CN113552664A

CN113552664A - Liquid crystal display device and polarizing plate

Info

Publication number: CN113552664A
Application number: CN202110761704.0A
Authority: CN
Inventors: 村田浩一; 佐佐木靖; 早川章太; 向山幸伸
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2014-10-30
Filing date: 2015-10-27
Publication date: 2021-10-26
Also published as: KR20170072222A; TW201621409A; KR102634613B1; JP2017138604A; JP6950731B2; TWI686642B; CN107077025A; JP2021193460A; JP2022003389A; JPWO2016068102A1; KR20240017143A; CN107077025B; JP6645420B2; JP2020034950A; WO2016068102A1

Abstract

Providing: a liquid crystal display device having a backlight source with a narrow half-value width of each peak in an emission spectrum, such as a backlight source including a light source emitting excitation light and quantum dots, wherein rainbow unevenness can be suppressed even when a polyester film is used as a polarizer protective film. A liquid crystal display device has: a backlight source having peaks of emission spectra in respective wavelength regions of 400nm or more and less than 495nm, 495nm or more and less than 600nm and 600nm or more and 780nm or less, the half-value width of each peak being 5nm or more and 100nm or less, at least one of the polarizing plates being obtained by laminating a polyester film on at least one surface of a polarizing plate, the polyester film having a refractive index of 1.53 to 1.62 in a direction parallel to a light transmission axis of the polarizing plate, and a liquid crystal cell disposed between the 2 polarizing plates, the retardation of the polyester film being 1500nm or more and less than 8000 nm.

Description

Liquid crystal display device and polarizing plate

This application is a divisional application filed on 2015, 10/27, with application number 201580058716X and title "liquid crystal display device and polarizing plate".

Technical Field

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 capable of reducing generation of iridescent stains.

Background

A polarizing plate used in a Liquid Crystal Display (LCD) is generally configured by sandwiching a polarizing plate obtained by dyeing iodine on polyvinyl alcohol (PVA) or the like with 2 sheets of a polarizing plate protective film, and a cellulose Triacetate (TAC) film is generally used as the polarizing plate protective film. In recent years, with the thinning of LCDs, the polarizing plate is required to be thin. However, if the thickness of the TAC film used as the protective film is reduced for this purpose, a sufficient mechanical strength cannot be obtained, and the moisture permeability deteriorates. In addition, TAC films are very expensive, and polyester films have been proposed as an inexpensive alternative material (patent documents 1to 3), but there is a problem in that iridescent unevenness is observed.

When an oriented polyester film having birefringence is disposed on one side of a polarizing plate, the polarization state of linearly polarized light emitted from a backlight unit or the polarizing plate changes when the linearly polarized light passes through the polyester film. The transmitted light exhibits a characteristic interference color according to the retardation amount which is the product of the birefringence and the 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, it shows different transmission light intensities depending on the wavelength and forms iridescent spots (see item 30 to 31, the 15 th Microoptic Congress Collection).

As a method for solving the above-mentioned problems, it has been proposed to use a white light source having a continuous and wide emission spectrum, such as a white light emitting diode, as a backlight light source, and further use an oriented polyester film having a certain retardation amount as a polarizer protective film (patent document 4). White light emitting diodes have a continuous and broad emission spectrum in the visible region. Therefore, it is proposed that when focusing on the shape of the envelope of the interference color spectrum of transmitted light transmitted through a birefringent body, a spectrum similar to the emission spectrum of a light source can be obtained by controlling the retardation amount of an oriented polyester film, and iridescence can be suppressed.

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 polarizing plate passes through the oriented polyester film while maintaining the polarization state. Further, the uniaxial orientation is improved by controlling the birefringence of the oriented polyester film, and light incident from an oblique direction also passes through the oriented polyester film while maintaining the polarization state. When the oriented polyester film is observed from an oblique direction, a shift occurs in the orientation main axis direction as compared with the case of observation from directly above, but when the uniaxial orientation is high, the shift in the orientation main axis direction when observed from an oblique direction becomes small. Therefore, it is considered that the deviation between the direction of the linearly polarized light and the orientation main axis direction is small, and the change of the polarization state is less likely to occur. As described above, it is considered that by controlling the emission spectrum of the light source, the orientation state of the birefringent body, and the orientation main axis direction, the change in the polarization state can be suppressed, and the visibility can be remarkably improved without generating rainbow-like color spots.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-116320

Patent document 2: japanese patent laid-open publication No. 2004-219620

Patent document 3: japanese patent laid-open publication No. 2004-205773

Patent document 4: WO2011/162198

Disclosure of Invention

Problems to be solved by the invention

In the case of industrially producing a liquid crystal display device using a polarizing plate using a polyester film as a polarizer protective film, the transmission axis of the polarizing plate and the fast axis direction of the polyester film are generally arranged so as to be perpendicular to each other. This is based on the following situation. The polyvinyl alcohol film as a polarizing plate is produced by uniaxial stretching in the machine direction. Thus, a polyvinyl alcohol film used as a polarizing plate is generally a film long in the stretching direction. On the other hand, since a polyester film as a protective film is produced by stretching in the machine direction and then stretching in the transverse direction, the orientation main axis direction of the polyester film is changed to the transverse direction. That is, the orientation major axis of the polyester film used as the polarizer protective film intersects the longitudinal direction of the film substantially perpendicularly. From the viewpoint of production efficiency, these films are generally bonded so that the longitudinal directions thereof are parallel to each other to produce a polarizing plate. Thus, the fast axis of the polyester film is generally perpendicular to the transmission axis of the polarizer. In the above case, by using an oriented polyester film having a specific retardation as the polyester film and using a light source having a continuous emission spectrum such as a white LED as the backlight light source, iridescent unevenness can be greatly improved. However, when it is found that the backlight light source is configured by a light source which emits excitation light and a light-emitting layer including quantum dots, there is still a new problem of occurrence of rainbow spots.

In addition to white light sources using quantum dot technology, liquid crystal display devices have been developed in which the emission spectrum of a white light source has a distinct peak of relative emission intensity in each of the wavelength regions of R (red), G (green), and B (blue) due to recent increasing demand for color gamut expansion. Liquid crystal display devices have been developed that can cope with a wider color gamut, using various light sources such as a phosphor type white LED light source using a phosphor having a clear emission peak in R (red) and G (green) regions by excitation light and a blue LED phosphor, a 3-wavelength type white LED light source, and a white LED light source combining a red laser beam. These white light sources have a narrower peak half-value width than a light source including a white light emitting diode using a YAG yellow phosphor which has been conventionally used in general. The following are found: among these white light sources, when a polyester film having a retardation is used as a polarizer protective film which is a constituent member of a polarizing plate, there is a problem similar to that in the case of the above-described liquid crystal display device having a backlight light source including a light source emitting excitation light and a light emitting layer including quantum dots.

That is, an object of the present invention is to provide: a liquid crystal display device having a backlight source with a narrow half-value width of each peak in an emission spectrum, such as a backlight source including a light source emitting excitation light and quantum dots, and a polarizing plate, wherein rainbow unevenness can be suppressed even when a polyester film is used as a polarizer protective film.

Means for solving the problems

Representative invention is described below.

Item 1.

A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

the backlight source comprises a light source emitting exciting light and quantum dots,

at least one of the polarizing plates is obtained by laminating a polyester film on at least one surface of a polarizer, and the refractive index of the polyester film in a direction parallel to the transmission axis of the polarizer is 1.53 to 1.62.

Item 2.

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and a half-value width of each peak is 5nm or more,

Item 3.

The liquid crystal display device according to item 2, wherein the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 750nm, and a half-value width of each peak is 5nm or more.

Item 4.

The liquid crystal display device according to any one of claims 1to 3, wherein a difference between a refractive index in a transmission axis direction of the polarizing plate and a refractive index of the polyester film in a direction parallel to the transmission axis of the polarizing plate is 0.12 or less.

Item 5.

A polarizing plate for a liquid crystal display device having a backlight source, which is obtained by laminating a polyester film on at least one surface of a polarizing plate,

the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizing plate is 1.53 to 1.62,

the backlight light source includes a light source emitting excitation light and quantum dots.

Item 6.

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and a half-value width of each peak is 5nm or more.

ADVANTAGEOUS EFFECTS OF INVENTION

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

Drawings

Fig. 1 shows an example when a plurality of peaks exist in a single wavelength region.

Fig. 2 shows an example when a plurality of peaks exist in a single wavelength region.

Fig. 3 shows an example in which a plurality of peaks exist in a single wavelength region.

Fig. 4 shows an example in which a plurality of peaks exist in a single wavelength region.

Detailed Description

In general, a liquid crystal display device has a rear module, a liquid crystal cell, and a front module in this order from a side where a backlight light source (also referred to as a "backlight unit") is arranged to a side where an image is displayed (visible 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, and a polarizing plate disposed on the opposite side. That is, the polarizing plate is disposed on the side opposite to the backlight light source in the rear module, and is disposed on the side (visible side) where an image is displayed in the front module.

The liquid crystal display device of the present invention uses at least a backlight source and a liquid crystal cell disposed between 2 polarizing plates as constituent members. The aforementioned backlight light source preferably has the following emission spectrum: has a peak top in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and has a half-value width of each peak of 5nm or more. It is known that the peak wavelengths of blue, green, and red defined in the CIE chromaticity diagram are 435.8nm (blue), 546.1nm (green), and 700nm (red), respectively. The wavelength regions of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less correspond to a blue region, a green region, and a red region, respectively. Examples of the light source having the emission spectrum include: a backlight light source including at least a light source emitting excitation light and quantum dots. Further, there may be mentioned: white LED light source of a phosphor system in which a phosphor having emission peaks in R (red) and G (green) regions by excitation light and a blue LED are combined, and white light of a 3-wavelength systemAn LED light source, a white LED light source combined with a red laser, and the like. Among the above phosphors, red phosphors include, for example: with CaAlSiN₃: eu, etc., and a phosphor of nitride system having CaS: eu, etc. as basic composition, and Ca₂SiO₄: eu, etc. as a basic composition. Among the phosphors, examples of the green phosphor include: taking the ratio of beta-SiAlON: eu, etc. as basic composition sialon phosphor, and (Ba, Sr)₂SiO₄: eu, etc. as a basic composition.

The liquid crystal display device may preferably have a configuration other than the backlight source, the polarizing plate, and the liquid crystal cell, for example, a color filter, a lens film, a diffusion sheet, and an antireflection film. A luminance improving film may be provided between the light source side polarizing plate and the backlight light source. As the luminance improving film, for example, a reflection type polarizing plate which transmits one linearly polarized light and reflects a linearly polarized light orthogonal thereto is exemplified. As the reflective polarizing plate, for example, a DBEF (registered trademark) series Brightness Enhancement Film manufactured by Sumitomo 3M Limited can be suitably used. In general, a reflective polarizing plate is arranged such that the absorption axis of the reflective polarizing plate is parallel to the absorption axis of the light source side polarizing plate.

At least one of the 2 polarizing plates disposed in the liquid crystal display device is obtained by laminating a polyester film on at least one surface of a polarizing plate dyed with iodine such as polyvinyl alcohol (PVA). The refractive index of the polyester film in a direction parallel to the transmission axis of the polarizing plate is preferably 1.53 to 1.62. A film (a polarizing plate composed of 3 layers) having no birefringence, such as a TAC film, an acrylic film, and a norbornene film, is preferably laminated on the other surface of the polarizer, but a film (a polarizing plate composed of 2 layers) is not necessarily laminated on the other surface of the polarizer. In the case of using polyester films as the protective films on both sides of the polarizing plate, the slow axes of the two polyester films are preferably substantially parallel to each other.

The polyester film may be laminated on the polarizing plate with an arbitrary adhesive or may be directly laminated without an adhesive. The adhesive is not particularly limited, and any adhesive can be used. As an example, an aqueous adhesive (i.e., a substance obtained by dissolving an adhesive component in water or a substance obtained by dispersing it in water) can be used. For example, an adhesive containing a polyvinyl alcohol resin and/or a urethane resin as a main component can be used. In order to improve the adhesiveness, an adhesive further containing an isocyanate compound, an epoxy compound, or the like may be used as necessary. As another example, a photocurable adhesive may be used. In one embodiment, a solvent-free ultraviolet curable adhesive is preferred. Examples of the photocurable resin include: a mixture of a photocurable epoxy resin and a photocationic polymerization initiator, and the like.

The backlight may be of an edge light type or a direct type, in which a light guide plate, a reflection plate, or the like is used as a constituent member. The backlight light source is preferably a "backlight light source having an emission spectrum having a peak top in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm and 600nm or more and 780nm or less, and a half-value width of each peak is 5nm or more" as a typical example of a backlight light source including a light source emitting excitation light and quantum dots. The quantum dots may be provided with a large number of layers containing quantum dots, for example, and used as light-emitting layers for backlights.

The application of quantum dot technology to LCDs is a technology that has attracted attention in recent years due to the increasing demand for color gamut expansion. In an LED using a general white LED as a backlight light source, only about 20% of a spectrum recognizable by human eyes can be reproduced. On the other hand, when a backlight light source including a light source that emits excitation light and a light-emitting layer including quantum dots is used, it can be said that 60% or more of the spectrum recognizable by the human eye can be reproduced. Practical quantum dot technology is QDEF of NanoSys Co., Ltd^TMColor IQ of QD Vision corporation^TMAnd the like.

The light-emitting layer including quantum dots is a layer including quantum dots in a resin material such as polystyrene, and emits light of each color in a pixel unit based on excitation light emitted from a light source. The light-emitting layer is composed of, for example, a red light-emitting layer disposed in a red pixel, a green light-emitting layer disposed in a green pixel, and a blue light-emitting layer disposed in a blue pixel, and the quantum dots in these light-emitting layers of the plurality of colors generate emitted light of different wavelengths (colors) from each other based on excitation light.

Examples of the material of such quantum dots include: CdSe, CdS, ZnS: mn, InN, InP, CuCl, CuBr, Si, etc., and the particle diameter (the dimension in one direction) of these quantum dots is, for example, about 2 to 20 nm. In the quantum dot material, InP may be used as a red light-emitting material, CdSc may be used as a green light-emitting material, and CdS may be used as a blue light-emitting material. In such a light-emitting layer, it was confirmed that the emission wavelength was changed by changing the size (particle diameter) of the quantum dot and the composition of the material. The size (particle diameter) and material of the quantum dot are controlled, and the quantum dot is mixed with a resin material and applied separately for each pixel. In addition, since the use of heavy metals such as cadmium tends to be limited in many applications, quantum dots which maintain the same brightness and stability as conventional ones and are free of cadmium have been developed.

As a light source for emitting excitation light, a blue LED is used, and a laser beam such as a semiconductor laser may be used. An excitation light emitted from a light source is allowed to pass through the light-emitting layer, thereby generating light emission spectra having peak tops in respective wavelength regions of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less. In this case, the color gamut is wider as the half width of the peak in each wavelength region is narrower, but the light emission efficiency is lowered as the half width of the peak is narrower, and therefore, the shape of the light emission spectrum is designed in consideration of the balance between the color gamut and the light emission efficiency required.

The light source using the quantum dot is not particularly limited, and there are roughly 2 mounting methods. An Edge (On Edge) method for mounting quantum dots along an end face (side face) of a light guide plate for backlight. Quantum dots, which are particles having a diameter of several n to several tens of nm, are put into a glass tube having a diameter of several mm, sealed, and disposed between the blue LED and the light guide plate. The glass tube is irradiated with light from a blue LED, wherein blue light colliding with the quantum dots is converted into green light, red light. The edge method has the advantage that the use amount of quantum dots can be reduced even for a large picture. The other is a surface mounting method in which quantum dots are placed on a light guide plate. Quantum dots are dispersed in a resin to form a sheet, and a quantum dot thin film sandwiched and sealed by 2 barrier films is laid on a light guide plate. The barrier film plays a role of suppressing the quantum dot degradation caused by water and oxygen. The blue LEDs are arranged on the end surface (side surface) of the light guide plate in the same manner as the edgewise method. Light from the blue LED enters the light guide plate and becomes planar blue light, and the quantum dot thin film is irradiated with the blue light. The surface mounting method has two features, and since light of one blue LED is irradiated to the quantum dot through the light guide plate, the influence of heat from the LED is small, and reliability is easily ensured. The other is a film shape, which is easy to cope with a wide screen size from a small size to a large size.

In the present invention, the backlight light source preferably has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and a half-value width of each peak is preferably 5nm or more. The wavelength region of 400nm or more and less than 495nm is more preferably 430nm or more and 470nm or less. The wavelength region of 495nm or more and less than 600nm is more preferably 510nm or more and 560nm or less. The wavelength region of 600nm to 780nm is more preferably 600nm to 750nm, more preferably 630nm to 700nm, and still more preferably 630nm to 680 mn. The lower limit of the half-value width of each peak is preferably 10nm or more, more preferably 15nm or more, and still more preferably 20nm or more. From the viewpoint of ensuring a suitable color gamut, the upper limit of the half-value width of each peak is preferably 140nm or less, preferably 120nm or less, preferably 100nm or less, more preferably 80nm or less, further preferably 60nm or less, and further preferably 45nm or less. Here, the half width means a peak width (nm) at 1/2 intensity of a peak intensity at a wavelength of a peak top. The upper and lower limits of the wavelength region described herein are assumed to be any combination thereof. The respective upper and lower limits of the half-value width described herein are assumed to be arbitrary combinations thereof. The peak intensity can be measured, for example, by using a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics K.K.

When a plurality of peaks are present in any wavelength region of a wavelength region of 400nm or more and less than 495nm, a wavelength region of 495nm or more and less than 600nm, or a wavelength region of 600nm or more and 780nm or less, the following is considered. When a plurality of peaks are independent peaks, the half-value width of the peak having the highest peak intensity is preferably in the above range. Further, the half-value width of the other peak having an intensity of 70% or more of the maximum peak intensity is also preferably in the above-described range. In the case where the half-value width of the peak having the highest peak intensity among the plurality of peaks can be directly measured for one independent peak having a shape in which the plurality of peaks overlap, the half-value width is used. Here, the independent peak means a peak having a region reaching 1/2 intensity of 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 1/2 intensity on both sides of the peak, the plurality of peaks are regarded as one peak as a whole. For one peak having such a shape that a plurality of peaks overlap, the width (nm) of the peak of the intensity of 1/2, which is the highest peak intensity among the peaks, is defined as the half-value width. The peak top is the point of the plurality of peaks at which the peak intensity is highest. In fig. 1to 4, the half-value width when a plurality of peaks exist in a single wavelength region is shown by a double-headed arrow.

In fig. 1, peaks a and B are starting points, and 1/2 that indicates peak intensity is present on the short wavelength side and the long wavelength side. Thus, peaks a and B are independent peaks. In the case of fig. 1, the half-value width may be evaluated as the width of the double-headed arrow having the peak a with the highest peak intensity.

In fig. 2, peak a has a point 1/2 reaching the peak intensity on the short wavelength side and the long wavelength side, and peak B has no point 1/2 reaching the peak intensity on the long wavelength side. Therefore, the peak a and the peak B are collectively regarded as 1 peak independently. In the case where the half-value width of the peak having the highest peak intensity among the plurality of peaks can be directly measured for one independent peak having such a shape that the plurality of peaks overlap with each other, the half-value width is defined as the half-value width of the independent peak. Therefore, in the case of fig. 2, the half-value width of the peak is the width of the double-headed arrow.

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

In fig. 4, peak a has a point 1/2 reaching the peak intensity on the short wavelength side and the long wavelength side, and peak B has no point 1/2 reaching the peak intensity on the long wavelength side. Therefore, the peak a and the peak B are collectively regarded as 1 peak independently. In the case where the half-value width of the peak having the highest peak intensity among the plurality of peaks can be directly measured for one independent peak having a shape in which the plurality of peaks overlap, the half-value width is used. Therefore, in the case of fig. 4, the half-value width thereof is the width shown by the double-headed arrow.

In FIGS. 1to 4, a wavelength range of 400nm or more and less than 495nm is exemplified, and the same concept is applied to other wavelength ranges.

It is preferable that a peak having the highest peak intensity in each of a wavelength region of 400nm or more and less than 495nm, a wavelength region of 495nm or more and less than 600nm, and a wavelength region of 600nm or more and 780nm or less be in a mutually independent relationship with peaks in other wavelength regions. In particular, it is preferable in terms of color clarity that a region having an intensity equal to or less than 1/3 of the peak intensity of the peak having the highest peak intensity in the wavelength region of 600nm or more and 780nm or less exists in the wavelength region between the peak having the highest peak intensity in the wavelength region of 495nm or more and less than 600nm and the peak having the highest peak intensity in the wavelength region of 600nm or more and 780nm or less.

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

The present inventors have conducted intensive studies and, as a result, have found that: in a case where a polarizing plate using a polyester film as a polarizer protective film is used in a liquid crystal display device having a backlight source with a narrow half-value width of each peak in an emission spectrum, such as a backlight source including a light source emitting excitation light and quantum dots as described above, if the refractive index of the polyester film in a direction parallel to the transmission axis of the polarizer constituting the polarizing plate is in a range of 1.53 or more and 1.62 or less, rainbow unevenness can be significantly suppressed. The mechanism of suppressing generation of iridescent stains by the above-described means is considered as follows.

When an oriented polyester film is disposed on one side of a polarizing plate, the polarization state changes when linearly polarized light emitted from a backlight unit or the polarizing plate passes through the oriented polyester film. One of the factors that cause the change in the polarization state is considered to be the possibility of the influence of the refractive index difference at the interface between the air layer and the oriented polyester film or the refractive index difference at the interface between the polarizing plate and the oriented polyester film. When linearly polarized light incident on the oriented polyester film passes through each interface, a part of the light is reflected by a refractive index difference in the interface. At this time, the polarization state of both the emitted light and the reflected light changes, which is considered to be one of the main causes of the occurrence of the rainbow-like color spots. Therefore, it is considered that reflection at each interface can be suppressed and iridescent unevenness can be suppressed by reducing the refractive index difference between the air layer and the oriented polyester film in the polarization direction (light transmission axis direction) of incident linearly polarized light and the refractive index difference between the polarizing plate and the oriented polyester film. The reduction of the refractive index difference between the air layer and the oriented polyester film in the polarization direction (light transmission axis direction) of incident linearly polarized light and the refractive index difference between the polarizing plate and the oriented polyester film can be achieved by adjusting the refractive index of the oriented polyester film in the direction parallel to the light transmission axis to about 1.53 to 1.62.

As described above, by combining a backlight source having a narrow half-value width of each peak in the emission spectrum, represented by a backlight source including a light source emitting excitation light and quantum dots, with a polarizing plate using an oriented polyester film as a polarizer protective film, a liquid crystal display device having excellent visibility with generation of rainbow color spots suppressed can be provided.

In the polarizing plate of the present invention, a polarizer protective film made of a polyester film is laminated on at least one surface of a polarizer. The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizing plate is preferably adjusted to be low so as to fall within the range of 1.53 to 1.62. This can suppress reflection at the interface between the air layer and the polyester film and at the interface between the polarizing plate and the polyester film, thereby suppressing rainbow-like color spots. When the refractive index exceeds 1.62, rainbow-like color unevenness may occur when viewed from an oblique direction. The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizing plate is preferably 1.61 or less, more preferably 1.60 or less, still more preferably 1.59 or less, and still more preferably 1.58 or less.

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 polarizing plate was 1.53. If the refractive index is less than 1.53, 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 1.54 or more, more preferably 1.55 or more, further preferably 1.56 or more, and further preferably 1.57 or more. An arbitrary range in which the upper limit and the lower limit of the refractive index are combined is assumed.

In order to set the refractive index of the polyester film in the range of 1.53 to 1.62 in the direction parallel to the transmission axis direction of the polarizer, the polarizing plate of the present invention is preferably such that the transmission axis of the polarizer is parallel to the fast axis (direction perpendicular to the slow axis) of the polyester film. The refractive index of the polyester film in the fast axis direction (direction perpendicular to the slow axis) can be adjusted to a range of 1.53 to 1.62 by stretching treatment in the film forming step described later. Further, the fast axis direction of the polyester film is made parallel to the transmission axis direction of the polarizer, whereby a polarizing plate having a refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizer of 1.53 to 1.62 can be produced. Here, the term "parallel" means that the angle formed by the transmission axis of the polarizing plate and the fast axis of the polarizing plate protective film is preferably-15 ° to 15 °, more preferably-10 ° to 10 °, still more preferably-5 ° to 5 °, still more preferably-3 ° to 3 °, still more preferably-2 ° to 2 °, and particularly preferably-1 ° to 1 °. In one embodiment, the parallelism is substantially parallel. Here, the term "substantially parallel" means that the transmission axis is parallel to the fast axis to such an extent that the polarizer and the protective film are inevitably deviated when they are bonded to each other. The direction of the slow axis can be determined by measurement using a molecular orientation meter (for example, an Oji Scientific Instruments Co., Ltd., manufactured by Ltd., MOA-6004 type molecular orientation meter).

That is, the refractive index of the polyester film used in the present invention in the fast axis direction is preferably 1.53 or more and 1.62 or less, and a polarizing plate having a refractive index of the polyester film in the direction parallel to the transmission axis of the polarizing plate of 1.53 or more and 1.62 or less can be manufactured by laminating the transmission axis of the polarizing plate and the fast axis of the polyester film in a substantially parallel manner.

The polarizing plate may be any one of those used in the art (polarizing film) and may be selected as appropriate. Typical examples of the polarizing plate include: the polarizing plate obtained by dyeing a dichroic material such as iodine on a polyvinyl alcohol film or the like is not limited to this, and a known polarizing plate or a polarizing plate that can be developed in the future can be appropriately selected and used.

The PVA film may be any one of commercially available films, for example: "Kuraray vinyl on (manufactured by KURARARAAY CO., LTD)", "Tohcello vinyl on (manufactured by Tohcello Inc.)," Nikki vinyl on (manufactured by Nippon synthetic chemical Co., Ltd) ", and the like. Examples of the dichroic material include: iodine, diazo compounds, polymethine dyes, and the like.

The polarizing plate can be obtained by any method, for example, as follows: a PVA film was dyed with a dichroic material, and the obtained material was uniaxially stretched in an aqueous boric acid solution, washed and dried while maintaining the stretched state, to obtain. The stretching ratio of the uniaxial stretching is usually about 4 to 8 times, but is not particularly limited. Other manufacturing conditions and the like may be appropriately set according to a known method.

It is more preferable that the difference between the refractive index of the polarizing plate in the transmission axis direction and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizing plate is 0.12 or less. The difference is more preferably 0.11 or less, more preferably 0.10 or less, more preferably 0.09 or less, still more preferably 0.08 or less, still more preferably 0.07 or less, particularly preferably 0.06 or less, and most preferably 0.05 or less. The smaller the difference in refractive index is, the more reflection at the interface of the polyester film can be suppressed, and the more rainbow unevenness can be suppressed, which is preferable. The lower limit of the difference is 0. The transmission axis direction of the polarizer may be determined using a known polarizing plate.

The polarizing plate is not particularly limited, and for example: conventionally known polarizing plates such as a polarizing plate dyed with iodine, such as polyvinyl alcohol (PVA). The refractive index of the polarizing plate in the transmission axis direction is preferably 1.41 to 1.56, more preferably 1.44 to 1.55, and still more preferably 1.47 to 1.54.

The polyester film used for the polarizer protective film preferably has a retardation of 1500 to 30000 nm. When the retardation amount is within the above range, the rainbow unevenness tends to be further reduced, which is preferable. The lower limit of the retardation is preferably 3000nm, and the lower limit thereof is preferably 3500nm, more preferably 4000nm, still more preferably 6000nm, and still more preferably 8000 nm. The preferable upper limit is 30000nm, and in the polyester film having a retardation of not less than this, the thickness tends to be considerably large, and the workability as an industrial material tends to be lowered. In the present specification, the retardation amount indicates an in-plane retardation amount unless otherwise specified.

The retardation may be determined by measuring the refractive index and the thickness in the 2-axis direction, or may be determined by using a commercially available automatic birefringence measurement 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) of the polyester film to the retardation (Rth) in the thickness direction is preferably 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more. As the ratio (Re/Rth) of the retardation to the retardation in the thickness direction is larger, the birefringence action becomes more isotropic, and the occurrence of rainbow-like color spots due to the observation angle tends to be less likely to occur. In a complete 1-axis (1-axis symmetric) film, the ratio of the retardation to the retardation in the thickness direction (Re/Rth) is 2.0, and therefore the upper limit of the ratio of the retardation to the retardation in the thickness direction (Re/Rth) is preferably 2.0. The thickness direction retardation is an average of the retardation obtained by multiplying each of the 2 birefringence Δ Nxz and Δ Nyz when the film is observed from a cross section in the thickness direction by the film thickness d.

The polarizer protective film formed of the polyester film can be used for polarizing plates on both the incident light side (light source side) and the outgoing light side (visible side). In the polarizing plate disposed on the incident light side, the polarizer protective film formed of the polyester film may be disposed on the incident light side from the polarizer, may be disposed on the liquid crystal cell side, or may be disposed on both sides, but is preferably disposed at least on the incident light side. The polarizing plate disposed on the light-emitting side may be a polarizer protective film made of the polyester film, which is disposed on the liquid crystal side from the polarizer as a starting point, may be disposed on the light-emitting side, or may be disposed on both sides.

The polyester used in the polyester film may be polyethylene terephthalate or polyethylene naphthalate, or may contain other copolymerizable components. These resins are excellent in transparency, thermal properties and mechanical properties, and the retardation can be easily controlled by stretching. In particular, polyethylene terephthalate has a large intrinsic birefringence, and is an optimum material because it can be stretched to suppress the refractive index in the fast axis direction (direction perpendicular to the slow axis direction) to a low level, and it can easily obtain a large retardation even when the film is thin.

In order to suppress deterioration of an optically functional dye such as an iodine dye, it is desirable that the polyester film has a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380nm is more preferably 15% or less, still more preferably 10% or less, and particularly preferably 5% or less. When the light transmittance is 20% or less, the deterioration of the optically functional dye by 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 type).

In order to make the transmittance of the polyester film at a wavelength of 380nm 20% or less, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber and the thickness of the film. The ultraviolet absorber used in the present invention is a known one. Examples of the ultraviolet absorber include an organic ultraviolet absorber and an inorganic ultraviolet absorber, and from the viewpoint of transparency, an organic ultraviolet absorber is preferable. Examples of the organic ultraviolet absorber include benzotriazole-based, benzophenone-based, cyclic imino ester-based, and combinations thereof, and the range of the absorbance is not particularly limited. However, benzotriazole and cyclic imino ester are particularly preferable from the viewpoint of durability. When 2 or more ultraviolet absorbers are used in combination, ultraviolet rays of respective wavelengths can be absorbed simultaneously, and thus the ultraviolet absorption effect can be further improved.

Examples of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and acrylonitrile-based ultraviolet 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 ' -dihydroxy-4, 4 ' -dimethoxybenzophenone, 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' -methylenebis (4- (1,1,3, 3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, etc. As cyclic imino ester ultraviolet absorbers, examples thereof include: 2, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazin-4-one), 2-methyl-3, 1-benzoxazin-4-one, 2-butyl-3, 1-benzoxazin-4-one, 2-phenyl-3, 1-benzoxazin-4-one, and the like, but is not particularly limited thereto.

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

In order to suppress scratches and the like, it is also preferable to provide various functional layers, i.e., a hard coat layer and the like, on the surface of the polyester film as the polarizer protective film used in the present invention. When various functional layers are provided, the polyester film preferably has an easy-adhesion layer on the surface thereof. In this case, from the viewpoint of suppressing interference due to reflected light, it is preferable to adjust the refractive index of the easy-adhesion layer to be in the vicinity of the geometric average of the refractive index of the functional layer and the refractive index of the polyester film. The refractive index of the easy-adhesion layer can be adjusted by a known method, and can be easily adjusted by, for example, adding titanium, germanium, or another metal substance to the binder resin.

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

In the present invention, in order to improve the adhesiveness to the polarizing plate, the film of the present invention preferably has an easy-adhesion layer containing at least 1 of a polyester resin, a polyurethane resin, or a polyacrylic resin as a main component on at least one surface thereof. Here, the "main component" means a component of 50 mass% or more of the solid component constituting 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 1 of a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin. Examples of these coating liquids include: water-soluble or water-dispersible copolyester resin solutions, acrylic resin solutions, or urethane resin solutions disclosed in japanese patent No. 3567927, japanese patent No. 3589232, japanese patent No. 3589233, japanese patent No. 3900191, and japanese patent No. 4150982, for example.

The easy adhesion layer can be obtained as follows: the coating liquid is applied to one side or both sides of a uniaxially stretched film in the longitudinal direction, dried at 100 to 150 ℃, and stretched in the transverse direction. The coating weight of the final easy-bonding layer is preferably controlled to be 0.05-0.20 g/m². If the coating weight is less than 0.05g/m²The adhesiveness to the obtained polarizing plate may be insufficient. On the other hand, if the coating amount exceeds 0.20g/m²Sometimes the blocking resistance is reduced. When the easy-adhesion layers are provided on both sides of the polyester film, the coating amounts of the easy-adhesion layers on both sides may be the same or different, and may be set within the above ranges independently.

In order to impart slidability, it is preferable to add particles to the easy-adhesion layer. It is preferable to use particles having an average particle diameter of 2 μm or less. If the average particle diameter of the particles exceeds 2 μm, the particles easily fall off from the coating layer. Examples of the particles contained in the easy adhesion layer include: inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer-based particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added alone to the easy-adhesion layer or in combination of 2 or more.

As a method for applying the coating liquid, a known method can be used. Examples thereof include: a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brush method, a spray coating method, an air knife coating method, a wire bar coating method, a tube blade method, and the like, which may be carried out alone or in combination.

The average particle size of the particles was measured by the following method. The particles were photographed by a Scanning Electron Microscope (SEM), and the maximum diameter (distance between 2 points at the farthest) of 300 to 500 particles was measured at a magnification of 2 to 5mm for the size of 1 smallest particle, and the average value was defined as the average particle diameter.

The polyester film used as the polarizer protective film can be produced by a usual method for producing a polyester film. For example, the following methods may be mentioned: a non-oriented polyester, which is obtained by melting a polyester resin and extrusion-molding the same into a sheet, is stretched in the longitudinal direction at a temperature not lower than the glass transition temperature by the speed difference of rolls, then stretched in the transverse direction by a tenter, and subjected to a heat treatment.

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

Specifically, the film forming conditions of the polyester film are preferably 80 to 135 ℃, more preferably 80 to 130 ℃, and particularly preferably 90 to 120 ℃. When the film is oriented so that the slow axis is in the TD direction, the longitudinal stretching magnification is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times. The transverse stretching magnification is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. When the film is oriented so that the slow axis is in the MD direction, the longitudinal stretching magnification is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. The stretching magnification in the transverse direction is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times.

In order to control the refractive index or retardation in the fast axis direction of the polyester film to the above range, it is preferable to control the ratio of the longitudinal stretching magnification to the transverse stretching magnification. If the difference in longitudinal and lateral draw ratios is too small, the refractive index of the polyester film in the fast axis direction tends to exceed 1.62, and the retardation tends to be difficult to increase, which is not preferable. When the stretching temperature is set to be low, it is preferable to increase the retardation. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250 ℃, particularly preferably 180 to 245 ℃.

In order to suppress the variation in retardation, it is preferable that the thickness variation of the thin film is small. Since the stretching temperature and the stretching ratio greatly affect the thickness unevenness of the film, it is preferable to optimize the film forming conditions from the viewpoint of reducing the thickness unevenness. In particular, in order to increase the retardation and decrease the longitudinal stretching magnification, the longitudinal thickness unevenness may be increased. Since the thickness variation in the machine direction has a region in which the thickness variation becomes very poor in a certain specific range of the stretch ratio, it is preferable to set film forming conditions after departing from this range.

The thickness variation of the polyester film is preferably 5.0% or less, more preferably 4.5% or less, still more preferably 4.0% or less, and particularly preferably 3.0% or less. The thickness unevenness of the film can be measured as follows. A strip-like film sample (3m) was collected, and the thickness of 100 points was measured at 1cm intervals using an electronic micrometer manufactured by SEIKO EM, MILLITRON 1240. The maximum value (dmax), the minimum value (dmin), and the average value (d) of the thickness were obtained from the measured values, and the thickness unevenness (%) was calculated by the following equation. The measurement is preferably performed 3 times, and the average value is obtained.

Thickness unevenness (%) ((dmax-dmin)/d) × 100

As described above, the retardation of the polyester film can be controlled to a specific range by appropriately setting the stretching ratio, the stretching temperature, and the film thickness. For example, a higher stretching ratio, a lower stretching temperature, and a thicker film thickness make it easier to obtain a higher retardation. Conversely, the lower the stretch ratio, the higher the stretching temperature, and the thinner the film thickness, the more easily a low retardation can be obtained. However, when the thickness of the film is increased, the retardation in the thickness direction tends to be increased. Therefore, it is desirable that the film thickness is appropriately set in the range described later. Further, it is preferable to set the final film forming conditions by examining physical properties and the like necessary for processing while controlling the retardation amount.

The thickness of the polyester film is arbitrary, and is preferably in the range of 15 to 300. mu.m, and more preferably in the range of 15 to 200. mu.m. Even a thin film having a thickness of less than 15 μm can in principle obtain a retardation of 1500nm or more. However, in this case, anisotropy of mechanical properties of the film becomes remarkable, and cracks, breakage, and the like are likely to occur, and the practicability as an industrial material is remarkably lowered. The lower limit of the thickness is particularly preferably 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 polarizer becomes too thick, which is not preferable. From the viewpoint of practical use as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. The upper limit of the thickness is particularly preferably 100 μm which is equivalent to that of a typical TAC film. In order to control the retardation within the above thickness range, the polyester used as the film base material is preferably polyethylene terephthalate.

The method of blending the ultraviolet absorber into the polyester film may be combined with a known method, and may be, for example, blended by the following method: the dried ultraviolet absorber and the polymer material are mixed in advance using a kneading extruder to prepare a master batch, and the master batch and the polymer material are mixed in a predetermined amount at the time of film formation.

In this case, the concentration of the ultraviolet absorber in the masterbatch is preferably 5 to 30 mass% in order to uniformly disperse the ultraviolet absorber and to economically blend the ultraviolet absorber. The master batch is preferably prepared by extrusion using a kneading extruder at an extrusion temperature of not less than the melting point of the polyester raw material and not more than 290 ℃ for 1to 15 minutes. When the temperature is 290 ℃ or higher, the decrease of the ultraviolet absorber increases, and the viscosity of the master batch decreases greatly. At the extrusion temperature, 1 minute or less, it becomes difficult to uniformly mix the ultraviolet absorber. In this case, a stabilizer, a color tone adjuster, and an antistatic agent may be added as needed.

Further, it is preferable that the polyester film is formed into a multilayer structure having at least 3 layers and an ultraviolet absorber is added to the intermediate layer of the film. Specifically, a 3-layer film having an ultraviolet absorber in the intermediate layer can be produced as follows. The pellets of the polyester for the outer layer were individually mixed with pellets of the polyester and a master batch containing an ultraviolet absorber for the intermediate layer at a predetermined ratio, dried, supplied to a known melt lamination extruder, extruded into a sheet form through a slit-shaped die, and cooled and solidified on a casting roll to produce an unstretched film. That is, using 2 or more extruders and 3-layer manifolds or confluence blocks (for example, confluence blocks having a square confluence part), film layers constituting both outer layers and film layers constituting an intermediate layer were laminated, 3-layer sheets were extruded from pipe headers, and cooled on casting rolls to produce unstretched films. In the present invention, it is preferable to perform high-precision filtration at the time of melt extrusion in order to remove foreign matters contained in the raw material polyester, which cause optical defects. The filter medium used for high-precision filtration of the molten resin preferably has a filter particle size (initial filtration efficiency 95%) of 15 μm or less. If the filter medium has a filter particle size of more than 15 μm, removal of foreign matter of 20 μm or more tends to be insufficient.

Examples

The present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples described below, and can be carried out by appropriately changing the examples within a range that can be adapted to the gist of the present invention, and these examples are included in the scope of protection of the present invention. The physical properties in the following examples were evaluated as follows.

(1) Refractive index of polyester film

The slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments co., ltd.) and a rectangle of 4cm × 2cm was cut out so that the slow axis direction was parallel to the long side to obtain a sample for measurement. For this sample, the refractive index (refractive index in the slow axis direction: Ny, refractive index in the fast axis direction (refractive index in the direction orthogonal to the slow axis direction: Nx) and refractive index in the thickness direction (Nz) of the orthogonal biaxial axes were obtained by using an Abbe refractometer (manufactured by ATAGO CO., LTD, NAR-4T, measurement wavelength 589 nm).

(2) Retardation (Re)

The retardation is a parameter defined by the product (Δ Nxy × d) of the refractive index anisotropy (Δ Nxy ═ Nx-Ny |) of the orthogonal biaxial refractive indices on the film and the film thickness d (nm), and is a standard indicating optical isotropy and anisotropy. The biaxial refractive index anisotropy (Δ Nxy) is obtained by the method (1) above. The absolute value (| Nx-Ny |) of the biaxial refractive index difference is calculated as the anisotropy of refractive index ([ delta ] Nxy). The thickness D (nm) of the film was measured by an electrometer (Fine Liu off Corp., Miritoron 1245D), and the unit was converted to nm. The retardation (Re) is determined from the product (Δ Nxy × d) of the anisotropy of the refractive index (Δ Nxy) and the thickness d (nm) of the thin film.

(3) Retardation in thickness direction (Rth)

The retardation in the thickness direction is a parameter representing an average of 2 birefringence values Δ Nxz (═ Nx-Nz |) and Δ Nyz (═ Ny-Nz |) obtained by multiplying the respective retardation values by the film thickness d when viewed from a cross section in the film thickness direction. Nx, Ny, Nz and the film thickness d (nm) were obtained by the same method as the measurement of the retardation amount, and the average value of (Δ Nxz × d) and (Δ Nyz × d) was calculated to obtain the retardation amount in the thickness direction (Rth).

(4) Measurement of emission spectrum of backlight light source

The liquid crystal display device used in each example was BRAVIA KDL-40W920A (a liquid crystal display device having a backlight source (edge system) including a light source emitting excitation light and quantum dots) manufactured by SONY corporation). The emission spectrum of the backlight light source of the liquid crystal display device was measured by using a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics K.K., and as a result, emission spectra having peaks were observed at around 450nm, 528nm, and 630nm, and the half-value width of each peak was 17nm to 34 nm. The exposure time during the spectrometry was set to 20 msec.

(5) Iridescent speckle Observation

The liquid crystal display devices obtained in the respective examples were visually observed in a dark place from the front and in the oblique direction, and the presence or absence of occurrence of rainbow unevenness was determined as follows. Here, the tilt direction is a range of 30 degrees to 60 degrees from the normal direction of the screen of the liquid crystal display device.

O: no iridescent plaques were observed

And (delta): slight iridescent spotting was observed

X: iridescent plaques were observed

X: obvious rainbow spots were observed

(6) Refractive index of polarizing plate

The refractive index of the polarizing plate in the direction of the transmission axis was measured by an Abbe refractometer (ATAGO CO., LTD, manufactured by NAR-4T SOLID, measurement wavelength 589 nm).

Production example 1 polyester A

The esterification reaction tank was heated, and when the temperature reached 200 ℃, 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 as a catalyst, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine were added while stirring. Subsequently, the esterification reaction was carried out under a pressure and temperature rise condition, and after the pressure esterification reaction was carried out under a gage pressure of 0.34MPa at 240 ℃, the esterification reaction tank was returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. Further, the temperature was raised to 260 ℃ over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, the resulting mixture was dispersed by a high-pressure disperser, and after 15 minutes, the esterification reaction product was transferred to a polycondensation reaction tank and subjected to polycondensation reaction at 280 ℃ under reduced pressure.

After the completion of the polycondensation reaction, the reaction mixture was filtered through a NASLON filter having a 95% cutoff diameter of 5 μm, extruded from a nozzle into a strand form, cooled and solidified with cooling water having been subjected to a filtration treatment (pore diameter: 1 μm or less), and cut into pellets. The resulting polyethylene terephthalate resin (A) had an intrinsic viscosity of 0.62dl/g and was substantially free of inactive particles and internally precipitated particles. (hereinafter abbreviated as PET (A))

Production example 2 polyester B

10 parts by mass of a dried ultraviolet absorber (2, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazin-4-one) and 90 parts by mass of a pellet-free PET (A) (intrinsic viscosity: 0.62dl/g) were mixed together, 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 preparation of coating liquid for adhesive Property modification

The ester exchange reaction and the polycondensation reaction were carried out by a conventional method to prepare a water-dispersible sulfonic acid-containing metal salt-based copolyester resin having a composition of a dicarboxylic acid component (with respect to the whole dicarboxylic acid component) 46 mol% of terephthalic acid, 46 mol% of isophthalic acid, and 8 mol% of sodium 5-sulfoisophthalate, and a diol component (with respect to the whole diol component) 50 mol% of ethylene glycol, and 50 mol% of neopentyl glycol. Subsequently, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butylcellosolve, and 0.06 part by mass of a nonionic surfactant were mixed, and then heated and stirred to 77 ℃. Further, after 3 parts by mass of aggregate silica particles (SILYSIA 310, manufactured by FUJI SILYSIA CHEMICAL ltd.) were dispersed in 50 parts by mass of water, 0.54 part by mass of an aqueous dispersion of SILYSIA 310 was added to 99.46 parts by mass of the water-dispersible copolyester resin solution, and 20 parts by mass of water was added thereto with stirring to obtain an adhesion-modifying coating solution.

(polarizing plate)

A rolled polyvinyl alcohol film having a thickness of 80 μm and continuously dyed in an aqueous iodine solution was stretched 5 times in the transport direction, and dried to obtain a long polarizing plate. The refractive index of the polarizing plate in the transmission axis direction was 1.51.

(polarizer protective film 1)

After 90 parts by mass of pellet-free PET (A) resin pellets and 10 parts by mass of UV absorber-containing PET (B) resin pellets as raw materials for the intermediate layer of the base film were dried under reduced pressure (1Torr) at 135 ℃ for 6 hours, the resultant was fed to the extruder 2 (for the intermediate layer II), and PET (A) was dried by a conventional method and fed to the extruder 1 (for the outer layer I and the outer layer III), respectively, and dissolved at 285 ℃. The 2 polymers were each filtered with a filter medium of a stainless steel sintered body (nominal filtration accuracy 10 μm particle 95% cutoff), laminated with 2 kinds of 3-layer flow blocks, extruded from a pipe head into a sheet shape, wound around a casting cylinder having a surface temperature of 30 ℃ by an electrostatic application casting method, cooled and solidified, and an unstretched film was produced. In this case, the ratio of the thicknesses of the layers I, II, and III is 10: 80: the discharge amount of each extruder was adjusted in the manner of 10.

Then, the coating weight after drying was set to 0.08g/m by the reverse roll method²The coating liquid for modifying adhesiveness was applied to both surfaces of the non-stretched PET film, and then dried at 80 ℃ for 20 seconds.

The unstretched film on which the coating layer was formed was introduced into a tenter stretcher, while holding the end of the film with clips, the film was introduced into a hot air zone at 125 ℃ and stretched 4.0 times in the width direction. Subsequently, the film was treated at 225 ℃ for 10 seconds while maintaining the stretching width in the width direction, and further subjected to a relaxation treatment of 3.0% in the width direction to obtain a uniaxially stretched PET film having a film thickness of about 100. mu.m. The Re of the resulting film was 10300nm, Rth was 12350nm, Re/Rth was 0.83, Nx was 1.588, and Ny was 1.691.

(polarizer protective film 2)

A uniaxially stretched PET film having a film thickness of about 80 μm was obtained by film formation in the same manner as in the polarizing plate protective film 1, except that the linear speed was changed and the thickness of the unstretched film was changed. The Re of the resulting film was 8080nm, Rth was 9960nm, Re/Rth was 0.81, Nx ═ 1.589, and Ny ═ 1.690.

(polarizer protective film 3)

A uniaxially stretched PET film having a film thickness of about 60 μm was obtained by film formation in the same manner as in the polarizing plate protective film 1, except that the linear speed was changed and the thickness of the unstretched film was changed. The Re of the resulting film was 6060nm, Rth 7470nm, Re/Rth 0.81, Nx ═ 1.589, Ny ═ 1.690.

(polarizer protective film 4)

A uniaxially stretched PET film having a film thickness of about 40 μm was obtained by film formation in the same manner as in the polarizing plate protective film 1, except that the linear speed was changed and the thickness of the unstretched film was changed. The Re of the obtained film was 4160nm, Rth was 4920nm, Re/Rth was 0.85, Nx was 1.587, and Ny was 1.691.

(polarizing plate protective film 5)

An unstretched film produced in the same manner as the polarizer protective film 1 was heated to 105 ℃ using a heated roll set and an infrared heater, stretched 1.5 times in the running direction using a roll set having a peripheral speed difference, introduced into a hot air zone having a temperature of 130 ℃ and stretched 4.0 times in the width direction, and a biaxially stretched PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 1. The Re of the obtained film was 7820nm, Rth was 13890nm, Re/Rth was 0.56, Nx was 1.608, and Ny was 1.686.

(polarizing plate protective film 6)

An unstretched film produced in the same manner as the polarizer protective film 1 was heated to 105 ℃ using a heated roll set and an infrared heater, stretched 2.0 times in the advancing direction using a roll set having a peripheral speed difference, introduced into a hot air zone having a temperature of 135 ℃ and stretched 4.0 times in the width direction, and a biaxially stretched PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 1. The film obtained had a Re of 6400nm, a Rth of 14600nm, a Re/Rth of 0.44, a Nx of 1.617 and a Ny of 1.681.

(polarizing plate protective film 7)

An unstretched film produced in the same manner as the polarizer protective film 1 was heated to 105 ℃ using a heated roll set and an infrared heater, stretched 2.8 times in the advancing direction using a roll set having a peripheral speed difference, introduced into a hot air zone having a temperature of 140 ℃ and stretched 4.0 times in the width direction, and a biaxially stretched PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 1. The Re of the resulting film was 5400nm, Rth was 15900nm, Re/Rth was 0.34, Nx ═ 1.631, and Ny ═ 1.685.

(polarizing plate protective film 8)

An unstretched film produced in the same manner as the polarizer protective film 1 was heated to 105 ℃ using a heated roll set and an infrared heater, stretched 3.3 times in the advancing direction using a roll set having a peripheral speed difference, introduced into a hot air zone having a temperature of 140 ℃ and stretched 4.0 times in the width direction, and a biaxially stretched PET film having a film thickness of about 100 μm was obtained in the same manner as the polarizer protective film 1. The Re of the resulting film was 4800nm, Rth 16700nm, Re/Rth 0.29, Nx ═ 1.640, Ny ═ 1.688.

Liquid crystal display devices were produced as described below using the polarizer protective films 1to 8.

(example 1)

A polarizer protective film 1 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to prepare a polarizing plate 1.

A liquid crystal display device was produced by replacing the polarizing plate on the visible side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation with the above-mentioned polarizing plate 1 so that the polyester film was on the opposite side (distal end) to the liquid crystal. The polarizing plate 1 was replaced so that the direction of the transmission axis was the same as the direction of the transmission axis of the polarizing plate before replacement.

(example 2)

A polarizer protective film 2 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to prepare a polarizing plate 2.

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate 1 was changed to the polarizing plate 2.

(example 3)

A polarizer protective film 3 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 3.

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate 1 was changed to the polarizing plate 3.

(example 4)

A liquid crystal display device was produced by replacing the polarizing plate on the light source side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation with the above-mentioned polarizing plate 3 so that the polyester film was on the side opposite to the liquid crystal (distal end). The direction of the light transmission axis of the polarizing plate 3 is replaced so as to be the same as the direction of the light transmission axis of the polarizing plate before replacement.

(example 5)

The polarizing plates on the visible side and the light source side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation were replaced with the above-mentioned polarizing plate 3 so that the polyester film was on the opposite side (distal end) to the liquid crystal, to manufacture a liquid crystal display device. The direction of the light transmission axis of the polarizing plate 3 is replaced so as to be the same as the direction of the light transmission axis of the polarizing plate before replacement.

(example 6)

A polarizer protective film 4 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 4.

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate 1 was changed to the polarizing plate 4.

(example 7)

A polarizer protective film 5 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 5.

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate 1 was changed to the polarizing plate 5.

(example 8)

A polarizer protective film 6 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 6.

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate 1 was changed to the polarizing plate 6.

Comparative example 1

A polarizer protective film 1 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was perpendicular to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 7.

A liquid crystal display device was produced by replacing the polarizing plate on the visible side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation with the above-mentioned polarizing plate 7 so that the polyester film was on the opposite side (distal end) to the liquid crystal. Note that the direction of the light transmission axis of the polarizing plate 7 is replaced so as to be the same as the direction of the light transmission axis of the polarizing plate before replacement.

Comparative example 2

A polarizer protective film 2 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was perpendicular to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 8.

A liquid crystal display device was produced in the same manner as in comparative example 1, except that the polarizing plate 7 was changed to the polarizing plate 8.

Comparative example 3

A polarizer protective film 3 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was perpendicular to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 9.

A liquid crystal display device was produced in the same manner as in comparative example 1, except that the polarizing plate 7 was changed to the polarizing plate 9.

Comparative example 4

A liquid crystal display device was produced by replacing the polarizing plate on the light source side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation with the above-mentioned polarizing plate 9 so that the polyester film was on the side opposite to the liquid crystal (distal end). Note that the direction of the light transmission axis of the polarizing plate 9 is replaced so as to be the same as the direction of the light transmission axis of the polarizing plate before replacement.

Comparative example 5

The polarizing plates on the visible side and the light source side of BRAVIA KDL-40W920A (liquid crystal display device having a backlight source including a light source emitting excitation light and quantum dots) manufactured by SONY corporation were replaced with the above-mentioned polarizing plate 9 so that the polyester film was on the opposite side (distal end) to the liquid crystal, to manufacture a liquid crystal display device. Note that the direction of the light transmission axis of the polarizing plate 9 is replaced so as to be the same as the direction of the light transmission axis of the polarizing plate before replacement.

Comparative example 6

A polarizer protective film 4 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was perpendicular to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 10.

A liquid crystal display device was produced in the same manner as in comparative example 1, except that the polarizing plate 7 was changed to the polarizing plate 10.

Comparative example 7

A polarizer protective film 7 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 11.

A liquid crystal display device was produced in the same manner as in comparative example 1, except that the polarizing plate 7 was changed to the polarizing plate 11.

Comparative example 8

A polarizer protective film 8 was attached to one side of a polarizer containing PVA and iodine so that the transmission axis of the polarizer was parallel to the fast axis of the film, and a TAC film (manufactured by Fujifilm Corporation, thickness 80 μm) was attached to the opposite side to obtain a polarizing plate 12.

A liquid crystal display device was produced in the same manner as in comparative example 1, except that the polarizing plate 7 was changed to the polarizing plate 12.

The results of observing the liquid crystal display devices obtained in the respective examples by measuring the rainbow unevenness are shown in table 1 below.

[ Table 1]

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 observation angle, and have extremely high industrial applicability.

Claims

1. A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and a half-value width of each peak is 5nm or more and 100nm or less,

at least one of the polarizing plates is obtained by laminating a polyester film on at least one surface of a polarizer, the polyester film has a refractive index of 1.53 to 1.62 in a direction parallel to a transmission axis of the polarizer,

the retardation of the polyester film is 1500nm or more and less than 8000 nm.

2. A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and less than 750nm, and a half-value width of each peak is 5nm or more and 120nm or less,

the retardation of the polyester film is 1500nm or more and less than 8000 nm.

3. A liquid crystal display device has: a backlight source, 2 polarizing plates, and a liquid crystal cell disposed between the 2 polarizing plates,

the backlight light source includes a light source emitting excitation light and quantum dots,

the retardation of the polyester film is 3000nm or more and less than 8000 nm.

4. The liquid crystal display device according to any one of claims 1to 3, wherein the polyester film has an easy-adhesion layer on at least one surface thereof.

5. The liquid crystal display device according to any one of claims 1to 3, wherein the polyester film is laminated on the polarizing plate via an adhesive.

6. A polarizing plate for a liquid crystal display device having a backlight source, which is obtained by laminating a polyester film on at least one surface of a polarizing plate,

the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is 1.53 to 1.62,

the retardation of the polyester film is 1500nm or more and less than 8000nm,

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 780nm or less, and a half-value width of each peak is 5nm or more and 100nm or less.

7. A polarizing plate for a liquid crystal display device having a backlight source, which is obtained by laminating a polyester film on at least one surface of a polarizing plate,

the retardation of the polyester film is 1500nm or more and less than 8000nm,

the backlight light source has a peak top of an emission spectrum in each wavelength region of 400nm or more and less than 495nm, 495nm or more and less than 600nm, and 600nm or more and 750nm, and a half-value width of each peak is 5nm or more and 120nm or less.

8. A polarizing plate for a liquid crystal display device having a backlight source, which is obtained by laminating a polyester film on at least one surface of a polarizing plate,

the retardation of the polyester film is 3000nm or more and less than 8000 nm.