WO2020066866A1

WO2020066866A1 - Surface-protection-sheet adhesive composition and surface protection sheet

Info

Publication number: WO2020066866A1
Application number: PCT/JP2019/036884
Authority: WO
Inventors: 達宏池谷; 一博佐々木; 中西　健一
Original assignee: 昭和電工株式会社
Priority date: 2018-09-26
Filing date: 2019-09-20
Publication date: 2020-04-02
Also published as: JPWO2020066866A1; KR20210042943A; JP7380577B2; TWI824013B; KR102567177B1; CN112752817A; TW202026385A

Abstract

Provided is a surface-protection-sheet adhesive composition for a surface protection sheet in which a crack does not occur when being cut, in addition to: exhibiting low haze; being easily laminated; being easily peeled off; and being capable of suppressing the occurrence of adhesive residue after being peeled off. The present invention provides a surface-protection-sheet adhesive composition that contains: 30-60% by mass of a polyurethane (A); 2-10% by mass of a polyfunctional monomer (B); 30-68% by mass of another monomer (C) that is polymerizable with the polyurethane (A) and the polyfunctional monomer (B); and 0.1-5 parts by mass of a photopolymerization initiator (D) with respect to the total amount, that is, 100 parts by mass, of the substances (A)-(C). The surface-protection-sheet adhesive composition is characterized in that the polyurethane (A) has a skeleton including a structure originating from a polyoxyalkylene polyol and a structure originating from a polyisocyanate, has (meth)acryloyl groups at a plurality of termini thereof, and has a weight average molecular weight of 30,000-200,000.

Description

Pressure-sensitive adhesive composition for surface protection sheet and surface protection sheet

The present invention relates to a pressure-sensitive adhesive composition for a surface protection sheet and a surface protection sheet, and more particularly to a pressure-sensitive adhesive composition for a surface protection sheet containing a compound having a (meth) acryloyl group, and a pressure-sensitive adhesive composition for the surface protection sheet. The present invention relates to a surface protection sheet having a cured product.
Priority is claimed on Japanese Patent Application No. 2018-180614, filed Sep. 26, 2018, the content of which is incorporated herein by reference.

種々 Various optical films are used for optical parts such as liquid crystal displays and touch panels such as smartphones, personal computers, and televisions. A protective sheet (surface protective sheet) is generally laminated on the surface of these optical films for the purpose of preventing dirt and damage in the transporting step, the manufacturing step, and the inspection step. This protective sheet is peeled off in a later step such as an assembling step. Various urethane pressure-sensitive adhesives have been proposed as pressure-sensitive adhesives for such protective sheets.

For example, in Patent Document 1, polyurethane having a polyoxyalkylene polyol as a skeleton and having a (meth) acryloyl group at a terminal and having a weight average molecular weight of 10,000 to 300,000, a hydroxy group-containing (meth) acrylate, and other A photocurable composition for a transparent pressure-sensitive adhesive sheet containing a photopolymerizable monomer and a photopolymerization initiator is described.

Further, in Patent Document 2, a polyurethane in which a (meth) acryloyl group is bonded to a terminal of a polyoxyalkylene chain via a urethane bond, a (meth) acrylate having a hydroxy group, and a (meth) acrylate having an aromatic ring And a photocurable composition for a transparent pressure-sensitive adhesive sheet, which contains another polymerizable monomer and a photopolymerization initiator.

In the inspection process of optical components, it is sometimes required to be able to sufficiently detect or detect fine foreign matter or scratches on the product or component in a state where the protective sheet is laminated on the product or component. Therefore, the protective sheet is required to be less fogged, that is, to have a lower haze.

In the manufacturing process of the optical component, the protective sheet may be repeatedly laminated and peeled off. Therefore, the protective sheet is required to be easily laminated to the adherend (high wettability to the adherend) and easily peeled. In recent years, the optical components themselves have been easily broken with the increase in the screen size of displays and the reduction in thickness of panel components and the like. For this reason, it is also required that the protective sheet has an appropriate tackiness (peeling strength) and can be peeled with a lighter force (light peeling property). Further, it is also required that a part of the pressure-sensitive adhesive layer or the like remains on the product surface (the adherend) after the protective sheet is peeled, that is, there is no so-called adhesive residue (removability).

JP 2014-210895 A JP 2016-20577 A

However, the compositions described in Patent Literature 1 and Patent Literature 2 are not intended for use as a protective sheet for peeling off in a manufacturing process, and pressure-sensitive adhesive sheets using these compositions have high peel strength. .

Therefore, the present inventors have made intensive studies to solve the above-mentioned problems, and include a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and having a (meth) acryloyl group at a plurality of terminals. A polyurethane having a weight average molecular weight of 30,000 to 200,000, a polyfunctional monomer having a plurality of (meth) acryloyl groups, another monomer polymerizable with the polyurethane and the polyfunctional monomer, and photopolymerization. By curing the pressure-sensitive adhesive composition for a photocurable surface protection sheet containing an initiator, a surface protection sheet that has a low haze, is easy to laminate, and is easy to peel off, and can further suppress adhesive residue after peeling is obtained. Was found. However, the surface protective sheet obtained from the pressure-sensitive adhesive composition for a photocurable surface protective sheet has a slightly hard pressure-sensitive adhesive layer. It has been found that cracks may occur on the end face.

Therefore, an object of the present invention is to provide a surface protection sheet having a low haze, easy to laminate, easy to peel, and capable of suppressing adhesive residue after peeling, and in which a pressure-sensitive adhesive layer does not crack 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 which has a low haze, is easy to laminate, is easy to peel off, can suppress the adhesive residue after peeling, and does not cause cracks in the pressure-sensitive adhesive layer at the time of cutting. 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 monomer (C) polymerizable with polyurethane (A) and polyfunctional monomer (B),
A photopolymerization initiator (D);
A pressure-sensitive 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) includes a 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 polyurethane (A) has a weight average molecular weight of 30,000 to 200,000;
The polyfunctional monomer (B) is a compound having a plurality of (meth) acryloyl groups, and is composed of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). For a 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,
For the total amount of 100 parts by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
The pressure-sensitive adhesive composition for a surface protective sheet, wherein the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass.
[2] The pressure-sensitive adhesive for a surface protective 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. Composition.
[3] The pressure-sensitive adhesive for a surface protective sheet according to any one of [1] and [2], wherein the skeleton included in the polyurethane (A) is a copolymer of the polyoxyalkylene glycol and the diisocyanate. Composition.
[4] the polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [3], wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate.
[5] The pressure-sensitive adhesive composition for a surface protective 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 pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [5], wherein the polyfunctional monomer (B) has three or more (meth) acryloyl groups.
[7] The pressure-sensitive adhesive composition for a surface protective sheet according to [6], wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate.
[8] The pressure-sensitive adhesive composition for a surface protective sheet according to [7], wherein the other monomer (C) has a (meth) acryloyl group.
[9] The pressure-sensitive adhesive composition for a surface protective sheet according to [8], wherein the other monomer (C) contains a (meth) alkyl acrylate.
[10] The polyurethane (A) further includes a polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and a polyurethane (a2) having a (meth) acryloyl group at only one terminal of the polyurethane (a2). The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [9].
[11] The surface protection according to any of [1] to [10], wherein a (meth) acryloyl group is introduced into 90 to 100% of the terminals of the polyurethane molecule contained in the polyurethane (A) on a numerical basis. An adhesive composition for a sheet.
[12] a sheet-like substrate,
Having an adhesive layer formed on the base material,
A surface protection sheet, characterized in that the pressure-sensitive adhesive layer comprises a photocured product of the pressure-sensitive adhesive composition for a surface protection sheet according to any one of [1] to [11].

Advantageous Effects of Invention According to the present invention, a surface protection sheet for a surface protection sheet that has a low haze, is easy to laminate, easily peels, and can suppress adhesive residue after peeling, and does not cause cracks in an adhesive layer during cutting processing. Pressure sensitive adhesive composition can be provided. Further, according to the present invention, in addition to providing a surface protective sheet that has a low haze, is easy to laminate, easily peels, and can suppress the adhesive residue after peeling, and does not cause cracking of an adhesive layer during cutting. Can be.

It is the top view which showed the lamination property evaluation method of the surface protection sheet. It is AA sectional drawing in FIG.

Hereinafter, an embodiment of the present invention will be described. Here, (meth) acryloyl group, the formula _CH 2 = _CH-CO-, a group represented by and the formula _{_{CH 2 = C (CH 3)}} -CO- with at least one member selected from the functional groups represented means, (meth) acrylate and the acryloyloxy group, the formula _CH 2 = _CH-CO-O-, a group represented by the and the formula _{_{CH 2 = C (CH 3)}} -CO-O- represented by functional group Means one or more selected from Further, the isocyanato group means a functional group represented by a chemical formula -N = C = O.

<1. Pressure-sensitive adhesive composition for surface protection sheet>
The pressure-sensitive adhesive composition for a surface protective sheet according to the present embodiment (hereinafter, also referred to as a “pressure-sensitive adhesive composition”) includes a polyurethane (A), a polyfunctional monomer (B), and a polyurethane (A). ) And other monomers (C) 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 the polyurethane (a1). The polyurethane (a1) has a skeleton containing 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. The content of the polyurethane (A) is 30 to 60% by mass based on the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C) being 100% by mass. 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 0.1 part by mass based on 100 parts by mass of the total of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). The amount is 1 to 5 parts by mass.
Further, the pressure-sensitive adhesive composition according to the present embodiment may include an additive such as a fatty acid ester, if necessary. Furthermore, the pressure-sensitive adhesive composition according to the present embodiment may not include a solvent, but may include a solvent as needed.
Hereinafter, each component contained in the pressure-sensitive adhesive composition will be described. In the following description, components composed of polyurethane (A), polyfunctional monomer (B), and other monomer (C) may be referred to as “components (A) to (C)”.

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

[Polyurethane (a1)]
The polyurethane (a1) is a polyurethane having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and having (meth) acryloyl groups at a plurality of terminals. The terminal (meth) acryloyl group of the polyurethane (a1) is preferably a part of a (meth) acryloyloxy group.

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

The “plurality of ends” of the present invention are two ends in the case of a linear polymer, and two or more ends in the same number of ends as each branched chain in the case of a branched polymer.
The polyurethane (A) contains no components other than the polyurethane (a1) and the polyurethane (a2).

ポリウレタン The polyurethane (a1) contained in the polyurethane (A) is preferably 80 to 100%, more preferably 90 to 100%, even more preferably 100% of the polyurethane (A) on a number basis. The polyurethane (a2) contained in the polyurethane (A) is preferably 0 to 20%, more preferably 0 to 10%, even more preferably 0% of the polyurethane (A) on a number basis. If the polyurethane (a1) contained in the polyurethane (A) is at least 80%, the cohesive force of the cured product of the pressure-sensitive adhesive composition will be sufficiently large.

"Polyoxyalkylene polyol"
As the polyoxyalkylene polyol, those having an alkylene chain having 2 to 4 carbon atoms are preferable, and specific examples thereof include polyoxyethylene polyol, polyoxypropylene polyol, and polyoxybutylene polyol. Further, 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 alkylene chains. Further, the polyurethane (A) may have a structure in which structures derived from two or more different polyoxyalkylene polyols are bonded via a polyisocyanate.

The number average molecular weight of the polyoxyalkylene polyol is preferably from 500 to 5,000, more preferably from 800 to 4,000, and even more preferably from 1,000 to 3,000. When the number average molecular weight is 500 or more, the peel strength of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition is improved. 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 pressure-sensitive 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 from 20 to 120 mgKOH / g, more preferably from 30 to 100 mgKOH / g, even more preferably from 40 to 80 mgKOH / g. As a specific example of the polypropylene glycol, Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type) of a polypropylene glycol having a hydroxyl group (hydroxy group) having a hydroxyl value of 56 mgKOH / g is exemplified.
Here, the hydroxyl value is a hydroxyl value of the polyoxyalkylene polyol measured according to JIS K0070, and is a 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, the hydroxyl group in the sample can be acetylated using acetic anhydride, and the free acetic acid generated at that time can be determined by titration with a potassium hydroxide solution.

"Polyisocyanate"
The polyisocyanate is not particularly limited as long as it is a compound having a plurality of isocyanato 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 Hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, norbornane diisocyanate, and the like.

Among these exemplified compounds, a hydrogenated product of isophorone diisocyanate or diphenylmethane diisocyanate is preferred from the viewpoint of control of light resistance and reactivity, and a hydrogenated product of diphenylmethane diisocyanate is more preferred from the viewpoint of reactivity. The structure derived from the polyisocyanate contained in the polyurethane (A) may be one kind or a structure containing two or more kinds.
Specific examples of the polyisocyanate include hydrogenated diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestourethane), and isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestourethane).

(4) The weight average molecular weight of the polyurethane (A) is from 30,000 to 200,000, preferably from 50,000 to 150,000, and more preferably from 70,000 to 100,000. When the weight average molecular weight of the polyurethane (A) is less than 30,000, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition has insufficient flexibility, and the surface protective sheet having this pressure-sensitive adhesive layer is laminated. It is hard to remove. On the other hand, when the weight average molecular weight of the polyurethane (A) is more than 200,000, handling becomes difficult, for example, the viscosity becomes high as the pressure-sensitive adhesive composition, and workability decreases.

The content of the polyurethane (A) is 30 to 60% by mass, preferably 35 to 55% by mass, and more preferably 40 to 50% by mass based on the total amount of the components (A) to (C). Is more preferred. When the content of the polyurethane (A) is less than 30% by mass, the cohesive force of the cured product of the pressure-sensitive adhesive composition is insufficient, the pressure-sensitive adhesive layer becomes too soft, and the pressure-sensitive adhesive surface (between the pressure-sensitive adhesive layer and the adherend). There is a concern that air bubbles may be trapped in the gap. When the content of the polyurethane (A) is more than 60% by mass, the cohesive force of the cured product of the pressure-sensitive adhesive composition is too high, the flexibility of the pressure-sensitive adhesive layer is insufficient, and the wettability of the pressure-sensitive adhesive layer to an adherend is low. There is concern that it will decline.

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

The polyfunctional monomer (B) is preferably a poly (meth) acrylate of a polyol compound, 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-dimethylhydantoindi ( (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, and the like.

Among these, 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol, from the viewpoint that the peel strength of the surface protective sheet using the pressure-sensitive adhesive composition is easily adjusted to be low. Trihydroxy (meth) acrylate and pentaerythritol tetra (meth) acrylate are more preferred, and trimethylolpropane tri (meth) acrylate is even more preferred. Further, the polyfunctional monomer (B) may be composed of one kind of compound, or may be composed of two or more kinds of compounds.

The content of the polyfunctional monomer (B) is 2 to 10% by mass, preferably 3 to 9% by mass, and preferably 4 to 8% by mass based on the total amount of the components (A) to (C). % Is more preferable. When the content is less than 2% by mass, the peel strength of the surface protective sheet is too high, and the light peelability is poor. When the content is more than 10% by mass, the pressure-sensitive adhesive layer using the cured product of the pressure-sensitive adhesive composition becomes hard, and cracks are easily generated at the time of cutting the sheet. If the content is more than 10% by mass, the haze tends to be high as a surface protective sheet.

<1-3. Other monomer (C)>
The other monomer (C) is a compound other than the polyurethane (A) and other than the polyfunctional monomer (B), and is polymerizable with the polyurethane (A) and the polyfunctional monomer (B). If it is, there is no particular limitation. However, the other monomer (C) preferably has a radically polymerizable ethylenically unsaturated bond as a functional group for polymerizing with the polyurethane (A) and the polyfunctional monomer (B). Above all, it preferably has a vinyl group or a (meth) acryloyl group, and more preferably has a (meth) acryloyl group.

The other monomer (C) is not particularly limited, but includes an alkyl (meth) acrylate, a cyclic alkyl (meth) acrylate, an alkoxyalkyl (meth) acrylate, an alkoxy (poly) alkylene glycol (meth) acrylate, and a hydroxy group-containing monomer. (Meth) acrylate, carboxy group-containing (meth) acrylate, fluorinated alkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylate, (meth) acrylamide, epoxy group-containing (meth) acrylate, unsaturated carboxylic acid, 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, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, n-hexyl (meth) acrylate, isooctyl (meth) acrylate, isostearyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, etc. No.

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) A) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentanyloxyethyl (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 and the like.

{Alkoxy (poly) alkylene glycol (meth) acrylates include, for example, methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, and methoxydipropylene glycol (meth) acrylate.

Examples of the hydroxy group-containing (meth) acrylate 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 and N, N-diethylaminoethyl (meth) acrylate.

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, diacetoneacrylamide and the like.

Examples of the epoxy group-containing (meth) acrylate include glycidyl (meth) acrylate.
Examples of the unsaturated carboxylic acid include (meth) acrylic acid, maleic acid, and itaconic acid.

Other monomers (C) other than the above compounds include, for example, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, Alkyl vinyl ether, vinyl toluene, N-vinyl pyridine, N-vinyl pyrrolidone, dialkyl itaconate, dialkyl fumarate, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether Or diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyl trime Le ammonium chloride, dimethyl allyl vinyl ketone.

Among these exemplified compounds, alkyl (meth) acrylate is preferable from the viewpoint of compatibility with the polyurethane (A), viscosity of the pressure-sensitive adhesive composition, and adjustment of peel strength, and 2-ethylhexyl (meth) acrylate and isooctyl are preferable. (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 kind of compound or two or more kinds of compounds.

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

<1-4. Photopolymerization initiator (D)>
The photopolymerization initiator (D) is not particularly limited, but includes a carbonyl-based photopolymerization initiator, a sulfide-based photopolymerization initiator, an acylphosphine oxide-based photopolymerization initiator, a quinone-based photopolymerization initiator, and a sulfochloride-based photopolymerization. Examples of the initiator include a thioxanthone-based photopolymerization initiator.

Examples of the carbonyl-based photopolymerization initiator include benzophenone, benzyl, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and 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, methylbenzoyl formate, 2,2-diethoxyacetophenone, 4-N, N'-dimethylacetophenone, 2-methyl-1- [4- (methylthio) phenyl] -2 -Morpholinopropan-1-one and the like.

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

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

(2) Examples of the quinone-based photopolymerization initiator include quinone-based photopolymerization initiators such as benzoquinone and anthraquinone.

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

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

Among these exemplified compounds, 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are preferred from the viewpoint of the transparency of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive 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 of components (A) to (C). And more preferably 0.3 to 2 parts by mass. When the content of the photopolymerization initiator (D) is less than 0.1 part by mass, the pressure-sensitive adhesive composition is not sufficiently cured by light. The releasability of the surface protective sheet tends to deteriorate.

<1-5. Additives>
To the pressure-sensitive adhesive composition, a fatty acid ester is added as necessary to improve the laminating property (wetting property) and the bubble-removing property (easiness of removing air bubbles trapped during bonding) of the obtained surface protective sheet. You may. Examples of the fatty acid ester include an ester of a monobasic acid or a polybasic acid having 8 to 18 carbon atoms and a branched alcohol having 18 or less carbon atoms, an unsaturated fatty acid having 14 to 18 carbon atoms, or a branched chain. And esters of the acid and a tetrahydric alcohol. A preferred specific example of the fatty acid ester is isopropyl myristate. The amount of the fatty acid ester to be added is preferably 1 to 40 parts by mass, more preferably 3 to 35 parts by mass, further preferably 5 to 30 parts by mass based on 100 parts by mass of the total of components (A) to (C). preferable.

In addition, other additives may be added to the pressure-sensitive adhesive composition as needed as long as the transparency is not impaired. Examples of the additive include a plasticizer, a surface lubricant, a leveling agent, a softener, an antioxidant, an antioxidant, a light stabilizer, an ultraviolet absorber, a polymerization inhibitor, a benzotriazole-based light stabilizer, Examples include acid ester-based and other flame retardants, antistatic agents such as surfactants, dyes, and the like.

<1-6. Solvent>
Since the pressure-sensitive adhesive composition contains a polyfunctional monomer (B) and another monomer (C) as low molecular weight components, the pressure-sensitive adhesive composition can be adjusted to a coatable viscosity without adding a solvent. That is, the pressure-sensitive adhesive composition comprises, in addition to the essential components consisting of the polyurethane (A), the polyfunctional monomer (B), the other monomer (C), and the photopolymerization initiator (D). And may not substantially contain a solvent. In that case, when manufacturing the surface protective sheet, the step of heating and drying the solvent can be omitted, and the productivity is increased. In particular, when producing a surface protective sheet having a thickness of more than 50 μm, it is preferable that the pressure-sensitive 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 pressure-sensitive adhesive composition of the present invention is 0 to 1% by mass, preferably 0 to 0.5% by mass, more preferably 0 to 0.5% by mass. ～ 0.1% by mass.
A solvent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the viscosity during coating. The solvent can be appropriately selected depending on other components and the like contained in the pressure-sensitive adhesive composition, but an organic solvent is preferable.
The organic solvent used is not particularly limited, but includes 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 as a mixture of two or more. The solvent is preferably removed by applying the pressure-sensitive adhesive composition to a substrate or the like, followed by drying, followed by photo-curing.

<2. Method for producing pressure-sensitive adhesive composition for surface protective sheet>
Here, an example of a method for synthesizing the polyurethane (A) will be described, but it is included in the polyfunctional monomer (B) and the other monomer (C) and the pressure-sensitive adhesive composition for a surface protective sheet. Other components are easy to purchase commercially and vary depending on the type of compound used, so that the description of the synthesis method is omitted.

<2-1. Method for synthesizing polyurethane (A)>
Hereinafter, an example of a preferred method for synthesizing the polyurethane (A) contained in the pressure-sensitive adhesive composition of the present embodiment will be described. However, the method for synthesizing the polyurethane (A) is not limited thereto, and conditions such as raw materials and equipment used for the synthesis are used. Can be changed as appropriate. Further, in this example, the reaction between the hydroxy group and the isocyanate group is carried out in any step in the presence of an organic solvent inert to the isocyanate group in the presence of an urethane such as dibutyltin dilaurate, dibutyltin diethylhexoate, or dioctyltin dilaurate. This is carried out using a catalyst for conversion. The reaction is preferably performed 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, a polyoxyalkylene polyol and a polyisocyanate are charged at a ratio where the amount of isocyanato groups (number basis, the same applies hereinafter) becomes larger than the amount of hydroxy groups (number basis, hereinafter the same), and these are reacted to form an isocyanato group at the terminal. Synthesize a polyurethane. Specific examples of the polyoxyalkylene polyol and the polyisocyanate are as exemplified in the section of the polyurethane (A).

At this time, the molecular weight (degree of polymerization) can be adjusted by adjusting the amount of the isocyanato group with respect to the amount of the hydroxy group. Specifically, the smaller the excess amount of the isocyanate group relative to the hydroxy group amount, the larger the molecular weight of the isocyanate group-containing polyurethane, and the larger the excess amount of the isocyanate group amount relative to the hydroxy group amount, the larger the isocyanate group-containing polyurethane. The molecular weight decreases.

Next, a polyurethane having an isocyanato group at a terminal and a compound having a hydroxy group and a (meth) acryloyl group are reacted to synthesize a polyurethane (A) having a (meth) acryloyl group at a molecular chain terminal. The (meth) acryloyl group contained in this compound is preferably a part of a (meth) acryloyloxy group.

Examples of the compound having a hydroxy group and a (meth) acryloyl group include, but are not particularly limited to, hydroxyalkyl (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 And monools having a (meth) acryloyl group derived from various polyols. These may be used alone or in combination of two or more. Among them, 2-hydroxyethyl (meth) acrylate is preferred in terms of reactivity with isocyanato groups and photocurability.

Further, in addition to a compound having a hydroxy group and a (meth) acryloyl group, an alkyl alcohol having no (meth) acryloyl group and having one hydroxy group is used in combination to react with a polyurethane having an isocyanate group at a terminal. This makes it possible to adjust the amount of the (meth) acryloyl group introduced. Examples of the alkyl alcohol include, but are not particularly limited to, linear, branched, and alicyclic alkyl alcohols, and these may be used alone or in combination of two or more. . As a result, a polyurethane having a structure derived from the above-mentioned alkyl alcohol at at least one end is produced. In this case, the polyurethane (A) includes a polyurethane having no (meth) acryloyl group at at least one end. Therefore, a polyurethane (a2) having a (meth) acryloyl group at only one terminal can also be included.

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

<2-2. Modification of Polyurethane (A) Synthesis Method>
A modified example of the method for synthesizing the polyurethane (A) will be described. In this example, as in the above example, the reaction between the hydroxy group and the isocyanato group was carried out in any step in the presence of an organic solvent inert to the isocyanato group, in the presence of dibutyltin dilaurate, dibutyltin diethylhexoate, This is performed using a urethanization catalyst such as dioctyltin dilaurate. The reaction is preferably performed 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 where the amount of hydroxy groups is larger than the amount of isocyanato groups, to synthesize a polyurethane having a hydroxy group at a terminal.

At this time, similarly to the above example, the molecular weight can be adjusted by adjusting the ratio of the amount of the hydroxy group to the amount of the isocyanate group. Specifically, the smaller the excess amount of the hydroxy group relative to the amount of the isocyanate group, the larger the molecular weight of the polyurethane having a hydroxy group, and the larger the excess amount of the hydroxy group relative to the amount of the isocyanate group, the greater the amount of the polyurethane having the hydroxy group. The molecular weight decreases.

Next, a polyurethane having a (meth) acryloyl group at a molecular chain terminal is synthesized by reacting a polyurethane having a hydroxy group at a terminal with a compound having an isocyanato group and a (meth) acryloyl group. The (meth) acryloyl group contained in this compound is preferably a part of a (meth) acryloyloxy group.

The compound having an isocyanato group and a (meth) acryloyl group is not particularly limited, but is 2- (meth) acryloyloxyethyl isocyanate, 2- (meth) acryloyloxypropyl isocyanate, 1,1-bis (acryloyloxymethyl) ethyl And isocyanate. Commercially available compounds having an isocyanato group and a (meth) acryloyl group include, for example, Karenz MOI (registered trademark) and Karenz AOI (registered trademark) manufactured by Showa Denko KK. These may be used alone or in combination of two or more. Among them, 2- (meth) acryloyloxyethyl isocyanate is preferred from the viewpoint of reactivity with a hydroxy group and photocurability.

Further, in addition to a compound having an isocyanate group and a (meth) acryloyl group, an alkyl isocyanate having no (meth) acryloyl group and having one isocyanato group is used in combination to react with a polyurethane having a hydroxy group at a terminal. This makes it possible to adjust the amount of the (meth) acryloyl group introduced. Examples of the alkyl isocyanate include, but are not particularly limited to, linear, branched, and alicyclic alkyl isocyanates. These may be used alone or in combination of two or more. . As a result, a polyurethane having a structure derived from the above-mentioned alkyl isocyanate at at least one end is produced. In this case, the polyurethane (A) includes a polyurethane having no (meth) acryloyl group at at least one end. Therefore, in this case, the polyurethane (A) may include a polyurethane having a (meth) acryloyl group at only one terminal.

It is preferable that a (meth) acryloyl group is introduced in 90 to 100% of the terminals of the polyurethane contained in the polyurethane (A), more preferably 95 to 100%, and still more preferably 100%, on a numerical basis. When the amount of the (meth) acryloyl group introduced is 90% or more based on the number of isocyanato groups, a sufficient cohesive force of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition can be obtained.

<2-3. Method for mixing components contained in pressure-sensitive adhesive composition for surface protective sheet>
A polyurethane (A), a polyfunctional monomer (B), another monomer (C), a photopolymerization initiator (D), a fatty acid ester added as required, and other additives, And an organic solvent to produce an adhesive composition. The mixing method is not particularly limited. For example, the mixing can be performed using a stirrer equipped with a stirrer such as a homodisper or a paddle blade.

Alternatively, all the components may be added and mixed at once, or the addition and mixing may be repeated for each component a plurality of times. In addition, when there is a solid component at room temperature, this component is added by dissolving it in a solvent or dispersing it in a dispersion medium, or by adding it by heating and melting it. It becomes easy to mix with high uniformity in the pressure-sensitive adhesive composition.

<3. Surface protection sheet>
<3-1. Configuration of Surface Protection Sheet>
The surface protective sheet according to the present embodiment has a pressure-sensitive adhesive layer containing a cured product of the pressure-sensitive adhesive composition formed on one surface of a substrate. The thickness of the pressure-sensitive adhesive layer is preferably from 3 to 150 μm, more preferably from 5 to 130 μm, even more preferably from 10 to 100 μm. When the film thickness of the pressure-sensitive adhesive layer is 3 μm or more, the strength of the pressure-sensitive adhesive layer is sufficient, and when the film thickness is 150 μm or less, control of the film thickness of the pressure-sensitive adhesive layer is easy.
Further, when it is desired to impart a function of protecting the adherend from impact (impact resistance) to the surface protective sheet, the thickness of the pressure-sensitive adhesive layer is preferably 50 μm or more.

The gel fraction of the cured product of the pressure-sensitive adhesive composition contained in the pressure-sensitive adhesive layer is preferably from 85 to 100% by mass, more preferably from 90 to 100% by mass, and preferably from 95 to 100% by mass. More preferred. Here, the gel fraction is a mass fraction of an extractable insoluble component with respect to a solvent. Here, the solvent is selected from among cured products of the pressure-sensitive adhesive composition that can dissolve components that are not crosslinked. An example of a specific method for measuring the gel fraction will be described later in Examples. When the gel fraction of the cured product of the pressure-sensitive adhesive composition is 85 to 100% by mass, a so-called glue residue can be suppressed, in which a part of the pressure-sensitive adhesive layer remains on the adherend when the surface protective sheet is peeled off. can do.

材質 The material of the substrate can be appropriately selected according to the use of the surface protection sheet, and examples thereof include a resin film. When the surface protection sheet is used, for example, as a protection sheet in a manufacturing process, and when the adherend, that is, a product is inspected for the presence of scratches or foreign matter, when the protection sheet is used in a laminated state, the base material is transparent. It is preferred that Examples of the transparent substrate include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, and cellulose.

The thickness of the base material can be appropriately selected according to the use of the surface protective sheet, and is not particularly limited. When the resin film is used, the thickness of the base material is preferably 5 μm or more from the viewpoint of handleability and strength. , More preferably at least 10 μm, even more preferably at least 20 μm. Considering the flexibility of the resin film, the thickness of the substrate is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less.

Further, as the substrate, a substrate which has been subjected to an antistatic treatment is preferably used. The antistatic treatment applied to the substrate is not particularly limited, and a method of providing an antistatic layer on at least one surface of the substrate, a method of kneading an antistatic agent into the substrate, or the like can be used. Further, the surface of the base material on which the pressure-sensitive adhesive layer is formed may be subjected to an easy adhesion treatment such as an acid treatment, an alkali treatment, a primer treatment, a corona treatment, a plasma treatment, an ultraviolet treatment, and an ozone treatment, if necessary. Good.

セパレータ The surface protective sheet can be laminated with a separator on the surface of the pressure-sensitive adhesive layer for the purpose of protecting the pressure-sensitive adhesive layer. As a material for the separator, for example, paper, a plastic film, or the like can be used, and a plastic film is preferable 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-mentioned pressure-sensitive adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, and polybutene.

<3-2. Manufacturing method of surface protection sheet>
The method for producing the surface protective sheet according to the present embodiment is, for example, by applying a pressure-sensitive adhesive composition to a base sheet, laminating a separator, and then irradiating the applied pressure-sensitive adhesive composition with ultraviolet light to cure the photocurable composition. Obtainable.

方法 The method for applying the pressure-sensitive adhesive composition to the substrate is not particularly limited, and can be appropriately selected. For example, as a method of applying the pressure-sensitive adhesive composition to a substrate, various coaters such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, and a direct coater. The method used, the screen printing method, and the like are included.

The light source for photocuring the pressure-sensitive adhesive composition includes 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 any value as long as the pressure-sensitive adhesive composition can be sufficiently cured, and is preferably, for example, 50 to 3000 mW / cm ² . If the light irradiation intensity is low, the curing takes a long time, and the productivity is reduced. Light irradiation can be performed from either the separator side or the substrate side as long as it is transparent.

<3-3. Use of surface protection sheet and required performance>
In the inspection process, it may be required that a fine foreign substance or a flaw of a product or a component can be sufficiently detected or detected in a state where a protective sheet is laminated on the product or the component. In addition, the protective sheet is a surface of a plastic film used as an optical component such as a polarizing plate, a wave plate, a retardation plate, an optical compensation film, a reflection sheet, and a brightness enhancement film used for a liquid crystal display such as a smartphone, a personal computer, and a television. May be suitably used for the purpose of protecting.

場合 When the surface protective sheet according to the present embodiment is used as such a protective sheet, the surface protective sheet is required to have little fogging, that is, low haze. In that case, the haze value of the surface protective 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 protective sheet will be described later in Examples.

When the surface protective sheet according to the present embodiment is used as the above protective sheet, the surface protective sheet has a minimum peel strength so as not to peel off from the product or part during handling such as transportation. Is required. On the other hand, when the surface protection sheet is peeled off from the product or component, it is necessary to reduce the peeling 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, the peel strength of the surface protective sheet depends on the thickness of the substrate and the pressure-sensitive adhesive layer when the peeling speed is 3.0 m / min, but is 1 when the pressure-sensitive adhesive layer is 50 to 100 μm. It is preferably from 50 to 50 gf / 25 mm, more preferably from 2 to 45 gf / 25 mm, even more preferably from 3 to 40 gf / 25 mm. A specific method for measuring the peel strength of the surface protective sheet will be described later in Examples.

Hereinafter, the present invention will be described in detail with reference to examples. The present invention is not limited in any way by the following examples. In the following examples, the weight average molecular weight of the obtained polyurethane (A) was determined by gel permeation chromatography (Showex (registered trademark) GPC-101 manufactured by Showa Denko KK; hereinafter, referred to as GPC). Is a value in terms of polystyrene measured by the following method. The GPC measurement conditions are as follows.
Column: LF-804 manufactured by Showa Denko KK
Column temperature: 40 ° C
Sample: 0.2 mass% polyurethane (A) tetrahydrofuran solution 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 diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestourethane), and a hydroxyl value Was charged with 40.1 kg (20 mol) of 56 mg KOH / g of a polypropylene glycol having a hydroxy group at the terminal, Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000). Thereafter, the reactor was heated to 60 ° C. and reacted 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, and the mixture was heated to 70 ° C. and reacted for 2 hours to obtain 45.8 kg of an acryloyl group-terminated polyurethane (A-1). . This polyurethane (A-1) was analyzed by IR, and it was confirmed that the peak derived from the isocyanato 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 the isocyanate group was confirmed by IR, 2-hydroxyethyl acrylate was added to all the terminals of the polyurethane having isocyanate groups at both terminals. That is, an acryloyl group is introduced into 100% of the terminal of the polyurethane molecule contained in the polyurethane (A-1) on a numerical basis.

(A-2)
Polyurethane having acryloyl groups at both ends in the same manner as in the method of synthesizing polyurethane (A-1) except that isophorone diisocyanate (Desmodur I, manufactured by Sumika Cobestourethane) is used instead of the hydrogenated diphenylmethane diisocyanate. (A-2) was obtained. The weight average molecular weight of the obtained polyurethane (A-2) was 67,000.

(A-3)
Polyurethane (except that the hydrogenated product of diphenylmethane diisocyanate was changed to 8 mol and the hydroxyl group having a hydroxyl group of 56 mgKOH / g and a hydroxyl-terminated polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) were changed to 7 mol. 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 the hydrogenated product of diphenylmethane diisocyanate was changed to 4 mol, and the hydroxyl value was 56 mgKOH / g, and the hydroxyl-terminated polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals) was changed to 3 mol. In the same manner as in the method, a polyurethane (A-4) having an acryloyl group at the terminal was obtained. The weight average molecular weight of the obtained polyurethane (A-4) was 12,000.

(A-5)
Except for using 1.8 mol of 2-hydroxyethyl acrylate and 0.2 mol of 1-octanol in place of 2 mol of 2-hydroxyethyl acrylate, an acryloyl group was added to both terminals or at both ends in the same manner as in the synthesis method of polyurethane (A-1). Polyurethane (A-5), which is a mixture of polyurethanes at one end, was obtained. The weight average molecular weight of the obtained polyurethane (A-5) was 69000.
Since the disappearance of the peak derived from the isocyanato group was confirmed by IR, 2-hydroxyethyl acrylate or 1-octanol was added to all the terminals of the polyurethane having the isocyanato group at both terminals. That is, an acryloyl group is introduced into 90% of the terminals of the polyurethane molecule contained in the polyurethane (A-5) on a numerical basis.
At this time, the polyurethane (a1) contained in the polyurethane (A-5) is 80% of the polyurethane (A) on a number basis, and the polyurethane (a2) is 20% of the polyurethane (A) on a number basis.

<Preparation of pressure-sensitive adhesive composition for surface protective sheet>
A polyurethane resin (A), a polyfunctional monomer (B), another monomer (C), a photopolymerization initiator (D), and an additive are blended in the composition shown in Table 1, and at 25 ° C. The resulting mixture was mixed using a disper to prepare pressure-sensitive adhesive compositions according to Examples 1 to 9 and Comparative Examples 1 to 4.

<Preparation of surface protection sheet>
In the same manner as in Examples 1 to 9 and Comparative Examples 1 to 4, surface protection sheets having a substrate of an optical PET film on one surface were produced. First, using an applicator, the prepared pressure-sensitive adhesive composition was applied as a separator on a 75-μm-thick optical PET film (A4300, manufactured by Toyobo Co., Ltd.), and the thickness of the applied pressure-sensitive adhesive composition was increased. It was covered with a 75 μm release PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, the sheet covered with the release PET film was irradiated with ultraviolet light from the surface on the release PET film side using an ultraviolet irradiation device (UV irradiation device, 3 kW, high-pressure mercury lamp, manufactured by Eye Graphics Co., Ltd.), and the adhesive was applied. The composition was light cured. The irradiation distance of the ultraviolet rays was 25 cm, the moving speed of the lamp was 1.0 m / min, and the irradiation amount was 1000 mJ / cm ² . The thickness of the cured pressure-sensitive adhesive layer was calculated by measuring the thickness of the surface protective sheet after the separator was peeled off using a dial gauge, and then subtracting the thickness of the substrate of 75 μm from the measured value. The measurement surface of the dial gauge was a circular flat surface having a diameter of 5 mm, and the measurement force was 0.8 N. The thickness was 75 μm in all of Examples 1 to 9 and Comparative Examples 1 to 4.

<Evaluation of pressure-sensitive adhesive composition for surface protective sheet and surface protective sheet>
For the pressure-sensitive adhesive compositions and surface protection sheets according to Examples 1 to 9 and Comparative Examples 1 to 4, the gel fraction, transparency (haze value), peel strength, laminating property (wetting property), and glue to the adherend The remaining and cracks in the pressure-sensitive adhesive layer at the time of cutting were evaluated by the methods described below. The results are shown in Table 1.

(Gel fraction)
First, using an applicator, the pressure-sensitive adhesive composition according to each of Examples 1 to 9 and Comparative Examples 1 to 4 was peeled off to a thickness of 50 μm so that the pressure-sensitive adhesive layer after curing had a thickness of 75 μm. HY-S10 manufactured by Higashiyama Film Co., Ltd.). In addition, the method of confirming the thickness of the pressure-sensitive adhesive layer is the same as the measuring method described above in the section of preparation of the surface protective sheet.

Next, the pressure-sensitive adhesive composition on the release PET film was covered with a release PET film having a thickness of 75 μm (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 pressure-sensitive adhesive composition having both surfaces covered with the release PET film was coated on the surface of the release PET film having a thickness of 75 μm. From above to light cure the pressure-sensitive adhesive composition. The irradiation distance of the ultraviolet rays was 25 cm, the moving speed of the lamp 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 peeled PET films on both sides were peeled off from the cured product of the pressure-sensitive adhesive composition to obtain a measurement sample. The measurement sample was immersed in 50 ml of toluene at 25 ° C. for 24 hours, 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 by the following equation (1). . The results are shown in Table 1.
Gel fraction (% by mass) = [A / B] × 100 (1)
A: Dry mass of sample for measurement after immersion in toluene (not including mass of toluene) B: Mass of sample for measurement before immersion in toluene

(Haze value)
The surface protective sheet with a separator produced in each of Examples 1 to 9 and Comparative Examples 1 to 4 was cut into a size of 50 mm × 50 mm, and the peeled PET film was peeled. Thereafter, the entire surface of the exposed pressure-sensitive adhesive layer was laminated on a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) having a mass of 2 kg (load: 19.6 N) was reciprocated once to prepare a measurement sample. . The haze value of this measurement sample was measured using a haze meter (NM-150 (manufactured by Murakami Color Research Laboratory Co., Ltd.)). The haze value (%) was calculated by dividing the diffuse transmittance by the total light transmittance and multiplying by 100. In addition, the measurement was performed in three places with the same sample, and those average values were set as the haze value.

(Peel strength)
The surface protective sheet with a separator produced in each of Examples 1 to 9 and Comparative Examples 1 to 4 was cut into a size of 25 mm × 150 mm, and the release PET film was peeled off. Thereafter, the entire surface of the exposed pressure-sensitive adhesive layer was laminated on a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) having a mass of 2 kg (load: 19.6 N) was reciprocated once to prepare a measurement sample. .
The obtained measurement sample was left for 1 hour in an environment at a temperature of 23 ° C. and a relative humidity of 50%. Thereafter, a 180 ° tensile test was performed at a peeling speed of 0.3 m / min and 3.0 m / min according to JIS K 6854-2, and the peel strength (gf / 25 mm) of the surface protective sheet to the glass plate was measured. Was measured.

(Laminating property)
FIG. 1 is a plan view showing a method for evaluating laminating property of the surface protective sheet 10, and FIG. 2 is a sectional view taken along the line AA in FIG. The surface protective sheet with a separator 10 is cut into a size of 20 mm × 100 mm, and the release PET film is peeled off. Next, the pressure-sensitive 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, and the adhesive portion is fixed to the glass plate 30, and as shown in FIG. Lift the other end of 10. As a method for fixing the adhesive portion, as shown in FIG. 1, the upper surface of the surface protection sheet 10 within a range of 15 mm from the one end of the surface protection sheet 10, and a glass plate on both outer sides in the width direction of the surface protection sheet 10. Cellophane tape 20 is stuck so as to cover.

From this state, the other end of the surface protection sheet 10 was released, and the time required for the entire pressure-sensitive adhesive layer to adhere to the glass plate 30 by the weight of the surface protection sheet 10 was measured. Examples 1 to 9 and Comparative Examples 1 to The lamination property of the surface protective sheet according to No. 4 was evaluated according to the following criteria.
(Evaluation criteria for laminating properties)
◎: less than 5 seconds until adhered ○: 5 seconds or more and less than 10 seconds until adhered △: 10 seconds or more and less than 15 seconds until adhered X: 15 seconds or more until adhered or not adhered

(Glue residue)
The surface protective sheet with a separator produced in each of Examples 1 to 9 and Comparative Examples 1 to 4 was cut into a size of 50 mm × 50 mm, and the release PET film was peeled off. Next, the exposed adhesive surface was laminated on a glass plate, and this was used as a sample. After the sample was allowed to stand at 85 ° C. and a relative humidity of 85% for 3 days, the surface protection sheet was peeled off from the glass plate, and the adhesive residue on the surface of the glass plate was visually observed and evaluated according to the following criteria.

(Evaluation criteria for glue residue)
：: No change was observed on the surface of the glass plate before the lamination.
Δ: Glue residue is slightly observed on the surface of the glass plate.
×: Adhesive residue is clearly confirmed on the surface of the glass plate.

(Crack of adhesive layer at cutting)
The surface protection sheets prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were cut with a pinnacle blade (height: 0.80 mm, blade angle: 50 ° (manufactured by Tsukaya Knife Manufacturing Co., Ltd.)), and after cutting. The end face of the pressure-sensitive adhesive layer was observed with a microscope (magnification: 800 times (RH-2000, manufactured by Hilox Corporation)) and evaluated according to the following criteria.

(Evaluation criteria for cracking)
：: Cracks are observed in the adhesive layer.
×: No crack was observed in the pressure-sensitive adhesive layer.

<Evaluation results of Examples and Comparative Examples>
According to the above Examples and Comparative Examples, the composition of Comparative Example 1 in which the content of the polyurethane (A) was 10% by mass showed adhesive residue. Further, the composition of Comparative Example 2 using polyurethane (A-4) having a weight average molecular weight of 12,000 as the polyurethane (A) had insufficient laminating properties and adhesive residue was observed. Furthermore, the composition of Comparative Example 3 containing no polyfunctional monomer (B) had too high peel strength and insufficient laminating properties. In the composition of Comparative Example 4 in which the polyfunctional monomer (B) was 15% by mass, the pressure-sensitive adhesive layer was hard and cracked when cut.

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

Claims

Polyurethane (A),
A polyfunctional monomer (B),
Other monomer (C) polymerizable with polyurethane (A) and polyfunctional monomer (B),
A photopolymerization initiator (D);
A pressure-sensitive 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) includes a 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 polyurethane (A) has a weight average molecular weight of 30,000 to 200,000;
The polyfunctional monomer (B) is a compound having a plurality of (meth) acryloyl groups,
With respect to a total amount of 100% by mass 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 2 to 10% by mass,
The content of the other monomer (C) is 30 to 68% by mass,
For the total amount of 100 parts by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
The pressure-sensitive adhesive composition for a surface protective sheet, wherein the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass.
The pressure-sensitive adhesive composition for a surface protective 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 protective sheet according to claim 1 or 2, wherein the skeleton contained in the polyurethane (A) is a copolymer of a polyoxyalkylene glycol and a diisocyanate.
The polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 3, wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate.
The pressure-sensitive adhesive composition for a surface protective 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 pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 5, wherein the polyfunctional monomer (B) has three or more (meth) acryloyl groups.
The pressure-sensitive adhesive composition for a surface protective sheet according to claim 6, wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate.
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 7, wherein the other monomer (C) has only one (meth) acryloyl group.
The pressure-sensitive adhesive composition for a surface protective 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 a polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and has a (meth) acryloyl group at only one terminal of the polyurethane (a2). 10. The pressure-sensitive adhesive composition for a surface protective sheet according to any one of 1 to 9.
The pressure-sensitive adhesive for a surface protective 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. Composition.
A sheet-like substrate,
Having an adhesive layer formed on the base material,
A surface protection sheet, wherein the pressure-sensitive adhesive layer comprises a photocured product of the pressure-sensitive adhesive composition for a surface protection sheet according to any one of claims 1 to 11.