JPWO2020066866A1 - Adhesive composition for surface protection sheet and surface protection sheet - Google Patents

Abstract

Provided is an adhesive composition for a surface protective sheet for a surface protective sheet that has a low haze, is easy to laminate, is easy to peel off, can suppress adhesive residue after peeling, and does not crack during cutting. Other monomers that can be polymerized with polyurethane (A) in an amount of 30 to 60% by mass, polyfunctional monomer (B) in an amount of 2 to 10% by mass, polyurethane (A) and polyfunctional monomer (B). A pressure-sensitive adhesive for a surface protective sheet containing 30 to 68% by mass of C) and 0.1 to 5 parts by mass of a photopolymerization initiator (D) with respect to 100 parts by mass of the total amount of (A) to (C). In the composition, the polyurethane (A) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has a (meth) acryloyl group at a plurality of terminals, and has a weight average molecular weight of 30. The pressure-sensitive adhesive composition for a surface protective sheet is 000 to 200,000.

Description

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

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

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, a (meth) acrylic acid ester having a hydroxy group, and the like. 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 the end of a polyoxyalkylene chain via a urethane bond, a (meth) acrylic acid ester having a hydroxy group, and a (meth) acrylic acid ester having an aromatic ring. , Other photocurable compositions for transparent pressure-sensitive adhesive sheets containing polymerizable monomers and photopolymerization initiators.

In the inspection process of an optical component, it may be required to sufficiently detect or detect fine foreign matter or scratches on the product or component with a protective sheet laminated on the product or component. Therefore, the protective sheet is required to have less fogging, that is, a low haze.

Further, 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 on the adherend (high wettability on the adherend) and easily peeled off. In addition, recently, as the screen of a display has become larger and the panel parts have become thinner, the optical parts themselves have become liable to crack. Therefore, it is also required that the protective sheet has an appropriate adhesiveness (peeling strength) and can be peeled with a lighter force (light peeling property). Further, it is also required that there is no so-called adhesive residue (removability) in which a part of the adhesive layer or the like remains on the product surface (adhesive body) after the protective sheet is peeled off.

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

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

Therefore, the present inventor has conducted diligent studies to solve the above problems, and includes a polyurethane having a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate and having a (meth) acryloyl group at a plurality of ends. Photopolymerization of polyurethane with a weight average molecular weight of 30,000 to 200,000, a polyfunctional monomer having a plurality of (meth) acryloyl groups, and a polyurethane and other monomers polymerizable with the polyfunctional monomer. By curing the pressure-sensitive adhesive composition for a photocurable surface protective sheet containing an initiator, a surface protective sheet having low haze, easy to laminate, easy to peel off, and capable of suppressing adhesive residue after peeling can be obtained. I found. However, the surface protective sheet obtained from the pressure-sensitive adhesive composition for a photocurable surface protective sheet has a slightly hard adhesive layer, so that when a sheet having a thick adhesive layer is laser-cut or knife-cut, the pressure-sensitive adhesive layer is formed. It was found that cracks may occur on the end face.

Therefore, an object of the present invention is that the haze is low, it is easy to laminate, it is easy to peel off, and the adhesive residue after peeling can be suppressed. 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 protective sheet having a low haze, easy to laminate, easy to peel off, and can suppress adhesive residue after peeling, and also to prevent cracks in the adhesive layer during cutting. To provide.

The configuration of the present invention for solving the above problems is as follows.
[1] Polyurethane (A) and
Polyfunctional monomer (B) and
With other monomers (C) that can polymerize with polyurethane (A) and polyfunctional monomer (B),
Photopolymerization initiator (D) and
A pressure-sensitive adhesive composition for a surface protective sheet containing
The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate.
The polyurethane (A) contains polyurethane (a1), and the polyurethane (A) contains 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 a (meth) acryloyl group 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 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, and the content 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, and the content 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 a surface protective sheet, wherein the content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass.
[2] The 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. Agent composition.
[3] Adhesive for surface protective sheet according to any one of [1] and [2], wherein the skeleton contained in the polyurethane (A) is a copolymer of the polyoxyalkylene glycol and the diisocyanate. Agent composition.
[4] The polyoxyalkylene glycol is polypropylene glycol, and 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 additive 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 the (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 (meth) alkyl acrylate.
[10] The polyurethane (A) further contains 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 only at one end 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 one 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. Adhesive composition for sheets.
[12] Sheet-shaped base material and
It has an adhesive layer formed on the base material and has.
A surface protective sheet, wherein the pressure-sensitive adhesive layer comprises a photocurable product of the pressure-sensitive adhesive composition for a surface-protecting sheet according to any one of [1] to [11].

According to the present invention, in addition to having low haze, easy laminating, easy peeling, and suppressing adhesive residue after peeling, a surface protective sheet for a surface protective sheet in which the adhesive layer does not crack during cutting. A pressure-sensitive adhesive composition for use can be provided. Further, according to the present invention, in addition to providing a surface protective sheet having a low haze, easy to laminate, easy to peel off, and can suppress adhesive residue after peeling, a surface protective sheet in which the adhesive layer does not crack during cutting is provided. Can be done.

It is a top view which showed the laminating property evaluation method of the surface protection sheet. FIG. 1 is a cross-sectional view taken along the line AA in FIG.

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

<1. Adhesive composition for surface protection sheet>
The pressure-sensitive adhesive composition for a surface protective sheet according to the present embodiment (hereinafter, may also be referred to as “pressure-sensitive adhesive composition”) includes polyurethane (A), a polyfunctional monomer (B), and polyurethane (A). ) And other monomers (C) that can be polymerized with the polyfunctional monomer (B), and a photopolymerization initiator (D). The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate. The polyurethane (A) contains polyurethane (a1). The polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has a (meth) acryloyl group 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 with respect to 100% by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C). The content of the polyfunctional monomer (B) is 2 to 10% by mass, and the content of the other monomer (C) is 30 to 68% by mass. Further, the content of the photopolymerization initiator (D) is 0. With respect to 100 parts by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B) and the other monomer (C). It is characterized by having 1 to 5 parts by mass.
In addition, the pressure-sensitive adhesive composition according to the present embodiment may contain an additive such as a fatty acid ester, if necessary. Further, the pressure-sensitive adhesive composition according to the present embodiment does not have to contain a solvent, but may contain a solvent if necessary.
Hereinafter, each component contained in the pressure-sensitive adhesive composition will be described. In the following description, the component composed of polyurethane (A), polyfunctional monomer (B), and other monomer (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 a polyoxyalkylene polyol and a polyisocyanate. The polyurethane (A) includes the polyurethane (a1) described later. The polyurethane (A) may further contain the polyurethane (a2) described below for the purpose of adjusting the cohesive force of the cured product of the pressure-sensitive adhesive composition.

[Polyurethane (a1)]
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 a (meth) acryloyl group at a plurality of ends. The (meth) acryloyl group at the end of the polyurethane (a1) is preferably a part of the (meth) acryloyloxy group.

[Polyurethane (a2)]
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 end of the polyurethane (a2) is preferably a part of the (meth) acryloyloxy group.
The content of the polyurethane (a1) and the polyurethane (a2) contained in the polyurethane (A), that is, the method for adjusting the number of (meth) acryloyl groups at the end of the polyurethane contained in the polyurethane (A) is as follows. , An example thereof will be described later in the section of the method for producing polyurethane (A).

Regarding the "plurality of ends" of the present invention, in the case of a linear polymer, there are two ends, and in the case of a branched polymer, there are two or more ends at the same number of ends as the number of each branched chain.
Polyurethane (A) does not contain components other than polyurethane (a1) and polyurethane (a2).

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) on a numerical basis. The polyurethane (a2) contained in the polyurethane (A) is preferably 0 to 20%, more preferably 0 to 10%, and even more preferably 0% of the polyurethane (A) on a numerical basis. When the polyurethane (a1) contained in the polyurethane (A) is 80% or more, the cohesive force of the cured product of the pressure-sensitive adhesive composition becomes sufficiently large.

"Polyoxyalkylene polyol"
The polyoxyalkylene polyol preferably has an alkylene chain having 2 to 4 carbon atoms, and specific examples thereof include polyoxyethylene polyol, polyoxypropylene polyol, and polyoxybutylene polyol. Further, among the polyoxyalkylene polyols, polyoxyalkylene glycol is preferably used, and polypropylene glycol is particularly preferably used.

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

The number average molecular weight of the polyoxyalkylene polyol is preferably 500 to 5,000, more preferably 800 to 4,000, and even more preferably 1,000 to 3,000. 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, the polyurethane contains a sufficient amount of urethane bonds, 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 end (diol or triol type polyoxyalkylene polyol). For example, in the case of diol-type polypropylene glycol, the hydroxyl value is preferably 20 to 120 mgKOH / g, more preferably 30 to 100 mgKOH / g, and even more preferably 40 to 80 mgKOH / g. Specific examples of polypropylene glycol include Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type) of polypropylene glycol having a hydroxyl group (hydroxy group) having a hydroxyl value of 56 mgKOH / g at the end.
Here, the hydroxyl value is the hydroxyl value of the polyoxyalkylene polyol measured according to JIS K0070, and the hydroxyl group required to neutralize free acetic acid when 1 g of the polyoxyalkylene polyol is acetylated. It means the number of mg of potassium. Specifically, it can be obtained by acetylating the hydroxyl group in the sample with acetic anhydride and titrating the free acetic acid generated at that time 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 preferable. Examples of the diisocyanate include tolylene diisocyanate and its hydrogen additive, xylylene diisocyanate and its hydrogen additive, diphenylmethane diisocyanate and its hydrogen additive, 1,5-naphthylene diisocyanate and its hydrogen additive, hexamethylene diisocyanate, and trimethyl. Hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyldiisocyanate, 1,3-bis (isocyanatemethyl) cyclohexane, norbornan diisocyanate and the like can be mentioned.

Among these exemplified compounds, a hydrogenated product of isophorone diisocyanate or diphenylmethane diisocyanate is preferable from the viewpoint of controlling light resistance and reactivity, and a hydrogenated product of diphenylmethane diisocyanate is more preferable from the viewpoint of reactivity. The polyisocyanate-derived structure contained in the polyurethane (A) may consist of one type or may include two or more types.
Specific examples of the polyisocyanate include hydrogenated diphenylmethane diisocyanate (Desmodule W, manufactured by Sumika Cobestrourethane), isophorone diisocyanate (Desmodule I, manufactured by Sumika Cobestrourethane), and the like.

The weight average molecular weight of polyurethane (A) is 30,000 to 200,000, preferably 50,000 to 150,000, and even more preferably 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 is insufficiently flexible, and the surface protective sheet having the pressure-sensitive adhesive layer is laminated. Difficult to remove. On the other hand, if the weight average molecular weight of the polyurethane (A) is larger than 200,000, the pressure-sensitive adhesive composition has a high viscosity and is difficult to handle, resulting in poor workability.

The content of the polyurethane (A) is 30 to 60% by mass, preferably 35 to 55% by mass, and 40 to 50% by mass with respect to the total amount of the components (A) to (C). Is more preferable. 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 (the pressure-sensitive adhesive layer and the adherend) There is a concern that air bubbles may get caught in the space. When the content of the polyurethane (A) is larger 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 the adherend becomes high. There is a 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 protective sheet) using the cured product of the pressure-sensitive adhesive composition. The polyfunctional monomer (B) is a compound other than polyurethane (A) and having a plurality of (meth) acryloyl groups. The number of (meth) acryloyl groups is not particularly limited as long as it is 2 or more, but from the viewpoint of curability, the polyfunctional monomer (B) preferably has 3 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-dimethylhydranthindi ( Meta) Acrylate, α, ω-di (Meta) Acrylic Bisdiethylene Glycolphthalate, Trimethylol Propanetri (Meta) Acrylate, Ethylene Glycol Di (Meta) Acrylate, Tetraethylene Glycol Di (Meta) Acrylate, Polyethylene Glycol Di (Meta) Acrylate , 1,4-Butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, diacryloxyethyl phosphate, dipentaerythritol trihydroxy (meth) acrylate, pentaerythritol tetra (meth) acrylate, etc. Can be mentioned.

Among these, 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and dipentaerythritol are easy to adjust because the peeling strength of the surface protective sheet using the pressure-sensitive adhesive composition is low and easy to adjust. Trihydroxy (meth) acrylate and pentaerythritol tetra (meth) acrylate are more preferable, and trimethylolpropane tri (meth) acrylate is further preferable. Further, the polyfunctional monomer (B) may be composed of one kind of compound or 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 4 to 8% by mass with respect to the total amount of the components (A) to (C). More preferably. If the content is less than 2% by mass, the peel strength of the surface protective sheet is too high and the light peelability is inferior. If 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 likely to occur during the cutting process of the sheet. Further, when the content is more than 10% by mass, the haze tends to be high as a surface protective sheet.

<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 can be polymerized with the polyurethane (A) and the polyfunctional monomer (B). If so, it is not particularly limited. 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). Among them, it is more preferable to have a vinyl group or a (meth) acryloyl group, and further preferably to have a (meth) acryloyl group.

The other monomer (C) is not particularly limited, but contains an alkyl (meth) acrylate, a cyclic alkyl (meth) acrylate, an alkoxyalkyl (meth) acrylate, an alkoxy (poly) alkylene glycol (meth) acrylate, and a hydroxy group. Examples thereof include (meth) acrylate, carboxy group-containing (meth) acrylate, fluorinated alkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylate, (meth) acrylamide, epoxy group-containing (meth) acrylate, and unsaturated carboxylic acid. ..

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. Can be mentioned.

Examples of the cyclic alkyl (meth) acrylate include cyclohexyl (meth) acrylate, norbornyl (meth) acrylate, isobornyl (meth) acrylate, norbornanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and dicyclopentenyloxyethyl (meth). ) Acrylate, dicyclopentanyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate and the like can be mentioned.

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

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

Examples of 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) acryloylmorpholin, diacetone acrylamide and the like.

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

In addition, as the other monomer (C), other than the above compounds, for example, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, and the like. Alkyl vinyl ether, vinyl toluene, N-vinyl pyridine, N-vinylpyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethylvinyl ether, triethylene glycol monovinyl ether Alternatively, diethylene glycol monovinyl ether, methyl vinyl ketone, N-acrylamide methyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallylvinyl ketone and the like can be mentioned.

Among these exemplified compounds, alkyl (meth) acrylate is preferable from the viewpoint of compatibility with polyurethane (A), viscosity of the pressure-sensitive adhesive composition, and adjustment of peel strength, 2-ethylhexyl (meth) acrylate, and isooctyl. (Meta) acrylate, isostearyl (meth) acrylate, and isobornyl (meth) acrylate are more preferable, and 2-ethylhexyl (meth) acrylate is even more preferable. 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 40 to 56% by mass with respect to the total amount of the components (A) to (C). More preferably. 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 concern that the wettability to the adherend is lowered. 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

<1-4. Photopolymerization initiator (D)>
The photopolymerization initiator (D) is not particularly limited, but is 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 thereof include an initiator and 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 ketone, benzoin methyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzylmethyl Ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropane-1-one, methyl Benzoylformates, 2,2-diethoxyacetophenone, 4-N, N'-dimethylacetophenone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1-one and the like can be mentioned. ..

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

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

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 and the like.

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

Among these exemplified compounds, 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are preferable from the viewpoint of 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 kind of compound or two or more kinds 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 with respect to 100 parts by mass of the total amount of the components (A) to (C). Is preferable, and it is more preferably 0.3 to 2 parts by mass. If the content of the photopolymerization initiator (D) is less than 0.1 parts by mass, the pressure-sensitive adhesive composition is not sufficiently photocured, and if it is larger than 5 parts by mass, a large amount of low molecular weight components are produced and obtained. The peelability of the surface protective sheet tends to deteriorate.

<1-5. Additives>
Fatty acid esters are added to the pressure-sensitive adhesive composition as necessary in order to improve the laminateability (wetting property) and foam removal property (easiness of removal of air bubbles sandwiched during bonding) of the obtained surface protection sheet. You may. Examples of fatty acid esters include monobasic acids having 8 to 18 carbon atoms, esters of polybasic acids with branched alcohols having 18 or less carbon atoms, unsaturated fatty acids having 14 to 18 carbon atoms, or branched chains. Examples thereof include an ester of a fatty acid and a tetravalent alcohol. Specific preferred examples of fatty acid esters include isopropyl myristate. The amount of the fatty acid ester added is preferably 1 to 40 parts by mass, more preferably 3 to 35 parts by mass, and further 5 to 30 parts by mass with respect to 100 parts by mass of the total amount of the components (A) to (C). preferable.

Further, 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 softening agent, an antioxidant, an antioxidant, a light stabilizer, an ultraviolet absorber, a polymerization inhibitor, a light stabilizer such as a benzotriazole, and phosphorus. Examples thereof include acid ester-based and other flame retardants, antistatic agents such as surfactants, and dyes.

<1-6. Solvent>
Since the pressure-sensitive adhesive composition contains the polyfunctional monomer (B) and other monomers (C) as low molecular weight components, the viscosity can be adjusted so that it can be applied without adding a solvent. That is, the pressure-sensitive adhesive composition includes the polyurethane (A), the polyfunctional monomer (B), the other monomer (C), and the photopolymerization initiator (D) in addition to the essential components. , The solvent may be substantially free. In that case, when the surface protective sheet is manufactured, 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 film thickness of more than 50 μm, it is preferable that the pressure-sensitive adhesive composition substantially does not contain the solvent. The meaning of "substantially free" of the present invention is 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, and more preferably 0. ~ 0.1% by mass.
A solvent may be added to the pressure-sensitive adhesive composition for the purpose of adjusting the viscosity at the time of coating. The solvent can be appropriately selected depending on other components contained in the pressure-sensitive adhesive composition and the like, but an organic solvent is preferable.
The organic solvent used is not particularly limited, and examples thereof include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol and the like. These organic solvents may be used alone or in combination of two or more. It is preferable that the solvent is removed by applying the pressure-sensitive adhesive composition to a base material or the like and then drying, and then photocuring.

<2. Method for Manufacturing Adhesive Composition for Surface Protective Sheet>
An example of the method for synthesizing polyurethane (A) will be described here, but it is contained in the polyfunctional monomer (B) and other monomers (C) and the pressure-sensitive adhesive composition for a surface protective sheet. Since it is easy to purchase commercially available products for other components and the components vary depending on the type of compound used, the description of the synthesis method will be omitted.

<2-1. Polyurethane (A) synthesis method>
Hereinafter, an example of a preferable synthesis method of polyurethane (A) contained in the pressure-sensitive adhesive composition of the present embodiment will be described, but the synthesis method of polyurethane (A) is not limited to this, and conditions such as raw materials and equipment used for synthesis are used. Can be changed as appropriate. Further, in this example, the reaction of the hydroxy group and the isocyanato group is carried out in any step in the presence of an organic solvent inert to the isocyanato group, such as urethane dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate and the like. It is carried out using a chemical catalyst. 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 mass ppm with respect to the total mass of the reactants.

First, a polyoxyalkylene polyol and a polyisocyanate are charged at a ratio in which the amount of isocyanato groups (number standard, the same applies hereinafter) is larger than the amount of hydroxy groups (number basis, the same applies hereinafter), and these are reacted to form isocyanato groups at the ends. Synthesize polyurethane to have. Specific examples of the polyoxyalkylene polyol and the polyisocyanate are as illustrated in the section of polyurethane (A).

At this time, the molecular weight (degree of polymerization) can be adjusted by adjusting the amount of isocyanato group with respect to the amount of hydroxy group. Specifically, the smaller the excess amount of the isocyanato group with respect to the hydroxy group amount, the larger the molecular weight of the polyurethane having an isocyanato group, and the larger the excess amount of the isocyanato group amount with respect to the hydroxy group amount, the more the polyurethane having an isocyanato group. The molecular weight becomes smaller.

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

The compound having a hydroxy group and a (meth) acryloyl group is not particularly limited, but is a hydroxyalkyl such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or 4-hydroxybutyl (meth) acrylate. Meta) acrylate; 1,3-butanediol mono (meth) acrylate, 1,4-butanediol mono (meth) acrylate, 1,6-hexanediol mono (meth) acrylate, 3-methylpentanediol mono (meth) acrylate Examples thereof include monool having a (meth) acryloyl group derived from various polyols such as. These may be used alone or in combination of two or more. Of these, 2-hydroxyethyl (meth) acrylate is preferable in terms of reactivity with an isocyanato group and photocurability.

Further, in addition to the 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 isocyanato group at the terminal. Therefore, the amount of (meth) acryloyl group introduced can be adjusted. The alkyl alcohol is not particularly limited, and examples thereof include linear type, branched type, and alicyclic type alkyl alcohols, which may be used alone or in combination of two or more types. .. As a result, a polyurethane having a structure derived from the above alkyl alcohol is produced at at least one of the terminals. In this case, the polyurethane (A) will contain at least one polyurethane having no (meth) acryloyl group at the end. Therefore, polyurethane (a2) having a (meth) acryloyl group at only one terminal can also be contained.

On a numerical basis, it is preferable that the (meth) acryloyl group is introduced into 90 to 100% of the ends of the polyurethane contained in the polyurethane (A), more preferably 95 to 100%, still more preferably 100%. When the amount of the (meth) acryloyl group introduced is 90% or more with respect to the isocyanato group on a numerical basis, the cohesive force of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition can be sufficiently obtained. The ratio of the number of terminals into which the (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 example of the method for synthesizing polyurethane (A)>
A modified example of the method for synthesizing polyurethane (A) will be described. In this example as well, as in the above example, the reaction of the hydroxy group and the isocyanato group is carried out in any step in the presence of an organic solvent inert to the isocyanato group, such as dibutyltin dilaurate, dibutyltin diethylhexoate. It is carried out using a urethanization catalyst such as dioctyltin 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 mass ppm with respect to 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 the terminal.

At this time, the molecular weight can be adjusted by adjusting the ratio of the hydroxy group amount to the isocyanato group amount as in the above example. Specifically, the smaller the excess amount of the hydroxy group amount with respect to the isocyanato group amount, the larger the molecular weight of the polyurethane having a hydroxy group, and the larger the excess amount of the hydroxy group amount with respect to the isocyanato group amount, the more the polyurethane having a hydroxy group. The molecular weight becomes smaller.

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

The compound having an isocyanato group and a (meth) acryloyl group is not particularly limited, but 2- (meth) acryloyloxyethyl isocyanate, 2- (meth) acryloyloxypropyl isocyanate, 1,1-bis (acryloyloxymethyl) ethyl. Examples thereof include isocyanate. 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 KK. These may be used alone or in combination of two or more. Of these, 2- (meth) acryloyloxyethyl isocyanate is preferable from the viewpoint of reactivity with a hydroxy group and photocurability.

Further, in addition to the compound having an isocyanato 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 the terminal. Therefore, the amount of the (meth) acryloyl group introduced can be adjusted. The alkyl isocyanate is not particularly limited, and examples thereof include a linear type, a branched type, and an alicyclic type alkyl isocyanate, which may be used alone or in combination of two or more. .. As a result, a polyurethane having a structure derived from the above alkyl isocyanate is produced at at least one of the terminals. In this case, the polyurethane (A) will contain at least one polyurethane having no (meth) acryloyl group at the end. Therefore, in this case, the polyurethane (A) may also contain a polyurethane having a (meth) acryloyl group at only one end.

On a numerical basis, it is preferable that the (meth) acryloyl group is introduced into 90 to 100% of the ends of the polyurethane contained in the polyurethane (A), more preferably 95 to 100%, still more preferably 100%. When the amount of the (meth) acryloyl group introduced is 90% or more with respect to the isocyanato group on a numerical basis, the cohesive force of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition can be sufficiently obtained.

<2-3. Method of mixing each component contained in the adhesive composition for surface protection sheet>
Polyurethane (A), polyfunctional monomer (B), other monomer (C), photopolymerization initiator (D), fatty acid ester added as needed, and other additives. And an organic solvent are mixed to produce a pressure-sensitive adhesive composition. The mixing method is not particularly limited, but for example, it can be performed using a stirring device equipped with a stirring blade such as a homodisper or a paddle blade.

Further, all the components may be added and mixed at one time, or the addition and mixing may be repeated in a plurality of times for each component. If there is a solid component at room temperature, this component can be added by dissolving it in a solvent, adding it as dispersed in a dispersion medium, or adding it as melted by heating. It is easy to mix in the pressure-sensitive adhesive composition with high uniformity.

<3. Surface protection sheet>
<3-1. Surface protection sheet configuration>
In the surface protective 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 even 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, the film thickness of the pressure-sensitive adhesive layer can be easily controlled.
Further, when it is desired to impart the function of protecting the adherend from impact (impact resistance) to the surface protective 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 contained in the pressure-sensitive adhesive layer is preferably 85 to 100% by mass, more preferably 90 to 100% by mass, and preferably 95 to 100% by mass. More preferred. Here, the gel fraction is the mass fraction of the extracted insoluble matter with respect to the solvent, and here, the solvent is selected from the cured products of the pressure-sensitive adhesive composition, which can dissolve the uncrosslinked component. An example of a specific method for measuring the gel fraction will be described later in Examples. If the gel fraction of the cured product of the pressure-sensitive adhesive composition is 85 to 100% by mass, a part of the pressure-sensitive adhesive layer or the like remains on the adherend when the surface protective sheet is peeled off, so-called adhesive residue is suppressed. can do.

The material of the base material can be appropriately selected depending on the use of the surface protective sheet, and examples thereof include a resin film. When the surface protective sheet is used as a protective sheet in the manufacturing process, for example, and the protective sheet is laminated when inspecting the adherend, that is, the product for scratches or foreign substances, the base material is transparent. Is preferable. Examples of the transparent base material include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, cellulose and the like.

The thickness of the base material can be appropriately selected depending on the use of the surface protective sheet and is not particularly limited, but in the case of a resin film, the thickness of the base material is preferably 5 μm or more from the viewpoint of handleability and strength. , More preferably 10 μm or more, still more preferably 20 μm or more. Further, considering the flexibility of the resin film, the thickness of the base material is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less.

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

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 the material of the separator, for example, paper, a plastic film, or the like can be used, but the plastic film is preferable from the viewpoint of 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 a surface protective sheet according to the present embodiment is, for example, by applying an pressure-sensitive adhesive composition to a base material sheet, laminating a separator, and then irradiating the applied pressure-sensitive adhesive composition with ultraviolet rays to photo-curing the coated pressure-sensitive adhesive composition. Obtainable.

The method for applying the pressure-sensitive adhesive composition to the base material 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 are used. Examples thereof include the method used and the screen printing method.

Further, examples of the light source for photocuring the pressure-sensitive adhesive composition include a black light, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, and a xenon lamp. The light irradiation intensity may be such that the pressure-sensitive adhesive composition can be sufficiently cured, and is preferably 50 to 3000 mW / cm ² . If the light irradiation intensity is weak, it takes a long time to cure, so that the productivity is lowered. Light irradiation can be performed from either the separator side or the base material side as long as it is transparent.

<3-3. Applications of surface protection sheet and required performance>
In the inspection process, it may be required to sufficiently detect or detect fine foreign matter or scratches on the product or part with the protective sheet laminated on the product or part. The protective sheet is the 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 reflective sheet, and a brightness improving film used for liquid crystal displays of smartphones, personal computers, televisions, etc. It may be preferably used for the purpose of protecting.

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 less fogging, that is, a 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 further preferably 1.0% or less. A specific method for measuring the haze value of the surface protective sheet will be described later in Examples.

Further, when the surface protective sheet according to the present embodiment is used as the protective sheet as described above, the surface protective sheet has a minimum peeling strength so as not to peel off from the product or parts during handling such as transportation. Is required. On the other hand, when the surface protective sheet is peeled off from the product or part, it is necessary to reduce the peeling strength in order to facilitate the peeling operation or to prevent the product or part from being deformed or damaged during the peeling. From these viewpoints, the peel strength of the surface protective sheet depends on the thickness of the base material and the pressure-sensitive adhesive layer when the peeling speed is 3.0 m / min, but when the pressure-sensitive adhesive layer is 50 to 100 μm, 1 It is preferably ~ 50 gf / 25 mm, more preferably 2 to 45 gf / 25 mm, and even more preferably 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 to the examples shown below. In the following examples, the weight average molecular weight of the obtained polyurethane (A) is gel permeation chromatography (Showa Denko Corporation Shodex® GPC-101, hereinafter referred to as GPC). It is a value in terms of polystyrene measured by. The measurement conditions of GPC are as follows.
Column: LF-804 manufactured by Showa Denko KK
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 thermometer, agitator, a dropping funnel, and a cooling tube with a drying tube, 5.5 kg (21 mol) of a hydrogen additive of diphenylmethane diisocyanate (Death Module W, manufactured by Sumika Cobestrolurethane) and a hydroxyl value 40.1 kg (20 mol) of polypropylene glycol Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) having a hydroxy group of 56 mgKOH / g at the end was charged. Then, 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 the reaction was carried out for 2 hours to obtain 45.8 kg of polyurethane (A-1) having an acryloyl group at the end. .. This polyurethane (A-1) was analyzed by IR, and it was confirmed that the peak derived from the isocyanato group disappeared. The weight average molecular weight of the obtained polyurethane (A-1) was 70,000.
Since the disappearance of the peak derived from the isocyanato group was confirmed by IR, 2-hydroxyethyl acrylate was added to all the ends of the polyurethane having the isocyanato group at both ends. That is, on a numerical basis, an acryloyl group is introduced into 100% of the terminals of the polyurethane molecule contained in polyurethane (A-1).

(A-2)
Polyurethane having acryloyl groups at both ends in the same manner as the method for synthesizing polyurethane (A-1) except that isophorone diisocyanate (Death Module I, manufactured by Sumika Cobestrourethane) 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 (manufactured by Mitsui Chemicals, number average molecular weight 2000) except that 8 mol of hydrogenated diphenylmethane diisocyanate and 7 mol of polypropylene glycol Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000) having a hydroxy group having a hydroxyl value of 56 mgKOH / g at the end were changed. 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 polypropylene glycol Actol D-2000 (manufactured by Mitsui Chemicals) having a hydroxy group having a hydroxyl value of 56 mgKOH / g at the end was changed to 3 mol. A polyurethane (A-4) having an acryloyl group at the end was obtained in the same manner as in the method. The weight average molecular weight of the obtained polyurethane (A-4) was 12,000.

(A-5)
Acryloyl groups are added to both ends or at the ends in the same manner as in the synthetic method of polyurethane (A-1) except that 1.8 mol of 2-hydroxyethyl acrylate and 0.2 mol of 1-octanol are used instead of 2 mol of 2-hydroxyethyl acrylate. Polyurethane (A-5), which is a mixture of polyurethane having one end, was obtained. The weight average molecular weight of the obtained polyurethane (A-5) was 69,000.
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 ends of the polyurethane having the isocyanato group at both ends. That is, on a numerical basis, an acryloyl group is introduced into 90% of the terminals of polyurethane molecules contained in polyurethane (A-5).
At this time, the polyurethane (a1) contained in the polyurethane (A-5) is 80% of the polyurethane (A) on a numerical basis, and the polyurethane (a2) is 20% of the polyurethane (A) on a numerical basis.

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

<Making a surface protection sheet>
A surface protective sheet having a base material of an optical PET film on one side was prepared by the same method for Examples 1 to 9 and Comparative Examples 1 to 4. First, using an applicator, the adjusted pressure-sensitive adhesive composition is applied as a separator on an optical PET film (A4300 manufactured by Toyobo Co., Ltd.) having a thickness of 75 μm, and the thickness of the pressure-sensitive adhesive composition is applied. It was covered with a 75 μm release PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp), the sheet covered with the release PET film is irradiated with ultraviolet rays from the surface on the release PET film side to form an adhesive. The composition was photocured. The irradiation distance of ultraviolet rays is 25 cm, the moving speed of the lamp is 1.0 m / min, and the irradiation amount is 1000 mJ / cm ² . The thickness of the pressure-sensitive adhesive layer after curing was calculated by measuring the thickness of the surface protective sheet after peeling off the separator using a dial gauge, and then subtracting the thickness of the base material of 75 μm from this 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 μm in both Examples 1 to 9 and Comparative Examples 1 to 4.

<Evaluation of Adhesive Composition for Surface Protective Sheet and Surface Protective Sheet>
Regarding the pressure-sensitive adhesive composition and the surface protective sheet according to Examples 1 to 9 and Comparative Examples 1 to 4, the gel fraction, transparency (haze value), peel strength, laminate property (wetting property), glue to the adherend. The remaining and cracks in the pressure-sensitive adhesive layer during 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 compositions of Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to a 50 μm-thick peeling PET film so that the thickness of the pressure-sensitive adhesive layer after curing was 75 μm. It was applied to HY-S10) manufactured by Higashiyama Film Co., Ltd. The method of confirming the thickness of the pressure-sensitive adhesive layer is the same as the measurement method described above in the section of preparing the surface protective sheet.

Next, the pressure-sensitive adhesive composition on the peeled PET film was covered with a 75 μm-thick peeled PET film (E7006 manufactured by Toyobo Co., Ltd.). Next, using an ultraviolet irradiation device (manufactured by Eye Graphics Co., Ltd., UV irradiation device 3 kW, high-pressure mercury lamp), an adhesive composition whose both sides were covered with a release PET film was applied to the surface of the release PET film side having a thickness of 75 μm. The pressure-sensitive adhesive composition was photo-cured by irradiating with ultraviolet rays. The irradiation distance of ultraviolet rays is 25 cm, the moving speed of the lamp is 1.0 m / min, and the irradiation amount is 1000 mJ / cm ² .

The prepared sheet was cut into a size of 100 mm × 100 mm, and the peeled PET films on both sides were peeled from the cured product of the pressure-sensitive adhesive composition to prepare a sample for measurement. This measurement sample was immersed in 50 ml of toluene at 25 ° C. for 24 hours, then dried at 80 ° C. for 5 hours, and the gel fraction was calculated from the mass of the measurement sample before and after immersion in toluene by the following formula (1). .. The results are shown in Table 1.
Gel fraction (mass%) = [A / B] x 100 (1)
A: Dry mass of the measurement sample after immersion in toluene (mass of toluene is not included) B: Mass of the measurement sample before immersion in toluene

(Haze value)
The surface protection sheet with a separator prepared 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 off. Then, the entire surface of the exposed 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 haze value of this measurement sample was measured using a haze meter (NM-150 (manufactured by Murakami Color Technology Laboratory Co., Ltd.)). The haze value (%) was calculated by dividing the diffusion transmittance by the total light transmittance and multiplying by 100. The measurement was performed at three points on the same sample, and the average value thereof was taken as the haze value.

(Peeling strength)
The surface protection sheet with a separator prepared 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 peeled PET film was peeled off. Then, the entire surface of the exposed 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 measurement sample was left to stand in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 1 hour. Then, according to JIS K 6854-2, a tensile test was performed in the 180 ° direction at a peeling speed of 0.3 m / min and 3.0 m / min, and the peel strength of the surface protective sheet against the glass plate (gf / 25 mm). Was measured.

(Laminated)
FIG. 1 is a plan view showing a method for evaluating the laminateability of the surface protective sheet 10, and FIG. 2 is a cross-sectional view taken along the line AA in FIG. The surface protection sheet 10 with a separator is cut into a size of 20 mm × 100 mm, and the peeling PET film is peeled off. Next, the adhesive layer 12 is attached to the glass plate 30 within a range of 15 mm from one end in the longitudinal direction of the surface protective sheet 10, the adhesive portion is fixed to the glass plate 30, and the surface protective sheet is as shown in FIG. Lift the other end of 10. As a method of fixing the adhesive portion, as shown in FIG. 1, the upper surface of the surface protective sheet 10 is provided in a range of 15 mm from the one end of the surface protective sheet 10, and a glass plate is provided on both outer sides of the surface protective sheet in the width direction. The cellophane tape 20 is attached so as to cover the glass.

From this state, the other end of the surface protective sheet 10 is released, and the time until the entire adhesive layer adheres to the glass plate 30 by the weight of the surface protective sheet 10 is measured, and Examples 1 to 9 and Comparative Examples 1 to 1 are measured. The laminateability of the surface protection sheet according to No. 4 was evaluated according to the following criteria.
(Evaluation criteria for laminateability)
⊚: Less than 5 seconds until close contact ○: 5 seconds or more and less than 10 seconds until close contact Δ: 10 seconds or more and less than 15 seconds until close contact ×: 15 seconds or more until close contact or no contact

(Remaining glue)
The surface protection sheet with a separator prepared 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 off. Next, the exposed adhesive surface was laminated on a glass plate, and this was used as a sample. After allowing this sample to stand at 85 ° C. and a relative humidity of 85% for 3 days, the surface protective sheet was peeled off from the glass plate, and the adhesive residue on the surface of the glass plate was visually confirmed and evaluated according to the following criteria.

(Evaluation criteria for adhesive residue)
◯: The surface of the glass plate does not change compared to before bonding.
Δ: A slight amount of adhesive residue is confirmed on the surface of the glass plate.
X: Adhesive residue is clearly confirmed on the surface of the glass plate.

(Cracking of adhesive layer during cutting)
The surface protection sheets produced in Examples 1 to 9 and Comparative Examples 1 to 4 are cut with a pinnacle blade (blade height: 0.80 mm, blade angle: 50 ° (manufactured by Tsukaya Knife Mfg. 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 Hirox Co., Ltd.)) and evaluated according to the following criteria.

(Evaluation criteria for cracks)
◯: Cracks are confirmed in the adhesive layer.
X: No crack is confirmed in the 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 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 12000 as polyurethane (A) had insufficient laminate property, and adhesive residue was also observed. Furthermore, the composition of Comparative Example 3 containing no polyfunctional monomer (B) had too high peel strength and insufficient laminateability. 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 the pressure-sensitive adhesive layer was cracked at the time of cutting.

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

Claims (12)

Polyurethane (A) and
Polyfunctional monomer (B) and
With other monomers (C) that can polymerize with polyurethane (A) and polyfunctional monomer (B),
Photopolymerization initiator (D) and
A pressure-sensitive adhesive composition for a surface protective sheet containing
The polyurethane (A) is a polyurethane having a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate.
The polyurethane (A) contains polyurethane (a1), and the polyurethane (A) contains 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 a (meth) acryloyl group 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 a compound having a plurality of (meth) acryloyl groups.
With respect to 100% by mass of the total amount of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C).
The content of the polyurethane (A) is 30 to 60% by mass, and the content 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, and the content 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 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 polyoxyalkylene glycol and 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 additive 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 the (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 contains polyurethane (a2).
Claim that the polyurethane (a2) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a polyisocyanate, and has a (meth) acryloyl group only at one end of the polyurethane (a2). The pressure-sensitive adhesive composition for a surface protective sheet according to any one of 1 to 9. The adhesive for a surface protective sheet according to any one of claims 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. Agent composition. Sheet-shaped base material and
It has an adhesive layer formed on the base material and has.
A surface protective sheet comprising the pressure-sensitive adhesive layer as a photocurable product of the pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 11.

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