KR102505572B1 - Liquid-crystal display, polarizing plate, and polarizer-protecting film - Google Patents

Abstract

An object of the present invention is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display realized therewith, which enable further thinning of the liquid crystal display while maintaining good visibility.
In order to solve the above problems, the liquid crystal display device of the present invention has a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, and the backlight light source is a white light source having a continuous emission spectrum, The polarizing plate has a structure in which polarizer protective films are laminated on both sides of the polarizer, and at least one of the polarizer protective films has the following physical properties (a) to (c): (a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less (b) a ratio (Re/Rth) of retardation (Re) and thickness direction retardation (Rth) of 1.0 or more; and (c) a degree of plane orientation (ΔP) of 0.12 or less; characterized in that it is a polyester film that satisfies do.

Description

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

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

Liquid crystal displays are widely used in mobile phones, tablet terminals, PCs, televisions, PDAs, electronic dictionaries, car navigation systems, music players, digital cameras, digital video cameras, and the like. As the miniaturization and weight reduction of liquid crystal display devices progress, their use is no longer limited to offices or indoors, and their use is also expanding outdoors and while moving in cars and trains.

In Patent Document 1, for the purpose of suppressing deterioration in image quality due to rainbow spots that may occur depending on the viewing angle when viewing a liquid crystal display device, a polyester film having a retardation of 3,000 to 30,000 nm is used as a polarizer protective film use has been disclosed.

WO2011/162198

However, in the market, additional thinness of the liquid crystal display is required, and simply controlling the retardation to 3,000 to 30,000 nm can solve the deterioration in visibility due to the occurrence of rainbow spots, but if the film thickness is thinned, Since the mechanical strength is remarkably lowered, it has been difficult to respond to the demand for thinning. Accordingly, one object of the present invention is to provide a polarizer protective film, a polarizing plate, and a liquid crystal display realized therewith that enable further thinning of the liquid crystal display while maintaining good visibility.

The inventors of the present invention have repeatedly studied intensively to solve the above problems. By controlling the degree of plane orientation of the polyester film to a certain level or less, the mechanical properties of the film while maintaining the retardation value at 3,000 or more and 30,000 or less and maintaining good visibility It was found that it was possible to increase the strength and make the thickness of the film thinner. Based on this knowledge, the present inventors have completed the present invention by repeating further examination and improvement.

A typical example of the present invention is as follows.

Section 1.

A backlight light source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, wherein the backlight light source is a white light source having a continuous emission spectrum,

The polarizing plate has a structure in which polarizer protective films are laminated on both sides of the polarizer,

At least one of the polarizer protective films has the following physical properties (a) to (c):

(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less;

(b) a ratio (Re/Rth) of retardation (Re) to thickness direction retardation (Rth) of 1.0 or more; and

(c) plane orientation degree (ΔP) of 0.12 or less;

A polyester film that satisfies

liquid crystal display.

clause 2.

The polyester film has the following physical properties (d):

(d) Birefringence (ΔNxy) greater than or equal to 0.1

The liquid crystal display device according to claim 1 that satisfies.

clause 3.

The liquid crystal display device according to claim 1 or 2, wherein the polyester film is a polarizer protective film constituting a polarizing plate positioned on a viewing side rather than the liquid crystal cell.

clause 4.

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

Section 5.

The liquid crystal display device according to any one of items 1 to 4, wherein the polyester film has a tear strength of 50 mN or more.

clause 6.

The following physical properties (a) to (c):

(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less;

(b) a ratio (Re/Rth) of retardation (Re) to thickness direction retardation (Rth) of 1.0 or more; and

(c) plane orientation degree (ΔP) of 0.12 or less;

A polarizing plate having a structure in which a polyester film satisfying the is laminated on at least one surface of the polarizer.

clause 7.

The polyester film has the following physical properties (d):

(d) Birefringence (ΔNxy) greater than or equal to 0.1

The polarizing plate according to claim 6, which satisfies.

Section 8.

The polarizing plate according to claim 6 or 7, wherein the polyester film has a thickness of 20 µm or more and 90 µm or less.

clause 9.

The polarizing plate according to any one of items 6 to 8, wherein the polyester film has a tear strength of 50 mN or more.

Section 10.

The following physical properties (a) to (c):

(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less;

(b) a ratio (Re/Rth) of retardation (Re) to thickness direction retardation (Rth) of 1.0 or more; and

(c) plane orientation degree (ΔP) of 0.12 or less;

A polarizer protective film that is a polyester film that satisfies.

Section 11.

The polyester film has the following physical properties (d):

(d) Birefringence (ΔNxy) greater than or equal to 0.1

The polarizer protective film according to claim 10, which satisfies.

Section 12.

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

Section 13.

The polarizer protective film according to any one of items 10 to 12, wherein the tear strength of the polyester film is 50 mN or more.

Section 14.

Including a step of simultaneously stretching the polyester film while performing a relaxation treatment in a direction orthogonal to the stretching direction,

The following physical properties (a) to (c):

(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less;

(b) a ratio (Re/Rth) of retardation (Re) to thickness direction retardation (Rth) of 1.0 or more; and

(c) plane orientation degree (ΔP) of 0.12 or less;

Method for producing a polarizer protective film that is a polyester film that satisfies the

Section 15.

The polarizing plate according to any one of items 6 to 9, which is for a liquid crystal display device having a white light source having a continuous emission spectrum.

Section 16.

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

Section 17.

The method according to claim 14, wherein the polarizer protective film is for a liquid crystal display device having a white light source having a continuous emission spectrum.

Since the polarizer protective film of the present invention has excellent mechanical strength (tear strength), it is suitable for thinning. In addition, the polarizer protective film of the present invention and the polarizing plate laminated thereon can suppress the occurrence of rainbow spots that may occur depending on the angle at which the image is viewed when an image is viewed by manufacturing a liquid crystal display device using the polarizer protective film. Therefore, according to the present invention, it is possible to provide a liquid crystal display device having excellent visibility and having a thinner shape. In addition, in this specification, "rainbow unevenness" is a concept including "color unevenness", "color shift", and "interference color".

1 is a schematic diagram of an observation angle θ.

The liquid crystal display device includes a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. In this specification, the side where the backlight source of the liquid crystal display device is located is referred to as the "light source side" for a person viewing an image, and the side for viewing an image is referred to as a "viewer's side". The order of arrangement of the constituent members of the liquid crystal display device is usually 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 a "visible-side polarizing plate") from the light source side to the viewing side.

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

The method or structure of the white light source having a continuous and broad emission spectrum is not particularly limited, and any white light source can be used as long as it can suppress the occurrence of rainbow spots, but a preferred light source is a white light emitting diode (LED). The white LED includes a phosphor-type one (ie, a device emitting white light by combining a light emitting diode emitting blue or ultraviolet light using a compound semiconductor and a phosphor), an organic light-emitting diode (OLED), and the like. In one embodiment, a preferable white LED is a phosphor type white LED, more preferably a white LED composed of a light emitting element combining a blue light emitting diode using a compound semiconductor and a yttrium aluminum garnet yellow phosphor.

The liquid crystal cell can be used by appropriately selecting any liquid crystal cell that can be used in a liquid crystal display device, and the method or structure is not particularly limited. For example, liquid crystal cells such as VA mode, IPS mode, TN mode, STN mode, and bend orientation (π type) can be appropriately selected and used. Therefore, the liquid crystal cell may appropriately select and use a liquid crystal made of known liquid crystal materials and liquid crystal materials that may be developed in the future. In one embodiment, a preferred liquid crystal cell is a transmissive liquid crystal cell.

The polarizing plate has a structure in which both sides of a film-shaped polarizer are sandwiched between two protective films (also referred to as "polarizer protective films"). The polarizer can be used by appropriately selecting any polarizer (or polarizing film) used in the technical field. A representative polarizer includes, but is not limited to, a polyvinyl alcohol (PVA) film in which a dichroic material such as iodine is dyed, and a known polarizer that can be developed in the future can be appropriately selected and used.

Commercially available products can be used for the PVA film used as the polarizer, for example, "Kuraray Vinylon (manufactured by Kuraray Co., Ltd.)", "Tosero Vinylon (manufactured by Tosero Co., Ltd.)", "Nichigo Vinylon (Nippon Corporation)" Synthetic Chemical Co., Ltd.)] etc. can be used. Examples of dichroic materials include iodine, diazo compounds, and polymethine dyes.

Since the liquid crystal display device usually includes two polarizing plates, and the polarizing plate is usually composed of two polarizer sheets and polarizer protective films stacked on both sides thereof, the liquid crystal display device may include four polarizer protective films. In the present invention, it is preferable that at least one of the four polarizer protective films is a polyester film satisfying the physical properties of (a) to (c) below.

(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less

(b) Ratio (Re/Rth) of retardation (Re) and thickness direction retardation (Rth) of 1.0 or more

(c) Planar orientation degree (ΔP) of 0.12 or less

It is preferable that the retardation of the polyester film used as a polarizer protective film is 3,000 nm or more and 30,000 nm or less from a viewpoint of reducing iridescence. The lower limit of retardation is preferably 4,500 nm or more, more preferably 5,000 nm or more, still more preferably 6,000 nm or more, even more preferably 8,000 nm or more, and still more preferably 10,000 nm or more. On the other hand, the upper limit of retardation is such that even if the retardation is made higher, the additional visibility improvement effect is not substantially obtained, and the thickness of the orientation film also tends to increase depending on the height of retardation. It is set to 30,000 nm from the point of view of reflection, but it is also possible to set it to a higher value. In addition, when simply describing as "retardation" in this specification, in-plane retardation is meant.

Retardation is expressed as the product of birefringence (ΔNxy) caused by light incident on the film plane (x-y plane) and thickness (d). Therefore, as the value of ΔNxy increases, higher retardation is obtained. On the other hand, since the retardation decreases relatively as the thickness of the film decreases, it is preferable that the value of ΔNxy is large in order to maintain a retardation value of a certain level or more while reducing the thickness. However, if the value of ΔNxy is too large, the tear strength of the film tends to decrease. Therefore, the value of ΔNxy of the polyester film is preferably 0.1 or more and less than 0.3. More specifically, in the case of a polyethylene terephthalate film, the values of ΔNxy are 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. 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, if the birefringence ΔNxy is low, it is necessary to increase the film thickness in order to increase the retardation. Therefore, in the case of a polyethylene naphthalate film, the birefringence ΔNxy is preferably 0.15 or more, more preferably 0.16 or more, It is more preferably 0.17 or more, still more preferably 0.18 or more, and particularly preferably 0.20 or more.

The value of the retardation of the polyester film changes depending on the viewing angle. Here, the observation angle refers to the difference (θ) between the direction perpendicular to the plane of the polyester film as a reference (zero degree) and the direction in which the observer looks at the polyester film (FIG. 1). The larger the observation angle, the lower the retardation value at that angle. For this reason, even if rainbow stains are not observed when observing from the front (ie, vertical direction) of the display device, there may be cases where rainbow stains are observed when observing from an oblique direction. Therefore, in order to ensure good visibility even when the display device is observed from an oblique direction, it is desirable to consider a decrease in retardation due to an increase in the viewing angle. In particular, since retardation is relatively low in the case of a polyester film having a thin thickness, the effect on visibility due to the decrease in retardation accompanying the increase in the viewing angle is relatively large. The ratio (Re/Rth) of the retardation (Re) of the polyester film to the retardation (Rth) in the thickness direction is used as an index indicating the degree of decrease in retardation accompanying an increase in the observation angle. As Re/Rth increases, the effect of birefringence increases isotropy, and since the degree of decrease in retardation due to an increase in the observation angle decreases, it is considered that rainbow unevenness depending on the observation angle becomes less likely to occur. From this point of view, Re/Rth is preferably 1.0 or more, more preferably 1.1 or more, still more preferably 1.2 or more, even more preferably 1.25 or more, still more preferably 1.3 or more. Retardation in the thickness direction means an average value of retardation obtained by multiplying two birefringences ΔNxz and ΔNyz by the film thickness (d), respectively, when viewed from a cross section in the film thickness direction.

The maximum value of the Re/Rth ratio is 2.0 (i.e., a perfect uniaxial symmetric film), but as it exceeds 1.0 and approaches a perfect uniaxial symmetric film, the mechanical strength in the direction orthogonal to the orientation principal axis direction may decrease, In that case, it is preferable to adjust so that the plane orientation degree mentioned later may become below a specific value. The Re/Rth ratio is preferably higher from the viewpoint of thinning and improving the viewing angle characteristics, but the upper limit is not required to be 2.0 of the maximum value, and is preferably 1.9 or less, more preferably 1.8 or less.

Retardation of an oriented film can be measured in accordance with a well-known method. Specifically, it can be determined by measuring the refractive index and thickness in the biaxial direction. In addition, it is also possible to obtain using a commercially available automatic birefringence measuring device (for example, KOBRA-21ADH: manufactured by Oji Instruments Co., Ltd.). In any measurement, the measurement wavelength is set to 589 nm, which is the wavelength of sodium D line.

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

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

When the degree of plane orientation is less than 0.04, the mechanical strength of the film is too low, so it is not preferable from the viewpoint of workability and the like. In addition, when the degree of plane orientation exceeds 0.12, it is difficult to achieve both retardation and mechanical strength under thin film conditions, which is not preferable because a problem may occur on either side.

The thickness (d) of the polyester film used as the polarizer protective film is not particularly limited, but is preferably 300 μm or less, more preferably 100 μm, from the viewpoint of providing a thinner polarizer protective film, polarizing plate and liquid crystal display device. or less, more preferably 90 μm or less, still more preferably 80 μm or less, even more preferably 60 μm or less, still more preferably 50 μm or less, still more preferably 45 μm or less, particularly preferably It is preferably 40 μm or less, and most preferably 35 μm or less. 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, still more preferably 25 μm or more, from the viewpoint of difficulty in maintaining sufficient tear strength.

Even if the polyester film used as the polarizer protective film is thin, it is preferable to maintain mechanical strength capable of withstanding handling in the manufacture of industrial liquid crystal display devices. From this point of view, the polyester film preferably has a tear strength of 50 mN or more. Preferably, the tear strength is 100 mN or more, more preferably 130 mN or more. The tear strength of the film can be measured according to the method of JIS P-8116, as shown in Examples to be described later.

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

For the purpose of suppressing deterioration of optical functional dyes such as iodine dyes, the polyester film used as a polarizer protective film preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance of 380 nm is more preferably 15% or less, further preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, deterioration of the optically functional dye by ultraviolet rays can be suppressed. In this specification, the transmittance is measured by a method perpendicular to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500 type). In addition, for example, inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light resistance agents, flame retardants, heat stabilizers, antioxidants, antigelling agents, surfactants, and the like interfere with the effects of the present invention. It is possible to add within a range that does not impair transparency.

A polyester film satisfying the physical properties described above can be obtained by controlling stretching conditions and the like in general polyester film manufacturing conditions. A polyester film is generally manufactured by the following procedure. That is, non-oriented polyester molded by melting a polyester resin and extruding into a sheet is stretched in the longitudinal direction using a speed difference of rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction by a tenter and heat treated. obtained by doing There are a method in which stretching in the longitudinal and transverse directions is performed separately for each direction, and a method in which the longitudinal and transverse directions are simultaneously stretched by changing the speed of the roll while widening the clip width after introduction into the tenter.

In order to obtain a polyester film satisfying the above-described physical properties, it is preferable to perform simple uniaxial stretching, and it is more preferable to perform a relaxation (relaxation) treatment in a direction perpendicular to the stretching direction simultaneously with stretching in an arbitrary direction. More specifically, a method of performing heat treatment after longitudinal stretching and transverse relaxation treatment, or transverse stretching and longitudinal relaxation treatment using a facility commonly referred to as a simultaneous biaxial stretching machine can be exemplified. there is. Although it is preferable to carry out the order of extending|stretching and a relaxation process at the same time, you may carry out also in the order of relaxation after extending|stretching, or extending|stretching after relaxation. A more preferred method is a method in which stretching in the transverse direction and relaxation treatment in the longitudinal direction are simultaneously performed. Although it is possible to perform relaxation in the process of heat treatment, care must be taken because thermal wrinkles occur when the relaxation rate increases.

It is also possible to manufacture using a sequential biaxial stretching machine. In that case, when relaxing in the machine direction, while heating with an external heater or the like, the roll after stretching is slower than the roll before stretching to relax in the machine direction, and then introduced into a tenter and stretched in the transverse direction. In addition, when relaxing in the transverse direction, it can be carried out by gradually narrowing the clip width in the transverse direction while heating in a tenter after performing longitudinal stretching by a method used in normal biaxial stretching. Moreover, when using a sequential biaxial stretching machine, the direction of uniaxial stretching is preferably horizontal stretching. Stretching in the longitudinal direction is also possible, but attention is required because there are problems such as easy occurrence of minute flaws on the film surface and easy occurrence of stretching unevenness during longitudinal stretching. Moreover, it is also possible to carry out the uniaxially stretched film by adding a relaxation process by any one of a simultaneous biaxial stretching machine, a tenter, and a roll equipment using the same principle as the above.

The film forming conditions (especially, stretching conditions) of the polyester film are explained more concretely. The stretching temperature is preferably 80 to 130°C, particularly preferably 90 to 120°C. The draw ratio is preferably 0.4 to 6 times, particularly preferably 0.6 to 5 times. It is preferable to set the draw ratio in the direction of relaxation to be 0.4 to 0.97 times, and the draw ratio in the direction perpendicular to the direction to be relaxed to be 3 to 6 times. In addition, it is more preferable to relax 0.6 to 0.9 times in one direction and stretch 3.5 to 5.5 times in the direction perpendicular thereto.

Magnifications in the relaxation direction and in the stretching direction can be arbitrarily set as long as they are within the above ranges. However, since the higher the stretching ratio, the uniaxiality increases, it is preferable to increase the degree of relaxation. On the other hand, when the draw ratio is low, it is preferable to lower the relaxation rate because the effect of wrinkles cannot be ignored if the relaxation is large.

In order to control the retardation within the above range, it is preferable to control the ratio of the longitudinal stretch magnification and the transverse stretch magnification. When the difference in draw ratio between longitudinal stretching and transverse stretching is too small, it becomes difficult to increase the retardation, which is not preferable. Further, when the magnification in the direction of softening is too low, generation of wrinkles and the like cannot be avoided, which is not preferable. In addition, when the magnification in the stretching direction is too high, it is not preferable because breakage is likely to occur. Setting the stretching temperature low is also a preferable response in increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250°C, particularly preferably 180 to 245°C.

The variation of retardation on the film is preferably small, and in order to suppress the variation, it is desirable to control the thickness variation of the film. Since the stretching temperature and the stretching ratio have a large influence on the thickness variation of the film, it is preferable to optimize the film forming conditions from the viewpoint of suppressing the thickness variation. In particular, when the longitudinal stretching magnification is lowered in order to increase the retardation, the longitudinal thickness variation may deteriorate. Since vertical thickness variation may deteriorate in a specific range of the stretching ratio, it is preferable to set the film forming conditions at a point outside such a range.

From the above viewpoint, the thickness variation of the polyester film is preferably 5.0% or less, more preferably 4.5% or less, even more preferably 4.0% or less, and particularly preferably 3.0% or less.

In order to control the retardation of a polyester film in a specific range, it can perform by setting a draw ratio, extending|stretching temperature, and the thickness of a film suitably. For example, it becomes easy to obtain high retardation, so that the thickness of a film is thick, so that extending|stretching temperature is low, so that a draw ratio is high. Conversely, it becomes easy to obtain low retardation, so that a draw ratio is low, a draw temperature is high, and the thickness of a film is thin, so that a draw ratio is low. However, when the thickness of the film is increased, the retardation in the thickness direction tends to increase. For this reason, it is preferable to set the film thickness appropriately to the range mentioned later. In addition to retardation control, it is necessary to set final film forming conditions in consideration of physical properties required for processing.

A polyester resin for obtaining a polyester film satisfying the above physical properties may be any polyester resin used in the art. That is, it can be obtained by condensing any dicarboxylic acid and diol. As dicarboxylic acid, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5 -naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2, and 2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

As the diol, for example, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1 , 4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, etc. are mentioned.

1 type or 2 or more types may be used for the dicarboxylic acid component and diol component which comprise a polyester film, respectively. Specific polyester resins constituting the polyester film include, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc., preferably polyethylene terephthalate and polyethylene naphthalate. , preferably polyethylene terephthalate. The polyester resin may contain other copolymerization components, and from the viewpoint of mechanical strength, the ratio of the copolymerization components is preferably 3 mol% or less, preferably 2 mol% or less, and more preferably 1.5 mol% or less.

A polyester film satisfying the above physical properties can be used as any of the four polarizer protective films used in liquid crystal displays. Preferably, the polyester film is used as a light source side polarizer protective film constituting a light source side polarizing plate and/or a viewer side polarizer protective film constituting a viewer side polarizing plate. More preferably, the said polyester film is a polarizer protective film arrange|positioned on the visual recognition side of the visual recognition side polarizing plate.

Any film conventionally used as a polarizer protective film may be used as a polarizer protective film that does not use a polyester film that satisfies the above physical properties. Preferably, it is preferable to use a film without retardation represented by a TAC film, an acrylic film, a norbornene-based resin film, and the like. The film without retardation can be used, for example, as a polarizer protective film on the viewer side constituting the light source side polarizing plate and/or a light source side polarizer protective film constituting the viewer side polarizing plate.

The polarizing plate constituted by the above-described polarizer and polarizer protective film 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 scratches.

The polarizer protective film preferably has an easily adhesive layer containing at least one type of polyester resin, polyurethane resin, or polyacrylic resin as a main component on at least one side in order to improve adhesion to the polarizer. Here, the "main component" refers to a component that is 50% by mass or more of the solid components constituting the easily bonding layer.

The coating liquid of the easily bonding layer formed on the polarizer protective film is preferably an aqueous coating liquid containing at least one of a water-soluble or water-dispersible co-polyester resin, an acrylic resin, and a polyurethane resin, and these coating liquids include Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, Japanese Patent No. 4150982, etc. Water-soluble or water-dispersible copolymerized polyester resin solutions and acrylic resin solutions disclosed , polyurethane resin solutions and the like are exemplified.

The easily adhesive layer formed on the polarizer protective film is a known method such as reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method alone may be applied individually or in combination.

As the functional layer laminated at any position on the visual 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, an antistatic layer, a silicone layer, an adhesive layer, an antifouling layer, At least one selected from the group consisting of a water repellent layer and a blue cut layer may be used.

In providing various functional layers, it is preferable to have an easily adhesive layer on the surface of the polarizer protective film. At that time, it is preferable to adjust the refractive index of the easily bonding layer to be near the geometric mean of the refractive index of the functional layer and the refractive index of the base film from the viewpoint of suppressing interference due to reflected light. Adjustment of the refractive index of an easily bonding layer can employ|adopt a well-known method, For example, it can adjust easily by making a binder resin contain titanium, zirconium, or other metal species.

(hard coat layer)

The hard coat layer may be a layer having hardness and transparency, and is usually formed as a cured resin layer of various curable resins such as ionizing radiation curable resins typically cured with ultraviolet rays or electron beams and thermosetting resins cured with heat. A thermoplastic resin or the like may be appropriately added to these curable resins in order to appropriately add flexibility and other physical properties. Among the curable resins, ionizing radiation-curable resins are preferable from the viewpoint of obtaining a typical and excellent hard coating film.

What is necessary is just to employ|adopt conventionally well-known resin suitably as said ionizing radiation-hardenable resin. In addition, as the ionizing radiation curable resin, a radical polymerizable compound having an ethylenic double bond, a cationic polymerizable compound such as an epoxy compound, etc. are typically used, and these compounds are monomers, oligomers, prepolymers, etc., and these compounds can be used alone or in combination of two or more as appropriate. Can be used in combination. Representative compounds are various (meth)acrylate-based compounds that are 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, acrylic (meth)acrylate, epoxy (meth)acrylate, Urethane (meth)acrylate etc. are mentioned.

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

A photopolymerization initiator is unnecessary when the ionizing radiation-curable resin is cured with electron beams, but a known photopolymerization initiator is used when cured with ultraviolet rays. For example, in the case of a radical polymerization system, acetophenones, benzophenones, thioxantones, benzoin, benzoin methyl ether, etc. can be used alone or in combination as a photopolymerization initiator. In the case of a cationic polymerization system, aromatic diazonium salts, aromatic sulfonium salts, aromatic iodonium salts, metallocene compounds, benzoin sulfonic acid esters and the like can be used alone or in combination as photopolymerization initiators.

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. In addition, the hard coat layer can be formed by employing appropriately known various coating methods.

A thermoplastic resin or a thermosetting resin can also be suitably added to the ionizing radiation curable resin for the purpose of appropriately adjusting the physical properties and the like. As a thermoplastic resin or a thermosetting resin, an acrylic resin, a urethane resin, a polyester resin etc. are mentioned, respectively, for example.

It is also preferable to add an ultraviolet absorber to the ionizing radiation curable resin in order to impart light resistance to the hard coat layer and prevent discoloration, strength deterioration, and cracking caused by ultraviolet rays included in sunlight. When an ultraviolet absorber is added, it is preferable to cure the ionizing radiation curable resin with an electron beam in order to reliably prevent curing of the hard coat layer from being inhibited by the ultraviolet absorber. As the ultraviolet absorber, organic ultraviolet absorbers such as benzotriazole-based compounds and benzophenone-based compounds, or inorganic ultraviolet absorbers such as particulate zinc oxide, titanium oxide, and cerium oxide having a particle size of 0.2 μm or less may be selected and used. The added amount of the ultraviolet absorber is about 0.01 to 5% by mass in the ionizing radiation curable resin composition. In order to further improve light resistance, it is preferable to add a radical scavenger such as a hindered amine radical scavenger in combination with an ultraviolet absorber. In addition, the electron beam irradiation has an acceleration voltage of 70 kV to 1 MV and an irradiation dose of 5 to 100 kGy (0.5 to 10 Mrad).

(Anti-glare layer)

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

The resin for dispersing and holding the antiglare agent preferably has as high a hardness as possible in the hard coat layer. Therefore, as said resin, curable resins, such as the ionizing-radiation-curable resin and thermosetting resin, etc. which were described in the said hard-coat layer, for example can be used.

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

(antireflection layer)

It is one of the preferred aspects that an antireflection layer is provided on the outermost surface side of the image display device and at the interface between each film and air. As the antireflection layer, a conventionally known one may be appropriately employed. In general, the antireflection layer is composed of at least a low refractive index layer, and is composed of multiple layers in which a low refractive index layer and a high refractive index layer (having a higher refractive index than the low refractive index layer) are alternately stacked adjacent to each other and the surface side is a low refractive index layer. . Each thickness of the low refractive index layer and the high refractive index layer may be an appropriate thickness according to the application, and is preferably around 0.1 μm when stacked adjacently, 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 layer containing a low refractive index substance such as silica and magnesium fluoride in a resin, a layer of a low refractive index resin such as a fluorine resin, a layer containing a low refractive index substance in a low refractive index resin, and a low refractive index such as silica and magnesium fluoride. A thin film formed by a thin film formation method (for example, a physical or chemical vapor phase growth method such as vapor deposition, sputtering, or CVD) of a layer composed of a material, a film formed by a sol-gel method in which a silicon oxide gel film is formed with a sol solution of silicon oxide, or a low A layer in which void-containing fine particles are contained in a resin as the refractive index substance, and the like are exemplified.

The void-containing microparticles refer to microparticles containing gas inside, microparticles with a porous structure containing gas, etc., and the apparent refractive index as a whole of the microparticles is lowered due to the voids in the gas compared to the original refractive index of the solid part of the microparticles. means particulate. Examples of such void-containing fine particles include silica fine particles disclosed in Japanese Unexamined Patent Publication No. 2001-233611. Further, as the void-containing fine particles, in addition to inorganic substances such as silica, hollow polymer fine particles disclosed in Japanese Unexamined Patent Publication No. 2002-805031 and the like can be cited. The particle size of the void-containing fine particles is, for example, about 5 to 300 nm.

Examples of the high refractive index layer include a layer containing a high refractive index substance such as titanium oxide, zirconium oxide, and zinc oxide in a resin, a layer of a high refractive index resin such as a fluorine-free resin, a layer containing a high refractive index substance in a high refractive index resin, and a titanium oxide layer. , a thin film formed by forming a layer made of a high refractive index material such as zirconium oxide or zinc oxide by a thin film formation method (eg, vapor deposition, sputtering, physical or chemical vapor deposition method such as CVD), and the like.

(antifouling layer)

As the antifouling layer, a conventionally known one may be appropriately employed, and in general, a paint containing a silicon-based compound such as silicone oil or silicone resin; a fluorine-based compound such as a fluorine-based surfactant or a fluorine-based resin; It can be formed by a known coating method. The thickness of the antifouling layer may be set to an appropriate thickness, and is usually about 1 to 10 µm.

(antistatic layer)

As the antistatic layer, a conventionally known one may be appropriately employed, and it is generally formed as a layer in which an antistatic layer is contained in a resin. As the antistatic layer, organic or inorganic compounds are used. For example, antistatic layers of organic compounds include cationic antistatic agents, anionic antistatic agents, amphoteric antistatic agents, nonionic antistatic agents, organometallic antistatic agents, and the like, and these antistatic agents are only used as low molecular weight compounds. It is also used as a polymer compound. Moreover, as an antistatic agent, conductive polymers, such as polythiophene and polyaniline, etc. are used. Further, as an antistatic agent, for example, conductive fine particles made of metal oxide and the like are also used. The particle diameter of the conductive fine particles is, for example, about 0.1 nm to 0.1 μm in average particle diameter from the viewpoint of transparency. Examples of the metal oxide include ZnO, CeO ₂ , Sb ₂ O ₂ , SnO ₂ , ITO (indium-doped tin oxide), In ₂ O ₃ , Al ₂ O ₃ , ATO (antimony-doped tin oxide), AZO ( aluminum-doped zinc oxide) etc. are mentioned.

As the resin containing the antistatic layer, for example, a curable resin such as an ionizing radiation curable resin or a thermosetting resin as described in the hard coat layer is used, and an antistatic layer is formed as an intermediate layer to increase the surface strength of the antistatic layer itself. When is unnecessary, a thermoplastic resin or the like is also 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 appropriately employing various well-known coating methods.

Although the liquid crystal display device of this invention has the above-mentioned backlight source, two polarizing plates, and the liquid crystal cell arrange|positioned between the said two polarizing plates, you may further have another member arbitrarily. For example, a color filter, a lens film, a diffusion sheet, an antireflection film or the like may be further provided.

Example

The present invention will be described in more detail with examples below, but the present invention is not limited by the following examples, and appropriate changes can be made within the scope suitable for the purpose of the present invention, all of which are technical aspects of the present invention. included in the scope

The methods for measuring physical properties employed in the examples are shown below.

(1) Thickness (d)

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

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

The MD refractive index (Nx), the TD refractive index (Ny), and the thickness direction refractive index (Nz) were determined in accordance with JIS K 7142 "Method for measuring the refractive index of plastics (Method A)". It was measured using a sodium D-line with a normal wavelength of 589 nm.

(3) Birefringence (ΔNxy) and retardation (Re)

Retardation is the refractive index (Nx, Ny, It is the phase difference represented by the product of the birefringence caused by Nz) and the film thickness (d). Here, the x-axis is the longitudinal direction (MD) and the y-axis is the transverse direction (TD). Dation was made into retardation (Re). Therefore, the birefringence (Δxy) and retardation (Re) were respectively obtained by the following formulas. Each refractive index was measured using an Abbe refractometer. The unit of retardation is nm.

△Nxy =｜Nx-Ny｜

Re　　=ΔNxy×d

(4) Thickness direction retardation (Rth)

Thickness direction retardation represents retardation caused by light incident from the thickness direction. Here, the product of the average of the two birefringences of the x-z plane and the y-z plane and the film thickness (d) was obtained from the following equation. Unit is nm.

Rth = (｜Nx-Nz｜+｜Ny-Nz｜)/2×d

(5) Plane orientation (ΔP)

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

ΔP = ((Nx＋Ny)/2)-Nz

(6) Observation of rainbow stains

On one side of a commercially available polarizer film, the films of each Example and Comparative Example described below were attached so that the absorption axis of the polarizer and the main axis of orientation of the film (higher Nx and Ny) were perpendicular to each other, and a commercially available TAC film was applied to the opposite side. It was stuck to produce a polarizing plate. Next, the polarizing plate on the viewing side of a commercially available liquid crystal display device having two polarizing plates and a liquid crystal cell having a white LED as a backlight and using two TAC films as a polarizer protective film was removed, and the polarizing plate produced as described above was replaced. . At this time, the said polarizing plate was installed so that the polarizer protective film of the visual recognition side of the produced polarizing plate might become the film of an Example or a comparative example. A white image was displayed on the thus produced liquid crystal display device, and visual observation was conducted from the front and in an oblique direction of the display, and the occurrence of rainbow spots was determined as follows. In addition, the observation angle is an angle formed by a line drawn in a normal direction (vertical) from the center of the display screen and a line connecting the center of the display and the position of the eyes when observing. ◎: No occurrence of rainbow spots in any direction. ○: When the observation angle is in the range of 0° to 55°, there is no occurrence of rainbow spots, and very light rainbow spots are observed in some parts in the range of the observation angle exceeding 55°. x: Rainbow spots were observed in the range of the observation angle of 0° to 55°.

(7) Tear strength

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

○: Tear strength is 50 mN or more

×: Tear strength less than 50 mN

(8) Transmittance

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

(9) Thermal contraction rate at 150°C

Based on JISC2318-19975.3.4 (dimensional change), the dimensional change rate (%) of the longitudinal direction and the width direction was measured. The film was cut to a width of 10 mm and a length of 250 mm in the direction to be measured, and marks were marked at intervals of 200 mm, and the gaps (A) of the marks were measured under a constant tension of 5 gf. Subsequently, the film was placed in an oven at 150° C., heated at 150 ± 3° C. for 30 minutes under no load, and then the mark spacing (B) was measured under a constant tension of 5 gf. Using these measured values, the thermal contraction rate was obtained from the formula below.

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

(Production Example 1-Polyester Resin A)

When the temperature of the esterification reaction can was raised and 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, 0.064 parts by mass of magnesium acetate tetrahydrate, and triethylamine were added as catalysts while stirring. 0.16 parts by mass was added. Subsequently, pressurized temperature was raised and pressurized esterification was carried out under conditions of a gauge pressure of 0.34 MPa and 240°C. Then, the esterification reaction can was returned to normal pressure and 0.014 parts by mass of phosphoric acid was added. Furthermore, it heated up to 260 degreeC over 15 minutes, and added 0.012 mass part of trimethyl phosphate. After 15 minutes, a dispersion treatment was performed with a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction can and polycondensation reaction was performed under reduced pressure at 280°C.

After the polycondensation reaction was completed, 95% was filtered with a Naslon filter having a cut diameter of 5 μm, extruded from a nozzle into a strand shape, and cooled using cooling water previously subjected to filtration treatment (pore diameter: 1 μm or less), It was solidified and cut into a pellet shape. The obtained resin had an intrinsic viscosity of 0.62 dl/g, and was substantially free of inert particles and internally precipitated particles. Below, the obtained polyethylene terephthalate resin is abbreviated as PET (A).

(Production Example 2-Polyester Resin B)

Dried UV absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) 10 parts by mass, particle-free PET (A) (intrinsic viscosity 0.62 dl/g) 90 mass parts were mixed, and a resin containing an ultraviolet absorber was obtained using a kneading extruder.The polyethylene terephthalate resin thus obtained is abbreviated as PET (B).

(Preparation Example 3 - Preparation of Adhesion Modifying Coating Solution)

46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 5-sulfonatoisophthalic acid (with respect to the total dicarboxylic acid component) as dicarboxylic acid components by transesterification and polycondensation by conventional methods A co-polyester resin containing a water-dispersible sulfonic acid metal base having a composition of 8 mol% sodium and 50 mol% ethylene glycol and 50 mol% neopentyl glycol as glycol components (relative to the total glycol component) was prepared. Subsequently, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 part by mass of a nonionic surfactant were mixed. After heating and stirring to reach 77°C, 5 parts by mass of the water-dispersible sulfonic acid metal base-containing co-polyester resin was added, and stirring was continued until lumps of the resin disappeared. Thereafter, the aqueous resin dispersion 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. Further, after dispersing 3 parts by mass of aggregate silica particles (Sylysia 310 manufactured by Fuji Silysia Co., Ltd.) in 50 parts by mass of water, 0.54 parts by mass of the aqueous dispersion of Silysia 310 in 99.46 parts by mass of the water-dispersible co-polyester resin solution. Part by mass was added, and 20 parts by mass of water was added while stirring to obtain an adhesion modifying coating liquid.

(Example 1)

As a raw material for the intermediate layer of the base film having a three-layer structure, 90 parts by mass of particle-free PET (A) resin pellets and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber are dried under reduced pressure at 135 ° C. for 6 hours (1 Torr ) and then supplied to the extruder (2) [for the middle layer (II layer)]. Further, PET (A) was dried by a conventional method, supplied to the extruder 1 (for outer layer (I layer) and outer layer (III layer)), and dissolved at 285°C. These two types of polymers were each filtered with a stainless steel sintered filter medium (nominal filtration accuracy of 10 μm particles, 95% cut), laminated in a two-type three-layer merged block, and extruded into a sheet form from a die, followed by an electrostatic application casting method. It was wound around a casting drum with a surface temperature of 30°C and cooled and solidified to make an unstretched film. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of the I layer, II layer, and III layer was 10:80:10.

Subsequently, the adhesion-modifying coating liquid was applied to both sides 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 on which this coating layer was formed was introduced into a simultaneous biaxial stretching machine, and while holding the end of the film with a clip, it was induced into a hot air zone at a temperature of 90°C, relaxed to a magnification of 0.8 in the longitudinal direction, and 4.0 in the transverse direction at the same time. double stretched. Next, treatment was performed at a temperature of 170° C. for 30 seconds, and further, a 3% relaxation treatment was performed in the width direction to obtain a uniaxially oriented PET film having a film thickness of about 50 μm.

(Example 2)

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

(Example 3)

Uniaxially oriented PET film in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 38 μm, the thickness was relaxed at a magnification of 0.7 times in the longitudinal direction, and heat treatment was performed at a temperature of 180 ° C. for 30 seconds. got

(Example 4)

Uniaxially oriented PET in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 25 μm, the draw ratio in the transverse direction was increased to 5.0 times, and heat treatment was performed at a temperature of 180 ° C. for 30 seconds. got the film

(Example 5)

By changing the thickness of the unstretched film, the thickness was set to about 80 μm, and the temperature at the time of stretching was set to 95 ° C. by relaxing at a magnification of 0.85 in the longitudinal direction, and heat treatment was performed at a temperature of 180 ° C. for 30 seconds. In the same manner as in 1, a uniaxially oriented PET film was obtained.

(Example 6)

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

(Comparative Example 1)

An unstretched film prepared in the same manner as in Example 1 was introduced into a tenter stretching machine, and while holding the end of the film with a clip, it was led to a hot air zone at a temperature of 125° C. and stretched 4.0 times in the width direction. Next, processing was performed at a temperature of 225° C. for 30 seconds while maintaining the stretched width in the width direction, and further, a 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, it was stretched 3.4 times in the running direction and 4.0 times in the width direction to obtain a biaxially oriented PET film having a film thickness of about 38 μm.

(Comparative Example 3)

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

(Comparative Example 4)

A uniaxially oriented PET film was obtained in the same manner as in Example 1 except that the thickness of the unstretched film was changed to about 38 μm and no longitudinal relaxation treatment 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 about 38 μm and no longitudinal relaxation treatment 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 about 25 μm and no longitudinal relaxation treatment was performed.

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 generation of rainbow spots was significantly suppressed and a liquid crystal display device having excellent visibility was obtained. In addition, the films of Examples 1 to 6 not only make it possible to provide an image display device with excellent visibility, but also have sufficient tear strength despite their relatively thin thickness, so that they can be used in the manufacture of industrial image display devices. It has been confirmed that it is suitable for use. On the other hand, when the films of Comparative Examples 1, 2 and 6 were used as polarizer protective films, it was impossible to obtain good visibility by generating rainbow spots when observed from the front. In addition, although the film of Comparative Example 3 has no problem in visibility when used as a polarizer protective film, it has been found to be unsuitable for production of an industrial and stable liquid crystal display device because the tear strength is insufficient. This is considered to be because the film of Comparative Example 3 has a relatively high Re value and Re/Rth ratio, but a high value of ΔP. When the films of Comparative Examples 4 and 5 were observed at an observation angle in the range of 0 ° to 55 °, rainbow stains were not observed, but very light rainbow stains were observed in some parts in the range of observation angles exceeding 55 °. This is considered to be because the films of Comparative Examples 4 and 5 had a relatively high Re/Rth ratio, but a low Re/Rth ratio. In Comparative Example 6, the tear strength was also insufficient because the value of ΔP was high.

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

1 polyester film
2 A line indicating the direction perpendicular to the plane of the polyester film.
3 A line connecting the position of the observer's eyes and the center of (the center of) the film plane.
4 Position of the observer's eyes

Claims (6)

A liquid crystal display device having a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
Among the two polarizing plates, the polarizing plate disposed on the visual side rather than the liquid crystal cell has a polarizer and the following physical properties (a) to (e):
(a) Retardation (Re) of 3,000 nm or more and 30,000 nm or less;
(b) a ratio of retardation (Re) to thickness direction retardation (Rth) (Re/Rth) of greater than 1.2 and less than or equal to 1.9;
(c) a plane orientation degree of 0.06 or more and 0.12 or less (ΔP);
(d) birefringence (ΔNxy) of 0.1 or more and 0.132 or less; and
(e) a thickness of 20 μm or more and 90 μm or less;
Including a polyester film that satisfies,
The absorption axis of the polarizer and the orientation main axis of the polyester film are perpendicular,
liquid crystal display. According to claim 1,
The polyester film is a polyethylene terephthalate film uniaxially stretched in the transverse direction, a liquid crystal display device. According to claim 1 or 2,
The tear strength of the polyester film is 50 mN or more, the liquid crystal display device. delete delete delete

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