Pressure-sensitive adhesive composition for polarizing plates, and pressure-sensitive adhesive for polarizing plates, pressure-sensitive adhesive sheet for polarizing plates, pressure-sensitive adhesive layer-attached polarizing plate, and image display device using the same

Abstract

To provide an adhesive composition for a polarizing plate comprising an acrylic resin and an ionic compound, and for forming an adhesive which has excellent long-term reworkability, causes no peeling even under a high temperature, humidity and a thermal shock environment and has excellent durability and antistatic property.SOLUTION: There is provided an adhesive composition for a polarizing plate which comprises an acrylic resin (A) having a weight-average molecular weight of 500,000 or more and less than 1,000,000 and an ionic compound (B), wherein the adhesive composition contains, as a polymerization component (a), 4 to 10 wt.% of a hydroxyl group-containing monomer (a1), 0.9 to 2.5 wt.% of a carboxy group-containing monomer (a2) and 5 to 10.5 wt.% of the hydroxyl group-containing monomer (a1) and the carboxy group-containing monomer (a2) in total.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition for polarizing plates, a pressure-sensitive adhesive for polarizing plates obtained using the pressure-sensitive adhesive composition for polarizing plates, and an image display device using the pressure-sensitive adhesive for polarizing plates. In particular, the present invention relates to a pressure-sensitive adhesive composition for polarizing plates that can provide a pressure-sensitive adhesive layer that is excellent in all of long-term reworkability, durability, and antistatic properties, and a pressure-sensitive adhesive for polarizing plates, a pressure-sensitive adhesive sheet for polarizing plates, a pressure-sensitive adhesive layer-attached polarizing plate, and an image display device that use the same. [Background technology]

[0002] Liquid crystal display devices are widely used as image display devices in liquid crystal televisions, computer displays, mobile phones, digital cameras, etc. Such liquid crystal display devices are configured such that polarizing plates are laminated on both sides of a glass substrate (liquid crystal cell) in which liquid crystal is sealed, and various optical elements such as retardation plates are further laminated as necessary.

[0003] In the manufacture of a liquid crystal display device, a pressure-sensitive adhesive layer containing an acrylic resin is typically provided on a release-treated film, and the surface of the pressure-sensitive adhesive layer opposite the release film is attached to a polarizing plate to produce a pressure-sensitive adhesive layer-attached polarizing plate.When attaching the polarizing plate to a liquid crystal cell, the release film is then peeled off and the pressure-sensitive adhesive layer and the glass substrate of the liquid crystal cell are attached to produce the polarizing plate.

[0004] Such polarizing plate adhesives used to bond a polarizing plate to the glass substrate of a liquid crystal cell are required to have removability (reworkability) that allows the polarizing plate to be easily peeled off from the liquid crystal cell without leaving any adhesive residue on the glass substrate, so that the polarizing plate can be peeled off from the liquid crystal cell and the liquid crystal cell can be reused if the bonding position is incorrect or if foreign matter is mixed in when bonding the polarizing plate to the liquid crystal cell.

[0005] Furthermore, adhesives for polarizing plates are required to have high durability so that the polarizing plate does not lift or peel off from the glass substrate even in high temperature environments (85°C dry), high temperature and high humidity environments (65°C 90% RH), and thermal shock environments (-30 ←→ 80°C cycles).

[0006] On the other hand, because liquid crystal cells are driven by controlling voltage, static electricity can cause problems such as display unevenness and breakdowns. Static electricity is easily generated when the adhesive layer, polarizing plate, and glass substrate of the liquid crystal cell are attached to or peeled off from each other, so adhesives are required to have antistatic properties.

[0007] A commonly known method for satisfying all of the above-mentioned reworkability, durability, and antistatic performance is to use an acrylic resin with a weight-average molecular weight of 1 million or more and add an ionic liquid, among other ionic compounds (see, for example, Patent Document 1). This method uses a high-molecular-weight acrylic resin with a molecular weight of 1 million or more to impart cohesive strength to the adhesive, ensuring reworkability and durability, and also forms an adhesive layer that can withstand the deterioration in durability caused by plasticization by the ionic liquid.

[0008] When an acrylic resin with a weight-average molecular weight of 1 million or more is used, the viscosity of the adhesive composition becomes high and handling becomes difficult, so it is used by diluting it with an organic solvent to reduce the solid content to 20% by weight or less. However, in recent years, growing awareness of environmental issues has made it necessary to reduce emissions of volatile organic compounds (VOCs), and there is also a demand for reducing the amount of organic solvent used in adhesives.

[0009] In response to this, Patent Document 2 proposes an adhesive composition in which a specific radical generator is added to a hydroxyl group-containing polymer having a solid content of 25% by weight or more and a weight average molecular weight of 500,000 to 1,000,000, thereby achieving a reduced amount of organic solvent used while maintaining excellent reworkability and durability, despite having a lower molecular weight than general adhesive compositions for polarizing plates. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2020-129103 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-57794 Summary of the Invention [Problem to be solved by the invention]

[0011] However, although the adhesive described in Patent Document 2 achieves both durability and reworkability as well as high solids content of the adhesive solution, the use of peroxide as a radical generator raises concerns about the stability of the formulation over time. In addition, while low-molecular-weight ionic compounds are typically added to adhesives for polarizing plates to impart antistatic properties, adding such compounds to low-molecular-weight acrylic resins with a weight-average molecular weight of less than 1 million causes more pronounced plasticization than adding such compounds to acrylic resins with a weight-average molecular weight of 1 million or more, resulting in a deterioration in durability and reworkability. Therefore, simply adding an ionic compound to Patent Document 2 makes it difficult to satisfy all of the requirements for durability, reworkability, and antistatic properties.

[0012] Therefore, under such circumstances, the present invention aims to provide a pressure-sensitive adhesive composition for polarizing plates that is excellent in all of long-term reworkability, durability, and antistatic properties, and a pressure-sensitive adhesive for polarizing plates, a pressure-sensitive adhesive sheet for polarizing plates, a polarizing plate with a pressure-sensitive adhesive layer, and an image display device that use the same. [Means for solving the problem]

[0013] In view of the above circumstances, the present inventors have conducted extensive research. In general, in a pressure-sensitive adhesive composition containing an acrylic resin, a common method for decreasing the solution viscosity and increasing the solid content is to decrease the weight-average molecular weight of the acrylic resin. Known methods for improving the durability of pressure-sensitive adhesive compositions include copolymerizing a monomer (high Tg monomer) used in the polymerization of an acrylic resin, the monomer having a glass transition temperature (Tg) of 0°C or higher, and copolymerizing a monomer having a polar functional group (hydroxyl group or carboxyl group). From the above, one method for achieving low solution viscosity, high solid content, and high durability is to use an acrylic resin with a low weight-average molecular weight and containing a high Tg monomer or a polar functional monomer as a copolymerization component. However, if an acrylic resin with a low weight-average molecular weight is simply copolymerized with a high Tg monomer, the entire pressure-sensitive adhesive layer will harden, reducing adhesion and resulting in peeling under high temperature conditions. Furthermore, if an acrylic resin with a low weight-average molecular weight is copolymerized with a polar functional group, the cohesive strength of the pressure-sensitive adhesive layer cannot be ensured, and the increased adhesion to the glass surface will result in poor reworkability. Furthermore, when an ionic compound is added to an acrylic resin having a low weight-average molecular weight in order to impart antistatic properties, significant plasticization occurs, resulting in problems such as deterioration of durability and reworkability.

[0014] The present inventors have discovered that a pressure-sensitive adhesive that is excellent in all of reworkability, durability, and antistatic properties can be obtained by using polar functional groups as copolymerization components in amounts that would normally be expected to deteriorate reworkability for acrylic resins with a weight-average molecular weight of less than 1,000,000, which would normally not provide sufficient cohesive strength and which, when containing ionic compounds, would further deteriorate reworkability and durability, but by using hydroxyl group and carboxyl group amounts within specific ranges, respectively, and have completed the present invention.

[0015] That is, the gist of the present invention is as follows. <1> A pressure-sensitive adhesive composition for polarizing plates, comprising an acrylic resin (A) having a weight average molecular weight of 500,000 or more and less than 1,000,000 and an ionic compound (B), A pressure-sensitive adhesive composition for polarizing plates, comprising, as polymerization components (a) of an acrylic resin (A), 4 to 10% by weight of a hydroxyl group-containing monomer (a1), 0.9 to 2.5% by weight of a carboxyl group-containing monomer (a2), and 5 to 10.5% by weight of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) in total. <2> The content of the ionic compound (B) is 2 to 30 parts by weight relative to 100 parts by weight of the acrylic resin (A). <1> The pressure-sensitive adhesive composition for polarizing plates according to claim 1. <3> Further, the composition is characterized in that it contains a crosslinking agent (C). <1> or <2> The pressure-sensitive adhesive composition for polarizing plates according to claim 1. <4> The composition further comprises a silane coupling agent (D). <1> ~ <3> 10. The pressure-sensitive adhesive composition for polarizing plates according to any one of the preceding items. <5> <1> ~ <4> 10. A pressure-sensitive adhesive for polarizing plates, which is formed from the pressure-sensitive adhesive composition for polarizing plates according to any one of the preceding claims. <6> <5> 10. A pressure-sensitive adhesive sheet for polarizing plates, comprising a pressure-sensitive adhesive layer for polarizing plates, the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive for polarizing plates according to claim 10. <7> <5> 10. A pressure-sensitive adhesive layer-attached polarizing plate, comprising a pressure-sensitive adhesive layer for a polarizing plate, the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive for a polarizing plate according to claim 1, and a polarizing plate laminated thereon. <8> The polarizing plate and the liquid crystal cell <5> 10. An image display device comprising a polarizing plate bonded together with the pressure-sensitive adhesive for polarizing plates according to claim 1. [Effects of the Invention]

[0016] The pressure-sensitive adhesive for polarizing plates of the present invention is a pressure-sensitive adhesive that is excellent in all of reworkability, durability, and antistatic properties despite having a low weight-average molecular weight of 500,000 or more and less than 1,000,000, and is therefore very useful as a pressure-sensitive adhesive for polarizing plates. Therefore, by using this pressure-sensitive adhesive composition for polarizing plates, not only is the long-term reworkability excellent, but the obtained pressure-sensitive adhesive sheet for polarizing plates, pressure-sensitive adhesive layer-attached polarizing plate, and image display device also have excellent durability and antistatic properties. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below. In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate. Furthermore, "acrylic resin" refers to a resin obtained by polymerizing a polymerization component containing at least one (meth)acrylate monomer. The "side chain structural portion of the acrylic resin" refers to a structural portion derived from alcohol in an ethylenically unsaturated group-containing ester contained in a polymerization component of the acrylic resin.

[0018] The "weight average molecular weight" and "number average molecular weight" are weight average molecular weights converted into standard polystyrene molecular weights. The samples were analyzed using a high performance liquid chromatograph (Waters Japan, "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 7 Separation range: 100 to 2 × 10 7 The measurement is performed using three columns in series (theoretical plate number: 10,000 columns / column, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm). The "dispersity" is determined by the weight average molecular weight / number average molecular weight.

[0019] The "glass transition temperature" is calculated from the types and mass fractions of the monomer units constituting the copolymer using the following Fox equation. In this specification, the glass transition temperature calculated using the Fox equation is also referred to as the "calculated glass transition temperature." 1 / (273+Tg)=Σ{Wi / (273+Tgi)} In the formula, Tg is the glass transition temperature (°C) of the copolymer, Wi is the weight fraction of the monomer units derived from monomer i that constitute the copolymer, and Tgi is the glass transition temperature (°C) of the homopolymer of monomer i. Tgi is usually measured by a differential scanning calorimeter (DSC) and can be measured by a method in accordance with JIS K7121-1987 or JIS K 6240. In addition, when the value of Tgi is described in the Polymer Handbook [Polymer Handbook, J. Brandrup, Interscience, 1989], this value can also be used to determine the value.

[0020] [Adhesive composition for polarizing plate] The pressure-sensitive adhesive composition for polarizing plates of the present invention contains an acrylic resin (A) and an ionic compound (B). First, the acrylic resin (A) will be described.

[0021] <Acrylic resin (A)> The acrylic resin (A) used in the present invention is a resin obtained by polymerizing a polymerization component (a), which contains at least a hydroxyl group-containing monomer (a1) and a carboxyl group-containing monomer (a2). In addition to the hydroxyl group-containing monomer and the carboxyl group-containing monomer, the polymerization component (a) preferably further contains a (meth)acrylic acid alkyl ester (a3), and optionally contains other polymerizable monomers (a4). Each of these monomers is described below. The acrylic resin (A) used in the present invention is a resin obtained by polymerizing a polymerization component (a) containing at least a hydroxyl group-containing monomer (a1) and a carboxyl group-containing monomer (a2), and therefore necessarily has a side chain structural portion.

[0022] [Hydroxyl group-containing monomer (a1)] Examples of the hydroxyl group-containing monomer (a1) include hydroxyalkyl acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth)acrylamide, and hydroxyethyl acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro-2-hydroxypropyl (meth)acrylate; and hydroxyl group-containing monomers such as 2,2-dimethyl-2-hydroxyethyl (meth)acrylate. These can be used alone or in combination of two or more.

[0023] Among the above hydroxyl group-containing monomers, primary hydroxyl group-containing monomers are preferred because of their excellent reactivity with the crosslinking agent (C), 2-hydroxyethyl (meth)acrylate is preferred because of its stability during polymerization, and 4-hydroxybutyl (meth)acrylate is preferred because of its rapid reactivity with the crosslinking agent (C) and short aging time. Furthermore, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred because they contain fewer impurities such as di(meth)acrylates during monomer preparation, resulting in high purity and ease of production.

[0024] The content of the hydroxyl group-containing monomer (a1) is 4 to 10% by weight, preferably 4.5 to 9% by weight, and more preferably 4.5 to 8% by weight, based on the total weight of the polymerizable components (a). If the content is too low, durability will decrease, and if the content is too high, reworkability will decrease.

[0025] [Carboxy group-containing monomer (a2)] Examples of the carboxy group-containing monomer (a2) include (meth)acrylic acid and dimer acids of acrylic acid such as β-carboxyethyl acrylate, among which (meth)acrylic acid is preferred in terms of heat resistance and stability during polymerization.

[0026] The content of the carboxyl group-containing monomer (a2) is 0.9 to 2.5 wt % of the total polymer component (a), preferably 1.0 to 2.4 wt %, more preferably 1.1 to 2.3 wt %, and particularly preferably 1.2 to 2.1 wt %. If the content is too low, durability will decrease, while if the content is too high, hydrolysis of the substrate will be promoted, thereby decreasing durability.

[0027] In the polymerization component (a) of the acrylic resin (A) of the present invention, the total amount of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) is 5 to 10.5 wt%, preferably 5.2 to 10.5 wt%, more preferably 5.5 to 10.3 wt%, and particularly preferably 5.7 to 10.0 wt%. If the total amount of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) is too high, reworkability will be poor, and if it is too low, durability will be poor.

[0028] [(Meth)acrylic acid alkyl ester (a3)] Examples of the (meth)acrylic acid alkyl ester (a3) ​​include those in which the alkyl group has usually 1 to 20 carbon atoms, preferably 2 to 18 carbon atoms, more preferably 2 to 12 carbon atoms, and even more preferably 3 to 8 carbon atoms, and aliphatic (meth)acrylic acid alkyl esters are preferred. Specific examples of the (meth)acrylic acid alkyl ester (a3) ​​include methyl acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, n-propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0029] Among these (meth)acrylic acid alkyl esters (a3), methyl acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, and n-butyl (meth)acrylate is particularly preferred, because of their excellent adhesive properties and excellent stability during polymerization. The content of the (meth)acrylic acid alkyl ester (a3) ​​is preferably 10% by weight or more, more preferably 30% by weight or more, even more preferably 50 to 97% by weight, and particularly preferably 60 to 95% by weight, based on the total weight of the polymer component (a). If the content is too low, the adhesive properties tend to decrease.

[0030] In order to achieve excellent compatibility with the ionic compound (B), the polymerization component (a) constituting the acrylic resin (A) preferably contains a C1 to C6 monomer such as methyl acrylate, ethyl (meth)acrylate, or n-butyl (meth)acrylate, and more preferably contains an alkyl (meth)acrylate having 2 to 4 carbon atoms. The content of these monomers is preferably 10% by weight or more, more preferably 30% by weight or more, even more preferably 50 to 97% by weight, particularly preferably 60 to 96% by weight, and especially preferably 80 to 95% by weight, based on the total polymerization component (a) constituting the acrylic resin (A).

[0031] [Other polymerizable monomers (a4)] The other polymerizable monomers (a4) are polymerizable ethylenically unsaturated monomers other than the hydroxyl group-containing monomers (a1), the carboxyl group-containing monomers (a2) and the (meth)acrylic acid alkyl esters (a3). For example, aromatic ring-containing monomers such as benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, and orthophenylphenoxyethyl (meth)acrylate; alicyclic ring-containing monomers such as cyclohexyl (meth)acrylate, cyclohexyloxyalkyl (meth)acrylate, t-butylcyclohexyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, and 2-butoxyethyl Ether chain-containing monomers such as (meth)acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol-mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, and stearoxypolyethylene glycol mono(meth)acrylate can be used alone or in combination of two or more.

[0032] Among these, aromatic ring-containing monomers are preferred in terms of ease of adjusting the refractive index and birefringence and excellent light leakage resistance, and benzyl (meth)acrylate, phenoxy (meth)ethyl acrylate, and phenoxy diethylene glycol (meth)acrylate are particularly preferred. Alicyclic ring-containing monomers are preferred in terms of ease of adjusting the refractive index and birefringence and excellent adhesion to low-polarity adherends (e.g., cycloolefins). The light leakage resistance refers to the ability of an adhesive to prevent backlight light from leaking after high temperature or moist heat tests when the adhesive is used to bond a polarizing plate to a liquid crystal cell or the like.

[0033] The content of the other polymerizable monomer (a4) is preferably 25% by weight or less based on the total polymerizable components (a) so as not to impair the effects of the present invention, and the lower limit is usually 0% by weight.

[0034] [Production of acrylic resin (A)] The acrylic resin (A) used in the present invention can be produced by using a polymerization component (a) which contains at least a hydroxyl group-containing monomer (a1) and a carboxy group-containing monomer (a2), and preferably further contains an alkyl (meth)acrylate (a3) ​​and other polymerizable monomers (a4) suitably selected and combined, for example, by mixing or dropping the polymerization component (a) and a polymerization initiator into an organic solvent and polymerizing them.

[0035] The polymerization reaction can be carried out by a conventionally known polymerization method such as solution radical polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization. Among these, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred.

[0036] Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane; esters such as ethyl acetate and butyl acetate; aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol; and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

[0037] Among these organic solvents, ethyl acetate, acetone, methyl ethyl ketone, butyl acetate, toluene, and methyl isobutyl ketone are preferably used, and particularly preferred are ethyl acetate, acetone, and methyl ethyl ketone, in view of the ease of polymerization reaction, chain transfer effect, ease of drying when applying the adhesive, and high safety. These organic solvents can be used alone or in combination of two or more. The amount of these organic solvents used is usually 10 to 900 parts by weight per 100 parts by weight of the total polymer component (a).

[0038] In addition, the polymerization initiator used in such solution radical polymerization can be a conventional radical polymerization initiator. Examples include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(methylpropionic acid); and organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide. These polymerization initiators can be selected appropriately depending on the monomer used. These polymerization initiators can be used alone or in combination of two or more. The amount of these polymerization initiators used is usually 0.01 to 5% by weight based on the total polymerizable component (a).

[0039] [Physical properties of acrylic resin (A)] The weight-average molecular weight of the acrylic resin (A) used in the present invention is 500,000 or more and less than 1,000,000, preferably 550,000 to 999,000, more preferably 600,000 to 995,000, particularly preferably 800,000 to 993,000, and especially preferably 900,000 to 990,000. If the weight-average molecular weight is too small, durability and reworkability will decrease, while if it is too large, a large amount of dilution solvent will be required during production, drying will decrease, and the amount of residual solvent will increase in the pressure-sensitive adhesive layer, resulting in decreased durability and making it impossible to reduce the amount of organic solvent used.

[0040] The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. If the degree of dispersion is too high, reworkability and durability tend to decrease. The lower limit of the degree of dispersion is usually 1.

[0041] The glass transition temperature (Tg) of the acrylic resin (A) is preferably −100 to 10° C., more preferably −70 to 0° C., and even more preferably −65 to −15° C. If the glass transition temperature is too high, adhesion tends to decrease and antistatic performance tends to decrease, while if the glass transition temperature is too low, the ionic compound (B) as an antistatic agent tends to move easily and bleed, resulting in decreased durability.

[0042] In the pressure-sensitive adhesive composition for polarizing plates of the present invention, the acrylic resin (A) is usually dissolved in a solvent or the like, and the viscosity is adjusted. As the solvent used to dissolve the acrylic resin (A), the organic solvent used in preparing the acrylic resin (A) is preferably used. The solid content (wt%) of the acrylic resin (A) solution is usually 15 to 45 wt%, preferably 20 to 40 wt%, more preferably 25 to 38 wt%, and particularly preferably 27 to 35 wt%.

[0043] From the viewpoint of ease of handling, the viscosity of the acrylic resin (A) solution is preferably 100 to 30,000 mPa·s / 25°C, more preferably 500 to 15,000 mPa·s / 25°C, even more preferably 1,000 to 8,000 mPa·s / 25°C, and particularly preferably 2,000 to 4,000 mPa·s / 25°C. If the viscosity is too high, the fluidity will decrease and handling will tend to be difficult, whereas if the viscosity is too low, coating of the resulting adhesive will tend to be difficult.

[0044] The viscosity of the acrylic resin (A) solution is measured by adjusting the temperature of the acrylic resin (A) solution to 25°C and by a rotational viscometer method using a B-type viscometer.

[0045] <Ionic Compound (B)> The pressure-sensitive adhesive composition for polarizing plates of the present invention further contains an ionic compound (B) from the viewpoint of antistatic properties. The ionic compound (B) is a compound consisting of a cationic component and an anionic component, and is a compound consisting of a combination of an organic cation or an inorganic cation as the cationic component and an anionic component. The ionic compound (B) can be used alone or in combination of two or more types.

[0046] As the inorganic cation, alkali metal cations are preferred in terms of antistatic performance, and lithium cations are particularly preferred. Examples of the organic cation include a pyridinium cation, a piperidinium cation, a pyrrolidinium cation, a cation having a pyrroline skeleton, a cation having a pyrrole skeleton, an imidazolium cation, a tetrahydropyrimidinium cation, a dihydropyrimidinium cation, a pyrazolium cation, a pyrazolinium cation, a tetraalkylammonium cation, a trialkylsulfonium cation, and a tetraalkylphosphonium cation. Among the cationic components, organic cations are preferred, and nitrogen-containing organic cations are particularly preferred in terms of compatibility with the resin. Tetraalkylammonium cations, pyridinium cations, and imidazolium cations are preferred in terms of compatibility with the acrylic resin (A), and tetraalkylammonium cations are particularly preferred in terms of low crystallinity of the ionic compound and resistance to precipitation.

[0047] The anion component includes monoatomic anions and polyatomic anions. Examples of the monoatomic anions include chloride anions, bromide anions, and iodide anions. Examples of the polyatomic anions include fluorine-based inorganic anions, fluorine-based organic anions, non-fluorine-based inorganic anions, and non-fluorine-based organic anions. Examples of fluorine-based inorganic anions include tetrafluoroborate anion and hexafluorophosphate anion, and examples of fluorine-based organic anions include fluorine-containing sulfonium anions such as trifluoromethanesulfonium anion; fluorine-containing imide anions; fluorine-containing sulfonylimide anions such as bis(trifluoromethanesulfonyl)imide anion and bis(pentafluoroethanesulfonyl)imide anion; and tris(trifluoromethanesulfonyl)methide anion. Examples of non-fluorine-based inorganic anions include perchlorate anion and nitrate anion, and examples of non-fluorine-based organic anions include acetate anion and dicyanamide anion.

[0048] Among the above, fluorine-containing organic anions are particularly preferred, and fluorine-containing sulfonium anions, fluorine-containing imide anions, and fluorine-containing sulfonylimide anions are more preferred in terms of antistatic performance, durability, and compatibility with the acrylic resin (A).

[0049] As the ionic compound (B), particularly preferred is a quaternary ammonium salt.Specific examples of quaternary ammonium salt include, for example, tributylmethylammonium N,N-bis(trifluoromethanesulfonyl)imide, tetrabutylammonium bis(trifluoromethylsulfonyl)imide, tetrabutylammonium bromide, tetrapentylammonium bromide, tetraoctylammonium bromide, ethyldimethylpropylammonium bis(trifluoromethylsulfonyl)imide, n-butyltrimethylammonium bis(trifluoromethanesulfonyl)imide, methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, tributylmethylammonium methyl sulfate, tributylmethylammonium methyl sulfate, tetraethylammonium trifluoromethanesulfonate, tetrabutylammonium benzoate, tetrabutylammonium methanesulfate, tetrabutylammonium nonafluorobutanesulfonate, tetra-n-butylammonium hexafluorophosphate, tetrabutylammonium trifluoroacetate, tetrahexylammonium tetrafluoroborate, tetrahexylammonium bromide etc.

[0050] From the viewpoint of the balance between antistatic performance and durability, ionic compounds in which the anion component of the ionic compound (B) is a fluorine-containing anion are preferred, and among these, tributylmethylammonium N,N-bis(trifluoromethanesulfonyl)imide (manufactured by 3M) is particularly preferred.

[0051] The melting point of the ionic compound (B) is preferably −100 to 150° C., more preferably 0 to 80° C., and even more preferably 25 to 50° C. If the melting point is too low, durability tends to decrease when bleeding out occurs, while if the melting point is too high, the compound tends to become cloudy when precipitated or to have reduced compatibility with resins.

[0052] The content of the ionic compound (B) is preferably 2 to 30 parts by weight, more preferably 2.2 to 15 parts by weight, and even more preferably 2.5 to 10 parts by weight, based on 100 parts by weight (solid content) of the acrylic resin (A). If the content of such ionic compound (B) is too low, the antistatic performance will be reduced, and static electricity will tend to cause malfunction of the touch panel and uneven display of the liquid crystal cell. If the content is too high, the adhesive layer will be plasticized, and durability will be reduced, and hydrolysis of the plastic substrate or the adherend will tend to occur more easily.

[0053] <Crosslinking agent (C)> The pressure-sensitive adhesive composition for polarizing plates of the present invention preferably contains a crosslinking agent (C) in addition to the acrylic resin (A) and the ionic compound (B). The crosslinking agent (C) is preferred in that it improves the elastic modulus of the pressure-sensitive adhesive when formed, prevents the migration of components contained in the substrate or adherend, and improves durability.

[0054] The crosslinking agent (C) is a compound that reacts with functional groups in the acrylic resin (A) to form a crosslinked structure, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, amine-based crosslinking agents, metal chelate-based crosslinking agents, etc. Among these, it is preferable to use an isocyanate-based crosslinking agent or an epoxy-based crosslinking agent, and isocyanate-based crosslinking agents are particularly preferable, in terms of improving adhesion to the adherend and having excellent reactivity with the acrylic resin (A). The crosslinking agent (C) can be used alone or in combination of two or more.

[0055] Examples of the isocyanate crosslinking agent include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds. Examples of the aromatic isocyanate compounds include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate; xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate; diphenylmethane compounds such as diphenylmethane-4,4-diisocyanate; and naphthalene diisocyanate compounds such as 1,5-naphthalene diisocyanate. Examples of the alicyclic isocyanate compounds include isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, and norbornane diisocyanate. Examples of the aliphatic isocyanate compounds include hexamethylene diisocyanate and trimethylhexamethylene diisocyanate. Further examples include adducts, biuret and isocyanurates of the above isocyanate compounds.

[0056] Among these isocyanate-based crosslinking agents, tolylene diisocyanate-based compounds are preferred in terms of pot life and durability, xylylene diisocyanate-based compounds and isocyanurate skeleton-containing isocyanate compounds are preferred in terms of shortening the aging time, and aromatic ring-free isocyanate compounds are preferred in terms of yellowing resistance. Specific examples of these include an adduct of an isocyanate compound selected from tolylene diisocyanate, xylylene diisocyanate, and hexamethylene diisocyanate with trimethylolpropane, and an isocyanurate of an isocyanate compound selected from tolylene diisocyanate, xylylene diisocyanate, and hexamethylene diisocyanate with trimethylolpropane, and these adducts and isocyanurates are preferred in terms of an excellent balance between durability, pot life, and crosslinking speed.

[0057] Examples of the epoxy crosslinking agent include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, and diglycerol polyglycidyl ether.

[0058] Examples of the aziridine crosslinking agent include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide).

[0059] Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

[0060] Examples of the aldehyde crosslinking agent include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0061] Examples of the amine-based crosslinking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0062] Examples of the metal chelate crosslinking agent include coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with ligands such as acetylacetone and acetoacetyl ester.

[0063] When a crosslinking agent (C) is used, its content is preferably 0.005 to 30 parts by weight, more preferably 0.01 to 10 parts by weight, even more preferably 0.03 to 5 parts by weight, and particularly preferably 0.05 to 3 parts by weight, relative to 100 parts by weight (solid content) of the acrylic resin (A). If the content is too low, it tends to be difficult to obtain the effect of improving durability, while if the content is too high, stress relaxation tends to decrease, making the adherend substrate more susceptible to warping and requiring long-term aging.

[0064] <Silane coupling agent (D)> The pressure-sensitive adhesive composition for polarizing plates of the present invention preferably further contains a silane coupling agent (D) in order to improve durability.

[0065] The silane coupling agent (D) is an organosilicon compound containing, in its structure, at least one reactive functional group and at least one alkoxy group bonded to a silicon atom, and examples thereof include monomeric and oligomeric types. Examples of the reactive functional group in the silane coupling agent (D) include an epoxy group, a (meth)acryloyl group, a mercapto group, a hydroxyl group, a carboxy group, an amino group, an amide group, an isocyanate group, and the like. Among these, an epoxy group and a mercapto group are preferred in terms of excellent durability and reworkability.

[0066] The content of the reactive functional group in the silane coupling agent (D) is preferably 50 to 3000 g / mol, more preferably 100 to 2000 g / mol, and even more preferably 150 to 1000 g / mol. If the functional group equivalent is too small, the adhesive strength tends to be high, and if it is too large, the durability tends to be reduced.

[0067] The weight-average molecular weight of the silane coupling agent (D) is preferably 300 to 10000, particularly preferably 500 to 5000, and further preferably 550 to 3000. If the molecular weight is too small, it tends to be easily volatilized during drying and to be less effective, whereas if it is too large, compatibility tends to decrease.

[0068] The weight average molecular weight is a weight average molecular weight converted into a standard polystyrene molecular weight, and can be measured by the following method. Apparatus: Gel permeation chromatograph Detector: Differential refractive index detector RI (Tosoh Corporation, RI-8020 type, sensitivity 32) Columns: TSKgel guard column HHR-H (1 column) (Tosoh Corporation, diameter 6 mm x 4 cm), TSKgel GMHHR-N (2 columns) (Tosoh Corporation, diameter 7.8 mm x 30 cm) Solvent: tetrahydrofuran (THF) Column temperature: 23℃ ·Flow rate: 1.0mL / min

[0069] As the silane coupling agent (D), an oligomeric organosilicon compound (organosiloxane compound) such as a dimer or trimer formed by partial hydrolysis and polycondensation of an organosilicon compound is preferred from the viewpoint of reworkability and durability. Examples of such oligomeric organosilicon compounds include mercapto group-containing oligomeric silane coupling agents having a structure in which siloxane skeletons (-Si-O-) are bonded to one another by an alkyl chain; mercapto group-containing oligomeric silane coupling agents obtained by partial hydrolysis and polycondensation of mercapto group-containing silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane; mercapto group-containing oligomeric silane coupling agents which are co-condensates of the above-mentioned mercapto group-containing silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropyltriethoxysilane; Examples of suitable silane coupling agents include epoxy group-containing oligomer-type silane coupling agents obtained by partial hydrolysis and polycondensation of epoxy group-containing silane compounds such as isethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; epoxy group-containing oligomer-type silane coupling agents which are co-condensates of the above epoxy group-containing silane compounds with alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane; and epoxy group-containing oligomer-type silane coupling agents obtained by ether-modifying a portion of these epoxy group-containing oligomer-type silane coupling agents. These can be used alone or in combination of two or more.

[0070] Specific examples of the monomeric or oligomeric silane coupling agent (D) include commercially available products such as the silane coupling agent "T-CURE" manufactured by Momentive Corporation, and silane coupling agents "KBM-403," "X-41-1053," "X-41-1059A," "X-24-9590," "KBM-803," "X-41-1805," "X-41-1810," and "X-41-1818" manufactured by Shin-Etsu Chemical Co., Ltd.

[0071] When the silane coupling agent (D) is used, the content thereof is preferably 0.001 to 3 parts by weight, more preferably 0.01 to 2 parts by weight, and even more preferably 0.05 to 1 part by weight, relative to 100 parts by weight (solid content) of the acrylic resin (A). If the content is too low, it will be difficult to obtain the effect of improving reworkability, whereas if the content is too high, the proportion of the low molecular weight compound will become too high, and durability will tend to decrease.

[0072] <Other ingredients> The pressure-sensitive adhesive composition for polarizing plates of the present invention may contain, as other components, within the range that does not impair the effects of the present invention, various additives such as a resin component, an acrylic monomer, a polymerization inhibitor, an antioxidant, a corrosion inhibitor, a crosslinking accelerator, a radical generator, a peroxide, a radical scavenger, an ultraviolet absorber, a plasticizer, a pigment, a stabilizer, a filler, metal particles, resin particles, etc. In addition to the above, the pressure-sensitive adhesive composition may contain small amounts of impurities contained in the production raw materials of the components of the pressure-sensitive adhesive composition. From the viewpoint of stability over time of the formulation, it is preferable that no radical generator, particularly peroxide, is contained, and even if it is contained, it is preferable that the amount is less than 0.03% by weight based on the total composition.

[0073] The content of other components is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, based on 100 parts by weight (solid content) of the acrylic resin (A). If the content is too high, the compatibility with the acrylic resin (A) decreases, and durability tends to decrease. The lower limit is 0 parts by weight.

[0074] Thus, by mixing the acrylic resin (A) and the ionic compound (B), preferably further a crosslinking agent (C), a silane coupling agent (D), and other components, the pressure-sensitive adhesive composition for polarizing plates of the present invention can be obtained.

[0075] The mixing method is not particularly limited, and various methods can be used, such as a method of mixing the components all at once, or a method of mixing any components and then mixing the remaining components all at once or sequentially.

[0076] [Adhesive for polarizing plate, adhesive sheet for polarizing plate, polarizing plate with adhesive layer, image display device] The pressure-sensitive adhesive composition for polarizing plates of the present invention can be crosslinked (cured) to form a pressure-sensitive adhesive for polarizing plates. A pressure-sensitive adhesive sheet for polarizing plates having such a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive layer made of such a pressure-sensitive adhesive, can be laminated on a polarizing plate to obtain a pressure-sensitive adhesive layer-attached polarizing plate. Furthermore, an image display device can be produced using such a pressure-sensitive adhesive layer-attached polarizing plate. It is preferable that the pressure-sensitive adhesive layer-attached polarizing plate further comprises a release sheet on the surface of the pressure-sensitive adhesive layer opposite to the surface facing the optical member.

[0077] Examples of methods for producing the above-mentioned pressure-sensitive adhesive layer-attached polarizing plate include [1] a method in which a pressure-sensitive adhesive composition for polarizing plates is applied to a polarizing plate, dried, and then a release sheet is attached, followed by aging at least at room temperature (23°C) or at a heated state, and [2] a method in which a pressure-sensitive adhesive composition for polarizing plates is applied to a release sheet, dried, and then a polarizing plate is attached, followed by aging at least at room temperature (23°C) or at a heated state. Among these, method [2] in which aging is performed at room temperature is preferred because it does not damage the polarizing plate and has excellent adhesion to the polarizing plate.

[0078] The aging treatment is carried out to balance the adhesive properties as the reaction time for chemical crosslinking of the adhesive. The aging conditions are a temperature of 20 to 70°C and a time of usually 1 to 30 days, and specific conditions include 1 to 20 days at 23°C, 3 to 10 days at 23°C, and 1 to 7 days at 40°C.

[0079] When applying the pressure-sensitive adhesive composition for polarizing plates, it is preferable to dilute the pressure-sensitive adhesive composition in a solvent and then apply the diluted composition. The dilution concentration is preferably 10 to 50% by weight, more preferably 15 to 30% by weight in terms of solid content.

[0080] The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition for polarizing plates, and examples thereof include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol solvents such as methanol, ethanol, and propyl alcohol. Among these, ethyl acetate and methyl ethyl ketone are preferably used in terms of solubility, drying properties, cost, etc. These solvents can be used alone or in combination of two or more.

[0081] The adhesive composition can be applied by a conventional method such as roll coating, die coating, gravure coating, comma coating, or screen printing.

[0082] The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 99 wt %, more preferably 40 to 98 wt %, even more preferably 50 to 97 wt %, and particularly preferably 60 to 96 wt %, from the viewpoints of durability and suppressing a decrease in polarization degree. If the gel fraction is too low, foaming tends to occur under harsh high-temperature conditions, while if it is too high, lifting and peeling tend to occur easily.

[0083] The gel fraction is a measure of the degree of crosslinking (degree of hardening) and is calculated, for example, by the following method. First, the adhesive is picked from the adhesive film on which the adhesive layer is formed. Next, the collected adhesive is wrapped in a 200-mesh SUS wire mesh and immersed in ethyl acetate adjusted to 23°C for 24 hours. The weight of the adhesive before immersion in ethyl acetate and the weight of the undissolved adhesive remaining in the wire mesh after immersion are measured, and the weight of the undissolved adhesive divided by the weight of the adhesive before immersion is taken as the gel fraction (%).

[0084] If the pressure-sensitive adhesive layer produced by the above method has a moderate tackiness when touched with the fingers, it tends to have good wettability when actually applied to an adherend, which tends to improve workability, and is therefore preferable.

[0085] As for the electrical properties of the pressure-sensitive adhesive layer obtained using the pressure-sensitive adhesive composition for polarizing plates of the present invention, a low surface resistivity is preferred as a countermeasure against static electricity, and more preferably 5.0×10 12 Ω / cm 2 or less, more preferably 5.0 × 10 11 Ω / cm 2 Below 1.0 × 10, particularly preferably 11 Ω / cm 2 If the surface resistivity is too high, the adhesive will be easily charged, and when used for liquid crystal displays, display unevenness due to static electricity will tend to occur.

[0086] In the present invention, a liquid crystal display panel is formed by bonding the pressure-sensitive adhesive layer surface of the polarizing plate with a pressure-sensitive adhesive layer directly, or after peeling off the release sheet if the polarizing plate has a release sheet, to, for example, a glass substrate of a liquid crystal cell.

[0087] The reworkability of the pressure-sensitive adhesive of the present invention is preferably such that the pressure-sensitive adhesive layer does not adhere to the adherend when peeled off. The adhesive strength during peeling is preferably 25 N / 25 mm or less, more preferably 0.1 to 20 N / mm, and particularly preferably 1 to 15 N / mm. If the adhesive strength is too high, the adherend tends to be easily damaged during rework, while if it is too low, the edges tend to peel off easily.

[0088] The adhesive strength is calculated as follows. A polarizing plate with an adhesive layer is cut to a width of 25 mm, the release sheet is peeled off, and the adhesive layer side is pressed against an alkali-free glass plate ("Eagle XG" manufactured by Corning Incorporated) to bond the polarizing plate and the glass plate. After that, autoclave treatment (50°C, 0.5 MPa, 20 minutes) is performed, and after leaving it at 23°C x 50% RH for 24 hours, a peel test is performed at a peel angle of 90° and a peel speed of 300 mm / min.

[0089] Regarding long-term reworkability, after autoclaving, the film is left to stand at 23°C x 50% RH for a specified period of time, and then a peel test is conducted at a peel angle of 90° and a peel speed of 300 mm / min.

[0090] The pressure-sensitive adhesive composition for polarizing plates of the present invention provides a pressure-sensitive adhesive for polarizing plates that has excellent durability even under high temperature and high temperature / high humidity environments and also has excellent long-term reworkability, and is therefore useful as a pressure-sensitive adhesive for polarizing plates for bonding a polarizing plate to a liquid crystal cell. In this specification, the term "liquid crystal cell" refers to a cell having a structure in which a liquid crystal material is sandwiched between a pair of substrates, and which does not have a polarizing plate.

[0091] A polarizing plate generally comprises a polyvinyl alcohol (PVA) film on which iodine molecules are adsorbed and aligned, and a protective film for protecting the PVA film, such as a triacetyl cellulose film, an acrylic film, a polyethylene film, a polypropylene film, or a cycloolefin film.

[0092] Furthermore, by using the pressure-sensitive adhesive for polarizing plates of the present invention, it is possible to produce an image display device such as a liquid crystal display device by bonding a polarizing plate and a liquid crystal cell, and the obtained image display device can be produced with high precision and has excellent durability. [Example]

[0093] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by weight.

[0094] First, various acrylic resins (A) were prepared as follows, and other raw materials for the pressure-sensitive adhesive composition were also prepared. The weight average molecular weight, polydispersity, and glass transition temperature of the acrylic resins (A) were measured according to the methods described above. The viscosity was measured at 25°C using a Brookfield viscometer.

[0095] <Acrylic resin (A)> As a raw material for the acrylic resin (A), the polymerization component (a) shown in Table 1 was prepared.

[0096] [Preparation of acrylic resin (A-1)] A five-necked round-bottom flask equipped with a reflux condenser, a dropping funnel, a stirrer, a nitrogen gas inlet, and a thermometer was charged with 70 parts of ethyl acetate, 20 parts of acetone, and 0.025 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator. The internal temperature was raised to the boiling point, and all of the polymerization components (a) were charged into the dropping funnel so as to give a monomer composition as shown in Table 1. A mixture of 5 parts of ethyl acetate and 0.025 parts of AIBN as a polymerization initiator was added dropwise while the reaction was carried out at reflux temperature for 2 hours. After that, a mixture containing 5 parts of ethyl acetate and 0.025 parts of AIBN was added, and the reaction was continued for another 2 hours and 30 minutes. The mixture was then diluted with ethyl acetate to obtain an acrylic resin (A-1) solution.

[0097] [Preparation of acrylic resins (A-2 to A-4, A'-1 to A'-4)] Acrylic resins (A-2 to A-4, A'-1 to A'-4) were prepared in the same manner as in the preparation of acrylic resin (A-1), except that the monomer composition of polymerization component (a) was changed as shown in Table 1.

[0098] [Table 1]

[0099] The monomers used above were from the following manufacturers: n-Butyl acrylate (BA) (Mitsubishi Chemical Corporation, glass transition temperature -56°C) 2-Hydroxyethyl acrylate (HEA) (Osaka Organic Chemical Industry, Ltd., glass transition temperature -15°C) Acrylic acid (AAc) (Osaka Organic Chemical Industry, Ltd., glass transition temperature 106°C) The above glass transition temperatures are those of homopolymers obtained from the respective monomers.

[0100] <Ionic Compound (B)> The following was prepared as the ionic compound (B): (B-1): Tributylmethylammonium N,N-bis(trifluoromethanesulfonyl)imide (3M, FC-4400) (melting point: 27.5°C)

[0101] <Crosslinking agent (C)> The following crosslinking agent (C) was prepared: (C-1): Adduct of tolylene diisocyanate and trimethylolpropane (Tosoh Corporation, Coronate L55E)

[0102] <Silane coupling agent (D)> The following silane coupling agent (D) was prepared. (D-1): T-CURE Momentive

[0103] <Examples 1 to 4, Comparative Examples 1 to 4> The above components were blended as shown in Table 2 below, and the solid content was adjusted with ethyl acetate to obtain a pressure-sensitive adhesive composition for polarizing plates.

[0104] Using the pressure-sensitive adhesive composition for polarizing plates obtained above, evaluation samples were prepared as follows, and the following performances were evaluated. The evaluation results are also shown in Table 2 below.

[0105] [Preparation of pressure-sensitive adhesive layer-attached polarizing plate [I]] The obtained adhesive composition was applied to a 38 μm thick release sheet (Toray Industries, Inc.'s "Cerapeel WZ") so that the dried thickness would be 20 μm, and after drying at 100°C for 3 minutes, the adhesive layer surface opposite the release sheet was attached to one of the triacetylcellulose (TAC) film surfaces of a polarizing plate laminated with TAC film on both sides, and aged for 7 days in an environment of 23°C x 50% RH to obtain an adhesive layer-attached polarizing plate [I] (layer structure: release sheet / adhesive layer / TAC film / polarizer / TAC film).

[0106] <Gel fraction> The release sheet was peeled off from the obtained pressure-sensitive adhesive layer-attached polarizing plate [I], and the pressure-sensitive adhesive was picked from the pressure-sensitive adhesive layer surface, wrapped in a 200-mesh SUS wire mesh, and then immersed for 24 hours in ethyl acetate adjusted to 23° C. The weight of the pressure-sensitive adhesive before immersion in ethyl acetate and the weight of the undissolved pressure-sensitive adhesive remaining in the wire mesh after immersion were each measured, and the weight of the undissolved pressure-sensitive adhesive divided by the weight of the pressure-sensitive adhesive before immersion was taken as the gel fraction (%).

[0107] <Reworkability: Adhesion, adhesive residue> The polarizing plate with adhesive layer [I] obtained above was cut to a width of 25 mm, the release sheet was peeled off, and the adhesive layer surface was pressed against alkali-free glass (Corning Eagle XG, thickness 1.1 mm) and laminated by rolling twice with a 2 kg roller. After that, autoclaving (0.5 MPa x 50 ° C x 20 minutes) was performed, and then the film was left to stand for 14 days in an environment of 23 ° C x 50% RH. After that, the film was peeled off at a peel angle of 90 ° and a peel speed of 300 mm / min, and the adhesive strength when peeled off was measured, and the state of adhesive remaining on the glass surface after peeling was visually confirmed and evaluated according to the following criteria. (Evaluation criteria) ◎ No glue residue is visible on the glass. 〇 No glue remains on the glass, but strings are visible when peeling off. △···Remains of the sticker can be seen on the glass surface. × Glue residue is visible on the glass surface.

[0108] <Durability> The obtained polarizing plate with adhesive layer [I] was cut to 165 mm x 95 mm, the release sheet was peeled off, and the adhesive layer surface was pressed against alkali-free glass (Corning Eagle XG, thickness 1.1 mm) and laminated by rolling twice back and forth with a 2 kg roller. After that, the film was autoclaved (0.5 MPa x 50°C x 20 minutes) to prepare a sample for durability evaluation. The obtained samples were exposed under the following conditions: (1) (85°C x 500 hours), (2) (65°C 90% RH x 500 hours), and (3) (-30°C ←→ 80°C x 500 cycles), and then evaluated according to the following criteria. (Evaluation criteria) ◎ No bubbles are observed on the entire surface of the polarizing plate or lifting at the edges. ○: Only a very slight lifting was observed at the corners of the polarizing plate. △: Slight lifting is observed at the edge of the polarizing plate. ×: Bubbles are observed on the entire surface of the polarizing plate or the edges are lifted by 1 mm or more.

[0109] <Anti-static performance: surface resistivity> The pressure-sensitive adhesive layer-attached polarizing plate [I] was left standing for 24 hours in an atmosphere of 23°C x 50% RH, and then the release sheet of the pressure-sensitive adhesive layer was removed. The surface resistivity (Ω / cm 2 ) was measured.

[0110] [Table 2]

[0111] From the above results, Examples 1 to 4, which used adhesives obtained from adhesive compositions containing an acrylic resin (A) containing a hydroxyl group-containing monomer (a1) and a carboxyl group-containing monomer (a2), each of which has a content within a specific range, and an ionic compound (B), exhibited excellent long-term reworkability, durability even under high temperature, high temperature and humidity, and thermal shock environments, and also excellent antistatic properties. On the other hand, Comparative Example 1, in which the total content of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) was outside the specific range, had poor long-term reworkability. Also, Comparative Examples 2 to 4, in which the total content of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) was within the specific range but either or both of them were outside the specific range, had satisfactory long-term reworkability but were poor in durability.

[0112] Furthermore, since the adhesive layer obtained using the adhesive composition of the embodiment of the present invention is excellent in all of long-term reworkability, durability, and antistatic properties, it is expected that an image display device formed by bonding a polarizing plate and an image display member such as a liquid crystal cell via the above-mentioned adhesive layer will be of excellent quality. [Industrial Applicability]

[0113] The pressure-sensitive adhesive composition of the present invention is capable of providing a pressure-sensitive adhesive that does not peel off even under high temperature, high temperature and high humidity, and thermal shock environments, has excellent durability, and further has excellent reworkability after aging. The pressure-sensitive adhesive composition of the present invention is useful as a pressure-sensitive adhesive for electronic components and optical components for bonding touch panels, displays, and the electronic and optical components that constitute them, and in particular as a pressure-sensitive adhesive for polarizing plates for bonding polarizing plates to glass substrates of liquid crystal cells, etc., and as a pressure-sensitive adhesive for touch sensors.

Claims

1. A pressure-sensitive adhesive composition for polarizing plates, comprising: an acrylic resin (A) having a weight-average molecular weight of 550,000 or more and less than 1,000,000; an ionic compound (B); a crosslinking agent (C); and a silane coupling agent (D), The acrylic resin (A) contains, as polymerization components (a), 4 to 10% by weight of a hydroxyl group-containing monomer (a1), 0.9 to 2.5% by weight of a carboxyl group-containing monomer (a2), and 5 to 10.5% by weight of the hydroxyl group-containing monomer (a1) and the carboxyl group-containing monomer (a2) in total, The acrylic resin (A) does not contain an alkyl (meth)acrylate having an alkyl group having 14 to 18 carbon atoms in the polymerization component (a), the content of the ionic compound (B) is 2 to 15 parts by weight based on 100 parts by weight of the acrylic resin (A), the content of the crosslinking agent (C) is 0.05 to 3 parts by weight based on 100 parts by weight of the acrylic resin (A); The pressure-sensitive adhesive composition for polarizing plates, wherein the content of the silane coupling agent (D) is 0.05 to 1 part by weight based on 100 parts by weight of the acrylic resin (A).

2. A pressure-sensitive adhesive for polarizing plates, which is formed from the pressure-sensitive adhesive composition for polarizing plates according to claim 1 .

3. A pressure-sensitive adhesive sheet for polarizing plates, comprising a pressure-sensitive adhesive layer for polarizing plates, which comprises the pressure-sensitive adhesive for polarizing plates according to claim 2 .

4. A pressure-sensitive adhesive layer-attached polarizing plate, comprising a pressure-sensitive adhesive layer for polarizing plates, the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive for polarizing plates according to claim 2, and a polarizing plate laminated thereon.

5. 3. An image display device comprising a polarizing plate and a liquid crystal cell bonded together with the pressure-sensitive adhesive for polarizing plates according to claim 2.

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