JP2643646B2 - Conductive epoxy paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive epoxy paste which gives a cured product having excellent properties such as thermal shock resistance and heat dissipation.

[0002]

2. Description of the Related Art Generally, a conductive paste is prepared by blending a heat-curable or ultraviolet-curable resin such as a low molecular weight epoxy resin, an epoxy acrylate resin or an unsaturated polyester resin with a conductive powder such as a metal powder or carbon. Manufactured. However, these conductive epoxy pastes have a low glass transition temperature (Tg) and thus have low heat resistance, and their applications are limited. In addition, a conductive paste having a high Tg is also commercially available, but in this case, the cured product has a small elongation and a low thermal shock resistance .

A method for producing a high-molecular-weight epoxy resin from a relatively low-molecular-weight bifunctional epoxy resin and a difunctional phenol is generally referred to as a two-stage method, and the first document relating to this method is disclosed in US Pat. No. 2,615,008, and in Japan, Japanese Patent Publication No. 28-4494 by the same applicant. In this document, sodium hydroxide is used as a polymerization catalyst, and 150 to 2
By reacting at 00 ° C., the epoxy equivalent becomes 5,6.
00 high molecular weight epoxy resin. The average molecular weight of this resin can be estimated to be about 11,000. As a reference described by using a solvent, there is US Pat. No. 3,306,872.

In US Pat. No. 3,306,872, either methyl ethyl ketone or ethylene glycol monomethyl ether is used as a solvent, and the solution has a solid content of 20 to 60%. As the catalyst, a hydroxide or phenolate of an alkali metal or benzyltrimethylammonium is used. Further, the polymerization reaction temperature is set to 75 to 150 ° C., and the reaction is continued until the weight average molecular weight of the produced high molecular weight epoxy resin becomes at least 40,000 or more. The average molecular weight is determined by a viscosity method, and is measured as 50,000 to 1,000,000. However, the viscosity method is known to greatly affect the calculated value depending on the setting of parameters used in the calculation, and therefore it cannot be said that accurate measurement is always performed.

An example in which a high molecular weight epoxy resin is considered to be obtained by polymerization in a solvent is disclosed in Japanese Patent Application Laid-Open No. 52200/1979 using ethylene glycol monoethyl ether as a solvent. To obtain a high molecular weight epoxy resin having a molecular weight of 45,000. JP-A-60-118575 describes that a high molecular weight epoxy resin having an average molecular weight of at most 31,000 is obtained by using methyl isobutyl ketone, cyclohexanone, and ethylene glycol monoethyl ether as a solvent. JP-A-60-144323 discloses that a high molecular weight epoxy resin having an average molecular weight of 53,200 can be obtained by using methyl ethyl ketone as a solvent, and JP-A-60-144324 discloses that methyl ethyl ketone is used as a solvent. To obtain a high molecular weight epoxy resin having an average molecular weight of 66,000. In the above four patent documents, the average molecular weight is measured by gel permeation chromatography, but the measurement conditions and calculation method are not described. The molecular weight obtained by gel and penetration chromatography, type of filler used, varies greatly depending on the measurement conditions and calculation methods such as the type of the eluent, not necessarily accurate value is measured. Such a conventionally known high molecular weight epoxy resin is not a linear high molecular epoxy resin but a branched high molecular epoxy resin, and cannot form a film having sufficient strength. .

[0006]

In the prior art, a conductive epoxy paper having both heat resistance and thermal shock resistance has been proposed.
The strike could not be made. The present invention applies a high-molecular-weight epoxy polymer, which has been polymerized linearly to have a film-forming ability, to a base material of a conductive epoxy paste, thereby achieving heat resistance and heat resistance that have not existed before. An object of the present invention is to provide a conductive epoxy paste having impact properties.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a bifunctional epoxy resin and a difunctional phenol which are prepared by mixing the bifunctional epoxy resin and the difunctional phenol with an equivalent ratio of epoxy group / phenol.
Hydroxyl group = 1: 0.9-1.1, obtained by heating and polymerizing in an amide-based or ketone-based solvent having a boiling point of 130 ° C. or more at a reaction solid concentration of 50% by weight or less in the presence of a catalyst. It is characterized in that a polyfunctional epoxy resin, a curing agent and a conductive powder or fiber are mixed with a linear high molecular weight epoxy polymer having a reduced viscosity of 0.70 dl / g or more . Hereinafter, the present invention will be described in detail.

The bifunctional epoxy resin in the present invention may be any compound as long as it is a compound having two epoxy groups in a molecule. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin , Bispheno-
S-type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, diglycidyl etherified bifunctional phenols, diglycidyl etherified bifunctional alcohols, and their halides, hydrogen There are additives and the like. These compounds can have any molecular weight. Some of these compounds can be used in combination, and components other than the bifunctional epoxy resin may be contained as impurities.

The bifunctional phenols in the present invention may be any compounds having two phenolic hydroxyl groups, such as hydroquinone, resorcinol and monocyclic bifunctional phenol. Examples include catechol, bisphenol A, which is a polycyclic bifunctional phenol, bisphenol F, naphthalene diols, bisphenols, and halides and alkyl-substituted products thereof. These compounds can have any molecular weight. Some of these compounds can be used in combination. Components other than the bifunctional phenols may be contained as impurities.

The catalyst which can be used in the present invention may be any compound having a catalytic ability to promote the etherification reaction between an epoxy group and a phenolic hydroxyl group.
For example, alkali metal compounds, alkaline earth metal compounds,
There are imidazoles, organic phosphorus compounds, secondary amines, tertiary amines, quaternary ammonium salts and the like. Of these, alkali metal compounds are the most preferred catalysts, and examples of alkali metal compounds include sodium, lithium, and potassium hydroxides , organic acid salts, alcoholates, phenolates, hydrides, borohydrides, and amides. These catalysts can be used in combination.

The reaction solvent used in the present invention is preferably an amide-based or ketone-based solvent. As the amide-based solvent, a solvent having a boiling point of 130 ° C. or more and dissolving the starting epoxy resin and phenols can be used. Without limitation, for example, formamide, N-methylformamide,
N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide,
N, N, N ', N'-tetramethylurea, 2-pyrrolidone, N-methylpyrrolidone, carbamic acid esters and the like. These solvents can be used in combination. Further, it may be used in combination with other solvents represented by ketone solvents, ether solvents and the like. Examples of the ketone-based solvent include cyclohexanone, acetylacetone, diisobutylketone, holon, isophorone, methylcyclohexanone, and acetophenone.

The conditions for synthesizing the polymer in the present invention are as follows: the blending equivalent ratio of the bifunctional epoxy resin to the bifunctional phenols is as follows: epoxy group / phenolic hydroxyl group = 1: 0.9
１．１1.1 . When the amount is less than 0.9 equivalent, a side reaction occurs without causing a high molecular weight in a linear form, resulting in crosslinking and insolubility in a solvent. If it is more than 1.1 equivalents, the high molecular weight does not progress.
The amount of the catalyst is not particularly limited, but is generally about 0.0001 to 0.2 mol per 1 mol of the epoxy resin. When the amount is less than this range, the reaction for increasing the molecular weight is remarkably slow. The polymerization temperature is desirably 60 to 150 ° C. When the temperature is lower than 60 ° C., the reaction for increasing the molecular weight is remarkably slow, and when the temperature is higher than 150 ° C., side reactions increase and the molecular weight is not increased linearly. The solid content concentration in the polymerization reaction using a solvent may be 50% or less, but is preferably 40% or less.
% Or less is good. More preferably, it is desirable to make it 30% or less. As the concentration increases, side reactions increase and it becomes difficult to increase the molecular weight in a linear manner. Therefore, when a polymerization reaction is performed at a relatively high concentration and a linear high molecular weight epoxy resin is to be obtained, it is necessary to lower the reaction temperature and reduce the amount of the catalyst.

The polyfunctional epoxy resin in the present invention may be any compound as long as it has two or more epoxy groups in the molecule. For example, bisphenol A epoxy resin, bisphenol F epoxy resin Resin, bisphenol S epoxy resin, phenol novolak epoxy resin, cresol novolak epoxy resin, bisphenol A novolak epoxy resin, bisphenol
Le F novolak type epoxy resin, alicyclic epoxy resin,
Aliphatic chain epoxy resin, glycidyl ester type epoxy resin, glycidylamine type epoxy resin, hydantoin type epoxy resin, isocyanurate type epoxy resin,
In addition, diglycidyl ether compounds of bifunctional phenols, diglycidyl ether compounds of bifunctional alcohols,
And their halides and hydrogenated products.
These compounds can have any molecular weight. Some of these compounds can be used in combination. Further, components other than the polyfunctional epoxy resin may be contained as impurities.

The curing agent used in the present invention may be any one as long as it can cure an epoxy resin. Representative examples thereof include polyfunctional phenols, amines, imidazole compounds, and acid anhydrides. and so on. Examples of polyfunctional phenols include monocyclic bifunctional phenols such as hydroquinone, resorcinol, catechol, and polycyclic bifunctional phenols such as bisphenol A and bisphenol F.
Examples include naphthalene diols, bisphenols and their halides and alkyl group-substituted products. Further, there are novolaks and resols which are polycondensates of these phenols and aldehydes. Examples of amines include aliphatic primary, secondary, and tertiary amines, aromatic primary,
There are secondary and tertiary amines, guanidines, urea derivatives and the like, and specific examples include triethylenetetramine, diaminodiphenylmethane, diaminodiphenylether, dicyandiamide, tolylbiguanide, guanylurea, and dimethylurea. Examples of imidazole compounds include:
Examples include alkyl-substituted imidazole and benzimidazole. Examples of the acid anhydride include phthalic anhydride, hexahydrophthalic anhydride, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride and the like. In addition to the above polyfunctional epoxy resin and curing agent, a curing accelerator, a flame retardant and the like may be blended. Curing accelerators include tertiary amines, imidazoles, and quaternary ammonium salts. Examples of the flame retardant include bromine compounds such as tetrabromobisphenol A, decabromodiphenyl ether, brominated epoxy resin and brominated phenol resin, and metal hydroxides such as aluminum hydroxide and magnesium hydroxide. These high molecular weight epoxy polymers, polyfunctional epoxy resins, curing agents, and curing accelerators may be mixed by any method.

As the conductive powder or fiber in the present invention, any conductive powder or fiber may be used, but those having relatively high electric conductivity and relatively high corrosion resistance are preferred. For example, metals such as gold, silver, copper, nickel,
In addition to transition metals such as cobalt, iron, chromium, tungsten, platinum, and zinc, there are aluminum, tin, indium, magnesium, and the like. Other examples include carbon, graphite, zinc oxide and tin oxide. The average particle size of these conductive powders may be 50 μm or less, but is preferably 10 μm or less. The average fiber length of these conductive fibers is 100
It is sufficient if it is not more than μm, but preferably not more than 20 μm. Some of the above conductive powders or fibers can be used in combination. The compounding amount may be 10% or more as the content in the conductive epoxy paste. However, in order to provide sufficient conductivity, it is necessary to mix 20% or more. In addition to all these ingredients, a new solvent may be added. The order of blending, the temperature during blending, and the blending method may be any methods. The conductive epoxy paste obtained by the above-mentioned method is a high thermal conductive paste having both heat resistance and thermal shock resistance and excellent characteristics which have not been obtained in the past.

[0016]

The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 177.5 g of bisphenol A type epoxy resin (epoxy equivalent: 177.5) as a bifunctional epoxy resin and bisphenol A (hydroxyl equivalent:
115.5) 115.5 g, and sodium hydroxide 1.77 g as an etherification catalyst were added to N, N-
It was dissolved in dimethylacetamide 547.9G, and the solid concentration in the reaction system with 35%. While mechanically stirring the mixture, the temperature in the reaction system was kept at 120 ° C. in an oil bath, and kept for 4 hours. As a result, the viscosity was 19,7
The reaction was saturated at 00 mPa · s, and the reaction was completed. The weight average molecular weight of the obtained high molecular weight epoxy polymer was 133,0 as a result of measurement by gel permeation chromatography.
00, 129,00 as a result of measurement by the light scattering method.
It was 0. The reduced viscosity of the diluted solution is 1.08 dl /
g. To this high molecular weight epoxy polymer solution, 146 g of a cresol novolak type epoxy resin (epoxy equivalent: 198) as a polyfunctional epoxy resin, 78 g of phenol novolak (hydroxyl equivalent: 106) as a curing agent,
Carbon black having an average particle size of 0.5 μm as conductive particles was blended at a ratio of 30 g with respect to 70 g of resin solid content, and stirred mechanically at 150 ° C. for 1 h. Next, 0.72 g of 2-ethyl-4-methylimidazole was added as a curing accelerator, and the mixture was mechanically stirred at 150 ° C. for 1 minute to obtain a conductive epoxy paste. The obtained paste was applied on an epoxy insulating plate, and heated and dried in a dryer at 170 ° C. for 1 hour to cure the conductive epoxy paste. The paste paste had a volume resistance of 8 Ω · cm, a Tg of 138 ° C, and a thermal decomposition temperature of 378 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 150 cycles.

[0018] Instead of blending the carbon black having an average particle diameter of 0.5μm in (Example 2) Example 1, except that the silver powder having an average particle size of 2.5μm was 80g formulated against resin solids 20g, Example 1 In the same manner as in the above, a conductive epoxy paste was obtained. Pe
The volume resistance of the cured cured product is 8.1 × 10 ⁻³ Ω · cm, T
g was 141 ° C and the thermal decomposition temperature was 375 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 120 cycles.

[0019] Instead of blending the carbon black having an average particle diameter of 0.5μm in (Example 3) Example 1, except that a nickel powder having an average grain size of 2.0μm and 80g formulated against resin solids 20g, Example In the same manner as in Example 1, a conductive epoxy paste was obtained. The paste has a volume resistance of 1.4 × 10 ⁻³ Ω ·
cm, Tg was 143 ° C., and the thermal decomposition temperature was 372 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 110 cycles.

( Example 4 ) Instead of blending carbon black having an average particle diameter of 0.5 μm in Example 1, 80 g of tin oxide powder having an average particle diameter of 4.0 μm was blended with respect to 20 g of a resin solid content.
In the same manner as in Example 1, a conductive epoxy paste was obtained.
The volume resistance of the cured paste is 6.9 × 10 ⁶ Ω · c.
m and Tg were 136 ° C, and the thermal decomposition temperature was 375 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 160 cycles.

[0021] was used in place N in (Example 5) Example 1, the N- dimethylacetamide in cyclohexanone, was subjected to the same synthesis of high molecular weight epoxy polymer of Example 1. As a result, the viscosity was saturated at 8,500 mPa · s, and the reaction was completed. The weight average molecular weight of the obtained high molecular weight epoxy polymer was 8 as measured by gel permeation chromatography.
9,000 and 84, according to the result measured by the light scattering method.
000. The reduced viscosity of the dilute solution is 0.91d
1 / g. In this high molecular weight epoxy polymer solution,
146 g of a cresol novolak type epoxy resin (epoxy equivalent: 198) as a polyfunctional epoxy resin, and phenol novolak (hydroxyl equivalent: 106) 78 as a curing agent
g, carbon black having an average particle size of 0.5 μm as conductive particles was blended at a ratio of 30 g to 70 g of resin solid content, and mechanically stirred at 150 ° C. for 1 h. Next, 2-ethyl-4-methylimidazole 0.72 as a curing accelerator
g was mechanically stirred at 150 ° C. for 1 minute to obtain a conductive epoxy paste. The obtained paste was applied on an epoxy insulating plate, and heated and dried in a dryer at 170 ° C. for 1 hour to cure the conductive epoxy paste. The cured paste has a volume resistance of 25 Ω · cm, Tg
Was 139 ° C and the thermal decomposition temperature was 370 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 170 cycles.

[0022] Instead of blending the carbon black having an average particle diameter of 0.5μm in Example 6 Example 5, except that the silver powder having an average particle size of 2.5μm was 80g formulated against resin solids 20g, Example 1 In the same manner as in the above, a conductive epoxy paste was obtained. Pe
The volume resistance of the cured product is 3.4 × 10 ⁻⁴ Ω · cm, T
g was 143 ° C, and the thermal decomposition temperature was 365 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 130 cycles.

( Example 7 ) Instead of blending carbon black having an average particle size of 0.5 μm in Example 5, 80 g of silver powder having an average particle size of 2.5 μm was blended with respect to 20 g of resin solid content, and tetrabromobisphenol A was further added. Was added in the same manner as in Example 5 except that 5 g was added to obtain a conductive epoxy paste. Pe
The volume resistance of the cured product is 7.6 × 10 ⁻⁴ Ω · cm, T
g was 131 ° C and the thermal decomposition temperature was 345 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 100 cycles.

[0024] (Comparative Example 1) except for not blending the carbon black in the first embodiment, in the same manner as in Example 1, Epokishipe - obtain a strike. The paste has a volume resistance of 3.2 × 10 ¹⁵ Ω · cm,
Tg was 140 ° C and thermal decomposition temperature was 380 ° C.

( Comparative Example 2 ) Phenoxy resin YP50 which is a high molecular weight epoxy polymer
The average molecular weight of P (Toto Kasei) was measured. The weight average molecular weight in terms of styrene by gel permeation chromatography is
68,000, average molecular weight by light scattering method is 58,000
00. The reduced viscosity of the dilute solution is 0.48 dl
/ G. This resin readily dissolved in methyl ethyl ketone. The viscosity of a 20% solution of N, N-dimethylacetamide was 200 mPa · s. A cresol novolak type epoxy resin (epoxy equivalent: 19) was added to this high molecular weight epoxy polymer solution as a polyfunctional epoxy resin.
8) 148 g, 78 g of phenol-novolak (hydroxyl equivalent: 106) as a curing agent, and aluminum having an average particle size of 1.5 μm as conductive particles were added to 20 g of resin solids.
0 g were blended and mechanically stirred at 150 ° C. for 1 h. Next, 2-ethyl-4-methylimidazole 0.1 as a curing accelerator was used.
72 g were blended and mechanically stirred at 150 ° C. for 1 minute to obtain a conductive epoxy paste. The paste obtained was applied on an epoxy insulating plate and dried at 170 ° C./1 in a drier.
The conductive epoxy paste was cured by heating and drying for h. The volume resistance of the cured paste is 8.2 × 1
0 ⁻³ Ω · cm 2 , Tg 134 ° C., thermal decomposition temperature 37
Was 6 ℃.

( Comparative Example 3 ) Phenoxy resin Epon, which is a high molecular weight epoxy polymer
The average molecular weight of o155L32 (shell) was measured. The weight average molecular weight in terms of styrene by gel permeation chromatography was 62,000, and the average molecular weight by light scattering method was 51,000. The reduced viscosity of the dilute solution was 0.44 dl / g. This resin readily dissolved in methyl ethyl ketone. The viscosity of the N, N-dimethylacetamide 20% solution was 180 mPa · s. To this high molecular weight epoxy polymer solution, 146 g of a cresol novolak type epoxy resin (epoxy equivalent: 198) as a polyfunctional epoxy resin, 78 g of phenol novolak (hydroxyl equivalent: 106) as a curing agent, and an average particle size of 0.1 as conductive particles. 5 μm of carbon black was blended at a ratio of 30 g to 70 g of the resin solid content, and the mixture was mechanically stirred at 150 ° C. for 1 h. Next, 0.72 g of 2-ethyl-4-methylimidazole was blended as a curing accelerator,
The mixture was stirred mechanically at C for 1 minute to obtain a conductive epoxy paste. The obtained paste was applied on an epoxy insulating plate, and heated and dried in a dryer at 170 ° C. for 1 hour to cure the conductive epoxy paste. The cured paste had a volume resistance of 11 Ω · cm, a Tg of 136 ° C, and a thermal decomposition temperature of 378 ° C. In the hot oil test, the number of cycles until the volume resistance doubled or more was 10 cycles.

The details of the experimental methods in the above Examples and Comparative Examples are described below. The phenol compounding equivalent is the compounding equivalent of the phenol relative to 1.000 equivalents of the epoxy resin. The viscosity was measured using an EMD type viscometer (Tokyo Keiki). The column used for gel permeation chromatography (GPC) was TSKgel G6000 + G5000.
+ G4000 + G3000 + G2000. N, N-dimethylacetamide was used as the eluent, and the sample concentration was 2%. After obtaining the relationship between the molecular weight and the elution time using styrene of various molecular weights, the molecular weight was calculated from the elution time, and the calculated weight average molecular weight was calculated as styrene. The light scattering photometer used was DLS-700 manufactured by Otsuka Electronics Co., Ltd., and the reduced viscosity of the diluted solution was measured using an Ubbelohde viscometer.
The glass transition temperature (Tg) was measured using a DuPont 910 differential scanning calorimeter (DSC). The pyrolysis temperature is
Using a differential thermal balance TGD-3000 manufactured by Vacuum Riko, the temperature at which weight loss started in air was defined as the thermal decomposition temperature. The hot oil test was performed by dipping in silicone oil at 260 ° C. for 20 seconds and dipping in water at 25 ° C. for 20 seconds to make one cycle. Volume resistance was measured every 10 cycles. As shown in Examples 1 to 7, it is clear that the conductive epoxy paste according to the present invention exhibits sufficient conductivity, heat resistance and thermal shock resistance. Further, as shown in Comparative Examples 2 and 3,
When a phenoxy resin which is a commercially available high molecular weight epoxy polymer is used, the Tg of the cured epoxy paste becomes high, but the thermal shock resistance is remarkably poor.

[0028]

The epoxy paste of the present invention has heat resistance,
Thermal shock resistance of any properties even superior conductivity Epokishipe - a strike.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01B 1/20 H01B 1/20 A (72) Inventor Hiroshi Shimizu 1500 Ogawa Oji, Shimodate-shi, Ibaraki Hitachi (72) Inventor Masami Arai, Shimodate-shi, Ibaraki, 1500, Oji, Hitachi, Ltd. Shimodate Research Laboratory, Hitachi Chemical Co., Ltd. (56) Reference JP-A-58-149914 (JP, A) JP 60-262819 (JP, A)

Claims (5)

(57) [Claims] 1. A blending ratio of a bifunctional epoxy resin and a bifunctional phenol to an epoxy group / phenol hydroxyl group = 1: 0.9 to between the bifunctional epoxy resin and the bifunctional phenol.
The reduced viscosity obtained by heating and polymerizing in an amide-based or ketone-based solvent having a boiling point of 130 ° C. or more at a reaction solid concentration of 50% by weight or less in the presence of a catalyst is 0.70.
A conductive epoxy paste comprising a dl / g or more linear high molecular weight epoxy polymer and a polyfunctional epoxy resin, a curing agent, and a conductive powder or fiber. 2. A high molecular weight epoxy polymer having a weight average molecular weight in terms of styrene of 7 as determined by gel permeation chromatography.
2. The conductive epoxy paste according to claim 1, which has a molecular weight of not less than 000. 3. The conductive epoxy paste according to claim 1, wherein the high molecular weight epoxy polymer has an average molecular weight determined by a light scattering method of 70,000 or more. 4. The conductive powder or fiber is a metal,
Carbon, graphite, zinc oxide, conductive according to any one of claims 1 to 3 is a member selected from the group of tin oxide Epokishipe - strike. 5. A curing agent is a polyfunctional phenol - le, amines or imidazo, - it is a member selected from the group Le compound of claims 1 to 4 according to any Shirubeshirube property Epokishipe - Strike.