JP2006260818A - Conductive paste and printed circuit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost conductive paste with improvement in an anti-migration property. <P>SOLUTION: The conductive paste contains scaly inorganic fine particles (A) surface-coated with a precious metal, and an organic resin (B). Especially, a core ingredient of the scaly inorganic fine particles (A) surface-coated with a precious metal is alumina. Moreover, an average particle size of the scaly inorganic fine particles (A) surface-coated with a precious metal as measured by a laser light scattering method is 0.5 to 50 μm, with an aspect ratio of 2 or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a conductive paste. More specifically, the conductive paste is applied, printed, or cured on a film or a substrate to impart conductivity, thereby forming a circuit, or a terminal or lead wire of an electronic component. The present invention relates to a conductive paste used for bonding or protecting an electronic device from electromagnetic interference (EMI).

  A membrane circuit obtained by printing a conductive paste on a PET film or the like is low-cost and lightweight, and is widely used for keyboards and switches. However, with the refinement of print patterns, the required characteristics have become stricter year by year, and migration resistance higher than before has been demanded. Furthermore, in recent years, there has been a growing demand for lower costs, and the conventional technology is sufficient. Instead, improvements are desired.

  Known conductive pastes include Patent Documents 1 and 2. Patent Document 1 describes a silver paste for a membrane circuit using flaky silver powder, a polyester resin, and a blocked isocyanate compound as a binder. However, this conductivity is relatively good, but because silver powder is used for the conductive filler, there is a shortage of the current requirements for migration resistance in a fine pattern, and the cost is high. There is. Patent Document 2 proposes a silver paste for a membrane circuit using silver powder having a three-dimensional higher-order structure as a conductive powder, but migration resistance is insufficient for modern demands and cost is high.

JP-A-1-159906 JP-A-9-306240

  An object of the present invention is to improve the migration resistance of these conventional conductive pastes, and to provide a low-cost conductive paste.

  As a result of intensive studies to solve the above problems, by using conductive powder mainly composed of scaly inorganic particles whose surface is coated with a noble metal such as silver, good conductivity is obtained, Surprisingly, the inventors have found that the migration resistance is greatly improved, and have reached the present invention. Furthermore, compared to known silver pastes, the amount of silver used can be greatly reduced, so the cost is low. Besides using for circuits, it is useful for electromagnetic shielding by thinly printing on the base material film by gravure printing. It is.

  That is, the present invention relates to a conductive paste containing scaly inorganic fine particles (A) whose surface is coated with a noble metal and an organic resin (B), and a printed circuit on which the conductive paste is printed on a substrate.

  The electrically conductive paste of this invention has favorable electroconductivity, and can further improve migration resistance significantly. Furthermore, it becomes possible to produce an excellent circuit material at a low cost.

  The shape of the scaly inorganic particles (A) whose surface is coated with a noble metal used in the present invention needs to be flakes. The flaky shape referred to here indicates that the 50% average particle diameter measured by the laser light scattering method is a value (aspect ratio) obtained by grading with an average thickness measured with an electron microscope, which will be described later, of 2 or more. More specifically, the 50% average particle size is 1 to 2 cups of the scaly inorganic fine particles (A) in a 100 ml tall beaker, 60 ml of ion-exchanged water is added, and the mixture is dispersed with an ultrasonic homogenizer for 1 minute. It can be measured with a particle size distribution meter (Microtrac FRA type (Nikkiso Co., Ltd.). The measurement time is measured twice in 30 seconds, and the average value of 50% cumulative diameter is taken as the average particle diameter. Measurement conditions are: light transmittance of particles (T, P); YES, particle shape (S, P); NO, particle refractive index (Pri); 1.76, dispersion medium refractive index (Cri); Specifically, the average thickness can be measured by the following method: 2 g of the scaly inorganic fine particles (A) and 10 cc of a water-soluble epoxy resin (Quetol 651 (manufactured by Nisshin EM Co., Ltd.)) 1 hour and 30 minutes in a constant temperature bath at 60 ° C After placement, the sample is sucked out with a syringe (1 ml of Nipro syringe (manufactured by Nipro Co., Ltd.)) and left in the syringe for 8 hours in a thermostatic bath at 60 ° C. The cured resin is taken out of the syringe and surfaced with a microtome After processing and carbon deposition, a photograph was taken at a magnification of 5000 times or 10,000 times with an electrolytic emission scanning electron microscope (S4500 type manufactured by Hitachi, Ltd.), and the thickness of the scaly inorganic particles (A) was measured. Measured, expressed as an average value of 50 measurements.

  The 50% average particle diameter of the scaly inorganic fine particles (A) whose surface is coated with a noble metal used in the present invention is preferably 50 μm or less, more preferably 40 μm or less, and most preferably 30 μm or less. The lower limit is preferably 0.5 μm or more, more preferably 1 μm or more. When the average particle diameter exceeds 50 μm, when screen printing is performed, the screen may be clogged or the storage stability of the paste due to sedimentation of the scaly inorganic fine particles (A) may be reduced. If the average particle size is 0.5 μm or less, the conductivity may be reduced, or the viscosity of the paste may be increased, and the scaly inorganic fine particles (A) may not be sufficiently filled.

  The scaly inorganic fine particles (A) whose surface is coated with a noble metal used in the present invention preferably have an average thickness of 2.0 μm or less, more preferably 1 μm or less. Although a minimum is not specifically limited, 0.1 micrometer or more is preferable. If it exceeds 2.0 μm, the aspect ratio becomes small and the conductivity may be lowered. If it is less than 0.1 μm, the amount of oil absorption of the scaly inorganic fine particles tends to increase, and there is a possibility that the adhesion may be lowered or the printability may be deteriorated.

  The aspect ratio of the scaly inorganic particles (A) whose surface is coated with a noble metal used in the present invention is preferably 5 or more, more preferably 10 or more. The upper limit is not particularly defined, but is preferably 200 or less, more preferably 150 or less.

  Examples of the scaly inorganic fine particles used as a base for producing the scaly inorganic fine particles (A) whose surface is coated with a noble metal used in the present invention include alumina, talc, mica, and graphite. Particularly preferred is scaly synthetic alumina with little or no cleavage. Examples of the flake shaped alumina include synthetic alumina such as Seraph YFA10030, 0525, and 05070 (all manufactured by Kinsei Matec Corporation). The flake shaped synthetic alumina is produced by a “hydrothermal synthesis method” in which aluminum hydroxide is allowed to react with water under high temperature and high pressure conditions. These base fine particles can be produced by surface-coating a precious metal by a known method such as electroless plating, sputtering, or vapor deposition. Examples of the noble metal include Ag, Au, Pt, and Pd. Ag is most preferable from the viewpoint of conductivity and cost. Further, the basis weight of the noble metal is preferably 10% or more, more preferably 20% or more with respect to the scaly inorganic fine particles (A). Although an upper limit is not specifically limited, 60% or less is preferable from a cost surface, More preferably, it is 50% or less.

  Other conductive powders used in the present invention include known flaky silver powder, spherical silver powder, three-dimensional higher order silver powder, dendritic silver powder, graphite powder, carbon powder, nickel powder, copper powder as long as the characteristics are not deteriorated. , Gold powder, palladium powder, aluminum powder, indium powder, etc. may be used in combination, but the scaly inorganic fine particles (A) whose surface is coated with a noble metal is at least 20% by weight of the total conductive powder amount, more preferably 30%. % Or more, more preferably 50% by weight or more, and most preferably 70% by weight or more. Among these, preferred conductive fillers include known flaky silver powder, graphite powder, and conductive carbon black. In addition, a small amount of non-conductive filler such as silica powder, fumed silica, colloidal silica, talc, and barium sulfate may be blended for the purpose of adjusting paste viscosity.

  The conductive paste of the present invention is used in combination with a scaly inorganic fine particle (A) whose surface is coated with a noble metal and an organic resin (B) as a binder resin. The type of the organic resin (B) is not limited, but the number average molecular weight is preferably 3000 or more, more preferably 8000 or more from the viewpoint of bending resistance. When the number average molecular weight is less than 3000, good flex resistance is difficult to obtain, and the paste viscosity is lowered, and the printability may be lowered.

  The types of organic resins (B) include polyester resins, urethane-modified polyester resins, epoxy-modified polyester resins, various modified polyester resins such as acrylic-modified polyester, polyether urethane resins, polycarbonate urethane resins, vinyl chloride / vinyl acetate. Examples thereof include polymers, epoxy resins, phenol resins, acrylic resins, polyamideimides, nitrocellulose, modified celluloses such as cellulose acetate acetate butyrate (CAB), cellulose acetate acetate propionate (CAP), and the like.

  Among them, epoxy resin and phenol resin can be used for flexible conductive adhesives, rigid substrate circuit conductive pastes, through-hole conductive pastes, etc., but PET film, ITO (indium tin Oxide) When using flexible and relatively difficult-to-adhere substrates such as vapor-deposited PET film and polyimide film, polyester resin, the above modified polyester resin, vinyl chloride A vinyl acetate copolymer or the like is preferable, and most preferable is a copolymerized polyester resin and / or a modified polyester resin (C), a vinyl chloride / vinyl acetate copolymer, particularly when used for such a flexible substrate. Its features can be demonstrated.

  More specifically, as the organic resin, it is preferable to use a polyester resin and / or a modified polyester resin (C) having a number average molecular weight of 3000 or more, and very excellent bending resistance and adhesion to a substrate are obtained. It is done. From the viewpoint of bending resistance, the number average molecular weight is preferably 8000 or more, more preferably 10,000 or more. When the number average molecular weight is less than 3,000, good bending resistance may not be obtained, and the paste viscosity may be lowered and printability may be poor. The glass transition temperature is preferably −20 ° C. or higher, more preferably −5 ° C. or higher, in terms of bending resistance and hardness. A preferable upper limit is 70 degrees C or less from an adhesive viewpoint. As the polyester resin of the present invention, those obtained by polycondensation by a known method under normal pressure or reduced pressure can be used. The polyester resin is preferably a saturated polyester. In addition, after polymerizing the polyester resin, a cyclic ester such as ε-caprolactone is post-added (ring-opening addition) at 180 to 230 ° C. to form a block, or an acid anhydride such as trimellitic anhydride or phthalic anhydride is post-added. Then, a carboxyl group may be imparted to the polyester molecule terminal.

  The dicarboxylic acid copolymerized with the resin and / or the modified polyester resin (C) used in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, orthophthalic acid, or 2,6-naphthalenedicarboxylic acid, succinic acid, or glutar. Acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, azelaic acid and other aliphatic dicarboxylic acids, dibasic acids having 12 to 28 carbon atoms, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2 -Cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogen Added dimer acid, hydrogenated naphthalene Carboxylic acid, alicyclic dicarboxylic acids such as tricyclodecane acid. Further, within the scope of not impairing the contents of the invention, polyvalent carboxylic acids such as trimellitic anhydride and pyromellitic anhydride, unsaturated dicarboxylic acids such as fumaric acid, and sulfonic acids such as sodium 5-sulfoisophthalic acid A metal base-containing dicarboxylic acid may be used in combination. Specifically, when the total amount of dicarboxylic acid is 100 mol%, a copolymer obtained by copolymerizing 50 mol% or more of aromatic dicarboxylic acid and / or alicyclic dicarboxylic acid is physical properties such as hardness and adhesion. From the viewpoint of moisture resistance. More preferably, it is 60 mol% or more.

  The glycol used in the polyester resin and modified polyester resin (C) of the present invention is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl- 1,3-propanediol, 1,9-nonanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, dimer diol, etc. It is done. Moreover, you may use together polyhydric polyols, such as a trimethylol ethane, a trimethylol propane, glycerol, a pentaerythritol, a polyglycerol, in the range which does not impair the content of invention. Among these, from the viewpoint of moisture resistance, when the total glycol component amount is 100 mol%, at least one selected from neopentyl glycol, alicyclic glycol, and aliphatic diol having 5 to 10 carbon atoms in the main chain. What was copolymerized 20 mol% or more is preferable from the point of hydrolysis resistance. More preferably, it is 30 mol% or more, and most preferably 40 mol% or more. Specific examples of the main chain glycol having 5 to 10 carbon atoms include 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, , 6-hexanediol, 1,9-nonanediol, 1,10-decanediol and the like. Examples of the alicyclic glycol include 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol and the like.

  Moreover, the polyester resin used for the electrically conductive paste of this invention can be modified | denatured and used by well-known methods, such as urethane modification, epoxy modification, (meth) acrylate modification, and (meth) acryl graft modification. Of these, urethane modification is particularly preferred from the viewpoint of bending resistance and adhesion. A urethane-modified resin synthesized by a known method by reacting with an isocyanate compound using a polyester polyol and, if necessary, a chain extender can be used.

  As the polyol used in the urethane-modified polyester resin, the above-described polyester polyol is used, but in addition to this, polyether polyol, (meth) acryl polyol, polycarbonate diol, polybutadiene polyol, and other polyols may be used in combination. As other polyols, polycarbonate diol is particularly preferable in view of adhesiveness, flex resistance, and durability. Examples of the polyol used as the chain extender include known polyols such as neopentyl glycol, 1,6-hexanediol, ethylene glycol, HPN (hydroxypivalate ester of neopentyl glycol), trimethylolpropane, and glycerin. Furthermore, carboxyl group-containing polyols such as dimethylolpropionic acid can also be used as chain extenders.

  Examples of the diisocyanate compound used for urethane modification include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and isophorone diisocyanate.

The lower limit of the urethane group concentration of the polyester urethane resin as the modified polyester resin (C) is preferably 500 equivalents / 10 ⁶ g or more from the viewpoint of adhesion and bending resistance, and the upper limit is 4000 equivalents / 10 ⁶ from the viewpoint of solubility. g or less is preferable.

  In the electrically conductive paste of this invention, you may use together other resin of a polyester resin and / or modified polyester resin (C). As other resins, vinyl chloride / vinyl acetate copolymers are particularly preferable, and known commercially available products can be used. The content of vinyl chloride in the polymer is preferably 85 to 95% in view of solubility and physical properties of the coating film. Further, a polar group may be introduced by copolymerizing a small amount of maleic acid, vinyl alcohol or the like as a monomer other than vinyl chloride or vinyl acetate. When a carboxyl group is introduced with maleic acid, adhesion to a metal is improved, and when a hydroxyl group is introduced with vinyl alcohol, an isocyanate compound can be used as a curing agent.

  The organic resin (B), polyester resin and / or modified polyester resin (C) used in the present invention may be used in combination with a curing agent. The curing agent capable of reacting with these resins is not particularly limited, but an isocyanate compound is particularly preferable from the viewpoint of adhesion, flex resistance, curability, and the like. Further, these isocyanate compounds are preferably used after being blocked from the viewpoint of storage stability. Examples of curing agents other than isocyanate compounds include known compounds such as amino resins such as methylated melamine, butylated melamine, benzoguanamine, and urea resin, acid anhydrides, imidazoles, epoxy resins, and phenol resins.

  Examples of the isocyanate compound include aromatic and aliphatic diisocyanates and trivalent or higher polyisocyanates, which may be either low molecular compounds or high molecular compounds. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate or trimers of these isocyanate compounds, and excess of these isocyanate compounds Amount of low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine or various polyester polyols, polyether polyols, polyamides Obtained by reacting with polymer active hydrogen compounds Terminal isocyanate group-containing compounds to be.

  Examples of the isocyanate group blocking agent include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol, and chlorophenol, oximes such as acetoxime, methyl ethyl ketoxime, and cyclohexanone oxime, Alcohols such as methanol, ethanol, propanol and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol; -Lactams such as caprolactam, δ-valerolactam, γ-butyrolactam, β-propylolactam and the like, and other aromatic amines, imides, acetylacetates Emissions, acetoacetic ester, active methylene compounds such as malonic acid ethyl ester, mercaptans, imines, imidazoles, ureas, diaryl compounds, sodium bisulfite, etc. can be mentioned. Of these, oximes, imidazoles, and amines are particularly preferable from the viewpoint of curability.

  These crosslinking agents may be used in combination with known catalysts or accelerators selected according to the type.

  There is no restriction | limiting in the kind in the solvent used for the electrically conductive paste of this invention, Ester type | system | group, ketone type | system | group, ether ester type | system | group, chlorine type | system | group, alcohol type | system | group, ether type, hydrocarbon type etc. are mentioned. Among these, in the case of screen printing, high boiling point solvents such as ethyl carbitol acetate, butyl cellosolve acetate, isophorone, cyclohexanone, and γ-butyrolactone are preferable.

  The conductive paste of the present invention is printed on a plastic film such as a PET film (sheet) by a known method such as screen printing, gravure printing, transfer printing, roll coating, flow coating, spray coating, etc. and used for a keyboard or a switch. Can be used for membrane circuits.

  Hereinafter, the present invention will be described using examples. In the examples, “parts” simply means “parts by weight”. Each measurement item followed the following method.

1. Molecular weight The number average molecular weight in terms of polystyrene was measured by GPC. Tetrahydrofuran was used as a measurement solvent.

2. Glass transition temperature (Tg)
5 mg of the sample was put in an aluminum sample pan, sealed, and measured using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc. up to 200 ° C. at a heating rate of 20 ° C./min. The temperature was obtained from the temperature at the intersection of the extended line of the base line below the glass transition temperature and the tangent indicating the maximum slope at the transition.

3. Acid value 0.2 g of a sample was precisely weighed and dissolved in 20 ml of chloroform. Subsequently, it titrated with 0.01N potassium hydroxide (ethanol solution). A phenolphthalein solution was used as an indicator.

4). Measurement of average particle size (50% D) by laser light scattering method One to two scaly fine particles coated with precious metal with a microspatera, put in a 100 ml tall beaker, add about 60 ml of ion-exchanged water, and an ultrasonic homogenizer And measured with a particle size distribution meter (Microtrac FRA type (Nikkiso Co., Ltd.). The measurement time was measured twice in 30 seconds, and the average value of 50% cumulative diameter was determined as the average particle diameter. The measurement conditions were
Light transmittance of particles (T, P); YES
Particle shape (S, P); NO
Particle refractive index (Pri); 1.76
Dispersion medium refractive index (Cri); 1.33
It was.

5. Measurement of average thickness of scaly fine particles surface-coated with noble metal 2 g of scaly fine particles surface-coated with noble metal were mixed well with 10 cc of water-soluble epoxy resin (Quetol 651 (Nisshin EM Co., Ltd.)), and 60 ° C. Then, the sample was sucked out with a syringe (1 ml of Nipro Syringe (manufactured by Nipro Co., Ltd.)) and placed in a constant temperature bath at 60 ° C. for 8 hours. Take out the cured resin from the syringe, chamfer the surface with a microtome, and after carbon deposition, take a picture at a magnification of 5000x or 10000x with an electrolytic emission scanning electron microscope (S4500, manufactured by Hitachi, Ltd.). The thickness of the silver powder was measured. It represented with the average value of 50 measurement numbers.

6). Adhesion A conductive paste was screen printed on a PET film that had been annealed to a thickness of 100 μm, a 25 × 200 mm pattern was printed, dried and cured at 150 ° C. for 30 minutes, and used as a test piece. The dry film thickness was adjusted to 6-8 μm. Evaluation was performed according to JIS K5400 6-15 using this test piece. Cellophane tape CT-12 (manufactured by Nichiban Co., Ltd.) was used as the adhesive tape.

7). Specific resistance The sheet resistance and film thickness were measured using the test piece produced in step 1, and the specific resistance was calculated. The sheet resistance was measured using a 4-terminal digital multimeter.

8). Migration resistance A conductive silver paste on an annealed polyester film having a thickness of 100 μm, a pattern having a line width of 2.0 mm and a length of 85 mm with a gap of 1.5 mm in the center shown in FIG. A sample was screen-printed to ˜8 μm and heat-cured (heat-dried) at 150 ° C./30 minutes. Next, 0.04 ml of distilled water was gently dropped with a syringe (Nipro syringe 1 ml (Nipro Co., Ltd.)) between the gaps, 10 V was applied with a constant voltage power source (Takasago Seisakusho Co., Ltd.), and a digital multimeter (Takeda Riken) The current value was measured by “Made by Co., Ltd.”, the time until the current value reached 0.1 mA was measured, and the average value of the five measured values was evaluated, and the larger the value, the better the migration resistance.

Synthesis example. 1 (Polyester resin I)
A four-necked flask equipped with a Gubileu fractionator is charged with 101 parts of dimethyl terephthalic acid, 35 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol, 0.068 parts of tetrabutyl titanate, and 180 ° C. for 3 hours. Exchange was performed. Subsequently, 61 parts of sebacic acid was added and esterification was further performed. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for 1 hour. The composition of the obtained copolyester was terephthalic acid / isophthalic acid / sebacic acid // ethylene glycol / neopentyl glycol = 52/18/30 // 55/45 (molar ratio), number average molecular weight 22,000, acid The value was 1.5 mgKOH / g and Tg was 7 ° C. The results are shown in Table 1.

Synthesis example. 2 to 4 (Polyester resins II to IV)
Synthesis example. 1 was synthesized in the same manner. The results are shown in Table 1. Synthesis Example IV is a base polyester for urethane modification.

Synthesis example. 6 (urethane-modified polyester resin V)
In a reaction vessel equipped with a thermometer, a stirrer, and a condenser, 100 parts of polyester resin IV of synthesis example, 3 parts of neopentyl glycol as a chain extender, ethyl carbitol acetate as a solvent were charged, dissolved at 80 ° C., and then diphenylmethane dii 19.4 parts of isocyanate (MDI) and 0.05 part of dibutyltin dilaurate were added and reacted at a solid concentration of 50% at 70-80 ° C. for 3 hours or more until there was no remaining isocyanate, and then with ethyl carbitol acetate. Dilution to a solid content concentration of 30% yielded urethane-modified polyester resin V. The number average molecular weight was 25000, the acid value was 1.0 mgKOH / g, and the glass transition temperature was 15 ° C.

Preparation of scaly inorganic fine particles a whose surface was coated with a noble metal Seraph YFA10030-50AG (manufactured by Kinsei Matec Co., Ltd.) was used as it was. The average particle diameter (50% D) was 15 μm, and the aspect ratio determined from the average particle diameter and average thickness was 30. The basis weight of silver was 50%.

Preparation of scaly inorganic fine particles b whose surface was coated with a noble metal Seraph 05070 (manufactured by Kinsei Matec Co., Ltd.) obtained by electrolessly plating Ag was used. The average particle diameter (50% D) was 7.5 μm, and the aspect ratio determined from the average particle diameter and average thickness was 70. The basis weight of silver was 30%.

Example. 1
85 parts of scaly fine particles a surface-coated with precious metal, 15 solid parts of polyester resin II dissolved in diethylene monoethyl ether acetate as organic resin, 0.5 parts of polyflow S (Kyoeisha Chemical Co., Ltd.) as leveling agent Then, the mixture was sufficiently premixed, and then dispersed three times with a chilled three roll to obtain a conductive paste. The obtained conductive paste had a slightly yellowish silver gray and good viscosity. The specific resistance was 7.6 × 10 ⁻⁴ Ω · cm, which was better than that of Comparative Example 1 in which Ag was used as the conductive filler with the same filler filling amount. This is presumably because the flake-shaped fine particles a of the present invention have a lower bulk specific gravity than Ag. Further, the migration property was 573 seconds, which was very good as compared with the Ag pastes shown in Comparative Examples 1 to 4. When a circuit with a line width of 0.4 mm produced with this conductive paste was bent five times by finger folding with the printed surface folded inward, there was almost no increase in resistance value and good bending resistance. Moreover, this paste had a favorable electromagnetic wave shielding property.

Example. 2-4
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

Comparative Examples 1-4
Prepared in the same manner as in Example 1. The results are shown in Table 3.

  The conductive paste of the present invention has basic physical properties such as good conductivity, adhesion, and bending resistance, and has extremely excellent migration resistance as compared with conventional Ag paste. Furthermore, since the Ag content can be greatly reduced, it is low-cost and resource-saving.

  The electrically conductive paste of this invention has favorable electroconductivity, and can further improve migration resistance significantly. Furthermore, it becomes possible to produce an excellent circuit material at a low cost.

This is a test pattern for evaluating migration resistance.

Explanation of symbols

1. 1. PET film Screen printing pattern

Claims (9)

  A conductive paste containing scaly inorganic fine particles (A) coated with a noble metal and an organic resin (B).   2. The conductive paste according to claim 1, wherein the core component is alumina in the scaly inorganic fine particles (A) whose surface is coated with a noble metal.   The average particle diameter measured by the laser light scattering method of the scaly inorganic fine particles (A) whose surface is coated with a noble metal is 0.5 to 50 µm and the aspect ratio is 2 or more. 2. The conductive paste according to 2.   Furthermore, carbon black and / or graphite fine powder are contained, The electrically conductive paste in any one of Claims 1-3 characterized by the above-mentioned.   The conductive paste according to any one of 1 to 4, wherein the organic resin (B) includes a polyester resin having a molecular weight of 3000 or more and / or a modified polyester resin (C).   When the total of all dicarboxylic acids and glycol components is 100 mol%, the polyester resin and / or modified polyester resin (C) contains 50 mol% or more of aromatic dicarboxylic acid and / or alicyclic dicarboxylic acid as the acid component. The conductive paste according to claim 5, wherein 20 mol% or more of at least one selected from neopentyl glycol and an aliphatic diol having 5 to 10 carbon atoms is copolymerized as a glycol component.   The conductive paste according to claim 1, wherein the organic resin (B) contains a vinyl chloride / vinyl acetate copolymer.   Furthermore, the hardening agent which can react with organic resin (B) is included, The electrically conductive paste in any one of Claims 1-7 characterized by the above-mentioned.   A printed circuit, wherein the conductive paste according to claim 1 is printed on a substrate.

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