JPH08129175A - Light control sheet and surface light emission device provided with the sheet - Google Patents

Abstract

PURPOSE: To provide a light control sheet provided with such condensing property that the front surface direction of a liquid crystal display, a liquid crystal television or an illuminated signboard becomes sufficiently bright and constituted so that they are viewed to be uniformly bright in all directions within the range of some visual field angle and emitting loss is eliminated when it is used for the liquid crystal display, the liquid crystal television or the illuminated signboard and a surface like light emission device provided with this light control sheet. CONSTITUTION: The light control sheet 10 is adjacently provided with many almost triangular pyramid-like projections 11 on at least on surface. It is desirable that the bottom surface of the projection 11 is an equilateral triangle and the length of one side thereof is >=30μm and <=150μm. It is desirable that an angle formed by the side surface of the projection 11 and the sheet surface of the sheet 10 is >=35 deg. and <=55 deg.. The apex of the projection may be round. It is desirable that the interval between the adjacent projections 11 is <=10μm. Also, the surface light emission device is provided with the light control sheet 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control used for a surface light emitting device which constitutes a liquid crystal display such as a personal computer and a word processor, a liquid crystal color television, or a surface light emitting device which is used for an illuminated signboard, facility lighting and the like. The present invention relates to a sheet and a planar light emitting device including the sheet.

[0002]

2. Description of the Related Art In an edge light type planar light emitting device, a fluorescent tube 1 is disposed on an end face 3 side of a light guide plate 2 as shown in FIG. The back surface of the light guide plate 2 is provided with a dot pattern 4 formed by dot printing of a paint, and the back surface of the light guide plate 2 is further provided with a reflection plate 5.

In the above structure, the light beam emitted from the fluorescent tube 1 enters the inside of the light guide plate 2 from the end surface 3 of the light guide plate 2, is diffusely reflected by the dot pattern 4 on the back surface of the light guide plate 2, and is reflected from the surface of the light guide plate 2. Is released. FIG. 3 shows the intensity distribution of the light rays emitted from the surface of the light guide plate 2 with respect to the emission angle. Most of the light rays are emitted in a direction largely deviated from the direction normal to the light guide plate 2, and the distribution thereof is extremely steep (intensity distribution 6). For this reason, the screen is usually very dark for the user who observes from the normal direction of the light guide plate 2.

In order to overcome this drawback, a method of installing a light diffusion sheet on the surface of the light guide plate has been devised. The light diffusion sheet is a transparent plastic sheet surface coated with white pigment, titanium oxide, glass short fibers, etc., or contained therein, or the surface of the transparent plastic sheet is processed to have fine irregularities (matting, It is obtained by graining). FIG. 4 shows the intensity distribution with respect to the emission angle of light rays when the light diffusion sheet 7 is used. in this case,
It can be seen that the emission of light rays in the normal direction is increased as compared with FIG. 3 (intensity distribution 8).

However, in the intensity distribution when the light diffusing sheet 7 is used, a large number of light rays are emitted in a direction unnecessary for the user, and diffuse reflection at the interface between the light diffusing sheet 7 and the light guide plate 2 occurs. The loss of rays due to is not negligible.

Therefore, as a method for improving these drawbacks, it has been attempted to use the prism sheet 9 having the structure shown in FIG. 5 instead of the light diffusing sheet. The prism sheet 9 is formed by arranging small prisms having a substantially triangular cross section in a flat plate shape, and is an optical function sheet having a function of refracting or reflecting a light ray incident on the prism. When the prism sheet 9 is used, the intensity distribution with respect to the emission angle of the light beam is as shown in FIG. 6, and the emission of the light beam in the normal direction is significantly increased (intensity distribution 10).

[0007]

However, when the prism sheet 9 is used, as shown in FIG. 6, the intensity distribution 10 at each emission angle of the light rays of the prism sheet 9 is such that the light rays are remarkably emitted in the normal direction. Although it increases, since the directivity of the emitted light is too strong, the viewing angle is very narrow, and the observed brightness sharply decreases when the position of the user moves slightly. In particular, the viewing angle in the direction perpendicular to the groove of the triangular cross section becomes extremely narrow. That is, the viewing angle characteristics differ depending on the left, right, front and back of the surface emission property, and there is a drawback in that a constant viewing angle cannot be obtained from any surface.

Further, since the cross-sectional shape of the prism is an isosceles triangle which is bilaterally symmetrical, unnecessary emission light such as emission light Y is emitted in addition to the effective emission light X in the normal direction as shown in FIG. Many occur. In addition, interference with the liquid crystal display element may cause a problem of (moire).

In view of the above points, the present invention has a condensing property that makes the front direction sufficiently bright when used in a liquid crystal display, a liquid crystal television, an illuminated signboard, or the like, and can be used in any viewing angle range. It is an object of the present invention to provide a light control sheet that looks evenly bright in the direction and has no emission loss, and a planar light emitting device including the light control sheet.

[0010]

The present invention provides a light control sheet characterized in that a large number of substantially triangular pyramid-shaped projections are provided adjacent to each other on at least one surface.

It is preferable that the bottom surface of the substantially triangular pyramid-shaped projection is an equilateral triangle, and the length of one side thereof is 30 μm or more.
It is preferably 50 μm or less. Further, the angle formed between the side surface of the protrusion and the sheet surface of the light control sheet is 35 ° or more 5
It is preferably 5 ° or less. Further, it is desirable to provide a roundness at the apex of the protrusion. Further, it is desirable that the gap between the adjacent protrusions is 10 μm or less.

The present invention also provides a planar light emitting device including the above light control sheet.

Next, the present invention will be described in more detail.

FIG. 1A shows an example of the light control sheet of the present invention. The light control sheet 10 of the present invention is provided with a plurality of substantially triangular pyramid-shaped protrusions 11 adjacent to each other on at least one surface. Specifically, a large number of substantially triangular pyramid shaped ridges 11 are arranged so that the bases 13 are adjacent to each other without a gap.

In the light control sheet of the present invention, the directional light incident from the back surface is emitted in the front direction while being refracted by the substantially triangular pyramidal projections 11 arranged on the structural surface, and the effect is obtained. It largely depends on the inclination angle of the side surface of the protrusion 11. In order to obtain good light emission characteristics, as shown in an enlarged view in FIG. 1B, it is desirable that the angle α formed by the side surface of the protrusion 11 and the sheet surface be 35 ° ≦ α ≦ 55 °, particularly 45. ° is optimal. The bottom surface of the protrusion 11 is preferably a regular triangle, and the length of one side thereof is 30 μm or more and 150 μm.
The following is desirable.

The distance b between the bases 13 of the adjacent protrusions 11 is preferably 10 μm or less. That is, since the space between adjacent bases 13 (valleys) does not contribute to light collection, the smaller the interval b, the better. If the distance b exceeds 10 μm, a problem occurs in the light-collecting density, leading to a decrease in front luminance and a decrease in image quality.

The apex 12 of the substantially triangular pyramidal protrusion 11
May be rounded, or may have a structure having a plane parallel to the bottom surface of the protrusion 11. This allows the absolute value of the viewing angle to be adjusted.

The material of the light control sheet is not particularly limited as long as it is a transparent resin, but a resin having good light transmittance such as polymethylmethacrylate or polycarbonate is preferable. Then, a predetermined sheet is obtained by shaping these resins by a method such as heat melting or photocuring, but the manufacturing method is not particularly limited.

The total thickness of the light control sheet is 0.10 to 0.
50 mm is preferable. If the thickness is 0.10 mm or less, the light control sheet is not stiff and is difficult to handle. If it is 0.50 mm or more, there is a problem in that it is difficult to miniaturize a planar light emitting device using the same and the like.

The surface of the light control sheet opposite to the structure surface provided with the protrusions may be matted for the purpose of imparting diffusibility or the like.

[0021]

Next, an embodiment of the present invention will be described. The present invention is not limited to the examples described below, and various configurations are possible without departing from the spirit of the present invention.

The planar light emitting device shown below was equipped with the light control sheet of each of the examples or comparative examples, and the front luminance, the viewing angle and the emission appearance quality were examined.

(Surface emitting device used) System: Edge light system on one side (1 lamp on short side) Light source: Cold cathode tube with thickness 3.5 mm, length 135 mm Light guide plate: Thickness 3 mm, width 205 mm, length 135 mm Of P
MMA plate Light diffusion sheet: A commercially available light diffusion sheet made of polycarbonate with a thickness of 0.20 mm (embossed with fine irregularities on the surface) is used to prevent the visibility of the dot pattern for imparting diffusivity to the back surface of the light guide plate. did. Applied pressure: 12V

(Evaluation method) Front brightness: The brightness (normal direction) from the front direction at 9 points where the backlight was determined was measured based on JIS-C761 and the average value was obtained. Viewing angle: An angle having a value of 50% of the front luminance (normal direction luminance), which is obtained by measuring the luminance of one point in the center of the backlight with the angle changed in both directions parallel and at right angles to the cold cathode tube. I asked.

Light control sheets of Examples and Comparative Examples having the following projection shapes and sheet thicknesses were prepared.

[Example 1] Angle formed between the side surface of the protrusion (slope) and the sheet surface (hereinafter referred to as α): 45 ° Length of one side of the bottom surface of the protrusion (hereinafter referred to as l): 80 μm Sheet thickness (hereinafter referred to as T) Yes): 200 μm Base is an equilateral triangle

[Example 2] α: 40 ° l: 100 μm T: 200 μm The bottom surface is an equilateral triangle.

Comparative Example 1 Prism Sheet Prism Vertical Angle: 90 ° Sheet Thickness: 200 μm Prism Pitch: 100 μm (Note) Arrangement of prism sheet: Prism grooves were arranged parallel to the cold cathode tubes.

Comparative Example 2 α: 25 ° l: 150 μm T: 200 μm

The evaluation results are shown in Table 1.

[0031]

[Table 1]

[0032]

As described above, according to the present invention, when used for a liquid crystal display, a liquid crystal television, an illuminated signboard, or the like, a light-collecting property is obtained such that the front direction is sufficiently bright.
If it is within a certain viewing angle range, it appears bright in all directions and emission loss can be suppressed.

[Brief description of drawings]

FIG. 1 shows an embodiment of a light control sheet according to the present invention,
(A) is a plan view and (B) is an explanatory view showing the projection 11 in an enlarged manner.

FIG. 2 is a perspective view showing an example of a planar light emitting device.

FIG. 3 is an explanatory diagram showing an outgoing light distribution of a conventional planar light emitting device that does not use a light control sheet.

FIG. 4 is an explanatory diagram showing an outgoing light distribution of a conventional planar light emitting device using a light diffusion sheet.

FIG. 5 is a perspective view showing an example of a prism sheet.

FIG. 6 is an explanatory diagram showing outgoing light distribution of a conventional planar light emitting device using a prism sheet.

FIG. 7 is an explanatory diagram showing a state of emitted light of a conventional planar light emitting device using a prism sheet.

[Explanation of symbols]

 1 Fluorescent Tube 2 Light Guide Plate 3 End Surface of Light Guide Plate 4 Dot Pattern 5 Reflective Plate 10 Light Control Sheet 11 Protrusion 12 Apex 13 Bottom

Claims (2)

[Claims] 1. A light control sheet comprising a plurality of substantially triangular pyramid-shaped protrusions provided adjacent to each other on at least one surface. 2. A planar light emitting device comprising the light control sheet according to claim 1.