WO2009031849A2

WO2009031849A2 - Conductive ink compositions incorporating nano glass frit and nano metal for enhanced adhesion with glass and ceramic substrates used in displays

Info

Publication number: WO2009031849A2
Application number: PCT/KR2008/005252
Authority: WO
Inventors: Jooho Moon; Daehwan Jang; Dongjo Kim; Byungyoon Lee; Yoonhyun Kim; Sungsoo Kim; Kyuyong Lee
Original assignee: Industry-Academic Cooperation Foundation, Yonsei University; Chang Sung Corporation
Priority date: 2007-09-07
Filing date: 2008-09-05
Publication date: 2009-03-12
Also published as: WO2009031849A4; WO2009031849A3; KR100905399B1; KR20090025894A

Abstract

The present invention relates to a conductive ink composition for ink jet printing, which can form a conductive pattern by an ink jet printing method using a glass or ceramic substrate such as a flat panel display and a laminated manual component in producing components and elements that require a thermal process at a relatively high temperature of 400-800°C. It relates to a method for synthesizing silver nano sol having a uniform particle size, an excellent dispersion and an excellent sinterability, and to a conductive ink composition to which is added nano glass frit for improving adhesion between a conductive pattern, which is closely relates to a panelt= long-term stability and reliability, and a glass substrate, the conductive ink composition being able to form patterns with excellent conductivity. According to the present invention, the conductive ink composition for ink jet printing comprising metal nano particles, a co-solvent and nano glass frit can form a conductive pattern using an ink jet printing method, and also enhance adhesion by fusing the nano glass frit, which is added during drying and heat treatment processes, with the substrate.

Description

[DESCRIPTION] [Invention Tit Ie]

CONDUCTIVE INK COMPOSITIONS INCORPORATING NANO GLASS FRIT AND NANO METAL FOR ENHANCED ADHESION WITH GLASS AND CERAMIC SUBSTRATES USED IN DISPLAYS [Technical Field]

<i> The present invention relates to a conductive ink composition applicable in a field where glass and dense or porous ceramic substrates are used instead of a plastic substrate because a thermal process at high temperatures of 400-800°C is required in the application fields of display, solar cell, biochip, manual chip component, multi-layered printing circuit substrate, sensor, light component, etc.

<2> The present invention relates to a conductive ink composition which can be used in a technology of manufacturing conductive patterns of various shapes with a maskless, easy direct-writing method through a drying, thermal process after selectively printing conductive ink on a substrate by an inkjet printing method. [Background Art]

<3> Conventionally, photolithography based on exposure and etching processes is mostly used in producing conductive fine patterns; however, because it is not only an energy-intensive, costly production technology going through many complex manufacturing steps but also can cause environmental pollution such as gas, waste water, etc. discharged during exposure and etching process, there has been a search for an alternative technology, and as an alternative technology, an inkjet printing application technology has been widely studied.

<4> Among various application fields which can produce metal wiring and conductive patterns through an inkjet printing, there is a field where a glass or dense/porous ceramic substrate is used instead of a plastic substrate due to a thermal process at high temperatures of 400-800^°C . Components and elements using glass substrates are flat panel displays, solar cells, sensors, biochips, etc.; and those using ceramic substrate, for example, dense substrates such as alumina, zirconia, aluminumnitride, etc. and pre-sintered porous ceramic green sheets prepared by tape casting, etc. are multi-layered printing circuit substrates, Low Temperature Cofired Ceramics (LTCC), laminated manual components, etc.

<5> For the purpose of forming metal wiring and conductive patterns of such components and elements, a conventional photo conductive paste is applied onto the surface of a substrate by a screen printing, and by means of an optical patterning and etching process, conductive patterns are formed on the substrate, which is then subjected to a high-temperature heat treatment to form a conductive film attached to the glass and ceramic substrate.

<6> A conventional conductive paste contains metal powder such as micro- size Ag, Ni, Au, Ag-Pd, etc. as components giving conductivity.

<7> The conductive ink of existing inkjet printers is for a thermal process at relatively low temperatures, i.e. thermal process at below 300^°C on a plastic substrate, and obtains conductive patterns where adhesion to the substrate depends mainly on organic components contained in the ink.

<8> After conductive ink for low-temperature is printed on a glass or ceramic substrate, the glass or ceramic substrate is subjected to a thermal treatment at high temperatures, which causes most of the organic materials provided to improve adhesion to be evaporated and thus the organic materials do not serve their purpose, and also the metal nano particles included in the conductive particles are excessively sintered and thus their volume shrinks greatly, thereby causing the substrate and the conductive pattern to be separated. Such defects are crucial because they are closely related to realizing the product by characteristics and credibility, and thus they must be considered in replacing the conventional conductive pattern process with an inkjet printing.

<9> During a thermal treatment at high temperatures, melting glass causes adhesion to the substrate. Since glass frit and metal powder used in a conventional conductive paste cannot be applied in producing conducive ink which can be used in inkjet printing due to a decrease in dispersion, nozzle blocking, differences in ink fluid properties, etc., conductive ink is required that is suitable for components and element, which require a thermal process at such a high temperature. The adhesion between a conductive pattern and a substrate is a very important factor determining the performance and reliability of the whole components and elements, and accordingly, a technology of thermal processing at high temperatures, in contrast to low-temperature type conductive ink, in order to secure conductivity and adhesion at the same time is crucial in achieving a successful application of the inkjet printing method in the current-and next- generation information/electronic component and element industries.

<io> The inkjet printing method according to the present invention is a non- contact printing method with less noise and low costs and can be divided into a continuous jet method and a drop-on-demand (DOD) method depending on the spraying type. The continuous jet method is a printing method adjusting the direction of ink by changing an electromagnetic field while continuously jetting the ink using a pump. The drop-on-demand method is a method dispersing ink only when needed on an electronic signal; it can be divided into a piezoelectric ink jet method generating pressure by using a piezoelectric plate causing a mechanical change by electricity, and a thermal ink jet method using pressures, which is generated by the expansion of bubbles produced by heat. Also, since ink is dispersed on a target spot by a non-contact method, patterns can be printed on substrates of various materials.

<ii> In the drying and thermal process after forming patterns on a substrate, for the purpose of superior conductivity free of defects from contraction, an ink composition comprising a high concentration of metal nano particles is required. For dispersion in ink at a high concentration level and maintenance of a stable dispersion state with nano glass frit, a technology of synthesizing metal particles in bulk and improving the quality of the surface of the synthesized particles is necessary. ^<12> Also, in the field that uses glass such as PDP (Plasma Display Panel), FEDs (Field Emission Displays), thermal coils for cars, etc., as a substrate, the firing temperature of a paste is set at 550°C or below, and many researches are under way to lower the firing temperature of a paste.

<'3> Accordingly, in trying to lower the firing temperature of the paste and ink, considering that silver powder has a characteristic of drastic decrease in its firing temperature as it becomes nano-sized, if that characteristic is used, a conductive paste and ink which can be used at low temperatures can be produced.

<i4> Silver particles of nanometer size have an improved performance because the surface area per unit mass increases as compared to bulk particles, and presents a different physicochemical characteristic from the bulk particle. And, this performance of silver particles improves the more as the particles become nanosized.

<15> Meanwhile, for the application of the inkjet method to a process of manufacturing displays, it is required to stably eject the ink material for inkjet, and to this end, the size of particles should be uniform; and the particles be uniformly dispersed. Further, for the purposes of formation of fine lines, connectabl ity of electrodes after sintering, and high conductivity, a high concentration of silver nano sol is required.

<16> For manufacturing silver particles, various methods such as an electrolysis method, an electric reduction method, an alcohol reduction method, a pyrolysis method, etc. are used. Among them, the electrolysis method (Laid-open Patent No. 2004-1005914) is not suitable for obtaining a high concentration of silver nano-sol because the time taken in manufacturing them is very long and the concentration of silver particles is very low.

<17> The chemical reduction method is a method of generating deposits using a reduction agent with a metal salt as a starting material, and can produce silver particles in high concentration; however, the generated silver particles are not stable, and tend to aggregate immediately, and thus it is difficult to obtain monodispersed silver particles. ^<18> For manufacturing monodispersed silver nano particles according to that method, Korean Laid-open Patent Nos. 2004-0025646, 2002-0022168, 2001- 0070070, etc. were filed with respect to a manufacturing process by adding dispersing agents such as PVP, PVA, surfactant, etc.

<'^9> However, using a dispersing agent as above makes it difficult to synthesize particles at high concentration; in addition, the amount of surfactant used should be increased for aggregation and dispersion.

<20> When using hydrazine as a reducing agent, and PVP, PAA and SDS as dispersing agent as in Korean Laid-open Patent No. 2004-0047100, the size of the particles increases to lOOnm or above, and it is difficult to obtain monodispersed nano-sol due to the aggregation of the particles.

<2i> Thus, further studies are needed for a method of producing monodispersed silver nanosol in high concentration. [Disclosure] [Technical Problem]

<22> The present invention is to provide a printable conductive ink composition, to which nano glass frit is added, which minimizes a loss of the conductive characteristic, improves adhesion to a substrate so as to prevent a conductive pattern from being separated from a glass or ceramic substrate, and presents excessive sintering between metal nano particles.

<23> Also, the present invention is to provide a conductive ink composition comprising metal nano particles and nano glass frit as main components, the conductive ink composition being able to minimize the decrease in conductivity and be used for jetting. To this end, metal nano particles that can control the characteristics of nano glass particles and their dispersion characteristic, and express conductivity as mixed with them are synthesized the surface characteristics of particles are controlled and then dispersed in an appropriate solvent. [Technical Solution]

<24> In order to achieve the above objectives, the present invention provides a conductive ink composition for inkjet printing, characterized in that the co-solvent of a first solvent and a second solvent comprises metal nano particles and nano glass frit.

^<25> Also, the present invention provides a conductive ink composition for inkjet printer, characterized in that the size of the metal nano particles is 50-100 nm.

<26> Also, the present invention provides a conductive ink composition for inkjet printer, characterized in that the content of said metal nano particles is 10 to 60 weight parts based on 100 weight parts of said ink composi t ion.

<27> Also, the present invention provides a conductive ink composition for inkjet printing, characterized in that the co-solvent comprises one or more selected from the group consisting of water, ethanol, methanol, isopropanol, and ethyl lactate as a first solvent, and one or more selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, and glycerine as a second solvent .

<28> Also, the present invention provides a conductive ink composition for inkjet printer chanracterized in that the nano glass frit is 0.5 to 20 weight parts based on 100 weight parts of the ink metal nano particle composition.

<29> Also, the present invention provides a conductive ink composition characterized in that the size of the nano glass frit is 200 nm or less.

<30> Also, the present invention provides a method for manufacturing silver nanosol of 50-100 nm, and the method is characterized by comprising the steps of: (A) melting silver (Ag) in nitric acid to make silver nitrate (AgN03), which is a silver precursor (pre-Ag); (B) diluting the silver nitrate obtained in step (A) and adding ammonia water to form a complex compound; (C) injecting a dispersion agent to make a silver complex compound which is monodispersed; (D) reducing the silver complex compound by using a reducing agent; (E) washing it by using an organic solvent and distilled water^; and (F) re-dispersing it in distilled water to obtain 10-50 w.t.% silver nanosol. [Advantageous Effects]

<32> The present invention adds nano glass frit to conductive ink for inkjet printer, and can form electrode patterns by using a simple, environment- friendly inkjet printing method for glass substrates such as flat display panels, solar cells, sensors, biochips, etc. or for ceramic substrates for example, dense substrates such as alumina, zirconia, aluminumnitride, etc. and pre-sintered porous ceramic green sheets prepared by tape casting, etc.

<33> The present invention can prevent excessive sintering of metal nano particles contained in the conductive ink of the present invention, and improve adhesion between a metal pattern and the substrate by fusion reaction between the nano glass frit and the substrate; it further solves the problem of adhesion between a substrate (for example, a glass substrate such as PDP and a dense or porous ceramic substrate) and a metal pattern, can quickly and freely form metal patterns having superior conductivity with a simple, environment-friendly inkjet printing method and obtain fine patterns.

<34> Also, the conductive ink composition of the present invention can be applied in various electric/electronic components industries such as next- generation displays, Radio Frequency Idenrif ication (RFID), manual components, electronic circuit substrates, sensors, etc.

<35> According to the present invention, nano sol having a silver concentration of 50 weight % and more can be produced and used in conductive ink that is used in an electronic circuit.

<36> Also, when using the synthesized silver nano sol as an electrode material for PDPs and displays, the particle size distribution and dispersion stability are superior. [Description of Drawings]

<37> Fig. 1 is a flow chart illustrating a preparation process using a conductive ink composition.

<38> Fig. 2 is a flow chart illustrating a preparation process of silver nano so1.

<39> Fig. 3 is a graph showing the change in viscosity when adding nano glass frit to a conductive ink according to the examples of the present invention.

^<40> Fig. 4a is an SEM photograph of the nano glass frit added to the conductive ink in the present invention, and Fig. 4b is its average size.

^<41> Fig. 5 is an SEM photograph of the silver nano particles prepared according to the present invention.

<^42> Fig. 6 is a result of TGA analysis of a dispersion agent and silver nano particles.

<43> Fig. 7 is sectional fine structures of comparative sample (a) and sample (b) prepared according to the present invention after they were heat treated at 600^°C . [Best Mode]

<44> Metal nano particles of the present invention may be Ag nano particles having superior dispersibi lity so that precipitation does not occur, the Ag nano particles being 50nm-100nm and having superior particle size distribution.

<45> If the size of the metal nano particles is less than 50nm, it can cause excessive volume contraction by oversintering during sintering after ink-jet printing, so it may cause a separation of a conductive pattern, and if the size is more than lOOnm, the particles dispersion stability is low, so that a nozzle is clogged during jetting, that maintenance of ink deteriorates, and that the density of the sintered structure after sintering is low and thus conductivity gets lower.

<46> 10-60 weight parts of the metal nano particles is mixed on the basis of 100 weight parts of the ink composition. If the amount of the metal nano particles is less than 10 weight parts with reference to the ink composition, sufficient conductivity cannot be achieved when a conductive pattern is obtained; and if the amount is more than 60 weight parts, a nozzle is clogged so that it is difficult to form a fine pattern.

<47> The co-solvent may be produced by a mixture of two solvents. It may consist of a solvent of a mixture of at least one first solvent with a relatively high evaporation rate and at least one second solvent with a relatively low evaporation rate.

^<48> The first solvent with a relatively high evaporation rate functions to obtain an accurate pattern by fixing the ink sprayed on a substrate before it spreads on the substrate because it evaporates fast after sprayed on the substrate. For example, it may be at least one solvent selected from a group consisting of water, ethanol, methanol, isopropanol, and ethyl lactate.

<49> The second solvent with a relatively low evaporation rate functions to keep the nozzle of an ink jet printer wet by preventing it from being clogged. The second solvent evaporates after the ink makes a pattern on the substrate and the first solvent evaporates. Such second solvent may be at least one solvent selected from a group consisting of ethylene glycol, dietylene glycol, triethlene glycol, propylene glycol, dipropylene glycol, hexylene glycol and glycerine.

<50> Here, the ratio of the first solvent to the second solvent is from 10:90 to 90:10. If the ratio of the first solvent is lower than 10:90, the drying rate of ink gets too high, so the nozzle can get easily clogged; and if the ratio of the first solvent is higher than 90:10, the drying time gets longer when forming a pattern by printing, so that the solvent is spread and thus it would be hard to obtain fine patterns.

<5i> In the present invention, it is preferred that the size of nano glass frit is 200nm or less and the glass transition temperature is lower than the process temperature in the process where conductive ink is used so that the nano glass frit can be adhered on the substrate. As shown in Table 4 of the following example 4, when nano glass frit is 200nm or less, jetting becomes stable and ink-jet printing is possible. According to the present invention, nano glass frit needs to have a glass transition temperature (T₈) that varies depending on the kind of the substrate used and the temperature condition of the heat treatment. In other words, the nano glass frit should have a glass transition temperature a little bit lower than the process temperature to be melted appropriately during the heat treatment. <52> For example, in case of a glass substrate for flat panel displays, it is preferred that the glass transition temperature of the nano glass frit is

O O

450-550 C, a little bit lower than 600 C which is the process temperature for flat panel displays. If the glass transition temperature of the nano

O glass frit is 600 C or higher, the melting reaction of the nano glass frit may not be complete, so adhesion is not expected to improve.

<53> 0.5 to 20 weight parts, more preferably 2 to 5 weight parts, of nano glass frit is added on the basis of 100 weight parts of the ink metal nano particle composition.

<54> In order that nano glass frit produces the effect of improving adhesion by being mixed with conductive ink, 0.5 weight parts or more of nano glass frit should be added on the basis of 100 weight parts of the ink metal nano particle composition. If the volume of the nano glass frit exceeds 20 weight parts, it is difficult for it to be uniformly dispersed in the conductive ink due to its big volume, so that it cannot have proper conductivity. As shown in Table 3 of example 3, ink-jet printing is possible with 20 weight parts or less, where a conductivity loss can be minimized. Example 5 shows the result of increasing adhesion, when the content of nano glass frit is 0.5 to 20 weight parts.

<55> Further, the present invention provides a process for producing Ag nano sol and an ink composition.

<56> Fig. 1 is a flow chart illustrating a process for producing a conductive ink composition.

<57> A co-solvent is mixed with metal nano sol to form a mixture, and nano glass frit is added to the mixture and thus obtained mixture is milled to produce a conductive ink composition.

<58> The present invention provides a process for producing a conductive ink composition for an ink-jet printer characterized in that the above produced metal nano sol is mixed with a dispersion agent in the co-solvent to form a mixture and then nano glass frit is added in the mixture and milling-mixed.

<59> According to one embodiment, nano glass frit is put into the mixture and then it is uniformly dispersed by wet corrosion Bead milling for 24 hours using 1 to 0.1-5 mm Zirconia Bead, so that it can have a viscosity of 1 to 20 (mPa-s) to allow ink-jet printing.

<60> Fig. 2 is a flow chart illustrating a process for producing silver nano sol .

<6i> The process comprises the steps of: (A) melting silver (Ag) in nitric acid to make silver nitrate (AgN03), which is a silver precursor (pre-Ag); (B) diluting the silver nitrate obtained in step (A) and adding ammonia water to form a complex compound; (C) injecting a dispersion agent to make a silver complex compound which is monodispersed; (D) reducing the silver complex compound by using a reducing agent; (E) washing it by using an organic solvent and distilled water; and (F) re-dispersing it in a distilled water to obtain 10-50 w.t.% silver nanosol .

<62> Step (A) is a step of melting pure Ag in nitric acid to produce AgNo₃, a silver precursor, where Ag and distilled water are put into the nitric acid and then ph of AgNo₃ is adjusted to 1.0-2.0 while boiling and stirring the mixture.

<63> Step (B) is a step of forming a complex ion of silver precursor and ammonia, where when a dispersion agent is added, the dispersion agent reacts with AgNo₃ to cause gellation so that silver particles may not be produced.

<64> Step (C) is a step of adding a dispersion agent to the product produced at step (B) to form a mono-dispersed Ag complex compound, where polysaccharide glucose such as acacia powder is used as the dispersion agent.

<65> Step (D) is a step of adding a reducing agent to the product produced at step (C) and then reducing the product to produce Ag nano particles, where hydrazine is the most preferable as an organic reducing agent and other reducing agents with high reducing potential such as formalin, NaBH4 etc., may be used, but if an organic reducing agent with low reducing potential is used, the reaction speed is slow and thus the particle size gets bigger. <66> Steps (E)-(F) are steps of precipitating the synthesized Ag nano particles using acetone to obtain a high concentration of Ag nanosol . Here, polysaccharide glucose used as dispersion agent causes strong aggregation induced by an organic solvent so that the reacted Ag nanosol can be easily precipitated. The organic solvent used for this should have a polarity that enables it to be easily mixed with water used as a reaction solvent and at the same time, be nonpolar such that it does not melt the dispersion agent. Here, alcohol such as ethanol, methanol, etc., and ketones such as acetone, etc. may be used, but in an economic aspect, acetone is the most preferable. The process of adding distilled water to the precipitated Ag nanosol, washing the non-reacted dispersion agent, and adding acetone again for precipitation is repeated three times. Here, the volume ratio of the organic solvent used to the added distilled water is 1:1.

<67> At step (F), the desired concentration of Ag nano sol can be obtained by adjusting the amount of distilled water. Step (F) is a step of adjusting the concentration of Ag nano sol, where distilled water is added and then re- dispersed using ultrasonic wave to produce a high concentration of Ag nano sol. Here, Ag concentration can be adjusted up to 50wt % depending on the added amount of distilled water.

<68> Acacia powder, which is polysaccharide glucose, is used as dispersion agent to suppress aggregation of particles.

<69> At the washing step, Ag nano particles are precipitated using acetone to synthesize a high concentration of silver nano sol (50 wt%).

<70> A conductive ink composition is produced using metal nano powder produced by the above preparation process.

<7i> The ink composition produced as above can be used to form an electrode pattern by using a simple, environmentally friendly ink-jet printing method on glass substrates necessary for producing flat panel displays, solar cells and laminated manual components, or ceramic green sheets, and to obtain highly adhesive conductive patterns by sintering the metal nano particles contained in conductive ink and inducing adhesion of nano glass frit added to prevent separation from the substrate <72> The conductive ink composition according to the present invention can be used in components and elements using glass substrates such as flat panel displays, solar cells, sensors, biochips, etc., and in those using ceramic substrates, for example, dense substrates such as alumina, zirconia, aluminumnitride, etc., and pre-sintered porous ceramic green sheets prepared by tape casting.

<73> Since, unlike a plastic substrate, such substrates are used in producing components and elements requiring a high heat treatment at 500-800

O

C, in case where conductive patterns are formed by ink-jet printing on those substrates, the conductive patterns also undergo the same heat treatment, and thus, nano glass frit is added to the conductive ink to prevent a substrate from being separated due to oversintering of the metal nano particles contained in the conductive ink, so that it can improve adhesion with the substrate.

<74> Conductive ink mixed with nano glass frit should indicate a Newtonian flow without a change in viscosity according to a shear rate.

<75> Fig. 3 illustrates the viscosity of conductive ink to which 2 weight parts of nano glass frit the particle size of which is 135 nm is added in example 5 of the present invention, and the Newtonian flow. The conductive ink should have dispersion stability to permit ink-jet printing.

<76> Fig. 4a is an SEM photography of the nano glass frit used in examples 4 and 6 of the present invention, and Fig. 4b is a graph illustrating the average size. It can be seen that the particles are dispersed with their size being regular averaging 135nm.

<77> Hereinafter, the present invention is specifically described with examples, but such examples are merely intended to merely describe the present invention, but not to restrict the scope of the present invention.

<78> Examples 1-5 are experimental examples of Ag nano particles among metal nano particles.

<79> (Example 1) <80> Ag nano particles are produced with a AgNo₃ aqueous solution as precursor, acacia powder as dispersion agent and hydrazine as reducing agent. <8i> Step (A): A reaction solution is produced by putting 78,75g of AgNo₃

(Ag 5Og) into distilled water 1000ml and stirring it at 400rpm for 10 minutes, and then a reduction solution is produced by putting hydrazine 22.5g (0.4M) into 1000ml of distilled water and stirring it at 400rpm.

<82> Step (B): A complex ion is formed by adding ammonia water 100ml in the reaction solution produced at step (A) and stirring it at 400rpm for 10 minutes. Here, the reaction solution is a transparent solution without Ag- precipitation.

<83> Step (C): A dispersion agent 1Og is added in the reaction solution produced at step (B) and the reduction solution produced at step (A), respectively, and is stirred at 400rpm for 30 minutes so that the dispersion agent is sufficiently mixed.

<84> Step (D): A reaction solution is temporarily put in the reduction solution produced at step (C) and then is stirred at 500rpm to reduce Ag ion. Here, Ag nano sol obtained after the reduction is blackish brown.

<85> Step (E): The concentration of the Ag nano sol is synthesized to be 2.5 wt% and it goes through the precipitation and cleaning processes for a high concentration. After the reaction, acetone is added to the reaction solution to precipitate Ag nano particles. Here, if the reaction solution is left for precipitation for 10 minutes, the upper layer is light yellow and all Ag nano particles are precipitated. After the precipitation, the upper layer is removed and then distilled water is added to the precipitated powder for re- dispersion. Here, non-reacted dispersion agents are eliminated by the distilled water and such washing process is repeated three times. The volume ratio of the used acetone to distilled water is 1:1.

<86> Step (F): Distilled water is added to the Ag nano particles washed at (E) step and then re-dispersed using ultrasonic wave. Here, the Ag concenstration can be adjusted up to 50 wt% according to the amount of the added distilled water.

<87> Fig. 5 shows an FE-SEM analysis result of the synthesized Ag nano particles, and as shown in the result, it can be seen that initial particles in the size of 30 nm are first aggregated so as to form Ag nano particles in the size of 50nm-100nm.

<88> Fig. 6 shows the measurement result of a heat analysis, where it can be seen that an organic material is completely decomposed at 300 °C or below.

<89> (Example 2) <90> Ag nano particles are produced in the same manner as in example 1 by adding Og, 5g, and 15g, of the dispersion agent at step (C) of example 1, respectively.

<91 > If acacia power as a dispersion agent is decreased to 5g, the size and dispersibi lity get abruptly worse.

<92> Meanwhile, if the amount of the dispersion agent is increased to 15g, it shows the same physical characteristic as when 1Og is added, and thus 1Og of the dispersion agent is preferable.

<93:> Table 1 is an analysis result of the size, zetapotential , specific surface area, tap density, and oxygen concentration of the nano particles.

<94> [Table 1] <95>

The dispersion agent used at step (c) of example 1 is replaced with PVP (Polyvinylpyrrolidone, Mw=13,000) and the amount of PVP used is 0.01M, 0.05M and 0.1M. Table 2 shows the analysis result of size and zetapotential when different amounts of PVP are used. When PVP is used as dispersion agent, dispersibi lity is generally superior but the particle size is big and irregular.

<96> [Table 2] <97>

(Example 3)

<98> A plasma di splay panel (PDP) , for which a glass substrate i s used o because it requires a process at the high temperature of about 550C, is selected among the flat panel displays as representative example.

<99> A 20 weight ratio of the above silver nano particles with respect to the solvent (water : ethylene glycol = 4:1) is completely mixed by Bead milling to obtain a high concentration of conductive ink composition that contains silver nano particles and can be used for printing. 0.1 to 30 weight parts of nano glass frit with a particle size 135nm is added on the basis of 100 weight parts of silver nano particles and mixed in the obtained ink, and then patterns are formed and it is heat- treated at 600C. Table 3 shows the result of the test for the ink-jet printing jetting possibility, and the test for dispersibility, conductivity and adhesion after 0.1 to 30 weight parts of nano glass frit on the basis of 100 weight parts of said conductive ink were added. When patterns are formed on a substrate with the conductive ink to which nano glass frit is added, it is necessary to control the amount of the glass frit to minimize the decrease of conductivity and secure sufficient adhesion to the substrate.

<100> [Table 3] :I01>

)'• Superior, O: good, Δ: normal, x: bad)

< I O2> (Example 4) <103> A plasma display panel (PDP), for which a glass substrate is used o because it requires a process at the high temperature of about 550C, is selected among the flat panel display as representative example.

< 104> A 20 weight ratio of the above silver nano particles with respect to the solvent (water ethylene glycol = 4:1) is completely mixed by Bead milling to obtain a high concentration of conductive ink composition that contains silver nano particles and can be used for printing. Nano glass frit with a particle size 10-500nm is added and mixed in the obtained ink to test Jetting possibility, dispersibi lity and adhesion. The table shows the respective result .

<105> [Table 4] <106>

<107> (Example 5) <108> A plasma display panel (PDP), for which a glass substrate is used

O because it requires a process at the high temperature of about 550C, is selected among the flat panel display as representative example. :109> A 20 weight ratio of the above silver nano particles with respect to the solvent ⁽water ethylene glycol = 4:1) is completely mixed by Bead milling to obtain a high concentration of conductive ink composition that contains silver nano particles and can be used for printing. cl lθ> 2 weight parts of nano glass frit with the glass transition temperature

O of 550 C and the particle size of 135nm is added to conductive ink with on the basis of 100 weight parts of Ag nano particles of the conductive ink, and the conductive ink is printed on glass substrates for PDP, and the patterned substrates are heat treated at 400°C, 500°C and 600°C, respectively. And then, they are compared with those to which nano glass frit is not added.

<1 1 1> Fig. 7 shows the sectional fine structures of a sample where nano glass frit is added to a conductive ink according example 7 and a sample where nano glass frit is not added after both samples are heat-treated at 600C. In case where frit is mixed, it shows that the frit has a close adhesion reaction with the glass substrate.

<U 2> After the conductive patterns formed with the above conductive ink for inkjet printers are heat-treated, the adhesion can be confirmed through ASTM D 3359 tape test. In the cross-cut tape test of ASTM D 3359 (Standard test methods for measuring adhesion by tape test), increase in adhesion is confirmed by tape test with 3M 610 tape on the scale of 0B-5B based on the rate of the eliminated area per unit area of the substrate.

<1 13> [Table 5] <l !4> Classification of the ASTM D 3359 test for measuring adhesion <1 15>

Table 6 shows the result of the adhesion test with 0-30 weight parts of naπo glass frit. When the amount of the nano glass is 0.5 weight parts to 20 weight parts and the heat treatment temperature of 600 °C is higher than the glass transition temperature of the nano glass frit, it improves adhesion, resulting in sufficient adhesion to the glass substrate, whereas when the glass transition temperature is 400 C or lower, the nano glass frit is not sufficiently adhered to the substrate, so that it cannot be expected to improve adhesion.

<1 I6> [Table 6] <1 17> Classification of adhesion according to the heat treatment temperature, ASTM D 3359

<! 18>

Claims

[CLAIMS] [Claim 1]

='20> A conductive ink composition for inkjet printing, characterized in that a co-solvent of a first solvent and a second solvent comprises metal nano particles and nano glass firt.

[Claim 2]

<i2i> The conductive ink composition for inkjet printer in claim 1, characterized in that the size of the metal nano particles is 50-100 nm.

[Claim 3]

<i22> The conductive ink composition for inkjet printer in claim 1 or 2, characterized in that the content of said metal nano particles is 10 to 60 weight parts based on 100 weight parts of said ink composition.

[Claim 4]

</23> The conductive ink composition for inkjet printing in claim 1 or 2, characterized in that the co-solvent comprises a first solvent, which is one or more selected from the group consisting of water, ethanol, methanol, isopropanol, and ethyl lactate, and a second solvent, which is one or more selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, hexylene glycol, and glycerine.

[Claim 5]

<I24> The conductive ink composition for inkjet printer in claim 1 or 2, characterized in that the nano glass frit is 0.5 to 20 weight parts based on 100 weight parts of the ink metal nano particle composition.

[Claim 6]

<125> The conductive ink composition for inkjet printer in claim 1 or 2, characterized in that the size of the nano glass frit is 200 nm or less.

[Claim 7]

<i26> A method for manufacturing silver nanosol of 50-100 nm, the method being characterized by comprising the steps of: (A) melting silver (Ag) in nitric acid to make silver nitrate (AgN03), which is a silver precursor (pre- Ag); (B) diluting the silver nitrate obtained in step (A) and adding ammonia water to form a complex compound; (C) injecting a dispersion agent to make a silver complex compound which is monodispersed; (D) reducing the silver complex compound by using a reducing agent; (E) washing it by using an organic solvent and distilled water; and (F) re-dispersing it in a distilled water to obtain 10-50 w.t.% silver nanosol.