JP7323564B2 - Liquid crystal display device and polarizing plate - Google Patents

Description

The present invention relates to a liquid crystal display device and a polarizing plate. More particularly, the present invention relates to a liquid crystal display device and a polarizing plate in which occurrence of rainbow-like color spots is reduced.

Polarizing plates used in liquid crystal displays (LCDs) generally have a structure in which a polarizer, such as polyvinyl alcohol (PVA) dyed with iodine, is sandwiched between two polarizer protective films. are mostly triacetyl cellulose (TAC) films. In recent years, along with the thinning of LCDs, thinning of polarizing plates is required. However, if the thickness of the TAC film used as a protective film is reduced for this reason, there arises a problem that sufficient mechanical strength cannot be obtained and moisture permeability is deteriorated. In addition, TAC film is very expensive, and polyester film has been proposed as an inexpensive alternative material (Patent Documents 1 to 3), but there is a problem that rainbow-like color spots are observed.

When an oriented polyester film having birefringence is arranged on one side of the polarizer, the polarization state of the linearly polarized light emitted from the backlight unit or the polarizer changes when passing through the polyester film. The transmitted light exhibits an interference color characteristic of the retardation, which is the product of the birefringence and thickness of the oriented polyester film. Therefore, when a discontinuous emission spectrum such as a cold-cathode tube or a hot-cathode tube is used as a light source, the intensity of transmitted light varies depending on the wavelength, resulting in rainbow-like color spots. 30-31).

As a means for solving the above problems, it is possible to use a white light source having a continuous and broad emission spectrum such as a white light emitting diode as a backlight source, and use an oriented polyester film having a certain retardation as a polarizer protective film. It has been proposed (Patent Document 4). A white light emitting diode has a continuous and broad emission spectrum in the visible light region. Therefore, focusing on the envelope shape of the interference color spectrum due to the transmitted light that has passed through the birefringent material, by controlling the retardation of the oriented polyester film, a spectrum similar to the emission spectrum of the light source can be obtained, and the rainbow spots can be suppressed. It is proposed that it is possible.

By making the orientation direction of the oriented polyester film and the polarization direction of the polarizing plate orthogonal or parallel to each other, the linearly polarized light emitted from the polarizer passes through the oriented polyester film while maintaining its polarization state. become. In addition, by controlling the birefringence of the oriented polyester film to enhance the uniaxial orientation, even light incident from an oblique direction can pass through while maintaining the polarization state. When an oriented polyester film is viewed obliquely, deviation occurs in the direction of the principal axis of orientation compared to when viewed from directly above. For this reason, it is considered that the deviation between the direction of linearly polarized light and the direction of the orientation main axis is reduced, and the change in polarization state is less likely to occur. In this way, by controlling the emission spectrum of the light source, the orientation state of the birefringent material, and the orientation principal axis direction, the change in the polarization state is suppressed, the rainbow-like color spots do not occur, and the visibility is significantly improved. It was thought that

JP-A-2002-116320 Japanese Patent Application Laid-Open No. 2004-219620 Japanese Patent Application Laid-Open No. 2004-205773 WO2011/162198

When industrially producing a liquid crystal display using a polarizing plate using a polyester film as a polarizer protective film, the directions of the transmission axis of the polarizer and the fast axis of the polyester film are usually arranged so as to be perpendicular to each other. be done. This is due to the following circumstances. A polyvinyl alcohol film, which is a polarizer, is manufactured by longitudinal uniaxial stretching. Therefore, the polyvinyl alcohol film used as a polarizer is usually a long film in the stretched direction. On the other hand, the polyester film, which is the protective film, is manufactured by longitudinally stretching and then transversely stretching, so that the orientation principal axis direction of the polyester film is the transverse direction. That is, the main orientation axis of the polyester film used as the polarizer protective film intersects the longitudinal direction of the film approximately perpendicularly. A polarizing plate is produced by laminating these films so that their longitudinal directions are generally parallel to each other. As a result, the fast axis of the polyester film and the transmission axis of the polarizer are generally perpendicular to each other. In this case, by using an oriented polyester film having a specific retardation as the polyester film and using a light source having a continuous and broad emission spectrum such as a white LED as the backlight source, the rainbow-like color spots are greatly improved. be. However, when the backlight source consists of a light source that emits excitation light and a light-emitting layer containing quantum dots, it was found that there is still a new problem that iridescence occurs.

Due to the increasing demand for expanding the color gamut in recent years, in addition to the white light source using quantum dot technology, the emission spectrum of the white light source is in each wavelength region of R (red), G (green), and B (blue). Liquid crystal display devices each having a distinct relative emission intensity peak have been developed. For example, a phosphor type white LED light source using a blue LED and a phosphor having distinct emission peaks in the regions of R (red) and G (green) by excitation light, a three-wavelength type white LED light source, and a red light source. A wide color gamut compatible liquid crystal display device has been developed using various types of light sources such as a white LED light source combined with a laser. All of these white light sources have a narrow half-value width of a peak compared to a light source composed of a white light-emitting diode using a YAG-based yellow phosphor, which has been widely used in the past. When a polyester film having retardation is used as a polarizer protective film which is a constituent member of a polarizing plate, these white light sources are back light sources composed of a light source for emitting excitation light and a light emitting layer containing quantum dots. It has been found that there is a problem similar to that in the case of liquid crystal display devices having

That is, one of the objects of the present invention is a liquid crystal having a backlight source in which the half width of each peak of the emission spectrum is relatively narrow, as typified by a backlight source that emits excitation light and a quantum dot. An object of the present invention is to provide a liquid crystal display device and a polarizing plate in which iridescence is suppressed even when a polyester film is used as a polarizer protective film in the display device.

A typical present invention is as follows.
Section 1.
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 includes a light source that emits excitation light and quantum dots,
At least one of the polarizing plates has a polyester film laminated on at least one surface of a polarizer,
The polyester film has a retardation of 1500 to 30000 nm,
An antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film,
Liquid crystal display.
Section 2.
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 has a peak top of an emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and emits light having a half width of 5 nm or more,
At least one of the polarizing plates has a polyester film laminated on at least one surface of a polarizer,
The polyester film has a retardation of 1500 to 30000 nm,
An antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film,
Liquid crystal display.
Item 3.
Item 2. Item 2, wherein the backlight source has peak tops of the emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 750 nm or less, and each peak has a half width of 5 nm or more. liquid crystal display.
Section 4.
Item 4. The liquid crystal display device according to any one of Items 1 to 3, wherein the antireflection layer surface has a surface reflectance of 2.0% or less at a wavelength of 550 nm.
Item 5.
A polarizing plate in which a polyester film is laminated on at least one surface of a polarizer,
The polyester film has a retardation of 1500 or more and 30000 nm or less, and an antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film.
A polarizing plate for a liquid crystal display device having a light source for emitting excitation light and a backlight source containing quantum dots.
Item 6.
A polarizing plate in which a polyester film is laminated on at least one surface of a polarizer,
The polyester film has a retardation of 1500 or more and 30000 nm or less, and an antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film.
For a liquid crystal display device having a backlight source having an emission spectrum having a peak top in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and a half width of each peak of 5 nm or more. Polarizer.
Item 7.
Item 7. The polarizing plate according to Item 5 or 6, wherein the antireflection layer surface has a surface reflectance of 2.0% or less at a wavelength of 550 nm.

The liquid crystal display device and the polarizing plate of the present invention can ensure good visibility in which the occurrence of rainbow-like color spots is significantly suppressed at any viewing angle.

An example is shown where multiple peaks exist within a single wavelength region. An example is shown where multiple peaks exist within a single wavelength region. An example is shown where multiple peaks exist within a single wavelength region. An example is shown where multiple peaks exist within a single wavelength region.

In general, a liquid crystal display device has a rear module, a liquid crystal cell, and a front module in order from the side on which a backlight source (also called a "backlight unit") is arranged to the side on which an image is displayed (viewing side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface of the substrate, and a polarizing plate disposed on the opposite side. That is, the polarizing plate is arranged on the side facing the backlight source in the rear module, and is arranged on the image display side (viewing side) in the front module.

The liquid crystal display device of the present invention includes at least a backlight source and a liquid crystal cell disposed between two polarizing plates as constituent members. The backlight source preferably has an emission spectrum having a peak top in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and having a half width of each peak of 5 nm or more. . It is known that the peak wavelengths of blue, green, and red defined in the CIE chromaticity diagram are 435.8 nm (blue), 546.1 nm (green), and 700 nm (red), respectively. The wavelength regions of 400 nm to less than 495 nm, 495 nm to less than 600 nm, and 600 nm to 780 nm correspond to the blue region, the green region, and the red region, respectively. As a light source having an emission spectrum as described above, there is a light source that emits excitation light and a backlight light source that includes at least quantum dots. In addition, a phosphor-type white LED light source combining a blue LED with a phosphor having emission peaks in the R (red) and G (green) regions by excitation light, a three-wavelength white LED light source, and a red laser are also available. A combined white LED light source and the like can be exemplified. Examples of the red phosphor among the phosphors include a nitride phosphor having a basic composition such as CaAlSiN ₃ :Eu, a sulfide phosphor having a basic composition such as CaS:Eu, and Ca ₂ SiO ₄ :Eu. and the like are exemplified as silicate-based phosphors having a basic composition of Among the above-described phosphors, the green phosphor may be, for example, a sialon-based phosphor having a basic composition of β-SiAlON:Eu or the like, a silicate-based phosphor having a basic composition of (Ba, Sr) ₂ SiO ₄ :Eu or the like. are exemplified.

In addition to the backlight source, the polarizing plate, and the liquid crystal cell, the liquid crystal display device may appropriately have other components such as a color filter, a lens film, a diffusion sheet, an antireflection film, and the like. A brightness enhancement film may be provided between the light source side polarizing plate and the backlight source. Examples of the brightness enhancement film include a reflective polarizing plate that transmits one linear polarized light and reflects the orthogonal linear polarized light. As the reflective polarizing plate, for example, brightness enhancement films of the DBEF (registered trademark) (Dual Brightness Enhancement Film) series manufactured by Sumitomo 3M Co., Ltd. are preferably used. Incidentally, the reflective polarizing plate is usually arranged so that the absorption axis of the reflective polarizing plate and the absorption axis of the light source side polarizing plate are parallel to each other.

Of the two polarizing plates placed in the liquid crystal display device, at least one of the polarizing plates is a polarizer in which polyvinyl alcohol (PVA) or the like is dyed with iodine, and a polyester film is laminated on at least one surface of the polarizer. is preferred. From the viewpoint of suppressing iridescent color spots, it is preferable that the polyester film has a specific retardation and has an antireflection layer and/or a low reflection layer laminated on at least one surface thereof. The antireflection layer and/or the low reflection layer may be provided on the surface of the polyester film opposite to the surface on which the polarizer is laminated, or may be provided on the surface of the polyester film on which the polarizer is laminated. It doesn't matter if it's both. Preferably, an antireflection layer and/or a low reflection layer is provided on the surface of the polyester film opposite to the surface on which the polarizer is laminated. When providing an antireflection layer and/or a low-reflection layer on the surface of the polyester film on which the polarizer is laminated, the layer is preferably provided between the polyester film and the polarizer. In addition, other layers (e.g., easy adhesion layer, hard coat layer, antiglare layer, antistatic layer, antifouling layer, etc.) are present between the antireflection layer and/or low reflection layer and the polyester film. may From the viewpoint of further suppressing rainbow-like color spots, the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is preferably 1.53 or more and 1.62 or less. On the other side of the polarizer, it is preferable to laminate a non-birefringent film typified by a TAC film, an acrylic film, and a norbornene-based film (a polarizing plate having a three-layer structure), but the polarizer is not necessarily It is not necessary to laminate a film on the other side of the film (two-layer polarizing plate). When polyester films are used as protective films on both sides of the polarizer, the slow axes of both polyester films are preferably substantially parallel to each other.

The polyester film may be laminated to the polarizer via any adhesive, or may be laminated directly without adhesive. Any adhesive can be used without any particular limitation. As an example, a water-based adhesive (that is, an adhesive component dissolved or dispersed in water) can be used. For example, an adhesive containing polyvinyl alcohol resin and/or urethane resin as a main component can be used. In order to improve adhesiveness, an adhesive further containing an isocyanate compound and/or an epoxy compound can be used, if necessary. As another example, a photocurable adhesive can also be used. In one embodiment, solventless UV curable adhesives are preferred. Examples of the photocurable resin include a mixture of a photocurable epoxy resin and a photocationic polymerization initiator.

The configuration of the backlight may be an edge-light type in which a light guide plate, a reflector, or the like is used as constituent members, or a direct type. A typical example of the backlight light source is a light source that emits excitation light and a backlight light source that includes quantum dots. and having an emission spectrum in which each peak has a half-value width of 5 nm or more. As for quantum dots, for example, a layer containing many quantum dots can be provided and used as a light-emitting layer for a backlight.

The application of quantum dot technology to LCDs is a technology that is attracting attention due to the growing demand for an expanded color gamut in recent years. An LED that uses a normal white LED as a backlight source can reproduce only about 20% of the spectrum recognizable by the human eye. On the other hand, it is said that when a backlight source consisting of a light source emitting excitation light and a light emitting layer containing quantum dots is used, it is possible to reproduce colors of 60% or more of the spectrum that can be recognized by the human eye. It is Quantum dot technologies that have been put into practical use include QDEF ^TM by Nanosys, Color IQ ^TM by QD Vision, and the like.

The light-emitting layer containing quantum dots is configured by containing quantum dots in a resin material such as polystyrene, for example, and is a layer that emits light of each color in pixel units based on excitation light emitted from a light source. . The light-emitting layer is composed of, for example, a red light-emitting layer arranged in the red pixel, a green light-emitting layer arranged in the green pixel, and a blue light-emitting layer arranged in the blue pixel. emit light of different wavelengths (colors) based on the excitation light.

Materials for such quantum dots include, for example, CdSe, CdS, ZnS:Mn, InN, InP, CuCl, CuBr, and Si. It is about 2 to 20 nm. Among the above quantum dot materials, red light emitting materials include InP, green light emitting materials include CdSc, and blue light emitting materials include CdS. In such a light-emitting layer, it has been confirmed that the emission wavelength is changed by changing the size (particle diameter) of the quantum dots and the composition of the material. The size (particle diameter) and material of the quantum dots are controlled, mixed with a resin material, and applied separately for each pixel. In addition, since the use of heavy metals such as cadmium is being restricted in many applications, cadmium-free quantum dots are being developed while maintaining the same brightness and stability as conventional ones.

A blue LED is used as a light source for emitting excitation light, but laser light such as a semiconductor laser may also be used. When the excitation light emitted from the light source passes through the light emitting layer, an emission spectrum having peak tops in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less is generated. At this time, the narrower the half-value width of the peak in each wavelength region, the wider the color gamut. is designed.

Although not limited to the following, the light source using quantum dots can be broadly classified into two mounting methods. One is an on-edge method in which quantum dots are mounted along the end surface (side surface) of the light guide plate of the backlight. A quantum dot, which is a particle with a diameter of several nanometers to several tens of nanometers, is placed in a glass tube with a diameter of several millimeters, sealed, and placed between a blue LED and a light guide plate. Light from a blue LED shines into the glass tube, and the blue light that collides with the quantum dots is converted into green or red light. The on-edge method has the advantage of reducing the amount of quantum dots used even on a large screen. The other is a surface mounting method in which quantum dots are placed on a light guide plate. Quantum dots are dispersed in resin to form a sheet, which is sandwiched between two barrier films for sealing. A quantum dot film is placed on the light guide plate. The barrier film plays a role in suppressing the deterioration of the quantum dots due to water and oxygen. The blue LED is placed on the edge (side) of the light guide plate as in the on-edge method. The light from the blue LED enters the light guide plate and becomes planar blue light, which illuminates the quantum dot film. The surface mount method has two major advantages. One is that the blue LED light passes through the light guide plate and hits the quantum dots, so the heat from the LED has little effect, making it easier to ensure reliability. Another advantage is that because it is in the form of a film, it is easy to adapt to a wide range of screen sizes, from small to large.

In the present invention, the backlight source has an emission spectrum peak top in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and the half width of each peak is 5 nm or more. is preferred. The wavelength region of 400 nm or more and less than 495 nm is more preferably 430 nm or more and 470 nm or less. The wavelength range of 495 nm or more and less than 600 nm is more preferably 510 nm or more and 560 nm or less. The wavelength region of 600 nm or more and 780 nm or less is more preferably 600 nm or more and 750 nm or less, more preferably 630 nm or more and 700 nm or less, and even more preferably 630 nm or more and 680 nm or less. A preferable lower limit of the half width of each peak is 10 nm or more, more preferably 15 nm or more, and still more preferably 20 nm or more. From the viewpoint of ensuring an appropriate color gamut, the upper limit of the half width of each peak is preferably 140 nm or less, preferably 120 nm or less, preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, and even more preferably 45 nm or less. Here, the half-value width is the peak width (nm) at half the intensity of the peak intensity at the wavelength of the peak top. Any combination of the individual upper and lower limits of the wavelength regions described herein is contemplated. Any combination of the individual upper and lower half-value width limits set forth herein is contemplated. The emission spectrum of the backlight light source can be measured using, for example, a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics.

If there are multiple peaks in any one of the wavelength range of 400 nm or more and less than 495 nm, the wavelength range of 495 nm or more and less than 600 nm, or the wavelength range of 600 nm or more and 780 nm or less, consider the following. When the plurality of peaks are independent peaks, the half width of the peak with the highest peak intensity is preferably within the above range. Furthermore, in a more preferred embodiment, other peaks having an intensity of 70% or more of the highest peak intensity also have half-value widths within the above range. For one independent peak having a shape in which multiple peaks overlap, if the half-value width of the peak with the highest peak intensity among the plurality of peaks can be measured as it is, that half-value width is used. Here, an independent peak has an intensity region of 1/2 of the peak intensity on both the short wavelength side and the long wavelength side of the peak. That is, when a plurality of peaks overlap and each peak does not have a region of intensity that is 1/2 of the peak intensity, the plurality of peaks as a whole is regarded as one peak. For one peak having such a shape in which a plurality of peaks are overlapped, the width (nm) of the peak at half the intensity of the highest peak intensity among them is defined as the half width. Let the peak top be the point with the highest peak intensity among a plurality of peaks. The double-headed arrows in FIGS.

In FIG. 1, the peaks A and B each have a point at which the intensity of the peak becomes 1/2 on the short wavelength side and the long wavelength side with the peak as the starting point. Therefore, peaks A and B are independent peaks. In the case of FIG. 1, the half-value width can be evaluated by the width of the double-headed arrow of peak A, which has the highest peak intensity.

In FIG. 2, peak A has points on the short wavelength side and long wavelength side where the peak intensity is 1/2, but peak B has a point on the long wavelength side where the peak intensity is 1/2. do not. Therefore, peak A and peak B are collectively regarded as one independent peak. For an independent peak having a shape in which multiple peaks overlap in this way, if the half-value width of the peak with the highest peak intensity among the multiple peaks can be measured as it is, the half-value width of the independent peak half width. Thus, in the case of FIG. 2, the half width of the peak is the width of the double arrow.

In FIG. 3, peak A does not have a point where the peak intensity is 1/2 on the short wavelength side, and peak B does not have a point where the peak intensity is 1/2 on the long wavelength side. Therefore, in FIG. 3, as in the case of FIG. 2, peak A and peak B are collectively regarded as one independent peak, and the half-value width thereof is the width indicated by the double-headed arrow.

In FIG. 4, peak A has points on the short wavelength side and long wavelength side where the peak intensity is 1/2, but peak B has a point on the long wavelength side where the peak intensity is 1/2. do not. Therefore, peak A and peak B are collectively regarded as one independent peak. For one independent peak having a shape in which multiple peaks overlap, if the half-value width of the peak with the highest peak intensity among the plurality of peaks can be measured as it is, that half-value width is used. Therefore, in the case of FIG. 4, the half width is the width indicated by the double-headed arrow.

1 to 4 show examples of the wavelength range of 400 nm or more and less than 495 nm, but the same concept applies to other wavelength ranges.

Let the peak with the highest peak intensity among the plurality of peaks be the peak top.
In addition, the peak having the highest peak intensity in the wavelength region of 400 nm or more and less than 495 nm, the wavelength region of 495 nm or more and less than 600 nm, or the wavelength region of 600 nm or more and 780 nm or less is independent of the peaks of other wavelength regions. is preferred. In particular, in the wavelength region between the peak with the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm and the peak with the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less, the intensity is 600 nm or more and 780 nm or less. From the standpoint of vividness of color, it is preferable that there is a region in which the peak intensity is ⅓ or less of the peak intensity of the highest peak in the region.

The emission spectrum of the backlight light source can be measured by using a spectroscope such as Hamamatsu Photonics multichannel spectroscope PMA-12.

As a result of intensive studies by the present inventors, a liquid crystal display device having a backlight source with a relatively narrow half-value width of each peak of the emission spectrum, such as a backlight source that emits excitation light and a quantum dot, To provide a liquid crystal display device in which iridescence is suppressed by using a polyester film having an antireflection layer and/or a low reflection layer as a polarizer protective film and having a specific retardation, and a polarizing plate useful for providing the liquid crystal display device. I found The mechanism by which the above aspect suppresses the occurrence of iridescent mottling is considered as follows.

When the oriented polyester film is placed on one side of the polarizer, the polarization state of the linearly polarized light emitted from the backlight unit or the polarizer changes when passing through the polyester film. One of the factors that change the polarization state may be the difference in refractive index at the interface between the air layer and the oriented polyester film or the difference in refractive index at the interface between the polarizer and the oriented polyester film. When the linearly polarized light incident on the oriented polyester film passes through each interface, part of the light is reflected due to the refractive index difference between the interfaces. At this time, the polarization states of both the emitted light and the reflected light change, and this is considered to be one of the factors causing the rainbow-like color spots. Therefore, by providing an antireflection layer or a low-reflection layer on the surface of the oriented polyester film to reduce the surface reflection, the reflection at the interface between the air layer and the oriented polyester film is suppressed, resulting in rainbow-like color spots. considered to be suppressed.

As described above, a backlight source with a relatively narrow half-value width of each peak of the emission spectrum, typified by a backlight source that emits excitation light and a quantum dot, and a polyester film as a polarizer protective film are used. By combining these polarizing plates, rainbow-like color spots can be suppressed and good visibility can be obtained.

The polarizing plate preferably has a polarizer protective film laminated on at least one surface of the polarizer, which is made of a polyester film. The polyester film used for the polarizer protective film preferably has a retardation of 1500 to 30000 nm. If the retardation is within the above range, the iridescence tends to be more easily reduced, which is preferable. A preferable lower limit of retardation is 3000 nm, a second preferable lower limit is 3500 nm, a more preferable lower limit is 4000 nm, a still more preferable lower limit is 6000 nm, and an even more preferable lower limit is 8000 nm. A preferable upper limit is 30000 nm, and a polyester film having a retardation of 30000 nm or more has a considerably large thickness, and tends to deteriorate in handleability as an industrial material. In this document, retardation means in-plane retardation unless otherwise indicated.

The retardation can be determined by measuring the refractive index and thickness in the biaxial directions, or can be determined using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). The refractive index can be determined by an Abbe refractometer (measurement wavelength: 589 nm).

The ratio (Re/Rth) of the retardation (Re: in-plane retardation) to the retardation (Rth) in the thickness direction of the polyester film is preferably 0.2 or more, preferably 0.3 or more, preferably 0.4 or more. , preferably 0.5 or more, more preferably 0.5 or more, and still more preferably 0.6 or more. As the ratio of the retardation to the thickness direction retardation (Re/Rth) increases, the birefringence action becomes more isotropic, and rainbow-like color spots tend to be less likely to occur depending on the viewing angle. Since the ratio of the retardation to the thickness direction retardation (Re/Rth) is 2.0 in a perfect uniaxial (uniaxially symmetric) film, the ratio of the retardation to the thickness direction retardation (Re/Rth) The upper limit is preferably 2.0. The thickness direction retardation means the average retardation obtained by multiplying the two birefringences ΔNxz and ΔNyz when the film is viewed from the thickness direction section by the film thickness d.

From the viewpoint of further suppressing rainbow-like color spots, the NZ coefficient of the polyester film is preferably 2.5 or less, more preferably 2.0 or less, still more preferably 1.8 or less, and even more preferably 1.8 or less. 6 or less. Since the NZ coefficient is 1.0 in a perfectly uniaxial (uniaxially symmetrical) film, the lower limit of the NZ coefficient is 1.0. However, it should be noted that the mechanical strength in the direction perpendicular to the orientation direction tends to decrease significantly as the film approaches a perfect uniaxial (uniaxially symmetrical) film.

The NZ coefficient is represented by |Ny−Nz|/|Ny−Nx|, where Ny is the refractive index in the slow axis direction, and Nx is the refractive index in the direction orthogonal to the slow axis (refraction in the fast axis direction). index), and Nz represents the refractive index in the thickness direction. The orientation axis of the film is obtained using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd.), and the biaxial refractive indices (Ny, Nx, where Ny>Nx) and the refractive index (Nz) in the thickness direction are determined by an Abbe refractometer (NAR-4T manufactured by Atago Co., Ltd., measuring wavelength 589 nm). The NZ coefficient can be obtained by substituting the value obtained in this way for |Ny-Nz|/|Ny-Nx|.

In addition, from the viewpoint of suppressing rainbow-like color spots, the Ny-Nx value of the polyester film is preferably 0.05 or more, more preferably 0.07 or more, still more preferably 0.08 or more, and even more preferably. is greater than or equal to 0.09, most preferably greater than or equal to 0.1. The upper limit is not particularly defined, but in the case of polyethylene terephthalate film, the upper limit is preferably about 1.5.

As a more preferred embodiment of the present invention, the refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer constituting the polarizing plate is preferably in the range of 1.53 or more and 1.62 or less. Thereby, it is possible to suppress the reflection at the interface between the polarizer and the polyester film, and to suppress rainbow-like color spots. If the refractive index exceeds 1.62, rainbow-like color spots may occur when observed from an oblique direction. The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer is preferably 1.61 or less, more preferably 1.60 or less, still more preferably 1.59 or less, and still more preferably is less than or equal to 1.58.

On the other hand, the lower limit of the refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer is 1.53. If the refractive index is less than 1.53, the crystallization of the polyester film becomes insufficient, and properties obtained by stretching such as dimensional stability, mechanical strength and chemical resistance become insufficient, which is not preferable. The refractive index is preferably 1.56 or higher, more preferably 1.57 or higher. Any range combining each upper limit and each lower limit of the refractive index noted above is envisioned.

In order to set the refractive index of the polyester film in the range of 1.53 or more and 1.62 or less in the direction parallel to the transmission axis direction of the polarizer, the polarizer has the transmission axis of the polarizer and the fast axis of the polyester film. (the direction perpendicular to the slow axis) is preferably parallel. The polyester film can be adjusted to have a low refractive index of about 1.53 to 1.62 in the fast axis direction, which is the direction perpendicular to the slow axis, by stretching in the film-forming process described later. By making the fast axis direction of the polyester film parallel to the transmission axis direction of the polarizer, the refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer can be set to 1.53 to 1.62. can. Here, being parallel means that the angle formed by the transmission axis of the polarizer and the fast axis of the polarizer protective film is -15° to 15°, preferably -10° to 10°, more preferably -5° to 5°, more preferably -3° to 3°, even more preferably -2° to 2°, even more preferably -1° to 1°. In one preferred embodiment, parallel is substantially parallel. Here, "substantially parallel" means that the transmission axis and the fast axis are parallel to the extent that a deviation that inevitably occurs when the polarizer and the protective film are stuck together is allowed. The direction of the slow axis can be obtained by measuring with a molecular orientation meter (for example, MOA-6004 type molecular orientation meter manufactured by Oji Instruments Co., Ltd.).

That is, the refractive index in the fast axis direction of the polyester film is preferably 1.53 or more and 1.62 or less. The polyester film may have a refractive index of 1.53 or more and 1.62 or less in a direction parallel to the transmission axis of the element.

The polarizer protective film made of the above polyester film can be used for both the polarizing plate on the incident light side (light source side) and the emitted light side (viewing side). In the polarizing plate arranged on the incident light side, the polarizer protective film made of the polyester film is placed on both sides of the polarizer regardless of whether it is arranged on the incident light side or the liquid crystal cell side with the polarizer as the starting point. Although it may be arranged, it is preferably arranged at least on the incident light side. Regarding the polarizing plate placed on the output light side, the polarizer protective film made of the polyester film is placed on both sides of the polarizer whether it is placed on the liquid crystal side or on the output light side. However, it is preferable that it is arranged at least on the output light side.

Polyethylene terephthalate and polyethylene naphthalate can be used as the polyester used for the polyester film, but other copolymer components may be included. These resins are excellent in transparency as well as in thermal and mechanical properties, and their retardation can be easily controlled by stretching. In particular, polyethylene terephthalate has a large intrinsic birefringence, and the refractive index in the fast axis direction (perpendicular to the slow axis direction) can be kept low by stretching the film. It is the most suitable material because a large retardation can be easily obtained.

For the purpose of suppressing deterioration of optically functional dyes such as iodine dyes, the polyester film preferably has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. If the light transmittance is 20% or less, deterioration of the optical functional dye due to ultraviolet rays can be suppressed. The transmittance is measured perpendicularly to the plane of the film, and can be measured using a spectrophotometer (for example, Hitachi U-3500).

In order to set the transmittance of the polyester film at a wavelength of 380 nm to 20% or less, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorbent and the thickness of the film. The ultraviolet absorbers used in the present invention are known substances. Examples of the UV absorber include organic UV absorbers and inorganic UV absorbers, but organic UV absorbers are preferred from the viewpoint of transparency. Examples of organic UV absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited as long as the absorbance is within the range defined by the present invention. However, from the viewpoint of durability, benzotriazole-based and cyclic iminoester-based agents are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be absorbed at the same time, so that the ultraviolet absorption effect can be further improved.

Examples of benzophenone UV absorbers, benzotriazole UV absorbers, and acrylonitrile UV absorbers include 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole, 2-[2' -hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-(methacryloyloxypropyl)phenyl]-2H-benzotriazole, 2,2'-dihydroxy- 4,4′-dimethoxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol, 2-( 2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl-6-( tert-butyl)phenol, 2,2′-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol, etc. Cyclic iminoesters Examples of UV absorbers include 2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one) and 2-methyl-3,1-benzoxazin-4-one. , 2-butyl-3,1-benzoxazin-4-one, 2-phenyl-3,1-benzoxazin-4-one, etc., but are not particularly limited thereto.

In addition to the ultraviolet absorber, it is also a preferred embodiment to contain various additives other than the catalyst within a range that does not impair the effects of the present invention. Examples of additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, and anti-gelling agents. , surfactants, and the like. In order to achieve high transparency, it is also preferred that the polyester film contains substantially no particles. The term "substantially contains no particles" means, for example, in the case of inorganic particles, a content of 50 ppm or less, preferably 10 ppm or less, particularly preferably a detection limit or less when the inorganic element is quantified by fluorescence X-ray analysis. means.

It is preferable to provide an antireflection layer and/or a low reflection layer on at least one surface of the polyester film which is the polarizer protective film. The surface reflectance of the antireflection layer is preferably 2.0% or less. If it exceeds 2.0%, rainbow-like color spots are likely to be visually recognized. The surface reflectance of the antireflection layer is more preferably 1.6% or less, still more preferably 1.2% or less, and particularly preferably 1.0% or less. Although the lower limit of the surface reflectance of the antireflection layer is not particularly limited, it is, for example, 0.01%. The reflectance can be measured by any method. For example, a spectrophotometer (Shimadzu Corporation, UV-3150) can be used to measure the light reflectance at a wavelength of 550 nm from the antireflection layer side surface.

The antireflection layer may be a single layer or multiple layers, and in the case of a single layer, the thickness of the low refractive index layer made of a material having a lower refractive index than that of the polyester film is set to a quarter wavelength of the light wavelength or less. An antireflection effect can be obtained by forming it so as to be an odd multiple. When the antireflection layer is multi-layered, an antireflection effect can be obtained by alternately forming two or more layers of a low refractive index layer and a high refractive index layer and appropriately controlling the thickness of each layer. Further, if necessary, a hard coat layer can be laminated between the antireflection layers, and an antifouling layer can be formed on the hard coat layer.

Examples of the antireflection layer include those using a moth-eye structure. A moth-eye structure is an uneven structure with a pitch smaller than the wavelength formed on the surface. make it possible to change. Therefore, by forming a moth-eye structure on the surface, light reflection on the surface of the film is reduced. Formation of an antireflection layer using a moth-eye structure can be performed, for example, with reference to Japanese Patent Publication No. 2001-517319.

Methods for forming an antireflection layer include, for example, a dry coating method in which an antireflection layer is formed on the substrate (polyester film) surface by vapor deposition or sputtering, and an antireflection coating liquid applied to the substrate surface and dried. A wet coating method for forming an antireflection layer, or a combination method using both of them can be mentioned. The composition and formation method of the antireflection layer are not particularly limited as long as the above characteristics are satisfied.

A known low-reflection layer can be used. For example, it is formed by a method of laminating at least one layer of metal or oxide thin films by vapor deposition or sputtering, or a method of coating one or more layers of organic thin films. As the low-reflection layer, one coated with an organic thin film having a refractive index lower than that of a polyester film or a hard coat layer laminated on a polyester film is preferably used. The surface reflectance of the low-reflection layer is preferably less than 5%, more preferably 4% or less, and even more preferably 3% or less. The lower limit is preferably about 0.8% to 1.0%.

The antireflection layer and/or the low reflection layer may further have an antiglare function. Thereby, iridescence can be further suppressed. That is, it may be a combination of an antireflection layer and an antiglare layer, a combination of a low reflection layer and an antiglare layer, or a combination of an antireflection layer, a low reflection layer and an antiglare layer. Particularly preferred is a combination of a low reflection layer and an antiglare layer. A known antiglare layer can be used as the antiglare layer. For example, from the viewpoint of suppressing the surface reflection of the film, it is preferable to laminate an antireflection layer or a low-reflection layer on the antiglare layer after laminating the antiglare layer on the polyester film.

When providing an antireflection layer or a low-reflection layer, the polyester film preferably has an easy-adhesion layer on its surface. At that time, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer so as to be close to the geometric mean of the refractive index of the antireflection layer and the refractive index of the polyester film. The adjustment of the refractive index of the easy-adhesion layer can employ a known method, and can be easily adjusted, for example, by adding titanium, germanium, or other metal species to the binder resin.

The polyester film may be subjected to corona treatment, coating treatment and/or flame treatment to improve adhesion to the polarizer.

In the present invention, in order to improve the adhesion to the polarizer, at least one surface of the film of the present invention has an easy-adhesion layer containing at least one of polyester resin, polyurethane resin or polyacrylic resin as a main component. is preferred. Here, the "main component" refers to a component that accounts for 50% by mass or more of the solid components that constitute the easy-adhesion layer. The coating liquid used for forming the easy-adhesion layer of the present invention is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolyester resins, acrylic resins and polyurethane resins. These coating liquids include, for example, water-soluble or water-dispersible liquids disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191, and Japanese Patent No. 4150982. A copolymer polyester resin solution, an acrylic resin solution, a polyurethane resin solution, or the like may be used.

The easy-adhesion layer can be obtained by applying the above-mentioned coating liquid to one or both sides of a uniaxially stretched film in the longitudinal direction, drying it at 100 to 150° C., and stretching it in the transverse direction. It is preferable to control the final coating amount of the easy-adhesion layer to 0.05 to 0.20 g/m ² . If the coating amount is less than 0.05 g/m ² , the adhesion to the resulting polarizer may be insufficient. On the other hand, if the coating amount exceeds 0.20 g/m ² , blocking resistance may deteriorate. When the easy-adhesion layer is provided on both sides of the polyester film, the coating amount of the easy-adhesion layer on both sides may be the same or different, and can be independently set within the above range.

Particles are preferably added to the easy-adhesion layer to impart lubricity. It is preferable to use particles having an average particle size of 2 μm or less. When the average particle size of the particles exceeds 2 μm, the particles tend to fall off from the coating layer. Particles contained in the easy-adhesion layer include, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and inorganic particles such as calcium fluoride, and organic polymer particles such as styrene, acrylic, melamine, benzoguanamine, and silicone particles. These may be added to the easy-adhesion layer singly, or two or more of them may be added in combination.

Moreover, a well-known method can be used as a method of apply|coating a coating liquid. Examples include reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire bar coating, pipe doctor, and the like. Or it can be performed in combination.

In addition, the measurement of the average particle size of the above particles is performed by the following method. The particles are photographed with a scanning electron microscope (SEM) and the largest diameter of 300-500 particles (between the two furthest Distance) is measured, and the average value is taken as the average particle size.

The polyester film used as the polarizer protective film can be produced according to a general polyester film production method. For example, a polyester resin is melted and a non-oriented polyester extruded into a sheet is stretched in the longitudinal direction using the speed difference between rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction with a tenter, A method of applying a heat treatment can be mentioned.

The polyester film used in the present invention may be a uniaxially stretched film or a biaxially stretched film.

Specifically, the film-forming conditions for the polyester film are preferably 80 to 130°C for the longitudinal stretching temperature and the transverse stretching temperature, and particularly preferably 90 to 120°C. In order to orient the film so that the slow axis is in the TD direction, the longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. Further, the transverse draw ratio is preferably 2.5 to 6.0 times, particularly preferably 3.0 to 5.5 times. In order to orient the film so that the slow axis is in the MD direction, the longitudinal draw ratio is preferably 2.5 to 6.0, more preferably 3.0 to 5.5. Further, the transverse draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times.

Setting the stretching temperature low is also a preferable measure for lowering the refractive index in the fast axis direction of the polyester film and increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably 100-250°C, particularly preferably 180-245°C.

In order to suppress variations in retardation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and the stretching ratio have a great effect on the thickness unevenness of the film, it is preferable to optimize the film-forming conditions from the viewpoint of reducing the thickness unevenness. In particular, if the longitudinal draw ratio is lowered in order to increase the retardation, longitudinal thickness unevenness may increase. Since there is a region in which the thickness unevenness in the machine direction becomes extremely poor within a certain range of the draw ratio, it is desirable to set the film-forming conditions outside this range.

Thickness unevenness of the polyester film is preferably 5.0% or less, more preferably 4.5% or less, even more preferably 4.0% or less, and 3.0% or less. is particularly preferred. The thickness unevenness of the film can be measured as follows. A tape-shaped film sample (3 m) is taken, and the thickness is measured at 100 points at a pitch of 1 cm using an electronic micrometer, Millitron 1240 manufactured by Seiko Em Corporation. The maximum value (dmax), minimum value (dmin), and average value (d) of the thickness are obtained from the measured values, and the thickness unevenness (%) is calculated by the following formula. It is preferable to perform the measurement three times and obtain the average value.
Thickness unevenness (%) = ((dmax-dmin)/d) x 100
As described above, the retardation of the polyester film can be controlled within a specific range by appropriately setting the draw ratio, draw temperature, and film thickness. For example, the higher the draw ratio, the lower the draw temperature, and the thicker the film, the easier it is to obtain a higher retardation. Conversely, the lower the draw ratio, the higher the drawing temperature, and the thinner the film, the easier it is to obtain a lower retardation. However, thickening the film tends to increase the retardation in the thickness direction. Therefore, it is desirable to appropriately set the film thickness within the range described later. In addition to retardation control, it is preferable to set the final film-forming conditions in consideration of the physical properties required for processing.

Although the thickness of the polyester film is arbitrary, it is preferably in the range of 15 to 300 μm, more preferably in the range of 15 to 200 μm. In principle, it is possible to obtain a retardation of 1500 nm or more even with a film having a thickness of less than 15 μm. However, in this case, the anisotropy of the mechanical properties of the film becomes conspicuous, and the film is likely to tear, tear, etc., and the practicality as an industrial material is remarkably lowered. A particularly preferable lower limit of the thickness is 25 μm. On the other hand, if the upper limit of the thickness of the polarizer protective film exceeds 300 μm, the thickness of the polarizing plate becomes too thick, which is not preferable. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. A particularly preferable upper limit of the thickness is 100 μm, which is equivalent to a general TAC film. In order to control the retardation within the range of the present invention even within the above thickness range, polyethylene terephthalate is suitable as the polyester used as the film substrate.

In addition, as a method for blending the ultraviolet absorber with the polyester film, a combination of known methods can be employed. For example, a masterbatch is prepared by blending the dried ultraviolet absorber and the polymer raw material using a kneading extruder in advance. It can be blended by, for example, a method of mixing the predetermined masterbatch and the polymer raw material at the time of film formation after preparation.

At this time, the concentration of the UV absorber in the masterbatch is preferably 5 to 30% by weight in order to uniformly disperse the UV absorber and to blend it economically. As conditions for preparing the masterbatch, a kneading extruder is preferably used, and the extrusion temperature is preferably the melting point of the polyester raw material or higher and 290° C. or lower for 1 to 15 minutes. At 290° C. or higher, the weight loss of the ultraviolet absorber is large, and the viscosity of the masterbatch is greatly lowered. If the extrusion temperature is less than 1 minute, it becomes difficult to uniformly mix the ultraviolet absorber. At this time, if necessary, a stabilizer, a color tone adjusting agent, and/or an antistatic agent may be added.

It is preferable that the polyester film has a multi-layered structure of at least three layers and that an ultraviolet absorber is added to an intermediate layer of the film. Specifically, a three-layer film containing an ultraviolet absorber in the intermediate layer can be produced as follows. For the outer layer, polyester pellets alone, and for the intermediate layer, a masterbatch containing an ultraviolet absorber and polyester pellets are mixed in a predetermined ratio, dried, fed to a known melt lamination extruder, and slit-shaped. A sheet is extruded through a die and cooled and solidified on a casting roll to form an unstretched film. That is, using two or more extruders, a three-layer manifold or a confluence block (for example, a confluence block having a square confluence portion), the film layers constituting both outer layers and the film layers constituting the intermediate layer are laminated, A three-layer sheet is extruded through a die and cooled on casting rolls to form an unstretched film. In addition, in the present invention, in order to remove foreign matter contained in the raw material polyester, which causes optical defects, it is preferable to perform high-precision filtration at the time of melt extrusion. The filtration particle size (initial filtration efficiency of 95%) of the filter medium used for high-precision filtration of molten resin is preferably 15 μm or less. If the filtration particle size of the filter medium exceeds 15 μm, the removal of foreign matter with a size of 20 μm or more tends to be insufficient.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by the following examples, and can be carried out with appropriate modifications within the scope of the gist of the present invention. Both of them are included in the technical scope of the present invention. Methods for evaluating physical properties in the following examples are as follows.

(1) Refractive index of polyester film A molecular orienter (MOA-6004 type molecular orienter manufactured by Oji Keisoku Co., Ltd.) is used to determine the slow axis direction of the film, and the slow axis direction is parallel to the long side. A rectangle of 4 cm x 2 cm was cut out so as to form a sample for measurement. For this sample, the refractive index in the orthogonal biaxial direction (refractive index in the slow axis direction: Ny, fast axis (refractive index in the direction perpendicular to the slow axis direction): Nx) and the refractive index in the thickness direction ( Nz) was determined by an Abbe refractometer (NAR-4T manufactured by Atago Co., measuring wavelength 589 nm).

(2) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|Nx−Ny|) on the film and the film thickness d (nm). It is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) is determined by the method (1) above, and the absolute value of the biaxial refractive index difference (|Nx−Ny|) is calculated as the refractive index anisotropy (ΔNxy ). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf Co.) and converted into nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

(3) Thickness direction retardation (Rth)
The retardation in the thickness direction refers to the two birefringences ΔNxz (=|Nx−Nz|) and ΔNyz (=|Ny−Nz|) when viewed from the cross section in the thickness direction of the film, and the film thickness d, respectively. It is a parameter indicating the average retardation obtained by multiplication. Nx, Ny, Nz and film thickness d (nm) are obtained in the same manner as in the measurement of retardation, and the average value of (ΔNxz × d) and (ΔNyz × d) is calculated to obtain the thickness direction retardation (Rth ).

(4) NZ Coefficient The values of Ny, Nx, and Nz obtained in (1) above were substituted into the formula (NZ=|Ny−Nz|/|Ny−Nx|) to obtain the value of the NZ coefficient.

(5) Measurement of emission spectrum of backlight light source The liquid crystal display device used in each example was BRAVIA KDL-40W920A manufactured by SONY (liquid crystal display having a light source for emitting excitation light and a backlight light source containing quantum dots. equipment) was used. When the emission spectrum of the backlight light source of this liquid crystal display device was measured using a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics, an emission spectrum having peak tops near 450 nm, 528 nm, and 630 nm was observed, and each peak top was 17 nm to 34 nm. The exposure time for spectrum measurement was 20 msec.

(6) Reflectance Using a spectrophotometer (Shimadzu Corporation, UV-3150), the 5-degree reflectance at a wavelength of 550 nm was measured from the antireflection layer side (or low reflection layer side) surface. In addition, after applying black marker on the side opposite to the antireflection layer (or low reflection layer) of the polyester film, black vinyl tape (Kyowa vinyl tape HF-737 width 50 mm) was attached and measured.

(7) Observation of iris spots The liquid crystal display device obtained in each example was visually observed from the front and oblique directions in a dark place, and the presence or absence of iris spots was determined as follows. Here, the oblique direction means a range of 30 to 60 degrees from the normal direction of the screen of the liquid crystal display device.

○: No iridescence observed △: Iridescence slightly observed ×: Iridescence observed XX: Iridescence markedly observed

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

After the completion of the polycondensation reaction, it is filtered through a NASLON filter with a 95% cut diameter of 5 μm, extruded from a nozzle in the form of a strand, and cooled and solidified using cooling water that has been previously filtered (pore size: 1 μm or less). , cut into pellets. The resulting polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62 dl/g and contained substantially no inert particles or internal precipitated particles. (Hereinafter abbreviated as PET (A).)

(Production Example 2-Polyester B)
10 parts by weight of dried UV absorber (2,2′-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one), particle-free PET (A) (intrinsic viscosity is 0.62 dl/g), and a kneading extruder was used to obtain a polyethylene terephthalate resin (B) containing an ultraviolet absorber (hereinafter abbreviated as PET (B)).

(Production Example 3-Adhesion-improving coating liquid preparation)
A transesterification reaction and a polycondensation reaction were carried out by a conventional method to obtain 46 mol % of terephthalic acid, 46 mol % of isophthalic acid and 8 mol % of sodium 5-sulfonatoisophthalate as dicarboxylic acid components (relative to the total dicarboxylic acid components). A water-dispersible sulfonic acid metal group-containing copolymer polyester resin was prepared having a composition of 50 mol % ethylene glycol and 50 mol % neopentyl glycol as the glycol component (relative to the total glycol component). Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant are mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal group-containing copolymerized polyester resin and continuing to stir until the lumps of the resin disappear, the resin aqueous dispersion was cooled to room temperature and the solid content concentration was 5.0% by mass. A homogeneous water-dispersible copolyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Silysia 310) in 50 parts by mass of water, Silysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added while stirring to obtain an adhesion-improving coating liquid.

(Production Example 4-Preparation of high refractive index coating agent)
80 parts of methyl methacrylate, 20 parts of methacrylic acid, 1 part of azoisobutyronitrile, and 200 parts of isopropyl alcohol are charged into a reaction vessel and reacted at 80° C. for 7 hours under a nitrogen atmosphere to produce isopropyl polymer having a weight average molecular weight of 30,000. An alcoholic solution was obtained. The resulting polymer solution was further diluted with isopropyl alcohol to a solid content of 5% to obtain an acrylic resin solution B. Next, the obtained acrylic resin solution B was mixed with the following components to obtain a coating liquid for forming a high refractive index layer.

・Acrylic resin solution B 5 parts by mass ・Bisphenol A diglycidyl ether 0.25 parts by mass ・Titanium oxide particles having an average particle size of 20 nm 0.5 parts by mass ・Triphenylphosphine 0.05 parts by mass ・Isopropyl alcohol 14.25 parts by mass

(Production Example 5-Preparation of low refractive index coating agent)
2,2,2-trifluoroethyl acrylate (45 parts by mass), perfluorooctylethyl acrylate (45 parts by mass), acrylic acid (10 parts by mass), azoisobutyronitrile (1.5 parts by mass), methyl ethyl ketone ( 200 parts by mass) was charged into a reaction vessel and reacted at 80° C. for 7 hours under a nitrogen atmosphere to obtain a methyl ethyl ketone solution of a polymer having a weight average molecular weight of 20.000. The obtained polymer solution was diluted with methyl ethyl ketone to a solid content concentration of 5% by mass to obtain a fluoropolymer solution C. The obtained fluoropolymer solution C was mixed as follows to obtain a coating liquid for forming a low refractive index layer.

・ Fluoropolymer solution C 4 4 parts by mass ・ 1,10-bis (2, 3-epoxypropoxy)
- 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7 ,
8,8,9,9-hexadecafluorodecane (manufactured by Kyoeisha Chemical Co., Ltd., Fluorite FE-16) 1 part by mass Triphenylphosphine 0.1 part by mass Methyl ethyl ketone 19 parts by mass

(Preparation Example 6-Preparation of Antiglare Layer Coating Agent-1)
Unsaturated double bond-containing acrylic copolymer Cychromer P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-20 (number average molecular weight 75000) (manufactured by Eastman Chemical Co.) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (2 parts by mass) , and Irgacure 184 (manufactured by BASF) (10 parts by mass) so that the solid content is 35% by mass, in addition to a mixed solvent of methyl ethyl ketone: 1-butanol = 3: 1, a coating solution for forming an antiglare layer Obtained.

(Preparation Example 7-Preparation of Antiglare Layer Coating Agent-2)
Unsaturated double bond-containing acrylic copolymer Cychromer P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.5 (number average molecular weight 25000) (Eastman Chemical Co.) ) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (4 mass part), and Irgacure 184 (manufactured by BASF) (10 parts by mass) so that the solid content is 35% by mass, in addition to a mixed solvent of methyl ethyl ketone: 1-butanol = 3: 1, coating for forming an antiglare layer I got the liquid.

(Production Example 8-Preparation of Antiglare Layer Coating Agent-3)
Unsaturated double bond-containing acrylic copolymer Cychromer P ACA-Z250 (manufactured by Daicel Chemical Industries, Ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.2 (number average molecular weight 15000) (Eastman Chemical Co.) ) (3 parts by mass), acrylic monomer AYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.) (49 parts by mass), acrylic-styrene copolymer (average particle size 4.0 μm) (manufactured by Sekisui Plastics Co., Ltd.) (2 mass Part), Irgacure 184 (manufactured by BASF) (10 parts by mass) so that the solid content is 35% by mass, in addition to a mixed solvent of methyl ethyl ketone: 1-butanol = 3: 1, a coating solution for forming an antiglare layer got

(Polarizer protective film 1)
After drying under reduced pressure (1 Torr) at 135° C. for 6 hours, 90 parts by mass of PET (A) resin pellets containing no particles and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber as raw materials for the base film intermediate layer. , supplied to extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method, supplied to extruder 1 (for outer layer I layer and outer layer III), and melted at 285 ° C. . These two types of polymers are each filtered with a stainless sintered filter material (nominal filtration accuracy: 10 μm, 95% cut of particles), laminated in a two-type, three-layer confluence block, extruded in a sheet form from a nozzle, An unstretched film was produced by winding the film around a casting drum having a surface temperature of 30° C. and solidifying it by cooling using an electrostatic casting method. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of the I layer, the II layer, and the III layer was 10:80:10.

Next, the adhesion-improving coating solution 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 with the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, was guided to a hot air zone at a temperature of 125° C. and stretched 4.0 times in the width direction. Next, while maintaining the stretched width in the width direction, it is treated at a temperature of 225 ° C. for 10 seconds, and further subjected to a relaxation treatment of 3.0% in the width direction to obtain a uniaxially stretched PET film with a film thickness of about 100 μm. rice field.

The coating solution for forming a high refractive index layer was applied to one coating surface of this uniaxially stretched PET film and dried at 150° C. for 2 minutes to form a high refractive index layer having a thickness of 0.1 μm. On this high refractive index layer, the coating liquid for forming a low refractive index layer obtained by the above method is applied and dried at 150° C. for 2 minutes to form a low refractive index layer having a thickness of 0.1 μm, and a reflective layer is formed. A polarizer protective film 1 laminated with an anti-layer was obtained.

(Polarizer protective film 2)
A polarizer protective film 2 having a film thickness of about 80 μm and having a film thickness of about 80 μm was obtained by forming a film in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. rice field.

(Polarizer protective film 3)
A polarizer protective film 3 having a film thickness of about 60 μm and having a film thickness of about 60 μm was obtained by forming a film in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. rice field.

(Polarizer protective film 4)
A polarizer protective film 4 having a film thickness of about 40 μm and having an antireflection layer laminated thereon was produced in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. rice field.

(Polarizer protective film 5)
An unstretched film produced by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then 3.3 degrees in the running direction with a roll group having a peripheral speed difference. After double-stretching, it is guided to a hot air zone at a temperature of 130° C. and stretched 4.0-fold in the width direction, and an antireflection layer is laminated in the same manner as the polarizer protective film 1. A polarizer protective film having a thickness of about 30 μm. Film 5 was obtained.

(Polarizer protective film 6)
A polarizer protective film 6 having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 1 except that the antireflection layer was not provided.

(Polarizer protective film 7)
Antiglare layer coating agent- 1 was applied and dried in an oven at 80° C. for 60 seconds. Thereafter, an ultraviolet irradiation apparatus (Fusion UV Systems Japan, Light Source H Bulb) was used to irradiate ultraviolet rays at an irradiation dose of 300 mJ/cm ² to laminate an antiglare layer. After that, an antireflection layer was laminated on the antiglare layer in the same manner as the polarizer protective film 1 to obtain a polarizer protective film 7 .

(Polarizer protective film 8)
An antiglare layer and an antireflection layer are formed in the same manner as the polarizer protective film 7 on one coated surface of the polarizer protective film prepared in the same manner as the polarizer protective film 3 except that the antireflection layer is not provided. A polarizer protective film 8 was obtained by lamination.

(Polarizer protective film 9)
Antiglare layer coating agent- 2 was applied and dried in an oven at 80° C. for 60 seconds. Thereafter, an ultraviolet irradiation apparatus (Fusion UV Systems Japan, Light Source H Bulb) was used to irradiate ultraviolet rays at an irradiation dose of 300 mJ/cm ² to laminate an antiglare layer. After that, an antireflection layer was laminated on the antiglare layer in the same manner as the polarizer protective film 1 to obtain a polarizer protective film 9 .

(Polarizer protective film 10)
Polarizer protective film 5 is prepared in the same manner as polarizer protective film 5, except that the antireflection layer is not provided. A child protective film 10 was obtained (no antireflection layer was laminated).

(Polarizer protective film 11)
An antiglare layer coating agent- 3 was applied and dried in an oven at 80° C. for 60 seconds. Thereafter, an ultraviolet irradiation device (Fusion UV Systems Japan, Light Source H Bulb) was used to irradiate ultraviolet rays at an irradiation dose of 300 mJ/cm ² to obtain a polarizer protective film 11 laminated with an antiglare layer.

(Polarizer protective film 12)
Antiglare layer coating agent- 1 was applied and dried in an oven at 80° C. for 60 seconds. Thereafter, an ultraviolet irradiation apparatus (Fusion UV Systems Japan, Light Source H Bulb) was used to irradiate ultraviolet rays at an irradiation dose of 300 mJ/cm ² to laminate an antiglare layer. After that, a low refractive index layer was laminated on the antiglare layer in the same manner as in the polarizer protective film 1 . In this way, a polarizer protective film 12 in which a low-reflection layer was laminated on the antiglare layer was obtained.

Using the polarizer protective films 1 to 12, a liquid crystal display device was produced as described later.

(Example 1)
A polarizer protective film 1 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare a polarizing plate 1. A polarizer was laminated on the surface of the polarizer protective film on which the antireflection layer was not laminated to prepare a polarizing plate. Sony's BRAVIA KDL-40W920A (liquid crystal display device having a light source that emits excitation light and a backlight source containing quantum dots), the polarizing plate on the viewing side, the polyester film is opposite to the liquid crystal (distal) and A liquid crystal display device was fabricated by replacing the polarizing plate 1 with the above polarizing plate 1. The direction of the transmission axis of the polarizing plate 1 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Example 2)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 2.

(Example 3)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 3.

(Example 4)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 4.

(Example 5)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 4 was used instead of the polarizer protective film 1, and the fast axis was attached so as to be parallel to the transmission axis of the polarizer. .

(Example 6)
A liquid crystal display device was produced in the same manner as in Example 1 except that the polarizer protective film 1 was changed to the polarizer protective film 7 .

(Example 7)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 8.

(Example 8)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 9.

(Example 9)
A liquid crystal display device was produced in the same manner as in Example 1 except that the polarizer protective film 1 was changed to the polarizer protective film 12 .

(Comparative example 1)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 5.

(Comparative example 2)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 6.

(Comparative Example 3)
A liquid crystal display device was produced in the same manner as in Example 1 except that the polarizer protective film 1 was changed to the polarizer protective film 10 .

(Comparative Example 4)
A liquid crystal display device was produced in the same manner as in Example 1, except that the polarizer protective film 1 was changed to the polarizer protective film 11 .

Table 1 below shows the results of iridescence observation of the liquid crystal display device obtained in each example.

INDUSTRIAL APPLICABILITY The liquid crystal display device and the polarizing plate of the present invention can ensure good visibility in which the occurrence of rainbow-like color spots is significantly suppressed at any angle, and greatly contribute to the industrial world.

Claims (8)

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 includes a light source that emits excitation light and quantum dots,
At least one of the polarizing plates has a polyester film on at least one surface of the polarizer, and the angle formed by the transmission axis of the polarizer and the fast axis of the polyester film is −15 degrees to 15 degrees. are laminated as
The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer is 1.53 or more and 1.62 or less,
The polyester film has an in-plane retardation of 4000 nm or more and 30000 nm or less,
A liquid crystal display device in which an antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film (however, it is a polyester film laminated with a hard code layer, and has an in-plane retardation of 8000 nm or more and a difference (nx -ny) is 0.07 to 0.20, and the refractive index (nh) of the hard coat layer, the refractive index (nx) in the slow axis direction and the fast axis direction of the polyester film (ny ) except for a liquid crystal display device having a polarizing plate in which a polyester film having a relationship of ny<nh<nx is laminated on a polarizer). 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 has a peak top of an emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and the half width of each peak is 5 nm or more and 80 nm or less,
At least one of the polarizing plates has a polyester film on at least one surface of the polarizer, and the angle formed by the transmission axis of the polarizer and the fast axis of the polyester film is −15 degrees to 15 degrees. are laminated as
The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer is 1.53 or more and 1.62 or less,
The polyester film has an in-plane retardation of 4000 nm or more and 30000 nm or less,
A liquid crystal display device in which an antireflection layer and / or a low reflection layer is laminated on at least one surface of the polyester film (however, it is a polyester film laminated with a hard code layer, and has an in-plane retardation of 8000 nm or more and a difference (nx -ny) is 0.07 to 0.20, and the refractive index (nh) of the hard coat layer, the refractive index (nx) in the slow axis direction and the fast axis direction of the polyester film (ny ) except for a liquid crystal display device having a polarizing plate in which a polyester film having a relationship of ny<nh<nx is laminated on a polarizer). 3. The liquid crystal display device according to claim 1, wherein said polyester film has an in-plane retardation of 6000 nm or more and 30000 nm or less. 4. The backlight source has a peak top of an emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 750 nm or less, and the half width of each peak is 5 nm or more and 80 nm or less. 3. The liquid crystal display device according to 2. 5. The liquid crystal display device according to claim 1, wherein the antireflection layer has a surface reflectance of 2.0% or less at a wavelength of 550 nm. The polyester film according to any one of claims 1 to 5 , wherein the ratio (Re/Rth) of the retardation (Re) and the retardation (Rth) in the thickness direction is 0.2 or more and 2.0 or less. Liquid crystal display. 7. The liquid crystal display device according to claim 1, further comprising another layer between said antireflection layer and/or low reflection layer and said polyester film. 7. The liquid crystal display device according to claim 1, further comprising an antiglare layer between said antireflection layer and/or low reflection layer and said polyester film.

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