KR20210111367A - Liquid crystal display device, polarizing plate, and polarizer protective film - Google Patents

Abstract

A liquid crystal display device using a polarizer protective film made of a polyester film and having good visibility is provided.
A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizer plates, wherein the backlight light source is a white light source having a continuous emission spectrum, and the polarizer plate has a structure in which polarizer protective films are laminated on both sides of the polarizer, , at least one of the polarizer protective films has a retardation of 3,000 to 30,000 nm, the center plane average roughness (SRa) of the outermost layer surface is 0.008 to 0.02 μm, and the ten-point average roughness (SRz) is 0.3 to 1.5 μm. A liquid crystal display that is an ester film.

Description

Liquid crystal display device, polarizing plate, and polarizer protective film {Liquid crystal display device, polarizing plate, and polarizer protective film}

The present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film. Specifically, it relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film having good visibility and suitable for thinning.

A polarizing plate used in a liquid crystal display device (LCD) has a structure in which a polarizer obtained by dyeing iodine in polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films, and triacetyl as a polarizer protective film is usually Cellulose (TAC) films are being used. In recent years, thinning of the polarizing plate is required along with the thinning of LCD. However, for this reason, when the thickness of the TAC film used as a protective film is made thin, sufficient mechanical strength cannot be acquired, and moisture permeability will become high and a polarizer will deteriorate easily. In addition, since TAC film is very expensive, there is a strong demand for an inexpensive alternative material.

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

Japanese Patent Laid-Open No. 2002-116320 Japanese Patent Laid-Open No. 2004-219620 Japanese Patent Laid-Open No. 2004-205773

The polyester film has excellent durability compared to the TAC film, but unlike the TAC film, it has birefringence, so that when it is used as a polarizer protective film, there is a problem that the image quality is deteriorated due to optical distortion. That is, since the polyester film having birefringence has a predetermined optical anisotropy (retardation), when it is used as a polarizer protective film, when viewed from an oblique direction, rainbow-like color unevenness occurs and the image quality deteriorates. Therefore, in patent documents 1-3, the countermeasure which makes retardation small is made|formed by using co-polyester as polyester. However, even in that case, it was not possible to completely remove the rainbow-shaped color spots.

The present invention has been made in order to solve these problems, and the object is to be able to cope with the reduction in thickness of the liquid crystal display device, and also to have a liquid crystal display device that does not cause deterioration of visibility due to rainbow-shaped color spots, and has high transparency and has no optical defects. It is to provide a little polarizer protective film.

MEANS TO SOLVE THE PROBLEM The present inventors earnestly examined about the generation|occurrence|production mechanism of the rainbow-shaped color unevenness which arises when a polyester film is used as a polarizer protective film. As a result, it turned out that rainbow-shaped color unevenness originates in the retardation of a polyester film, and the emission spectrum of a backlight light source. As a backlight light source of a conventional liquid crystal display device, a fluorescent tube such as a cold cathode tube or a hot cathode tube is used. The spectral distribution of a fluorescent lamp such as a cold cathode tube or a hot cathode tube shows an emission spectrum having a plurality of peaks, and these discontinuous emission spectra are combined to obtain a white light source. When light passes through a film with high retardation, the transmitted light intensity is different depending on the wavelength. For this reason, if the backlight light source had a discontinuous emission spectrum, only a specific wavelength was strongly transmitted, and it was thought that rainbow-like color spots were generated.

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said problem could be solved by using in combination the polyester film which has a specific backlight light source and specific retardation, as a result of earnestly examining in order to achieve the said subject. In addition, it was found that it is effective to provide a specific surface shape in order to secure high transparency while suppressing optical defects of the polyester film.

That is, a typical present invention is as follows.

(1) A liquid crystal display device having a backlight light source and a liquid crystal cell disposed between two polarizing plates, wherein the backlight light source is a white light source having a continuous emission spectrum, and the polarizing plate is a polarizing plate in which polarizer protective films are laminated on both sides of the polarizer and at least one of the polarizer protective films has a retardation of 3,000 to 30,000 nm, a central surface average roughness (SRa) of the outermost layer surface is 0.008 to 0.02 µm, and a ten-point average roughness (SRz) is 0.3 to 1.5 µm A liquid crystal display device that is a polyester film.

(2) the exit light side polarizer protective film of the polarizing plate disposed on the exit light side with respect to the liquid crystal cell has a retardation of 3,000 to 30,000 nm, and the central surface average roughness (SRa) of the surface of the outermost layer is 0.008 to 0.02 μm, In addition, the liquid crystal display device is a polyester film having a ten-point average roughness (SRz) of 0.3 to 1.5 μm.

(3) The liquid crystal display device in which the ratio (Re/Rth) of the retardation in the thickness direction to the retardation of the polyester film is 0.2 or more.

(4) a polarizing plate in which a polarizer protective film is laminated on both sides of a polarizer, wherein the polarizer protective film on at least one side has a retardation of 3,000 to 30,000 nm, and the central surface average roughness (SRa) of the surface of the outermost layer is 0.008 to 0.02 μm; , Also, a polarizing plate for a liquid crystal display using a white light source having a continuous emission spectrum, which is a polyester film having a ten-point average roughness (SRz) of 0.3 to 1.5 μm, as a backlight light source.

(5) a continuous polyester film having a retardation of 3,000 to 30,000 nm, a center plane average roughness (SRa) of the outermost layer surface of 0.008 to 0.02 µm, and a ten-point average roughness (SRz) of 0.3 to 1.5 µm A polarizer protective film for a liquid crystal display using a white light source having an emission spectrum as a backlight light source.

(6) The said polarizer protective film whose ratio (Re/Rth) of retardation of the said polyester film and thickness direction retardation is 0.2 or more.

(7) The said polarizer protective film in which the said polyester film has an easily adhesive layer.

(8) The polarizer protective film in which the polyester film is made of at least three layers, the outermost layer contains inert particles having an average particle diameter of 1.0 to 3.5 μm, and the thickness of the outermost layer is equal to or greater than the average particle diameter of the inert particles.

(9) The said polarizer protective film whose inert particle content in the outermost layer of the said polyester film is 0.005-0.05 mass %, and the haze of the said polyester film is 3 % or less.

(10) The above-mentioned polarizer protective film, wherein a UV absorber is contained in a layer other than the outermost layer of the polyester film, and the light transmittance at 380 nm is 20% or less.

The liquid crystal display device, the polarizing plate, and the polarizer protective film of the present invention can obtain a spectrum similar to the light source as for the spectrum of transmitted light at any observation angle, and can ensure good visibility without rainbow-like color unevenness. Moreover, since the polarizer protective film of this invention has a specific surface roughness, it is excellent in handleability, and it is hard to generate|occur|produce a flaw by friction etc. Therefore, the polarizer protective film of the present invention has high transparency and has very few optical defects such as scratches.

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

The liquid crystal display device of the present invention comprises at least a backlight light source and a liquid crystal cell disposed between two polarizing plates as constituent members. 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.

As the configuration of the backlight light source, an edge light method using a light guide plate, a reflecting plate, etc. as a constituent member may be used, or a direct type method may be used. However, it is preferable to use a white light source having a continuous and broad emission spectrum. Here, the continuous and broad emission spectrum means an emission spectrum in which there is no wavelength at which the intensity of light becomes zero in a wavelength region of at least 450 nm to 650 nm, preferably in a visible light region. As a white light source which has such a continuous and wide emission spectrum, a white light emitting diode (white LED) is mentioned, for example. The white LED includes an element that emits white light by combining a phosphor method, that is, a blue light using a compound semiconductor, or a light emitting diode that emits ultraviolet light, and an organic light-emitting diode (OLED). 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 yellow phosphor of yttrium, aluminum, and garnet system has a continuous and wide emission spectrum and excellent luminous efficiency. It is suitable as a backlight light source. By using a light source, such as a white LED, which consumes less power, it is effective for energy saving.

Fluorescent tubes, such as cold cathode tubes and hot cathode tubes, which are conventionally widely used as backlight light sources, have only discontinuous emission spectra in which the emission spectrum has a peak at a specific wavelength, so it is difficult to obtain the effects of the present invention as described above.

The polarizing plate has a configuration in which both sides of a polarizer dyed with iodine in PVA or the like are sandwiched between two polarizer protective films. It is characterized by using

As a mechanism by which generation|occurrence|production of a rainbow-like color unevenness is suppressed by the said aspect, it is thought as follows. When a polyester film having birefringence is disposed on one side of the polarizer, the linearly polarized light emitted from the polarizer is disturbed when passing through the polyester film. The transmitted light exhibits an interference color characteristic of retardation, which is the product of birefringence and thickness of the polyester film. Therefore, when a discontinuous emission spectrum such as a cold cathode tube or a hot cathode tube is used as a light source, the transmitted light intensity differs depending on the wavelength, resulting in rainbow-like color spots (refer to: 15th Microoptics Conference Summary, pages 30-31) ).

On the other hand, a white light emitting diode has a continuous and wide emission spectrum in the wavelength range of at least 450 nm - 650 nm, and preferably in the visible light range normally. And since the interference color spectrum by the transmitted light which has passed through the birefringent body becomes an envelope shape, it becomes possible to obtain a spectrum similar to the emission spectrum of a light source by controlling the retardation of a polyester film. As described above, it is thought that by making the luminescence spectrum of the light source and the envelope shape of the interference color spectrum by the transmitted light passing through the birefringent have a similar shape, rainbow-like color unevenness does not occur and visibility is remarkably improved.

From the above principle, in the present invention, by using a white light emitting diode having a wide emission spectrum as a light source, the envelope shape of the spectrum of transmitted light is approximated to the emission spectrum of the light source only with a relatively simple configuration, and consequently, rainbow spots on the liquid crystal display are suppressed. It is thought to be possible.

(polyester film)

It is preferable that the polyester film used for a polarizer protective film is an orientation polyester film which has 3,000-30,000 nm retardation. When the retardation is less than 3,000 nm, when it is used as a polarizer protective film, a strong interference color is exhibited when observed from an oblique direction. A preferable lower limit of the retardation is 4,500 nm or more, more preferably 6,000 nm or more, still more preferably 8,000 nm or more, even more preferably 10,000 nm or more.

On the other hand, the upper limit of the retardation is 30,000 nm. Even if a polyester film having a retardation higher than that is used, an additional effect of improving visibility is not substantially obtained, and the thickness of the film is also considerably increased, which is undesirable because handling as an industrial material is deteriorated.

The retardation of the polyester film can be obtained by measuring the refractive index and thickness in the biaxial direction, and can also be obtained using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Instruments Co., Ltd.). In this specification, retardation means in-plane retardation.

In this invention, at least one of a polarizer protective film is a polarizer protective film which has the said specific retardation, It is characterized by the above-mentioned. The arrangement of the polarizer protective film having the specific retardation is not particularly limited, but the polarizer protective film on the incident light side of the polarizing plate arranged on the incident light side of the liquid crystal display device, or the polarizer on the exit light side of the polarizing plate arranged on the emitted light side It is preferable that a protective film is a polarizer protective film which consists of a polyester film which has the said specific retardation. An especially preferable aspect is an aspect which uses the polarizer protective film on the side of the exit light of the polarizing plate arrange|positioned on the side of the exit light as the polyester film which has the said specific retardation. When a polyester film is arrange|positioned at positions other than the above, the polarization characteristic of a liquid crystal cell may be changed.

The polarizing plate of the present invention has a configuration in which both sides of a polarizer in which iodine is dyed with polyvinyl alcohol (PVA) or the like is sandwiched between two polarizer protective films, and any one of the polarizer protective films has the above specific retardation. characterized by being. It is preferable to use a film without birefringence as typified by a TAC film, an acrylic film, and a norbornene-type film for the other polarizer protective film.

It is preferable that the polarizing plate used for this invention has various functional layers on the surface for the purpose of reflection prevention, glare suppression, flaw suppression, etc. Although it does not restrict|limit especially as such a functional layer, For example, a hard-coat layer, a glare-proof layer (AG), an anti-reflection layer (AR), a low reflection layer (LR), a low reflection anti-glare layer (AG/LR), and an anti-reflection anti-glare layer (AG) /AR) and the like. It is preferable to provide a functional layer in the surface on the opposite side to the side which contact|connects the polarizer of a polyester film. As for these layers, only 1 type may be provided on the polyester film, and may be laminated|stacked in combination of 2 or more type as needed. By forming these layers, it is also possible to expect the effect of further reducing rainbow-like color unevenness.

When providing various functional layers, it is preferable to provide an easily bonding layer in advance on the surface of an oriented polyester film. In that case, it is preferable to adjust the refractive index of an easily bonding layer from a viewpoint of suppressing the interference by reflected light so that it may become near a rising average of the refractive index of a functional layer, and the refractive index of a polyester film. A well-known method can be employ|adopted for adjustment of the refractive index of an easily bonding layer, For example, it can adjust easily by containing titanium, germanium, and other metal species in binder resins, such as polyester and polyurethane.

A polyester film can be obtained by condensing dicarboxylic acid and diol. As a dicarboxylic acid component usable for manufacture of a polyester film, For example, 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-cyclopentane Dicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-di Ethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, sveric acid, dodecanedi Carboxylic acid etc. are mentioned.

Examples of the diol component usable in the production of the polyester film include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and decamethylene glycol. , 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl) propane, bis(4-hydroxyphenyl) Sulfone etc. are mentioned.

The dicarboxylic acid component and diol component which comprise a polyester film may use 1 type, or 2 or more types, respectively. Specific examples of the polyester resin constituting the polyester film include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, preferably polyethylene terephthalate and polyethylene naphthalate. . These resins are excellent in transparency and also excellent in thermal and mechanical properties, and retardation can be easily controlled by stretching. In particular, polyethylene terephthalate is the most suitable material because it has a large intrinsic birefringence and relatively easily obtains a large retardation even if the thickness of the film is thin.

It is preferable that the polyester film of this invention contains an inert particle in both outermost layers as a laminated constitution of three or more layers by a co-extrusion method. Thereby, it becomes possible to provide an uneven|corrugated shape to the outermost layer surface, and the workability (activity) by film processing becomes favorable. As the laminated structure of the present invention, for example, when the outermost layer is B layer and the other layers are A layer and C layer, the layer structure in the film thickness direction is B/A/B, B/A/C/B or B/ A configuration such as A/C/A/B is conceivable. Each of the layers of the A to C layers may have the same or different polyester resin composition, but in order to suppress the occurrence of curls due to the bimetallic composition, the polyester resin of each layer may have the same composition and/or B/A/B It is preferable to set it as a structure (two types, three layer structure).

In the present invention, the polyester resin constituting the central layer other than the outermost layer (for example, layer A in the case of B/A/B configuration) may contain particles, but in order to obtain high transparency, the polyester resin constituting the central layer It is preferable that the resin contains substantially no particles. By containing an inert particle only in an outermost layer, high transparency can be acquired more suitably. When adding particles to the central layer other than the outermost layer, it is preferably 50 ppm or less, preferably 10 ppm or less.

Examples of the inert particles contained in the outermost layer include calcium carbonate, calcium phosphate, amorphous silica, spherical silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, Inorganic particles such as zeolite, molybdenum sulfide, mica, crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate particles, benzoguanamine/formaldehyde condensate particles, melamine/formaldehyde condensate particles, polytetrafluoro Heat-resistant polymer microparticles|fine-particles, such as ethylene particle|grains, are mentioned. Among them, silica is most suitable because it has a relatively close refractive index to polyester, so that a film with more excellent transparency can be secured.

It is preferable that the average particle diameter of the inert particle contained in the outermost layer of the film of this invention is 1.0-3.5 micrometers, More preferably, it is 1.5-3.0 micrometers, More preferably, it is the range of 2.1-2.5 micrometers. When the average particle diameter of the inert particles is less than 1.0 µm, the cohesive force of the particles is very large, and coarse abnormal particles are easily generated due to the aggregation of the particles, which is not preferable. In this case, a flock|aggregate becomes a factor and the optical fault which can visually recognize on the film surface may arise.

Moreover, when an average particle diameter exceeds 3.5 micrometers, content of the coarse particle as a particle|grain single-piece|unit increases, and it is unpreferable. In this case, coarse particles may become a factor, and optical defects may occur on the surface of the film. It is preferable to use such a specific range of particles in order to reduce to the limit the coarse particles that cause optical defects.

The range of the average particle diameter of the inert particle here is measured by the measuring method mentioned later. In addition, for example, in the case of secondary particles in which primary particles as described below are aggregated, the average particle diameter of the secondary particles is referred to. That is, the average particle diameter of the inert particles here is the average particle diameter in the aspect that can actually exist as a lump as inert particles in the film.

It is preferable that content of the inert particle in outermost layer is 0.005-0.05 mass %, More preferably, it is 0.010-0.04 mass %, More preferably, it is 0.015-0.03 mass %. When content of an inert particle is 0.005 mass % or more, it is preferable from showing the effective activity of the grade which reduces a micro flaw. When content of an inert particle is 0.05 mass % or less, when maintaining high transparency, it is preferable.

The upper limit of the thickness of the outermost layer is not particularly set, but when the thickness is too thick, the amount of inert particles inside the film is excessively increased, and the scattering of light generated inside the film increases, which is not preferable because transparency is lowered. When the thickness of an outermost layer becomes very thin compared with an inert particle, the optical fault visually visually recognizable may arise on the film surface by the powder fall of particle|grains. For this reason, the thickness of the outermost layer is preferably equal to or more than the average particle diameter of the inert particles, more preferably 2 times or more, and particularly preferably 5 times or more. The surface projections are formed by inert particles present in the outermost layer. In order to form a smooth surface protrusion, it is preferable that the inert particles are not located directly below the surface, but particles having a size larger than a certain level are present at an appropriate depth of the film. When the thickness of the outermost layer is equal to or greater than the average particle diameter of the inert particles, more preferably 2 times or more, and still more preferably 5 times or more, the shape of the surface protrusions due to the inert particles becomes relatively gentle, so that powder fall hardly occurs. lose In addition, the thickness of the outermost layer means the thickness of one side of the outermost layer laminated|stacked on both surfaces of a film here.

As described above, by controlling the thickness of the inert particles and the inert particle-containing layer, the shape of the projections on the surface of the film can be suitably adjusted, and optical defects can be reduced more suitably while suppressing the decrease in transparency as much as possible.

Further, in order to more suitably form the specific surface shape, for example, (1) a method of smoothing the surface shape by increasing the intrinsic viscosity of the polyester resin, (2) treating the surface shape at a high temperature to change the surface shape It is also possible by combining a method of softening and the like. In addition, as will be described later (3), it is also suitable to use inert particles that are easily deformed by stretching of the film.

As the inert particles, which are likely to be deformed following film stretching, are secondary particles in which primary particles of several nm to several hundreds of nm are aggregated, and the pore volume is preferably 1.5 ml/g or more. In particular, from the viewpoints of transparency, handleability, and price, an amorphous lumped silica is suitable. When the pore volume of the inert particles is 1.5 ml/g or more, deformation of the particles due to stretching tends to occur, and the projection deformation is easily controlled. In addition, the pore volume of an inert particle can be computed by well-known nitrogen desorption methods, such as a BJH method. When the inert particles are in the film, for example, they are dissolved with a phenol/tetrachloroethane mixed solution or the like, and the residual inert particles are recovered and dried sufficiently, and can be calculated by known nitrogen desorption such as the BJH method.

As a method of mix|blending the said inert particle with polyester, a well-known method is employable. For example, it can be added in any step of producing the polyester, preferably after the esterification step or the transesterification reaction is completed, and then added as a slurry dispersed in ethylene glycol or the like in the step before the start of the polycondensation reaction to perform polycondensation. The reaction may proceed. In addition, it can be carried out by a method of blending a polyester raw material with a slurry of particles dispersed in ethylene glycol or water using a kneading extruder with a vent, or a method of blending a polyester raw material with dried particles using a kneading extruder.

Among them, in the present invention, after homogeneously dispersed the aggregated inorganic particles in the monomer liquid which becomes a part of the polyester raw material, the filtered product is added to the remainder of the polyester raw material before, during or after the esterification reaction. desirable. According to this method, since the monomer solution has a low viscosity, homogeneous dispersion of particles and high-precision filtration of the slurry can be easily performed, and at the same time, when added to the remainder of the raw material, the dispersibility of the particles is good, and new agglomerates are hardly generated.

In particular, in the case of using the amorphous aggregate-like silica, the particles may agglomerate due to the addition and mixing of the slurry to generate agglomerated coarse particles. Since silica aggregation tends to occur at high temperatures, when adding an ethylene glycol solution containing the amorphous agglomerated silica to reduce agglomerated coarse particles that cause optical defects, an esterification reaction or transesterification reaction is performed to form an oligomer It is preferable to blend with the polyester raw material while maintaining it in the range of preferably 10 to 50° C., more preferably 10 to 30° C. By adding the slurry at this timing, it becomes possible to add while maintaining the slurry temperature at a low temperature, and it is possible to suppress the formation of new aggregates.

In general, the particle size of the inert particles shows a distribution having a certain width, and the inert particles used in the present invention preferably contain 1% or less of the inert particles having a particle size of 10 μm or more. When the amount of inert particles having a particle size of 10 µm or more exceeds 1%, the number of coarse particles that cause optical defects may increase. As a method of making the distribution of inert particles within the above range, (1) a method of microfiltration of ethylene glycol or polyester in which inert particles are dispersed, (2) a batch or intermittent method of ethylene glycol or polyester in which inert particles are dispersed is applied. A method of treating with a centrifugal separator of (3) a method of selecting inert particles having a predetermined particle size distribution, etc. can be used.

The three-dimensional center plane average roughness (SRa) of the film of the present invention is preferably 0.008 to 0.02 μm, more preferably 0.009 to 0.015 μm. Moreover, it is preferable that it is 0.3-1.5 micrometers, and, as for ten-point average roughness (SRz), it is more preferable that it is 0.5-1.0 micrometer. When the three-dimensional center plane average roughness (SRa) or the ten-point average roughness (SRz) is within the above range, it is preferable because transparency can be maintained while effectively suppressing micro scratches.

It is preferable that the haze of the film of this invention is 3 % or less. More preferably, it is 2.5 % or less, More preferably, it is 2 % or less. When the haze exceeds 3%, it is not preferable because there is a risk of lowering the screen luminance of the liquid crystal display device.

Further, in order to suppress deterioration of optically functional dyes such as iodine dye, the film of the present invention preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance of 380 nm is more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, it is possible to suppress the deterioration of the optical functional dye due to ultraviolet rays. In addition, the transmittance|permeability in this invention is measured by the method perpendicular|vertical with respect to the plane of a film, and can be measured using the spectrophotometer (for example, Hitachi U-3500 type|mold).

Making the transmittance of the film of the present invention at a wavelength of 380 nm 20% or less includes adding an ultraviolet absorber in the film, applying a coating solution containing the ultraviolet absorber to the film surface, the type, concentration and film of the ultraviolet absorber. It can be achieved by adjusting the thickness appropriately. The ultraviolet absorber used in the present invention is a known substance. Although an organic type ultraviolet absorber and an inorganic type ultraviolet absorber are mentioned as a ultraviolet absorber, From a transparency viewpoint, an organic type ultraviolet absorber is preferable.

Examples of the organic ultraviolet absorbent include benzotriazole-based, benzophenone-based, cyclic iminoester-based and combinations thereof, but it is not particularly limited as long as it is within the absorbance range specified in the present invention. From a durable viewpoint, a benzotriazole type and a cyclic iminoester type are especially preferable. When two or more types of ultraviolet absorbers are used in combination, the ultraviolet absorption effect of ultraviolet rays can be further improved because ultraviolet rays of respective wavelengths can be simultaneously absorbed. When mix|blending a ultraviolet absorber with a polyester film, it is preferable to make a polyester film into a structure of three or more layers, and to mix|blend a ultraviolet absorber in layers other than the outermost layer (namely, an intermediate|middle layer).

Examples of the benzophenone-based ultraviolet absorber, the benzotriazole-based ultraviolet absorber and the acrylonitrile-based ultraviolet absorbent include 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotria Sol, 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. As a cyclic iminoester type|system|group ultraviolet absorber, for example, 2,2'-(1,4-phenylene) ) bis (4H-3,1-benzoxazinone-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazin-4-one, etc. However, it is not particularly limited thereto.

Moreover, it is also preferable to contain various additives other than a ultraviolet absorber in the range which does not impair the effect of this invention. Examples of the additive include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light resistance agents, flame retardants, heat stabilizers, antioxidants, anti-gelling agents, surfactants, and the like. Moreover, in order to show high transparency, it is also preferable not to contain particle|grains substantially in a polyester film. "Substantially not containing particles" means, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescence X-ray analysis, 50 ppm or less by weight, preferably 10 ppm or less, particularly preferably detected Content used below the limit is meant.

Furthermore, in order to make adhesiveness with a polarizer favorable to the polyester film of this invention, it is also possible to perform corona treatment, a coating process, a flame treatment, etc.

In this invention, in order to improve adhesiveness with a polarizer, it is preferable to have an easily adhesive layer which has at least one type of polyester resin, a polyurethane resin, or a polyacrylic resin as a main component on at least one side of the film of this invention. Here, the "main component" refers to a component of 50 mass % or more among the solid components constituting the easily adhesive layer. As for the coating liquid used for formation of an easily adhesive layer, the aqueous coating liquid containing 1 or more types of water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin is preferable. As these coating liquids, for example, the water-soluble disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, etc. Or a water-dispersible copolymer polyester resin solution, an acrylic resin solution, a polyurethane resin solution, etc. are mentioned.

The easily adhesive layer can be obtained by applying the coating solution to one or both surfaces of an unstretched or longitudinal uniaxially oriented film, followed by drying at 100 to 150° C., and further stretching in the transverse direction. It is preferable to manage the application amount of the final easily adhesive layer to 0.05-0.20 g/m<2>. Adhesiveness with the polarizer obtained as an application amount is less than 0.05 g/m<2> may become inadequate. On the other hand, when an application amount exceeds 0.20 g/m<2>, blocking resistance may fall. When providing an easily bonding layer on both surfaces of a polyester film, the application amount of the easily bonding layer of both surfaces may be same or different, and can each independently set within the said range.

It is preferable to add particle|grains in order to provide easy activity to an easily adhesive layer. The average particle diameter of the fine particles is preferably 2 µm or less. When the average particle diameter of the particles exceeds 2 mu m, the particles easily fall off from the easily adhesive layer. As particle|grains made to contain in an easily bonding layer, the thing similar to the microparticles|fine-particles mentioned above is illustrated.

Moreover, as a method of apply|coating a coating liquid, a well-known method can be used. For example, the reverse roll coating method, the gravure coating method, the kiss coating method, the roll brush method, the spray coating method, the air knife coating method, the wire bar coating method, the pipe doctor method, etc. are mentioned, These methods are mentioned individually or in combination. so it can be done

In addition, the measurement of the average particle diameter of the said particle|grains can be performed by the following method. Take a picture of the particles with a scanning electron microscope (SEM) and measure the maximum diameter (distance between the two most distant points) of 300 to 500 particles at a magnification such that the size of one smallest particle is 2 to 5 mm. Let the average value be the average particle diameter.

As a manufacturing method of a polyester film, the most common manufacturing method is to melt a polyester resin, extrude the molded unoriented polyester into a sheet shape, and stretch it in the longitudinal direction at a temperature above the glass transition temperature by using the speed difference of the roll. , a method of stretching in the transverse direction by means of a tenter and performing heat treatment is exemplified.

The polyester film of the present invention may be a uniaxially oriented film or a biaxially oriented film, but when the biaxially oriented film is used as a polarizer protective film, rainbow-like color spots are not seen even when viewed from directly above the film surface, but a rainbow when observed from an oblique direction Because shape color unevenness may be observed, it is necessary to be careful.

This phenomenon is that the biaxially oriented film consists of a fracture-rate ellipsoid having different refractive indices in the running direction, width direction, and thickness direction, and the retardation becomes zero depending on the direction of light transmission inside the film (the refractive index ellipsoid appears as a true circle). ) because there is a direction. Therefore, when the liquid crystal display screen is observed from a specific direction in the oblique direction, a point at which the retardation becomes zero may occur, and rainbow-like color spots are generated concentrically around that point. And when the angle from directly above the film plane (normal direction) to the position where the rainbow-shaped color unevenness is seen is θ, the angle θ increases as the birefringence in the film plane increases, making it difficult to see the rainbow-shaped color unevenness. Since the angle θ tends to be small in the biaxially oriented film, the uniaxially oriented film is preferable because it is difficult to see rainbow-like color irregularities.

However, in a perfectly uniaxial (uniaxially symmetric) film, the mechanical strength in the direction orthogonal to the orientation direction is significantly lowered, which is not preferable. It is preferable that the present invention has biaxiality (biaxial symmetry) in a range that does not substantially generate rainbow-like color unevenness or does not generate rainbow-like color unevenness in a viewing angle range required for a liquid crystal display screen.

As an index for judging the difficulty in seeing the rainbow-like color unevenness, there is a method of evaluating the difference between the retardation (in-plane retardation) and the retardation (Rth) in the thickness direction. This thickness direction retardation means the average of the retardation obtained by multiplying the film thickness d by two birefringence (DELTA)Nxz, (DELTA)Nyz, respectively, when viewed from the cross section in the film thickness direction. The smaller the difference between the in-plane retardation and the thickness direction retardation, the smaller the change in retardation depending on the observation angle is because the action of birefringence according to the observation angle increases isotropy. Therefore, it is thought that it becomes difficult to generate|occur|produce the rainbow-like color unevenness according to an observation angle.

Ratio (Re/Rth) of retardation and thickness direction retardation of the polyester film of this invention becomes like this. Preferably it is 0.2 or more, More preferably, it is 0.5 or more, More preferably, it is 0.6 or more. The larger the ratio (Re/Rth) of the retardation and the thickness direction retardation, the more the birefringence action increases the isotropy, and it becomes difficult to generate a rainbow-like color irregularity according to the observation angle. And in the case of a perfect uniaxial (uniaxial symmetry) film, the ratio (Re/Rth) of the retardation and the retardation in the thickness direction becomes 2. However, as described above, the mechanical strength in the direction orthogonal to the orientation direction significantly decreases as the film approaches the perfect uniaxial (uniaxial symmetry) film.

On the other hand, the ratio (Re/Rth) of the retardation and thickness direction retardation of the polyester film of this invention becomes like this. Preferably it is 1.2 or less, More preferably, it is 1 or less. In order to completely suppress the occurrence of rainbow-like color unevenness depending on the observation angle, the ratio (Re/Rth) of the retardation and the thickness direction retardation does not need to be 2, but is sufficient if it is 1.2 or less. In addition, even if the ratio is 1.0 or less, it is sufficiently possible to satisfy the viewing angle characteristics (about 180 degrees left and right, 120 degrees up and down) required for the liquid crystal display device.

When the film forming conditions of this invention are demonstrated concretely, 80-130 degreeC is preferable and, as for the longitudinal stretching temperature and transverse stretching temperature, it is 90-120 degreeC especially preferably. As for the longitudinal draw ratio, 1.0-3.5 times are preferable, Especially preferably, it is 1.0-3.0 times. Moreover, as for the lateral draw ratio, 2.5 to 6.0 times are preferable, Especially preferably, it is 3.0 to 5.5 times. In order to control the retardation within the above range, it is preferable to control the ratio of the longitudinal stretch magnification to the lateral stretch magnification. When the difference of the draw ratio of length and breadth is too small, it becomes difficult to provide a difference in retardation, and it is unpreferable. Moreover, setting extending|stretching temperature low is also a preferable correspondence when making retardation high. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250°C, particularly preferably 180 to 245°C.

In order to suppress the fluctuation|variation of retardation, it is preferable that the thickness dispersion|variation of a film is small. Since the stretching temperature and the stretching ratio have a large influence on the thickness variation of the film, it is necessary to optimize the film forming conditions also from the viewpoint of the thickness variation. In particular, when a longitudinal draw ratio is made low in order to provide a difference in retardation, the value of vertical thickness dispersion|variation may become high. Since there is a region where the value of the vertical thickness deviation becomes very high in a certain specific range of the draw ratio, it is preferable to set the film forming conditions at a point outside this range.

The thickness variation of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and particularly preferably 3.0% or less. The thickness deviation of the film can be measured by any means, for example, a tape-shaped sample (length 3 m) continuous in the flow direction of the film is taken, and an electric micrometer (Millitron) manufactured by Seiko EM Co., Ltd. 1240), measure the thickness of 100 points at a pitch of 1 cm, obtain the maximum value (dmax), minimum value (dmin), and average value (d) of the thickness, and calculate the thickness deviation (%) by the following formula can

As described above, controlling the retardation of the film to a specific range can be performed by appropriately setting the draw ratio, the stretching temperature, and the thickness of the film. For example, it becomes easy to obtain high retardation, so that the draw ratio difference between longitudinal stretching and transverse stretching is high, extending|stretching temperature is low, and the thickness of a film is thick. Conversely, it becomes easy to obtain low retardation, so that the draw ratio difference between longitudinal stretching and transverse stretching is low, extending|stretching temperature is high, and the thickness of a film is thin. Moreover, it becomes easy to obtain the film with low ratio (Re/Rth) of retardation and thickness direction retardation, so that a total draw ratio is low, so that extending|stretching temperature is high. Conversely, it becomes easy to obtain a film with high ratio (Re/Rth) of retardation and thickness direction retardation, so that a total draw ratio is high, so that a extending|stretching temperature is low. The final film forming conditions need to be set in consideration of the physical properties required for processing in addition to retardation control.

Although the thickness of the polyester film of this invention is arbitrary, the range of 15-200 micrometers is preferable. Even for a film with a thickness of less than 15 mu m, in principle, it is possible to obtain a retardation of 3,000 nm or more. However, in that case, the anisotropy of the mechanical properties of the film becomes remarkable, it becomes easy to generate a tear, a crack, etc., and the practicality as an industrial material falls remarkably. A particularly preferred lower limit of the thickness is 25 μm. On the other hand, from a practical viewpoint as a polarizer protective film, the upper limit of thickness is 200 micrometers. When it exceeds 200 micrometers, the thickness of a polarizing plate becomes too thick, and it is unpreferable. A particularly preferable upper limit of the thickness is 100 μm, which is equivalent to that of a general TAC film. In order to control retardation within the range of this invention also in the said thickness range, polyethylene terephthalate is suitable as polyester used as a film base material.

In addition, as a method of blending the ultraviolet absorber with the polyester film in the present invention, a known method can be employed in combination. For example, a masterbatch by blending the ultraviolet absorber and polymer raw material dried in advance using a kneading extruder. can be prepared and blended by a method of mixing a predetermined masterbatch and a polymer raw material at the time of film forming. The addition weight of the ultraviolet absorber added in a film becomes like this. Preferably it is 0.3 to 1.5 %, More preferably, it is 0.4 to 1.0 %.

At this time, the concentration of the UV absorber in the masterbatch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and to mix it economically. As conditions for producing a master batch, a kneading extruder is used, and the extrusion temperature is preferably greater than or equal to the melting point of the polyester raw material and extruded at a temperature of 290° C. or less for 1 to 15 minutes. At 290°C or higher, the loss of the ultraviolet absorber is large, and the viscosity of the masterbatch is also decreased. If the residence time is less than 1 minute, uniform mixing of the ultraviolet absorber becomes difficult. At this time, you may add a stabilizer, a color tone adjuster, and an antistatic agent as needed.

In this invention, it is preferable to make a film into a multilayer structure of at least three layers or more, to add an inert particle to a surface layer, and to add a ultraviolet absorber to the intermediate|middle layer of a film. A film having a three-layer structure including inert particles in the surface layer and an ultraviolet absorber in the intermediate layer can be specifically produced as follows. For the outer layer, the masterbatch containing inert particles and polyester pellets are mixed in a predetermined ratio, and for the intermediate layer, the masterbatch containing the ultraviolet absorber and polyester pellets are mixed in a predetermined ratio and dried, followed by a known melt lamination. It is supplied to an extruder for extruding from a slit-shaped die to a sheet form, and is cooled and solidified on a casting roll to make an unstretched film. That is, by using two or more extruders, a three-layer manifold or a merging block (for example, a merging block having a square confluence), the film layers constituting both outer layers and the film layers constituting the intermediate layer are laminated, An unstretched film is made by extruding a layered sheet and cooling it with a casting roll. Further, in the present invention, in order to remove foreign substances contained in the polyester as a raw material that causes optical defects, it is preferable to perform high-precision filtration at the time of melt extrusion. The filter particle size (initial filtration efficiency 95%) of the filter medium used for high-precision filtration of molten resin is preferably 15 µm or less. When the filter particle size of the filter medium exceeds 15 µm, the removal of foreign substances of 20 µm or more tends to be insufficient.

Example

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited by the following examples, and may be implemented with appropriate modifications within the scope suitable for the spirit of the present invention, all of which are the present invention included in the technical scope of In addition, in the following examples, the evaluation method of the physical properties is as follows.

(1) Retardation (Re)

It is a parameter defined as the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|Nx-Ny|) of the orthogonal biaxial refractive index on the film and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) is obtained by the following method. The orientation axial direction of the film was calculated|required using two polarizing plates, and a 4 cm x 2 cm rectangle was cut out so that an orientation axial direction might be orthogonal to it, and it was set as the sample for a measurement. The refractive index (Nx,Ny) and the refractive index (Nz) in the thickness direction of the biaxial orthogonal to this sample were obtained by an Abbe refractometer (manufactured by Atago Corporation, NAR-4T), and the absolute value (|Nx) of the difference in refractive index of the biaxial -Ny|) was taken as the anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Lup Corporation, Miltron 1245D), and the unit was converted into nm. Retardation (Re) was calculated|required from the product (ΔNxy×d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(2) Thickness direction retardation (Rth)

It is a parameter representing the average of the retardation obtained by multiplying the film thickness d by the two birefringence ΔNxz (= | Nx-Nz |) and ΔNyz (= | Ny-Nz |) when viewed from a cross section in the film thickness direction. The thickness direction retardation (Rth) is obtained by calculating Nx, Ny, Nz and the film thickness d (nm) in the same manner as the retardation measurement, and calculating the average value of (ΔNxz × d) and (ΔNyz × d) did.

(3) Light transmittance at a wavelength of 380 nm

Using a spectrophotometer (manufactured by Hitachi, Ltd., U-3500 type), the light transmittance in the wavelength range of 300 to 500 nm of each film was measured using the air layer as a standard, and the light transmittance at a wavelength of 380 nm was determined.

(4) Observation of rainbow blotches

The polyester film of the present invention is affixed on one side of a polarizer made of PVA and iodine so that the absorption axis of the polarizing film and the main axis of orientation of the film are perpendicular, and on the opposite side, a TAC film (manufactured by Fujifilm Co., Ltd., 80 µm in thickness) to prepare a polarizing plate. A liquid crystal display device (two TAC films on the side of the liquid crystal cell and incident light) using a white LED composed of a light emitting device combining the obtained polarizing plate with a blue light emitting diode and a yttrium/aluminum/garnet-based yellow phosphor as a light source (Nicia Chemical, NSPW500CS) It has a polarizing plate used as a polarizer protective film), and it installed so that a polyester film might become a visual recognition side on the exit light side. It was visually observed from the front and the oblique direction of the polarizing plate of the liquid crystal display device, and it was determined as follows about the occurrence of rainbow_pattern|erythema.

In Comparative Example 3, a backlight light source using a cold cathode tube as a light source was used instead of the white LED.

(double-circle) : There is no generation|occurrence|production of a rainbow_pattern|erythema from any direction.

(circle): When it observes from the diagonal direction, some very light rainbow spots can be observed.

x: When it observes from the diagonal direction, a rainbow_pattern|erythema can be observed clearly.

(5) Mechanical strength

The obtained film was cut to a width of 10 mm, and in accordance with JIS-K-7127 (2000), using "Tensilon Universal Testing Machine RTA-T-4M" manufactured by Orient Co., Ltd., the initial length was 50 mm, and the tensile rate was 200 mm/min. Thus, a tensile test was performed. The tensile modulus of elasticity was obtained by dividing the difference in stress between two points on the straight line by the difference in strain between the same two points using the first straight portion of the stress-strain curve obtained by the tensile test. The measurement was carried out in a standard environment adjusted to a temperature of 23±2° C. and a relative humidity of 50±15% RH, and measurements were made in the longitudinal and transverse directions. With respect to the tensile modulus of elasticity in the longitudinal direction or the transverse direction, those having a smaller value of 5% or more were denoted as (circle) and those less than 5% were denoted by x.

(6) Thickness of outermost layer (layer containing inert particles)

The produced film was cut out perpendicular to the flow direction of the film and embedded with a photocurable resin. The embedded sample was made into ultra-thin sections with a thickness of about 70 to 100 nm with a microtome and stained for 30 minutes in ruthenium tetroxide vapor. The dyed ultrathin section was observed for cross section using a transmission electron microscope (manufactured by Nippon Electronics Co., Ltd., TEM2010), and the thickness of the outermost layer (inactive particle-containing layer) was determined from the position of the inert particles. In addition, the observation magnification was appropriately set in the range of 1,500 times to 10,000 times.

(7) Haze

According to JIS-K7105, the haze of the film was measured using a turbidimeter (NHD2000, manufactured by Nippon Denshi Kogyo).

(8) Three-dimensional surface roughness (SRa, SRz) of the surface of the outermost layer

In each Example and Comparative Example, a polarizer protective film produced without providing an application layer was prepared, and the surface of the outermost layer of the film was measured using a stylus-type three-dimensional illuminometer (SE-3AK, manufactured by Kosaka Laboratories Co., Ltd.) of the needle. Under the condition of a radius of 2 µm and a load of 30 mg, a cut-off value of 0.25 mm in the longitudinal direction of the film and a needle feeding speed of 0.1 mm/sec over a measurement length of 1 mm were measured and divided into 500 points at a 2 µm pitch, each point The height was input to the 3D roughness analysis device (SPA-11). The same operation was performed 150 times continuously at intervals of 2 µm with respect to the width direction of the film, that is, over 0.3 mm in the width direction of the film, and data was inputted into the analysis device. Next, the center plane average roughness (SRa) and the ten-point average roughness (SRz) were obtained using an analysis device.

(9) The average particle diameter of the inert particles, the number of particles of 10 μm or more

The inert particles were observed with a scanning electron microscope (manufactured by Hitachi, Ltd., S-510 type), and the magnification was appropriately changed according to the size of the particles, and the photographed ones were enlarged and copied. Then, for at least 200 or more randomly selected particles, the outer periphery of each particle was traced, and the equivalent circle diameter of the particles was measured from these traces with an image analysis device, and the average of these was taken as the average particle diameter. Further, the proportion of particles of 10 µm or more was calculated from the particle diameters of 200 or more particles thus obtained.

(10) scratch evaluation

About the obtained polyester film, the film was taken out from the film roll of width 1m and length 100m, and it was hung up vertically. At this time, 100 m of the surface layer of the film roll was removed, and the continuous 100 m was used as a sample. Next, a matte black cloth was placed on the entire surface of the back side of the film and observed from the front side to detect and mark a defect (locally shiny dot). Next, the size of the major axis was measured at the marked location using a magnifying glass with a scale (SCALE LUPE×10 manufactured by PEAK) having a magnification of 10 times. Judgment was made on the basis of the following criteria.

○ The number of optical defects of size 1 mm or larger is 0/m2

△ The number of optical defects of size 1 mm or larger is 1-3 pieces/m2

× Number of optical defects of size 1 mm or more 3/m2 or more

(Production Example 1-Polyester A)

When the temperature of the esterification reaction tube is raised to 200° C., 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol are added and stirred while stirring as a catalyst, 0.017 parts by mass of antimony trioxide, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine. parts by mass were added. Then, after pressurizing temperature rise and performing pressure esterification on the conditions of 0.34 MPa of gauge pressure and 240 degreeC, the esterification reaction tube was returned to normal pressure, and 0.014 mass parts of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and added 0.012 mass part of trimethyl phosphates. Subsequently, 15 minutes later, dispersion treatment is performed with a high-pressure disperser, and an aqueous sodium tripolyphosphate solution is further contained as sodium atoms in an amount of 0.1% by mass relative to the silica particles, and the coarse portions are cut by centrifugal separation treatment by 35%, and further, the mesh 0.2 parts by mass of an ethylene glycol slurry of silica particles having an average particle diameter of 2.3 μm and a pore volume of 1.60 ml/g, which was filtered through a metal filter having a diameter of 5 μm, was added as a particle content. After 15 minutes, the obtained esterification product was transferred to a polycondensation reaction tube, and polycondensation reaction was performed at 280°C under reduced pressure.

After completion of the polycondensation reaction, filtration is performed with a 95% cut diameter filter manufactured by Naslon of 5 µm, extruded from the nozzle into a strand shape, and cooled using cooling water that has been previously filtered (pore diameter: 1 µm or less); It was solidified and cut into pellets. The obtained polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g (hereinafter abbreviated as PET (A)).

(Preparation Example 2-Polyester B)

Meanwhile, in the production of PET (A), a polyethylene terephthalate resin (B) having an intrinsic viscosity of 0.62 dL/g containing no silica particles was obtained (hereinafter abbreviated as PET (B)).

(Production Example 3-Polyester C)

A polyethylene terephthalate resin (C) having an intrinsic viscosity of 0.62 dl/g was obtained in the same manner except for using silica particles having an average particle diameter of 2.8 μm in the production of PET (A) (hereinafter abbreviated as PET (C)). ).

(Production Example 4-Polyester D)

A polyethylene terephthalate resin (D) having an intrinsic viscosity of 0.62 dl/g was obtained in the same manner except that silica particles having an average particle diameter of 3.7 µm were used in the production of PET (A) (hereinafter abbreviated as PET (D)). ).

(Production Example 5-Polyester E)

A polyethylene terephthalate resin (E) having an intrinsic viscosity of 0.62 dl/g was obtained in the same manner except that calcium carbonate particles having an average particle diameter of 0.5 μm were used in the production of the PET (A) (hereinafter abbreviated as PET (E)). .).

(Preparation Example 6-Polyester F)

10 parts by mass of dried ultraviolet absorbent (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), particle-free PET(B) (intrinsic viscosity) 0.62 dl/g) 90 parts by mass were mixed, and a polyethylene terephthalate resin (F) containing an ultraviolet absorber was obtained using a kneading extruder (hereinafter abbreviated as PET (F)).

(Preparation Example 7-Preparation of coating liquid for easily adhesive layer formation)

Transesterification reaction and polycondensation reaction were carried out in a conventional manner, and as a dicarboxylic acid component (relative to the whole dicarboxylic acid component), 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and sodium 5-sulfonatoisophthalate 8 A water-dispersible sulfonic acid metal base-containing copolymerized polyester resin having a composition of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol (relative to the total glycol component) as a mol% and glycol component was prepared. Subsequently, 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 are mixed and stirred with heat, and when it reaches 77° C., the water-dispersible sulfonic acid metal base contains After adding 5 mass parts of copolyester resin and stirring continuously until the resin lump disappears, the resin aqueous dispersion was cooled to room temperature, and the uniform water-dispersible copolyester resin liquid with a solid content concentration of 5.0 mass % was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silicia Co., Ltd., Silicia 310) in 50 parts by mass of water, an aqueous dispersion of Silicia 310 in 99.46 parts by mass of the water-dispersible co-polyester resin solution 0.54 parts by mass was added, and 20 parts by mass of water was added while stirring to obtain an adhesive modifying coating solution.

(Example 1)

As a raw material for the intermediate layer of the base film, 90 parts by mass of PET(B) resin pellets without particles and 10 parts by mass of PET(F) resin pellets containing a UV absorber were dried under reduced pressure (1 Torr) at 135° C. for 6 hours, followed by an extruder 2 [for intermediate layer (II layer)], further mixing and adjusting PET (A) and PET (B) so that the silica particle content is 0.020 mass %, drying in a conventional manner, and extruder 1 [outer layer (I layer)] and for the outer layer (layer III)], and dissolved at 285°C. Each of these two types of polymers was filtered with a stainless steel sintered filter medium (nominal filtration precision of 10 μm, 95% of particles cut), laminated with 2 types and 3 layer merging blocks, extruded from a nozzle into a sheet shape, and then electrostatic applied casting method It was wound around a casting drum having a surface temperature of 30° C. and solidified by cooling to make an unstretched film. At this time, the discharge amount of each extruder was adjusted so that ratio of the thickness of I layer, II layer, and III layer might be set to 10:80:10.

Next, the coating liquid for forming an easily adhesive layer was applied to both surfaces of the unstretched PET film by a reverse roll method so that the application 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 guided to a hot air zone having a temperature of 125°C while gripping the end of the film with a clip, and stretched 4.0 times in the width direction.

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

(Example 2)

A uniaxially oriented PET film having a thickness of about 100 μm was obtained by changing the thickness of the unstretched film in the same manner as in Example 1 except that the silica concentration of the outer layers (I and III layers) was 400 ppm.

(Example 3)

The unstretched film produced in the same manner as in Example 1 was heated to 105° C. using a heated roll group and an infrared heater, and then stretched 1.5 times in the traveling direction with a roll group having a peripheral speed difference, followed by the same method as in Example 1 was stretched 4.0 times in the width direction to obtain a biaxially oriented PET film having a film thickness of about 50 μm.

(Example 4)

A biaxially oriented PET film having a film thickness of about 50 μm was obtained by stretching 2.0 times in the running direction and 4.0 times in the width direction in the same manner as in Example 3 except that polyester C was used instead of polyester A.

(Example 5)

The film was stretched 3.3 times in the running direction and 4.0 times in the width direction in the same manner as in Example 3 except that polyester C was used instead of polyester A and the silica concentration of the outer layers (I and III layers) was 50 ppm. A biaxially oriented PET film having a thickness of about 75 μm was obtained.

(Example 6)

In the same manner as in Example 1, a uniaxially oriented PET film having a film thickness of 50 µm was obtained without using the PET resin (B) containing the ultraviolet absorber for the intermediate layer (II layer).

(Example 7)

A biaxially-oriented PET film having a film thickness of about 250 μm was obtained by stretching 3.5 times in the running direction and 3.7 times in the width direction in the same manner as in Example 3 except that the silica concentration of the outer layers (I and III layers) was 100 ppm. Although the obtained film had Re of 4,500 nm or more, since the Re/Rth ratio was less than 0.2, very light rainbow spots in the oblique direction were confirmed.

(Example 8)

A uniaxially oriented PET film having a thickness of about 275 μm was obtained by changing the thickness of the unstretched film using the same method as in Example 1.

(Example 9)

The same test as in Example 1 was performed except that rainbow blotch observation was performed using a liquid crystal display device in which an organic light emitting diode (OLED) was a light source.

(Comparative Example 1)

In the same manner as in Example 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.

(Comparative Example 2)

A uniaxially oriented PET film having a thickness of about 10 μm was prepared by changing the thickness of the unstretched film using the same method as in Example 1 except that polyester A was not used and silica was not added to the outer layers (layers I and III). got it

(Comparative Example 3)

It carried out similarly to Example 1 except having made the light source of a liquid crystal display device into a cold cathode tube and performing rainbow_pattern|erythema observation.

(Comparative Example 4)

Except for using polyester D instead of polyester A, it was stretched 4.0 times in the running direction and 1.0 times in the width direction in the same manner as in Example 3 to obtain a uniaxially oriented PET film having a film thickness of about 100 μm.

(Comparative Example 5)

A uniaxially-oriented PET film having a film thickness of about 75 μm was obtained by stretching 1.0 times in the running direction and 3.5 times in the width direction in the same manner as in Example 1 except that polyester E was used instead of polyester A.

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

Claims (3)

A liquid crystal display device having a liquid crystal cell disposed between a backlight light source and two polarizing plates, the liquid crystal display device comprising:
A polarizing plate disposed on the incident light side with respect to the liquid crystal cell,
A polarizer protective film having a polyester film is a polarizing plate laminated on a polarizer,
The polyester film has an in-plane retardation of 8,000 nm or more and less than 10,000 nm, and a ratio (Re/Rth) of in-plane retardation and thickness-direction retardation of 0.2 or more and 1.2 or less, and the average roughness of the center plane of the surface of the outermost layer (SRa) ) is 0.008 to 0.02 μm, and the ten-point average roughness (SRz) is 0.3 to 1.5 μm.
liquid crystal display. According to claim 1,
A liquid crystal display device having a ratio (Re/Rth) of in-plane retardation to thickness-direction retardation of the polyester film of 0.5 or more and 1.2 or less. 3. The method of claim 1 or 2,
A liquid crystal display in which a TAC film, an acrylic film, or a norbornene-based film is laminated on the opposite side of the polarizer to the side on which the polarizer protective film having the polyester film is laminated.