JP2020098344A - Liquid crystal display device, polarizing plate, and polarizer protective film - Google Patents

Abstract

To provide a liquid crystal display device that prevents formation of an iridescent speckle when an oriented polyester film is used as a polarizer protective film on both of polarizing plates provided in a pair.SOLUTION: A liquid crystal display device includes a back light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The back light source is a white light source having a continuous emission spectrum. A polarizer protective film on an incident light side of a polarizing plate disposed on the incident light side and a polarizer protective film on a projection light side of a polarizing plate disposed on the projection light side are oriented polyester films having an in-plane retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.SELECTED DRAWING: None

Description

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

A polarizing plate used in a liquid crystal display device (LCD) is usually constituted by sandwiching a polarizer obtained by dyeing polyvinyl alcohol (PVA) or the like with iodine between two polarizer protective films. Is usually a triacetyl cellulose (TAC) film. In recent years, as LCDs have become thinner, there has been a demand for thinner polarizing plates. However, if the thickness of the TAC film used as a protective film is reduced for this reason, sufficient mechanical strength cannot be obtained and the moisture permeability deteriorates. Further, the TAC film is very expensive, and there is a strong demand for an inexpensive alternative material.

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

The polyester film is more durable than the TAC film, but has a birefringence unlike the TAC film. Therefore, when this is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since a polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, rainbow-like color spots occur when observed from an oblique direction, and the image quality deteriorates. .. Therefore, in Patent Documents 1 to 3, measures are taken to reduce the retardation by using a copolyester as the polyester. However, even in that case, it was not possible to completely eliminate the iridescent color spot.

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 of the present invention have made further studies on the liquid crystal display device having such a configuration, and even in the liquid crystal display device thus improved, polyester is used as a polarizer protective film for both of the pair of polarizing plates. In the case of using a film, we found that there is a new problem that iris may still occur 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 both polarizer protective films of a pair of polarizing plates of a liquid crystal display device.

The present inventors have studied the above problems day and night, and as a result, by controlling the retardation of an oriented polyester film used as a polarizer protective film and the Nz coefficient represented by |ny-nz|/|ny-nx| The inventors have found that 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 occurrence of iris can be effectively suppressed. The present invention is an invention completed as a result of further research and improvement based on such findings.

The representative present invention is as follows.
Item 1.
A liquid crystal display device comprising a backlight light source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates,
The backlight light 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 30000 nm and an 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 30,000 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 degree of plane orientation 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 the continuous emission spectrum is a white light emitting diode.
Item 5.
It 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, in which at least one polarizer protective film is an oriented polyester film having a retardation of 4000 to 30,000 nm and an Nz coefficient of 1.7 or less.
Item 6.
Item 6. A polarizing plate for a liquid crystal display device, which uses a white light source having a continuous emission spectrum as a backlight light source, 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 a white light source having a continuous emission spectrum as a backlight light source, which is composed of an oriented polyester film having a retardation of 4000 to 30000 nm and an Nz coefficient of 1.7 or less.
Item 8.
Item 8. The polarizer protective film for a liquid crystal display device, wherein the white light source having a continuous emission spectrum as a backlight source is used as a backlight source, wherein the degree of plane orientation of the oriented polyester film is 0.13 or less.
Item 9.
Item 9. A polarizer protective film for a liquid crystal display device, which uses a white light source having a continuous emission spectrum as a backlight light source, wherein the oriented polyester film has an easily adhesive layer.
Item 10.
Item 10. The continuous emission spectrum according to any one of Items 7 to 9, wherein the oriented polyester film is composed of 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, which uses a white light source as a backlight light 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 both polarizer protective films of a pair of polarizing plates without the problem of rainbow spots. Therefore, the present invention enables further thinning while maintaining sufficient mechanical strength of the liquid crystal display device, which in turn makes it possible to reduce the manufacturing cost. Further, 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. Liquid Crystal Display Device In general, a liquid crystal display device includes a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight light source toward the side displaying an image (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 thereof, and a polarizing plate arranged on the opposite side thereof. Here, the polarizing plate is arranged on the side facing the backlight light source in the rear surface module, and is arranged on the image display side (viewing side or emitted light side) in the front surface 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 arranged between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may appropriately have other components other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like.

The structure of the backlight may be an edge light system using a light guide plate, a reflection plate or the like as a constituent member, or a direct type system. In the present invention, it is preferable to use a white light source having a continuous and wide emission spectrum as the backlight light source of the 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. Examples of such a white light source having a continuous and wide emission spectrum include, but are not limited to, white LEDs.

The white LED that can be used in the present invention includes a phosphor type, that is, an element that emits white light by combining a phosphor with a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor, or an organic light emitting diode (Organic light). -Emitting diode (OLED) and the like are included. Examples of the phosphors include yttrium/aluminum/garnet-based yellow phosphors and terbium/aluminum/garnet-based yellow phosphors. Among white LEDs, a white light emitting diode composed of a light emitting element combining a blue light emitting diode using a compound semiconductor and a yttrium-aluminum-garnet-based yellow phosphor has a continuous and wide emission spectrum and 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 also contributes to energy saving.

A fluorescent tube such as a cold cathode tube or a hot cathode tube, which has been widely used as a backlight light source, has a discontinuous emission spectrum having an emission spectrum having a peak at a specific wavelength. Therefore, it is difficult to obtain the intended effect of the present invention, which is not preferable as the light source of the liquid crystal display device of the present invention.

3. Polarizer Protective Film A polarizing plate has a structure in which two polarizer protective films are laminated on both sides of a polarizer in which PVA or the like is dyed with iodine. The polarizing plate used in the present invention is an oriented polyester that satisfies at least one of two polarizer protective films and has physical properties of retardation in a specific range and 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 30,000 nm. This is because if the retardation is less than 4000 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, preferably 5000 nm or more, more preferably 6000 nm or more, still more preferably 8000 nm or more, still more preferably 10,000 nm or more.

The upper limit of retardation of the oriented polyester film is 30,000 nm. Even if an oriented polyester film having a retardation of more than that is used, the effect of further improving the visibility cannot be substantially obtained, and the thickness of the film becomes considerably thicker as the retardation increases, which makes it easier to handle as an industrial material. This is because it will decrease.

The retardation value of the oriented polyester film can be determined by measuring the biaxial direction refractive index and the thickness according to a known method. In addition, for example, it can be measured using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.).

As shown in Patent Document 4, when the 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 to be in the range of 3000 to 30,000 nm and is continuously used as a light source. By adopting a white light source having a specific and wide emission spectrum, the occurrence of iris is suppressed. The principle is considered as follows.

That is, when an oriented polyester film having birefringence is arranged on one side of the polarizer, the linearly polarized light emitted from the polarizer is disturbed when passing through the polyester film. Then, the transmitted light exhibits an interference color peculiar to retardation which is a product of 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, and a rainbow-like color spot appears.

On the other hand, when the light having a continuous and wide emission spectrum in the 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 has an envelope shape. Therefore, by controlling the retardation of the polyester film, it becomes 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 by the transmitted light transmitted through the birefringent body similar to each other, iridescent color spots do not occur, and the visibility is remarkable. 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, the occurrence of iris may still be observed. The present invention enables suppression of such iris generation, but its principle has not yet 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, in the orientation axis direction and the direction orthogonal to the orientation axis direction). However, ny>nx) and the refractive index (nz) in the thickness direction are obtained by an Abbe refractometer (NAR-4T, manufactured by Atago Co., measurement wavelength 589 nm). The Nz coefficient can be obtained by substituting the nx, ny, and nz thus obtained in the expression represented by |ny-nz|/|ny-nx|.

When 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, still more preferably 1.63 or less. The lower limit of the Nz coefficient is 1.2. This is because it is difficult to obtain a film of less than 1.2 in terms of manufacturing technology. Further, 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, 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 above specific retardation and Nz coefficient is used as both polarizer protective films of the pair of polarizing plates. The pair of polarizing plates means a combination of a polarizing plate arranged on the incident light side of the liquid crystal and a polarizing plate arranged on the outgoing light side of the liquid crystal. That is, the oriented polyester film is used as both a polarizing plate on the incident light side and a 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 for both of them.

In a preferred embodiment, the oriented polyester film is used as a polarizer protective film on the incident light side of a polarizing plate on the incident light side, and as a polarizer protective film on the outgoing light side of a 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, any polarizer protective film (for example, TAC film) 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, 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, a norbornene-based film, etc.). It is preferable to use a film having no birefringence).

3-4. Plane orientation coefficient In addition to controlling the retardation value and the Nz coefficient of the oriented polyester film within the above-mentioned specific ranges, by setting the plane orientation degree represented by (nx+ny)/2-nz to a specific value or less, more reliable It is possible to completely eliminate rainbow spots 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 obtained by the same method as 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 further preferably 0.12 or less. By setting the plane orientation degree to 0.13 or less, it is possible to completely eliminate the rainbow spots that are 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 plane of the film.

3-5. Retardation ratio The oriented polyester film has a ratio (Re/Rth) of its retardation (Re) to thickness direction retardation (Rth) of preferably 0.2 or more, more preferably 0.5 or more, and further preferably 0.6. That is all. This is because the larger the ratio of the retardation to the retardation in the thickness direction (Re/Rth), the more isotropic the birefringence action becomes, and the more unlikely rainbow-like color spots are generated depending on the observation angle. In a perfect uniaxial (uniaxially symmetric) film, the ratio (Re/Rth) between the retardation and the thickness direction retardation is 2. However, as will be described later, the mechanical strength in the direction orthogonal to the orientation direction remarkably decreases as the film approaches a completely uniaxial (uniaxially symmetric) film.

Therefore, the upper limit of the ratio between the retardation and the retardation in the thickness direction (Re/Rth) is preferably 1.2 or less, more preferably 1 or less. In order to completely suppress the generation of iridescent color spots due to the observation angle, the ratio of the retardation to the thickness direction retardation (Re/Rth) does not need to be 2, but 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 (horizontal 180 degrees, vertical 120 degrees) required for the liquid crystal display device.

3-6. Thickness unevenness In order to suppress variation in retardation of the oriented polyester film, it is preferable that the thickness unevenness of the film is small. From this viewpoint, 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 further preferably 3% or less. Particularly preferred.

3-7. Thickness The thickness of the oriented polyester film is not particularly limited as long as it does not impair the effects of the present invention, but is usually 15 to 300 μm, and preferably 15 to 200 μm. When the film thickness is less than 15 μm, the anisotropy of mechanical properties of the film becomes remarkable, and tearing or tearing 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 that of 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 the dicarboxylic acid component that can be used for producing the polyester resin include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1 ,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, 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 Examples thereof include adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid and dodecadicarboxylic acid.

Examples of the diol component that can be used for producing the polyester resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, and 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 either individually or in combination of two or more. Suitable polyester resin constituting the polyester film includes, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and the like, more preferably polyethylene terephthalate and polyethylene naphthalate, but these are Further, other copolymerization component may be contained. These resins have excellent transparency as well as thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most preferable material because it has a large intrinsic birefringence and a relatively large retardation can be obtained relatively easily even when 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 an optical functional dye such as an iodine dye contained in a polarizer. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optically functional dye due to ultraviolet rays can be suppressed. 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 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 absorber to be blended and the thickness of the film. As the ultraviolet absorber used in the present invention, a known ultraviolet absorber can be appropriately selected and used. Specific UV absorbers include organic UV absorbers and inorganic UV absorbers, and organic UV absorbers are preferred from the viewpoint of transparency.

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

Examples of the benzophenone-based UV absorber, the benzotriazole-based UV absorber, and the acrylonitrile-based UV absorber include 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole and 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. may be mentioned. Examples of the cyclic iminoester-based ultraviolet absorber include 2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 2-methyl-3,1-benzo. Oxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazin-4-one, etc. These UV absorbers are only one kind. May be used, or two or more kinds may be used in combination.

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

3-10. Other Components In addition to the ultraviolet absorber, it is also preferable that the oriented polyester film contains various additives within a range that does not impair the effects of the present invention. As additives, for example, inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, anti-gelling agents , Surfactants and the like. It is also preferable that the polyester film contains substantially no particles in order to achieve high transparency. "Substantially free of particles" means, for example, in the case of inorganic particles, a content of 50 ppm or less, preferably 10 ppm or less, particularly preferably a detection limit or less when the inorganic element is quantified by fluorescent X-ray analysis. means.

4. Easy-Adhesion Layer In the present invention, an easy-adhesion layer containing at least one of a polyester resin, a polyurethane resin or a polyacrylic resin as a main component is provided on at least one surface of the oriented polyester film in order to improve the adhesiveness with the polarizer. It is preferable to have. Here, the "main component" refers to a component that is 50% by mass or more of the solid components that form 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 a water-soluble or water-dispersible copolyester resin, an acrylic resin and a polyurethane resin. Examples of these coating liquids include water-soluble or water-dispersible compounds disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, and the like. Examples include polymerized polyester resin solutions, acrylic resin solutions, polyurethane resin solutions, and the like.

The easy-adhesion layer can be obtained by applying the above-mentioned coating solution on one or both sides of an unstretched film or a uniaxially stretched film in the longitudinal direction, drying at 100 to 150°C, and further stretching in the transverse direction. The final coating amount of the easily adhesive layer is preferably controlled to 0.05 to 0.2 g/m ² . When the coating amount is less than 0.05 g/m ² , the adhesiveness to the obtained polarizer may be insufficient. On the other hand, if the coating amount exceeds 0.2 g/m ² , the blocking resistance may decrease. When the easy-adhesion layers are provided on both sides of the polyester film, the coating amounts of the easy-adhesion layers on both sides 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 diameter of 2 μm or less. When the average particle size of the particles exceeds 2 μm, the particles are likely to fall off the coating layer. The particles to be 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 thereof include inorganic particles such as calcium fluoride and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added alone to the easy-adhesion layer, or two or more kinds may be added in combination.

The coating solution can be applied using a known method. Examples thereof include a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method and a pipe doctor method. These methods can be performed alone 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 maximum diameter of 300 to 500 particles (between the two most distant points) is used at a magnification such that the size of one of the smallest particles is 2 to 5 mm. The 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 the adhesiveness to the polarizer.

5. Functional Layer The polarizing plate used in the present invention has 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 glare, suppressing glare, and suppressing scratches. It is also a preferred mode to provide one or more functional layers selected from the group consisting of an anti-reflection layer and an antireflection antiglare 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. A known method can be used to adjust the refractive index of the easy-adhesion layer. For example, the binder resin can be easily adjusted by adding titanium, zirconium, or another metal species.

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 and molded into a sheet is stretched in the longitudinal direction by utilizing the speed difference of rolls at a temperature of the glass transition temperature or higher, and then stretched in the lateral direction by a tenter, A method of applying heat treatment may 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 directly from the film surface. Although not visible, care should be taken as rainbow-like color spots may be observed when observed from an oblique direction.

This phenomenon is 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 light transmission direction inside the film (refractive index ellipse). 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 iridescent color spots are concentrically formed around the point. If the angle from just above the film surface (in the normal direction) to the position where the iridescent color spot is visible is θ, this angle θ increases as the birefringence in the film surface increases, and the iridescent color The spots are hard to see. Since the angle θ tends to be small in the biaxially stretched film, the uniaxially stretched film is preferable because the rainbow-shaped color spots are less visible.

However, a completely uniaxial (uniaxially symmetric) film is not preferable because the mechanical strength in the direction perpendicular to the orientation direction is significantly reduced. INDUSTRIAL APPLICABILITY The present invention has biaxiality (biaxial symmetry) in a range in which substantially no rainbow-shaped color spots are generated, or in a range in which a viewing angle range required for a liquid crystal display screen is not generated. Preferably. Such biaxial symmetry can be obtained by producing an oriented polyester film under the following conditions.

The oriented polyester film having the above-mentioned specific retardation and Nz coefficient can be obtained by adjusting the conditions during film formation (for example, stretching ratio, stretching temperature, film thickness, etc.). For example, the higher the draw ratio, the lower the draw temperature, and the thicker the film, the higher the retardation is likely to be obtained. On the other hand, the lower the stretch ratio, the higher the stretching temperature, and the thinner the film, the easier it is to obtain low retardation.

As specific film forming conditions, for example, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 145°C, and particularly preferably 90 to 140°C. The longitudinal stretching ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 times to 3.0 times. 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 above-mentioned specific range, it is preferable to control the ratio of the longitudinal stretching ratio and the lateral stretching ratio. If the difference between the stretching ratios in the length and width 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 bring the Nz coefficient to the above-mentioned specific value, it is preferable to control the ratio of the longitudinal stretching ratio and the transverse stretching ratio, and it is most preferable to use a uniaxially stretched film. Further, in order to lower the Nz coefficient, it is also preferable to increase the molecular weight of the polymer and to add a copolymerization component to lower 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 stretching ratio and the higher the stretching temperature, the lower the Nz coefficient can be obtained.

In order to bring the degree of plane orientation to the above-mentioned 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 stretching ratio and the lateral stretching ratio, setting the total stretching ratio low, and setting the stretching temperature high, it is possible to set the Nz coefficient and the degree of plane orientation 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 also from the viewpoint of the thickness unevenness. In particular, if the longitudinal stretching ratio is lowered in order to increase the retardation, the unevenness in the longitudinal thickness may be deteriorated. Since there is a region where the vertical thickness unevenness becomes extremely bad in a certain range of the draw ratio, it is desirable to set the film forming conditions outside this range.

The UV absorber may be added to the oriented polyester film 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 masterbatch and the polymer raw material are mixed by a method of mixing the predetermined masterbatch and the polymer raw material during film formation. be able to.

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

The ultraviolet absorber can be compounded in the intermediate layer of the oriented polyester film having a multilayer structure of three or more layers by the following method. Polyester pellets alone for the outer layer, a masterbatch containing a UV absorber for the intermediate layer and polyester pellets are mixed at a predetermined ratio, and after drying, the mixture is fed to a known melt-laminating extruder and slit-shaped. An unstretched film is produced by extruding from a die into a sheet and then cooling and solidifying on a casting roll. 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), the film layers constituting both outer layers and the film layer constituting the intermediate layer are laminated, A three-layer sheet is extruded from the die and cooled with a casting roll to produce an unstretched film.

In order to remove foreign matter contained in the raw material polyester, which causes optical defects, it is preferable to perform high-precision filtration during melt extrusion in the process of producing the oriented polyester film. The filtration particle size (initial filtration efficiency 95%) of the filter material used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filtration particle size of the filter material exceeds 15 μm, the removal of foreign matter of 20 μm or more 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 may be implemented with appropriate modifications within a range compatible with the gist of the present invention. It is possible, and all of them are included in the technical scope of the present invention.

The evaluation methods of physical properties in the examples are as follows.
(1) Retardation (Re)
Retardation is a parameter defined by a product (ΔNxy×d) of anisotropy (ΔNxy=|nx−ny|) of biaxial refractive indexes on the film and film thickness d (nm). Yes, it is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. 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 a 4 cm×2 cm rectangle is cut out so that the orientation axis direction is the long side, and for measurement It was used as a sample. About this sample, the refractive index (nx, ny) of two orthogonal axes and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer (manufactured by Atago Co., NAR-4T, measurement wavelength 589 nm). The absolute value (|nx-ny|) of the difference between the biaxial refractive indexes was defined as the refractive index anisotropy (ΔNxy). The film thickness d (nm) was measured by using an electric micrometer (Millitron 1245D, manufactured by Fine Luff Co.), and the unit was converted to nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the anisotropy of refractive index (ΔNxy) and the film thickness d (nm).

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

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

(4) Thickness direction retardation (Rth)
The thickness direction retardation means two birefringences ΔNxz (=|nx-nz|) and ΔNyz (=|ny-nz|) multiplied by the film thickness d, respectively, when viewed from the cross section in the film thickness direction. It is a parameter indicating the average of the retardation obtained. The film thickness d (nm) and nx, ny, nz are obtained by the same method as the measurement of retardation, and the average value of (ΔNxz×d) and (ΔNyz×d) is calculated to calculate the thickness direction retardation (Rth). ) Was asked.

(5) Observation of rainbow spots A polyester film prepared by the method described below is attached to one side of a polarizer made of PVA and iodine so that the polarization axis of the polarizer and the orientation main axis of the polyester film are perpendicular to each other, and the surface on the opposite side. A TAC film (manufactured by FUJIFILM Corporation, thickness 80 μm) was attached to the plate to prepare a polarizing plate. A liquid crystal display device was manufactured by arranging the obtained polarizing plates one by one on both sides with a liquid crystal interposed therebetween so that each polarizing plate was under the crossed Nicols condition. Each polarizing plate was arranged such that the polyester film was on the opposite side (distal) from the 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-based yellow phosphor were combined was used as a light source (NSPW500CS, Nichia). The liquid crystal display device was visually observed from the front and oblique directions, and the presence/absence of rainbow spots was determined as follows.

A: Iridescent spots did not occur from any direction.
A′: When observed from an oblique direction, an extremely thin iris is observed depending on the angle.
B: When observed from an oblique direction, a thin iris is observed depending on the angle.
C: Iridescent spots are observed when observed from an oblique direction.
D: Iridescent spots are observed when observed from the front and oblique directions.

(6) Tear strength The tear strength of each film was measured in accordance with JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho. The tearing direction was set so as to be parallel to the orientation main axis direction of the film, and the following judgment was made. In addition, the measurement of the orientation main axis direction was performed with a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Scientific 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 reaction vessel 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 were added while stirring. 0.064 parts by mass of magnesium acetate tetrahydrate and 0.16 parts by mass of triethylamine were charged. Then, the pressure and temperature were raised to carry out the pressure esterification reaction under the conditions of a gauge pressure of 0.34 MPa and 240° C., the esterification reaction vessel was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, the temperature was raised to 260° C. over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. Then, 15 minutes later, a dispersion treatment was carried out 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 under reduced pressure at 280°C.

After completion of the polycondensation reaction, a 95% cut diameter was filtered through a Naslon filter with a diameter of 5 μm, extruded in a strand form from a nozzle, and cooled and solidified with cooling water that had been subjected to a filtration treatment (pore diameter: 1 μm or less) in advance. , Cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g, and substantially did not contain inert particles and internally precipitated particles. (Hereafter, abbreviated as PET(A).)

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

(Production Example 3-Adjustment of Adhesive Modification Coating Liquid)
Performing an ester exchange reaction and a polycondensation reaction by a conventional method, as a dicarboxylic acid component (to the entire dicarboxylic acid component), 46 mol% of terephthalic acid, 46 mol% of isophthalic acid and 8 mol% of sodium 5-sulfonatoisophthalate, A water-dispersible metal sulfonate-containing copolymerized polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol as a glycol component (based on the whole glycol component) was prepared. Then, after mixing 51.4 parts by mass of water, 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, the mixture is heated and stirred, and when reaching 77° C., the above. After adding 5 parts by mass of the water-dispersible metal sulfonate-containing copolyester resin and continuing stirring until the resin clumps out, the resin water dispersion is cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A uniform water-dispersible copolyester resin solution was obtained. Furthermore, after dispersing 3 parts by mass of aggregate silica particles (manufactured by Fuji Silysia Chemical Ltd., Silysia 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolyester resin solution is mixed with Silysia 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 modification coating liquid.

(Polarizer protective film 1)
After 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 a raw material for the base film intermediate layer were dried under reduced pressure at 135° C. for 6 hours (1 Torr). , Extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method and supplied to Extruder 1 (for outer layer I layer and outer layer III) and melted at 285°C. .. These two types of polymers were respectively filtered with a stainless sintered filter medium (nominal filtration accuracy: 10 μm particles 95% cut), laminated with a type 2 three-layer confluent block, and extruded into a sheet form from a die. The film was wound around a casting drum having a surface temperature of 30° C. and cooled and solidified by using an electrostatic applied casting method to prepare 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.

Then, the above-mentioned adhesive property modification coating liquid was applied to both surfaces of this 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 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 holding the end portion of the film with 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 protection 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 that for the polarizer protective film 1 was heated to 105° C. by using a heated roll group and an infrared heater, and then, in a running direction with a roll group having a peripheral speed difference of 1.5. After being double-stretched, it was stretched 4.0 times in the width direction in the same manner as in the polarizer protective film 1, to obtain a biaxially oriented PET film having a film thickness of about 50 μm.

(Polarizer protective film 4)
By a method similar to that 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 by the same method as that for the polarizer protective film 1, without using the PET resin (B) containing an ultraviolet absorber in the intermediate layer.

(Polarizer protection film 6)
By a method similar to that for 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)
By a method similar to that 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 that for the polarizer protective film 1, the thickness of the unstretched film was changed, the transverse stretching ratio was 3.8 times, and the stretching temperature was 135° C. to obtain a uniaxially oriented PET film having a thickness of about 100 μm.

(Polarizer protective film 9)
A uniaxially oriented PET film having a thickness of about 50 μm was obtained by using the same method as that for the polarizer protective film 1, the transverse stretching ratio was 3.8 times, and the stretching temperature was 135° C.

(Polarizer protective film 10)
A uniaxially oriented PET film having a thickness of 50 μm was obtained by using the same method as that for the polarizer protective film 1 and adjusting the transverse stretching ratio to 3.8 times.

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

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

(Polarizer protective film 13)
A uniaxially oriented PET film having a thickness of 38 μm was obtained by changing the thickness of the unstretched film using the same method as that for the polarizer protective film 1.

(Polarizer protective film 14)
By a method similar to that for the polarizer protective film 3, the film was stretched 1.8 times in the running direction and 2.0 times in the width direction to obtain a biaxially oriented PET film having a film thickness of about 275 μm.

(Polarizer protective film 15)
By a method similar to that 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 that 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 device manufactured 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 the organic light emitting diode (OLED) is used as the light source. 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 the cold cathode tube is used as the light source. In Table 1, the 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, and uses the polarizer protective film on the incident light side of the outgoing light side polarizing plate and both sides of the incident light side polarizing plate. The case where a TAC film is used as the 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 thereof is 1.7 or less, the occurrence of iris is remarkably suppressed. .. Further, it was shown that by controlling the plane orientation degree of the oriented polyester film to 0.13 or less in addition to this condition, it is possible to more effectively suppress the occurrence of iris.

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 the LCD without lowering the visibility due to rainbow-shaped color spots. Therefore, the industrial applicability of the present invention is extremely high.

Claims (3)

A liquid crystal display device comprising a backlight light source, two polarizing plates, and a liquid crystal cell arranged between the two polarizing plates,
The backlight light source is a white light source having 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 4000 to 30,000 nm and 1. An oriented polyester film having an Nz coefficient of 7 or less,
Liquid crystal display device. The liquid crystal display device according to claim 1, wherein the oriented polyester film has a degree of plane orientation of 0.13 or less. The liquid crystal display device according to claim 1 or 2, wherein the white light source having the continuous emission spectrum is a white light emitting diode.