば、銀ペーストを印刷法により基材に供給する場合は、おおよその目安として、銀粉末の割合が、銀ペースト全体の約５０質量％以上とすることができ、６０質量％以上が好ましく、例えば７０質量％以上であってよい。また、銀粉末の割合は、銀ペースト全体の９０質量％以下とすることができ、８５質量％以下が好ましく、例えば８０質量％以下となるように調製することが例示される。また、溶剤の割合としては、銀ペースト全体の約１０質量％以上とすることができ、１５質量％以上が好ましく、例えば２０質量％以上であってよい。また、溶剤の割合は、銀ペースト全体の５０質量％以下とすることができ、４０質量％以下が好ましく、例えば３０質量％以下であってよい。このように銀粉末の占める割合を高めることで、導電膜の緻密性を向上させることができる。その結果、低温で短時間の焼成であっても、導電性に優れる導電膜を安定して形成することができる。また、比較的薄い（例えば厚みが３μｍ以下の）導電膜を形成する場合においても、ムラのない均質な導電膜を形成することができる。 The ratio of the (C) solvent in the silver paste is not particularly limited as long as it is an amount capable of dissolving the thermoplastic polyester resin. For example, it can be appropriately adjusted according to the supply method so that the workability and supply performance when supplying the silver paste to the substrate are good. For example, when supplying a silver paste to a substrate by a printing method, as a rough guide, the ratio of the silver powder can be about 50% by mass or more of the entire silver paste, preferably 60% by mass or more. It may be 70% by mass or more. Moreover, the ratio of a silver powder can be 90 mass% or less of the whole silver paste, 85 mass% or less is preferable, for example, preparing so that it may become 80 mass% or less is illustrated. Moreover, as a ratio of a solvent, it can be set as about 10 mass% or more of the whole silver paste, 15 mass% or more is preferable, for example, it may be 20 mass% or more. Moreover, the ratio of a solvent can be 50 mass% or less of the whole silver paste, 40 mass% or less is preferable, for example, it may be 30 mass% or less. Thus, by increasing the proportion of silver powder, the denseness of the conductive film can be improved. As a result, a conductive film having excellent conductivity can be stably formed even when baking is performed at a low temperature for a short time. Further, even when a relatively thin conductive film (for example, having a thickness of 3 μm or less) is formed, a uniform conductive film without unevenness can be formed.
　（Ｄ）その他の成分
　ここに開示される銀ペーストは、本質的に、上記の（Ａ）銀粉末、（Ｂ）熱可塑性ポリエステル樹脂および（Ｃ）溶剤以外の成分を含む必要はない。しかしながら、本願の目的を逸脱しない範囲において、上述した（Ａ）銀粉末と、（Ｂ）熱可塑性ポリエステル樹脂と、（Ｃ）溶剤の他に、種々の成分の含有は許容される。これらの成分としては、フレキシブル基板用銀ペーストの性状を改善する目的で添加される添加剤や、硬化物としての導電膜の特性を改善する目的で添加される添加剤等を考慮することができる。一例として、界面活性剤、分散剤、充填材（有機充填材、無機充填材）、粘度調整剤、消泡剤、可塑剤、安定剤、酸化防止剤、防腐剤等が挙げられる。これらの添加剤（化合物）は１種が単独で含まれていてもよく、２種以上が組み合わせて含まれていてもよい。しかしながら、（Ａ）銀粉末の焼結と（Ｂ）熱可塑性ポリエステル樹脂によるバインダ性能とを阻害する成分や、これらを阻害するような量での添加剤の含有は好ましくない。かかる観点から、例えば、不適切な銀粒子の保護剤や、無機充填材の含有は好ましくない。また、添加剤を含む場合は、これらの成分の総含有量が、銀ペースト全体の約５質量％以下であるのが好ましく、３質量％以下がより好ましく、１質量％以下が特に好ましい。 (D) Other component The silver paste disclosed here does not need to contain components other than said (A) silver powder, (B) thermoplastic polyester resin, and (C) solvent essentially. However, in the range which does not deviate from the purpose of the present application, the inclusion of various components in addition to the above-mentioned (A) silver powder, (B) thermoplastic polyester resin, and (C) solvent is allowed. As these components, an additive added for the purpose of improving the properties of the silver paste for a flexible substrate, an additive added for the purpose of improving the properties of the conductive film as a cured product, and the like can be considered. . Examples include surfactants, dispersants, fillers (organic fillers, inorganic fillers), viscosity modifiers, antifoaming agents, plasticizers, stabilizers, antioxidants, preservatives, and the like. One of these additives (compounds) may be contained alone, or two or more thereof may be contained in combination. However, it is not preferable to contain components that inhibit (A) sintering of silver powder and (B) binder performance by the thermoplastic polyester resin, and additives in amounts that inhibit these components. From such a viewpoint, for example, an inappropriate silver particle protective agent or inorganic filler is not preferable. When the additive is included, the total content of these components is preferably about 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 1% by mass or less based on the total silver paste.
　フレキシブル基板用銀ペーストは、上記構成成分を所定の割合で配合し、均一に混合および混練することで、調製することができる。混合に際しては、各構成材料を同時に混合してもよいが、例えば、（Ｂ）熱可塑性ポリエステル樹脂と（Ｃ）溶剤とを混合してベヒクルを調製したのち、かかるベヒクルに（Ａ）銀粉末を混ぜ込むようにしてもよい。その他の添加剤を添加する場合は、その添加のタイミングに特に制限はない。混合には、例えば３本ロールミルを使用することができる。 The silver paste for flexible substrates can be prepared by blending the above components in a predetermined ratio, and uniformly mixing and kneading. In mixing, each constituent material may be mixed at the same time. For example, after (B) a thermoplastic polyester resin and (C) solvent are mixed to prepare a vehicle, (A) silver powder is added to the vehicle. You may make it mix. When other additives are added, there is no particular limitation on the timing of the addition. For mixing, for example, a three-roll mill can be used.
　このように調製されたフレキシブル基板用銀ペーストは、例えば、従来に比べて低い温度（典型的には１４０℃以下、例えば１１０～１３５℃）で硬化させることができる。そしてフレキシブル基板用銀ペーストを任意の基板上に所望のパターンで供給したのち、硬化させることで、基板上に所望のパターンの導電膜（硬化物）を形成することができる。 The silver paste for a flexible substrate thus prepared can be cured at a lower temperature (typically 140 ° C. or lower, for example, 110 to 135 ° C.), for example. And after supplying the silver paste for flexible substrates with a desired pattern on arbitrary board | substrates and making it harden | cure, the electrically conductive film (hardened | cured material) of a desired pattern can be formed on a board | substrate.
［導電膜］
　なお、この導電膜は、バインダとして上記の熱可塑性エポキシ樹脂を使用していることから、導電膜自体がフレキシブル性を備えている。導電膜の平均厚みは、厳密には限定されない。しかしながら、フレキシブル基板に対して成膜された場合であって、基板を湾曲させたときの導電膜の接着性および基板追随性を優れたものとするためには、導電膜の厚みを３μｍ以下とすることが好ましい。このように導電膜の厚みを制御することで、基板を繰り返し湾曲させた場合はもとより、基板を繰り返し折り曲げた場合においても、基材に対する優れた密着性を維持することができる。 [Conductive film]
In addition, since this electrically conductive film uses said thermoplastic epoxy resin as a binder, electrically conductive film itself is provided with flexibility. The average thickness of the conductive film is not strictly limited. However, in order to improve the adhesion of the conductive film and the substrate followability when the substrate is bent, the thickness of the conductive film is 3 μm or less. It is preferable to do. By controlling the thickness of the conductive film in this manner, excellent adhesion to the base material can be maintained not only when the substrate is repeatedly bent but also when the substrate is repeatedly bent.
　また、導電膜の導電性を優れたものとするためには、導電膜の厚みを０．２μｍ以上とすることが好ましい。これにより、銀粉末が厚み方向で積層して導電膜を構成することができ、良好な導電パスを形成することができる。このような導電膜の導電性は、導電膜の形状や厚みにもよるため一概には言えないが、例えば、導電膜の厚みを１０μｍに換算したときのシート抵抗が１００ｍΩ／□以下のものとして得ることができる。シート抵抗は、例えば、８０ｍΩ／□以下とすることができ、好ましくは６０ｍΩ／□以下とすることができる。 In order to make the conductive film excellent in conductivity, the thickness of the conductive film is preferably 0.2 μm or more. Thereby, silver powder can be laminated | stacked on the thickness direction, a conductive film can be comprised, and a favorable conductive path can be formed. Although the conductivity of such a conductive film depends on the shape and thickness of the conductive film, it cannot be generally stated. For example, the sheet resistance when the thickness of the conductive film is converted to 10 μm is 100 mΩ / □ or less. Obtainable. The sheet resistance can be, for example, 80 mΩ / □ or less, and preferably 60 mΩ / □ or less.
［基板］
　ここに開示されるフレキシブル基板用銀ペーストが適用される基板としては、その材質は厳密には制限されない。例えば、ポリマー（プラスチック）、紙、布等からなる薄層（フィルム）状であって、柔軟性を有する基板を対象とする場合に、ここに開示される銀ペーストの優れた特性が顕著に発現されるために好ましい。フレキシブルフィルム基板（以下、単に「フレキシブル基板」という場合がある。）としては、通常、ポリエチレンテレフタレート（ＰＥＴ）等のポリエステル樹脂、ポリプロピレン、エチレン－プロピレン共重合体等のポリオレフィン樹脂、ポリイミド樹脂、ポリ塩化ビニル等の熱可塑性樹脂からなるポリマーフィルムが好適に用いられている。これらの基材は、単層、複層のいずれの形態を有していてもよい。複層である場合は、異なる素材のフィルム基材が貼り合わされていてもよいし、同種の素材のフィルム基材が貼り合わされていてもよい。かかるフレキシブル基板は、部品などを実装するリジッド部と屈曲をするフレックス部とからなるリジッドフレキシブル基板のうちのフレックス部を構成していてもよい。 [substrate]
The material to which the silver paste for flexible substrate disclosed herein is applied is not strictly limited. For example, when the target is a flexible substrate made of polymer (plastic), paper, cloth, etc., the excellent characteristics of the silver paste disclosed here are remarkably exhibited. To be preferred. As a flexible film substrate (hereinafter, sometimes simply referred to as “flexible substrate”), polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polypropylene and ethylene-propylene copolymers, polyimide resins, polychlorinated resins are generally used. A polymer film made of a thermoplastic resin such as vinyl is preferably used. These base materials may have any form of a single layer or a multilayer. In the case of multiple layers, film base materials of different materials may be bonded together, or film base materials of the same kind of material may be bonded together. Such a flexible substrate may constitute a flex portion of a rigid flexible substrate including a rigid portion for mounting components and the like and a flex portion for bending.
　また「フレキシブル」とは、柔軟であって、撓ませたり折り曲げたりすることが可能であることを意味する。通常は、常温でその物自体を損傷させることなく、比較的弱い力で撓ませたり折り曲げたりすることが可能であることを意味する。フレキシブル基板とは、温度変化や被覆層の存在なしに撓むことのない硬質基板に対する用語である。フレキシブル基板の撓み量（撓むことができる撓み可能量）に特に制限はない。しかしながら、必要であれば、例えば常温で、片持ち梁状の基板の先端に荷重をかけたときのたわみ量が、基板寸法に対して０．００１以上（典型的には０．１以上、例えば１以上）の変形を生じ得る基板として把握することができる。なお、ここに開示される銀ペーストは、極めて柔軟性の高いフレキシブル基板への適用が可能とされている。例えば、そのような基板とは、断面の直径が２０ｍｍ以下の巻き芯（コア）に巻き取り可能な湾曲性を備えるフィルム基材であり得る。この湾曲性については、例えば、好ましくは直径が１０ｍｍ以下、特に好ましくは６ｍｍ以下のコアに巻き取り可能なフィルムで基材であってよい。また、ここに開示される銀ペーストは、極めて屈曲性に優れたフレキシブル基板への適用が可能とされている。このような基板とは、例えば、折り返し角度が９０°～１２０°での繰り返しの折り曲げによっても損傷を受けない基板であり得る。フレキシブル基板の厚みは特に制限されないが、例えば、可撓性の観点から約３～２００μｍ（例えば５～１００μｍ、典型的には１０～５０μｍ）の厚みのものが広く採用される。 Also, “flexible” means that it is flexible and can be bent or bent. Usually, it means that it can be bent or bent with a relatively weak force without damaging the object itself at room temperature. The flexible substrate is a term for a hard substrate that does not bend without temperature change or the presence of a coating layer. There is no restriction | limiting in particular in the bending amount (the amount which can be bent which can be bent) of a flexible substrate. However, if necessary, the deflection amount when a load is applied to the tip of the cantilevered substrate at room temperature, for example, is 0.001 or more (typically 0.1 or more, for example, 1 or more) can be grasped as a substrate that can be deformed. In addition, the silver paste disclosed here can be applied to a flexible substrate with extremely high flexibility. For example, such a substrate may be a film base material having a curvature that can be wound around a winding core (core) having a cross-sectional diameter of 20 mm or less. For example, the base material may be a film that can be wound around a core with a diameter of preferably 10 mm or less, particularly preferably 6 mm or less. Further, the silver paste disclosed here can be applied to a flexible substrate having extremely excellent flexibility. Such a substrate can be, for example, a substrate that is not damaged by repeated folding at a folding angle of 90 ° to 120 °. The thickness of the flexible substrate is not particularly limited. For example, a substrate having a thickness of about 3 to 200 μm (for example, 5 to 100 μm, typically 10 to 50 μm) is widely used from the viewpoint of flexibility.
　なお、フレキシブル基板は、繰り返し湾曲したり、折り曲げたりし得ることから、所定の剛性（強度）を有していることが好ましい。かかる観点から、フレキシブル基板としてはポリエステルフィルムを好ましく用いることができ、なかでもＰＥＴフィルム基板を特に好ましく用いることができる。ＰＥＴフィルム基板は、フレキシブルプリント回路基板（Flexible printed circuits：ＦＰＣ）や、フレキシブルケーブルの基板として多用されている点においても好ましい。そこで、以下に、例えばＰＥＴフィルム基板上に、ここに開示されるフレキシブル基板用銀ペーストを用いて導電膜を形成し、電子素子を好適に製造する手法について説明する。 Note that the flexible substrate preferably has a predetermined rigidity (strength) because it can be repeatedly bent and bent. From such a viewpoint, a polyester film can be preferably used as the flexible substrate, and a PET film substrate can be particularly preferably used among them. The PET film substrate is also preferable in that it is frequently used as a flexible printed circuit board (FPC) or a flexible cable substrate. Therefore, a method for suitably manufacturing an electronic device by forming a conductive film on a PET film substrate using the silver paste for flexible substrate disclosed herein will be described below.
［電子素子の製造方法］
　ここに開示される電子素子の製造方法は、本質的に、下記の（１）～（５）の工程を含む。
（１）フレキシブル基板を用意する。
（２）ここに開示される銀ペーストを用意する。
（３）フレキシブル基板上に、銀ペーストを供給する。
（４）銀ペーストが供給されたフレキシブル基板を乾燥させる。
（５）乾燥された銀ペーストが供給されたフレキシブル基板を熱処理して、導電膜を形成する。 [Method for Manufacturing Electronic Device]
The electronic device manufacturing method disclosed herein essentially includes the following steps (1) to (5).
(1) A flexible substrate is prepared.
(2) Prepare the silver paste disclosed here.
(3) A silver paste is supplied on the flexible substrate.
(4) Dry the flexible substrate supplied with the silver paste.
(5) The flexible substrate supplied with the dried silver paste is heat-treated to form a conductive film.
　なお、工程（１）および（２）については上述の銀ペーストと基板との説明により理解できるため、ここでは再度の説明を省略する。
　工程（３）では、用意したフレキシブル基板上に、ここに開示される銀ペーストを供給する。銀ペーストの供給手法は特に制限されない。例えば、インクジェット印刷、グラビア印刷、スクリーン印刷、フレキソ印刷、オフセット印刷、スピンコート、エアロゾル・ジェット印刷等の各種の印刷方法を採用することができる。これらの印刷は、ステップ（間欠）方式で行ってもよいし、ロールｔｏロール等の連続方式でおこなってもよい。銀ペーストは、各々の印刷手法に適した性状に調製される。ここに開示される銀ペーストは、例えば、スクリーン印刷により、フレキシブル基板上に比較的広い面積に亘って任意のパターンの導電膜を形成する用途で好ましく用いることができる。 Steps (1) and (2) can be understood from the description of the silver paste and the substrate described above, and thus the description thereof is omitted here.
In step (3), the silver paste disclosed here is supplied onto the prepared flexible substrate. The method for supplying the silver paste is not particularly limited. For example, various printing methods such as ink jet printing, gravure printing, screen printing, flexographic printing, offset printing, spin coating, and aerosol / jet printing can be employed. These printings may be performed by a step (intermittent) method or a continuous method such as roll-to-roll. The silver paste is prepared in a property suitable for each printing method. The silver paste disclosed here can be preferably used for the purpose of forming a conductive film having an arbitrary pattern over a relatively wide area on a flexible substrate by, for example, screen printing.
　尚、上述のとおり、焼成後の導電膜に十分な可撓性（フレキシブル性）を持たせるためには、熱処理後に得られる導電膜の厚みが３μｍ以下（例えば３μｍ未満）となるように、銀ペーストの供給量を制御することが好ましい。導電膜の厚みが３μｍを超えると、導電性の観点では好ましい。しかしながら、例えば、フレキシブル基板の僅かな撓みに対しては問題ない場合であっても、フレキシブル基板を大きく撓ませた場合に、導電膜に割れやクラックが発生してしまう可能性が高まるために好ましくない。導電膜の損傷は、導電膜の導電性の低下につながるために避けるべき形態である。導電膜の厚みは２．７μｍ以下がより好ましく、２．５μｍ以下が特に好ましい。また、熱処理後に得られる導電膜の厚みが０．２μｍ未満であると、導電膜とフレキシブル基板との十分な密着性が実現され難いために好ましくない。また、導電膜の導電性が低下する虞がある点においても好ましくない。導電膜の厚みは０．２μｍ以上とするのが好ましく、０．５μｍ以上とするのがより好ましく、０．７μｍ以上とするのが特に好ましい。 As described above, in order to give the fired conductive film sufficient flexibility (flexibility), the thickness of the conductive film obtained after the heat treatment is 3 μm or less (for example, less than 3 μm). It is preferable to control the supply amount of the paste. When the thickness of the conductive film exceeds 3 μm, it is preferable from the viewpoint of conductivity. However, for example, even if there is no problem with slight bending of the flexible substrate, it is preferable because the possibility that the conductive film is cracked or cracked increases when the flexible substrate is greatly bent. Absent. Damage to the conductive film is a form to avoid because it leads to a decrease in the conductivity of the conductive film. The thickness of the conductive film is more preferably 2.7 μm or less, and particularly preferably 2.5 μm or less. Moreover, it is not preferable that the thickness of the conductive film obtained after the heat treatment is less than 0.2 μm because sufficient adhesion between the conductive film and the flexible substrate is difficult to be realized. Moreover, it is not preferable also in the point that the electroconductivity of an electrically conductive film may fall. The thickness of the conductive film is preferably 0.2 μm or more, more preferably 0.5 μm or more, and particularly preferably 0.7 μm or more.
　なお、導電膜の厚みは、基板表面に対して垂直な方向の寸法を、１０点以上測定したときの算術平均値（つまり平均厚み）として得ることができる。 The thickness of the conductive film can be obtained as an arithmetic average value (that is, average thickness) when the dimension in the direction perpendicular to the substrate surface is measured at 10 points or more.
　続く工程（４）および（５）では、それぞれ、フレキシブル基板上に供給された銀ペーストに対し「乾燥」と「熱処理」とを施す。この乾燥と熱処理とにより導電膜が形成される。導電膜の形成に際して、銀ペーストに含まれる各成分は、溶剤については揮発し、樹脂については軟化したのちに硬化し、銀粉末は焼結する。焼結された銀粉末と硬化した樹脂とにより、導電膜が形成される。 In subsequent steps (4) and (5), “drying” and “heat treatment” are performed on the silver paste supplied on the flexible substrate, respectively. A conductive film is formed by this drying and heat treatment. When forming the conductive film, each component contained in the silver paste volatilizes the solvent, softens the resin and then hardens, and the silver powder sinters. A conductive film is formed by the sintered silver powder and the cured resin.
　ここで、溶剤の揮発と、樹脂の軟化および硬化ならびに銀粉末の焼結とが、同時に進行することは好ましくない。つまり、溶剤が完全に揮発して、基板上に銀ペーストの固形分のみが密に残された状態で銀粉末が焼結することで、銀粒子同士がより多くの接点で結合し、低抵抗な導電膜を得ることが可能となるために好ましい。また、溶剤が完全に揮発して、基板上に銀ペーストの固形分のみが残された状態で樹脂が軟化・硬化することで、より少ない樹脂量で適切なバインダ機能を発現することが可能となるために好ましい。さらに、樹脂は、銀粉末が完全に焼結を終えてから硬化することで、銀粉末の焼結の阻害を抑制しつつ、焼結した銀を基板に結合できるために好ましい。 Here, it is not preferable that the volatilization of the solvent, the softening and hardening of the resin, and the sintering of the silver powder proceed simultaneously. In other words, the silver powder sinters in a state where the solvent is completely volatilized and only the solid content of the silver paste remains densely on the substrate. It is preferable because a conductive film can be obtained. In addition, since the solvent is completely volatilized and the resin is softened and cured with only the solid content of the silver paste remaining on the substrate, an appropriate binder function can be expressed with a smaller amount of resin. This is preferable. Further, the resin is preferable because the silver powder is cured after the sintering is completely completed, so that the sintered silver can be bonded to the substrate while suppressing the inhibition of the sintering of the silver powder.
　なお、工程（４）における「乾燥」は、主として、銀ペーストに含まれる溶剤を揮発させて、基板上に銀ペーストの固形分のみを残す目的で実施する工程である。また、工程（５）における「熱処理」は、主として基板上の銀粉末を焼結させる目的で実施する工程である。そして、工程（４）の後、工程（５）に至る途中で樹脂が軟化され、工程（５）の加熱が終了して冷却される途中に樹脂が硬化する。したがって、ここに開示される電子素子の製造に際しては、工程（４）における乾燥と工程（５）における熱処理との温度を、銀ペーストに合わせてそれぞれ適切に制御することが肝要である。 The “drying” in the step (4) is a step mainly performed for the purpose of leaving only the solid content of the silver paste on the substrate by volatilizing the solvent contained in the silver paste. In addition, the “heat treatment” in the step (5) is a step performed mainly for the purpose of sintering the silver powder on the substrate. Then, after the step (4), the resin is softened on the way to the step (5), and the resin is cured while the heating in the step (5) is finished and cooled. Therefore, when manufacturing the electronic device disclosed herein, it is important to appropriately control the temperatures of the drying in the step (4) and the heat treatment in the step (5) according to the silver paste.
　工程（４）の乾燥は、自然乾燥であってもよいし、送風乾燥、加熱乾燥、真空乾燥、凍結乾燥等の手段を利用してもよい。より短時間で簡便に乾燥を行えることから、加熱乾燥が好ましい。加熱乾燥における加熱手段は特に制限されず、公知の各種の乾燥機を利用して乾燥することができる。 The drying in the step (4) may be natural drying, or may utilize means such as blow drying, heat drying, vacuum drying, freeze drying and the like. Heating and drying are preferable because drying can be easily performed in a shorter time. The heating means in the heat drying is not particularly limited, and it can be dried using various known dryers.
　この乾燥工程は、銀ペーストに使用される熱可塑性エポキシ樹脂のガラス転移点（Ｔｇ）よりも低い温度で行うようにする。乾燥時間の短縮の観点から、例えば、乾燥工程は、ガラス転移点よりも２℃～３０℃程度低い温度にまで加熱して実施することが好ましい。乾燥温度は、ガラス転移点よりも低い温度であって、例えば、６０℃±１０℃程度の範囲に設定することが好適である。 This drying step is performed at a temperature lower than the glass transition point (Tg) of the thermoplastic epoxy resin used for the silver paste. From the viewpoint of shortening the drying time, for example, the drying step is preferably performed by heating to a temperature lower by about 2 ° C. to 30 ° C. than the glass transition point. The drying temperature is lower than the glass transition point, and is preferably set to a range of about 60 ° C. ± 10 ° C., for example.
　工程（５）の熱処理は、銀粉末の焼結が実現できる温度であって、かつ、熱可塑性エポキシ樹脂のガラス転移点よりも高い温度で行う。ここに開示される技術では、より低温での熱処理により導電膜の形成を行うことから、１４０℃以下の温度範囲で熱処理を行うことができる。また、ここに開示される技術では、熱可塑性エポキシ樹脂としてガラス転移点が６０℃以上９０℃以下のものを使用するようにしていることから、熱処理温度は、銀ペーストに含まれる熱可塑性エポキシ樹脂のガラス転移点に応じて設定することができる。なお、熱処理温度は、銀ペーストに使用する熱可塑性エポキシ樹脂のガラス転移点に応じて、（ガラス転移点＋２０）℃以上の温度を目安に行うことが好ましい。例えば、熱処理温度は、おおよそ１００℃～１３５℃が好ましく、１００℃～１３０℃がより好ましく、１００℃～１２０℃が特に好ましい。この熱処理は、公知の各種の加熱装置や乾燥装置等を用いて実施することができる。 The heat treatment in step (5) is performed at a temperature at which the silver powder can be sintered and higher than the glass transition point of the thermoplastic epoxy resin. In the technique disclosed herein, the conductive film is formed by a heat treatment at a lower temperature, and thus the heat treatment can be performed in a temperature range of 140 ° C. or lower. In the technique disclosed herein, a thermoplastic epoxy resin having a glass transition point of 60 ° C. or higher and 90 ° C. or lower is used, so that the heat treatment temperature is the thermoplastic epoxy resin contained in the silver paste. It can be set according to the glass transition point. In addition, it is preferable to perform the heat processing temperature on the basis of the temperature of (glass transition point +20) degree C or more according to the glass transition point of the thermoplastic epoxy resin used for a silver paste. For example, the heat treatment temperature is preferably about 100 ° C. to 135 ° C., more preferably 100 ° C. to 130 ° C., and particularly preferably 100 ° C. to 120 ° C. This heat treatment can be carried out using various known heating devices and drying devices.
　この熱処理により、銀ペーストの固形成分である銀粉末は焼結し、銀粒子同士が良好な電気コンタクトを形成する。また、この熱処理後の冷却により、熱可塑性エポキシ樹脂が硬化して、銀粉末の焼結体同士の接合をより確実なものにサポートするとともに、焼結体とＰＥＴ基板のとの柔軟かつ強固な接着を実現する。このことにより、フレキシブルな基板に対しても、導電性が高くかつ接着性の良好な導電膜を、低温で簡便に形成することができる。この導電膜は、印刷技術を利用して形成されているため、任意のパターンで均一な膜厚のものとして実現される。 By this heat treatment, the silver powder which is a solid component of the silver paste is sintered, and the silver particles form a good electrical contact. In addition, the cooling after the heat treatment cures the thermoplastic epoxy resin to support the joining of the sintered bodies of the silver powder more reliably, and the flexible and strong bonding between the sintered body and the PET substrate. Realize adhesion. Thus, a conductive film having high conductivity and good adhesiveness can be easily formed at a low temperature even on a flexible substrate. Since this conductive film is formed using a printing technique, it is realized as a film having a uniform thickness with an arbitrary pattern.
　したがって、かかる導電膜が形成されたフレキシブル基板は、変形された後も基板と導電膜とが極めて良好な接着性を維持し得る。また、導電膜は、変形後も導電性を維持し得る。具体的には、基板を繰り返し大きく撓ませた場合であっても、導電膜の剥離や割れが高度に抑制されている。また、後述の実施例にも示されるように、基板を繰り返し折り曲げた場合であっても、導電膜の剥離や割れが高度に抑制されている。したがって、ここに開示される技術によると、例えば、ヒンジ部等において繰り返し屈曲するフレキシブル基板に対して、可動部配線等の導電膜を印刷により好適に形成することができる。延いては、凹凸部や省スペースでの配設が可能な電子素子（例えばＦＰＣ）が実現される。また、繰り返し屈曲性に優れ、駆動部等における省スペースでの配線が可能なフレキシブルケーブルが実現される。 Therefore, the flexible substrate on which such a conductive film is formed can maintain extremely good adhesion between the substrate and the conductive film even after being deformed. Moreover, the conductive film can maintain conductivity even after deformation. Specifically, even when the substrate is repeatedly bent greatly, peeling and cracking of the conductive film are highly suppressed. In addition, as shown in Examples described later, even when the substrate is repeatedly bent, peeling and cracking of the conductive film are highly suppressed. Therefore, according to the technology disclosed herein, for example, a conductive film such as movable part wiring can be suitably formed by printing on a flexible substrate that bends repeatedly at a hinge part or the like. As a result, an electronic element (for example, FPC) that can be arranged in a concavo-convex portion or in a space-saving manner is realized. In addition, a flexible cable that is excellent in repeated bendability and can be wired in a space-saving manner in the drive unit or the like is realized.
　かかるフレキシブルな導電膜付き基板は、例えば、電気機器、半導体機器、太陽電池、ディスプレイ、センサーおよびバイオメディカルデバイス等の多様な分野において使用される電子素子として好適に利用することができる。 Such a flexible substrate with a conductive film can be suitably used as an electronic element used in various fields such as electric devices, semiconductor devices, solar cells, displays, sensors, and biomedical devices.
　以下、本発明に関するいくつかの実施例を説明するが、本発明をかかる実施例に示すものに限定することを意図したものではない。 Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the examples shown in the examples.
（実施形態１）
　［銀粉末の用意］
　平均粒子径の異なる３通りの銀粉末Ａ～Ｃを用意した。具体的には、室温（２５℃）にて、表面修飾剤としてのブチルアミンと、溶媒兼粒径制御剤としてのブタノールとを所定のモル比で混合し、シュウ酸銀を添加したのち、撹拌しながら約１００℃まで加熱することで、表面を有機アミンで安定化させた略球形の銀粉末Ｂ，Ｃを得た。銀粉末の平均粒子径は、粒径制御剤の添加量（有機アミンと粒径制御剤とのモル比）を調整し、さらに分級することで制御した。また、銀粉末Ａは、市販のフレーク状の銀粉末であり、平面視での平均粒子径が２０００ｎｍと比較的大きいことから、表面修飾剤は使用されていない。このようにして用意した銀粉末Ａ～Ｃの平均粒子径（Ｄ５０）と形状とを、ＳＥＭ観察により算出し、下記の表１に示した。 (Embodiment 1)
[Preparation of silver powder]
Three types of silver powders A to C having different average particle diameters were prepared. Specifically, butylamine as a surface modifier and butanol as a solvent and particle size control agent are mixed at a predetermined molar ratio at room temperature (25 ° C.), and after adding silver oxalate, the mixture is stirred. While heating to about 100 ° C., substantially spherical silver powders B and C having surfaces stabilized with organic amines were obtained. The average particle size of the silver powder was controlled by adjusting the addition amount of the particle size control agent (molar ratio of the organic amine and the particle size control agent) and further classifying. Further, the silver powder A is a commercially available flaky silver powder, and since the average particle diameter in a plan view is relatively large at 2000 nm, no surface modifier is used. The average particle diameters (D50) and shapes of the silver powders A to C thus prepared were calculated by SEM observation and are shown in Table 1 below.
　［ベヒクルの用意］
　次いで、銀粉末を分散させるベヒクルを調整した。具体的には、まず、バインダ樹脂として、結晶性のエポキシ樹脂（ＥＰ）と、非結晶性のポリエステル樹脂（ＰＥｓ）との２通りの樹脂を用意した。エポキシ樹脂としては、熱硬化型導電ペーストのバインダとして汎用されている、軟化点が６５℃で、数平均分子量（Ｍｎ）が１×１０３のものを用いた。ポリエステル樹脂としては、熱可塑性で数平均分子量（Ｍｎ）が２３×１０３、ガラス転移点（Ｔｇ）が６５°のものを用いた。また溶剤として、分子構造中にフェニル基を有し、上記のバインダ樹脂を好適に溶解できるプロピレングリコールモノフェニルエーテルを用意した。プロピレングリコールモノフェニルエーテルの沸点（Ｔｂ）は２４３℃である。そしてそれぞれの樹脂と溶剤とをガラス瓶容器に所定量秤量し、手撹拌したのち、約１００℃のスチームオーブンで１０～２０時間程度加熱した。加熱中は、必要に応じて手撹拌を行った。これにより２通りのベヒクルを得た。 [Vehicle preparation]
Next, a vehicle for dispersing the silver powder was prepared. Specifically, first, two types of resins, a crystalline epoxy resin (EP) and an amorphous polyester resin (PEs), were prepared as binder resins. As the epoxy resin, a resin having a softening point of 65 ° C. and a number average molecular weight (Mn) of 1 × 10 3 , which is widely used as a binder for a thermosetting conductive paste, was used. As the polyester resin, a thermoplastic resin having a number average molecular weight (Mn) of 23 × 10 3 and a glass transition point (Tg) of 65 ° was used. As a solvent, propylene glycol monophenyl ether having a phenyl group in the molecular structure and capable of suitably dissolving the binder resin was prepared. The boiling point (Tb) of propylene glycol monophenyl ether is 243 ° C. Then, a predetermined amount of each resin and solvent was weighed into a glass bottle container, stirred manually, and then heated in a steam oven at about 100 ° C. for about 10 to 20 hours. During the heating, hand stirring was performed as necessary. This gave two vehicles.
　［銀ペーストの調製］
　準備した銀粉末Ａ～Ｃとベヒクルとを所定の割合で調合し、三本ロールミルを用いて混合・混練することで、例１～５の銀ペーストを用意した。なお、銀粉末とベヒクルとは、表１に示すように、ベヒクル中の樹脂が銀粉末の質量（１００質量部）に対して、１０質量部または６質量部となる割合とした。銀ペーストは、溶剤を加えることで、２５℃－２０ｒｐｍにおける粘度が５０～１５０Ｐａ・ｓになるように調整した。 [Preparation of silver paste]
The prepared silver powders A to C and a vehicle were mixed at a predetermined ratio, and mixed and kneaded using a three-roll mill to prepare silver pastes of Examples 1 to 5. In addition, as shown in Table 1, the silver powder and the vehicle were set to a ratio in which the resin in the vehicle was 10 parts by mass or 6 parts by mass with respect to the mass of the silver powder (100 parts by mass). The silver paste was adjusted to have a viscosity of 50 to 150 Pa · s at 25 ° C.-20 rpm by adding a solvent.
　［導電膜の形成］
　このように用意した例１～５の銀ペーストを、ＰＥＴ樹脂製のフィルム状基板（厚み１００μｍ）の表面にスクリーン印刷法により塗布した。スクリーン印刷には、カレンダー処理された＃６４０のステンレスメッシュを用い、熱処理（焼成）後の膜厚がおおよそ１μｍとなるように薄層状に印刷した。印刷パターンは、３ｃｍ×１．５ｃｍの長方形のベタ塗りパターンを１つと、後述のシート抵抗測定用のパターンを並べて配置するものとした。なお、シート抵抗測定用のパターンは、焼成後の寸法が、総長さが１０ｃｍ以上で幅が０．５ｍｍとなるように調整した線状パターンとした。例４の銀ペーストについては、ステンレスメッシュを変えて熱処理後の厚みが１０μｍとなるように印刷した（これを例４＊とする）。印刷後の基板は、乾燥器にて６０℃で１０分間乾燥させたのち、１２０℃で２０分間の熱処理を施すことで、例１～５の導電膜を形成した。得られた導電膜の膜厚を測定し、下記の表１の「焼成厚み」の欄に示した。また、得られた導電膜について、下記の手法により、シート抵抗、接着性および曲げ接着性の各特性を評価し、その結果を下記表１の当該欄に示した。 [Formation of conductive film]
The silver pastes of Examples 1 to 5 prepared in this way were applied to the surface of a PET resin film substrate (thickness 100 μm) by screen printing. For screen printing, a calendered # 640 stainless mesh was used and printed in a thin layer so that the film thickness after heat treatment (firing) was approximately 1 μm. The printing pattern was arranged by arranging one rectangular solid coating pattern of 3 cm × 1.5 cm and a sheet resistance measurement pattern described later side by side. The sheet resistance measurement pattern was a linear pattern in which the dimensions after firing were adjusted so that the total length was 10 cm or more and the width was 0.5 mm. The silver paste of Example 4 was printed by changing the stainless steel mesh so that the thickness after the heat treatment was 10 μm (this is Example 4 * ). The printed substrate was dried in a dryer at 60 ° C. for 10 minutes and then heat-treated at 120 ° C. for 20 minutes to form the conductive films of Examples 1 to 5. The film thickness of the obtained conductive film was measured and shown in the column of “Firing thickness” in Table 1 below. Moreover, about the obtained electrically conductive film, each characteristic of sheet resistance, adhesiveness, and bending adhesiveness was evaluated with the following method, and the result was shown in the said column of the following Table 1.
　［シート抵抗］
　上記のように形成したシート抵抗測定用の導電膜のシート抵抗を測定した。具体的には、デジタルマルチメーターを用い、２端子法により、端子間隔（導体長さ）１００ｍｍ、ライン幅（導体幅）０．５００ｍｍの条件で線状の導電膜の抵抗値を測定した。そしてこの抵抗値から、下式に基づき、シート抵抗値を算出した。なお、換算厚みは、１０μｍとした。その結果を表１に示した。なお、シート抵抗値が１０００ｍΩ／□を超過した膜については、導電膜としての使用が困難なレベルであることから、実測値ではなく「＞１０００」と表示した。
　　シート抵抗値（ｍΩ／□）＝抵抗値（Ω）×｛導体幅（ｍｍ）／導体長さ（ｍｍ）｝×｛導体厚み（μｍ）／換算厚み（μｍ）｝ [Sheet resistance]
The sheet resistance of the conductive film for measuring sheet resistance formed as described above was measured. Specifically, the resistance value of the linear conductive film was measured by a two-terminal method using a digital multimeter under the conditions of a terminal interval (conductor length) of 100 mm and a line width (conductor width) of 0.500 mm. From this resistance value, the sheet resistance value was calculated based on the following equation. The converted thickness was 10 μm. The results are shown in Table 1. A film having a sheet resistance value exceeding 1000 mΩ / □ is indicated as “> 1000” instead of an actual measurement value because it is difficult to use as a conductive film.
Sheet resistance value (mΩ / □) = resistance value (Ω) × {conductor width (mm) / conductor length (mm)} × {conductor thickness (μm) / converted thickness (μm)}
　［接着性］
　上記のように形成した導電膜について、両面テープを用いた接着性試験を行うことにより、導電膜の基板に対する接着性を評価した。具体的には、まず、試験台の上に両面テープ（ニチバン（株）製、ナイスタック一般用ＮＷ－１０、幅１ｃｍ×長さ１．５ｃｍ）を貼り付けた。そして台上に貼り付けた両面テープの上方側の粘着面に、ＰＥＴ基板上に形成した導電膜部分を張り付け、ＰＥＴ基板の裏面上から指で押して十分に接着させた。そしてＰＥＴ基板の端部を指でつまみ、両面テープの長手方向に沿う方向で、かつ、ＰＥＴ基板の初期貼り付け位置から１２０°～１５０°の方向（すなわち、ＰＥＴ基板の為す角が６０°～３０°となる斜め上後方）に引っ張ることで、両面テープからフィルム基板を剥離させた。 [Adhesiveness]
About the electrically conductive film formed as mentioned above, the adhesiveness test with respect to the board | substrate of a electrically conductive film was evaluated by performing the adhesive test using a double-sided tape. Specifically, a double-sided tape (manufactured by Nichiban Co., Ltd., NW-10 for general use, width 1 cm × length 1.5 cm) was attached on the test stand. And the electrically conductive film part formed on the PET board | substrate was affixed on the adhesive surface of the upper side of the double-sided tape affixed on the stand, and it was made to adhere | attach sufficiently by pushing with the finger from the back surface of the PET board | substrate. Then, the edge of the PET substrate is pinched with a finger, and the direction along the longitudinal direction of the double-sided tape is 120 ° to 150 ° from the initial attachment position of the PET substrate (ie, the angle formed by the PET substrate is 60 ° to The film substrate was peeled from the double-sided tape by pulling it diagonally upward and rearward at 30 °.
　剥離後のフィルム基板の導電膜を観察し、両面テープに接着した部分のうち、はく離後にフィルム基板に残った部分の面積割合が９５％以上の場合を「○」、残った部分の面積割合が９５％未満８０％以上の場合を「△」、残った部分の面積割合が８０％未満の場合を「×」とし、その結果を表１に示した。 Observe the conductive film of the film substrate after peeling, and among the parts adhered to the double-sided tape, “○” when the area ratio of the part remaining on the film substrate after peeling is 95% or more, the area ratio of the remaining part is The case of less than 95% and 80% or more is indicated by “Δ”, and the case where the remaining area ratio is less than 80% is indicated by “X”.
　［折り曲げ耐性］
　上記のように形成した導電膜について、基板を折り曲げたときの導電性膜の耐久性を評価した。具体的には、まず、ＰＥＴ基板に形成した導電膜のシート抵抗（初期シート抵抗）を上記のとおり測定した。次いで、導電膜を備えたＰＥＴ基板を、直角（９０°）の角部を有する試験台の表面にぴたりと沿わせて、導電膜の部分でＰＥＴ基板ごと直角に折り曲げた。その後、折り曲げたＰＥＴ基板をまっすぐに延ばし、再び同じ折り曲げ位置でＰＥＴ基板および導電膜を直角に折り曲げた。この操作を、折り曲げ回数が計６回となるまで繰り返し行った。 [Bending resistance]
For the conductive film formed as described above, the durability of the conductive film when the substrate was bent was evaluated. Specifically, first, the sheet resistance (initial sheet resistance) of the conductive film formed on the PET substrate was measured as described above. Next, the PET substrate provided with the conductive film was bent along the surface of the test table having a right angle (90 °) corner, and the PET substrate was bent at a right angle at the conductive film portion. Thereafter, the bent PET substrate was straightened, and the PET substrate and the conductive film were again bent at a right angle at the same folding position. This operation was repeated until the total number of bendings was six.
　６回折り曲げ後の導電膜に対し、デジタルマルチメーターの２つの端子を、端子間に折り曲げ部が挟まれるように接触させて、折り曲げ部を含む導電膜のシート抵抗を上記のとおり測定した。そして次式から、シート抵抗上昇率を測定し、６回折り曲げ後のシート抵抗が、初期シート抵抗の１２０％以上である場合を「×」、１２０％未満である場合を「〇」として、導電膜の折り曲げ耐性を評価した。なお、シート抵抗上昇率は、初期シート抵抗が１０００ｍΩ／□を超過した膜についても同様に測定した。その結果を表１に示した。
　　シート抵抗上昇率（％）＝｛（６回折り曲げ後のシート抵抗）－（初期シート抵抗）｝÷（初期シート抵抗）×１００ Two terminals of the digital multimeter were brought into contact with the conductive film after being bent six times so that the bent portion was sandwiched between the terminals, and the sheet resistance of the conductive film including the bent portion was measured as described above. Then, the sheet resistance increase rate is measured from the following equation, and the sheet resistance after bending 6 times is defined as “X” when the sheet resistance is 120% or more of the initial sheet resistance, and “◯” when the sheet resistance is less than 120%. The bending resistance of the film was evaluated. Note that the sheet resistance increase rate was measured in the same manner for a film having an initial sheet resistance exceeding 1000 mΩ / □. The results are shown in Table 1.
Rate of increase in sheet resistance (%) = {(sheet resistance after 6-fold bending) − (initial sheet resistance)} ÷ (initial sheet resistance) × 100
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
（評価）
　表１に示すように、例１の銀ペーストは、平均粒子径が２０００ｎｍのフレーク型の銀粉末Ａと、エポキシ樹脂とを用いた、汎用されている熱硬化型の銀ペーストの一例である。従来の一般的な熱硬化型の銀ペーストによると、厚みが１０μｍ程度の導電性膜を好適に形成することができる。この例１の銀ペーストを使用すると、印刷条件が同じであっても厚みが１μｍにまで薄い導電膜を印刷することはできず、導電膜の膜厚は銀粒子の粒径に基づいて厚くなってしまうことが確認できた。本例では、銀粒子の平均粒子径と同程度の厚みが約２μｍの導電膜の形成が可能であることがわかった。 (Evaluation)
As shown in Table 1, the silver paste of Example 1 is an example of a widely used thermosetting silver paste using a flake-type silver powder A having an average particle diameter of 2000 nm and an epoxy resin. According to a conventional general thermosetting silver paste, a conductive film having a thickness of about 10 μm can be suitably formed. When the silver paste of Example 1 is used, it is not possible to print a conductive film as thin as 1 μm even under the same printing conditions, and the film thickness of the conductive film becomes thicker based on the particle size of the silver particles. I was able to confirm. In this example, it was found that a conductive film having a thickness approximately equal to the average particle diameter of the silver particles and having a thickness of about 2 μm can be formed.
　このような例１の導電膜は、１２０℃での熱処理では銀粒子同士の焼結は進行せず、銀粒子が熱硬化性のバインダを介してあるいはバインダで固定されることで膜が形成されている。そのため膜形成のために必要なバインダ量が１０質量部と比較的多く、例えば１０μｍの厚みの導電膜を形成する場合であっても、シート抵抗を低くすることは困難であった。本例では、膜厚が５μｍとさらに厚みの薄い導電膜を形成した。そのため、厚み方向でも銀粒子同士の電気コンタクトが悪く、シート抵抗は導電膜としては適さない程度にまで著しく高くなることがわかった。また、例１の導電膜は、銀粒子同士が焼結していないことに加えて銀粒子の大きさに対して厚みが薄いことから、膜強度が弱く、接着性試験では大部分の導電膜が剥離してしまうことがわかった。さらに、熱硬化性樹脂は結晶性であるため、硬化後の硬度が高い。したがって、導電膜の厚みが比較的薄いにもかかわらず、一度の折り曲げによって導電膜にクラックの形成や基板からの剥離が確認され、折り曲げ耐性も悪いことがわかった。つまり、例１の銀ペーストによると、耐熱性の低いフレキシブルな基板に対して、シート抵抗が低く接着性の良好な導電薄膜の形成は困難であることがわかった。 In such a conductive film of Example 1, the sintering of silver particles does not proceed by heat treatment at 120 ° C., and the film is formed by fixing the silver particles via a thermosetting binder or with a binder. ing. For this reason, the amount of binder required for film formation is relatively large at 10 parts by mass. For example, even when a conductive film having a thickness of 10 μm is formed, it is difficult to reduce sheet resistance. In this example, a thin conductive film having a thickness of 5 μm was formed. Therefore, it was found that the electrical contact between the silver particles was poor even in the thickness direction, and the sheet resistance was remarkably increased to such an extent that it was not suitable as a conductive film. In addition, the conductive film of Example 1 has a low film strength due to the fact that the silver particles are not sintered with each other and has a small thickness with respect to the size of the silver particles. Was found to peel off. Furthermore, since the thermosetting resin is crystalline, the hardness after curing is high. Therefore, although the thickness of the conductive film was relatively thin, formation of cracks in the conductive film and peeling from the substrate were confirmed by one-time bending, and it was found that the bending resistance was poor. In other words, according to the silver paste of Example 1, it was found that it was difficult to form a conductive thin film having a low sheet resistance and good adhesion on a flexible substrate having low heat resistance.
　例２および例４の銀ペーストは、ガラス転移点が６５℃のポリエステル樹脂を用いた低温硬化型の銀ペーストであって、用いた銀粉末の平均粒子径が、（例２）銀粉末Ｂ：５００ｎｍと（例４）銀粉末Ｃ：７０ｎｍとで異なっている。これらの銀ペーストを使用すると、目標である１μｍの厚みの導電膜の形成が可能であることが確認できた。また、バインダ樹脂のガラス転移点が６５℃であるため、１２０℃の熱処理によりバインダ樹脂が十分に軟化したのち硬化して、銀粒子同士ならびに銀粒子と基板とを良好に結合し、接着性の良好な導電膜が形成できることが確認できた。また、バインダとして用いたポリエステル樹脂は非結晶性のため導電膜に柔軟性と基板追随性とが備わり折り曲げ耐性が高く、基材を繰り返し折り曲げても導電膜のシート抵抗に大幅な上昇が見られないことが確認できた。このことから、バインダ樹脂としてガラス転移点が適正な熱可塑性樹脂を使用することで、耐熱性が低くフレキシブルな基板に対して接着性の良好な導電薄膜を形成できることがわかった。 The silver pastes of Examples 2 and 4 are low-temperature curable silver pastes using a polyester resin having a glass transition point of 65 ° C., and the average particle diameter of the silver powder used is (Example 2) Silver Powder B: It is different between 500 nm and (Example 4) silver powder C: 70 nm. When these silver pastes were used, it was confirmed that a target conductive film having a thickness of 1 μm could be formed. In addition, since the glass transition point of the binder resin is 65 ° C., the binder resin is sufficiently softened by heat treatment at 120 ° C. and then hardened, and the silver particles and the silver particles and the substrate are well bonded to each other. It was confirmed that a good conductive film could be formed. The polyester resin used as the binder is non-crystalline, so the conductive film has flexibility and substrate followability and high bending resistance. Even when the base material is repeatedly bent, the sheet resistance of the conductive film is significantly increased. It was confirmed that there was no. From this, it was found that by using a thermoplastic resin having an appropriate glass transition point as the binder resin, a conductive thin film having low heat resistance and good adhesion to a flexible substrate can be formed.
　その一方で、表１には表れていないが、微細な銀粉末Ｃを使用した例４の導電膜は、熱処理により銀粉末の一部が焼結しており、例２の導電膜よりも高い接着性を示すものであった。また、例４の導電膜のシート抵抗が５０ｍΩ／□と低いのに対し、平均粒子径が５００ｎｍの銀粉末Ｂを使用した例２の導電膜のシート抵抗は依然として１０００ｍΩ／□を超過していた。これは、例４の導電膜では、平均粒子径が十分に小さいために銀粒子同士が焼結し、導電膜内に良好なコンタクトを形成していることによると考えらえる。しかしながら、例２で用いた銀粒子Ｂは、低温での熱処理では焼結しないため、例えば１μｍ程度の限られた厚みの膜内では銀粒子が良好なコンタクトを形成できないことを示している。このことから、銀粉末の平均粒子径は、例えば１００μｍ以下程度とするのが好ましいことがわかった。 On the other hand, although not shown in Table 1, the conductive film of Example 4 using fine silver powder C is partly sintered by heat treatment and is higher than the conductive film of Example 2. It showed adhesiveness. In addition, the sheet resistance of the conductive film of Example 4 was as low as 50 mΩ / □, whereas the sheet resistance of the conductive film of Example 2 using silver powder B having an average particle diameter of 500 nm still exceeded 1000 mΩ / □. . It can be considered that this is because, in the conductive film of Example 4, since the average particle diameter is sufficiently small, the silver particles are sintered to form a good contact in the conductive film. However, since the silver particles B used in Example 2 are not sintered by heat treatment at a low temperature, the silver particles cannot form a good contact in a film having a limited thickness of about 1 μm, for example. From this, it was found that the average particle diameter of the silver powder is preferably about 100 μm or less, for example.
　例３、４、５の銀ペーストは、銀粉末Ｃを用い、ガラス転移点が６５℃のポリエステル樹脂の量を、（例３）０質量部（使用しない）、（例４）６質量部、（例５）１０質量部、で変化させたものである。これらの銀ペーストを使用すると、目標である１μｍの厚みの導電膜の形成が可能であることが確認できた。また、導電膜のシート抵抗は、バインダ樹脂の使用量がゼロの例３の導電膜については１０ｍΩ／□と極めて低く、バインダ樹脂が増えるほどシート抵抗が高くなることがわかった。ここで、バインダ樹脂量が６質量部の例４の導電膜のシート抵抗は５０ｍΩ／□と十分低いものの、バインダ樹脂量が１０質量部の例５の導電膜は、例１の導電膜と同様、シート抵抗が１０００ｍΩ／□超過と極めて高くなることがわかった。このことから、バインダ樹脂は、銀粉末に対して１０質量部よりも少なく、例えば８質量部以下とするのが好ましいことがわかった。また、ガラス転移点が適正な熱可塑性のバインダ樹脂を使用することで、樹脂量を削減しながらも低温焼成で接着性の良好な膜を形成することができ、低シート抵抗と接着性とを高度なレベルで両立し得ることがわかった。 The silver paste of Examples 3, 4, and 5 uses silver powder C, and the amount of the polyester resin having a glass transition point of 65 ° C. is (Example 3) 0 part by mass (not used), (Example 4) 6 parts by mass, (Example 5) It is changed at 10 parts by mass. When these silver pastes were used, it was confirmed that a target conductive film having a thickness of 1 μm could be formed. In addition, the sheet resistance of the conductive film was extremely low at 10 mΩ / □ for the conductive film of Example 3 in which the amount of binder resin used was zero, and it was found that the sheet resistance increased as the binder resin increased. Here, although the sheet resistance of the conductive film of Example 4 having a binder resin amount of 6 parts by mass is sufficiently low as 50 mΩ / □, the conductive film of Example 5 having a binder resin amount of 10 parts by mass is the same as the conductive film of Example 1. The sheet resistance was found to be extremely high, exceeding 1000 mΩ / □. From this, it was found that the binder resin is preferably less than 10 parts by mass, for example, 8 parts by mass or less with respect to the silver powder. In addition, by using a thermoplastic binder resin with an appropriate glass transition point, it is possible to form a film with good adhesion by low-temperature firing while reducing the amount of resin, and to achieve low sheet resistance and adhesiveness. It turns out that they can be compatible at a high level.
　なお、バインダ樹脂量が０質量部の例３の導電膜は、１２０℃での熱処理により銀粒子が焼結するため、厚みが１μｍの導電膜の形成は可能であった。しかしながら、例３の導電膜にはバインダ樹脂が存在しないため、導電膜と基板との接着性および折り曲げ耐性は悪くなることがわかった。このことから、フレキシブルな基板に対して導電性薄膜を形成するためには、ガラス転移点が適正な熱可塑性のバインダ樹脂の使用が必須である（例えば０．２質量部以上）ことがわかった。 In addition, since the silver particle sinters by the heat processing at 120 degreeC about the electrically conductive film of Example 3 whose binder resin amount is 0 mass part, formation of the electrically conductive film with a thickness of 1 micrometer was possible. However, it was found that since the binder resin does not exist in the conductive film of Example 3, the adhesion and bending resistance between the conductive film and the substrate deteriorate. From this, it was found that in order to form a conductive thin film on a flexible substrate, it is essential to use a thermoplastic binder resin having an appropriate glass transition point (for example, 0.2 parts by mass or more). .
　以上のとおり、例４の銀ペーストを用いることで、低耐熱性でフレキシブルなＰＥＴ基板に対して、接着性が極めて良好な導電膜を形成できることがわかった。そこで、例４の銀ペーストを用い、従来の熱硬化型銀ペーストを用いたときと同様に厚みが１０μｍの例４＊の導電膜を形成した。その結果、例４＊の導電膜は、例４の導電膜と同様に、低温焼成でありながら、シート抵抗が低く、接着性に優れるものであった。しかしながら、膜厚が１０μｍと厚かったため、折り曲げにより導電膜に浮きや割れが生じ、本例では折り曲げ耐性については満足な結果が得られなかった。なお具体的なデータは示さないが、例４の銀ペーストは、フレキシブル性を備えるためには１０μｍよりも薄い、例えば膜厚が３μｍ以下の薄膜を形成するのに特に好適に用い得ることがわかった。 As described above, it was found that by using the silver paste of Example 4, it is possible to form a conductive film having extremely good adhesion to a flexible PET substrate with low heat resistance. Therefore, using the silver paste of Example 4, a conductive film of Example 4 * having a thickness of 10 μm was formed in the same manner as when a conventional thermosetting silver paste was used. As a result, like the conductive film of Example 4, the conductive film of Example 4 * had low sheet resistance and excellent adhesiveness while being fired at a low temperature. However, since the film thickness was as thick as 10 μm, the conductive film was floated or cracked by bending, and in this example, satisfactory results were not obtained with respect to bending resistance. Although specific data is not shown, it is understood that the silver paste of Example 4 can be particularly suitably used to form a thin film having a thickness of less than 10 μm, for example, a film thickness of 3 μm or less in order to have flexibility. It was.
（実施形態２）
　［銀ペーストの調製］
　上記の実施形態１と同様にして、表面修飾剤としてのブチルアミンを使用した平均粒子径が７０ｎｍの略球形の銀粉末Ｃを用意した。なお、ここで用意した銀粉末Ｃは、概ね全ての粒子が略球形であったものの、１０質量％以下程度の割合で、アスペクト比が１．５を超過する非球形銀微粒子が存在することが確認できた。
　また、バインダ樹脂として、表２に示すように、ガラス転移点（Ｔｇ）が７～８４の異なる５種類の非結晶性ポリエステル樹脂（ＰＥｓ）Ａ～Ｅを用意した。溶剤としては、以下に示すように、プロピレングリコールモノフェニルエーテルの他に、沸点（Ｔｂ）の異なる３通りの有機溶剤を用意した。 (Embodiment 2)
[Preparation of silver paste]
In the same manner as in Embodiment 1 above, a substantially spherical silver powder C having an average particle diameter of 70 nm using butylamine as a surface modifier was prepared. In addition, although the silver powder C prepared here was almost spherical in shape, non-spherical silver fine particles having an aspect ratio exceeding 1.5 were present at a ratio of about 10% by mass or less. It could be confirmed.
As binder resins, as shown in Table 2, five types of amorphous polyester resins (PEs) A to E having different glass transition points (Tg) of 7 to 84 were prepared. As the solvent, as shown below, in addition to propylene glycol monophenyl ether, three kinds of organic solvents having different boiling points (Tb) were prepared.
（ａ）プロピレングリコールモノフェニルエーテル（沸点：２４３℃）
（ｂ）酢酸２－（２－ブトキシエトキシ）エチル（沸点：２５５℃）
（ｃ）エチレングリコールモノフェニルエーテル（沸点：２４５℃）
（ｄ）ジエチレングリコールモノフェニルエーテル（沸点：２９８℃）
　そしてまず、用意した樹脂と溶剤とを、表２に示す組みあわせで、樹脂：溶剤が重量比で４：２１となる割合で配合し、適宜手撹拌しながら、約１００℃のスチームオーブンで１０～２０時間程度加熱することで、ベヒクルを調製した。 (A) Propylene glycol monophenyl ether (boiling point: 243 ° C.)
(B) 2- (2-butoxyethoxy) ethyl acetate (boiling point: 255 ° C.)
(C) Ethylene glycol monophenyl ether (boiling point: 245 ° C.)
(D) Diethylene glycol monophenyl ether (boiling point: 298 ° C.)
First, the prepared resin and solvent are combined in the combination shown in Table 2 at a ratio of resin: solvent of 4:21 by weight, and 10 times in a steam oven at about 100 ° C. with appropriate manual stirring. The vehicle was prepared by heating for ~ 20 hours.
　準備した銀粉末とベヒクルとを、銀粉末：樹脂が重量比で７５：４（つまり、１００質量部：５．３質量部）となる割合で配合し、三本ロールミルを用いて混合・混練することで、例６～１３の銀ペーストを用意した。銀ペーストは、溶剤を加えることで、２５℃－２０ｒｐｍにおける粘度が５０～１５０Ｐａ・ｓになるように調製した。 The prepared silver powder and vehicle are blended at a ratio of silver powder: resin of 75: 4 (that is, 100 parts by mass: 5.3 parts by mass), and mixed and kneaded using a three-roll mill. Thus, the silver pastes of Examples 6 to 13 were prepared. The silver paste was prepared by adding a solvent so that the viscosity at 25 ° C.-20 rpm was 50 to 150 Pa · s.
　［導電膜の形成］
　このように用意した例６～１３の銀ペーストを、実施形態１と同様にして、ＰＥＴ樹脂製のフィルム状基板（厚み１００μｍ）の表面にスクリーン印刷法により塗布した。スクリーン印刷には、カレンダー処理された＃６４０のステンレスメッシュを用い、焼成後の膜厚がおおよそ１．５μｍとなるように薄層状に印刷した。印刷後の基板は、乾燥器にて６０℃で１０分間乾燥させたのち、１０５℃，１１５℃または１２５℃の温度で２０分間の熱処理を施すことで、異なる熱処理温度で作製した例６～１３の導電膜を形成した。
　得られた導電膜の膜厚を測定し、その平均値を下記の表２の「焼成厚み」の欄に示した。また、得られた導電膜について、実施形態１と同様にしてシート抵抗および接着性を評価し、その結果を下記表２の当該欄に示した。 [Formation of conductive film]
The silver pastes of Examples 6 to 13 prepared in this way were applied to the surface of a PET resin film-like substrate (thickness: 100 μm) by screen printing in the same manner as in Embodiment 1. For the screen printing, a calendered # 640 stainless mesh was used and printed in a thin layer so that the film thickness after firing was approximately 1.5 μm. The printed substrates were dried at 60 ° C. for 10 minutes in a drier and then heat-treated at 105 ° C., 115 ° C. or 125 ° C. for 20 minutes, thereby producing Examples 6 to 13 at different heat treatment temperatures. The conductive film was formed.
The film thickness of the obtained conductive film was measured, and the average value was shown in the column of “Firing thickness” in Table 2 below. Further, the obtained conductive film was evaluated for sheet resistance and adhesiveness in the same manner as in Embodiment 1, and the results are shown in the corresponding column of Table 2 below.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
（評価）
　表２の例６～１０は、ガラス転移点が異なるポリエステル樹脂Ａ～Ｅを使用した点以外は同じ条件で調製した銀ペーストである。
　これらの銀ペーストにより形成された導電膜のシート抵抗は、バインダ樹脂のガラス転移点が乾燥温度よりも低い例６，７において小さい値となった。この点のみを見ると、バインダ樹脂のガラス転移点は、例えば５０℃以下の低い値であることが好ましいように思われる。しかしながら、シート抵抗の低い例６，７の導電膜は、樹脂量が同じであるにも関わらず基材への接着性が極めて低い。これは、例えば６０℃での銀ペーストの乾燥の際に、溶剤の揮発とバインダの軟化とが同時に起こり、安定した成膜ができないことによると考えられる。 (Evaluation)
Examples 6 to 10 in Table 2 are silver pastes prepared under the same conditions except that polyester resins A to E having different glass transition points were used.
The sheet resistance of the conductive film formed from these silver pastes was small in Examples 6 and 7, where the glass transition point of the binder resin was lower than the drying temperature. From this point alone, it seems that the glass transition point of the binder resin is preferably a low value of, for example, 50 ° C. or less. However, the conductive films of Examples 6 and 7 having a low sheet resistance have extremely low adhesion to the base material despite the same resin amount. This is considered to be because, for example, when the silver paste is dried at 60 ° C., volatilization of the solvent and softening of the binder occur at the same time, and stable film formation cannot be performed.
　これに対し、バインダ樹脂のガラス転移点が乾燥温度よりも高い例８～１０の銀ペーストについては、銀ペーストの乾燥と焼成とが別の工程で（２段階で）実施され、溶剤が十分に揮発した塗布体について焼成を行うことができる。このことにより、例８～１０の導電膜は、シート抵抗がやや高くなるものの、基材への接着性が高く、低シート抵抗と基材接着性とを両立し得ることがわかった。特に、例８および９の銀ペーストについては、焼成温度に大きく影響を受けることなく、安定してシート抵抗特性と接着性とに優れた導電膜を形成できることがわかった。 On the other hand, for the silver pastes of Examples 8 to 10 where the glass transition point of the binder resin is higher than the drying temperature, the drying and firing of the silver paste are performed in separate steps (in two steps), and the solvent is sufficient. Firing can be performed on the volatilized application body. From this, it was found that the conductive films of Examples 8 to 10 have a slightly high sheet resistance, but have high adhesion to the substrate, and can achieve both low sheet resistance and substrate adhesion. In particular, for the silver pastes of Examples 8 and 9, it was found that a conductive film having excellent sheet resistance characteristics and adhesiveness can be stably formed without being greatly affected by the firing temperature.
　なお、例１０の導電膜については、熱処理温度が１２５℃と高温であったサンプルについて、やや密着性が低下した。これは、バインダ樹脂のガラス転移点が熱処理温度に近づきすぎたため、バインダの軟化と銀粒子の焼成とが同時に進行して安定性が低下したためであると考えられる。このことから、耐熱性の低いフィルム状基板に導電膜を形成するためには、バインダ樹脂のガラス転移点は熱処理温度よりも十分に低いことが好ましい傾向にあると言える。例えば、熱処理温度よりも３０℃程度以上低いことが好ましい。 In addition, about the electrically conductive film of Example 10, about the sample whose heat processing temperature was as high as 125 degreeC, adhesiveness fell a little. This is thought to be because the glass transition point of the binder resin was too close to the heat treatment temperature, so that the softening of the binder and the firing of the silver particles proceeded simultaneously and the stability was lowered. From this, it can be said that the glass transition point of the binder resin tends to be preferably lower than the heat treatment temperature in order to form a conductive film on a film-like substrate having low heat resistance. For example, it is preferably about 30 ° C. lower than the heat treatment temperature.
　例１１～１３は、溶剤の種類を変えて銀ペーストを調製した例である。
　例１１では、溶剤として（ｂ）の酢酸２－（２－ブトキシエトキシ）エチルを用いた。溶剤として酢酸２－（２－ブトキシエトキシ）エチルを用いた場合、バインダ樹脂を溶解させて銀ペーストを作製することはできたものの、得られた銀ペーストの粘性が低すぎて印刷を行うことはできなかった。これは酢酸２－（２－ブトキシエトキシ）エチルがフェニル気を有さないためであると考えらえる。なお、このような粘性の低い銀ペーストに増粘剤を添加すると、得られる導電膜の特性が著しく悪化してしまうために実用的ではない。 Examples 11 to 13 are examples in which silver paste was prepared by changing the type of solvent.
In Example 11, (b) 2- (2-butoxyethoxy) ethyl acetate was used as the solvent. When 2- (2-butoxyethoxy) ethyl acetate was used as the solvent, the binder resin was dissolved to produce a silver paste, but the resulting silver paste was too viscous to perform printing. could not. This is thought to be because 2- (2-butoxyethoxy) ethyl acetate does not have a phenyl group. In addition, when a thickener is added to such a low-viscosity silver paste, the properties of the resulting conductive film are significantly deteriorated, which is not practical.
　例１２では、溶剤として（ｃ）のエチレングリコールモノフェニルエーテルを用いた。この場合、銀ペーストを印刷に適した粘度に調整することができた。また、加熱処理の温度を１０５℃～１２５℃の範囲とすることで、シート抵抗および接着性に優れた導電膜を形成できることがわかった。なお、加熱処理の温度を１０５℃～１１５℃と低めにすることで接着性がより改善され、シート抵抗と接着性とのバランスがより良い導電膜とすることができ、加熱処理の温度を１２５℃と高めにすることでよりシート抵抗の低い導電膜を形成できることも確認できた。 In Example 12, (c) ethylene glycol monophenyl ether was used as a solvent. In this case, the silver paste could be adjusted to a viscosity suitable for printing. It was also found that a conductive film having excellent sheet resistance and adhesiveness can be formed by setting the temperature of the heat treatment to a range of 105 ° C. to 125 ° C. Note that by reducing the temperature of the heat treatment to 105 ° C. to 115 ° C., the adhesiveness can be further improved, and a conductive film with a better balance between sheet resistance and adhesiveness can be obtained. It was also confirmed that a conductive film having a lower sheet resistance can be formed by increasing the temperature to 0C.
　例１３では、溶剤として（ｄ）のジエチレングリコールモノフェニルエーテルを用いた。溶剤としてジエチレングリコールモノフェニルエーテルを用いた場合、バインダ樹脂を溶剤に溶解させることができず、銀ペーストの調製自体が不可能であった。（ｄ）ジエチレングリコールモノフェニルエーテルは、（ｃ）エチレングリコールモノフェニルエーテルと同様にアルキレングリコール類であるが、沸点が２５０℃を大幅に超過する。沸点は分子構造やその特性をも反映し得るため、沸点が２５０℃を超えるジエチレングリコールモノフェニルエーテルは、ここに開示されるフレキシブル基板用銀ペーストの溶剤としては不適切であると考えられる。 In Example 13, (d) diethylene glycol monophenyl ether was used as a solvent. When diethylene glycol monophenyl ether was used as the solvent, the binder resin could not be dissolved in the solvent, and the silver paste itself could not be prepared. (D) Diethylene glycol monophenyl ether is an alkylene glycol similar to (c) ethylene glycol monophenyl ether, but its boiling point greatly exceeds 250 ° C. Since the boiling point may reflect the molecular structure and its characteristics, diethylene glycol monophenyl ether having a boiling point exceeding 250 ° C. is considered to be inappropriate as a solvent for the silver paste for flexible substrates disclosed herein.
　以上、本発明の具体例を詳細に説明したが、これらは例示にすぎず、請求の範囲を限定するものではない。請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。 Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (7)

  1. 　フレキシブルフィルム基板に導電膜を形成するための銀ペーストであって、
    　（Ａ）銀粉末と、（Ｂ）バインダとしての熱可塑性ポリエステル樹脂と、（Ｃ）前記熱可塑性ポリエステル樹脂を溶解させる溶剤と、を含み、
    （Ａ）前記銀粉末は、平均粒子径が４０ｎｍ以上１００ｎｍ以下であり、
    （Ｂ）前記熱可塑性ポリエステル樹脂は、
    　　ガラス転移点が６０℃以上９０℃以下であって、
    　　前記銀粉末１００質量部に対して、５質量部以上８質量部以下の割合で含まれ、
    （Ｃ）前記溶剤は、
    　　沸点が１８０℃以上２５０℃以下であって、
    　　分子構造にフェニル基を含む、
    ことを特徴とする、フレキシブル基板用銀ペースト。     A silver paste for forming a conductive film on a flexible film substrate,
    (A) silver powder, (B) a thermoplastic polyester resin as a binder, and (C) a solvent that dissolves the thermoplastic polyester resin,
    (A) The silver powder has an average particle size of 40 nm or more and 100 nm or less,
    (B) The thermoplastic polyester resin is
    The glass transition point is 60 ° C. or higher and 90 ° C. or lower,
    It is contained at a ratio of 5 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the silver powder.
    (C) The solvent is
    The boiling point is 180 ° C. or higher and 250 ° C. or lower,
    Including phenyl group in the molecular structure,
    The silver paste for flexible substrates characterized by the above-mentioned.
  2. 　（Ａ）前記銀粉末は、アスペクト比が１．５以下の球形銀微粒子と、アスペクト比が１．５超過の非球形銀微粒子とを含む、請求項１に記載のフレキシブル基板用銀ペースト。 (A) The silver paste for flexible substrates according to claim 1, wherein the silver powder includes spherical silver fine particles having an aspect ratio of 1.5 or less and non-spherical silver fine particles having an aspect ratio exceeding 1.5.
  3. 　（Ａ）前記銀粉末の表面には、炭素数５以下の有機アミンからなる保護剤が付着している、請求項１または２に記載のフレキシブル基板用銀ペースト。 (A) The silver paste for flexible substrates according to claim 1 or 2, wherein a protective agent made of an organic amine having 5 or less carbon atoms is attached to the surface of the silver powder.
  4. 　フレキシブルフィルム基板と、
    　前記フレキシブルフィルム基板上に備えられた導電膜と、
    を含み、
    　前記導電膜は、請求項１～３のいずれか１項に記載のフレキシブル基板用銀ペーストの硬化物である、電子素子。     A flexible film substrate;
    A conductive film provided on the flexible film substrate;
    Including
    The electronic device, wherein the conductive film is a cured product of the silver paste for flexible substrates according to any one of claims 1 to 3.
  5. 　前記導電膜の平均厚みは、０．２μｍ以上３μｍ以下である、請求項４に記載の電子素子。 The electronic element according to claim 4, wherein the conductive film has an average thickness of 0.2 μm to 3 μm.
  6. 　前記導電膜のシート抵抗は、１００ｍΩ／□以下である、請求項４または５に記載の電子素子。 The electronic element according to claim 4 or 5, wherein a sheet resistance of the conductive film is 100 mΩ / □ or less.
  7. 　フレキシブルフィルム基板を用意すること、
    　請求項１～３のいずれか１項に記載のフレキシブル基板用銀ペーストを用意すること、
    　前記フレキシブルフィルム基板上に、前記フレキシブル基板用銀ペーストを供給すること、
    　前記フレキシブル基板用銀ペーストが供給された前記フレキシブルフィルム基板を、乾燥させること、
    　前記乾燥された前記フレキシブル基板用銀ペーストが供給された前記フレキシブルフィルム基板を、熱処理して導電膜を形成すること、
    を含み、
    　前記フレキシブル基板用銀ペーストの供給は、形成される前記導電膜の平均厚みが３μｍ以下となるように実施し、
    　前記乾燥のための温度は、前記フレキシブル基板用銀ペーストに含まれる前記熱可塑性ポリエステル樹脂のガラス転移点よりも低い温度であり、
    　前記熱処理の温度は、前記ガラス転移点よりも２０℃以上高い温度である、
    電子素子の製造方法。     Preparing a flexible film substrate;
    Preparing a silver paste for a flexible substrate according to any one of claims 1 to 3,
    Supplying the silver paste for a flexible substrate on the flexible film substrate;
    Drying the flexible film substrate supplied with the silver paste for flexible substrate,
    Heat-treating the flexible film substrate supplied with the dried silver paste for a flexible substrate to form a conductive film;
    Including
    The supply of the silver paste for flexible substrate is carried out so that the average thickness of the conductive film to be formed is 3 μm or less,
    The temperature for the drying is a temperature lower than the glass transition point of the thermoplastic polyester resin contained in the silver paste for flexible substrate,
    The temperature of the heat treatment is a temperature that is 20 ° C. or more higher than the glass transition point.
    A method for manufacturing an electronic device.
PCT/JP2017/031811 2016-09-16 2017-09-04 Silver paste for flexible substrate WO2018051830A1 (en)

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