JP7380577B2 - Adhesive composition for surface protection sheet and surface protection sheet - Google Patents

Description

The present invention relates to an adhesive composition for a surface protection sheet and a surface protection sheet, and in particular, an adhesive composition for a surface protection sheet containing a compound having a (meth)acryloyl group, and an adhesive composition for this surface protection sheet. The present invention relates to a surface protection sheet having a cured product.
This application claims priority based on Japanese Patent Application No. 2018-180614 filed in Japan on September 26, 2018, the contents of which are incorporated herein.

Various optical films are used in optical components such as liquid crystal displays and touch panels of 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, in Patent Document 1, polyurethane with a weight average molecular weight of 10,000 to 300,000, which has a polyoxyalkylene polyol as a backbone and has a (meth)acryloyl group at the end, (meth)acrylic acid ester having a hydroxy group, and other A photocurable composition for a transparent adhesive sheet containing a photopolymerizable monomer and a photopolymerization initiator is described.

In addition, Patent Document 2 describes polyurethane in which a (meth)acryloyl group is bonded to the terminal of a polyoxyalkylene chain via a urethane bond, a (meth)acrylic ester having a hydroxy group, and a (meth)acrylic ester having an aromatic ring. , a photocurable composition for a transparent adhesive sheet containing other polymerizable monomers and a photopolymerization initiator is described.

In the inspection process of optical components, it is sometimes required to be able to sufficiently discover or detect fine foreign objects or scratches on the product or component while the product or component is laminated with a protective sheet. Therefore, the protective sheet is required to have little cloudiness, that is, low haze.

Furthermore, in the manufacturing process of optical components, the protective sheet may be repeatedly laminated and peeled off. Therefore, the protective sheet is required to be easy to laminate onto the adherend (high wettability to the adherend) and easy to peel off. In addition, recently, as displays have become larger and panel parts have become thinner, optical parts 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). Furthermore, it is also required that there is no so-called adhesive residue (removability), in which a part of the adhesive layer remains on the surface of the product (adherent) after the protective sheet is peeled off.

Japanese Patent Application Publication No. 2014-210895 JP 2016-20477 Publication

However, the compositions described in Patent Document 1 and Patent Document 2 are not intended for use in protective sheets to be peeled off during the manufacturing process, and adhesive sheets using these compositions have high peel strength. .

Therefore, the present inventor conducted extensive studies to solve the above problems, and found that the present inventors have a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and a polyurethane containing a (meth)acryloyl group at a plurality of terminals. Polyurethane with a weight average molecular weight of 30,000 to 200,000, a polyfunctional monomer having multiple (meth)acryloyl groups, other monomers that can be polymerized with polyurethane and the polyfunctional monomer, and photopolymerization By curing a pressure-sensitive adhesive composition for a photocurable surface protection sheet containing an initiator, it is possible to obtain a surface protection sheet that has low haze, is easy to laminate, is easy to peel, and can suppress adhesive residue after peeling. I found out. However, the surface protection sheet obtained from this photocurable adhesive composition for surface protection sheets has a slightly hard adhesive layer, so when a sheet with a thick adhesive layer is laser cut or knife cut, the adhesive layer is It was found that cracks may occur on the end face.

Therefore, an object of the present invention is to provide a surface protection sheet that has low haze, is easy to laminate, is easy to peel, and can suppress adhesive residue after peeling, and also does not cause cracks in the adhesive layer during cutting. An object of the present invention is to provide a pressure-sensitive adhesive composition for a protective sheet. Another object of the present invention is to provide a surface protection sheet that has low haze, is easy to laminate, is easy to peel, and can suppress adhesive residue after peeling, and which does not cause cracks in the adhesive layer during cutting. It is to provide.

The configuration of the present invention for solving the above problems is as follows.
[1] Polyurethane (A) and
A polyfunctional monomer (B),
Other monomers (C) that can be polymerized with the polyurethane (A) and the polyfunctional monomer (B),
A photopolymerization initiator (D),
An adhesive composition for a surface protection sheet comprising:
The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate,
The polyurethane (A) contains polyurethane (a1),
The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals of the polyurethane (a1),
The weight average molecular weight of the polyurethane (A) is 30,000 to 200,000,
The polyfunctional monomer (B) is a compound having a plurality of (meth)acryloyl groups, and is a compound of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). With respect to the total amount of 100% by mass,
The content of the polyurethane (A) is 30 to 60% by mass,
The content of the polyfunctional monomer (B) is 2 to 10% by mass,
The content of the other monomer (C) is 30 to 68% by mass,
Based on 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
An adhesive composition for a surface protection sheet, characterized in that the content of a photopolymerization initiator (D) is 0.1 to 5 parts by mass.
[2] The adhesive for a surface protection sheet according to [1], wherein the structure derived from the polyoxyalkylene polyol contained in the polyurethane (A) is a structure derived from a polyoxyalkylene polyol having a number average molecular weight of 500 to 5,000. agent composition.
[3] The adhesive for a surface protection sheet according to any one of [1] or [2], wherein the skeleton contained in the polyurethane (A) is a copolymer of the polyoxyalkylene glycol and the diisocyanate. agent composition.
[4] The polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for a surface protection sheet according to any one of [1] to [3], wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate.
[5] The adhesive composition for a surface protection sheet according to any one of [1] to [4], wherein the (meth)acryloyl group in the polyurethane (A) is a part of a (meth)acryloyloxy group. .
[6] The adhesive composition for a surface protection sheet according to any one of [1] to [5], wherein the polyfunctional monomer (B) has three or more (meth)acryloyl groups.
[7] The adhesive composition for a surface protection sheet according to [6], wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate.
[8] The adhesive composition for a surface protection sheet according to [7], wherein the other monomer (C) has a (meth)acryloyl group.
[9] The adhesive composition for a surface protection sheet according to [8], wherein the other monomer (C) contains (meth)alkyl acrylate.
[10] The polyurethane (A) further includes polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and has a (meth)acryloyl group at only one terminal of the polyurethane (a2). The pressure-sensitive adhesive composition for a surface protection sheet according to any one of [1] to [9], comprising:
[11] The surface protection according to any one of [1] to [10], wherein (meth)acryloyl groups are introduced into 90 to 100% of the ends of the polyurethane molecules contained in the polyurethane (A), based on number. Adhesive composition for sheets.
[12] Sheet-like base material;
an adhesive layer formed on the base material,
A surface protection sheet, wherein the pressure-sensitive adhesive layer is made of a photocured product of the pressure-sensitive adhesive composition for a surface protection sheet according to any one of [1] to [11].

According to the present invention, a surface protection sheet for a surface protection sheet that has low haze, is easy to laminate, is easy to peel, can suppress adhesive residue after peeling, and does not cause cracks in the adhesive layer during cutting. can provide a pressure-sensitive adhesive composition for Further, according to the present invention, there is provided a surface protection sheet that has low haze, is easy to laminate, is easy to peel, can suppress adhesive residue after peeling, and does not cause cracking of the adhesive layer during cutting. I can do it.

FIG. 2 is a plan view showing a method for evaluating lamination properties of a surface protection sheet. 2 is a sectional view taken along line AA in FIG. 1. FIG.

An embodiment of the present invention will be described 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-. (meth)acryloyloxy group refers to 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- means one or more selected from. Further, the isocyanato group means a functional group represented by the chemical formula -N=C=O.

<1. Adhesive composition for surface protection sheet>
The adhesive composition for a surface protection sheet according to the present embodiment (hereinafter also referred to as "adhesive composition") contains polyurethane (A), a polyfunctional monomer (B), and polyurethane (A). ), other monomers (C) that are polymerizable with the polyfunctional monomer (B), and a photopolymerization initiator (D). The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate. The polyurethane (A) includes polyurethane (a1). The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals of the polyurethane (a1). The weight average molecular weight of the polyurethane (A) is 30,000 to 200,000. The polyfunctional monomer (B) is a compound having multiple (meth)acryloyl groups. The content of the polyurethane (A) is 30 to 60% by mass relative to 100% by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). The content of the polyfunctional monomer (B) is 2 to 10% by mass, and the content of the other monomer (C) is 30 to 68% by mass. Further, the content of the photopolymerization initiator (D) is 0.00 parts by mass with respect to 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). It is characterized by being 1 to 5 parts by mass.
Furthermore, the adhesive composition according to the present embodiment may contain additives such as fatty acid esters, if necessary. Furthermore, the adhesive composition according to this embodiment does not need to contain a solvent, but may contain a solvent as necessary.
Each component contained in the adhesive composition will be explained below. In the following description, the components consisting of polyurethane (A), polyfunctional monomer (B), and other monomers (C) may be referred to as "components (A) to (C)."

<1-1. Polyurethane (A)>
Polyurethane (A) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate. Polyurethane (A) includes polyurethane (a1) described below. For the purpose of adjusting the cohesive force of the cured product of the adhesive composition, the polyurethane (A) may further contain polyurethane (a2) described below.

[Polyurethane (a1)]
Polyurethane (a1) is a polyurethane that has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals. In addition, it is preferable that the (meth)acryloyl group at the terminal of polyurethane (a1) is a part of (meth)acryloyloxy group.

[Polyurethane (a2)]
Polyurethane (a2) is a polyurethane that has a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and has a (meth)acryloyl group at only one terminal. In addition, it is preferable that the terminal (meth)acryloyl group of polyurethane (a2) is a part of (meth)acryloyloxy group.
In addition, the method for adjusting the content of polyurethane (a1) and polyurethane (a2) contained in polyurethane (A), that is, the number of terminal (meth)acryloyl groups of polyurethane contained in polyurethane (A), is as follows. An example thereof will be described later in the section on the method for producing polyurethane (A).

In the case of a linear polymer, "a plurality of terminals" in the present invention refers to two terminals, and in the case of a branched polymer, it refers to two or more terminals in the same number of terminals as the number of each branch chain.
Polyurethane (A) does not contain any components other than polyurethane (a1) and polyurethane (a2).

The polyurethane (a1) contained in the polyurethane (A) is preferably 80 to 100% of the polyurethane (A), more preferably 90 to 100%, and even more preferably 100%. The polyurethane (a2) contained in the polyurethane (A) is preferably 0 to 20% of the polyurethane (A), more preferably 0 to 10%, and even more preferably 0%. If the polyurethane (a1) contained in the polyurethane (A) is 80% or more, the cohesive force of the cured product of the adhesive composition will be sufficiently large.

"Polyoxyalkylene polyol"
The polyoxyalkylene polyol preferably has an alkylene chain having 2 to 4 carbon atoms, and specific examples thereof include polyoxyethylene polyol, polyoxypropylene polyol, polyoxybutylene polyol, and the like. Moreover, among polyoxyalkylene polyols, polyoxyalkylene glycol is preferably used, and polypropylene glycol is particularly 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 500 to 5,000, more preferably 800 to 4,000, and even more preferably 1,000 to 3,000. If the number average molecular weight is 500 or more, the peel strength of the adhesive layer obtained by curing the adhesive composition will improve. When the number average molecular weight is 5,000 or less, a sufficient amount of urethane bonds are contained in the polyurethane, so that the cohesive force of the adhesive layer is improved.

The polyoxyalkylene polyol preferably has two or three hydroxyl groups at the terminal (diol or triol type polyoxyalkylene polyol). For example, in the case of diol type polypropylene glycol, the hydroxyl value is preferably 20 to 120 mgKOH/g, more preferably 30 to 100 mgKOH/g, and even more preferably 40 to 80 mgKOH/g. A specific example of polypropylene glycol is Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type), which is a polypropylene glycol having a hydroxyl group (hydroxyl group) at the end with a hydroxyl value of 56 mgKOH/g.
Here, the hydroxyl value is the hydroxyl value of the polyoxyalkylene polyol measured according to JIS K0070, and is the hydroxyl value required to neutralize free acetic acid when 1 g of the polyoxyalkylene polyol is acetylated. It means the number of mg of potassium. Specifically, it can be determined by acetylating hydroxyl groups in a sample using acetic anhydride and titrating the free acetic acid produced at that time with a potassium hydroxide solution.

"Polyisocyanate"
The polyisocyanate is not particularly limited as long as it is a compound having multiple isocyanate groups, but diisocyanate is preferred. Examples of the diisocyanate 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, trimethyl Examples include hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, norbornane diisocyanate.

Among these exemplified compounds, hydrogenated products of isophorone diisocyanate or diphenylmethane diisocyanate are preferred from the viewpoint of controlling light resistance and reactivity, and hydrogenated products of diphenylmethane diisocyanate are more preferred from the viewpoint of reactivity. The polyisocyanate-derived structure contained in the polyurethane (A) may be composed of one type, or may be a structure containing two or more types.
Specific examples of polyisocyanates include hydrogenated diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethane), isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane), and the like.

The weight average molecular weight of the polyurethane (A) is 30,000 to 200,000, preferably 50,000 to 150,000, and more preferably 70,000 to 100,000. If the weight average molecular weight of the polyurethane (A) is less than 30,000, the adhesive layer obtained by curing the adhesive composition will have insufficient flexibility, and the surface protection sheet having this adhesive layer will not be laminated. Difficult to remove. Furthermore, if the weight average molecular weight of the polyurethane (A) is greater than 200,000, the viscosity of the adhesive composition increases, making it difficult to handle and reducing workability.

The content of polyurethane (A) is 30 to 60% by mass, preferably 35 to 55% by mass, and 40 to 50% by mass based on the total amount of components (A) to (C). is more preferable. If the content of polyurethane (A) is less than 30% by mass, the cohesive force of the cured product of the adhesive composition will be insufficient, the adhesive layer will become too soft, and the adhesive surface (between the adhesive layer and the adherend) will be insufficient. There is a concern that air bubbles may become trapped between the two. When the content of polyurethane (A) is greater than 60% by mass, the cohesive force of the cured product of the adhesive composition is too high, the flexibility of the adhesive layer is insufficient, and the wettability of the adhesive layer to the adherend is poor. There are concerns that this will decline.

<1-2. Polyfunctional monomer (B)>
The polyfunctional monomer (B) adjusts the peel strength of the adhesive layer (surface protection sheet) using the cured product of the adhesive composition. The polyfunctional monomer (B) is a compound other than polyurethane (A) that has a plurality of (meth)acryloyl groups. There is no particular restriction as long as the number of (meth)acryloyl groups is two or more, but from the viewpoint of curability, it is preferable that the polyfunctional monomer (B) has three or more (meth)acryloyl groups.

The polyfunctional monomer (B) is preferably a poly(meth)acrylate of a polyol compound, such as 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, 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, etc. can be mentioned.

Among these, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol are used because they are easy to adjust the peel strength of the surface protection sheet using the adhesive composition to be low. Trihydroxy(meth)acrylate and pentaerythritol tetra(meth)acrylate are more preferred, and trimethylolpropane tri(meth)acrylate is even more preferred. Moreover, the polyfunctional monomer (B) may consist of one type of compound, or may consist of two or more types of compounds.

The content of the polyfunctional monomer (B) is 2 to 10% by mass, preferably 3 to 9% by mass, and 4 to 8% by mass based on the total amount of components (A) to (C). % is more preferable. If the content is less than 2% by mass, the peel strength of the surface protection sheet will be too high and the easy peelability will be poor. When the content is more than 10% by mass, the adhesive layer using the cured product of the adhesive composition becomes hard, and cracks are likely to occur during cutting of the sheet. Moreover, when the content is more than 10% by mass, the surface protection sheet tends to have a high haze.

<1-3. Other monomers (C)>
Other monomer (C) is a compound other than polyurethane (A) and other than polyfunctional monomer (B), and is polymerizable with polyurethane (A) and polyfunctional monomer (B). If so, there are no particular limitations. However, the other monomer (C) preferably has an ethylenically unsaturated bond capable of radical polymerization as a functional group for polymerizing with the polyurethane (A) and the polyfunctional monomer (B). Among these, it is more preferable to have a vinyl group or a (meth)acryloyl group, and even more preferable to have a (meth)acryloyl group.

Other monomers (C) include, but are not limited to, alkyl (meth)acrylates, cyclic alkyl (meth)acrylates, alkoxyalkyl (meth)acrylates, alkoxy(poly)alkylene glycol (meth)acrylates, and hydroxy group-containing Examples include (meth)acrylate, carboxy group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylate, (meth)acrylamide, epoxy group-containing (meth)acrylate, unsaturated carboxylic acid, etc. .

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, and the like.

Examples of alkoxyalkyl (meth)acrylates 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, and 1,3-butanediol mono(meth)acrylate. , 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, 3-methylpentanediol mono(meth)acrylate, and the like.

Examples of the carboxy group-containing (meth)acrylate include β-carboxyethyl (meth)acrylate.

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.
Examples of unsaturated carboxylic acids include (meth)acrylic acid, maleic acid, itaconic acid, and the like.

Other monomers (C) other than the above-mentioned compounds include, for example, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, Alkyl vinyl ether, vinyltoluene, N-vinylpyridine, N-vinylpyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether Or diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, and the like.

Among these exemplified compounds, from the viewpoint of compatibility with polyurethane (A), viscosity of the adhesive composition, and adjustment of peel strength, alkyl (meth)acrylates are preferred, and 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isostearyl (meth)acrylate, and isobornyl (meth)acrylate are more preferred, and 2-ethylhexyl (meth)acrylate is even more preferred. Further, the other monomer (C) may be composed of one type of compound, or may be composed of two or more types of compounds.

The content of other monomers (C) is 30 to 68% by mass, preferably 35 to 62% by mass, and 40 to 56% by mass based on the total amount of components (A) to (C). % is more preferable. If the content is less than 30% by mass, the cohesive force of the cured product of the pressure-sensitive adhesive composition will be too high, the flexibility of the pressure-sensitive adhesive layer will be insufficient, and there is a concern that the wettability to the adherend may be reduced. If the content is higher than 68% by mass, the cohesive force of the cured product of the adhesive composition will be small, the adhesive layer will be too soft, and air bubbles will be trapped on the adhesive surface (between the adhesive layer and the adherend). There is a concern that this may occur.

<1-4. Photopolymerization initiator (D)>
Examples of the photopolymerization initiator (D) include, but are not limited to, carbonyl photopolymerization initiators, sulfide photopolymerization initiators, acylphosphine oxide photopolymerization initiators, quinone photopolymerization initiators, and sulfochloride photopolymerization initiators. Examples include initiators, thioxanthone photopolymerization initiators, and the like.

Examples of carbonyl photopolymerization initiators 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 photopolymerization initiator include diphenyl disulfide, dibenzyl disulfide, tetraethylthiuram disulfide, and tetramethylammonium monosulfide.

Examples of the acylphosphine oxide photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide.

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 photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone.

Among these exemplified compounds, 1-hydroxycyclohexyl phenyl ketone and 2,4,6-trimethylbenzoyl diphenylphosphine oxide are preferred from the viewpoint of transparency of the adhesive layer obtained by curing the adhesive composition. . Further, the photopolymerization initiator (D) 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 (D) is 0.1 to 5 parts by mass, and 0.2 to 3 parts by mass, based on 100 parts by mass of the total amount of components (A) to (C). The amount is preferably 0.3 to 2 parts by mass, and more preferably 0.3 to 2 parts by mass. If the content of the photoinitiator (D) is less than 0.1 part by mass, the adhesive composition will not be sufficiently photocured, and if it is more than 5 parts by mass, a large amount of low molecular weight components will be produced, resulting in The removability of the surface protection sheet tends to deteriorate.

<1-5. Additive>
If necessary, a fatty acid ester may be added to the adhesive composition in order to improve the lamination properties (wettability) and bubble removal properties (easiness of air bubbles trapped during lamination) of the resulting surface protection sheet. It's okay. Examples of fatty acid esters include esters of monobasic acids with 8 to 18 carbon atoms or polybasic acids and branched alcohols with 18 or less carbon atoms, unsaturated fatty acids with 14 to 18 carbon atoms, or esters with branched alcohols with 14 to 18 carbon atoms. Examples include esters of acids and tetrahydric alcohols. A specific example of the fatty acid ester is isopropyl myristate. The amount of fatty acid ester added is preferably 1 to 40 parts by weight, more preferably 3 to 35 parts by weight, and further 5 to 30 parts by weight, based on 100 parts by weight of the total amount of components (A) to (C). preferable.

Further, 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 plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, and phosphorus. Examples include acid ester and other flame retardants, antistatic agents such as surfactants, and dyes.

<1-6. Solvent>
Since the adhesive composition contains the polyfunctional monomer (B) and other monomers (C) as low molecular weight components, the viscosity can be adjusted to allow coating without adding a solvent. That is, the adhesive composition contains, in addition to the essential components consisting of the polyurethane (A), the polyfunctional monomer (B), the other monomer (C), and the photopolymerization initiator (D). , may be substantially free of solvent. In that case, when manufacturing the surface protection sheet, the step of heating and drying the solvent can be omitted, increasing productivity. In particular, when producing a surface protection 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 free" 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, and more preferably 0 to 1% by mass. ~0.1% by mass.
A solvent may be added to the adhesive composition for the purpose of adjusting the 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.

<2. Method for producing adhesive composition for surface protection sheet>
Here, an example of the method for synthesizing polyurethane (A) will be explained, but polyfunctional monomer (B) and other monomers (C) and those contained in the adhesive composition for surface protection sheet The other components are easily available commercially and vary depending on the type of compound used, so a description of the synthesis method will be omitted.

<2-1. Synthesis method of 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, polyoxyalkylene polyol and polyisocyanate are charged in such a proportion that the amount of isocyanato 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 isocyanate groups at the terminals. Synthesize polyurethane with Specific examples of the polyoxyalkylene polyol and polyisocyanate are as exemplified in the section of polyurethane (A).

At this time, it is possible to adjust the molecular weight (degree of polymerization) by adjusting the amount of isocyanate groups relative to the amount of hydroxy groups. Specifically, the smaller the excess amount of isocyanate groups with respect to the amount of hydroxy groups, the larger the molecular weight of the polyurethane having isocyanate groups becomes. The molecular weight becomes smaller.

Next, the polyurethane having an isocyanato group at the end is reacted with a compound having a hydroxyl group and a (meth)acryloyl group to synthesize a polyurethane (A) having a (meth)acryloyl group at the end of the molecular chain. Note that the (meth)acryloyl group contained in this compound is preferably part of a (meth)acryloyloxy group.

Examples of compounds having a hydroxy group and (meth)acryloyl group include, but are not limited to, hydroxyalkyl (meth)acrylate, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. meth)acrylate; 1,3-butanediol mono(meth)acrylate, 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, 3-methylpentanediol mono(meth)acrylate Examples include monools having (meth)acryloyl groups derived from various polyols such as. These may be used alone or in combination of two or more. Among these, 2-hydroxyethyl (meth)acrylate is preferred in terms of reactivity with isocyanate groups and photocurability.

In addition to a compound having a hydroxyl group and a (meth)acryloyl group, an alkyl alcohol having one hydroxyl group but not having a (meth)acryloyl group is used in combination to react with a polyurethane having an isocyanato group at the terminal. By doing so, the amount of (meth)acryloyl group introduced can be adjusted. Examples of the alkyl alcohol include, but are not limited to, linear, branched, and alicyclic alkyl alcohols, and these may be used alone or in combination of two or more types. . As a result, a polyurethane having a structure derived from the alkyl alcohol at at least one of the ends is produced. In this case, the polyurethane (A) includes a polyurethane that does not have a (meth)acryloyl group at at least one of its ends. Therefore, polyurethane (a2) having a (meth)acryloyl group only at one end may also be included.

On a numerical basis, (meth)acryloyl groups are preferably introduced into 90 to 100% of the terminals of the polyurethane contained in polyurethane (A), more preferably 95 to 100%, and even more preferably 100%. When the amount of (meth)acryloyl groups introduced is 90% or more based on the number of isocyanato groups, sufficient cohesive force can be obtained in the adhesive layer obtained by curing the adhesive composition. The ratio of the number of terminals into which (meth)acryloyl groups have been introduced to the number of terminals of all polyurethane molecular chains can be measured by IR, NMR, or the like.

<2-2. Modification of the synthesis method of polyurethane (A)>
A modification of the method for synthesizing polyurethane (A) will be described. In this example, as in the above 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 in each step, using dibutyltin dilaurate, dibutyltin diethylhexoate, dibutyltin diethylhexoate, This is carried out using a urethanization catalyst such as dioctyltin dilaurate. 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. In this modification, first, a polyoxyalkylene polyol and a polyisocyanate are reacted at a ratio such that the amount of hydroxy groups is greater than the amount of isocyanate groups to synthesize a polyurethane having a hydroxy group at the terminal.

At this time, as in the above example, it is possible to adjust the molecular weight by adjusting the ratio of the amount of hydroxy groups to the amount of isocyanate groups. Specifically, the smaller the excess amount of hydroxy groups relative to the amount of isocyanate groups, the larger the molecular weight of the polyurethane having hydroxy groups, and the larger the excess amount of hydroxy groups relative to the amount of isocyanate groups, the higher the molecular weight of the polyurethane having hydroxy groups. The molecular weight becomes smaller.

Next, the polyurethane having a hydroxy group at the end is reacted with a compound having an isocyanato group and a (meth)acryloyl group to synthesize a polyurethane (A) having a (meth)acryloyl group at the end of the molecular chain. Note that the (meth)acryloyl group contained in this compound is preferably part of a (meth)acryloyloxy group.

Compounds having an isocyanato group and a (meth)acryloyl group include, but are not particularly limited to, 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropylisocyanate, 1,1-bis(acryloyloxymethyl)ethyl Examples include isocyanates. Examples of commercially available compounds having an isocyanato group and a (meth)acryloyl group include Karenz MOI (registered trademark) and Karenz AOI (registered trademark) manufactured by Showa Denko K.K. These may be used alone or in combination of two or more. Among these, 2-(meth)acryloyloxyethyl isocyanate is preferred from the viewpoint of reactivity with hydroxy groups and photocurability.

In addition to a compound having an isocyanato group and a (meth)acryloyl group, an alkyl isocyanate having no (meth)acryloyl group and one isocyanato group is used in combination to react with a polyurethane having a hydroxyl group at the end. By doing so, the amount of (meth)acryloyl group introduced can be adjusted. Examples of the alkyl isocyanate include, but are not limited to, linear, branched, and alicyclic alkyl isocyanates, which may be used alone or in combination of two or more types. . This produces polyurethane having a structure derived from the alkyl isocyanate at at least one of its ends. In this case, the polyurethane (A) includes a polyurethane that does not have a (meth)acryloyl group at at least one of its ends. Therefore, in this case, the polyurethane (A) may also include a polyurethane having a (meth)acryloyl group only at one end.

On a numerical basis, (meth)acryloyl groups are preferably introduced into 90 to 100% of the terminals of the polyurethane contained in polyurethane (A), more preferably 95 to 100%, and even more preferably 100%. When the amount of (meth)acryloyl groups introduced is 90% or more based on the number of isocyanato groups, sufficient cohesive force can be obtained in the adhesive layer obtained by curing the adhesive composition.

<2-3. Method for mixing each component contained in the adhesive composition for surface protection sheet>
Polyurethane (A), polyfunctional monomer (B), other monomer (C), photopolymerization initiator (D), fatty acid ester added as necessary, 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.

Moreover, all the components may be added and mixed at once, or the addition and mixing may be repeated in multiple steps 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.

<3. Surface protection sheet＞
<3-1. Composition of surface protection sheet>
In the surface protection sheet according to this embodiment, a pressure-sensitive adhesive layer containing a cured product of the pressure-sensitive adhesive composition is formed on one side of a 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 surface protection 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 gel fraction of the cured product of the adhesive composition contained in the adhesive layer is preferably 85 to 100% by mass, more preferably 90 to 100% by mass, and preferably 95 to 100% by mass. More preferred. Here, the gel fraction is the mass fraction of extractable insoluble matter with respect to a solvent, and a solvent is selected that can dissolve non-crosslinked components of the cured adhesive composition. Note that a specific example of a method for measuring the gel fraction will be described later in Examples. If the gel fraction of the cured product of the adhesive composition is 85 to 100% by mass, it will suppress so-called adhesive residue, in which part of the adhesive layer remains on the adherend when the surface protection sheet is removed. can do.

The material of the base material can be appropriately selected depending on the use of the surface protection sheet, and examples thereof include resin films. For example, if the surface protection sheet is used as a protection sheet in the manufacturing process and the adherend, that is, the product, is inspected for scratches or foreign matter with the protection sheet laminated, the base material is transparent. It is preferable that 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 surface protection 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 10 μm or more, 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 on which the adhesive layer is formed 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., if necessary. good.

A separator can be laminated onto the surface of the adhesive layer in the surface protection sheet for the purpose of protecting the adhesive layer. As the material for the separator, 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 separator 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.

<3-2. Manufacturing method of surface protection sheet>
The method for manufacturing the surface protection sheet according to the present embodiment includes, for example, applying an adhesive composition to a base sheet, laminating a separator, and then irradiating the applied adhesive composition with ultraviolet rays to photocure it. Obtainable.

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. Light irradiation can be performed from either the separator side or the base material side as long as the material is transparent.

<3-3. Applications and required performance of surface protection sheets>
In an inspection process, it may be required to be able to sufficiently discover or detect fine foreign objects or scratches on a product or component with a protective sheet laminated thereon. In addition, protective sheets are used for the surfaces of plastic films used as optical components such as polarizing plates, wavelength plates, retardation plates, optical compensation films, reflective sheets, and brightness enhancement films used in liquid crystal displays of smartphones, computers, televisions, etc. It may also be suitably used for the purpose of protecting.

When the surface protection sheet according to the present embodiment is used as such a protection sheet, the surface protection sheet is required to have little cloudiness, that is, low haze. In that case, the haze value of the surface protection sheet is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.0% or less. A specific method for measuring the haze value of the surface protection sheet will be described later in Examples.

In addition, when the surface protection sheet according to the present embodiment is used as a protection sheet as described above, the surface protection sheet must have a minimum peel strength to prevent it from peeling off from the product or parts during handling such as transportation. is required. On the other hand, when peeling the surface protection 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 3.0 m/min, the peel strength of the surface protection sheet is 1.0 m/min. It is preferably 50 gf/25 mm, more preferably 2 to 45 gf/25 mm, even more preferably 3 to 40 gf/25 mm. A specific method for measuring the peel strength of the surface protection sheet will be described later in Examples.

Hereinafter, the present invention will be explained in detail with reference to Examples. The present invention is not limited in any way by the examples shown below. In addition, in the following 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)

<Synthesis of polyurethane (A)>
(A-1)
In a reactor equipped with a thermometer, a stirrer, a dropping funnel, and a cooling tube with a drying tube, 5.5 kg (21 mol) of a hydrogenated product of diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethane) and a hydroxyl value 40.1 kg (20 mol) of polypropylene glycol Actokol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) having a hydroxyl group at the end of 56 mg KOH/g was charged. Thereafter, the temperature of the reactor was raised to 60° C. and the reaction was carried out for 4 hours to obtain a polyurethane having isocyanate groups at both ends.

Subsequently, 232.2 g (2 mol) of 2-hydroxyethyl acrylate was added to the reactor, the temperature was raised to 70°C, and the reaction was carried out for 2 hours to obtain 45.8 kg of polyurethane (A-1) having an acryloyl group at the end. . This polyurethane (A-1) 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 (A-1) was 70,000.
Since the disappearance of the peak derived from isocyanate groups was confirmed by IR, 2-hydroxyethyl acrylate was added to all ends of the polyurethane having isocyanate groups at both ends. That is, on a numerical basis, acryloyl groups are introduced into 100% of the terminals of the polyurethane molecules contained in polyurethane (A-1).

(A-2)
A polyurethane having acryloyl groups at both ends was prepared in the same manner as the synthesis method for polyurethane (A-1) except that isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane) was used in place of the hydrogenated product of diphenylmethane diisocyanate. (A-2) was obtained. The weight average molecular weight of the obtained polyurethane (A-2) was 67,000.

(A-3)
Polyurethane ( A polyurethane (A-3) having acryloyl groups at both ends was obtained in the same manner as in the synthesis method of A-1). The weight average molecular weight of the obtained polyurethane (A-3) was 35,000.

(A-4)
Synthesis of polyurethane (A-1) except that 4 mol of hydrogenated diphenylmethane diisocyanate and 3 mol of polypropylene glycol Actocol D-2000 (manufactured by Mitsui Chemicals) having a hydroxyl group at the end with a hydroxyl value of 56 mgKOH/g were used. Polyurethane (A-4) having acryloyl groups at the ends was obtained in the same manner as in the method. The weight average molecular weight of the obtained polyurethane (A-4) was 12,000.

(A-5)
The method for synthesizing polyurethane (A-1) was repeated, except that 1.8 mol of 2-hydroxyethyl acrylate and 0.2 mol of 1-octanol were used instead of 2 mol of 2-hydroxyethyl acrylate. Polyurethane (A-5), which is a mixture of polyurethanes having one end thereof, was obtained. The weight average molecular weight of the obtained polyurethane (A-5) was 69,000.
Since the disappearance of the peak derived from isocyanate groups was confirmed by IR, 2-hydroxyethyl acrylate or 1-octanol was added to all ends of the polyurethane having isocyanate groups at both ends. That is, on a numerical basis, acryloyl groups are introduced into 90% of the terminals of the polyurethane molecules contained in polyurethane (A-5).
At this time, the polyurethane (a1) contained in the polyurethane (A-5) is 80% of the polyurethane (A) on a numerical basis, and the polyurethane (a2) is 20% of the polyurethane (A) on a numerical basis.

<Preparation of adhesive composition for surface protection sheet>
A polyurethane resin (A), a polyfunctional monomer (B), other monomers (C), a photopolymerization initiator (D), and additives were blended in the composition shown in Table 1, and the mixture was heated at 25°C. By mixing using a disper, adhesive compositions according to Examples 1 to 9 and Comparative Examples 1 to 4 were prepared.

<Preparation of surface protection sheet>
In Examples 1 to 9 and Comparative Examples 1 to 4, surface protection sheets having an optical PET film base material on one side were produced in the same manner. First, using an applicator, the prepared adhesive composition was applied onto an optical PET film (A4300 manufactured by Toyobo Co., Ltd.) with a thickness of 75 μm as a separator. It was covered with a 75 μm release PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3kW, 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 remove the adhesive. The composition was photocured. 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 was calculated by measuring the thickness of the surface protection sheet after peeling off the separator using a dial gauge, and then subtracting the thickness of the base material, 75 μm, from this measured value. The measuring surface of the dial gauge was a circular plane with a diameter of 5 mm, and the measuring force was 0.8 N. In all of Examples 1 to 9 and Comparative Examples 1 to 4, it was 75 μm.

<Evaluation of adhesive composition for surface protection sheet and surface protection sheet>
Regarding the adhesive compositions and surface protection sheets according to Examples 1 to 9 and Comparative Examples 1 to 4, gel fraction, transparency (haze value), peel strength, lamination property (wettability), and adhesiveness to adherends The residue and cracking of the adhesive layer upon cutting were evaluated by the method described below. The results are shown in Table 1.

(gel fraction)
First, using an applicator, the adhesive compositions of Examples 1 to 9 and Comparative Examples 1 to 4 were applied to a 50 μm thick release PET film ( It was coated on HY-S10) manufactured by Higashiyama Film Co., Ltd. Note that the method for checking the thickness of the adhesive layer is the same as the measuring method described above in the section of the preparation of the surface protection sheet.

Next, the pressure-sensitive adhesive composition on the release PET film was covered with a release PET film (E7006 manufactured by Toyobo Co., Ltd.) having a thickness of 75 μm. Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high pressure mercury lamp), the adhesive composition whose both sides were covered with a release PET film was applied to the surface of the 75 μm thick release PET film side. The adhesive composition was photocured by irradiating it with ultraviolet rays. 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 prepared sheet was cut into a size of 100 mm x 100 mm, and the release PET films on both sides were peeled off from the cured product of the adhesive composition to prepare a sample for measurement. This measurement sample was immersed in 50 ml of toluene at 25°C for 24 hours, then dried at 80°C for 5 hours, and the gel fraction was calculated from the mass of the measurement sample before and after immersion in toluene using the following formula (1). . The results are shown in Table 1.
Gel fraction (mass%) = [A/B] x 100 (1)
A: Dry mass of measurement sample after immersion in toluene (does not include mass of toluene) B: Mass of measurement sample before immersion in toluene

(Haze value)
The surface protection sheets with separators prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were cut into a size of 50 mm x 50 mm, and the release PET film was peeled off. Thereafter, the exposed entire surface of the adhesive layer was laminated onto a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load: 19.6 N) was made to reciprocate once to prepare a sample for measurement. . The haze value of this measurement sample was measured using a haze meter (NM-150 (manufactured by Murakami Color Research Institute, Inc.)). The haze value (%) was calculated by dividing the diffuse transmittance by the total light transmittance and multiplying by 100. Note that measurements were performed at three locations on the same sample, and the average value thereof was taken as the haze value.

(Peel strength)
The surface protection sheets with separators prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were cut into a size of 25 mm x 150 mm, and the release PET film was peeled off. Thereafter, the exposed entire surface of the adhesive layer was laminated onto a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) with a mass of 2 kg (load: 19.6 N) was made to reciprocate once to prepare a sample for measurement. .
The obtained measurement sample was left in an environment with a temperature of 23° C. and a relative humidity of 50% for 1 hour. Thereafter, according to JIS K 6854-2, a tensile test was performed in a 180° direction at a peeling speed of 0.3 m/min and 3.0 m/min to determine the peel strength (gf/25 mm) of the surface protection sheet against the glass plate. was measured.

(Lamination property)
FIG. 1 is a plan view showing a method for evaluating the lamination properties of the surface protection sheet 10, and FIG. 2 is a sectional view taken along line AA in FIG. The surface protection sheet with separator 10 is cut into a size of 20 mm x 100 mm, and the release PET film is peeled off. Next, the adhesive layer 12 is bonded to the glass plate 30 within a range of 15 mm from one end in the longitudinal direction of the surface protection sheet 10, the adhesive part is fixed to the glass plate 30, and as shown in FIG. Lift the other end of 10. As shown in FIG. 1, the adhesive part can be fixed using a glass plate on the top surface of the surface protection sheet 10 within a range of 15 mm from the one end of the surface protection sheet 10, and on both sides of the surface protection sheet in the width direction. Cellophane tape 20 is pasted to cover.

From this state, the other end of the surface protection sheet 10 was released, and the time required for the entire adhesive layer to come into close contact with the glass plate 30 due to the weight of the surface protection sheet 10 was measured. The lamination properties of the surface protection sheet according to No. 4 were evaluated based on the following criteria.
(Evaluation criteria for lamination properties)
◎: Less than 5 seconds until adhesion ○: More than 5 seconds, less than 10 seconds until adhesion △: More than 10 seconds, less than 15 seconds until adhesion ×: More than 15 seconds until adhesion, or no adhesion

(glue residue)
The surface protection sheets with separators prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were cut into pieces of 50 mm x 50 mm, and the release PET films were peeled off. Next, the exposed adhesive surface was laminated onto a glass plate, and this was used as a sample. After this sample was left at 85° C. and 85% relative humidity for 3 days, the surface protection sheet was removed from the glass plate, and the adhesive residue on the surface of the glass plate was visually confirmed and evaluated according to the following criteria.

(Evaluation criteria for adhesive residue)
○: There is no change in the surface of the glass plate compared to before bonding.
Δ: Slight adhesive residue is observed on the surface of the glass plate.
×: Adhesive residue is clearly observed on the surface of the glass plate.

(Cracked adhesive layer when cutting)
The surface protection sheets prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were cut with a pinnacle blade (blade height: 0.80 mm, blade angle: 50° (manufactured by Tsukatani Hamono Seisakusho Co., Ltd.)), and after cutting. The end face of the adhesive layer was observed with a microscope (magnification: 800 times (RH-2000, manufactured by Hirox Co., Ltd.)) and evaluated according to the following criteria.

(Crack evaluation criteria)
○: Cracks are observed in the adhesive layer.
×: No cracks are observed in the adhesive layer.

<Evaluation results of Examples and Comparative Examples>
According to the above Examples and Comparative Examples, adhesive residue was observed in the composition of Comparative Example 1 in which the content of polyurethane (A) was 10% by mass. Furthermore, the composition of Comparative Example 2 in which polyurethane (A-4) having a weight average molecular weight of 12,000 was used as polyurethane (A) had insufficient lamination properties and adhesive residue was observed. Furthermore, the composition of Comparative Example 3, which did not contain the polyfunctional monomer (B), had too high peel strength and insufficient lamination properties. In the composition of Comparative Example 4 containing 15% by mass of the polyfunctional monomer (B), the adhesive layer was hard and cracked when cut.

10... Surface protection sheet 12... Adhesive layer 14... Base material 20... Cellophane tape 30... Glass plate

Claims (13)

polyurethane (A),
A polyfunctional monomer (B),
Other monomers (C) that can be polymerized with the polyurethane (A) and the polyfunctional monomer (B),
A photopolymerization initiator (D),
An adhesive composition for a surface protection sheet comprising:
The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate,
The polyurethane (A) contains polyurethane (a1),
The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth)acryloyl groups at a plurality of terminals of the polyurethane (a1),
The weight average molecular weight of the polyurethane (A) is 30,000 to 200,000,
The polyfunctional monomer (B) is a compound having multiple (meth)acryloyl groups,
Based on 100% by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
The content of the polyurethane (A) is 30 to 60% by mass,
The content of the polyfunctional monomer (B) is 4 to 8 % by mass,
The content of the other monomer (C) is 30 to 68% by mass,
Based on 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
An adhesive composition for a surface protection sheet, characterized in that the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass. The adhesive composition for a surface protection sheet according to claim 1, wherein the structure derived from the polyoxyalkylene polyol contained in the polyurethane (A) is a structure derived from a polyoxyalkylene polyol having a number average molecular weight of 500 to 5,000. . The pressure-sensitive adhesive composition for a surface protection sheet according to claim 1 or 2, wherein the skeleton contained in the polyurethane (A) is a copolymer of polyoxyalkylene glycol and diisocyanate. The polyoxyalkylene glycol is polypropylene glycol,
The adhesive composition for a surface protection sheet according to claim 3, wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate. The pressure-sensitive adhesive composition for a surface protection sheet according to any one of claims 1 to 4, wherein the (meth)acryloyl group in the polyurethane (A) is a part of a (meth)acryloyloxy group. The adhesive composition for a surface protection sheet according to any one of claims 1 to 5, wherein the polyfunctional monomer (B) has three or more (meth)acryloyl groups. The adhesive composition for a surface protection sheet according to claim 6, wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate. The adhesive composition for a surface protection sheet according to any one of claims 1 to 7, wherein the other monomer (C) has only one (meth)acryloyl group. The adhesive composition for a surface protection sheet according to any one of claims 1 to 8, wherein the other monomer (C) contains an alkyl (meth)acrylate. The polyurethane (A) further includes polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and has a (meth)acryloyl group at only one terminal of the polyurethane (a2). The pressure-sensitive adhesive composition for a surface protection sheet according to any one of 1 to 9. The adhesive for a surface protection sheet according to any one of claims 1 to 10, wherein (meth)acryloyl groups are introduced into 90 to 100% of the terminals of the polyurethane molecules contained in the polyurethane (A) on a numerical basis. agent composition. Furthermore, it contains fatty acid ester,
The content of the fatty acid ester is 1 to 40 parts by mass based on 100% by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C).
The adhesive composition for a surface protection sheet according to any one of claims 1 to 11. A sheet-like base material,
an adhesive layer formed on the base material,
A surface protection sheet, wherein the adhesive layer is made of a photocured product of the adhesive composition for a surface protection sheet according to any one of claims 1 to 12 .

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