TWI415918B - Adhesive composition for optical film protective sheet and protective film for optical film - Google Patents

Abstract

A pressure-sensitive adhesive composition capable of giving protective sheets for optical films which exhibit small peel strength in high-speed peeling and little dependence of peel strength on peel rate and cause neither zipping nor staining of the films in peeling. The composition comprises the following components (A), (B) and (C): (A) 100 parts by weight of a (meth)acrylic polymer obtained by copolymerizing (a1) an alkyl (meth)acrylate and (a2) a (meth)acrylic monomer having a hydroxyl or carboxyl group, (B) 0.1 to 20 parts by weight of dibutyl sebacate, and (C) 1 to 10 parts by weight of an isocyanate crosslinking agent and/or 1 to 10 parts by weight of an aziridine crosslinking agent and/or 0.01 to 5 parts by weight of an epoxy crosslinking agent.

Description

Adhesive composition for optical film protection sheet and optical film protection sheet

The present invention relates to an adhesive composition for an optical film protective sheet, and more specifically relates to an optical film protective sheet and an adhesive having good peelability when used as a protective sheet for an optical film such as a polarizing film used for a liquid crystal display or the like. The composition and the optical film protection sheet using the same.

As an optical film used for a liquid crystal display or the like, such as a polarizing film, a phase difference film, and a brightness enhancement film, many of them are well known, and most of them are laminated.

However, before the final composition of the display, the optical films are usually subjected to steps of punching, transporting, inspecting, etc., but the steps are not to cause damage or contamination, and the protective sheet is usually attached to the surface.

After the end of each step, the protective sheets are peeled off and discarded when not in use. However, the peeling operation is mainly performed manually because of the mechanical operation. On the other hand, the peeling speed of the protective sheet by manual operation is relatively high, and the speed is not easily controlled from the peeling to the end.

In general, the faster the peeling speed, the larger the force required for peeling (hereinafter referred to as "adhesion"), and therefore, the work efficiency of peeling off the protective sheet is deteriorated, and problems such as damage and contamination of the optical film during peeling occur. Moreover, it is impossible to peel off smoothly, and the sound of a creaking sound causes a problem called a close phenomenon. Further, this problem is solved, and after the adhesive force of the protective sheet is made small, the problem that the optical film is lifted and peeled off occurs in the working step. Therefore, being It is strictly required that the high-speed peeling or the low-speed peeling does not cause a peeling force reduction, a problem of lifting and peeling, and a protective sheet having good adhesion to the covering.

In the prior art, in the adhesive sheet for an adhesive sheet which is generally used for the surface of glass or plastic, it is known to reduce the adhesion when the adhesive sheet is re-peeled (Patent Document 1). Moreover, it is well known that plasticizers can be blended in such compositions. However, those who are the coverings are not particularly targeted to optical films, and those having various properties required for a protective film that satisfies an optical film such as a polarizing film are not provided. Therefore, in order to improve the above-described properties required for the optical film, a plasticizer is not desirable.

Further, it is also known that the above-mentioned compounding plasticity is in the adhesive composition for an optical film protective sheet. However, usually, when a plasticizer is blended, a plasticizer of a low molecular weight body is printed, causing a problem of contaminating the optical film. Further, at the time of low-speed peeling, even if the low peeling force can be controlled, the peeling force tends to increase as the peeling speed increases, so that the use of the plasticizer in the optical film protective sheet which is required to be peeled off at a high speed causes problems. .

Patent Document 1: Japanese Patent Publication No. Hei 10-310745

Therefore, when it is used for an optical film protective sheet, it is expected to provide a peeling force at the time of high-speed peeling, and at the same time, the peeling force change by peeling speed is small, and there is no adhesion, and the adhesive composition of the optical film is not contaminated at the time of peeling. The present invention provides the adhesive composition as a subject.

In order to solve this problem, the inventors of the present invention conducted a detailed study and found that The above problem can be solved by blending a polymer copolymerized with a specific component as a specific substance of a plasticizer, and the present invention has been completed.

That is, the present invention provides an adhesive composition for an optical film protective sheet comprising the following components (A), (B), and (C).

(A) 100 parts by weight of a (meth)acrylic polymer obtained by copolymerizing at least the following components (a1) and (a2)

(a1) alkyl (meth)acrylate

(a2) a (meth)acrylic monomer having a hydroxyl group or a carboxyl group

(B) Dibutyl sebacate 0.1 to 20 parts by weight

(C) Isocyanate-based crosslinking agent 1 to 10 parts by weight and/or 1 to 10 parts by weight of the aziridine-based crosslinking agent and/or 0.01 to 5 parts by weight of the epoxy-based crosslinking agent.

Moreover, the present invention provides an optical film protective sheet having an adhesive which is obtained by applying an adhesive composition for an optical film protective sheet to a support and crosslinking the adhesive.

According to the present invention, it is possible to obtain an adhesive composition for an optical film protective sheet which is suitable for manual work, has a small peeling force at high-speed peeling, and has little change in peeling force by peeling speed. Further, the optical film protective sheet using the adhesive composition does not cause adhesion, and does not contaminate the optical film when peeled off.

[Best form of implementation of the invention]

The component (A) which is an essential component of the adhesive composition for an optical film protective sheet of the present invention is obtained by copolymerizing at least the following components (a1) and (a2) ( Methyl) acrylic polymer.

(a1) (meth)acrylic acid ester

(a2) a (meth)acrylic monomer having a hydroxyl group or a carboxyl group

In the present specification, "(meth)acrylyl" means both a propenyl group and a methacryl group. Therefore, the "alkyl (meth)acrylate" of the copolymer component (a1) means the alkyl acrylate or the alkyl methacrylate.

The alkyl group of the (meth)acrylic acid alkyl ester of the copolymer component (a1) may be linear or branched, and is not particularly limited, and is a main monomer of the component (a1). The glass transition point (hereinafter referred to as "Tg") is preferably an alkyl (meth)acrylate of 0 ° C or lower. It is particularly preferable that the homopolymer has a Tg of an alkyl (meth)acrylate of -30 ° C or less. Further, in order to measure the molecular weight of the homopolymer of Tg, the Tg is a constant value.

When a large amount of a (meth)acrylic acid alkyl ester having a Tg higher than 0 ° C in a homopolymer is used, the Tg of the obtained component (A) is too high, and the desired adhesiveness cannot be obtained.

As an example of the copolymerization component (a1), specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. N-butyl (meth)acrylate, n-butyl (meth)acrylate, third-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, N-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, Examples of decyl (meth)acrylate and lauryl (meth)acrylate. These may be used alone or in combination of two or more.

Specific examples of the particularly preferable copolymer component (a1) include n-butyl acrylate and 2-ethylhexyl acrylate.

Further, the copolymer component (a2) of the other essential component of the component (A) is a (meth)acrylic monomer having a hydroxyl group or a carboxyl group. After the hydroxyl group or the carboxyl group is introduced into the (meth)acrylic polymer, the groups are bonded to the component (C) crosslinking agent.

The copolymerization component (a2) is not particularly limited as long as it has a hydroxyl group or a carboxyl group in the molecule, and is generally a functional group having a carboxyl group, such as (meth)acrylic acid. , β-carboxyethyl (meth)acrylate, mono(methyl)propenyloxyethyl succinate, ω-carboxypolycaprolactone mono(meth)acrylate, 2-(methyl)propene oxide Base ethyl hydrogen phthalate, 2-(meth) acrylate oxypropyl hydrogen phthalate, 2-(methyl) propylene methoxy propyl hexahydro phthalate, 2-(methyl) propylene hydride Examples of the oxypropyl tetrahydrohydrophthalic acid ester and the like, which have a hydroxyl group as a functional group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, or (methyl) ) 3-hydroxypropyl acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxy-3-chloropropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate Etc.

Among them, those having a carboxyl group as a functional group are exemplified by acrylic acid, methacrylic acid, etc., and those having a hydroxyl group as a functional group are, for example, 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate. Examples of 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate.

The component (A) used in the present invention may also copolymerize only the essential copolymerization component. Further, when the copolymerized vinyl acetate is applied to the protective sheet as a component (a3), it is less likely to be warped, and the peeling is particularly preferable.

The copolymerization composition ratio of each monomer in the case of producing the component (A) is not particularly limited. Generally, in the case of the component (A) as a whole, the composition range of the desired copolymerization is as follows (hereinafter referred to as "% by mass" is "%").

(I) when vinyl acetate is not used to form a copolymerization component

(II) When vinyl acetate is used as a copolymerization component

Further, when the component (A) is produced, a polymerizable monomer other than the above may be used. Examples of the vinyl-containing compound such as styrene, vinyl toluene, α-methylstyrene, allyl acetate, and maleic anhydride are exemplified as the polymerizable monomer. These are copolymerized in the range of 0 to 20% for the entire component (A).

The production method of the component (A) using the above components is not particularly limited, and generally, a known method can be used, and a radical polymerization method is preferred, and the solution polymerization method can easily adjust the molecular weight and reduce the impurities. for Ideal.

The Tg of the obtained component (A) is not particularly limited, and is generally preferably -80 ° C to -30 ° C, and particularly preferably -60 ° C to -40 ° C. When it is less than -80 ° C, the adhesive is too soft and prone to contamination. Conversely, when it is greater than -30 ° C, the adhesion increases to more than necessary, causing adhesion.

Further, the molecular weight of the component (A) is not particularly limited, and the weight average molecular weight is generally 100,000 or more, and more preferably 200,000 or more. When the molecular weight is too small, it will cause pollution and it is difficult to achieve balanced performance. More preferably, the weight average molecular weight is from 300,000 to 1,000,000.

The component (A) may be a single polymer having a certain molecular weight distribution, or may be a copolymer composition, a mixture of two or more different Tg or molecular weight polymers.

The adhesive composition for an optical film protective sheet of the present invention must contain a component (B) which is a dibutyl sebacate. Dibutyl phthalate is particularly effective in achieving the above effects in a poly-plasticizer.

The compounding amount of the dibutyl sebacate of the component (B) is 0.1 to 20 parts per 100 parts by weight of the component (A) (hereinafter referred to as "parts"). When the amount is less than 0.1 part, the peeling force is increased at the time of high-speed peeling, and the above-described effect is not exhibited in addition to the peeling speed dependency of the peeling force. On the other hand, when it exceeds 20 parts, the phenomenon of the contaminated covering body occurs. The ideal is 1 to 15 servings, especially 1 to 10 servings.

The component (C) which is an essential component of the adhesive composition for an optical film protective sheet of the present invention is an isocyanate crosslinking agent and/or an aziridine crosslinking agent and/or an epoxy crosslinking agent. The crosslinking agent is functional with the component (A) After the chemical reaction or interaction, the component (A) is crosslinked.

The isocyanate-based crosslinking agent is not particularly limited, and specific examples thereof include tolene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, and a compound having two isocyanate groups in a molecule such as phenylmethane diisocyanate or hydrogenated diphenylmethane diisocyanate; a compound which is subjected to an addition reaction with a polyvalent alcohol such as trimethylolpropane or pentaerythritol, an isocyanate compound, and a triheteropoly group. The cyanate compound and the biuret type compound are more commonly known to carry out an addition reaction with a polyether polyol, a polyester polyol, a propylene polyol, a polybutadiene polyol, a polyisoprene polyol, and the like. An example of a compound having two or more isocyanate groups in the molecule of the urethane prepolymer type. These may be used alone or in combination of two or more.

The aziridine-based crosslinking agent is not particularly limited, and is generally, for example, 1,1'-(methylene-di-P-phenylene)bis-3,3-azacyclopropane urea, 1 , 1'-(hexamethylene)bis-3,3-azetidine urea, 2,4,6-triazacyclopropene-1,3,5-triazine, trimethylolpropane-three -(2-Azacyclopropanepropionate) and the like. These may be used alone or in combination of two or more.

The epoxy-based crosslinking agent is not particularly limited, and specific examples thereof include a bisphenol A epichlorohydrin type epoxy resin, ethylene diglycidyl ether, and polyethylene glycol diglycidyl ether. Glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diepoxypropyl aniline, diamine glycidylamine , N, N, N', N'-tetraepoxy A compound having two or more epoxy groups in a molecule such as propyl-m-xylylenediamine or 1,3-bis(N,N'-diaminoglycidylmethyl)cyclohexane. These may be used alone or in combination of two or more.

Among the above components (C), an isocyanate crosslinking agent or an epoxy crosslinking agent is preferred. Further, when the copolymer component (a2) of the component (A) is a (meth) propylene group monomer having a hydroxyl group, the component (C) is preferably an isocyanate crosslinking agent, and the copolymer component (a2) of the component (A). When it is a (meth) propylene-based monomer having a carboxyl group, it is preferred to use an epoxy-based crosslinking agent in the component (C).

Further, the amount of the component (C) is preferably from 1 to 10 parts, preferably from 1 to 5 parts, per 100 parts of the component (A), and the component (C) is an isocyanate crosslinking agent. Further, when the component (C) is an aziridine-based crosslinking agent, it is preferably 1 to 10 parts, preferably 1 to 5 parts. Further, when the component (C) is an epoxy-based crosslinking agent, it is preferably 0.01 to 5 parts, more preferably 0.5 to 3 parts. When the component (C) is too small, the adhesion is too large, and conversely, most of the time, it is easily peeled off by the covering.

After the combination with the component (C), a metal chelate compound as a crosslinking agent can be further used. As the metal chelate compound, such as aluminum, iron, copper, zinc, tin, titanium, nickel, ruthenium, magnesium, vanadium, chromium, zirconium and other polyvalent metals, such as ethyl acetone, ethyl acetate, etc. Examples of compounds such as coordination. These may be used in combination with 0 to 5 parts (C) for 100 parts of the ingredient (A).

The adhesive composition for an optical film protective sheet of the present invention may contain, in addition to the above components, an ultraviolet absorber, an antioxidant, an antifoaming agent, a preservative, etc., without impairing its properties.

The adhesive composition for an optical film protective sheet of the present invention is produced by mixing the above components (A), component (B) and component (C) in a usual manner.

The adhesive composition for an optical film protective sheet containing the component (A) to the component (C) as an essential component can be applied to a support by a solvent according to a usual method, and after distilling off the solvent, if necessary, the outer film is attached. After being placed for a certain period of time, an optical film protection sheet is formed. The solvent to be used is not particularly limited, and examples thereof include ethyl acetate, toluene, and methyl ethyl ketone. Further, the support to be used is not particularly limited, and polyester such as polyethylene terephthalate (PET), polyethylene, polypropylene, and ethylene-vinyl acetate copolymer can be generally used. Plastic film such as objects.

The optical film protective sheet of the present invention obtained as described above preferably has an adhesive force of 10,000 mm/min of 10 to 60 gf/25 mm, particularly preferably 10 to 40 gf/25 mm. Further, the optical film protective sheet of the present invention preferably has an adhesive force of from 1 to 10 gf/25 mm at 150 mm/min. When the optical film protective sheet of the adhesive composition for an optical film protective sheet of the component (B) dibutyl sebacate of the present invention is used, no adhesion is caused, and the optical film is not contaminated when peeled off, and 150 mm can be obtained. The peeling force of the low peeling of /min is maintained in the above range, and the adhesive force of the high speed peeling of 10000 mm/min is set to the above low range. That is, it is possible to reduce the increase in peeling force by an increase in the peeling speed.

The optical film protective sheet of the present invention is used for all optical films, but is particularly preferred for the purpose of surface protection of a polarizing film for liquid crystal display. Further, in particular, when the surface material is polyethylene terephthalate or a cellulose derivative such as triacetyl cellulose, the effect of the present invention is most remarkable. do The surface of the optical film protective sheet of the present invention is a polarizing film of triacetyl cellulose.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited by the examples.

[Example 1] Modulation of optical film protection sheet:

In the reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen introduction tube, the copolymerizable monomer shown in Table 1 (hereinafter also abbreviated as "parts") and 150 parts of ethyl acetate were placed. Thereafter, 0.2 part of azobisisobutyronitrile (AIBN) was added. Further, polymerization was carried out at 68 ° C for 8 hours in a nitrogen stream to obtain a (meth)acrylic polymer (ingredient (A)).

Further, 100 parts of the (meth)acrylic polymer (component (A)) was added to the solid content of the plasticizer and the crosslinking agent in Table 1, and the adhesive composition of 1 to 12 was obtained.

Each of the adhesive compositions was applied onto a polyethylene terephthalate film having a thickness of 50 μm to a thickness of 20 μm after drying, and after removing the solvent at 80 ° C, the crosslinking reaction was carried out while drying. Further, a polyethylene terephthalate film having a thickness of 38 μm thick was applied to the dried surface, and then placed in an environment of 23° C. and a humidity of 65% for 7 days to obtain an optical film protective sheet.

The abbreviations of the copolymer component monomers of Table 1 and the names of the crosslinking agents are as follows.

2EHA: 2-ethylhexyl acrylate

2HEA: 2-hydroxyethyl acrylate

AA: Acrylic

VAc: vinyl acetate

Colonate L: Isocyanate crosslinker made by Japan Polyurethane Company

Tetrad X: epoxy crosslinking agent made by Mitsubishi Gas Chemical Co., Ltd.

chemitytePZ-33: Nitrogen heterocyclopropane crosslinker manufactured by Nippon Shokubai Co., Ltd.

[Evaluation of Optical Film Protective Sheets]

The optical film protective sheet obtained above was evaluated by the following evaluation method. The results are shown in Table 2.

<Method for evaluating adhesion>

After the optical film protective sheets were cut into 25 mm × 150 mm, the film for the outer cover was peeled off, adhered to one surface of a polarizing film having a surface of triacetyl cellulose, and left at 23 ° C for 24 hours. Thereafter, the peeling speed was changed in the range of 150 to 10000 mm/min, and the tension was applied in the direction of 180°, and the peeling force was started to obtain an adhesive force.

<Method of evaluation of peeling>

Each of the optical film protective sheets was cut into 25 mm × 150 mm, and the film for the outer cover was peeled off, adhered to one surface of a polarizing film having a surface of triethylene fluorene fiber, and left at 40 ° C for 24 hours. Subsequently, it was visually observed and protected by each optical film. The peeling state of the surface of the polarizing film (triethylene glycol surface) of the sheet was determined as follows.

○: Peeling did not occur at all

×: peeling occurs

<Evaluation method of pollution>

The film for the outer cover was peeled off from each of the optical film protective sheets, and then attached to a stainless steel plate, and left at 23 ° C for 24 hours. Then, the optical film protective sheet was peeled off from the stainless steel plate to visually observe the contamination on the surface of the stainless steel plate, and the following determination was made. . In addition, the contamination of the polyethylene film or the cellulose derivative formed on the optical film on the surface thereof can be more clearly determined by the presence or absence of contamination on the surface of the stainless steel plate.

○: No pollution at all

×: There is pollution

As a result of the evaluation shown in Table 2, the optical film protective sheet using the adhesive composition compositions 1 to 5 of the optical film protective sheet of the present invention did not cause an increase in adhesion even at a high-speed peeling of 10000 mm/min, and the contamination was good. Further, when a dibutyl phthalate is used as the plasticizer (adhesive composition 6 to 10), the adhesive force is increased in high-speed peeling, and the staining property is also poor.

More adhesive composition 11 having too little cross-linking agent in high-speed peeling The adhesive force is too large. On the contrary, the adhesive composition 12 having too much cross-linking agent is peeled off from the surface of the polarizing film.

[Industrial availability]

The optical film protective sheet of the present invention has a small peeling force in high-speed peeling, a small change in peeling force by peeling speed, no adhesion, no contamination of the optical film during peeling, and good workability, and therefore, it is used as various optical films. It is widely used as a protective sheet for a polarizing film and a liquid crystal display.

Claims (11)

An adhesive composition for a polarizing film protective sheet, characterized by comprising the following components (A), (B), and (C) (A) a glass transition point obtained by copolymerizing at least the following components (a1) and (a2)- 100 parts by weight of (meth)acrylic polymer at 80 ° C to -30 ° C (a1) alkyl (meth)acrylate (a2) (meth)acrylic monomer (B) dibutyl having a hydroxyl group or a carboxyl group 0.1 to 20 parts by weight of the sebacate (C) 1 to 10 parts by weight of the isocyanate crosslinking agent and/or 1 to 10 parts by weight of the aziridine crosslinking agent and/or the epoxy crosslinking agent 0.01 to 5 Parts by weight. The adhesive composition for a polarizing film protective sheet according to claim 1, wherein the (meth)acrylic polymer of the component (A) is at least 90 to 99.5% by mass of the (a1) alkyl (meth)acrylate. (a2) 0.5 to 10% by mass of a (meth)acrylic monomer having a hydroxyl group or a carboxyl group, which is formed by copolymerization. The adhesive composition for a polarizing film protective sheet according to claim 1, wherein the (meth)acrylic polymer of the component (A) is a copolymer of vinyl acetate as the component (a3). The adhesive composition for a polarizing film protective sheet according to claim 3, wherein the (meth)acrylic polymer of the component (A) is at least 50 to 98.5% by mass of the (a1) alkyl (meth)acrylate. (a2) a (meth)acrylic monomer having a hydroxyl group or a carboxyl group 0.5 to 10% by mass (a3) of vinyl acetate 1 to 40% by mass, which is formed by copolymerization. The adhesive composition for a polarizing film protective sheet according to claim 1, wherein the component (a1) is a (meth)acrylic acid alkyl ester having a homopolymer glass transition temperature of 0 ° C or less. An adhesive composition for a polarizing film protective sheet according to claim 3, wherein the component (a1) is a (meth)acrylic acid alkyl ester having a homopolymer glass transition temperature of 0 ° C or less. An adhesive composition for a polarizing film protective sheet according to claim 1, wherein the component (a2) is selected from the group consisting of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate and A One or more of a group of 4-hydroxybutyl acrylates. An adhesive composition for a polarizing film protective sheet according to claim 3, wherein the component (a2) is selected from the group consisting of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate and A One or more of a group of 4-hydroxybutyl acrylates. A polarizing film protective sheet characterized in that the adhesive composition for a polarizing film protective sheet according to any one of claims 1 to 8 is coated on a support to be crosslinked. Into the adhesive layer. The polarizing film protective sheet of claim 9, wherein the polarizing film to be attached is a surface material of polyethylene terephthalate, a cycloolefin derivative or a cellulose derivative. For example, apply polarized film protection in item 9 or item 10 of the patent scope. A protective sheet in which a polarizing film to be attached is a polarizing film for liquid crystal display.