JP4498711B2 - Pressure-sensitive adhesive composition for optical member surface protective film and optical member surface protective film - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition for a protective film used for primary protection of the surface of an optical member such as a liquid crystal display panel, and more specifically, is temporarily attached to the surface of an optical member during a manufacturing process. The present invention relates to a pressure-sensitive adhesive composition for a surface protective film that protects the surface during a process requiring protection and is peeled off after completion of the process, and a surface protective film in which the adhesive composition is applied to a substrate.

In recent years, liquid crystal display panels have been used as screen display devices for various information-related devices such as word processors and notebook personal computers because they are thin and light and consume less power. In such a liquid crystal display plate, an optical member such as a polarizing plate or a retardation plate is used together with a glass cell (liquid crystal cell) containing liquid crystal as a main body. Among these optical members, for example, a polarizing plate is usually a polarizing element made of a polyvinyl alcohol (PVA) film, and a saponified triacetyl cellulose bonded to both surfaces of the polarizing element to maintain its mechanical strength. (TAC) Consists of a protective layer made of a film, and the surface of the polarizing plate on the front side of the liquid crystal display panel is to protect the polarizing plate from scratches and contamination, and to provide functions according to its use. In many cases, a functional layer is formed. This functional layer has an anti-glare layer that forms fine irregularities on the surface in order to diffuse the reflected image of a fluorescent lamp on the polarizing plate and make the display easy to see; scratch resistance by increasing the surface hardness of the polarizing plate A hard coat layer that imparts a property; an anti-reflection layer that suppresses reflection of external light on the surface of the polarizing plate to make the display easier to see. The polarizing plate is attached to the liquid crystal cell via a pressure sensitive adhesive.

These optical members are usually further coated with a surface protective film so that the surface is not contaminated or damaged during each process such as punching, inspection, transportation, and assembly of the liquid crystal display panel. And formed as a long optical member laminate, and after these steps, the surface protective film is peeled off from the optical member when surface protection is no longer necessary. In addition, in the process of assembling the liquid crystal display panel or the like, a heating and pressing process called an autoclave process is often performed for the purpose of stabilizing the adhesion state between the optical member and the liquid crystal cell. In order to release the distortion generated in the autoclave process, an aging process is performed at a certain high temperature such as 90 ° C. for several hours.

Such a surface protective film has a pot life sufficient for coating work, and while the surface protection of the optical member is required, the surface of the member is displaced or dropped from the surface. Adhering to the surface to such an extent that it does not interfere with various inspections such as the performance of the liquid crystal, it must be highly transparent and within the adhesive layer such as bulge, tunneling, peeling, etc. It is required that the interface between the agent layer and the optical member is free from defects. When such a defective portion exists, the surface of the optical member in that portion often has spider or contamination. When the film is peeled off from the optical member, the optical member and the liquid crystal cell are not damaged by the distortion caused by the peeling, and the optical member is not peeled off from the liquid crystal cell. It must be easily peelable. In recent years, there has been a tendency for the speed of peeling of the surface protective film to be increased for the purpose of improving working efficiency, and workability in high speed peeling has also been required as a characteristic of the adhesive.

Many of the conventional surface protective films are peeled off by increasing the adhesive force to the optical member over time when the above-mentioned processing steps have sufficient adhesiveness for protecting the surface of the optical member. There is a tendency that the adhesive force at the time becomes too high. For this reason, when the separation is performed at a particularly high speed, the working efficiency is poor, and in addition, the distortion associated with the separation may cause inconveniences such as disorder of the alignment of the optical member and the liquid crystal cell and expansion of the cell gap. Especially in the polarizing plate provided with the anti-glare layer and the like, the adhesive force is likely to increase, and in particular, when the wetting is sufficient to prevent the occurrence of bulge by the aging treatment, the adhesive force tends to be too high, Furthermore, when the peeling of the surface protective film is mechanized and speeded up, a larger peeling force is applied than at the conventional peeling speed.

In order to solve these problems, many proposals have been known. For example, Patent Document 1 (Japanese Patent Laid-Open No. 9-208910) discloses a pressure-sensitive adhesive composition that has moderate adhesive strength and excellent removability and does not cause swelling or tunneling, and uses the same. A surface protection film was disclosed. The pressure-sensitive adhesive in this proposal is mainly composed of an acrylic acid alkyl ester having 1 to 9 carbon atoms in the alkyl group, a copolymerizable unsaturated monomer containing a hydroxyl group and / or a carboxyl group, and the carbon number of the alkyl group. Is obtained by blending a specific amount of a crosslinking agent such as an isocyanate into an acrylic copolymer obtained by copolymerizing a specific amount of each of 16 to 22 (meth) acrylic acid alkyl esters and reactive emulsifiers.

However, with the surface protective film using the above-mentioned pressure-sensitive adhesive, it was possible to suppress the occurrence of swelling and tunneling, but the re-peelability is not always sufficient, especially as an adherend. It has been found that when a polarizing plate having an antiglare layer is used, the peeling force becomes so large that it cannot be practically used.

Furthermore, for example, in Patent Document 2 (Japanese Patent Laid-Open No. 2001-33624), the optical member does not peel even when the environment changes such as temperature and humidity, and it can be peeled and separated from the optical member without any adhesive residue at the time of peeling. A surface protective film intended to obtain a surface protective film that can be easily separated by separation without damaging the optical member or peeling from the liquid crystal cell even after heat treatment such as aging while satisfying basic performance, A surface protective film is disclosed in which, at a peeling speed of 300 mm / min, 180 ° peeling, the adhesive strength at 80 ° C. is within 1.3 times that at room temperature. Specific examples of the second proposal include a tetrafunctional epoxy crosslinking agent for 100 parts by weight of an acrylic copolymer of 2-ethylhexyl acrylate / vinyl acetate / acrylic acid = 54.1 / 43.2 / 2.7 (% by weight). An acrylic pressure-sensitive adhesive composed of 3 parts by weight is described.

However, according to the results of a further test by the present inventors, the above-mentioned pressure-sensitive adhesive of the above-mentioned second proved that the adhesive strength test using a stainless steel plate as an adherend is an adhesive that is allowed to stand at 80 ° C. Although it was within 1.3 times the force, for example, when a polarizing plate having an antiglare layer on the surface was used as an adherend, an aging treatment was performed at 90 ° C. for 2 hours after the autoclave treatment. It has been found that there are problems such as the occurrence of numerous blisters between the surface protective film.

In order to solve the problems of the pressure-sensitive adhesive composition for the conventional optical member surface protective film, the present inventors have conducted an improvement study on an acrylic pressure-sensitive adhesive. (Japanese Patent Laid-Open No. 2003-41229), for example, 2-ethylhexyl acrylate is mainly used and 4-hydroxybutyl acrylate and acrylic acid are copolymerized thereto, and the weight average molecular weight (Mw) is about 600,000, and the weight average molecular weight ( 2 types including a bifunctional isocyanate compound (b ₁ ) having a specific molecular structure in an acrylic copolymer having a molecular weight distribution of a ratio Mw / Mn of about 10 (Mw) to number average molecular weight (Mn) The acrylic pressure sensitive adhesive composition obtained by mix | blending the polyisocyanate compound derived from the above aliphatic isocyanate was proposed.

However, in this proposal, when the protective film is peeled off at a peeling speed of 0.3 m / s or less in the prior art, good performance is shown. However, in peeling at a high speed of 30 m / s or more, the peeling force is too large. The problem was not solved enough.
JP-A-9-208910 JP 2001-33624 A Japanese Patent Laid-Open No. 2003-41229

The problems to be solved by the present application are pot life, anti-swelling properties, transparency, wettability, etc., satisfying the conventional physical properties of pressure-sensitive adhesive compositions, and without greatly reducing the adhesive force, It is to provide a low pressure sensitive adhesive composition and a surface protection film.

As a result of further research, the inventors of the present invention have, as a pressure-sensitive adhesive composition having no increase in peeling force even at high speed peeling, containing a hydroxyl group and a carboxyl group as reactive functional groups, and a glass transition temperature (Tg). −40 ° C. or lower A pressure-sensitive adhesive composition for an optical member surface protective film comprising an acrylic copolymer having a temperature of −80 ° C. or higher and an aromatic polyfunctional isocyanate compound as essential components solves all of the above problems. It was found that this was an excellent pressure-sensitive adhesive composition that could be made, and further research was advanced to complete the present invention.

The pressure-sensitive adhesive composition for an optical member surface protective film of the present invention has a specific amount of hydroxyl group and carboxyl group as a reactive functional group, and a specific copolymer and an acrylic copolymer in a specific SP value range. It comprises an aromatic isocyanate compound having a structure as an essential component.

By being configured in this manner, the surface protective film of the present invention has surface protection and high transparency of the optical member, and, for example, a polarizing plate provided with a layer having fine irregularities such as an antiglare layer on the surface, etc. Even when used for optical members, adhesive layer defects such as bulge, tunneling and peeling are not observed after autoclave treatment and subsequent work and heat history during use. When the film is peeled from the film, it exhibits good peeling characteristics even at high-speed peeling, causing problems such as disordered orientation of the optical member or liquid crystal cell, expansion of the cell gap, peeling of the optical member from the liquid crystal cell, etc. And can be easily peeled off.

  The acrylic copolymer (A) used in the present invention is an acrylic ester or an acrylic ester and a methacrylic ester as a main component, for example, a total of 50 weights based on the weight of the acrylic copolymer (A). % Is copolymerized and contains a hydroxyl group and a carboxyl group in the molecule. The acrylic copolymer (A) can further contain other functional groups in the molecule as necessary.

The acrylic copolymer (A) particularly preferably used in the present invention specifically includes the following monomers (a ₁ ) and (a ₂ ) as essential components:

An acrylic ester (a ₁ ) represented by the following general formula (2) and having a glass transition temperature (Tg) of the homopolymer of −50 ° C. or lower (hereinafter referred to as an acrylic ester (a ₁ ) or simply a monomer) (It may be called (a ₁ ))
H ₂ C = CHCOOR ¹
(2)
(Wherein R ¹ represents a linear or branched alkyl group having 4 to 10 carbon atoms), and

A monomer having a hydroxyl group in the molecule (a ₂ ) (hereinafter sometimes referred to as a hydroxyl group-containing monomer (a ₂ ) or simply a monomer (a ₂ )), and

A monomer having a carboxyl group in the molecule (a ₃ ) (hereinafter sometimes referred to as a carboxyl group-containing monomer (a ₃ ) or simply a monomer (a ₃ )),

The monomer _{(a 1) ~ (a 3} ) copolymerizable with the, the monomer _{(a 1) ~ (a 3} ) other than the monomer (a ₄₎ [hereinafter, the monomer (a ₄ ) Or simply the monomer (a ₄ )] is preferably copolymerized as necessary.

The acrylic acid ester (a ₁ ) of the general formula (2) has a linear or branched alkyl group having 4 to 10 carbon atoms, and the glass transition temperature (Tg) of the homopolymer is −50 ° C. or lower. Specific examples thereof include n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylate, and isononyl acrylate. Among these, n-Butyl acrylate, 2-ethylhexyl acrylate and isooctyl acrylate are preferred. These acrylic acid esters may be used alone or in combination of two or more.

  As used herein, “glass transition temperature (Tg) of homopolymer” refers to the monomer glass described in LE Nielsen, translated by Nojiharu Onoki, “Mechanical Properties of Polymers” on pages 11-35. A transition temperature is applied.

The copolymerization amount of the acrylic ester (a ₁ ) is generally based on a total of 100% by weight of the monomer components (a ₁ ) to (a ₄ ) constituting the acrylic acid copolymer (A). The range is 60 to 98% by weight, preferably 65 to 95% by weight. If the copolymerization amount of the acrylate ester (a ₁ ) is less than or equal to the above upper limit value, the adhesive force during re-peeling will not be too high, and even when heat treatment or the like is performed, damage to optical members or liquid crystal cells The surface protective film can be easily peeled off without causing inconvenience such as peeling of the optical member from the surface. On the other hand, if it is at least the lower limit, the surface of the polarizing plate and the surface protective film can be obtained by autoclave treatment or aging treatment. This is preferable because no swelling occurs between the pressure-sensitive adhesive layer.

Specific examples of the hydroxyl group-containing monomer (a ₂ ) include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene glycol monoacrylate, 2-hydroxyethyl. Methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, polyethylene glycol monomethacrylate, allyl alcohol, methallyl alcohol, and the like, among these, monomer (a ₁ ) and From the viewpoint of copolymerization, it is preferable to use a hydroxyl group-containing (meth) acrylic acid ester, and it is particularly preferable to use 4-hydroxybutyl acrylate. These monomers (a ₂ ) may be used alone or in combination of two or more.

The amount of copolymerization of these hydroxyl group-containing monomers (a ₂ ) is generally 1 to 10% by weight, preferably 4 based on the total 100% by weight of the monomer components (a ₁ ) to (a ₄ ). It should be in the range of -8% by weight, more preferably 5-7% by weight. If the copolymerization amount of the monomer (a ₂ ) is equal to or greater than the lower limit value, the adhesive force at the time of re-peeling does not become too large. The surface protective film can be easily peeled off without causing inconvenience such as peeling of the optical member from the surface. On the other hand, if it is not more than the upper limit, the surface of the polarizing plate and the surface protective film can be obtained by autoclaving or aging treatment. This is preferable because no swelling occurs between the pressure-sensitive adhesive layer.

Specific examples of the carboxyl group-containing monomer (a ₃ ) used together with these monomers (a ₁ ) and (a ₂ ) in the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid , Crotonic acid, citraconic acid, maleic anhydride, and the like, may include α, β-unsaturated mono- or di-carboxylic acids having 3 to 5 carbon atoms, and among these, the use of acrylic acid and methacrylic acid is preferable. . These monomers (a ₃ ) may be used alone or in combination of two or more.

The copolymerization amount of these carboxyl group-containing monomers (a ₃ ) is 0.001 to 2.0% by weight, preferably 0.003 to based on a total of 100% by weight of the monomer components (a ₁ ) to (a ₄ ). It is good that it is in the range of 0.05% by weight, more preferably 0.004 to 0.04% by weight. If the copolymerization amount of the monomer (a ₃ ) is less than or equal to the upper limit, the pot life wettability of the pressure-sensitive adhesive composition after blending the polyisocyanate compound is sufficient to withstand use. On the other hand, if it is above the lower limit value, the adhesive force at the time of re-peeling does not become excessive, and inconveniences such as damage to the optical member and peeling of the optical member from the liquid crystal cell even when heat treatment is performed. This is preferable because the surface protective film can be easily peeled off without causing any problems.

Specific examples of the monomer (a ₄ ) that are used together with these monomers (a ₁ ) and (a ₂ ) or with the monomers (a ₁ ) to (a ₃ ) as necessary in the present invention. As the acrylic ester other than (a ₁ ), for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, i-butyl acrylate, t-butyl acrylate, tridecyl acrylate, stearyl acrylate, oleyl Acrylate, etc. (preferably methyl acrylate); Methacrylate, for example, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate , Benzyl methacrylate, etc. Methyl methacrylate); saturated fatty acid vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, “vinyl versatate” (trade name), etc. (preferably vinyl acetate); aromatic vinyl monomers such as styrene , Α-methylstyrene, vinyltoluene and the like; and vinyl cyanide monomers such as acrylonitrile, methacrylonitrile and the like.

Examples of the monomer (a ₄ ) include dimethyl malate, di-n-butyl malate, di-2-ethylhexyl malate, di-n-octyl malate, dimethyl fumarate, and di-n-butyl fumarate. , Diesters of maleic acid or fumaric acid such as di-2-ethylhexyl fumarate and di-n-octyl fumarate can also be used.

Furthermore, as the monomer (a ₄ ), if necessary, a monomer having at least one functional group in addition to one radical polymerizable unsaturated group in the molecule, Monomers other than (a ₂ ) and (a ₃ ) (hereinafter sometimes referred to as functional monomers ) can also be copolymerized.

Examples of such a functional monomer include a monomer having an amide group or a substituted amide group, an amino group or a substituted amino group, a lower alkoxyl group, or an epoxy group as a functional group, A monomer having two or more radically polymerizable unsaturated groups in the molecule can also be used.

Specific examples of these functional monomers include acrylamide, methacrylamide, diacetone acrylamide, N-methylol acrylamide, N-methylol methacrylamide, Nn-butoxymethyl acrylamide, Ni-butoxymethyl acrylamide, N, N-dimethyl acrylamide. Amide group or substituted amide group-containing monomers such as N-methylacrylamide (preferably acrylamide and methacrylamide); for example, aminoethyl acrylate, N, N-dimethylaminoethyl acrylate, N, N-diethylaminoethyl acrylate, N Amino group- or substituted amino group-containing monomers such as N, N-dimethylaminoethyl methacrylate and N, N-diethylaminoethyl methacrylate;

  For example, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-n-butoxyethyl acrylate, 2-methoxyethoxyethyl acrylate, 2-ethoxyethoxyethyl acrylate, 2-n-butoxyethoxyethyl acrylate, 2-methoxyethyl methacrylate 2-ethoxyethyl methacrylate, 2-n-butoxyethyl methacrylate, 2-methoxyethoxyethyl methacrylate, 2-ethoxyethoxyethyl methacrylate, 2-n-butoxyethoxyethyl methacrylate, methoxypolyethylene glycol monoacrylate, methoxypolyethylene glycol monomethacrylate, etc. Lower alkoxyl group-containing monomers; for example, glycidyl acrylate, glycidyl methacrylate, glycidyl allyl ether, glycidyl methallyl ether Epoxy group-containing monomers;

For example, divinylbenzene, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, ethylene glycol di (meth) acrylate, 1,2-propylene glycol di (meth) acrylate, 1,3-propylene glycol di (meth) acrylate, 2,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate, etc. A monomer group such as a monomer having one or more radically polymerizable unsaturated groups;

The copolymerization amount of these monomers (a ₄ ) is generally 0 to 35% by weight, preferably 0 to 30% by weight, based on the total 100% by weight of the monomer components (a ₁ ) to (a ₄ ). % Should be in the range. If the copolymerization amount of the monomer (a ₄ ) is less than or equal to the upper limit value, there will be no swelling between the polarizing plate surface and the pressure-sensitive adhesive layer of the surface protective film even by autoclaving or aging treatment. Therefore, it is preferable.

  The acrylic copolymer used in the present invention also needs to have a glass transition temperature (Tg) of −40 ° C. or lower and −80 ° C. or higher, preferably −45 ° C. or lower and −65 ° C. or higher. Is good. If the Tg is too high above the temperature, the pressure-sensitive adhesive layer is hard and difficult to flow, especially when used for a polarizing plate having an anti-glare layer on the surface, the pressure-sensitive adhesive has sufficient anti-glare layer unevenness. Therefore, the air remaining slightly between the pressure-sensitive adhesive layer and the anti-glare layer is expanded by autoclaving or aging treatment, and the pressure-sensitive adhesive layer of the polarizing plate surface and the surface protective film Since it may cause a bulge during

  In the present invention, the glass transition temperature (Tg) of the acrylic copolymer is a value determined and measured by the following.

Glass transition temperature (Tg)
Measure according to (1) to (3) below.
(1) An acrylic copolymer solution is applied to release paper and dried at 100 ° C. for 1 minute to obtain a film-like acrylic copolymer.
(2) About 10 mg of the sample obtained in (1) is weighed in a cylindrical cell made of aluminum foil with a thickness of about 0.05 mm and an inner diameter of about 5 mm and a depth of about 5 mm.
(3) Using a SSC-5000 differential scanning calorimeter manufactured by Seiko Denshi Kogyo Co., Ltd., the temperature is measured from −150 ° C. at a heating rate of 10 ° C./min.

The acrylic copolymer used in the present invention has a weight average molecular weight (Mw) of generally 300,000 or more, preferably 350,000 or more, and more preferably 400,000 to 800,000. If the weight average molecular weight (Mw) is equal to or greater than the lower limit value, the adhesive force during re-peeling does not become excessively large. This is preferable because the surface protective film can be easily peeled without causing inconvenience such as peeling. On the other hand, if it is less than or equal to the upper limit value, the resulting pressure-sensitive adhesive layer has excellent fluidity, and even when used in a polarizing plate having minute irregularities on the surface, the pressure-sensitive adhesive sufficiently covers the polarizing plate surface. Since it can be wetted, it is preferable that no swelling occurs between the polarizing plate surface and the pressure-sensitive adhesive layer of the surface protective film even by autoclaving or aging.

The acrylic copolymer suitably used in the present invention generally has a molecular weight distribution represented by a ratio Mw / Mn of weight average molecular weight (Mw) and number average molecular weight (Mn) of generally 15 or less, preferably 2 to 2. It should be in the range of 12. If the value of Mw / Mn is less than or equal to the above upper limit value, the adhesive force at the time of re-peeling will not be too great, especially damage to the optical member or peeling of the optical member from the liquid crystal cell even if heat treatment etc. This is preferable because the surface protective film can be easily peeled off without causing the above disadvantages.

In addition, the value measured by the gel permeation chromatography (GPC) method according to a usual method is used for the value of the said weight average molecular weight (Mw) and number average molecular weight (Mn) in this specification.

  The polymerization method of the acrylic copolymer (A) used in the present invention is not particularly limited and can be polymerized by a known method such as solution polymerization, emulsion polymerization, suspension polymerization, etc., but obtained by polymerization. In producing the pressure-sensitive adhesive composition of the present invention using a copolymer mixture, it is preferable to perform polymerization by solution polymerization since the treatment process is relatively simple and can be performed in a short time.

  In solution polymerization, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent used as needed are generally charged in a polymerization tank, and stirred in a nitrogen stream or at the reflux temperature of the organic solvent. The reaction is performed by heating for several hours. In this case, at least a part of the organic solvent, the monomer and / or the polymerization initiator may be sequentially added.

  Examples of the organic solvent for polymerization include aromatics such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha. Hydrocarbons; for example, aliphatic or alicyclic hydrocarbons such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, turpentine oil; Esters such as ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, methyl benzoate; for example, acetone, methyl ethyl ketone, methyl-i- Ketones such as butyl ketone, isophorone, cyclohexanone, methylcyclohexanone; for example, ethylene glycol monomethyl ester Glycol ethers such as ter, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether; for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n -Alcohols such as butyl alcohol, i-butyl alcohol, s-butyl alcohol and t-butyl alcohol; These organic solvents can be used alone or in admixture of two or more.

  Of these organic solvents for polymerization, when the acrylic copolymer (A) is polymerized, it is preferable to use an organic solvent that hardly causes chain transfer during the polymerization reaction, for example, esters and ketones. In view of the solubility of the acrylic copolymer (A) and the ease of the polymerization reaction, it is preferable to use ethyl acetate, methyl ethyl ketone, acetone or the like.

  As said polymerization initiator, it is possible to use the organic peroxide, an azo compound, etc. which can be used by normal solution polymerization.

  Examples of such organic peroxides include t-butyl hydroperoxide, cumene hydroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, and di-i-propyl peroxydicarbonate. , Di-2-ethylhexyl peroxydicarbonate, t-butyl peroxybivalate, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,4- Di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) propane, 2,2-bis (4,4-di-α-cumylperoxycyclohexyl) ) Propane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) butane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) butane, etc. As a compound For example, 2,2'-azobis-i-butyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, etc. Can do.

  Among these organic peroxides, when the acrylic copolymer (A) is polymerized, a polymerization initiator that does not cause a graft reaction during the polymerization reaction is preferable, and an azobis type is particularly preferable. The amount used is usually 0.01 to 2 parts by weight, preferably 0.1 to 1.0 parts by weight, based on 100 parts by weight of the total amount of monomers.

  Further, in the production of the acrylic copolymer (A) used in the present invention, it is normal not to use a chain transfer agent, as long as it does not impair the purpose and effect of the present invention. It is possible to use.

  Examples of such chain transfer agents include cyanoacetic acid; alkyl esters having 1 to 8 carbon atoms of cyanoacetic acid; bromoacetic acid; alkyl esters having 1 to 8 carbon atoms of bromoacetic acid; anthracene, phenanthrene, fluorene, 9 -Aromatic compounds such as phenylfluorene; aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, p-nitrotoluene; benzoquinone, 2,3,5, Benzoquinone derivatives such as 6-tetramethyl-p-benzoquinone; Borane derivatives such as tributylborane; carbon tetrabromide, carbon tetrachloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloro Halogenated hydrocarbons such as methane, tribromomethane, 3-chloro-1-propene; chloral, Aldehydes such as furaldehyde: alkyl mercaptans having 1 to 18 carbon atoms; aromatic mercaptans such as thiophenol and toluene mercaptan; mercaptoacetic acid, alkyl esters having 1 to 10 carbon atoms of mercaptoacetic acid; And hydroxyalkyl mercaptans; terpenes such as vinylene and terpinolene; and the like.

  The polymerization temperature is generally in the range of about 30 to 180 ° C, preferably 40 to 150 ° C, more preferably 50 to 90 ° C.

  When an unreacted monomer is contained in a polymer obtained by a solution polymerization method or the like, it can be purified by a reprecipitation method using methanol or the like in order to remove the monomer.

  The pressure-sensitive adhesive composition for an optical member surface protective film of the present invention contains a polyfunctional aromatic isocyanate compound (B).

  Examples of the polyisocyanate compound (B) that can be used in the present invention include aromatic polyfunctional isocyanate crosslinking agents, such as tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate-3 functional alcohol. Examples thereof include adducts and tolylene diisocyanate trimers.

  Among these isocyanate-based crosslinking agents, tolylene diisocyanate-3 functional alcohol adducts and the like are preferable from the viewpoint of peeling rate dependency and reaction rate, and specific examples include products such as Coronate L and Takenate D262.

The amount of these polyisocyanate compounds (b ₁ ) used is generally in the range of 0.3 to 1.5 equivalents, preferably 0.4 to 1.2, particularly preferably 0.5 to 1.1, with respect to 1 equivalent of the reactive functional group in the acrylic copolymer. It is good to be. If the amount used is greater than or equal to the lower limit value, the adhesive force during re-peeling does not become excessively large, and inconveniences such as damage to the optical member and peeling of the optical member from the liquid crystal cell even when heat treatment is performed. It is preferable because the surface protective film can be easily peeled off without causing slag, and if it is less than or equal to the upper limit value, the surface of the polarizing plate and the pressure-sensitive adhesive layer of the surface protective film can be obtained by autoclaving or aging treatment. It is preferable because no blisters are generated between them.

  In addition to the acrylic copolymer (A) and the polyisocyanate compound (B) described above, the pressure-sensitive adhesive composition for an optical member surface protective film of the present invention, if necessary, a pressure-sensitive adhesive for a protective film. For example, a weather resistance stabilizer, a tackifier, a plasticizer, a softening agent, a dye, a pigment, an inorganic filler, and the like can be appropriately blended in the adhesive composition.

  Here, the peak temperature is a temperature at which the crosslinked resin composition exhibits a maximum logarithmic decay rate.

  The pressure-sensitive adhesive composition for an optical member surface protective film of the present invention thus obtained is prepared on at least one surface of an appropriate transparent surface protective substrate by a conventionally known method in order to produce an optical member surface protective film. Used to form a pressure sensitive adhesive layer.

  The substrate used for the surface protective film of the present invention needs to be a substrate to which a pressure sensitive adhesive can be applied. From the viewpoint of inspection and management of optical members by fluoroscopy as the base resin, for example, polyester resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, A film made of an acrylic resin can be exemplified, but a polyester resin is preferable from the viewpoint of surface protection performance, and a polyethylene terephthalate resin is particularly preferable in consideration of practicality.

  The thickness of the substrate is generally 500 μm or less, preferably 5 to 300 μm, more preferably about 10 to 200 μm. An antistatic layer may be provided on one or both surfaces of these base materials for the purpose of preventing antistatic during peeling. The surface of the substrate on the side where the pressure-sensitive adhesive layer is provided may be subjected to a corona discharge treatment or the like in order to improve the adhesion with the pressure-sensitive adhesive layer.

It is necessary to have a sufficient adhesive force to the optical member (adhesive force for low speed peeling is sufficiently large) and to be easily peeled at high speed peeling (the adhesive force for high speed peeling does not increase).
That is, the adhesive force of 180 ° peel to the optical member at 23 ° C. is 0.05 N / 25 mm or more, preferably 0.07 N / 25 mm or more, particularly preferably 0.09 N / 25 mm or more at a peeling speed of 0.3 m / min (low speed peeling). It is preferable that the adhesive force for low-speed peeling is less than 0.05 N / 25 mm because turning and shifting are likely to occur.

In addition, since the workability of the peeling work is lowered when the adhesive force is increased, it is important that 2N / 25 mm or more, preferably 1.5 N / 25 mm or more is not required during high-speed peeling.
Therefore, the adhesive force at a peeling speed of 30 m / min (high speed peeling) is 3.5 times to 15 times, preferably 4 times to 10 times, particularly preferably 5 times to 8 times that of low speed peeling. If the adhesive force at the time of high-speed peeling is 15 times or more that of low-speed peeling, the high-speed peeling work will be hindered and the peeling work must be done at a low speed, resulting in a significant reduction in productivity. In addition, an adhesive having a high-speed peel adhesive strength that is less than 3.5 times the low-speed peel adhesive strength is not preferable, although the peelability is satisfactory, but the resin is too hard, resulting in insufficient wettability and poor coating.

  The thickness of the pressure-sensitive adhesive layer formed on the substrate can be appropriately set according to the required adhesive strength of the protective film, the surface roughness of the optical member, etc., and is generally 1 to 100 μm, preferably 5 to A thickness of about 50 μm, more preferably about 15 to 30 μm can be exemplified.

  As a method for forming the pressure-sensitive adhesive layer, the pressure-sensitive adhesive composition of the present invention is used as it is or diluted with an appropriate solvent as necessary, and this is directly applied to a surface protective base film and dried to obtain a solvent. It is possible to adopt a method of removing In addition, first, the pressure-sensitive adhesive composition of the present invention is applied on a release sheet made of an appropriate film such as paper or polyester film that has been subjected to a release treatment with a silicone resin or the like, and then heat-dried for pressure-sensitive adhesion. An adhesive layer may be formed, and then the adhesive layer side of the release sheet may be pressed against a surface protective base film to transfer the adhesive layer to the protective film.

  The protective film thus obtained is laminated on the surface of the optical member to protect the surface of the optical member from being contaminated or damaged, and when the optical member is processed into a liquid crystal display panel or the like, While the protective film is laminated on the optical member, it is used in various processes such as punching, inspection, transportation, and assembly of the liquid crystal display panel. If necessary, heat and pressure such as autoclaving and high-temperature aging When the surface treatment is no longer necessary, the optical member is peeled off and removed.

Next, the optical member in which the surface protective film in the present invention is used will be described.
In general, the optical member in which the surface protective film in the present invention is used includes a polarizing plate and a retardation plate.

  As a specific example of the polarizing plate, the main component of the polarizer is usually a hydrophilic polymer such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene / vinyl acetate copolymer partially saponified film. It is formed by a polyene oriented film such as a film obtained by adsorbing iodine and / or a dichroic dye to the film and stretched, a polyvinyl alcohol dehydrated product, a polyvinyl chloride dehydrochlorinated product, etc. The transparent protective layer similar to what is used for the said surface protection base material, for example may be provided in the surface of one or both of the polarizer. Although the thickness of a transparent protective layer is not specifically limited, Generally it is 500 micrometers or less, Preferably it is 5-300 micrometers, More preferably, the thickness of about 10-200 micrometers can be illustrated.

  In addition, the surface on the viewing side of the transparent protective layer contains, as necessary, transparent fine particles of about 0.5 to 20 μm in order to impart light diffusibility, antiglare properties, etc. Further, the surface on the viewing side of the transparent protective layer may be roughened by buffing or the like. Furthermore, an anti-glare layer having a fine concavo-convex structure on the surface or having a roughened surface may be further laminated on the surface on the viewing side of the transparent protective layer.

  Specific examples of the retardation plate include a birefringent film obtained by stretching a film of polyolefin such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, and polypropylene, polyarylate, and polyamide, and an alignment film of a liquid crystal polymer. Can be mentioned.

  The retardation plate has an appropriate retardation according to the purpose of use, such as various wavelength plates such as 1/2, 1/4, etc., and those for the purpose of compensation such as coloring or vision due to birefringence of the liquid crystal layer. It may be a thing, and the inclination orientation film which controlled the refractive index of the thickness direction may be sufficient. Moreover, what laminated | stacked 2 or more types of phase difference plates may be used.

  In the surface protective film of the present invention, the pressure-sensitive adhesive layer made of the above-described pressure-sensitive adhesive composition of the present invention is formed on the surface of the surface protective substrate that is in contact with the optical member (the side opposite to the viewing side). Conventional surface protection except that the pressure-sensitive adhesive layer for adhering the surface protective film to the surface of the optical member is formed of the pressure-sensitive adhesive composition of the present invention described above. It is comprised similarly to a film. That is, for example, as shown in FIG. 1, the surface protective film 1 in the present invention is composed of a surface protective substrate 2 and a pressure-sensitive adhesive layer 3 formed on the surface of the substrate.

  The pressure-sensitive adhesive layer 3 has a dry thickness of 10 to 50 μm, particularly preferably 15 to 30 μm.

  The surface protective film is affixed to the optical member 4 by the pressure-sensitive adhesive layer 3, and the optical member 4 is bonded to a glass cell (not shown) such as a liquid crystal cell by the pressure-sensitive adhesive layer 5. Before being applied, the surface of the pressure-sensitive adhesive layer 5 is usually protected by the release paper 6.

  EXAMPLES Examples and comparative examples will be described below to specifically describe the effects of the present invention, but the present invention is not limited to these examples. In addition, preparation of a test piece and various test methods and evaluation methods used in Examples and Comparative Examples are as follows.

(1) Preparation of pressure-sensitive adhesive sheet for testing Pressure-sensitive adhesive so that the coating amount after drying is 25 g / m ² on the release paper surface-treated with silicone release agent After applying the composition and drying with a hot air circulating dryer at 100 ° C. for 60 seconds to form a pressure-sensitive adhesive layer, a polyethylene terephthalate (PET) film [trade name; E5001; manufactured by Toyobo Co., Ltd.] The pressure-sensitive adhesive layer surface was placed on top and bonded by pressing through a pressure nip roll, followed by curing at 23 ° C. and 65% RH for 10 days to obtain a test surface protective film.

(2) Measurement of adhesive strength
After the test surface protective film prepared in the previous section (1) was cut to 25 mm × 150 mm, this surface protective film piece was antiglare-treated with a desktop laminator [trade name; SQ-1852AP- AG6; manufactured by Sumitomo Chemical Co., Ltd.] was used as a test sample. This sample is allowed to stand for 24 hours under conditions of 23 ° C and 65% RH (conditioning treatment), and then the adhesive strength at 180 ° peeling is measured at peeling speeds of 0.3 m / min (low speed peeling conditions) and 3 m / min (high speed peeling conditions). Each was measured with.

(3) Peeling speed dependence of adhesive strength The following evaluation was made based on the measurement result of the peeling speed.
A: The peel force under the high speed peel condition is less than 10 times the peel force under the low speed peel condition. ○: The peel force under the high speed peel condition is 10 times or more and less than 15 times the peel force under the low speed peel condition. More than 15 times the peel force under low speed peel conditions

(4) Before observing the surface state of the polarizing film after peeling The surface state of the polarizing film after peeling the test sample tested in (2) was observed.
○: Abnormalities such as adhesive residue on the surface are not observed.
X: Abnormalities such as adhesive residue are observed on the surface.

(5) Evaluation of pot life The pot life of the samples was evaluated according to the following criteria.
(Evaluation criteria)
○: Does not gel for 12 hours or more at 25 ° C. △: Does not gel for 8 hours or more at 25 ° C. ×: Gels in less than 8 hours at 25 ° C.

(6) Before the evaluation of heat resistance After cutting the test surface protective film prepared in (1) above to 60mm x 80mm, the same two types of polarized light are applied to the surface protective film piece in the same manner as in the previous item (2). Crimped to film. Next, using a commercially available pressure-sensitive adhesive composition (Nissetsu Q-1851: manufactured by Nippon Carbide Industries Co., Ltd.), a pressure-sensitive adhesive having a thickness of about 25 μm on the release paper in the same manner as in the previous item (1). After forming a layer and transferring this pressure-sensitive adhesive layer to the back surface of each polarizing film, these were pressure-bonded to a glass plate having a thickness of about 2 mm using a table laminating machine to prepare a test sample. This sample was allowed to stand for 1 week at 23 ° C. and 65% RH, and then autoclaved (70 ° C., 490 kPa). 30 minutes), followed by further heat treatment at 90 ° C. for 2 hours. By visual observation from the surface of the surface protective film side of this test sample, generation of bubbles in the pressure-sensitive adhesive layer of the surface protective film, The state of peeling was evaluated. The evaluation criteria are as follows.

(Evaluation criteria)
A: Generation of bubbles is not recognized at all.
○: Some bubbles are observed in the test sample (width of about 5 mm).
Δ: Bubbles are observed in the test sample (width of about 5 mm), but there is no peeling.
X: Bubbles are observed on the entire surface of the test sample.

(7) Evaluation of wettability The surface protective film for test prepared in the previous item (1) was cut to 25 mm × 100 mm under the condition of 23 ° C. × 65% RH so that the adhesive would be in contact with the polarizing plate (antiglare). When placed gently, evaluate the wet spread area under its own weight.

(Evaluation criteria)
○: 80% or more wet spread within 10 seconds △: 30% or more wet spread within 10 seconds ×: Less than 30% wet spread within 10 seconds

Production of acrylic copolymer (A) Production Example 1
In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube and a reflux condenser, 35 parts by weight of ethyl acetate and 15 parts by weight of toluene were placed, and in another container, butyl acrylate (monomer (a ₁ )) BA) 65.6 parts by weight and 2-ethylhexyl acrylate (2EHA) 28.2 parts by weight, monomer (a ₂ ) 4-hydroxybutyl acrylate (HBA) 6.0 parts by weight, monomer (a ₃ ) acrylic acid (AA) Add 0.03 part by weight to make a monomer mixture, add 25% of the mixture to the reaction vessel, and then replace the air in the reaction vessel with nitrogen gas, and then use 1,1′-azobis as a polymerization initiator. The initial reaction was initiated by adding 0.0875 parts by weight of -1-cyclohexanecarbonitrile (ACHN) and raising the temperature of the mixture in the reaction vessel to 87 ° C. in a nitrogen atmosphere with stirring. After the initial reaction was almost completed, 75% of the remaining monomer mixture and a mixture of 25 parts by weight of ethyl acetate and 0.075 part by weight of ACHN were sequentially added for about 2 hours at reflux, followed by another 2 hours. Reacted. Thereafter, a solution in which 0.25 parts by weight of azobisisobutyronitrile (AIBN) was dissolved in 25 parts by weight of ethyl acetate was added dropwise over 1 hour, and the mixture was further reacted for 1.5 hours. After completion of the reaction, the reaction mixture was diluted with 154 parts by weight of toluene to obtain an acrylic copolymer solution having a solid content of 28.9% by weight.

The resulting acrylic copolymer solution has a viscosity of 360 mPa · s, and the acrylic copolymer has a glass transition temperature (Tg) of −60.0 ° C., a weight average molecular weight (Mw) of about 552,000 and a weight. The ratio of average molecular weight (Mw) to number average molecular weight (Mn) was Mw / Mn of about 9.0.

In Production Example 1, as shown in Table 1, the amount of the monomer (a ₁ ), monomer (a ₂ ), monomer (a ₃ ) used was changed, and the monomer (a except for using a ₄₎ in the same manner as in preparation example 1 to obtain an acrylic copolymer solution. Table 1 shows the viscosity, solid content, Tg, Mw and Mw / Mn of the resulting acrylic copolymer solution.

In addition, the symbol of the monomer in Table 1 is as follows.
EHA: 2-ethylhexyl acrylate
BA: Butyl acrylate
EA: Ethyl acrylate
AA: Acrylic acid
HBA: 4-hydroxybutyl acrylate

Preparation of pressure-sensitive adhesive composition for surface protective film Example 1
As the acrylic copolymer (A), 100 parts by weight of the acrylic copolymer (A) solution of Production Example 1 (28.9 parts by weight as a copolymer; 0.01216 equivalent parts by functional group) was used, and an isocyanate compound (B Product name: Takenate D262 [TDI type, solid content 49.8% by weight, isocyanate (NCO) content 7.58% by weight; manufactured by Mitsui Takeda Chemical Co., Ltd.] 6.69 parts by weight (corresponding to 1.0 equivalent ratio of NCO to functional groups) ) Was added and sufficiently stirred to obtain a solution of the pressure-sensitive adhesive composition for optical member surface protective film. The obtained pressure-sensitive adhesive composition had a solid content of about 28.9% by weight and a viscosity of 400 mPa · s. Using this pressure-sensitive adhesive composition, a test surface protective film was prepared according to the above-described method for preparing a test pressure-sensitive adhesive sheet, and the above-described various physical property tests were conducted. The obtained results are shown in Table 3.

Comparative Example 1
In Example 1, instead of using 6.69 parts by weight (1.0 equivalent part) of “D262” as the polyisocyanate compound (B), “Duranate D201” (HMDI type, solid content 100% by weight, NCO content 16.1% by weight; Asahi Kasei) Co., Ltd.] was used in the same manner as in Example 1 except that 3.15 parts by weight (corresponding to 1.0 equivalent part of NCO with respect to the functional group) was used to obtain a pressure-sensitive adhesive composition solution for optical member surface protective film. . Table 1 shows the blended composition of the obtained pressure-sensitive adhesive composition and the characteristic values such as the solid content and viscosity thereof.

  Using this pressure-sensitive adhesive composition, a test surface protective film was prepared according to the above-described method for preparing a test pressure-sensitive adhesive sheet, and the above-described various physical property tests were conducted. The obtained results are shown in Table 3.

Examples 2-4 and Comparative Examples 2-3
In Example 1, instead of using the acrylic copolymer solution of Production Example 1 as the acrylic copolymer (A), any one of the acrylic copolymer solutions of Production Examples 2 to 6 was used, and a polyisocyanate compound was used. The amount of (B) used was changed as shown in Table 2, and a solution of a pressure-sensitive adhesive composition for an optical member surface protective film was obtained in the same manner as in Example 1.
Using this pressure-sensitive adhesive composition, a test surface protective film was prepared in accordance with the above-described method for preparing a test pressure-sensitive adhesive sheet, and the results of the above various physical property tests are shown in Table 3.

The abbreviations of the polyfunctional compound of the polyisocyanate compound (B) in Table 2 are as follows.
D262: “Takenate D-262” TDI type polyisocyanate, solid content 49.8% by weight, NCO content 7.58% by weight (manufactured by Mitsui Takeda Chemical Co., Ltd.)
D201: “Duranate D-201” HMDI type polyisocyanate, solid content 100% by weight, NCO content 16.1% by weight (manufactured by Asahi Kasei Corporation)

Claims (6)

An acrylic copolymer (A) containing a hydroxyl group and a carboxyl group as a reactive functional group and having a glass transition temperature (Tg) of −40 ° C. or lower and −80 ° C. or higher; and an aromatic polyfunctional isocyanate compound (B) in the comprising as essential components an optical member surface protective film pressure-sensitive adhesive composition,
The acrylic copolymer (A) is
Acrylic acid ester monomer (a ₁ ) represented by the following general formula (2) and having a glass transition temperature (Tg) of the homopolymer of −50 ° C. or less ,
H ₂ C = CHCOOR ¹
(2)
(Wherein R ¹ represents a linear or branched alkyl group having 4 to 10 carbon atoms)
1 to 10% by weight of a monomer (a ₂ ) having a hydroxyl group in the molecule ;
0.003 to 0.05% by weight of a monomer (a ₃ ) having a carboxyl group in the molecule ;
Copolymerizable with the above monomers (a ₁ ) to (a ₃ ) and 0 to 35% by weight of monomers (a ₄ ) other than the monomers (a ₁ ) to (a ₃ ) A pressure-sensitive adhesive composition for a surface protective film for an optical member.
[However, the total of the monomers (a ₁ ) to (a ₄ ) is 100% by weight] The acrylic copolymer (A) has a weight average molecular weight (Mw) of 300,000 or more and a molecular weight distribution represented by a ratio Mw / Mn of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of 15 The pressure-sensitive adhesive composition for an optical member surface protective film according to claim 1, wherein: Monomers having a hydroxyl group in the molecule (a ₂₎ is a hydroxyl group-containing (meth) optical element surface protective films for pressure sensitive adhesive according to claim 1 or claim 2 which is an acrylic acid ester Composition. The pressure-sensitive adhesive composition for an optical member surface protective film according to claim 3 , wherein the hydroxyl group-containing (meth) acrylic acid ester is 4-hydroxybutyl acrylate. Monomers having a carboxyl group in the molecule (a ₃₎ is, alpha 3 to 5 carbon atoms, beta-unsaturated monocarboxylic - carboxylic acid or di - any one of claims 1 is a carboxylic acid of claim 4 one The pressure-sensitive adhesive composition for an optical member surface protective film according to the item. The content of the aromatic polyfunctional isocyanate compound (B) is in the range of 0.5 to 1.5 equivalents with respect to 1 equivalent of the reactive functional group in the acrylic copolymer (A) . The pressure-sensitive adhesive composition for an optical member surface protective film according to any one of the above.