JP2000075135A - Light diffusion polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarizing plate which allows the formation of a liquid crystal display device making it possible to lower bulk in spite of omission of a light diffusion sheet and substantially preventing the generation of interference fringes in spite of control of the optical path via a condenser sheet, does not damage the device in site of the arrangement thereof on the condenser sheet and does give rise to a sticking problem. SOLUTION: This light diffusion polarizing plate has light diffusion layers 1 of a surface fine rugged structure formed in tight contact with the one or both surfaces of the polarizing plate 2 and has a cloud value of >=60%. The cloud value of the case the surface is smoothed by embedding the surface fine rugged structure described above by a transparent polymer is 40 to 60%. As a result, the display device of good visibility which is of a thin type and substantially prevents the generation of the interference fringes may be formed. The light diffusion layer preferably consists of a UV curing resin layer contg. particulates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing polarizing plate suitable for forming a thin liquid crystal display device with good visibility by preventing the occurrence of interference fringes by a light-collecting sheet.

[0002]

2. Description of the Related Art There is known a liquid crystal display device in which liquid crystal cells are sequentially disposed on a side light type light guide plate via a light condensing sheet, a light diffusion sheet, a polarizing plate or an elliptically polarizing plate. Such an arrangement structure controls the optical path of light emitted from the light guide plate by a single-layer or multilayer light-condensing sheet made of a prism sheet or the like, and the optical path control light interferes with the pixels of the liquid crystal cell to generate interference fringes such as moire. In this case, the light is diffused by a light diffusion sheet and introduced into a polarizing plate, and the object is to improve the viewing angle characteristics of a liquid crystal display device. However, in such a configuration, the number of stacked sheets and the like is large, and there is a problem that the display device is bulky due to the interposition of an adhesive layer for fixing the sheets and the like, and a reduction in thickness is required.

The present inventors believe that the method of reducing the thickness of a sheet or the like has a limit from the point of strength and the like, and cannot achieve the above-mentioned reduction in thickness. The antiglare polarizing plate to be arranged was arranged on the light source side of the liquid crystal cell, and an attempt was made to reduce the thickness essentially by omitting the light diffusion sheet on the condensing sheet.

However, it has been found that when such an anti-glare polarizing plate is arranged on a light-collecting sheet, there is a problem that the light-collecting sheet is damaged due to surface irregularities of the anti-glare polarizing plate. As described above, the light-collecting sheet is intended to control the optical path, and damage such as surface flaws becomes a scattering point and the like, which makes the optical path control impossible and is fatal. Simply preventing damage can be achieved by smoothing the surface of the anti-glare polarizing plate, but in that case, it causes problems such as insufficient diffusion ability and sticking due to close contact with the light-collecting sheet. Problems are also induced.

[0005]

According to the present invention, it is possible to form a liquid crystal display device which can reduce the bulk by omitting a light diffusing sheet and hardly cause interference fringes even when an optical path is controlled via a light condensing sheet. It is an object of the present invention to develop a polarizing plate that does not damage the light-collecting sheet even when it is arranged on the light-collecting sheet and does not cause sticking.

[0006]

According to the present invention, a light diffusion layer having a fine surface uneven structure is adhered to one or both surfaces of a polarizing plate, and the haze value is 6 or less.
The present invention provides a light-diffusing polarizing plate characterized by having a haze value of 40% to 60% when the surface fine unevenness structure is filled with a transparent polymer to make the surface smooth at 0% or more.

[0007]

According to the present invention, the light diffusion layer adhered to the polarizing plate shows the necessary diffusion effect of incident light such as light path control light by the light-collecting sheet without greatly changing the control light path by the light-collecting sheet. Therefore, the arrangement of a separate light diffusing sheet can be omitted by preventing the occurrence of interference fringes, and the adhesive layer can be omitted because it is in close contact with the polarizing plate, so that the bulk can be reduced. It is possible to form a display device that is difficult and has good visibility. Further, even if it is arranged on the light-collecting sheet, it is not damaged and the sticking problem does not occur in the fine uneven structure on the surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The light diffusing polarizing plate according to the present invention comprises a light diffusing layer having a fine surface irregularity structure adhered to one or both surfaces of the polarizing plate. Is embedded in a transparent polymer to make the surface smooth and has a haze value of 40 to 60%. Examples thereof are shown in FIGS. Reference numerals 1 and 3 are light diffusion layers, and 2 is a polarizing plate.

Any suitable polarizing plate can be used as a supporting base of the light diffusion layer, and the type thereof is not particularly limited. By the way, for example, hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, ethylene-vinyl acetate copolymer-based partially saponified films, and dichroic dyes such as iodine and dichroic dyes Stretched by adsorbing substances,
Examples of the polarizing film include dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride. The thickness of the polarizing film is generally 5 to 80 μm,
It is not limited to this.

Further, as shown in FIG.
A transparent protective layer 2 comprising a polymer coating layer or a film laminating layer on one or both sides for the purpose of protection such as water resistance.
There are also those provided with 1, 23 and the like. For forming the transparent protective layer, an appropriate material such as a transparent polymer can be used, but a material having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like can be preferably used. In many cases, the transparent protective layer is preferably as small as possible in optical anisotropy such as retardation. The thickness of the transparent protective layer is generally from 10 to 300 μm, but is not limited thereto.

The polymer forming the transparent protective layer is, for example, a polyester polymer such as polyethylene terephthalate or polyethylene naphthalate, a cellulose polymer such as cellulose diacetate or cellulose triacetate, a polycarbonate polymer or a PMM.
Examples include acrylic polymers such as A, and styrene polymers such as polystyrene and acrylonitrile / styrene copolymer (AS resin).

Further, olefin polymers such as polyethylene and polypropylene, polyolefins having a cyclo or norbornene structure, and ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, and the like. Sulfone polymer, polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer And a blend of the above-mentioned polymers are also examples of the polymer forming the transparent protective layer.

The light diffusing polarizing plate according to the present invention has a light diffusing layer having a fine surface uneven structure adhered to one side or both sides of the polarizing plate, and has a light transmitting side when perpendicular light is incident on its reference plane. The haze value is 60% or more, and the haze value is 40 to 60% when the surface fine unevenness structure is filled with a transparent polymer to smooth the surface.

If the haze value is less than 60%, the diffusion effect is poor, and it is difficult to prevent the occurrence of interference fringes when light path control light is incident on the light-collecting sheet. Therefore, the light diffusion layer in the present invention is required to have a diffusion characteristic that maintains the directivity as much as possible without the light path control light from the light-collecting sheet being diffused at a large angle, and effectively prevents the generation of interference fringes. Is done. From this point, the haze value is preferably 65% or more, especially 70% or more, particularly 75% or more.

On the other hand, if the haze value is less than 40% when the latter surface is smoothed, it is difficult to prevent the optical layers, such as the light-condensing sheet, which are superposed, from being damaged. The haze value when the surface is smoothed is preferable from the viewpoint of prevention of damage and the like.
0% or more, especially 55% or more. The haze value is
In the incident light perpendicular to the reference plane, the ratio of the transmitted light of the polarizing plate to the incident light is Tt (total light transmittance), the ratio of the light parallel to the incident light in the transmitted light is Tp (parallel light transmittance), The ratio is Td (diffuse light transmittance = Tt−T)
p) is defined as Td / Tt.

In the above, it is assumed that a degree of polarization of 80% or more, especially 85% or more, especially 90% or more based on a polarizing plate is achieved, rather than achieving a bright display in a liquid crystal display device or the like. It is preferable that the light-diffusing polarizing plate exhibit as high a light transmittance as possible. In particular, it is preferable that the transmittance of light incident perpendicular to the reference plane be 35% or more, particularly 40% or more.

The above-mentioned reference plane is assumed based on the entire light-diffusing polarizing plate in which the uneven structure on the surface of the light-diffusing layer and the variation in the layer thickness are leveled, as exemplified by the imaginary line H in FIG. Means the plane to be set.

The light-diffusing layer for imparting the above-mentioned diffusion properties such as haze value may be provided on one side of a polarizing plate for the purpose of eliminating the necessity of providing a separately arranged light-diffusing sheet as described above and achieving a thin thickness. It is provided in close contact with both surfaces, and it may be formed into a structure having fine irregularities on the surface by an appropriate method.

Examples thereof include a resin layer containing fine particles having a difference in refractive index dispersed therein, a resin layer having a fine unevenness formed on the surface by roughening treatment by an appropriate method such as sand blasting, embossing roll, or chemical etching. Craze generated by application of mechanical stress or solvent treatment, etc.
Examples thereof include those in which a fine uneven structure is provided on the surface by a transfer method using a mold or the like.

Therefore, the light diffusion layer provided in close contact is, for example, as shown in FIG.
As described in Example 1 above, an additional layer composed of a coating layer or the like of the resin layer on the transparent protective layer 21 of the polarizing plate 2 or a fine uneven structure is provided on the surface of the polymer layer applied to the transparent protective layer. It can be formed as a processed layer obtained by applying a fine uneven structure or the like to the surface of a transparent protective layer, or a layer provided with a polymer coating layer on the processed layer.

Further, like the light diffusion layer 3 illustrated in FIG. 2, the light diffusion layer can be formed as a light diffusion layer instead of the transparent protective layer or also serving as the transparent protective layer. In this case, a light diffusion film may be bonded in advance to a polarizing film or the like via an adhesive layer. The light diffusion layer may be formed as a layer in which two or more of the above-described states are combined.

The method of forming the light diffusion layer, which is preferable from the viewpoints of the above-described properties of imparting the diffusion characteristics, easy attachment and thin film processing, is a method using the resin layer, that is, for example, a method in which fine particles are dispersed and contained in a resin solution. This is a method in which an appropriate method such as a doctor blade method or a gravure roll coater method is applied on a polarizing plate to form a coating film.

The resin layer to be formed may have a fine uneven structure on the surface based on the fine particles contained therein,
The polarizing plate to be coated may have a fine uneven structure on the surface in a state where the surface unevenness is reflected on the resin layer surface, or may have a fine uneven structure on the surface in a state where they are combined. Is also good.

As the resin forming the resin layer, an appropriate resin such as the polymer exemplified in the above-mentioned transparent protective layer can be used, but an ultraviolet curable resin is preferably used. According to this, a light diffusion layer composed of an ultraviolet-curable resin layer containing fine particles can be efficiently formed by a simple processing operation by a curing treatment of the coating layer by irradiation with ultraviolet light.
It is also easy to form an ultraviolet-curable resin layer on the surface of the roughened transparent protective layer and reflect the surface irregularities of the transparent protective layer on the surface.

Examples of the UV-curable resin include polyester-based, acrylic-based, urethane-based and amide-based resins.
An appropriate compound such as a compound obtained by compounding an ultraviolet polymerization initiator with a monomer, oligomer, or polymer capable of forming a resin such as a silicone-based or epoxy-based resin and forming a resin layer by a curing treatment by ultraviolet irradiation is used. sell.

The UV-curable resin which can be preferably used is, for example, an acrylic monomer or oligomer having 3 to 6 UV-polymerizable functional groups as a component, such as adhesion and transparency to the polarizing plate surface to be provided. In the case where fine particles are contained, hard coat properties and fine particles are excellent in dispersibility.

Examples of the fine particles include inorganic particles which may be conductive, such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, and antimony oxide, and polymethyl methacrylate (PMMA). ) Or crosslinked or uncrosslinked organic particles made of various polymers such as polyurethane.

The fine particles which can be preferably used are those which have excellent transparency and do not dissolve in a UV-curable resin before forming a cured film. The fine particles that can be preferably used from the viewpoint of the above-mentioned diffusion characteristics such as formability and dispersibility have an average particle size of 3%.
0 μm or less, especially 0.1 to 15 μm, especially 0.5 to 10 μm
m spherical particles, especially organic spherical particles.

The thickness of the light diffusion layer can be determined as appropriate.
In general, the average diameter of the particles used is 100 μm, particularly 50 μm or less, and particularly 30 μm or less from the viewpoint of achieving the above-mentioned diffusion characteristics and reducing the thickness.

As shown in FIG. 2, the light diffusion polarizing plate may be provided with an adhesive layer 4 on one side or both sides as needed. The purpose of such an adhesive layer is to adhere the light diffusion polarizing plate to another member such as a liquid crystal cell or a light condensing sheet. The adhesive layer can be formed with an appropriate adhesive such as an acrylic-based, rubber-based, or silicone-based adhesive or a hot-melt-based adhesive, and preferably has excellent transparency and weather resistance.

The light-diffusing polarizing plate according to the present invention can be used for various conventional applications such as display devices. In particular, as in a liquid crystal display device, pixels are arranged at predetermined intervals, and interference fringes such as moiré are easily generated by light path control light or the like through a light-collecting sheet. Therefore, it can be preferably used for a display device in which an increase in thickness is not desirable.

[0032]

EXAMPLE 1 UV curable acrylic monomer 1 having a refractive index of 1.52
A UV-curable resin composed of 00 parts (parts by weight, hereinafter the same) and 3 parts of a benzophenone-based photopolymerization initiator has a refractive index of 1.
In step 49, 20 parts of resin particles having an average particle diameter of 10 μm were added, and the solid content concentration was adjusted to 50% by weight by adding a viscosity adjusting solvent, followed by mixing with a high-speed stirrer. A 50 μm-thick triacetylcellulose film is adhered to both sides of the film via a polyvinyl alcohol-based adhesive layer. One side of the polarizing plate is coated, the solvent is volatilized, and the film is cured by irradiating ultraviolet rays to a thickness of 10 μm.
A light diffusion layer having a fine uneven surface structure was formed at a thickness of μm to obtain a light diffusion polarizing plate.

When vertical light was made incident on the light diffusing polarizing plate, the total light transmittance was 42%, and the haze value on the light transmitting side was 81%. The cloudiness was 69% when the fine irregularities on the surface were filled with an acrylic resin to make it smooth.
In addition, the light-diffusing polarizing plate is disposed on a sidelight-type light guide plate via two light-condensing sheets made of a prism sheet, and a liquid crystal cell and a polarizing plate are disposed thereon. When a liquid crystal color display panel was formed, it was possible to obtain a panel excellent in the clarity and brightness of the screen and thinner than the conventional panel. Also, no damage occurred to the light-collecting sheet.

Comparative Example 1 A light-diffusing polarizing plate was obtained by forming a light-diffusing layer having a fine surface irregularity structure in the same manner as in Example 1 except that the amount of resin particles used was changed to 10 parts. When perpendicular light was incident on this polarizing plate, the total light transmittance was 42%, the haze value on the light transmission side was 53%, and the haze when the fine irregularities on the surface were filled with acrylic resin to make it smooth. The value was 44%. When a liquid crystal color display panel without a light diffusing sheet was formed using the light diffusing polarizing plate according to Example 1, the light collecting sheet was not damaged, but the sharpness of the screen was inferior and it was difficult to see. .

Comparative Example 2 A light diffusion layer having a thickness of 3 μm and a surface irregular structure was formed in the same manner as in Example 1 except that the used amount of the resin particles was 10 parts and the solid content concentration was 20% by weight. I got a board. When perpendicular light was made incident on this light diffusing polarizing plate, the total light transmittance was 43%, the haze value on the light transmitting side was 70%, and the unevenness on the surface was filled with an acrylic resin to make it smooth. Haze value is 12
%Met. However, using the light diffusing polarizing plate, Example 1
When a liquid crystal color display panel omitting the light diffusion sheet was formed according to the method described above, the sharpness of the screen was good, but the light-collecting sheet was damaged.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is a cross-sectional view of another embodiment.

[Explanation of symbols]

 1,3: light diffusion layer 2: polarizing plate 21, 23: transparent protective layer 22: polarizing film 4: adhesive layer

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor: Masami Masada 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H042 AA04 AA26 BA02 BA03 BA20 2H049 BA13 BA25 BA26 BB16 BB63 BC22 2H091 FA08X FA08Z FA31X FA31Z FB02 FB04 FB12 FB13 FC14 FC23 FC25 GA16 LA02 LA06 LA11 LA16 LA21 4F100 AJ06 AK01D AK01E AK21 AK21G AK25 AR00A AR00B AR00C BA05 BA06 BA07 BA10D BA10E DE01B DE01C EJ54 EJ542 GB41 JB14B JB14C JK14B JK14C JK15D JK15E JN01D JN01E JN02B JN02C JN02D JN02E JN10 JN10A JN30 JN30B JN30C YY00B YY00C YY00D YY00E

Claims (2)

[Claims] 1. A light diffusing layer having a fine surface unevenness structure is adhered to one or both surfaces of a polarizing plate, and has a haze value of 60% or more. The surface fine unevenness structure is filled with a transparent polymer to smooth the surface. Wherein the haze value is 40 to 60%. 2. The light-diffusing polarizing plate according to claim 1, wherein the light-diffusing layer comprises an ultraviolet-curable resin layer containing fine particles.