WO2014021242A1 - Liquid crystal display device, polarizing plates, and polarizer protection film - Google Patents

Abstract

Provided is a liquid crystal display device wherein rainbow spots that occur when an oriented polyester film is used as a polarizer protection film for both of a pair of polarizing plates are minimized. The liquid crystal display device has a background light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The backlight light source is a white light source having a continuous emission spectrum. The polarizing plates have a structure obtained by laminating a polarizer protection film on both sides of a polarizer. At least one of the polarizer protective films of the polarizing plate disposed on the incoming light side, and at least one of the polarizer protective films of the polarizing plate disposed on the outgoing light side are oriented polyester films having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.

Description

Liquid crystal display device, polarizing plate and polarizer protective film

The present invention relates to a liquid crystal display device. Specifically, the present invention relates to a liquid crystal display device in which generation of rainbow spots is improved.

A polarizing plate used in a liquid crystal display device (LCD) is usually composed of a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like and sandwiched 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 used as the protective film is reduced for this purpose, sufficient mechanical strength cannot be obtained and moisture permeability deteriorates. Further, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

Therefore, it has been proposed to use a polyester film instead of the TAC film so that the polarizing plate can be made thin so that high durability can be maintained even if the thickness is small as a polarizer protective film (Patent Documents 1 to 3). ).

The polyester film is superior to the TAC film in durability, but unlike the TAC film, it has birefringence. Therefore, when it 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, a rainbow-like color spot is generated when observed from an oblique direction, and the image quality is deteriorated. . Therefore, Patent Documents 1 to 3 take measures to reduce retardation by using a copolyester as the polyester. However, even in that case, the iridescent color spots could not be completely eliminated.

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

As a means for solving the above problems, the present inventors have found that a white light emitting diode is used as a backlight light source, and an oriented polyester film having a certain retardation is used as a polarizer protective film (Patent Document 4). . However, the inventors have made further studies on the liquid crystal display device having such a configuration, and even in such an improved liquid crystal display device, polyester as a polarizer protective film is provided on both of the pair of polarizing plates. In the case of using a film, we discovered the existence of a new problem that, when observed from an oblique direction, there may still be rainbow spots depending on the angle. Then, this invention makes it a main subject to suppress generation | occurrence | production of the iridescence at the time of using an oriented polyester film as a polarizer protective film of both of a pair of polarizing plate of a liquid crystal display device.

As a result of studying the above problem day and night, the present inventor has controlled retardation of an oriented polyester film used as a polarizer protective film and a characteristic of Nz coefficient represented by | ny-nz | / | ny-nx |. The present inventors have found that the occurrence of rainbow spots can be effectively suppressed when a polyester film is used as the polarizer protective film for both of the pair of polarizing plates of the liquid crystal display device. The present invention has been completed as a result of further research and improvement based on such knowledge.

The representative present invention is as follows.
Item 1.
A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
At least one of the polarizer protective films of the polarizing plate arranged on the incident light side, and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side have a retardation of 4000 to 30,000 nm and Nz of 1.70 or less. An oriented polyester film having a coefficient,
Liquid crystal display device.
Item 2.
The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side have a retardation of 4000 to 30000 nm and 1.7. Item 2. The liquid crystal display device according to item 1, which is an oriented polyester film having the following Nz coefficient.
Item 3.
Item 3. The liquid crystal display device according to item 1 or 2, wherein the orientation degree of the oriented polyester film is 0.13 or less.
Item 4.
Item 4. The liquid crystal display device according to any one of Items 1 to 3, wherein the white light source having a continuous emission spectrum is a white light emitting diode.
Item 5.
Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
A polarizing plate for a liquid crystal display device using a white light source having a continuous emission spectrum as a backlight light source, wherein the polarizer protective film on at least one side is an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.
Item 6.
The polarizing plate for liquid crystal display devices which uses the white light source which has the continuous emission spectrum of claim | item 5 whose planar orientation degree of the said oriented polyester film is 0.13 or less as a backlight light source.
Item 7.
A polarizer protective film for a liquid crystal display device comprising a white light source having a continuous emission spectrum, which comprises an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less, as a backlight source.
Item 8.
Item 8. The polarizer protective film for a liquid crystal display device using the white light source having a continuous emission spectrum according to Item 7 as a backlight light source, wherein the oriented polyester film has a plane orientation degree of 0.13 or less.
Item 9.
Item 9. The polarizer protective film for a liquid crystal display device using the white light source having a continuous emission spectrum according to Item 7 or 8, wherein the oriented polyester film has an easy-adhesion layer.
Item 10.
Item 10. The continuous emission spectrum according to any one of Items 7 to 9, wherein the oriented polyester film comprises at least three layers, contains an ultraviolet absorber in a layer other than the outermost layer, and has a light transmittance of 380 nm of 20% or less. A polarizer protective film for a liquid crystal display device using a white light source having a backlight as a backlight source.

The liquid crystal display device of the present invention has excellent visibility because the occurrence of rainbow spots is suppressed. In addition, the liquid crystal display device of the present invention makes it possible to use an oriented polyester film as a polarizer protective film for both of a pair of polarizing plates without the problem of rainbow spots. Therefore, the present invention makes it possible to further reduce the thickness of the liquid crystal display device while maintaining sufficient mechanical strength, and in turn reduce the manufacturing cost. Furthermore, the polarizing plate and the polarizer protective film of the present invention enable the production of the liquid crystal display device of the present invention.

1. 2. Liquid Crystal Display Device In general, a liquid crystal display device is composed of a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight light source toward the image display side (viewing side or outgoing light side). The rear module and the front module are generally composed of 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 side facing the backlight light source in the rear module, and is disposed on the image display side (viewing side or outgoing light side) in the front module.

2. Backlight Light Source The liquid crystal display device of the present invention 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 the 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). -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.

Conventionally, 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.

3. Polarizer Protective Film The polarizing plate has a structure in which two polarizer protective films are laminated on both sides of a polarizer in which iodine is dyed on PVA or the like. The polarizing plate used in the present invention is an oriented polyester satisfying at least one of two polarizer protective films having a specific range of retardation and a physical property of Nz coefficient represented by | ny-nz | / | ny-nx |. Use film.

3-1. Retardation The oriented polyester film used for the polarizer protective film used in the present invention preferably has a retardation of 4000 to 30000 nm. This is because when the retardation is less than 4000 nm, an interference color is exhibited when the liquid crystal display device is observed from an oblique direction, so that good visibility cannot always be ensured. The preferred retardation of the oriented polyester film 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 oriented polyester film is 30000 nm. Even if an oriented polyester film having a retardation higher than that is used, a further improvement effect of visibility is not substantially obtained, and as the retardation increases, the thickness of the film is considerably increased, and the handleability as an industrial material is improved. It is because it falls.

The retardation value of the oriented polyester film can be determined by measuring the biaxial refractive index and thickness according to a known method. Further, for example, measurement can be performed using a commercially available automatic birefringence measuring apparatus such as KOBRA-21ADH (Oji Scientific Instruments).

As shown in Patent Document 4, when an oriented polyester film is used as a polarizer protective film for only one of a pair of polarizing plates, the retardation of the oriented polyester film is controlled in the range of 3000 to 30000 nm and is continuously used as a light source. By adopting a white light source having a broad spectrum of emission, the generation of rainbow spots is suppressed. The principle is considered as follows.

That is, when an oriented polyester film having birefringence is disposed on one side of the polarizer, the linearly polarized light emitted from the polarizer is disturbed when passing through the polyester film. And the transmitted light shows the interference color peculiar to the retardation which is the product of the birefringence and the thickness of the polyester film. Therefore, when a light source having a discontinuous emission spectrum, such as a cold cathode tube or a hot cathode tube, is used as the light source, the transmitted light intensity varies depending on the wavelength, and a rainbow-like color spot is exhibited.

On the other hand, when light having a continuous and broad emission spectrum in a wavelength region of at least 450 nm to 650 nm, preferably in the visible light region, passes through the birefringent body, the interference color spectrum becomes an envelope shape. Therefore, by controlling the retardation of the polyester film, a spectrum similar to the emission spectrum of the light source can be obtained. In this way, by making the emission spectrum of the light source similar to the envelope shape of the interference color spectrum by the transmitted light that has passed through the birefringent body, visibility is not noticeable without rainbow-like color spots. It is thought to improve.

However, as described above, when the oriented polyester film is used as the polarizer protective film in both of the pair of polarizing plates, rainbow spots may still be observed. Although the present invention makes it possible to suppress the occurrence of such rainbow spots, the principle has not been fully elucidated.

3-2. Nz coefficient The oriented polyester film used for the polarizer protective film 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 obtained using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), and the biaxial refractive index (ny, nx, However, ny> nx) and the refractive index (nz) in the thickness direction are determined by an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm). 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 |.

If the Nz coefficient of the oriented polyester film exceeds 1.7, rainbow spots may occur depending on the angle when the liquid crystal display device is observed from an oblique direction. 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.

3-3. Arrangement of Polarizer Protective Film In the liquid crystal display device of the present invention, the oriented polyester film having the specific retardation and the Nz coefficient is used as both polarizer protective films of a pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate disposed on the incident light side with respect to the liquid crystal and a polarizing plate disposed on the outgoing light side with respect to the liquid crystal. That is, the oriented polyester film is used for both a polarizing plate on the incident light side and a polarizing plate on the outgoing light side. The oriented polyester film only needs to be used as at least one of the two polarizer protective films constituting each polarizing plate, and may be used for both.

In a preferred embodiment, the oriented polyester film is used as a polarizer protective film on the incident light side of the polarizing plate on the incident light side, and as a polarizer protective film on the outgoing light side of the polarizing plate on the outgoing light side. used. When the oriented polyester film is used for only one of the two polarizer protective films constituting the polarizing plate, an arbitrary polarizer protective film (for example, a TAC film) can be used for the other. When the oriented polyester film is used as the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the incident light side and the polarizer protective film on the liquid crystal cell side of the polarizing plate arranged on the outgoing light side, the polarization of the liquid crystal cell Since there is a possibility of changing the characteristics, the polarizer protective film at these positions is a polarizer protective film other than the oriented polyester film (for example, a TAC film, an acrylic film, or a norbornene-based film). It is preferable to use a film having no birefringence.

3-4. Planar orientation coefficient In addition to controlling the retardation value and Nz coefficient of the oriented polyester film to the above specific range, the plane orientation degree represented by (nx + ny) / 2-nz is made to be less than the specific value, thereby ensuring more certainty. Iridescents can be completely eliminated when a polyester film is used as a polarizer protective film for both of the pair of polarizing plates. Here, the values of nx, ny, and nz are obtained by the same method as for the Nz coefficient. The degree of plane orientation of the oriented polyester 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.

3-5. Retardation ratio The ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) of the oriented polyester film 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 will be described later, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered as the film approaches a complete uniaxial (uniaxial symmetry) film.

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.

3-6. Thickness unevenness In order to suppress the variation in retardation of the oriented polyester film, it is preferable that the thickness unevenness of the film is small. In this respect, the uneven thickness of the oriented polyester film is preferably 5% or less, more preferably 4.5% or less, still more preferably 4% or less, and more preferably 3% or less. Particularly preferred.

3-7. Thickness The thickness of the oriented polyester film is not particularly limited as long as the effects of the present invention are not hindered, but is usually 15 to 300 μm, preferably 15 to 200 μm. 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 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.

3-8. Polyester resin The oriented polyester film used in the present invention can be obtained from any polyester resin. The type of the polyester resin is not particularly limited, and any polyester resin obtained by condensing dicarboxylic acid and diol can be used.

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, , 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 Adipi Acid, 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 in 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.

The dicarboxylic acid component and the diol component constituting the polyester resin can be used alone or in combination of two or more. 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.

3-9. Light Transmittance The oriented polyester film desirably has a light transmittance of 20% or less at a wavelength of 380 nm from the viewpoint of suppressing deterioration of optical functional dyes such as iodine dyes 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 measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

The transmittance at a wavelength of 380 nm of the oriented polyester 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 used in the present invention, 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 ′ Methylphenyl) -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 the cyclic imino ester UV absorber 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 -One, 2-phenyl-3,1-benzoxazin-4-one, etc. These ultraviolet absorbers may be used alone or in combination of two or more.

In the case where an ultraviolet absorbent is blended with the oriented polyester film, it is preferable that the oriented polyester film has a multilayer structure of three or more layers, and the ultraviolet absorbent is added to a layer other than the outermost layer (ie, the intermediate layer) of the film.

3-10. Other components, etc. In addition to the ultraviolet absorber, it is also preferable to add various additives to the oriented polyester film 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 polyester film does not contain a particle | grain 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.

4). In the present invention, in order to improve the adhesion to the polarizer, at least one surface of the oriented polyester film is provided with an easy adhesion layer mainly composed of at least one of polyester resin, polyurethane resin or polyacrylic resin. It is preferable to have. 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 of the present invention is preferably an aqueous coating solution containing at least one of water-soluble or water-dispersible copolymerized polyester resin, acrylic resin, and 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 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 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 average particle diameter of the above particles can be measured by 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 oriented polyester film can be subjected to corona treatment, coating treatment, flame treatment or the like in order to improve the adhesion to the polarizer.

5. Functional layer The polarizing plate used in the present invention has various functional layers, that is, a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection layer, for the purpose of preventing reflection, suppressing glare, suppressing scratches, and the like. It is also preferable to provide one or more functional layers selected from the group consisting of an anti-reflection layer and an anti-reflection anti-glare layer on the oriented polyester surface. When providing various functional layers, the oriented polyester film preferably has an easy adhesion layer on the surface thereof. At that time, 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 oriented polyester 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.

6). The manufacturing method of an oriented polyester film The oriented polyester film which is a protective film of this invention can be manufactured in accordance with the manufacturing method of a general polyester film. For example, the polyester resin is melted and the non-oriented polyester extruded and formed into a sheet shape is stretched in the longitudinal direction by utilizing the speed difference of the roll at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. The method of performing heat processing is mentioned.

The oriented polyester film of the present invention may be a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as a polarizer protective film, even if observed from directly above the film surface, rainbow-like color spots are observed. Although it is not seen, it should be noted that rainbow-like color spots may be observed when observed from an oblique direction.

This phenomenon is that a biaxially stretched film is composed of refractive index ellipsoids having different refractive indexes in the running direction, width direction, and thickness direction, and the retardation becomes zero depending on the light transmission direction inside the film (refractive index ellipse). This is because there is a direction in which the body appears to be a perfect circle. Therefore, when the liquid crystal display screen is observed from a specific oblique direction, a point where the retardation becomes zero may be generated, and a rainbow-like color spot is generated concentrically around that point. When the angle from the position directly above the film surface (normal direction) to the position where the rainbow-like color spots are visible is θ, the angle θ increases as the birefringence in the film increases, and the rainbow-like color increases. Spots are difficult to see. The biaxially stretched film tends to reduce the angle θ, and therefore the uniaxially stretched film is more preferable because rainbow-like color spots are less visible.

However, a perfect uniaxial (uniaxial symmetry) film is not preferable because the mechanical strength in the direction orthogonal to the orientation direction is significantly reduced. The present invention has biaxiality (biaxiality) in a range that does not substantially cause rainbow-like color spots or a range that does not cause rainbow-like color spots in the viewing angle range required for a liquid crystal display screen. It is preferable. Such biaxial objectivity is obtained by producing an oriented polyester film under the following conditions.

The oriented polyester film having the specific retardation and Nz coefficient described above can be obtained by adjusting the conditions during film formation (for example, the draw ratio, the draw temperature, the thickness of the film, 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., 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 between 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 specific value described above, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio, and most preferably 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 plane orientation degree 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 blending of the ultraviolet absorber into the oriented polyester film can be carried out 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 concentration of the UV absorber in 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 the master batch, a kneading extruder is used, and the extrusion temperature is preferably from 1 to 15 minutes at a temperature not lower than the melting point of the polyester raw material and not higher than 290 ° C. 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 oriented polyester film having a multilayer structure of three or more layers can be carried out by the following method. Polyester pellets alone for the outer layer, master batches containing UV absorbers for the intermediate layer and polyester pellets are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder, which is slit-shaped. Extruded into a sheet form from a die 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 that cause optical defects, it is preferable to perform high-precision filtration during melt extrusion in the process of producing an oriented polyester 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.

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) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | nx−ny |) on the film and the film thickness d (nm). Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), 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. For this sample, the biaxial refractive index (nx, ny) perpendicular to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., 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).

(2) The value obtained by Nz coefficient | ny-nz | / | ny-nx | was defined as Nz coefficient. However, the values of ny and nx were selected so that ny> nx.

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

(4) Thickness direction retardation (Rth)
Thickness direction retardation refers to two birefringences ΔNxz (= | nx−nz |) and ΔNyz (= | ny−nz |), respectively, when viewed from the cross section in the film thickness direction. It is a parameter which shows the average of retardation obtained. Thickness direction retardation (Rth) is calculated by calculating nx, ny, nz and film thickness d (nm) in the same manner as the retardation measurement, and calculating an average value of (ΔNxz × d) and (ΔNyz × d). )

(5) Observation of rainbow spots A polyester film prepared by the method 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 main axis of orientation of the polyester film are perpendicular to each other. A TAC film (manufactured by FUJIFILM Corporation, thickness 80 μm) was attached to the substrate to prepare a polarizing plate. 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 was arrange | positioned so that the said polyester film might be on the opposite side (distal) from a liquid crystal. 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.

(6) Tear Strength The tear strength of each film was measured according to JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho. The tearing direction was performed so as to be parallel to the orientation main axis direction of the film, and was determined as follows. The measurement in the orientation main axis direction was performed with a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments).
○: 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 Adhesive Modification Coating Solution)
A transesterification reaction and a polycondensation reaction were carried out 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 a 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.

(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, 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, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

(Polarizer protective film 2)
By changing the thickness of the unstretched film, 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.

(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 the polarizer protective film 1 to obtain a biaxially oriented PET film having a film thickness of about 50 μm.

(Polarizer protective film 4)
In the same manner as for the polarizer protective film 3, the film was stretched 2.0 times in the running direction and 4.0 times in the width direction to obtain a biaxially oriented PET film having a film thickness of about 50 μm.

(Polarizer protective film 5)
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.

(Polarizer protective film 6)
In the same manner as the polarizer protective film 3, the film was stretched 4.0 times in the running direction and 1.0 times in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 100 μm.

(Polarizer protective film 7)
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 uniaxially oriented PET film having a film thickness of about 75 μm.

(Polarizer protective film 8)
Using the same method as for the polarizer protective film 1, the thickness of the unstretched film was changed, the transverse stretch ratio was 3.8 times, the stretch temperature was 135 ° C., and a uniaxially oriented PET film having a thickness of about 100 μm was obtained.

(Polarizer protective film 9)
A method similar to that for the polarizer protective film 1 was used to obtain a uniaxially oriented PET film having a thickness of about 50 μm at a lateral stretching ratio of 3.8 times and a stretching temperature of 135 ° C.

(Polarizer protective film 10)
A method similar to that for the polarizer protective film 1 was used, and the transverse stretch ratio was 3.8 times to obtain a uniaxially oriented PET film having a thickness of 50 μm.

(Polarizer protective film 11)
A method similar to that for the polarizer protective film 1 was used, and a lateral stretching ratio of 4.2 times and a stretching temperature of 135 ° C. were obtained to obtain a uniaxially oriented PET film having a thickness of about 50 μm.

(Polarizer protective film 12)
Using the same method as for the polarizer protective film 1, the thickness of the unstretched film was changed, and the lateral stretch ratio was changed to 3.8 times to obtain a uniaxially oriented PET film having a thickness of 38 μm.

(Polarizer protective film 13)
Using a method similar to that for the polarizer protective film 1 and changing the thickness of the unstretched film, a uniaxially oriented PET film having a thickness of 38 μm was obtained.

(Polarizer protective film 14)
In the same manner as 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 biaxially oriented PET film having a film thickness of about 275 μm.

(Polarizer protective film 15)
In the same manner as for 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 biaxially oriented PET film having a film thickness of about 38 μm.

(Polarizer protective film 16)
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.

Table 1 below shows the results of rainbow spot observation and tear strength measurement of the liquid crystal display devices fabricated as described above using the polarizer protective films 1 to 17.

In Table 1, 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 1, 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. In Table 1, polarizer protective film No. 1 * uses the polarizer protective film 1 as a polarizer protective film on the outgoing light side of the outgoing light side polarizing plate, on both sides of the polarizer protective film on the incident light side of the outgoing light side polarizing plate and the incident light side polarizing plate. The case where a TAC film is used for a polarizer protective film is shown.

From the results shown in Table 1, 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.

By using the liquid crystal display device, the polarizing plate and the polarizer protective film of the present invention, it becomes possible to contribute to the reduction in thickness and cost of the LCD without lowering the visibility due to rainbow-like color spots. Therefore, the industrial applicability of the present invention is extremely high.

Claims (10)

1. A liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
   The backlight source is a white light source having a continuous emission spectrum;
   The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
   At least one of the polarizer protective films of the polarizing plate arranged on the incident light side, and at least one of the polarizer protective films of the polarizing plate arranged on the outgoing light side have a retardation of 4000 to 30,000 nm and Nz of 1.7 or less. An oriented polyester film having a coefficient,
   Liquid crystal display device.
2. The polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side and the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side have a retardation of 4000 to 30000 nm and 1.7. The liquid crystal display device according to claim 1, which is an oriented polyester film having the following Nz coefficient.
3. The liquid crystal display device according to claim 1 or 2, wherein the orientation degree of the oriented polyester film is 0.13 or less.
4. The liquid crystal display device according to any one of claims 1 to 3, wherein the white light source having a continuous emission spectrum is a white light emitting diode.
5. Consists of a structure in which a polarizer protective film is laminated on both sides of the polarizer,
   A polarizing plate for a liquid crystal display device using a white light source having a continuous emission spectrum as a backlight light source, wherein the polarizer protective film on at least one side is an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.
6. The polarizing plate for liquid crystal display devices which uses as a backlight light source the white light source which has the continuous emission spectrum of Claim 5 whose surface orientation degree of the said oriented polyester film is 0.13 or less.
7. A polarizer protective film for a liquid crystal display device comprising a white light source having a continuous emission spectrum, which comprises an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less, as a backlight source.
8. The polarizer protective film for a liquid crystal display device using a white light source having a continuous emission spectrum according to claim 7 as a backlight light source, wherein the orientation degree of the oriented polyester film is 0.13 or less.
9. The polarizer protective film for liquid crystal display devices which uses as a backlight light source the white light source which has the continuous emission spectrum of Claim 7 or 8 in which the said orientation polyester film has an easily bonding layer.
10. The continuous light emission according to any one of claims 7 to 9, wherein the oriented polyester film comprises at least three layers, contains an ultraviolet absorber in a layer other than the outermost layer, and has a light transmittance of 380 nm of 20% or less. A polarizer protective film for a liquid crystal display device using a white light source having a spectrum as a backlight source.