WO2014171386A1

WO2014171386A1 - Liquid-crystal display, polarizing plate, and polarizer-protecting film

Info

Publication number: WO2014171386A1
Application number: PCT/JP2014/060377
Authority: WO
Inventors: 芳紀斎宮; 林原　幹也
Original assignee: 東洋紡株式会社
Priority date: 2013-04-19
Filing date: 2014-04-10
Publication date: 2014-10-23
Also published as: CN105143967A; JP6586727B2; TWI557447B; KR102505572B1; KR20210095974A; CN105143967B; TW201441679A; KR20150143590A; JP2020073951A; JPWO2014171386A1; KR102285068B1; JP6658954B1

Abstract

To provide the following: a polarizer-protecting film and polarizing plate that make it possible to further reduce the thickness of a liquid-crystal display while maintaining good visibility; and such a liquid-crystal display. A liquid-crystal display that has a backlight light source, two polarizing plates, and liquid-crystal cells laid out between said polarizing plates. The backlight light source is a white light source that has a continuous emission spectrum. Each of the polarizing plates has a structure wherein a polarizer-protecting film is laminated to each side of a polarizer, with at least one of said polarizer-protecting films being a polyester film with the following properties: (a) a retardation (Re) between 3,000 and 30,000 nm, inclusive; (b) a ratio (Re/Rth) between retardation (Re) and thickness-direction retardation (Rth) of at least 1.0; and (c) a degree of planar orientation (ΔP) of at most 0.12.

Description

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. More specifically, the present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film that have good visibility and are suitable for thinning.

Liquid crystal display devices are widely used in mobile phones, tablet terminals, personal computers, televisions, PDAs, electronic dictionaries, car navigation systems, music players, digital cameras, digital video cameras, and the like. As liquid crystal display devices become smaller and lighter, their use is no longer limited to offices and indoors, but is also being used outdoors and while moving by car or train.

Patent Document 1 discloses that a polyester film having a retardation of 3000 to 30000 nm is protected by a polarizer for the purpose of suppressing deterioration in image quality caused by rainbow spots or the like that may occur depending on the viewing angle when the liquid crystal display device is viewed. Use as a film is disclosed.

WO2011 / 162198

However, in the market, liquid crystal display devices are required to be thinner, and by simply controlling the retardation to 3000 to 30000 nm, the deterioration of visibility due to the occurrence of rainbow spots can be eliminated, but the thickness of the film is reduced. When the thickness is reduced, the mechanical strength is remarkably lowered, so that it is difficult to meet the demand for thickness reduction. Therefore, the present invention provides a polarizer protective film, a polarizing plate, and a liquid crystal display device in which the liquid crystal display device is realized that enables further thinning of the liquid crystal display device while maintaining good visibility. One purpose.

The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems. By controlling the degree of surface orientation of the polyester film to a certain level or less, the retardation value is maintained at 3000 or more and 30000 or less, and good visual recognition is achieved. The present inventors have found that it is possible to increase the mechanical strength of the film and reduce the thickness of the film while maintaining the properties. Based on such knowledge, the inventors have further studied and improved, and have completed the present invention.

The representative present invention is as follows.
Item 1.
A backlight light source, two polarizing plates, a liquid crystal cell disposed between the two polarizing plates, the backlight light source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
At least one of the polarizer protective films has the following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
It is a polyester film that satisfies
Liquid crystal display device.
Item 2.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
2. The liquid crystal display device according to item 1, wherein
Item 3. The liquid crystal display device according to item 1 or 2, wherein the polyester film is a polarizer protective film constituting a polarizing plate located closer to the viewing side than the liquid crystal cell.
Item 4.
Item 4. The liquid crystal display device according to any one of Items 1 to 3, wherein the polyester film has a thickness of 20 μm to 90 μm.
Item 5.
Item 5. The liquid crystal display device according to any one of Items 1 to 4, wherein the polyester film has a tear strength of 50 mN or more.
Item 6.
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
The polarizing plate which has the structure where the polyester film which satisfy | fills was laminated | stacked on the at least 1 surface of the polarizer.
Item 7.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
Item 7. The polarizing plate according to Item 6, wherein
Item 8.
Item 8. The polarizing plate according to Item 6 or 7, wherein the polyester film has a thickness of 20 μm or more and 90 μm or less.
Item 9.
Item 9. The polarizing plate according to any one of Items 6 to 8, wherein the polyester film has a tear strength of 50 mN or more.
Item 10.
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
A polarizer protective film, which is a polyester film satisfying the requirements.
Item 11.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
Item 11. The polarizer protective film according to Item 10, wherein
Item 12.
Item 12. The polarizer protective film according to Item 10 or 11, wherein the polyester film has a thickness of 20 μm or more and 90 μm or less.
Item 13.
Item 13. The polarizer protective film according to any one of Items 10 to 12, wherein the polyester film has a tear strength of 50 mN or more.
Item 14.
Including a step of simultaneously stretching the polyester film while performing relaxation treatment on the direction orthogonal to the stretching direction,
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
The manufacturing method of the polarizer protective film which is a polyester film which satisfy | fills.
Item 15.
Item 10. The polarizing plate according to any one of Items 6 to 9, which is for a liquid crystal display device having a white light source having a continuous emission spectrum.
Item 16.
Item 14. The polarizer protective film according to any one of Items 10 to 13, which is for a liquid crystal display device having a white light source having a continuous emission spectrum.
Item 17.
Item 15. The method according to Item 14, wherein the polarizer protective film is for a liquid crystal display device having a white light source having a continuous emission spectrum.

The polarizer protective film of the present invention is suitable for thinning because it is excellent in mechanical strength (tear strength). In addition, the polarizer protective film of the present invention and the polarizing plate laminated with the polarizer film can be produced by producing a liquid crystal display device using the same, and when the image is viewed, rainbow spots can occur depending on the angle at which the image is viewed. Can be suppressed. Therefore, according to the present invention, it is possible to provide a liquid crystal display device that is excellent in visibility and thinner. In this document, “rainbow spot” is a concept including “color spot”, “color shift”, and “interference color”.

It is a schematic diagram of an observation angle ((theta)).

The liquid crystal display device includes a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. In this document, the side where the backlight light source of the liquid crystal display device is located is referred to as the “light source side” with respect to the side where the person views the image, and the side where the person views the image is referred to as the “viewing side”. The arrangement order of the constituent members of the liquid crystal display device is usually from a light source side to a viewing side, a backlight source, a polarizing plate (also referred to as “light source side polarizing plate”), a liquid crystal cell, and a polarizing plate (“viewing side”). Also referred to as “polarizing plate”.

The backlight light source is preferably a white light source having a continuous and broad emission spectrum from the viewpoint of suppressing the occurrence of rainbow spots when an image is visually recognized. “Continuous and broad emission spectrum” means an emission spectrum in which there is no wavelength region where the light intensity is zero in the wavelength region of at least 450 to 650 nm, preferably in the visible light region. The visible light region is, for example, a wavelength region of 400 to 760 nm, and may be 360 to 760 nm, 400 to 830 nm, or 360 to 830 nm.

Any white light source can be used as long as the method and structure of the white light source having a continuous and broad emission spectrum are not particularly limited and the generation of rainbow spots can be suppressed, but the preferred light source is a white light emitting diode. (LED). White LEDs include phosphor-type LEDs (that is, elements that emit white light by combining phosphors with light emitting diodes that emit blue light or ultraviolet light using compound semiconductors) and organic light-emitting diodes (Organic light-emitting diodes). : OLED) and the like. In one embodiment, the preferred white LED is a phosphor-type white LED, more preferably a white LED comprising a light emitting element in which a blue light emitting diode using a compound semiconductor and a yttrium, aluminum, garnet yellow phosphor are combined. It is.
As the liquid crystal cell, any liquid crystal cell that can be used in a liquid crystal display device can be appropriately selected and used, and the method and structure thereof are not particularly limited. For example, a liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be appropriately selected and used. Therefore, the liquid crystal cell can be used by appropriately selecting a known liquid crystal material and a liquid crystal made of a liquid crystal material that can be developed in the future. In one embodiment, a preferred liquid crystal cell is a transmissive liquid crystal cell.

The polarizing plate has a structure in which both sides of a film-like polarizer are sandwiched between two protective films (also referred to as “polarizer protective film”). As the polarizer, any polarizer (or polarizing film) used in the technical field can be appropriately selected and used. Representative polarizers include those obtained by dyeing a dichroic material such as iodine on a polyvinyl alcohol (PVA) film or the like, but are not limited to this, and are known and will be developed in the future. A polarizer to be obtained can be appropriately selected and used.

Commercially available products can be used as the PVA film used as the polarizer. For example, “Kuraray Vinylon (manufactured by Kuraray Co., Ltd.)”, “Tosero Vinylon (manufactured by Toh Cello Co., Ltd.)”, “Nichigo Vinylon (Nihon Gosei) Chemical Co., Ltd.) etc. Examples of dichroic materials include iodine, diazo compounds, and polymethine dyes.

The liquid crystal display device usually includes two polarizing plates, and the polarizing plate is usually composed of two polarizers and a polarizer protective film laminated on both sides thereof. A sheet of polarizer protective film may be included. In the present invention, at least one of the four polarizer protective films is preferably a polyester film satisfying the following physical properties (a) to (c).
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less
(B) Ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) being 1.0 or more
(C) Plane orientation degree (ΔP) of 0.12 or less

It is preferable that the retardation of the polyester film used as a polarizer protective film is 3000 nm or more and 30000 nm or less from a viewpoint of reducing iridescence. The lower limit of retardation is preferably 4500 nm or more, more preferably 5000 nm or more, further preferably 6000 nm or more, still more preferably 8000 nm or more, and still more preferably 10,000 nm or more. On the other hand, the upper limit of the retardation is substantially not improved even if the retardation is further increased, and the thickness of the oriented film tends to increase depending on the height of the retardation. From the viewpoint that it may be contrary to the demand for thinning, the thickness is set to 30000 nm, but it can be set to a higher value. In this document, when simply described as “retardation”, it means in-plane retardation.

Retardation is represented by the product of birefringence (ΔNxy) caused by light incident on the film surface (xy plane) and thickness (d). Therefore, higher retardation is obtained as the value of ΔNxy increases. On the other hand, since the retardation becomes relatively smaller as the film becomes thinner, it is desirable that the value of ΔNxy is larger in order to maintain the retardation value above a certain level while reducing the thickness. However, if the value of ΔNxy is excessively increased, the tear strength of the film tends to decrease. Therefore, the value of ΔNxy of the polyester film is preferably 0.1 or more and less than 0.3. More specifically, in the case of a polyethylene terephthalate film, the value of ΔNxy is preferably 0.1 or more and 0.16 or less, more preferably 0.105 or more and 0.15 or less, and further preferably 0.11 or more and 0.145 or less. It is. In the case of a polyethylene naphthalate film, the value of ΔNxy is preferably less than 0.3, more preferably less than 0.27, still more preferably less than 0.25, and still more preferably less than 0.24. On the other hand, if the birefringence index ΔNxy is low, it is necessary to increase the film thickness in order to increase the retardation. Therefore, in the case of a polyethylene naphthalate film, the birefringence index ΔNxy is preferably 0.15 or more, more preferably It is 0.16 or more, more preferably 0.17 or more, still more preferably 0.18 or more, and particularly preferably 0.20 or more.

The retardation value of the polyester film changes depending on the observation angle. Here, the observation angle means a deviation (θ) between the direction perpendicular to the plane of the polyester film (zero degree) and the direction in which the observer views the polyester film (FIG. 1). The larger the observation angle, the lower the retardation value at that angle. For this reason, even when rainbow spots are not observed when viewed from the front (that is, in the vertical direction) of the display device, rainbow spots may be observed when observed from an oblique direction. Therefore, in order to ensure good visibility even when the display device is observed from an oblique direction, it is preferable to consider a decrease in retardation due to an increase in observation angle. In particular, in the case of a polyester film having a small thickness, since the retardation is relatively low, the influence on the visibility due to a decrease in retardation accompanying an increase in observation angle is relatively large. The ratio (Re / Rth) of the retardation (Re) and the thickness direction retardation (Rth) of the polyester film is used as an index representing the degree of retardation reduction accompanying the increase in the observation angle. It is considered that as the Re / Rth increases, the birefringence action becomes more isotropic, and the degree of retardation decrease due to the increase in the observation angle becomes smaller, so that rainbow spots due to the observation angle are less likely to occur. From such a viewpoint, Re / Rth is preferably 1.0 or more, more preferably 1.1 or more, still more preferably 1.2 or more, still more preferably 1.25 or more, and still more preferably 1. 3 or more. Thickness direction retardation means an average value of retardation obtained by multiplying two birefringences ΔNxz and ΔNyz, respectively, when viewed from a cross section in the film thickness direction, with the film thickness (d).

The maximum value of the Re / Rth ratio is 2.0 (that is, a complete uniaxial symmetry film), but the machine is in a direction orthogonal to the orientation main axis direction as it approaches 1.0 and a complete uniaxial symmetry film. In such a case, it is preferable to adjust the degree of plane orientation described below to be a specific numerical value or less. The Re / Rth ratio is preferably as high as possible from the viewpoint of thin film formation and improved viewing angle characteristics, but the upper limit is not required up to the maximum value of 2.0, preferably 1.9 or less, more preferably 1.8. It is as follows. *

The retardation of the oriented film can be measured according to a known method. Specifically, it can be determined by measuring the refractive index and thickness in the biaxial direction. It can also be determined using a commercially available automatic birefringence measuring apparatus (for example, KOBRA-21ADH: manufactured by Oji Scientific Instruments). In any measurement, the measurement wavelength is 589 nm which is the wavelength of the sodium D line.

The film thickness is made thinner while satisfying the retardation and Re / Rth ratio for suppressing rainbow spots and maintaining the mechanical strength (tear strength) that can withstand the production of industrial liquid crystal display devices. From the viewpoint, the degree of plane orientation (ΔP) is preferably 0.12 or less. The degree of plane orientation is the difference between the average value of the refractive index (Nx) in the longitudinal direction and the refractive index (Ny) in the width direction of the film and the value of the refractive index (Nz) in the thickness direction. Can be represented: ΔP = ((Nx + Ny) / 2) −Nz.

The upper limit of the degree of plane orientation is more preferably 0.11 or less, still more preferably 0.102 or less, still more preferably 0.1 or less, still more preferably 0.098 or less, and much more. Preferably it is 0.095 or less, More preferably, it is 0.09 or less. On the other hand, the lower limit of the degree of plane orientation is preferably 0.04 or more, more preferably 0.05 or more, and still more preferably 0.06 or more.

When the degree of plane orientation is less than 0.04, the mechanical strength of the film is too low, which is not preferable in terms of workability. In addition, when the degree of plane orientation exceeds 0.12, it is difficult to achieve both retardation and mechanical strength under the thin film condition, and any one of the problems may occur.

The thickness (d) of the polyester film used as the polarizer protective film is not particularly limited, but is preferably 300 μm or less from the viewpoint of providing a thinner polarizer protective film, a polarizing plate, and a liquid crystal display device. Is not more than 100 μm, more preferably not more than 90 μm, still more preferably not more than 80 μm, still more preferably not more than 60 μm, still more preferably not more than 50 μm, still more preferably not more than 45 μm, particularly preferably not more than 40 μm, most preferably not more than 35 μm. It is as follows. The lower limit of the thickness of the polyester film is 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more, and further preferably 25 μm or more, from the viewpoint that it is difficult to maintain sufficient tear strength.

The polyester film used as the polarizer protective film preferably has a mechanical strength that can withstand handling in the production of an industrial liquid crystal display device even when the thickness is small. From this viewpoint, the polyester film preferably has a tear strength of 50 mN or more. Preferably, the tear strength is 100 mN or more, more preferably 130 mN or more. The tear strength of the film can be measured according to the method of JIS P-8116 as shown in the examples described later.

The polyester film used as the polarizer protective film preferably has heat resistance that can withstand handling of an industrial liquid crystal display device. From this viewpoint, the polyester film preferably has a heat shrinkage of −5.0% to 5.0%, more preferably −3.0% to 3.0%, and still more preferably − 2.0% to 2.0%. The heat shrinkage rate of the film can be measured according to the method of JIS C-2318 as shown in the examples described later.

For the purpose of suppressing deterioration of optical functional dyes such as iodine dyes, it is desirable that the polyester film used as the polarizer protective film 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 this document, the transmittance is measured in a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type). Further, for example, 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, antigelling agents, interfaces An activator or the like can be added within a range that does not impair the effects of the present invention and does not impair the transparency.

A polyester film satisfying the above physical properties can be obtained by controlling stretching conditions and the like in general polyester film production conditions. A polyester film is generally produced by the following procedure. That is, the polyester resin is melted, and the non-oriented polyester extruded and formed into a sheet shape is stretched in the machine direction at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. Obtained by heat treatment. Stretching in the machine direction and the transverse direction can be performed separately for each direction, and by extending the clip width while guiding the tenter and changing the speed of the roll to stretch the machine direction and the transverse direction simultaneously. is there.

In order to obtain a polyester film satisfying the above-described physical properties, it is preferable to perform simple uniaxial stretching, and it is more preferable to perform relaxation (relaxation) treatment in a direction perpendicular to the stretching direction simultaneously with stretching in any direction. More specifically, an equipment generally called a simultaneous biaxial stretching machine is used, and the heat treatment is performed after the longitudinal stretching and the transverse relaxation treatment, or the transverse stretching and the longitudinal relaxation treatment. A method can be exemplified. The order of stretching and relaxation treatment is preferably performed at the same time, but it may be performed in the order of relaxing after stretching or stretching after relaxing. A more preferable method is a method in which the stretching in the transverse direction and the relaxation treatment in the longitudinal direction are simultaneously performed. Although it is possible to relax during the heat treatment, it should be noted that heat wrinkles occur when the relaxation rate increases.

It is also possible to manufacture using a sequential biaxial stretching machine. In that case, when relaxing in the longitudinal direction, the roll after stretching is slower than the roll before stretching while being heated by an external heater or the like, and then relaxed in the longitudinal direction and then guided to the tenter and stretched in the lateral direction. Can be implemented. Moreover, when relaxing in the lateral direction, it can be carried out by gradually narrowing the lateral clip width while heating in the tenter after performing longitudinal stretching by the method used in normal biaxial stretching. When a sequential biaxial stretching machine is used, the direction of uniaxial stretching is preferably stretching in the transverse direction. Although the film can be stretched in the machine direction, there are problems such as the occurrence of minute flaws on the film surface and the occurrence of stretching unevenness during the longitudinal stretching, and attention should be paid. Furthermore, using the same principle as described above, the uniaxially stretched film can be subjected to a relaxation treatment with any one of a simultaneous biaxial stretching machine, a tenter, and a roll.

The film forming conditions (particularly stretching conditions) of the polyester film will be described more specifically. The stretching temperature is preferably from 80 to 130 ° C, particularly preferably from 90 to 120 ° C. The draw ratio is preferably 0.4 to 6 times, particularly preferably 0.6 to 5 times. It is preferable to set the stretching ratio in the direction perpendicular to the relaxing direction to 3 to 6 times so that the stretching ratio in the relaxing direction is 0.4 to 0.97 times. Furthermore, it is more preferable that one direction is relaxed by 0.6 to 0.9 times and the film is stretched by 3.5 to 5.5 times in the direction perpendicular thereto.

The magnification in the direction of relaxation and the direction of stretching can be arbitrarily set as long as it is within the above range, but uniaxiality increases as the stretching ratio increases, so that the degree of relaxation can be increased. preferable. On the other hand, when the draw ratio is lowered, if the effect is greatly relaxed, the effect of wrinkles cannot be ignored. Therefore, it is preferable to lower the relaxation rate.

In order to control the retardation within the above range, 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 increase the retardation, which is not preferable. Moreover, if the magnification in the relaxing direction is too low, generation of wrinkles cannot be avoided, which is not preferable. Furthermore, if the magnification in the extending direction is too high, breakage tends to occur, which is not preferable. Setting the stretching temperature low is also a preferable measure for increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably from 100 to 250 ° C., particularly preferably from 180 to 245 ° C.

The fluctuation of retardation on the film is preferably small, and in order to suppress the fluctuation, it is preferable to control the thickness variation of the film. Since the stretching temperature and the stretching ratio greatly affect the thickness variation of the film, it is preferable to optimize the film forming conditions from the viewpoint of suppressing the thickness variation. In particular, if the longitudinal stretching ratio is lowered to increase the retardation, the longitudinal thickness unevenness may be deteriorated. Since the vertical thickness unevenness may deteriorate in a specific range of the draw ratio, it is desirable to set the film forming conditions outside such a range.

From the above viewpoint, the thickness unevenness of the polyester 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 is particularly preferable.

In order to control the retardation of the polyester 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.

The polyester resin for obtaining a polyester film satisfying the above physical properties can be any polyester resin used in the field. That is, it can be obtained by condensing an arbitrary dicarboxylic acid and a diol. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and diphenylcarboxylic acid. Acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalate Acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, Dimer , It may be mentioned sebacic acid, suberic acid, dodecamethylene dicarboxylic acid.

Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4 -Butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone and the like.

The dicarboxylic acid component and the diol component constituting the polyester film may each be used alone or in combination of two or more. Specific polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc., preferably polyethylene terephthalate and polyethylene naphthalate, preferably polyethylene terephthalate. . The polyester resin may contain other copolymer components. From the viewpoint of mechanical strength, the proportion of the copolymer components is preferably 3 mol% or less, preferably 2 mol% or less, more preferably 1.5 mol% or less. .

The polyester film satisfying the above physical properties can be used as an arbitrary polarizer protective film among the four polarizer protective films used in the liquid crystal display device. Preferably, the polyester film is used as a light source side polarizer protective film constituting the light source side polarizing plate and / or a visual recognition side polarizer protective film constituting the visual recognition side polarizing plate. More preferably, the said polyester film is a polarizer protective film arrange | positioned at the visual recognition side of the visual recognition side polarizing plate.

Any film conventionally used as a polarizer protective film can be used as a polarizer protective film that does not use a polyester film that satisfies the above physical properties. Preferably, it is preferable to use a film having no retardation, such as a TAC film, an acrylic film, and a norbornene resin film. The film without retardation can be used as, for example, a viewing-side polarizer protective film constituting the light source-side polarizing plate and / or a light source-side polarizer protecting film constituting the viewing-side polarizing plate.

The polarizing plate composed of the polarizer and the polarizer protective film described above has various functional layers (for example, a hard coat layer) on the surface for the purpose of preventing reflection, suppressing glare, and / or suppressing scratches. May be.

The polarizer protective film preferably has an easy-adhesion layer mainly composed of at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin on at least one surface in order to improve the adhesion with the polarizer. . 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 liquid for the easy-adhesion layer formed on the polarizer protective film is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. These coating liquids are water-soluble or water-dispersible as disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, and the like. Examples thereof include a copolymerized polyester resin solution, an acrylic resin solution, and a polyurethane resin solution.

The easy adhesion layer formed on the polarizer protective film is a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, It can apply | coat by well-known methods, such as these individually or in combination.

Examples of the functional layer laminated at an arbitrary position on the viewing side of the polarizer protective film include, for example, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, an antistatic layer, and silicone. One or more selected from the group consisting of a layer, an adhesive layer, an antifouling layer, a water repellent layer, a blue cut layer, and the like can be used.

When providing various functional layers, it is preferable to have an easy-adhesion layer on the surface of the polarizer protective film. At this time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so that it is close to the geometric mean of the refractive index of the functional layer and the refractive index of the basic film. The refractive index of the easy-adhesion layer can be adjusted by a known method. For example, the refractive index of the easy-adhesion layer can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

(Hard coat layer)
The hard coat layer only needs to be a layer having hardness and transparency. Usually, various curable properties such as an ionizing radiation curable resin typically cured by ultraviolet rays or an electron beam, and a thermosetting resin cured by heat. What was formed as a cured resin layer of resin is used. In order to appropriately add flexibility and other physical properties to these curable resins, thermoplastic resins and the like may be added as appropriate. Among the curable resins, ionizing radiation curable resins are preferable because they are representative and an excellent hard coating film can be obtained.

As the ionizing radiation curable resin, a conventionally known resin may be appropriately employed. As the ionizing radiation curable resin, a radical polymerizable compound having an ethylenic double bond, a cationic polymerizable compound such as an epoxy compound, and the like are typically used. These compounds include monomers, oligomers, prepolymers, and the like. These can be used alone or in appropriate combination of two or more. Typical compounds are various (meth) acrylate compounds that are radical polymerizable compounds. Among the (meth) acrylate compounds, compounds used at a relatively low molecular weight include, for example, polyester (meth) acrylate, polyether (meth) acrylate, acrylic (meth) acrylate, epoxy (meth) acrylate, urethane (meth) ) Acrylate, etc.

Examples of the monomer include monofunctional monomers such as ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methylstyrene, and N-vinylpyrrolidone; or, for example, trimethylolpropane tri (meth) acrylate, tripropylene glycol diester (Meth) acrylate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, etc. These polyfunctional monomers are also used as appropriate. (Meth) acrylate means acrylate or methacrylate.

When the ionizing radiation curable resin is cured with an electron beam, a photopolymerization initiator is not required, but when it is cured with ultraviolet rays, a known photopolymerization initiator is used. For example, in the case of a radical polymerization system, acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether, or the like can be used alone or in combination as a photopolymerization initiator. In the case of a cationic polymerization system, an aromatic diazonium salt, aromatic sulfonium salt, aromatic iodonium salt, metatheron compound, benzoin sulfonate, or the like can be used alone or in combination as a photopolymerization initiator.

The thickness of the hard coat layer may be an appropriate thickness, for example, 0.1 to 100 μm, but usually 1 to 30 μm. The hard coat layer can be formed by appropriately adopting various known coating methods.

In the ionizing radiation curable resin, a thermoplastic resin, a thermosetting resin, or the like can be appropriately added for the purpose of adjusting physical properties as appropriate. Examples of the thermoplastic resin or thermosetting resin include an acrylic resin, a urethane resin, and a polyester resin, respectively.

In order to impart light resistance to the hard coat layer and prevent discoloration, strength deterioration, cracking, and the like due to ultraviolet rays contained in sunlight, it is also preferable to add an ultraviolet absorber in the ionizing radiation curable resin. When an ultraviolet absorber is added, the ionizing radiation curable resin is preferably cured with an electron beam in order to reliably prevent the ultraviolet coater from inhibiting the curing of the hard coat layer. Examples of the ultraviolet absorber include organic ultraviolet absorbers such as benzotriazole compounds and benzophenone compounds, or inorganic ultraviolet absorbers such as fine particles of zinc oxide, titanium oxide, and cerium oxide having a particle size of 0.2 μm or less, What is necessary is just to select and use from well-known things. The addition amount of the ultraviolet absorber is about 0.01 to 5% by mass in the ionizing radiation curable resin composition. In order to further improve the light resistance, it is preferable to add a radical scavenger such as a hindered amine radical scavenger in combination with an ultraviolet absorber. The electron beam irradiation has an acceleration voltage of 70 kV to 1 MV and an irradiation dose of about 5 to 100 kGy (0.5 to 10 Mrad).

(Anti-glare layer)
It is one of the preferred embodiments that an antiglare layer is provided on the most visible side of the image display device. As the antiglare layer, a conventionally known layer may be appropriately employed, and it is generally formed as a layer in which an antiglare agent is dispersed in a resin. As the antiglare agent, inorganic or organic fine particles are used. These fine particles have a spherical shape, an elliptical shape, or the like. The fine particles are preferably transparent. Examples of such fine particles include silica beads as inorganic fine particles and resin beads as organic fine particles. Examples of the resin beads include styrene beads, melamine beads, acrylic beads, acrylic-styrene beads, polycarbonate beads, polyethylene beads, and benzoguanamine-formaldehyde beads. The fine particles can be usually added in an amount of about 2 to 30 parts by mass, preferably about 10 to 25 parts by mass with respect to 100 parts by mass of the resin.

The resin for dispersing and holding the antiglare agent is preferably as hard as possible as in the hard coat layer. Therefore, as the resin, for example, a curable resin such as an ionizing radiation curable resin or a thermosetting resin described in the hard coat layer can be used.

The thickness of the antiglare layer may be an appropriate thickness, and is usually about 1 to 20 μm. The antiglare layer can be formed by appropriately adopting various known coating methods. In addition, it is preferable to add well-known anti-settling agents such as silica to the coating liquid for forming the anti-glare layer in order to prevent precipitation of the anti-glare agent.

(Antireflection layer)
It is also one of preferable modes that an antireflection layer is provided on the outermost surface side of the image display device and the interface of each film with air. As the antireflection layer, a conventionally known layer may be appropriately employed. In general, the antireflection layer is composed of at least a low refractive index layer, and a low refractive index layer and a high refractive index layer (having a higher refractive index than the low refractive index layer) are alternately stacked adjacent to each other and the surface side has a low refractive index. It consists of multiple layers as the rate layer. Each thickness of the low refractive index layer and the high refractive index layer may be appropriately determined according to the application, and is about 0.1 μm when adjacent layers are stacked, and about 0.1 to 1 μm when the low refractive index layer alone is used. It is preferable.

As a low refractive index layer, a layer containing a low refractive index material such as silica or magnesium fluoride in a resin, a layer of a low refractive index resin such as a fluorine-based resin, or a low refractive index material in a low refractive index resin A thin film formed by a thin film forming method (for example, physical or chemical vapor deposition such as vapor deposition, sputtering, CVD, or the like), an oxidation layer, or a layer made of a low refractive index material such as silica or magnesium fluoride. Examples thereof include a film formed by a sol-gel method in which a silicon oxide gel film is formed from a silicon sol solution, or a layer in which void-containing fine particles are contained in a resin as a low refractive index substance.

The void-containing fine particles are fine particles containing gas inside, fine particles having a porous structure containing gas, etc., and with respect to the original refractive index of the fine particle solid portion, It means fine particles whose refractive index is apparently lowered. Examples of such void-containing fine particles include silica fine particles disclosed in JP-A No. 2001-233611. Examples of the void-containing fine particles include hollow polymer fine particles disclosed in JP-A No. 2002-805031, in addition to inorganic substances such as silica. The particle diameter of the void-containing fine particles is, for example, about 5 to 300 nm.

As the high refractive index layer, a layer containing a high refractive index material such as titanium oxide, zirconium oxide or zinc oxide in a resin, a layer of a high refractive index resin such as a fluorine-free resin, or a high refractive index material is highly refracted. A layer formed of a high-refractive-index material such as titanium oxide, zirconium oxide, or zinc oxide in a thin film forming method (for example, vapor deposition, sputtering, CVD, etc., physical or chemical vapor deposition) Method).

(Anti-fouling layer)
As the antifouling layer, a conventionally known layer may be appropriately employed. Generally, in the resin, a silicon compound such as silicone oil or silicone resin; a fluorine compound such as fluorine surfactant or fluorine resin. It can be formed by a known coating method using a paint containing a stain-proofing agent such as wax. The thickness of the antifouling layer may be set appropriately, and can usually be about 1 to 10 μm.

(Antistatic layer)
As the antistatic layer, a conventionally known layer may be appropriately employed, and it is generally formed as a layer containing an antistatic layer in a resin. As the antistatic layer, an organic or inorganic compound is used. For example, the antistatic layer of an organic compound includes a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, a nonionic antistatic agent, an organometallic antistatic agent, and the like. The inhibitor is used not only as a low molecular compound but also as a high molecular compound. As the antistatic agent, conductive polymers such as polythiophene and polyaniline are also used. Further, as the antistatic agent, for example, conductive fine particles made of a metal oxide are used. The particle diameter of the conductive fine particles is, for example, about 0.1 nm to 0.1 μm in average particle diameter in terms of transparency. Examples of the metal oxide include ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , ITO (indium doped tin oxide), In ₂ O ₃ , Al ₂ O ₃ , ATO (antimony doped tin oxide), AZO (aluminum doped zinc oxide) etc. are mentioned.

Examples of the resin containing the antistatic layer include curable resins such as ionizing radiation curable resins and thermosetting resins as described in the hard coat layer. When the layer is formed as a layer and the surface strength of the antistatic layer itself is unnecessary, a thermoplastic resin or the like is also used. The thickness of the antistatic layer may be set appropriately, and is usually about 0.01 to 5 μm. The antistatic layer can be formed by appropriately adopting various known coating methods.

The liquid crystal display device of the present invention includes the above-described backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, but may optionally further include other members. . For example, a color filter, a lens film, a diffusion sheet, an antireflection film, and the like may be further provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and can be appropriately modified within a scope that fits the gist of the present invention. They are all included in the technical scope of the present invention.

The physical property measurement methods employed in the examples are shown below.
(1) Thickness (d)
The thickness (d) was determined in accordance with JIS K 7130 “Plastic Film and Sheet Thickness Measurement Method (Method A)”.

(2) Refractive index (Nx, Ny, Nz)
Based on JIS K 7142 “Plastic Refractive Index Measurement Method (Method A)”, MD refractive index (Nx), TD refractive index (Ny), and thickness direction refractive index (Nz) were determined. It was measured using a sodium D line with a normal wavelength of 589 nm.

(3) Birefringence (ΔNxy) and retardation (Re)
Retardation is the direction of each axis when the thickness direction is the z-axis with respect to the film surface, and the two axis directions perpendicular to the z-axis and perpendicular to each other are the x-axis and the y-axis. Is a phase difference represented by the product of birefringence caused by the refractive index (Nx, Ny, Nz) and the film thickness d. Here, the product of birefringence (ΔNxy) and thickness (d) generated by light incident on the film surface (xy plane), where the vertical direction (MD) is the x-axis and the width direction (TD) is the y-axis. The in-plane retardation which is is defined as retardation (Re). Accordingly, the birefringence (Δxy) and retardation (Re) were determined by the following formulas for each. Each refractive index was measured using an Abbe refractometer. The unit of retardation is nm.

ΔNxy = | Nx−Ny |
Re = ΔNxy × d

(4) Thickness direction retardation (Rth)
Thickness direction retardation indicates retardation generated by light incident from the thickness direction. Here, the product of the average of the two birefringences in the xz plane and the yz plane and the film thickness (d) was obtained from the following equation. The unit is nm.

Rth = (| Nx−Nz | + | Ny−Nz |) / 2 × d

(5) Degree of plane orientation (ΔP)
Using the values of the refractive index (Nx) in the longitudinal direction, the refractive index (Ny) in the width direction, and the refractive index (Nz) in the thickness direction of the film, the degree of plane orientation (ΔP) was calculated according to the following formula.

ΔP = ((Nx + Ny) / 2) −Nz

(6) Iridescent observation On one side of a commercially available polarizer film, the film of each example and comparative example described later is perpendicular to the absorption axis of the polarizer and the orientation axis of the film (the higher of Nx and Ny). A polarizing plate was prepared by attaching a commercially available TAC film to the opposite surface. Next, two polarizing plates having a white LED as a backlight and two TAC films as a polarizer protective film and a polarizing plate on the viewing side of a commercially available liquid crystal display device having a liquid crystal cell are removed, The polarizing plate produced as described above was replaced. Under the present circumstances, the said polarizing plate was installed so that the polarizer protective film at the side of visual recognition of the produced polarizing plate might turn into a film of an Example or a comparative example. A white image was displayed on the liquid crystal display device thus fabricated, and visual observation was performed from the front of the display and from an oblique direction, and the occurrence of rainbow spots was determined as follows. The observation angle is an angle formed by a line drawn in the normal direction (vertical) from the center of the display screen and a line connecting the display center and the eye position at the time of observation. A: No occurrence of rainbow spots from any direction B: No generation of rainbow spots when the observation angle is in the range of 0 ° to 55 °. A very thin rainbow is observed in part in the range where the observation angle exceeds 55 °. X: Iridescents are observed when the observation angle is in the range of 0 ° to 55 °.

(7) Tear Strength The tear strength of each film was measured according to JIS P-8116 using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho. The tearing direction was performed so as to be parallel to the orientation main axis direction of the film, and evaluated according to the following criteria. The measurement in the orientation main axis direction was performed with a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments).

○: Tear strength is 50 mN or more ×: Tear strength is less than 50 mN

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

(9) Thermal contraction rate at 150 ° C. The dimensional change rate (%) in the longitudinal direction and the width direction was measured in accordance with JIS C2318-19975.3.4 (dimensional change). With respect to the direction to be measured, the film was cut into a width of 10 mm and a length of 250 mm, marked at intervals of 200 mm, and the distance (A) between the marks was measured under a constant tension of 5 gf. The film was then placed in an oven at 150 ° C. and heat-treated at 150 ± 3 ° C. for 30 minutes under no load, and the mark interval (B) was measured under a constant tension of 5 gf. Using these measured values, the heat shrinkage rate was obtained from the following equation.
Thermal shrinkage (%) = (AB) / A × 100

(Production Example 1—Polyester resin 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. Subsequently, the pressure was raised and the esterification reaction was performed under the conditions of a gauge pressure of 0.34 MPa and 240 ° C., and then the esterification reaction vessel 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 resin had an intrinsic viscosity of 0.62 dl / g and contained substantially no inert particles and internally precipitated particles. Hereinafter, the polyethylene terephthalate resin thus obtained is abbreviated as PET (A).

(Production Example 2-Polyester resin 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 0.62 dl / g) was mixed with 90 parts by mass, and a kneading extruder was used to obtain a resin containing an ultraviolet absorber, and the polyethylene terephthalate resin thus obtained is abbreviated as PET (B).

(Production Example 3-Adjustment of Adhesive Modification Coating Solution)
Using a transesterification reaction and a polycondensation reaction in a conventional manner, the dicarboxylic acid component (based on the total dicarboxylic acid component) is 46 mol% terephthalic acid, 46 mol% isophthalic acid and 8 mol% sodium 5-sulfonatoisophthalate. A water-dispersible sulfonic acid metal group-containing copolymer polyester resin having a composition of 50 mol% ethylene glycol and 50 mol% neopentyl glycol 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, and 0.06 parts by mass of a nonionic surfactant were mixed. Then, the mixture was heated and stirred, and when the temperature reached 77 ° C., 5 parts by mass of the water-dispersible sulfonic acid metal base-containing copolymer polyester resin was added, and stirring was continued until the resin no longer solidified. Thereafter, the resin water dispersion was cooled to room temperature to obtain a uniform water dispersible copolyester resin liquid having a solid concentration of 5.0% by mass. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (Silicia 310, manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 99.46 parts by mass of the water-dispersible copolyester resin solution was mixed with 99.46 parts by mass of the silicia 310. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added with stirring to obtain an adhesive modified coating solution.

(Example 1)
90 parts by mass of PET (A) resin pellets containing no particles as a raw material for a base film intermediate layer having a three-layer structure and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber were dried under reduced pressure at 135 ° C. for 6 hours. (1 Torr), and then supplied to the extruder 2 (for the intermediate layer II layer). Moreover, PET (A) was dried by a conventional method, supplied to the extruder 1 (for the outer layer I layer and outer layer III), and melted 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 ratio of the thicknesses of the I layer, the II layer, and the III layer was 10:80:10.

Next, the above-mentioned adhesive property-modified coating solution was applied on both sides of this unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g / m ^2, and then dried at 80 ° C. for 20 seconds. did.

The unstretched film on which this coating layer is formed is guided to a simultaneous biaxial stretching machine, and the end of the film is held by a clip while being guided to a hot air zone at a temperature of 90 ° C. so that the magnification is 0.8 times in the vertical direction. It was relaxed and simultaneously stretched 4.0 times in the transverse direction. Next, it was treated at a temperature of 170 ° C. for 30 seconds and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

(Example 2)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 58 μm and relaxed at a magnification of 0.9 times in the longitudinal direction.

(Example 3)
By changing the thickness of the unstretched film, the thickness was about 38 μm, the thickness was relaxed at a magnification of 0.7 times, and the heat treatment was performed at a temperature of 180 ° C. for 30 seconds, as in Example 1. A uniaxially oriented PET film was obtained.

Example 4
By changing the thickness of the unstretched film, the thickness was about 25 μm, the transverse stretch ratio was 5.0 times, and uniaxial in the same manner as in Example 1 except that the heat treatment was performed at a temperature of 180 ° C. for 30 seconds. An oriented PET film was obtained.

(Example 5)
By changing the thickness of the unstretched film, the thickness was about 80 μm, relaxed at a magnification of 0.85 times in the longitudinal direction, the stretching temperature was 95 ° C., and heat treatment was performed at a temperature of 180 ° C. for 30 seconds. A uniaxially oriented PET film was obtained in the same manner as Example 1 except for the above.

(Example 6)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 38 μm and relaxed at a magnification of 0.6 times in the longitudinal direction.

(Comparative Example 1)
The unstretched film produced by the same method as in Example 1 was guided to a tenter stretching machine, and the end of the film was guided with a clip while being guided to a hot air zone at a temperature of 125 ° C., and stretched 4.0 times in the width direction. . Next, while maintaining the width stretched in the width direction, the film was treated at a temperature of 225 ° C. for 30 seconds and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 25 μm.

(Comparative Example 2)
In the same manner as in Example 1, the film was stretched 3.4 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 3)
In the same manner as in Comparative Example 1, the film was stretched 4.0 times in the running direction and 1.0 times in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 100 μm. Due to the uniaxially stretched film, minute scratches were observed on the film surface.

(Comparative Example 4)
A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 38 μm and the longitudinal relaxation treatment was not performed.

(Comparative Example 5)
A uniaxially oriented PET film was obtained in the same manner as in Example 3 except that the thickness of the unstretched film was changed to about 38 μm and the longitudinal relaxation treatment was not performed.

(Comparative Example 6)
A uniaxially oriented PET film was obtained in the same manner as in Example 4 except that the thickness of the unstretched film was changed to about 25 μm and the longitudinal relaxation treatment was not performed.

The results of evaluating the films of the above Examples and Comparative Examples are shown in Table 1 below.

As described above, when the films of Examples 1 to 6 were used as a polarizer protective film, it was confirmed that the generation of rainbow spots was significantly suppressed and a liquid crystal display device having excellent visibility was obtained. Further, the films of Examples 1 to 6 not only make it possible to provide an image display device with excellent visibility, but also have a sufficient tear strength despite being relatively thin, It has been confirmed that it is suitable for use in the manufacture of typical image display devices. On the other hand, when the films of Comparative Examples 1, 2, and 6 were used as polarizer protective films, rainbow spots were produced when observed from the front, and good visibility could not be obtained. In addition, the film of Comparative Example 3 has no problem in visibility when used as a polarizer protective film, but is not suitable for the production of an industrial and stable liquid crystal display device because of insufficient tear strength. Not found out. This is considered to be because the film of Comparative Example 3 has a relatively high Re value and Re / Rth ratio but a high ΔP value. In the films of Comparative Examples 4 and 5, the generation of rainbow spots was not observed when the observation angle was observed in the range of 0 ° to 55 °, but it was extremely thin in part in the range where the observation angle exceeded 55 °. Iridae was observed. This is presumably because the films of Comparative Examples 4 and 5 have a relatively high Re but a low Re / Rth ratio. In Comparative Example 6, the tear strength was insufficient due to the high ΔP value.

By using the liquid crystal display device, the polarizing plate and the polarizer protective film of the present invention, it is possible to provide a thin liquid crystal display device with excellent visibility. Therefore, the industrial applicability of the present invention is extremely high.

DESCRIPTION OF SYMBOLS 1 Polyester film 2 Line | wire which shows the orthogonal | vertical direction with respect to the surface of a polyester film 3 Line | wire which connects the position of an observer's eye and film surface (center) 4 Position of an observer's eye

Claims

A backlight light source, two polarizing plates, a liquid crystal cell disposed between the two polarizing plates, the backlight light source is a white light source having a continuous emission spectrum;
The polarizing plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer,
At least one of the polarizer protective films has the following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
It is a polyester film that satisfies
Liquid crystal display device.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
The liquid crystal display device according to claim 1, wherein
The liquid crystal display device of Claim 1 or 2 whose said polyester film is a polarizer protective film which comprises the polarizing plate located in the visual recognition side rather than the said liquid crystal cell.
The liquid crystal display device according to claim 1, wherein the polyester film has a thickness of 20 袖 m to 90 袖 m.
The liquid crystal display device according to any one of claims 1 to 4, wherein the tear strength of the polyester film is 50 mN or more.
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
The polarizing plate which has the structure where the polyester film which satisfy | fills was laminated | stacked on the at least 1 surface of the polarizer.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
The polarizing plate of Claim 6 which satisfy | fills.
The polarizing plate of Claim 6 or 7 whose thickness of the said polyester film is 20 micrometers or more and 90 micrometers or less.
The polarizing plate according to any one of claims 6 to 8, wherein the tear strength of the polyester film is 50 mN or more.
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
A polarizer protective film, which is a polyester film satisfying the requirements.
The polyester film has the following physical properties (d):
(D) Birefringence index (ΔNxy) of 0.1 or more
The polarizer protective film of Claim 10 which satisfy | fills.
The polarizer protective film according to claim 10 or 11 whose thickness of said polyester film is 20 micrometers or more and 90 micrometers or less.
The polarizer protective film according to any one of claims 10 to 12, wherein the tear strength of the polyester film is 50 mN or more.
Including a step of simultaneously stretching the polyester film while performing relaxation treatment on the direction orthogonal to the stretching direction,
The following physical properties (a) to (c):
(A) Retardation (Re) which is 3000 nm or more and 30000 nm or less;
(B) ratio (Re / Rth) of retardation (Re) and thickness direction retardation (Rth) which is 1.0 or more; and (c) degree of plane orientation (ΔP) which is 0.12 or less;
The manufacturing method of the polarizer protective film which is a polyester film which satisfy | fills.