JP2003145585A - Light guide plate for surface light source device, molded intermediate object of light guide plate, surface light source device, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a light guide plate, which has an incident surface having a light source arranged in the vicinity thereof and an emitting surface emitting the incident light arriving from the incident surface and is used in a state incorporated in a surface light source device along with the light source. SOLUTION: A gate is arranged on the side of the incident surface of the light guide plate and a molten material is injected in a cavity for forming the light guide plate from the position corresponding to the incident surface of the light guide plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate for a surface light source device manufactured by injection molding suitable for use as a backlight mainly in liquid crystal displays such as office automation equipment, televisions, measuring instruments and watches, and its molding. Regarding intermediates.

[0002]

2. Description of the Related Art A surface light source device has been known for a long time, and a small one is used as a backlight of a wrist watch for liquid crystal display.
Large ones have been used as backlights for advertisement display boards and lighting devices for product display. As the light sources, LEDs are used for small ones, and fluorescent tubes are used for large ones, and 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 thinned, the light source is usually arranged at a lateral position of the light guide plate. Deformation into a special shape, roughening the surface as desired using sandpaper, special equipment, or equipment to form a reflective surface, or polishing the incident surface of the light source to a mirror surface. It was made.

With the recent breakthrough in liquid crystal display technology and the development of office automation equipment, electronic and communication equipment, etc.
The demand for a surface light source device used for a liquid crystal display device of about 0 inch is rapidly increasing. Therefore, on the one hand, an ultra-thin and long-life fluorescent tube with a diameter of 4 mm or less was developed as a light source, and on the other hand, the light guide plate is manufactured by injection molding that has fewer steps than before and is of stable quality and can be mass-produced. It's starting to happen.

By the way, in such a light guide plate, various measures are required in order to allow the light source light incident from the lateral 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 them are provided with some means (formation of uneven surface or coating, printing, etc.) on the surface opposite to the emission surface, that is, the reflection surface to distribute the reflectance. May be changed, or the reflective surface may be formed by various flat surfaces or curved surfaces instead of being parallel to the emission surface, or a combination of both.

Of these, those not having a reflecting surface formed in parallel with the exit surface have a large thickness at or near the entrance surface of the light from the light source, and become thinner as the distance from the entrance surface decreases. As such examples, JP-A-3-59526, JP-A-3-104906, JP-A-5-75738 and JP-A-5-7573.
In addition to those disclosed in Japanese Patent Publication No. 9 and the like, there are those having the shapes shown in FIGS. 4 and 5. 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 surface is the exit surface.

Therefore, how the conventional light guide plate is molded will be described with reference to the typical shape of the 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, in any of the drawings, the upper surface becomes the entrance surface 1 and is perpendicular to the exit surface 2 in FIG. 7. The thickness of the light guide plate on this incident surface is because the fluorescent tubes are arranged along the longitudinal direction of the incident surface at a position near the outside thereof,
The size of the fluorescent tube is taken into consideration. Since the reflecting surface 3 is formed obliquely with respect to the exit surface 2 so that it can also directly reflect the incident light from the entrance surface 1, the thickness of the light guide plate becomes thinner as it goes downward in the drawing. Is formed.

When such a light guide plate is injection-molded, it is necessary to first decide on which side of which surface the gate position of the mold is to be provided. In the conventional case, the side surfaces 5 and 6 in FIG. Either way, it was usual to place the gate at a thick position near the entrance surface. As shown in FIG. 8, the reflecting surface 3 is inclined with respect to the emitting surface 2 from the central portion in the opposite direction, the lower surface 4 is formed to have substantially the same thickness as the incident surface 1, and the fluorescent light is provided near the outside thereof. The same applies to molding a two-lamp type light guide plate in which tubes are arranged.

It is necessary that the emitting surface and the reflecting surface are as effective as possible. Particularly, in order to obtain uniform emitted light, the reflecting surface is formed with uneven surfaces of various shapes such as a mesh pattern. In many cases, painting or printing is applied, and thus it has been avoided to arrange gates on these surfaces.

Further, although it is conceivable to arrange a gate on the lower surface 4 in FIG. 7, the thickness of this surface is usually about 10 inches, and is 1 to 2 in the case of an ultra-thin light guide plate for OA equipment.
Since it is about mm, it is difficult to arrange the gate itself, but even if it is arranged, the injection pressure cannot be sufficiently obtained with a normal molding machine and the acrylic melt cannot flow well into the cavity. The transferability of is significantly deteriorated.
Therefore, in order to increase the injection pressure or increase the mold temperature to make it easier to flow, an expensive molding machine that enables highly accurate control is required, which increases the cost of the light guide plate. I could not escape. It is also possible to increase the number of gates, but in that case, not only the cost of the mold is increased but also the occurrence of so-called weld lines cannot be prevented, which is a fatal problem in uniforming the emitted light. Therefore, it is difficult to consider arranging the gate on this surface.

[0010]

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 path B flows at the time of material injection.
Since the flow of the material becomes slower, the flow of the material flowing from the incident surface 1 side to the lower surface 4 side varies in various ways depending on the place where the flow direction of the material is constant. And will be very different. Therefore, the pressure difference and the temperature difference between the respective regions are different, and when the uneven surface of various shapes is formed on the reflecting surface, the transfer of the shape cannot be obtained in a predetermined manner. The problem of warpage is likely to occur, and in the ultra-thin light guide plate as shown in the figure, the phenomenon that the cavity cannot be completely filled with the normal molding machine and molding method also occurs. Depending on the difference, it was necessary to make a considerable examination each time when setting the conditions for molding.

The object of the present invention is to produce a moldable product using an ordinary molding machine under normal conditions, even if it is an ultra-thin product, without causing the above problems. Obtaining a light guide plate for a surface light source device and a molded intermediate thereof,
Another object of the present invention is to provide a surface light source device and a liquid crystal display device using them.

[0012]

In order to achieve the above-mentioned object, a light guide plate for a surface light source device according to the present invention has an incident surface on which a light source is arranged in close proximity and incident light from the incident surface. A light guide plate having an emission surface and used by being incorporated in a surface light source device together with the light source, using a molding die in which a gate is arranged on the incident surface side of a cavity forming the light guide plate, It is characterized in that a molten material is injected into the cavity from a position corresponding to the incident surface and injection molding is performed.

The light guide plate for a surface light source device of the present invention is preferably injection-molded by injecting a molten material into the cavity from a position corresponding to a substantially central portion in the longitudinal direction of the incident surface.

Further, in the light guide plate for a surface light source device of the present invention, a gate is provided at a position separated from the incident surface by a predetermined dimension, and the molten material injected from the gate is directed toward the incident surface toward the incident surface. It can be manufactured by injection molding using a molding die provided with an auxiliary cavity that flows substantially symmetrically in the longitudinal direction, and then removing an unnecessary portion formed by the auxiliary cavity. In this case, preferably, the gate is provided toward the extension surface of the emission surface or the surface parallel to the emission surface.

Further, the molded intermediate of the light guide plate for a surface light source device according to the present invention has an incident surface on which the light sources are arranged in close proximity and an emission surface from which the incident light from the incident surface is emitted. A molding intermediate of a light guide plate used together with a surface light source device, wherein a gate is provided at a position separated from the incident surface by a predetermined dimension, and molten material injected from the gate is directed toward the incident surface. After injection molding is performed using a molding die provided with an auxiliary cavity that flows substantially symmetrically in the longitudinal direction of the incident surface, the unnecessary portion formed by the auxiliary cavity is not removed. It is characterized by being taken out from the molding die.

A surface light source device according to the present invention is characterized by incorporating the above-mentioned light guide plate for a surface light source device.

The liquid crystal display device according to the present invention is characterized in that the liquid crystal display panel is illuminated by the surface light source device.

[0018]

The light guide plate for a surface light source device of the present invention is manufactured by arranging a gate on the incident surface side, and preferably by the following manufacturing method. In the mold used, a gate is provided at a position substantially in the center of the incident surface of the light guide plate to be manufactured and at a position separated from the incident surface by a predetermined dimension, in the same direction as or parallel to the exit surface of the light guide plate. An additional cavity is provided so that the material injected from the gate flows symmetrically in the longitudinal direction of the incident surface.

Therefore, the material injected from the gate travels 90 degrees in a direction and spreads in the auxiliary cavity, and the cavity portion forming the thick portion near the incident surface of the light guide plate is wider than the gate area. Inflow from the area with a substantially uniform pressure. Then, the material is filled in a parallel flow from the thick portion to the thin portion at the tip. Therefore, in each region of the cavity, a substantially equal regular flow and a substantially uniform pressure can be obtained, incomplete filling and weld lines can be prevented, and the transferability of the phase surface shape formed on the reflecting surface can be prevented. No defects will occur.

After the molding, the light guide plate is manufactured by cutting and removing the unnecessary portion molded by the auxiliary cavity.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention are shown in FIGS.
Will be explained. 1 is a plan view of a semifinished state of a light guide plate, that is, a state in which a material of a runner part is removed after molding, that is, a plan view of a molding intermediate body, FIG. 2 is a right side view of FIG. 1, and FIG. It is a right side view of the light guide plate which shows the completed product state which cut off. The same parts as those shown in FIGS. 6 and 7 are designated by the same reference numerals.

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. 6 and 7.

Although the reflecting surface 3 is shown as a flat surface in FIGS. 2 and 3, it is actually formed into a fine uneven shape, and the light source light incident from the incident surface is reflected in multiple directions, and the final surface is reflected. Specifically, the light is emitted from the emission surface 2 as uniform light. Since various ideas and proposals have been made for the uneven shape, detailed description is omitted here. Further, 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 so as to face one surface of the projecting portion 7, that is, the same surface as the emitting surface 2. Therefore, after the material supplied from the runner R is injected from the gate G into the cavity, the course of the material can be bent by about 90 degrees.

As described above, the light guide plate in this embodiment is ultrathin, but its dimensions will be described here. In FIG. 1, the lengths of the incident surface 1 and the lower surface 4 are each 180
mm, the side surfaces 5 and 6 each have a length of 143 mm, and in FIG. 3, the thick portion has a thickness of 3.5 mm and the thin portion has a thickness of 1.5 mm.
Is. In addition, the distance from the center of the gate mark 9 to the incident surface 1 is 18
mm.

Next, a method of manufacturing such a light guide plate by injection molding will be described. In describing the manufacturing method, it is essential to show the mold structure, but in the sense of omitting complicated drawings, a semi-finished product of the light guide plate shown in FIGS. 1 and 2, that is, a molding intermediate. Will be described as a mold cavity. Therefore, the cavity forming the projecting portion 7 will be referred to as an incidental cavity from the viewpoint that the projecting portion 7 is cut off 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. Since the incidental cavity has a spread in the traveling direction as shown in FIG. 1, it 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 laterally and has a fan shape, but as a whole flows from the thick portion on the incident surface side toward the thin portion on the lower surface side. Although the flow directions are not strictly parallel, they flow in a much more parallel and uniform pressure as compared with the conventional example described in FIG.

In this way, although the light guide plate is ultra-thin in the present embodiment, the material in each cavity is controlled by the usual pressure control and the usual temperature control using the usual molding machine. It flowed regularly through the area and was completely filled in every corner. In addition, the transfer of the uneven shape formed on the reflecting surface was good, no weld line was generated, and there was no problem in terms of warpage that easily occurs because of the ultrathin shape. In this embodiment, the inflow portion from the incidental cavity to the thick wall portion occupies about 1/7 of the length of the incident surface 1 as shown in FIG. In order to further improve the above, the ratio may be increased and the incidental cavity may be formed as shown by the chain double-dashed 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 molding intermediate is molded in this manner, the overhang 7 is cut. There is no problem in this cutting if a diamond cutter or the like is used, but in the present example, the cutting was carried out with a usual acrylic cutting cutter having a rotary blade.

In the above embodiment, the gate G is arranged so as to face the extension surface of the emission surface 2 as shown in FIG. 2, which is the size of the gate mark 9 shown in FIG. As can be seen from the 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 its thickness, and the material spreads from the incidental cavity to the thick wall portion. This is because there is an effect that the pressure can be averaged to some extent as it flows. However, the present invention is not limited to such an arrangement and the gate G
May be arranged so as to face downward in the figure.

The thickness of the overhanging portion 7 does not have to be the same as the thickness of the thick portion of the light guide plate. Further, the gate position is ideally located at the center of the light guide plate in the left-right direction as shown in FIG. 1, but even if the gate position is moved to the left or right, the uniformity of the emitted light is not significantly affected. Absent.

Further, in the present invention, as shown in FIG. 1, the side surfaces 5 and 6 may be provided with overhang portions 5a and 6a having an appropriate thickness. The protrusions 5a and 6a are normally used for positioning the light guide plate when incorporated in a surface light source device, but in the light guide plate according to the conventional manufacturing method shown in FIG. Since the filling was difficult, the shape transfer was not performed as desired when the overhanging portions 5a and 6a were provided in the vicinity of the overhanging portions 5a and 6a, which caused a uniform distribution of the emitted light in the thin portion. could not. Considering the uniformity of the brightness distribution on the exit surface 2,
It is desirable that the projecting portions 5a and 6a be provided at positions apart from the incident surface 1, at least on the lower surface 4 side from the middle between the incident surface 1 and the lower surface 4, that is, near the thin portion.

When a mold having a structure in which the molten material injected from the gate flows toward the incident surface 1 side or the lower surface 4 side as in the present invention, a lower surface is formed between the incident surface 1 and the lower surface 4. When the protruding portions 5a and 6a are provided on the fourth side, the shape transferability of the protruding portions 5a and 6a is good from the flow of the molten material, and the protruding portions 5a and 6a having excellent shape accuracy can be easily formed. You can When the shape accuracy of the overhanging 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 molten material injected from the gate flows from the incident surface 1 toward the lower surface 4 in the structure of the mold. It is desirable that the structure is such that the projecting portions 5a and 6a are provided on the lower surface 4 side with respect to the middle of the incident surface 1 and the lower surface 4. Further, in FIG. 1, the bulged portions 5a and 6a are provided on the side surfaces 5 and 6, but similar bulged portions may be provided on the emitting surface 2, the reflecting surface 3 and the lower surface 4 in some cases.

Further, the shape of the light guide plate of the present invention is not limited to that shown in the embodiments, and the light guide plate having the shape described in the above-mentioned publicly known publication is also shown in FIGS. 4, 5 and 8. It goes without saying that it can be applied to a light guide plate having a different shape. In particular, FIG.
In the case of the light guide plate having the shape shown in Fig. 2, two incident surfaces are formed on the upper and lower sides, but the molten metal flows through the mold structure from one incident surface side to the other incident surface side. Then,
The material flow is almost the same as in the embodiment of FIG. 1 until it reaches the central position in the material flow direction, that is, the thin portion, and is parallel to the fan-shaped flow having a certain spread. The flow becomes closer to the flow, but after passing through the thin part, the wall thickness gradually increases and it becomes fan-shaped again. However, the degree thereof is extremely small, and substantially, as in the case of the embodiment of FIG. 1, the particles are completely filled in parallel flow.

[0035]

As described above, according to the present invention, even with an ultra-thin light guide plate, there is no filling in the mold cavity or transfer defects of various irregularities, and there is no wald line or warp. It is possible to obtain a light guide plate for a surface light source device with good moldability, in which the occurrence of light does not occur and the uniformity of emitted light is not impaired.

[Brief description of drawings]

FIG. 1 is a plan view showing a semi-finished product of a light guide plate according to an embodiment of the present invention.

FIG. 2 is a right side view of FIG.

FIG. 3 is a right side view showing a completed product state of the light guide plate shown in FIG.

FIG. 4 is a side view of a light guide plate having a shape different from that of the embodiment.

FIG. 5 is a side view of a light guide plate having a different shape from the light guide plate shown in the embodiment and FIG.

FIG. 6 is a plan view for explaining a conventional example in the case of molding an ultrathin light guide plate similar to that of the example.

FIG. 7 is a right side view of FIG.

FIG. 8 is a side view of an ultra-thin light guide plate having different shapes shown in connection with the description of FIG.

[Explanation of symbols]

1 incident surface 2 Exit surface 3 reflective surface 4 Lower surface 5, 6 side 7 Overhanging part 9 Gate mark G Gate R runner

Claims (7)

[Claims] 1. A light guide plate, which has an incident surface on which a light source is arranged in close proximity and an emission surface from which incident light is emitted from the incident surface, and which is used together with the light source in a surface light source device. Then, using a molding die in which a gate is arranged on the incident surface side of the cavity forming the light guide plate, a molten material is injected into the cavity from a position corresponding to the incident surface, and injection molding is performed. A characteristic light guide plate for a surface light source device. 2. The light guide plate for a surface light source device according to claim 1, wherein a molten material is injected into the cavity from a position corresponding to a substantially central portion of the incident surface in the longitudinal direction and injection molding is performed. 3. A gate is provided at a position distant from the entrance surface by a predetermined dimension, and the molten material injected from the gate flows toward the entrance surface substantially symmetrically in the longitudinal direction of the entrance surface. The injection molding is performed using a molding die provided with an objective cavity, and then an unnecessary portion formed by the incidental cavity is removed.
The light guide plate for the surface light source device described. 4. The light guide plate for a surface light source device according to claim 3, wherein the gate is provided toward an extension surface of the emission surface or a surface parallel to the emission surface. 5. A light guide plate having an incident surface on which a light source is disposed in close proximity and an exit surface from which incident light is emitted from the incident surface, and which is used together with the light source in a surface light source device. The intermediate body is provided with a gate at a position separated from the incident surface by a predetermined dimension, and the molten material injected from the gate flows toward the incident surface substantially symmetrically in the longitudinal direction of the incident surface. A surface light source device characterized in that, after injection molding is performed using a molding die provided with an accessory cavity, the unnecessary portion formed by the accessory cavity is taken out from the molding die without being removed. Intermediate for light guide plates for automobiles. 6. A surface light source device comprising the light guide plate for a surface light source device according to claim 1, 2, 3, or 4. 7. A liquid crystal display device, which illuminates a liquid crystal display panel with the surface light source device according to claim 6.