JPH06186562A - Light transmission plate for surface light source - Google Patents

Abstract

PURPOSE:To reduce the cost of production and to simultaneously attain high brightness and high uniformity of the brightness by forming a prescribed irregular reflection structure directly on the base of a transparent substrate. CONSTITUTION:Rugged shapes are formed in prescribed plane patterns on the base 11 of the transparent substrate 10 made of acryl. The surfaces 12a of the projecting parts 12 thereof are formed as rough surfaces having ruggedness. A light reflection plate 13 is stuck onto the bases thereof. On the other hand, the entire surface of the front surface 14 of the transparent substrate 10 is also formed to the rough surface having the very small rugged shapes and a light diffusion plate 15 is stuck thereon. This light transmission plate is higher in brightness than the conventional products and the uniformity of light is improved; in addition, the need for forming a printing layer like heretofore is eliminated. Since the light transmission plate is produced by integral molding, the cost of the production is reduced; in addition, the durability is enhanced and the change with lapse of time is lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is designed to introduce light from the side surface of a transparent substrate and reflect the introduced light by a diffused reflection structure on the bottom surface modulated in the incident direction of the light to emit the light from the surface. The present invention relates to a light guide plate for a planar light source, and more particularly to a technique for obtaining a flat light emitting body with high brightness and high uniformity as a backlight in a liquid crystal display device or the like.

[0002]

2. Description of the Related Art In a backlight of a conventional liquid crystal display device, as shown in FIG. 2, for example, an LED array 1 in which LEDs are arranged in parallel in a line is provided on an incident side surface 2a of a rectangular transparent substrate 2 (for example, acrylic). The light diffusing plate made of polycarbonate is attached to the side of the transparent substrate 2 and the reflecting plate 22 is attached to the bottom surface of the transparent substrate 2 and the reflecting tape 25 is attached to the other side surface of the transparent substrate 2, and the upper surface of the transparent substrate 2 is roughened. A planar light-emitting body formed by attaching 23 and 24 is used. In this case, as shown in FIG. 3, the light diffuse reflection layer 21 is printed on the bottom surface of the transparent substrate 2 in various plane patterns, and the light reflection plate 22 is attached thereon. The plane pattern of the diffused light reflection layer 21 includes a chain dot in addition to a circular dot pattern,
There is a so-called square dot, which increases the dot area according to the distance from the incident side surface 2a and makes the amount of reflected light toward the upper surface side uniform with respect to the incident direction.
On the other hand, the light diffusion plates 23 and 24 attached to the upper surface scatter the reflected light to make the distribution of the emitted light amount uniform over the entire surface.

[0003]

In the above-mentioned conventional light guide plate, the step of printing the diffused reflection layer 21 on the transparent substrate 2, the step of attaching the light reflection plate 22 and the two light diffusion plates 23, 24 to each other. In addition, since the diffused reflection layer 21 must be formed with a precise thickness, area, etc., by using a special material in consideration of various characteristics such as light scattering efficiency and refractive index.
There was a problem that the cost would be high. In addition, deterioration of the printed layer due to aging and deterioration such as peeling may occur. Then, after overcoming these problems, higher brightness and higher uniformity of brightness must be achieved as an essential issue. Therefore, in view of the above problems, the present invention can reduce the cost by simplifying the manufacturing process, and it is possible to improve the uniformity of the emitted light amount and the brightness as compared with the conventional product without hindering the durability. The purpose is to obtain a light guide plate for a planar light source.

[0004]

The first means taken by the present invention to achieve the above object is as a diffused light reflection structure.
A reflection layer disposed in contact with or opposite to the bottom surface and a concavo-convex pattern formed directly on the bottom surface are provided, and the area of the concavities or convexities in the concavo-convex pattern is gradually increased along the incident direction, and the concavities or The surface of the convex portion is formed as a rough surface having irregularities with a period sufficiently smaller than the period of forming the irregular pattern. The second aspect of the present invention
The means of (1) provides, as a diffuse reflection structure, a reflection layer arranged in contact with or opposite to the bottom surface and a plurality of grooves or ridges formed directly on the bottom surface, and the grooves or ridges are formed in the incident direction. It extends in at least two directions inclined with respect to, and is formed in a plane lattice shape. In each of these means,
The upper surface is formed as a rough surface having unevenness with a period sufficiently smaller than the formation cycle of the uneven pattern, or a plurality of concave grooves or ridges extending along the incident direction are directly formed on the upper surface in parallel. Is desirable.

[0005]

According to such means, irregular reflection light is uniformly generated in the incident direction by the rough surface formed in the concave or convex portion of the concave-convex pattern on the bottom surface. In this case, the surface of the concavo-convex pattern and its concavities or convexities is processed into a rough surface having minute concavo-convex shapes without forming a printing layer, or a plurality of concave grooves or convex stripes formed in a planar lattice are directly formed. Therefore, it can be easily manufactured by integral molding, and since it does not use a printing layer, it has a diffuse reflection structure with little change over time. Further, since only the space or the interface with the reflective layer exists on the bottom surface, extra light absorption does not occur, and light loss can be reduced. Here, the upper surface is directly roughened, or concave grooves or ridges extending in the incident direction are formed in parallel to improve the uniformity of the emitted light amount while maintaining the ease of manufacturing by integral molding. Can be made.

[0006]

EXAMPLE 1 Next, Example 1 of the light guide plate according to the first invention will be described with reference to the drawings. As shown in FIG. 1, an acrylic transparent substrate 10 having a rectangular thin plate shape and a thickness of 3.5 mm and a flat surface of 30 × 60 mm has a bottom surface 11 and a continuous inclination angle of 45 ° with respect to the incident side surface. A plurality of convex portions 12 are formed in a substantially rhombic plane pattern (chain dots) having directions, and the plane patterns are formed so that the area of the convex portions 12 gradually increases along the light incident direction L. .

When a transparent substrate having a plane dimension of 30 × 60 mm (the incident side surface is along the long side) is used, the width of the widened portion of the convex portion 12 is about 80 with respect to the continuous direction of the plane pattern.
0 to 1100 μm, the width of the narrow portion is about 200 to 300
μm. However, if the shorter side along the incident direction becomes longer,
The range of these numbers also increases. That is, when a substrate that is long in the incident direction is used, for example, in the portion near the incident side surface, independent small area rhombuses are connected in series in a state of being separated in the continuous direction, and the area of the rhombus increases as the distance from the incident side surface increases. Eventually, they are connected to each other in the continuous direction.

The height of the convex portion 12 is about 50 μm, and the surface 12a of the convex portion 12 is a rough surface having an irregular shape with a period of about 175 μm. The surface of the bottom surface 11 other than the convex portion 12 is a mirror surface, and the light reflection plate 13 is attached thereon. On the other hand, the upper surface 14 of the transparent substrate 10 is about 200 μm.
The light diffusing plate 15 is formed on a rough surface having a concave and convex shape of m periods, and a light diffusing plate 15 made of a resin such as polycarbonate having fine unevenness on both front and back surfaces is attached on the rough surface.

Next, a method by injection molding will be described as an example of a method for manufacturing the above-mentioned embodiment. A mask with a chain dot-shaped plane pattern is formed on the cavity surface of the mold, and the lower mold surface is etched through this mask.
Form a recess. At this time, the surface state of the concave portion can be controlled to have the surface roughness of the convex portion 12 under a predetermined etching condition.

On the other hand, the upper mold surface of the mold is finished to a predetermined surface roughness by sandblasting. By injecting acrylic resin into the mold thus formed and molding, the bottom surface 1
It is possible to manufacture the transparent substrate 10 having the convex portion 12 having the surface 12a as the rough surface and the rough surface 14 having the concave and convex shape on the upper surface 14. As described above, in this embodiment, if a predetermined mold is formed, it can be manufactured extremely easily in a single process.
A significant cost reduction can be expected.

Here, it is also possible to finish the surface of the convex portion 12 and the upper surface 14 of the transparent substrate 10 taken out from the mold after molding to a predetermined surface roughness by sandblasting, without forming the rough surface by molding. On the other hand, the surface of the concave portion on the bottom surface 12 of the light guide plate is reversed, contrary to the above embodiment, by chemically polishing the concave surface of the lower surface of the mold into a mirror surface and finishing the convex surface to a predetermined surface roughness. It is also possible to manufacture a light guide plate having a rough surface (the surface of the convex portion becomes a mirror surface). However, in this case, it is necessary to form a plane pattern that gradually increases the area of the concave portion in the incident direction.

The LED array 1 shown in FIG. 2 was connected to the light guide plate thus formed, and the brightness was measured with the conventional product shown in FIG. 3 having the same area and the same pattern as that of the comparative example. While the average brightness of the conventional product is 14.1cd / m ^2, it was possible to obtain an average luminance of 21.5cd / m ² under the same conditions in the present embodiment. Here, when two light diffusion plates are attached as in the conventional product, the average brightness is 25.3c.
It was d / m ² . Regarding the uniformity of brightness,
A single light diffusing plate was sufficiently superior to the conventional product.

The effect of this embodiment is that, in addition to the geometrical scattering due to the uneven pattern formed on the bottom surface, the minute unevenness on the surface of the convex portion disperses the incident light, and the light is efficiently absorbed without light absorption. The reason is that the light can be deflected to the upper surface side. Here, the surface roughness of the convex surface 12a is sufficient if light scattering is sufficient as compared with the bottom surface other than the convex portion, and therefore the convex surface 12a can be formed with a period up to the order of the wavelength of the incident light. , Should be appropriately set in relation to the cycle of the concavo-convex pattern and the relationship with the scattering portion on the upper surface.

The upper limit of the cycle of the rough surface 12a of the convex portion 12 is smaller than the cycle of forming the concavo-convex pattern.
From the viewpoint of scattering efficiency, it is desirable to be smaller than the formation period by one digit or more. In forming the unevenness by etching the mold, it is considered that the depth of the concave portion on the mold surface corresponding to the convex portion 12 and the surface roughness thereof have a positive correlation, so that the depth of the concave portion should be adjusted. It is possible to control so as to obtain desired brightness and uniformity.

Next, a second embodiment according to the second invention will be described with reference to FIG. In this embodiment, similar to the first embodiment, a large number of ridges 31 and 32 each having a height and a width of about 200 μm are formed on the bottom surface of a transparent substrate 30 at a period of about 300 μm. They are almost orthogonal to each other, and both sides are incident side surfaces
It is formed in a plane lattice so as to form an angle of about 45 degrees with respect to 0a. In this embodiment, since the transparent substrate 30 having a plane size of 30 × 60 mm is used, the ridges 31 and 3 are
2 is made constant, but when a substrate longer in the incident direction is used, as shown in FIG.
It is desirable that the periods 32 and 32 are formed with a short period and a high density as they proceed in the light incident direction.

This transparent substrate 30 is preferably formed by forming grooves having a width of about 200 μm on the die surface of the die by mechanical grinding (polishing). The mold surface may be formed by a chemical treatment such as etching. Further, instead of the convex stripe, a concave groove may be directly formed on the bottom surface of the transparent substrate 30. In addition, the inclination angle of the concave groove or the convex line with respect to the traveling direction of the light is 45
It may be formed by appropriately changing the angle other than degrees.

The same light reflecting plate and one light diffusing plate as in Example 1 were attached to this example, and the same luminance measurement as above was performed. The average luminance was 15.0 cd / m ² , and even though only one light diffusing plate was attached, higher luminance than the conventional product under the same conditions was obtained. Also, the uniformity was comparable to that of the conventional product.

Next, a third embodiment will be described which has the same bottom surface as that of the first embodiment but has a different diffusion surface on the top surface. In this embodiment, as shown in FIG. 5C, the convex portions 42 are formed on the bottom surface 41 of the transparent substrate 40 having a thickness of 3.5 mm and a plane size of 60 × 62 mm in the same plane pattern of chain dots as in the first embodiment. Is formed. On the other hand, its upper surface is
As shown in FIGS. 5A and 5B, a plurality of convex stripes 44 and concave grooves 45, each extending in the incident direction, are formed in parallel (hereinafter referred to as striation knurls 46).

The period of the corrugated section formed by the convex stripes 44 and the concave grooves 45 is about 0.2 mm, and the height difference between the apex of the convex stripes 44 and the bottom of the concave grooves 45 is about 0.1 mm. This perforated knurl 46 can be manufactured by a mold as in the above embodiment. The streak knurls 46 have an effect of uniformizing the diffused reflected light that is uniformized in the incident direction by the plane pattern formed on the bottom surface 41 in the direction orthogonal to the incident direction. In this case, it is considered that the amount of light traveling in a direction other than the emission direction can be reduced and the light can be efficiently radiated from the rough surface or the light diffusing plate, so that it also contributes to the improvement of brightness.

Luminance measurement was performed by comparing the above-mentioned Example 3 with the conventional example and Example 1 which were manufactured by using a transparent substrate of the same size. The result is shown in FIG. The measurement points are nine points shown in FIG. As described above, the present example is superior in brightness and uniformity to the first example as well as the conventional example. As the crease knurls 46, only convex ridges having a semicircular cross section or a mountain shape may be formed at predetermined intervals on the upper surface of the transparent substrate, or only concave grooves having a semicircular cross section or a V shape may be formed. You may.

In the first to third embodiments described above, since the incident light is diffusely reflected and diffused by the surface structure of the transparent substrate itself, it can be easily manufactured by injection molding or the like, and the manufacturing cost can be reduced. Since the scattering efficiency is good and there is no excess light absorption, high brightness and high uniformity can be obtained. This ease of processing is also due to the fact that there is no need for gradation processing (the formation of gradually increasing shapes such as the depth of grooves or inclined surfaces with respect to the incident direction).

Further, each embodiment is characterized in that the step of forming the print layer is not required and the print layer is not deteriorated as in the conventional case, so that the change with time is small. Further, since the rough surface or the streak knurls formed by minute irregularities is directly formed on the upper surface, the upper surface portion functions as a light scattering layer, and sufficient in-plane uniformity of brightness can be obtained without stacking a plurality of light diffusion plates. Since it is obtained, the step of attaching the diffusion plate can be reduced.

[0023]

As described above, according to the present invention, a concavo-convex pattern composed of concave portions or convex portions having a roughened surface is formed directly on the bottom surface of a transparent substrate, or is inclined with respect to the incident direction of light. Since it is characterized in that the concave grooves or ridges extending in the above-mentioned direction are formed in a plane lattice shape, the following effects are obtained. The manufacturing cost can be reduced and the brightness can be improved as compared with the related art. Further, since the diffused reflection structure is formed on the transparent substrate itself, there is little change in characteristics over time, and durability can be improved. Since the upper surface is roughened or formed into streak knurls, the upper surface layer itself of the transparent substrate functions as a light scattering layer, and the uniformity of the emitted light amount can be improved. In addition, since it is unnecessary to attach the light diffusion plate or the number of the attached light diffusion plates is reduced, the labor and cost of assembly are reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of Example 1 of a light guide plate for a planar light source according to the present invention.

FIG. 2 is a perspective view showing a schematic structure of a planar light source using a light guide plate.

FIG. 3 is a vertical sectional view showing a structure of a conventional light guide plate for a planar light source.

FIG. 4 is a partial bottom view showing the structure of Example 2 of the light guide plate for the planar light source according to the invention.

5A is a partial plan view of a third embodiment of a planar light source light guide plate according to the present invention, and FIG. 5B is a partial sectional view of the same embodiment.
(C) is a partial bottom view of the embodiment.

FIG. 6A is a schematic diagram showing the measurement points of the brightness of the light guide plate,
(B) is a table showing the measurement results.

[Explanation of symbols]

 10, 30 and 40 light guide plate for planar light source 11, 41 bottom surface 12, 42 convex portion 12a convex surface (rough surface) 13 light reflecting plate 14 upper surface (rough surface) 15 light diffusing plate 31, 32, 44 convex strip 45 Grooves 46 Streak knurls

Claims (4)

[Claims] 1. A light guide plate for a planar light source, wherein light is introduced from a side surface of a transparent substrate, and light is emitted from an upper surface by a light diffuse reflection structure on a bottom side that is modulated in an incident direction of the light. The structure has a reflection layer arranged in contact with or opposite to the bottom surface, and an uneven pattern formed directly on the bottom surface, and the area of the concave portion or the convex portion in the uneven pattern is along the incident direction. The light guide plate for a planar light source, wherein the surface of the concave portion or the convex portion is gradually increased and is formed into a rough surface having irregularities having a period sufficiently smaller than the formation period of the concave-convex pattern. 2. A light guide plate for a planar light source, wherein light is introduced from a peripheral surface of a transparent substrate and is emitted from an upper surface by a diffused reflection structure on a bottom surface that is modulated in an incident direction of the light. The irregular reflection structure has a reflection layer arranged in contact with or opposite to the bottom surface, and a plurality of concave grooves or convex stripes formed directly on the bottom surface, and the concave grooves or convex stripes in the incident direction. A planar light source light guide plate extending in at least two directions inclined with respect to each other and formed in a planar lattice shape. 3. The light guide plate for a planar light source according to claim 1, wherein the upper surface of the light source plate is a rough surface having irregularities with a period sufficiently smaller than the period of forming the irregular pattern. 4. The light guide plate for a planar light source according to claim 1, wherein a plurality of grooves or ridges extending along the incident direction are directly formed in parallel on the upper surface of the light guide plate.