JP2020152862A - Film-like adhesive - Google Patents

Abstract

To provide a new film-like adhesive using an epoxy resin which can preferably maintain peeling strength and shear strength even after through heating and cooling in a state of being inserted between members to be joined.SOLUTION: A film-like adhesive includes a resin layer A composed of an epoxy resin composition a and a resin layer B composed of an epoxy resin composition b, is a film-like adhesive having the resin layer A provided on front and rear sides of the resin layer B, and has storage elastic modulus Ea of the epoxy resin composition a at 30°C after curing and storage elastic modulus Eb of the epoxy resin composition b at 30°C after curing satisfying a relationship of Ea>Eb.SELECTED DRAWING: None

Description

The present invention relates to a film-like adhesive using an epoxy resin.

In recent years, from the viewpoint of suppressing global warming and protecting the environment, studies on weight reduction of structures have been advanced for the purpose of reducing fuel consumption in transporters such as automobiles and aircraft. As a method for reducing the weight, thinning is performed by using an ultra-high-strength steel plate with high strength instead of the commonly used steel plate, and materials such as aluminum and CFRP, which are lightweight materials instead of the steel plate, are used. It is widely considered for its utilization.

However, while these materials contribute to weight reduction, they have problems such as inferiority to steel sheets in terms of cost, strength, fatigue resistance, electrical characteristics, etc., so these materials should be used alone. There are few, and replacement from steel sheets is being considered, focusing on the parts where various characteristics can be used as alternatives. As a result, a plurality of members are joined and used, which makes it difficult to join with a general welding technique.

Further, when such a plurality of members are joined by welding or metal fastening, metal corrosion (electrolytic corrosion) occurs due to different potentials between the joined members, so that the joining using an insulating material is used. Is required.
Further, it is expected that the efficiency of the work of joining by welding in the production line including the process of joining members in the factory will be improved. As described above, in recent years, it has become important to introduce a joining technology that replaces welding.

As one of the joining techniques that replaces this welding, there is a method of joining using a liquid or film-like structural adhesive. Among them, the film-like adhesive does not need to be applied with an adhesive and can make the thickness of the adhesive layer uniform, so that uneven coating of the adhesive is unlikely to occur, and thus the reliability after adhesion is high. It is especially useful in production lines that include the process of joining parts in a factory.
Epoxy-based adhesives, second-generation acrylic adhesives (hereinafter referred to as SGA), urethane resin-based adhesives, silicone resin-based adhesives, and the like are known as such structural adhesives, and among them, epoxy-based adhesives. Adhesives are widely used because of their high adhesiveness to various members such as metals and CFRP and their high heat resistance.

Conventionally, regarding a film-like adhesive using an epoxy resin, for example, in Patent Document 1, a flexible epoxy resin, a flexible curing agent, a silane coupling agent, and a latent catalyst are blended into a three-layer or multi-layered adhesive. The central layer does not contain a silane coupling agent and has an excellent function of relieving stress, and the outermost layer contains a silane coupling agent so that the adhesive force with the adherend is increased before bonding. Discloses a flexible adhesive in which all layers are uncured and heated and adhered during use.

Patent Document 2 describes that the first layer is an adhesive composition composed of an epoxy resin, a rubber component, and a curing agent component, and the second layer is an adhesive component composed of an epoxy resin, a rubber component, and a curing agent component. An adhesive composition containing up to 90% by volume of an inorganic filler is applied to a base film as a third layer, and an adhesive composition consisting of an epoxy resin, a rubber component, and a curing agent is applied to a semi-cured state. A thermosetting adhesive sheet that has been heat-treated to have a three-layer structure is disclosed.

Patent Document 3 has a three-layer structure in which a thermosetting epoxy-based adhesive layer that is flexible even in a completely cured state is formed on both sides of a base material made of a heat-resistant flexible resin sheet. Disclosed is an adhesive sheet in which the epoxy-based adhesive layer is heat-treated to a semi-cured state and is in a solid state having flexibility at 25 ° C.

JP-A-11-124557 Japanese Unexamined Patent Publication No. 2000-290613 Japanese Unexamined Patent Publication No. 2013-64078

When a film-like adhesive using an epoxy resin is used as a structural adhesive, for example, a film-like adhesive is inserted between two structural members (for example, a steel material), and the film-like adhesive is heated and cooled in a laminated state. The film-like adhesive is cured to join the two structural members.
Generally, since the structural member is heated and cooled at the same time as the film-like adhesive using a thermosetting resin such as epoxy resin, the structural member and the film-like adhesive are affected by the difference in expansion and contraction during heating and cooling. There is a problem that stress is generated at the interface with and the peel strength after joining tends to decrease. As shown in Patent Documents 1 to 3, by arranging the flexible member at the joint portion between the structural member and the film-like adhesive, the stress due to the difference in linear expansion coefficient and the stress generated in the peeling mode can be relaxed. And the peel strength can be improved. On the other hand, when the cohesive force of the adhesive is reduced by imparting the flexibility of the material, there is a problem that the shear strength, which is affected by the interfacial adhesion and the rigidity of the adhesive, tends to be reduced.

Therefore, the present invention relates to a film-like adhesive using an epoxy resin, and is a new film capable of suitably maintaining peel strength and shear strength even when heated and cooled while being inserted between members to be joined. It is intended to provide a state adhesive.

The present invention is a film-like adhesive comprising a resin layer A composed of an epoxy resin composition a and a resin layer B composed of an epoxy resin composition b, and the resin layer A provided on the front and back sides of the resin layer B. Therefore, the storage elasticity Ea of the epoxy resin composition a at 30 ° C. after curing and the storage elasticity Eb of the epoxy resin composition b at 30 ° C. after curing have a relationship of Ea> Eb. We propose a film-like adhesive characterized by.

Since the film-like adhesive proposed by the present invention has a structure in which resin layers A and B composed of epoxy resin compositions a and b having different storage elastic moduli are laminated, both peel strength and shear strength can be obtained. Can be combined. Moreover, by designing the resin layers A having a high storage elastic modulus Ea to be arranged on the front and back sides, it is possible to increase the bonding strength with structural materials such as ultra-high strength steel plates, aluminum, CFRP, and steel materials. Therefore, it can be suitably used for various purposes, especially as a structural adhesive. Further, since it is a film-like adhesive, it has high reliability after bonding, and is particularly suitable for use in a production line for joining members in a factory.

Next, the present invention will be described based on examples of embodiments. However, the present invention is not limited to the embodiments described below.

<This film-like adhesive>
The film-like adhesive (referred to as "the present film-like adhesive") according to an example of the embodiment of the present invention comprises a resin layer A made of an epoxy resin composition a and a resin layer B made of an epoxy resin composition b. It is a film-like adhesive provided with the resin layer A on both the front and back sides of the resin layer B.

This film-like adhesive is in an uncured state, and by inserting it between the members to be joined and heating and cooling it to form a cured product, the adhesive strength is increased and the adhesives can be joined together. It is an agent.

In the present invention, the state in which the film-like adhesive is heated and cooled and cured is referred to as "after curing". The degree of curing may be any of a state closer to uncured than the B stage, a state of being B-staged (semi-cured), and a state of being completely cured.
Further, what is cured by heating and cooling this film-like adhesive is referred to as a "cured product". The cured product shall be a "cured product" regardless of the degree of curing.

(Storage modulus)
In this film-like adhesive, the storage elastic modulus Ea of the epoxy resin composition a at 30 ° C. after curing and the storage elastic modulus Eb of the epoxy resin composition b at 30 ° C. after curing are Ea>. It is preferable to have an Eb relationship.
When a film-like adhesive is inserted between the members to be joined and the laminated state is heated and cooled to cure the film-like adhesive to join the members, the storage elastic modulus on the side to be joined with the members is higher. In other words, the higher the rigidity, the higher the cohesive force of the adhesive, so that it has high adhesion at the interface with the member, and also expands during heating and shrinks during cooling between the member to be joined and the adhesive. Since the strain generated due to the above and the like is reduced, the shear strength can be suitably maintained.

Among them, Ea is preferably 5 times or more larger than Eb, and more preferably 10 times or more, and more preferably 100 times or more.

From the viewpoint of increasing the shear strength of the film-like adhesive, the epoxy resin composition a preferably has a storage elastic modulus Ea at 30 ° C. after curing of 1000 MPa or more, particularly 1200 MPa or more, and among them 1500 MPa or more. Is even more preferable. If the storage elastic modulus Ea is too high, the peel strength may be significantly reduced due to the increase in stress due to the difference in expansion coefficient with the member to be joined, or it may be the starting point of peeling due to impact. Therefore, 50 GPa ( It is preferably 50,000 MPa) or less, and more preferably 30 GPa (30,000 MPa) or less, and more preferably 20 GPa (20,000 MPa) or less.

On the other hand, from the viewpoint of mainly increasing the shear strength, the epoxy resin composition b preferably has a storage elastic modulus Eb at 30 ° C. after curing of 0.1 MPa or more, particularly 0.5 MPa or more, and among them 1. It is more preferably 0 MPa or more. If the storage elastic modulus Ea is too high, the peel strength may be insufficient. Therefore, it is preferably 1000 MPa or less, more preferably 800 MPa or less, and even more preferably 500 MPa or less.

In order to adjust the storage elasticity Ea and Eb at 30 ° C. after curing of the epoxy resin compositions a and b within the above range, for example, the types of the epoxy resins and the curing agents constituting the epoxy resin compositions a and b. To introduce a flexible and rigid skeleton by polymerization or reaction into each epoxy resin and curing agent constituting the epoxy resin compositions a and b, a plasticizer, a reactive silane oligomer, a urethane oligomer, etc. Other compatible materials may be blended, or a soft component such as a rubber component or a hard component such as an inorganic filler may be added to the epoxy resin compositions a and b. However, the method is not limited to these methods.

(Coefficient of linear expansion)
In the present film-like adhesive, the linear expansion coefficient Ka of the epoxy resin composition a in the in-plane direction at 25 to 160 ° C. after curing and the linear expansion coefficient Kb of the epoxy resin composition b in the in-plane direction are The relationship is preferably Ka <Kb.
Above all, Kb is preferably 20 ppm / K or more larger than Ka, and more preferably 30 ppm / K or more, and more preferably 50 ppm / K or more.

The linear expansion coefficient Ka of the epoxy resin composition a at 25 to 160 ° C. after curing in the in-plane direction is 1. From the viewpoint of reducing the difference in expansion coefficient with members such as steel plates, aluminum, and CFRP to be generally bonded. It is preferably 0 ppm / K or more, and more preferably 3.0 ppm / K or more, and more preferably 5.0 ppm / K or more. However, if the coefficient of linear expansion Ka is too high, the difference in expansion coefficient with members such as steel plates, aluminum, and CFRP to be joined is large, which may cause a decrease in adhesive strength. Therefore, it is 200 ppm / K or less. It is preferably 150 ppm / K or less, and more preferably 100 ppm / K or less.

On the other hand, the linear expansion coefficient Kb of the epoxy resin composition b at 25 to 160 ° C. after curing in the in-plane direction is preferably 1.0 ppm / K or more from the viewpoint of reducing the difference from the linear expansion coefficient Ka. Among them, 3.0 ppm / K or more, and more preferably 5.0 ppm / K or more. However, if the coefficient of linear expansion Kb is too high, the difference from the coefficient of linear expansion Ka increases and internal stress is generated. From this point of view, it is preferably 200 ppm / K or less, more preferably 150 ppm / K or less, and more preferably 100 ppm / K or less.

In order to adjust the linear expansion coefficients Ka and Kb of the epoxy resin compositions a and b within the above range, for example, the types and amounts of the epoxy resins and the curing agents constituting the epoxy resin compositions a and b may be adjusted. , A flexible structure such as an ethylene skeleton or a tough structure such as a benzene skeleton can be introduced into each of the epoxy resins and curing agents constituting the epoxy resin compositions a and b by polymerization or reaction, or a plasticizer, a reactive silane oligomer, or a urethane oligomer. Other compatible materials such as the above may be blended, or a high thermal expansion material such as a rubber component or a low thermal expansion material such as an inorganic filler may be added to the epoxy resin compositions a and b. However, the method is not limited to these methods.

(Glass-transition temperature)
Regarding the glass transition temperature of the epoxy resin compositions a and b after curing, the glass transition temperature of the epoxy resin composition a after curing is preferably 10 to 180 ° C. higher than that of the epoxy resin composition b.
If the glass transition temperature of the epoxy resin composition a after curing is 10 ° C. or higher higher than that of the epoxy resin composition b, the storage elastic modulus of the epoxy resin composition a after curing tends to be higher than that of the epoxy resin composition b. Therefore, it is preferable. On the other hand, if the difference between the two is within 180 ° C., curling or warpage occurs due to the difference between the linear expansion coefficient Ka after curing of the epoxy resin composition a and the linear expansion coefficient Kb after curing of the epoxy resin composition b. It is preferable because it is suppressed.
From this point of view, the glass transition temperature of the epoxy resin composition a after curing is preferably 10 ° C. or higher higher than that of the epoxy resin composition b, particularly 30 ° C. or higher, and more preferably 50 ° C. or higher. .. On the other hand, the difference between the two is preferably 180 ° C. or lower, more preferably 150 ° C. or lower, and more preferably 120 ° C. or lower.

The glass transition temperature of the epoxy resin composition a after curing is preferably 50 to 300 ° C., more preferably 70 ° C. or higher or 280 ° C. or lower, and more preferably 80 ° C. or higher or 250 ° C. or lower.
On the other hand, the glass transition temperature of the epoxy resin composition b after curing is preferably −60 to 150 ° C., particularly −50 ° C. or higher or 130 ° C. or lower, and particularly −40 ° C. or higher or 120 ° C. or lower. Is even more preferable.

In order to adjust the glass transition temperature (Tg) of the epoxy resin compositions a and b after curing within the above range, for example, the types and amounts of the epoxy resins and the curing agents constituting the epoxy resin compositions a and b are adjusted. In addition, a low Tg component such as an olefin structure or a high Tg component such as a benzene skeleton can be introduced into each of the epoxy resins and curing agents constituting the epoxy resin compositions a and b by polymerization or reaction, or a plasticizer or a reactive silane oligomer can be introduced. , Other compatible materials such as urethane oligomers may be blended, or surface treatment or finely divided rubber components, inorganic fillers, etc. may be added to the epoxy resin compositions a and b. However, the method is not limited to these methods.

<Epoxy resin compositions a and b>
Each of the epoxy resin compositions a and b preferably contains an epoxy resin and a curing agent, and preferably contains other components as necessary. The types of the epoxy resin and the curing agent are different so as to have the above physical properties, respectively. It is preferable to adjust the amount.

(Epoxy resin)
Next, the epoxy resin that can be used for the epoxy resin compositions a and b will be described. It is preferable to select and use a type of these epoxy resins so that the physical properties can be adjusted.

Examples of the epoxy resin used in the epoxy resin composition a include bisphenols such as bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol AD, and bisphenol acetophenone, and bifunctional phenols such as biphenol, catechol, resorcin, hydroquinone, and dihydroxynaphthalene. Type epoxy resin, other bifunctional glycidyl ether type epoxy resin, bifunctional glycidyl ester type epoxy resin, bifunctional glycidylamine type epoxy resin, bifunctional linear aliphatic epoxy resin, bifunctional alicyclic epoxy resin, bifunctional complex It is possible to use an epoxy resin such as a hydrogenated epoxy resin such as a ring-type epoxy resin or a hydrogenated bisphenol A type epoxy resin. Of these, bisphenol A type epoxy resin and bisphenol F type epoxy resin are particularly preferable from the viewpoint of rigidity and heat resistance.

If the number average molecular weight of the epoxy resin is 200 or more, a sufficient effect of improving flexibility can be obtained, and if it is 100,000 or less, the resin will not be difficult to handle, which is preferable. .. Therefore, the number average molecular weight of the epoxy resin is preferably 200 or more and 100,000 or less, and more preferably 300 or more or 90,000 in terms of both heat resistance and handling of the resin. It is more preferably 400 or more or 80,000 or less.
The method for measuring the molecular weight (Mn) is not particularly limited, but can be measured by, for example, gel permeation chromatography.

On the other hand, as the epoxy resin used in the epoxy resin composition b, those obtained by mixing and reacting two or more kinds of the epoxy resins described in the epoxy resin composition a can be preferably used. Above all, from the viewpoint of the flexibility of the obtained epoxy resin, at least one of the two or more kinds of epoxy resins is preferably a bifunctional aliphatic epoxy resin.
As such a bifunctional linear aliphatic epoxy resin, those having a molecular weight of 200 to 100,000, particularly 400 or more or 50,000 or less, and among them, 500 or more or 10,000 or less are particularly preferable.

The bifunctional aliphatic epoxy compound may be an aliphatic epoxy resin having a purity of 90% by mass or more derived from diglycidyl ether obtained by reacting a diol having 2 to 12 carbon atoms with epihalohydrin and then distilling and purifying it. For example, ethylene glycol glycidyl ether, propylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, 1,6-hexanediol glycidyl ether, 1,8 octane diol glycidyl ether, 1,10-decanediol. Glysidyl ether, glycidyl ether of 2,2-dimethyl-1,3-propanediol, glycidyl ether of diethylene glycol, glycidyl ether of triethylene glycol, glycidyl ether of tetraethylene glycol, glycidyl ether of hexaethylene glycol, 1,4-cyclohexane Dimethanol glycidyl ether and the like. Among these, glycidyl ether of 1,4-butanediol, glycidyl ether of 1,6-hexanediol, 1,4 from the viewpoint of the large effect of reducing the viscosity of the liquid epoxy resin and the small decrease in heat resistance of the cured product. -Cyclohexanedimethanol glycidyl ether or 2,2-dimethyl-1,3-propanediol glycidyl ether is particularly preferred. That is, those obtained by mixing and reacting these bifunctional aliphatic epoxy compounds with the epoxy resins listed as the epoxy resins of the epoxy resin composition a are particularly preferable as the epoxy resins of the epoxy resin composition b.

Further, the epoxy resin compositions a and b may contain curing agents having the same composition as each other, or may contain curing agents having different compositions from each other. However, since it is preferable that the epoxy resin compositions a and b behave in the same manner at the same temperature, it is preferable to use the same curing agent in the epoxy resin compositions a and b, and among them, the curing agent is contained in the same proportion. It is preferable to do so.

(Hardener)
Next, the curing agent that can be used for the epoxy resin compositions a and b will be described. It is preferable to select and use a type of these curing agents so that the physical properties can be adjusted.

The curing agent may be any of an aliphatic compound, an alicyclic compound, an aromatic compound or a heterocyclic compound, and may be polyamines, tertiary amines, triphenylphosphines, phenols, acid anhydrides or carboxylics. Two-component reaction-type curing agents such as acids and one-component mixed-type latent curing agents such as dicyandiamides, imidazoles, and ureas can be used as general curing agents.
More specifically, for example, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, dodecenylsuccinic anhydride, pyromerit anhydride. Acid anhydrides such as acids; dicyandiamide compounds such as dicyandiamide, ortho-tolylbiguanide, phenylbiguanide, para-chlorophenylbiguanide, ethylenebisbiguanide hydrochloride, uralylbiguanide hydrochloride, phenylbiguanidooxalate; boron trifluoride-amine Complex; Phenylmethylamine, Triethanolamine, Dimethylaminomethylphenol, Tris (dimethylaminomethyl) phenol, Triethyltetramine, 3,9-bis (3-aminopropyl) -2,4,8,10-Tetraoxaspiro ( 5,5) Tertiary amines such as undecane; 1,2,3-benzotriazole, 5-methyltriazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-ethylimidazole, 2,4-Dimethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-vinyl-2-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methylimidazole, 2 Imidazoles such as −isopropylimidazole, 1-cyanomethyl-2-methylimidazole; 3- (3,4-dichlorophenyl) -1,1-dimethylurea, 3-phenyl-1,1-dimethylurea, toluenebis (dimethylurea) ), 4,4'-Methylenebis (phenyldimethylurea) and other urea compounds. However, among these, there are also compounds that function as co-curing agents and curing accelerators.
As the curing agent, one type of compound may be used alone, or two or more types of compounds such as a combination of the curing agent and a co-curing agent or a curing accelerator may be used in combination.

Among them, a latent curing agent is preferable in terms of storage stability, and among them, dicyandiamide, ortho-tolylbiguanide, phenylbiguanide, para-chlorophenylbiguanide, ethylenebisbiguanide hydrochloride, and uralylbiguanide hydrochloride are preferable in terms of curability. , Dicyandiamides such as phenylbiguanideoxalate and 3- (3,4-dichlorophenyl) -1,1-dimethylurea, 3-phenyl-1,1-dimethylurea, toluenebis (dimethylurea), 4,4'- Urea compounds such as methylenebis (phenyldimethylurea) are more preferred.

Among the above, it is preferable to use a latent curing agent having a melting point of 120 ° C. or higher because of its high storage stability.
Examples of such a latent curing agent include dicyandiamide and 3- (3,4-dichlorophenyl) -1,1-dimethylurea.
These latent curing agents may be used alone or in combination of two or more.

The contents of the epoxy resin and the curing agent may be determined in consideration of the mechanical strength of the desired effect product and the reaction mechanism of each curing agent. The larger the amount of the curing agent, the faster the heat curing rate, and the smaller the amount, the longer the pot life tends to be.
For curing agents having functional groups such as primary amines, secondary amines, acid anhydrides, and active hydrogens such as carboxylic acids, the number of epoxy groups and the number of curable functional groups are equal. It is preferable to do so.
For example, as a guide, it is preferable to add the curing agent in a ratio of 0.1 to 20 parts by mass with respect to 100 parts by mass of the epoxy resin composition, and in particular, it is added in a ratio of 1 part by mass or more or 10 parts by mass or less. Is more preferable.
As for the curing agent that becomes a catalyst curing system such as tertiary amine, imidazole, dicyandiamide, and dimethylurea, the reaction proceeds even in a small amount, so about 1 to 10 parts by mass should be added to 100 parts by mass of the epoxy resin. Is preferable.

If necessary, it is preferable to use a reaction accelerator in combination with a curing agent. For example, when dicyandiamide is used as the latent curing agent, it is preferable to use other basic compounds such as an imidazole compound and dimethylurea at the same time. When an acid anhydride is used as the two-component reaction type curing agent, it is preferable to contain a reaction accelerator that promotes ring opening of the acid anhydride.
Examples of the reaction accelerator include imidazole compounds, tertiary amines, dicyandiamides, Lewis acids, and organometallic compounds.

(solvent)
The epoxy resin compositions a and b may also contain a solvent, if necessary.
Examples of the solvent include alcohols such as methanol, ethanol and isopropyl alcohol, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and dimethylformamide. These solvents can be appropriately used as a mixed solvent of two or more kinds.

(Other ingredients)
The epoxy resin compositions a and b may contain other components, such as a sensitizer, a cross-linking agent, an ultraviolet absorber, a polymerization inhibitor, a silane coupling agent, a filler, an antioxidant, a leveling agent, a slip agent, and fine particles, if necessary. , Dispersants, organic peroxides, reducing agents, radically polymerizable compounds; various additives such as antioxidants, plasticizing agents, defoaming agents, polymerization initiators, inorganic fine particles, and elastomers can be contained.
For example, by blending an elastomer, the viscosity of the film-like adhesive and the flexibility and impact resistance of the cured product can be adjusted. Further, by blending a thermal polymerization initiator such as a peroxide or an azo compound or a polymerization initiator such as a photopolymerization initiator, the strength of the cured product obtained by curing the present film-like adhesive can be adjusted.

<Thickness>
From the viewpoint of being used as a structural adhesive, the thickness of this film-like adhesive is preferably 5 μm or more and 2000 μm or less, particularly 10 μm or more or 1500 μm or less, among which 50 μm or more or 1200 μm or less, especially 100 μm or more or 1000 μm or less. Is more preferable.

Regarding the thickness ratio between the resin layer A and the resin layer B, from the viewpoint of the balance between the shear strength and the peel strength, the thickness of each resin layer A is 1% or more and 90% of the thickness of the resin layer B (100%). It is preferably% or less, more preferably 10% or more or 80% or less, and further preferably 20% or more or 70% or less.

<Characteristics of this film-like adhesive>
(Shear strength)
The tensile shear adhesive strength (JIS K6850) with respect to the cold-rolled steel sheet (SPCC) after curing of the film-like adhesive is preferably 20 N / mm ² or more, and the film-like adhesive has such a tensile shear adhesive strength. Can have.
If the tensile shear adhesive strength (JIS K6850) to the cold-rolled steel sheet (SPCC) after curing of this film-like adhesive is 20 N / mm ² or more, it is sufficient for applications that require high bonding strength such as automobiles and aircraft. It is preferable from the viewpoint of obtaining excellent adhesive strength. However, if the tensile shear adhesive strength (JIS K6850) is too large, there is a concern that the rigidity of the material is too high as a result, and there is a possibility that the peel strength may decrease due to insufficient stress relaxation.
Therefore, the tensile shear adhesive strength (JIS K6850) of the present film-like adhesive to the cold-rolled steel sheet (SPCC) after curing is preferably 20 N / mm ² or more, particularly 23 N / mm ² or more, and 25 N / mm among them. It is more preferably mm ² or more. On the other hand, it is preferably 60 N / mm ² or less, more preferably 50 N / mm ² or less, and more preferably 40 N / mm ² or less.

In order to adjust the tensile shear adhesive strength (JIS K6850) of this film-like adhesive to a cold-rolled steel sheet (SPCC), the composition of the epoxy resin compositions a and b, the thickness of each resin layer A and B, and the present film The overall thickness of the adhesive may be adjusted. However, the method is not limited to such a method.

(Peeling strength)
The film-like adhesive preferably has a T-type peel strength (JIS K6854-3) of 20 N / 25 mm width or more with respect to the cold-rolled steel sheet (SPCC) after curing, and the film-like adhesive has such peeling. Can have strength.
If the T-type peel strength (JIS K6854-3) with respect to the cold-rolled steel sheet (SPCC) after curing of this film-like adhesive is 20 N / 25 mm width or more, applications requiring high bonding strength such as automobiles and aircraft. It is preferable from the viewpoint of obtaining sufficient adhesive strength. However, if the peel strength (JIS K6854-3) is too large, there is a concern that the flexibility of the material will be too high as a result, the cohesive force of the material will decrease, and the material will easily break during tensile shearing. There is a possibility that the adhesive strength will decrease.
Therefore, the T-type peel strength (JIS K6854-3) with respect to the cold-rolled steel sheet (SPCC) after curing of this film-like adhesive is preferably 20 N / 25 mm width or more, particularly 30 N // 25 mm width or more. Above all, it is more preferable that the width is 40 N // 25 mm or more. On the other hand, it is preferably 400 N // 25 mm width or less, more preferably 350 N // 25 mm width or less, and more preferably 300 N // 25 mm width or less.

In order to adjust the T-type peel strength (JIS K6854-3) against the cold-rolled steel sheet (SPCC) after curing of this film-like adhesive, the compositions of the epoxy resin compositions a and b and the resin layers A and B are used. The thickness and the overall thickness of the film-like adhesive may be adjusted. However, the method is not limited to such a method.

<Manufacturing method of this film-like adhesive>
In this film-like adhesive, for example, epoxy resin films a and b are prepared from epoxy resin compositions a and b, respectively, and the films are bonded to each other by pressurizing and adhering them to each other to form a resin layer A / resin layer B /. The present film-like adhesive formed by laminating the resin layer A in this order can be produced.

Further, for example, an epoxy resin film b is prepared from the epoxy resin composition b, and the epoxy resin composition a is applied to and dried on the front and back surfaces of the epoxy resin film b to form a resin layer A / resin layer B / resin layer. This film-like adhesive formed by laminating in the order of A can be produced.

Furthermore, the resin layer A / b is formed by extruding the epoxy resin compositions a and b onto a release film or the like in a laminated state of two or three layers using a mouthpiece such as a T-die, and then molding the epoxy resin composition a / b with a cast roll or the like. The present film-like adhesive formed by laminating the resin layer B and the resin layer A in this order can be produced.
However, the manufacturing method of the present film-like adhesive is not limited to such a manufacturing method.

<Cured product>
This film-like adhesive can be made into a cured product by heating and cooling.

The heating temperature during the curing treatment is preferably 60 ° C. or higher. However, if the heating temperature is too high, the adhesive properties and reliability may deteriorate due to decomposition and oxidative deterioration of the epoxy resin composition.
Therefore, the heating temperature is preferably 60 ° C. or higher, more preferably 80 ° C. or higher, and more preferably 100 ° C. or higher. On the other hand, it is more preferably 250 ° C. or lower, and more preferably 200 ° C. or lower.
The heating time is not particularly limited as long as the curing reaction of the composition constituting the film-like adhesive proceeds sufficiently. Usually, it is 5 minutes or more and 200 hours or less, and preferably 10 minutes or more and 150 hours or less.

Further, from the viewpoint of productivity and the like, the cooling rate during the curing treatment is preferably 0.1 ° C./min or more, particularly 0.5 ° C./min or more, and among them, 1 ° C./min or more. Is even more preferable.
On the other hand, the decrease in adhesiveness, uneven adhesion, uneven appearance, warpage, etc. due to the occurrence of cooling strain inside the member or adhesive, and the cooling time is preferably 40 ° C./min or less, especially 30 ° C./min or less. Above all, it is preferably 20 ° C./min or less.

<Laminated body>
The present film-like adhesive can be laminated on a member, and the present film-like adhesive can be provided as a laminated body in an uncured or cured state.
At this time, the film-like adhesive may be laminated on one side or both sides of the member, or the film-like adhesive may be laminated with the film-like adhesive inserted between the two members.

<Use>
The film-like adhesive can be joined between the joining members by inserting the adhesive between the joining members and heating and cooling the bonding members.
This film-like adhesive can have both peel strength and shear strength, and by designing the resin layer A with a high storage elastic modulus Ea to be arranged on the front and back sides, it can be used with structural materials such as steel materials. The joint strength of the Therefore, it can be suitably used for various purposes, especially as a structural adhesive. Further, since it is a film-like adhesive, it does not require a step and an apparatus for applying the adhesive, so that it can be particularly preferably used in a production line for joining members in a factory.

<Explanation of words>
When expressed as "X to Y" (X, Y are arbitrary numbers) in the present specification, unless otherwise specified, it means "X or more and Y or less" and "preferably larger than X" or "preferably Y". It also includes the meaning of "smaller".
Further, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it means "preferably larger than X" or "preferably less than Y". Including intention.

Hereinafter, the present invention will be further described with reference to Examples. However, the following examples are not intended to limit the present invention in any way.

[Epoxy resin composition a]
20 parts by mass of bisphenol A type epoxy resin "JER828" (manufactured by Mitsubishi Chemical Co., Ltd., number average molecular weight 370) and 80 parts of bisphenol A type epoxy resin "JER1001" (manufactured by Mitsubishi Chemical Co., Ltd., number average molecular weight 900) The parts by mass were heated to 80 ° C. and mixed. After that, 6 parts by mass of dicyandiamide "DYCY7" (manufactured by Mitsubishi Chemical Corporation, melting point 209 ° C.) as a latent curing agent and 3- (3,4-dichlorophenyl) -1,1-dimethylurea as a curing accelerator " Dimethylurea (manufactured by Nacalai Tesque, melting point 159 ° C.) was mixed with 1 part by mass to prepare an epoxy resin composition a.

The prepared epoxy resin composition a is sandwiched between a release film "Fluorouge RL" (manufactured by Mitsubishi Chemical Corporation) and introduced into a heated biaxial roll heated at 60 ° C. to form a film having a thickness of 50 μm. As a result, an epoxy resin film a was produced.
The produced epoxy resin film a was cured at 160 ° C. for 60 minutes, and as a result of dynamic viscoelasticity measurement, the glass transition temperature (Tg) due to the tan δ peak was 115 ° C., and linear expansion at 25 to 160 ° C. in TMA measurement. The coefficient was 94 ppm / K. The storage elastic modulus (E') at 30 ° C. after curing was 1850 MPa.

[Epoxy resin composition b]
In addition to 100 parts by mass of the epoxy resin described below, 6 parts by mass of dicyandiamide "DYCY7" as a latent curing agent and 3- (3,4-dichlorophenyl) -1,1-dimethylurea "DCMU" 1 as a curing accelerator The parts by mass were mixed to prepare an epoxy resin composition b.

For the epoxy resin used in the epoxy resin composition b, 1,6-hexanediol diglycidyl ether, bisphenol F, a catalyst and cyclohexanone were placed in a pressure resistant reaction vessel, and a polymerization reaction was carried out at 180 ° C. for 5 hours in a nitrogen gas atmosphere. The obtained epoxy resin.

The prepared epoxy resin composition b is sandwiched between a release film "Fluorouge RL" (manufactured by Mitsubishi Chemical Co., Ltd.) and introduced into a heated biaxial roll heated at 60 ° C. to form a film having a thickness of 50 μm. As a result, an epoxy resin film b was produced.
The produced epoxy resin film b was cured at 160 ° C. for 60 minutes, and as a result of dynamic viscoelasticity measurement, the glass transition temperature (Tg) due to the tan δ peak was 25 ° C., and linear expansion at 25 to 160 ° C. in TMA measurement. The coefficient was 202 ppm / K. The storage elastic modulus (E') at 30 ° C. after curing was 6.8 MPa.

[Example 1]
The epoxy resin film a was bonded to both sides of the epoxy resin film b, and then pressed and adhered with a hand roller to prepare a film-like adhesive.
The obtained film-like adhesive had a thickness of 150 μm composed of a resin layer A (thickness 50 μm) / resin layer B (thickness 50 μm) / resin layer A (thickness 50 μm). Table 1 shows the results of various physical property evaluations using this film-like adhesive.

[Comparative Example 1]
A film composed of a resin layer B (thickness 50 μm) / resin layer B (thickness 50 μm) / resin layer B (thickness 50 μm), which was carried out in the same manner as in Example 1 except that the epoxy resin film b was laminated and bonded in three layers. A plastic adhesive was prepared.
Table 1 shows the results of various physical property evaluations using this film-like adhesive.

[Comparative Example 2]
A film composed of resin layer A (thickness 50 μm) / resin layer A (thickness 50 μm) / resin layer A (thickness 50 μm), which was carried out in the same manner as in Example 1 except that the epoxy resin film a was laminated in three layers. A plastic adhesive was prepared.
Table 1 shows the results of various physical property evaluations using this film-like adhesive.

[Comparative Example 3]
The same procedure as in Example 1 was carried out except that the epoxy resin film b was bonded to both sides of the epoxy resin film a, and the resin layer B (thickness 50 μm) / resin layer A (thickness 50 μm) / resin layer B ( A film-like adhesive having a thickness of 50 μm) was produced.
Table 1 shows the results of various physical property evaluations using this film-like adhesive.

[Evaluation method]
For the samples prepared in Examples and Comparative Examples, the physical properties and the like were measured and evaluated by the methods shown below.

(Peeling strength)
The evaluation method of the T-type peel strength for the cold-rolled steel sheet (SPCC) was carried out in accordance with JIS-K 6854-3. That is, the film-like adhesive produced in Examples and Comparative Examples was cut into a width of 25 mm and a length of 200 mm. A cold-rolled steel sheet (also referred to as "SPCC") having a width of 25 mm, a length of 250 mm, and a thickness of 0.5 mm is degreased and washed with ethanol, and then the cut film-like adhesive is inserted between the two SPCCs and peeled off. The film is placed in a constant temperature bath with the release film inserted at a white of 50 mm, heated at 160 ° C for 60 minutes, and cooled to 50 ° C while slowly cooling at a cooling rate of 1 to 20 ° C / min in a circulating oven. A peeling test piece was prepared by curing the adhesive.

The prepared peeling test piece was subjected to a T-type peeling test at a speed of 100 mm / min using a high-temperature constant-humidity tensile tester "INTEXCO 200X" (manufactured by INTEXCO Co., Ltd.) with a test number of n = 5, and the measured strength was measured. Based on the lower limit, it was evaluated according to the following criteria.
〇 (good): Peeling strength is 40N / 25mm width or more Δ (usual): Peeling strength is 20N / 25mm width or more and less than 40N / 25mm width × (poor): Peeling strength is less than 20N / 25mm width

In addition, the state of destruction of the sample after the peeling test was also evaluated, and the case where the adhesive resin adhered to only one surface of the member and the interface between the member and the adhesive was visible was defined as "interface". The case where the adhesive resin adhered to the surfaces on both sides of the member and the adhesive layer was broken was evaluated as "aggregation".

(Shear strength)
The method for evaluating the tensile shear adhesive strength of a cold-rolled steel sheet (SPCC) was carried out in accordance with JIS-K 6850. That is, the film-like adhesive produced in Examples and Comparative Examples was cut into a width of 25 mm and a length of 12.5 mm. After degreasing and cleaning a cold-rolled steel sheet (SPCC) having a width of 25 mm, a length of 100 mm, and a thickness of 1.6 mm with ethanol, the cut film-like adhesive is inserted between the two SPCCs and placed in a constant temperature bath. The film was heated at 160 ° C. for 60 minutes and cooled to 50 ° C. while slowly cooling at a cooling rate of 1 to 20 ° C./min in a circulating oven to cure the film-like adhesive to prepare a peeling test piece.

The prepared peeling test piece was subjected to a tensile shear test using a tensile tester "INTERXCO 2050X" (manufactured by INTEXCO Co., Ltd.) at a speed of 5 mm / min with a test number of n = 5, and evaluated from the measured strength according to the following criteria. did.
〇 (good): Tensile shear strength is 20 N / mm ² or more × (poor): Tensile shear strength is less than 20 N / mm ^2.

In addition, the fracture state of the sample after the tensile shear test was also evaluated, and the case where the adhesive resin adhered only to one side surface of the member and the interface between the member and the adhesive was visible was the "interface". The case where the adhesive resin adhered to the surfaces on both sides of the member and the adhesive layer was broken was evaluated as "aggregation".

(Measurement of glass transition temperature and storage elastic modulus)
The glass transition temperature and storage elastic modulus are measured by a dynamic viscoelasticity measuring device (“DVA-200” manufactured by IT Measurement Control Co., Ltd.) using a tension jig at a measurement temperature of -100 to 250 ° C. and a frequency. From the results measured at 10 Hz and a heating rate of 3 ° C./min, the glass transition temperature (Tg) due to the tan δ peak and the storage elastic modulus (E') at 30 ° C. were read.

(Measurement of coefficient of linear expansion)
The film-like adhesive produced in Examples and Comparative Examples was cut into a width of 25 mm and a length of 12.5 mm, the cut film-like adhesive was inserted, and the film-like adhesive was placed in a constant temperature bath and heated at 160 ° C. for 60 minutes. A peeling test piece was prepared by cooling to 50 ° C. while slowly cooling at a cooling rate of 1 to 20 ° C./min in a circulating oven to cure the film-like adhesive.
Then, using a thermal expansion meter "DL1500" (manufactured by ULVAC), the coefficient of thermal expansion in the in-plane direction was measured by heating at a measurement temperature of -100 ° C to 250 ° C and a heating rate of 10 ° C / min. Based on the above, the coefficient of linear expansion in the in-plane direction at 25 ° C. to 160 ° C. was measured.

It was found that the film-like adhesive of Example 1 can obtain excellent properties of both peel strength and shear strength.
On the other hand, when a film-like adhesive obtained by laminating only the epoxy resin composition b having a low storage elastic modulus was used as in Comparative Example 1, the shear strength was insufficient. Further, as in Comparative Example 2, when a film-like adhesive obtained by laminating only the epoxy resin composition a having a high storage elastic modulus was used, the peel strength was insufficient. Further, when a film-like adhesive obtained by changing the laminated structure of the epoxy resin composition a and the epoxy resin composition b and laminating them as in Comparative Example 3 is used, the shear strength is insufficient. ..

Claims (9)

A film-like adhesive comprising a resin layer A made of an epoxy resin composition a and a resin layer B made of an epoxy resin composition b, and having the resin layer A on the front and back sides of the resin layer B.
The storage elastic modulus Ea of the epoxy resin composition a at 30 ° C. after curing and the storage elastic modulus Eb of the epoxy resin composition b at 30 ° C. after curing are characterized in that Ea> Eb. Film-like adhesive to be used. The film-like adhesive according to claim 1, wherein the epoxy resin composition a has a storage elastic modulus Ea of 1000 MPa or more at 30 ° C. after curing. The relationship between the linear expansion coefficient Ka of the epoxy resin composition a in the in-plane direction at 25 to 160 ° C. after curing and the linear expansion coefficient Kb of the epoxy resin composition b in the in-plane direction is Ka <Kb. The film-like adhesive according to claim 1 or 2, wherein the adhesive is characterized by. The film-like adhesive according to claim 3, wherein the epoxy resin composition a has a linear expansion coefficient Ka of 1.0 ppm / K or more in the in-plane direction at 25 to 160 ° C. after curing. The film-like adhesive according to any one of claims 1 to 4, which has a thickness of 5 μm to 2000 μm. The film-like adhesive according to any one of claims 1 to 5, wherein the tensile shear adhesive strength (JIS K6850) to the cold-rolled steel sheet (SPCC) after curing is 20 N / mm ² or more. The film-like adhesive according to any one of claims 1 to 6, wherein the T-type peel strength (JIS K6854-3) with respect to the cold-rolled steel sheet (SPCC) after curing is 20 N / 25 mm width or more. A cured product obtained by curing the film-like adhesive according to any one of claims 1 to 7. A laminate comprising the film-like adhesive according to any one of claims 1 to 7.