CN113608384A

CN113608384A - Liquid crystal display device having a plurality of pixel electrodes

Info

Publication number: CN113608384A
Application number: CN202110787266.5A
Authority: CN
Inventors: 村田浩一; 佐佐木靖; 向山幸伸
Original assignee: Toyobo Co Ltd
Current assignee: Toyobo Co Ltd
Priority date: 2014-11-25
Filing date: 2015-11-20
Publication date: 2021-11-05
Also published as: JP2023059869A; KR102690508B1; TW201621422A; TW202229997A; TWI777916B; CN107003562B; JPWO2016084729A1; JP7323564B2; CN107003562A; WO2016084729A1; KR20240118192A; JP2021099521A; KR20170086477A

Abstract

Provided is a liquid crystal display device which has a backlight source including a light source emitting excitation light and quantum dots, and which can suppress rainbow unevenness 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, 2 polarizing plates, at least one of which has a polyester film having a retardation of 6000nm or more and 30000nm or less laminated on at least one surface of a polarizing plate so that a transmission axis of the polarizing plate is perpendicular to a fast axis of the polyester film, and a liquid crystal cell disposed between the 2 polarizing plates, wherein an antireflection layer and/or a low reflection layer are laminated on at least one surface of the polyester film.

Description

Liquid crystal display device having a plurality of pixel electrodes

This application is a divisional application filed on 2015, 11/20, with application number 2015800642294, entitled "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 the shape of the envelope of the interference color spectrum of transmitted light transmitted through a birefringent body is focused, 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 substantially perpendicularly intersects with the longitudinal direction of the film. These films are generally bonded so that their longitudinal directions 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 and wide 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. For example, liquid crystal display devices have been developed which are adapted to a wider color gamut by 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 phosphor type blue LED, 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, one of the problems 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 polarizing plate,

the polyester film has a retardation of 1500 to 30000nm,

an antireflection layer and/or a low reflection layer is laminated on at least one surface of the polyester film.

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,

the polyester film has a retardation of 1500 to 30000nm,

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 surface reflectance of the anti-reflection layer surface at a wavelength of 550nm is 2.0% 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 polyester film has a retardation of 1500 to 30000nm inclusive, and an antireflection layer and/or a low reflection layer is laminated on at least one surface of the polyester film,

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

Item 6.

the backlight light source has the following light 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.

Item 7.

The polarizing plate according to item 5 or 6, wherein the surface reflectance of the antireflection layer surface at a wavelength of 550nm is 2.0% or less.

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 above emission spectrum include: a backlight light source including at least a light source emitting excitation light and quantum dots. Further, there may be mentioned: a 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, a white LED light source of a 3-wavelength system, a white LED light source combined with a red laser beam, 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 preferably a polarizing plate obtained by laminating a polyester film on at least one surface of a polarizing plate dyed with iodine such as polyvinyl alcohol (PVA). From the viewpoint of suppressing the iridescent unevenness, it is preferable that the polyester film has a specific retardation amount 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 of the laminated polarizing plate, may be provided on the surface of the polyester film of the laminated polarizing plate, or may be both of them. 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 polarizing plate is laminated. When an antireflection layer and/or a low reflection layer is provided on the surface of the polyester film on which the polarizing plate is laminated, the layer is preferably provided between the polyester film and the polarizing plate. Further, other layers (for example, an easy adhesion layer, a hard coat layer, an antiglare layer, an antistatic layer, an antifouling layer, and the like) may be present between the antireflection layer and/or the low reflection layer and the polyester film. From the viewpoint of further suppressing the rainbow-like color spots, the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizing plate is preferably 1.53 or more and 1.62 or less. 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 and/or an epoxy compound 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 a side-light type in which a light guide plate, a reflection plate, or the like is used as a constituent member, or of a direct-type. 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 formed by including quantum dots in a resin material such as polystyrene, for example, 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 passed through the light-emitting layer, thereby generating 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. 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 quantum dots is not limited to the following, and there are roughly 2 types of 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 advantages, and since light of one blue LED is irradiated to the quantum dots 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 by using, for example, a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics k.k. or the like, to measure the emission spectrum of the backlight source.

When a plurality of peaks exist 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, it is more preferable that the half width is in the above range similarly for other peaks having an intensity of 70% or more of the maximum peak intensity. 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 of 1/2 intensity reaching 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 1/2 intensity that reaches the peak intensity, the plurality of peaks as a whole are regarded as one peak. For such a peak having a shape in which a plurality of peaks overlap, the width (nm) of the peak of 1/2 intensity, which is the highest peak intensity among the peaks, is defined as the half-value width. The point of the plurality of peaks at which the peak intensity is highest is taken as the peak top. 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.

Among the plurality of peaks, the peak having the highest peak intensity is set as the peak top.

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

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 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, when a polyester film having an antireflection layer and/or a low reflection layer and having a specific retardation is used as a polarizer protective film, a liquid crystal display device with suppressed rainbow unevenness and a polarizing plate useful for providing the liquid crystal display device can be provided. 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 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 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 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 between the interfaces. 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 by applying an antireflection layer and/or a low reflection layer to 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 can be suppressed, and the rainbow-like color unevenness can be suppressed.

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 a polyester film as a polarizer protective film, it is possible to suppress iridescent unevenness and have good visibility.

In the polarizing plate, a polarizer protective film made of a polyester film is preferably laminated on at least one surface of the polarizer. The polyester film used for the polarizer protective film preferably has a retardation of 1500 to 30000nm inclusive. 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, 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 (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 completely uniaxial (uniaxially 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.

From the viewpoint of further suppressing the rainbow-like color spots, the NZ coefficient of the polyester film is preferably 2.5 or less, more preferably 2.0 or less, further preferably 1.8 or less, and further preferably 1.6 or less. Further, in a completely uniaxial (uniaxially symmetric) film, the NZ coefficient is 1.0, and therefore the lower limit of the NZ coefficient is 1.0. However, as the film approaches perfect uniaxiality (uniaxial symmetry), the mechanical strength in the direction perpendicular to the orientation direction tends to be significantly reduced, and attention is required.

The NZ coefficient is represented by | Ny-NZ |/| Ny-Nx |, where Ny represents the refractive index in the slow axis direction, Nx represents the refractive index in the direction orthogonal to the slow axis (the refractive index in the fast axis direction), and NZ represents the refractive index in the thickness direction. The orientation axis of the film was determined using a molecular orientation meter (MOA-6004 type molecular orientation meter, manufactured by Oji Scientific Instruments co., ltd., measured at a wavelength of 589nm) and the biaxial refractive indices (Ny, Nx, where Ny > Nx) in the orientation axis direction and the direction orthogonal thereto and the refractive index (Nz) in the thickness direction were determined using an abbe refractometer (ATAGO co., ltd., manufactured by NAR-4T, measured at a wavelength of 589 nm). The value thus obtained may be substituted into | Ny-Nz |/| Ny-Nx | to obtain the Nz coefficient.

From the viewpoint of further suppressing the rainbow-like color spots, the value Ny-Nx of the polyester film is preferably 0.05 or more, more preferably 0.07 or more, still more preferably 0.08 or more, still more preferably 0.09 or more, and most preferably 0.1 or more. The upper limit is not particularly limited, but in the case of a polyethylene terephthalate film, the upper limit is preferably about 1.5.

In a more preferred embodiment of the present invention, the refractive index of the polyester film in a direction parallel to the transmission axis direction of the polarizer constituting the polarizing plate is preferably in a range of 1.53 to 1.62. This can suppress reflection at the interface between the polarizing plate and the polyester film, thereby suppressing rainbow unevenness. 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 1.56 or more, more 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 transmission axis of the polarizer is preferably parallel to the fast axis (direction perpendicular to the slow axis) of the polyester film. The polyester film can be adjusted to have a low refractive index in the fast axis direction, which is a direction perpendicular to the slow axis, of about 1.53 to 1.62 by stretching in a film forming step to be described later. The refractive index of the polyester film in the direction parallel to the transmission axis direction of the polarizing plate can be set to 1.53 to 1.62 by making the fast axis direction of the polyester film parallel to the transmission axis direction of the polarizing plate. 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-15 ° to 15 °, preferably-10 ° to 10 °, more preferably-5 ° to 5 °, still more preferably-3 ° to 3 °, still more preferably-2 ° to 2 °, and still more preferably-1 ° to 1 °. In a preferred 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 deviation inevitably occurs when the polarizing plate and the protective film are bonded. 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 in the fast axis direction is preferably 1.53 or more and 1.62 or less, and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizing plate can be 1.53 or more and 1.62 or less by laminating the transmission axis of the polarizing plate and the fast axis of the polyester film so as to be substantially parallel to each other.

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 absorbance defined in the present invention 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.

Preferably, an antireflection layer and/or a low reflection layer is provided on at least one surface of the polyester film as the polarizer protective film. The surface reflectance of the antireflection layer is preferably 2.0% or less. When the content exceeds 2.0%, iridescent stains are easily observed. 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. The lower limit of the surface reflectance of the antireflection layer is not particularly limited, and is, for example, 0.01%. The reflectance can be measured by any method, and for example, the reflectance of light at a wavelength of 550nm can be measured from the surface on the side of the anti-reflection layer using a spectrophotometer (UV-3150, manufactured by Shimadzu corporation).

The antireflection layer may be a single layer or a plurality of layers, and in the case of a single layer, the antireflection effect can be obtained if the low refractive index layer formed of a material having a lower refractive index than the polyester film is formed so that the thickness thereof is 1/4 wavelengths or an odd multiple thereof, which is the wavelength of light. In the case where the antireflection layer is a multilayer, an antireflection effect can be obtained if the low refractive index layer and the high refractive index layer are alternately laminated in 2 or more layers and the thickness of each layer is appropriately controlled. Further, if necessary, a hard coat layer may be laminated between the antireflection layers, and an antifouling layer may be formed on the hard coat layer.

Examples of the antireflection layer include those using a moth-eye structure. The moth-eye structure is an uneven structure having a pitch smaller than a wavelength formed on a surface thereof, and is capable of changing a rapid and discontinuous refractive index change at a boundary with air into a continuous and gradual refractive index change. Therefore, by forming the moth-eye structure on the surface, light reflection on the surface of the film is reduced. The formation of the antireflection layer using the moth-eye structure can be performed, for example, with reference to japanese patent application laid-open No. 2001-517319.

Examples of the method for forming the antireflection layer include: a dry coating method of forming an antireflection layer on the surface of a base material (polyester film) by vapor deposition or sputtering; a wet coating method of applying a coating liquid for antireflection on a surface of a base material and drying the coating liquid to form an antireflection layer; or a combination of both of them. The composition of the antireflection layer and the method for forming the antireflection layer are not particularly limited as long as the above characteristics are satisfied.

The low reflection layer may be formed using a known material. For example, by the following method: a method of laminating at least 1 or more thin films of a metal or an oxide by an evaporation method or a sputtering method; a method of coating one or more layers of organic thin films, and the like. As the low reflection layer, a polyester film or an organic film coated with a layer having a lower refractive index than that of the hard coat layer to be laminated is preferably used. The surface reflectance of the low reflection layer is preferably less than 5%, more preferably 4% or less, and still more preferably 3% or less. The lower limit is preferably about 0.8% to 1.0%.

For the antireflection layer and/or the low reflection layer, it may also be preferable to impart an antiglare function. This can further suppress the rainbow unevenness. That is, a combination of an antireflection layer and an antiglare layer, a combination of a low-reflection layer and an antiglare layer, and a combination of an antireflection layer and a low-reflection layer and an antiglare layer may be used. Particularly preferred is a combination of a low reflection layer and an antiglare layer. As the antiglare layer, a known antiglare layer can be used. For example, from the viewpoint of suppressing the surface reflection of the film, a mode is preferred in which an antiglare layer is laminated on a polyester film, and then an antireflection layer or a low reflection layer is laminated on the antiglare layer.

When the antireflection layer and/or the low reflection layer is 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 anti-reflection 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 easy slidability to the easy-adhesion layer, it is preferable to add particles. 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 longitudinal stretching temperature and the transverse stretching temperature are preferably 80 to 130 ℃, and more 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.

When the stretching temperature is set to be low, it is also preferable to lower the refractive index of the polyester film in the fast axis direction and 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 variation in retardation amount, it is preferable that the thickness unevenness of the 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 the film forming conditions in a case where the thickness variation deviates from the 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, uniform mixing of the ultraviolet absorber becomes difficult in 1 minute or less. At this time, a stabilizer, a color tone adjuster and/or an antistatic agent may be added as needed.

Preferably, the polyester film is made into a multilayer structure with at least 3 layers, and the ultraviolet absorbent is added in the middle 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 criterion indicating optical isotropy and anisotropy. The biaxial refractive index anisotropy (Δ Nxy) was 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 (Δ 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) was determined from the product (Δ Nxy × d) of the anisotropy of refractive index (Δ Nxy) and the thickness d (nm) of the film.

(3) Retardation in thickness direction (Rth)

The thickness-direction retardation 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) Coefficient of NZ

The value of the Nz coefficient is obtained by substituting the values of Ny, Nx, and Nz obtained in (1) above into an equation (Nz | Ny-Nz |/| Ny-Nx |).

(5) 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 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.

(6) Reflectivity of light

The 5-degree reflectance at a wavelength of 550nm was measured from the surface on the side of the anti-reflection layer (or on the side of the low-reflection layer) using a spectrophotometer (UV-3150, manufactured by Shimadzu corporation). A black marker was applied to the surface of the polyester film opposite to the side provided with the antireflection layer (or low reflection layer), and then a black vinyl tape (vinyl tape HF-737 having a width of 50mm, from KYOWA lifetime) was attached thereto for measurement.

(7) 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

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 metal sulfonate-containing 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.

Production example 4 preparation of high refractive index coating agent

In a reaction vessel, 80 parts of methyl methacrylate, 20 parts of methacrylic acid, 1 part of azoisobutyronitrile and 200 parts of isopropyl alcohol were charged and reacted at 80 ℃ for 7 hours in a nitrogen atmosphere to obtain an isopropyl alcohol solution of a polymer having a weight average molecular weight of 30000. 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.

Production example 5 preparation of Low refractive index coating agent

2,2, 2-trifluoroethyl acrylate (45 parts by mass), perfluorooctyl ethyl acrylate (45 parts by mass), acrylic acid (10 parts by mass), azoisobutyronitrile (1.5 parts by mass), and methyl ethyl ketone (200 parts by mass) were put into a reaction vessel, and reacted at 80 ℃ 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 low refractive index layer forming coating liquid.

Production example 6 preparation of anti-glare layer coating agent-1

An acrylic copolymer CYCLOMER P ACA-Z250(DAICEL CHEMICAL INDUSTRIES, ltd.) (49 parts by mass), cellulose acetate propionate CAP482-20 (number average molecular weight 75000) (Eastman Chemical Company, 3 parts by mass), an acrylic monomer AYARAD DPHA (Nippon Kayaku co., ltd.) (49 parts by mass), an acrylic-styrene copolymer (average particle diameter 4.0 μm) (Sekisui Plastics co., ltd.) (2 parts by mass), and Irgacure 184(BASF CORPORATION) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone: 1-butanol: 3:1 so that the solid content became 35% by mass, to obtain an antiglare layer-forming coating liquid.

Production example 7 production of anti-glare layer coating agent-2

An acrylic copolymer CYCLOMER P ACA-Z250(DAICEL CHEMICAL INDUSTRIES, ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.5 (number average molecular weight 25000) (Eastman Chemical Company, 3 parts by mass), an acrylic monomer AYARAD DPHA (Nippon Kayaku co., ltd.) (49 parts by mass), an acrylic-styrene copolymer (average particle size 4.0 μm) (Sekisui Plastics co., ltd.) (4 parts by mass), and Irgacure 184(BASF CORPORATION) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone: 1-butanol: 3:1 so that the solid contents became 35% by mass, to obtain an antiglare coating liquid.

Production example 8 production of anti-glare layer coating agent-3

An acrylic copolymer CYCLOMER P ACA-Z250(DAICEL CHEMICAL INDUSTRIES, ltd.) (49 parts by mass), cellulose acetate propionate CAP482-0.2 (number average molecular weight 15000) (Eastman Chemical Company, 3 parts by mass), an acrylic monomer AYARAD DPHA (Nippon Kayaku co., ltd.) (49 parts by mass), an acrylic-styrene copolymer (average particle diameter 4.0 μm) (Sekisui Plastics co., ltd.) (2 parts by mass), and Irgacure 184(BASF CORPORATION) (10 parts by mass) were added to a mixed solvent of methyl ethyl ketone: 1-butanol: 3:1 so that the solid content became 35% by mass, to obtain an antiglare layer-forming coating liquid.

(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, they were supplied to the extruder 2 (for the intermediate layer II), and further, pet (a) was dried by a conventional method and supplied to the extruder 1 (for the outer layer I and the outer layer III), respectively, and melted 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 coating liquid for forming a high refractive index layer was applied to one coated surface of the uniaxially stretched PET film, and dried at 150 ℃ for 2 minutes to form a high refractive index layer having a thickness of 0.1. mu.m. The coating liquid for forming a low refractive index layer obtained by the above method was applied on the high refractive index layer, and dried at 150 ℃ for 2 minutes to form a low refractive index layer having a film thickness of 0.1 μm, thereby obtaining a polarizer protective film 1 in which an antireflection layer was laminated.

(polarizer protective film 2)

Film formation was performed in the same manner as for the polarizing plate protective film 1 except that the linear velocity was changed and the thickness of the unstretched film was changed, to obtain a polarizing plate protective film 2 having a film thickness of about 80 μm in which an antireflection layer was laminated.

(polarizer protective film 3)

A polarizing plate protective film 3 having a film thickness of about 60 μm and an antireflection layer laminated thereon was obtained by film formation in the same manner as the polarizing plate protective film 1 except that the linear velocity was changed and the thickness of the unstretched film was changed.

(polarizer protective film 4)

A polarizing plate protective film 4 having a film thickness of about 40 μm and an antireflection layer laminated thereon was obtained by film formation in the same manner as in the polarizing plate protective film 1 except that the linear velocity was changed and the thickness of the unstretched film was changed.

(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 3.3 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 polarizer protective film 5 having an antireflection layer laminated thereon and having a film thickness of about 30 μm was obtained in the same manner as the polarizer protective film 1.

(polarizing plate protective film 6)

A polarizing plate protective film 6 having a film thickness of about 100 μm was obtained by the same method as the polarizing plate protective film 1 except that no antireflection layer was provided.

(polarizing plate protective film 7)

An anti-glare layer coating agent 1 was applied to one coated surface of a polarizer protective film produced in the same manner as the polarizer protective film 2, except that no anti-reflection layer was provided, so that the cured film thickness became 8 μm, and the coating was dried in an oven at 80 ℃ for 60 seconds. Then, an ultraviolet irradiation apparatus (Fusion UV Systems Japan Co., Ltd., light source H tube (valve)) was used to irradiate 300mJ/cm of radiation²The anti-glare layer is laminated by irradiating ultraviolet rays. Then, an antireflection layer was laminated on the antiglare layer in the same manner as in the polarizing plate protection film 1to obtain a polarizing plate protection film 7.

(polarizing plate protective film 8)

An anti-glare layer and an anti-reflection layer were laminated on one coated surface of a polarizer protective film produced in the same manner as the polarizer protective film 3 in the same manner as the polarizer protective film 7, except that no anti-reflection layer was provided, thereby obtaining a polarizer protective film 8.

(polarizer protective film 9)

An anti-glare layer coating agent 2 was applied to one coated surface of a polarizer protective film produced in the same manner as the polarizer protective film 4, except that no anti-reflection layer was provided, so that the cured film thickness became 8 μm, and the coating was dried in an oven at 80 ℃ for 60 seconds. Then, an ultraviolet irradiation apparatus (Fusion UV Systems Japan Co., Ltd., light source H tube) was used to irradiate 300mJ/cm of radiation²The anti-glare layer is laminated by irradiating ultraviolet rays. Then, an antireflection layer was laminated on the antiglare layer in the same manner as in the polarizing plate protection film 1to obtain a polarizing plate protection film 9.

(polarizer protective film 10)

An antiglare layer was laminated on one coated surface of the polarizer protective film produced by the same method as the polarizer protective film 5 in the same method as the polarizer protective film 7, to obtain a polarizer protective film 10 (no antireflection layer was laminated) except that no antireflection layer was provided.

(polarizing plate protective film 11)

An anti-glare layer coating agent 3 was applied to one coated surface of a polarizer protective film produced in the same manner as the polarizer protective film 1, except that no anti-reflection layer was provided, so that the cured film thickness became 8 μm, and the coating was dried in an oven at 80 ℃ for 60 seconds. Then, an ultraviolet irradiation apparatus (Fusion UV Systems Japan Co., Ltd., light source H tube) was used to irradiate 300mJ/cm of radiation²The polarizing plate protective film 11 on which the antiglare layer was laminated was obtained by irradiation with ultraviolet rays.

(polarizing plate protective film 12)

An anti-glare layer coating agent 1 was applied to one coated surface of a polarizer protective film produced in the same manner as the polarizer protective film 2, except that no anti-reflection layer was provided, so that the cured film thickness became 8 μm, and the coating was dried in an oven at 80 ℃ for 60 seconds. Then, an ultraviolet irradiation apparatus (Fusion UV Systems Japan Co., Ltd., light source H tube) was used to irradiate 300mJ/cm of radiation²The anti-glare layer is laminated by irradiating ultraviolet rays. Then, a low refractive index layer was laminated on the antiglare layer by the same method as the polarizer protective film 1. Thus, a polarizing plate protective film 12 in which a low reflection layer was laminated on the antiglare layer was obtained.

A liquid crystal display device was produced as described below using the polarizer protective films 1to 12.

(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 prepare a polarizing plate 1. The polarizing plate is produced by laminating a polarizing plate on the surface of the polarizer protective film on which the antireflection layer is not laminated. 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 liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 2.

(example 3)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 3 was replaced with the polarizing plate protective film 1.

(example 4)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protection film 1 was replaced with the polarizing plate protection film 4.

(example 5)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 4 was used instead of the polarizing plate protective film 1 and attached so that the fast axis thereof was parallel to the transmission axis of the polarizing plate.

(example 6)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 7.

(example 7)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 8 was replaced with the polarizing plate protective film 1.

(example 8)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 9.

(example 9)

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 12.

Comparative example 1

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 5.

Comparative example 2

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 6 was replaced with the polarizing plate protective film 1.

Comparative example 3

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizer protective film 10 was replaced with the polarizer protective film 1.

Comparative example 4

A liquid crystal display device was produced in the same manner as in example 1, except that the polarizing plate protective film 1 was replaced with the polarizing plate protective film 11.

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 generation of rainbow-like color spots is significantly suppressed at any angle, and contribute significantly to the industry.

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 has a polyester film laminated on at least one surface of a polarizer, and is laminated so that a transmission axis of the polarizer and a fast axis of the polyester film are perpendicular to each other,

the polyester film has a retardation of 6000nm to 30000nm,

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 polyester film has a retardation of 6000nm to 30000nm,

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 polyester film has a retardation of 8000nm or more and 30000nm or less,

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

the polyester film has a retardation of 6000nm to 30000nm,

the ratio Re/Rth of the retardation Re to the retardation Rth in the thickness direction of the polyester film is 0.6 to 2.0,

5. The liquid crystal display device according to any one of claims 1to 4, wherein another layer is provided between the antireflection layer and/or the low reflection layer and the polyester film.

6. The liquid crystal display device according to any one of claims 1to 4, wherein an easy adhesion layer is provided between the antireflection layer and/or the low reflection layer and the polyester film.

7. The liquid crystal display device according to any one of claims 1to 4, wherein a hard coat layer is provided between the antireflection layer and/or the low reflection layer and the polyester film.

8. The liquid crystal display device according to any one of claims 1to 4, wherein an antiglare layer is provided between the antireflection layer and/or low reflection layer and the polyester film.

9. The liquid crystal display device according to any one of claims 1to 4, wherein the polyester film is laminated on the polarizing plate via an adhesive.

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