Adhesive composition and protective film

Abstract

This invention provides an adhesive composition that can suppress changes in the gel fraction of a hardened material even under high humidity conditions. The adhesive composition of this invention comprises: an urethane polymer (A) containing vinyl unsaturated groups, a monomer (B) containing vinyl unsaturated groups, and a photopolymerization initiator (C). The aforementioned urethane polymer (A) containing vinyl unsaturated groups is a reaction product of a polyol (a1) and a polyisocyanate (a2) with an vinyl unsaturated compound (a3-1) having only one hydroxyl group or an vinyl unsaturated compound (a3-2) containing an isocyanate group. The aforementioned polyol (a1) comprises: a polyol (a1-1) containing vinyl unsaturated groups and a polyoxyethylene polyol (a1-2) without vinyl unsaturated groups.

Description

Technical Field

[0001] This invention relates to an adhesive composition and a protective sheet of a hardened material having the adhesive composition. This case is based on the priority claim made in Japan under Special Purpose No. 2021-209991 filed on December 23, 2021, the contents of which are hereby cited. Prior Technology

[0002] Optical components in LCD displays or touch panels of smartphones, personal computers, televisions, etc., utilize various optical thin films. To prevent contamination or damage during transport, manufacturing, and inspection processes, the surface of these optical thin films is typically laminated with a protective film. This protective film is peeled off in the later stages of the aforementioned processes.

[0003] The protective film requires that, after peeling, a portion of the adhesive layer constituting the protective film remains on the surface of the product (the adhered object), which is called no adhesive residue (re-peelability) (Patent Document 1). In recent years, the performance requirements have become increasingly stringent, assuming harsh conditions during transportation or long-term storage. Furthermore, various adhesives are proposed to address this problem.

[0004] For example, Patent Document 2 describes an adhesive comprising a hydroxyl-containing urethane prepolymer and a nonionic sulfonate, which satisfies the requirements of re-peelability and resistance to contamination of the adhered object under high temperature and humidity. Patent Document 3 discloses an adhesive composition comprising a base polymer and polysiloxane additives and / or fluorine additives, which describes that even under harsh conditions and long-term storage, re-peeling over time can be sufficiently suppressed, and the contamination of the adhered object surface is sufficiently low. [Previous Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2021-41711 [Patent Document 2] Japanese Patent Application Publication No. 2020-75978 [Patent Document 3] Japanese Patent Application Publication No. 2019-218472 Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] However, from the perspective of stain resistance, there are higher performance requirements for protecting thin films, and previous adhesives have failed to meet these requirements.

[0008] The present invention was made to solve the problems described above. The object of the present invention is to provide a protective sheet that is not easily contaminated with the adhered material. Furthermore, the object of the present invention is to provide an adhesive composition suitable for the protective sheet. More specifically, the object of the present invention is to provide an adhesive composition that can suppress changes in the gel fraction of the hardened material even under high temperature and high humidity conditions. [Methods used to solve problems]

[0009] The present invention includes the following states. [1] An adhesive composition comprising: an urethane polymer containing an ethylene unsaturated group (A), a monomer containing an ethylene unsaturated group (B), and a photopolymerization initiator (C). The aforementioned urethane polymer (A) containing vinyl unsaturated groups is a reactant of a polyol (a1) and a polyisocyanate (a2) with a vinyl unsaturated compound having only one hydroxyl group (a3-1) or a vinyl unsaturated compound containing an isocyanate group (a3-2). The polyol (a1) is a polyol containing an ethylene unsaturated group (a1-1) and a polyoxyethylene polyol (a1-2) not containing an ethylene unsaturated group. [2] As in [1], the aforementioned urethane polymer (A) containing an ethylene unsaturated group is an urethane polymer with an ethylene unsaturated compound (a3-1) having only one hydroxyl group or an ethylene unsaturated compound (a3-2) containing an isocyanate group added to the end of an urethane prepolymer of a reaction product of polyol (a1) and polyisocyanate (a2). [3] Adhesive compositions such as [1] or [2], wherein the aforementioned polyol (a1) is a compound having two hydroxyl groups, The aforementioned polyisocyanate (a2) is a compound having two isocyanate groups. [4] An adhesive composition as described in any of [1] to [3], wherein the aforementioned urethane polymer (A) containing an vinyl unsaturated group is an urethane polymer containing (meth)acryloxy groups. The aforementioned polyol containing an vinyl unsaturated group (a1-1) is a polyol containing a (meth)acrylic acid group. The aforementioned vinyl unsaturated compound (a3-1), which has only one hydroxyl group, is a (meth)acrylate containing a hydroxyl group. The aforementioned vinyl unsaturated compound (a3-2) containing isocyanate groups is a (meth)acrylate containing isocyanate groups. [5] An adhesive composition of any one of [1] to [4], wherein the weight average molecular weight of the aforementioned urethane polymer (A) containing an ethylene unsaturated group is 5,000 to 150,000. [6] The adhesive composition of any one of [1] to [5], wherein the number average molecular weight of the polyoxyethylene polyol (a1-2) that does not contain vinyl unsaturated groups is 500 to 5,000. [7] The adhesive composition of any one of [1] to [6], wherein the aforementioned urethane polymer (A) containing an ethylene unsaturated group is a reaction product of the aforementioned polyol (a1), the aforementioned polyisocyanate (a2), and the aforementioned ethylene unsaturated compound (a3-1) having only one hydroxyl group. Compared to the total amount of hydroxyl groups in the aforementioned polyol (a1) being 1 mole, the total amount of isocyanate groups in the aforementioned polyisocyanate (a2) is 1.1 to 1.8 moles. The ratio of the aforementioned polyol containing vinyl unsaturated groups (a1-1) and polyoxyethylene polyols not containing vinyl unsaturated groups (a1-2) (molar ratio (a1-1) / (a1-2)) is 0.03~0.8. [8] The adhesive composition of any one of [1] to [6], wherein the aforementioned urethane polymer (A) containing vinyl unsaturated groups is a reaction product of the aforementioned polyol (a1), the aforementioned polyisocyanate (a2), and the aforementioned vinyl unsaturated compound (a3-2) containing isocyanate groups. Compared to the total amount of isocyanate groups in the aforementioned polyisocyanate (a2) being 1 mole, the total amount of hydroxyl groups in the polyol (a1) is 1.1~1.8 moles. The ratio of the aforementioned polyol containing vinyl unsaturated groups (a1-1) and polyoxyethylene polyols not containing vinyl unsaturated groups (a1-2) (molar ratio (a1-1) / (a1-2)) is 0.03~0.8. [9] An adhesive composition of any one of [1] to [8], wherein the monomer (B) containing an ethylene unsaturated group contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2).

[10] The adhesive composition as in [9], wherein the aforementioned monofunctional (meth)acrylate (B1) is a chain alkyl (meth)acrylate with 6 to 18 carbon atoms.

[11] such as [9] or

[10] adhesive composition, wherein the aforementioned polyfunctional (meth)acrylate (B2) is a 3- to 6-functional (meth)acrylate.

[12] The adhesive composition of any one of [9] to

[11] , wherein relative to the total mass of the aforementioned urethane polymer (A) containing an ethylene unsaturated group and the monomer (B) containing an ethylene unsaturated group, the aforementioned urethane polymer (A) containing an ethylene unsaturated group is 30 to 70% by mass and the monomer (B) containing an ethylene unsaturated group is 30 to 70% by mass.

[13] The adhesive composition of any one of [9] to

[12] , wherein, relative to 100% by mass of the aforementioned urethane polymer (A) containing an ethylene unsaturated group and the aforementioned monomer (B) containing an ethylene unsaturated group, the monofunctional (meth)acrylate (B1) is 25 to 60% by mass and the polyfunctional (meth)acrylate (B2) is 1 to 30% by mass.

[14] An adhesive composition as described in any of [1] to

[13] , wherein the adhesive further comprises a plasticizer (D).

[15] In the adhesive composition of

[14] , when the total mass of the aforementioned urethane polymer (A) containing an ethylene unsaturated group and the aforementioned monomer (B) containing an ethylene unsaturated group is 100 parts by mass, the aforementioned photopolymerization initiator (C) is 0.05 to 5 parts by mass and the aforementioned plasticizer (D) is 1 to 30 parts by mass.

[16] A protective sheet having an adhesive layer on one side of a substrate having a hardened adhesive composition of any one of [1] to

[15] . [Invention Effects]

[0010] According to the present invention, an adhesive composition can be provided that suppresses changes in the gel fraction of the cured material even under high temperature and high humidity conditions. Therefore, the present invention can provide an adhesive layer of a cured material having the above-mentioned adhesive composition, which is less likely to contaminate the adhered material. [Forms of Invention Implementation]

[0011] The embodiments of the present invention will now be described in detail. However, the present invention is not limited to the embodiments shown below. Here, (meth)acrylic acid refers to one or more groups selected from those represented by the chemical formula CH2=CH-CO- and CH2=C(CH3)-CO-. (meth)acrylic acid oxy refers to one or more groups selected from those represented by the chemical formula CH2=CH-CO-O- and CH2=C(CH3)-CO-O-. Furthermore, isocyanate group refers to a group represented by the chemical formula -N=C=O. Vinyl refers to a group represented by the chemical formula CH2=CH-. Allyl refers to a group represented by the chemical formula CH2=CH-CH2-.

[0012] <Adhesive composition> The adhesive composition of this embodiment contains: an urethane polymer (A) containing vinyl unsaturated groups (hereinafter referred to as "component (A)"), a monomer (B) containing vinyl unsaturated groups (hereinafter referred to as "component (B)"), and a photopolymerization initiator (C) (hereinafter referred to as "component (C)"). The aforementioned adhesive composition may also contain, if necessary, a plasticizer (D) (hereinafter referred to as "component (D)").

[0013] [Ammonium carbamate polymer containing vinyl unsaturated groups (A)] The urethane polymer (A) containing vinyl unsaturated groups used in this embodiment is a reaction product of a polyol (a1), a polyisocyanate (a2), and an vinyl unsaturated compound (a3-1) having only one hydroxyl group or an vinyl unsaturated compound (a3-2) containing an isocyanate group. Because the adhesive composition of this embodiment contains the urethane polymer (A) containing vinyl unsaturated groups, the cured product of the aforementioned adhesive composition can suppress changes in the gel fraction even under high temperature and high humidity conditions. Therefore, when the aforementioned cured product is used as a protective film for the adhesive layer, it becomes less likely to contaminate the adhered object when peeled off. Furthermore, the urethane polymer (A) containing vinyl unsaturated groups in this embodiment uses two types of polyols (a1) as the polyol (a1): polyol (a1-1) containing vinyl unsaturated groups (a1-1) and polyoxyethylene polyol (a1-2) without vinyl unsaturated groups. Therefore, these two types of compounds coexist in the polymer chain. Also, since the ratio of polyol (a1) to polyisocyanate (a2) is determined by using either a vinyl unsaturated compound (a3-1) having only one hydroxyl group or a vinyl unsaturated compound (a3-2) containing an isocyanate group, the urethane polymer (A) containing vinyl unsaturated groups has a complex structure, making it difficult to define precisely by structural formulas, etc. The aforementioned urethane polymer (A) containing an vinyl unsaturated group is preferably at least one of a vinyl urethane polymer, an allyl urethane polymer, and a (meth)acryloxy urethane polymer. More preferably, the aforementioned urethane polymer (A) containing an vinyl unsaturated group is a (meth)acryloxy urethane polymer.

[0014] The urethane polymer (A) containing an ethylene unsaturated group may be exemplified by the first urethane polymer (A-1) or the second urethane polymer (A-2) containing an ethylene unsaturated group described below.

[0015] [The first urethane polymer containing vinyl unsaturated groups (A-1)] The first urethane polymer (A-1) containing an vinyl unsaturated group used in this embodiment is a reaction product of a polyol (a1), a polyisocyanate (a2), and an vinyl unsaturated compound (a3-1) having only one hydroxyl group. Preferably, the first urethane polymer (A-1) containing an vinyl unsaturated group is an urethane polymer to which the vinyl unsaturated compound (a3-1) having only one hydroxyl group is added to the end of the aforementioned urethane prepolymer. The aforementioned urethane prepolymer is a reaction product of a polyol (a1) and a polyisocyanate (a2). The aforementioned first urethane polymer (A-1) containing an vinyl unsaturated group is preferably an urethane polymer containing (meth)acrylic acid oxy groups.

[0016] [Polyol (a1)] The polyol (a1) used in this embodiment is a compound having two or more hydroxyl groups but not an isocyanate group, and includes a polyol (a1-1) containing an vinyl unsaturated group and a polyoxyethylene polyol (a1-2) not containing an vinyl unsaturated group. From the viewpoint of inhibiting gelation during synthesis or ensuring uniform stretchability of the polymer, the polyol (a1) preferably has two hydroxyl groups.

[0017] Polyols containing vinyl unsaturated groups (a1-1) are not particularly limited as long as they have two or more hydroxyl groups and one or more vinyl unsaturated groups.

[0018] These polyols containing vinyl unsaturated groups (a1-1) can be used alone or in combination of two or more. By using polyols containing vinyl unsaturated groups (a1-1), vinyl unsaturated groups can also be introduced into the portion of the urethane polymer (A) containing vinyl unsaturated groups, excluding the ends (within the molecular chain). Therefore, when the adhesive composition is used as a cured material, the crosslinking points increase, and the gel fraction of the cured material does not easily change even under high temperature and high humidity conditions.

[0019] The aforementioned polyol containing an vinyl unsaturated group (a1-1) is preferably at least one of a polyol containing a vinyl group, an allyl group, and a (meth)acryloxy group. The aforementioned polyol containing an vinyl unsaturated group (a1-1) is more preferably a polyol containing a (meth)acryloxy group, and even more preferably a polyol having two or more (meth)acryloxy groups.

[0020] Polyols containing (meth)acryloxy groups, such as epoxy compounds containing (meth)acryloxy groups, undergo acid-catalyzed cleavage reactions, and are synthesized as compounds with two hydroxyl groups. Examples of epoxy compounds containing (meth)acryloxy groups include glycidyl (meth)acrylates, 3,4-epoxycyclohexyl meth (meth)acrylates, (meth)acrylates with alicyclic epoxy groups and their lactone adducts, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, epoxides of dicyclopentenyl (meth)acrylates, and epoxides of dicyclopentenoxyethyl (meth)acrylates.

[0021] Polyols containing (meth)acryloxy groups can be commercially available products, such as glycerol monomethacrylate (BLEMMERS (registered trademark) GLM), which causes the epoxy groups of glycidyl methacrylates to crack. These polyols containing (meth)acryloxy groups can be used alone or in combination of two or more. By using a polyol containing an vinyl unsaturated group (a1-1), (meth)acryloxy groups can also be introduced into the molecular chain, except at the ends of the amino carbamate polymer (A) containing (meth)acryloxy groups. Therefore, when the adhesive composition is used as a cured material, the crosslinking points increase, and the gel fraction of the cured material does not easily change even under high temperature and high humidity conditions.

[0022] When a polyoxyethylene polyol (a1-2) without vinyl unsaturated groups has a polyoxyethylene chain, does not have an isocyanate group, and has two or more hydroxyl groups, there is no particular limitation, but it is preferred to have two hydroxyl groups. The number of carbon atoms in the alkyl chain constituting the polyoxyethylene chain is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 4. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, and polyoxybutene polyol. The first urethane polymer (A-1) containing vinyl unsaturated groups, by having a polyoxyethylene chain, can lower the glass transition temperature (Tg) and improve the wettability of the adhesive layer constituting the protective film to the adhered object. Polyoxyethylene polyols (a1-2) that do not contain ethylene unsaturated groups can be commercially available, such as Ripoxy (trademark) SP-16LDA (Showa Denko).

[0023] The content ratio (molar ratio (a1-1) / (a1-2)) of the aforementioned polyol containing vinyl unsaturated groups (a1-1) and the aforementioned polyoxyethylene polyol not containing vinyl unsaturated groups (a1-2) is preferably 0.03~0.8, more preferably 0.08~0.7, even more preferably 0.1~0.6, and particularly preferably 0.1~0.4.

[0024] [Polyisocyanate (a2)] When polyisocyanate (a2) is a compound having two or more isocyanate groups, there is no particular limitation. Examples include methylbenzyl diisocyanate and its hydride, xylene diisocyanate and its hydride, diphenylmethane diisocyanate and its hydride, 1,5-naphthyl diisocyanate and its hydride, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, norbornene diisocyanate, etc. From the perspective of ease of reaction control during the synthesis of the urethane polymer (A) containing vinyl unsaturated groups, or from the viewpoint of lightfastness as a cured product, a polyisocyanate having a cyclic hydrocarbon structure is preferred, more preferably selected from one or more of isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, and norcamphene diisocyanate, and even more preferably isophorone diisocyanate. These polyisocyanates without vinyl unsaturated groups can be used alone or in combination of two or more.

[0025] Compared to the total amount of hydroxyl groups of the aforementioned polyol (a1) being 1 mole, the total amount of isocyanate groups of the aforementioned polyisocyanate (a2) is preferably 1.1 to 1.8 moles, more preferably 1.2 to 1.7 moles, and even more preferably 1.3 to 1.6 moles. When the total amount of isocyanate groups is 1.1 moles or more, the weight average molecular weight of the first urethane polymer containing vinyl unsaturated groups (A-1) becomes an appropriate range, and the amount of vinyl unsaturated compound (a3-1) having only one hydroxyl group introduced can be sufficiently ensured.

[0026] [Ethylene unsaturated compounds with only one hydroxyl group (a3-1)] The vinyl unsaturated compound (a3-1) having only one hydroxyl group is not particularly limited to compounds having an isocyanate group, while compounds having one hydroxyl group and an vinyl unsaturated group are not particularly limited. From the viewpoint of curability, the vinyl unsaturated group is preferably selected from at least one of the group consisting of vinyl, allyl, and (meth)acryloxy, with (meth)acryloxy being more preferred.

[0027] <Methacrylates containing hydroxyl groups> The ethylene unsaturated compound (a3-1) of this embodiment, having only one hydroxyl group, is preferably a (meth)acrylate containing a hydroxyl group. There is no particular limitation on whether the (meth)acrylate containing a hydroxyl group is a compound without an isocyanate group or a compound having both a hydroxyl group and a (meth)acryloxy group. Examples include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and monools containing a (meth)acryl group from various polyols such as 1,3-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. From the viewpoints of reactivity with the isocyanate groups of polyisocyanate (a2) and photocurability as an adhesive component, hydroxyalkyl (meth)acrylate is preferred, more preferably hydroxyalkyl (meth)acrylate having alkyl groups having 2 to 6 carbon atoms, and even more preferably 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate. These can be used alone or in combination of two or more. By using an ethylene unsaturated compound (a3-1) having only one hydroxyl group, ethylene unsaturated groups can be introduced at the end of the molecular chain of the first urethane polymer (A-1) containing ethylene unsaturated groups. As a result, during the photocuring of the adhesive composition, polymerization occurs from the ethylene unsaturated groups of the ethylene unsaturated compound (a3-1) having only one hydroxyl group, the ethylene unsaturated groups of the polyol (a1-1) containing ethylene unsaturated groups, and the ethylene unsaturated groups of component (B) described later, and the gel fraction becomes less prone to change. Therefore, contamination of the adhered material is less likely to occur when peeling off the protective film.

[0028] <Compounds containing hydroxyl and vinyl groups> The ethylene unsaturated compound (a3-1) of this embodiment, which has only one hydroxyl group, can also be a compound having both a hydroxyl group and a vinyl group. Examples of compounds having both a hydroxyl group and a vinyl group include polyvinyl alcohol monovinyl ether, hydroxyalkyl vinyl ether, hydroxycarboxylic acid vinyl ester, and hydroxyalkyl vinyl ester.

[0029] Polyethylene glycol monoethylene ethers can include diethylene glycol monoethylene ether, triethylene glycol monoethylene ether, etc. Hydroxyalkyl vinyl ethers include, for example, 4-hydroxybutyl vinyl ether and 4-hydroxycyclohexyl vinyl ether. Hydroxycarboxylic acid vinyl esters include, for example, hydroxyacetic acid vinyl ester, hydroxypropionic acid vinyl ester, hydroxybutyric acid vinyl ester, hydroxyhexanoic acid vinyl ester, and 4-hydroxycyclohexylacetic acid vinyl ester. Hydroxyalkyl vinyl esters, such as hydroxycyclohexylcarboxylic acid vinyl ester, are examples.

[0030] <Compounds containing hydroxyl and allyl groups> The ethylene unsaturated compound (a3-1) of this embodiment, which has only one hydroxyl group, can also be a compound that does not have an isocyanate group but has a hydroxyl and an allyl group. Examples of compounds having a hydroxyl and an allyl group include hydroxyalkyl allyl ethers, hydroxycarboxylic acid allyl esters, and hydroxyalkyl allyl esters.

[0031] Hydroxyalkyl allyl ethers include, for example, 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, glycerol monoallyl ether, and 4-hydroxycyclohexyl allyl ether. Hydroxycarboxylic acid allyl esters include, for example, allyl glycolate, allyl hydroxypropionate, allyl hydroxybutyrate, allyl hydroxyhexanoate, and allyl 4-hydroxycyclohexylacetate. Hydroxyalkyl allyl esters include, for example, hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, hydroxyisobutyl allyl ester, and hydroxycyclohexyl allyl ester.

[0032] The aforementioned ratio of the vinyl unsaturated compound (a3-1) having only one hydroxyl group is preferably such that the total amount of hydroxyl groups in compounds (a1) and (a3-1) is equal to the total amount of isocyanate groups in compound (a2). "Equal" means that the difference in mole numbers between the two is preferably 0.05 moles or less, and more preferably 0.01 moles or less. When the difference in mole numbers is 0.05 moles or less, the amount of unreacted compounds (a1) to (a3-1) can be sufficiently reduced, and the amount of unreacted hydroxyl or isocyanate groups can also be sufficiently reduced. Therefore, when used as a cured material, changes in gel fraction over time can be suppressed.

[0033] The weight-average molecular weight of the aforementioned first urethane polymer containing vinyl unsaturated groups (A-1) is preferably 5,000 to 150,000, more preferably 10,000 to 100,000, and particularly preferably 20,000 to 50,000. When the weight-average molecular weight is 5,000 or higher, the cured adhesive composition has sufficient flexibility, and this cured composition, as a protective film for the adhesive layer, has sufficient lamination properties. When the weight-average molecular weight is 150,000 or lower, the adhesive composition is easy to handle, improving workability.

[0034] [Second type: urethane polymer containing vinyl unsaturated groups (A-2)] The second urethane polymer (A-2) containing an vinyl unsaturated group used in this embodiment is a reactant of a polyol (a1), a polyisocyanate (a2), and an vinyl unsaturated compound (a3-2) containing an isocyanate group. Preferably, the aforementioned second urethane polymer (A-2) containing an vinyl unsaturated group is an urethane polymer containing a (meth)acrylic acid group.

[0035] [Polyol (a1)] The polyol (a1) used in the second urethane polymer (A-2) containing an ethylene unsaturated group can be the polyol (a1) used in the first urethane polymer (A-1) containing an ethylene unsaturated group described above, or a preferred example thereof.

[0036] [Polyisocyanate (a2)] The polyisocyanate (a2) used in the second urethane polymer containing an ethylene unsaturated group (A-2) can be the polyisocyanate (a2) used in the first urethane polymer containing an ethylene unsaturated group (A-1) of the aforementioned embodiment, or a preferred example thereof.

[0037] The total amount of hydroxyl groups in the aforementioned polyol (a1) is 1 mole relative to the total amount of isocyanate groups in the aforementioned polyisocyanate (a2), preferably 1.1 to 1.8 moles, more preferably 1.2 to 1.7 moles, and even more preferably 1.3 to 1.6 moles. When the total amount of hydroxyl groups is 1.1 moles or more, the weight average molecular weight of the second urethane polymer (A-2) containing vinyl unsaturated groups is within an appropriate range, which can sufficiently ensure the introduction of the vinyl unsaturated compound (a3-2) containing isocyanate groups.

[0038] The content ratio (molar ratio (a1-1) / (a1-2)) of the aforementioned polyol containing vinyl unsaturated groups (a1-1) and the aforementioned polyoxyethylene polyol not containing vinyl unsaturated groups (a1-2) is preferably 0.03~0.8, more preferably 0.08~0.7, even more preferably 0.1~0.6, and particularly preferably 0.1~0.4.

[0039] [Ethylene unsaturated compounds containing isocyanate groups (a3-2)] The isocyanate-containing vinyl unsaturated compound (a3-2) is not particularly limited to compounds that do not have hydroxyl groups, but have both isocyanate and vinyl unsaturated groups. The isocyanate-containing vinyl unsaturated compound (a3-2) is preferably a (meth)acrylate containing an isocyanate group. Examples include isocyanate-based alkyl (meth)acrylates such as 2-isocyanoethyl (meth)acrylate, 2-isocyanopropyl (meth)acrylate, 4-isocyanobutyl (meth)acrylate, and 6-isocyanohexyl (meth)acrylate. From the viewpoint of reactivity with the hydroxyl groups of the polyol (a1) and photocurability as an adhesive component, isocyanate-based alkyl (meth)acrylates having alkyl groups with 2 to 6 carbon atoms are preferred, and 2-isocyanoethyl (meth)acrylate and 4-isocyanobutyl (meth)acrylate are more preferred. These can be used alone or in combination of two or more. By using an isocyanate-containing vinyl unsaturated compound (a3-2), vinyl unsaturated groups can be introduced into the terminal portion of the molecular chain of the second vinyl unsaturated urethane polymer (A-2). As a result, during the photocuring of the adhesive composition, the vinyl unsaturated groups from the isocyanate-containing vinyl unsaturated compound (a3-2), the vinyl unsaturated groups from the polyol (a1-1) containing vinyl unsaturated groups, and the vinyl unsaturated groups of component (B) described later polymerize, and the gel fraction becomes less prone to change. Therefore, contamination of the adhered material during the peeling of the protective film becomes less likely to occur.

[0040] The aforementioned ratio of the vinyl unsaturated compound (a3-2) containing isocyanate groups is preferably set such that the total amount of isocyanate groups in compound (a2) and compound (a3-2) is equal to the total amount of hydroxyl groups in compound (a1). "Equal" means that the difference in mole count between the two is preferably 0.05 moles or less, and more preferably 0.01 moles or less. When the difference in mole count is 0.05 moles or less, the amount of unreacted compounds (a1) to (a3-2) can be sufficiently reduced, and the amount of unreacted hydroxyl or isocyanate groups can also be sufficiently reduced. Therefore, when used as a cured material, changes in gel fraction over time can be suppressed.

[0041] The weight-average molecular weight of the aforementioned second urethane polymer containing vinyl unsaturated groups (A-2) is preferably 5,000 to 150,000, more preferably 10,000 to 100,000, and particularly preferably 20,000 to 50,000. When the weight-average molecular weight is 5,000 or higher, the cured adhesive composition has sufficient flexibility, and this cured composition, as a protective film for the adhesive layer, has sufficient lamination properties. When the weight-average molecular weight is 150,000 or lower, the adhesive composition is easy to handle, improving workability.

[0042] [Monomers containing vinyl unsaturated groups (B)] When the monomer (B) containing an vinyl unsaturated group is a monomer with an vinyl unsaturated group, there is no particular limitation. From the viewpoint of curability, it is preferable to have a vinyl or (meth)acrylic group, and more preferably to have a (meth)acrylic group. Among these, from the viewpoint of the dilution of the adhesive composition, low tack, and punching processability of the protective film, the monomer (B) containing an vinyl unsaturated group is preferably a monofunctional (meth)acrylate (B1) and / or a polyfunctional (meth)acrylate (B2). "Monofunctional" means having only one (meth)acrylic oxygen group, and "polyfunctional" means having multiple (meth)acrylic oxygen groups. By using a monofunctional (meth)acrylate (B1), the cohesiveness of the cured adhesive composition can be suppressed, making the adhesive layer soft and improving the wettability to the adhered object. By using polyfunctional (meth)acrylate (B2), the cohesiveness of the cured adhesive composition is enhanced, maintaining appropriate hardness of the adhesive layer and suppressing air bubbles trapped between the adhesive surface (the adhesive layer and the substrate). By using components (B1) and (B2) together, the peel strength when peeling off the protective film can be adjusted.

[0043] Monofunctional (meth)acrylates (B1) can be exemplified by alkyl (meth)acrylates, cyclic alkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, alkoxy (poly)alkylene glycol (meth)acrylates, hydroxyl-containing (meth)acrylates, carboxyl-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, (meth)acrylamide, epoxy-containing (meth)acrylates, etc.

[0044] Alkyl (meth)acrylates, such as meth (meth)acrylates, ethyl (meth)acrylates, n-propyl (meth)acrylates, n-butyl (meth)acrylates, tert-butyl (meth)acrylates, isobutyl (meth)acrylates, 2-ethylhexyl (meth)acrylates, isodecyl (meth)acrylates, n-hexyl (meth)acrylates, isooctyl (meth)acrylates, isooctadecyl (meth)acrylates, lauryl (meth)acrylates, tridecyl (meth)acrylates, etc.

[0045] Cycloalkyl (meth)acrylates include, for example, cyclohexyl (meth)acrylate, norcamphenyl (meth)acrylate, isocamphenyl (meth)acrylate, northoalkyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenoxyethyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentoxyethyl (meth)acrylate, tricyclodecane dihydroxymethyl di(meth)acrylate, etc.

[0046] Alkoxyalkyl (meth)acrylates, such as ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, 2-ethoxyethoxyethyl (meth)acrylate, etc.

[0047] Alkoxy (poly)alkylene glycol (meth)acrylates, such as methoxy diethylene glycol (meth)acrylate, ethoxy diethylene glycol (meth)acrylate, and methoxy dipropylene glycol (meth)acrylate, are examples of such methoxy acrylates.

[0048] Examples of hydroxyl-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,3-butanediol (meth)acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate.

[0049] Examples of (meth)acrylates containing carboxyl groups include (meth)acrylic acid and β-carboxyethyl (meth)acrylate.

[0050] Fluorinated alkyl (meth)acrylates, such as octafluoropentyl (meth)acrylate, etc.

[0051] Dialkylaminoalkyl (meth)acrylates, such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.

[0052] Examples of (meth)acrylamide include (meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-isopropylacrylamide, N-hexyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, (meth)acrylamide morpholine, diacetone acrylamide, etc.

[0053] Examples of (meth)acrylates containing epoxy groups include glycidyl (meth)acrylates.

[0054] Among these, from the viewpoint of compatibility with the (meth)acryloxy amino ester polymer (A), viscosity of the adhesive composition, and adjustment of peel strength, alkyl (meth)acrylates are preferred, and more preferably, chain alkyl (meth)acrylates with 6 to 18 carbon atoms. More specifically, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, isooctyl (meth)acrylate, isooctadecyl (meth)acrylate, isocamphenyl (meth)acrylate, and more preferably 2-ethylhexyl (meth)acrylate. Furthermore, monofunctional (meth)acrylates (B1) may be composed of one type of compound or of two or more types of compounds.

[0055] The polyfunctional (meth)acrylate (B2) is preferably a polyol compound and an ester compound of (meth)acrylate, and more preferably a 3- to 6-functional (meth)acrylate. Examples include polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane ether neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acrylamide di(diethylene glycol phthalate), trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diallyloxyethyl phosphate, dipentaerythritol trihydroxy(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc.

[0056] Among these, from the viewpoint of reducing the peel strength of the protective film, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol trihydroxy(meth)acrylate, pentaerythritol tetra(meth)acrylate, and even more preferably trimethylolpropane tri(meth)acrylate. Furthermore, the polyfunctional (meth)acrylate (B2) can be composed of one type of compound or of two or more types of compounds.

[0057] Monomers containing vinyl unsaturated groups (B) may also contain monomers (B3) containing vinyl unsaturated groups other than those in (B1) and (B2). Examples of monomers (B3) containing vinyl unsaturated groups other than those in (B1) and (B2) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyltoluene, N-vinylpyridine, N-vinylpyrrolidone, dialkyl ivonate, dialkyl fumarate, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether or diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamide methyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, etc.

[0058] [Photopolymerization Initiator (C)] Photopolymerization initiators (C) are not specifically limited to any polymerization initiator that generates free radicals through light irradiation. Examples include carbonyl photopolymerization initiators, sulfide photopolymerization initiators, acetylated phosphorus oxides, quinone photopolymerization initiators, sulfonylurea photopolymerization initiators, and thioxanone photopolymerization initiators.

[0059] Examples of carbonyl-based photopolymerization initiators include benzophenone, diphenylethylene glycol, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylaminoacetophenone, p-dimethylaminoacetophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bis(diethylamino)benzophenone, michleone, benzoin methyl ether, and benzoin isocyanate. Butyl ether, benzoin-n-butyl ether, benzyl methyl acetal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, methylbenzoylcarbamate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinylpropane-1-one, etc.

[0060] Examples of sulfur-based photopolymerization initiators include diphenyl disulfide, bibenzyl disulfide, tetraethylthiuram disulfide, and tetramethylammonium monosulfide.

[0061] Phosphorus oxide [(]phosphine oxide Examples of such examples include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide.

[0062] Quinone-based photopolymerization initiators include, for example, benzoquinone and anthraquinone.

[0063] Sulfochloride-based photopolymerization initiators include, for example, 2-naphthalenesulfonyl chloride.

[0064] Thioxanone is a photopolymerization initiator, and examples include thioxanone, 2-chlorothioxanone, and 2-methylthioxanone.

[0065] Among these exemplified compounds, from the viewpoint of improving the transparency of the adhesive layer obtained by curing the adhesive composition, carbonyl photopolymerization initiators and phosphine oxides are preferred, and 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzyldiphenylphosphine oxide are even more preferred. Furthermore, the photopolymerization initiator (C) may be composed of one type of compound or may be composed of two or more types of compounds.

[0066] [Plasticizer (D)] The plasticizer (D) can be any known material without particular limitation. For example, fatty acid esters are preferred. The plasticizer (D) can improve the lamination (wetting) and defoaming (ease of removing air bubbles carried during lamination) of the protective film.

[0067] Examples of fatty acid esters include monobasic acids with 8 to 18 carbon atoms, esters of polybasic acids and branched alcohols with 18 or fewer carbon atoms, unsaturated fatty acids with 14 to 18 carbon atoms, and esters of branched acids and tetravalent alcohols. A preferred specific example of a fatty acid ester is ethylhexyl stearate.

[0068] Furthermore, other additives may be added to the adhesive composition if necessary, without compromising transparency. Examples of additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazoles, phosphate esters and other flame retardants, antistatic agents such as surfactants, and dyes.

[0069] [solvent] Because the adhesive composition contains a monomer (B) with an ethylene-unsaturated group as a low molecular weight component, it can be adjusted to a coatable viscosity even without the addition of a solvent. That is, the adhesive composition can be substantially solvent-free. In this case, the step of heating and drying the solvent can be omitted when manufacturing the protective film, improving productivity. Especially when manufacturing protective films with a film thickness exceeding 50 μm, it is preferable that the adhesive composition is substantially solvent-free. In this invention, "substantially solvent-free" means that the content of the aforementioned solvent in the adhesive composition of this invention is 0-1% by mass, preferably 0-0.5% by mass or less, and more preferably 0-0.1% by mass or less. To adjust the viscosity of the adhesive composition during coating, solvents may be added. The solvent can be chosen appropriately based on other components contained in the adhesive composition, but organic solvents are preferred. There are no particular limitations on the organic solvents that can be used, but examples include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, and isopropanol. These organic solvents can be used alone or in mixtures of two or more. It is preferable to apply the adhesive composition to the substrate, remove it after drying, and then perform photocuring.

[0070] [Adhesive composition formulation] When the total mass percentage of components (A) and (B) is 100%, the content of the urethane polymer (A) containing vinyl unsaturated groups is preferably 30-70% by mass, more preferably 40-60% by mass, and even more preferably 50-60% by mass. When the content is 30% by mass or more, the cohesiveness of the hardened adhesive composition is improved, resulting in an adhesive layer with appropriate hardness, thus suppressing air bubble entrainment on the adhesive surface of the protective sheet (between the adhesive layer and the adhered object). When the content is 70% by mass or less, the cohesiveness of the hardened adhesive composition is suppressed, the adhesive layer becomes soft, and the wettability of the adhesive layer to the adhered object is improved.

[0071] When the total mass percentage of components (A) and (B) is 100%, the content of monomer (B) containing ethylene unsaturated groups is preferably 30-70% by mass, more preferably 40-60% by mass, and even more preferably 40-50% by mass. When the monomer (B) containing an ethylene unsaturated group contains both monofunctional (meth)acrylate (B1) and polyfunctional (meth)acrylate (B2), the content of monofunctional (meth)acrylate (B1) is preferably 20-60% by mass, more preferably 25-55% by mass, and even more preferably 35-45% by mass. When the content of monofunctional (meth)acrylate (B1) is 20% by mass or more, the cohesive force of the hardened adhesive composition is suppressed, resulting in a soft hardened material, thus improving the wettability of the adhesive layer to the adhered object. When the content of monofunctional (meth)acrylate (B1) is 60% by mass or less, the cohesive force of the hardened adhesive composition is improved, resulting in an adhesive layer with appropriate hardness, thus suppressing the entrainment of air bubbles on the adhesive surface of the protective sheet (between the adhesive layer and the adhered object). When the total mass percentage of components (A) and (B) is 100%, the content of polyfunctional (meth)acrylate (B2) is preferably 1-30% by mass, more preferably 3-20% by mass, and even more preferably 5-15% by mass. When the content of polyfunctional (meth)acrylate (B2) is 1% by mass or more, the peel strength during the peeling of the protective film can be suppressed. When the content of polyfunctional (meth)acrylate (B2) is 30% by mass or less, the flexibility of the hardened adhesive composition can be maintained, and the haze can be reduced.

[0072] When the total mass of components (A) and (B) is 100 parts by mass, the content of photopolymerization initiator (C) is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.3 to 1 part by mass. When the content of photopolymerization initiator (C) is 0.05 parts by mass or more, the adhesive composition has sufficient photocurability, and the gel fraction of the cured product does not easily change even under high temperature and high humidity conditions. When the content of photopolymerization initiator (C) is 5 parts by mass or less, contamination of the adhered material during the peeling of the protective film can be suppressed.

[0073] When the total mass of components (A) and (B) is 100 parts by mass, the content of plasticizer (D) is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 to 23 parts by mass. When the content of plasticizer (D) is 1 part by mass or more, it is expected that the effects of adding plasticizer (D) will be sufficiently manifested, such as improved lamination (wetting properties) or improved defoaming properties (removal of air bubbles carried during bonding). When the content of plasticizer (D) is 30 parts by mass or less, it can sufficiently suppress contamination of the adhered material during the peeling of the protective film.

[0074] Furthermore, an example of a synthesis method for an urethane polymer (A) containing an ethylene unsaturated group is described here. Additionally, explanations are provided regarding the synthesis method of a monomer (B) containing an ethylene unsaturated group and the synthesis method of other components contained in the adhesive composition, omitting the latter. Because various types of compounds are used, commercially available products can be used.

[0075] <Synthetic Method of Uracarbamate Polymer (A) Containing Ethylene Unsaturated Groups> The following describes an example of a preferred method for synthesizing the urethane polymer (A) containing vinyl unsaturated groups in the adhesive composition of this embodiment. The method for synthesizing the urethane polymer (A) containing vinyl unsaturated groups is not particularly limited, and can be appropriately modified by changing the conditions such as the raw materials or equipment used in the synthesis. Furthermore, in this example, in any step, the reaction between the hydroxyl and isocyanate groups is carried out using an urethane esterification catalyst such as dibutyltin dilaurate, dibutyltin diethylhexanoate, or dioctyltin dilaurate in the presence of an organic solvent inactive to the isocyanate groups. The reaction is preferably carried out at 30-100°C for 1-5 hours continuously. The amount of urethane esterification catalyst used is preferably 50-500 ppm by mass relative to the total mass of the reactants.

[0076] <Synthetic Method of the First Uracarbamate Polymer Containing Ethylene Unsaturated Groups (A-1)> First, polyol (a1) and polyisocyanate (a2) are added in a ratio in which the amount of isocyanate groups (by number, the same below) of polyisocyanate (a2) is greater than the amount of hydroxyl groups (by number, the same below) of polyol (a1), and the reaction is carried out to synthesize an aminocarbamate prepolymer with isocyanate groups at the ends. The amount of hydroxyl groups in the polyol (a1) mentioned above is the total amount of hydroxyl groups in polyol (a1-1) containing vinyl unsaturated groups and polyoxyethylene polyol (a1-2) not containing vinyl unsaturated groups. Specific examples of polyols and polyisocyanates are shown in the example of polyaminocarbamate (A).

[0077] At this point, as the polyol (a1), a polyol containing vinyl unsaturated groups (a1-1) and a polyoxyethylene polyol without vinyl unsaturated groups (a1-2) are used, but they can be added simultaneously or separately, and the order of addition is not particularly limited. The position of the vinyl unsaturated groups in the main chain of the first urethane polymer containing vinyl unsaturated groups (A-1) can also be adjusted by adding the polyol containing vinyl unsaturated groups (a1-1) and the polyoxyethylene polyol without vinyl unsaturated groups (a1-2). From the viewpoint of shortening the distance between crosslinking points of the first urethane polymer containing vinyl unsaturated groups (A-1) through the polymerization of vinyl unsaturated groups, and suppressing changes in the gel fraction as a cured product, it is preferable to also introduce vinyl unsaturated groups near the center of the main chain of the first urethane polymer containing vinyl unsaturated groups (A-1). That is, the order of adding polyols (a1) is preferably to add the polyol containing ethylene unsaturated groups (a1-1) first, or to add the polyol containing ethylene unsaturated groups (a1-1) and the polyoxyethylene polyol without ethylene unsaturated groups (a1-2) at the same time, and more preferably to add the polyol containing ethylene unsaturated groups (a1-1) first.

[0078] Next, the urethane prepolymer containing isocyanate groups is reacted with an ethylene unsaturated compound (a3-1) having only one hydroxyl group to synthesize a first urethane polymer (A-1) containing ethylene unsaturated groups with ethylene unsaturated groups introduced at the end of the molecular chain. On a numerical basis, it is preferable, more preferably 95-100%, and even more preferably 100%, to incorporate ethylene unsaturated groups into the ends of the polyurethane molecules in the first polyurethane polymer containing ethylene unsaturated groups (A-1). When the amount of ethylene unsaturated groups introduced relative to isocyanate groups is 90% or more on a numerical basis, sufficient cohesiveness of the adhesive layer obtained by curing the adhesive composition is obtained. The proportion of ends with ethylene unsaturated groups relative to the total number of polyurethane molecular chains can be determined by IR, NMR, etc.

[0079] <Synthetic Method of the Second Uracarbamate Polymer Containing Ethylene Unsaturated Groups (A-2)> First, the polyol (a1) and polyisocyanate (a2) are added in a ratio where the amount of hydroxyl groups (based on numbers, the same below) is greater than the amount of isocyanate groups (based on numbers, the same below) in the polyisocyanate (a2), and the reaction is carried out to synthesize a urethane prepolymer with hydroxyl groups at the ends. The amount of hydroxyl groups in the polyol (a1) is the total amount of hydroxyl groups in the polyol (a1-1) containing vinyl unsaturated groups and the polyoxyethylene polyol (a1-2) not containing vinyl unsaturated groups. Specific examples of polyols and polyisocyanates are illustrated in the section on polyurethane (A).

[0080] At this point, as the polyol (a1), a polyol containing vinyl unsaturated groups (a1-1) and a polyoxyethylene polyol without vinyl unsaturated groups (a1-2) are used. However, they can be added simultaneously or separately, and the order of addition is not particularly limited. Similar to the first urethane polymer containing vinyl unsaturated groups (A-1), from the viewpoint of suppressing the change in gel fraction as a cured product, it is preferable to add it simultaneously or by the polyol containing vinyl unsaturated groups (a1-1), and more preferably by the polyol containing vinyl unsaturated groups (a1-1).

[0081] Secondly, the hydroxyl-containing urethane prepolymer is reacted with the isocyanate-containing vinyl unsaturated compound (a3-2) to synthesize a second urethane polymer (A-2) containing vinyl unsaturated groups with vinyl unsaturated groups introduced at the ends of the molecular chains. Based on numerical standards, it is preferable, more preferably 95-100%, and even more preferably 100%, to incorporate ethylene unsaturated groups into the ends of the polyurethane polymer (A-2) containing ethylene unsaturated groups. When the amount of ethylene unsaturated groups introduced relative to hydroxyl groups is 90% or more, sufficient cohesiveness of the adhesive layer obtained by curing the adhesive composition can be obtained. The proportion of ends with ethylene unsaturated groups relative to the total number of polyurethane molecular chains can be determined by IR, NMR, etc.

[0082] <Manufacturing Method of Adhesive Composition> An adhesive composition is prepared by mixing an urethane polymer (A) containing vinyl unsaturated groups, a monomer (B) containing vinyl unsaturated groups, a photopolymerization initiator (C), a plasticizer (D) if necessary, other additives, and an organic solvent. The mixing method is not particularly limited; for example, a homogenizer or a stirring device equipped with impellers can be used.

[0083] Furthermore, all components can be added and mixed at once, or each component can be added and mixed repeatedly in multiple batches. Also, when there are solid components at room temperature, they can be added by means of those dissolved in a solvent or dispersed in a dispersion medium, or by means of those that can be melted by heating. These components are easily mixed with high homogeneity in the adhesive composition.

[0084] <3. Protective Film> <3-1. Composition of the Protective Sheet> In this embodiment, the protective sheet has an adhesive layer formed on one side of a substrate, comprising a hardened copy of the aforementioned adhesive composition. The thickness of the adhesive layer is preferably 3-150 μm, more preferably 5-130 μm, and even more preferably 10-100 μm. When the adhesive layer thickness is 3 μm or more, the adhesive layer has sufficient strength; when the thickness is 150 μm or less, the thickness of the adhesive layer is easily controlled. In addition, when the protective film is intended to provide the adhesive layer with the function of protecting the adhered object from impact (impact resistance), the thickness of the adhesive layer is preferably 50 μm or more.

[0085] The gel fraction of the hardened adhesive composition contained in the adhesive layer is preferably 60-100% by mass, more preferably 70-90% by mass. Here, gel fraction refers to the mass fraction of extractable components in the solvent, where the solvent is selected to dissolve the uncrosslinked components in the hardened adhesive composition. Furthermore, examples of specific methods for measuring the gel fraction are described later in the embodiments. When the gel fraction of the hardened adhesive composition is 60-100% by mass, it can suppress the residue of a portion of the adhesive layer on the adhered material, the so-called adhesive residue, during the peeling of the protective film.

[0086] The material of the substrate can be appropriately selected based on the intended use of the protective film; examples include resin films. For instance, when the protective film is used as a protective film in the manufacturing process, or when inspecting the adhered material (i.e., the product) for damage or foreign objects, a transparent substrate is preferable when the protective film is being laminated. Examples of transparent substrates include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, and cellulose.

[0087] The thickness of the substrate can be appropriately selected based on the intended use of the protective film and is not particularly limited. For resin films, from the viewpoint of operability and strength, the substrate thickness is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, considering the flexibility of the resin film, the substrate thickness is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0088] Furthermore, it is preferable to use a substrate that has undergone antistatic treatment. The antistatic treatment applied to the substrate is not particularly limited; methods such as providing an antistatic layer on at least one side of the substrate or incorporating an antistatic agent into the substrate may be used. In addition, if necessary, easy-bonding treatments such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, or ozone treatment may be applied to the substrate surface where the adhesive layer is formed.

[0089] For protective films, a separator can be applied to the surface of the adhesive layer to protect it. The separator can be made of materials such as paper or plastic film; however, plastic film is preferred for its superior surface smoothness. There are no particular limitations on the type of plastic film used as the separator, as long as it can protect the adhesive layer; examples include polyethylene, polypropylene, polyethylene terephthalate, and polybutene.

[0090] <3-2. Method for manufacturing protective films> The protective film of this embodiment can be manufactured by, for example, coating an adhesive composition onto a substrate and irradiating the coated adhesive composition with ultraviolet light to achieve photocuring.

[0091] There are no particular limitations on the method of applying the adhesive composition to the substrate, and any suitable method can be selected. For example, methods of applying the adhesive composition to the substrate include various coating machines such as gravure roller coating machines, reverse roller coating machines, roller kissing coating machines, dip roller coating machines, coating rods, doctor blade coating machines, spray coating machines, corner wheel coating machines, and direct coating machines, as well as screen printing.

[0092] Furthermore, light sources used for photocuring adhesive components include black light, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and xenon lamps. The light intensity should be sufficient to fully cure the adhesive component; for example, 50–3000 mW / cm² is preferable. However, weaker light intensity results in longer curing times, thus reducing productivity.

[0093] <3-3. Applications and required performance of protective films> During the inspection process, when a protective film is deposited on a product or part, it is required that minute foreign objects or damage to the product or part be sufficiently detected. Furthermore, the protective film is also suitable, for example, for protecting the surface of plastic films used in optical components such as those found in LCD displays for smartphones, personal computers, and televisions. Examples of such optical components include polarizing plates, wavelength plates, retardation plates, optical compensation films, reflective films, and brightness-enhancing films.

[0094] When used as a protective sheet in this embodiment, the protective sheet is required to cause minimal contamination to the adhered object. In this case, it is preferable to have minimal changes in the gel fraction of the adhesive layer constituting the protective sheet or minimal changes in the water contact angle of the adhered object surface before and after the protective sheet is applied. Specific methods for measuring the contamination of the adhered object surface by the adhesive layer of the protective sheet are described later in the embodiments.

[0095] Furthermore, when the protective sheet of this embodiment is used as the protective sheet described above, it requires a minimum peel strength to prevent the product or part from peeling off during handling such as conveying. In addition, when peeling the protective sheet off the product or part, the peel strength needs to be reduced to facilitate the peeling operation or to prevent deformation or damage to the product or part during peeling. From these perspectives, the peel strength of the protective sheet, when the peeling speed is 2.4 m / min, although varying depending on the thickness of the substrate and adhesive layer, is preferably 1~50 gf / 25 mm, more preferably 2~45 gf / 25 mm, and even more preferably 2~40 gf / 25 mm. The specific method for measuring the peel strength of the protective sheet is described later in the embodiments. Implementation

[0096] [Example]

[0097] The present invention will be described in detail below with reference to the embodiments. The present invention is not limited to the embodiments shown below.

[0098] (Determination of weight-average molecular weight) In the following examples, the weight-average molecular weight of the obtained urethane polymer (A) containing vinyl unsaturated groups was a value converted from polystyrene by colloidal permeation chromatography (Shodex GPC-101 manufactured by Showa Denko Co., Ltd., hereinafter referred to as GPC). The determination conditions of GPC are as follows. Tube column: LF-804 manufactured by Showa Denko Co., Ltd. Column temperature: 40℃ Sample: 0.2% by mass tetrahydrofuran solution of polyurethane (A) Flow rate: 1 ml / min Dissolution solution: Tetrahydrofuran Detector: RI detector (Differential Refractive Index Detector)

[0099] Synthesis of urethane polymer (A) containing vinyl unsaturated groups (Synthesis example 1) In a four-necked flask equipped with a thermometer, stirrer, dropping funnel, and condenser with a drying tube, 0.9 mol of BLEMMERM (registered trademark) GLM (manufactured by Nippon Oil) and 6 mol of isophorone diisocyanate (manufactured by DesmodurI, Sumika Covestro Urethane) were added. The flask was then heated to 80°C and reacted for 2 hours. Next, 4.1 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) with hydroxyl groups at both ends (56 mg KOH / g) was added, and the reaction was carried out at 80°C for 6 hours to obtain a carbamate prepolymer with isocyanate groups at both ends.

[0100] 2 mol of 2-hydroxyethyl acrylate was added to the obtained carbamate prepolymer. The reaction was then allowed to proceed for 2 hours to obtain a carbamate polymer (Ai) containing (meth)acryloxy groups at the ends. IR analysis confirmed the disappearance of the peak from the isocyanate group in this carbamate polymer (Ai). The weight-average molecular weight of the obtained carbamate polymer (Ai) containing (meth)acryloxy groups was 27,000. See Table 1.

[0101] (Synthesis example 2) Except for replacing 0.25 mol of BLEMMERM (registered trademark) GLM (manufactured by Nippon Oil) with Ripoxy (trademark) SP-16LDA (manufactured by Showa Denko), 3.75 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) with polypropylene glycol D-1000 (manufactured by Mitsui Chemicals, number average molecular weight 1000), and 5 mol of isophorone diisocyanate with 6 mol, the synthesis method was the same as that for the aminocarbamate polymer (Ai) containing (meth)acryloxy groups, resulting in an aminocarbamate polymer (A-ii) with acryloxy groups at the end. The weight average molecular weight of the obtained aminocarbamate polymer (A-ii) was 12,000. See Table 1.

[0102] (Synthesis example 3) Except for changing the components and formulation amounts as described in Table 1, the same method was used to synthesize the (meth)acryloxy-containing aminocarbamate polymer (Ai) to obtain the aminocarbamate polymer (A-iii) with terminal acryloxy groups. The weight-average molecular weight of the obtained aminocarbamate polymer (A-iii) was 13,000. See Table 1.

[0103] (Comparative Synthesis Example 1) Except for changing BLEMMERM (registered trademark) GLM (Nippon Oil Manufacturing) to 0 mol and polypropylene glycol D-2000 to 5 mol, the method for synthesizing urethane polymers (Ai) containing (meth)acryloxy groups was the same as that for synthesizing urethane polymers (Ai) with acryloxy groups at the ends, resulting in urethane polymers (cA-i). The weight average molecular weight of the obtained urethane polymer (cA-i) was 38,000. See Table 1.

[0104] (Comparative Synthesis Example 2) Except for changing the components and formulation amounts as described in Table 1, the same method was used to synthesize the (meth)acryloxy-containing aminocarbamate polymer (Ai) to obtain the aminocarbamate polymer (cA-ii) with terminal acryloxy groups. The weight-average molecular weight of the obtained aminocarbamate polymer (cA-ii) was 20,000. It is shown in Table 1.

[0105]

[0106] In Table 1, "BLEMMERM GLM" refers to BLEMMERM (registered trademark) GLM, the compound represented by the following formula (1).

[0107]

[0108] In Table 1, "RipoxySP-16LDA" is Ripoxy (trademark) SP-16LDA, a compound represented by the following formula (2).

[0109]

[0110] (Examples 1-4, Comparative Examples 1-5) <Preparation of Adhesive Composition> The urethane polymer (A) containing vinyl unsaturated groups, the monomer (B) containing vinyl unsaturated groups, the photopolymerization initiator (C), and the plasticizer (D) were formulated according to the composition listed in Table 2 and mixed using a disperser at 25°C to prepare the adhesive compositions of Examples 1-4 and Comparative Examples 1-5.

[0111] <Making of Protective Sheets> For Examples 1-4 and Comparative Examples 1-5, protective sheets with a substrate having an optical PET film on one side were prepared using the same method. First, using a coater, a prepared adhesive composition was coated onto a 75 μm thick optical PET film (Toyobo Co., Ltd., A4300). A 75 μm thick release PET film (Toyobo Co., Ltd., E7006) was then placed over the coated adhesive composition. Next, using an ultraviolet irradiation device (EYE GRAPHICS Co., Ltd., 3kW UV irradiation device, high-pressure mercury lamp), the sheet covered with the release PET film was irradiated with ultraviolet light from the side covered by the release PET film to photocur the adhesive composition. The irradiation distance was 25 cm, the lamp moving speed was 1.0 m / min, and the irradiation dose was 1000 mJ / cm². The thickness of the hardened adhesive layer was calculated by subtracting the thickness of the optical PET film (75 μm) and the thickness of the peeling PET film (75 μm) from the measured value using a dial gauge. The measuring surface of the dial gauge was a circular plane with a diameter of 5 mm, and the measuring force was 0.8 N. In any one of Examples 1-4 and Comparative Examples 1-5, the thickness of the adhesive layer was 75 μm.

[0112]

[0113] The compounds listed in the table use the following substances. EHA: Compound name (2-ethylhexyl acrylate, manufactured by Dong-A Synthetic Co., Ltd.) TMPTA: Compound name (Trimethylolpropane triacrylate M-309, manufactured by Dong-A Synthetic Co., Ltd.) Irg-184: Compound name (1-Hydroxycyclohexyl Phenyl Ketone, manufactured by Tokyo Chemical Industry Co., Ltd.) IPM: Compound name (EXEPARL IPM, manufactured by Kao Corporation)

[0114] Evaluation of Adhesive Composition and Protective Film For the adhesive compositions and protective films of Examples 1-4 and Comparative Examples 1-5, the changes in gel fraction and water contact angle after placement under initial conditions and high temperature and humidity conditions were evaluated using the methods described below. Furthermore, the presence or absence of contamination on the glass test plate after peeling off the protective film under high temperature and humidity conditions was evaluated using the methods described below. The results are shown in Table 2.

[0115] (Gel fraction) First, using a coater, the adhesive compositions of Examples 1-4 and Comparative Examples 1-5 were coated onto a 50 μm thick release PET film (HY-S10 manufactured by Dongshan Film Co., Ltd.) to achieve a cured adhesive layer thickness of 75 μm. Furthermore, the method for confirming the thickness of the adhesive layer was the same as the method described above for determining the thickness of the protective film.

[0116] Next, a 75μm thick release PET film (Toyobo Co., Ltd. E7006) is applied over the adhesive composition on the aforementioned release PET film. Then, using an ultraviolet irradiation device (EYE GRAPHICS Co., Ltd., 3kW UV irradiation device, high-pressure mercury lamp), ultraviolet light is applied to both sides of the adhesive composition covered with the release PET film from the side covered by the 75μm thick release PET film to photocur the adhesive composition. The irradiation distance is 25cm, the lamp moving speed is 1.0m / min, and the irradiation dose is 1000mJ / cm².

[0117] The prepared sheet was cut into strips of 150mm × 80mm. The hardened adhesive composition was used to peel off the PET film from both sides to obtain the test sample. This test sample was immersed in 50ml of tetrahydrofuran at 25°C for 24 hours, then dried at 80°C for 5 hours. The gel fraction under the initial conditions was calculated from the mass of the test sample before and after tetrahydrofuran immersion using the following formula (1). The results are shown in Table 2.

[0118] Gel fraction (mass %) = [A / B] × 100 (1)

[0119] A: Determine the dried mass of the sample after impregnation with tetrahydrofuran (excluding the mass of tetrahydrofuran). B: Determination of the mass of the sample before tetrahydrofuran impregnation.

[0120] Prepare another sample under the same conditions as the sample used in the previous test, and place it in an air environment with a temperature of 85°C and a relative humidity of 85% for 250 hours. Use the same steps as the gel fraction determination described above to determine the gel fraction after being placed under high temperature and high humidity conditions.

[0121] The gel fraction under the initial conditions and the gel fraction after being placed under the aforementioned high temperature and high humidity conditions were calculated using the following formula (2). The results are shown in Table 2.

[0122] Change in gel fraction (Δ) = AB (2)

[0123] A: Gel fraction under initial conditions B: Gel fraction after placement under high temperature and high humidity conditions

[0124] (Water contact angle) The test plate, made of glass, was immersed overnight in an alkaline cleaning solution of 3% Semi Clean L.GL (made by Yokohama Resin) aqueous solution and then ultrasonically cleaned for 1 hour. Next, the test plate was immersed in ion-exchange water and ultrasonically cleaned for 30 minutes, repeated twice. The water contact angle of the test plate surface was then measured at 200°C in air for 2 hours. Five points on each sample were measured using a contact angle meter (DMo-601, Kyowa Interface Science Co., Ltd.), and the average value was used as a blank test. The protective films prepared in Examples 1-4 and Comparative Examples 1-5 were cut into strips of 25mm × 150mm, and the PET film was peeled off. The exposed adhesive layer was laid on a cleaned and dried test plate, and a rubber roller 1 was used to reciprocate to prepare the test sample. This test sample was placed in an environment with an air temperature of 85°C and a relative humidity of 85% for 250 hours. Then, after peeling off the protective film from the test sample, the water contact angle of the test plate surface formed by the glass plate after being placed under high temperature and high humidity conditions was measured using the same procedure as the aforementioned blank test.

[0125] The changes in water contact angle under initial conditions and under high temperature and humidity conditions were calculated using the following formula (3) by comparing the water contact angle from the blank test with the water contact angle after placement under the aforementioned high temperature and humidity conditions. The results are shown in Table 2.

[0126] Water contact angle change (Δ) = BA (°) (3)

[0127] A: Water contact angle (°) in blank test B: Water contact angle (°) after placement under high temperature and high humidity conditions.

[0128] (Contamination of the glass test plate) Similar to the water contact angle test, the test sample was placed in an air environment with a temperature of 85°C and a relative humidity of 85% for 250 hours. Then, after peeling off the protective film from the test sample, the surface of the glass test plate was observed at 400x magnification using a digital optical microscope (Hirox Corporation, RH-2000) to check for contamination.

[0129] <Peel strength of protective film> Cut the prepared protective sheet to a size of 25mm × 150mm and peel off the PET film. Next, attach the exposed adhesive side to the glass plate and roll it back and forth once with a 2kg rubber roller (width: about 50mm) to prepare the sample for testing. After pressing for 30 minutes, a tensile test was conducted in the 180° direction at a peeling speed of 2.4 m / min. The peel strength (g / 25 mm) of the protective film to the glass plate was determined according to JIS Z0237.

[0130] As shown in Table 2, it was found that even when Examples 1-4 were placed under high temperature and high humidity conditions, the change in the gel fraction of the hardened adhesive composition was suppressed. Furthermore, it was found that no contamination was identified on the surface of the glass test plate after the protective film was peeled off following placement under high temperature and high humidity conditions, and the change in water contact angle was also suppressed, demonstrating a high level of contamination suppression through the protective film. Furthermore, as shown in Table 2, Comparative Examples 1-5 exhibited high variations in gel fraction and water contact angle, and contamination of the glass test plates was identified. Therefore, it was determined that the performance required for the protective film was insufficient. The above explanation suggests that as the water contact angle changes significantly, the surface of the glass test plate becomes contaminated by the adhesive layer of the protective film, leading to changes in the surface properties of the test plate. The above explanation also suggests that for those with large variations in gel fraction, significant contamination of the glass test plate was identified. The increase in solvent-soluble components, which contribute to contamination of the test plate surface through hydrolysis of the adhesive layer or deterioration of acid value, is undesirable. Moreover, a large variation in gel fraction indicates changes in the properties of the adhesive layer of the protective film, i.e., deterioration, which is also undesirable. [Industrial Applicability]

[0131] According to the present invention, an adhesive composition can be provided that suppresses changes in the gel fraction of the cured material even under high temperature and high humidity conditions. Therefore, an adhesive layer of the cured material having the above-mentioned adhesive composition can be provided, which is a protective sheet that is less likely to contaminate the adhered material.

Claims

1. An adhesive composition comprising: an urethane polymer (A) containing an ethylene unsaturated group, a monomer (B) containing an ethylene unsaturated group, and a photopolymerization initiator (C), wherein the aforementioned urethane polymer (A) containing an ethylene unsaturated group is a reactant of a polyol (a1) and a polyisocyanate (a2) and an ethylene unsaturated compound (a3-1) having only one hydroxyl group or an ethylene unsaturated compound (a3-2) containing an isocyanate group, and the polyol (a1) is a polyol (a1-1) containing an ethylene unsaturated group and a polyoxyethylene polyol (a1-2) not containing an ethylene unsaturated group.

2. The adhesive composition of claim 1, wherein the aforementioned urethane polymer (A) containing an ethylene unsaturated group is an urethane polymer in which an ethylene unsaturated compound (a3-1) having only one hydroxyl group or an ethylene unsaturated compound (a3-2) containing an isocyanate group is added to the end of an urethane prepolymer of a reaction product of polyol (a1) and polyisocyanate (a2).

3. The adhesive composition of claim 1 or 2, wherein the aforementioned polyol (a1) is a compound having two hydroxyl groups, and the aforementioned polyisocyanate (a2) is a compound having two isocyanate groups.

4. The adhesive composition as claimed in claim 1 or 2, wherein the aforementioned urethane polymer (A) containing an vinyl unsaturated group is an urethane polymer containing (meth)acryloxy groups, the aforementioned polyol (a1-1) containing an vinyl unsaturated group is a polyol containing (meth)acryloxy groups, the aforementioned vinyl unsaturated compound (a3-1) having only one hydroxyl group is a (meth)acrylate containing a hydroxyl group, and the aforementioned vinyl unsaturated compound (a3-2) containing an isocyanate group is a (meth)acrylate containing an isocyanate group.

5. The adhesive composition of claim 1 or 2, wherein the weight average molecular weight of the aforementioned urethane polymer (A) containing vinyl unsaturated groups is 5,000 to 150,000.

6. The adhesive composition of claim 1 or 2, wherein the number average molecular weight of the aforementioned polyoxyethylene polyols (a1-2) that do not contain vinyl unsaturated groups is 500 to 5,000.

7. The adhesive composition of claim 1 or 2, wherein the aforementioned urethane polymer (A) containing vinyl unsaturated groups is a reactant of the aforementioned polyol (a1), the aforementioned polyisocyanate (a2), and the aforementioned vinyl unsaturated compound (a3-1) having only one hydroxyl group, wherein the total amount of isocyanate groups in the aforementioned polyisocyanate (a2) is 1.1 to 1.8 mol relative to the total amount of hydroxyl groups in the aforementioned polyol (a1) being 1 mol, and the content ratio (molar ratio (a1-1) / (a1-2)) of the aforementioned polyol (a1-1) containing vinyl unsaturated groups and the polyoxyethylene polyol (a1-2) without vinyl unsaturated groups is 0.03 to 0.

8.

8. The adhesive composition of claim 1 or 2, wherein the aforementioned urethane polymer (A) containing vinyl unsaturated groups is a reactant of the aforementioned polyol (a1), the aforementioned polyisocyanate (a2), and the aforementioned vinyl unsaturated compound (a3-2) containing isocyanate groups, wherein the total amount of hydroxyl groups in the polyol (a1) is 1.1 to 1.8 moles relative to the total amount of isocyanate groups in the aforementioned polyisocyanate (a2) of 1 mole, and the content ratio (mole ratio (a1-1) / (a1-2)) of the aforementioned polyol (a1-1) containing vinyl unsaturated groups and the polyoxyethylene polyol (a1-2) without vinyl unsaturated groups is 0.03 to 0.

8.

9. The adhesive composition of claim 1 or 2, wherein the monomer (B) containing the vinyl unsaturated group contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2).

10. The adhesive composition of claim 9, wherein the aforementioned monofunctional (meth)acrylate (B1) is a chain alkyl (meth)acrylate having 6 to 18 carbon atoms.

11. The adhesive composition of claim 9, wherein the aforementioned polyfunctional (meth)acrylate (B2) is a 3- to 6-functional (meth)acrylate.

12. The adhesive composition of claim 9, wherein, relative to the total of the aforementioned 100% by mass of the urethane polymer (A) containing an ethylene unsaturated group and the monomer (B) containing an ethylene unsaturated group, the aforementioned urethane polymer (A) containing an ethylene unsaturated group is 30 to 70% by mass and the monomer (B) containing an ethylene unsaturated group is 30 to 70% by mass.

13. The adhesive composition of claim 9, wherein, relative to 100% by mass of the aforementioned urethane polymer (A) containing an ethylene unsaturated group and the aforementioned monomer (B) containing an ethylene unsaturated group, the monofunctional (meth)acrylate (B1) is 25 to 60% by mass and the polyfunctional (meth)acrylate (B2) is 1 to 30% by mass.

14. An adhesive composition as claimed in claim 1 or 2, further comprising a plasticizer (D).

15. The adhesive composition of claim 14, wherein, relative to a total of 100 parts by mass of the aforementioned urethane polymer (A) containing an ethylene unsaturated group and the aforementioned monomer (B) containing an ethylene unsaturated group, the aforementioned photopolymerization initiator (C) is 0.05 to 5 parts by mass and the aforementioned plasticizer (D) is 1 to 30 parts by mass.

16. A protective sheet having an adhesive layer on one side of a substrate having a hardened copy of an adhesive composition as described in any one of claims 1 to 15.