JPH07198913A - Prism sheet - Google Patents

Abstract

PURPOSE:To bend the diffused light to its inner side and to lessen the loss of light quantity by reflection on an incident surface by forming specific projecting parts on both surfaces of a sheet and varying the direction where the vertexes of the respective projecting parts elongate with both surfaces. CONSTITUTION:The many projecting parts 11, 11 are respectively formed on both surfaces of the sheet 10. The sectional shape of these projecting parts 11, 12 is triangular; for example, the vertexes 11a of the projecting parts 11 of the surface in the upper part of Fig. are lined up and arranged. Similarly, the vertexes 12a of the projecting parts 12 of the rear sheet of the prism sheet are also lined up and arranged. In addition, the direction where the vertexes 11a of the projecting parts 11 of the front surface and the direction where the vertexes 12a of the projecting parts 12 of the rear surface elongate face the directions varying by 90 deg. from each other. The diffused light in any directions is bent inward and is directed into the surface desired to be illuminated of a liquid crystal display plate, etc., if such prism sheet is used in place of the prism sheet of for example, a surface light source device. Brighter illumination of the display plate is thus possible.

Description

Detailed Description of the Invention

[0001]

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.

[0002]

2. Description of the Related Art FIG. 5 is a view showing a structure of a conventional surface light source device using a prism sheet, in which light from a linear light source 1 is made incident on a light guide 2 made of a transparent material and is incident from an incident end face 2a. While transmitting light to the opposite side, the light is partially diffused by the reflecting surface provided on the lower surface 2c and having a partial diffusing action, and is emitted from the upper emission surface 2b and then passes through the diffusion plate 3 to become diffused light. Reference numeral 4 denotes a reflecting surface, which is arranged on the side opposite to the emitting surface of the light guide 2 (the surface on the side of the diffusion plate 3). This makes it possible to obtain illumination light having a relatively uniform luminance distribution. However, when this surface light source device is used as a backlight of a liquid crystal display plate, for example, the diffused light travels from the diffuser plate 3 in all directions, so that part of the diffused light deviates from the liquid crystal display plate and the amount of light is lost.
In particular, since the liquid crystal display plate is observed in a direction substantially perpendicular to the liquid crystal display plate, there is much light that does not reach the eyes of the observer even when the light illuminates the liquid crystal display plate.

[0003]

In order to solve such a drawback, there is a prism sheet 5 in front of the diffusion plate 3 of the surface light source device as shown in FIG. As shown, the prism sheet 5 has a large number of triangular cross sections and extends in a direction perpendicular to the plane of the drawing. With this, for example, a light beam traveling in the L ₁ direction is bent inward, and the diffusion plate 3 is The diffused light that has passed is directed in a direction perpendicular or nearly perpendicular to the diffuser plate 3 so that the light that deviates from the liquid crystal display plate is incident on the display plate by directing it toward the observer, 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, in the direction in which the apex 5a of the prism sheet 5 extends, that is, in the direction perpendicular to the paper surface, the action of bending the light beam inward does not occur.

In order to solve this drawback, it is conceivable to dispose two prism sheets so that the directions in which the vertices of the prisms extend are different from each other. However, when two prism sheets are arranged, an air gap is created between the sheets, and the transmitted light is reduced due to reflection on the incident surface, resulting in loss of light quantity.

Further, during the manufacturing process, dust or dirt may be caught between the sheets, which may reduce the brightness 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 reflection plate 6, and this case also has the above-mentioned drawbacks.

An object of the present invention is a prism sheet for use in a surface light source device that uses light from a light source as diffused light through a diffuser plate, which can bend diffused light traveling in any direction through the diffuser plate to the inside thereof, and Another object of the present invention is to provide a prism sheet with a small amount of light loss due to reflection on the incident surface.

[0009]

The prism sheet of the present invention is used in a surface light source device using a light guide or a reflector, and has a triangular or corrugated cross-section extending continuously in one direction on both sides of the sheet. A large number of protrusions are formed, and the directions in which the vertices of the protrusions extend are different on both sides. As a result, the diffused light that enters the prism sheet on the side where the diffused light enters is bent inward in one direction, and the surface on the side where the light exits bends the diffused light that spreads in a different direction from the incident side. The object of the invention can thereby be achieved.

[0010]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a perspective view showing an embodiment of the present invention, in which a large number of convex portions 11 and 12 are formed on both sides of a sheet 10. The cross-sectional shape of the convex portion 11 or 12 is triangular, and, for example, the convex portions 11 on the upper surface of the drawing are arranged with their vertices 11a aligned. Similarly, the apexes 12a of the convex portions 12 on the lower surface of the prism sheet are also arranged. Moreover, the extending direction of the apex 11a of the convex portion 11 on the upper surface and the apex 12a of the convex portion 12 on the lower surface
Are different from each other by 90 °.

Such a prism sheet is shown in FIG.
Alternatively, when used instead of the prism sheet 5 of the surface light source device shown in FIG. 6, the prism sheet 1 as shown in FIG.
Of the diffused light entering 0, the light L ₁ that spreads in the x direction travels as shown in FIG. 2A, and the light L _{2 that} spreads in the y direction.
Proceeds as shown in FIG. As shown in these figures, in both the x direction and the y direction, the diffused light is bent inward and directed toward the surface of the liquid crystal display plate or the like to be illuminated, so that the display plate can be illuminated brighter. Further, since the light emitted from the prism sheet 10 is mostly in the direction substantially perpendicular to the sheet surface, it is possible for an observer who observes the display plate to view a brighter image. Further, since there is no void in the prism sheet, there is little loss of light quantity due to reflection. In addition, since the spread is small despite the diffused light, the amount of light per unit area does not decrease even if the light source is far from the light source, and a bright image can be observed even at a distant position.

FIG. 3 is a diagram showing another embodiment of the prism sheet of the present invention. The apex 11 of each prism 11 and 12 is shown.
The directions in which a and 12a extend are inclined with respect to the four sides of the prism sheet 10. Also vertex 11a
The direction in which the point extends and the direction in which the apex 12a extends are offset by 90 °.

Even in this embodiment, if the x-direction and the y-direction are considered as oblique directions with respect to the sides of the prism sheet 10, it is clear that the same operation as the embodiment shown in FIG.

In both of the above embodiments, the direction of the apex 11a of the prism 11 on one surface of the prism sheet 10 and the direction of the apex 12a of the prism 12 on the other surface of the prism sheet 10 are 90 °.
Although they are formed to be deviated from each other, the angle is not limited to 90 °, but may be an angle other than 90 °, and may be appropriately determined according to the purpose of use and the like.

The apex angle θ is preferably 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 cross-sectional shape of each prism is not limited to a triangular shape, but may be a waveform as shown in FIG. In the case of such a waveform, the angle θ of the triangle formed by connecting the apex A of the crest of the wave and the bottom B of the trough may satisfy the above range. Further, in any of the embodiments of FIG. 1 and FIG. 3, it is possible to form a waveform, and the angle of deviation in the extending direction of the vertices A on both sides is 90 ° or another angle. Further, waveforms with different θ on both sides may be used.

[0017]

When the prism sheet of the present invention is used together with a surface light source device, the diffused light that spreads can be directed in a direction substantially perpendicular to the prism sheet surface as a whole, and there is little reflection on the surface and it is bright. It can be used as a surface light source.

Further, when two prism sheets are used, foreign matter such as dust or dust may be caught between the prism sheets during the manufacturing process. However, in the case of the present invention,
Since such a thing does not occur, quality control becomes easy.

[Brief description of 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 refraction state of light rays in the embodiment.

FIG. 3 is a perspective view of another embodiment of the prism sheet of the present invention.

FIG. 4 is a diagram showing another shape of the prism of the prism sheet of the present invention.

FIG. 5 is a diagram showing a configuration of a surface light source device using a light guide.

FIG. 6 is a diagram showing a configuration of a surface light source device using a reflector.

[Explanation of symbols]

 10 Prism sheet 11 Prism 12 Prism

Claims (1)

[Claims] 1. A prism sheet having an emission surface disposed on the emission surface side of a surface light source device having a certain area, wherein the prism sheet has a triangular or corrugated cross-sectional shape on both sides in one direction. It has a large number of convex portions in which the respective extensions are arranged side by side, and the extending direction of the convex portions of one surface of the prism sheet and the extending direction of the convex portions of the other surface are different directions. Prism sheet to do.