JP6658954B1 - Liquid crystal display, polarizing plate and polarizer protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer protective film, a polarizing plate, and a liquid crystal display device having the same, which enables further thinning of a liquid crystal display device while maintaining good visibility. A backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, wherein the backlight light source is a white light source having a continuous emission spectrum, The plate has a structure in which a polarizer protective film is laminated on both sides of a polarizer, and at least one of the polarizer protective films has the following physical properties (a) to (c): (a) 3000 nm or more. Retardation (Re) of 30,000 nm or less; (b) Ratio (Re / Rth) of retardation (Re) of 1.0 or more and thickness direction retardation (Rth); and (c) surface of 0.12 or less. A liquid crystal display device, which is a polyester film satisfying an orientation degree (ΔP). [Selection diagram] None

Description

  The present invention relates to a liquid crystal display, 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 having good visibility and 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 the size and weight of liquid crystal display devices have been reduced, their use is no longer limited to offices and indoors, and their use has been expanding both outdoors and while traveling by car or train.

  Patent Document 1 discloses a method of protecting a polyester film having a retardation of 3000 to 30000 nm with a polarizer for the purpose of suppressing a decrease in image quality due to a rainbow spot or the like that may occur depending on a viewing angle when viewing a liquid crystal display device. It is disclosed for use as a film.

WO2011 / 162198

  However, in the market, there is a demand for an even thinner liquid crystal display device. 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. If the thickness is reduced, the mechanical strength is remarkably reduced, and it has been difficult to respond to a demand for a reduction in the thickness. Therefore, the present invention provides a polarizer protective film, a polarizing plate, and a liquid crystal display device in which the same is realized, which enables further reduction in the thickness of the liquid crystal display device while maintaining good visibility. One purpose.

  The present inventors have conducted intensive studies in order to solve the above-mentioned problems. As a result, by controlling the degree of plane orientation of the polyester film to be equal to or less than a certain value, the retardation value was maintained at 3,000 or more and 30,000 or less. It has been found that it is possible to increase the mechanical strength of the film and to reduce the thickness of the film while maintaining the properties. Based on such knowledge, the present inventors have conducted further studies and improvements, and have completed the present invention.

A typical 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) a retardation (Re) of 3000 nm or more and 30000 nm or less;
(B) the ratio (Re / Rth) between the retardation (Re) of 1.0 or more and the retardation in the thickness direction (Rth); and (c) the degree of plane orientation (ΔP) of 0.12 or less;
Is a polyester film that satisfies
Liquid crystal display.
Item 2.
The polyester film has the following physical properties (d):
(D) Birefringence (ΔNxy) of 0.1 or more
Item 2. The liquid crystal display device according to item 1, which satisfies item 3.
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 on the viewing side of the liquid crystal cell.
Item 4.
Item 4. The liquid crystal display device according to any one of Items 1 to 3, wherein a thickness of the polyester film is 20 μm or more and 90 μm or less.
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) a retardation (Re) of 3000 nm or more and 30000 nm or less;
(B) the ratio (Re / Rth) between the retardation (Re) of 1.0 or more and the retardation in the thickness direction (Rth); and (c) the degree of plane orientation (ΔP) of 0.12 or less;
A polarizing plate having a structure in which a polyester film satisfying the above is laminated on at least one surface of the polarizer.
Item 7.
The polyester film has the following physical properties (d):
(D) Birefringence (ΔNxy) of 0.1 or more
Item 7. The polarizing plate according to Item 6, which satisfies the following.
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 10. 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) a retardation (Re) of 3000 nm or more and 30000 nm or less;
(B) the ratio (Re / Rth) between the retardation (Re) of 1.0 or more and the retardation in the thickness direction (Rth); and (c) the degree of plane orientation (ΔP) of 0.12 or less;
A polarizer protective film that is a polyester film that satisfies the following.
Item 11.
The polyester film has the following physical properties (d):
(D) Birefringence (ΔNxy) of 0.1 or more
Item 11. The polarizer protective film according to item 10, which satisfies the following.
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.
The polyester film includes a step of simultaneously stretching while performing relaxation treatment in a direction perpendicular to the stretching direction,
The following physical properties (a) to (c):
(A) a retardation (Re) of 3000 nm or more and 30000 nm or less;
(B) the ratio (Re / Rth) between the retardation (Re) of 1.0 or more and the retardation in the thickness direction (Rth); and (c) the degree of plane orientation (ΔP) of 0.12 or less;
A method for producing a polarizer protective film, which is a polyester film satisfying the following.
Item 15.
Item 10. The polarizing plate according to any one of Items 6 to 9, which is used 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 used 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.

  Since the polarizer protective film of the present invention has excellent mechanical strength (tear strength), it is suitable for thinning. Further, the polarizer protective film of the present invention and the polarizing plate obtained by laminating the polarizer protective film can be used to produce a liquid crystal display device. Can be suppressed. Therefore, according to the present invention, it is possible to provide a thinner liquid crystal display device having excellent visibility. In this document, the term “rainbow spot” is a concept including “color spot”, “color shift”, and “interference color”.

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

  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 of the liquid crystal display device where the backlight light source 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 components of the liquid crystal display device is generally such that, from the light source side to the viewing side, a backlight light source, a polarizing plate (also referred to as a “light source side polarizing plate”), a liquid crystal cell, and a polarizing plate (“viewing side”). Polarizing plate ").

  The backlight light source is preferably a white light source having a continuous and wide 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 light intensity becomes zero in a wavelength region of at least 450 to 650 nm, preferably in a 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.

The method and structure of the white light source having a continuous and wide emission spectrum is not particularly limited, and any white light source can be used as long as the occurrence of rainbow spots can be suppressed. (LED). Examples of the white LED include a phosphor type (that is, an element that emits white light by combining a light emitting diode that emits blue light or ultraviolet light using a compound semiconductor and a phosphor) and an organic light emitting diode (Organic light-emitting diode). : OLED) and the like. In one embodiment, a preferred white LED is a phosphor-based white LED, and 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-based 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 system and structure are not particularly limited. For example, a liquid crystal cell of 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, for the liquid crystal cell, a liquid crystal made of a known liquid crystal material and a liquid crystal material that can be developed in the future can be appropriately selected and used. 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-shaped polarizer are sandwiched between two protective films (also referred to as “polarizer protective films”). 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 thereto, and are known and will be developed in the future. The polarizer to be obtained can be appropriately selected and used.

  As the PVA film used as the polarizer, commercially available products can be used. For example, “Kuraray Vinylon (manufactured by Kuraray Co., Ltd.)”, “Tocellovinylon (manufactured by Tosero Co., Ltd.)”, “Nichigo Vinylon (Nihon Gosei) And dichroic materials include iodine, diazo compounds, and polymethine dyes.

A liquid crystal display device usually includes two polarizing plates, and the polarizing plate is generally composed of two polarizers and a polarizer protective film laminated on both sides thereof. One polarizer protective film may be included. In the 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) of 3000 nm or more and 30000 nm or less
(B) Ratio (Re / Rth) of retardation (Re) of 1.0 or more to retardation in the thickness direction (Rth)
(C) Plane orientation degree (ΔP) of 0.12 or less

 The retardation of the polyester film used as the polarizer protective film is preferably from 3,000 nm to 30,000 nm from the viewpoint of reducing iridescence. The lower limit of the retardation is preferably 4500 nm or more, more preferably 5000 nm or more, still more preferably 6000 nm or more, even more preferably 8000 nm or more, and further preferably 10,000 nm or more. On the other hand, the upper limit of the retardation, even if the retardation is further increased, further improvement effect of visibility is not substantially obtained, and the thickness of the oriented film tends to increase depending on the height of the retardation. The thickness is set to 30,000 nm from the viewpoint that it may be against the demand for thinning, but it can be set to a higher value. In this document, when simply referred to as “retardation”, it means in-plane retardation.

  The retardation is represented by the product of the birefringence (ΔNxy) generated by light incident on the film surface (xy plane) and the thickness (d). Therefore, a higher retardation is obtained as the value of ΔNxy increases. On the other hand, the smaller the thickness of the film, the smaller the retardation. Therefore, in order to maintain a certain or more retardation value while reducing the thickness, it is desirable that the value of ΔNxy is large. However, if the value of ΔNxy is too large, 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 even more 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, further preferably less than 0.25, and still more preferably less than 0.24. On the other hand, if the birefringence 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 ΔNxy is preferably 0.15 or more, more preferably It is 0.16 or more, further 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 as a reference (zero degree) and the direction in which the observer views the polyester film (FIG. 1). As the observation angle increases, the value of the retardation at that angle decreases. Therefore, even when no iris is observed when viewed from the front of the display device (that is, in the vertical direction), an iris may be observed when viewed 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 the observation angle. In particular, in the case of a polyester film having a small thickness, the retardation is relatively low, and thus, the visibility is relatively largely affected by the decrease in the retardation as the observation angle increases. The ratio (Re / Rth) between the retardation (Re) of the polyester film and the retardation in the thickness direction (Rth) is used as an index indicating the degree of reduction of the retardation as the observation angle increases. It is considered that the larger the value of Re / Rth is, the more the effect of birefringence is isotropic, and the degree of retardation decrease due to the increase of the observation angle is small, 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, further preferably 1.2 or more, further preferably 1.25 or more, and still more preferably 1. 3 or more. The retardation in the thickness direction means an average value of retardation obtained by multiplying two birefringences △ Nxz and そ れ ぞ れ Nyz by the film thickness (d) when viewed from a cross section in the film thickness direction.

  The maximum value of the Re / Rth ratio is 2.0 (that is, a completely uniaxially symmetric film), but the machine direction in the direction orthogonal to the orientation principal axis direction exceeds 1.0 and approaches a completely uniaxially symmetric film. In some cases, the target strength is reduced. In such a case, it is preferable to adjust the degree of plane orientation described below to a specific value or less. The Re / Rth ratio is preferably higher from the viewpoint of thinning and improvement of viewing angle characteristics, but the upper limit is not required to be 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 technique. Specifically, it can be determined by measuring the refractive index and the thickness in the biaxial directions. In addition, it can also be determined using a commercially available automatic birefringence measurement device (for example, KOBRA-21ADH: manufactured by Oji Scientific Instruments). In each measurement, the measurement is performed at a wavelength of 589 nm, which is the wavelength of the sodium D line.

  It is intended to reduce the thickness of the film while satisfying the retardation and Re / Rth ratio for suppressing rainbow spots, and maintaining the mechanical strength (tearing strength) that can withstand industrial liquid crystal display device production. From the viewpoint, the degree of plane orientation (ΔP) is preferably 0.12 or less. The degree of plane orientation is a 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. It can be represented: ΔP = ((Nx + Ny) / 2) −Nz.

  The upper limit of the degree of plane orientation is more preferably 0.11 or less, further preferably 0.102 or less, still more preferably 0.1 or less, and still more preferably 0.098 or less. Preferably it is 0.095 or less, and still more preferably 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.

  If the degree of plane orientation is less than 0.04, the mechanical strength of the film is too low, which is not preferred in terms of processability and the like. On the other hand, when the degree of plane orientation exceeds 0.12, it is difficult to achieve both the retardation and the mechanical strength under thin film conditions, and one of them may cause a problem, which is not preferable.

  The thickness (d) of the polyester film used as the polarizer protective film is not particularly limited, but is preferably 300 μm or less, and more preferably from the viewpoint of providing thinner polarizer protective films, polarizing plates, and liquid crystal display devices. Is 100 μm or less, further preferably 90 μm or less, still more preferably 80 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, even more preferably 45 μm or less, particularly preferably 40 μm or less, and most preferably 35 μm or less. 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 still more preferably 25 μm or more, from the viewpoint that it is difficult to maintain sufficient tear strength.

  It is preferable that the polyester film used as the polarizer protective film retains mechanical strength enough to withstand handling in industrial production of a liquid crystal display device even if the thickness is small. In this respect, the polyester film preferably has a tear strength of 50 mN or more. Preferably, the tear strength is at least 100 mN, more preferably at least 130 mN. The tear strength of the film can be measured according to the method of JIS P-8116, as shown in Examples described later.

  The polyester film used as the polarizer protective film preferably has heat resistance enough to withstand industrial liquid crystal display device handling. In this respect, 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 of the film can be measured according to the method of JIS C-2318, as shown in Examples described later.

  For the purpose of suppressing deterioration of an optical functional dye such as an iodine dye, a polyester film used as a polarizer protective film desirably has a light transmittance at a wavelength of 380 nm of 20% or less. The light transmittance at 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optical functional dye due to ultraviolet rays can be suppressed. In this document, the transmittance is measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500). Further, for example, inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, gelling agents, interfaces An activator or the like can be added as long as the effect of the present invention is not hindered and transparency is not impaired.

  A polyester film satisfying the above physical properties can be obtained by controlling the stretching conditions and the like in general polyester film production conditions. A polyester film is generally manufactured 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 longitudinal direction using a speed difference between the rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter. Obtained by performing heat treatment. Stretching in the vertical and horizontal directions is performed separately for each direction, and the method of simultaneously stretching in the vertical and horizontal directions by changing the roll speed while expanding the clip width after guiding to the tenter is available. is there.

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

  It is also possible to produce using a sequential biaxial stretching machine. In that case, when relaxing in the vertical direction, the roll after stretching is made slower than the roll before stretching by heating with an external heater or the like, so that it is relaxed in the vertical direction and then guided to the tenter and stretched in the horizontal direction. Can be carried out. In addition, in the case of relaxing in the horizontal direction, after performing longitudinal stretching by a method used in ordinary biaxial stretching, the width of the clip in the horizontal direction can be gradually reduced while heating in a tenter. When a sequential biaxial stretching machine is used, the uniaxial stretching is preferably performed in a transverse direction. Although stretching in the longitudinal direction is possible, there is a problem that minute scratches are likely to occur on the film surface during stretching in the longitudinal direction and stretching unevenness is likely to occur. Furthermore, using the same principle as described above, the uniaxially stretched film may be subjected to a relaxation treatment by using any 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 stretching ratio is preferably from 0.4 to 6 times, particularly preferably from 0.6 to 5 times. It is preferable that the stretching ratio in the relaxing direction is set to 0.4 to 0.97 times, and the stretching ratio in the direction perpendicular to the relaxing direction is 3 to 6 times. Further, 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 a direction perpendicular thereto.

  Regarding the magnification in the direction of relaxation and the direction of stretching, it can be arbitrarily set as long as it is within the above range, but the higher the stretching ratio, the higher the uniaxiality, so the degree of relaxation can be increased. preferable. On the other hand, when the stretching ratio is reduced, the effect of the wrinkles cannot be ignored if the ratio is largely relaxed. Therefore, it is preferable to reduce the relaxation ratio.

  In order to control the retardation within the above range, it is preferable to control the ratio between the longitudinal stretching ratio and the transverse stretching ratio. If the difference between the longitudinal and transverse stretching ratios is too small, it is difficult to increase the retardation, which is not preferable. On the other hand, if the magnification in the relaxing direction is too low, generation of wrinkles and the like cannot be avoided, which is not preferable. Further, if the magnification in the stretching 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 250C, particularly preferably from 180 to 245C.

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

  In light of the above, the unevenness in thickness 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 to a specific range, the retardation can be controlled by appropriately setting a stretching ratio, a stretching temperature, and a film thickness. For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the easier it is to obtain high retardation. Conversely, the lower the draw ratio, the higher the draw temperature, and the thinner the film, the easier it is to obtain low retardation. However, when the thickness of the film is increased, the phase difference in the thickness direction tends to increase. Therefore, it is desirable that the film thickness is appropriately set in the range described below. Further, in addition to controlling the retardation, it is necessary to set final film forming conditions in consideration of physical properties and the like required for processing.

  The polyester resin for obtaining a polyester film satisfying the above physical properties may be any polyester resin used in the art. 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, diphenoxyethane dicarboxylic acid, diphenyl sulfone carboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid 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, and 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 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 and the like, preferably polyethylene terephthalate and polyethylene naphthalate, and preferably polyethylene terephthalate. . The polyester resin may contain another copolymer component. From the viewpoint of mechanical strength, the proportion of the copolymer component 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 a light source side polarizing plate and / or a viewing side polarizer protecting film constituting a viewing side polarizing plate. More preferably, the polyester film is a polarizer protective film disposed on the viewing side of the viewing side polarizing plate.

  Any film conventionally used as a polarizer protective film can be used as the polarizer protective film not using a polyester film satisfying the above physical properties. Preferably, a film without retardation, such as a TAC film, an acrylic film, or a norbornene-based resin film, is preferably used. The film without retardation can be used, for example, as a viewing-side polarizer protective film constituting a light source-side polarizing plate and / or a light source-side polarizer protecting film constituting a 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, on at least one side, a polyester resin, a polyurethane resin, or an easy-adhesion layer containing at least one kind of polyacrylic resin as a main component, in order to improve the adhesiveness 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 a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating solutions include water-soluble or water-dispersible compounds disclosed in Japanese Patent Nos. 3,567,927, 3,589,232, 3,589,233, 3,900,191 and 4,150,982. 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 includes a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brushing method, a spray coating method, an air knife coating method, a wire bar coating method, a pipe doctor method, A known method such as the above method can be applied alone or in combination.

  Examples of the functional layer to be laminated at any 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 a silicone. One or more selected from the group consisting of a layer, an adhesive layer, an antifouling layer, a water-repellent layer, and a blue cut layer 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 that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so as to be near the geometric mean of the refractive index of the functional layer and the refractive index of the basic film. A known method can be used to adjust the refractive index of the easy-adhesion layer. For example, the refractive index can be easily adjusted by adding titanium, zirconium, or other metal species to the binder resin.

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

  As the ionizing radiation-curable resin, a conventionally known resin may be appropriately used. In addition, 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, and these compounds include monomers, oligomers, prepolymers, and the like. May be used alone or in combination of two or more. Representative compounds are various (meth) acrylate compounds that are radically polymerizable compounds. Among the (meth) acrylate-based compounds, compounds used at a relatively low molecular weight include, for example, polyester (meth) acrylate, polyether (meth) acrylate, acryl (meth) acrylate, epoxy (meth) acrylate, urethane (meth) A) acrylate, and the like.

  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 diacrylate. (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. Is 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 unnecessary, but when it is cured with an ultraviolet ray, a known photopolymerization initiator is used. For example, in the case of a radical polymerization system, acetophenones, benzophenones, thioxanthones, benzoin, benzoin methyl ether and 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, an aromatic sulfonium salt, an aromatic iodonium salt, a metatheron compound, a benzoin sulfonic acid ester, 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 is usually 1 to 30 μm. Further, the hard coat layer can be formed by appropriately employing various known coating methods.

  To the ionizing radiation-curable resin, a thermoplastic resin, a thermosetting resin, or the like can be appropriately added for the purpose of appropriately adjusting physical properties. Examples of the thermoplastic resin or thermosetting resin include, for example, acrylic resin, urethane resin, polyester resin, and the like.

  In order to impart light resistance to the hard coat layer and prevent discoloration, strength deterioration, crack generation, and the like due to ultraviolet light contained in sunlight or the like, it is also preferable to add an ultraviolet absorber to 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 hardening of the hard coat layer from being inhibited by the ultraviolet absorber. As the ultraviolet absorber, an organic ultraviolet absorber such as a benzotriazole-based compound and a benzophenone-based compound, or an inorganic ultraviolet absorber such as zinc oxide, titanium oxide, and cerium oxide having a particle diameter of 0.2 μm or less, What is necessary is just to select and use from well-known things. The amount of the ultraviolet absorber added 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 preferred embodiments that an antiglare layer is provided on the most visible side of the image display device. As the anti-glare layer, a conventionally known anti-glare layer may be appropriately employed, and is generally formed as a layer in which an anti-glare agent is dispersed in a resin. As the antiglare agent, inorganic or organic fine particles are used. The shape of these fine particles is a true sphere, an ellipse, 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, acryl-styrene beads, polycarbonate beads, polyethylene beads, and benzoguanamine-formaldehyde beads. Fine particles can be added usually in an amount of 2 to 30 parts by mass, preferably about 10 to 25 parts by mass, per 100 parts by mass of the resin component.

  It is preferable that the resin that disperses and holds the antiglare agent has as high a hardness as possible, like the hard coat layer. Therefore, as the resin, for example, a curable resin such as the ionizing radiation curable resin and the 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 employing various known coating methods. It is preferable that a known anti-settling agent such as silica is appropriately added to the coating liquid for forming the anti-glare layer in order to prevent precipitation of the anti-glare agent.

(Anti-reflective layer)
It is also a preferable embodiment that an antireflection layer is provided on the outermost surface side of the image display device, at the interface between each film and air. As the antireflection layer, a conventionally known one may be appropriately adopted. 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 laminated adjacently and the surface side has a low refractive index. It is composed of multiple layers as a rate layer. The thickness of each 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 adjacently laminated, and about 0.1 to 1 μm when the low refractive index layer is used alone. Is preferred.

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

  The above-mentioned void-containing fine particles are fine particles containing a gas therein, fine particles having a porous structure containing a gas, and the like. It means fine particles having apparently reduced refractive index. Examples of such void-containing fine particles include silica fine particles disclosed in JP-A-2001-233611. Examples of the void-containing fine particles include, in addition to inorganic materials such as silica, hollow polymer fine particles disclosed in JP-A-2002-85031 and the like. The particle size 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, and zinc oxide in a resin, a layer of a high refractive index resin such as a resin containing no fluorine, and a high refractive index of a high refractive index material Layer formed of a high refractive index material such as titanium oxide, zirconium oxide, zinc oxide, etc., into a thin film by a thin film forming method (for example, physical or chemical vapor deposition such as vapor deposition, sputtering, CVD, etc.) And the like).

(Antifouling layer)
As the antifouling layer, conventionally known ones may be appropriately adopted, and generally, in the resin, a silicon-based compound such as silicone oil or silicone resin; a fluorine-based compound such as a fluorine-based surfactant or a fluorine-based 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 appropriately set, and usually about 1 to 10 μm.

(Antistatic layer)
As the antistatic layer, a conventionally known antistatic layer may be appropriately employed, and 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, examples of the antistatic layer of an organic compound include a cationic antistatic agent, an anionic antistatic agent, an amphoteric antistatic agent, a nonionic antistatic agent, and an organometallic antistatic agent. The inhibitor is used as a low molecular compound and also as a high molecular compound. In addition, conductive polymers such as polythiophene and polyaniline are also used as the antistatic agent. Further, as the antistatic agent, for example, conductive fine particles made of a metal oxide or the like are used. The particle diameter of the conductive fine particles is, for example, about 0.1 nm to 0.1 μm in terms of transparency. Note that, as the metal oxide, for example, 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) and the like can be mentioned.

  As the resin to contain the antistatic layer, for example, as described in the hard coat layer, a curable resin such as an ionizing radiation curable resin and a thermosetting resin is used. When 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 appropriately set, and is usually about 0.01 to 5 μm. The antistatic layer can be formed by appropriately employing 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 further include another member arbitrarily. . 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 more specifically with reference to examples. However, the present invention is not limited to the following examples, and can be appropriately changed within a range that conforms to the purpose of the present invention. And they are all included in the technical scope of the present invention.

Hereinafter, methods for measuring physical properties adopted in the examples will be described.
(1) Thickness (d)
The thickness (d) was determined according to JIS K 7130 “Method for measuring thickness of plastic film and sheet (method A)”.

(2) Refractive index (Nx, Ny, Nz)
The refractive index of MD (Nx), the refractive index of TD (Ny), and the refractive index in the thickness direction (Nz) were determined based on JIS K7142 “Method of measuring the refractive index of plastic (Method A)”. It was usually measured using a sodium D line having a wavelength of 589 nm.

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

ΔNxy = | Nx−Ny |
Re = ΔNxy × d

(4) Thickness direction retardation (Rth)
Thickness direction retardation indicates retardation caused by light incident from the thickness direction. Here, the product of the average of two birefringence indices on 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) Plane orientation (ΔP)
Using the values of the refractive index (Nx), 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 equation.

  ΔP = ((Nx + Ny) / 2) −Nz

(6) Observation of rainbow spots On one surface of a commercially available polarizer film, the films of Examples and Comparative Examples to be described later were arranged such that the absorption axis of the polarizer and the main orientation axis of the film (the higher of Nx and Ny) were perpendicular to each other. And a commercially available TAC film was pasted on the opposite side to produce a polarizing plate. Next, two polarizing plates having a white LED as a backlight and two TAC films as polarizer protective films, and a polarizing plate on a viewing side of a commercially available liquid crystal display device having a liquid crystal cell were removed. The polarizing plate manufactured as described above was replaced. At this time, the polarizing plate was installed such that the polarizer protective film on the viewing side of the manufactured polarizing plate was the film of the example or the comparative example. A white image was displayed on the liquid crystal display device thus manufactured, 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. Note that the observation angle is an angle formed by a line drawn in the normal direction (vertical) from the center of the screen of the display, and a line connecting the center of the display and the position of the eye during observation. ：: No rainbow spots are generated from any direction. ：: No rainbow spots are generated when the observation angle is in the range of 0 ° to 55 °. In the range where the observation angle exceeds 55 °, an extremely thin iris is partially observed. ×: Iridescence is observed when the observation angle is in the range of 0 ° to 55 °.

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

：: tear strength of 50 mN or more ×: tear strength of less than 50 mN

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

(9) Heat Shrinkage Rate at 150 ° C. The dimensional change rate (%) in the longitudinal direction and the width direction was measured in accordance with JISC2318-19975.3.4 (dimensional change). The film was cut into a width of 10 mm and a length of 250 mm in the direction to be measured, marked at intervals of 200 mm, and measured under a constant tension of 5 gf to measure the interval (A) between the marks. Next, the film was placed in an oven in an atmosphere of 150 ° C. and heat-treated at 150 ± 3 ° C. for 30 minutes under no load, and then the mark interval (B) was measured under a constant tension of 5 gf. Using these measured values, the heat shrinkage was determined from the following equation.
Heat shrinkage (%) = (AB) / A × 100

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

  After completion of the polycondensation reaction, the mixture is filtered with a NASLON filter having a 95% cut diameter of 5 μm, extruded into a strand form 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 intrinsic viscosity of the obtained resin was 0.62 dl / g, and substantially no inert particles or internally precipitated particles were contained. Hereinafter, the polyethylene terephthalate resin thus obtained is abbreviated as PET (A).

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

(Production Example 3-Preparation of Adhesion Modification Coating Solution)
Utilizing a transesterification reaction and a polycondensation reaction by a conventional method, 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol% of sodium 5-sulfonatoisophthalate as the dicarboxylic acid component (based on the whole dicarboxylic acid component) A water-dispersible sulfonic acid metal base-containing copolymerized polyester resin having a composition of ethylene glycol 50 mol% and neopentyl glycol 50 mol% (based on the whole glycol component) as a 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 salt group-containing copolymerized polyester resin was added thereto, and the mixture was continuously stirred until the resin did not solidify. Thereafter, the aqueous resin dispersion was cooled to room temperature to obtain a uniform aqueous dispersible copolymerized polyester resin liquid having a solid content of 5.0% by mass. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia K.K., Sylysia 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolymerized polyester resin solution was used to disperse thyricia 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 adhesion-modified coating solution.

(Example 1)
90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for a base film intermediate layer having a three-layer structure 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). Further, PET (A) was dried by a conventional method, supplied to extruder 1 (for outer layer I and outer layer III), and melted at 285 ° C. The two types of polymers are respectively filtered with a stainless steel sintered body filter medium (nominal filtration accuracy: 10 μm, particles cut by 95%), laminated in a two-type three-layer merging block, extruded into a sheet from a die, and extruded. It was wound around a casting drum having a surface temperature of 30 ° C. using an electrostatic application casting method, and cooled and solidified to form an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

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

  The unstretched film having the coating layer formed thereon is guided to a simultaneous biaxial stretching machine, and while holding the end of the film with a clip, guided to a hot air zone at a temperature of 90 ° C. so that the magnification becomes 0.8 times in the longitudinal direction. The film was relaxed and simultaneously stretched 4.0 times in the transverse direction. Next, treatment was performed at a temperature of 170 ° C. for 30 seconds, and a relaxation treatment of 3% 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 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 in the longitudinal direction.

(Example 3)
By changing the thickness of the unstretched film, the thickness was reduced to about 38 μm, relaxed by a factor of 0.7 in the longitudinal direction, and the same as in Example 1 except that the heat treatment was performed at a temperature of 180 ° C. for 30 seconds. A uniaxially oriented PET film was obtained.

(Example 4)
By changing the thickness of the unstretched film, the thickness was set to about 25 μm, the stretching ratio in the transverse direction was set to 5.0 times, and 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 reduced to about 80 μm, relaxed at a magnification of 0.85 times in the longitudinal direction, the stretching temperature was set to 95 ° C., and heat treatment was performed at 180 ° C. for 30 seconds. Except for the above, a uniaxially oriented PET film was obtained in the same manner as in Example 1.

(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 in the longitudinal direction.

(Comparative Example 1)
The unstretched film produced in the same manner as in Example 1 was guided to a tenter stretching machine, and while holding the end of the film with a clip, 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 a relaxation treatment of 3% was performed 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 longitudinally uniaxially stretched film, fine 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 relaxation treatment in the longitudinal direction 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)
By changing the thickness of the unstretched film, the thickness was set to about 25 μm, and a uniaxially oriented PET film was obtained in the same manner as in Example 4 except that the longitudinal relaxation treatment was not performed.

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

  As described above, it was confirmed that when the films of Examples 1 to 6 were used as the polarizer protective film, the occurrence of rainbow spots was significantly suppressed, and a liquid crystal display device having excellent visibility was obtained. In addition, the films of Examples 1 to 6 not only enable provision of an image display device with excellent visibility, but also have a sufficient tear strength despite their relatively small thickness. It has been confirmed that it is suitable for use in the production of a typical image display device. On the other hand, when the films of Comparative Examples 1, 2 and 6 were used as polarizer protective films, rainbow spots were formed when viewed from the front, and good visibility could not be obtained. Further, although the film of Comparative Example 3 has no problem in visibility when used as a polarizer protective film, it has an insufficient tear strength and is suitable for industrially and stably producing a liquid crystal display device. Turned out not to be. This is probably because the film of Comparative Example 3 had a relatively high Re value and a high Re value, although the Re / Rth ratio was relatively high. In the films of Comparative Examples 4 and 5, the occurrence of rainbow spots was not observed when the observation angle was observed in the range of 0 ° to 55 °, but the film was partly extremely thin in the range where the observation angle exceeded 55 °. A rainbow spot was observed. This is probably because the films of Comparative Examples 4 and 5 have a relatively high Re but a low Re / Rth ratio. In Comparative Example 6, since the value of ΔP was high, the tear strength was insufficient.

  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 having excellent visibility. Therefore, the industrial applicability of the present invention is extremely high.

DESCRIPTION OF SYMBOLS 1 Polyester film 2 Line showing direction perpendicular to polyester film surface 3 Line connecting observer's eye position and (center of) film surface 4 Observer's eye position

Claims (7)

The following physical properties (a) to (c):
(A) a retardation (Re) of 3000 nm or more and 30000 nm or less;
(B) a ratio (Re / Rth) of retardation (Re) of 1.0 or more to 1.6 or less and retardation in the thickness direction (Rth); and (c) plane orientation of 0.04 or more and 0.12 or less. Degree (ΔP);
A liquid crystal display device including a polarizing plate having a structure in which a polyethylene terephthalate film that satisfies the above is laminated on at least one surface of a polarizer (except when Re is 10,000 nm or more and 30,000 nm or less). The polyethylene terephthalate film has the following physical properties (d):
(D) Birefringence (ΔNxy) of 0.1 or more
The liquid crystal display device according to claim 1, wherein the following conditions are satisfied. The liquid crystal display device according to claim 1, wherein the thickness of the polyethylene terephthalate film is from 20 μm to 90 μm. The liquid crystal display device according to any one of claims 1 to 3, wherein the polyethylene terephthalate film has a tear strength of 50 mN or more. 5. The polyethylene terephthalate film according to claim 1, wherein the degree of plane orientation (ΔP) is 0.04 or more and 0.098 or less, and the birefringence (ΔNxy) is 0.11 or more and 0.145 or less. A liquid crystal display device according to any one of the above. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a white light emitting diode as a backlight light source. The liquid crystal display device according to any one of claims 1 to 5, wherein the liquid crystal display device has a backlight light source (however, the liquid crystal display device in which the backlight light source is a cold cathode tube, and the backlight light source is a hot cathode). Excluding the liquid crystal display device which is a tube).

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