JP2007169329A - Adhesive composition for optical use and adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition for optical use, which not only reduces distortion by displacement of an adhesive, provided that the distortion specifically results from expansion and contraction of a polarizing plate, but also approximates the birefringence of an adhesive layer to zero, provided that the birefringence results from orientation of a polymer in the adhesive layer induced by the displacement, thus preventing color heterogeneity or white spot phenomenon in a liquid crystal element. <P>SOLUTION: The adhesive composition for optical use contains a copolymer (A) and a crosslinking agent (B), wherein the amount of the crosslinking agent (B) is adjusted so that the adhesive layer formed achieves a coefficient of viscosity at 90°C of 0.5×10<SP>7</SP>-10×10<SP>7</SP>Pa s. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical pressure-sensitive adhesive composition used for attaching an optical functional film such as a polarizing plate or a retardation plate to an optical component such as a liquid crystal cell of a liquid crystal display device.

  A liquid crystal display device (hereinafter referred to as a liquid crystal element) has a structure in which a liquid crystal component oriented in a predetermined direction is sandwiched between two substrates. The laminated body with a phase difference plate is stuck. In recent years, liquid crystal elements have been widely used due to the reduction in weight and thickness of display devices such as those mounted on vehicles, outdoor instruments, personal computer displays and televisions, and the demand for such devices is increasing. Along with this, the usage environment has become very severe both indoors and outdoors.

  A polarizing plate used for a liquid crystal element has a three-layer structure in which both surfaces of a polyvinyl alcohol-based polarizer are sandwiched between triacetyl cellulose-based protective films, but dimensional stability is poor due to the characteristics of these materials. Further, since the polarizing plate is formed by stretching, dimensional changes with time are likely to occur. If the internal stress generated by such a dimensional change cannot be absorbed and relaxed, the distribution of residual stress acting on the polarizing plate becomes non-uniform, and stress is concentrated particularly on the peripheral portion of the polarizing plate. As a result, color unevenness and white spotting occur on the surface of the liquid crystal element such that the peripheral edge of the liquid crystal element is brighter or darker than the center.

  On the other hand, birefringence of the pressure-sensitive adhesive layer can be considered as another factor that causes uneven color and white spots. That is, the pressure-sensitive adhesive layer formed by coating the optical film in a form in which the pressure-sensitive adhesive is dissolved in the solvent is macroscopically isotropic because many polymer chains are intertwined therein, Does not generate birefringence. However, after bonding the polarizing plate to the liquid crystal panel, etc., when the dimensional change of the polarizing plate occurs over time, the adhesive layer follows the dimensional change of the deflecting plate, and thus distortion occurs. When the polymer in the agent layer is partially oriented, birefringence occurs, which causes the above-described uneven color / whitening phenomenon.

  Many means have been studied in order to solve the above problems. For example, in Patent Document 1, an outline “100 parts by mass of a high molecular weight (meth) acrylic copolymer having a weight average molecular weight of 1,000,000 or more and a low molecular weight (meth) acrylic copolymer having a weight average molecular weight of 30,000 or less. An invention of “adhesive composition for polarizing plate comprising 20 to 200 parts by mass of coalescence and 0.005 to 5 parts by mass of a polyfunctional compound” is disclosed. The invention describes that a pressure-sensitive adhesive layer that can follow the dimensional change of the polarizing plate is formed, and color unevenness and white spotting phenomenon hardly occur in the liquid crystal element. However, as a result of investigations by the present inventors, in the present invention, the addition amount of the polyfunctional compound is wide, and it is very difficult to adjust the addition amount in order to prevent the occurrence of uneven color and white spots. Therefore, it is difficult to produce a polarizing plate or a retardation plate having a stable pressure-sensitive adhesive layer.

  Patent Documents 2 and 3 disclose a pressure-sensitive adhesive having a high refractive index, for example, an invention that is generally “a pressure-sensitive adhesive containing an aromatic monomer having a refractive index of at least 1.48”. Is disclosed. In the invention, since the pressure-sensitive adhesive having a high refractive index can match the refractive index of the adhesive and the refractive index of the substrate, it is used for a specific optical application, particularly, a substrate having a high refractive index. It is stated that it is useful if you do. However, in the invention, there is no description that the addition amount of the polyfunctional compound is in a wide range, the occurrence of uneven color / whitening phenomenon is prevented, and the optical characteristics can be improved.

  Patent Document 4 discloses a low-polarity film pressure-sensitive adhesive comprising a (meth) acrylic acid alkyl ester, an alicyclic monomer or an aromatic ring-containing monomer, and a functional group-containing monomer. However, Patent Document 4 does not describe that the optical characteristics can be improved by controlling the birefringence of the adhesive to prevent uneven color and white spots when used in a polarizing plate.

Japanese Patent No. 3533589 Special table 2003-535921 gazette JP 2002-173656 A JP 2005-053976 A

  The purpose of the present invention is not only to relieve distortion of the optical substrate, particularly due to expansion and contraction of the polarizing plate, by shifting the pressure sensitive adhesive, but also for the pressure sensitive adhesive layer produced by the orientation of the polymer in the pressure sensitive adhesive layer due to displacement. An object of the present invention is to provide an optical pressure-sensitive adhesive composition that does not cause uneven color and white spots in a liquid crystal element by making birefringence close to zero.

The above object is achieved by the present invention described below. That is, the present invention comprises at least a (meth) acrylic acid alkyl ester monomer unit (a) having 1 to 18 carbon atoms, a copolymerizable monomer unit (b) having an aromatic ring, a carboxyl group and / or A copolymerizable monomer unit (c) containing a hydroxyl group, and the unit (c) is 0.1 to 4 parts by mass per 100 parts by mass in total of the unit (a) and the unit (b), The unit (a) is an amount occupying 40 to 80% by mass in the total 100% by mass of the unit (a) and the unit (b), and the unit (b) is a total of 100 of the unit (a) and the unit (b). It contains 20% to 60% by mass of the copolymer (A) and the crosslinking agent (B) having a weight average molecular weight of 1,000,000 to 2,000,000, and contains the crosslinking agent (B). amount, 90 ° C. of formed adhesive layer viscosity coefficient 0.5 × 10 ⁷ to 1 Providing an optical pressure-sensitive adhesive composition characterized (hereinafter referred to as "pressure-sensitive adhesive composition") that is an amount to be × 10 ⁷ Pa · s.

In the pressure-sensitive adhesive composition of the present invention, the monomer unit (b) is at least one selected from the group consisting of 2-phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, styrene, and α-methylstyrene. A monomer unit of the species: and the monomer unit (b) is represented by the following general formula (I): a monomer having n of 1 and a monomer having n of 2 or more The mixture is preferably a monomer mixture in which the content of the monomer having n of 2 or more occupies 1 to 5% by mass of the total amount of the mixture.

  The pressure-sensitive adhesive composition of the present invention further comprises 1 to 50 parts by mass of a low molecular weight copolymer (C) per 100 parts by mass of the copolymer (A), and the copolymer (C) Includes a (meth) acrylic acid alkyl ester monomer unit (a) and a copolymerizable monomer unit (b) having an aromatic ring, and has a weight average molecular weight of 1,000 to 30,000. The dispersity (MW / MN) is preferably 1.0 to 2.5 and is a copolymer compatible with the copolymer (A).

  Moreover, in the said adhesive composition of this invention, 0.01-2 mass of silane compounds (D) which contain a mercaptoalkyl group and an alkoxy group simultaneously in a molecule | numerator per 100 mass parts of said copolymers (A) further. It is preferable that a part is included.

  Moreover, this invention provides the adhesive sheet characterized by having an adhesive layer which consists of an adhesive composition of the said this invention on the surface of an optical functional film.

  As a result of intensive studies to solve the problems of the prior art, the present inventors can copolymerize the adhesive resin of the adhesive composition with an alkyl acrylate ester monomer and a specific aromatic ring. By co-polymerizing with a certain monomer at a certain ratio, and by adjusting the viscosity coefficient of the pressure-sensitive adhesive composition containing the pressure-sensitive adhesive resin, it is possible to follow the dimensional change of the polarizing plate. The inventors have found that a pressure-sensitive adhesive composition that does not cause peculiar color unevenness and white spots when used for an optical substrate such as a plate can be obtained.

  The above phenomenon is caused by a pressure-sensitive adhesive resin obtained by copolymerizing an acrylic acid alkyl ester monomer and a copolymerizable monomer having a specific aromatic ring at a certain ratio, and the orientation birefringence is close to zero in the pressure-sensitive adhesive layer. For this reason, it is considered that even if a deviation occurs due to expansion and contraction of the polarizing plate, it was achieved by not causing birefringence.

  Therefore, according to the present invention, the polarizing plate has a suitable adhesive force, good adhesion to the optical functional film, and further contains a copolymerizable monomer having an aromatic ring as a constituent component. Provided is a pressure-sensitive adhesive composition that can prevent the occurrence of uneven color and white spots due to expansion and contraction.

Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention. The pressure-sensitive adhesive composition of the present invention contains a specific copolymer (A) and a crosslinking agent (B) as essential components, and the content of the crosslinking agent is such that the 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer is 0.5 × 10. ^The amount is ⁷ to 10 × 10 ⁷ Pa · s.

  Specific examples of the (meth) acrylic acid alkyl ester monomer (a) used in the production of the copolymer (A) include (methyl) methyl (meth) acrylate and ethyl (meth) acrylate. , Propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate And at least one selected from these groups can be used. The amount used is 40 to 80% by mass when the total of the monomer (a) constituting the copolymer (A) and the monomer (b) described below is 100% by mass. It is necessary. Preferably it is 50-70 mass%. When the amount used is less than 40% by mass, the adhesiveness of the finally obtained pressure-sensitive adhesive composition to the polarizing plate is lowered. On the other hand, when the amount of the monomer (a) used exceeds 80% by mass, the effect on the uneven color / whitening phenomenon is deteriorated.

The monomer (b) to be copolymerized with the monomer (a) is a monomer having an aromatic ring, which reduces the orientation birefringence of the pressure-sensitive adhesive composition of the present invention, thereby polarizing the polarizing plate. Even if the dimensional change occurs, the pressure-sensitive adhesive composition of the present invention is provided with a function that does not cause uneven color / whitening phenomenon and does not cause foaming or peeling due to the dimensional change.
Examples of the monomer (b) include 2-phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, styrene, and α-methylstyrene, and at least one selected from these groups is used. be able to. A particularly preferable monomer (b) is a mixture of a monomer having n of 1 and a monomer having n of 2 or more represented by the following general formula (I), wherein n is 2 or more. It is a monomer mixture in which the content of the monomer occupies 1 to 5% by mass of the total amount of the mixture.

  In the above, when a mixture in which the content of the monomer having n of 2 or more exceeds 5% by mass in the total amount of the monomer (b) is used, the finally obtained copolymer (A) is gelled. Therefore, the viscosity of the pressure-sensitive adhesive composition also deteriorates. Further, a mixture in which the content of the monomer having n of 2 or more is less than 1% is not preferable because it requires a purification cost during production and is expensive.

  The amount of the monomer (b) used is 20 to 60 when the total of the monomer (a) and the monomer (b) constituting the copolymer (A) is 100% by mass. It is necessary to be mass%. Preferably it is 30-50 mass%. When the amount of the monomer (b) used is less than 20% by mass or exceeds 60% by mass, the use of the pressure-sensitive adhesive composition formed by the copolymer (A) may cause uneven color and white spots. The occurrence cannot be suppressed.

  Specific examples of the carboxyl group-containing monomer among the carboxyl group and / or hydroxyl group-containing monomer (c) constituting the copolymer (A) include (meth) acrylic acid, itaconic acid, maleic acid, Maleic anhydride, fumaric acid, fumaric anhydride, carboxyethyl acrylate and the like can be mentioned, and at least one selected from these groups can be used. (Meth) acrylic acid and carboxyethyl acrylate are preferred. Specific examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, caprolactone-modified (meth) acrylate, polyethylene glycol (meta ) Acrylate, polypropylene glycol (meth) acrylate, etc., and at least one selected from these groups can be used.

  The carboxyl group-containing monomer and the hydroxyl group-containing monomer can be used alone or in combination. The usage-amount is 0.1-4 mass parts per 100 mass parts of total amounts of the monomer (a) and monomer (b) which comprise a copolymer (A). Preferably it is 0.5-3 mass parts. When the amount used is less than 0.1 parts by mass, the obtained copolymer (A) has few crosslinking points, and the optical member using the pressure-sensitive adhesive composition containing the copolymer has a deviation at room temperature. On the other hand, when the amount of the monomer (c) used exceeds 4 parts by mass, in the optical member using the pressure-sensitive adhesive composition containing the copolymer, it is caused by expansion and contraction of the polarizing plate layer. It is not possible to sufficiently absorb or relax the stress concentration. Moreover, it cannot polymerize stably because gelation occurs during the reaction.

  The weight average molecular weight of the copolymer (A) constituting the pressure-sensitive adhesive composition of the present invention needs to be 1 million to 2 million. When the copolymer (A) has a weight average molecular weight of less than 1,000,000, the cohesive force of the pressure-sensitive adhesive layer is insufficient even if it is crosslinked using a crosslinking agent, and foaming or peeling from the polarizing plate is likely to occur. . When the weight average molecular weight exceeds 2 million, the stress concentration resulting from the expansion and contraction of the polarizing plate cannot be sufficiently absorbed and relaxed. Moreover, the viscosity of an adhesive composition becomes high too much and the workability | operativity at the time of using an adhesive composition is inferior.

  In addition, a weight average molecular weight (MW) is G.G. P. Polystyrene equivalent molecular weight measured by C. Specifically, the coating film obtained by drying the copolymer at room temperature was dissolved in tetrahydrofuran, and then a high performance liquid chromatograph (Shimadzu Corporation, LC-10ADvp, column; KF-G + KF-806 × 2). The weight average molecular weight (MW) was determined in terms of polystyrene.

  As the crosslinking agent (B) used in the pressure-sensitive adhesive composition of the present invention, a compound that reacts with a carboxyl group and / or a hydroxyl group can be used, and is necessary for increasing the cohesive strength of the pressure-sensitive adhesive. As the crosslinking agent that can be used, a glycidyl compound having at least two glycidyl groups in one molecule, an isocyanate compound having two or more isocyanate groups in one molecule, an aziridine compound having at least two aziridinyl groups in one molecule, 1 An oxazoline compound having an oxazoline group in the molecule, a metal chelate compound, a butylated melamine compound, or the like can be used. Preferred are glycidyl compounds, isocyanate compounds and aziridine compounds.

The amount of the crosslinking agent used is such that the 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer formed from the copolymer (A) and the crosslinking agent (B) is 0.5 × 10 ⁷ to 10 × 10 ⁷ Pa · s. Amount. When the 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer is lower than 0.5 × 10 ⁷ Pa · s, the cohesive force of the pressure-sensitive adhesive layer is low, which causes foaming and peeling, while the pressure-sensitive adhesive layer has a 90 ° C. viscosity. When the coefficient is higher than 10 × 10 ⁷ Pa · s, it becomes difficult for the pressure-sensitive adhesive layer to sufficiently absorb and relax the stress concentration caused by the expansion and contraction of the polarizing plate layer. The 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer can be adjusted to the above range by changing the amount of the crosslinking agent (B) used in various ways. The amount of the crosslinking agent (B) used cannot be defined unconditionally depending on the properties of the copolymer (A), the type of the crosslinking agent (B), etc., but is 0.01% per 100 parts by mass of the copolymer (A). It is -1 mass part, Preferably it is 0.05-0.5 mass part. By using this amount, the 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer can be in the above range.

  Specific examples of the glycidyl compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6 -Hexanediol diglycidyl ether, N, N, N ', N'-tetraglycidyl m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, trimethylolpropane polyglycidyl ether, diglycerol Polyfunctional glycidyl compounds such as polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, and the group Ri at least one selected may be used.

Specific examples of the isocyanate compound include tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and prepolymers modified from these, and at least one selected from these groups should be used. Can do.
Specific examples of the aziridine compound include 1,1 ′-(methylene-di-p-phenylene) bis-3,3-aziridylurea and 1,1 ′-(hexamethylene) bis-3,3-aziridyl. Urea, ethylenebis- (2-aziridinylpropionate), tris (1-aziridinyl) phosphine oxide, 2,4,6-triaziridinyl-1,3,5-triazine, trimethylolpropane-tris- (2- Aziridinylpropionate) and the like, and at least one selected from these groups can be used.

  In the adhesive composition of this invention, it is preferable that 1-50 mass parts low molecular weight copolymer (C) is further included per 100 mass parts of said copolymers (A). The copolymer (C) includes a (meth) acrylic acid alkyl ester monomer unit (a) and a copolymerizable monomer unit (b) having an aromatic ring, and has a weight average molecular weight of 1, It is a copolymer having a dispersity (MW / MN) of 1.0 to 2.5 and compatibility with the copolymer (A).

  The (meth) acrylic acid alkyl ester monomer (a) used for the synthesis of the low molecular weight copolymer (C) is the same as the monomer (a) used for the synthesis of the copolymer (A). is there. The copolymerization ratio is preferably an amount occupying 40 to 80% by mass when the total monomer constituting the obtained copolymer (C) is 100% by mass. The monomer (b) is the same as the monomer (b) used for the synthesis of the copolymer (A). The copolymerization ratio is preferably an amount occupying 20 to 60% by mass when the total monomer constituting the copolymer (C) to be obtained is 100% by mass.

  The copolymer (C) does not exacerbate color unevenness / whitening phenomenon due to minute stress caused by dimensional change of the polarizing plate in the pressure-sensitive adhesive composition of the present invention, and causes foaming or peeling with dimensional change. It is an effective component to prevent it from being generated. Since the copolymer (C) has a small weight average molecular weight and does not contain a functional group, the copolymer (C) does not contribute to the formation of a network structure by the crosslinking agent and gives the adhesive composition high flexibility. That is, the pressure-sensitive adhesive composition partially reacts with the cross-linking agent, so that not only foaming and peeling do not occur, but also an effect of preventing color unevenness and white spot phenomenon.

  The weight average molecular weight of the copolymer (C) needs to be 1,000 to 30,000. When the weight average molecular weight is less than 1,000, the cohesive force of the pressure-sensitive adhesive layer is lowered, which causes foaming and peeling. On the other hand, when the weight average molecular weight exceeds 30,000, the flexibility of the pressure-sensitive adhesive layer is lowered, and it is difficult to prevent the color unevenness and white spots.

  Further, the degree of dispersion (MW / MN) of the copolymer (C) needs to be 1.0 to 2.5. When the degree of dispersion of the copolymer (C) exceeds 2.5, the influence of the low molecular weight component is increased, and the cohesive force of the pressure-sensitive adhesive layer is reduced, causing foaming and peeling. The weight average molecular weight (MW) and number average molecular weight (MN) P. Polystyrene equivalent molecular weight measured by C. Specifically, the coating film obtained by drying the copolymer at room temperature was dissolved in tetrahydrofuran, and a high performance liquid chromatograph (manufactured by Shimadzu Corporation, LC-10ADvp, column; KF-G + KF-806 × 2) The weight average molecular weight (MW) and the number average molecular weight (MN) were determined in terms of polystyrene.

  The usage-amount of the said copolymer (C) is 1-50 mass parts with respect to 100 mass parts of said copolymers (A), Preferably it is 5-40 mass parts, More preferably, it is 10-18. Part by mass. When the amount used is less than 1 part by mass, the effect of sufficiently absorbing and relaxing the stress concentration of the pressure-sensitive adhesive layer due to expansion and contraction of the polarizing plate layer is small. When the amount used exceeds 50 parts by mass, the cohesive force of the pressure-sensitive adhesive layer is reduced, causing foaming and peeling.

  The pressure-sensitive adhesive composition of the present invention can further contain a silane compound (D) containing a mercaptoalkyl group and an alkoxy group simultaneously in the molecule. By using a silane compound containing a mercaptoalkyl group and an alkoxy group at the same time in the molecule, the adhesiveness of the pressure-sensitive adhesive layer to the glass substrate surface as the adherend can be further improved. Specific examples of the compound (D) used in the present invention include γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptobutyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, and mercapto group-containing alkoxy. A silane oligomer etc. are mentioned. At least one selected from these groups can be used.

  The usage-amount of the said compound (D) is 0.01-2 mass parts per 100 mass parts of said copolymers (A), Preferably it is 0.05-1 mass part. When the amount used is less than 0.01 parts by mass, the effect of increasing the adhesiveness of the pressure-sensitive adhesive layer to the glass substrate surface, which is the adherend, is small. On the other hand, when the amount used exceeds 2 parts by mass, It may cause peeling of the agent layer.

  The copolymer (A) can be usually produced by bulk polymerization or solution polymerization. Solution polymerization is preferred. As the solvent to be used, organic solvents such as ethyl acetate, toluene, n-hexane, acetone, methyl ethyl ketone and the like which are usually used for solution polymerization reaction are used. Polymerization initiators used in the polymerization are peroxides such as benzoyl peroxide and lauryl peroxide, azobis compounds such as azobisisobutyronitrile and azobisvaleronitrile, and polymer azo polymerization initiators alone or in combination. Can be used. The low molecular weight copolymer (C) can also be produced by the same method as that for the copolymer (A).

  You may mix | blend various things with the adhesive composition of this invention as needed in order to adjust the adhesiveness of the copolymer (A) in the adhesive composition of this invention. Specific examples used for blending include terpene-based, terpene-phenol-based, coumarone indene-based, styrene-based, rosin-based, xylene-based, phenol-based, petroleum-based tackifier resins, antioxidants, ultraviolet absorbers, etc. , Fillers, pigments and the like.

Furthermore, the pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive layer obtained from the amount of deviation in holding force measurement at 90 ° C. when the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is attached to a glass plate. It is necessary that the viscosity coefficient is 0.5 × 10 ⁷ to 10 × 10 ⁷ Pa · s. Preferably, it is 1 × 10 ^{7 to} 5 × 10 ⁷ Pa · s. Within the range of this viscosity coefficient, a polarizing plate in which uneven color, white spots, foaming and peeling are unlikely to occur can be obtained.

In addition, said viscosity coefficient can be calculated | required with the following method. In accordance with the holding power measurement method of JIS Z-0237, the polarizing plate sample is cut into 25 mm × 55 mm so that the absorption axis is 90 ° with respect to the long side of the polarizing plate, and the pressure-sensitive adhesive composition of the present invention is used. Then, a test sample is prepared by applying a pressure of 5 kg / cm ² at 50 ° C. to the glass plate so that the adhesion area becomes 25 mm × 10 mm and holding it for 18 minutes. The test sample is suspended in a 90 ° C. atmosphere at a load of 9.8 N, and the amount of deviation after 1 hour is measured. From the amount of deviation, the viscosity coefficient (Pa · s) of the pressure-sensitive adhesive layer is calculated according to the following [Equation 1].
[Formula 1]
Displacement stress (N / m ² ) = Load / Adhesion area = 9.8 N / 0.025 m × 0.01 m
Deviation speed (1 / s) = deviation amount / time / thickness = deviation amount (m) / 3600 seconds / 0.000025 m
Viscosity coefficient (Pa · s) = Deviation stress / Deviation speed

  The pressure-sensitive adhesive sheet of the present invention may use a general plastic film as a base film, and in particular, has a pressure-sensitive adhesive layer comprising the optical pressure-sensitive adhesive composition of the present invention on the surface of the optical functional film. It is characterized by that. Examples of the optical functional film include optical films such as a film light guide plate, an antireflection film, a conductive film, a viewing angle widening film, a retardation film, a polarizing plate, and the like. When used, it is possible to produce a pressure-sensitive adhesive sheet having good optical functionality without causing uneven color and white spots.

  The pressure-sensitive adhesive sheet having such optical functionality is applied by using a commonly used coating apparatus, for example, a roll coating apparatus, dried, and heated and crosslinked as necessary. It can be obtained by a method of curing by, for example. Moreover, it is preferable that the application quantity of the optical adhesive of this invention is about 10-50 micrometers normally.

  The color unevenness / white spot test of the pressure-sensitive adhesive sheet obtained by the above method is evaluated by measuring the total light transmittance (%) of the whole 35 points by visual observation and using NDH2000 haze meter manufactured by Nippon Denshoku Industries Co., Ltd. it can. The total light transmittance difference Δ is a difference between the maximum total light transmittance and the minimum total light transmittance, and can be calculated from the following [Equation 2].

[Formula 2]
Difference in total light transmittance Δ = maximum total light transmittance−minimum total light transmittance The difference Δ in total light transmittance of the pressure-sensitive adhesive sheet of the present invention is preferably 0.1 or less, more preferably 0.05. It is as follows. When Δ is 0.1 or more, color unevenness and white spots cannot be suppressed when used for a polarizing plate.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not restrict | limited by these. In the examples and comparative examples, “parts” and “%” are based on mass unless otherwise specified.

[Production Example 1 (low molecular weight copolymer C)]
After nitrogen gas is sealed in a reactor equipped with a stirrer, thermometer, reflux condenser and nitrogen introduction tube, 20 parts of ethyl acetate, 60 parts of toluene, 5 parts of α-methylstyrene dimer, 60 parts of butyl acrylate, the above general formula In (1), a mixed phenoxyethyl acrylate (hereinafter referred to as “PHEA1”) 40 in which the monomer having n = 1 is 98%, the monomer having n = 2 is 1%, and the monomer having n = 3 is 1% 40 Part, 0.5 parts of polymerization initiator azobisisobutyronitrile. The reaction is carried out for 8 hours at reflux temperature in a nitrogen gas stream while stirring. After completion of the reaction and 20 parts of ethyl acetate are added and cooled to room temperature. A low molecular weight copolymer C having a viscosity of 20 mPa · s, a solid content of 50%, a weight average molecular weight of 10,000, a number average molecular weight of 5,900, and a dispersity of 1.7 was obtained.

[Example 1]
A reactor equipped with a stirrer, thermometer, reflux condenser and nitrogen inlet tube is charged with nitrogen gas, and then 100 parts of ethyl acetate, 60 parts of butyl acrylate, 40 parts of PHEA1, 2 parts of acrylic acid and polymerization initiator azobis Charge 0.1 part of isobutyronitrile. It reacts at 68 degreeC in nitrogen gas stream for 8 hours, stirring. After completion of the reaction, 300 parts of ethyl acetate is added and cooled to room temperature. As a result, a copolymer (A) having a viscosity of 1,800 mPa · s, a solid content of 20%, and a weight average molecular weight of 1,220,000 was obtained. As a crosslinking agent, 0.2 parts of polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) is used as a silane coupling agent for 100 parts of the solid content of the obtained copolymer (A). 0.1 parts of γ-mercaptopropylmethyltrimethoxysilane (trade name: KBM-803, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and mixed to obtain the pressure-sensitive adhesive composition of the present invention.

  The pressure-sensitive adhesive composition obtained above is applied onto a silicon-coated polyethylene terephthalate film (PET film) so that the thickness after drying is 25 μm, and the solvent is removed at 90 ° C., followed by drying and a crosslinking reaction. Thus, an adhesive layer was formed. A polarizing film having a thickness of 250 μm, which is an optical functional film, was bonded to the obtained pressure-sensitive adhesive layer to produce a pressure-sensitive adhesive sheet of the present invention. This adhesive sheet was cured at 23 ° C. and 50% RH for 7 days, and then evaluated for durability, adhesive strength, holding power, viscosity coefficient, and white spot (measured according to the test method described later). All the results were good. The results are shown in Table 2.

[Examples 2 and 3]
As shown in Table 1, a pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that the amount of butyl acrylate, the amount of PHEA1 and the amount of acrylic acid were changed, and a pressure-sensitive adhesive sheet was prepared and evaluated in the same manner. It was. All the results were good. The results are shown in Table 2.

[Example 4]
As shown in Table 1, a pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that PHEA1 of Example 1 was changed to benzyl acrylate and acrylic acid was changed to carboxyethyl acrylate. Went. All the results were good. The results are shown in Table 2.

[Example 5]
As shown in Table 1, the amount of butyl acrylate was changed to 50 parts, PHEA1 was changed to 15 parts, benzyl acrylate was changed to 35 parts, and γ-mercaptopropylmethyldimethoxysilane (trade name: KBM-802) was used as a silane coupling agent. Except for using Shin-Etsu Chemical Co., Ltd.), a pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, and a pressure-sensitive adhesive sheet was prepared and evaluated in the same manner. All the results were good. The results are shown in Table 2.

[Example 6]
As shown in Table 1, the pressure-sensitive adhesive composition was the same as Example 1 except that 0.1 part of a polyfunctional glycidyl compound (trade name: Tetrad X, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used as a crosslinking agent. A pressure-sensitive adhesive sheet was prepared in the same manner and evaluated. All the results were good. The results are shown in Table 2.

[Example 7]
As shown in Table 1, the pressure-sensitive adhesive composition was the same as in Example 1 except that 10 parts of the low molecular weight copolymer (C) obtained in Production Example 1 was further added when the pressure-sensitive adhesive composition was blended. An adhesive sheet was prepared in the same manner and evaluated. All the results were good. The results are shown in Table 2.

[Example 8]
As shown in Table 1, the cross-linking agent used in Example 7 was changed to polyisocyanate (trade name: Takenate D-160N, manufactured by Mitsui Takeda Chemical Co., Ltd.), and the low molecular weight copolymer obtained in Production Example 1 was used. A pressure-sensitive adhesive composition was obtained in the same manner as in Example 7 except that the amount of the polymer (C) used was changed to 30 parts and the amount of the silane coupling agent KBM-803 used was changed to 0.2 parts. The pressure-sensitive adhesive sheet of the present invention was prepared and evaluated. All the results were good. The results are shown in Table 2.

[Example 9]
As shown in Table 1, 18 parts of the low molecular weight copolymer (C) used in Example 7 and a mercapto group-substituted alkoxy oligomer (trade name: X-41-1805, Shin-Etsu Chemical (as a silane coupling agent) The adhesive composition was exactly the same as in Example 7 except that 0.1 part was used as a cross-linking agent and polyisocyanate (trade name: Takenate D-160N, manufactured by Mitsui Takeda Chemical Co., Ltd.) was used. In the same manner, the pressure-sensitive adhesive sheet of the present invention was produced and evaluated. All the results were good. The results are shown in Table 2.

[Example 10]
As shown in Table 1, the acrylic acid of Example 1 is hydroxyethyl acrylate, the crosslinking agent is 0.1 part of polyisocyanate (trade name: Takenate D-110N, manufactured by Mitsui Takeda Chemical Co., Ltd.), and a silane cup. A pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that a mercapto group-substituted alkoxy oligomer (trade name: X-41-1810, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the ring agent. A pressure-sensitive adhesive sheet was prepared and evaluated. All the results were good. The results are shown in Table 2.

[Example 11]
As shown in Table 1, the pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that the acrylic acid of Example 1 was changed to carboxyethyl acrylate and no silane coupling agent was added. The pressure-sensitive adhesive sheet of the invention was prepared and evaluated. All the results were good. The results are shown in Table 2.

[Comparative Example 1]
Comparative Example 1 is an example in which the composition of the monomer unit of the copolymer (A) is outside the scope of the present invention. As shown in Table 1, the same procedure as in Example 1 was performed except that the amount of butyl acrylate used in Example 1 was changed to 90 parts, the amount of PHEA1 used was changed to 10 parts, and the amount of acrylic acid used was changed to 0.1 parts. Thus, a pressure-sensitive adhesive composition was obtained, and a pressure-sensitive adhesive sheet was similarly prepared and evaluated. As a result, durability, viscosity coefficient, and white spots were bad. The results are shown in Table 2.

[Comparative Example 2]
Comparative Example 2 is an example in which the amount of acrylic acid used in the copolymer (A) is outside the scope of the present invention. As shown in Table 1, the amount of butyl acrylate used in Example 1 was 20 parts, the amount of PHEA 1 was 80 parts, the amount of acrylic acid was 5 parts, and the crosslinking agent was polyisocyanate (trade name: Takenate D-160N). Except for changing to 0.1 part by Mitsui Takeda Chemical Co., Ltd.), a pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, and a pressure-sensitive adhesive sheet was prepared and evaluated in the same manner. As a result, durability peeling, viscosity coefficient, and white spots were bad. The results are shown in Table 2.

[Comparative Example 3]
Comparative Example 3 is an example in which the weight average molecular weight of the copolymer (A) is outside the scope of the present invention. As shown in Table 1, the pressure-sensitive adhesive was exactly the same as in Example 1 except that the weight average molecular weight of the copolymer (A) of Example 1 was adjusted to 500,000 and coronate L was changed to 0.1 part. A composition was obtained, an adhesive sheet was prepared in the same manner, and evaluated. As a result, durability, viscosity coefficient, and white spots were bad. The results are shown in Table 2.

[Comparative Example 4]
Comparative Example 4 is an example in which no crosslinking agent is used in Example 1. As shown in Table 1, a pressure-sensitive adhesive composition was obtained in the same manner as in Example 1 except that no cross-linking agent was added to Example 1, and a pressure-sensitive adhesive sheet was prepared and evaluated in the same manner. As a result, everything except white spots was bad. The results are shown in Table 2.

The monomers shown in Table 1 are described by the following abbreviations.
Monomer (a): Butyl acrylate BZA: Benzyl acrylate AA: Acrylic acid CEA: Carboxyethyl acrylate HEA: Hydroxyethyl acrylate

[Test method]
1. Durability The adhesive sheets of Examples and Comparative Examples were cut into 90 mm × 150 mm, peeled off PET film, pasted on a glass substrate, autoclaved, 80 ° C. DRY, and 60 ° C. 95% RH. Using the samples after being allowed to stand for 500 hours in the environment, the state of bubbles and peeling generated on the pressure-sensitive adhesive sheet is visually observed, and the durability is evaluated according to the following criteria.

<Evaluation criteria>
[Foaming]
◯: Foaming was not confirmed on the adhesive sheet.
Δ: Slight foaming was confirmed on the adhesive sheet.
X: Foaming was confirmed in the adhesive sheet.
[Peeling]
◯: No peeling occurred on the adhesive sheet.
Δ: Slight peeling was confirmed on the adhesive sheet.
X: Peeling was confirmed on the adhesive sheet.

2. Adhesive strength The adhesive sheets of the examples and comparative examples were peeled 180 ° in accordance with JIS Z-0237, and the adhesive strength was measured. A glass plate is used as the adherend.

3. Holding power The amount of deviation of the pressure-sensitive adhesive sheets of Examples and Comparative Examples is measured according to the holding power measurement method of JIS Z-0237. That is, it is cut into 25 mm × 55 mm so that the absorption axis is 90 ° with respect to the long side of the polarizing plate, and a pressure of 5 kg / cm ² is applied to the glass plate at 50 ° C. so that the bonding area is 25 mm × 10 mm. Then, a test sample is prepared by holding for 18 minutes and sticking, and the sample is suspended in an atmosphere of 90 ° C. under a load of 9.8 N, and the deviation after 1 hour is measured.

4). Viscosity coefficient The viscosity coefficient of the adhesive layer is calculated according to the following [Equation 1] from the amount of deviation measured according to the holding force measurement method.
[Formula 1]
Displacement stress (N / m ² ) = Load / Adhesion area = 9.8 N / 0.025 m × 0.01 m
Deviation speed (1 / s) = deviation amount / time / thickness = deviation amount (m) / 3600 seconds / 0.000025 m
Viscosity coefficient (Pa · s) = Deviation stress / Deviation speed

5. Evaluation of white spots (1) Visual observation After the 80 ° C. durability test using the pressure-sensitive adhesive sheets of the examples and comparative examples, two sheets of the same sample were bonded together in a crossed Nicol state and placed on the backlight of the liquid crystal monitor. Were visually observed and evaluated according to the following criteria.
<Evaluation criteria>
◯: No white spots were found on the adhesive sheet.
Δ: Slight white spots were confirmed on the adhesive sheet.
X: White spots were confirmed on the adhesive sheet.

(2) Total light transmittance evaluation The total light transmittance (%) of 35 points was measured using the NDH2000 haze meter made from Nippon Denshoku Industries Co., Ltd. for the adhesive sheet of the above-mentioned white spot visual evaluation. Of the 35 points, the difference between the maximum total light transmittance and the minimum total light transmittance was defined as the difference Δ of the total light transmittance, and the total light transmittance was calculated from the following [Equation 2] to evaluate white spots.
[Formula 2]
Difference in total light transmittance Δ = maximum total light transmittance−minimum total light transmittance

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the adhesive composition which has moderate adhesive force, the adhesiveness with respect to an optical functional film is good, and does not raise | generate an uneven color and a white spot phenomenon. In particular, when the pressure-sensitive adhesive composition is used for an optical functional film such as a polarizing film, it is difficult to improve with conventional pressure-sensitive adhesives. Can be suppressed, and a high-quality polarizing plate can be formed and produced.

Claims (6)

Copolymer containing at least (meth) acrylic acid alkyl ester monomer unit (a) having 1 to 18 carbon atoms, copolymerizable monomer unit (b) having an aromatic ring, and carboxyl group and / or hydroxyl group Possible monomer unit (c), unit (c) is 0.1 to 4 parts by mass per 100 parts by mass of unit (a) and unit (b), and unit (a) is unit It is an amount that occupies 40 to 80% by mass in the total 100% by mass of (a) and the unit (b), and the unit (b) is 20 to 60 in the total 100% by mass of the unit (a) and the unit (b). Including the copolymer (A) and the crosslinking agent (B) having a weight average molecular weight of 1,000,000 to 2,000,000, the content of the crosslinking agent (B) is formed. The 90 ° C. viscosity coefficient of the pressure-sensitive adhesive layer is 0.5 × 10 ⁷ to 10 × 10 ⁷ Pa · s. An optical pressure-sensitive adhesive composition characterized by the above-mentioned amount.   2. The monomer unit (b) is at least one monomer unit selected from the group consisting of 2-phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, styrene, and α-methylstyrene. An optical pressure-sensitive adhesive composition as described in 1. The monomer unit (b) is a mixture of a monomer having n of 1 and a monomer having n of 2 or more, represented by the following general formula (I), wherein n is a unit of 2 or more. 2. The optical pressure-sensitive adhesive composition according to claim 1, comprising a monomer mixture in which the content of the monomer occupies 1 to 5 mass% of the total amount of the mixture.

  Further, the copolymer (A) contains 1 to 50 parts by mass of a low molecular weight copolymer (C) per 100 parts by mass of the copolymer (A), and the copolymer (C) is a (meth) acrylic acid alkyl ester monomer unit. (A) and a copolymerizable monomer unit (b) having an aromatic ring, having a weight average molecular weight of 1,000 to 30,000 and a dispersity (MW / MN) of 1.0 to The optical pressure-sensitive adhesive composition according to claim 1, which is 2.5 and is compatible with the copolymer (A).   Furthermore, 0.01-100 mass parts of silane compounds (D) which contain a mercaptoalkyl group and an alkoxy group simultaneously in a molecule | numerator per 100 mass parts of said copolymers (A) are included. An optical pressure-sensitive adhesive composition as described in 1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the optical pressure-sensitive adhesive composition according to claim 1 on the surface of the optical functional film.