JP2008171828A - Conductive paste, and printed circuit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste improving migration resistance which is a defect of conductive paste, decreasing resistance, improving surface smoothness, resistance to insertion and pulling out of a connector, and blocking resistance, and especially increasing elasticity. <P>SOLUTION: The conductive paste contains silver powder (A) having a flake shape, a thickness of 100-1300 Å, a tap density of 1.0-2.5 g/cm<SP>3</SP>, and a specific surface area of 1.2-4 m<SP>2</SP>/g, and organic resin (B). <P>COPYRIGHT: (C)2008,JPO&INPIT

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), and particularly relates to a conductive paste suitable for a circuit requiring high conductivity and bending resistance.

  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, the demanded characteristics have become stricter year by year due to the refinement of the printed pattern, and higher bending resistance, conductivity, and migration resistance than ever before are desired, as well as surface smoothness, when using connectors. Insertion / extraction resistance, blocking resistance, etc. are not sufficient in the prior art, and improvements are desired. Known conductive pastes include JP-A-1-159906 and JP-A-9-306240. Japanese Patent Application Laid-Open No. 1-159906 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 it is not enough for the current requirements, and it is not enough for the modern requirements with fine patterns of migration resistance, bending resistance and connector insertion / removal. Yes. Japanese Patent Laid-Open No. 9-306240 proposes a silver paste for a membrane circuit that uses silver powder of a three-dimensional higher order structure as conductive powder, but both flex resistance and conductivity are insufficient for the current demands. Yes.

  The object of the present invention is to improve the migration resistance possessed by these conventional conductive pastes, and further to improve the surface smoothness, resistance to insertion / removal when using connectors, and blocking resistance at low resistance. In particular, it is to provide a conductive paste imparted with a high degree of bending resistance.

  As a result of intensive studies to solve the above problems, surprisingly, by using conductive powder mainly composed of organic resin and flaky silver powder having an average thickness of 1300 angstroms or less, bending resistance is surprisingly achieved. As a result, the inventors have found that the migration resistance is further improved and have reached the present invention. In addition, by using this conductive powder, even when a hard binder is used compared to the flaky silver powder used in known polymer type conductive paste, it is possible to obtain a good bending resistance. Compatibility with connector blocking resistance and insertion / removal properties is also possible. In addition, even when a curing agent such as a blocked isocyanate compound is not blended, good bending resistance can be obtained, so that low temperature rapid curing can be achieved as compared with the prior art. Moreover, since favorable electroconductivity is obtained also in a thin area | region with a film thickness of about 1-3 micrometers, it prints thinly by gravure printing etc. on a base film, and is useful as an electromagnetic wave shield.

  That is, the present invention relates to the following conductive paste and a printed circuit using the same.

(1) shape is flake, and a thickness is 1300 angstroms or less than 100 angstroms, a tap density of not more than 1.0 g / cm ³ or more 2.5 g / cm ^3, specific surface area of 1.2 m ² A conductive paste containing silver powder (A) that is not less than / g and not more than 4 m ² / g, and an organic resin (B).
(2) The conductive paste according to (1), wherein the silver powder (A) has a 50% average particle diameter of 1 μm or more and 20 μm or less.
(3) The conductive paste according to (1) or (2), wherein the organic resin (B) contains a polyester resin having a molecular weight of 3000 or more and / or a modified polyester resin (C).
(4) The conductive paste according to (3), wherein the organic resin (B) contains a vinyl chloride / vinyl acetate copolymer.
(5) The conductive paste according to (1) or (2), wherein the organic resin (B) is a polyester resin having a molecular weight of 3000 or more and / or a modified polyester resin (C).
(6) When the total of all dicarboxylic acids and glycol components is 100 mol%, the polyester resin and / or modified polyester resin (C) contains 50 aromatic dicarboxylic acids and / or alicyclic dicarboxylic acids as acid components. It is characterized in that at least one selected from the group consisting of neopentyl glycol, alicyclic glycol, and aliphatic diol having 5 to 10 carbon atoms in the main chain is copolymerized in an amount of 20 mol% or more. The conductive paste according to any one of claims (3) to (5).
(7) A printed circuit, wherein the conductive paste according to any one of (1) to (6) is printed on a substrate.

  With the conductive paste of the present invention, it is possible to significantly improve the bending resistance with a low resistance, and to produce an excellent circuit material having an excellent migration resistance.

  The silver powder (A) used in the present invention needs to have a flake shape. 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 diameter is 1 to 2 cups of silver powder in a microspatella, taken in a 100 ml tall beaker, 60 ml of isopropyl alcohol, dispersed with an ultrasonic homogenizer for 1 minute, and a particle size distribution meter (Microtrac FRA). It can be measured with a mold (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. (T, P): YES, particle shape (S, P): NO, particle refractive index (Pri): 2.25, dispersion medium refractive index (Cri): 1.37 The average thickness is Specifically, it can be measured by the following method: 2 g of silver powder is mixed well with 10 cc of a water-soluble epoxy resin (Quetol 651 (Nisshin EM Co., Ltd.)) and left in a constant temperature bath at 60 ° C. for 1 hour and 30 minutes. , Syringe (Nipro Syringe Draw out the sample with ml (manufactured by Nipro Co., Ltd.) and place it in a syringe for 8 hours in a thermostatic bath at 60 ° C. Take out the cured resin from the syringe, perform surface processing with a microtome, and after carbon deposition The photograph was taken with an electrolytic emission scanning electron microscope (S4500, manufactured by Hitachi, Ltd.) at a magnification of 5000 or 10,000 times, and the thickness of the silver powder was measured.

  The silver powder (A) used in the present invention must further have an average thickness of 1300 angstroms or less. Surprisingly, when the shape is flaky and the average thickness is 1300 angstroms or less, remarkably good bending resistance can be obtained with low resistance. Furthermore, migration resistance and connector insertion / removal resistance can be improved as compared with conventional flaky silver powder and other shapes of silver powder. The upper limit of the average thickness is more preferably 1100 angstroms, more preferably 900 angstroms. The lower limit is not particularly limited, but 100 angstrom is preferable. When the upper limit exceeds 1300 angstroms, the migration resistance, the bending resistance, the conductivity, and the like are lowered. If the lower limit is less than 100 angstroms, the oil absorption of silver powder tends to increase, and there is a possibility that adhesion, flex resistance, etc. may be lowered or printability may be deteriorated.

  As a method of making the thickness of the silver powder (A) used in the present invention 1300 angstroms or less, the 50% average particle diameter by laser light scattering of primary silver particles prepared by reduction of silver nitrate is preferably 5 μm or less, More preferably, it is obtained by milling a material having a size of 3 μm or less and a lower limit of preferably 0.01 μm or more at a high speed using a known apparatus such as a bead mill, a ball mill or an attritor in the presence of a lubricant by a wet method. The beads used for dispersion preferably have a diameter of 3 mm or less, more preferably 2 mm or less. Most preferably, zirconia or silica beads having a small diameter of 1.5 mm or less and a lower limit of 0.1 mm or more are preferred. As the disperser, a bead mill is preferable because it can take a high share, and as a trade name, dyno mill (manufactured by WILLYA. BACHOFE AG), K series (manufactured by Buehler Co., Ltd.) and the like can be mentioned.

As other powder characteristics of the silver powder (A) of the present invention, the tap density is 2.5 g / cm ³ or less, the specific surface area is 1.2 m ² / g or more, and the 50% average particle diameter by the laser light scattering method is 20 μm. The following is preferred. The tap density is more preferably 2.0 g / cm ³ or less, and the lower limit is not particularly defined but is preferably 1.0 g / cm ³ or more. The specific surface area is more preferably 1.5 m ² / g or more, and the upper limit is not particularly defined, but is preferably 4 m ² / g or less, more preferably 3 m ² / g or less. The 50% average particle diameter is more preferably 15 μm or less, and most preferably 10 μm or less. The lower limit is not particularly defined, but is preferably 1 μm or more from the viewpoint of conductivity and adhesion. If the tap density exceeds 2.2 g / cm ³ , the specific surface area is less than 1.5 m ² / g, or the 50% average particle diameter is less than 1 μm, the thickness of the flaky silver powder can exceed 1300 angstroms. In some cases, the electrical conductivity, the bending resistance, the migration resistance and the like may be deteriorated.

  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 silver powder (A) having a flake shape and a thickness of 1300 angstroms or less is preferably at least 20% by weight or more of the total conductive powder amount. Is preferably 30% by weight 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 the silver powder (A) of the present invention 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. Of these, epoxy resin and phenolic resin can be used for applications such as flexible conductive adhesives, rigid circuit board conductive pastes, and through-hole conductive pastes. In the case of using a flexible and relatively difficult-to-adhere base material such as polyimide film, polyester resin, the above modified polyester resin, vinyl chloride / vinyl acetate copolymer from the viewpoint of flex resistance and adhesion to the base material The most preferred is a copolyester resin and / or a modified polyester resin (C), and the characteristics can be exhibited particularly when used for such a flexible substrate.

  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. Acids, 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 dicarboxylic acid amount is 100 mol%, 50 mol% or more of an aromatic dicarboxylic acid and an alicyclic dicarboxylic acid are copolymerized, and the coating film properties such as hardness and adhesion and moisture resistance. From the viewpoint of sex. 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 flex resistance, and the upper limit is 4000 equivalents / 10 ⁶ from the viewpoint of solubility. g or less is preferable. The unit equivalent / 10 ⁶ g represents the number of equivalents of urethane groups per 10 ⁶ g (1 ton) of resin.

  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.

  The conductive paste of the present invention can obtain good bending resistance and adhesion without using a curing agent by using silver powder (A) and polyester resin and / or modified polyester resin (C). it can. When the curing agent is not blended (thermoplastic type), drying at a lower temperature is possible than the thermosetting type, but the conventional thermoplastic type has poor bending resistance. The conductive paste of the present invention can provide significantly superior bending resistance as compared with the thermoplastic type of the prior art.

  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 | system | group, 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)
It measured with the temperature increase rate of 20 degree-C / min using the differential scanning calorimeter (DSC). As a sample, 5 mg of a sample was placed in an aluminum press-lid container and crimped.

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). Specific surface area 15g of silver powder is taken in a sample tube and pretreated under the conditions of 60 ± 5 ° C, 60 ± 5 minutes in a specific surface area automatic measuring device (Micronetics 2300 Tsushima Seisakusho; BET method N ₂ gas adsorption one point method) The total surface area was then measured. The specific surface area per gram was calculated by dividing the total surface area by the sample amount.

5. Tap density 100 g of silver powder was weighed and gently dropped into a 100 cc graduated cylinder with a funnel. The sample was placed on a tap density measuring machine, dropped 600 times at a drop distance of 20 mm and a speed of 60 times / minute, the volume of the compressed silver powder was measured, and calculated from the weight and volume of the silver powder.

6). Measurement of average particle size (50% D) by laser light scattering method Take 1 to 2 cups of silver powder with a microspatella and place in a 100 ml tall beaker, add about 60 ml of isopropyl alcohol, and disperse with an ultrasonic homogenizer for 1 minute. (Measured with Microtrac FRA type (Nikkiso Co., Ltd.) The measurement time was measured twice in 30 seconds, and the average value of 50% cumulative diameter was defined as the average particle diameter. Permeability (T, P); YES particle shape (S, P); NO particle refractive index (Pri); 2.25 dispersion medium refractive index (Cri); 1.37.

7). Measurement of average thickness of flaky silver powder 2 g of silver powder was mixed well with 10 cc of water-soluble epoxy resin (Quetol 651 (Nisshin EM Co., Ltd.)), left in a constant temperature bath at 60 ° C. for 1 hour and 30 minutes, and then syringe The sample was sucked out with 1 ml of Nipro Syringe (manufactured by Nipro Co., Ltd.) and placed in a constant temperature bath at 60 ° C. for 8 hours while being put in the syringe. 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.

8). Specific resistance The sheet resistance of the conductive paste heated and cured at 150 ° C. for 30 minutes was measured using a 4 deep needle resistance measuring device, and the specific resistance was calculated from the sheet resistance and film thickness.

9. Adhesiveness It evaluated according to JIS K5400 6-15. Cellophane tape CT-12 (manufactured by Nichiban Co., Ltd.) was used as the adhesive tape.

10. Bending resistance A conductive silver paste screen-printed with a pattern of 0.5 mm line width and 75 mm length on an annealed polyester film with a thickness of 100 μm and heat-cured (heat-dried) at 150 ° C./30 minutes as a sample Then, 360 ° bending was repeated at the same location under the conditions of a load of 50 g / cm ² and R = 0, and the number of times until the resistance value of the conductor reached the KΩ order was evaluated. The dry film thickness of the printed pattern was evaluated at 6 to 8 μm.

11. Connector Insertion / Removal Resistance The connector was inserted and removed 10 times on the back of a test piece prepared in the same manner as in Example 10 with a 125 μm reinforcing film adhered, and the degree of peeling of the conductive paste coating film was evaluated.
○: No peeling Δ: Slight peeling ×: Peeling

12 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 85.5 mm with a gap of 1.5 mm in the center shown in FIG. The sample was screen-printed so as to be 6 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. 6 (urethane-modified polyester resin V)
In a reaction vessel equipped with a thermometer, a stirrer, and a cooler, 100 parts of polyester resin IV of synthesis example, 3 parts of neopentyl glycol as 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 to 80 ° C. for 3 hours or more until there was no residual 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 silver powder A-1 Commercial tap density of 2.8 g / cm ³ , specific surface area of 1.3 m ² / g, 100 parts by weight of spherical silver powder having an average particle size of 0.5 μm by laser scattering method, ethylene glycol 60 Part by weight, 0.3 parts by weight of oleic acid as a lubricant, zirconia beads having a diameter of 1 mm and a dyno mill KDL-special type (manufactured by WILLYA. BACHOFE AG), a shaft speed of 3200 rpm, an agitator disk peripheral speed of 16 m / s Three-pass milling was performed with a disk diameter of 96 mm. Next, after filtration under reduced pressure, washing was repeated twice with methanol, and dried under reduced pressure at 80 ° C. for 24 hours to obtain flaky silver powder (A-1). The thickness of the obtained flaky silver powder was measured and found to be 640 angstrom. The tap density was 1.7 g / cm ³ , the specific surface area was 2.1 m ² / g, the average particle size was 5.5 μm, and the aspect ratio was 86. The shape is shown in FIG.

Adjustment of Silver Powder A-2 Using a granular silver powder having a commercially available tap density of 2.8 g / cm ³ , a specific surface area of 1.3 m ² / g and an average particle diameter of 0.1 μm by a laser scattering method, silver powder (A Milling, washing and drying were performed in the same manner as in -1). However, the rotation speed was 2500 rpm. When the thickness of the obtained flaky silver powder (A-2) was measured, it was 1000 angstroms. The tap density was 2.2 g / cm ³ , the specific surface area was 1.8 m ² / g, the average particle diameter was 4.0 μm, and the aspect ratio was 40.

Adjustment of silver powder A-3 Commercially available flaky silver powder (AgC-A, manufactured by Fukuda Metal Foil Co., Ltd.) was used as it was. The thickness of the silver flakes was 1540 angstroms. The average particle diameter measured by the laser light scattering method was 4.5 μm, the specific surface area was 0.7 m ² / g, the tap density was 3.1 g / cm ³ , and the aspect ratio was 29.

Adjustment of silver powder A-4 Commercially available flaky silver powder (SF7, manufactured by Ferro Japan Co., Ltd.) was used as it was. The thickness of the silver flakes was 2520 angstroms. The average particle diameter measured by the laser light scattering method was 6.1 μm, the specific surface area was 0.94 m ² / g, the tap density was 2.8 g / cm ³ , and the aspect ratio was 24.

Preparation of silver powder A-5 275 parts of a 37% strength aqueous silver nitrate solution and 220 parts of a 18% strength aqueous sodium hydroxide solution were allowed to react at 40-50 ° C. with stirring, and 70 parts of distilled water was added after completion of the reaction. Then, 60 parts of a 23% concentration formalin aqueous solution was added thereto and reacted at 30 to 40 ° C. The pH after completion of the reaction was 8. The obtained silver powder was filtered, washed with water and dehydrated repeatedly, washed with methanol, filtered, and dried under reduced pressure at 80 ° C. for 24 hours. The obtained silver powder has a three-dimensional higher order structure in which spherical primary particles are three-dimensionally bonded, and the average particle diameter of the primary particles is 0.5 μm from the scanning electron micrograph, The average particle diameter was 11 μm, the specific surface area was 1.62 m ² / g, and the tap density was 0.8 g / cm ³ as measured by the light scattering method. However, since this silver powder has a three-dimensional higher order structure rather than flakes, the thickness cannot be measured. The shape is shown in FIG.

Example. 1
Silver powder A-1, 87 parts, 11.1 solid part of ethyl acetate carbitol solvent of polyester resin (I), blocked isocyanate compound (methyl ethyl ketoxime block of biuret trimer of hexamethylene diisocyanate, solid content 80%) 9 solid parts, polyflow S (manufactured by Kyoeisha Resin Chemical Co., Ltd.) 0.5 solid part as a leveling agent, 0.02 part by weight of dibutyltin dilaurate as a curing catalyst were mixed and fully premixed, and then chilled 3 rolls In a kneader, the mixture was dispersed three times. The obtained silver paste had a very low resistance of 1.8 × 10 −5 Ω · cm, and the bending resistance was very good at 30 times or more. Further, the migration resistance was superior to the case of using conventional silver powder, the surface smoothness was good, and the connector insertion / extraction resistance was also good. The results are shown in Table 2.

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

Comparative Examples 1-5
Prepared in the same manner as in Example 1. The results are shown in Table 3.

  From Tables 1 and 2, Examples 1 to 4 had very low specific resistance as compared to Comparative Examples 1 to 5, and also had good bending resistance, migration resistance, and connector insertion / removal resistance. In Comparative Examples 1 and 2 using conventional silver flakes, the bending resistance is slightly insufficient, and the migration resistance and the connector insertion / removal resistance are inferior. Also, the specific resistance is insufficient. Furthermore, the connector insertion / removability is also poor. About Comparative Examples 3-5, the bending resistance is remarkably inferior and the migration resistance is also insufficient.

This is a test pattern for evaluating migration resistance. It is a scanning electron micrograph of flaky silver powder (A-1). It is a scanning electron micrograph of silver powder (A-5) having a three-dimensional higher order structure in which spherical primary particles are combined three-dimensionally.

Explanation of symbols

1. 1. PET film Screen printing pattern

Claims (7)

Shape is flake, and a thickness is 1300 angstroms or less than 100 angstroms, tap density 1.0 g / cm ³ or more 2.5 g / cm ³ Ri der or less and a specific surface area of 1.2 m ² / g more ^4m 2 / g Ru der less silver powder (a), and the organic resin (B) a conductive paste containing. The conductive paste according to claim 1, wherein the silver powder (A) has a 50% average particle diameter of 1 μm or more and 20 μm or less. The conductive paste according to claim 1 or 2, wherein the organic resin (B) contains a polyester resin having a molecular weight of 3000 or more and / or a modified polyester resin (C). 4. The conductive paste according to claim 3, wherein the organic resin (B) contains a vinyl chloride / vinyl acetate copolymer .   The conductive paste according to claim 1 or 2, wherein the organic resin (B) is 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. And 20 mol% or more of at least one selected from neopentyl glycol, alicyclic glycol, and aliphatic diol having 5 to 10 carbon atoms in the main chain as a glycol component. The electrically conductive paste in any one of 3-5. Printed circuit conductive paste according to any one of claims 1 to 6, characterized in that it is printed on a substrate.