JPH0720459A - Light guide plate for back light - Google Patents

Abstract

PURPOSE:To shift chromaticity coordinates to lower values while holding constant luminance by providing the light guide plate with titanium oxide which has anatase-type crystal structure as a light diffusing material. CONSTITUTION:The light guide plate 1 is provided with the titanium oxide which has the anatase-type crystal structure as the light diffusing material. Further, a linear light source 4 is arranged having its center axis almost in parallel to its end surface preferably so that light is made incident on an end part of the light guide plate 1; and the surfaces of the linear light source 4 other than the surface facing the end surface of the light guide plate 1 are covered with a light reflecting plate or film 5. A light diffusion sheet 2 diffuses and passes the light projected from a surface of the light guide plate 1 and one or plural light diffusion sheets 2 are used at need. Further, the light reflection sheet 3 is arranged covering the entire surface of the light guide plate 1 which is provided with the light diffusion material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive or semi-transmissive panel, and more particularly to a light guide plate used for an edge light type backlight for illuminating a liquid crystal display from the back side.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a backlight mechanism which is thin and easy to see has been used as a display device for a laptop or book type word processor, a computer or the like. For such a backlight, there is an edge light system in which a linear light source (4 in the figure) such as a fluorescent tube is provided at one end of a light-transmitting light guide plate (1 in the figure) as shown in FIG. It is used. In the case of this edge light system, as shown in FIG. 2, one side of the light guide plate is partially covered with ink or paint containing a light diffusing substance such as white pigment in a dot shape, a stripe shape, and the like. In many cases, the light diffusing reflection sheet (3 in the figure) covers almost the entire surface and the light emitting surface (2 in the figure) covers the light output surface.

Further, in order to make the brightness on the light emitting surface of the backlight uniform, when the light diffusing material is partially coated on the light guide plate, the ratio of the coating to the unit area of the light guide plate gradually increases as the distance from the light source increases. As described above, it is partially covered in a dot shape, a stripe shape, or the like.

Conventionally, the above-mentioned white light diffusing material is Si
O ₂ , BaSO ₄ , TiO _{2 and the} like are used. Especially, regarding TiO ₂ , so-called rutile (Rutil) is used.
The main type is e) type TiO ₂ .

In particular, in recent years, it has been desired to further reduce the power consumption and the brightness of these word processors and personal computers, and in the backlight, the efficiency is reduced while suppressing the power consumption of the linear light source to a low level. It is currently being investigated whether the surface light emission is good. The emission color of the backlight is generally expressed by chromaticity coordinates x and y obtained from the tristimulus values X, Y, and Z of the color system recommended by CIE (International Commission on Illumination). The chromaticity coordinates x and y of the luminescent color of the backlight tended to shift to higher values than the chromaticity coordinates x and y of the luminescent color of.

Therefore, in order to achieve the required chromaticity coordinates x and y of the light emission color of the backlight, the chromaticity value d that shifts the chromaticity coordinates x and y of the light emission color of the fluorescent tube by the backlight.
It was reduced by x and dy. However, when the chromaticity coordinates x and y of the emission color of the fluorescent tube are shifted to lower values, there is a problem in that the efficiency of conversion into total luminous flux with respect to power consumption is reduced, and as a result, the brightness of the backlight is reduced.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light guide plate for a backlight capable of shifting chromaticity coordinates x and y to low values while maintaining constant brightness with constant power consumption. It is in.

[0008]

The inventors of the present invention have made various studies on the state of a light diffusing material, particularly titanium oxide, partially applied to the surface of a light guide plate. As a result, titanium oxide having a certain crystal structure is obtained. It has been found that the light guide plate for a backlight that can shift the chromaticity coordinates x and y to low values while maintaining constant brightness with constant power consumption.

That is, the present invention is a light guide plate made of a translucent material having a linear light source in the vicinity of a side end, and a light diffusion plate having a refractive index higher than that of the translucent material on a wide surface thereof. The substance is partially applied and said substance is anatase (An
The present invention relates to a light guide plate for a backlight, which is a titanium oxide of atase) type. Next, the present invention will be described in more detail with reference to the drawings.

The structure of the present invention is basically the same as that shown in FIGS. The light guide plate of the present invention may be any substance that allows light to efficiently pass therethrough, and may be quartz, glass, translucent natural or synthetic resin such as acrylic resin.
A method of applying a light diffusing substance (6 in the figure) that causes the light rays incident from the side surface end portion to be emitted from a wide surface on the surface of the light guide plate is as follows. A medium such as a printing ink dispersed in a resin or a vinyl resin is printed on the surface of the light guide plate in a dot shape or a stripe shape by a method such as screen printing.

A feature of the present invention is that titanium oxide having an anatase type crystal structure is applied to the light guide plate as a light diffusing substance. Conventionally, as described above, titanium oxide having a rutile type crystal structure, which has been used as a paint or a printing ink because of its excellent hiding power and weather resistance, is used as a light diffusing substance. It was applied to the light board.

However, as a result of the research conducted by the inventors of the present invention, when titanium oxide having an anatase type crystal structure is used in place of titanium oxide having a rutile type crystal structure, a constant luminance can be obtained at a constant power consumption. It has been found that it is possible to shift the chromaticity coordinates x and y to lower values while maintaining the same. The titanium oxide to be used has only to have an anatase type crystal structure, and the production method thereof is not particularly limited, but the anatase type can be identified by, for example, an X-ray diffraction pattern.

Reference numeral 4 is a linear light source, and in a preferred embodiment,
Arrange the linear light source so that the central axis of the linear light source is substantially parallel to the end face of the light guide plate so that light is incident on the end face of the light guide plate. It is arranged in a state of being covered with the reflection plate or the film 5. The linear light source 4
, There are fluorescent tubes, tungsten incandescent tubes, optical rods, LED arrays, etc., but fluorescent tubes are preferable, and in terms of the uniformity of the luminance distribution of the effective light emitting area and the aspect of power saving, it is uniform except for the electrode part. It is preferable that the length of the light emitting portion is substantially equal to the length of the end portion of the light guide plate adjacent to the light emitting portion.

The main part of the present invention has such a constitution and is used as a backlight of a panel, particularly a liquid crystal panel. In the present invention, it is preferable to have the following configuration.

The light diffusion sheet (2 in the figure) scatters the light emitted from the light guide plate surface and allows it to pass therethrough, and one or more light diffusion sheets are used as necessary.

The light reflection sheet (3 in the figure) is arranged so as to cover the entire surface of the light guide plate of the light guide plate on which the light diffusion material is applied, and reflects light.

[0017]

INDUSTRIAL APPLICABILITY The present invention can be used as a light guide plate for a backlight capable of shifting chromaticity coordinates x and y to low values while maintaining constant brightness with constant power consumption.

[0018]

COMPARATIVE EXAMPLES AND EXAMPLES Next, the present invention will be described in more detail with reference to Comparative Examples and Examples.

Comparative Examples and Examples A rectangular acrylic plate (225 having a thickness of 2 mm as shown in FIG.
mm × 127 mm, Asahi Kasei Co., Ltd. delagrass A), a cold cathode fluorescent tube (made by Harrison Electric Co., Ltd.) with a diameter of 3 mm is arranged at the short end of the Ag film (Nakai Kogyo It was placed so that light emitted from a slit having a width of 2 mm facing the end portion of the light guide plate of the Ag film enters the light guide plate from the end portion of the light guide plate.

On the other hand, on the surface of the light guide plate, an ink containing titanium oxide having a rutile type crystal structure as a light diffusing substance and a light-transmitting substance (acrylic vinyl resin) is circular dot pattern at a pitch of 1 mm. 220mm x 12 on acrylic plate
Screen-printed over an area of 5 mm. Under the screen printing, the coverage of the light diffusion material is 3.8% at the minimum point (near the linear light source) and 95% at the maximum point (farthest portion of the light guide plate).
%, In the middle, the values were created such that these ratios were sequentially increased from the point where the coverage was the minimum. The weight ratio of titanium oxide to acrylic vinyl resin was about 1: 1, the solvent contained in the ink was removed in the drying process, and the thickness of the dots printed on the light guide plate after drying was 5 to 8 μm. It was The particle diameter of titanium oxide was 2 μm or less.

White light diffuse reflector made of polyester with a thickness of 0.125 mm (Melinex 329 manufactured by ICI)
Was arranged so as to cover the entire surface of the light guide plate coated with the light diffusion material. The light diffusion plate (8B36 manufactured by GE) made of polycarbonate with a thickness of 0.18 mm is arranged so that the rough surface side is the opposite side to the light guide plate side and covers almost the entire light exit surface of the light guide plate. Two sheets were placed on top of each other. Invert the cold cathode tube.
The surface luminance when an alternating voltage of 30 KHz was applied to drive at a constant current (tube current of 5 mA) was measured with a luminance meter (Topcon BM-7).

The measured average luminance in the light emitting surface is 588 cd / m.
² , the chromaticity coordinate x was 0.3734, and y was 0.4058. (Comparative Example) Next, a backlight was constructed in the same manner as in Comparative Example except that titanium oxide having an anatase type crystal structure was used in place of titanium oxide having a rutile type crystal structure. It was measured at.

The average luminance measured on the light emitting surface is 590 cd / m 2.
² , the chromaticity coordinate x was 0.3714, and y was 0.4018. That is, by using titanium oxide having an anatase type crystal structure instead of the rutile type, the chromaticity coordinate x, while maintaining the brightness of the backlight at a constant power consumption,
We were able to shift y to a lower value. (Example) Incidentally, when the chromaticity coordinates of the cold cathode fluorescent tubes used in the comparative example and the example were measured in the same manner as in the comparative example, x = 0.3610, y =
It was 0.3775.

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional (invention) backlight.

FIG. 2 is a sectional view of a conventional (invention) backlight.

[Explanation of symbols]

 1: Light guide plate 2: Light diffusion sheet 3: Light reflection sheet 4: Linear light source 5: Light reflection plate or film 6: Light diffusion material

Claims (1)

[Claims] 1. A light guide plate made of a translucent material having a linear light source in the vicinity of an end portion of a side surface, and a light diffusing substance having a refractive index higher than that of the translucent material is partly formed on a wide surface thereof. A light guide plate for a backlight, wherein the light guide plate is applied specifically and the substance is an anatase type titanium oxide.