JPH07318709A - Light control sheet - Google Patents

Abstract

PURPOSE:To obtain a light control sheet having excellent light condensability and excellent handling quality by specifying the difference in the refractive indices of materials forming respective layers to a specific value or above and providing the front and rear surfaces of a sheet with surfaces which are smooth in shape optically and geometrically. CONSTITUTION:This light control sheet has double structures in which the boundary surfaces of an upper layer 22 and a lower layer 21 are prism parts having an approximately triangular shape in section or many peak parts of an approximately triangular shape in section having an projecting arc shape at the top parts. The difference in the refractive indices of the materials forming the respective layers 21, 22 is >=0.05 and the front and rear surfaces of the sheet have the surfaces which are optically flat in shape. Namely, the upper layer 22 consisting of the low-refractive material is formed on the lower layer 21 consisting of the prism sheet of the high-refractive material or the sheet having a waveform structural surface, by which the handling quality is enhanced while the light condensability is maintained. A better result is obtd. as the difference in the i-&-j refractive indices between the lower layer 21 and the upper layer 22 is larger. The refraction at the boundary between the upper and lower layers 22, 21 is small and the light condensability is poor if the difference in the refractive indices is below 0.05.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge light type planar light emitting device used for liquid crystal displays such as personal computers and word processors, liquid crystal color televisions, etc., and more particularly to a light control sheet constituting the same.

[0002]

2. Description of the Related Art In an edge light type sheet emitting device, a fluorescent tube 1 is disposed on an end face 3 side of a light guide plate 2 as shown in FIG. The back surface of the light guide plate 2 is provided with a dot pattern 4 formed by dot printing of a paint, and the back surface of the light guide plate 2 is further provided with a reflection plate 5.

In the above structure, the light beam emitted from the fluorescent tube 1 enters the inside of the light guide plate 2 from the end surface 3 of the light guide plate 2, is diffusely reflected by the dot pattern 4 on the back surface of the light guide plate 2, and is reflected from the surface of the light guide plate 2. Is released. FIG. 3 shows the intensity distribution of the light rays emitted from the surface of the light guide plate 2 with respect to the emission angle. Most of the light rays are emitted in a direction largely deviated from the direction normal to the light guide plate 2, and the distribution thereof is extremely steep (intensity distribution 6). For this reason, the screen is usually very dark for the user who observes from the normal direction of the light guide plate 2.

In order to overcome this drawback, a method of installing a light diffusion sheet on the surface of the light guide plate has been devised. For the light diffusion sheet, a transparent plastic sheet surface is coated with or contains titanium oxide, a short fiber of glass, etc. containing a white pigment, or the transparent plastic sheet surface is processed to have an irregular triangular fine cross section. It is obtained by things (mat processing, texture processing). FIG. 4 shows the intensity distribution with respect to the emission angle of light rays when the light diffusion sheet 7 is used. In this case, it can be seen that the emission of light rays in the normal direction is increased as compared with FIG. 3 (intensity distribution 8).

[0005]

However, in the intensity distribution when the above-mentioned light diffusing sheet 7 is used, the emission of light rays in a direction unnecessary for the user is still large, and the light diffusing sheet 7 and the light diffusing sheet 7 are used. The loss of light rays due to diffused reflection at the interface of the light plate 2 cannot be ignored. That is, the light diffusing sheet 7 has a strong light diffusing ability and is inferior in the so-called light collecting ability to direct light in the normal direction of the light guide plate 2.

Therefore, as a method for improving these drawbacks, it has been attempted to use the prism sheet 9 having the structure shown in FIG. 5 instead of the light diffusing sheet. The prism sheet 9 is formed by arranging small prisms having a substantially triangular cross section in a flat plate shape, and is an optical function sheet having a function of refracting or reflecting a light ray incident on the prism. When the prism sheet 9 is used, the intensity distribution with respect to the emission angle of the light beam is as shown in FIG. 6, and the emission of the light beam in the normal direction is significantly increased (intensity distribution 10).

However, although this prism sheet 9 has an excellent light-collecting ability, it is apt to be scratched on the structural surface due to its shape. Further, since the triangles are regularly arranged, the scratches are likely to be conspicuous, and the appearance defects often occur on the light emitting surface during mass production, which makes mass production difficult. further,
The adhering foreign matter that has entered the groove portion of the structure surface is adsorbed by static electricity and cannot be easily removed, which is a serious problem when it is incorporated into the planar light emitting device.

Therefore, it is an object of the present invention to provide a light control sheet which is excellent in light collecting ability and handling suitability.

[0009]

According to the present invention, a light control of a two-layer structure in which a boundary surface between an upper layer and a lower layer is a prism portion having a substantially triangular cross section or a large number of mountain portions having a substantially triangular cross section having a convex arc shape at the top. The sheet is characterized in that the difference in the refractive index of the material forming each layer is 0.05 or more, and the front and back surfaces of the sheet have optically and geometrically smooth surfaces. Less than,
The present invention will be described in more detail.

In the present invention, as shown in FIG. 1A or 1B, an upper layer of a low refractive index material is formed on a lower layer 21 formed of a prism sheet of a high refractive index material or a sheet having a corrugated structure surface. By forming No. 22, handling suitability was improved while leaving the light collecting ability.

The larger the difference in refractive index between the lower layer 21 and the upper layer 22, the better. When the difference in the refractive index is less than 0.05, the refraction at the interface between the upper and lower layers is small and the light collecting ability becomes poor. When a low refractive index material is arranged in the lower layer 21 and a high refractive index material is arranged in the upper layer 22, the light entering from below is diffused at the interface between the upper and lower layers and has no light collecting ability.

[0012]

EXAMPLE The light control sheet of each of the examples or comparative examples was attached to the planar light emitting device described below, and the front luminance thereof was examined, as well as the adhesion of foreign matter and the easiness of scratching.

(Surface emitting device used) Method: Edge light method on one side (1 lamp on short side) Light source: Cold cathode tube having a thickness of 3.5 mm and a length of 135 mm Light guide plate: a thickness of 3 mm, a width of 205 mm, and a length of 135 mm Of P
MMA plate Light diffusion sheet: A commercially available light diffusion sheet made of polycarbonate with a thickness of 0.20 mm (embossed with fine irregularities is provided on the surface) to prevent the visibility of the dot pattern for providing the diffusivity of the back surface of the light guide plate. It was used. Applied pressure: 12V

(Evaluation method) Front brightness: The brightness (normal direction) from the front direction at 9 points where the backlight was determined was measured based on JIS-C761 and the average value was calculated.

(Preparation of Light Control Sheet) Light control sheets of Examples and Comparative Examples in which the material, the thickness of the sheet, and the shape of the structural surface were as follows were prepared.

[Example 1] Material: Upper layer base material: trifluoroisopropyl methacrylate (refractive index 1.418) Lower layer base material: polycarbonate (refractive index 1.586) Structural surface: A prism shape is applied to a boundary surface between upper and lower layers. . Prism apex angle: 90 ° Prism pitch: 50 μm Sheet thickness: 300 μm

Example 2 Material: Same as Example 1. Structural surface: A sinusoidal shape is applied to the boundary surface between the upper and lower layers. Vertical angle: 80 ° Pitch: 100 μm Sheet thickness: 300 μm

[Comparative Example 1] Material: Polycarbonate Structure surface: A prism shape is applied to the sheet surface. Prism apex angle: 90 ° Prism pitch: 50 μm Sheet thickness: 250 μm

Comparative Example 2 Material: Polycarbonate Structure surface: A sine wave shape is applied to the sheet surface. Prism apex angle: 80 ° Pitch: 100 μm Sheet thickness: 250 μm

[Comparative Example 3] Material: Polycarbonate Structure surface: Random unevenness on the sheet surface (Ra = 100 to
150 μm). Sheet thickness: 250 μm

[Comparative Example 4] Material: Upper layer base material: Polycarbonate (refractive index 1.586) Lower layer base material: trifluoroisopropyl methacrylate (refractive index 1.418) Structural surface: prismatic shape is applied to the boundary surface between upper and lower layers . Prism apex angle: 90 ° Prism pitch: 50 μm Sheet thickness: 300 μm

[Comparative Example 5] Material: Upper layer base material: p-cyclohexylphenyl methacrylate (refractive index 1.558) Lower layer base material: polycarbonate (refractive index 1.586) Structural surface: A prism shape is formed on the boundary surface between the upper and lower layers. Give. Prism apex angle: 90 ° Prism pitch: 50 μm Sheet thickness: 300 μm

The evaluation results are shown in Table 1.

[0024]

[Table 1]

[0025]

As described above, according to the present invention, it is possible to improve the handling aptitude by smoothing the structural surface while maintaining the light collecting ability by the prism effect.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an example of a light control sheet of the present invention.

FIG. 2 is a configuration diagram of an edge light type planar light emitting device.

FIG. 3 is an explanatory diagram showing emission light characteristics of a light guide plate alone of a planar light emitting device.

FIG. 4 is an explanatory diagram showing outgoing light characteristics when a light diffusion sheet is used in the planar light emitting device.

FIG. 5 is an external view of a prism sheet.

FIG. 6 is an explanatory diagram showing emission light characteristics when a prism sheet is used for the planar light emitting device.

[Explanation of symbols]

 1 Fluorescent Tube 2 Light Guide Plate 3 End Surface of Light Guide Plate 4 Dot Pattern 5 Reflector 7 Light Diffusing Sheet 9 Prism Sheet 21 Lower Layer 22 Upper Layer

Claims (1)

[Claims] 1. A light control sheet having a two-layer structure, wherein an interface between an upper layer and a lower layer is a prism portion having a substantially triangular cross section or a plurality of peaks having a substantially triangular cross section having a convex arc shape. The light control sheet, wherein the difference in the refractive index between the materials is 0.05 or more, and the front and back surfaces of the sheet have optically and geometrically smooth surfaces.