JP2009090539A - Multi-cavity injection mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of gas marks in molding thin light guiding plate. <P>SOLUTION: In the injection mold 1, each of cavities 5 is formed between a fixed side cavity 2 and a movable side cavity 3. A resin flowing path in communication from four gates 8 to the side face of each of cavities 5 from a sprue section 6 through a runner section 7 is formed. An overflow section 9 is formed in the side face center of the opposite gate side of the cavities 5. The connecting portion of the side faces of the cavities 5 and the overflow section 9 and the gates 8 are rounded. A gas vent A 10 is formed in the terminal end face of the overflow section 9 and the gas vent A 10 is formed parallel to the long side of the cavities 5 and is in communication with the gas vent C 12 in communication with the outside of the mold. The gas vents B 11 are formed in both sides of the overflow section 9 sandwiching the same in the side face of the opposite side of the cavities 6 and are in communication with the gas vent C 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plastic injection mold, and more particularly to a multi-cavity injection mold for injection molding a thin light guide plate used as a backlight of a liquid crystal display.

  2. Description of the Related Art Conventionally, an edge-type backlight device in which a light source is arranged at an edge portion of a light guide plate is generally used 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, or the like. Such an edge type backlight device is a system in which a light source such as a cold cathode tube or an LED is disposed on an edge portion of a light guide plate made of an injection molded product such as a transparent acrylic resin plate. This is useful because the device can be realized. However, the trace of the gate always remains on the light guide plate which is an injection molded product, which causes luminance unevenness and becomes an obstacle to obtaining a uniform display screen. For this reason, various attempts have been made to avoid the adverse effects of gate traces. (For example, refer to Patent Document 1).

  FIG. 5 is a plan view showing a configuration of a main part of a conventional molding die for a thin light guide plate and showing a movable cavity below a parting line (hereinafter abbreviated as PL) 54. FIG. 6 is a cross-sectional view showing the XX cross section of FIG. 5 and 6, the injection mold 51 is a mold for taking four rectangular thin light guide plates. A cavity 55 is formed on the movable cavity block 53 of the injection mold 51 with a PL 54 interposed between the fixed cavity block 52 and the movable cavity block 53. A resin flow path is formed that branches in two directions from the sprue portion 56 through the runner portion 57, branches left and right from both ends of the runner portion 57, and communicates with each cavity 55 through four gates 58.

  Since the gate 58 is not allowed to weld due to the properties of the thin light guide plate, one gate 58 is provided on each long side. On the long side opposite to the gate 58, there is provided a gas vent A60 which is a thin groove for facilitating removal of gas generated from the resin together with the air in the cavity 55 (hereinafter, this gas is simply referred to as air or gas). The gas vent A60 further leads to a gas vent B61 which is a thin groove provided parallel to the long side of the cavity 55 and leading to the outside of the mold. Although there is no restriction | limiting in the depth of gas vent B61, the depth of gas vent A60 is shallower than the depth of gas vent B61.

  The molten resin injected from the nozzle 71 of the molding machine enters the gates 58 on both sides from the runner portion 57 through the sprue portion 56 as shown by arrows in FIG. Subsequently, as shown by an arrow in FIG. 5, the molten resin flows into the cavity 55 through the gate 58 and is filled in the cavity 55. During this time, the air in the cavity 55 is pushed by the resin as indicated by the arrow, and is pushed out of the mold from the gas vent A60 through the gas vent B61.

In molds for injection molding of thin molded products, a gas vent, which is a groove formed on the parting surface of the cavity, is generally provided in order to discharge gas out of the mold. Because of its deep depth, it is easy to be crushed. Once crushed, gas remains in the mold and leads to defective molding. Therefore, an injection mold for improving gas release performance has been developed (for example, see Patent Document 2).
JP 2003-53798 A Patent application 2006-287203

  However, in molding the thin light guide plate, in order to flow the resin through the thin space of the cavity 55, it is necessary to increase the injection speed of the molding or use a resin with very good fluidity. As the injection speed increases, the air in the cavity 55 is less likely to go out of the cavity 55 and remains as a gas mark on the product, which deteriorates the performance of the light guide plate. Further, if the depth of the gas vent A60 is increased in order to improve gas escape, the resin flows out to the resin together with the gas in the cavity 55 to generate burrs, so that the process of burr processing becomes necessary.

  The present invention has been made to solve such a conventional problem, and an object thereof is to provide a multi-piece injection mold that can eliminate the generation of gas marks in the formation of a thin light guide plate. That is.

  The means of the present invention for solving the above-mentioned problem is a multi-cavity injection molding in which a cavity is formed with a parting line between a fixed side cavity and a movable side cavity, and a thin rectangular light guide plate is formed. In the mold, a gate is connected to the side surface on the long side of the cavity, and a resin overflow portion in which a part of the side surface bulges is formed on the side surface on the opposite gate side. The first gas vent is connected, and the second gas vent is connected to the opposite side of the gate on both sides of the overflow portion, and the first and second gas vents are outside the mold. Connected to a third gas vent leading to

  The connecting portion between the cavity and the gate, and the connecting portion between the cavity and the overflow portion are each provided with an R.

  Further, the dimension in the width direction of the overflow portion is 7% to 70% of the total length in the longitudinal direction of the cavity.

  Further, the depth of the third gas vent is formed deeper than the depths of the first gas vent and the second gas vent.

  According to the present invention, in a multi-cavity injection mold in which a cavity is formed with a parting line between a fixed side cavity and a movable side cavity and a thin light guide plate having a flat rectangular shape is formed, A gate is connected to the side surface on the long side, and an overflow portion of the resin in which a part of the side surface bulges is formed on the side surface on the opposite gate side, and a first gas vent is connected to the end side surface of this overflow portion A second gas vent is connected to the opposite side surfaces of the gate on both sides of the overflow portion, and the first and second gas vents are connected to the outside of the mold. Since it is connected to the gas vent, the overflow part provided on the side opposite to the gate of the cavity becomes the final filling part of the resin, and the pushed-out air gathers here. The air in the cavity is released from the first gas vent and the second gas vent to the outside of the mold through the third gas vent. In this way, the outgassing is improved and the generation of gas marks is suppressed.

  In addition, since the connection portion between the cavity and the gate and the connection portion between the cavity and the overflow portion are respectively R-attached, the gate resin and the overflow resin are slightly separated from the side surface of the product. By cutting at the position, bright lines are not generated by the reflected light inside the light guide plate, and the performance of the light guide plate is not impaired.

  Moreover, since the dimension in the width direction of the overflow portion is 7% or more and 70% or less of the total length in the longitudinal direction of the cavity, the air in the cavity can easily escape.

  Further, since the depth of the third gas vent is formed deeper than the depth of the first gas vent and the second gas vent, the third gas vent smoothly flows from the first and second gas vents. To flow into. The depth is in the relationship of third gas vent> first gas vent> second gas vent. The depth of the second gas vent is the shallowest because it is in contact with the cavity, so that the burr must be suppressed most. Because of the flow resistance, the depth works more effectively than the cross-sectional area.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing a configuration of a main part of an injection mold according to an embodiment of the present invention and showing a movable cavity below a PL. FIG. 2 is a cross-sectional view showing the XX cross section of FIG. 3 is a cross-sectional view showing the YY cross section of FIG. FIG. 4 is an enlarged plan view showing a part of a molded product by a mold according to an embodiment of the present invention.

  First, the configuration of this mold will be described. In FIG. 1, an injection mold 1 is for taking four thin light guide plates having a rectangular planar shape, and each cavity 5 is formed with a PL 4 interposed between a fixed cavity 2 and a movable cavity 3. Has been. The light guide plate size to which the present invention is applied is 3.5 inches or less, and the thickness is 0.1 mm to 0.35 mm. A resin flow path that branches in two directions from the sprue part 6 through the runner part 7, branches left and right from both end parts of the runner part 7, and passes through four gates 8 to the long side of each cavity 5. Is formed. A resin overflow portion 9 is formed on the opposite side of the cavity 5 from the side of the cavity 5, which is a bulging portion. The arrangement positions of the gate 8 and the overflow portion 9 in the cavity 5 are on the positions opposite to each other. The dimension in the width direction of the overflow part 9 is preferably 7% or more and 70% or less of the entire length of the cavity 5 in the longitudinal direction. If it is less than 7%, the effect becomes too small. If it exceeds 70%, the cutting distance becomes long, so that higher accuracy is required for cutting, and more material is wasted. The optimum value is around 50%. The connection portion between the base of the overflow portion 9 and the side surface of the cavity 5 and the connection portion between the gate 8 and the side surface on the long side are each provided with an R as shown by an arrow in FIG.

  A gas vent A10, which is a first gas vent, which is a thin groove for venting gas, is formed on the end face of the overflow portion 9, and the gas vent A10 is formed in parallel to the long side of the cavity 5 and leads out of the mold. To a gas vent C12 which is a third gas vent which is a thin groove. The depth of the gas vent A10 is such an amount that burrs appear on the end face of the overflow portion 9. FIG. 3 shows a cross section of a gas vent B11 that is a second gas vent that is a thin groove that allows air in the cavity 5 to pass to the gas vent C12 on both sides of the overflow portion 9 on both sides of the cavity 5 on the side opposite to the gate. It is formed as follows. The depth of the gas vent C12 is deeper than the depths of the gas vent A10 and the gas vent B11.

  Next, the operation of this injection mold will be described. As shown by the arrows in FIG. 1, the molten resin is injected from the sprue part 6 through the runner part 7 through the gate 8 into the cavity 5 and then cooled and solidified. At this time, the molten resin is filled in the overflow portion 9 which is the final filling portion, and the air in the cavity 5 is discharged from the gas vent A10 and the gas vent C12 to the outside of the mold through the gas vent B11.

  As shown in FIG. 4, the molded product taken out from the mold after the molding is first cut at the cut line 23 at a position slightly away from the side surface of the cavity, and then the overflow 24 is generated. A light guide plate 26 that is a product is formed by cutting along a cut line 25 that is located slightly away from the side surface of the light guide plate 26.

  Next, effects of the embodiment of the present invention will be described. In the injection mold 1, the molten resin is filled into the cavity 5 and filled into the overflow portion 9 of the final filling portion. During this time, the air in the cavity 5 is pushed out of the mold through the gas vent B11 and the gas vent A10 and further through the gas vent C12. This improves gas escape and suppresses the generation of gas marks. In addition, in order to improve gas escape, the depth of the gas vent A10 is increased, and the generation of burrs at portions other than the overflow portion 9 can be suppressed. Even if a burr 27 is generated at the end of the overflow portion 9, there is no problem because it is cut off together with the overflow 24. Further, since the gate 8 and the overflow portion 9 and the cavity 5 are connected to each other at the connection portion R, if the gate 8 and the overflow portion 9 are cut at the cut lines 23 and 25, the light guide plate 26 is connected to the connection portion. Since the bright line due to the internal reflected light does not remain, the performance of the light guide plate is not deteriorated.

It is a principal part top view which shows the bottom from the parting line of the injection mold which is embodiment of this invention. It is sectional drawing which shows the XX cross section of FIG. It is sectional drawing which shows the YY cross section of FIG. It is an enlarged plan view which shows the part of the molded article by the metal mold | die which is embodiment of this invention. It is a principal part top view which shows the bottom from the parting line of the conventional injection molding die. It is principal part sectional drawing which shows the XX cross section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection mold 2 Fixed side cavity 3 Movable side cavity 4 Parting line 5 Cavity 8 Gate 9 Overflow part 10 Gas vent A
11 Gas Vent B
12 Gas vent C

Claims (4)

  In a multi-cavity injection mold in which a cavity is formed with a parting line between a stationary cavity and a movable cavity, and a thin light guide plate with a flat rectangular shape is formed, on the side of the long side of the cavity A gate is connected, and an overflow portion of a resin in which a part of the side surface bulges is formed on a side surface on the side opposite to the gate, and a first gas vent is connected to a terminal side surface of the overflow portion. A second gas vent is connected to the opposite side faces of the gate on both sides of the part, and the first and second gas vents are connected to a third gas vent that communicates outside the mold. This is a multi-cavity injection mold.   2. The multi-cavity injection mold according to claim 1, wherein R is attached to a connection portion between the cavity and the gate and a connection portion between the cavity and the overflow portion.   3. The multi-cavity injection mold according to claim 1, wherein a dimension of the overflow portion in a width direction is 7% or more and 70% or less of a total length in a longitudinal direction of the cavity.   The multi-cavity injection molding according to any one of claims 1 to 3, wherein the depth of the third gas vent is deeper than the depths of the first gas vent and the second gas vent. Mold.

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