Adhesive composition and use thereof

Abstract

To provide an adhesive composition that produces an adhesive having superior durability and reworkability under hot and humid conditions, as well as superior substrate adhesion and processability.SOLUTION: An adhesive composition comprises an acrylic resin (A) and a crosslinking agent (B), wherein the acrylic resin (A) contains structural units derived from a hydroxyl group-containing monomer (a2-1), the content of the structural units derived from the hydroxyl group-containing monomer (a2-1) accounts for 2.7 to 8 wt.% of the total structural units constituting the acrylic resin (A), the crosslinking agent (B) has an isocyanate group, and the isocyanate group content in 100 wt.% solids of the crosslinking agent (B) is 15 wt.% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and its use, more particularly to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive composition for optical members, and a pressure-sensitive adhesive and an optical member using the same. More particularly, the present invention relates to a pressure-sensitive adhesive composition that can provide a highly practical pressure-sensitive adhesive that can achieve not only durability and reworkability under humid and hot conditions, but also adhesion to a substrate and processability, when used as a pressure-sensitive adhesive for bonding an optical member such as a polarizing plate to a glass substrate or the like. [Background technology]

[0002] In general, a liquid crystal display panel is manufactured by laminating polarizing plates on both sides of a liquid crystal cell, and the polarizing plate is formed by covering both sides of a polarizer made of a polyvinyl alcohol-based film or the like to which polarizing properties have been imparted with a protective film such as a triacetyl cellulose (TAC)-based film, and the liquid crystal cell is formed by sandwiching an oriented liquid crystal component between two glass plates. The lamination of the polarizing plates on both sides of the liquid crystal cell is usually performed by abutting and pressing an adhesive layer provided on the surface of the polarizing plate against the surface of the liquid crystal cell.

[0003] Since liquid crystal display panels using polarizing plates are used in various environments, the adhesive layer provided on the polarizing plate surface is required to have durability so that it does not foam or peel off even in high temperature and high humidity environments. For example, Patent Document 1 describes an acrylic adhesive that uses an acrylic resin copolymerized with a larger amount of hydroxyl group monomer than usual as an adhesive with excellent durability, particularly excellent resistance to moist heat, and describes that this acrylic adhesive has excellent resistance to moist heat whitening. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-213203 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the present inventors have found that although the adhesive described in Patent Document 1 has excellent resistance to wet heat whitening, it has too much hydroxyl group content, which makes the polymer highly polar. When an aromatic crosslinking agent, which also has high polarity, is used, there is a risk of poor adhesion to a substrate (such as a polarizing plate) which has low polarity. As a result, there is a risk of problems with processability, such as the adhesive protruding from the substrate during the slit processing step of the polarizing plate.

[0006] Under these circumstances, the present invention aims to provide a pressure-sensitive adhesive composition which not only has excellent durability and reworkability under humid and hot conditions but also provides a pressure-sensitive adhesive having good adhesion to substrates and processability, a pressure-sensitive adhesive obtained by crosslinking this composition, and an optical component using this pressure-sensitive adhesive. [Means for solving the problem]

[0007] However, in view of these circumstances, the present inventors have conducted extensive research and found that, in a pressure-sensitive adhesive composition containing an acrylic resin and a crosslinking agent, by using an acrylic resin containing a specific amount of structural units derived from a hydroxyl group-containing monomer and a crosslinking agent having a specific concentration of isocyanate groups, a pressure-sensitive adhesive composition can be created that not only has excellent durability and reworkability under moist and hot conditions, but also has good adhesion to substrates and processability, and thus completed the present invention.

[0008] That is, the present invention includes the following aspects. Aspect (1) of the present invention is a pressure-sensitive adhesive composition comprising an acrylic resin (A) and a crosslinking agent (B), wherein the acrylic resin (A) contains structural units derived from a hydroxyl group-containing monomer (a2-1), and the content of the structural units derived from the hydroxyl group-containing monomer (a2-1) is 2.7 to 8 wt % of all structural units constituting the acrylic resin (A), and the crosslinking agent (B) has an isocyanate group, and the concentration of the isocyanate group per 100 wt % solids content of the crosslinking agent (B) is 15 wt % or less.

[0009] In an embodiment (2) of the present invention, in the pressure-sensitive adhesive composition of the embodiment (1), the crosslinking agent (B) has a structure derived from lactone.

[0010] In an embodiment (3) of the present invention, the pressure-sensitive adhesive composition of the embodiment (1) or (2) further contains a silane coupling agent (C).

[0011] In an embodiment (4) of the present invention, in the pressure-sensitive adhesive composition of the embodiment (3), the silane coupling agent (C) contains an epoxy group and / or a mercapto group.

[0012] Aspect (5) of the present invention is the pressure-sensitive adhesive composition of aspect (3) or (4), wherein the silane coupling agent (C) is an oligomer type silane compound.

[0013] In an embodiment (6) of the present invention, the pressure-sensitive adhesive composition of any of the embodiments (1) to (5) further contains an ionic compound (D).

[0014] In an aspect (7) of the present invention, in the pressure-sensitive adhesive composition of the aspect (6), the ionic compound (D) has a melting point of 25° C. or higher.

[0015] In an embodiment (8) of the present invention, in the pressure-sensitive adhesive composition of the embodiment (6) or (7), the cationic component (d1) of the ionic compound (D) is an onium cation containing nitrogen.

[0016] An embodiment (9) of the present invention is a pressure-sensitive adhesive composition for optical members, comprising the pressure-sensitive adhesive composition of any one of embodiments (1) to (8).

[0017] An embodiment (10) of the present invention is a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of embodiments (1) to (6).

[0018] Aspect (12) of the present invention is an optical member with a pressure-sensitive adhesive layer, in which a pressure-sensitive adhesive layer is laminated on an optical member, and the pressure-sensitive adhesive layer contains the pressure-sensitive adhesive of aspect (10).

[0019] In the present invention, the term "optical member" refers to a member that selectively transmits a part of incident light, and examples thereof include a polarizing plate, a retardation plate, and a light-reducing plate. A "polarizing plate" generally refers to a polarizer made of a polyvinyl alcohol-based film or the like, both sides of which are covered with a protective film such as a TAC film. An "optical member with a pressure-sensitive adhesive layer" is an optical member having a pressure-sensitive adhesive layer laminated on one surface thereof, and is generally commercially available with a peelable release liner laminated on the pressure-sensitive adhesive layer. Additionally, the term "film" conceptually encompasses sheets, films, and tapes. Effect of the Invention

[0020] The adhesive obtained by using the adhesive composition of the present invention has excellent durability and reworkability under moist and hot conditions, and also has good adhesion to substrates and processability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 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. Also, the acrylic resin is a resin obtained by polymerizing a polymerization component containing at least one (meth)acrylate monomer. In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), it means "X or more and Y or less" unless otherwise specified. In the present specification, in which multiple numerical ranges are described in stages, each upper limit and each lower limit may be the upper limit or lower limit of any combination of numerical ranges. For example, when the content of a certain component is described as "5-20% by weight, 10-15% by weight," each of the numerical ranges may be "5-15% by weight," "10-20% by weight," "5-10% by weight," and "15-20% by weight."

[0022] (1) Pressure-sensitive adhesive composition The pressure-sensitive adhesive composition of the present invention contains, as essential components, an acrylic resin (A) and a crosslinking agent (B). First, these essential components will be described in order.

[0023] <Acrylic resin (A)> The acrylic resin (A) used in the present invention is a polymer obtained by polymerizing a copolymerization component (a), which contains a (meth)acrylic acid alkyl ester monomer (a1) as a main component and at least a hydroxyl group-containing monomer (a2-1) as a functional group-containing monomer (a2). The copolymerization component (a) may contain a functional group-containing monomer (a2) other than the hydroxyl group-containing monomer (a2-1) and other copolymerizable monomers (a3) ​​as necessary. The main component is the component that is most abundant in the copolymerization component (a), and is usually 40% by weight or more, preferably 50% by weight or more, of the copolymerization component (a).

[0024] The content of each monomer relative to the entire copolymerization component (a) can be regarded as the content of structural units derived from that monomer in all structural units constituting the acrylic resin (A), which is a copolymer. For example, the content of the hydroxyl-containing monomer (a2-1) relative to the entire copolymerization component (a) can be regarded as the content of structural units derived from the hydroxyl-containing monomer (a2-1) in all structural units constituting the acrylic resin (A). Furthermore, when the pressure-sensitive adhesive composition of the present invention contains two or more acrylic resins (including acrylic resins that do not contain structural units derived from the hydroxyl-containing monomer (a2-1)) having different constituent monomers or different contents thereof, the contents of various monomers such as the hydroxyl-containing monomer (a2-1) are the contents in the two or more acrylic resins as a whole.

[0025] The (meth)acrylic acid alkyl ester monomer (a1) preferably has an alkyl group having a carbon number of usually 1 to 20, particularly 1 to 12, further 1 to 8, and particularly 4 to 8. Specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-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, isostearyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0026] Among such (meth)acrylic acid alkyl ester monomers (a1), n-methyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred from the standpoints of copolymerizability, adhesive properties, ease of handling, and ease of availability of raw materials. In particular, it is preferred to contain 50% by weight or more of n-butyl acrylate based on the total amount of (meth)acrylic acid alkyl ester monomers (a1) from the standpoints of excellent stability during polymerization and adhesive properties.

[0027] The content of the (meth)acrylic acid alkyl ester monomer (a1) is preferably 40 to 99.9% by weight, more preferably 50 to 99% by weight, and even more preferably 60 to 98% by weight, based on the total weight of the copolymerization component (a). If the content is too low, the adhesive properties and durability tend to decrease, and if the content is too high, the adhesive properties tend to decrease.

[0028] The acrylic resin (A) in the present invention uses a functional group-containing monomer (a2) as the copolymerization component (a), and this functional group becomes a crosslinking point of the acrylic resin (A), which can further increase the adhesion to the substrate or the adherend. Furthermore, by using a copolymerization component (a) containing a hydroxyl group-containing monomer (a2-1) as the functional group-containing monomer (a2), durability, particularly wet heat resistance, can be improved.

[0029] Examples of the hydroxyl group-containing monomer (a2-1) include acrylic acid hydroxyalkyl esters 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; and primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl 2-hydroxyethyl phthalate and N-methylol (meth)acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-chloro 2-hydroxypropyl (meth)acrylate; and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate. These may be used alone or in combination of two or more. Among the above hydroxyl group-containing monomers, primary hydroxyl group-containing monomers are preferred because they have excellent reactivity with the crosslinking agent (B) and good compatibility with hydroxyl group-containing ionic compounds. In particular, 2-hydroxyethyl acrylate is preferred because it contains less impurities such as di(meth)acrylates and is easy to produce.

[0030] In addition, as the hydroxyl group-containing monomer (a2-1) used in the present invention, it is also preferable to use one having a content of di(meth)acrylate as an impurity of 0.5% by weight or less, more preferably 0.2% by weight or less, and even more preferably 0.1% by weight or less.

[0031] Examples of the functional group-containing monomer (a2) other than the hydroxyl group-containing monomer (a2-1) include carboxyl group-containing monomer, amino group-containing monomer, acetoacetyl group-containing monomer, isocyanate group-containing monomer, and glycidyl group-containing monomer. Among these, carboxyl group-containing monomer is preferred in terms of efficient crosslinking reaction. In addition, it is also preferred to use an amino group-containing monomer in terms of promoting the reaction between the hydroxyl group and the isocyanate-based crosslinking agent (B) described later, and it is also preferred to use an amide group-containing monomer in terms of improving heat resistance and reworkability.

[0032] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, acrylic acid dimer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamido-N-glycolic acid, and cinnamic acid. Of these, (meth)acrylic acid is preferably used.

[0033] Examples of the amino group-containing monomer include primary amino group-containing monomers such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing monomers such as t-butylaminoethyl (meth)acrylate; and tertiary amino group-containing monomers such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. Among the above amino group-containing monomers, tertiary amino group-containing monomers are preferred in terms of the storage stability of the resin solution and the crosslinking promoting effect, and dimethylaminoethyl (meth)acrylate is particularly preferred.

[0034] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0035] Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

[0036] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0037] The content of the functional group-containing monomer (a2) is preferably 2.7 to 30% by weight, more preferably 2.8 to 20% by weight, and even more preferably 3 to 8% by weight, based on the total weight of the copolymerization component (a). If the content is too low, the durability tends to decrease, while if the content is too high, the adhesion to the substrate, processability, polarization degree, and reworkability tend to decrease.

[0038] In the present invention, the content of the hydroxyl group-containing monomer (a2-1) is 2.7 to 8 wt %, particularly preferably 2.8 to 7 wt %, further preferably 2.9 to 6 wt %, and particularly preferably 3 to 5 wt %, based on the total copolymerization component (a). When the content of the hydroxyl group-containing monomer (a2-1) is within the above range, it is possible to improve all of the adhesion to substrates, processability, reworkability, and durability under moist and hot conditions.

[0039] When a carboxyl group-containing monomer is used as the functional group-containing monomer (a2), the content of the carboxyl group-containing monomer is preferably 0.01 to 5 wt %, more preferably 0.1 to 3 wt %, and even more preferably 0.5 to 1.5 wt %, based on the total weight of the copolymerization component (a). If the content of the carboxyl group-containing monomer is too low, the crosslinking promotion effect will be low and crosslinking will tend to be inhibited by the influence of alcohol or moisture contained in the polarizing plate or moisture in the environment. If the content is too high, the adherend etc. will tend to be easily corroded.

[0040] When an amino group-containing monomer is used as the functional group-containing monomer (a2), the content of the amino group-containing monomer is preferably 0.01 to 1 wt %, more preferably 0.05 to 0.5 wt %, and even more preferably 0.1 to 0.2 wt %, based on the total weight of the copolymerization component (a). If the content of the amino group-containing monomer is too low, the crosslinking promotion effect is low, and crosslinking tends to be inhibited due to the influence of alcohol or moisture contained in the polarizing plate or moisture in the environment, and the catalytic effect of the amino group is difficult to obtain, aging is prolonged, and crosslinking efficiency tends to decrease. If the content is too high, yellowing tends to occur easily and the pot life tends to be shortened.

[0041] When an amide group-containing monomer is used as the functional group-containing monomer (a2), the content of the amide group-containing monomer is preferably 0.01 to 5 wt %, more preferably 0.01 to 3 wt %, and even more preferably 0.1 to 1 wt %, based on the total copolymerization component (a). If the amount of the amide group-containing monomer is too large, when the film is used for a polarizing plate, resistance to light leakage and reworkability tend to decrease.

[0042] Such functional group-containing monomers (a2) may be used alone or in combination of two or more, preferably in combination of two or more, and particularly preferably in combination of a hydroxyl group-containing monomer (a2-1) and a carboxyl group-containing monomer, or a hydroxyl group-containing monomer (a2-1) and an amino group-containing monomer (preferably a tertiary amino group-containing monomer).

[0043] Examples of the other copolymerizable monomers (a3) ​​include aromatic ring-containing monomers such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, ethoxylated o-phenylphenyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and styrene; and alicyclic ring-containing monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate.

[0044] Among these, aromatic ring-containing monomers are preferred because they can efficiently increase the refractive index and efficiently adjust the birefringence of the adhesive to be positive, and particularly preferred are phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate.

[0045] The content of the other copolymerizable monomer (a3) ​​is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less, based on the total weight of the copolymerization component (a). If the content is too high, reworkability and durability, particularly wet heat resistance, tend to decrease.

[0046] [Production of acrylic resin (A)] The acrylic resin (A) used in the present invention can be produced by appropriately selecting and polymerizing the copolymerization components (a) from the above (a1) to (a3). Such polymerization can be carried out by a conventionally known method such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. However, from the viewpoint of stably obtaining a high molecular weight acrylic resin (A), solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is more preferred. Specifically, for example, copolymerization components such as (meth)acrylic acid alkyl ester monomer (a1), functional group-containing monomer (a2), and other copolymerizable monomers (a3), and a polymerization initiator are mixed or dropped into an organic solvent, and polymerized under reflux or at 50 to 90° C. for 2 to 20 hours.

[0047] Examples of the organic solvent used in such polymerization include aromatic hydrocarbons such as toluene and xylene; esters such as methyl acetate, 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.

[0048] Specific examples of the polymerization initiator used in the radical polymerization include azo-based polymerization initiators such as azobisisobutyronitrile and azobisdimethylvaleronitrile, which are ordinary radical polymerization initiators; and peroxide-based polymerization initiators such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide. These polymerization initiators may be used alone or in combination of two or more.

[0049] [Physical properties of acrylic resin (A)] The weight average molecular weight of the acrylic resin (A) is usually 200,000 to 3,000,000, preferably 500,000 to 2,000,000, particularly preferably 800,000 to 1,900,000, and further preferably 1,000,000 to 1,800,000. If the weight average molecular weight is too small, reworkability and durability tend to decrease, whereas if the weight average molecular weight is too high, a large amount of dilution solvent is required during production, drying property decreases, and the amount of residual solvent in the pressure-sensitive adhesive layer increases, tending to decrease durability.

[0050] The degree of dispersion (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 10 or less, particularly preferably 8 or less, further preferably 7 or less, and particularly preferably 6 or less. If the degree of dispersion is too high, the resin contains a large amount of low molecular weight components, and the cohesive force tends to decrease and the durability tends to decrease. The lower limit of the degree of dispersion is usually 1.

[0051] The weight-average molecular weights mentioned above are those calculated based on the molecular weight of standard polystyrene. The samples were analyzed using a high-performance liquid chromatograph (manufactured by Japan Waters, Inc., "Waters 2695 (main unit)" and "Waters 2414 (detector)") with a Shodex GPC KF-806L column (molecular weight exclusion limit: 2×10 7 , Separation range: 100~2×10 7 The number average molecular weight can also be measured in a similar manner. The degree of dispersion can be calculated from the weight average molecular weight and the number average molecular weight.

[0052] The glass transition temperature of the acrylic resin (A) is preferably −70 to 0° C., particularly preferably −60 to −20° C., and further preferably −55 to −30° C. If the glass transition temperature is too low, the heat resistance tends to decrease, and if it is too high, the adhesive performance tends to decrease.

[0053] The glass transition temperature (Tg) of the copolymer is calculated by the following Fox formula. Tg: Glass transition temperature of the copolymer (K) Tga: Glass transition temperature (K) of homopolymer consisting of monomer A Wa: Weight fraction of monomer A Tgb: Glass transition temperature (K) of homopolymer consisting of monomer B Wb: Weight fraction of monomer B Tgn: Glass transition temperature (K) of homopolymer consisting of monomer N Wn: Weight fraction of monomer N (Wa+Wb+···+Wn=1)

[0054] That is, it is a value calculated by applying the glass transition temperature and weight fraction of a homopolymer prepared from each of the monomers constituting the acrylic resin (A) to the Fox formula. The glass transition temperature of a homopolymer prepared from each of the monomers constituting the acrylic resin (A) is usually measured by a differential scanning calorimeter (DSC) and can be measured by a method in accordance with JIS K7121-1987 or JIS K6240.

[0055] <Crosslinking agent (B)> The crosslinking agent (B) used in the present invention is a compound that reacts with the functional group in the acrylic resin (A) to form a crosslinked structure, and at least an isocyanate-based crosslinking agent having an isocyanate group is used as the crosslinking agent (B). The crosslinking agent (B) has an isocyanate group concentration of 15% by weight or less, preferably 12% by weight or less, and more preferably 10% by weight or less per 100% by weight of solid content. Usually, the lower limit is 0.01% by weight. If the concentration is too high, the polarity of the pressure-sensitive adhesive composition will be high, and the storage modulus (G') of the pressure-sensitive adhesive composition in the 0 to 25°C region will be too high, which may reduce adhesion to polarizing plate substrates and the like having low polarity and reduce processability, making it difficult to achieve the effects of the present invention.

[0056] The method for calculating the isocyanate group concentration defined in the present invention is as follows. Isocyanate group concentration (wt%) per 100 wt% solid content of crosslinking agent (B) = Concentration of isocyanate groups in crosslinking agent (B) (wt%) / Solid content of crosslinking agent (B) (wt%) × 100 (wt%) The isocyanate group concentration in the crosslinking agent (B) is the weight ratio of the molecular weight (42) of the isocyanate group (-N=C=O) to the molecular weight of the isocyanate-based crosslinking agent, and when the crosslinking agent (B) contains a solvent, it is the isocyanate group concentration in a compound including the solvent.

[0057] Examples of the crosslinking agent (B) having an isocyanate group concentration of 15% by weight or less include a trimethylolpropane adduct of isophorone diisocyanate, a reaction product of hexamethylene diisocyanate and caprolactone-modified polyol, a reaction product of hexamethylene diisocyanate and polytetramethylene ether glycol, and a reaction product of hexamethylene diisocyanate and polypropylene glycol.

[0058] These crosslinking agents (B) may be used alone or in combination of two or more kinds. Among such crosslinking agents (B), those having a lactone-derived structure are preferred, and those having a caprolactone-derived structure are particularly preferred, in terms of low polarity and high reaction rate. For example, a reaction product of hexamethylene diisocyanate and caprolactone-modified polyol (isocyanate group concentration: 9.0% by weight) is preferred.

[0059] In the present invention, it is preferable that the crosslinking agent (B) contains at least an aliphatic polyisocyanate, and it is particularly preferable that the crosslinking agent (B) contains an aliphatic polyisocyanate in an amount of 10% by weight or more, more preferably 50% by weight or more, and especially preferably 80% by weight or more, the upper limit of which is usually 100% by weight.

[0060] The content of the crosslinking agent (B) is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, and particularly preferably 0.4 to 4 parts by weight, based on 100 parts by weight of the acrylic resin (A). If the content of the crosslinking agent (B) is too low, the durability tends to decrease, whereas if it is too high, the stress relaxation property tends to decrease and aging for a long period of time tends to be required.

[0061] In addition to the isocyanate-based crosslinking agent, a small amount of an epoxy-based crosslinking agent, an aziridine-based crosslinking agent, a melamine-based crosslinking agent, an aldehyde-based crosslinking agent, an amine-based crosslinking agent, a metal chelate-based crosslinking agent, etc. may be contained. The amount of these crosslinking agents is preferably 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less relative to 100 parts by weight of the crosslinking agent (B). The lower limit is 0 parts by weight.

[0062] 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.

[0063] Examples of the aziridine-based 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).

[0064] Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, melamine resins, and the like.

[0065] Examples of the aldehyde crosslinking agent include glyoxal, malondialdehyde, succindialdehyde, maleic dialdehyde, glutaric dialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0066] Examples of the amine-based crosslinking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0067] Examples of the metal chelate crosslinking agent include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

[0068] [Silane coupling agent (C)] The pressure-sensitive adhesive composition of the present invention may further contain a silane coupling agent (C). The silane coupling agent (C) is a silane compound having a functional group-containing substituent and an alkoxy group as a substituent.

[0069] Examples of the functional group include an epoxy group, a mercapto group, a hydroxyl group, a carboxyl group, an amino group, an amide group, an isocyanate group, a (meth)acryloyl group, etc., and the epoxy group and the mercapto group are preferred. The silane coupling agent (C) may have one type selected from these functional groups alone or two or more types in combination.

[0070] In addition, from the viewpoints of durability and storage stability, the alkoxy group is preferably an alkoxy group having 1 to 8 carbon atoms, more preferably an alkoxy group having 2 or more carbon atoms, and particularly preferably an ethoxy group. The content of the alkoxy group is preferably 30% by weight or more based on the silane coupling agent (C) from the viewpoints of maintaining the resistance to moist heat for a long period of time and of storage stability.

[0071] Furthermore, the silane coupling agent (C) may be either a monomeric silane compound or an oligomeric silane compound that is partially hydrolyzed and polycondensed. However, it is preferable to use an oligomeric silane compound because it has excellent durability and reworkability and is less likely to volatilize during drying after application of the adhesive.

[0072] Examples of the silane coupling agent (C) include epoxy group-containing silane coupling agents, (meth)acryloyl group-containing silane coupling agents, mercapto group-containing silane coupling agents, hydroxyl group-containing silane coupling agents, carboxyl group-containing silane coupling agents, amino group-containing silane coupling agents, amide group-containing silane coupling agents, isocyanate group-containing silane coupling agents, etc. These may be used alone or in combination of two or more. Among these, epoxy group-containing silane coupling agents and mercapto group-containing silane coupling agents are preferably used, and it is also preferable to use an epoxy group-containing silane coupling agent and a mercapto group-containing silane coupling agent in combination, in terms of improving the wet heat durability and preventing an excessive increase in adhesive strength.

[0073] Specific examples of the epoxy group-containing silane coupling agent include silane compounds such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, methyltri(glycidyl)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, oligomeric silane compounds (such as epoxy group-containing silicone alkoxy oligomers) obtained by hydrolyzing and polycondensing a portion of the silane compounds, and silane compounds obtained by ether-modifying a portion of these silane compounds. Among these, preferred are oligomeric silane compounds such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and silane compounds, or silane compounds obtained by partially ether-modifying these silane compounds.

[0074] Specific examples of the mercapto group-containing silane coupling agent include silane compounds such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-mercaptopropyldimethoxymethylsilane, and oligomeric silane compounds (such as mercapto group-containing silicone alkoxy oligomers) obtained by partial hydrolysis and polycondensation of silane compounds.

[0075] As the silane coupling agent (C), among the above silane compounds, it is preferable to use an oligomeric silane compound as described above, and furthermore, it is most preferable to use an oligomeric silane compound having an epoxy group or a mercapto group in terms of excellent reworkability and durability. Specific examples of oligomeric silane compounds having an epoxy group or a mercapto group include commercially available products such as "X-24-9590" manufactured by Shin-Etsu Chemical Co., Ltd. and "T-cure" manufactured by Momentive Performance Materials, Inc.

[0076] The content of the silane coupling agent (C) is usually 0.001 to 2 parts by weight, preferably 0.005 to 0.5 parts by weight, and particularly preferably 0.01 to 0.2 parts by weight, based on 100 parts by weight of the acrylic resin (A). If the content of the silane coupling agent (C) is too low, the effect tends not to be obtained, whereas if the content is too high, bleeding tends to occur, resulting in reduced durability.

[0077] [Ionic compounds (D)] The pressure-sensitive adhesive composition of the present invention may further contain an ionic compound (D), regardless of the presence or absence of the silane coupling agent (C). The ionic compound (D) used in the present invention is an ionic compound consisting of a cationic component (d1) and an anionic component (d2).

[0078] Examples of the cationic component (d1) include alkali metal cations and onium cations, and one type may be used alone or two or more types may be used in combination. Examples of the alkali metal cation include lithium cation and sodium cation. Examples of the onium cation include nitrogen-containing onium cation, phosphorus-containing onium cation, sulfur-containing onium cation, etc. Examples of the onium cation containing nitrogen include imidazolium cation, pyrrolidinium and other 5-membered ring compound onium cation, pyridinium cation, piperidinium and other 6-membered ring compound onium cation, quaternary ammonium cation, etc. Examples of the onium cation containing phosphorus include phosphonium cation, and examples of the onium cation containing sulfur include sulfonium cation. Among such onium cations, from the viewpoints of compatibility with the acrylic resin (A) and antistatic performance, nitrogen-containing onium cations are preferred, and in particular ammonium cations, and more preferably quaternary ammonium cations.

[0079] The anion component (d2) of the ionic compound (D) can be selected from metal anions and organic anions, and one type can be used alone or two or more types can be used in combination. Specific examples include metal anions such as hexafluorophosphate anion, bromide anion, and chloride anion, and organic anions such as trifluoromethanesulfonylimide anion and bisfluorosulfonylimide anion. Among these, from the viewpoints of antistatic performance and lowering the melting point, organic anions are preferred, and trifluoromethanesulfonylimide is more preferred from the viewpoints of compatibility with the acrylic resin (A) and lowering the melting point.

[0080] The melting point of the ionic compound (D) is preferably 25°C or higher, more preferably 26°C or higher, and particularly preferably 27°C or higher. If the melting point is too low, the polarization degree tends to decrease in a humid and hot environment. The upper limit of the melting point is usually 100°C, preferably 80°C, more preferably 60°C, and particularly preferably 40°C. If the melting point is too high, the compatibility with the acrylic resin (A) tends to decrease, or precipitation tends to occur at low temperatures.

[0081] As the ionic compound (D), for example, it is preferable to use methyltri-n-butylammonium bis(trifluoromethanesulfonyl)imide ("FC-4400" manufactured by 3M, melting point: 27.5° C.).

[0082] The content of the ionic compound (D) is preferably 1 to 10 parts by weight, particularly 1.5 to 5 parts by weight, and further preferably 2 to 4 parts by weight, based on 100 parts by weight of the acrylic resin (A). If the content of the ionic compound (D) is too small, sufficient antistatic performance tends not to be obtained, whereas if it is too large, the degree of polarization tends to decrease under humid and hot conditions.

[0083] The ionic compound (D) used in the present invention has excellent compatibility with the acrylic resin (A) and the crosslinking agent (B), and therefore inhibits migration of the ionic compound in a humid and hot environment, and has excellent antistatic properties and durability.

[0084] <Other ingredients> The adhesive composition of the present invention may contain, within the scope of the present invention, acrylic adhesives other than the acrylic resin (A), other adhesives, tackifiers such as urethane resins, rosins, rosin esters, hydrogenated rosin esters, phenolic resins, aliphatic petroleum resins, alicyclic petroleum resins, and styrene resins, colorants, fillers, antioxidants, ultraviolet absorbers, and various additives such as functional dyes, and compounds that change color or undergo color change when exposed to ultraviolet light or radiation. In addition to the above additives and compounds, the adhesive composition may contain small amounts of impurities contained in the raw materials for producing the components of the adhesive composition.

[0085] The content of the other components may be appropriately set so as to obtain desired physical properties, but is preferably 5 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, relative to 100 parts by weight of the acrylic resin (A). If the content is too high, the compatibility with the acrylic resin (A) decreases, and transparency tends to be impaired.

[0086] Thus, the pressure-sensitive adhesive composition of the present invention can be obtained. The pressure-sensitive adhesive composition of the present invention can exhibit excellent optical properties (degree of polarization) even under humid and hot conditions when used as a pressure-sensitive adhesive composition for bonding an optical component such as a polarizing plate to a glass substrate or the like, and can provide a pressure-sensitive adhesive having excellent antistatic properties. The pressure-sensitive adhesive composition of the present invention is useful as a pressure-sensitive adhesive composition for optical components for bonding displays and optical components that constitute the displays, and in particular as a pressure-sensitive adhesive composition for polarizing plates for bonding a polarizing plate to a glass substrate or the like of a liquid crystal cell.

[0087] (2) Pressure-sensitive adhesive, optical component with pressure-sensitive adhesive layer The pressure-sensitive adhesive composition of the present invention can be made into a pressure-sensitive adhesive by crosslinking with a crosslinking agent (B). Furthermore, a pressure-sensitive adhesive layer made of such a pressure-sensitive adhesive can be laminated on an optical member (optical laminate) to obtain an optical member with a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer-attached optical member preferably further has a release sheet provided on the surface of the pressure-sensitive adhesive layer opposite to the optical member surface.

[0088] The method for producing the pressure-sensitive adhesive layer-attached optical member includes the steps of: [1] A method in which a pressure-sensitive adhesive composition is applied onto an optical member, dried, a release sheet is attached, and the adhesive composition is subjected to at least one of aging treatments at room temperature or at an elevated temperature; [2] There is a method in which a pressure-sensitive adhesive composition is applied onto a release sheet, dried, and then an optical member is attached to the sheet, followed by aging at least one of at room temperature or at an elevated temperature. Among these, the method [2], which involves aging at room temperature, is preferred because it does not damage the substrate and provides excellent adhesion to the substrate.

[0089] The aging treatment is carried out to balance the adhesive properties as the reaction time of the chemical crosslinking of the adhesive, and the aging conditions are usually room temperature to 70°C and the time is usually 1 to 30 days. Specifically, the aging treatment can be carried out under conditions such as 1 to 20 days at 23°C, 3 to 10 days at 23°C, or 1 to 7 days at 40°C.

[0090] When applying the pressure-sensitive adhesive composition, it is preferable to dilute the pressure-sensitive adhesive composition in a solvent and apply the composition, and the dilution concentration is preferably 5 to 60% by weight, particularly preferably 10 to 30% by weight, as a heating residue concentration. The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, and for example, ester-based solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate; ketone-based solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic solvents such as toluene and xylene; and alcohol-based solvents such as methanol, ethanol, and propyl alcohol can be used. Among these, ethyl acetate and methyl ethyl ketone are preferably used in terms of solubility, drying property, price, and the like.

[0091] The pressure-sensitive adhesive composition can be applied by a conventional method such as roll coating, die coating, gravure coating, comma coating, screen printing, or the like.

[0092] The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 95%, particularly preferably 40 to 90%, and further preferably 55 to 85%, from the viewpoints of durability and suppression of a decrease in the degree of polarization. If the gel fraction is too low, the movement of the ionic compound (D) cannot be suppressed, and the degree of polarization tends to decrease, whereas if the gel fraction is too high, the antistatic performance tends to decrease.

[0093] The gel fraction is a measure of the degree of crosslinking (degree of curing) and is calculated, for example, by the following method: the adhesive layer is scraped off from an adhesive sheet (without a separator) in which an adhesive layer is formed on an optical member serving as a substrate, the adhesive layer is wrapped in a 200-mesh SUS wire netting and immersed in ethyl acetate at 23°C for 24 hours, and the weight percentage of the insoluble adhesive component remaining in the wire netting is taken as the gel fraction. The gel fraction can be adjusted to fall within the above range by adjusting the type and amount of the crosslinking agent (B), for example.

[0094] If the pressure-sensitive adhesive layer produced by the above method has an appropriate tackiness when touched with the fingers, it is preferred since it has good wettability when actually applied to an adherend, which tends to improve workability.

[0095] The thickness of the adhesive layer in the obtained optical member with the adhesive layer is preferably 5 to 300 μm, particularly preferably 10 to 50 μm, and further preferably 10 to 30 μm. If the thickness of this adhesive layer is too thin, the adhesive properties tend to be difficult to stabilize, whereas if it is too thick, the amount of the ionic compound (D) contained increases, which tends to cause a decrease in the degree of polarization or a deterioration in wet heat whitening (haze value).

[0096] The pressure-sensitive adhesive layer-attached optical member of the present invention is used, for example, as a liquid crystal display panel, by laminating the pressure-sensitive adhesive layer surface to a glass substrate directly, or after peeling off a release sheet if one is provided.

[0097] The initial adhesive strength of the adhesive layer is appropriately determined depending on the material of the adherend, etc. For example, when adhering to a glass substrate, the adhesive strength is preferably 0.2 to 20 N / 25 mm, particularly preferably 1 to 10 N / 25 mm, and further preferably 2 to 8 N / 25 mm.

[0098] The initial adhesive strength is calculated, for example, as follows: A polarizing plate with an adhesive layer is cut to a width of 25 mm, the release film is peeled off, and the adhesive layer side is pressed against an alkali-free glass plate (manufactured by Corning (registered trademark), "Eagle XG (registered trademark)") to bond the polarizing plate and the glass plate. After that, autoclave treatment (50°C, 0.5 MPa, 20 minutes) is performed, and then the specimen is left at 23°C and 50% RH for 24 hours before undergoing a 180°C peel test.

[0099] The polarizing plate used in the present invention is usually a polarizing film having triacetyl cellulose (TAC)-based films laminated on both sides as protective films. The polarizing film is a uniaxially stretched film (usually stretched 2 to 10 times, preferably 3 to 7 times) dyed with an aqueous solution of iodine-potassium iodide or a dichroic dye, using a film made of a polyvinyl alcohol-based resin having an average degree of polymerization of 1,500 to 10,000 and a degree of saponification of 85 to 100 mol% as a raw film.

[0100] The polyvinyl alcohol resin is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but may contain a small amount of a component copolymerizable with vinyl acetate, such as unsaturated carboxylic acid (including salt, ester, amide, nitrile, etc.), olefin, vinyl ether, unsaturated sulfonate, etc. Also included are so-called polyvinyl acetal resins and polyvinyl alcohol derivatives, such as polybutyral resin and polyvinyl formal resin, which are produced by reacting polyvinyl alcohol with aldehydes in the presence of an acid.

[0101] Examples of the protective film for the polarizing plate include, in addition to conventional TAC films, acrylic films, polyethylene films, polypropylene films, cycloolefin films, and the like. The pressure-sensitive adhesive of the present invention can be suitably used for any protective film selected from low polarity films such as TAC films, acrylic films, cycloolefin films, and PET films. EXAMPLES

[0102] 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.

[0103] First, various acrylic resins were prepared as follows: The weight average molecular weight, dispersity and glass transition temperature of the acrylic resin (A) were measured according to the methods described above. The viscosity was measured in accordance with JIS K5400 (1990) 4.5.3 Rotational Viscometer Method.

[0104] <Preparation of acrylic resin (A)> [Production of acrylic resin (A-1)] In a four-necked round-bottom flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet, and a thermometer, 96.3 parts of butyl acrylate (a1), 3.0 parts of 2-hydroxyethyl acrylate (a2-1), 0.7 parts of acrylic acid (a2), 54.3 parts of ethyl acetate, and 20 parts of acetone were charged, and a mixture of 0.029 parts of azobisisobutyronitrile (AIBN) and 60 parts of ethyl acetate was added dropwise over 2 hours while heating and refluxing. After further reacting for 1.5 hours, the mixture was diluted with 129.4 parts of ethyl acetate to obtain an acrylic resin (A-1) solution (solid concentration 23.6% by weight, viscosity 7,500 mPa·s / 25℃, weight average molecular weight 1.4 million, dispersity 3.6, glass transition temperature -53.3℃).

[0105] For the acrylic resins (A-1) to (A-3) and (A'-1) to (A'-2) prepared as described above, the contents of the monomer components, the weight average molecular weight (Mw) and the dispersity are shown in Table 1 below.

[0106] [Table 1]

[0107] <Crosslinking agent (B)> The following compound was prepared as the crosslinking agent (B). B-1: Reaction product of hexamethylene diisocyanate and caprolactone-modified polyol (solid content concentration 100% by mass, isocyanate group concentration 9.0% by weight) B'-1: Toluene diisocyanate and trimethylolpropane adduct (solid content concentration 75% by mass, isocyanate group concentration 17.7% by weight (per 100% by mass of solid content))

[0108] <Silane coupling agent (C)> The following silane coupling agent (C) was prepared: C-1: Oligomeric silane compound ("X-24-9590" manufactured by Shin-Etsu Chemical Co., Ltd., functional group: epoxy group) C-2: Oligomeric silane compound ("T-cure" manufactured by Momentive Performance Materials, Inc., functional group: mercapto group)

[0109] <Ionic Compound (D)> The following was prepared as the ionic compound (D). D-1: Methyltri-n-butylammonium bis(trifluoromethanesulfonyl)imide (3M "FC-4400", melting point: 27.5°C)

[0110] <Examples 1 to 3 and Comparative Examples 1 to 4> The above components (A) to (D) were mixed as shown in Table 2 below, and the solid content was adjusted to 15% by weight with ethyl acetate to obtain a pressure-sensitive adhesive composition. In Table 2, the amounts of the crosslinking agent (B), silane coupling agent (C), and ionic compound (D) are calculated based on 100 parts by weight of the entire acrylic resin (A).

[0111] [Preparation of Polarizing Plate with Pressure-Sensitive Adhesive Layer] The obtained adhesive composition was applied to a 38 μm separator ("Lumirror (registered trademark) SP-0138BU" manufactured by Mitsui Chemicals Tocello Inc.) so that the film thickness after drying would be 25 μm, and after drying at 100°C for 3 minutes, the adhesive layer surface opposite the separator was bonded to one of the TAC surfaces of a polarizing plate having TAC film laminated on both sides, and cured for 7 days in an environment of 23°C x 50% RH to obtain a polarizing plate with an adhesive layer (layer structure: separator / adhesive layer / TAC film / polarizer / TAC film). The obtained polarizing plate with the pressure-sensitive adhesive layer was evaluated for adhesion to a substrate, processability, durability, reworkability, gel fraction, and surface resistance. The results are shown in Table 3.

[0112] <Adhesion to substrate> After peeling off the separator from the polarizing plate with the adhesive layer obtained above, the edge of the adhesive applied to the polarizing plate was rubbed with a finger 10 times, and the condition was observed and evaluated according to the following evaluation criteria. (Evaluation Criteria) No peeling of the adhesive was observed. ○ Slight peeling of adhesive was observed. △ Peeling was observed. ×: Peeling was evident.

[0113] <Workability> Five sheets of the polarizing plate with the adhesive layer obtained above were stacked together to produce a laminate, and the laminate was then cut with a blade. The cut sheets were observed to determine whether the sheets were adhered to each other and whether the adhesive was adhered to the cutting blade, and evaluated according to the following evaluation criteria. (Evaluation Criteria) ◎ No adhesive was found to adhere to the blade or to the other sheets. ○: A small amount of adhesive was found to be attached to the blade, but no adhesion between the sheets was found. △: Slight adhesion of adhesive to the blade and between the sheets was observed. ×: Significant adhesion between sheets was observed.

[0114] <Durability> The polarizing plate with the adhesive layer obtained above was cut to 15 cm x 10 cm, the separator was peeled off, and the adhesive layer side was pressed against an alkali-free glass plate (Corning (registered trademark) "Eagle XG (registered trademark): thickness 1.1 mm) to bond the polarizing plate and the glass plate, and then autoclaving (50°C, 0.5 MPa, 20 minutes) was performed to prepare a sample for a durability test. The durability test samples obtained above were left to stand for 500 hours in an 85°C dry (heat-resistant) environment and in a 60°C x 90% RH environment, respectively, and then observed after being taken out and evaluated according to the following evaluation criteria. (Evaluation Criteria) ○ The area where floating or peeling is observed is less than 0.1 mm from the edge, or the diameter of the bubbles observed is less than 0.1 mm. △: Floating or peeling was observed in the area 0.1 mm or more but less than 1.0 mm from the edge, or the diameter of the bubbles observed was 0.1 mm or more but less than 1.0 mm. × Lifting or peeling is observed in the area 1.0 mm or more from the edge, or the diameter of the bubbles observed is 1.0 mm or more.

[0115] <Reworkability> The polarizing plate with the adhesive layer obtained above was cut to a width of 2.5 cm × 12 cm, the separator was peeled off, and the adhesive layer side was pressed against an alkali-free glass plate (Corning (registered trademark) "Eagle XG (registered trademark): thickness 1.1 mm) to bond the polarizing plate and the glass plate, and then autoclaving (50°C, 0.5 MPa, 20 minutes) was performed to prepare a sample for evaluating reworkability. The reworkability evaluation samples obtained above were subjected to an adhesive strength evaluation 30 days after bonding using an autograph peel test (300 mm / min), and the reworkability was evaluated according to the following evaluation criteria. (Evaluation Criteria) ○ Less than 5N / 25mm and adherend interface peeling × 5N / 25mm or more, or cohesive peeling or substrate interface peeling

[0116] <Gel fraction> After peeling off the separator from the polarizing plate with the adhesive layer obtained above, the adhesive layer was rinsed off, wrapped in a 200-mesh SUS wire mesh, and immersed in ethyl acetate at 23°C for 24 hours. The weight percentage of the insoluble adhesive component remaining in the wire mesh was determined as the "gel fraction."

[0117] <Surface resistivity> The separator was peeled off from the polarizing plate with the adhesive layer obtained above, and the surface resistivity (Ω / sq.) of the adhesive layer was measured using a surface resistivity meter (manufactured by Nitto Seiko Analytech Co., Ltd., device name "Hiresta-UP MCP-HT450").

[0118] [Table 2]

[0119] [Table 3]

[0120] From the results in Table 3, the pressure-sensitive adhesives of Examples 1 to 3, which were made of the pressure-sensitive adhesive composition of the present invention, were excellent in terms of adhesion to substrates, processability, durability, and reworkability in a well-balanced manner. In contrast, the pressure-sensitive adhesive of Comparative Example 1, in which a crosslinking agent (B) having an isocyanate group concentration of more than 15 mass % in 100% solids was used, was found to be inferior in adhesion to substrates and processability. It is clear that the pressure-sensitive adhesive of Comparative Example 2, in which the structural unit derived from the hydroxyl group-containing monomer (a2-1) in the acrylic resin (A) was less than 2.7% by weight, was poor in durability. It can be seen that the adhesives of Comparative Examples 3 and 4, in which the structural units derived from the hydroxyl group-containing monomer (a2-1) in the acrylic resin (A) exceed 8 mass%, are significantly inferior in adhesion to substrates and processability, and are inferior in either durability or reworkability. [Industrial Applicability]

[0121] The pressure-sensitive adhesive composition of the present invention has excellent processability, durability and reworkability when used as an adhesive for bonding a polarizing plate to a glass substrate or the like, and is therefore useful as an adhesive for optical components for bonding optical components, in particular as an adhesive for polarizing plates for bonding a polarizing plate to a glass substrate or the like of a liquid crystal cell.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic resin (A) and a crosslinking agent (B), the acrylic resin (A) contains a structural unit derived from a hydroxyl group-containing monomer (a2-1), and the content of the structural unit derived from the hydroxyl group-containing monomer (a2-1) is 2.7 to 8% by weight of all structural units constituting the acrylic resin (A); The pressure-sensitive adhesive composition, wherein the crosslinking agent (B) has an isocyanate group, and the concentration of the isocyanate group per 100% by weight of the solid content of the crosslinking agent (B) is 15% by weight or less.

2. The pressure-sensitive adhesive composition according to claim 1 , wherein the crosslinking agent (B) has a structure derived from a lactone.

3. The pressure-sensitive adhesive composition according to claim 1, further comprising a silane coupling agent (C).

4. The pressure-sensitive adhesive composition according to claim 3, wherein the silane coupling agent (C) contains an epoxy group and / or a mercapto group.

5. 4. The pressure-sensitive adhesive composition according to claim 3, wherein the silane coupling agent (C) is an oligomer type silane compound.

6. The pressure-sensitive adhesive composition according to claim 1, further comprising an ionic compound (D).

7. The pressure-sensitive adhesive composition according to claim 6, wherein the ionic compound (D) has a melting point of 25°C or higher.

8. The pressure-sensitive adhesive composition according to claim 6, wherein the cationic component (d1) of the ionic compound (D) is an onium cation containing nitrogen.

9. A pressure-sensitive adhesive composition for optical members, comprising the pressure-sensitive adhesive composition according to any one of claims 1 to 8.

10. A pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 8.

11. An optical member with a pressure-sensitive adhesive layer, comprising an optical member and a pressure-sensitive adhesive layer laminated thereon, the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to claim 10.

Images