TWI557447B - Liquid crystal display device, polarizing plate and polarizer - Google Patents

Description

Liquid crystal display device, polarizing plate and polarizer protective film

The present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film. More specifically, the present invention relates to a liquid crystal display device, a polarizing plate, and a polarizer protective film which are excellent in visibility and are suitable for thinning.

The liquid crystal display device is widely used in mobile phones, tablet terminals, personal computers, televisions, PDAs, electronic dictionaries, computers, music players, digital cameras, digital cameras, and the like. In view of the progress of miniaturization and weight reduction of the liquid crystal display device, the use thereof has not been limited to an office or an indoor space, and has been expanded to outdoor use and use in the movement of a car or a train.

Patent Document 1 discloses that a polyester film having a hysteresis of 3,000 to 30,000 nm is used as a polarizer for the purpose of suppressing image quality deterioration due to a rainbow ray or the like which may occur depending on the angle of gaze in the case of gazing at the liquid crystal display device. Protective film.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] WO2011/162198

However, there is a need in the market for a thinner liquid crystal display device. Although the hysteresis is controlled to only 3,000 to 30,000 nm, the visibility of the rainbow spot can be degraded, but the mechanical strength is remarkably lowered by thinning the thickness of the film. Therefore, it is difficult to correspond to the requirements for thinning. Therefore, an object of the present invention is to provide a polarizing mirror protective film, a polarizing plate, and a liquid crystal display device which are excellent in visibility and which can reduce the thickness of a liquid crystal display device.

In order to solve the above problems, the inventors of the present invention have repeatedly observed the above-mentioned problems and found that the surface alignment degree of the polyester film is controlled to be constant or lower, and the hysteresis value can be maintained at 3,000 or more and 30,000 or less, while maintaining good visibility. , to improve the mechanical strength of the film, and to make the thickness of the film thinner. Based on such findings, the present inventors have completed the present invention by further reviewing and improving them.

Representative inventions are as follows.

Item 1. A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, wherein the backlight source is a white light source having continuous emission mass spectrum, and the polarizing plate 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 is a polyester film satisfying the following physical properties (a) to (c): (a) 3000 nm or more Hysteresis (Re) of 30000 nm or less; (b) ratio of retardation (Re) of 1.0 or more to retardation of thickness direction (Rth) (Re/Rth); and (c) plane alignment degree (ΔP) of 0.12 or less.

The liquid crystal display device of item 1, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more.

The liquid crystal display device of item 1 or 2, wherein the polyester film is a polarizer protective film which is formed on the polarizing plate on the viewing side of the liquid crystal cell.

The liquid crystal display device according to any one of items 1 to 3, wherein the polyester film has a thickness of 20 μm or more and 90 μm or less.

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. A polarizing plate having a structure in which a polyester film satisfying the following physical properties (a) to (c) is laminated on at least one surface of a polarizer: (a) hysteresis (Re) of 3000 nm or more and 30,000 nm or less; (b) a ratio of retardation (Re) of 1.0 or more to a retardation (Rth) in the thickness direction (Re/Rth); and (c) a plane alignment degree (ΔP) of 0.12 or less.

The polarizing plate of item 6, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more.

The polarizing plate of item 6 or 7, wherein the polyester film has a thickness of from 20 μm to 90 μm.

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. A polarizer protective film which is a polyester film which satisfies the following physical properties (a) to (c): (a) hysteresis (Re) of 3000 nm or more and 30000 nm or less; (b) ratio of retardation (Re) of 1.0 or more to retardation of thickness direction (Rth) (Re/Rth); and (c) plane alignment of 0.12 or less (ΔP) ).

Item 11. The polarizer protective film according to Item 10, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more.

The polarizer protective film of item 10 or 11, wherein the polyester film has a thickness of from 20 μm to 90 μm.

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. A method for producing a polarizer protective film, comprising the step of simultaneously stretching a polyester film while being relaxed in a direction orthogonal to the extending direction, and satisfying the following physical properties (a)~ (c) polyester film: (a) hysteresis (Re) of 3000 nm or more and 30,000 nm or less; (b) ratio of retardation (Re) of 1.0 or more to thickness direction retardation (Rth) (Re/Rth); and (c) The surface orientation (ΔP) of 0.12 or less.

Item 15. The polarizing plate according to any one of items 6 to 9, which is for use in a liquid crystal display device having a white light source including continuous luminescence mass spectrum.

The polarizer protective film according to any one of items 10 to 13, which is for use in a liquid crystal display device having a white light source including continuous luminescence mass spectrum.

Item 17. The method of item 14, wherein the polarizer protective film is used for a liquid crystal display device having a white light source containing a continuous luminescence mass spectrum.

Since the polarizer protective film of the present invention is excellent in mechanical strength (tear strength), it is suitable for thinning. Further, the polarizer protective film of the present invention and the polarizing plate formed by laminating the same are used to produce a liquid crystal display device, and in the case of gazing at an image, it is possible to suppress a rainbow spot which may occur depending on the angle of the gaze image. It happened. Therefore, according to the present invention, it is possible to provide a liquid crystal display device which is excellent in visibility and thinner. In addition, in this specification, the so-called "rainbow" includes the concepts of "spot", "color shift", and "interference color".

1‧‧‧ polyester film

2‧‧‧ indicates the line perpendicular to the face of the polyester film

3‧‧‧Connect the line of the observer's eye to the line of the film (center)

4‧‧‧The position of the observer's eyes

Fig. 1 is a pattern diagram of the observation angle (θ).

[Formation of the Invention]

The liquid crystal display device includes a backlight source, two polarizing plates, and liquid crystal cells disposed between the two polarizing plates. In the present specification, the side of the backlight source position of the liquid crystal display device is referred to as the "light source side" with respect to the side on which the person views the image, and the side where the person views the image is referred to as the "view side". The arrangement order of the constituent members of the liquid crystal display device is generally a backlight source, a polarizing plate (also referred to as a "light source side polarizing plate"), a liquid crystal cell, and a polarizing plate (also referred to as "visual recognition" from the light source side toward the viewing side. The order of the side polarizers").

From the standpoint of suppressing the generation of rainbow spots in the case of visualizing images, the backlight source is preferably a white light source having a continuous and extensive illumination mass spectrum. "Continuous and extensive luminescence mass spectrometry" means at least 450 to 650 nm The wavelength region, preferably in the region of visible light, does not have an illuminating mass spectrum of a wavelength region where the intensity of light is zero. The visible light region may be, for example, a wavelength region of 400 to 760 nm, 360 to 760 nm, 400 to 830 nm, or 360 to 830 nm.

The manner or configuration of a white light source having a continuous and extensive luminescence mass spectrum is not particularly limited. Any white light source may be used as long as the generation of rainbow spots can be suppressed, but a preferred light source is a white light emitting diode (LED). The white LED includes a phosphor (that is, a device that emits blue light or a light-emitting diode and a phosphor to emit white light by using a compound semiconductor in combination) and an organic light-emitting diode. (Organic light-emitting diode: OLED). In one embodiment, the preferred white LED is a white LED of a phosphor type, and more preferably a blue light emitting diode and a germanium comprising a compound semiconductor in combination. aluminum. A white LED of a garnet-based yellow phosphor light-emitting element.

The liquid crystal cell system can be appropriately selected and used in any liquid crystal cell which can be used in a liquid crystal display device, and the mode or structure thereof is not particularly limited. For example, a liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a curved alignment (π type) can be appropriately selected and used. Therefore, the liquid crystal cell system can be suitably selected by using a well-known liquid crystal material and a liquid crystal produced by developing a liquid crystal material obtained in the future. In one embodiment, the preferred liquid crystal cell is a transmissive liquid crystal cell.

The polarizing plate has a structure in which two protective film (also referred to as "polarizing mirror protective film") are sandwiched between both sides of the film-shaped polarizing mirror. The polarizer can be appropriately selected from any of the polarizers (or polarizing films) used in the technical field. As for the representative polarizer, the iodine and the like can be cited. The coloring material is dyed with a polyvinyl alcohol (PVA) film or the like, but is not limited thereto, and a polarizing lens which is well known and developed in the future can be appropriately selected and used.

Commercially available products can be used as the PVA film used as the polarizer. For example, "Kuraray Vinylon (Kuraray Co., Ltd.)", "Tohcello Vinylon (manufactured by Tohcello)", "Nikkei Vinylon" (Japanese Synthetic Chemistry (" The dichroic material may, for example, be iodine, a diazo compound or a polymethine dye.

The liquid crystal display device usually includes two polarizing plates, and the polarizing plate is usually composed of two polarizing mirrors and a polarizing mirror protective film laminated on both sides thereof. Therefore, the liquid crystal display device can include four polarizing mirror protective films. . In the present invention, at least one of the four polarizer protective films is preferably a polyester film satisfying the following physical properties (a) to (c): (a) a retardation of 3000 nm or more and 30,000 nm or less ( Re); (b) ratio of retardation (Re) of 1.0 or more to retardation of thickness direction (Rth) (Re/Rth); (c) plane alignment degree (ΔP) of 0.12 or less.

From the viewpoint of reducing the rainbow spot, the hysteresis of the polyester film used as the polarizer protective film is preferably from 3,000 nm to 30,000 nm. The lower limit of the hysteresis is preferably 4,500 nm or more, more preferably 5,000 nm or more, further preferably 6,000 nm or more, still more preferably 8,000 nm or more, and still more preferably 10,000 nm or more. On the other hand, even if the hysteresis is further increased, the effect of improving the visibility is substantially not obtained, and the thickness of the alignment film tends to increase depending on the magnitude of the hysteresis. Therefore, it may not conform to the demand for thinning. , the department will be late The upper limit of the hysteresis is set to 30000 nm, but it can also be set to a higher value. In addition, in this specification, only the case of "hysteresis" means the in-plane retardation.

The hysteresis is expressed by the product of the birefringence (ΔNxy) and the thickness (d) generated by light incident on the film surface (x-y plane). Therefore, the larger the value of ΔNxy, the higher the hysteresis can be obtained. On the other hand, the thinner the thickness of the film, the smaller the relative hysteresis becomes, and in order to reduce the thickness while maintaining a certain hysteresis value or more, it is preferable that the value of ΔNxy is large. However, when 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 from 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, still more preferably 0.11 or more and 0.145 or less. Further, in the case of a polyethylene naphthalate film, the value of ΔNxy is preferably less than 0.3, more preferably less than 0.27, still more preferably less than 0.25, still more preferably less than 0.24. On the other hand, when the birefringence ΔNxy is low, the necessity of increasing the thickness of the film in order to increase the hysteresis occurs, so in the case of the polyethylene naphthalate film, the birefringence ΔNxy is preferably 0.15. The above is more preferably 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 hysteresis value of the polyester film varies depending on the viewing angle. Here, the observation angle means a deviation (θ) from the plane of the polyester film with respect to the direction of the vertical direction (zero degree) in the direction in which the observer gazes at the polyester film (Fig. 1). The larger the observation angle becomes, the lower the value of the hysteresis in this angle. For this reason, there will be even if it is from the display device The front side (ie, the vertical direction) is not observed when the rainbow spot is observed, but the rainbow spot may be observed when viewed from the oblique direction. Therefore, in order to ensure good visibility even when the display device is viewed from the oblique direction, it is preferable to consider the decrease in hysteresis caused by an increase in the observation angle. In particular, in the case of a polyester film having a small thickness, since the hysteresis is relatively low, the influence on the visibility due to the decrease in the hysteresis with an increase in the observation angle is relatively large. The ratio (Re/Rth) of the hysteresis (Re) to the thickness direction retardation (Rth) of the polyester film is used as an index indicating the degree of decrease in hysteresis accompanying an increase in the observation angle. It is generally considered that the larger the Re/Rth becomes, the more isotropic due to the action of birefringence, and the degree of decrease in hysteresis caused by the increase of the observation angle becomes small, so that the rainbow spot caused by the observation angle becomes difficult to produce. . From such a viewpoint, the Re/Rth system 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 further preferably 1.3 or more. The retardation in the thickness direction means the average value of the hysteresis obtained by multiplying the film thickness (d) by the two birefringences ΔNxz and ΔNyz when viewed from the cross section of the film thickness direction.

The maximum value of the Re/Rth ratio is 2.0 (that is, a complete 1-axis symmetrical film), but there is a machine that is oriented in a direction orthogonal to the direction of the alignment main axis with a completely 1-axis symmetrical film close to more than 1.0. In the case where the strength is lowered, in this case, it is preferable to adjust the surface alignment degree to be described later to a specific value or less. From the viewpoint of improvement in film formation and viewing angle characteristics, the Re/Rth ratio is preferably higher, but the upper limit is not necessarily as large as 2.0, and is preferably 1.9 or less, more preferably 1.8 or less.

The hysteresis of the alignment film can be in accordance with well-known techniques. Determination. Specifically, the refractive index and thickness in the two-axis direction can be measured. Further, it can be obtained by using a commercially available automatic birefringence measuring device (for example, KOBRA-21ADH: manufactured by Oji Scientific Instruments Co., Ltd.). In any of the measurements, the measurement wavelength can be set to 589 nm which is the wavelength of the sodium D line.

From the viewpoint of satisfying the hysteresis of the rainbow spot and the Re/Rth ratio, while maintaining the mechanical strength (tear strength) of the liquid crystal display device which can withstand industrial production, the thickness of the film is thinner, and the surface alignment degree is improved. (ΔP) is preferably 0.12 or less. The surface alignment is a difference between the average value of the refractive index (Nx) in the longitudinal direction of the film and the refractive index (Ny) in the width direction, and the value of the refractive index (Nz) in the thickness direction, which can be expressed by the following formula: ΔP = ( (Nx+Ny)/2)-Nz.

The upper limit of the surface alignment degree is more preferably 0.11 or less, further preferably 0.102 or less, still more preferably 0.1 or less, still more preferably 0.098 or less, still more preferably 0.095 or less, still more preferably 0.09 or less. On the other hand, the lower limit of the surface alignment degree is preferably 0.04 or more, more preferably 0.05 or more, still more preferably 0.06 or more.

In the case where the surface alignment degree is less than 0.04, the mechanical strength of the film is too low, and the workability is not preferable. In addition, in the case where the surface alignment degree exceeds 0.12, it is difficult to have hysteresis and mechanical strength in the film condition, and it is not preferable in any case that a defect occurs.

The thickness (d) of the polyester film used as the polarizer protective film is not particularly limited, but from the viewpoint of providing a thinner polarizer protective film, a polarizing plate, and a liquid crystal display device, it is preferably 300 μm or less, and more preferably It is 100 μm or less, further preferably 90 μm or less, and further It is preferably 80 μm or less, more preferably 60 μm or less, still more preferably 50 μm or less, still more preferably 45 μm or less, particularly preferably 40 μm or less, and most preferably 35 μm or less. From the viewpoint of maintaining sufficient tear strength, 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.

It is preferable that the polyester film used as the polarizer protective film maintains mechanical strength capable of withstanding handling in the manufacture of industrial liquid crystal display devices even when the thickness is small. From this viewpoint, the polyester film preferably has a tear strength of 50 mN or more. Preferably, the tear strength is 100 mN or more, more preferably 130 mN or more. The tear strength of the film is measured in accordance with the method of JIS P-8116 as shown in the examples described later.

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

For the purpose of suppressing the deterioration of the optical functional dye such as iodine dye, the polyester film used as the polarizer protective film preferably has a light transmittance of 380 nm or less of 20% or less. The light transmittance at 380 nm is 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 the present specification, the transmittance is determined by the vertical method with respect to the plane of the film. A photometer (for example, Hitachi U-3500 type) is measured. 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, gelation inhibitors, interfaces The active agent or the like can be added within a range that does not impair the effects of the present invention and does not impair transparency.

The polyester film which satisfies the above physical properties can be obtained by controlling the stretching conditions and the like in the production conditions of a general polyester film. Polyester film is generally produced by the following procedure. That is, the molten polyester resin is extruded and formed into a sheet-like unaligned polyester at a temperature higher than the glass transition temperature, and is extended in the longitudinal direction by the difference in speed of the rolls, and then extended in the lateral direction by a tenter, and Obtained by applying heat treatment. The extension in the longitudinal direction and the lateral direction is a method of individually performing in each direction, and a method of changing the speed of the roller while extending the width of the jig after guiding the tenter, and simultaneously extending the longitudinal direction and the lateral direction.

In order to obtain a polyester film which satisfies the above physical properties, it is preferred to carry out simple uniaxial stretching, and it is more preferred to extend in an arbitrary direction while performing a relaxation treatment in a direction perpendicular to the extending direction. More specifically, a method of applying heat treatment after stretching in the longitudinal direction and relaxation treatment in the lateral direction, or stretching in the transverse direction and relaxation treatment in the longitudinal direction, using a device called a simultaneous biaxial stretching machine, can be generally exemplified. The order of stretching and relaxation treatment is preferably carried out simultaneously, but may be carried out in the order of stretching after stretching, or stretching after stretching. A more preferred method is a method of simultaneously performing the lateral direction extension and the longitudinal direction relaxation treatment. Although it is also possible to apply relaxation during the heat treatment, it is necessary to pay attention to the occurrence of heat wrinkles due to an increase in the relaxation rate.

It can also be manufactured using a sequential biaxial stretching machine. In this case, when it is relaxed in the longitudinal direction, the extended roller can be made slower than the roller before the extension by heating with an external heater or the like, and after being relaxed in the longitudinal direction, the guide tenter is oriented in the lateral direction. Implemented by extension. Further, in the case where it is slack in the lateral direction, it can be carried out by applying a longitudinal extension by a normal biaxial stretching, and then slowly heating the inside of the tenter while shortening the width of the jig in the lateral direction. Further, in the case of using a sequential biaxial stretching machine, the direction of the uniaxial extension is preferably an extension in the lateral direction. It may be an extension in the longitudinal direction, but it is easy to cause a slight flaw on the surface of the film when it is extended in the longitudinal direction, and there is a problem that an extended spot is likely to occur, and it is necessary to pay attention to it. Further, it is also possible to apply a relaxation treatment to the uniaxially stretched film by using any one of a simultaneous biaxial stretching machine, a tenter, and a roller, using the same principle as described above.

The film forming conditions (especially the stretching conditions) of the polyester film are more specifically described. The elongation temperature is preferably from 80 to 130 ° C, particularly preferably from 90 to 120 ° C. The stretching ratio is preferably 0.4 to 6 times, and particularly preferably 0.6 to 5 times. Preferably, the stretching ratio in the relaxation direction is set to 0.4 to 0.97 times, and the stretching ratio in the vertical direction with respect to the relaxation direction is 3 to 6 times. Furthermore, it is better to relax one direction by 0.6 to 0.9 times, and to extend it by 3.5 to 5.5 times in the vertical direction.

The magnification of the direction of relaxation and the direction of extension can be arbitrarily set within the above range. However, since the uniaxiality is increased as the stretching ratio is increased, it is preferable to increase the degree of slack. On the other hand, in the case where the stretching ratio is lowered, since it is impossible to ignore the influence of wrinkles when it is largely slackened, it is preferable to lower the relaxation rate.

In order to control the hysteresis within the above range, it is preferred to control the ratio of the longitudinal stretching ratio to the lateral stretching ratio. When the difference between the vertical and horizontal stretching ratios is too small, it becomes difficult to increase the hysteresis and it is not preferable. Further, when the magnification in the relaxation direction is too low, the occurrence of wrinkles or the like cannot be avoided, which is not preferable. Further, when the magnification in the extending direction is too high, it is not preferable because the breaking is likely to occur. It is a better correspondence to lower the set extension temperature and increase the hysteresis. Then, in the heat treatment, the treatment temperature is preferably from 100 to 250 ° C, particularly preferably from 180 to 245 ° C.

The variation in hysteresis on the film is preferably small, and it is preferable to control the thickness of the film in order to suppress variation. Since the stretching temperature and the stretching ratio greatly affect the thickness of the film, it is preferable to optimize the film forming conditions from the viewpoint of suppressing the thickness. In particular, when the longitudinal stretching ratio is lowered in order to increase the hysteresis, there is a case where the longitudinal thickness spot is deteriorated. Since the longitudinal thickness spot may be deteriorated within a certain range of the stretching ratio, it is preferable to set the film forming conditions while avoiding such a range.

From the above viewpoints, the 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 particularly preferably 3.0% or less.

In order to control the hysteresis of the polyester film to a specific range, it can be carried out by appropriately setting the stretching ratio or the stretching temperature and the thickness of the film. For example, the higher the stretching ratio, the lower the stretching temperature, and the thicker the film, the higher the hysteresis is easily obtained. Conversely, the lower the stretching ratio, the higher the stretching temperature, and the thinner the thickness of the film, the easier the hysteresis is obtained. However, when thickening the thickness of the film, the thickness direction is different. It is easy to become bigger. For this reason, it is preferable that the thickness of the film is appropriately set within the range described later. Further, in addition to the control of the hysteresis, it is necessary to set the final film forming conditions in consideration of the physical properties necessary for the processing.

The polyester resin for obtaining a polyester film satisfying the above physical properties may be any polyester resin used in the field. That is, it can be obtained by condensing an arbitrary dicarboxylic acid and a diol. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 1,4-naphthalene dicarboxylic acid. Acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylic acid, diphenoxy ethane dicarboxylic acid, diphenyl hydrazine carboxylic acid, hydrazine dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid , 3,3-diethyl succinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipate, trimethyl adipate, pimelic acid, Azelaic acid, dimer acid, sebacic acid, suberic acid, dodeca-dicarboxylic acid and the like.

Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and tenthylene. Glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis ( 4-hydroxyphenyl) hydrazine and the like.

One type or two types or more of the dicarboxylic acid component and the diol component which are constituting the polyester film can be used. Specific examples of the polyester resin constituting the polyester film include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Esters and the like, preferably polyethylene terephthalate and polyethylene naphthalate, Preferred is polyethylene terephthalate. The polyester resin may contain other copolymerization components, and the ratio of the copolymerization component is preferably 3 mol% or less, preferably 2 mol% or less, and more preferably 1.5 mol% or less from the viewpoint of mechanical strength. .

A polyester film which satisfies the above physical properties can be used as any of the polarizer protective films of the four polarizer protective films used in the liquid crystal display device. It is preferable that the polyester film is used as a polarizer protective film constituting a light source side of a light source side polarizing plate, and/or a viewing side polarizer protective film constituting a viewing side polarizing plate. More preferably, the polyester film is disposed on the viewing side of the viewing side polarizing plate.

In the polarizer protective film which does not use the polyester film which satisfies the above physical properties, any film which has hitherto been used as a polarizer protective film can be used. It is preferable to use a film having no hysteresis represented by a TAC film, an acrylic film, a norbornene-based resin film or the like. The film having no hysteresis can be used, for example, as a polarizer protective film constituting the viewing side of the light source side polarizing plate and/or a polarizer protective film constituting the light source side of the viewing side polarizing plate.

The polarizing plate comprising the polarizer and the polarizer protective film described above may have various functional layers (for example, a hard coat layer) on the surface for the purpose of preventing reflection, suppressing glare, and/or suppressing flaws. ).

In order to improve the adhesion to the polarizer, the polarizer protective film preferably has at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin as a main component at least on one side. Floor. Here, the "main component" means a component which is 50% by mass or more among the solid components constituting the easy-adhesion layer.

Coating liquid for easy adhesion layer formed in polarizer protective film 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 is preferable, and as such a coating liquid, Japan can be exemplified. Water-soluble or water-dispersible copolymerized polyester disclosed in Japanese Patent No. 3, 567, 927, Japanese Patent No. 3,589, 232, Japanese Patent No. 3,589, 233, Japanese Patent No. 3,900, 191, and Japanese Patent No. 4,150,982. A resin solution, an acrylic resin solution, a polyurethane resin solution, or the like.

The easy-adhesive layer formed in the polarizer protective film may be a single or combined 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 metal bar coating method, or a tube. Coating is carried out by a well-known method such as a doctor blade method.

For the functional layer laminated at any position on the viewing side of the polarizer protective film, for example, an antiglare layer, an antireflection layer, a low reflection layer, a low reflection antiglare layer, an antireflection antiglare layer, and an anti-glare layer can be used. One or more of the group of the electrostatic layer, the ruthenium layer, the adhesion layer, the antifouling layer, the water repellent layer, and the blue light blocking layer.

When a wide variety of functional layers are provided, it is preferred to have an easy adhesion layer on the surface of the polarizer protective film. At this time, from the viewpoint of suppressing interference caused by the reflected light, it is preferred to adjust the refractive index of the easy-adhesion layer to be near the geometric mean of the refractive index of the functional layer and the refractive index of the basic film. The refractive index of the easy-adhesion layer can be adjusted by well-known methods, for example, by adjusting the binder resin to contain titanium or zirconium and other metal sources.

(hard coating)

The hard coat layer may be a layer having hardness and transparency, and is usually made of various curable resins such as an ionizing radiation curable resin represented by ultraviolet rays or electron beams, and a thermosetting resin which is hardened by heat. Formed by a hardened resin layer. A thermoplastic resin or the like may be appropriately added to the curable resin in order to add appropriate flexibility and other physical properties. Among the curable resins, a point which is representative and can provide an excellent hard coating film is preferably an ionizing radiation curable resin.

In the ionizing radiation curable resin, a conventionally known resin may be suitably used. In addition, as the ionizing radiation-curable resin, a radically polymerizable compound having an ethylenic double bond, a cationically polymerizable compound such as an epoxy compound, or the like is typically used, and these compounds are used as monomers, oligomers, and the like. The polymer prepolymer or the like may be used alone or in combination of two or more. Representative compounds are various (meth)acrylate compounds of radically polymerizable compounds. Among the (meth) acrylate-based compounds, examples of the compound used at a relatively low molecular weight include polyester (meth) acrylate, polyether (meth) acrylate, and acrylic (meth) acrylate. Ester, epoxy (meth) acrylate, urethane (meth) acrylate, and the like.

As the monomer, for example, a monofunctional single such as ethyl (meth) acrylate, ethyl hexyl (meth) acrylate, styrene, methyl styrene or N-vinyl pyrrolidone can be suitably used. Or; for example, trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylic acid Polyester, dipentaerythritol hexa(meth) acrylate, 1,6-hexanediol di(meth) acrylate, neopentyl glycol di(meth) acrylate, etc. Can be monomeric and so on. The (meth) acrylate system means acrylate or methacrylate.

In the case where the ionizing radiation curable resin is cured by an electron beam, although a photopolymerization initiator is not required, in the case of curing by ultraviolet rays, a well-known photopolymerization initiator is used. For example, in the case of a radical polymerization system, as a photopolymerization initiator, acetophenones, benzophenones, and 9-oxosulfurate can be used. , benzoin, benzoin methyl ether, etc., used alone or in combination. In the case of the cationic polymerization system, an aromatic diazonium salt, an aromatic sulfonium salt, an aromatic iodonium salt, a metallocene compound, a benzoin sulfonate or the like may be used singly or in combination as a photopolymerization initiator.

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

A thermoplastic resin, a thermosetting resin, or the like may be appropriately added to the ionizing radiation curable resin in order to adjust the appropriate physical properties and the like. Examples of the thermoplastic resin or the thermosetting resin include an acrylic resin, a urethane resin, a polyester resin, and the like.

In order to impart light resistance to the hard coat layer, prevent discoloration due to ultraviolet rays contained in sunlight or the like, deterioration in strength, cracking, and the like, it is also preferred to add an ultraviolet absorber to the ionizing radiation curable resin. When the ultraviolet absorber is added, in order to prevent the hardening of the hard coat layer from being impeded by the ultraviolet absorber, the ionizing radiation curable resin is preferably cured by an electron beam. The ultraviolet absorber may be an organic ultraviolet absorber such as a benzotriazole compound or a benzophenone compound or a fine particle zinc oxide having a particle diameter of 0.2 μm or less. A well-known thing, such as an inorganic ultraviolet absorber, such as a titanium oxide and a cerium oxide, is selected and used. 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 light resistance, it is preferred to use a radical scavenger such as a hindered amine-based radical scavenger in combination with an ultraviolet absorber. In addition, the electron beam irradiation system has an accelerating voltage of 70 kV to 1 MV and an irradiation line amount of about 5 to 100 kGy (0.5 to 10 Mrad).

(anti-glare layer)

It is one of the preferable forms to provide an anti-glare layer on the most visible side of the image display device. As the antiglare layer, those conventionally known can be suitably used, and generally, it is formed as a layer in which an antiglare agent is dispersed in a resin. As the antiglare agent, inorganic or organic fine particles are used. The shape of these fine particles is a true spherical shape, an elliptical shape, or the like. The microparticle system is preferably transparent. Examples of such fine particles include vermiculite beads as the inorganic fine particles, and resin beads as the organic fine particles. Examples of the resin beads include styrene beads, melamine beads, acrylic beads, acrylic styrene beads, polycarbonate beads, polyethylene beads, benzoguanamine-formaldehyde beads, and the like. The fine particles are usually added 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 portion.

The above-mentioned resin in which the antiglare agent is dispersed and retained is preferably as high as possible as in the case of the hard coat layer. Therefore, as the resin, for example, a curable resin such as an ionizing radiation curable resin or a thermosetting resin described in the above hard coat layer can be used.

The thickness of the anti-glare layer may be an appropriate thickness, usually It is about 1~20μm. The antiglare layer can be formed by suitably using various well-known coating methods. Further, in the coating liquid for forming the antiglare layer, in order to prevent precipitation of the antiglare agent, a well-known anti-settling agent such as vermiculite is preferably added.

(anti-reflection layer)

It is also preferable to provide an antireflection layer on the outermost surface side of the image display device and the interface between each film and air. As the antireflection layer, those well known in the art can be suitably used. In general, the anti-reflective layer comprises at least a low refractive index layer, and further comprising a low refractive index layer and a (high refractive index than the low refractive index layer) high refractive index layer alternately adjacent to the laminate and the surface side as a low refractive index A layer of multiple layers of layers. The respective thicknesses of the low refractive index layer and the high refractive index layer may be appropriately thick depending on the application, and are preferably about 0.1 μm before and after the laminate, and about 0.1 to 1 μm when the low refractive index layer is used alone.

Examples of the low refractive index layer include a film formation method (for example, physical or chemical vapor phase growth method such as vapor deposition, sputtering, CVD, etc.), and a low refractive index of vermiculite, magnesium fluoride, or the like. a layer containing a substance in a resin; a layer of a low refractive index resin such as a fluorine resin; a layer containing a low refractive index substance in a low refractive index resin; and a layer containing a low refractive index substance such as vermiculite or magnesium fluoride. The formed film, a film formed by a sol-gel method in which a cerium oxide film is formed from a cerium oxide sol solution, or a layer containing a void-containing fine particle as a low refractive index substance in a resin.

The void-containing fine particles mean fine particles containing a gas inside, fine particles having a porous structure containing a gas, and the like, and the refractive index due to the gas is based on the original refractive index of the solid portion of the fine particles. As for the entire microparticles, there are microparticles whose apparent refractive index is lowered. Examples of such void-containing fine particles include vermiculite fine particles disclosed in Japanese Laid-Open Patent Publication No. 2001-233611. In addition, as for the fine particles containing voids, in addition to the inorganic material such as vermiculite, the hollow polymer fine particles disclosed in JP-A-2002-805031 can be used. The particle diameter of the void-containing fine particles is, for example, about 5 to 300 nm.

Examples of the high refractive index layer include a film formation method (for example, physical or chemical vapor phase growth methods such as vapor deposition, sputtering, CVD, etc.), and the titanium oxide, zirconium oxide, zinc oxide, and the like are made high. a layer containing a refractive index substance in a resin; a layer of a high refractive index resin such as a resin not containing fluorine; a layer containing a high refractive index substance in a high refractive index resin; and containing titanium oxide, zirconium oxide, zinc oxide, or the like A film formed of a layer of a high refractive index material or the like.

(anti-fouling layer)

As the antifouling layer, a conventionally known one can be suitably used. In general, an anthraquinone compound such as an eucalyptus oil or a polyfluorene resin; a fluorine-based surfactant such as a fluorine-based surfactant or a fluorine-based resin; A coating material containing an anti-fouling agent such as wax is formed by a well-known coating method. The thickness of the antifouling layer may be any thickness as long as it is an appropriate thickness, and is usually about 1 to 10 μm.

(antistatic layer)

The antistatic layer can be suitably used as a conventionally known one, 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 the 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 antistatic agent is used as a polymer compound in addition to being used as a low molecular compound. Further, as the antistatic agent, a conductive polymer such as polythiophene or polyaniline or the like is also used. Further, as the antistatic agent, for example, conductive fine particles containing a metal oxide or the like are used. The particle diameter of the conductive fine particles is, for example, an average particle diameter of about 0.1 nm to 0.1 μm. Further, examples of the metal oxide include ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , ITO (tin oxide doped with indium), In ₂ O ₃ , Al ₂ O ₃ , ATO (doping Oxide tin oxide, AZO (doped zinc oxide of aluminum), and the like.

In the above-mentioned resin containing the antistatic layer, for example, an antistatic layer such as an ionizing radiation curable resin or a thermosetting resin as described in the above hard coat layer is used, and an antistatic layer is formed as an intermediate layer. In the case where the surface strength of the antistatic layer itself is not required, a thermoplastic resin or the like can also be used. The thickness of the antistatic layer may be an appropriate thickness, and is usually about 0.01 to 5 μm. The antistatic layer can be formed by suitably using various well-known coating methods.

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

[Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the following examples, and may be suitable for the present invention. Appropriate changes are added to the scope of the present invention, and they are all included in the technical scope of the present invention.

Hereinafter, the measurement method of the physical properties used in the examples will be described.

(1) Thickness (d)

The thickness (d) was determined in accordance with JIS K 7130 "Method for Measuring Thickness of Plastic Film and Sheet (Method A)".

(2) Refractive index (Nx, Ny, Nz)

The refractive index (Nx) of MD, the refractive index (Ny) of TD, and the refractive index (Nz) in the thickness direction were determined in accordance with JIS K 7142 "Method for Measuring Refractive Index of Plastic (A Method)". It is usually determined using a sodium D line having a wavelength of 589 nm.

(3) Birefringence (ΔNxy) and hysteresis (Re)

The hysteresis is a case where the film surface is set to the z-axis in the thickness direction and is orthogonal to the z-axis, and the two axial directions orthogonal to each other are the x-axis and the y-axis, and the refraction is based on the axial directions. The phase difference represented by the product of the birefringence (Nx, Ny, Nz) and the film thickness d. Here, the birefringence (ΔNxy) and the thickness (d) which are generated by the light incident on the film surface (xy plane) are set in the longitudinal direction (MD) as the x-axis and the width direction (TD) as the y-axis. The hysteresis in the surface of the product is set to hysteresis (Re). Therefore, the birefringence (Δxy) and the hysteresis (Re) are each obtained by the following formula. Each refractive index was measured using an Abbe refractometer. The unit of hysteresis is nm.

ΔNxy=|Nx-Ny|

Re=ΔNxy×d

(4) Thickness direction hysteresis (Rth)

The thickness direction retardation is expressed by light incident from the thickness direction Delayed. Here, the product of the average of the two birefringences in the x-z plane and the y-z plane and the film thickness (d) is obtained by the following formula. The unit is nm.

Rth=(|Nx-Nz|+|Ny-Nz|)/2×d

(5) Surface alignment (ΔP)

The surface alignment degree (ΔP) was calculated from the following equation using the values of the refractive index (Nx) in the longitudinal direction of the film, the refractive index (Ny) in the width direction, and the refractive index (Nz) in the thickness direction.

ΔP=((Nx+Ny)/2)-Nz

(6) Rainbow spot observation

The film of each of the examples and the comparative examples described below was attached to one side of a commercially available polarizing film film such that the absorption axis of the polarizer and the alignment main axis of the film (the higher of Nx and Ny) were perpendicular to each other. On the opposite side, a commercially available TAC film was attached to make a polarizing plate. Then, two polarizing plates having a white LED as a backlight, two TAC films as a polarizer protective film, and a polarizing plate on the viewing side of a commercially available liquid crystal display device having a liquid crystal cell are removed and exchanged as before. The polarizing plate produced. At this time, the polarizer protective film on the viewing side of the produced polarizing plate was provided as the film of the example or the comparative example. The liquid crystal display device thus produced was displayed with a white image, and visually observed from the front side and the oblique direction of the display, and the occurrence of the rainbow spot was determined as follows. Further, the viewing angle is an angle formed by a line drawn from the center of the screen of the display to the normal direction (vertical), and a line connecting the center of the display and the position of the eye at the time of observation. ◎: No rainbow spots occurred from any direction. ○: When the observation angle is in the range of 0° to 55°, no rainbow spots occur. in When the observation angle exceeded the range of 55°, a part of the extremely pale rainbow spot was observed. ×: A rainbow spot was observed in a range in which the observation angle was 0° to 55°.

(7) tear strength

The tear strength of each film was measured in accordance with JIS P-8116 using an Aifufu tear tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The tear direction was performed in parallel with the direction of the alignment main axis of the film, and was evaluated according to the following criteria. The measurement in the direction of the main axis was measured by a molecular alignment meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004 molecular alignment meter).

○: tear strength is 50mN or more

×: tear strength is less than 50mN

(8) penetration rate

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

(9) Thermal shrinkage at 150 ° C

The dimensional change rate (%) in the longitudinal direction and the width direction was measured in accordance with JIS C2318-19975.3.4 (dimension change). For the direction to be measured, the film was cut into a width of 10 mm and a length of 250 mm, and printed at intervals of 200 mm, and the printing interval (A) was measured under a constant tension of 5 gf. Next, the film was placed in an oven at 150 ° C, and heat-treated at 150 ± 3 ° C for 30 minutes under no load, and then the printing interval (B) was measured under a constant tension of 5 gf. Using these measured values, the heat shrinkage ratio was determined by the following formula.

Heat shrinkage rate (%) = (A-B) / A × 100

(Manufacturing Example 1 - Polyester Resin A)

When the esterification reactor was heated up to 200 ° C, the feed was 86.4 mass. The terephthalic acid and 64.6 parts by mass of ethylene glycol were fed as 0.017 parts by mass of antimony trioxide, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine as a catalyst while stirring. Next, the pressure-increasing temperature was raised, and after the pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C, the esterification reaction tank 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. Then, after 15 minutes, the dispersion treatment was carried out by a high-pressure disperser. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tank, and a polycondensation reaction was carried out under reduced pressure at 280 °C.

After completion of the polycondensation reaction, it was filtered by a 95% Naslon filter having a diameter of 5 μm, and extruded into a stripe shape from a nozzle, and cooled and solidified by using a cooling water subjected to pre-filtration treatment (pore diameter: 1 μm or less). Cut into pellets. The obtained resin had an intrinsic viscosity of 0.62 dl/g and contained substantially no inert particles and internal precipitated particles. Hereinafter, the polyethylene terephthalate resin thus obtained is simply referred to as PET (A).

(Production Example 2 - Polyester Resin B)

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

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

The transesterification reaction and the polycondensation reaction are carried out by a conventional method to prepare 46 mol% of terephthalic acid as a dicarboxylic acid component (to the entire dicarboxylic acid component), 46 mol% of isophthalic acid, and 5- Sodium sulfoisophthalate 8 mol%, a copolymerized polyester containing a water-dispersible sulfonic acid metal salt as a composition of a diol component (to the total of a diol component) of 50 mol% of ethylene glycol and 50 mol% of neopentyl glycol Resin. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl celecoxime, and 0.06 parts by mass of a nonionic surfactant were mixed. Further, while heating and stirring, 5 parts by mass of the above-mentioned copolymerized polyester resin containing a water-dispersible sulfonic acid metal salt was added at a time point of reaching 77 ° C, and stirring was continued until the agglomeration of the resin was not observed. Then, the aqueous resin dispersion liquid was cooled to room temperature to obtain a uniform water-dispersible copolymerized polyester resin liquid having a solid content concentration of 5.0% by mass. In addition, after dispersing 3 mass parts of aggregated vermiculite particles (Fuji SILYSIA Co., Ltd., SYLYSIA 310) in 50 parts by mass of water, 99.46 parts by mass of the above water-dispersible copolymerized polyester resin liquid is added. 0.54 parts by mass of an aqueous dispersion of SYLYSIA 310 was added with 20 parts by mass of water while stirring to obtain a binder-modified coating liquid.

(Example 1)

90 parts by mass of the particle-free PET (A) resin pellets and 10 parts by mass of the PET (B) resin pellets containing the ultraviolet absorber as a raw material for the base film intermediate layer of the three-layer structure at 135 ° C After drying under reduced pressure (1 Torr) for 6 hours, it was supplied to the extruder 2 (for the intermediate layer II layer). Further, the PET (A) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I and the outer layer III), respectively, and dissolved at 285 °C. Each of the two kinds of polymers was filtered with a filter material of a stainless steel sintered body (manufactured by a nominal filtration rate of 10 μm particles and cut by 95%), and laminated by two types of three-layered flow blocks, and extruded into a sheet shape by a nozzle, and then an electrostatic casting method was used. The casting drum wound to a surface temperature of 30 ° C was cooled and solidified to produce an unstretched film. At this time, I layer, II layer The discharge ratio of each extruder was adjusted in such a manner that the ratio of the thickness of the III layer was 10:80:10.

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

The unstretched film forming the coating layer is guided to the simultaneous biaxial stretching machine, and the end portion of the film is held by the jig while being guided to the hot air region at a temperature of 90 ° C, and the longitudinal direction is relaxed at a magnification of 0.8 times while extending in the lateral direction. 4.0 times. Subsequently, the film was treated at a temperature of 170 ° C for 30 seconds, and further subjected to a relaxation treatment of 3% in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

(Example 2)

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

(Example 3)

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 a thickness of about 38 μm, and the film was relaxed at a magnification of 0.7 times in the longitudinal direction and at a temperature of 180 ° C for 30 seconds. .

(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 a thickness of about 25 μm, a stretching ratio in the transverse direction was 5.0 times, and heat treatment was performed at a temperature of 180 ° C for 30 seconds.

(Example 5)

Except that the thickness of the unstretched film was changed, the thickness was made to be about 80 μm, the longitudinal direction was relaxed at a magnification of 0.85 times, the temperature at the time of stretching was 95° C., and the heat treatment was applied at a temperature of 180° C. for 30 seconds. A uniaxially oriented PET film was obtained in the same manner.

(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 a thickness of about 38 μm and a magnification of 0.6 times in the longitudinal direction.

(Comparative Example 1)

The unstretched film produced by the same method as in Example 1 was guided to a tenter stretching machine, and the end portion of the film was held by a jig while being guided to a hot air region having a temperature of 125 ° C, and extended 4.0 times in the width direction. Subsequently, the width extending in the width direction was maintained, and the treatment was carried out at a temperature of 225 ° C for 30 seconds, and further 3% relaxation treatment was performed in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 25 μm.

(Comparative Example 2)

In the same manner as in Example 1, a biaxially oriented PET film having a film thickness of about 38 μm was obtained by extending 3.4 times in the traveling direction and 4.0 times in the width direction.

(Comparative Example 3)

In the same manner as in Comparative Example 1, a uniaxially oriented PET film having a film thickness of about 100 μm was obtained by stretching 4.0 times in the traveling direction and 1.0 times in the width direction. Since the film was uniaxially stretched in the longitudinal direction, minute defects were observed on the surface of the film.

(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 a thickness of about 38 μm and no relaxation treatment in the longitudinal direction was 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 a thickness of about 38 μm and no relaxation treatment in the longitudinal direction was performed.

(Comparative Example 6)

A uniaxially oriented PET film was obtained in the same manner as in Example 4 except that the thickness of the unstretched film was changed to a thickness of about 25 μm and no relaxation treatment in the longitudinal direction was carried out.

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

As described above, when the films of Examples 1 to 6 were used as a polarizer protective film, it was confirmed that the occurrence of rainbow spots was intentionally suppressed, and a liquid crystal display device having excellent visibility was obtained. Further, the films of Examples 1 to 6 can provide not only an image display device having excellent visibility, but also a relatively thin thickness. However, since the film has sufficient tear strength, it has been confirmed to be suitable for use in industrial image display devices. On the other hand, in the case of using the films of Comparative Examples 1, 2, and 6 as a polarizer protective film, rainbow spots were generated when viewed from the front, and good visibility was not obtained. Further, in the film of Comparative Example 3, it is clear that there is no problem in visibility in the case of being used as a polarizer protective film, but the tear strength is insufficient, and it is not suitable for the production of an industrial and stable liquid crystal display device. It is considered that the film of Comparative Example 3 has a high Re value and a Re/Rth ratio, but the value of ΔP is also high. In the films of Comparative Examples 4 and 5, when the observation angle was in the range of 0° to 55°, although the occurrence of rainbow spots was not observed, a part of the extremely pale rainbow spots was observed in the range where the observation angle exceeded 55°. It is considered that the films of Comparative Examples 4 and 5 are relatively high in Re, but the Re/Rth ratio is lower. Further, in Comparative Example 6, since the value of ΔP was high, the tear strength was also insufficient.

[Industrial availability]

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 liquid crystal display device which is excellent in visibility and thin. Therefore, the industrial use of the present invention is extremely high.

Claims (14)

A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, the backlight source being a white light source having continuous emission mass spectrum, the polarizing plate having A structure in which a polarizer protective film is laminated on both sides of the polarizer, and at least one of the polarizer protective films is a polyester film satisfying the following physical properties (a) to (c): (a) 3000 nm or more and 30000 nm or less. Hysteresis (Re); (b) ratio of retardation (Re) of 1.0 or more to thickness direction retardation (Rth) (Re/Rth); and (c) plane alignment degree (ΔP) of 0.12 or less; hysteresis (Re) is ΔNxy×d, thickness direction retardation (Rth) is (|Nx-Nz|+|Ny-Nz|)/2×d, ΔP is ((Nx+Ny)/2)-Nz, where Nx is a film The refractive index in the longitudinal direction, Ny is the refractive index in the width direction of the film, Nz is the refractive index in the thickness direction of the film, ΔNxy is |Nx-Ny|, and d is the film thickness. The liquid crystal display device of claim 1, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more. The liquid crystal display device of claim 1 or 2, wherein the polyester film constitutes a polarizer protective film of a polarizing plate which is located on the viewing side of the liquid crystal cell. The liquid crystal display device of claim 1 or 2, wherein the polyester film has a thickness of from 20 μm to 90 μm. The liquid crystal display device of claim 1 or 2, wherein the polyester film has a tear strength of 50 mN or more. A polarizing plate having a structure in which a polyester film satisfying the following physical properties (a) to (c) is laminated on at least one surface of a polarizer: (a) hysteresis (Re) of 3000 nm or more and 30,000 nm or less; (b) Ratio of hysteresis (Re) of 1.0 or more to retardation of thickness direction (Rth) (Re/Rth); and (c) plane alignment degree (ΔP) of 0.12 or less; hysteresis (Re) of ΔNxy×d, hysteresis in thickness direction (Rth) is (|Nx-Nz|+|Ny-Nz|)/2×d, and ΔP is ((Nx+Ny)/2)-Nz, where Nx is the refractive index in the longitudinal direction of the film, and Ny is The refractive index in the width direction of the film, Nz is the refractive index in the thickness direction of the film, ΔNxy is |Nx-Ny|, and d is the film thickness. The polarizing plate of claim 6, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more. The polarizing plate of claim 6 or 7, wherein the polyester film has a thickness of from 20 μm to 90 μm. The polarizing plate of claim 6 or 7, wherein the polyester film has a tear strength of 50 mN or more. A polarizer protective film which is a polyester film satisfying the following physical properties (a) to (c): (a) hysteresis (Re) of 3,000 nm or more and 30,000 nm or less; (b) hysteresis (Re) and thickness of 1.0 or more Directional retardation (Rth) ratio (Re/Rth); and (c) Surface orientation degree (ΔP) of 0.12 or less; hysteresis (Re) is ΔNxy×d, and thickness direction retardation (Rth) is (|Nx-Nz|+|Ny-Nz|)/2×d, △ P is ((Nx+Ny)/2)-Nz, where Nx is the refractive index in the longitudinal direction of the film, Ny is the refractive index in the width direction of the film, Nz is the refractive index in the thickness direction of the film, and ΔNxy is |Nx -Ny|, d is the film thickness. The polarizer protective film according to claim 10, wherein the polyester film satisfies the following physical properties (d): (d) a birefringence (?Nxy) of 0.1 or more. The polarizer protective film of claim 10 or 11, wherein the polyester film has a thickness of from 20 μm to 90 μm. The polarizer protective film of claim 10 or 11, wherein the polyester film has a tear strength of 50 mN or more. A method for producing a polarizer protective film, comprising the steps of simultaneously stretching a polyester film while being relaxed in a direction orthogonal to an extending direction, and satisfying the following physical properties (a) to (c) Polyester film: (a) hysteresis (Re) of 3000 nm or more and 30000 nm or less; (b) ratio of retardation (Re) of 1.0 or more to retardation of thickness direction (Rth) (Re/Rth); and (c) of 0.12 or less Surface alignment (ΔP); hysteresis (Re) is ΔNxy×d, thickness direction hysteresis (Rth) is (|Nx-Nz|+|Ny-Nz|)/2×d, ΔP is ((Nx+ Ny)/2)-Nz, where Nx is the refractive index in the longitudinal direction of the film, Ny is the refractive index in the width direction of the film, Nz is the refractive index in the thickness direction of the film, ΔNxy is |Nx-Ny|, and d is membrane thickness.