JP2008144125A - Acrylate-based pressure-sensitive adhesive, and polarizing plate and liquid crystal display device obtained using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive capable of improving light leakage at a peripheral part of a screen, caused by changes in temperature or humidity or by continuous lighting of a liquid crystal display device, and peeling of a polarizing plate, and a polarizing plate and a liquid crystal display device obtained using the same. <P>SOLUTION: The acrylate-based pressure-sensitive adhesive comprises a copolymer formed from a composition comprising at least one monomer having a positive inherent birefringence in itself, at least one acrylate monomer having a negative inherent birefringence in itself and at least one monomer having a crosslinkable part. The polarizing plate and the liquid crystal display device are obtained using the same. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acrylate-based pressure-sensitive adhesive, and a polarizing plate and a liquid crystal display device using the same, and more specifically, an acrylate that can maintain optical properties of a polarizing plate or the like stably over time when used in a polarizing plate or the like. The present invention relates to a PSA adhesive, a polarizing plate produced using the same, and a liquid crystal display device.

  Recently, liquid crystal display devices (hereinafter referred to as LCDs) are widely used in place of CRTs because of their thinness, light weight, and low power consumption. The demand for polarizing plates is rapidly increasing with the spread of LCDs. The field of use is also expanding from small products such as conventional calculators and watches to large products such as automotive instruments, PC monitors, and televisions. Since the display device is often in use for a long time at all times, the polarizing plate has been required to have long-term durability so that the image quality of the LCD does not deteriorate even after long-term use.

  In the TN (Twisted Nematic) type display system, generally two transparent electrode substrates on which an alignment layer is formed are arranged with a alignment layer inside so as to have a predetermined interval through a spacer, and the periphery is sealed. A liquid crystal cell is formed by sandwiching a liquid crystal material in the gap between the electrode substrates, and a polarizing plate is attached to the outer surfaces of the two electrode substrates via adhesive layers, respectively. Note that the transmission axis of the polarizing plate is 45 ° and 135 ° (crossed Nicols) with respect to the edge of the screen. When the polarizing plate used in such a liquid crystal cell is processed under high temperature and high humidity conditions, the internal stress generated in the polarizing plate distorts the absorption axis at the peripheral edge of the polarizing plate, the light transmittance changes, and light leakage occurs. The phenomenon is likely to occur.

  In order to solve such a problem, as for light leakage by the TN liquid crystal method, a means for appropriately softening an adhesive and imparting stress relaxation properties has been reported (see Patent Document 1). However, acrylate-based pressure-sensitive adhesives that have a stress relieving function are generally so flexible that they are fatal to the liquid crystal display function such as foaming or peeling due to stress that occurs during prolonged use or high temperature and humidity. Have some problems. In addition, when a highly flexible adhesive layer is used, there is a problem that the adhesive is easily stretched when the polarizing plate adhesive product is precisely cut, and the product is contaminated.

In order to solve these problems, a technique for improving the light leakage phenomenon by creating a polarizing plate using an acrylate adhesive for polarizing plate containing a component having a positive photoelastic coefficient is disclosed. (See Patent Document 2).
Japanese Patent Laid-Open No. 9-137143 JP-T-2004-516359

  The method of imparting stress relaxation to the pressure-sensitive adhesive disclosed in Patent Document 1 can be suppressed to some extent if it is a small size, but in recent years, IPS and MVA have become widespread as modes corresponding to large-sized liquid crystal televisions. Compared to the TN mode, the system and the like are large and have not yet reached the quality required for a large-size liquid crystal television, such as light leakage cannot be sufficiently suppressed. Further, the acrylate-based pressure-sensitive adhesive for polarizing plate described in Patent Document 2 is characterized by including a component having a positive photoelastic coefficient, but specific numerical values and signs of the photoelastic coefficient are not disclosed, Also, the effect of the photoelastic coefficient on light leakage is unclear. Furthermore, the component having a positive photoelastic coefficient exemplified in Patent Document 2 generally has low solubility, and is added when a large amount is added in order to make the photoelastic coefficient of the adhesive a desired value. The elution of the material causes peeling of the polarizing plate, which may cause a problem in durability particularly for a large-sized liquid crystal television. It has also been found that if the amount of the component having a positive photoelastic coefficient is reduced, a sufficient effect against light leakage cannot always be obtained.

  Accordingly, an object of the present invention is to provide a pressure-sensitive adhesive capable of improving light leakage at the periphery of the screen due to temperature and humidity changes and continuous lighting of the liquid crystal display device, and peeling of the polarizing plate, and a polarizing plate and a liquid crystal using the same. It is to provide a display device.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors usually obtained a copolymer obtained by copolymerizing a monomer having a positive intrinsic birefringence with an acrylate monomer having a negative intrinsic birefringence. By using the base polymer of the pressure-sensitive adhesive, it was found that the retardation generated due to the distortion of the pressure-sensitive adhesive can be controlled with time, and peeling of the polarizing plate can be suppressed, and the present invention has been completed.

Means for solving the above problems are as follows.
(1) A composition comprising at least one monomer having positive intrinsic birefringence alone, at least one acrylate monomer having alone negative intrinsic birefringence, and at least one monomer having a crosslinking site. An acrylate-based pressure-sensitive adhesive comprising a copolymer formed from
(2) The acrylate-based pressure-sensitive adhesive according to (1), wherein the monomer having positive intrinsic birefringence alone has at least one aromatic ring.
(3) The acrylate-based pressure-sensitive adhesive according to (1), wherein the monomer having positive intrinsic birefringence alone has a benzene ring, a naphthalene ring or a biphenyl structure.
(4) The total amount of the monomer having positive intrinsic birefringence alone is 0.5 to 30% by mass with respect to the total amount of the acrylate monomer having negative intrinsic birefringence alone (1) to ( The acrylate pressure-sensitive adhesive according to any one of 3).
(5) The acrylate pressure-sensitive adhesive according to any one of (1) to (4), further comprising at least one compound having positive intrinsic birefringence.
(6) The acrylate-based pressure-sensitive adhesive according to (5), wherein the compound having positive intrinsic birefringence is a rod-like liquid crystal compound.
(7) The acrylate pressure-sensitive adhesive according to (5), wherein the compound having positive intrinsic birefringence is a crosslinking agent.
(8) The acrylate-based pressure-sensitive adhesive according to (7), wherein the crosslinking agent has two or more aromatic rings.
(9) The acrylate pressure-sensitive adhesive according to (7) or (8), wherein the crosslinking agent is a polymer.
(10) A polarizing plate in which an adhesive layer formed of the acrylate-based adhesive according to any one of (1) to (9) is coated.
(11) In an image display device having two polarizing plates, wherein the transmission axes of the two polarizing plates are perpendicular to each other, at least one of the two polarizing plates is the polarizing plate according to (10) A liquid crystal display device characterized by
(12) The polarizing plate is bonded so that the transmission axis of the polarizing plate is in a 45-degree direction with respect to the side of the display screen, and any one of (1) to (9) is provided. The liquid crystal display device according to (11), wherein the in-plane photoelastic coefficient of the pressure-sensitive adhesive layer formed using the acrylate-based pressure-sensitive adhesive is +250 to +800 (× 10 ⁻¹² Pa ⁻¹ ).
(13) The liquid crystal display device according to (12), wherein the display mode of the liquid crystal cell is a TN mode.
(14) The polarizing plate is bonded so that the transmission axis of the polarizing plate is in the direction of 0 degree or 90 degrees with respect to the side of the display screen, and any one of (1) to (9). (11) The liquid crystal display device according to (11), wherein the in-plane photoelastic coefficient of the pressure-sensitive adhesive layer formed using the acrylate-based pressure-sensitive adhesive according to the item is −400 to +250 (× 10 ⁻¹² Pa ⁻¹ ).
(15) The liquid crystal display device according to (14), wherein a display mode of the liquid crystal cell is an IPS mode or a VA mode.
(16) Any one of (11) to (15), in which the distance between the central point of the polarizing plate according to (10) and the central point of the liquid crystal cell is 0 to 10 mm in the polarizing plate surface direction. The liquid crystal display device according to one item.
(17) The distance in the polarizing plate surface direction between each of the four sides of the polarizing plate according to (10) and each of the corresponding four sides of the glass constituting the liquid crystal cell to which the polarizing plate is bonded is The liquid crystal display device according to any one of (11) to (16), which is 0.0 to 5.0 mm.

  By forming the pressure-sensitive adhesive layer using the pressure-sensitive adhesive of the present invention, a pressure-sensitive adhesive layer having a desired photoelastic coefficient can be obtained, and the polarizing plate of the present invention having the pressure-sensitive adhesive layer can be obtained over time. Light leakage can be prevented and peeling of the polarizing plate can be suppressed.

  The acrylate pressure-sensitive adhesive of the present invention comprises at least one monomer having positive intrinsic birefringence alone, at least one acrylate monomer having negative intrinsic birefringence alone, and at least one monomer having a crosslinking site. It contains the copolymer formed from the composition containing these. The monomer used in the acrylate copolymer that is the base polymer of the conventional acrylate adhesive has a negative intrinsic birefringence, and the acrylate copolymer has a negative photoelastic coefficient. Thereby, when distortion of an adhesive layer arises, retardation will generate | occur | produce and light leakage etc. will arise. The present invention uses a monomer having a positive intrinsic birefringence alone, in addition to the conventionally used acrylate monomer, as a monomer used for the base polymer, and copolymerizes it, thereby causing distortion of the pressure-sensitive adhesive layer. It controls the retardation that occurs and prevents light leakage. By copolymerizing, as described in Patent Document 2, it is possible to prevent peeling of the polarizing plate that occurs when a compound having positive intrinsic birefringence is added separately.

  By adjusting the kind, ratio and amount of the monomer having positive intrinsic birefringence alone and the acrylate monomer having negative intrinsic birefringence used alone when synthesizing the copolymer according to the present invention, The photoelastic coefficient of the agent layer can be set as desired. For example, when increasing the value of the photoelastic coefficient, increase the monomer component having positive intrinsic birefringence constituting the copolymer, or the acrylate system having negative intrinsic birefringence constituting the copolymer It can be adjusted by reducing the monomer component, and conversely, when the value of the photoelastic coefficient is decreased, the monomer component having positive intrinsic birefringence constituting the copolymer is reduced, or It can be adjusted by increasing the acrylate monomer component having negative intrinsic birefringence constituting the coalescence.

  The intrinsic birefringence is intrinsic birefringence depending on the molecular structure, and is caused by the anisotropy of the polarizability in the molecule. The magnitude of macro birefringence is governed by intrinsic birefringence and molecular orientation. If the orientation is completely random, the macroscopic birefringence is zero even when the intrinsic birefringence of a single molecule is large. Positive intrinsic birefringence means that a slow axis can be formed in the same direction with respect to the stretching direction of the molecule (rubbing direction in the case of liquid crystal or the like), and negative intrinsic birefringence has a slow axis in the vertical direction. It can be done. The measurement method is to determine the slow axis of the color change when a sample of each composition is observed through a sensitive color plate using a polarizing microscope at an ambient temperature and humidity of 25 ° C. and 60%. It can be determined from the direction of the slow axis when a shearing force is applied, and in the case of a low-molecular liquid crystal or the like, the direction of the slow axis when the polyvinyl alcohol surface is rubbed with acrylic hair and oriented thereon. In the present invention, a monomer having a positive intrinsic birefringence alone and an acrylate monomer having a negative intrinsic birefringence alone according to the present invention, the numerical values of the intrinsic birefringence of each, without being strictly specified, can be appropriately selected. The pressure-sensitive adhesive layer can be adjusted to a desired photoelastic coefficient by the method described above.

The photoelastic coefficient is defined by birefringence (Δn) generated when stress (σ) is applied, and can be expressed as follows.
Photoelastic coefficient (C) = Δn / σ Formula (1-1)
Photoelastic coefficient (Cth) in thickness direction = Δnth / σ Formula (1-2)

  In the present specification, unless otherwise described, the measurement method of the photoelastic coefficient in the in-plane direction is performed as follows. Using an ellipsometer M-220 manufactured by JASCO Corporation in an environment of 25 ° C and 60%, a 2 cm square sample is subjected to a tensile force in the range of 0 to 10 N (measurement wavelength is 630 nm), and measurement is performed. When the load area changes due to deformation of the sample, the area is corrected and an accurate stress is calculated.

  Measurement of the photoelastic coefficient (Cth) in the thickness direction assumes that the adhesive can be expressed by a uniaxial or biaxial refractive index ellipse, and the adhesive was tilted at 0 and 40 degrees when a tensile force was applied. Based on the retardation of time, it computed by following formula (2), (3). Using the slow axis as the tilt axis (rotation axis) (in the case where there is no slow axis, the arbitrary direction in the film plane is the rotation axis), the retardation value is measured from any two tilted directions, Cth was calculated from formulas (1-2), (2), and (3) based on the assumed average refractive index and the input film thickness value.

Note: Re (θ) above represents the retardation value in the direction inclined at an angle θ from the normal direction. In formula (2), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny. .
Δnth = ((nx + ny) / 2-nz) --- Formula (3)

  In a situation in which peripheral unevenness occurs, shear deformation occurs in the adhesive, and the refractive index ellipsoid in the adhesive is inclined in an oblique direction. Therefore, in the case of shear deformation, not only C but also Cth are important parameters.

  As the pressure-sensitive adhesive, a material that is excellent in optical transparency, exhibits appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and is excellent in weather resistance, heat resistance, and the like is preferably used. An acrylate-based pressure-sensitive adhesive is known to exhibit such characteristics, and the pressure-sensitive adhesive of the present invention is an acrylate-based pressure-sensitive adhesive, and is a copolymer formed from a composition containing an acrylate-based monomer (hereinafter, “ It is also referred to as an “acrylate polymer”) as an essential component. That is, the acrylate polymer is based on an acrylate polymer having a monomer unit of (meth) acrylic acid alkyl ester as a main skeleton. In addition, (meth) acrylic acid alkyl ester means acrylic acid alkyl ester and / or methacrylic acid alkyl ester, and (meth) of the present invention has the same meaning. In addition, if it is the acrylate polymer generally used, it will not restrict | limit in particular, As (meth) acrylic-acid alkylester which comprises the main frame | skeleton of an acrylate polymer, for example, (meth) Examples include methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and the like. These are generally used in acrylate-based pressure-sensitive adhesives, and these monomers usually have a negative intrinsic birefringence at 25 ° C. and 60%. Preferred examples of acrylate monomers having

Further, the copolymer according to the present invention is formed from a composition containing a monomer having a positive intrinsic birefringence alone, in addition to a monomer having a negative intrinsic negative refraction used for an acrylate-based pressure-sensitive adhesive. The monomer having a positive intrinsic birefringence alone is not particularly limited, but an acrylate monomer is preferred in the same manner as the monomer having a negative intrinsic birefringence. Preferred examples of the acrylate monomer include compounds having a side chain containing a fluorine atom in the alcohol component portion of the ester. An example is fluorohexyl methacrylate. In addition, it is preferable to have a conjugated system or the like in the main chain. Moreover, it is also preferable that it is liquid crystalline. Furthermore, it is preferable to have at least one aromatic ring. In the case of having such a substituent, in the case of a polymer, a compound in which an aromatic ring is bonded through a bond that is allowed to rotate around a bond axis such as sp3 bond, not directly to the main chain. Used. Although it does not restrict | limit especially as an aromatic ring, Aromatic hydrocarbon is preferable and benzene, naphthalene, etc. can be mentioned. Furthermore, in the case of an aromatic system, a thing with high aromaticity is preferable. There is a topological resonance energy (TRE) as a measure of aromaticity, and the higher this energy, the higher the aromaticity. The calculation method of TRE is described in J. Aihara, J. Am. Chem. Soc., 2048, 99 (7) (1999). From this viewpoint, the monomer having positive intrinsic birefringence according to the present invention preferably has a benzene ring, naphthalene ring or biphenyl structure, and the TRE values of benzene, naphthalene and biphenyl are 0.273, 0.389, It is 0.502, and the aromaticity is higher in this order. Here, when it has two or more aromatic rings, such as a benzene ring, it is preferable that these several aromatic rings are directly connected or condensed. From these viewpoints, those having a naphthalene ring or a biphenyl structure are preferred, and those having a benzene ring are preferred from the viewpoint of cost.
For example, benzyl acrylate, foxyethyl acrylate, acrylic acid (2-naphthyl) methyl, N-substituted maleimide (such as cyclohexylmaleimide) and the following compounds are exemplified.

  In synthesizing the copolymer, those having good compatibility between the monomer having positive intrinsic birefringence and the monomer having negative intrinsic birefringence are preferable. As an indication of compatibility, for example, an octanol-water partition coefficient (log P value) can be used, and a difference in log P value of 5 or less is preferable.

  The octanol-water partition coefficient (log P value) can be measured by a flask soaking method described in JIS Z-7260-107 (2000). Further, the octanol-water partition coefficient (log P value) can be estimated by a computational chemical method or an empirical method instead of the actual measurement.

  As a calculation method, Crippen's fragmentation method ("J. Chem. Inf. Comput. Sci.", 27, p21 (1987)), Viswanadhan's fragmentation method ("J. Chem. Inf. Comput. Sci."). ", 29, p163 (1989)), Broto's fragmentation method (" Eur. J. Med. Chem.-Chim. Theor. ", 19, p71 (1984)) and the like are preferably used. Crippen's fragmentation method ("J. Chem. Inf. Comput. Sci.", 27, p21 (1987)) is more preferable.

  When the log P value of a certain compound varies depending on the measurement method or calculation method, it is preferable to determine whether or not the compound is within the above range by the Crippen's fragmentation method.

  Furthermore, the copolymer according to the present invention is formed from a composition containing a monomer having a crosslinking site in addition to the monomer having the intrinsic birefringence. The cross-linking site becomes a reaction point with the cross-linking agent. The monomer having a crosslinking site is not particularly limited, and those used for the base polymer of conventional acrylate-based pressure-sensitive adhesives can be suitably used. Preferred examples of the optical film include α, β-unsaturated carboxylic acid-containing monomers from the viewpoint of adhesion to liquid crystal cells and durability. For example, acrylic acid is preferably used. The α, β-unsaturated carboxylic acid-containing monomer imparts adhesive strength or adhesive strength. Furthermore, a hydroxyl group-containing monomer is also preferably used as the monomer having a crosslinking site, and the hydroxyl group-containing monomer imparts adhesive force due to a chemical bond so that the adhesive force of the adhesive does not break at high temperatures by itself or reacting with a crosslinking agent. To do. Examples thereof include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxyethylene glycol (meth) acrylate, 2-hydroxypropylene glycol (meth) acrylate, and mixtures thereof.

  In the composition, the ratio of the monomer having positive intrinsic birefringence alone and the monomer having negative intrinsic birefringence alone is appropriately selected depending on the type of monomer used and the desired photoelastic coefficient. However, the total amount of the monomer having positive intrinsic birefringence alone is preferably 0.5 to 30% by mass, more preferably 1 to the total amount of the monomer having negative intrinsic birefringence alone. It is 20 mass%, More preferably, it is 1-10 mass%. The content of the monomer having a crosslinking site is not particularly limited, but is preferably 0.01 to 5% by mass, more preferably 1 to 5% by mass, and still more preferably 2 to 2%, based on the entire monomer. 5% by mass. If it is less than 0.01, the effect of improving the adhesive strength may be reduced.

  The average molecular weight of the acrylate polymer is not particularly limited, but the weight average molecular weight is preferably about 300,000 to 2.5 million. The acrylate polymer can be produced by various known methods. For example, a radical polymerization method such as a bulk polymerization method, a solution polymerization method, or a suspension polymerization method can be appropriately selected. As the radical polymerization initiator, various known azo and peroxide initiators can be used. The reaction temperature is usually about 50 to 80 ° C., and the reaction time is 1 to 8 hours. Of these production methods, the solution polymerization method is preferred, and ethyl acetate, toluene and the like are generally used as the solvent for the acrylate polymer. The solution concentration is usually about 20 to 80% by weight.

  Further, when adjusting the photoelastic coefficient of the pressure-sensitive adhesive layer, not only the polymer according to the present invention but also an acrylate-based pressure-sensitive adhesive is further contained by containing at least one compound having positive intrinsic birefringence. You can also Furthermore, it can also be carried out by containing at least one compound having negative intrinsic birefringence. It is preferable to adjust by adding a compound having positive intrinsic birefringence alone. By adding a compound having intrinsic birefringence in addition to the copolymer, it is possible to easily adjust the desired photoelastic coefficient of the pressure-sensitive adhesive layer. For example, with the copolymer according to the present invention, the photoelastic coefficient of the pressure-sensitive adhesive layer can be approximated to a desired value, and a compound having intrinsic birefringence can be added to perform fine adjustment. . Thereby, for example, the addition amount of the compound having positive intrinsic birefringence is small, and it is possible to suppress peeling of the polarizing plate.

  Although it does not restrict | limit especially as a compound which has a positive intrinsic birefringence independently, A rod-shaped liquid crystal compound etc. are effective. Furthermore, in the case of an aromatic system, a thing with high aromaticity is preferable. Moreover, the crosslinking agent mentioned later can also be used as a compound which has a positive intrinsic birefringence. Furthermore, the monomer having positive intrinsic birefringence can be used alone as a compound having positive intrinsic birefringence. The compound having intrinsic birefringence does not need to be an organic molecule, and there is no problem even if it is an inorganic substance or an organic-inorganic composite. Specific examples of the compound having positive intrinsic birefringence alone will be shown below. The following compounds are liquid crystal compounds, and LC-1 and LC-2 can also be used as monomers having positive intrinsic birefringence according to the present invention.

  The addition amount of the compound having positive intrinsic birefringence of the present invention is such that a positive intrinsic birefringence component (a monomer having positive intrinsic birefringence and a positive intrinsic birefringence is added to 100 parts by mass of the negative intrinsic birefringence monomer). The total amount of the compound having) is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, and still more preferably 1 to 10% by mass.

  A compound having positive intrinsic birefringence is more preferable as the intrinsic birefringence is higher. In addition, the orientation of the compound having a positive intrinsic birefringence and the copolymer of the present invention is an important factor, and by aligning in the same way, for example, the intermolecular interaction of each component is strong. By doing so, the effect of addition of the compound having positive intrinsic birefringence can be further obtained. Thereby, the compatibility is remarkably improved, the effect is exhibited with a low addition amount, and the durability is further improved. For example, the effect can be obtained when the difference in the log P value is 5 or less.

  In addition to the copolymer and the compound having intrinsic birefringence, the pressure-sensitive adhesive of the present invention can arbitrarily use components used in conventional acrylate-based pressure-sensitive adhesives. For example, the addition of a surfactant or the like is also effective for improving the compatibility, and the effect of suppressing the peeling of the adhesive can be obtained.

  Moreover, when using the adhesive of this invention and forming an adhesive layer, a crosslinking agent is used. Further, as described above, in the present invention, the crosslinking agent can also function as a compound having positive intrinsic birefringence. Examples of the polyfunctional compound that can be blended in the pressure-sensitive adhesive include organic crosslinking agents and polyfunctional metal chelates. Examples of the organic crosslinking agent include an epoxy crosslinking agent, an isocyanate crosslinking agent, an imine crosslinking agent, and a peroxide crosslinking agent. These crosslinking agents can be used alone or in combination of two or more. As the organic crosslinking agent, an isocyanate crosslinking agent is preferable. Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and methylol adducts thereof. A polymerized product is also preferable. A polyfunctional metal chelate is one in which a polyvalent metal is covalently or coordinately bonded to an organic compound. Examples of polyvalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, Ti, and the like. can give. An atom in the organic compound that is covalently or coordinately bonded includes an oxygen atom, and examples of the organic compound include an alkyl ester, an alcohol compound, a carboxylic acid compound, an ether compound, and a ketone compound.

  In the pressure-sensitive adhesive of the present invention, it is particularly preferable that 0.5 to 20 parts by weight of an isocyanate-based crosslinking agent is contained with respect to 100 parts by weight of the base polymer (solid content). Further, it is preferable that the cross-linking agent has positive intrinsic birefringence from the viewpoints of compatibility, durability, and the like, while minimizing changes in the pressure-sensitive adhesive preparation process. When using in order to adjust the photoelastic coefficient of an adhesive layer in a desired range, the thing containing two or more aromatic rings in the crosslinking agent is preferable. Furthermore, in the case of an aromatic system, a thing with high aromaticity is preferable. For example, Nippon Urethane Coronate L, Millionate MR, Millionate MT, 1,6-naphthalenediyl diisocyanate, (1,3,5-benzenetriyl) tris (4,1-phenylene) trisisocyanate are preferably used. It is done.

  Moreover, when a crosslinking agent is added in a large amount (1% or more), the crosslinking reaction proceeds too much, and the relaxation property of the pressure-sensitive adhesive may be reduced. In order to prevent this, the content of the monomer having a crosslinking site of the acrylate polymer (α, β unsaturated carboxylic acid monomer or hydroxyl group, etc.) is preferably 0.1 to 3% by mass relative to the whole monomer, More preferably, it is 0.1-2 mass%, More preferably, it is 0.1-1 mass%. Further, as another method for maintaining the relaxation property, a method of adding an acrylate polymer having no cross-linking site can be mentioned, and the addition amount is preferably 1 to 30% by mass with respect to the copolymer according to the present invention, More preferably, it is 1-20 mass%, More preferably, it is 1-10 mass%, and the combination with the said method is also possible.

  Furthermore, the pressure-sensitive adhesive of the present invention includes a tackifier, a plasticizer, a glass fiber, a glass bead, a metal powder, a filler composed of other inorganic powders, a pigment, a colorant, a filler, if necessary. Various additives can be appropriately used for the antioxidant, the ultraviolet absorber, the silane coupling agent and the like without departing from the object of the present invention. Moreover, it is good also as an adhesive layer etc. which contain microparticles | fine-particles and show light diffusibility.

  As the additive, a silane coupling agent is suitable, and the silane coupling agent (solid content) is preferably about 0.001 to 10 parts by weight with respect to 100 parts by weight of the base polymer (solid content). It is preferable to add about 005 to 5 parts by weight. As the silane coupling agent, those conventionally known can be used without particular limitation. For example, epoxy groups such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4 epoxycyclohexyl) ethyltrimethoxysilane -Containing silane coupling agent, 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N- (1,3-dimethylbutylidene) propylamine Amino group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane, (meth) acrylic group-containing silane coupling agents such as 3-methacryloxypropyltriethoxysilane, and isocyanates such as 3-isocyanatopropyltriethoxysilane It can be exemplified containing silane coupling agent.

The polarizing plate of the present invention is characterized in that an adhesive layer formed of the above-mentioned adhesive of the present invention is coated. When applying the pressure-sensitive adhesive of the present invention to the polarizing plate, it is important that no components remain on the glass surface during rework and that each component does not phase separate. Phase separation results from the compatibility of each component. The better the compatibility of each component, the less likely it is to cause phase separation, and the effects of the present invention can be effectively obtained. The method for improving the compatibility is as described above. When judging the presence or absence of phase separation, the pressure sensitive adhesive alone is 80 ℃ dry 1000h or 60 ℃ 90% 1000h.
This can be confirmed by microscopic observation after the treatment.

The gel fraction of the pressure-sensitive adhesive of the present invention is preferably 70% or more and 90% or less, more preferably 80% or more and 90% or less. If the gel fraction is smaller than the above range, the amount of deviation of the polarizing plate after the durability test may be increased and the light leakage may be increased. On the other hand, if the gel fraction is exceeded, appropriate relaxation and adhesion cannot be obtained. There is a fear. By adding an acrylate polymer having no cross-linked site, the gel fraction can be lowered, and the gel fraction can be adjusted. The gel fraction is measured by taking out the pressure-sensitive adhesive bulk, measuring the weight (w1), and leaving it in ethyl acetate for 1 day. Next, the polymer (gel content) insoluble in ethyl acetate is taken out, dried in an oven at 100 ° C. for 2 hours, the weight (w2) of the remaining solid content is measured, and can be calculated by the following formula.
Gel fraction (%) = (w2 / w1) × 100

  The method of forming the pressure-sensitive adhesive layer on the polarizing plate is not particularly limited, and the pressure-sensitive adhesive film is directly applied to the surface of the polarizing film using a bar coater and dried, or the pressure-sensitive adhesive is temporarily peelable. A method of transferring the pressure-sensitive adhesive layer formed on the surface of the peelable substrate to the surface of the polarizing film and subsequently aging after applying to the material surface and drying can also be employed.

  The thickness of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 10 μm to 40 μm, more preferably 10 μm to 30 μm, and still more preferably 10 μm to 20 μm. If the thickness is smaller than the above range, the adhesive force may not be sufficiently obtained. On the other hand, if the thickness exceeds the above range, the amount of displacement of the polarizing plate after the durability test may be increased and light leakage may be increased.

  If the adhesive strength of the pressure-sensitive adhesive is too high, adhesive residue or panel breakage occurs during rework, and therefore the adhesive strength in the 180 ° peel test is preferably 20 N / 25 mm or less. Moreover, since durability is inferior in it being 0.5 N / 25mm or less, it is unpreferable. A more preferable range is 1 to 10 N / 25 mm.

After fixing to the substrate with an adhesive area of 10 mm x 25 mm through the pressure-sensitive adhesive layer, the strain amount of the pressure-sensitive adhesive layer obtained from a creep test in which a load of 1 kg is applied for 1 hour at 80 ° C dry is A: μm, and the load is removed. When the strain amount of the pressure-sensitive adhesive layer after 1 minute is B: μm, a pressure-sensitive adhesive having {(A−B) / A} × 100 of 50 (%) or less is preferable. More preferably, 20 (%) or less is good.
The amount of strain (D: μm) of the pressure-sensitive adhesive layer obtained from a creep test that is fixed to the substrate with an adhesive area of 10 mm × 25 mm through the pressure-sensitive adhesive layer and that applies a load of 1 kg at 25 ° C. and 60% for 1 minute is preferably 20 μm or less. . The strain amount (A: μm) of the pressure-sensitive adhesive layer obtained from a creep test in which a load of 1 kg is applied for 1 hour at 80 ° C. is preferably 30 μm or more and 100 μm or less.

  The Tg of the pressure-sensitive adhesive layer is preferably −40 ° C. ≦ Tg ≦ −10 ° C. If it is −40 ° C. or lower, the amount of deviation of the polarizing plate after the durability test may increase and light leakage may increase. On the other hand, if it is −10 ° C. or higher, it may cause peeling in a durability test such as heat shock. Cause.

  The polarizing plate of the present invention is characterized in that an adhesive layer formed of the acrylate-based adhesive of the present invention is coated.

(Polarizing plate protective film)
The polarizing plate of the present invention has protective films on both sides of the polarizer. As the protective film, any protective film that is usually used as a protective film for a polarizing plate can be used. In the present invention, it is preferable to use a cellulose acylate film or a cycloolefin polymer. The protective films on both sides may be the same or different. For example, among the protective films on both sides of the polarizer, a cellulose acylate film can be used on one side and a cycloolefin polymer can be used on the other side. Also, films having different compositions and different optical characteristics can be used. Furthermore, it is good also as a protective film by providing a polymer layer on a cellulose acylate film, a cycloolefin type polymer film, etc. For example, a polyimide layer can be provided on a cellulose acylate film to form a protective film. In the polarizing plate of the present invention, an adhesive layer is provided on at least one surface (one side of the polarizer) of the protective film (1) or the surface of the protective film via another functional layer. In this case, the selection of the photoelastic coefficient of the pressure-sensitive adhesive is preferably adjusted as appropriate according to the photoelastic coefficient of the polarizing plate protective film. In particular, when the absorption axis of the polarizing plate is 45 degrees with respect to the side of the screen, the retardation generated in the polarizing plate protective film must be offset in order to reduce light leakage. It is necessary to change according to the photoelastic coefficient of the plate protective film.

(Cellulose acylate film)
Next, a cellulose acylate film that is preferably used as a protective film will be described.
The cellulose acylate film can be formed using a specific cellulose acylate as a raw material. The cellulose acylate used for increasing the optical anisotropy and for decreasing the optical anisotropy may be used properly. The raw material cotton and the synthesis method of the cellulose acylate are described in detail in JIII Journal of Technical Disclosure No. 2001-1745 (issued on March 15, 2001, pages 7-12, JIII). And synthetic methods can be adopted.

(Manufacture of cellulose acylate film)
The cellulose acylate film can be produced by any method as long as the cellulose acylate film is usually produced, but it is particularly preferred to produce the cellulose acylate film by a solvent cast method. In the solvent cast method, a film can be produced using a solution (dope) in which cellulose acylate is dissolved in an organic solvent.

  The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain. The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group. Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon. Two or more organic solvents may be mixed and used.

  The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35% by mass. The surface of the drum or band is preferably finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310, 2,367,603, 2,429,078, 2,429,297, 2,429,978, 2,607,704, 2,739,69, British Patent 6,407,331, No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.

  The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

  A plasticizer can be added to the cellulose acylate film in order to improve mechanical properties or to increase the drying speed. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.

The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of cellulose acylate.
Degradation inhibitors (for example, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) may be added to the cellulose acylate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The amount of the deterioration inhibitor added is 0.01 to 1 of the solution (dope) to be prepared from the viewpoint that the effect of the addition of the deterioration inhibitor is manifested and the bleeding out of the deterioration inhibitor to the film surface is suppressed. The content is preferably mass%, more preferably 0.01 to 0.2 mass%. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

(Cycloolefin polymer)
As the norbornene-based addition (co) polymer, those disclosed in JP-A No. 10-7732, JP-A No. 2002-504184, US2004229157A1 or International Publication No. 2004 / 070463A1 may be used. it can. It can be obtained by addition polymerization of norbornene-based polycyclic unsaturated compounds. If necessary, norbornene-based polycyclic unsaturated compounds and conjugated dienes such as ethylene, propylene, butene, butadiene and isoprene; non-conjugated dienes such as ethylidene norbornene; acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride It is also possible to carry out addition polymerization with linear diene compounds such as acid, acrylic acid ester, methacrylic acid ester, maleimide, vinyl acetate and vinyl chloride. As this norbornene type addition (co) polymer, a commercial item can also be used. Specifically, grades such as APL8008T (Tg70 ° C), APL6013T (Tg125 ° C), or APL6015T (Tg145 ° C), which are sold under the trade name of Apel from Mitsui Chemicals, Inc. and have different glass transition temperatures (Tg), are used. There is. Pellets such as TOPAS 8007, 6013 and 6015 are sold by Polyplastics Co., Ltd. Furthermore, Appear 3000 is marketed by Promerus.

  Norbornene-based polymer hydrides are disclosed in JP-A-1-240517, JP-A-7-196736, JP-A-60-26024, JP-A-62-19807, JP-A-2003-1159767, or As disclosed in Japanese Patent Application Laid-Open No. 2004-309979 and the like, it is possible to use those produced by hydrogenation after addition polymerization or metathesis ring-opening polymerization of a polycyclic unsaturated compound. Specifically, JSR Co., Ltd. is sold under the trade name Arton G or Arton F, and from Zeon Japan, Zeonor ZF14, ZF16, Zeonex 250 or Zeonex 280. These are commercially available under the trade name and can be used.

(Polarizer)
The polarizing plate is composed of a polarizer and two transparent protective films disposed on both sides thereof. Examples of the polarizer include an iodine polarizer, a dye polarizer using a dichroic dye, and a polyene polarizer. The iodine polarizer and the dye polarizer are generally produced using a polyvinyl alcohol film. When a cellulose acylate film is used as a polarizing plate protective film, the method for producing the polarizing plate is not particularly limited, and can be produced by a general method. There is a method in which the obtained cellulose acylate film is treated with an alkali and bonded to both sides of a polarizer prepared by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Instead of alkali treatment, easy adhesion processing as described in JP-A-6-94915 and JP-A-6-118232 may be performed. Examples of the adhesive used to bond the protective film-treated surface and the polarizer include polyvinyl alcohol adhesives such as polyvinyl alcohol and polyvinyl butyral, vinyl latexes such as butyl acrylate, and the like. The polarizing plate is composed of a polarizer and a protective film that protects both surfaces of the polarizer, and is further constructed by laminating a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. Moreover, a separate film is used in order to cover the contact bonding layer bonded to a liquid crystal plate, and is used for the surface side which bonds a polarizing plate to a liquid crystal plate.

UV3100PC (made by Shimadzu Corp.) was used for the single plate transmittance TT, the parallel transmittance PT, and the orthogonal transmittance CT of the polarizing plate. In the measurement, measurement was performed in the range of 380 nm to 780 nm, and the average value of 10 measurements was used for each of the single plate, parallel, and orthogonal transmittance. The polarizing plate durability test was performed as follows in two types of forms in which (1) only the polarizing plate and (2) the polarizing plate were bonded to glass via an adhesive. For the measurement of only the polarizing plate, two orthogonal and identical ones were prepared and measured so that the optical compensation film was sandwiched between the two polarizers. Two samples (approx. 5 cm × 5 cm) are prepared by attaching a polarizing plate on glass so that the optical compensation film is on the glass side. In single-plate transmittance measurement, the sample is set with the film side facing the light source. Each of the two samples is measured, and the average value is taken as the transmittance of the single plate. The preferable range of polarization performance is 40.0 ≦ TT ≦ 45, 0, 30.0 ≦ PT ≦ 40.0, CT ≦ 2 in the order of single plate transmittance TT, parallel transmittance PT, and orthogonal transmittance CT, respectively. 0.0, and more preferable ranges are 41.0 ≦ TT ≦ 44.5, 34 ≦ PT ≦ 39.0, and CT ≦ 1.3 (the unit is%). In the polarizing plate durability test, the amount of change is preferably smaller.
In addition, the polarizing plate of the present invention has an orthogonal single plate transmittance change ΔCT (%) and a polarization degree change ΔP when left at 60 ° C. and 95% RH for 500 hours, with the following formulas (j) and (k ) Is satisfied.
(J) −6.0 ≦ ΔCT ≦ 6.0
(K) -10.0 ≦ ΔP ≦ 0.0
Here, the amount of change is a value obtained by subtracting the measured value before the test from the measured value after the test.
Satisfying this requirement ensures stability during use or storage of the polarizing plate.

(Optical compensation)
It is also preferred that the protective film is an optical compensation film having an optical compensation layer comprising an optical anisotropic layer. The optical compensation film (retardation film) can improve the viewing angle characteristics of the liquid crystal display screen. A known film can be used as the optical compensation film, but the optical compensation film described in JP-A-2001-100042 is preferable in terms of widening the viewing angle.

(Optically anisotropic layer made of polymer film)
The optically anisotropic layer may be formed from a polymer film. The polymer film is formed from a polymer that can exhibit optical anisotropy. Examples of such polymers include polyolefins (eg, polyethylene, polypropylene, norbornene polymers), polycarbonates, polyarylate, polysulfone, polyvinyl alcohol, polymethacrylic acid esters, polyacrylic acid esters and cellulose esters (eg, cellulose triacetate, Cellulose diacetate), polyaryletherketone, polyamide, polyester, polyimide, polyamideimide or polyesterimide. Specifically, polyamides and polyimides described in JP-A No. 2004-4474 and JP-A No. 61-162512 can be used. Moreover, a copolymer or a polymer mixture of these polymers may be used.

  The optical anisotropy of the polymer film is preferably obtained by stretching. The stretching is preferably uniaxial stretching or biaxial stretching. Specifically, longitudinal uniaxial stretching using a difference in peripheral speed between two or more rolls, tenter stretching for grasping both sides of the polymer film and stretching in the width direction, or biaxial stretching in combination of these is preferable. In addition, using two or more polymer films, the optical properties of the entire two or more films may satisfy the above conditions. The polymer film is preferably produced by a solvent cast method in order to reduce unevenness in birefringence. The thickness of the polymer film is preferably 20 to 500 μm, and most preferably 40 to 100 μm. Specifically, for example, the method described in Japanese Patent Application No. 2005-302992 can be used.

It is preferable that the Reλ retardation value and the Rthλ retardation value satisfy the following formulas (2) and (3), respectively, in order to widen the viewing angle of a liquid crystal display device, particularly a VA mode liquid crystal display device. In particular, a cellulose acylate film is preferable when used for a protective film on the liquid crystal cell side of the polarizing plate.
Formula (2): 0 nm ≦ Re ₅₉₀ ≦ 200 nm
Formula (3): 0 nm ≦ Rth ₅₉₀ ≦ 400 nm
[In the formula, Re ₅₉₀ and Rth ₅₉₀ are values at a wavelength λ = 590 nm (unit: nm). ]

When it is desired to reduce the influence of the optical anisotropy of the cellulose acylate film, Re (λ) and Rth (λ) of the protective film (cellulose acylate film) disposed on the liquid crystal cell side are expressed by the following formula (8). It is preferable to satisfy (11).
Formula (8): 0 ≦ Re ₅₉₀ ≦ 10
Formula (9): | Rth ₅₉₀ | ≦ 25
Formula (10): | Re ₄₀₀ −Re ₇₀₀ | ≦ 10
Formula (11): | Rth ₄₀₀ −Rth ₇₀₀ | ≦ 35
[Wherein Re ₅₉₀ and Rth ₅₉₀ are values at wavelength λ = 590 nm, Re ₄₀₀ and Rth ₄₀₀ are values at wavelength λ = 400 nm, Re ₇₀₀ and Rth ₇₀₀ are values at wavelength λ = 700 nm (both units: nm). ]

When cellulose acylate film is used in the VA mode, a mode in which a total of two sheets are used on each side of the cell (two-sheet type) and a mode in which only one of the upper and lower sides of the cell is used (one-sheet type) There are two ways. In the case of the two-sheet type, Re ₅₉₀ is preferably 20 to 100 nm, and more preferably 30 to 70 nm. Rth ₅₉₀ is preferably 70 to 300 nm, and more preferably 100 to 200 nm. In the case of a single sheet type, Re ₅₉₀ is preferably 30 to 150 nm, and more preferably 40 to 100 nm. Rth ₅₉₀ is preferably from 100 to 300 nm, more preferably from 150 to 250 nm.

  Further, as the polymer film forming the optically anisotropic layer, at least one polymer material selected from the group consisting of polyamide, polyimide, polyester, polyetherketone, polyamideimide polyesterimide, and polyaryletherketone is used, A method in which a solution obtained by dissolving this in a solvent is applied to a substrate and the solvent is dried to form a film can be preferably used. At this time, a method of stretching the polymer film and the base material to develop optical anisotropy and using it as an optical anisotropic layer can be preferably used. In addition, it is also preferable that the polymer film is prepared on another substrate, the polymer film is peeled from the substrate, and then bonded to the film, and used as an optically anisotropic layer. In this method, the thickness of the polymer film can be reduced, and is preferably 50 μm or less, and more preferably 1 to 20 μm.

(Optically anisotropic layer (discotic compound))
Further, the protective film may be a polymer film provided with an optically anisotropic layer. The optically anisotropic layer preferably has an alignment layer and an optically anisotropic layer in this order on a transparent polymer film. The alignment layer can be provided by means such as a rubbing treatment of an organic compound (preferably a polymer), oblique deposition of an inorganic compound, or formation of a layer having a microgroup. Furthermore, an alignment layer in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known, but an alignment layer formed by a rubbing treatment of a polymer is particularly preferable. The rubbing treatment is preferably performed by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. As the polymer used for the alignment layer, polyimide, polyvinyl alcohol, a polymer having a polymerizable group described in JP-A-9-152509, and the like can be preferably used. The thickness of the alignment layer is preferably 0.01 to 5 μm, and more preferably 0.05 to 2 μm.

  The optically anisotropic layer preferably contains a liquid crystalline compound. It is particularly preferable that the liquid crystal compound has a discotic compound (discotic liquid crystal). The discotic liquid crystal molecule has a disk-like core portion like the triphenylene derivative of D-1, and has a structure in which side chains extend radially therefrom. Further, in order to fix the once aligned state, it is also preferable to further introduce a group that reacts with heat, light or the like. Preferred examples of the discotic liquid crystal are described in JP-A-8-50206.

  The discotic liquid crystal molecules are aligned almost parallel to the film plane with a pretilt angle in the rubbing direction in the vicinity of the alignment layer, and the discotic liquid crystal molecules are oriented so that they are perpendicular to the plane on the opposite air side. is doing. The tilt angle of the discotic liquid crystal molecules near the alignment layer and near the air interface can be controlled by the type of the discotic liquid crystal material, the type of the alignment layer material, the rubbing conditions, and the use of additives. The discotic liquid crystal layer as a whole has a hybrid orientation, and this layer structure can realize a viewing angle expansion of a liquid crystal display device using a protective film.

  The optically anisotropic layer is generally a discotic compound and another compound (for example, a polymerizable monomer, a photopolymerization initiator) dissolved in a solvent, coated on the alignment layer, dried, and then discotic nematic. After heating to the phase formation temperature, it is obtained by polymerization by irradiation with UV light or the like and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, particularly preferably 70 to 170 ° C.

In addition to the discotic compound added to the optically anisotropic layer, the compound has compatibility with the discotic compound and can give a preferable change in tilt angle to the liquid crystalline discotic compound or inhibit the alignment. Any compound can be used as long as it is not. Among these, additives for controlling the orientation on the air interface side such as polymerizable monomers (eg, compounds having vinyl group, vinyloxy group, acryloyl group and methacryloyl group), fluorine-containing triazine compounds, cellulose acetate, cellulose acetate Mention may be made of polymers such as pionate, hydroxypropylcellulose and cellulose acetate butyrate. These compounds are generally used in an amount of 0.1 to 50% by mass, preferably 0.1 to 30% by mass, based on the discotic compound.
The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm.

  The optically anisotropic layer may be a non-liquid crystalline polymer layer prepared by dissolving a non-liquid crystalline compound in a solvent, applying the solution onto a support, and drying by heating. In this case, for example, the non-liquid crystalline compound is excellent in heat resistance, chemical resistance, transparency, and has high rigidity, so polyamide, polyimide, polyester, polyether ketone, polyaryl ether ketone, polyamide imide, polyester imide, etc. These polymers can be used. Any one of these polymers may be used alone, or a mixture of two or more having different functional groups such as a mixture of polyaryletherketone and polyamide may be used. . Among such polymers, polyimide is preferable because of its high transparency, high orientation, and high stretchability. Moreover, as a support body, a TAC film is preferable.

  In addition, it is also preferable that the laminate of the non-liquid crystal layer and the support is stretched in the horizontal direction of the tenter from 1.05 times to 1.50 times and the support side is bonded to a polarizer.

  Furthermore, the optically anisotropic layer may be an alignment solidified layer of cholesteric liquid crystal having a selective reflection wavelength region of 350 nm or less. Examples of the cholesteric liquid crystal are described in JP-A-3-67219, JP-A-3-140921, JP-A-5-61039, JP-A-6-186534, JP-A-9-133810, and the like. Any suitable material showing the selective reflection characteristics can be used. What can be preferably used from the viewpoint of stability of the alignment solidified layer is, for example, a cholesteric liquid crystal composed of a cholesteric liquid crystal polymer, a nematic liquid crystal polymer containing a chiral agent, a compound that forms such a liquid crystal polymer by polymerization treatment with light, heat, or the like. A layer can be formed.

  In this case, the optically anisotropic layer can be formed by, for example, a method of coating a cholesteric liquid crystal on a support substrate. In that case, for the purpose of controlling the phase difference or the like, a method of overcoating the same type or different types of cholesteric liquid crystals may be employed as necessary. For the coating treatment, for example, an appropriate method such as a gravure method, a die method, or a dipping method can be adopted. An appropriate material such as a TAC film or other polymer film can be used as the support substrate.

  In the above, when forming the optically anisotropic layer, a means for aligning the liquid crystal is employed. The alignment means is not particularly limited, and any appropriate means that can align the liquid crystal compound can be adopted. Incidentally, as an example, there is a method in which liquid crystal is coated on the alignment film and aligned. As the alignment film, a rubbing treatment film made of an organic compound such as a polymer, an oblique deposition film of an inorganic compound, a film having a microgroove, or an organic material such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, or methyl stearylate. Examples thereof include a film obtained by accumulating LB films by the Langmuir-Blodgett method of compounds. Further examples include an alignment film that generates an alignment function by light irradiation. On the other hand, a method of aligning liquid crystal on a stretched film (Japanese Patent Application Laid-Open No. 3-9325), a method of aligning liquid crystal under application of an electric field or magnetic field, and the like are also included. The alignment state of the liquid crystal is preferably as uniform as possible, and is preferably a solidified layer fixed in the alignment state.

(Liquid crystal display device)
The polarizing plate can be advantageously used in an image display device such as a liquid crystal display device.
The liquid crystal display device has a liquid crystal cell and two polarizing plates arranged on both sides thereof, and the liquid crystal cell carries a liquid crystal between two electrode substrates. Furthermore, one optically anisotropic layer may be disposed between the liquid crystal cell and one polarizing plate, or two optically anisotropic layers may be disposed between the liquid crystal cell and both polarizing plates. The liquid crystal cell is preferably in TN mode, VA mode, OCB mode, IPS mode or ECB mode. In the VA mode and the IPS mode, it is general and preferable that the transmission axes of the polarizing plates are perpendicular to each other and are bonded in the direction of 0 or 90 degrees with respect to the side of the display screen.

The liquid crystal display device of the present invention has two polarizing plates, and in the image display device in which the transmission axes of the two polarizing plates are orthogonal to each other, at least one of the two polarizing plates is the present invention. It is a polarizing plate. In addition, it is preferable that both of the two polarizing plates are the polarizing plates of the present invention. In the liquid crystal display of the present invention, the in-plane photoelastic coefficient is set to −400 to +800 (× 10 ⁻¹² Pa ⁻¹ ) using the acrylate-based pressure-sensitive adhesive composition of the present invention. Even a large display device can sufficiently reduce light leakage. In the liquid crystal display device of the present invention, the polarizing plate is bonded so that the transmission axis of the polarizing plate is in the direction of 45 degrees with respect to the side of the display screen (see FIG. 1A). The solid line arrow indicates the absorption axis direction of the front polarizing plate, and the dotted line arrow indicates the absorption axis direction of the rear polarizing plate.) The in-plane photoelastic coefficient of the adhesive layer formed using the adhesive of the present invention is +250. It is preferable that it is ˜ + 800 (× 10 ⁻¹² Pa ⁻¹ ), more preferably +300 to +600 (× 10 ⁻¹² Pa ⁻¹ ). As a display mode of the liquid crystal cell of the liquid crystal display device, a TN mode can be preferably exemplified. In addition, if the photoelastic coefficient of the pressure-sensitive adhesive layer can be within the above range, the same effect of suppressing light leakage can be obtained even if the pressure-sensitive adhesive layer is not formed using the acrylate-based pressure-sensitive adhesive composition of the present invention. Can do.

Further, in the liquid crystal display device of the present invention, the transmission axis of the polarizing plate is oriented at 0 degrees or 90 degrees with respect to the side of the display screen (see FIG. 1B). The absorption axis direction of the polarizing plate, the dotted arrow indicates the absorption axis direction of the rear polarizing plate.), The polarizing plate is bonded, and in the plane of the adhesive layer formed using the adhesive of the present invention Those having a photoelastic coefficient of −400 to +250 (× 10 ⁻¹² Pa ⁻¹ ) are preferable, more preferably −200 to +100 (× 10 ⁻¹² Pa ⁻¹ ), and −100 to +50 (× 10 ^-12 Pa ^-1 ) is more preferred. As a display mode of the liquid crystal cell of the liquid crystal display device, an IPS mode or a VA mode can be preferably exemplified. In addition, if the photoelastic coefficient of the pressure-sensitive adhesive layer can be within the above range, the same effect of suppressing light leakage can be obtained even if the pressure-sensitive adhesive layer is not formed using the acrylate-based pressure-sensitive adhesive composition of the present invention. Can do.

The preferred photoelastic coefficient is preferably satisfied at a wavelength of 400 to 700 nm, and the photoelastic coefficient at 630 nm can be used as a guide. The photoelastic coefficient is preferably −800 to +800 (× 10 ⁻¹² Pa ⁻¹ ) with respect to the photoelastic coefficient (Cth) in the thickness direction of the pressure-sensitive adhesive. The suitable photoelastic coefficient is preferably satisfied at a wavelength of 400 to 700 nm, and the photoelastic coefficient at 630 nm can be used as a guide.

  When the polarizing plate of the present invention is bonded to a liquid crystal cell of various modes on a panel, the polarizing plate surface direction distance between the central point of the polarizing plate of the present invention and the central point of the liquid crystal cell is 0 to 10 mm. It is preferable to combine, and it is more preferable to bond at 0 to 5 mm. Here, the center point of the polarizing plate means the point where the diagonal lines intersect when two diagonal lines of the polarizing plate are drawn, as shown in FIG. Furthermore, when two diagonal lines of the liquid crystal cell are drawn, it means a point where the diagonal lines intersect. By doing so, the strain applied to the cell and the polarizing plate can be evenly dispersed, and the effect of improving the unevenness of the present adhesive becomes more prominent. As shown in FIG. 2, the distance in the polarizing plate surface direction is a distance that considers only the component in the polarizing plate surface direction without considering the distance in the thickness direction of the polarizing plate. In FIG. 2, the straight line indicates the shape and diagonal of the cell, and the thick broken line indicates the shape and diagonal of the polarizing plate.

  Moreover, the distance of the said polarizing plate surface direction of each 4 sides of the polarizing plate of this invention and each corresponding 4 sides of the glass which comprises the liquid crystal cell by which this polarizing plate was bonded is 0.0-. It is preferably 5.0 mm. Here, the side of the polarizing plate and the corresponding side of the glass mean the side closest to the distance, as shown in FIG. Here, the distances (a, b, c, d) on all four sides are preferably 0.0 to 5.0 mm, and more preferably 0 to 2.0 mm. By setting it as the said range, the retardation which generate | occur | produces with the stress of each member cancels, and the nonuniformity improvement effect of this adhesive comes out more notably. The distance in the polarizing plate surface direction has the same meaning as described above.

The acrylate polymer according to the present invention was prepared according to the following procedure.
Add 100 parts of butyl acrylate, 3 parts of acrylic acid and 0.3 part of 2,2'-azobisisobutyronitrile together with ethyl acetate to a reaction vessel equipped with a condenser, nitrogen inlet, thermometer and stirrer. Thus, the solid content concentration was adjusted to 30%, and the mixture was reacted at 60 ° C. for 4 hours under a nitrogen gas stream to obtain an acrylate polymer (A1) solution. In addition, acrylate polymers (A2 to A8) shown in Table 1 below were prepared by the same operation as A1. Further, the intrinsic birefringence of the obtained acrylate polymer was measured by the following method. The measurement results are also shown in Table 1.

(Measurement of intrinsic birefringence of acrylate polymer) Each single film is made and stretched at 25 ° C 60% at 25 ° C (for acrylic acid) or sandwiched between glass plates (butyl acrylate, benzyl acrylate, 2 -Hydroxyethyl methacrylate) was added to the sample and observed at a magnification of 5 times with a polarizing microscope set to crossed Nicols, and observed through a sensitive color plate equipped with the microscope, and the positive and negative of the intrinsic birefringence was determined from the color change. .

Next, the acrylate-based adhesive of the present invention was produced from the obtained acrylate-based polymer according to the following procedure.
2 parts of trimethylolpropane tolylene diisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) and 0.1 part of 3-glycidoxypropyltrimethoxysilane per 100 parts of acrylate polymer solid content and surface-treated with a silicone release agent The film was applied using a die coater and dried at 150 ° C. for 3 hours to obtain an acrylate-based pressure-sensitive adhesive. The composition of the acrylate adhesive is shown in Table 2 below. Although an attempt was made to prepare a pressure-sensitive adhesive with the acrylate polymers A1 and A8, the two did not mix well and a good pressure-sensitive adhesive could not be obtained. Coronate L (Nippon Polyurethane), which is a cross-linking agent, is a cross-linking agent having two or more aromatic rings, and ALCH-TR (Kawaken) is an aluminum chelate.

The gel fraction, intrinsic birefringence and photoelastic coefficient were measured by the following methods. It shows together in Table 2. (Measurement of gel fraction)
The pressure-sensitive adhesive bulk is taken out, the weight (w1) is measured, and it is left in ethyl acetate for 1 day. Next, the polymer (gel content) insoluble in ethyl acetate is taken out, dried in an oven at 100 ° C. for 2 hours, and the weight (w2) of the remaining solid content is measured. The gel fraction is calculated by the following formula.
Gel fraction (%) = (w2 / w1) × 100 (measurement of intrinsic birefringence of LC3)
In the case of LC3, a sample oriented on PVA rubbed with acrylic hair is observed at a magnification of 5 times with a polarizing microscope set to crossed Nicols, and is observed through a sensitive color plate provided with the microscope. Refractive sign was determined. (Measurement of photoelastic coefficient)
Measurement was performed at a wavelength of 630 nm by applying a tensile force in the range of 0 to 10 N from both ends to an adhesive sample with a thickness of 0.5 μm and a 2 cm square using an ellipsometer M-220 manufactured by JASCO at an ambient temperature and humidity of 25 ° C. . When the load area of the sample changed due to deformation, the amount of deformation was measured with a measure, the area was corrected, and an accurate stress was calculated.

The liquid crystal display device (TV for evaluation) of the present invention was produced according to the following procedure.
A 120 μm-thick polyvinyl alcohol film was immersed in an aqueous solution containing 1 part by mass of iodine, 2 parts by mass of potassium iodide, and 4 parts by mass of boric acid, and stretched 4 times at 50 ° C. to produce a polarizer. The polarizing plate protective film includes a commercially available WV film (manufactured by FUJIFILM Corporation), WVBZ438 film (manufactured by FUJIFILM Corporation), Z-TAC film (manufactured by FUJIFILM Corporation), and TD80 (FUJIFILM Corporation). TF80 (manufactured by FUJIFILM Corporation) was used. LC-26GD3 (manufactured by Sharp Corporation) is purchased for VA mode, 32LC100 (manufactured by Toshiba Corporation) is purchased for IPS mode, and MRT-191S (manufactured by Mitsubishi Electric Corporation) is purchased for TN mode. The plate was peeled off to make an evaluation TV.

(Preparation of polarizing plate for VA mode evaluation)
After TD80 was immersed in a sodium hydroxide aqueous solution at a concentration of 1.5 mol / L and 55 ° C., the sodium hydroxide was sufficiently washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at a concentration of 0.005 mol / L for 1 minute for 1 minute, it was immersed in water to sufficiently wash away the diluted sulfuric acid aqueous solution. Finally, the sample was thoroughly dried at 120 ° C. The same processing was performed for TF80. The obtained saponified tack film was laminated using a polyvinyl alcohol adhesive so as to sandwich the polarizer, thereby producing an optical film. Next, the pressure-sensitive adhesive was bonded to the surface of the optical film in the order of TD80 / polarizer / TF80 / pressure-sensitive adhesive / separator, and then aged for 7 days at 25 ° C. and 60% RH to prepare a polarizing plate. . The obtained polarizing plate was used as a front polarizing plate. A rear polarizing plate was produced in the same manner as the front polarizing plate except that TF80 was changed to WVBZ438. The used adhesive is shown in Table 3 below.

(Preparation of polarizing plate for IPS mode evaluation)
The production of the front polarizing plate is performed in the same manner as in the VA mode except that a Z-TAC film is used instead of TF80, and the production of the rear polarizing plate is performed except that a Z-TAC film is used instead of WVBZ438. This was performed in the same manner as in the VA mode.

(Preparation of polarizing plate for TN mode evaluation)
The front polarizing plate is manufactured in the same manner as in the VA mode except that a WV film is used instead of TF80, and the rear polarizing plate is manufactured in the VA mode except that a WV film is used instead of WVBZ438. The same was done.

Using the obtained polarizing plate for evaluation, light leakage was evaluated by the following method.
The produced polarizing plate is cut into each screen size, and the transmission axis of the polarizing plate is 45 ° for the TN mode, 135 ° for the rear, 0 ° for the VA mode and IPS mode with respect to the periphery of the panel. It was attached to both sides of the panel so that the absorption axis of the polarizing plate was perpendicular to the front and back so that the rear was 90 °, and autoclaved at 50 ° C. and a pressure of 0.5 MPa for 30 minutes. Table 3 shows the distance from the four sides (a, b, c, d: synonymous with FIG. 2) and the center shift position of the polarizing plate attachment position. Then, the sample for 1000-hour process evaluation was obtained at 80 degreeCdry or 60 degreeC90% RH. After the sample was stored at 25 ° C. and 60% for 24 hours, the presence or absence of light leakage around the sample was visually observed and evaluated. The evaluation criteria are shown below. Moreover, the peeling state of the polarizing plate after wet heat processing was observed. The obtained results are shown in Table 3 below. The light leakage before the wet heat treatment was evaluated as “5” with no problem in any sample. It can also be seen that it is effective that the bonding position with respect to the panel is in the center and that the interval of 5 mm or more is not left.

(Evaluation criteria)
5: When no light leakage occurred
4: The occurrence of light leakage is slightly observed but there is no practical problem 3: The occurrence of light leakage is recognized weak but there is no problem in practical use 2: The occurrence of light leakage is strongly recognized, but there is no practical problem When there is no 1: When light leakage is observed at a level that is problematic in practice

From Table 3 above, simply adding a compound having a positive intrinsic birefringence to a normal acrylate-based pressure-sensitive adhesive suppresses light leakage but causes peeling of the polarizing plate. It can be seen that such a problem does not occur when a polymer is added with liquid crystal. In addition, it is preferable that the photoelastic coefficient is −400 to +250 (× 10 ⁻¹² Pa ⁻¹ ) when 0/90 degrees is applied, and further effective when it is −100 to +50 (× 10 ⁻¹² Pa ⁻¹ ). I understand that. On the other hand, it was found that when it was pasted at 45 degrees, +250 to +800 (× 10 ⁻¹² Pa ⁻¹ ) was preferable, and when it was +300 to +600 (× 10 ⁻¹² Pa ⁻¹ ), the effect was high. From the comparison of pressure-sensitive adhesives 3 and 12, the effect of increasing the photoelastic coefficient is higher as the amount of addition is smaller and the higher the aromaticity is conjugated like naphthalene than when the phenyl group is not conjugated like benzyl acrylate. I understand that. Furthermore, it can be seen that it is effective that the bonding position with respect to the panel is the center and that the interval of 5 mm or more is not left.

It is the schematic which shows the absorption-axis direction of the polarizing plate of this invention. It is the schematic which shows the center point of the polarizing plate of this invention, and a liquid crystal cell, and the distance of a surface direction.

Claims (17)

  It is formed from a composition containing at least one monomer having positive intrinsic birefringence alone, at least one acrylate monomer having alone negative intrinsic birefringence, and at least one monomer having a crosslinking site. An acrylate-based pressure-sensitive adhesive comprising a copolymer.   The acrylate-based pressure-sensitive adhesive according to claim 1, wherein the monomer having positive intrinsic birefringence alone has at least one aromatic ring.   The acrylate-based pressure-sensitive adhesive according to claim 1, wherein the monomer having positive intrinsic birefringence alone has a benzene ring, a naphthalene ring or a biphenyl structure.   The total amount of the monomer having positive intrinsic birefringence alone is 0.5 to 30% by mass with respect to the total amount of the acrylate monomer having independent negative birefringence alone. The acrylate-based pressure-sensitive adhesive according to claim 1.   Furthermore, the acrylate-type adhesive as described in any one of Claims 1-4 which contains at least 1 type of compound which has a positive intrinsic birefringence.   The acrylate pressure-sensitive adhesive according to claim 5, wherein the compound having positive intrinsic birefringence is a rod-like liquid crystal compound.   The acrylate-based pressure-sensitive adhesive according to claim 5, wherein the compound having positive intrinsic birefringence is a crosslinking agent.   The acrylate pressure-sensitive adhesive according to claim 7, wherein the crosslinking agent has two or more aromatic rings.   The acrylate pressure-sensitive adhesive according to claim 7 or 8, wherein the crosslinking agent is a polymer.   A polarizing plate, wherein a pressure-sensitive adhesive layer formed of the acrylate-based pressure-sensitive adhesive according to claim 1 is applied.   In the image display apparatus which has two polarizing plates and the transmission axes of the two polarizing plates are perpendicular to each other, at least one of the two polarizing plates is the polarizing plate according to claim 10. A liquid crystal display device. The said polarizing plate is bonded so that the transmission axis of the said polarizing plate may become a 45 degree direction with respect to the edge | side of a display screen, The acrylate-type adhesive as described in any one of Claims 1-9. The liquid crystal display device according to claim 11, wherein the in-plane photoelastic coefficient of the pressure-sensitive adhesive layer formed is +250 to +800 (× 10 ⁻¹² Pa ⁻¹ ).   The liquid crystal display device according to claim 12, wherein a display mode of the liquid crystal cell is a TN mode. The acrylate system according to any one of claims 1 to 9, wherein the polarizing plate is bonded so that a transmission axis of the polarizing plate is in a direction of 0 degree or 90 degrees with respect to a side of the display screen. The liquid crystal display device according to claim 11, wherein an in-plane photoelastic coefficient of the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive is −400 to +250 (× 10 ⁻¹² Pa ⁻¹ ).   The liquid crystal display device according to claim 14, wherein a display mode of the liquid crystal cell is an IPS mode or a VA mode.   The distance between the central point of the polarizing plate according to claim 10 and the central point of the liquid crystal cell in the direction of the polarizing plate surface is bonded at 0 to 10 mm, according to any one of claims 11 to 15. Liquid crystal display device.   The distance in the polarizing plate surface direction between each four sides of the polarizing plate according to claim 10 and each corresponding four sides of the glass constituting the liquid crystal cell to which the polarizing plate is bonded is 0.0. The liquid crystal display device according to claim 11, which has a size of ˜5.0 mm.

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