JP5579510B2 - Conductive epoxy resin composition and conductive epoxy resin sheet - Google Patents

Description

The present invention relates to a conductive epoxy resin composition having high conductivity and flexibility, and a conductive epoxy resin sheet.

Epoxy resins become infusible and insoluble three-dimensional cross-linked cured products when reacted, and are widely used as high-performance, multifunctional resins with features such as high mechanical strength, high heat resistance, high insulation, and high chemical resistance. It is used for various purposes.

On the other hand, since epoxy resins generally have hard and brittle properties, it is difficult to form into a sheet, and even if it can be formed, cracking and chipping of the sheet during handling become a problem.
Patent Document 1 discloses a technique in which an epoxy resin is formed into a sheet shape, and flexibility and flexibility imparting by adding an elastomer component is a common technique for improving the brittleness of the epoxy resin.

JP 2008-260845 A

However, the softening by the addition of these elastomer components has a problem of greatly reducing the heat resistance and chemical resistance of the epoxy resin. Further, when it is desired to impart high conductivity to the resin sheet, it is necessary to add about tens of parts by mass of an inorganic substance generally called a conductive filler. In this case, the flexibility of the resin sheet has been remarkably lowered.

The present invention is a conductive epoxy resin composition having excellent conductivity and flexibility that can be formed into a sheet shape, and a conductive epoxy resin sheet.

The present invention is a conductive epoxy resin composition containing an epoxy resin, an acid anhydride curing agent, a curing catalyst, and carbon fiber, and the epoxy resin has a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, and a triazine skeleton. The epoxy resin has an epoxy equivalent of 200 or less, the acid anhydride curing agent has an ether bond in the molecule, and (acid anhydride equivalent number) / (epoxy equivalent) Number) is 0.1 to 1.0,
The curing catalyst is tetrabutylphosphonium decanoate capable of curing epoxy resin alone, the average fiber length of carbon fibers is 100 μm or less, and the value of (carbon fiber length) / (carbon fiber diameter) is 50 or more. It is a conductive epoxy resin composition.

The average fiber length of the carbon fiber is preferably 100 μm or less, and the value of (carbon fiber length) / (carbon fiber diameter) is preferably 50 or more.

Another invention is a conductive epoxy resin sheet in which the above-described conductive epoxy resin composition is formed into a sheet shape.

The conductive epoxy resin composition concerning this invention has high electroconductivity by the said structure. The conductive epoxy resin sheet which is another invention has high conductivity and flexibility.

Hereinafter, the present invention will be described in detail.

The present invention is a conductive epoxy resin composition containing an epoxy resin, an acid anhydride curing agent, a curing catalyst, and carbon fiber, and the epoxy resin has a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, and a triazine skeleton. The epoxy resin has an epoxy equivalent of 200 or less, the acid anhydride curing agent has an ether bond in the molecule, and (acid anhydride equivalent number) / (epoxy equivalent) Number) is 0.1 to 1.0,
The curing catalyst is tetrabutylphosphonium decanoate capable of curing epoxy resin alone, the average fiber length of carbon fibers is 100 μm or less, and the value of (carbon fiber length) / (carbon fiber diameter) is 50 or more. It is a conductive epoxy resin composition.

In the present invention, the epoxy resin has an epoxy equivalent of 200 or less, and examples thereof include bisphenol A type epoxy resins, bisphenol F type epoxy resins, epoxy resins having a triazine skeleton, and mixtures thereof. Since these have a benzene ring or triazine skeleton in the molecular skeleton, they can have a rigid structure when cured, and use these epoxy resins with a relatively short molecular chain with an epoxy equivalent of 200 or less. As a result, the crosslink density was increased, and various physical properties such as mechanical strength, heat resistance, and chemical resistance could be increased.

In the present invention, examples of the acid anhydride curing agent include compounds having an ether bond in the molecule. By including an ether bond, the molecular skeleton of the entire epoxy resin composition is made flexible, and the glass transition temperature of the entire epoxy resin composition is lowered, thereby giving the flexibility to mold the epoxy resin composition into a sheet. I was able to.

Examples of the acid anhydride having an ether bond in the molecule include a compound obtained by reacting an acid anhydride at the end of a polyether skeleton having propylene oxide, ethylene oxide or the like as a repeating unit, and preferably an acid anhydride having a propylene oxide skeleton. It is a thing.

In the present invention, the addition amount of the acid anhydride curing agent having an ether bond in the molecule can be selected within the range where (acid anhydride equivalent number) / (epoxy equivalent number) is 0.1 to 1.0. Since the resin composition has a flexible ether bond in the structure, the resin composition can have a sheet forming flexibility.
Since the equivalent weight is the molecular weight per functional group, the number of equivalents is a value obtained by dividing the weight of the resin used by the equivalent weight. For example, when the epoxy resin is 100 parts by mass and the acid anhydride curing agent is 20 parts by mass, the epoxy resin has an epoxy equivalent of 185 and the acid anhydride has an acid anhydride equivalent of 330.
The epoxy equivalent number is 100/185 = 0.541.
The number of acid anhydride equivalents is 20/330 = 0.061
And (acid anhydride equivalent number) / (epoxy equivalent number) is 0.112.
The closer the value of (acid anhydride equivalent number) / (epoxy equivalent number) is to 0.1, the better the heat resistance and chemical resistance, and the value of (acid anhydride equivalent number) / (epoxy equivalent number) is 1.0. The closer it is, the more flexible it is. In the case of the addition amount of the curing agent having a value of (acid anhydride equivalent number) / (epoxy equivalent number) of 0.1 or less, the epoxy resin composition is hard because the number of ether bonds contained in the structure is too small. It becomes brittle and cracks and chips occur during sheet molding. In the case of the addition amount of the curing agent having a value of (acid anhydride equivalent number) / (epoxy equivalent number) of 1.0 or more, the unreacted curing agent remains, which may hinder the performance of the epoxy resin composition. There is.

In the present invention, examples of the curing catalyst include tetrabutylphosphonium decanoate capable of curing the epoxy resin according to claim 1 alone. These compounds not only promote the reaction between the epoxy resin and the acid anhydride curing agent, but can be cured by the epoxy resin alone, so the amount of acid anhydride curing agent added is less than the equivalent of the epoxy resin However, a cured product can be produced without leaving an uncured epoxy resin.

Examples of imidazole compounds include 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5- Examples thereof include hydroxymethylimidazole and 2-phenyl-4,5-dihydroxymethylimidazole. Examples of the tetraalkylphosphonium carboxylate of formula 1 include tetra-n-butylphosphonium acetate.

When the addition amount of the curing catalyst is small, there is a problem that the epoxy resin curing is not sufficiently progressed or the curing is very slow, and when it is large, there is a problem that the usable time is shortened. Therefore, the lower limit of the addition amount of the curing accelerator with respect to 100 parts by mass of the compounding member in which the epoxy resin and the curing agent are mixed is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and the upper limit is preferably 20 parts by mass or less, more preferably 10 parts by mass or less.

In the present invention, examples of the material imparting conductivity include carbon fibers having an average fiber length of 100 μm or less and a value of (carbon fiber length) / (carbon fiber diameter) of 50 or more. By adding carbon fiber having a large ratio of carbon fiber length to carbon fiber diameter, contact between carbon fibers is increased, and dispersion for obtaining conductivity is facilitated. Therefore, (carbon fiber length) / (carbon The value of the fiber diameter) is preferably 50 or more, more preferably 100 or more.

The amount of carbon fiber added is preferably 100 parts by mass of the compounding member in which the epoxy resin and the curing agent are mixed. Thus, the amount added is preferably 0.5 parts by mass to 20 parts by mass, more preferably 3 parts by mass to 10 parts by mass. If the amount of carbon fiber added is small, the volume resistivity tends to increase, and the necessary conductivity cannot be obtained in some cases. If the amount of carbon fiber added is large, a problem arises in that it cannot be formed into a sheet due to an increase in viscosity.

Moreover, the flexible conductive epoxy resin sheet was able to be obtained by forming the above-mentioned conductive epoxy resin composition in a sheet form. Here, although described as a sheet, a film having a thickness of several μm is also included.
Forming into a sheet form includes a method of coating a release film, extrusion molding, injection molding, and laminate molding.

A curing accelerator, a discoloration inhibitor, and a surfactant can be appropriately blended with the above-described epoxy resin composition as long as the composition is not affected.

Examples of the present invention will be described with reference to Table 1 using comparative examples.
(Reference Example 1)

<Preparation of conductive epoxy resin composition>
The conductive epoxy resin composition according to this example is composed of 100 parts by mass of a bisphenol A type epoxy resin (ep828, epoxy equivalent 185 manufactured by Japan Epoxy Resin Co.) as an epoxy resin, and an acid anhydride curing agent (manufactured by Shin Nippon Rika Co., Ltd.). 20 parts by mass of Ricacid HF-08 (registered trademark), acid anhydride equivalent 330), 5 parts by mass of an imidazole compound (2E4MZ-CN manufactured by Shikoku Kasei Co., Ltd.) as a curing catalyst, carbon fiber (VGCF-S manufactured by Showa Denko KK) (Registered Trademark)) 10 parts by mass and a leveling agent (BYK300 (Registered Trademark) manufactured by Big Chemie) as an additive are produced in 1 part by mass. In production, members other than carbon fiber were mixed in advance, and then the carbon fiber was mixed using a planetary mixer in an environment of 25 ° C. and passed through a 25 ° C. three roll.
The number of epoxy equivalents in Reference Example 1 is 100 parts by mass / 185 epoxy equivalents = 0.541.
The number of acid anhydride equivalents is 20 parts by mass / 330 acid anhydride equivalents = 0.061.
And (number of acid anhydride equivalents) / (epoxy equivalent number) is 0.112.
The carbon fiber has an average fiber length of 12.5 μm and a value of (carbon fiber length) / (carbon fiber diameter) of 156.3.

<Preparation of conductive epoxy resin sheet>
This epoxy resin composition was applied onto a 0.05 mm thick PET (polyethylene terephthalate) film so that the thickness after curing was 0.10 mm, and dried by heating at 150 ° C. for 180 minutes. Thus, a conductive epoxy resin sheet was produced.

<Evaluation of conductive epoxy resin sheet>
The following methods were used to evaluate (1) volume resistivity (2) sheet bendability.
(1) The volume resistivity of the volume resistivity sheet was measured according to JIS K 6911, 5.13. 1.0 × 10 ⁴ Ω · cm or less is preferable.
(2) Sheet bendability A sheet cut into a strip shape having a width of 10 cm and a length of 20 cm was wound around a cylinder with a radius of 2 cm, and the presence or absence of cracking of the sheet was evaluated. The fact that there is no sheet cracking is indicated as “good” in Table 1 as acceptable for the bendability, and x when the sheet cracking was confirmed visually.
As shown in Table 1, Reference Example 1 was good in both volume resistivity and sheet bendability.
(Reference Example 2)

Reference Example 2, the epoxy resin of Example 1, bisphenol F type epoxy resin (Japan Epoxy Resins Co., Ltd. Ep807, epoxy equivalent 173) except that in, those similar to Reference Example 1. In Reference Example 2, both volume resistivity and sheet bendability were good.
(Reference Example 3)

Reference Example 3, the epoxy resin of Reference Example 1, an epoxy resin having a triazine skeleton (manufactured by Nissan Chemical Industries, Ltd. TEPIC-PAS B26 (registered trademark), epoxy equivalent 138) except that in, those similar to Reference Example 1 . In Reference Example 3, both volume resistivity and sheet bendability were good.
(Reference Example 4)

Reference Example 4, except that the blending ratio of the acid anhydride curing agent of Example 1 was 178 parts by mass, that of Example 1. In Reference Example 4, both volume resistivity and sheet bendability were good.
(Example 5)

Example 5, a curing catalyst of Reference Example 1, except that the tetraalkylphosphonium carboxylates (Hokko Chemical Co., Ltd. TBP-DA) 3 mass, those similar to Reference Example 1. In Example 5, both volume resistivity and sheet bendability were good.
(Reference Example 6)

Reference Example 6, the carbon fiber of Example 1 and manufactured by Showa Denko KK VGCF-X (TM), except that the the mixing ratio 6 parts by those similar to Reference Example 1. In Reference Example 6, both volume resistivity and sheet bendability were good.

(Comparative Example 2)
Comparative Example 2, a curing catalyst of Reference Example 1, except that the phosphorus compound (Hokko Chemical Industry Co., Ltd. TPP) 3 parts by mass, those similar to Reference Example 1. In Comparative Example 2, the reaction of the epoxy resin did not proceed and the sheet could not be molded.

(Comparative Example 3)
Comparative Example 3, carbon black (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha Denka Black (registered trademark)) of carbon fiber of Reference Example 1 except for using 33 wt those similar to Reference Example 1. Comparative Example 3 had a remarkably high viscosity and could not be formed into a sheet.

(Comparative Example 4)
Comparative Example 4, the carbon fiber of Example 1, and Teijin Ltd. Raheama (registered trademark) 201, except that the blending ratio of 40 wt those similar to Reference Example 1. In Comparative Example 4, the volume resistivity was large and the conductivity was insufficient.
(Reference Example 7)

Although Reference Example 7 was not described in Table 1, the average fiber length of the carbon fiber of Reference Example 1 was 110 μm, and the value of (carbon fiber length) / (carbon fiber diameter) was 50. . In this configuration, the volume resistivity and the sheet bendability were both good, but when there was an aggregate of carbon fibers due to insufficient kneading, appearance defects such as protrusions on the surface during sheet formation The point that was seen was a drawback.

(Comparative Example 5)
Although Comparative Example 5 was not described in Table 1, the compounding ratio of the acid anhydride curing agent of Reference Example 1 was 200 parts by mass, and (acid anhydride equivalent number) / (epoxy equivalent number) was 1.121. Other than the above, it is that of Reference Example 1. In Comparative Example 5, the acid anhydride curing agent that did not react remained, and the sheet was poorly folded.

The present invention is a conductive epoxy resin composition and a conductive epoxy resin sheet that have excellent conductivity and can be molded into a sheet shape, and are applied as a conductive member of an electronic circuit board.

Claims (3)

An epoxy resin, an acid anhydride curing agent, a curing catalyst, and a conductive epoxy resin composition containing carbon fiber,
The epoxy resin includes one or more of a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, and an epoxy resin having a triazine skeleton,
The epoxy equivalent of the epoxy resin is 200 or less, the acid anhydride curing agent has an ether bond in the molecule, and (acid anhydride equivalent number) / (epoxy equivalent number) is 0.1 to 1.0. ,
The curing catalyst is tetrabutylphosphonium decanoate capable of curing epoxy resin alone,
The conductive epoxy resin composition whose average fiber length of carbon fiber is 100 micrometers or less, and the value of (carbon fiber length) / (diameter of carbon fiber) is 50 or more. The conductive epoxy resin composition according to claim 1, wherein the curing catalyst is 3 to 5 parts by mass with respect to 100 parts by mass of the epoxy resin. The electroconductive epoxy resin sheet which formed the electroconductive epoxy resin composition of Claim 1 or Claim 2 in the sheet form.