KR102567177B1 - Pressure-sensitive adhesive composition for surface protection sheet and surface protection sheet - Google Patents

Abstract

To provide a pressure-sensitive adhesive composition for a surface protection sheet for a surface protection sheet having low haze, easy to laminate, easy to peel, capable of suppressing adhesive residue after peeling, and not generating cracks during cutting. 30 to 60% by mass of polyurethane (A), 2 to 10% by mass of polyfunctional monomer (B), and 30 to 68 mass% of other monomers (C) polymerizable with polyurethane (A) and polyfunctional monomer (B) %, a pressure-sensitive adhesive composition for a surface protection sheet containing 0.1 to 5 parts by mass of a photopolymerization initiator (D) based on 100 parts by mass of the total amount of (A) to (C), wherein the polyurethane (A) is polyoxyalkylene An adhesive composition for a surface protection sheet characterized by having a skeleton containing a structure derived from a polyol and a structure derived from a polyisocyanate, and having (meth)acryloyl groups at a plurality of terminals, and having a weight average molecular weight of 30,000 to 200,000. include

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, particularly comprising a pressure-sensitive adhesive composition for a surface protection sheet containing a compound having a (meth)acryloyl group, and a cured product of the pressure-sensitive adhesive composition for a surface protection sheet. It relates to a surface protection sheet.

This application claims priority based on Japanese Patent Application No. 2018-180614 for which it applied to Japan on September 26, 2018, and uses the content here.

BACKGROUND ART Various optical films are used for optical components such as liquid crystal displays and touch panels of smart phones, 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 contamination or scratches in a transportation process, a manufacturing process, or an inspection process. This protective sheet is peeled off in a post-process such as an assembling process. As an adhesive for such a protective sheet, various urethane adhesives have been proposed.

For example, in Patent Document 1, a polyurethane having a polyoxyalkylene polyol as a skeleton and having a (meth)acryloyl group at the terminal and having a weight average molecular weight of 10,000 to 300,000, and a (meth)acrylic acid ester having a hydroxy group , a photocurable composition for a transparent adhesive sheet comprising other photopolymerizable monomers and a photopolymerization initiator.

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

[0003] In an optical component inspection step, it is sometimes required to be able to sufficiently detect or detect minute foreign matter or flaws in a product or component in a state where a protective sheet is laminated on the product or component. Therefore, the protective sheet is required to have little blur, that is, low haze.

In addition, in the manufacturing process of an optical component, the protective sheet may be laminated and peeled repeatedly. For this reason, the protective sheet is required to be easily laminated to an adherend (high wettability to an adherend) and easily peelable. Moreover, in recent years, optical components themselves are becoming prone to cracking with the increase in screen size of displays and thinning of panel components and the like. For this reason, protective sheets are also required to be capable of being peeled with a lighter force (light peelability) while having appropriate adhesiveness (peel strength). In addition, it is also required that there is no so-called adhesive residue (repeelability), in which a part of the pressure-sensitive adhesive layer or the like remains on the product surface (adherent) after peeling of the protective sheet.

Japanese Unexamined Patent Publication No. 2014-210895 Japanese Unexamined Patent Publication No. 2016-20477

However, the compositions described in Patent Literature 1 and Patent Literature 2 are not intended to be used for a protective sheet for peeling in the manufacturing process, and the adhesive sheet using these compositions has high peel strength.

Therefore, the inventors of the present invention conducted intensive studies to solve the above problems, and included a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate and having (meth)acryloyl groups 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, other monomers polymerizable with the polyurethane and the polyfunctional monomer, and a photopolymerization initiator. It was found that, by curing the pressure-sensitive adhesive composition for sheets, a surface protection sheet having a low haze, easy to laminate, and easy to peel, and capable of suppressing adhesive residue after peeling, was obtained. However, since the surface protection sheet obtained from this photocurable pressure-sensitive adhesive composition for surface protection sheet has a slightly hard pressure-sensitive adhesive layer, when a sheet with a thicker pressure-sensitive adhesive layer is laser cut or knife-cut, cracks occur on the end face of the pressure-sensitive adhesive layer. It turned out that there is

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

The configuration of the present invention for solving the above problems is as follows.

[1] polyurethane (A),

A multifunctional monomer (B);

Polyurethane (A) and other monomers (C) polymerizable with the multifunctional monomer (B);

Photopolymerization initiator (D)

A pressure-sensitive adhesive composition for a surface protection sheet comprising

The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate,

The polyurethane (A) comprises 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 ends 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 100 mass% of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomers (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;

With respect to 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),

A pressure-sensitive adhesive composition for surface protection sheets characterized in that the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass.

[2] The pressure-sensitive adhesive for 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. composition.

[3] The pressure-sensitive adhesive composition for surface protection sheets according to any one of [1] or [2], wherein the backbone contained in the polyurethane (A) is a copolymer of the polyoxyalkylene glycol and the diisocyanate. .

[4] The polyoxyalkylene glycol is polypropylene glycol,

The pressure-sensitive adhesive composition for surface protection sheets 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 surface protection sheets according to any one of [1] to [4], wherein the (meth)acryloyl group in the polyurethane (A) is a part of the (meth)acryloyloxy group.

[6] The pressure-sensitive adhesive composition for surface protection sheets 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 surface protection sheets according to [6], wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate.

[8] The pressure-sensitive adhesive composition for surface protection sheets according to [7], wherein the other monomer (C) has a (meth)acryloyl group.

[9] The pressure-sensitive adhesive composition for surface protection sheets 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 polyoxyalkylene polyol and polyisocyanate, and has a (meth)acryloyl group only at either end of the polyurethane (a2) ( The pressure-sensitive adhesive composition for surface protection sheets according to any one of [1] to [9], including a2).

[11] The surface according to any one of [1] to [10], in which (meth)acryloyl groups are introduced to 90 to 100% of the ends of the polyurethane molecules contained in the polyurethane (A), by number. An adhesive composition for protective sheets.

[12] a sheet-like substrate;

Pressure-sensitive adhesive layer formed on the substrate

have

The surface protection sheet characterized in that the pressure-sensitive adhesive layer contains a photocured product of the pressure-sensitive adhesive composition for surface protection sheets according to any one of [1] to [11].

ADVANTAGE OF THE INVENTION According to the present invention, surface protection sheets for surface protection sheets that have low haze, are easy to laminate, are easy to peel, can suppress adhesive residue after peeling, and do not generate cracks in the pressure-sensitive adhesive layer during cutting. An adhesive composition can be provided. Further, according to the present invention, it is possible to provide a surface protection sheet that has a low haze, is easy to laminate, is easy to peel, can suppress adhesive residue after peeling, and does not cause cracks in the pressure-sensitive adhesive layer during cutting. .

1 is a plan view showing a method for evaluating the laminability of a surface protection sheet.
Fig. 2 is a AA sectional view in Fig. 1 .

Hereinafter, one embodiment of the present invention will be described. Here, the (meth)acryloyl group means at least one selected from groups represented by the chemical formula CH ₂ =CH-CO- and functional groups represented by the chemical formula CH ₂ =C(CH ₃ )-CO-, and Royloxy group means at least one selected from groups represented by the chemical formula CH ₂ =CH-CO-O- and functional groups represented by the chemical formula CH ₂ =C(CH ₃ )-CO-O-. In addition, an isocyanato group means a functional group represented by chemical formula -N=C=O.

<1. Pressure-sensitive adhesive composition for surface protection sheet>

The pressure-sensitive adhesive composition for surface protection sheets according to the present embodiment (hereinafter sometimes referred to as "pressure-sensitive adhesive composition") includes polyurethane (A), a polyfunctional monomer (B), a polyurethane (A) and a polyfunctional monomer ( B), other polymerizable monomers (C), and a photopolymerization initiator (D) are included. The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate. The polyurethane (A) includes polyurethane (a1). The polyurethane (a1) has a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate, and has (meth)acryloyl groups at a plurality of ends of the polyurethane (a1). The polyurethane (A) has a weight average molecular weight of 30,000 to 200,000. The said polyfunctional monomer (B) is a compound which has 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), and 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 to 5 parts 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).

Moreover, the adhesive composition concerning this embodiment may also contain additives, such as a fatty acid ester, as needed. In addition, although the adhesive composition concerning this embodiment does not have to contain a solvent, it may contain a solvent as needed.

Hereinafter, each component contained in the pressure-sensitive adhesive composition will be described. In the following description, components containing polyurethane (A), polyfunctional monomers (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 pressure-sensitive adhesive composition, the polyurethane (A) may further include a polyurethane (a2) described below.

[Polyurethane (a1)]

Polyurethane (a1) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate, and having (meth)acryloyl groups at a plurality of ends. Moreover, it is preferable that the terminal (meth)acryloyl group of polyurethane (a1) is a part of (meth)acryloyloxy group.

[Polyurethane (a2)]

Polyurethane (a2) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and having a (meth)acryloyl group only at one end. Moreover, it is preferable that the terminal (meth)acryloyl group of polyurethane (a2) is a part of (meth)acryloyloxy group.

In addition, control of 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) As for the method, an example thereof in the section of the method for producing polyurethane (A) will be described later.

Regarding the "plural terminals" of the present invention, in the case of a straight chain polymer, it is two terminals, and in the case of a branched polymer, it is two or more terminals in the same number of terminals as the number of each branched chain.

Components other than polyurethane (a1) and polyurethane (a2) are not contained in polyurethane (A).

The polyurethane (a1) contained in the polyurethane (A) is preferably 80 to 100%, more preferably 90 to 100%, still more preferably 100% of the polyurethane (A) by number. The polyurethane (a2) contained in the polyurethane (A) is preferably 0 to 20%, more preferably 0 to 10%, still more preferably 0%, of the polyurethane (A) by number. The cohesive force of the hardened|cured material of an adhesive composition becomes large enough that the polyurethane (a1) contained in polyurethane (A) is 80 % or more.

"Polyoxyalkylene polyol"

As the polyoxyalkylene polyol, those having an alkylene chain of 2 to 4 carbon atoms are preferable, and specific examples thereof include polyoxyethylene polyol, polyoxypropylene polyol, and polyoxybutylene polyol. Among polyoxyalkylene polyols, polyoxyalkylene glycol is preferably used, and polypropylene glycol is particularly preferably used.

Moreover, as polyoxyalkylene polyol, you may also include 2 or more types of alkylene chains. Moreover, as polyurethane (A), the structure derived from 2 or more types of different polyoxyalkylene polyols couple|bonded with polyisocyanate may be sufficient.

The number average molecular weight of the polyoxyalkylene polyol is preferably 500 to 5,000, more preferably 800 to 4,000, still more preferably 1,000 to 3,000. When the number average molecular weight is 500 or more, the peeling strength of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition is improved. If the number average molecular weight is 5,000 or less, the cohesive force of the pressure-sensitive adhesive layer is improved because a sufficient amount of urethane bonds are contained in the polyurethane.

The polyoxyalkylene polyol preferably has 2 or 3 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 still more preferably 40 to 80 mgKOH/g do. As a specific example of polypropylene glycol, Actcol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type) of polypropylene glycol having a hydroxyl group (hydroxyl group) at the terminal with a hydroxyl value of 56 mgKOH/g can be given. there is.

Here, the hydroxyl value is the hydroxyl value of polyoxyalkylene polyol measured according to JISK0070, and means the number of milligrams of potassium hydroxide required to neutralize free acetic acid when 1 g of the polyoxyalkylene polyol is acetylated. . Specifically, it can be determined by acetylating the hydroxyl group in the sample using acetic anhydride and titrating the free acetic acid formed at that time with a potassium hydroxide solution.

"Polyisocyanate"

As polyisocyanate, if it is a compound which has two or more isocyanato groups, it will not specifically limit, but diisocyanate is preferable. As diisocyanate, for example, 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, hexamethylenedi Isocyanate, trimethylhexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, norbornane diisocyanate etc. can be mentioned.

Among these exemplified compounds, a hydrogenated product of isophorone diisocyanate or diphenylmethane diisocyanate is preferable in light resistance and reactivity control, and a hydrogenated product of diphenylmethane diisocyanate is more preferable in terms of reactivity. The structure derived from the polyisocyanate contained in polyurethane (A) may contain one type or a structure containing two or more types.

Specific examples of the polyisocyanate include hydrogenated diphenylmethane diisocyanate (Desmodur W, manufactured by Sumica Covestro Urethane), isophorone diisocyanate (Desmodur I, manufactured by Sumica Covestro Urethane), and the like.

The weight average molecular weight of polyurethane (A) is 30,000 to 200,000, preferably 50,000 to 150,000, more preferably 70,000 to 100,000. When the weight average molecular weight of polyurethane (A) is less than 30,000, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition has insufficient flexibility, and it is difficult to laminate the surface protection sheet having this pressure-sensitive adhesive layer. Moreover, when the weight average molecular weight of polyurethane (A) is larger than 200,000, handling as an adhesive composition becomes difficult, such as a viscosity becoming high, and workability|operativity falls.

The content of polyurethane (A) is 30 to 60% by mass, preferably 35 to 55% by mass, and more preferably 40 to 50% by mass with respect to the total amount of components (A) to (C). If 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 there is a possibility that air bubbles may be entrapped into the pressure-sensitive adhesive surface (between the pressure-sensitive adhesive layer and the adherend). there is. When the content of the polyurethane (A) is greater 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 not sufficient, and the wettability of the pressure-sensitive adhesive layer to an adherend may decrease.

<1-2. Multifunctional Monomer (B)>

The polyfunctional monomer (B) adjusts the peel strength of the pressure-sensitive adhesive layer (surface protective sheet) using the cured product of the pressure-sensitive adhesive composition. The polyfunctional monomer (B) is a compound other than the polyurethane (A) and has a plurality of (meth)acryloyl groups. Although there is no particular restriction as long as the number of (meth)acryloyl groups is two or more, 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, such as polyethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. Acrylates, 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)acrylbisdiethylene glycol phthalate, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol Di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, diacryloxyethyl phosphate, dipentaeryth Litol trihydroxy (meth)acrylate, pentaerythritol tetra (meth)acrylate, etc. are mentioned.

Among these, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and dipentaerythritol trihyd in that the peeling strength of the surface protective sheet using the pressure-sensitive adhesive composition can be easily adjusted to a low level. Roxy (meth)acrylate and pentaerythritol tetra(meth)acrylate are more preferable, and trimethylolpropane tri(meth)acrylate is still more preferable. Moreover, the polyfunctional monomer (B) may contain one type of compound or may contain 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 more preferably 4 to 8% by mass with respect to the total amount of components (A) to (C). If the content is less than 2% by mass, the peel strength of the surface protective sheet is too high and the easy 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 tend to occur during cutting of the sheet. Moreover, when the content is more than 10% by mass, the haze as a surface protection sheet tends to increase.

<1-3. Other monomers (C)>

The other monomer (C) is a compound other than the polyurethane (A) and other than the polyfunctional monomer (B), and is not particularly limited as long as it can be polymerized with the polyurethane (A) and the polyfunctional monomer (B). However, the other monomer (C) preferably has an ethylenically unsaturated bond capable of radical polymerization as a functional group for polymerization with the polyurethane (A) and the multifunctional monomer (B), and among them, a vinyl group or a (meth)acryl What has a loyl group is more preferable, and what has a (meth)acryloyl group is still more preferable.

Other monomers (C) are not particularly limited, but alkyl (meth) acrylates, cyclic alkyl (meth) acrylates, alkoxyalkyl (meth) acrylates, alkoxy (poly) alkylene glycol (meth) acrylates, hydroxy group-containing (meth) ) acrylate, carboxyl group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, dialkylaminoalkyl (meth)acrylate, (meth)acrylamide, epoxy group-containing (meth)acrylate, unsaturated carboxylic acid, etc. can be heard

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

Examples of the cyclic alkyl (meth)acrylate include cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, norbornanyl (meth)acrylate, and dicyclophene. tenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)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, and 2-methoxyethoxyethyl (meth)acrylate. rate, 2-ethoxyethoxyethyl (meth)acrylate, and the like.

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

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, etc. are mentioned.

As a carboxy group-containing (meth)acrylate, (beta)-carboxyethyl (meth)acrylate etc. are mentioned, for example.

As fluorinated alkyl (meth)acrylate, octafluoropentyl (meth)acrylate etc. are mentioned, for example.

As dialkyl aminoalkyl (meth)acrylate, N,N- dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc. are mentioned, for example.

Examples of (meth)acrylamide include (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropylacrylamide, N-hexyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, (meth)acryloylmorpholine, diacetone acrylamide, etc. are mentioned. .

As an epoxy group-containing (meth)acrylate, glycidyl (meth)acrylate etc. are mentioned, for example.

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

In addition, as other monomers (C), other than the above compounds, 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, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclo hexyl methyl vinyl ether, triethylene glycol monovinyl ether or diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamide methyl trimethyl ammonium chloride, allyl trimethyl ammonium chloride, dimethyl allyl vinyl ketone and the like.

Among these exemplified compounds, from the viewpoints of compatibility with polyurethane (A), viscosity of the pressure-sensitive adhesive composition, and adjustment of peel strength, alkyl (meth) acrylates are preferred, 2-ethylhexyl (meth) acrylate, isooctyl ( Meth) acrylate, isostearyl (meth) acrylate, and isobornyl (meth) acrylate are more preferable, and 2-ethylhexyl (meth) acrylate is still more preferable. Moreover, the other monomer (C) may contain one type of compound or may contain two or more types of compounds.

The content of the other monomers (C) is 30 to 68% by mass, preferably 35 to 62% by mass, and more preferably 40 to 56% by mass with respect to the total amount of components (A) to (C). If the content is less than 30% 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 there is a risk that wettability to an adherend may decrease. If the content is higher than 68% by mass, the cohesive force of the cured product of the pressure-sensitive adhesive composition is reduced, the pressure-sensitive adhesive layer is too soft, and there is a possibility that air bubbles may be entrapped into the pressure-sensitive adhesive surface (between the pressure-sensitive adhesive layer and the adherend).

<1-4. Photopolymerization Initiator (D)>

The photopolymerization initiator (D) is not particularly limited, but includes carbonyl-based photopolymerization initiators, sulfide-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, quinone-based photopolymerization initiators, sulfochloride-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. can

Examples of the carbonyl photopolymerization initiator include benzophenone, benzyl, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, and 2,2-dimethoxy-2-phenyl. Acetophenone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, Michler's ketone, benzo Inmethyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, methylbenzoylformate, 2,2-diethoxyacetophenone, 4-N,N'-dimethylacetophenone, 2 -Methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one etc. are mentioned.

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.

As a quinone-type photoinitiator, quinone-type photoinitiators, such as benzoquinone and anthraquinone, are mentioned, for example.

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

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 preferable in view of the transparency of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition. In addition, the photoinitiator (D) may contain one type of compound or may contain two or more types of compounds.

The content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass, preferably 0.2 to 3 parts by mass, and more preferably 0.3 to 2 parts by mass, based on 100 parts by mass of the total amount of components (A) to (C). When the content of the photopolymerization initiator (D) is less than 0.1 part by mass, the pressure-sensitive adhesive composition is not sufficiently photocured, and when it is greater than 5 parts by mass, many low-molecular-weight components are generated, and the peelability of the surface protection sheet obtained tends to deteriorate.

<1-5. Additives>

A fatty acid ester may be added to the pressure-sensitive adhesive composition, if necessary, in order to improve the laminating properties (wetting properties) and bubble release properties (the degree to which bubbles trapped during bonding are easily released) of the resulting surface protection sheet. Examples of fatty acid esters include esters of monobasic acids with 8 to 18 carbon atoms or polybasic acids with branched alcohols with 18 or less carbon atoms, unsaturated fatty acids with 14 to 18 carbon atoms, or esters with branched-chain acids and tetrahydric alcohols. can A preferable specific example of the fatty acid ester is isopropyl myristate. The addition amount of the fatty acid ester is preferably 1 to 40 parts by mass, more preferably 3 to 35 parts by mass, still more preferably 5 to 30 parts by mass, based on 100 parts by mass of the total amount of components (A) to (C).

Further, other additives may be added to the pressure-sensitive adhesive composition as needed within a range not impairing transparency. As additives, for example, plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazoles, phosphate esters and other flame retardants, surfactants and The same antistatic agent, dye, etc. are mentioned.

<1-6. Solvent>

Since the pressure-sensitive adhesive composition contains the polyfunctional monomer (B) and other monomers (C) as low-molecular-weight components, it can be adjusted to an applicable viscosity without adding a solvent. That is, the pressure-sensitive adhesive composition need not substantially contain a solvent other than the essential components consisting of the polyurethane (A), the polyfunctional monomer (B), the other monomer (C), and the photopolymerization initiator (D). In that case, when manufacturing a surface protection sheet, the process of heat-drying a solvent can be omitted, and productivity improves. In particular, when producing a surface protective sheet having a film thickness exceeding 50 µm, it is preferable that the pressure-sensitive adhesive composition does not substantially contain a solvent thereof. The meaning of "substantially not included" 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 0.1% by mass. %am.

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 according to other components included in the pressure-sensitive adhesive composition, but an organic solvent is preferable.

The organic solvent used is not particularly limited, but methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol and the like are exemplified. These organic solvents may be used alone or in combination of two or more. The solvent is preferably removed by applying the pressure-sensitive adhesive composition to a substrate or the like and then drying, followed by photocuring.

<2. Method for producing pressure-sensitive adhesive composition for surface protection sheet>

In addition, although the method for synthesizing polyurethane (A) is described here as an example, purchase of commercially available products is required for the polyfunctional monomer (B) and other monomers (C) and other components contained in the pressure-sensitive adhesive composition for surface protection sheets. Since it is easy and varies depending on the type of compound used, the description of the synthesis method is omitted.

<2-1. Method for synthesizing polyurethane (A)>

Hereinafter, an example of a preferable method for synthesizing polyurethane (A) included in the pressure-sensitive adhesive composition of the present embodiment will be described, but the method for synthesizing polyurethane (A) is not limited to this, and conditions such as raw materials and equipment used for synthesis can be changed accordingly. In this example, in any step, the reaction between the hydroxyl group and the isocyanato group is carried out in the presence of an organic solvent inactive to the isocyanato group, such as dibutyltin dilaurate, dibutyltin diethylhexoate, or dioctyltin. It is performed using a urethanization catalyst, such as dilaurate. The reaction is preferably carried out continuously 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 added in a ratio such that the amount of isocyanato groups (number basis, hereinafter the same) is greater than the amount of hydroxy groups (number basis, hereinafter the same), and these are reacted to form an isocyanato group at the terminal 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 isocyanato groups relative to the amount of hydroxyl groups. Specifically, as the excess amount of isocyanato groups relative to hydroxy groups decreases, the molecular weight of polyurethane having isocyanato groups increases, and as the excess amount of isocyanato groups relative to hydroxy groups increases, polyurethane having isocyanato groups molecular weight becomes smaller.

Next, a polyurethane having an isocyanato group at the terminal and a compound having a hydroxyl group and a (meth)acryloyl group are reacted to synthesize a polyurethane (A) having a (meth)acryloyl group at the molecular chain terminal. . Moreover, it is preferable that the (meth)acryloyl group contained in this compound is a part of (meth)acryloyloxy group.

Although the compound having a hydroxyl group and a (meth)acryloyl group is not particularly limited, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. hydroxyalkyl (meth)acrylates; 1,3-butanediol mono(meth)acrylate, 1,4-butanediol mono(meth)acrylate, 1,6-hexanediol mono(meth)acrylate, 3-methylpentanediol mono(meth)acrylate, etc. The monool which has a (meth)acryloyl group derived from various polyols, etc. are mentioned. These may be used independently or may be used in combination of two or more types. Among them, 2-hydroxyethyl (meth)acrylate is preferable in terms of reactivity with isocyanato groups and photocurability.

Further, in addition to a compound having a hydroxyl group and a (meth)acryloyl group, an alkyl alcohol having no (meth)acryloyl group and one hydroxyl group is used in combination and reacted with a polyurethane having an isocyanato group at the terminal (meth ) The introduction amount of the acryloyl group can be adjusted. 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 alkyl alcohol at least at one of the terminals is produced. In this case, the polyurethane (A) includes a polyurethane having no (meth)acryloyl groups at least at either terminal. Therefore, polyurethane (a2) having a (meth)acryloyl group only at one end can be included.

In terms of number, it is preferable that 90 to 100% of the ends of the polyurethane included in the polyurethane (A) have (meth)acryloyl groups introduced, more preferably 95 to 100%, and still more preferably 100%. do. When the introduced amount of (meth)acryloyl groups is 90% or more on a number basis with respect to isocyanato groups, the cohesive force of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition is sufficiently obtained. The ratio of the number of terminals into which (meth)acryloyl groups are introduced to the number of terminals of all polyurethane molecular chains can be measured by IR, NMR or the like.

<2-2. Modification of synthesis method of polyurethane (A)>

A modified example of the method for synthesizing polyurethane (A) will be described. Also in this example, in the same way as in the above example, the reaction between the hydroxyl group and the isocyanato group is carried out in the presence of an organic solvent inactive to the isocyanato group in either dibutyltin dilaurate or dibutyltin diethylhexoate. , It is performed using a urethanization catalyst, such as dioctyl tin dilaurate. The reaction is preferably carried out continuously 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, polyoxyalkylene polyol and polyisocyanate are reacted at a ratio such that the amount of hydroxy groups is greater than the amount of isocyanato groups, thereby synthesizing 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 hydroxyl groups to the amount of isocyanato groups. Specifically, the molecular weight of the polyurethane having a hydroxy group increases as the excess amount of hydroxyl groups relative to the amount of isocyanato groups decreases, and the molecular weight of the polyurethane having a hydroxy group decreases as the excess amount of hydroxy groups relative to the amount of isocyanato groups increases.

Next, a polyurethane having a hydroxyl group at the terminal and a compound having an isocyanato group and a (meth)acryloyl group are reacted to synthesize a polyurethane (A) having a (meth)acryloyl group at the molecular chain terminal. . Moreover, it is preferable that the (meth)acryloyl group contained in this compound is a part of (meth)acryloyloxy group.

Although the compound having an isocyanato group and a (meth)acryloyl group is not particularly limited, 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, 1,1-bis(acrylic acid) Royloxymethyl) ethyl isocyanate etc. are mentioned. 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 Co., Ltd. there is. These may be used independently or may be used in combination of 2 or more types. Among them, 2-(meth)acryloyloxyethyl isocyanate is preferable from the viewpoint of reactivity with a hydroxyl group and photocurability.

Further, 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 polyurethane having a hydroxyl group at the terminal By doing so, the introduction amount of the (meth)acryloyl group can be adjusted. Alkyl isocyanates are not particularly limited, but include straight-chain, branched, and alicyclic alkyl isocyanates, which may be used alone or in combination of two or more. As a result, a polyurethane having a structure derived from the alkyl isocyanate at least at one of the terminals is produced. In this case, the polyurethane (A) includes a polyurethane having no (meth)acryloyl groups at least at either terminal. Therefore, in this case, the polyurethane (A) can also contain a polyurethane having a (meth)acryloyl group at only one terminal.

In terms of number, it is preferable that 90 to 100% of the ends of the polyurethane included in the polyurethane (A) have (meth)acryloyl groups introduced, more preferably 95 to 100%, and still more preferably 100%. do. When the introduced amount of (meth)acryloyl groups is 90% or more on a number basis with respect to isocyanato groups, the cohesive force of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition is sufficiently obtained.

<2-3. Mixing method of each component included in the pressure-sensitive adhesive composition for surface protection sheet>

A pressure-sensitive adhesive composition is prepared by mixing polyurethane (A), polyfunctional monomer (B), other monomer (C), photopolymerization initiator (D), fatty acid ester, other additives and organic solvent added as needed. Although the mixing method is not particularly limited, for example, it can be performed using a stirring device equipped with stirring blades such as a homodisper or a paddle blade.

In addition, all components may be added and mixed at once, or addition and mixing may be repeated for each component in a plurality of times. In addition, when there is a solid component at room temperature, it is easily mixed with high uniformity in the pressure-sensitive adhesive composition by adding it as dissolved in a solvent or dispersed in a dispersion medium, or added as a substance melted by heating. lose

<3. Surface Protection Sheet>

<3-1. Composition of Surface Protection Sheet>

In the surface protection sheet according to the present 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 pressure-sensitive adhesive layer is preferably 3 to 150 μm, more preferably 5 to 130 μm, and still more preferably 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, in the case where the function of protecting adherends from impact (impact resistance) is to be imparted to the surface protection sheet, the film 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 included in the pressure-sensitive adhesive layer is preferably 85 to 100% by mass, more preferably 90 to 100% by mass, and still more preferably 95 to 100% by mass. Here, the gel fraction is the mass fraction of the extraction insoluble content with respect to the solvent, and the solvent is selected from among the cured products of the pressure-sensitive adhesive composition that can dissolve the uncrosslinked component. In addition, an example of a specific method for measuring the gel fraction will be described later in the Examples. When the gel fraction of the cured product of the pressure-sensitive adhesive composition is 85 to 100% by mass, so-called adhesive residue, which is a part of the pressure-sensitive adhesive layer or the like remaining on the adherend when the surface protection sheet is peeled off, can be suppressed.

The material of the base material can be appropriately selected according to the use of the surface protection sheet, and a resin film is exemplified. When the surface protection sheet is used, for example, as a protection sheet in a manufacturing process, and the presence or absence of scratches or foreign matter on an adherend, that is, a product is inspected, when the protection sheet is laminated, the base material is transparent. it is desirable 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 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, more preferably 10 μm from the viewpoints of handleability and strength. or more, more preferably 20 μm or more. In view of the flexibility of the resin film, the thickness of the substrate is preferably 200 µm or less, more preferably 150 µm or less, still more preferably 100 µm or less.

Moreover, as a base material, what is antistatically treated is used preferably. The antistatic treatment applied to the substrate is not particularly limited, but a method of providing an antistatic layer on at least one side of the substrate, a method of injecting an antistatic agent into the substrate, and the like can be used. In addition, the surface of the base material forming the pressure-sensitive adhesive layer may be subjected to an adhesion-facilitating treatment such as acid treatment, alkali treatment, priming treatment, corona treatment, plasma treatment, ultraviolet treatment, or ozone treatment, if necessary.

In the surface protection sheet, it is possible to laminate a separator on the surface of the pressure-sensitive adhesive layer for the purpose of protecting the pressure-sensitive adhesive layer. As the material of the separator, for example, paper, plastic film, etc. can be used, but a plastic film is suitable 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 pressure-sensitive adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, and polybutene.

<3-2. Manufacturing Method of Surface Protection Sheet>

The manufacturing method of the surface protection sheet according to the present embodiment can be obtained, for example, by applying an adhesive composition to a base sheet, laminating a separator, and then irradiating the applied adhesive composition with ultraviolet rays to photocur it.

The method of applying the pressure-sensitive adhesive composition to the substrate is not particularly limited and can be selected appropriately. For example, as a method of applying an adhesive composition to a substrate, a method using 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, a direct coater, A screen printing method etc. are mentioned.

Moreover, as a light source at the time of photocuring the adhesive composition, a black light, a low-pressure mercury-vapor lamp, a high-pressure mercury-vapor lamp, an ultra-high-pressure mercury-vapor lamp, a metal halide lamp, a xenon lamp, etc. are mentioned. As light irradiation intensity, what is necessary is just to be able to fully harden an adhesive composition, and it is preferable that it is 50-3000 mW/cm<2> for example. In addition, when the irradiation intensity of light is low, productivity decreases because hardening takes time. Light irradiation can be performed from either the separator side or the base material side as long as it is transparent.

<3-3. Uses of Surface Protection Sheets and Required Performance>

In the inspection process, it is sometimes required to be able to sufficiently detect or detect minute foreign matter or scratches on a product or part in a state where a protective sheet is laminated on the product or part. In addition, the protective sheet protects the surface of plastic films used as optical components such as polarizers, wave plates, retardation plates, optical compensation films, reflective sheets, and brightness enhancement films used in liquid crystal displays such as smartphones, personal computers, and televisions. There are also things that are used appropriately for the purpose.

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 a low blur, that is, a 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, still 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 the above protection sheet, the minimum peel strength is required so that the surface protection sheet does not peel from products or parts during handling such as transportation. On the other hand, when peeling the surface protection sheet from a product or component, it is necessary to lower the peeling strength in order to facilitate the peeling operation or to prevent deformation or damage to the product or component during peeling. From these points of view, the peel strength of the surface protective sheet varies depending on the thickness of the substrate and the pressure-sensitive adhesive layer when the peeling speed is 3.0 m/min, but is preferably 1 to 50 gf/25 mm when the pressure-sensitive adhesive layer is 50 to 100 μm. It is more preferable that it is - 45 gf/25 mm, and it is still more preferable that it is 3 - 40 gf/25 mm. A specific method for measuring the peel strength of the surface protective sheet will be described later in Examples.

Example

Hereinafter, the present invention will be described in detail by examples. This invention is not limited at all by the Example shown below. Further, in the following examples, the weight average molecular weight of the obtained polyurethane (A) is measured by gel permeation chromatography (Showa Denko Co., Ltd. Shodex (registered trademark) GPC-101, hereinafter referred to as GPC) is the polystyrene equivalent. The measurement conditions of GPC are as follows.

Column: LF-804 manufactured by Showa Denko Co., Ltd.

Column temperature: 40°C

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 cooling tube having a thermometer, stirrer, dropping funnel, and drying tube, 5.5 kg (21 mol) of a hydrogenated diphenylmethane diisocyanate (Desmodur W, manufactured by Sumika Covestro Urethane) and oxalic acid were added to the reactor. 40.1 kg (20 mol) of polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight: 2000) having a hydroxyl group of 56 mgKOH/g at the terminal 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 isocyanato 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 it was made to react for 2 hours to obtain 45.8 kg of polyurethane (A-1) having an acryloyl group at the terminal. This polyurethane (A-1) was analyzed by IR, and it was confirmed that the peak derived from the isocyanato group disappeared. The weight average molecular weight of the obtained polyurethane (A-1) was 70,000.

Since disappearance of peaks derived from isocyanato groups was confirmed by IR, 2-hydroxyethyl acrylate was added to all ends of polyurethane having isocyanato groups at both ends. That is, acryloyl groups are introduced at 100% of the terminals of the polyurethane molecules contained in polyurethane (A-1) on a number basis.

(A-2)

Except for using isophorone diisocyanate (Desmodur I, manufactured by Sumika Covestro Urethane) instead of the hydrogenated diphenylmethane diisocyanate, in the same manner as in the synthesis method of polyurethane (A-1), acryloyl groups were added to both ends. Polyurethane (A-2) having The weight average molecular weight of the obtained polyurethane (A-2) was 67,000.

(A-3)

8 mol of hydrogenated diphenylmethane diisocyanate, and 7 mol of polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight: 2000) having a hydroxyl group at the terminal with a hydroxyl value of 56 mgKOH/g Polyurethane (A-3) having acryloyl groups at both ends was obtained in the same manner as in the method for synthesizing polyurethane (A-1) except for changing. The weight average molecular weight of the obtained polyurethane (A-3) was 35,000.

(A-4)

Polyurethane (with the exception of changing 4 mol of hydrogenated diphenylmethane diisocyanate and 3 mol of polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals) having a hydroxyl group at the terminal with a hydroxyl value of 56 mgKOH/g Polyurethane (A-4) having an acryloyl group at the terminal was obtained in the same manner as in the synthesis method of A-1). 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 instead of 2 mol of 2-hydroxyethyl acrylate, in the same manner as in the method for synthesizing polyurethane (A-1), acryloyl groups were added at both ends or 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 69,000.

Since disappearance of peaks derived from isocyanato groups was confirmed by IR, 2-hydroxyethyl acrylate or 1-octanol was added to all ends of the polyurethane having isocyanato groups at both ends. That is, acryloyl groups are introduced at 90% of the terminals of the polyurethane molecules contained in polyurethane (A-5) on a number basis.

At this time, the polyurethane (a1) included in the polyurethane (A-5) is 80% of the polyurethane (A) by number, and the polyurethane (a2) is 20% of the polyurethane (A) by number.

<Preparation of pressure-sensitive adhesive composition for surface protection sheet>

Polyurethane resin (A), polyfunctional monomer (B), other monomers (C), photopolymerization initiator (D) and additives were formulated in the composition shown in Table 1 and mixed using a disper at 25 ° C. 1 to 9 and the pressure-sensitive adhesive composition according to Comparative Examples 1 to 4 were prepared.

<Production of surface protection sheet>

In the same manner as for Examples 1 to 9 and Comparative Examples 1 to 4, a surface protection sheet having an optical PET film substrate on one side was produced. First, using an applicator, the prepared adhesive composition is applied as a separator on a 75 μm-thick optical PET film (A4300 manufactured by Toyobo Co., Ltd.), and a 75 μm-thick peeling PET film is formed from the applied adhesive composition. (E7006 manufactured by Toyobo Co., Ltd.). Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp), the sheet covered with the release PET film was irradiated with ultraviolet rays from the surface on the side of the release PET film, and the adhesive composition was pissed off The irradiation distance of ultraviolet rays was 25 cm, the lamp movement speed was 1.0 m/min, and the irradiation amount was 1000 mJ/cm 2 . The thickness of the pressure-sensitive 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 subtracting the thickness of the base material of 75 µm from the measured value. The measuring surface of the dial gauge was a circular flat surface with a diameter of 5 mm, and the measuring force was 0.8 N. It was 75 micrometers also in any of Examples 1-9 and Comparative Examples 1-4.

<Evaluation of pressure-sensitive adhesive composition for surface protection sheet and surface protection sheet>

For the pressure-sensitive 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 (wetting property), adhesive residue to adherends, and cutting Cracking of the pressure-sensitive adhesive layer upon application was evaluated by the method described below. The results are shown in Table 1.

(gel fraction)

First, using an applicator, the adhesive composition according to Examples 1 to 9 and Comparative Examples 1 to 4 was applied to a 50 μm-thick release PET film (manufactured by Higashiyama Film Co., Ltd.) so that the thickness of the adhesive layer after curing was 75 μm. of HY-S10). The method for confirming the thickness of the pressure-sensitive adhesive layer is the same as the method for measuring the thickness of the surface protection sheet described above.

Next, from the top of the adhesive composition on the release PET film, it 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 covered with the release PET film on both sides was irradiated with ultraviolet rays from the surface on the side of the release PET film having a thickness of 75 μm. was irradiated to photocur the pressure-sensitive adhesive composition. The irradiation distance of ultraviolet rays was 25 cm, the lamp movement speed was 1.0 m/min, and the irradiation amount was 1000 mJ/cm 2 .

The produced sheet was cut into a size of 100 mm × 100 mm, and the release PET film on both sides was peeled off from the cured product of the pressure-sensitive adhesive composition to obtain a sample for measurement. This sample for measurement 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 by the following formula (1) from the mass of the sample for measurement before and after immersion in toluene. The results are shown in Table 1.

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

A: Dry mass of the sample for measurement after toluene immersion (not including the mass of toluene) B: Mass of the sample for measurement before toluene immersion

(Haze value)

The surface protection sheets with separators prepared in each of 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 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 sample for measurement. About this sample for a measurement, the haze value was measured using the haze meter (NM-150 (made by Murakami Shikisai Kijutsu Genkyujo)). 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 at three locations in the same sample, and the average value thereof was made into the haze value.

(peel strength)

The surface protection sheets with separators prepared in each of 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 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 sample for measurement.

The obtained sample for measurement was left to stand for 1 hour in an environment of a temperature of 23°C and a relative humidity of 50%. Then, in accordance with JIS K 6854-2, a tensile test in the 180° direction was conducted at a peeling rate of 0.3 m/min and 3.0 m/min, and the peel strength (gf/25 mm) of the surface protection sheet to the glass plate was measured. .

(lamination)

Fig. 1 is a plan view showing a method for evaluating the laminability of the surface protection sheet 10, and Fig. 2 is a cross-sectional view taken along A-A in Fig. 1 . The surface protection sheet 10 having a separator is cut into a size of 20 mm x 100 mm, and the release PET film is peeled off. Next, the pressure-sensitive adhesive layer 12 is bonded to the glass plate 30 in a range of 15 mm from one end of the surface protection sheet 10 in the longitudinal direction, and the adhesive portion is fixed to the glass plate 30, as shown in FIG. As described above, the other end of the surface protection sheet 10 is lifted. As a method of fixing the adhesive portion, as shown in FIG. 1, the upper surface of the surface protection sheet 10 is fixed within a range of 15 mm from the end of the surface protection sheet 10, and both sides of the surface protection sheet in the width direction are fixed. On the outside, cellophane tape 20 is affixed so as to cover the glass plate.

The other end of the surface protection sheet 10 was released from this state, and the time until the entire pressure-sensitive adhesive layer adhered to the glass plate 30 with the weight of the surface protection sheet 10 was measured. Examples 1 to 9 and Comparative Examples The lamination properties of the surface protection sheets according to 1 to 4 were evaluated according to the following criteria.

(Evaluation Criteria for Laminating Properties)

◎: Less than 5 seconds to adhere

○: 5 seconds or more and less than 10 seconds until adherence

△: 10 seconds or more and less than 15 seconds until adherence

×: 15 seconds or more until adhered or not adhered

(adhesive residue)

The surface protection sheets with separators produced in each of 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. Next, the exposed adhesive side was laminated to a glass plate, and this was used as a sample. After the sample was left at 85°C and 85% relative humidity for 3 days, the surface protection sheet was peeled off from the glass plate, and adhesive residue on the surface of the glass plate was visually confirmed and evaluated according to the following criteria.

(Evaluation Criteria for Adhesive Residue)

○: The surface of the glass plate has no change compared to before bonding

△: Slightly confirmed adhesive residue on the surface of the glass plate

×: adhesive residue is clearly observed on the surface of the glass plate

(Cracks in the adhesive layer at the time of cutting)

The surface protection sheets produced in each of 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.)) , The end surface of the pressure-sensitive adhesive layer after cutting was observed with a microscope (magnification: 800 times (RH-2000 manufactured by Hyrox Co., Ltd.)) and evaluated according to the following criteria.

(crack evaluation criteria)

○: Cracks were confirmed in the pressure-sensitive adhesive layer

×: No cracks were observed in the pressure-sensitive 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. Further, the composition of Comparative Example 2 using polyurethane (A-4) having a weight average molecular weight of 12000 as the polyurethane (A) had insufficient lamination properties and adhesive residue was also observed. Further, the composition of Comparative Example 3 containing no polyfunctional monomer (B) had excessively high peel strength and insufficient lamination properties. In the composition of Comparative Example 4 containing 15% by mass of the polyfunctional monomer (B), the pressure-sensitive adhesive layer was hard and cracked during cutting.

10: surface protection sheet
12: adhesive layer
14: substrate
20: cellophane tape
30: glass plate

Claims (12)

polyurethane (A);
A multifunctional monomer (B);
Polyurethane (A) and other monomers (C) polymerizable with the multifunctional monomer (B);
A photopolymerization initiator (D);
fatty acid ester
A pressure-sensitive adhesive composition for a surface protection sheet comprising
The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from polyoxyalkylene polyol and a structure derived from polyisocyanate,
The polyurethane (A) comprises 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 ends 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 100 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;
With respect to 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass;
The pressure-sensitive adhesive composition for surface protection sheet characterized in that the content of the fatty acid ester is 1 to 40 parts by mass. According to claim 1,
The pressure-sensitive adhesive composition for surface protection sheet, 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. According to claim 1 or 2,
The pressure-sensitive adhesive composition for surface protection sheet, wherein the skeleton contained in the polyurethane (A) is a copolymer of polyoxyalkylene glycol and diisocyanate. According to claim 3,
The polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for surface protection sheets, wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate. According to claim 1 or 2,
The pressure-sensitive adhesive composition for surface protection sheets, wherein the (meth)acryloyl group in the polyurethane (A) is a part of the (meth)acryloyloxy group. According to claim 1 or 2,
The pressure-sensitive adhesive composition for surface protection sheets, wherein the polyfunctional monomer (B) has three or more (meth)acryloyl groups. According to claim 6,
The pressure-sensitive adhesive composition for surface protection sheets, wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate. According to claim 1 or 2,
The pressure-sensitive adhesive composition for surface protection sheets, wherein the other monomer (C) has only one (meth)acryloyl group. According to claim 1 or 2,
The other monomer (C) comprises an alkyl (meth) acrylate, the pressure-sensitive adhesive composition for surface protection sheet. According to claim 1 or 2,
The polyurethane (A) further comprises polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and has a (meth)acryloyl group only at either end of the polyurethane (a2),
An adhesive composition for surface protection sheets. According to claim 1 or 2,
The pressure-sensitive adhesive composition for surface protection sheet, in which (meth)acryloyl groups are introduced to 90 to 100% of the terminals of the polyurethane molecules included in the polyurethane (A) on a number basis. A sheet-type substrate;
Pressure-sensitive adhesive layer formed on the substrate
have
A surface protection sheet characterized in that the pressure-sensitive adhesive layer contains a photocured product of the pressure-sensitive adhesive composition for surface protection sheets according to claim 1 or 2.

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