Active energy ray-curable adhesive composition and use thereof

Abstract

To provide an active energy ray-curable adhesive composition that exhibits excellent hot-melt coating performance and is capable of yielding an adhesive with superior adhesive properties such as adhesion and holding power to olefin adherends in an adhesive sheet employing a polyvinyl chloride base sheet.SOLUTION: An active energy ray-curable adhesive composition comprises a (meth)acrylic resin (A) and a plasticizer (B), the (meth)acrylic resin (A) containing a structural unit derived from a monomer (a1) having an active energy ray-reactive site.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an active energy ray-curable pressure-sensitive adhesive composition and uses thereof, and more particularly to an active energy ray-curable pressure-sensitive adhesive composition that can be used for laminates and pressure-sensitive adhesive sheets for hot melt coating, a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition, and a laminate or pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive. [Background technology]

[0002] Rubber-based adhesives and acrylic-based adhesives are known as adhesives used in adhesive layers of adhesive tapes, adhesive sheets, etc. As acrylic-based adhesives, (co)polymers containing specific alkyl (meth)acrylates as essential structural units have been developed.

[0003] In recent years, with growing concern about the environment, attention has been focused on pressure-sensitive adhesive compositions that do not use organic solvents. For example, hot-melt pressure-sensitive adhesive compositions have been proposed in which a heat-molten resin is applied to a substrate sheet without using an organic solvent. Patent Document 1 and the like describe crosslinking of a hot-melt-applied acrylic pressure-sensitive adhesive composition by irradiation with active energy rays. However, the acrylic pressure-sensitive adhesive described in Patent Document 1 has a high melt viscosity, so it is necessary to apply it at a high temperature.

[0004] To solve this problem, Patent Document 2 proposes a pressure-sensitive adhesive composition containing an acrylic copolymer having structural units derived from a macromonomer. This pressure-sensitive adhesive composition provides a pressure-sensitive adhesive that has excellent low-temperature application properties, excellent holding power even with low UV exposure, and reduced adhesive residue upon re-peeling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2018-501397 [Patent Document 2] International Publication No. 2020 / 158475 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, olefins such as polypropylene are used in a wide variety of applications, including automotive parts, building materials, electronic components, and office equipment, and are used in a wide range of environments. Despite their versatility, olefins have low surface energy and therefore exhibit poor adhesion, so there is a demand for improved adhesion to olefin-based substrates.

[0007] Although Patent Document 1 describes adhesive strength to olefin adherends, the pressure-sensitive adhesive described therein has a high melt viscosity and poor coatability, which is thought to result in productivity problems. Also, while the pressure-sensitive adhesive composition described in Patent Document 2 has a low melt viscosity and excellent coatability, the same document describes adhesive strength to SUS plates but makes no mention of adhesive strength to olefin adherends.

[0008] The present invention aims to provide an active energy ray-curable pressure-sensitive adhesive composition that provides a pressure-sensitive adhesive sheet using a polyvinyl chloride (PVC) substrate sheet with excellent hot-melt coatability and excellent adhesive properties such as adhesion and holding power to olefin adherends. The present invention also aims to provide a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition, and a laminate or pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive. [Means for solving the problem]

[0009] However, in view of the above circumstances, the present inventors have conducted extensive research and have found that the above object can be achieved by combining a (meth)acrylic resin containing a structural unit derived from a monomer having an active energy ray-active site with a plasticizer, and have thus completed the present invention.

[0010] That is, the present invention includes the following aspects. Aspect (1) of the present invention is an active energy ray-curable pressure-sensitive adhesive composition (hereinafter also simply referred to as "pressure-sensitive adhesive composition") comprising a (meth)acrylic resin (A) and a plasticizer (B), wherein the (meth)acrylic resin (A) contains a structural unit derived from a monomer (a1) having an active energy ray-active site.

[0011] Aspect (2) of the present invention is the pressure-sensitive adhesive composition of aspect (1), wherein the plasticizer (B) is an aliphatic plasticizer.

[0012] Aspect (3) of the present invention is the PSA composition of aspect (1) or (2), further comprising a tackifier (C).

[0013] Aspect (4) of the present invention is the pressure-sensitive adhesive composition of aspect (3), wherein the tackifier (C) is a rosin-based resin.

[0014] In an aspect (5) of the present invention, in the pressure-sensitive adhesive composition of any one of aspects (1) to (4), the content of the thermal crosslinking agent (D) is less than 0.05 mass %.

[0015] Aspect (6) of the present invention is a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition of any one of aspects (1) to (5).

[0016] A seventh aspect of the present invention is a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of the sixth aspect.

[0017] An embodiment (8) of the present invention is a pressure-sensitive adhesive sheet having a polyvinyl chloride substrate sheet and a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive of embodiment (6).

[0018] Aspect (9) of the present invention is a laminate in which a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive of aspect (6) and a member are laminated together.

[0019] In this specification, the term "(meth)acrylic resin" refers to an acrylic resin or a methacrylic resin. Furthermore, "(meth)acrylic" refers to "acrylic" or "methacrylic," "(meth)acryloyl" refers to "acryloyl" or "methacryloyl," and "(meth)acrylate" refers to "acrylate" or "methacrylate." [Effects of the Invention]

[0020] The pressure-sensitive adhesive obtained using the pressure-sensitive adhesive composition of the present invention has good hot-melt coatability and high heat resistance. Furthermore, when a pressure-sensitive adhesive sheet produced using the pressure-sensitive adhesive composition is used, the pressure-sensitive adhesive not only has high adhesion to polyolefins, which are difficult to adhere to, but also has excellent holding power. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below. In this specification, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more, Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also means that "it is preferably greater than X" or "it is preferably less than Y." In this specification, in multiple numerical ranges described in stages, each upper limit and each lower limit can be the upper limit or lower limit of any combined numerical range. For example, when the content of a certain component is described as "5 to 20 wt %, 10 to 15 wt %, "it can constitute each of the numerical ranges of "5 to 15 wt %, " "10 to 20 wt %, " "5 to 10 wt %, " and "15 to 20 wt %.

[0022] (1) Pressure-sensitive adhesive composition The pressure-sensitive adhesive composition of the present invention contains, as essential components, a (meth)acrylic resin (A) and a plasticizer (B). First, these essential components will be described in order.

[0023] <(Meth)acrylic resin (A)> The (meth)acrylic resin (A) used in the present invention is a polymer obtained by polymerizing a copolymerization component (a), and the copolymerization component (a) contains a monomer (a1) having an active energy ray-active site, and further contains an alkyl (meth)acrylate (a2), a functional group-containing monomer (a3), and other copolymerizable monomers (a4), as necessary.

[0024] [Monomer (a1) having an active energy ray-active site] The active energy ray active site refers to a site that can form a crosslinked structure with another site in the same molecule or with another molecule when irradiated with active energy rays, and the monomer (a1) having an active energy ray active site is a monomer having such an active site in its molecule. The monomer (a1) having an active energy ray active site can be used alone or in combination of two or more. The monomer (a1) having an active energy ray active site is not limited, but for example, a (meth)acrylate having such an active site can be used.

[0025] Examples of active energy ray-active moieties include a benzophenone structure, a benzyl structure, an o-benzoylbenzoic acid ester structure, a thioxanthone structure, a 3-ketocoumarin structure, a 2-ethylanthraquinone structure, and a camphorquinone structure. Each of these structures can be excited by irradiation with active energy rays, and in the excited state, it can abstract hydrogen radicals from the (meth)acrylic resin (A) molecules. In this way, radicals are generated on the (meth)acrylic resin (A) molecules. Various reactions occur in the system, such as the formation of crosslinked structures by the generated radicals bonding with each other, the generation of peroxide radicals by reaction with oxygen molecules, the formation of crosslinked structures via the generated peroxide radicals, and the abstraction of other hydrogen radicals by the generated radicals, ultimately resulting in crosslinking of the (meth)acrylic resin (A).

[0026] Among the above structures, a benzophenone structure is preferred in consideration of transparency, reactivity, etc. Examples of (meth)acrylates having such a benzophenone structure include, but are not limited to, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy-4'-methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'-methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof.

[0027] The content of the monomer (a1) having an active energy ray-active site is usually 0.05 to 5 wt %, preferably 0.1 to 3 wt %, and more preferably 0.2 to 2 wt %, based on the copolymerization component (a). If the content is too low, the curability upon irradiation with active energy rays tends to be low, while if the content is too high, the gel fraction increases too much, which tends to reduce the adhesive strength to olefins.

[0028] The content of each monomer relative to the entire copolymerization component (a) can be considered as the content of structural units derived from that monomer in all structural units constituting the (meth)acrylic resin (A) which is a copolymer.

[0029] [Alkyl (meth)acrylate (a2)] The alkyl(meth)acrylate (a2) does not have an active energy ray active site or a polar group, has 1 to 20 carbon atoms, preferably 2 to 12 carbon atoms, and has a linear or branched alkyl group. Examples of the alkyl(meth)acrylate (a2) include methyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, iso-butyl(meth)acrylate, tert-butyl(meth)acrylate, n-propyl(meth)acrylate, n-hexyl(meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, and stearyl(meth)acrylate. Among these, n-butyl(meth)acrylate and ethyl(meth)acrylate are preferred from the viewpoint of adhesive strength. The alkyl(meth)acrylate (a2) can be used alone or in combination of two or more.

[0030] The alkyl(meth)acrylate (a2) preferably contains at least one monomer having a glass transition temperature of −30° C. or higher. Examples of the monomer (a2-1) having a glass transition temperature of −30° C. or higher include ethyl(meth)acrylate and methyl(meth)acrylate. The content of the alkyl (meth)acrylate (a2-1) having a glass transition temperature of -30°C or higher is 0 to 75% by weight, preferably 10 to 60% by weight, and more preferably 20 to 40% by weight, relative to the alkyl (meth)acrylate (a2). If the content is too low, the plasticizer resistance of the polyvinyl chloride substrate tends to decrease, while if the content is too high, the adhesive properties tend to decrease, the glass transition temperature increases, and the melt viscosity increases, which tends to decrease hot-melt coatability. The glass transition temperature of the alkyl (meth)acrylate (a2) is the glass transition temperature of a homopolymer prepared from the monomer (a2), and is usually a value measured by a differential scanning calorimeter (DSC) according to a method in accordance with JIS K7121-1987 or JIS K6240, or a value listed in a catalog.

[0031] The content of the alkyl (meth)acrylate (a2) relative to the copolymerization component (a) is usually 1 to 99 wt%, preferably 50 to 97 wt%, more preferably 70 to 95 wt%. If the content is too low, the glass transition temperature will increase, and the adhesive properties of the resulting adhesive will tend to deteriorate overall, while if the content is too high, the holding power of the resulting adhesive will tend to deteriorate.

[0032] [Polar Group-Containing Ethylenically Unsaturated Monomer (a3)] The polar group-containing ethylenically unsaturated monomer (a3) ​​is an ethylenically unsaturated monomer containing a polar group other than an active energy ray-active site, excluding the monomer (a1) having an active energy ray-active site and alkyl (meth)acrylate (a2). Examples of the polar group-containing ethylenically unsaturated monomer (a3) ​​include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, and cyano group-containing monomers. The polar group-containing ethylenically unsaturated monomer (a3) ​​can be used alone or in combination of two or more. Among these, monomers having at least one of a carboxyl group, a hydroxyl group, and an amide group are preferred, and carboxyl group-containing monomers are more preferred, in terms of excellent adhesive strength of the (meth)acrylic resin (A) obtained by copolymerization.

[0033] The hydroxyl group-containing monomers include primary hydroxyl group-containing monomers, secondary hydroxyl group-containing monomers, and tertiary hydroxyl group-containing monomers. Examples of primary hydroxyl group-containing monomers include (meth)acrylic acid hydroxyalkyl ester monomers such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and others such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth)acrylamide, and hydroxyethyl acrylamide. Examples of the secondary hydroxyl group-containing monomer include 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro 2-hydroxypropyl (meth)acrylate. Examples of the tertiary hydroxyl group-containing monomer include 2,2-dimethyl 2-hydroxyethyl (meth)acrylate.

[0034] Examples of the carboxy group-containing monomer include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, N-glycolic acid, cinnamic acid, etc. Among these, acrylic acid is more preferred because of its high versatility.

[0035] Examples of the amino group-containing monomer include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and quaternized products thereof.

[0036] Examples of the amide group-containing monomer include (meth)acrylamide, N-(n-butoxyalkyl)(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, vinylpyrrolidone, and acryloylmorpholine.

[0037] Examples of the cyano group-containing monomer include acrylonitrile and methacrylonitrile.

[0038] The content of the polar group-containing ethylenically unsaturated monomer (a3) ​​is usually 20% by weight or less, preferably 0.1% by weight or more and 15% by weight or less, more preferably 0.5% by weight or more and 10% by weight or less, even more preferably 1% by weight or more and 8% by weight or less, and particularly preferably 2% by weight or more and 7% by weight or less, based on the copolymerization component (a) in order to achieve both thermal stability and adhesive properties of the resin. If the content is too high, the thermal stability of the (meth)acrylic resin (A) obtained by copolymerization tends to decrease. If the content is too low, the adhesive strength of the adhesive obtained by crosslinking tends to decrease.

[0039] [Other polymerizable monomers (a4)] The other polymerizable monomer (a4) may be any polymerizable monomer other than the above (a1), (a2), and (a3), and examples thereof include alicyclic structure-containing monomers, aromatic monomers, alkoxy group-containing monomers, vinyl monomers, etc. These may be used alone or in combination of two or more.

[0040] Examples of the alicyclic structure-containing monomer include (meth)acrylates having an alicyclic structure, such as cyclohexyl (meth)acrylate, isobornyl acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and 2-adamantyl (meth)acrylate.

[0041] Examples of the aromatic monomer include (meth)acrylates having one aromatic ring, such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxydipropylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and phenoxypolypropylene glycol (meth)acrylate; and (meth)acrylates having two aromatic rings, such as phenoxybenzyl (meth)acrylate and ethoxylated o-phenylphenol (meth)acrylate.

[0042] Examples of the alkoxy group-containing monomer include alkoxyalkyl (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, and 2-butoxyethyl (meth)acrylate.

[0043] Examples of the vinyl monomer include vinyl propionate, vinyl stearate, vinyl acetate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, methyl vinyl ketone, and dimethyl allyl vinyl ketone.

[0044] The other polymerizable monomers (a4) may be contained within a range that does not impair the effects of the present invention, but the amount is preferably 20% by weight or less, more preferably 15% by weight or less, based on the total copolymerization component (a).

[0045] <Method for producing (meth)acrylic resin (A)> The method for producing the (meth)acrylic resin (A) is not particularly limited, and known polymerization methods using the copolymerization component (a) can be used, such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. For example, a method in which an appropriately selected copolymerization component (a) and a polymerization initiator are mixed or dropped into an organic solvent and polymerized under predetermined polymerization conditions can be used. Among the above polymerization methods, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is more preferred because it allows the stable production of the (meth)acrylic resin (A).

[0046] Examples of organic solvents used in the above polymerization method 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, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. These organic solvents can be used alone or in combination of two or more.

[0047] Among these organic solvents, esters such as ethyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone are preferred from the standpoints of ease of polymerization reaction, chain transfer effect, ease of drying when the pressure-sensitive adhesive composition is applied, and safety, with ethyl acetate being particularly preferred. These may be used alone or in combination of two or more. The amount of the organic solvent used is usually 10 to 900 parts by weight per 100 parts by weight of the copolymerization component (a).

[0048] In addition, a conventional radical polymerization initiator can be used for such solution radical polymerization. Examples of radical polymerization initiators include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(methylpropionic acid); organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide; and the like. These polymerization initiators can be appropriately selected and used depending on the monomer used. These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used is usually 0.01 to 10 parts by weight based on 100 parts by weight of the copolymerization component (a).

[0049] In this way, the (meth)acrylic resin (A) used in the present invention is obtained.

[0050] <Physical properties of (meth)acrylic resin (A)> The weight-average molecular weight (Mw) of the (meth)acrylic resin (A) is preferably from 30,000 to 1,500,000, more preferably from 50,000 to 1,000,000, particularly preferably from 70,000 to 500,000, and even more preferably from 100,000 to 300,000. If the weight-average molecular weight is too small, the cohesive strength tends to be low and the adhesiveness tends to decrease, whereas if it is too large, the melt viscosity tends to be too high and the resin tends to be unsuitable for hot-melt coating.

[0051] The dispersity of the (meth)acrylic resin (A) [weight average molecular weight (Mw) / number average molecular weight (Mn)] is preferably 10 or less, more preferably 7 or less. If the dispersity is too high, the cohesive force tends to decrease. The lower limit of the dispersity is usually 1.

[0052] The weight-average molecular weight of the (meth)acrylic resin (A) is a weight-average molecular weight converted into a standard polystyrene molecular weight. The weight-average molecular weight was measured using a high-performance liquid chromatograph (manufactured by Japan Waters, Inc., "Waters 2695 (main body)" and "Waters 2414 (detector)") with a column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 × 10 7 The molecular weight can be measured using a system in which three columns (theoretical plate number: 10,000 columns / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm) are connected in series, and the number average molecular weight can also be measured in a similar manner. The dispersity can also be determined from the measured values ​​of the weight average molecular weight and number average molecular weight.

[0053] The glass transition temperature (Tg) of the (meth)acrylic resin (A) is preferably −85° C. or higher, more preferably −80 to 20° C., particularly preferably −70 to 0° C., even more preferably −60 to −10° C., and especially preferably −50 to −20° C. If the glass transition temperature is too low, the adhesive strength of the pressure-sensitive adhesive sheet after curing tends to decrease, leading to peeling, whereas if the glass transition temperature is too high, the tack before curing tends to decrease, making it difficult to apply to the adherend.

[0054] The glass transition temperature is calculated by the following Fox formula.

[0055]

number

[0056] That is, it is a value calculated by applying the glass transition temperature and weight fraction of a homopolymer prepared from each of the monomers constituting the (meth)acrylic resin (A) to Fox's formula. The glass transition temperature of the homopolymer prepared from the monomers constituting the (meth)acrylic resin (A) is usually a value measured by a differential scanning calorimeter (DSC) according to a method in accordance with JIS K7121-1987 or JIS K6240, or a value listed in a catalog.

[0057] The (meth)acrylic resin (A) is the main component of the pressure-sensitive adhesive composition, and its content in the pressure-sensitive adhesive composition is preferably 50% by weight or more, more preferably 60 to 98% by weight, particularly preferably 70 to 95% by weight, and even more preferably 75 to 93% by weight. If the content is outside this range, the effects of the present invention tend to be difficult to achieve.

[0058] The (meth)acrylic resin (A) obtained by the above-described production method contains an organic solvent, and its solids concentration is usually 10 to 80% by weight, preferably 30 to 70% by weight. When the solids concentration is within the range of 10 to 80% by weight, the viscosity of the diluted (meth)acrylic resin (A) is preferably 500 to 30,000 mPa·s / 25°C, 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 as the plasticizer (B) or tackifier (C) described below, the component tends to settle, resulting in a non-uniform concentration of the component in the (meth)acrylic resin (A).

[0059] <Plasticizer (B)> The pressure-sensitive adhesive composition of the present invention contains a plasticizer (B) as an essential component. The plasticizer (B) is not particularly limited as long as it has good miscibility and compatibility with the (meth)acrylic resin (A), and any conventionally known plasticizer can be appropriately selected and used. Non-limiting examples of such plasticizers include phthalic acid compounds, terephthalic acid compounds, trimellitic acid compounds, cyclohexanedicarboxylic acid ester compounds, phosphoric acid compounds, adipic acid compounds, citric acid compounds, ether compounds, and polyester compounds.

[0060] Examples of the phthalic acid compounds include dialkyl phthalates such as bis(2-ethylhexyl) phthalate, dioctyl phthalate, diisononyl phthalate, and diisodecyl phthalate; alkylbenzyl phthalates such as butylbenzyl phthalate; alkylaryl phthalates; dibenzyl phthalate; and diaryl phthalates. An example of the terephthalic acid compound is bis(2-ethylhexyl) terephthalate. Examples of the trimellitic acid-based compounds include trialkyl trimellitates such as tris(2-ethylhexyl) trimellitate. An example of the cyclohexanedicarboxylic acid ester compound is diisononyl cyclohexane-1,2-dicarboxylate. Examples of the phosphoric acid compounds include triaryl phosphates such as tricresyl phosphate; trialkyl phosphates; and alkylaryl phosphates. Examples of the adipic acid compound include adipic acid esters such as bis(2-ethylhexyl) adipate. Examples of the citric acid compounds include citrate esters such as acetyl tributyl citrate. Examples of the ether compounds include polyalkylene glycols such as polyethylene glycol and polypropylene glycol. Examples of the polyester compounds include polyesters of dibasic acids such as adipic acid, sebacic acid, or phthalic acid and glycols such as 1,2-propanediol or butanediol.

[0061] The plasticizer (B) is preferably at least one selected from the group consisting of phthalic acid compounds, terephthalic acid compounds, trimellitic acid compounds, cyclohexanedicarboxylic acid ester compounds, phosphoric acid compounds, adipic acid compounds, citric acid compounds, ether compounds, and polyester compounds, more preferably at least one selected from the group consisting of bis(2-ethylhexyl) phthalate, bis(2-ethylhexyl) terephthalate, tris(2-ethylhexyl) trimellitate, bis(2-ethylhexyl) adipate, tributyl acetylcitrate, and diisononyl cyclohexane-1,2-dicarboxylate, and even more preferably bis(2-ethylhexyl) adipate and tributyl acetylcitrate because they are less inhibited by active energy ray curing.

[0062] The content of the plasticizer (B) used in the present invention is preferably 0.1 to 100 parts by weight, more preferably 1 to 50 parts by weight, particularly preferably 2 to 30 parts by weight, and even more preferably 4 to 20 parts by weight, relative to 100 parts by weight (solid content) of the (meth)acrylic resin (A). If the content is too high or too low, the effects of the present invention tend to be difficult to achieve.

[0063] The molecular weight of the plasticizer (B) used in the present invention is preferably 250 to 2000, more preferably 300 to 1000, and particularly preferably 350 to 500. When the molecular weight is within the above range, compatibility with the (meth)acrylic resin (A) is good, and not only can the plasticizer be imparted with appropriate wettability to polyolefins, but the melt viscosity is also likely to be reduced, thereby improving hot-melt coatability.

[0064] <Tackifier (C)> The pressure-sensitive adhesive composition of the present invention may further contain a tackifier (C). Examples of the tackifier (C) include rosin-based resins, phenol-based resins, terpene-based resins, modified terpene-based resins, hydrocarbon-based resins, epoxy-based resins, polyamide-based resins, elastomer-based resins, and ketone-based resins. From the viewpoint of adhesive strength to low-polarity adherends such as polyethylene (PE), rosin-based resins are preferred. Examples of rosin resins include modified rosin resins such as hydrogenated rosin, disproportionated rosin, and polymerized rosin; and rosin esters obtained by esterifying unmodified rosin with alcohols. The tackifier (C) can be used alone or in combination of two or more.

[0065] The softening point of the tackifier (C) is preferably 20 to 180° C., more preferably 50 to 160° C., and particularly preferably 70 to 130° C. If the softening point is too high or too low, the adhesiveness of the pressure-sensitive adhesive composition tends to decrease. Furthermore, if the softening point is too high, the melt viscosity of the pressure-sensitive adhesive composition increases, which tends to decrease hot-melt coatability. The softening point of the tackifier (C) is determined by the R&B (ring and ball) method in accordance with JIS K59025.3 (1969). The softening point can be measured, for example, using an automatic softening point measuring device (manufactured by Elex Scientific Co., Ltd.) that automates heating and softening point measurement. When the softening point has a range, the average value of the sum of the upper and lower limits is taken as the softening point.

[0066] When the pressure-sensitive adhesive composition of the present invention contains a tackifier (C), the content of the tackifier (C) is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, particularly preferably 30 parts by weight or less, and even more preferably 20 parts by weight or less, relative to 100 parts by weight (solid content) of the (meth)acrylic resin (A). If the content is too high, the effects of the present invention tend to be difficult to achieve.

[0067] <Thermal crosslinking agent (D)> The pressure-sensitive adhesive composition of the present invention may contain a thermal crosslinking agent (D), and in such a case, the content of the thermal crosslinking agent (D) is preferably less than 0.05% by weight, more preferably less than 0.01% by mass, of the total pressure-sensitive adhesive composition. Most preferably, the pressure-sensitive adhesive composition does not contain a thermal crosslinking agent (D).

[0068] Examples of the thermal crosslinking agent (D) include isocyanate-based curing agents, epoxy-based curing agents, metal chelate curing agents, and aziridine-based curing agents.

[0069] <Optional ingredients> In addition to the above components, the pressure-sensitive adhesive composition of the present invention may also contain various additives as optional components, such as conductive agents such as carbon and metals, inorganic fillers such as metal particles and glass particles, bulking agents, antioxidants, ultraviolet absorbers, crosslinking accelerators such as ionic compounds, peroxides, silane coupling agents, and urethane catalysts, crosslinking retarders such as acetylacetone, monofunctional monomers, and polyfunctional monomers. These may be used alone or in combination of two or more.

[0070] In addition to the optional components described above, the pressure-sensitive adhesive composition of the present invention may contain impurities contained in the raw materials for producing the components of the pressure-sensitive adhesive composition, to the extent that the effects of the present invention are not impaired.

[0071] When the optional components are used, the content thereof is preferably 5 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, relative to 100 parts by weight of the (meth)acrylic resin (A). If the content is too high, the effects of the present invention tend to be impaired.

[0072] <Method of manufacturing pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition of the present invention can be obtained by mixing at least the (meth)acrylic resin (A) and the plasticizer (B), and, if necessary, further mixing optional components such as the tackifier (C).

[0073] 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 all at once, or a method in which any component is mixed and then the remaining components are mixed all at once or sequentially.

[0074] The total content of the (meth)acrylic resin (A) and the plasticizer (B) in the pressure-sensitive adhesive composition is preferably 80% by weight or more, more preferably 85% by weight or more, and particularly preferably 90% by weight or more.

[0075] The pressure-sensitive adhesive composition of the present invention is useful as a pressure-sensitive adhesive component, particularly as a hot-melt pressure-sensitive adhesive component. When used for hot-melt applications, the above components are blended to obtain a pressure-sensitive adhesive composition solution, and then the organic solvent (hereinafter sometimes simply referred to as "solvent") is distilled off.

[0076] The step of distilling off the solvent from the solution of the PSA composition obtained by blending can be carried out by a known method. Methods for distilling off the solvent include a method of distilling off the solvent by heating and a method of distilling off the solvent by reducing pressure, but from the viewpoint of efficiently distilling off the solvent, a method of distilling off the solvent by heating under reduced pressure is preferred.

[0077] The temperature when distilling off the solvent by heating is preferably 60 to 150° C. In particular, it is preferable to hold the reaction solution after polymerizing the (meth)acrylic resin (A) at 60 to 80° C. to distill off the solvent, and then distill off the solvent at 80 to 150° C., in order to minimize the amount of remaining solvent. Note that in order to prevent gelation of the (meth)acrylic resin (A), it is preferable that the temperature during solvent distillation is not 150° C. or higher.

[0078] The pressure when distilling off the solvent under reduced pressure is preferably 20 to 101.3 kPa. In particular, it is preferred to maintain the pressure in the range of 50 to 101.3 kPa to distill off the solvent in the reaction solution, and then distill off the remaining solvent at 0 to 50 kPa, in order to minimize the amount of remaining solvent. In this manner, the active energy ray-curable pressure-sensitive adhesive composition of the present invention can be produced.

[0079] The pressure-sensitive adhesive composition of the present invention preferably contains substantially no solvent, and more preferably the solvent content of the pressure-sensitive adhesive composition is 2 wt % or less, particularly preferably 0.00001 to 2 wt %, further preferably 0.0001 to 1 wt %, and most preferably 0.001 to 0.1 wt %. If the solvent content is too high, bubbles tend to form and the physical properties after curing with active energy rays tend to deteriorate.

[0080] The melt viscosity of the pressure-sensitive adhesive composition of the present invention is preferably 1 to 1500 Pa·s, more preferably 2 to 500 Pa·s, particularly preferably 3 to 90 Pa·s, even more preferably 4 to 60 Pa·s, and most preferably 5 to 30 Pa·s. If the melt viscosity of the pressure-sensitive adhesive composition is too high, the coatability during hot-melt coating tends to decrease. On the other hand, if the melt viscosity of the pressure-sensitive adhesive composition is too low, the adhesive properties after curing with active energy rays tend to decrease due to a decrease in molecular weight.

[0081] The melt viscosity of the pressure-sensitive adhesive composition is measured using a solvent-free pressure-sensitive adhesive composition obtained by distilling off the solvent, with a rotational rheometer under the following conditions. Measuring equipment: MCR301 (manufactured by Anton Paar) Cone plate diameter: 25mm Measurement distance: 0.5mm Measurement shear rate: 0.002 (1 / S) ·Measurement temperature: 130℃

[0082] <Adhesive, adhesive sheet, and laminate> The pressure-sensitive adhesive composition of the present invention can be made into a pressure-sensitive adhesive by crosslinking the (meth)acrylic resin (A). Furthermore, by laminating a pressure-sensitive adhesive layer containing this pressure-sensitive adhesive onto a substrate sheet such as a plastic film, a pressure-sensitive adhesive sheet having a substrate sheet / pressure-sensitive adhesive layer laminate structure can be obtained. Furthermore, by laminating this pressure-sensitive adhesive layer onto an adherend, a laminate having an adherend / pressure-sensitive adhesive layer laminate structure can be obtained. Hereinafter, the substrate sheet and adherend will be collectively referred to as "members." In other words, the concept of a laminate encompasses the concept of a pressure-sensitive adhesive sheet.

[0083] The pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer laminated on a substrate sheet, as well as a substrate-less double-sided pressure-sensitive adhesive sheet having separators (release sheets) laminated on both sides of the pressure-sensitive adhesive layer, with the double-sided pressure-sensitive adhesive sheet being preferred from the viewpoint of ease of handling. When using the pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet, the release sheet is peeled off from the pressure-sensitive adhesive layer before use.

[0084] The pressure-sensitive adhesive layer may be the pressure-sensitive adhesive composition of the present invention itself, or may be obtained by curing (crosslinking) the pressure-sensitive adhesive composition of the present invention. Examples of the curing method include a method of curing by irradiation with active energy rays, a method of curing by crosslinking using a crosslinking agent, and a combination of these methods.

[0085] The pressure-sensitive adhesive sheet can be produced, for example, as follows. In this specification, the term "sheet" is not particularly distinguished from "film" or "tape" and is used to include these terms.

[0086] First, a pressure-sensitive adhesive layer having a predetermined thickness is formed on one or both sides of a substrate sheet by a method such as coating the pressure-sensitive adhesive composition in a melted state by heating onto one or both sides of a substrate sheet and then cooling, or by melting the pressure-sensitive adhesive composition by heating and extruding it onto the substrate sheet using a T-die or the like and laminating it, or by drying the solvent after coating if a solvent is contained in the composition, etc. Next, a pressure-sensitive adhesive sheet can be produced by laminating a release sheet to the surface of the pressure-sensitive adhesive layer, if necessary.

[0087] Furthermore, after forming the adhesive layer on the base sheet, if necessary, an active energy ray irradiation treatment is carried out, and then an aging treatment is carried out, whereby an adhesive sheet having an adhesive layer in which the adhesive composition is cured (crosslinked) can be produced.

[0088] Examples of substrate sheets include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene (PP), and polymethylpentene; polyethylene fluoride resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; and synthetic resin sheets such as polyimide; metal foils such as aluminum, copper, and iron; paper such as fine paper and glassine paper; and woven and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, etc. These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated together. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and the like.

[0089] As the release sheet, for example, a release-treated synthetic resin sheet, paper, cloth, nonwoven fabric, etc., exemplified above as the base sheet, can be used. As the release sheet, it is preferable to use a silicone-based release sheet.

[0090] As a method for applying the pressure-sensitive adhesive composition, a general application method can be adopted, and examples thereof include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0091] By irradiating the pressure-sensitive adhesive composition with active energy rays, the (meth)acrylic resin (A) in the pressure-sensitive adhesive composition forms intramolecular and / or intermolecular crosslinked structures.

[0092] When irradiating with active energy rays, light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and gamma rays, as well as electron beams, proton beams, neutron beams, etc. can be used. However, curing by ultraviolet irradiation is advantageous in terms of curing speed, ease of obtaining irradiation equipment, cost, etc.

[0093] The aging treatment is preferably carried out particularly when the pressure-sensitive adhesive composition contains a thermal crosslinking agent (D), and the conditions for the aging treatment are typically room temperature (25°C) to 100°C and typically 1 to 30 days. Specifically, the aging treatment can be carried out, for example, at 23°C for 1 to 20 days, preferably at 23°C for 3 to 10 days, or at 40°C for 1 to 7 days.

[0094] The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 10 to 90%, more preferably 20 to 80%, and particularly preferably 40 to 60%, from the viewpoint of the balance of physical properties such as adhesive strength, holding power, and adhesion to PVC substrates. If the gel fraction is too low, the cohesive strength tends to decrease, resulting in a decrease in durability. On the other hand, if the gel fraction is too high, the cohesive strength tends to increase, resulting in a decrease in adhesive strength.

[0095] The gel fraction can be adjusted to fall within the above range by, for example, adjusting the active energy ray irradiation dose or the type and amount of the monomer (a1) having an active energy ray-active site, or, when a thermal crosslinking agent (D) is used, adjusting the type and amount of the thermal crosslinking agent (D).

[0096] The gel fraction is a measure of the degree of crosslinking (degree of cure) and is calculated, for example, by the following method. A pressure-sensitive adhesive sheet (without a separator) consisting of a substrate polymer sheet (e.g., polyethylene terephthalate (PET) film, etc.) on which a pressure-sensitive adhesive layer is formed is wrapped in a 200-mesh SUS wire netting and immersed in toluene at 23°C for 24 hours, and the weight percentage of the undissolved pressure-sensitive adhesive component remaining in the wire netting is taken as the gel fraction. The weight of the pressure-sensitive adhesive component is calculated by subtracting the weight of the substrate from the weight of the pressure-sensitive adhesive sheet.

[0097] The thickness of the adhesive layer of the adhesive sheet is preferably 5 to 2000 μm, more preferably 10 to 100 μm, and particularly preferably 20 to 30 μm. If the thickness of the adhesive layer is too thin, the adhesiveness tends to decrease, and if it is too thick, the adhesive tends to overflow when used as an adhesive label.

[0098] The thickness of the adhesive layer was determined by subtracting the measured thickness of the components other than the adhesive layer from the measured thickness of the entire adhesive sheet containing the adhesive layer using a Mitutoyo ID-C112B.

[0099] The pressure-sensitive adhesive composition of the present invention provides a pressure-sensitive adhesive having excellent hot-melt coating properties and excellent adhesive properties such as adhesive strength and holding power to olefin adherends of pressure-sensitive adhesive sheets using polyvinyl chloride (PVC) substrate sheets.

[0100] Therefore, the pressure-sensitive adhesive composition of the present invention is useful for various applications, even among hot melt coatings, such as adhesive applications for caution labels, labels for frozen foods, building materials, automobile parts, electronic parts, heat dissipation sheets, FPC manufacturing, semiconductor manufacturing processes, component sealing, aircraft parts, and sporting goods, and is particularly suitable for use in automobile parts and marking films (pressure-sensitive adhesive sheets and pressure-sensitive adhesive tapes). [Example]

[0101] 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. The weight average molecular weight, dispersity, and glass transition temperature (Tg) of the (meth)acrylic resin (A) in the following examples were measured according to the methods described above. The viscosity was measured according to JIS K5400 (1990) 4.5.3 Rotational Viscosity Method. First, prior to the examples, the following components were prepared.

[0102] <(Meth)acrylic resin (A)> The following were used as raw material monomers for the (meth)acrylic resin. Monomer (a1) having an active energy ray active site MBP: 4-methacryloyloxybenzophenone (Tg = 118°C, manufactured by Shinryo Corporation) Alkyl (meth)acrylate (a2) BA: normal butyl acrylate (Tg = -55°C, manufactured by Mitsubishi Chemical Corporation) EA: Ethyl acrylate (Tg = -22°C, manufactured by Mitsubishi Chemical Corporation) Polar group-containing ethylenically unsaturated monomer (a3) Aac: acrylic acid (Tg = 106°C, manufactured by Nippon Shokubai Co., Ltd.)

[0103] [Production of (meth)acrylic resin (A-1)] A four-necked round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 42.9 parts of methyl ethyl ketone (MEK) and 0.007 parts of azobis(2,4-dimethylvaleronitrile) (ADVN) as a polymerization initiator. After heating and refluxing in the flask, a mixed solution of 64.7 parts of BA, 30 parts of EA, 0.3 parts of MBP, 5 parts of Aac, 2.9 parts of MEK, and 0.093 parts of ADVN was added dropwise over 2 hours. One hour after the monomer addition was completed, 0.057 parts of polymerization initiator (ADVN) and 2.9 parts of MEK were added and the reaction was continued for 1 hour. After that, 0.057 parts of polymerization initiator (ADVN) and 2.9 parts of MEK were added and the reaction was continued for 1 hour. Further, 0.029 parts of a polymerization initiator (ADVN) and 2.9 parts of methyl ethyl ketone were added, and the mixture was allowed to react for 2 hours to obtain a (meth)acrylic resin (A-1) solution [solids concentration 59.4%, viscosity 2520 mPa s, weight average molecular weight (Mw) 150,000, dispersity 2.73 (Mw / Mn), calculated Tg = -40.6°C].

[0104] The proportions of the various copolymerization components (a) in the (meth)acrylic resin (A-1) were changed as shown in Table 1, and (meth)acrylic resin (A-2) was also obtained in the same manner.

[0105] [Table 1]

[0106] <Plasticizer (B)> The following plasticizers (B) were prepared: (B-1) Acetyl tributyl citrate (Tokyo Chemical Industry Co., Ltd., molecular weight 402.5) (B-2) Bis(2-ethylhexyl) adipate (Tokyo Chemical Industry Co., Ltd., molecular weight 371)

[0107] <Tackifier (C)> (C-1) Pine Crystal KE100 (Arakawa Chemical Industries, ultra-light-colored rosin, softening point 95-105°C (catalog value), acid value 2-10 (catalog value))

[0108] <Examples 1 to 5, Comparative Examples 1 and 2> The above (meth)acrylic resin (A), plasticizer (B), and tackifier (C) were blended according to Table 2. All blending amounts are solid contents. The blended solution was placed in a flask equipped with a U-shaped connecting tube so that the solvent could be distilled out of the system, and the mixture was left at a jacket temperature of 80°C for 1 hour, and then reduced to 10 kPa and left at a jacket temperature of 90°C for 2 hours to distill off the solvent, thereby obtaining the active energy ray-curable pressure-sensitive adhesive compositions described in Examples 1 to 5 and Comparative Examples 1 and 2. The obtained active energy ray-curable pressure-sensitive adhesive compositions were evaluated for hot-melt coatability as described below.

[0109] <Hot melt coatability> The melt viscosity of the pressure-sensitive adhesive composition was measured to evaluate whether it could be applied in a molten state as follows. (Melt viscosity measurement) The active energy ray-curable pressure-sensitive adhesive composition which had been made solvent-free by distilling off the solvent as described above was measured using a rotational rheometer under the following conditions. Measuring equipment: MCR301 (manufactured by Anton Paar) Cone plate diameter: 25mm Measurement distance: 0.5mm Measurement shear rate: 0.002 (1 / S) ·Measurement temperature: 130℃ The evaluation was carried out according to the following criteria, and the results are summarized in Table 2.

[0110] (Evaluation criteria) ◎··30Pa·s or less ○ More than 30 Pa·s and less than 60 Pa·s △: More than 60 Pa·s and less than 90 Pa·s ×··Greater than 90 Pa·s

[0111] [Table 2]

[0112] [Preparation of adhesive sheet (PVC substrate)] Each of the active energy ray-curable pressure-sensitive adhesive compositions of Examples 1 to 5 and Comparative Examples 1 and 2 was blended with ethyl acetate and diluted to a solids concentration of 50%, and then coated using an applicator onto a 38 μm-thick light-release silicone separator (Mitsui Chemicals Tohcello, Inc., "SPPET01 38BU") so that the thickness after drying would be 25 μm, forming a layer of the pressure-sensitive adhesive composition. A UV irradiation device using a high-pressure mercury lamp was used to apply the composition at a predetermined dose (130 mW / cm 2 , XmJ / cm 2 where X is the value shown in the irradiation conditions column in Table 3), to form a pressure-sensitive adhesive layer. A pressure-sensitive adhesive sheet was produced by laminating the surface of the pressure-sensitive adhesive layer to a soft PVC film having a thickness of 80 μm (a laminate of soft PVC film / pressure-sensitive adhesive layer / easy-release silicone separator).

[0113] <Adhesive strength> A 25mm x 200mm test piece was prepared from the PVC-backed pressure-sensitive adhesive sheet. After removing the separator, the piece was pressed onto the adherend (PE plate or PP plate) using a 2kg rubber roller, which was rolled back and forth twice under pressure at 23°C and 50% RH. The piece was then left to stand at 23°C for 30 minutes. The 180° peel strength (N / 25mm) was then measured at a peel rate of 300mm / min in accordance with JIS Z 0237, and evaluated as follows. The results are summarized in Table 3.

[0114] (Evaluation criteria, against PE board and PP board) ◎ 12.0N / 25mm or more and peeling at the adherend interface ○ 8.0N / 25mm or more, less than 12.0N / 25mm, and peeling occurs at the adherend interface △ 8.0N / 25mm or more and cohesive peeling, substrate interface peeling or zipping × Less than 8.0N / 25mm

[0115] <Holding force> A 25mm x 25mm test piece was prepared from the PVC-backed adhesive sheet. After removing the separator, the test piece was pressed against a sandpaper-polished stainless steel plate (SUS304) using a 2kg roller back and forth (25mm x 25mm area). The holding strength was measured using a creep tester (Tester Sangyo Co., Ltd., BE-501 high-temperature, constant-humidity chamber-equipped holding strength tester) under a 1kg load in a 40°C atmosphere for 24 hours. The holding strength was evaluated using the following criteria. The results are summarized in Table 3. The values ​​in Table 3 represent the distance (mm) the test piece was rubbed, and "NC" indicates that measurement was not possible.

[0116] (Evaluation criteria) ◎ Maintains for 1440 minutes or more without misalignment ○··Maintained for 1440 minutes or more, but there was a discrepancy △··Maintained for 30 minutes or more and less than 1440 minutes ×: held for less than 30 minutes

[0117] [Preparation of adhesive sheet (heavy release separator / adhesive / light release separator)] Each of the active energy ray-curable pressure-sensitive adhesive compositions of Examples 1 to 5 and Comparative Examples 1 and 2 was blended with ethyl acetate and diluted to a solids concentration of 50%, and then coated using an applicator onto a 38 μm-thick light-release silicone separator (Mitsui Chemicals Tohcello, Inc., "SPPET01 38BU") so that the thickness after drying would be 25 μm, forming a layer of the pressure-sensitive adhesive composition. A UV irradiation device using a high-pressure mercury lamp was used to apply the composition at a predetermined dose (130 mW / cm 2 , XmJ / cm 2 where X is the value listed in the irradiation conditions column in Table 3), to form a pressure-sensitive adhesive layer. A 38 μm-thick heavy release silicone separator (manufactured by Mitsui Chemicals Tocello, Inc., "SPPET03 38BU") was attached to the surface of the pressure-sensitive adhesive layer to produce a pressure-sensitive adhesive sheet (a laminate of heavy release separator / pressure-sensitive adhesive layer / light release separator).

[0118] <Gel fraction> The adhesive was picked from the heavy release separator / adhesive layer / light release separator configuration obtained above, wrapped in a 200-mesh SUS wire mesh, and immersed in toluene adjusted to 23°C for 24 hours. The weight of the adhesive before immersion in toluene and the undissolved adhesive components remaining in the wire mesh after immersion were weighed, and the weight of the undissolved adhesive components divided by the weight of the adhesive before immersion was taken as the gel fraction (%). The results are summarized in Table 3.

[0119] [Table 3]

[0120] Examples 1 to 5, which used the pressure-sensitive adhesive composition of the present invention, contained a (meth)acrylic resin (A) containing a structural unit derived from a monomer having an active energy active site and a plasticizer (B), and therefore resulted in excellent hot-melt coating properties and adhesive properties such as adhesion and holding power to olefins (PE board and PP board).

[0121] On the other hand, Comparative Examples 1 and 2 did not contain the plasticizer (B), and therefore the hot melt coatability and adhesive strength to olefin (particularly PP plate) were not excellent. [Industrial Applicability]

[0122] The adhesive obtained using the adhesive composition of the present invention has good hot-melt coatability, so that the organic solvent is less likely to volatilize after use, reducing harmfulness to humans and animals. Furthermore, the adhesive of the present invention has high adhesion to polyolefins, which are difficult to adhere to, and also has excellent holding power, so it can be used in a variety of applications such as automobile parts, building materials, electronic parts, and office automation equipment.

Claims

1. An active energy ray-curable pressure-sensitive adhesive composition comprising a (meth)acrylic resin (A) and a plasticizer (B), The (meth)acrylic resin (A) is an active energy ray-curable pressure-sensitive adhesive composition containing a structural unit derived from a monomer (a1) having an active energy ray-active site.

2. 2. The active energy ray-curable pressure-sensitive adhesive composition according to claim 1, wherein the plasticizer (B) is an aliphatic plasticizer.

3. The active energy ray-curable pressure-sensitive adhesive composition according to claim 1 or 2, further comprising a tackifier (C).

4. 4. The active energy-curable pressure-sensitive adhesive composition according to claim 3, wherein the tackifier (C) is a rosin-based resin.

5. The active energy ray-curable pressure-sensitive adhesive composition according to claim 1 or 2, wherein the content of the thermal crosslinking agent (D) is less than 0.05% by mass.

6. A pressure-sensitive adhesive obtained by crosslinking the active energy ray-curable pressure-sensitive adhesive composition according to claim 1 or 2.

7. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 6.

8. A pressure-sensitive adhesive sheet comprising a polyvinyl chloride substrate sheet and a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 6.

9. A laminate comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 6 and a member laminated thereon.

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