Urethane polymers containing ethylenically unsaturated groups, methods for their manufacture, and adhesive compositions

Abstract

This invention provides a urethane polymer containing olefinic unsaturated groups that can suppress changes in the gel fraction of the cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition containing the urethane polymer. The urethane polymer containing olefinic unsaturated groups of this invention is a urethane prepolymer that is the product of the reaction of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2), and a product of the reaction of a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2). The polyisocyanate (a2) comprises a polyisocyanate (a2-1) containing olefinic unsaturated groups and a polyisocyanate (a2-2) without olefinic unsaturated groups, wherein at least a structure derived from the polyisocyanate (a2-1) containing olefinic unsaturated groups is present in the central region of the main chain of the urethane polymer containing olefinic unsaturated groups.

Description

Technical Field

[0001] The present invention relates to urethane polymers containing olefinic unsaturated groups, methods for manufacturing the same, adhesive compositions comprising the urethane polymers, and protective sheets having the cured adhesive compositions.

[0002] This application claims priority based on Japanese Patent Application No. 2021-108810, filed in Japan on June 30, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Various optical films are used in optical components such as LCD displays and touch panels in smartphones, personal computers, and televisions. Protective sheets are typically laminated onto the surface of these optical films to prevent contamination and damage during transport, manufacturing, and inspection processes. These protective sheets are peeled off in subsequent processes.

[0004] For protective sheets, it is required that after peeling, no residue, including part of the adhesive layer constituting the protective sheet, should remain on the surface of the product (the adhered object), i.e., there should be no so-called residual adhesive (repeatingability) (Patent Document 1). In recent years, considering that they will be placed under harsh conditions during transportation and long-term storage, the required performance has become increasingly stringent. Therefore, various adhesives have been proposed to solve this problem.

[0005] For example, Patent Document 2 discloses an adhesive comprising a urethane prepolymer with hydroxyl groups and a nonionic sulfonate, which describes properties that satisfy re-peelability and resistance to contamination of the adhered surface under high temperature and humidity. Patent Document 3 discloses an adhesive composition comprising a base polymer and silicone-based and / or fluorinated additives. It describes that even when stored for a long time in harsh environments, it can sufficiently suppress severe peeling after prolonged exposure and has sufficiently low contamination of the adhered surface.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-41711

[0009] Patent Document 2: Japanese Patent Application Publication No. 2020-75978

[0010] Patent Document 3: Japanese Patent Application Publication No. 2019-218472 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, in terms of stain resistance, the protective film is required to have higher performance, which previous adhesives did not meet.

[0013] This invention was made to solve the problems described above, and its object is to provide a protective sheet that is less likely to contaminate the adhered material. Furthermore, it aims to provide an adhesive composition suitable for providing this protective sheet. More specifically, it aims to provide an adhesive composition that can suppress changes in the gel fraction of the cured product even under high temperature and high humidity conditions. Additionally, it aims to provide a urethane polymer containing olefinically unsaturated groups suitable for providing this adhesive composition, and a method for manufacturing the same.

[0014] Problem-solving methods

[0015] The present invention includes the following solutions.

[0016] [1] A urethane polymer containing olefin unsaturated groups, characterized in that it is a urethane prepolymer that is the product of the reaction of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2), or a urethane polymer containing olefin unsaturated groups that is the product of the reaction of a hydroxyl-containing olefin unsaturated compound (a3-1) or an isocyanate-containing olefin unsaturated compound (a3-2). The polyisocyanate (a2) comprises a polyisocyanate (a2-1) containing an olefinic unsaturated group and a polyisocyanate (a2-2) without an olefinic unsaturated group, wherein at least a structure derived from the polyisocyanate (a2-1) containing the olefinic unsaturated group exists in the central region of the backbone of the urethane polymer containing the olefinic unsaturated group.

[0017] [2] According to [1], the urethane polymer containing olefinic unsaturated groups, wherein the structure of the polyisocyanate (a2-1) containing olefinic unsaturated groups is biased in the central region of the main chain of the urethane polymer containing olefinic unsaturated groups, and the structure of the polyisocyanate (a2-2) without olefinic unsaturated groups is biased in the terminal region of the main chain of the urethane polymer containing olefinic unsaturated groups.

[0018] [3] The urethane polymer containing olefinic unsaturated groups according to [1], wherein the structure derived from the polyisocyanate (a2-1) containing olefinic unsaturated groups and the structure derived from the polyisocyanate (a2-2) without olefinic unsaturated groups are uniformly present in the urethane polymer containing olefinic unsaturated groups.

[0019] [4] The urethane polymer containing olefinic unsaturated groups according to any one of [1] to [3], wherein the polyoxyalkylene polyol (a1) is a compound having two hydroxyl groups and the polyisocyanate (a2) is a compound having two or more isocyanate groups.

[0020] [5] The urethane polymer containing an olefinic unsaturated group according to any one of [1] to [4], wherein the urethane polymer containing an olefinic unsaturated group is an urethane polymer containing (meth)acryloyloxy group. The polyisocyanate (a2-1) containing olefinic unsaturated groups is a polyisocyanate (a2-1) containing (meth)acryloyloxy groups. The hydroxyl-containing olefinic unsaturated compound (a3-1) is a hydroxyl-containing (meth)acrylate. The isocyanate-containing olefinic unsaturated compound (a3-2) is an isocyanate-containing (meth)acrylate.

[0021] [6] The urethane polymer containing olefinic unsaturated groups according to any one of [1] to [5], wherein the weight-average molecular weight of the urethane polymer containing olefinic unsaturated groups is 30,000 to 250,000.

[0022] [7] The urethane polymer containing olefinic unsaturated groups according to any one of [1] to [6], wherein the number average molecular weight of the polyoxyalkylene polyol (a1) is 500 to 5,000.

[0023] [8] The urethane polymer containing olefinic unsaturated groups according to any one of [1] to [7], wherein the urethane polymer containing olefinic unsaturated groups is the reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the hydroxyl-containing olefinic unsaturated compound (a3-1). Relative to 1 mole of the total number of hydroxyl groups in the polyoxyalkylene polyol (a1), the total number of isocyanate groups in the polyisocyanate (a2) is 1.1 to 1.5 moles. The molar ratio (a2-1) of the polyisocyanate containing olefinic unsaturated groups (a2-1) to the polyisocyanate without olefinic unsaturated groups (a2-2) is 0.03 to 0.8.

[0024] [9] The urethane polymer containing olefinic unsaturated groups according to any one of [1] to [8], wherein the urethane polymer containing olefinic unsaturated groups is the reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the olefinic unsaturated compound containing isocyanate groups (a3-2). Relative to 1 mole of the total isocyanate groups in the polyisocyanate (a2), the total hydroxyl groups in the polyoxyalkylene polyol (a1) are 1.1 to 1.5 moles. The molar ratio (a2-1) of the polyisocyanate containing olefinic unsaturated groups (a2-1) to the polyisocyanate without olefinic unsaturated groups (a2-2) is 0.03 to 0.8.

[0025]

[10] The urethane polymer containing olefin unsaturated groups according to any one of [1] to [9], wherein the polyisocyanate (a2-1) containing olefin unsaturated groups is a reaction product of an olefin unsaturated compound containing hydroxyl groups and a diisocyanate.

[0026]

[11] A method for preparing a urethane polymer containing olefinic unsaturated groups, characterized in that it involves reacting a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) in a reactor to generate a urethane prepolymer, and then reacting the urethane prepolymer with a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2) to prepare a urethane polymer containing olefinic unsaturated groups. The polyisocyanate (a2) comprises a polyisocyanate (a2-1) containing olefin unsaturated groups and a polyisocyanate (a2-2) without olefin unsaturated groups. First, a polyoxyalkylene polyol (a1) is added to the reactor, then the polyisocyanate (a2-1) containing olefin unsaturated groups and the polyisocyanate (a2-2) without olefin unsaturated groups are added to the reactor separately. The start time for the addition of the polyisocyanate containing olefinic unsaturated groups (a2-1) is set to be earlier than the start time for the addition of the polyisocyanate without olefinic unsaturated groups (a2-2).

[0027]

[12] According to the method for preparing the urethane polymer containing olefin unsaturated groups as described in

[11] , the addition of the polyisocyanate (a2-1) containing olefin unsaturated groups is started after the addition of the polyisocyanate (a2-2) without olefin unsaturated groups is completed.

[0028]

[13] A method for preparing a urethane polymer containing olefinic unsaturated groups, characterized in that it involves reacting a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) in a reactor to generate a urethane prepolymer, and then reacting the urethane prepolymer with a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2) to prepare a urethane polymer containing olefinic unsaturated groups. The polyisocyanate (a2) comprises a polyisocyanate (a2-1) containing an olefin unsaturated group and a polyisocyanate (a2-2) without an olefin unsaturated group. The polyisocyanate (a2-1) containing an olefin unsaturated group and the polyisocyanate (a2-2) without an olefin unsaturated group are premixed and added to the reactor.

[0029]

[14] An adhesive composition characterized in that it comprises a urethane polymer (A) containing an olefinically unsaturated group as described in any one of [1] to

[10] , a monomer (B) containing an olefinically unsaturated group, and a photopolymerization initiator (C).

[0030]

[15] The adhesive composition according to

[14] further comprises a plasticizer (D).

[0031]

[16] According to the adhesive composition of

[15] , wherein, relative to a total of 100 parts by mass of the urethane polymer (A) containing olefinic unsaturated groups and the monomer (B) containing olefinic unsaturated groups, the urethane polymer (A) containing olefinic unsaturated groups is 30 to 70 parts by mass, the monomer (B) containing olefinic unsaturated groups 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.

[0032]

[17] A protective sheet having an adhesive layer on one side of a substrate, said adhesive layer being a cured product of any of the adhesive compositions described in any one of

[14] to

[16] .

[0033] Invention Effects

[0034] According to the present invention, a urethane polymer containing olefinically unsaturated groups, capable of suppressing changes in the gel fraction of the cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition using the urethane polymer can be provided. Therefore, an adhesive layer having a cured product as the aforementioned adhesive composition and a protective sheet that is less prone to contaminating the adhered object can be provided. Detailed Implementation

[0035] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments shown below. Here, (meth)acryloyl group refers to one or more groups selected from those represented by the chemical formula CH2=CH-CO- and those represented by the chemical formula CH2=C(CH3)-CO-. (meth)acryloyloxy group refers to one or more groups selected from those represented by the chemical formula CH2=CH-CO-O- and those represented by the chemical formula CH2=C(CH3)-CO-O-. In addition, isocyanate group refers to a group represented by the chemical formula -N=C=O. Vinyl group refers to a group represented by the chemical formula CH2=CH-. Allyl group refers to a group represented by the chemical formula CH2=CH-CH2-.

[0036] (A) A urethane polymer containing olefin unsaturated groups

[0037] The urethane polymer (A) containing olefinic unsaturated groups in this embodiment is a reaction product of a urethane prepolymer and a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2). The aforementioned urethane prepolymer is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2). By including the urethane polymer (A) containing olefinic unsaturated groups in the adhesive composition described later, changes in the gel fraction of the cured adhesive composition can be suppressed even when exposed to high temperature and high humidity conditions. Therefore, the protective sheet having the cured product as an adhesive layer is less likely to contaminate the adhered object when peeled off.

[0038] It should be noted that in the urethane polymer (A) containing olefin unsaturated groups in this embodiment, two substances are used as the polyisocyanate (a2): the polyisocyanate (a2-1) containing olefin unsaturated groups (described later) and the polyisocyanate (a2-2) without olefin unsaturated groups. Therefore, these compounds are introduced into the polymer chain in a mixed manner. Furthermore, whether to use the hydroxyl-containing olefin unsaturated compound (a3-1) or the isocyanate-containing olefin unsaturated compound (a3-2) depends on the ratio of the polyoxyalkylene polyol (a1) and the polyisocyanate (a2), etc., and the urethane polymer (A) containing olefin unsaturated groups has a complex structure. Therefore, it is difficult to define it uniquely using structural formulas, etc.

[0039] The urethane polymer (A) containing an olefinically unsaturated group is preferably at least one of a vinyl-containing urethane polymer, an allyl-containing urethane polymer, and a (meth)acryloyloxy-containing urethane polymer. From the perspective of the reactivity of free radical polymerization, the urethane polymer (A) containing an olefinically unsaturated group is more preferably a (meth)acryloyloxy-containing urethane polymer.

[0040] As a urethane polymer (A) containing an olefin unsaturated group, examples include a first urethane polymer (A-1) containing an olefin unsaturated group or a second urethane polymer (A-2) containing an olefin unsaturated group, which will be described later.

[0041] [First urethane polymer containing olefinic unsaturated groups (A-1)]

[0042] The first urethane polymer (A-1) containing an olefinically unsaturated group in this embodiment is a reaction product of a urethane prepolymer and a hydroxyl-containing olefinically unsaturated compound (a3-1). The aforementioned urethane prepolymer is a reaction product of a polyoxyalkylene polyol (a1) and a polyisocyanate (a2). The aforementioned first urethane polymer (A-1) containing an olefinically unsaturated group is preferably a urethane polymer containing a (meth)acryloyloxy group.

[0043] [Polyoxyalkylene polyols (a1)]

[0044] For polyoxyalkylene polyols (a1), there are no particular limitations as long as they are compounds having polyoxyalkylene chains, not isocyanate groups, and having two or more hydroxyl groups; compounds having two hydroxyl groups are preferred. The number of carbon atoms in the alkylene chains constituting the polyoxyalkylene chains is preferably 2 to 8, more preferably 2 to 6, and even more preferably 2 to 4. Specific examples include polyoxyethylene polyols, polyoxypropylene polyols, and polyoxybutene polyols. By giving the first urethane polymer (A-1) containing olefinic unsaturated groups a polyoxyalkylene chain, the glass transition temperature (Tg) can be suppressed to a lower level, thereby improving the wettability of the adhesive layer constituting the protective sheet to the adhered object.

[0045] The polyoxyalkylene polyol (a1) has two or more hydroxyl groups, preferably a diol with two hydroxyl groups. Specific examples include polyethylene glycol, polypropylene glycol, and polybutane glycol. Among these, polyethylene glycol and polypropylene glycol are preferred from the perspective of availability, and polypropylene glycol is more preferred from the perspective of the flexibility of the first urethane polymer containing an olefinic unsaturated group (A-1).

[0046] The aforementioned polyoxyalkylene polyol (a1) can be used alone or in combination of two or more. Alternatively, a copolymer of two or more polyoxyalkylene polyols can be used as the polyoxyalkylene polyol (a1).

[0047] 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 higher, sufficient adhesion can be obtained when forming the protective sheet. If the number-average molecular weight is 5,000 or lower, the number of urethane bonds in the first olefin-unsaturated urethane polymer (A-1) can be sufficiently ensured, thus sufficiently improving the cohesive strength of the adhesive layer constituting the protective sheet.

[0048] The hydroxyl value of the polyoxyalkylene polyol (a1) is preferably 30-300 mgKOH / g, more preferably 40-200 mgKOH / g, and even more preferably 50-150 mgKOH / g. A hydroxyl value of 30 mgKOH / g or higher has the advantage of low staining after durability testing. A hydroxyl value of 300 mgKOH / g or lower has the advantage of yielding a cured product with moderate adhesion. It should be noted that the hydroxyl value is determined by method B based on JIS K1557-1.

[0049] [Polyisocyanate (a2)]

[0050] The polyisocyanate (a2) used in this embodiment is a compound that has two or more isocyanate groups but no hydroxyl groups, including polyisocyanates (a2-1) containing olefinic unsaturated groups and polyisocyanates (a2-2) that do not contain olefinic unsaturated groups. From the perspective of suppressing gelation during synthesis and enabling the polymer to stretch uniformly, the polyisocyanate (a2) preferably has two isocyanate groups.

[0051] The polyisocyanate (a2-1) containing an olefinically unsaturated group is present at least in the central region of the backbone of the first olefinically unsaturated urethane polymer (A-1). The "central region" refers to the region containing 50% of the monomer units derived from the monomer units of the compounds (a1), (a2), (a3-1), and (a3-2) constituting the backbone. That is, counting the number of monomer units from the end of the backbone of the first olefinically unsaturated urethane polymer (A-1), the range from 25% to 75% of the total number of monomer units is designated as the "central region." At least the structure of the aforementioned polyisocyanate (a2-1) containing an olefinically unsaturated group is present in the central region. Therefore, when polymerized as an adhesive composition described later, the distance between the crosslinking points of the first olefinically unsaturated urethane polymer (A-1) becomes shorter, resulting in a cured product that is less prone to changes in gel fraction even when exposed to high temperature and high humidity conditions.

[0052] The structures derived from polyisocyanates containing olefinic unsaturated groups (a2-1) and polyisocyanates without olefinic unsaturated groups (a2-2) can exist uniformly or non-uniformly in the first olefinic unsaturated urethane polymer (A-1). "Uniformly" as used herein refers to the state in which the structures derived from compounds (a2-1) and (a2-2) are randomly and unbiasedly incorporated into the backbone of the first olefinic unsaturated urethane polymer (A-1). If both exist uniformly, it means that the olefinic unsaturated groups are uniformly introduced into the first olefinic unsaturated urethane polymer (A-1), and a first olefinic unsaturated urethane polymer (A-1) without fluctuations in physical properties can be obtained.

[0053] When the structures derived from compound (a2-1) and compound (a2-2) are not homogeneous, it is preferable that the structure derived from the polyisocyanate containing the olefinic unsaturated group (a2-1) is concentrated in the central region of the main chain of the first olefinic unsaturated urethane polymer (A-1), and the structure derived from the aforementioned polyisocyanate without the olefinic unsaturated group (a2-2) is concentrated in the terminal region of the main chain of the first olefinic unsaturated urethane polymer (A-1). "Terminal region" refers to the portion of the main chain of the first olefinic unsaturated urethane polymer (A-1) outside the central region. The structure of the polyisocyanate (a2-1) derived from the olefin unsaturated group is "biased" in the central region of the main chain of the first urethane polymer (A-1) containing the olefin unsaturated group. This means that the number of monomer units in the central region corresponding to the structure of the polyisocyanate (a2-1) containing the olefin unsaturated group is more than 1.5 times the number of monomer units in the terminal region corresponding to the structure of the polyisocyanate (a2-1) containing the olefin unsaturated group.

[0054] For polyisocyanates containing olefin unsaturated groups (a2-1), there are no particular restrictions as long as the compound has two or more isocyanate groups and one or more olefin unsaturated groups.

[0055] These polyisocyanates (a2-1) containing olefinic unsaturated groups can be used alone or in combination of two or more. By using the polyisocyanate (a2-1) containing olefinic unsaturated groups, olefinic unsaturated groups are also introduced into the portion (molecular chain) of the first urethane polymer (A-1) containing olefinic unsaturated groups, beyond the ends. Therefore, the crosslinking points increase when the adhesive composition described later is cured, and the gel fraction of the cured product does not easily change even under high temperature and high humidity conditions.

[0056] The polyisocyanate (a2-1) containing an olefinic unsaturated group is preferably at least one of a vinyl polyisocyanate, an allyl polyisocyanate, and a (meth)acryloyloxy polyisocyanate. From the perspective of the reactivity of free radical polymerization, the polyisocyanate (a2-1) containing an olefinic unsaturated group is more preferably a (meth)acryloyloxy polyisocyanate.

[0057] Examples of polyisocyanates containing (meth)acryloyloxy groups include the reaction product of a hydroxyl-containing (meth)acrylate and a polyisocyanate. Polyisocyanates containing (meth)acryloyloxy groups can be synthesized as compounds having urea-formate bonds by urethane esterification and ureoformation, according to methods described in Japanese Patent Application Publication No. 2002-533542 and Japanese Patent Application Publication No. 2012-111851. Specifically, the same substance as compound (a3-1) described later can be cited as a hydroxyl-containing (meth)acrylate. The same substance as compound (a2-2) described later can be cited as a polyisocyanate. Preferably, compounds containing urea-formate bonds are obtained by reacting a hydroxyl-containing (meth)acrylate with a diisocyanate in excess of diisocyanate. More preferably, it is a compound containing a urea-formate bond obtained by reacting (meth)acrylate hydroxyalkyl ester and alkylene diisocyanate in excess of alkylene diisocyanate. Even more preferably, it is a reaction product obtained by urea-formate esterification of one or more selected from (meth)acrylate 2-hydroxyethyl ester, (meth)acrylate 2-hydroxypropyl ester, and (meth)acrylate 2-hydroxybutyl ester with one or more selected from hexamethylene diisocyanate and trimethylhexamethylene diisocyanate.

[0058] The aforementioned polyisocyanate (a2-1) containing olefinic unsaturated groups preferably comprises 2 isocyanate groups, an average of 1.1 to 2.0 (meth)acryloyloxy groups, and 1 to 3 urea-formate bonds. More preferably, the aforementioned polyisocyanate (a2-1) containing olefinic unsaturated groups comprises 2 isocyanate groups, an average of 1.2 to 1.6 (meth)acryloyloxy groups, and 1 to 2 urea-formate bonds.

[0059] Polyisocyanates containing (meth)acryloyloxy groups can be commercially available. For example, BASF's Laromer (registered trademark) LR9000, which contains a urethane bond, is an example of a reaction product of 2-hydroxyethyl acrylate and hexamethylene diisocyanate.

[0060] These (meth)acryloyloxy-containing polyisocyanates can be used alone or in combination of two or more. By using the (meth)acryloyloxy-containing polyisocyanate (a2-1), (meth)acryloyloxy groups are also introduced into the portion of the first (meth)acryloyloxy-containing urethane polymer (A-1) beyond its ends (within the molecular chain). Therefore, the crosslinking points increase when the adhesive composition is cured, and the gel fraction of the cured product does not easily change even when subjected to high temperature and high humidity conditions.

[0061] For polyisocyanates (a2-2) that do not contain olefinically unsaturated groups, there are no particular restrictions as long as the compound has two or more isocyanate groups and does not contain olefinically unsaturated groups. Examples include toluene diisocyanate and its hydrides, phenylene diisocyanate and its hydrides, diphenylmethane diisocyanate and its hydrides, 1,5-naphthalene diisocyanate and its hydrides, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylphenylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, norbornane diisocyanate, etc. Among these, considering the ease of reaction control during the synthesis of the first olefinically unsaturated urethane polymer (A-1) and the lightfastness of the cured product, polyisocyanates with cyclic hydrocarbon structures are preferred. More preferably, it is selected from one or more of isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornene diisocyanate. Isophorone diisocyanate is even more preferred. These polyisocyanates, which do not contain olefinic unsaturated groups, can be used alone or in combination of two or more.

[0062] Relative to the total amount of hydroxyl groups in the aforementioned polyoxyalkylene polyol (a1) being 1 mole, the total amount of isocyanate groups in the aforementioned polyisocyanate (a2) is preferably 1.1 to 1.5 moles, more preferably 1.15 to 1.4 moles, and even more preferably 1.2 to 1.3 moles. If the total amount of isocyanate groups is 1.1 moles or more, the weight-average molecular weight of the first olefin-unsaturated urethane polymer (A-1) reaches an appropriate range, which can sufficiently ensure the introduction amount of the hydroxyl-containing olefin-unsaturated compound (a3-1).

[0063] The molar ratio (a2-1) of the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (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.

[0064] (hydroxyl-containing olefinic unsaturated compounds (a3-1))

[0065] For hydroxyl-containing olefinic unsaturated compounds (a3-1), there are no particular restrictions as long as the compound has hydroxyl and olefinic unsaturated groups but not isocyanate groups. From the perspective of curability, the olefinic unsaturated group is preferably selected from at least one of vinyl, allyl, and (meth)acryloyloxy, and preferably (meth)acryloyloxy.

[0066] Hydroxyl-containing (meth)acrylates

[0067] The hydroxyl-containing olefinic unsaturated compound (a3-1) in this embodiment is preferably a hydroxyl-containing (meth)acrylate. As for the hydroxyl-containing (meth)acrylate, there are no particular limitations as long as the compound has hydroxyl and (meth)acryloyloxy groups but not isocyanate groups. Examples include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and monohydric alcohols with (meth)acryloyl groups derived from various polyols such as 1,3-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, and 3-methylpentanediol mono(meth)acrylate. Considering the reactivity with the isocyanate groups of the polyisocyanate (a2) and the photocurability as an adhesive composition, hydroxyalkyl (meth)acrylates are preferred, more preferably hydroxyalkyl (meth)acrylates having alkyl groups with 2 to 6 carbon atoms, and even more preferably 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate. They can be used individually or in combination of two or more.

[0068] By using a hydroxyl-containing olefinic unsaturated compound (a3-1), olefinic unsaturated groups can be introduced into the end portion of the molecular chain of the first olefinic unsaturated urethane polymer (A-1). As a result, when the adhesive composition described later is photocured, the olefinic unsaturated groups derived from the hydroxyl-containing olefinic unsaturated compound (a3-1), the olefinic unsaturated groups derived from the olefinic unsaturated polyisocyanate (a2-1), and the olefinic unsaturated groups of component (B) described later polymerize, and the gel fraction does not easily change even when exposed to high temperature and high humidity conditions. Therefore, contamination of the adhered material is less likely to occur when peeling off as a protective sheet.

[0069] <Compounds containing hydroxyl and vinyl groups>

[0070] The hydroxyl-containing olefinic unsaturated compound (a3-1) in this embodiment can be a compound having both hydroxyl and vinyl groups. Examples of compounds having both hydroxyl and vinyl groups include polyalkylene glycol monovinyl ether, hydroxyalkyl vinyl ether, hydroxycarboxylic acid vinyl ester, and hydroxyalkyl vinyl ester.

[0071] Examples of polyalkylene glycol monovinyl ethers include diethylene glycol monovinyl ether and triethylene glycol monovinyl ether.

[0072] Examples of hydroxyalkyl vinyl ethers include 4-hydroxybutyl vinyl ether and 4-hydroxycyclohexyl vinyl ether.

[0073] Examples of hydroxycarboxylic acid vinyl esters include hydroxyvinyl acetate, hydroxypropionic acid vinyl ester, hydroxybutyrate vinyl ester, hydroxyhexanoate vinyl ester, and 4-hydroxycyclohexylvinyl acetate.

[0074] Examples of hydroxyalkyl vinyl esters include hydroxycyclohexylcarboxylic acid vinyl ester.

[0075] <Compounds containing hydroxyl and allyl groups>

[0076] The hydroxyl-containing olefinic unsaturated compound (a3-1) in this embodiment can be a compound that has hydroxyl and allyl groups but no isocyanate group. Examples of compounds having hydroxyl and allyl groups include hydroxyalkyl allyl ethers, hydroxycarboxylic acid allyl esters, and hydroxyalkyl allyl esters.

[0077] Examples of hydroxyalkyl allyl ethers include 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, glyceryl monoallyl ether, and 4-hydroxycyclohexyl allyl ether.

[0078] Examples of hydroxycarboxylic acid allyl esters include allyl glycolate, allyl hydroxypropionate, allyl hydroxybutyrate, allyl hydroxyhexanoate, and allyl 4-hydroxycyclohexylacetate.

[0079] Examples of hydroxyalkyl allyl esters include hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, hydroxyisobutyl allyl ester, and hydroxycyclohexyl allyl ester.

[0080] The proportion of the aforementioned hydroxyl-containing olefinic unsaturated compound (a3-1) is preferably set such that the total amount of hydroxyl groups in compounds (a1) and (a3-1) is equal to the total amount of isocyanate groups in compound (a2). "Equal" means that the difference in molar numbers between the two is preferably 0.05 mol or less, more preferably 0.01 mol or less. If the difference in molar numbers is 0.05 mol or less, the amount of unreacted compounds (a1) to (a3-1) can be sufficiently reduced, as can the amount of unreacted hydroxyl and isocyanate groups. Therefore, even when a cured product is formed, the change in gel fraction over time can be suppressed.

[0081] The weight-average molecular weight of the first urethane polymer (A-1) containing olefinic unsaturated groups 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 43,000 to 150,000. When the weight-average molecular weight is 30,000 or higher, the cured adhesive composition has sufficient flexibility, and the protective sheet having the cured composition as an adhesive layer has sufficient lamination properties. When the weight-average molecular weight is 250,000 or lower, the adhesive composition is easy to handle and has improved workability.

[0082] [Second urethane polymer containing olefinic unsaturated groups (A-2)]

[0083] The second urethane polymer (A-2) containing an olefinic unsaturated group used in this embodiment is a reaction product of a polyoxyalkylene polyol (a1), a polyisocyanate (a2), and an olefinic unsaturated compound (a3-2) containing an isocyanate group. The second urethane polymer (A-2) containing an olefinic unsaturated group is preferably an urethane polymer containing a (meth)acryloyloxy group.

[0084] [Polyalkylene oxide polyols (a1)]

[0085] As the polyoxyalkylene polyol (a1) used in the second urethane polymer (A-2) containing olefinic unsaturated groups, the polyoxyalkylene polyol (a1) used in the first urethane polymer (A-1) containing olefinic unsaturated groups described in this embodiment, or preferred examples thereof, can be used.

[0086] (Polyisocyanate (a2))

[0087] As the polyisocyanate (a2) for the second olefin-unsaturated urethane polymer (A-2), the polyisocyanate (a2) for the first olefin-unsaturated urethane polymer (A-1) described in this embodiment or a preferred example thereof can be used.

[0088] Relative to the total amount of isocyanate groups of the aforementioned polyisocyanate (a2) being 1 mole, the total amount of hydroxyl groups of the aforementioned polyoxyalkylene polyol (a1) is preferably 1.1 to 1.5 moles, 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 urethane polymer (A-2) containing olefinic unsaturated groups reaches an appropriate range, which can sufficiently ensure the introduction amount of the olefinic unsaturated compound (a3-2) containing isocyanate groups.

[0089] The molar ratio (a2-1) of the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (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.

[0090] [Isocyanate-containing olefinic unsaturated compounds (a3-2)]

[0091] As for the isocyanate-containing olefinic unsaturated compound (a3-2), there are no particular limitations as long as it is a compound that does not have hydroxyl groups but has isocyanate groups and olefinic unsaturated groups. The isocyanate-containing olefinic unsaturated compound (a3-2) is preferably a (meth)acrylate containing an isocyanate group. Examples include, for instance, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, alkyl (meth)acrylate, and alkyl (meth)acrylate isocyanate, etc. Considering the reactivity with the hydroxyl groups of the polyoxyalkylene polyol (a1) and the photocurability as an adhesive composition, alkyl (meth)acrylate isocyanate having alkyl groups with 2 to 6 carbon atoms is preferred, and ethyl (meth)acrylate and butyl (meth)acrylate are more preferred. They can be used alone or in combination of two or more. By using an isocyanate-containing olefin unsaturated compound (a3-2), olefin unsaturated groups can be introduced into the end-chain portion of a second olefin unsaturated urethane polymer (A-2). As a result, during photocuring of the adhesive composition, the olefin unsaturated groups derived from the isocyanate-containing olefin unsaturated compound (a3-2), the olefin unsaturated groups derived from the polyisocyanate (a2-1) containing olefin unsaturated groups, and the olefin unsaturated groups of component (B) described later polymerize, and the gel fraction does not easily change even when exposed to high temperature and humidity conditions. Therefore, contamination of the adhered material is less likely to occur when peeling off as a protective sheet.

[0092] The proportion of the aforementioned isocyanate-containing olefinic unsaturated compound (a3-2) is preferably set such that the total amount of isocyanate groups in compound (a2) and compound (a3-2) is equal to the total amount of hydroxyl groups in compound (a1). "Equal" means that the difference in molar numbers between the two is preferably 0.05 mol or less, more preferably 0.01 mol or less. If the difference in molar numbers is 0.05 mol or less, the amount of unreacted compounds (a1) to (a3-2) can be sufficiently reduced, as can the amount of unreacted hydroxyl and isocyanate groups. Therefore, even when a cured product is formed, the change in gel fraction over time can be suppressed.

[0093] The weight-average molecular weight of the second urethane polymer (A-2) containing olefinically unsaturated groups 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 43,000 to 150,000. When the weight-average molecular weight is 30,000 or higher, the cured adhesive composition has sufficient flexibility, and the protective sheet having this cured composition as an adhesive layer has sufficient lamination properties. When the weight-average molecular weight is 250,000 or lower, the adhesive composition is easy to handle and has improved workability.

[0094] [Synthetic method of urethane polymer (A) containing olefinic unsaturated groups]

[0095] The following describes an example of a preferred synthesis method for the urethane polymer (A) containing olefinically unsaturated groups in the adhesive composition of this embodiment. However, the synthesis method for the urethane polymer (A) containing olefinically unsaturated groups is not limited to this and can be appropriately modified depending on the raw materials, equipment, and other conditions used in the synthesis. Furthermore, in this example, the reaction between the hydroxyl and isocyanate groups is carried out in any step using a carbamate catalyst such as dibutyltin dilaurate, dibutyltin diethylhexanoate, or dioctyltin dilaurate in the presence of an organic solvent inert to the isocyanate groups. The reaction is preferably carried out at 30–100°C for 1–5 hours. The amount of carbamate catalyst used is preferably 50–500 ppm by mass relative to the total mass of the reaction product.

[0096] The method for manufacturing the urethane polymer (A) containing olefinic unsaturated groups according to this embodiment may, for example, include the following basic steps in sequence.

[0097] S1 process: Polyoxyalkylene polyol (a1) and polyisocyanate (a2) are reacted in a reactor to generate urethane prepolymer.

[0098] S2 step: React the above urethane prepolymer with a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2).

[0099] The aforementioned polyisocyanate (a2) comprises a polyisocyanate containing olefinic unsaturated groups (a2-1) and a polyisocyanate without olefinic unsaturated groups (a2-2). In the S1 step described above, the polyoxyalkylene polyol (a1) is first added to the reactor, and the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (a2-2) are added to the reactor at different times. That is, the start time of adding the polyisocyanate containing olefinic unsaturated groups (a2-1) is set earlier than the start time of adding the polyisocyanate without olefinic unsaturated groups (a2-2).

[0100] In the above S1 process, it is preferable to start the addition of the above polyisocyanate (a2-2) without olefinic unsaturated groups after the addition of the above polyisocyanate (a2-1) containing olefinic unsaturated groups is completed.

[0101] The method for manufacturing the urethane polymer (A) containing olefinic unsaturated groups according to this embodiment may, for example, include the following basic steps in sequence.

[0102] S1 process: Polyoxyalkylene polyol (a1) and polyisocyanate (a2) are reacted in a reactor to generate urethane prepolymer.

[0103] S2 step: React the above urethane prepolymer with a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2).

[0104] In the above-mentioned S1 process, the above-mentioned polyisocyanate (a2) includes polyisocyanate (a2-1) containing olefin unsaturated groups and polyisocyanate (a2-2) without olefin unsaturated groups. The above-mentioned polyisocyanate (a2-1) containing olefin unsaturated groups and the above-mentioned polyisocyanate (a2-2) without olefin unsaturated groups are premixed and fed into the above-mentioned reactor.

[0105] <Synthetic Method of the First Carbamate Polymer Containing an Alkenyl Unsaturated Group (A-1)>

[0106] First, a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) are added in a ratio in which the total amount of isocyanate groups (by quantity, the same below) of the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (a2-2) is greater than the amount of hydroxyl groups (by quantity, the same below). They are then reacted to synthesize a urethane prepolymer with isocyanate groups at the ends. Specific examples of polyoxyalkylene polyols and polyisocyanates are illustrated in section (A) on urethane polymers containing olefinic unsaturated groups.

[0107] At this point, as polyisocyanate (a2), polyisocyanate (a2-1) containing olefinic unsaturated groups and polyisocyanate (a2-2) without olefinic unsaturated groups are used. They can be added simultaneously or first. The position of the olefinic unsaturated group in the main chain of the first urethane polymer (A-1) containing olefinic unsaturated groups, i.e., the position of the structure in the main chain originating from the polyisocyanate (a2-1) containing olefinic unsaturated groups, can be adjusted by the timing of adding polyisocyanate (a2-1) containing olefinic unsaturated groups and polyisocyanate (a2-2) without olefinic unsaturated groups. Therefore, in order to ensure that the structure derived from the polyisocyanate (a2-1) containing the olefinic unsaturated group exists at least in the central region of the backbone of the first urethane polymer (A-1) containing the olefinic unsaturated group, it is necessary to add at least the polyisocyanate (a2-1) containing the olefinic unsaturated group from the beginning of the reaction between the polyoxyalkylene polyol (a1) and the polyisocyanate (a2). Thus, during polymerization as an adhesive composition, the distance between the crosslinking points of the first urethane polymer (A-1) containing the olefinic unsaturated group can be appropriately adjusted, and changes in the gel fraction can be suppressed even when the cured product is exposed to high temperature and high humidity conditions.

[0108] The polyisocyanate (a2-2) without olefinic unsaturated groups can be added simultaneously with the polyisocyanate (a2-1) containing olefinic unsaturated groups, or it can be added after pre-mixing with the polyisocyanate (a2-1) containing olefinic unsaturated groups. If it is added after pre-mixing with the polyisocyanate (a2-1) containing olefinic unsaturated groups, both the polyisocyanate (a2-1) containing olefinic unsaturated groups and the polyisocyanate (a2-2) without olefinic unsaturated groups are uniformly incorporated into the first urethane polymer (A-1) containing olefinic unsaturated groups. Therefore, the physical properties as an adhesive are stable without fluctuations, which is preferred.

[0109] Furthermore, the timing of adding the polyisocyanate (a2-2) without olefinic unsaturated groups can be set after the timing of adding the polyisocyanate (a2-1) containing olefinic unsaturated groups. This allows the structure derived from the polyisocyanate (a2-1) containing olefinic unsaturated groups to be concentrated in the central region of the main chain of the first urethane polymer (A-1) containing olefinic unsaturated groups, while the structure derived from the polyisocyanate (a2-2) without olefinic unsaturated groups is concentrated in the terminal region of the main chain of the first urethane polymer (A-1) containing olefinic unsaturated groups. This allows for adjustment of the mesh size and crosslinking density of the three-dimensional mesh structure during curing, suppressing changes in gel fraction under high temperature and high humidity conditions, improving stain resistance, and obtaining a first urethane polymer (A-1) containing olefinic unsaturated groups with balanced physical properties such as peel strength and flexibility.

[0110] After the addition of the polyisocyanate (a2-1) containing olefinic unsaturated groups is completed, the addition of the polyisocyanate (a2-2) without olefinic unsaturated groups can be started, allowing the timing of the additions to be completely staggered. This is preferred because the structures derived from the polyisocyanate (a2-1) containing olefinic unsaturated groups and the polyisocyanate (a2-2) without olefinic unsaturated groups can exist more significantly and unevenly in the main chain of the first urethane polymer (A-1) containing olefinic unsaturated groups, and the three-dimensional structure of the cured product can be controlled to remain stable.

[0111] Next, the urethane prepolymer containing isocyanate groups is reacted with a hydroxyl-containing olefinic unsaturated compound (a3-1) to synthesize the first urethane polymer containing olefinic unsaturated groups (A-1) with olefinic unsaturated groups introduced at the ends of the molecular chains.

[0112] Preferably, in terms of quantity, olefinic unsaturated groups are introduced into 90% to 100% of the polyurethane ends contained in the first olefinic unsaturated urethane polymer (A-1), more preferably 95% to 100%, and even more preferably 100%. When the amount of olefinic unsaturated groups introduced is 90% or more relative to the isocyanate groups, sufficient cohesive strength of the adhesive layer obtained by curing the adhesive composition can be obtained. The ratio of the number of ends with introduced olefinic unsaturated groups to the total number of ends of the polyurethane molecular chains can be determined by IR, NMR, etc.

[0113] <Synthetic Method of Second Carbamate Polymer Containing Alkenyl Unsaturated Groups (A-2)>

[0114] First, polyoxyalkylene polyol (a1) and polyisocyanate (a2) are added in a ratio where the amount of hydroxyl groups (by quantity, the same below) is greater than the total amount of isocyanate groups (by quantity, the same below) of the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (a2-2). They are then reacted to synthesize a urethane prepolymer with hydroxyl groups at the ends. Specific examples of polyoxyalkylene polyols and polyisocyanates are illustrated in section (A) on urethane polymers containing olefinic unsaturated groups.

[0115] At this point, as polyisocyanate (a2), both polyisocyanate (a2-1) containing olefinic unsaturated groups and polyisocyanate (a2-2) without olefinic unsaturated groups can be used. They can be added simultaneously or first. Similar to the first urethane polymer (A-1) containing olefinic unsaturated groups, as long as the polyisocyanate (a2-1) containing olefinic unsaturated groups is added at the start of the reaction between the polyoxyalkylene polyol (a1) and the polyisocyanate (a2), such that at least a structure originating from the polyisocyanate (a2-1) exists in the central region of the main chain of the second urethane polymer (A-2), there is no particular restriction on the timing of adding the polyisocyanate (a2-2) without olefinic unsaturated groups. The timing of adding the polyisocyanate (a2-2) without olefinic unsaturated groups starts from...

[0116] 1) Added simultaneously with polyisocyanates containing olefinic unsaturated groups (a2-1)

[0117] 2) Add after pre-mixing with polyisocyanates (a2-1) containing olefinic unsaturated groups.

[0118] 3) The addition should begin at a later time than that of polyisocyanates containing olefinic unsaturated groups (a2-1).

[0119] 4) Options include adding the polyisocyanate (a2-1) containing olefinic unsaturated groups after its addition is completed. Among these, methods 2) and 4) are preferred, and method 4) is more preferred in terms of suppressing changes in the gel fraction of the cured product when exposed to high temperature and high humidity conditions and the stain resistance of the adhered material.

[0120] Next, the hydroxyl-containing urethane prepolymer is reacted with an isocyanate-containing olefin unsaturated compound (a3-2) to synthesize a second urethane polymer (A-2) with olefin unsaturated groups introduced at the ends of the molecular chain.

[0121] In terms of quantity, it is preferable to introduce olefinic unsaturated groups into 90% to 100% of the polyurethane ends contained in the second olefinic unsaturated urethane polymer (A-2), more preferably 95% to 100%, and even more preferably 100%. When the amount of olefinic unsaturated groups introduced is 90% or more relative to the number of hydroxyl groups, sufficient cohesive strength of the adhesive layer obtained by curing the adhesive composition can be obtained. The ratio of the number of ends with introduced olefinic unsaturated groups to the total number of ends of the polyurethane molecular chains can be determined by IR, NMR, etc.

[0122] (Adhesive composition)

[0123] The adhesive composition of this embodiment comprises a urethane polymer (A) containing olefinic unsaturated groups (hereinafter also referred to as "(A) component"), a monomer (B) containing olefinic unsaturated groups (hereinafter also referred to as "(B) component"), and a photopolymerization initiator (C) (hereinafter also referred to as "(C) component"). The above adhesive composition may contain a plasticizer (D) (hereinafter also referred to as "(D) component") as needed.

[0124] [Monomers containing olefinic unsaturated groups (B)]

[0125] For monomers (B) containing olefinic unsaturated groups, there are no particular restrictions as long as the monomer contains olefinic unsaturated groups. From the perspective of curability, monomers containing vinyl or (meth)acryloyl groups are preferred, and (meth)acryloyl groups are more preferred. Specifically, considering the dilution properties, low tackiness, and die-cutting processability of the adhesive composition, monomers (B) containing olefinic unsaturated groups are preferably monofunctional (meth)acrylates (B1) and / or polyfunctional (meth)acrylates (B2). "Monofunctional" means having only one (meth)acryloyloxy group, and "polyfunctional" means having multiple (meth)acryloyloxy groups. By using monofunctional (meth)acrylates (B1), the cohesiveness of the cured adhesive composition can be suppressed, making the adhesive layer softer and improving the wettability to the adhered object. By using polyfunctional (meth)acrylates (B2), the cohesiveness of the cured adhesive composition is increased, maintaining a suitable hardness of the adhesive layer and suppressing air bubbles from being trapped at the adhesive surface (between the adhesive layer and the adhered object). By combining components (B1) and (B2), the peel strength when peeling off the protective film can be adjusted.

[0126] Examples of monofunctional (meth)acrylates (B1) include alkyl (meth)acrylates, cyclic (meth)acrylates, alkoxyalkyl (meth)acrylates, alkoxy (poly)alkylene glycol (meth)acrylates, hydroxyl-containing (meth)acrylates, carboxyl-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, (meth)acrylamide, and epoxy-containing (meth)acrylates.

[0127] Examples of alkyl methacrylates include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, isodecanyl methacrylate, n-hexyl methacrylate, isooctyl methacrylate, isostearyl methacrylate, lauryl methacrylate, and tridecyl methacrylate.

[0128] Examples of cycloalkyl esters of (meth)acrylate include cyclohexyl methacrylate, norbornyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, dicyclopentenyl methacrylate, dicyclopentenoxyethyl methacrylate, dicyclopentyl methacrylate, dicyclopentoxyethyl methacrylate, tricyclodecane dihydroxymethyl di(meth)acrylate, etc.

[0129] Examples of alkoxyalkyl esters of (meth)acrylate include ethoxyethyl ester of (meth)acrylate, methoxyethyl ester of (meth)acrylate, butoxyethyl ester of (meth)acrylate, 2-methoxyethoxyethyl ester of (meth)acrylate, and 2-ethoxyethoxyethyl ester of (meth)acrylate.

[0130] Examples of alkoxy (poly)alkylene glycol (meth)acrylates include, for example, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate.

[0131] Examples of hydroxyl-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,3-butanediol (meth)acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate.

[0132] Examples of carboxyl-containing (meth)acrylates include (meth)acrylic acid and β-carboxyethyl (meth)acrylate.

[0133] Examples of fluoroalkyl esters of (meth)acrylate include, for example, octafluoropentyl (meth)acrylate.

[0134] Examples of dialkylaminoalkyl esters of (meth)acrylate include N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate.

[0135] 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, diacetone acrylamide, etc.

[0136] Examples of epoxy-containing (meth)acrylates include glycidyl (meth)acrylate and the like.

[0137] Among these, considering compatibility with the urethane polymer (A) containing (meth)acryloyloxy group, the viscosity of the adhesive composition, and the adjustment of peel strength, alkyl (meth)acrylates are preferred, and chain alkyl esters with 6 to 18 carbon atoms in (meth)acrylate 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) can be composed of one compound or two or more compounds.

[0138] As a polyfunctional (meth)acrylate (B2), it is preferably an ester compound of a polyol compound and (meth)acrylate, and more preferably a (meth)acrylate with 3 to 6 functions. Examples include polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, hydroxypentaenoate neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acrylate di(diethylene glycol) phthalate, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diacryloyloxyethyl phosphate, dipentaerythritol trihydroxy(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc.

[0139] From the perspective of suppressing the peel strength of the protective sheet to a low level, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol trihydroxy(meth)acrylate, and pentaerythritol tetra(meth)acrylate are more preferred, and trimethylolpropane tri(meth)acrylate is even more preferred. In addition, the polyfunctional (meth)acrylate (B2) can be composed of one compound or two or more compounds.

[0140] Monomers (B) containing olefinic unsaturated groups can also include monomers (B3) containing olefinic unsaturated groups other than those in (B1) and (B2). Examples of monomers (B3) containing olefinic unsaturated groups other than those in (B1) and (B2) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyltoluene, N-vinylpyridine, N-vinylpyrrolidone, dialkyl itaconic acid, 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-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, etc.

[0141] [Photopolymerization Initiator (C)]

[0142] For photopolymerization initiators (C), there are no particular restrictions as long as the polymerization initiator generates free radicals through light irradiation. Examples include carbonyl photopolymerization initiators, thioether photopolymerization initiators, acylphosphine oxides, quinone photopolymerization initiators, sulfonyl chloride photopolymerization initiators, thioxanone photopolymerization initiators, etc.

[0143] Examples of carbonyl-based photopolymerization initiators include benzophenone, benzoin, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylaminoacetophenone, p-dimethylaminoacetophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bis(diethylamino)benzophenone, michalcone, benzoin methyl ether, and benzoin isobenzophenone. Butyl ether, benzoin n-butyl ether, benzyl methyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, methyl benzoyl carbamate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one, etc.

[0144] Examples of thioether photopolymerization initiators include diphenyl disulfide, dibenzyl disulfide, tetraethylthiuram disulfide, and tetramethylammonium monosulfide.

[0145] Examples of acylphosphine oxides include 2,4,6-trimethylbenzoyl diphenylphosphine oxide and 2,4,6-trimethylbenzoyl phenyl ethoxyphosphine oxide.

[0146] Examples of quinone photopolymerization initiators include benzoquinone and anthraquinone.

[0147] Examples of sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride.

[0148] Examples of thioxanthone photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone.

[0149] Among these exemplified compounds, carbonyl photopolymerization initiators and acyl phosphine oxides are preferred from the perspective of the transparency of the adhesive layer obtained by curing the adhesive composition; 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are more preferred. Furthermore, the photopolymerization initiator (C) may consist of one compound or two or more compounds.

[0150] [Plasticizer (D)]

[0151] Plasticizer (D) can be any known substance without particular restriction. For example, fatty acid esters are preferred. Plasticizer (D) can improve the lamination (wetting) and defoaming (ease of removing air bubbles trapped during lamination) of the protective sheet.

[0152] Examples of fatty acid esters include esters of monocarboxylic or polycarboxylic acids with 8 to 18 carbon atoms and branched alcohols with 18 or fewer carbon atoms, and esters of unsaturated fatty acids or branched acids with 14 to 18 carbon atoms and tetrahydric alcohols. A preferred example of a fatty acid ester is ethylhexyl stearate.

[0153] In addition, other additives may be added to the adhesive composition as needed, without compromising transparency. Examples of additives include, for instance, plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, light stabilizers such as benzotriazoles, phosphate esters and other flame retardants, antistatic agents such as surfactants, and dyes.

[0154] [solvent]

[0155] Because the adhesive composition contains a monomer (B) with an olefinically unsaturated group as a low molecular weight component, it can be adjusted to a coatable viscosity even without the addition of a solvent. That is, the adhesive composition can be substantially solvent-free. In this case, the step of heating and drying the solvent can be omitted when manufacturing the protective film, increasing productivity. Particularly when manufacturing protective films with a film thickness exceeding 50 μm, it is preferable that the adhesive composition substantially does not contain the solvent. In this invention, "substantially solvent-free" means that the content of the aforementioned solvent in the adhesive composition of this invention is 0 to 1% by mass, preferably 0 to 0.5% by mass or less, and more preferably 0 to 0.1% by mass or less.

[0156] For adhesive compositions, solvents may be added to adjust the viscosity during coating. The solvent can be appropriately selected based on other components contained in the adhesive composition, with organic solvents being preferred. There are no particular limitations on the organic solvents used; examples include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, and isopropanol. These organic solvents can be used alone or in combination of two or more. The solvent is preferably removed by drying the adhesive composition after coating it onto a substrate, followed by photocuring.

[0157] [Formulation of the adhesive composition]

[0158] Relative to 100% by mass of the total amount of components (A) and (B), the content of the urethane polymer (A) containing olefinic unsaturated groups is preferably 30-70% by mass, more preferably 40-60% by mass, and even more preferably 50-60% by mass. If the content is 30% by mass or more, the cohesiveness of the cured adhesive composition can be improved, resulting in an adhesive layer with moderate hardness, thus suppressing air bubbles from being trapped in the adhesive surface of the protective sheet (between the adhesive layer and the adhered object). When the content is 70% by mass or less, the cohesiveness of the cured adhesive composition can be suppressed, the adhesive layer becomes soft, and the wettability of the adhesive layer to the adhered object is improved.

[0159] The content of monomer (B) containing olefinic unsaturated groups is preferably 30 to 70% by mass relative to the total mass of components (A) and (B), more preferably 40 to 65% by mass, and even more preferably 50 to 60% by mass.

[0160] When the monomer (B) containing an olefinically unsaturated group comprises a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2), the content of the monofunctional (meth)acrylate (B1) is preferably 20-60% by mass, more preferably 25-55% by mass, and even more preferably 35-50% by mass. If the content of the monofunctional (meth)acrylate (B1) is 20% by mass or more, the cohesiveness of the cured adhesive composition can be suppressed, resulting in a soft cured product, thus improving the wettability of the adhesive layer to the adhered object. When the content of the monofunctional (meth)acrylate (B1) is 60% by mass or less, the cohesiveness of the cured adhesive composition can be improved, forming an adhesive layer with moderate hardness, thus suppressing air bubbles from being trapped at the adhesive surface of the protective sheet (between the adhesive layer and the adhered object).

[0161] The content of polyfunctional (meth)acrylate (B2) relative to 100% by mass of the total of components (A) and (B) is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 15% by mass. If the content of polyfunctional (meth)acrylate (B2) is 1% by mass or more, the peel strength during the release of the protective film can be suppressed. When the content of polyfunctional (meth)acrylate (B2) is 30% by mass or less, the curing material of the adhesive composition can maintain its flexibility, and haze can be suppressed to a low level.

[0162] The content of photopolymerization initiator (C) is preferably 0.05 to 5 parts by mass relative to the total 100 parts by mass 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. When the content of photopolymerization initiator (C) is 0.05 parts by mass or more, the adhesive composition has sufficient photocurability, and the gel fraction of the cured product does not easily change even under high temperature and high humidity conditions. If the content of photopolymerization initiator (C) is 5 parts by mass or less, contamination of the adhered object can be suppressed when peeling off the protective film.

[0163] The content of plasticizer (D) is preferably 1 to 30 parts by mass relative to a total of 100 parts by mass 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 plasticizer (D) is 1 part by mass or more, the effects of adding plasticizer (D) on the lamination (wetting properties) and defoaming properties (ease of removing air bubbles trapped during bonding) of the protective film can be fully expected to appear. If the content of plasticizer (D) is 30 parts by mass or less, contamination of the adhered material during peeling off the protective film can be sufficiently suppressed.

[0164] It should be noted that the example of the synthesis method of the urethane polymer (A) containing olefinic unsaturated groups is as described above. Here, the monomer (B) containing olefinic unsaturated groups and other components contained in the adhesive composition vary depending on the type of compound used. In addition, since commercially available products can be used, the description of the synthesis method is omitted.

[0165] [Method for manufacturing adhesive composition]

[0166] An adhesive composition is prepared by mixing a urethane polymer (A) containing olefinically unsaturated groups, a monomer (B) containing olefinically unsaturated groups, a photopolymerization initiator (C), a plasticizer (D) if necessary, other additives, and an organic solvent. There are no particular limitations on the mixing method; for example, a homogenizer or a stirring device equipped with paddle blades can be used.

[0167] Alternatively, all ingredients can be added and mixed at once, or each ingredient can be added and mixed repeatedly in multiple batches. It should be noted that when an ingredient is solid at room temperature, it can be added in a highly uniform manner in the adhesive composition by means of dissolving it in a solvent, dispersing it in a dispersion medium, or melting it by heating.

[0168] (Protective film)

[0169] [Structure of the protective sheet]

[0170] The protective sheet of this embodiment has an adhesive layer containing a cured product of the above-described adhesive composition formed on one side of the substrate. 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; if the film thickness is 150 μm or less, the film thickness of the adhesive layer is easy to control.

[0171] Furthermore, if it is desired to give the protective sheet the function of protecting the adhered object from impact (impact resistance), the film thickness of the adhesive layer is preferably 50 μm or more.

[0172] The gel fraction of the cured adhesive composition contained in the adhesive layer is preferably 60-100% by mass, more preferably 70-90% by mass. Here, gel fraction refers to the mass fraction of insoluble components during solvent extraction. The solvent selected here is one capable of dissolving the uncrosslinked components in the cured adhesive composition. It should be noted that examples of specific methods for determining the gel fraction are described later in the examples. When the gel fraction of the cured adhesive composition is 60-100% by mass, so-called residual adhesive, such as a portion of the adhesive layer remaining on the adhered surface, can be suppressed when the protective sheet is peeled off.

[0173] The material of the substrate can be appropriately selected according to the intended use of the protective film; for example, a resin film can be used. When the protective film is used, for example, in a manufacturing process, to inspect the adhered object (i.e., the product) for damage or foreign matter, and this is done while the protective film is laminated, a transparent substrate is preferred. Examples of transparent substrates include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, and cellulose.

[0174] The thickness of the substrate can be appropriately selected according to the application of the protective film and is not particularly limited. In the case of a resin film, considering operability and strength, 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. 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.

[0175] Furthermore, an antistatic treatment substrate is preferred as the substrate. There are no particular limitations on the antistatic treatment applied to the substrate; methods such as providing an antistatic layer on at least one side of the substrate or mixing an antistatic agent into the substrate can be used. Moreover, the surface of the substrate to which the adhesive layer will form can be subjected to easy-to-bond treatments such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, or ozone treatment, as needed.

[0176] For the purpose of protecting the adhesive layer, a separator can be laminated onto the surface of the adhesive layer on the protective sheet. Materials used for the separator include, for example, paper or plastic film; plastic film is preferred due to its superior surface smoothness. There are no particular limitations on the plastic film used as the separator, as long as it can protect the adhesive layer; examples include polyethylene, polypropylene, polyethylene terephthalate, and polybutene.

[0177] [Manufacturing method of protective film]

[0178] The protective sheet of this embodiment can be manufactured, for example, by coating an adhesive composition onto a substrate and then irradiating the coated adhesive composition with ultraviolet light to cure it.

[0179] There are no particular limitations on the method of applying the adhesive composition to the substrate, and appropriate methods can be selected. For example, methods for applying the adhesive composition to the substrate include various coating machines such as gravure roller coating machines, reverse roller coating machines, licker roller coating machines, dip roller coating machines, bar coating machines, doctor blade coating machines, spray coating machines, comma coating machines, direct coating machines, and screen printing.

[0180] In addition, examples of light sources for photocuring the adhesive composition include black light, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and xenon lamps. The light intensity is only required to ensure sufficient curing of the adhesive composition; for example, 50 to 3000 mW / cm² is preferred. 2 It should be noted that if the light intensity is weak, curing will take longer, thus reducing productivity.

[0181] [Uses and required performance of protective films]

[0182] During the inspection process, it is sometimes necessary to be able to fully detect or inspect small foreign objects or damage to products or components even when a protective film is laminated onto them. Additionally, protective films are also suitable for protecting the surface of plastic films used as optical components. Examples of such optical components include polarizers, wavelength plates, phase retardation plates, optical compensation films, reflective films, and brightness enhancement films. These optical components are used in, for example, liquid crystal displays in smartphones, personal computers, and televisions.

[0183] When using the protective sheet of this embodiment as such a protective sheet, it is desirable that the protective sheet causes minimal contamination to the adhered object. In this case, it is preferable that the gelation rate of the adhesive layer constituting the protective sheet changes little, and that the water contact angle of the adhered object surface changes little before and after the protective sheet is applied. Specific methods for measuring the contamination of the adhesive layer of the protective sheet on the adhered object surface are described later in the examples.

[0184] Furthermore, when the protective sheet of this embodiment is used as the protective sheet described above, a minimum peel strength is required to prevent the protective sheet from peeling off from the product or component during transportation or other handling. On the other hand, when peeling the protective sheet from the product or component, a lower peel strength is needed to facilitate the peeling operation or to prevent deformation or damage to the product or component during peeling. Considering these aspects, at a peeling speed of 2.4 m / min, the peel strength of the protective sheet, while also depending on the thickness of the substrate and adhesive layer, is preferably 1~50 gf / 25 mm, more preferably 2~45 gf / 25 mm, and even more preferably 2~40 gf / 25 mm. Specific methods for measuring the peel strength of the protective sheet will be described later in the examples.

[0185] Example

[0186] The present invention will now be described in detail through examples. The present invention is not limited to the examples shown below.

[0187] (Determination of weight-average molecular weight)

[0188] In the following examples, the weight-average molecular weight of the urethane polymer (A) containing olefinic unsaturated groups was determined by gel permeation chromatography (Shodex GPC-101 manufactured by Showa Denko Corporation, hereinafter referred to as GPC), which is a polystyrene equivalent. The determination conditions for GPC are described below.

[0189] Pillar: LF-804 manufactured by Showa Denko Co., Ltd.

[0190] Column temperature: 40℃

[0191] Sample: 0.2% by mass tetrahydrofuran solution of polyurethane (A)

[0192] Flow rate: 1 ml / min

[0193] Eluent: Tetrahydrofuran

[0194] Detector: RI detector (differential refractive index detector)

[0195] Synthesis of urethane polymers (A) containing olefinically unsaturated groups

[0196] (Synthesis example 1)

[0197] In a four-necked flask equipped with a thermometer, stirrer, dropping funnel, and cooling tube with a drying tube, 1 mol of Laromer (registered trademark) PR9000 (manufactured by BASF) and 5 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) with hydroxyl groups at the ends (hydroxyl value 56 mg KOH / g) were added. The flask was then heated to 80°C and reacted for 2 hours. Next, 5 mol of isophorone diisocyanate (Desmojule I, manufactured by Sumitomo Chemical Covestro Uretan) was added, and the reaction was carried out at 80°C for 6 hours, yielding a urethane prepolymer with isocyanate groups at both ends and a structure derived from Laromer (registered trademark) PR9000 concentrated in the central region.

[0198] 2 mol of 2-hydroxyethyl acrylate was added to the obtained urethane prepolymer. The mixture was then reacted at 80 °C for 2 hours to obtain a urethane polymer (Ai) terminally terminal with an acryloyloxy group. IR analysis of this urethane polymer (Ai) confirmed the disappearance of the peak originating from the isocyanate group. The weight-average molecular weight of the obtained urethane polymer (Ai) was 70,000. (See Table 1 for details.)

[0199] (Synthesis example 2)

[0200] Except for the simultaneous addition of Laromer (registered trademark) PR9000, isophorone diisocyanate, and polypropylene glycol D-2000 at the beginning, the same procedures as the synthesis of the (meth)acryloyloxy-containing urethane polymer (Ai) were followed, reacting at 80°C for 8 hours to obtain the (meth)acryloyloxy-containing urethane polymer (A-ii) with Laromer (registered trademark) PR9000 and isophorone diisocyanate uniformly present in the main chain. The weight-average molecular weight of the obtained (meth)acryloyloxy-containing urethane polymer (A-ii) was 65,000. (See Table 1.)

[0201] (Synthesis Examples 3~5)

[0202] Except for the compounds and complexing amounts shown in Table 1, the same procedures were performed as for the synthesis of (meth)acryloyloxy-containing urethane polymers (Ai) to obtain (A-iii)~(Av) urethane polymers (A-iii)~(Av) with structures segregated in the central region of the main chain, derived from Laromer (registered trademark) PR9000. The values, along with the weight-average molecular weights, are shown in Table 1.

[0203] (Comparative Synthesis Example 1)

[0204] By changing Laromer (registered trademark) PR9000 to 0 mol and isophorone diisocyanate to 6 mol, the reaction was carried out at 80 °C for 8 hours in the same manner as the synthesis of (meth)acryloyloxy-terminated urethane polymers (Ai), yielding urethane polymers (cA-i) with terminal acryloyloxy groups. The weight-average molecular weight of the obtained urethane polymer (cA-i) was 42,000. See Table 1.

[0205] (Comparative Synthesis Example 2)

[0206] Except for changing the components and proportions as described in Table 1, the same procedure as for synthesizing the (meth)acryloyloxy-containing urethane polymer (Ai) was performed to obtain the urethane polymer (cA-ii) with terminal acryloyloxy groups. The resulting urethane polymer (cA-ii) had a weight-average molecular weight of 20,000, as shown in Table 1.

[0207] (Comparative Synthesis Example 3)

[0208] In a four-necked flask equipped with a thermometer, stirrer, dropping funnel, and cooling tube with a drying tube, 5 mol of isophorone diisocyanate (Desmojule I, manufactured by Sumitomo Chemical Co., Ltd.) and 5 mol of polypropylene glycol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) with hydroxyl groups at the ends (hydroxyl value 56 mg KOH / g) were added. The flask was then heated to 80°C and reacted for 2 hours. Next, 1 mol of Laromer PR9000 (manufactured by BASF) was added, and the reaction was carried out at 80°C for 6 hours to obtain a urethane prepolymer with isocyanate groups at both ends and Laromer PR9000 concentrated in the terminal regions.

[0209] Similar to the synthesis of the (meth)acryloyloxy-containing urethane polymer (Ai), the obtained urethane prepolymer was reacted with 2-hydroxyethyl acrylate. This resulted in a (meth)acryloyloxy-containing urethane polymer (cA-iii) with Laromer (registered trademark) PR9000 segregated in the terminal regions of the main chain. The resulting urethane polymer (cA-iii) had a weight-average molecular weight of 90,000. See Table 1.

[0210]

[0211] In Table 1, “PR9000” refers to the compound represented by formula (1) below. In formula (1), n ​​= 0.32~0.45.

[0212]

[0213] <Preparation of Adhesive Compositions>

[0214] The urethane polymer (A) containing olefin unsaturated groups, the monomer (B) containing olefin unsaturated groups, the photopolymerization initiator (C) and the plasticizer (D) were mixed according to the compositions described in Tables 2-3 and mixed at 25°C using a disperser to prepare the adhesive compositions of Examples 1-13 and Comparative Examples 1-10.

[0215] <Production of Protective Film>

[0216] Regarding Examples 1-13 and Comparative Examples 1-10, protective sheets with an optical PET film substrate on one side were prepared using the same method. First, using a coating machine, a prepared adhesive composition was coated onto a 75 μm thick optical PET film (Toyobo Co., Ltd. A4300). Then, a 75 μm thick PET release film (Toyobo Co., Ltd. E7006) was applied over the coated adhesive composition. Next, using an ultraviolet irradiation device (Igura Films, 3kW UV irradiation device, high-pressure mercury lamp), ultraviolet light was irradiated onto the sheet covered with the PET release film from the surface of the PET release film side, causing the adhesive composition to photocur. The irradiation distance was 25 cm, the lamp moving speed was 1.0 m / min, and the irradiation dose was 1000 mJ / cm². 2 The thickness of the cured adhesive layer was calculated by subtracting the thickness of the optical PET film (75 μm) and the thickness of the peeling PET film (75 μm) from the measured value using a dial indicator. The dial indicator's measuring surface was a circular plane with a diameter of 5 mm, and the measuring force was set to 0.8 N. In Examples 1-13 and Comparative Examples 1-10, the thickness of the adhesive layer was 75 μm.

[0217]

[0218] The compounds in the table use the following substances.

[0219] EHA: Compound name (2-ethylhexyl acrylate, manufactured by Toa Synthetic Co., Ltd.)

[0220] LA: Compound name (Lauryl acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.)

[0221] TMPTA: Compound name (Trimethylolpropane triacrylate M-309, manufactured by Toa Synthetic Co., Ltd.)

[0222] Irg-184: Compound name (1-hydroxycyclohexylphenyl ketone, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0223] IPM: Compound name (IPM, manufactured by Kao Corporation)

[0224] <Evaluation of Adhesive Compositions and Protective Sheets>

[0225] For the adhesive compositions and protective sheets of Examples 1-13 and Comparative Examples 1-10, the changes in gel fraction and water contact angle after placement under initial conditions and high temperature and humidity conditions were evaluated using the methods described below. Furthermore, the presence of contamination on the glass test plates after peeling off the protective sheets under high temperature and humidity conditions was evaluated using the methods described below. The results are shown in Tables 2-3.

[0226] (Gel fraction)

[0227] First, using a coating machine, the adhesive compositions of Examples 1-13 and Comparative Examples 1-10 were coated onto a 50 μm thick PET release film (HY-S10 manufactured by Higashiyama Film Co., Ltd.) to achieve a cured adhesive layer thickness of 75 μm. It should be noted that the method for confirming the thickness of the adhesive layer is the same as the measurement method described in the section on the production of the protective film.

[0228] Next, a 75μm thick PET release film (Toyobo Co., Ltd. E7006) was applied over the adhesive composition on the aforementioned PET release film. Then, using an ultraviolet (UV) irradiation device (Igura Films, 3kW UV irradiation device, high-pressure mercury lamp), UV light was irradiated onto the adhesive composition covered on both sides of the PET release film from one side of the 75μm thick PET release film, causing the adhesive composition to photocur. The UV irradiation distance was 25cm, the lamp moving speed was 1.0 m / min, and the irradiation dose was 1000mJ / cm². 2 .

[0229] The prepared sheet was cut into strips of 150mm × 80mm. The PET release films on both sides were peeled off from the cured adhesive composition to obtain the test samples. These test samples were immersed in 50ml of tetrahydrofuran at 25°C for 24 hours, and then dried at 80°C for 5 hours. The gel fraction under the initial conditions was calculated from the mass of the test samples before and after tetrahydrofuran immersion using the following formula (1). The results are shown in Tables 2-3.

[0230] Gel fraction (mass%) = [A / B] × 100 (1)

[0231] A: Determine the dried mass of the sample after impregnation with tetrahydrofuran (excluding the mass of tetrahydrofuran).

[0232] B: Determine the mass of the sample before it is impregnated with tetrahydrofuran.

[0233] Prepare another sample with the same conditions as the sample used in the above test, and place it in air at a temperature of 85°C and a relative humidity of 85% for 250 hours. Then, determine the gel rate after placing it under high temperature and high humidity conditions according to the same procedure as the gel rate determination above.

[0234] The changes in gel fraction under the initial conditions and after placement under the aforementioned high temperature and high humidity conditions were calculated using the following formula (2). The results are shown in Tables 2-3.

[0235] Change in gel fraction (Δ) = AB (2)

[0236] A: Gel fraction under initial conditions

[0237] B: Gel fraction after placement under high temperature and high humidity conditions

[0238] (Water contact angle)

[0239] The test plate, made of glass, was immersed overnight in an alkaline cleaning solution (3% Semiclean LGL, manufactured by Yokohama Resin) and then cleaned for 1 hour using an ultrasonic cleaner. Next, the test plate was immersed in ion-exchange water and cleaned twice for 30 minutes each time using an ultrasonic cleaner, followed by drying in air at 150°C for 2 hours. The water contact angle of the dried test plate surface was measured at 5 points on one sample using a contact angle meter (DMo-601, manufactured by Kyowa Interface Science Co., Ltd.), and the average value was used as a blank. Pure water was used. The protective sheets prepared in Examples 1-13 and Comparative Examples 1-10 were cut into strips of 25mm × 150mm, and the PET release film was peeled off. The entire exposed adhesive layer was pressed onto the cleaned and dried test plate, and a rubber roller was used to repeat the process once to prepare a test sample. This test sample was placed in an environment with an air temperature of 85°C and a relative humidity of 85% for 250 hours. Then, after peeling the protective film off the sample for testing, the water contact angle of the test plate surface made of glass plate was measured under the same procedure as the blank sample above.

[0240] The changes in water contact angle under the initial conditions and under the high temperature and humidity conditions were calculated using the blank water contact angle and the water contact angle after placement under the aforementioned high temperature and humidity conditions, using the following formula (3). The results are shown in Tables 2-3.

[0241] Water contact angle change (Δ) = BA (°) (3)

[0242] A: Water contact angle (°) in blank space

[0243] B: Water contact angle (°) after placement under high temperature and high humidity conditions.

[0244] (Contamination of the glass test plate)

[0245] Similar to the water contact angle test, the test sample was placed in an air environment at 85°C and 85% relative humidity for 250 hours. Then, after peeling off the protective film from the test sample, the surface of the glass test plate was observed at 400x magnification using a digital optical microscope (manufactured by Hylocks Co., Ltd., RH-2000) to check for contamination.

[0246] <Peel strength of protective sheet>

[0247] Cut the prepared protective sheet into 25mm × 150mm pieces and peel off the PET release film. Next, attach the exposed adhesive surface to the glass plate and roll it back and forth once with a 2kg rubber roller (width: approximately 50mm) to prepare the sample for testing.

[0248] Thirty minutes after the start of pressing, a tensile test in the 180° direction was performed at a peeling speed of 2.4 m / min, and the peel strength (g / 25 mm) of the protective sheet relative to the glass plate was determined according to JIS Z0237.

[0249] As shown in Table 2, it can be seen that in Examples 1-13, even under high temperature and high humidity conditions, the change in gel fraction of the cured adhesive composition was suppressed. Furthermore, regarding the evaluation of the test panel surface after the protective sheet was peeled off under high temperature and high humidity conditions, no visual contamination was observed, and the change in water contact angle was also suppressed to a low degree, indicating that contamination caused by the protective sheet was suppressed at a high level.

[0250] On the other hand, as shown in Table 3, it can be seen that Comparative Examples 2-10 exhibited significant variations in gel fraction or water contact angle, or showed signs of contamination of the test plates, thus failing to meet the required performance as protective sheets. The large variation in water contact angle suggests contamination of the test plate surface by the adhesive layer of the protective sheet, resulting in changes in the surface properties of the test plate. The large variation in gel fraction indicates significant contamination of the test plate, suggesting an increase in solvent-soluble components on the test plate surface due to hydrolysis of the adhesive layer, acid value degradation, etc., which is undesirable. Furthermore, a large variation in gel fraction signifies changes in the properties of the adhesive layer of the protective sheet, i.e., degradation, which is also undesirable.

[0251] Regarding Comparative Example 1, the protective film peeled off the glass plate due to decreased peel strength during placement under high temperature and humidity conditions, making it impossible to measure the change in water contact angle. In other words, it did not reach a level suitable for use as a protective film.

[0252] Industrial availability

[0253] According to the present invention, a urethane polymer containing olefinic unsaturated groups, capable of suppressing changes in the gel fraction of the cured product even under high temperature and high humidity conditions, a method for manufacturing the same, and an adhesive composition comprising the urethane polymer can be provided. Therefore, a protective sheet can be provided having an adhesive layer having cured as the aforementioned adhesive composition and not easily contaminating the adhered object.

Claims

1. A urethane polymer containing olefinically unsaturated groups, characterized in that, It is a urethane prepolymer that is the product of the reaction between polyoxyalkylene polyol (a1) and polyisocyanate (a2), and a urethane polymer containing olefinic unsaturated groups that is the product of the reaction between hydroxyl-containing olefinic unsaturated compound (a3-1) or isocyanate-containing olefinic unsaturated compound (a3-2). The polyisocyanate (a2) comprises a polyisocyanate containing an olefinic unsaturated group (a2-1) and a polyisocyanate not containing an olefinic unsaturated group (a2-2). The polyisocyanate (a2-1) structure, derived from the olefinically unsaturated group, is present at least in the central region of the backbone of the urethane polymer. The structures derived from the polyisocyanate containing olefinic unsaturated groups (a2-1) are biased in the central region of the main chain of the urethane polymer containing olefinic unsaturated groups, while the structures derived from the polyisocyanate without olefinic unsaturated groups (a2-2) are biased in the terminal region of the main chain of the urethane polymer containing olefinic unsaturated groups.

2. The urethane polymer containing olefinically unsaturated groups according to claim 1, The polyoxyalkylene polyol (a1) is a compound having two hydroxyl groups. The polyisocyanate (a2) is a compound having two or more isocyanate groups.

3. The urethane polymer containing olefinically unsaturated groups according to claim 1 or 2, The urethane polymer containing olefinic unsaturated groups is an urethane polymer containing (meth)acryloyloxy groups. The polyisocyanate (a2-1) containing olefinic unsaturated groups is a polyisocyanate (a2-1) containing (meth)acryloyloxy groups. The hydroxyl-containing olefinic unsaturated compound (a3-1) is a hydroxyl-containing (meth)acrylate. The isocyanate-containing olefinic unsaturated compound (a3-2) is an isocyanate-containing (meth)acrylate.

4. The urethane polymer containing olefinic unsaturated groups according to claim 1 or 2, wherein the weight-average molecular weight of the urethane polymer containing olefinic unsaturated groups is 30,000 to 250,000.

5. The urethane polymer containing olefinic unsaturated groups according to claim 1 or 2, wherein the number-average molecular weight of the polyoxyalkylene polyol (a1) is 500 to 5,000.

6. The urethane polymer containing olefinically unsaturated groups according to claim 1 or 2, The urethane polymer containing olefinic unsaturated groups is the reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the hydroxyl-containing olefinic unsaturated compound (a3-1). Relative to 1 mole of the total number of hydroxyl groups in the polyoxyalkylene polyol (a1), the total number of isocyanate groups in the polyisocyanate (a2) is 1.1 to 1.5 moles. The molar ratio (a2-1) / (a2-2) of the polyisocyanate containing olefinic unsaturated groups to the polyisocyanate without olefinic unsaturated groups is 0.03~0.

8.

7. The urethane polymer containing olefinically unsaturated groups according to claim 1 or 2, The urethane polymer containing olefinic unsaturated groups is the reaction product of the polyoxyalkylene polyol (a1), the polyisocyanate (a2), and the olefinic unsaturated compound containing isocyanate groups (a3-2). Relative to 1 mole of the total isocyanate groups in the polyisocyanate (a2), the total hydroxyl groups in the polyoxyalkylene polyol (a1) are 1.1 to 1.5 moles. The molar ratio (a2-1) / (a2-2) of the polyisocyanate containing olefinic unsaturated groups to the polyisocyanate without olefinic unsaturated groups is 0.03~0.

8.

8. The urethane polymer containing olefin unsaturated groups according to claim 1 or 2, wherein the polyisocyanate (a2-1) containing olefin unsaturated groups is a reaction product of an olefin unsaturated compound containing hydroxyl groups and a diisocyanate.

9. The method for preparing the urethane polymer containing olefinically unsaturated groups according to claim 1, characterized in that, A method for preparing a urethane polymer containing olefinic unsaturated groups by reacting a polyoxyalkylene polyol (a1) and a polyisocyanate (a2) in a reactor to generate a urethane prepolymer, and then reacting the urethane prepolymer with a hydroxyl-containing olefinic unsaturated compound (a3-1) or an isocyanate-containing olefinic unsaturated compound (a3-2). First, the polyoxyalkylene polyol (a1) is added to the reactor. Then, the polyisocyanate containing olefinic unsaturated groups (a2-1) and the polyisocyanate without olefinic unsaturated groups (a2-2) are added to the reactor separately. After the addition of the polyisocyanate containing olefin unsaturated groups (a2-1) is completed, the addition of the polyisocyanate without olefin unsaturated groups (a2-2) begins.

10. An adhesive composition, characterized in that... The product comprises the urethane polymer (A) containing an olefinically unsaturated group as described in any one of claims 1 to 8, the monomer (B) containing an olefinically unsaturated group, and the photopolymerization initiator (C).

11. The adhesive composition of claim 10, further comprising a plasticizer (D).

12. The adhesive composition according to claim 11, wherein, relative to a total of 100 parts by mass of the urethane polymer (A) containing olefinic unsaturated groups and the monomer (B) containing olefinic unsaturated groups, the urethane polymer (A) containing olefinic unsaturated groups is 30 to 70 parts by mass, the monomer (B) containing olefinic unsaturated groups 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.

13. A protective sheet having an adhesive layer on one side of a substrate, said adhesive layer being a cured product of the adhesive composition of any one of claims 10 to 12.

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