WO1997012009A1

WO1997012009A1 - Thermosetting composition

Info

Publication number: WO1997012009A1
Application number: PCT/US1996/014492
Authority: WO
Inventors: Yoshihiko Tasaka; Yuji Hiroshige
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1995-09-29
Filing date: 1996-09-06
Publication date: 1997-04-03
Also published as: JPH0995600A; JP3641033B2

Abstract

A thermosetting film adhesive according to the present invention is obtained by irradiating a precursor composition and converting it into a film shape, the precursor composition including: a) an epoxy resin not having a radiation-polymerizable functional group; b) a curing agent for curing the epoxy resin; c) a first radiation-polymerizable compound capable of reacting with one, or both, of the epoxy resin and the curing agent at the time of heat-curing; d) a second radiation-polymerizable compound not chemically reacting with the epoxy resin and the curing agent; and e) solid rubber particles; wherein the components b) and e) are dispersed in a matrix phase comprising the components a), c) and d), and which is liquid at a normal temperature.

Description

THERMOSETTING COMPOSITION

Detailed Description ofthe Invention The present invention relates to a thermosetting composition containing a radiation polymerized copolymer, such as an acrylic polymer, and a thermosetting epoxy resin, and also to a precursor composition suitable for preparing such a thermosetting composition.

The thermosetting composition according to the present invention is suitable, for example, for producing a thermosetting film adhesive.

Prior Art Epoxy compositions primarily contains an epoxy resin and a curing agent, and its cured product is excellent in bondability, heat-resistance, chemical resistance and electrical characteristics. The epoxy resin compositions can be cured at relatively low temperature and low pressure, and are useful for adhesives in that by-products are not emitted during the curing reaction. Accordingly, the epoxy resin composition has gained a wide application as the adhesive in the field of electric and civil engineering. However, the adhesives comprising the epoxy resin composition are mostly of a liquid two-pack type or a liquid one-pack type. Therefore, the workability is low, and reliability of bonding performance is likely to drop due to variance ofthe thickness at the time of application. Moreover, the two-pack type adhesive involves the problem that accurate weighing and mixing ofthe epoxy resin and the curing agent are necessary, and the one-pack type adhesive involves the problem of limited shelf stability.

An improvement; a film which contains the epoxy resin composition and which is shaped into a film (hereinafter referred to as the "film adhesive") is known. This adhesive has a high workability, and because the epoxy resin and the curing agent are mixed in advance, the bonding performance variability is low. Further, because the epoxy resin composition exists in the solid film, a diffusion proportion ofthe components is smaller than a liquid adhesive and its shelf stability is also improved. Such a film adhesive can be produced by, for example, irradiation by means of e.g., ultraviolet rays, of a film precursor consisting of a epoxy containing liquid mixture and a radiation-polymerizable acrylic compound. The acrylic only is polymerizee to form a solid continuous film. In such a film adhesive, the epoxy resin and the curing agent are contained in the substantially unreacted state in the film, and bonding is completed by interposing the film adhesive between adherends and heating so as to react the epoxy resin and the curing agent.

Such a film adhesive comprising the mixture ofthe acrylic compound and the epoxy resin composition is disclosed, for example, in U.S. Patent No. 4,552,604 (granted to Green and corresponding to Japanese Examined Patent Publication (Kokoku) No. 61-15112). Such a film adhesive is prepared from a composition containing an epoxy resin, its curing agent and acrylic acid ester as its principal components. In the film adhesive, the content ofthe epoxy resin is increased so as to improve heat-resistance and bonding performance but in such a case, cohesion performance ofthe film itself after the acrylic acid ester is polymerized drops, so that tack becomes excessively strong, the film becomes more stretchable, or oozing occurs while the film is wound on a roll. In consequence, the film adhesive becomes difficult to handle. Because the chemical reaction between the acrylic acid ester and the epoxy resin or bewteen the acrylic acid ester, the epoxy resin and the curing agent is not directed, the polymer ofthe acrylic acid ester and the cured product ofthe epoxy resin undergoes phase separation when the adhesive is thermally cured, and the bonding strength is likely to drop. Even when such phase separation is not extreme, the cured film itself is brittle, due to the high cross-linking density of the cured high epoxy product, so that the decrease in bonding performance such as shear adhesion strength, peel adhesion strength, etc., due to this brittleness cannot be improved easily.

Japanese Unexamined Patent Publication (Kokai) No. 63-10680 (Irii et al.) discloses an adhesive composition prepared from a composition containing an epoxy resin, a curing agent therefor, a monofunctional acrylate and a polyfunctional acrylate as the principal components. Because the polyfunctional acrylate is introduced, cohesion performance of the film itself can be improved. However, fluidity ofthe film is sacrificed at the state where the film is sandwiched between the adherends and is heated, and wettability to the surface ofthe adherend drops. As a result, bonding performance drops, too. As a matter of fact, shear adhesion strength no greater than 150 kg/cm² is observed in most cases. Japanese Unexamined Patent Publication (Kokai) No. 63-142084 (Sato et al.) discloses a radiation-polymerizable semicurable adhesive film prepared from a varnish containing a) an epoxy resin, b) a thermal epoxy curing agent contained as a dispersion in the phase containing the epoxy resin, c) a monomer containing a free-radical polymerizable unsaturated group and an epoxy group in the molecule thereof, and d) a free-radical photoinitiator. Component c), that is, the monomer, prevents the phase separation ofthe epoxy-cured product in the radiation copolymer, improving bonding performance. A form of film containing a liquid rubber component such as an epoxidated liquid rubber is also proposed for this adhesive film. However, because the radiation-polymerizable monomer also reacts with the epoxy resin through the curing agent, the cross-linking density ofthe film adhesive after heat curing becomes high, and it also becomes brittle.

Japanese Unexamined Patent Publication (Kokai) Nos. 63-10680, 63-142084, etc. described above, suggest the addition of a filler into the film adhesive, but do not suggest (1) improvement of cohesion performance ofthe film without attendent deterioration of its fluidity at the time of heat-curing and/or (2) bonding improvement performance while preventing film brittleness. To improve cohesion performance of the film, ordinary organic or inorganic fillers must be added in large quantities, and this will lower bonding performance and/or impede transmission of the radiation such as the ultraviolet rays for thicker film adhesives.

The adhesive tape disclosed in Japanese Unexamined Patent Publication (Kokai) No. 7-102223 (Nagase) is an example ofthe combination of an epoxy resin composition with a filler. This adhesive tape comprises an epoxy resin, a curing agent therefor, an adhesive layer requiring core/shell type resin particles as its essential component and a substrate of a fiber cloth. In this adhesive layer, the core/shell type resin particles are swelled inside the epoxy resin by heating at the formation stage of the adhesive layer so as to prevent oozing ofthe adhesive before application and at the time of application. To form a film adhesive having good handling properties, however, relatively large quantities of resin particles must be present, which decreases fluidity ofthe film at the time of heat curing and bonding performance drops. Further, heat-treatment for a predetermined time is necessary so as to allow the resin particles to swell in the filming process, so that the use of a fast-setting curing agent, that is, a curing agent sensitive to heat, becomes difficult, restricting the type of applicable curing agents.

As described above, the prior art technologies do not at all propose any improvement for the following required performances (1) and (2) ofthe film adhesive: (1) to improve cohesion performance without decreasing fluidity at the time of heat curing; and

(2) to improve bonding performance while preventing the adhesive from becoming brittle after heat curing.

It is an object ofthe present invention to provide a thermosetting film adhesive which simultaneously satisfies the requirements (1) and (2) described above.

The present invention provides a novel thermosetting composition containing a radiation-polymerizable copolymer, such as an acrylic polymer, and a thermosetting epoxy resin, and also a precursor composition suitable for preparing such a thermosetting composition.

Means for Solving the Problems

The object ofthe present invention to provide the novel thermosetting composition described above can be accomplished by a thermosetting composition obtained by irradiating a precursor composition, the precursor composition including: a) an epoxy resin not having a radiation-polymerizable functional group; b) a curing agent for thermally curing the epoxy resin; c) a first polymerizable compound containing at least one radiation- polymerizable functional group and at least one functional group capable of reacting, at the time of heat-curing, at least one of, the epoxy resin and the curing agent; d) a second polymerizable compound having at least one radiation- polymerizable functional group in the molecule thereof but not containing a functional group capable of reacting with the epoxy resin and the curing agent at the time of heat-curing; and e) solid rubber particles; wherein the components b) and c) are dispersed in the matrix phase consisting ofthe components a), c) and d), and wherein the precursor composition is liquid at ambient temperatures, to thereby polymerize the compounds c) and d).

A precursor composition according to the present invention suitable for preparing the thermosetting composition is a composition which contains: a) an epoxy resin not having a radiation-polymerizable functional group; b) a curing agent for thermally curing the epoxy resin; c) a first polymerizable compound containing, in the molecule thereof, at least one radiation-polymerizable functional group and at least one functional group capable of reacting, at the time of heat-curing, with one, or both, ofthe epoxy resin and the curing agent; d) a second polymerizable compound containing at least one radiation- polymerizable functional group in the molecule thereof but not containing a functional group capable of reacting with the epoxy resin and the curing agent at the time of heat-curing; and e) solid rubber particles; wherein the components b) and e) form a dispersion phase in the matrix phase comprising the components a), c) and d), and the composition is liquid at a normal temperature. Further, the present invention provides a thermosetting film adhesive comprising the composition described above which is shaped into a film having a predetermined thickness.

In the present invention, the solid rubber particles are contained, with the curing agent for the epoxy resin, in the matrix phase comprising the radiation copolymer formed by the first and second polymerizable compounds and the epoxy resin, as the dispersion phase. Therefore, in the thermosetting composition ofthe present invention, cohesion performance can be improved without decreasing fluidity at the time of heat-curing.

The thermosetting composition ofthe present invention contains the radiation copolymer formed by the first polymerizable compound capable of reacting with the epoxy resin and/or the curing agent and the second polymerizable compound not reacting with both ofthe epoxy resin and the curing agent. This controls the crosslinking density ofthe heat-cured product, prevents the cured product from becoming brittle, and so functions as to improve bonding performance, particularly shear adhesion strength and peel adhesion strength

The epoxy resin and the curing agent for thermally curing the epoxy resin so function as to easily improve the heat resistance and bonding performance ofthe thermosetting composition ofthe present invention

When the first polymerizable compound is a compound containing an acryloyl group or methacryloyl group and the solid rubber particles contain either i) fine particles substantially comprising an acrylic rubber and/or ii) rubber particles having an acrylic shell portion, the function of improving cohesion performance without deteriorating fluidity at the time of heat-curing can be further improved This is presumably because a physical interaction partially exists between the radiation copolymer containing the acrylic component in the matrix and the rubber particles, and this interaction operates in such a manner as to disappear at a temperature higher than heat-curing temperature

Embodiments ofthe Invention Hereinafter, embodiments ofthe present invention will be explained in further detail

The thermosetting composition according to the present invention is prepared by irradiating a precursor composition as a precursor of the thermosetting composition. It is a solid composition which contains an unreacted epoxy resin and a curing agent for heat-curing the epoxy resin, wherein the epoxy resin and the curing agent are subjected to the curing reaction by heating The thermosetting composition is solid at a normal temperature (i e about 25°C, hereinafter the terms "normal temperature" and "ambient temperature" mean a temperature of about 25°C). In this composition, the matrix phase comprises the radiation copolymer formed from the first and second polymerizable compounds by irradiating the precursor composition, and the epoxy resin. The curing agent for the epoxy resin and the solid rubber particles exists as the dispersion phase in the matrix This composition is generally heat-curable at a temperature within the range of 80 to 200°C The thermosetting composition is generally prepared by applying the precursor composition to a substrate such as an adherend and then polymerizing the radiation-polymerizable components.

The "radiation" that can be utilized for the preparation ofthe thermosetting composition according to the present invention is suitably a ultraviolet ray, but electron beams, visible rays and X-rays can also be utilized so long as the object ofthe invention is not spoiled.

The precursor composition for preparing the thermosetting composition according to the present invention is a composition which contains an epoxy resin, a curing agent for the epoxy resin, a radiation-polymerizable component (whose detail will be later described) and solid rubber particles (whose detail will be later described), and which is liquid at the normal temperature. Its viscosity is suitably 500 to 100,000 cP (centi-poise) as the measurement value at 25°C using a Brookfield viscometer, and particularly preferably 1,000 to 50,000 cPs. If the viscosity is less than 500 cP, fluidity is too excessive to form film having a uniform thickness, and a film having a large thickness (e.g. at least 250 μm) cannot be formed easily. If the viscosity exceeds

100,000 cPs, on the contrary, the coating operation or the mixing operation tends to become difficult, and defoaming at the time of film formation is likely to become difficult, if defoaming is not carried out sufficiently, uniform adhesive products cannot be produced as a whole due to the formation of bubbles, hindrance of radiation polymerization by oxygen, and so forth.

The "epoxy resin not having a radiation-polymerizable functional group" (hereinafter merely called the "epoxy resin") is the component which imparts thermosettability to the thermosetting composition in cooperation with the curing agent, and exhibits suitable tackiness (or adhesiveness) before heat-curing and high bonding performance after heat-curing when used as the adhesive. Here, the term "epoxy resin" means a compound which contains at least one epoxy group in the molecule thereof. The term "radiation-polymerizable functional group" means a group which has a polymerizable unsaturated bond, such as an acrylic group, a methacrylic group, and so forth. The epoxy resin is a monomer or oligomer having suitably at least two glycidyl groups per molecule. They easily exhibit suitable tack and high bonding performance. Its viscosity is suitably 500 to 5,000,000 cP (centi-poise), particularly suitably 1,000 to 1,000,000 cP, as a measurement value at 25°C using a Brookfield viscometer. The epoxy resin may be used either alone or as a mixture of two or more kinds, and can contain a solid epoxy compound within the viscosity range described above.

The epoxy equivalent ofthe epoxy resin affects the viscosity ofthe precursor composition, and the epoxy equivalent suitable for improving the handling property of the precursor composition is 150 to 1,000 and particularly suitably 170 to 500.

Examples ofthe epoxy resins that can be used in the present invention are bis¬ phenol type epoxy, a phenol novolak type epoxy, a cresol novolak type epoxy, an aliphatic epoxy, and so forth. The "curing agent for heat-curing the epoxy resin" (hereinafter merely called the "curing agent") is contained in the matrix phase containing the epoxy resin while forming the dispersion phase. The curing agent dispersed in the matrix phase containing the epoxy resin is solid at the normal temperature or is separated from the matrix. Accordingly, the thermosetting composition according to the present invention has latency. The shape ofthe curing agent in the dispersion phase is generally particles, and the mean particle diameter is suitably 1 to 100 μm and particularly suitably 5 to 50 μm. Latency tends to drop if the size ofthe dispersion phase is too small, and when the size is excessively great, on the other hand, the thermosetting reaction is likely to be heterogeneous or reactivity is likely to drop. Examples ofthe curing agents that can be used in the present invention include dicyandiamide type curing agents (inclusive of dicyandiamide and its derivatives), organic acid hydrazides, BF₃ complexes, imidazole derivatives, diaminomaleonitrile and its derivatives, and melamine and its derivatives.

Among them, the dicyandiamide type curing agent or the organic acid hydrazide type curing agent is suitable so as to exhibit high bonding performance.

When high latency and fast curability are taken into consideration, the dicyandiamide type curing agent is particularly suitable. The reason why the dicyandiamide type curing agent exhibits such excellent functions is because it is a so-called "heat- promotion type" latent curing agent which is not dissolved in the epoxy resin in the matrix but is contained as the dispersion phase at the normal temperature, and when heated to a temperature above the melting point ofthe curing agent, it is dissolved in the epoxy resin and quickly starts the reaction A specific example ofthe dicayndiamide derivative is "H3842" (trade name) available from A C R K K

The amount ofthe curing agent is suitably from 0 1 to 80 parts by weight, particularly suitably from 1 to 50 parts by weight, on the basis of 100 parts by weight ofthe epoxy resin If the amount is less than 0 1 part by weight, the curing reaction of the epoxy resin is likely to becomes inferior and if it exceeds 80 parts by weight, on the contrary, the unreacted curing agent is likely to remain in the heat-cured product The unreacted curing agent reduces the mechanical strength, moisture resistance and electrical characteristics ofthe heat-cured product A curing promoter can be used in combination with the curing agent in order to lower the curing temperature and to reduce the curing time Tertiary amine, imidazole or polyamine is a suitable example ofthe curing promoter for dicyandiamide or the dicyandiamide derivatives "HX3O88" (trade name) commercially vailable from Asahi Kasei K K is a specific example ofthe imidazole type promoter The amount ofthe curing promoter should be appropriately determined in accordance with the object of its use, but is suitably 0 1 to 20 parts by weight, particularly suitably 0 5 to 10 parts by weight, per 100 parts by weight ofthe epoxy resin If the amount is less than 0 1 part by weight, the promotion effect is low, and if it exceeds 20 parts by weight, latency will drop. The "first polymerizable compound" used in the present invention is the

"radiation-polymerizable compound containing, in the molecule thereof, at least one radiation-polymerizable functional group and at least one functional group capable of reacting, at the time of heat-curing, with one, or both, ofthe epoxy resin and the curing agent" The first polymerizable compound is polymerized with the second polymerizable compound (whose detail will be later described) when the radiation is irradiated to the precursor composition, and forms a solid thermosetting composition Here, the term "radiation-polymerizable functional group" represents a group having a polymerizable unsaturated bond such as (meth)acryhc group The first polymerizable compound has at least one radiation-polymerizable functional group, and can have two or more such groups to the extent that fluidity ofthe thermosetting composition is not deteriorated at the time of heat-curing The term "fluidity at the time of heat-curing" means the property ofthe thermosetting composition such that when it is sandwiched between two bonded articles and is pressed with heating, the thermosetting composition can easily increase its bonding area while following up concavoconvexities or undulation ofthe surfaces ofthe bonded article, or the property such that the adhesive layer comprising the thermosetting resin can undergo deformation and it thickness can be reduced easily to a desired value. Such a property is one ofthe requisites for the bonding operation of compact electronic or electrical or mechanical components such as miniature motors for vehicles, ferrite magnets for speakers, and so forth The capability ofthe first polymerizable compound to be chemically reacted with the epoxy resin or the curing agent improves compatibility between the radiation copolymer formed from the first and second polymerizable compounds and the epoxy cured product (the reaction product between the epoxy resin and the curing agent), increases the cohesion force ofthe thermosetting composition after heat-curing, and provides high bonding performance Here, the term "functional group capable of reacting, at the time of heat-curing, with one, or both, of the epoxy resin and the curing agent" represents a) functional groups capable of reacting with the epoxy group ofthe epoxy resin, such as a carboxyl group, a hydroxyl group, an amino group, etc., or b) functional groups capable of reacting with the curing agent, such as a glycidyl group, a ketone group, an alicyclic epoxy group (oxysilane group), etc Such a functional group is a member selected from the functional groups belonging to (a) or (b) or at least two kinds of functional groups belonging to (a) and (b)

Examples of such first polymerizable compounds include a carboxyl group- containing type such as acrylic acid and methacrylic acid, a hydroxyl group-containing type such as 2-hydroxy-3-phenoxypropyl acrylate, and glycidyl group-containing type such as glycidyl acrylate, glycidyl methacrylate, N-[4-(2,3-epoxypropoxy)-3,5- dimethylbenzyl]-acrylamide

A suitable first polymerizable compound is the glycidyl group-containing type described above Reactivity of the compounds of this type to the curing agent is substantially equal to that ofthe epoxy resin Therefore, the radiation copolymer does not first react with the curing agent in the thermosetting composition to spoil shelf stability, its reactivity is not inferior to that ofthe epoxy resin at the time of heat - curing, and the phase separation does not occur between the radiation copolymer and the epoxy cured product, either.

The "second polymerizable compound" used in the present invention is "the radiation polymerizable compound containing at least one radiation-polymerizable functional group in the molecule thereof but not containing a functional group capable of reacting the epoxy resin and the curing agent at the time of heat-curing, and not substantially undergoing the thermosetting reaction with the epoxy resin and the curing agent". This second polymerizable compound contributes to the formation ofthe solid thermosetting composition by the radiation treatment in the same way as the first polymerizable compound, but because it does not react with both ofthe epoxy resin and the curing agent, it prevents the heat-cured product from becoming brittle.

The term "radiation-polymerizable functional group" is defined in the same way as in the case ofthe first polymerizable compound. The second polymerizable compound also has at least one radiation-polymerizable functional group, and can contain two or more such groups to the extent that fluidity ofthe thermosetting composition is not deteriorated at the time of heat-curing

Here, the term "functional group capable of reacting with the epoxy resin and the curing agent at the time of heat-curing" can be defined in the same way as in the case ofthe first polymerizable compound. In other words, examples ofthe second polymerizable compound include (meth)acrylic acid alkyl esters, N,N- dialkyl(meth)acryal amides, (meth)acryloylmorpholine, N-vinylpyrolidone and N- vinylcaprolactam.

The second characterizing feature brought forth by the use ofthe second polymerizable compound is that the properties of the radiation copolymer formed by the first and second polymerizable compounds such as a glass transition temperature can be easily controlled. The glass transition temperature ofthe radiation copolymer is suitably 25 to 180°C, particularly suitably 40 to 120°C. If the glass transition temperature ofthe copolymer is less than 25°C, the handling property ofthe thermosetting composition tends to drop and bonding performance after heat-curing tends to drop, too. If it exceeds 180°C, on the contrary, fluidity after heat-curing tends to drop, and initial tack at normal temperature is likely to drop. A suitable second polymerizable compound, which makes it easy to control the glass transition temperature of the radiation copolymer, is a (meth)acrylic acid alkyl ester whose homopolymer has a glass transition temperature of 25 to 200°C Specific examples of such (meth)acrylic acid alkyl esters include isobornyl acrylate (whose homopolymer has a glass transition temperature of 94°C (hereinafter, the numeric figure in parentheses represents similarly the glass transition temperature ofthe homopolymer)), cyclohexyl methacrylate (66°C), isobornyl methacrylate (180°C), dicyclopentanyl acrylate (120°C, this is also called "tricyclo[5,2, l,0²⁶]deca-8-il- acrylate"), and dicyclopentanyl methacrylate ( 175°C, this is also called "tricyclo[5,2, l,0²⁶]deca-8-il-methacrylate") Here, the "glass transition temperature" is defined by the Fox's equation (T G Fox, Bull Am Phys Soc 1, 123(1956))

The blend proportion ofthe second polymerizable compound and the first polymerizable compound is generally within the range of 9 1 to 1 9 in terms ofthe weight ratio (first polymerizable compound second polymerizable compound) This blend proportion can be suitably determined so as to obtain good balance of latency of the thermosetting composition, brittleness of the heat-cured product, fluidity at the time of heat-curing, compatibility between the epoxy cured product and the radiation copolymer, and bonding performance, and so forth

The "solid rubber particles" used in the present invention are solid at the normal temperature and can be contained in the matrix phase comprising the radiation copolymer and the epoxy resin while forming the dispersion phase Depending on the matrix components, the portion ofthe particles near the surface sometimes undergoes swelling, but the particles are not dissolved as a whole in the matrix components even at the time of heat-curing The solid rubber particles improve cohesion performance without spoiling fluidity ofthe thermosetting composition at the time of heat-curing, also improve the handling property as the film adhesive when the content ofthe epoxy resin is increased so as to improve the heat-resistance, etc , and advantageously function to improve the impact resistance and peel adhesive strength ofthe cured product after heat-curing The addition ofthe solid rubber particles is also advantageous so as to adjust the viscosity ofthe precursor composition to the suitable range described already The shape ofthe dispersion phase of the solid rubber particles is generally granular and the size is suitably 0.1 to 20 μm. If it is less than 0.1 μm, the viscosity of the precursor composition will be excessively increased and the application and the formation ofthe film precursor will become difficult. If it exceeds 20 μm, on the contrary, the effect of improvement ofthe impact resistance, etc., cannot be expected. Solid rubber particles containing one, or both, ofthe following particles i) and ii) can be used as the solid rubber particles: i) fine particles substantially consisting of an acrylic rubber; and ii) core/shell type fine particles comprising acrylic type shell portion and core portion substantially consisting of rubber.

When the solid rubber particles contain the fine particles i), the acrylic fine particles preferably comprise substantially a (meth)acrylate type rubber having a glass transition temperature of not higher than O°C. This is advantageous in order to easily exhibit the improving effect of cohesion performance. When the thermosetting composition is used as the film adhesive, the glass translation temperature ofthe acrylic fine particles should be set generally to a lower temperature than the temperature of use and in this case, the glass transition temperature ofthe (meth)acrylate type rubber should be set to -20°C or below.

Copolymers from ethyl acrylate and n-butyl acrylate homopolymers or monomer components containing them can be used as the (meth)acrylate type rubber. A crosslinked rubber formed from the monomer components containing polyfunctional acrylic monomers can also be used. The crosslinked rubber is advantageous to prevent excessive swelling due to the matrix components, the increase ofthe viscosity ofthe precursor composition and the drop ofthe properties ofthe heat-cured product. An emulsifier can be allowed to exist on the surface of the acrylic type fine particles in order to further improve dispersibility in the matrix and to improve interaction with the epoxy cured product.

When the solid rubber particles contain the component ii) described above, the core/shell type fine particles suitably comprise a core portion substantially consisting of a rubber having a glass transition temperature of not higher than O°C and an acrylic shell portion consisting ofa (meth)acrylic polymer having a glass transition temperature of not lower than 25°C. Such core/shell type fine particles are advantageous because the improvement effect such as the improvement of cohesion performance can be easily obtained.

Besides the (meth)acrylate type rubber described above, the core portion ofthe core/shell type fine particles can use a diene type rubber substantially consisting of butadiene homopolymers, butadiene-styrene copolymers, etc., can be used, too.

Polymethyl methacrylate is generally used for the shell portion, and its shell portion is suitably crosslinked in order to prevent excessive swelling due to the matrix components. The glass transition temperature ofthe shell porion is suitably 30 to 150°C and particularly suitably 50 to 130°C. If it is less than 30°C, cohesion ofthe fine particles is likely to occur and dispersion tends to become difficult. If the glass transition temperature exceeds 150°C, on the contrary, swelling tends to be insufficient due to the matrix components. Further, it is also possible to use core/shell type fine particles containing the shell portion, which has a functional group (carboxyl group, hydroxyl group, glycidyl group, etc.) capable of reacting with the epoxy resin and/or the curing agent on the surface thereof, to the extent that fluidity at the time of heat- curing is not deteriorated.

The weight ratio (core-to-shell ratio) ofthe core component and the shell component in the core/shell type fine particles is generally within the range of 10: 1 to 1:2.

Proportion of each component:

A suitable proportion of each component in the precursor composition for preparing the thermosetting composition according to the present invention is as follows. When the sum ofthe epoxy resin (component a), the curing agent (component b), the first polymerizable compound (component c), the second polymerizable compound (component d) and the solid rubber particles (component e) is calculated as 100 wt%, the sum ofthe components a) and b) is within the range of 38 to 90 wt%, the sum ofthe components c) and d) is 5 to 60 wt%, and the content of e) is 2 to 40 wt%.

If the sum ofthe components a) and b) is less than 38 wt%, bonding performance after heat-curing and fluidity at the time of heat-curing tend to drop and the viscosity ofthe precursor composition cannot be adjusted to the suitable range, so that the film having a large thickness cannot be obtained easily. If the sum exceeds 90 wt%, on the contrary, tack becomes so strong that the handling property tends to drop.

If the sum ofthe components c) and d) is less than 5 wt%, tack becomes so strong that the handling property tends to drop. If it exceeds 60 wt%, on the contrary, the contents ofthe epoxy resin and the curing agent drop relatively, and the viscosity ofthe precursor composition cannot be regulated to a suitable range, so that a film having a large thickness cannot be obtained easily.

If the content ofthe component e) is less than 2 wt%, the effect of improvement of cohesion performance, etc., tends to be insufficient and if it exceeds 40 wt%, on the contrary, the viscosity ofthe precursor composition excessively increases, so that the application and the formation ofthe film precursor tend to become difficult.

When the balance of overall performance is taken into consideration, a suitable content of each component is as follows. Namely, when the sum ofthe components a) to e) is calculated as 100 wt%, the sum ofthe contents ofthe components a) and b) is within the range of 46 to 80 wt%, the sum ofthe contents ofthe components c) and d) is within the range of 10 to 50 wt%, and the content ofthe component e) is 4 to 30 wt%.

Radical initiator:

To promote the radiation polymerization ofthe first and second polymerizable compounds, a radical initiator is generally added to the precursor composition.

Utilization ofthe radical promoter is advantageous to uniformly and quickly complete the radiation polymerization throughout the precursor composition formed into a relatively large film thickness particularly when the radiation having relatively weak transmission force such as the ultraviolet rays is utilized.

A cleavage type or a hydrogen abstraction type is effective as the radical initiator for the ultraviolet rays. Specific examples include benzoethyl ether, diethoxy- acetophenone, benzyl methyl ketal, 2-hydroxy-2-methyl-l-phenylpropane-l-one, 1- hydroxycyclohexyl phenyl ketone, etc., for the cleavage type, and benzyl, benzophenone, 2,4-diethylthioxanthone, etc., for the hydrogen abstraction type. The content ofthe radical initiator is suitably from 0 01 to 5 wt% on the basis ofthe weight ofthe composition as a whole if it is less than 0 01 wt%, the radiation polymerization cannot be completed uniformly and quickly and if it exceeds 5 wt%, on the contrary, the initiator remains even after the radiation polymerization and tends to lower bonding performance

Further, a photo-initiator adjuvant, a photo-sensitizer and a chain transfer agent can be added in order to promote the radiation polymerization

Other additives, etc Besides the additives described above such as the curing promoter, the radical initiator, etc , those additives which are used for general liquid epoxy resin compositions can be added, whenever necessary, to the precursor composition according to the present invention Examples of such additives include an organic or inorganic filler other than the solid rubber particles, a flow controlling agent, a pigment, a defoaming agent, a modifier (silane coupling agent), etc For example, a heat conductive filler or an electrically conductive filler can be added in order to impart heat conductivity or electrical conductivity

Production method of precursor composition The precursor composition for the thermosetting composition according to the present invention can be produced in the following way First, the epoxy resin, the first polymerizable compound, the second polymerizable compound, and the additives, whenever necessary, are mixed in a stirrer Stirring is continued until these components form a uniform solution, so as to prepare a preliminary mixture. The curing agent and the solid rubber particles are not generally added at the preparation stage ofthe preliminary mixture Subsequently, the curing agent and the solid rubber particles are added to the preliminary mixture and are uniformly dispersed, thereby obtaining the intended precursor composition In this case, the solid rubber particles are first added to, and dispersed into, the preliminary mixture and then the curing agent is added so as to complete dispersion The radical initiator is not generally added at the preparation stage of preliminary mixture, and is better added at the final production stage ofthe precursor composition in the same way as the curing agent. An apparatus generally used for the production ofthe adhesives can be used as the stirrer.

Preparation method of thermosetting composition: The thermosetting composition according to the present invention is prepared by applying radiation polymerization treatment to the precursor composition as described above. For example, the thermosetting composition is obtained by disposing a coating layer consisting ofthe precursor composition on the surface ofa substrate such as release paper (liner, etc.), a plastic film, a fiber cloth, etc., and then irradiating so as to solidify the coating layer. In this case, customary coating means such as a knife coater, a roll coater, etc., can be employed for disposing the coating layer. When the thermosetting composition is used as the adhesive layer while it remains fixed on the substrate such as the plastic film, the fiber cloth, etc., it can be used as an adhesive tape, etc.

Further, a film-like thermosetting composition having a predetermined thickness can be formed in the following way. First, the precursor composition is sandwiched between two transparent substrates and a predetermined pressure is applied so as to attain a predetermined thickness. In this way, a film precursor ofthe precursor composition sandwiched between the two transparent substrates is formed. After irradiating the film precursor from above the transparent substrates to solidify the composition, the film is taken out from between the transparent substrates, thereby providing the thermosetting composition. In this case, it is advisable to apply release treatment using a silicone releasing agent to the surfaces ofthe transparent substrates which come into contact with the preparation substrate. The transparent substrates are advantageously used when radiations having a relatively low transmission force such as the ultraviolet rays are used, and when the polymerization reaction is likely to be impeded by oxygen, in order to carry out the radiation polymerization uniformly and quickly. Further, in the case ofthe preparation method using such transparent substrates, the irradiation can be effected either sequentially or simultaneously from one, or both, ofthe surfaces ofthe two transparent substrates. The dose ofthe radiation should be suitably determined in accordance with the precursor composition or with a radiation source used. Nonetheless, when the ultraviolet rays are used as the radiation, for example, the dose is generally within the range of 100 to 3,000 mJ/cm²

Application of thermosetting composition The thermosetting composition according to the present invention has excellent bonding performance and handling property as described above. Therefore, it can be suitably utilized as an adhesive material The form of the adhesive material includes an adhesive tape having a substrate, and a thermosetting film adhesive which will be later described.

The thermosetting composition according to the present invention can also be utilized as a base-impregnated film adhesive containing a substrate consisting of a fiber fabric existing in the film of the thermosetting composition The fiber fabric may be a non-woven fabric or a woven fabric, and examples of the fiber materials are polyester, nylon, glass, carbon, alumina, and so forth The base-impregnated film adhesive can further improve cohesion performance of the thermosetting composition and can effectively prevent oozing

The thermosetting film adhesive according to the present invention can be used for the application, to which ordinary epoxy adhesives are applied, such as bonding of metals, glass, plastics, ceramics and other adherends Since this thermosetting composition has both high shear adhesive strength and high peel adhesive strength, it is useful as a structural adhesive

Thermosetting film adhesive The thermosetting film adhesive according to the present invention comprises the thermosetting composition according to the present invention, and since it does not require a substrate, it is economically advantageous from the aspect of materials and production process Such a thermosetting film adhesive can be produced by forming the film-like thermosetting composition having a predetermined thickness as described above.

The thickness of the film adhesive is generally at least 10 μm, suitably 250 to 10,000 μm, and most suitably 300 to 5,000 μm According to the present invention, when a film comprising the thermosetting composition prepared from the precursor composition is formed, a film having a relatively large thickness can be formed easily. This is because the curing agent for thermally curing the epoxy resin forms the dispersion phase inside the matrix phase, therefore reflects uniformly the radiation on the surface of its dispersion phase and so functions as to allow the radiation to reach the depth ofthe film through the gaps between the dispersion phases. Such a function is particularly effective when the radiation has a low transmission force such as the ultraviolet rays. When the thickness of the film adhesive is at least 250 μm, handling at the time of bonding to the adherend becomes easy, and bonding can be easily made to adherend having vigorous concavoconvexities or between the adherends having mutually different radii of curvature on their surfaces. However, when the thickness exceeds 10,000 μm, the strength in the direction of the thickness of the film becomes non-uniform, and reliability of the adhesive is likely to drop.

When suitable tack is provided to the surface of the film adhesive, provisional bonding to the boded article and the adjustment of the bonding position becomes easy. Tack of the film surface can be easily controlled by selecting the kind ofthe epoxy resin and/or adjusting the contents in the composition to the suitable ranges.

Examples Hereinafter, the present invention will be explained in further detail with reference to the following Examples.

Examples 1 to 3: Comparative Examples 1 to 4

Precursor compositions for thermosetting compositions of Examples 1 to 3 were produced by preparing each of the compounds shown in Table 1 in the amount also tabulated in Table 1, in the following way. The amount of each component in the table is expressed by parts by weight. The components used in Examples 1 to 3 and Comparative Examples 1 to 4 and tabulated in Table 1 were as follows. ( 1) Compound a) (epoxy resin):

(i) YD 134: glycidylether bis-phenol A type epoxyresin (Type "YD 134"; epoxy equivalent = about 260), a product of Toto Kasei K.K. (ii) YD128 glycidylether bis-phenol A type epoxy resin (Type "YD128", epoxy equivalent = about 186), a product of Toto Kasei K K

(2) Compound b) (curing agent) (i) H3842 a product of A C R K K , modified dicyandiamide type curing agent (Type "H3842")

(ii) AH162 a product of Ajinomoto K K , modified dicyandiamide type curing agent (Type "AH 162")

(iii) H3615S a product of A C R K K , polyamine type curing promoter (Type "H3615S")

(iv) HX3088 a product of Asahi Kasei K K , imidazole type curing agent (Type "HX3088")

(3) Compound c) (first polymerizable compound) GMA glycidyl methacrylate (4) Compound d) (second polymerizable compound)

(i) DCPMA a product of Hitachi Kasei Kogyo K K , dicyclopentanyl methacrylate (Type "FA513M")

(ii) ACMO a product ofKojin K K , acryloyl morpholine (Type

"ACMO") (iii) IOA isooctyl acrylate

(5) Compound e) (solid rubber particles)

(i) EXL2655 a product of Kureha Kagaku K K , consisting of core portion of styrene-butadiene copolymer and shell portion of uncrosslinked methyl methacrylate type polymer, mean particle size = about 0 2 μm, core-shell type rubber fine particles ("Paraloid

EXL2655")

(ii) BPA328 a product of Nippon Shokubai K K , a mixture containing 20 wt% of crosslinked acrylic rubber fine particles (mean particle size = about 0 3 μm) in liquid glycidylether bis-phenol A type epoxy resin (epoxy equivalent = about 230) (Type "acrylic rubber fine particle-dispersed epoxy resin BPA328") (iii) AC3355 a product of Takeda Yakuhin Kogyo K K., core/shell type solid rubber fine particles having mean particle size of about 0.5 μm and consisting of core portion of n-butyl acrylate-ethyl acrylate copolymer and shell portion of crosslinked methyl methacrylate polymer ("Stafiloid AC3355")

(6) Compound f) (radical initiator) D1 173 a product of Ciba Geigy AG, 2-hydroxy-2-methyl-l-phenylpropane-l-one ("Darocur 1 173")

(7) Inorganic filler A200 a product of Nippon Aerosil K.K., anhydrous silica fine particles ("Aerosil A200") (8) Organic filler S2464 a product of Nippon Synthetic Rubber K.K., crosslinked polystyrene particles (mean particle diameter of about 10 μm, "S2464-100")

First, the epoxy resin (compound a), the first polymerizable (compound c) and the second polymerizable (compound d) were mixed and stirred to obtain a preliminary mixture consisting of a uniform solution Next, this preliminary mixture and the solid rubber particles (compound e) were mixed in a homomixer and high speed stirring was continued for several hours After uniform dispersion ofthe solid rubber particles in the preliminary mixture was confirmed, the curing agent (compound b) and the radical initiator (compound f) were added and stirring was further continued so as to uniformly disperse the curing agent and to obtain the intended precursor composition. The viscosity of this precursor composition was adjusted to the range of 1,000 to 50,000 cP in terms ofthe measurement value at 25°C using a Brookfield viscometer

The precursor composition of each of Comparative Examples 1 to 4 was obtained in the same way as in Examples described above, with the proviso that the addition ofthe solid rubber particles was omitted in Comparative Examples 1 and 2, and the fillers tabulated in the table were added in place ofthe solid rubber particles in Comparative Examples 3 and 4

Subsequently, a film adhesive comprising the thermosetting composition was produced by using the precursor composition obtained in each ofthe examples. First, vacuum defoaming treatment was applied to the precursor composition and then the precursor composition was sandwiched between two PET films into a total thickness of 300 μm so as to produce a film precursor sandwiched between the two films. Each film surface was subjected to releasing treatment by a silicone releasing agent. Next, the film precursor was irradiated with ultraviolet rays from both surfaces of the film to solidify the film precursor and the two films were removed to obtain the object film adhesive. The irradiation was carried out using a high pressure mercury lamp in the dose of about 1,250 mj/cm². This dose was measured by using a light quantity integrator "UV Actinointegrator UV350", a product of ORC K.K.

The shear adhesion strength, the T-peel adhesion strength, tackiness, flow capability at 150°C and oozing at 25°C of the film adhesive obtained in the manner described above were evaluated by the following method. The results were also tabulated in Table 1. The glass transition temperature ofthe acrylic copolymer (radiation copolymer) contained in the film adhesive was measured by the aforementioned Fox's equation and the result of calculation was also tabulated in Table 1. The glass transition temperatures of the homopolymers of respective acrylic component were GMA = 46°C, DCPMA = 175°C, ACMO = 145°C and IOA = -55°C. Next, the measurement method of each evaluation item will be explained.

(1) Shear adhesion strength:

A film adhesive prepared into a predetermined size was interposed between two steel plates having a length of 150 mm, a width of 25 mm and a length of 1.6 mm, and while both ends ofthe steel plates in the longitudinal direction were clipped by two clips, a pressure was applied to the film and the film was left standing in an oven at 150°C for 30 minutes so as to cure the adhesive, in accordance with JIS K6850. The tensile shear adhesive strength was measured for this sample. The measurement temperature was 25°C and a tensile speed was 5 mm/min.

The film adhesives (Examples 1 to 3) containing the solid rubber particles according to the present invention exhibited a higher adhesive strength than that of Comparative Example 1.

(2) T-peel adhesive strength:

A film adhesive prepared into a predetermined size was inteφosed between two steel plates having a length of 150 mm, a width of 25 mm and a thickness of 0.5 mm in such a manner that only the portion having a distance of 90 mm from one ofthe ends in the longitudinal direction was clamped, and while a pressure was applied by clamping both ends ofthe steel plates in the longitudinal direction by two clips, the film was left standing in an oven at 150°C for 30 minutes so as to cure the adhesive, in accordance with JIS K6850. The T- peel adhesive strength was measured for this sample. Measurement was carried out by opening the unbounded portions ofthe two steel plates into a T-shape and pulling the two plates in the separating direction at a tensile speed of 50 mm/min. The measurement temperature was 25°C.

The film adhesives containing the solid rubber particles according to the present invention (Examples 1 to 3) exhibited the adhesive strength of about 4 to 6 times higher than that of Comparative Example 1 not containing the solid rubber particles. (3) Tackiness:

The degree of tackiness ofthe surface ofthe film adhesive was judged by the feel ofthe finger tip. The case where the film adhesive had suitable tackiness so as to handle it was judged as "moderate (M)", and the case where it was too tacky to handle was judged as "strong (S)". In Comparative Example 2, since tackiness was too strong and the film adhesive could not be peeled easily from the PET film used for the production process ofthe film adhesive, it was judged as "excessive (E)".

(4) Flow capability at 150°C:

The film adhesive was sandwiched between two steel plates in the same way as in the measurement ofthe shear adhesive strength in the item (1), the degree of flow of the adhesive was observed with the naked eye while pressure and heating were applied thereto. The case where the adhesive quickly spread between the two steel plates and a sufficient bonding area could be secured was judged as "excellent (E)" and the case where a certain time was necessary before spreading was judged as "normal (N)". In Comparative Example 3, the viscosity of the precursor composition and its thixotropy were so high that vacuum defoaming and the application were difficult to practice.

(5) Oozing at 25°C:

A film adhesive was slitted into a width of 20 mm without removing the two PET films during the production process ofthe film adhesive, and a tape comprising the film adhesive equipped with the PET films having a predetermined length was produced. The tape was taken up into a roll, and this roll was evaluated as the sample. The case where the sample was left standing at 25°C for one hour and oozing occurred to a remarkable extent was judged as "remarkable (R)", and the case where oozing occurred to the extent such that no problem occurred in appearance was judged as "slight (S)"

Table 1

Claims

What is claimed is:

1. A thermosetting composition obtained by irradiating a precursor composition, said precursor composition comprising: a) an epoxy resin containing no radiation-polymerizable functional group; b) a curing agent for thermally curing said epoxy resin; c) a first polymerizable compound containing, in the molecule thereof, at least one radiation-polymerizable functional group and at least one functional group capable of reacting, at the time of heat-curing, with at least one of said epoxy resin and said curing agent; d) a second polymerizable compound containing at least one radiation- polymerizable functional group in the molecule thereof but not containing a functional group capable of reacting with said epoxy resin and said curing agent at the time of heat-curing; and e) solid rubber particles; wherein each of said components b) and e) is dispersed in a matrix phase consisting of said components a), c) and d), and wherein said precursor composition is liquid at a normal temperature, to thereby polymerize the compounds c) and d).

2. A thermosetting composition according to claim 1, wherein said radiation-polymerizable functional group of said first polymerizable compound is an acryloyl group or a methacryloyl group, and said solid rubber particles comprise at least one of a) fine particles substantially consisting of an acrylic rubber and b) core/shell type fine particles comprising an acrylic type shell portion and a core portion substantially consisting of a rubber.

3. A thermosetting composition according to claim 1, wherein when the sum ofthe content of each of said components a) to e) in said precursor composition is calculated as 100 wt%, components a) and b) comprise from 38 to 90 wt%, components c) and d) comprise 5 to 60 wt%, and component e) comprises 2 to 40 wt%.

4. A precursor composition for preparing a thermosetting composition according to claim 1 including: a) an epoxy resin not having a radiation-polymerizable functional group; b) a curing agent for thermally curing said epoxy resin; c) a first polymerizable compound containing, in the molecule thereof, at least one radiation-polymerizable functional group and at least one functional group capable of reacting, at the time of heat-curing, with one, or both, of said epoxy resin and said curing agent; d) a second polymerizable compound having at least one radiation- polymerizable functional group in the molecule thereof but not having a functional group capable of reacting with said epoxy resin and said curing agent at the time of heat-curing; and e) solid rubber particles; wherein each of said components b) and e) form a dispersion phase in a matrix phase consisting of said components a), c) and d), and which is a liquid at a normal temperature.

5. A thermosetting film adhesive consisting of said thermosetting composition of claim 1, which is shaped into a film having a thickness of from 250 to 10,000 μm.