JPH08262206A - Prism sheet - Google Patents

Abstract

PURPOSE: To improve transmittance for light and to decrease the production cost by forming a rugged pattern on both sides of a sheet so that enough condensing effect is obtd. in one sheet. CONSTITUTION: A rugged pattern necessary to form a prism is formed on both sides of a sheet 1 in such a manner that the ridge lines of prisms on top and back sides are perpendicular to each other. In this case, light is condensed in the plane perpendicular to the ridge of the prism on each surface. Namely, light can be condensed in the vertical direction and the horizontal direction. Thus, light is condensed on both surfaces of the prism sheet 1 in contact with air in the plane perpendicular to each other (perpendicular to each of the prism ridge) so that light can be efficiently condensed. Thereby, the effect to condense light in the vertical and horizontal directions can be performed in one prism sheet l, which improves the brightness and decreases manhour and the production cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is arranged between a light guide for a backlight (back illumination light source) of a liquid crystal display device and the back surface of a liquid crystal display element, and the surface of the light guide body is moved from the surface to the back surface of the liquid crystal display element. The present invention relates to a prism sheet that equivalently enhances the brightness of a backlight by making the direction of light rays emitted toward a direction closer to the normal direction of the display surface of a liquid crystal display element and collecting light fluxes.

[0002]

2. Description of the Related Art For some time after the development of a liquid crystal display device, it has been considered desirable to arrange a plurality of ordinary fluorescent lamps for illumination on the back surface of a liquid crystal display element in order to realize bright display. However, such a method makes the liquid crystal display device thicker and consumes a large amount of electric power, so that it has been replaced by the light guide method described later. That is, since the liquid crystal display device is often used as a display element of a portable information processing device or the like, in order to reduce the thickness of the liquid crystal display device, the tube diameter arranged at the end of the display surface is thin and has a long life. A cold cathode fluorescent tube is used as a light source, and the light is incident on the end face of a so-called light guide placed on the back surface of the liquid crystal display element (edge light method) and guided to the back surface of the liquid crystal display element to guide the light as much as possible. It has become possible to convert the light into a direction perpendicular to the body surface and emit the light with uniform brightness. However, it is quite difficult to obtain a bright liquid crystal display screen using the light guide body, and various efforts are still being made. In one of them, a so-called prism sheet is interposed between the light guide and the rear surface of the liquid crystal display element, and the light flux emitted from the light guide is collected by the prism sheet as much as possible in the normal direction of the liquid crystal display surface, There are some that try to use the light from the light source efficiently.

For example, a flat panel display '9
2 (Nikkei BP) p. 209-p. 212 and JP-A-6-
In the specification of No. 18879, a large number of prisms (a convex portion having a triangular cross-section with a protruding ridge that is an intersection line of two inclined surfaces as an apex) is formed on one surface of a resin sheet that absorbs light as little as possible and has a high refractive index. Of a prism sheet in which the prisms are repeatedly formed in parallel, the uneven surface on which the prism is formed faces the light guide side, and the smooth surface of the prism sheet faces the back surface side of the liquid crystal display element. It is described that, due to the action of the prism sheet, the light beam emitted from the light guide is refracted so as to come close to the normal line of the display surface of the liquid crystal display element, and a light-collecting effect is produced. On the other hand, please refer to the "Development and Commercialization Trend of LCD Backlight" document of JIEC Seminar (March 1, 1994) p. 10-p. 28 and “Flat Panel Display '94” (Nikkei BP) p. In 217,
When the surface of the prism sheet on which the prism is formed faces the back surface of the liquid crystal display element, and the smooth surface of the prism sheet faces the light guide, the prism sheet also causes the emitted light to exit. It is described that the light is refracted so as to come close to the normal line of the display surface, and a condensing effect occurs. In addition, it is stated that a plurality of prism sheets may be stacked to enhance the condensing action of the prism sheet, and in that case, the prisms may have different directions. As the material of the prism sheet, for example, polycarbonate (refractive index 1.58) or acrylic (refractive index 1.49) is used. Acrylic is preferable in terms of easy light transmission, but polycarbonate having a high refractive index is preferable in terms of concentrating light.

[0004]

As described above, the conventionally used prism sheet has a prism formed only on one side. In this case, the prism sheet is collected only in a plane orthogonal to the extending direction of the ridge of the prism. Light action takes place. Therefore,
If the conventional prism sheet is used to perform the light condensing action in the up, down, left and right directions, two prism sheets in which the ridge extension directions of the prism are different by 90 ° must be used in a stacked manner. It was However, when a plurality of prism sheets are stacked, the light transmittance of one prism sheet is about 90%, so that the light transmittance becomes 81% when two sheets are stacked. Further, since the prism sheet is quite expensive, using a large number of prism sheets causes an increase in cost.

The present invention condenses light in a direction that was not sufficiently controlled by using only one conventional prism sheet, and has one condensing function that was conventionally realized by using a plurality of sheets. It is an object of the present invention to provide a prism sheet which can be used at the same time to improve the light transmittance and reduce the cost at the same time.

[0006]

In order to solve the above problems, in the present invention, the unevenness necessary for prism formation is formed on both sides of the sheet, and the ridges of the prisms extend on both the front and back sides of the sheet. The directions in which they exist are orthogonal to each other.

[0007]

According to the above means, the condensing action in the two directions of up, down, left and right can be performed with only one prism sheet, and the brightness can be improved, the man-hours can be reduced, and the cost can be reduced at the same time.

At the interface where different substances come into contact, light is refracted in a substance having a high refractive index so as to come closer to the normal line of the interface than in a substance having a low refractive index. Utilizing this phenomenon, the prism sheet performs a light condensing action. In the present invention, both sides of the prism sheet are brought into contact with air, and the condensing action is performed in the planes orthogonal to each other (perpendicular to the ridges of the respective prisms), so that the light can be efficiently condensed.

If the distribution of the light incident on the prism sheet from the light guide is asymmetrical, the peaks of the prisms can also be formed in an optimum asymmetrical shape, so that light can be efficiently condensed.

If a conventional prism sheet having one flat surface is placed on a flat light guide plate, the prism sheet is in direct contact with the light guide plate at a certain location, while the prism sheet is at another location. An extremely thin air layer may be formed in the middle. If the prism sheet and the light guide plate are made of the same material, no refraction of the light beam occurs at the point where they are in direct contact and nothing appears on the display, but at the point where a thin air layer is interposed between the two Part of the light from the light body is totally reflected, and there may be a difference in the amount of light reaching the display portion (and thus brightness) between the direct contact portion and the portion where a thin air layer is interposed. On the other hand, when the prism sheet according to the present invention is used, the prism is always formed on the surface of the prism sheet which is in contact with the light guide body, and the flat surface of the substance forming the prism sheet is in direct contact with the light guide body surface. In principle, there are no such places, so the above uneven brightness does not appear.

Japanese Patent Publication No. 1-37801 discloses that
Two sheets each having a corrugated surface having a smooth surface on one side and a smooth surface on the other side and forming a 45 ° crossing each other at 90 ° (apex angle) are used to form two sheets having a predetermined angle α (actual Most of the light that passes through the panel is overlapped with each other by intersecting at 90 °), the smooth surface of the first sheet faces the light source side, and the corrugated surface of the first sheet contacts the smooth surface of the second sheet. A "lighting panel" is described which is controlled in an angular direction within 30 ° with respect to the normal line of the panel. Is the purpose of the present invention to reduce the glare of light from a fluorescent lamp? There is no problem with light absorption, as in the present invention.
It is of course not considered that a single prism sheet has a light-collecting effect comparable to that of two conventional prism sheets, and that the light absorption is reduced by half.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. FIG. 1 is a perspective view of the most typical prism sheet 1 according to the present invention. In this case, the light is condensed in the plane orthogonal to the ridges of the prisms on both sides. That is, light can be collected in the vertical direction and the horizontal direction.

2 and 3 are views showing the behavior of light in the most typical arrangement. FIG. 2 is a view of the XZ plane. A light beam 5 emitted from a light source 3 is a lamp reflector 4
It is reflected by and enters the light guide plate 2. Then, it goes out, enters the prism sheet 1, is refracted and reflected by the lower surface, is condensed, and goes out.

FIG. 3 is a view of the YZ plane. It goes out from the light guide plate 2, enters the prism sheet 1, is refracted and reflected by the upper surface, and is condensed and goes out.

Further, as shown in FIG. 4, prisms are formed in a plurality of directions perpendicular to one surface (pyramidal protrusions are formed), or as shown in FIG. If it is made asymmetrical according to the incident direction, the light can be condensed more efficiently.

FIG. 6 is a basic block diagram of a backlight according to the present invention. At the bottom is a reflection plate 7, on which is located a light source 3, a lamp reflector 4 and a light guide plate 2. Further, if it is necessary to diffuse the light, the diffusion sheet 6 is arranged. The prism sheet 1 is arranged on it.

[0017]

As described above, according to the present invention, the light converging property is improved, the brightness of the display screen is improved, and since only one prism sheet is required, the light absorption by the sheet is reduced. It helps improve brightness and reduces man-hours and costs. Further, in the prism sheet of the present invention, since the prism is also formed on the lower surface and the lower surface is not in close contact with the surface of the object below, local unevenness of light does not appear on the liquid crystal display.

[Brief description of drawings]

FIG. 1 is a perspective view of a most typical prism sheet according to the present invention.

FIG. 2 is a diagram illustrating a path where light travels on a plane orthogonal to a tube axis of a tubular light source when a prism sheet is arranged.

FIG. 3 is a diagram illustrating a path that light travels on a plane parallel to the tube axis of the light source and orthogonal to the light guide plate when the prism sheet is arranged.

FIG. 4 is a plan view showing a state where a plurality of prisms orthogonal to each other are formed on one surface of a prism sheet.

FIG. 5 is a diagram illustrating a cross section when the shape of a prism is left-right asymmetric.

FIG. 6 is a basic configuration diagram of a backlight system according to the present invention.

[Explanation of symbols]

1 ... Prism sheet, 2 ... Light guide plate, 3 ... Light source, 4
… Lamp reflector, 5… Rays, 6… Diffusing sheet,
7 ... Reflector

Claims (2)

[Claims] 1. A prism sheet, wherein irregularities necessary for forming a prism are formed on both sides of the sheet. 2. The prism sheet according to claim 1, wherein the directions in which the ridges of the prisms extend on both front and back surfaces of the sheet are orthogonal to each other.