JP7272474B2 - Liquid crystal display device, polarizing plate and polarizer protective film - Google Patents

Description

The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device in which generation of iridescence is improved.

Polarizing plates used in liquid crystal displays (LCDs) are usually polyvinyl alcohol (PVA)
A polarizer dyed with iodine is sandwiched between two polarizer protective films, and a triacetyl cellulose (TAC) film is usually used as the polarizer protective film. In recent years, along with the thinning of LCDs, thinning of polarizing plates is required. However, if the thickness of the TAC film used as the protective film is reduced for this reason, there arises a problem that sufficient mechanical strength cannot be obtained and moisture permeability is deteriorated. again,
TAC films are very expensive and there is a strong demand for cheaper alternatives.

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

A polyester film is more durable than a TAC film, but unlike a TAC film, it has birefringence. Therefore, when it is used as a polarizer protective film, there is a problem that the image quality deteriorates due to optical distortion. That is, since a polyester film having birefringence has a predetermined optical anisotropy (retardation), when it is used as a polarizer protective film, rainbow-like color spots occur when observed from an oblique direction, and image quality deteriorates. . Therefore, in Patent Documents 1 to 3, copolyester is used as the polyester to reduce the retardation. However, even in that case, the rainbow-like color spots could not be completely eliminated.

JP-A-2002-116320 Japanese Patent Application Laid-Open No. 2004-219620 Japanese Patent Application Laid-Open No. 2004-205773 WO2011-162198

The present inventors have found that as a means for solving the above problems, a white light emitting diode is used as a backlight source, and an oriented polyester film having a certain retardation is used as a polarizer protective film (Patent Document 4). . However, the inventors
After further studies on the liquid crystal display device having such a configuration, even in the liquid crystal display device thus improved, when a polyester film is used as a polarizer protective film for both of a pair of polarizing plates, We discovered the existence of a new problem that iridescence still occurs depending on the angle when observed from an oblique direction. Therefore, the main object of the present invention is to suppress the occurrence of rainbow spots when an oriented polyester film is used as a polarizer protective film for both of a pair of polarizing plates of a liquid crystal display device.

As a result of studying the above problems day and night, the present inventors found that by controlling the retardation of the oriented polyester film used as a polarizer protective film and the Nz coefficient represented by |ny-nz|/|ny-nx| found that the occurrence of iridescence can be effectively suppressed when a polyester film is used as a polarizer protective film for both of a pair of polarizing plates of a liquid crystal display device. The present invention is an invention completed as a result of further research and improvements based on such findings.

A typical present invention is as follows.
Section 1.
A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates,
The backlight source is a white light source with a continuous emission spectrum,
The polarizing plate has a structure in which polarizer protective films are laminated on both sides of the 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 30000 nm and an Nz of 1.70 or less. is an oriented polyester film having a modulus of
Liquid crystal display.
Section 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 1. 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 degree of plane orientation of the oriented polyester film is 0.13 or less.
Section 4.
Items 1 to 1, wherein the white light source having a continuous emission spectrum is a white light emitting diode
4. The liquid crystal display device according to any one of 3.
Item 5.
It consists of a polarizer protective film laminated on both sides of the polarizer,
A polarizing plate for a liquid crystal display device, 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, and a white light source having a continuous emission spectrum is used as the backlight source.
Item 6.
Item 6. A polarizing plate for a liquid crystal display device using a white light source having a continuous emission spectrum as a backlight source according to item 5, wherein the degree of plane orientation of the oriented polyester film is 0.13 or less.
Item 7.
A polarizer protective film for a liquid crystal display device, comprising an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less, and having a continuous emission spectrum and using a white light source as a backlight source.
Item 8.
Item 8. The polarizer protective film for a liquid crystal display device using a white light source having a continuous emission spectrum as a backlight source according to item 7, wherein the degree of plane orientation of the oriented polyester film is 0.13 or less.
Item 9.
Item 9. The polarizer protective film for a liquid crystal display device according to Item 7 or 8, wherein the oriented polyester film has an easy-adhesion layer, and a white light source having a continuous emission spectrum is used as a backlight source.
Item 10.
Item 9. The continuous emission spectrum according to any one of Items 7 to 9, wherein the oriented polyester film consists of at least three layers, contains an ultraviolet absorber in layers other than the outermost layer, and has a light transmittance of 20% or less at 380 nm. A polarizer protective film for a liquid crystal display device using a white light source having

The liquid crystal display device of the present invention has excellent visibility because the generation of iridescence 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 iridescence. Therefore, the present invention makes it possible to further reduce the thickness of the liquid crystal display device while maintaining sufficient mechanical strength, thereby reducing the manufacturing cost. Furthermore, the polarizing plate and polarizer protective film of the present invention enable the production of the liquid crystal display device of the present invention.

1. 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 source toward the image display side (viewing side or emitted 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 of the substrate, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is arranged on the side facing the backlight source in the rear module,
The front module is arranged on the image display side (viewing side or emitted light side).

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 arranged between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may appropriately have other constituent members other than these, such as color filters, lens films, diffusion sheets, antireflection films, and the like.

The configuration of the backlight may be an edge-light type in which a light guide plate, a reflector, or the like is used as constituent members, or a direct type. In the present invention, it is preferable to use a white light source having a continuous broad emission spectrum as the backlight source of the liquid crystal display device. here,
A continuous broad emission spectrum means an emission spectrum in which there is no wavelength at which the light intensity is zero in at least the wavelength range of 450 nm to 650 nm, preferably in the visible light range. Examples of white light sources having such a wide continuous emission spectrum include, but are not limited to, white LEDs.

The white LED that can be used in the present invention includes a phosphor system, 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, and an organic light emitting diode (Organic light). - emitting
diode: OLED) and the like. Examples of the phosphor include an yttrium-aluminum-garnet-based yellow phosphor and a terbium-aluminum-garnet-based yellow phosphor. Among white LEDs, white light emitting diodes composed of light emitting elements that combine blue light emitting diodes using compound semiconductors and yttrium-aluminum-garnet-based yellow phosphors have a continuous and wide emission spectrum and high luminous efficiency. Also, it is suitable as a backlight source of the present invention. Since the power consumption of the white LED is small, 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, which have been widely used as backlight sources, have discontinuous emission spectra with peaks at specific wavelengths. Therefore, since it is difficult to obtain the desired effect of the present invention, it is not preferable as a light source for 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 made by dyeing PVA or the like with iodine. The polarizing plate used in the present invention has at least one of the two polarizer protective films, an oriented polyester that satisfies the physical properties of Nz coefficient represented by retardation in a specific range and |ny-nz|/|ny-nx| Use film.

3-1. Retardation The oriented polyester film used for the polarizer protective film used in the present invention has 4
It preferably has a retardation of 000 to 30000 nm. retardation is 4
This is because if the thickness is less than 000 nm, an interference color is exhibited when the liquid crystal display device is observed from an oblique direction, and 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, even more preferably 8000 nm or more, even more preferably 1000 nm or more.
0 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 higher retardation is used, the effect of further improving visibility is not substantially obtained, and the thickness of the film becomes considerably thicker as the retardation increases,
This is because the handleability as an industrial material is lowered.

The retardation value of the oriented polyester film can be obtained by measuring the refractive index and thickness in biaxial directions according to known methods. Also, for example, KOBRA-21ADH (
It can also be measured using a commercially available automatic birefringence measuring device such as Oji Keisokuki Co., Ltd.).

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 a continuous light source is used. By employing a white light source with a bright and broad emission spectrum, the occurrence of iridescence is suppressed. The principle is
It can be considered as follows.

That is, when an oriented polyester film having birefringence is placed 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 an interference color peculiar to the retardation, which is the product of the birefringence and 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, resulting in rainbow-like color spots.

On the other hand, when light having a continuous and broad emission spectrum in at least the wavelength range of 450 nm to 650 nm, preferably in the visible light range, passes through the birefringent material, the interference color spectrum has an envelope shape. Therefore, by controlling the retardation of the polyester film, it is possible to obtain a spectrum similar to the emission spectrum of the light source. In this way, by making the emission spectrum of the light source and the envelope shape of the interference color spectrum due to the transmitted light that has passed through the birefringent material similar, the visibility is remarkable without the occurrence of rainbow-like color spots. It is considered to be improved.

However, as described above, when an oriented polyester film is used as a polarizer protective film in both of a pair of polarizing plates, iridescence still occurs in some cases. The present invention makes it possible to suppress such iridescence, but the principle has not yet been fully elucidated.

3-2. Nz coefficient The oriented polyester film used for the polarizer protective film has |ny-nz|/|ny-
The Nz coefficient represented by nx| is preferably 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 Keisoku Co., Ltd.), and the biaxial refractive indices (ny, nx, ny>nx) and the refractive index (nz) in the thickness direction are determined by an Abbe refractometer (NAR-4T manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The Nz coefficient can be obtained by substituting nx, ny, and nz obtained in this way into the expression represented by |ny-nz|/|ny-nx|.

When the Nz coefficient of the oriented polyester film exceeds 1.7, iridescence may occur depending on the angle when the liquid crystal display device is viewed obliquely. The Nz coefficient is more preferably 1.65 or less, still more preferably 1.63 or less. The lower limit of the Nz coefficient is 1.2. This is because it is technically difficult to obtain a film of less than 1.2. In order to maintain the mechanical strength of the film, the lower limit of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and still more 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 Nz coefficient is used as the polarizer protective film for both of the pair of polarizing plates. A pair of polarizing plates means a combination of a polarizing plate arranged on the incident light side with respect to the liquid crystal and a polarizing plate arranged on the exiting light side with respect to the liquid crystal. That is, the oriented polyester film is used for both the polarizing plate on the incident light side and the polarizing plate on the outgoing light side. The oriented polyester film may be used as at least one of the two polarizer protective films constituting each polarizing plate, or may be used as both.

In a preferred embodiment, the oriented polyester film is used as the incident light side polarizer protective film of the incident light side polarizer and as the exit light side polarizer protective film of the exit light side polarizer. used. When the oriented polyester film is used for only one of the two polarizer protective films constituting the polarizing plate, any polarizer protective film (for example, TAC film, etc.) can be used for the other. When the oriented polyester film is adopted 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 should not be used as a polarizer protective film other than the oriented polyester film (for example, TAC film, acrylic film, norbornene-based film, etc.). It is preferable to use a film with no birefringence.

3-4. Plane orientation coefficient In addition to controlling the retardation value and Nz coefficient of the oriented polyester film within the above specific ranges, the degree of plane orientation represented by (nx + ny) / 2-nz is set to a specific value or less, thereby more reliably It is possible to completely eliminate iridescence when a polyester film is used as a polarizer protective film for both of a pair of polarizing plates. Here, the values of nx, ny and nz are determined in the same manner as the Nz coefficient. The plane orientation degree of the oriented polyester film is 0.13
The following is preferable, 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 iridescence observed depending on the angle when the liquid crystal display device is observed from an oblique direction. The degree of plane orientation is preferably 0.08 or more, more preferably 0.10 or more. If the degree of plane orientation is less than 0.08, the film thickness may fluctuate and the retardation value may become non-uniform in the film plane.

3-5. Retardation ratio The oriented polyester film has a ratio (Re/Rth) of retardation (Re) to thickness direction retardation (Rth) of preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.6. That's it. This is because the greater the ratio of the retardation to the thickness direction retardation (Re/Rth), the more isotropic the birefringent action becomes, and the more difficult it is for rainbow-like color spots to occur depending on the viewing angle. A perfect uniaxial (uniaxially symmetric) film has a ratio (Re/Rth) of 2 between the retardation and the retardation in the thickness direction. However, as will be described later, the mechanical strength in the direction perpendicular to the orientation direction decreases significantly as the film approaches a perfect uniaxial (uniaxially symmetrical) film.

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

3-6. Thickness unevenness In order to suppress variations in retardation of the oriented polyester film, it is preferable that the thickness unevenness of the film is small. From this viewpoint, the thickness unevenness of the oriented polyester film is preferably 5% or less, more preferably 4.5% or less, even more preferably 4% or less, and 3% or less. Especially preferred.

3-7. Thickness The thickness of the oriented polyester film is not particularly limited as long as it does not interfere with the effects of the present invention. film thickness is 1
If the thickness is less than 5 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 equivalent to 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 polyester resin is not particularly limited, and any polyester resin obtained by condensing a dicarboxylic acid and a diol can be used.

Examples of dicarboxylic acid components that can be used in the production of polyester resins 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, anthracenedicarboxylic 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 adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecadicarboxylic acid and the like.

Examples of diol components that can be used in the production of polyester resins 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 and the like.

Both the dicarboxylic acid component and the diol component that constitute the polyester resin are one or two
More than one species can be used. 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, thermal,
It also has excellent 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 preferably 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, more preferably 10% or less.
% or less is particularly preferred. If the light transmittance is 20% or less, deterioration of the optical functional dye due to ultraviolet rays can be suppressed. The light transmittance is measured perpendicular to the plane of the film and can be measured using a spectrophotometer (eg Hitachi U-3500).

The transmittance of the oriented polyester film at a wavelength of 380 nm can be controlled to 20% or less by appropriately adjusting the type and concentration of the ultraviolet absorbent to be blended and the thickness of the film.
Known ultraviolet absorbents can be appropriately selected and used as the ultraviolet absorbent used in the present invention. Specific examples of UV absorbers include organic UV absorbers and inorganic UV absorbers, but organic UV absorbers are preferred from the viewpoint of transparency.

Examples of organic UV absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. However, from the viewpoint of durability, benzotriazole-based and cyclic iminoester-based agents are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be absorbed at the same time, so that the ultraviolet absorption effect can be further improved.

Benzophenone UV absorbers, benzotriazole UV absorbers, and acrylonitrile UV absorbers include, for example, 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. Cyclic imino esters Examples of UV absorbers include 2,2′-(1,4-phenylene)
Bis(4H-3,1-benzoxazinone-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl -3,1-benzoxazin-4-one and the like. These ultraviolet absorbers may be used alone or in combination of two or more.

When the oriented polyester film is blended with an ultraviolet absorber, it is preferable that the oriented polyester film has a multi-layered structure of three or more layers and that the ultraviolet absorber is added to a layer other than the outermost layer (that is, an intermediate layer) of the film.

3-10. Other Ingredients It is also a preferred embodiment that the oriented polyester film contains various additives other than the ultraviolet absorber as long as the effects of the present invention are not impaired. Examples of additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, and anti-gelling agents. , surfactants, and the like. In order to achieve high transparency, it is also preferred that the polyester film contains substantially no particles. "Do not substantially contain particles" means, for example, in the case of inorganic particles,
It means a content of 50 ppm or less, preferably 10 ppm or less, particularly preferably a detection limit or less when the inorganic elements are quantified by fluorescence X-ray analysis.

4. Easy-Adhesion Layer In the present invention, an easy-adhesion layer containing at least one of polyester resin, polyurethane resin, or polyacrylic resin as a main component is provided on at least one side of the oriented polyester film in order to improve adhesion to the polarizer. It is preferable to have Here, the "main component" refers to a component that accounts for 50% by mass or more of the solid components that constitute the easy-adhesion layer. The coating liquid used for forming the easy-adhesion layer of the present invention is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolyester resins, acrylic resins and polyurethane resins. Examples of these coating liquids include Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No.
Examples thereof include water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, and polyurethane resin solutions disclosed in Japanese Patent No. 589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, and the like.

The easy-adhesion layer can be obtained by applying the above coating liquid to 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 transverse direction. It is preferable to control the final coating amount of the easy-adhesion layer to 0.05 to 0.2 g/m ² .
If the coating amount is less than 0.05 g/m ² , the adhesion to the resulting polarizer may be insufficient. On the other hand, if the coating amount exceeds 0.2 g/m ² , blocking resistance may deteriorate. When the easy-adhesion layer is provided on both sides of the polyester film, the coating amount of the easy-adhesion layer on both sides may be the same or different, and can be independently set within the above range.

Particles are preferably added to the easy-adhesion layer to impart lubricity. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle size of the particles exceeds 2 μm, the particles tend to fall off from the coating layer. Particles contained in the easy-adhesion layer include, 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 particles. These may be added to the easy-adhesion layer singly, or two or more of them may be added in combination.

The coating liquid can be applied using a known method. For example, 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 can be mentioned. These methods can be performed singly or in combination.

The average particle size of the above particles can be measured by the following method. The particles are photographed with a scanning electron microscope (SEM) and the largest diameter of 300-500 particles (between the two furthest Distance) is measured, and the average value is taken as the average particle size.

The oriented polyester film may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve adhesion to the polarizer.

5. Functional Layer The polarizing plate used in the present invention includes various functional layers such as a hard coat layer, an antiglare layer, an antireflection layer, a low reflection layer, and a low reflection layer for the purpose of preventing reflection, suppressing glare, suppressing scratches, and the like. It is also a preferred embodiment 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 surface of the oriented polyester. When providing various functional layers, the oriented polyester film preferably has an easy-adhesion layer on its surface. 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 as to be close to the geometric mean of the refractive index of the functional layer and the refractive index of the oriented polyester film. The adjustment of the refractive index of the easy-adhesion layer can employ a known method, and can be easily adjusted, for example, by adding titanium, zirconium, or other metal species to the binder resin.

6. Method for Producing Oriented Polyester Film The oriented polyester film, which is the protective film of the present invention, can be produced according to a general method for producing a polyester film. For example, a polyester resin is melted and a non-oriented polyester extruded into a sheet is stretched in the longitudinal direction using the speed difference between rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction with a tenter, A method of applying a heat treatment can be 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, rainbow-like color spots are observed even when viewed from directly above the film surface. Although not visible, it is necessary to pay attention to the fact that rainbow-like color spots may be observed when observed from an oblique direction.

This phenomenon occurs because the biaxially stretched film consists of a refractive index ellipsoid having different refractive indices in the running direction, the width direction, and the thickness direction, and the retardation becomes zero depending on the direction of light transmission inside the film (refractive index ellipsoid This is because there is a direction in which the body looks like a perfect circle. Therefore, when the liquid crystal display screen is observed from a specific oblique direction, there may be a point where the retardation becomes zero, and rainbow-like color spots appear concentrically around that point. Assuming that the angle from directly above the film surface (normal direction) to the position where the rainbow-like color spots appear is θ, this angle θ
increases as the in-plane birefringence of the film increases, making it difficult to see rainbow-like color spots. Since the angle θ tends to be small in a biaxially stretched film, a uniaxially stretched film is preferable because rainbow-like color spots are less visible.

However, a completely uniaxial (uniaxially symmetrical) film is not preferable because the mechanical strength in the direction perpendicular to the orientation direction is remarkably lowered. The present invention is a range in which rainbow-like color spots do not occur substantially, or a range in which rainbow-like color spots do not occur in the viewing angle range required for a liquid crystal display screen.
It preferably has axiality (biaxial symmetry). Such biaxial symmetry can be obtained by producing an oriented polyester film under the following conditions.

An oriented polyester film having the specific retardation and Nz coefficient described above can be obtained by adjusting the film forming conditions (eg, draw ratio, draw temperature, film thickness, etc.). For example, the higher the draw ratio, the lower the draw temperature, and the thicker the film, the easier it is to obtain a higher retardation. On the other hand, the lower the draw ratio, the higher the drawing temperature, and the thinner the film, the easier it is to obtain a low 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. Further, the transverse draw ratio is preferably 2.5 to 6.0 times, 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 in draw ratio between the vertical and horizontal directions 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 100-250°C, particularly preferably 180-245°C.

In order to set the Nz coefficient to the specific value described above, it is preferable to control the ratio between the longitudinal draw ratio and the transverse draw ratio, and it is most preferred to use a uniaxially stretched film. It is also preferable to increase the molecular weight of the polymer in order to lower the Nz coefficient, and to add a copolymerization component to lower the crystallinity. Furthermore, the Nz coefficient of the film can be controlled within a specific range by appropriately setting the total draw ratio and draw temperature. 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 specific value described above, 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. Controlling the stretching temperature is also preferable for lowering 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 drawing temperature high, it is possible to set the Nz coefficient and the degree of plane orientation to a specific value or less.

Since the stretching temperature and the stretching ratio have a great effect on the thickness unevenness of the film, it is preferable to optimize the film-forming conditions also from the viewpoint of the thickness unevenness. In particular, if the longitudinal draw ratio is lowered in order to increase the retardation, longitudinal thickness unevenness may become worse. Since there is a region in which the longitudinal thickness unevenness becomes extremely poor within a certain range of the draw ratio, it is desirable to set the film-forming conditions outside this range.

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 ultraviolet absorber and the polymer raw material are blended to prepare a masterbatch in advance, and the predetermined masterbatch and the polymer raw material are mixed at the time of film formation. be able to.

The concentration of the UV absorber in the masterbatch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and to blend it economically. A kneading extruder is used as the conditions for preparing the masterbatch, and the extrusion temperature is the melting point of the polyester raw material or higher, 290 ° C.
It is preferable to extrude for 1 to 15 minutes at the following temperature. At 290° C. or higher, the weight loss of the ultraviolet absorber is large, and the viscosity of the masterbatch is greatly lowered. Extrusion for 1 minute or less makes it difficult to uniformly mix the ultraviolet absorber. At this time, a stabilizer, a color tone adjusting agent, and an antistatic agent may be added as necessary.

Incorporation of an ultraviolet absorber into an intermediate layer of an oriented polyester film having a multi-layered structure of three or more layers can be carried out by the following method. For the outer layer, polyester pellets alone, and for the intermediate layer, a masterbatch containing an ultraviolet absorber and polyester pellets are mixed in a predetermined ratio, dried, then supplied to a known melt lamination extruder, and slit-shaped. A sheet is extruded through a die and cooled and solidified on a casting roll to form an unstretched film. That is, using two or more extruders, a three-layer manifold or a confluence block (for example, a confluence block having a square confluence portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, A three-layer sheet is extruded through a die and cooled on casting rolls to form an unstretched film.

In order to remove foreign matter contained in the raw material polyester that causes optical defects, it is preferable to perform high-precision filtration during melt extrusion in the production process of the oriented polyester film. Filtration particle size of filter material used for high-precision filtration of molten resin (initial filtration efficiency 95%
) is preferably 15 μm or less. If the filtration particle size of the filter media exceeds 15 μm, 20 μm
Removal of the foreign matter described above tends to be insufficient.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples, and can be carried out with appropriate modifications within the scope of the gist of the present invention. It is possible and all of them are included in the technical scope of the present invention.

Methods for evaluating physical properties in Examples are as follows.
(1) Retardation (Re)
Retardation is defined as the anisotropy of the refractive index of two orthogonal axes on the film (ΔNxy=|nx
−ny|) and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. Biaxial refractive index anisotropy (ΔNxy)
was obtained by the following method. Obtain the orientation axis direction of the film using a molecular orientation meter (manufactured by Oji Keisoku Co., Ltd., MOA-6004 type molecular orientation meter), and 4c so that the orientation axis direction is the long side.
A rectangle of m×2 cm was cut out and used as a measurement sample. For this sample, the biaxial refractive indices (nx, ny) orthogonal to each other and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (manufactured by Atago, NAR-4T, measurement wavelength 589 nm). , the absolute value of the biaxial refractive index difference (|nx−ny|) was defined as the refractive index anisotropy (ΔNxy). Film thickness d(n
m) was measured using an electric micrometer (Millitron 1245D manufactured by Finereuf Co.) and converted into nm. Refractive index anisotropy (ΔNxy) and film thickness d (nm)
Retardation (Re) was obtained from the product of (ΔNxy×d).

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

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

(4) Thickness direction retardation (Rth)
The retardation in the thickness direction is defined as the two birefringences ΔN
It is a parameter indicating the average retardation obtained by multiplying xz (=|nx−nz|) and ΔNyz (=|ny−nz|) by the film thickness d. Obtain nx, ny, nz and film thickness d (nm) in the same manner as for measuring retardation, and calculate the average value of (ΔNxz × d) and (ΔNyz × d) to obtain thickness direction retardation (Rth ).

(5) Observation of iridescence 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 orientation axis of the polyester film are perpendicular to each other, and the surface on the opposite side is attached. A TAC film (manufactured by Fuji Film Co., Ltd., thickness: 80 μm) was adhered to the substrate to prepare a polarizing plate. A liquid crystal display device was fabricated by arranging the obtained polarizing plates one by one on both sides of the liquid crystal so that each polarizing plate satisfies the crossed Nicols condition. Each polarizer was positioned with the polyester film facing away from the liquid crystal (distal). The light source of the liquid crystal display device includes:
A white LED composed of a light-emitting element combining a blue light-emitting diode and an yttrium-aluminum-garnet-based yellow phosphor was used as a light source (NSPW500CS, Nichia Corporation).
Such a liquid crystal display device was visually observed from the front and oblique directions, and the presence or absence of iridescence was determined as follows.

A: No iridescence from any direction.
A': When observed from an oblique direction, a very thin iridescence is observed depending on the angle.
B: When observed from an oblique direction, a thin iridescence is observed depending on the angle.
C: Iridescent spots are observed when observed obliquely.
D: Iridescent spots are observed when viewed from the front and oblique directions.

(6) Tear strength Using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho, according to JIS P-8116,
The tear strength of each film was measured. The direction of tearing was parallel to the principal axis of orientation of the film, and the evaluation was made as follows. The orientation principal axis direction was measured with a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Instruments Co., Ltd.).
○: 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 was added while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, pressurization was performed to raise the temperature, and the gauge pressure was 0.34 MPa and 24
After performing the pressure esterification reaction at 0 ° C., the pressure in the esterification reaction vessel is returned to normal pressure, and the phosphoric acid is zero.
. 014 parts by weight were added. Furthermore, the temperature was raised to 260° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, dispersion treatment was performed with a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reactor, and polycondensation reaction was performed at 280°C under reduced pressure.

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

(Production Example 2-Polyester B)
10 parts by weight of dried UV absorber (2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), particle-free PET (A) (intrinsic viscosity is 0.62 dl/g), and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter abbreviated as PET (B)).

(Production Example 3-Adhesion-improving coating liquid preparation)
An ester exchange reaction and a polycondensation reaction were carried out by a conventional method to obtain 46 mol % terephthalic acid, 46 mol % isophthalic acid and 5-
A water-dispersible sulfonic acid metal group-containing copolymer polyester resin was prepared with a composition of 8 mol% sodium sulfonatoisophthalate and 50 mol% ethylene glycol and 50 mol% neopentyl glycol as glycol components (relative to the entire glycol component). . then water 5
1.4 parts by mass, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant are mixed, then heated and stirred, and when the temperature reaches 77 ° C., the water dispersibility After adding 5 parts by mass of a sulfonic acid metal base-containing copolymerized polyester resin and continuing to stir until the lumps of the resin disappear, the resin aqueous dispersion is cooled to room temperature and mixed with uniform water having a solid content concentration of 5.0% by mass. A dispersible copolyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Silysia 310) in 50 parts by mass of water, Silysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid. Aqueous dispersion 0
. 54 parts by mass was added, and 20 parts by mass of water was added while stirring to obtain an adhesion-improving coating liquid.

(Polarizer protective film 1)
After drying under reduced pressure (1 Torr) at 135° C. for 6 hours, 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for the base film intermediate layer. , extruder 2 (for intermediate layer II layer), and PET (A
) is dried by a conventional method and fed to extruder 1 (for outer layer I and outer layer III), 28
Dissolved at 5°C. These two types of polymers are each filtered with a stainless sintered filter material (nominal filtration accuracy: 10 μm, 95% cut of particles), laminated in a two-type, three-layer confluence block, extruded in a sheet form from a nozzle, An unstretched film was produced by winding the film around a casting drum having a surface temperature of 30° C. and solidifying it by cooling using an electrostatic casting method. At this time, I layer, II layer,
The discharge rate of each extruder was adjusted so that the thickness ratio of the III layer was 10:80:10.

Next, the adhesion-improving coating solution was applied to both sides of the unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g/m ² , and then dried at 80°C for 20 seconds. .

The unstretched film with the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, was guided to a hot air zone at a temperature of 125° C. and stretched 4.0 times in the width direction.
Next, while maintaining the stretched width 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 thickness of about 50 μm.

(Polarizer protective film 2)
A uniaxially oriented PET film was obtained in the same manner as the polarizer protective film 1 except that the thickness of the unstretched film was changed to about 100 μm.

(Polarizer protective film 3)
An unstretched film produced by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then 1.5° C. in the running direction with a roll group having a peripheral speed difference. After being stretched twice, it 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)
A biaxially oriented PET film having a film thickness of about 50 μm was obtained by stretching 2.0 times in the running direction and 4.0 times in the width direction in the same manner as in the polarizer protective film 3 .

(Polarizer protective film 5)
In the same manner as the polarizer protective film 1, a PET resin (
A uniaxially oriented PET film having a film thickness of 50 μm was obtained without using B).

(Polarizer protective film 6)
A uniaxially oriented PET film having a film thickness of about 100 μm was obtained by stretching 4.0 times in the running direction and 1.0 times in the width direction in the same manner as in the polarizer protective film 3 .

(Polarizer protective film 7)
A uniaxially oriented PET film having a film thickness of about 75 μm was obtained by stretching 1.0 times in the running direction and 3.5 times in the width direction in the same manner as in the polarizer protective film 1 .

(Polarizer protective film 8)
A uniaxially oriented PET film having a thickness of about 100 μm was obtained by using the same method as for the polarizer protective film 1, changing the thickness of the unstretched film, setting the lateral stretching ratio to 3.8 times, and stretching temperature to 135°C.

(Polarizer protective film 9)
Using the same method as for the polarizer protective film 1, the lateral stretching ratio is 3.8 times and the stretching temperature is 135.
℃, a uniaxially oriented PET film having a thickness of about 50 µm was obtained.

(Polarizer protective film 10)
Using the same method as for the polarizer protective film 1, the lateral stretch ratio is 3.8 times, and the thickness is 50 μm.
A uniaxially oriented PET film with a thickness of m was obtained.

(Polarizer protective film 11)
Using the same method as the polarizer protective film 1, the lateral stretching ratio is 4.2 times, and the stretching temperature is 135.
℃, a uniaxially oriented PET film having a thickness of about 50 µm was obtained.

(Polarizer protective film 12)
A uniaxially oriented PET film with a thickness of 38 μm was obtained by changing the thickness of the unstretched film and changing the lateral stretching ratio to 3.8 times using the same method as for the polarizer protective film 1 .

(Polarizer protective film 13)
A uniaxially oriented PET film with 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 .

(Polarizer protective film 14)
A biaxially oriented PET film having a film thickness of about 275 μm was obtained by stretching 1.8 times in the running direction and 2.0 times in the width direction in the same manner as for the polarizer protective film 3 .

(Polarizer protective film 15)
By the same method 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 biaxially oriented PET film with 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 produced as described above using the polarizer protective films 1 to 17.

In Table 1, the polarizer protective film No. 7* indicates the case where the polarizer protective film 7 is used as the polarizer protective film and an organic light emitting diode (OLED) is used as the light source. again,
In Table 1, the polarizer protective film No. 7** indicates the case where the polarizer protective film 7 is used as the polarizer protective film and a cold cathode tube is used as the light source. In Table 1, the polarizer protective film N
o. 1* uses the polarizer protective film 1 as the polarizer protective film on the output light side of the output light side polarizing plate, and the polarizer protective film on the incident light side of the output light side polarizing plate and on both sides of the incident light side polarizing plate. A case where a TAC film is used as 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 occurrence of iridescence is remarkably suppressed. . In addition to these conditions, the degree of plane orientation of the oriented polyester film was set to 0.0.
It was shown that by controlling the number to 13 or less, it is possible to more effectively suppress the development of iridescence.

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

Claims (2)

A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates,
The backlight source is a white light source with a continuous emission spectrum,
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 in-plane retardation of 8000 to 10500 nm, An oriented polyester film having a degree of plane orientation of 13 or less and an Nz coefficient of 1.62 or less,
Liquid crystal display. 2. The liquid crystal display device according to claim 1, wherein the orientation degree of the oriented polyester film is 0.08 or more.