JPH038397B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to heat-resistant adhesives. Polyimide adhesives have conventionally been known as adhesives with excellent heat resistance. For example, adhesives whose main component is polyamic acid obtained by reacting pyromellitic acid dianhydride and 4,4-diaminodiphenyl ether, and biphenyltetracarboxylic acid which has a perfluoroisopropylidene group bonded to a phthalic anhydride structure. Adhesives obtained by reacting acid dianhydrides and aromatic diamines are known. However, these aromatic polyamic acid adhesives have poor storage stability in polyamic acid organic solvents, and the molecular weight decreases during storage and insoluble components precipitate, so they must be stored at low temperatures. There were problems with handling. Moreover, although these polyamic acid adhesives are somewhat satisfactory in terms of heat resistance after curing, they cannot be said to be satisfactory in terms of adhesive strength. Furthermore, adhesives made of epoxy resin/silver powder, phenolic resin/silver powder, phenolic resin/carbon black, etc. are conventionally known as conductive adhesives. Among these, Epokin resin adhesives have high adhesive strength, but have a low heat resistance temperature of 150℃, and because they are two-component type, workability is poor, and adhesive strength may vary depending on preparation conditions such as blending ratio. It had the following drawbacks. In addition, phenolic resin adhesive is a one-component type, has strong adhesive strength, and has a heat resistance of 200°C, which is higher than Epoquin resin adhesive.
For the purpose of bonding conductors of electronic materials, conductive adhesives with extremely excellent heat resistance are required, and these adhesives have not been satisfactory for this purpose. For this reason, attempts have been made to add conductive fillers such as metal powder to polyimide adhesives in order to impart conductivity to the polyamic acid adhesives, but this tends to further reduce the adhesive strength. ,
There was a drawback that the amount of conductive filler added was limited due to its relationship with adhesive strength. As a result of intensive research aimed at improving the drawbacks of the above-mentioned conventional adhesives, the present inventors found that an adhesive whose main component is polyamic acid with a specific structure has excellent storage stability, and can be stored for long periods at room temperature. It also has excellent adhesive strength and heat resistance.
Furthermore, the inventors have discovered that even when a conductive filler is added to the adhesive, the adhesive strength is extremely reduced and the adhesive has excellent heat resistance, and the present invention has been achieved. The heat-resistant adhesive of the present invention is characterized in that its main component is polyamic acid obtained by reacting 2,3,5-tricarboxycyclopentyl acetic acid or its anhydride with a diamine. In the present invention, heat resistance and conductivity can be imparted by incorporating a conductive filler into the polyamic acid. 2,3,5-tricarboxycyclopentyl acetic acid (hereinafter referred to as TCA) used in the present invention
For example, a method of ozonolyzing dicyclopentadiene and oxidizing it with hydrogen peroxide (UK patent no.
No. 872355, J.Org.Chem.28(10) 2537-41,
1963), or a method in which hydroxy-dicyclopentadiene obtained by hydrating dicyclopentadiene is oxidized with nitric acid (West German Patent No. 1078120). It is preferable to use TCA in the form of an anhydride (usually dianhydride) from the viewpoint of polymerization reaction. The diamine to be reacted with TCA or its anhydride is a compound represented by the general formula H ₂ N-R-NH ₂ (R is a divalent aliphatic, alicyclic, or aromatic group).
It is. Preferred R in the above general formula is, for example,

【formula】 【formula】

(In the formula, X ₁ , X ₂ , X ₃ , and X ₄ are the same or different and are H or CH ₃ , and Y is CH ₂ , C ₂ H ₄ ,
O,S,

【formula】

[Formula] SO ₂ or CONH, n represents 0 or 1), such as -(CH ₂ ) ₂ -, -(CH ₂ ) ₃ -, -(CH ₂ ) ₄
−, −(CH ₂ ) ₅ −, −(CH ₂ ) ₆ −, −(CH ₂ ) ₇ −, −
(CH ₂ ) ₈ −, −(CH ₂ ) ₉ −,

【formula】

【formula】

【formula】

【formula】

[Formula] It is an aliphatic or alicyclic hydrocarbon group having 6 to 13 carbon atoms or a norbornane derivative hydrocarbon group, and the heat resistance when the adhesive of the present invention is imidized by heat treatment. In order to further improve the properties, R is preferably an aromatic group. Specific examples of the above diamine include paraphenylenediamine, metaphenylenediamine, 4,4'-
Diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 2,2-di(p-aminophenyl)hexafluoropropane, 4,4'-diaminodiphenylpropane, benzidine, 4,4'-diaminodiphenylene Nyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene, 3,
3'-dimethyl-4,4'-diaminobiphenyl,
3,4-diaminobenznialide, 3,4'-diaminodiphenyl ether, 2,3-diaminotoluene, 2,4,-diaminotoluene, 3,4-diaminotoluene, 2,6-diaminotoluene,
3,5-diaminotoluene, 2,5-diaminotoluene, metaxylylenediamine, and paraxylylenediamine, ethylenediamine, propanediamine, tetramethylenediamine, hexamethylenediamine, heptamethylene, octethylenediamine, nonamethylenediamine, 4 , 4'-dimethylheptamethylenediamine, 1,4-diaminocyclohexane, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanilene dimethylenediamine, tricyclo[6,2,1,0 ^2.7 ]- Undecylendimethyldiamine and the like can be mentioned. These can be used alone or in combination. The solvent used for the reaction of these TCA or anhydride with the diamine, or the solvent that can be contained in the adhesive of the present invention, is not particularly limited as long as it dissolves the polyamic acid to be produced. Examples of these solvents include dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone,
Dimethyl sulfoxide, tetramethylurea, γ-
A dipolar polar solvent such as butyrolactone is used. In addition to these solvents, which generally have high boiling points,
A low boiling point solvent can also be mixed and used within a range in which the polyamic acid does not precipitate. Specific examples of these low boiling point solvents include alcohols, phenols, ketones, and ethers, such as ethyl alcohol, isopropyl alcohol, propylene glycol, 1,4'-butanediol, triethylene glycol, and ethylene glycol monomethyl ether. , phenol, cresol, methyl ethyl ketone, tetrahydrofuran, dioxane and the like. Although the reaction ratio of TCA or its anhydride and diamine is preferably carried out in equimolar amounts, the ratio of these monomers may be slightly varied as long as the object of the present invention is achieved. For example, in order to obtain a high molecular weight polyamic acid, a diamine compound is usually added per mole of tetracarboxylic acid or its anhydride.
It is preferable to use about 0.7 to 1.3 mol. Furthermore, the molecular weight can be adjusted by adding a diamine, dicarboxylic acid, or anhydride thereof at one end. In addition, the reaction is usually carried out in a solvent, and the amount of solvent used is 0.5 to TCA or its anhydride and diamine.
~20 times by weight is preferred. The reaction temperature when producing the polyamic acid used in the present invention varies depending on whether TCA or its anhydride is used as a starting material. When TCA is used as a starting material, in order to perform dehydration condensation, It is usually effective to carry out the reaction at a temperature of 50 to 300°C, preferably 100 to 250°C. On the other hand, when TCA anhydride is used as a raw material, it is a polyaddition reaction, and the reaction does not necessarily need to be carried out at a high temperature, and the reaction may normally be carried out at 0 to 100°C. The polyamic acid obtained by the above reaction generally has a repeating structural unit represented by the following general formula () or a repeating structural unit represented by the following general formula () and a repeating structural unit represented by the following general formula (). −R ₂ −CO−HH−R ₁ )−……() (In the formula, R ₁ is a divalent aliphatic, alicyclic or aromatic group, R ₂ is

[expression] or

[Formula]) In addition to the above, there may be some repeating structural units represented by the following general formulas (), (), (), or (). The polyamic acid obtained as described above is easily soluble in a solvent, and even if a part of the polyamic acid is imidized, it is soluble in the solvent, so it is very stable in a solution state. Reduced viscosity of this polyamic acid (concentration 1g/100ml solvent, solvent dimethylacetamide,
The measurement temperature (30° C.) is preferably 0.05 dl/g or more, particularly preferably 0.1 to 100 dl/g. In the present invention, examples of the conductive filler added to polyamic acid include metal powders such as silver, copper, and aluminum, butcher black, acetylene black,
Carbon black such as furnace black, graphite, etc. are used. The form of these conductive fillers is preferably as fine as possible, and is used by adding them to the solvent of the polyamic acid and stirring them to uniformly disperse them in the adhesive. Conductive adhesive is
Generally, the volume resistivity of the adhesive after curing is 1Ω・cm
As shown below, the volume resistivity can be adjusted by adjusting the amount of conductive filler added. The amount of conductive filler added depends on the properties of the conductive filler, but it is 3 parts by weight per 100 parts by weight of polyamic acid.
~150 parts by weight is preferred. If the amount added is less than 3 parts by weight, it will not be possible to obtain a product with excellent conductivity, and if it is more than 150 parts by weight, the adhesive strength will be significantly reduced. In the adhesive of the present invention, preferably 5 to 80% by weight, particularly preferably 10 to 50% by weight of polyamic acid is dissolved in the solvent. It is preferable to use the polymerization solution obtained by the reaction as it is as the adhesive of the present invention from the viewpoint of ease of handling. When using the adhesive of the present invention, usually
After dispensing a solution of polyamic acid or a suspension of a mixture of polyamic acid and a conductive filler on the adhesive surface, it is heated and cured by heat treatment while being pressed onto the adhesive surface. At this time, polyamic acid is imidized to become polyimide. Before thermal curing, preliminary heating may be performed to remove the solvent and dry the material. Although the imidization temperature depends on the structure of the polyamic acid, it is generally preferably higher than the glass transition temperature of the polyamic acid, and is usually 100 to 500°C. When the imidization temperature is high, it is preferable to carry out the imidization under a nitrogen atmosphere from the viewpoint of preventing thermal deterioration. The adhesive of the present invention exhibits extremely high adhesive strength and excellent heat resistance, and has an excellent effect on bonding heat-resistant materials. Examples of heat-resistant materials include metal materials such as aluminum, copper, titanium, and steel, non-metallic inorganic materials such as silicon and ceramics, heat-resistant organic materials such as aromatic polyamide, polyamide-imide, and polyimide, and composite materials thereof. Examples include molded products such as. The adhesive of the present invention is particularly useful as a heat-resistant adhesive in the aviation and space industries, and as a heat-resistant adhesive in the electronics industry. Furthermore, the adhesive of the present invention containing a conductive filler exhibits high conductivity in addition to the above-mentioned high adhesive strength and heat resistance, and is suitable for bonding conductive materials. This adhesive is effective for bonding metal-to-metal materials, particularly aluminum, copper, titanium, steel, etc., and silicon-to-metal, silicon-to-silicon materials, etc., where soldering is not possible. Adhesives containing this conductive filler are particularly effective in the fields of die bonding and wire bonding as assembly techniques for semiconductor ICs in the electronic industry. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Example 1 14.1 parts by weight (0.1 mol) of 4,4'-diaminodiphenyl ether and 15.9 parts by weight (0.1 mol) of 2,3,5-tricarboxycyclopentyl acetic acid were mixed in 70 parts by weight of dimethylacetraamide at 25°C. The mixture was allowed to react for 8 hours. The obtained polyamic acid solution (reduced viscosity of polyamic acid 0.67 dl/g, polyamic acid concentration 30% by weight) was applied to the circular cross section of two aluminum rods polished according to JISK6849, and dried while being crimped and fixed. , and was further heat-treated at 300°C for 1 hour to thermally cure it. After adhesion, a tensile test was conducted at room temperature to cause tensile breakage, and the adhesive strength was measured. In addition, to evaluate heat resistance, after adhesion, the adhesive was left in an air atmosphere at 450°C for 15 minutes to heat age, and the adhesive strength at room temperature after aging was measured. These results are shown in Table 1. Example 2 Using a polyamic acid solution prepared in the same manner as in Example 1 (reduced viscosity of polyamic acid: 16.4 dl/g, polyamic acid concentration: 16.2% by weight), tests were conducted in the same manner as in Example 1. Table 1 shows the results. Shown below. Example 3 Using 4,4'-diaminodiphenylmethane instead of 4,4'-diaminodiphenyl ether,
Otherwise, a polyamic acid solution (reduced viscosity of polyamic acid: 0.17 dl/g, polyamic acid concentration: 30% by weight) was prepared in the same manner as in Example 1. Table 1 shows the results of the test conducted in the same manner as in Example 1. Example 4 A polyamic acid solution (polyamic acid A polyamic acid with a reduced viscosity of 0.73 dl/g and a polyamic acid concentration of 30% by weight was prepared. Table 1 shows the results of the test conducted in the same manner as in Example 1. Comparative Example 1 7.4 parts by weight (0.1 mol) of pyromellitic anhydride and 8.6 parts by weight (0.1 mol) of 4,4'-diaminodiphenyl ether were reacted in 84.0 parts by weight of dimethylformamide at 25°C for 8 hours. Obtained polyamic acid solution (reduced viscosity of polyamic acid 34.2 dl/
g, polyamic acid concentration 16% by weight), and the adhesive strength was tested in the same manner as in Example 1. Four out of 10 adhesive samples were broken during handling after adhesion, indicating that the adhesive strength was extremely weak. Table 1 shows the sample results for the samples that were not damaged. Comparative Example 2 Using a polyamic acid solution prepared in the same manner as in Comparative Example 1 (reduced viscosity of polyamic acid 1.56 dl/g, polyamic acid concentration 30% by weight), the imidization conditions were set to 125°C for 30 minutes at 300°C. ℃ for 30 minutes, 400℃ for 20 minutes
Heat curing was carried out in a stepwise manner for 30 minutes, and the test was carried out in the same manner as in Example 1. In this adhesive sample, 6 out of 10 were broken during handling during adhesion, indicating that the adhesive strength was extremely weak. Table 1 shows the test results for the samples that were not damaged.

[Table] As is clear from Table 1, the adhesive of the present invention has extremely excellent heat resistance and adhesive performance. Example 5 7.5 parts by weight (0.1 mol) of 4,4'-diaminodiphenyl ether and 8.5 parts by weight (0.1 mol) of 2,3,5-tricarboxycyclopentyl acetic acid were mixed in 84 parts by weight of dimethylacetamide at 25°C for 8 hours. Made it react. Obtained polyamic acid solution (reduced viscosity
1.12dl/g, polyamic acid concentration 16% by weight) with silver powder
12.8 parts by weight was added and stirring continued until uniformly dispersed. Using the obtained suspension, the adhesive strength was tested in the same manner as in Example 1. In addition, volume resistivity was measured as a measure of conductivity. These results are shown in Table 2. Example 6 Table 2 shows the results of a test conducted in the same manner as in Example 5 using a suspension prepared in the same manner as in Example 5 except that the amount of silver powder was 8 parts by weight. Example 7 Table 2 shows the results of a test conducted in the same manner as in Example 5 using a polyamic acid solution prepared in the same manner as in Example 5 without adding silver powder. Comparative Example 3 7.4 parts by weight (0.1 mol) of pyromellitic anhydride and 8.6 parts by weight (0.1 mol) of 4,4'-diaminodiphenyl ether were mixed with 84.0 parts by weight of dimethylformamide.
The reaction was carried out in parts by weight. Obtained polyamic acid solution (reduced viscosity 3.42 dl//g, polyamic acid concentration 16
A test was carried out in the same manner as in Example 1 using a suspension obtained by adding 12.8 parts by weight of silver powder to (% by weight) in the same manner as in Example 5. After bonding, 6 out of 10 pieces of the adhesive material broke during handling, indicating that the adhesive strength was extremely weak. Table 2 shows the test results for the samples that did not break.

[Table] As is clear from Table 2, the adhesive containing the conductive filler of the present invention has excellent heat resistance as well as excellent adhesive performance and conductivity.

Claims (1)

[Claims] 1. A heat-resistant adhesive characterized in that its main component is a polyamic acid obtained by reacting 2,3,5-tricarboxycyclopentyl acetic acid or its anhydride with a diamine.