JPH06108031A - Adhesive composition for polarizing plate - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a pressure-sensitive adhesive composition for adhering a polarizing film coated with a protective layer such as a cellulosic material to a glass substrate of a liquid crystal cell, which has a high adhesive strength under normal use conditions. When it is necessary to remove the polarizing plate because defects such as foaming and peeling are prevented from occurring, and when the polarizing plate is attached to the liquid crystal cell surface, the attachment position shifts. In particular, there is provided a pressure-sensitive adhesive composition in which the adhesive strength is lowered by heating to a high temperature and the peeling operation can be easily performed. A pressure-sensitive adhesive composition comprising an acrylic resin containing a blocked polyisocyanate compound.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive composition useful for adhering a polarizing film coated with a protective layer such as a cellulosic material and a glass substrate of a liquid crystal cell.

[0002]

2. Description of the Related Art Conventionally, a polarizing film, such as a polyvinyl alcohol film having a polarizing property, is coated with a protective film of a cellulosic film such as a cellulose triacetate film on both sides of a polarizing film. The liquid crystal display plate is applied to the surface, and the application to the liquid crystal cell surface is performed by bringing the pressure-sensitive adhesive layer provided on the polarizing plate surface into contact with the cell surface and pressing it. It is normal. As the above-mentioned pressure-sensitive adhesive, one made of an acrylic resin is often used because of its excellent adhesiveness and transparency. As such an adhesive, one having a high adhesive strength is generally used for the purpose of preventing the appearance of abnormal appearance such as foaming or peeling of the adhesive when used in a high humidity and high temperature environment.

[0003]

When a polarizing film is attached to the surface of a liquid crystal cell, if the attachment position is misaligned or an attachment defect occurs, the liquid crystal cell is expensive and the polarizing film is peeled off. It is common practice to reuse such liquid crystal cells. However, the conventional pressure-sensitive adhesive made of acrylic resin has a high adhesive strength as described above, which makes the peeling operation very difficult. However, under normal conditions of use, it is desired to develop a pressure-sensitive adhesive that has a high adhesive strength and prevents foaming, peeling, etc., and reduces the adhesive strength when a peeling operation is required so that the peeling operation can be performed easily. .

[0004]

The inventors of the present invention have conducted extensive studies to solve such problems, and as a result, an acrylic resin containing a blocked polyisocyanate compound was coated with a protective layer of cellulose or the like. The present invention has been completed by finding that the use as a pressure-sensitive adhesive composition for adhering a polarizing film and a glass substrate of a liquid crystal cell meets the above purpose.

That is, since the pressure-sensitive adhesive composition of the present invention has a high pressure-sensitive adhesive strength under ordinary heating conditions of about 40 to 100 ° C., it exhibits extremely good durability even in a high-humidity and high-temperature environment. When heated to 120 ° C. or higher, the blocking agent of the blocked polyisocyanate compound is dissociated to generate an active isocyanate group, so that the functional group of the acrylic resin and the isocyanate group are crosslinked, and the pressure-sensitive adhesive composition is cured. It has the property that the adhesive strength decreases. Therefore, when peeling is required, the peeling operation can be easily performed by leaving it at a temperature of 120 ° C. or higher. Hereinafter, the present invention will be described in detail.

As described above, the adhesive of the present invention comprises a composition of an acrylic resin and a blocked polyisocyanate compound. Examples of the constituent component of the acrylic resin of the present invention include a soft monomer component having a low glass transition temperature, a hard comonomer component having a high glass transition temperature and a small amount of a functional group-containing monomer component.

The main monomer components include ethyl acrylate, n-butyl acrylate, iso-acrylate
Butyl, 2-ethylhexyl acrylate, lauryl acrylate, benzyl acrylate, cyclohexyl acrylate, etc. Alkyl acrylates having 2 to 12 carbon atoms, n-butyl methacrylate, iso-butyl methacrylate, methacrylic acid 2-ethylhexyl,
Carbon number of alkyl group such as lauryl methacrylate, benzyl methacrylate and cyclohexyl methacrylate is 4 to 12
Examples include methacrylic acid alkyl ester,
Examples of the comonomer component include methyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid alkyl ester having 1 to 3 carbon atoms of an alkyl group such as propyl methacrylate, vinyl acetate, acrylonitrile, methacrylonitrile, and styrene. Can be mentioned.

In addition to the above, as the functional group-containing monomer component, monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, polycarboxylic acids such as maleic acid, fumaric acid, citraconic acid, glutaconic acid and itaconic acid, and Carboxyl group-containing monomers such as anhydrides, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-chloro-2-hydroxylpropyl (meth) acrylate, diethylene glycol mono (meth) acrylate, and the like. Examples thereof include hydroxyl group-containing monomers such as N-methylol acrylamide.

The content of the main monomer component cannot be unconditionally specified depending on the types and contents of the comonomer component and the functional group-containing monomer component to be contained, but generally, the main monomer should be contained in an amount of 50% by weight or more. Is preferred. The acrylic resin of the present invention is easily produced by a method well known to those skilled in the art, such as radical copolymerization of a main monomer, a comonomer, and a functional group-containing monomer in an organic solvent.

The organic solvent used for the above polymerization is
Examples thereof include aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Specific examples of the polymerization catalyst used for the radical polymerization include azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide and the like which are ordinary radical polymerization catalysts.

The acrylic resin thus obtained has a glass transition temperature (hereinafter abbreviated as Tg) of -20 ° C or lower, preferably -30 to -60 ° C, and has an average molecular weight of 50.
50,000 or more, preferably 600,000 to 900,
It is 000. If the Tg exceeds -20 ° C, the adhesive strength is poor, and if the average molecular weight is less than 500,000, the adhesive may cause foaming, peeling, or other abnormal appearance.

Such an acrylic resin can be used alone or of course, but a curing agent may be used in combination if necessary. The addition amount is about 0.5 to 5.0% by weight.
Representative examples of the curing agent include isocyanate compounds, epoxy compounds, aldehyde compounds, amine compounds, metal salts, metal alkoxides, metal chelate compounds, ammonium salts and hydrazine compounds.

Among the curing agents, the isocyanate compounds include tolylene diisocyanate, hydrogenated tolylene diisocyanate, tolylene diisocyanate adduct of trimethylol propane, xylylene diisocyanate adduct of trimethylol propane, triphenyl methane triisocyanate, methylene bis (4 -Phenylmethane) triisocyanate, isophorone diisocyanate and the like.

Examples of the epoxy compound include bisphenol A / epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin di- or triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane. Triglycidyl ether, diglycidyl aniline, diglycidyl amine, N, N, N ′, N′-tetraglycidyl m-xylene diamine, 1,3-bis (N, N′-diglycidylaminomethyl) cyclohexane and the like can be mentioned. .

Examples of the aldehyde compounds include glyoxal, malondialdehyde, succindialdehyde, maleindialdehyde, glutardialdehyde, formaldehyde, acetaldehyde, benzaldehyde and the like. Examples of the amine compound include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetramine, diethylenetriamine, triethyltetramine, isophoronediamine, amino resin and melamine resin.

As the metal salt, aluminum, iron, copper,
Salts of polyvalent metals such as zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium, salts such as bromide, nitrate, sulfate and acetate, such as cupric chloride, aluminum chloride and chloride. Examples thereof include ferric iron, stannic chloride, zinc chloride, nickel chloride, magnesium chloride, aluminum sulfate, copper acetate and chromium acetate. Examples of metal alkoxides include tetraethyl titanate, tetraethyl zirconate, and aluminum isopropionate.

Examples of the metal chelate compound include acetylacetone and acetoacetic acid ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium. . Examples of ammonium salts include ammonium chloride, ammonium sulfate, ammonium acetate, and ammonium propionate.
Examples of the hydrazine compound include hydrazine, hydrazine hydrate, and their inorganic salts such as base salts, sulfates and phosphates, and organic acid salts such as formic acid and oxalic acid.

The blocked polyisocyanate used in the present invention means that the free isocyanate group of the polyisocyanate undergoes an addition reaction to inactivate it.
It refers to an addition reaction product of a compound (hereinafter referred to as a blocking agent) that is easily dissociated by heating to form a bond that regenerates a polyisocyanate having a free isocyanate group again. As the polyisocyanate for the blocked polyisocyanate compound, any conventionally known polyisocyanate is used.

Therefore, examples of such polyisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatocaproic acid. Aliphatic diisocyanates such as methyl, 3-isocyanatomethyl-3,5,5-trimethylcyclohexane, 1,3- or 1,4-bis (isocyanatomethyl)
Cyclohexane, methylcyclohexane-2,4- or 2,6-diisocyanate, dicyclohexylmethane-
Aliphatic diisocyanates such as 4,4'-diisocyanate, 1,3- or 1,4-diisocyanatocyclohexane, m- or p-phenylene diisocyanate, diphenylmethane-4,4'-diisocyanate, 2,4- or 2 Aromatic diisocyanates such as 1,6-tolylene diisocyanate, 1,3′- or 1,4-bis (isocyanatomethyl) benzene, 1,3- or 1,4-bis (α-
Diisocyanates such as araliphatic diisocyanates such as isocyanatoisopropyl) benzene can be mentioned.

As the triisocyanate, triphenylmethane-4,4,4 "-triisocyanate,
1,3,5-triisocyanatobenzene, 1,3,5-
Tris (isocyanatomethyl) cyclohexane, 1,
3,5-tris (isocyanatomethyl) benzene, 2,
Examples thereof include 6-diisocyanatocaproic acid-2-isocyanatoethyl.

Further, as the polyisocyanate that can be used in the present invention, for example, polymerized polyisocyanate such as diisocyanate and trimer of diisocyanate, polymethylene polyphenylene polyisocyanate, and excess of the above isocyanate compound, for example, ethylene glycol, propylene Glycol, dipropylene glycol, diethylene glycol, triethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, neopentyl glycol, hexanediol, cyclohexanedimethanol, cyclohexanediol, hydrogenated bisphenol A,
Xylylene glycol, glycerin, trimethylolethane, trimethylolpropane, hexanetriol,
Pentaerythritol, sorbitol, sorbit, sucrose, castor oil, ethylenediamine, hexamethylenediamine, diethanolamine, triethanolamine, water, ammonia, low molecular weight compounds containing active hydrogen such as urea, or various polyether polyols, polyester polyols, polyurethanes Polyisocyanate obtained by reacting with active hydrogen-containing high molecular weight compound such as polyol, acrylic polyol and epoxy polyol,
Or these allophanatized polyisocyanates,
Examples thereof include biuretized polyisocyanate.

The above-mentioned isocyanate compounds are used alone or as a mixture of two or more kinds. As the blocking agent, any conventionally known blocking agent is used. Examples of the blocking agent include phenol, cresol, p-nonylphenol,
Phenolic blocking agents such as hydroxybenzoate, ε-caprolactam, lactam blocking agents such as γ-butyrolactam, diethyl malonate, methyl acetoacetate, active methylene blocking agents such as acetylacetone, ethanol, isopropyl alcohol, Alcohol-based blocking agents such as t-butyl alcohol, lauryl alcohol, ethylene glycol monoethyl ether, benzyl alcohol, glycolic acid, glycolic acid ester, lactic acid, lactate ester, diacetone alcohol, ethylene chlorohydrin, butyl mercaptan, octyl mercaptan , T-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol and other mercaptan blocking agents, acetanilide, acetic acid amide, acrylamide, benz Acid amide blocking agents such as amides, succinimide, imide blocking agents such as phthalimide, diphenylamine, carbazole, aniline,
Amine-based blocking agents such as dibutylamine, imidazole-based blocking agents such as imidazole and 2-ethylimidazole, urea-based blocking agents such as urea, thiourea, and ethylenethiourea, 2-oxazolidone, phenyl N-phenylcarbamate, etc. Carbamic acid ester blocking agents, formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime, cyclohexanone oxime, benzophenone oxime, etc., or sulfites such as sodium hydrogen sulfite and potassium hydrogen sulfite. Examples thereof include salt-based blocking agents.

These blocking agents may be used alone or in combination of two or more. The blocked polyisocyanate can be obtained by reacting the polyisocyanate and the blocking agent in a conventional manner, as described above. This reaction can be carried out in a solvent having no active hydrogen or in the absence of solvent. As the solvent having no active hydrogen, for example, ethyl acetate, butyl acetate, cellosolve acetate, carbitol acetate, ester type such as dimethyl ester of dibasic acid, methyl ethyl ketone, methyl isobutyl ketone, ketone type such as cyclohexanone, toluene, Aromatic solvents such as xylene, sorbetso # 100, sorbetso # 150 and the like can be mentioned. When a sulfite-based blocking agent is used as the blocking agent, it is often preferable to use water as the solvent.

The blocking reaction of polyisocyanate is
As described above, a conventional method may be used, but more specifically, for example, polyisocyanate and a blocking agent may be added to NCO.
/ Blocking agent (equivalent ratio) of about 0.9 to 1.1, preferably about 0.95 to 1.0, and reacting, polyisocyanate and blocking agent NCO / blocking agent (equivalent ratio) About 1.1 to 3.0, preferably about 1.2 to
After reacting as 2.0, a method of reacting the above-mentioned active hydrogen-containing low molecular weight compound and / or active hydrogen-containing high molecular weight compound, polyisocyanate and active hydrogen-containing low molecular weight compound and / or active hydrogen-containing high molecular weight compound The compound has an NCO / active hydrogen (equivalent ratio) of about 1.5 to 10.0,
Preferably, after reacting at about 2.0 to 7.0, the polyisocyanate is removed if necessary, and then a blocking agent is reacted with it. But,
It is not limited to these. In the blocking reaction of polyisocyanate, a conventionally known catalyst such as a tertiary amine or an organometallic compound may be used.

It is appropriate that the blocked polyisocyanate is contained in an amount of 0.5 to 10 parts by weight, preferably 1.0 to 5 parts by weight, based on 100 parts by weight of the acrylic resin (as solid content). When the content is less than 0.5 parts by weight, when the peeling operation between the polarizing film and the glass substrate is required, the curing reaction of the pressure-sensitive adhesive layer is not sufficient even if heated to 120 ° C. or higher, and the peeling force No decrease is observed.
On the other hand, if the amount exceeds 10 parts by weight, the pressure-sensitive adhesive layer acts as a plasticizer, and abnormal appearance such as foaming or peeling of the pressure-sensitive adhesive layer occurs when used in a high humidity and high temperature environment, which is not preferable.

The pressure-sensitive adhesive composition of the present invention is applied to the surface of a cellulose-based protective film of a polarizing film. The coating method is, for example, an organic solvent such as toluene, ethyl acetate or methyl cellosolve alone. Alternatively, a solution having a resin solid content of about 15 to 40% by weight dissolved in the mixed solution is applied with an applicator or the like and dried. The film thickness after drying is 10
40 μm, preferably 20-30 μm is suitable. In addition, there is also a method in which the pressure-sensitive adhesive composition is once applied to a base material such as release paper to form a coating film, and then transfer coating is applied to a polarizing film.

[0027]

[Operation] The pressure-sensitive adhesive composition of the present invention is used for adhering a polarizing film coated with a protective layer such as a cellulosic material and a glass substrate of a liquid crystal cell. Such an adhesive has a high adhesive strength under normal use conditions, prevents appearance abnormalities such as foaming and peeling, and reduces the adhesive strength by heating at a higher temperature when a peeling operation is required. The pressure-sensitive adhesive composition is characterized in that it can be easily peeled off.

[0028]

The present invention will be described in more detail below with reference to examples. Incidentally, “%” and “part” are based on weight unless otherwise specified. Example 1 An acrylic resin (Tg = -44) having a resin composition (%) of n-butyl acrylate / methyl acrylate / acrylic acid / 2-hydroxyethyl methacrylate = 82/15 / 2.7 / 0.3 ℃, average molecular weight = 800,000)
30% ethyl acetate solution (viscosity = 5000 cps / 25
C) 100 parts (as solid content), Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd., trimethylolpropane tolylene diisocyanate adduct) 1.0 part and hexamethyldiisocyanate phenol block 3.0.
Parts were mixed and mixed. Such a pressure-sensitive adhesive composition is formed on a release paper so as to have a film thickness after drying of 20 to 30 μm, and after drying, a polyvinyl alcohol-based polarizing film having a cellulose triacetate protective layer (average degree of polymerization 1700, average ken) A cellulose film having a degree of conversion of 99.7 mol% and a degree of polarization of 99.9 was laminated on the side of the cellulose film and pressed by a roller to produce a polarizing film. The polarizing film and a glass plate at 50 ° C for 5k
Adhesion was performed in an autoclave at g / cm ² pressure, and the adhesive force at that time was measured. Further, in order to evaluate the peeling operability of the adhesive layer, the adhesive strength after heat treatment at 130 ° C. for 30 minutes was measured. Further, in order to evaluate the durability as a polarizing plate, a heat resistance test (180 ° C, left for 500 hours) and a humidity resistance test (6
The evaluation was performed at 0 ° C., 90% RH, and left for 500 hours). The results are summarized in Table 1. Adhesion measuring method is 2
The 90 ° peel force was measured at a peel speed of 300 mm / min at 3 ° C.

Example 2 An experiment was conducted in the same manner as in Example 1 except that the blocked isocyanate was an ε-caprolactam block of 2,4-tolylene diisocyanate. The results are summarized in Table 1. Example 3 An experiment was conducted according to Example 1 except that the blocked isocyanate was a phenol block of tetramethylene diisocyanate. The results are summarized in Table 1. Example 4 An experiment was conducted according to Example 1, except that the blocked hexaisone was a cyclohexanone oxime block of ethylene diisocyanate. The results are summarized in Table 1. Comparative Example 1 An experiment was performed according to Example 1 except that Coronate 2507 was not added. The results are summarized in Table 1.

[0030]

[Table 1]

[0031]

INDUSTRIAL APPLICABILITY The present invention has a high adhesive strength under normal use conditions, prevents appearance abnormalities such as foaming and peeling, and heats it to a high temperature when peeling operation is required. A pressure-sensitive adhesive composition for a polarizing film, which has a reduced force and can be easily peeled off.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C08G 18/80 NFM 8620-4J

Claims (1)

[Claims] 1. A pressure-sensitive adhesive composition for a polarizing plate comprising a polarizing film covered with a protective layer of cellulose or the like and a glass plate, which is composed of an acrylic resin containing a blocked polyisocyanate compound.