WO2020066870A1

WO2020066870A1 - Surface-protection-sheet adhesive composition and surface protection sheet

Info

Publication number: WO2020066870A1
Application number: PCT/JP2019/036892
Authority: WO
Inventors: 達宏池谷; 一博佐々木; 中西　健一
Original assignee: 昭和電工株式会社
Priority date: 2018-09-26
Filing date: 2019-09-20
Publication date: 2020-04-02
Also published as: KR20210041021A; JP7380578B2; KR102535559B1; JPWO2020066870A1; CN112673072A; TW202026386A; TWI824017B

Abstract

Provided are: a surface-protection-sheet adhesive composition for a surface protection sheet that is easily laminated on an adherend, that is easily peeled off therefrom, that is capable of preventing the occurrence of adhesive residue on the adherend after being peeled off, and that is capable of suppressing the peeling chargeability when being peeled off; and a surface protection sheet having an adhesive layer consisting of a cured product of the adhesive composition. The present invention provides a surface-protection-sheet adhesive composition containing: a polyurethane (A); a polyfunctional monomer (B); another monomer (C) that is polymerizable with the polyurethane (A) and the polyfunctional monomer (B); a photopolymerization initiator (D); and an ionic liquid (E). The polyurethane (A) has a skeleton including a structure originating from a polyoxyalkylene polyol and a structure originating from a polyisocyanate; (meth)acryloyl groups are included at a plurality of termini of the polyurethane (A); and the polyurethane (A) has a weight average molecular weight of 30,000-200,000.

Description

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

The present invention relates to a pressure-sensitive adhesive composition for a surface protection sheet, and a surface protection sheet having a pressure-sensitive adhesive layer formed of a cured product of the pressure-sensitive adhesive composition.
Priority is claimed on Japanese Patent Application No. 2018-180613, filed Sep. 26, 2018, the content of which is incorporated herein by reference.

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

For example, Patent Document 1 describes that a removable pressure-sensitive adhesive containing a specific urethane resin has improved removability and wettability to an adherend. Further, in order to suppress adhesion of fine dust in the air in a step of peeling these protective sheets, it is also disclosed that an ionic liquid is contained in an adhesive to impart antistatic properties to the surface protective sheet. .

JP 2017-155249 A

However, in the urethane surface protective sheet as disclosed in Patent Document 1, easiness of lamination to the adherend (high wettability to the adherend), easiness of peeling, difficulty of adhesive residue, and difficulty in peeling Although the antistatic property has been improved, it has not been sufficient yet.
The present invention has been made in view of the above circumstances, and is easy to laminate on an adherend (high wettability to an adherend), easy to peel, difficult to leave glue, It is an object of the present invention to provide a pressure-sensitive adhesive composition which further enhances the antistatic property of a sheet, and a surface protective sheet having a pressure-sensitive adhesive layer obtained by curing the same.

The configuration of the present invention for solving the above problems is as follows.
[1] Polyurethane (A),
A polyfunctional monomer (B),
Other monomers (C) polymerizable with the polyurethane (A) and the polyfunctional monomer (B),
A photopolymerization initiator (D);
An ionic liquid (E);
A pressure-sensitive adhesive composition for a surface protection sheet comprising:
The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate,
The polyurethane (A) includes a polyurethane (a1),
The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth) acryloyl groups at a plurality of terminals of the polyurethane (a1);
The polyurethane (A) has a weight average molecular weight of 30,000 to 200,000;
The polyfunctional monomer (B) is a compound having a plurality of (meth) acryloyl groups,
With respect to a total amount of 100% by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
30 to 60% by mass of the polyurethane (A),
2 to 10% by mass of the polyfunctional monomer (B),
30 to 68% by mass of the other monomer (C)
Containing
For the total amount of 100 parts by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
0.1 to 5 parts by mass of the photopolymerization initiator (D),
0.5 to 5 parts by mass of the ionic liquid (E),
A pressure-sensitive adhesive composition for a surface protective sheet, comprising:
[2] The pressure-sensitive adhesive for a surface protective sheet according to [1], wherein the structure derived from the polyoxyalkylene polyol contained in the polyurethane (A) is a structure derived from a polyoxyalkylene polyol having a number average molecular weight of 500 to 5,000. Composition.
[3] The ionic liquid (E) is
The pressure-sensitive adhesive composition for a surface protective sheet according to [1] or [2], which is a combination of an organic cation selected from the group consisting of quaternary nitrogen atoms, ammonium, immonium, and sulfonium, and a fluorinated organic anion.
[4] The ionic liquid (E) is
Ionic liquid composed of 1-ethyl-3-methylimidazolium cation and bis (fluorosulfonyl) imide anion ((FSO ₂ ) ₂ N ⁻ ), and 4-methyl-1-octyl-pyridinium cation and bis (fluorosulfonyl) imide The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [3], including at least one selected from the group consisting of an ionic liquid comprising an anion ((FSO ₂ ) ₂ N ⁻ ).
[5] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [4], wherein the skeleton contained in the polyurethane (A) is a copolymer with a polyoxyalkylene glycol and a diisocyanate.
[6] The polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [5], wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate.
[7] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [6], wherein the (meth) acryloyl group in the polyurethane (A) is a part of a (meth) acryloyloxy group. .
[8] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [7], wherein the polyfunctional monomer (B) has three or more (meth) acryloyl groups.
[9] The pressure-sensitive adhesive composition for a surface protective sheet according to [8], wherein the polyfunctional monomer (B) is trimethylolpropane triacrylate.
[10] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [9], wherein the other monomer (C) has only one (meth) acryloyl group.
[11] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [1] to [10], wherein the other monomer (C) contains an alkyl (meth) acrylate.
[12] The polyurethane (A) further contains a polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and has a (meth) acryloyl group at only one terminal of the polyurethane (a2) [1 ] The pressure-sensitive adhesive composition for a surface protective sheet according to any one of [11] to [11].
[13] The surface protection according to any of [1] to [12], wherein a (meth) acryloyl group is introduced into 90 to 100% of the terminals of the polyurethane molecules contained in the polyurethane (A) on a numerical basis. An adhesive composition for a sheet.
[14] a sheet-like base material;
Having an adhesive layer formed on the base material,
A surface protection sheet, characterized in that the pressure-sensitive adhesive layer comprises a photocured product of the pressure-sensitive adhesive composition for a surface protection sheet according to any one of [1] to [13].

ADVANTAGE OF THE INVENTION According to this invention, it is easy to laminate on an adherend (it has high wettability to an adherend), and it is easy to peel off. It is possible to provide a pressure-sensitive adhesive composition for a surface protective sheet, which can suppress the peeling chargeability at the time. Further, according to the present invention, it is possible to provide a surface protection sheet which can be easily laminated and peeled, and can further suppress the peeling chargeability at the time of peeling.

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

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

<1. Pressure-sensitive adhesive composition for surface protection sheet>
The pressure-sensitive adhesive composition for a surface protective sheet according to the present embodiment (hereinafter, also sometimes referred to as “pressure-sensitive adhesive composition”) includes a polyurethane (A), a polyfunctional monomer (B), and the polyurethane ( A) and another monomer (C) polymerizable with the polyfunctional monomer (B), a photopolymerization initiator (D), and an ionic liquid (E). The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate. The polyurethane (A) includes the polyurethane (a1). The polyurethane (a1) has a skeleton containing a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth) acryloyl groups at a plurality of terminals of the polyurethane (a1). The weight average molecular weight of the polyurethane (A) is 30,000 to 200,000. Components of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C) (hereinafter sometimes referred to as “components (A) to (C)”). The polyurethane (A) is 30 to 60% by mass, the polyfunctional monomer (B) is 2 to 10% by mass, and the other monomer (C) is 30 to 68% by mass with respect to the total amount of 100% by mass. %contains. Further, based on 100 parts by mass of the total of the components (A) to (C), 0.1 to 5 parts by mass of the photopolymerization initiator (D) and 0.5 to 5 parts by mass of the ionic liquid (E). Parts, are contained.
Further, the pressure-sensitive adhesive composition according to the present embodiment may include an additive such as a fatty acid ester, if necessary. Furthermore, the pressure-sensitive adhesive composition according to the present embodiment may not include a solvent, but may include a solvent as needed.
Hereinafter, each component contained in the pressure-sensitive adhesive composition will be described.

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

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

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

The “plurality of ends” of the present invention are two ends in the case of a linear polymer, and two or more ends in the same number of ends as each branched chain in the case of a branched polymer.
The polyurethane (A) contains no components other than the polyurethane (a1) and the polyurethane (a2).
The polyurethane (a1) contained in the polyurethane (A) is preferably 80 to 100%, more preferably 90 to 100%, even more preferably 100% of the polyurethane (A) on a number basis. The polyurethane (a2) contained in the polyurethane (A) is preferably 0 to 20%, more preferably 0 to 10%, even more preferably 0% of the polyurethane (A) on a number basis. If the polyurethane (a1) contained in the polyurethane (A) is at least 80%, the cohesive force of the cured product of the pressure-sensitive adhesive composition will be sufficiently large.

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

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

The number average molecular weight of the polyoxyalkylene polyol is preferably from 500 to 5,000, more preferably from 800 to 4,000, and even more preferably from 1,000 to 3,000. When the number average molecular weight is 500 or more, the peel strength of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition is improved. When the number average molecular weight is 5,000 or less, a sufficient amount of urethane bonds are contained in the polyurethane, so that the cohesive force of the pressure-sensitive adhesive layer is improved.
The polyoxyalkylene polyol preferably has two or three hydroxyl groups at the terminal (diol or triol type polyoxyalkylene polyol). For example, in the case of diol type polypropylene glycol, the hydroxyl value is preferably from 20 to 120 mgKOH / g, more preferably from 30 to 100 mgKOH / g, even more preferably from 40 to 80 mgKOH / g. As a specific example of the polypropylene glycol, Actol D-2000 (manufactured by Mitsui Chemicals, number average molecular weight 2000, diol type) of a polypropylene glycol having a hydroxyl group (hydroxy group) having a hydroxyl value of 56 mgKOH / g is exemplified.
Here, the hydroxyl value is a hydroxyl value of the polyoxyalkylene polyol measured according to JIS K0070, and is a hydroxyl value required to neutralize free acetic acid when 1 g of the polyoxyalkylene polyol is acetylated. It means the number of mg of potassium. Specifically, the hydroxyl group in the sample can be acetylated using acetic anhydride, and the free acetic acid generated at that time can be determined by titration with a potassium hydroxide solution.

"Polyisocyanate"
The polyisocyanate is not particularly limited as long as it is a compound having a plurality of isocyanato groups, but diisocyanate is preferred. Examples of the diisocyanate include tolylene diisocyanate and its hydrogenated product, xylylene diisocyanate and its hydrogenated product, diphenylmethane diisocyanate and its hydrogenated product, 1,5-naphthylene diisocyanate and its hydrogenated product, hexamethylene diisocyanate, trimethyl Hexamethylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, norbornane diisocyanate, and the like.

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

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

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

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

The polyfunctional monomer (B) is preferably a poly (meth) acrylate of a polyol compound, for example, polyethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate , Triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, hydroxypivalic acid ester neopentyl glycol di (meth) acrylate, 1,3-bis (hydroxyethyl) -5,5-dimethylhydantoindi ( (Meth) acrylate, α, ω-di (meth) acrylic bisdiethylene glycol phthalate, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, tetraethylene glycol Di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, diacryloxyethyl phosphate, dipentaerythritol trihydroxy (Meth) acrylate, pentaerythritol tetra (meth) acrylate, and the like.

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

The content of the polyfunctional monomer (B) is 2 to 10% by mass, preferably 3 to 9% by mass, and preferably 4 to 8% by mass based on the total amount of the components (A) to (C). % Is more preferable. When the content is less than 2% by mass, the peel strength of the surface protective sheet is too high, and the light peelability is poor. If the content is more than 10% by mass, the compatibility with the ionic liquid (E) is deteriorated, so that the antistatic property and the transparency (haze value) are deteriorated.

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

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

Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, and isobutyl (meth). Acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, n-hexyl (meth) acrylate, isooctyl (meth) acrylate, isostearyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, etc. No.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Among these exemplified compounds, from the viewpoint of the transparency of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition, a carbonyl-based photopolymerization initiator and an acylphosphine oxide-based photopolymerization initiator are preferable, and 1-hydroxy Cyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide are more preferred. Further, the photopolymerization initiator (D) may be composed of one type of compound, or may be composed of two or more types of compounds.

The content of the photopolymerization initiator (D) is 0.1 to 5 parts by mass, and 0.2 to 3 parts by mass based on 100 parts by mass of the total of components (A) to (C). And more preferably 0.3 to 2 parts by mass. When the content of the photopolymerization initiator (D) is less than 0.1 part by mass, the pressure-sensitive adhesive composition is not sufficiently cured by light. The releasability of the surface protective sheet tends to deteriorate.

<1-5. Ionic liquid (E)>
The ionic liquid (E) contained in the pressure-sensitive adhesive composition of the present embodiment improves the antistatic property of the pressure-sensitive adhesive composition. The ionic liquid refers to a molten salt compound (ionic compound) having a melting point of 100 ° C. or less. The ionic liquid preferably has a melting point of room temperature (25 ° C.) or lower. The ionic liquid (E) may be composed of one type of compound, or may be composed of two or more types of compounds.

As the ionic liquid (E), it is preferable to use an organic salt compound in which an organic cation is combined with an inorganic anion or an organic anion.
Onium is mentioned as an organic cation constituting the ionic liquid (E). Specifically, as the organic cation, ammonium quaternary nitrogen atom (representative ^structure: _Q 1 ^{4 N} +), immonium (representative ^{_{^{^{structure: Q 2 2 C = N +}}}} Q 1 2), sulfonium (representative structure: Q ¹ ₃ S ^+), oxonium (representative ^structure: _Q 1 ^{2 O} +), phosphonium quaternary phosphorus atom (representative ^structure: _Q 1 ^{4 P} +), iodonium (representative ^structure: _Q 1 2 ^{I +)} and the like No.

In the above representative structure of the organic cation, Q ¹ represents a substituent such as an alkyl group, an aryl group, or a heterocyclic group. Q ² represents a hydrogen atom or a substituent. A plurality of Q ^{1 in} the molecule, a plurality of Q ^{2 in} the molecule, or Q ¹ and Q ² in the molecule may be bonded to each other to form a ring. Furthermore, two for ^{Q 1} or 2 ^{Q 2} 'is jointly double bond group in the molecule (e.g., = O, = S, = NQ 2) may be formed.

中でも Among the above organic cations, quaternary nitrogen atoms such as ammonium, immonium and sulfonium are preferred. As these organic cations, for example, pyridinium cation, piperidinium cation, pyrrolidinium cation, imidazolium cation, tetrahydropyrimidinium cation, dihydropyrimidinium cation, pyrazolium cation, tetraalkylammonium cation, trialkyl And a sulfonium cation. Among these organic cations, an imidazolium cation and a pyridinium cation are preferably used.

粘着 The pressure-sensitive adhesive composition containing the ionic liquid (E) using an imidazolium cation or a pyridinium cation as the organic cation has excellent antistatic properties.

Specific examples of the imidazolium cation used as the organic cation include, for example, 1-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-ethyl-2,3-dimethylimidazolium cation, 1-butyl -3-methylimidazolium cation, 1,2,3-trimethylimidazolium cation and the like. Among these imidazolium cations, 1-ethyl-3-methylimidazolium cation is preferably used.

Specific examples of the pyridinium cation used as the organic cation include, for example, 1-ethylpyridinium cation, 1-butylpyridinium cation, 1-hexylpyridinium cation, 1-butyl-3-methylpyridinium cation, 1-butyl-4- Examples thereof include a methylpyridinium cation, a 1-hexyl-3-methylpyridinium cation, a 1-hexyl-4-methylpyridinium cation, and a 1-butyl-3,4-dimethylpyridinium cation. Among these pyridinium cations, a 1-hexyl-4-methylpyridinium cation, a 4-methyl-1-octyl-pyridinium cation and the like are preferably used.

The inorganic anion constituting the ionic liquid (E) is not particularly limited as long as it satisfies that it becomes an ionic liquid. Examples of the inorganic anion include Cl ⁻ , Br ⁻ , I ⁻ , AlCl ₄ ⁻ , Al ₂ Cl ₇ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , NO ₃ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , NbF ₆ ⁻ , TaF ₆ ⁻ , F (HF) _m ⁻ (m is an integer of 0 or more), (CN) ₂ N ^{− and the} like.

The organic anion constituting the ionic liquid (E) is not particularly limited as long as the organic anion satisfies the ionic liquid. Examples of the organic anion include CH ₃ COO ⁻ , CF ₃ COO ⁻ , CH ₃ SO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (FSO ₂ ) ₂ N ⁻ , and (CF _3). SO ₂ ) ₃ C ⁻ , C ₄ F ₉ SO ₃ ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , C ₃ F ₇ COO ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ^{− and the} like. Can be

As the inorganic anion or organic anion constituting the ionic liquid (E), it is particularly preferable to use an anion containing a fluorine atom among the above. By using an anion containing a fluorine atom, an ionic liquid (E) having excellent ion conductivity is obtained. Among the anions containing a fluorine atom, a fluorine-containing organic anion is preferable, and (FSO ₂ ) ₂ N ⁻ and (CF ₃ SO ₂ ) ₂ N ⁻ are particularly preferably used. The pressure-sensitive adhesive composition containing the ionic liquid (E) using (FSO ₂ ) ₂ N ⁻ or (CF ₃ SO ₂ ) ₂ N ⁻ as an organic anion has particularly excellent antistatic properties.

As the ionic liquid (E), a commercially available ionic liquid may be used. Among commercially available ionic liquids (E), ionic liquids composed of 1-ethyl-3-methylimidazolium cation and bis (fluorosulfonyl) imide anion ((FSO ₂ ) ₂ N ⁻ ) (Daiichi Kogyo Seiyaku Co., Ltd.) (Trade name: AS-110), an ionic liquid composed of 4-methyl-1-octyl-pyridinium cation and bis (fluorosulfonyl) imide anion ((FSO ₂ ) ₂ N ⁻ ) (Daiichi Kogyo Seiyaku Co., Ltd.) , Trade name: AS-804). An adhesive composition containing the above-mentioned AS-110 and AS-804 as the ionic liquid (E) is preferable because of its excellent antistatic properties.

The content of the ionic liquid (E) contained in the pressure-sensitive adhesive composition is 0.5 to 5 parts by mass with respect to 100 parts by mass of the total of components (A) to (C), and 1 to 3 parts by mass. It is preferred that When the content of the ionic liquid (E) is less than 0.5 parts by mass, the antistatic performance is insufficient. As a result, there is a concern that the surface resistance of the surface protective sheet having the pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition will not be sufficiently low. Further, when the content of the ionic liquid (E) is more than 5 parts by mass, when the surface protective sheet having the pressure-sensitive adhesive layer containing the pressure-sensitive adhesive composition is peeled off after being attached to the adherend, Contamination may occur.

<1-6. Additives>
The pressure-sensitive adhesive composition may have, as necessary, a laminating property (wetting property to an adherend) and a bubble removing property (easiness of removing bubbles trapped during bonding) of the obtained surface protective sheet. Fatty acid esters may be added. Examples of the fatty acid ester include an ester of a monobasic acid or a polybasic acid having 8 to 18 carbon atoms and a branched alcohol having 18 or less carbon atoms, an unsaturated fatty acid having 14 to 18 carbon atoms, or a branched chain. And esters of the acid and a tetrahydric alcohol. Specific preferred examples of the fatty acid ester include isopropyl myristate and isopropyl palmitate. The amount of the fatty acid ester to be added is preferably 1 to 40 parts by mass, more preferably 3 to 35 parts by mass, further preferably 5 to 30 parts by mass based on 100 parts by mass of the total of components (A) to (C). preferable.

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

<1-7. Solvent>
Since the pressure-sensitive adhesive composition contains a polyfunctional monomer (B) and another monomer (C) as low molecular weight components, the pressure-sensitive adhesive composition can be adjusted to a coatable viscosity without adding a solvent. That is, the pressure-sensitive adhesive composition for a surface protective sheet of the present invention comprises the polyurethane (A), the polyfunctional monomer (B), the other monomer (C), and the photopolymerization initiator (D ) And the ionic liquid (E), a solvent may not be substantially contained. In that case, when manufacturing the surface protection sheet, the step of heating and drying the solvent can be omitted, and the productivity is increased. In particular, when producing a surface protective sheet having a thickness exceeding 50 μm, it is preferable that the pressure-sensitive adhesive composition for a surface protective sheet does not substantially contain the solvent. The meaning of “substantially free” in the present invention means that the content of the solvent in the pressure-sensitive adhesive composition for a surface protective sheet 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.
A solvent may be added for the purpose of adjusting the viscosity during coating. The solvent can be appropriately selected depending on other components and the like contained in the pressure-sensitive adhesive composition, but an organic solvent is preferable. The organic solvent used is not particularly limited, but includes methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol and the like. These organic solvents may be used alone or as a mixture of two or more. The solvent is preferably removed by applying the pressure-sensitive adhesive composition to a substrate or the like, followed by drying, followed by photo-curing.

<2. Method for producing pressure-sensitive adhesive composition for surface protective sheet>
Here, an example of a method for synthesizing the polyurethane (A) contained in the pressure-sensitive adhesive composition of the present invention will be described. Regarding the polyfunctional monomer (B), the other monomer (C), and other components contained in the pressure-sensitive adhesive composition for a surface protective sheet, it is easy to purchase a commercially available product, and the type of compound used Therefore, the description of the synthesis method is omitted.

<2-1. Method for synthesizing polyurethane (A)>
Hereinafter, an example of a preferred method for synthesizing the polyurethane (A) contained in the pressure-sensitive adhesive composition of the present embodiment will be described. However, the method for synthesizing the polyurethane (A) is not limited thereto, and conditions such as raw materials and equipment used for the synthesis are used. Can be changed as appropriate. In this example, the reaction between the hydroxy group and the isocyanato group is performed using a urethanization catalyst such as dibutyltin dilaurate, dibutyltin diethylhexoate, or dioctyltin dilaurate. The reaction is preferably performed at 30 to 100 ° C. for 1 to 5 hours. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass based on the total mass of the reactants.

First, a polyoxyalkylene polyol and a polyisocyanate are charged at a ratio where the amount of isocyanato groups (number basis, the same applies hereinafter) becomes larger than the amount of hydroxy groups (number basis, hereinafter the same), and these are reacted to form an isocyanato group at the terminal. Synthesize a polyurethane. Specific examples of the polyoxyalkylene polyol and the polyisocyanate are as exemplified in the section of the polyurethane (A).

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

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

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

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

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

<2-2. Modification of Polyurethane (A) Synthesis Method>
A modified example of the method for synthesizing the polyurethane (A) will be described. In this example, similarly to the above example, the reaction between the hydroxy group and the isocyanate group is performed using a urethanization catalyst such as dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. The reaction is preferably performed at 30 to 100 ° C. for 1 to 5 hours. The amount of the urethanization catalyst used is preferably 50 to 500 ppm by mass based on the total mass of the reactants. In this modification, first, a polyoxyalkylene polyol and a polyisocyanate are reacted at a ratio where the amount of hydroxy groups is larger than the amount of isocyanato groups, to synthesize a polyurethane having a hydroxy group at a terminal.

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

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

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

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

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

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

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

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

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

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

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

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

セパレータ The surface protective sheet can be laminated with a separator on the surface of the pressure-sensitive adhesive layer for the purpose of protecting the pressure-sensitive adhesive layer. As a material for the separator, for example, paper, a plastic film, or the like can be used, and a plastic film is preferable because of its excellent surface smoothness. The plastic film used as the separator is not particularly limited as long as it can protect the above-mentioned pressure-sensitive adhesive layer, and examples thereof include polyethylene, polypropylene, polyethylene terephthalate, and polybutene.

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

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

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

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

場合 When the surface protective sheet according to the present embodiment is used as such a protective sheet, the surface protective sheet is required to have little fogging, that is, low haze. In that case, the haze value of the surface protective sheet is preferably 1.5% or less, more preferably 1.3% or less, and even more preferably 1.0% or less. A specific method for measuring the haze value of the surface protective sheet will be described later in Examples.

When the surface protective sheet according to the present embodiment is used as the above protective sheet, the surface protective sheet has a minimum peel strength so as not to peel off from the product or part during handling such as transportation. Is required. On the other hand, when the surface protection sheet is peeled off from the product or component, it is necessary to reduce the peeling strength in order to facilitate the peeling operation or to prevent the product or component from being deformed or damaged during peeling. From these viewpoints, the peel strength of the surface protective sheet depends on the thickness of the substrate and the pressure-sensitive adhesive layer when the peeling speed is 3.0 m / min. It is preferably from 30 to 30 gf / 25 mm, more preferably from 3 to 27 gf / 25 mm, even more preferably from 5 to 25 gf / 25 mm. A specific method for measuring the peel strength of the surface protective sheet will be described later in Examples.

Hereinafter, the present invention will be described in detail with reference to examples. The present invention is not limited in any way by the following examples. In the following examples, the weight average molecular weight of the obtained polyurethane (A) was determined by gel permeation chromatography (Showex (registered trademark) GPC-101 manufactured by Showa Denko KK; hereinafter, referred to as GPC). Is a value in terms of polystyrene measured by the following method. The GPC measurement conditions are as follows.
Column: LF-804 manufactured by Showa Denko KK
Column temperature: 40 ° C
Sample: 0.2 mass% polyurethane (A) tetrahydrofuran solution flow rate: 1 ml / min Eluent: tetrahydrofuran detector: RI detector (differential refractive index detector)

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

Subsequently, 232.2 g (2 mol) of 2-hydroxyethyl acrylate was added to the reactor, and the mixture was heated to 70 ° C. and reacted for 2 hours to obtain 45.8 kg of an acryloyl group-terminated polyurethane (A-1). . This polyurethane (A-1) was analyzed by IR, and it was confirmed that the peak derived from the isocyanato group had disappeared. The weight average molecular weight of the obtained polyurethane (A-1) was 70,000.
Since the disappearance of the peak derived from the isocyanate group was confirmed by IR, 2-hydroxyethyl acrylate was added to all the terminals of the polyurethane having isocyanate groups at both terminals. That is, an acryloyl group is introduced into 100% of the terminal of the polyurethane molecule contained in the polyurethane (A-1) on a numerical basis.

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

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

(A-4)
Synthesis of polyurethane (A-1) except that the hydrogenated product of diphenylmethane diisocyanate was changed to 4 mol, and the hydroxyl value was 56 mgKOH / g, and the hydroxyl-terminated polypropylene glycol Actcol D-2000 (manufactured by Mitsui Chemicals) was changed to 3 mol. In the same manner as in the method, a polyurethane (A-4) having an acryloyl group at the terminal was obtained. The weight average molecular weight of the obtained polyurethane (A-4) was 12,000.

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

<Preparation of adhesive composition>
The polyurethane resin (A), polyfunctional monomer (B), other monomer (C), photopolymerization initiator (D), ionic liquid (E), and additives are listed in Tables 1 and 2. The compositions were blended and mixed at 25 ° C. using a disper to prepare pressure-sensitive adhesive compositions according to Examples 1 to 15 and Comparative Examples 1 to 4.

<Preparation of surface protection sheet>
In the same manner as in Examples 1 to 15 and Comparative Examples 1 to 4, surface protection sheets having a substrate of an optical PET film on one side were produced. First, the prepared pressure-sensitive adhesive composition was applied on a 75 μm-thick optical PET film (A4300 manufactured by Toyobo Co., Ltd.) using an applicator, and a 75 μm-thick separator was formed on the applied pressure-sensitive adhesive composition as a separator. (E7006 manufactured by Toyobo Co., Ltd.). Next, the sheet covered with the release PET film was irradiated with ultraviolet light from the surface on the release PET film side using an ultraviolet irradiation device (UV irradiation device, 3 kW, high-pressure mercury lamp, manufactured by Eye Graphics Co., Ltd.), and the adhesive was applied. The composition was light cured. The irradiation distance of the ultraviolet rays was 25 cm, the moving speed of the lamp was 1.0 m / min, and the irradiation amount was 1000 mJ / cm ² . The thickness of the cured pressure-sensitive adhesive layer was calculated by measuring the thickness of the surface protective sheet after the separator was peeled off using a dial gauge, and then subtracting the thickness of the substrate of 75 μm from the measured value. The measurement surface of the dial gauge was a circular flat surface having a diameter of 5 mm, and the measurement force was 0.8 N. The thickness was 20 μm in each of Examples 1 to 15 and Comparative Examples 1 to 4.

In Tables 1 and 2, the notation of each component is shown below.
TMPTA: Trimethylolpropane triacrylate EHA: 2-Ethylhexyl acrylate IOA: Isooctyl acrylate ISTA: Isostearyl acrylate IBOA: Isobornyl acrylate ACMO: Acryloylmorpholine I-184: Irgacure 184 (1-hydroxycyclohexyl phenyl ketone, manufactured by BASF) )
Elexel AS-110: 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide (Daiichi Kogyo Seiyaku Co., Ltd.)
Elexel AS-804: 1-octyl-4-methylpyridinium bis (fluorosulfonyl) imide (Daiichi Kogyo Seiyaku Co., Ltd.)
Exepearl IPM: Isopropyl myristate (manufactured by Kao Corporation)

<Evaluation of pressure-sensitive adhesive composition and surface protection sheet>
For the pressure-sensitive adhesive compositions and surface protection sheets according to Examples 1 to 15 and Comparative Examples 1 to 4, transparency (haze value), peel strength, laminating property (wetting property), peeling chargeability, and glue to adherends The remainder was evaluated by the method described below. The results are shown in Tables 1 and 2.

(Haze value)
The surface protective sheet with a separator prepared in each of Examples 1 to 15 and Comparative Examples 1 to 4 was cut into a size of 50 mm × 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 measurement sample. . The haze value of this measurement sample was measured using a haze meter (manufactured by Murakami Color Research Laboratory Co., Ltd., NM-150). The haze value (%) was calculated by dividing the diffuse transmittance by the total light transmittance and multiplying by 100. In addition, the measurement was performed in three places with the same sample, and those average values were set as the haze value.

(Peel strength)
The surface protective sheet with a separator produced in each of Examples 1 to 15 and Comparative Examples 1 to 4 was cut into a size of 25 mm × 150 mm, and the release PET film was peeled off. Thereafter, the entire surface of the exposed pressure-sensitive adhesive layer was laminated on a glass plate, and a rubber roller (diameter: 85 mm, width: 50 mm) having a mass of 2 kg (load: 19.6 N) was reciprocated once to prepare a measurement sample. .
The obtained measurement sample was left for 1 hour in an environment at a temperature of 23 ° C. and a relative humidity of 50%. Thereafter, a high-speed peeling tester (Light Load Type Adhesion and Film Peeling Analyzer VPA-3, manufactured by Kyowa Interface Science Co., Ltd.) was used, and the peeling speed was 0.3 m / min and 3.0 m according to JIS K 6854-2. The peel strength (gf / 25 mm) of the surface protective sheet with respect to the glass plate was measured by performing a tensile test in the 180 ° direction at a rate of / °.

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

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

(Evaluation of peeling chargeability (measurement of surface resistivity))
The surface protective sheet with a separator prepared in each of Examples 1 to 15 and Comparative Examples 1 to 4 was cut into a size of 120 mm in length and 120 mm in width, and was subjected to a temperature of 23 ° C. and a relative humidity (RH) of 50% for 3 hours. It was left to humidify. Thereafter, the peelable PET film was peeled off to expose the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer was exposed using a high resistivity meter (manufactured by Mitsubishi Chemical Analytech, Hiresta-UX) under the conditions of an applied voltage of 100 V × 60 seconds. The side surface resistivity was measured. And it evaluated based on the following criteria.

Evaluation criteria ◎: Surface resistivity is less than 1 × 10 ¹² Ω / □ ○: Surface resistivity is 1 × 10 ¹² Ω / □ or more and less than 5 × 10 ¹² Ω / □ Δ: Surface resistivity is 5 × 10 ¹² Ω / □ or more and less than 1 × 10 ¹³ Ω / □ ×: Surface resistivity is 1 × 10 ¹³ Ω / □ or more

(Glue residue)
The surface protective sheet with a separator prepared in each of Examples 1 to 15 and Comparative Examples 1 to 4 was cut into a size of 50 mm × 50 mm, and the release PET film was peeled off. Next, the exposed adhesive surface was laminated on a glass plate, and this was used as a sample. After the sample was allowed to stand at 85 ° C. and a relative humidity of 85% for 3 days, the surface protection sheet was peeled off from the glass plate, and the adhesive residue on the surface of the glass plate was visually observed and evaluated according to the following criteria.
(Evaluation criteria for glue residue)
：: The surface of the glass plate did not change as compared to before bonding.
Δ: Glue residue is slightly observed on the surface of the glass plate.
×: Adhesive residue is clearly confirmed on the surface of the glass plate.

<Evaluation results of Examples and Comparative Examples>
According to the above Examples and Comparative Examples, the composition of Comparative Example 1 using polyurethane (A-4) having a weight-average molecular weight of 12,000 as the polyurethane (A) has insufficient laminating properties and adhesive residue. Was also seen. The composition of Comparative Example 2, which did not contain the polyfunctional monomer (B), had too high peel strength and insufficient laminating properties. The composition of Comparative Example 3 containing 30% by mass of the polyfunctional monomer (B) had a high haze value of 1.7. In addition, the composition of Comparative Example 4 containing no ionic liquid (E) had an overrange in the surface resistivity and was inferior in peeling chargeability.

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

Claims

Polyurethane (A),
A polyfunctional monomer (B),
Other monomers (C) polymerizable with the polyurethane (A) and the polyfunctional monomer (B),
A photopolymerization initiator (D);
An ionic liquid (E);
A pressure-sensitive adhesive composition for a surface protection sheet comprising:
The polyurethane (A) is a polyurethane having a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate,
The polyurethane (A) includes a polyurethane (a1),
The polyurethane (a1) has a skeleton including a structure derived from a polyoxyalkylene polyol and a structure derived from a polyisocyanate, and has (meth) acryloyl groups at a plurality of terminals of the polyurethane (a1);
The polyurethane (A) has a weight average molecular weight of 30,000 to 200,000;
The polyfunctional monomer (B) is a compound having a plurality of (meth) acryloyl groups,
With respect to a total amount of 100% by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
30 to 60% by mass of the polyurethane (A),
2 to 10% by mass of the polyfunctional monomer (B),
30 to 68% by mass of the other monomer (C)
Containing
For the total amount of 100 parts by mass of the polyurethane (A), the polyfunctional monomer (B), and the other monomer (C),
0.1 to 5 parts by mass of the photopolymerization initiator (D),
0.5 to 5 parts by mass of the ionic liquid (E),
A pressure-sensitive adhesive composition for a surface protective sheet, comprising:
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 ionic liquid (E) is
The pressure-sensitive adhesive composition for a surface protective sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive composition is a combination of an organic cation selected from the group consisting of quaternary nitrogen atoms, ammonium, immonium, and sulfonium, and a fluorine-containing organic anion.
The ionic liquid (E) is
Ionic liquid composed of 1-ethyl-3-methylimidazolium cation and bis (fluorosulfonyl) imide anion ((FSO 2 ) 2 N − ), and 4-methyl-1-octyl-pyridinium cation and bis (fluorosulfonyl) imide The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 3, comprising at least one selected from the group consisting of an ionic liquid comprising an anion ((FSO 2 ) 2 N − ).
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 4, wherein the skeleton contained in the polyurethane (A) is a copolymer of a polyoxyalkylene glycol and a diisocyanate.
The polyoxyalkylene glycol is polypropylene glycol,
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 5, wherein the diisocyanate is a hydrogenated product of diphenylmethane diisocyanate.
粘着 The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 6, wherein the (meth) acryloyl group in the polyurethane (A) is a part of a (meth) acryloyloxy group.
The pressure-sensitive adhesive composition for a surface protective sheet according to any one of claims 1 to 7, 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 8, 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 9, 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 10, wherein the other monomer (C) contains an alkyl (meth) acrylate.
The polyurethane (A) further includes a polyurethane (a2),
The polyurethane (a2) has a skeleton containing a structure derived from polyoxyalkylene polyol and polyisocyanate, and has a (meth) acryloyl group at only one terminal of the polyurethane (a2). 12. The pressure-sensitive adhesive composition for a surface protective sheet according to any one of 1 to 11.
The pressure-sensitive adhesive for a surface protective sheet according to any one of claims 1 to 12, wherein (meth) acryloyl groups are introduced into 90 to 100% of the terminals of the polyurethane molecules contained in the polyurethane (A) on a numerical basis. Composition.
A sheet-like substrate,
Having an adhesive layer formed on the base material,
14. A surface protection sheet, wherein the pressure-sensitive adhesive layer comprises a photocured product of the pressure-sensitive adhesive composition for a surface protection sheet according to any one of claims 1 to 13.