JP2008107376A - Thin type light guide plate and its molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten flow length of resin, to stabilize molding and to make multiple quantity molding easy, in molding of a thin light guide plate. <P>SOLUTION: In the edge light type thin light guide plate comprising a transparent resin member and having a light incident surface 3 at the side surface of the light guide plate 1 whose planar surface has a nearly rectangular shape and its molding method, the sectional shape of the light guide plate has a wedge shape inclined from a thick part side to a thin part side in the vicinity of the light incident surface and a flat plate shape whose thickness is uniform from the end of the wedge shape to the thin part on the side opposite to the light incident surface. The light incident surface 3 of the light guide plate 1 is provided to the side of a short side of the rectangular shape and the gate 9 of an injection molding product is disposed by being offset from the nearly central part of a side of a long side of the rectangular shape to the light incident surface 3 side to shorten the flow length of resin. An offset quantity C is so set as to be 0% of the total length of the product<the offset quantity<30% of the total length of the product. By the position of the gate 9, a molding material can be reduced, a molding pressure loss can be reduced and multiple quantity molding is made possible. Thereby, reduction of a molding cost and stabilization of molding can be attained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an edge light type thin light guide plate manufactured by injection molding suitable for use as a backlight in a liquid crystal display and a molding method thereof.

Conventionally, as a backlight device for a liquid crystal display device on a display screen of a personal computer, a flat-screen TV, a car navigation system, etc., an edge light type backlight device in which a light source is arranged at an edge portion of a light guide plate, and a light source with a light diffusion plate In general, a direct-type backlight device disposed directly below the display screen is used. The above-mentioned edge light type backlight device is a method in which a light source such as a cold cathode tube or an LED is arranged on the light incident surface of the edge portion of a light guide plate made of an injection molded product such as a transparent acrylic resin plate. A backlight device can be realized. However, the gate mark always remains in the injection molded product, causing unevenness in brightness and hindering obtaining a uniform display screen. For this reason, various attempts have been made to avoid the adverse effects of the gate trace. Even when viewed from the gate position, the light incident surface, the surface facing the light incident surface (anti-light incident surface), the side surface adjacent to the light incident surface, etc. An injection molding method for providing a gate has been proposed. For example, a method of forming a light guide plate that uses an ordinary molding machine and is ultra-thin and does not generate weld lines or warpage and obtains uniform emitted light has been proposed. (For example, refer to Patent Document 1) Further, the cross-sectional shape of the light guide plate manufactured by the above molding method is a wedge shape inclined from the light incident surface to the anti-light incident surface or a flat plate shape having a uniform thickness. is there. (For example, see Patent Document 2)
JP 2001-96583 (pages 4-5, FIG. 1, FIG. 2, FIG. 3) Japanese Patent Laying-Open No. 2005-153488 (Page 4, FIGS. 1 and 2)

  The thin light guide plate forming method disclosed in Patent Document 1 is shown in FIGS. 4 (a) and 4 (b). FIG. 4A is a plan view showing a semi-finished product state of the light guide plate, and FIG. 4B is a side view of the lower side of FIG. In FIG. 4, the light guide plate is made of a transparent resin member, the plane has a substantially rectangular shape, and has a light incident surface 11 on the long side of the rectangle for incident light from the light source in the direction of arrow A. The exit surface 13 is a reflective surface provided with a fine prism pattern and uneven pattern. The light incident from the light incident surface 11 is reflected in many directions and finally emitted from the exit surface 12 as uniform light. Reference numeral 14 denotes a light incident surface. As shown in FIG. 4B, the thickness of the thick portion on the light incident surface 11 side is, for example, about t1 = 3.5 mm, and the thickness of the thin portion on the light incident surface 14 side. For example, the thickness is set to about t2 = 1.5 mm, and the cross-sectional shape viewed from the rectangular short side is a thin light guide plate having a substantially wedge shape. A gate mark 16 is formed on the extended portion 15 provided on the light incident surface 11 on the rectangular long side of the light guide plate. The gate 17 in the mold is disposed on one surface of the overhang portion 15. Therefore, after the material supplied from the runner 18 is filled into the cavity from the gate 17, the path is bent by approximately 90 degrees. In FIG. 4 (b), the acrylic resin-based molten material filled in the gate 17 through the runner 18 spreads in the resin flow direction B in the incidental cavity where the overhanging portion 15 is cut off after molding, and is substantially uniform. It flows into the cavity near the light incident surface 11 by pressure and flows from the thick portion t1 on the light incident surface 11 side toward the thin portion t2 on the anti-light incident surface 14 side as a whole, and is completely filled up to every corner. . In this way, after the semi-finished product 19 is formed, the overhanging portion 15 is cut using a diamond cutter or a normal acrylic cutting cutter having a rotary blade.

  In the above-described method for forming a thin light guide plate, a cost is increased because a projecting portion 15 is provided on the light incident surface 11 on the long side of the rectangle and an unnecessary projecting portion 15 is cut after the molding. Further, if the cut surface is rough, the brightness of the emitted light is uneven, which is an obstacle to obtaining a uniform display screen. There are problems such as.

  As shown in FIG. 5, the light guide plate 20 disclosed in Patent Document 2 is a molded product made of a transparent thermoplastic resin. The light guide plate shown in FIG. (For example, t1 = 3.5 mm), the light incident surface 21 is formed, and the anti-light incident surface 22 is thin (for example, t2 = 1.5 mm) and has a substantially wedge shape. The light guide plate 20A shown in FIG. 5B is a flat plate having a uniform overall thickness (for example, t1 = 3.5 mm). A light source (for example, LED) 25 is disposed close to the light incident surface 21 of the light guide plate 20 (20A) and is surrounded by a reflector. The light emitted from the light source 25 enters from the light incident surface 21, repeats total reflection in the light guide plate 20 (20 </ b> A), and emits uniform light from the light emitting surface 23 to the liquid crystal display element. The light reflecting surface 24 is provided with a fine prism pattern and uneven pattern in order to reflect light.

  In the light guide plate described above, the light incident surface on which the light source (for example, LED) is arranged cannot be made thinner than the thickness of the light source. Therefore, the wedge-shaped light guide plate shown in FIG. 5A and the flat light guide plate shown in FIG. 5B are difficult to obtain a thin light guide plate in consideration of the thickness of the LED. Therefore, a thin backlight cannot be achieved.

  FIG. 6 shows a conventional method for forming a thin thin light guide plate that does not require a gate cutting step. Reference numeral 20 denotes a light guide plate, and a plane made of a transparent resin member has a substantially rectangular shape. The cross-sectional shape seen from the long side has a substantially wedge shape, with the surface 21 side being thick and the light incident surface 22 side being thin. It has a light incident surface 21 through which light from a light source arranged on the rectangular short side is incident in the direction of arrow A. Reference numeral 23 denotes an exit surface, and 24 denotes a reflective surface having a fine prism pattern and an uneven pattern. The light incident from the light incident surface 21 is reflected in many directions, and finally emitted from the exit surface 23 as uniform light. To do. As shown in FIG. 6 (b), the thin light guide plate is molded by the molten resin injected from the injection molding machine passing through the sprue 25 and runner 26, passing through the gate 27, and entering the mold cavity 28. Filled. Arrow B indicates the resin flow direction. The gate 27 is arranged on the thin-walled thin-walled portion side of the thin light guide plate, that is, on the reflection light incident surface 22 side.

  As a problem to be solved, in the above-described thin light guide plate molding method, injection molding of a thin light guide plate having a thickness of 0.35 mm or less increases the flow length of the molten resin, and the pressure loss of the molten resin. And the filling property of the molten resin into the molding cavity is deteriorated, and in particular, the surface state of the light incident surface on the side opposite to the gate is hardly molded into a mirror surface. In addition, it is difficult to accurately transfer a fine prism pattern or uneven pattern for reflecting light onto the light reflecting surface of the light guide plate. Furthermore, when molding is performed at a high pressure and a high speed, the molten resin is brought into close contact with the mold surface, making it difficult to release the mold. Still further, the thin light guide plate is molded at a high pressure and high speed, but it is difficult to obtain a large number of pieces.

  The present invention eliminates the above-mentioned drawbacks. The purpose of the present invention is to reduce the resin flow length in the thin light guide plate and the molding method thereof, and to the mold surface under normal molding conditions such as filling speed and pressure. Accordingly, the present invention provides a thin light guide plate that is excellent in releasability and transferability by relaxing the adhesion of the light, has uniform emission light, is easy to produce in large numbers, and is inexpensive, and a method for forming the same.

  In order to achieve the above object, the thin light guide plate according to the present invention is made of a transparent resin member, has a light incident surface on the side surface of the light guide plate having a substantially rectangular plane, and a light source is arranged on the light incident surface. In the edge light type thin light guide plate to be provided, the light incident surface of the light guide plate is provided on the short rectangular side, and the cross-sectional shape of the light guide plate viewed from the long rectangular side is the thick part side. And a thin plate portion having a uniform thickness from the end of the wedge shape to the thin portion on the side of the light incident surface.

  Further, the thickness of the thick portion on the light incident surface side of the light guide plate is about 0.5 mm or less, the thickness of the thin portion on the anti-light incident surface side is about 0.35 mm or less, and the length of the wedge portion is about 2 mm. It is characterized by.

  The thin light guide plate molding method according to the present invention includes a light incident surface on a side surface of a light guide plate made of a transparent resin member and having a substantially rectangular plane, and a light source is disposed on the light incident surface. In the method of forming a light-type thin light guide plate, the light incident surface of the light guide plate is provided on the short rectangular side, and the cross-sectional shape of the light guide plate viewed from the long rectangular side is the thick portion side. From the edge of the wedge shape to the thin-walled portion on the light-incident surface side, and a flat plate shape with a uniform thickness, offset from the approximate center on the long side of the rectangle to the light-incident surface side In this case, an injection molded product gate is provided.

  The offset amount set on the light incident surface side from the approximate center on the long side of the rectangle is 0% of the total product length <offset amount <30% of the total product length with respect to the total product length. It is.

  In addition, the gate position arranged in the injection molded product shortens the distance from the sprue to the gate of each product, reduces molding pressure loss due to the runner, and molds multiple pieces. is there.

  By making the cross-sectional shape of the thin light guide plate of the present invention “wedge shape” + “flat plate shape”, the thickness of the light incident surface on which the light source is arranged in “wedge shape” is secured, and at the same time, “flat plate shape” is thin. A light guide plate can be realized. Moreover, in order to improve the filling property of the light incident surface, the flow length of the molten resin is shortened and the thickness is 0.35 mm or less by offsetting the position of the gate from the center of the long side to the light incident surface side. In the formation of the thin light guide plate, filling in a short time is possible, and sinking of the thick part is suppressed. Further, the filling pressure can be lowered, the moldability is improved, and a large number of pieces can be obtained, and an inexpensive light guide plate can be obtained. In addition, it is possible to provide a thin light guide plate having excellent optical characteristics and quality stability as a light guide plate for a liquid crystal display device and a method for forming the same, such that the reflected light can be effectively used because the reflection light incident surface side can be a mirror surface. It is.

  A method for forming a thin light guide plate of the present invention will be described with reference to the drawings.

  1 to 3 relate to an embodiment of the present invention, FIG. 1 is an explanatory view of a light guide plate for a liquid crystal display device, FIG. 2 is an explanatory view showing a method of forming the light guide plate, and FIG. It is explanatory drawing in the case of taking.

  1 (a) and 1 (b), the light guide plate 1 is a molded product having a substantially rectangular plane made of, for example, PC, PMMA, or polyolefin resin as a transparent resin material. However, it is a light guide plate having a thickness of 3.5 inches or less and a thickness of 0.35 mm or less.

  As shown in FIG. 1A, a light source 2 such as a cold cathode tube or an LED is arranged close to the rectangular short side of the light guide plate 1, and light incident from the light source 2 in the direction of arrow A is incident. A surface 3 is provided, 4 is an exit surface, and 5 is a reflective surface provided with a fine prism pattern and concavo-convex pattern. The light incident from the light incident surface 3 is reflected in many directions, and finally the exit surface 4. To be emitted as uniform light. Reference numeral 6 denotes a reflection light incident surface. The cross-sectional shape viewed from the long side of the rectangle is a wedge shape that inclines from the thick portion t1 side to the thin portion t2 side in the vicinity of the light incident surface 3, and the thin wall on the side of the light incident surface 6 from the end of the wedge shape. A flat plate shape having a uniform thickness from the portion t2 to “wedge shape” + “flat plate shape”. The thickness of the thick portion on the light incident surface 3 side of the light guide plate 1 is, for example, t1 = approximately 0.5 mm or less, the thickness of the thin portion is, for example, t2 = approximately 0.35 mm or less, and the length of the wedge portion is For example, L = about 2 mm.

  A method for forming the thin light guide plate will be described. As shown in FIG. 2B, the position of the gate 9 is offset from the approximate center on the long side of the rectangle to the light incident surface 3 side. For example, PC, PMMA, polyolefin-based molten resin injected from the injection molding machine passes through the sprue 7, the runner 8, and the gate 9 and proceeds in the resin flow direction indicated by the arrow B. Until completely filled. After the molten resin is cooled and solidified, the mold is opened and the light guide plate 1 is exposed. Since the gate trace is not on the light incident surface 3 and the light incident surface 6 side but on the long rectangular side, the gate end surface can be processed using a hot nipper or a cutting jig having an equivalent function. good. The offset amount C set on the light incident surface side from the approximate center on the long side of the rectangle is a result of various experiments conducted by the applicant. As a result, 0% (center) of the total product length <offset amount C (long) The optimum condition is that the amount of deviation from the center of the side to the center of the gate) <30% of the total product length. An injection molded product having excellent optical characteristics and quality stability for a liquid crystal display device described later can be efficiently produced.

  FIG. 3 shows a layout in the case of taking a large number (for example, four). In FIG. 3, arrow A indicates the light incident direction on the light incident surface 3 side, arrow B indicates the resin flow direction, and C indicates the offset amount. As described above, the acrylic resin-based molten resin injected from the injection molding machine is diverted in two directions from the sprue 7, passes through the runner 8 and the gate 9, and proceeds in the resin flow direction indicated by the arrow B. Every corner of the cavity 10 is completely filled.

  The operation and effect of the thin light guide plate having the above-described configuration and the molding method will be described. First, by making the cross-sectional shape of the light guide plate "wedge shape" + "flat plate shape", the thickness of the light incident surface on which the light source is arranged in "wedge shape" is secured, and at the same time, the thin plate light guide plate in "flat plate shape" Can be realized. Furthermore, the resin flow length is shortened and the filling speed and filling pressure are increased by disposing the gate position offset from the approximate center of the long rectangular side, which is not related to the light incident surface, to the light incident surface. Even if it is not, it is possible to completely fill every corner of the mold cavity in a short time. Further, since the position of the gate is moved closer to the thick part t1, the sink of the thick part t1 is suppressed, and a molded product having an optically high quality can be obtained. Furthermore, since the reflection light incident surface side can be a mirror surface, the reflected light can be effectively used. Furthermore, the fine prism pattern and uneven pattern formed on the reflecting surface can be reliably transferred, and the light incident from the light incident surface can be efficiently reflected in many directions. In addition, as for the size, it is possible to take a large number of thin light guide plates whose diagonal dimensions of the active area are, for example, 3.5 inches or less and the thickness is 0.35 mm or less. Furthermore, the distance from the sprue to each molded product can be shortened, and the molding material can be reduced. At the same time, the loss of molding pressure by the runner can be reduced, leading to a reduction in molding cost and stabilization of molding. It is possible to provide an excellent thin light guide plate and a molding method thereof.

It is explanatory drawing of the thin-shaped light-guide plate concerning the Example of this invention. It is explanatory drawing which shows the shaping | molding method of the thin light-guide plate of FIG. It is explanatory drawing in the case of taking many thin light-guide plates of FIG. It is explanatory drawing which shows the shaping | molding method of the conventional thin light-guide plate. It is sectional drawing of the conventional light-guide plate. It is explanatory drawing which shows the shaping | molding method of the other conventional thin light-guide plate.

Explanation of symbols

1 Light guide plate 2 Light source (LED)
3 Light incident surface 4 Emission surface 5 Reflecting surface 6 Anti-light incident surface 7 Sprue 8 Runner 9 Gate 10 Cavity
A Light incident direction
B Resin flow direction
C Offset amount t1 Thick part t2 Thin part L Length of wedge part

Claims (5)

  An edge light type thin light guide plate comprising a transparent resin member and having a light incident surface on a side surface of a light guide plate having a substantially rectangular shape on a flat surface, and a light source disposed on the light incident surface. The incident surface is provided on the rectangular short side, and the cross-sectional shape of the light guide plate viewed from the rectangular long side is a wedge shape in which the vicinity of the light incident surface is inclined from the thick portion side to the thin portion side, and the end portion of the wedge shape A thin light guide plate having a flat plate shape with a uniform thickness from the thin portion on the side opposite to the light incident surface.   The thickness of the thick portion on the light incident surface side of the light guide plate is approximately 0.5 mm or less, the thickness of the thin portion on the light incident surface side is approximately 0.35 mm or less, and the length of the wedge portion is approximately 2 mm. The thin light guide plate according to claim 1.   In the method for forming an edge light type thin light guide plate, which is made of a transparent resin member and has a light incident surface on a side surface of a light guide plate having a substantially rectangular shape on a flat surface, and a light source is disposed on the light incident surface. The light incident surface of the light plate is provided on the rectangular short side, and the cross-sectional shape of the light guide plate viewed from the rectangular long side is a wedge shape in which the vicinity of the light incident surface is inclined from the thick portion side to the thin portion side, and the wedge shape A flat plate shape with a uniform thickness is formed from the end of the light-incident surface to the thin-walled portion on the side opposite to the light incident surface, and an injection molded product gate is disposed offset from the approximate center on the long side of the rectangle toward the light incident surface. A method for forming a thin light guide plate. The offset amount set on the light incident surface side from the approximate center on the long side of the rectangle is the total length of the product,
0% of total product length <offset amount <30% of total product length
The method for forming a thin light guide plate according to claim 3. 4. The gate position arranged in the injection molded product shortens the distance from the sprue to the gate of each molded product, reduces molding pressure loss due to the runner, and molds multiple pieces. Or the shaping | molding method of the thin-shaped light-guide plate of 4.

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