JP2002090508A - Light diffusing sheet and optical element - Google Patents

Abstract

(57) [Problem] To provide a light diffusing sheet which suppresses a glare phenomenon on a screen while maintaining anti-glare properties, and hardly recognizes white blur. SOLUTION: One or more resin coating layers (a) are formed as light diffusion layers on one surface of a transparent substrate, and further, a resin coating layer having an uneven surface on the resin coating layer (a). Light diffusion sheet (1) on which (b) is superimposed
In the above, when only the resin coating layer (a) is formed as a light diffusion layer on one surface of the transparent substrate, the haze value of the sheet (2) is 15 to 55%, and the haze value of the sheet (1) is 35. A light diffusing sheet, wherein the haze value of the sheet (2) <the haze value of the sheet (1) is 35 to 75%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-diffusing sheet used in a liquid crystal display, EL, PDP, or the like to suppress a glare phenomenon on a screen caused by high-definition pixels. Optical element.

[0002]

2. Description of the Related Art The visibility of an image is hindered on the surface of an image display device such as a liquid crystal display by indoor lighting such as a fluorescent lamp, sunlight incident from a window, and a shadow of an operator. Therefore, on the display surface, in order to improve the visibility of an image, the surface reflected light is diffused, the specular reflection of external light is suppressed, and reflection of an external environment can be prevented (having anti-glare properties). A light diffusion layer having an uneven structure is provided. As a method of forming the light diffusion layer, a method of forming a resin film layer by coating a resin in which fine particles are dispersed has been mainly used because the structure can be easily miniaturized and the productivity is good.

However, in the case of a high-definition liquid crystal display, when the light diffusion layer is mounted, random strong and weak light appears as bright spots, and glare of an image (light passing through pixels is distorted by unevenness on the surface and transmitted light is distorted). The phenomenon that spot variations occur randomly) becomes serious, and there is a problem that image quality is reduced. In order to suppress such glare, for example, it has been proposed that the resin film has two or more layers, and the improvement has been promoted.

[0004] However, with the improvement of the glare, the surface treatment layer causes a phenomenon of white blur (whitening: whiteness of the surface layer when the display is viewed from all angles up, down, left, and right) in the surface treatment layer. This is a problem that the visibility of black display is reduced particularly in a display device such as a liquid crystal display.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a light-diffusing sheet which suppresses the glare phenomenon on the screen while maintaining the anti-glare property and hardly recognizes white blur. . Still another object is to provide an optical element provided with the light diffusing sheet.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found that the above object can be achieved by a light diffusing sheet having the following structure, thereby completing the present invention. Reached.

That is, according to the present invention, one side of a transparent substrate is provided.
One or more resin film layers (a) are formed as light diffusion layers, and a resin film layer (b) having an uneven surface is superposed on the resin film layer (a). In the diffusible sheet (1), when only the resin film layer (a) is formed as a light diffusing layer on one surface of the transparent substrate, the haze value of the sheet (2) is 15 to 55%, and the sheet ( The light-diffusing sheet, wherein the haze value of 1) is 35 to 75%, and the haze value of the sheet (2) <the haze value of the sheet (1).

As described above, according to the present invention, when the light diffusion layer is a superposed layer of the resin film layer (a) and the resin film layer (b), and only the resin film layer (a) is formed as the light diffusion layer. The haze value of the sheet (2) and the haze value of the sheet (1) in which the resin film layer (a) and the resin film layer (b) are formed so as to overlap each other are adjusted to be within the above-mentioned predetermined range. Thus, the state of light diffusion is separated between the outermost resin film layer (b) and the other resin film layer (a), thereby suppressing glare and white blur.

The haze value of the sheet (1) and the haze value of the sheet (2) can be appropriately set within the above ranges. However, the haze value of the sheet (1) can be controlled in a well-balanced manner. Is preferably set to 40 to 70%, and the haze value of the sheet (2) is set to 20 to 50%.

In the light diffusing sheet, the difference ((1)-(2)) between the haze value of the sheet (1) and the haze value of the sheet (2) is preferably 40% or less.

By controlling the difference between the haze values to 40% or less, glare and blurring can be suppressed in a well-balanced manner. Particularly, the difference between the haze values is preferably set to 10 to 30%.

In the light diffusing sheet, the resin film layer (a) and the resin film layer (b) have an average particle size of 0.05
It preferably comprises fine particles of up to 5 μm.

When the resin coating layer (a) and the resin coating layer (b) serving as the light diffusion layer contain the fine particles having the above-mentioned average particle size, anti-glare properties, anti-glare properties and anti-blur can be effectively exhibited. Become like The average particle diameter of the fine particles is more preferably from 2 to 3 μm.

Further, the present invention relates to an optical element, wherein the light diffusing sheet is provided on one side or both sides of the optical element.

The light-diffusing sheet of the present invention can be used for various applications, for example, for optical elements.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a light diffusing property in which a lower resin coating layer 2 (a) and a resin coating layer 2 (b) having an uneven surface are formed as a light diffusing layer on a transparent substrate 1. It is a sheet. FIG. 2 is a sheet in which only the lower resin coating layer 2 (a) is formed on a transparent substrate 1. Although FIGS. 1 and 2 show a case where the lower resin coating layer 2 (a) is a single layer, the resin coating layer 2 (a) may have a plurality of layers.

Examples of the transparent substrate 1 include transparent polymers such as polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, polycarbonate polymers, and acrylic polymers such as polymethyl methacrylate. Film. Styrene polymers such as polystyrene and acrylonitrile-styrene copolymer; polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure; olefin polymers such as ethylene-propylene copolymer; vinyl chloride polymers; nylon and aromatic polyamides And a film made of a transparent polymer such as an amide-based polymer. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers A film made of a transparent polymer such as a polymer, an epoxy-based polymer or a blend of the above-mentioned polymers may also be used. Particularly, those having low optical birefringence are preferably used.

The thickness of the transparent substrate can be appropriately determined.
Generally, the thickness is about 10 to 500 μm from the viewpoint of workability such as strength and handleability, and thinness. In particular, 20 to 300 μm is preferable, and 30 to 200 μm is more preferable.

As the resin for forming the resin coating layers 2 (a) and 2 (b), a resin corresponding to the hardness of the polymer or the like exemplified in the transparent substrate 1 may be appropriately selected and used. Preferably, an ultraviolet curable resin is used. The ultraviolet-curable resin can efficiently form the light diffusion layer by a simple processing operation in a curing treatment by irradiation with ultraviolet light.

The UV-curable resin includes, for example, various resins such as polyester, acrylic, urethane, amide, silicone and epoxy, and includes UV-curable monomers, oligomers and polymers. It is. The UV-curable resin preferably used is, for example, a resin having a UV-polymerizable functional group, particularly a resin containing an acrylic monomer or oligomer having two or more, particularly 3 to 6 functional groups. Further, an ultraviolet polymerization initiator is blended with the ultraviolet curing resin. The resins forming the resin coating layers 2 (a) and 2 (b) may be the same or different.

The resin coating layers 2 (a) and 2 (b) can contain fine particles 3 (a) and 3 (b). The average particle diameter of the fine particles is 0.05 to 5 μm as described above.
Is preferred. The ratio of the fine particles 3 (a) and 3 (b) is not particularly limited, but is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the resin in view of the balance between anti-glare and anti-blur.

Fine particles 3 (a) in resin coating layer 2 (a)
May be inside the layer, and the upper resin coating layer 2
It may be at the interface with (b) or with the transparent substrate 1. Also, the particles 3 (b) in the resin coating layer 2 (b) may be inside the layer, and the light diffusing layer surface may have an uneven shape.

Examples of the fine particles 3 (a) and 3 (b) 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 two or more of appropriate ones such as crosslinked or uncrosslinked organic particles or silicone particles made of various polymers such as polymethyl methacrylate and polyurethane can be used. Note that the particles 3 (a) and 3 (b) may be the same or different.

The method for forming the resin film layer 2 (a) and the resin film layer 2 (b) having an uneven surface on the transparent substrate 1 is not particularly limited, and an appropriate method can be adopted.

The resin film layer 2 (a) can be formed by applying a resin (for example, an ultraviolet curable resin: a coating liquid) on the transparent substrate 1, drying and then curing the resin. it can. The coating liquid is applied by an appropriate method such as fountain, die coater, casting, spin coating, fountain metalling, and gravure. Although the thickness of the resin film layer 2 (a) is not particularly limited, it is 1 to 10 μm.
It is preferable to set the degree.

The formation of the surface irregularities relating to the resin film layer 2 (b) is performed by, for example, adding fine particles 3 (b) to the resin forming the resin film layer 2 (b) as shown in FIG. There is a method of applying a coating liquid by the above-mentioned appropriate method so that the fine particles 3 (b) are reflected on the unevenness of the surface. The surface irregularities are formed by roughening the surface of the resin film layer 2 (a) in advance by an appropriate method such as sandblasting, embossing roll, etching, or the like, and applying a coating liquid to the roughened surface sequentially. Various means, such as performing by coating, can also be adopted.

The thickness of the resin film layer 2 (b) is not particularly limited, but is usually preferably about 1 to 10 μm.
When the surface irregularities are formed by the fine particles 3 (b), it is preferable that the average particle diameter of the fine particles 3 (b) is equal to or smaller than the average particle diameter.

An antireflection layer can be further provided on the uneven surface of the resin film layer (b), which is the outermost surface of the light diffusion layer. The antireflection layer has a lower refractive index than that of the resin film layer (b). For example, a low refractive index material can be used. Although the thickness of the antireflection layer is not particularly limited, it is about 0.05 to 0.3 μm, particularly 0.1 μm.
It is preferable to set it to 0.3 μm.

The light diffusing sheet of the present invention can bond an optical element (not shown). Examples of the optical element include a polarizing plate, an elliptically polarizing film, a retardation plate, and a conductive optical film. These can be used as a laminate. The adhesion of the optical element can be carried out through an appropriate adhesive layer having excellent transparency and weather resistance, such as an adhesive such as an acrylic, rubber, or silicone, or a hot-melt adhesive, if necessary.

As the polarizing plate, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene / vinyl acetate copolymer-based partially saponified film, etc. was drawn by adsorbing iodine or a dye. And polarizing films such as dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride. Examples of the retardation plate include a uniaxially or biaxially stretched film of a polymer film exemplified as the transparent substrate and a liquid crystal polymer film. 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.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and the like specifically showing the configuration and effects of the present invention will be described below.

The haze value is based on JIS-K7105,
Haze meter (Model TC-H3D manufactured by Tokyo Denshoku Industries Co., Ltd.)
P).

Example 1 (Formation of Resin Coating Layer (a)) 10 parts by weight of silica spherical particles having an average particle diameter of 5 μm and benzophenone-based photopolymerization were started with respect to 100 parts by weight of an ultraviolet-curable resin (urethane acrylate monomer). A coating solution obtained by mixing 3 parts by weight of the agent via a mixed solvent of toluene and methyl ethyl ketone was applied on a triacetyl cellulose film (80 μm),
After drying, the coating was cured by irradiation with ultraviolet rays to form a coating film (6 μm) having a smooth surface. When the haze value of the obtained light diffusing sheet (2) was measured, it was 20%.

(Formation of Resin Coating Layer (b)) Similarly, an ultraviolet curable resin (urethane acrylate monomer) 10
A coating liquid obtained by mixing 8 parts by weight of silica spherical particles having an average particle diameter of 5 μm and 3 parts by weight of a benzophenone-based photopolymerization initiator via a mixed solvent of toluene and methyl ethyl ketone is applied to the coating film based on 0 part by weight. After drying, the coating is cured by irradiation with ultraviolet light to form a coating having an uneven surface (10 μm).
m) was formed. The haze value of the resulting light-diffusing sheet (1) having a two-layer structure was 40%.

Examples 2 to 12 Light diffusing sheet (2) and light diffusing sheet were prepared in the same manner as in Example 1 except that the amount of the silica spherical particles used was changed as shown in Table 1. (1) was prepared sequentially. Table 1 shows the haze values of the obtained light diffusing sheet (2) and light diffusing sheet (1).

Comparative Examples 1 to 16 Light-diffusing sheet (2) and light-diffusing sheet were prepared in the same manner as in Example 1 except that the amount of the silica spherical particles used was changed as shown in Table 2. (1) was prepared sequentially. Table 2 shows the haze values of the obtained light diffusing sheet (2) and light diffusing sheet (1).

The polarizing plate (185 μm) bonded to the light diffusing sheet (2) obtained in the above Examples and Comparative Examples was bonded to a glass substrate, and a mask pattern (opening ratio) fixed on a light table was used. (25%), and the degree of glare (anti-glare) was visually evaluated according to the following criteria. Further, a black tape was attached to the surface of the glass substrate opposite to the surface to which the polarizing plate was bonded, and white blur (anti-white blur) was visually evaluated according to the following criteria. The results are shown in Tables 1 and 2.

As Comparative Examples 17 to 22, Examples 1 to
The light-diffusing sheet (2) prepared in 6 was evaluated for anti-glare and anti-blur in the same manner as described above. Table 3 shows the results.

(Anti-glare)…: There is no glare at all. ○: There is almost no glare. Δ: The glare is small and there is no practical problem. ×: There is glare. (Anti-blur)…: There is no white blur. …: Almost no blurring. Δ: There is white blurring, but there is little effect on visibility. ×: There is white blur. XX: Very white blur.

[0041]

[Table 1]

[Table 2]

[Table 3] As can be seen from Tables 1 and 3, the light-diffusing sheet (2) having two light-diffusing layers has reduced glare and reduced white blur as compared with the single-light-diffusing sheet (1). I have. Further, as can be seen from Tables 1 and 2, the resin film layer (a) as the light diffusion layer and the resin film layer (b) as the surface unevenness layer were adjusted to form the light diffusion sheets (1) and (2). When the haze value was within a predetermined range (Example: Table 1), the balance between the glare and the white blur was good, and both the performance of the glare and the white blur were “△” or more, and one of them was “「 ”. Yes,
A clear image can be obtained. On the other hand, when the haze value of at least one of the light diffusing sheets (1) and (2) is out of the above-mentioned range (Comparative Example: Table 2), the balance between the glare and the white blur is poor, and one of the light diffusing sheets is “×”. Or less, or both of the glare and white blur performances do not show a particularly excellent “◎”.

[Brief description of the drawings]

FIG. 1 is an example of a light diffusing sheet (1) having a resin film layer (b) formed on a resin film layer (a).

FIG. 2 is an example of a sheet (2) on which a resin film layer (a) is formed.

[Explanation of symbols]

 1: transparent substrate 2 (a): resin film layer 2 (b): resin film layer 3 (a): fine particles 3 (b): fine particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C08L 101/00 C08L 101/00 (72) Inventor Masayuki Satake 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Inside Nitto Denko Corporation (72) Inventor Shigeo Kobayashi 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Inside Nitto Denko Corporation (72) Takayuki Shigematsu 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Takuya Matsunaga 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H042 BA02 BA03 BA12 BA15 BA20 2H049 BA02 BA04 BA25 BA27 BB43 BB51 BB63 BC03 BC04 BC14 BC22 2H091 FA32X FB02 FB04 FB13 FC12 FC25 FC26 FD06 FD23 4F006 AA12 AA15 AA22 AA35 AA36 AB24 AB34 AB35 AB37 AB39 BA15 CA05 DA04 EA03 4F100 AA20H AH02H AJ06 AK01B AK01C AK25 AR00A BA03 BA07 CA23B CA23C CA30 EJ54 GB41 HB21C JN01A JN02 JN18B JN18C JN30 YY00 YY00B YY00C YY00H

Claims (4)

[Claims] At least one resin coating layer (a) is formed as a light diffusing layer on one surface of a transparent substrate, and a resin coating having an uneven surface is formed on the resin coating layer (a). Light diffusing sheet (1) on which layer (b) is superposed
In the above, when only the resin coating layer (a) is formed as a light diffusion layer on one surface of the transparent substrate, the haze value of the sheet (2) is 15 to 55%, and the haze value of the sheet (1) is 35. A light diffusing sheet, wherein the haze value of the sheet (2) <the haze value of the sheet (1) is 35 to 75%. 2. Haze value of sheet (1) and sheet (2)
3. The light diffusing sheet according to claim 1, wherein the difference ((1)-(2)) in the haze value is 40% or less. 3. The light diffusing sheet according to claim 1, wherein the resin coating layer (a) and the resin coating layer (b) contain fine particles having an average particle diameter of 00.5 to 5 μm. . 4. An optical element, wherein the light diffusing sheet according to claim 1 is provided on one side or both sides of an optical element.