JP2002008441A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit material that applies conductive paste having excellent heat resistance, moisture resistance, thermal shock resistance, flexibility and excellent adhesion to an organic film, a metal substrate and a glass substrate and the like. SOLUTION: This conductive paste composed of a binder containing a conductive powder (A) and polyester resin (B) of number average molecular weight more than 3000 and a solvent (C) as main components, characterized in that the polyester resin (B) contains aromatic dicarboxylic acid more than 80% by mole based on total acid components and alkyleneglycol (a) having carbon atoms of a main chain more than 5 and/or alicyclic glycol (b) more than 50% by mole based on total glycol components and alkyleneglycol (c) having carbon atoms of a main chain less than 4 and a side chain 0-50% by mole based on total glycol components, and sum of (a)-(c) is more than 70% by mole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste, and more particularly, to coating or printing a conductive paste on a film such as polyethylene terephthalate, vinyl chloride or nylon, a metal substrate, or a glass substrate.
By giving conductivity by curing, to form a circuit,
It relates to conductive paste used for bonding terminals and lead wires of electronic components and for protecting electronic devices from electromagnetic interference (EMI). / Or 85 ° C, 85% RH
The present invention relates to a conductive paste suitable for circuit formation of components such as automobiles and OA equipment and adhesives which require the above-mentioned heat resistance, moisture resistance, and thermal shock resistance.

[0002]

2. Description of the Related Art A membrane circuit formed by printing a conductive paste on a PET film or the like is lightweight and widely used for keyboards and switches. However, the required characteristics are becoming stricter year by year, and in a higher environment than before, ie, 85 ° C. or higher and / or 85 ° C., 85% RH
With the above conductivity and low temperature bending resistance, and heat resistance,
There is a strong demand for compatibility with both moisture resistance and thermal shock resistance.

A known conductive paste is disclosed in
No. 9-206449. This is a silver paste for a membrane circuit using a polybutadiene resin and a blocked isocyanate compound obtained by blocking an isocyanate group with an oxime compound or caprolactam as a binder, but has a relatively good bending resistance. However, the durability in heat resistance, moisture resistance, and thermal shock resistance is poor.

Japanese Patent Application Laid-Open No. 1-159906 discloses a silver paste having excellent flexing resistance using flake-like (flake-like) silver powder, a copolymerized polyester resin and a blocked isocyanate compound as a binder. However, durability in heat resistance, moisture resistance, and thermal shock resistance is poor.

[0005] Japanese Patent Application Laid-Open No. 60-223871 discloses a known conductive paste of the fast-curing type. Although it is a conductive paste using a blocked isocyanate blocked with imidazole as a curing agent, it has a drawback in pot life, and further has poor heat resistance, moisture resistance, and heat shock resistance.

[0006] Epoxy resins, phenol resins, and the like are examples of resins that exhibit good adhesiveness to films such as polyethylene terephthalate, vinyl chloride, and nylon, and metals. JP-A-8-245754, JP-A-7-245
JP-A-278274 is a conductive paste having excellent moisture resistance comprising an epoxy resin and a phenol resin, and JP-A-9-259636 discloses a conductive paste comprising an epoxy resin and a sulfonium salt and having excellent heat resistance and moisture resistance. It is. These conductive pastes are unsatisfactory in severe bending properties such as 360 ° where R of the bent portion is 0 mm. Also, good adhesion to metal foils and films cannot be obtained.

Japanese Patent Application Laid-Open No. 55-149356 discloses a conductive paste made of an acrylic resin and having excellent heat resistance, but has a drawback that its reliability under high temperature and high humidity is poor.

JP-A-6-116517 discloses a heat-resistant and moisture-resistant conductive paste made of a polyamide-imide silicone polymer. JP-A-6-136300 discloses a polyamide-imide silicone polymer and an epoxy resin. It is a conductive paste which is excellent in heat resistance and moisture resistance. Also in these conductive pastes, the R at the bent portion is 0 m.
A severe bending property such as m of 360 ° is not good.

JP-A-7-41706 discloses a resol type phenol resin and an epoxy resin, a polyester resin,
The conductive paste is made of at least one resin selected from polyvinyl butyral resins and has excellent moisture resistance and temperature cycle resistance.
A severe bending property such as 360 ° in mm is bad.

[0010]

In order to obtain good adhesiveness and flexibility in the resin composition used for the conductive paste, the glass transition temperature usually needs to be 10 ° C. or less. Performance deteriorates in durability of moisture resistance. On the other hand, when trying to obtain durability, there is a problem that sufficient flexibility cannot be obtained.

[0011]

In order to solve these problems, the present inventors have excellent adhesiveness and flexibility, and have a combination of durability such as heat resistance, moisture resistance and thermal shock resistance. As a result of diligent study of a resin composition suitable for a conductive paste having a number average molecular weight of 3000 or more, the aromatic dicarboxylic acid is 80 mol% or more of all the acid components, and the main chain carbon number of all glycol components is 5 or more. Containing at least 50 mol% of an alkylene glycol and / or an alicyclic glycol, and 0 to 50 mol% of an alkylene glycol having a main chain having 3 or less carbon atoms and having a side chain, and a total of 70 mol% or more thereof The inventors have discovered that the resin has excellent adhesiveness and flexibility, and has surprising physical properties that combine durability such as heat resistance, moisture resistance, and thermal shock resistance, and have reached the present invention. The conductive paste of the present invention has high conductivity and low-temperature bending resistance, and also has durability such as heat resistance, moisture resistance and thermal shock resistance, and can overcome the problems of the prior art.

That is, the present invention relates to a conductive paste containing a conductive powder (A), a binder containing a polyester resin (B) having a number average molecular weight of 3000 or more and a solvent (C) as main components, and a polyester resin (B). Is an alkylene glycol (a) having an aromatic dicarboxylic acid content of 80 mol% or more, wherein the total number of the dicarboxylic acid component and the lactone component is 100 mol%, and having at least 5 carbon atoms in the main chain of all glycol components. Or 5 alicyclic glycols (b)
0 to 50 mol%, containing 0 to 50 mol% of alkylene glycol (c) having 4 or less carbon atoms in the main chain and having a side chain;
A conductive paste, wherein the total of (a) to (c) is 70 mol% or more.

The conductive powder (A) used in the present invention is preferably silver powder alone or mainly composed of silver powder. Examples of the shape of the silver powder include known flakes (flakes), spheres, dendrites (dendrites), and three-dimensionally aggregated spherical primary particles described in JP-A-9-306240. Among them, flake silver powder and silver powder in which the above-mentioned spherical primary particles are three-dimensionally aggregated are particularly preferable. The flake silver powder preferably has an average particle diameter (50% D) of 1 to 15 μm, more preferably 2 to 8 μm, and still more preferably 2 to 5 μm as measured by a light scattering method.
In addition to silver powder, conductive powders include carbon fillers such as carbon black and graphite powder, precious metal powders such as gold powder, platinum powder and palladium powder, base metal powders such as copper powder, nickel powder, aluminum powder and brass powder, and silver. Plating with precious metals such as
Inorganic fillers such as alloyed base metal powders, silica, talc, mica, barium sulfate, etc. can be mixed with silver powder and used. However, carbon black and / or graphite can be used due to environmental characteristics such as conductivity and moisture resistance and cost. It is preferred that the powder be blended in 20% by weight or less, more preferably 10% by weight or less, in all conductive powders mainly composed of silver powder. Of course, those mainly composed of carbon black and / or graphite have a considerably higher resistance value than silver-based materials, but they are inexpensive and chemically stable, so that they can be used in some applications.

The compounding ratio of the conductive powder (A) and the binder used in the present invention varies depending on the kind of the conductive powder. When (A) is mainly composed of silver powder, the ratio of (A) / binder is 60/40 to 40%. 95 /
5 (weight ratio) is preferred, and more preferably 80/20 to
90/10. If (A) has a (A) / binder ratio of less than 60/40, good conductivity, bending resistance, heat resistance, moisture resistance, heat shock resistance, and other durability cannot be obtained. It is not preferable because the bending resistance and the adhesion are reduced. When the conductive powder (A) is mainly composed of carbon black and / or graphite, the ratio of (A) / binder is 40 to 7
0 (weight ratio) is preferred, and more preferably 45 to 65. If the ratio (A) is less than 60/40 in the ratio (A) / binder, good conductivity, bending resistance, heat resistance, moisture resistance and thermal shock resistance cannot be obtained. It is not preferable because the bending resistance and the adhesion are reduced.

[0015] The binder used in the present invention is composed of at least 80 mol% of aromatic dicarboxylic acid when the synthesis amount of the dicarboxylic acid component and the lactone component is 100 mol%, and the carbon number of the main chain of the total glycol component is at least 80 mol%. 5 or more alkylene glycols (a) and / or alicyclic glycols (b)
0 to 50 mol% of alkylene glycol (c) having 0 to 3 mol% and having 3 or less carbon atoms and having a side chain;
The polyester resin (B) contains a total of 70 mol% or more of (c) to (c) as a main component. The use of this polyester as a binder results in surprisingly good flex resistance and high environmental properties.

The number average molecular weight of the polyester resin (B) is at least 3,000, preferably at least 8,000, more preferably at least 15,000. Number average molecular weight is 3,
If it is less than 000, the bending resistance is reduced. Further, the paste viscosity is undesirably reduced. The reduced viscosity of the polyester resin (B) is preferably at least 0.2 dl / g, more preferably at least 0.4 dl / g, even more preferably at least 0.5 dl / g.

The polyester resin (B) has an aromatic dicarboxylic acid content of 80 mol% or more, preferably 90 mol% or more, of all the acid components. If the amount of the aromatic dicarboxylic acid is less than 80 mol%, the strength of the coating film is reduced, and the low-temperature bending resistance, heat resistance, moisture resistance, heat shock resistance and other durability are reduced.

The polyester resin (B) used in the present invention
The glycol component which is copolymerized with the above is an aliphatic glycol (a) and / or an alicyclic glycol (b) having a main chain having 5 or more carbon atoms in an amount of 50 mol% or more, a main chain having 4 or less carbon atoms and a side chain. It is necessary to contain 0 to 50 mol% of the alkylene glycol (c) having the following formula: The preferred content of (a) and / or (b) is 70 mol% or more,
The preferred content of (c) is 0 to 30 mol%. By using these glycols, a resin having good solvent solubility, bending resistance, and durability such as heat resistance, moisture resistance, and thermal shock resistance can be obtained. Has high conductivity and low-temperature bending resistance, and also has durability such as heat resistance, moisture resistance, and thermal shock resistance.

The glass transition temperature of the polyester resin (B) is preferably 25 ° C. or lower, more preferably -20 to 15 ° C.
° C.

As the aliphatic glycol (a) having a main chain having 5 or more carbon atoms which is copolymerized with the polyester resin (B),
1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,5-pentanediol, 1,9-nonanediol, 1,10-decanediol, etc. And used alone or in combination of two or more. By using these long-chain glycols, good adhesion, flexibility and heat resistance can be obtained and, more surprisingly, the moisture resistance is significantly improved. In particular, 1,5-pentanediol,
1,6-hexanediol and 3-methyl-1,5-pentanediol are preferred, and these are preferably used in an amount of 70 mol% or more. .

As the alicyclic glycol (b), 1,4-
Cyclohexane dimethanol, 1,3-cyclohexane dimethanol, 1,2-cyclohexane dimethanol,
Tricyclodecane glycol, dimer diol and the like. Of these, 1,4-cyclohexanedimethanol is preferred from the viewpoint of moisture resistance, but is preferably used in an amount of 20 mol% or less because the glass transition temperature increases.

The alkylene glycol (c) having a main chain having 4 or less carbon atoms and having a side chain includes propylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol, 2,2-diethyl-1,3. -Propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,3-butanediol and the like.
By using an appropriate amount of these glycols, solvent solubility can be imparted to the polyester resin and the glass transition temperature can be adjusted. Of these, neopentyl glycol and 2-methyl-1,3-propanediol are preferably used in an amount of 30 mol% or less from the viewpoints of physical properties of the coating film and moisture resistance.

Other glycols such as ethylene glycol, 1,3-propanediol, and 1,4-butanediol include alkylene glycols having no main chain having less than 5 carbon atoms, diethylene glycol, polyethylene glycol, and polytetramethylene. And polyether diols such as glycol. If these glycols are contained in a large amount, environmental properties such as moisture resistance are remarkably deteriorated. Further, an alkylene oxide adduct of bisphenol A, an alkylene oxide adduct of bisphenol F or trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, or a polyhydric polyol such as polyglycerin is used in combination without impairing the content of the invention. Is also good.

Examples of the aromatic dicarboxylic acid copolymerized with the polyester resin (B) include terephthalic acid, isophthalic acid, orthophthalic acid and 2,6-naphthalenedicarboxylic acid. Of these, terephthalic acid and isophthalic acid are preferably used in combination from the viewpoint of physical properties and solvent solubility.
Other dicarboxylic acids include succinic acid, glutaric acid, adipic acid, sebacic acid, dodecanedicarboxylic acid,
Aliphatic dicarboxylic acids such as azelaic acid, having 12 to 12 carbon atoms
28 dibasic acids, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2
Alicyclic dicarboxylic acids such as methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalenedicarboxylic acid, tricyclodecanedicarboxylic acid, hydroxy Hydroxycarboxylic acids such as benzoic acid and lactic acid. Further, a lactone such as caprolactone may be copolymerized, but the total amount of the dicarboxylic acid and the lactone may be 100 mol%.
, The aromatic dicarboxylic acid component needs to be 80 mol% or more.

In addition, polycarboxylic acids such as trimellitic anhydride and pyromellitic anhydride, unsaturated dicarboxylic acids such as fumaric acid, and sodium 5-sulfoisophthalate may be used within the scope of the invention. May be used in combination. Also, after polymerizing the polyester resin, trimellitic anhydride,
An acid anhydride such as phthalic anhydride may be added later to give an acid value.

It is preferable that the polyester resin (B) of the present invention does not have a melting point (amorphous) in view of adhesiveness, flexibility and solvent solubility.

The polyester resin (B) of the present invention may be a polyester resin other than the polyester resin (B) of the present invention, a polyester urethane resin, a polyether urethane resin, a polycarbonate urethane resin, a vinyl chloride resin. Vinyl acetate copolymer, epoxy resin, phenol resin, acrylic resin, polyacrylonitrile resin, polybutadiene resin, hydrogenated polybutadiene resin, nitrocellulose, cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP) Such modified celluloses and polyamide-imide resins may be blended as long as the properties are not deteriorated.

The polyester resin (B) is polymerized by a known method such as a transesterification method and a direct polymerization method. Further, it is preferable to blend a curing agent that can react with the polyester resin (B). The preferable compounding amount of the curing agent is 5 to 40 parts by weight based on 100 parts by weight of the polyester resin (B). Although the kind of the curing agent is not limited, an isocyanate compound is particularly preferable in terms of adhesiveness and low-temperature bending resistance. Further, it is preferable that these isocyanate compounds are used after being blocked, from the viewpoint of storage stability. Examples of the curing agent other than the isocyanate compound include known compounds such as methylated melamine, butylated melamine, benzoguanamine, amino resins such as urea resins, acid anhydrides, imidazoles, epoxy resins, and phenol resins. These may be used alone or in combination.

As the isocyanate compound, aromatic,
There are aliphatic diisocyanate and trivalent or higher polyisocyanate, and either low molecular weight compound or high molecular weight compound may be used. 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 The amount and, for example, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, low molecular active hydrogen compounds such as triethanolamine or various polyester polyols, polyether polyols, polyamides By reacting with a high molecular weight active hydrogen compound, etc. Terminal isocyanate group-containing compounds to be.

Examples of the blocked isocyanate agent include phenols such as phenol, thiophenol, methylthiophenol, ethylthiophenol, cresol, xylenol, resorcinol, nitrophenol and chlorophenol, and oximes such as acetoxime, methylethylketoxime and cyclohexanone oxime. Alcohols such as methanol, ethanol, propanol and butanol, ethylene chlorohydrin,
Halogen-substituted alcohols such as 1,3-dichloro-2-propanol, tertiary alcohols such as t-butanol and t-pentanol, ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propyrolactam And other active amines such as aromatic amines, imides, acetylacetone, acetoacetate, and malonic acid ethyl ester, mercaptans, imines, imidazoles, ureas, and diaryl compounds. And sodium bisulfite. Of these, oximes, imidazoles, and amines are particularly preferred over curability. These crosslinkers include:
A well-known catalyst or promoter selected according to the type can be used in combination.

The type of the solvent (C) used in the present invention is not limited, and examples thereof include ester type, ketone type, ether ester type, chlorine type, alcohol type, ether type, and hydrocarbon type. Among them, when screen printing is performed, a high boiling point solvent such as ethyl carbitol acetate, butyl cellosolve acetate, isophorone, cyclohexanone, and γ-butyrolactone is preferable.

The conductive paste of the present invention may contain known additives such as an antifoaming agent, a leveling agent and a dispersant.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. In the examples, “parts” simply means “parts by weight”. Each measurement item followed the following method.

1. Reduced viscosity, ηsp / c (dl / g) 0.10 g of a polyester resin was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (weight ratio: 6/4) and measured at 30 ° C.

2. Molecular weight The number average molecular weight in terms of polystyrene was measured by GPC.

3. Glass transition point temperature (Tg) Measured at a heating rate of 20 ° C./min using a differential scanning calorimeter (DSC). As a sample, 5 mg of the sample was placed in an aluminum holding lid type container and crimped.

4. Acid value (mgKOH / g) 0.2 g of a sample was precisely weighed and dissolved in 20 ml of chloroform. Then, it was determined by titration with 0.01 N potassium hydroxide (ethanol solution). A phenolphthalein solution was used as an indicator.

5. Preparation of test piece Conductive paste with 100 μm thickness annealed PET
A pattern with a line width of 0.5 mm and a length of 75 mm (for bending resistance test) and a pattern with a width of 25 mm and a length of 50 mm (for specific resistance measurement, heat resistance measurement so that the film thickness after drying becomes 8 to 10 μm) , Moisture resistance measurement, and thermal shock resistance) were screen printed. Using a conveyor type far-infrared oven, the surface temperature of the
What was dried under the conditions of minutes was used as a test piece.

6. Specific resistance5. Using the test piece prepared in the above section, the film thickness and the sheet resistance film thickness were measured using a 4-deep needle resistance measuring instrument, and the specific resistance was calculated from these.

7. 4. Flex resistance Test piece prepared at 25 ° C, load 50g / c
Under the conditions of m ² and R = 0, bending at 360 ° at the same location was repeated five times, and the resistance change rate of the conductor was evaluated. Flex resistance (%) = {(R− _Ro ) / _Ro } × 100 where R ₀ = initial circuit resistance R = resistance value after flex test

8. Heat resistance 5. After heat-treating the test piece prepared in the above at 100 ° C. for 1,000 hours in a hot air oven, the adhesion of the conductor, the pencil hardness, and the low-temperature flexibility were evaluated.

9. 4. Moisture resistance 85% relative humidity 85%
After heat treatment in a thermo-hygrostat at RH for 1,000 hours, the adhesiveness of the conductor, pencil hardness and low-temperature flexibility were evaluated.

10. 4. Thermal shock resistance Test pieces prepared at -40 ° C and 85 ° C for 1 each
After being left alternately for a total of 1,000 hours, the adhesion of the conductor, pencil hardness, and low-temperature flexibility were evaluated.

11. Adhesion 5. The test piece prepared in the above was evaluated by a cellophane peel test.

12. Pencil hardness5. SUS30 2mm thick test piece
The sample was placed on four plates, measured using a high-grade pencil specified in JIS-6006 in accordance with JIS K-5400, and judged by the presence or absence of scratches.

Synthesis Example 1 (Polyester resin I) 97 parts of dimethyl terephthalic acid, 97 parts of dimethyl isophthalic acid,
208 parts of 5-pentanediol and 0.102 parts of tetrabutyl titanate were charged, and the mixture was exchanged at 180 ° C. for 3 hours. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for 2 hours. The composition of the obtained polyester resin is terephthalic acid / isophthalic acid // 1,5
-Pentanediol = 50/50 // 100 (molar ratio), reduced viscosity 0.45 dl / g, number average molecular weight 12,
000, acid value 0.7 mgKOH / g, glass transition temperature 5 ° C. Table 1 shows the results.

Synthesis Example 2 (Polyester resin II) Synthesis example. In the same manner as in Example 1, a polyester resin II was synthesized.
The composition of the obtained polyester resin is as follows: terephthalic acid / isophthalic acid / 1,4-cyclohexanedicarboxylic acid / trimellitic acid // 1,6-hexanediol / neopentyl glycol = 50/29/20/1 // 75 / 25
(Molar ratio), reduced viscosity 0.55 dl / g, number average molecular weight 17,000, acid value 0.8 mg KOH / g, and glass transition point temperature 0 ° C. Table 1 shows the results.

Synthesis Example 3 (Polyester resin III) 97 parts of dimethyl terephthalic acid, 87 parts of dimethyl isophthalic acid,
236 parts of methyl-1,5-pentanediol, 1,4-
29 parts of cyclohexane dimethanol and 0.102 part of tetrabutyl titanate were charged, and the mixture was exchanged at 180 ° C. for 3 hours. Next, 10 parts of sebacic acid was charged, and transesterification was further performed. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for 2 hours. The composition of the obtained polyester resin is as follows: terephthalic acid / isophthalic acid / sebacic acid // 3-methyl-1,5-pentanediol diol / 1,4-cyclohexanedimethanol = 50/45/5 // 80/20 ( Molar ratio), reduced viscosity 0.65 dl / g, number average molecular weight 21,000, acid value 0.9 mg KOH / g, glass transition temperature -3 ° C. Table 1 shows the results.

Synthesis Example 4 (Polyester resin IV) Synthesis example. In the same manner as in Example 1, a polyester resin IV was synthesized.
The composition of the obtained polyester resin is as follows: terephthalic acid / isophthalic acid / trimellitic acid // 1,6-hexanediol / 2-methyl-1,3-propanediol / 1,4
-Cyclohexanedimethanol = 50/49/1 // 5
0/24/26 (molar ratio), reduced viscosity 0.70 dl /
g, number average molecular weight 25,000, acid value 0.7 mg KOH
/ G, and the glass transition temperature was 35 ° C. Table 1 shows the results.

Comparative Synthesis Example 1 (Comparative polyester resin V) Synthesis example. Comparative polyester resin V was synthesized in the same manner as in Comparative Example 2. The composition of the obtained polyester resin is as follows: terephthalic acid / isophthalic acid / sebacic acid // neopentyl glycol / 1,6-hexanediol = 50/20/30 //
14/86 (molar ratio), reduced viscosity 0.70 dl / g, number average molecular weight 24,000, acid value 1.1 mgKOH / g,
Glass transition temperature was -26 ° C. Table 2 shows the results.

Comparative synthesis example. 2 (Comparative polyester ether resins VI and VII) Comparative polyester resins VI and VI were synthesized in the same manner as the polyester resin I of the synthesis example. Table 2 shows the results.

Comparative Synthesis Example 3 (Comparative polyester urethane resin VIII) Aliphatic polyester diol OD-X in a four-necked flask
100 parts of -688 (manufactured by Dainippon Ink and Chemicals, Inc.), 6 parts of neopentyl glycol as a chain extender, 2 parts of 1,6-hexanediol, 105 parts of methyl ethyl ketone, and 105 parts of toluene are charged, and the mixture is charged with nitrogen gas to 60 parts. C., 31 parts of diphenylmethane diisocyanate was further charged, and the mixture was slowly heated to 80.degree. C. and reacted for 5 hours until no residual isocyanate was detected. The resulting polyurethane resin had a reduced viscosity of 1.10 dl / g, a number average molecular weight of 38,000, an acid value of 0.2 mgKOH / g, and a glass transition temperature of -25 ° C. Table 3 shows the results.

Preparation of Silver Powder A-1 Commercial flake silver powder was used as it was. The average particle diameter (50% D) by a light scattering method is 4.5 μm, and the specific surface area is 0.4 μm.
It was 7 m ² / g.

Preparation of Silver Powder A-2 275 parts of a 37% aqueous silver nitrate solution and 220 parts of an 18% aqueous sodium hydroxide solution were reacted with stirring at 40 to 50 ° C., and after the reaction was completed, 70 parts of distilled water was added. did. Then, 60 parts of a formalin aqueous solution having a concentration of 23% was added thereto and reacted at 30 to 40 ° C. PH after the reaction is 8
Met. The obtained silver powder was filtered, washed and dehydrated repeatedly, replaced with methanol, and filtered.
It dried under reduced pressure for 4 hours. The obtained silver powder has a shape in which the spherical primary particles shown in FIG. 1 are three-dimensionally aggregated, the average particle diameter of the primary particles is 0.5 μm from a scanning electron micrograph, and The average particle size measured by a light scattering method was 11 μm, and the specific surface area was 1.62 m ² / g. The secondary particles are not destroyed in the three-roll dispersing step, and can maintain their structure.

Example 1 89 parts of silver powder A-1, 9.6 solid parts of a solution of polyester resin I in butyl cellosolve acetate, 1.4 solid parts of a curing agent, and 0.5 part of a leveling agent were sufficiently mixed and premixed. Thereafter, the mixture was dispersed three times with a chilled three-roll kneader. 4. The obtained silver paste is Printed, dried and evaluated by the method described in (1). Specific resistance is 5.0 × 10 ⁻⁵ Ω · cm
Was good. Flex resistance: 25 ° C., R = 0, 360
The rate of change in resistance after 5 degrees of bending was + 35%, no disconnection was observed, and it was very good. Further, heat resistance, moisture resistance and thermal shock resistance were also good. Table 4 shows the results.

In the same manner as in Example 1, the conductive pastes of Examples 2 to 5 were prepared and evaluated. Table 4 shows the results.

In the same manner as in Example 1, the conductive pastes of Comparative Examples 1 to 5 were prepared and evaluated. Table 5 shows the results.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3] 1) OD-X-688 (manufactured by Dainippon Ink Industries, Ltd.)

[0061]

[Table 4] 1) Conductive carbon black (manufactured by Lion Co., Ltd.) 2) Hexamethylene diisocyanate biuret trimer methylethyl ketoxime block 3) Hexamethylene diisocyanate isocyanurate adduct methyl ethyl ketoxime block

[0062]

[Table 5] 1) Methylethylketoxime block of hexamethylenediisocyanate biuret trimer 2) Methylethylketoxime block of hexamethylenediisocyanate isocyanurate adduct 3) Vinyl chloride / vinyl acetate copolymer (Union Carbide Co., Ltd.)

[0063]

The conductive paste of the present invention has excellent adhesion and flexibility to films such as polyethylene terephthalate, vinyl chloride, nylon, etc., metal substrates, glass substrates, etc., and cannot be obtained by conventional techniques. Has excellent durability such as excellent heat resistance, moisture resistance and thermal shock resistance. As a result, it is possible to meet high required quality in extremely severe fields such as electric products, electronic components, and applications between automobiles.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph of silver powder A-2.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/24 H01B 1/24 A F term (Reference) 4J002 CF041 DA026 DA076 ER007 FD007 FD116 FD147 GJ01 5G301 DA03 DA18 DA19 DA42 DA53 DD01

Claims (2)

[Claims] 1. A conductive paste comprising a conductive powder (A), a binder containing a polyester resin (B) having a number average molecular weight of 3,000 or more and a solvent (C) as main components, wherein the polyester resin (B) is a dicarboxylic acid. When the total amount of the acid component and the lactone component is 100 mol%, the aromatic dicarboxylic acid is at least 80 mol%, and the alkylene glycol (a) having at least 5 carbon atoms in the main chain of all glycol components and / or an alicyclic group Glycol (b) in an amount of 50 mol% or more, alkylene glycol (c) having a main chain having 4 or less carbon atoms and having a side chain in an amount of 0 to 50 mol%, and the total of (a) to (c) being 70 mol% The conductive paste as described above. 2. The conductive paste according to claim 1, further comprising a curing agent capable of reacting with the polyester resin (B).