KR20240158372A - Polyester film, and polarizing plate comprising polyester film - Google Patents

Abstract

A polyester film is provided which reduces the occurrence of rainbow spots when applied to a display device and can also contribute to improving the durability of a polarizing plate. The polyester film of the present invention has a coefficient of linear expansion of 3.0×10 ^-5 /°C or less in a first direction, a coefficient of linear expansion of 3.5×10 ^-5 /°C to 7.5× ^{10 -5} /°C in a second direction orthogonal to the first direction, and has a ground axis in a direction of -5° to 5° with respect to the first direction.

Description

Polyester film and polarizing plate comprising the polyester film {POLYESTER FILM, AND POLARIZING PLATE COMPRISING POLYESTER FILM}

The present invention relates to a polyester film and a polarizing plate comprising the polyester film.

In image display devices (e.g., liquid crystal display devices, organic EL display devices), due to the image formation method, in many cases, a polarizing plate is arranged on at least one side of the display cell. Recently, image display devices have tended to diversify their functions and uses, and they are required to be able to withstand use in harsher environments. Polarizing plates generally have a configuration in which a polarizer is sandwiched between two protective films, and triacetyl cellulose, acrylic resin, cycloolefin resin, etc. are widely used as the protective films. On the other hand, from the viewpoint of durability as described above, it has been proposed to use a polyester film, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), which has excellent mechanical properties, chemical resistance, and moisture barrier properties, as a polarizer protective film (e.g., Patent Document 1). However, while polyester films have excellent mechanical properties, they have birefringence, and thus may cause deterioration of visibility, such as the occurrence of rainbow spots. In particular, with the recent advancement in high brightness and color purity of display devices, the problem of rainbow spots has become more prominent.

On the other hand, polarizing plates formed using protective films made of conventionally used triacetyl cellulose, acrylic resin or cycloolefin resin may cause cracks in the polarizer due to temperature changes. Recently, as image display devices become thinner, thinner polarizers are required, and as image display devices that are expected to be used at high temperatures are increasing, polarizing plates that do not cause cracks in the polarizer and have excellent durability are strongly demanded.

Japanese Patent Publication No. 8-271733

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to provide a polyester film that reduces the occurrence of rainbow spots when applied to an image display device and can also contribute to improving the durability of a polarizing plate.

The polyester film of the present invention has a coefficient of linear expansion of 3.0×10 ^-5 /°C or less in a first direction, a coefficient of linear expansion of 3.5×10 ^-5 /°C to 7.5 ^{×10 -5} /°C in a second direction orthogonal to the first direction, and has a ground axis in a direction of -5° to 5° with respect to the first direction.

In one embodiment, the polyester film is a polyester film according to claim 1, wherein the degree of crystallinity as measured by DSC is 30% or more.

According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate comprises a polarizer and the polyester film disposed on one side of the polarizer.

In one embodiment, the absolute value of the difference between the coefficient of linear expansion of the polyester film in the first direction and the coefficient of linear expansion of the polarizer in the direction parallel to the first direction, and the absolute value of the difference between the coefficient of linear expansion of the polyester film in the second direction orthogonal to the first direction and the coefficient of linear expansion of the polarizer in the direction parallel to the second direction are all 2.0×10 ^-5 /°C or less.

In one embodiment, the thickness of the polarizer is 20 μm or less.

In one embodiment, the polarizing plate further includes an adhesive layer disposed on the polarizer side of the polyester film.

In one embodiment, the adhesive layer comprises microparticles.

In one embodiment, the thickness of the adhesive layer is 0.35 μm or less.

In one embodiment, the refractive index of the adhesive layer is 1.55 or less.

According to the present invention, by selectively reducing the coefficient of linear expansion in a predetermined direction, a polyester film can be provided which reduces the occurrence of rainbow spots when combined with a polarizer and can also contribute to improving the durability of a polarizing plate.

Figure 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.
Figure 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Polyester film

The polyester film of the present invention has a coefficient of linear expansion of 3.0×10 ^-5 /°C or less in the first direction, and a coefficient of linear expansion of 3.5×10 ^-5 /°C to 7.5 ^{×10 -5} /°C in the second direction orthogonal to the first direction. When a polyester having anisotropy in dimensional change is used in this way, the polarizer can be effectively protected while preventing cracks from occurring by laminating it on a polarizer. More specifically, a polarizer is usually manufactured to have an absorption axis through a stretching process and has anisotropy in dimensional change (for example, dimensional change due to temperature change), so when the absorption axis of the polarizer and the first direction of the polyester film are made substantially parallel, and the polarizer and the polyester film are laminated, the polyester film and the polarizer can desirably change shape in synchronization. As a result, by using the polyester film of the present invention, cracking of the polarizer can be prevented even under harsh environments such as high temperatures and large temperature changes, and a polarizing plate with excellent durability can be obtained. In one embodiment, the first direction corresponds to the conveying direction (MD) when manufacturing the polyester film. Further, the second direction may correspond to TD orthogonal to MD. The coefficient of linear expansion can be determined by TMA measurement according to JIS K 7197. In addition, the expression "approximately parallel" includes a case where the angle formed by two directions is 0°±10°, preferably 0°±7°, and more preferably 0°±5°.

The coefficient of linear expansion in the first direction of the polyester film is preferably 2.8×10 ^-5 /℃ or less, preferably 0.0×10 ^-5 /℃ to 2.5× ^{10 -5} /℃, and more preferably 0.5×10 ^-5 /℃ to 1.8× ^{10 -5} /℃. In this range, the above effect becomes more remarkable.

The coefficient of linear expansion of the polyester film in the second direction is preferably 3.3×10 ^-5 /℃ to 7.3 ^{×10 -5} /℃. In this range, the above effect becomes more remarkable.

In one embodiment, the coefficient of linear expansion in the first direction is lower by 1.0×10 ^-5 /℃ or more (preferably 2.0×10 ^-5 /℃ or more) than the coefficient of linear expansion in the second direction. In this range, the effect becomes more remarkable.

The polyester film of the present invention has a ground axis in the direction of -5° to 5° with respect to the first direction. Within this range, a polyester film can be made with a reduced occurrence of rainbow spots when combined with a polarizer. More specifically, as described above, when a polarizer and a polyester film are laminated to form a polarizing plate so that the absorption axis of the polarizer and the first direction are approximately parallel, rainbow spots can be effectively prevented.

The angle formed by the first direction and the ground axis is preferably -3° to 3°, more preferably -1° to 1°, particularly preferably -0.5° to 0.5°, and most preferably 0°. In this range, the effect becomes more remarkable.

Typically, the polyester film may be a stretched film obtained through a stretching process. By appropriately adjusting the manufacturing conditions in the stretching process, and the coefficient of linear expansion in the first direction and the second direction (and the in-plane retardation Re(590) described later) can be favorably controlled, and as a result, a polyester film having excellent properties as a polarizer protective film in terms of rainbow spots and durability as described above can be obtained. As the manufacturing conditions, stretching conditions (stretching temperature, stretching ratio, stretching speed, MD/TD stretching order), preheating temperature before stretching, heat treatment temperature after stretching, heat treatment time after stretching, relaxation rate in the MD/TD direction after stretching, and the like are exemplified. The stretching temperature, stretching ratio, and stretching speed can be appropriately adjusted for each MD/TD.

The in-plane retardation Re(590) of the polyester film is, for example, greater than 0 nm and less than or equal to 10000 nm. In addition, the in-plane retardation Re(λ) is the in-plane retardation of the film measured under light having a wavelength of λ㎚ at 23℃. Therefore, Re(590) is the in-plane retardation of the film measured under light having a wavelength of 590 nm. Re(λ) is obtained by the formula: Re(λ) = (nx-ny) × d, where d(nm) is the thickness of the film. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the direction of the slow axis), and ny is the refractive index in the direction orthogonal to the slow axis in the plane.

The above polyester film preferably has a crystallinity of 30% or more, more preferably 40% or more, and even more preferably 50% or more as measured by differential scanning calorimetry (DSC). The upper limit of the crystallinity is, for example, 70%. Within this range, a polyester film having excellent heat resistance and mechanical properties and suitable as a polarizer protective film can be obtained.

The thickness of the above polyester film is typically 10 µm to 100 µm, preferably 20 µm to 80 µm, and more preferably 20 µm to 50 µm.

The total light transmittance of the above polyester film is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more. The haze of the above polyester film is preferably 1.0% or less, more preferably 0.7% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less.

The moisture permeability of the polyester film is preferably 100 g/m2·24 hr or less, more preferably 50 g/m2·24 hr or less, and even more preferably 15 g/m2·24 hr or less. Within this range, a polarizing plate having excellent durability and moisture resistance can be obtained.

The polyester film of the present invention is formed of a polyester resin. The polyester resin can be obtained by condensation polymerization of a carboxylic acid component and a polyol component.

Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Examples of the aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, benzylmalonic acid, 1,4-naphthalic acid, diphenic acid, 4,4'-oxybenzoic acid, and 2,5-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acids include malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, thiodipropionic acid, and diglycolic acid. Examples of the alicyclic dicarboxylic acid include 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, and adamantanedicarboxylic acid. The carboxylic acid component may be a derivative such as an ester, chloride, or acid anhydride, and examples thereof include dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl terephthalate, and diphenyl terephthalate. The carboxylic acid component may be used alone or in combination of two or more.

As a polyol component, a dihydric alcohol is typically exemplified. As a dihydric alcohol, aliphatic diol, alicyclic diol, and aromatic diol are exemplified. As aliphatic diol, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,6-hexanediol are exemplified. Examples of the alicyclic diols include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Examples of the aromatic diols include 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-(2-norbornylidene)diphenol, 4,4'-dihydroxybiphenol, o-, m-, and p-dihydroxybenzene, 4,4'-isopropylidenephenol, 4,4'-isopropylidenebis(2,6-dichlorophenol)2,5-naphthalenediol, and p-xylenediol. Polyol components can be used alone or in combination of two or more.

As the polyester resin, polyethylene terephthalate and/or modified polyethylene terephthalate are preferably used, and polyethylene terephthalate is more preferably used. By using these resins, a polyester film having excellent mechanical properties and a low occurrence of rainbow spots can be obtained. Polyethylene terephthalate and modified polyethylene terephthalate may be used in a blended form.

As the modified polyethylene terephthalate, for example, a modified polyethylene terephthalate containing a structural unit derived from diethylene glycol, 1,4-butanediol, 1,3-propanediol or isophthalic acid is exemplified. The proportion of diethylene glycol in the polyol component is preferably more than 0 mol% and not more than 10 mol%, more preferably more than 0 mol% and not more than 3 mol%. The proportion of 1,4-butanediol in the polyol component is preferably more than 0 mol% and not more than 10 mol%, more preferably more than 0 mol% and not more than 3 mol%. The proportion of 1,3-propanediol in the polyol component is preferably more than 0 mol% and not more than 10 mol%, more preferably more than 0 mol% and not more than 3 mol%. The proportion of isophthalic acid in the carboxylic acid component is preferably more than 0 mol% and not more than 10 mol%, more preferably more than 0 mol% and not more than 8 mol%. Within this range, a polyester film having good crystallinity can be obtained. In addition, the mol% described above is the mol% relative to the total of repeating units of the entire polymer.

The weight average molecular weight of the polyester resin is preferably 10,000 to 100,000, more preferably 20,000 to 75,000. With such a weight average molecular weight, a film that is easy to handle during molding and has excellent mechanical strength can be obtained. The weight average molecular weight can be measured by GPC (solvent: THF).

In one embodiment, a polyester film having a double-sided adhesive layer is provided. The double-sided adhesive layer comprises, for example, a water-based polyurethane and an oxazoline-based crosslinking agent. Details of the double-sided adhesive layer are described in, for example, Japanese Patent Application Laid-Open No. 2010-55062, which is incorporated herein by reference in its entirety.

In one embodiment, the adhesive layer includes any suitable fine particles. By forming the adhesive layer including the fine particles, blocking that occurs during winding can be effectively suppressed. The fine particles may be inorganic fine particles or organic fine particles. Examples of the inorganic fine particles include inorganic oxides such as silica, titania, alumina, and zirconia, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate. Examples of the organic fine particles include silicone resins, fluorine resins, (meth)acrylic resins, and the like. Among these, silica is preferable.

The particle diameter (number average primary particle diameter) of the above fine particles is preferably 10 nm to 200 nm, more preferably 20 nm to 60 nm.

The thickness of the above adhesive layer is preferably 2 µm or less, more preferably 1 µm or less, and even more preferably 0.35 µm or less. Within this range, a polyester film having an adhesive layer that is unlikely to impede the optical properties of other components when applied to an image display device can be obtained.

In one embodiment, the refractive index of the adhesive layer is preferably 1.45 to 1.60. Within this range, a polyester film having an adhesive layer that is unlikely to impede the optical properties of other components when applied to an image display device can be obtained. In one embodiment, the refractive index of the adhesive layer is 1.54 or more.

In one embodiment, the polyester film may have an anti-block layer on at least one side thereof. The composition of the anti-block layer may adopt the composition of the adhesive layer described above. Preferably, the anti-block layer includes the fine particles.

(Method for manufacturing polyester film)

The above polyester film can be obtained through a forming process of forming a film-forming material (resin composition) including the polyester resin into a film shape, and a stretching process of stretching the formed film. Preferably, the stretching process includes a preheating treatment of the film performed before film stretching, and a heat treatment performed after film stretching. In one embodiment, the polyester film is provided in a long form (or in a shape cut from a long body).

In addition to the polyester resin, the film forming material may contain an additive and a solvent. Any appropriate additive may be employed as the additive depending on the purpose. Specific examples of the additive include a reactive diluent, a plasticizer, a surfactant, a filler, an antioxidant, an anti-aging agent, an ultraviolet absorber, a leveling agent, a thixotropic agent, an antistatic agent, a conductive agent, and a flame retardant. The number, type, combination, addition amount, and the like of the additives may be appropriately set depending on the purpose.

Any suitable molding processing method can be adopted as a method for forming a film from a film-forming material. Specific examples thereof include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., flexible), calendar molding, and heat press. Extrusion molding or cast coating is preferable. This is because the smoothness of the resulting film can be improved and good optical uniformity can be obtained.

The film stretching method may be either uniaxial stretching or biaxial stretching.

In one embodiment, as a method for stretching the film, uniaxial stretching is employed, and stretching is performed in the longitudinal direction (MD) of the film.

Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter stretching machine. Therefore, the stretching direction of the film is typically the longitudinal direction (MD) and the transverse direction (TD) of the film.

In one embodiment, sequential biaxial stretching is employed as the stretching method of the film. It is preferable to perform MD stretching after TD stretching to obtain the polyester film. By doing so, it becomes possible to alleviate the effect of bowing occurring during TD stretching and to set the angle formed by the first direction (MD) and the ground axis in the polyester film to an appropriate value.

The stretching temperature is preferably Tg+5℃ to Tg+50℃ relative to the glass transition temperature (Tg) of the film, more preferably Tg+5℃ to Tg+30℃, and even more preferably Tg+6℃ to Tg+10℃. By stretching at such a temperature, a polyester film in which the direction of the ground axis and the coefficient of linear expansion are well balanced can be obtained. In addition, a polyester film having excellent transparency can be obtained.

The stretching ratio in MD is preferably 2 to 7 times, more preferably 2.5 to 6.5 times, and even more preferably 3 to 6 times. In this range, a polyester film having good crystallinity and excellent durability while having a coefficient of linear expansion within a desired range can be obtained.

The stretching ratio in TD is preferably 1 to 4.5 times, more preferably 1.2 to 4 times, and even more preferably 1.5 to 3.5 times. In this range, a polyester film having excellent crystallinity and durability while having a coefficient of linear expansion within a desired range can be obtained.

The ratio of the stretching ratio in TD to the stretching ratio in MD (MD stretching ratio/TD stretching ratio) is preferably greater than 1 and not more than 7, more preferably 1 to 6, and even more preferably 1 to 3. Within this range, a polyester film with particularly low occurrence of rainbow spots can be obtained. In addition, by using the obtained polyester film, occurrence of cracks in the polarizer can be prevented, and a polarizing plate with excellent durability can be obtained.

The stretching speed in MD is preferably 5%/sec to 100%/sec, more preferably 8%/sec to 80%/sec, and even more preferably 8%/sec to 60%/sec. Within this range, a polyester film having excellent optical properties, good crystallinity, and excellent durability can be obtained.

The stretching speed in TD is preferably 5%/sec to 100%/sec, more preferably 8%/sec to 80%/sec, and even more preferably 8%/sec to 60%/sec. In this range, a polyester film having excellent optical properties and good crystallinity and excellent durability can be obtained.

The temperature of the preheating treatment is preferably 80°C to 150°C, more preferably 90°C to 130°C. In addition, the time of the preheating treatment is preferably 10 seconds to 100 seconds, more preferably 15 seconds to 80 seconds. In this range, a polyester film having excellent optical properties and good crystallinity and excellent durability can be obtained.

The temperature of the heat treatment is preferably 100°C to 250°C, more preferably 120°C to 200°C, and even more preferably 130°C to 180°C. In this range, a polyester film having excellent transparency, good crystallinity, and excellent durability can be obtained. The time of the heat treatment is preferably 2 seconds to 50 seconds, more preferably 5 seconds to 40 seconds, and even more preferably 8 seconds to 30 seconds. In this range, a polyester film having excellent transparency, good crystallinity, and excellent durability can be obtained.

B. Polarizing plate

FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate (100) has a polarizer (10) and a polyester film (20) arranged on one side of the polarizer (10). As the polyester film (20), the polyester film of the present invention described in the above paragraph A is used. Any other appropriate polarizer protective film may be arranged on the other side of the polarizer, and the polarizer protective film may not be arranged. In one embodiment, the polarizer (10) and the polyester film (20) (or another polarizer protective film) are laminated via an adhesive layer (30).

In one embodiment, the polarizing plate may be applied to an image display device such that the side on which the polyester film is arranged becomes the viewing side. In addition, when the polarizing plate is applied to a liquid crystal display device, the polarizing plate having the polyester film may be arranged on the viewing side of the liquid crystal cell or may be arranged on the back side.

Any suitable polarizer may be employed as the polarizer. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films, which have been dyed and stretched with a dichroic substance such as iodine or a dichroic dye, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Preferably, a polarizer obtained by dyeing a PVA film with iodine and then uniaxially stretching it is used because of its excellent optical properties.

The above dyeing with iodine is performed, for example, by immersing the PVA film in an iodine aqueous solution. The stretching ratio of the above uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or while dyeing. In addition, dyeing may be performed after stretching. If necessary, the PVA film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc. For example, by immersing the PVA film in water before dyeing and then washing it, not only can contamination or anti-blocking agent on the surface of the PVA film be washed away, but also the PVA film can be swollen to prevent dyeing spots, etc.

Specific examples of polarizers obtained using a laminate include polarizers obtained using a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by: applying a PVA-based resin solution to a resin substrate, drying to form a PVA-based resin layer on the resin substrate, and obtaining a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. In the present embodiment, the stretching typically includes stretching by immersing the laminate in a boric acid aqueous solution. Furthermore, the stretching may further include stretching the laminate in the air at a high temperature (for example, 95° C. or higher) before stretching in the boric acid aqueous solution, if necessary. The obtained laminate of the resin substrate/polarizer may be used as is (i.e., the resin substrate may be used as a protective layer of the polarizer), or the resin substrate may be peeled off from the laminate of the resin substrate/polarizer, and any appropriate protective layer may be laminated on the peeled surface according to the purpose for use. Details of the method for producing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire disclosure of the publication is incorporated herein by reference.

The thickness of the polarizer is, for example, 1 µm to 80 µm. In one embodiment, the thickness of the polarizer is preferably 20 µm or less, and more preferably 3 µm to 15 µm. Since cracks in the polarizer can be effectively prevented by using the polyester film of the present invention, it becomes possible to use a thin polarizer even in harsh environments such as high temperatures and large temperature changes.

The polarizer and the polarizer protective film (polyester film) can be laminated via any suitable adhesive layer. Preferably, the adhesive layer is formed of an adhesive composition containing a polyvinyl alcohol-based resin.

It is preferable that the absorption axis direction of the polarizer and the first direction (typically MD) of the polyester film are approximately parallel. If a polarizing plate is formed so that the absorption axis of the polarizer and the first direction of the polyester film are approximately parallel, the polyester film and the polarizer can be synchronized and change shape preferably. As a result, cracking of the polarizer is prevented.

The ground axis angle of the polyester film is preferably the same as the angle formed by the absorption axis direction of the polarizer, and the angle formed by the two axes is preferably 0°±10°, more preferably 0°±7°, and even more preferably 0°±5°. Within this range, a polyester film with reduced occurrence of rainbow spots when applied to an image display device can be obtained. In addition, the ground axis angle is the angle when the roll flow direction is set to 0°.

In the above polarizing plate, the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction is preferably 2.0×10 ^-5 /℃ or less, more preferably 1.5×10 ^-5 /℃ or less, and even more preferably 1.0×10 ^-5 /℃ or less. In this range, cracking of the polarizer can be prevented even under harsh environments such as high temperatures and large temperature changes. The lower limit of the absolute value of the difference between the linear expansion coefficient of the polyester film in the first direction and the linear expansion coefficient of the polarizer in the direction parallel to the first direction is preferably smaller, but may be, for example, 0.1×10 ^-5 /℃.

In the above polarizing plate, the absolute value of the difference between the coefficient of linear expansion of the polyester film in the second direction (the direction orthogonal to the first direction) and the coefficient of linear expansion of the polarizer in the direction parallel to the second direction is preferably 2.0×10 ^-5 /°C or less, more preferably 1.5×10 ^-5 /°C or less, and even more preferably 1.0×10 ^-5 /°C or less. In this range, cracking of the polarizer can be prevented even under harsh environments such as high temperatures and large temperature changes. The lower limit of the absolute value of the difference between the coefficient of linear expansion of the polyester film in the second direction and the coefficient of linear expansion of the polarizer in the direction parallel to the second direction is preferably smaller, but may be, for example, 0.1×10 ^-5 /°C.

In one embodiment, the absolute value of the difference between the coefficient of linear expansion of the polyester film in the first direction and the coefficient of linear expansion of the polarizer in the direction parallel to the first direction, and the absolute value of the difference between the coefficient of linear expansion of the polyester film in the second direction (the direction orthogonal to the first direction) and the coefficient of linear expansion of the polarizer in the direction parallel to the second direction are all 2.0× ^10-5 /°C or less (preferably 1.0× ^10-5 /°C or less). Within these ranges, cracking of the polarizer can be prevented even under harsh environments such as high temperatures and large temperature changes.

Fig. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention. The polarizing plate (200) further includes an adhesive layer (40) arranged on the polarizer (10) side of a polyester film (20). In one embodiment, the adhesive layer (40) is arranged on the polarizer (10) side, and a polyester film A having the adhesive layer is arranged on the polarizer (10). As the adhesive layer, the adhesive layer described in the above section A can be employed.

C. Video display device

The above polarizing plate can be applied to an image display device. Representative examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Since the image display device adopts a configuration well-known in the industry, a detailed description is omitted.

Example

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to these examples. The measurement method of each characteristic in the examples is as follows. In addition, unless specifically stated, "part" and "%" in the examples are based on weight.

(1) Orientation angle (direction of expression of ground axis)

A sample was prepared by cutting the central portion of the polyester film used in the examples and comparative examples into a square shape with a width of 50 mm and a length of 50 mm with one side parallel to the width direction of the film. The sample was measured using a Muller matrix polarimeter (manufactured by Axometrics, product name “Axoscan”), and the orientation angle (θ) at a wavelength of 550 nm and 23°C was measured. In addition, the orientation angle (θ) was measured in a state where the sample was placed parallel to the measuring stage.

(2) Coefficient of linear expansion

The coefficient of linear expansion of polyester films and polarizers was measured using a thermomechanical analyzer "TMA7000" manufactured by Hitachi High-Tech Science Corporation in accordance with JIS K 7197, by increasing the temperature from 30°C to 150°C at a rate of 10°C/min, and measuring the amount of deformation of the test film at each temperature. Then, the coefficient of linear expansion of the film was obtained from the amount of deformation in the temperature range of 30°C to 70°C. In addition, a case where the film dimension increased (expanded) with an increase in temperature was considered positive (plus), and a case where the film dimension decreased (shrank) with an increase in temperature was considered negative (minus).

For polyester films, the coefficients of linear expansion in MD (first direction) and TD (second direction) were measured. For polarizers, the coefficients of linear expansion in the direction parallel to MD and the direction parallel to TD in the polarizing plate were measured.

(3) Crystallinity

The crystallinity of the polyester films used in the examples and comparative examples was measured by differential scanning calorimetry (DSC). The calorific value and heat of fusion observed during the temperature increase of the sample up to 300°C at 10°C/min were obtained, and the crystallinity was obtained by the following formula. In addition, the calorific value and heat of fusion were measured using Q-2000 manufactured by TA instruments.

Crystallinity (%) = (Measured heat of fusion - Measured heat of calorific value) / Crystallinity 100% Heat of fusion of polyethylene terephthalate (119 mJ/mg) × 100

(4) Rainbow Spots

The liquid crystal cell was extracted from the liquid crystal TV "45UH7500" manufactured by LGD, and the polarizing plate on the backlight side was separated. The polarizing plates obtained in the examples and comparative examples were bonded to the surface of the liquid crystal TV from which the polarizing plate was separated, using an adhesive, so that the absorption axis of the polarizer was on the short side of the liquid crystal TV. The liquid crystal cell to which the polarizing plates obtained in the examples and comparative examples were bonded was reinstalled, and the TV was turned on with a white display.

The LCD TV was visually inspected from all directions at a 60° angle and the presence or absence of rainbow spots was observed. The evaluation was made according to the following criteria.

○: No rainbow spots were confirmed

△: Rainbow spots were slightly confirmed

×: Rainbow spots were clearly visible

(5) Dimensional changes

The polyester film used in the examples and comparative examples was cut to 100 mm x 100 mm. After that, it was placed in a heating oven at 100°C for 24 hours, the film was taken out, the dimensions were accurately measured again, the dimensions were confirmed with a gold ruler, and the changes in the dimensions were determined. In addition, the condition of the sample was visually checked and evaluated according to the following criteria.

○: No significant shrinkage of 1mm or more

×: There is shrinkage of 1mm or more or deformation

(6) Crack test (heat shock acceleration test)

The polarizing plates obtained in the examples and comparative examples were evaluated using a cold-heat shock tester (manufactured by ESPEC).

The polarizing plates obtained in the examples and comparative examples were cut to 50 mm wide × 150 mm long. At that time, samples were produced in which the absorption axis direction of the polarizer was parallel to the transverse direction (short side) of the polarizing plate after cutting, and samples in which the transmission axis direction of the polarizer was parallel to the transverse direction (short side) of the polarizing plate after cutting. Samples were produced by bonding the side of the polarizing plate on which the protective film (polyester film) was not laminated and 0.5 mm thick alkali-free glass using an acrylic adhesive.

The obtained sample was placed in the test area of a cold-heat shock tester, and the temperature inside the test area was lowered from room temperature to -40°C over 30 minutes. Then, the temperature inside the test area was raised to 85°C over 30 minutes, and then lowered again to -40°C over 30 minutes. This process of raising the temperature from -40°C to 85°C and then lowering the temperature again to -40°C was considered one cycle, and after repeating 100 and 200 cycles, the laminate was taken out, and the presence or absence of crack occurrence was visually confirmed, and evaluated according to the following criteria.

◎: No cracks were observed even after 300 cycles.

○: No cracks were observed after 200 cycles, but cracks were occurring after 300 cycles.

△: No cracks were observed after 100 cycles, but cracks were occurring after 200 cycles.

×: Cracks were occurring after 100 cycles.

[Manufacturing Example 1] Manufacturing of polarizer A

As a substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having an elongated shape, an absorption rate of 0.75%, and a Tg of 75°C was used. One side of the substrate was subjected to corona treatment, and an aqueous solution containing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (degree of polymerization 1200, degree of acetoacetyl modification 4.6%, degree of saponification 99.0 mol% or higher, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z200") in a ratio of 9:1 was applied and dried at 25°C, thereby forming a PVA-based resin layer having a thickness of 11 μm, and a laminate was produced.

The obtained laminate was stretched uniaxially in the longitudinal direction (length direction) 2.0 times between rolls of different speeds in an oven at 120°C (air-assisted stretching).

Next, the laminate was immersed in an insolubilizing bath (boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid per 100 parts by weight of water) at a temperature of 30°C for 30 seconds (insolubilizing treatment).

Next, the polarizing plate was immersed in a dyeing bath having a temperature of 30°C while adjusting the iodine concentration and immersion time so that the polarizing plate has a predetermined transmittance. In this example, 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide were mixed with 100 parts by weight of water, and the polarizing plate was immersed in an iodine aqueous solution for 60 seconds (dyeing treatment).

Next, it was immersed in a crosslinking bath (boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) at a temperature of 30°C for 30 seconds (crosslinking treatment).

Thereafter, the laminate was immersed in a boric acid solution (an aqueous solution obtained by mixing 4 parts by weight of boric acid and 5 parts by weight of potassium iodide per 100 parts by weight of water) at a temperature of 70°C, and uniaxial stretching was performed between rolls of different speeds so that the total stretching ratio in the transverse direction (longitudinal direction) was 5.5 times (underwater stretching).

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a temperature of 30°C (washing treatment), and a polarizer A having a peelable substrate was obtained.

[Manufacturing Example 2] Manufacturing of Polarizer B

A polarizer B having a peelable substrate was obtained in the same manner as in Manufacturing Example 1, except that the stretching ratio in underwater stretching was increased to 4.6 times.

[Manufacturing Example 3] Manufacturing of polyester film A

Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, Inc., IV value 0.75 dl/g (phenol: 1,1,2,2,-tetrachloroethane = 6:4 mixed solvent solution concentration 0.4 g/dl) was vacuum dried at 100°C for 10 hours, and then a film forming device equipped with a single-screw extruder (manufactured by TOYO SEIKI CO., LTD., screw diameter 25 mm, cylinder set temperature: 280°C), a T-die (width 500 mm, set temperature: 280°C), a chill roll (set temperature: 50°C), and a winder was used to produce an amorphous polyester resin film having a thickness of 200 μm.

The obtained non-crystalline polyester resin film was simultaneously biaxially stretched using a stretching machine KARO IV manufactured by Bruckner, to obtain polyester film A (ground axis angle with respect to the longitudinal direction: -1.3°, in-plane phase Re(590): 142 nm, thickness: 20 μm). The stretching ratio was 5 times in the longitudinal direction (MD) and 2 times in the transverse direction (TD). The stretching temperature was 90°C, and the stretching speed was 30%/sec in both MD and TD. In addition, after the stretching treatment, heat treatment was performed at 180°C for 10 seconds while maintaining the dimensions.

[Manufacturing Example 4] Manufacturing of polyester film B

Polyester film B (ground axis angle with respect to the longitudinal direction: -0.5°, in-plane phase Re(590): 78 nm, thickness: 17 μm) was obtained in the same manner as in Manufacturing Example 3, except that the stretching ratio was 4 times in the longitudinal direction (MD) and 3 times in the transverse direction (TD) and that the stretching speed was 50%/sec in both MD and TD.

[Manufacturing Example 5] Manufacturing of polyester film I

A polyester film I (ground axis angle with respect to the longitudinal direction: -2.5°, in-plane phase Re(590): 271 nm, thickness: 22 μm) was obtained in the same manner as in Manufacturing Example 3, except that the stretching ratio was 3 times in the longitudinal direction (MD) and 3 times in the transverse direction (TD), the stretching speed was 2%/sec in both MD and TD, and heat treatment was performed at 140°C for 10 seconds after the stretching treatment.

[Manufacturing Example 6] Manufacturing of polyester film II

A polyester film II (ground axis angle with respect to the longitudinal direction: -11.9°, in-plane phase Re(590): 54 nm, thickness: 50 μm) was obtained in the same manner as in Manufacturing Example 4, except that the stretching ratio was doubled in the longitudinal direction (MD) and doubled in the transverse direction (TD), the stretching speed was 2%/sec in both MD and TD, and heat treatment was performed at 140°C for 10 seconds after the stretching treatment.

[Manufacturing Example 7] Manufacturing of polyester film III

A polyester film III (ground axis angle with respect to the longitudinal direction: -0.6°, in-plane phase Re(590): 2823 nm, thickness: 41 μm) was obtained in the same manner as in Manufacturing Example 4, except that the stretching ratio was set to 6 times in the longitudinal direction (MD) and 1 time in the transverse direction (TD), the stretching speed was set to 2%/sec in both MD and TD, and heat treatment was performed at 140°C for 10 seconds after the stretching treatment.

[Manufacturing Example 8] Manufacturing of polyester film IV

Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, Inc., isophthalic acid modification amount: 2.5 mol% (the number of moles based on the total number of repeating units of the entire polymer), diethylene glycol modification amount: 1.0 mol% (the number of moles based on the total number of repeating units of the entire polymer), IV value: 0.77 dl/g (phenol: 1,1,2,2,-tetrachloroethane = 6:4 mixed solvent solution concentration: 0.4 g/dl) was dried in vacuum at 100°C for 10 hours, and then a film forming apparatus equipped with a single-screw extruder (manufactured by TOYO SEIKI CO., LTD., screw diameter: 25 mm, cylinder set temperature: 280°C), T-die (width: 500 mm, set temperature: 280°C), chill roll (set temperature: 50°C), and winder was used to produce an amorphous polyester resin film having a thickness of 100 μm.

The obtained non-crystalline polyester resin film was simultaneously biaxially stretched with a stretching machine KARO IV manufactured by Bruckner, to obtain a polyester film IV (ground axis angle with respect to the longitudinal direction: -0.9°, in-plane phase Re(590): 3191 nm, thickness: 38 μm). The stretching ratio was fixed-end stretching, and was 7 times in the longitudinal direction (MD) and 1 time in the transverse direction (TD). The stretching temperature was 90°C, and the stretching speed was 10%/sec for both MD and TD. In addition, after the stretching treatment, heat treatment was performed at 140°C for 10 seconds while maintaining the dimensions.

[Manufacturing Example 9] Manufacturing of polyester film V

A polyester film V (ground axis angle with respect to the longitudinal direction: 3.0°, in-plane phase Re(590): 17 nm, thickness: 50 μm) was obtained in the same manner as in Manufacturing Example 7, except that the film thickness was 50 μm and stretching was not performed.

[Manufacturing Example 10] Manufacturing of polyester film VI

Polyester resin (polyethylene terephthalate, manufactured by Bell Polyester Products, Inc., isophthalic acid modification content 2.5 mol% (number of moles based on the total number of repeating units of the entire polymer), IV value 0.77 dl/g (phenol: 1,1,2,2,-tetrachloroethane = 6:4 mixed solvent solution concentration 0.4 g/dl) was dried in vacuum at 100°C for 10 hours, and then an amorphous polyester resin film having a thickness of 170 μm was produced using a film forming apparatus equipped with a single-screw extruder (manufactured by TOYO SEIKI CO., LTD., screw diameter 25 mm, cylinder set temperature: 280°C), T-die (width 500 mm, set temperature: 280°C), chill roll (set temperature: 50°C), and winder.

This film was stretched uniaxially in the longitudinal direction (length direction) 2.0 times between rolls of different speeds in an oven at 120°C.

Next, after immersing in water having a temperature of 30°C for 120 seconds, the sample was immersed in water having a temperature of 73°C, and then uniaxially stretched between rolls at different speeds so that the total elongation ratio was 5.5 times in the longitudinal direction (length direction) (underwater stretching).

The obtained stretched film was heat-treated at 90°C for 10 seconds using a stretching machine KARO IV manufactured by Bruckner, and a polyester film VI (ground axis angle with respect to the longitudinal direction: -0.2°, in-plane phase Re(590): 3243 nm, thickness: 35 μm) was obtained.

[Manufacturing Example 11] Manufacturing of polyester film VII

A stretched film was obtained in the same manner as in Manufacturing Example 10.

The obtained stretched film was heat-treated at 90°C for 10 seconds and further at 140°C for 10 seconds using a stretching machine KARO IV manufactured by Bruckner, to obtain a polyester film VII (ground axis angle with respect to the longitudinal direction: -0.4°, in-plane phase Re(590): 4052 nm, thickness: 35 μm).

[Example 1]

A polyester film A manufactured in Manufacturing Example 3 was subjected to corona treatment, and an aqueous solution containing 15.2 wt% of "Super Flex 210R" (trade name) manufactured by DKS Co. Ltd. and 2.7 wt% of "WS-700" (trade name) manufactured by Nippon Shokubai Co., Ltd. was applied so that the film thickness became 300 ㎛ after drying, and the film was dried at 80° C. for 1 minute, thereby obtaining a polyester film A having an adhesive layer.

A PVA resin solution (manufactured by The Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosephimer (registered trademark) Z-200", resin concentration: 3 wt%) was applied to the polarizer surface of the polarizer having the substrate obtained in Manufacturing Example 1, and a polyester film having the above-described adhesive layer was bonded. The obtained laminate was heated in an oven maintained at 60°C for 5 minutes. Thereafter, the substrate was peeled off from the PVA resin layer, and a polarizing plate (polarizer (transmittance 42.3%, thickness 5 μm)/protective film (polyester film)) was obtained. In addition, the polyester film A and the polarizer were laminated so that the MD direction of the polyester film A and the absorption axis direction of the polarizer were approximately parallel.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Example 2]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film B manufactured in Manufacturing Example 4 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Example 3]

A polarizing plate was obtained in the same manner as in Example 1, except that the polarizer obtained in Manufacturing Example 2 was used instead of the polarizer having the substrate obtained in Manufacturing Example 1. The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Example 4]

A polarizing plate was obtained in the same manner as in Example 2, except that the polarizer obtained in Manufacturing Example 2 was used instead of the polarizer having the substrate obtained in Manufacturing Example 1.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 1]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film I manufactured in Manufacturing Example 5 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 2]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film II manufactured in Manufacturing Example 6 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 3]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film III manufactured in Manufacturing Example 7 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 4]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film IV manufactured in Manufacturing Example 8 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 5]

A polarizing plate was obtained in the same manner as in Example 1, except that polyester film a (manufactured by TOYOBO CO., LTD., trade name “Cosmoshine A 4100”, ground axis angle with respect to the longitudinal direction: 90°, in-plane phase Re(590): 7800 nm, thickness: 75 μm) was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 6]

A polarizing plate was obtained in the same manner as in Example 1, except that polyester film b (manufactured by Mitsubishi Chemical Corporation, trade name “T100-J25”, ground axis angle with respect to the longitudinal direction: 27°, in-plane phase Re(590): 525 nm, thickness: 25 μm) was used instead of polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 7]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film V manufactured in Manufacturing Example 9 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 8]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film VI manufactured in Manufacturing Example 10 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 9]

A polarizing plate was obtained in the same manner as in Example 1, except that the polyester film VII manufactured in Manufacturing Example 11 was used instead of the polyester film A manufactured in Manufacturing Example 3.

The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 10]

A polarizing plate was obtained in the same manner as in Comparative Example 1, except that the polarizer obtained in Manufacturing Example 2 was used instead of the polarizer having the substrate obtained in Manufacturing Example 1. The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 11]

A polarizing plate was obtained in the same manner as in Comparative Example 3, except that the polarizer obtained in Manufacturing Example 2 was used instead of the polarizer having the substrate obtained in Manufacturing Example 1. The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

[Comparative Example 12]

A polarizing plate was obtained in the same manner as in Comparative Example 8, except that the polarizer obtained in Manufacturing Example 2 was used instead of the polarizer having the substrate obtained in Manufacturing Example 1. The obtained polarizing plate was subjected to the above evaluations (1) to (6). The results are shown in Table 1.

10: Polarizer 20: Polyester film
30: Adhesive layer 40: Adhesive layer
100, 200: Polarizing plate

Claims (9)

Equipped with a polarizer and a polyester film arranged on one side of the polarizer,
The coefficient of linear expansion of the polyester film in the first direction is 0.5×10 ^-5 /℃ to 1.8 ^{×10 -5} /℃,
The coefficient of linear expansion of the polyester film in the second direction orthogonal to the first direction is 3.5×10 ^-5 /℃ to 7.5 ^{×10 -5} /℃,
The above polyester film has a ground axis in a direction of -5° to 5° with respect to the first direction,
A polarizing plate in which the absorption axis of the polarizer and the first direction of the polyester film are approximately parallel. In paragraph 1,
A polarizing plate having a crystallinity of 30% or more as measured by DSC of the above polyester film. In claim 1 or 2,
A polarizing plate wherein the above polyester film is a biaxially stretched film. In claim 1 or 2,
A polarizing plate, wherein the absolute value of the difference between the coefficient of linear expansion of the polyester film in the first direction and the coefficient of linear expansion of the polarizer in the direction parallel to the first direction, and the absolute value of the difference between the coefficient of linear expansion of the polyester film in the second direction orthogonal to the first direction and the coefficient of linear expansion of the polarizer in the direction parallel to the second direction are both 2.0×10 ^-5 /℃ or less. In claim 1 or 2,
A polarizing plate having a thickness of the polarizer of 20㎛ or less. In claim 1 or 2,
A polarizing plate further comprising an adhesive layer disposed on the polarizer side of the polyester film. In paragraph 6,
A polarizing plate wherein the above adhesive layer contains fine particles. In paragraph 6,
A polarizing plate having a thickness of the above adhesive layer of 0.35㎛ or less. In paragraph 6,
A polarizing plate having a refractive index of the above-mentioned adhesive layer of 1.55 or less.