TWI675226B - Liquid crystal display device, polarizing plate and polarizer protective film - Google Patents

Abstract

The present invention provides a polarizer protective film including a polyester film, which can suppress light leakage even when two polarizing plates are arranged in a crossed Nicols environment.

The polarizer protective film includes a polyester film having an absolute value of an inclination of a thermal shrinkage rate of 15 degrees or less with respect to a film flow direction or a width direction.

Description

Liquid crystal display device, polarizing plate and polarizer protective film

The present invention relates to a polarizer protective film for a polarizing plate used in a liquid crystal display device.

A polarizing plate used in a liquid crystal display device (LCD) is generally composed of two polarizer protective films sandwiched with a polarizer such as polyvinyl alcohol (PVA) dyed with iodine. As a polarizer protective film, three polarizers are usually used. Acetyl cellulose (TAC) film. In recent years, with the thinning of LCDs, thinning of polarizing plates is required. However, if the thickness of the TAC film used as a protective film is reduced, sufficient mechanical strength cannot be obtained, and the problem of poor moisture permeability may occur. In addition, TAC films are very expensive, and there is a strong demand for inexpensive alternative materials.

Therefore, in order to reduce the thickness of a polarizing plate, it has been proposed to use a polyester film instead of a TAC film as a protective film for a polarizer. This polyester film can maintain high durability even with a thin thickness (Patent Documents 1 to 3).

Polyester films are more durable than TAC films, but because they have birefringence different from TAC films, when they are used as polarizer protective films, there is a problem that the image quality is lowered due to optical distortion. That is, since a polyester film having birefringence has specific optical anisotropy (retardation), when it is used as a protective film for a polarizer, when viewed from an oblique direction, a rainbow-like color spot occurs, The picture quality is degraded. therefore In Patent Documents 1 to 3, countermeasures are taken to reduce the retardation by using a copolymerized polyester as the polyester.

Furthermore, Patent Document 4 discloses that by using a white light-emitting diode as a backlight light source and using an alignment polyester film having a certain retardation as a protective film for a polarizer, an iridescent stain can be solved.

Patent Document 5 discloses that the polarizer protective film has good dimensional stability through a number of heat treatment steps during the manufacture of the polarizing plate or the step of recombining the obtained polarizing plate with the liquid crystal cell, etc., specifically, The shrinkage ratio of the polyester film after unconstrained heat treatment at 120 ° C for 30 minutes is preferably 5% or less in both the MD direction and the TD direction of the film.

[Prior technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2002-116320

[Patent Document 2] Japanese Patent Laid-Open No. 2004-219620

[Patent Document 3] Japanese Patent Laid-Open No. 2004-205773

[Patent Document 4] WO2011-162198

[Patent Document 5] Japanese Patent Laid-Open No. 2010-277028

As described above, the polyester film used as the polarizer protective film has been improved repeatedly from various viewpoints, but the inventors have found that there is room for further improvement. That is, the present inventors have found that a polarizing plate using another modified polyester film as a polarizer protective film and another sheet are used. When the polarizing plates are arranged in the relationship of crossed Nicols, there is a new problem that some slight light leakage occurs and the visibility is deteriorated. Therefore, an object of the present invention is to provide a polarizer protective film including a polyester film, which can suppress the above-mentioned slight light leakage.

In order to solve the above-mentioned problems, the present inventors repeated their dedication research, and found that the angle formed by the direction in which the thermal shrinkage of the polyester film becomes maximum and the flow direction or width direction of the polyester film (that is, relative to In the film flow direction or the film width direction, the absolute value of the inclination of the direction in which the heat shrinkage rate is the maximum) is controlled to 15 degrees or less, and the above problem is solved. Based on this knowledge, further review is repeated to provide inventions represented by the following.

Item 1. A polarizer protective film, which is a polyester film having an absolute value of an angle formed by an angle between a film flow direction or a width direction and a direction in which a film's thermal shrinkage ratio becomes maximum at 15 degrees or less.

Item 2. The polarizer protective film according to item 1, wherein the retardation of the polyester film is 4000 to 30,000 nm, and the Nz coefficient is 1.7 or less.

Item 3. The polarizer protective film according to Item 1 or 2, wherein the surface alignment degree of the polyester film is 0.13 or less.

Item 4. A polarizing plate comprising a structure in which polarizer protective films are laminated on both sides of a polarizer, and at least one side of the polarizer protective film is the polarizer protective film according to any one of items 1 to 3.

Item 5. A polarizing plate comprising a polarizer protective film according to any one of items 1 to 3 laminated on one side of a polarizer.

Item 6. A liquid crystal display device having a backlight source, two polarizers A light plate and a liquid crystal display device with a liquid crystal cell disposed between the two polarizing plates. The backlight light source is a white light source with a continuous light emission spectrum. The polarizing plate is a layer with a polarizer protective film laminated on both sides of the polarizer. At least one of the polarizer protective film of the polarizer disposed on the incident light side and at least one of the polarizer protective film of the polarizer disposed on the outgoing light side is configured as described in any one of items 1 to 3. Polarizer protective film.

Item 7. The liquid crystal display device according to Item 6, wherein the polarizer protective film on the incident light side of the polarizer disposed on the incident light side and the polarizer protective film on the exit light side of the polarizer disposed on the exit light side Is the polarizer protective film according to any one of items 1 to 3.

Item 8. A liquid crystal display device, which is a liquid crystal display device having a backlight light source, two polarizing plates, and 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 is a polarizing plate as described in item 5.

According to the present invention, when the two polarizing plates are arranged in a cross-Nicol relationship, it is possible to suppress some light leakage that has occurred in the past. In addition, according to a suitable embodiment, a liquid crystal display device can be provided which is not only suitable for thinning and does not cause iridescence, but also can reduce the deterioration of visibility due to the light leakage, and has excellent visibility.

FIG. 1 shows an example of the results of measuring the thermal shrinkage of a film by setting the flow direction of the film to 0 degrees and 360 degrees at 5 degree intervals. In this example, the angle at which the thermal shrinkage rate becomes the largest is about 15 degrees.

The second figure is to determine the angle at which the thermal contraction rate becomes the largest with an accuracy of 1 degree or more from the thermal contraction rate measured at 5 degree intervals. Let the angle be the X axis and the thermal contraction rate be the Y axis. And draw the picture.

FIG. 3 schematically shows the interval between the jigs used in the method 1 for reducing the inclination of the heat shrinkage rate.

FIG. 4 shows the relationship between the distance in the lengthwise direction of the tenter and the tenter temperature which can be used in the method 4 for reducing the gradient of the heat shrinkage rate.

[Form of Implementing Invention]

Polarizer protective film

The absolute value of the inclination of the direction in which the thermal shrinkage rate becomes the largest with respect to the flow direction or width direction of the film of the polarizer protective film polyester film of the present invention (hereinafter, also referred to as the inclination of the thermal shrinkage rate for simplicity) It is preferably 15 degrees or less. The absolute value of the inclination of the aforementioned heat shrinkage ratio is preferably 12 degrees or less, more preferably 10 degrees or less, even more preferably 8 degrees or less, even more preferably 6 degrees or less, particularly preferably 4 degrees or less, and most preferably 2 Degrees below. The smaller the absolute value of the slope of the thermal shrinkage, the better, so the lower limit is 0 degrees.

Although the above-mentioned correct mechanism of some slight light leakage has not yet been clarified, the judgment is as follows. Generally, in a liquid crystal display device, two polarizing plates are arranged in a relationship of crossed Nicols. If two polarizers are arranged in a cross-Nicol relationship, light normally does not pass through the two polarizers. However, if the polarizer protective film shrinks due to heat treatment, the polarizer will follow Micro shrinkage or warping occurs, and as a result, the relationship of the full cross Nicols collapses, and light leaks. According to such a principle, when the direction in which the thermal contraction rate of the polarizer protective film is the largest is inclined with respect to the film flow direction or the film width direction, light leakage becomes significant. Moreover, the flow direction of the polarizer protective film is generally parallel or perpendicular to the polarization axis of the polarizer.

Patent Document 5 discloses a polarizer protective film composed of a polyester film having a thermal shrinkage of 5% or less in both the MD direction and the TD direction. However, as is clear from the above mechanism, even if the thermal contraction rate in the MD direction and the thermal contraction rate in the TD direction are small, when the direction in which the thermal contraction rate becomes the maximum is inclined with respect to the film flow direction or the film width direction, the foregoing occurs. The problem of leakage of polarized light.

In addition, Patent Document 5 also discloses that for the two ends of the film, the angle and deviation between the retardation axis and the TD direction of the film in the plane of the film are reduced to prevent the color shift and color spots of the liquid crystal display. However, the direction of the retardation axis in the film plane and the inclination of the thermal shrinkage may not be parallel. Even for a film in which the retardation axis in the film plane is controlled, the aforementioned problem of leakage of polarized light may occur.

The polyester film used in the polarizer protective film of the present invention can be obtained from any polyester resin. The type of the polyester resin is not particularly limited, and any polyester resin obtained by condensing a dicarboxylic acid and a diol can be used.

Examples of the dicarboxylic acid component that can be used in the production of polyester resins include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. Acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylfluorenecarboxylic acid Acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydrogen Phthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyl Adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecane dicarboxylic acid, and the like.

Examples of the diol component that can be used in the production of polyester resins include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, and 1,4- Cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis (4 -Hydroxyphenyl) propane, bis (4-hydroxyphenyl) fluorene and the like.

As the dicarboxylic acid component and the diol component constituting the polyester resin, one type or two or more types can be used. Examples of the polyester resin suitable for constituting the polyester film include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like. It is more preferably polyethylene terephthalate or polyethylene naphthalate, but these may also contain other copolymerization components. These resins are excellent in transparency, and also excellent in thermal and mechanical properties, and can easily control hysteresis by extension processing. In particular, polyethylene terephthalate is the most suitable material because it has a large inherent birefringence and can obtain relatively large hysteresis relatively easily even if the thickness of the film is thin.

(Heat shrinkage)

The thermal shrinkage of the polyester film is preferably 5% or less in all directions. The thermal shrinkage of the polyester film in all directions was measured as follows.

A 21 cm square shape was cut out from the polyester film. Store at 23 ° C and 65% RH for more than 2 hours. On this polyester film, a circle with a diameter of 80 mm is drawn around the center of the polyester film. Using a two-dimensional image measuring machine (for example, QUICK IMAGE by MITUTOYO), the diameter of the film is taken as 0 degrees, and the diameter is measured at 5 degree intervals . Here, the flow direction of the film is regarded as 0 degree. When viewing the film from above in the tenter, the clockwise rotation (turn right) is regarded as a positive angle, and the counterclockwise rotation (turn left) is regarded as a negative angle. When measured in the range of -90 degrees to 85 degrees, the diameter can be measured in all directions.

Next, after heat-treating the polyester film in water at 85 ° C. for 30 minutes, the moisture attached to the surface of the film was wiped and air-dried, and then left in an environment of 23 ° C. and 65% RH for more than 2 hours. Then, in the same manner as described above, the diameter of the circle was measured at 5-degree intervals. Let the diameter before the heat treatment be Lo, and the diameter in the same direction after the heat treatment as L, and the heat shrinkage in each direction was determined according to the following formula.

Thermal shrinkage (%) = ((L ₀ -L) / L ₀ ) × 100

If the thermal contraction rate measured at a 360-degree interval of 5 degrees is shown in a graph, for example, it is like the first figure. In FIG. 1, the center of the circle shows a thermal contraction rate of 0%. As the distance from the center of the circle becomes longer, the thermal contraction rate becomes larger. The circle indicates the angle when the film flow direction is regarded as 0 degrees. Therefore, the 90 degree system is parallel to the film width direction.

The maximum value of the thermal shrinkage obtained by the above measurement method is preferably 5% or less, more preferably 3% or less, even more preferably 1% or less, and most preferably 0.5% or less. The lower limit of the thermal shrinkage ratio is not particularly limited, but is, for example, 0.01% or more.

(Inclination of heat shrinkage)

As described above, the thermal shrinkage ratio is measured at intervals of 5 degrees, but the direction in which the thermal shrinkage ratio becomes the maximum is determined with the accuracy of 1 degree in accordance with the following procedure. That is, as shown in FIG. 2, the horizontal axis is taken as the angle when the film flow direction is set to 0 degrees, and the vertical axis is taken as the heat shrinkage rate at this angle. The measurement results of the heat shrinkage rate are plotted (-90 degrees to 85 degrees). Range of thermal shrinkage results). At this time, the values of -180 degrees to -95 degrees and 90 degrees to 175 degrees are also interpolated (a thermal contraction rate of -90 degrees corresponds to a thermal contraction rate of 90 degrees, and a thermal contraction rate of 0 degrees corresponds to -180 degrees Heat shrinkage). Next, draw an approximate curve connecting the trace points, and read the direction in which the thermal shrinkage ratio becomes the largest with an accuracy of 1 degree, and define this as α. Moreover, -90 degrees ≦ α ≦ 90 degrees.

When the direction α in which the heat shrinkage ratio becomes the maximum is in the range of -45 degrees to 45 degrees, this value is taken as the slope of the heat shrinkage ratio. In addition, when the direction in which the heat shrinkage ratio is maximum α is 45 degrees or more and -45 degrees or less, it is understood that the film width direction is not inclined to the reference, but the film width direction is inclined to the reference, and α-90 degrees (α When it is 45 degrees or more), 90 degrees + α (when α is -45 degrees or less) are taken as the slopes of the thermal contraction rate. When the difference between the maximum value and the minimum value of the thermal contraction rate is 0.1% or less, the thermal contraction rate in almost all directions is almost equal, and there is no gradient in the thermal contraction rate. Therefore, the gradient of the thermal contraction rate is regarded as 0 degree.

(Light leakage evaluation method)

The light leakage was obtained by arranging two polarizing plates in a cross-Nicol relationship, and measuring the maximum transmittance of light having a wavelength of 550 to 600 nm. The measurement of light transmittance can be performed using an arbitrary spectrophotometer. The measured maximum transmittance is preferably 0.02% or less, and more preferably 0.015% or less.

Next, from the viewpoint of suppressing iridescence, the hysteresis, Nz coefficient, and surface orientation of the polyester film will be described.

(Lag)

The polyester film used for the polarizer protective film preferably has a retardation of 4000 to 30,000 nm. When the hysteresis is 4000 nm or more, rainbow spots that may occur when the liquid crystal display device is viewed from an oblique direction can be suppressed, and good visibility can be ensured. The preferred hysteresis of the polyester film is 4500 nm or more, more preferably 5000 nm or more, even more preferably 6000 nm or more, even more preferably 8000 nm or more, and even more preferably 10,000 nm or more. Here, the so-called 4000 to 30000 nm means that 4000 nm is included as the lower limit value and 30,000 nm is included as the upper limit value, but a range not included is also envisaged.

The upper limit of the retardation of the polyester film is not particularly limited, but is, for example, 30,000 nm. Even if a polyester film with a retardation of more than this is used, further improvement of the visibility is not substantially obtained, and as the retardation increases, the thickness of the film becomes considerably thicker, which reduces the operability as an industrial material. Fear.

The hysteresis value of an oriented polyester film was calculated | required by the following procedure. Using a molecular alignment meter (for example, MOA-6004 molecular alignment meter manufactured by Oji Instruments Co., Ltd.), the alignment axis direction of the thin film is determined. The refractive index (ny) in the alignment axis direction and the refractive index (nx) in the direction orthogonal to the in-plane direction of the film were measured at a measurement wavelength of 589 nm. The absolute value (| ny-nx |) of the difference (anisotropy) of the refractive index in these biaxial directions is obtained, and it is multiplied by the thickness of the film to obtain the value of the hysteresis. The retardation of a thin film can be measured using, for example, a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Measurement Co., Ltd.). Refraction The ratio can be measured using, for example, a commercially available measuring instrument such as an Abbe refractometer (NAR-4T manufactured by ATAGO).

(Nz coefficient)

In addition to the above-mentioned hysteresis range of the polyester film used for the polarizer protective film, it is preferable that the Nz coefficient represented by | ny-nz | / | ny-nx | is 1.7 or less. The Nz coefficient can be obtained as follows. Using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 molecular alignment meter), the orientation axis direction of the thin film was determined, and it was determined by an Abbe refractometer (NAR-4T manufactured by ATAGO, measuring wavelength: 589 nm). The biaxial refractive index (ny, nx, but ny> nx) and thickness refractive index (nz) of the alignment axis direction and the direction orthogonal to it are obtained. By substituting nx, ny, and nz thus obtained into the formula shown by | ny-nz | / | ny-nx |, the Nz coefficient can be obtained.

Even if the retardation of a polyester film is 4000 nm to 30,000 nm, if the Nz coefficient exceeds 1.7, when a polyester film is used as a protective film for a polarizer in both of a pair of polarizing plates (for example, polarized light disposed on the incident light side) When the polarizer protective film on the incident light side of the plate and the polarizer protective film on the outgoing light side of the polarizing plate disposed on the outgoing light side are polyester films), the liquid crystal display device is still obliquely viewed from an oblique direction. Iris occurs. From the viewpoint of suppressing the occurrence of such rainbow spots, the Nz coefficient is more preferably 1.65 or less, and even more preferably 1.63 or less. The lower limit of the Nz coefficient is 1.2. This is because it is technically difficult to obtain a thin film of less than 1.2. In order to maintain the mechanical strength of the film, the lower limit value of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and even more preferably 1.45 or more.

(Face alignment coefficient)

In addition to controlling the hysteresis value and Nz coefficient of polyester film In a fixed range, the surface alignment degree represented by (nx + ny) / 2-nz is set to a specific value or less. When a polyester film is used as a polarizer protective film in both of a pair of polarizing plates, it is more reliable. Eliminate rainbow spots. Here, the values of nx, ny, and nz are obtained by the same method as the Nz coefficient. The surface alignment degree of the oriented polyester film is preferably 0.13 or less, more preferably 0.125 or less, and even more preferably 0.12 or less. By setting the surface alignment degree to 0.13 or less, when the liquid crystal display device is viewed from an oblique direction, the rainbow spots observed due to the angle can be more completely eliminated. The surface alignment degree is preferably 0.08 or more, and more preferably 0.1 or more. When the surface alignment degree is less than 0.08, the thickness of the film changes, and the hysteresis value may become uneven in the film surface.

(Hysteresis ratio)

The polyester film has a retardation (Re) and a thickness direction retardation (Rth) ratio (Re / Rth) of preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 0.6 or more. This is because the larger the ratio (Re / Rth) of the hysteresis to the thickness direction retardation (Rth), the more the effect of birefringence increases the isotropy, and the more difficult the occurrence of iridescent stains due to the observation angle. In a completely uniaxial (uniaxially symmetric) film, the ratio (Re / Rth) of the hysteresis to the thickness direction hysteresis is two. However, as described later, the mechanical strength decreases significantly in a direction orthogonal to the alignment direction as the film is almost completely uniaxial (uniaxially symmetric). Therefore, the upper limit of the ratio of the hysteresis to the hysteresis in the thickness direction (Re / Rth) is preferably 1.2 or less, and more preferably 1 or less. In order to completely suppress the occurrence of iridescent stains caused by the observation angle, the ratio of the retardation to the thickness direction phase difference (Re / Rth) does not need to be 2, but 1.2 or less is sufficient. In addition, even if the ratio is 1.0 or less, the viewing angle characteristics (180 degrees left and right, and 120 degrees up and down) required by the liquid crystal display device can be sufficiently satisfied.

(Uneven thickness)

In order to suppress the variation of the hysteresis of a polyester film, it is preferable that the thickness of each film is small. From this viewpoint, the thickness unevenness of the polyester film is preferably 5% or less, more preferably 4.5% or less, particularly preferably 4% or less, and particularly preferably 3% or less. The thickness unevenness of the film can be measured by the following procedure. A 40 mm wide film was cut from the film roll in the TD direction. About the cut out sample, the thickness in the TD direction was continuously measured with a contact continuous thickness gauge (feed speed: 1.5 m / min, sampling period: 100 ms) made by ANRITSU, and the average value, maximum value, and minimum value were obtained. The thickness unevenness is an absolute value of a value calculated by the following formula.

Thickness non-uniformity = ((maximum value of measurement result)-(minimum value of measurement result)) / (average value of measurement result) × 100 (%)

(membrane thickness)

The thickness of the polyester film is not particularly limited, but is usually 15 to 300 μm, and preferably 15 to 200 μm. When the thickness of the film is less than 15 μm, the anisotropy of the mechanical properties of the film becomes significant, and cracks and breakage may occur. A particularly preferred lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes excessively thick, which is not suitable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. The upper limit of the particularly preferred thickness is 100 μm which is equivalent to that of a general TAC film.

(Light transmittance)

From the viewpoint of suppressing the deterioration of optically functional pigments such as iodine pigments contained in the polarizer, it is preferable that the light transmittance of the polyester film at a wavelength of 380 nm is 20% or less. 15% better light transmittance at 380nm Below, particularly preferred is 10% or less, and particularly preferred is 5% or less. When the light transmittance is 20% or less, deterioration of the optically functional pigment due to ultraviolet rays can be suppressed. The light transmittance is measured in a direction perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Japan Spectrophotometer V-7100).

The transmittance of the aligned polyester film at a wavelength of 380 nm can be controlled to 20% or less by appropriately adjusting the type and concentration of the ultraviolet absorber and the thickness of the film. Among the ultraviolet absorbents used in the present invention, a well-known ultraviolet absorbent can be appropriately selected and used. Specific examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber. From the viewpoint of transparency, an organic ultraviolet absorber is preferred.

Examples of the organic ultraviolet absorber include a benzotriazole system, a diphenyl ketone system, a cyclic imine ester system, and any combination thereof, and are not particularly limited. From the viewpoint of durability, particularly preferred are benzotriazole-based or cyclic iminoester-based. When two or more kinds of ultraviolet absorbers are used in combination, since ultraviolet rays of respective wavelengths can be absorbed at the same time, the ultraviolet absorption effect can be further improved.

Examples of the diphenylketone-based ultraviolet absorber, benzotriazole-based ultraviolet absorber, and acrylonitrile-based ultraviolet absorber include 2- [2'-hydroxy-5 '-(methacryloxymethyl) ) Phenyl] -2H-benzotriazole, 2- [2'-hydroxy-5 '-(methacryloxyethyl) phenyl] -2H-benzotriazole, 2- [2'- Hydroxy-5 '-(methacryloxypropyl) phenyl] -2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxydiphenyl ketone, 2, 2 ', 4,4'-tetrahydroxydiphenyl ketone, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2- (2'-hydroxy- 3'-Third-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (5-chloro (2H) -benzotriazol-2-yl) -4-methyl- 6- (third butyl) phenol, 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2- Group) phenol, etc. Examples of the cyclic imide-based ultraviolet absorber include 2,2 '-(1,4-phenylene) bis (4H-3,1-benzo -4-one), 2-methyl-3,1-benzo 4-one, 2-butyl-3,1-benzo 4-one, 2-phenyl-3,1-benzo -4-ketone, etc. These ultraviolet absorbers may be used alone or in combination of two or more.

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

(Other ingredients, etc.)

In the oriented polyester film, in addition to the ultraviolet absorber, those containing various additives are also preferred as long as the effects of the present invention are not hindered. Examples of the additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light-resistant agents, flame retardants, heat stabilizers, antioxidants, and gelation prevention Agents, surfactants, etc. In order to achieve high transparency, it is also preferable that the polyester film does not substantially contain particles. The term "substantially free of particles" means, for example, in the case of inorganic particles, when the inorganic element is quantified by fluorescent X-ray analysis, it means 50 ppm or less, preferably 10 ppm or less, and particularly preferably content below the detection limit.

(Easy adhesion layer)

In the present invention, in order to improve the adhesion with the polarizer, it is preferable to have polyester resin and polyamine on at least one side of the oriented polyester film. At least one type of urethane resin or polyacrylic resin is used as a main component of an easy-adhesion layer. The "main component" as referred to herein means a component of 50% by mass or more of the solid content constituting the easily-adhesive layer. The coating liquid for forming an easy-adhesive layer is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible copolymerized polyester resin, acrylic resin, and polyurethane resin. Examples of such coating liquids include Japanese Patent Application No. 3567927, Japanese Patent Application No. 3589232, Japanese Patent Application No. 3589233, Japanese Patent Application No. 3900191, and Japanese Patent Application No. 4150982. The water-soluble or water-dispersible copolymerized polyester resin solution, acrylic resin solution, and polyurethane resin solution disclosed in the et al.

The easy-adhesion layer can be obtained by coating the above coating solution on one or both sides of an unstretched film or a uniaxially stretched film in the longitudinal direction, and drying at 100 to 150 ° C, and extending in the transverse direction. The coating amount of the final easy-adhesive layer is preferably controlled at 0.05 to 0.2 g / m ² . When the coating amount is less than 0.05 g / m ² , the adhesiveness with the obtained polarizer may become insufficient. On the other hand, if the coating amount exceeds 0.2 g / m ² , the blocking resistance may be reduced. When the easy-adhesion layer is provided on both sides of the polyester film, the coating amount of the double-sided easy-adhesion layer can be the same or different, and can be independently set within the above range.

In the easy-adhesion layer, particles are preferably added in order to impart slipperiness. It is preferred to use particles having an average particle diameter of 2 μm or less. When the average particle diameter of a particle exceeds 2 micrometers, a particle will fall easily from a coating layer. Examples of particles contained in the easy-adhesion layer include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silicon dioxide, and aluminum oxide. , Talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride and other inorganic particles, or styrene, acrylic, melamine, benzoguanamine Based, silicon based, and other organic polymer based particles. These systems may be added to the easy-adhesive layer alone, or two or more of them may be added in combination.

The average particle diameter of a particle can be taken by a scanning electron microscope (SEM). The maximum diameter of 300 to 500 particles (with the distance between the two most distant points) can be measured at a magnification of 2 to 5 mm with the size of one of the smallest particles. Distance), and calculate the average value.

The coating liquid system can be applied by a known method. Examples thereof include a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire rod coating method, and a pipe doctoring method. These methods can be performed individually or in combination.

The polyester film may be subjected to a corona treatment, a coating treatment, a flame treatment, or the like in order to improve the adhesion to the polarizer.

(Functional layer)

On the side of the polyester film opposite to the side on which the polarizer is arranged, for the purpose of preventing writing, suppressing glare, suppressing damage, etc., various functional layers are composed of a hard coating layer, an anti-glare layer, and an anti-reflection. One or more functional layers selected from the group consisting of a layer, a low-reflection layer, an anti-low-reflection layer, an anti-reflection anti-glare layer, and an antistatic layer are also preferable when they are arranged on the surface of the alignment polyester. When providing various functional layers, the oriented polyester film preferably has an easy-adhesion layer on the surface. 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 to the geometry of the refractive index of the functional layer and the refractive index of the oriented polyester film. Near average. The refractive index of the easy-adhesion layer can be adjusted by a well-known method. For example, the adhesive resin can be easily adjusted by containing titanium, zirconium, or other metal species.

(Manufacturing method of polyester film)

The polyester film used as a polarizer protective film can be manufactured in accordance with a general polyester film manufacturing method. For example, the polyester resin is melted, extruded into a sheet shape, and the formed non-oriented polyester is stretched in a longitudinal direction by a speed difference of a roll at a temperature equal to or higher than a glass transition temperature, and then stretched by stentering. The machine extends in the transverse direction and is subjected to heat treatment. It can be a uniaxially stretched film or a biaxially stretched film.

(The slope of the heat shrinkage is reduced)

The means for controlling the absolute value of the inclination of the direction in which the heat shrinkage ratio becomes the largest with respect to the flow direction or width direction of the film is not more than 15 degrees, but it is preferable to pay attention to the following points. That is, in the cooling section after the heat treatment step in the tenter, there are shrinkage stress associated with elongation that has not been completely removed by heat setting, and thermal stress associated with cooling. In addition, the thin film system at the end is restrained by the jig, and the thin film system at the center is more likely to expand and contract. Therefore, in the cooling section, the stress distribution in the film flow direction and the width direction is biased. These are the main causes, and the inclination of the heat shrinkage rate occurs. In view of such circumstances, specific means for reducing the inclination of the heat shrinkage rate are exemplified below.

(Method 1 for reducing the slope of the heat shrinkage ratio)

In the cooling section after heat setting, the clamp interval is narrowed in the film flow direction, so that the stress in the film flow direction in the cooling section of the tenter can be made uniform, and the inclination of the heat shrinkage can be reduced. So for In order to reduce the inclination of the heat shrinkage ratio, it is preferable to appropriately adjust the temperature band that narrows the interval between the clamps. There is no particular limitation as it varies depending on the film composition or film manufacturing conditions, but when the temperature is too high, the inclination of the thermal contraction rate of the film system at the left end (when viewing the film from above) relative to the flow direction is It becomes larger in the positive direction (the right end portion becomes larger in the negative direction). In addition, when the temperature is too low, the thermal shrinkage of the film is too small, and the planarity is not good. In this way, by setting the temperature for narrowing the clamp interval to an appropriate range, the stress in the flow direction in the tenter cooling zone can be made uniform, and the inclination of the thermal shrinkage can be reduced.

In order to reduce the inclination of the heat shrinkage rate, it is also important to reduce the relaxation rate of narrowing the clamp interval in the film flow direction. It is not particularly limited because it varies depending on the film composition or film manufacturing conditions, but the relaxation rate is preferably 0.01 to 3%, and more preferably 0.05 to 1.5%. When the relaxation rate is too high, the flatness is not suitable because the film is not completely shrunk. When the relaxation rate is too low, the effect of reducing the slope of the heat shrinkage rate becomes low. The so-called relaxation rate can be calculated by the following formula using the distance between the centers of the clamps as shown in FIG. 3.

Relaxation rate = (((distance between fixtures before relaxation)-(distance between fixtures after relaxation)) / (distance between fixtures before relaxation)) × 100 (%)

When the thermal contraction rate in the width direction is too high, the gradient of the thermal contraction rate tends to increase. Therefore, it is more preferable to adjust the rail patten of the tenter, and to appropriately adjust the relaxation rate and temperature for narrowing the clamp interval in the film width direction. In this way, by setting the temperature band and the relaxation rate that narrow the clamp interval in the film flow direction, and adjusting the pattern of the tenter guide rail appropriately as needed without narrowing the width direction If the shrinkage becomes too large, the stress in the flow direction in the cooling section of the tenter can be made uniform, and the inclination of the heat shrinkage can be reduced.

(Method 2 for reducing the slope of the heat shrinkage rate)

In the cooling section after heat setting, the end of the film is separated from the clamp and released from the restraint of the clamp, so that the stress in the width direction in the cooling section of the tenter can be made uniform. In addition, by adjusting the tension in the winding step to an appropriate value, the stress in the flow direction in the cooling section of the tenter can be made uniform. In this way, by making the stress in the flow direction in the tenter cooling zone uniform, the inclination of the heat shrinkage rate can be reduced.

The method of separating the film end portion from the jig is not particularly limited, and a conventionally well-known method can be used. Specifically, the method of cutting a film from a jig and the method of releasing a jig can be mentioned. The method for cutting the film from the jig is arbitrary, and examples thereof include cutting with a cutter or fusing with a laser. These methods can also be implemented in combination. When cutting the film from the clamp, it should be performed near the clamp at both ends of the film.

The temperature of the film when separating the end of the film from the clamp is preferably 50 ° C to 300 ° C. The higher the film temperature relative to the melting point Tm of the film, the more difficult it is to maintain the planarity of the film, and when the film temperature is too low relative to the glass transition temperature Tg of the film, the slope of the thermal shrinkage becomes difficult to decrease. Therefore, it is preferable to cut the separation film from the jig at a temperature higher than (glass transition temperature Tg-20 ° C) and lower than (melting point Tm-10 ° C). The film temperature here is a measurement value of a radiation thermometer.

When separating the film end portion from the jig, it is preferable to appropriately adjust the tension in the winding step. The appropriate tension is different depending on the film composition, thickness, and film manufacturing conditions, so it is not particularly limited, but is preferably 0.01 to 3 kg / mm ² , and more preferably 0.1 to 2 kg / mm ² . When the tension is too high, the inclination of the heat shrinkage rate of the film system at the left end portion becomes larger in the positive direction (the right end portion becomes larger in the negative direction) with respect to the flow direction. When the tension is too low, the gradient of the heat shrinkage rate of the film system at the left end portion becomes larger in the negative direction (the right end portion becomes larger in the positive direction) with respect to the flow direction. However, when these tendencies are based on the direction of flow and the angle is evaluated, the situation based on the width direction is the opposite tendency.

When the thermal contraction rate in the width direction is too high, the gradient of the thermal contraction rate becomes large. Therefore, it is preferable to adjust the pattern of the guide rail before separating the end portion of the film from the clamp, and adjust the relaxation rate and temperature for narrowing the clamp interval in the film width direction as described above. In this way, by setting the tension in an appropriate range, the stress in the flow direction in the tenter cooling zone can be made uniform, and the inclination of the thermal shrinkage can be reduced.

(Method 3 for Reducing the Inclination of Thermal Shrinkage)

In the same way as reduction method 2, the temperature of the film at the tenter exit is higher than the specified temperature (ie, the glass transition temperature Tg-20 ° C) and lower than the specified temperature (melting point Tm-70 ° C) , Can reduce the slope of the thermal shrinkage. At this time, since the effect is controlled by room temperature, room temperature should be controlled.

(Method 4 for Reducing the Inclination of Thermal Shrinkage)

Adjusting the temperature setting of the cooling step after heat setting of the tenter can also reduce the inclination of the heat shrinkage rate. For example, as shown in FIG. 4, it is preferable to set the heat setting temperature to the tenter exit temperature along the tenter length direction to -15 / X to -100 / X (° C / m). Here, X represents the tenter exit width (m). Therefore, for example, when the width of the tenter exit is 2m, it is better. In order to advance 1m in the tenter length direction, the temperature is decreased in the range of -7.5 ° C to -50 ° C. Since the above temperature represents the temperature per width of the tenter exit, this is hereinafter referred to as the temperature setting per unit width.

The tenter exit temperature is generally preferably set to be lower than Tg. When the temperature per unit width is set to -100 / X (° C / m) or less in the longitudinal direction, it is not suitable because the slope of the heat shrinkage rate exceeds 15 degrees. The inclination of the heat shrinkage rate can be sufficiently reduced, but it is not suitable due to the excessive investment in tenter equipment.

(Method 5 for Reducing the Inclination of Thermal Shrinkage)

Even for a film having a gradient of thermal shrinkage, the gradient of the thermal shrinkage can be reduced by subjecting the reel once wound to an offline annealing treatment at 80 ° C to 120 ° C for 10 seconds to 90 minutes, for example. In the offline annealing treatment, it is preferably adjusted to sufficiently ensure the temperature and time of the annealing treatment. In addition, the conventional annealing process between the tenter exit and the winding drum is also suitable. At this time, as with the offline annealing treatment described above, it is preferable to sufficiently ensure the temperature and time of the annealing treatment, and it is more preferable to use an air can roll to maintain the heat treatment efficiency or flatness.

These reduction methods 1 to 5 can be implemented individually or in combination. By these methods, the gradient of the thermal shrinkage can be made 15 degrees or less.

The polyester film is subjected to a heat treatment step after longitudinal stretching and lateral stretching, and the two edges are cut to form a mill roll, and the slit roll is cut by cutting if necessary. When the so-called two-edge portion uses the entire length of the wide surface of the film as 100%, it is preferably in the range of 1% to 10%, and more preferably in the range of 1% to 5% from both ends of the film. Further The two ends mentioned here are the same as the two ends of the film before the cutting described in the reduction method 2 described above. Among these, when the rolling reel is divided into three equal parts, the absolute value of the gradient of the heat shrinkage ratio tends to become larger, so it is preferable to set the gradient of the heat shrinkage ratio of this area. The absolute value is controlled below 15 degrees.

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

As specific film forming conditions, for example, the longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 145 ° C, and more preferably 90 to 140 ° C. The longitudinal stretching magnification is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times. The lateral extension ratio is preferably 2.5 to 6.0 times, and more preferably 3.0 to 5.5 times.

In order to control the hysteresis in the above-mentioned specific range, it is preferable to control the ratio of the longitudinal stretching magnification and the lateral stretching magnification. If the difference between the stretching ratios in the vertical and horizontal directions is too small, it is difficult to improve the hysteresis. In addition, setting the elongation temperature to a low level is also preferable for improving the hysteresis. The temperature of the subsequent heat treatment is preferably 100 to 250 ° C, and particularly preferably 180 to 245 ° C.

In order to make the Nz coefficient a specific value as described above, it is preferable to control the ratio of the longitudinal stretching magnification and the lateral stretching magnification, and it is preferable to form a uniaxially stretched film. In order to reduce the Nz coefficient, it is preferable to add a copolymerization component in order to increase the molecular weight of the polymer and reduce the crystallinity. Furthermore, in order to control the Nz coefficient of the film to a specific range, It is performed by setting the total stretching ratio and stretching temperature. For example, the lower the total extension ratio and the higher the extension temperature, the lower the Nz coefficient can be obtained.

In order to make the surface alignment degree the specific value mentioned above, it is preferable to control the total extension ratio. If the total stretching ratio is too high, it is not suitable because the surface alignment degree becomes too high. It is also preferable to control the elongation temperature in reducing the surface alignment. By increasing the difference between the longitudinal stretching magnification and the lateral stretching magnification, and setting the total stretching magnification to be low and the stretching temperature to be high, the Nz coefficient and the surface alignment degree can be made below specific values.

Since the elongation temperature and elongation ratio greatly affect the thickness unevenness of the film, it is also preferable to optimize the film forming conditions from the viewpoint of the thickness unevenness. In particular, if the longitudinal stretching ratio is lowered in order to increase the hysteresis, unevenness in the longitudinal thickness is deteriorated. The vertical thickness unevenness is a very poor region in a specific range of the stretch magnification, and therefore it is appropriate to set film forming conditions outside this range.

The blending of the ultraviolet absorber to the oriented polyester film can be carried out by combining well-known methods. For example, a masterbatch can be prepared by mixing a dried ultraviolet absorber and a polymer raw material in advance by using a kneading extruder, and mixing the specified masterbatch and polymer raw material during film formation, etc. Together.

In order to uniformly disperse and economically mix the ultraviolet absorber, the concentration of the ultraviolet absorbent of the master batch is preferably 5 to 30% by mass. As a condition for preparing the master batch, it is preferable to use a kneading extruder, and extrude at a temperature of from the melting point of the polyester raw material to 290 ° C. or lower and for 1 to 15 minutes. When the temperature is 290 ° C or higher, the reduction of the ultraviolet absorber is large, and the viscosity reduction of the master batch becomes large. During extrusion under 1 minute It is difficult to uniformly mix ultraviolet absorbers. In this case, a stabilizer, a hue adjusting agent, and an antistatic agent may be added as needed.

The blending of the ultraviolet absorber to the intermediate layer of the oriented polyester film having a multilayer structure of three or more layers can be carried out by the following method. Separate the particles of polyester for the outer layer, the master batch containing the ultraviolet absorber for the middle layer, and the particles of the polyester at a specified ratio, dry them, and then supply them to a well-known extruder for melt-lamination. The die was extruded into a sheet shape, and cooled and solidified on a casting roll to produce an unstretched film. That is, using two or more extruders, three-layer collecting pipes, or a junction block (for example, a junction block having a corner junction portion), the film layers constituting the two outer layers and the film layers constituting the intermediate layer are laminated. A three-layer sheet was extruded by a nozzle and cooled on a casting roll to produce an unstretched film.

In order to remove the foreign matter contained in the raw polyester which is the cause of the optical defects, it is preferable to perform high-precision filtration during melt extrusion in the manufacturing process of the oriented polyester film. The filter particle size (initial filtration efficiency 95%) of the filter material for high-precision filtration of molten resin is preferably 15 μm or less. If the filter particle size of the filter material exceeds 15 μm, the removal system of foreign matter of 20 μm or more is liable to be insufficient.

Polarizing plate

The polarizing plate is formed by sandwiching two sides of a polarizer made of an iodine-dyed polyvinyl alcohol film, etc., with at least one of the two polarizer protective films. The absolute value of the gradient of the heat shrinkage rate is a polyester film in a specific range. Moreover, in one embodiment, the polarizing plate preferably has a structure in which a polarizer protective film is laminated on one surface of the polarizer. Polarizer and polarizer protective film are laminated through an adhesive In general, a polarizing plate is obtained by heat treatment in a range of 70 ° C to 120 ° C for about 10 minutes to 60 minutes.

(Configuration of Polarizer Protective Film)

In the liquid crystal display device, the specific polyester film described above is preferably a polarizer protective film using both of a pair of polarizing plates. The pair of polarizing plates refers to a combination of a polarizing plate disposed on the incident light side with respect to the liquid crystal and a polarizing plate disposed on the outgoing light side with respect to the liquid crystal. That is, the polyester film is preferably a polarizing plate used for both a polarizing plate on the incident light side and a polarizing plate on the outgoing light side. This polyester film may be laminated on at least one side of a polarizer constituting each polarizing plate.

In a suitable embodiment, the polyester film uses a polarizer protective film on the incident light side of the polarizer on the incident light side, and uses a polarizer protective film on the exit light side of the polarizer on the outgoing light side. When the alignment polyester film is laminated only on one side of the polarizer constituting the polarizing plate, any polarizer protective film (such as a TAC film, etc.) can be used on the other side, or no polarizer is provided. Protective film. If the polyester film is used as the polarizer protective film on the liquid crystal cell side of the polarizer disposed on the incident light side and the polarizer protective film on the liquid crystal cell side (that is, the incident light side) of the polarizer disposed on the outgoing light side, Since there is a possibility that the polarization characteristics of the liquid crystal cell may be changed, the polarizer protective film at these positions is preferably a polarizer protective film other than the polyester film (for example, TAC film, acrylic film, norbornene-based film). The film is representative of a film without birefringence). These films are also preferably those in which the absolute value of the inclination of the thermal shrinkage is small.

2. Liquid crystal display device

Generally speaking, a liquid crystal display device faces a display image side (visual recognition side or outgoing light side) from a side facing a backlight light source, and has a rear module, a liquid crystal cell, and a front module in this order. The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is arranged on the side opposite to the backlight light source in the rear module, and is arranged on the display image side (visual recognition side or outgoing light side) in the front module.

(Backlight source)

The liquid crystal display device includes at least a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates as constituent members. The liquid crystal display device of the present invention may suitably have other constituent members other than these, such as a color filter, a lens film, a diffusion sheet, an anti-reflection film, and the like.

The constitution of the backlight may be an edge light method using a light guide plate or a reflection plate as a constituent member, or a direct type. The backlight light source is preferably a white light source with a continuous broad emission spectrum. Here, the continuous broad light emission spectrum refers to a light emission spectrum having a wavelength at which light intensity becomes zero in a wavelength region of at least 450 nm to 650 nm, preferably in a visible light region. As a white light source having such a continuous broad light emission spectrum, a white LED is mentioned, for example, but it is not limited to this.

The white LED that can be used in the present invention includes a phosphor method, that is, a device that emits white by using a compound semiconductor emitting blue or ultraviolet light emitting diode and a phosphor, or an organic light emitting diode Body (Organic light-emitting diode: OLED) and the like. Examples of the phosphor include yttrium, aluminum, and garnet yellow phosphors. Or yellow phosphor of 鋱 ‧aluminum garnet series. Among the white LEDs, a white light emitting diode composed of a light emitting element using a compound semiconductor blue light emitting diode and a yttrium, aluminum, and garnet yellow phosphor is a continuous and wide light emitting diode. The light emission spectrum and the light emission efficiency are also excellent, so it is suitable as the backlight light source of the present invention. Since the white LED consumes less power, the liquid crystal display device of the present invention using it also contributes to energy saving.

Fluorescent tubes such as cold-cathode tubes or hot-cathode tubes, which have been widely used as backlight light sources in the past, are discontinuous light-emission spectra in which the emission spectrum has a peak at a specific wavelength. Therefore, since it is difficult to obtain the effect of suppressing iridescence, it is not suitable as a light source of the liquid crystal display device of the present invention.

[Example]

Hereinafter, the present invention will be described more specifically with reference to the examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate changes within the scope suitable for the purpose of the present invention. They are all included in Within the technical scope of the present invention.

The evaluation method of the physical property in an Example is as follows.

(1) Thermal shrinkage and its inclination

The polyester film cut from each cut-out portion of the slitting roll was cut into a 21 cm square shape, and left for more than 2 hours in an environment of 23 ° C and 65% RH. A circle with a diameter of 80 mm was drawn with the center of the polyester film as the center, and the diameter was measured at a 5 degree interval using a two-dimensional image measuring machine (QUICK IMAGE by MITUTOYO) as the flow direction of the film as 0 degrees. Here, the flow direction of the film is taken as 0 degrees, the clockwise rotation (right turn) of the upper surface of the film is set to a positive angle, and the counterclockwise rotation (turn left) Set to a negative angle. In order to measure the diameter, the measurement is performed in the range of -90 degrees to 85 degrees in all directions. Next, after heat-treating this polyester film in water at 85 ° C for 30 minutes, the moisture attached to the surface of the film was wiped and air-dried, and then left in an environment of 23 ° C and 65% RH for more than 2 hours. Then, in the same manner as described above, the diameter of the circle was measured at 5-degree intervals. Let the diameter before the heat treatment be Lo, and the diameter in the same direction after the heat treatment as L, and the heat shrinkage in each direction was determined according to the following formula.

Thermal shrinkage (%) = ((L ₀ -L) / L ₀ ) × 100

(Maximum thermal shrinkage)

The maximum value of the thermal contraction rate in all directions was taken as the maximum thermal contraction rate. For each slit roll (L, C, R), three points were sampled in the film width direction (three points at the center and both ends), and the same evaluation was performed. The average of the three maximum heat shrinkage ratios was taken as The maximum values of the thermal shrinkage are shown in Table 1. Furthermore, in this embodiment, the maximum thermal shrinkage of any slitting roll at the three points of the center and both ends is 5% or less.

(Reading of the maximum direction (α) of thermal shrinkage)

From the results of obtaining the thermal shrinkage in all directions, the slope of the thermal shrinkage was measured as follows. As shown in Figure 2, the horizontal axis is taken as the angle, the vertical axis is taken as the thermal shrinkage rate corresponding to the angle, and the measured values (-90 degrees to 85 degrees) are plotted, and -180 degrees to -95 degrees are interpolated. 90 degrees to 175 degrees. (The thermal contraction rate of -90 degrees corresponds to a thermal contraction rate of 90 degrees, and the thermal contraction rate of 0 degrees corresponds to a thermal contraction rate of -180 degrees). Next, draw an approximate curve connecting the trace points, and read the direction in which the thermal shrinkage rate becomes the largest with an accuracy of 1 degree, and define it as α. However, -90 degrees ≦ α ≦ 90 degrees.

(Inclination of heat shrinkage)

When the direction α in which the heat shrinkage ratio becomes the maximum is in the range of -45 degrees to 45 degrees, this value is taken as the slope of the heat shrinkage ratio. In addition, when the direction in which the heat shrinkage ratio becomes the maximum α is 45 degrees or more and -45 degrees or less, it is understood that instead of tilting the film flow direction to the reference, the film width direction is tilted to the reference, and α-90 degrees ( When α is 45 degrees or more), 90 degrees + α (when α is -45 degrees or less) are taken as the slopes of the heat shrinkage rate. For each slit roll (L, C, R), three points were sampled (three points at the center and both ends) in the film width direction, and the above measurement was performed in the same manner, and the inclination of the three heat shrinkage rates was The average value of the absolute value of is shown in Table 1 as the gradient of the thermal shrinkage. Furthermore, in this embodiment, the absolute value of the inclination of the thermal contraction rate at three points at the center and both ends is 15 degrees or less.

(2) Light leakage evaluation method

On one side of a polarizer made of a PVA film, a triethyl cellulose film (manufactured by Fujifilm (stock), thickness 80 μm) was bonded, and on the other side, a polyester produced by a method described later was bonded. film. An adhesive was used for bonding, and a heat treatment was performed at 85 ° C. for 30 minutes in an oven to manufacture a polarizing plate. Furthermore, the polarizing axis of the polarizer and the main alignment axis of the polyester film are bonded to each other so as to be perpendicular to each other. The two polarizing plates thus obtained were arranged as crossed Nicols. At this time, two polarizers are arranged so that each polyester film is located outside the polarizer. Then, the maximum light transmittance of light having a wavelength of 550 nm to 600 nm that passed through the two polarizing plates was measured using a spectrophotometer V7100 made by Japan Spectroscopy. The measurement results were evaluated as follows.

○: Maximum light transmittance is 0.02% or less

×: Maximum light transmittance is 0.02% or more

(3) Hysteresis (Re)

The so-called hysteresis is a parameter defined by the product of the anisotropy (△ Nxy = | nx-ny |) of the orthogonal biaxial refractive index on the film and the film thickness d (nm) (△ Nxy × d). It is a scale representing optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) is obtained by the following method. Using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 molecular alignment meter), the orientation axis direction of the film is obtained, and a 4 cm × 2 cm rectangle is cut out so that the orientation axis direction becomes a long side. Measurement samples. For this sample, an Abbe refractometer (NAR-4T manufactured by ATAGO, measuring wavelength: 589 nm) was used to measure the refractive index (nx, ny) and the refractive index (Nz) in the thickness direction of the orthogonal biaxial direction. The absolute value (| nx-ny |) of the difference between the refractive indices of the axes is taken as the anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (Militron 1245D, manufactured by Feinpruef, Inc.), and the unit was converted to nm. The hysteresis (Re) is obtained from the product of the anisotropy (ΔNxy) of the refractive index and the thickness d (nm) of the film (ΔNxy × d).

(4) Nz coefficient

Let the value obtained from | ny-nz | / | ny-nx | be used as the Nz coefficient. However, in order to become ny> nx, the values of ny and nx are selected.

(5) Plane orientation (△ P)

The value obtained from (nx + ny) / 2-nz is taken as the surface alignment degree (ΔP).

(6) Thickness Hysteresis (Rth)

The so-called thickness-direction hysteresis is obtained by multiplying the two birefringences ΔNxz (= | nx-nz |) and △ Nyz (= | ny-nz |) by the film thickness d when viewed from a section in the thickness direction of the film. The average parameter of the hysteresis. With and late The method of measuring the hysteresis is to calculate nx, ny, nz and the film thickness d (nm), calculate the average value of (ΔNxz × d) and (ΔNyz × d), and obtain the thickness direction hysteresis (Rth).

(7) Rainbow spot observation

On one side of a polarizer made of PVA and iodine, a polyester film made by the method described below is attached so that the polarizing axis of the polarizer and the alignment main axis of the polyester film are perpendicular to each other. A TAC film (manufactured by Fujifilm (strand), thickness: 80 μm) was attached on the surface, and a polarizing plate was produced. The obtained polarizing plates were arranged so that liquid crystals were sandwiched on each of the two sides, and the polarizing plates were arranged in a relationship of crossed Nicols to produce a liquid crystal display device. Each polarizing plate is arrange | positioned so that the said polyester film may become the opposite side (remote position) to a liquid crystal. As the light source of the liquid crystal display device, a white LED composed of a light emitting element combining a blue light emitting diode and a yttrium, aluminum, and garnet yellow phosphor is used as the light source (Nichia Chemicals, NSPW500CS). From the front and oblique directions of such a liquid crystal display device, visual observation was performed, and the presence or absence of iridescence was determined as follows.

A: From any direction, no rainbow spots occurred.

A ': When viewed from an oblique direction, an extremely pale rainbow spot was observed depending on the angle.

B: When viewed from an oblique direction, a pale rainbow spot was observed depending on the angle.

C: When viewed from an oblique direction, a rainbow spot was observed.

D: When viewed from the front direction and oblique direction, rainbow spots were observed.

(8) Tear strength

The tear strength of each film was measured using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho in accordance with JIS P-8116. Tear direction system and film The direction of the main axis of alignment is performed in parallel, and it is determined as follows. The measurement in the direction of the alignment main axis was performed using a molecular alignment meter (manufactured by Oji Instruments Co., Ltd., MOA-6004 molecular alignment meter).

○: Tear strength is 50 mN or more

×: Tear strength is less than 50mN

(Production Example 1-Polyester A)

The esterification reaction tank was heated up, and when it reached 200 ° C, 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were added, and 0.017 parts by mass of antimony trioxide and 0.064 as catalysts were added while stirring. Parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine. Next, the temperature was increased under pressure, and the pressure esterification reaction was performed under the conditions of a gauge pressure of 0.34 MPa and 240 ° C. Then, the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. 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, dispersion treatment was performed using a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tank, and a polycondensation reaction was performed at 280 ° C under reduced pressure.

After completion of the polycondensation reaction, a 95% cut-off filter made of Naslon with a diameter of 5 μm was used for filtering treatment, a strand was extruded from a nozzle, and cooling was performed using cooling water that had been previously filtered (pore diameter: 1 μm or less) , Curing, cutting into granules. The obtained polyethylene terephthalate resin (A) had an inherent viscosity of 0.62 dl / g, and substantially contained no inert particles and internally precipitated particles. (Hereinafter referred to as PET (A)).

(Production Example 2-Polyester B)

10 parts by mass of the dried ultraviolet absorber (2,2 '-(1,4-phenylene) bis (4H-3,1-benzo -4-ketone), 90 parts by mass of particle-free PET (A) (inherent viscosity 0.62 dl / g), and using a kneading extruder, a polyethylene terephthalate resin containing an ultraviolet absorber was obtained (B). (Hereinafter, referred to as PET (B)).

(Production Example 3-Adjustment of Adhesive Modification Coating Liquid)

The transesterification reaction and the polycondensation reaction are performed by a common method to prepare 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol of dicarboxylic acid (relative to the entire dicarboxylic acid component). Water dispersion of mole% of sodium 5-sulfonate isophthalate, 50 mole% of ethylene glycol and 50 mole% of neopentyl glycol as a diol component (relative to the entire diol component) Copolymer polyester resin containing sulfonic acid metal base. Next, after mixing 51.4 parts by mass of water, 38 parts by mass of isopropanol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a non-ionic surfactant, heat and stir. Once it reaches 77 ° C, add 5 parts by mass Parts of the water-dispersible copolymerized polyester resin containing a metal sulfonic acid base, and stirring was continued until the agglomerates of the resin disappeared, and then the resin aqueous dispersion was cooled to normal temperature to obtain a uniform water having a solid content concentration of 5.0% by mass. Dispersive copolymerized polyester resin solution. Furthermore, 3 parts by mass of aggregated silica particles (Silysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water, and then 99.46 parts by mass of the above-mentioned water-dispersible copolymerized polyester resin solution. 0.54 parts by mass of a water dispersion of Silysia 310 was added, and 20 parts by mass of water was added while stirring to obtain an adhesive modified coating solution.

(Polarizer protective film 1)

90 parts by mass of non-particle PET (A) resin particles and 10 parts by mass of PET (B) resin particles containing an ultraviolet absorber as raw materials for the intermediate layer of the base film were dried under reduced pressure at 135 ° C (1 Torr) 6 After hours, supply It goes to the extruder 2 (for the intermediate layer II layer), and the PET (A) is dried by a common method, and is respectively supplied to the extruder 1 (for the outer layer I layer and the outer layer III), and is dissolved at 285 ° C. These two kinds of polymers were respectively filtered with a filter material of a stainless steel sintered body (95% of particles with a nominal filtering accuracy of 10 μm retained), and were laminated in two kinds of three-layer converging blocks, extruded into a sheet form by a nozzle, and then electrostatically applied. In the casting method, it is wound on a casting drum having a surface temperature of 30 ° C, and is cooled and solidified to produce an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer became 10:80:10.

Next, on both sides of the unstretched PET film, the adhesive modified coating liquid was applied on both sides of the unstretched PET film so that the coating amount after drying became 0.08 g / m ² , and then dried at 80 ° C for 20 seconds.

The unstretched film on which the coating layer was formed was guided to a tenter stretcher, and while holding the end of the film with a jig, it was guided to a hot air zone having a temperature of 125 ° C, and stretched 4.0 times in the width direction. Next, while maintaining the stretched width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and then cut the film cooled to 130 ° C with a cutter at a position of 2% from both ends, at 0.5 kg / mm. Take up the tension of ² and remove both edges by cutting to obtain a rolled roll made of a uniaxially oriented PET film with a film thickness of about 50 μm. This rolled roll was divided into three equal parts to obtain three slit rolls (L, C, R). Furthermore, let the slitting roll on the left with respect to the film flow direction be L, let the slitting roll on the right be R, and let the center be C.

(Polarizer protective film 2)

In addition to changing the thickness of the unstretched film, Except for 100 μm, similar to the polarizer protective film 1, a slit roll (L, C, R) made of a uniaxially oriented PET film was obtained.

(Polarizer protective film 3)

Except for cutting without using a cutter after heat setting, as in the case of the polarizer protective film 1, three slit rolls (L, C, and R) formed by a uniaxially aligned PET film were obtained.

(Polarizer protective film 4)

Using a heated roller group and an infrared heater, the unstretched film produced by the same method as the polarizer protective film 1 is heated to 105 ° C, and then the roller group having a peripheral speed difference is extended twice in the traveling direction. In the same way as the polarizer protective film 1, it was extended 4.0 times in the width direction, and then the film cooled to 140 ° C was cut with a cutter at a position of 2% from both ends, and 0.65 Take up a tension of kg / mm ² and adjust the thickness of the unstretched film to obtain three slit rolls (L, C, R) formed by a biaxially oriented PET film with a film thickness of about 50 μm.

(Polarizer protective film 5)

Except as a method of separating the film from the jig, and changing the method of cutting with a cutter to a method of releasing the jig, as in the case of the polarizer protective film 1, three slitting rolls made of a uniaxially aligned PET film were obtained. (L, C, R).

(Polarizer protective film 6)

By the same method as that of the polarizer protective film 1, extending 1.0 times in the traveling direction and 3.5 times in the width direction, three slitting rolls made of a biaxially oriented PET film with a film thickness of about 75 μm were obtained ( L, C, R).

(Polarizer protective film 7)

Using the same method as that of the polarizer protective film 1, changing the thickness of the unstretched film, setting the lateral stretching magnification to 3.8 times, and setting the stretching temperature to 135 ° C, 3 of a uniaxially oriented PET film having a thickness of about 100 μm was obtained. Supported slitting rolls (L, C, R).

(Polarizer protective film 8)

Using the same method as the polarizer protective film 1, the lateral stretching magnification was set to 3.8 times, and the stretching temperature was set to 135 ° C. Three slitting rolls made of a uniaxially oriented PET film with a thickness of about 50 μm were obtained ( L, C, R).

(Polarizer protective film 9)

Except for cutting without using a cutter after heat setting, three slit rolls (L, C, and R) formed from a uniaxially aligned PET film were obtained in the same manner as in the polarizer protective film 8.

(Polarizer protective film 10)

Using the same method as that of the polarizer protective film 1, setting the lateral stretching magnification to 4.2 times and the stretching temperature to 135 ° C, three slitting rolls made of a uniaxially oriented PET film with a thickness of about 50 μm were obtained ( L, C, R).

(Polarizer protective film 11)

Except for setting the take-up tension after cutting the cutter to 0.2 kg / mm ² , similar to the polarizer protective film 10, three slit rolls (L, C, R).

(Polarizer protective film 12)

Except for cutting without using a cutter after heat setting, similar to the polarizer protective film 10, three slit rolls (L, C, and R) made of a uniaxially aligned PET film were obtained.

(Polarizer Protective Film 13)

By the same method as that of the polarizer protective film 4, it is extended 1.8 times in the traveling direction and 2.0 times in the width direction, and the winding tension after the cutter is cut is set to 0.2 kg / mm ² to obtain a film thickness of about Three slit rolls (L, C, R) made of 275 μm biaxially oriented PET film.

(Polarizer protective film 14)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, then maintain the extended width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and shorten the 0.2% clamp interval in the flow direction in a temperature range of 90 ° C to 70 ° C to obtain a uniaxial film with a thickness of about 75 μm Three slitting rolls (L, C, R) formed by aligning PET film.

(Polarizer protective film 15)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, then maintain the extended width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and shorten the 0.1% clamp interval in the flow direction in a temperature range of 90 ° C to 70 ° C to obtain a uniaxial film with a thickness of about 75 μm Three slitting rolls (L, C, R) formed by aligning PET film.

(Polarizer Protective Film 16)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, and then maintain the extended width in the width direction, at a temperature of 225 ° C After processing for 30 seconds, the clamping interval of 0.2% in the flow direction was reduced in the temperature range of 110 ° C to 70 ° C, and three slit rolls (L, C, and L) formed by a uniaxially oriented PET film with a film thickness of about 75 μm were obtained. R).

(Polarizer Protective Film 17)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, then maintain the extended width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and reduce the 0.4% clamp interval in the flow direction in a temperature range of 150 ° C to 100 ° C to obtain a uniaxial film with a thickness of about 75 μm Three slitting rolls (L, C, R) formed by aligning PET film.

(Polarizer Protective Film 18)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, then maintain the extended width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and cool at a temperature setting of -55 ° C / m per unit width to obtain a uniaxially oriented PET film with a film thickness of about 75 μm Into 3 slit rolls (L, C, R).

(Polarizer Protective Film 19)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Extend 3.5 times, then maintain the extended width in the width direction, treat at a temperature of 225 ° C for 30 seconds, and cool at a temperature setting of -35 ° C / m per unit width. To three slit rolls (L, C, R) formed by a uniaxially oriented PET film with a film thickness of about 75 μm.

(Polarizer protective film 20)

The unstretched film produced by the same method as the polarizer protective film 1 is guided to a tenter stretcher, while holding the end of the film with a clamp, it is guided to a hot air zone with a temperature of 125 ° C in the width direction Stretched 3.5 times, followed by maintaining the stretched width in the width direction, treated at a temperature of 225 ° C for 30 seconds, and cooled at a temperature setting of -120 ° C / m per unit width to obtain a uniaxially oriented PET film with a film thickness of about 75 μm Into 3 slit rolls (L, C, R).

Regarding the polarizer protective films 1 to 20, Table 1 shows the absolute value of the gradient of the thermal shrinkage rate, the maximum value of the thermal shrinkage rate, and the results of the light leakage evaluation.

In Table 1, the "film" refers to the above-mentioned polarizer protective film.

Regarding the liquid crystal display device manufactured as described above using the polarizer protective films 1 to 20, the results of the rainbow spot observation and the measurement of the tear strength are shown in Table 2 below.

According to the results shown in Table 1, if the absolute value of the gradient showing the thermal shrinkage is 15 degrees or less, it is possible to suppress slight light leakage when the two polarizing plates are arranged in a relationship of orthogonal Nicols. In addition, the maximum value of the thermal shrinkage of the polarizer protective films 1 to 20 is less than 1%.

According to the results shown in Table 2, when the hysteresis of the oriented polyester film was 4,000 or more and the Nz coefficient was 1.7 or less, the occurrence of iridescence was significantly suppressed. In addition, in addition to this condition, The surface orientation is controlled below 0.13, showing that the occurrence of rainbow spots can be suppressed more effectively.

[Industrial availability]

According to the present invention, it is possible to provide a polyester film containing a liquid crystal display device suitable for obtaining a liquid crystal display device having excellent visibility when suppressing the occurrence of slight light leakage when two polarizing plates are arranged in a cross-Nicol relationship. Polarizer protective film. Therefore, the industrial possibility of the present invention is extremely high.

Claims (8)

A polarizer protective film comprising a polyester film having an absolute value of an inclination of 15 degrees or less with respect to the direction in which the heat shrinkage ratio becomes the largest with respect to the flow direction or width direction of the film. For example, the polarizer protective film of claim 1, wherein the polyester film has a hysteresis of 4000 to 30,000 nm and an Nz coefficient of 1.7 or less. For example, the polarizer protective film of claim 1 or 2, wherein the surface alignment of the polyester film is 0.13 or less. A polarizing plate includes a structure in which a polarizer protective film is laminated on both sides of the polarizer, and the polarizer protective film on at least one side is the polarizer protective film according to any one of claims 1 to 3. A polarizing plate is formed by laminating a polarizer protective film according to any one of claims 1 to 3 on one side of a polarizer. A liquid crystal display device is a liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The backlight light source is a white light source having a continuous light emission spectrum, and the polarizing plate. The polarizer protective film is laminated on both sides of the polarizer, and at least one of the polarizer protective film of the polarizer disposed on the incident light side and at least one of the polarizer protective film of the polarizer disposed on the outgoing light side. One is the polarizer protective film according to any one of claims 1 to 3. The liquid crystal display device according to claim 6, wherein the polarizer protective film on the incident light side of the polarizing plate disposed on the incident light side and the outgoing light The polarizer protective film on the light-emitting side of the polarizer on the side is the polarizer protective film according to any one of claims 1 to 3. A liquid crystal display device is a liquid crystal display device having a backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The backlight light source is a white light source having a continuous light emission spectrum, and the polarizing plate. The polarizing plate as in item 5.