TW202409226A - Adhesive composition and protective sheet - Google Patents

Abstract

Provided is an adhesive composition that reduces the generation of cutting scraps and adhesive layer damage during cutting, and with which an adhesive layer having suitable peel strength and strength can be obtained. The adhesive composition according to the present invention contains a polyurethane (A), an ethylenically unsaturated group-containing monomer (B), and a photopolymerization initiator (C). The polyurethane (A) has a skeleton including a polyol-derived structure and a polyisocyanate structure, and has an ethylenically unsaturated group at a terminal end. The weight-average molecular weight of the polyurethane (A) in the adhesive composition is 3000-30,000.

Description

Adhesive composition and protective sheet

The invention relates to an adhesive composition and a protective sheet. This application claims priority based on Japanese Patent Application No. 2022-110520 filed in Japan on July 8, 2022, the contents of which are incorporated herein by reference.

Optical components such as LCDs and touch panels of smartphones, personal computers, and televisions use various optical films. In order to prevent contamination and damage during transportation, manufacturing, and inspection, a protective sheet (surface protection sheet) is generally laminated on the surface of these optical films. This protective sheet will be peeled off in subsequent steps such as assembly. Various urethane adhesives have been proposed as adhesives for such protective sheets.

For example, Patent Document 1 discloses an ultraviolet curable adhesive composition for protective films, which contains polyurethane (A) and an alkyl mono(meth)acrylate with an alkyl group having 6 to 18 carbon atoms. (B), multifunctional (meth)acrylate (C), plasticizer (D). The aforementioned polyurethane (A) is a reaction product of polyol (a1), polyisocyanate (a2), hydroxyl-containing (meth)acrylate (a3), and hydroxyl-containing photopolymerization initiator (a4) . [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2020-164840

[Problem to be solved by the invention]

These protective sheets can be cut into a desired shape with a cutting machine or the like in a step before or after being attached to the body. At this time, chips of the adhesive layer will be generated on the cross section of the protective sheet, which may contaminate the surface of the adhered object. In addition, when the laminating and peeling operations of protective sheets are repeated, or when external impacts are applied, the adhesive layer may be damaged and contaminate the adherend, or the adhesive layer may be insufficient in strength to transmit the impact to the adherend and be damaged. . In recent years, as display screens have become larger and panel parts and the like have become thinner, optical components themselves have become prone to breakage. Therefore, it is required that a protective sheet has moderate adhesiveness (peel strength) and can be peeled off with a lighter force (light peelability).

The present invention was made to solve the above-mentioned problems, and its object is to provide an adhesive composition that can reduce the generation of chips during cutting and damage to the adhesive layer, and has an adhesive that has appropriate peeling force and strength. layer. Another object of the present invention is to provide a protective sheet that reduces the generation of chips and damage to the adhesive layer during cutting, and has an adhesive layer with moderate peeling force and strength. [Means used to solve problems]

The present invention includes the following aspects. [1] An adhesive composition containing: polyurethane (A), an ethylenically unsaturated group-containing monomer (B), and a photopolymerization initiator (C), wherein the polyamine group Formate (A) is a polyurethane having a skeleton including a structure derived from polyol and a structure derived from polyisocyanate, and has an ethylenically unsaturated group at the terminal, and the aforementioned polyurethane ( The weight average molecular weight of A) is 3000~30000. [2] The adhesive composition according to [1], wherein the polyol is a polyoxyalkylene polyol with a number average molecular weight of 300 to 1800. [3] The adhesive composition according to [1] or [2], wherein the ethylenically unsaturated group equivalent of the polyurethane (A) is 900 to 3000 g/mol. [4] The adhesive composition according to any one of [1] to [3], wherein the concentration of the urethane bond of the polyurethane (A) is 1.0 to 5 mol/kg. [5] The adhesive composition according to any one of [1] to [4], wherein the polyurethane (A) has an ethylenically unsaturated group at a position other than the terminal. [6] The adhesive composition according to any one of [1] to [5], wherein the polyisocyanate includes a polyisocyanate containing an ethylenically unsaturated group and a polyisocyanate not containing an ethylenically unsaturated group. [7] The adhesive composition according to any one of [1] to [6], wherein the ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1), The aforementioned monofunctional (meth)acrylate (B1) is a chain alkyl (meth)acrylate having 6 to 18 carbon atoms. [8] The adhesive composition according to any one of [1] to [7], wherein the ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1) and Polyfunctional (meth)acrylate (B2). [9] The adhesive composition according to [8], which contains a monomer based on 100% by mass of the total of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). Functional (meth)acrylate (B1) is 5 to 89 mass%, and polyfunctional (meth)acrylate (B2) is contained in 0.1 to 30 mass%. [10] The adhesive composition according to [1], which contains polyurethane (A) and the ethylenically unsaturated group-containing monomer (B) in an amount of 100% by mass based on the total of 100% by mass. 10 to 90 mass % of urethane (A), and 10 to 90 mass % of ethylenically unsaturated group-containing monomer (B). [11] The adhesive composition according to any one of [1] to [9], further containing a plasticizer (D). [12] The adhesive composition according to [11], which contains light based on 100% by mass of the total of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). The polymerization initiator (C) is 0.05 to 5 parts by mass, and the plasticizer (D) mentioned above is contained in 1 to 30 parts by mass. [13] A hardened product of the adhesive composition according to [1] or [11]. [14] The hardened material described in [13] has an elongation at break of 92 to 300% and a breaking strength of 300 to 800 g/mm ² . [15] A protective sheet having a base material and an adhesive layer formed on one surface of the base material and including the cured product according to [13]. [Effects of the invention]

According to the present invention, an adhesive composition can be provided, which can reduce the generation of chips during cutting and the damage of the adhesive layer, and has an appropriate peeling force and strength of the adhesive layer. In addition, a protective sheet can be provided, which can reduce the generation of chips during cutting and the damage of the adhesive layer, and has an appropriate peeling force and strength of the adhesive layer.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments shown below. Here, the so-called (meth)acrylyl group refers to one selected from the group represented by the chemical formula CH ₂ =CH-CO- and the functional group represented by the chemical formula CH ₂ =C(CH ₃ )-CO- above. The (meth)acryloxy group refers to a group selected from the group represented by the chemical formula CH ₂ =CH-CO-O- and the functional group represented by the chemical formula CH ₂ =C(CH ₃ )-CO-O- More than one of them.

＜Adhesive composition＞ The adhesive composition of this embodiment contains polyurethane (A), an ethylenically unsaturated group-containing monomer (B), and a photopolymerization initiator (C). Plasticizer (D) may also be included if necessary. By using the adhesive composition of this embodiment as the adhesive layer of the protective sheet, the generation of chips during cutting and damage to the adhesive layer can be reduced. Multiple factors are considered to have a complex relationship with the occurrence of chips and damage to the adhesive layer. Examples include various external factors including the type and thickness of the base material and adhesive layer, the type and conditions of the steps when using the protective sheet, the type of the object to be adhered, and the type of impact from the outside. Among these factors, by using a combination of components that are significantly related to the occurrence of chips and breakage of the adhesive layer, the chips and breakage of the adhesive layer can be effectively reduced.

[Polyurethane (A)] The polyurethane (A) used in the present embodiment is a polyurethane having a skeleton including a structure derived from a polyol and a structure derived from a polyisocyanate, and having an ethylenically unsaturated group at the terminal. The so-called "structure derived from a polyol" refers to a structure introduced by using a polyol of a compound having two or more hydroxyl groups as a raw material for polyurethane. The so-called "structure derived from a polyisocyanate" refers to a structure introduced by using a polyisocyanate of a compound having two or more isocyanate groups as a raw material for polyurethane. As a method for introducing an ethylenic unsaturated group at the terminal, there are: a method of adding an ethylenic unsaturated compound containing a hydroxyl group to an isocyanate-terminated urethane prepolymer, and a method of adding an ethylenic unsaturated compound containing an isocyanate group to a hydroxyl-terminated urethane prepolymer. From the viewpoint of reducing the peeling force when peeling the protective sheet from the body, the polyurethane (A) may also have an ethylenic unsaturated group at a position other than the terminal as required. As a method for introducing an ethylenic unsaturated group at a position other than the terminal, there are: a method of using a polyol containing an ethylenic unsaturated group and a polyisocyanate containing an ethylenic unsaturated group as a raw material for synthesizing the polyurethane (A).

"Polyol" The polyol used in this embodiment is a compound having no isocyanate group but having two or more hydroxyl groups. From the viewpoint of suppressing gelation during synthesis and making the polymer uniformly elongated, the number of hydroxyl groups possessed by the polyol is preferably two.

From the viewpoint of increasing the elongation of the adhesive layer and more effectively suppressing the generation of chips during cutting, preferred polyols include polyoxyalkylene polyols having polyoxyalkylene chains. In particular, when the base material constituting the protective sheet is hard or thick, chips and breakage are likely to occur due to the brittleness of the adhesive layer during cutting or external impact. As a polyol, Preferably, polyoxyalkylene polyol is used. The carbon number of the alkylene chain constituting the polyoxyalkylene chain is preferably 2 to 8, more preferably 2 to 6, and still more preferably 2 to 4. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, and the like. Among the polyoxyalkylene polyols, polyoxyalkylene glycol is preferably used, polypropylene glycol and polytetramethylene glycol are particularly preferably used, and polypropylene glycol is further preferably used.

Note that the polyoxyalkylene polyol may contain two or more alkylene chains. Furthermore, the polyurethane (A) may have a structure in which structures derived from two or more different polyoxyalkylene polyols are mixed and bonded with polyisocyanate.

The number average molecular weight of the polyoxyalkylene polyol is preferably 300 to 1800, more preferably 330 to 1500, and further preferably 360 to 1200. When the number average molecular weight of the polyoxyalkylene polyol is 300 or more, the peeling force when peeling the protective sheet from the adhered object can be reduced. When the number average molecular weight of the polyoxyalkylene polyol is 1800 or less, the weight average molecular weight of the polyurethane (A) can be reduced to obtain an adhesive layer with good hardness. Therefore, the generation of chips and damage can be reduced in the case of external impact on the protective sheet, as well as the force applied during cutting, attachment and peeling operations.

The hydroxyl value of the polyoxyalkylene polyol is preferably 30 to 400 mgKOH/g, more preferably 50 to 350 mgKOH/g, and further preferably 80 to 300 mgKOH/g. When the hydroxyl value is 30 mgKOH/g or more, there is an advantage that the generation of chips during cutting can be reduced. When the hydroxyl value is 300 mgKOH/g or less, there is an advantage that a cured product having moderate adhesive force can be obtained. Note that the hydroxyl value is measured by method B according to JIS K1557-1.

From the perspective of reducing the peeling force when peeling the protective sheet from the adhered object, other preferred examples of polyols include: polyols containing ethylenic unsaturated groups. In particular, under any of the following conditions, polyols containing ethylenic unsaturated groups are preferred. The above conditions are conditions that require lower peeling from the perspective of the strength of the adhered object such as miniaturization and film formation of the adhered object, or conditions that are easy to cause chips and damage due to insufficient crosslinking and insufficient cohesion of the adhesive layer due to high peeling strength. As the ethylenic unsaturated group possessed by the polyol containing ethylenic unsaturated groups, there can be listed: (meth)acryloyloxy, vinyl, allyl, etc. From the perspective of reducing the peeling force, (meth)acryloyloxy is preferred. By using a polyol containing ethylenic unsaturated groups, ethylenic unsaturated groups can be introduced into a part other than the terminal of the polyurethane (A) (in the molecular chain). Thereby, the peeling strength of the adhesive layer can be reduced, especially the peeling strength during high-speed peeling. In addition, by improving the crosslinking density and cohesive force of the adhesive layer, it is possible to suppress chipping and damage.

As a polyol containing a (meth)acryloyloxy group, for example, the epoxy group of an epoxy compound containing a (meth)acryloyloxy group can be synthesized as a compound having two hydroxyl groups by subjecting the epoxy group to an acid-catalyzed cleavage reaction. As an epoxy compound containing a (meth)acryloyloxy group, for example, there can be listed: glycidyl (meth)acrylate, 3,4-epoxyepoxyhexylmethyl (meth)acrylate, (meth)acrylate having an alicyclic epoxy group and its lactone adduct, 3,4-epoxyepoxyhexylmethyl-3',4'-epoxyepoxyhexanecarboxylate, epoxide of dicyclopentenyl (meth)acrylate, and epoxide of dicyclopentenyloxyethyl (meth)acrylate. In addition, as a polyol containing a (meth)acryloyloxy group, a compound obtained by adding a carboxyl group-containing ethylenically unsaturated compound such as (meth)acrylic acid to a polyepoxide such as 1,6-hexanediol diglycidyl ether can be used.

As the polyol containing a (meth)acryloyloxy group, commercial products can be used. Examples of the commercial products include glyceryl monomethacrylate obtained by cleaving the epoxy group of glycidyl methacrylate (Blemmer (registered trademark) GLM manufactured by NOF Corporation), and acrylic acid adduct of 1,6-hexanediol diglycidyl ether (Ripoxy (trademark) SP-16LDA manufactured by Showa Denko K.K.).

These polyols may be used alone or in combination of two or more. From the viewpoint of achieving a balance among multiple properties such as suppressing chip generation during cutting and reducing peeling force, it is preferred to use a polyol containing an ethylenically unsaturated group and a polyoxyalkylene polyol in combination. The ratio (molar ratio) of the polyol containing an ethylenically unsaturated group/polyoxyalkylene polyol is preferably 0.03 to 0.8, more preferably 0.08 to 0.7, further preferably 0.1 to 0.6, and particularly preferably 0.1 to 0.4.

"Polyisocyanate" The polyisocyanate used in this embodiment is not particularly limited as long as it is a compound that does not have a hydroxyl group and has two or more isocyanate groups. From the perspective of suppressing gelation during synthesis and making the polymer uniformly elongated, the number of isocyanate groups possessed by the polyisocyanate is preferably two.

Examples of the polyisocyanate include polyisocyanates not containing an ethylenically unsaturated group, such as toluene diisocyanate and hydrogenates thereof, xylene diisocyanate and hydrogenates thereof, diphenylmethane diisocyanate and hydrogenates thereof, 1,5-naphthalene diisocyanate and hydrogenates thereof, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornane diisocyanate. Among them, from the viewpoint of facilitating reaction control during synthesis of polyurethane (A) and imparting rigidity to the adhesive, polyisocyanates having a cyclic hydrocarbon structure are preferred, more preferably at least one selected from isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornane diisocyanate, and further preferably isophorone diisocyanate.

From the viewpoint of reducing the peeling force when peeling the protective sheet from the adhered object, the polyisocyanate is preferably a polyisocyanate containing an ethylenically unsaturated group. In particular, under any of the following conditions, the polyol is preferably a polyol containing an ethylenically unsaturated group. The above conditions are conditions that require lower peeling from the viewpoint of the strength of the adhered object such as miniaturization and thin filmization of the adhered object, and conditions that easily generate chips and damage due to insufficient crosslinking and insufficient cohesion of the adhesive layer due to high peeling strength. As the ethylenic unsaturated group of the polyisocyanate containing ethylenic unsaturated groups, there can be listed: (meth)acryloyloxy, vinyl, allyl, etc. From the viewpoint of reducing the peeling force, (meth)acryloyloxy is preferred. By using the polyisocyanate containing ethylenic unsaturated groups, the ethylenic unsaturated groups can be introduced into the part other than the terminal of the polyurethane (A) (in the molecular chain). Thereby, the peeling strength of the adhesive layer can be reduced, especially the peeling strength during high-speed peeling can be reduced. In addition, by improving the crosslinking density and cohesive force of the adhesive layer, it is possible to suppress chipping and damage.

Examples of polyisocyanates containing a (meth)acryloyloxy group include: reaction products of (meth)acrylates containing a hydroxyl group and polyisocyanates. According to the methods described in Japanese Unexamined Patent Publication No. 2002-533542 and Japanese Patent Application Laid-Open No. 2012-111851, the polyisocyanates can be obtained by synthesizing compounds having an allophanate bond through urethanization and allophanation. Specifically, examples of (meth)acrylates containing a hydroxyl group include: compounds identical to the (meth)acrylates containing a hydroxyl group exemplified as the ethylenically unsaturated compound containing a hydroxyl group as a raw material for the polyurethane (A) described later. Examples of polyisocyanates include compounds identical to the aforementioned compounds. Among them, preferably, a compound containing an allophanate bond obtained by reacting a (meth)acrylate containing a hydroxyl group with an excess of diisocyanate. More preferably, a compound containing an allophanate bond obtained by reacting a hydroxyalkyl (meth)acrylate with an excess of alkylene diisocyanate. In addition, further preferably, one or more selected from 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and one or more selected from hexamethylene diisocyanate and trimethylhexamethylene diisocyanate are allophanated to produce a reaction product.

Commercially available polyisocyanates containing (meth)acryloxy groups can be used. Examples of the commercially available products include BASF's Laromer (registered trademark) PR9000, which is a reaction product of 2-hydroxyethylacrylate and hexamethylene diisocyanate and contains an allophanate bond.

These polyisocyanates may be used alone or in combination of two or more. From the viewpoint of achieving a balance among multiple properties such as suppressing the generation of chips during cutting and reducing the peeling force, it is preferred to use a polyisocyanate containing an ethylenic unsaturated group and a polyisocyanate not containing an ethylenic unsaturated group in combination. The ratio (molar ratio) of polyisocyanate containing an ethylenic unsaturated group/polyisocyanate not containing an ethylenic unsaturated group is preferably 0.03 to 0.8, more preferably 0.08 to 0.7, further preferably 0.1 to 0.6, and particularly preferably 0.1 to 0.4.

When an isocyanate group-terminated urethane prepolymer is obtained, the total amount of isocyanate groups of the polyisocyanate is preferably 1.05 to 1.8 moles relative to 1 mol of the total amount of hydroxyl groups of the polyol. More preferably, it is 1.1~1.7, and further more preferably, it is 1.15~1.6. As long as the total amount of isocyanate groups is 1.05 mol or more, the weight average molecular weight of the polyurethane (A) can be within an appropriate range.

When a hydroxyl-terminated urethane prepolymer is obtained, the total amount of hydroxyl groups of the polyol is preferably 1.05 to 1.8 moles relative to 1 mole of the total amount of isocyanate groups of the polyisocyanate, and more preferably 1.05 to 1.8 moles. Preferably, it is 1.1~1.7, and further more preferably, it is 1.15~1.6. As long as the total amount of hydroxyl groups is 1.05 mol or more, the weight average molecular weight of the polyurethane (A) can be within an appropriate range.

[Ethylenically unsaturated compounds containing hydroxyl groups] The ethylenic unsaturated compound containing a hydroxyl group is not particularly limited as long as it does not have an isocyanate group and has a hydroxyl group and an ethylenically unsaturated group. From the viewpoint of hardening properties, the ethylenically unsaturated group is preferably at least one selected from the group consisting of vinyl, allyl and (meth)acryloxy groups, preferably (methyl) Acryloxy.

"(Meth)acrylate containing hydroxyl group" The hydroxyl-containing ethylenically unsaturated compound of this embodiment is preferably a hydroxyl-containing (meth)acrylate. The hydroxyl-containing (meth)acrylate is not particularly limited as long as it does not have an isocyanate group and has a hydroxyl group and a (meth)acryloxy group. Examples include: (meth)acrylic acid hydroxyalkyl groups such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. Esters; such as 1,3-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, 3-methylpentanediol mono(meth)acrylate, etc. Monohydric alcohols having (meth)acrylyl groups from various polyhydric alcohols, etc. From the viewpoint of reactivity with the isocyanate group of polyisocyanate and photocurability as an adhesive composition, hydroxyalkyl (meth)acrylate is more preferred, and an alkyl group having a carbon number of 2 to 6 is more preferred. Hydroxyalkyl (meth)acrylate, more preferably 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate. These may be used individually by 1 type, and may use 2 or more types together.

"Compounds with hydroxyl and vinyl groups" The ethylenic unsaturated compound containing a hydroxyl group in this embodiment may be a compound that does not have an isocyanate group but has a hydroxyl group and a vinyl group. Examples of compounds having a hydroxyl group and a vinyl group include polyalkylene glycol monovinyl ether, hydroxyalkyl vinyl ether, hydroxycarboxylic acid vinyl ester, hydroxyalkyl vinyl ester, and the like.

Examples of polyalkylene glycol monovinyl ethers include diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, and the like. Examples of hydroxyalkyl vinyl ethers include 4-hydroxybutyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, and the like. Examples of hydroxyl carboxylic acid vinyl esters include hydroxyl vinyl acetate, hydroxyl vinyl propionate, hydroxyl vinyl butyrate, hydroxyl vinyl hexanoate, and 4-hydroxycyclohexyl vinyl acetate. Examples of hydroxyl alkyl vinyl esters include hydroxyl cyclohexyl vinyl carboxylate, and the like.

"Compounds having hydroxyl and allyl groups" The ethylenically unsaturated compound containing a hydroxyl group in this embodiment may be a compound having a hydroxyl and an allyl group without an isocyanate group. Examples of compounds having a hydroxyl and an allyl group include hydroxyalkyl allyl ethers, hydroxyalkyl carboxylic acid allyl esters, hydroxyalkyl allyl esters, and the like.

Examples of hydroxyalkyl allyl ethers include 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, glycerol monoallyl ether, 4-hydroxycyclohexyl allyl ether, etc. Examples of hydroxycarboxylic acid allyl esters include hydroxyacetic acid allyl ester, hydroxypropionic acid allyl ester, hydroxybutyric acid allyl ester, hydroxyhexanoic acid allyl ester, 4-hydroxycyclohexyl acetate allyl ester, etc. Examples of hydroxyalkyl allyl esters include hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, hydroxyisobutyl allyl ester, hydroxycyclohexyl allyl ester, etc.

The ratio of the hydroxyl-containing ethylenically unsaturated compound is preferably set so that the total amount of hydroxyl groups in the polyol and the hydroxyl-containing ethylenically unsaturated compound is equal to the total amount of isocyanate groups in the polyisocyanate. Being equal means that the difference between the molar numbers of the two is preferably 0.05 mole or less, more preferably 0.01 mole or less. As long as the difference in molar number between the two is 0.05 mol or less, the amount of unreacted monomer can be sufficiently reduced. Since the amount of unreacted hydroxyl and isocyanate groups can be sufficiently reduced, the time-lapse of the cured product can be suppressed. changes in gel fraction.

[Ethylenically unsaturated compounds containing isocyanate groups] As ethylenically unsaturated compounds containing isocyanate groups, there are no particular restrictions as long as they do not have a hydroxyl group but have an isocyanate group and an ethylenically unsaturated group. Ethylenically unsaturated compounds containing isocyanate groups are preferably (meth)acrylates containing isocyanate groups. For example, alkyl isocyanate (meth)acrylates such as 2-isocyanate (meth) ethyl acrylate, 2-isocyanate (meth) propyl acrylate, 4-isocyanate (meth) butyl acrylate, 6-isocyanate (meth) hexyl acrylate, etc. can be cited. From the perspective of reactivity with the hydroxyl group of the polyoxyalkylene polyol (a1) and the photocurability of the adhesive composition, an isocyanate (meth) alkyl ester having an alkyl group with 2 to 6 carbon atoms is preferred, and 2-isocyanate (meth) ethyl acrylate and 4-isocyanate (meth) butyl acrylate are more preferred. These can be used alone or in combination of two or more.

The ratio of the aforementioned ethylenically unsaturated compound containing an isocyanate group is preferably set in such a way that the total amount of the isocyanate groups of the polyisocyanate and the isocyanate groups of the ethylenically unsaturated compound containing an isocyanate group is equal to the total amount of the hydroxyl groups of the polyol. Equal means that the difference in the molar number of the two is preferably 0.05 mol or less, and more preferably 0.01 mol or less. As long as the difference in the molar number of the two is 0.05 mol or less, the amount of unreacted monomers can be sufficiently reduced. Since the amount of unreacted hydroxyl groups and isocyanate groups can be sufficiently reduced, the change in the gel fraction over time when the cured product is formed can be suppressed.

The weight average molecular weight of polyurethane (A) is 3000~30000, preferably 5000~28000, and more preferably 6000~25000. When the weight average molecular weight is 3000 or more, the cured product of the adhesive composition has sufficient flexibility, and the cured product has sufficient lamination properties as a protective sheet of the adhesive layer. When the weight average molecular weight is 3000 or less, it has appropriate hardness as an adhesive layer, suppresses the generation of chips during cutting, and can reduce the damage to the adhesive layer, damage to the adhered object, and contamination caused by external impact. The weight average molecular weight of polyurethane (A) can be in the range of 3000 to less than 10000. In this case, the coating film surface strength can be relatively high by increasing the proportion of the polyurethane (A) in the adhesive composition while maintaining the coating properties of the adhesive composition.

The concentration of urethane bonds of the polyurethane (A) is preferably 1.0 to 5 mol/kg, more preferably 1.5 to 5 mol/kg, and further preferably 1.85 to 3.5 mol/kg. When the concentration of urethane bonds is 1.0 mol/kg or more, the adhesive layer has a moderate elongation and can have good hardness and tensile strength. When the concentration of urethane bonds is 5 mol/kg or less, the protective sheet has good low peeling properties and can prevent damage to the adhered object when being peeled off from the adhered object.

The ethylenically unsaturated group equivalent of the polyurethane (A) is preferably 900~3000g/mol, more preferably 950~2700g/mol, further preferably 1000~2500g/mol, further preferably 1100~ 2300g/mol. When the ethylenically unsaturated group equivalent is above 900g/mol, the adhesive layer has good flexibility and elongation. When the ethylenically unsaturated group equivalent is less than 3000g/mol, the adhesive layer has good hardness and tensile strength.

The lower limit of the ethylene unsaturated group equivalent of polyurethane (A) is preferably 900 g/mol or more, more preferably 950 g/mol or more, further preferably 1000 g/mol or more, and further preferably 1100 g/mol or more. When the ethylene unsaturated group equivalent is 900 g/mol or more, the adhesive layer has good flexibility and elongation. The upper limit of the ethylene unsaturated group equivalent of polyurethane (A) is preferably 3000 g/mol or less, more preferably 2700 g/mol or less, further preferably 2500 g/mol or less, and further preferably 2300 g/mol. When the ethylene unsaturated group equivalent is 3000 g/mol or less, the adhesive layer has good hardness and tensile strength. The above upper and lower limits can be combined arbitrarily.

The content of the polyurethane (A) is preferably 10 to 90 mass %, more preferably 25 to 80 mass %, further preferably 35 to 75 mass %, further more preferably 40 to 70 mass % relative to the total of 100 mass % of the polyurethane (A) and the monomer (B) containing an ethylenically unsaturated group. When the content of the polyurethane (A) is 10 mass % or more, the elongation and tensile strength of the adhesive layer are good. When the content of the polyurethane (A) is 90 mass % or less, the low peeling property as a protective sheet is good.

The lower limit of the content of polyurethane (A) is preferably 10% by mass relative to 100% by mass of the total of polyurethane (A) and ethylenically unsaturated group-containing monomer (B) % or more, more preferably 25 mass % or more, further preferably 35 mass % or more, still more preferably 40 mass % or more. When the content of the polyurethane (A) is 10% by mass or more, the adhesive layer has good elongation and tensile strength. The upper limit of the content of polyurethane (A) is preferably 90 mass % relative to 100 mass % of the total of polyurethane (A) and ethylenically unsaturated group-containing monomer (B). % or less, more preferably 80 mass% or less, further preferably 75 mass% or less, still more preferably 70 mass% or less. When the content of the polyurethane (A) is 90% by mass or less, the protective sheet has good low peelability. The above-mentioned upper limit value and lower limit value can be combined arbitrarily.

[Ethylenically unsaturated group-containing monomer (B)] The ethylenically unsaturated group-containing monomer (B) is not particularly limited as long as it is a monomer having an ethylenically unsaturated group. From the viewpoint of curability, it is preferable to have a vinyl group or a (meth)acrylyl group, and it is more preferable to have a (meth)acrylyl group. Among them, the monomer (B) containing an ethylenically unsaturated group is preferably a monomer containing a monofunctional (methyl ) Acrylate (B1). Furthermore, the ethylenically unsaturated group-containing monomer (B) may optionally contain a polyfunctional (meth)acrylate (B2) from the viewpoint of protecting the low peelability of the sheet and improving the hardness and tensile strength. The term "monofunctional" means having only one (meth)acryloxy group, and the term "polyfunctional" means having a plurality of (meth)acryloxy groups.

Examples of the monofunctional (meth)acrylate (B1) include alkyl (meth)acrylates, cyclic alkyl (meth)acrylates, alkoxy alkyl (meth)acrylates, alkoxy (poly)alkylene glycol (meth)acrylates, hydroxyl group-containing (meth)acrylates, carboxyl group-containing (meth)acrylates, fluorinated alkyl (meth)acrylates, dialkylaminoalkyl (meth)acrylates, (meth)acrylamides, and epoxy group-containing (meth)acrylates.

Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, n-hexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, lauryl (meth)acrylate, and tridecyl (meth)acrylate.

Examples of the cyclic alkyl (meth)acrylate include cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isoborneol (meth)acrylate, norbornenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentyl (meth)acrylate, dicyclopentyloxyethyl (meth)acrylate, tricyclodecanedihydroxymethyl di(meth)acrylate, and the like.

Examples of alkoxy(meth)acrylic acid alkyl esters include: (meth)acrylic acid ethoxyethyl ester, (meth)acrylic acid methoxyethyl ester, (meth)acrylic acid butoxyethyl ester, 2-Methoxyethoxy(meth)ethyl acrylate, 2-ethoxyethoxy(meth)ethyl acrylate, etc.

Examples of alkoxy (poly)alkylene glycol (meth)acrylate include methoxydiethylene glycol (meth)acrylate and ethoxydiethylene glycol (meth)acrylate. , methoxydipropylene glycol (meth)acrylate, etc.

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

Examples of the carboxyl group-containing (meth)acrylate include (meth)acrylic acid and β-carboxyethyl (meth)acrylate.

Examples of the fluorinated alkyl (meth)acrylate include octafluoropentyl (meth)acrylate and the like.

Examples of the dialkylaminoalkyl (meth)acrylate include N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate.

Examples of the (meth)acrylamide include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropylacrylamide, N-hexyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, (meth)acryloylmorpholine, and diacetoneacrylamide.

Examples of the epoxy group-containing (meth)acrylate include glycidyl (meth)acrylate and the like.

Among these, from the viewpoint of reducing chips when cutting the protective sheet, alkyl (meth)acrylate is preferred, and alkyl (meth)acrylate having a carbon number of 6 to 18 is more preferred. More specifically, preferred are 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate, isooctyl(meth)acrylate, isostearyl(meth)acrylate, and (meth)acrylate. ) isocamphenyl acrylate, more preferably 2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate. In addition, the monofunctional (meth)acrylate (B1) may be composed of one type of compound or two or more types of compounds.

As the polyfunctional (meth)acrylate (B2), an ester compound of a polyol compound and (meth)acrylic acid is preferred, and a 3- to 6-functional (meth)acrylate is more preferred. Examples include polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. Ester, tripropylene glycol di(meth)acrylate, hydroxypivalate neopentyl glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylalantoin Di(meth)acrylate, α,ω-di(meth)acrylate bisdiethylene glycol phthalate, trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxy Chemical tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanedi Alcohol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diacryloyloxyethyl phosphate, dipentaerythritol trihydroxy(meth)acrylate, pentaerythritol tetra(methyl)acrylate Acrylic etc.

Among these, from the viewpoint of suppressing the decrease in the peel strength of the protective sheet, 1,6-hexanediol di(meth)acrylate, trihydroxymethylpropane tri(meth)acrylate, trihydroxymethylpropane ethoxylate tri(meth)acrylate, dipentaerythritol trihydroxy(meth)acrylate, and pentaerythritol tetra(meth)acrylate are more preferred, and trihydroxymethylpropane tri(meth)acrylate and trihydroxymethylpropane ethoxylate tri(meth)acrylate are further preferred. In addition, the multifunctional (meth)acrylate (B2) may be composed of one type of compound or may be composed of two or more types of compounds.

The monomer (B) containing an ethylenically unsaturated group may have an ethylenically unsaturated group-containing monomer (B3) other than the components (B1) and (B2). Examples of the monomer (B3) containing an ethylenically unsaturated group other than the components (B1) and (B2) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, N-vinyl pyridine, N-vinyl pyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexyl methyl vinyl ether, triethylene glycol monovinyl ether or diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, and the like.

The content of the monomer (B) containing an ethylenic unsaturated group is preferably 10 to 90% by mass, more preferably 20 to 75% by mass, further preferably 25 to 65% by mass, and further more preferably 30 to 60% by mass, relative to the total of 100% by mass of the polyurethane (A) and the monomer (B) containing an ethylenic unsaturated group. When the content of the monomer (B) containing an ethylenic unsaturated group is 10% by mass or more, the low peeling property as a protective sheet is good. When the content of the monomer (B) containing an ethylenic unsaturated group is 90% by mass or less, the elongation and tensile strength of the adhesive layer are good.

The lower limit of the content of the monomer (B) containing an ethylenic unsaturated group relative to the total of 100 mass % of the polyurethane (A) and the monomer (B) containing an ethylenic unsaturated group is preferably 10 mass % or more, more preferably 20 mass % or more, further preferably 25 mass % or more, and further preferably 30 mass % or more. When the content of the monomer (B) containing an ethylenic unsaturated group is 10 mass % or more, the low peeling property as a protective sheet is good. The upper limit of the content of the monomer (B) containing an ethylenic unsaturated group is preferably 90% by mass or less, more preferably 75% by mass or less, further preferably 65% by mass or less, and further preferably 60% by mass or less, relative to the total of 100% by mass of the polyurethane (A) and the monomer (B) containing an ethylenic unsaturated group. When the content of the monomer (B) containing an ethylenic unsaturated group is 90% by mass or less, the low peeling property as a protective sheet is good. The above upper limit and lower limit can be arbitrarily combined.

When the ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2), compared to the aforementioned polyurethane ( The content of the monofunctional (meth)acrylate (B1) is preferably 5 to 89 mass %, more preferably 15 to 74 mass % of the total 100 mass % of A) and the aforementioned ethylenically unsaturated group-containing monomer (B). %, more preferably 25 to 57 mass %. When the content of the monofunctional (meth)acrylate (B1) is 5% by mass or more, the protective sheet has good low peelability. When the content of the monofunctional (meth)acrylate (B1) is 89% by mass or less, the adhesive has a moderate viscosity, and application when forming an adhesive sheet becomes easy. The content of the polyfunctional (meth)acrylate (B2) is preferably 0.1~ 30 mass%, more preferably 1 to 20 mass%, further preferably 3 to 15 mass%. When the content of the monofunctional (meth)acrylate (B1) is 0.1% by mass or more, the generation of chips and damage to the adhesive layer are suppressed, and the protective sheet has good low peelability. When the content of the monofunctional (meth)acrylate (B1) is 30% by mass or less, the adhesive layer has good elongation.

[Photopolymerization initiator (C)] The photopolymerization initiator (C) is not particularly limited as long as it generates radicals by light irradiation, and examples thereof include carbonyl-based photopolymerization initiators, thioether-based photopolymerization initiators, Cylphosphine oxides, quinone-based photopolymerization initiators, sulfonic acid chloride-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, etc.

Examples of carbonyl photopolymerization initiators include benzophenone, benzyl, 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, michler's ketone, benzoin methyl ether, benzoin isobutyl ether, and benzoin methyl ether. ether, benzoin n-butyl ether, benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, methyl benzoylformate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one, and the like.

Examples of the thioether-based photopolymerization initiator include diphenyl disulfide, bibenzyl disulfide, tetraethylthiuram disulfide, tetramethylammonium monosulfide, and the like.

Examples of the acylphosphine oxides include 2,4,6-trimethylbenzyldiphenylphosphine oxide and 2,4,6-trimethylbenzylphenylethoxyphosphine oxide.

Examples of the quinone-based photopolymerization initiator include benzoquinone, anthraquinone and the like.

Examples of the sulfonic acid chlorine-based photopolymerization initiator include 2-naphthalenesulfonyl chloride and the like.

Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, and the like.

Among these exemplified compounds, from the viewpoint of the transparency of the adhesive layer obtained by curing the adhesive composition, carbonyl photopolymerization initiators and acylphosphine oxides are preferred, and 1-hydroxyl is more preferred. Cyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide. In addition, the photopolymerization initiator (C) may be composed of one type of compound or two or more types of compounds.

The content of the photopolymerization initiator (C) is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and further preferably 0.3 to 1 part by mass, relative to 100% by mass of the total of the polyurethane (A) and the monomer (B) containing an ethylenically unsaturated group. As long as the content of the photopolymerization initiator (C) is 0.05 parts by mass or more, the adhesive composition can have sufficient photocurability. When the content of the photopolymerization initiator (C) is 5 parts by mass or less, contamination of the object to be adhered to can be suppressed when the protective sheet is peeled off.

[Plasticizer (D)] As the plasticizer (D), known substances can be used without particular limitation. For example, fatty acid esters can be preferably used. The plasticizer (D) can improve the layering property (wetting property) and bubble removal property (removal property of bubbles trapped during lamination) of the protective sheet.

Examples of fatty acid esters include monobasic acids having 8 to 18 carbon atoms, esters of polybasic acids and branched-chain alcohols having 18 or less carbon atoms, unsaturated fatty acids having 14 to 18 carbon atoms, or branched fatty acids. Esters of acids and tetravalent alcohols, etc. Preferable specific examples of the fatty acid ester include ethylhexyl stearate.

When using a plasticizer (D), its content is preferably 1 to 30 parts by mass relative to 100% by mass of the total of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). More preferably, it is 5-25 parts by mass, and still more preferably, it is 10-23 parts by mass. When the content of the plasticizer (D) is 1 part by mass or more, the addition of plasticization can be expected to improve the lamination properties (wetness) and bubble removable properties (removal of air bubbles sandwiched during lamination) of the protective sheet. The effect brought about by agent (D). When the content of the plasticizer (D) is 30 parts by mass or less, contamination of the adherend when the protective sheet is peeled off can be sufficiently suppressed.

[Solvent] The adhesive composition of the present embodiment, because it contains the monomer (B) containing an ethylenically unsaturated group as a low molecular weight component, can be adjusted to a coatable viscosity without adding a solvent. That is, the adhesive composition can contain substantially no solvent. In this case, when manufacturing a protective sheet, the step of heating and drying the solvent can be omitted, thereby improving productivity. In particular, when manufacturing a protective sheet with a film thickness exceeding 50 μm, the adhesive composition preferably does not substantially contain the solvent. The meaning of "substantially not containing" in the present invention means that the content of the aforementioned solvent in the adhesive composition of the present invention is 0~1 mass%, preferably 0~0.5 mass% or less, and more preferably 0~0.1 mass% or less. For the purpose of adjusting the viscosity during application, a solvent may be added to the adhesive composition. The solvent may be appropriately selected according to other components contained in the adhesive composition, and an organic solvent is preferred. The organic solvent used is not particularly limited, and may include: methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol, etc. These organic solvents may be used alone or in combination of two or more. After applying the adhesive composition to a substrate, it is preferred to remove the solvent by drying, and then perform photocuring.

In addition, other additives can be added to the adhesive composition as needed within the scope that does not impair the transparency. Examples of additives include surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazole series, and phosphoric acid. Ester and other flame retardants, such as surfactants, antistatic agents, dyes, etc.

Note that in the present invention, an example of the synthesis method of the ethylenically unsaturated group-containing polyurethane (A) will be described, but the ethylenically unsaturated group-containing monomer (B) and adhesive Since other components contained in the composition vary depending on the type of compound used, or commercially available products can be used, description of the synthesis method is omitted.

<Synthesis method of polyurethane (A)> Below, an example of a preferred synthesis method of polyurethane (A) contained in the adhesive composition of the present embodiment is described, but the synthesis method of polyurethane (A) is not limited thereto and can be appropriately changed according to the conditions of the raw materials, equipment, etc. used for synthesis. In addition, in this example, the reaction between the hydroxyl group and the isocyanate group is carried out in any step in the presence of an inert organic solvent using a carbamate catalyst such as dibutyltin dilaurate, dibutyltin diethylhexanoate, and dioctyltin dilaurate for the isocyanate group. The reaction is preferably carried out at 30~100°C for 1~5 hours. Relative to the total mass of the reactants, the preferred amount of carbamate catalyst used is 50~500 mass ppm.

＜First synthesis method＞ First, polyol and polyisocyanate are fed in such a ratio that the amount of isocyanate groups (based on number, the same below) is greater than the amount of hydroxyl groups (based on number, the same below), and allowed to react. To synthesize urethane prepolymers with terminal isocyanate groups. Specific examples of polyols and polyisocyanates are those exemplified in the polyurethane (A) section.

At this time, when a polyisocyanate containing an ethylenically unsaturated group and a polyisocyanate not containing an ethylenically unsaturated group are used together as the polyisocyanate, these may be added simultaneously or separately, and the order of addition may be arbitrary. The introduction position of the ethylenically unsaturated group in the main chain of the polyurethane (A) can be determined in the order of adding the polyisocyanate containing the ethylenically unsaturated group and adding the polyisocyanate not containing the ethylenically unsaturated group. Adjust. From the viewpoint of shortening the distance between cross-linking points of the polyurethane (A) and reducing peeling of the adhesive layer, it is preferable to introduce an ethylenically unsaturated group also near the center of the main chain. That is, it is preferable to add the polyisocyanate containing an ethylenically unsaturated group first, or to add the polyisocyanate containing an ethylenically unsaturated group and the polyisocyanate not containing an ethylenically unsaturated group at the same time. It is more preferable to add the polyisocyanate containing an ethylenically unsaturated group first. Unsaturated polyisocyanate.

Similarly, when a polyoxyalkylene polyol and an ethylenically unsaturated group-containing polyol are used together as the polyol, these may be added simultaneously or separately, and the order of addition may be arbitrary. From the viewpoint of reducing peeling of the adhesive layer, it is preferable to add the polyol containing an ethylenically unsaturated group first, or to add the polyol containing an ethylenically unsaturated group and the polyoxyalkylene polyol simultaneously, and more preferably The polyol containing ethylenically unsaturated groups is added first.

Next, the urethane prepolymer containing an isocyanate group is reacted with an ethylenically unsaturated compound containing a hydroxyl group to synthesize a polyurethane (A) having an ethylenically unsaturated group introduced at the end of the molecular chain. Based on the number, it is preferred that the ethylenically unsaturated group be introduced into 90 to 100% of the ends of the polyurethane contained in the polyurethane (A) containing the ethylenically unsaturated group, more preferably 95 to 100%, and further preferably 100%. As long as the amount of ethylenically unsaturated groups introduced is 90% or more based on the number of isocyanate groups, the cohesive force of the adhesive layer obtained by curing the adhesive composition can be sufficiently obtained. The ratio of the number of ends with introduced ethylenically unsaturated groups to the number of ends of the entire polyurethane molecular chain can be measured by IR, NMR, etc.

<Second synthesis method> First, polyol and polyisocyanate are fed in a ratio such that the amount of hydroxyl groups (based on the number, the same below) is greater than the amount of isocyanate groups (based on the number, the same below), and reacted to synthesize a urethane prepolymer having a hydroxyl group at the end. Specific examples of polyoxyalkylene polyol and polyisocyanate are those exemplified in the section of polyurethane (A).

Next, the urethane prepolymer containing a hydroxyl group is reacted with an ethylenically unsaturated compound containing an isocyanate group to synthesize a polyurethane (A) having an ethylenically unsaturated group introduced at the end of the molecular chain. Based on the number, it is preferred that the ethylenically unsaturated group be introduced into 90 to 100% of the ends of the polyurethane contained in the polyurethane (A), more preferably 95 to 100%, and further preferably 100%. As long as the amount of ethylenically unsaturated groups introduced is 90% or more based on the number of hydroxyl groups, the cohesive force of the adhesive layer obtained by curing the adhesive composition can be fully obtained. The ratio of the number of ends with introduced ethylenically unsaturated groups to the number of ends of the entire polyurethane molecular chain can be measured by IR, NMR, etc.

<Method for producing adhesive composition> The adhesive composition is produced by mixing polyurethane (A) containing ethylenically unsaturated groups, monomer (B) containing ethylenically unsaturated groups, photopolymerization initiator (C), plasticizer (D) added as needed, other additives and organic solvent. The mixing method is not particularly limited, and for example, a homodispersor or a stirring device with stirring blades such as paddles attached can be used.

In addition, all components may be added and mixed at once, or may be added and mixed repeatedly for each component in multiple times. Note that when there is a component that is solid at room temperature, it may be added by dissolving it in a solvent, dispersing it in a dispersion medium, or adding it by heating and melting it, so that the component can be easily mixed in the adhesive composition with high uniformity.

<Protective sheet> <Constitution of protective sheet> The protective sheet of the present embodiment includes a substrate and an adhesive layer, and an adhesive layer composed of a cured product of the adhesive composition is formed on one surface of the substrate. The thickness of the adhesive layer is preferably 3 to 150 μm, more preferably 5 to 130 μm, and further preferably 10 to 100 μm. As long as the thickness of the adhesive layer is 3 μm or more, the strength of the adhesive layer is sufficient, and as long as the thickness is 150 μm or less, the thickness of the adhesive layer can be easily controlled. Furthermore, when the protective sheet is given a function of protecting the adherend from impact (impact resistance), the thickness of the adhesive layer is preferably 50 μm or more.

The material of the base material can be appropriately selected according to the purpose of the protective sheet, and examples thereof include resin films. The protective sheet is used, for example, as a protective sheet for a display surface in the manufacturing process of optical components. When inspecting the object, that is, the presence of foreign matter, for scratches and foreign matters, when the protective sheet is in a laminated state, the base material is preferably transparent. . Examples of the transparent base material include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, cellulose, and the like.

The thickness of the substrate can be appropriately selected according to the purpose of the protective sheet, and is not particularly limited. In the case of a resin film, from the perspective of operability and strength, the thickness of the substrate is preferably 5 μm or more, more preferably 10 μm or more, and further 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 further preferably 100 μm or less.

In addition, as a substrate, it is preferred to use one that has been treated with antistatic. There is no particular limitation on the antistatic treatment applied to the substrate, and a method of providing an antistatic layer on at least one surface of the substrate, a method of mixing an antistatic agent on the substrate, etc. can be used. Furthermore, the surface of the substrate on which the adhesive layer is formed can be subjected to an easy-to-bond treatment such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet treatment, ozone treatment, etc. as required.

For the purpose of protecting the adhesive layer, a peeling film may be layered on the surface of the adhesive layer. As the material of the peeling film, for example, paper, plastic film, etc. may be used. From the viewpoint of excellent surface smoothness, plastic film is more suitable. The plastic film used for the peeling film is not particularly limited as long as it can protect the above-mentioned adhesive layer. For example, polyethylene, polypropylene, polyethylene terephthalate, polybutylene, etc. may be listed. In addition, it is preferred to apply an easy-peeling treatment to the surface in contact with the adhesive layer.

<Method for producing a protective sheet> The method for producing a protective sheet of the present embodiment can be obtained by, for example, applying an adhesive composition to a substrate and laminating a peeling film as required, and then irradiating the adhesive composition with ultraviolet light to photoharden it. The ultraviolet light can be irradiated from a transparent peeling film, or from the substrate side when the substrate is transparent.

The method for applying the adhesive composition to the substrate is not particularly limited and can be appropriately selected. For example, as the method for applying the adhesive composition to the substrate, there can be listed: a method using various coating machines such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a rod coater, a doctor blade coater, a spray coater, a comma coater, a direct coater, etc.; a screen printing method, etc.

When the adhesive composition is subjected to light curing, the light source may be black light, low-pressure mercury lamp, high-pressure mercury lamp, ultra-high-pressure mercury lamp, metal halide lamp, xenon lamp, etc. The light irradiation intensity may be any light that can sufficiently cure the adhesive composition, and is preferably 50 to 3000 mW/cm ² . Note that when the light irradiation intensity is low, curing takes a long time, resulting in reduced productivity.

<Application and required performance of protective sheet> In the manufacturing process of optical components, the protective sheet can be cut according to the shape of the product or part before laminating it on the product or part. In addition, the product or part laminated with the protective sheet can be punched. In addition, the protective sheet can be suitably used for the purpose of protecting the surface of the plastic film used as an optical component. As the aforementioned optical components, for example, polarizing plates, wavelength plates, phase difference plates, optical compensation films, reflective sheets, brightness enhancement films, etc. used in liquid crystal displays of smartphones, personal computers, and televisions can be listed.

When the protective sheet of the present embodiment is used as such a protective sheet, in order to prevent contamination of the adhered object, the protective sheet is required not to generate chips when cut. In addition, when external impact is applied or force is applied during peeling, it is also required to have a hardness and tensile strength that do not damage the adhesive layer and the adhered object. In this case, the adhesive layer constituting the protective sheet preferably has a hardness above a certain level and has appropriate elongation and tensile strength. From these viewpoints, the pencil hardness (coating surface strength) of the adhesive layer is preferably a hardness of 4B or more. The elongation at break of the adhesive layer is preferably 40-300%, preferably 50-300%, more preferably 92-300%, and further preferably 92-250%. The breaking strength (tensile strength) of the adhesive layer is preferably 100-800 g/mm ² , more preferably 200-800 g/mm ² , further preferably 300-800 g/mm ² , and further more preferably 330-600 g/mm ² . The specific determination methods of these physical properties in the adhesive layer of the protective sheet will be described in the subsequent examples.

Furthermore, when the protective sheet of the present embodiment is used as the protective sheet described above, it is necessary to have a minimum peeling strength in order to prevent the protective sheet from being peeled off from a product or part during transportation, etc. On the other hand, when the protective sheet is peeled off from a product or part, a lower peeling strength is required in order to facilitate the peeling operation or to prevent the product or part from being deformed or damaged during the peeling. From these viewpoints, when the peeling speed is 0.3 m/min, the peeling force of the protective sheet is preferably 0.1-10 gf/25 mm, more preferably 0.2-8 gf/25 mm, further preferably 0.2-3 gf/25 mm, further more preferably 0.2-1 gf/25 mm, although it depends on the thickness of the substrate and the adhesive layer. When the peeling speed is 2.4 m/min, although it depends on the thickness of the substrate and the adhesive layer, it is preferably 1-50 gf/25 mm, more preferably 1.5-40 gf/25 mm, further preferably 1.5-10 gf/25 mm, further more preferably 1.5-4.5 gf/25 mm. The specific method for measuring the peel strength of the protective sheet will be described in the subsequent examples.

As described above, the protective sheet requires multiple properties, and the optimal range of the necessary properties will change depending on the thickness and type of the substrate and adhesive used for the protective sheet. For example, when the thickness of the substrate is changed to be thicker and the pencil hardness of the substrate is changed to be higher, the impact when the protective sheet is cut is more likely to be transmitted to the adhesive layer, and it is more likely to generate chips. From this point of view, as the physical properties of the adhesive layer to further reduce the generation of chips, it is preferred that the elongation is 92% or more and the tensile strength is 300gf/ ^mm2 or more. For example, when a (meth)acrylate alkyl ester of a monofunctional (meth)acrylate (B1) is used as the monomer (B) containing an ethylenically unsaturated group, the elongation tends to be improved when the alkyl chain contained in the (meth)acrylate alkyl ester is longer. From this viewpoint, it is preferred to use a chain (meth)acrylate alkyl ester having 8 to 18 carbon atoms, more preferably a chain (meth)acrylate alkyl ester having 12 to 18 carbon atoms, and even more preferably lauryl (meth)acrylate.

In addition, by using a polyoxyalkylene polyol as the polyol used for the polyurethane (A), the number average molecular weight of the polyoxyalkylene polyol is reduced, and the concentration of the urethane bond of the polyurethane (A) is increased, thereby increasing the elongation of the adhesive layer. From this point of view, it is preferred to use a polyoxyalkylene polyol having a number average molecular weight of 360 to 1200, and the concentration of the urethane bond of the polyurethane (A) is preferably 1.9 to 5 mol/kg, more preferably 2 to 5 mol/kg, and further preferably 2.3 to 5 mol/kg.

On the other hand, when the elongation of the adhesive layer increases, the peeling force increases, making the adherend easy to break, and the tensile strength decreases, causing the adhesive layer to break. When the protective sheet is peeled off, the adherend may be contaminated. From this point of view, when a multifunctional (meth)acrylate (B2) is used as the monomer (B) containing an ethylenically unsaturated group, the adhesive layer can be reduced in peeling resistance while improving hardness and tensile strength. In this case, the elongation of the protective sheet decreases when the multifunctional (meth)acrylate (B2) is used. Therefore, from the perspective of achieving a balance between the two performances, it is necessary to adjust the amount of the multifunctional (meth)acrylate (B2) so that the elongation of the protective sheet is not less than 92%. In this case, the content of the multifunctional (meth)acrylate (B2) is preferably 0.1 to 15% by mass, more preferably 1 to 12% by mass, and even more preferably 3 to 10% by mass, relative to 100% by mass of the total of the polyurethane (A) and the monomer (B) containing an ethylenically unsaturated group. Furthermore, various properties can be adjusted according to the mixing ratio of the polyurethane (A) and the monofunctional (meth)acrylate (B1).

From the viewpoint of achieving a balance of various properties and further reducing the generation of chips, based on 100% by mass of the total of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), it is preferable to Contains 50% by mass or more of polyurethane (A). Within the aforementioned range, when the amount of monofunctional (meth)acrylate (B1) is increased, the elongation of the adhesive layer increases and the peeling force tends to be lowered. When the amount of polyurethane (A) is increased, When the amount is increased, the hardness and strength of the adhesive layer tend to increase. From the viewpoint of achieving a balance of various properties and suppressing the generation of chips regardless of the type of base material, the content of the polyurethane (A) is preferably 50 to 70% by mass, and the monofunctional (meth)acrylic acid The content of ester (B1) is 20 to 50% by mass. [Example]

Hereinafter, the present invention will be further described in more detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

<Synthesis of polyurethane (A)> (Synthesis Example 1)

Into a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel, and a cooling tube with a drying tube attached, polypropylene glycol D-1000 (manufactured by Mitsui Chemicals, number average molecular weight) having a hydroxyl group at the end with a hydroxyl value of 111 mgKOH/g was fed. 1000) 2 mol, isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane) 3 mol, and the temperature was raised to 80°C to react for 7 hours. To the obtained urethane prepolymer, 2 mol of 2-hydroxyethylacrylate was added. Thereafter, the reaction was carried out at 80° C. for 2 hours to obtain polyurethane (A-i) having an acryloxy group at the terminal. This polyurethane (A-i) was analyzed by IR, and it was confirmed that the peak derived from the isocyanate group disappeared. The weight average molecular weight of the obtained polyurethane (A-i) was 7,000. The weight average molecular weight, urethane bond concentration, and ethylenically unsaturated group equivalent were each evaluated according to the following method, and the results are shown in Table 1 and Table 2.

(Determination of weight average molecular weight) In the synthesis examples and comparative synthesis examples, the weight average molecular weight of the obtained polyurethane (A) is a value converted to polystyrene measured by gel/permeation/chromatography (Shodex (registered trademark) GPC-101 manufactured by Showa Denko Co., Ltd., hereinafter referred to as GPC). The measurement conditions of GPC are as follows. Column: LF-804 manufactured by Showa Denko Co., Ltd. Column temperature: 40°C Sample: 0.2 mass% tetrahydrofuran solution of polyurethane (A) Flow rate: 1 ml/min Washing liquid: tetrahydrofuran Detector: RI detector (differential refractometer detector)

(Concentration of urethane bonds) Theoretical value calculated from the feed amount of each raw material.

(ethylenically unsaturated group equivalent) The theoretical value calculated from the feed amount of each raw material.

(Synthesis Examples 2 to 9, Comparative Synthesis Examples 1 to 6) Polyurethanes (A-ii) to (A-) were obtained in the same manner as in Synthesis Example 1 except that the polyols and polyisocyanates described in Tables 1 and 2 were used in the amounts specified in Tables 1 and 2. ix), (cA-i)~(cA-vi). In the same manner as in Synthesis Example 1, the weight average molecular weight, urethane bond concentration, and ethylenically unsaturated group equivalent of each polyurethane were evaluated. The results are shown in Table 1 and Table 2.

In Table 1 and Table 2, "PR9000" is a compound represented by the following formula (1).

The following compounds were used as compounds described in Table 1 and Table 2. ・Polypropylene glycol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) ・Polypropylene glycol D-1000 (manufactured by Mitsui Chemicals, number average molecular weight 1000) ・Polypropylene glycol D-400 (manufactured by Mitsui Chemicals, number average molecular weight 400) ・Epoxy acrylate (manufactured by Showa Denko Co., Ltd., Ripoxy (trademark) SP-16LDA) ・PR9000: Laromer (registered trademark) PR9000 (manufactured by BASF) ・Isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane) ・Coronate HX: Isocyanurate body of hexamethylene diisocyanate (manufactured by TOSOH) ・Hydride of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethane) ・Hexamethylene diisocyanate (manufactured by Asahi Kasei) ・2-Hydroxyethylacrylate (manufactured by Osaka Organic Chemical Industry)

(Example 1) <Preparation of adhesive composition PU1> Let 50 parts by mass of the polyurethane (A-i) obtained in Synthesis Example 1 be the polyurethane (A), and 50 parts by mass of the EHA of the monofunctional (meth)acrylate be the ethylenically unsaturated group-containing The monomer (B), 0.6 parts by mass of Irg-184 as the photopolymerization initiator (C) and 20 parts by mass of IPM as the plasticizer (D) were prepared, and mixed at 25°C using a disperser to The adhesive composition PU1 of Example 1 was prepared.

<Preparation 1 of protective sheet PUS1> A protective sheet having an adhesive layer on one surface of a substrate of an optical PET film is prepared. First, the above-adjusted adhesive composition PU1 is applied using an applicator onto a 75 μm thick optical PET film (A4300 manufactured by Toyobo Co., Ltd.) or a 75 μm thick PET film (HY-S10 manufactured by Higashiyama Film Co., Ltd.) as a substrate. The applied adhesive composition is covered with a 75 μm thick release PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, a UV irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3kW, high-pressure mercury lamp) was used to irradiate the sheet covered with the peelable PET film from the peelable PET film side to photoharden the adhesive composition and produce an adhesive layer. The UV irradiation distance was 25 cm, the lamp movement speed was 1.0 m/min, and the irradiation amount was 1000 mJ/cm ² . After measuring the thickness of the protective sheet with a micrometer, the thickness of the optical PET film 75 μm and the thickness of the peelable PET film 75 μm were subtracted from the measured value to calculate the thickness of the cured adhesive layer. The measuring surface of the micrometer was a circular plane with a diameter of 5 mm, and the measuring force was 0.8 N. The protective sheet PUS1 of Example 1 having an adhesive layer thickness of 71 μm was obtained. The protective sheet PUS1 was evaluated for the coating surface strength (pencil hardness) of the adhesive layer, the peeling strength of the protective sheet, and the chipping and cracking of the adhesive layer using the following evaluation method. The results are shown in Table 3.

<Preparation of Sample PUS1 for Tensile Test 2> In the same manner as in Preparation 1 of the protective sheet, except using a peelable PET film (E7006 manufactured by Toyobo Co., Ltd.) with a thickness of 75 μm as the base material, a tensile test sample in which both sides of the adhesive layer are peelable PET films is produced. PUS1. A tensile test (elongation, tensile strength) was performed for evaluation using the following evaluation method. The results are shown in Table 3.

(Examples 2 to 21, Comparative Examples 1 to 15) <Preparation of adhesive composition> Except for using the components and their blending amounts listed in Tables 3 to 7, the adhesive compositions PUS2 to 21 and cPS1 to 15 of Examples 2 to 21 and Comparative Examples 1 to 15 were prepared in the same manner as in Example 1.

<Preparation of protective sheet 1> Except for using the above-obtained adhesive compositions PUS2~21 and cPS1~15, the protective sheets PUS2~21 and cPUS1~15 of Examples 2~21 and Comparative Examples 1~15 were obtained in the same manner as in Example 1. The protective sheets were evaluated for the coating surface strength (pencil hardness) of the adhesive layer and the peeling strength of the protective sheets in the same evaluation method as in Example 1. The results are shown in Tables 3~7.

<Preparation of samples for tensile test 2> Except for using the adhesive compositions PUS2~21 and cPS1~15 obtained above, the samples PUS2~21 and cPUS1~15 for tensile test of Examples 2~21 and Comparative Examples 1~15 were obtained in the same manner as in Example 1. The tensile test (elongation, tensile strength) was evaluated for the samples for tensile test using the same evaluation method as in Example 1. The results are shown in Tables 3~7.

The following compounds were used as the compounds in the table. EHA: 2-ethylhexyl acrylate (manufactured by Toagosei Co., Ltd.) LA: Lauryl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.) TMPTA: Trihydroxymethylpropane triacrylate (M-309, manufactured by Toagosei Co., Ltd.) Irg-184: 1-Hydroxycyclohexyl Phenyl Ketone (manufactured by Tokyo Chemical Industry Co., Ltd.) IPM: EXCEPARL IPM (manufactured by Kao Corporation) HY-S10: manufactured by Higashiyama Film Co., Ltd. A4300: manufactured by Toyobo Co., Ltd.

＜Coating film surface strength (pencil hardness)＞ The prepared protective sheet was cut into a size of 100 mm × 100 mm, and the PET film was peeled off. The device used is an electric pencil scratch hardness testing machine (manufactured by Yasuda Seiki Manufacturing Co., Ltd., product name "No. 553-M"). In addition, the pencil used is Mitsubishi Pencil Co., Ltd.'s pencil "Uni (trade name)". Then, in accordance with JIS K 5600-5-4, the pencil hardness of the adhesive layer surface of the protective sheet was measured under the condition of a load of 100 g.

＜Peel strength of protective sheet＞ Cut the produced protective sheet into a size of 25 mm × 150 mm, and peel off the PET film. Next, the exposed adhesive surface was bonded to the glass plate, and a 2kg rubber roller (width: approximately 50mm) was reciprocated once to prepare a sample for measurement. After 30 minutes of pressure bonding, a tensile test was performed in the 180° direction at peeling speeds of 0.3m/min and 2.4m/min, and the peeling strength (g/25mm) of the protective sheet relative to the glass plate was measured in accordance with JISZ0237.

＜Tensile test (elongation, tensile strength)＞ Cut the prepared tensile test sample into a dumbbell shape with a width of 5mm and a length of 50mm as shown in Figure 1, and peel off the peeling PET film on both sides to expose the adhesive layer. The elongation at break and the breaking strength (tensile strength) were measured according to the method of JIS K 7161-1:2014. The device used was a tensile testing machine (manufactured by Stable MicroSystems). Conduct a tensile test on the adhesive layer under the conditions that the distance between the marking lines is 20mm and the tensile speed is 100mm/min. The elongation was calculated according to the following formula (A).

Test piece dimensions: Total length: 50mm Parallel length: 25mm Line spacing: 20mm Parallel width: 5mm Thickness see Tables 3~7 Grip width: 20mm Distance between grips: 30mm

Elongation = {(distance between marking lines at break) - (initial distance between marking lines 20mm)}/(initial distance between marking lines 20mm) x 100 (A)

＜Chips and cracks in the adhesive layer＞ Cut the prepared protective sheet with a sharp edge blade (blade height: 0.80 mm, blade angle: 50° (Tsukatani Hamono Seisakusho Co., Ltd.)), and peel off the PET film. Use a microscope (magnification: 800 times (Hirox Co., Ltd.) RH-2000 (manufactured by the company)) observes the end surface of the adhesive layer after cutting, the upper side is the adhesive layer, and the lower side is the base material layer, and evaluates based on the following standards.

"Evaluation Criteria for Chips and Adhesive Layer Cracks" 1: No chips or cracks are observed in the adhesive layer (for example, the cross-sectional view shown in Figure 2) 2: Chips are observed in part of the adhesive layer, but no cracks are observed (for example, the cross-sectional view shown in Figure 3) 3: Cracks were observed in part of the adhesive layer, but no chips were observed. 4: Chips or cracks are observed throughout the adhesive layer (for example, the cross-sectional view shown in Figure 4) [Industrial applicability]

According to the present invention, an adhesive composition can be provided, which can reduce the generation of chips during cutting and the damage of the adhesive layer, and has an appropriate peeling force and strength. Therefore, a protective sheet can be provided, which has an adhesive layer of a cured product of the above-mentioned adhesive composition, and has a reduced generation of chips during cutting and the damage of the adhesive layer, and has an appropriate peeling force and strength.

[Fig. 1] is a schematic diagram showing the dimensions of a test piece used in the tensile test of the Example. [Figure 2] is a cross-sectional micrograph of the adhesive sheet (upper layer: adhesive layer, lower layer: base material) obtained by an evaluation test for chips and cracks in the adhesive layer of the protective sheet of Example 1 (using A4300). [Figure 3] is a cross-sectional micrograph of the adhesive sheet (upper layer: adhesive layer, lower layer: base material) obtained by an evaluation test for chipping and cracks in the adhesive layer of the protective sheet of Comparative Example 1 (using A4300). [Figure 4] is a cross-sectional micrograph of the protective sheet of Comparative Example 4 (using A4300), obtained by an evaluation test for chips and cracks in the adhesive layer (upper layer: adhesive layer, lower layer: base material).

Claims (15)

An adhesive composition containing: Polyurethane (A), Monomer (B) containing ethylenically unsaturated groups, and Photopolymerization initiator (C), wherein The aforementioned polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyol and a structure derived from a polyisocyanate, and has an ethylenically unsaturated group at the terminal, and The weight average molecular weight of the aforementioned polyurethane (A) is 3,000 to 30,000. The adhesive composition of claim 1, wherein the polyol is a polyoxyalkylene polyol having a number average molecular weight of 300 to 1800. Such as the adhesive composition of claim 1 or 2, wherein the ethylenically unsaturated group equivalent of the aforementioned polyurethane (A) is 900~3000g/mol. The adhesive composition of claim 1 or 2, wherein the concentration of the urethane bonds of the polyurethane (A) is 1.0~5 mol/kg. The adhesive composition of claim 1 or 2, wherein the polyurethane (A) has an ethylenically unsaturated group at a position other than a terminal. Such as the adhesive composition of claim 1 or 2, wherein the aforementioned polyisocyanate includes a polyisocyanate containing an ethylenically unsaturated group and a polyisocyanate that does not contain an ethylenically unsaturated group. The adhesive composition of claim 1 or 2, wherein the aforementioned monomer (B) containing an ethylenically unsaturated group contains a monofunctional (meth)acrylate (B1), and the aforementioned monofunctional (meth)acrylate (B1) ) is a chain alkyl (meth)acrylate with a carbon number of 6 to 18. Such as the adhesive composition of claim 1 or 2, wherein the aforementioned monomer (B) containing an ethylenically unsaturated group contains a monofunctional (meth)acrylate (B1) and a multifunctional (meth)acrylate (B2) . The adhesive composition of claim 8, which contains a monofunctional (methyl) compound based on 100% by mass of the total of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). Acrylate (B1) 5 to 89 mass %, and polyfunctional (meth)acrylate (B2) 0.1 to 30 mass %. The adhesive composition of claim 1 or 2, which contains polyurethane methyl based on 100% by mass of the total of the aforementioned polyurethane (A) and the aforementioned ethylenically unsaturated group-containing monomer (B). Acid ester (A) 10 to 90 mass %, and ethylenically unsaturated group-containing monomer (B) 10 to 90 mass %. The adhesive composition of claim 1, further comprising a plasticizer (D). The adhesive composition of claim 11, wherein the photopolymerization initiator (C) is contained in an amount of 0.05 to 5 parts by weight, and the plasticizer (D) is contained in an amount of 1 to 30 parts by weight, relative to 100% by weight of the total of the polyurethane (A) and the monomer (B) containing an ethylenically unsaturated group. A hardened product of the adhesive composition of claim 1 or 11. For example, the hardened material of claim 13 has an elongation at fracture of 92-300% and a fracture strength of 300-800 g/mm ² . A protective sheet having a base material and an adhesive layer formed on one surface of the base material and including the cured product according to claim 13.

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