JPH11326611A - Light diffusion layer, optical element, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light diffusion plate, optical element, and liquid crystal display device which has superior preventablilty against glares and dizziness performance, while maintaining a preventing function against ghost. SOLUTION: This light diffusion layer has on one surface a fine uneven structure 11, having a surface roughness such that a 60 deg. mirror surface luster is 10 to 70%, the center line mean roughness is 0.1 to 0.35 μm, and a mean top to bottom interval is 18 to 60 μm, the optical element has a light diffusion layer 1 on one or both the surfaces of an optical layer, and the liquid crystal display device has a light diffusion layer on the viewing side of a liquid crystal display element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing layer and an optical element which can form a liquid crystal display device which is excellent in ghost and glare prevention and non-glare and has good visibility.

[0002]

2. Description of the Related Art In a display device such as a liquid crystal display device, a light diffusion layer is generally provided on the surface thereof. Such a light diffusion layer functions as a non-glare (anti-glare) layer that diffuses surface reflected light, and the ghost phenomenon that external light such as illumination light such as a fluorescent lamp or sunlight or a keyboard is reflected on a screen is displayed. The purpose is to prevent the obstruction. Conventionally,
As the light diffusing layer, a layer in which a fine uneven structure is provided on the surface by a roughening method such as sandblasting or mixing of transparent particles has been known.

However, with the miniaturization of pixels due to the high definition and colorization of display devices, especially liquid crystal display devices, glare in which strong display light portions are randomly generated and display light distortion become remarkable. The problem that visibility deteriorates remarkably has come to arise.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop a light diffusion layer, an optical element and a liquid crystal display device which are excellent in glare prevention and anti-glare properties while maintaining a ghost prevention function.

[0005]

According to the present invention, a 60-degree specular gloss is 10
~ 70%, and the center line average roughness is 0.1 ~ 0.35μ
m, a light diffusion layer comprising a UV-curable resin film having a fine uneven structure having a surface roughness of 18 to 60 μm on average on one surface, and the light diffusion layer on one or both surfaces of the optical layer. And a liquid crystal display device having the light diffusion layer on the viewing side of the liquid crystal display element.

[0006]

According to the present invention, it is possible to obtain a light diffusion layer and an optical element having excellent anti-glare properties as well as preventing ghosting in a liquid crystal display device and the like, and to provide a display device having excellent visibility. Can be formed. Although the reason is unknown, the present inventors believe that the distortion of display light is suppressed by the above-mentioned specular glossiness and surface roughness characteristics.

That is, the glare problem and the like caused by the above-mentioned conventional light diffusion layer is caused by the fact that the pitch of the pixel becomes more compatible with the uneven structure of the light diffusion layer due to the miniaturization of the pixel, and the display light passing through the pixel becomes uneven. The structure is susceptible to distortion such as refraction and diffusion, and the distortion significantly reduces the sharpness of the displayed image,
It is considered that the intensity difference of the display light becomes large and a strong display light portion is generated at random, thereby causing a glare phenomenon.

On the other hand, in the light diffusion layer according to the present invention,
Based on the surface characteristics and the structural characteristics of the fine irregularities, the display light transmitted through the pixel is unlikely to be distorted, so that the above-described good optical characteristics are expected to be obtained. The mechanism of the structural characteristics and the distortion of the display light is unknown.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The light diffusing layer according to the present invention has a 60 ° specular gloss of 10 to 70% and a center line average roughness of 0.5%.
It is made of an ultraviolet-curable resin film having a fine uneven structure on one side having a surface roughness of 1 to 0.35 μm and an average peak-to-valley interval of 18 to 60 μm.

FIGS. 1 and 2 show examples of the light diffusion layer. 1 is a light diffusion layer made of an ultraviolet curable resin film, 11 and 12 are fine irregularities, 2 is a transparent substrate, and 3 is an adhesive layer as required. As shown in the figure, the light diffusion layer 1 may be composed of a single layer of an ultraviolet curable resin film, or may be composed of a light diffusion sheet in which the ultraviolet curable resin film is supported on one or both surfaces of a transparent substrate 2. Is also good.

The UV-curable resin for forming the resin film includes, for example, a monomer, oligomer or polymer capable of forming a resin such as polyester, acrylic, urethane, amide, silicone or epoxy, and an ultraviolet polymerization initiator. And an appropriate material such as a resin film formed by curing treatment by ultraviolet irradiation.

The UV-curable resin which can be preferably used is, for example, one having an acrylic monomer or oligomer having 3 to 6 UV-polymerizable functional groups as a component, such as adhesion to an object to be provided, transparency, and hard coat property. And when transparent particles are contained, they are excellent in dispersibility and the like.

The light diffusion layer according to the present invention has a 60 ° specular gloss of 10-70% and a center line average roughness of 0.1-0. 3
A fine uneven structure having a surface roughness of 5 μm and an average peak-to-valley interval of 18 to 60 μm is provided. If the 60-degree specular gloss, the center line average roughness, and the average peak-to-valley interval are out of the above-mentioned ranges, the antiglare property is poor, and the visibility is likely to deteriorate.

The formation of the UV-curable resin film having the fine uneven structure on one side is carried out by, for example, dispersing and containing transparent particles having a different refractive index in the UV-curable resin and subjecting it to a doctor blade method or a gravure roll coater method. Coating on a predetermined surface by an appropriate method, and curing the applied layer through ultraviolet irradiation to form a fine uneven structure reflecting the unevenness of the transparent particles, or sand blasting or embossing roll on the surface of the transparent substrate Roughening by an appropriate method such as etching, coating and forming an ultraviolet curable resin film on the roughened surface, and forming a fine uneven structure by reflecting the unevenness of the roughened surface on the film surface. Can be performed by an appropriate method.

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

The transparent particles which can be preferably used are those which are excellent in transparency and do not dissolve in a UV-curable resin before forming a cured film. The transparent particles that can be preferably used from the viewpoint of the formation of the surface roughness characteristics described above have an average particle diameter of 30.
μm or less, especially 0.1 to 15 μm, especially 0.5 to 10 μm
belongs to.

On the other hand, as the transparent substrate for supporting the light diffusion layer composed of the above-mentioned ultraviolet curable resin film, for example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, and cellulose polymers such as cellulose diacetate and cellulose triacetate are used. And films made of transparent polymers such as polycarbonate polymers and acrylic polymers such as PMMA.

Styrene polymers such as polystyrene and acrylonitrile-styrene copolymer (AS resin); polyethylene and polypropylene; polyolefins having cyclo or norbornene structure; olefin polymers such as ethylene / propylene copolymer; vinyl chloride Films made of transparent polymers such as polymers and amide polymers such as nylon and aromatic polyamide are also included.

Further, imide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, A film made of a transparent polymer such as an oxymethylene-based polymer, an epoxy-based polymer, or a blend of the above polymers is also used.

In particular, it is composed of a polymer having excellent transparency,
A film having a phase difference as small as possible due to birefringence is preferably used. The thickness of the transparent substrate can be determined as appropriate, but is generally from 10 to 500 μm, preferably from 30 to 300 μm, especially from 5 to 5 from the viewpoint of workability such as strength and handleability and thinness.
The thickness is 0 to 200 μm.

The preferable 60-degree specular gloss in the light diffusion layer is from 15 to 65%, especially from 20 to 60%, especially from 25 to 5 in view of the ability to form a clear image by preventing glare and the like.
5%. Further, the center line average roughness more preferable than the above points is 0.33 μm or less, especially 0.12 to 0.30 μm,
Particularly, it is 0.15 to 2.5 μm, and the average interval between peaks and valleys is 2
It is at least 0 μm, especially 25 to 55 μm, especially 30 to 50 μm. It is preferable that the peak-to-valley interval is as constant as possible.

The thickness of the light diffusion layer can be determined as appropriate.
In general, from the viewpoint of the formability of the fine uneven structure having the above-described characteristics, 50 μm or less, particularly 1 to 30 μm, particularly 3 to 10 μm
m. As shown in FIG. 2, the purpose of the adhesive layer 3 provided as needed is to adhere to another member such as an optical layer. The adhesive layer can be formed of an appropriate adhesive such as an acrylic, rubber, or silicone adhesive or a hot-melt adhesive, and preferably has excellent transparency and weather resistance.

The light diffusion layer according to the present invention can be used for various purposes in accordance with the prior art. In particular, it can be preferably used for a display device having pixels arranged at predetermined intervals, such as a liquid crystal display device. Upon application, the optical element can be used as an optical element having a light diffusion layer provided on one or both sides of the optical layer.

FIGS. 3 and 4 show examples of the optical element according to the present invention. Reference numeral 4 denotes a polarizing plate, reference numeral 5 denotes a retardation plate, and reference numeral 6 denotes an elliptically polarizing plate comprising a laminate of the polarizing plate 4 and the retardation plate 5.
Therefore, the optical layer may be a suitable one such as a polarizing plate, a retardation plate, or an elliptically polarizing plate made of a laminate thereof.

An appropriate polarizing plate can be used as the above-mentioned polarizing plate.
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 Examples of the polarizing film include a film obtained by adsorbing a substance and stretching, a dehydration product of polyvinyl alcohol, and a dehydrochlorination product of polyvinyl chloride. The thickness of the polarizing film is generally from 5 to 80 μm, but is not limited thereto.

Further, there may be mentioned a polarizing film in which a transparent protective layer composed of a polymer coating layer, a film laminating layer or the like is provided on one or both sides of the polarizing film for the purpose of protecting water resistance or the like. For the formation of the transparent protective layer, an appropriate material such as the above-mentioned transparent base material such as a polymer can be used, but a material having excellent transparency, mechanical strength, heat stability, moisture shielding property, and the like can be preferably used.

On the other hand, an appropriate retardation plate can be used. Incidentally, examples thereof include a stretched film and a liquid crystal polymer film by an appropriate method such as uniaxial or biaxial of the polymer film exemplified by the transparent substrate. The retardation plate may be formed as a superimposed body of two or more stretched films.

The elliptically polarizing plate can be formed by laminating a polarizing plate and a retardation plate. In this case, it is preferable that the light diffusion layer is provided at least on the polarizing plate side from the viewpoint of practicality and the like. It is preferable that the polarizing plate and the retardation plate in the elliptically polarizing plate are bonded and laminated via the above-described bonding layer from the viewpoint of stability of optical characteristics due to prevention of displacement and the like.

The light diffusing layer in the optical element may be provided directly on the optical layer 4 as shown in FIG. 3 or as a light diffusing sheet integrated with the transparent substrate 2 as shown in FIG. It may be. Also in the case of the light diffusion sheet, it is preferable that the light diffusion sheet is adhesively laminated with the optical layer via the above-mentioned adhesive layer from the viewpoint of stability of optical characteristics due to prevention of displacement and the like.

As described above, the light diffusion layer and the optical element according to the present invention can be used for a display device in which the distortion of display light through a pixel becomes a problem, especially for a liquid crystal display device in a personal computer such as a notebook type or a desktop type. And the like. In particular, like TFT type and STN type liquid crystal display devices,
Pixels as display units are light-shielding parts (black matrix)
It can be preferably used for a liquid crystal display or the like, which is formed at a predetermined pitch while being divided at equal intervals, and has a pixel pitch of, for example, 50 to 500 μm.

In the above description, the light diffusing layer and the optical element are provided on the viewing side of the liquid crystal display device. In this case, the light diffusing layer should be as large as possible on the outermost surface of the device in terms of preventing glare and non-glare action. It is preferred to be located on the outer surface. The liquid crystal display device is not particularly limited except that at least one light diffusion layer or optical element according to the present invention is arranged, and can be formed as a conventional one.

[0032]

EXAMPLE 1 An ultraviolet-curable resin comprising 100 parts (parts by weight, hereinafter the same) of an ultraviolet-curable urethane acrylate monomer and 3 parts of a benzophenone-based photopolymerization initiator was added with an average particle diameter of 1.4 μm.
Of silica particles was added to the mixture, and the solid content was adjusted to 50% by weight by adding a solvent for adjusting the viscosity, followed by mixing with a high-speed stirrer. After coating and volatilization of the solvent, the coating was cured by irradiating ultraviolet rays to obtain a light diffusion sheet having a light diffusion layer having a thickness of 7 μm.

The light-diffusing layer has a light-diffusing property of 9%, a 60-degree specular gloss of 44%, and a center line average roughness (based on a stylus-type surface roughness measuring instrument) in a fine uneven structure. The same shall apply hereinafter) was 0.16 μm, and the average peak-to-valley interval (the same applies hereinafter) according to the surface roughness curve was 39 μm.

Comparative Example A light diffusion sheet having a light diffusion layer having a thickness of 7 μm was obtained in the same manner as in Example 1 except that three parts of silica particles having an average particle diameter of 2.5 μm were used. The light-diffusing layer exhibits a light-diffusing property of 9%, a 60-degree specular gloss of 86%, an average center line roughness of 0.42 μm in the fine uneven structure, and an average peak-to-valley interval of 12%.
It was 0 μm.

Evaluation Test Strain The light diffusion sheets obtained in Examples and Comparative Examples were placed on a transparent glass plate drawn in a straight line, illuminated from the glass plate side, and observed when viewed from the light diffusion sheet side. The curve due to the straight line distortion was defined as a valley curve, and the variation in the distance between the valley center line and the valley peak was examined, and the degree of the variation was evaluated as the skewness via the light diffusion sheet. As a result, it was 2.8 μm in Example 1, but 3.7 μm in Comparative Example.

Clarity of Image The light diffusion sheet obtained in each of the examples and comparative examples was applied to a liquid crystal display element (size 12.1 inches, resolution XG) for a notebook personal computer.
A) The display image was visually recognized by being installed on top of (A). In that case, in the liquid crystal display device using the light diffusion sheet of Example 1, a very clear display image was obtained and glare was small. However, in the liquid crystal display device using the light diffusion sheet of the comparative example,
The display image was inferior in sharpness, and many glare occurred.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a light diffusion layer.

FIG. 2 is a cross-sectional view of another example of a light diffusion layer.

FIG. 3 is a cross-sectional view of an example of an optical element.

FIG. 4 is a cross-sectional view of another example of an optical element.

[Explanation of symbols]

 1: light diffusion layer composed of an ultraviolet curable resin film 11, 12: fine uneven structure 2: transparent base material 4: polarizing plate 5: retardation plate 6: elliptically polarizing plate

Claims (6)

[Claims] 1. A fine uneven structure having a surface roughness of 60-degree mirror glossiness of 10 to 70%, a center line average roughness of 0.1 to 0.35 μm, and an average peak-to-valley interval of 18 to 60 μm. A light diffusion layer comprising an ultraviolet-curable resin film as described above. 2. The method according to claim 1, wherein the 60-degree specular gloss is 20 to 70%, and the center line average roughness is 0.15 to 0.5.
A light diffusion layer having a fine uneven structure with a surface roughness of 35 μm and an average peak-to-valley interval of 30 to 60 μm. 3. The light diffusion layer according to claim 1, wherein the light diffusion layer is supported on one or both surfaces of the transparent substrate. 4. An optical element comprising the optical diffusion layer according to claim 1 on one or both sides of the optical layer. 5. The optical element according to claim 4, wherein the optical layer is a polarizing plate, a retardation plate, or an elliptically polarizing plate made of a laminate thereof. 6. A liquid crystal display device comprising the light diffusion layer according to claim 1 on the viewing side of a liquid crystal display element.