JP3923508B2 - Light guide plate for surface light source device, surface light source device, and liquid crystal display device - Google Patents

Description

  The present invention mainly incorporates a light guide plate for a surface light source device manufactured by injection molding suitable for use as a backlight in liquid crystal displays such as office automation equipment, televisions, measuring instruments and watches, and the light guide plate for the surface light source device. And a liquid crystal display device using the surface light source device.

  A surface light source device has been known for a long time, and a small one has been used as a backlight of a wristwatch for a liquid crystal display, and a large one has been used as a backlight for an advertisement display board or a lighting device for displaying products. As the light sources, LEDs are used for the small ones and fluorescent tubes are used for the large ones. As the light guide plate, an acrylic plate material cut into an appropriate size is used. It was. On the other hand, since the surface light source device is required to emit uniform light from a predetermined plane and to be thin, the light source is usually disposed at a side position of the light guide plate. By deforming into a special shape, using a sandpaper or special equipment or device to roughen the surface as desired to form a reflective surface, or polishing the incident light source surface to a mirror surface It was made.

  In recent years, with the breakthrough advances in liquid crystal display technology and the development of OA equipment and electronic / communication equipment, the demand for surface light source devices mainly used for liquid crystal display devices of around 10 inches has increased rapidly. Yes. Therefore, on the one hand, an ultra-fine and long-life fluorescent tube with a diameter of 4 mm or less has been developed as a light source. On the other hand, the light guide plate is manufactured by injection molding capable of mass production with stable quality and fewer steps. It has become like this.

  By the way, in such a light guide plate, various devices are required to allow the light source light incident from the side position to be emitted as a uniform plane light from a plane having a predetermined area. Therefore, many proposals have been made so far, but most of the distribution of the reflectivity by taking some means (formation of uneven surface or painting, printing, etc.) on the surface opposite to the exit surface, that is, the reflection surface. It may be considered that the surface is changed, or the reflecting surface is not a surface parallel to the exit surface, but formed by various planes or curved surfaces, or a combination of both.

  Among these, those that do not form a reflecting surface parallel to the exit surface have a large thickness at or near the incident surface of the light source light, and are thinned away from it. Examples include those disclosed in Patent Documents 1 to 4 and the like, as well as those having the shapes shown in FIGS. 4 and 5 are side views of the light guide plate, and in each case, the upper surface is the entrance surface and the left side is the exit surface.

  Therefore, how such a light guide plate is conventionally formed will be described with reference to a typical light guide plate shown in FIGS. 6 is a plan view seen from the exit surface side, and FIG. 7 is a right side view of FIG. Therefore, in this case, the upper surface is the incident surface 1 in any drawing, and is perpendicular to the emission surface 2 in FIG. The thickness of the light guide plate on the incident surface is determined in consideration of the thickness of the fluorescent tube in view of the arrangement of the fluorescent tube along the longitudinal direction of the incident surface near the outside. Since the reflection surface 3 is formed obliquely with respect to the emission surface 2 so that the incident light from the incidence surface 1 can be directly reflected, the thickness of the light guide plate decreases as it goes downward in the drawing. It is formed to become.

  When such a light guide plate is injection-molded, it is first necessary to determine at which position on which surface the gate position of the mold is provided. Conventionally, either one of the side surfaces 5 and 6 in FIG. It was usual to place the gate at a thick position, which is also close to the incident surface. As shown in FIG. 8, the reflecting surface 3 is inclined with respect to the emission surface 2 in the opposite direction from the center, and the lower surface 4 is substantially the same thickness as the incident surface 1, and fluorescent light is also present in the vicinity of the outside. The same applies to the molding of a two-lamp type light guide plate in which tubes are arranged.

  In addition, it is necessary to take the effective surface as much as possible between the exit surface and the reflective surface. In particular, in order to obtain uniform exit light on the reflective surface, various uneven surfaces such as a mesh pattern can be formed or painted. In many cases, it is difficult to place gates on these surfaces.

  Furthermore, although it is conceivable to arrange a gate on the lower surface 4 in FIG. 7, the thickness of this surface is usually about 1 to 2 mm in the case of an ultra thin light guide plate for OA equipment of about 10 inches, Although it is difficult to arrange the gate itself, even if it is temporarily arranged, the injection pressure cannot be sufficiently obtained with a normal molding machine, and the acrylic melt cannot flow well into the cavity, so the surface transferability is remarkably high. Deteriorate. Therefore, in order to increase the injection pressure or to make it easy to flow by raising the temperature of the mold, an expensive molding machine capable of high-precision control is required, which increases the cost of the light guide plate. I couldn't escape. Although it is conceivable to increase the number of gates, in that case, it is not possible to prevent the so-called weld line from being generated as well as the cost of the mold, which is a fatal problem for the uniformization of the emitted light. Therefore, it is difficult to consider a gate on this surface.

Japanese Patent Laid-Open No. 3-59526 Japanese Utility Model Publication No. 3-104906 Japanese Utility Model Publication No. 5-75738 Japanese Utility Model Publication No. 5-75739

  However, in the conventional molding method, when the gate G is arranged on the side surface 5 as shown in FIG. 6, the flow path A flows quickly and the flow of the flow path B becomes slow at the time of material injection. In this case, the flow of the material flowing from the incident surface 1 side toward the lower surface 4 side is not constant, and the flow direction varies depending on the location, and is greatly different between the side surface 5 side and the side surface 6 side. For this reason, the pressure difference and temperature difference between each region vary, and when the uneven surface of various shapes is formed on the reflective surface, the transfer of the shape cannot be obtained as prescribed, and after the generation of the weld line and the molding The problem of warping is likely to occur, and in the ultra-thin light guide plate as shown in the figure, the phenomenon that the normal molding machine and molding method cannot completely fill the cavity also occurs, and the light guide plate has a slight shape and size. Due to these differences, it was necessary to consider each time to set the conditions for molding.

  An object of the present invention is to provide a surface light source that can be manufactured with good moldability without causing the above-mentioned problems even if it is ultra-thin, using a normal molding machine and based on normal condition settings. A light guide plate for a device, a surface light source device using the light guide plate for a surface light source device, and a liquid crystal display device are provided.

The invention of claim 1 relates to a light guide plate for a surface light source device having an incident surface on which light sources are arranged close to each other and an exit surface from which incident light from the incident surface is emitted. In the present invention, the light guide plate is (1) a plate-like body having a substantially quadrangular planar shape as viewed from the exit surface side, and (2) one side surface is a thick portion and faces the one side surface. The other side surface is a thin-walled portion, and has a shape in which the plate thickness is reduced from the one side surface toward the other side surface. (3) Light from the light source is incident only on the one side surface that is the thick-walled portion. (4) Concave and convex shapes that reflect light in the process of entering the incident surface and propagating toward the other side surface in multiple directions, and finally exiting as uniform light from the exit surface Is formed on the reflection surface located on the opposite side of the emission surface. Further, the incident surface is (1) a gate disposed in a semi-finished product at a position that is a substantially central portion in a direction in which the incident surface spreads and is separated by a predetermined dimension in a direction orthogonal to the incident surface. An overhanging portion for connecting to the incident surface is integrally formed, and (2) in a finished product state, has a cut surface after the overhanging portion is cut. The planar shape of the overhanging portion is a shape that widens from the gate side toward the incident surface side so as to be connected to the incident surface with an area larger than the area of the gate, and The shape is such that the molten resin injected from the gate flows symmetrically with respect to a substantially central portion in the direction in which the incident surface spreads.

The invention of claim 2 relates to a surface light source device characterized by comprising incorporating a surface light source device for a light guide plate according to the invention of claim 1.

A third aspect of the present invention relates to a liquid crystal display device that illuminates a liquid crystal display panel with the surface light source device according to the second aspect of the present invention.

According to the present invention , in the state of the semi-finished product of the light guide plate, the molten resin injected from the gate to the portion corresponding to the overhanging portion (ancillary cavity) corresponds to the overhanging portion from the gate toward the incident surface. The part flows in contrast to the approximately central part of the direction in which the incident surface spreads, and the inside of the cavity that forms a plate-like body whose planar shape is a substantially rectangular shape from the incident surface (thick part) side to the other side (thin part) ) And filled in a parallel flow toward the side. Therefore, according to the present invention, a normal molding machine is used, and a normal pressure control and a normal temperature control are used to obtain a substantially equal regular flow and a substantially uniform pressure of the molten resin in each region in the cavity. Incomplete filling and weld lines are not generated, and various irregularities formed on the reflecting surface are not transferred. Then, by cutting and removing the projecting portion of the semi-finished product of the light guide plate, an incident surface having a cut surface after the projecting portion is cut is formed, and the light guide plate for the surface light source device is completed. Goods will be formed.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a semi-finished state of a light guide plate showing a state in which the material of a runner portion after molding is removed, that is, a plan view of a molding intermediate, FIG. 2 is a right side view of FIG. 1, and FIG. It is a right view of the light-guide plate which shows the completed-product state which cut out. In addition, the same code | symbol is attached | subjected to the same part as the part shown in FIG.6 and FIG.7.

  The light guide plate for the surface light source device of this embodiment is an ultra-thin light guide plate as described with reference to FIGS.

  2 and 3, the reflecting surface 3 is shown as a flat surface. However, the reflecting surface 3 actually has a fine uneven shape, and reflects the light source light incident from the incident surface in multiple directions. The light can be emitted as uniform light from the emission surface 2. Since various contrivances and proposals have been made for the concavo-convex shape, a detailed description is omitted here. In FIG. 1, a gate mark 9 is formed on the overhang portion 7. As can be seen from this, the gate G in the mold is arranged toward one surface of the overhanging portion 7, that is, the same surface as the emission surface 2. Therefore, after the material supplied from the runner R is injected from the gate G into the cavity, the path is bent by approximately 90 degrees.

  As described above, the light guide plate in the present embodiment is ultra-thin, but the dimensions will be described here. In FIG. 1, the length of the incident surface 1 and the lower surface 4 is 180 mm, the length of the side surfaces 5 and 6 is 143 mm, and in FIG. 3, the thickness of the thick portion is 3.5 mm and the thickness of the thin portion is 1.5 mm. It is. The distance from the center of the gate mark 9 to the incident surface 1 is 18 mm.

  Next, a method for manufacturing such a light guide plate by injection molding will be described. In explaining the manufacturing method, the mold structure is originally shown and explained, but in the sense of omitting complicated drawings, a semi-finished product of the light guide plate shown in FIGS. Is described as a mold cavity. Therefore, the cavity that forms the overhanging portion 7 will be referred to as an incidental cavity from the viewpoint that the overhanging portion 7 is removed after molding as described above.

  At the time of molding, in FIG. 2, the acrylic resin-based molten material injected from the gate G through the runner R advances at an angle of 90 degrees in the incidental cavity. As shown in FIG. 1, the incidental cavity expands in the traveling direction, so that the incident cavity flows into the cavity near the incident surface with a substantially uniform pressure from an area larger than the area of the gate G. After that, the molten material spreads widely in the side and exhibits a fan shape, but as a whole flows from the thick part on the incident surface side toward the thin part on the lower surface side. Although the flow direction is not strictly parallel, it flows much more parallel and under a uniform pressure than the conventional example described in FIG.

  In this way, in this embodiment, despite the fact that it is an ultra-thin light guide plate, the material is defined in each area in the cavity by a normal pressure control and a normal temperature control using a normal molding machine. It flowed and it was completely filled to every corner. In addition, the uneven shape formed on the reflecting surface is excellent, no weld line is generated, and there is no problem with respect to the warp that easily occurs due to the ultra-thin shape. In this embodiment, the inflow part from the incidental cavity to the thick part occupies about 1/7 with respect to the length of the incident surface 1 as shown in FIG. In order to further improve the ratio, the ratio may be increased, and an incidental cavity may be formed as shown by a two-dot chain line, for example. Even in this case, no abnormality was found in the uniformity of the light emitted from the emission surface as in the case described later.

  After the semi-finished product, that is, the forming intermediate is formed in this way, the overhang portion 7 is cut. This cutting has no problem if a diamond cutter or the like is used, but in this embodiment, the cutting was performed with a normal acrylic cutting cutter having a rotary blade.

  In the above embodiment, as shown in FIG. 2, the gate G is arranged toward the extended surface of the emission surface 2, but this can also be seen from the size of the gate mark 9 shown in FIG. As described above, even if the light guide plate is ultra-thin, there is an effect that the size of the gate G can be determined regardless of the thickness thereof, and the material flows from the incidental cavity to the thick wall portion. This is because the pressure can be averaged somewhat. However, the present invention is not limited to such an arrangement, and the gate G may be arranged so as to face downward from above in the drawing.

  Further, the thickness of the overhang 7 need not be equal to that of the thick portion of the light guide plate. In addition, the gate position is ideally located at the center in the left-right direction of the light guide plate as shown in FIG. 1, but even if the position is moved slightly to the left and right, the uniformity of the emitted light is not affected much. Absent.

  Furthermore, in the present invention, as shown in FIG. 1, overhang portions 5 a and 6 a having appropriate thicknesses may be provided on the side surfaces 5 and 6. The overhang portions 5a and 6a are used for positioning the light guide plate when it is normally incorporated in a surface light source device. In the light guide plate according to the conventional manufacturing method shown in FIG. Due to the difficulty in filling, when the overhanging portions 5a and 6a are provided in the vicinity thereof, the shape transfer is not performed as desired, and this can cause uniform distribution of the emitted light in the thin-walled portion. could not. Considering the uniformity of the luminance distribution on the exit surface 2, the overhang portions 5a and 6a are located at a position distant from the entrance surface 1, at least from the middle between the entrance surface 1 and the bottom surface 4, that is, near the thin portion. It is desirable to provide in.

  When a mold having a structure in which the molten material injected from the gate flows in the direction of the incident surface 1 or toward the lower surface 4 as in the present invention is used, the intermediate surface between the incident surface 1 and the lower surface 4 is moved to the lower surface 4 side. When the overhang portions 5a and 6a are provided, the overhang portions 5a and 6a having excellent shape accuracy can be easily formed from the flow of the molten material, and the shape transferability of the overhang portions 5a and 6a is excellent. Thus, when the shape accuracy of the overhang portions 5a and 6a is high, the positioning accuracy of the light guide plate can be increased.

  Even in the case of a light guide having a uniform thickness from the incident surface 1 to the lower surface 4, the mold structure has a structure in which the molten material injected from the gate flows from the incident surface 1 toward the lower surface 4. It is desirable to provide the overhang portions 5 a and 6 a on the lower surface 4 side from the middle between the incident surface 1 and the lower surface 4. In FIG. 1, the overhang portions 5 a and 6 a are provided on the side surfaces 5 and 6, but similar overhang portions may be provided on the emission surface 2, the reflection surface 3, and the lower surface 4 depending on circumstances.

  Further, the shape of the light guide plate of the present invention is not limited to that shown in the embodiment, and the light guide plate having the shape described in the above-mentioned publicly known publication is also used in the shape shown in FIGS. Needless to say, the present invention can also be applied to a light guide plate. In particular, in the case of the light guide plate having the shape shown in FIG. 8, two incident surfaces are formed on the upper and lower sides, but the mold material is directed from one incident surface side to the other incident surface side. 1, the flow of the material is almost the same as that in the embodiment of FIG. 1 until the center of the flow direction of the material, that is, the thin portion is reached, and the fan-shaped direction having a certain extent of spread. The flow becomes close to a parallel flow, but after passing through the thin-walled portion, the wall thickness gradually increases, so it becomes fan-shaped again. However, the degree is extremely small, and substantially completely filled in parallel flow as in the embodiment of FIG.

It is a top view which shows the semi-finished product state of the light-guide plate which is embodiment of this invention. It is a right view of FIG. It is a right view which shows the finished product state of the light-guide plate shown in FIG. It is a side view of the light-guide plate of a shape different from embodiment. FIG. 5 is a side view of a light guide plate having a shape different from that of the embodiment and the light guide plate shown in FIG. 4. It is a top view for demonstrating the prior art example in the case of shape | molding the ultra-thin light-guide plate similar to embodiment. FIG. 7 is a right side view of FIG. 6. It is a side view of the ultra-thin light-guide plate of a different shape shown in relation to description of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Incident surface, 2 ... Output surface, 3 ... Reflective surface, 4 ... Lower surface, 5, 6 ... Side surface, 7 ... Overhang | projection part, G ... Gate

Claims (3)

In a light source plate for a surface light source device having an incident surface on which a light source is disposed close to and an exit surface from which incident light from the incident surface is emitted,
What planar shape substantially rectangular plate-like body der viewed from the exit surface,
One side is a thick part, the other side facing this one side is a thin part, and exhibits a shape that reduces the plate thickness from the one side toward the other side,
Only the one side surface that is the thick portion becomes the incident surface on which light from the light source is incident,
The concave and convex shape that reflects the light in the process of entering from the incident surface and propagating toward the other side surface in multiple directions, and finally emits the light as uniform light from the emitting surface is the opposite side of the emitting surface. Is formed on the reflective surface located at
The incident surface is
(1) In a semi-finished product state, the entrance surface is connected to a gate disposed at a position that is a substantially central portion in the direction in which the entrance surface spreads and is separated by a predetermined dimension in a direction orthogonal to the entrance surface. The overhang is integrally formed,
(2) In the state of the finished product, it has a cut surface after the protruding portion is cut,
The planar shape of the overhanging portion is a shape that widens from the gate side toward the incident surface side so as to be connected to the incident surface with an area larger than the area of the gate, and from the gate. The injected molten resin is shaped to flow symmetrically with respect to the substantially central portion in the direction in which the incident surface spreads.
A light guide plate for a surface light source device. A surface light source device comprising the light guide plate for a surface light source device according to claim 1 incorporated therein. A liquid crystal display device that illuminates a liquid crystal display panel with the surface light source device according to claim 2.

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