Ethylene unsaturated group-containing urethane polymer, method of manufacturing the same, and adhesive composition

Abstract

The present invention provides an ethylene unsaturated group-containing urethane polymer that enables the suppression of changes in the gel fraction of a cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition using the said urethane polymer. The ethylene unsaturated group-containing urethane prepolymer of the present invention is a urethane prepolymer that is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2), and a reaction product of a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2). The above polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-non-containing polyisocyanate (a2-2), and at least a structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) exists in the central region of the main chain of the ethylene unsaturated group-containing urethane polymer.

Description

Technology Field

[0001] The present invention relates to an ethylene-containing unsaturated urethane polymer, a method for manufacturing the same, an adhesive composition containing the said urethane polymer, and a protective sheet having a cured product of the said adhesive composition.

[0002] The present application claims priority based on Japanese Patent Application No. 2021-108810 filed in Japan on June 30, 2021, and incorporates the contents thereof herein by reference. Background Technology

[0003] Various optical films are used in optical components such as liquid crystal displays or touch panels for smartphones, personal computers, and televisions. Generally, a protective sheet is laminated to the surface of these optical films to prevent contamination or scratches during transport, manufacturing, and inspection processes. This protective sheet is peeled off in subsequent processes of each of the above processes.

[0004] Protective sheets are required to be free of so-called adhesive residues (re-peelability), such as parts of the adhesive layer constituting the protective sheet remaining on the product surface (adherent) after peeling (Patent Document 1). In recent years, assuming that they will be subjected to harsh conditions during transportation or long-term storage, the required performance has become stricter year by year. And, various adhesives have been proposed to address this.

[0005] For example, Patent Document 2 discloses an adhesive comprising a urethane prepolymer having hydroxyl groups and a nonionic sulfonic acid ester, which satisfies re-peeling properties and resistance to contamination of the substrate under high temperature and high humidity. Patent Document 3 discloses an adhesive composition comprising a base polymer and a silicone-based additive and / or a fluorine-based additive. It is described that even when stored for a long time under harsh environments, heavy peeling over time can be sufficiently suppressed, and the contamination of the substrate surface is sufficiently low. Prior art literature

[0006] Japanese Patent Publication No. 2021-41711 Japanese Patent Publication No. 2020-75978 Japanese Patent Publication No. 2019-218472 The problem to be solved

[0007] However, in terms of stain resistance, higher performance is required for protective sheets, and conventional adhesives have not satisfied these performance requirements.

[0008] The present invention is made to solve the above-mentioned problems and aims to provide a protective sheet that is difficult to contaminate a substrate. In addition, it aims to provide an adhesive composition suitable for providing said protective sheet. More specifically, it aims to provide an adhesive composition that enables the suppression of changes in the gel fraction of the cured product even under high temperature and high humidity conditions. In addition, it aims to provide an ethylene-containing unsaturated group urethane polymer suitable for providing said adhesive composition and a method for manufacturing the same. means of solving the problem

[0009] The present invention includes the following aspects.

[0010] [1] A urethane prepolymer that is a reaction product of polyoxyalkylene polyol (a1) and polyisocyanate (a2), and

[0011] Hydroxyl group-containing ethylenically unsaturated compound (a3-1) or isocyanate group-containing ethylenically unsaturated compound (a3-2)

[0012] It is an ethylenedimethyl unsaturated group-containing urethane polymer that is a reactant of, and

[0013] An ethylene unsaturated group containing urethane polymer, characterized in that the polyisocyanate (a2) contains an ethylene unsaturated group containing polyisocyanate (a2-1) and an ethylene unsaturated group non-containing polyisocyanate (a2-2), and at least a structure derived from the ethylene unsaturated group containing polyisocyanate (a2-1) exists in the central region of the main chain of the ethylene unsaturated group containing urethane polymer.

[0014] [2] An ethylene unsaturated group-containing urethane polymer described in [1], wherein the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) is localized in the central region of the main chain of the ethylene unsaturated group-containing urethane polymer, and the structure derived from the ethylene unsaturated group-free polyisocyanate (a2-2) is localized in the terminal region of the main chain of the ethylene unsaturated group-containing urethane polymer.

[0015] [3] An ethylene unsaturated group-containing urethane polymer described in [1], wherein the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) and the structure derived from the ethylene unsaturated group-free polyisocyanate (a2-2) are uniformly present in the ethylene unsaturated group-containing urethane polymer.

[0016] [4] The above polyoxyalkylene polyol (a1) is a compound having two hydroxyl groups, and

[0017] An ethylene unsaturated group containing urethane polymer described in any one of [1] to [3], wherein the above polyisocyanate (a2) is a compound having two or more isocyanate groups.

[0018] [5] The above ethylene unsaturated group-containing urethane polymer is a (meth)acryloyloxy group-containing urethane polymer, and

[0019] The above ethylene unsaturated group-containing polyisocyanate (a2-1) is a (meth)acryloyloxy group-containing polyisocyanate (a2-1), and

[0020] The above hydroxyl group-containing ethylenically unsaturated compound (a3-1) is a hydroxyl group-containing (meth)acrylate, and

[0021] An ethylene unsaturated urethane polymer described in any one of [1] to [4], wherein the above isocyanate-containing ethylene unsaturated compound (a3-2) is an isocyanate-containing (meth)acrylate.

[0022] [6] An ethylene unsaturated group-containing urethane polymer described in any one of [1] to [5], wherein the weight average molecular weight of the ethylene unsaturated group-containing urethane polymer is 30,000 to 250,000.

[0023] [7] An ethylenically unsaturated urethane polymer described in any one of [1] to [6], wherein the number average molecular weight of the above polyoxyalkylene polyol (a1) is 500 to 5,000.

[0024] [8] The above ethylene unsaturated group-containing urethane polymer is a reaction product of the above polyoxyalkylene polyol (a1), the above polyisocyanate (a2), and the above hydroxyl group-containing ethylene unsaturated compound (a3-1), and

[0025] The total amount of isocyanate groups of the above polyisocyanate (a2) is 1.1 to 1.5 moles per 1 mole of the total amount of hydroxyl groups of the above polyoxyalkylene polyol (a1), and

[0026] An ethylene unsaturated group containing urethane polymer described in any one of [1] to [7], wherein the ratio of the ethylene unsaturated group containing polyisocyanate (a2-1) and the ethylene unsaturated group not containing polyisocyanate (a2-2) (molar ratio (a2-1) / (a2-2)) is 0.03 to 0.8.

[0027] [9] The above ethylene unsaturated group-containing urethane polymer is a reaction product of the above polyoxyalkylene polyol (a1), the above polyisocyanate (a2), and the above isocyanate group-containing ethylene unsaturated compound (a3-2), and

[0028] The total amount of hydroxyl groups of the above polyoxyalkylene polyol (a1) is 1.1 to 1.5 moles per 1 mole of the total amount of isocyanate groups of the above polyisocyanate (a2), and

[0029] An ethylene unsaturated group-containing urethane polymer described in any one of [1] to [8], wherein the ratio of the ethylene unsaturated group-free polyisocyanate (a2-2) and the ethylene unsaturated group-containing polyisocyanate (a2-1) (molar ratio (a2-2) / (a2-1)) is 0.03 to 0.8.

[0030]

[10] An ethylene unsaturated group-containing urethane polymer described in any one of [1] to [9], wherein the above ethylene unsaturated group-containing polyisocyanate (a2-1) is a reaction product of a hydroxyl group-containing ethylene unsaturated compound and a diisocyanate.

[0031]

[11] Polyoxyalkylene polyol (a1) and,

[0032] Polyisocyanate (a2)

[0033] react in a reactor to produce a urethane prepolymer, and then

[0034] The above urethane prepolymer and,

[0035] Hydroxyl group-containing ethylenically unsaturated compound (a3-1) or isocyanate group-containing ethylenically unsaturated compound (a3-2)

[0036] A method for manufacturing an ethylenedimethyl unsaturated group-containing urethane polymer by reacting,

[0037] The above polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-free polyisocyanate (a2-2), and first, a polyoxyalkylene polyol (a1) is introduced into a reactor, and the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-free polyisocyanate (a2-2) are each introduced separately into the reactor.

[0038] A method for manufacturing an ethylene unsaturated group-containing urethane polymer, characterized by setting the start time of input of the above-mentioned ethylene unsaturated group-containing polyisocyanate (a2-1) faster than the start time of input of the above-mentioned ethylene unsaturated group-non-containing polyisocyanate (a2-2).

[0039]

[12] A method for producing an ethylene unsaturated urethane polymer as described in

[11] , wherein, after the addition of the ethylene unsaturated polyisocyanate (a2-1) is finished, the addition of the ethylene unsaturated polyisocyanate (a2-2) is started.

[0040]

[13] Polyoxyalkylene polyol (a1) and,

[0041] Polyisocyanate (a2)

[0042] react in a reactor to produce a urethane prepolymer, and then

[0043] The above urethane prepolymer and,

[0044] Hydroxyl group-containing ethylenically unsaturated compound (a3-1) or isocyanate group-containing ethylenically unsaturated compound (a3-2)

[0045] A method for manufacturing an ethylenedimethyl unsaturated group-containing urethane polymer by reacting,

[0046] A method for manufacturing an ethylene unsaturated group-containing urethane polymer, characterized in that the polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-free polyisocyanate (a2-2), and the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-free polyisocyanate (a2-2) are mixed in advance and introduced into the reactor.

[0047]

[14] An ethylene unsaturated group-containing urethane polymer (A) described in any one of [1] to

[10] ,

[0048] Ethylene unsaturated group containing monomer (B), and,

[0049] Photopolymerization initiator (C)

[0050] An adhesive composition characterized by containing

[0051]

[15] A pressure-sensitive adhesive composition described in

[14] , further containing a plasticizer (D).

[0052]

[16] A pressure-sensitive adhesive composition as described in

[15] , wherein, for a total of 100 parts by mass of the ethylene unsaturated group-containing urethane polymer (A) and the ethylene unsaturated group-containing monomer (B), the ethylene unsaturated group-containing urethane polymer (A) is 30 to 70 parts by mass, the ethylene unsaturated group-containing monomer (B) is 30 to 70 parts by mass, the photopolymerization initiator (C) is 0.05 to 5 parts by mass, and the plasticizer (D) is 1 to 30 parts by mass.

[0053]

[17] A protective sheet having an adhesive layer on one side of a substrate, which is a cured product of the adhesive composition described in any of

[14] to

[16] . Effects of the invention

[0054] According to the present invention, an ethylene-containing unsaturated group urethane polymer that enables suppression of changes in the gel fraction of a cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition using the said urethane polymer can be provided. Accordingly, a protective sheet having an adhesive layer which is a cured product of the said adhesive composition and which is difficult to contaminate a substrate can be provided. Specific details for implementing the invention

[0055] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below. Here, the term (meth)acryloyl group refers to one or more selected from the group represented by the chemical formula CH2=CH-CO- and the group represented by the chemical formula CH2=C(CH3)-CO-. The term (meth)acryloyloxy group refers to one or more selected from the group represented by the chemical formula CH2=CH-CO-O- and the group represented by the chemical formula CH2=C(CH3)-CO-O-. Additionally, the term isocyanato group refers to a group represented by the chemical formula N=C=O. The term vinyl group refers to a group represented by the chemical formula CH2=CH-. The term allyl group refers to a group represented by the chemical formula CH2=CH-CH2-.

[0056] (Ethylene unsaturated group containing urethane polymer (A))

[0057] The ethylene unsaturated group-containing urethane polymer (A) of the present embodiment is a reaction product of a urethane prepolymer and a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2). The urethane prepolymer is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2). By including the ethylene unsaturated group-containing urethane polymer (A) in the adhesive composition described below, the change in the gel fraction of the cured product of the adhesive composition can be suppressed even if the cured product is exposed to high temperature and high humidity conditions. Therefore, when the protective sheet having the cured product as an adhesive layer is peeled off from the substrate, it becomes difficult to contaminate the substrate.

[0058] In addition, the ethylene unsaturated group-containing urethane polymer (A) of the present embodiment uses two types of polyisocyanates as polyisocyanates (a2): the ethylene unsaturated group-containing polyisocyanate (a2-1) described later and the ethylene unsaturated group-non-containing polyisocyanate (a2-2). Therefore, these compounds are introduced mixed within the polymer chain. Furthermore, the ethylene unsaturated group-containing urethane polymer (A) has a complex structure, such as determining whether to use the hydroxyl group-containing ethylene unsaturated compound (a3-1) or the isocyanate group-containing ethylene unsaturated compound (a3-2) based on the ratio of the polyoxyalkylene polyol (a1) and the polyisocyanate (a2). Therefore, it is difficult to define it uniquely using a structural formula or the like.

[0059] The above ethylene unsaturated group-containing urethane polymer (A) is preferably at least one of a vinyl group-containing urethane polymer, an allyl group-containing urethane polymer, and a (meth)acryloyloxy group-containing urethane polymer. From the perspective of the reactivity of radical polymerization, the above ethylene unsaturated group-containing urethane polymer (A) is more preferably a (meth)acryloyloxy group-containing urethane polymer.

[0060] As an ethylene unsaturated group containing urethane polymer (A), the first ethylene unsaturated group containing urethane polymer (A-1) or the second ethylene unsaturated group containing urethane polymer (A-2) described below may be used.

[0061] [1st Ethylene Unsaturated Group Containing Urethane Polymer (A-1)]

[0062] The first ethylene unsaturated group-containing urethane polymer (A-1) of the present embodiment is a reaction product of a urethane prepolymer and a hydroxyl group-containing ethylene unsaturated compound (a3-1). The urethane prepolymer is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2). It is preferable that the first ethylene unsaturated group-containing urethane polymer (A-1) is a (meth)acryloyloxy group-containing urethane polymer.

[0063] [Polyoxyalkylene polyol (a1)]

[0064] Polyoxyalkylene polyol (a1) is not particularly limited to a compound having a polyoxyalkylene chain, not an isocyanate group, and having two or more hydroxyl groups, and it is preferable that it be a compound having two hydroxyl groups. The number of carbon atoms in the alkylene chain constituting the polyoxyalkylene 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, polyoxybutylene polyol, etc. By having a polyoxyalkylene chain in the first ethylene unsaturated group-containing urethane polymer (A-1), the glass transition temperature (Tg) is kept low, thereby improving the wettability of the adhesive layer constituting the protective sheet described later to the substrate.

[0065] The polyoxyalkylene polyol (a1) has two or more hydroxyl groups, and it is preferable that it be a glycol having two hydroxyl groups. Specific examples include polyethylene glycol, polypropylene glycol, and polybutylene glycol. Among these, polyethylene glycol and polypropylene glycol are preferred due to ease of availability, and polypropylene glycol is more preferred due to the flexibility of the first ethylene unsaturated group-containing urethane polymer (A-1).

[0066] The above polyoxyalkylene polyol (a1) may be used alone or in combination with two or more types. Additionally, a copolymer of two or more polyoxyalkylene polyols may be used as the polyoxyalkylene polyol (a1).

[0067] The number average molecular weight of the polyoxyalkylene polyol (a1) is preferably 500 to 5,000, more preferably 800 to 4,000, and even more preferably 1,000 to 3,000. If the number average molecular weight is 500 or more, sufficient adhesive strength is obtained when used as a protective sheet. If the number average molecular weight is 5,000 or less, sufficient urethane-bound water in the first ethylenically unsaturated group-containing urethane polymer (A-1) can be secured, so the cohesive strength of the adhesive layer constituting the protective sheet is sufficiently improved.

[0068] The hydroxyl value of the polyoxyalkylene polyol (a1) is preferably 30 to 300 mgKOH / g, more preferably 40 to 200 mgKOH / g, and even more preferably 50 to 150 mgKOH / g. If the hydroxyl value is 30 mgKOH / g or higher, there is an advantage in low contamination after a durability test. If the hydroxyl value is 300 mgKOH / g or lower, there is an advantage in obtaining a cured product with appropriate adhesive strength. In addition, the hydroxyl value is measured by a method conforming to Method B of JIS K1557-1.

[0069] [Polyisocyanate (a2)]

[0070] The polyisocyanate (a2) used in the present embodiment is a compound having two or more isocyanato groups and not having a hydroxyl group, and contains an ethylene unsaturated polyisocyanate (a2-1) and an ethylene unsaturated polyisocyanate (a2-2). The number of isocyanato groups in the polyisocyanate (a2) is preferably two, in order to suppress gelation during synthesis and to allow the polymer to be stretched uniformly.

[0071] The ethylene unsaturated group-containing polyisocyanate (a2-1) is present in at least the central region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1). The "central region" is a region containing 50% of the monomer units derived from compounds (a1), (a2), (a3-1), and (a3-2) constituting the main chain. That is, the monomer units are counted from the end of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1), and the range from the 25th to the 75th of the total monomer units is defined as the "central region." At least a structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) is present in the central region. Accordingly, when polymerizing with the adhesive composition described below, the distance between the crosslinking points of the first ethylene unsaturated group-containing urethane polymer (A-1) is shortened, and a cured product is obtained in which changes in gel fraction are difficult to occur even when exposed to high temperature and high humidity conditions.

[0072] The structure derived from the polyisocyanate containing ethylene unsaturated groups (a2-1) and the structure derived from the polyisocyanate not containing ethylene unsaturated groups (a2-2) may be uniformly present in the first ethylene unsaturated group-containing urethane polymer (A-1), or both may be localized. The term "uniformly" as used here means a state in which the structure derived from the compound (a2-1) and the structure derived from the compound (a2-2) are introduced randomly into the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1) without being biased. If both are uniformly present, it means that ethylene unsaturated groups are introduced throughout the first ethylene unsaturated group-containing urethane polymer (A-1), and a first ethylene unsaturated group-containing urethane polymer (A-1) with no change in physical properties is obtained.

[0073] (a2-1) When the structure derived from the compound and (a2-2) the structure derived from the compound are localized, it is preferable that the structure derived from the polyisocyanate containing an ethylene unsaturated group (a2-1) be localized in the central region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1), and the structure derived from the polyisocyanate not containing an ethylene unsaturated group (a2-2) be localized in the terminal region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1). "Terminal region" refers to a part of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1) other than the central region. The definition that the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) is “localized” in the central region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1) means that the number of monomer units corresponding to the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) present in the central region is 1.5 times or more the number of monomer units corresponding to the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) present in the terminal region.

[0074] The polyisocyanate containing ethylene unsaturated groups (a2-1) is not particularly limited to compounds having two or more isocyanate groups and one or more ethylene unsaturated groups.

[0075] These polyisocyanates containing ethylene unsaturated groups (a2-1) may be used alone or in combination of two or more types. By using polyisocyanates containing ethylene unsaturated groups (a2-1), ethylene unsaturated groups are introduced into parts other than the ends (in the molecular chain) of the first ethylene unsaturated group-containing urethane polymer (A-1). Therefore, when the adhesive composition described later is cured, the crosslinking points increase, and even when placed under high temperature and high humidity conditions, the gel fraction of the cured product becomes less likely to change.

[0076] It is preferable that the above ethylene unsaturated group-containing polyisocyanate (a2-1) is at least one of a vinyl group-containing polyisocyanate, an allyl group-containing polyisocyanate, and a (meth)acryloyloxy group-containing polyisocyanate. From the perspective of the reactivity of radical polymerization, it is more preferable that the above ethylene unsaturated group-containing polyisocyanate (a2-1) is a (meth)acryloyloxy group-containing polyisocyanate.

[0077] Examples of (meth)acryloyloxy group-containing polyisocyanates include, for instance, reaction products of hydroxyl group-containing (meth)acrylates and polyisocyanates. (Met)acryloyloxy group-containing polyisocyanates can be obtained by synthesizing a compound having an allophanate bond by performing urethane and allophanate according to the methods described in Japanese Patent Publication No. 2002-533542, Japanese Patent Publication No. 2012-111851, etc. Specifically, as a hydroxyl group-containing (meth)acrylate, the same as the compound (a3-1) described below can be cited. As a polyisocyanate, the same as the compound (a2-2) described below can be cited. Among these, an allophanate bond-containing compound obtained by reacting a hydroxyl group-containing (meth)acrylate and a diisocyanate with an excess of diisocyanate is preferred. A compound containing an allophanate bond, obtained by reacting a hydroxyalkyl (meth)acrylate and an alkylene diisocyanate with an excess of alkylene diisocyanate, is more preferable. A reaction product obtained by allophanating one or more selected from 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate, and one or more selected from hexamethylene diisocyanate and trimethylhexamethylene diisocyanate is even more preferable.

[0078] The above ethylene unsaturated group-containing polyisocyanate (a2-1) is preferred and comprises two isocyanate groups, an average of 1.1 to 2.0 (meth)acryloyloxy groups, and one to three allophanate bonds. The above ethylene unsaturated group-containing polyisocyanate (a2-1) is more preferred and comprises two isocyanate groups, an average of 1.2 to 1.6 (meth)acryloyloxy groups, and one to two allophanate bonds.

[0079] Commercially available polyisocyanates containing (meth)acryloyloxy groups may be used. Examples include BASF’s Laromer (registered trademark) LR9000, which is a reaction product of 2-hydroxyethyl acrylate and hexamethylene diisocyanate and contains an allophanate bond.

[0080] These (meth)acryloyloxy group-containing polyisocyanates may be used as a single type or in combination of two or more types. By using the (meth)acryloyloxy group-containing polyisocyanate (a2-1), (meth)acryloyloxy groups are introduced into parts other than the terminals (in the molecular chain) of the first (meth)acryloyloxy group-containing urethane polymer (A-1). As a result, the crosslinking points increase when the adhesive composition is cured, making it difficult for the gel fraction of the cured product to change even when placed under high temperature and high humidity conditions.

[0081] Polyisocyanates (a2-2) that do not contain ethylenically unsaturated groups are not particularly limited as long as they have two or more isocyanato groups and do not have ethylenically unsaturated groups. Examples include tolylene diisocyanate and its hydrogenated derivatives, xylylene diisocyanate and its hydrogenated derivatives, diphenylmethane diisocyanate and its hydrogenated derivatives, 1,5-naphthylene diisocyanate and its hydrogenated derivatives, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, norbornane diisocyanate, etc. Among these, a polyisocyanate having a cyclic hydrocarbon structure is preferred from the perspective of ease of reaction control when synthesizing the first ethylene unsaturated group-containing urethane polymer (A-1) and light resistance as a cured product. One or more selected from isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornane diisocyanate are more preferred. Isophorone diisocyanate is even more preferred. One of these ethylene unsaturated group-free polyisocyanates may be used alone, or two or more may be used in combination.

[0082] The total amount of isocyanato groups of the above polyisocyanate (a2) is preferably 1.1 to 1.5 moles per 1 mole of the total amount of hydroxyl groups of the above polyoxyalkylene polyol (a1), more preferably 1.15 to 1.4 moles, and even more preferably 1.2 to 1.3 moles. If the total amount of isocyanato groups is 1.1 moles or more, the weight average molecular weight of the first ethylene unsaturated group-containing urethane polymer (A-1) is within the appropriate range, and the amount of hydroxyl group-containing ethylene unsaturated compound (a3-1) introduced can be sufficiently secured.

[0083] The content ratio (molar ratio (a2-1) / (a2-2)) of the above ethylene unsaturated group-containing polyisocyanate (a2-1) and the above ethylene unsaturated group-non-containing polyisocyanate (a2-2) is preferably 0.03 to 0.8, more preferably 0.08 to 0.7, even more preferably 0.1 to 0.6, and particularly preferably 0.4 to 0.6.

[0084] [Hydroxyglycerid-containing ethylenically unsaturated compound (a3-1)]

[0085] The hydroxyl group-containing ethylenically unsaturated compound (a3-1) is not particularly limited as long as it is a compound having a hydroxyl group and an ethylenically unsaturated group, and does not have an isocyanato group. From the perspective of curability, it is preferable that the ethylenically unsaturated group be at least one selected from the group consisting of vinyl group, allyl group and (meth)acryloyloxy group, and it is preferable that it be a (meth)acryloyloxy group.

[0086] Hydroxyl group-containing (meth)acrylates

[0087] The hydroxyl group-containing ethylenically unsaturated compound (a3-1) of the present embodiment is preferably a hydroxyl group-containing (meth)acrylate. As for the hydroxyl group-containing (meth)acrylate, it is not particularly limited as long as it is a compound having a hydroxyl group and a (meth)acryloyloxy group, without having an isocyanato group. Examples include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and monools having a (meth)acryloyl group derived from various polyols such as 1,3-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. In terms of the reactivity of polyisocyanate (a2) with the isocyanate group and the photocurability as an adhesive composition, hydroxyalkyl (meth)acrylate is preferred, hydroxyalkyl (meth)acrylate having an alkyl group having 2 to 6 carbon atoms is more preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are more preferred. One of these may be used alone, or two or more may be used in combination.

[0088] By using a hydroxyl group-containing ethylene unsaturated compound (a3-1), ethylene unsaturated groups can be introduced into the molecular chain end portions of the first ethylene unsaturated group-containing urethane polymer (A-1). As a result, when the adhesive composition described below is photocured, the ethylene unsaturated groups derived from the hydroxyl group-containing ethylene unsaturated compound (a3-1), the ethylene unsaturated groups derived from the ethylene unsaturated group-containing polyisocyanate (a2-1), and the ethylene unsaturated groups of component (B) described below are polymerized, making it difficult for the gel fraction to change even when exposed to high temperature and high humidity conditions. Therefore, it is difficult for contamination of the adherend to occur when peeled off as a protective sheet.

[0089] Compounds having hydroxyl and vinyl groups

[0090] The hydroxyl group-containing ethylene unsaturated compound (a3-1) of the present embodiment may be a compound having a hydroxyl group and a vinyl group. Examples of compounds having a hydroxyl group and a vinyl group include polyalkylene glycol monovinyl ether, hydroxyalkyl vinyl ether, hydroxycarboxylic acid vinyl ester, hydroxyalkyl vinyl ester, etc.

[0091] Examples of polyalkylene glycol monovinyl ethers include diethylene glycol monovinyl ether and triethylene glycol monovinyl ether.

[0092] Examples of hydroxyalkyl vinyl ethers include 4-hydroxybutyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, etc.

[0093] Examples of vinyl hydroxycarboxylate esters include vinyl hydroxyacetate, vinyl hydroxypropanoate, vinyl hydroxybutanoate, vinyl hydroxyhexanoate, and 4-vinyl hydroxycyclohexylacetate.

[0094] Examples of hydroxyalkyl vinyl esters include vinyl hydroxycyclohexylcarboxylate.

[0095] Compounds having hydroxyl and allyl groups

[0096] The hydroxyl group-containing ethylenically unsaturated compound (a3-1) of the present embodiment may not have an isocyanate group and may be a compound having a hydroxyl group and an allyl group. Examples of compounds having a hydroxyl group and an allyl group include hydroxyalkylallyl ether, hydroxycarboxylic acid allyl ester, hydroxyalkylallyl ester, etc.

[0097] Examples of hydroxyalkylallyl ethers include 2-hydroxyethylallyl ether, 4-hydroxybutylallyl ether, glycerol monoallyl ether, 4-hydroxycyclohexylallyl ether, etc.

[0098] Examples of hydroxycarboxylic acid allyl esters include allyl hydroxyacetate, allyl hydroxypropanoate, allyl hydroxybutanoate, allyl hydroxyhexanoate, and allyl 4-hydroxycyclohexylacetate.

[0099] Examples of hydroxyalkylallyl esters include hydroxyethylallyl ester, hydroxypropylallyl ester, hydroxybutylallyl ester, hydroxyisobutylallyl ester, hydroxycyclohexylallyl ester, etc.

[0100] It is preferable to set the ratio of the above hydroxyl group-containing ethylenically unsaturated compound (a3-1) such that the total amount of hydroxyl groups of compound (a1) and compound (a3-1) is equal to the total amount of isocyanate groups of compound (a2). If they are equal, the difference in the number of moles of the two is preferably 0.05 moles or less, more preferably 0.01 moles or less. If the difference in the number of moles of the two 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 groups or isocyanate groups can also be sufficiently reduced, so that changes in the gel fraction over time can be suppressed even when the product is cured.

[0101] The weight average molecular weight of the first ethylene unsaturated group-containing urethane polymer (A-1) is preferably 30,000 to 250,000, more preferably 30,000 to 200,000, even more preferably 40,000 to 150,000, and particularly preferably 430 to 150,000. If the weight average molecular weight is 30,000 or more, the cured product of the adhesive composition has sufficient flexibility, and the protective sheet having this cured product as an adhesive layer has sufficient lamination properties. If the weight average molecular weight is 250,000 or less, it is easy to handle as an adhesive composition, and workability is improved.

[0102] [Second Ethylene Unsaturated Group Containing Urethane Polymer (A-2)]

[0103] The second ethylene unsaturated group-containing urethane polymer (A-2) used in this embodiment is a reaction product of a polyoxyalkylene polyol (a1), a polyisocyanate (a2), and an isocyanate group-containing ethylene unsaturated compound (a3-2). It is preferable that the second ethylene unsaturated group-containing urethane polymer (A-2) is a (meth)acryloyloxy group-containing urethane polymer.

[0104] [Polyoxyalkylene polyol (a1)]

[0105] The polyoxyalkylene polyol (a1) used in the second ethylene unsaturated group-containing urethane polymer (A-2) may be the polyoxyalkylene polyol (a1) used in the first ethylene unsaturated group-containing urethane polymer (A-1) of the above embodiment or a preferred example thereof.

[0106] [Polyisocyanate (a2)]

[0107] The polyisocyanate (a2) used in the second ethylene unsaturated group-containing urethane polymer (A-2) may be the polyisocyanate (a2) used in the first ethylene unsaturated group-containing urethane polymer (A-1) of the above embodiment or a preferred example thereof.

[0108] The total amount of hydroxyl groups of the above polyoxyalkylene polyol (a1) is preferably 1.1 to 1.5 moles per 1 mole of the total amount of isocyanato groups of the above polyisocyanate (a2), more preferably 1.15 to 1.4 moles, and even more preferably 1.2 to 1.3 moles. If the total amount of hydroxyl groups is 1.1 moles or more, the weight average molecular weight of the second ethylene unsaturated group-containing urethane polymer (A-2) is within the appropriate range, and the amount of isocyanato group-containing ethylene unsaturated compound (a3-2) introduced can be sufficiently secured.

[0109] The content ratio (molar ratio (a2-1) / (a2-2)) of the above ethylene unsaturated group-containing polyisocyanate (a2-1) and the above ethylene unsaturated group-non-containing polyisocyanate (a2-2) is preferably 0.03 to 0.8, more preferably 0.08 to 0.7, even more preferably 0.1 to 0.6, and particularly preferably 0.4 to 0.6.

[0110] [Isocyanato group-containing ethylenically unsaturated compound (a3-2)]

[0111] As for the isocyanato group-containing ethylenically unsaturated compound (a3-2), it is not particularly limited to a compound having an isocyanato group and an ethylenically unsaturated group, provided that it does not have a hydroxyl group. It is preferable that the isocyanato group-containing ethylenically unsaturated compound (a3-2) be an isocyanato group-containing (meth)acrylate. Examples include isocyanatoalkyl (meth)acrylates such as 2-isocyanatoethyl (meth)acrylate, 2-isocyanatopropyl (meth)acrylate, 4-isocyanatobutyl (meth)acrylate, and 6-isocyanatohexyl (meth)acrylate. From the perspective of reactivity with the hydroxyl groups of the polyoxyalkylene polyol (a1) and photocurability as an adhesive composition, an isocyanatocycloalkyl (meth)acrylate having an alkyl group having 2 to 6 carbon atoms is preferred, and 2-isocyanatoethyl (meth)acrylate and 4-isocyanatobutyl (meth)acrylate are more preferred. One of these may be used alone, or two or more may be used in combination. By using an isocyanato group-containing ethylenically unsaturated compound (a3-2), an ethylenically unsaturated group can be introduced to the molecular chain end portion of the second ethylenically unsaturated urethane polymer (A-2). As a result, when the adhesive composition is photocured, the ethylene unsaturated group derived from the isocyanate-containing ethylene unsaturated compound (a3-2), the ethylene unsaturated group derived from the ethylene unsaturated polyisocyanate (a2-1), and the ethylene unsaturated group of component (B) described below are polymerized, and the gel fraction becomes less likely to change even when exposed to high temperature and high humidity conditions. Therefore, it becomes less likely for contamination of the adherend to occur when peeled off as a protective sheet.

[0112] It is preferable to set the ratio of the above isocyanato group-containing ethylenically unsaturated compound (a3-2) such that the total amount of isocyanato groups of compound (a2) and compound (a3-2) is equal to the total amount of hydroxyl groups of compound (a1). If they are equal, the difference in the number of moles of the two is preferably 0.05 moles or less, more preferably 0.01 moles or less. If the difference in the number of moles of the two 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 groups or isocyanato groups can also be sufficiently reduced, so that changes in the gel fraction over time can be suppressed even when the product is cured.

[0113] The weight average molecular weight of the second ethylene unsaturated group-containing urethane polymer (A-2) is preferably 30,000 to 250,000, more preferably 30,000 to 200,000, even more preferably 40,000 to 150,000, and particularly preferably 430 to 150,000. If the weight average molecular weight is 30,000 or more, the cured product of the adhesive composition has sufficient flexibility, and the protective sheet having this cured product as an adhesive layer has sufficient lamination properties. If the weight average molecular weight is 250,000 or less, it is easy to handle as an adhesive composition, and workability is improved.

[0114] [Method for synthesizing urethane polymer (A) containing ethylene unsaturated groups]

[0115] Hereinafter, an example of a preferred synthesis method for the ethylene unsaturated group-containing urethane polymer (A) included in the adhesive composition of the present embodiment will be described; however, the synthesis method of the ethylene unsaturated group-containing urethane polymer (A) is not limited to this and can be appropriately modified depending on conditions such as raw materials or equipment used in the synthesis. In addition, in this example, the reaction between the hydroxyl group and the isocyanate group is carried out in any process using a urethane catalyst such as dibutyltin dilaurate, dibutyltin diethyl exoate, or dioctyltin dilaurate in the presence of an organic solvent inert to the isocyanate group. It is preferable that the reaction be carried out continuously for 1 to 5 hours at 30 to 100°C. It is preferable that the amount of urethane catalyst used be 50 to 500 mass ppm relative to the total mass of the reactants.

[0116] The method for manufacturing the ethylene unsaturated group-containing urethane polymer (A) of the present embodiment may include, for example, the following basic processes in this order.

[0117] S1 Process: Polyoxyalkylene polyol (a1) and polyisocyanate (a2) are reacted in a reactor to produce a urethane prepolymer.

[0118] S2 Process: The above urethane prepolymer is reacted with a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2).

[0119] The above polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-free polyisocyanate (a2-2). In the above S1 process, the polyoxyalkylene polyol (a1) is first introduced into the reactor, and the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-free polyisocyanate (a2-2) are introduced into the reactor at separate timings, respectively. That is, the start time for introducing the ethylene unsaturated group-containing polyisocyanate (a2-1) is set earlier than the start time for introducing the ethylene unsaturated group-free polyisocyanate (a2-2).

[0120] In the above S1 process, it is preferable to start the introduction of the ethylene unsaturated group non-containing polyisocyanate (a2-2) after the introduction of the ethylene unsaturated group-containing polyisocyanate (a2-1) is finished.

[0121] The method for manufacturing the ethylene unsaturated group-containing urethane polymer (A) of the present embodiment may include, for example, the following basic processes in this order.

[0122] S1 Process: Polyoxyalkylene polyol (a1) and polyisocyanate (a2) are reacted in a reactor to produce a urethane prepolymer.

[0123] S2 Process: The above urethane prepolymer is reacted with a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2).

[0124] In the above S1 process, the polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-free polyisocyanate (a2-2), and the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-free polyisocyanate (a2-2) are mixed in advance and introduced into the reactor.

[0125] <Synthesization method of urethane polymer containing 1st ethylenically unsaturated group (A-1)>

[0126] First, polyoxyalkylene polyol (a1) and polyisocyanate (a2) are added in a ratio such that the amount of isocyanate groups (based on number, hereinafter the same) of the total of polyisocyanate containing ethylene unsaturated groups (a2-1) and polyisocyanate not containing ethylene unsaturated groups (a2-2) is greater than the amount of hydroxyl groups (based on number, hereinafter the same). These are reacted to synthesize a urethane prepolymer having isocyanate groups at the terminals. Specific examples of polyoxyalkylene polyol and polyisocyanate are as exemplified in the section on urethane polymer containing ethylene unsaturated groups (A).

[0127] At this time, polyisocyanate (a2) containing an ethylene unsaturated group (a2-1) and polyisocyanate (a2-2) not containing an ethylene unsaturated group are used as polyisocyanates (a2), but they may be added simultaneously or the polyisocyanate (a2-1) containing an ethylene unsaturated group may be added first. The position of the introduction of the ethylene unsaturated group in the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1), that is, the position of the structure derived from the polyisocyanate (a2-1) containing an ethylene unsaturated group in the main chain, can be controlled by the timing of adding the polyisocyanate (a2-1) containing an ethylene unsaturated group and the polyisocyanate (a2-2) not containing an ethylene unsaturated group. Accordingly, in order to have at least a structure derived from an ethylene unsaturated group-containing polyisocyanate (a2-1) present in the central region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1), it is necessary to add at least the ethylene unsaturated group-containing polyisocyanate (a2-1) from the start of the reaction between the polyoxyalkylene polyol (a1) and the polyisocyanate (a2). By doing so, the distance between the crosslinking points of the first ethylene unsaturated group-containing urethane polymer (A-1) is appropriately adjusted during polymerization as an adhesive composition, thereby suppressing changes in the gel fraction even when the cured product is exposed to high temperature and high humidity conditions.

[0128] The timing for adding the polyisocyanate (a2-2) that does not contain ethylene unsaturated groups may be simultaneous with the polyisocyanate (a2-1) that contains ethylene unsaturated groups, or it may be added after mixing with the polyisocyanate (a2-1) that contains ethylene unsaturated groups. If it is added after mixing with the polyisocyanate (a2-1) that contains ethylene unsaturated groups, the polyisocyanate (a2-1) that contains ethylene unsaturated groups and the polyisocyanate (a2-2) that does not contain ethylene unsaturated groups are uniformly introduced into the first urethane polymer (A-1) that contains ethylene unsaturated groups. Therefore, it is desirable that the physical properties as an adhesive remain stable without changing.

[0129] In addition, the timing for adding the polyisocyanate (a2-2) that does not contain an ethylene unsaturated group can be set later than the timing for adding the polyisocyanate (a2-1) that contains an ethylene unsaturated group. By doing so, the structure derived from the polyisocyanate (a2-1) that contains an ethylene unsaturated group can be localized in the central region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1), and the structure derived from the polyisocyanate (a2-2) that does not contain an ethylene unsaturated group can be localized in the terminal region of the main chain of the first ethylene unsaturated group-containing urethane polymer (A-1). As a result, the mesh size and crosslinking density of the three-dimensional mesh structure can be controlled when the product is cured, thereby suppressing changes in gel fraction when exposed to high temperature and high humidity conditions, and improving stain resistance, while also obtaining a first ethylene unsaturated group containing urethane polymer (A-1) with balanced physical properties such as peel strength and flexibility.

[0130] After the addition of the polyisocyanate containing an ethylene unsaturated group (a2-1) is finished, the addition of the polyisocyanate not containing an ethylene unsaturated group (a2-2) can be started, and the timing of adding both can be completely staggered. By doing so, the structure derived from the polyisocyanate containing an ethylene unsaturated group (a2-1) and the structure derived from the polyisocyanate not containing an ethylene unsaturated group (a2-2) can be more significantly localized within the main chain of the first urethane polymer containing an ethylene unsaturated group (A-1), which is desirable because the three-dimensional structure as a cured product can be controlled without variation.

[0131] Next, an isocyanate-containing urethane prepolymer is reacted with a hydroxyl-containing ethylenically unsaturated compound (a3-1) to synthesize a first ethylenically unsaturated urethane polymer (A-1) in which an ethylenically unsaturated group is introduced at the end of the molecular chain.

[0132] Based on the number, it is preferable that ethylene unsaturated groups be introduced to 90 to 100% of the terminals of the polyurethane included in the first ethylene unsaturated group-containing urethane polymer (A-1), more preferable to 95 to 100%, and even more preferable to 100%. If the amount of ethylene unsaturated groups introduced is 90% or more based on the number relative to the isocyanate groups, sufficient cohesive strength is obtained in the adhesive layer obtained by curing the adhesive composition. The ratio of the number of terminals to which ethylene unsaturated groups are introduced to the total number of terminals of the polyurethane molecular chains can be measured by IR, NMR, etc.

[0133] <Method for synthesizing a urethane polymer containing a second ethylenically unsaturated group (A-2)>

[0134] First, a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) are added in a ratio such that the amount of hydroxyl groups (based on number, hereinafter the same) is greater than the amount of isocyanate groups (based on number, hereinafter the same) of the total of the polyisocyanate containing ethylene unsaturated groups (a2-1) and the polyisocyanate not containing ethylene unsaturated groups (a2-2). These are reacted to synthesize a urethane prepolymer having hydroxyl groups at the ends. Specific examples of the polyoxyalkylene polyol and polyisocyanate are as exemplified in the section on the urethane polymer containing ethylene unsaturated groups (A).

[0135] At this time, polyisocyanate containing an ethylene unsaturated group (a2-1) and polyisocyanate not containing an ethylene unsaturated group (a2-2) are used as polyisocyanate (a2), but they may be added simultaneously or the polyisocyanate containing an ethylene unsaturated group (a2-1) may be added first. Similar to the first ethylene unsaturated group-containing urethane polymer (A-1), the polyisocyanate containing an ethylene unsaturated group (a2-1) is added from the start of the reaction between the polyoxyalkylene polyol (a1) and the polyisocyanate (a2), so that a structure derived from the polyisocyanate containing an ethylene unsaturated group (a2-1) exists in the central region of the main chain of the second ethylene unsaturated group-containing urethane polymer (A-2), and the timing of adding the polyisocyanate not containing an ethylene unsaturated group (a2-2) is not particularly limited. The timing of adding the ethylenically unsaturated polyisocyanate (a2-2) is,

[0136] 1) Add simultaneously with ethylenically unsaturated polyisocyanate (a2-1).

[0137] 2) Add by pre-mixing with ethylenically unsaturated polyisocyanate (a2-1).

[0138] 3) Start adding at a later timing than the ethylenically unsaturated polyisocyanate (a2-1).

[0139] 4) Options can be selected from options such as starting to add after the addition of the ethylene unsaturated group-containing polyisocyanate (a2-1) is finished. Among these, the method of 2) and the method of 4) are preferred, and the method of 4) is more preferred from the perspective of suppressing changes in the gel fraction of the cured product when exposed to high temperature and high humidity conditions, or from the perspective of the anti-contamination properties of the substrate.

[0140] Next, a hydroxyl group-containing urethane prepolymer is reacted with an isocyanate group-containing ethylenically unsaturated compound (a3-2) to synthesize a second ethylenically unsaturated group-containing urethane polymer (A-2) in which an ethylenically unsaturated group is introduced at the end of the molecular chain.

[0141] Based on the number, it is preferable that ethylene unsaturated groups be introduced to 90 to 100% of the terminals of the polyurethane included in the second ethylene unsaturated group-containing urethane polymer (A-2), more preferable to 95 to 100%, and even more preferable to 100%. If the amount of ethylene unsaturated groups introduced is 90% or more based on the number relative to the hydroxyl groups, sufficient cohesive strength is obtained in the adhesive layer obtained by curing the adhesive composition. The ratio of the number of terminals to which ethylene unsaturated groups are introduced to the total number of terminals of all polyurethane molecular chains can be measured by IR, NMR, etc.

[0142] (Adhesive composition)

[0143] The adhesive composition of the present embodiment contains an ethylene unsaturated group-containing urethane polymer (A) (hereinafter simply referred to as "Component (A)"), an ethylene unsaturated group-containing monomer (B) (hereinafter simply referred to as "Component (B)"), and a photopolymerization initiator (C) (hereinafter simply referred to as "Component (C)"). The adhesive composition may also contain a plasticizer (D) (hereinafter simply referred to as "Component (D)") as needed.

[0144] [Ethylene unsaturated group containing monomer (B)]

[0145] The monomer (B) containing an ethylene unsaturated group is not particularly limited as long as it is a monomer having an ethylene unsaturated group. From the perspective of curability, it is preferable to have a vinyl group or a (meth)acryloyl group, and more preferable to have a (meth)acryloyl group. Among these, from the perspective of the dilutability of the adhesive composition, low tack, and punching processability of the protective sheet, it is preferable that the monomer (B) containing an ethylene unsaturated group is a monofunctional (meth)acrylate (B1) and / or a polyfunctional (meth)acrylate (B2). "Monofunctional" means having only one (meth)acryloyloxy group, and "polyfunctional" means having multiple (meth)acryloyloxy groups. By using a monofunctional (meth)acrylate (B1), the cohesive force of the cured product of the adhesive composition can be suppressed, the adhesive layer can be made flexible, and the wettability to the substrate can be improved. By using a multifunctional (meth)acrylate (B2), the cohesive strength of the cured product of the adhesive composition is improved, and the appropriate hardness of the adhesive layer is maintained, thereby suppressing the ingress of air bubbles into the adhesive surface (between the adhesive layer and the substrate). By using components (B1) and (B2) together, the peel strength when peeling the protective sheet can be adjusted.

[0146] Examples of monofunctional (meth)acrylates (B1) include alkyl (meth)acrylates, cyclic alkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, alkoxy(poly)alkylene glycol (meth)acrylates, hydroxyl group-containing (meth)acrylates, carboxyl group-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, (meth)acrylamides, epoxy group-containing (meth)acrylates, etc.

[0147] Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, n-hexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, etc.

[0148] Examples of cyclic alkyl (meth)acrylates include cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, norbornanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclofentanyl (meth)acrylate, dicyclofentanyl (meth)acrylate, dicyclofentanyloxyethyl (meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, etc.

[0149] Examples of alkoxyalkyl (meth)acrylates include ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, 2-ethoxyethoxyethyl (meth)acrylate, etc.

[0150] Examples of alkoxy(poly)alkylene glycol(meth)acrylates include methoxydiethylene glycol(meth)acrylate, ethoxydiethylene glycol(meth)acrylate, methoxydipropylene glycol(meth)acrylate, etc.

[0151] Examples of hydroxyl group-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, 3-methylpentanediol (meth)acrylate, etc.

[0152] Examples of carboxyl group-containing (meth)acrylates include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, etc.

[0153] Examples of fluoroalkyl (meth)acrylates include octafluoropentyl (meth)acrylate.

[0154] Examples of dialkylaminoalkyl (meth)acrylates include N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.

[0155] Examples of (meth)acrylamides 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)acryloylmorpholine, diacetoneacrylamide, etc.

[0156] Examples of epoxy group-containing (meth)acrylates include glycidyl (meth)acrylate.

[0157] Among these, alkyl (meth)acrylates are preferred in terms of compatibility with the (meth)acryloyloxy group-containing urethane polymer (A), viscosity of the adhesive composition, and adjustment of peel strength, and chain alkyl (meth)acrylates having 6 to 18 carbon atoms are more preferred. More specifically, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, and isobornyl (meth)acrylate are preferred, and 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate are more preferred. In addition, the monofunctional (meth)acrylate (B1) may include one type of compound or two or more types of compounds.

[0158] As for the polyfunctional (meth)acrylate (B2), it is preferable that it be an ester compound of a polyol compound and (meth)acrylic acid, and more preferable that it be a (meth)acrylate with 3 to 6 functions. For example, 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, hydroxypivalsan ester neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acrylbisdiethylene 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, diacryloxyethyl phosphate, Examples include dipentaerythritol trihydroxy(meth)acrylate and pentaerythritol tetra(meth)acrylate.

[0159] Among these, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol trihydroxy(meth)acrylate, and pentaerythritol tetra(meth)acrylate are more preferred from the perspective of keeping the peel strength of the protective sheet low, and trimethylolpropane tri(meth)acrylate is even more preferred. In addition, the polyfunctional (meth)acrylate (B2) may include one type of compound or may include two or more types of compounds.

[0160] The ethylene unsaturated group-containing monomer (B) may also have an ethylene unsaturated group-containing monomer (B3) other than the components (B1) and (B2). Examples of monomers (B3) containing ethylenically unsaturated groups other than components (B1) and (B2) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyltoluene, N-vinylpyridine, N-vinylpyrrolidone, dialkyl ester of itaconate, 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.

[0161] [Photopolymerization initiator (C)]

[0162] The photopolymerization initiator (C) is not particularly limited as long as it is a polymerization initiator that generates radicals upon light irradiation, but examples include carbonyl-based photopolymerization initiators, sulfide-based photopolymerization initiators, acylphosphine oxides, quinone-based photopolymerization initiators, sulfochloride-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, etc.

[0163] As carbonyl-based photopolymerization initiators, for example, benzophenone, benzyl, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, mihler ketone, benzoin methyl ether, benzoin sobutyl ether, benzoin-n-butyl ether, benzylmethyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, Examples include 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, methylbenzoyl formate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

[0164] Examples of sulfide-based photopolymerization initiators include diphenyl disulfide, dibenzyl disulfide, tetraethylthiuram disulfide, tetramethylammonium monosulfide, etc.

[0165] Examples of acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide.

[0166] Examples of quinone-based photopolymerization initiators include quinone-based photopolymerization initiators such as benzoquinone and anthraquinone.

[0167] Examples of sulfochloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride.

[0168] Examples of thioxantone-based photopolymerization initiators include thioxantone, 2-chlorothioxantone, 2-methylthioxantone, etc.

[0169] Among these exemplified compounds, carbonyl-based photopolymerization initiators and acylphosphine oxides are preferred in terms of the transparency of the adhesive layer obtained by curing the adhesive composition, and 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are more preferred. In addition, the photopolymerization initiator (C) may include one type of compound or two or more types of compounds.

[0170] [Plasticizer (D)]

[0171] The plasticizer (D) may be any known material without particular limitation. For example, fatty acid esters may be preferably used. The plasticizer (D) can improve the lamination (wetting) and bubble wicking properties (ease of wicking of bubbles trapped during bonding) of the protective sheet.

[0172] Examples of fatty acid esters include esters of a monobasic acid having 8 to 18 carbon atoms or a polybasic acid and a branched alcohol having 18 or fewer carbon atoms, esters of an unsaturated fatty acid having 14 to 18 carbon atoms or an acid having a branched chain and a tetravalent alcohol. A specific example preferred as a fatty acid ester is ethylhexyl stearate.

[0173] In addition, other additives may be added to the adhesive composition as needed, provided that transparency is not impaired. Examples of additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, light stabilizers such as benzotriazole-based ones, phosphate ester-based and other flame retardants, antistatic agents such as surfactants, dyes, etc.

[0174] [menstruum]

[0175] Since the adhesive composition contains an ethylenically unsaturated group-containing monomer (B) as a low molecular weight component, the viscosity can be adjusted to a level that allows for application without adding a solvent. In other words, the adhesive composition does not substantially need to contain a solvent. In this case, when manufacturing a protective sheet, the process of heating and drying the solvent can be omitted, thereby increasing productivity. In particular, when manufacturing a protective sheet with a film thickness exceeding 50 μm, it is desirable that the adhesive composition does not substantially contain the solvent. The meaning of "substantially not containing" in the present invention is that the content of the solvent in the adhesive composition of the present invention is 0 to 1 mass%, preferably 0 to 0.5 mass% or less, and more preferably 0 to 0.1 mass% or less.

[0176] A solvent may be added to the adhesive composition for the purpose of adjusting viscosity during coating. The solvent can be appropriately selected based on other components included in the adhesive composition, but an organic solvent is preferred. Examples of organic solvents used are not particularly limited, but include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol, etc. These organic solvents may be used alone or in a mixture of two or more types. It is preferable to remove the solvent by drying the adhesive composition after it has been applied to a substrate, etc., and then perform photocuring.

[0177] [Mixing ratio of adhesive composition]

[0178] The content of the ethylene unsaturated group-containing urethane polymer (A) is preferably 30 to 70 mass% with respect to 100 mass% of the total of component (A) and component (B), more preferably 40 to 60 mass%, and even more preferably 50 to 60 mass%. If the content is 30 mass% or more, the cohesive force of the cured product of the adhesive composition can be improved, and since it becomes an adhesive layer with appropriate hardness, the ingress of air bubbles into the adhesive surface of the protective sheet (between the adhesive layer and the substrate) can be suppressed. If the content is 70 mass% or less, the cohesive force of the cured product of the adhesive composition is suppressed, and the adhesive layer becomes flexible, thereby improving the wettability of the adhesive layer to the substrate.

[0179] The content of the monomer (B) containing an ethylenically unsaturated group is preferably 30 to 70 mass% with respect to 100 mass% of the total of components (A) and (B), more preferably 40 to 65 mass%, and even more preferably 50 to 60 mass%.

[0180] When the monomer (B) containing an ethylenically unsaturated group contains monofunctional (meth)acrylate (B1) and polyfunctional (meth)acrylate (B2), the content of monofunctional (meth)acrylate (B1) is preferably 20 to 60 mass%, more preferably 25 to 55 mass%, and even more preferably 35 to 50 mass%. If the content of monofunctional (meth)acrylate (B1) is 20 mass% or more, the cohesive force of the cured product of the adhesive composition is suppressed, and a flexible cured product is obtained, so the wettability of the adhesive layer on the substrate can be improved. If the content of monofunctional (meth)acrylate (B1) is 60 mass% or less, the cohesive strength of the cured product of the adhesive composition can be improved, and since it becomes an adhesive layer with appropriate hardness, the ingress of bubbles into the adhesive surface of the protective sheet (between the adhesive layer and the adherend) can be suppressed.

[0181] The content of the polyfunctional (meth)acrylate (B2) is preferably 1 to 30 mass% with respect to 100 mass% of the total of component (A) and component (B), more preferably 3 to 20 mass%, and even more preferably 5 to 15 mass%. If the content of the polyfunctional (meth)acrylate (B2) is 1 mass% or more, the peel strength when peeling the protective sheet can be suppressed. If the content of the polyfunctional (meth)acrylate (B2) is 30 mass% or less, the flexibility of the cured product of the adhesive composition can be maintained, and haze can also be suppressed to a low level.

[0182] The content of the photopolymerization initiator (C) is preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the total of components (A) and (B), more preferably 0.1 to 3 parts by mass, and even more preferably 0.3 to 1 part by mass. If the content of the 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 is difficult to change even under high temperature and high humidity conditions. If the content of the photopolymerization initiator (C) is 5 parts by mass or less, contamination of the adherend when peeling off the protective sheet can be suppressed.

[0183] When using a plasticizer (D), the content is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the total of components (A) and (B), more preferably 5 to 25 parts by mass, and even more preferably 10 to 23 parts by mass. If the content of the plasticizer (D) is 1 part by mass or more, sufficient effects resulting from the addition of the plasticizer (D), such as improved lamination properties (wetting properties) of the protective sheet or improved bubble wicking properties (ease of wicking of bubbles trapped during bonding), can be expected. If the content of the plasticizer (D) is 30 parts by mass or less, contamination of the substrate when peeling off the protective sheet can be sufficiently suppressed.

[0184] In addition, an example of the synthesis method for the ethylene unsaturated group-containing urethane polymer (A) has been described in detail. Here, regarding the ethylene unsaturated group-containing monomer (B) and other components included in the adhesive composition, the description of the synthesis method is omitted because they vary depending on the type of compound used and commercially available products can be used.

[0185] [Method for preparing an adhesive composition]

[0186] An adhesive composition is prepared by mixing an ethylene-unsaturated group-containing urethane polymer (A), an ethylene-unsaturated group-containing monomer (B), a photopolymerization initiator (C), a plasticizer (D) as needed, other additives, and an organic solvent. The mixing method is not particularly limited, but can be carried out using a stirring device equipped with stirring blades such as a homodisperser or paddle blades, for example.

[0187] In addition, all components may be added and mixed at once, or the addition and mixing may be repeated in multiple stages for each component. Furthermore, if there are components that are solid at room temperature, they may be added by dissolving them in a solvent, dispersing them in a dispersion medium, or adding them by heating and melting them, thereby making it easier for these components to be mixed into the adhesive composition with high uniformity.

[0188] (Protective sheet)

[0189] [Composition of the protective sheet]

[0190] The protective sheet according to the present embodiment has an adhesive layer formed on one side of a substrate, the adhesive layer comprising a cured product of the adhesive composition. The thickness of the adhesive layer is preferably 3 to 150 μm, more preferably 5 to 130 μm, and even more preferably 10 to 100 μm. If the film thickness of the adhesive layer is 3 μm or more, the strength of the adhesive layer is sufficient, and if the film thickness is 150 μm or less, the film thickness of the adhesive layer is easy to control.

[0191] In addition, if the protective sheet is to be provided with the function of protecting the substrate from impact (impact resistance), it is preferable that the thickness of the adhesive layer be 50㎛ or more.

[0192] The gel fraction of the cured adhesive composition included in the adhesive layer is preferably 60 to 100 mass%, and more preferably 70 to 90 mass%. Here, the gel fraction is the mass fraction of the extractable insoluble matter relative to the solvent, and the solvent is selected to be capable of dissolving the uncrosslinked component among the cured adhesive composition. In addition, examples of specific measurement methods for the gel fraction will be described later in the examples. If the gel fraction of the cured adhesive composition is 60 to 100 mass%, so-called adhesive residue, which remains on the substrate when the protective sheet is peeled off, can be suppressed.

[0193] The material of the substrate can be appropriately selected depending on the application of the protective sheet, but examples include resin films. When the protective sheet is used, for example, as a protective sheet in a manufacturing process, and the inspection of the presence or absence of scratches or foreign matter on the substrate, i.e., the product, is performed while the protective sheet is laminated, it is preferable that the substrate be transparent. Examples of transparent substrates include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, cellulose, etc.

[0194] The thickness of the substrate can be appropriately selected according to the application of the protective sheet and is not particularly limited, but in the case of a resin film, the thickness of the substrate is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more from the perspective of handling properties and strength. In addition, considering the flexibility of the resin film, the thickness of the substrate is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0195] In addition, it is preferable to use a substrate that has been treated with an antistatic agent. The antistatic treatment applied to the substrate is not particularly limited, but methods such as providing an antistatic layer on at least one side of the substrate or mixing an antistatic agent into the substrate may be used. Furthermore, the surface of the substrate forming the adhesive layer may be subjected to adhesion-facilitating treatments such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, or ozone treatment, if necessary.

[0196] In the protective sheet, it is possible to laminate a separator onto the surface of the adhesive layer for the purpose of protecting the adhesive layer. As a material for the separator, for example, paper or plastic film can be used, but plastic film is suitable due to its excellent surface smoothness. The plastic film used as a separator is not particularly limited as long as it can protect the adhesive layer mentioned above, and examples include polyethylene, polypropylene, polyethylene terephthalate, polybutene, etc.

[0197] [Method for manufacturing a protective sheet]

[0198] A method for manufacturing a protective sheet according to the present embodiment can be obtained, for example, by applying an adhesive composition to a substrate and photocuring the applied adhesive composition by irradiating it with ultraviolet light.

[0199] The method of applying the adhesive composition to the substrate is not particularly limited and can be appropriately selected. For example, as a method of applying the adhesive composition to the substrate, methods using various coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, and direct coaters, as well as screen printing methods, may be cited.

[0200] In addition, light sources for photocuring the adhesive composition may include black lights, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, etc. As for the light irradiation intensity, it is sufficient to sufficiently cure the adhesive composition, for example, 50 to 3000 mW / cm² 2 It is desirable. In addition, if the light irradiation intensity is weak, curing takes time, which reduces productivity.

[0201] [Applications and Required Performance of Protective Sheets]

[0202] In the inspection process, it is sometimes required to sufficiently detect or identify minute foreign particles or scratches on a product or part while the product or part is laminated with a protective sheet. Additionally, the protective sheet may be suitably used to protect the surface of a plastic film used as an optical component. Examples of the optical components include polarizers, wave plates, phase difference plates, optical compensation films, reflective sheets, brightness enhancement films, etc. The optical components are used, for example, in liquid crystal displays for smartphones, personal computers, televisions, etc.

[0203] When the protective sheet according to the present embodiment is used as such a protective sheet, the protective sheet is required to have minimal contamination of the substrate. In this case, it is desirable that the change in the gel fraction of the adhesive layer constituting the protective sheet and the change in the water contact angle of the substrate surface before and after the protective sheet is peeled off be small. A specific method for measuring contamination of the substrate surface by the adhesive layer of the protective sheet will be described later in the examples.

[0204] In addition, when the protective sheet according to the present embodiment is used as such a protective sheet, a minimum peel strength is required to prevent the protective sheet from peeling off from the product or part during handling, such as transportation. On the other hand, when peeling the protective sheet off from the product or part, it is necessary to lower the peel strength to facilitate the peeling process or to prevent the product or part from being deformed or damaged during peeling. In this regard, the peel strength of the protective sheet, when the peeling speed is 2.4 m / min, varies depending on the thickness of the substrate and the adhesive layer, but is preferably 1 to 50 gf / 25 mm, more preferably 2 to 45 gf / 25 mm, and even more preferably 2 to 40 gf / 25 mm. A specific method for measuring the peel strength of the protective sheet will be described later in the examples.

[0205] Examples

[0206] The present invention will be described in detail below by way of examples. The present invention is not in any way limited by the examples shown below.

[0207] (Measurement of weight-average molecular weight)

[0208] In the following examples, the weight average molecular weight of the obtained ethylene unsaturated group-containing urethane polymer (A) is a polystyrene equivalent value measured by gel permeation chromatography (Showa Denko Co., Ltd. Shodex (registered trademark) GPC-101, hereinafter referred to as GPC). The measurement conditions of the GPC are as follows.

[0209] Column: Showa Denko Co., Ltd. LF-804

[0210] Column temperature: 40℃

[0211] Sample: 0.2 mass% tetrahydrofuran solution of polyurethane (A)

[0212] Flow rate: 1 ml / min

[0213] Eluent: Tetrahydrofuran

[0214] Detector: RI detector (parallax refractive index detector)

[0215] <Synthesis of ethylene unsaturated group-containing urethane polymer (A)>

[0216] (Synthesized Example 1)

[0217] 1 mol of Laromer (registered trademark) PR9000 (manufactured by BASF) and 5 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemical, number average molecular weight 2000) having hydroxyl groups at the ends with a hydroxyl value of 56 mgKOH / g were added to a 4-neck flask equipped with a thermometer, a stirrer, a dropping funnel, and a drying tube. Subsequently, the temperature of the 4-neck flask was raised to 80°C and the reaction was carried out for 2 hours. Then, 5 mol of isophorone diisocyanate (Desmodul I, manufactured by Sumika Covestro Urethane) was added and the reaction was carried out at 80°C for 6 hours to obtain a urethane prepolymer having isocyanate groups at both ends and a structure derived from Laromer (registered trademark) PR9000 localized in the central region.

[0218] Two mol of 2-hydroxyethyl acrylate was added to the obtained urethane prepolymer. Subsequently, the mixture was reacted at 80°C for 2 hours to obtain a (meth)acryloyloxy group-containing urethane polymer (Ai) having acryloyloxy groups at the terminals. This (meth)acryloyloxy group-containing urethane polymer (Ai) was analyzed by IR, and it was confirmed that the peaks originating from the isocyanate groups had disappeared. The weight-average molecular weight of the obtained (meth)acryloyloxy group-containing urethane polymer (Ai) was 70,000. This is shown in Table 1.

[0219] (Synthesized Example 2)

[0220] Except for the simultaneous addition of Laromer (registered trademark) PR9000, isophorone diisocyanate, and polypropylene glycol D-2000 from the beginning, the reaction was carried out at 80°C for 8 hours in the same manner as the synthesis method of the (meth)acryloyloxy group-containing urethane polymer (Ai), thereby obtaining a (meth)acryloyloxy group-containing urethane polymer (A-ii) in which Laromer (registered trademark) PR9000 and isophorone diisocyanate were uniformly present in the main chain. The weight average molecular weight of the obtained (meth)acryloyloxy group-containing urethane polymer (A-ii) was 65,000. This is shown in Table 1.

[0221] (Synthesized Examples 3 to 5)

[0222] Except for using the compounds and formulations shown in Table 1, (meth)acryloyloxy group-containing urethane polymers (A-iii) to (Av) were obtained in the same manner as the synthesis method of (meth)acryloyloxy group-containing urethane polymer (Ai), in which a structure derived from Laromer (registered trademark) PR9000 is localized in the central region of the main chain. The values ​​of weight average molecular weight are shown in Table 1.

[0223] (Comparative Synthesis Example 1)

[0224] Except for replacing Laromer (registered trademark) PR9000 with 0 mol and isophorone diisocyanate with 6 mol, the reaction was carried out at 80°C for 8 hours in the same manner as the synthesis method for the (meth)acryloyloxy group-containing urethane polymer (Ai) to obtain a urethane polymer (cA-i) having acryloyloxy groups at the ends. The weight average molecular weight of the obtained urethane polymer (cA-i) was 42,000. This is shown in Table 1.

[0225] (Comparative Synthesis Example 2)

[0226] A urethane polymer (cA-ii) having acryloyloxy groups at the ends was obtained by the same synthesis method as for the (meth)acryloyloxy group-containing urethane polymer (Ai), except that each component and its composition amount was changed to those listed in Table 1. The weight average molecular weight of the obtained urethane polymer (cA-ii) was 20,000. It is shown in Table 1.

[0227] (Comparative Synthesis Example 3)

[0228] 5 mol of isophorone diisocyanate (Desmodul I, manufactured by Sumika Covestro Urethane) and 5 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemical, number average molecular weight 2000) having hydroxyl groups at the ends with a hydroxyl value of 56 mgKOH / g were added to a 4-neck flask equipped with a thermometer, a stirrer, a dropping funnel, and a cooling tube equipped with a drying tube. Subsequently, the temperature of the 4-neck flask was raised to 80°C and the reaction was carried out for 2 hours. Then, 1 mol of Laromer (registered trademark) PR9000 (manufactured by BASF) was added and the reaction was carried out at 80°C for 6 hours to obtain a urethane prepolymer having isocyanate groups at both ends and having Laromer (registered trademark) PR9000 localized in the terminal region.

[0229] 2-hydroxyethyl acrylate was reacted with the obtained urethane prepolymer in the same manner as the synthesis method for the (meth)acryloyloxy group-containing urethane polymer (Ai). As a result, a (meth)acryloyloxy group-containing urethane polymer (cA-iii) was obtained in which Laromer (registered trademark) PR9000 was localized in the terminal region of the main chain. The weight average molecular weight of the obtained urethane polymer (cA-iii) was 90,000. This is shown in Table 1.

[0230]

[0231] In Table 1, “PR9000” is a compound represented by the following formula (1). In formula (1), n=0.32 to 0.45.

[0232]

[0233] <Preparation of Adhesive Composition>

[0234] An ethylene-unsaturated urethane polymer (A), an ethylene-unsaturated monomer (B), a photopolymerization initiator (C), and a plasticizer (D) were combined according to the compositions described in Tables 2 and 3, mixed using a disperser at 25°C, and adhesive compositions according to Examples 1 to 13 and Comparative Examples 1 to 10 were prepared.

[0235] Production of protective sheets

[0236] For Examples 1 to 13 and Comparative Examples 1 to 10, a protective sheet having an optical PET film substrate on one side was prepared in the same manner. First, using an applicator, a prepared adhesive composition was applied onto an optical PET film (A4300, manufactured by Toyobo Corporation) with a thickness of 75 μm, and then covered over the applied adhesive composition with a release PET film (E7006, manufactured by Toyobo Corporation) with a thickness of 75 μm. Subsequently, using an ultraviolet irradiation device (iGraphics Corporation, UV irradiation device 3 kW, high-pressure mercury lamp), the sheet covered with the release PET film was irradiated with ultraviolet light from the side facing the release PET film to photocur the adhesive composition. The irradiation distance of the ultraviolet light was 25 cm, the lamp travel speed was 1.0 m / min, and the irradiation dose was 1000 mJ / cm². 2 The thickness of the adhesive layer after curing was calculated by measuring the thickness of the protective sheet using a dial gauge, and then subtracting the thickness of the optical PET film (75 μm) and the thickness of the release PET film (75 μm) from this measurement. The measuring surface of the dial gauge was a circular flat surface with a diameter of 5 mm, and the measuring force was set to 0.8 N. In any of Examples 1 to 13 and Comparative Examples 1 to 10, the thickness of the adhesive layer was 75 μm.

[0237]

[0238]

[0239] The compounds in the table used the following substances.

[0240] EHA: Compound name (2-ethylhexyl acrylate, manufactured by Doa Gose Co., Ltd.)

[0241] LA: Compound name (Lauryl acrylate, manufactured by Osaka Yuki Kagaku Kogyo Co., Ltd.)

[0242] TMPTA: Compound name (Trimethylolpropane triacrylate M-309, manufactured by Doa Kose Co., Ltd.)

[0243] Irg-184: Compound name (1-Hydroxycyclohexyl Phenyl Ketone, manufactured by Tokyo Kasei High School Co., Ltd.)

[0244] IPM: Compound name (Exepal IPM, manufactured by Kao Co., Ltd.)

[0245] <Evaluation of Adhesive Composition and Protective Sheet>

[0246] For the adhesive compositions and protective sheets of Examples 1 to 13 and Comparative Examples 1 to 10, changes in gel fraction and water contact angle after storage under initial conditions and high temperature and high humidity conditions were evaluated by the method described below. In addition, the presence or absence of contamination on the glass test plate after peeling off the protective sheet following storage under high temperature and high humidity conditions was evaluated by the method described below. The results are shown in Tables 2 and 3.

[0247] (Gel fraction)

[0248] First, using an applicator, the adhesive compositions for Examples 1 to 13 and Comparative Examples 1 to 10, respectively, were applied to a 50 μm thick release PET film (HY-S10 manufactured by Higashiyama Film Co., Ltd.) such that the thickness of the adhesive layer after curing was 75 μm. In addition, the method for verifying the thickness of the adhesive layer is the same as the measurement method described above in the section on the production of the protective sheet.

[0249] Next, the adhesive composition on the above-mentioned release PET film was covered with a 75 μm thick release PET film (Toyobo Co., Ltd. E7006). Subsequently, using an ultraviolet irradiation device (iGraphics Co., Ltd., 3 kW UV irradiation device, high-pressure mercury lamp), the adhesive composition covered on both sides by release PET films was photocured by irradiating ultraviolet light from the side facing the 75 μm thick release PET film. The irradiation distance was 25 cm, the lamp travel speed was 1.0 m / min, and the irradiation dose was 1000 mJ / cm². 2 am.

[0250] The prepared sheet was cut into a 150mm × 80mm rectangle, and the release PET films on both sides were peeled off from the cured product of the adhesive composition to serve as a measurement sample. This measurement sample was immersed in 50ml of tetrahydrofuran at 25°C for 24 hours, then dried at 80°C for 5 hours, and the gel fraction under initial conditions was calculated using the following formula (1) from the mass of the measurement sample before and after immersion in tetrahydrofuran. The results are shown in Tables 2 and 3.

[0251] Gel fraction (mass%) = [A / B] × 100 (1)

[0252] A: Dry mass of the sample for measurement after immersion in tetrahydrofuran (excluding the mass of tetrahydrofuran)

[0253] B: Mass of the measurement sample before tetrahydrofuran immersion

[0254] One more measurement sample under the same conditions as the above measurement sample was prepared, and it was left in air at a temperature of 85°C and a relative humidity of 85% for 250 hours, and the gel fraction after leaving it under high temperature and high humidity conditions was measured in the same procedure as the above gel fraction measurement.

[0255] From the gel fraction under initial conditions and the gel fraction after leaving under high temperature and high humidity conditions, the change in gel fraction under initial conditions and after leaving under high temperature and high humidity conditions was calculated by the following formula (2). The results are shown in Tables 2 and 3.

[0256] Change in gel fraction (Δ) = AB (2)

[0257] A: Gel fraction under initial conditions

[0258] B: Gel fraction after storage under high temperature and high humidity conditions

[0259] (Water contact angle)

[0260] A test plate containing a glass plate was immersed overnight in an alkaline cleaning solution, which was a 3% Semiclean LGL (manufactured by Yokohama Juicy), and cleaned with an ultrasonic cleaner for 1 hour. Afterward, the test plate was immersed in ion-exchanged water, and the cleaning process was repeated twice for 30 minutes with an ultrasonic cleaner, followed by drying at an air temperature of 150°C for 2 hours. After drying, the water contact angle of the surface of the test plate was measured at 5 locations per sample using a contact angle meter (DM-601, manufactured by Kyowa Kaimen Chemical Co., Ltd.), and the average value was used as a blank. Pure water was used. The protective sheets prepared in Examples 1 to 13 and Comparative Examples 1 to 10 were cut into a 25 mm × 150 mm rectangle, and the release PET film was peeled off. The entire surface of the exposed adhesive layer was laminated onto the cleaned and dried test plate, and a rubber roller was passed back and forth once to produce a sample for measurement. For this measurement sample, it was left for 250 hours in an environment with an air temperature of 85°C and a relative humidity of 85%. After that, the protective sheet was peeled off from the measurement sample, and the water contact angle of the surface of the test plate, including the glass plate, was measured in the same procedure as with the blank above after being left under high temperature and high humidity conditions.

[0261] From the water contact angle of the blank and the water contact angle after being left under the above high temperature and high humidity conditions, the change in water contact angle under initial conditions and after being left under high temperature and high humidity conditions was calculated by the following equation (3). The results are shown in Tables 2 and 3.

[0262] Change in water contact angle (Δ) = BA(°) (3)

[0263] A: Water contact angle of the blank (°)

[0264] B: Water contact angle (°) after being left under high temperature and high humidity conditions

[0265] (Contamination of the glass test plate)

[0266] In the same manner as the water contact angle test, the measurement sample was left for 250 hours in an environment with an air temperature of 85°C and a relative humidity of 85%. Subsequently, after peeling off the protective sheet from the measurement sample, the surface of the glass test plate was observed at a magnification of 400x using a digital optical microscope (Hyrox Co., Ltd., RH-2000) to check for the presence or absence of contamination on the glass test plate.

[0267] <Peel strength of the protective sheet>

[0268] The protective sheet produced was cut to a size of 25 mm × 150 mm, and the release PET film was peeled off. Then, the exposed adhesive surface was bonded to a glass plate, and a 2 kg rubber roller (width: approximately 50 mm) was used once to produce a sample for measurement.

[0269] After 30 minutes from compression, a tensile test was performed in the 180° direction at a peeling speed of 2.4 m / min, and the peel strength (g / 25 mm) of the protective sheet against the glass plate was measured in accordance with JIS Z0237.

[0270] As shown in Table 2, it was found that in all of Examples 1 to 13, the change in the gel fraction of the cured adhesive composition was suppressed even when left under high temperature and high humidity conditions. In addition, regarding the evaluation of the surface of the test plate after peeling off the protective sheet following leaving under high temperature and high humidity conditions, no contamination was observed, and the change in the water contact angle was suppressed to a low level, indicating that contamination by the protective sheet was suppressed to a high level.

[0271] Meanwhile, as shown in Table 3, Comparative Examples 2 to 10 were found to have insufficient performance required as protective sheets, as either the change in gel fraction or the change in water contact angle was high, or contamination of the test plate was observed. Regarding the large change in water contact angle, it is suggested that the surface of the test plate is contaminated by the adhesive layer of the protective sheet, and that the properties of the test plate surface are changing due to this influence. Regarding the large change in gel fraction, significant contamination of the test plate is observed, and it is undesirable as it suggests that the solvent-soluble components causing contamination of the test plate surface are increasing due to hydrolysis of the adhesive layer or acid value degradation. Furthermore, a large change in gel fraction is also undesirable in that it implies a change in the properties of the adhesive layer of the protective sheet, i.e., degradation.

[0272] Regarding Comparative Example 1, while left under high temperature and high humidity conditions, the peel strength of the protective sheet decreased and it peeled off from the glass plate, making it impossible to measure the change in water contact angle. In other words, it was not at a level suitable for use as a protective sheet. Industrial applicability

[0273] According to the present invention, an ethylene-containing unsaturated group urethane polymer that enables suppression of changes in the gel fraction of a cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition containing the said urethane polymer can be provided. Accordingly, a protective sheet having an adhesive layer which is a cured product of the said adhesive composition and which is difficult to contaminate a substrate can be provided.

Claims

Claim 1 A urethane prepolymer which is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2), and an ethylene unsaturated group-containing urethane polymer which is a reaction product of a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2), wherein the polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-non-containing polyisocyanate (a2-2), wherein at least a structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) is present in the central region of the main chain of the ethylene unsaturated group-containing urethane polymer, and the structure derived from the ethylene unsaturated group-containing polyisocyanate (a2-1) is localized in the central region of the main chain of the ethylene unsaturated group-containing urethane polymer, and wherein the ethylene An ethylene unsaturated group-containing urethane polymer characterized in that a structure derived from an unsaturated group-free polyisocyanate (a2-2) is localized in the terminal region of the main chain of the ethylene unsaturated group-containing urethane polymer. Claim 2 An ethylene unsaturated group-containing urethane polymer according to claim 1, wherein the polyoxyalkylene polyol (a1) is a compound having two hydroxyl groups and the polyisocyanate (a2) is a compound having two or more isocyanato groups. Claim 3 An ethylene unsaturated group containing urethane polymer according to claim 1 or 2, wherein the ethylene unsaturated group containing urethane polymer is a (meth)acryloyloxy group containing urethane polymer, the ethylene unsaturated group containing polyisocyanate (a2-1) is a (meth)acryloyloxy group containing polyisocyanate (a2-1), the hydroxyl group containing ethylene unsaturated compound (a3-1) is a hydroxyl group containing (meth)acrylate, and the isocyanato group containing ethylene unsaturated compound (a3-2) is an isocyanato group containing (meth)acrylate. Claim 4 An ethylene unsaturated group-containing urethane polymer according to claim 1 or 2, wherein the weight average molecular weight of the ethylene unsaturated group-containing urethane polymer is 30,000 to 250,000. Claim 5 An ethylenically unsaturated urethane polymer according to claim 1 or 2, wherein the number average molecular weight of the polyoxyalkylene polyol (a1) is 500 to 5,000. Claim 6 The ethylene unsaturated group-containing urethane polymer according to claim 1 or 2, wherein the ethylene unsaturated group-containing urethane polymer is a reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the hydroxyl group-containing ethylene unsaturated compound (a3-1), the total amount of isocyanato groups of the polyisocyanate (a2) is 1.1 to 1.5 moles per 1 mole of the total amount of hydroxyl groups of the polyoxyalkylene polyol (a1), and the content ratio (molar ratio (a2-1) / (a2-2)) of the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-non-containing polyisocyanate (a2-2) is 0.03 to 0.

8. Claim 7 The ethylene unsaturated group-containing urethane polymer according to claim 1 or 2, wherein the ethylene unsaturated group-containing urethane polymer is a reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the isocyanate group-containing ethylene unsaturated compound (a3-2), the total amount of hydroxyl groups of the polyoxyalkylene polyol (a1) is 1.1 to 1.5 moles per 1 mole of the total amount of isocyanate groups of the polyisocyanate (a2), and the content ratio (molar ratio (a2-1) / (a2-2)) of the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-non-containing polyisocyanate (a2-2) is 0.03 to 0.

8. Claim 8 An ethylene unsaturated group containing urethane polymer according to claim 1 or 2, wherein the ethylene unsaturated group containing polyisocyanate (a2-1) is a reaction product of a hydroxyl group containing ethylene unsaturated compound and a diisocyanate. Claim 9 A method for manufacturing an ethylene unsaturated group-containing urethane polymer by reacting a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) in a reactor to produce a urethane prepolymer, and then reacting the urethane prepolymer with a hydroxyl group-containing ethylene unsaturated compound (a3-1) or an isocyanate group-containing ethylene unsaturated compound (a3-2), wherein the polyisocyanate (a2) contains an ethylene unsaturated group-containing polyisocyanate (a2-1) and an ethylene unsaturated group-non-containing polyisocyanate (a2-2), wherein the polyoxyalkylene polyol (a1) is first introduced into a reactor, and the ethylene unsaturated group-containing polyisocyanate (a2-1) and the ethylene unsaturated group-non-containing polyisocyanate (a2-2) are each introduced separately into the reactor, and the ethylene unsaturated group-containing A method for manufacturing an ethylene unsaturated group-containing urethane polymer, characterized by setting the start time of adding polyisocyanate (a2-1) faster than the start time of adding polyisocyanate (a2-2) that does not contain ethylene unsaturated groups. Claim 10 A method for manufacturing an ethylene unsaturated group-containing urethane polymer according to claim 9, wherein, after the addition of the ethylene unsaturated group-containing polyisocyanate (a2-1) is finished, the addition of the ethylene unsaturated group-free polyisocyanate (a2-2) is initiated. Claim 11 An adhesive composition characterized by containing an ethylene unsaturated group-containing urethane polymer (A) described in claim 1 or 2, an ethylene unsaturated group-containing monomer (B), and a photopolymerization initiator (C). Claim 12 In claim 11, an adhesive composition further containing a plasticizer (D). Claim 13 An adhesive composition according to claim 12, wherein, for a total of 100 parts by mass of the ethylene unsaturated group-containing urethane polymer (A) and the ethylene unsaturated group-containing monomer (B), the ethylene unsaturated group-containing urethane polymer (A) is 30 to 70 parts by mass, the ethylene unsaturated group-containing monomer (B) is 30 to 70 parts by mass, the photopolymerization initiator (C) is 0.05 to 5 parts by mass, and the plasticizer (D) is 1 to 30 parts by mass. Claim 14 A protective sheet having an adhesive layer on one side of a substrate, which is a cured product of the adhesive composition described in claim 11. Claim 15 delete Claim 16 delete Claim 17 delete

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