JP2001166137A - Polarizer - Google Patents

Abstract

(57) [Problem] To develop a polarizing plate capable of forming a liquid crystal display device or the like that has a small chromaticity change between the front and the perspective when arranged in crossed Nicols and is unlikely to cause a color change due to the perspective. SOLUTION: A polarizing film containing a dichroic substance and having a light transmittance of 40% or more and a polarization degree of 99% or more has transparent protective layers on both sides, and is arranged in crossed Nicols to allow vertical light to enter. x ₀ the xy chromaticity in transmitted light _if, y _0, and x in transmitted light when the orientation of 45 degrees to the polarization axis of the oblique incident light is incident at an angle of 40 degrees to the normal line
When y chromaticity is x ₄₀ and y ₄₀ , {x ₀ −x ₄₀ }
<0.200, and ┃y ₀ -y ₄₀ ┃ <polarizer is 0.130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate capable of forming a liquid crystal display device having a small change in chromaticity between the front and the perspective when arranged in crossed Nicols.

[0002]

BACKGROUND OF THE INVENTION There has been a demand for an increase in the viewing angle at which a liquid crystal display can be viewed in a good display state. It has been found that there is a cause of lowering the quality. That is, conventionally, as a polarizing plate, a polarizing film containing a dichroic substance and transparent protective layers provided on both sides is used. However, in a conventional polarizing plate, when it is arranged in crossed Nicols, the front (normal line) There is a problem that the chromaticity greatly differs between the direction (1) and the perspective direction.

[0003] Incidentally, a conventional polarizing plate is generally formed by bonding a triacetyl cellulose film having a thickness of about 80 µm to both sides of a polyvinyl alcohol-based polarizing film. In this case, the polarizing plate is arranged in crossed Nicols to transmit vertical light. Xy chromaticity x ₀ , y ₀ in transmitted light when incident
When, ┃X difference between xy chromaticity x _40, y _{4 0} in the transmitted light in the case of orientation of 45 degrees to the polarization axis of the oblique incident light is incident at an angle of 40 degrees with respect to the normal ₀ - x ₄₀ ┃ about 0.243 mm, is about 0.174 about at ┃y ₀ -y ₄₀ ┃, the display color is greatly different in front and perspective.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop a polarizing plate capable of forming a liquid crystal display device or the like which has a small chromaticity change between the front and the perspective when arranged in crossed Nicols and is unlikely to cause a color change due to the perspective. I do.

[0005]

According to the present invention, a polarizing film containing a dichroic substance and having a light transmittance of 40% or more and a polarization degree of 99% or more has transparent protective layers on both sides, and is arranged in crossed Nicols. Xy chromaticity in transmitted light when vertical light is incident on the optical axis is x ₀ , y ₀ , and oblique incident light incident at an angle of 40 degrees with respect to the normal from an azimuth of 45 degrees with respect to the polarization axis. When the xy chromaticity in the transmitted light of x is x ₄₀ and y ₄₀ , ┃
In x ₀ -x ₄₀ ┃ <0.200, and ┃y ₀ -y ₄₀ ┃
The present invention provides a polarizing plate characterized by <0.130.

[0006]

According to the polarizing plate of the present invention, the change in chromaticity between the front and the perspective when arranged in crossed Nicols is small,
It is possible to form a liquid crystal display device or the like in which a color change when viewed obliquely is small.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A polarizing plate according to the present invention comprises a polarizing film containing a dichroic substance and having a light transmittance of 40% or more and a polarization degree of 99% or more, and a transparent protective layer on both sides of the polarizing film. x ₀ the xy chromaticity in transmitted light when made incident vertically light is _disposed, y _0, and the oblique incidence from the orientation of 45 degrees with respect to the polarization axis is incident at an angle of 40 degrees to the normal line when the xy chromaticity in the transmitted light when the light was _{x 40, y 40,} with ┃x ₀ -x ₄₀ ┃ <0.200, and ┃y
₀₋ y ₄₀ ┃ <0.130.

[0008] As the polarizing film, for example, polyvinyl alcohol, partially formalized polyvinyl alcohol,
A film made of a suitable hydrophilic polymer according to the prior art such as a partially saponified ethylene / vinyl acetate copolymer may be appropriately dyed with a dichroic substance such as iodine or a dichroic dye, stretched, or cross-linked. When natural light is incident thereon, it transmits linearly polarized light and has a light transmittance of 40% or more and a degree of polarization of 99% or more.

As described above, a liquid crystal display which is bright and excellent in contrast and the like can be achieved. A polarizing plate that is preferable from the viewpoint of improvement of display quality and the like has a light transmittance of 41% or more, particularly 42% or more, particularly 43% or more, and a polarization degree of 99.2%.
Above all, it is 99.5% or more. The thickness of the polarizing film is generally from 5 to 80 μm, but in the present invention, the thickness is preferably from 10 to 50 μm, particularly preferably from 15 to 40 μm.

For forming the transparent protective layer provided on both sides of the polarizing film, a film made of an appropriate transparent polymer can be used, and the polymer is not particularly limited.
Above all, a film made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property, and the like is preferably used. Examples of the polymer include an acetate resin such as triacetyl cellulose, a polyester resin, a polyether sulfone resin, a polycarbonate resin, a polyamide resin, a polyimide resin, a polyolefin resin, and an acrylic resin.

A transparent protective layer that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film. The thickness of the transparent protective layer is an important factor for achieving the above-mentioned change in chromaticity, and in the present invention, it is preferable that at least one transparent protective layer has a thickness of 50 μm or less, particularly 45 μm or less. The thickness of the other transparent protective layer is 50
Although it can be more than μm, from the point of achieving the above chromaticity change, 160 μm or less based on the total thickness of the polarizing plate,
The thickness is preferably set to 0 μm or less, particularly 140 μm or less. Such a thickness is more advantageous than the thickness of the polarizing plate. The transparent protective layers provided on both sides of the polarizing film may be formed of a combination of different polymers on the front and back.

The film for forming the transparent protective layer is bonded to the polarizing film by, for example, a polyvinyl alcohol-based adhesive, a water-soluble crosslinking agent for a vinyl alcohol-based polymer such as boric acid or borax, glutaraldehyde, melamine or oxalic acid. It can be carried out using one or more appropriate transparent adhesives such as an adhesive composed of At the time of the bonding treatment, an appropriate surface treatment such as a method of saponifying the bonding surface of the transparent protective layer or the like can be performed for the purpose of improving the adhesion.

The polarizing film and the transparent protective layer forming the polarizing plate are treated with an ultraviolet absorbent such as a salicylate compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex salt compound, or the like. For example, a material having an ultraviolet absorbing ability by an appropriate method such as a method may be used.

The polarizing plate according to the invention, the xy chromaticity in transmitted light when made incident vertically light by placing it in a cross nicol state by the above-mentioned configuration x _0, y _0, and with respect to the polarization axis 45 Assuming that xy chromaticity in transmitted light in the case of obliquely incident light incident at an angle of 40 degrees with respect to the normal from the azimuth of degrees is x ₄₀ , y ₄₀ , {x ₀ −x ₄₀ } <0.2.
00 and {y ₀ −y ₄₀ } <0.130.

[0015] It is more preferable to suppress chromaticity change due to oblique view.
A good polarizing plate is ┃x₀-X₄₀０．１ is 0.190 or less,
Especially below 0.170, especially below 0.150, and
┃y ₀-Y₄₀┃ is 0.120 or less, especially 0.110 or less
Below, especially below 0.100. Note that both polarizers
If the thickness of the transparent protective layer is different on the side,
The above-mentioned xy chromaticity is obtained by the cross Nicol arrangement with the side inside.
Measured.

The polarizing plate according to the present invention can be preferably used for forming various devices such as a liquid crystal display device. The liquid crystal display device can be formed as a transmission type or reflection type in which polarizing plates are arranged on both sides of a liquid crystal cell, or a device having an appropriate structure according to the related art, such as a transmission / reflection type. Therefore, the liquid crystal cell forming the liquid crystal display device is arbitrary, and may be an appropriate type such as an active matrix driving type represented by a thin film transistor type, a simple matrix driving type represented by a twisted nematic type or a super twisted nematic type, and the like. A liquid crystal cell of a type may be used.

The polarizing plates provided on both sides of the liquid crystal cell may be the same or different.
Further, when forming a liquid crystal display device, one or more layers, which are appropriate components used for forming a liquid crystal display device, such as a retardation plate, a light-collecting sheet, a light diffusion plate, and a backlight, are arranged at appropriate positions. be able to.

[0018]

EXAMPLE 1 While continuously transporting a long polyvinyl alcohol film through a guide roll, the film was immersed in a dyeing bath containing iodine and potassium iodide to perform a dyeing treatment, and then boric acid and potassium iodide were removed. A cross-linking treatment and a stretching treatment of a total of 6 times were performed in the added acidic bath, followed by drying to obtain a polarizing film having a thickness of 40 μm, a light transmittance of 42%, and a degree of polarization of 99.3%. An adhesive consisting of an aqueous solution of polyvinyl alcohol was applied, and a 40 μm-thick triacetyl cellulose film whose adhesive surface was saponified with an aqueous solution of caustic soda was adhered to obtain a polarizing plate having a total thickness of 130 μm.

Comparative Example A polarizing plate was obtained in the same manner as in Example 1 except that the thickness of the triacetyl cellulose film was changed to 80 μm.

Evaluation Test The polarizing plates obtained in Examples and Comparative Examples were arranged in crossed Nicols, and perpendicular light or oblique incident light at an angle of 45 degrees with respect to the polarization axis and obliquely incident at an angle of 40 degrees with respect to the normal line was transmitted and transmitted. Spectrophotometer with integrating sphere for light (UV-2400, manufactured by Shimadzu Corporation)
The transmittance is measured at xy chromaticity x ₀ , y ₀ and x ₄₀ ,
Investigate y ₄₀ and find {x ₀ −x ₄₀ } and {y ₀ −y
₄₀ were asked to ┃.

The results are shown in the following table. _{x 0 y 0 x 40 y 40} ┃x 0 -x 40 ┃ ┃y 0 - y 40 ┃ Example 1 0.194 0.225 0.328 0.314 0.134 0.089 comparisons Example 0.099 0.155 0.342 0.329 0.243 0.174

Continued on the front page (72) Inventor Eiji Hamamoto 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Inside Nitto Denko Corporation (72) Inventor Tomomori Masada 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Within TEPCO (72) Inventor Kenji Nakahara 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA25 BA27 BB33 BB43 BB51 BC03 BC22 2H091 FA08X FA08Z GA16 LA15 LA20

Claims (1)

[Claims] 1. A polarizing film containing a dichroic substance, having a light transmittance of 40% or more and a degree of polarization of 99% or more, having transparent protective layers on both sides thereof, and arranging in a crossed Nicols to allow vertical light to enter. The xy chromaticity of the transmitted light in the case of being made is x ₀ , y ₀ , and x of the transmitted light in the case of the oblique incident light which is made to enter from the azimuth of 45 degrees to the polarization axis at an angle of 40 degrees to the normal line
When y chromaticity is x ₄₀ and y ₄₀ , {x ₀ −x ₄₀ }
<Polarizing plate, wherein the at 0.200, and is ┃y ₀ -y ₄₀ ┃ <0.130.