JP2009169447A - Polarizing plate and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve display quality (particularly grayscale characteristics) of a VA mode liquid crystal display device. <P>SOLUTION: The following polarizing plate is used. The polarizing plate is composed of a polarizing film and two transparent protective films disposed on both sides of the polarizing film, wherein one transparent protective film is a retardation film having a Re retardation value of 20 to 70 nm and a Rth retardation value of 70 to 200 nm, the retardation film is made of an oriented polymer film and is disposed to allow the slow phase axis of the retardation film to be substantially parallel to the transmission axis of the polarizing film, and the other transparent protective film has a light diffusing function. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing plate capable of improving the viewing angle dependency of a liquid crystal display device, particularly the gradation characteristics depending on the viewing angle. The present invention also relates to a VA mode liquid crystal display device having a wide range of viewing angles.

Conventionally, as a liquid crystal display (LCD) using an active matrix, a liquid crystal material having a positive dielectric anisotropy is twisted by 90 degrees horizontally between the substrates and between the opposing substrates. A TN (Twisted Nematic) mode liquid crystal display device oriented in a wide range is widely used. However, the TN mode liquid crystal display device has a big problem that the viewing angle characteristic is poor, and various studies have been made to improve the viewing angle characteristic.
On the other hand, as an alternative to the TN mode, a liquid crystal material having negative dielectric anisotropy is vertically aligned, and a protrusion provided on the substrate surface regulates the liquid crystal molecule tilt direction when a voltage is applied. A domain vertical alignment) type liquid crystal display device has been proposed, and the viewing angle characteristics have been greatly improved.

The MVA type liquid crystal display device is a VA (Vertically Aligned) mode liquid crystal display device in which a liquid crystal material having a negative dielectric anisotropy is vertically aligned. By restricting the obliquely oriented directions to be in a plurality of directions within one pixel and improving the viewing angle characteristics, the viewing angle characteristics have been remarkably improved.
However, the conventional liquid crystal display device using the MVA method has a problem that the gradation characteristics are deteriorated depending on the viewing angle. Specifically, if the viewing angle is tilted in the vertical and horizontal directions, the gradation interval on the high luminance side becomes small, and the gradation cannot be displayed well.
In order to solve this problem, it has been shown that the display quality can be improved by using a light diffusion means having a highly controlled lens structure or diffractive structure as described in Patent Documents 1 and 2. However, these specific means have a problem that they are expensive and very difficult to mass-produce.
On the other hand, with respect to light diffusing means that is inexpensive and can be mass-produced, for example, as disclosed in Patent Documents 3 and 4, a resin containing a filler such as silicon dioxide (silica) is provided on the surface of a transparent substrate film. Examples thereof include those formed by coating, and those using a light diffusion layer containing a translucent resin and translucent fine particles as in Patent Documents 5 to 10.

JP 2001-33783 A JP 2001-56461 A JP-A-6-18706 Japanese Patent Laid-Open No. 10-20103 JP-A-11-160505 Japanese Patent Laid-Open No. 11-305010 JP 11-326608 A JP 2000-121809 A JP 2000-180611 A JP 2000-338310 A

  In the conventional technology, although a certain degree of viewing angle improvement effect is recognized with respect to the VA mode liquid crystal display device, only an effect that cannot be said to be practically sufficient is obtained.

An object of the present invention is to provide a polarizing plate capable of remarkably improving the display quality (particularly gradation characteristics) of a VA mode liquid crystal display device.
An object of the present invention is also to significantly improve the display quality (particularly gradation characteristics) of the VA mode, which is a wide viewing angle liquid crystal display device, using a light scattering layer.

The object of the present invention was achieved by the following polarizing plates (1) to (9) and the liquid crystal display device (10) below.
(1) A polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof, wherein one transparent protective film has a Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm. The retardation film comprises a stretched polymer film, and is arranged so that the slow axis of the retardation film and the transmission axis of the polarizing film are substantially parallel to each other. And the other transparent protective film has a light-diffusion function, The polarizing plate characterized by the above-mentioned.

(2) The polarizing plate according to (1), wherein the transparent protective film having a light diffusing function comprises a light diffusing layer containing translucent fine particles in a transparent support and a translucent resin.
(3) The polarizing plate according to (2), wherein the difference between the refractive index of the translucent fine particles and the refractive index of the translucent resin is 0.02 or more and 0.15 or less.
(4) The polarizing plate according to (2) or (3), wherein the translucent fine particles have a particle size distribution having at least two peaks.
(5) One peak of the particle size distribution of the translucent fine particles is in the range of 0.5 to 2.0 μm, and the other peak is in the range of 2.5 to 5.0 μm. Polarizer.

(6) The polarizing plate according to any one of (1) to (5), wherein the transparent protective film having a light diffusion function has a haze value of 40% or more.
(7) The low refractive index layer having a refractive index of 1.35 to 1.45 is provided on the transparent protective film having a light diffusion function, according to any one of (1) to (6) Polarizer.
(8) The polarizing plate according to (7), wherein the low refractive index layer is formed of a crosslinked cured product obtained by heat or ionizing radiation of a composition containing a fluorine-containing compound and inorganic fine particles.
(9) The polarizing plate according to (7) or (8), wherein the low refractive index layer has an integrating sphere average reflectance of 2.5% or less in a wavelength range of 450 to 650 nm.

  (10) A VA mode liquid crystal cell, two polarizing plates arranged on both sides thereof, and a backlight, and the two polarizing plates are respectively a polarizing film and two transparent protection pieces arranged on both sides thereof. A liquid crystal display device comprising a film, wherein two transparent protective films between a polarizing film and a liquid crystal cell each have a Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm. A phase difference film, which is composed of a stretched polymer film, arranged so that the slow axis of the phase difference film on the display surface side and the transmission axis of the polarizing film on the display surface side are substantially parallel to each other. The phase difference film on the backlight side is arranged so that the slow axis of the retardation film and the transmission axis of the polarizing film on the backlight side are substantially parallel to each other. The liquid crystal display device which has a transparent protective film is characterized by having a light diffusing function.

In the present specification, the Re retardation value is a value defined by the following formula (I), and the Rth retardation value is a value defined by the following formula (II):
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
[Where nx is the refractive index in the slow axis direction in the film plane; ny is the refractive index in the fast axis direction in the film plane; nz is the refractive index in the thickness direction of the film] And d is the thickness of the film].

It is a graph which shows the gradation characteristic of the left-right direction in a commercially available MVA mode liquid crystal display device. It is a cross-sectional schematic diagram which shows the typical aspect of the liquid crystal display device according to this invention. It is a cross-sectional schematic diagram which shows the typical form of the transparent protective film which has a light-diffusion function.

[Basic configuration of liquid crystal display]
When the polarizing plate according to the present invention is used in a transmissive liquid crystal display device, particularly a VA mode transmissive display device, a remarkable effect can be obtained.
The transmissive liquid crystal display device includes a liquid crystal cell and two polarizing plates disposed on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates.

  In a VA mode liquid crystal cell, rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied. The VA mode liquid crystal cell includes (1) a narrowly defined VA mode liquid crystal cell in which rod-like liquid crystalline molecules are aligned substantially vertically when no voltage is applied, and substantially horizontally when a voltage is applied (Japanese Patent Laid-Open No. Hei 2-). 176625) (2) Liquid crystal cell (SID97, Digest of tech. Papers (Preliminary Proceed) 28 (1997) 845 in which the VA mode is made into a multi-domain (MVA mode) for widening the viewing angle ), (3) Liquid crystal cell in a mode (n-ASM mode) in which rod-like liquid crystalline molecules are substantially vertically aligned when no voltage is applied and twisted multi-domain alignment is applied when a voltage is applied (Preliminary collections 58-59 of the Japanese Liquid Crystal Society) (1998)), and (4) SURVAIVAL mode liquid crystal cells (announced at LCD International 98).

FIG. 1 is a graph showing the gradation characteristics in the left-right direction in a commercially available MVA mode liquid crystal display device.
In the liquid crystal display device shown in FIG. 1, the gradation on the high luminance side (L7, L8) converges at a viewing angle of about 50 °, and the gradation characteristics (luminance (brightness) in the voltage for displaying each gradation depend on the viewing angle). Gender) gets worse. Therefore, when the display image is viewed from the direction of 50 °, a high-intensity image such as an X-ray image cannot be displayed accurately. The angle at which deterioration of gradation characteristics becomes a problem in practice is 20 °. The gradation characteristic at 20 ° on the high luminance side (L7, L8) is preferably 40 ° or more, more preferably 50 ° or more, and most preferably 60 ° or more.

A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. In the present invention, at least the polarizing plate on the display surface side is used in combination with a transparent protective film having a function as a retardation film and a transparent protective film having a function as a light diffusion film, and functions as a light diffusion film. It arrange | positions so that the direction of the transparent protective film which has may be the display surface side most.
For the polarizing plate on the side opposite to the display surface (usually the backlight side), a transparent protective film having a function as a retardation film can be used as the transparent protective film on the liquid crystal cell side. However, the transparent protective film having a function as a light diffusion film is not necessary for the polarizing plate on the side opposite to the display surface.

FIG. 2 is a schematic cross-sectional view showing a typical embodiment of the liquid crystal display device according to the present invention.
In the liquid crystal display device shown in FIG. 2A, a transparent protective film (1), a polarizing film (2), a transparent protective film (3p) having a function as a retardation film, in order from the backlight (BL) side, A VA mode liquid crystal cell (4), a transparent protective film (5p) having a function as a retardation film, a polarizing film (6), and a transparent protective film (7d) having a function as a light diffusion film.
The transparent protective film (5p) having a function as a retardation film, the polarizing film (6), and the transparent protective film (7d) having a function as a light diffusion film constitute a polarizing plate according to the present invention.

The liquid crystal display device shown in FIG. 2 (b) has a transparent protective film (1), a polarizing film (2), a transparent protective film (3), and a VA mode liquid crystal cell (4) in this order from the backlight (BL) side. The transparent protective film (5p) having a function as a retardation film, the polarizing film (6), and the transparent protective film (7d) having a function as a light diffusion film.
The transparent protective film (5p) having a function as a retardation film, the polarizing film (6), and the transparent protective film (7d) having a function as a light diffusion film constitute a polarizing plate according to the present invention.

The transparent protective film having a function as a retardation film may be obtained by laminating a retardation film on a normal transparent protective film. However, it is preferable to impart a function as a retardation film to the transparent protective film itself.
A transparent protective film having a function as a light diffusing film can impart a function as a light diffusing film to the transparent protective film itself. However, it is preferable to laminate a light diffusion film (light diffusion layer) on an ordinary transparent protective film (functioning as a transparent support).

[Transparent protective film functioning as a light diffusion film]
The light diffusion film is a film that refracts and scatters light. Specifically, a microlens film with a fine lens, a lenticular film, a film mixed with fine particles, a diffusion film with a random irregular surface, an internal refractive index distribution film, or a diffraction grating layer is used. can do. A film mixed with fine particles can be preferably used as a light diffusing film that can be mass-produced at low cost. The transparent protective film having a light diffusing function is particularly preferably composed of a transparent support and a light diffusing layer (light diffusing film) containing translucent fine particles in a translucent resin.

FIG. 3 is a schematic cross-sectional view showing a representative form of a transparent protective film having a light diffusion function.
The transparent protective film (10) shown in FIG. 3 is formed by laminating a transparent support (20) and a light diffusion layer (30) containing translucent fine particles (41, 42) in a translucent resin (31). It becomes. The light diffusing layer (30) shown in FIG. 3 includes two types of first light-transmitting fine particles (41) and second light-transmitting fine particles (42) having two types of peaks in the particle size distribution (with different refractive indexes). ). One kind of translucent fine particles may be used. Further, translucent fine particles of the same type (having the same refractive index) and having two particle size distribution peaks may be used for the light diffusion layer.

The first light transmissive fine particles (41) are made of a light transmissive resin (for example, silica, refractive index: 1.51) (average particle diameter: 1.0 μm). The second translucent fine particles (42) are composed of another translucent resin (for example, styrene, refractive index: 1.61) (average particle diameter of 3.5 μm).
The light diffusing function is obtained by the difference in refractive index between the translucent fine particles (41, 42) and the translucent resin (31). The difference in refractive index is preferably 0.02 to 0.15. If the difference in refractive index is less than 0.02, the light diffusion effect may not be obtained. When the refractive index difference is larger than 0.15, the light diffusibility is too high, and the entire film may be whitened. The difference in refractive index is more preferably 0.03 to 0.13, and most preferably 0.04 to 0.10.

One peak of the particle size distribution of the translucent fine particles is preferably in the range of 0.5 to 2.0 μm, and the other peak is preferably in the range of 2.5 to 5.0 μm. Such a particle size distribution can be easily achieved by mixing two types of fine particle groups having different mode particle sizes.
With a peak in the range of 0.5 to 2.0 μm (the mode particle diameter of the light-transmitting fine particles (41) in FIG. 3), an appropriate light scattering angle distribution as the light diffusion film can be obtained. In the light diffusion film, it is necessary to diffuse the incident light to some extent in order to improve the display quality (improve the viewing angle in the downward direction). The greater the diffusion effect, the better the viewing angle characteristic. However, in order to maintain the front brightness in terms of display quality, it is necessary to increase the transmittance as much as possible.
By setting the particle size peak to 0.1 μm or more, backscattering can be reduced, and a reduction in brightness can be suppressed. In addition, by setting the particle size peak to 2.0 μm or less, a large scattering effect is obtained, and the viewing angle characteristics are improved. This peak is more preferably in the range of 0.3 to 1.8 μm, and most preferably in the range of 0.4 to 1.6 μm.

A surface scattering suitable for a light diffusion film can be obtained by a peak in the range of 2.5 to 5.0 μm (in FIG. 3, the mode particle diameter of the light-transmitting fine particles (42)). In a light diffusion film, it is also important to prevent external light from being reflected by appropriate surface scattering in order to improve display quality.
As described above, the mode (mode) particle size is more important as the particle size of the fine particles (rather than the average particle size). In the present specification, the mode particle size means a particle size in which fine particles are classified by particle size (0.1 μm unit) and the maximum number of fine particles is classified. The particle size of the fine particles described below (including the examples) means the mode particle size.

The lower the haze value of the surface, the smaller the display blur and the clear display can be obtained. However, when the haze value is too low, the reflection and the glittering brightness called surface glare (scintillation) occur. On the contrary, if the haze value is too high, it becomes whitish and whitening (black density reduction) occurs. The surface haze value (hs) is preferably 0.5 <hs <30, more preferably 7 ≦ hs ≦ 20, and most preferably 7 ≦ hs ≦ 15.
In order to control the surface haze value, it is preferable to provide appropriate irregularities on the surface of the resin layer with fine particles. The haze value (cloudiness value) can be measured using a measuring device (for example, HR-100, manufactured by Murakami Color Research Laboratory) according to JIS-K-7105.
When the particle diameter of the translucent fine particles is 2.0 μm or less, the surface unevenness becomes small, the effect of surface scattering is small, and reflection due to external light cannot be sufficiently suppressed. On the other hand, when the particle diameter is 5.0 μm or more, the surface unevenness is increased, and the reflection is suppressed, but it is markedly whitened and the display quality is lowered. The particle diameter is preferably 2.2 to 4.7 μm, more preferably 2.4 to 4.5 μm.

The surface unevenness is preferably 1.2 μm or less as an average surface roughness (Ra), more preferably 0.5 μm or less, and most preferably 0.2 μm or less.
There is a correlation between the haze value of the light diffusion film, particularly the internal scattering haze that contributes greatly to the diffusion of transmitted light and the viewing angle improvement effect. That is, if the light emitted from the backlight is diffused by the light diffusion film provided on the surface of the polarizing plate on the viewing side, the viewing angle characteristics are improved. However, if it is diffused too much, backscattering will increase and the front brightness will decrease. Further, if the scattering is too large, there arises a problem that the image clarity is deteriorated. The internal scattering haze is preferably 30 to 80%, more preferably 35 to 70%, and most preferably 40 to 60%.
As a method for increasing the internal scattering haze, a method for increasing the concentration of particles having a particle diameter of 0.5 μm to 1.5 μm, a method for increasing the difference in refractive index between the light transmitting resin and the light transmitting fine particles, or the light transmitting A method of reducing the conductive fine particles can be employed.
From the viewpoint of visibility, it is also necessary to provide surface haze by surface irregularities. In the state where internal scattering haze and surface haze exist, the surface haze is preferably 40 to 90%, more preferably 45 to 80%, and most preferably 50 to 70%.

  As described above, when the light-transmitting fine particles having at least two particle size distribution peaks are used, the viewing angle characteristics related to display quality and the reflection of external light can be independently optimized. Compared with single-peak fine particles, the light diffusion function of the transparent protective film is finely set by the intensity of two particle size distribution peaks (substantially, the mixing ratio of two kinds of light-transmitting fine particles). be able to.

The translucent fine particles are preferably used by mixing two or more kinds of monodisperse fine particles having different particle diameters. If the fine particles before mixing are monodispersed (no variation in particle size) (although not monodispersed after mixing), the haze can be easily adjusted with respect to the scattering characteristics.
The variation is reduced, and the haze value can be easily designed.
As the translucent fine particles, organic fine particles or inorganic fine particles can be used.
As the organic fine particles, plastic beads are preferable. It is preferable to select and use a material having a refractive index difference from the light-transmitting resin as described above from a plastic having high transparency. Examples of plastic beads include acrylic-styrene copolymer beads (refractive index: 1.55), melamine beads (refractive index: 1.57), polycarbonate beads (refractive index: 1.57), styrene beads (refractive index). : 1.60), cross-linked polystyrene beads (refractive index: 1.61), polymethyl methacrylate beads (refractive index: 1.49), silica beads (refractive index: 1.44), benzoguanamine-melamine formaldehyde beads (refractive index) : 1.68) and polyvinyl chloride beads (refractive index: 1.60).
The particle size of the plastic beads is preferably 0.1 to 5 μm. The plastic beads are preferably used in an amount of 5 to 30 parts by mass with respect to 100 parts by mass of the translucent resin.

  When translucent fine particles are likely to settle in the resin composition (translucent resin), an inorganic filler (eg, silica) may be added to prevent sedimentation. In addition, an inorganic filler will have a bad influence on the transparency of a coating film, if the addition amount increases. Accordingly, it is preferable to add an inorganic filler having a particle size of 0.5 μm or less to the cylindrical enemy in an amount of less than 0.1% by mass so as not to impair the transparency of the coating film with respect to the translucent resin.

As the translucent resin, a resin that is cured by ultraviolet rays or an electron beam is generally used. Specifically, it can be classified into three types: an ionizing radiation curable resin, an ionizing radiation curable resin, a mixture of a thermoplastic resin and a solvent, and a thermosetting resin.
The thickness of the light diffusion layer is preferably 0.5 to 50 μm, more preferably 1 to 20 μm, further preferably 2 to 10 μm, and most preferably 3 to 7 μm.

  The refractive index of the translucent resin is preferably 1.50 to 2.00, more preferably 1.57 to 1.90, and most preferably 1.64 to 1.80. In addition, the refractive index of translucent resin is the value measured without including translucent fine particles. When the refractive index is too small, the antireflection property is lowered. When the refractive index is too large, the color of the reflected light becomes strong.

  The binder used for the translucent resin is preferably a polymer having a saturated hydrocarbon or polyether as the main chain, and more preferably a polymer having a saturated hydrocarbon as the main chain. The binder is preferably crosslinked. The polymer having a saturated hydrocarbon as the main chain is preferably obtained by a polymerization reaction of an ethylenically unsaturated monomer. In order to obtain a crosslinked binder, it is preferable to use a monomer having two or more ethylenically unsaturated groups.

  Examples of monomers having two or more ethylenically unsaturated groups include esters of polyhydric alcohols and (meth) acrylic acid (eg, ethylene glycol di (meth) acrylate, 1,4-dichlorohexane diacrylate, penta Erythritol tetra (meth) acrylate), pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) Acrylate, dipentaerythritol hexa (meth) acrylate, 1,3,5-cyclohexanetriol trimethacrylate, polyurethane polyacrylate, polyester polyacrylate), vinylbenzene derivatives Examples include 1,4-divinylbenzene, 4-vinylbenzoic acid-2-acryloylethyl ester, 1,4-divinylcyclohexanone), vinyl sulfone (eg, divinyl sulfone), acrylamide (eg, methylenebisacrylamide) and methacrylamide. included. A (meth) acrylate of a pentafunctional or higher alcohol can form a film having high hardness, that is, high scratch resistance. Commercially available monomers (for example, a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate) are also preferably used.

The monomer having an ethylenically unsaturated group can be cured by a polymerization reaction by ionizing radiation or heat after being dissolved in a solvent together with various polymerization initiators and other additives, applied and dried.
Instead of or in addition to the monomer having two or more ethylenically unsaturated groups, a crosslinked structure may be introduced into the binder by a reaction of a crosslinkable group. Examples of the crosslinkable functional group include isocyanate group, epoxy group, aziridine group, oxazoline group, aldehyde group, carbonyl group, hydrazine group, carboxyl group, methylol group and active methylene group. Vinylsulfonic acid, acid anhydride, cyanoacrylate derivative, melamine, etherified methylol, ester and urethane, and metal alkoxide such as tetramethoxysilane can also be used as a monomer for introducing a crosslinked structure. A functional group that exhibits crosslinkability as a result of the decomposition reaction, such as a block isocyanate group, may be used. That is, the crosslinkable functional group may be in a precursor state (reactive as a result of decomposition).
The binder having a crosslinkable functional group can form a crosslinked structure by heating after coating.

In addition to the binder polymer, the binder of the translucent resin is formed from a polymer obtained by copolymerizing a monomer having a high refractive index or metal oxide ultrafine particles having a high refractive index.
Examples of high refractive index monomers include bis (4-methacryloylthiophenyl) sulfide, vinyl naphthalene, vinyl phenyl sulfide and 4-methacryloxyphenyl-4′-methoxyphenyl thioether.
Examples of the metal used for the metal oxide ultrafine particles having a high refractive index include zirconium, titanium, aluminum, indium, zinc, tin and antimony. As the metal _{oxide, ZrO 2, TiO 2, Al} 2 O 3, In 2 O 3, ZnO, SnO 2, Sb 2 O 3 , and ITO is preferable. ZrO ₂ is particularly preferred. The particle diameter of the ultrafine particles is preferably 100 nm or less, and more preferably 50 nm or less. The addition amount of the metal oxide ultrafine particles is preferably 10 to 90% by mass of the translucent resin, and more preferably 20 to 80% by mass.

  When cellulose triacetate is used as a transparent support, the solvent of the coating solution for forming the light-transmitting resin is preferably used by mixing a solvent in which cellulose triacetate is dissolved with a solvent in which cellulose triacetate is not dissolved. It is preferable that the boiling point of the solvent in which cellulose triacetate is not dissolved is higher than the boiling point of the solvent in which cellulose triacetate is dissolved. The temperature difference between the boiling point of the solvent in which cellulose triacetate is not dissolved and the boiling point of the solvent in which cellulose triacetate is dissolved is preferably 30 ° C. or higher, and preferably higher than 50 ° C. When two types of solvents in which cellulose triacetate dissolves or a solvent in which cellulose triacetate does not dissolve are used in combination, it is sufficient that at least one type of solvent satisfies the above rules. About the temperature difference of a boiling point, it is preferable to satisfy the said prescription | regulation by the comparison of the solvent which has the highest boiling point.

The solvent in which cellulose triacetate is dissolved means a solvent in which the solubility of cellulose triacetate having an acetylation degree of 60% at 25 ° C. is 1% by mass or more. The solvent in which cellulose triacetate does not dissolve means a solvent in which the solubility of cellulose triacetate having an acetylation degree of 60% at 25 ° C. is less than 1% by mass.
Examples of solvents in which cellulose triacetate is dissolved include ethers having 3 to 12 carbon atoms (eg, dibutyl ether, dimethoxymethane, dimethoxyethane, diethoxyethane, propylene oxide, 1,4-dioxane, 1,3-dioxolane. 1,3,5-trioxane, tetrahydrofuran, anisole, phenetole), ketones having 3 to 12 carbon atoms (eg, acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methylcyclohexanone) Methylcyclohexanone), esters having 3 to 12 carbon atoms (eg, ethyl formate, propyl formate, n-pentyl formate, methyl acetate, ethyl acetate, methyl propionate, propion brewed ethyl, n-pentyl acetate, γ Ptylolactone) and organic solvents having two or more types of functional groups (eg, methyl 2-methoxyacetate, methyl 2-ethoxyacetate, ethyl 2-ethoxyacetate, ethyl 2-ethoxypropionate, 2-methoxyethanol, 2-propoxyethanol) 2-butoxyethanol, 1,2-diacetoxyacetone, acetylacetone, diacetone alcohol, methyl acetoacetate, ethyl acetoacetate).

  Examples of solvents in which cellulose triacetate does not dissolve include alcohols (eg, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-methyl-2- Butanol, cyclohexanol), ester (eg, isobutyl acetate), ketone (eg, methyl isobutyl ketone, 2-octanone, 2-pentanone, 2-hexanone, 2-heptanone, 3-pentanone, 3-heptanone, 4-heptanone) Is included.

  The mass ratio (A / B) of the amount (A) of the solvent in which the cellulose triacetate is dissolved and the amount (B) of the solvent in which the cellulose triacetate is not dissolved is preferably 5/95 to 50/50, 10/90 to 40 / 60 is more preferable, and 15/85 to 30/70 is most preferable.

  The ionizing radiation curable resin composition can be cured by electron beam or ultraviolet irradiation.

In the case of electron beam curing, use an electron beam emitted from an electron beam accelerator (for example, Cockrowalton type, bandegraph type, resonant transformer type, insulated core transformer type, linear type, dynamitron type, high frequency type) To do. The electron beam energy is preferably 50 to 1000 KeV, more preferably 100 to 300 KeV.
In the case of ultraviolet curing, ultraviolet rays emitted from a light source (for example, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a carbon arc, a xenon arc, a metal halide lamp) are used.

In the transparent protective film having a light diffusion function, it is preferable to use a polymer film or a glass plate as a transparent support, and it is more preferable to use a polymer film. Examples of polymers that form polymer films include cellulose esters (cellulose triacetate, cellulose diacetate, cellulose acetate butyrate), cellulose films, polyesters (eg, polyethylene terephthalate), polyethersulfones, polyolefins (eg, polyacrylic acid) Ester, polymethylpentene), polyurethane, polycarbonate, polysulfone, polyether, polyetherketone and poly (meth) acrylonitrile.
The thickness of the transparent support is preferably 25 to 1000 μm.

Since the transparent support is used on the outermost surface of the polarizing plate, a cellulose acetate film generally used as a protective film for the polarizing plate is particularly preferable. The cellulose acetate film is preferably cellulose triacetate having an acetylation degree of 59.0 to 61.5%. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more.
Cellulose acetate preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.3 to 1.65, and most preferably 1.4 to 1.6. preferable.

In general, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not uniformly substituted by acetyl groups, but the substitution degree at the 6-position tends to be smaller than the substitution degree at the 2-position and the 3-position. . In the cellulose acetate used for the transparent support, the substitution degree at the 6-position is preferably the same or higher than those at the 2-position and the 3-position.
The ratio of the 6-position substitution degree to the total of the substitution degrees at the 2-position, the 3-position and the 6-position is preferably 32% or more, more preferably 33% or more, and most preferably 34% or more. . The 6-position substitution degree of cellulose acetate is also preferably 0.88 or more.
The degree of substitution at each position can be determined by NMR.
Paragraph Nos. [0043] to [0044] [Example] [Synthesis Example 1], Paragraph Numbers [0048] to [0049] [Synthesis Example 2], Paragraph Numbers [0051] to [0052] The cellulose acetate obtained by the method of [Synthesis Example 3] can be used for the transparent support.

It is preferable to produce a cellulose acetate film by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent.
The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of the ketone having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the ester having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.
The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon.
Two or more organic solvents may be mixed and used.

A cellulose acetate solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent.
The amount of cellulose acetate is adjusted so that it is contained in an amount of 10 to 40% by mass in the resulting solution. The amount of cellulose acetate is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring cellulose acetate and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, cellulose acetate and an organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.

Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acetate with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method.
In the cooling dissolution method, first, cellulose acetate is gradually added to an organic solvent with stirring at room temperature.
The amount of cellulose acetate is preferably adjusted so as to be contained in the mixture at 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acetate and organic solvent solidifies.
The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

Furthermore, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acetate is dissolved in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath.
The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .
A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
In addition, according to differential scanning calorimetry (DSC), a 20 mass% solution obtained by dissolving cellulose acetate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) in methyl acetate by the cooling dissolution method is 33 There exists a quasi-phase transition point between a sol state and a gel state in the vicinity of ° C., and a uniform gel state is obtained below this temperature. Therefore, it is necessary to keep this solution at a temperature equal to or higher than the pseudo phase transition temperature, preferably about 10 ° C. plus the gel phase transition temperature. However, this pseudo phase transition temperature varies depending on the degree of acetylation of cellulose acetate, the degree of viscosity average polymerization, the concentration of the solution, and the organic solvent used.

A cellulose acetate film is produced from the prepared cellulose acetate solution (dope) by a solvent cast method.
The dope is cast on a drum or band, and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

  The prepared cellulose acetate solution (dope) can be used to form a film by casting two or more layers. In this case, it is preferable to produce a cellulose acetate film by a solvent cast method. The dope is cast on a drum or band, and the solvent is evaporated to form a film. The dope before casting is preferably adjusted in concentration so that the solid content is 10 to 40%. The surface of the drum or band is preferably finished in a mirror state.

  When casting a plurality of cellulose acetate solutions of two or more layers, produce a film while casting and laminating a plurality of cellulose acetate solutions from a plurality of casting openings provided at intervals in the traveling direction of the support. (Japanese Patent Laid-Open Nos. 61-158414, 1-122419, and 11-198285). The film can also be formed by casting a cellulose acetate solution from two casting ports (Japanese Patent Publication Nos. 60-27562, 61-94724, 61-947245, 61-104813). No. 61-158413 and JP-A-6-134933). Also, a cellulose acetate film casting method (described in JP-A-56-162617) in which a flow of a high-viscosity cellulose acetate solution is wrapped with a low-viscosity cellulose acetate solution and the high- and low-viscosity cellulose acetate solutions are simultaneously extruded. It may be adopted.

Using two casting ports, the film cast on the support is peeled off by the first casting port, and the second casting is performed on the side that is in contact with the support surface, thereby producing the film. (Japanese Patent Publication No. 44-20235).
The plurality of cellulose acetate solutions may have the same composition. In order to give a function to a plurality of cellulose acetate layers, a cellulose acetate solution corresponding to the function may be extruded from each casting port.
The cellulose acetate solution can also be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, a UV absorption layer, a polarizing layer).

  In the case of a monolayer liquid, it is necessary to extrude a cellulose acetate solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In that case, the stability of the cellulose acetate solution is poor, and solid matter is generated, which often causes problems due to defects or poor flatness. By casting a plurality of cellulose acetate solutions from the casting port, a highly viscous solution can be simultaneously extruded onto the support. Further, not only can the flatness be improved and an excellent planar film can be produced, but also the use of a concentrated cellulose acetate solution can achieve a reduction in drying load and increase the production speed of the film.

A plasticizer can be added to the cellulose acetate film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethyl hexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by mass, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass of the amount of the cellulose ester.

  A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acetate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. When the addition amount is less than 0.01% by mass, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by mass, bleeding-out (bleeding) of the deterioration preventing agent to the film surface may be observed. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

The cellulose acetate film is preferably subjected to a surface treatment. Specific examples include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment. Further, an undercoat layer (described in JP-A-7-333433) may be provided.
From the viewpoint of maintaining the flatness of the film, the temperature of the cellulose acetate film in these treatments is preferably Tg (glass transition temperature) or lower, specifically 150 ° C. or lower.
When used as a transparent protective film of a polarizing plate, it is particularly preferable to carry out acid treatment or alkali treatment, that is, saponification treatment on cellulose acetate, from the viewpoint of adhesiveness with the polarizing film.
The surface energy is preferably 55 mN / m or more, and more preferably 60 mN / m or more and 75 mN / m or less.

Alkali saponification is most preferred. The alkali saponification treatment is preferably performed in a cycle in which the film surface is immersed in an alkali solution, neutralized with an acidic solution, washed with water and dried.
Examples of the alkaline solution include a potassium hydroxide solution and a sodium hydroxide solution, and the prescribed concentration of hydroxide ions is preferably 0.1 to 3.0N, more preferably 0.5 to 2.0N. preferable. The alkaline solution temperature is preferably in the range of room temperature to 90 ° C, more preferably 40 to 70 ° C.
From the viewpoint of productivity, it is preferable to apply an alkali solution and remove the alkali from the film surface by washing with water after saponification treatment. From the viewpoint of wettability, alcohol (eg, IPA, n-butanol, methanol, ethanol) is preferable as a coating solvent, and an alkali dissolution aid (eg, water, propylene glycol, ethylene glycol) is also preferably added. .

The surface energy of a solid can be determined by a contact angle method, a wet heat method, and an adsorption method as described in “Basics and Applications of Wetting” (issued by Realize 1989.12.10). In the case of the cellulose acetate film of the present invention, the contact angle method is preferably used.
Specifically, two types of solutions having known surface energies are dropped on a cellulose acetate film, and at the intersection of the surface of the droplet and the surface of the film, the angle formed by the tangent line drawn on the droplet and the surface of the film The surface angle of the film can be calculated by defining the angle containing the droplet as the contact angle.

[Low refractive index layer]
A low refractive index layer can be provided on the transparent protective film having a light diffusion function. The low bending rate layer can function as an antireflection layer.
By providing the low refractive index layer, an integrating sphere average reflectance of 2.5% or less can be achieved in the wavelength range of 450 to 650 nm.
The refractive index of the low refractive index layer is preferably 1.35 to 1.45.
The refractive index of the low refractive index layer preferably satisfies the following formula (I).
(I) (mλ / 4) × 0.7 <n1d1 <(mλ / 4) × 1.3
In the formula, m is a positive odd number (generally 1), n1 is the refractive index of the low refractive index layer, and d1 is the film thickness (nm) of the low refractive index layer. Further, λ is the wavelength of visible light, and is a value in the range of 450 to 650 (nm).
Satisfying the above formula (I) means that m (positive odd number, usually 1) satisfying the formula (I) exists in the above wavelength range.

The low refractive index layer is preferably composed of a cured cured product of heat or ionizing radiation of a composition containing a fluorine-containing compound and inorganic fine particles. It is preferable to perform a crosslinking reaction using a crosslinkable fluorine-containing compound as the fluorine-containing compound, and as a result, form a cured fluorine-containing resin. The dynamic friction coefficient of the cured fluorine-containing resin is preferably 0.03 to 0.15. The contact angle of the cured fluorine-containing resin with respect to water is preferably 90 to 120 degrees.
As the crosslinkable fluorine-containing compound, a perfluoroalkyl group-containing silane compound (eg, (heptadecafluoro-1,1,2,2-tetradecyl) triethoxysilane) is preferably used. Moreover, you may use the fluorine-containing copolymer which has a fluorine-containing monomer and the monomer for crosslinkable group provision as a structural unit.

Examples of fluorine-containing monomers include fluoroolefins (eg, fluoroethylene, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoro-2,2-dimethyl-1,3-dioxole), (meta ) Partially or fully fluorinated alkyl esters of acrylic acid and fully or partially fluorinated vinyl ethers. Etc. Regarding the (meth) acrylic acid moiety or the fully fluorinated alkyl ester, commercially available products (eg, Biscoat 6FM, manufactured by Osaka Organic Chemical Co., Ltd .; M-2020, manufactured by Daikin Co., Ltd.) can also be used.
Monomers for imparting a crosslinkable group include (meth) acrylate monomers (eg, glycidyl methacrylate, (meth) acrylic acid) having a crosslinkable functional group (eg, glycidyl group, carboxyl, hydroxyl, amino, sulfo) in the molecule. , Methylol (meth) acrylate, hydroxyalkyl (meth) acrylate, allyl acrylate). A crosslinked structure may be introduced after forming the polymer (described in JP-A-10-25388 and JP-A-10-147739).

Further, in the low refractive index layer, not only a copolymer of the above-mentioned fluorine-containing monomer and a monomer for imparting a crosslinkable group, but also a polymer obtained by copolymerizing other monomers may be used.
Examples of other monomers that can be copolymerized include olefins (eg, ethylene, propylene, isoprene, vinyl chloride, vinylidene chloride), acrylic esters (eg, methyl acrylate, methyl acrylate, ethyl acrylate, 2-acrylic acid 2- Ethylhexyl), methacrylic acid esters (eg, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene glycol dimethacrylate), styrene, styrene derivatives (eg, divinylbenzene, vinyltoluene, α-methylstyrene), vinyl ethers (eg, Methyl vinyl ether), vinyl esters (eg, vinyl acetate, vinyl propionate, vinyl cinnamate), acrylamides (eg, N-tert-butylacrylamide, N-cyclohexylacrylamide), methacrylamide and Ronitoriru are included.

In order to impart scratch resistance to the fluorine-containing resin used for the low refractive index layer, Si oxide ultrafine particles having an average particle diameter of preferably 0.1 μm or less, more preferably 0.001 to 0.05 μm are added. And preferably used. From the viewpoint of antireflection properties, the lower the refractive index, the better. However, as the refractive index of the fluororesin is lowered, the scratch resistance deteriorates. Therefore, by optimizing the refractive index of the fluorine-containing resin and the addition amount of Si oxide ultrafine particles, it is possible to find the best point of the balance between scratch resistance and low refractive index.
As the ultrafine particles of Si, silica sol dispersed in a commercially available organic solvent may be added to the coating solution as it is, or various commercially available silica powders may be dispersed in an organic solvent.

[Transparent protective film functioning as retardation film]
The Re retardation value and Rth retardation value of the retardation film are defined by the following formulas (I) and (II), respectively. The measurement wavelength is 550 nm.
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
In the formulas (I) and (II), nx is the refractive index in the slow axis direction (the direction in which the refractive index is maximum) in the film plane. In formulas (I) and (II), ny is the refractive index in the fast axis direction (the direction in which the refractive index is minimized) in the film plane. In the formula (II), nz is a refractive index in the thickness direction of the film. In the formulas (I) and (II), d is the thickness of the film whose unit is nm.

In the transparent protective film functioning as a retardation film, the Re retardation value is adjusted to 20 to 70 nm, and the Rth retardation value is adjusted to 70 to 400 nm.
When two transparent protective films functioning as a retardation film are used in the liquid crystal display device, the Rth retardation value of the film is preferably 70 to 200 nm.
When a single transparent protective film functioning as a retardation film is used in a liquid crystal display device, the Rth retardation value of the film is preferably 150 to 400 nm.
The birefringence (Δn: nx−ny) of the retardation film is preferably 0.00025 to 0.00088. The birefringence {(nx + ny) / 2−nz} in the thickness direction of the retardation film is preferably 0.00088 to 0.005.

As the retardation film, a transparent polymer film has been conventionally used. Examples of resin films and polymers include norbornene resins, cellulose esters (eg, cellulose triacetate, cellulose diacetate, cellulose acetate butyrate), polyesters (eg, polyethylene terephthalate, polycarbonate), polyethersulfones, polyolefins (eg, poly Methylpentene, polyacrylate), polyurethane, polysulfone, polyether, polyetherketone and poly (meth) acrylonitrile. Commercially available norbornene resins (Arton, manufactured by JSR Corporation; Zeonex, Zeonoa, manufactured by Nippon Zeon Corporation) may be used.
The thickness of the transparent protective film functioning as a retardation film is preferably 25 to 300 μm.

As the transparent protective film functioning as a retardation film, it is preferable to use a cellulose acetate film generally used as a protective film for a polarizing plate. That is, in order not to increase the thickness of the liquid crystal display device, it is preferable to use a single cellulose acetate film having both a function as a retardation film and a function as a transparent protective film (a protective function of a polarizing film).
Cellulose acetate films are generally less susceptible to birefringence. Therefore, in order to provide the retardation value, it is preferable to further perform a stretching treatment using the following retardation increasing agent.

As a retardation increasing agent for cellulose acetate film, an aromatic compound having at least two aromatic rings can be used.
The aromatic compound is preferably used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of cellulose acetate. The aromatic compound is more preferably used in the range of 0.05 to 15 parts by mass and most preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of cellulose acetate. Two or more aromatic compounds may be used in combination.
The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring).
The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring.
As the aromatic ring, benzene ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring, imidazole ring, triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring are preferable, More preferred are a benzene ring and a 1,3,5-triazine ring.
It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.

The number of aromatic rings contained in the aromatic compound is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. .
The bond relationship between two aromatic rings can be classified into (a) a condensed ring, (b) a direct bond with a single bond, and (c) a bond through a linking group (for aromatic rings). , Spiro bonds cannot be formed). The connection relationship may be any of (a) to (c).

Examples of the condensed ring (a condensed ring of two or more aromatic rings) include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a naphthacene ring, a pyrene ring, Indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline ring, quinolidine Ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thianthrene ring Be Naphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The linking group in (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right in the following examples of the linking group may be reversed.
c1: -CO-O-
c2: —CO—NH—
c3: -alkylene-O-
c4: —NH—CO—NH—
c5: —NH—CO—O—
c6: —O—CO—O—
c7: -O-alkylene-O-
c8: -CO-alkenylene-
c9: -CO-alkenylene-NH-
c10: -CO-alkenylene-O-
c11: -alkylene-CO-O-alkylene-O-CO-alkylene-
c12: -O-alkylene-CO-O-alkylene-O-CO-alkylene-O-
c13: -O-CO-alkylene-CO-O-
c14: -NH-CO-alkenylene-
c15: -O-CO-alkenylene-

The aromatic ring and the linking group may have a substituent.
Examples of the substituent include halogen atom (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl group, alkenyl group, alkynyl group, aliphatic acyl group , Aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.

The alkyl group preferably has 1 to 8 carbon atoms. A chain alkyl group is preferable to a cyclic alkyl group, and a linear alkyl group is particularly preferable. The alkyl group may further have a substituent (eg, hydroxy, carboxy, alkoxy group, alkyl-substituted amino group). Examples of alkyl groups (including substituted alkyl groups) include methyl, ethyl, n-butyl, n-hexyl, 2-hydroxyethyl, 4-carboxybutyl, 2-methoxyethyl and 2-diethylaminoethyl.
The alkenyl group preferably has 2 to 8 carbon atoms. A chain alkenyl group is preferable to a cyclic alkenyl group, and a linear alkenyl group is particularly preferable. The alkenyl group may further have a substituent. Examples of alkenyl groups include vinyl, allyl and 1-hexenyl.
The alkynyl group preferably has 2 to 8 carbon atoms. A chain alkynyl group is preferable to a cyclic alkynyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of alkynyl groups include ethynyl, 1-butynyl and 1-hexynyl.

The aliphatic acyl group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl. The aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy.
The number of carbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy group may further have a substituent (eg, alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy.
The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl.
The number of carbon atoms of the alkoxycarbonylamino group is preferably 2 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The alkylthio group preferably has 1 to 12 carbon atoms. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl.
The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide.
The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino.
The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl.
The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl.
The number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido. Examples of non-aromatic heterocyclic groups include piperidino and morpholino.
The molecular weight of the retardation increasing agent is preferably 300 to 800.
Specific examples of the retardation increasing agent are described in JP 2000-1111914 A, JP 2000-275434 A and WO 00/65384.

The cellulose acetate film is preferably stretched to adjust retardation and further reduce distortion. Since stretching can reduce strain in the stretching direction, biaxial stretching is more preferable in order to reduce strain in all directions in the plane.
Biaxial stretching includes simultaneous biaxial stretching method and sequential biaxial stretching method, but sequential biaxial stretching method is preferable from the viewpoint of continuous production. After dope is cast, it is peeled off from the band or drum, and the width direction. After stretching in the (longitudinal method), it is stretched in the longitudinal direction (width direction).

The methods of stretching in the width direction are described in JP-A-62-115035, JP-A-4-152125, JP-A-4284221, JP-A-298310, and JP-A-11-48271. The film is stretched at room temperature or under heating conditions. The heating temperature is preferably not higher than the glass transition temperature of the film. The film can be stretched by a treatment during drying, and is particularly effective when the solvent remains. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of the film transport roller so that the film winding speed is higher than the film peeling speed. In the case of stretching in the width direction, the film can also be stretched by conveying the film while holding it with a tenter and gradually increasing the width of the tenter. After the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine). The draw ratio of the film (ratio of increase due to stretching relative to the original length) is preferably 5 to 50%, more preferably 10 to 40%, and most preferably 15 to 35%.
When the stretched cellulose acetate film is used as a protective film for the polarizing plate, the transmission axis of the polarizing plate and the slow axis of the cellulose acetate film are made parallel. For that purpose, it is preferable that the draw ratio in the width direction is larger than the draw ratio in the longitudinal direction.

[Polarizer]
A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides.
In the polarizing plate (on the display surface side) according to the present invention, the transparent protective film functioning as the retardation film is used as one transparent protective film, and the transparent protective film functioning as the light diffusion film as the other transparent protective film Is used.
In the polarizing plate on the backlight side, the transparent protective film functioning as the retardation film can be used as one transparent protective film. A normal cellulose acetate film may be used as the other transparent protective film.
Examples of the polarizing film include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. The iodine polarizing film and the dye polarizing film are generally manufactured using a polyvinyl alcohol film.
The slow axis of the retardation film and the transmission axis of the polarizing film are arranged so as to be substantially parallel.

For the productivity of the polarizing plate, the moisture permeability of the transparent protective film is important. The polarizing film and the protective film are bonded with a water-based adhesive, and the adhesive solvent is dried by diffusing in the transparent protective film. The higher the moisture permeability of the transparent protective film, the faster the drying and the higher the productivity, but if it becomes too high, moisture will enter the polarizing film depending on the usage environment (under high humidity) of the liquid crystal display device. As a result, the polarization ability decreases.
The moisture permeability of the transparent protective film is determined by the thickness, free volume, hydrophilicity / hydrophobicity, etc. of the polymer film (and polymerizable liquid crystal compound).
When the polymer film is used as a transparent protective film for a polarizing plate, the moisture permeability is preferably 100 to 1000 g / m ² · 24 hrs, and more preferably 300 to 700 g / m ² · 24 hrs.
In the case of film formation, the thickness of the film can be adjusted by lip flow rate and line speed, or stretching and compression. Since the moisture permeability varies depending on the main material to be used, it is possible to make a preferable range by adjusting the thickness.
In the case of film formation, the free volume of the film can be adjusted by the drying temperature and time. Also in this case, moisture permeability varies depending on the main material to be used, so that a preferable range can be obtained by adjusting the free volume.
The hydrophilicity / hydrophobicity of the retardation film can be adjusted by an additive. The moisture permeability can be increased by adding a hydrophilic additive to the free volume, and conversely, the moisture permeability can be lowered by adding a hydrophobic additive.
By independently controlling the moisture permeability, a polarizing plate having an optical compensation ability can be manufactured at low cost with high productivity.

[Example 1]
(Preparation of transparent protective film functioning as retardation film)
A commercially available norbornene (Arton, manufactured by JSR Corporation) film (thickness: 100 μm) is obtained, stretched 30% in the width direction at a temperature of 180 ° C., and then stretched 10% in the longitudinal direction to function as a retardation film. A transparent protective film was prepared. About the produced transparent protective film, Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). As a result, Re was 40 nm and Rth was 110 nm.

(Preparation of a transparent protective film that functions as a light diffusion film)
100 parts by mass of an ultraviolet curable resin (Z7526, manufactured by JSR Corporation) having a refractive index of 1.51, 5 parts by mass of a curing initiator (Irgacure 184, manufactured by Ciba Geigy), and a refractive index as the first light-transmitting fine particles 1.61, 17 parts by mass of crosslinked styrene beads (manufactured by Soken Chemical Co., Ltd.) having a particle diameter of 1.3 μm, and a second translucent fine particle having a refractive index of 1.61 and a particle diameter of 3.5 μm 7 parts by mass of styrene beads (manufactured by Soken Chemical Co., Ltd.) was dispersed in a mixed solvent of methyl ethyl ketone / methyl isobutyl ketone (mass ratio 3/7) to prepare a dispersion having a solid content of 24% by mass. The dispersion was applied onto a cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) so as to have a dry film thickness of 6.0 μm. After drying, using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.), irradiating with ultraviolet rays having an illuminance of 400 mW / cm ² and an irradiation amount of 300 mJ / cm ² to cure the coating layer to form a light diffusion film. A functional transparent protective film was prepared.
According to JIS-K-7105, the haze (cloudiness value) of the transparent protective film was measured using a measuring instrument (manufactured by Murakami Color Research Laboratory, HR-100), and it was 67%.

(Preparation of viewing side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
The transparent protective film functioning as a light diffusing film was saponified, and attached to one side of the polarizing film using a polyvinyl alcohol adhesive so that the transparent support (cellulose triacetate film) was on the polarizing film side.
Next, the transparent protective film functioning as a retardation film was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive.
In this way, a viewing side polarizing plate according to the present invention was produced.

(Preparation of backlight side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
A commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to one side of the polarizing film using a polyvinyl alcohol adhesive.
Next, the transparent protective film functioning as a retardation film was subjected to saponification treatment and attached to the opposite side using a polyvinyl alcohol-based adhesive. In this way, a backlight side polarizing plate was produced.

(Production of liquid crystal display device)
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell were peeled off.
And the produced visual recognition side polarizing plate was affixed through the adhesive so that the transparent protective film which functions as a phase difference film might become a liquid crystal cell side.
Next, the produced backlight side polarizing plate was affixed through the adhesive so that the transparent protective film which functions as a phase difference film might become the liquid crystal cell side.
The crossed Nicols were arranged so that the transmission axis of the viewing side polarizing plate was in the vertical direction and the transmission axis of the backlight side polarizing plate was in the left and right direction.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 1.

[Example 2]
(Preparation of transparent protective film functioning as retardation film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

────────────────────────────────────
Cellulose acetate solution composition ────────────────────────────────────
Cellulose acetate having an acetylation degree of 60.9% 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 300 parts by weight Methanol (No. 1) 2 solvents) 54 parts by mass 1-butanol (third solvent) 11 parts by mass ───────────────────────────────── ───

In another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution.
A dope was prepared by mixing 474 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band casting machine. A cellulose acetate film (thickness: 80 μm) was produced by laterally stretching a film having a residual solvent amount of 15% by mass at a stretching ratio of 25% using a tenter under the conditions of 130 ° C.
About the produced transparent protective film (cellulose acetate film), Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). As a result, Re was 40 nm and Rth was 110 nm.

(Preparation of a transparent protective film that functions as a light diffusion film)
100 parts by mass of an ultraviolet curable resin (Z7526, manufactured by JSR Corporation) having a refractive index of 1.61, 5 parts by mass of a curing initiator (Irgacure 184, manufactured by Ciba Geigy), and a refractive index as the first light-transmitting fine particles 1.49, 8 parts by mass of polymethyl methacrylate beads (manufactured by Soken Chemical Co., Ltd.) having a particle size of 1.5 μm, and a refractive index of 1.61 and a particle size of 3.5 μm as the second translucent fine particles 5 parts by mass of crosslinked styrene beads (manufactured by Soken Chemical Co., Ltd.) was dispersed in a mixed solvent of methyl ethyl ketone / methyl isobutyl ketone (mass ratio 1/9) to prepare a dispersion having a solid content of 45% by mass. The dispersion was applied on a cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) so as to have a dry film thickness of 3.5 μm. After drying, using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.), irradiating with ultraviolet rays having an illuminance of 400 mW / cm ² and an irradiation amount of 300 mJ / cm ² to cure the coating layer to form a light diffusion film. A functional transparent protective film was prepared.
According to JIS-K-7105, the haze (cloudiness value) of the transparent protective film was measured using a measuring instrument (manufactured by Murakami Color Research Laboratory, HR-100), which was 48%.

(Preparation of viewing side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
The transparent protective film functioning as a light diffusing film is saponified, and the transparent support (cellulose triacetate film) of the transparent protective film functioning as a light diffusing film is placed on the polarizing film side using a polyvinyl alcohol adhesive. Affixed to one side of the polarizing film.
Next, the transparent protective film functioning as a retardation film was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. The slow axis of the retardation film and the transmission axis of the polarizing film were arranged in parallel.
In this way, a viewing side polarizing plate according to the present invention was produced.

(Preparation of backlight side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
A commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to one side of the polarizing film using a polyvinyl alcohol adhesive.
Next, the transparent protective film functioning as a retardation film was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. The slow axis of the retardation film and the transmission axis of the polarizing film were arranged in parallel.
Thus, the backlight side polarizing plate was produced.

(Production of liquid crystal display device)
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell were peeled off.
And the produced visual recognition side polarizing plate was affixed through the adhesive so that the transparent protective film which functions as a phase difference film might become a liquid crystal cell side.
Next, the produced backlight side polarizing plate was affixed through the adhesive so that the transparent protective film which functions as a phase difference film might become the liquid crystal cell side.
The crossed Nicols were arranged so that the transmission axis of the viewing side polarizing plate was in the vertical direction and the transmission axis of the backlight side polarizing plate was in the left and right direction.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 1.

[Example 3]
(Preparation of transparent protective film functioning as retardation film)
A dope was prepared by mixing 474 parts by mass of a cellulose acetate solution with 56 parts by mass of a retardation increasing agent solution (use 7.8 parts by mass of a retardation increasing agent with respect to 100 parts by mass of cellulose acetate), and adjusting the draw ratio. A cellulose acetate film was produced in the same manner as in Example 2 except that the content was changed to 14%.
About the produced transparent protective film (cellulose acetate film), Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). As a result, Re was 50 nm and Rth was 240 nm.

(Preparation of a transparent protective film that functions as a light diffusion film)
100 parts by mass of an ultraviolet curable resin (DPHA, Nippon Kayaku Co., Ltd.) having a refractive index of 1.54, 3 parts by mass of a curing initiator (Irgacure 907, Ciba Geigy), and refractive index as translucent fine particles Is 11 parts by weight of a crosslinked styrene bead (manufactured by Soken Chemical Co., Ltd.) in a mixed solvent of methyl ethyl ketone / cyclohexanone (mass ratio 6/4). A mass% dispersion was prepared. The dispersion was applied onto a cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) so as to have a dry film thickness of 2.0 μm. After drying, 140 mJ was irradiated with ultraviolet rays.
Furthermore, 100 parts by mass of an ultraviolet curable resin (DPHA, manufactured by Nippon Kayaku Co., Ltd.) having a refractive index of 1.54, 3 parts by mass of a curing initiator (Irgacure 907, manufactured by Ciba Geigy), first light-transmitting fine particles 6 parts by mass of a crosslinked styrene bead (manufactured by Soken Chemical Co., Ltd.) having a refractive index of 1.61 and a particle size of 3.5 μm, and the second light transmitting fine particles have a refractive index of 1.61 and a particle size of 16 parts by mass of 3 μm crosslinked styrene beads (manufactured by Soken Chemical Co., Ltd.) were dispersed in methyl ethyl ketone / cyclohexanone (mass ratio 6/4) to prepare a dispersion having a solid content of 22% by mass. The dispersion was applied on the first layer so as to have a dry film thickness of 3.0 μm. After drying, using a 160 W / cm air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.), ultraviolet rays having an illuminance of 400 mW / cm ² and an irradiation amount of 300 mJ / cm ² were irradiated to cure the coating layer. In this way, a light diffusion layer was formed.
According to JIS-K-7105, the haze (cloudiness value) was measured using a measuring instrument (manufactured by Murakami Color Research Laboratory, HR-100) and found to be 56%.

An average particle size of 10 to 20 nm and a solid content concentration of 2240 g of a methyl ethyl ketone solution (solid content concentration of 6% by mass) of a heat-crosslinkable fluoropolymer having a refractive index of 1.42 (JN-7228, manufactured by JSR Corporation) 192 g of methyl ethyl ketone dispersion (MEK-ST, manufactured by Nissan Chemical Co., Ltd.) of 30% by mass of SiO ₂ sol, 2224 g of methyl ethyl ketone, and 144 g of cyclohexanone were added, and after stirring, a polypropylene filter (PPE-01) having a pore size of 1 μm was used. Filtration was performed to prepare a coating solution for a low refractive index layer.
The coating solution for the low refractive index layer is applied onto the light diffusion layer using a bar coater, dried at 80 ° C., and then thermally crosslinked at 120 ° C. for 8 minutes to form a low refractive index layer having a thickness of 0.096 μm. Formed.
In this way, a transparent protective film functioning as a light diffusion film with a low refractive index layer was produced.

(Preparation of viewing side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
The transparent protective film functioning as a light diffusing film is saponified, and the transparent support (cellulose triacetate film) of the transparent protective film functioning as a light diffusing film is placed on the polarizing film side using a polyvinyl alcohol adhesive. Affixed to one side of the polarizing film.
Next, the transparent protective film functioning as a retardation film was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive. The slow axis of the retardation film and the transmission axis of the polarizing film were arranged in parallel.
In this way, a viewing side polarizing plate according to the present invention was produced.

(Preparation of backlight side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
A commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to one side of the polarizing film using a polyvinyl alcohol adhesive.
Next, a commercially available triacetylcellulose film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive.
Thus, the backlight side polarizing plate was produced.

(Production of liquid crystal display device)
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell were peeled off.
And the produced visual recognition side polarizing plate was affixed through the adhesive so that the transparent protective film which functions as a phase difference film might become a liquid crystal cell side.
Next, the produced backlight side polarizing plate was affixed on the opposite side of the liquid crystal cell with an adhesive.
The crossed Nicols were arranged so that the transmission axis of the viewing side polarizing plate was in the vertical direction and the transmission axis of the backlight side polarizing plate was in the left and right direction.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 1.

[Comparative Example 1]
(Preparation of a transparent protective film that does not function as a retardation film)
A cellulose acetate film was produced in the same manner as in the production of the transparent protective film functioning as the retardation film in Example 2 except that the cellulose acetate solution was used as it was as a dope and no stretching treatment was performed.
About the produced transparent protective film (cellulose acetate film), Re retardation value and Rth retardation value in wavelength 550nm were measured using the ellipsometer (M-150, JASCO Corporation make). As a result, Re was 4 nm and Rth was 48 nm.

(Preparation of viewing side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
A commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to one side of the polarizing film using a polyvinyl alcohol adhesive.
Next, the produced transparent protective film that does not function as a retardation film was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive.
In this way, a comparative viewing side polarizing plate was produced.

(Backlight side polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film.
A commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to one side of the polarizing film using a polyvinyl alcohol adhesive.
Next, a commercially available cellulose triacetate film (Fujitac TD80, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side using a polyvinyl alcohol adhesive.
Thus, the backlight side polarizing plate was produced.

(Production of liquid crystal display device)
A pair of polarizing plates and a pair of optical compensation sheets provided in a liquid crystal display device (VL-1530S, manufactured by Fujitsu Limited) using a vertical alignment type liquid crystal cell were peeled off.
And the produced visual recognition side polarizing plate was affixed through the adhesive so that the transparent protective film which does not function as a phase difference film may become a liquid crystal cell side.
Next, the produced backlight side polarizing plate was affixed on the opposite side of the liquid crystal cell with an adhesive.
The crossed Nicols were arranged so that the transmission axis of the viewing side polarizing plate was in the vertical direction and the transmission axis of the backlight side polarizing plate was in the left and right direction.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). The results are shown in Table 1.

Table 1 ────────────────────────────────────
Range with liquid crystal contrast ratio of 10 or more Range with good gradation characteristics
Display device Transmission axis direction From transmission axis Transmission axis direction From transmission axis
45 ° direction 45 ° direction ─────────────────────────────────────
Example 1> 80 °> 80 ° 47 ° 45 °
Example 2> 80 °> 80 ° 50 ° 49 °
Example 3> 80 °> 80 ° 51 ° 50 °
Comparative Example 1> 80 ° 44 ° 20 ° 15 °
────────────────────────────────────
(Ii) “Good gradation characteristic” means an angle equivalent to the high luminance gradation (L7, L8) at the left and right viewing angles of 20 degrees shown in the detailed description.

BL Backlight 1, 3 Transparent protective film 2, 6 Polarizing film 3p, 5p Transparent protective film having a function as a phase difference film 4 VA mode liquid crystal cell 7d, 10 Transparent protective film having a function as a light diffusion film 10 Light Transparent protective film having a diffusion function 20 Transparent support 31 Translucent resin 41 First translucent fine particles 42 Second translucent fine particles

Claims (10)

  A polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof, one transparent protective film having a Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm A retardation film, wherein the retardation film is a stretched polymer film, and is arranged so that a slow axis of the retardation film and a transmission axis of the polarizing film are substantially parallel to each other; and The other transparent protective film has a light-diffusion function, The polarizing plate characterized by the above-mentioned.   The polarizing plate according to claim 1, wherein the transparent protective film having a light diffusing function comprises a light diffusing layer containing translucent fine particles in a transparent support and a translucent resin.   The polarizing plate according to claim 2, wherein the difference between the refractive index of the translucent fine particles and the refractive index of the translucent resin is 0.02 or more and 0.15 or less.   The polarizing plate according to claim 2 or 3, wherein the translucent fine particles have a particle size distribution having at least two peaks.   The polarizing plate according to claim 4, wherein one peak of the particle size distribution of the translucent fine particles is in the range of 0.5 to 2.0 μm and the other peak is in the range of 2.5 to 5.0 μm.   The polarizing plate as described in any one of Claims 1 thru | or 5 with which the transparent protective film which has a light-diffusion function has a haze value of 40% or more.   The polarizing plate according to claim 1, wherein a low refractive index layer having a refractive index of 1.35 to 1.45 is provided on a transparent protective film having a light diffusion function.   The polarizing plate according to claim 7, wherein the low refractive index layer comprises a crosslinked cured product of a composition containing a fluorine-containing compound and inorganic fine particles by heat or ionizing radiation.   The polarizing plate according to claim 7 or 8, wherein the low refractive index layer has an integrating sphere average reflectance of 2.5% or less in a wavelength range of 450 to 650 nm.   VA mode liquid crystal cell and two polarizing plates arranged on both sides thereof, and a backlight, each of the two polarizing plates comprising a polarizing film and two transparent protective films arranged on both sides thereof In a liquid crystal display device, two transparent protective films between a polarizing film and a liquid crystal cell are both retardation films having a Re retardation value of 20 to 70 nm and an Rth retardation value of 70 to 200 nm. The retardation film is made of a stretched polymer film, and is arranged so that the slow axis of the retardation film on the display surface side and the transmission axis of the polarizing film on the display surface side are substantially parallel to each other. The slow axis of the retardation film on the backlight side and the transmission axis of the polarizing film on the backlight side are arranged so as to be substantially parallel to each other, and are provided on the most display surface side. The liquid crystal display device bright protective film is characterized by having a light diffusing function.

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