JP2005044771A - Conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive paste excellent in heat resistance against reflow solder, conductivity, heat resistance, heat cycle resistance or the like. <P>SOLUTION: The conductive paste made by dispersing a conductive filler (A) in binder resin contains polyester resin and/or denatured polyester resin copolymerized with aromatic dicarboxylic acid by 50 mol% or more (B) and epoxy resin (C), when the acid number of the binder resin is not less than 10 equivalent weight/t, and when a total amount of carboxylic acid component is 100 mol%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a conductive paste, and more particularly to a conductive coating agent or a conductive adhesive for a circuit or a conductive element, metal or the like.

In recent years, lead-free solder has been used as an environmental measure, and the heat resistance of electronic devices has been increasingly required, and the conductive paste used for these applications also requires heat resistance higher than before. It has come to be. Various binder resins are used for the conductive paste, but those using polyester resins as binders are superior in terms of adhesion to the substrate, flex resistance, heat cycle resistance, pigment dispersibility, etc. Yes. For example, in Patent Document 1, a conductive paste using a saturated copolymerized polyester resin and a blocked isocyanate compound as a binder is known, and in Patent Document 2, a conductive paste in which silver powder and carbon black are dispersed in a similar binder system is known. Yes.
JP-A-1-159906 Japanese Patent No. 2802622

  However, since the former is designed mainly for circuits and uses an isocyanate compound as a curing agent, it is insufficient for the recent high heat resistance such as reflow soldering heat resistance. The latter has good dispersibility of carbon black and can provide excellent characteristics in terms of conductivity mainly for circuit use, but also has a problem of poor heat resistance.

  On the other hand, epoxy-based conductive pastes, which are widely used mainly for bonding applications, have good heat resistance and adhesiveness, but are basically inferior in heat cycle resistance due to the hard binder resin and low molecular weight. In addition, when fine powder fillers such as carbon black and resin-like or spherical metal fine powder having a large specific surface area are used alone or in combination with other metal powders such as flakes, the dispersibility is inferior and high solid differentiation is caused. There are problems such as difficulty, thixotropic property (thixotropic property) is too strong, and workability is poor.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have an acid value, that is, a carboxyl group as a binder resin used in the conductive paste, and aromatic dicarboxylic acid is 50 mol% in all carboxylic acid components. If the polyester resin and the epoxy resin are used in combination, the dispersibility and conductivity of the filler are good, and the heat resistance is greatly reduced without deteriorating various physical properties such as adhesion, bending resistance, and heat cycle resistance. The present invention has been found out.

That is, the present invention is the following conductive paste.
(1) In a conductive paste in which a conductive filler (A) is dispersed in a binder resin, the binder resin has an acid value of 10 equivalents / t or more, and when the total carboxylic acid component is 100 mol%, aromatic A conductive paste comprising a polyester resin and / or a modified polyester resin (B) copolymerized with 50 mol% or more of dicarboxylic acid and an epoxy resin (C).
(2) As said polyester resin and / or modified polyester resin (B), as a glycol component, neopentyl glycol, 2-methyl-1,3-propanediol, alicyclic glycol, having 5 to 10 carbon atoms in the main chain It is preferable that at least one selected from aliphatic glycols is copolymerized in an amount of 20 mol% or more.
(3) As said epoxy resin (C), a novolak-type epoxy resin is preferable.
(4) The blending mass ratio (B) / {(B) + (C)} of the polyester resin and / or modified polyester resin (B) and the epoxy resin (C) is 0.3 or more and 0.95 or less. Preferably there is.
(5) The conductive paste of the present invention may further contain an imidazole compound.
(6) The conductive filler (A) preferably contains silver powder and carbon black and / or graphite.

  The conductive paste of the present invention is excellent in heat resistance and heat cycle resistance, which has been difficult to achieve at the same time, and even when a conductive filler having a high specific surface area such as conductive carbon black is used because of its excellent dispersibility. Good workability with low viscosity. The conductive paste of the present invention is suitable as a conductive adhesive or conductive coating agent for various electronic components as well as for rigid substrates, flexible substrates such as polyimide, and PET membrane circuits.

  Examples of the conductive filler (A) used in the present invention include noble metal powders such as silver powder, gold powder, platinum powder and palladium powder, noble metal powders such as copper powder, nickel powder, aluminum powder, brass powder and stainless steel powder, silver, etc. And carbon-based fillers such as carbon black and graphite powder plated and alloyed with noble metals. Examples of the shape of these metal powders include a flake shape (flaky shape), a spherical shape, a cocoon shape, a dendritic shape (dendritic shape), and a shape in which spherical primary particles are aggregated three-dimensionally. Among these, silver powder is preferably the main component from the viewpoint of conductivity, cost, and reliability, and it is more preferable to use a small amount of carbon black and / or graphite powder in combination with the silver powder from the viewpoint of conductivity. Further, in terms of conductivity and reliability, it is preferable to use flaky and spherical silver powder, and it is most preferable to use flaky and spherical silver powder in combination.

  Moreover, you may mix | blend a small amount of inorganic fillers, such as a silica, a talc, a mica, barium sulfate, and an indium oxide, as needed.

  The preferable blending ratio (mass ratio) of silver powder and carbon black and / or graphite fine powder is preferably 99. The upper limit of silver powder is preferably 99. When the total amount of silver powder and carbon black and / or graphite fine powder is 100 mass ratio. It is 5 mass ratio or less, More preferably, it is 99 or less. The lower limit as silver powder is 85 mass ratio or more, more preferably 90 or more.

  The blending ratio of the conductive powder and the binder resin is such that when the total amount of the silver powder and other conductive powder and the total amount of the binder resin is 100 mass ratio, the lower limit of the conductive powder is preferably 75 mass ratio or more, more preferably. Is 80 mass ratio or more. The upper limit is preferably 95 mass ratio or less, more preferably 90 or less, from the viewpoint of adhesiveness and ink viscosity.

  As the binder resin, when the acid value is 10 equivalent / t or more and the total carboxylic acid component is 100 mol%, the polyester resin and / or the modified polyester resin (B) in which the aromatic dicarboxylic acid is copolymerized 50 mol% or more. And epoxy resin (C) must be used in combination. By applying an acid value, that is, a carboxyl group to the polyester resin, a tough coating film is obtained. In addition, with the synergistic effect of improving heat resistance by introducing an aromatic component, without lowering the adhesion to the base material, the bending resistance, the heat cycle resistance, the pigment dispersibility, etc., which are the characteristics of the polyester resin , Heat resistance can be improved. In general, heat resistance means changes in physical properties such as adhesive strength and adhesion before and after heat history, but heat resistance here also means that there is little change in resistance value after bonding with conductive paste. Including. In applications such as application of conductive paste to chip parts, mounting on a substrate, adhesion to a lead frame, and the like, particularly important characteristics include a change in conductivity after adhesion. In applications such as application of conductive paste to chip parts, solid electrolytic capacitor elements, etc., mounting on substrates, adhesion to lead frames, and the like, particularly important characteristics include changes in conductivity after adhesion. The conductive paste of the present invention is excellent in initial conductivity and particularly excellent in stability of conductivity after heat history.

  As the polyester resin (B), those obtained by polycondensation by a known method under normal pressure or reduced pressure can be used. Further, modification as described later may be performed.

  The dicarboxylic acid copolymerized with the polyester resin (B) is desirably copolymerized with 50 mol% or more of aromatic dicarboxylic acid in the total acid component from the viewpoint of heat resistance, adhesive strength, and durability, and more preferably 60 The mol% or more, most preferably 70 mol% or more. The upper limit is not particularly limited, and may be 100 mol%. When the aromatic dicarboxylic acid is less than 50 mol%, the heat resistance, adhesive strength, durability, and the like may be lowered.

  Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, and 2,6-naphthalenedicarboxylic acid. Among these, it is preferable to use terephthalic acid and isophthalic acid in combination in view of characteristics such as heat resistance and adhesiveness and solvent solubility.

  Examples of other dicarboxylic acids include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and other aliphatic dicarboxylic acids, C12-C28 dibasic acids, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxyhydrogenated bisphenol A, Examples thereof include alicyclic dicarboxylic acids such as dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalene dicarboxylic acid, and tricyclodecanedicarboxylic acid, which can be copolymerized with aromatic dicarboxylic acid.

  Among these, from the viewpoint of durability, as the aliphatic dicarboxylic acid, those having 9 or more carbon atoms in the main chain such as azelaic acid and sebacic acid are preferable. As other dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid is preferable.

  The alkylene glycol used for the polyester resin (B) is ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-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 Examples include diols. 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 durability, neopentyl glycol, 2-methyl-1,3-propanediol, and a long-chain aliphatic diol having 5 to 10 carbon atoms are particularly preferable, and 20 mol% or more of all glycol components is preferable, More preferably, it is 30 mol% or more. The upper limit is not particularly defined and may be 100 mol%. The composition ratio referred to in this specification can be determined by ¹ H-NMR analysis.

  The polyester resin (B) needs to have an acid value of 10 equivalent / t or more. A preferable acid value is 30 equivalents / t or more, more preferably 50 equivalents / t or more. If the acid value is less than 10 equivalents / t, curability is lowered and good heat resistance may not be obtained. The upper limit is preferably 800 equivalents / t or less, more preferably 500 equivalents / t or less. If it exceeds 800 equivalents / t, the coating film tends to be brittle, and heat cycle resistance and heat resistance may be reduced. In addition, the acid value said here shows the equivalent number of the carboxyl group (or other acidic substituent) contained in 1 ton of resin.

  As a method for imparting an acid value to the polyester resin (B), it can be imparted by hydrolyzing and stirring in the air while being melted and heated after polymerization. However, trimellitic anhydride, phthalic anhydride, ethylene glycol bis (anne) Hydrotrimellitate), pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride, bicycloheptanetetracarboxylic dianhydride, 3,3 ′, 4,4 ′ -Acid anhydrides such as biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic dianhydride are polyester resins A method of post-addition after polymerization is preferred. Among these, as the acid anhydride, trimellitic anhydride and ethylene glycol bis (anhydro trimellitate) are particularly preferable.

  The lower limit of the number average molecular weight of the polyester resin (B) is preferably 2,000 or more, more preferably 3,000 or more, and most preferably 4,000 or more. Although the upper limit is not particularly limited, when the conductive paste of the present invention is used as a conductive adhesive, high solid differentiation is preferable to reduce the influence of the solvent, and 15,000 or less is required to achieve high solid differentiation. Is more preferable, and 10,000 or less is more preferable. When the molecular weight is less than 2,000, the bending resistance and heat cycle resistance tend to decrease.

  Further, after polymerization of the polyester resin, a cyclic ester such as ε-caprolactone may be post-added (ring-opening addition) at 180 to 230 ° C. to form a block shape.

  In addition, within the scope of not impairing the content of the invention, a branched structure is introduced by copolymerizing a polyvalent carboxylic acid such as trimellitic anhydride or pyromellitic anhydride, an unsaturated dicarboxylic acid such as fumaric acid, A sulfonic acid metal base-containing dicarboxylic acid such as 5-sulfoisophthalic acid sodium salt may be used in combination.

  The polyester resin used in the present invention can be modified and used. Examples of the modification method include urethane modification, epoxy modification, and acrylic modification.

  When the polyester resin is urethane-modified, it can be synthesized by reacting the above-described polyester polyol and, if necessary, a chain extender with an isocyanate compound. It is preferable to use a polyol having a molecular weight of less than 500 as the chain extender, such as neopentyl glycol, 1,6-hexanediol, ethylene glycol, HPN (hydroxypivalate ester of neopentyl glycol), trimethylolpropane, glycerin and the like. A well-known polyol is mentioned. Furthermore, since a carboxyl group can be introduced into a molecular chain by using a carboxyl group-containing polyol such as dimethylolpropionic acid as a chain extender, an acid value of 10 equivalents can be obtained by adjusting the amount of copolymerization thereof. / T or more can be adjusted.

  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 urethane group concentration of the urethane-modified polyester resin is preferably 500 to 4000 equivalents / 10 ⁶ g in terms of adhesion and flex resistance. The number average molecular weight is preferably 8,000 to 20,000 in view of bending resistance and paste viscosity.

  When the polyester resin is epoxy-modified, as described above, a polyester to which an acid anhydride such as trimellitic anhydride or phthalic anhydride is post-added to give an acid value is used, and a catalyst such as triphenylphosphine is used in the solution. It can be produced by reacting with an epoxy resin in the presence.

  Of these modified polyester resins, epoxy modification is preferred from the viewpoint of heat resistance.

  Examples of the epoxy resin (C) used in the present invention include phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, NC manufactured by Nippon Kayaku Co., Ltd. Novolak type epoxy resin containing biphenol skeleton such as -3000, epoxy resin containing biphenol skeleton such as CER-3000L manufactured by Nippon Kayaku Co., Ltd., high molecular weight phenoxy resin, water-added bisphenol A type epoxy resin, dimer acid Examples include modified epoxy resins, rubber-modified epoxy resins, and brominated epoxy resins. From the viewpoint of heat resistance and curability, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A type epoxy resins, biphenols Novolak type epoxy resin containing skeleton, epoxy resin is preferably contained biphenol skeleton. Of these, novolac type epoxy resins are preferred.

  The blending ratio (mass ratio) of the polyester resin (B) and the epoxy resin (C) is preferably (B) / {(B) + (C)} = 0.3 or more, more preferably 0.4 or more. is there. The upper limit is preferably 0.95 or less, more preferably 0.90 or less. If this blending ratio is less than 0.3, the bending resistance and heat cycle resistance may be lowered, and if it is less than 0.05, the curability may be deteriorated.

  The conductive paste of the present invention can contain a curing catalyst such as an imidazole compound, an acid anhydride, or triphenylphosphine. Of these, imidazole compounds are particularly preferred because of their good curability and low corrosivity. Examples of imidazole compounds include 2-phenyl-4,5-dihydroxymethylimidazole, 2-methylimidazole, 1-cyanoethyl-2-methylimidazolium trimellitate, 1-benzyl-2-methylimidazole, 2,4 -Diamino-6- [2'-methylimidazolyl- (1 ')]-ethyl-s-triazine, 2-methylimidazole isocyanuric acid adduct, 2-phenylimidazole, 2-methylimidazoline and the like. Among these, from the viewpoint of curability and storage stability, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6- [2 ′ -Methylimidazolyl- (1 ')]-ethyl-s-triazine isocyanuric acid adduct is preferred.

  Moreover, you may mix | blend the hardening | curing agent which can react with a polyester resin and / or a modified polyester resin, and an epoxy resin. Examples of the curing agent include phenol resol resins, alkyl etherified amino resins, isocyanate compounds, blocked isocyanate compounds, acid anhydrides, and the like.

  These curing agents can be used in combination with a known catalyst or accelerator selected according to the type.

  Other resins may be used in combination with the conductive paste of the present invention. Examples of other resins include polyether urethane resins, polycarbonate urethane resins, vinyl chloride / vinyl acetate copolymers, epoxy resins, phenol resins, cellulose resins, acrylic resins, polyimide resins, and polyamideimide resins.

  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, a high boiling point solvent having a boiling point of 140 ° C. or higher is preferable from the viewpoint of workability. Examples of the high boiling point solvent include ethyl carbitol acetate, butyl cellosolve acetate, butyl carbitol, butyl carbitol acetate, isophorone, cyclohexanone, γ-butyrolactone, N-methyl-2-pyrrolidone, and dimethylacetamide.

  When the conductive paste of the present invention is used as a conductive adhesive, the solid content is preferably 75% or more, more preferably 80% or more in order to reduce the adverse effects of the solvent. In this case, the viscosity of the conductive paste is preferably 1000 dP · s or less, more preferably 800 dPa · s or less at a Brookfield BH type rotational viscometer, 20 rpm, 25 ° C. The lower limit is preferably 100 dPa · s or more, and more preferably 200 dPa · s or more. If it exceeds this range, printability and workability with a dispenser tend to deteriorate.

  In addition, the degree of throttling (thixotropy) is also important, and is preferably 2.0 or higher, more preferably 3.0 or higher in the measurement method described later. The upper limit is preferably 7.0 or less, and more preferably 6.0 or less. If the degree of change is less than 2.0, there is a tendency to sag at the time of application of the dispenser, and if it exceeds 7.0, it tends to stop flowing.

Hereinafter, the present invention will be described using examples. In the examples, the term “part” simply means “part by mass”. Each measurement item followed the following method.
1. Molecular weight The number average molecular weight in terms of polystyrene was measured by GPC.
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
A 0.2 g 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. The unit was expressed in equivalent / t (t = 1000 kg).
4). Measurement of Viscosity and Thickness (Thixotropic) of Conductive Paste Viscosity was measured at 20 rpm using a Brookfield BH type rotational viscometer. Similarly, the viscosity was measured by measuring the viscosity at 2 rpm and calculated by the following formula. The measurement was performed at 25 ° C.
Deflection = viscosity (2 rpm) / viscosity (20 rpm)
5. Measurement of specific resistance A pattern having a width of 25 mm and a length of 50 mm was screen-printed on a polyimide film having a thickness of 50 μm so that the film thickness after drying was 8 to 10 μm. This was heat cured in a hot air oven at 170 ° C. for 1 hour. Using the prepared test piece, the sheet resistance and the film thickness were measured separately using a film thickness and 4 deep needle resistance measuring device, and the specific resistance was calculated from these.
6). Measurement of Initial Resistance and Evaluation of Heat Resistance A 100 μm thick copper foil was polished in water with Scotch Bright, washed with ion-exchanged water, and dried. This copper foil is cut to 10 × 25 mm, and a conductive paste is applied to a portion 10 mm from the tip in the longitudinal direction so that the dry thickness is 50 ± 5 μm, and the overlapping portion of the same copper foil is 10 × 10 mm Then, the non-bonded portions were bonded in the opposite direction. After the bonding, it was cured by heating in a hot air oven at 170 ° C. for 1 hour. Then, using a 4 deep needle resistance measuring device, a terminal was connected to the upper and lower copper foil portions that were not bonded (copper foils were not overlapped), and the initial resistance (R ₀ ) was measured. Next, after heating once at 250 ° C. for 1 minute assuming solder reflow, the resistance value (R ₁ ) was measured, and the resistance change rate of R ₁ with respect to R ₀ was evaluated. The average value of the number of repeated measurements (hereinafter referred to as N) = 5. The calculation formula is shown below.
Resistance change rate (%) = {(R ₁ −R ₀ ) / R ₀ } × 100
7. 5. Measurement of shear adhesive strength The initial shear adhesive force (F ₀ ) was measured at 20 ° C. and a pulling speed of 10 mm / min using the adhesion test piece prepared in ₁ . Expressed as an average value of N = 5.
8). 5. Heat cycle resistance The adhesive test piece prepared in the same manner was prepared in the same manner, and the initial resistance (R ₀ ) and the initial shear adhesive force (F ₀ ) were measured. The same test piece was subjected to 250 cycles of −40 ° C. × 30 minutes and 80 ° C. × 30 minutes, and the resistance value (R ₂ ) and shearing adhesive force (F ₂ ) after the test were measured. It was evaluated with. Each was represented by an average value of N = 5. The calculation formula is shown below.
Resistance change rate (%) = {(R ₂ −R ₀ ) / R ₀ } × 100
Change rate of shear adhesive force (%) = {(F ₁ −F ₀ ) / F ₀ } × 100

Synthesis example 1 (polyester resin a)
A four-necked flask equipped with a Gubileu fractionator is charged with 97 parts of dimethyl terephthalic acid, 97 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol and 0.068 parts of tetrabutyl titanate, and 180 ° C. for 3 hours. Exchange was performed. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for about 2 hours. After the polymerization, the mixture was stirred for 20 minutes at 200 ° C. in normal pressure and air, and partially hydrolyzed to give an acid value. The composition of the copolymerized polyester a is terephthalic acid / isophthalic acid // ethylene glycol / neopentyl glycol = 50/50 // 55/45 (molar ratio), number average molecular weight 15,000, acid value 35 equivalents / T, Tg = 65 ° C. The results are shown in Table 1.

Synthesis example 2 (polyester resin b)
A four-necked flask equipped with a Gubileu rectification column was charged with 97 parts of dimethyl terephthalic acid, 78 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol and 0.068 parts of tetrabutyl titanate. Exchange was performed. Subsequently, 20 parts of sebacic acid was charged to carry out an esterification reaction. Next, the pressure was gradually reduced to 1 mmHg or less, and polymerization was performed at 240 ° C. for about 1 hour. Subsequently, it cooled to 200 degreeC in normal pressure and nitrogen, 2.9 parts of trimellitic anhydride was prepared, it reacted for 30 minutes, and was added after that, and the carboxyl group (acid value) was provided. The composition of the obtained copolymer polyester b is terephthalic acid / isophthalic acid / sebacic acid / trimellitic acid (post-addition) // ethylene glycol / neopentyl glycol = 50/40/10 / 1.5 (post-addition) / The number average molecular weight was 8,000, the acid value was 135 equivalents / t, and Tg was 45 ° C./55/45 (molar ratio). The results are shown in Table 1.

Synthesis example 3,
Polyester resins c and d were synthesized in the same manner as in Synthesis Example 2. The results are shown in Table 1.

Synthesis example 4 (epoxy-modified polyester resin e)
In the same manner as in Synthesis Example 2, the composition is terephthalic acid / isophthalic acid / trimellitic acid (post-addition) // ethylene glycol / bisphenol A ethylene oxide 2.2 mol adduct = 50/50 / 2.0 (post-addition) // 50/50 (molar ratio), an acid value of 120 equivalents / t, and a number average molecular weight of 6,500 polyester were obtained. 100 parts of this polyester and 15 parts of Epicoat 1004 (Japan Epoxy Resin Co., Ltd.), which is a bisphenol A epoxy resin, were dissolved in ethyl carbitol acetate at a solid content of 60%, and 0.16 part of triphenylphosphine was added as a catalyst. Then, after reacting at 120 ° C. for 4 hours in a nitrogen stream and reacting until the acid value becomes 60% of the initial acid value, it is diluted with ethyl carbitol acetate to a solid content of 40% to obtain an epoxy-modified polyester resin e. It was. The obtained resin solution was a light yellow transparent liquid.

Comparative Synthesis Example 1 (Comparative polyester resin f)
A four-necked flask equipped with a Gubileu fractionator is charged with 97 parts of dimethyl terephthalic acid, 97 parts of dimethyl isophthalic acid, 93 parts of ethylene glycol, 73 parts of neopentyl glycol and 0.068 parts of tetrabutyl titanate, and 180 ° C. for 3 hours. Exchange was performed. Next, the pressure was gradually reduced to 1 mmHg or lower, polymerized at 240 ° C. for about 2 hours, and blown immediately in a nitrogen stream. The composition of the obtained copolymer polyester a is terephthalic acid / isophthalic acid // ethylene glycol / neopentyl glycol = 50/50 // 55/45 (molar ratio), number average molecular weight 22,000, acid value 5 equivalents / T, Tg = 67 ° C. The results are shown in Table 1.

Silver powder A
Commercially available flaky silver powder (Fukuda Metal Foil Powder Industry Co., Ltd.) was used as it was. The average particle size determined by the light scattering method was 4.5 μm, the specific surface area was 0.8 m ² / g, and the tap density was 3.3 g / cm ³ .

Silver powder B
Commercially available spherical and fine silver powder K-ED (manufactured by Fellow) was used as it was. The average particle diameter by the light scattering method was 0.6 μm, the specific surface area was 1.9 m ² / g, and the tap density was 3.1 g / cm ³ .

Example 1
Silver powder A, 88 parts, polyester resin a, 8.4 solid part, 3.6 parts of phenol novolac type epoxy resin having an epoxy equivalent of 180 g / equivalent, 2MA-OK as an imidazole catalyst (manufactured by Shikoku Chemicals Co., Ltd.) 0 .36 parts, 0.5 part of Polyflow S (manufactured by Kyoeisha Chemical Co., Ltd.) as a leveling agent and ethyl carbitol acetate as a solvent were blended to adjust the solid content to 83%. After sufficiently premixing, the mixture was dispersed three times with a chilled three-roll kneader. The obtained silver paste had a specific resistance of 5.5 × 10 ⁻⁵ Ω · cm. The initial shear adhesive strength was good at 380 N / cm ² . The heat resistance was better than the epoxy-based conductive adhesive (Comparative Examples 4 and 5) used for comparison at a resistance change rate of + 18%. The heat cycle resistance was stable with a resistance value change rate of ± 0% and a shear adhesive force change rate of ± 0%. The formulation and evaluation results are shown in Table 2.

Example 2
In the same manner as in Example 1, the composition shown in Table 2 is used, and in addition to silver powder, Vulcan XC-72 and Vulcan VXC-305 (both manufactured by Cabot Corporation) are blended in addition to silver powder. It was created. Very large specific surface area, good dispersibility can be obtained even if fine carbon black is blended, it has an appropriate viscosity of 450dPa · s at a solid content of 83%, and workability in screen printing and dispenser is also good Met. Moreover, the initial resistance after adhesion (R ₀ ) was 56 mΩ, which was a lower value than Example 1 in the case of using only silver powder as the conductive filler. As shown in Table 2, other physical properties were also good.

Examples 3-6
In the same manner as in Example 1, the compositions shown in Tables 2 and 3 were evaluated. In Example 4, a combination of flaky silver powder and fine spherical silver powder was examined as a conductive filler, but better initial resistance was obtained than in Example 1 of the flaky silver powder alone system. In Example 5, a novolak type epoxy resin having a biphenol structure as a skeleton was used, but a superior shear adhesive force was obtained, and the resistance change rate in heat resistance was extremely good at + 4%. In Example 6, an example in which an epoxy-modified polyester resin was used as a binder resin was shown, but good shear adhesion was obtained. In all the examples, the heat cycle resistance, which was a defect of the conventional epoxy-based conductive adhesive, was also good. The results are shown in Table 2.

Comparative Examples 1-5
A conductive paste was prepared and evaluated in the same manner as in the examples. In Comparative Examples 1 and 2, the binder resin is a combination of a polyester resin and a blocked isocyanate as a curing agent, but the heat cycle resistance is good, but the initial shear adhesion is insufficient, and the heat resistance is remarkably high. It is bad. Although the comparative example 3 uses comparative polyester resin with a low acid value, the adhesive force and heat resistance are getting worse. Comparative Example 4 is an example of a silver paste using a bisphenol A epoxy resin, but the shear adhesive strength and heat resistance are relatively good, but the heat cycle resistance is poor. Comparative Example 5 is a silver carbon paste using a phenol novolac-type epoxy resin, but it is difficult to achieve high solid differentiation required as a conductive adhesive, its viscosity is remarkably high, its variability is high, and its workability is poor. Even in this example, the heat cycle resistance is poor. The results are shown in Tables 4 and 5.

  The conductive paste of the present invention is a polyester resin and / or modified copolymer of aromatic dicarboxylic acid of 50 mol% or more when the acid value as binder resin is 10 equivalent / t or more and the total carboxylic acid component is 100 mol%. A conductive paste characterized in that it contains a polyester resin (B) and an epoxy resin (C). It has excellent heat resistance and heat cycle resistance, both of which have been difficult to achieve at the same time. Even when a conductive filler having a high specific surface area such as black is used, a conductive paste having low viscosity and good workability can be obtained. The conductive paste of the present invention is suitable as a conductive adhesive or conductive coating agent for various electronic components as well as for rigid substrates, flexible substrates such as polyimide, and PET membrane circuits.

Claims (6)

  In the conductive paste in which the conductive filler (A) is dispersed in the binder resin, when the acid value as the binder resin is 10 equivalent / t or more and the total carboxylic acid component is 100 mol%, the aromatic dicarboxylic acid is A conductive paste comprising a polyester resin and / or a modified polyester resin (B) copolymerized by 50 mol% or more and an epoxy resin (C).   The polyester resin and / or the modified polyester resin (B) is selected from neopentyl glycol, 2-methyl-1,3-propanediol, alicyclic glycol, and aliphatic glycol having 5 to 10 carbon atoms in the main chain as a glycol component. The conductive paste according to claim 1, wherein at least one kind is copolymerized in an amount of 20 mol% or more.   The conductive paste according to claim 1 or 2, wherein the epoxy resin (C) is a novolac type epoxy resin.   The blending mass ratio (B) / {(B) + (C)} of the polyester resin and / or the modified polyester resin (B) and the epoxy resin (C) is 0.3 or more and 0.95 or less. The conductive paste according to any one of claims 1 to 3.   Furthermore, an imidazole-type compound is contained, The electrically conductive paste in any one of Claims 1-4 characterized by the above-mentioned.   The conductive paste according to any one of claims 1 to 5, wherein the conductive filler (A) contains silver powder and carbon black and / or graphite.