WO2012173245A1 - Silver powder and method for producing same - Google Patents

Silver powder and method for producing same Download PDF

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Publication number
WO2012173245A1
WO2012173245A1 PCT/JP2012/065411 JP2012065411W WO2012173245A1 WO 2012173245 A1 WO2012173245 A1 WO 2012173245A1 JP 2012065411 W JP2012065411 W JP 2012065411W WO 2012173245 A1 WO2012173245 A1 WO 2012173245A1
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WIPO (PCT)
Prior art keywords
silver
silver powder
paste
particles
powder
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PCT/JP2012/065411
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French (fr)
Japanese (ja)
Inventor
井上　雅仁
川上　裕二
知倫 二瓶
俊昭 寺尾
Original Assignee
住友金属鉱山株式会社
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.)
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Application filed by 住友金属鉱山株式会社 filed Critical 住友金属鉱山株式会社
Priority to CN201280002704.1A priority Critical patent/CN103079730B/en
Priority to JP2012548249A priority patent/JP5344099B2/en
Priority to KR1020137005227A priority patent/KR20140024829A/en
Priority to KR1020187016842A priority patent/KR20180069930A/en
Publication of WO2012173245A1 publication Critical patent/WO2012173245A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/148—Agglomerating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/16—Metallic particles coated with a non-metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2301/00—Metallic composition of the powder or its coating
    • B22F2301/25—Noble metals, i.e. Ag Au, Ir, Os, Pd, Pt, Rh, Ru
    • B22F2301/255—Silver or gold

Definitions

  • the present invention relates to silver powder and a method for producing the same, and more particularly to silver powder as a main component of silver paste used for forming a wiring layer or an electrode of an electronic device and a method for producing the same.
  • a silver paste such as a resin type silver paste or a baking type silver paste is often used to form a wiring layer, an electrode and the like in an electronic device.
  • a conductive film to be a wiring layer, an electrode, or the like can be formed by applying or printing these silver pastes on various types of substrates and then heat curing or heating and firing.
  • resin-type silver paste is made of silver powder, resin, curing agent, solvent, etc., printed on a conductor circuit pattern or terminal, heat cured at 100 ° C. to 200 ° C. to form a conductive film, wiring layer or electrode Form
  • the baking type silver paste is made of silver powder, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at 600 ° C. to 800 ° C. to form a conductive film to form a wiring layer or an electrode. .
  • the silver powder used for these silver pastes has a particle diameter of 0.1 ⁇ m to several ⁇ m, and the particle diameter of the silver powder used differs depending on the thickness of the wiring layer to be formed, the thickness of the electrode, and the like. Further, by uniformly dispersing silver powder in silver paste, it is possible to form a wiring layer of uniform thickness and an electrode of uniform thickness.
  • each component is weighed and placed in a predetermined container, prekneaded using a universal stirrer, a kneader or the like, and then main kneading is carried out using a triple roll or the like.
  • pre-kneading it is important to sufficiently wet and disperse the respective constituents, and by sufficiently performing this pre-kneading, the generation of silver foil in the main-kneading is prevented, and the particle size of silver powder in the silver paste is aimed at It is possible to quickly reduce the particle size and disperse the silver powder uniformly in the silver paste.
  • the silver powder which occupies most of the weight in the silver paste is not only uniform in particle diameter and less aggregation, but also conforms well to the vehicle comprising a solvent, resin or the like, and the dispersibility in the silver paste is high. Characteristics are required. Such characteristics change depending not only on the structural properties of the powder such as bulk density and particle size distribution but also on the chemical properties of the silver powder surface such as slipperiness, hydrophilicity and hydrophobicity of the powder surface.
  • Patent Document 1 describes that spherical silver powder has a specific bulk density and a formed body density to improve the compatibility with a vehicle or a resin. There is. However, Patent Document 1 does not describe the surface chemical properties, and it is difficult to control the compatibility with a vehicle or a resin only with such structural parameters. In addition, Patent Document 1 does not describe a method of producing silver powder, such as a method of crushing silver powder that greatly affects the chemical properties of the surface.
  • Patent Document 2 the ratio D50 / DIA between the D50 value by particle size distribution measurement and the particle diameter DIA obtained by image analysis is used as a measure of the degree of aggregation of the powder, and if this is less than a specific value It is stated that Certainly, if this value is small, it is considered that the number of aggregates in the powder is small.
  • Patent Document 2 describes, as in Patent Document 1, a description of the chemical properties of the surface of silver powder that affects the compatibility with a vehicle or resin when pasted, and a production method that affects the chemical properties. There is no.
  • an object of the present invention is to provide silver powder excellent in compatibility with a solvent, resin, etc. of silver paste, resin, etc., and its manufacturing method.
  • the silver powder according to the present invention for achieving the above-mentioned object is characterized in that the internal friction angle is 20 ° or less and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more.
  • the crushing process is sufficiently sufficient not to damage the organic film layer. It is characterized by doing.
  • the internal friction angle of silver powder is 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more, so that the compatibility with solvents, resins, etc. is high and the dispersibility is excellent. And can be easily pasted. Thereby, in the present invention, the quality and productivity of silver paste can be improved.
  • the silver powder 1 shown in FIG. 1 is contained in a resin-type silver paste composed of a curing agent, a resin, a solvent and the like, and a fired silver paste composed of glass, a solvent and the like.
  • the resin type silver paste and the baking type silver paste in which the silver powder 1 is contained are used for formation of a wiring layer and an electrode. For this reason, the silver powder 1 has good compatibility with the solvent of silver paste and resin so that electrical connection can be achieved, and it is necessary to disperse it evenly in the paste.
  • Silver powder 1 is particularly suitable for silver paste using a hydrophobic solvent.
  • the silver powder 1 has an internal friction angle of 20 ° or less, and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more. Furthermore, it is preferable that the silver powder 1 is 18 or less in surface SP value by an acetone titration method.
  • the silver powder 1 has good chemical compatibility with a vehicle such as a solvent of a silver paste or a resin by making the chemical property of the powder surface low hydrophilic to improve sliding.
  • the silver powder 1 also includes secondary particles and aggregates.
  • the primary particles refer to individual spherical silver particles 2, and as shown in FIG. 1 (B), a plurality of primary particles are connected by fusion, fixation, etc.
  • the silver particles 2 are called secondary particles.
  • aggregation of silver particles 2 of these primary particles and secondary particles is referred to as an aggregate.
  • primary particles preferably have an average particle diameter in the range of 0.1 ⁇ m to 1.5 ⁇ m.
  • the average particle diameter of the primary particles is 0.1 ⁇ m or more, resistance can not be generated when the silver paste (conductive paste) is used, and conductivity can be improved. Further, by setting the average particle diameter of the primary particles to 1.5 ⁇ m or less, silver flakes are not generated at the time of kneading without deteriorating the dispersibility, and the printability is also improved.
  • the average particle size of primary particles can be measured by scanning electron microscope (SEM) observation.
  • the particle size of silver powder 1 is preferably 0.5 ⁇ m to 5 ⁇ m, and more preferably 1.0 ⁇ m to 4.0 ⁇ m in terms of D50 (volume integration 50% diameter) measured using a laser diffraction scattering method. preferable.
  • D50 volume integration 50% diameter
  • the internal friction angle of the silver powder 1 is a parameter indicating the slipperiness of the powder, and can be measured by a commercially available powder layer shear force measuring device.
  • the internal friction angle exceeds 20 °, slippage between particles (primary particles, secondary particles or aggregates independently present in silver powder 1) becomes worse.
  • the solvent or resin can not be split between the particles of silver powder 1 and only part of the surface of silver powder 1 can be wetted. In such a state, even if stirring is performed, the particles are not easily loosened, and the dispersibility of the silver powder 1 is poor.
  • the silver powder 1 having poor dispersibility not only takes time for prekneading to wet and disperse the respective constituents, but also the silver powder 1 aggregated during main kneading with a three-roll mill or the like is crushed and silver flakes are easily generated. Become. Accordingly, when the internal friction angle of the silver powder 1 is 20 ° or less, the slip becomes better, the solvent and the resin enter between the particles, and the compatibility becomes better, so the dispersibility in the silver paste becomes better.
  • the silver powder 1 has an internal friction angle of 20 ° or less immediately after production and, of course, maintains an internal friction angle of 20 ° or less after production, and is mixed with a solvent or resin to be paste It is preferable that it is 20 degrees or less also in For example, even after one month has passed at room temperature after producing the silver powder 1, for example, the internal friction angle of the silver powder 1 is 20 ° or less.
  • the internal friction angle is a parameter that changes due to the aggregation of particles, and even if it is a powder with a low degree of aggregation immediately after production, the internal friction angle increases due to the progress of aggregation between particles over time There is.
  • the internal friction angle changes over time and the internal friction angle exceeds 20 °, the dispersibility decreases when the paste is formed, which causes various problems such as aggregation of the silver powder 1. Therefore, if the internal friction angle of 20 ° or less can be maintained, the progress of aggregation can be suppressed, so that the occurrence of a problem can be prevented at the time of paste formation.
  • the silver powder 1 has a contact angle of 100 ° or more with a 50% by volume aqueous solution of methanol.
  • the contact angle is a parameter representing the wettability of the surface of silver powder 1 to the solvent, and for example, the larger the contact angle to water, the easier it is to wet a hydrophobic paste solvent. On the contrary, the smaller the contact angle to water, the more hydrophilic it is, and the more it gets wet to the hydrophobic paste solvent.
  • the contact angle of the silver powder 1 is generally measured on the molded surface, but when the measurement is performed with water, in the case of a powder with high hydrophobicity, the water droplets become spherical on the surface of the molded powder, It is difficult to measure accurately because the water droplets slide and move. For this reason, a method of performing measurement by adding a low polarity solvent such as methanol to water to lower the polarity of the solvent is performed. In producing a silver paste, generally a hydrophobic solvent is often used.
  • the silver powder 1 has a hydrophilic surface having a contact angle of less than 100 °, the compatibility of the paste with the solvent or resin is poor, and the silver powder 1 does not get wet with the solvent or resin, making it paste It will be difficult.
  • the paste is forcibly kneaded to form a paste, the dispersion stability is poor and separation of the paste is likely to occur due to reaggregation.
  • Silver powder 1 has a surface SP value of 18 or less.
  • the surface SP value is a parameter representing the polarity of the surface of silver powder 1, and is smaller as it is smaller and more as it is larger.
  • This surface SP value can be measured with a commercially available powder wettability tester or the like, but in a simple manner, the acetone titration method as described in "Color material, 62 (9) 524-528" But measurement is possible.
  • this acetone titration method hydrophobic powder is added to water (A [ml]) and suspended. While stirring gently with a stirrer, acetone is added dropwise with a burette, and the amount of acetone (B [ml]) required for the powder to wet and settle is measured.
  • the SP value of the silver powder 1 is calculated from the equation 1 below using the SP value of water 23.43, the SP value of acetone 9.75, the volume of water used and the volume of acetone used from the equation 1 below. Let it be the surface SP value.
  • the hydrophilicity of the silver powder 1 When the surface SP value of the silver powder 1 is larger than 18, the hydrophilicity is too large, the compatibility of the paste with the solvent or resin is deteriorated, and the silver powder 1 does not get wet with the solvent or resin, making it into a paste Is difficult. In addition, even if the paste is forcedly kneaded, the dispersion stability is poor, and separation of the paste is likely to occur due to reaggregation. On the other hand, when the surface SP value of the silver powder 1 is 18 or less, the hydrophilicity of the silver powder 1 does not become too large, the compatibility with the solvent and the resin becomes good, and the dispersibility becomes excellent. Becomes easier.
  • the silver powder 1 is surface-treated with the silver particles 2 obtained by the wet reduction method to form the organic coating layer 3 on the surfaces of the primary particles or the secondary particles as shown in FIG. Can be made 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol can be made 100 ° or more, and furthermore, the surface SP value by the acetone titration method can be made 18 or less.
  • the organic coating layer 3 can be formed of a surfactant, or a surfactant and a dispersant.
  • the organic coating layer 3 is preferably formed of a surfactant and a dispersant.
  • aggregation can be suppressed by adsorbing the surfactant to silver particles 2 in the ionized state, but in order to suppress aggregation only by the surfactant, the addition amount becomes too large . Therefore, even if a good dispersion state is obtained in the silver paste, the conductivity of the wiring layer or the electrode may not be sufficient. Therefore, in order to suppress the aggregation of the silver powder 1 and to make the conductivity of the wiring layer or the electrode sufficient, it is effective to use a surfactant and a dispersant in combination.
  • the organic coating layer 3 is formed by further adsorbing the dispersant to the surfactant adsorbed to the silver particles 2 by adding the dispersant during or after adsorption of the surfactant to the silver particles 2.
  • the organic coating layer 3 is strongly attached to the surface of the silver particles 2, while the solvent or resin is Good compatibility with Thereby, even if the silver powder 1 in which the organic film layer 3 is formed almost uniformly on the surface of the silver particle 2 is mixed with the solvent or the resin, the organic film layer 3 can be prevented from peeling off.
  • a cationic surfactant for example, in the case of silver powder 1 using silver chloride as a starting material, it is preferable to use a cationic surfactant as a surfactant.
  • the cationic surfactant ionizes into positive ions without being affected by pH, so that the adsorptivity to the silver powder 1 can be improved.
  • the cationic surfactant is not particularly limited, but is an alkyl monoamine salt type represented by a monoalkylamine salt, and an alkyl diamine salt represented by an N-alkyl (C14 to C18) propylene diamine dioleate.
  • alkyl trimethyl ammonium salt type represented by alkyl trimethyl ammonium chloride
  • alkyl dimethyl benzyl ammonium salt type represented by coc alkyl dimethyl benzyl ammonium chloride
  • quaternary ammonium salt type represented by alkyl dipolyoxyethylene methyl ammonium chloride
  • Alkyl pyridinium salt type tertiary amine type represented by dimethyl stearyl amine
  • polyoxyethylene alkyl amine type represented by polyoxypropylene / polyoxyethylene alkylamine
  • at least one selected from oxyethylene addition forms of diamines represented by N, N ′, N′-tris (2-hydroxyethyl) -N-alkyl (C14-18) 1,3-diaminopropane A quaternary ammonium salt type, a tertiary amine salt type or a mixture thereof is more preferred.
  • the cationic surfactant preferably has at least one alkyl group having a carbon number of C4 to C36 represented by methyl group, butyl group, cetyl group, stearyl group, beef tallow, hardened beef tallow, and vegetable stearyl.
  • the alkyl group is preferably one to which at least one selected from polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid and polycarboxylic acid is added. Since these alkyl groups have strong adsorption with the fatty acid used as the dispersant, when the dispersant is adsorbed to the silver particles 2 via the surfactant, the fatty acid can be strongly adsorbed.
  • the cationic surfactant is not particularly limited, but is preferably at least one selected from fluoride, bromide, iodide, chloride, sulfate, nitrate and phosphate. These are generally contained as main components of surfactants, and are preferable because they are easily available.
  • protective colloids such as fatty acids, organic metals, gelatin and the like can be used, but fatty acids or salts thereof may be used in view of the possibility of contamination with impurities and in view of the adsorptivity with surfactants. preferable.
  • the fatty acid used as the dispersant is not particularly limited, but is preferably at least one selected from stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid and linolenic acid. Because these fatty acids have a relatively low boiling point, they have little adverse effect on wiring layers and electrodes formed using silver paste.
  • the fatty acid is originally hydrophobic, and by causing the dispersant to be adsorbed to the surface of the silver particle 2 via the surfactant, a large amount of the fatty acid is present on the outer surface side of the organic coating layer 3 and the silver powder 1 is hydrophobic. It is thought that it comes to have sex.
  • the dispersant is sufficiently adsorbed through the surfactant.
  • the silver powder 1 becomes sufficiently hydrophobic.
  • the addition amount of the surfactant is preferably in the range of 0.002% by mass to 1.000% by mass with respect to the silver particles 2. Since almost all of the surfactant is adsorbed to the silver particles 2, the addition amount of the surfactant and the adsorption amount are almost equal. When the addition amount of the surfactant is less than 0.002% by mass, the effects of the aggregation suppression of the silver particles 2 and the adsorptivity improvement of the dispersant may not be obtained. On the other hand, when the addition amount exceeds 1.000% by mass, the conductivity of the wiring layer or the electrode formed using the silver paste is unfavorably lowered.
  • the addition amount of the dispersant is preferably in the range of 0.01% by mass to 3.00% by mass, and more preferably 0.01% by mass to 1.00% by mass with respect to the silver particles 2.
  • the amount of adsorption onto silver particles 2 varies depending on the type of dispersant, but if the amount added is less than 0.01% by mass, the amount of dispersant of which the effect of suppressing aggregation of silver particles 2 is sufficiently obtained is silver particles 2 may not be adsorbed.
  • the addition amount of the dispersing agent exceeds 3.00 mass%, the dispersing agent adsorbed to the silver particles 2 increases, and the conductivity of the wiring layer and the electrode formed using the silver paste is sufficiently It can not be obtained.
  • the adsorptivity of the surfactant to the silver particles 2 is significantly improved, so the surfactant can be strongly adsorbed to the silver powder 1. More preferably, by stably adsorbing the surfactant adsorbed to the silver particles 2, it is possible to obtain the silver powder 1 which is further suppressed from aggregation and excellent in the dispersibility in the paste.
  • the method of producing the silver powder 1 is as follows, for example, in the case of using silver chloride as a starting material.
  • a silver particle slurry is prepared by a wet reduction method in which a silver complex solution containing a silver complex obtained by dissolving silver chloride with a complexing agent and a reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles 2.
  • a nitrous gas recovery device required by the conventional method using silver nitrate as a starting material and a treatment device for nitric acid-based nitrogen in waste water, and to the environment. Since the process is less affected, the manufacturing cost can be reduced.
  • silver chloride is dissolved using a complexing agent to prepare a silver complex solution containing a silver complex.
  • the complexing agent is not particularly limited, but it is preferable to use ammonia water which easily forms a complex with silver chloride and does not contain a component remaining as an impurity.
  • silver chloride having high purity As such silver chloride, high purity silver chloride having a purity of 99.9999% by mass is stably manufactured for industrial use.
  • a slurry of silver chloride may be prepared and ammonia water may be added, but ammonia is increased to increase the concentration of the complex to improve productivity. It is preferable to add and dissolve silver chloride in water.
  • Ammonia water which dissolves silver chloride may be a conventional one which is used industrially, but one having as high purity as possible is preferable in order to prevent impurity contamination.
  • a reducing agent solution to be mixed with the silver complex solution is prepared.
  • the reducing agent general hydrazine, formalin or the like can be used. Ascorbic acid is particularly preferable because the crystal grains in the silver particles 2 easily grow because the reducing action is slow. Because hydrazine and formalin have strong reducing power, crystals in silver particles 2 tend to be small.
  • the reducing agent may be used as an aqueous solution in which the concentration is adjusted by dissolving or diluting it with pure water or the like.
  • the water-soluble polymer to be added is not particularly limited, but is preferably at least one of polyethylene oxide, polyethylene glycol, polyvinyl alcohol or polyvinyl pyrrolidone.
  • the water-soluble polymer is adsorbed on the surface of the silver particles 2 so that the primary or secondary particles of the silver do not excessively aggregate when the silver complex is reduced to precipitate the silver particles 2. Act as a dispersing agent to be dispersed. In the case where the water-soluble polymer is not added, the silver particles 2 generated by the reduction of the silver complex and the nuclei generated by the reduction may cause excessive aggregation, and the dispersibility may be poor.
  • the particle size of silver powder 1 can be adjusted to the extent preferable for silver paste depending on the reducing conditions, but the addition of water-soluble polymer makes the particle size more preferable for silver paste. It becomes possible to adjust.
  • the addition amount of the water-soluble polymer may be appropriately determined according to the type of the water-soluble polymer and the particle size of the silver powder 1 to be obtained, but 1% by mass to 10% by mass with respect to silver contained in the silver complex solution It is preferable to make it the range of%. By setting the content of the water-soluble polymer to 1% by mass to 10% by mass, excessive aggregation of primary particles or secondary particles of silver does not occur, and the silver particles 2 are The organic coating layer 3 can be appropriately formed on the surface.
  • the water-soluble polymer can also be added to the silver complex solution and / or the reducing agent solution.
  • the addition of the water-soluble polymer to the silver complex solution and / or the reducing agent solution may be previously added to the solution to be added prior to the reduction treatment, and the silver complex-containing solution for the reduction treatment And may be added when mixing the reducing agent solution. More preferably, it is better to previously mix the water-soluble polymer in the reducing agent solution. This is an experimentally confirmed result, but the mixing of the reducing agent solution and the water-soluble polymer results in the presence of the water-soluble polymer at the site of nucleation or growth, and the nucleus or silver formed.
  • concentration at the time of mixing a water-soluble polymer with silver complex solution sets it as 10 mass% or less exceeding 3 mass%.
  • an antifoaming agent may be added to the silver complex solution or the reducing agent mixed solution.
  • the antifoaming agent is not particularly limited, and may be one usually used at the time of reduction. However, in order not to inhibit the reduction reaction, it is preferable to set the amount of the antifoaming agent to a minimum level at which the defoaming effect can be obtained.
  • water used when preparing a silver complex solution and a reducing agent solution in order to prevent mixing of an impurity, it is preferable to use the water from which the impurity was removed, and it is especially preferable to use a pure water.
  • the silver complex solution prepared as described above and the reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles 2 by a wet reduction method.
  • This reduction reaction may be a batch method or may be performed using a continuous reduction method such as a tube reactor method or an overflow method.
  • the particle size of the silver particles 2 can be controlled by the mixing speed of the silver complex solution and the reducing agent solution or the reduction speed of the silver complex, and can be easily controlled to the target particle size.
  • the obtained silver particle slurry is filtered with a filter etc., solid-liquid separation of the silver particle 2 is carried out.
  • the silver particles 2 obtained in this step a large amount of chlorine ions and a surplus water-soluble polymer are adsorbed on the surface. Therefore, in order to make the conductivity of the wiring layer and electrodes formed using silver paste sufficient, the obtained slurry of silver particles 2 is washed in the next washing step, and these surface adsorbates are It needs to be removed by washing.
  • the washing method is not particularly limited, but silver particles 2 solid-liquid separated from the slurry are added to the washing liquid, stirred using a stirrer or an ultrasonic cleaner, and then solid-liquid separated again A method of recovering silver particles 2 is generally used. Moreover, in order to fully remove a surface adsorbate, it is preferable to repeat the operation which consists of injection
  • the cleaning solution water may be used, but an alkaline aqueous solution may be used to efficiently remove chlorine.
  • the alkaline solution is not particularly limited, but it is preferable to use an inexpensive aqueous solution of sodium hydroxide with few residual impurities.
  • sodium hydroxide aqueous solution as a washing
  • the concentration of the aqueous sodium hydroxide solution used for washing is preferably 0.01 mol / l to 1 mol / l. If it is less than 0.01 mol / l, the cleaning effect is insufficient, and if it exceeds 1 mol / l, sodium may be left in the silver particles 2 more than acceptable.
  • the water used for the cleaning solution is preferably water containing no impurity element harmful to the silver particles 2, and particularly preferably pure water.
  • the surface treatment process of forming the organic film layer 3 on the surface of the silver particle 2 is performed.
  • the silver particles 2 are treated with a surfactant, or more preferably with a surfactant and a dispersant.
  • This surface treatment may be performed at any stage before the silver particles 2 are dried, but when the chlorine and the water-soluble polymer are completely removed, the silver particles 2 aggregate, and in the surface treatment after removal the silver Since uniform surface treatment to the surface of the particles 2 may be difficult, surface treatment at the same time or immediately after reduction, after solid-liquid separation of the silver particles 2 from the silver particle slurry and before the washing step It is preferable to carry out the surface treatment simultaneously with the treatment or washing step.
  • the surface treatment step for example, solid-liquid separation of the silver particles 2 from the silver particle slurry is followed by surface treatment to prevent the adsorption of the surfactant and the dispersant from being inhibited by the residual organic matter or the like caused by the reducing agent.
  • Surface treatment can be performed efficiently. Therefore, a sufficient organic coating layer 3 is formed, and compatibility and dispersibility with a solvent, a resin, and the like are secured.
  • surface treatment may be performed during any washing, but chlorine remaining in silver particles 2 and excess water-soluble polymer do not affect the surface treatment. It is preferable that removal be performed to a certain extent and aggregation of the silver particles 2 not proceed, for example, surface treatment be performed after one or more washings.
  • a silver particle 2 obtained by solid-liquid separation from a silver particle slurry is used as a surfactant and It may be poured into water to which the dispersant has been added and stirred, or may be poured into water to which the surfactant has been added and stirred, and then the dispersant may be added and stirred.
  • the washing and the surface treatment may be performed simultaneously by adding the surfactant and the dispersing agent simultaneously to the washing solution, or adding the dispersing agent after the addition of the surfactant.
  • the silver particles 2 are added to water or a washing solution to which the surfactant is added and stirred, and then the dispersing agent is further added and stirred. Is preferred.
  • cleaning and surface treatment may be an apparatus normally used for washing
  • a recovery step of recovering the silver particles 2 having the organic coating layer 3 formed on the surface is performed.
  • solid-liquid separation is performed to recover silver particles 2.
  • An apparatus used for solid-liquid separation may be a commonly used apparatus, and for example, a centrifuge, a suction filter, a filter press, etc. can be used.
  • washing and surface treatment are completed, and a drying step of evaporating and drying the water of the silver particles 2 obtained by solid-liquid separation is performed.
  • a drying method for example, silver particles 2 collected after completion of washing and surface treatment are placed on a stainless steel pad, and a temperature of 40 ° C. to 80 ° C. using a commercially available drying device such as an atmospheric oven or vacuum dryer. It may be heated.
  • the silver powder 1 is obtained.
  • the crushing method is not particularly limited as long as the organic coating layer 3 is not damaged, and it is preferable to use an apparatus having a weak crushing power such as a jet mill or a high speed stirrer. In an apparatus with high crushing power, not only damage to the organic coating layer 3 but also the silver powder 1 may be deformed, which is not preferable.
  • the classifier is not particularly limited, and an air flow classifier, a sieve or the like can be used.
  • the crushing process refers to an operation of disaggregating dried aggregate powder into a state of primary particles or secondary particles before surface treatment.
  • a means of crushing it is possible to use various things such as a ball mill, a collision type air flow type crusher, an impact type crusher, a cylindrical high speed stirrer, etc., but when the energy of crushing is too weak.
  • the aggregates formed during the wet processing and the drying process can not be sufficiently disintegrated, and the internal friction angle can not be made 20 ° or less.
  • the crushing energy is excessively strong, the organic film layer 3 on the surface of the silver powder 1 is damaged, or the primary particles in the secondary particles are broken.
  • the newly exposed surface of silver metal on the surface of silver powder 1 increases the hydrophilicity of the surface, and the contact angle with a 50% by volume aqueous solution of methanol becomes less than 100 °, and the surface SP value by acetone titration method is 18 It gets bigger. Furthermore, the exposed new surface may be an active point, reaggregated during storage, and the internal friction angle may increase over time.
  • the crushing conditions are adjusted while confirming parameters such as the internal friction angle, contact angle, surface SP value, and the destruction of the bond where primary particles are bonded is suppressed.
  • the crushing conditions the number of rotations of the crushing device, the crushing time, the temperature and the like are appropriately determined depending on the size of the crushing device, the state of the produced silver powder 1 and the like.
  • the peripheral speed and stirring time of the stirrer are adjusted according to the input amount of silver particles 2 so as not to damage the organic coating layer 3 .
  • a crushing condition in the case of using a high-speed stirrer for example, it is preferable to set the peripheral speed to 10 m / s to 40 m / s and set the crushing time to about 10 to 60 minutes.
  • classification processing such as air flow type or sieving type is performed for the purpose of removing massive silver powder aggregates which are generated or mixed in the silver particle slurry forming step or the crushing / classifying step. Is preferred.
  • the method for producing silver powder 1 described above after the organic coating layer 3 is formed on the surface of the silver particles 2 obtained in the silver particle slurry forming step, generation of a new surface of metallic silver on the silver particles 2 is suppressed
  • a low hydrophilic silver powder 1 having an internal friction angle of 20 ° or less and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more.
  • the silver powder 1 has a surface SP value of 18 or less by the acetone titration method.
  • the internal friction angle of silver powder 1 is 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more, whereby the wettability of the silver paste to the solvent, resin, etc. Is excellent in dispersibility and can be easily pasted to prepare a silver paste.
  • the silver powder 1 produced by this production method is subjected to sufficient surface treatment, so that the internal friction angle is 20 ° or less not only immediately after production but also when it is mixed with a silver paste resin or solvent. Because of the above, even when mixing with a solvent after a while after production, compatibility with the solvent, resin, etc. is good, and since it is excellent in dispersibility, it can be easily made into a paste. .
  • the silver powder 1 described above is dispersed evenly in the silver paste, and therefore, when the wiring layer or the electrode is formed by the silver paste, the electrical connection can be made favorable.
  • Example 1 In Example 1, first, 2490 g of silver chloride (Sumitomo Metal Mining Co., Ltd.) is added while being stirred to 36 L of 25% by mass ammonia water kept at a liquid temperature of 36 ° C. in a 38 ° C. water bath and a silver complex solution And kept at 36.degree. C. in a warm water bath.
  • silver chloride Suditomo Metal Mining Co., Ltd.
  • the silver complex solution and the reducing agent solution are sent to the inside of the crucible at 2.44 L / min and 0.90 L / min, respectively, using a Mono pump (manufactured by HIROSHI KOGYO CO., LTD.) To obtain a silver complex Reduced.
  • the reduction rate at this time is 127 g / min in silver amount.
  • the pipe made from polyvinyl chloride of internal diameter 25 mm and length 725 mm was used for the said crucible.
  • the slurry containing the silver particles obtained by the reduction of the silver complex was received in the receiving vessel with stirring. After receiving, the stirring in the receiving tank was continued for 60 minutes.
  • the silver particle slurry after completion of the stirring was filtered by a filter press to separate the silver particles into solid and liquid.
  • the silver particles were put into a 0.05 mol / L aqueous NaOH solution, stirred for 15 minutes and washed, and then filtered and collected by a filter press. Thereafter, the washing operation and the solid-liquid separation operation by filtration were repeated three times.
  • the solid-liquid separated silver particles were introduced into 20 L of pure water, stirred and filtered, and then the silver particles were transferred to a stainless steel pad and dried in a vacuum drier at 60 ° C. for 10 hours.
  • the silver powder of Example 1 was obtained as mentioned above.
  • the internal friction angle, the contact angle, and the surface SP value were measured for the obtained silver powder.
  • a powder layer shear force measuring apparatus (NS-S300 manufactured by Nano Seas Co., Ltd.) was used. After filling 18 g of silver powder into a SUS cell with an inner diameter of 15 mm at normal temperature, the setting value of the pressing load was set to 20 N, and the load was applied at a pressing speed of 0.2 mm / sec. After reaching the set load, lateral movement was started at a speed of 10 ⁇ m / sec after 100 seconds. The sampling frequency was 10 Hz.
  • the value obtained by dividing the indentation load at the start of sliding by the cross-sectional area of the cell is the vertical stress ⁇ (N / cm 2 ), and obtained by dividing the maximum value of shear force measured after sliding by the cross-sectional area of the cell
  • the shear stress ⁇ (N / cm 2 ) was taken as the value.
  • the set value of indentation load was set to 40 N, and the normal stress ⁇ and the shear stress ⁇ were similarly measured. Furthermore, the normal stress ⁇ and the shear stress ⁇ were similarly measured with the setting value of indentation load being 60N.
  • the vertical stress ⁇ obtained under the above three conditions is plotted on the horizontal axis, and the shear stress ⁇ is plotted on the vertical axis, and the inclination (degree) of the approximate straight line obtained using the least squares method is taken as the internal friction angle.
  • the internal friction angle of the silver powder of Example 1 measured by the above method was 7.1 °.
  • the silver powder was allowed to stand at room temperature for 1 month, and the internal friction angle was measured in the same manner as described above.
  • a contact angle measurement device (CA-X150, manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the contact angle with a 50% by volume aqueous solution of methanol.
  • the silver powder was press-formed at a normal temperature and a load of about 1 MPa to obtain a flat plate-like test body in which the silver powder was consolidated and filled.
  • the contact angle at which a 50% by volume aqueous solution of methanol is formed was measured on this test sample.
  • the contact angle of the silver powder of Example 1 measured by this method was 110 °.
  • the measurement of the surface SP value by the acetone titration method was performed as follows. 50 ml of water is added to 0.5 g of silver powder, and acetone is continuously dropped into water containing silver powder while stirring gently, and silver particles suspended on the water surface are dispersed to cause the solution to become cloudy. And The surface SP value of the acetone aqueous solution calculated from the addition volume of acetone at this time was taken as the surface SP of the silver powder. The surface SP value of the silver particles of Example 1 measured by this method was 16.7.
  • this paste was kneaded for 5 minutes at 2000 rpm using a self-revolution kneader (AREA-250 manufactured by Shinky Co., Ltd.) to obtain a uniform silver paste.
  • a self-revolution kneader (AREA-250 manufactured by Shinky Co., Ltd.) to obtain a uniform silver paste.
  • the maximum particle size Dmax was as small as 7 ⁇ m and showed excellent dispersibility.
  • Example 2 was the same as Example 1 except that the amount of polyvinyl alcohol was 75 g (4.00 mass% with respect to silver particles), and the rotating blade of the high speed stirrer was rotated at a peripheral speed of 28 m / sec. Silver powder was obtained and evaluated in the same manner. The average particle diameter of primary particles of the obtained silver powder was 1.01 ⁇ m, and the particle diameter (D50) was 2.73 ⁇ m.
  • the internal friction angle of the silver powder of Example 2 was 10.4 °, and the internal friction angle after being left at room temperature for one month was 10.6 °.
  • the contact angle of the silver powder of Example 2 was 109 °, and the surface SP value was 17.4.
  • Example 2 Evaluation of paste formation similar to Example 1 was performed using the obtained silver powder.
  • the surface of the silver powder was observed to be wet quickly by the vehicle.
  • this was mixed using a metallic spatula, mixing, dispersion proceeded easily, and it could be made into a paste.
  • this paste was kneaded with a revolution / revolution type kneader in the same manner as in Example 1 to obtain a uniform silver paste.
  • the maximum particle diameter Dmax was as small as 6 ⁇ m and showed excellent dispersibility.
  • Comparative Example 1 In Comparative Example 1, silver powder was obtained and evaluated in the same manner as in Example 1 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 42 m / sec. The average particle diameter of the primary particles of the obtained silver powder was 0.99 ⁇ m, and the particle diameter (D50) was 1.82 ⁇ m. Further, the internal friction angle of the silver powder of Comparative Example 1 was 20.8 °, which was considerably higher than that of the example. Moreover, the contact angle of the silver powder of Comparative Example 1 was 85 °, and the surface SP value was 18.7.
  • Example 2 Evaluation of paste formation similar to Example 1 was performed using the obtained silver powder. Wetting of the surface of the silver powder by the vehicle was hardly observed. Moreover, when this was stirred using a metallic spatula, it could not be made into a paste-like while remaining large clay-like. Further, this silver paste was kneaded with a self-revolution type kneader in the same manner as in Example 1 to form a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle diameter Dmax was as large as 20 ⁇ m and the dispersibility was poor.
  • Comparative Example 2 In Comparative Example 2, silver powder was obtained and evaluated in the same manner as in Example 2 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 7 m / sec.
  • the average particle diameter of primary particles of the obtained silver powder was 1.00 ⁇ m, and the particle diameter (D50) was 3.52 ⁇ m.
  • the internal friction angle of the silver powder of Comparative Example 2 was 25.8 °, which was considerably higher than that of the example.
  • the contact angle of the silver powder of Comparative Example 2 was 110 °, and the surface SP value was 17.4 °.
  • Example 2 Evaluation of paste formation similar to Example 1 was performed using the obtained silver powder. Wetting of the surface of the silver powder by the vehicle was hardly observed. Moreover, when this was stirred using a metallic spatula, it could not be made into a paste-like while remaining large clay-like. Further, this paste was kneaded with a revolution / revolution type kneader in the same manner as in Example 1 to form a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle diameter Dmax was as large as 18 ⁇ m and the dispersibility was poor.
  • Example 1 and Examples were sufficiently crushed to the extent that the film formed on the surface of the silver powder was not damaged even in the silver powder produced by the same method, as compared with the Comparative Example.
  • the internal friction angle was 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol was 100 ° or more, and a silver powder having good compatibility with the vehicle and excellent dispersibility was obtained.
  • surface SP value by acetone titration method was 18 or less.
  • Example 1 and Example 2 even after the silver powder was left to stand at room temperature for 1 month, the internal friction angle was 20 ° or less, and aggregation was suppressed.
  • Comparative Example 1 the crushing condition was too strong, the organic coating layer formed on the surface of the silver powder was damaged, the internal friction angle was larger than 20 °, and the contact angle was also smaller than 100 °. . In addition, the surface SP value was also greater than 18. Further, in Comparative Example 2, since the crushing conditions were weak and the aggregates could not be sufficiently loosened, the internal friction angle was considerably increased to 25.8 °. Thereby, in Comparative Example 1 and Comparative Example 2, the compatibility with the vehicle was poor, and the dispersibility of the silver powder was poor.

Abstract

In order to provide a silver powder which has excellent compatibility with a solvent, a resin, etc. in a silver paste, and excellent dispersibility, and a method for producing the same, a silver powder according to the invention has an organic coating layer formed on the surface thereof and has an internal friction angle of 20º or less and a contact angle with an aqueous solution of 50 vol% methanol of 100º or more, and a method for producing a silver powder according to the invention comprises performing a surface treatment of silver particles, thereby forming an organic coating layer on the surfaces thereof, and thereafter, performing a sufficient crushing treatment to such an extent that the organic coating layer is not damaged.

Description

銀粉及びその製造方法Silver powder and method for producing the same
　本発明は、銀粉及びその製造方法に関するものであり、更に詳しくは、電子機器の配線層や電極等の形成に利用される銀ペーストの主たる成分となる銀粉及びその製造方法に関するものである。
　本出願は、日本国において２０１１年６月１６日に出願された日本特許出願番号特願２０１１－１３４３３７を基礎として優先権を主張するものであり、これらの出願を参照することにより、本出願に援用される。 The present invention relates to silver powder and a method for producing the same, and more particularly to silver powder as a main component of silver paste used for forming a wiring layer or an electrode of an electronic device and a method for producing the same.
This application claims priority based on Japanese Patent Application No. 2011-134337 filed on Jun. 16, 2011 in Japan, and the present application is directed to this application by reference. It is incorporated.
　電子機器における配線層や電極等の形成には、樹脂型銀ペーストや焼成型銀ペーストのような銀ペーストが多用されている。これらの銀ペーストを各種基材上に塗布又は印刷した後、加熱硬化又は加熱焼成することによって、配線層や電極等となる導電膜を形成することができる。 A silver paste such as a resin type silver paste or a baking type silver paste is often used to form a wiring layer, an electrode and the like in an electronic device. A conductive film to be a wiring layer, an electrode, or the like can be formed by applying or printing these silver pastes on various types of substrates and then heat curing or heating and firing.
　例えば、樹脂型銀ペーストは、銀粉、樹脂、硬化剤、溶剤等からなり、導電体回路パターン又は端子の上に印刷し、１００℃～２００℃で加熱硬化させて導電膜とし、配線層や電極を形成する。 For example, resin-type silver paste is made of silver powder, resin, curing agent, solvent, etc., printed on a conductor circuit pattern or terminal, heat cured at 100 ° C. to 200 ° C. to form a conductive film, wiring layer or electrode Form
　また、焼成型銀ペーストは、銀粉、ガラス、溶剤等からなり、導電体回路パターン又は端子の上に印刷し、６００℃～８００℃に加熱焼成して導電膜とし、配線層や電極を形成する。 In addition, the baking type silver paste is made of silver powder, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at 600 ° C. to 800 ° C. to form a conductive film to form a wiring layer or an electrode. .
　これらの銀ペーストで形成された配線層や電極では、銀粉が連なることで電気的に接続された電流パスが形成される。 In the wiring layers and electrodes formed of these silver pastes, current paths electrically connected are formed by silver powder being continuous.
　これらの銀ペーストに使用される銀粉は、粒径が０．１μｍから数μｍであり、形成する配線層の太さや電極の厚さ等によって使用される銀粉の粒径が異なる。また、銀ペースト中に均一に銀粉を分散させることにより、均一な太さの配線層、均一な厚さの電極を形成することができる。 The silver powder used for these silver pastes has a particle diameter of 0.1 μm to several μm, and the particle diameter of the silver powder used differs depending on the thickness of the wiring layer to be formed, the thickness of the electrode, and the like. Further, by uniformly dispersing silver powder in silver paste, it is possible to form a wiring layer of uniform thickness and an electrode of uniform thickness.
　一般に、銀ペーストを製造方法は、各構成要素を計量して所定の容器に入れ、万能撹拌器やニーダー等を用いて予備混練した後、３本ロール等で本混練を行う。予備混練では、各構成要素同士を十分に濡らし分散させることが重要であり、この予備混練を十分に行うことによって、本混練における銀箔の発生を防止し、銀ペースト中の銀粉の粒度を目的の粒度まで速やかに下げ、銀ペースト中に銀粉を均一に分散させることが可能となる。 Generally, in the production method of silver paste, each component is weighed and placed in a predetermined container, prekneaded using a universal stirrer, a kneader or the like, and then main kneading is carried out using a triple roll or the like. In the pre-kneading, it is important to sufficiently wet and disperse the respective constituents, and by sufficiently performing this pre-kneading, the generation of silver foil in the main-kneading is prevented, and the particle size of silver powder in the silver paste is aimed at It is possible to quickly reduce the particle size and disperse the silver powder uniformly in the silver paste.
　したがって、銀ペースト中で重量の大部分を占める銀粉には、粒径が均一で凝集が少ないことだけでなく、溶剤や樹脂等からなるビヒクルに対するなじみが良く、銀ペースト中での分散性が高いといった特性が求められる。このような特性は、嵩密度や粒度分布といった粉体の構造的な性質だけでなく、粉体表面の滑り易さや親水性、疎水性といった銀粉表面の化学的性質によっても変化する。 Therefore, the silver powder which occupies most of the weight in the silver paste is not only uniform in particle diameter and less aggregation, but also conforms well to the vehicle comprising a solvent, resin or the like, and the dispersibility in the silver paste is high. Characteristics are required. Such characteristics change depending not only on the structural properties of the powder such as bulk density and particle size distribution but also on the chemical properties of the silver powder surface such as slipperiness, hydrophilicity and hydrophobicity of the powder surface.
　銀ペーストに使用される銀粉について、例えば特許文献１では、球状銀粉が特定の嵩密度且つ成形体密度を有していることで、ビヒクル又は樹脂との相溶性を良好にすることが記載されている。しかしながら、特許文献１では、表面の化学的性質に関する記載はなく、このような構造的なパラメータだけではビヒクルや樹脂との相溶性を制御することは困難である。また、特許文献１には、銀粉の製造方法について、上記表面の化学的性質に大きく影響する銀粉の解砕方法等の製造方法については記載されていない。 With respect to silver powder used for silver paste, for example, Patent Document 1 describes that spherical silver powder has a specific bulk density and a formed body density to improve the compatibility with a vehicle or a resin. There is. However, Patent Document 1 does not describe the surface chemical properties, and it is difficult to control the compatibility with a vehicle or a resin only with such structural parameters. In addition, Patent Document 1 does not describe a method of producing silver powder, such as a method of crushing silver powder that greatly affects the chemical properties of the surface.
　一方、特許文献２には、粒度分布測定によるＤ５０値と画像解析によって得られる粒径ＤＩＡとの比Ｄ５０／ＤＩＡを粉体の凝集度の目安とし、これが特定の値以下であれば低凝集性であると記載されている。確かに、この値が小さければ粉体中における凝集体の数は少ないと考えられる。しかしながら、特許文献２には、特許文献１と同様に、ペースト化するときのビヒクルや樹脂との相溶性に影響を及ぼす銀粉表面の化学的性質に関する記載や化学的性質に影響する製造方法に関する記載はない。 On the other hand, in Patent Document 2, the ratio D50 / DIA between the D50 value by particle size distribution measurement and the particle diameter DIA obtained by image analysis is used as a measure of the degree of aggregation of the powder, and if this is less than a specific value It is stated that Certainly, if this value is small, it is considered that the number of aggregates in the powder is small. However, Patent Document 2 describes, as in Patent Document 1, a description of the chemical properties of the surface of silver powder that affects the compatibility with a vehicle or resin when pasted, and a production method that affects the chemical properties. There is no.
　銀ペーストに用いる銀粉については、特許文献１や特許文献２のように、嵩密度や成形体密度、粉体の凝集度等、構造的な性質だけでは十分に銀ペーストの溶剤や樹脂等との相溶性、分散性を良くすることはできない。このため、銀粉については、相溶性及び分散性の更なる向上が求められている。 With regard to silver powder used for silver paste, as in Patent Document 1 and Patent Document 2, only structural properties such as bulk density, compact density, powder cohesion degree, etc. are sufficient with silver paste solvent, resin, etc. Compatibility and dispersibility can not be improved. For this reason, the silver powder is required to further improve the compatibility and the dispersibility.
特開２００６－０９７０８６公報JP, 2006-097086, A 特開２００４－１０００１３公報Japanese Patent Application Publication No. 2004-100013
　そこで、本発明は、上記した従来の事情に鑑み、銀ペーストの溶剤や樹脂等との相溶性及び分散性が優れた銀粉及びその製造方法を提供することを目的とする。 Then, in view of the above-mentioned conventional situation, an object of the present invention is to provide silver powder excellent in compatibility with a solvent, resin, etc. of silver paste, resin, etc., and its manufacturing method.
　上述した目的を達成する本発明に係る銀粉は、内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上であることを特徴とする。 The silver powder according to the present invention for achieving the above-mentioned object is characterized in that the internal friction angle is 20 ° or less and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more.
　上述した目的を達成する本発明に係る銀粉の製造方法は、銀粒子に表面処理を行うことによって表面に有機皮膜層を形成した後、有機被膜層に損傷を与えない程度で十分な解砕処理を行うことを特徴とする。 In the method for producing silver powder according to the present invention for achieving the above-mentioned object, after an organic film layer is formed on the surface by performing surface treatment on silver particles, the crushing process is sufficiently sufficient not to damage the organic film layer. It is characterized by doing.
　本発明では、銀粉の内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上であることによって、溶媒や樹脂等との相溶性が高く、分散性に優れ、容易にペースト化が可能なものである。これにより、本発明では、銀ペーストの品質及び生産性を向上させることができる。 In the present invention, the internal friction angle of silver powder is 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more, so that the compatibility with solvents, resins, etc. is high and the dispersibility is excellent. And can be easily pasted. Thereby, in the present invention, the quality and productivity of silver paste can be improved.
銀粒子形態と粒子の表面状体について模式的に示す図である。It is a figure which shows typically about silver particle form and the surface-like body of particle | grains.
　以下に、本発明を適用した銀粉及び銀粉の製造方法について詳細に説明する。なお、本発明は、特に限定がない限り、以下の詳細な説明に限定されるものではない。 Below, the manufacturing method of silver powder and silver powder to which this invention is applied is demonstrated in detail. The present invention is not limited to the following detailed description unless otherwise specified.
　図１に示す銀粉１は、硬化剤、樹脂、溶剤等から構成される樹脂型銀ペーストやガラス、溶剤等から構成される焼成型銀ペーストに含有される。銀粉１が含有された樹脂型銀ペーストや焼成型銀ペーストは、配線層や電極の形成に用いられる。このため、銀粉１は、電気的接続が図られるように、銀ペーストの溶剤や樹脂との相溶性が良く、ペースト中に偏りなく分散させる必要がある。銀粉１は、特に疎水的な溶剤を用いた銀ペーストに好適である。 The silver powder 1 shown in FIG. 1 is contained in a resin-type silver paste composed of a curing agent, a resin, a solvent and the like, and a fired silver paste composed of glass, a solvent and the like. The resin type silver paste and the baking type silver paste in which the silver powder 1 is contained are used for formation of a wiring layer and an electrode. For this reason, the silver powder 1 has good compatibility with the solvent of silver paste and resin so that electrical connection can be achieved, and it is necessary to disperse it evenly in the paste. Silver powder 1 is particularly suitable for silver paste using a hydrophobic solvent.
　銀粉１は、内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上である。更に、銀粉１は、アセトン滴定法による表面ＳＰ値が１８以下であることが好ましい。この銀粉１は、粉体表面の化学的性質を低親水性にして滑りを良くすることで、銀ペーストの溶剤や樹脂といったビヒクルとの相溶性が良いものである。なお、銀粉１とは、一次粒子の他に、二次粒子及び凝集体も含むものとする。ここで、図１（Ａ）に示すように、一次粒子とは球状の銀粒子２の個々のことをいい、図１（Ｂ）に示すように、融着、固着などによって一次粒子が複数連結した銀粒子２を二次粒子という。図１（Ｃ）に示すように、これらの一次粒子や二次粒子の銀粒子２が凝集したものを凝集体という。 The silver powder 1 has an internal friction angle of 20 ° or less, and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more. Furthermore, it is preferable that the silver powder 1 is 18 or less in surface SP value by an acetone titration method. The silver powder 1 has good chemical compatibility with a vehicle such as a solvent of a silver paste or a resin by making the chemical property of the powder surface low hydrophilic to improve sliding. In addition to the primary particles, the silver powder 1 also includes secondary particles and aggregates. Here, as shown in FIG. 1 (A), the primary particles refer to individual spherical silver particles 2, and as shown in FIG. 1 (B), a plurality of primary particles are connected by fusion, fixation, etc. The silver particles 2 are called secondary particles. As shown in FIG. 1 (C), aggregation of silver particles 2 of these primary particles and secondary particles is referred to as an aggregate.
　銀粉１は、一次粒子が平均粒径０．１μｍ～１．５μｍの範囲であることが好ましい。一次粒子の平均粒径が０．１μｍ以上であることにより、銀ペースト（導電性ペースト）にした場合に抵抗を生じさせず導電性を良好なものとすることができる。また、一次粒子の平均粒径を１．５μｍ以下とすることにより、分散性を悪化させることなく、混練の際に銀フレークが発生せず、印刷性も良好となる。一次粒子の平均粒径は、走査型電子顕微鏡（ＳＥＭ）観察により測定することができる。また、銀粉１の粒度は、レーザー回折散乱法を用いて測定したＤ５０（体積積算５０％径）で、０．５μｍ～５μｍであることが好ましく、１．０μｍ～４．０μｍであることがより好ましい。Ｄ５０をこの範囲とすることで、銀ペースト用として好ましいものとなり、内部摩擦角が最適化され、ペースト中での分散性が改善される。 In the silver powder 1, primary particles preferably have an average particle diameter in the range of 0.1 μm to 1.5 μm. When the average particle diameter of the primary particles is 0.1 μm or more, resistance can not be generated when the silver paste (conductive paste) is used, and conductivity can be improved. Further, by setting the average particle diameter of the primary particles to 1.5 μm or less, silver flakes are not generated at the time of kneading without deteriorating the dispersibility, and the printability is also improved. The average particle size of primary particles can be measured by scanning electron microscope (SEM) observation. The particle size of silver powder 1 is preferably 0.5 μm to 5 μm, and more preferably 1.0 μm to 4.0 μm in terms of D50 (volume integration 50% diameter) measured using a laser diffraction scattering method. preferable. By setting D50 in this range, it becomes preferable for silver paste, the internal friction angle is optimized, and the dispersibility in the paste is improved.
　銀粉１の内部摩擦角とは、粉体の滑りやすさを表すパラメータであり、市販されている粉体層せん断力測定装置によって測定することが可能である。銀ペースト用の銀粉１の場合では、内部摩擦角が２０°を超えると粒子（銀粉１中において独立して存在する一次粒子、二次粒子もしくは凝集体）間の滑りが悪くなる。その結果、ペースト化するときに、溶剤や樹脂が銀粉１の粒子間に割って入ることができず、銀粉１の表面の一部しか濡らすことができなくなる。このような状態では、攪拌を行っても粒子同士がほぐれにくく銀粉１の分散性が悪いものとなる。分散性が悪い銀粉１は、各構成要素同士を濡らして分散させる予備混練に時間がかかるだけでなく、３本ロールミル等による本混練時に凝集した銀粉１が押し潰されて銀フレークが発生し易くなる。したがって、銀粉１は、内部摩擦角が２０°以下であることによって、滑りが良くなり、溶剤や樹脂が粒子間に入り込み、相溶性が良くなるため、銀ペースト中における分散性が良くなる。 The internal friction angle of the silver powder 1 is a parameter indicating the slipperiness of the powder, and can be measured by a commercially available powder layer shear force measuring device. In the case of silver powder 1 for silver paste, when the internal friction angle exceeds 20 °, slippage between particles (primary particles, secondary particles or aggregates independently present in silver powder 1) becomes worse. As a result, when it is made into a paste, the solvent or resin can not be split between the particles of silver powder 1 and only part of the surface of silver powder 1 can be wetted. In such a state, even if stirring is performed, the particles are not easily loosened, and the dispersibility of the silver powder 1 is poor. The silver powder 1 having poor dispersibility not only takes time for prekneading to wet and disperse the respective constituents, but also the silver powder 1 aggregated during main kneading with a three-roll mill or the like is crushed and silver flakes are easily generated. Become. Accordingly, when the internal friction angle of the silver powder 1 is 20 ° or less, the slip becomes better, the solvent and the resin enter between the particles, and the compatibility becomes better, so the dispersibility in the silver paste becomes better.
　また、銀粉１は、製造直後に内部摩擦角が２０°以下であることはもちろんのこと、製造後においても内部摩擦角が２０°以下であることが維持され、溶剤や樹脂に混合してペースト化する際においても２０°以下となっていることが好ましい。例えば、銀粉１を製造した後、例えば室温にて１月経過後であっても、銀粉１の内部摩擦角が２０°以下である。内部摩擦角は、粒子の凝集によって変化するパラメータであり、製造直後は凝集の程度の低い粉体であっても、経時的に粒子間の凝集が進行することによって、内部摩擦角が大きくなることがある。経時的に変化して内部摩擦角が２０°を超えた場合には、ペースト化するときに分散性が低下し、銀粉１が凝集するなどの様々な問題を引き起こしてしまう。そこで、２０°以下の内部摩擦角が維持できていれば、凝集の進行が抑えられるため、ペースト化の際に問題が発生することを防止できる。 In addition, the silver powder 1 has an internal friction angle of 20 ° or less immediately after production and, of course, maintains an internal friction angle of 20 ° or less after production, and is mixed with a solvent or resin to be paste It is preferable that it is 20 degrees or less also in For example, even after one month has passed at room temperature after producing the silver powder 1, for example, the internal friction angle of the silver powder 1 is 20 ° or less. The internal friction angle is a parameter that changes due to the aggregation of particles, and even if it is a powder with a low degree of aggregation immediately after production, the internal friction angle increases due to the progress of aggregation between particles over time There is. If the internal friction angle changes over time and the internal friction angle exceeds 20 °, the dispersibility decreases when the paste is formed, which causes various problems such as aggregation of the silver powder 1. Therefore, if the internal friction angle of 20 ° or less can be maintained, the progress of aggregation can be suppressed, so that the occurrence of a problem can be prevented at the time of paste formation.
　次に、銀粉１の接触角について説明する。銀粉１は、メタノール５０容量％水溶液での接触角が１００°以上である。接触角は、銀粉１の表面の溶剤に対する濡れやすさを表すパラメータであり、例えば、水に対する接触角が大きいほど、疎水的なペースト溶剤に濡れやすくなる。逆に水に対する接触角が小さいほど親水性であり、疎水的なペースト溶剤に対する濡れは悪くなる。銀粉１の接触角は、成形した表面上で測定するのが一般的であるが、水で測定を行う場合、疎水性が大きい粉体では、成形粉体の表面上で水滴が真球状となり、水滴が滑って動いてしまうため精度良く計測することが困難である。このため、メタノール等の極性の低い溶媒を水に加え、溶媒の極性を下げて測定を行う方法が行われる。銀ペーストを作製する際には、一般的に疎水的な溶剤を用いることが多い。したがって、銀粉１が、接触角が１００°未満の親水的な表面を有する場合、ペーストの溶剤や樹脂に対する相溶性が悪く、銀粉１と溶剤や樹脂との濡れが起こらず、ペースト化することが困難となる。また、無理に混練してペースト化した場合には、分散安定性が悪く再凝集によってペーストの分離が起こり易くなる。 Next, the contact angle of the silver powder 1 will be described. The silver powder 1 has a contact angle of 100 ° or more with a 50% by volume aqueous solution of methanol. The contact angle is a parameter representing the wettability of the surface of silver powder 1 to the solvent, and for example, the larger the contact angle to water, the easier it is to wet a hydrophobic paste solvent. On the contrary, the smaller the contact angle to water, the more hydrophilic it is, and the more it gets wet to the hydrophobic paste solvent. The contact angle of the silver powder 1 is generally measured on the molded surface, but when the measurement is performed with water, in the case of a powder with high hydrophobicity, the water droplets become spherical on the surface of the molded powder, It is difficult to measure accurately because the water droplets slide and move. For this reason, a method of performing measurement by adding a low polarity solvent such as methanol to water to lower the polarity of the solvent is performed. In producing a silver paste, generally a hydrophobic solvent is often used. Therefore, when the silver powder 1 has a hydrophilic surface having a contact angle of less than 100 °, the compatibility of the paste with the solvent or resin is poor, and the silver powder 1 does not get wet with the solvent or resin, making it paste It will be difficult. In addition, when the paste is forcibly kneaded to form a paste, the dispersion stability is poor and separation of the paste is likely to occur due to reaggregation.
　次に、銀粉１の表面ＳＰ値について説明する。銀粉１は、表面ＳＰ値が１８以下である。表面ＳＰ値は、銀粉１の表面の極性を表すパラメータであり、小さいほど疎水性であり、大きいほど親水性である。 Next, the surface SP value of the silver powder 1 will be described. Silver powder 1 has a surface SP value of 18 or less. The surface SP value is a parameter representing the polarity of the surface of silver powder 1, and is smaller as it is smaller and more as it is larger.
　この表面ＳＰ値は、市販されている粉体濡れ性試験機等で測定可能であるが、簡易的には「色材、６２（９）５２４－５２８」に記載されているようなアセトン滴定法でも測定が可能である。このアセトン滴定法では、疎水性の粉体を水（Ａ［ｍｌ］）に加え浮遊させる。スターラーで緩やかに攪拌をしながら、ビュレットでアセトンを滴下していき、粉体が濡れて沈降をするまでに要したアセトンの滴下量（Ｂ［ｍｌ］）を計測する。水のＳＰ値２３．４３、アセトンのＳＰ値９．７５、使用した水の体積及び使用したアセトンの体積から沈降したアセトン溶液のＳＰ値を下記の式１より計算し、この値を銀粉１の表面ＳＰ値とする。 This surface SP value can be measured with a commercially available powder wettability tester or the like, but in a simple manner, the acetone titration method as described in "Color material, 62 (9) 524-528" But measurement is possible. In this acetone titration method, hydrophobic powder is added to water (A [ml]) and suspended. While stirring gently with a stirrer, acetone is added dropwise with a burette, and the amount of acetone (B [ml]) required for the powder to wet and settle is measured. The SP value of the silver powder 1 is calculated from the equation 1 below using the SP value of water 23.43, the SP value of acetone 9.75, the volume of water used and the volume of acetone used from the equation 1 below. Let it be the surface SP value.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　銀粉１の表面ＳＰ値が１８より大きい場合には、親水性が大きすぎて、ペーストの溶剤や樹脂に対する相溶性が悪くなり、銀粉１と溶剤や樹脂との濡れが起こらず、ペースト化することが困難となる。また、無理に混練してペースト化しても、分散安定性が悪く再凝集によってペーストの分離が起こり易くなる。一方、銀粉１の表面ＳＰ値が１８以下であることによって、銀粉１の親水性が大きくなり過ぎず、溶剤や樹脂との相溶性が良好となり、分散性が優れたものとなるため、ペースト化が容易になる。 When the surface SP value of the silver powder 1 is larger than 18, the hydrophilicity is too large, the compatibility of the paste with the solvent or resin is deteriorated, and the silver powder 1 does not get wet with the solvent or resin, making it into a paste Is difficult. In addition, even if the paste is forcedly kneaded, the dispersion stability is poor, and separation of the paste is likely to occur due to reaggregation. On the other hand, when the surface SP value of the silver powder 1 is 18 or less, the hydrophilicity of the silver powder 1 does not become too large, the compatibility with the solvent and the resin becomes good, and the dispersibility becomes excellent. Becomes easier.
　銀粉１は、湿式還元法により得られた銀粒子２を表面処理して、図１のように一次粒子あるいは二次粒子の表面に有機被膜層３が形成されることによって、上述した内部摩擦角を２０°以下にでき、且つメタノール５０容量％水溶液での接触角を１００°以上にすることができ、更にはアセトン滴定法による表面ＳＰ値も１８以下とすることができる。この有機被膜層３は、界面活性剤、又は界面活性剤及び分散剤によって形成することができる。 The silver powder 1 is surface-treated with the silver particles 2 obtained by the wet reduction method to form the organic coating layer 3 on the surfaces of the primary particles or the secondary particles as shown in FIG. Can be made 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol can be made 100 ° or more, and furthermore, the surface SP value by the acetone titration method can be made 18 or less. The organic coating layer 3 can be formed of a surfactant, or a surfactant and a dispersant.
　有機被膜層３は、界面活性剤及び分散剤によって形成することが好ましい。銀粉１では、電離状態で界面活性剤を銀粒子２に吸着させることで凝集を抑制することが可能であるが、界面活性剤のみで凝集を抑制するためには添加量が多くなり過ぎてしまう。そのため、銀ペースト中で良好な分散状態が得られても配線層や電極の導電性が十分でないことがある。そこで、銀粉１の凝集を抑制し且つ配線層や電極の導電性を十分なものとするために、界面活性剤と分散剤を併用することが有効である。 The organic coating layer 3 is preferably formed of a surfactant and a dispersant. In silver powder 1, aggregation can be suppressed by adsorbing the surfactant to silver particles 2 in the ionized state, but in order to suppress aggregation only by the surfactant, the addition amount becomes too large . Therefore, even if a good dispersion state is obtained in the silver paste, the conductivity of the wiring layer or the electrode may not be sufficient. Therefore, in order to suppress the aggregation of the silver powder 1 and to make the conductivity of the wiring layer or the electrode sufficient, it is effective to use a surfactant and a dispersant in combination.
　有機被膜層３は、界面活性剤の銀粒子２への吸着時又は吸着後に分散剤を添加することによって、銀粒子２に吸着した界面活性剤に分散剤を更に吸着させて形成することが特に好ましい。銀粒子２の表面に界面活性剤を介して分散剤を吸着させて有機被膜層３を形成することによって、有機被膜層３は、銀粒子２の表面に強く付いている一方で、溶剤や樹脂との相溶性が良好なものとなる。これにより、銀粒子２の表面にほぼ一様に有機被膜層３が形成された銀粉１を溶剤や樹脂に混ぜても有機被膜層３が剥がれたりすることを抑制できる。 Particularly, the organic coating layer 3 is formed by further adsorbing the dispersant to the surfactant adsorbed to the silver particles 2 by adding the dispersant during or after adsorption of the surfactant to the silver particles 2. preferable. By causing the dispersant to be adsorbed to the surface of the silver particles 2 via a surfactant to form the organic coating layer 3, the organic coating layer 3 is strongly attached to the surface of the silver particles 2, while the solvent or resin is Good compatibility with Thereby, even if the silver powder 1 in which the organic film layer 3 is formed almost uniformly on the surface of the silver particle 2 is mixed with the solvent or the resin, the organic film layer 3 can be prevented from peeling off.
　例えば、塩化銀を出発原料とした銀粉１の場合、界面活性剤としては、カチオン系界面活性剤を用いることが好ましい。カチオン系界面活性剤は、ｐＨの影響を受けることなく正イオンに電離するため、銀粉１への吸着性の改善効果が得られる。 For example, in the case of silver powder 1 using silver chloride as a starting material, it is preferable to use a cationic surfactant as a surfactant. The cationic surfactant ionizes into positive ions without being affected by pH, so that the adsorptivity to the silver powder 1 can be improved.
　カチオン系界面活性剤は、特に限定されるものではないが、モノアルキルアミン塩に代表されるアルキルモノアミン塩型、Ｎ－アルキル（Ｃ１４～Ｃ１８）プロピレンジアミンジオレイン酸塩に代表されるアルキルジアミン塩型、アルキルトリメチルアンモニウムクロライドに代表されるアルキルトリメチルアンモニウム塩型、ヤシアルキルジメチルベンジルアンモニウムクロライドに代表されるアルキルジメチルベンジルアンモニウム塩型、アルキルジポリオキシエチレンメチルアンモニウムクロライドに代表される４級アンモニウム塩型、アルキルピリジニウム塩型、ジメチルステアリルアミンに代表される３級アミン型、ポリオキシプロピレン・ポリオキシエチレンアルキルアミンに代表されるポリオキシエチレンアルキルアミン型、Ｎ、Ｎ’、Ｎ’－トリス（２－ヒドロキシエチル）－Ｎ－アルキル（Ｃ１４～１８）１，３－ジアミノプロパンに代表されるジアミンのオキシエチレン付加型から選択される少なくとも１種が好ましく、４級アンモニウム塩型、３級アミン塩型のいずれか又はその混合物がより好ましい。 The cationic surfactant is not particularly limited, but is an alkyl monoamine salt type represented by a monoalkylamine salt, and an alkyl diamine salt represented by an N-alkyl (C14 to C18) propylene diamine dioleate. Type, alkyl trimethyl ammonium salt type represented by alkyl trimethyl ammonium chloride, alkyl dimethyl benzyl ammonium salt type represented by coc alkyl dimethyl benzyl ammonium chloride, quaternary ammonium salt type represented by alkyl dipolyoxyethylene methyl ammonium chloride , Alkyl pyridinium salt type, tertiary amine type represented by dimethyl stearyl amine, polyoxyethylene alkyl amine type represented by polyoxypropylene / polyoxyethylene alkylamine Preferably, at least one selected from oxyethylene addition forms of diamines represented by N, N ′, N′-tris (2-hydroxyethyl) -N-alkyl (C14-18) 1,3-diaminopropane, A quaternary ammonium salt type, a tertiary amine salt type or a mixture thereof is more preferred.
　カチオン系界面活性剤は、メチル基、ブチル基、セチル基、ステアリル基、牛脂、硬化牛脂、植物系ステアリルに代表されるＣ４～Ｃ３６の炭素数を持つアルキル基を少なくとも１個有することが好ましい。また、アルキル基としては、ポリオキシエチレン、ポリオキシプロピレン、ポリオキシエチレンポリオキシプロピレン、ポリアクリル酸、ポリカルボン酸から選択される少なくとも１種を付加されたものであることが好ましい。これらのアルキル基は、分散剤として用いる脂肪酸との吸着が強いため、界面活性剤を介して銀粒子２に分散剤を吸着させる場合に脂肪酸を強く吸着させることができる。 The cationic surfactant preferably has at least one alkyl group having a carbon number of C4 to C36 represented by methyl group, butyl group, cetyl group, stearyl group, beef tallow, hardened beef tallow, and vegetable stearyl. The alkyl group is preferably one to which at least one selected from polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene, polyacrylic acid and polycarboxylic acid is added. Since these alkyl groups have strong adsorption with the fatty acid used as the dispersant, when the dispersant is adsorbed to the silver particles 2 via the surfactant, the fatty acid can be strongly adsorbed.
　カチオン系界面活性剤は、特に限定されるものではないが、フッ化物、臭化物、ヨウ化物、塩化物、硫酸塩、硝酸塩、リン酸塩から選択される少なくとも１種であることが好ましい。これらは一般的に界面活性剤の主成分として含まれ、入手が容易であることから好ましい。 The cationic surfactant is not particularly limited, but is preferably at least one selected from fluoride, bromide, iodide, chloride, sulfate, nitrate and phosphate. These are generally contained as main components of surfactants, and are preferable because they are easily available.
　分散剤としては、例えば、脂肪酸、有機金属、ゼラチン等の保護コロイドを用いることができるが、不純物混入の恐れがなく且つ界面活性剤との吸着性を考慮すると、脂肪酸若しくはその塩を用いることが好ましい。なお、脂肪酸若しくはその塩は、エマルジョンとして添加してもよい。 As the dispersant, for example, protective colloids such as fatty acids, organic metals, gelatin and the like can be used, but fatty acids or salts thereof may be used in view of the possibility of contamination with impurities and in view of the adsorptivity with surfactants. preferable. In addition, you may add a fatty acid or its salt as an emulsion.
　分散剤として用いる脂肪酸としては、特に限定されるものではないが、ステアリン酸、オレイン酸、ミリスチン酸、パルミチン酸、リノール酸、ラウリン酸、リノレン酸から選択される少なくとも１種であることが好ましい。これらの脂肪酸は、沸点が比較的低いため、銀ペーストを用いて形成された配線層や電極への悪影響が少ないからである。脂肪酸は、元来、疎水性であり、銀粒子２の表面に界面活性剤を介して分散剤を吸着させることで、有機被膜層３の外面側に多く存在するようになり、銀粉１が疎水性を有するようになると考えられる。特に、銀粒子２に吸着しやすい、例えば、電荷的に銀粒子２表面と逆の電荷に電離する界面活性剤を選択することで、十分に界面活性剤を介して分散剤を吸着させることができ、銀粉１が十分な疎水性を示すようになる。 The fatty acid used as the dispersant is not particularly limited, but is preferably at least one selected from stearic acid, oleic acid, myristic acid, palmitic acid, linoleic acid, lauric acid and linolenic acid. Because these fatty acids have a relatively low boiling point, they have little adverse effect on wiring layers and electrodes formed using silver paste. The fatty acid is originally hydrophobic, and by causing the dispersant to be adsorbed to the surface of the silver particle 2 via the surfactant, a large amount of the fatty acid is present on the outer surface side of the organic coating layer 3 and the silver powder 1 is hydrophobic. It is thought that it comes to have sex. In particular, by selecting a surfactant which is easily adsorbed to the silver particles 2, for example, a surfactant which is ionized to a charge opposite to that of the surface of the silver particles 2 in charge, the dispersant is sufficiently adsorbed through the surfactant. As a result, the silver powder 1 becomes sufficiently hydrophobic.
　界面活性剤の添加量は、銀粒子２に対して０.００２質量％～１.０００質量％の範囲が好ましい。界面活性剤は、ほぼ全量が銀粒子２に吸着されるため、界面活性剤の添加量と吸着量はほぼ等しいものとなる。界面活性剤の添加量が０.００２質量％未満の場合には、銀粒子２の凝集抑制や分散剤の吸着性改善の効果が得られないことがある。一方、添加量が１.０００質量％を超える場合には、銀ペーストを用いて形成された配線層や電極の導電性が低下するため好ましくない。 The addition amount of the surfactant is preferably in the range of 0.002% by mass to 1.000% by mass with respect to the silver particles 2. Since almost all of the surfactant is adsorbed to the silver particles 2, the addition amount of the surfactant and the adsorption amount are almost equal. When the addition amount of the surfactant is less than 0.002% by mass, the effects of the aggregation suppression of the silver particles 2 and the adsorptivity improvement of the dispersant may not be obtained. On the other hand, when the addition amount exceeds 1.000% by mass, the conductivity of the wiring layer or the electrode formed using the silver paste is unfavorably lowered.
　分散剤の添加量は、銀粒子２に対して０.０１質量％～３.００質量％の範囲が好ましく、０.０１質量％～１.００質量％がより好ましい。分散剤の種類により銀粒子２への吸着量は異なるが、添加量が０.０１質量％未満の場合には、銀粒子２の凝集抑制の効果が十分に得られる量の分散剤が銀粒子２に吸着されないことがある。一方、分散剤の添加量が３.００質量％を超える場合には、銀粒子２に吸着される分散剤が多くなり、銀ペーストを用いて形成された配線層や電極の導電性が十分に得られないことがある。 The addition amount of the dispersant is preferably in the range of 0.01% by mass to 3.00% by mass, and more preferably 0.01% by mass to 1.00% by mass with respect to the silver particles 2. The amount of adsorption onto silver particles 2 varies depending on the type of dispersant, but if the amount added is less than 0.01% by mass, the amount of dispersant of which the effect of suppressing aggregation of silver particles 2 is sufficiently obtained is silver particles 2 may not be adsorbed. On the other hand, when the addition amount of the dispersing agent exceeds 3.00 mass%, the dispersing agent adsorbed to the silver particles 2 increases, and the conductivity of the wiring layer and the electrode formed using the silver paste is sufficiently It can not be obtained.
　銀粉１では、カチオン系界面活性剤を用いることで、銀粒子２に対する界面活性剤の吸着性が大幅に改善されるため、界面活性剤を銀粉１に強固に吸着させることができる。更に好ましくは、銀粒子２に吸着する界面活性剤を安定的に吸着させることによって、より一層凝集が抑制され且つペースト中での分散性に優れた銀粉１を得ることができる。 In the silver powder 1, by using the cationic surfactant, the adsorptivity of the surfactant to the silver particles 2 is significantly improved, so the surfactant can be strongly adsorbed to the silver powder 1. More preferably, by stably adsorbing the surfactant adsorbed to the silver particles 2, it is possible to obtain the silver powder 1 which is further suppressed from aggregation and excellent in the dispersibility in the paste.
　次に、本発明の銀粉１の製造方法について、工程毎に説明する。 Next, the manufacturing method of the silver powder 1 of this invention is demonstrated for every process.
　銀粉１の製造方法は、例えば、塩化銀を出発原料とするものの場合以下の通りである。先ず、塩化銀を錯化剤により溶解して得た銀錯体を含む銀錯体溶液と還元剤溶液とを混合し、銀錯体を還元して銀粒子２を析出させる湿式還元法により銀粒子スラリーを生成する工程を行う。この銀粒子スラリーを生成する工程では、硝酸銀を出発原料とする従来の方法で必要とされた亜硝酸ガスの回収装置や廃水中の硝酸系窒素の処理装置を設置する必要がなく、環境への影響も少ないプロセスであることから、製造コストの低減を図ることができる。 The method of producing the silver powder 1 is as follows, for example, in the case of using silver chloride as a starting material. First, a silver particle slurry is prepared by a wet reduction method in which a silver complex solution containing a silver complex obtained by dissolving silver chloride with a complexing agent and a reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles 2. Perform the process of generating. In the process of producing this silver particle slurry, there is no need to install a nitrous gas recovery device required by the conventional method using silver nitrate as a starting material and a treatment device for nitric acid-based nitrogen in waste water, and to the environment. Since the process is less affected, the manufacturing cost can be reduced.
　具体的に、銀粒子スラリーを生成する工程では、先ず、錯化剤を用いて塩化銀を溶解し、銀錯体を含む銀錯体溶液を調製する。錯化剤としては、特に限定されるものではないが、塩化銀と錯体を形成しやすく且つ不純物として残留する成分が含まれないアンモニア水を用いることが好ましい。また、塩化銀は高純度のものを用いることが好ましい。このような塩化銀として、純度９９.９９９９質量％の高純度塩化銀が工業用に安定的に製造されている。 Specifically, in the step of producing a silver particle slurry, first, silver chloride is dissolved using a complexing agent to prepare a silver complex solution containing a silver complex. The complexing agent is not particularly limited, but it is preferable to use ammonia water which easily forms a complex with silver chloride and does not contain a component remaining as an impurity. In addition, it is preferable to use silver chloride having high purity. As such silver chloride, high purity silver chloride having a purity of 99.9999% by mass is stably manufactured for industrial use.
　塩化銀の溶解方法としては、例えば錯化剤としてアンモニア水を用いる場合、塩化銀のスラリーを作製してアンモニア水を添加してもよいが、錯体濃度を高めて生産性を上げるためにはアンモニア水中に塩化銀を添加して溶解することが好ましい。塩化銀を溶解するアンモニア水は、工業的に用いられる通常のものでよいが、不純物混入を防止するため可能な限り高純度のものが好ましい。 As a method of dissolving silver chloride, for example, when using ammonia water as a complexing agent, a slurry of silver chloride may be prepared and ammonia water may be added, but ammonia is increased to increase the concentration of the complex to improve productivity. It is preferable to add and dissolve silver chloride in water. Ammonia water which dissolves silver chloride may be a conventional one which is used industrially, but one having as high purity as possible is preferable in order to prevent impurity contamination.
　次に、銀錯体溶液と混合する還元剤溶液を調製する。還元剤としては、一般的なヒドラジンやホルマリン等を用いることができる。アスコルビン酸は、還元作用が緩やかであるため、銀粒子２中の結晶粒が成長しやすく特に好ましい。ヒドラジンやホルマリンは、還元力が強いため、銀粒子２中の結晶が小さくなりやすい。また、反応の均一性又は反応速度を制御するために、還元剤を純水等で溶解又は希釈して濃度調整した水溶液として用いてもよい。 Next, a reducing agent solution to be mixed with the silver complex solution is prepared. As the reducing agent, general hydrazine, formalin or the like can be used. Ascorbic acid is particularly preferable because the crystal grains in the silver particles 2 easily grow because the reducing action is slow. Because hydrazine and formalin have strong reducing power, crystals in silver particles 2 tend to be small. Further, in order to control the uniformity of the reaction or the reaction rate, the reducing agent may be used as an aqueous solution in which the concentration is adjusted by dissolving or diluting it with pure water or the like.
　還元反応を行う際には、水溶性高分子を添加することが好ましい。添加する水溶性高分子としては、特に限定はされないが、ポリエチレンオキシド、ポリエチレングリコール、ポリビニルアルコール又はポリビニルピロリドンの少なくとも１種であることが好ましい。水溶性高分子は、銀錯体を還元して銀粒子２を析出させる際に、銀の一次粒子もしくは二次粒子が過度に凝集しないように、銀粒子２の表面に吸着し、銀粒子２を分散させる分散剤の役割をする。水溶性高分子を添加しない場合には、銀錯体の還元により発生した核や核が成長した銀粒子２が過度に凝集を起こし、分散性が悪いものとなってしまうことがある。水溶性高分子を添加しない場合であっても、還元条件によって銀ペースト用として好ましい程度に銀粉１の粒度調整が可能であるが、水溶性高分子の添加によって、銀ペースト用としてより好ましい粒度に調整することが可能となる。水溶性高分子の添加量は、水溶性高分子の種類及び得ようとする銀粉１の粒径により適宜決めればよいが、銀錯体溶液中に含有される銀に対して１質量％～１０質量％の範囲とすることが好ましい。水溶性高分子の含有量を１質量％～１０質量％とすることによって、銀の一次粒子もしくは二次粒子の過度の凝集が生じず、銀粉１の粒度調整とともに後の工程において銀粒子２の表面に有機被膜層３を適切に形成することができる。 When performing a reduction reaction, it is preferable to add a water-soluble polymer. The water-soluble polymer to be added is not particularly limited, but is preferably at least one of polyethylene oxide, polyethylene glycol, polyvinyl alcohol or polyvinyl pyrrolidone. The water-soluble polymer is adsorbed on the surface of the silver particles 2 so that the primary or secondary particles of the silver do not excessively aggregate when the silver complex is reduced to precipitate the silver particles 2. Act as a dispersing agent to be dispersed. In the case where the water-soluble polymer is not added, the silver particles 2 generated by the reduction of the silver complex and the nuclei generated by the reduction may cause excessive aggregation, and the dispersibility may be poor. Even when no water-soluble polymer is added, the particle size of silver powder 1 can be adjusted to the extent preferable for silver paste depending on the reducing conditions, but the addition of water-soluble polymer makes the particle size more preferable for silver paste. It becomes possible to adjust. The addition amount of the water-soluble polymer may be appropriately determined according to the type of the water-soluble polymer and the particle size of the silver powder 1 to be obtained, but 1% by mass to 10% by mass with respect to silver contained in the silver complex solution It is preferable to make it the range of%. By setting the content of the water-soluble polymer to 1% by mass to 10% by mass, excessive aggregation of primary particles or secondary particles of silver does not occur, and the silver particles 2 are The organic coating layer 3 can be appropriately formed on the surface.
　水溶性高分子は、銀錯体溶液及び還元剤溶液の両方、又はいずれか一方に添加することも可能である。銀錯体溶液及び還元剤溶液の両方、又はいずれか一方への水溶性高分子の添加については、還元処理に先立ち予め添加対象の溶液に添加してもよく、還元処理のための銀錯体含有溶液及び還元剤溶液の混合時に添加するようにしてもよい。より好ましくは予め還元剤溶液に水溶性高分子を混合しておく方がよい。このことは実験的に確認された結果であるが、還元剤溶液と水溶性高分子を混合しておくことで核発生又は核成長の場に水溶性高分子が存在し、生成した核又は銀粒子２の表面に迅速に水溶性高分子が吸着するため過度の凝集が抑えられると考えられる。また、銀錯体溶液に水溶性高分子を混合する際の濃度は、３質量％を超えて、１０質量％以下とすることがより好ましい。水溶性高分子を、予め銀錯体含有溶液に添加した場合には、核発生あるいは核成長の場に水溶性高分子が供給され難く、銀粒子２の表面に適度に水溶性高分子を吸着させることができないおそれがあるため、３質量％よりも多く添加する。 The water-soluble polymer can also be added to the silver complex solution and / or the reducing agent solution. The addition of the water-soluble polymer to the silver complex solution and / or the reducing agent solution may be previously added to the solution to be added prior to the reduction treatment, and the silver complex-containing solution for the reduction treatment And may be added when mixing the reducing agent solution. More preferably, it is better to previously mix the water-soluble polymer in the reducing agent solution. This is an experimentally confirmed result, but the mixing of the reducing agent solution and the water-soluble polymer results in the presence of the water-soluble polymer at the site of nucleation or growth, and the nucleus or silver formed. It is thought that excessive aggregation is suppressed because the water-soluble polymer is rapidly adsorbed to the surface of the particles 2. Moreover, it is more preferable that the density | concentration at the time of mixing a water-soluble polymer with silver complex solution sets it as 10 mass% or less exceeding 3 mass%. When a water-soluble polymer is previously added to the silver complex-containing solution, it is difficult to supply the water-soluble polymer to the place of nucleation or growth, and the water-soluble polymer is adsorbed to the surface of the silver particles 2 appropriately. Because it may not be possible, it is added more than 3% by mass.
　水溶性高分子を添加した場合には、還元反応時に発泡することがあるため、銀錯体溶液又は還元剤混合液に消泡剤を添加するようにしてもよい。消泡剤は、特に限定されるものではなく、通常還元時に用いられるものでよい。ただし、還元反応を阻害させないため、消泡剤の添加量は、消泡効果が得られる最小限程度にしておくことが好ましい。 When a water-soluble polymer is added, a foam may be generated during the reduction reaction, so an antifoaming agent may be added to the silver complex solution or the reducing agent mixed solution. The antifoaming agent is not particularly limited, and may be one usually used at the time of reduction. However, in order not to inhibit the reduction reaction, it is preferable to set the amount of the antifoaming agent to a minimum level at which the defoaming effect can be obtained.
　なお、銀錯体溶液及び還元剤溶液を調製する際に用いる水については、不純物の混入を防止するため、不純物が除去された水を用いることが好ましく、純水を用いることが特に好ましい。 In addition, as water used when preparing a silver complex solution and a reducing agent solution, in order to prevent mixing of an impurity, it is preferable to use the water from which the impurity was removed, and it is especially preferable to use a pure water.
　銀粒子スラリーを生成する工程では、上記のごとく調製した銀錯体溶液と還元剤溶液とを混合し、銀錯体を還元して銀粒子２を湿式還元法により析出させる。この還元反応は、バッチ法でもよく、チューブリアクター法やオーバーフロー法のような連続還元法を用いて行ってもよい。また、銀粒子２の粒径は、銀錯体溶液と還元剤溶液の混合速度や銀錯体の還元速度で制御することが可能であり、目的とする粒径に容易に制御することができる。そして、得られた銀粒子スラリーをフィルター等でろ過し、銀粒子２を固液分離する。 In the step of producing a silver particle slurry, the silver complex solution prepared as described above and the reducing agent solution are mixed, and the silver complex is reduced to precipitate silver particles 2 by a wet reduction method. This reduction reaction may be a batch method or may be performed using a continuous reduction method such as a tube reactor method or an overflow method. In addition, the particle size of the silver particles 2 can be controlled by the mixing speed of the silver complex solution and the reducing agent solution or the reduction speed of the silver complex, and can be easily controlled to the target particle size. And the obtained silver particle slurry is filtered with a filter etc., solid-liquid separation of the silver particle 2 is carried out.
　この工程で得られた銀粒子２は、表面に多量の塩素イオン及び余剰の水溶性高分子が吸着している。従って、銀ペーストを用いて形成される配線層や電極の導電性を十分なものとするためには、得られた銀粒子２のスラリーを次の洗浄工程において洗浄し、これらの表面吸着物を洗浄により除去する必要がある。 In the silver particles 2 obtained in this step, a large amount of chlorine ions and a surplus water-soluble polymer are adsorbed on the surface. Therefore, in order to make the conductivity of the wiring layer and electrodes formed using silver paste sufficient, the obtained slurry of silver particles 2 is washed in the next washing step, and these surface adsorbates are It needs to be removed by washing.
　洗浄方法としては、特に限定されるものではないが、スラリーから固液分離した銀粒子２を洗浄液に投入し、撹拌機又は超音波洗浄器を使用して撹拌した後、再び固液分離して銀粒子２を回収する方法が一般的に用いられる。また、表面吸着物を十分に除去するためには、洗浄液への投入、撹拌洗浄、及び固液分離からなる操作を、適宜数回繰り返して行うことが好ましい。 The washing method is not particularly limited, but silver particles 2 solid-liquid separated from the slurry are added to the washing liquid, stirred using a stirrer or an ultrasonic cleaner, and then solid-liquid separated again A method of recovering silver particles 2 is generally used. Moreover, in order to fully remove a surface adsorbate, it is preferable to repeat the operation which consists of injection | throwing-in to a washing | cleaning liquid, stirring washing | cleaning, and solid-liquid separation several times suitably, and to perform it.
　洗浄液は、水を用いてもよいが、塩素を効率よく除去するためにアルカリ水溶液を用いてもよい。アルカリ溶液としては、特に限定されるものではないが、残留する不純物が少なく且つ安価な水酸化ナトリウム水溶液を用いることが好ましい。洗浄液として水酸化ナトリウム水溶液を用いる場合には、水酸化ナトリウム水溶液での洗浄後、ナトリウムを除去するために銀粒子２又はそのスラリーを更に水で洗浄することが望ましい。 As the cleaning solution, water may be used, but an alkaline aqueous solution may be used to efficiently remove chlorine. The alkaline solution is not particularly limited, but it is preferable to use an inexpensive aqueous solution of sodium hydroxide with few residual impurities. When using sodium hydroxide aqueous solution as a washing | cleaning liquid, after washing | cleaning with sodium hydroxide aqueous solution, in order to remove sodium, it is desirable to wash silver particle 2 or its slurry with water further.
　洗浄に用いる水酸化ナトリウム水溶液の濃度は、０．０１ｍｏｌ／ｌ～１ｍｏｌ／ｌが好ましい。０．０１ｍｏｌ／ｌ未満では、洗浄効果が不十分であり、１ｍｏｌ／ｌを超えると、銀粒子２にナトリウムが許容以上に残留することがある。なお、洗浄液に用いる水は、銀粒子２に対して有害な不純物元素を含有していない水が好ましく、特に純水が好ましい。 The concentration of the aqueous sodium hydroxide solution used for washing is preferably 0.01 mol / l to 1 mol / l. If it is less than 0.01 mol / l, the cleaning effect is insufficient, and if it exceeds 1 mol / l, sodium may be left in the silver particles 2 more than acceptable. The water used for the cleaning solution is preferably water containing no impurity element harmful to the silver particles 2, and particularly preferably pure water.
　更に、銀粒子２の表面に有機被膜層３を形成する表面処理工程を行う。銀粒子２への表面処理工程では、銀粒子２を界面活性剤で処理するか、より好ましくは界面活性剤と分散剤で処理する。この表面処理は、銀粒子２が乾燥する前であればいずれの段階で行ってもよいが、塩素及び水溶性高分子を完全に除去すると銀粒子２が凝集し、除去後の表面処理では銀粒子２の表面への一様な表面処理が困難となることがあるため、還元同時若しくは還元直後に表面処理、銀粒子スラリーから銀粒子２を固液分離した後であって洗浄工程前に表面処理、又は洗浄工程と同時に表面処理を行うことが好ましい。 Furthermore, the surface treatment process of forming the organic film layer 3 on the surface of the silver particle 2 is performed. In the surface treatment step to the silver particles 2, the silver particles 2 are treated with a surfactant, or more preferably with a surfactant and a dispersant. This surface treatment may be performed at any stage before the silver particles 2 are dried, but when the chlorine and the water-soluble polymer are completely removed, the silver particles 2 aggregate, and in the surface treatment after removal the silver Since uniform surface treatment to the surface of the particles 2 may be difficult, surface treatment at the same time or immediately after reduction, after solid-liquid separation of the silver particles 2 from the silver particle slurry and before the washing step It is preferable to carry out the surface treatment simultaneously with the treatment or washing step.
　表面処理工程では、例えば銀粒子スラリーから銀粒子２を固液分離した後に表面処理を行うことによって、還元剤起因の残留有機物等によって、界面活性剤や分散剤の吸着が阻害されることを防ぎ、効率的に表面処理を行うことができる。このため、十分な有機被膜層３が形成され、溶剤や樹脂等との相溶性及び分散性が確保される。 In the surface treatment step, for example, solid-liquid separation of the silver particles 2 from the silver particle slurry is followed by surface treatment to prevent the adsorption of the surfactant and the dispersant from being inhibited by the residual organic matter or the like caused by the reducing agent. Surface treatment can be performed efficiently. Therefore, a sufficient organic coating layer 3 is formed, and compatibility and dispersibility with a solvent, a resin, and the like are secured.
　また、洗浄を複数回繰り返して行う場合には、いずれの洗浄時に表面処理を行ってもよいが、銀粒子２に残留している塩素及び余剰の水溶性高分子が表面処理に影響を及ぼさない程度に除去され、銀粒子２の凝集が進行しない状態で行うこと、例えば洗浄を１回以上行った後に表面処理することが好ましい。 When washing is repeated several times, surface treatment may be performed during any washing, but chlorine remaining in silver particles 2 and excess water-soluble polymer do not affect the surface treatment. It is preferable that removal be performed to a certain extent and aggregation of the silver particles 2 not proceed, for example, surface treatment be performed after one or more washings.
　例えば、界面活性剤と分散剤を用いる好ましい表面処理の具体的方法としては、洗浄前の表面処理を行う場合、銀粒子スラリーから固液分離して得られた銀粒子２を、界面活性剤及び分散剤を添加した水中に投入して撹拌するか、界面活性剤を添加した水中に投入して撹拌した後、更に分散剤を添加して撹拌すればよい。また、洗浄液に界面活性剤及び分散剤を同時に添加するか、又は界面活性剤の添加後に分散剤を添加することで、洗浄と表面処理を同時に行ってもよい。銀粒子２への界面活性剤及び分散剤の吸着性を改善するためには、界面活性剤を添加した水又は洗浄液に銀粒子２を投入して撹拌した後、分散剤を更に添加し撹拌することが好ましい。 For example, as a specific method of preferable surface treatment using a surfactant and a dispersant, in the case of performing surface treatment before washing, a silver particle 2 obtained by solid-liquid separation from a silver particle slurry is used as a surfactant and It may be poured into water to which the dispersant has been added and stirred, or may be poured into water to which the surfactant has been added and stirred, and then the dispersant may be added and stirred. Alternatively, the washing and the surface treatment may be performed simultaneously by adding the surfactant and the dispersing agent simultaneously to the washing solution, or adding the dispersing agent after the addition of the surfactant. In order to improve the adsorptivity of the surfactant and the dispersing agent to the silver particles 2, the silver particles 2 are added to water or a washing solution to which the surfactant is added and stirred, and then the dispersing agent is further added and stirred. Is preferred.
　なお、洗浄及び表面処理に用いられる装置は、通常、洗浄や表面処理に用いられる装置でよく、例えば撹拌機付の反応槽等を用いることができる。 In addition, the apparatus used for washing | cleaning and surface treatment may be an apparatus normally used for washing | cleaning and surface treatment, for example, the reaction tank with a stirrer etc. can be used.
　次に、表面に有機被膜層３を形成した銀粒子２を回収する回収工程を行う。この回収工程は、表面処理及び洗浄を行った後、固液分離して銀粒子２を回収する。固液分離に用いられる装置は、通常用いられるものでよく、例えば遠心機、吸引濾過機、フィルタープレス等を用いることができる。 Next, a recovery step of recovering the silver particles 2 having the organic coating layer 3 formed on the surface is performed. In this recovery step, after surface treatment and washing, solid-liquid separation is performed to recover silver particles 2. An apparatus used for solid-liquid separation may be a commonly used apparatus, and for example, a centrifuge, a suction filter, a filter press, etc. can be used.
　次に、洗浄及び表面処理が終了し、固液分離して得られた銀粒子２の水分を蒸発させて乾燥させる乾燥工程を行う。乾燥方法としては、例えば、洗浄及び表面処理の終了後に回収した銀粒子２をステンレスパッド上に置き、大気オーブン又は真空乾燥機等の市販の乾燥装置を用いて、４０℃～８０℃の温度で加熱すればよい。 Next, washing and surface treatment are completed, and a drying step of evaporating and drying the water of the silver particles 2 obtained by solid-liquid separation is performed. As a drying method, for example, silver particles 2 collected after completion of washing and surface treatment are placed on a stainless steel pad, and a temperature of 40 ° C. to 80 ° C. using a commercially available drying device such as an atmospheric oven or vacuum dryer. It may be heated.
　次に、乾燥後の銀粒子２を表面に形成した有機皮膜層３に損傷を与えない程度の十分弱いエネルギーで銀ペースト用として好ましい粒度まで十分に解砕し、分級処理する解砕・分級工程を行い、銀粉１が得られる。解砕方法は、有機皮膜層３に損傷を与えない程度であれば、特に限定されるものではなく、ジェットミル、高速撹拌機等の解砕力が弱い装置を用いることが好ましい。解砕力が強い装置では、有機皮膜層３に損傷を与えるばかりでなく銀粉１が変形することがあり好ましくない。分級装置は、特に限定されるものではなく、気流式分級機、篩い等を用いることができる。 Next, a crushing / classification step of sufficiently crushing to a particle size preferable for silver paste with sufficiently weak energy that does not damage the organic coating layer 3 formed on the surface of the silver particles 2 after drying, and classification processing The silver powder 1 is obtained. The crushing method is not particularly limited as long as the organic coating layer 3 is not damaged, and it is preferable to use an apparatus having a weak crushing power such as a jet mill or a high speed stirrer. In an apparatus with high crushing power, not only damage to the organic coating layer 3 but also the silver powder 1 may be deformed, which is not preferable. The classifier is not particularly limited, and an air flow classifier, a sieve or the like can be used.
　解砕処理とは、乾燥後の凝集粉を、表面処理前の一次粒子もしくは二次粒子の状態に解きほぐす操作をいう。解砕の手段としては、ボールミルや衝突式気流型粉砕器、衝撃式粉砕器、筒型高速攪拌機等種々のものを用いることが可能であるが、解砕のエネルギーが過度に弱すぎる場合には、湿式処理中や乾燥過程で生じた凝集体を十分に解きほぐすことができず、内部摩擦角を２０°以下にすることはできない。一方で、解砕のエネルギーを過度に強くしすぎた場合には、銀粉１の表面の有機皮膜層３に損傷を与え、あるいは二次粒子における一次粒子同士の結合部が破壊されることにより、銀粉１の表面に金属銀の新生面が新たに露出することで表面の親水性が大きくなり、メタノール５０容量％水溶液での接触角が１００°未満になったり、アセトン滴定法による表面ＳＰ値が１８より大きくなってしまう。更に、露出した新生面が活性点となり、保管中に再凝集し、経時的に内部摩擦角が大きくなる場合もある。 The crushing process refers to an operation of disaggregating dried aggregate powder into a state of primary particles or secondary particles before surface treatment. As a means of crushing, it is possible to use various things such as a ball mill, a collision type air flow type crusher, an impact type crusher, a cylindrical high speed stirrer, etc., but when the energy of crushing is too weak. The aggregates formed during the wet processing and the drying process can not be sufficiently disintegrated, and the internal friction angle can not be made 20 ° or less. On the other hand, when the crushing energy is excessively strong, the organic film layer 3 on the surface of the silver powder 1 is damaged, or the primary particles in the secondary particles are broken. The newly exposed surface of silver metal on the surface of silver powder 1 increases the hydrophilicity of the surface, and the contact angle with a 50% by volume aqueous solution of methanol becomes less than 100 °, and the surface SP value by acetone titration method is 18 It gets bigger. Furthermore, the exposed new surface may be an active point, reaggregated during storage, and the internal friction angle may increase over time.
　したがって、いずれの解砕処理機を使用する場合においても、内部摩擦角、接触角、表面ＳＰ値といったパラメータを確認しながら解砕条件を調整し、一次粒子同士が結合した結合部の破壊を抑制するとともに銀粉１の表面の有機皮膜層３に損傷を与えない程度、即ち有機被膜層３が剥がれて銀粒子２が露出しないような解砕処理を加える必要がある。解砕条件は、解砕する装置の大きさや作製した銀粉１の状態等によって、適宜、解砕装置の回転数、解砕時間、温度等を決めるようになる。 Therefore, when using any crushing processing machine, the crushing conditions are adjusted while confirming parameters such as the internal friction angle, contact angle, surface SP value, and the destruction of the bond where primary particles are bonded is suppressed. At the same time, it is necessary to add a crushing treatment to the extent that the organic coating layer 3 on the surface of the silver powder 1 is not damaged, that is, the organic coating layer 3 is peeled off and the silver particles 2 are not exposed. As for the crushing conditions, the number of rotations of the crushing device, the crushing time, the temperature and the like are appropriately determined depending on the size of the crushing device, the state of the produced silver powder 1 and the like.
　例えば、高速撹拌機を用いる場合には、攪拌機の容量により条件は異なるが、銀粒子２の投入量に応じて、有機被膜層３が損傷しないように攪拌機の周速と撹拌時間等を調整する。高速攪拌機を用いた場合の解砕条件としては、例えば、周速を１０ｍ／秒～４０ｍ／秒にし、解砕時間を１０分～６０分程度にすることが好ましい。 For example, when using a high-speed stirrer, conditions vary depending on the capacity of the stirrer, but the peripheral speed and stirring time of the stirrer are adjusted according to the input amount of silver particles 2 so as not to damage the organic coating layer 3 . As a crushing condition in the case of using a high-speed stirrer, for example, it is preferable to set the peripheral speed to 10 m / s to 40 m / s and set the crushing time to about 10 to 60 minutes.
　なお、解砕処理後は、銀粒子スラリー生成工程や解砕・分級工程中に生成又は混入してしまった塊状の銀粉凝集体を除去する目的で、気流式又は篩い式等の分級処理を行うことが好ましい。 In addition, after crushing, classification processing such as air flow type or sieving type is performed for the purpose of removing massive silver powder aggregates which are generated or mixed in the silver particle slurry forming step or the crushing / classifying step. Is preferred.
　上述した銀粉１の製造方法では、銀粒子スラリー生成工程によって得られた銀粒子２の表面に有機被膜層３を形成した後、銀粒子２に金属銀の新生面が新たに生成することを抑制するように解砕することによって、内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上である低親水性の銀粉１を得ることができる。更に、この銀粉１は、アセトン滴定法による表面ＳＰ値が１８以下である。これにより、この製造方法では、銀粉１の内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上であることによって、銀ペーストの溶剤や樹脂等に対する濡れ性が優れているため、分散性が良く、容易にペースト化して銀ペーストを作製することができる。 In the method for producing silver powder 1 described above, after the organic coating layer 3 is formed on the surface of the silver particles 2 obtained in the silver particle slurry forming step, generation of a new surface of metallic silver on the silver particles 2 is suppressed By crushing as described above, it is possible to obtain a low hydrophilic silver powder 1 having an internal friction angle of 20 ° or less and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more. Furthermore, the silver powder 1 has a surface SP value of 18 or less by the acetone titration method. Thereby, in this manufacturing method, the internal friction angle of silver powder 1 is 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol is 100 ° or more, whereby the wettability of the silver paste to the solvent, resin, etc. Is excellent in dispersibility and can be easily pasted to prepare a silver paste.
　また、この製造方法により製造した銀粉１は、十分な表面処理が行われているため、製造直後だけではなく、銀ペーストの樹脂や溶剤と混合する際にも、内部摩擦角が２０°以下となっているため、製造後しばらくしてから溶剤と混合する場合であっても、溶剤や樹脂等との相溶性が良好であり、分散性に優れているため、容易にペースト化することができる。 In addition, the silver powder 1 produced by this production method is subjected to sufficient surface treatment, so that the internal friction angle is 20 ° or less not only immediately after production but also when it is mixed with a silver paste resin or solvent. Because of the above, even when mixing with a solvent after a while after production, compatibility with the solvent, resin, etc. is good, and since it is excellent in dispersibility, it can be easily made into a paste. .
　したがって、上述した銀粉１は、銀ペースト中で偏りなく分散されるため、銀ペーストで配線層や電極を形成した際には電気的接続を良好にすることができる。 Accordingly, the silver powder 1 described above is dispersed evenly in the silver paste, and therefore, when the wiring layer or the electrode is formed by the silver paste, the electrical connection can be made favorable.
　以下、本発明を適用した具体的な実施例について説明するが、本発明は、これらの実施例に限定されるものではない。 EXAMPLES Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.
　＜実施例１＞
　実施例１では、先ず、３８℃の温浴中で液温３６℃に保持した２５質量％アンモニア水３６Ｌに、塩化銀２４９０ｇ（住友金属鉱山（株）製）を撹拌しながら投入して銀錯体溶液を作製し、温浴中で３６℃に保持した。 Example 1
In Example 1, first, 2490 g of silver chloride (Sumitomo Metal Mining Co., Ltd.) is added while being stirred to 36 L of 25% by mass ammonia water kept at a liquid temperature of 36 ° C. in a 38 ° C. water bath and a silver complex solution And kept at 36.degree. C. in a warm water bath.
　一方、還元剤のアスコルビン酸１３１８ｇ（関東化学（株）製、試薬）を、３６℃の純水１０Ｌに溶解して還元剤溶液を作製した。 On the other hand, 1318 g of ascorbic acid as a reducing agent (Kanto Chemical Co., Ltd., reagent) was dissolved in 10 L of pure water at 36 ° C. to prepare a reducing agent solution.
　次に、水溶性高分子のポリビニルアルコール１８７．５ｇ（（株）クラレ製、ＰＶＡ２０５、銀粒子に対して１０．０質量％）を分取し、３６℃の純水４．６Ｌに溶解した溶液を上記還元剤溶液に混合した。 Next, 187.5 g of a water-soluble polymer polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA 205, 10.0% by mass with respect to silver particles) was separated and dissolved in 4.6 L of pure water at 36 ° C. Was mixed into the above reducing agent solution.
　次に、上記銀錯体溶液と還元剤溶液を、モーノポンプ（兵神装備（株）製）を使用し、それぞれ２．４４Ｌ／ｍｉｎ及び０．９０Ｌ／ｍｉｎで樋内に送液して、銀錯体を還元した。この時の還元速度は、銀量で１２７ｇ／ｍｉｎである。なお、上記樋には、内径２５ｍｍ及び長さ７２５ｍｍの塩ビ製パイプを使用した。銀錯体の還元により得られた銀粒子を含むスラリーは、撹拌しながら受槽に受け入れた。受け入れ終了後、受槽内での撹拌を６０分継続した。撹拌終了後の上記銀粒子スラリーをフィルタープレスで濾過し、銀粒子を固液分離した。 Next, the silver complex solution and the reducing agent solution are sent to the inside of the crucible at 2.44 L / min and 0.90 L / min, respectively, using a Mono pump (manufactured by HIROSHI KOGYO CO., LTD.) To obtain a silver complex Reduced. The reduction rate at this time is 127 g / min in silver amount. In addition, the pipe made from polyvinyl chloride of internal diameter 25 mm and length 725 mm was used for the said crucible. The slurry containing the silver particles obtained by the reduction of the silver complex was received in the receiving vessel with stirring. After receiving, the stirring in the receiving tank was continued for 60 minutes. The silver particle slurry after completion of the stirring was filtered by a filter press to separate the silver particles into solid and liquid.
　次に、固液分離した銀粒子に対して表面処理を行った。表面処理剤として市販のカチオン系界面活性剤であるポリオキシエチレン付加４級アンモニウム塩０．９０ｇ（クローダジャパン（株）製、商品名　シラソル、銀粒子に対して０．０４８質量％）及び分散剤であるステアリン酸エマルジョン１６．８７ｇ（中京油脂（株）製、セロゾール９２０、銀粒子に対して０．９０質量％）とを２０Ｌの純水に投入し、撹拌して銀粒子の表面に表面処理した。この後、０．０５ｍｏｌ／Ｌの濃度になるようにＮａＯＨを加え、１５分間攪拌して洗浄した後、フィルタープレスで濾過して銀粒子を回収した。 Next, surface treatment was performed on the solid-liquid separated silver particles. 0.90 g of a polyoxyethylene type quaternary ammonium salt which is a commercially available cationic surfactant as a surface treatment agent (manufactured by Croda Japan Co., Ltd., trade name: silasol, 0.048 mass% with respect to silver particles), and a dispersant 16.20 g of stearic acid emulsion (manufactured by Chukyo Yushi Co., Ltd., Cellosol 920, 0.90% by mass with respect to silver particles), which is an aqueous solution, is added to 20 L of pure water and stirred to surface-treat the surface of the silver particles. did. After this, NaOH was added to a concentration of 0.05 mol / L, and after stirring for 15 minutes for washing, filtration was performed with a filter press to recover silver particles.
　引き続き、回収した銀粒子を乾燥する前に、銀粒子を０．０５ｍｏｌ／ＬのＮａＯＨ水溶液に投入し、１５分間撹拌して洗浄した後、フィルタープレスで濾過して回収した。その後、この洗浄操作と濾過による固液分離操作を３回繰り返した。 Subsequently, before drying the collected silver particles, the silver particles were put into a 0.05 mol / L aqueous NaOH solution, stirred for 15 minutes and washed, and then filtered and collected by a filter press. Thereafter, the washing operation and the solid-liquid separation operation by filtration were repeated three times.
　固液分離した銀粒子を、２０Ｌの純水中に投入し、撹拌及び濾過した後、銀粒子をステンレスパッドに移し、真空乾燥機にて６０℃で１０時間乾燥した。 The solid-liquid separated silver particles were introduced into 20 L of pure water, stirred and filtered, and then the silver particles were transferred to a stainless steel pad and dried in a vacuum drier at 60 ° C. for 10 hours.
　乾燥後、解砕及び分級を行った。解砕は、乾燥後の銀粒子を１．５ｋｇ取り、５Ｌの高速攪拌機（日本コークス（株）製ＦＭ５Ｃ／Ｉ）に投入し、回転羽根を１５ｍ／秒の周速で３０分間回転させて解砕処理を行った。更に、解砕後の銀粒子を、気流式分級機（日本鉱業（株）ＥＪ－３型）を用いて、分級点７μｍで分級処理して銀粉を得た。得られた銀粉のＳＥＭ観察による一次粒子の平均粒径は、０．９８μｍであり、レーザー回折散乱法を用いて測定した粒度（Ｄ５０）は２．３５μｍであった。 After drying, crushing and classification were performed. Disintegration is carried out by taking 1.5 kg of dried silver particles and charging it into a 5 L high-speed stirrer (Nippon Coke Co., Ltd. FM5C / I) and rotating the rotating blade at a circumferential speed of 15 m / sec for 30 minutes to dissolve The crushing process was done. Furthermore, the crushed silver particles were classified at a classification point of 7 μm using an air flow classifier (Japan Mining & Mining Co., Ltd. Model EJ-3) to obtain silver powder. The average particle diameter of the primary particles by SEM observation of the obtained silver powder is 0.98 μm, and the particle diameter (D50) measured using a laser diffraction scattering method is 2.35 μm.
　以上のようにして、実施例１の銀粉を得た。得られた銀粉について、内部摩擦角、接触角、表面ＳＰ値を測定した。 The silver powder of Example 1 was obtained as mentioned above. The internal friction angle, the contact angle, and the surface SP value were measured for the obtained silver powder.
　内部摩擦角の測定には、粉体層せん断力測定装置（（株）ナノシーズ社製ＮＳ－Ｓ３００型）を用いた。常温で銀粉１８ｇを内径１５ｍｍのＳＵＳ製セルに充填した後、押し込み荷重の設定値を２０Ｎとし、押し込み速度０．２ｍｍ／秒で荷重を加えた。設定荷重に達した後、１００秒後に１０μｍ／秒の速度で横摺りを開始した。なお、サンプリングの周波数は１０Ｈｚとした。横摺り開始時の押し込み加重をセルの断面積で除した値を垂直応力σ（Ｎ／ｃｍ２）とし、横摺り後に測定されたせん断力の最大値をセルの断面積で除して得られた値をせん断応力τ（Ｎ／ｃｍ２）とした。 For measurement of the internal friction angle, a powder layer shear force measuring apparatus (NS-S300 manufactured by Nano Seas Co., Ltd.) was used. After filling 18 g of silver powder into a SUS cell with an inner diameter of 15 mm at normal temperature, the setting value of the pressing load was set to 20 N, and the load was applied at a pressing speed of 0.2 mm / sec. After reaching the set load, lateral movement was started at a speed of 10 μm / sec after 100 seconds. The sampling frequency was 10 Hz. The value obtained by dividing the indentation load at the start of sliding by the cross-sectional area of the cell is the vertical stress σ (N / cm 2 ), and obtained by dividing the maximum value of shear force measured after sliding by the cross-sectional area of the cell The shear stress τ (N / cm 2 ) was taken as the value.
　次に、押し込み加重の設定値を４０Ｎとし、垂直応力σ及びせん断応力τを同様に測定した。更に、押し込み加重の設定値を６０Ｎとして垂直応力σ及びせん断応力τを同様に測定した。以上の３つの条件において得られた垂直応力σを横軸に、せん断応力τを縦軸にプロットし、最小二乗法を用いて得られた近似直線の傾き（度）を内部摩擦角とした。 Next, the set value of indentation load was set to 40 N, and the normal stress σ and the shear stress τ were similarly measured. Furthermore, the normal stress σ and the shear stress τ were similarly measured with the setting value of indentation load being 60N. The vertical stress σ obtained under the above three conditions is plotted on the horizontal axis, and the shear stress τ is plotted on the vertical axis, and the inclination (degree) of the approximate straight line obtained using the least squares method is taken as the internal friction angle.
　以上の方法で測定した実施例１の銀粉の内部摩擦角は、７．１°であった。この銀粉を室温で１ヶ月放置後、上記と同様の方法で内部摩擦角の測定を行ったところ７．８°であった。 The internal friction angle of the silver powder of Example 1 measured by the above method was 7.1 °. The silver powder was allowed to stand at room temperature for 1 month, and the internal friction angle was measured in the same manner as described above.
　メタノール５０容量％水溶液での接触角の測定には、接触角測定装置（協和界面科学（株）製ＣＡ－Ｘ１５０）を用いて行った。常温で銀粉を荷重約１ＭＰａでプレス成形して、銀粉が圧密充填された平板状の試験体を得た。この試験体に対して、メタノール５０容量％水溶液が形成する接触角を測定した。この方法で測定した実施例１の銀粉の接触角は、１１０°であった。 A contact angle measurement device (CA-X150, manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the contact angle with a 50% by volume aqueous solution of methanol. The silver powder was press-formed at a normal temperature and a load of about 1 MPa to obtain a flat plate-like test body in which the silver powder was consolidated and filled. The contact angle at which a 50% by volume aqueous solution of methanol is formed was measured on this test sample. The contact angle of the silver powder of Example 1 measured by this method was 110 °.
　アセトン滴定法による表面ＳＰ値の測定は、次のようにして行った。銀粉０．５ｇに水５０ｍｌを加え、緩やかに撹拌をしながら、銀粉を入れた水にアセトンを連続的に滴下し、水面に浮遊している銀粒子が分散し、溶液が白濁したところを終点とした。この時のアセトンの添加体積から計算されるアセトン水溶液の表面ＳＰ値を銀粉の表面ＳＰとした。この方法で測定した実施例１の銀粒子の表面ＳＰ値は、１６．７であった。 The measurement of the surface SP value by the acetone titration method was performed as follows. 50 ml of water is added to 0.5 g of silver powder, and acetone is continuously dropped into water containing silver powder while stirring gently, and silver particles suspended on the water surface are dispersed to cause the solution to become cloudy. And The surface SP value of the acetone aqueous solution calculated from the addition volume of acetone at this time was taken as the surface SP of the silver powder. The surface SP value of the silver particles of Example 1 measured by this method was 16.7.
　次に、得られた銀粉を用いてペースト化の評価を行った。ペースト化の評価は、先ず、ステンレス製の小皿に銀粉９．２ｇと、エポキシ樹脂（三菱化学（株）製、ＪＥＲ　８１９）とターピネオールの重量比が１：７のビヒクル０．８ｇを秤量した。このとき、銀粉の表面がビヒクルによって速やかに濡れていることが観察された。次に、これを金属性のヘラを用いて混合したところ、容易に混合、分散が進み、ペースト状にすることができた。更に、このペーストを自公転型混練機（（株）シンキー製ＡＲＥ－２５０型）を用いて２０００ｒｐｍで５分間混練し、均一な銀ペーストを得た。得られた銀ペーストの分散性をグラインドゲージを用いて評価したところ、最大粒径Ｄｍａｘは、７μmと小さく優れた分散性を示した。 Next, evaluation of paste formation was performed using the obtained silver powder. For evaluation of the formation of paste, first, 9.2 g of silver powder and 0.8 g of a vehicle having a weight ratio of an epoxy resin (Mitsubishi Chemical Co., Ltd., JER 819) to terpineol of 1: 7 were weighed in a small dish made of stainless steel. At this time, it was observed that the surface of the silver powder was quickly wetted by the vehicle. Next, when this was mixed using a metallic spatula, mixing, dispersion proceeded easily, and it could be made into a paste. Furthermore, this paste was kneaded for 5 minutes at 2000 rpm using a self-revolution kneader (AREA-250 manufactured by Shinky Co., Ltd.) to obtain a uniform silver paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle size Dmax was as small as 7 μm and showed excellent dispersibility.
　＜実施例２＞
　実施例２では、ポリビニルアルコールの量を７５ｇ（銀粒子に対して４．００質量％）にしたこと、高速攪拌機の回転羽根を２８ｍ／秒の周速で回転させた以外は、実施例１と同様の方法で銀粉を得るとともに評価した。得られた銀粉の一次粒子の平均粒径は、１．０１μｍであり、粒度（Ｄ５０）は２．７３μｍであった。 Example 2
Example 2 was the same as Example 1 except that the amount of polyvinyl alcohol was 75 g (4.00 mass% with respect to silver particles), and the rotating blade of the high speed stirrer was rotated at a peripheral speed of 28 m / sec. Silver powder was obtained and evaluated in the same manner. The average particle diameter of primary particles of the obtained silver powder was 1.01 μm, and the particle diameter (D50) was 2.73 μm.
　実施例２の銀粉の内部摩擦角は、１０．４°であり、室温で１ヶ月放置後の内部摩擦角は、１０．６°であった。また、実施例２の銀粉の接触角は、１０９°であり、表面ＳＰ値は、１７．４であった。 The internal friction angle of the silver powder of Example 2 was 10.4 °, and the internal friction angle after being left at room temperature for one month was 10.6 °. The contact angle of the silver powder of Example 2 was 109 °, and the surface SP value was 17.4.
　次に、得られた銀粉を用いて実施例１と同様のペースト化の評価を行った。銀粉の表面は、ビヒクルによって速やかに濡れていることが観察された。これを金属性のヘラを用いて混合したところ、容易に混合、分散が進み、ペースト状にすることができた。更に、このペーストを実施例１と同様に自公転型混練機で混練し、均一な銀ペーストを得た。得られた銀ペーストの分散性をグラインドゲージを用いて評価したところ、最大粒径Ｄｍａｘは６μｍと小さく優れた分散性を示した。 Next, evaluation of paste formation similar to Example 1 was performed using the obtained silver powder. The surface of the silver powder was observed to be wet quickly by the vehicle. When this was mixed using a metallic spatula, mixing, dispersion proceeded easily, and it could be made into a paste. Furthermore, this paste was kneaded with a revolution / revolution type kneader in the same manner as in Example 1 to obtain a uniform silver paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle diameter Dmax was as small as 6 μm and showed excellent dispersibility.
　＜比較例１＞
　比較例１では、高速攪拌機の回転羽根を４２ｍ／秒の周速で回転させた以外は、実施例１と同様の方法で銀粉を得るとともに評価した。得られた銀粉の一次粒子の平均粒径は、０．９９μｍであり、粒度（Ｄ５０）は１．８２μｍであった。また、比較例１の銀粉の内部摩擦角は、２０．８°と実施例と比較してかなり高かった。また、比較例１の銀粉の接触角は、８５°であり、表面ＳＰ値は、１８．７であった。 Comparative Example 1
In Comparative Example 1, silver powder was obtained and evaluated in the same manner as in Example 1 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 42 m / sec. The average particle diameter of the primary particles of the obtained silver powder was 0.99 μm, and the particle diameter (D50) was 1.82 μm. Further, the internal friction angle of the silver powder of Comparative Example 1 was 20.8 °, which was considerably higher than that of the example. Moreover, the contact angle of the silver powder of Comparative Example 1 was 85 °, and the surface SP value was 18.7.
　次に、得られた銀粉を用いて実施例１と同様のペースト化の評価を行った。銀粉の表面のビヒクルによる濡れはほとんど観察されなかった。また、これを金属性のヘラを用いて攪拌したところ、大きな粘土状になったままで、ペースト状にすることができなかった。更に、この銀ペーストを実施例１と同様に自公転型混練機で混練し、ペースト状にした。得られた銀ペーストの分散性を、グラインドゲージを用いて評価したところ、最大粒径Ｄｍａｘは２０μｍと大きく分散性が悪かった。 Next, evaluation of paste formation similar to Example 1 was performed using the obtained silver powder. Wetting of the surface of the silver powder by the vehicle was hardly observed. Moreover, when this was stirred using a metallic spatula, it could not be made into a paste-like while remaining large clay-like. Further, this silver paste was kneaded with a self-revolution type kneader in the same manner as in Example 1 to form a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle diameter Dmax was as large as 20 μm and the dispersibility was poor.
　＜比較例２＞
　比較例２では、高速攪拌機の回転羽根を７ｍ／秒の周速で回転させた以外は、実施例２と同様の方法で銀粉を得るとともに評価した。得られた銀粉の一次粒子の平均粒径は、１．００μｍであり、粒度（Ｄ５０）は３．５２μｍであった。また、比較例２の銀粉の内部摩擦角は、２５．８°と実施例と比較してかなり高かった。また、比較例２の銀粉の接触角は、１１０°であり、表面ＳＰ値は、１７．４°であった。 Comparative Example 2
In Comparative Example 2, silver powder was obtained and evaluated in the same manner as in Example 2 except that the rotating blades of the high-speed stirrer were rotated at a peripheral speed of 7 m / sec. The average particle diameter of primary particles of the obtained silver powder was 1.00 μm, and the particle diameter (D50) was 3.52 μm. Further, the internal friction angle of the silver powder of Comparative Example 2 was 25.8 °, which was considerably higher than that of the example. The contact angle of the silver powder of Comparative Example 2 was 110 °, and the surface SP value was 17.4 °.
　次に、得られた銀粉を用いて実施例１と同様のペースト化の評価を行った。銀粉の表面のビヒクルによる濡れはほとんど観察されなかった。また、これを金属性のヘラを用いて攪拌したところ、大きな粘土状になったままで、ペースト状にすることができなかった。更に、このペーストを実施例１と同様に自公転型混練機で混練し、ペースト状にした。得られた銀ペーストの分散性を、グラインドゲージを用いて評価したところ、最大粒径Ｄｍａｘは１８μｍと大きく分散性が悪かった。 Next, evaluation of paste formation similar to Example 1 was performed using the obtained silver powder. Wetting of the surface of the silver powder by the vehicle was hardly observed. Moreover, when this was stirred using a metallic spatula, it could not be made into a paste-like while remaining large clay-like. Further, this paste was kneaded with a revolution / revolution type kneader in the same manner as in Example 1 to form a paste. When the dispersibility of the obtained silver paste was evaluated using a grind gauge, the maximum particle diameter Dmax was as large as 18 μm and the dispersibility was poor.
　以上の実施例及び比較例から、同じ方法によって作製した銀粉であっても、比較例に比べて、銀粉の表面に形成された被膜を損傷しない程度で十分に解砕した実施例１及び実施例２では、内部摩擦角は２０°以下であり、且つ、メタノール５０容量％水溶液での接触角が１００°以上となり、ビヒクルとの相溶性が良く、分散性に優れた銀粉が得られた。また、実施例１及び実施例２では、更に、アセトン滴定法による表面ＳＰ値が１８以下であった。更には、実施例１及び実施例２では、銀粉を室温で１ヶ月放置後であっても、内部摩擦角が２０°以下であり、凝集することが抑制されていた。 From the above Examples and Comparative Examples, Example 1 and Examples were sufficiently crushed to the extent that the film formed on the surface of the silver powder was not damaged even in the silver powder produced by the same method, as compared with the Comparative Example. In No. 2, the internal friction angle was 20 ° or less, and the contact angle with a 50% by volume aqueous solution of methanol was 100 ° or more, and a silver powder having good compatibility with the vehicle and excellent dispersibility was obtained. Moreover, in Example 1 and Example 2, surface SP value by acetone titration method was 18 or less. Furthermore, in Example 1 and Example 2, even after the silver powder was left to stand at room temperature for 1 month, the internal friction angle was 20 ° or less, and aggregation was suppressed.
　一方、比較例１では、解砕条件が強すぎ、銀粉の表面に形成した有機被膜層が損傷してしまい、内部摩擦角が２０°よりも大きくなり、接触角も１００°よりも小さくなった。さらに、表面ＳＰ値も１８よりも大きくなった。また、比較例２では解砕条件が弱く、凝集体を十分にほぐすことができなかったため、内部摩擦角が２５．８°とかなり大きくなった。これにより、比較例１及び比較例２では、ビヒクルとの相溶性が悪く、銀粉の分散性が悪くなった。 On the other hand, in Comparative Example 1, the crushing condition was too strong, the organic coating layer formed on the surface of the silver powder was damaged, the internal friction angle was larger than 20 °, and the contact angle was also smaller than 100 °. . In addition, the surface SP value was also greater than 18. Further, in Comparative Example 2, since the crushing conditions were weak and the aggregates could not be sufficiently loosened, the internal friction angle was considerably increased to 25.8 °. Thereby, in Comparative Example 1 and Comparative Example 2, the compatibility with the vehicle was poor, and the dispersibility of the silver powder was poor.

Claims (5)

  1. 　内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上であることを特徴とする銀粉。 Silver powder having an internal friction angle of 20 ° or less and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more.
  2. 　更に、アセトン滴定法による表面ＳＰ値が１８以下であることを特徴とする請求項１記載の銀粉。 Furthermore, silver powder according to claim 1, wherein the surface SP value by the acetone titration method is 18 or less.
  3. 　銀ペーストの溶剤と混合する際の上記内部摩擦角が２０°以下であることを特徴とする請求項１又は請求項２記載の銀粉。 The silver powder according to claim 1 or 2, wherein the internal friction angle at the time of mixing with a solvent of silver paste is 20 ° or less.
  4. 　湿式還元法を用いて合成した銀粒子に表面処理を行うことによって表面に有機皮膜層を形成した後、上記有機被膜層に損傷を与えない程度で十分な解砕処理を行い、
    　内部摩擦角が２０°以下であり、且つメタノール５０容量％水溶液での接触角が１００°以上である銀粉を製造することを特徴とする銀粉の製造方法。     After an organic film layer is formed on the surface by performing surface treatment on silver particles synthesized using a wet reduction method, a sufficient crushing process is performed to the extent that the organic film layer is not damaged.
    A method for producing a silver powder comprising producing a silver powder having an internal friction angle of 20 ° or less and a contact angle with a 50% by volume aqueous solution of methanol of 100 ° or more.
  5. 　上記解砕処理の方法は、高速攪拌機を用い、攪拌羽根の周速が１０ｍ／秒以上、４０ｍ／秒以下の条件であることを特徴とする請求項４記載の銀粉の製造方法。 The method for producing a silver powder according to claim 4, wherein the method of the crushing treatment uses a high speed stirrer and the peripheral speed of the stirring blade is 10 m / s to 40 m / s.
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