JP6459176B2 - Liquid crystal display device and polarizing plate - Google Patents

Description

  The present invention relates to a liquid crystal display device and a polarizing plate.

  A polarizing plate used for a liquid crystal display device (LCD) is usually configured by sandwiching a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like between two polarizer protective films. In general, a triacetyl cellulose (TAC) film is used. In recent years, with the thinning of LCDs, there has been a demand for thinner polarizing plates. However, if the thickness of the TAC film is reduced for that purpose, sufficient mechanical strength cannot be obtained, and the problem that moisture permeability deteriorates occurs. Moreover, the TAC film used as a polarizer protective film is very expensive, and an inexpensive alternative material is strongly demanded.

  Therefore, it has been proposed to use a polyester film that can maintain high durability even if the thickness is thin as a polarizer protective film for thinning the polarizing plate (Patent Documents 1 to 3).

  The polyester film is superior to the TAC film in durability, but unlike the TAC film, the polyester film has birefringence. Therefore, when the polyester film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, when observed from an oblique direction, a rainbow-like color spot is generated and the image quality is deteriorated. Therefore, in patent documents 1-3, the countermeasure which makes retardation small is made by using copolyester as polyester.

  Patent Document 4 discloses that a rainbow-like color unevenness can be solved by using a white light emitting diode as a backlight light source and further using an oriented polyester film having a certain retardation as a polarizer protective film. .

  In Patent Document 5, it is preferable that the polarizer protective film has good dimensional stability because it undergoes many heat-receiving processes, for example, during the production of a polarizing plate and when combined with a liquid crystal cell. Discloses that the shrinkage ratio of the polyester film after non-constrained heat treatment at 120 ° C. for 30 minutes is preferably 5% or less in both the film MD direction and the TD direction.

  On the other hand, there are a plurality of types of liquid crystal driving methods of the liquid crystal display device, and typical examples include a twisted nematic (TN) method, a vertical alignment (VA) method, and an in-plane switching (IPS) method. In liquid crystal display devices employing these methods, each method is used to reduce the light leakage, color unevenness, color shift, or color tone reversal observed when the image is viewed obliquely, and to widen the viewing angle. A conventional optical compensator is used, and a film having an optical compensation function is also used as a polarizer protective film.

JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A WO2011-162198 JP 2010-277028 A

  The inventors have further studied the conventional liquid crystal display device, and when using an alignment film as a polarizer protective film, observe an image even if an alignment film having an optical compensation function is used. We discovered the existence of a new problem that light leakage still occurs depending on the angle.

  In particular, when two polarizing plates having at least one of the two polarizer protective films made of a polyester film are prepared and arranged so that the two polarizing plates are in a crossed Nicol environment, a slight amount of light is emitted. The present inventors have discovered that there is a new problem that leakage may occur and visibility may deteriorate. Therefore, an object of the present invention is to provide a polarizing plate and a liquid crystal display device that can suppress such slight light leakage.

  As a result of studying the above problems day and night, the present inventors have found that the difference between the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the -45 degree direction with respect to the film flow direction is 0.4. It has been found that the above-mentioned problems can be solved by using a polyester film that is not more than% as a polarizer protective film. The present invention has been completed based on such knowledge.

The representative present invention is as follows.
Item 1.
A light source side polarizing plate and a viewing side polarizing plate, and a liquid crystal display device including a liquid crystal cell disposed between these polarizing plates,
At least one of the light source side polarizer protective film of the light source side polarizing plate or the viewer side polarizer protective film of the viewer side polarizing plate satisfies the following condition A,
At least one of the liquid crystal cell side polarizer protective film of the light source side polarizing plate or the liquid crystal cell side polarizer protective film of the viewing side polarizing plate satisfies the following condition B.
Liquid crystal display device.
Condition A: The difference between the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the −45 degree direction with respect to the film flow direction is 0.4% or less. Condition B: Compound having a discotic structural unit The disc surface of the discotic structural unit is inclined with respect to the surface of the transparent film, and the disc surface of the discotic structural unit and the surface of the transparent film Item 2. The angle between and increases with increasing distance from the surface of the transparent film.
Item 2. The liquid crystal display device according to item 1, wherein at least one liquid crystal cell side polarizer protective film of the light source side polarizing plate and the viewer side polarizing plate satisfies the condition B and the other polarizer protective film satisfies the condition A.
Item 3.
Item 3. The liquid crystal display device according to item 1 or 2, wherein the liquid crystal cell is a twisted nematic liquid crystal cell.
Item 4.
A polarizing plate in which a polarizer protective film is provided on both sides of a polarizer, wherein one polarizer protective film satisfies the following condition A, and the other polarizer protective film satisfies the following condition B.
Condition A: The difference between the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the −45 degree direction with respect to the film flow direction is 0.4% or less. Condition B: Compound having a discotic structural unit And a disc surface of the discotic structural unit is inclined with respect to the transparent film surface, and the disc surface of the discotic structural unit and the surface of the transparent film The angle formed by increases as the distance from the surface of the transparent film increases

  According to the present invention, there is provided a liquid crystal display device having excellent visibility in which the occurrence of slight light leakage is suppressed while using an alignment film for the polarizer protective film, and such a liquid crystal display device. A polarizing plate is provided.

In the optically anisotropic layer provided on the transparent film, the disc surface of the discotic structural unit of the discotic compound is inclined with respect to the surface of the transparent film, and the disc surface of the discotic structural unit and the transparent film A state is schematically shown in which the angle formed by the surface increases with an increase in the distance from the surface.

1. Polarizer Protective Film A polarizer protective film that satisfies the condition A (hereinafter also referred to as “polarizer protective film A”) will be described below.

  The polarizer protective film A has a difference between a heat shrinkage rate in the +45 degree direction with respect to the film flow direction and a heat shrinkage rate in the -45 degree direction with respect to the film flow direction (“difference in heat shrinkage rate in the oblique direction”). It is preferable that the ratio is 0.4% or less (hereinafter, this characteristic may be referred to as “condition A”). The difference in heat shrinkage rate in the oblique direction is preferably 0.30% or less, and more preferably 0.20% or less. Since the smaller the value of the difference in heat shrinkage rate is, the lower limit is 0%. The direction of +45 degrees with respect to the film flow direction and the direction of −45 degrees with respect to the film flow direction are orthogonal to each other. The difference in the heat shrinkage rate is obtained by dividing the smaller value from the larger value of the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the −45 degree direction with respect to the film flow direction. Is required.

  The thermal shrinkage in the +45 degree direction with respect to the film flow direction is preferably 1% or less, more preferably 0.8% or less, and particularly preferably 0.6% or less. There is no particular lower limit, but it can be about 0.001%. Here, the “flow direction” means the traveling direction of the film in the film forming process.

  The heat shrinkage rate of the film for determining the difference in heat shrinkage rate in the oblique direction is a value obtained when the film is heated in water at 85 ° C. for 30 minutes. More specifically, the degree of shrinkage of + 45 ° with respect to the film flow direction by heat treatment is measured using the length before treatment as a reference (100%), and is defined as the heat shrinkage rate. Similarly, a thermal shrinkage of −45 ° with respect to the film flow direction is also measured. The difference between the heat shrinkage rate in the + 45 ° direction with respect to the film flow direction and the heat shrinkage rate in the −45 ° direction with respect to the film flow direction is determined.

  Usually, in a liquid crystal display device, two polarizing plates are arranged in a crossed Nicols state. When two polarizing plates are arranged in a crossed Nicol state, light usually does not pass through the two polarizing plates. However, light may leak depending on the difference in thermal contraction rate in the oblique direction of the polarizer protective film. The mechanism is considered as follows, but the present invention is not limited to this theory.

  When manufacturing a polarizing plate, a polarizer protective film and a polarizer are normally heat-processed in the range of 70 to 120 degreeC for 10 to 60 minutes via an adhesive agent. At this time, if the thermal contraction rate difference in the oblique direction of the polarizer protective film is large, the polarizer protective film warps obliquely during the heat treatment, and accordingly, the polarizing plate itself is slightly warped in the oblique direction. It is considered that the polarization axis is slightly distorted in the oblique direction as the polarizing plate is warped in the oblique direction. In this way, the polarizing plate whose polarization axis is slightly distorted in an oblique direction cannot be arranged in a complete crossed Nicols relationship with the other polarizing plate, and thus it is considered that light leaks slightly. Moreover, when the curvature of the polarizing plate at the time of the above heat treatment becomes remarkable when two films (for example, a PET film and a TAC film) having different characteristics are used as a polarizer protective film constituting one polarizing plate. Conceivable.

  Patent Document 5 discloses a polarizer protective film made of a polyester film having a thermal shrinkage rate of 5% or less in both the MD direction and the TD direction. However, as is clear from the mechanism described above, even if the thermal contraction rate in the MD direction and the thermal contraction rate in the TD direction are small, if the thermal contraction rate difference in the oblique direction is large, the polarizing plate warps in the oblique direction. The light leakage problem cannot be solved.

  As the resin used for the polarizer protective film A, any thermoplastic resin is used. Examples thereof include polyester, polycarbonate, and polystyrene (for example, syndiotactic polystyrene). Among these, polyester is preferable. The polyester film can be obtained from any polyester resin. Suitable polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and more preferably polyethylene terephthalate and polyethylene naphthalate. Furthermore, other copolymer components may be included. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and a large retardation can be obtained relatively easily even if the film is thin. The polyester resin is obtained by condensing a dicarboxylic acid and a diol. The dicarboxylic acid component and the diol component constituting the polyester resin can be used alone or in combination of two or more.

  Examples of the dicarboxylic acid component that can be used in the production of the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 , 5-Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid , Hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyl Adipine , Pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecamethylene dicarboxylic acid and the like.

  Examples of the diol component that can be used for the production of the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1 , 3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. Can be mentioned.

  Hereinafter, the retardation, Nz coefficient, and degree of plane orientation of the preferred polarizer protective film A will be described from the viewpoint of suppressing irises.

(Retardation)
Although the polarizer protective film A is not specifically limited, It is preferable to have a retardation of 4000-30000 nm. When the retardation is 4000 nm or more, the interference color is suppressed when the liquid crystal display device is observed from an oblique direction, and good visibility can be secured. The preferred retardation of the polarizer protective film A is 4500 nm or more, then preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, and even more preferably 10,000 nm or more.

  The upper limit of the retardation of the polarizer protective film A is preferably 30000 nm. Even if a film having a retardation higher than that is used, the effect of further improving visibility is not substantially obtained, and as the retardation increases, the thickness of the film is considerably increased, and the handling property as an industrial material is reduced. Because there is a fear.

  The retardation value of the polarizer protective film A is determined by measuring the biaxial refractive index and thickness at a wavelength of 589 nm according to a known method. For example, it can measure at a wavelength of 589 nm using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments).

(Nz coefficient)
In addition to the retardation range described above, the polarizer protective film A preferably has an Nz coefficient represented by | ny-nz | / | ny-nx | of 1.7 or less. The Nz coefficient can be obtained as follows. The orientation axis direction of the film is determined using a molecular orientation meter (for example, MOA-6004 type molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), and the biaxial refractive index (ny, in the direction perpendicular to the orientation axis direction). nx, where ny> nx) and the refractive index (nz) in the thickness direction are determined by an Abbe refractometer (NAGO-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.). The Nz coefficient can be obtained by substituting nx, ny, and nz obtained in this way into an expression represented by | ny-nz | / | ny-nx |.

  Even when the retardation of the polarizer protective film A is 4000 nm to 30000 nm, when the Nz coefficient exceeds 1.7, when such a film is used for both of a pair of polarizing plates (for example, disposed on the incident light side). When the liquid crystal display device is observed from an oblique direction in the polarizer protective film on the incident light side of the polarizing plate and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side) Depending on the angle, there is a risk of rainbow spots. From such a viewpoint, the Nz coefficient is more preferably 1.65 or less, and still more preferably 1.63 or less. The lower limit value of the Nz coefficient is 1.2. This is because it is difficult in terms of manufacturing technology to obtain a film of less than 1.2. In order to maintain the mechanical strength of the film, the lower limit value of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and further preferably 1.45 or more.

(Plane orientation coefficient)
In addition to controlling the retardation value and the Nz coefficient of the polarizer protective film A to the above specific range, the plane orientation degree represented by (nx + ny) / 2−nz is made to be not more than the specific value, so that the rainbow can be surely obtained. Spots can be eliminated. Here, the values of nx, ny, and nz are obtained by the same method as for the Nz coefficient. The plane orientation degree of the film is preferably 0.13 or less, more preferably 0.125 or less, and still more preferably 0.12 or less. By setting the degree of plane orientation to 0.13 or less, it is possible to completely eliminate rainbow spots observed depending on the angle when the liquid crystal display device is observed from an oblique direction. The plane orientation degree is preferably 0.08 or more, and more preferably 0.10 or more. If the degree of plane orientation is less than 0.08, the film thickness varies, and the retardation value may be non-uniform in the film plane.

(Retardation ratio)
In the polarizer protective film A, the ratio (Re / Rth) between the retardation (Re) and the thickness direction retardation (Rth) is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6. That's it. This is because as the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is larger, the birefringence action is more isotropic, and the occurrence of rainbow-like color spots due to the observation angle is less likely to occur. In a complete uniaxial (uniaxial symmetry) film, the ratio of the retardation to the retardation in the thickness direction (Re / Rth) is 2. However, as the film approaches a perfect uniaxial (uniaxial symmetry) film, the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced.

  Therefore, the upper limit of the ratio of retardation to retardation in the thickness direction (Re / Rth) is preferably 1.2 or less, more preferably 1 or less. In order to completely suppress the occurrence of rainbow-like color spots due to the observation angle, the ratio of retardation to thickness direction retardation (Re / Rth) does not have to be 2, and 1.2 or less is sufficient. Even if the ratio is 1.0 or less, it is possible to satisfy the viewing angle characteristics (180 degrees left and right, 120 degrees up and down) required for the liquid crystal display device.

(Thickness unevenness)
From the viewpoint of suppressing rainbow spots due to the observation angle, it is preferable to suppress fluctuations in retardation of the polarizer protective film A, and for this purpose, it is preferable that the thickness unevenness of the film is small. The thickness unevenness of the film is preferably 5% or less, more preferably 4.5% or less, still more preferably 4% or less, and particularly preferably 3% or less.

(Film thickness)
Although the thickness in particular of the polarizer protective film A is not restrict | limited, Usually, it is 15-300 micrometers, Preferably it is 15-200 micrometers. When the film thickness is less than 15 μm, the anisotropy of the mechanical properties of the film becomes remarkable, and tearing, tearing, and the like may occur. A particularly preferable lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film A exceeds 300 μm, the thickness of the polarizing plate becomes too thick, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. A particularly preferable upper limit of the thickness is 100 μm, which is about the same as a general TAC film.

(Light transmittance)
It is desirable that the polarizer protective film A has a light transmittance of 20% or less at a wavelength of 380 nm from the viewpoint of suppressing deterioration of an optical functional dye such as iodine dye contained in the polarizer. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the optical functional dye can be prevented from being deteriorated by ultraviolet rays. The light transmittance is a value measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, a spectrophotometer V7100 manufactured by JASCO Corporation).

  The transmittance at a wavelength of 380 nm of the film can be controlled to 20% or less by appropriately adjusting the type, concentration, and thickness of the ultraviolet absorber to be blended. As the ultraviolet absorber, a known ultraviolet absorber can be appropriately selected and used. Specific examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency.

  Examples of the organic ultraviolet absorber include benzotriazole, benzophenone, and cyclic imino ester, and combinations thereof. However, the organic ultraviolet absorber is not particularly limited as long as it is within the absorbance range defined in the present invention. However, from the viewpoint of durability, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

  Examples of the benzophenone ultraviolet absorber, benzotriazole ultraviolet absorber, and acrylonitrile ultraviolet absorber include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2′-hydroxy-5 ′-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2 ′ -Dihydroxy-4,4'-dimethoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- (2′-Hydroxy-3′-tert-butyl-5′- Tilphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2′-methylenebis (4- ( 1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, etc. Examples of cyclic imino ester UV absorbers include 2,2 ′-(1 , 4-phenylene) bis (4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazine-4- ON, 2-phenyl-3,1-benzoxazin-4-one, etc. These UV absorbers may be used alone or in combination of two or more.

  When a UV absorber is blended in a film used as a polarizer protective film, it is preferable that the film has a multilayer structure of three or more layers, and the UV absorber is added to a layer other than the outermost layer (that is, the intermediate layer) of the film.

(Other ingredients)
It is also a preferable aspect that the film used as the polarizer protective film contains various additives in addition to the ultraviolet absorber as long as the effects of the present invention are not hindered. Examples of additives include inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants, and antigelling agents. And surfactants. Moreover, in order to show high transparency, it is also preferable that a film does not contain particle | grains substantially. “Substantially free of particles” means, for example, in the case of inorganic particles, a content that is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less when inorganic elements are quantified by fluorescent X-ray analysis. means.

(Easily adhesive layer)
When a polyester film is used as the polarizer protective film A, in order to improve the adhesion with the polarizer, at least one of a polyester resin, a polyurethane resin or a polyacrylic resin is a main component on at least one surface of the polyester film. It is preferable to have an easy adhesion layer. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating solution used for forming the easy-adhesion layer is preferably an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating liquids include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying the coating solution on one or both sides of an unstretched film or a uniaxially stretched film in the longitudinal direction, drying at 100 to 150 ° C., and further stretching in the lateral direction. The final coating amount of the easy adhesion layer is preferably controlled to 0.05 to 0.2 g / m ² . If the coating amount is less than 0.05 g / m ² , the adhesion with the resulting polarizer may be insufficient. On the other hand, when the coating amount exceeds 0.2 g / m ² , blocking resistance may be lowered. When providing an easily bonding layer on both surfaces of a polyester film, the application quantity of an easily bonding layer on both surfaces may be the same or different, and can be independently set within the above range.

  It is preferable to add particles to the easy-adhesion layer in order to impart easy slipperiness. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the coating layer. As particles to be included in the easy adhesion layer, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, Examples include inorganic particles such as calcium fluoride, and organic polymer particles such as styrene, acrylic, melamine, benzoguanamine, and silicone. These may be added alone to the easy-adhesion layer, or may be added in combination of two or more.

  The coating solution can be applied using a known method. Examples include reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method and the like. These methods can be performed alone or in combination.

  The measurement of the average particle diameter of said particle | grain can be performed with the following method. Take a picture of the particles with a scanning electron microscope (SEM) and at a magnification such that the size of one smallest particle is 2-5 mm, the maximum diameter of 300-500 particles (between the two most distant points) Distance) is measured, and the average value is taken as the average particle diameter.

  The polarizer protective film A can be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the adhesion to the polarizer.

(Functional layer)
Various functional layers, that is, a hard coat layer, an anti-glare layer, and a reflection, are provided on the surface of the polarizer protective film A opposite to the surface on which the polarizer is disposed for the purpose of preventing reflection, suppressing glare, and suppressing scratches. It is also preferable to provide one or more functional layers selected from the group consisting of an anti-reflection layer, a low reflection layer, a low anti-reflection layer, an anti-reflection glare layer and an antistatic layer on the oriented polyester surface. When providing various functional layers, the polarizer protective film preferably has an easy adhesion layer on the surface thereof. In that case, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the functional layer and the refractive index of the polarizer protective film. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

(Method for producing oriented polyester film)
The film used as the polarizer protective film can be produced according to a general film production method. For example, in the case of a polyester film, a non-oriented polyester obtained by melting a polyester resin and extruding into a sheet is stretched in the machine direction at a temperature equal to or higher than the glass transition temperature by using a speed difference of a roll, and then stretched by a tenter. The method of extending | stretching to a direction and giving heat processing is mentioned. The polarizer protective film may be a uniaxially stretched film or a biaxially stretched film.

  In order to reduce the difference between the heat shrinkage rate in the direction of 45 ° with respect to the flow direction of the film used as the polarizer protective film and the heat shrinkage rate in the direction of 45 ° with respect to the flow direction, the above-described method can be used. In the film forming process of the uniaxially stretched film and the biaxially stretched film, it is preferable to relieve the stress in the oblique direction generated in the process of cooling after the heat treatment. For this reason, it is preferable to adjust the relaxation rate and temperature to an appropriate range after the heat treatment step and relax in the TD direction. Also effective is an off-line annealing treatment of the roll once wound, for example, at 80 ° C. to 120 ° C. for 10 seconds to 90 minutes.

  In order to reduce the difference between the heat shrinkage rate in the direction of 45 ° with respect to the flow direction of the film used as the polarizer protective film and the heat shrinkage rate in the direction of 45 ° with respect to the flow direction, the above-described method can be used. In the film forming process of the uniaxially stretched film and the biaxially stretched film, it is preferable to relieve the stress in the oblique direction generated in the process of cooling after the heat treatment.

  For this reason, it is preferable to adjust the relaxation rate and temperature to an appropriate range after the heat treatment step and relax in the TD direction. Furthermore, it is preferable to adjust the tension in the MD direction to an optimum range. It is preferable to control the tension in the MD direction by adjusting the difference between the speed of the tenter clip and the speed of the take-up roll within an appropriate range. It is also preferable to adjust the relaxation rate and temperature to an appropriate range after the heat treatment step and relax by reducing the clip interval in the MD direction while relaxing in the TD direction.

  A method of cutting or releasing the film from the tenter clip during the cooling step and cooling the film while relaxing in the MD direction and the TD direction is also preferable. Also effective is an off-line annealing treatment of the roll once wound, for example, at 80 ° C. to 120 ° C. for 10 seconds to 90 minutes.

  After the polarizer protective film A is stretched longitudinally and / or laterally, it is possible to obtain a slit roll by cutting both edges into a mill roll through a heat treatment step and slitting as necessary. Of these, the 33% range (33% from the right end of the film and 33% from the left end of the film) of the both ends of the mill roll tends to increase the heat shrinkage difference particularly in the oblique direction. In the case of treatment, it is preferable to adjust the temperature and time of annealing treatment sufficiently.

  The film having the specific retardation and Nz coefficient described above can be obtained by adjusting the conditions during film formation (for example, stretching ratio, stretching temperature, film thickness, etc.). For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the higher the retardation. On the other hand, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation.

  As specific film forming conditions, for example, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 145 ° C, and particularly preferably 90 to 140 ° C. The longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. The transverse draw ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times.

  In order to control the retardation within the specific range described above, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio. If the difference between the vertical and horizontal draw ratios is too small, it is difficult to increase the retardation, which is not preferable. It is also preferable to set the stretching temperature low in order to increase the retardation. The temperature of the subsequent heat treatment is preferably 100 to 250 ° C, particularly preferably 180 to 245 ° C.

  In order to set the Nz coefficient to the above-described specific value, it is preferable to control the ratio of the longitudinal stretch ratio and the lateral stretch ratio, and it is preferable to use a uniaxially stretched film. In order to reduce the Nz coefficient, it is also preferable to add a copolymer component in order to increase the molecular weight of the polymer and to decrease the crystallinity. Furthermore, in order to control the Nz coefficient of the film within a specific range, the total stretching ratio and the stretching temperature can be appropriately set. For example, the lower the total draw ratio and the higher the drawing temperature, the lower the Nz coefficient can be obtained.

  In order to set the degree of plane orientation to the above specific value, it is preferable to control the total draw ratio. If the total draw ratio is too high, the degree of plane orientation becomes too high, which is not preferable. It is also preferable to control the stretching temperature in order to reduce the degree of plane orientation. By increasing the difference between the longitudinal draw ratio and the transverse draw ratio, setting the total draw ratio low, and setting the draw temperature high, the Nz coefficient and the degree of plane orientation can be made to be below specific values.

  Since the stretching temperature and the stretching ratio have a great influence on the thickness unevenness of the film, it is preferable to optimize the film forming conditions from the viewpoint of the thickness unevenness. In particular, if the longitudinal stretching ratio is lowered to increase the retardation, the longitudinal thickness unevenness may be deteriorated. Since there is a region where the vertical thickness unevenness becomes very bad in a specific range of the draw ratio, it is desirable to set the film forming conditions outside this range.

  The ultraviolet absorber can be blended into the film by combining known methods. For example, using a kneading extruder, the dried UV absorber and polymer raw material are blended to prepare a master batch in advance, and blended by a method of mixing the predetermined master batch and polymer raw material during film formation. be able to.

  The UV absorber concentration of the master batch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and economically blend it. As a condition for producing a master batch, it is preferable to use a kneading extruder and extrude at a temperature not lower than the melting point of the resin and not higher than 290 ° C. for 1 to 15 minutes. Above 290 ° C, the weight loss of the UV absorber is large, and the viscosity of the master batch is greatly reduced. Extrusion for 1 minute or less makes it difficult to uniformly mix the UV absorber. At this time, if necessary, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added.

  The blending of the ultraviolet absorber into the intermediate layer of the film having a multilayer structure of three or more layers can be carried out by the following method. The resin pellet for the outer layer alone, the master batch containing the UV absorber for the intermediate layer and the resin pellet are mixed at a predetermined ratio, dried and then fed to a known melt laminating extruder, from the slit die Extruded into a sheet and cooled and solidified on a casting roll to make an unstretched film. That is, using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, An unstretched film is formed by extruding a three-layer sheet from the die and cooling with a casting roll.

  In order to remove foreign substances contained in the raw material polyester, which cause optical defects, it is preferable to perform high-precision filtration during melt extrusion in the production process of a film used as a polarizer protective film. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filter particle size of the filter medium exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

  Next, a polarizer protective film satisfying the condition B (hereinafter sometimes referred to as “polarizer protective film B”) will be described.

  The polarizer protective film B is a polarizer protective film in which an optically anisotropic layer containing a compound having a discotic structural unit (discotic compound) is provided on a transparent film.

  Examples of the discotic compound include a benzene derivative, a truxene derivative, a cyclohexane derivative, an azacrown type, a phenylacetylene type macrocycle and the like, and a compound having a triphenylene ring represented by the following general formula (1) is preferably used.

Here, R _{1 to} R ₆ are each independently hydrogen, halogen, an alkyl group, or a group represented by —O—X (where X is an alkyl group, an acyl group, an alkoxybenzyl group, an epoxy-modified group) An alkoxybenzyl group, an acryloyloxy-modified alkoxybenzyl group, and an acryloyloxy-modified alkyl group). R _{1 to} R ₆ are preferably acryloyloxy-modified alkoxybenzyl groups represented by the following general formula (2) (where m is 4 to 10).

  In the optically anisotropic layer provided on the transparent film, the discotic compound is such that the disc surface of the discotic structural unit is inclined with respect to the surface of the transparent film, and the disc surface of the discotic structural unit is The angle formed by the surface of the transparent film increases as the distance from the surface increases. Such a state is schematically shown in FIG.

  The lower limit of the range of the angle formed by the disc surface of the discotic structural unit of the discotic compound and the surface of the transparent film is preferably 5 degrees, and more preferably 10 degrees. The upper limit of this angle range is preferably 85 degrees, more preferably 80 degrees.

  The lower limit of the difference between the minimum and maximum angles formed by the disc surface of the discotic structural unit of the discotic compound and the transparent film is preferably 10 degrees, more preferably 15 degrees. The upper limit is preferably 60 degrees, and more preferably 55 degrees. By setting it as the said range, when a display apparatus is seen from diagonally, the light leakage and the change of a color tone can be prevented effectively, and a viewing angle can be expanded.

  The lower limit of the thickness (d) of the optically anisotropic layer is preferably 0.1 μm, more preferably 0.5 μm, and even more preferably 1 μm. If it is less than the above, it may be difficult to obtain a compensation effect. The upper limit of the thickness of the optically anisotropic layer is preferably 10 μm, more preferably 7 μm, and even more preferably 5 μm. If the above is exceeded, it may be difficult to obtain a compensation effect.

  The lower limit of the retardation in the thickness direction of the optically anisotropic layer (Rth: ((nx + ny) / 2-nz) × d) is preferably 20 nm, more preferably 50 nm, and even more preferably 100 nm. The upper limit of Rth is preferably 400 nm, more preferably 380 nm, and even more preferably 350 nm. By setting it as the said range, when a display apparatus is seen from diagonally, the light leakage and the change of a color tone can be prevented effectively, and a viewing angle can be expanded.

  The optically anisotropic layer does not have a specific optical axis, but has a minimum absolute value of retardation in a direction inclined from the normal direction of the transparent film. The lower limit of the angle between the direction in which the absolute value of retardation is minimum and the normal direction of the transparent film is preferably 5 degrees, and more preferably 10 degrees. The upper limit is preferably 50 degrees, more preferably 40 degrees. By setting it as the said range, when a display apparatus is seen from diagonally, the light leakage and the change of a color tone can be prevented effectively, and a viewing angle can be expanded.

  For optically anisotropic layers, plasticizers and surfactants are used as long as they do not inhibit the orientation of the discotic compound in order to control the angle of the discotic compound, the discotic nematic phase formation temperature, the compatibility, the coating property, etc. , Polymerizable monomers, polymer compounds, and the like can be added.

  As the polymerizable monomer, those having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group are preferable. The amount of the polymerizable monomer is preferably 1 to 50% by weight, more preferably 5 to 30% by weight, based on the amount of the discotic compound.

  The polymer compound is not particularly limited as long as it has compatibility with the discotic compound. As the polymer compound, cellulose ester is preferable, and cellulose acetate butyrate is particularly preferable. The polymer compound can be used in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the amount of the discotic compound. The degree of butyrylation of cellulose acetate butyrate is preferably 30 to 80%, and the degree of acetylation is preferably 30 to 80%.

  The transparent film constituting the polarizer protective film B is not particularly limited as long as it is formed of a transparent resin. Examples of the resin used for forming the transparent film include cellulose esters such as triacetyl cellulose, acetyl-propionyl cellulose, and acetyl-butyryl cellulose, polyesters such as polyamide, polycarbonate, polyethylene terephthalate, and polyethylene naphthalate, polystyrene, and syndiotactic polystyrene. , Polyolefins such as polypropylene and polymethylpentene, alicyclic polyolefins such as polynorbornene, and polymethyl methacrylate. Among these, cellulose esters such as triacetyl cellulose, acetyl-propionyl cellulose, and acetyl-butyryl cellulose are preferable.

  The lower limit of the absolute value of retardation in the thickness direction of the transparent film is preferably 0 nm, more preferably 20 nm, and even more preferably 30 nm. The upper limit of the absolute value of retardation in the thickness direction is preferably 400 nm, more preferably 300 nm, and even more preferably 150 nm. By making it within the above range, it is easy to secure economical production stability and to secure appropriate optical characteristics as the polarizing plate protective film B.

  The lower limit of the absolute value of the in-plane retardation of the transparent film is preferably 0 nm, more preferably 5 nm, and even more preferably 10 nm. The upper limit of the absolute value of in-plane retardation is preferably 100 nm, more preferably 50 nm, and even more preferably 30 nm. By making it within the above range, it is easy to secure economical production stability and to secure appropriate optical characteristics as the polarizing plate protective film B.

  The lower limit of the thickness (D) of the transparent film is preferably 10 μm, more preferably 20 μm, and even more preferably 30 μm. If it is less than the above, the strength as a film is insufficient, and processing such as lamination may be difficult. The upper limit of the thickness (D) is preferably 200 μm, more preferably 170 μm, and even more preferably 150 μm. If the above is exceeded, the display device may become thick.

  An undercoat layer may be provided on the transparent film in order to impart adhesion. For the undercoat layer, gelatin, poly (meth) acrylate resin and its substitute, styrene-butadiene resin or the like is used. Surface treatment such as corona treatment may be performed on the surface of the transparent film.

  It is preferable to provide an alignment layer between the transparent film and the optically anisotropic layer in order to control the alignment direction of the discotic compound. The resin used for the alignment layer is not particularly limited as long as it is a transparent resin, but one or more selected from polyimide, polystyrene, polyvinyl alcohol, and alkyl-modified polyvinyl alcohol is preferable. Among these, at least one selected from polyimide and alkyl-modified polyvinyl alcohol modified with an alkyl group having 6 or more carbon atoms is preferable.

  The surface of the alignment layer can be provided with fine grooves in one direction by rubbing treatment. The rubbing treatment is performed by rubbing in a certain direction using a cloth on which, for example, paper, gauze, felt, rubber, nylon, and polyester fiber are flocked on average. The rubbing treatment can use a treatment method used as a liquid crystal alignment treatment of the liquid crystal panel.

  An optically anisotropic layer containing a discotic compound can be provided on the alignment layer. The optically anisotropic layer can be formed by applying a coating solution prepared by dissolving the above discotic compound and, if necessary, a polymerizable monomer, a polymer compound, and other additives in a solvent onto the alignment layer and then drying. it can. As the solvent, one or more selected from methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, cyclohexanone, toluene, methanol, ethanol, isopropanol, butanol, a mixed solvent thereof and the like are preferably used.

  After drying, the discotic compound can be oriented by heating to the phase transition temperature. The lower limit of the heating temperature for the phase transition is preferably 50 ° C, more preferably 70 ° C. The upper limit is preferably 250 ° C, more preferably 170 ° C.

  In order to maintain the orientation state, the discotic compound is preferably fixed by reacting a reactive group introduced into the discotic compound. Preferable reactive groups include a glycidyl group, an isocyanate group, a hydroxyl group, a carboxylic acid group, and a vinyl group, and among these, a vinyl group is preferable. The immobilization reaction is performed by a method suitable for the reactive group and the reaction catalyst, and examples thereof include heating or radiation irradiation. In particular, when a vinyl group is used, ultraviolet rays or electron beam irradiation is preferable.

  The lower limit of the light transmittance of the polarizer protective film B is preferably 80%, more preferably 86%. If it is less than the above, the brightness of the display device may decrease.

  The upper limit of the haze of the polarizer protective film B is preferably 3%, more preferably 2%, and further preferably 1%. If the above is exceeded, the image may become unclear.

  The polarizer protective film B has Nx ≧ Ny> Nz (Nx is the refractive index in the direction where the maximum refractive index is seen from the film plane, Ny is the refractive index in the direction orthogonal to Nx on the film plane, and Nz is the thickness direction. The refractive index ellipsoidal structure having a thick disc shape to an oval shape.

  The lower limit of the retardation in the thickness direction of the polarizer protective film B on which the optically anisotropic layer is laminated is preferably 20 nm, more preferably 50 nm, and even more preferably 100 nm. The upper limit is preferably 500 nm, more preferably 400 nm, still more preferably 300 nm, and particularly preferably 200 nm. By making it within the above range, it is easy to secure economical production stability and to secure appropriate optical characteristics as the polarizing plate protective film B.

  The lower limit of the absolute value of the in-plane retardation of the polarizer protective film B on which the optically anisotropic layer is laminated is preferably 0 nm, more preferably 5 nm, and further preferably 10 nm. The upper limit is preferably 100 nm, more preferably 50 nm, and even more preferably 30 nm. The retardation in the thickness direction and the in-plane retardation of the polarizer protective film B can effectively prevent light leakage and color change when the display device is viewed from an oblique direction, and widen the viewing angle. .

2. Polarizing plate The polarizing plate has a configuration in which both sides of a polarizer made of a polyvinyl alcohol film dyed with iodine are sandwiched between two polarizer protective films. The combination of the two polarizer protective films includes a combination of a polarizer protective film A and a general polarizer protective film, a combination of a general polarizer protective film and a polarizer protective film B, and a polarizer protective film A and a polarized light. The combination with the child protective film B can be mentioned. Any of these polarizing plates can be used as a constituent member of the liquid crystal display device of the present invention. Among these, the polarizing plate which combined the polarizer protective film A and the polarizer protective film B is preferable. Here, the general polarizer protective film is a polarizer protective film that does not satisfy any of the conditions A and B described above, and preferably a TAC film, a COP film, an acrylic film, or the like having a relatively low retardation. .

  The polarizer and the polarizer protective film are laminated via an adhesive. As the adhesive, a water-based adhesive, a radiation curable adhesive, or the like is selected and used in accordance with a polarizer or a polarizer protective film. In the case of an aqueous adhesive, a polarizing plate is usually obtained by heat treatment in the range of 70 ° C. to 120 ° C. for about 10 minutes to 60 minutes.

  The liquid crystal display device has a liquid crystal cell and a pair of polarizing plates on both sides thereof. In this document, a polarizing plate disposed on the light source side of the liquid crystal cell is referred to as a light source side polarizing plate, and a polarizing plate disposed on the viewing side (the side opposite to the light source) from the liquid crystal cell is referred to as a viewing side polarizing plate. At least one of the light source side polarizing plate protective film of the light source side polarizing plate or the viewing side polarizer protective film of the visual side polarizing plate is the polarizer protective film A, and the liquid crystal cell side polarizer protective film of the light source side polarizing plate or At least one of the liquid crystal cell side polarizer protective films of the viewing side polarizing plate is a polarizer protective film B.

  In a more preferred embodiment, both the light source side polarizing plate protective film of the light source side polarizing plate and the visual side polarizer protective film of the visual side polarizing plate are the polarizer protective film A. Moreover, it is also a preferable form that both the liquid crystal cell side polarizer protective film of the light source side polarizing plate and the liquid crystal cell side polarizer protective film of the viewing side polarizing plate are the polarizer protective film B. As a particularly preferred embodiment, both the light source side polarizing plate protective film of the light source side polarizing plate and the viewing side polarizer protective film of the viewing side polarizing plate are the polarizer protective film A, and the liquid crystal cell side of the light source side polarizing plate. Both the polarizer protective film and the liquid crystal cell side polarizer protective film of the viewing side polarizing plate are the polarizer protective film B. In this case, the polarizer protective film A does not have to have the same characteristics, and the polarizer protective film B does not necessarily have the same characteristics.

  The polarizer protective film provided on the surface opposite to the polarizer protective film A constituting the polarizing plate may be either the polarizer protective film B or the general polarizer protective film. It is preferable that the difference in shrinkage rate is small. Specifically, the difference between the heat shrinkage rate in the + 45 ° direction with respect to the film flow direction and the heat shrinkage rate in the −45 ° direction with respect to the film flow direction is preferably 0.4% or less.

3. 2. Liquid Crystal Display Device Generally, a liquid crystal display device includes a rear module, a liquid crystal cell, and a front module in order from the backlight light source side toward the image display side (viewing side or outgoing light side). The rear module and the front module generally include a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the backlight source side in the rear module, and is disposed on the image display side in the front module.

  The liquid crystal display device includes at least a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may have other constituent members other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film and the like as appropriate.

  The configuration of the backlight may be an edge light method using a light guide plate, a reflection plate, or the like as a constituent member, or a direct type. In the present invention, it is preferable to use a white light source having a continuous broad emission spectrum as a backlight light source of a liquid crystal display device. Here, the continuous broad emission spectrum means an emission spectrum in which there is no wavelength at which light intensity becomes zero in a wavelength region of at least 450 nm to 650 nm, preferably in the visible light region. As such a white light source having a continuous broad emission spectrum, for example, a white LED can be exemplified, but the present invention is not limited thereto.

  The white LED usable in the present invention includes a phosphor type, that is, an element that emits white light by combining a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor, or an organic light emitting diode (Organic light diode). -Emitting diode (OLED). Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. Among white LEDs, white light-emitting diodes, consisting of light-emitting elements that combine blue light-emitting diodes using compound semiconductors with yttrium, aluminum, and garnet-based yellow phosphors, have a continuous and broad emission spectrum and have a luminous efficiency. Therefore, it is suitable as the backlight light source of the present invention. Since the white LED has low power consumption, the liquid crystal display device of the present invention using the white LED contributes to energy saving.

  Fluorescent tubes such as cold-cathode tubes and hot-cathode tubes that have been widely used as backlight light sources have a discontinuous emission spectrum whose emission spectrum has a peak at a specific wavelength. Therefore, since it is difficult to obtain the desired effect of the present invention, it is not preferable as the light source of the liquid crystal display device of the present invention.

  As the liquid crystal cell, any liquid crystal cell that can be used in a liquid crystal display device can be appropriately selected and used, and the method and structure thereof are not particularly limited. For example, a liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be appropriately selected and used. Therefore, the liquid crystal cell can be used by appropriately selecting a known liquid crystal material and a liquid crystal made of a liquid crystal material that can be developed in the future. In one embodiment, a preferred liquid crystal cell is a transmissive liquid crystal cell.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all possible and are within the scope of the present invention.

  The physical property evaluation methods in the examples are as follows.

(1) Difference in heat shrinkage rate in oblique direction A polarizer protective film 1 to 15 described later cut out from each cut-out part of a slit roll is cut out into a square shape with a side of 21 cm, and the atmosphere is 23 ° C. and 65% RH for 2 hours or more. I left it alone. Draw a circle with a diameter of 20 cm centered on the center of this sample, draw a straight line passing through the center of the circle in the + 45 ° and -45 ° directions, with the vertical direction (film flow direction) as 0 °, and measure the diameter in each direction And the length before processing. Next, the cut sample was heated in water at 85 ° C. for 30 minutes, and then water adhering to the cut surface was wiped off and air-dried, and then left in an atmosphere of 23 ° C. and 65% RH for 2 hours or more. As described above, the length of the straight line drawn in each diameter direction was measured to obtain the length after treatment. Next, the thermal shrinkage rate was determined according to the following formula.
Thermal shrinkage = ((length of sample before treatment) − (length of sample after treatment)) / (length of sample before treatment) × 100 In addition, three points in the film width direction with the same slit roll Sampling was performed, and the average was taken as the heat shrinkage difference. By subtracting the smaller value from the larger value of the heat shrinkage rate in the + 45 ° and −45 ° directions, the difference in heat shrinkage rate in the oblique direction was obtained.

(2) Light Leakage Evaluation Method A triacetyl cellulose film having a thickness of 120 μm having an optically easy layer having a thickness of 1.8 μm prepared in Production Example 4 described later on one surface of a polarizer made of a PVA film ( One of the polarizer protective films 1 to 15 produced by the method described later is bonded to the other surface with an adhesive so that the surface of the triacetyl cellulose film is on the polarizer side, and 85 ° C. 30 in an oven. The polarizing plate was manufactured by heat-processing for minutes. In addition, it bonded together so that the polarizing axis of a polarizer and the main orientation axis | shaft of a polyester film (any one of polarizer protective films 1-15) might become perpendicular | vertical. The two polarizing plates thus obtained are positioned so that the polyester film (any one of the polarizer protective films 1 to 5) is outside the two polarizers (that is, the triacetyl cellulose film is on the polarizer side). The maximum light transmittance at a wavelength of 550 to 600 nm was measured using a spectrophotometer V7100 manufactured by JASCO Corporation.
○: Maximum light transmittance is 0.02% or less ×: Maximum light transmittance exceeds 0.02%

(3) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | nx−ny |) and the film thickness d (nm) on the film. Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) of the polarizer protective films 1 to 15 described later was determined by the following method. Using a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes the long side, for measurement A sample was used. About this sample, the biaxial refractive index (nx, ny) orthogonal to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm), The absolute value (| nx−ny |) of the difference between the biaxial refractive indexes was defined as the refractive index anisotropy (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (ΔNxy × d) of refractive index anisotropy (ΔNxy) and film thickness d (nm).

(4) Nz coefficient | ny-nz | / | ny-nx | However, the values of ny and nx were selected so that ny> nx.

(5) Degree of plane orientation (ΔP)
The value obtained by (nx + ny) / 2−nz was defined as the degree of plane orientation (ΔP).

(6) Thickness direction retardation (Rth)
Thickness direction retardation is obtained by multiplying two birefringences ΔNxz (= | nx-nz |) and ΔNyz (= | ny-nz |), respectively, when viewed from the cross section in the film thickness direction. This is a parameter indicating an average of retardation to be obtained. Thickness direction retardation (Rth) is obtained by calculating nx, ny, nz and film thickness d (nm) by the same method as the measurement of retardation, and calculating an average value of (ΔNxz × d) and (ΔNyz × d). Asked.

(7) Iridescent observation One of the polarizer protective films 1 to 15 described later is attached to one side of a polarizer made of PVA and iodine so that the polarization axis of the polarizer and the orientation main axis of the polyester film are perpendicular to each other. A 120 μm-thick triacetyl cellulose film having a 1.8 μm-thick optically easy-to-use layer produced in Production Example 4 to be described later is attached to the opposite surface so that the triacetyl cellulose film surface is on the polarizer side. A polarizing plate was created. The obtained polarizing plate was placed on both sides of the liquid crystal so that each polarizing plate was in a crossed Nicols condition to produce a liquid crystal display device. Each polarizing plate is such that the polyester film (any one of the polarizer protective films 1 to 15) is on the opposite side (distal) to the liquid crystal (that is, the triacetyl cellulose film is on the polarizer side). Arranged. As a light source of the liquid crystal display device, a white LED composed of a light emitting element in which a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor were combined was used as a light source (Nichia Chemical, NSPW500CS). The liquid crystal display device was visually observed from the front and oblique directions, and the presence or absence of rainbow spots was determined as follows.

A: No iridescence from any direction.
A ′: When observed from an oblique direction, very thin rainbow spots are observed depending on the angle.
B: When observed from an oblique direction, a thin iridescence is observed depending on the angle.
C: When observed from an oblique direction, rainbow spots are observed.
D: When observed from the front direction and the oblique direction, rainbow spots are observed.

(8) Tear Strength Using a Toyo Seiki Seisakusho Elmendorf Tear Tester, the tear strength of each film was measured according to JIS P-8116. The tearing direction was performed so as to be parallel to the orientation main axis direction of the film, and was determined as follows. In addition, the measurement of the orientation main axis direction was measured with a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter).
○: Tear strength is 50 mN or more ×: Tear strength is less than 50 mN

(Production Example 1-Polyester A)
When the temperature of the esterification reactor was raised to 200 ° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged and 0.017 parts by mass of antimony trioxide as a catalyst while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Next, the pressure was raised and the pressure esterification reaction was carried out under the conditions of gauge pressure 0.34 MPa and 240 ° C., then the esterification reaction can was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and 0.012 mass part of trimethyl phosphate was added. Then, after 15 minutes, dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and subjected to polycondensation reaction at 280 ° C. under reduced pressure.

  After completion of the polycondensation reaction, it is filtered through a NASRON filter with a 95% cut diameter of 5 μm, extruded into a strand from a nozzle, and cooled and solidified using cooling water that has been filtered (pore diameter: 1 μm or less) in advance. And cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles and internally precipitated particles. (Hereafter, abbreviated as PET (A).)

(Production Example 2-Polyester B)
10 parts by weight of a dried UV absorber (2,2 ′-(1,4-phenylene) bis (4H-3,1-benzoxazinon-4-one), PET (A) containing no particles (inherent viscosity Was 0.62 dl / g) and 90 parts by mass were mixed, and a polyethylene terephthalate resin (B) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (B)).

(Production Example 3-Adjustment of Adhesiveness Modification Coating Solution)
A transesterification reaction and a polycondensation reaction are performed by a conventional method, and as a dicarboxylic acid component (based on the whole dicarboxylic acid component) 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate, A water-dispersible sulfonic acid metal group-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol (relative to the entire glycol component) was prepared as a glycol component. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, 0.06 parts by mass of nonionic surfactant were mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal base-containing copolymer polyester resin and continuing to stir until the resin is no longer agglomerated, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolymerized polyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin solution was mixed with 99.46 parts by mass of the silicia 310. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modified coating solution.

(Production Example 4: Film satisfying characteristic B)
A triacetyl cellulose film having a thickness of 120 μm on which an optically anisotropic layer having a thickness of 1.8 μm was formed was obtained in accordance with the description in the section for producing an optical compensation film in Example 1 of JP-A-2001-100043. As described in Example 1 of Japanese Patent Application Laid-Open No. 2001-100043, the triacetyl cellulose film used was formed by forming a rubbing-treated alignment layer having a thickness of 0.5 μm. An optically anisotropic layer was formed. As the discotic compound, a structure in which R _{1 to} R ₆ are acryloyloxy-modified alkoxybenzyl groups (m = 8) represented by the general formula (2) in the structure represented by the general formula (1) described above was used. . The change in the tilt angle of the discotic compound from the surface of the triacetyl cellulose film was 20 ° to 50 °.

  The change in tilt angle was evaluated as follows. That is, with respect to the optical compensation film, the retardation from any direction on the plane that includes the rubbing axis and is perpendicular to the optical compensation film surface is measured with an ellipsometer (AEP-100, manufactured by Shimadzu Corporation), and the optical portion of the measurement portion is further measured. The retardation of only the support and the alignment layer after removing the side layer was measured in the same manner. By obtaining the optical characteristics of the optically anisotropic layer only from these two measured values (retardation angle dependence), the direction of zero retardation was taken as the optical axis and the presence or absence of the optical axis was examined. Further, the tilt (change in tilt angle) of the discotic compound from the support surface was calculated by fitting the optical characteristics.

As films corresponding to the polarizer protective film A, the following polarizer protective films 1 to 15 were produced.
(Polarizer protective film 1)
After drying 90 parts by mass of PET (A) resin pellets containing no particles as a raw material for the base film intermediate layer and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber at 135 ° C. for 6 hours under reduced pressure (1 Torr) , And supplied to the extruder 2 (for the intermediate layer II layer). Also, the PET (A) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I layer and the outer layer III) and dissolved at 285 ° C. . After filtering these two kinds of polymers with a filter medium made of a sintered stainless steel (nominal filtration accuracy of 10 μm particles 95% cut), laminating them in a two-kind / three-layer confluence block, and extruding them into a sheet form from a die, The film was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and then cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, after applying the adhesive property-modifying coating solution on the both sides of this unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m ² , the coating was dried at 80 ° C. for 20 seconds. .

  The unstretched film on which this coating layer was formed was guided to a tenter stretching machine, and the film was guided to a hot air zone at a temperature of 125 ° C. while being gripped by a clip, and stretched 4.0 times in the width direction. Next, a mill roll made of a uniaxially oriented PET film having a film thickness of about 50 μm was obtained by processing at a temperature of 225 ° C. for 30 seconds while keeping the width stretched in the width direction, and cutting and removing both edges. . This mill roll was divided into three equal parts to obtain three slit rolls (L (left position), C (center position), R (right position)). For each slit roll, two types were prepared: one that was offline annealed at 90 ° C. for 5 minutes and one that was not offline annealed.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, a slit roll made of a uniaxially oriented PET film was obtained in the same manner as the polarizer protective film 1 except that the thickness was about 100 μm. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 3)
An unstretched film produced by the same method as that for the polarizer protective film 1 is heated to 105 ° C. using a heated roll group and an infrared heater, and then 1.5 rolls in the traveling direction with a roll group having a difference in peripheral speed. After being double-stretched, the film was stretched 4.0 times in the width direction in the same manner as for the polarizer protective film 1 to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 50 μm. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 4)
By a method similar to that for the polarizer protective film 3, the slit roll made of a biaxially oriented PET film having a film thickness of about 50 μm was stretched 2.0 times in the running direction and 4.0 times in the width direction. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 5)
A slit roll made of a uniaxially oriented PET film having a film thickness of 50 μm was obtained in the same manner as in the polarizer protective film 1 without using a PET resin (B) containing an ultraviolet absorber in the intermediate layer. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 6)
In the same manner as for the polarizer protective film 1, the film was stretched 1.0 times in the running direction and 3.5 times in the width direction to obtain a slit roll made of a uniaxially oriented PET film having a film thickness of about 75 μm. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 7)
A slit roll made of a uniaxially oriented PET film having a thickness of about 100 μm is used by changing the thickness of the unstretched film using the same method as that for the polarizer protective film 1, setting the transverse stretch ratio to 3.8 times, and the stretching temperature to 135 ° C. Obtained. Two types were prepared, one that was offline annealed in the same manner as the polarizer protective film 1 and one that was offline annealed.

(Polarizer protective film 8)
A slit roll made of a uniaxially oriented PET film having a thickness of about 50 μm was obtained using the same method as for the polarizer protective film 1 with a lateral stretching ratio of 3.8 times and a stretching temperature of 135 ° C. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 9)
A slit roll made of a uniaxially oriented PET film having a thickness of 50 μm was obtained using the same method as for the polarizer protective film 1 with a lateral stretch ratio of 3.8 times. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 10)
A slit roll made of a uniaxially oriented PET film having a thickness of about 50 μm was obtained using the same method as for the polarizer protective film 1 with a transverse draw ratio of 4.2 times and a draw temperature of 135 ° C. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 11)
A slit roll made of a uniaxially oriented PET film having a thickness of 38 μm was obtained by changing the thickness of the unstretched film and changing the lateral stretch ratio to 3.8 times using the same method as for the polarizer protective film 1. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 12)
A slit roll made of a uniaxially oriented PET film having a thickness of 38 μm was obtained by changing the thickness of the unstretched film using the same method as for the polarizer protective film 1. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 13)
By a method similar to that for the polarizer protective film 3, the film was stretched 1.8 times in the running direction and 2.0 times in the width direction to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 275 μm. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 14)
In the same manner as the polarizer protective film 3, the film was stretched 3.6 times in the running direction and 4.0 times in the width direction to obtain a slit roll made of a biaxially oriented PET film having a film thickness of about 38 μm. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

(Polarizer protective film 15)
A slit roll made of a uniaxially oriented PET film having a thickness of about 10 μm was obtained by changing the thickness of the unstretched film using the same method as for the polarizer protective film 1. Two types were prepared: one that was subjected to offline annealing in the same manner as the polarizer protective film 1 and one that was not subjected to offline annealing.

  About the polarizer protective films 1-15, the result of light leakage evaluation is shown in Table 1 (sample processed by offline annealing) and Table 2 (sample which was not processed by offline annealing). In addition, Table 3 below shows the results of rainbow spot observation and tear strength measurement of the liquid crystal display device manufactured as described above using the polarizer protective films 1 to 15 (samples processed by offline annealing).

  In Table 3, polarizer protective film No. 7 * shows the case where the polarizer protective film 7 is used as the polarizer protective film and the organic light emitting diode (OLED) is used as the light source. In Table 3, the polarizer protective film No. 7 ** shows the case where the polarizer protective film 7 is used as the polarizer protective film and the cold cathode tube is used as the light source.

  From the results shown in Table 3, it was shown that when the retardation of the oriented polyester film is 4000 or more and the Nz coefficient is 1.7 or less, the generation of rainbow spots is remarkably suppressed. . In addition to this condition, it has been shown that by controlling the degree of plane orientation of the oriented polyester film to 0.13 or less, it is possible to more effectively suppress the occurrence of rainbow spots.

  According to the present invention, when two polarizing plates are arranged in a crossed Nicol environment, the occurrence of slight light leakage is suppressed, and a polyester film suitable for obtaining a liquid crystal display device having excellent visibility. The polarizer protective film which consists of can be provided. Therefore, the industrial applicability of the present invention is extremely high.

Claims (4)

A light source side polarizing plate and a viewing side polarizing plate, and a liquid crystal display device including a liquid crystal cell disposed between these polarizing plates,
At least one of the light source side polarizer protective film of the light source side polarizing plate or the viewer side polarizer protective film of the viewer side polarizing plate satisfies the following condition A,
At least one of the liquid crystal cell side polarizer protective film of the light source side polarizing plate or the liquid crystal cell side polarizer protective film of the viewing side polarizing plate satisfies the following condition B.
Liquid crystal display device.
Condition A: The difference between the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the -45 degree direction with respect to the film flow direction is 0.4% or less, and has a retardation of 4500 to 30000 nm. Polyester film condition B: a transparent film provided with a layer containing a compound having a discotic structural unit, the disc surface of the discotic structural unit being inclined with respect to the transparent film surface, the discotic structural unit The angle formed by the disk surface of the transparent film and the surface of the transparent film increases as the distance from the surface of the transparent film increases. The liquid crystal cell side polarizer protective film of at least one of the light source side polarizing plate and the viewing side polarizing plate satisfies the condition B, and the other polarizer protective film of the at least one polarizing plate satisfies the condition A. Liquid crystal display device. The liquid crystal display device according to claim 1, wherein the liquid crystal cell is a twisted nematic liquid crystal cell. A polarizing plate in which a polarizer protective film is provided on both sides of a polarizer, wherein one polarizer protective film satisfies the following condition A, and the other polarizer protective film satisfies the following condition B. Condition A: The difference between the heat shrinkage rate in the +45 degree direction with respect to the film flow direction and the heat shrinkage rate in the -45 degree direction with respect to the film flow direction is 0.4% or less, and has a retardation of 4500 to 30000 nm. Polyester film condition B: a transparent film provided with a layer containing a compound having a discotic structural unit, the disc surface of the discotic structural unit being inclined with respect to the transparent film surface, and the discotic The angle formed by the disk surface of the structural unit and the surface of the transparent film increases as the distance from the surface of the transparent film increases.

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