WO2024009593A1 - 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 present 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.

Various optical films are used in optical components such as liquid crystal displays and touch panels for smartphones, personal computers, televisions, etc. A protective sheet (surface protection sheet) is generally laminated on the surface of these optical films for the purpose of preventing stains and scratches during transportation, manufacturing, and inspection steps. This protective sheet is peeled off in a subsequent process such as an assembly process. Various urethane adhesives have been proposed as adhesives for such protective sheets.

For example, Patent Document 1 describes polyurethane (A), alkyl mono(meth)acrylate (B) whose alkyl group has 6 to 18 carbon atoms, polyfunctional (meth)acrylate (C), and plasticizer (D). ) A UV-curable adhesive composition for a protective film is disclosed. The polyurethane (A) is a reaction product of a polyol (a1), a polyisocyanate (a2), a hydroxyl group-containing (meth)acrylate (a3), and a hydroxyl group-containing photopolymerization initiator (a4).

JP2020-164840A

These protective sheets may be cut into a desired shape with a cutter or the like in a process before or after pasting them onto the adherend. At this time, cutting debris of the adhesive layer is generated on the cross section of the protective sheet, which may lead to contamination of the surface of the adherend. In addition, if the protective sheet is repeatedly laminated or peeled off, or if an impact is applied from the outside, the adhesive layer may be damaged and the adherend may be contaminated, or the adherend may be damaged due to insufficient strength of the adhesive layer. In some cases, the shock was transmitted to the device and the device was damaged. In recent years, as displays have become larger and panel components have become thinner, optical components themselves have become more susceptible to breakage. Therefore, the protective sheet is required to have appropriate adhesiveness (peel strength) and to be able to be peeled off with a lighter force (light peelability).

The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the generation of cutting chips and damage to the adhesive layer during cutting, and to obtain an adhesive layer with appropriate peeling force and strength. The purpose of the present invention is to provide a pressure-sensitive adhesive composition that can be used as an adhesive composition.
A further object of the present invention is to provide a protective sheet having an adhesive layer that reduces generation of cutting debris during cutting and damage to the adhesive layer, and has appropriate peeling force and strength.

The present invention includes the following aspects.
[1] Polyurethane (A) and
an ethylenically unsaturated group-containing monomer (B),
Contains a photopolymerization initiator (C),
The polyurethane (A) is a polyurethane having a skeleton including a polyol-derived structure and a polyisocyanate-derived structure, and has an ethylenically unsaturated group at the terminal,
An adhesive composition in which the polyurethane (A) has a weight average molecular weight of 3,000 to 30,000.
[2] The adhesive composition according to [1], wherein the polyol is a polyoxyalkylene polyol having a number average molecular weight of 300 to 1,800.
[3] The adhesive composition according to [1] or [2], wherein the polyurethane (A) has an ethylenically unsaturated group equivalent of 900 to 3000 g/mol.
[4] The adhesive composition according to any one of [1] to [3], wherein the polyurethane (A) has a urethane bond concentration of 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 site other than the terminal end.
[6] The adhesive composition according to any one of [1] to [5], wherein the polyisocyanate contains an ethylenically unsaturated group-containing polyisocyanate and an ethylenically unsaturated group-free polyisocyanate.
[7] The ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1), and the monofunctional (meth)acrylate (B1) is a chain alkyl group having 6 to 18 carbon atoms. The adhesive composition according to any one of [1] to [6], which is a (meth)acrylate.
[8] The ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2) according to [1] to [7]. The pressure-sensitive adhesive composition according to any one of the above.
[9] Contains 5 to 89 mass% of monofunctional (meth)acrylate (B1) based on the total of 100 mass% of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and contains polyfunctional (meth)acrylate (B1) in an amount of 5 to 89 mass%. The adhesive composition according to [8], containing 0.1 to 30% by mass of meth)acrylate (B2).
[10] Contains 10 to 90% by mass of polyurethane (A) based on a total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and contains the ethylenically unsaturated group-containing monomer ( The adhesive composition according to claim 1, containing 10 to 90% by mass of B).
[11] The adhesive composition according to any one of [1] to [9], further containing a plasticizer (D).
[12] Contains 0.05 to 5 parts by mass of a photopolymerization initiator (C) based on a total of 100 parts by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and the plasticizer The adhesive composition according to [11], containing 1 to 30 parts by mass of (D).
[13] A cured product of the pressure-sensitive adhesive composition according to [1] or [11].
[14] The cured product according to [13], which has an elongation at break of 92 to 300% and a breaking strength of 300 to 800 g/mm ² .
[15] A protective sheet comprising a base material and an adhesive layer formed on one side of the base material and made of the cured product according to [13].

According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that reduces the generation of cutting debris during cutting and damage to the pressure-sensitive adhesive layer, and provides a pressure-sensitive adhesive layer having appropriate peeling force and strength. Furthermore, it is possible to provide a protective sheet having an adhesive layer that reduces generation of cutting debris during cutting and damage to the adhesive layer, and has appropriate peeling force and strength.

FIG. 2 is a mock diagram showing the dimensions of a test piece used in a tensile test in an example. This is a cross-sectional micrograph of the adhesive sheet obtained in an evaluation test for cutting debris and cracks in the adhesive layer for the protective sheet of Example 1 (using A4300) (upper layer: adhesive layer, lower layer: base material). This is a cross-sectional micrograph of the adhesive sheet obtained in an evaluation test for cutting debris and cracks in the adhesive layer for the protective sheet of Comparative Example 1 (using A4300) (upper layer: adhesive layer, lower layer: base material). This is a cross-sectional micrograph of the adhesive sheet obtained in an evaluation test for cutting debris and cracks in the adhesive layer for the protective sheet of Comparative Example 4 (using A4300) (upper layer: adhesive layer, lower layer: base material).

Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments shown below. Here, the (meth)acryloyl group refers to one or more types selected from a group represented by the chemical formula CH ₂ =CH-CO- and a functional group represented by the chemical formula CH ₂ =C(CH ₃ )-CO-. means. The (meth)acryloyloxy group is selected from a group represented by the chemical formula CH ₂ =CH-CO-O- and a functional group represented by the chemical formula CH ₂ =C(CH ₃ )-CO-O-. It means more than one type.

<Adhesive composition>
The adhesive composition of this embodiment includes a polyurethane (A), an ethylenically unsaturated group-containing monomer (B), and a photopolymerization initiator (C). A plasticizer (D) may be included if necessary.
By using the adhesive composition of this embodiment as an adhesive layer of a protective sheet, generation of cutting debris during cutting and damage to the adhesive layer can be reduced. It is thought that multiple factors are intricately related to the occurrence of cutting debris and damage to the adhesive layer. For example, there are various factors including external factors, such as the type and thickness of the base material and adhesive layer, the type and conditions of the process when using the protective sheet, the type of adherend, and the type of impact applied from the outside. . Among these factors, by using a combination of ingredients to reduce the factors that are significantly related to the occurrence of cutting debris and damage to the adhesive layer, it is possible to effectively reduce cutting debris and damage to the adhesive layer. be able to.

[Polyurethane (A)]
The polyurethane (A) used in this embodiment 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 end. A "polyol-derived structure" is a structure introduced by using a polyol, which is a compound having two or more hydroxy groups, as a raw material for polyurethane. "Structure derived from polyisocyanate" is a structure introduced by using polyisocyanate, which is a compound having two or more isocyanate groups, as a raw material for polyurethane. Methods for introducing ethylenically unsaturated groups at the terminals include adding a hydroxy group-containing ethylenically unsaturated compound to an isocyanate group-terminated urethane prepolymer; Examples include a method of adding a compound. Polyurethane (A) may have ethylenically unsaturated groups at sites other than the terminals as necessary, from the viewpoint of reducing the peeling force when peeling the protective sheet from the adherend. Examples of methods for introducing ethylenically unsaturated groups into sites other than the terminals include methods using ethylenically unsaturated group-containing polyols or ethylenically unsaturated group-containing polyisocyanates as raw materials for synthesizing polyurethane (A). It will be done.

"Polyol"
The polyol used in this embodiment is a compound that does not have an isocyanate group and has two or more hydroxy groups. The number of hydroxyl groups in the polyol is preferably 2 from the viewpoint of suppressing gelation during synthesis and uniformly elongating the polymer.

Preferred polyols include polyoxyalkylene polyols having a polyoxyalkylene chain, from the viewpoint of improving the elongation rate of the adhesive layer and more effectively suppressing the generation of cutting debris during cutting. Particularly in conditions where the base material that makes up the protective sheet is hard or thick, cutting chips and damage are likely to occur due to the brittleness of the adhesive layer when cutting or when external impact is applied. It is preferable to use polyoxyalkylene polyol as the polyol. The alkylene chain constituting the polyoxyalkylene chain preferably has 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and even more preferably 2 to 4 carbon atoms. Specific examples include polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, and the like. Moreover, among polyoxyalkylene polyols, polyoxyalkylene glycol is preferably used, polypropylene glycol and polytetramethylene glycol are particularly preferable, and polypropylene glycol is even more preferably used.

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

The number average molecular weight of the polyoxyalkylene polyol is preferably from 300 to 1,800, more preferably from 330 to 1,500, even more preferably from 360 to 1,200. When the number average molecular weight of the polyoxyalkylene polyol is 300 or more, the peeling force when peeling the protective sheet from the adherend 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, and an adhesive layer having good hardness can be obtained. Therefore, it is possible to reduce the occurrence of cutting chips and damage when an external impact is applied to the protective sheet, or when a force is applied during cutting, pasting, or peeling operations.

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

Another preferred example of the polyol is an ethylenically unsaturated group-containing polyol from the viewpoint of reducing the peeling force when peeling the protective sheet from the adherend. In particular, under any of the following conditions, it is preferable to contain an ethylenically unsaturated group-containing polyol as the polyol. The above conditions are conditions that require lower peeling from the viewpoint of the strength of the adherend, such as miniaturization and thinning of the adherend, or conditions such as high peel strength, insufficient crosslinking of the adhesive layer, and low cohesive force. This is a condition where cutting chips and damage are likely to occur due to shortages.
Examples of the ethylenically unsaturated group contained in the ethylenically unsaturated group-containing polyol include a (meth)acryloyloxy group, a vinyl group, an allyl group, and the like, and a (meth)acryloyloxy group is preferable from the viewpoint of reducing peeling force. By using the ethylenically unsaturated group-containing polyol, it is possible to introduce the ethylenically unsaturated group into sites other than the terminals (in the molecular chain) of the polyurethane (A). Thereby, the peel strength of the adhesive layer can be reduced, particularly the peel strength during high-speed peeling. Further, by improving the crosslinking density and cohesive force of the adhesive layer, cutting debris and damage can be suppressed.

The (meth)acryloyloxy group-containing polyol can be obtained, for example, by performing an acid-catalyzed cleavage reaction of the epoxy group of a (meth)acryloyloxy group-containing epoxy compound to synthesize a compound having two hydroxy groups. can.
Examples of the (meth)acryloyloxy group-containing epoxy compound include glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, (meth)acrylate having an alicyclic epoxy group and its lactone adduct, 3 , 4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate, epoxidized products of dicyclopentenyl (meth)acrylate, and epoxidized products of dicyclopentenyloxyethyl (meth)acrylate.
Furthermore, as the (meth)acryloyloxy group-containing polyol, a compound obtained by adding a carboxy group-containing ethylenically unsaturated compound such as (meth)acrylic acid to a polyepoxy compound such as 1,6-hexanediol diglycidyl ether is used. It's okay.

A commercially available product may be used as the (meth)acryloyloxy group-containing polyol. Examples of the commercially available products include glycerin monomethacrylate (Blenmer (registered trademark) GLM, manufactured by NOF), which is obtained by cleaving the epoxy group of glycidyl methacrylate, and an acrylic acid adduct of 1,6-hexanediol diglycidyl ether (Showa Denko). Co., Ltd., Ripoxy (trademark) SP-16LDA).

These polyols may be used alone or in combination of two or more. From the viewpoint of balancing multiple performances, such as suppressing the generation of cutting debris during cutting and reducing peeling force, it is preferable to use an ethylenically unsaturated group-containing polyol and a polyoxyalkylene polyol in combination. The ratio (mole ratio) of ethylenically unsaturated group-containing polyol/polyoxyalkylene polyol is preferably 0.03 to 0.8, more preferably 0.08 to 0.7, and 0.1 It is more preferably 0.6 to 0.6, 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. The number of isocyanate groups that the polyisocyanate has is preferably 2 from the viewpoint of suppressing gelation during synthesis and uniformly elongating the polymer.

Examples of the polyisocyanate include tolylene diisocyanate and its hydrogenated product, xylylene diisocyanate and its hydrogenated product, diphenylmethane diisocyanate and its hydrogenated product, 1,5-naphthylene diisocyanate and its hydrogenated product, hexamethylene diisocyanate, Polyisocyanates that do not contain ethylenically unsaturated groups such as trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanate methyl)cyclohexane, and norbornane diisocyanate can be mentioned. . Among these, polyisocyanates having a cyclic hydrocarbon structure are preferred from the viewpoint of easy reaction control when synthesizing polyurethane (A) and imparting rigidity to the adhesive, such as isophorone diisocyanate, 4,4'- More preferred are at least one selected from dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and norbornane diisocyanate, and isophorone diisocyanate is even more preferred.

The polyisocyanate preferably contains an ethylenically unsaturated group-containing polyisocyanate from the viewpoint of reducing the peeling force when peeling the protective sheet from the adherend. In particular, under any of the following conditions, it is preferable to contain an ethylenically unsaturated group-containing polyol as the polyol. The above conditions include conditions that require lower peeling from the viewpoint of the strength of the adherend, such as miniaturization and thinning of the adherend, high peel strength, insufficient crosslinking of the adhesive layer, insufficient cohesive force, etc. This is a condition where cutting chips and damage are likely to occur. Examples of the ethylenically unsaturated group contained in the ethylenically unsaturated group-containing polyisocyanate include a (meth)acryloyloxy group, a vinyl group, an allyl group, and the like, and a (meth)acryloyloxy group is preferred from the viewpoint of reducing peeling force. By using the ethylenically unsaturated group-containing polyisocyanate, it is possible to introduce the ethylenically unsaturated group to sites other than the terminals (in the molecular chain) of the polyurethane (A). Thereby, the peel strength of the adhesive layer can be reduced, particularly the peel strength during high-speed peeling. Further, by improving the crosslinking density and cohesive force of the adhesive layer, cutting debris and damage can be suppressed.

Examples of the (meth)acryloyloxy group-containing polyisocyanate include a reaction product of a hydroxy group-containing (meth)acrylate and a polyisocyanate. It can be obtained by performing urethanization and allophanate formation according to the methods described in Japanese Patent Publication No. 2002-533542, JP2012-111851, etc., and synthesizing a compound having an allophanate bond. Specifically, examples of hydroxy group-containing (meth)acrylates include those similar to the hydroxy group-containing (meth)acrylates exemplified as hydroxy group-containing ethylenically unsaturated compounds that are raw materials for polyurethane (A) described below. can. As the polyisocyanate, the same compounds as mentioned above can be mentioned. Among these, an allophanate bond-containing compound obtained by reacting a hydroxy group-containing (meth)acrylate and a diisocyanate with an excess of diisocyanate is preferable. More preferred is an allophanate bond-containing compound obtained by reacting a hydroxyalkyl (meth)acrylate and an alkylene diisocyanate with an excess of the alkylene diisocyanate. Also, one or more selected from 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate, and one or more selected from hexamethylene diisocyanate and trimethylhexamethylene diisocyanate. A reaction product obtained by converting and into an allophanate is more preferable.

A commercially available product may be used as the (meth)acryloyloxy group-containing polyisocyanate. Examples of the commercially available product include Laromer (registered trademark) PR9000 manufactured by BASF, which is a reaction product of 2-hydroxyethyl acrylate and hexamethylene diisocyanate and contains an allophanate bond.

These polyisocyanates may be used alone or in combination of two or more.
From the perspective of balancing multiple properties, such as suppressing the generation of cutting debris during cutting and reducing peeling force, it is possible to use polyisocyanates containing ethylenically unsaturated groups and polyisocyanates not containing ethylenically unsaturated groups together. preferable. The ratio (mole ratio) of ethylenically unsaturated group-containing polyisocyanate/ethylenic unsaturated group-free polyisocyanate is preferably 0.03 to 0.8, and preferably 0.08 to 0.7. is more preferable, even more preferably from 0.1 to 0.6, particularly preferably from 0.1 to 0.4.

When obtaining an isocyanate group-terminated urethane prepolymer, the total amount of isocyanate groups in the polyisocyanate is preferably 1.05 to 1.8 mol per 1 mol of the hydroxyl groups in the polyol. It is more preferably from 1 to 1.7, and even more preferably from 1.15 to 1.6. If the total amount of isocyanate groups is 1.05 moles or more, the weight average molecular weight of the polyurethane (A) will be within the appropriate range.

When obtaining a hydroxy group-terminated urethane prepolymer, the total amount of hydroxy groups in the polyol is preferably 1.05 to 1.8 mol per 1 mol of the total isocyanate groups in the polyisocyanate. It is more preferably from 1 to 1.7, and even more preferably from 1.15 to 1.6. If the total amount of hydroxy groups is 1.05 moles or more, the weight average molecular weight of the polyurethane (A) will be within the appropriate range.

[Hydroxy group-containing ethylenically unsaturated compound]
The hydroxy group-containing ethylenically unsaturated compound is not particularly limited as long as it does not have an isocyanato group and has a hydroxy group and an ethylenically unsaturated group. From the viewpoint of curability, the ethylenically unsaturated group is preferably at least one selected from the group consisting of a vinyl group, an allyl group, and a (meth)acryloyloxy group; It is preferable that there be.

"Hydroxy group-containing (meth)acrylate"
The hydroxy group-containing ethylenically unsaturated compound of this embodiment is preferably a hydroxy group-containing (meth)acrylate. The hydroxy group-containing (meth)acrylate is not particularly limited as long as it is a compound that does not have an isocyanato group and has a hydroxy group and a (meth)acryloyloxy group. For example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; 1,3-butanediol mono(meth)acrylate, 1 , 6-hexanediol mono(meth)acrylate, 3-methylpentanediol mono(meth)acrylate, and other monools having a (meth)acryloyl group derived from various polyols. From the viewpoint of reactivity with the isocyanate group of polyisocyanate and photocurability as an adhesive composition, hydroxyalkyl (meth)acrylate is preferable, and hydroxyalkyl (meth)acrylate having an alkyl group having 2 to 6 carbon atoms is preferable. More preferred are 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate. These may be used alone or in combination of two or more.

"Compounds with hydroxyl and vinyl groups"
The hydroxy group-containing ethylenically unsaturated compound of this embodiment may be a compound that does not have an isocyanato group but has a hydroxy group and a vinyl group. Examples of the compound 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 the polyalkylene glycol monovinyl ether include diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, and the like.
Examples of the hydroxyalkyl vinyl ether include 4-hydroxybutyl vinyl ether and 4-hydroxycyclohexyl vinyl ether.
Examples of the hydroxycarboxylic acid vinyl ester include vinyl hydroxyacetate, vinyl hydroxypropanoate, vinyl hydroxybutanoate, vinyl hydroxyhexanoate, vinyl 4-hydroxycyclohexyl acetate, and the like.
Examples of the hydroxyalkyl vinyl ester include vinyl hydroxycyclohexylcarboxylate.

"Compounds with hydroxyl group and allyl group"
The hydroxy group-containing ethylenically unsaturated compound of this embodiment may be a compound that does not have an isocyanato group but has a hydroxy group and an allyl group. Examples of the compound having a hydroxy group and an allyl group include hydroxyalkyl allyl ether, hydroxycarboxylic acid allyl ester, hydroxyalkyl allyl ester, and the like.

Examples of the hydroxyalkyl allyl ether include 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, glycerol monoallyl ether, and 4-hydroxycyclohexyl allyl ether.
Examples of the hydroxycarboxylic acid allyl ester include allyl hydroxyacetate, allyl hydroxypropanoate, allyl hydroxybutanoate, allyl hydroxyhexanoate, allyl 4-hydroxycyclohexyl acetate, and the like.
Examples of the hydroxyalkyl allyl ester include hydroxyethyl allyl ester, hydroxypropyl allyl ester, hydroxybutyl allyl ester, hydroxyisobutyl allyl ester, hydroxycyclohexyl allyl ester, and the like.

The proportion of the hydroxy group-containing ethylenically unsaturated compound is preferably set so that the total amount of hydroxy groups in the polyol and the hydroxy group-containing ethylenically unsaturated compound is equivalent to the total amount of isocyanate groups in the polyisocyanate. Equivalent means that the difference in the number of moles between the two is preferably 0.05 mol or less, more preferably 0.01 mol or less. If the difference in the number of moles between the two is 0.05 mole or less, the amount of unreacted monomers can be sufficiently reduced, and the amount of unreacted hydroxy groups and isocyanate groups can also be sufficiently reduced, so even if it is made into a cured product, it will not change over time. Changes in gel fraction can be suppressed.

[Isocyanato group-containing ethylenically unsaturated compound]
The isocyanato group-containing ethylenically unsaturated compound is not particularly limited as long as it is a compound that does not have a hydroxyl group and has an isocyanato group and an ethylenically unsaturated group. It is preferable that the isocyanato group-containing ethylenically unsaturated compound is an isocyanato group-containing (meth)acrylate. For example, isocyanatoalkyl (meth)acrylates such as 2-isocyanatoethyl (meth)acrylate, 2-isocyanatopropyl (meth)acrylate, 4-isocyanatobutyl (meth)acrylate, and 6-isocyanatohexyl (meth)acrylate. etc. From the viewpoint of reactivity with the hydroxyl group of the polyoxyalkylene polyol (a1) and photocurability as an adhesive composition, isocyanatosialkyl (meth)acrylates having an alkyl group having 2 to 6 carbon atoms are preferred; -isocyanatoethyl (meth)acrylate and 4-isocyanatobutyl (meth)acrylate are more preferred. These may be used alone or in combination of two or more.

The proportion of the isocyanato group-containing ethylenically unsaturated compound can be set such that the total amount of isocyanato groups in the polyisocyanate and the isocyanato groups in the isocyanato group-containing ethylenically unsaturated compound is equivalent to the total amount of hydroxy groups in the polyol. preferable. Equivalent means that the difference in the number of moles between the two is preferably 0.05 mol or less, more preferably 0.01 mol or less. If the difference in the number of moles between the two is 0.05 mole or less, the amount of unreacted monomers can be sufficiently reduced, and the amount of unreacted hydroxy groups and isocyanate groups can also be sufficiently reduced, so even if it is made into a cured product, it will not change over time. Changes in gel fraction can be suppressed.

The weight average molecular weight of the polyurethane (A) is 3,000 to 30,000, preferably 5,000 to 28,000, and more preferably 6,000 to 25,000. When the weight average molecular weight is 3000 or more, the cured product of the pressure-sensitive adhesive composition has sufficient flexibility, and the protective sheet having this cured product as the pressure-sensitive adhesive layer has sufficient lamination properties. When the weight average molecular weight is 30,000 or less, when used as an adhesive layer, it has appropriate hardness, suppresses the generation of cutting chips during cutting, and prevents the adhesive layer from forming when external impact is applied. Breakage, damage to adherends, and contamination can be reduced. The weight average molecular weight of the polyurethane (A) may range from 3,000 to less than 10,000. In this case, the proportion of polyurethane (A) in the pressure-sensitive adhesive composition can be increased while maintaining the coatability of the pressure-sensitive adhesive composition, so that the surface strength of the coating film is relatively high.

The urethane bond concentration of polyurethane (A) is preferably 1.0 to 5 mol/kg, more preferably 1.5 to 5 mol/kg, and even more preferably 1.85 to 3.5 mol/kg. When the urethane bond concentration is 1.0 mol/kg or more, the adhesive layer has an appropriate elongation rate and has good hardness and tensile strength. When the urethane bond concentration is 5 mol/kg or less, the protective sheet has good low releasability and can prevent damage to the adherend when peeled from the adherend.

The ethylenically unsaturated group equivalent of the polyurethane (A) is preferably 900 to 3000 g/mol, more preferably 950 to 2700 g/mol, even more preferably 1000 to 2500 g/mol, even more preferably 1100 to 2300 g/mol. When the ethylenically unsaturated group equivalent is 900 g/mol or more, the adhesive layer has good flexibility and elongation. When the ethylenically unsaturated group equivalent is 3000 g/mol or less, the pressure-sensitive adhesive layer has good hardness and tensile strength.

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

The content of the polyurethane (A) is preferably 10 to 90% by mass, and preferably 25 to 80% by mass, based on the total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). The amount is more preferably 35 to 75% by weight, even more preferably 40 to 70% by weight. When the content of polyurethane (A) is 10% by mass or more, the elongation rate and tensile strength of the adhesive layer are good. When the content of polyurethane (A) is 90% by mass or less, the protective sheet has good low releasability.

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

[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)acryloyl group, and more preferably to have a (meth)acryloyl group. Among them, the ethylenically unsaturated group-containing monomer (B) is monofunctional (meth)acrylate (B1) from the viewpoints of dilubility of the adhesive composition, punching workability of the protective sheet, reduction of cutting debris during cutting, etc. It is preferable to contain. Furthermore, from the viewpoint of improving the peelability, hardness, and tensile strength of the protective sheet, the ethylenically unsaturated group-containing monomer (B) may contain a polyfunctional (meth)acrylate (B2) as necessary. . "Monofunctional" means having only one (meth)acryloyloxy group, and "polyfunctional" means having multiple (meth)acryloyloxy groups.

Examples of the monofunctional (meth)acrylate (B1) include alkyl (meth)acrylate, cyclic alkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, alkoxy(poly)alkylene glycol (meth)acrylate, and hydroxy group-containing (meth)acrylate. ) acrylate, carboxy group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylate, (meth)acrylamide, epoxy group-containing (meth)acrylate, and the like.

Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, and isobutyl (meth)acrylate. Acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, n-hexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, etc. Can be mentioned.

Examples of the cyclic alkyl (meth)acrylate include cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, norbornanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyloxyethyl (meth)acrylate. ) acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclodecane dimethyloldi(meth)acrylate, and the like.

Examples of the alkoxyalkyl (meth)acrylate include ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, and 2-ethoxyethoxyethyl (meth)acrylate. Examples include acrylate.

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

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

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

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

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

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

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

Among these, from the viewpoint of reducing cutting debris when cutting the protective sheet, alkyl (meth)acrylates are preferred, and chain alkyl (meth)acrylates having 6 to 18 carbon atoms are more preferred. More specifically, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, and isobornyl (meth)acrylate are preferred, and 2-ethylhexyl (meth)acrylate and lauryl (Meth)acrylate is more preferred. Furthermore, the monofunctional (meth)acrylate (B1) may be composed of one type of compound, or may be composed of two or more types of compounds.

The polyfunctional (meth)acrylate (B2) is preferably an ester compound of a polyol compound and (meth)acrylic acid, more preferably a tri- to hexa-functional (meth)acrylate. For example, polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, hydroxypivalic acid ester neopentyl Glycol di(meth)acrylate, 1,3-bis(hydroxyethyl)-5,5-dimethylhydantoin di(meth)acrylate, α,ω-di(meth)acrylic bisdiethylene glycol phthalate, trimethylolpropane tri(meth)acrylate , trimethylolpropane ethoxylate tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1 , 6-hexanediol di(meth)acrylate, diacryloxyethyl phosphate, dipentaerythritol trihydroxy(meth)acrylate, pentaerythritol tetra(meth)acrylate, and the like.

Among these, from the viewpoint of keeping the peel strength of the protective sheet low, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane ethoxylate tri(meth)acrylate, dipentaerythritol Trihydroxy(meth)acrylate and pentaerythritol tetra(meth)acrylate are more preferred, and trimethylolpropane tri(meth)acrylate and trimethylolpropane ethoxylate tri(meth)acrylate are even more preferred. Further, the polyfunctional (meth)acrylate (B2) may be composed of one type of compound, or may be composed of two or more types of compounds.

The ethylenically unsaturated group-containing monomer (B) may contain an ethylenically unsaturated group-containing monomer (B3) other than the components (B1) and (B2). Ethylenically unsaturated group-containing monomers (B3) other than components (B1) and (B2) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, and chloride. Vinylidene, alkyl vinyl ether, vinyltoluene, N-vinylpyridine, N-vinylpyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol Examples include 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 ethylenically unsaturated group-containing monomer (B) is preferably 10 to 90% by mass with respect to the total 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), It is more preferably 20 to 75% by weight, even more preferably 25 to 65% by weight, even more preferably 30 to 60% by weight. When the content of the ethylenically unsaturated group-containing monomer (B) is 10% by mass or more, the protective sheet has good low peelability. When the content of the ethylenically unsaturated group-containing monomer (B) is 90% by mass or less, the elongation rate and tensile strength of the adhesive layer are good.

The lower limit of the content of the ethylenically unsaturated group-containing monomer (B) may be 10% by mass or more based on the total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). It is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more. When the content of the ethylenically unsaturated group-containing monomer (B) is 10% by mass or more, the protective sheet has good low peelability.
The upper limit of the content of the ethylenically unsaturated group-containing monomer (B) is 90% by mass or less based on the total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). It is preferably 75% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less. When the content of the ethylenically unsaturated group-containing monomer (B) is 90% by mass or less, the protective sheet has good low peelability.
The above upper limit value and lower limit value can be arbitrarily combined.

When the ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2), the content of the monofunctional (meth)acrylate (B1) is preferably 5 to 89% by mass, more preferably 15 to 74% by mass, based on the total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). , more preferably 25 to 57% by mass. When the content of the monofunctional (meth)acrylate (B1) is 5% by mass or more, the protective sheet has good low releasability. When the content of the monofunctional (meth)acrylate (B1) is 89% by mass or less, the adhesive has an appropriate viscosity, making it easy to apply when creating a pressure-sensitive adhesive sheet. The content of the polyfunctional (meth)acrylate (B2) should be 0.1 to 30% by mass with respect to the total 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). The amount is preferably from 1 to 20% by weight, more preferably from 3 to 15% by weight. When the content of the monofunctional (meth)acrylate (B1) is 0.1% by mass or more, generation of cutting debris and damage to the adhesive layer are suppressed, and the protective sheet has good low releasability. When the content of monofunctional (meth)acrylate (B1) is 30% by mass or less, the elongation rate of the adhesive layer is good.

[Photopolymerization initiator (C)]
The photopolymerization initiator (C) is not particularly limited as long as it is a polymerization initiator that generates radicals when irradiated with light, but includes carbonyl photopolymerization initiators, sulfide photopolymerization initiators, acylphosphine oxides, and quinone photopolymerization initiators. Examples include initiators, sulfochloride photopolymerization initiators, thioxanthone photopolymerization initiators, and the like.

Examples of the carbonyl photopolymerization initiator include benzophenone, benzyl, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylamino Acetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, Michler's ketone, benzoin methyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl Ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, methyl Examples include benzoyl formate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, etc. .

Examples of the sulfide-based photopolymerization initiator include diphenyl disulfide, dibenzyl disulfide, tetraethylthiuram disulfide, and tetramethylammonium monosulfide.

Examples of the acylphosphine oxides include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, and the like.

Examples of the quinone photopolymerization initiator include quinone photopolymerization initiators such as benzoquinone and anthraquinone.

Examples of the sulfochloride photopolymerization initiator include 2-naphthalenesulfonyl chloride.

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

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

The content of the photopolymerization initiator (C) is preferably 0.05 to 5 parts by mass, and preferably 0.1 to 5 parts by mass, based on a total of 100 parts by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). More preferably 3 parts by mass, and even more preferably 0.3 to 1 part by mass. When the content of the photopolymerization initiator (C) is 0.05 parts by mass or more, the pressure-sensitive adhesive composition has sufficient photocurability. When the content of the photopolymerization initiator (C) is 5 parts by mass or less, contamination of the adherend when the protective sheet is peeled off can be suppressed.

[Plasticizer (D)]
As the plasticizer (D), any known plasticizer can be used without particular limitation. For example, fatty acid esters can be preferably used. The plasticizer (D) can improve the lamination properties (wettability) and bubble removal properties (ease of releasing air bubbles trapped during lamination) of the protective sheet.

Fatty acid esters include monobasic acids with 8 to 18 carbon atoms, esters of polybasic acids and branched alcohols with 18 or less carbon atoms, unsaturated fatty acids with 14 to 18 carbon atoms, or acids with branched chains. Examples include esters of and tetrahydric alcohols. A preferred specific example of the fatty acid ester is ethylhexyl stearate.

When using the plasticizer (D), the content is preferably 1 to 30 parts by mass, and 5 to 25 parts by mass, based on a total of 100 parts by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). is more preferable, and 10 to 23 parts by mass is even more preferable. When the content of the plasticizer (D) is 1 part by mass or more, the plasticizer (D) can improve the lamination properties (wettability) of the protective sheet and the bubble release properties (ease of releasing air bubbles caught during lamination). It can be fully expected that the addition of D) will bring out the effects. When the content of the plasticizer (D) is 30 parts by mass or less, contamination of the adherend when peeling off the protective sheet can be sufficiently suppressed.

[solvent]
Since the adhesive composition of this embodiment contains the ethylenically unsaturated group-containing monomer (B) as a low molecular weight component, it can be adjusted to a viscosity that allows coating without adding a solvent. That is, the adhesive composition does not need to substantially contain a solvent. In that case, when manufacturing the protective sheet, the step of heating and drying the solvent can be omitted, increasing productivity. In particular, when manufacturing a protective sheet with a thickness of more than 50 μm, it is preferable that the adhesive composition does not substantially contain the solvent. The meaning of "substantially not included" in the present invention means that the content of the solvent in the adhesive composition of the present invention is 0 to 1% by mass, preferably 0 to 0.5% by mass or less, and more preferably 0 to 0.5% by mass. ~0.1% by mass or less.
A solvent may be added to the adhesive composition for the purpose of adjusting viscosity during coating. The solvent can be appropriately selected depending on other components contained in the adhesive composition, but organic solvents are preferred. Examples of the organic solvent used include, but are not limited to, methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol, and the like. These organic solvents may be used alone or in combination of two or more. It is preferable that the solvent is removed by drying after applying the adhesive composition to a base material, etc., and then photocuring is performed.

Additionally, other additives may be added to the pressure-sensitive adhesive composition as necessary within a range that does not impair transparency. Examples of additives include surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, and phosphoric acid ester-based light stabilizers. and other flame retardants, antistatic agents such as surfactants, dyes, etc.

Here, an example of the method for synthesizing the ethylenically unsaturated group-containing polyurethane (A) will be explained, but the ethylenically unsaturated group-containing monomer (B) and other components contained in the adhesive composition will be explained below. The synthesis methods vary depending on the type of compound used, and commercially available products can be used, so a description of the synthesis method will be omitted.

<Method of synthesizing polyurethane (A)>
An example of a preferred method for synthesizing polyurethane (A) contained in the adhesive composition of the present embodiment will be described below, but the method for synthesizing polyurethane (A) is not limited to this, and the conditions such as raw materials and equipment used for synthesis are described below. It can be changed as appropriate. In addition, in this example, the reaction between the hydroxyl group and the isocyanate group is carried out in the presence of an organic solvent inert to the isocyanate group, using a urethane such as dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate, etc. It is carried out using a chemical catalyst. The reaction is preferably continuously carried out at 30 to 100°C for 1 to 5 hours. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass based on the total mass of the reactants.

<First synthesis method>
First, polyol and polyisocyanate are charged in such a ratio that the amount of isocyanate groups (based on numbers, the same applies hereinafter) is greater than the amount of hydroxyl groups (based on numbers, the same applies below), and these are reacted to form a urethane polymer having isocyanate groups at the terminals. Synthesize polymers. Specific examples of the polyol and polyisocyanate are as exemplified in the section of polyurethane (A).

At this time, if a polyisocyanate containing an ethylenically unsaturated group and a polyisocyanate not containing an ethylenically unsaturated group are used together as the polyisocyanate, they may be added at the same time or separately, and the order in which they are added may be changed. good. The introduction position of the ethylenically unsaturated group in the main chain of the polyurethane (A) can also be adjusted in the order in which the ethylenically unsaturated group-containing polyisocyanate and the ethylenically unsaturated group-free polyisocyanate are added. From the viewpoint of shortening the distance between crosslinking points of polyurethane (A) and reducing peeling of the adhesive layer, it is preferable that an ethylenically unsaturated group is also introduced near the center of the main chain. That is, it is preferable to add the ethylenically unsaturated group-containing polyisocyanate first, or to add the ethylenically unsaturated group-containing polyisocyanate and the ethylenically unsaturated group-free polyisocyanate at the same time. It is more preferable to add it first.

Similarly, when a polyoxyalkylene polyol and an ethylenically unsaturated group-containing polyol are used together as polyols, they may be added at the same time or separately, and the order of addition may be either. From the viewpoint of reducing the peeling of the adhesive layer, it is preferable to add the ethylenically unsaturated group-containing polyol first, or to add the ethylenically unsaturated group-containing polyol and the polyoxyalkylene polyol simultaneously. It is more preferable to add the polyol first.

Next, the isocyanato group-containing urethane prepolymer and the hydroxy group-containing ethylenically unsaturated compound are reacted to synthesize a polyurethane (A) in which an ethylenically unsaturated group is introduced at the end of the molecular chain.
Ethylenically unsaturated groups are preferably introduced into 90 to 100% of the terminals of the polyurethane contained in the ethylenically unsaturated group-containing polyurethane (A), more preferably 95 to 100%, and 100% is even more preferable. When the amount of ethylenically unsaturated groups introduced is 90% or more based on the number of isocyanate groups, sufficient cohesive force can be obtained in the adhesive layer obtained by curing the adhesive composition. The ratio of the number of ends into which ethylenically unsaturated groups have been introduced to the number of ends of all polyurethane molecular chains can be measured by IR, NMR, or the like.

<Second synthesis method>
First, polyol and polyisocyanate are prepared in such a ratio that the amount of hydroxy groups (on a number basis, the same applies hereinafter) is greater than the amount of isocyanate groups (on a number basis, the same below), and these are reacted to form a urethane polymer having a hydroxy group at the end. Synthesize polymers. Specific examples of the polyoxyalkylene polyol and polyisocyanate are as exemplified in the section of polyurethane (A).

Next, the hydroxy group-containing urethane prepolymer and the isocyanato group-containing ethylenically unsaturated compound are reacted to synthesize a polyurethane (A) in which an ethylenically unsaturated group is introduced at the end of the molecular chain.
Ethylenically unsaturated groups are preferably introduced into 90 to 100% of the terminals of the polyurethane contained in the polyurethane (A), more preferably 95 to 100%, and even more preferably 100%. When the amount of ethylenically unsaturated groups introduced is 90% or more based on the number of hydroxyl groups, sufficient cohesive force can be obtained in the adhesive layer obtained by curing the adhesive composition. The ratio of the number of ends into which ethylenically unsaturated groups have been introduced to the number of ends of all polyurethane molecular chains can be measured by IR, NMR, or the like.

<Method for producing adhesive composition>
Ethylenically unsaturated group-containing polyurethane (A), ethylenically unsaturated group-containing monomer (B), photopolymerization initiator (C), if necessary, a plasticizer (D), and other additives, A pressure-sensitive adhesive composition is produced by mixing the organic solvent and the organic solvent. The mixing method is not particularly limited, but can be carried out using, for example, a stirring device equipped with a stirring blade such as a homodisper or a paddle blade.

Furthermore, all the components may be added and mixed at once, or the addition and mixing may be repeated multiple times for each component. In addition, if there is a component that is solid at room temperature, this component can be dissolved by adding it as a solution in a solvent or dispersing in a dispersion medium, or adding it as a component that has been heated and melted. It becomes easier to mix into the adhesive composition with high uniformity.

<Protective sheet>
<Configuration of protective sheet>
The protective sheet according to this embodiment includes a base material and an adhesive layer, and the adhesive layer made of a cured product of the above-mentioned adhesive composition is formed on one side of the base material. 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 thickness of the adhesive layer is 3 μm or more, the strength of the adhesive layer is sufficient, and if the thickness is 150 μm or less, the thickness of the adhesive layer can be easily controlled.
Furthermore, when it is desired that the protective sheet has the 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 selected as appropriate depending on the use of the protective sheet, and examples include resin films. The protective sheet is used, for example, as a protective sheet for the display surface in the manufacturing process of optical components, etc., and when inspecting the adherend, that is, the presence of scratches or foreign matter on the product, the protective sheet is laminated. In this case, the substrate 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 base material can be appropriately selected depending on the use of the protective sheet and is not particularly limited, but in the case of a resin film, the thickness of the base material is preferably 5 μm or more from the viewpoint of handling properties and strength. More preferably, it is 10 μm or more, and still more preferably 20 μm or more. Moreover, considering the flexibility of the resin film, the thickness of the base material is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

Furthermore, as the base material, one that has been subjected to antistatic treatment is preferably used. The antistatic treatment applied to the base material is not particularly limited, but a method of providing an antistatic layer on at least one side of the base material, a method of kneading an antistatic agent into the base material, etc. can be used. Furthermore, the surface of the base material forming the adhesive layer may be subjected to adhesion-facilitating treatment such as acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, ultraviolet ray treatment, ozone treatment, etc., as necessary. good.

A release film can be laminated on the surface of the adhesive layer in the protective sheet for the purpose of protecting the adhesive layer. As the material for the release film, for example, paper, plastic film, etc. can be used, but plastic film is preferred because of its excellent surface smoothness. The plastic film used as the release film is not particularly limited as long as it can protect the above-described adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, polybutene, and the like. Moreover, it is preferable that the surface in contact with the adhesive layer is subjected to easy-peel treatment.

<Production method of protective sheet>
The method for manufacturing the protective sheet according to the present embodiment includes, for example, applying an adhesive composition to a base material, laminating a release film if necessary, and then irradiating the adhesive composition with ultraviolet rays to photocure it. It can be obtained by The ultraviolet rays may be irradiated from a transparent release film, or if the base material is transparent, the ultraviolet rays may be irradiated from the base material side.

The method of applying the adhesive composition to the base material is not particularly limited and can be selected as appropriate. For example, various coaters such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, and direct coater can be used to apply the adhesive composition to the base material. Examples of methods used include screen printing.

In addition, examples of the light source for photocuring the adhesive composition include a black light, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, and the like. The light irradiation intensity may be sufficient as long as it can sufficiently cure the adhesive composition, and is preferably, for example, 50 to 3000 mW/cm ² . Note that if the light irradiation intensity is low, curing takes time, resulting in a decrease in productivity.

<Applications and required performance of the protective sheet>
In the manufacturing process of optical components and the like, the protective sheet may be cut to match the shape of the product or component before it is laminated onto the product or component. In some cases, the product or component is laminated with a protective sheet and then punched out. Moreover, a protective sheet may be suitably used for the purpose of protecting the surface of a plastic film used as an optical component. Examples of the optical components include polarizing plates, wavelength plates, retardation plates, optical compensation films, reflective sheets, brightness enhancement films, etc. used in liquid crystal displays of smartphones, personal computers, televisions, and the like.

When the protective sheet according to the present embodiment is used as such a protective sheet, it is required that the protective sheet does not generate cutting debris during cutting in order to prevent contamination of the adherend. It is also required to have hardness and tensile strength to the extent that the adhesive layer and the adherend will not be damaged when external impact or peeling force is applied.
In that case, it is preferable that the adhesive layer constituting the protective sheet has a hardness of a certain level or higher, and has appropriate elongation and tensile strength.
From these viewpoints, the pencil hardness (coating film surface strength) of the adhesive layer is preferably 4B or higher. The elongation rate at break of the adhesive layer is preferably 40 to 300%, preferably 50 to 300%, more preferably 92 to 300%, and preferably 92 to 250%. Even more preferred. The breaking strength (tensile strength) of the adhesive layer is preferably 100 to 800 g/mm ² , more preferably 200 to 800 g/mm ² , even more preferably 300 to 800 g/mm ² , Even more preferably, it is 330 to 600 g/mm ² . Specific methods for measuring these physical properties in the adhesive layer of the protective sheet will be described later in Examples.

Further, when the protective sheet according to the present embodiment is used as the above-mentioned protective sheet, the protective sheet needs to have a minimum peel strength in order to prevent it from peeling off from the product or component during handling such as transportation. become. On the other hand, when peeling the protective sheet from a product or component, it is necessary to reduce the peel strength in order to facilitate the peeling operation or to prevent the product or component from being deformed or damaged during peeling. From these viewpoints, when the peeling speed is 0.3 m/min, the peeling force of the protective sheet is preferably 0.1 to 10 gf/25 mm, depending on the thickness of the base material and the adhesive layer. It is more preferably 0.2 to 8 gf/25 mm, even more preferably 0.2 to 3 gf/25 mm, even more preferably 0.2 to 1 gf/25 mm. When the peeling speed is 2.4 m/min, it is preferably 1 to 50 gf/25 mm, more preferably 1.5 to 40 gf/25 mm, although it depends on the thickness of the base material and the adhesive layer. It is more preferably 1.5 to 10 gf/25 mm, even more preferably 1.5 to 4.5 gf/25 mm. A specific method for measuring the peel strength of the protective sheet will be described later in Examples.

As mentioned above, a protective sheet is required to have a plurality of performances, and the optimal range of required performance may change depending on the thickness and type of the base material and adhesive used in the protective sheet. For example, if the thickness of the base material is increased or the pencil hardness of the base material is increased, the impact when cutting the protective sheet is more easily transmitted to the adhesive layer, and cutting debris is more likely to be generated. From this viewpoint, the physical properties of the adhesive layer that further reduce the generation of cutting debris are preferably an elongation rate of 92% or more and a tensile strength of 300 gf/mm ² or more. For example, when using an alkyl (meth)acrylate that is a monofunctional (meth)acrylate (B1) as the ethylenically unsaturated group-containing monomer (B), if the alkyl chain contained in the alkyl (meth)acrylate is made longer, There is a tendency for the elongation rate to improve. From that point of view, it is preferable to use a chain alkyl (meth)acrylate having 8 to 18 carbon atoms, more preferably a chain alkyl (meth)acrylate having 12 to 18 carbon atoms, and using lauryl (meth)acrylate. It is even more preferable.

The elongation rate of the adhesive layer can also be improved by using a polyoxyalkylene polyol as the polyol used in the polyurethane (A), lowering the number average molecular weight of the polyoxyalkylene polyol, and increasing the urethane bond concentration as the polyurethane (A). can be improved. From that point of view, it is preferable to use a polyoxyalkylene polyol with a number average molecular weight of 360 to 1200, and the urethane bond concentration of polyurethane (A) is preferably 1.9 to 5 mol/kg, and preferably 2 to 5 mol/kg. It is more preferable that the amount is 2.3 to 5 mol/kg.

On the other hand, if the elongation rate of the adhesive layer is improved, the peeling force will increase and the adherend will be more likely to be damaged, the tensile strength will decrease and the adhesive layer will be damaged, or the adherend will be damaged when the protective sheet is removed. may become contaminated. From this point of view, when polyfunctional (meth)acrylate (B2) is used as the ethylenically unsaturated group-containing monomer (B), it is possible to reduce the peeling of the adhesive layer and to improve the hardness and tensile strength. can. In this case, since the elongation rate of the protective sheet decreases with the use of polyfunctional (meth)acrylate (B2), from the viewpoint of balancing both performances, the elongation rate of the protective sheet should not be less than 92%. It is necessary to adjust the blending amount of the functional (meth)acrylate (B2). In this case, the content of the polyfunctional (meth)acrylate (B2) is 0.1 to 15% by mass based on the total 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B). The amount is preferably from 1 to 12% by weight, more preferably from 3 to 10% by weight. Furthermore, various performances can also be adjusted by changing the blending ratio of polyurethane (A) and monofunctional (meth)acrylate (B1).

From the perspective of further reducing the generation of cutting debris while balancing various performances, 50% by mass of polyurethane (A) is % or more is preferable. In the above range, increasing the amount of monofunctional (meth)acrylate (B1) tends to increase the elongation rate of the adhesive layer and lowering the peeling force, and increasing the amount of polyurethane (A) increases the hardness and strength of the adhesive layer. It tends to rise. From the viewpoint of balancing various performances and suppressing the generation of cutting debris regardless of the type of substrate, the content of polyurethane (A) should be 50 to 70% by mass, and the content of monofunctional (meth)acrylate (B1) should be 50 to 70% by mass. The content is preferably 20 to 50% by mass.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Synthesis of polyurethane (A)>
(Synthesis example 1)
In a four-necked flask equipped with a thermometer, a stirrer, a dropping funnel, and a cooling tube with a drying tube, add polypropylene glycol D-1000 (manufactured by Mitsui Chemicals, number average molecular weight 1000) having a hydroxyl group at the end and a hydroxyl value of 111 mgKOH/g. ) and 3 mol of isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane) were added, and the mixture was heated to 80° C. and reacted for 7 hours. 2 mol of 2-hydroxyethyl acrylate was added to the obtained urethane prepolymer. Thereafter, the mixture was reacted at 80° C. for 2 hours to obtain polyurethane (Ai) having an acryloyloxy group at the end. This polyurethane (A-i) was analyzed by IR, and it was confirmed that the peak derived from the isocyanate group had disappeared. The weight average molecular weight of the obtained polyurethane (Ai) was 7,000. The weight average molecular weight, urethane bond concentration, and ethylenically unsaturated group equivalent were evaluated using the following methods, and the results are shown in Tables 1 and 2.

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

(Urethane bond concentration)
This is a theoretical value calculated from the amount of each raw material charged.

(Ethylenically unsaturated group equivalent)
This is a theoretical value calculated from the amount of each raw material charged.

(Synthesis Examples 2 to 9, Comparative Synthesis Examples 1 to 6)
Polyurethanes (A-ii) to (A-ix), (cA-i ) to (cA-vi) were obtained. In the same manner as in Synthesis Example 1, each polyurethane was evaluated for weight average molecular weight, urethane bond concentration, and ethylenically unsaturated group equivalent. The results are shown in Tables 1 and 2.

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

Regarding the compounds listed in Tables 1 and 2, the following were used.
・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 aquarylate (manufactured by Showa Denko K.K., Lipoxy (trademark) SP-16LDA) ・PR9000: Laromer (registered trademark) PR9000 (manufactured by BASF)
・Isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestrourethane)
・Coronate HX: Isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh) ・Hydrogenated product of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestrourethane)
・Hexamethylene diisocyanate (manufactured by Asahi Kasei)
・2-Hydroxyethyl acrylate (manufactured by Osaka Organic Chemical Industry)

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

<Production 1 of protective sheet PUS1>
A protective sheet having an adhesive layer on one side of a base material of an optical PET film was produced. First, using an applicator, apply the adhesive composition PU1 prepared above as a base material to a 75 μm thick optical PET film (A4300 manufactured by Toyobo Co., Ltd.) or a 75 μm thick PET film (Higashiyama Film Co., Ltd. HY- S10). The applied adhesive composition was covered with a 75 μm thick release PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high pressure mercury lamp), the sheet covered with the release PET film is irradiated with ultraviolet rays from the side of the release PET film to make it stick. The adhesive composition was photocured to prepare an adhesive layer. The ultraviolet irradiation distance was 25 cm, the lamp moving speed was 1.0 m/min, and the irradiation amount was 1000 mJ/cm ² . The thickness of the adhesive layer after curing is determined by measuring the thickness of the protective sheet using a dial gauge, then subtracting the thickness of the optical PET film, 75 μm, and the thickness of the release PET film, 75 μm from this measured value. Calculated. The measuring surface of the dial gauge was a circular plane with a diameter of 5 mm, and the measuring force was 0.8 N. A protective sheet PUS1 of Example 1 with an adhesive layer having a thickness of 71 μm was obtained. The protective sheet PUS1 was evaluated in terms of coating surface strength (pencil hardness) of the adhesive layer, peel strength of the protective sheet, cutting debris, and cracking of the adhesive layer using the following evaluation methods. The results are shown in Table 3.

<Preparation 2 of sample PUS1 for tensile test>
Sample PUS1 for the tensile test, in which both sides of the adhesive layer are made of release PET film, was prepared in the same manner as in Preparation 1 of the protective sheet, except that a 75 μm thick release PET film (E7006 manufactured by Toyobo Co., Ltd.) was used as the base material. Created. A tensile test (elongation rate, tensile strength) was evaluated 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>
Adhesive compositions PUS2-21 and cPS1-15 according to Examples 2-21 and Comparative Examples 1-15 were prepared in the same manner as in Example 1 except that the components and their blending amounts listed in Tables 3-7 were used. did.

<Production of protective sheet 1>
Protective sheets PUS2-21, cPUS1-15 of Examples 2-21 and Comparative Examples 1-15 were prepared in the same manner as in Example 1, except that the adhesive compositions PUS2-21 and cPS1-15 obtained above were used. I got it. Using the same evaluation method as in Example 1, the protective sheet was evaluated for the coating surface strength (pencil hardness) of the adhesive layer and the peel strength of the protective sheet. The results are shown in Tables 3-7.

<Preparation of sample for tensile test 2>
Tensile test samples PUS2-21 of Examples 2-21 and Comparative Examples 1-15 were prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive compositions PUS2-21 and cPS1-15 obtained above were used. cPUS1-15 were obtained. The tensile test samples were evaluated using the same evaluation method as in Example 1 regarding the tensile test (elongation rate, tensile strength). The results are shown in Tables 3-7.

The following compounds were used in the table.
EHA: 2-ethylhexyl acrylate (manufactured by Toagosei Co., Ltd.)
LA: Lauryl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.)
TMPTA: Trimethylolpropane triacrylate (M-309, manufactured by Toagosei Co., Ltd.)
Irg-184:1-Hydroxycyclohexyl Phenyl Ketone (manufactured by Tokyo Chemical Industry Co., Ltd.)
IPM: Exepal 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 produced protective sheet was cut into a size of 100 mm x 100 mm, and the release PET film was peeled off. The device used was an electric pencil scratch hardness tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd., product name "No. 553-M"). In addition, the pencil used was Mitsubishi Pencil Co., Ltd.'s pencil "Uni (product name)." Then, the pencil hardness of the surface of the adhesive layer of the protective sheet was measured under the condition of 100 g load according to JIS K 5600-5-4.

<Peel strength of protective sheet>
The prepared protective sheet was cut into a size of 25 mm x 150 mm, and the release PET film was peeled off. Next, the exposed adhesive surface was bonded to a glass plate, and a 2 kg rubber roller (width: approximately 50 mm) was moved back and forth once to prepare a measurement sample.
30 minutes after crimping, a tensile test was performed in a 180° direction at a peeling speed of 0.3 m/min and 2.4 m/min, and the peel strength (g/25 mm) of the protective sheet against the glass plate was measured according to JIS Z0237. did.

<Tensile test (elongation rate, tensile strength)>
As shown in FIG. 1, the sample prepared for the tensile test was cut into a dumbbell shape with a width of 5 mm and a length of 50 mm, and the release PET film on both sides was peeled off to expose the adhesive layer. The elongation at break and the strength at break (tensile strength) were measured according to the method of JIS K 7161-1:2014. A tensile tester (manufactured by Stable MicroSystems) was used as the device. A tensile test of the adhesive layer was conducted under conditions of a distance between gauge lines of 20 mm and a tensile speed of 100 mm/min. The elongation rate was calculated according to the following formula (A).

Specimen dimensions:
Total length: 50mm
Parallel length: 25mm
Distance between gauge lines: 20mm
Parallel part width: 5mm
See Tables 3 to 7 for thickness Grip width: 20mm
Gripping distance: 30mm

Elongation rate = {(distance between gauge lines at break) - (initial distance between gauge lines 20 mm)} / (initial distance between gauge lines 20 mm) × 100 (A)

<Cut chips and cracks in the adhesive layer>
The prepared protective sheet was cut with a pinnacle blade (blade height: 0.80 mm, blade angle: 50° (manufactured by Tsukatani Hamono Seisakusho Co., Ltd.)), and the release PET film was peeled off. The end face of the adhesive layer after cutting was observed with a microscope (magnification: 800 times (RH-2000, manufactured by Hirox Co., Ltd.)) with the adhesive layer on the upper side and the base layer on the lower side, and evaluated according to the following criteria. .

"Evaluation criteria for cutting chips and cracks in adhesive layer"
1: No cutting debris or cracks are observed in the adhesive layer (for example, cross-sectional view shown in Figure 2)
2: Cutting debris is observed in a part of the adhesive layer, and no cracks are observed (for example, the cross-sectional view shown in Figure 3)
3: Cracks are observed in a part of the adhesive layer, but no cutting debris is observed. 4: Cutting debris or cracks are observed throughout the adhesive layer (for example, the cross-sectional view shown in FIG. 4).

According to the present invention, it is possible to provide a pressure-sensitive adhesive composition that reduces the generation of cutting debris during cutting and damage to the pressure-sensitive adhesive layer, and provides a pressure-sensitive adhesive layer having appropriate peeling force and strength. Therefore, the protection has an adhesive layer that is a cured product of the above-mentioned adhesive composition, reduces the generation of cutting chips during cutting and damage to the adhesive layer, and has an appropriate peeling force and strength. sheets can be provided.

Claims (15)

1. polyurethane (A),
   an ethylenically unsaturated group-containing monomer (B),
   Contains a photopolymerization initiator (C),
   The polyurethane (A) is a polyurethane having a skeleton including a polyol-derived structure and a polyisocyanate-derived structure, and has an ethylenically unsaturated group at the terminal,
   An adhesive composition in which the polyurethane (A) has a weight average molecular weight of 3,000 to 30,000.
2. The adhesive composition according to claim 1, wherein the polyol is a polyoxyalkylene polyol having a number average molecular weight of 300 to 1,800.
3. The adhesive composition according to claim 1 or 2, wherein the polyurethane (A) has an ethylenically unsaturated group equivalent of 900 to 3000 g/mol.
4. The adhesive composition according to claim 1 or 2, wherein the concentration of urethane bonds in the polyurethane (A) is 1.0 to 5 mol/kg.
5. The adhesive composition according to claim 1 or 2, wherein the polyurethane (A) has an ethylenically unsaturated group at a site other than the terminal end.
6. The adhesive composition according to claim 1 or 2, wherein the polyisocyanate contains an ethylenically unsaturated group-containing polyisocyanate and an ethylenically unsaturated group-free polyisocyanate.
7. The ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1), and the monofunctional (meth)acrylate (B1) is a chain alkyl (meth) having 6 to 18 carbon atoms. The adhesive composition according to claim 1 or 2, which is an acrylate.
8. The adhesive composition according to claim 1 or 2, wherein the ethylenically unsaturated group-containing monomer (B) contains a monofunctional (meth)acrylate (B1) and a polyfunctional (meth)acrylate (B2). thing.
9. Contains 5 to 89% by mass of monofunctional (meth)acrylate (B1) based on a total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and contains polyfunctional (meth)acrylate. The adhesive composition according to claim 8, containing 0.1 to 30% by mass of (B2).
10. The polyurethane (A) is contained in an amount of 10 to 90% by mass based on the total of 100% by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and the ethylenically unsaturated group-containing monomer (B) is The adhesive composition according to claim 1 or 2, containing 10 to 90% by mass.
11. The adhesive composition according to claim 1, further comprising a plasticizer (D).
12. Contains 0.05 to 5 parts by mass of a photopolymerization initiator (C) with respect to a total of 100 parts by mass of the polyurethane (A) and the ethylenically unsaturated group-containing monomer (B), and the plasticizer (D). The adhesive composition according to claim 11, containing 1 to 30 parts by mass of.
13. A cured product of the adhesive composition according to claim 1 or 11.
14. The cured product according to claim 13, having an elongation at break of 92 to 300% and a breaking strength of 300 to 800 g/mm ² .
15. A protective sheet comprising a base material and an adhesive layer formed on one side of the base material and made of the cured product according to claim 13.

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