JP2000056104A - Light diffusing layer, optical device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusing layer, an optical device and a liquid crystal display device having excellent glare preventing property and antidazzle property while maintaining a function to prevent ghost. SOLUTION: A light diffusing layer 1 comprised an ultraviolet curing resin film 1 of a finely projected and recessed surface structure 11, the film contains particles having 1-2 μm average particle diameter and a thixotrophy agent and the finely projected and recessed surface structure is formed based on the contained particles. An optical device is provided with the light diffusing layer on one or both surfaces of its optical layer and a liquid crystal display device is provided with the light diffusing layer on a viewing side of its liquid crystal 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 for diffusing surface reflected light, and provides visibility due to a ghost phenomenon in which external light such as illumination light such as a fluorescent lamp or sunlight or a keyboard is reflected on a screen. 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 high definition and colorization of display devices, especially liquid crystal display devices of the dot matrix display type, glare at which random intensity is generated in display light becomes remarkable, and visibility becomes high. Was significantly reduced.

[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, there is provided an ultraviolet-curable resin film having a fine irregular surface structure, wherein the film has an average particle size of 1 to 2 μm.
a light-diffusing layer, characterized in that the light-diffusing layer contains the particles of m and a thixotropy agent and forms the above-mentioned surface fine uneven structure based on the contained particles, and that the light-diffusing layer is provided on one or both sides 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. The details of the reason are unknown, but the present inventors believe that the distortion of display light is suppressed due to the distribution characteristics of the surface fine uneven structure of the particles based on the inclusion of the thixotropy agent. I have.

That is, the glare problem caused by the above-mentioned conventional light diffusion layer is caused by the fact that the pitch of the pixel becomes smaller and the correspondence with the surface unevenness structure of the light diffusion layer becomes higher due to the miniaturization of the pixel. The unevenness of the surface makes it more susceptible to distortions such as refraction and diffusion, and the distortions cause random differences in the intensity of the display light from the pixels that have been partitioned by the black matrix and turned into parallel light, causing a glare phenomenon. Conceivable.

On the other hand, in the light diffusion layer according to the present invention,
The sedimentation of the particles is prevented by the inclusion of the thixotropic agent, and a large number of particles are present on the surface of the UV-curable resin film, and a high-density particle structure can be formed on the surface that is impossible with the conventional forming method. Based on the fine uneven structure where the particles are distributed at high density on the surface, the display light from the pixels parallelized in the partition by the black matrix, the sufficiently small surface fine uneven structure is formed for each pixel, It is considered that distortion of display light is prevented, glare is suppressed, and good visibility is achieved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The light diffusing layer according to the present invention comprises an ultraviolet-curable resin film having a finely uneven surface structure, and the film contains particles having an average particle size of 1 to 2 μm and a thixotropic agent. To form a surface fine uneven structure. Examples thereof are shown in FIGS. 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 FIG. 1, the light diffusion layer 1 may be formed as an independent layer such as a sheet made of an ultraviolet-curable resin film itself, or may be formed on one or both surfaces thereof via a transparent substrate 2. 1 may be made of a light diffusion sheet in a form supporting the light diffusion sheet. Further, according to the latter, it may be formed as a subordinate layer attached to a supporting base.

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 excellent dispersibility of the blended particles.

The formation of the UV-curable resin film having a fine surface irregularity structure is carried out, for example, by dispersing transparent particles having a different refractive index and a thixotropy agent into the UV-curable resin and subjecting the dispersion to an appropriate method such as a doctor blade method or a gravure roll coater method. It can be performed by a method of applying a coating on a predetermined surface by a suitable method, curing the applied layer through ultraviolet irradiation, and forming a fine uneven structure in which unevenness due to transparent particles is reflected on the surface. In addition, the above-mentioned surface fine uneven structure is obtained by roughening the surface of a supporting base such as a transparent base material by an appropriate method such as sandblasting, embossing roll, etching, or the like, and coating and forming an ultraviolet-curable resin film on the roughened surface. The surface of the coating may also reflect the irregularities of the roughened surface, and may be combined with the irregularities of the particles to reflect the fine irregularities on the surface.

Examples of the particles to be contained in the ultraviolet curable resin film include inorganic particles which may be conductive, such as silica, alumina, titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, and antimony oxide; One or more kinds of appropriate ones such as crosslinked or uncrosslinked organic particles made of various polymers such as methyl methacrylate (PMMA) and polyurethane can be used. The particles that can be preferably used are those that have excellent transparency and do not dissolve in the ultraviolet-curable resin before forming a cured film.

The particles used have an average particle size of 1 to 2 μm. As a result, it is possible to achieve a fine surface unevenness structure that is sufficiently small with respect to display light from pixels.

In forming the ultraviolet-curable resin film, a thixotropic agent is used together with the particles.
Thereby, it is possible to suppress the sedimentation of the contained particles until the coating layer is cured by ultraviolet rays, a large number of particles remain on the surface portion, are distributed at a high density, are excellent in fineness, and are small pixels. Can form a sufficiently small uneven structure for the display light.

Accordingly, as the thixotropic agent, any suitable thixotropic agent which can suppress the sedimentation of the contained particles by thickening the coating solution or the like can be used, and any known thixotropic agent can be used. Incidentally, examples thereof include aerosil, layered organic clay, polyacrylic acid and ethyl cellulose.

The light diffusing layer, which is preferable from the viewpoint of improving the sharpness of an image by preventing glare, has a UV-curable resin film having a center line average roughness of 0.07 to 0.5 μm, particularly 0.08
~ 0.4μm, average peak-to-valley spacing 20 ~ 80μm, especially 25 ~
It has a surface micro unevenness structure with a surface roughness of 70 μm,
It shows a light diffusion of 3% or more, especially 5% or more, based on haze inside the film, and 10-80%, especially 20-
It shows a 60% specular gloss of 75%. Preferably, the peak-to-valley interval is as constant as possible.

The amount of the particles used can be appropriately determined according to the light diffusivity and surface roughness, etc., but is generally 1 to 100 parts by weight, preferably 2 to 100 parts by weight, per 100 parts by weight of the ultraviolet curable resin.
To 70 parts by weight, especially 3 to 50 parts by weight.

The amount of the thixotropic agent to be used can be appropriately determined depending on the effect of preventing sedimentation of the particles and the like, but is generally 50 parts by weight or less per 100 parts by weight of the ultraviolet curable resin.
Especially 0.1 to 30 parts by weight, especially 0.5 to 10 parts by weight.

Further, the thickness of the light diffusion layer can be determined as appropriate. However, in general, from the viewpoint of the formability of the light diffusion layer having the above-described characteristics, the thickness is preferably 50 μm or less, and ３０30 μm, especially 3 to 10 μm.

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

Styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymer (AS resin), polyethylene and polypropylene, olefin-based polymers such as polyolefin having a cyclo- or norbornene structure and ethylene-propylene copolymer, and vinyl chloride-based polymers 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.

As shown in FIG. 2, the adhesive layer 3 provided as needed has the purpose of adhering to another member such as an optical layer. A material which can be formed with an appropriate adhesive such as a melt-based adhesive and has excellent transparency and weather resistance is preferable.

The light diffusion layer according to the present invention can be used for various purposes according to the prior art. In particular, it can be preferably used for a display device in which pixels are arranged at predetermined intervals, such as a liquid crystal display device of a dot matrix display type. Upon its application,
It can also 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.
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 such as a polymer coating layer or a film laminating layer 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 diffusion layer in the optical element may be provided directly on the optical layer 4 as shown in FIG. 3 or as a light diffusion 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 display light distortion due to pixels is 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 is preferably used for a liquid crystal display device of a dot matrix display type in which the pixel pitch is, 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.

[0036]

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.
5 parts of silica particles and 2 parts of a thixotropic agent were added, the solid content was adjusted to 50% by weight by adding a solvent, and then mixed with a high-speed stirrer. The mixed solution was applied to one surface of a 50 μm-thick triacetyl cellulose film. After coating with a bar coater and evaporating the solvent, the film was cured by irradiating ultraviolet rays to obtain a light diffusion sheet having a light diffusion layer composed of a 7 μm-thick ultraviolet-curable resin film having a fine surface unevenness structure.

The light diffusion layer has a center line average roughness (hereinafter the same applies) of 0.10 μm based on a stylus type surface roughness measuring device in a fine uneven structure on the surface, and an average peak-to-valley interval (hereinafter referred to as an average) based on a surface roughness curve. Same) was 47 μm, had a 60 ° specular gloss of 67%, and exhibited a light diffusion of 6% based on haze inside the film.

Comparative Example 1 A light diffusing sheet having a light diffusing layer was obtained in the same manner as in Example 1 except that the thixotropic agent was not used. The light diffusion layer,
Center line average roughness 0.07μm, average peak-to-valley interval 80μm, 6
It had a 0-degree specular gloss of 82% and a light diffusing property of 8% inside the film.

Comparative Example 2 A light diffusing sheet having a light diffusing layer was obtained in the same manner as in Example 1 except that three parts of silica particles having an average particle size of 2.5 μm were used and no thixotropic agent was used. The light diffusion layer has a center line average roughness of 0.42 μm and an average peak-to-valley interval of 120 μm.
μm, 60 degree specular gloss 86%, light diffusion inside the film 9
%.

Evaluation Test The light diffusion sheets obtained in Example 1 and Comparative Examples 1 and 2 were placed on a liquid crystal display element (size 12.1 inches, resolution XGA) for a notebook personal computer, and the displayed image was visually observed. . In that case, in the liquid crystal display device using the light diffusion sheet of Example 1, a very clear display image with little glare was obtained, but in Comparative Examples 1 and 2, the degree of the glare was large and the display image was clear. It was inferior.

[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 diffusing layer composed of an ultraviolet curable resin film 11, 12: fine uneven structure surface 2: transparent substrate 4: polarizing plate 5: retardation plate 6: elliptically polarizing plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Masami Masada 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H042 BA02 BA03 BA15 BA20 2H049 BA02 BA04 BA06 BA26 BA27 BB22 BB43 BB50 BB62 BB63 BC21 2H091 FA08X FA08Z FA11X FA11Z FA31X FA31Z FB04 FB12 FB13 FC23 LA03 LA16

Claims (5)

[Claims] 1. An ultraviolet-curable resin film having a fine surface irregularity structure, wherein the film contains particles having an average particle size of 1 to 2 μm and a thixotropic agent, and the fine surface irregularity structure is formed on the basis of the contained particles. A light diffusion layer characterized by the following. 2. The light diffusion layer according to claim 1, which is supported on one or both sides of a transparent substrate. 3. An optical element comprising the optical diffusion layer according to claim 1 on one or both sides of the optical layer. 4. The optical element according to claim 3, wherein the optical layer is a polarizing plate, a retardation plate, or an elliptically polarizing plate made of a laminate thereof. 5. The liquid crystal display device according to claim 1, wherein
A liquid crystal display device comprising the light diffusing layer according to claim 1.