JP5505766B2 - Adhesive composition for polarizing plate and polarizing plate using the same - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition for polarizing plates, and more specifically, a pressure-sensitive adhesive composition for polarizing plates that achieves both effective prevention of light leakage and high durability without using high-energy rays, and The present invention relates to a polarizing plate using the same.

  The liquid crystal element has a structure in which a liquid crystal material is sandwiched between two substrates, and a polarizing plate is attached to the surface of the substrate via an adhesive layer. In recent years, the use of liquid crystal elements for mounting on vehicles, for outdoor instruments, personal computer displays, televisions, and the like has been expanded, and the usage environment has become very severe.

  Under such high-temperature and high-humidity heat environment, stress due to contraction of the polarizing plate concentrates and induces birefringence of the polarizing plate, and the adhesive itself is oriented due to the stress concentration. Color unevenness (light leakage) occurs at the end where the light is concentrated. In order to prevent this, it is effective not to concentrate the stress of the pressure-sensitive adhesive, specifically to reduce the amount of the crosslinking agent, etc., but on the other hand, foaming at the interface between the polarizing plate and the glass or peeling of the polarizing plate, or Problems such as poor workability and reduced yield may occur. Therefore, conversely, a method of making the adhesive highly crosslinked and making the polarizing plate and the adhesive itself difficult to move is effective. However, in the case of high crosslinking, the relaxability and adhesiveness are lowered, so that the durability is inferior, and problems such as peeling are likely to occur under wet heat conditions.

  As a method for solving such a decrease in durability, a pressure-sensitive adhesive has been developed in which a UV curable monomer is mixed with a main polymer, applied to a polarizing plate, and then UV cured. A pressure-sensitive adhesive for a polarizing film obtained by adding a UV curable polyfunctional monomer, a photoinitiator, an isocyanate crosslinking agent and an epoxy crosslinking agent to a polymerized acrylic polymer and irradiating with UV has been proposed (Patent Document 1). However, when such a UV cross-linking pressure-sensitive adhesive is used, a UV irradiation device is required for the polarizing plate coating line, and the performance changes depending on irradiation conditions, or a separator that forms a pressure-sensitive adhesive sheet by UV light. There is a risk that problems such as cost and quality may occur due to adverse effects on such materials.

  On the other hand, by using a cross-linking agent having a positive intrinsic birefringence such as an isocyanate-based cross-linking agent, the photoelastic coefficient of the pressure-sensitive adhesive is set to a positive value, thereby adjusting birefringence caused by stress concentration and preventing light leakage. A technique is disclosed (Patent Document 2). However, although this technique can provide a certain light leakage prevention effect, it has not been practically sufficient.

JP 2008-31212 A JP 2008-144126 A

  Therefore, a pressure-sensitive adhesive composition for a polarizing plate that can effectively prevent light leakage without causing foaming or peeling even under severe use environment is desired, and the present invention has such durability and It is an object of the present invention to provide a pressure-sensitive adhesive composition for polarizing plates that has an effect of preventing light leakage.

  As a result of intensive investigations to solve the above-mentioned problems, the present inventors have obtained an acrylic polymer obtained by copolymerizing a carboxyl group-containing monomer having a specific range of molecular weight and dispersity (Mw / Mn) with an epoxy crosslinking agent. By adding a specific amount of an isocyanate compound, it was found that excellent durability and a high light leakage prevention effect were obtained, and the present invention was completed.

That is, the present invention
Next component (A) thru | or (C)
(A) It is obtained by polymerizing a monomer mixture containing 1 to 8% by mass of a carboxyl group-containing monomer, and has a weight average molecular weight of 250,000 to 600,000 and a weight average molecular weight (M
The ratio (Mw / Mn) of w) to the number average molecular weight (Mn) is 3.5 or less (meth)
Acrylic polymer 100 parts by mass (B) Epoxy cross-linking agent 0.01 to 10 parts by mass (C) An isocyanate compound 6 to 20 parts by mass.

  Moreover, this invention is a polarizing plate which provides the adhesive layer formed from the said adhesive composition for polarizing plates on the at least one surface of a polarizing film.

  The pressure-sensitive adhesive composition of the present invention can effectively prevent the occurrence of light leakage even under high-temperature and high-humidity conditions by using this for a polarizing plate, and has excellent durability and a pressure-sensitive adhesive layer. It is possible to suppress the occurrence of foaming or peeling. Furthermore, this pressure-sensitive adhesive layer is highly transparent without whitening.

  The acrylic polymer of component (A) used in the pressure-sensitive adhesive composition for polarizing plates of the present invention is obtained by polymerizing a monomer mixture containing at least a carboxyl group-containing monomer.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, 2-carboxyethyl (meth) acrylate, 3-carboxypropyl (meth) acrylate, 4-carboxybutyl (meth) acrylate, itaconic acid, crotonic acid, maleic acid, Examples thereof include fumaric acid and maleic anhydride.

  The content of the carboxyl group-containing monomer in the monomer mixture is 1 to 8% by mass (hereinafter referred to as “%”), preferably 1.5 to 6%. If it is less than 1%, the number of crosslinking points is small, so that the gel fraction is lowered and wet heat durability may be lowered and light leakage may occur. If it is more than 8%, the crosslinking density becomes too high. Since there are too many carboxyl groups not involved, there is a risk that the adhesive force will increase and the reworkability will deteriorate, or the adhesiveness will decrease and peeling will occur.

  Other constituent monomers of the acrylic polymer of component (A) include (meth) acrylic acid alkyl ester, hydroxyl group-containing monomer, benzene ring-containing monomer, (meth) acrylic acid alkoxy ester, amino group-containing monomer, amide-containing monomer, etc. Is mentioned.

  As said (meth) acrylic-acid alkylester, what has a C1-C12 alkyl group which may be branched is preferable, and, specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl ( (Meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl ( Examples include meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, and lauryl (meth) acrylate. Of these, butyl acrylate and methyl acrylate are preferably used because of a good balance between adhesive strength and durability.

  The content of the (meth) acrylic acid alkyl ester in the monomer mixture is 50 to 99%, preferably 60 to 98.5%. If it is less than 50%, the balance between the adhesive strength and the durability may not be achieved, and if it exceeds 99%, the durability may be deteriorated.

  The hydroxyl group-containing monomer can form an appropriate crosslinked structure by copolymerization thereof. Specifically, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, Examples include 1,4-cyclohexanedimethanol mono (meth) acrylate, chloro-2-hydroxypropyl acrylate, diethylene glycol mono (meth) acrylate, and allyl alcohol. Of these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferably used in terms of good copolymerizability with the (meth) acrylic acid alkyl ester.

  The content of the hydroxyl group-containing monomer in the monomer mixture is 0 to 0.5%, preferably 0 to 0.3%. If it exceeds 0.5%, it will react with the isocyanate compound described later to form an excessive cross-linked structure, and the balance between adhesive strength and durability will not be achieved, or the reaction between the isocyanate compounds described later will be inhibited. The effect may not be obtained.

  The benzene ring-containing monomer has positive intrinsic birefringence, and the birefringence of the (meth) acrylic polymer can be reduced by copolymerizing the monomer. Specifically, phenyl acrylate, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate, hydroxyethylated β-naphthol acrylate, biphenyl (meth) acrylate , Styrene, vinyltoluene, α-methylstyrene and the like. Of these, benzyl acrylate and phenoxyethyl acrylate are preferably used in that they have good compatibility and copolymerization with (meth) acrylic acid alkyl esters and do not deteriorate transparency.

  The content of the benzene ring-containing monomer in the monomer mixture is 0 to 40%, preferably 0 to 30%. If it exceeds 40%, the benzene ring-containing monomer has a relatively high glass transition temperature, so that the pressure-sensitive adhesive coating film becomes hard and the stress relaxation property decreases, or due to the steric hindrance of the benzene ring, This is not preferable because it is thought to inhibit the formation of an IPN structure with polyurea, which is a reaction product of an isocyanate compound.

  Examples of the (meth) acrylic acid alkoxy ester include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-methoxypropyl (meth) acrylate, and 3-methoxypropyl (meth) acrylate. And 2-methoxybutyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, and the like.

  Examples of the amino group-containing monomer include dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate.

  Examples of the amide-containing monomer include (meth) acrylamide and (meth) N-methylolacrylamide. These amino group-containing monomers and amide group-containing monomers, such as monomers having functional groups that react with epoxy crosslinking agents, may cause excessive crosslinking of the (meth) acrylic polymer. Can be used as appropriate in consideration of the amount used.

  Component (A) of the present invention is produced by polymerizing a monomer mixture containing the above monomer components by a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, a suspension polymerization method, or the like. Can do. Among these, those produced by a solution polymerization method or a bulk polymerization method that does not contain a polymerization stabilizer such as an emulsifier and a suspending agent are more preferable.

  The weight average molecular weight (Mw) of the component (A) obtained as described above is 25 to 600,000, preferably 300 to 500,000. If the weight average molecular weight is less than 250,000, sufficient cohesive force of the pressure-sensitive adhesive layer may not be obtained, and light leakage may occur or durability may be lowered. Since compatibility with polyurea, which is a product, decreases, whitening is likely to occur. In addition, in this specification, a weight average molecular weight means the value calculated | required by the measuring method described in the Example.

  In addition, the ratio (Mw / Mn; degree of dispersion) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the component (A) is 3.5 or less, preferably 3.2 or less. When the ratio is larger than 3.5, a polymer having a relatively low weight average molecular weight of Mw 250,000 to 600,000 as in the present invention results in an excessive increase in the amount of low molecular weight, resulting in deterioration of light leakage. The number average molecular weight (Mn) of the component (A) is also a value determined by the measurement method described in the examples.

  The epoxy crosslinking agent of component (B) used in the present invention includes bisphenol A epichlorohydrin type epoxy resin, ethylene diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6- Hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N ′ -A compound having two or more epoxy groups in a molecule such as diamineglycidylaminomethyl) cyclohexane. Among these, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N′-diamineglycidylaminomethyl) cyclohexane has good reactivity and well-balanced crosslinking. Since a structure can be formed, it is preferably used.

  The compounding quantity of the component (B) in the adhesive composition for polarizing plates of this invention is 0.01-10 parts with respect to 100 mass parts (henceforth "part" only) of a component (A). And preferably 0.02 to 1 part. When the amount is less than 0.01 part, the formation of the crosslinked structure becomes insufficient, the durability is deteriorated, and light leakage occurs. On the other hand, when the amount is more than 10 parts, the crosslink density becomes too high, the adhesive force is increased and the adhesiveness is lowered, and the adhesiveness and durability cannot be balanced.

  Examples of the isocyanate compound of component (C) used in the present invention include tolylene diisocyanate, xylylene diisocyanate, chlorophenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate. Compounds having two isocyanate groups in the molecule; isocyanate compounds, isocyanurate compounds, burette type compounds obtained by addition reaction of these with polyhydric alcohols such as trimethylolpropane and pentaerythritol, and further known polyether polyols and polyesters Addition reaction with polyol, acrylic polyol, polybutadiene polyol, polyisoprene polyol, etc. It may be mentioned derivatives of the isocyanate compound or the like of the urethane prepolymer type. Among these, tolylene diisocyanate compounds including tolylene diisocyanate (TDI) and derivatives thereof are preferably used because they have low reactivity with carboxyl groups and hardly participate in the formation of crosslinks of (meth) acrylic polymers.

  The compounding quantity of the component (C) in the adhesive composition for polarizing plates of this invention is 6-20 parts with respect to 100 parts of components (A), Preferably it is 8-16 parts. If it is less than 6 parts, light leakage cannot be improved, and if it exceeds 20 parts, the isocyanate compound reacts with the carboxyl group of the (meth) acrylic polymer to form an excessive cross-linked structure, The reaction product is not taken into the (meth) acrylic polymer cross-linked structure, causing problems such as bleeding, and the balance between adhesive force and durability deteriorates.

  The pressure-sensitive adhesive composition for polarizing plates of the present invention preferably further contains a silane coupling agent (D) containing a group that reacts with a carboxyl group contained in the acrylic polymer of component (A). By using this, the pressure-sensitive adhesive can be firmly adhered to the glass, and peeling can be prevented in a humid heat environment. Specifically, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4 epoxy cyclohexyl) ethyltrimethoxysilane, etc. And an amino group-containing silane coupling agent such as 3-aminopropyltrimethoxysilane and N-2 (aminoethyl) 3-aminopropyltrimethoxysilane.

  The compounding quantity of the silane coupling agent (D) in the adhesive composition for polarizing plates of this invention is 0.05-1 part with respect to 100 parts of components (A), Preferably it is 0.1-0. 5 parts. If it is less than 0.05 part, peeling is likely to occur in a moist heat environment, and if it is more than 1 part, the silane coupling agent bleeds in a high temperature environment, and conversely, peeling is liable to occur.

  The polarizing plate pressure-sensitive adhesive composition of the present invention is prepared by blending the above components (A) to (C) and, if necessary, the component (D) and other optional components, and mixing them according to a conventional method. . Examples of optional components that can be used include antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, and the like, and these can be blended as long as the effects of the present invention are not impaired.

  In order to obtain the polarizing plate pressure-sensitive adhesive sheet of the present invention from the polarizing plate pressure-sensitive adhesive composition thus obtained, the pressure-sensitive adhesive composition was applied to at least one surface on the support according to a conventional method, and after coating, The pressure-sensitive adhesive layer may be formed by drying and crosslinking treatment. As the support, a polyester film having a surface peel-treated can be used. The thickness of an adhesive layer is 10-30 micrometers normally, Preferably it is about 15-25 micrometers.

  Moreover, the polarizing plate of this invention can be obtained by providing the adhesive layer formed from the said adhesive composition for polarizing plates in at least one surface of a polarizing film. The thickness of the pressure-sensitive adhesive layer provided on the polarizing film is usually 10 to 30 μm, preferably about 15 to 25 μm.

  In providing the pressure-sensitive adhesive layer on the polarizing film, the pressure-sensitive adhesive composition is applied on the polarizing film and dried or aged, or the coated film dried on the support is pasted onto the polarizing film, An adhesive layer can be formed by aging this. The gel fraction of the pressure-sensitive adhesive layer after aging is preferably 80 to 99%, more preferably 90 to 97%. If it is lower than 80%, light leakage may occur due to insufficient cohesion.

  Moreover, as a polarizing film used for this invention, the layer which has another function may be laminated | stacked, and an ellipse polarizing film, retardation film, etc. are specifically included.

  The type of the liquid crystal element in which the polarizing plate of the present invention obtained as described above is used is not particularly limited, and any of TN mode, VA mode, IPS mode, OCB mode, and the like may be used.

  The polarizing plate pressure-sensitive adhesive composition of the present invention has excellent light leakage prevention properties and durability, and the reason is considered as follows. That is, since the epoxy group of the epoxy crosslinking agent (B) reacts faster than the isocyanate group of the isocyanate compound (C) with respect to the carboxyl group in the acrylic polymer (A), the acrylic polymer (A) is It is mainly crosslinked with an epoxy crosslinking agent (B). In contrast, the isocyanate compound (C) reacts with moisture that has migrated from the substrate or the substrate or the adherend to the pressure-sensitive adhesive layer, and forms polyurea with little bonding to the acrylic polymer (A). . It is presumed that this polyurea has an IPN (interpenetrating network polymer) structure that is intertwined with the acrylic polymer (A) and is different from simple hypercrosslinking.

  This point is supported by the photoelastic coefficient. That is, when the isocyanate compound is bonded to the acrylic polymer (A), the photoelastic coefficient increases with an increase in the addition amount of the isocyanate compound, but the pressure-sensitive adhesive composition of the present invention increases the addition amount of the isocyanate compound. However, the photoelastic coefficient hardly changes. On the other hand, even if the acrylic polymer (A) and polyurea are simply mixed, they are not mixed uniformly. Therefore, the acrylic polymer (A) and polyurea have an IPN structure, and this structure suppresses the movement of the adhesive while maintaining the adhesive performance, so it has excellent durability and excellent light leakage prevention. It is considered that an effect can be obtained.

  In forming such an IPN structure, if the acrylic polymer (A) has a high molecular weight, the movement of the polyurea is suppressed. On the other hand, if the acrylic polymer (A) has a large number of low molecular weight substances, the polyurea is added to the acrylic polymer (A). Although the entanglement is inhibited, in the present invention, the weight average molecular weight (Mw) and the dispersity (Mw / Mn) of the acrylic polymer (A) are in a specific range, so that these are appropriately entangled efficiently. It is assumed that an IPN structure is formed. Furthermore, when the isocyanate compound (C) is excessively mixed with the acrylic polymer (A), it tends to be whitened due to the difference in compatibility. In the present invention, the weight average molecular weight of the acrylic polymer (A) is set to a specific range. This is considered to suppress whitening.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples.

Manufacturing example 1
Acrylic polymer production:
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 97.8 parts by weight of butyl acrylate, 2 parts by weight of acrylic acid, 0.2 parts by weight of 2-hydroxyethyl acrylate, 50 parts by weight of ethyl acetate Then, 0.1 part by weight of normal dodecyl mercaptan (NDM) was charged, and the contents of the flask were heated to 60 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part by mass of a polymerization initiator azobisisobutyronitrile (AIBN) sufficiently substituted with nitrogen gas was added to the flask under stirring. Heating and cooling were performed for 10 hours so that the temperature of the contents in the flask could be maintained at 60 ° C., and finally 150 parts of ethyl acetate was added to obtain an acrylic polymer A1 solution. About this acrylic polymer A1, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured according to the following GPC measurement conditions, and dispersity (Mw / Mn) was determined. Further, the nonvolatile content (nV) and viscosity were also measured by the following methods. The measurement results are shown in Table 1 together with the monomer composition.

<GPC measurement conditions>
Measuring device: HLC-8120GPC (manufactured by Tosoh Corporation)
GPC column configuration: The following five columns (all manufactured by Tosoh Corporation)
(1) TSK-GEL HXL-H (guard column)
(2) TSK-GEL G7000HXL
(3) TSK-GEL GMHXL
(4) TSK-GEL GMHXL
(5) TSK-GEL G2500HXL
Diluted with tetrahydrofuran so that the sample concentration is 1.0 mg / cm ³ Mobile phase solvent: Tetrahydrofuran Flow rate: 1 ml / min
Column temperature: 40 ° C

<Measurement method of non-volatile content>
About 1 g of the acrylic copolymer solution was placed in a precisely weighed tin plate (n1), the total weight (n2) was precisely weighed, and then heated at 105 ° C. for 3 hours. Thereafter, the tin plate was allowed to stand in a desiccator at room temperature for 1 hour, and then precisely weighed again to measure the total weight (n3) after heating. The nonvolatile content was calculated from the following formula using the obtained weight measurement values (n1 to n3).
Nonvolatile content (%) = 100 × [weight after heating (n3-n1) / weight before heating (n2-n1)]

<Measurement method of viscosity>
Measurement was performed at room temperature using a B-type viscometer.

Manufacturing example 2
An acrylic polymer A2 solution was obtained in the same manner as in Production Example 1 except that the blending amounts of butyl acrylate and acrylic acid were changed to 95.4 parts by mass and 4 parts by mass, respectively. Mw, Mn, nonvolatile content and viscosity of this polymer were measured in the same manner as in Production Example 1. The results are shown in Table 1.

Manufacturing example 3
An acrylic polymer A3 solution was obtained in the same manner as in Production Example 1 except that the monomer composition was changed to 92.95 parts by mass of butyl acrylate, 7 parts by mass of acrylic acid, and 0.05 parts by mass of 2-hydroxyethyl acrylate. Mw, Mn, nonvolatile content and viscosity of this polymer were measured in the same manner as in Production Example 1. The results are shown in Table 1.

Manufacturing example 4
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 67.8 parts by mass of butyl acrylate, 25 parts by mass of benzyl acrylate, 3 parts by mass of phenoxyethyl acrylate, 4 parts by mass of acrylic acid, 2-hydroxy 0.2 parts by mass of ethyl acrylate, 0.1 part by mass of NDM and 70 parts by mass of ethyl acetate were added, and the contents of the flask were heated to 60 ° C. while introducing nitrogen gas. Subsequently, 0.1 mass part of AIBN as an initiator was added into the flask under stirring with sufficient nitrogen gas replacement. Heating and cooling were carried out for 10 hours so that the temperature of the contents in the flask could be maintained at 60 ° C., and finally 110 parts of ethyl acetate was added to obtain an acrylic polymer A4 solution. About this polymer, it carried out similarly to manufacture example 1, and measured Mw, Mn, the non volatile matter, and the viscosity. The results are shown in Table 1.

Comparative production example 1
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 95.8 parts by mass of butyl acrylate, 4 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, 90 parts by mass of ethyl acetate The flask contents were heated to 60 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part by mass of AIBN sufficiently substituted with nitrogen gas was added to the flask with stirring. Heating and cooling were performed for 5 hours so that the temperature of the contents in the flask could be maintained at 60 ° C, and then the temperature was raised to 65 ° C and stirred for 4 hours. Finally, 110 parts of ethyl acetate was added to obtain an acrylic polymer B1 solution. About this polymer, it carried out similarly to manufacture example 1, and measured Mw, Mn, the non volatile matter, and the viscosity. The results are shown in Table 1.

Comparative production example 2
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 95.5 parts by mass of butyl acrylate, 0.5 parts by mass of acrylic acid, 4 parts by mass of 2-hydroxyethyl acrylate, 90 parts by mass of ethyl acetate And the contents of the flask were heated to 70 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part by mass of AIBN sufficiently substituted with nitrogen gas was added to the flask with stirring. Heating and cooling were carried out for 10 hours so that the temperature of the contents in the flask could be maintained at 60 ° C., and finally 110 parts of ethyl acetate was added to obtain an acrylic polymer B2 solution. About this polymer, it carried out similarly to manufacture example 1, and measured Mw, Mn, the non volatile matter, and the viscosity. The results are shown in Table 1.

Comparative production example 3
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 95.8 parts by mass of butyl acrylate, 4 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, 0.2 parts of NDM, 50 parts by mass of ethyl acetate was charged, and the contents of the flask were heated to 60 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part by mass of AIBN sufficiently substituted with nitrogen gas was added to the flask with stirring. Heating and cooling were carried out for 10 hours so that the temperature of the contents in the flask could be maintained at 60 ° C., and finally 150 parts of ethyl acetate was added to obtain an acrylic polymer B3 solution. About this polymer, it carried out similarly to manufacture example 1, and measured Mw, Mn, the non volatile matter, and the viscosity. The results are shown in Table 1.

Comparative production example 4
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 95.8 parts by mass of butyl acrylate, 4 parts by mass of acrylic acid, 0.2 parts by mass of 2-hydroxyethyl acrylate, 50 parts by mass of ethyl acetate The flask contents were heated to 60 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part by mass of AIBN sufficiently substituted with nitrogen gas was added to the flask with stirring. Heating and cooling were carried out for 10 hours so that the temperature of the contents in the flask could be maintained at 60 ° C., and finally 190 parts of ethyl acetate was added to obtain an acrylic polymer B4 solution. About this polymer, it carried out similarly to manufacture example 1, and measured Mw, Mn, the non volatile matter, and the viscosity. The results are shown in Table 1.

Example 1
Production of polarizing plate having an adhesive layer:
(Preparation of adhesive composition)
8 parts by mass of TDI coronate L (manufactured by Nippon Polyurethane Co., Ltd.) as an isocyanate compound with respect to 100 parts by mass of acrylic polymer A1 (solid content) of the acrylic polymer A1 solution obtained in Production Example 1, an epoxy curing agent As tetrad X (Mitsubishi Gas Chemical Co., Ltd.) 0.2 parts by mass, and silane coupling agent as KBM-403 (Shin-Etsu Chemical Co., Ltd.) 0.2 parts by mass, and these are mixed well to produce an adhesive composition. I got a thing.

(Preparation of polarizing plate)
After defoaming, it was applied to a peeled polyester film using a doctor blade and immediately dried at 90 ° C. for 3 minutes. After drying, it was pasted on a polarizing plate and allowed to stand for 7 days at room temperature of 23 ° C. and a humidity of 50% for aging to obtain a polarizing plate having an adhesive layer.

Examples 2-6, Comparative Examples 1-8
A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that the acrylic polymer, epoxy crosslinking agent and isocyanate compound were changed as shown in Table 2 below. Moreover, the polarizing plate which has an adhesive layer was produced like Example 1 using the obtained adhesive composition.

Test example 1
For the pressure-sensitive adhesive compositions and polarizing plates obtained in Examples 1 to 6 and Comparative Examples 1 to 8, the following evaluation methods were used for the adhesive strength, gel fraction, photoelastic coefficient, durability, light leakage prevention property, and the presence or absence of whitening. It was evaluated with. These results are summarized in Tables 2 and 3.

<Measurement method of adhesive strength>
A polarizing plate having an adhesive layer was cut into a size of 70 mm × 25 mm to prepare a test piece. After peeling the polyester film from the test piece and sticking it on one side of the glass plate using a laminator roll, it was kept in an autoclave adjusted to 50 ° C. and 5 atm for 20 minutes. Next, after being left in an environment of 23 ° C. and 50% RH for 1 hour, the film was pulled in the 90 ° direction at a speed of 300 mm / min, and the peel strength was measured.

<Method for measuring gel fraction>
The obtained pressure-sensitive adhesive composition was applied to the surface of the polyester that had been subjected to a release treatment so that the thickness after drying was 20 μm, and after drying, the polyester film that had been subjected to the release treatment was laminated to the other surface, A test piece was prepared by aging for 7 days at 50% RH. About 0.1 g of adhesive was collected from the test piece into a sample bottle, 30 cc of ethyl acetate was added and shaken for 24 hours, and then the contents of the sample bottle were filtered off with a 200 mesh stainless steel wire, and the residue on the metal wire The product was dried at 100 ° C. for 2 hours, and the dry weight was measured.
Gel fraction (%) = (dry weight / weight of collected adhesive) × 100

<Measuring method of photoelastic coefficient>
The obtained pressure-sensitive adhesive composition was applied onto a release-treated polyester film so that the thickness after drying was 125 μm, and dried at 80 ° C. for 2 minutes to prepare a pressure-sensitive adhesive film. Two pressure-sensitive adhesive films were laminated together with the pressure-sensitive adhesive layers. Using the obtained pressure-sensitive adhesive layer having a thickness of 250 μm, the same operation was further repeated to prepare a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer thickness of 1 mm. The pressure-sensitive adhesive sheet was aged for 7 days in an environment of 23 ° C. and 50% RH to prepare a test piece. The test piece is cut into a size of 15 mm × 50 mm, and this is attached to a photoelasticity measuring apparatus M-220 (Ellipsometer manufactured by Otsuka Electronics Co., Ltd.) using a jig, and the retardation is measured at a measurement wavelength of 633 nm while changing the stress. did. The slope when the stress is plotted on the horizontal axis and the retardation is plotted on the vertical axis is the photoelastic coefficient.

<Durability evaluation method>
A polarizing plate having an adhesive layer is cut into a size of 150 mm × 250 mm, stuck on one side of a glass plate using a laminator roll, and then held in an autoclave adjusted to 50 ° C. and 5 atm for 20 minutes. A test plate was prepared. Two similar test plates were prepared and left for 500 hours under conditions of a temperature of 60 ° C. and a humidity of 95% RH and for 500 hours under a temperature of 85 ° C., respectively. It was visually observed and evaluated.
(Standard)
○: Foaming, peeling, cracks are not seen △: Foaming, peeling, cracks are slightly seen ×: Foaming, peeling, cracks are seen over the entire surface

<Evaluation method for light leakage prevention>
Two polarizing plates having a pressure-sensitive adhesive layer were attached to the front and back surfaces of a 19-inch wide TN monitor (model number: BenQ FP93VW) using a laminator roll so as to be mutually orthogonal Nicol positions, and then 50 ° C., 5 atm. A test plate was prepared by holding in an autoclave adjusted to 20 minutes for 20 minutes. The prepared test plate was allowed to stand for 500 hours at 70 ° C., and light leakage was visually observed and evaluated according to the following criteria.
(Standard)
○: No light leakage is observed △: Light leakage is partially observed ×: Light leakage is observed on the entire surface

<Evaluation method of whitening>
The obtained pressure-sensitive adhesive composition was applied onto a polyester film that had been subjected to a release treatment so that the thickness after drying was 20 μm. After drying at 80 ° C. for 2 minutes, the pressure-sensitive adhesive coating film was visually observed.

In Comparative Examples 1 and 3 where the amount of the isocyanate compound used is small, light leakage cannot be sufficiently suppressed, and in Comparative Example 2 where no epoxy crosslinking agent is used, the isocyanate compound reacts with the (meth) acrylic polymer. Since the cross-linked structure is formed, the effect of the present invention cannot be obtained and light leakage cannot be suppressed.
In Comparative Example 5 in which the molecular weight distribution of the (meth) acrylic polymer is wide and Comparative Example 7 in which the weight average molecular weight is small, there are many low molecular weight substances, and there is little entanglement of the polymer chain with polyurea, and the cohesive force is also reduced. Therefore, light leakage cannot be effectively suppressed, and in Comparative Example 8 having a large weight average molecular weight, the compatibility between the polyurea and the polymer is deteriorated. Therefore, the adhesive force is decreased due to whitening of the coating film or bleeding of the polyurea. Arise.

In general, when an isocyanate compound having an aromatic ring is added, the photoelastic coefficient increases in the positive direction. Further, when the polymer is crosslinked with such an isocyanate compound, the orientation of the polymer is controlled, so that the photoelastic coefficient is remarkable. It is known to increase.
In this example, although a large amount of an isocyanate compound was added, the photoelastic coefficient hardly increased except for Example 6 in which a benzene ring-containing monomer was copolymerized. This is thought to be because the isocyanate compound hardly participates in the crosslinking of the polymer, forms polyurea by the reaction between the isocyanate compounds, and has an IPN structure with the (meth) acrylic polymer chain. By adopting a simple structure, sufficient light leakage resistance is obtained.

The pressure-sensitive adhesive composition of the present invention effectively prevents light leakage, has excellent durability, and can suppress the occurrence of foaming and peeling even under high temperature and high humidity conditions. Therefore, this can be suitably used as a pressure-sensitive adhesive composition for polarizing plates.
that's all

Claims (6)

Next component (A) thru | or (C)
(A) It is obtained by polymerizing a monomer mixture containing 1 to 8% by mass of a carboxyl group-containing monomer, and has a weight average molecular weight of 250,000 to 600,000 and a weight average molecular weight (M
The ratio (Mw / Mn) of w) to the number average molecular weight (Mn) is 3.5 or less (meth)
100 mass parts of acrylic polymers (B) 0.01-10 mass parts of epoxy crosslinking agents (C) 6-20 mass parts of isocyanate compounds, The adhesive composition for polarizing plates characterized by the above-mentioned.   The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the monomer mixture contains 50 to 99 mass% of (meth) acrylic acid alkyl ester.   The pressure-sensitive adhesive composition for polarizing plates according to claim 1 or 2, wherein the isocyanate compound is tolylene diisocyanate and derivatives thereof.   The pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 3, further comprising a component (D) a silane coupling agent.   The adhesive sheet for polarizing plates which provides the adhesive layer formed from the adhesive composition for polarizing plates in any one of Claims 1 thru | or 4 in the at least one surface of a support body.   The polarizing plate which provides the adhesive layer formed from the adhesive composition for polarizing plates of Claim 1 thru | or 4 on the at least one surface of a polarizing film.