Adhesive composition and adhesive sheet using same

1. An adhesive composition comprising: resin components that include:

a bisphenol A epoxy resin;

a tri- or higher-functional epoxy resin in addition to the bisphenol A epoxy resin;

an acrylic particle having a core-shell structure containing a butadiene-based rubber, and epoxy-modified polymethacrylate or epoxy-modified polyacrylate; and

a curing agent, wherein:

the content of the bisphenol A epoxy resin and tri- or higher-functional epoxy resin ranges from 40 parts by mass to 90 parts by mass with respect to the total amount of the resin components in the adhesive composition;

the blending ratio of the acrylic particle is 3% to 33% by mass with respect to the total mass of the adhesive composition; and

an adhesive layer formed from the adhesive composition has an adhesive strength retaining rate of not less than 68% after immersion in each of water at 80° C. 10% NaCl solution at 80° C., and 50% CaCl 2 solution at 80° C. for 200 hours following adhesion of a metal to a composite resin through the adhesive layer.

2. The adhesive composition according to claim 1 , further comprising an acrylic resin that is a binary copolymer including a methyl methacrylate (MMA) block and butyl acrylate (BA) block optionally modified with a functional group that is a carboxylic acid, hydroxyl group, or amide group introduced to part of the BA block or MMA block.

3. The adhesive composition according to claim 1 , wherein the acrylic particle has an average particle size of not more than 200 nm.

4. An adhesive sheet comprising an adhesive layer between a first release film and a second release film, the adhesive layer formed from the adhesive composition of claim 1 .

5. The adhesive sheet according to claim 4 , wherein the acrylic particle has an average particle size of not more than 200 nm.

6. The adhesive composition according to claim 1 , further comprising an epoxy-modified silane compound.

7. The adhesive composition according to claim 6 , wherein the epoxy-modified silane compound is:

γ-glycidoxypropyltrimethoxysilane;

γ-glycidoxypropyltriethoxysilane;

2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane;

2-(3,4-epoxycyclohexyl)ethyltriethoxysilane;

(γ-glycidoxypropyl)(methyl)dimethoxysilane;

(γ-glycidoxypropyl)(ethyl)dimethoxysilane;

(γ-glycidoxypropyl)(methyl)diethoxysilane;

(γ-glycidoxypropyl)(ethyl)diethoxysilane;

[2-(3,4-epoxycyclohexyl)ethyl](methyl)dimethoxysilane;

[2-(3,4-epoxycyclohexyl)ethyl](ethyl)dimethoxysilane;

[2-(3,4-epoxycyclohexyl)ethyl](methyl)diethoxysilane;

[2-(3,4-epoxycyclohexyl)ethyl](ethyl)diethoxysilane;

(γ-glycidoxypropyl)(methoxy)dimethylsilane;

(γ-glycidoxypropyl)(methoxy)diethylsilane;

(γ-glycidoxypropyl)(ethoxy)dimethylsilane;

(γ-glycidoxypropyl)(ethoxy)diethylsilane;

[2-(3,4-epoxycyclohexyl)ethyl](methoxy)dimethylsilane;

[2-(3,4-epoxycyclohexyl)ethyl](methoxy)diethylsilane;

[2-(3,4-epoxycyclohexyl)ethyl](ethoxy)dimethylsilane;

[2-(3,4-epoxycyclohexyl)ethyl](ethoxy)diethylsilane;

a partial condensate thereof; or

any combination thereof.

8. The adhesive composition according to claim 2 , wherein a ratio of the bisphenol A epoxy resin and tri- or higher-functional epoxy resin to the acrylic resin is 100:4 to 100:100 on a mass basis.

9. The adhesive composition according to claim 2 , wherein the bisphenol A epoxy resin, tri- or higher-functional epoxy resin, and acrylic resin have a sea-island structure before curing in which particles of the acrylic resin are dispersed in the bisphenol A epoxy resin and tri- or higher-functional epoxy resin.

10. The adhesive composition according to claim 1 , further comprising an epoxy-modified silicone resin having a polyorganosiloxane skeleton.

11. The adhesive composition according to claim 1 , wherein the bisphenol A epoxy resin has a glass transition temperature ranging from 50° C. to 150° C.

12. The adhesive composition according to claim 1 , wherein the bisphenol A epoxy resin has a backbone with 2 to 10 units.

13. The adhesive composition according to claim 1 , wherein the tri- or higher-functional epoxy resin has a tris(hydroxyphenyl)methane structure, a tetrakis(hydroxyphenyl)ethane structure, an aminophenol structure, or a bis(aminophenyl)methane structure.

14. The adhesive composition according to claim 1 , wherein the tri- or higher-functional epoxy resin has not less than three glycidyl ether groups.

15. The adhesive composition according to claim 1 , wherein the content of the tri- or higher-functional epoxy resin is 5% to 50% by mass with respect to the total mass of the adhesive composition.

16. A method of adhering adherends, comprising: providing an adhesive sheet comprising an adhesive layer and a release film on a surface of the adhesive layer;

exposing the adhesive layer of the adhesive sheet by the release-film removal;

sandwiching the adhesive layer between a first adherend and a second adherend to provide initial adhesion between the first and second adherends; and

curing the adhesive layer by heat or under pressure and heat to strengthen adhesion between the first and second adherends, wherein:

the first and second adherends are each a metal or composite resin; and

the adhesive layer is formed from the adhesive composition according to claim 1 .

17. A laminated body obtained by the method according to claim 16 .

18. The adhesive composition according to claim 1 , wherein the curing agent comprises a dicyandiamide-based curing agent in combination with a blocked isocyanate.

19. An adhesive composition comprising: resin components that include:

a bisphenol A epoxy resin;

a tri- or higher-functional epoxy resin in addition to the bisphenol A epoxy resin;

an acrylic particle having a core-shell structure containing a butadiene-based rubber, and polymethacrylate or polyacrylate; and

a curing agent, wherein:

the content of the bisphenol A epoxy resin and tri- or higher-functional epoxy resin ranges from 40 parts by mass to 90 parts by mass with respect to the total amount of the resin components in the adhesive composition; the blending ratio of the acrylic particle is 3% to 33% by mass with respect to the total mass of the adhesive composition;

the acrylic particle is the only particle present in the adhesive composition; and

an adhesive layer formed from the adhesive composition has an adhesive strength retaining rate of not less than 68% after immersion in each of water at 80° C., 10% NaCl solution at 80° C., and 50% CaCl 2 solution at 80° C. for 200 hours following adhesion of a metal to a composite resin through the adhesive layer.