JPH10339815A - Light guide plate, manufacture of light guide plate, and surface light source using the light guid plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use one lenticular lend sheet or eliminates the need of it and to eliminate the need to print a light scatter dot pattern on the reverse surface of the light guide plate by forming grooves at intervals decreasing with the distance from a light incidence surface and then optimizing the reverse surface structure of the light guide plate. SOLUTION: The light emitted by a light source enters the light guide plate 1 from its light incidence surface 5 and is reflected by a light reflecting surface 3, grooves 4a1 to 4a4, and the flank to exit from its light projection surface 2. On the light reflecting surface, groove 4a1 to 4a4 which are triangularly sectioned and nearly equal in groove width 4c are formed almost in parallel to the light incidence surface 5. The grooves 4a1 to 4a4 have groove intervals 4da to 4d3 decreased gradually with the distance from the light incidence surface. Here, the reverse surface structure of the light guide plate 1 is so optimized so that, specially, the interval 4d1 from the far end of the groove 4a1 closest to the light incidence surface 5 to the near end of the next groove 4a2 is 5 to 15 times as large as the groove width 4c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate, a method for manufacturing the light guide plate, and a surface light source using the light guide plate.
The present invention relates to a surface light source used for a traffic sign, a light guide plate provided in the surface light source, and a method for manufacturing the light guide plate.

[0002]

2. Description of the Related Art As a surface light source for a backlight of a liquid crystal display (LCD), a side light type using a light-transmitting flat plate as a light guide plate is known. In such a surface light source,
Light is incident from one of the side end surfaces of a light guide plate made of a transparent parallel plate or a wedge-shaped flat plate, and the light is propagated throughout the light guide plate using the total internal reflection inside the light-transmitting plate. Is made into diffusely reflected light of less than the critical angle by a light scattering reflector on the back surface of the light guide plate, and diffused light is emitted from the surface of the light guide plate (Japanese Utility Model Laid-Open No. 55-162201).

Further, a lens sheet having a triangular prism type lenticular lens protrusion on one surface and a smooth surface on the other surface is superposed on the light guide plate surface of the above-mentioned surface light source with the protrusion surface facing upward. , Utilizing the light focusing action of the lens
There is also known one that diffuses the diffused radiation uniformly and isotropically within a desired angle range (Japanese Utility Model Laid-Open No. 4-10720).
1).

When this lens sheet is used in combination with a matte transparent diffuser (matte transparent sheet), the lens sheet uses only a matte transparent diffuser (US Pat. No. 4,729,067).
), The light energy of the light source can be more preferentially distributed within a desired limited angle range, and diffused light having high uniform isotropy can be obtained within that angle range. In addition, as a measure against high luminance of a backlight used in a liquid crystal display device, as shown in FIG. 1, there is a tendency to adopt a configuration in which two lenticular lens sheets are stacked at right angles (Monthly Display, May 1996, pages P35 to P39). ).

[0005]

However, the conventional surface light source for a backlight of a liquid crystal display device not only has a problem that the visual characteristics are relatively narrow, but also uses two lenticular lens sheets. In addition to the cost of parts, it is necessary to mount two lenticular lens sheets at right angles to each other, which leads to a large production cost, and the surface light source for the backlight becomes very expensive. There is a point,
A research and development report has been made on a surface light source for a backlight that does not require the printing of a lenticular lens sheet, a diffuser plate, or a light scattering dot pattern on the back surface of a light guide plate (The Institute of Electronics, Information and Communication Engineers, IEICE Technical Report EID98-79 Page 67-7).
2).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. By optimizing the back surface structure of a light guide plate, the number of lenticular lens sheets used can be reduced to one or no. An object of the present invention is to provide a surface light source for a backlight, which does not require printing of a light-scattering dot pattern on the back surface and reduces component costs and manufacturing costs, a light guide plate provided in the surface light source, and a method for manufacturing the light guide plate.

[0007]

According to a first aspect of the present invention, there is provided a light guide plate, comprising:
One side end surface constitutes a light incident surface, and one surface of the light guide plate that intersects the light incident surface constitutes a light exit surface, and a plurality of grooves having substantially equal groove widths are formed on the opposing surface of the light exit surface. The grooves are substantially parallel to each other, and are formed such that the distance between the grooves increases as the distance from the light incident surface increases.

According to a second aspect of the present invention, in the light guide plate according to the first aspect, the first light guide plate includes a plurality of first grooves, each of the plurality of grooves being arranged from the far end of the first groove close to the light incident surface. The distance between the groove and the near end of the second groove adjacent in the direction away from the light incident surface is 5 to 15 times the width of the groove. The light guide plate of the present invention according to claim 3 is the light guide plate according to claim 1 or 2,
The cross-sectional shape of the plurality of grooves may be any one of the following (a), (b) or (c).

A) an N-sided polygon (where N is a natural number of 3 or more) b) an isosceles triangle c) a part of an ellipse (the ellipse includes a circle); Is claim 1
4. The method for manufacturing a light guide plate according to claim 3, further comprising a step of molding the light guide plate with a mold.

According to a fifth aspect of the present invention, there is provided a surface light source comprising: the light guide plate according to any one of the first to third aspects; and a light source provided adjacent to a light incident surface of the light guide plate. It is characterized by doing.

[0011]

FIG. 2 is a schematic view of a light guide plate according to the present invention. FIG. 2 (a) is a partial sectional view of the light guide plate, and FIG. 2 (b) is an enlarged sectional view of a main part of the light guide plate. . The following terms are defined using this diagram. The term “groove” refers to a plurality of grooves 4 a (see FIG. 2A) dug on the opposite surface 3 of the light exit surface 2 of the light guide plate 1 to a length approximately equal to the length of the light source.

The cross-sectional shape of the groove 4a refers to a cross-sectional shape 4b (see FIGS. 2B and 2C) corresponding to the groove 4a, and in this case, it is a half of a quadrangle or an ellipse. In FIG. 2B, the cross-sectional shape 4b of the groove 4a may be an N-sided polygon (where N is a natural number of 3 or more). In particular, when N is 3, the cross-sectional shape 4b of the groove 4a is It becomes V-shaped. Note that the intersection of the N-gons of the cross-sectional shape 4b may be smoothly rounded and rounded.

The near end of the groove is defined as a point P1 of the groove 4a when there is a light incident surface (not shown) on the left side of FIG.
Say. The far end of the groove refers to a point P2 of the groove 4a when a light incident surface (not shown) is on the left side of the drawing in FIG. The groove width refers to a groove width 4c (see FIG. 2B).

The distance from the far end of the groove to the near end of the adjacent groove (hereinafter simply referred to as "groove distance") refers to the groove distance 4d (see FIG. 2B). Next, an embodiment of the present invention will be described.
This will be described in detail with reference to the drawings. FIG. 3 is a schematic view of a light guide plate according to the present invention. FIG. 3A is a perspective view of the light guide plate, and FIG.
(B) is a front view of a light guide plate.

Reference numeral 1 denotes a light guide plate. The light guide plate 1 is manufactured by resin molding using a mold, and a plurality of grooves 4a are formed at the same time.
(In this case, a triangular cross section) is formed on the light reflecting surface 3. Reference numeral 5 denotes a light incident surface, and as will be described below, light emitted from a light source (not shown) arranged substantially parallel to the light incident surface 5 is incident. Reference numeral 3 denotes a light reflecting surface. As described above, a plurality of grooves 4a are formed on the light reflecting surface 3 substantially in parallel with the light incident surface 5, and a groove interval 4d between the grooves 4a is 4a gradually narrows as the distance from the light incident surface 5 increases. In addition, after the resin molding, an aluminum reflective film is formed on the light reflecting surface 3 by sputtering, vapor deposition, or the like to prevent light from leaking and to increase the reflection efficiency (not shown).

Reference numeral 2 denotes a light exit surface, on which light incident from the light incident surface 5 is reflected by the light reflecting surface 3 and the three side surfaces 6 of the light guide plate 1.
Most of the incident light is finally reflected from the light exit surface 2 as light having uniform directivity after being reflected by a, 6b and 6c. Incidentally, a leakage preventing member such as a white tape is attached to the side surfaces 6a, 6b and 6c in order to prevent light leakage.

The material of the light guide plate 1 is selected from light-transmissive materials, and usually acrylic or polycarbonate resin is used. The shape of the light guide plate is a parallel flat plate or a flat wedge-shaped flat plate, and the thickness thereof is generally about 1 to 10 mm. Other translucent materials include acrylate or methacrylate homo- or copolymers such as polymethyl methacrylate and polymethyl acrylate, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonates, and the like. Thermoplastic resins such as polystyrene and polymethylpentene, or acrylates such as polyfunctional urethane acrylates and polyester acrylates cross-linked by ultraviolet rays or electron beams, transparent resins such as unsaturated polyesters, transparent glass, transparent ceramics, etc. are used. Can be

Next, the operation of the light guide plate according to the present invention will be described with reference to FIG.
This will be described with reference to FIG. Light (left side in FIG. 2B) emitted from a light source (not shown) provided adjacent to the light incident surface 5 of the light guide plate 1 enters the inside of the light guide plate 1 from the light incident surface 5, Light reflecting surface 3, a plurality of grooves 4a and side surfaces 6a, 6b and 6
c and is emitted from the light emitting surface 2 (FIG. 2B)
Upward).

FIG. 4 is a partial sectional view of a light guide plate according to the present invention. The light reflecting surface 3 has a triangular cross section (in this case, an isosceles triangle) substantially parallel to the light incident surface 5 and a groove width 4.
A plurality of grooves having substantially the same c are formed, and the grooves 4a1, 4a2, 4a3, and 4a are arranged in the order closer to the light incident surface 5.
4. . . Thus, as the distance from the light incident surface 5 increases, the groove interval 4d1, the groove interval 4d2, the groove interval 4d3. . . Is gradually narrowing.

FIG. 5 is a graph showing luminance distribution characteristics. The horizontal axis represents the distance of the light guide plate from the light source (lamp), and the position of the value 0 is the end face position of the lamp. The vertical axis does not show a unit, but is a luminance, and a larger value means a brighter.

This graph shows that, in the light guide plate according to the present invention, in which the groove interval shown in FIG. 4 gradually narrows as the distance from the light incident surface 5 increases, the groove width 4c is fixed and the groove interval 4d1 closest to the light incident surface 5 is obtained. Of the luminance distribution characteristics when the width of the light guide plate is changed, and the luminance distribution characteristics of the light guide plate are analyzed using CODEV, which is an optical design evaluation software developed by ORA, USA.

The evaluation parameters are as follows: 1) The shape of the light guide plate is as follows: length L = 190 (mm), W = width 260 (mm), thickness d1 = 3 (mm), thickness d2 =
1.2 (mm) cross section of wedge-shaped flat plate (see FIG. 6) 2) The wavelength of light emitted from the light source (lamp) is 600
3) The material of the light guide plate is PMMA having a refractive index of 1.49. 4) The groove 4a on the light reflecting surface 3 has a bottom groove width 4c of 0.2.
(Mm) is an isosceles triangle with a vertical angle of 150 degrees in cross section. 5) The light reflecting surface 3 and the groove 4a form a reflecting film of aluminum.

6) The width of change of the groove interval 4d1 is five steps of 2.5 to 20 times the groove width 4c, ie, five points in the range of 0.5 (mm) to 4 (mm). We are simulating the characteristics. As is apparent from FIG. 5, when the groove interval 4d1 is 2.5 times and 20 times the groove width 4c, the characteristics are biased at a position near or far from the light source, and the luminance distribution characteristic is extremely low. On the other hand, when the groove width is 4 times, 10 times, and 15 times the groove width 4c, the characteristics are improved so as to be distributed more uniformly than when the groove width is 4 times and 20 times. It can be easily understood that the objective effect has appeared. However, even if the wavelength of light or the refractive index of the material of the light guide plate is slightly changed, there is no significant effect on the luminance distribution characteristics found here.

The inventor of the present application paid attention to the length relationship between the groove width 4c and the groove interval 4d1, and independently performed a basic optical design simulation of the light guide plate. As a result, the groove width 4c and the groove interval 4d1 were obtained.
It has been found that the luminance distribution characteristics are significantly improved when the length ratio is between 5 and 15 times, and based on the results, a completely new light guide plate is proposed. FIG. 7 is a schematic view showing a liquid crystal display device including the surface light source according to the present invention.

The liquid crystal display device comprises a liquid crystal panel 7 and a surface light source 8, and the surface light source 8 comprises a light guide plate 1, a light source 9 such as a fluorescent tube, and various control circuits (not shown) according to the present invention. Have been. The light emitted from the light source 9 is
The light enters the inside from the light incident surface, is reflected by the light reflecting surface and the side end surface, repeatedly converges, and the diffuse radiation is uniformly and isotropically diffused within a desired angle range and is guided to the liquid crystal panel 7.

Further, the method for manufacturing a light guide plate according to the present invention comprises:
The method includes a step of molding the above light guide plate using a mold in which a fine pattern of the light reflecting surface is processed.

[0027]

As described above, according to the light guide plate and the method of manufacturing the light guide plate according to the present invention, the groove interval is formed so as to become denser as the distance from the light incident surface increases. Since the back surface structure of the light guide plate is optimized such that the distance from the far end of the first groove closest to the close end of the second groove is 5 to 15 times the groove width. In addition, the number of lenticular lens sheets to be used becomes one or unnecessary, and furthermore, it becomes unnecessary to print the light scattering dot pattern on the back surface of the light guide plate, so that the cost of parts and the cost of manufacturing can be greatly reduced.

Further, according to the surface light source of the present invention, since the light guide plate is used, the component cost of the surface light source is greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a conventional liquid crystal display device.

FIG. 2 is a schematic view of a light guide plate according to the present invention.

FIG. 3 is a schematic view of a light guide plate according to the present invention.

FIG. 4 is a partial sectional view of a light guide plate according to the present invention.

FIG. 5 is a graph showing luminance distribution characteristics.

FIG. 6 is a perspective view showing a light guide plate according to the present invention.

FIG. 7 is a schematic view showing a liquid crystal display device including a surface light source according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 light guide plate 2 light emitting surface 3 light reflecting surface 4a groove 4b sectional shape 4c groove width 4d groove interval 5 light incident surface 7 liquid crystal panel 8 surface light source 9 light source

Claims (5)

[Claims] 1. A light guide plate, wherein one side end surface of the light guide plate constitutes a light incident surface, and one surface of the light guide plate intersecting with the light incident surface constitutes a light exit surface; A plurality of grooves having substantially the same groove width are formed substantially parallel to each other on the opposite surface of the surface, and the grooves are formed so that the distance between the grooves becomes smaller as the distance from the light incident surface increases. . 2. The light guide plate according to claim 1, wherein, of the plurality of grooves, a direction away from the far end of the first groove close to the light incident surface to the first groove and the light incident surface. The distance to the near end of the second groove adjacent to the groove is 5 to 15 times the groove width. 3. The light guide plate according to claim 1, wherein a cross-sectional shape of the plurality of grooves is any one of the following shapes (a), (b), and (c). A light guide plate, characterized in that: a) N-gon (where N is a natural number of 3 or more) b) Isosceles triangle c) Part of an ellipse (however, the ellipse includes a circle) 4. The method for manufacturing a light guide plate according to claim 1, further comprising a step of molding the light guide plate with a mold. . 5. A surface light source, comprising: the light guide plate according to claim 1; and a light source provided adjacent to a light incident surface of the light guide plate.