Active energy ray-curable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet using the same

Abstract

Provided is an active energy ray-curable and peelable pressure-sensitive adhesive composition which has pressure-sensitive adhesive properties capable of protecting and fixing a member to be processed with a strong pressure-sensitive adhesive force during processing, has a very low pressure-sensitive adhesive force by active energy ray irradiation after processing, can be peeled off with a light force, has high surface curability with excellent curability even in the presence of oxygen, and further has excellent low pressure-sensitive adhesive force-maintaining properties with a small increase in pressure-sensitive adhesive force over time after active energy ray irradiation.SOLUTION: Disclosed is an active energy ray-curable removable adhesive composition containing at least a (meth) acrylic resin (A), a photopolymerization initiator (C) and a crosslinking agent (D), wherein the photopolymerization initiator (C) contains at least an oxime ester photopolymerization initiator (C-1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an active energy ray-curable release-type pressure-sensitive adhesive composition and a release-type pressure-sensitive adhesive sheet using the same, and more particularly to an active energy ray-curable release-type pressure-sensitive adhesive composition used in the pressure-sensitive adhesive layer of a release-type pressure-sensitive adhesive sheet for temporary protection during processing of workpieces such as semiconductor wafers, printed circuit boards, processed glass products, metal plates, and plastic plates, and a release-type pressure-sensitive adhesive sheet obtained using the composition. [Background technology]

[0002] Peel-off adhesive sheets, which have traditionally been used in processes for dividing various components such as electronic components and glass into individual pieces or for grinding them into thin films, are required to protect and secure the processed components from external forces applied during processing, and to be easily peelable after processing so as not to damage the divided or thinned components.

[0003] As such a peel-off pressure-sensitive adhesive sheet, for example, Patent Document 1 discloses that a dicing sheet can be obtained that can simultaneously reduce chip scattering during the dicing process and reduce the amount of material remaining in the recesses by setting the storage modulus and adhesive strength of the pressure-sensitive adhesive layer before irradiation with energy rays within specific ranges and increasing the flex resistance of the pressure-sensitive adhesive layer after irradiation with energy rays. Furthermore, Patent Document 1 discloses a dicing sheet having a pressure-sensitive adhesive layer obtained from a pressure-sensitive adhesive composition containing, as a main component, an acrylic polymer having a carboxyl group and an energy ray-polymerizable compound. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-91903 Summary of the Invention [Problem to be solved by the invention]

[0005] Peel-off adhesive sheets used in the above-mentioned electronic components, etc., are required to have strong adhesive strength to the workpiece to protect it from chipping and breakage during cutting. However, when peeling off after completing their protective role, they are also required to be peeled off with extremely weak force and without leaving any adhesive residue on the workpiece. Furthermore, in recent years, they have also been used to process components of various shapes. On uneven workpieces, the tape does not conform to the adhesive surface, leaving gaps between the adhesive surface and the workpiece. Even when exposed to active energy rays, the adhesive surface in contact with the gaps is inhibited from curing due to oxygen inhibition, causing adhesive residue. Therefore, the adhesive layer is required to have high surface curing properties that allow it to cure even in the presence of oxygen. Furthermore, in some processing processes, the adhesive layer may remain attached for several days after being irradiated with active energy rays to reduce its adhesive strength. Therefore, the adhesive layer must be able to maintain its low adhesive strength during this period.

[0006] However, in Patent Document 1, although the flexibility of the pressure-sensitive adhesive layer after irradiation with active energy rays is excellent, because the flexibility is maintained, the adhesive strength is likely to increase when the adhesive layer is left standing for several days without being peeled off after irradiation with active energy rays, which is not satisfactory. Furthermore, when used on a member having an uneven surface, adhesive residue occurs in the recesses, which is not satisfactory.

[0007] Under these circumstances, the present invention aims to provide an active energy ray-curable peel-type pressure-sensitive adhesive composition which has adhesive properties that enable it to protect and fix workpieces with strong adhesive strength during processing, and which, after processing, has extremely low adhesive strength when irradiated with active energy rays, allowing it to be peeled off with light force, has high surface curability that allows it to be cured even in the presence of oxygen, and further has excellent low adhesive strength retention, with only a small increase in adhesive strength over time after irradiation with active energy rays, and a peel-type pressure-sensitive adhesive sheet using the same. [Means for solving the problem]

[0008] It is generally known that in coating applications, etc., it is easy to improve surface curing properties by using a photopolymerization initiator that is less susceptible to oxygen inhibition. However, in adhesive sheets in which an adhesive layer is formed on the surface of a substrate sheet, the absorption wavelength of the photopolymerization initiator is blocked by the substrate sheet when irradiated with active energy rays, and therefore the original performance of the photopolymerization initiator is often not fully exhibited. Therefore, the present inventors have found that by using an oxime ester-based photopolymerization initiator, among other hypoxia-inhibiting photopolymerization initiators, it is possible to obtain an active energy ray-curable peel-type pressure-sensitive adhesive composition that is less susceptible to the blockage of the absorption wavelength of the substrate sheet even when various substrate sheets are used, has excellent surface curing properties, and is also excellent in maintaining low adhesive strength.

[0009] That is, the present invention includes the following aspects. Aspect (1) of the present invention is an active energy ray-curable removable pressure-sensitive adhesive composition (hereinafter also simply referred to as "pressure-sensitive adhesive composition") that contains at least a (meth)acrylic resin (A), a photopolymerization initiator (C), and a crosslinking agent (D), and the photopolymerization initiator (C) contains at least an oxime ester photopolymerization initiator (C-1).

[0010] In an aspect (2) of the present invention, in the pressure-sensitive adhesive composition of the aspect (1), the (meth)acrylic resin (A) has a glass transition temperature of -70 to 10°C.

[0011] In an embodiment (3) of the present invention, the pressure-sensitive adhesive composition of the embodiment (1) or (2) further contains an active energy ray-curable compound (B).

[0012] Aspect (4) of the present invention is the pressure-sensitive adhesive composition of any one of aspects (1) to (3), wherein the (meth)acrylic resin (A) contains a structural unit derived from a carboxyl group-containing monomer.

[0013] Aspect (5) of the present invention is the pressure-sensitive adhesive composition of aspect (3) or (4), wherein the active energy ray-curable compound (B) has three or more unsaturated groups per molecule.

[0014] Aspect (6) of the present invention is the pressure-sensitive adhesive composition of any one of aspects (1) to (5), wherein the content of the oxime ester photopolymerization initiator (C-1) in the photopolymerization initiator (C) is 5 mass % or more.

[0015] Aspect (7) of the present invention is the pressure-sensitive adhesive composition of any one of aspects (1) to (6), wherein the content of the oxime ester photopolymerization initiator (C-1) is 0.1 to 20 parts by mass per 100 parts by mass of the (meth)acrylic resin (A) or the active energy ray-curable compound (B).

[0016] An embodiment (8) of the present invention is an active energy ray-curable peelable pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition of any one of embodiments (1) to (7) is crosslinked. [Effects of the Invention]

[0017] The active energy ray-curable peel-type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition of the present invention is crosslinked has excellent adhesive properties and surface curability, and low adhesive strength retention before and after exposure to active energy rays, and can therefore be suitably used, for example, as an active energy ray-curable peel-type pressure-sensitive adhesive sheet using a substrate sheet that reflects ultraviolet rays. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments for carrying out the present invention will be specifically described, but the present invention is not limited to these. In this specification, "(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. The term "active energy ray-curable peelable type" means that the purpose is to peel off the pressure-sensitive adhesive layer obtained by curing through irradiation with active energy rays, the term "active energy ray-curable peelable pressure-sensitive adhesive composition" refers to a pressure-sensitive adhesive composition used for such a purpose, and the term "active energy ray-curable peelable pressure-sensitive adhesive sheet" refers to a sheet having a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition has been crosslinked. The term "sheet" is not particularly intended to be distinguished from film or tape, and is used to include these. 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 mass%, 10 to 15 mass%, "it can constitute each of the numerical ranges "5 to 15 mass%, " "10 to 20 mass%, " "5 to 10 mass%, " and "15 to 20 mass%.

[0019] <Active energy ray-curable peel-type pressure-sensitive adhesive composition> The active energy ray-curable peel-type pressure-sensitive adhesive composition of the present invention is generally used in the pressure-sensitive adhesive layer of a peel-type pressure-sensitive adhesive sheet that is intended to be peeled off after being attached to a workpiece such as a metal plate, a plastic plate, a semiconductor wafer, etc. In the above-mentioned peel-type pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer is formed by coating the pressure-sensitive adhesive composition on a substrate sheet, and after being attached to the workpiece, the pressure-sensitive adhesive layer is cured by irradiating it with active energy rays, thereby reducing the adhesive strength and allowing it to be easily peeled off from the workpiece.

[0020] The active energy ray-curable peelable pressure-sensitive adhesive composition is a composition containing an unsaturated group-containing compound such as a (meth)acrylic resin having an unsaturated group that is curable with active energy rays. An example of a method for adding an unsaturated group to a (meth)acrylic resin is to urethanize a hydroxyl group-containing (meth)acrylic resin with 2-ethyl isocyanate methacrylate, thereby adding an unsaturated group to the side chain of the (meth)acrylic resin. Another example of a method for incorporating a compound having an unsaturated group is to mix a (meth)acrylic resin with a bifunctional or higher functional active energy ray-curable compound. In the present invention, it is preferable to contain an unsaturated group-containing compound that is curable with active energy rays. Hereinafter, a pressure-sensitive adhesive composition containing an active energy ray-curable unsaturated group-containing compound will be described.

[0021] In such a case, the pressure-sensitive adhesive composition contains at least a (meth)acrylic resin (A), a photopolymerization initiator (C), and a crosslinking agent (D). Each component will be explained in turn below.

[0022] [(Meth)acrylic resin (A)] The (meth)acrylic resin (A) contains structural units derived from at least one (meth)acrylic monomer (a1) as a main component, and may contain structural units derived from various other polymerizable monomers. In other words, the (meth)acrylic resin (A) is a (meth)acrylic resin obtained by polymerizing a polymerization component (a) containing at least one (meth)acrylic monomer (a1) and, in some cases, various other polymerizable monomers. The phrase "containing structural units derived from the (meth)acrylic monomer (a1) as a "main component"" means that the (meth)acrylic resin (A) contains structural units derived from the (meth)acrylic monomer (a1) in an amount of usually 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, based on the total structural units constituting the (meth)acrylic resin (A). The content of the structural unit derived from the (meth)acrylic monomer (a1) in the (meth)acrylic resin (A) can also be expressed as the content of the (meth)acrylic monomer (a1) relative to the total polymerization components (a) constituting the (meth)acrylic resin (A).

[0023] Next, the (meth)acrylic resin (A) obtained by polymerizing the polymerization component (a) containing at least one (meth)acrylic monomer (a1), a carboxyl group-containing monomer (a2), and a hydroxyl group-containing monomer (a3) ​​will be described.

[0024] [(Meth)acrylic monomer (a1)] Examples of the (meth)acrylic monomer (a1) (excluding the monomers (a2) and (a3)) used in the present invention include derivatives of (meth)acrylic acid, (meth)acrylamide and derivatives thereof.

[0025] 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.

[0026] 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, and the like. ) acrylate, 3-methyl-2-norbornylmethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate and other polycyclic (meth)acrylates; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxymethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate Alkoxy group- or phenoxy group-containing (meth)acrylates such as ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl (meth)acrylate, and alkylphenoxypolyethylene glycol (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;Examples include 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.

[0027] Examples of the (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 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; and heterocycle-containing (meth)acrylamide derivatives such as N-acryloylmorpholine, N-acryloylpiperidine, N-methacryloylpiperidine, and N-acryloylpyrrolidine.

[0028] These (meth)acrylic monomers (a1) may be used alone or in combination of two or more. Among these (meth)acrylic monomers (a1), 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 2 to 18, and more preferably 4 to 12. Among these, methyl (meth)acrylate and n-butyl acrylate are preferred in terms of easily stable adhesive properties and compatibility with urethane (meth)acrylate, which will be described later.

[0029] The content of the structural units derived from the (meth)acrylic monomer (a1) is usually 40% by mass, preferably 50% by mass or more, more preferably 60% by mass or more, with the upper limit usually being 100% by mass, based on all the structural units constituting the (meth)acrylic resin (A). In particular, when an alkyl group-containing (meth)acrylate is used, the content of structural units derived from the alkyl group-containing (meth)acrylate relative to the total structural units of the (meth)acrylic resin (A) is usually 40 mass% or more, preferably 50 mass% or more, more preferably 60 mass% or more, and the upper limit is usually 100 mass%.

[0030] [Carboxyl group-containing monomer (a2)] Examples of the carboxyl group-containing monomer (a2) (excluding the (meth)acrylic monomer (a1)) used in the present invention include (meth)acrylic acid, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxyethyl phthalic acid, crotonic acid, maleic acid, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, cinnamic acid, etc. These carboxyl group-containing monomers (a2) may be used alone or in combination of two or more. Among these, (meth)acrylic acid is preferred because it is easily copolymerized and can easily improve the adhesive strength before irradiation with active energy rays.

[0031] The content of the structural units derived from the carboxyl group-containing monomer (a2) is preferably 0.1 to 40 mass%, more preferably 1 to 30 mass%, and even more preferably 3 to 25 mass%, based on the total amount of structural units constituting the (meth)acrylic resin (A), in order to easily increase the adhesive strength before irradiation with active energy rays. If the content of the structural unit derived from the carboxyl group-containing monomer (a2) is too low, the adhesive strength before irradiation with active energy rays tends to be low, which may easily cause chipping or breakage.On the other hand, if the content is too high, the glass transition temperature (Tg) of the (meth)acrylic resin (A) tends to be too high, which may easily reduce the adhesion and adhesive properties to the workpiece.

[0032] [Hydroxyl group-containing monomer (a3)] Examples of the hydroxyl group-containing monomer (a3) ​​(excluding the (meth)acrylic monomer (a1)) used in the present invention include 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; and hydroxyl group-containing (meth)acrylates such as [4-(hydroxymethyl)cyclohexyl]methyl acrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. These hydroxyl group-containing monomers (a3) ​​may be used alone or in combination of two or more. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred because they are easily copolymerized, have good crosslinkability with the crosslinking agent (D) described below, and can easily improve stain resistance after irradiation with active energy rays.

[0033] The content of the structural units derived from the hydroxyl group-containing monomer (a3) ​​is preferably 0.01 to 30 mass %, more preferably 0.02 to 20 mass %, and even more preferably 0.05 to 10 mass %, of all the structural units constituting the (meth)acrylic resin (A), from the viewpoint of improving adhesion to the substrate sheet and stain resistance when peeled off after irradiation with active energy rays. If the content of the structural unit derived from the hydroxyl group-containing monomer (a3) ​​is too low, the adhesion to the substrate sheet tends to decrease and the cohesive strength of the pressure-sensitive adhesive layer formed tends to decrease, whereas if the content is too high, the stability of the (meth)acrylic resin (A) tends to decrease and the pot life tends to be shortened.

[0034] [Other polymerizable monomers (a4)] The (meth)acrylic resin (A) used in the present invention may contain a structural unit derived from a polymerizable monomer (a4) other than the (meth)acrylic monomer (a1), the carboxyl group-containing monomer (a2), and the hydroxyl group-containing monomer (a3) ​​(hereinafter referred to as "other polymerizable monomer (a4)"). Examples of the other polymerizable monomer (a4) include unsaturated carboxylic acids such as maleic anhydride, itaconic anhydride, and acrylamido-N-glycolic acid; vinyl 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 other polymerizable monomers (a4) may be used alone or in combination of two or more.

[0035] The other polymerizable monomer (a4) may also contain a photocrosslinkable monomer, which is a monomer that generates radicals when exposed to active energy rays such as light. As the photocrosslinkable monomer, for example, (meth)acrylate monomers having a benzophenone structure such as 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 can be used. By using such a photocrosslinkable monomer as the polymerization component (a), a photocrosslinkable structural moiety can be formed in the (meth)acrylic resin (A).

[0036] The content of the structural units derived from the other polymerizable monomers (a4) is usually 0 to 30% by mass, and preferably 0 to 20% by mass, based on the total structural units constituting the (meth)acrylic resin (A). Of the structural units derived from the other polymerizable monomers (a4), the structural units derived from the photocrosslinkable monomers generally account for 0 to 10 mass %, preferably 0 to 5 mass %, of the total structural units constituting the (meth)acrylic resin (A).

[0037] [Method for producing (meth)acrylic resin (A)] The polymerization method for the (meth)acrylic resin (A) used in the present invention can be a conventionally known method such as solution radical polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. For example, a method in which an appropriately selected polymerization component (a) and a thermal polymerization initiator are mixed or dropped into an organic solvent and polymerized under predetermined polymerization conditions can be used. Among these, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred because it allows the stable production of an acrylic resin. An example of a preferred method for producing the (meth)acrylic resin (A) used in the present invention will be described below.

[0038] First, the above-mentioned polymerization component (a) and a thermal polymerization initiator are mixed or dropped into an organic solvent, and solution polymerization is carried out to obtain an acrylic resin solution.

[0039] (organic solvent) 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; and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. One of these may be used alone, or two or more may be used in combination. Among these solvents, it is preferable to use an organic solvent having a boiling point of 80° C. or less, since this allows for efficient production of a solventless (meth)acrylic resin (A) by distilling off the solvent from the solution of the (meth)acrylic resin (A) obtained by solution polymerization.

[0040] Examples of organic solvents having a boiling point of 80°C or lower include hydrocarbon solvents such as n-hexane (67°C), alcohol solvents such as methanol (65°C), ester solvents such as ethyl acetate (77°C) and methyl acetate (54°C), ketone solvents such as methyl ethyl ketone (80°C) and acetone (56°C), diethyl ether (35°C), methylene chloride (40°C), tetrahydrofuran (66°C), etc. Among these, in terms of versatility and safety, it is preferable to use ethyl acetate, acetone, and methyl acetate, and it is particularly preferable to use ethyl acetate and acetone. The numerical values ​​in parentheses following the names of the above organic solvents are the boiling points of the respective organic solvents at 1 atmosphere.

[0041] (thermal polymerization initiator) The thermal polymerization initiator used in the polymerization reaction may be a typical radical polymerization initiator such as an azo polymerization initiator or a peroxide polymerization initiator. Examples of the azo polymerization initiator include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide polymerization initiators include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, diisobutyryl peroxide, etc. Among these, one type may be used alone, or two or more types may be used in combination.

[0042] The amount of the thermal polymerization initiator used is usually 0.001 to 10% by mass, preferably 0.1 to 8% by mass, particularly preferably 0.5 to 6% by mass, even more preferably 1 to 4% by mass, especially preferably 1.5 to 3% by mass, and most preferably 2 to 2.5% by mass, based on 100% by mass of the polymerization component (a). If the amount of the thermal polymerization initiator used is too small, the polymerization rate of the (meth)acrylic resin (A) tends to decrease, the amount of residual monomer increases, and the mass average molecular weight of the (meth)acrylic resin (A) tends to increase. If the amount used is too large, the time required for the follow-up heating described below becomes long, which is not productive.

[0043] (Polymerization conditions, etc.) The polymerization conditions for solution polymerization are not particularly limited, and polymerization can be carried out according to conventionally known polymerization conditions. For example, polymerization component (a) and a thermal polymerization initiator can be mixed or dropped into a solvent and polymerized under predetermined polymerization conditions.

[0044] The polymerization temperature in the above polymerization reaction is usually 40 to 120° C., but in the present invention, from the viewpoint of ensuring a stable reaction, it is preferably 50 to 90° C., particularly preferably 55 to 75° C., and even more preferably 60 to 70° C. If the polymerization temperature is too high, the (meth)acrylic resin (A) tends to gel easily, while if it is too low, the activity of the thermal polymerization initiator decreases, so that the polymerization rate of the (meth)acrylic resin (A) decreases and the amount of residual monomer tends to increase.

[0045] The polymerization time in the polymerization reaction (the time until the start of the follow-up heating, if follow-up heating is performed as described below) is not particularly limited, but is preferably 0.5 hours or more from the addition of the final thermal polymerization initiator, particularly preferably 1 hour or more, further preferably 2 hours or more, and particularly preferably 5 hours or more. The upper limit of the polymerization time is usually 72 hours. The polymerization reaction is preferably carried out while refluxing the solvent, since this facilitates heat removal.

[0046] In the production of the acrylic resin, it is preferable to thermally decompose the thermal polymerization initiator by follow-up heating in order to reduce the amount of the remaining thermal polymerization initiator.

[0047] The drive-in heating temperature is preferably higher than the 10-hour half-life temperature of the thermal polymerization initiator, and specifically is usually 40 to 150°C, preferably 55 to 130°C from the viewpoint of suppressing gelation, and particularly preferably 75 to 95°C. If the drive-in heating temperature is too high, the (meth)acrylic resin (A) tends to yellow, while if it is too low, the polymerization component (a) and the thermal polymerization initiator remain, and the stability over time and thermal stability of the (meth)acrylic resin (A) tend to decrease. In this way, a solution of the (meth)acrylic resin (A) can be obtained.

[0048] [Physical Properties of (Meth)acrylic Resin (A)] The mass-average molecular weight (Mw) of the (meth)acrylic resin (A) obtained as described above is preferably 50,000 or more, more preferably 100,000 to 3,000,000, even more preferably 200,000 to 2,000,000, and particularly preferably 400,000 to 1,500,000. If the mass-average molecular weight (Mw) is too small, the cohesive strength of the resulting pressure-sensitive adhesive layer tends to decrease, and the adhesive properties before curing with active energy rays and the stain resistance after exposure to active energy rays tend to decrease. On the other hand, if the mass-average molecular weight (Mw) is too large, the compatibility with the urethane (meth)acrylate described below tends to decrease, and the adhesive strength before exposure to active energy rays tends to decrease.

[0049] The dispersity of the (meth)acrylic resin (A) [mass 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.

[0050] The mass average molecular weight (Mw) of the (meth)acrylic resin (A) is the mass average molecular weight converted into the molecular weight of standard polystyrene. The mass average molecular weight was measured by a high performance liquid chromatograph (manufactured by Japan Waters, "Waters2695 (main body)" and "Waters2414 (detector)") using a Shodex GPCKF-806L column (molecular weight exclusion limit: 2 × 10 7 Separation range: 100 to 2 × 10 7The measurement can be performed using three tubes connected in series (theoretical plate number: 10,000 / tube, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm), and the number average molecular weight (Mn) can also be measured in a similar manner. The dispersity can be determined from the measured values ​​of the mass average molecular weight (Mw) and number average molecular weight (Mn).

[0051] The glass transition temperature (Tg) of the (meth)acrylic resin (A) is preferably 20° C. or lower, more preferably −70° C. to 10° C., even more preferably −65° C. to 0° C., and particularly preferably −60° C. to −10° C. If the glass transition temperature (Tg) is too low, the cohesive strength of the pressure-sensitive adhesive layer tends to decrease and the adhesive properties before irradiation with active energy rays tend to be easily reduced, whereas if the glass transition temperature (Tg) is too high, the adhesion to the workpiece tends to decrease and the adhesive properties tend to be reduced.

[0052] The glass transition temperature (Tg) is calculated by the following Fox formula.

number

[0053] That is, the glass transition temperature (Tg) is a value calculated by applying the glass transition temperature and mass fraction of a homopolymer obtained by forming the homopolymer using each of the monomers constituting the (meth)acrylic resin (A) to the above Fox's formula. The glass transition temperature of a homopolymer formed using each of the monomers constituting the (meth)acrylic resin (A) is usually measured by a differential scanning calorimeter (DSC) and can be measured by a method conforming to JIS K7121-1987 or JIS K6240. Alternatively, a value listed in a catalog can be used as the glass transition temperature (Tg).

[0054] The refractive index of the (meth)acrylic resin (A) is usually 1.440 to 1.600. It is preferable to reduce the difference in refractive index between the (meth)acrylic resin (A) and the workpiece to be laminated, as this reduces optical loss at the interface between the workpiece and the (meth)acrylic resin (A). The refractive index is a value measured by measuring a thin film layer of the (meth)acrylic resin (A) using a refractive index measuring device (Abbe refractometer NAR-1T SOLID manufactured by Atago Co., Ltd.) with NaD rays at 23°C.

[0055] [Active energy ray-curable compound (B)] When the (meth)acrylic resin (A) does not have an active energy ray-curable unsaturated group, the pressure-sensitive adhesive composition of the present invention preferably further contains a difunctional or higher active energy ray-curable compound (B). Examples of the active energy ray-curable compound (B) include urethane (meth)acrylate compounds, monofunctional (meth)acrylates, and polyfunctional (meth)acrylates.

[0056] [Urethane (meth)acrylate compound (b)] The urethane (meth)acrylate compound (b) may be a urethane (meth)acrylate compound (b-1) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1) and a polyvalent isocyanate compound (b2); a urethane (meth)acrylate compound (b-2) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1), a polyvalent isocyanate compound (b2), and a polyol compound (b3); or a urethane (meth)acrylate compound (b-3) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1), a polyvalent isocyanate compound (b2), a monofunctional alcohol (b4), and, if necessary, a polyol compound (b3).

[0057] Among these, in the present invention, a urethane (meth)acrylate compound (b-1) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1) and a polyvalent isocyanate compound (b2), or a urethane (meth)acrylate compound (b-2) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1), a polyvalent isocyanate compound (b2), and a polyol compound (b3) is preferred in terms of compatibility with the (meth)acrylic resin (A) and adhesion properties and contamination resistance before and after irradiation with active energy rays. In the present invention, the urethane (meth)acrylate compounds may be used alone or in combination of two or more.

[0058] The hydroxyl group-containing (meth)acrylate compound (b1) is preferably one having one hydroxyl group, and examples thereof include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, 2-hydroxyethyl acryloyl phosphate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, dipropylene glycol (meth)acrylate, fatty acid-modified glycidyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and 2-hydroxy-3-(meth)acrylate. Examples of the hydroxyl group-containing (meth)acrylate compounds include those containing one ethylenically unsaturated group, such as aryloyloxypropyl (meth)acrylate; those containing two ethylenically unsaturated groups, such as glycerin di(meth)acrylate and 2-hydroxy-3-acryloyloxypropyl methacrylate; and those containing three or more ethylenically unsaturated groups, such as pentaerythritol tri(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, and ethylene oxide-modified dipentaerythritol penta(meth)acrylate. These hydroxyl group-containing (meth)acrylate compounds (b) can be used alone or in combination of two or more.

[0059] Of the hydroxyl group-containing (meth)acrylate compounds (b1), those containing three or more ethylenically unsaturated groups per molecule are preferred, in terms of excellent reactivity and versatility, with pentaerythritol tri(meth)acrylate and dipentaerythritol penta(meth)acrylate being more preferred, and pentaerythritol tri(meth)acrylate being even more preferred.

[0060] Examples of the polyisocyanate compound (b2) include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane polyisocyanate, modified diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, and lysine triisocyanate; Examples of the polyisocyanate include diisocyanates; alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and norbornene diisocyanate; isocyanurates or polymeric compounds of these polyisocyanates, allophanate polyisocyanates, biuret polyisocyanates, and water-dispersible polyisocyanates (for example, "AQUANATE 105," "AQUANATE 130," "AQUANATE 200," and "AQUANATE 210," manufactured by Tosoh Corporation).

[0061] Among these, in terms of excellent reactivity and versatility, aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate; and alicyclic diisocyanates such as hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and norbornene diisocyanate are preferred, more preferably isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, and hexamethylene diisocyanate, and even more preferably isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate.

[0062] The polyol compound (b3) may be any compound containing two or more hydroxyl groups, and examples thereof include aliphatic polyols, alicyclic polyols, polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, polybutadiene polyols, polyisoprene polyols, (meth)acrylic polyols, polysiloxane polyols, etc. One of these may be used alone, or two or more may be used in combination.

[0063] Examples of the aliphatic polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, dimethylolpropane, neopentyl glycol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-tetramethylenediol, 1,3-tetramethylenediol, 2-methyl-1,3-trimethylenediol, 1,5-pentamethylenediol, 1, Examples include aliphatic alcohols containing two hydroxyl groups, such as 6-hexamethylenediol, 3-methyl-1,5-pentamethylenediol, 2,4-diethyl-1,5-pentamethylenediol, pentaerythritol diacrylate, 1,9-nonanediol, and 2-methyl-1,8-octanediol; sugar alcohols, such as xylitol and sorbitol; and aliphatic alcohols containing three or more hydroxyl groups, such as glycerin, trimethylolpropane, and trimethylolethane.

[0064] Examples of the alicyclic polyol include cyclohexanediols such as 1,4-cyclohexanediol and cyclohexyldimethanol, hydrogenated bisphenols such as hydrogenated bisphenol A, and tricyclodecane dimethanol.

[0065] Examples of the polyether polyol include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene glycol, polypentamethylene glycol, and polyhexamethylene glycol, as well as random or block copolymers of these polyalkylene glycols.

[0066] Examples of the polyester polyol include a condensation polymer of a polyhydric alcohol and a polycarboxylic acid, a ring-opening polymer of a cyclic ester (lactone), and a reaction product of three components: a polyhydric alcohol, a polycarboxylic acid, and a cyclic ester. In this specification, a polyester polyol that further has a carbonate bond in the molecule is considered to belong to the polycarbonate polyol category. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,4-tetramethylene diol, 1,3-tetramethylene diol, 2-methyl-1,3-trimethylene diol, 1,5-pentamethylene diol, neopentyl glycol, 1,6-hexamethylene diol, 3-methyl-1,5-pentamethylene diol, 2,4-diethyl-1,5-pentamethylene diol, glycerin, trimethylolpropane, trimethylolethane, cyclohexanediols (such as 1,4-cyclohexanediol), bisphenols (such as bisphenol A), and sugar alcohols (such as xylitol and sorbitol). Examples of the polycarboxylic acid include aliphatic dicarboxylic acids such as malonic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, and trimellitic acid. Examples of the cyclic ester include propiolactone, β-methyl-δ-valerolactone, and ε-caprolactone.

[0067] Examples of the polycarbonate polyol include a reaction product of a polyhydric alcohol with phosgene; a ring-opening polymer of a cyclic carbonate (such as alkylene carbonate); and the like. Examples of the polyhydric alcohol include the polyhydric alcohols exemplified in the description of the polyester polyol, and examples of the alkylene carbonate include ethylene carbonate, trimethylene carbonate, tetramethylene carbonate, and hexamethylene carbonate. The polycarbonate polyol may be any compound having a carbonate bond in the molecule and a hydroxyl group at the end, and may have an ester bond in addition to the carbonate bond.

[0068] The polyolefin polyols include those having a homopolymer or copolymer of ethylene, propylene, butene, or the like as a saturated hydrocarbon skeleton and having hydroxyl groups at the molecular terminals.

[0069] The polybutadiene polyol may be a polybutadiene polyol having a butadiene copolymer as a hydrocarbon skeleton and hydroxyl groups at its molecular terminals. The polybutadiene polyol may be a hydrogenated polybutadiene polyol in which all or part of the ethylenically unsaturated groups contained in the polybutadiene polyol structure have been hydrogenated.

[0070] The polyisoprene-based polyol may be a polyisoprene polyol having an isoprene copolymer as a hydrocarbon backbone and hydroxyl groups at the molecular terminals. The polyisoprene-based polyol may be a hydrogenated polyisoprene polyol in which all or part of the ethylenically unsaturated groups contained in the polyisoprene-based polyol structure have been hydrogenated.

[0071] The (meth)acrylic polyols include those having at least two hydroxyl groups in the molecule of a (meth)acrylic acid ester polymer or copolymer thereof. Examples of such (meth)acrylic acid esters include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

[0072] Examples of the polysiloxane polyol include dimethylpolysiloxane polyol and methylphenylpolysiloxane polyol.

[0073] Among these polyol compounds (b3), aliphatic polyols and alicyclic polyols are preferably used from the viewpoint of cost, and polyester polyols, polyether polyols and polycarbonate polyols are preferably used from the viewpoint of versatility.

[0074] The mass average molecular weight of the polyol compound (b3) is preferably 60 to 10,000, more preferably 100 to 5,000, and even more preferably 200 to 4,000. If the mass average molecular weight of the polyol compound (b3) is too large, the compatibility between the resulting urethane (meth)acrylate compounds (b-2, b-3) and the (meth)acrylic resin (A) tends to decrease, and the adhesive properties after irradiation with active energy rays tend to decrease.

[0075] The monofunctional alcohol (b4) is not particularly limited, but examples thereof include alcohols containing a linear or branched alkyl group having 1 to 36 carbon atoms, aromatic ring-containing alcohols, alicyclic group-containing alcohols, and heterocycle-containing alcohols, and from the viewpoint of versatility, alcohols containing a linear or branched alkyl group having 1 to 36 carbon atoms are preferred, and alcohols containing a linear or branched alkyl group having 4 to 18 carbon atoms are more preferred. One of these may be used alone, or two or more may be used in combination.

[0076] The urethane (meth)acrylate compound (b) can be produced by reacting the above components by known reaction means. An example is shown below. (1) To obtain urethane (meth)acrylate compound (b-1) A method in which the hydroxyl group-containing (meth)acrylate compound (b1) is subjected to a urethane reaction with a polyisocyanate compound (b2). (2) To obtain urethane (meth)acrylate compound (b-2) A method in which the hydroxyl group-containing (meth)acrylate compound (b1), a polyvalent isocyanate compound (b2), and a polyol compound (b3) are subjected to a urethane reaction. (3) To obtain urethane (meth)acrylate compound (b-3) A method of subjecting the hydroxyl group-containing (meth)acrylate compound (b1), the polyisocyanate compound (b2), the polyol compound (b3), and further the monofunctional alcohol (b4) to a urethane reaction. The urethane-forming reaction can be carried out by charging the above components into a reactor all at once or separately and carrying out the urethane-forming reaction by a known reaction means. When producing the urethane (meth)acrylate compounds (b-2, b-3), a method of reacting a polyol compound (b3) with a polyvalent isocyanate compound (b2) in advance to obtain a reaction product, and then reacting the resulting product with a hydroxyl group-containing (meth)acrylate compound (b1) or a monofunctional alcohol (b4) is useful in terms of the stability of the urethane-forming reaction and the reduction of by-products.

[0077] In the reaction between the hydroxyl group-containing (meth)acrylate compound (b1) and the polyvalent isocyanate compound (b2), it is preferable to use a reaction catalyst in order to promote the reaction. Examples of such reaction catalysts include organometallic compounds such as dibutyltin dilaurate, trimethyltin hydroxide, and tetra-n-butyltin; metal salts such as zinc octenoate, tin octenoate, tin octoate, cobalt naphthenate, stannous chloride, and stannic chloride; triethylamine, benzyldiethylamine, 1,4-diazabicyclo[2,2,2]octane, 1,8-diazabicyclo[5,4,0]undecene, N,N,N',N' Examples of suitable catalysts include amine catalysts such as tetramethyl-1,3-butanediamine and N-ethylmorpholine; bismuth nitrate, bismuth bromide, bismuth iodide, and bismuth sulfide; organic bismuth compounds such as dibutyl bismuth dilaurate and dioctyl bismuth dilaurate; and organic bismuth salts such as bismuth 2-ethylhexanoate, bismuth naphthenate, bismuth isodecanoate, bismuth neodecanoate, bismuth laurate, bismuth maleate, bismuth stearate, bismuth oleate, bismuth linoleate, bismuth acetate, bismuth bisneodecanoate, bismuth disalicylate, and bismuth digallate; zirconium catalysts such as inorganic zirconium, organic zirconium, and simple zirconium; and combinations of two or more catalysts such as zinc 2-ethylhexanoate / zirconium tetraacetylacetonate. Among these, dibutyltin dilaurate and organic bismuth compounds are preferred. These catalysts can be used alone or in combination of two or more.

[0078] In the urethane-forming reaction, organic solvents that do not have a functional group that reacts with an isocyanate group, such as esters such as ethyl acetate and butyl acetate; ketones such as methyl ethyl ketone and methyl isobutyl ketone; and aromatics such as toluene and xylene, can be used.

[0079] The reaction temperature for the urethane-forming reaction is usually 30 to 90° C., preferably 40 to 80° C., and the reaction time is usually 2 to 10 hours, preferably 3 to 8 hours.

[0080] The urethane-forming reaction is terminated when the content of residual isocyanate groups in the reaction system reaches 0.5% by mass or less, thereby obtaining the urethane (meth)acrylate compound (b).

[0081] The (meth)acryloyl group concentration of the urethane (meth)acrylate compound (b) obtained in this manner is 0.5 mmol / g or more, preferably 1.0 to 35 mmol / g, more preferably 1.5 to 20 mmol / g, and even more preferably 2.0 to 15 mmol / g. By adjusting the (meth)acryloyl group concentration of the urethane (meth)acrylate compound (b) to fall within the above range, it is possible to obtain an urethane (meth)acrylate compound (b) with excellent releasability after irradiation with active energy rays.

[0082] In addition, from the viewpoint of adhesive properties after irradiation with active energy rays, the urethane (meth)acrylate compound (b) preferably has three or more ethylenically unsaturated groups per molecule. If the number of such ethylenically unsaturated groups is too small, sufficient crosslinking density cannot be obtained, and adhesive properties and contamination resistance after irradiation with active energy rays tend to decrease.

[0083] The mass average molecular weight (Mw) of the urethane (meth)acrylate compound (b) is usually 200 to 10,000, preferably 400 to 5,000, and more preferably 600 to 4,000. If the mass average molecular weight (Mw) is too large, the active energy ray-curable compound (B) and the (meth)acrylic resin (A) will not be uniformly mixed, and the adhesive properties before and after active energy ray irradiation will tend to deteriorate. If the mass average molecular weight is too small, the cohesive strength of the adhesive layer will tend to decrease, and the adhesive properties will tend to deteriorate.

[0084] The mass average molecular weight (Mw) is the mass average molecular weight converted to standard polystyrene molecular weight, and is measured using a high performance liquid chromatograph (Waters, "ACQUITY APC System") with four columns arranged in series: one ACQUITY APCXT450, one ACQUITY APCXT200, and two ACQUITY APCXT45.

[0085] The viscosity of the urethane (meth)acrylate compound (b) used in the present invention at 60°C is preferably 50 to 10,000 mPa·s, more preferably 100 to 7,000 mPa·s, and even more preferably 200 to 4,000. If the viscosity is too low, the cohesive force tends to decrease, and if it is too high, the coatability tends to decrease. The viscosity can be measured using an E-type viscometer.

[0086] As the active energy ray-curable compound (B), in addition to the urethane (meth)acrylate-based compound (b), monofunctional (meth)acrylates and polyfunctional (meth)acrylates can also be used.

[0087] [Monofunctional (meth)acrylate] Examples of such monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, acrylonitrile, 2-methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, phenoxyethyl (meth)acrylate, 2-phenoxy-2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, glycerin mono(meth)acrylate, glycidyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Peroxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)-methyl (meth)acrylate, cyclohexanespiro-2-(1,3-dioxolan-4-yl)-methyl (meth)acrylate, 3-ethyl-3-oxetanylmethyl (meth)acrylate, γ-butyrolactone (meth)acrylate, n-butyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, n-stearyl (meth)acrylate, benzyl (meth)acrylate, phenol ethylene oxide modified (n=2) (meth)acrylate, nonylphenol propylene oxide modified (n=2).5) (Meth)acrylate monomers such as half (meth)acrylates of phthalic acid derivatives, such as 2-(meth)acryloyloxyethyl acid phosphate and 2-(meth)acryloyloxy-2-hydroxypropyl phthalate, furfuryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, carbitol (meth)acrylate, benzyl (meth)acrylate, butoxyethyl (meth)acrylate, allyl (meth)acrylate, (meth)acryloylmorpholine, and polyoxyethylene secondary alkyl ether acrylate, 2-hydroxyethyl acrylamide, N-methylol (meth)acrylamide, N-vinylpyrrolidone, 2-vinylpyridine, and vinyl acetate.

[0088] [Multifunctional (meth)acrylate] Examples of polyfunctional (meth)acrylates include bifunctional (meth)acrylates and trifunctional or higher acrylates.

[0089] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, cyclohexanedimethanol di(meth)acrylate, Examples of the diglycidyl acrylate include acrylate, ethoxylated cyclohexanedimethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, phthalic acid diglycidyl ester di(meth)acrylate, hydroxypivalic acid-modified neopentyl glycol di(meth)acrylate, and isocyanuric acid ethylene oxide-modified diacrylate.

[0090] Examples of trifunctional or higher functional acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tri(meth)acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly(meth)acrylate, isocyanuric acid ethylene oxide modified triacrylate, caprolactone modified dipentaerythritol penta(meth) ... Examples of the copolymer include lactone-modified dipentaerythritol hexa(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, caprolactone-modified pentaerythritol tetra(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified dipentaerythritol hexa(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, and ethoxylated (15) glycerin triacrylate.

[0091] Furthermore, Michael adducts of acrylic acid or 2-acryloyloxyethyl dicarboxylic acid monoesters can also be used in combination, and examples of such Michael adducts of acrylic acid include (meth)acrylic acid dimer, (meth)acrylic acid trimer, and (meth)acrylic acid tetramer. The 2-acryloyloxyethyl dicarboxylic acid monoester is a carboxylic acid having a specific substituent, and examples of such monoesters include 2-acryloyloxyethyl succinic acid monoester, 2-methacryloyloxyethyl succinic acid monoester, 2-acryloyloxyethyl phthalic acid monoester, 2-methacryloyloxyethyl phthalic acid monoester, 2-acryloyloxyethyl hexahydrophthalic acid monoester, 2-methacryloyloxyethyl hexahydrophthalic acid monoester, etc. Furthermore, other examples include oligoester acrylates, etc. These monofunctional (meth)acrylates and polyfunctional (meth)acrylates can be used alone or in combination of two or more.

[0092] The content of the urethane (meth)acrylate compound (b) in the active energy ray-curable compound (B) is 50% by mass or more, preferably 80% by mass or more, with the upper limit being 100% by mass. If the content is too low, the adhesive properties before active energy ray irradiation and the contamination resistance after active energy ray irradiation tend to decrease.

[0093] The content of monofunctional (meth)acrylates and polyfunctional (meth)acrylates other than the urethane (meth)acrylate compound (b) in the active energy ray-curable compound (B) is less than 50% by mass, preferably less than 20% by mass, with the lower limit being 0% by mass. If this content is too high, the adhesive properties before active energy ray irradiation and the contamination resistance after active energy ray irradiation tend to decrease.

[0094] In the pressure-sensitive adhesive composition of the present invention, the content of the active energy ray-curable compound (B) is 10 to 200 parts by mass, preferably 30 to 180 parts by mass, more preferably 50 to 150 parts by mass, and even more preferably 75 to 120 parts by mass, relative to 100 parts by mass of the (meth)acrylic resin (A). If the content of the active energy ray-curable compound (B) is too low, the peelability after irradiation with active energy rays tends to be easily reduced, while if it is too high, the cohesive strength of the pressure-sensitive adhesive layer tends to be reduced, and the adhesive properties before and after irradiation with active energy rays tend to be reduced.

[0095] [Photopolymerization initiator (C)] The photopolymerization initiator (C) used in the present invention contains at least one oxime ester-based photopolymerization initiator (C-1). Examples of such oxime ester photopolymerization initiators (C-1) include 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime) (Irgacure OXE01), 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone-1-(O-acetyloxime) (Irgacure OXE02), Irgacure OXE03, Irgacure OXE04 (all manufactured by BASF Japan Ltd.), Adeka Arcles N-1919T, Adeka Arcles NCI-831E, Adeka Arcles NCI-930, Adeka Arcles NCI-730 (all manufactured by Adeka Corporation). These photopolymerization initiators (C) can be used alone or in combination of two or more. Among these, Irgacure OXE01 and Irgacure OXE02 are preferred because they are readily available and have an absorption wavelength that is easy to handle.

[0096] The photopolymerization initiator (C) may contain a photopolymerization initiator (C-2) other than the oxime ester-based photopolymerization initiator (C-1). Examples of such photopolymerization initiators (C-2) include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl ketone, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-methyl-2-morpholino(4-thiomethylphenyl)propan-1-one, and the like. Acetophenones such as propan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomer; benzoins such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, and 4-benzoyl-4' benzophenones such as 4-benzoylbenzyl)trimethylammonium chloride; thioxanthones such as 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-(3-dimethylamino-2-hydroxy)-3,4-dimethyl-9H-thioxanthone-9-one mesochloride; acylphosphine oxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; and the like. Among these, it is preferable to use acylphosphine oxides such as 2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide in combination with the oxime ester photopolymerization initiator (C-1), because they have high internal curing properties and tend to maintain adhesive strength over time after irradiation with active energy rays. These photopolymerization initiators (C-2) can be used alone or in combination of two or more.

[0097] As an auxiliary for these photopolymerization initiators (C), for example, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. can also be used in combination. These auxiliary agents can be used alone or in combination of two or more. When an auxiliary is used, the content of the auxiliary per 100 parts by mass of the photopolymerization initiator (C) is preferably 0.1 to 50 parts by mass.

[0098] The content of the photopolymerization initiator (C) is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 25 parts by mass, even more preferably 1 to 20 parts by mass, and particularly preferably 1.5 to 10 parts by mass, per 100 parts by mass of the (meth)acrylic resin (A) if the (meth)acrylic resin (A) has an unsaturated group curable with active energy rays, or per 100 parts by mass of the active energy ray-curable compound (B) if the (meth)acrylic resin (A) does not have an unsaturated group curable with active energy rays. If the content of the photopolymerization initiator (C) is too low, curing failure occurs even after irradiation with active energy rays, and easy peelability tends to decrease. If the content is too high, it tends to migrate to the workpiece during peeling and cause contamination as particles.

[0099] The content of the oxime ester photopolymerization initiator (C-1) in the photopolymerization initiator (C) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 30% by mass or more. If the content of the oxime ester photopolymerization initiator (C-1) is too low, the surface curing property decreases, and adhesive residue tends to easily occur when the film is applied to an uneven surface.

[0100] [Crosslinker (D)] The crosslinking agent (D) used in the present invention is not particularly limited as long as it crosslinks the (meth)acrylic resins (A) together, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, and amine-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred in terms of improving the adhesion of the peel-type pressure-sensitive adhesive sheet to the substrate sheet and reactivity with the (meth)acrylic resin (A). These crosslinking agents (D) may be used alone or in combination of two or more.

[0101] Examples of the isocyanate crosslinking agent include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, adducts of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret and isocyanurate forms of these polyisocyanate compounds. Among these, in terms of chemical resistance and reactivity with functional groups, an isocyanurate of hexamethylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, an adduct of 2,6-tolylene diisocyanate and trimethylolpropane, an isocyanurate of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and an adduct of tetramethylxylylene diisocyanate and trimethylolpropane are preferred.

[0102] Examples of the epoxy crosslinking agent include bisphenol A-epichlorohydrin epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0103] Examples of the aziridine crosslinking agent include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0104] Examples of the oxazoline crosslinking agent include 2,2' and polymers of one or more of the following addition-polymerizable oxazolines: 1,2-bis(2-oxazoline), 1,2-bis(2-oxazolin-2-yl)ethane, 1,4-bis(2-oxazolin-2-yl)butane, 1,8-bis(2-oxazolin-2-yl)butane, 1,4-bis(2-oxazolin-2-yl)cyclohexane, 1,2-bis(2-oxazolin-2-yl)benzene, 1,3-bis(2-oxazolin-2-yl)benzene, and the like.

[0105] Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0106] Examples of the aldehyde crosslinking agent include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0107] Examples of the amine-based crosslinking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0108] The content of the crosslinking agent (D) is preferably 0.1 to 30 parts by mass, more preferably 0.2 to 20 parts by mass, and even more preferably 0.3 to 15% by mass, relative to 100 parts by mass of the (meth)acrylic resin (A). If the content of the crosslinking agent (D) is too low, the cohesive strength of the adhesive layer tends to decrease, and the adhesive properties tend to decrease. If the content of the crosslinking agent (D) is too high, the adhesive properties before irradiation with active energy rays tend to decrease, and lifting or peeling tends to occur during processing.

[0109] [Other ingredients] The pressure-sensitive adhesive composition of the present invention may further contain additives within the range that does not impair the effects of the present invention. Examples of additives include antistatic agents, antioxidants, plasticizers, fillers, pigments, diluents, antioxidants, UV absorbers, UV stabilizers, etc., and these additives can be used alone or in combination of two or more. Antioxidants in particular are effective in maintaining the stability of the pressure-sensitive adhesive layer. The content of other components varies depending on the components used, but is preferably 10% by mass or less relative to the pressure-sensitive adhesive composition. For example, when an antioxidant is added, its content is not particularly limited, but is preferably 0.01 to 5% by mass relative to the pressure-sensitive adhesive composition. In addition to the above-mentioned additives, the pressure-sensitive adhesive composition of the present invention may contain small amounts of impurities contained in the raw materials for producing the components of the pressure-sensitive adhesive composition.

[0110] Furthermore, the pressure-sensitive adhesive composition of the present invention preferably does not contain a tackifying resin such as a terpene-based resin, a rosin-based resin, a chroman-based resin, a phenol-based resin, a styrene-based resin, or a petroleum-based resin, since this may reduce the contamination resistance of the workpiece after irradiation with active energy rays.

[0111] <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), the photopolymerization initiator (C), and the crosslinking agent (D), and, if necessary, further mixing optional components such as the active energy ray-curable compound (B) and other components.

[0112] 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.

[0113] The pressure-sensitive adhesive composition of the present invention has strong adhesive properties before irradiation with active energy rays, but its adhesive strength is significantly reduced by crosslinking the (meth)acrylic resin (A) via the crosslinking agent (D) upon irradiation with active energy rays, and is therefore suitable for use in forming a pressure-sensitive adhesive layer of a release-type pressure-sensitive adhesive sheet. More specifically, after a release-type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed thereon using the pressure-sensitive adhesive composition of the present invention is bonded to a workpiece, the pressure-sensitive adhesive layer is cured by irradiation with active energy rays, resulting in a decrease in adhesive strength and thereby exhibiting releasability from the workpiece. Therefore, the properties of this release-type pressure-sensitive adhesive sheet can be utilized to temporarily protect the surface of various workpieces when processing the workpieces. Hereinafter, an active energy ray-curable peelable pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer is formed on a substrate sheet using the pressure-sensitive adhesive composition of the present invention will be described.

[0114] <Active energy ray curable peel-off adhesive sheet> The active energy ray-curable peel-type adhesive sheet according to the present invention (hereinafter also simply referred to as "peel-type adhesive sheet") has an adhesive layer in which the adhesive composition of the present invention is crosslinked, and can be used for the purpose of temporarily protecting a workpiece.

[0115] Examples of workpieces that can be protected by the peelable pressure-sensitive adhesive sheet include semiconductor wafers, printed circuit boards, processed glass products, metal plates, and plastic plates.

[0116] The above-mentioned peelable pressure-sensitive adhesive sheet usually has a structure in which a base sheet, a pressure-sensitive adhesive layer consisting of the pressure-sensitive adhesive composition of the present invention, and a release film are arranged in this order, and other layers may be interposed between the base sheet, the pressure-sensitive adhesive layer, and the release film. A method for producing a peelable pressure-sensitive adhesive sheet having a structure in which a substrate sheet, a pressure-sensitive adhesive layer, and a release film are laminated in this order will be described below. First, the pressure-sensitive adhesive composition of the present invention is applied directly onto a release film or a substrate sheet, either as is or as a solution of the pressure-sensitive adhesive composition whose concentration has been adjusted with an appropriate organic solvent. This is then dried, for example, by heat treatment at 80 to 105°C for 0.5 to 10 minutes, and the dried pressure-sensitive adhesive layer is attached to the substrate sheet or release film.

[0117] Furthermore, to balance the adhesive properties, an aging treatment may be further carried out after drying. The aging treatment conditions are typically room temperature (25°C) to 100°C, and the treatment time is typically 1 to 30 days. Specifically, for example, the treatment can be carried out at 40°C for 1 to 7 days.

[0118] Examples of the substrate sheet include polyester-based resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymer; polyolefin-based resins such as polyethylene, polypropylene, 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.

[0119] Furthermore, as the release film, for example, various synthetic resin sheets, paper, woven fabrics, nonwoven fabrics, etc. exemplified above as the base sheet can be used which have been subjected to a release treatment.

[0120] The method for applying the pressure-sensitive adhesive composition or a solution thereof is not particularly limited, and any common application method can be used, such as roll coating, die coating, gravure coating, comma coating, and screen printing.

[0121] The thickness of the pressure-sensitive adhesive layer in the above-mentioned peelable pressure-sensitive adhesive sheet is preferably 1 to 200 μm, and more preferably 10 to 100 μm. The thickness of the adhesive layer can be determined using a Mitutoyo ID-C112B 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.

[0122] By irradiating the pressure-sensitive adhesive layer with active energy rays, the (meth)acrylic resin (A) in the pressure-sensitive adhesive composition forms intramolecular and / or intermolecular crosslinked structures. As the active energy rays, generally, 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, it is advantageous to use ultraviolet rays in terms of curing speed, ease of availability of irradiation equipment, cost, etc.

[0123] The cumulative dose of ultraviolet light is usually 50 to 3000 mJ / cm 2 , preferably 100 to 1000 mJ / cm 2 The irradiation time varies depending on the type of light source, the distance between the light source and the adhesive layer, the thickness of the adhesive layer, and other conditions, but is usually a few seconds, and in some cases may be a very short time of less than one second.

[0124] The adhesive strength of the peel-type adhesive sheet varies depending on the type of substrate sheet, the type of workpiece, etc., but is adjusted so that the 180-degree peel strength before irradiation with active energy rays is usually 1 N / 25 mm or more, preferably 3 N / 25 mm or more. The adhesive strength can be adjusted by adjusting the glass transition temperature (Tg) of the (meth)acrylic resin (A) or the type and amount of the crosslinking agent (D).

[0125] The peel strength of the above-mentioned release-type pressure-sensitive adhesive sheet after irradiation with active energy rays is usually lower than the peel strength before irradiation with active energy rays. The 180-degree peel strength of the above-mentioned release-type pressure-sensitive adhesive sheet after irradiation with active energy rays is usually 1 N / 25 mm or less, preferably 0.5 N / 25 mm or less, and more preferably 0.05 N / 25 mm or less.

[0126] A peelable adhesive sheet using the adhesive composition of the present invention as an adhesive layer can be easily peeled off from a workpiece by laminating it to a workpiece to temporarily protect the surface of the workpiece, and then irradiating it with active energy rays from the base sheet side, whereby the adhesive layer hardens and the adhesive strength decreases. Furthermore, even when a peel-off pressure-sensitive adhesive sheet is attached to a workpiece having an uneven surface, the pressure-sensitive adhesive layer of the peel-off pressure-sensitive adhesive sheet is less susceptible to the effects of oxygen in the voids caused by the unevenness when irradiated with active energy rays, resulting in high surface curing properties, and the sheet also has excellent low adhesive strength retention, with only a small increase in adhesive strength over time after irradiation with active energy rays. Therefore, the pressure-sensitive adhesive composition of the present invention can be suitably used to form a pressure-sensitive adhesive layer in a peel-off pressure-sensitive adhesive sheet for temporary protection when processing workpieces such as semiconductor wafers, printed circuit boards, processed glass products, metal plates, and plastic plates. [Example]

[0127] 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 based on mass. In the following examples, the mass average molecular weight and glass transition temperature (Tg) were measured according to the methods described above. Viscosity was measured according to JIS K5400 (1990) 4.5.3 Rotational Viscometer Method. First, prior to the examples, the following components were prepared.

[0128] <Preparation of (meth)acrylic resin (A) solution> [(Meth)acrylic resin (A-1)] A reactor equipped with a temperature controller, a thermometer, a stirrer, a dropping funnel, and a reflux condenser was charged with 70 parts of ethyl acetate and 0.04 parts of 2,2'-azobisisobutyronitrile (AIBN (thermal polymerization initiator)) as a polymerization catalyst, and the temperature was raised to reflux with stirring. When the internal temperature stabilized, a mixture of 91.9 parts of n-butyl acrylate (a1), 8.0 parts of acrylic acid (a2), and 0.1 parts of 2-hydroxyethyl methacrylate (a3) ​​as polymerization component (a) was added dropwise over 2 hours, and the reaction was carried out under reflux. Next, 3 hours after the start of the reaction, 13.3 parts of toluene and 0.08 parts of AIBN were added, and the reaction was terminated 5.5 hours after the start of the reaction, yielding a (meth)acrylic resin (A-1) solution [glass transition temperature (Tg) -48.2°C, resin content 35.0%, viscosity 7,000 mPa s (25°C), mass average molecular weight (Mw) 877,000].

[0129] <Preparation of active energy ray-curable compound (B)> [Preparation of urethane (meth)acrylate (B-1)] A four-neck flask equipped with a temperature controller, a thermometer, a stirrer, a water-cooled condenser, and a nitrogen gas inlet was charged with 18.3 parts of isophorone diisocyanate (isocyanate group content: 37.8%) (manufactured by Evonik Japan Co., Ltd.), 81.7 parts of a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (hydroxyl value: 119.1 mg KOH / g), 0.04 parts of 2,6-di-tert-butylcresol as a polymerization inhibitor, and 0.02 parts of dibutyltin dilaurate, a tin compound, as a reaction catalyst, and reacted at 60°C. The reaction was terminated when the residual isocyanate groups reached 0.3% or less, yielding a mixture of urethane (meth)acrylate (B-1) (6 ethylenically unsaturated groups, mass average molecular weight 1,300, acryloyl group concentration 25.4 mmol / g).

[0130] <Examples 1 to 3 and Comparative Examples 1 to 7> An active energy ray-curable peel-type pressure-sensitive adhesive composition was obtained by blending the (meth)acrylic resin (A), active energy ray-curable compound (B), and the following components in the amounts shown in Table 1. The blending amounts of components (B), (C), and (D) are the blending amounts per 100 parts by mass (solid content) of the (meth)acrylic resin (A).

[0131] [Table 1]

[0132] [Photopolymerization initiator (C)] Photopolymerization initiator (C-1): 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(O-benzoyloxime) (BASF Japan: Irgacure OXE01) Photopolymerization initiator (C-2): 1-hydroxycyclohexyl phenyl ketone (IGM Resins BV: Omnirad 184) Photopolymerization initiator (C-3): 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Omnirad 127, manufactured by IGM Resins BV) Photopolymerization initiator (C-4): Methyl phenylglyoxylate (Omnirad MBF, manufactured by IGM Resins BV) Photopolymerization initiator (C-5): 2-(dimethylamino)-2-(4-methylbenzyl)-1-[4-(4-morpholinyl)phenyl]-1-butanone (Omnirad 379EG, manufactured by IGM Resins BV) Photopolymerization initiator (C-6): Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (IGM Resins BV: Omnirad 819) Photopolymerization initiator (C-7): Ethyl (2,4,6-trimethylbenzoyl)phenylphosphine oxide (Omnirad TPO-L, manufactured by IGM Resins BV)

[0133] [Crosslinking agent (D)] Isocyanate-based crosslinking agent (D-1): Trimethylolpropane adduct of tolylene diisocyanate (Mitsui Chemicals: Takenate D-101E) Epoxy crosslinker (D-2): 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane (Tetrad C, manufactured by Mitsubishi Gas Chemical Company, Inc.)

[0134] [Preparation of Peelable Pressure-Sensitive Adhesive Sheet] The obtained active energy ray-curable peel-type pressure-sensitive adhesive composition was applied with an applicator onto a polyethylene terephthalate film (film thickness 38 μm) (manufactured by Toray Industries, Inc., "T60 Lumirror") as a substrate sheet, and then dried at 100°C for 3 minutes. The coated film was then attached to a release film (manufactured by Mitsui Chemicals Tocello, Inc., "SP-PET3801-BU") and aged at 40°C for 3 days to obtain a peel-type pressure-sensitive adhesive sheet (adhesive layer thickness 25 μm). The peelable pressure-sensitive adhesive sheets obtained were subjected to the following evaluations, and the results are shown in Table 2.

[0135] [Initial adhesive strength (before exposure to active energy rays)] A 25mm x 100mm test piece was prepared from the peel-off pressure-sensitive adhesive sheet obtained above, and after peeling off the release film, the piece was pressed onto a stainless steel plate (SUS304BA plate) by rolling a 2kg rubber roller back and forth twice in an atmosphere of 23°C and 50% relative humidity. After leaving the piece to stand in the same atmosphere for 30 minutes, the 180-degree peel strength (N / 25mm) was measured at a peel speed of 300mm / min in accordance with JIS Z 0237, and evaluated according to the following criteria. ○:10N / 25mm or more △: 3N / 25mm or more, less than 10N / 25mm ×: Less than 3N / 25mm

[0136] [Initial adhesive strength (after exposure to active energy rays)] A 25mm x 100mm test piece was prepared from the peel-off pressure-sensitive adhesive sheet obtained above, and after peeling off the release film, it was pressed onto a stainless steel plate (SUS304BA plate) by rolling a 2kg rubber roller back and forth twice in an atmosphere of 23°C and 50% relative humidity. After leaving it in the same atmosphere for 30 minutes, it was irradiated with ultraviolet light (cumulative irradiation dose 180mJ / cm) from a height of 18cm at a conveyor speed of 51.0m / min using one 80W high-pressure mercury lamp. 2 After leaving the sample to stand for 30 minutes in an atmosphere of 23°C and 50% relative humidity, the 180-degree peel strength (N / 25 mm) was measured at a peel rate of 300 mm / min in accordance with JIS Z 0237 and evaluated according to the following criteria. ◎: Less than 0.05N / 25mm ○: 0.05N / 25mm or more, less than 0.10N / 25mm ×:0.10N / 25mm or more

[0137] [Low adhesive strength maintenance] After application and irradiation with active energy rays in the same manner as for the initial adhesive strength (after active energy ray irradiation), the tape was left standing for 7 days in an atmosphere of 23°C and 50% relative humidity. The 180-degree peel strength (N / 25 mm) was then measured at a peel rate of 300 mm / min in accordance with JIS Z 0237 (adhesive strength after standing). The rate of increase in adhesive strength after standing relative to the initial adhesive strength (after UV irradiation) was calculated based on the adhesive strength after standing, and evaluated according to the following criteria. ◎: Adhesive strength after standing is less than 0.10N / 25mm and the rate of increase is less than 200% ○: Adhesive strength after standing is less than 0.10 N / 25 mm, and the increase rate is 200% or more but less than 250% ×: Adhesive strength after standing is 0.10N / 25mm or more and the rate of increase is 250% or more In addition, if adhesive residue was observed, the evaluation was also given as "x".

[0138] [Surface hardening] A 5 mm high step was formed on both ends of a 70 mm x 150 mm stainless steel plate in the long side direction, and the peelable adhesive sheet obtained above was attached to the formed step with the adhesive side facing down in a bridge-like manner to create a test specimen with a raised adhesive side. The obtained test specimen was irradiated with ultraviolet light (cumulative irradiation dose 180 mJ / cm ) in air from a height of 18 cm from the substrate side at a conveyor speed of 51.0 m / min. 2 After the application, the stickiness of the adhesive surface was evaluated by touching with a finger according to the following criteria. ○: No stickiness was felt. ×: Stickiness was felt.

[0139] [Table 2]

[0140] Although Examples 1 to 3 showed extremely high adhesive strength before irradiation with active energy rays, the adhesive strength was sufficiently reduced after irradiation with active energy rays, resulting in excellent peelability.Furthermore, they also exhibited excellent compatibility between low adhesive strength retention and surface curability. On the other hand, Comparative Examples 1 to 7 were excellent in easy peelability but had poor low adhesive strength maintenance or adhesive residue occurred, and the surface curability was not satisfactory in any case.

[0141] The above results show that by using an adhesive composition containing a (meth)acrylic resin (A), a photopolymerization initiator (C), and a crosslinking agent (D), in which the photopolymerization initiator (C) contains at least an oxime ester-based photopolymerization initiator (C-1), a peelable adhesive sheet with excellent peelability, low adhesive strength retention, and surface hardening properties can be obtained. [Industrial Applicability]

[0142] The active energy ray-curable peelable pressure-sensitive adhesive composition of the present invention can be suitably used for the pressure-sensitive adhesive layer of a temporary surface-protective pressure-sensitive adhesive film when processing semiconductor wafers, printed circuit boards, processed glass products, metal plates, plastic plates, etc.

Claims

1. The active energy ray-curable removable pressure-sensitive adhesive composition contains at least a (meth)acrylic resin (A), a photopolymerization initiator (C), and a crosslinking agent (D), wherein the photopolymerization initiator (C) contains at least an oxime ester photopolymerization initiator (C-1).

2. 2. The active energy ray-curable peelable pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic resin (A) has a glass transition temperature of −70 to 10° C.

3. The active energy ray-curable peelable pressure-sensitive adhesive composition according to claim 1 or 2, further comprising an active energy ray-curable compound (B).

4. The active energy ray-curable peelable pressure-sensitive adhesive composition according to claim 1 or 2, wherein the (meth)acrylic resin (A) contains a structural unit derived from a carboxyl group-containing monomer.

5. The active energy ray-curable peelable pressure-sensitive adhesive composition according to claim 3 , wherein the active energy ray-curable compound (B) has three or more unsaturated groups per molecule.

6. 3. The active energy ray-curable peel-type pressure-sensitive adhesive composition according to claim 1, wherein a content ratio of the oxime ester photopolymerization initiator (C-1) in the photopolymerization initiator (C) is 5 mass% or more.

7. 4. The active energy ray-curable peel-type pressure-sensitive adhesive composition according to claim 3, wherein a content of the oxime ester photopolymerization initiator (C-1) is 0.1 to 20 parts by mass per 100 parts by mass of the (meth)acrylic resin (A) or the active energy ray-curable compound (B).

8. An active energy ray-curable peelable pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer crosslinked with the active energy ray-curable peelable pressure-sensitive adhesive composition according to claim 1 or 2.

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