JPH09178912A - Light diffusing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-cost light diffusing sheet hard to scratch and well fittable with a plane light emitter by blending a transparent thermosetting elastomer obtd. by adding an org. peroxide with solid light scattering nuclei. SOLUTION: The back light unit of a liq. crystal display device has a light diffusing sheet 6 laminated on a light guiding plate 1 and light from a lamp 4 is sent from the light guiding plate 1 to the display of the display device through the light diffusing sheet 6. The sheet 6 is made of a blend of a transparent thermosetting elastomer obtd. by adding an org. peroxide with solid light scattering nuclei. A thermoplastic elastomer used as a base material is preferably a flexible elastomer (polymer) such as polyurethane, PE or an ethylene-vinyl acetate copolymer. The light scattering nuclei are formed by blending polymers different from each other in refractive index or mixing the transparent thermosetting elastomer with inorg. solid particles or powder.

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 for a backlight for a liquid crystal display device, and more particularly to a transparent thermosetting elastomer containing an organic peroxide in a solid state. The present invention relates to a light diffusion sheet containing the above light scattering nucleus.

[0002]

2. Description of the Related Art Internally illuminated panel-shaped lighting devices, traces, and foreign matter inspections that have been conventionally used for applications such as backlights for liquid crystal display devices, advertisements, road signs, and displays. When uniform light is required, such as for light boxes used for applications such as light boxes and surface light source devices such as photographic exposure devices, it is necessary to add scattering particles to transparent resin or glass, or to add embossing to the surface. The light diffusion sheet or the light diffusion plate obtained by the method was used. However, these conventional light diffusion sheets (plates) are based on a hard resin such as transparent polycarbonate resin, polyester resin, acrylic resin, styrene resin. Although this light diffusing sheet (plate) has no problem with respect to its ability to diffuse light uniformly, it has a problem that it is easily scratched, and in order to solve this point, a complicated process such as hard coating on the surface is performed. In addition, when used for a flat light source such as a backlight for a liquid crystal display device, the rigidity as a sheet is high, and even if there is a slight warp, it is unfamiliar to the light emitting body such as the light guide plate and the uniformity of light is improved. Sheet (plate) as it may be damaged
Were difficult to manufacture and tended to be more and more expensive.

Further, in the manufacturing process of the liquid crystal display device, since the light diffusion sheet (plate) is made of a hard resin, the coefficient of friction with the light guide plate made of the same material is low, and if it is not held for some time, it slips and shifts its position. There was a problem with, and the improvement was awaited.

The present invention has been made in view of the above circumstances, and has improved the problems of the conventional light diffusing sheet (plate), is hard to be scratched, is well adapted to a flat light emitting body, and has an appropriate resistance. Therefore, it is an object of the present invention to provide an inexpensive light diffusing sheet (plate) that can be flown to the next process without being held in the assembly process.

[0005]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that a solid light-scattering nucleus is added to a transparent thermosetting elastomer containing an organic peroxide. It was found that the above problems can be solved by using a light diffusion sheet (plate) containing More specifically, a transparent thermosetting elastomer containing an organic peroxide is not easily scratched by stress within its elastic recovery range and is highly flexible, so that it can be used, for example, in a backlight for a liquid crystal display device. When applied, it easily fits on the surface of the light guide plate of the backlight, and because it has an appropriate frictional resistance, it does not slip even if it is placed on the light guide plate, it does not shift the position, and if necessary, spot the peripheral part etc. We found that this light diffusion sheet can be adhered to a light guide plate or a frame that holds the light guide plate by thermocompression bonding, and that it can solve the problems of conventional light diffusion sheets (plates). Then, the present invention has been completed.

That is, the present invention provides (1) a light diffusing sheet comprising a transparent thermosetting elastomer containing an organic peroxide and a solid light-scattering nucleus, and (2) a solid light. The light scattering sheet according to (1), wherein the scattering nuclei are light scattering nuclei produced by blending a polymer having a refractive index different from that of the thermosetting elastomer, and (3) the solid light scattering nuclei are inorganic solid fine particles ( 1) The light diffusion sheet, (4) The light diffusion sheet according to (1), wherein the solid light scattering nuclei are crosslinked polymer fine particles, (5) The fine particles are transparent, (3) or (4) A diffusion sheet, (6) the light diffusion sheet according to any one of (1) to (5) having an embossed pattern on its surface, (7) a backlight for a liquid crystal display device (1), (8) The light diffusion sheet according to any one of (6), (8 Providing a light diffusing sheet of the liquid crystal display part of the device for the backlight of the light guide plate or adhered by thermocompression bonding to all (7), wherein.

As described above, the present invention uses the transparent thermosetting elastomer containing the organic peroxide,
This is a completely new technology that solves the problems of the conventional light diffusion sheet (plate) without deteriorating the light diffusion performance.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The transparent thermoplastic elastomer as a base material of the light diffusion sheet of the present invention may be a transparent elastomer having flexibility at around room temperature. Any of them may be used, for example, polyurethane, polyethylene, polypropylene, poly-1,2-butadiene, silicone elastomer, copolymerized fluoroelastomer, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid copolymer. And metal salts thereof, ethylene-based copolymers such as ethylene- (meth) acrylic acid ester copolymers, styrene-butadiene block copolymers, styrene-isoprene block copolymers, styrene-ethylene block copolymers,
Diene-based block copolymers such as styrene-ethylene butylene block copolymers and hydrogenated products thereof, homopolymers and copolymers of (meth) acrylic acid esters with alcohols having 6 or more carbon atoms, and those having 5 or less carbon atoms. A flexible elastomer (polymer) such as an acrylic elastomer (polymer) such as a copolymer of (meth) acrylic acid ester with alcohol and a monomer copolymerizable therewith is preferable. Further, a hard resin such as polyvinyl chloride, polyamide, polyester, polystyrene or the like which is mixed with a plasticizer to give flexibility, can also be suitably used.

An organic peroxide is added to the transparent thermoplastic elastomer in order to make it thermosetting. As the organic peroxide, benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-
Butyl peroxybenzoate, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexane, 2,5
-Dimethyl-2,5-di-t-butylperoxyhexyne-3,1,1-bis (t-butylperoxy) 3,
One type of 3,5-trimethylcyclohexane, lauroyl peroxide and the like can be used alone or in combination of two or more types. The amount of these organic peroxides added is 0.1 to 10 per 100 parts by weight of the transparent thermoplastic elastomer.
Parts by weight are sufficient.

Further, it is preferable to add a silane coupling agent represented by the following general formula to the thermoplastic elastomer from the viewpoint of further imparting adhesiveness.

[0011]

Embedded image (In the formula, R ₁ is selected from an amino group, a mercapto group, a (meth) acryl group, a phenyl group, a glycidyl group, a halogen atom and the like. Further, n is 2 or 3, and m is 1,2,3. The integers q and p are selected from positive integers such that q + p = 3.)

Next, in order to form a scattering nucleus for efficiently scattering light, a blend of polymers having different refractive indexes, a mixture of inorganic solid particles or powder with the transparent thermoplastic elastomer, the transparent thermoplastic elastomer. Can be by mixing cross-linked polymer particles or powders into.

As for the above-mentioned transparent resin, an optically non-uniform structure having a light-scattering nucleus can be formed by melt-mixing or mixing two or more kinds having different refractive indexes in the form of particles (powder). . In this case, since the polymer to be mixed does not need to have flexibility, a hard resin containing no plasticizer can also be used. Further, the addition amount thereof is 0.1 to 50 parts, preferably 0.5 to 20 parts, and more preferably 0.5 to 10 parts with respect to 100 parts of thermosetting elastomer (weight part, the same applies hereinafter).

As the material of the inorganic solid particles or powder of (1), transparent or white materials such as glass, quartz, silicon oxide, calcium carbonate, titanium oxide and zinc oxide are most common, but they are colored. The existing ones can also be used. The average particle diameter is preferably 0.01 to 100 μm, particularly preferably 0.1 to 20 μm. Further, a material obtained by surface-treating these can also be preferably used. In this case, the addition amount is 0.0 with respect to 100 parts of the thermosetting elastomer.
5 to 20 parts, preferably 0.1 to 15 parts, more preferably 0.5 to 10 parts.

As the material of the particles or powder made of the crosslinked polymer, resin particles or powder of silicone, acrylic, polyethylene, polystyrene, polyurethane, etc. can be preferably used. The addition amount is 0.05 to 20
Parts, preferably 0.1 to 15 parts, more preferably 0.5.
-10 parts is good. The average particle size is 0.01 to 100 μ
m, particularly preferably 0.1 to 20 μm.

An embossed pattern can be provided on one side or both sides of the surface of the sheet containing the above-mentioned light scattering nucleus. This not only improves the light diffusing performance, but when applied to a backlight for a liquid crystal display device, for example, the friction coefficient with the light guide plate is adjusted by applying it to the light guide plate side of the backlight to adjust the liquid crystal display device. It can be adapted to the manufacturing process. The depth of the embossed pattern in this case is 1 to
100 μm, preferably 2 to 50 μm is suitable.

Next, as a method for obtaining the light diffusing sheet of the present invention, an organic peroxide and a light scattering nucleus are mixed with a transparent thermoplastic elastomer by a kneading device such as Banbury, kneader, mixing roll, etc., and then the extruder is used. Or calendar,
It may be formed into a sheet using a means such as a press.
Further, in order to impart an embossed pattern to the surface, pressure may be applied using an embossing roll or a template after forming the sheet. Then, a light diffusion sheet can be obtained by cutting into a predetermined size. It is also possible to make a product of a predetermined size at a time using an injection molding machine. Further, if necessary, it is possible to carry out heat curing at the time of forming the sheet and use it as a crosslinked sheet in advance. It should be noted that it is possible to add an antioxidant, an ultraviolet absorber, a coloring agent, etc. depending on the application.

The light diffusing sheet of the present invention is a backlight used for liquid crystal display devices, an internally illuminating panel type lighting device used for advertisements, road signs, displays and the like, a light used for traces, foreign matter inspection and the like. It is suitable for use in applications where uniform light is required, such as box and photolithography surface light source devices, and is particularly effective as a light diffusion sheet (plate) for a backlight for liquid crystal display devices as shown in the figure. is there. Here, the drawing shows a backlight unit of a liquid crystal display device, 1 is a light guide plate, 2 and 3 are high reflection films, 4 is a lamp, 5 is a reflector film, and a light diffusion sheet 6 is laminated on the light guide plate 1. The light from the lamp is sent from the light guide plate 1 to the display of the liquid crystal display device through the light diffusion sheet 6. By using the light diffusing sheet of the present invention as the light diffusing sheet 6 of such a backlight unit, since it has an appropriate frictional resistance when placed on the light guide plate 1, it is difficult to slip and position shift is less likely to occur. It is easy to fabricate, and since the base of the light diffusion sheet is a thermoplastic elastomer, it is not easily scratched by the stress within its elastic recovery range, and it is rich in flexibility, so it easily fits on the surface of the light guide plate. At this point, the light uniformity is not impaired, and a good light diffusion effect is provided.

Next, an experimental example will be shown.

[Experimental Example 1] 2,5-Dimethyl-2,5 as an organic peroxide based on 100 parts by weight of an ethylene-vinyl acetate copolymer (EVA: vinyl acetate content: 26%, melt index: 4). -Add 1 part by weight of di (t-butylperoxy) hexane and 5 parts by weight or 10 parts by weight of surface-treated calcium carbonate (Chemipron A manufactured by Chemipro Kasei), and knead thoroughly with a mixing roll at a temperature of 90 ° C. After that, a sheet having a thickness of 0.2 mm was created using a press.

This sheet is placed on a light guide plate of a backlight obtained by disassembling a Sharp 4-inch LCD TV,
The effect was measured. The backlight used here is a type in which a slit (slit) with a controlled density is formed in the lower part of the light guide plate in order to uniformly emit light. If the light diffusing sheet created above was not present, this cut was recognized from the exit side, and there was a problem with uniformity.However, when this light diffusing sheet was placed, this cut was not visible, and there was an overall uniformity. It became luminous. Further, as a result of measuring the luminance from the front with a luminance meter (CS-100 manufactured by Minolta), as shown in Table 1, the light mixing effect by the diffusion sheet was also clear.

[0022]

[Table 1]

The conventional light diffusing sheet (PC: polycarbonate) used in the backlight of the liquid crystal television and the EVA light diffusing sheet prepared above are placed on the light guide plate and gradually inclined. The sliding angle was measured. As for the result, in the case of PC, it started to slip at about 30 °, but E
In the case of VA, it did not slip to 37 °.

[Experimental Example 2] In the same manner as in Experimental Example 1, a light diffusion sheet having the same size as the frame of the backlight was used. Here, the four corners of the light diffusion sheet were thermocompression-bonded using a spot type ultrasonic heater and bonded to the frame. There was no effect on the part of the luminous body, and the light diffusing sheet did not fall even when inverted.

[Experimental Example 3] 2 parts by weight of crosslinked silicone resin particles having an average particle diameter of 2 μm were added to 100 parts by weight of ethylene-vinyl acetate copolymer (EVA: vinyl acetate content: 26%, melt index: 4). Then, after sufficiently kneading with a mixing roll at a temperature of 90 ° C., a sheet having a thickness of 0.2 mm and a thickness of 0.4 mm was prepared using a press. Place this sheet on the back light guide plate obtained by disassembling the same Sharp 4-inch LCD TV as above,
The effect was measured. As a result, when this light diffusing sheet was placed, the cuts were not visible and the light emission was uniform throughout. The results of measuring the luminance from the front in this case are shown in Table 2. Also in this case, as in Experimental Example 1, the effect of increasing the front luminance was recognized, and the light mixing effect was clear.

[0026]

[Table 2]

[0027]

According to the present invention, it is possible to provide a light diffusing sheet that is not easily scratched, has a good compatibility with a light emitting body, and can easily manufacture a light diffusing unit.

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight for a liquid crystal display device.

[Explanation of reference numerals] 1 light guide plate 2 high reflection film 3 high reflection film 4 lamp 5 reflector film 6 light diffusion sheet

Claims (8)

[Claims] 1. A light diffusion sheet comprising a transparent thermosetting elastomer containing an organic peroxide and solid light scattering nuclei. 2. The light-diffusing sheet according to claim 1, wherein the solid light-scattering nucleus is a light-scattering nucleus generated by blending a polymer having a refractive index different from that of the thermosetting elastomer. 3. The light diffusion sheet according to claim 1, wherein the solid light scattering nuclei are inorganic solid fine particles. 4. The light diffusion sheet according to claim 1, wherein the solid light scattering nuclei are crosslinked polymer fine particles. 5. The light diffusion sheet according to claim 3, wherein the fine particles are transparent. 6. An embossed pattern is applied to the surface of the sheet.
6. The light diffusion sheet according to any one of items 1 to 5. 7. The light diffusion sheet according to claim 1, which is used for a backlight for a liquid crystal display device. 8. The light diffusion sheet according to claim 7, wherein the light guide plate of the backlight for a liquid crystal display device is bonded by heating and pressure bonding to a part or all of the light guide plate.