JP2016099553A - Liquid crystal display device and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device and polarizing plates that can ensure good visibility while suppressing rainbow-like color irregularity at any observation angle.SOLUTION: There is provided a liquid crystal display device that has a backlight light source and a liquid crystal cell arranged between two polarizing plates, where the backlight light source is a white light source having a continuous emission spectrum; at least one polarizing plate of the polarizing plates has an alignment polyester film having a retardation of 1500 nm or more and less than 3000 nm laminated on at least one face of a polarizer; an absorption axis of the polarizer is substantially parallel to a slow axis of the alignment polyester film.SELECTED DRAWING: None

Description

  The present invention relates to a liquid crystal display device and a polarizing plate. Specifically, the present invention relates to a liquid crystal display device and a polarizing plate that have favorable visibility and are suitable for thinning.

  A polarizing plate used in a liquid crystal display (LCD) usually has a configuration in which a polarizer in which iodine is dyed on polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films. As the film, a triacetyl cellulose (TAC) film is usually used. In recent years, with the thinning of LCDs, there has been a demand for thinner polarizing plates. However, if the thickness of the TAC film used as the protective film is reduced for this purpose, sufficient mechanical strength cannot be obtained and moisture permeability deteriorates. Further, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

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

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

  The polyester film is superior to the TAC film in durability, but unlike the TAC film, the polyester film has birefringence. Therefore, when the polyester film is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when used as a polarizer protective film, a rainbow-like color spot is generated when observed from an oblique direction, and the image quality is deteriorated. . Therefore, in patent documents 1-3, the countermeasure which makes retardation small is made by using copolyester as polyester. However, even in that case, the iridescent color spots could not be completely eliminated.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a liquid crystal display that can cope with the thinning of the liquid crystal display device and suppress deterioration in visibility due to rainbow-like color spots. An apparatus and a polarizing plate are provided.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors used a combination of a specific backlight light source and an oriented polyester film having a specific retardation, and an absorption axis of a polarizer constituting the polarizing plate. It has been found that the above problem can be solved by making the slow axis of the oriented polyester film substantially parallel, and the present invention has been completed.

That is, the present invention is as follows.
Item 1.
A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
Among the polarizing plates, at least one polarizing plate is obtained by laminating an oriented polyester film having a retardation of 1500 nm or more and less than 3000 nm on at least one surface of the polarizer, and the absorption axis of the polarizer and the oriented polyester film. The slow axis of is substantially parallel,
Liquid crystal display device.
Item 2.
Item 2. The liquid crystal display device according to item 1, wherein the oriented polyester film has an NZ coefficient of 2.5 or less.
Item 3.
A polarizing plate in which an oriented polyester film having a retardation of 1500 nm or more and less than 3000 nm is laminated on at least one surface of a polarizer,
The absorption axis of the polarizer and the slow axis of the oriented polyester film are substantially parallel.
A polarizing plate for a liquid crystal display device having a white light source having a continuous emission spectrum.

  The liquid crystal display device and polarizing plate of the present invention can ensure good visibility in which rainbow-like color spots are suppressed at any viewing angle.

  In general, the liquid crystal panel includes a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight light source toward the image display side (viewing side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is arranged on the side facing the backlight light source in the rear module, and is arranged on the side (viewing side) displaying the image in the front module.

  The liquid crystal display device of the present invention comprises at least a backlight source and a liquid crystal cell disposed between two polarizing plates. Moreover, you may have suitably other structures other than these, for example, a color filter, a lens film, a diffusion sheet, an antireflection film etc. suitably.

  The configuration of the backlight may be an edge light method using a light guide plate or a reflection plate as a constituent member, or may be a direct type, but in the present invention, it is a continuous light source for a liquid crystal display device. Specifically, it is preferable to use a white light source having an emission spectrum. Especially, it is preferable to use a white light emitting diode (white LED). In the present invention, the white LED is an element that emits white by combining a phosphor with a phosphor system, that is, a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor. Examples of the phosphor include yttrium / aluminum / garnet yellow phosphor and terbium / aluminum / garnet yellow phosphor. In particular, white light-emitting diodes, which are composed of light-emitting elements that combine blue light-emitting diodes using compound semiconductors with yttrium, aluminum, and garnet-based yellow phosphors, have a continuous and broad emission spectrum and are also efficient in light emission. Since it is excellent, it is suitable as the backlight light source of the present invention. Here, the continuous emission spectrum means that there is no wavelength at which the light intensity becomes zero at least in the visible light region. In addition, since the white LED with low power consumption can be widely used by the method of the present invention, it is possible to achieve an energy saving effect.

  Conventional fluorescent tubes such as cold cathode tubes and hot cathode tubes, which have been widely used as backlight light sources, have only a discontinuous emission spectrum having a peak at a specific wavelength. It is difficult to obtain the desired effect.

  The polarizing plate has a configuration in which a polarizer protective film is bonded to at least one surface of a polarizer in which iodine is dyed on PVA or the like. In the present invention, at least one of the polarizer protective films constituting the polarizing plate, an oriented polyester film having a specific range of retardation is used as the polarizer protective film, and the absorption axis of the polarizer and the slow phase of the oriented polyester film are used. It is preferable to laminate so that the axes are in a substantially parallel relationship.

  The oriented polyester film used as the polarizer protective film preferably has a retardation of 1500 nm or more and less than 3000 nm. When the retardation is less than 1500 nm, when used as a polarizer protective film, a strong interference color is observed when observed from an oblique direction, and thus good visibility cannot be ensured. The preferred lower limit of retardation is 1800 nm, and the next preferred lower limit is 2000 nm.

  On the other hand, the upper limit of retardation is 3000 nm. When a polyester film having a retardation higher than that is used, it is difficult to obtain a polarizer protective film comprising a thin polyester film.

  In addition, the retardation of this invention can also be calculated | required by measuring the refractive index and thickness of a biaxial direction, and can also be calculated | required using commercially available automatic birefringence measuring apparatuses, such as KOBRA-21ADH (Oji Scientific Instruments). it can. The refractive index can be measured using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm).

  In the present invention, at least one of the polarizer protective films is a polarizer protective film having the specific retardation. The arrangement of the polarizer protective film having the specific retardation is not particularly limited, but a polarizing plate disposed on the incident light side (light source side), a liquid crystal cell, and a polarizing plate disposed on the outgoing light side (viewing side). In the case of the liquid crystal display device, the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side or the polarizer protective film on the outgoing light side of the polarizing plate arranged on the outgoing light side It is preferable that it is a polarizer protective film which consists of an oriented polyester film which has the said specific retardation. A particularly preferred embodiment is an embodiment in which the polarizer protective film on the exit light side of the polarizing plate disposed on the exit light side is an oriented polyester film having the specific retardation. When the polyester film is disposed at a position other than the above, the polarization characteristics of the liquid crystal cell may be changed. Since it is not preferable to use the polymer film of the present invention at a place where polarization characteristics are required, it is preferably used as a protective film for a polarizing plate at such a specific position.

  The polarizing plate of the present invention has a structure in which a polarizer protective film is attached to at least one surface of a polarizer in which polyvinyl alcohol (PVA) is dyed with iodine, and one of the polarizer protective films is It is a polarizer protective film which has the said specific retardation, It is characterized by the above-mentioned. As the other polarizer protective film, it is preferable to use a film having no birefringence such as a TAC film, an acrylic film, and a norbornene-based film.

  It is preferable that the absorption axis of the polarizer constituting the polarizing plate and the slow axis of the oriented polyester film as the polarizer protective film are substantially parallel. Here, “substantially parallel” means that the angle formed between the absorption axis of the polarizer and the slow axis of the oriented polyester film may be shifted from 0 degree within an allowable range of ± 20 degrees. In some cases, an inevitable angle shift is allowed when laminating a polarizer and a polyester film as a polarizer protective film. The allowable range is preferably within ± 15 degrees, more preferably within ± 10 degrees, further preferably within ± 7 degrees, and particularly preferably within ± 5 degrees.

  In the oriented polyester film used as the polarizer protective film, it is also preferable to provide various hard coats on the surface for the purpose of preventing reflection, suppressing glare, suppressing scratches, and the like. In addition, providing a low reflection layer or an antireflection layer is also a preferable embodiment from the viewpoint of further reducing rainbow-like color spots. The low reflection layer and the antireflection layer may be laminated on any surface of the polyester film, but are preferably laminated on the polyester film opposite to the surface on which the polarizer is laminated. It is also a preferable aspect that another layer (for example, an easy-adhesion layer, a hard coat layer, an antiglare layer, an antistatic layer, etc.) is laminated between the low reflection layer or antireflection layer and the polyester film. .

  The polyester used in the present invention may be polyethylene terephthalate or polyethylene naphthalate, but may contain other copolymerization components. These resins are excellent in transparency and excellent in thermal and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate has a large intrinsic birefringence and is the most suitable material.

  For the purpose of suppressing deterioration of optical functional dyes such as iodine dyes, the oriented polyester film preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, the optical functional dye can be prevented from being deteriorated by ultraviolet rays. In addition, the transmittance | permeability in this invention is measured by the perpendicular | vertical method with respect to the plane of a film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type).

  In order to reduce the transmittance of the oriented polyester film at a wavelength of 380 nm to 20% or less, it is desirable to appropriately adjust the type, concentration and thickness of the ultraviolet absorber. The ultraviolet absorber used in the present invention is a known substance. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency. Examples of the organic ultraviolet absorber include benzotriazole, benzophenone, cyclic imino ester, 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, benzotoazole and cyclic imino ester are particularly preferable. When two or more kinds of ultraviolet absorbers are used in combination, ultraviolet rays having different wavelengths can be absorbed simultaneously, so that the ultraviolet absorption effect can be further improved.

  Examples of benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, and acrylonitrile ultraviolet absorbers include 2- [2′-hydroxy-5 ′-(methacryloyloxymethyl) phenyl] -2H-benzotriazole, 2- [2 ′. -Hydroxy-5 '-(methacryloyloxyethyl) phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5'-(methacryloyloxypropyl) phenyl] -2H-benzotriazole, 2,2'-dihydroxy- 4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- ( 2'-hydroxy-3'-tert-butyl-5'-methyl Enyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl-6- (tert-butyl) phenol, 2,2′-methylenebis (4- ( 1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, etc. Examples of cyclic imino ester UV absorbers include 2,2 ′-(1,4 -Phenylene) bis (4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, Examples thereof include 2-phenyl-3,1-benzoxazin-4-one, but are not particularly limited thereto.

  Moreover, it is also a preferable aspect to contain various additives in the range which does not prevent the effect of this invention other than an ultraviolet absorber. Examples of additives include inorganic particles, heat resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light proofing agents, flame retardants, thermal stabilizers, antioxidants, and antigelling agents. And surfactants. Moreover, in order to show high transparency, it is also preferable that a polyester film does not contain a particle | grain substantially. “Substantially free of particles” means, for example, in the case of inorganic particles, a content that is 50 ppm or less, preferably 10 ppm or less, particularly preferably the detection limit or less when inorganic elements are quantified by fluorescent X-ray analysis. means.

  Furthermore, the oriented polyester film used in the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc. in order to improve the adhesion to the polarizer.

  In the present invention, in order to improve the adhesion to the polarizer, the oriented polyester film may have an easy adhesion layer mainly comprising at least one of a polyester resin, a polyurethane resin or a polyacrylic resin on at least one side. preferable. Here, the “main component” refers to a component that is 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating solution used for forming the easy-adhesion layer is preferably an aqueous coating solution containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible co-polymers disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. Examples thereof include a polymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy-adhesion layer can be obtained by applying the coating solution on one or both sides of a longitudinal uniaxially stretched film, drying at 100 to 150 ° C., and further stretching in the transverse direction. The final coating amount of the easy adhesion layer is preferably controlled to 0.05 to 0.20 g / m ² . If the coating amount is less than 0.05 g / m ² , the adhesion with the resulting polarizer may be insufficient. On the other hand, when the coating amount exceeds 0.20 g / m ² , blocking resistance may be lowered. When providing an easily bonding layer on both surfaces of a polyester film, the application quantity of an easily bonding layer on both surfaces may be the same or different, and can be independently set within the above range.

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

  Moreover, a well-known method can be used as a method of apply | coating a coating liquid. 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, etc. can be mentioned. Or it can carry out in combination.

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

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

  The oriented polyester film may be either a uniaxially stretched film or a biaxially stretched film, but when the biaxially stretched film is used as a polarizer protective film, it is rainbow-like even when observed from directly above the film surface. However, it should be noted that rainbow-like color spots may be observed when observed from an oblique direction.

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

That is, the polyester film used as the polarizer protective film in the present invention is not necessarily required to be completely uniaxial, but preferably has a certain degree of uniaxiality from the viewpoint of suppressing iridescent color spots. . An NZ coefficient can be used as this index.
The oriented polyester film used in the present invention preferably has an NZ coefficient of 2.5 or less, more preferably 2.0 or less, still more preferably 1.8 or less, and still more preferably 1.6 or less. When the NZ coefficient is 2.5 or less, the birefringence action increases uniaxiality, and rainbow-like color spots are less likely to occur due to the observation angle. And since a NZ coefficient will be 1.0 in a perfect uniaxial (uniaxial symmetry) film, the minimum of a Nz coefficient is 1.0. However, it should be noted that the mechanical strength in the direction perpendicular to the orientation direction tends to decrease significantly as the film approaches a perfect uniaxial (uniaxial symmetry) film.

  The NZ coefficient is represented by | Ny−Nz | / | Ny−Nx |, where Ny is the refractive index in the slow axis direction, and Nx is the refractive index in the direction perpendicular to the slow axis (the refractive index in the fast axis direction). Index) and Nz represent the refractive index in the thickness direction. The orientation axis of the film is obtained using a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter), and the biaxial refractive index (Ny, Nx, where the orientation axis direction is perpendicular to the orientation axis direction) Ny> Nx) and the refractive index (Nz) in the thickness direction are determined by Abbe's refractometer (NAGO-4T, measurement wavelength 589 nm, manufactured by Atago Co., Ltd.). The value obtained in this way can be substituted for | Ny−Nz | / | Ny−Nx | to obtain the Nz coefficient.

  In order to satisfy the retardation in the thin film polarizer protective film, the value of Ny-Nx is preferably 0.05 or more, more preferably 0.07 or more, further preferably 0.08 or more, and still more preferably. Is 0.09 or more, most preferably 0.1 or more. The upper limit is not particularly defined, but in the case of a polyethylene terephthalate film, the upper limit is preferably about 1.5.

Describing specifically the film forming conditions of the oriented polyester film, the longitudinal stretching temperature and the transverse stretching temperature are preferably from 80 to 130 ° C, particularly preferably from 90 to 120 ° C.
In order to orient the film so that the slow axis is in the TD direction (film width direction), the longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. is there. The transverse draw ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times.
In order to orient the film so that the slow axis is in the MD direction (film flow direction), the longitudinal draw ratio is preferably 2.5 to 6.0 times, particularly preferably 3.0 to 5.5 times. In addition, the transverse draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times.
In order to control the retardation within the above range in the thin film, it is preferable to control the ratio of the longitudinal draw ratio and the transverse draw ratio. If the difference between the vertical and horizontal draw ratios is too small, it is difficult to make the retardation within the above range, which is not preferable. In addition, setting the stretching temperature low is also a preferable measure for setting the retardation in the above range in the thin film. In the subsequent heat treatment, the treatment temperature is preferably from 100 to 250 ° C, particularly preferably from 180 to 245 ° C.

  In order to suppress retardation fluctuation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and the stretching ratio greatly affect the thickness variation of the film, it is necessary to optimize the film forming conditions from the viewpoint of the thickness variation.

  The thickness unevenness of the film is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and 3.0% or less. Particularly preferred.

  As described above, in order to control the retardation of the film within a specific range, the stretching ratio, the stretching temperature, and the thickness of the film can be appropriately set. For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the higher the retardation. Conversely, the lower the stretching ratio, the higher the stretching temperature, and the thinner the film, the lower the retardation. However, when the thickness of the film is increased, the thickness direction retardation tends to increase. Therefore, it is desirable to set the film thickness appropriately within the range described below. In addition to controlling the retardation, it is necessary to set final film forming conditions in consideration of physical properties necessary for processing.

  Although the thickness of an oriented polyester film is arbitrary, the range of 15-300 micrometers is preferable, More preferably, it is 15-100 micrometers, More preferably, it is 15-60 micrometers, Especially preferably, it is 25-50 micrometers. In order to control the retardation within the range of the present invention even in the above thickness range, the polyester used as the film substrate is preferably polyethylene terephthalate.

  In addition, as a method of blending the ultraviolet absorber into the polyester film, a known method can be used in combination. For example, a master batch is prepared by blending the dried ultraviolet absorber and the polymer raw material in advance using a kneading extruder. It can be prepared and blended by, for example, a method of mixing a predetermined master batch and a polymer raw material during film formation.

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

  In the present invention, it is preferable that the film has a multilayer structure of at least three layers and an ultraviolet absorber is added to the intermediate layer of the film. A film having a three-layer structure containing an ultraviolet absorber in the intermediate layer can be specifically produced as follows. Polyester pellets alone for the outer layer, master batches containing UV absorbers for the intermediate layer and polyester pellets are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder, which is slit-shaped. Extruded into a sheet form from a die and cooled and solidified on a casting roll to make an unstretched film. That is, using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square merging portion), a film layer constituting both outer layers and a film layer constituting an intermediate layer are laminated, An unstretched film is formed by extruding a three-layer sheet from the die and cooling with a casting roll. In the present invention, it is preferable to perform high-precision filtration during melt extrusion in order to remove foreign substances contained in the raw material polyester that cause optical defects. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of the molten resin is preferably 15 μm or less. When the filter particle size of the filter medium exceeds 15 μm, removal of foreign matters of 20 μm or more tends to be insufficient.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. These are all included in the technical scope of the present invention. In addition, the evaluation method of the physical property in the following examples is as follows.

(1) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy × d) of the biaxial refractive index anisotropy (ΔNxy = | Ny−Nx |) on the film and the film thickness d (nm). Yes, a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using a molecular orientation meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 type molecular orientation meter), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes the long side, A sample was used. For this sample, the biaxial refractive index (Ny: refractive index in the slow axis direction, Nx: refractive index in the direction perpendicular to the slow axis direction in the plane (refractive index in the fast axis direction)), and The refractive index (Nz) in the thickness direction was measured using an Abbe refractometer (NAGO-4T manufactured by Atago Co., Ltd., measurement wavelength 589 nm), and the absolute value of the difference between the biaxial refractive indices (| Ny−Nx | ) Is the refractive index anisotropy (ΔNxy). The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Reef, Millitron 1245D), and the unit was converted to nm. Retardation (Re) was determined from the product (ΔNxy × d) of refractive index anisotropy (ΔNxy) and film thickness d (nm).

(2) NZ coefficient The values of Ny, Nx, and Nz obtained above were substituted into | Ny−Nz | / | Ny−Nx | to obtain an NZ coefficient.

(3) Iridescent observation Visual observation was performed from the front side and the oblique direction of the polarizing plate of the liquid crystal display device obtained in the examples, and the presence or absence of the occurrence of iridescence was determined as follows.

◎: No rainbow spots from any direction.
○: When observed from an oblique direction, a partly extremely thin rainbow can be observed.
Δ: When observed from an oblique direction, rainbow unevenness can be observed in part.
X: When observing from an oblique direction, rainbow spots can be clearly observed.

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

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

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

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

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

  Next, the adhesive modified coating solution was applied on 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 on which this coating layer was formed was guided to a tenter stretching machine, and the film was guided to a hot air zone at a temperature of 125 ° C. while being gripped by a clip, and stretched 4.0 times in the width direction. Next, 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 3% relaxation treatment in the width direction to obtain an oriented polyester film having a film thickness of about 25 μm.

  An oriented polyester film prepared by the method described above is attached to one side of a polarizer composed of PVA and iodine so that the absorption axis of the polarizer and the slow axis of the film are parallel, and a TAC film (Fuji Film) is placed on the opposite side. A polarizing plate was prepared by pasting (manufactured by Co., Ltd., thickness: 80 μm). The resulting polarizing plate is made of polyester on the outgoing light side of a liquid crystal display device using a white LED composed of a light emitting element in which a blue light emitting diode and a yttrium / aluminum / garnet yellow phosphor are combined as a light source (Nichia Chemical, NSPW500CS). The film was placed so that the film was on the viewing side. This liquid crystal display device had a polarizing plate having two TAC films as polarizer protective films on the incident light side of the liquid crystal cell.

(Example 2)
An oriented polyester film was obtained in the same manner as in Example 1, except that the thickness of the unstretched film was changed to about 20 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

(Example 3)
An unstretched film produced by the same method as in Example 1 is heated to 105 ° C. using a heated roll group and an infrared heater, and then stretched 1.5 times in the running direction with a roll group having a difference in peripheral speed. Then, the film was stretched 4.0 times in the width direction in the same manner as in Example 1 to obtain an oriented polyester film having a film thickness of about 25 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

Example 4
In the same manner as in Example 3, the polyester film was stretched 2.0 times in the running direction and 4.0 times in the width direction to obtain an oriented polyester film having a film thickness of about 45 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

(Example 5)
An oriented polyester film having a film thickness of about 15 μm was obtained in the same manner as in Example 1.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

(Example 6)
In the same manner as in Example 3, the film was stretched 4.0 times in the running direction and 1.0 times in the width direction to obtain an oriented polyester film having a film thickness of about 15 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

(Example 7)
In the same manner as in Example 1, the polyester film was stretched 1.0 times in the running direction and 3.5 times in the width direction to obtain an oriented polyester film having a film thickness of about 30 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

(Comparative Example 1)
A liquid crystal display device was produced in the same manner as in Example 1 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 2)
A liquid crystal display device was produced in the same manner as in Example 2 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 3)
A liquid crystal display device was produced in the same manner as in Example 3 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 4)
A liquid crystal display device was produced in the same manner as in Example 4 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 5)
A liquid crystal display device was produced in the same manner as in Example 5 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 6)
A liquid crystal display device was produced in the same manner as in Example 6 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 7)
A liquid crystal display device was produced in the same manner as in Example 7 except that a polarizing plate was produced by vertically laminating the absorption axis of the polarizer and the slow axis of the oriented polyester film.

(Comparative Example 8)
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that the rainbow spots were observed using the light source of the liquid crystal display device as a cold cathode tube.

(Comparative Example 9)
In the same manner as in Example 3, the polyester film was stretched 3.6 times in the running direction and 4.0 times in the width direction to obtain an oriented polyester film having a film thickness of about 38 μm.
A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1 except that this oriented polyester film was used.

  Table 1 below shows the results of rainbow spot observation of the liquid crystal display devices obtained in Examples 1 to 7 and Comparative Examples 1 to 9.

  As shown in Table 1, when rainbow spots were observed for the liquid crystal display devices of Examples 1 to 7, when observed from the front direction, no rainbow spots were observed in any of the films. With respect to the liquid crystal display device of Example 3, rainbow unevenness may be partially observed when observed from an oblique direction. About the liquid crystal display device of Example 4, when observing from the diagonal, a rainbow spot might be observed partially. For the liquid crystal display devices of Examples 1-2 and 5-7, no rainbow spots were observed even when observed obliquely. About Examples 3-4, since the NZ coefficient is comparatively high, it is considered that spots were sometimes observed when observed obliquely. On the other hand, in the liquid crystal display devices of Comparative Examples 1 to 9, rainbow spots were observed when observed from an oblique direction.

  By using the liquid crystal display device and the polarizing plate of the present invention, it is possible to contribute to the thinning and cost reduction of the LCD without lowering the visibility due to the rainbow-like color spots, and industrial applicability. Is extremely expensive.

Claims (3)

A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates,
The backlight source is a white light source having a continuous emission spectrum;
Among the polarizing plates, at least one polarizing plate is obtained by laminating an oriented polyester film having a retardation of 1500 nm or more and less than 3000 nm on at least one surface of the polarizer, and the absorption axis of the polarizer and the oriented polyester film. The slow axis of is substantially parallel,
Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein an NZ coefficient of the oriented polyester film is 2.5 or less. A polarizing plate in which an oriented polyester film having a retardation of 1500 nm or more and less than 3000 nm is laminated on at least one surface of a polarizer,
The absorption axis of the polarizer and the slow axis of the oriented polyester film are substantially parallel.
A polarizing plate for a liquid crystal display device having a white light source having a continuous emission spectrum.