JP2004079418A - Light guide plate and backlight device using the same - Google Patents

Abstract

Provided is a light guide plate capable of facilitating processing of a molding die for forming a thinned light guide plate and improving the life of the mold, and a backlight device using the same.
A plurality of V-grooves (2g) are formed on the bottom surface of a reflector of a light guide plate (2). The V-shaped groove 2g is formed by being divided by a plurality of protrusions 2p formed in the orthogonal direction. Due to the division of the V-groove 2g, the reflection inclined surface 2s formed by the side surface of the V-groove 2g on the light incident surface side is also divided and formed. The depth of the V-groove 2g can be increased by dividing the V-groove 2g formed on the reflector bottom surface of the light guide plate 2 by the protrusion 2p to form the reflection slope 2s. That is, the processing accuracy of the mold for forming the light guide plate 2 can be reduced, and the life of the mold can be extended.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light guide plate used as a backlight in a display device such as a liquid crystal display device, and a backlight device using the same.
[0002]
[Prior art]
In recent years, liquid crystal displays have been widely used as display devices for personal computers, mobile terminals, mobile phones, television devices, and the like. This liquid crystal display is required to be lighter, smaller, thinner, lower in power consumption, higher in brightness, and lower in price. Therefore, a backlight device mounted as a backlight source of the liquid crystal display is also required. Similar improvements are required.
[0003]
The structure of a conventional backlight device will be described with reference to FIG. FIG. 9 is a perspective view showing the structure of a conventional backlight device, and in order to simplify the description, only a reflection surface formed inside is shown in perspective.
[0004]
In FIG. 9, the conventional backlight device includes a light source 100, a light guide plate 101, a reflection sheet 102, and a diffusion sheet 103. The light guide plate 101 is formed of a flat light guide member, and light emitted from the light source 100 enters from one side surface (hereinafter, referred to as a light incident surface). On a flat surface (hereinafter referred to as a reflector bottom surface) formed perpendicular to the light incident surface of the light guide plate 101, a plurality of grooves 101g whose extension direction is provided in parallel with the light incident surface are formed. Is done. Generally, the groove 101g is formed in a V-shape, and is hereinafter referred to as a V-shaped groove 101g. A plurality of reflecting slopes 101s are formed by the side surfaces of the plurality of V-grooves 101g on the light incident surface side (surfaces indicated by oblique dashed lines in FIG. 9). Light incident on the light guide plate 101 from the light source 100 is emitted from a surface (hereinafter, referred to as a light emission surface) perpendicular to the light source 100 by being reflected by the plurality of reflection slopes 101s. , Led to the liquid crystal panel. In the vicinity of the light exit surface of the light guide plate 101, there is provided a diffusion sheet 103 for diffusing light emitted from the light exit surface to make the light uniform and to guide the light to the liquid crystal panel. Further, a reflection sheet 102 is provided near the reflector bottom surface of the light guide plate 101 for reflecting light leaking from the reflector bottom surface of the light guide plate 101 and returning the light to the inside of the light guide plate 101 again. As described above, in the conventional backlight device, the light of the light source 100 enters from the light incident surface of the light guide plate 101 and propagates in the light guide plate 101 by the reflection slopes 101s of the plurality of V-grooves 101g formed on the bottom surface of the reflector. By emitting light in the front direction (light emission surface) of the backlight device, directivity is increased and luminance in the front direction is improved without using a condensing sheet such as a prism sheet.
[0005]
[Problems to be solved by the invention]
However, as described above, the backlight device is required to be smaller and thinner, and the light guide plate 101 of a portable terminal, a mobile phone, or the like is required to have a thickness of 1 mm or less. As described above, when the thickness of the light guide plate 101 is reduced, the distance between the V-shaped groove 101g of the light guide plate 101 and the diffusion sheet 103 is shortened, and the light reflected from the reflection slope 101s of the light guide plate 101 is not diffused. Spots such as moiré tend to appear between them. For this reason, the pitch of the V grooves 101g of the light guide plate 101 must be sufficiently smaller than the pixel pitch of the liquid crystal panel. For example, if the pixel pitch of the liquid crystal panel is 200 μm, the pitch of the V-groove 101 g of the light guide plate 101 needs to be 100 μm or less. Further, the depth of the V-shaped groove 101g must be formed shallower in proportion to the pitch of the V-shaped groove 101g.
[0006]
On the other hand, the amount of light emitted from the light exit surface of the light guide plate 101 is proportional to the area of the reflection slope 101s formed on the reflector bottom surface. Further, since more light propagates in the light guide plate 101 as the light source 100 is closer to the light source 100, in order to make the luminance emitted from the light exit surface of the light guide plate 101 uniform, the area of the reflection inclined surface 101s is closer to the light source 100. It is necessary to decrease it gradually. Therefore, the depth of the V-groove 101g must be gradually reduced as the distance from the light source 100 increases.
[0007]
As described above, the V-groove 101g formed in the light guide plate 101 needs to be formed to have a narrow and shallow groove pitch in accordance with the performance required of the display device. 1 μm. The light guide plate 101 is generally formed by injection molding. However, when the depth of the V groove 101g is 1 μm or less, it becomes difficult to form a groove by a molding die, the life of the die is shortened, and mass productivity is reduced. It was getting worse.
[0008]
Therefore, an object of the present invention is to provide a light guide plate capable of facilitating the processing of a molding die for forming a thinned light guide plate and improving the life of the mold, and a backlight device using the same. To provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following features.
In the light guide plate of the present invention, light emitted from a light source is incident on a side surface, and light incident on the side surface is reflected on a bottom surface and emitted toward an upper surface. The light guide plate has a plurality of grooves and a plurality of reflection reducing portions on the bottom surface. The plurality of grooves are formed on the bottom surface so that their extending directions are parallel to the side surfaces, and form a reflecting surface that reflects light incident from the side surfaces toward the upper surface. The plurality of reflection reducing portions are formed on the bottom surface so that the extending direction is perpendicular to the side surfaces and in contact with the grooves. Then, the amount of light emitted from the reflection reducing section is smaller than the amount of light emitted from the groove.
[0010]
According to the configuration of the present invention described above, the bottom surface of the light guide plate has a plurality of grooves parallel to the side surface and a plurality of reflection reduction portions formed perpendicular to the side surface and in contact with the groove. Since the amount of light radiated from the reflection reducing portion is smaller than the amount of light radiated from the groove, the depth of the groove can be increased. Therefore, the convex portion for forming the groove in the molding die for injection-molding the light guide plate can be formed high, so that the mold can be easily formed, the mold life is prolonged, and mass productivity is improved. .
[0011]
Further, the groove may be arranged by being divided by the reflection reducing portion. Thereby, the plurality of grooves parallel to the side surface formed on the bottom surface of the light guide plate for forming the reflection surface are separated by the plurality of reflection reduction portions formed perpendicular to the side surface, so that the reflection surface Since the reflection surface corresponding to the portion where the light-reflection portion overlaps with the light-reflection portion is reduced, the amount of light emitted from the groove can be easily reduced, and the depth of the groove can be similarly increased. Therefore, the convex portion for forming the groove in the molding die for injection-molding the light guide plate can be formed high, so that the mold can be easily formed, the mold life is prolonged, and mass productivity is improved. .
[0012]
The reflection reducing portion may be formed so that the width in a direction parallel to the side surface gradually decreases as the distance from the side surface increases. As a result, the area of the reflection surface formed by the groove gradually increases as the distance from the light source increases, and the luminance emitted from the light exit surface of the light guide plate at a constant groove depth can be made uniform. In other words, the projections for forming the grooves in the molding die for injection-molding the light guide plate can be formed at a certain height, so that it becomes easy. Light plates can be manufactured.
[0013]
Further, the reflection reducing section may be configured by a convex protrusion formed parallel to the bottom surface of the light guide plate. In this case, in a molding die for injection-molding the light guide plate, a groove parallel to a surface for forming the bottom surface may be formed to form the reflection-reducing portion. On the other hand, cutting can be easily performed only by cutting. Further, since the groove in the mold is cut in a concave shape with respect to the surface for forming the bottom surface, an overlapping portion of the convex portion in the mold can be completely removed, so that the light guide plate is formed. It is possible to completely remove the portion where the reflection surface to be formed is desired to be reduced.
[0014]
Further, the protrusion may have a rectangular cross section in a direction parallel to the side surface. In this case, since the light incident on the projection is almost totally reflected, light loss propagating through the light guide plate can be prevented.
[0015]
Note that the present invention can also be realized as a backlight device using the above-described light guide plate.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
A backlight device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a side view showing the structure of the backlight device.
[0017]
In FIG. 1, the backlight device of the present embodiment includes a light source 1, a light guide plate 2, a diffusion sheet 3, and a reflection sheet 4. The light source 1 includes an LED (Light Emitting Diode) that emits diffused light, a fluorescent tube, an incandescent lamp, and the like. The light guide plate 2 is a light guide member made of a transparent resin such as a flat acrylic or polycarbonate, and light emitted from the light source 1 is incident on one side surface (hereinafter, referred to as a light incident surface). The light guide plate 2 guides light propagating inside the light guide plate 2 in a direction perpendicular to the light source 1 and emits the light from a flat plate surface (hereinafter referred to as a light emission surface) formed in the front direction of the backlight device. Let it. On the other flat surface (hereinafter referred to as a reflector bottom surface), which is the back surface opposite to the light exit surface of the light guide plate 2, a plurality of grooves 2g whose extending direction is provided in parallel with the light incidence surface are formed. Is done. For example, the groove 2g is formed in a V-shape, and is hereinafter referred to as a V groove 2g. A plurality of reflection slopes 2s are formed by the side surfaces on the light incident surface side of the plurality of V grooves 2g. A plurality of projections 2p are formed on the bottom surface of the reflector of the light guide plate 2 in a direction orthogonal to the V-groove 2g. The detailed shapes of the V-groove 2g, the reflecting slope 2s, and the protrusion 2p formed on the bottom surface of the reflector of the light guide plate 2 will be described later.
[0018]
The light L that has entered the light guide plate 2 from the light source 1 is reflected by the plurality of reflection slopes 2s, is emitted in the direction of the light emission surface opposite to the bottom surface of the reflector, and is guided to a liquid crystal panel (not shown). In the vicinity of the light emitting surface of the light guide plate 2, light L emitted from the light emitting surface is diffused to be uniform, and fine beads for guiding the light to the liquid crystal panel are flat and fine beads are dispersed on the upper surface. A diffusion sheet 3 is provided. A reflection sheet 4 is provided near the reflector bottom surface of the light guide plate 2 for reflecting light leaking from the reflector bottom surface of the light guide plate 2 and returning the light to the inside of the light guide plate 2 again. As described above, in the backlight device according to the present embodiment, the light L of the light source 1 is incident from the light incident surface of the light guide plate 2, and the reflection slope 2 s of the plurality of V-grooves 2 g formed on the bottom surface of the reflector makes the light guide plate 2 inside the light guide plate 2. Is emitted from the front direction (light emitting surface) of the backlight device while guiding the light L propagating through the light emitting device toward the light emitting surface.
[0019]
Next, a detailed structure of the light guide plate 2 according to the first embodiment will be described with reference to FIGS. FIG. 2 is a perspective view of the light guide plate 2 as viewed from the light exit surface with the light incident surface toward the front, and FIG. 3 is a perspective view of the light guide plate 2 with the side facing the light incident surface as viewed from the bottom of the reflector. . In FIG. 2, in order to explain the internal structure of the light guide plate 2, a reflection surface and a projection formed inside are shown through.
[0020]
2 and 3, a plurality of V-grooves 2g whose extending direction is provided in parallel with the light incident surface are formed on the reflector bottom surface of the light guide plate 2. Further, on the reflector bottom surface of the light guide plate 2, each V-groove 2g is divided and formed by a plurality of protrusions 2p formed in a direction orthogonal to the V-groove 2g. That is, since the protrusion 2p is formed at the portion where the V groove 2g and the protrusion 2p overlap, the V groove 2g is divided by the protrusion 2p. Therefore, by the division of the V-grooves 2g, a plurality of reflection slopes 2s formed by the side surfaces on the light incident surface side of the plurality of V-grooves 2g are also formed by division (the surfaces indicated by the hatched broken lines in FIG. 3).
[0021]
Here, the light guide plate 2 used in a mobile phone or the like has a screen size of about 40 mm × 35 mm and a thickness of 1 mm or less. Further, the amount of light emitted from the light exit surface of the light guide plate 2 is proportional to the area of the reflection slope 2s formed on the reflector bottom surface. Further, since the light propagating in the light guide plate 2 becomes closer to the light source 1, the area of the reflection slope 2 s becomes closer to the light source 1 in order to make the luminance emitted from the light exit surface of the light guide plate 2 uniform. It is necessary to decrease it gradually. Therefore, the depth of the V-groove 2g must be gradually reduced toward the light source 1. Further, in order to avoid moire or the like between the pixels of the liquid crystal panel, the pitch of the V-grooves 2g and the pitch of the projections 2p of the light guide plate 2 must be sufficiently smaller than the pixel pitch of the liquid crystal panel. In the light guide plate 101 (see FIG. 9) used in the conventional backlight device, the pitch of the V-groove 101g is about 100 μm because the pitch of the V-groove 101g is at least half or less of the pixel pitch of the liquid crystal panel. Further, in order to make the luminance of the light guide plate 2 uniform, it is necessary that h = about 0.5 μm, where h is the depth of the V groove 101g on the light source 100 side.
[0022]
On the other hand, the area of the reflection inclined surface 2s formed inside the light guide plate 2 used in the backlight device according to the present embodiment is divided by the protrusion 2p, and thus corresponds to an area corresponding to a portion overlapping the protrusion 2p. Will be reduced. Assuming that the width of the light incident surface of the light guide plate 2 is W and the widths of the n projections 2p are all constant widths Wp, the ratio (duty) Dw occupied by the width Wp relative to the width W is:
Dw (%) = n × Wp / W × 100
Is represented by When the same area as the reflection slope 101s formed by the V-groove 101g of the depth h in the conventional light guide plate 101 is formed by the reflection slope 2s of the light guide plate 2 of the present embodiment, the V-groove 2g of the light guide plate 2 is formed. The depth H of
H = h / (1-Dw / 100)
It becomes. For example, when the duty Dw occupied by the width Wp of the projection 2p of the light guide plate 2 is 90%, the depth H of the V groove 2g of the light guide plate 2 is set to be greater than the depth h of the V groove 101g of the conventional light guide plate 101. It can be 10 times. That is, the light guide performance of the conventional light guide plate 101 formed at the depth h = 0.5 μm of the V groove 101g of the conventional light guide plate 101 is changed to the V groove 2g with the duty Dw = 90% in the light guide plate 2 according to the present embodiment. With a depth H = 5 μm. The pitch of the V-grooves 2g and the pitch of the protrusions 2p of the light guide plate 2 are set to be equal to or less than half the pixel pitch of the liquid crystal panel, similarly to the pitch of the V-grooves 101g of the conventional light guide plate 101. In addition, it is possible to avoid moire or the like between pixels of the liquid crystal panel. Further, since the cross-sectional shape of the projection 2p is rectangular, the light incident on the projection 2p is substantially totally reflected, so that light loss propagating through the light guide plate 2 can be prevented. In the light guide plate 2 as well, the depth of the other V-grooves 2g is gradually increased in order to gradually increase the area of the reflection slope 2s as the distance from the light source 1 increases. It can be formed at a ratio based on the depth of the V-groove 101g of the conventional light guide plate 101.
[0023]
Next, a method for manufacturing the light guide plate 2 will be described. The light guide plate 2 is preferably formed by injection molding using a light guide member. Referring to FIGS. 4 and 5, a method of forming the reflector bottom surface of the light guide plate 2 by injection molding, which is a feature of the present invention, will be described. explain. FIG. 4 is a perspective view showing a first stage of forming a mold 20 used in injection molding for forming the reflector bottom surface of the light guide plate 2, and FIG. 5 is a second stage of forming the mold 20. FIG.
[0024]
In the mold 20 used by injection molding for forming the shape of the reflector bottom surface of the light guide plate 2, the V-groove 2g has a convex shape and the protrusion 2p has a concave shape. In FIG. 4, first, in forming the mold 20, in order to form a plurality of V-grooves 2 g by injection molding, the mold 20 has a plurality of V-grooves with respect to a plane for molding the reflector bottom surface of the light guide plate 2. Is formed (first stage). Since the V-groove forming portion 20g is a convex portion for forming the V-groove 2g, a convex similar to the shape of the V-groove 2g is formed based on the above-described pitch of the V-groove 2g and the depth according to the duty Dw. Form a shape. Therefore, as described above, the light guide plate 2 can form the V-grooves 2g deeper at a rate based on the duty Dw, so that the V-groove forming portion 20g can be formed higher. The height of the V-groove forming portion 20g is formed gradually and deeply so as to gradually increase the area of the reflection slope 2s as the distance from the light incident surface increases. The V-groove forming portion 20g in the mold 20 can be cut by a conventional processing method such as a cutting process.
[0025]
In FIG. 5, a plurality of groove shapes for forming a plurality of protrusions 2p are formed on the surface on which the V-groove forming portion 20g is formed by using the mold 20 on which the formation in the first stage is completed. Is formed (second stage). Since the protrusion forming portion 20p is a concave portion for forming the protrusion 2p, the protrusion forming portion 20p is cut as a groove having a direction perpendicular to the V-groove forming portion 20g as an extending direction. Therefore, the groove width of the projection forming portion 20p is cut with a width based on the above-described duty Dw. The groove depth of the projection forming portion 20p is formed by shaving the V-groove forming portion 20g by the above-mentioned groove width, and further driving the V-groove forming portion 20p to have a groove depth of 5 to 10 μm.
[0026]
In this manner, the protrusion forming portion 20p can be easily cut only by cutting in the mold 20 on which the V-groove forming portion 20g is formed. Further, as described above, the height of the V-groove forming portion 20g can be formed to be higher and larger in accordance with the duty Dw as compared with the related art, so that it is easy to form the convex portion in the molding die, and the mold life And the mass productivity is improved.
[0027]
In addition, since the protrusion 2p in the light guide plate 2 is provided to divide the V groove 2g, the shaping of the protrusion forming portion 20p is originally performed by only the V groove forming portion 20g with respect to the mold 20 by the groove width. If the cutting process is performed (that is, the groove depth of the projection forming portion 20p is 0), the function can be sufficiently satisfied. However, in the case where the projection forming portion 20p is cut by cutting the mold 20 provided with the V-groove forming portion 20g, it is not possible to completely remove only the V-groove forming portion 20g in consideration of a processing error or the like. difficult. Therefore, by further processing the groove so as to have a groove depth of 5 to 10 μm, it is possible to prevent a part of the portion of the V-groove forming portion 20 g that is desired to be reduced from remaining. However, when such an effect is not expected, a part of the V groove forming portion 20g to be reduced may be left partially. Even if a part of the V-groove forming portion 20g to be reduced remains partially, the reflection slope 2s in the V-groove 2g of the light guide plate 2 formed by the mold 20 is reduced as a result. The height of the forming portion 20g can be increased. Such a die processing can be performed by cutting the groove depth of the projection forming portion 20p to 0 or the like. In this case, the projection 2p is not formed on the bottom surface of the reflector of the light guide plate 2, but a V-groove 2g divided according to the duty Dw is formed. Further, the groove depth of the projection forming portion 20p may be minus (that is, convex in the mold 20). In this case, in the first stage of the generation of the mold 20 described above, the V-groove 2g can be similarly divided by forming the convex-shaped protrusion forming portion 20p simultaneously with the V-groove forming portion 20p. In this case, a groove is formed on the bottom surface of the reflector of the light guide plate 2 instead of the protrusion 2p, but a V-groove 2g divided according to the duty Dw can be formed.
[0028]
In addition, a plurality of V-grooves 2g whose extending directions are provided in parallel with the light incident surface are formed on the reflector bottom surface of the light guide plate 2 by connecting the right and left sides as viewed from the light incident surface in a straight line. As described above, the V-groove 2g does not have to connect the right and left side surfaces in a straight line. If the extending direction is parallel to the light incident surface, the V-groove 2g may be terminated at the intersection with the protrusion 2p. For example, the V-groove 2g and the protrusion 2p may be formed on the bottom surface of the reflector. It may be formed. Further, the V-groove 2g of the light guide plate 2 does not have to be a single triangular cross-sectional groove. Further, the bottom surface of the reflector of the light guide plate 2 may be stepped, and a plurality of triangular grooves may be formed in the step portion. Further, the light guide plate 2 does not have to be a flat plate, and may have a wedge shape.
[0029]
(Second embodiment)
In the backlight device according to the above-described first embodiment, the V-groove is formed gradually deeper in order to gradually increase the area of the reflection slope as the light guide plate used therein is separated from the light source. As a second embodiment, a backlight device using a light guide plate that makes the luminance emitted from the light exit surface uniform by gradually reducing the width of the projection as the distance from the light source increases is described. The structure of the backlight device according to the second embodiment differs from the structure described in the first embodiment with reference to FIG. 1 only in the structure of the light guide plate. The light guide plate used is a light guide plate 2i, and other similar components are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0030]
Next, a detailed structure of the light guide plate 2i according to the second embodiment will be described with reference to FIGS. FIG. 6 is a perspective view of the light guide plate 2i as viewed from the light exit surface with the light incident surface toward the front, and FIG. 7 is a perspective view of the light guide plate 2i with the side opposite to the light incident surface as viewed from the bottom of the reflector. . In FIG. 6, in order to explain the internal structure of the light guide plate 2i, a reflection surface and a projection formed inside are shown through.
[0031]
6 and 7, a plurality of V-grooves 2gi whose extending direction is provided in parallel with the light incident surface are formed on the reflector bottom surface of the light guide plate 2i. Also, on the reflector bottom surface of the light guide plate 2i, each V-groove 2gi is divided and formed by a plurality of protrusions 2pi formed in a direction orthogonal to the V-groove 2gi. That is, since the protrusion 2pi is formed at the portion where the V groove 2gi and the protrusion 2pi overlap, the V groove 2gi is divided by the protrusion 2pi. Therefore, by the division of the V-grooves 2gi, the plurality of reflection slopes 2si formed by the side surfaces on the light incident surface side of the plurality of V-grooves 2gi are also formed by division (the surfaces indicated by the hatched broken lines in FIG. 6 and the figures). 7).
[0032]
Here, as described above, the amount of light emitted from the light emission surface of the light guide plate 2i is proportional to the area of the reflection slope 2si formed on the reflector bottom surface. Since the amount of light propagating in the light guide plate 2i increases as the distance from the light source 1 increases, the area of the reflection slope 2si decreases as the distance from the light source 1 increases. It is necessary to decrease it gradually. In the light guide plate 2i, the width of the projection 2pi is gradually increased in order to gradually reduce the area of the reflection slope 2si. That is, the width of the protrusion 2pi formed on the reflector bottom surface of the light guide plate 2i is formed with the largest width Wpw on the light incident surface and the smallest width Wpn on the side surface facing the light incident surface. The protrusions 2pi are formed by gradually changing the widths of the protrusions 2pi. Then, as described above, the reflection slope 2si formed inside the light guide plate 2i is divided by the projection 2pi, and as a result, a portion overlapping the projection 2pi is reduced from the area of the reflection slope 2si. Therefore, as the width Wp of the projection 2pi gradually changes from Wpw to Wpn, the area of the reflection slope 2si reduced by the projection 2pi gradually increases. Then, the area of each reflection slope 2si is adjusted by the width change amount of the projection 2pi (that is, the widths Wpw and Wpn are adjusted) so that the luminance emitted from the light emission surface of the light guide plate 2i becomes uniform. In other words, in the light guide plate 2i, even if the depth of the V-groove 2gi is formed to be constant by gradually narrowing the width of the protrusion 2pi, the luminance emitted from the light exit surface of the light guide plate 2i can be made uniform. can do.
[0033]
Note that, similarly to the light guide plate 2 (see FIGS. 2 and 3) in which the protrusion 2p having the constant width Wp is formed as described in the first embodiment, the pitch of the V-grooves 2gi and the protrusion 2pi By forming the pitch at a half or less of the pixel pitch of the liquid crystal panel, it is possible to avoid moire and the like between the pixels of the liquid crystal panel. Further, since the cross-sectional shape of the projection 2pi is rectangular, the light incident on the projection 2pi is almost totally reflected, so that light loss propagating through the light guide plate 2i can be prevented. The duty Dw of the light guide plate 2i may be calculated in the same manner as in the first embodiment, using the average width (Wpw + Wpn) / 2 of the protrusion 2pi. Therefore, similarly to the light guide plate 2 according to the first embodiment, the depth of the V-groove 2gi of the light guide plate 2i is a ratio based on the duty Dw using the average width of the protrusions 2pi. Needless to say, it can be formed deeper than the depth of the V groove 101g.
[0034]
Next, a method for manufacturing the light guide plate 2i will be described. The light guide plate 2i can also be formed by injection molding using a light guide member. A method of forming the reflector bottom surface of the light guide plate 2i by injection molding, which is a feature of the present invention, will be described with reference to FIG. I do. FIG. 8 is a perspective view showing a second stage of generating a mold 20i used in injection molding for forming the reflector bottom surface of the light guide plate 2i.
[0035]
First, in the generation of the mold 20i, a plurality of convex V-groove forming portions 20gi are formed as a first step in order to form the plurality of V-grooves 2g by injection molding. The method is the same as the method described in the first embodiment with reference to FIG. 4 except that the height of the portion 20gi is constant. Therefore, a detailed description of the method of generating the mold 20i in the first stage is omitted.
[0036]
In FIG. 8, a plurality of groove shapes for forming a plurality of protrusions 2pi are formed on the surface on which the V-groove forming portion 20gi is formed by using the mold 20i on which the formation of the first stage is completed. Is formed (second stage). Since the projection forming portion 20pi is a concave portion for forming the projection 2pi, it is cut as a groove having a direction perpendicular to the V-groove forming portion 20gi as an extending direction. Therefore, the groove width of the projection forming portion 20pi is cut so as to have the largest width Wpw on the light incident surface and the smallest width Wpn on the side surface facing the light incident surface. Such a groove whose groove width changes gradually can be easily formed by cutting a plurality of times while shifting the angle of the cutting direction. Further, the groove depth of the projection forming portion 20pi is formed by shaving the V-groove forming portion 20gi by a groove width, and further driving the V-groove forming portion 20gi to have a groove depth of 5 to 10 μm.
[0037]
As described above, the protrusion forming portion 20pi can be easily cut only by cutting in the mold 20i in which the V-groove forming portion 20gi is formed. Further, as described above, the height of the V-groove forming portion 20gi can be formed to be higher and larger in accordance with the duty Dw with respect to the average width of the projection 2pi as compared with the related art, so that it is easier to form the convex portion in the molding die. Yes, the mold life is prolonged, and mass productivity is improved. Furthermore, since the light guide plate 2i can be molded by the mold 20i having a constant height of the V-groove forming portion 20gi, the mold 20i can be easily formed in the first stage, and a highly accurate mold can be formed. By doing so, a highly accurate light guide plate 2i can be manufactured.
[0038]
Since the projections 2pi on the light guide plate 2i are provided to divide the V-grooves 2gi, the shaping of the projection-forming portions 20pi is essentially performed by only the V-groove forming portions 20gi by the groove width with respect to the mold 20i. If cutting is performed (that is, the groove depth of the projection forming portion 20pi is 0), the function can be sufficiently satisfied. However, when the projection forming portion 20pi is cut by cutting in the mold 20i provided with the V-groove forming portion 20gi, it is not possible to completely remove only the V-groove forming portion 20gi in consideration of a processing error or the like. difficult. Therefore, by further processing the groove so as to have a groove depth of 5 to 10 μm, it is possible to prevent a part of the portion of the V-groove forming portion 20gi to be reduced from remaining. However, when such an effect is not expected, a portion of the V-groove forming portion 20gi to be reduced may be left partially. Even if a part of the V-groove forming portion 20gi to be reduced remains partially, the reflection slope 2si in the V-groove 2gi of the light guide plate 2i formed by the mold 20i is reduced as a result. The formation part 20gi can be formed high. Such die processing can be performed by cutting the groove depth of the projection forming portion 20pi to 0 or the like. In this case, the protrusion 2pi is not formed on the reflector bottom surface of the light guide plate 2i, but the V groove 2gi divided according to the duty Dw and the change in the groove width can be formed. The groove depth of the projection forming portion 20pi may be minus (that is, convex in the mold 20i). In this case, in the above-described first stage of the generation of the mold 20i, the V-groove 2gi can be similarly divided by forming the convex-shaped protrusion forming portion 20pi simultaneously with the V-groove forming portion 20pi. In this case, a groove is formed on the bottom surface of the reflector of the light guide plate 2i instead of the protrusion 2pi, but a V-groove 2gi divided according to the duty Dw and the groove width change can be formed.
[0039]
In addition, a plurality of V-grooves 2gi whose extending directions are provided in parallel with the light incident surface are formed on the reflector bottom surface of the light guide plate 2i by connecting the right and left sides as viewed from the light incident surface in a straight line. However, the V-groove 2gi does not have to connect the right and left sides in a straight line. If the extending direction is parallel to the light incident surface, the V-groove 2gi may be terminated at the intersection with the projection 2pi. For example, the V-groove 2gi and the projection 2pi may be formed on the bottom surface of the reflector. It may be formed. Further, the V-groove 2gi of the light guide plate 2i may not be a single triangular cross-sectional groove. Further, the reflector bottom surface of the light guide plate 2i may be stepped, and a plurality of triangular grooves may be formed in the step portion. In addition, the light guide plate 2i does not have to be a flat plate shape, and may be a wedge shape.
[0040]
【The invention's effect】
As described above, by dividing the groove parallel to the light incident surface formed on the reflector bottom surface of the light guide plate to form the reflecting surface by the projection formed perpendicular to the light incident surface, The depth can be increased. Therefore, it is easy to form the convex portion for forming the groove in the molding die for injection-molding the light guide plate, the life of the mold is prolonged, and mass productivity is improved. In addition, the die processing for forming the projections can be easily performed only by cutting. Further, by gradually changing the width of the projection, it is possible to make the luminance emitted from the light exit surface of the light guide plate uniform at a constant groove depth.
[Brief description of the drawings]
FIG. 1 is a side view showing a structure of a backlight device according to a first embodiment of the present invention.
FIG. 2 is a perspective view of the light guide plate 2 according to the first embodiment of the present invention as viewed from a light exit surface with a light incident surface in front.
FIG. 3 is a perspective view of the light guide plate 2 of FIG. 2 when viewed from the bottom of the reflector with a side surface facing a light incident surface facing the user;
FIG. 4 is a perspective view showing a first stage of generating a mold 20 used in injection molding for forming a reflector bottom surface of the light guide plate 2 of FIG.
FIG. 5 is a perspective view showing a second stage of generating a mold 20 used in injection molding for forming a reflector bottom surface of the light guide plate 2 of FIG. 2;
FIG. 6 is a perspective view of a light guide plate 2i according to a second embodiment of the present invention as viewed from a light exit surface with a light entrance surface in front.
FIG. 7 is a perspective view of the light guide plate 2i of FIG. 6 when viewed from the bottom of the reflector with a side surface facing a light incident surface facing the front;
8 is a perspective view showing a second stage of generating a mold 20i used for injection molding for forming a reflector bottom surface of the light guide plate 2i of FIG.
FIG. 9 is a perspective view showing the structure of a conventional backlight device.
[Explanation of symbols]
1. Light source
2, 2i ... Light guide plate
2g, 2gi ... V groove
2p, 2pi ... projection
2s, 2si ... Reflective slope
20, 20i ... mold
20g, 20gi ... V groove forming part
20p, 20pi ... protrusion formation part
3. Diffusion sheet
4: Reflective sheet

Claims (6)

A light guide plate that emits light from a light source from a side surface and reflects the light incident from the side surface on a bottom surface and emits the light toward an upper surface,
A plurality of grooves on the bottom surface, the extending direction of which is formed parallel to the side surface, and a reflection surface that reflects light incident from the side surface toward the top surface,
The bottom surface has a plurality of reflection reducing portions, the extending direction of which is perpendicular to the side surface, and is formed in contact with the groove,
The light guide plate, wherein an amount of light emitted from the reflection reducing unit is smaller than an amount of light emitted from the groove. The light guide plate according to claim 1, wherein the groove is divided and arranged by the reflection reduction unit. The light guide plate according to claim 2, wherein the reflection reducing portion is formed so that a width in a direction parallel to the side surface gradually decreases as the distance from the side surface increases. The light guide plate according to claim 2, wherein the reflection reduction unit is configured by a convex protrusion formed parallel to the bottom surface. The light guide plate according to claim 4, wherein the protrusion has a rectangular cross section in a direction parallel to the side surface. A light guide plate according to claim 1,
A light source,
And a diffusion sheet for diffusing light emitted from the light guide plate.

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