JP7484557B2 - Adhesive composition, adhesive sheet and laminate - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive sheet, and a laminate. More specifically, the present invention relates to a pressure-sensitive adhesive composition for forming a pressure-sensitive adhesive layer that has adhesiveness under normal conditions and is firmly bonded to an adherend by curing by heating or the like after application to the adherend. The present invention also relates to a pressure-sensitive adhesive sheet and a laminate having a pressure-sensitive adhesive layer that has excellent room temperature transferability to an adherend and also has excellent adhesion and heat resistance after curing.

Conventionally, liquid adhesives using epoxy compounds have been used to bond metals and plastics. Recently, there has been an increasing demand for adhesives that have the properties of both pressure sensitive adhesives and pressure sensitive adhesives, i.e., adhesive properties under normal conditions, and that cure and firmly bond when heated after application to an adherend. As such adhesives, thermosetting pressure sensitive adhesive compositions using acrylic resins, epoxy resins, and epoxy curing agents have been proposed (see, for example, Patent Document 1).

Furthermore, in recent years, excellent adhesive strength is required in applications of flexible printed circuit boards (FPCs), particularly in applications where FPCs are bonded to reinforcing plates. For example, terminals of flexible printed circuit boards made of polyimide film are backed with a reinforcing substrate such as a polyimide film, glass epoxy plate, or metal plate to increase their strength. In such applications, the polyimide film of the flexible printed circuit board and the reinforcing substrate are bonded by hardening a thermosetting adhesive placed between them (see, for example, Patent Document 2).

JP 2013-203795 A JP 2017-17131 A

However, the thermosetting pressure-sensitive adhesive composition disclosed in Patent Document 1 does not take into consideration the adhesive strength after heat curing at all, and when this composition is used to produce an adhesive sheet, for example, there is a problem that the elastic modulus after curing becomes too high, resulting in insufficient adhesive strength.

In addition, the above-mentioned Patent Document 2 describes an adhesive sheet obtained by adding an epoxy resin and an epoxy resin curing agent to an acrylic resin having a glass transition temperature of -5 to 15°C, and this adhesive sheet had excellent adhesive strength. However, this adhesive sheet requires the use of heat attachment (thermal lamination) to attach to the adherend, and does not have excellent transferability at room temperature. From the perspective of process optimization in the future, room temperature transferability that allows attachment to the adherend at room temperature will be required. Furthermore, when used in electronic devices, heat resistance that does not easily change adhesiveness even when exposed to high temperatures is also required.

In light of this background, the present invention aims to provide a pressure-sensitive adhesive composition that provides a pressure-sensitive adhesive layer that has excellent room temperature transferability and coating appearance before curing, and excellent adhesion to adherends after curing, as well as excellent heat resistance.

However, the present inventors have conducted extensive research in light of the above circumstances, and as a result have discovered that a pressure-sensitive adhesive composition containing an acrylic resin (A), an epoxy compound (B), a curing agent (C) that reacts with the epoxy compound (B), and a crosslinking agent (D) can be obtained, and that by specifying the physical properties of a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition when cured under predetermined conditions, a pressure-sensitive adhesive layer can be obtained that has excellent room temperature transferability and coating appearance before curing, and has moderate viscosity after curing, excellent adhesion to an adherend, and further has excellent heat resistance, thereby completing the present invention.

That is, the first gist of the present invention is a pressure-sensitive adhesive composition containing an acrylic resin (A), an epoxy compound (B), a curing agent (C) that reacts with the epoxy compound (B), and a crosslinking agent (D), characterized in that when a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is heated at 160°C for 1 hour to be cured, the loss tangent (tan δ) at 23°C obtained by dynamic viscoelasticity measurement is 1.5 to 5.

The second aspect of the present invention is an adhesive sheet having an adhesive layer formed from the adhesive composition of the first aspect described above.

The third aspect of the present invention is a laminate in which an adhesive layer formed from the adhesive composition of the first aspect is laminated on an adherend.

The adhesive composition of the present invention can form an adhesive layer that has excellent coating appearance and room temperature transferability before curing, and excellent adhesion to an adherend after curing, and also has excellent heat resistance. Therefore, the adhesive layer formed from the adhesive composition of the present invention can be suitably used for various adhesive applications, such as building materials, in-vehicle parts, electronic parts, semiconductor manufacturing processes, component sealing, aviation parts, and sporting goods, and is particularly useful for bonding FPCs and reinforcing plates.

In pressure-sensitive adhesive compositions, it is common to incorporate an epoxy compound into an acrylic resin, and as the epoxy compound, epoxy resins such as bisphenol A type and bisphenol F type are used from the viewpoints of curability, handling, etc., and solid epoxy resins such as multifunctional type, novolac phenol type, biphenyl type, etc. are used from the viewpoint of creep properties. When these epoxy resins are blended with an acrylic resin, there is a concern that the tack is easily lost and transferability at room temperature is poor, and a solution to this problem is required.
[0023] In view of this, in the present invention, the inventors have focused on the loss tangent (tan δ) at 23°C obtained by measuring the dynamic viscoelasticity after curing, and have investigated the relationship between the viscosity of the adhesive composition, the hardness and softness of the adhesive layer after curing, and the effects of the present invention. As a result, they have found that by adjusting the adhesive composition so that the loss tangent (tan δ) after curing is within a predetermined range, it is possible to obtain an adhesive layer that has room temperature transferability before curing, and excellent adhesion after curing, and furthermore, surprisingly has excellent heat resistance.

The present invention will be described in detail below.
In the present invention, (meth)acrylic means acrylic or methacrylic, (meth)acryloyl means acryloyl or methacryloyl, and (meth)acrylate means acrylate or methacrylate, respectively.

The adhesive composition of the present invention contains an acrylic resin (A), an epoxy compound (B), a curing agent (C) that reacts with the epoxy compound (B) (hereinafter may be abbreviated as curing agent (C) for epoxy compounds or simply curing agent (C)), and a crosslinking agent (D) (hereinafter may be abbreviated as crosslinking agent (D) for acrylic resins). Hereinafter, the adhesive composition of the present invention may be abbreviated as "adhesive composition [I]".

[Adhesive composition [I]]
As described above, the pressure-sensitive adhesive composition [I] of the present invention contains the acrylic resin (A), the epoxy compound (B), the curing agent for the epoxy compound (C) and the crosslinking agent for the acrylic resin (D). Each component constituting the pressure-sensitive adhesive composition [I] will be described.

<Acrylic resin (A)>
The acrylic resin (A) is a resin obtained by polymerizing a polymerization component containing at least one kind of (meth)acrylic monomer, and examples thereof include acrylic resins obtained by polymerizing a polymerization component containing a (meth)acrylic monomer as a main component and, in some cases, various other polymerizable monomers.

The phrase "mainly composed of" a (meth)acrylic monomer means that the (meth)acrylic monomer is generally present in an amount of 40% by weight or more, preferably 50% by weight or more, and more preferably 60% by weight or more of the total polymerizable components.

Examples of the (meth)acrylic monomer include (meth)acrylic acid or a derivative thereof, and (meth)acrylamide or a derivative thereof.

Examples of the derivatives of (meth)acrylic acid include alkyl group-containing (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-methyl-2-nitropropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, t-pentyl (meth)acrylate, 3-pentyl (meth)acrylate, 2,2-dimethylbutyl (meth)acrylate, n-hexyl (meth)acrylate, cetyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 4-methyl-2-propylpentyl (meth)acrylate, and n-octadecyl (meth)acrylate.

Other examples of the derivatives of (meth)acrylic acid include cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate and cyclopentyl (meth)acrylate; aralkyl (meth)acrylates such as benzyl (meth)acrylate; biphenyloxy structure-containing (meth)acrylates such as biphenyloxyethyl (meth)acrylate; 2-isobornyl (meth)acrylate, 2-norbornylmethyl (meth)acrylate, 5-norbornen-2-yl-methyl (meth)acrylate, 3-methyl-2-norbornylmethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. polycyclic (meth)acrylates such as dicyclopentanyl (meth)acrylate; alkoxy or phenoxy group-containing (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, and alkylphenoxypolyethylene glycol (meth)acrylate; and the like.

Further, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; further, hydroxyl group-containing (meth)acrylates such as [4-(hydroxymethyl)cyclohexyl]methyl acrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate; epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate glycidyl ether. ; halogen-containing (meth)acrylates such as 2,2,2-trifluoroethyl (meth)acrylate, 2,2,2-trifluoroethylethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropentyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; alkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate; oxetane group-containing (meth)acrylates such as 3-oxetanylmethyl (meth)acrylate, 3-methyl-oxetanylmethyl (meth)acrylate, 3-ethyl-oxetanylmethyl (meth)acrylate, 3-butyl-oxetanylmethyl (meth)acrylate, and 3-hexyl-oxetanylmethyl (meth)acrylate; and the like.

Examples of the above-mentioned (meth)acrylamide derivatives include N-alkyl group-containing (meth)acrylamide derivatives such as N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N-hexyl(meth)acrylamide; N-hydroxyalkyl group-containing (meth)acrylamide derivatives such as N-methylol(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, and N-methylol-N-propane(meth)acrylamide; aminomethyl(meth)acrylamide; N-aminoalkyl group-containing (meth)acrylamide derivatives such as aminoethyl (meth)acrylamide; N-alkoxy group-containing (meth)acrylamide derivatives such as N-methoxymethyl (meth)acrylamide and N-ethoxymethyl (meth)acrylamide; N-mercaptoalkyl group-containing (meth)acrylamide derivatives such as mercaptomethyl (meth)acrylamide and mercaptoethyl (meth)acrylamide; heterocyclic ring-containing (meth)acrylamide derivatives such as N-acryloylmorpholine, N-acryloylpiperidine, N-methacryloylpiperidine, and N-acryloylpyrrolidine.

These (meth)acrylic monomers may be used alone or in combination of two or more. Among these (meth)acrylic monomers, alkyl group-containing (meth)acrylates are preferably used. The number of carbon atoms in the alkyl group in the alkyl group-containing (meth)acrylate is usually 1 to 20, preferably 1 to 12, more preferably 1 to 8, and even more preferably 1 to 4. The alkyl group having a smaller number of carbon atoms is preferred because it has better compatibility with the epoxy compound (B) described below.

Of these (meth)acrylic monomers, the monomer having an acryloyl group is preferably contained in an amount of 25% by weight or more, more preferably 35% by weight or more, based on the total polymerization components of the acrylic resin (A). The upper limit of the content of the monomer having an acryloyl group based on the total polymerization components of the acrylic resin (A) is 100% by weight. By increasing the content ratio of the monomer having an acryloyl group, the transferability after the formation of the adhesive layer is excellent without impairing the adhesion before curing, and the handling properties are good.

As such a monomer having an acryloyl group, acrylic acid or a derivative thereof, acrylamide or a derivative thereof, etc., can be selected from the various (meth)acrylic monomers mentioned above and used.

When an acrylic acid derivative is used as the monomer having an acryloyl group, for example, an acrylic acid derivative having a glass transition temperature of 0°C or higher when a homopolymer is prepared is preferred because it has a high glass transition temperature and is easy to increase the molecular weight of the acrylic resin (A). In particular, methyl acrylate is preferred in terms of polymerizability.

In addition, taking into consideration the reactivity with the crosslinking agent (D) for acrylic resins described below, acrylates containing hydroxyl groups are preferred, for example, hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. For the same reasons why acrylates containing hydroxyl groups are preferred, it is also preferred to use acrylic acid.

When an acrylamide derivative is used as the monomer having an acryloyl group, for example, dialkylacrylamide or N-acryloylmorpholine is preferred because it has a high glass transition temperature and is highly compatible with the epoxy compound (B). In particular, it is preferred to use an acrylamide derivative whose glass transition temperature when the homopolymer is prepared is 0°C or higher, because the glass transition temperature of the resulting acrylic resin (A) can be maintained high and the adhesion to the adherend can be improved.

The polymerization components constituting the acrylic resin (A) may contain polymerizable monomers other than the (meth)acrylic monomers (hereinafter referred to as "other polymerizable monomers").
Examples of the other polymerizable monomers include unsaturated carboxylic acids such as crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamide-N-glycolic acid, and cinnamic acid; carboxylic acid vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl stearate, and vinyl benzoate; aromatic ring-containing monomers such as styrene and α-methylstyrene; acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, allyl trimethyl ammonium chloride, and dimethyl allyl vinyl ketone. These may be used alone or in combination of two or more.

The polymerization components constituting the acrylic resin (A) preferably contain, in particular, a functional group-containing monomer. As such a functional group-containing monomer, it is preferable to contain at least one type of functional group-containing monomer selected from the above-mentioned hydroxyl group-containing (meth)acrylates and other hydroxyl group-containing monomers and carboxyl group-containing monomers such as acrylic acid. Among these, functional group-containing monomers containing a (meth)acryloyl group are preferred, and functional group-containing monomers containing an acryloyl group are even more preferred. Among these, 2-hydroxyethyl acrylate and acrylic acid are particularly preferred, and 2-hydroxyethyl acrylate is even more preferred.

The content of such functional group-containing monomer is preferably 0.1 to 30% by weight, more preferably 1 to 25% by weight, and even more preferably 3 to 20% by weight, based on the total polymeric components constituting the acrylic resin (A). If the amount of the functional group-containing monomer is too small, the cohesive force tends to decrease, and the adhesive strength after curing tends to decrease. Conversely, if the amount is too large, the storage stability of the adhesive layer tends to decrease and the pot life tends to be shortened.

As a polymerization method for the acrylic resin (A), a conventionally known method such as solution radical polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. For example, a method in which appropriately selected polymerization components and a polymerization initiator are mixed or dropped into an organic solvent and polymerized under predetermined polymerization conditions can be mentioned. Among them, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred because it can stably obtain the acrylic resin (A).

Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These organic solvents may be used alone or in combination of two or more.

Among these organic solvents, esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone are preferred from the standpoint of ease of polymerization reaction, chain transfer effect, ease of drying when applying the adhesive composition, and safety, and ethyl acetate is particularly preferred.

In addition, examples of polymerization initiators used in such solution radical polymerization include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(methylpropionic acid), which are typical radical polymerization initiators; organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide; and the like, which can be appropriately selected and used according to the monomer to be used. These polymerization initiators may be used alone or in combination of two or more kinds.

In this way, the acrylic resin (A) used in the present invention is obtained.

The weight average molecular weight (Mw) of the acrylic resin (A) is preferably 100,000 or more, more preferably 150,000 to 1,500,000, particularly preferably 200,000 to 1,000,000, and even more preferably 250,000 to 800,000. If the weight average molecular weight is too small, the toughness and cohesive strength of the resulting adhesive layer tend to decrease. If the weight average molecular weight is too large, the viscosity tends to become too high, causing more scaling during polymerization, and the compatibility with the epoxy compound (B) and handling properties tend to decrease.

The dispersity of the acrylic resin (A) [weight average molecular weight (Mw)/number average molecular weight (Mn)] is preferably 10 or less, more preferably 7 or less, and even more preferably 5.5 or less. If the dispersity is too high, the cohesive force tends to decrease. The lower limit of the dispersity is usually 1.

The weight average molecular weight of the acrylic resin (A) is a weight average molecular weight converted to standard polystyrene molecular weight, and can be measured by connecting three columns in series: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical plate number: 10,000 plates / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm) to a high performance liquid chromatograph (manufactured by Japan Waters, "Waters 2695 (main body)" and "Waters 2414 (detector)"), and the number average molecular weight can also be measured by the same method. The degree of dispersion can be determined from the measured values of the weight average molecular weight and the number average molecular weight.

The glass transition temperature (Tg) of the acrylic resin (A) is preferably -50°C or higher, more preferably -20 to 100°C, even more preferably 0 to 75°C, particularly preferably 10 to 50°C, and especially preferably 15 to 40°C. If the glass transition temperature is outside the specified range, the tan δ value at 23°C after curing will be low, and the adhesive strength will tend to decrease.

The glass transition temperature is calculated using the Fox formula below.

Tg: glass transition temperature of the polymer (K)
Tga: Glass transition temperature (K) of homopolymer of monomer A Wa: Weight fraction of monomer A Tgb: Glass transition temperature (K) of homopolymer of monomer B Wb: Weight fraction of monomer B Tgn: Glass transition temperature (K) of homopolymer of monomer N Wn: Weight fraction of monomer N (Wa + Wb + ... + Wn = 1)

That is, the glass transition temperature of the acrylic resin is a value calculated by applying the glass transition temperature and weight fraction when a homopolymer is prepared from each monomer constituting the acrylic resin to Fox's formula.
The glass transition temperature of a homopolymer prepared from monomers constituting an acrylic resin can be determined by using the value described in Polymer Handbook (J. Brandrup, Interscience, 1989) in the case where the glass transition temperature is described in Polymer Handbook (J. Brandrup, Interscience, 1989). The glass transition temperature of a homopolymer prepared from monomers constituting an acrylic resin can also be measured by a differential scanning calorimeter (DSC) according to JIS K7121-1987 or JIS K 6240.

The refractive index of the acrylic resin (A) is usually 1.440 to 1.600. It is preferable to reduce the difference in refractive index between the resin and the laminated member, as this reduces optical loss at the interface between the resin and the laminated member.

The refractive index above was measured for a thin film of the acrylic resin (A) using a refractive index measuring device (Abbe Refractometer 1T manufactured by Atago Co., Ltd.) at NaD line and 23°C.

<Epoxy Compound (B)>
The epoxy compound (B) used in the present invention may be an epoxy compound having one or more epoxy groups in one molecule, preferably an epoxy compound having one to two epoxy groups, more preferably an epoxy compound having two epoxy groups. These compounds may be used alone or in combination of two or more. If the number of epoxy groups in one molecule is too large, the product becomes too hard after curing, and the adhesive strength tends to decrease.

In the present invention, among the epoxy compounds (B), those which are liquid at 25° C. are preferred, and among these, it is preferred to contain an epoxy compound which has a low viscosity and a high epoxy equivalent.
As such an epoxy compound, an epoxy compound (b1) having a viscosity of 2000 mPa·s or less at 25°C and an epoxy equivalent of 300 g/eq or more is particularly preferred. The viscosity of the epoxy compound (b1) at 25°C is preferably 2000 mPa·s or less in terms of easily imparting tack to the adhesive layer before curing, more preferably 1 to 1500 mPa·s, particularly preferably 1 to 1200 mPa·s, and even more preferably 50 to 1000 mPa·s. If the viscosity is too high, room temperature transferability tends to decrease. If the viscosity is too low, it tends to volatilize during heat curing and generate bubbles.
The above viscosity is a value measured using a B-type viscometer in accordance with JIS K 7233.

Furthermore, the epoxy equivalent of the epoxy compound (b1) is preferably 300 g/eq or more in terms of adhesive strength after curing, more preferably 310 to 10,000 g/eq, particularly preferably 320 to 5,000 g/eq, even more preferably 350 to 2,500 g/eq, and particularly preferably 400 to 2,000 g/eq. If the epoxy equivalent is too low, the adhesive strength after curing tends to decrease. If the epoxy equivalent is too high, the compatibility with the acrylic resin (A) tends to decrease.
The epoxy equivalent is a value measured in accordance with JIS K 7236 using a potentiometric titrator.

The weight average molecular weight of the epoxy compound (b1) is preferably 300 to 5000, more preferably 350 to 4000, and particularly preferably 400 to 2000. If the molecular weight is too small, it will volatilize during heat curing, and bubbles will easily form in the coating film, tending to deteriorate the appearance of the coating film, whereas if the molecular weight is too large, it will tend to increase the viscosity and deteriorate the room temperature transferability.
The weight average molecular weight of the epoxy compound (b1) is measured by the same method as that for the weight average molecular weight of the acrylic resin (A).

Specific examples of the epoxy compound (b1) include "jER (registered trademark) 871" and "jER (registered trademark) YX7400" manufactured by Mitsubishi Chemical Corporation, "EP-4005", "ED-502", "ED-502S", and "ED-506" manufactured by ADEKA Corporation, and "EPICLON (registered trademark) 1650-75MPX" and "EPICLON (registered trademark) 1051-75M" manufactured by DIC Corporation.

In the present invention, it is preferable that the epoxy compound (B) contains the above-mentioned epoxy compound (b1), but it is also possible to use a known epoxy compound other than the epoxy compound (b1) that is generally used for adhesive applications, etc., in combination, as long as the transferability before curing is not impaired.

Examples of such known epoxy compounds include monofunctional epoxy compounds having one epoxy group in the molecule, and polyfunctional epoxy compounds having two or more epoxy groups. These compounds may be used alone or in combination of two or more.

Examples of the monofunctional epoxy compounds include alkyl glycidyl ethers, alkoxy glycidyl ethers, phenol glycidyl ethers, EO (ethylene oxide)-modified phenol glycidyl ethers, and allyl glycidyl ethers.

Among the above multifunctional epoxy compounds, examples of bifunctional epoxy compounds having two epoxy groups include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, diglycidyl terephthalate, diglycidyl-o-phthalate, diglycidyl resorcinol ether, bisphenol A diglycidyl compounds and hydrogenated products thereof, bisphenol F diglycidyl compounds and hydrogenated products thereof, biphenyl diglycidyl compounds and derivatives thereof, etc.

Examples of the polyfunctional epoxy compounds having three or more epoxy groups include trifunctional epoxy compounds such as glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, triglycidyl isocyanurate and its derivatives, and pentaerythritol triglycidyl ether; tetrafunctional epoxy compounds such as pentaerythritol tetraglycidyl ether, diglycerol tetraglycidyl ether, and ditrimethylolpropane tetraglycidyl ether; pentafunctional epoxy compounds such as polyglycerol pentaglycidyl ether, pentaerythritol pentaglycidyl ether, and dipentaerythritol pentaglycidyl ether; hexafunctional epoxy compounds such as sorbitol hexaglycidyl ether and dipentaerythritol hexaglycidyl ether; polyglycidyl ether, phenol novolac type epoxy compounds, and cresol novolac type epoxy compounds.

In the present invention, the content of the epoxy compound (b1) relative to the total epoxy compound (B) is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 60% by weight or more, in terms of room temperature transferability before curing and adhesive strength after curing. If the content of the epoxy compound (b1) is too low, the room temperature transferability before curing tends to decrease, and the tan δ value after curing also tends to decrease. The upper limit of this content is 100% by weight.

The viscosity of the epoxy compound (B) including the epoxy compound (b1) as a whole is preferably 1 to 10,000 mPa·s, more preferably 10 to 5,000 mPa·s, and particularly preferably 50 to 2,500 mPa·s, from the viewpoint of room temperature transferability before curing. If the viscosity is too low, the cohesive force before curing tends to decrease, and if the viscosity is too high, the room temperature transferability before curing tends to decrease.
The above viscosity is a value measured using a B-type viscometer in accordance with JIS K 7233.

The content of the epoxy compound (B) is preferably 1 to 150 parts by weight, more preferably 3 to 120 parts by weight, particularly preferably 5 to 100 parts by weight, and even more preferably 10 to 75 parts by weight, relative to 100 parts by weight of the acrylic resin (A). If the content of the epoxy compound (B) relative to the acrylic resin (A) is too low, the room temperature transferability before curing tends to decrease, while if it is too high, it tends to cause a decrease in the cohesive force before curing and a decrease in the adhesive strength after curing.

<Curing agent for epoxy compounds (C)>
The epoxy compound curing agent (C) is used as a curing agent for the epoxy compound (B) and is a compound having a functional group capable of reacting with the epoxy group of the epoxy compound (B).
Examples of the curing agent (C) include amines, polyamides, imidazoles, polymercaptan curing agents, acid anhydrides, etc. These may be used alone or in combination of two or more. Among the curing agents (C), it is preferable to use amine compounds, particularly in terms of excellent storage stability and curing properties when the adhesive is formed, and among these, dicyandiamide and organic acid hydrazides are preferable, and among the organic acid hydrazides, adipic acid dihydrazide and sebacic acid dihydrazide are particularly preferable in terms of excellent curing speed.

The curing agent (C) may be either liquid or solid, but is preferably solid in terms of storage stability when the adhesive is formed and the pot life of the adhesive composition, and is preferably dispersed in a powder state in terms of the coating film becoming smooth and increasing the adhesive area with the member when cured, thereby increasing the adhesive strength after curing. When a powder is used as the curing agent (C), the particle size of the powder is preferably set to 1.2 times or less the thickness of the adhesive layer when it is formed, and more preferably 1 time or less.

The content of the curing agent (C) is preferably 1 to 100 parts by weight, more preferably 3 to 80 parts by weight, particularly preferably 5 to 70 parts by weight, and even more preferably 7 to 50 parts by weight, relative to 100 parts by weight of the epoxy compound (B). If the content ratio of the curing agent (C) relative to the epoxy compound (B) is too low, the curing speed tends to be slow or the curing temperature tends to be high, and if it is too high, streaks tend to occur during coating or the pot life of the adhesive composition tends to be shortened.

<Crosslinking Agent (D)>
The adhesive composition [I] of the present invention further contains a crosslinking agent (D) (crosslinking agent (D) for acrylic resin) that crosslinks the acrylic resin (A) in addition to the above-mentioned acrylic resin (A), epoxy compound (B) and curing agent for epoxy compound (C). By containing the crosslinking agent (D), the adhesive composition [I] can be crosslinked, and the cohesive strength of the adhesive can be improved. Since the acrylic resin (A) is also crosslinked by the epoxy compound (B), the crosslinking agent (D) in the present invention excludes the epoxy compound (B).

As the crosslinking agent (D), a known crosslinking agent can be used, and examples thereof include an isocyanate-based crosslinking agent, an aziridine-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, and a metal chelate-based crosslinking agent.
These crosslinking agents (D) may be used alone or in combination of two or more.

Examples of the isocyanate crosslinking agent include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate; xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethyl xylylene diisocyanate; aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate; hexamethylene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate, and adducts of these isocyanate compounds with polyol compounds such as trimethylolpropane, biuret compounds and isocyanurates of these polyisocyanate compounds, etc.

Examples of the aziridine-based crosslinking agent include tetramethylolmethane-tri-β-aziridinyl propionate, trimethylolpropane-tri-β-aziridinyl propionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), etc.

Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexabutoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, melamine resins, etc.

Examples of the aldehyde crosslinking agents include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of the metal chelate crosslinking agent include coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or acetoacetyl ester.

In the present invention, the content of the crosslinking agent (D) is preferably 0.01 to 15 parts by weight, more preferably 0.1 to 10 parts by weight, particularly preferably 0.5 to 5 parts by weight, and even more preferably 1 to 3 parts by weight, per 100 parts by weight of the acrylic resin (A). If the content of the crosslinking agent (D) is too low, the adhesion to the substrate after curing tends to be poor and the adhesive strength tends to decrease, whereas if the content is too high, the tack before curing tends to decrease and the room temperature transferability tends to decrease.

<Optional ingredients>
The pressure-sensitive adhesive composition [I] of the present invention may contain, in addition to the above-mentioned components, various additives as optional components, such as conductive agents such as carbon and metal, inorganic fillers such as metal particles and glass particles, tackifiers such as urethane resins, rosin, rosin esters, hydrogenated rosin esters, phenolic resins, aliphatic petroleum resins, alicyclic petroleum resins, and styrene resins, fillers, antioxidants, ultraviolet absorbers, silane coupling agents, crosslinking accelerators such as ionic compounds, peroxides, and urethane catalysts, and crosslinking retarders such as acetylacetone. These may be used alone or in combination of two or more.

In addition to the above-mentioned optional components, the adhesive composition [I] of the present invention may contain impurities contained in the raw materials for producing the components of the adhesive composition [I], to the extent that the effects of the present invention are not impaired.

[0043] The pressure-sensitive adhesive composition [I] of the present invention can be obtained by mixing the acrylic resin (A), the epoxy compound (B), the curing agent for the epoxy compound (C), and the crosslinking agent for the acrylic resin (D), as well as other optional components.
The method for mixing these components is not particularly limited, and various methods can be used, such as a method in which the components are mixed together at once, or a method in which any component is mixed and then the remaining components are mixed together or sequentially.
Thus, the pressure-sensitive adhesive composition [I] of the present invention is obtained.

The pressure-sensitive adhesive composition [I] of the present invention has a function of being cured by heating at preferably 100 to 250°C, more preferably 120 to 200°C, and particularly preferably 130 to 185°C. If the temperature is too low, the storage stability tends to decrease, and if the temperature is too high, the versatility tends to be poor because the adherends that can be used are limited.

The present invention is characterized in that when an adhesive layer formed from the adhesive composition [I] is heated at 160°C for 1 hour to be cured, the loss tangent (tan δ) at 23°C obtained by dynamic viscoelasticity measurement is 1.5 to 5.
The loss tangent (tan δ) is preferably in the range of 1.55 to 4.8, more preferably 1.6 to 4.5, particularly preferably 1.7 to 4.2, further preferably 1.8 to 4, and particularly preferably 1.9 to 3. If the loss tangent (tan δ) is too small, the viscosity at 23° C. will be insufficient, resulting in a decrease in adhesive strength, whereas if the loss tangent (tan δ) is too large, the viscosity will be too high, resulting in a decrease in cohesive strength.

Here, the loss tangent (tan δ) at 23°C obtained by dynamic viscoelasticity measurement means an index of the strength of the viscous tendency of the adhesive layer at that temperature, and is measured as follows.

First, the adhesive layer formed to a thickness of 100 μm or more is heated at 160°C for 1 hour to harden. Next, using a humidity-controlled viscoelasticity device, dynamic viscoelasticity measurements are performed under the following conditions: adhesive tool: 20 mm diameter parallel plate, distortion: 0.1%, frequency: 1 Hz, heating rate: 3°C/min, measurement temperature: -100 to 150°C, and the tan δ value at 23°C is read from the obtained viscoelasticity curve to measure.

In the present invention, the loss tangent (tan δ) can be adjusted to the above range by, for example, (1) adjusting the glass transition temperature of the acrylic resin (A), (2) adjusting the epoxy equivalent of the epoxy compound (B), or (3) adjusting by combining (1) and (2). Among these, method (3) is preferred because it is easy to align the peak top temperatures of the loss tangent (tan δ) of the acrylic resin (A) and the epoxy compound (B), that is, it is easy to make the peak sharp.

Moreover, the glass transition temperature of a cured product obtained by curing the adhesive layer formed from the adhesive composition [I] at 160° C. for 1 hour is preferably −20 to 100° C., more preferably 0 to 75° C., particularly preferably 10 to 50° C., and further preferably 15 to 35° C. If the temperature is outside this range, the value of the loss tangent (tan δ) tends to decrease, and the adhesive strength tends to decrease.
The glass transition temperature of the cured product can be measured using a dynamic viscoelasticity device in the same manner as in the measurement of loss tangent, and the tan δ peak top temperature in the obtained viscoelasticity curve is taken as the glass transition temperature.

[Adhesive sheet and laminate]
The adhesive composition [I] of the present invention can be made into an adhesive by crosslinking the acrylic resin (A). In addition, an adhesive sheet having a laminated structure of substrate/adhesive layer can be obtained by laminating an adhesive layer containing this adhesive on a substrate such as a plastic film. Furthermore, a laminate having a laminated structure of adherend/adhesive layer can be obtained by laminating this adhesive layer on an adherend. In the following, the substrate and the adherend are collectively referred to as "members".

The above-mentioned adhesive sheets include adhesive sheets in which an adhesive layer is laminated to a substrate, as well as substrate-less double-sided adhesive sheets in which separators (release sheets) are laminated to both sides of the adhesive layer, and the double-sided adhesive sheets are preferred in terms of ease of handling.

The above-mentioned adhesive sheet can be produced, for example, by coating the adhesive composition [I] on a substrate, drying the composition, attaching a separator, and performing an aging treatment at least one of aging at room temperature (unheated state) and aging at a temperature. In addition, a substrate-less double-sided adhesive sheet can be produced by coating the adhesive composition [I] on a separator, drying the composition, attaching another separator having a different peel strength from the separator, and performing an aging treatment.

The aging treatment is a treatment carried out to chemically crosslink the acrylic resin (A) and the crosslinking agent (D) to give the adhesive an appropriate level of adhesiveness. The aging conditions are, for example, a temperature that is usually between room temperature (20±10°C) and 40°C, and a time that is usually between 1 and 30 days. Specific examples include conditions such as 1 to 20 days at 23°C and 1 to 7 days at 40°C.

When applying the adhesive composition [I], it is preferable to dilute the adhesive composition [I] with a solvent before application, and the solids concentration is preferably 5 to 65% by weight, more preferably 20 to 60% by weight, and particularly preferably 30 to 55% by weight.

The solvent is not particularly limited as long as it dissolves the adhesive composition. For example, ester-based solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol-based solvents such as methanol, ethanol, and propyl alcohol; etc. can be used. Among these, ethyl acetate is preferably used in terms of solubility, drying property, cost, etc.

The viscosity of the diluted adhesive composition [I] is preferably 500 to 15,000 mPa·s/25°C, and more preferably 1,000 to 10,000 mPa·s/25°C. If the viscosity is too low, when a component with a high specific gravity is used, the component tends to settle, and the concentration of the component in the adhesive composition [I] tends to be non-uniform.

Examples of the coating method for the adhesive composition [I] include roll coating, die coating, gravure coating, comma coating, and screen printing.

The thickness of the adhesive layer in the adhesive sheet is preferably 5 to 250 μm, more preferably 25 to 200 μm, and even more preferably 50 to 175 μm. If the adhesive layer is too thin, the thickness precision and adhesive strength tend to decrease, and if the adhesive layer is too thick, the adhesive layer tends to protrude from the edges when the adhesive sheet is rolled.

The gel fraction of the adhesive layer is preferably 1 to 99% by weight, more preferably 5 to 95% by weight, and even more preferably 10 to 90% by weight, in terms of adhesion to the substrate and adherend, and adhesion before curing. If the gel fraction of the adhesive layer is too low, the adhesion to the substrate after curing tends to be poor and the adhesive strength tends to decrease, and if the gel fraction is too high, sufficient adhesion between the adhesive layer and the interface of the member cannot be obtained when the adhesive sheet is attached to the adherend, and the adhesive strength after curing tends to decrease.

The above gel fraction is an indication of the degree of crosslinking (degree of hardening) and is calculated, for example, by the following method. First, an adhesive is picked from an adhesive sheet in which an adhesive layer is laminated on the surface of a substrate, and the adhesive is wrapped in a 200-mesh SUS wire mesh and immersed in ethyl acetate adjusted to 23°C for 24 hours. The weights of the adhesive layer before and after immersion in ethyl acetate are measured, and the difference between the two weights is taken as the weight of the insoluble adhesive component remaining in the wire mesh. The gel fraction is the weight percentage of the insoluble adhesive component remaining in the wire mesh relative to the weight of the adhesive layer before immersion in ethyl acetate.

In the present invention, the adhesive composition [I] has the function of being cured by heating at a predetermined temperature, so that the adhesive strength of the adhesive layer in the adhesive sheet increases, and the adhesive sheet is fixed to the adherend.
The heating temperature when curing the pressure-sensitive adhesive is preferably 100 to 250°C, more preferably 120 to 200°C, and even more preferably 130 to 185°C. If the temperature is too low, the curing time becomes long and the workability tends to decrease, and if the temperature is too high, the epoxy compound (B) tends to volatilize or ignite. The heating time is preferably 5 to 180 minutes, more preferably 30 to 120 minutes, and even more preferably 45 to 90 minutes. If the time is too short, the curing is insufficient and the adhesive strength tends to decrease, and if the time is too long, the workability tends to decrease.

The adhesive sheet, which has an adhesive layer laminated on the surface of a separator, allows the adhesive layer to be easily transferred by simply peeling off the separator and adhering the adhesive layer to the desired adherend surface, resulting in very efficient work.

Furthermore, in a laminate obtained by laminating another member via the above-mentioned adhesive layer, i.e., a laminate having a laminate structure of adherend/adhesive layer/another member, the adhesive layer has high adhesion before curing and exhibits high adhesive strength after curing, so that the other member is unlikely to easily shift or peel off from the adherend. Therefore, by using the adhesive composition [I] of the present invention, a laminate having high adhesive reliability and excellent quality in appearance can be obtained.

The adhesive composition [I] of the present invention has adhesion under normal conditions, and the adhesive layer made of the adhesive composition [I] has excellent room temperature transferability before curing. In addition, when the adhesive layer is applied to an adherend and cured by heating or the like, it adheres firmly and has excellent adhesion to the adherend. Therefore, the adhesive composition [I] of the present invention can be suitably used for various adhesive applications, such as building materials, automotive parts, electronic parts, semiconductor manufacturing processes, component sealing, aviation parts, and sporting goods.
The present invention is particularly useful in applications involving flexible printed circuit boards (FPCs), for example, bonding an FPC to a reinforcing plate. In applications involving bonding an FPC to a reinforcing plate, there is no need to use heat application (thermal lamination) to attach the adhesive to the adherend, and the adhesive can be attached to the adherend at room temperature. Even after curing, the adhesive has good heat resistance and moist heat resistance as well as good adhesion, and is therefore expected to be of great promise in the future.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight.
In the following examples, the weight average molecular weight, dispersity, glass transition temperature and other physical properties of the acrylic resins were measured according to the methods described above.
First, prior to the examples, the following components were prepared.

<Acrylic resin (A)>
[Preparation of acrylic resin (A-1)]
A four-neck round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 80 parts of ethyl acetate, 6 parts of methyl ethyl ketone, and 0.036 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator, and heated until the internal temperature reached the boiling point. Then, a mixed solution of 40 parts of methyl acrylate (MA), 10 parts of methyl methacrylate (MMA), 45 parts of n-butyl methacrylate, 5 parts of 2-hydroxyethyl acrylate (2HEA), 4 parts of ethyl acetate, and 0.036 parts of the polymerization initiator (AIBN) was added dropwise over a period of 2 hours while maintaining the boiling state. Thereafter, while continuing the reaction, 0.05 parts of a polymerization initiator (AIBN) was added twice, and the reaction was continued for 7 hours. After that, the mixture was diluted to obtain an acrylic resin (A-1) solution (solid concentration 45.1%, viscosity 12,400 mPa·s/25°C, acrylic resin (A-1): weight average molecular weight (Mw) 288,000, dispersity (Mw/Mn) 2.2, glass transition temperature (Tg) 19.7°C).

[Preparation of acrylic resin (A-2)]
A four-neck round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 80 parts of ethyl acetate, 6 parts of methyl ethyl ketone, and 0.036 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator, and heated until the internal temperature reached the boiling point. Then, a mixed solution of 40 parts of methyl acrylate (MA), 20 parts of methyl methacrylate (MMA), 35 parts of n-butyl methacrylate, 5 parts of 2-hydroxyethyl acrylate (2HEA), 4 parts of ethyl acetate, and 0.036 parts of the polymerization initiator (AIBN) was added dropwise over a period of 2 hours while maintaining the boiling state. Thereafter, while continuing the reaction, 0.05 parts of a polymerization initiator (AIBN) was added twice, and the reaction was continued for 7 hours. After that, the mixture was diluted to obtain an acrylic resin (A-2) solution (solid content concentration 43.6%, viscosity 10,800 mPa·s/25°C, acrylic resin (A-2): weight average molecular weight (Mw) 267,000, dispersity (Mw/Mn) 1.98, glass transition temperature (Tg) 26.3°C).

<Epoxy Compound (B)>
The following epoxy compound (B) was prepared.
(B-1): jER (registered trademark) YX7400 (manufactured by Mitsubishi Chemical Corporation), viscosity at 25°C 200 mPa·s, epoxy equivalent 440 g/eq, number of functional groups 2
(B-2): jER (registered trademark) YX7105 (manufactured by Mitsubishi Chemical Corporation), viscosity at 25°C: 53,000 mPa·s, epoxy equivalent: 480 g/eq, number of functional groups: 2
(B-3): Denacol EX-321 (manufactured by Nagase Chemtex Corporation), viscosity at 25°C 140 mPa·s, epoxy equivalent 140 g/eq, number of functional groups 2 to 3
(B-4): jER 828 (manufactured by Mitsubishi Chemical Corporation), viscosity at 25°C 13,500 mPa·s, epoxy equivalent 189 g/eq, number of functional groups 2
(B-5): jER 1032H80 (manufactured by Mitsubishi Chemical Corporation), solid at 25°C, epoxy equivalent 160g/eq, functional group number 3

<Curing agent for epoxy compounds (C)>
The following was prepared as the epoxy compound curing agent (C).
(C-1): Adipic acid dihydrazide (ADH-S: manufactured by Otsuka Chemical Co., Ltd.)

<Crosslinking Agent (D)>
The following was prepared as the crosslinking agent (D).
(D-1): Coronate L55E (manufactured by Tosoh Corporation: adduct of trimethylolpropane and tolylene diisocyanate)

<Examples 1 to 3 and Comparative Examples 1 to 5>
The above components were mixed according to Table 1 below, and the solid content was adjusted to a range of 30 to 60% using ethyl acetate to obtain a pressure-sensitive adhesive composition.

Using the obtained adhesive composition, an adhesive sheet having an adhesive layer was produced according to the procedure described below. Then, using this adhesive sheet, the gel fraction of the adhesive sheet before curing, room temperature transferability, loss tangent (tan δ) after curing, glass transition temperature (Tg) of the cured product, and adhesive strength after curing and after a heat resistance test were evaluated as described below.
The evaluation methods and evaluation criteria for each item are as follows. The results are also shown in Table 1 below.

<Preparation of adhesive sheet>
The adhesive composition was applied to a 38 μm-thick heavy release silicone separator (manufactured by Mitsui Chemicals Tohcello, Inc., "SPPET03 38BU") using a comma coater so that the thickness after drying would be 50 μm, and dried at 100° C. for 3 minutes to form an adhesive layer. A 38 μm-thick light release silicone separator (manufactured by Mitsui Chemicals Tohcello, Inc., "SPPET01 38BU") was attached to the surface of the adhesive layer, and then aging was performed at 40° C. for 3 days to produce an adhesive sheet (a laminate of light release silicone separator/adhesive layer/heavy release silicone separator).

[Gel fraction]
The adhesive layer was collected from the obtained adhesive sheet by picking, and the adhesive was wrapped in a 200 mesh SUS wire netting and immersed in ethyl acetate adjusted to 23°C for 24 hours, and the weight percentage of the insoluble adhesive component remaining in the wire netting relative to the weight of the adhesive layer before immersion in ethyl acetate was defined as the gel fraction.

[Coating film appearance]
The appearance of the obtained adhesive sheet was visually inspected and evaluated as follows.
○: No bubbles or unevenness △: A few bubbles ×: Many bubbles and unevenness

[Room temperature transferability]
The light release silicone separator of the adhesive sheet prepared above was peeled off, and the adhesive layer side was attached to a polyimide film (Kapton 200H: manufactured by Toray DuPont Co., Ltd.) at room temperature to obtain an adhesive sheet with a film substrate. When the heavy release silicone separator was peeled off from the obtained adhesive sheet with a film substrate, it was visually confirmed whether the adhesive layer was transferred to the polyimide film, and evaluated according to the following criteria.
○: Transferred ×: Not transferred

[Loss tangent (tan δ)]
The light release silicone separator was peeled off from the produced adhesive sheet, laminated so that the adhesive layer had a thickness of 150 to 200 μm, and further heated and cured at 160° C. for 1 hour to obtain a test piece. Thereafter, the loss tangent (tan δ) value at 23° C. was measured for the test piece cut into a size of 5 mm x 30 mm using a humidity-controlled viscoelasticity device (DVA-225) under conditions of a frequency of 1 Hz and a temperature rise of 3° C./min from −100 to 150° C.

[Glass transition temperature (Tg) of cured product]
The glass transition temperature was determined as the tan δ peak top temperature in the viscoelasticity curve obtained in the above loss tangent (tan δ) measurement.

[Adhesive strength after curing]
The light release silicone separator of the adhesive sheet prepared above was peeled off, and the adhesive layer side was attached to a polyimide film (Kapton 200H: manufactured by Toray DuPont Co., Ltd.) at room temperature to obtain an adhesive sheet with a film substrate. The obtained adhesive sheet with a film substrate was cut into a width of 25 mm, and then the heavy release silicone separator was peeled off, and the adhesive layer side was attached to a SUS-BA plate at room temperature by rolling a 1 kg roller twice back and forth, and then heat cured at 160 ° C for 1 hour. After that, the temperature was adjusted in a 23 ° C × 50% RH environment, and the adhesive strength (unit: N / cm) of 180 ° peeling was measured at a speed of 300 mm / min using AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation), and evaluated according to the following criteria.
◎: Higher than 15N/cm ○: 10-15N/cm
×...less than 10N/cm

[Adhesive strength after heat resistance test]
The light release silicone separator of the adhesive sheet prepared above was peeled off, and the adhesive layer side was attached to a polyimide film (Kapton 200H: manufactured by Toray DuPont Co., Ltd.) at room temperature to obtain an adhesive sheet with a film substrate. The obtained adhesive sheet with a film substrate was cut into a width of 25 mm, and then the heavy release silicone separator was peeled off, and the adhesive layer side was attached to a SUS-BA plate at room temperature by rolling a 1 kg roller twice, and then heat cured at 160 ° C. for 1 hour. It was further left to stand at 150 ° C. for 250 hours, and then the temperature was adjusted in a 23 ° C. × 50% RH environment, and then the adhesive strength (unit: N / cm) of 180 ° peeling was measured at a speed of 300 mm / min using AUTO Graph AG-X Plus (manufactured by Shimadzu Corporation) and evaluated according to the following criteria.
◎: Higher than 15N/cm ○: 10-15N/cm
×...less than 10N/cm

From the above results, in the examples where the loss tangent (tan δ) when cured was within a specific range, the coating film appearance and room temperature transferability were excellent, and the adhesion and heat resistance after curing were also excellent. In contrast, the comparative examples that did not satisfy the loss tangent (tan δ) were all poor in adhesion and heat resistance, and some were poor in coating film appearance and room temperature transferability.

According to the adhesive composition [I] of the present invention, it is possible to form an adhesive layer that has excellent room temperature transferability and coating appearance before curing, and excellent adhesion to the adherend after curing, and also has excellent heat resistance. Therefore, the adhesive layer formed from the adhesive composition [I] of the present invention can be suitably used for various adhesive applications, such as for building materials, for in-vehicle parts, for electronic parts, for semiconductor manufacturing processes, for sealing components, for aviation parts, and for sporting goods, and is particularly useful for bonding FPCs and reinforcing plates.

Claims (9)

A pressure-sensitive adhesive composition comprising an acrylic resin (A), an epoxy compound (B), a curing agent (C) reactive with the epoxy compound (B), and a crosslinking agent (D),
when the adhesive layer formed from the adhesive composition is heated at 160°C for 1 hour to be cured, the loss tangent (tan δ) at 23°C obtained by dynamic viscoelasticity measurement is 1.5 to 5,
A pressure-sensitive adhesive composition , comprising: a curing agent (C) in an amount of 1 to 100 parts by weight based on 100 parts by weight of the epoxy compound (B) . The adhesive composition according to claim 1, characterized in that the weight average molecular weight of the acrylic resin (A) is 100,000 or more. The adhesive composition according to claim 1 or 2, characterized in that the epoxy compound (B) contains an epoxy compound (b1) having a viscosity at 25°C of 2000 mPa·s or less and an epoxy equivalent of 300 g/eq or more. The adhesive composition according to any one of claims 1 to 3, characterized in that the content of the epoxy compound (B) is 1 to 150 parts by weight per 100 parts by weight of the acrylic resin (A). The adhesive composition according to any one of claims 1 to 4, characterized in that the curing agent (C) is an amine compound. The pressure-sensitive adhesive composition according to any one of claims 1 to 5 , characterized in that the content of the crosslinking agent (D) is 0.01 to 15 parts by weight based on 100 parts by weight of the acrylic resin (A). The pressure-sensitive adhesive composition according to any one of claims 1 to 6 , which has a function of being cured by heating at 100 to 250°C. An adhesive sheet comprising an adhesive layer formed from the adhesive composition according to any one of claims 1 to 7 . A laminate comprising an adhesive layer formed from the adhesive composition according to any one of claims 1 to 7 laminated on an adherend.