JP2008307882A5 - - Google Patents

Description

Light guide plate molding die and molding method

The present invention relates to a molding die and a molding method for a light guide plate, and more particularly to a molding die and a molding method for a light guide plate that have been devised for the shape of the sprue portion and the shaping of the sprue portion.

As a method of forming the light guide plate by injection molding, it is roughly divided into a molding method using a molding die provided with a hot runner as described in Patent Document 1, and as described in Patent Document 2. There is a molding method using a molding die provided with a cold runner (including a sprue). The former mold provided with the hot runner has the advantage that the resin molding loss is small, but has the following disadvantages.
(1) The mold structure is complicated.
(2) It takes time to adjust at the start of molding.
(3) Flow loss during injection is large.
(4) Since the vicinity of the nozzle of the cavity is difficult to cool, the molding cycle time becomes long.
Therefore, it is relatively used for injection molding of a large light guide plate having a long total length of sprues and runners, but is hardly used for a small light guide plate (7 inches or less).

On the other hand, the mold with the latter cold runner has a problem that the resin in the cold runner part consisting of the runner and sprue is a molding loss, but the mold structure is relatively simple and adjustment until the molding starts. Is also widely used because it is easy. What is described in Patent Document 2 is a so-called three-plate system, and a runner can be taken out between the plates 32 and 33. The plate 32 is provided with a cooling pipe dedicated to the spool, and the cooling process time is shortened in order to efficiently cool the spool. However, the method of Patent Document 2 has a complicated mold structure and is only suitable for forming a large-sized light guide plate. In addition, the cooling time cannot be significantly shortened for the following reasons.
(1) Since it is molded by an injection mold that is clamped with a constant volume of the cavity, it is necessary to inject and fill the resin into the cavity substantially equal to the thickness of the light guide plate. Therefore, the molten resin cannot be uniformly filled up to the end of the light guide plate unless the injection speed is increased and the resin is injected and filled into the cavity. In order to allow the molten resin to reach the cavity at a high injection speed, it is necessary to reduce the flow loss of the molten resin as much as possible, and it is necessary to increase the diameter of the spool.
(2) Since the runner is bent, the flow loss of the molten resin is increased, and in order to eliminate this, it is necessary to further increase the diameter of the spool and the runner.
(3) In order to prevent sink marks due to the shrinkage of the molten resin in the cavity, it is necessary to continue to apply pressure from the injection device, and as a result, the spool portion is molded without shrinkage at a high pressure. Is difficult to release.
Therefore, in Patent Document 2, even if a cooling pipe dedicated to the spool is provided, it is necessary to increase the diameter of the spool because of the reasons (1) and (2). In addition, for the reason of (3) above, it is necessary to cool the spool to a further lower temperature in order to prevent the spool from being cut and remaining in the inner hole of the sprue bush when the spool is pulled out. There was a problem.

Patent Document 3 discloses an example in which an injection speed of 500 mm / sec or more is required when a light guide plate having a thickness of 0.65 mm and a diagonal size of 10.6 inches is formed. And in patent document 3, the weight of a molded product is 29g with respect to 65g of 1 shot weight, and the weight ratio of a molded product is 44.6%. Referring to FIG. 1, it is understood that Patent Document 3 is a direct gate type without a runner, and the weight ratio of the sprue is 50% or more. In other words, it is necessary to increase the cross-sectional area of the sprue in order to ensure the injection speed, and it will be well understood from the above that the weight of the sprue portion is heavy. Incidentally, neither Patent Document 2 nor Patent Document 3 mentions the molding cycle time at all. However, it is common knowledge that a molding cycle time of 20 seconds or more is necessary for a device having the above-described sprue. .

Furthermore, Patent Document 4 describes that a light guide plate or the like is formed using an injection mold having a sprue bush having an effective diameter of 1 to 10 mm at a portion of the sprue that is in contact with the injection molding nozzle. ing. In Example 1 of Patent Document 4, it is described that a wedge-shaped light guide plate having a plate thickness of 2.0 to 6.0 mm is formed with a cycle time of 40 seconds as a target. However, Patent Document 4 is also molded by an injection mold that is clamped with a constant volume of the cavity, and resin must be injected and filled into a cavity that is substantially equal to the thickness of the light guide plate. Therefore, it is difficult to form a non-defective product from a light guide plate having a thin plate thickness at a relatively low injection speed. In addition, in relation to the effective diameter of the portion of the sprue bush that is in contact with the nozzle, when the effective diameter is 3 mm or less, it is difficult to mold a thin light guide plate with a plate thickness of 0.6 mm or less. It was. In other words, when the effective diameter of the sprue bush is 3 mm or less, it is difficult to fill the end of the light guide plate with a thin plate thickness even if high-speed injection of 500 mm / sec or more is performed. There is a problem that distortion occurs in the image and unevenness in the luminance distribution occurs. Therefore, Patent Document 4 is difficult to apply in a portion where the inner diameter of the sprue is small, and can be applied only to a portion having an effective diameter of about 4.2 mm in contact with a sprue injection molding nozzle as shown in FIG. It was a thing. Moreover, although patent document 4 does not have description of the temperature control piping which cools a sprue separately, it seems that it cools by combining with other parts, but cools a molded article and a sprue separately at appropriate temperature, respectively. I couldn't. Further, in Patent Document 4, cooling is promoted by using a sprue bushing made of a material having a thermal conductivity of 35 W / m · k or more. Therefore, when the effective diameter of the sprue bushing is 3 mm or less, local sprue is used. Due to the progress of cooling and solidification, there is a problem that the holding pressure cannot be sufficiently applied from the injection device, and there is a possibility that sink marks may occur in the molded light guide plate. Furthermore, since the heat conductivity of the sprue bush is high, if the nozzle is always touched to the sprue bushing and molding, the heat at the nozzle tip is taken away too much, so it is required to retreat the nozzle for each molding, and the molding cycle time is improved. I couldn't.

JP 2003-145593 A (0016, FIG. 1) JP 2004-90555 A (Claim 1, FIG. 2) JP 2006-341512 A (0026, FIG. 7) JP 2007-83462 A (Claim 1, 0016, FIG. 6)

In the present invention, in view of the above problems, the light guide plate is conventionally formed by injection molding. Therefore, in order to inject and fill the resin into a thin cavity substantially equal to the thickness of the light guide plate at high speed, the diameter of the sprue is set. It is necessary to reduce the flow loss of the molten resin as much as possible and to apply pressure to the cavity and the sprue, and as a result, to solve the problem that it takes too much time until the sprue is completely cooled and solidified. An object of the present invention is to provide a molding die and a molding method for a light guide plate that can be used. At the same time, the mold structure of the cold runner type light guide plate that can be easily adjusted at the start of molding is simple. It is an object of the present invention to provide a light guide plate molding die and a molding method capable of reducing the yield and improving the yield. It is another object of the present invention to provide a light guide plate molding die and a molding method capable of reliably pulling out the sprue even if the sprue cooling time is shortened.

The light guide plate molding die according to claim 1 of the present invention is a light guide plate molding die for forming a light guide plate in a cavity forming portion formed between a fixed die and a movable die. A cavity forming portion capable of compression molding, a sprue bush connected to the cavity forming portion via a runner forming portion, and a cooling medium flow path disposed around the sprue bush for cooling the cavity forming portion And a cooling medium flow path independent of the weight of the sprue formed by the inner hole of the sprue bush is 1.4 to 6.1 weight relative to the weight of the light guide plate formed in the cavity forming portion. It is characterized by becoming%.

The molding die for the light guide plate according to claim 2 of the present invention is the molding die for the light guide plate according to claim 1, wherein the injection hole has a cross-sectional area of 5. 5 when the molded product volume is 7.8 cm ³ or less. and a 31 mm ² or less, the cross-sectional area of the runner connecting portion is characterized by at 10.17Mm ² or less.

The light guide plate forming method according to claim 3 of the present invention is a light guide plate forming method in which a light guide plate is formed in a cavity forming portion formed between a fixed mold and a movable mold. A moldable cavity forming part, a sprue bush connected to the cavity forming part via a runner forming part, and a cooling medium flow path arranged around the sprue bushing and cooling the cavity forming part An independent cooling medium flow path, and the weight of the sprue formed by the inner hole of the sprue bush is 1.4 to 6.1% by weight with respect to the weight of the light guide plate formed in the cavity forming portion. The light guide plate is formed by injecting molten resin into the cavity through the inner hole of the sprue bush.

According to a fourth aspect of the present invention, there is provided the light guide plate molding method according to the third aspect, wherein the sprue injection hole has a cross-sectional area of 5.31 mm when the light guide plate having a molded product volume of 7.8 cm ³ or less is formed. ² or less, and the cross-sectional area of the runner connection portion is 10.17 mm ² or less.

A light guide plate molding die and a molding method according to the present invention include: a light guide plate molding mold that molds a light guide plate in a cavity forming portion formed between a fixed mold and a movable mold; Possible cavity forming portion, sprue bush connected to the cavity forming portion via a runner forming portion, and a cooling medium flow path disposed around the sprue bushing for cooling the cavity forming portion. The weight of the sprue formed by the inner hole of the sprue bush is 1.4 to 6.1% by weight with respect to the weight of the light guide plate formed in the cavity forming portion. As a result, even if the sprue is reduced, the molten resin can be compressed in response to the cooling shrinkage of the molten resin in the cavity, and at the same time, the cooling time and the molding cycle time can be shortened. It can be. In addition, the yield can be improved by reducing the ratio of parts other than the light guide plate, such as runners and sprues, that cause molding loss.

The light guide plate molding die and the injection molding machine of this embodiment will be described with reference to FIGS. FIG. 1 is a front view of a light guide plate injection molding machine according to the present embodiment. FIG. 2 is a cross-sectional view of the molding die for the light guide plate of the present embodiment, showing a state where the movable die is stopped at a position before the start of injection. FIG. 3 is a cross-sectional view of the light guide plate molding die of the present embodiment, showing a state in which the resin in the cavity is compressed. FIG. 4 is a cross-sectional view of the molding die for the light guide plate of the present embodiment, showing a state where the gate is cut. FIG. 5 is an enlarged view of a main part of the sprue bush in FIG. FIG. 6 is a chart showing a method for forming the light guide plate of the present embodiment. FIG. 7 is a perspective view of the sprue and runner obtained by the light guide plate molding method of the present embodiment. FIG. 9 is an enlarged side view of a sprue obtained by the light guide plate forming method of the present embodiment.

The injection molding machine 1 according to the present embodiment is a molding machine capable of injection compression molding that is formed by a cavity having a variable volume after injection and injection press molding that is one of the fields. In the injection molding machine 1, an injection device 3 provided with a heating cylinder 2 a and a nozzle 2 b in which a screw is incorporated is disposed on a bed 4. In the present embodiment, the diameter of the nozzle hole of the nozzle 2b is 1.5 mm. The injection device 3 is controlled by a measuring servo motor of a measuring mechanism (not shown) and an injection servo motor of an injection mechanism, and controls an injection speed, a pressure holding switching position, a pressure at holding pressure, an injection amount, and the like. In the mold clamping device 5, four tie bars 8 are arranged between a fixed plate 6 fixed to the bed 4 and a pressure receiving plate 7 arranged on the bed 4, and a movable plate 9 moves to the tie bar 8. It is inserted as possible. The pressure receiving plate 7 is provided with a mold clamping cylinder 10 which is a mold opening / closing / clamping mechanism for performing mold opening / closing and clamping, and a ram 10 a of the mold clamping cylinder 10 is fixed to the back surface of the movable plate 9. A mold clamping cylinder 10 which is a mold opening / closing / clamping mechanism controls a mold clamping speed and a mold clamping force during mold clamping. In this embodiment, the mold opening / closing / clamping mechanism is an example of a mold clamping cylinder 10 controlled by a servo valve, but a toggle mechanism operated by a servo motor and a ball screw mechanism or the like may be used.

The light guide plate molding die 11 is formed by injection press molding of two mobile phone light guide plates having a diagonal size of 4 inches in the plane direction (effective area 3.5 inches), a plate thickness of 0.38 mm, and a uniform plate thickness. This is a molding die 11 to be molded. (Hereafter, the light guide plate for mobile phones is simply abbreviated as the light guide plate P.) In the injection press molding, the distance between the cavity forming portion 42a of the fixed mold 13 and the cavity forming portion 16a of the movable mold 12 is set before the injection starts. The movable mold 12 is stopped at a position A (a position where a certain mold opening amount is secured) that is a value obtained by adding a predetermined amount to the thickness B of the light guide plate P, and at the start of injection, after the start of injection, or after injection In this method, the molten resin in the cavity 14 is compressed and molded after completion. In injection press molding, injection is performed with the cavity 14 slightly opened as compared to the completion of molding, and therefore there is less flow loss compared to general injection molding. Therefore, there is no need for an injection device having a high-speed injection capability, and the molten resin can be injected at a relatively low speed and low pressure. In addition, since the injection speed is relatively slow as described above, it is possible to mold the light guide plate P having a thin plate thickness while reducing the residual stress in the vicinity of the gate P3 as much as possible. As a result, it is possible to form a light guide plate with very little warpage after molding and excellent brightness balance. Furthermore, the problem of silver and burning as formed by high-speed injection can be solved, and sprues and runners having a small cross-sectional area can be used, so that there is an advantage that the cooling time can be shortened. Furthermore, since the movable mold 12 is moved in the mold clamping direction with or after the start of injection to compress the molten resin, the flow of the molten resin is accelerated at a position far from the gate portion of the cavity 14 to eliminate insufficient filling. In addition, there is an advantage that fine transfer can be performed well. After the gate P3 is cut, the normal injection mold cannot apply pressure from the injection device. However, in the case of injection press molding, the molten resin in the cavity 14 is compressed and cooled and solidified. It can cope with the contraction by. The molding die 11 used for injection press molding can also be used for injection compression molding in which the cavity 14 is slightly opened and recompressed by injection from the mold clamping completion position, and the present invention covers both of them.

2 to 4 are cross sections of the molding die 11 of the present embodiment. The molding die 11 includes a movable die 12 that is a first die and a fixed die 13 that is a second die. Two cavities 14 of variable length are formed. In this embodiment, an example of the two-piece mold 11 is shown, but even in the case of a single mold, the sprue P1 can be molded using the same mold. A movable mold 12 attached to the movable plate 9 of the injection molding machine 1 is provided with a mold main body portion 15, a core portion 16, a movable frame portion 19 and the like. A core portion 16 is fixed substantially at the center of the surface of the mold main body portion 15 on the fixed mold side. The surface of the core portion 16 that faces the fixed mold 13 is a cavity forming portion 16a that is a mirror surface and forms a light output surface, and has a substantially quadrilateral shape including protrusions that substantially match the shape of the light guide plate P. Yes. A plurality of cooling medium channels 17 are formed in the core portion 16 in parallel with the cavity forming portion 16a. In addition, the part which forms the cavity formation part of a core part, and another part may consist of a separate block. Further, the cavity forming portion 16a is shown as an example of a mirror surface, but it may be subjected to pattern processing such as dots, grooves, holograms, rough surface processing, etc., and does not exclude those with a stamper attached.

Concave portions are formed at four positions in the upper and lower portions of the surface of the mold main body 15 on the fixed mold side, and springs 18 are attached to the fixed mold side toward the fixed mold side. Then, the fixed mold side of the spring 18 is in contact with a movable frame portion 19 disposed so as to surround the core portion 16. Therefore, in other words, the core portion 16 is disposed in the hollow portion formed by the movable frame portion 19. The entire movable frame portion 19 is movable in the mold opening / closing direction with respect to the mold main body portion 15 and the core portion 16 by the spring 18. The surface of the movable frame portion 19 that faces the fixed mold 13 is a contact surface 19a. A light incident surface forming block 20 for forming a light incident surface is detachably disposed on the side of the movable frame portion 19 opposite to the gate. The front inner portion of the movable frame portion 19 including the light incident surface forming block 20 also constitutes a cavity forming portion that forms the cavity 14 together with the cavity forming portion 16a. FIG. 2 shows a state in which the movable mold 12 is stopped at a position before the start of injection. FIG. 3 shows a state in which molten resin (not shown) in the cavities 14 and 14 is compressed after the start of injection. Furthermore, FIG. 4 shows a state in which it is further compressed and gate-cut. 2 to 4 all depict the shape of the sprue P1, the positional relationship between the core portion 16 and the movable frame portion 19, the contraction of the spring, and the like exaggerated from the actual situation.

A heat insulating plate 21 is attached to the movable platen 9 side of the mold body 15, and a protruding pin 23 that is moved forward and backward through the ejector plate of the ejector device is disposed in the internal space and hole. The protruding pin 23 is disposed in a hole formed over the inside of the mold main body 15 and the core portion 16, and the tip thereof faces the runner forming portion 32 so that the sprue P1 and the runner P2 can be easily held. The biting portion 23a is provided in a Z shape. The ejector pin 23 is driven by an ejector driving device disposed in the movable platen 9 or on the ram 10 a side of the clamping cylinder 10 from the movable platen 9.

Further, gate cutter members 24 and 24 are disposed inside the mold main body 15. Each gate cutter member 24 is formed of a rectangular thin plate, the front surface thereof is a gate forming portion, and the corner portion on the cavity side of the gate forming portion is a gate cutter 24a for cutting the molten gate. Yes. And as FIG. 4 shows, a part of side surface by the side of the cavity in the said gate cutter member 24 comprises a cavity formation part after a gate cut. As for the dimensions of the gate cutter member 24, the width (gate width) in the direction orthogonal to the flow direction of the molten resin is 12 mm. It is desirable that the thickness of the molten resin in the flow direction is about 1.2 to 2.0 mm when the light guide plate P having the size of this embodiment is formed.

The gate cutter member 24 is driven by a gate cutter driving device disposed in the movable platen 9 or on the ram 10a side from the movable platen 9. The gate cutter driving device uses a hydraulic cylinder controlled by a servo valve, or a servo motor and a ball screw mechanism. In the case of a hydraulic cylinder controlled by a servo valve, closed loop control during forward movement of the gate cutter member 24 is performed by speed control or pressure control. The gate cutter member 24 can be retracted by a spring 25.

Further, in the core portion 16, a surface facing the sprue bush 44 and the insert block 43 of the fixed mold 13 described later is a runner forming portion 32. As for the runner forming portion 32, a convex portion is formed in a portion adjacent to the protruding pin 23 side from the gate cutter member 24, and a portion facing the sprue bush 44 and facing the protruding pin 23 is a concave portion. The gate forming portion of the gate cutter member 24 is located at a position (movable platen 9 side) lower than the convex portion except when protruding. The reason for this is that the resin solidified at the tip of the passage of the nozzle of the injection device is not received by the cold slug well-like recesses at the time of injection and does not flow into the cavities 14, 14. This is to prevent the burr and the like from being excessively applied to the front surface.

Further, the runner forming portion 32 is connected to the sprue P1 from the connecting portion P2a with the sprue P1, as can be understood by looking at the sprue P1 and the runner P2 (gate cut and separated from the light guide plates P and P) shown in FIG. Although it is formed so that the width becomes wider toward the cutting portions P2b and P2b, it is about 7 mm at the connection portion P2a (substantially equal to the diameter of the protruding pin 23) with the sprue P1, and at the cutting portion P2b of the gate P3. Since it is 12 mm as described above, it spreads 5 mm. The width of the connecting portion P2a of the sprue P1 is desirably about 3 to 9 mm. The plate thickness P2c of the runner P2 is preferably about 0.6 to 1.5 mm from the viewpoint of achieving both shortening the cooling time and ensuring the fluidity of the resin. In the present embodiment, the runner forming portion 32 is provided as a part of the core portion 16, and the runner P2 and the gate P3 are also provided such that the cross-sectional areas are variable after injection, but the runner forming portion is the movable frame. The cross-sectional areas of the runner and the gate may be unchangeable so as to be a part of the portion. The runner and the gate may be linearly connected to the cavity, and the width and length of the runner are appropriately selected, but it is desirable to use a film gate.

A cooling medium flow path 33 is formed around the protrusion pin 23 and in the vicinity of the gate cutter member 24 so as to promote cooling of the runner P2. An air passage 34 that is blown at the time of mold release is formed between the core portion 16 and the movable frame portion 19. The air passage may also be provided between the gate cutter member 24 and the hole. Note that when the sprue is held and taken out with the light guide plate and the sprue integrated, the gate cutter member is unnecessary, and the gate cutter member is not essential in the present invention.

Next, the fixed mold 13 will be described. As shown in FIGS. 2 to 4, the fixed mold 13 attached to the fixed plate 6 of the injection molding machine 1 includes a mold main body 41, a cavity forming block 42, The insert block 43, the sprue bush 44, the gate cutter members 45 and 45, the contact block 46, and the like are formed. A heat insulating plate 47 is attached to the fixed plate side of the mold main body 41, and a hole 48 into which the nozzle 2b of the injection device 3 is inserted is formed, and a locating ring 49 is attached around the hole 48. A cavity forming block 42 is attached to the movable mold side of the mold body 41, and the surface of the cavity forming block 42 that faces the movable mold 12 is a main portion forming portion 42a of the cavity forming portion. Yes. In the present embodiment, the main portion forming portion 42a is a portion that forms a reflective surface, and fine dots are engraved therein. In the cavity forming block 42, a plurality of cooling medium flow paths 50 are formed in parallel with the main part forming part 42a of the cavity forming part. In addition, an air passage 53 is formed between the cavity forming block 42 and the insert block 43 and the contact block 46 for ejecting air at the time of mold release.

Further, an insert block 43 is disposed in the mold main body 41 together with the cavity forming block 42. As shown in FIG. 5 in which the two-dot chain line portion of FIG. 4 is enlarged, a sprue bush 44 is disposed in the center hole of the insert block 43. The sprue bush 44 has a small-diameter portion on the movable mold 12 side and a large-diameter portion on the nozzle touch surface 44b side with a stepped portion as a boundary, and an inner hole 44a for forming the sprue P1 is provided on the central axis. Yes. The sprue bush 44 is made of martensitic SUS420J2 which is stainless steel or steel having hardness similar to that. The thermal conductivity of SUS420J2 is 24.9 W / m ° C. However, if a thermal conductivity that is too good is used for the sprue bush 44, the tip of the nozzle is too cold to hinder injection, and the sprue bush 44 Since the cooling and solidification of the molten resin proceeds excessively, the width of the thermal conductivity of various stainless steels (13 to 30 W / m ° C.) is not essential but desirable. In addition, the Young's modulus of stainless steel is 180 to 210 kN / mm ² , and if the Young's modulus is too low, a problem may occur in a state where the nozzle touch force is continuously received.

The inner hole 44a of the sprue bush 44 is enlarged in a taper shape from the injection hole 44c facing the nozzle touch surface 44b toward the runner connection portion 44d. In this embodiment, the angle θ of the draft (referred to as draft because it is an inclination necessary for pulling out the sprue) is 1 ° with respect to the center line L as shown in the cross section of FIG. It has become. However, the angle θ is preferably 0.5 to 2.0 ° (1 to 4 ° on both sides), and the angle θ is 0.8 to 1.4 ° to optimize the diameter of the runner connecting portion 44d. 1 ° is most desirable because it is possible. This is because when the draft angle is less than 0.5 °, the friction with the inner hole becomes too large and the sprue P1 may be cut off when the sprue P1 is released, and thread drawing occurs. It becomes easy. When the draft angle is greater than 2.0 °, the diameter in the vicinity of the runner connection portion becomes too thick, and when the sprue P1 is released, the cooling in the vicinity of the runner connection portion is delayed, and in the vicinity of the runner connection portion. There arises a problem that the sprue P1 is cut. However, even when the draft angle θ is 2 ° or in the vicinity of 2 °, there is a problem that it takes too much cooling time if the diameter P1b of the runner connecting portion 44d of the sprue P1 is a certain value or more.

In the present embodiment, the diameter P1a of the injection hole 44c in the inner hole 44a of the sprue bush 44 is 2.0 mm (cross-sectional area 3.14 mm ² : rounded off below), and the diameter P1b of the runner connection portion 44d is about 2.87 mm ( The cross-sectional area is 6.47 mm ² : the following are rounded off). The diameter P1a of the injection hole 44c is provided larger than the diameter of the nozzle hole of the nozzle 2b (1.5 mm in this embodiment). If the diameter P1a of the injection hole 44c is too small, a flow loss of the molten resin and defects due to excessive cooling of the sprue are caused. If it is too large, the molding cycle time becomes long, and sprue breakage and stringing are caused. In this embodiment, the cross-sectional shape of the inner hole 44a of the sprue bush 44 is a perfect circle. However, since the shape other than the perfect circle is not excluded, the diameters P1a and P1b are effective diameters. For example, at least one of the injection hole and the runner connection portion may be a non-circular shape (an ellipse, a polygon, a combination of an arc and a straight line, a shape formed by a combination of different arcs, and the like. As long as it satisfies the range of the cross-sectional areas of the injection hole 44c and the runner connection portion 44d of the sprue bush 44 shown in FIG.

And 25 mm is employ | adopted as the optimal value for the full length P1c of the inner hole 44a of the sprue bush 44. FIG. If the overall length P1c of the inner hole 44a of the sprue bush 44 is short, it is advantageous from the viewpoint of preventing the flow loss of the molten resin. However, in order to provide the cooling mold 50 or the like in the fixed mold 13, the insert block 43 is used as a nozzle. Considering the necessary thickness for receiving the touch pressure, 20 mm or more is required. The total length P1c of the inner hole 44a of the sprue bush 44 is desirably 30 mm or less in order to reduce the flow loss of the molten resin. The surface of the inner hole 44a of the sprue bush 44 is roughened by sandblasting, for the purpose of facilitating release of the sprue bush 44.

Accordingly, in the present embodiment, the volume of the sprue P1 that is separated from the runner P2 by the one-dot chain line in FIG. 5 and is molded in the inner hole 44a is 116.6 mm ³ without considering a portion caused by a slight sink or rough surface. When the specific gravity of the polycarbonate used for molding is multiplied by 1.2, the weight g2 of the sprue P1 is 0.14 g (the following is rounded off). Moreover, the weight (average value of the actual measurement value) including the sprue P1 and the runner P2 shown in FIG. 7 is 0.50 g. When the volume is obtained by dividing by the specific gravity, it is about 416.7 mm ³ (the following rounded off). It has become. Accordingly, the weights of the runners P2 and P2 of this embodiment are 0.36 g (calculated value) for both sides, and the volume is 300.0 mm ³ (calculated value). The molded product weight g1 (average value of the actual measurement values) of the light guide plate P having a diagonal dimension of 3 inches, a plate thickness of 0.3 mm and a uniform plate thickness is 2.20 g, and its volume is about 1,833. .3 mm ³ (the following are rounded off). Therefore, in this embodiment, since two light guide plates are simultaneously formed, the molded product weight g1 of the two light guide plates P is 4.40 g, and its volume is 3,666.6 mm ³ (volume). 3.7 cm ³ : The following is rounded off). Therefore, the weight% of the weight g2 of the sprue P1 formed by the sprue bush 44 with respect to the molded product weight g1 of the light guide plate P (the calculation formula is g2 / g1) is 3.2% (the following are rounded off). This value is about 1/3 to about 1/6 of the weight% of the sprue P1 with respect to the light guide plate P when the light guide plate P is formed by conventional injection molding (fixing the volume of the cavity). The sprue P1 can be reduced in size and volume.

In FIG. 9, a solid line shows an enlarged side view of a sprue obtained by the light guide plate forming method of the present embodiment. Also, the broken lines in FIG. 9 indicate the minimum and maximum cases of the sprue P1 obtained by the present invention. Further, in FIG. 9, a two-dot chain line indicates a sprue obtained by a conventional method of forming a light guide plate, and it can be clearly understood how small the capacity of the sprue P1 of the present invention is. When two light guide plates (volume 3,876 mm ³ , weight 4.65 g) having a diagonal size (actual size) of 5 inches and a thickness of 0.5 mm are taken (volume 7,752 mm ³ (7.8 cm ³ ( Rounded off to the third decimal place)), weight 9.3 g), or 7 inch diagonal dimension (actual dimension), 0.5 mm plate thickness (volume 7,526 mm ³ (7.5 cm ³ ( ^third decimal place)) It was confirmed that the sprue bushing 44 of the present invention can be molded up to rounding off))) and a weight of 9.03 g).

As described above, the diameter and taper angle (draft angle) θ of the sprue P1 as shown in FIG. 5 have the most influence as factors determining the cooling time in the molding cycle time in the present invention. The diameter of the nozzle hole (not shown) of the nozzle of the injection device is 1.5 mm. The diameter of the injection hole 44c on the nozzle hole side of the sprue bush 44 needs to be larger than the diameter of the nozzle hole in order for the resin at the nozzle tip to be satisfactorily removed when the sprue is pulled out. It is desirable to use holes. FIGS. 10 to 14 show a small light guide plate injection compression molding die (of the sprue bushing 44) that takes two small light guide plates P having a diagonal size of 2.8 inches, a plate thickness of 0.4 mm, and a volume of 0.94 cm ³ . The structure is the same as in FIG. 5, and the temperature of the cooling water in the cooling medium flow path for cooling the cavity forming surface is 90 ° C., the nozzle temperature is 325 ° C., the heating cylinder front temperature is 355 ° C., and the heating cylinder middle temperature is 370 It is the result of having performed the test at ℃, heating tube rear temperature 360 ℃, injection speed 300mm / sec.

In FIG. 10, the diameter of the injection hole 44c is 1.6 mm (cross-sectional area 2.01 mm ² : rounded down below), the taper angle θ as shown in FIG. 5 is 1 °, and the diameter of the runner connection 44d is 2.5 mm. FIG. 9 shows data when using a sprue bush 44 having a length of 25 mm, and the sprue P1 to be molded is indicated by the innermost broken line in FIG. In this example, when the cooling temperature of the sprue bush 44 is 70 ° C. or 80 ° C., if the molding cycle time becomes long (more than 5 seconds), the injection hole 44c of the sprue bush 44 and the nozzle hole of the nozzle are overcooled. As a result, there was a problem that the next injection could not be performed or cold slag was mixed with the molded product. Even when the cooling temperature of the sprue bushing was 90 ° C., it became defective in 6 seconds or more. Accordingly, the diameter of the injection hole 44c of the sprue bush 44 is 1.6 mm, so that the practical range is extremely narrow, and if it is less than that, a practical setting adjustment cannot be made.

FIG. 11 shows data when a sprue bushing 44 having a diameter of the injection hole 44c of 2.0 mm, a taper angle θ of 1 °, a diameter of the runner connection portion 44d of 2.9 mm, and a length of 25 mm is used. The sprue P1 is indicated by the solid line in FIG. In this example, even at each cooling temperature, when the molding cycle time is 2 seconds, the cooling of the sprue P1 may not catch up and sprue breakage may occur. However, it is not economical to extend the molding cycle time more than necessary. And if the molding cycle time is extended too much, the nozzle is cooled and the fluidity of the molten resin is lowered, and the residence of the molten resin in the heating cylinder becomes too long, and the resin deteriorates (yellowing or black spots). Problems also arise. As for the temperature of the cooling water, when the temperature is 40 ° C., cold slag begins to mix with the molded product, so the cooling temperature used for molding is desirably 50 ° C. or higher. In the case of 120 ° C., sprue breakage occurs in 4 seconds. Therefore, the cooling temperature used for molding is preferably 110 ° C. or lower (particularly, the cooling temperature of the cavity forming surface or lower).

FIG. 12 shows data when a sprue bush 44 having a diameter of the injection hole 44c of 2.3 mm, a taper angle θ of 1 °, a diameter of the runner connection portion 44d of 3.2 mm, and a length of 25 mm is used. In this example, when the cooling temperature is 70 ° C., sprue breakage occurs when the molding cycle time is 3 seconds, and when the cooling temperature is 80 ° C. and 90 ° C., sprue breakage occurs even when the molding cycle time is 5 seconds.

FIG. 13 shows data when a sprue bushing 44 having a diameter of the injection hole 44c of 2.6 mm, a taper angle θ of 1 °, a diameter of the runner connection portion 44d of 3.5 mm, and a length of 25 mm is used. In this example, the diameter of the runner connection portion 44d is 3.47 mm, and it takes time to cool and solidify this portion. In this example, when the cooling temperature is 70 ° C., sprue breakage or stringing occurs when the molding cycle time reaches 5 seconds. When the cooling temperature is 80 ° C. or 90 ° C., sprue breakage occurs even when the molding cycle time is 6 seconds. Or stringing occurred. Therefore, when the diameter of the injection hole is 2.6 mm, it can be said that it is the upper limit diameter among the above-described cases where the desired molding cycle time is within 6 seconds as described above.

In addition, FIG. 14 uses a sprue bush 44 having a diameter of the injection hole 44c of 1.6 mm, 2.0 mm, 2.3 mm, 2.6 mm, a taper angle θ of 1.5 °, and a length of 25 mm, It is the data at the time of testing by setting a cooling temperature as 70 degreeC. In this example, the diameter of the runner connection portion is 2.9 mm, 3.3 mm, 3.6 mm, and 3.9 mm corresponding to the above, respectively, and there is a problem that cooling and solidification of this thickest portion is particularly delayed. . In the example in which the injection hole 44c has a diameter of 2.6 mm and the taper angle θ is 1.5 °, when the cooling temperature is 70 ° C., sprue breakage occurs when the molding cycle time is 5 seconds, Elongation and bending were observed. Further, in the case of other diameters of the injection holes 44c, molding failure occurred unless the molding cycle time that is the shortest was extended as compared with the case where the taper angle θ of the inner hole 44a of the sprue bush 44 was 1 °. Accordingly, the diameter of the runner connection portion 44d of the sprue bush 44 with the slowest cooling was determined to be 3.6 mm in the practical range with the maximum diameter.

Therefore, even if the diameter of the injection hole 44c shown in FIG. 13 is 2.6 mm, the upper limit of the diameter of the runner connection portion 44d is 3.6 mm as shown in FIG. Is done. Therefore, as shown by a broken line outside the solid line in FIG. 9, the diameter of the injection hole 44c is 2.6 mm (cross-sectional area 5.31 mm ² : rounded down below), and the runner connection portion 44d has a diameter of 3.6 mm (cross-sectional area of 10.3). The sprue P1 of 17 mm ² (rounded off below) is the maximum capacity sprue P1 in the present invention.

The preferable taper angle θ of the inner hole 44a of the sprue bush 44 is preferably increased by 0.5 to 2.0 ° from the injection hole 44c toward the runner connection portion 44d. However, if the diameter of the runner connection 44d exceeds 3.6 mm, even if the molding cycle time is 6 seconds (cooling time 3.9 seconds), the cooling and solidification in the vicinity of the runner connection 44d is delayed, and the sprue P1 is cut when the mold is opened. May occur. Once the sprue P1 remains in the sprue bush 44, continuous molding is interrupted, and a skilled worker must work in a narrow space to take out the sprue P1 and possibly damage the mold. is there.

Based on the above example, the weight and volume of the light guide plate P and the sprue P1 of 4.40 g (volume 3.7 cm ³ ) in the two sheets of this embodiment will be described. In the case where the sprue P1 is the smallest, the sprue bush 44 having an inner hole 44a having a diameter P1a of the injection hole 44c of 1.6 mm, a draft angle θ: 0.5 ° with respect to the center line, and a total length P1c of 20 mm. The volume of the sprue P1 formed by the above is 49.5 mm ³ (the following is rounded off), and the weight g2 of the sprue P1 is 0.06 g (the following is rounded off). And the weight% of the weight g2 of the sprue P1 with respect to 4.40 g which is the molded product weight g1 of the light guide plate P which is a molded product is 1.4% (rounded off below) (the volume ratio is the same). In the case where the weight and volume of the sprue P1 are the largest, the inner hole 44a having a diameter P1a of the injection hole 44c of 2.6 mm, a diameter P1b of the runner connection portion 44d of 3.6 mm, and a total length P1c of 30 mm is provided. The volume of the sprue P1 formed by the sprue bushing 44 is 226.3 mm ³ (the following is rounded off), and the weight g2 of the sprue P1 is 0.27 g (the following is rounded off). The weight% of the weight g2 of the sprue P1 with respect to 4.40 g which is the molded product weight g1 of the light guide plate P is 6.1% (the following are rounded off). Therefore, the weight% of the sprue P1 with respect to the light guide plate P is within the range of 1.4 to 6.1% as a range that satisfies the cooling efficiency and the state of the molded product.

Furthermore, when the draft angle θ and the total length of the sprue P1 (matching the full length P1c of the inner hole 44a) are more desirable, the diameter P1a of the injection hole 44c is 1.6 mm, and the draft angle θ is When a sprue bush 44 having an inner hole 44a having an angle of 1 ° and a total length P1c of 25 mm is selected with respect to the center line L represented by the alternate long and short dash line, the volume of the sprue P1 is 81.4 mm ³ (the following are rounded off) And the weight g2 of the sprue P1 is 0.10 g (the following are rounded off). And the weight% of the weight g2 of the sprue P1 with respect to 4.40 g which is the molded product weight g1 of the light guide plate P is 2.3% (the following are rounded off). In addition, when the sprue bush 44 having the inner hole 44a having the diameter P1a of the injection hole 44c of 2.6 mm, the draft angle θ of 1 ° with respect to the center line L, and the total length P1c of 25 mm is selected. The volume of the sprue P1 is 181.0 mm ³ (the following are rounded off), and the weight g2 of the sprue P1 is 0.22 g (the following are rounded off). And the weight% of the weight g2 of the sprue P1 with respect to 4.40 g which is the molded product weight g1 of the light guide plate P is 5.0% (the following are rounded off). Therefore, the weight% of the sprue P1 with respect to the light guide plate P is set to 2.3 to 5.0% in the above range, the cooling rate until the sprue P1 can be released, the flow of the molten resin, and the moldability. From the point of view, it is even more desirable.

When two light guide plates (volume 3,876 mm ³ , weight 4.65 g) having a diagonal size (actual size) of 5 inches and a thickness of 0.5 mm are taken, the diameter P1a of the injection hole 44c is 2.6 mm, When a sprue bush 44 having an inner hole 44a having an inclination angle θ of 1 ° with respect to the center line L and an overall length P1c of 25 mm is selected, the weight g2 of the sprue P1 is 0.22 g as described above. The sprue P1 is 2.4% by weight.

The sprue P1 and the runner P2 can be reduced in size and weight by performing injection press or injection compression molding as described above, so that the injection speed may be relatively slow. There is no need to increase the area. Further, in the injection press and injection compression molding, the resin in the cavities 14 and 14 can be eliminated by compressing the resin in the cavities 14 and 14 with a mold opening / closing and clamping mechanism. Since it is not necessary to apply a strong holding pressure from the side, the sprue P1 may be cooled and solidified first, and as a result, there is no need to increase the cross-sectional area of the sprue P1. In particular, in the type that performs gate cut, holding pressure is applied through the sprue P1 until the gate cut, and after holding the gate cut, the holding pressure is stopped to lower the internal pressure of the sprue P1 and cause a slight sink in the sprue P1. By doing so, the sprue P1 can be more easily released from the inner hole 44a of the sprue bush 44.

A cooling medium passage 51 for cooling the sprue P1 and the runner P2 is formed around the small diameter portion of the sprue bush 44. Specifically, the cooling medium flow path 51 is formed in a concave shape in the portion of the insert block 43 facing the sprue bush 44 in a longitudinal direction of 5 to 10 mm of the sprue P1 and a width of 3 to 6 mm in a direction orthogonal to the longitudinal direction. O-rings 51a and 51a are fitted between the bush 44 and the insert block 43 to prevent leakage of the cooling medium. In this embodiment, since the total length of the sprue P1 is as short as 25 mm, the cooling medium flow path 51 is formed in one place. However, the injection hole side and the runner connection part side may be separately cooled. In this embodiment, water whose temperature is controlled is used as the cooling medium, but oil may be used.

Further, as shown in FIGS. 2 to 4, a runner forming portion 54 is connected to the surface of the insert block 43 facing the movable mold 12 from the runner connecting portion 44 d of the sprue bush 44 toward the cavity forming portion. Is formed. The runner forming portion 54 is formed in a groove-like lower position (a position on the stationary platen side) in a groove shape with respect to the abutting surface 46a of the abutting block 46, and constitutes a surface forming the runner P2 on the stationary mold 13 side. To do. The width of the runner forming portion 54 in the direction orthogonal to the flow direction of the molten resin gradually increases from the portion adjacent to the sprue bush 44 toward the cavities 14 and 14. The runner forming portion 54 is also formed with a convex portion facing the concave portion and formed with a concave portion facing the convex portion so as to keep the same distance from the runner forming portion 32 of the movable mold 12.

The recessed portion of the runner forming portion 54 is connected to the gate forming portion on the same continuous surface. Therefore, there is no clear distinction between the runner P2 and the gate P3 and its formation part. Further, a gate forming portion made of an end face of the gate cutter member 24 is formed continuously with the runner forming portion 32 of the core portion 16. And the width | variety (width | variety of the gate cutter member 24) of the direction orthogonal to the flow direction of the molten resin of a gate formation part is provided more widely than the diameter of the sprue P1. Therefore, the gate P3 of this embodiment is a kind of film gate, and has a length (width) of about 2/3 to 1/4 of the length of the side surface (side surface opposite to the light incident surface) of the light guide plate. The runner and the cavity are connected via the film gate.

A gate cutter member 45 is fixed between the runner forming portion 54 of the insert block 43 and the main portion forming portion 42 a of the cavity forming portion of the cavity forming block 42. The gate cutter member 45 is a rectangular thin plate made of a hard metal member such as an alloy tool steel (SKD steel) having a Rockwell C scale hardness of 55 to 63 HRC, and is more than a member forming the main portion forming portion 42a of the cavity forming portion. A metal having a high hardness is used. The width of the gate cutter member 45 in the direction orthogonal to the flowing direction of the molten resin is the same as or slightly wider than the gate forming portion. The thickness of the gate cutter member 45 is about 0.4 to 0.8 mm. The front surface of the gate cutter member 45 faces the cavity forming portion 16a and is a part of the cavity forming portion. Further, a gate cutter 45a having a blade at the corner of the gate cutter member 45 on the gate portion side is formed. The surface on the gate portion side is a surface where the gate cutter member 24 of the movable mold 12 is opposed to the movable mold 12 at a slight interval when moving forward.

Next, a molding method (injection press molding method) using the molding die 11 of the present embodiment will be described with reference to the chart of FIG. In the present embodiment, a light guide plate having a uniform plate thickness of 4 inches in the plane direction and a thickness of 0.38 mm is formed in a molding cycle time of 4.2 seconds. The breakdown is as follows: mold opening / closing time (including mold opening time, removal time, mold closing time) 1.4 seconds, intermediate time (including decompression time) 0.1 seconds, injection time 0.05 seconds, pressure holding time 0 .45 seconds, cooling time 2.2 seconds (substantially cooling starts from the start of injection). Therefore, in the present embodiment, the cooling medium flow path 17 that cools the cavity forming portion 16a of the movable mold 12, the cooling medium flow path 33 that cools the vicinity of the protrusion pin 23 and the runner forming portion 32, and the cavity formation of the fixed mold 13 are formed. The temperature was controlled to about 80 to 120 ° C., which is 30 to 70 ° C. lower than the glass transition temperature Tg of polycarbonate, which is a resin molded by the temperature controller, into the cooling medium flow path 50 for cooling the main part forming portion 42a of the part. Cooling medium (cooling water) is flowing. Moreover, it is 30-100 degreeC lower than the glass transition temperature Tg of the polycarbonate which is resin shape | molded by the temperature controller to the cooling-medium flow path 51 which cools the sprue bush 44 vicinity and the runner formation part 54 vicinity. A temperature-controlled cooling medium (cooling water) is flowing. It is desirable that the temperature of the cooling medium sent to the cooling medium flow path 51 is equal to or lower than the temperature of the cooling medium sent to the cooling medium flow path 50. That is, as shown in FIG. 11, when the temperature of the cooling water to the cooling medium flow path 51 of the sprue bush 44 is 40 ° C., the sprue bush 44 is too cold in the molding cycle time of 7 seconds or more, and the molded product is cold. A defect with mixed slag occurred. Further, if there is an excessive temperature difference from the cavity forming block 42 in the fixed mold 13, a difference in thermal expansion occurs in each part, and there is a problem with transfer. Therefore, it is not desirable to perform molding at 40 ° C. or less. Further, when the temperature of the cooling water to the cooling medium flow path 51 is 120 ° C., sprue breakage occurs in 4 seconds, and in practice, there is a meaning that the risk of sprue breakage is violated at such temperature. Absent.

The front zone of the injection device (zone closest to the nozzle) is set to 350 ° C., and the molten resin of polycarbonate is measured. When polycarbonate is used, it is desirable that the temperature setting of the front zone of the injection device is set to a relatively high temperature of 320 to 380 ° C. from the viewpoint of the flow of the molten resin. Then, the mold clamping cylinder 10 is operated, and the mold is closed by bringing the movable mold 12 attached to the movable plate 9 into contact with the fixed mold 13 attached to the fixed plate 6. At this time, the core portion 16 is once advanced to the most advanced position, the spring 18 is contracted, and the movable platen 9 and the like are advanced to the mold closing completion position (0 position) where the movable frame portion 19 and the mold main body portion 15 come into contact with each other. After that, the movable platen 9 and the like are moved back by a small amount again by the mold clamping cylinder 10, and the position is controlled and stopped at the position A at the start of injection in FIG. As a result, the core portion 16 of the movable mold 12 can be stopped at a position in the mold opening direction from the molding completion position. If the position of the movable plate can be determined with higher accuracy by a servo motor or the like, the movable plate may be moved from the beginning to the position A at the start of injection.

At this time, the position A at the start of injection of the movable plate 9 and the core portion 16 of the movable mold 12 is guided so that the distance of the cavity forming portion 16a of the movable mold 12 relative to the cavity forming portion 42a of the fixed mold 13 is formed. Control is performed so that the thickness of the optical plate P is 0.1 to 0.3 mm. Further, the distance between the cavity forming portion 42a and the cavity forming portion 16a is preferably 120% to 200% with respect to the plate thickness of the light guide plate P. When the plate thickness is thin, a high numerical value in the above ratio. When the plate is thick, a low value is desirable. When the injection is stopped at the position A at the start of injection, a mold clamping force is exerted slightly to the extent that the position is not changed by the mold clamping cylinder 10 which is a mold opening / closing / clamping mechanism. When a servo motor is used, position control is performed so as to stop at the stop position.

When the movable mold 12 is stopped and the variable thickness cavities 14 and 14 connected to the runner including the variable thickness gate are formed, the air in the cavities 14 and 14 is sucked. For air suction, an electromagnetic opening / closing valve between a vacuum device (not shown) and the air passages 34 and 53 is opened, and the air passage 34 and the gap between the core portion 16 and the movable frame portion 19 connected thereto, the air passage 53 and the air passage 53 and connection thereto. The air in the cavities 14 and 14 is sucked from the gap between the cavity forming block 42 and the contact block 46. The reason why the cavities 14 and 14 are depressurized before the start of injection is that the molten resin does not receive air resistance in the cavities 14 and 14 at the time of injection and quickly reaches the end on the light incident surface forming block 20 side. This is to make it possible to flow, and is particularly effective when a thin light guide plate P having a thickness of 0.2 to 1.0 mm is formed. In the present embodiment, since the nozzle 2b is always in contact with the sprue bush 44, air is not sucked from the sprue bush 44 side during decompression.

Next, when a predetermined intermediate time (decompression time) elapses, an injection mechanism (not shown) of the injection device 3 is operated, and the screw in the heating cylinder 2a is advanced to inject the molten resin. The molten resin is injected into the cavity 14 through the sprue P1, the runner P2, and the gate P3 formed by the nozzle hole of the nozzle 2b and the inner hole 44a of the sprue bush 44. In this embodiment, the injection speed is set to be 200 mm / sec at the peak, and the screw advance speed is controlled by the injection servo motor of the injection mechanism. However, the injection speed is desirably 150 to 400 mm / sec. Since the cavities 14 and 14 can be injected and filled at a relatively low injection speed in this way, the weight and volume of the sprue P1 and the runner P2 can be reduced as described above, and the vicinity of the gate of the light guide plate P to be formed can be reduced. Internal stress can be reduced

When the injection is performed, the mold clamping force is close to 0 as described above. Therefore, the core portion 16 and the movable platen 9 of the movable mold 12 are retracted by the injection pressure, and the cavities 14 and 14 are retreated. The interval of is widened. After injection (substantially at the same time as the completion of injection), the mold clamping cylinder 10 which is a mold opening / closing and clamping mechanism is operated on the mold clamping device 5 side, and the movable platen 9 and the movable mold 12 are moved in the mold closing direction. As a result, the core part 16 is moved forward relative to the movable frame part 19, and the distance of the cavity forming part 16a of the movable mold 12 from the cavity forming part 42a of the fixed mold 13 of the cavities 14 and 14 is shortened. The molten resin in the cavities 14 is compressed. At this time, the pressure of the mold clamping cylinder 10 is controlled, and the hydraulic pressure is detected and controlled so that the setting is 400 KN. This value is about 150 MPa in terms of the resin pressure in the cavities 14 and 14. The boosting speed at this time is increased rapidly in 0.03 seconds to the set value. Note that it is desirable that the pressure increase speed is high, and it is desirable that the pressure is increased in 0.02 to 0.05 seconds. In the case where the mechanism using the mold clamping cylinder 10 is substantially the same scale as the mechanism using the servo motor, the rise is faster and a high mold clamping speed can be achieved. In the example of forming a light guide plate having a diagonal size of 4 inches according to this embodiment, clamping is performed at 300 KN. In some cases, the mold clamping may be started simultaneously with the start of the injection or during the injection (after the start of the injection). In this case, the interval between the cavities 14 and 14 may not be widened at all. In addition, the movable platen is moved by position control until a predetermined position at which compression starts from the start of the mold opening / closing / clamping mechanism or until a predetermined mold clamping force (or detected resin pressure) is reached, and then the pressure is changed to pressure control. Also good.

When the screw position reaches a predetermined holding pressure switching position by the injection device, the injection control is switched to the holding pressure control by pressure control. The holding pressure is preferably 5 to 20 MPa (resin pressure), but injection and holding pressure are performed with almost no cushion. In this embodiment, when a predetermined time elapses, each gate cutter member 24 of the movable mold 12 is advanced by 0.45 to 0.8 mm by a gate cutter member driving device (not shown) to cut the gates P3 and P3. At this time, the gates P3 and P3 are cut between the gate cutter 24a which is the blade of the gate cutter member 24 of the movable mold 12 and the gate cutter 45a which is the blade of the gate cutter member 45 of the fixed mold 13 respectively. Needless to say, the molten resin of the gate P3 is not completely solidified when the gate is cut.

Then, after the gate P3 is cut by the gate cutter member 24, the gate cutter member 24 is held at the advanced position. However, in the present invention, even if the holding pressure does not reach from the injection device, the core portion 16 of the movable mold 12 is advanced by the driving of the mold clamping cylinder 10 which is a mold opening / closing / clamping mechanism. Therefore, even if shrinkage due to cooling occurs, sink marks do not occur and good transfer molding can be performed. Then, the core portion 16 is advanced, and finally the advancement is stopped at the position of the thickness B of the light guide plate P. On the other hand, the injection device side can stop holding pressure and start measuring after a predetermined time. Further, since the holding pressure does not reach the sprue P1 side from the injection device 3, the pressure in the sprue P1 can be reduced. The sprue P1 is cooled and contracted by the cooling medium, causing a slight sink, and a gap is easily formed between the sprue bush 44 and the inner hole 44a. It becomes easy to pull out the sprue P1.

In the present embodiment, the sprue P1 is provided with an angle θ of 1 ° with respect to the center line L, so that the sprue P1 can be more easily extracted. If the draft angle θ is too small (smaller than 0.5 ° each), the sprue P1 will not come out. If the draft angle θ is too large (greater than 2 ° each), the sprue P1 near the injection hole 44c. Since the progress of cooling and solidification of the sprue P1 in the vicinity of the runner connecting portion 44d is delayed with respect to the progress of the cooling and solidifying, the possibility that the sprue P1 is cut in the vicinity of the runner P2 increases when the sprue P1 is forcibly pulled out. In addition, the diameter P1a of the injection hole 44c is 2.0 mm, which prevents stringing when the sprue P1 is pulled out. If the diameter of the injection hole 44c exceeds 3.0 mm, stringing occurs, and if it is smaller than 1.6 mm, the flow loss of the resin increases, so that a higher injection speed than that of the present embodiment is required. Therefore, the possibility that a defective product is generated in the light guide plate P is increased.

When a predetermined time elapses, the mold clamping force is reduced, the air passage 34 between the movable frame portion 19 and the core portion 16 of the movable mold 12, the contact block 46 of the fixed mold 13, the cavity forming block 42, and Release air is applied to the cavities 14 and 14 and the runner P2 from the air passage 53 between the insert block 43 and the like. Next, the mold clamping device is operated to perform pressure release and mold opening in order. At that time, the sprue P1 is taken out from the sprue bush 44 because the runner P2 integrated with the sprue P bites into the biting portion 23a, and is taken out while being held on the movable mold 12 side together with the runner P2. Is done. Further, the light-guide plates P and P that are gate-cut are also taken out from the mold shape while being held on the movable mold 12 side.

At the same time when the movable mold 12 stops at the mold opening completion position, an unillustrated take-out robot is operated and the ejector pin 23 of the ejector device is advanced. The take-out robot used in this embodiment can hold the sprue P1 and the runner P2 and the light guide plate separately. At the time of the removal, the gate cutter member 24 is stopped at the advanced position. In addition, since the gate P3 of the light guide plate of this embodiment is not a portion that becomes a light incident surface, the gate P3 can be used as a light guide plate without performing a finishing process. Further, the sprue P1 and the runner P2 are extremely small in weight percent as described above, but can be recycled separately. Also in this case, since the diameter of the sprue P1 is thin, it can be pulverized by a small pulverizer and the ratio of the virgin material can be increased.

Next, the relationship between the diagonal dimension and thickness of the light guide plate and the molding conditions will be described. The relationship between the diagonal dimension of the light guide plate and the plate thickness can be covered depending on the resin and its molding conditions, so there is no strict division, but the outline is divided as follows. A light guide plate having a diagonal size of 2 to 5 inches can be molded in a free range of 0.3 to 0.5 mm, and a light guide plate of 0.2 mm or more can be formed depending on conditions. Incidentally, when two light guide plates having a diagonal size of 2 inches and a plate thickness of 0.3 mm are taken, the volume is 744 mm ³ and the molded product weight g1 is 0.89 g.
For a light guide plate having a diagonal size of 5 to 6 inches, a plate thickness of 0.3 to 0.6 mm is particularly desirable from the relationship between the resin flow and the cooling rate, and for a light guide plate having a diagonal size of 6 to 7 inches, the plate thickness is 0.4. -0.6 mm is particularly desirable. For example, in a 7-inch light guide plate, the distance from the gate to the farthest corner from the gate is about 15 cm. Therefore, a larger light guide plate requires a higher injection speed and a higher mold clamping speed. In order to improve the flow of the resin as the light guide plate is larger, it is desirable that the temperature of the molten resin is higher. The mold clamping force is preferably 200 to 500 KN in the case of one or two pieces with a diagonal dimension of 2 to 5 inches, and 500 to 1000 KN in the case of one piece of light guide plate of 6 inches or more. The mold clamping force is determined so as to realize 300 to 600 mm / sec at a desired mold clamping speed peak in consideration of the projected area of the light guide plate.

The molding cycle time of the light guide plate requires the following time. When two light guide plates having a diagonal size of 2 to 5 inches and a thickness of 0.2 to 0.5 mm are taken, one light guide plate having a diagonal size of 5 to 7 inches and a thickness of 0.4 to 0.6 mm is provided. In the case of removing, the time (molding time) from the completion of mold closing to the start of mold opening (molding time) is 1.75 to 4.0 seconds, and from the start of mold opening to the completion of mold closing after taking out the light guide plate It is possible to perform the time (die opening / closing time) within 0.75 to 2.2 seconds and the total molding cycle time within 6.2 seconds. FIG. 15 is a chart when the cycle time for forming the light guide plate by injection compression molding included in the present invention is performed in the shortest 2.5 seconds. The breakdown is as follows: mold opening / closing time (take-out time, intermediate time) 0.75 seconds, injection delay time (pressure increase time) 0.1 seconds, injection time 0.05 seconds, pressure holding time 0.4 seconds, The cooling time is 1.2 seconds. In the formation of the light guide plate of the present invention, the plate thickness of the light guide plate is 1.0 mm or less at the maximum, and the size of the light guide plate in the planar direction does not significantly affect the molding cycle time. The thickest sprue P1 (particularly the runner connection portion) has the greatest influence on the molding cycle time. If an attempt is made to shorten the molding cycle time further, the cooling time of the sprue P1 is insufficient and the solidification is insufficient. Therefore, the sprue P1 is cut off. As shown in the chart of FIG. 16, a light guide plate having a transfer pattern having a diagonal size of 3 inches and a plate thickness of 0.6 mm (equal plate thickness) may be molded by injection compression molding with a molding cycle time of 6.0 seconds. In this case, the cooling time is 3.9 seconds. There is a tendency that the molding cycle time becomes longer as the area and thickness of the light guide plate to be molded increases, but extending the molding cycle time further has a problem from the economical point of view. When exceeding, problems also arise from nozzle cooling and deterioration of the resin in the heating cylinder.

Further, in the present invention, injection compression molding or injection press molding may be performed by using a light guide plate molding die 61 of still another embodiment as shown in FIG. The molding die 61 is a so-called inlay die. Specifically, a cavity forming block 64 having a cavity forming portion 64a formed on the front surface and a fitting surface 64b formed on the side surface is fixed to the mold body 63 of the movable mold 62. Further, a runner forming block 65 on which an ejector protruding pin or the like is disposed is fixed to the mold main body 63, and the side surface of the runner forming block 65 is also a fitting surface 65a. The cavity forming block 64 and the runner forming block 65 are each cooled by a separate coolant flow path, and a movable gate cutter member is disposed between the cavity forming block 64 and the runner forming block 65. . The cavity forming block 64 and the runner forming block 65 form a convex portion toward the fixed mold 66 side.

On the other hand, in the fixed mold 66, a cavity forming block 68 having a cavity forming portion 68a formed on the front surface and an insert block 70 having a sprue bush 69 disposed at the center are fixed to the mold main body 67. Yes. A frame forming block 71 is fixed so as to surround the cavity forming block 68 and the insert block 70. The inside of the frame forming block 71 on the movable mold 62 side is a cavity side surface forming portion 71a. A fixed gate cutter member is disposed between the cavity forming block 68 and the insert block 70. A recess is formed toward the movable mold 62 by the cavity forming portion 68 a of the cavity forming block 68 and the cavity side surface forming portion 71 a of the frame forming block 71.

A cooling medium flow path 70 a of a different system from the cooling medium flow path 68 b of the cavity forming block 68 is also formed around the sprue bush 69 of the fixed mold 66. Also in this embodiment, the diameter P1a of the injection hole 69a of the sprue P1 is 20 mm, the draft angle θ is 1 °, and the total length P1c of the inner hole 44a is 25 mm. The weight g2 of the sprue P1 and the runner P2 can be the same as that of the embodiment shown in FIG.

Even when the convex part of the movable mold 62 is fitted into the concave part of the fixed mold 66, the fitting surfaces 64b and 65a and the cavity side surface forming part 71a have a slight gap between which the molten resin does not leak. A cavity 72 is formed between the molds 62 and 66. The distance between the cavity forming portion 68a of the fixed mold 66 and the cavity forming portion 64a of the movable mold 62 in a state where the frame forming block 71 of the fixed mold 66 and the mold main body 63 of the movable mold 62 are not in contact with each other. The volume of the cavity 72 (cavity forming portion) is variable.

Therefore, when performing injection press molding according to another embodiment shown in FIG. 8, first, the distance between the cavity forming portion 64a of the movable mold 62 and the cavity forming portion 68a of the fixed mold 66 is changed during molding. As a result, injection filling is possible even when the injection speed is set to 150 to 400 mm / sec, and the molten resin in the cavity 72 is compressed after the gate cut to obtain a plate thickness of 0.3 to 0.5 mm and a diagonal dimension. It is possible to mold a 2-7 inch light guide plate. As described above, the diameter of the sprue P1 may be relatively small. By cooling the sprue P1 with the independent cooling medium flow path 70a, the sprue P1 can be cooled early and the molding cycle time can be shortened.

The present invention is not enumerated one by one, but is not limited to that of the above-described embodiment, and it goes without saying that those skilled in the art also apply modifications made in accordance with the spirit of the present invention. is there. In the present embodiment, the molding die 11 for a light guide plate for a mobile phone having a diagonal size of 4 inches has been described, but the shape and type of the light guide plate are not limited. Therefore, a light guide plate having a uniform thickness may be a wedge-type light guide plate whose thickness decreases from the light incident surface side toward the other side. The wedge-shaped light guide plate can be molded in such a manner that a gate is formed in a portion other than the light incident surface and the thickness of the thin portion is 0.2 to 0.6 mm. In addition, for incident light, a sidelight-type light guide plate that is incident from the side surface, a backlight-type light guide plate that is incident from the back surface and exits to the front surface (including what is called a light diffusing plate), and external light is reflected. It may be a thing. Various shapes such as a mirror surface, a dot, a groove, and a hologram can be considered for the shape of the reflecting surface and the light emitting surface. Furthermore, it is envisaged that the present invention performs lenses and other thin plates with incident and outgoing light. In any case, at least one of the transfer surfaces is effective for the injection press molding or injection compression molding of the present invention.

In the present embodiment, the molding die 11 attached to the injection molding machine in which the mold is opened and closed in the horizontal direction has been described. However, the mold may be opened and closed in the vertical direction. Further, in the above embodiment, the description has been given of the one in which the molten resin is compressed by changing the distance between the cavity forming portion of the fixed mold and the cavity forming portion of the movable mold by the mold opening / closing / clamping mechanism of the injection molding machine. Alternatively, a hydraulic cylinder for injection press may be provided in the movable mold, and the core portion may be moved by the hydraulic cylinder to compress the molten resin.

Further, as the resin used for molding, polycarbonate (Teflon LC1500 from Idemitsu Kosan Co., Ltd.) is described as an example, but other resins may be used as long as they have excellent optical performance and fluidity. For example, methacrylic resin (specific gravity 1 .2), cycloolefin polymer resin (specific gravity 1.0) and the like. In the present invention, the light guide plate may include a light-transmitting resin plate such as a light diffusion plate.

It is a front view of the injection molding machine used for the shaping | molding method of the light-guide plate of this embodiment. It is sectional drawing of the shaping die used for the shaping | molding method of the light-guide plate of this embodiment, Comprising: It is a figure which shows the state by which the movable die was stopped in the position before the injection start. It is sectional drawing of the shaping die used for the shaping | molding method of the light-guide plate of this embodiment, Comprising: It is a figure which shows the state which compressed the resin in a cavity. It is sectional drawing of the shaping | molding die used for the shaping | molding method of the light-guide plate of this embodiment, and is a figure which shows the state by which the gate was cut. It is a principal part enlarged view of the sprue bush in FIG. It is a chart figure which shows the shaping | molding method of the light-guide plate of this embodiment. It is a perspective view of the sprue and runner obtained by the shaping | molding method of the light-guide plate of this embodiment. It is sectional drawing of the shaping die used for the shaping | molding method of the light-guide plate of another embodiment. It is an enlarged side view of the sprue obtained by the light guide plate forming method of the present embodiment. It is a figure which shows the relationship between the sprue shape of the injection compression molding metal mold | die of the light-guide plate of another embodiment, and molding cycle time. It is a figure which shows the relationship between the sprue shape of the injection compression molding metal mold | die of the light-guide plate of another embodiment, and molding cycle time. It is a figure which shows the relationship between the sprue shape of the injection compression molding metal mold | die of the light-guide plate of another embodiment, and molding cycle time. It is a figure which shows the relationship between the sprue shape of the injection compression molding metal mold | die of the light-guide plate of another embodiment, and molding cycle time. It is a figure which shows the relationship between the sprue shape of the injection compression molding metal mold | die of the light-guide plate of another embodiment, and molding cycle time. It is a chart figure which shows the shaping | molding method of the light-guide plate of another embodiment. It is a chart figure which shows the shaping | molding method of the light-guide plate of another embodiment.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 3 Injection apparatus 5 Clamping apparatus 6 Fixed board 9 Movable board 10 Clamping cylinder 11,61 Molding mold 12,62 Movable mold 13,66 Fixed mold 14,72 Cavity 15,41 Mold main-body part 16, Core part 16a, 42a Cavity forming part 19 Movable frame part 24, 45 Gate cutter member 44, 69 Sprue bush 44a Inner hole 44b Nozzle touch surface 44c, 69a Injection hole 44d Runner connecting part 17, 33, 50, 51, 68b , 70a Cooling medium flow path P Light guide plate P1 Sprue P1a Injection hole diameter P1b Runner connection diameter P1c Total length P2 Runner P3 Gate

Claims (4)

In the mold of the light guide plate for forming the light guide plate in the cavity forming part formed between the fixed mold and the movable mold,
A cavity forming portion capable of compression-molding the light guide plate, a sprue bush connected to the cavity forming portion via a runner forming portion, and a cooling medium disposed around the sprue bush and cooling the cavity forming portion A cooling medium flow path independent of the flow path,
The weight of the sprue formed by the inner hole of the sprue bush is 1.4 to 6.1% by weight with respect to the weight of the light guide plate formed in the cavity forming portion. Light plate mold. The cross-sectional area of the sprue injection hole when molding a light guide plate having a molded product volume of 7.8 cm ³ or less is 5.31 mm ² or less, and the cross-sectional area of the runner connection portion is 10.17 mm ² or less. The molding die for the light guide plate according to claim 1, wherein In the light guide plate forming method of forming the light guide plate in the cavity forming portion formed between the fixed mold and the movable mold,
A cavity forming portion capable of compression-molding the light guide plate, a sprue bush connected to the cavity forming portion via a runner forming portion, and a cooling medium disposed around the sprue bush and cooling the cavity forming portion A cooling medium flow path independent of the flow path,
The weight of the sprue formed by the inner hole of the sprue bush is 1.4 to 6.1% by weight with respect to the weight of the light guide plate formed in the cavity forming portion. A light guide plate is formed by injecting molten resin into a cavity through a mold. The cross-sectional area of the sprue injection hole when molding a light guide plate having a molded product volume of 7.8 cm ³ or less is 5.31 mm ² or less, and the cross-sectional area of the runner connection portion is 10.17 mm ² or less. The method for forming a light guide plate according to claim 3.