JP2010167594A - Molding method and molding system for thin plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method and a molding system for a thin plate which mold a thin plate in an allowable range while pursuing the productivity by pressing an injection molded thin plate. <P>SOLUTION: In the molding system 11 for the thin plate, the thin plate L molded by an injection machine 12 is gate-cut by a gate-cut device 13 during or after injection molding, the plurality of gate cut thin plates L are piled by a piling device 15 directly or through other members P and are held in a pressed state by a pressing device 16 for a fixed time to mold the thin plate L having warpage in the allowable range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming an injection-molded thin plate and a system for forming the thin plate.

  In general, thin plates such as light guide plates that have been injection-molded (including injection compression molding and injection presses in one field thereof) have residual internal stress when molded by injection of molten resin into the cavity, differential shrinkage due to temperature distribution, Warpage occurs after molding due to physical force applied at the time of take-out and moisture absorption after take-out. However, many of the conventional light guide plates are relatively thick with a thickness of 2 to 10 mm, and warpage is difficult to occur. In addition, as described in Patent Document 1, warpage has been prevented by providing a groove for preventing warpage in the light guide plate. However, as the light guide plate becomes thinner, it becomes difficult to make the light guide plate itself in a shape suitable for warpage prevention, and the problem of warpage has been further highlighted.

  Moreover, what is described in patent document 2 and patent document 3 is known as what prevents the curvature of a thin plate although it is not a light-guide plate. Patent Document 2 corrects distortion by applying a load in the opposite direction to the molding distortion of a thin plate molded by an injection mold using a distortion correction mold. However, a large molding distortion as shown in Patent Document 2 is a problem to be solved in the injection molding process, and usually a large warp does not occur in the thin plate immediately after being taken out from the injection molding machine. And the curvature which generate | occur | produces after shaping | molding does not necessarily correspond with the shaping | molding distortion immediately after injection molding. Therefore, in some cases, applying a load in the direction of correcting the forming distortion is not effective for obtaining a thin plate having good flatness. In Patent Document 2, since correction is performed for each thin plate, the time required for correcting one thin plate is within the time required for the injection molding process. However, even when a load in the direction opposite to the molding strain direction is applied in a short time as described above, the warp that occurs after molding occurs over a certain period of time, so a thin plate with good flatness can be obtained. Was difficult. Furthermore, since a load is applied to a part of the thin plate, there is a problem that the optically molded product having a fine transfer surface such as a light guide plate is damaged. Furthermore, in the case of an optical molded product made of a transparent resin having a plate thickness of 1.0 mm or less using a resin material that is relatively easy to break, such as acrylic, the thin plate breaks when a strong load is applied to only a part thereof. There was a problem that there was a possibility.

  Moreover, although patent document 3 is not related to injection molding or a light guide plate, it discloses a thin plate supply device that pressurizes a plurality of thin plates and corrects the warp. According to this apparatus, both the warped end surfaces of the substrate are pressed by the pair of thin plate pressing devices, and the warp is corrected by the movement of the storage rack, so that a plurality of sheets can be corrected simultaneously. However, since the entire surface of the substrate is not pressed by the pressing device, the entire substrate cannot have a good flatness, and the same problem as in Patent Document 2 due to a strong load being applied only to the pressed portion. I had it.

WO2006-85526 (0164, FIG. 43) JP 2007-290313 A (Claim 1, FIG. 4) JP-A-5-167292 (0014, FIG. 1)

  In the present invention, in view of the above-described problems, when pressurizing an injection-molded thin plate to make the warpage within an allowable range, the thin plate capable of forming a thin plate within the allowable range while pursuing productivity. It is an object of the present invention to provide a forming method and a thin plate forming system.

  The method for forming a thin plate of the present invention is a method for forming a thin plate in which an injection-molded thin plate is pressed to form a thin plate with a warp within an allowable range, and the gate of the thin plate is cut during or after injection molding, A plurality of gate-cut thin plates are stacked directly or via another member, held for a certain period of time in a state of being pressed by a pressure device, and a thin plate having a warpage within an allowable range is formed.

The thin plate molding system of the present invention is a thin plate molding system that pressurizes an injection-molded thin plate to form a thin plate whose warpage is within an allowable range, and is attached to the post-process of the injection molding machine or the injection molding machine. A gate cutting device that is provided in a molding die and performs gate cutting of a thin plate;
A stacking device for stacking a plurality of gate-cut thin plates directly or via other members;
And a pressurizing device that holds the stacked thin plates in a pressurized state for a predetermined time.

  The thin plate forming method and thin plate forming system according to the present invention includes performing gate cutting of a thin plate during or after injection molding by an injection molding machine, and stacking a plurality of thin plates gate-cut by a stacking device directly or via other members. And by hold | maintaining for a certain period of time in the state pressurized with the pressurization apparatus, the thin board in which a curvature is a tolerance | permissible_range can be shape | molded, pursuing productivity.

FIG. 1 is a schematic plan view of a light guide plate forming system according to the first embodiment. FIG. 2 is a schematic front view of the light guide plate molding system (excluding the injection molding machine) according to the first embodiment. FIG. 3 is a partially enlarged view of the stacking device of the light guide plate forming system according to the first embodiment.

  Stacked multiple sheets of gate-cut thin plates at a higher temperature than the atmosphere taken out from the injection molding machine and placed in the injection molding machine directly or via a cushioning material, and pressurized in the atmosphere where the injection molding machine was placed To form a thin plate having warpage within an allowable range. In particular, it is intended for an optically molded article made of a substantially uniform transparent resin having a thin plate thickness formed from a material that easily warps after molding, such as acrylic molded by injection compression molding including an injection press.

  A light guide plate forming system and a light guide plate forming method of Example 1 will be described with reference to FIGS. 1 to 3. A light guide plate forming system 11 which is a thin plate forming system is composed of an injection molding machine 12 and a gate cut device 13 formed on one side thereof, a transport device 14 for transporting the light guide plate while being placed thereon, a stack of light guide plates and the like. The device 15 includes a pressure device 16 that pressurizes the light guide plate L to be flat or keeps the flat state.

  The injection molding machine 12 is provided with a material drying device and an automatic material supply device (not shown). An injection device 17 and a mold clamping device 18 are disposed on the bed of the injection molding machine 12. One fixed mold 21 of the molding die 20 is disposed on the fixed plate 19 of the mold clamping device 18, and the other movable mold 23 of the molding die 20 is disposed on the movable plate 22. The molding die 20 is temperature-controlled by flowing a cooling medium from a temperature control device (not shown). The injection molding machine 12 and the molding die 20 can be injection compression molded including an injection press. In the cavity 37 of the molding die 20 of Example 1, one light guide plate L having a diagonal dimension of 14 inches and a plate thickness of 0.7 mm (uniform thickness) and having a transfer surface on at least one surface is taken. Note that the number, size, shape, resin material, and the like of the light guide plate, which is an optical molded product made of transparent resin, are not limited.

  On one side of the injection molding machine 12, a gate cut device 13 is provided. The mold clamping device 18 is provided with a take-out device (not shown) for transferring the molded light guide plate L to the gate cut device 13. Further, on one side of the gate cut device 13, a transport device 14 that transports the light-guide plate L that has been gate-cut on the pallet P, and the light guide plate L that is transferred from the gate cut device 13 to the transport device 14 is illustrated. A non-transfer device is provided. Alternatively, the gate cutting device 13 for the light guide plate L may not be provided in the subsequent process of the injection molding machine 12, but a gate cutting device may be provided inside the molding die 20 to perform gate cutting in the mold. In that case, the light guide plate L is directly taken out from the injection molding machine 12 to the conveying device 14 by the take-out device. Further, the conveying device 14 may be placed on the pallet P after the light guide plate L is placed in a vertical direction and placed in a state where both surfaces are exposed to the atmosphere. That way, both sides can be cooled evenly.

  The pallet P shown in FIG. 3 is made of resin, and in the first embodiment, a placement portion P1 on which the entire surface of the two light guide plates L is placed and holding portions P2 on both sides thereof are provided. It is one step higher than the mounting portion P1. The mounting portion P1 has a high flatness on both the front surface and the back surface. The pallet P, which is another member, is not limited to resin, but may be metal, glass, wood, or the like. The conveying device 14 is composed of a belt conveyor, and a pallet supply device 24 for supplying the pallets P one by one onto the belt conveyor is disposed at the start end portion 14a. As shown in FIG. 2, a pallet feeding device 25 that supplies the pallet P and the light guide plate L to the stacking device 15 one by one is provided in the vicinity of the end portion 14 b of the transport device 14. The stacking device 15 is a device that stacks a plurality of pallets P on which the light guide plates L are placed in the vertical direction. In the first embodiment, the pallets P on which about 20 light guide plates L are placed are stacked.

  As shown in FIG. 3, the pallet stacking device 15 is configured such that a holding claw portion 27 is provided on a circulation type chain 26 provided on each side of the conveying device 14 on the end portion 14 b side. The holding part P2 of the pallet P is held. When the chain 26 moves downward and approaches the conveyor 28 toward the pressurizing device 16, the chain 26 moves outward to cancel the holding of the pallet P and the like. The first one of the pallet P and the light guide plate L from which the holding of the stacking device 15 is released is placed on the conveyor 28, and the pallet P and the light guide plate L are stacked one after another. When a predetermined number of pallets P and light guide plates L are stacked, the conveyor 28 is intermittently moved to the pressure device 16. A transfer device such as a multi-axis robot that transfers the light guide plate L from the gate cut device 13 may also serve as a stacking device, and only the light guide plate L and the pallet P or the light guide plate L may be stacked.

  In the first embodiment, the pressurizing device 16 is provided with a flat plate 30 that is moved up and down by an air cylinder 29 and a fixed flat plate 31 below the conveyor 28, and between the flat plates 30 and 31. Of the stacked pallet P and light guide plate L, at least the entire surface of the light guide plate L is pressurized. The flat plate 30 and the flat plate 31, which are pressure plates, do not exclude those having a hole in the portion corresponding to the central portion of the light guide plate L, but it is desirable to cover the entire surface, and at least the four corners can be pressurized. It is desirable that The air cylinder 29 is connected to a high-pressure air supply device via a regulator (not shown) so that the pressure can be controlled. The pressurizing device 16 of Example 1 does not pressurize in a heated atmosphere. The pressurizing device 16 may be of any type as long as it can hold the stacked light guide plates L and the like for a certain period of time in a pressurized state. May be held under pressure from the beginning to the end. The pressurizing drive means of the pressurizing device 16 may be one using a hydraulic cylinder or an electric motor in addition to the air cylinder 29, or may be one that applies a load to the stacked light guide plates L using a heavy object. Further, with respect to the direction of pressurization, the light guide plate L may be stacked and pressed in the horizontal direction in a standing state.

  The stacked light guide plates L and the like are pressurized by a plurality of pressure stages 16a, 16b, and 16c, and then sent to the stack cancellation device 32. The stacking cancellation device 32 inserts a claw portion between the holding portions P2 on both sides of the stacked pallets P, holds all the pallets P, moves up the chain once, moves horizontally, and has no conveyor 28. Then, the chain again moves downward, and the pallets P on which the light guide plates L are placed are placed one by one on the placement position 33a of the return conveyor 33 by the same structure as FIG. The light guide plate L is taken out by the loading / unloading device 34 at the loading / unloading position 33 b in the middle of the return conveyor 33 and transferred to the finishing device 35. The pallet P from which the light guide plate L has been taken out is again conveyed upward from the position 33c near the end of the return conveyor 33 by the pallet supply device 24 and sent to the conveying device 14.

  Next, a method for forming the light guide plate L using the light guide plate forming system 11 of the first embodiment will be described. First, dried acrylic resin (PMMA) pellets are supplied to the injection device 17 of the injection molding machine 12. The acrylic resin used is particularly excellent in optical performance such as fluidity and transmittance of the grade exclusive for the light guide plate, and is particularly suitably used for a large light guide plate L having a diagonal dimension of 8 inches or more. . However, the acrylic resin is easy to absorb moisture, and there is a problem that warping and cracking are likely to occur during or after molding if the orientation becomes non-uniform due to internal stress. As a resin material of the light guide plate L, an olefin resin such as polycarbonate, zeonore or cycloolefin polymer (all including a polymer blend) may be used in addition to an acrylic resin.

  When the acrylic resin is used, the temperature of the heating cylinder 36 of the injection device 17 is more desirably 230 ° C. to 290 ° C. as an example. Further, since the acrylic resin easily absorbs moisture as described above, the moisture may be further removed by sucking the inside of the heating cylinder 36 in a vacuum state. The temperature of the cooling medium sent to the molding die 20 is more desirably about 40 ° C. to 90 ° C. as an example. (In order to improve the fluidity and transferability of the molten resin in the cavity 37, the mold temperature is raised, but the molding cycle time becomes longer and warping due to subsequent shrinkage is likely to occur. The lowering is advantageous in terms of shortening the molding cycle time and warping, but is disadvantageous in terms of the fluidity and transferability of the molten resin in the cavity 37.) A molten resin is injected and filled into the cavity 37 to form a light guide plate L having a diagonal dimension of 14 inches, a plate thickness of 0.7 mm (uniform thickness), and having a transfer surface on at least one surface. The molding cycle time is 30 seconds in Example 1 (more desirably, in the range of 15 seconds to 40 seconds as an example). The position of the movable mold 23 at the start of injection is slightly in front of the completion of mold clamping, and the volume of the cavity 37 is enlarged. When the molten resin is injected and filled into the cavity 37, injection core molding is performed in which the core block of the movable mold 23 moves forward and compresses the molten resin. Note that injection compression molding may be performed in which the cavity 37 is slightly opened after injection and then compressed. In these injection compression molding and injection press molding, which is one of the fields, injection is performed in a state where the gaps of the cavities 37 are widened, the internal stress of the light guide plate L is reduced. Even when the thin light guide plate L having a large internal stress is flat when taken out from the molding die 20, warping occurs over time. In particular, when acrylic is used, the occurrence of warpage becomes prominent or cracked easily if the alignment unevenness is large. In some cases, the light guide plate L molded by the injection molding machine 12 is molded in a slightly warped state and flattened due to a contraction difference due to cooling of the upper surface and the lower surface during the transport by the transport device 14.

  The gate of the light guide plate L taken out from the molding die 20 of the injection molding machine 12 is cut by a laser or the like by the gate cut device 13. The reason for cutting the gate first is that, in the light guide plate L having a plate thickness of 0.1 mm to 1.0 mm or less (0.7 mm in Example 1), the gate or runner has a larger plate thickness and a larger heat capacity. This is because if the gate is not cut, the temperature distribution of the light guide plate L is higher on the gate side than on the opposite side, causing warping. Then, two light guide plates L with the gates cut are placed on the resin pallet P on the transport device 14. Although the number of sheets to be placed is not limited, the reason for placing a plurality of sheets in Example 1 is to increase the pressurization time in the pressurizer 16. The area around the injection molding machine 12 is an atmosphere in the factory (in many cases, an air-conditioned clean room). The light guide plate L of about 50 ° C. to 80 ° C. immediately after being taken out is deprived of heat by the pallet P or atmosphere on the transport device 14 and is lowered to about 30 ° C. to 60 ° C. It is hotter than the atmosphere in which it is placed.

The light guide plate L placed on the pallet P is stacked by the stacking device 15 and sent to the pressurizing device 16. In the pressurizing device 16, a load of about 30 kg (surface pressure 0.025 kg / cm ² ) is applied to the pallet P and the light guide plate L between the flat plates 30 and 31 by the air cylinder 29. The surface pressure is more desirably 0.025 kg / cm ^{2 to 1} kg / cm ² , and the pressure may be further increased, but the effect is not changed. Rather, an optical product such as a light guide plate having a transfer surface may adversely affect the transfer surface when a pressure higher than 1 kg / cm ² is applied. In the case of an acrylic light guide plate or the like, there is a possibility of cracking if the pressure is too high. The surface pressure can be optimally controlled by controlling the high-pressure air supplied to the air cylinder 29 according to the state of the light guide plate L by a regulator. In the first embodiment, pressurization is performed by the pressurization device 16 in an atmosphere where the injection molding machine 12 is placed, and cooling proceeds while the pressurization is performed. Accordingly, the present invention is different from the annealing step performed at a temperature lower by 10 ° C. to 30 ° C. than the heat deformation temperature, and does not lose energy or deteriorate the light guide plate or the like due to extra heat.

  The pressurization time by the pressurizer 16 in Example 1 is 20 minutes for each pressurization stage, and the total time is 3 hours for 3 stages. The pressurization time may be one hour on the pressurization stage, and more desirable time (total time) for achieving good flatness while pursuing productivity is, for example, about 30 minutes to 3 hours. is there. Further, the number of stacked sheets when pressing is 20 in Example 1, but the number of stacked sheets is not limited. However, if the number of stacked sheets is small, it is necessary to greatly increase the number of pressurizing devices 16 in order to secure a desired pressurizing time, which is inefficient. Further, if the number of stacked sheets is too large, a pressure difference due to a temperature difference or a weight is generated between the light guide plate L stacked first and the light guide plate L stacked last, and therefore the number of stacked sheets of about 10 to 100 is more preferable. In addition, the light guide plates L may be stacked so that the gate traces overlap (direction), or the gate traces may be alternately stacked. When the light guide plate L is substantially symmetrical and warps at a certain position, it is preferable to alternately stack the light guide plates L in order to cancel the warpage. Also, when taking two light guide plates with a molding die, mixing light guide plates formed in different cavities and stacking them alternately is rather than stacking parts formed in the same part of the same cavity. It can be expected to cancel the warpage in the same way as when stacking. Also, in the case of a wedge-shaped light guide plate, it is desirable to stack them alternately.

  The light guide plate L that has been pressurized for a predetermined time by the pressurizing device 16 is lowered from the pallet P on the return conveyor 33, sent to the next finishing device 35, and a gate finishing process is performed. However, in the case of a film gate, since the heat capacity of the gate portion is small, the gate cutting and finishing may be performed simultaneously after pressurizing with the pressurizing device 16. Then, the light guide plate that has been finished and has reached the atmospheric temperature in the factory is packed. In Example 1, the standard for warpage of a light guide plate having a diagonal size of 14 inches and a plate thickness of 0.7 mm is based on whether a thin plate such as a shim or the like is flat if a warp of 0.03 mm occurs in each part with respect to the plane. The product is inspected according to whether or not it can be inserted, and if it cannot be inserted, it is judged as a non-defective product (within the allowable range). The pressure-treated light guide plate of the present invention has very good flatness and improved yield. Note that the standard for optical molded products such as light guide plates may allow a certain amount of warping to one side but not to the other at all, but in this case also injection molding and subsequent cooling shrinkage and pressurizing device By adjusting the shape of the pressure plate and the pressing time, a molded product corresponding to the standard can be formed.

  The light guide plate forming system 11 of the first embodiment has been described with respect to a system that circulates the pallet P. However, a system that does not automatically circulate the pallet P using a part or all of the hands may be used. Further, a plurality of light guide plates L may be stacked and pressed through other members other than the pallet P. Examples of other members sandwiched when the light guide plate L is pressed may be a ceramic plate such as paper, cloth, metal plate, resin plate, wood plate, and glass in addition to the pallet. Further, the light guide plate L may be stacked and pressed so as to be in direct contact without using other members. When the light guide plates are directly stacked, the light guide plates L that have been gate-cut by the injection molding machine 12 or the gate cut device 13 may be stacked as they are by the stack device, or depending on the material and type of the light guide plate L, You may make it stack after cooling to about 30 to 70 degreeC above.

  According to the present invention, it is possible to form a warp of an injection-molded thin plate other than the light guide plate within an allowable range. In particular, it is effective for optical molded products made of transparent resins such as light diffusion plates and lenses, acrylic glass, resin window materials for vehicles, and the like. In addition, the thin plate is not necessarily limited to a thin plate having a flat surface. In the case of a thin plate having a curved surface or a thin plate in which a curved surface is allowed, pressurization is performed for a predetermined time so as to be within an allowable range. The thickness of the thin plate is not necessarily limited to a thin plate having a uniform thickness. The material of the thin plate is mainly assumed to be a resin material, but if it is injection-molded, it is another paper, an organic material such as wood, an inorganic material such as ceramic, or a metal material such as magnesium or aluminum. Also good.

11 Light guide plate molding system (thin plate molding system)
DESCRIPTION OF SYMBOLS 12 Injection molding machine 13 Gate cut apparatus 14 Conveyance apparatus 15 Stacking apparatus 16 Pressurization apparatus 20 Molding die 29 Air cylinder (pressure drive means)
30 Flat plate (Pressure plate)
L Light guide plate P Pallet

Claims (5)

A method for forming a thin plate, in which a thin plate that has been warped within an allowable range is formed by pressurizing the injection-molded thin plate,
Perform gate cutting of thin plate during or after injection molding,
Stacking multiple sheets of gate-cut thin plates directly or through other members,
Hold for a certain period of time under pressure with a pressure device,
A method of forming a thin plate, characterized by forming a thin plate having warpage within an allowable range. The thin plate taken out from the injection molding machine and pressed at a higher temperature than the atmosphere in which the injection molding machine is placed is pressed in the atmosphere to form a thin plate with a warpage within the standard. Forming method of thin plate. The thin plate molding method according to claim 1 or 2, wherein the thin plate is an optical molded product made of a transparent resin having a plate thickness of 1.0 mm or less. A thin plate molding system that pressurizes an injection molded thin plate to form a thin plate with a warp within an allowable range,
A gate cut device for performing a gate cut of a thin plate provided in a post mold of an injection molding machine or in a molding die attached to the injection molding machine;
A stacking device for stacking a plurality of gate-cut thin plates directly or via other members;
And a pressurizing device for holding the stacked thin plates under pressure for a certain period of time. The thin plate molding system according to claim 4, wherein the thin plate is an optical molded product made of a transparent resin having a thickness of 1.0 mm or less.

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