JP3886072B2 - Light guide plate for planar light source - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a light source plate used for a planar light source device used as a backlight of various display devices or a planar light source device for a display such as an electric signboard, and in particular, a light source is disposed on at least one side end surface of the light guide plate. The present invention relates to a light guide plate suitable for a so-called edge light type planar light source device.
[0002]
[Prior art]
The edge light type planar light source device has a structure in which the light source 2 is arranged on the side end surface of the light guide plate 1 and the reflection plate 3 is arranged around the light source 2 and on the lower surface of the light guide plate, as shown in FIG. The upper surface of the light guide plate 1 is a light emitting surface. Such a planar light source device tends to reduce the amount of light emitted as it moves away from the light source, and is required to prevent this, and among the light emitted from the light emitting surface in order to obtain high luminance , More light is required to be directed in the vertical direction (direction perpendicular to the light exit surface).
[0003]
In order to satisfy the former requirement, the light diffusion pattern is formed so that the area increases as the distance from the light source plate (Japanese Patent Laid-Open No. 51-88042) or the light source is reduced so that the cross section becomes thinner as the distance from the light source increases. Known light guide plates (Japanese Patent Laid-Open No. Hei 1-241590, etc.) are known. In order to make the light diffusion pattern inconspicuous, a diffusion sheet or a diffusion film is used in combination. The light diffusion sheet is disposed on the normal light exit surface as indicated by 4 in FIG.
[0004]
On the other hand, in order to satisfy the latter requirement, a light guide plate having a roughened surface opposite to the light emitting surface and a planar light source device in which a prism sheet is disposed on the upper surface or the lower surface of the light guide plate are well known. The light emitted from the light guide plate is redirected by the prism sheet and directed in a direction close to a direction perpendicular to the light emitting surface. Thereby, the brightness | luminance of a planar light source device can be improved significantly.
[0005]
However, in general, the prism sheet is expensive, and there is a problem that the assembly work of the planar light source device is increased due to the increase in the number of parts. To improve this, the light guide plate is manufactured by injection molding, and the light guide plate itself It has been proposed to form a light emission pattern such as a prism (Japanese Patent Laid-Open No. 7-168026, Utility Model Registration 3039669, etc.). The light guide plate described in Japanese Patent Application Laid-Open No. 7-168026 is formed by forming a V-shaped groove parallel to the light source on the surface opposite to the light emitting surface and increasing the groove as the distance from the light source increases. The parallel V-shaped groove increases the amount of light directed to the light exit surface to improve the brightness, and the size of the V-shaped groove is changed so that the area distribution of the emitted light is substantially uniform over the entire surface. Yes.
[0006]
[Problems to be solved by the invention]
In the conventional light guide plate, when the pattern for emitting light is a dot-like rough surface, there is a problem that the uniformity as a surface light source is high but the luminance is low. On the other hand, in order to obtain high luminance, when a groove having a V-shaped cross section is provided deep inside the light guide plate, the difference in luminance between the portion where the groove is formed (light emitting portion) and the other portion (non-light emitting portion) It was difficult to erase the pattern even when a diffusion film was used. In the case of a V-shaped groove, it is difficult to obtain a uniform luminance distribution, and the light guide plate described in JP-A-7-168026 has not been sufficient.
[0007]
Recently, in addition to the uniform luminance distribution, there is a demand for fine adjustment of the luminance distribution, such as brightening only the central part when moving images are projected. However, with the conventional light guide plate, the luminance distribution is finely adjusted. I couldn't.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a light guide plate that can obtain high luminance and a uniform luminance distribution when used in a planar light source. Another object of the present invention is to provide a light guide plate capable of fine adjustment of luminance distribution.
[0009]
[Means for Solving the Problems]
As a result of research to solve the above problems, by forming a pattern in which a straight groove having a V-shaped cross section and a conical concave portion are formed on the back surface of the light emitting surface of the light guide plate, It has been found that fine adjustment can be easily performed, and an arbitrary luminance distribution can be obtained such as a uniform luminance distribution on the entire surface or a higher luminance at the center as in the case of moving images. In this description, luminance means luminance as a planar light source when the light guide plate of the present invention is applied to a planar light source.
[0010]
That is, in the light guide plate of the present invention, at least one side surface is a light incident surface, one surface substantially orthogonal to the light incident surface is a light output surface, and a light output pattern is provided on at least one of the light output surface and the back surface thereof. In the light guide plate formed, the light emission pattern is a combination of a linear groove having a V-shaped cross section and a conical concave portion. In a preferred embodiment, the linear groove is perpendicular to the light incident surface. The area of the inclined surface of the groove is formed so as to increase as the distance from the light incident surface increases.
[0011]
In a preferred aspect of the present invention, the conical recess is disposed between adjacent grooves, and is formed so that the conical shape increases as the distance from the light incident surface increases.
[0012]
By combining the linear groove and the conical recess, the light traveling in various directions in the light guide plate can be directed almost in the direction of the light exit surface, thereby obtaining high brightness. The luminance distribution can be arbitrarily adjusted by changing the distribution and shape of the conical recesses. Further, since the conical concave portion exists between the grooves, the luminance difference between the portion having the linear groove and the portion therebetween can be eliminated, and the light emission pattern can be made inconspicuous. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the light guide plate of the present invention will be described in detail with reference to the drawings.
[0014]
FIG. 1 is a perspective view showing an embodiment of a light guide plate 10 according to the present invention. In this figure, in order to understand the light output pattern that is a feature of the present invention, the light output surface 10b is placed downward and the back surface 10c is displayed. Shown above. In addition, the pattern for light emission is illustrated in an enlarged manner than the actual size.
[0015]
The light guide plate 10 is formed of a wedge-shaped plate having a thick one-side end surface 10a and a thickness that decreases with increasing distance from the light-emitting plate 10. The light source 2 is disposed on the side end surface 10a side to form a light incident surface. For example, the thickness of the light guide plate on the light incident surface side is usually 10 to 2 mm, while the thickness on the end surface side opposite to the light incident surface is thinner than that, preferably in the range of 3 to 0.2 mm. In the illustrated embodiment, the light guide plate has a wedge shape. However, in the present invention, the upper and lower surfaces of the light guide plate may be parallel or partially parallel and have a wedge shape from the middle. It may be. In the case of a wedge shape, the luminance area distribution can be made more uniform.
[0016]
The light emitting pattern 30 provided on the back surface 10c includes a large number of V-shaped linear grooves 31 formed in a direction perpendicular to the light emitting surface 10b (hereinafter referred to as Y direction), and these linear grooves. The conical recess 32 formed between 31 and the light traveling in the Y direction within the critical angle within the light guide plate is directed toward the light emitting surface 10b.
[0017]
As shown in FIG. 2A, the straight groove 31 has a V shape in which the angles A and B formed by the inclined surfaces 31a and 31b on both sides and the back surface 10c are equal or substantially equal, and the apex angle θ1 is 60 to 120 °. The range is preferably 70 to 100 °. When the apex angle θ1 is smaller than 60 °, the effect of directing light perpendicular to the exit surface is weak. Further, 60 ° or more is preferable from the viewpoint of production when the light guide plate of the present invention is produced by injection molding or the like. That is, when the angle is less than 60 °, the durability of the blade for cutting the molding die is deteriorated, and it is difficult to take out the light guide plate from the die. If the apex angle θ1 is larger than 120 °, the light emission effect by the groove is weakened.
[0018]
Moreover, the linear groove | channel 31 is formed so that the area of an inclined surface may become large, as it leaves | separates from the light-incidence surface 10a side. The area of the inclined surface is changed by changing the width or depth of the groove. In this case, the shape of the cross section parallel to the light incident surface 10a is similar, and the width and depth of the groove are increased. Thus, by changing the size of the groove, it is possible to improve the uniformity of luminance along the Y direction.
[0019]
The depth of the linear groove 31 varies depending on the overall size and configuration of the light guide plate. For example, in a light guide plate having a length of about 45 mm and a width of about 60 mm, it is preferably about 50 to 200 μm at the shallowest position (on the light incident surface 10 a side) and about 300 to 350 μm at the deepest position.
[0020]
The distance (pitch) between the grooves of the linear grooves 31 is preferably such that the pattern is not visible when the diffusion film is passed through, and the distance between the center lines (valley parts) of the grooves is preferably 1000 μm or less.
[0021]
The conical recess 32 has a function of directing light in the light exit surface direction with respect to light directed in various directions within the light guide plate, thereby improving the luminance as compared with the case of only the linear groove, There is an effect of making the linear pattern due to the linear groove inconspicuous.
[0022]
The apex angle θ2 of the conical recess 32 is preferably 45 to 90 °, and more preferably 60 to 80 °, as shown in FIG. When the apex angle θ2 is smaller than 45 °, it is difficult to remove from the mold at the time of molding. If it is larger than 90 °, the pitch of the linear grooves 31 is increased, and fine adjustment of the luminance distribution becomes difficult.
[0023]
The conical recess 32 is formed so as to increase as the distance from the light incident surface 10a side increases. Also in this case, “becomes larger” means that the shape of the cross section parallel to the light incident surface 10a is similar and the bottom diameter and depth of the cone increase, and thus the size of the concave portion. It is possible to improve the uniformity of luminance along the Y direction by changing.
[0024]
The depth varies depending on the overall size and configuration of the light guide plate. As an example, in a light guide plate having a length of about 45 mm and a width of about 60 mm, the depth of the smallest conical recess 32 is preferably about 10 to 50 μm, and the depth of the deepest recess 32 is preferably about 300 to 600 μm.
[0025]
The pitch in the groove direction (Y direction) of the conical recess 32 may be uniform or may be changed according to the size of the recess, and is set to several tens to several hundreds μm at the interval between the apexes.
[0026]
The light exit surface 10b may be smooth, but it is preferable to provide a light diffusion pattern such as a dot, stripe, or satin in order to efficiently emit light from the light exit surface. The light diffusion pattern can be formed on the light emitting surface 10b by printing. However, when the light guide plate of the present invention is manufactured by injection molding as will be described later, the light emitting pattern is emitted simultaneously with the light emitting pattern on the back surface 10c. It is preferable to provide a light diffusion pattern on the surface 10b.
[0027]
The material of the light guide plate is not particularly limited, but it is possible to manufacture polymethylmethacrylate (PMMA), methylmethacrylate and other (meth) acrylates from the manufacturing advantage of being able to be manufactured by injection molding and optical properties such as transparency and refractive index. It is preferable to use a transparent resin such as a polymer or polycarbonate.
[0028]
The light guide plate of the present invention can be manufactured by injection molding or compression molding using the resin, and at this time, the light emitting pattern 30 and the light diffusion pattern described above are formed on both surfaces of the light guide plate 10. Can do.
[0029]
The light guide plate having such a configuration can be used as the light guide plate 1 of the planar light source device shown in FIG. The light that has entered the light guide plate 1 from the light source 2 is changed in the traveling direction on each inclined surface of the linear groove 31 or the conical recess 32, and is directed toward the light emitting surface 10b. At this time, the inclined surface of the linear groove 31 faces a certain direction, whereas the inclined surface of the conical recess 32 is a curved surface, so that light traveling in various directions is directed to the light emitting surface side. be able to. The amount of light in the light guide plate decreases as the distance from the light incident surface 10a decreases, but the area of each inclined surface of the V-shaped groove 31 and the conical recess 32 increases as the distance from the light incident surface 10a increases. The ratio of the light toward the light increases, and light is emitted from the light emitting surface 10b with a uniform distribution as a whole. Thereby, a uniform luminance distribution of the planar light source device can be achieved.
[0030]
As described above, the light guide plate of the present invention can improve the luminance of the planar light source device and have a uniform luminance distribution even when used alone, but further makes the light emitting pattern 30 invisible, In order to increase the uniformity of light, it is preferable to place a diffusion film on the light exit surface. Further, a known prism sheet may be used in combination on the light emitting surface or the back surface, and in that case, higher luminance can be obtained.
[0031]
【Example】
Example 1
Using PMMA resin, a light guide plate having a vertical and horizontal size of 3 inches and a wedge-shaped cross section (thickness: 3 mm thickest part, 0.5 mm thinnest part) was formed by injection molding. By this injection molding, a V-shaped groove and a conical recess were formed on the back surface of the light guide plate as shown in FIG. 1, and a rough dot pattern was formed on the light exit surface. The V-shaped groove has an angle between both inclined surfaces of 70 °, the depth of the light incident surface is 150 μm, and the width and depth increase with increasing distance from the incident surface, and the depth of the opposite surface of the light incident surface. The thickness was set to 350 μm. The interval between the grooves (between the groove valleys) was 500 μm.
[0032]
On the other hand, the conical recess has an apex angle of 60 °, the depth of the light incident surface is set to 35 μm, the depth increases as the distance from the light incident surface increases, and the depth of the surface opposite to the light incident surface is set to 450 μm. The pitch between the recesses (the distance between the vertices) was uniformly 500 μm.
[0033]
A 2.6 mm cold-cathode tube was installed on the thicker side of the light guide plate, and a reflective film (trade name GR38W: Kimoto Co., Ltd.) was wound around the cold-cathode tube. In addition, a reflector (trade name: Ref White: Kimoto Co., Ltd.) is installed under the light guide plate, and a diffusion film (product name: Light Up MX: Kimoto Co., Ltd.) is installed on the light exit surface side of the light guide plate. A backlight was manufactured by laminating.
[0034]
A tube current of 5 mA was passed through the backlight, the backlight was turned on, and the luminance was measured. As shown in FIG. 4, the luminance measurement was performed using an luminance meter BM-8 (manufactured by Topcon Co., Ltd.). As a result, an average luminance of 3600 cd / m ² was obtained.
Comparative Example A comparative backlight was produced in the same manner as in Example 1 except that the rear surface of the comparative light guide plate was flat and the same structure as in Example 1 was used. As a result of measuring the luminance of this backlight in the same manner as in Example 1, only an average luminance of 3000 cd / m ² was obtained.
[0035]
【The invention's effect】
The light guide plate according to the present invention can obtain a high luminance in the front direction and a uniform luminance distribution by combining a linear groove having a V-shaped cross section and a conical concave portion as a light emitting pattern.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a light guide plate of the present invention.
2A and 2B are diagrams showing a main part of a light emission pattern in a light guide plate of the present invention, wherein FIG. 2A is a cross-sectional view of a V-shaped linear groove, and FIG.
FIG. 3 is a schematic configuration diagram of a planar light source device to which the present invention and a conventional light guide plate are applied.
FIG. 4 is a diagram for explaining a luminance measurement method of a planar light source device (backlight).
[Explanation of symbols]
10. Light guide plate 10a ... Light incident surface 10b ... Light exit surface 10c ... Back surface 20 ... Light source 30 ... ..Light emitting pattern 31 ... Linear groove 32 ... Conical recess

Claims (5)

In the light guide plate in which at least one side surface is a light incident surface, and one surface substantially orthogonal to the light incident surface is a light emitting surface, and a light emitting pattern is formed on at least one of the light emitting surface or the back surface thereof, A plurality of patterns for light emission arranged in the same direction, a plurality of linear grooves having a V-shaped cross section , and a plurality of patterns arranged between the grooves, the apex angle being in the range of 60 to 80 °. A light guide plate comprising a combination with a recess.   The light guide plate according to claim 1, wherein the linear groove is disposed in a direction perpendicular to the light incident surface, and an area of the inclined surface of the groove increases as the distance from the light incident surface increases.   The light guide plate according to claim 1, wherein the conical recess is disposed between the grooves, and the conical shape increases as the distance from the light incident surface increases.   4. The light guide plate according to claim 1, wherein the shape of a cross section perpendicular to the light emitting surface is a wedge shape.   The light guide plate according to claim 1, wherein an angle formed by two inclined surfaces of the linear groove is in a range of 60 to 120 °.

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