JPH07174909A - Light diffusing plate - Google Patents

Abstract

PURPOSE:To obtain a light diffusing plate having a light scattering coefft. (degree of haze) comparable to that of a conventional plate and having a higher light transmissivity than the conventional plate at a low cost of production by carrying out application to one side of a transparent substrate. CONSTITUTION:This light diffusing plate has a light diffusing layer contg. an org. macromolecular binder and org. macromolecular particles on one side of the transparent substrate. The difference between the refractive index of the binder and that of the particles if <=0.05, the weight average particle diameter of the particles if 10 to 21mum and the weight ratio of the particles to the binder is 1.9 to 3.6. The total amt. of the particles and the binder applied is 10 to 17g/m<2> and the extent of the size distribution of the particles if <=3.5mum as standard deviation value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing plate, and more particularly to a light diffusing plate used in liquid crystal displays or the like, or a light diffusing plate used in projection screens, OHP sheet supports, and advertising signboard bags. Light sheet support,
Also, the present invention relates to a light diffusing plate used for display using light transmission and diffusion.

[0002]

2. Description of the Related Art For a backlight of a liquid crystal display,
Alternatively, a light diffusion plate is used as a screen for images of televisions, movies and the like. In the present age of colorization, this light diffusing plate is particularly required to diffuse light well, have no coloring, and have good light transmittance. Conventionally, a sheet in which a light diffusion layer containing a matting agent of inorganic particles is formed on a polyester base has been used as a diffusion plate for a liquid crystal display backlight. However, since such a conventional diffuser plate has a small amount of transmitted light and is not suitable for today's color age, improvement of its characteristics has been desired. On the other hand, recently, a polycarbonate sheet having a transmittance higher than that of a polyester base and having its surface embossed has been used as a diffusion plate for a liquid crystal display backlight. However, since this sheet is embossed, it is necessary to increase the thickness of the support, and in order to prevent its static charge, it is necessary to apply an antistatic agent by spraying or the like when incorporating the liquid crystal. The recent embossed surface of this polycarbonate sheet is 2-3 times more expensive than the conventional product, and there is a problem in that point as well. On the other hand, it is possible to increase the power of the light itself in order to increase the amount of transmitted light, but in the age when cost reduction is required, it is disadvantageous to increase the power of the light for the purpose of brightening the image surface. Recently,
Nikkei Microdevice (February 1993 issue) introduces a diffusion plate containing an organic polymer binder and organic polymer particles. However, the organic polymer particles used in this diffusion plate have a large particle diameter, and the weight ratio of the polymer particles and the binder is too small, resulting in low brightness.

[0003]

The object of the present invention is to provide a light-scattering rate (haze degree) equivalent to that of the conventional one by coating on one surface of a transparent support, while at the same time providing a light transmission higher than that of the conventional product. To obtain a light diffusing plate having high efficiency and low manufacturing cost.

[0004]

As a result of the research conducted by the present inventors, the above-mentioned object is to provide an organic polymer binder having a refractive index difference of 0.05 or less and a specific particle size on one surface of a transparent support. It was found to be achieved by providing a light diffusing layer containing organic polymer particles in a specific ratio and satisfying various other requirements. That is, the difference in refractive index between the organic polymer binder and the organic polymer particles is 0.05 or less, and the weight average particle diameter of the organic polymer particles is 10 to 21 μm. Weight ratio 1.9
When the total weight of the both (total coating weight) per 1 m ^{2 is} 10 to 17 g, a light diffusion plate having a high light transmittance, that is, a high brightness can be obtained. The standard deviation of the size distribution of the organic polymer particles is 3.5 μm
When it is within the range, a light diffusing plate having higher brightness can be obtained.
In addition, it is further obtained by coating and drying an ion conductive resin layer (eg, JULIMER SP-50T manufactured by Nippon Pure Chemical Industries, Ltd.) on the surface of the support (the surface on the side where the light diffusion layer is provided and / or the surface opposite thereto). It has also been found that by applying a layer thickness of 0.1 to 2.0 μm, the reflection is further reduced and the brightness is further increased.

The present invention will be described in more detail below. As the transparent support used in the present invention, a generally known plastic film can be appropriately used as long as it has good transparency and mechanical strength. Usually 0.02 mm or more,
A sheet-shaped resin for film having a thickness of 4.0 mm or less is used, but a glass plate or the like may be used. As the resin for this film, polyester, polyolefin, polyamide, polyether, polystyrene, polyesteramide, polycarbonate, polyphenylene sulfide, polyether ester, polyvinyl chloride, polymethacrylic acid ester and the like are preferable.

As the organic polymer binder used in the light diffusion layer of the present invention, an organic polymer having a volume resistivity of 10 ¹² Ω · cm or more is preferably used. Specific examples thereof include vinyl acetate resin, ethylene-vinyl acetate copolymer resin, vinyl chloride resin, vinyl chloride-vinylidene chloride copolymer resin, acrylic ester resin, methacrylic ester resin, butyral resin, silicone resin, polyester resin, Vinylidene fluoride resin, nitrocellulose resin,
Examples thereof include styrene resin, styrene / acrylic copolymer resin, urethane resin, polyethylene resin, polypropylene resin, chlorinated polyethylene, rosin derivative and mixtures thereof.

The weight average particle diameter of the organic polymer particles used in the light diffusion layer is 10 to 21 μm (preferably 15 to 21 μm).
m). If it is less than 10 μm, the brightness becomes low,
If it exceeds 21 μm, the brightness is lowered in this case as well. And, the closer the refractive index of the organic polymer particles to the organic polymer binder is, the more preferable the point is that the reflection at the interface of the organic polymer particles decreases, but the difference in the refractive index is particularly 0.05.
It must be: For example, for polypropylene particles and polymethylmethacrylate particles, a combination with an organic polymer binder such as polymethylmethacrylate, cellulose acetate or polyvinyl butyral is used. The weight ratio of the organic polymer particles and the organic polymer binder is also an important factor for obtaining the desired high brightness. If it is less than 1.9, the surface condition (surface condition) is fine, but the brightness is not high. When it exceeds 3.6, the surface condition deteriorates and the brightness also starts to deteriorate. The total coating weight of the organic polymer particles and the organic polymer binder is also an important factor for the brightness given by the light diffusion plate. In addition, it cannot be said that the light diffusing plate has sufficient practicality only when the brightness is high. For example, for use in a liquid crystal display device, it is necessary to have a light diffusing property (referred to as visibility) at a level that guides light by a liquid crystal system and hides so-called dot printing on a light guide plate. A matting agent composed of inorganic particles may be added to the light diffusion layer for the purpose of increasing the light diffusion property. As the matting agent for the inorganic particles used in the light diffusing layer, inorganic fine powders having a particle size of 1 μm to 5 μm, such as silica, calcium carbonate, and alumina, which have been conventionally used in the light diffusing layer are used. As described above, it is necessary to set a limited range for each material because the light transmittance has a delicate relationship with reflection and refraction, and the angular distribution of incident light is limited to a specific range. Is understood. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0008]

EXAMPLES All of the polyethylene terephthalate (PET) bases used in the examples were subjected to double-side glow discharge treatment in order to enhance the adhesion of the coating layer. The PET bases used in the following examples were all made of the following [1] ion conductive resin liquid on the surface of the support on which the light diffusion layer was provided and on the opposite surface except for the No23 light diffusion plate sample. Application,
After drying, an ion conductive resin layer was formed so that the thickness after drying was 0.4 μm. Drying was performed by air drying at 130 ° C for 1 minute. Hereinafter, the PET base coated with the ion conductive resin solution [1] on both sides will be referred to as a treated base. [1] Liquid Ion conductive resin (Nippon Pure Chemical Co., Ltd., Julimer SP-50T) 44.0 g Methanol 44.0 g Cyclohexanone 12.0 g (The above ion conductive resin is dimethylaminoethyl methacrylate quaternary compound 25. 4 parts by weight, 7.6 parts by weight of 2-hydroxyethyl methacrylate, 46 parts by weight of methyl methacrylate and 21 parts by weight of ethyl acrylate are emulsion-copolymerized to prepare an aqueous solution of an ion conductive resin. Glycerol polyglycidyl ether was added as a crosslinkable compound in an amount of 4% by weight based on the solid content of the ion conductive resin, and 2-methylimidazole was added to the glycerol polyglycidyl ether at 2.5% by weight.
By adding and mixing by weight%, an ion conductive resin-containing aqueous solution having a solid content of 20% by weight was obtained. )

[Experimental Example 1] Preparation and evaluation of No. 1 to No. 6 light-diffusing plate samples By changing the wire diameter of the Mayer bar on one side of the treatment base, the following [2] liquid (coating liquid for manufacturing the diffusion layer) was prepared.
Was applied by changing the coating amount, and light diffusion plate samples No. 1 to 6 having different solid weights of the diffusion layers were prepared. Drying at 130 ° C
By air-drying for 1 minute. [2] Liquid Toluene 61.7 g Modified acrylic polymer (manufactured by Mitsubishi Rayon Co., Ltd., BR-79, copolymer of methacrylic acid and acrylic monomer) 12.1 g PMMA particles (Nippon Pure Chemical Co., Ltd., Julimer MB20X) , Weight average particle size 17.5 μm, standard deviation 3.1 μm) 26.2 g The particle size and particle size distribution of PMMA (polymethylmethacrylate) particles were evaluated with a Coulter counter (Multisizer). Coulter counter measurement concentration is 3
%.

To measure the brightness, two of these light diffusion plates are used.
Both of the diffusion layers were placed so as to face the light source side of the light guide plate, and a luminance meter (BM-7, manufactured by Topcon Corp.) was used. And, the brightness value is the light diffusing film D20 which has been conventionally used in the current commercial product.
4 (light diffusion film product of Kimoto Co., Ltd.) was considered as a control. In measurement, this D204 gave a brightness of 960 cd / m ² . Then, a film showing a brightness sufficiently higher than the D204 (based on 270 cd / m ² or more where a visually distinct difference is seen) was judged to be an excellent light diffusion film (that is, 1230 cd / m ² or more is required). Performance). The brightness value of the control light diffusion film D204 is shown as No. 29 in Table 1. The visibility was evaluated by setting two light diffusion plates on an edge light type light guide plate having a thickness of 4.0 mm and setting it on a normal liquid crystal display, and using the dot printing pattern of the light guide plate with the naked eye. It was carried out by checking whether or not identification was possible. Regarding the visibility, the one in which the dot printing pattern of the light guide plate having a thickness of 4 mm with two films was clearly found was x, the marginal limit was Δ, and the one in which the dot printing pattern was not completely visible was rated as ◯. The measurement results are shown in Table 1. In the light diffusion plate samples Nos. 1 to 6, the total coating weight of the organic polymer binder and the organic polymer particles was gradually increased. In the No. 1 light diffusion plate sample, the total weight of the organic polymer binder and the organic polymer particles is insufficient, and sufficient brightness cannot be obtained. On the other hand, it can be seen that the light diffusion plate samples of Nos. 5 and 6 do not provide sufficient brightness because the total coating weight of the organic polymer binder and the organic polymer particles is too large.

[Experimental Example 2] Preparation and Evaluation of Light Diffusing Plate Samples Nos. 7 to 12 PMMA particles having different weight average particle diameters were appropriately mixed with four kinds of PMMA (polymethylmethacrylate) particles having different weight average particle diameters. Created. All of these four types of PMMA particles are products of Nippon Pure Chemical Co., Ltd., and the product number is Mb1.
X, Mb10X, Mb20X, and Mb30X. The weight average particle diameters and the standard deviation values thereof are shown below. When the weight average particle diameter is represented by D and the standard deviation value is represented by σ, Mb1X is D = 7.9 μm, σ = 1.6 μm, Mb
10X has D = 12 μm, σ = 2.1 μm, Mb20X has D = 17.1 μm, σ = 2.8 μm, and Mb30X has D =
28 μm and σ = 5.2 μm. These four types of PMMA
The light diffusing plate of Nos. 7 to 12 was obtained by using six kinds of PMMA particles having different weight average particle diameters prepared by appropriately mixing the particles, and the brightness and visibility thereof were evaluated by the method described in Experimental Example 1. evaluated. The evaluation results are shown in Table 1. When the light diffusing plate was produced, the total weight of the organic polymer binder and the organic polymer particles was adjusted to be in the range of 14.76 to 14.94 g / m ² . From the results in Table 1, the weight average particle size is 1
It can be seen that particles in the range of 0 to 21 μm give high brightness. In the sample of No. 7 light diffusion plate, it was found that the particle size of PMMA particles was small and sufficient brightness could not be obtained.
It can also be seen that in the light diffusion plate samples 1 and 12, the particle size of the PMMA particles is too large and sufficient brightness cannot be obtained.

[Experimental Example 3] Preparation and evaluation of light diffusing plate samples of Nos. 13 to 17 The weight average particle diameter of PMMA particles was kept constant, and variations in particle diameter, that is, fluctuations in luminance when the standard deviation value was changed. Examined. The results are shown in Table 1. Σ of PMMA particles is 3.5
When the thickness was within μm, the brightness was 1.00 or more and the brightness was bright. That is, No16, 17 (No3
The same). In addition, the light diffusion plate sample (No. 1 when the standard deviation value of PMMA particles was increased)
3, 14, 15) have slightly lower brightness.

[Experimental Example 4] Preparation and Evaluation of Light Diffusing Plate Samples No. 18 to 26: Polymer particles were prepared by making the weight average particle diameter, the variation of the particle diameter, ie, the standard deviation value, and the total solid content of the diffusion layer coating solution constant. The brightness and the visibility were examined when the weight ratio with the binder was changed. The results are shown in Table 1. It can be seen that high brightness can be obtained when the ratio value of the polymer particles and the binder is in the range of 1.9 to 3.6. The brightness is lowered if it is higher or lower than this value. That is, No18, 19, 20,
The light diffusion plate samples of No. 26 are low in brightness, and the light diffusion plate samples of Nos. 21 to 25 are high in brightness.

[Experimental Example 5] Preparation and evaluation of No. 27 light-diffusing plate sample In the case where there is no 0.4 μm undercoat layer and back layer on both sides of the PET base, the PET base itself has No.
The same diffusion layer as the light diffusion plate sample of No. 4 was applied to prepare a light diffusion plate sample, and its brightness and visibility were examined. The results are shown in Table 1. Even in this case, the brightness was relatively high, but the brightness was lower than that of the No. 4 light diffusion plate sample. The light diffusion plate sample of No. 27 is an example.

Experimental Example 6 Preparation and Evaluation of No. 28 Light Diffusing Plate Sample Finally, in the No. 12 light diffusing plate sample of Experimental Example 2, the refractive index was 1. in place of the organic polymer particles (PMMA) in this case. 54, polystyrene particles having a refractive index difference of 0.5 from PMMA particles (SGP-10, Soken Chemical Industry Co., Ltd.)
0) was used to examine the change in luminance. The polystyrene particles had a weight average particle diameter of 29.1 μm and a variation σ value of 5.6 μm. The specific gravity of polystyrene particles is 1.0
Since it was 6, the added weight of 4% polystyrene particles was reduced to match the volume of PMMA particles having a specific gravity of 1.10.
Since the polystyrene particles swell slightly with a solvent, a coating solution was prepared and immediately applied to prepare a light diffusing plate, and its brightness and visibility were examined. The results are shown in Table 1. The brightness is 3 as compared with the case of No. 12 PMMA particles of Experimental Example 2.
It fell about%. It is understood that when the refractive index of the particles is different from that of the binder, reflection and refraction occur at the interface, and as a result, the brightness is further lowered. The light diffusion plate sample of No. 28 is an example.

Table 1 ──────────────────────────────────── Light spread Weight average Organic polymer Organic high Molecular particles Organic polymer particles Undercoating plate Average particle size Particle size and organic high molecular weight and brightness of organic high molecular weight Sample (μm) distribution Standard deviation binder Presence or absence of child binder (cd / m ² ) Approval No Weight ratio of difference value (μm) Total weight g / m ² property ──────────────────────────────────── ─ 1 17.1 2.8 2.17 9.4 Yes 1150 × 2 17.1 2.8 2.17 10.0 Yes 1232 △ 3 17.1 2.8 2.17 14.76 Yes 1298 ○ 4 17.1 2.8 2.17 16.5 Yes 1270 ○ 5 17.1 2.8 2.17 18.00 Yes 1200 ○ 6 17.1 2.8 2.17 20.32 Yes 170 ○ 7 7.91 1.63 2.17 14.80 Yes 1195 ○ 8 12.05 2.10 2.17 14.91 Yes 1230 ○ 9 15.02 2.53 2.17 14.87 Yes 1240 ○ 10 20.9 2.90 2.17 14.83 Yes 1250 ○ 11 22.0 3.1 2.17 14.94 Yes 1190 ○ 12 30.2 5.2 2.17 14.78 Yes 1170 △ 13 17 1 7.6 2.09 14.80 Yes 1160 ○ 14 17.1 5.0 5.05 5.97 14.97 Yes 1180 ○ 15 17.1 3.7 2.16 14.73 Yes 1200 ○ 16 17.1. 3.5 2.14 14.67 Yes 1234 ○ 17 17.1 1.9 2.11 14.88 Yes 1290 ○ 18 17.1 2.8 1.20 14.56 Yes 1088 ○ 19 17. 1 2.8 1.52 14.48 Yes 1109 ○ 20 17.1 2.8 1.77 14.90 Yes 1140 ○ 21 17.1 2.8 1.90 14.58 Yes 1230 ○ 22 17.1 2 2.8 2.39 14.74 Yes 1270 ○ 23 17.1 2.8 2.60 14.69 Yes 1240 ○ 24 17.1 2.8 3.26 14.59 Yes 1238 ○ 25 17.1 2.8 3.59 14.80 Yes 1231 ○ 26 17.1 2.8 3.81 14.66 Yes 1210 ○ 27 17.1 2.8 2.17 14.76 No 1238 ○ 28 29.1 5.2 2. 30 14.20 Yes 1130 △ 29 −−−−−−−−− 960 ○ ─────────────────────────────── ─────

[0017]

The light diffusing plate having the light diffusing layer containing the organic polymer binder and the organic polymer particles satisfying the specific requirements of the present invention is a transparent support such as a polyethylene terephthalate film which is relatively inexpensive and easily available. High brightness can be given while using the body. Therefore, a light diffusing plate used for a liquid crystal display or a light scattering plate used for a projection screen, a support for an OHP sheet,
It can be advantageously used in practical use as a support for a backlit sheet of an illuminated signboard for advertisement, and a light diffusing plate used for other display utilizing light transmission and diffusion.

Claims (2)

[Claims] 1. A light diffusing plate having a light diffusing layer containing an organic polymer binder and organic polymer particles on one surface of a transparent support, wherein the organic polymer binder and the organic polymer particles have a refractive index. The difference is 0.05 or less, the weight average particle diameter of the organic polymer particles is 10 to 21 μm, and the weight ratio of the organic polymer particles to the organic polymer binder is 1.9.
˜3.6, the total coating weight of the organic polymer particles and the organic polymer binder is 10 to 17 g / m ² , and the spread of the size distribution of the organic polymer particles is 3 as a standard deviation value. Light diffusion plate within 0.5 μm. 2. The light diffusion plate according to claim 1, wherein an ion conductive resin layer is provided on the surface of the transparent support on which the light diffusion layer is provided and / or on the surface opposite thereto.