JP7201026B2 - liquid crystal display - Google Patents

Description

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

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

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

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

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

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

Due to the increasing demand for expanding the color gamut of liquid crystal display devices in recent years, the emission spectrum peaks in each wavelength region of the blue region (400 nm or more and less than 495 nm), the green region (495 nm or more and less than 600 nm), and the red region (600 nm or more and 780 nm or less). A liquid crystal display device has been developed that uses, as a backlight source, a white light emitting diode that has an emission spectrum with a relatively narrow peak half width in the red region (600 nm or more and 780 nm or less).

When industrially producing a liquid crystal display using a polarizing plate using a polyester film as a polarizer protective film, the directions of the transmission axis of the polarizer and the fast axis of the polyester film are usually arranged so as to be perpendicular to each other. be done. This is because the polyvinyl alcohol film that is the polarizer is manufactured by longitudinal uniaxial stretching, while the polyester film that is the protective film is manufactured by longitudinally stretching and then laterally stretching. This is because the main axis direction is the horizontal direction, and when a polarizing plate is produced by laminating these elongated objects, the fast axis of the polyester film and the transmission axis of the polarizer are usually perpendicular to each other. In this case, an oriented polyester film having a specific retardation is used as the polyester film, and the backlight source is represented by, for example, a white LED composed of a light-emitting element combining a blue light-emitting diode and an yttrium-aluminum-garnet-based yellow phosphor. , By using a light source having a continuous and broad emission spectrum, the rainbow-like color spots are greatly improved, but the half width of the peak in the red region (600 nm or more and 780 nm or less) is relatively narrow (less than 5 nm). We have discovered that when using a backlight source consisting of a white light emitting diode with a spectrum, there is still a new problem of iridescence.

That is, an object of the present invention is to have an emission spectrum peak top in each wavelength region of the blue region (400 nm or more and less than 495 nm), the green region (495 nm or more and less than 600 nm), and the red region (600 nm or more and 780 nm or less). In a liquid crystal display device having a white light emitting diode having an emission spectrum with a relatively narrow (less than 5 nm) peak half width in the region (600 nm or more and 780 nm or less) as a backlight source, when a polyester film is used as a polarizer protective film Another object of the present invention is to provide a liquid crystal display device and a polarizing plate in which iridescence is suppressed.

A typical present invention is as follows.
Section 1.
A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source has a peak top of the emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and has the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less. A white light source having an emission spectrum with a peak half width of less than 5 nm,
At least one polarizing plate of the two polarizing plates has a polyester film laminated on at least one surface of a polarizer,
The polyester film has an easy-adhesion layer on at least one surface,
The difference between the refractive index of the easily adhesive layer and the refractive index of the polyester film in a direction parallel to the transmission axis of the polarizer is 0.10 or less.
Liquid crystal display.
Section 2.
The emission spectrum of the backlight light source is
The half width of the peak with the highest peak intensity in the wavelength region of 400 nm or more and less than 495 nm is 5 nm or more,
Item 2. The liquid crystal display device according to item 1, wherein the half width of the peak having the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm is 5 nm or more.
Item 3.
Item 3. The liquid crystal display device according to Item 1 or 2, wherein the polyester film has a retardation of 1500 to 30000 nm.
Section 4.
A polarizing plate in which a polyester film is laminated via an adhesive layer on at least one surface of a polarizer,
The polyester film has a retardation of 1500 to 30000 nm,
The polyester film has an easy-adhesion layer on at least one surface, and the difference between the refractive index of the easy-adhesion layer and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is 0. .10 or less,
Polarizer.
Item 5.
Item 5. The polarizing plate according to item 4, wherein the angle formed by the transmission axis of the polarizer and the fast axis of the polyester film is -15° to 15°.

INDUSTRIAL APPLICABILITY The liquid crystal display device of the present invention has a wide color gamut and can ensure good visibility in which the occurrence of rainbow-like color spots is significantly suppressed at any viewing angle.

(Liquid crystal display device)
In general, a liquid crystal display device is composed of a rear module, a liquid crystal cell, and a front module in order from the side facing the backlight source to the side where an image is displayed (viewing side). The rear module and the front module are generally composed of a transparent substrate, a transparent conductive film formed on the liquid crystal cell side surface of the substrate, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is arranged on the side facing the backlight light source in the rear module, and is arranged on the image display side (viewing side) in the front module. The configuration of the backlight may be an edge-light type in which a light guide plate, a reflector, or the like is used as constituent members, or a direct type. In addition to the backlight source, polarizing plate, and liquid crystal cell, the liquid crystal display device may appropriately have other components such as a color filter, lens film, diffusion sheet, antireflection film, and the like. A brightness enhancement film may be provided between the light source side polarizing plate and the backlight source. Examples of the brightness enhancement film include a reflective polarizing plate that transmits one linear polarized light and reflects the orthogonal linear polarized light. As the reflective polarizing plate, for example, brightness enhancement films of the DBEF (registered trademark) (Dual Brightness Enhancement Film) series manufactured by Sumitomo 3M Co., Ltd. are preferably used. Incidentally, the reflective polarizing plate is usually arranged so that the absorption axis of the reflective polarizing plate and the absorption axis of the light source side polarizing plate are parallel to each other.

(backlight light source)
The liquid crystal display device of the present invention includes at least a backlight source and a liquid crystal cell disposed between two polarizing plates as constituent members. The backlight source is a white light source having an emission spectrum having a peak top in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 750 nm or less, and a half width of each peak of 5 nm or more. preferable.

The structure of the backlight may be of an edge light system or a direct type system, in which a light guide plate, a reflector, etc. are used as constituent members. 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less have peak tops of the emission spectrum in each wavelength region, and the half width of the peak with the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less A backlight source consisting of white light emitting diodes with an emission spectrum that is less than 5 nm is preferred. The upper limit of the half width of the peak having the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less is preferably less than 5 nm, more preferably less than 4 nm, and even more preferably less than 3.5 nm. The lower limit is preferably 1 nm or more, more preferably 1.5 nm or more. A peak half width of less than 5 nm is preferable because the color gamut of the liquid crystal display device is widened. Moreover, when the half width of the peak is less than 1 nm, the luminous efficiency may deteriorate, which is not preferable. The shape of the emission spectrum is designed from the balance between the required color gamut and luminous efficiency. Here, the half-value width is the peak width (nm) at half the intensity of the peak intensity at the wavelength of the peak top.

Application of a backlight source having an emission spectrum having the above characteristics to an LCD is a technique that has been attracting attention due to the growing demand for an expanded color gamut in recent years. LEDs that use conventionally used white LEDs (for example, light-emitting elements that combine blue light-emitting diodes and yttrium-aluminum-garnet-based yellow phosphors) as backlight sources have a spectrum that can be recognized by the human eye. Only about 20% of colors can be reproduced. On the other hand, it is said that 60% or more colors can be reproduced when a backlight light source having an emission spectrum having the characteristics described above is used.

The wavelength region of 400 nm or more and less than 495 nm is more preferably 430 nm or more and 470 nm or less. The wavelength range of 495 nm or more and less than 600 nm is more preferably 510 nm or more and 560 nm or less. The wavelength region of 600 nm or more and 780 nm or less is more preferably 600 nm or more and 700 nm or less, and even more preferably 610 nm or more and 680 nm or less.

The peak half width at the peak top of each wavelength region of 400 nm or more and less than 495 nm and 495 nm or more and less than 600 nm in the emission spectrum (the half width of the peak having the highest peak intensity in each wavelength region) is not particularly limited, but is 400 nm or more and less than 495 nm. The half-value width of the peak having the highest peak intensity in the wavelength region of is preferably 5 nm or more, and the half-value width of the peak having the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm is preferably 5 nm or more. From the viewpoint of ensuring an appropriate color gamut, the upper limit of the peak half-value width at the peak top of each wavelength region of 400 nm or more and less than 495 nm and 495 nm or more and less than 600 nm (the half-value width of the peak having the highest peak intensity in each wavelength region) is It is preferably 140 nm or less, preferably 120 nm or less, preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, and even more preferably 50 nm or less.

A specific example of the white light source having the emission spectrum having the characteristics described above is a phosphor type white light emitting diode in which a blue light emitting diode and a phosphor are combined. Examples of the red phosphor among the phosphors include a fluoride phosphor (also referred to as “KSF”) having a composition formula of K ₂ SiF ₆ :Mn ⁴⁺ and others. The Mn ⁴⁺ -activated fluoride complex phosphor is a phosphor containing Mn ⁴⁺ as an activator and a fluoride complex salt of an alkali metal, an amine or an alkaline earth metal as a base crystal. Fluoride complexes forming host crystals include those with coordination centers of trivalent metals (B, Al, Ga, In, Y, Sc, lanthanide), tetravalent metals (Si, Ge, Sn, Ti, Zr, Re, Hf) and pentavalent metals (V, P, Nb, Ta), and the number of fluorine atoms coordinated therearound is 5-7.

Preferred examples of the Mn ⁴⁺ -activated fluoride complex phosphor include A ₂ [MF ₆ ]:Mn (A is one or more selected from Li, Na, K, Rb, Cs and NH ₄ ; M is Ge, Si, At least one selected from Sn, Ti, and Zr), E[MF ₆ ]: Mn (E is at least one selected from Mg, Ca, Sr, Ba, and Zn; M is selected from Ge, Si, Sn, Ti, and Zr. _Ba0.65 , _Zr0.35F2.70 :Mn _{, A3} [ _ZrF7 ]:Mn ₍ A is one or more selected from Li, Na, K, Rb, Cs, and NH4) , A ₂ [MF ₅ ]: Mn (A is at least one selected from Li, Na, K, Rb, Cs and NH ₄ ; M is at least one selected from Al, Ga and In), A ₃ [MF ₆ ] : Mn (A is at least one selected from Li, Na, K, Rb, Cs and NH4 _; M is at least one selected from Al, Ga and _In ), Zn2[ _MF7 ]:Mn (M is Al, one or more selected from Ga and _In ), A[ _In2F7 ]:Mn ₍ A is one or more selected from Li, Na, K, Rb, Cs and NH4), and the like.

One of the preferable Mn ⁴⁺ -activated fluoride complex phosphors is A ₂ MF ₆ :Mn (A is selected from Li, Na, K, Rb, Cs, NH ₄ one or more; M is one or more selected from Ge, Si, Sn, Ti and Zr). Among them, A is one or more selected from K (potassium) or Na (sodium), and M is Si (silicon) or Ti (titanium). Among them, it is particularly preferable that A is K (the ratio of K to the total amount of A is 99 mol % or more) and M is Si. The activating element is desirably 100% Mn (manganese), but Ti, Zr, Ge, Sn, Al, Ga, B, In, Cr, Al, Ga, B, In, Cr, Fe, Co, Ni, Cu, Nb, Mo, Ru, Ag, Zn, Mg, etc. may be included. When M is Si, the proportion of Mn in the sum of Si and Mn is preferably in the range of 0.5 mol % to 10 mol %. Another preferred Mn ⁴⁺ -activated fluoride complex phosphor has the chemical formula A _2+x M _y Mn _z F _n (A is Na and K; M is Si and Al; −1≦x≦1 and 0.9≦y+z≦1 .1 and 0.001≤z≤0.4 and 5≤n≤7).

The backlight source is preferably a white light emitting diode having a blue light emitting diode and at least a fluoride phosphor as a phosphor, particularly preferably a blue light emitting diode and at least a fluoride K ₂ SiF ₆ :Mn ⁴⁺ as a phosphor. A white light emitting diode having a phosphor. For example, commercially available products such as NSSW306FT, which is a white LED manufactured by Nichia Corporation, can be used.

Among the above-described phosphors, the green phosphor may be, for example, a sialon-based phosphor having a basic composition of β-SiAlON:Eu or the like, a silicate-based phosphor having a basic composition of (Ba, Sr) ₂ SiO ₄ :Eu or the like. , and others.

If there are multiple peaks in any one of the wavelength range of 400 nm or more and less than 495 nm, the wavelength range of 495 nm or more and less than 600 nm, or the wavelength range of 600 nm or more and 750 nm or less, consider the following.
When the plurality of peaks are independent peaks, the half width of the peak with the highest peak intensity is preferably within the above range. Furthermore, in a more preferred embodiment, other peaks having an intensity of 70% or more of the highest peak intensity also have half-value widths within the above range. Here, an independent peak has an intensity region of 1/2 of the peak intensity on both the short wavelength side and the long wavelength side of the peak. That is, when a plurality of peaks overlap and each peak does not have a region of intensity that is 1/2 of the peak intensity, the plurality of peaks as a whole is regarded as one peak. For one peak having such a shape in which a plurality of peaks are overlapped, the width (nm) of the peak at half the intensity of the highest peak intensity among them is defined as the half width.
A peak having the highest peak intensity among the plurality of peaks is defined as a peak top.
In addition, the peak having the highest peak intensity in the wavelength region of 400 nm or more and less than 495 nm, the wavelength region of 495 nm or more and less than 600 nm, or the wavelength region of 600 nm or more and 750 nm or less has a mutually independent relationship with the peaks of other wavelength regions. is preferred. In particular, in the wavelength region between the peak with the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm, or the peak with the highest peak intensity in the region of 600 nm or more and 750 nm or less, the intensity is 600 nm or more and 750 nm or less. From the standpoint of vividness of color, it is preferable that there is a region where the peak intensity is ⅓ of the peak intensity of the highest peak in the wavelength region.

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

(Polarizer)
Of the two polarizing plates placed in the liquid crystal display device, at least one of the polarizing plates is a polarizer in which polyvinyl alcohol (PVA) or the like is dyed with iodine, and a polyester film is laminated on at least one surface of the polarizer. is. On the other surface of the polarizer, it is preferable to laminate a non-birefringent film such as a TAC film, an acrylic film, or a norbornene film (a polarizing plate having a three-layer structure). There is no need to laminate a film on the other side (two-layer polarizer). When polyester films are used as protective films on both sides of the polarizer, the slow axes of both polyester films are preferably substantially parallel to each other.

As a result of intensive studies by the present inventors, it was found that each of the wavelength regions of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less has a peak top, and the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less. In a liquid crystal display device in which a white light emitting diode having an emission spectrum in which the half-value width of a high peak is less than 5 nm is used as a backlight source, even when a polarizing plate using a polyester film is used as a polarizer protective film, at least one side can be easily Using a polyester film having an adhesive layer, if the difference between the refractive index of the easy-adhesive layer and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is 0.10 or less, significant iridescence is produced. I have found that it can be suppressed. The mechanism by which the above-described mode suppresses the occurrence of rainbow-like color spots is thought to be as follows.

When the oriented polyester film is placed on one side of the polarizer, the polarization state of the linearly polarized light emitted from the backlight unit or the polarizer changes when passing through the polyester film. One of the factors that changes the polarization state of the linearly polarized light emitted from the backlight unit or the polarizer when it passes through the oriented polyester film is the difference in the refractive index at the interface between the easy-adhesion layer and the oriented polyester film. I found a possibility. When linearly polarized light incident from an oblique direction passes through each interface, part of the light is reflected due to the refractive index difference between the interfaces. At this time, the polarization states of both the emitted light and the reflected light are considered to change, which is considered to be one of the factors that cause the rainbow-like color spots. Therefore, by reducing the difference in refractive index between the easy-adhesion layer and the oriented polyester film in the polarization direction (transmission axis direction) of the incident linearly polarized light, reflection at each interface is suppressed, resulting in rainbow-like color spots. is thought to be suppressed.

As described above, in the present invention, each wavelength region of the blue region (400 nm or more and less than 495 nm), the green region (495 nm or more and less than 600 nm) and the red region (600 nm or more and 780 nm or less) has a peak top of the emission spectrum, Polarization using a polyester film as a polarizer protective film in a liquid crystal display device using a white light emitting diode having an emission spectrum with a relatively narrow half-value width (less than 5 nm) of a peak in the red region (600 nm or more and 780 nm or less) as a backlight source. Even if a plate is used, it is possible to have good visibility without generating rainbow-like color spots.

The difference between the refractive index of the easily adhesive layer and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is preferably 0.10 or less, preferably 0.09 or less, and preferably 0.08 or less. , preferably 0.07 or less, preferably 0.06 or less. The smaller the refractive index difference, the more preferable it is because the reflection at the interface of the polyester film can be suppressed and the iridescence can be suppressed. The lower limit is 0.

The difference between the refractive index of the easily adhesive layer layer in the direction parallel to the transmission axis of the polarizer and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is preferably 0.10 or less, and more It is preferably 0.09 or less, more preferably 0.08 or less, preferably 0.07 or less, preferably 0.06 or less. The smaller the refractive index difference, the more preferable it is because the reflection at the interface of the polyester film can be suppressed and the iridescence can be suppressed. The lower limit is 0.

The method of laminating the polyester film and the polarizer is not particularly limited. An arrangement in which the axial directions are substantially parallel is preferable. Lamination may be carried out with care so that the difference between the refractive index of the adhesive and the refractive index of the polyester film in the direction parallel to the transmission axis of the polarizer is within a preferable range.

Here, "substantially parallel" means that the angle formed by the transmission axis of the polarizer and the fast axis (or slow axis) of the polarizer protective film is preferably -15° to 15°, more preferably -10°. ~10°, more preferably -5° to 5°, even more preferably -3° to 3°, even more preferably -2° to 2°, particularly preferably -1° to 1°. In one preferred embodiment, substantially parallel is substantially parallel. Here, "substantially parallel" means that the transmission axis and the fast axis (or the slow axis) are parallel to the extent that a deviation that inevitably occurs when the polarizer and the protective film are laminated is allowed. means The direction of the slow axis can be obtained by measuring with a molecular orientation meter (for example, MOA-6004 type molecular orientation meter manufactured by Oji Instruments Co., Ltd.).

(polyester film)
The polyester film used for the polarizer protective film preferably has a retardation of 1500-30000 nm. If the retardation is within the above range, the iridescence tends to be more easily reduced, which is preferable. A preferable lower limit of retardation is 3000 nm, a second preferable lower limit is 3500 nm, a more preferable lower limit is 4000 nm, a still more preferable lower limit is 6000 nm, and an even more preferable lower limit is 8000 nm. A preferable upper limit is 30000 nm, and a polyester film having a retardation of 30000 nm or more has a considerably large thickness, and tends to deteriorate in handleability as an industrial material.

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

The ratio (Re/Rth) of the retardation (Re: in-plane retardation) to the thickness direction retardation (Rth) of the polyester film is preferably 0.2 or more, more preferably 0.5 or more, and still more preferably 0.5. 6 or more. As the ratio of the retardation to the thickness direction retardation (Re/Rth) increases, the birefringence action becomes more isotropic, and rainbow-like color spots tend to be less likely to occur depending on the viewing angle. Since the ratio of the retardation to the thickness direction retardation (Re/Rth) is 2.0 in a perfect uniaxial (uniaxially symmetric) film, the ratio of the retardation to the thickness direction retardation (Re/Rth) The upper limit is preferably 2.0. The thickness direction retardation means the average retardation obtained by multiplying the two birefringences ΔNxz and ΔNyz when the film is viewed from the thickness direction section by the film thickness d.

The refractive index in the fast axis direction of the polyester film is preferably 1.53 or more and 1.62 or less. If the refractive index is less than 1.53, the crystallization of the polyester film becomes insufficient, and properties obtained by stretching such as dimensional stability, mechanical strength and chemical resistance become insufficient, which is not preferable. The upper limit of the refractive index in the fast axis direction of the polyester film is more preferably 1.61 or less, still more preferably 1.60 or less, still more preferably 1.59 or less, and particularly preferably 1.61 or less. 58 or less. The lower limit of the refractive index in the fast axis direction of the polyester film is more preferably 1.54 or more, still more preferably 1.55 or more, even more preferably 1.56 or more, and particularly preferably 1.56 or more. 57 or more.
The refractive index in the slow axis direction of the polyester film is preferably 1.67 or more and 1.75 or less. The upper limit of the refractive index in the slow axis direction of the polyester film is more preferably 1.74 or less, still more preferably 1.73 or less, even more preferably 1.72 or less, and particularly preferably 1.74 or less. 71 or less. The lower limit of the refractive index of the slow axis of the polyester film is more preferably 1.68 or more. The adjustment of the refractive index can be easily adjusted by stretching treatment in the film-forming process, which will be described later.
The difference between the refractive index in the slow axis direction and the refractive index in the fast axis direction of the polyester film is preferably 0.05 or more, more preferably 0.07 or more, and still more preferably 0.09 or more.

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

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

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

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

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

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

On the surface of the polyester film, which is the polarizer protective film used in the present invention, various functional layers such as a hard coat layer, an antiglare layer, an antireflection layer, and the like are applied for the purpose of preventing reflection, suppressing glare, and suppressing scratches. It is also a preferred mode to provide a low-reflection layer or the like. When providing various functional layers, the polyester film preferably has an easy-adhesion layer on its surface.

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

(Easy adhesion layer)
In the present invention, it is preferable that at least one side of the film of the present invention has an easy-adhesion layer in order to improve the adhesion to the functional layer and the polarizer described above.

As the easy-adhesion layer, conventionally known easy-adhesion layers used for optical films can be used. It is not particularly limited as long as it satisfies the condition of the refractive index difference from the polyester film described above. Among others, it is preferable to have an easy-adhesion layer containing at least one of polyester resin, polyurethane resin, polyacrylic resin, and polyvinyl alcohol-based resin as a main component. Here, the "main component" refers to a component that accounts for 50% by mass or more of the solid components that constitute the easy-adhesion layer.
A conventionally known cross-linking agent can be added to these resins. The coating liquid used for forming the easy-adhesion layer of the present invention is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolyester resins, acrylic resins, polyurethane resins and polyvinyl alcohol resins. Polyester resins, polyurethane resins, acrylic resins, and polyvinyl alcohol resins may be used singly or in combination of two or more. For example, in order to improve the adhesion to the polarizer, a combination of one or more selected from the group consisting of polyester resins, polyurethane resins and acrylic resins and a polyvinyl alcohol-based resin is preferred, and polyester resins are particularly preferred. It is a combination of resin and polyvinyl alcohol resin. Examples of these coating liquids include water-soluble or water-dispersible coating liquids disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, Japanese Patent No. 3900191 and Japanese Patent No. 4150982. A polymerized polyester resin solution, an acrylic resin solution, a polyurethane resin solution and the like can be used.

Examples of polyester resins include acid components such as terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyro mellitic acid, dimer acid, 5-sodium sulfoisophthalic acid, and glycol components such as ethylene glycol, dimethylene glycol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4 -Butanediol, neopentyl glycol, xylene glycol, dimethylolpropane, and copolymers selected from poly(ethylene oxide) glycol, poly(tetramethylene oxide) glycol, and the like. When these are used as water-based resins as coating liquids, it is preferable to copolymerize a compound containing a carboxylic acid group or a sulfonic acid group in order to facilitate water solubility and improve the adhesiveness of the polyester resin. Examples of polyurethane resins include those composed of polyols, polyisocyanates, chain extenders, cross-linking agents, and the like. Examples of the above polyol include polyethers such as polyoxyethylene glycol, polyoxypropylene glycol and polyoxytetramethylene glycol, polyethylene adipate, polyethylene-butylene adipate, polycaprolactone, and the like. Examples include polyesters produced, polycarbonates having carbonate bonds, acrylic polyols, castor oil, and the like. Examples of the polyisocyanate include tolylene diisocyanate, phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate. Examples of the chain extender or crosslinker include ethylene glycol, propylene glycol, diethylene glycol, trimethylolpropane, hydrazine, ethylenediamine, diethylenetriamine, triethylenetetramine, 4,4'-diaminodiphenylmethane, 4,4'-diamino. dicyclohexylmethane, water and the like. Acrylic resins include copolymers selected from methyl methacrylate, ethyl acrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, acrylamide, n-methylolacrylamide, glycidyl methacrylate, acrylic acid, and the like. When used as a coating liquid made into a water-based resin, copolymerization with a monomer having a hydrophilic group (acrylic acid, methacrylic acid, acrylamide, vinylsulfonic acid and its salts, etc.) or emulsion polymerization using a reactive emulsifier or surfactant , suspension polymerization, or soap-free polymerization. Moreover, a cross-linking agent or the like may be contained in order to improve coatability. The cross-linking agent is not particularly limited as long as it is a compound that causes a cross-linking reaction. A coupling agent etc. can be illustrated.

In addition, high refractive index fine particles, chelate compounds, and the like can be added in order to adjust the refractive index of the easy-adhesion layer. As the high refractive index fine particles, for example, metal oxide fine particles having a refractive index of 1.60 to 2.80 can be suitably used. Specific examples of metal oxide fine particles include titanium oxide (TiO ₂ , refractive index: 2.71), zirconium oxide (ZrO ₂ , refractive index: 2.10), tin oxide (SnO ₂ , refractive index : 2.00), antimony tin oxide (ATO, refractive index: 1.75 to 1.95), cerium oxide (CeO ₂ , refractive index: 2.20), indium tin oxide (ITO, refractive index: 1 .95 to 2.00), phosphorus tin compound (PTO, refractive index: 1.75 to 1.85), antimony oxide (Sb ₂ O ₅ , refractive index: 2.04), aluminum zinc oxide (AZO, refractive index index: 1.90-2.00), niobium pentoxide (Nb ₂ O ₅ , refractive index: 2.33), gallium zinc oxide (GZO, refractive index: 1.90-2.00), tantalum oxide ( Ta ₂ O ₅ : refractive index 2.16) and zinc antimonate (ZnSb ₂ O ₆ , refractive index: 1.90 to 2.00). Although the average primary particle size of the high refractive index fine particles is not particularly limited, it is preferably 5 to 100 nm. Although the content of the high refractive index fine particles is not particularly limited, it may be adjusted so that the refractive index of the easy-adhesion layer has a desired value. Examples of the chelate compound include water-soluble titanium chelate compounds, water-soluble titanium acylate compounds, and water-soluble zirconium compounds. Examples of the water-soluble titanium chelate compounds include isopropoxy(2-ethyl-1,3-hexanediolate)titanium, diisopropoxybis(acetylacetonato)titanium, and diisopropoxybis(triethanolaminato). titanium, di-n-butoxybis(triethanolamineto)titanium, hydroxybis(lactato)titanium, ammonium salts of hydroxybis(lactato)titanium, titanium beroxocitrate ammonium salts and the like. Examples of water-soluble titanium acylate compounds include oxotitanium bis(monoammonium oxalate). Examples of water-soluble zirconium compounds include zirconium tetraacetylacetonate and zirconium acetate.

In one embodiment, the easy adhesion layer preferably has a refractive index of 1.42 to 1.70. It is more preferably 1.42 to 1.65, still more preferably 1.45 to 1.60, even more preferably 1.47 to 1.55, and particularly preferably 1.48 to 1.54.
When a functional layer (or polarizer) is further laminated on the easy-adhesion layer of the polyester film, the refractive index of the easy-adhesion layer is the same as the refractive index of the functional layer (or polarizer) and the refractive index of the polyester film (slow phase It is preferable to adjust so as to be close to the geometric mean of the average value of the refractive index in the axial direction and the refractive index in the fast axis direction).
Furthermore, in the polarizing plate laminated so that the transmission axis of the polarizer and the slow axis of the polyester film are parallel, the refractive index of the easily adhesive layer is the same as the refractive index of the slow axis direction of the polyester film and the functional layer ( or polarizer), and in a polarizing plate laminated so that the transmission axis of the polarizer and the fast axis of the polyester film are parallel, the refractive index of the easily adhesive layer More preferably, the index is the geometric mean of the refractive index in the fast axis direction of the polyester film and the refractive index of the functional layer (or polarizer). The refractive index of the easy-adhesion layer can be adjusted by a known method, for example, by adjusting the copolymerization component of the binder resin or by adding titanium, germanium, or other metal species to the binder resin. can be adjusted to

In the above embodiment, the relationship of refractive index of the functional layer (or polarizer)≦refractive index of the easily adhesive layer≦refractive index of the polyester film, and it is more preferable that the refractive index difference between the layers is small. In the polarizing plate laminated so that the transmission axis of the polarizer and the slow axis of the polyester film are parallel, the refractive index of the functional layer (or polarizer) ≤ the refractive index of the easily adhesive layer ≤ the slow phase of the polyester film It is more preferable that there is a relationship between the refractive indices in the axial direction and that the refractive index difference between the layers is small. In the polarizing plate laminated so that the transmission axis of the polarizer and the fast axis of the polyester film are parallel, the refractive index of the functional layer (or polarizer) ≤ the refractive index of the easily adhesive layer ≤ the fast phase of the polyester film It is more preferable that there is a relationship between the refractive indices in the axial direction and that the refractive index difference between the layers is small.

In one embodiment, the refractive index of the easy-adhesion layer preferably satisfies the relationship: refractive index in the fast axis direction of the polyester film<refractive index of the easy-adhesion layer<refractive index in the slow axis direction of the polyester film. . When a functional layer is further laminated on the easy-adhesion layer of the polyester film, the relationship of refractive index in the fast axis direction of the polyester film<refractive index of the functional layer<refractive index in the slow axis direction of the polyester film must be satisfied. is preferred.
In one embodiment, the thickness of the easy-adhesion layer is 3 to 30 nm, and the relationship of refractive index in the fast axis direction of the polyester film<refractive index of the functional layer<refractive index in the slow axis direction of the polyester film is satisfied. is preferred. At this time, the refractive index of the easily adhesive layer is preferably smaller than the refractive index of the polyester film in the fast axis direction, and the difference between the refractive index of the polyester film in the fast axis direction and the refractive index of the easily adhesive layer is 0.05. The following are more preferable. The difference between the refractive index of the polyester film in the fast axis direction and the refractive index of the functional layer, and the difference between the refractive index of the polyester film in the slow axis direction and the refractive index of the functional layer are 0.025 or more. It is more preferable to have

The easy-adhesion layer can be obtained by applying the coating solution to one or both sides of a uniaxially stretched film or an unstretched film in the longitudinal direction, drying at 100 to 150° C., and stretching in the transverse direction. The final thickness of the easy-adhesion layer is preferably 3 nm or more and 200 nm or less, more preferably 50 nm or more and 150 nm or less, and still more preferably 80 nm or more and 130 nm or less. If the thickness is less than 3 nm, the adhesiveness to the functional layer or polarizer may be insufficient. On the other hand, if the thickness exceeds 200 nm, the blocking resistance may deteriorate. When the easy-adhesion layer is provided on both sides of the polyester film, the coating amount of the easy-adhesion layer on both sides may be the same or different, and can be independently set within the above range.

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

Moreover, a well-known method can be used as a method of apply|coating a coating liquid. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, etc., and these methods can be used alone. Or it can be performed in combination.

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

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

The polyester film used in the present invention may be a uniaxially stretched film or a biaxially stretched film, but when a biaxially stretched film is used as a polarizer protective film, the film is observed from directly above the film surface. Although rainbow-like color spots are not observed even when observed from an oblique direction, it is necessary to pay attention to the fact that rainbow-like color spots may be observed in some cases.

Specifically, the film-forming conditions for the polyester film are preferably 80 to 135°C, more preferably 80 to 130°C, and particularly preferably 90 to 120°C for the longitudinal stretching temperature and the transverse stretching temperature. In order to orient the film so that the slow axis is in the TD direction, the longitudinal draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times. Further, the transverse draw ratio is preferably 2.5 to 6.0 times, particularly preferably 3.0 to 5.5 times. In order to orient the film so that the slow axis is in the MD direction, the longitudinal draw ratio is preferably 2.5 to 6.0, more preferably 3.0 to 5.5. Further, the transverse draw ratio is preferably 1.0 to 3.5 times, particularly preferably 1.0 to 3.0 times.
In order to control the refractive index or retardation in the fast axis direction of the polyester film within the above range, it is preferable to control the ratio between the longitudinal draw ratio and the transverse draw ratio. If the difference between the draw ratios in the vertical and horizontal directions is too small, the refractive index in the fast axis direction of the polyester film tends to exceed 1.62, and it becomes difficult to increase the retardation, which is not preferable. Setting the stretching temperature low is a preferable measure for increasing the retardation. In the subsequent heat treatment, the treatment temperature is preferably 100-250°C, particularly preferably 180-245°C.

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

Thickness unevenness of the polyester film is preferably 5.0% or less, more preferably 4.5% or less, even more preferably 4.0% or less, and 3.0% or less. is particularly preferred.

As described above, the retardation of the polyester film can be controlled within a specific range by appropriately setting the draw ratio, draw temperature, and film thickness. For example, the higher the draw ratio, the lower the draw temperature, and the thicker the film, the easier it is to obtain a higher retardation. Conversely, the lower the draw ratio, the higher the drawing temperature, and the thinner the film, the easier it is to obtain a lower retardation. However, thickening the film tends to increase the retardation in the thickness direction. Therefore, it is desirable to appropriately set the film thickness within the range described later. In addition to retardation control, it is necessary to set the final film forming conditions in consideration of the physical properties required for processing.

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

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

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

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

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

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

(2) Retardation (Re)
Retardation is a parameter defined by the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy=|Nx−Ny|) on the film and the film thickness d (nm). It is a measure of optical isotropy and anisotropy. The biaxial refractive index anisotropy (ΔNxy) was obtained by the following method. Using a molecular orientation meter (MOA-6004 type molecular orientation meter manufactured by Oji Keisoku Co., Ltd.), the slow axis direction of the film was determined, and the slow axis direction was 4 cm so that it was parallel to the long side of the sample for measurement. A 2 cm x 2 cm rectangle was cut out and used as a measurement sample. For this sample, the refractive index in the biaxial direction perpendicular to each other (refractive index in the slow axis direction: Ny, refractive index in the direction perpendicular to the slow axis direction: Nx) and the refractive index in the thickness direction (Nz) were measured by the Abbe refractor. The absolute value of the biaxial refractive index difference (|Nx−Ny|) was defined as the anisotropy of the refractive index (ΔNxy) by using an index meter (NAR-4T, manufactured by Atago Co., measuring wavelength: 589 nm). The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Finereuf Co.) and converted into nm. The retardation (Re) was obtained from the product (ΔNxy×d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

(3) Thickness direction retardation (Rth)
The retardation in the thickness direction is obtained by multiplying the two birefringences ΔNxz (=|Nx−Nz|) and ΔNyz (=|Ny−Nz|) when viewed from the cross section in the thickness direction of the film by the film thickness d. is a parameter that indicates the average retardation obtained by Obtain Nx, Ny, Nz and film thickness d (nm) in the same manner as in the measurement of retardation, calculate the average value of (ΔNxz × d) and (ΔNyz × d), and calculate the thickness direction retardation (Rth ).

(4) Measurement of Emission Spectrum of Backlight Light Source REGZA 43J10X manufactured by Toshiba Corporation was used as a liquid crystal display device used in each example. When the emission spectrum of the backlight light source (white light emitting diode) of this liquid crystal display device was measured using a multichannel spectrometer PMA-12 manufactured by Hamamatsu Photonics, an emission spectrum having peak tops near 450 nm, 535 nm, and 630 nm was observed. was done. The half-value width of each peak top (the half-value width of the peak having the highest peak intensity in each wavelength region) was 17 nm for the peak at 450 nm, 45 nm for the peak at 535 nm, and 2 nm for the peak at 630 nm. Although this light source had a plurality of peaks in the wavelength region of 600 nm or more and 780 nm or less, the half width was evaluated at the peak near 630 nm, which has the highest peak intensity in this region. The exposure time for spectrum measurement was 20 msec.

(5) Observation of iris spots The liquid crystal display device obtained in each example was visually observed from the front and oblique directions in a dark place, and the presence or absence of iris spots was determined as follows.

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

(6) Refractive Index of Easy Adhesion Layer After applying the adhesion-improving coating liquid to a glass plate, it was cured under predetermined conditions to prepare a coating film having a thickness of about several μm. The coating film was peeled off from the glass plate, and the refractive index was measured with an Abbe refractometer (NAR-1T SOLID manufactured by Atago, measurement wavelength 589 nm).

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

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

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

(Production Example 3-Adhesion-improving coating liquid preparation)
A transesterification reaction and a polycondensation reaction were carried out by a conventional method to obtain 46 mol % of terephthalic acid, 46 mol % of isophthalic acid and 8 mol % of sodium 5-sulfonatoisophthalate as dicarboxylic acid components (relative to the total dicarboxylic acid components). A water-dispersible sulfonic acid metal group-containing copolymer polyester resin was prepared having a composition of 50 mol % ethylene glycol and 50 mol % neopentyl glycol as the glycol component (relative to the total glycol component). Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant are mixed and then heated and stirred. After adding 5 parts by mass of a water-dispersible sulfonic acid metal group-containing copolymerized polyester resin and continuing to stir until the lumps of the resin disappear, the resin aqueous dispersion was cooled to room temperature to obtain a solid content concentration of 5.0% by mass. A homogeneous water-dispersible copolyester resin liquid was obtained. Furthermore, after dispersing 3 parts by mass of aggregated silica particles (manufactured by Fuji Silysia Co., Ltd., Silysia 310) in 50 parts by mass of water, Silysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin liquid. 0.54 parts by mass of the aqueous dispersion was added, and 20 parts by mass of water was added while stirring to obtain an adhesion-improving coating liquid. The easy-adhesion layer obtained by using this easy-adhesion modifying coating liquid had a refractive index of 1.530.

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

Next, the adhesion-improving coating solution was applied to both sides of the unstretched PET film by a reverse roll method so that the coating amount after drying was 0.08 g/m ² , and then dried at 80°C for 20 seconds. .

The unstretched film with the coating layer formed thereon was guided to a tenter stretching machine, and while holding the ends of the film with clips, was guided to a hot air zone at a temperature of 125° C. and stretched 4.0 times in the width direction. Next, while maintaining the stretched width in the width direction, it is treated at a temperature of 225 ° C. for 10 seconds, and further subjected to a relaxation treatment of 3.0% in the width direction to obtain a uniaxially stretched PET film with a film thickness of about 100 μm. rice field. The obtained film had an Re of 10,300 nm, an Rth of 12,350 nm, an Re/Rth of 0.83, Nx=1.588, and Ny=1.691.

(Polarizer protective film 2)
A uniaxially stretched PET film having a film thickness of about 80 μm was obtained in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. The obtained film had Re of 8080 nm, Rth of 9960 nm, Re/Rth of 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 in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. The obtained film had Re of 6060 nm, Rth of 7470 nm, Re/Rth of 0.81, Nx=1.589 and Ny=1.690.

(Polarizer protective film 4)
A uniaxially stretched PET film having a film thickness of about 40 μm was obtained in the same manner as the polarizer protective film 1 except that the line speed was changed to change the thickness of the unstretched film. The obtained film had Re of 4160 nm, Rth of 4920 nm, Re/Rth of 0.85, Nx=1.587 and Ny=1.691.

(Polarizer protective film 5)
An unstretched film produced by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then 1.5° C. in the running direction with a roll group having a peripheral speed difference. After double-stretching, the film was led to a hot air zone at a temperature of 130° C. and stretched 4.0-fold in the width direction to obtain a biaxially stretched PET film having a film thickness of about 100 μm in the same manner as the polarizer protective film 1 . The obtained film had Re of 7820 nm, Rth of 13890 nm, Re/Rth of 0.56, Nx=1.608 and Ny=1.686.

(Polarizer protective film 6)
An unstretched film produced by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then a roll group having a peripheral speed difference of 2.0 in the running direction. After double-stretching, the film was led to a hot air zone at a temperature of 135° C. and stretched 4.0-fold in the width direction. The obtained film had Re of 6400 nm, Rth of 14600 nm, Re/Rth of 0.44, Nx=1.617 and Ny=1.681.

(Polarizer protective film 7)
An unstretched film prepared by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then a roll group with a peripheral speed difference of 2.8 in the running direction. After being double-stretched, the film was led to a hot air zone at a temperature of 140° C. and stretched 4.0-fold in the width direction. The obtained film had Re of 5400 nm, Rth of 15900 nm, Re/Rth of 0.34, Nx=1.631 and Ny=1.685.

(Polarizer protective film 8)
An unstretched film produced by the same method as the polarizer protective film 1 was heated to 105° C. using a heated roll group and an infrared heater, and then 3.3 degrees in the running direction with a roll group having a peripheral speed difference. After being double-stretched, the film was led to a hot air zone at a temperature of 140° C. and stretched 4.0-fold in the width direction. The obtained film had Re of 4800 nm, Rth of 16700 nm, Re/Rth of 0.29, Nx=1.640 and Ny=1.688.

Using the polarizer protective films 1 to 8, a liquid crystal display device was produced as described later.

(Example 1)
A polarizer protective film 1 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the opposite side. (thickness: 80 μm) was adhered to prepare a polarizing plate 1.
A liquid crystal display device was fabricated by replacing the polarizing plate on the visible side of REGZA 43J10X manufactured by Toshiba with the above polarizing plate 1 so that the polyester film was on the opposite side (distal) to the liquid crystal. The direction of the transmission axis of the polarizing plate 1 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Example 2)
A polarizer protective film 2 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the opposite side. (thickness: 80 μm) was adhered to prepare the 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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the 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 polarizer protective film 3 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the polarizing plate 3 .
A liquid crystal display device was fabricated by replacing the polarizing plate on the light source side of REGZA 43J10X manufactured by Toshiba with the above polarizing plate 3 so that the polyester film was on the opposite side (distal) to the liquid crystal. The direction of the transmission axis of the polarizing plate 3 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Example 5)
A polarizer protective film 3 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the polarizing plate 3 .
A liquid crystal display device was fabricated by replacing the polarizing plates on the viewing side and the light source side of REGZA 43J10X manufactured by Toshiba with the polarizing plate 3 so that the polyester film was on the opposite side (distal) to the liquid crystal. The direction of the transmission axis of the polarizing plate 3 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Example 6)
A polarizer protective film 4 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the 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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the 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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the opposite side. (thickness: 80 μm) was attached to prepare 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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare the polarizing plate 7 .
A liquid crystal display device was fabricated by replacing the polarizing plate on the visible side of REGZA 43J10X manufactured by Toshiba with the polarizing plate 7 so that the polyester film was on the opposite side (distal) to the liquid crystal.
The direction of the transmission axis of the polarizing plate 7 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Comparative example 2)
A polarizer protective film 2 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare a polarizing plate 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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare a polarizing plate 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 polarizer protective film 3 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare a polarizing plate 9 .
A liquid crystal display device was fabricated by replacing the polarizing plate on the light source side of REGZA 43J10X manufactured by Toshiba with the above polarizing plate 9 so that the polyester film was on the opposite side (distal) to the liquid crystal. The direction of the transmission axis of the polarizing plate 9 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Comparative Example 5)
A polarizer protective film 3 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. (thickness: 80 μm) was adhered to prepare a polarizing plate 9 .
A liquid crystal display device was fabricated by replacing the polarizing plates on the viewing side and the light source side of REGZA 43J10X manufactured by Toshiba with the polarizing plate 9 so that the polyester film was on the opposite side (distal) to the liquid crystal. The direction of the transmission axis of the polarizing plate 9 was replaced so as to be the same as the direction of the transmission axis of the polarizing plate before replacement.

(Comparative Example 6)
A polarizer protective film 4 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer is perpendicular to the fast axis of the film, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. A polarizing plate 10 was prepared by affixing a polarizing plate 10 with a thickness of 80 μm.
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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the other side. A polarizing plate 11 was prepared by affixing a film (80 μm thick).
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 is attached to one side of a polarizer made of PVA and iodine so that the transmission axis of the polarizer and the fast axis of the film are parallel, and a TAC film (manufactured by Fuji Film Co., Ltd.) is attached to the opposite side. (thickness: 80 μm) was attached to prepare the 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 .

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

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

Claims (5)

A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source has a peak top of the emission spectrum in each wavelength region of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and 780 nm or less, and has the highest peak intensity in the wavelength region of 600 nm or more and 780 nm or less. A white light source having an emission spectrum with a peak half width of less than 5 nm,
At least one polarizing plate of the two polarizing plates has a polyester film laminated on at least one surface of a polarizer,
The polyester film has an easy-adhesion layer on at least one surface,
The difference between the refractive index of the easily adhesive layer and the refractive index of the polyester film in a direction parallel to the transmission axis of the polarizer is 0.087 or less ,
A liquid crystal display device , wherein the polyester film has a retardation of 1500 to 30000 nm . In the emission spectrum of the backlight light source, the half width of the peak with the highest peak intensity in the wavelength region of 400 nm or more and less than 495 nm is 5 nm or more, and the half width of the peak with the highest peak intensity in the wavelength region of 495 nm or more and less than 600 nm is 2. The liquid crystal display device according to claim 1, wherein the thickness is 5 nm or more. The backlight source contains Mn as a red phosphor ⁴⁺ 3. A liquid crystal display device according to claim 1, comprising an activated fluoride complex phosphor. A liquid crystal display device comprising a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates,
The backlight source contains Mn as a red phosphor. ⁴⁺ A white light source having an activated fluoride complex phosphor,
At least one polarizing plate of the two polarizing plates has a polyester film laminated on at least one surface of a polarizer,
The polyester film has an easy-adhesion layer on at least one surface,
The difference between the refractive index of the easily adhesive layer and the refractive index of the polyester film in a direction parallel to the transmission axis of the polarizer is 0.087 or less,
A liquid crystal display device, wherein the polyester film has a retardation of 1500 to 30000 nm. 5. The liquid crystal display device according to claim 1, wherein the angle formed by the transmission axis of said polarizer and the fast axis of said polyester film is -15° to 15°.