JP3455884B2 - Prism sheet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism sheet used in a surface light source device for illuminating an object with diffused light. 2. Description of the Related Art FIG. 5 is a view showing the structure of a conventional surface light source device using a prism sheet. Light from a linear light source 1 is made incident on a light guide 2 made of a transparent material. While transmitting light from the end face 2a to the opposite side, the light is partially diffused by the reflective surface provided on the lower surface 2c and having a partial diffusing action, and is emitted from the upper exit surface 2b and then becomes diffused light through the diffuser plate 3. . Reference numeral 4 denotes a reflection surface, which is arranged on the side opposite to the exit surface of the light guide 2 (the surface on the side of the diffusion plate 3). Thereby, illumination light having a relatively uniform luminance distribution can be obtained. However, when this surface light source device is used, for example, as a backlight of a liquid crystal display panel, a part of the diffused light goes away from the liquid crystal display panel because the light goes in all directions from the diffuser plate 3 and the amount of light is lost.
In particular, since the liquid crystal display panel is observed in a direction substantially perpendicular to the liquid crystal display panel, there is a lot of light that does not reach the observer's eyes even if the light illuminates the liquid crystal display panel. [0005] In order to solve such a drawback, there is a surface light source device using a prism sheet 5 in front of a diffusion plate 3 as shown in FIG. The prism sheet 5 is of a shape in cross section extending in a direction perpendicular to the paper surface without a large number of triangular shape as shown, thereby to bend inward the beam, for example proceed to L ₁ direction, the diffuser plate 3 The diffused light that has passed is directed in a direction perpendicular or substantially perpendicular to the diffuser plate 3 and directed toward the observer, so that light that deviates from the liquid crystal display panel is made incident on the display plate, and diffused light in all directions can be generated. As far as possible, it is aimed at the observer. However, when such a prism sheet 5 is used, there is no effect of bending light rays inward in the direction in which the apex 5a of the prism sheet 5 extends, that is, in the direction of a plane perpendicular to the paper surface. In order to solve this drawback, it is conceivable to arrange two prism sheets so that the apexes of the prisms extend in mutually different directions. However, when two prism sheets are arranged, an air gap is formed between the sheets, and light transmitted due to reflection on the incident surface is reduced, resulting in a loss of light amount. Further, during the manufacturing process, dust and dirt may be caught between the sheets, which may lower the luminance of the surface light source device. FIG. 6 shows a conventional example in which a prism sheet 5 is arranged in a surface light source device using a reflecting plate 6, and this case also has the above-mentioned disadvantages. An object of the present invention is to provide a prism sheet for use in a surface light source device in which light from a light source is used as diffused light through a diffuser plate, whereby the diffused light passing through the diffuser plate in all directions can be bent inward. It is an object of the present invention to provide a prism sheet having a small light amount loss due to reflection on an incident surface. [0009] The prism sheet of the present invention is used in a surface light source device using a light guide or a reflection plate, and has a triangular or wavy cross section on both sides of the sheet in one direction. A large number of convex portions are formed so that the directions in which the vertices of each convex portion extend are different from each other on both surfaces. As a result, the diffused light that spreads in one direction on the surface on which the diffused light entering the prism sheet is incident is bent inward, and the diffused light that spreads in a different direction from the incident side on the surface on the side from which light is emitted is bent inward. Thereby, the object of the invention can be achieved. Next, an embodiment of the present invention will be described. FIG. 1 is a perspective view showing an embodiment of the present invention, in which a large number of convex portions 11, 12 are formed on both surfaces of a sheet 10, respectively. The cross-sectional shape of the protrusions 11 or 12 is triangular. For example, the protrusions 11 on the upper surface of the drawing have their vertexes 11a arranged side by side. Similarly, the vertexes 12a of the projections 12 on the lower surface of the prism sheet are also arranged. Moreover, the direction in which the apex 11a of the protrusion 11 on the upper surface extends and the apex 12a of the protrusion 12 on the lower surface
Are different from each other by 90 °. Such a prism sheet is, for example, shown in FIG.
Alternatively, if the prism sheet 5 is used in place of the prism sheet 5 of the surface light source device shown in FIG.
0 light L ₁ that extends in the x direction in the diffused light incident on, the process proceeds as shown in FIG. 2 (A), also light L ₂ extending in y-direction
Proceeds as shown in FIG. As shown in these figures, the diffused light in both the x direction and the y direction is bent inward and directed to the surface of the liquid crystal display panel or the like to be illuminated, so that the display panel can be illuminated more brightly. Further, the amount of light emitted from the prism sheet 10 in the direction substantially perpendicular to the sheet surface increases, so that an observer who observes from the direction perpendicular to the display panel can observe a brighter image. Further, since there is no gap in the prism sheet, the loss of light amount due to reflection is small. In addition, since the light spreads little even though the light is diffused, a decrease in the amount of light per unit area is small even at a distance from the light source, and a bright image can be observed even at a remote position. FIG. 3 shows another embodiment of the prism sheet of the present invention.
The directions in which a and 12a extend are oblique to the four sides of the prism sheet 10. Also vertex 11a
Is different from the direction in which the apex 12a extends by 90 °. In this embodiment, if the x direction and the y direction are considered to be oblique to the sides of the prism sheet 10, it is apparent that the same operation as the embodiment shown in FIG. In both of the above embodiments, the direction of the vertex 11a of the prism 11 on one surface of the prism sheet 10 and the direction of the vertex 12a of the prism 12 on the other surface are 90 °.
Although formed to be shifted, the angle is not limited to 90 °, and may be another angle other than 90 °, and may be appropriately determined depending on the purpose of use and the like. The apex angle θ is desirably in the range of 50 ° to 110 °, and the apex angle of the prism 11 and the apex angle of the prism 12 can be different from each other within the above range. Further, the sectional shape of each prism is not limited to a triangle but may be a waveform as shown in FIG. In this case, the angle θ of the triangle formed by connecting the peak A of the peak of the wave and the bottom B of the trough satisfies the above range. In each of the embodiments shown in FIGS. 1 and 3, it is possible to form a waveform, and the angle of deviation of the apex A on both surfaces in the extending direction is 90 ° or another angle. Further, waveforms having different θ on both surfaces may be used. According to the prism sheet of the present invention, when it is used together with a surface light source device, it is possible to direct the spread diffused light in a direction substantially perpendicular to the prism sheet surface as a whole, and to reflect the light on the surface. Less bright light source. In the case where two prism sheets are used, foreign substances such as dust and dirt may be interposed between the prism sheets during the manufacturing process.
Since such a thing does not occur, quality control becomes easy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an embodiment of a prism sheet of the present invention. FIG. 2 is a diagram showing an outline of a state of refraction of light rays of the embodiment. FIG. FIG. 4 is a view showing another shape of the prism of the prism sheet of the present invention. FIG. 5 is a view showing a configuration of a surface light source device using a light guide. FIG. Diagram showing the configuration of a surface light source device that has been placed [Description of References] 10 Prism sheet 11 Prism 12 Prism

Continuation of the front page (56) References JP-A-3-37614 (JP, A) JP-A-5-313156 (JP, A) JP-A-5-203950 (JP, A) , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 5/02 G02B 5/04

Claims (1)

(1) A prism sheet used on a surface light source device having an exit surface having an area and having an area on an exit surface side, wherein the prism sheet has a triangular or corrugated cross section on both surfaces. In the same cross-sectional shape, it has a number of convex portions each extending in one direction while being arranged in the same direction, and the direction in which the convex portions on one surface of the prism sheet extend and the direction in which the convex portions on the other surface extend. different directions der Ri further the extending direction of the protrusions the pre
A prism sheet characterized by being oblique to four sides of the prism sheet.