JPH08292324A - Light transmission body - Google Patents

Abstract

PURPOSE: To practically vertically and efficiently emit light incident from a light source and to equalize the luminance distribution of an emitting plane by successively increasing the area rates of plural recessed reflecting planes away from a light incident end face. CONSTITUTION: Plural recessed parts 6 are provided in parallel with a light incident end face 2 on a rear face 5 of a light transmission body 1, and the area rates of respective recessed reflecting planes 6a are successively increased away from the light incident end face 2. The cross-sectional shape of recessed part 6 is formed by the recessed reflecting plane 6a and its confronted plane 6b. When the apex angle formed by the recessed reflecting plane 6a and the confronted plane 6b is defined as θ, concerning the range of size for angles θ1 and θ2 divided by its normal, the cases of 30 deg.<=θ1 <=45 deg. and 0 deg.<=θ2 <=45 deg. are preferable from the character of full reflection of light. Thus, since the recessed reflecting plane 6a is arranged so that its area rate can be successively increased away from the light incident end face 2 as the function of a light transmission distance (x), the light can be uniformly emitted over all the light emitting plane 4 regardlessly of the light transmission distance in macro manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide for a charge eliminating light source for a photoconductor drum of a copying machine, a light source for reading an original document of a fax machine or an image scanner, or a light guide device for surface light emission of a liquid crystal display, a signboard, a lighting fixture or the like. Regarding the body

[0002]

2. Description of the Related Art As conventional surface light source devices, there are known a direct type in which a light source is arranged directly below the back surface of a display plate and an edge light type in which a light source is arranged on a side surface. The edge light type is now the mainstream because the device is favored to be lightweight and thin. An example of the edge light type surface light source device is shown in FIG.

In order to efficiently emit light, the light guide body made of a transparent material used here is printed with a white paint or the like on its back surface to form a light diffusion pattern.
The light diffusion pattern changes a dot-shaped or mesh-shaped dot pattern pattern in accordance with the distance from the light source for the purpose of making the brightness distribution on the light emitting surface uniform. (For example, Japanese Patent Application Laid-Open No. 57-12838) However, in this method, when the composition of the coating material changes, the light reflection performance changes and the brightness is not uniform, and there is light absorption loss due to the pigment. If the screen mesh used for screen is clogged, dot-like or mesh-like patterns will not be printed accurately, and uniform brightness distribution cannot be reproduced. This also reduces productivity and hinders cost reduction. .

[0004]

SUMMARY OF THE INVENTION Accordingly, the problem to be solved by the present invention is to solve the problems of the prior art, and to make the light incident from the light source substantially vertical in spite of its simple structure. It is to provide a light guide body that efficiently emits light, has a uniform luminance distribution on the exit surface, and has high productivity.

[0005]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, as a result, a plurality of transparent light guides having a plurality of surfaces parallel to the light incident end surface are formed on the back surface facing the light emitting surface. When the area ratio of the plurality of concave reflecting surfaces is gradually increased with increasing distance from the light incident end face, and the light is emitted from the light emitting surface while sequentially reflecting the light by the plurality of concave reflecting surfaces, the light is emitted. The present invention has been completed by finding that a light guide body having uniform brightness over the entire surface can be obtained.

Although not limited thereto, the present invention will be described in detail with reference to the drawings in order to facilitate understanding of the contents.

FIG. 1 is a side cross-sectional view showing an example of a one-side incident type light guide used by installing a light source on one end face,
(A) is an enlarged view of part A. In the figure, 1 is a transparent light guide, 2 is a light incident end face, 3 is an end face facing the light incident end face 2, 4 is a light emitting face, 5 is a back face facing the light emitting face, 6
Indicates a concave portion provided on the back surface.

The light guide 1 is made of a transparent resin such as methacrylic resin, polycarbonate or polyvinyl chloride having a high light transmittance, and the incident end face 2 is smooth because it is necessary to efficiently introduce light into the light guide 1. I'm on the surface.

The end face 3 facing the incident end face 2 is also preferably a smooth surface. The light emitting surface 4 is preferably mirror-finished so that the light can be emitted smoothly. The back surface 5 is the surface facing the light emitting surface 4, and it is preferable that the portion having no recess is mirror-finished.

As shown in FIG. 1, in the light guide according to the present invention, a plurality of recesses are provided on the back surface 5 of the light guide 1 in parallel with the light incident end face 2, and the area ratio of each recess reflection surface is large. , Light incident end face 2
It is designed to increase gradually as it moves away from.

As shown in FIG. 1A, the cross-sectional shape of the concave portion 6 is formed by a concave reflecting surface 6a and a facing surface 6b thereof. The apex angle formed by the concave reflecting surface 6a and the facing surface 6b is θ
Where the range of the angles θ ₁ and θ ₂ divided by the normal is 30 ° ≦ θ ₁ ≦ 4 due to the property of total internal reflection of light.
The case of 5 ° and 0 ≦ θ ₂ ≦ 45 ° is preferable.

That is, θ is 30 to 90 °, preferably 6
It is 0 to 90 °. In addition, the concave reflecting surface 6a and the facing surface 6
b is preferably a substantially mirror surface obtained by molding, cutting or polishing of the light guide.

The number of recesses provided in the light guide, the distance between adjacent recesses, the area of the reflection surface of the recesses, etc. can be appropriately adjusted and determined according to the material of the light guide and the dimensions such as thickness and length. In any case, the light propagating in the light guide body by total reflection is reflected by each concave part reflecting surface by a certain amount, is emitted from the light emitting surface 4, and leaks and reaches the end face 3 facing the light incident end face. It is preferable to design so that the amount of

In the light guide shown in FIG. 1, the inventor of the present invention finds that most of the light emitted from the light emitting surface 4 is reflected light from the concave reflecting surface 6a, and the concave portion. When the pattern is defined indirectly by one-dimensional dimensions such as the depth and width of the recess, it is affected by errors due to processing accuracy during pattern formation. The area ratio was defined as the following formula (1), and it was considered to directly define it. Further, by providing a plurality of concave portions so that the area ratio of the concave reflecting surface 6a satisfies the following expression (2),
It was found that a more uniform luminance distribution can be obtained over the entire light emitting surface.

Area ratio of concave reflecting surface = (area of reflecting surface of concave / projected area per pitch) × 100 (1) m = {K / (L−x + l ₀ )} × 100 (2) where m = concave Area ratio of reflecting surface K = 5.66 (constant determined by experience) L = length of light guide, x = light guiding distance l ₀ = distance from light incident end face to first concave portion That is, the above formula ( As seen in 2), by making the area ratio of the concave reflecting surface a function of the light guide distance x, a certain amount of light can be emitted from the light emitting surface 4 regardless of the light guide distance. .

In the light guide of the present invention, the thickness (T) of the light incident end surface 2 is usually 2 though it depends on the size of the light source used.
6 mm is preferred. The interval (pitch) between adjacent recesses is preferably 600 μm or less at the maximum in order to make the uneven brightness of the recesses 6 and the back surface 5 inconspicuous. Further, it is not necessary to make it constant over the entire length of the light guide body, but rather it is partially changed so that the pitch becomes smaller as it goes away from the light incident end surface 2, and the concave portion is made so as to satisfy the area ratio of the above formula (2). It is easier to form the film in order to make the brightness uniform.

The light guide body in which the light source is arranged on one end face has been described above, but as shown in FIG.
It may be a light guide body in which a light source is arranged on both of the two light incident end faces 2 and the side end faces 7 facing the two light incident end faces 2.

In FIG. 2, 1 is a transparent light guide, 2 and 7
Is a light incident end surface, 4 is a light emitting surface, 5 is a back surface, and 6 is a recess.

In the light guide of the both-end surface light source type as shown in FIG. 2, the central portion of the light guide has the maximum distance from the incident end face, and the lack of brightness is most likely to occur. Are provided so that the area ratio thereof gradually increases so that the area ratio becomes maximum in the central portion, and the area ratio of each concave reflecting surface is symmetrical with respect to the center line.

In the light guide of the both-end surface light source type shown in FIG. 2, the area ratio of the concave reflecting surface can be obtained according to the above equation (2).

Further, as shown in FIG. 3, the back surface facing the light emitting surface may be formed to be inclined. In FIG. 3, 1 is a transparent light guide plate, 2 is a light incident end face, 3 is an end face facing the light incident end face 2, 4 is a light emitting face, 5 is a back face, and 6 is a recess.
In the light guide body whose back surface is inclined as shown in FIG.
In the light incident on the light guide from the light, the light propagating in the light guide and reaching the end face 3 facing the light incident end face 2 is reduced, and the light exit face 4 is reduced.
The effect is to increase the amount of light emitted from.

Further, as shown in FIG. 4, a light guide of the both-end surface light source type may also be formed so that the back surface facing the light emission surface is inclined. As for the light guide body as shown in FIG. 4, the light emitting surface 4 is the same as the light guide body of the one end face light source type shown in FIG.
The effect is to increase the amount of light emitted from.

Further, as shown in FIG. 5, the light incident end face may be formed in a convex lens shape toward the light source. In FIG. 5, the thickness (R) of the lens-like portion of the light incident end face is empirically 0 ≦ R ≦ T / 2 (T: thickness of the incident end face). Since the light is condensed, it has an effect of improving the incidence efficiency.

The method for producing the light guide of the present invention is not particularly limited, and it may be produced by cutting a flat plate of a transparent synthetic resin such as acrylic resin, polycarbonate or polyvinyl chloride, and injecting the resin. Depending on the molding material, transfer manufacturing may be performed by injection molding using a patterned die. In particular, when the injection molding method is adopted, it is possible to manufacture with high yield and high productivity.

[0025]

In the light guide of the present invention, the light from the light source enters the light guide 1 from the light incident end face 2 and is guided according to the law of total reflection (critical angle: 42 ° for acrylic resin, 39 ° for polycarbonate). Propagate in the light body. When this light is incident on the concave reflecting surface 6a, most of the light is directly emitted to the light emitting surface 4 due to reflection.

Further, since the area ratio of the concave reflecting surface is arranged so as to gradually increase as it goes away from the light incident end face 2 as a function of the light guiding distance x, the light emitting surface 4 is macroscopically independent of the light guiding distance. Can be emitted uniformly over the entire surface. Compared with the conventional technique of forming a light diffusion pattern by printing paint or the like, light absorption by paint or the like can be eliminated, so that the brightness is improved and the brightness distribution becomes uniform.

[0027]

EXAMPLES Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1 A substantially triangular recess (vertical angle θ = 85) was formed on the back surface of a transparent methacrylic resin plate having a thickness of 5 mm, a width of 204 mm and a length of 156 mm.
°, was prepared theta ₁ = theta ₂₎ light guides formed by cutting as the area ratio of the concave reflecting surface satisfies the equation (2).
M = 3.5 at x = 4 mm in the first recess of the light guide
4%, x = 150 mm in final recess m = 56.
It was 6%. Using this light guide, a cold cathode type fluorescent tube having a tube diameter of 3 mm is arranged on the light incident end face 2 side, and the remaining surface of the light guide except the light incident end face and the light emitting face and the outer circumference of the tubular light source are arranged. By covering with a white polyester reflective film, a general surface light source device shown in FIG. 6 was produced. In the surface light source device produced above, the brightness on the light emitting surface 4 of the light guide was measured with a brightness meter BM-8 manufactured by Topcon.

As a result, it was found that the luminance level was high over the entire surface, and the luminance uniformity was calculated according to the following equation (3) to be 85%, which was almost uniform.

Luminance uniformity ratio = {(minimum luminance) / (maximum luminance)} × 100 (3) Example 2 Formed so that the back surface facing the light exit surface as shown in FIG. 3 is inclined, and otherwise A light guide was prepared in the same manner as the light guide of Example 1. When a surface light source device similar to that of Example 1 was manufactured using the light guide and luminance was measured by the same method as in Example 1, the luminance uniformity ratio was 84 as compared with Example 1.
%, It was almost the same, but it was found that the brightness level was improved by about 2%.

Example 3 A back surface of a rod-shaped transparent methacrylic resin having a thickness of 6 mm, a width of 10 mm and a length of 308 mm was cut into a shape in which the back surface is inclined as shown in FIG. An incident light guide was created.

The concave portion of the light guide is the same as that of the first embodiment, m = 3.
The area ratio was 54% to 56.6%, and the area ratio was maximized at the center in the longitudinal direction of the light guide. Example 1 A double-sided incident type rod-shaped surface light source device in which LED light sources each having a diameter of 5 mm are arranged on both light incident end surfaces of the light guide is manufactured, and
When the luminance was measured in the same manner as in 1., the central portion was not dark and the luminance uniformity was 85%, which was almost uniform.

Comparative Example 1 A surface illuminant device was produced by using a transparent methacrylic resin plate without recess formation (the same methacrylic resin plate used in Example 1) as it was as a light guide, and producing a surface light source device in the same manner as in Example 1. When the luminance was measured by the method, there was almost no light emitted in the plane direction, and the luminance level was extremely low over almost the entire light emitting surface.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the area ratio of the concave reflecting surface formed on the back surface of the light guide was m = 10% (constant) regardless of the light guide distance. A light guide was produced by Using this light guide, a surface light source device similar to that in Example 1 was produced and luminance was measured in the same manner as in Example 1. As a result, the luminance in the vicinity of the light incident end face was high and It was found that the luminance was low at the positions where the luminance was uniform and the luminance uniformity was 15%.

[0035]

According to the light guide of the present invention, it is possible to uniformly emit light over the entire surface of the light exit surface without unevenness of brightness, and even the angle of the reflected light in the light guide that becomes the exit light. You can control. Further, since light is not absorbed as compared with a conventional light guide plate using a light diffusion pattern formed by painting or the like, light can be efficiently emitted. Further, since the injection molding method can be adopted for manufacturing the light guide, productivity is improved. Therefore,
The light guide of the present invention is a useful light guide for a general sidelight type surface light source device.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a one-side incidence type light guide, and FIG. 1 (a) is an enlarged view of part A.

FIG. 2 is a side cross-sectional view showing an example of a both-end surface incident type light guide.

FIG. 3 is a side cross-sectional view showing an example of a light guide body of a one-sided incidence type in which a back surface facing a light emission surface is inclined.

FIG. 4 is a side cross-sectional view showing an example of a light guide body which is formed in such a manner that the back surface facing the light exit surface is inclined in a both-end surface incident type.

FIG. 5 is a partial cross-sectional view showing an example of a light guide body in which a light incident end face is formed in a convex lens shape toward a light source.

FIG. 6 is a side sectional view of an example of a flat light source device using the light guide of the present invention.

FIG. 7 is a side sectional view showing the structure of a conventional surface light source device,
(B) is a plan view showing an example of a light diffusion pattern.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light guide 2 ... Light incident end surface 3 ... End surface 4 ... Light emission surface 5 ... Back surface 6 ... Recessed part, 6a ... Recessed reflective surface, 6b ... Opposing surface 7 ... Side end surface 8 ... Light source 9 ... Reflective sheet (or film) 11 ... Diffusion sheet (or film) 12 ... Specular reflection layer 13 ... Light diffusion pattern 14 ... Light emitting surface 15 ... Light scattering material

Claims (3)

[Claims] 1. A transparent light guide body is provided with a plurality of concave portions parallel to a light incident end surface on a surface facing a light emitting surface, and an area ratio of the concave reflecting surface to a projected area per pitch is calculated from the incident end surface. A light guide characterized by being increased in sequence as the distance increases. 2. The light guide according to claim 1, wherein the back surface facing the light emitting surface is inclined. 3. The light guide according to claim 1, wherein the light incident end face is formed in a convex lens shape toward the light source.