JPH05313004A - Light adjusting sheet and liquid crystal display device provided with the sheet - Google Patents

Abstract

PURPOSE:To improve luminance in the front direction by disposing numerous protrusions with the tip thereof rounded into protruding arc shape in cross section and numerous recessions with the root parts thereof rounded into recessed arc shape in cross section alternately and approximately parallel on one face of a sheet. CONSTITUTION:Numerous protrusi6ns 9 with the top parts 9a thereof rounded into protruding. arc shape in cross section, and numerous recessions 12 with the root parts 12a thereof rounded into recessed arc shape in cross section are disposed alternately and approximately parallel on the light outgoing face of a square sheet. It is desirable that one slant face of the protrusion 9 and recession 12 is curved or bent to some extent within a range of not lowering converging performance, and the approximately parallel state means that the respective top parts 9a of numerous protrusions 9 and the respective root parts 12 of numerous recessions 12 are approximately parallel. The back face of the sheet is formed into the fine irregular face by a mat-rolling method so as to be made into the optically unsmooth face. The luminance in the front direction is thereby improved, and the angle of visibility is enlarged, and that there is no fear of optical adherence to a light guide plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display such as a liquid crystal display such as a personal computer or a word processor or a liquid crystal color television, and a light control sheet constituting the same.

[0002]

2. Description of the Related Art Word processors and personal computers have become smaller, lighter and thinner year after year, and so-called notebook size has become the mainstream. A liquid crystal display device called a notebook type or a laptop type does not normally have a self-luminous property, and therefore a planar light source device is provided on the back surface thereof to improve visibility. Among them,
A type called an edge light system in which a light source is arranged on one side surface or both side surfaces of the device is widely used from the viewpoints of thinness, light weight, and power saving.

An edge light type planar light source device is shown in FIG.
It has the basic structure shown in. That is, in this device, the cathode tubes (1) as light sources are arranged on both side surfaces of the light guide plate (6) made of a transparent plate. A dot pattern (5) is formed on the back surface of the light guide plate (6). The light guide plate (6) has a reflector plate (3) on the back side, and the light guide plate (6) has a light diffuser sheet on the front side, which is made of a resin plate containing a light diffusing agent or a resin plate with a textured surface. (4) is provided (JP-A-3-7)
8701, JP-A-63-75053).

Edge light type dot pattern (5)
Is a light-scattering print pattern formed on the back surface of the light guide plate (6) in order to allow the light incident from the side fluorescent lamp (1) to be emitted uniformly from any position on the screen. It can be said that.

When the liquid crystal display screen is used, the light diffusing sheet is a light source for the rear surface through the liquid crystal display element (2), that is, a dot pattern which is a pseudo light source in the edge light system.
(5) is not visually recognized, and functions so that it can be regarded as a uniformly emitting surface.

In this system, when the brightness (luminance) of the screen is insufficient, the front surface of the light guide plate (6) has a prism shape as shown in FIG. A light control sheet (8) consisting of a prism sheet is arranged to limit the emission direction, and the light diffused by the light diffusion plate is collected in the direction of the user such as the word processor, that is, the direction of the screen direction, and a higher brightness is obtained. A device for obtaining a screen has been devised (JP-A-62-144102, JP-A-2-25).
No. 7188, Japanese Utility Model Laid-Open No. 2-78924).

[0007]

In the surface light source device of the type shown in FIG. 6 which does not use the light control sheet, the amount of light emitted in a direction other than the direction of the user (the normal direction of the screen) is large and the brightness is high. Was large and the amount of light emitted toward the user was small, so the brightness of the screen was not sufficient as shown by the broken line (D) in FIG.

Further, in the planar light source device having the prism sheet shown in FIG. 7, since the incident direction and the outgoing direction of light are excessively determined, the outgoing direction is deflected in the front direction within a narrow angle range, and The viewing angle tended to be too narrow (see the luminance distribution for each observation direction shown by the solid line (C) in Fig. 5).

Further, when the light control sheet made of a prism sheet is arranged so that the flat rear surface thereof and the light guide plate are in direct contact with each other, both of them partially cause optical contact, and only that portion shines abnormally bright, Interference patterns may occur,
There is a drawback that the light diffusivity becomes low and the dot pattern on the back surface of the light guide plate can be seen, and further, the grid-like division lines on the liquid crystal display surface and the ridge lines and valley lines of the prism sheet cause interference (moire phenomenon). It was

In view of the above points, the present invention improves the brightness in the front direction as compared with the case where the light control sheet is not used, and has a wider viewing angle than the conventional light control sheet.
Moreover, it is an object of the present invention to provide a light control sheet for a planar light source device that does not cause optical contact with the light guide plate.

[0011]

The light control sheet according to the present invention has been devised to achieve the above-mentioned object. It has a large number of ridges whose tops are rounded in a convex arc shape in cross section and valleys on one side. Are arranged alternately and substantially in parallel with each other, and a large number of concave lines rounded in a concave arc shape in cross section, and the other surface is optically non-smooth.

At least one of the ridges and the ridges is preferably slightly curved or bent within a range that does not deteriorate the light-collecting performance. Throughout this specification, “substantially parallel” means that the tops of the multiple ridges and the valleys of the multiple ridges are substantially parallel.

A method for measuring the emission light brightness of the planar light emitting device will be described.

In FIG. 2, the normal direction of the light emitting surface of the planar light emitting device (7) is 0 °, and the brightness of a point P on the light emitting device (7) passes through P and is parallel to the light source (1). With a straight line as the axis −
From several positions in the range of 90 ° to + 90 °, the luminance meter (1
Measure each according to 0). Of the values obtained in this way, the maximum brightness value is set to 100%, and the values at other positions are set to%.
Is displayed, and the relationship between the measurement position and the brightness is plotted in the figure.

The solid line (A) and the broken line (B) in FIG.
FIG. 3 shows a luminance distribution in an edge lamp type light emitting device having a basic structure as shown in FIG. Solid line in Figure 4
(A) shows the luminance distribution with a wide viewing angle, and the broken line (B) in FIG.
Indicates a luminance distribution in which a large amount of light is emitted in the direction of the user (the normal direction of the screen).

The large number of ridges on the light control sheet serve to collect more of the light emitted from the light control sheet in the direction normal to the screen. The angle between the two slopes of each ridge is 30 to 150.
And preferably in the range of about 60-120 °. 30 °
If it is less than 150 ° C., it is difficult to form ridges, and if it exceeds 150 °, the light-collecting ability may be reduced.

The material of the light control sheet is not particularly limited as long as it is a transparent organic material or inorganic material. Examples of transparent organic materials include resins such as polycarbonate, polyester, polymethylmethacrylate, and polyvinyl chloride.
A typical example of a transparent inorganic material is glass. The light control sheet is
Preferably, it is made of the same resin as the base resin of the light diffusion sheet described later.

The formation of a large number of ridges is usually carried out on the light exit surface of the sheet, but it may also be carried out on the light entrance surface. The tops of the ridges are rounded in a convex arc shape in cross section in a range that does not impair the light-collecting performance, and the troughs of each ridge are rounded in a concave arc shape in cross section in a range that does not impair the light-collecting performance. The radius of curvature of these convex arcs and concave arcs is determined by the groove depth, apex angle, pitch, etc. of the convex stripes, but is preferably 10 to 100 μm.

The sheet production means and the method for forming the ridges and the ridges include casting, solvent casting, profile extrusion, roll embossing while extrusion, hot pressing to a flat plate, monomer casting, There are injection molding methods and the like, but the forming method is not limited to these.

The other surface, that is, the surface having no convex stripes or concave stripes is a non-smooth surface. The non-smooth surface is preferably, for example, one on which fine and random uneven surfaces are formed. The size and depth of the unevenness are not particularly limited as long as the surface is in contact with a smooth surface and optical contact does not occur with a size that is visible to the naked eye. The non-smooth surface may also be a gentle corrugated surface.

As a method for forming a non-smooth surface, a method of transferring a pattern of a roll, a mold or the like at the same time as molding the surface,
A method of shaping the formed sheet by calendering, sandblasting, chemical etching, mat processing, pressing or the like can be applied. Particularly preferable examples of the method for forming the non-smooth surface are a mat processing method, a sandblast method, a pressing method and the like.

The thickness of the light control sheet is 50 μm or more, preferably 90 to 300 μm. If this thickness is less than 50 μm, it may be difficult to shape the ridge.

The light control sheet thus constructed is used as an element of a planar light emitting device. That is, as shown in FIG. 2, the light control sheet (8) having the above structure, the light guide plate (6) provided behind the light control sheet and having the printed dot pattern (5) on the back surface, and the light guide plate (6). ) Light sources on both sides (1)
Thus, the planar light emitting device (7) including the light guide plate (6) and the reflection plate (3) provided on the rear side of the light guide plate (6) can be obtained. Planar light emitting device (7)
A liquid crystal display element is provided on the front side of.

Next, each element constituting the planar light emitting device (7) will be described.

First, the light control sheet (8) has the above-mentioned structure. The light control sheet (8) may be used by stacking a plurality of sheets, or may be used together with a conventional type light diffusion sheet (4) described later.

A cathode ray tube is usually used as the light source (1). The cathode tube may be a cold cathode tube or a hot cathode tube. The size of the cathode tube and the like are not limited. Cathode tube is a light guide plate
It is provided on both the left and right side surfaces of (6) or on one of the side surfaces. Further, it may be provided on three sides or all four sides of the light guide plate (6).

The light guide plate (6) is made of a material with good transparency such as glass, polycarbonate, polyester, polymethylmethacrylate, etc., and the light from the light source (1) is emitted on its rear surface, that is, the surface on the reflector side. It has a printed dot pattern (5) that causes irregular reflection so that light is emitted uniformly from any position. The thickness and the like of the light guide plate (6) are not limited.

As the reflection plate (3), a resin plate mixed with a white pigment, a foamed resin plate, a metal deposition resin plate, a metal plate, etc.
Any plate-shaped member having a function of blocking light rays can be applied without limitation. The reflector (3) is arranged on the non-light emitting surface side of the light guide plate (6) and is in contact with the printed dot pattern (5) of the light guide plate (6).

The light diffusing sheet (4) is provided so that the shape of the printed dot pattern (5) of the light guide plate (6) is not visible to the user.
It diffuses light rays, and there are conventionally known light diffusing agent kneading type and random unevenness processing type. The thickness of this sheet is not limited, but is usually 10 μm or more, preferably 20 to 300 μm. If this thickness is less than 10 μm, sufficient diffusivity may not be obtained. The resin constituting the light diffusion sheet (4) is not particularly limited as long as it is a transparent resin, and as the transparent resin, polycarbonate,
Examples include polyester and polymethylmethacrylate. As the light diffusing agent, a conventionally known one can be applied,
For example, titanium oxide, glass fiber, glass beads, silica / alumina, etc. are exemplified. The compounding amount of the light diffusing agent is
It is preferably 5 to 100 relative to 100 parts by weight of the transparent resin.
Parts by weight, more preferably 10 to 50 parts by weight. Light diffusion sheet (4) As a method of forming a sheet for manufacturing, a method of hot pressing a material, a method of extruding the material with a T-die, a flow casting method, or any other known method can be applied and formed. Haze value from 50 to 9
The molding method is not particularly limited as long as it is 0%, preferably 70 to 85%.

[0030]

The present invention will be described in detail with reference to the following examples.

Example 1 In FIG. 1, melt index (290 ° C., 1.9 k)
g) A large number of convex stripes (9) and a large number of concave stripes (12) are formed alternately and in parallel on the light emitting surface of a rectangular sheet of polycarbonate of 4.0. The top (9a) of each ridge (9) is rounded in a convex arc shape in cross section, and the trough (12a) of each ridge (12) is rounded in a concave arc shape in cross section. The angle formed by the two slopes of the ridge (9) is approximately a right angle. The total thickness of the sheet is 200μ
m, the height from the top (9a) of the ridge (9) to the valley (12a) of the groove (12) is 120 μm, the pitch of the ridge (9) and the groove (12)
The pitch of each is 350 μm. The radius of curvature of each crest (9a) of each ridge (9) and each trough (12a) of each groove (12) is 6
It is 7 μm. The ridges (9) and the ridges (12) are molded by the hot pressing method. The back surface (11) of the sheet is shaped into a fine uneven surface by a mat roll method. Thus, a light control sheet (a) having a large number of ridges (9) on the front surface and an uneven surface on the back surface (11) is formed.

Performance Test Regarding the planar light emitting device equipped with the above-mentioned light control sheet, the front luminance and the luminance ratio were measured, and the appearance was observed.

I) Luminance In order to measure the brightness of the screen, the cathode tube (1) and the light guide plate (8)
A planar light emitting device was manufactured by using the following as the reflection plate (3) and the light diffusion sheet (4).

Cathode tube: diameter 3.0 mm, length 130 mm
Cold cathode tube Light guide plate: length 130mm, width 260mm, thickness 3.0m
m, material acrylic resin, dot printing for irregular reflection is applied on the lower surface Reflector: thickness 100 μm, white pigment (titanium oxide) 20
Polycarbonate in which wt% is kneaded Light diffusion sheet: Polycarbonate in which 10 wt% of calcium carbonate is kneaded.

In FIG. 2 showing the basic structure of the edge-light type planar light emitting device, the cathode tube (1) as a light source is arranged on both sides of the light guide plate (6) having the printed dot pattern (5) on the back surface. Has been done. The light guide plate (6) is provided with the reflection plate (3) on the rear side, and the light control plate according to the present invention is provided on the front side of the light guide plate (6).
(8) is located. The light control sheet (8) is installed such that the surface provided with the ridges (9) becomes the light emitting surface and the ridges (9) are parallel to the cathode tube (1).

In the planar light emitting device (7), the normal (0
The brightness was measured from the () direction and from the normal direction at 30 °. The luminance measurement is as described above.

II)) Appearance In the above-mentioned planar light emitting device (7), it was examined whether or not there was a problem in appearance on the screen. Examples 2 to 4 In the same manner as in the case of the sheet (a), the light control sheet (b) (c) was changed in the same manner as in the case of the sheet (a) by changing the sheet material, the size of the convex stripes and the concave stripes, and the shaping method of the back surface. ) (d) was obtained. A performance test was conducted on the planar light emitting device provided with the light control sheet in the same manner as in Example 1. The light control sheet (d) of Example 4
Is as shown in FIG. 3, and the non-smooth surface (11) is formed into a gentle corrugated surface by the pressing method.

Comparative Example 1 A performance test was conducted in the same manner as in Example 1 with respect to the planar light emitting device having no light control sheet according to the present invention.

Comparative Examples 2 to 3 The sheet material, the size of the ridges, and the method of shaping the back surface were changed to the values shown in Table 1, and the light control sheets (e) and (f) were obtained in the same manner as in the case of the sheet (a). ) Got. A performance test was conducted on the planar light emitting device provided with the light control sheet in the same manner as in Example 1.

Table 1 shows the sheet materials of the light control sheets of Examples and Comparative Examples, the size of the ridges, the shaping method of the back surface, and the performance test results.

[0041]

[Table 1] As is clear from Table 1, the light-control sheets of the examples are 30 ° from the normal (0 °) direction and from the normal, as compared with those of the comparative examples.
It shows excellent brightness in the direction of ° and is superior in appearance.

[0042]

The light control sheet according to the present invention has one surface
A large number of ridges whose tops are rounded in a convex arc shape in cross section and a large number of ridges whose valleys are rounded in a concave arc shape in cross section are arranged alternately and substantially in parallel. The planar light emitting device used can improve the brightness in the front direction as compared with the case where the light control sheet is not used, and ensures that the dot pattern on the back surface of the light guide plate cannot be seen,
It exhibits an appropriate light diffusivity and can maintain the same viewing angle as a liquid crystal display element. Furthermore, the grid-like division lines on the liquid crystal display surface interfere with the ridge lines and valley lines of the prism sheet (moire phenomenon). You can keep coming.

Further, since the other surface of the light control sheet is optically non-smooth, the light control sheet does not come into optical contact with the light guide plate to cause interference, and is also effective for light diffusion. Contribute.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a light control sheet.

FIG. 2 is a schematic diagram showing a method of measuring brightness in an edge light type planar light emitting device using the light control sheet of FIG.

FIG. 3 is a cross-sectional view showing a light control sheet.

FIG. 4 is a diagram showing a luminance distribution in an edge lamp type light emitting device.

FIG. 5 is a diagram showing a luminance distribution in an edge lamp type light emitting device.

FIG. 6 is a cross-sectional view showing a conventional edge light type planar light emitting device.

FIG. 7 is a cross-sectional view showing a conventional edge light type planar light emitting device.

[Explanation of symbols]

 (1) Light source (2) Liquid crystal display element (3) Reflector (4) Light diffusion sheet (5) Dot pattern (6) Light guide plate (7) Planar light emitting device (8) Light control sheet (9) Convex strip ( 9a) Top part (10) Luminance meter (11) Back surface (12) Recessed line (12a) Valley part

Claims (4)

[Claims] 1. A plurality of ridges whose tops are rounded in a convex arc shape in cross section and a plurality of ridges in which troughs are rounded in a concave arc shape in cross section are arranged alternately and substantially in parallel on one surface. The light control sheet, wherein the other surface is optically non-smooth. 2. The light control sheet according to claim 1, wherein the non-smooth surface is a fine uneven surface formed by a mat processing method, a sandblast method or a pressing method. 3. The light control sheet according to claim 1, wherein the non-smooth surface is a gently corrugated surface. 4. A liquid crystal display device comprising the light control sheet according to claim 1.