JP5071794B2 - Injection press molding method for thin plate-shaped optical moldings - Google Patents

Description

  The present invention relates to an injection press molding method for a thin plate-shaped optical molded product, and particularly suitable for molding a thin plate-shaped optical molded product to be an optical product such as a light guide plate disposed on the back surface of a liquid crystal display device. The present invention relates to an injection press molding method.

  As a thin optical product, for example, in an electronic device such as a mobile phone, a light guide plate is disposed to guide light from a light source to the back surface of a liquid crystal display device. In the case of molding a thin plate-shaped optical molded product that becomes an optical product such as a light guide plate, not only is there a lack of filling, but the yield is good, as well as sinks, warps, and residuals that cause uneven brightness. There is no stress or the like, and it is required to mold the optical characteristics well. In addition, if the shape is transferred to the surface of an optical molded product by patterning or roughening the surface of the cavity or placing a stamper, etc., the shape is transferred with high accuracy. Therefore, it is required to have good yield and good optical characteristics.

  In order to satisfy these requirements, in the conventional injection molding, as a countermeasure against insufficient filling, the injection speed of the molding material into the cavity is set high, for example, 600 mm / sec to 1000 mm / sec. .

  In addition, it is also conventionally known to mold a thin plate-like optical molded product that becomes an optical product by using injection molding or an injection compression molding method or injection press molding method (injection compression molding) which is one of the fields. Here, the injection compression molding method is a method in which a molding material is injected and filled in a cavity with the mold closed, the mold is allowed to open by a predetermined amount by the pressure of the injection filling, and the mold is clamped again. Thus, the molding material is compressed. In the injection press molding, a molding material is injected and filled into a cavity with a predetermined amount of the mold opened, and the molding material is clamped at a predetermined timing to compress the molding material. For example, Patent Document 1 and Patent Document 2 disclose conventional techniques for injection press molding.

  Patent Document 1 particularly relates to a method of forming a light guide plate used for a surface light emitting device of a liquid crystal monitor having a maximum wall thickness of 4 mm or more or an uneven wall thickness of 15 inches or more (0001). Patent Document 1 discloses that when a thermoplastic resin is injection-molded, the mold cavity is opened in excess in the thickness direction, and the volume of the cavity is 1.09 times or more and 1.20 times or less. The resin is injected in an amount, and the mold starts to be compressed while the molten resin in the cavity exceeds the solidification temperature to fill the mold cavity. The mold clamping force is weakened when it becomes 1.005 times or more and 1.07 times or less with respect to the volume of the mold, and after further compression with weakened mold clamping force or weaker mold clamping force, cooling and solidifying Further, an injection compression molding method (in the present invention, referred to as an injection press molding method as described above) characterized by opening a mold and taking out a molded product is disclosed.

  Further, Patent Document 1 states that “the cylinder temperature is 240 ° C., the mold temperature is 60 ° C., the filling time is 5 seconds, and the gate seal seals the resin supply by closing the shut-off mechanism of the nozzle after completion of the injection. Used a light guide plate mold 1 having a six-sided mirror surface, and the mold cavity was opened with a force of 285 t, and the opening amount was 1 mm (16 mm for the maximum thickness of the mold cavity of 6.0 mm). The force of 285t was stopped at the mold at the position of 6% extra opening) Next, carbon dioxide gas was injected into this extra open mold cavity from the PL surface at a pressure of 2 MPa from 2 seconds before the acrylic resin was injected. Acrylic resin was injected 1.12 times the volume of the original mold cavity, and when the injection was completed 99%, the mold clamping force was compressed at 285 t. Finished After the mold cavity is filled, when the opening amount of the mold cavity is 0.3 mm (1.05 times the volume of the mold cavity), the mold clamping force is reduced to 150 t, and the compression is continued. It was allowed to cool and solidify for 2 seconds, and then the mold was opened and taken out. At this time, the time from the start of injection until the mold was opened and taken out was 2 minutes. ”(0034).

  Further, in Patent Document 2, in a method for manufacturing a plate-shaped light guide plate made of a transparent plastic member that constitutes a planar light source unit, a metal plate in a resin molding machine is preliminarily heated and softened in a substantially strip-shaped resin sheet. Production of a light guide plate characterized by forming a light guide plate of a desired shape by inserting into a product cavity disposed in a mold and then compressing and molding for a predetermined time and discharging the cooled and solidified molded product A method is disclosed.

  Patent Document 2 discloses that in normal injection molding in which a molten resin (molding material) heated and melted is filled and injected into a mold and then cooled and solidified, the product thickness is, for example, 0.6 mm or less. The thinner it becomes, the more insufficient filling and sinking occur ”(0008), and“ as the molding material, the resin sheet 1A is compressed and molded in the mold, so that the resin does not flow in conventional injection molding. Such a thin product, for example, a product having a thickness of 0.3 mm or less has been made possible "(0014).

JP 2000-229343 A JP 2001-191348 A

  However, among the above conventional techniques, in the case of injection molding, when the injection speed of the molding material into the cavity is set fast, for example, set to 600 mm / sec to 1000 mm / sec, as a countermeasure for insufficient filling, FIG. As shown in FIG. 1, there is a big problem that the residual stress in the vicinity of the gate portion becomes non-uniform. When the residual stress is large, the light guide plate having a small thickness is likely to be warped, and there is a problem in optical characteristics such as luminance distribution. Conventionally, there has been a problem that by increasing the injection speed, defects such as silver and burn are likely to occur.

  Furthermore, in the conventional technique for setting the injection speed of the molding material into the cavity fast as described above, the injection device including the heating cylinder and the screw must be enlarged in order to obtain the injection speed. There was a problem such as cost. As disclosed in Patent Document 1 and the like, particularly in the injection press molding method, the mold clamping device for clamping against the injection filling speed must be increased in size and further costly. There was a problem.

  In addition, when the injection speed of the molding material into the cavity is set to be high, it is generally necessary to use a sprue or runner having a relatively large cross-sectional area in order to suppress pressure loss. The cross-sectional area of the molding material in the runner also increases, it takes time for the temperature to drop and solidify, and a cooling time of, for example, 10 seconds or more is required, which increases the molding cycle and makes it difficult to improve productivity. There were also problems such as becoming.

  Of the conventional techniques described above, Patent Document 1 relates to a method for forming a light guide plate used in a surface light emitting device of a liquid crystal monitor having a maximum thickness of 4 mm or more or an uneven thickness of 15 inches or more. As described in Patent Document 2 (“0008”), it is described that “the thinner the product is, for example, 0.6 mm or less, the less filling or sinking occurs”. Based on the inventions described in (2) and (2), it was not possible to mold a comparatively thin plate-like optical molded product, particularly a light guide plate for use in a mobile phone or the like, to be molded. Patent Document 1 for forming such a relatively thick and large light guide plate (it is unknown whether it is a diagonal dimension in the plane direction or the length of one side is 15 inches) Compared with the present invention for forming a relatively small and thin light guide plate (for example, the diagonal dimension in the plane direction is 3 inches and the plate thickness is 0.3 mm). However, in Patent Document 1, it takes 2 minutes from the start of injection until the mold is opened and taken out (0034), and it takes a long time for one molding cycle, and it is hoped that productivity can be improved. There wasn't.

  Further, among the above conventional techniques, in Patent Document 2, when forming a thin light guide plate of 0.6 mm or less, it is molded as a molding material in order to eliminate insufficient filling and sinks that cause poor optical characteristics. A resin sheet that is slightly thicker than the thickness of the light guide plate to be molded is molded in advance, and is not injection molding in which a molten molding material is injected and filled into the cavity. This is not injection press molding in which a molding material is injected and filled, and a mold is clamped at a predetermined timing to compress the molding material. And in patent document 2, it is necessary to shape | mold a molding material in a sheet form beforehand, and also it is necessary to prepare the resin sheet of the thickness according to the thickness of the light-guide plate to shape | mold, When the light guide plate is formed, the thickness of the resin sheet must be changed, which causes a problem such as labor and cost. Further, in Patent Document 2, it is necessary to heat and soften the molding material once after being molded into a sheet shape before molding in the mold, and there is a problem that it takes time and cost.

  The present invention has been made in view of the above-described problems. For example, a relatively thin plate shape such as a sidelight type light guide plate for a mobile phone having a diagonal dimension of 3 inches in a planar direction, a thickness of 0.3 mm, and a uniform thickness. It is an object of the present invention to provide an injection press molding method for a thin plate-like optical molded product that can be molded with good yield, good optical characteristics, and can be molded at a short molding cycle and at a low cost. And

In order to achieve the above object, the invention according to claim 1 injects and fills the molding material into the cavity with a predetermined amount of the mold opened, and clamps the mold with a mold clamping device to inject into the cavity. An injection press molding method for molding a thin plate-like optical molded article by injection press molding for compressing the molded material, and increasing the pressure from the start of compression of the molding material until reaching a set clamping force Clamping is performed at a mold clamping speed set based on time and the amount of mold opening at the start of injection.
In order to achieve the above object, the invention according to claim 2 is characterized in that, in the invention according to claim 1, the mold clamping is performed at a mold clamping speed of 5.7 to 25.0 mm / sec. is there.
In order to achieve the above object, the invention according to claim 3 is the invention according to any one of claims 1 and 2, wherein the thickness of the thin plate-like optical molded product is formed to 0.2 to 0.7 mm. It is characterized by doing.
According to a fourth aspect of the present invention, in order to achieve the above object, in the invention according to any one of the first to third aspects, the mold clamping device is positioned by detecting the position of the mold before starting compression. By controlling, the mold is stopped at a position where the mold is opened by a predetermined amount, and after the start of compression, the mold clamping force is detected and the mold clamping force is controlled.
In order to achieve the above object, the invention according to claim 5 is the mold clamping force according to any one of claims 1 to 4, wherein the pressure exerted on the molding material in the cavity is 25 to 80 MPa. It is characterized by controlling.

According to the first aspect of the present invention, the mold is clamped at a mold clamping speed set based on the pressurization time from the start of compression of the molding material until reaching the set mold clamping force and the amount of mold opening at the start of the injection. By clamping, the molding material injected and filled into the cavity with the mold opened by a predetermined amount can be clamped at an appropriate speed by the clamping device to compress the molding material in the cavity. A relatively thin plate-like optical molded article can be molded in a short molding cycle with reduced cost, good yield, good optical characteristics.
According to a second aspect of the invention, in the first aspect of the invention, the mold clamping in the cavity is appropriately compressed by performing the mold clamping at a mold clamping speed of 5.7 to 25.0 mm / sec. Therefore, a relatively thin plate-like optical molded article can be molded with good cost and good yield and good optical characteristics.
According to the invention of claim 3, in the invention according to claim 1 or 2, a thin plate-like optical molded product having a plate thickness of 0.2 to 0.7 mm can be manufactured at a reduced yield. Therefore, the optical characteristics can be molded well.
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the mold clamping device detects the position of the mold and controls the position of the mold before starting the compression. Is stopped at a position where the mold opens for a predetermined amount, and after starting compression, the mold clamping force is detected and the mold clamping force is controlled to maintain the set mold clamping force. The tightening force can be accurately controlled. Therefore, a comparatively thin plate-like optical molded article can be molded at a low cost, with a good yield, and with good optical characteristics.
According to the invention of claim 5, in the invention according to any one of claims 1 to 4, by controlling the clamping force so that the pressure exerted on the molding material in the cavity is 25 to 80 MPa, The molding material in the cavity can be compressed with an appropriate clamping force. Therefore, a relatively thin plate-like optical molded article can be molded at a low cost, with a high yield and good optical properties. be able to.

  An embodiment of an injection press molding method for a thin plate-like optical molded product according to the present invention is an example of a thin plate-shaped optical molded product having a diagonal size of 3 inches in a plane direction and a thickness of 0.2 to 0.3 mm. The case of forming a side-light type light guide plate for a cellular phone having a plate thickness will be described in detail with reference to the drawings. In the drawings, the same reference numerals are given to similar or corresponding parts.

  Initially, the structure of the injection molding machine 1 used for the injection press molding method of the thin plate-shaped optical molded product of this embodiment will be described. FIG. 1 is a front view of an injection molding machine 1 used in an injection press molding method for a thin plate-like optical molded article of the present embodiment. FIG. 2 is a system diagram shown for explaining an example of the mold clamping device 5 of the injection molding machine 1 used in the injection press molding method of the thin plate-like optical molded article of the present embodiment. FIG. 3 is a cross-sectional view of a molding die 11 used in the injection press molding method for a thin plate-like optical molded article of the present embodiment, and shows a state where the movable die 12 is stopped at a position before the start of injection. is there. FIG. 4 is a cross-sectional view of a molding die 11 used in the injection press molding method for a thin plate-like optical molded article of the present embodiment, and shows a state in which the resin in the cavity 14 is compressed. FIG. 5 is a cross-sectional view of the molding die 11 used in the injection press molding method for the thin plate-like optical molded article of the present embodiment and shows a state where the gate is cut. FIG. 6 is a chart for illustrating an injection press molding method for a thin plate-like optical molded product of the present embodiment. FIG. 7 is a graph showing the position of the movable mold 12 and the change with time of the clamping force shown for explaining the injection press molding method of the thin plate-like optical molded article of the present embodiment. . FIG. 8 shows a light guide plate formed by the injection press molding method of this embodiment. FIG. 9 is a test result showing the relationship between the injection speed and the resin temperature when a light guide plate having a thickness of 0.3 mm is formed by injection press molding. FIG. 10 shows test results showing the relationship between the injection speed and the resin temperature when a light guide plate having a thickness of 0.2 mm is formed by injection press molding. FIG. 11 is a test result showing the relationship between the injection speed and the mold opening amount at the start of injection. FIG. 12 shows test results showing the relationship between the pressurization time at the start of mold clamping and transferability.

  As shown in FIG. 1, an injection molding machine 1 used in an injection press molding method of a thin plate-like optical molded product according to this embodiment includes an injection device 3 for plasticizing and melting a molding material and injecting a predetermined amount, and molding. A mold clamping device 5 that opens and closes the mold 11 and clamps the mold 11 with a predetermined pressure is provided.

  The injection device 3 has a screw (not shown) inserted in the heating cylinder 2a so as to be rotatable about an axis and capable of moving forward and backward in the axial direction, and a predetermined amount of plasticized and melted molding material Is provided at the tip of the heating cylinder 2 a and is disposed on the bed 4. The injection device 3 is controlled by a metering servo motor of a metering mechanism (not shown) and an injection servo motor of the injection mechanism, and the molding speed is determined by the rotational speed of the screw in the heating cylinder 2a, the backward and forward positions of the screw, and the forward movement of the screw. The injection speed, holding pressure switching position, holding pressure, injection amount, etc. are controlled. In this embodiment, the diameter of the screw is 28 mm. In addition, the injection device 3 using a servo motor as described above is preferably used, but it may also be a hydraulic mechanism.

  A fixed plate 6 and a pressure receiving plate 7 are fixedly arranged on the bed 4, and tie bars 8 are arranged at the corners of the fixed plate 6 and the pressure receiving plate 7, respectively. The board 9 is slidably inserted. As shown in FIG. 2, the mold clamping device 5 in this embodiment includes a mold clamping cylinder 10 that drives the movable plate 9 to move toward and away from the fixed plate 6, and the mold clamping cylinder 10. A driving device 200 that supplies hydraulic oil to drive the ram 10a to extend and retract, and a control device 300 that controls supply of the hydraulic oil to the clamping cylinder 10 by the driving device 200 are provided. A mold clamping cylinder 10 is disposed on the pressure receiving plate 7, and a ram 10 a of the mold clamping cylinder 10 is fixed to the back surface of the movable plate 9.

  In this embodiment, as shown in FIG. 2, a booster ram type clamping device 5 is employed. At the base end portion of the ram 10a, a flange portion 10b that is slidably inserted into the mold clamping cylinder 10 to form a main mold clamping drive cylinder chamber 114a and a mold opening drive cylinder chamber 115 is formed. Further, a booster cylinder ram chamber 114b into which a booster ram 113 provided inside the mold clamping cylinder 10 is inserted is formed on the base end surface of the ram 10a. In addition, pressure detectors 121a, 121b, and 121c are disposed on the pipes that send hydraulic oil to the main mold clamping drive cylinder chamber 114a, the booster cylinder ram chamber 114b, and the mold opening drive cylinder chamber 115, respectively. It is connected.

  A driving device 200 for supplying hydraulic oil to the mold clamping cylinder 10 includes a tank 130 that stores the hydraulic oil, a pump 128 that pumps the hydraulic oil stored in the tank 130, and the hydraulic oil that is pumped by the pump 128. An accumulator 123 for temporarily storing and supplying at a predetermined pressure, and a servo valve 118 for switching and supplying hydraulic oil from the accumulator 123 to predetermined cylinder chambers 114a, 114b, and 115 of the clamping cylinder 10 are provided. Yes.

  The pump 128 sucks and pressurizes the hydraulic oil stored in the tank 130 and discharges the hydraulic oil. An AC induction motor is preferably employed as the motor 129 that rotationally drives the pump 128. A relief valve 125 is connected to the tank 130, and a switching valve 126 that is ON / OFF controlled by a signal from the control device 300 is connected to the control port 132 of the relief valve 125. When the switching valve 126 is OFF (the switching state shown in FIG. 2), the control port 132 communicates with the tank 130 and the control port 132 becomes no pressure. Therefore, the relief valve 125 discharges all the hydraulic oil discharged from the pump 128. It will be returned to the tank 130. On the other hand, when the switching valve 126 is ON, the control port 132 is shut off, and the control port 132 is controlled to the hydraulic pressure manually set in the relief valve 125 in advance, so that the hydraulic oil discharged from the pump 128 by the relief valve 125 is controlled. Is limited to a predetermined hydraulic pressure. That is, when the switching valve 126 is ON, the pump 128 is in a load state, and the entire amount of the discharge hydraulic oil of the pump 128 flows out to the pipe line 122 through the check valve 124 until the set pressure of the relief valve 125 is reached. Is accumulated. When the hydraulic oil pressure reaches the set pressure of the relief valve 125, excess hydraulic oil is returned to the tank 130 through the relief valve 125.

  An accumulator 123, a pressure detector 121 d constituting a sensor for detecting a mold clamping force, and a cartridge valve 119 are connected to the pipe line 122. The accumulator 123 is composed of a rubber bag or a cylinder and a piston, and pressurizes the hydraulic oil stored in the rubber bag or the cylinder with the pressure of nitrogen gas to discharge the hydraulic oil. The pressure detector 121 transmits an electric signal of the pressure of hydraulic oil supplied to the clamping cylinder 10 converted by a strain gauge or a semiconductor to the control device 300 or the like. The pressure detector 121d or the control device 300 has two set values of low pressure and high pressure, and turns on the switching valve 126 when the pressure by the accumulator 123, that is, the pressure of the hydraulic fluid in the pipe 122 drops to the low pressure set value. Then, the control valve 126 is controlled to be turned off when the pressure of the hydraulic oil in the pipe line 122 rises to a high pressure set value. That is, the hydraulic oil discharged from the pump 128 is accumulated in the accumulator 123 while the switching valve 126 is ON.

  The cartridge valve 119 is a check valve that can be controlled to be opened and closed by the switching valve 120. The cartridge valve 119 is closed when the switching valve 120 is OFF, and is opened when the switching valve 120 is ON. The outlet of the cartridge valve 119 is connected to the inlet P port of the servo valve 118. Accordingly, the hydraulic oil discharged from the accumulator 123 is supplied to the mold clamping cylinder 10 via the pipe line 122, the cartridge valve 119 and the servo valve 118. When hydraulic oil is supplied from the booster ram 113 to the booster cylinder ram chamber 114b and the mold is closed and the movable mold 12 comes into contact with the fixed mold 13, the switching valve 116 is turned on to operate the main mold clamping drive cylinder chamber 114a. Supply oil and clamp. At this time, since the check valve 117 provided between the main clamping drive cylinder chamber 114a and the tank 130 is in the reverse direction from the main clamping drive cylinder chamber 114a, the hydraulic oil in the main clamping drive cylinder chamber 114a is retained. The After the injection process of the molten resin into the cavity 14 in the mold 11 and the solidification / cooling process of the molten resin injected into the mold are completed, the servo valve 118 depressurizes the main mold clamping drive cylinder chamber 114a. The servo valve 118 supplies the hydraulic oil to the mold opening drive cylinder chamber 115 to perform mold opening. At this time, the check valve 117 is controlled to forcibly open, and the hydraulic oil in the main mold clamping drive cylinder chamber 114 a returns to the tank 130.

  The pressure of the hydraulic oil supplied to the mold clamping cylinder 10 from the accumulator 123 via the servo valve 118 is detected by the pressure detectors 121a and 121b. The position of the movable platen 9 to which the movable mold 12 is attached (the amount of extension of the ram 10a) is detected by a sensor (not shown) such as a linear scale. Based on the detection results of these sensors, the mold clamping cylinder 10 of the mold clamping device 5 stops the movable platen 9 before injection filling of the molding material (that is, the mold opening amount), the mold clamping start timing, the mold clamping. The mold clamping speed, mold clamping force, and the amount by which the movable platen 9 moves backward by the pressure generated by injecting the molding material of the injection device 3 are controlled. The mold clamping device 5 in this embodiment is an example of the mold clamping cylinder 10 controlled by the servo valve 118, but may be a toggle mechanism operated by a servo motor and a ball screw mechanism or the like.

The light guide plate molding die 11 in this embodiment is formed by injection press molding a mobile phone sidelight type light guide plate having a diagonal dimension in the plane direction of 3 inches, a plate thickness of, for example, 0.3 mm, and a uniform plate thickness. (Hereafter, the side light type light guide plate for mobile phones is simply abbreviated as the light guide plate P).
As shown in cross-sectional views in FIGS. 3 to 5, the molding die 11 is composed of a movable die 12 that is a first die and a fixed die 13 that is a second die. A cavity 14 having a variable volume and thickness is formed between the molds 12 and 13. In the present invention, the light guide plate P having a plate thickness of about 0.2 mm to 0.7 mm and a diagonal size of about 1.5 to 13 inches (including those having round corners) can be formed.

  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 facing the fixed mold 13 is a cavity forming surface 16a that is a mirror surface and forms a light exit 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 surface 16a. In addition, the part which forms the cavity formation surface of a core part, and another part may consist of a separate block. In addition, although the cavity forming surface 16a is an example of a mirror surface, the cavity forming surface 16a may be subjected to pattern processing such as dots, grooves, holograms, or rough surface processing, and does not exclude those having a stamper attached thereto.

  Concave portions are formed at four positions on the surface of the mold main body 15 on the fixed mold 13 side, and springs 18 are attached to the fixed mold 13 side in the concave portions. Then, the fixed mold 13 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. In the case of the embodiment shown in FIGS. 3 to 4, the gate P <b> 3 is formed between the lower portion of the cavity 14 and the runner P <b> 2, i.e., at a position that becomes the end face of the light guide plate P to be molded. A light incident surface forming block 20 for forming a light incident surface is detachably disposed on the opposite side of the movable frame portion 19 to the gate P3. FIG. 3 shows a state in which the movable mold 12 is stopped at a position before the start of injection. FIG. 4 shows a state in which a molten resin (not shown) in the cavity 14 is compressed after the start of injection. Further, FIG. 5 shows a state where the gate is cut. In FIGS. 3 to 5, the positional relationship between the core portion 16 and the movable frame portion 19, the contraction of the spring, and the like are exaggerated from the actual values. By injecting a molding material into the cavity through a gate provided at a position opposite to the light incident surface of the light guide plate P, the light guide plate P having good optical characteristics can be formed. it can.

  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 an ejector plate 22 of an 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 body 15 and the core 16, and its tip faces the runner forming surface 32, so that the sprue P 1 and the runner P 2 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.

  In addition, a hole 25 and a space 26 for disposing the gate cutter member 24 are formed inside the mold body 15. On the other hand, guide pins 27 are disposed in the holes 25 of the mold body 15. The guide pin 27 is supported by a ball guide 28 provided in contact with the hole 25. When the guide pin 27 moves back and forth, the ball of the ball guide 28 rolls to keep the guide pin 27 core. While being moved. A disc-shaped plate 29 is disposed in the space 26 of the mold main body 15 so that the guide pin 27 is brought into contact therewith. A gate cutter member 24 is inserted and engaged from the movable platen 9 side at the center of the plate 29 on the fixed platen 6 side. The gate cutter member 24 is formed of a rectangular thin plate, and is disposed in the hole 31 having a rectangular cross section of the core portion 16 so as to be movable forward and backward. The front surface (tip surface) of the gate cutter member 24 is a gate forming surface, and the corner on the cavity side (upper side in the figure) is a gate cutter 24b for cutting the molten gate. And as FIG. 5 shows, a part of side surface by the side of the cavity in the said gate cutter member 24 comprises a cavity formation surface after a gate cut. The base 24d of the gate cutter member 24 has a cylindrical shape, and a spring 30 is provided in the space 26 so as to urge the plate 29 and the gate cutter member 24 toward the movable platen 9 around the base 24d. It is arranged. In the present embodiment, the gate cutter member 24 is made of a hard metal member such as high-speed steel having a Rockwell C scale hardness of 55 to 65 HRC. The dimensions of the gate cutter member 24 are such that the width in the direction perpendicular to the flow direction of the molten resin is 10 to 20 mm, and the thickness in the flow direction of the molten resin is about 1.2 to 2.0 mm. It is desirable when the light guide plate P having a size 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. When the gate cutter driving device is a servo motor, position control or speed control of the gate cutter member 24 is performed. The forward stop position of the gate cutter member 24 may be adjusted by disposing a stopper block or shim in the movable mold 12 and replacing the stopper block with a stopper block having a different thickness.

  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 surface 32. A rectangular hole 31 through which the gate cutter member 24 advances and retreats is formed between the runner forming surface 32 and the cavity forming surface 16a, and the gap between the hole 31 and the gate cutter member 24 is an interval at which no resin enters. Is formed. Further, with respect to the runner forming surface 32, a convex portion is formed at 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 surface of the gate cutter member 24 is located at a position lower than the convex portion (on the movable platen 9 side) except when protruding. The reason is that the resin solidified at the end of the passage of the nozzle 2b of the injection device 3 is not received by the cold slug well-shaped recess during injection, and the injection pressure of the gate cutter member 24 This is to prevent the occurrence of burrs or the like between the front surface and the hole 31. The runner and the gate may be linearly connected to the cavity.

  A cooling medium flow path 33 is formed around the protrusion pin 23 and in the vicinity of the gate cutter member 24. An air passage 34 through which air is blown at the time of mold release is formed between the core portion 16 and the movable frame portion 19. The air passage 34 may also be provided between the gate cutter member 24 and the hole 31. Note that the gate cutter member 24 is not necessary when the light guide plate P and the sprue P1, etc. are grasped and taken out, and the gate cutter member 24 is not essential in the present invention.

  Next, the fixed mold 13 will be described. As shown in FIGS. 3 to 5, 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 member 45, the contact block 46, and the like are formed. A heat insulating plate 47 is attached to the fixed plate 6 side of the mold main body 41 and a hole 48 into which the nozzle 2b (see FIG. 1) of the injection device 3 is inserted is formed around the locating ring. 49 is attached. A cavity forming block 42 is attached to the mold body 41 on the movable mold 12 side, and a surface of the cavity forming block 42 facing the movable mold 12 is a cavity forming surface 42a. In the present embodiment, the cavity forming surface 42a is a portion that forms the reflecting surface of the light guide plate P, and fine dots are engraved therein. A plurality of cooling medium channels 50 are formed in the cavity forming block 42 in parallel with the cavity forming surface 42a. Further, 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. The insert block 43 has a sprue bush 44 provided with a hole whose diameter is increased toward the movable platen 9 at the center thereof. A cooling medium flow path 51 for cooling the sprue P1 and the runner P2 is formed around the sprue bush 44. As shown in FIGS. 3 to 5, a runner forming surface 54 is formed on the surface of the insert block 43 facing the movable mold 12 from the tip of the sprue bush 44 toward the cavity forming surface. . The runner forming surface 54 is formed in a groove-like lower position (position on the stationary platen 6 side) on the contact surface 46 a of the contact block 46, and together with the runner formation surface of the contact block 46, the fixed mold 13 side. The surface that forms the runner P2 is formed. The width of the runner forming surface 54 in the direction orthogonal to the flowing direction of the molten resin gradually increases from the portion adjacent to the sprue bush 44 toward the cavity 14. The runner forming surface 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 surface 32 of the movable mold 12.

  The concave portion of the runner formation surface 54 is connected to the gate formation surface on the same continuous surface. Therefore, there is no clear distinction between the runner P2 and the gate P3 and their formation surface. Of the continuous same surface, a portion facing the gate forming surface of the gate cutter member 24 of the movable mold 12 is a portion forming the fixed mold gate forming surface. A gate forming surface is formed continuously with the runner forming surface of the contact block 46. The gate forming surface is provided at a position (position on the fixed platen side) that is one step lower than the cavity forming surface 42a and the gate cutter member 45, which will be described later, and the convex portion. And the width | variety of the direction orthogonal to the flow direction of the molten resin of the gate formation surface is provided more widely than the diameter of the sprue P1. Therefore, the gate P3 of the present 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 P. ).

  A gate cutter member 45 is fixed between the gate forming surface connected to the runner forming surface 54 of the insert block 43 and the cavity forming surface 42 a of the cavity forming block 42. The gate cutter member 45 is a rectangular thin plate made of a hard metal member such as alloy tool steel (SKD steel) having a Rockwell C scale hardness of 55 to 63 HRC, and has a higher hardness than the member forming the cavity forming surface 42a. Is used. The width of the gate cutter member 45 in the direction perpendicular to the flow direction of the molten resin is the same as or slightly wider than the gate forming surface. The thickness of the gate cutter member 45 is about 0.4 to 0.8 mm. The front surface (tip surface) of the gate cutter member 45 is opposed to the cavity forming surface 16a and is a part of the cavity forming surface. Further, a gate cutter 45b in which a corner portion on the gate portion side of the gate cutter member 45 is a blade is formed. The surface on the gate portion side is a surface where the gate cutter member 24 of the movable mold 12 faces with a slight gap when moving forward. Therefore, the distance of the gate forming surface of the present embodiment is variable by the advancement / retraction of the movable mold 12 as well as the distance of the cavity 14 of the fixed mold 13 and the movable mold 12, and further by the forward / backward movement of the gate cutter member 24. Is also variable.

Next, when using the injection molding machine configured as described above, a light guide plate P having an arbitrary plate thickness of 3 inches in a planar direction and a plate thickness of 0.2 to 0.7 mm is formed. The injection press molding method for the thin plate-like optical molded product of the present embodiment will be described.
The injection press molding method for a thin plate-like optical molded product according to the present invention is roughly performed by injecting and filling a molding material into the cavity 14 with a predetermined amount of the mold 11 opened, and clamping by the mold clamping device 5. The injection molding is performed to compress the molding material injected into the cavity 14 to form a thin plate-like optical molded product, and the mold clamping force set from the start of molding material compression is reached. The mold is clamped at a mold clamping speed set based on the pressurizing time until completion and the amount of mold opening at the start of injection.

FIG. 6 is a chart diagram showing an outline of the injection press molding method of the present embodiment in the case of forming a light guide plate P having an equal plate thickness of 3 inches in a planar direction and a thickness of 0.3 mm. 7 is a graph showing a change in mold opening amount and a change in mold clamping pressure of the movable mold 12 with respect to the fixed mold 13 by the mold clamping device 5.
As shown in FIG. 6, in this embodiment, a light guide plate P having an equal thickness of 3 inches (area of about 27 cm ² ) and a thickness of 0.3 mm is formed in a planar cycle time of 4.2 seconds in this embodiment. is doing. The breakdown is a mold opening / closing time (including a mold opening time, a removal time, and a mold closing time) of 1.4 seconds and a total time of 2.8 seconds for injection / holding pressure and mold clamping. For this reason, in this embodiment, the cooling medium flow path 17 for cooling the cavity forming surface 16a of the movable mold 12, the cooling medium flow path 33 for cooling the vicinity of the protrusion pin 23 and the runner forming surface 32, and the cavity formation of the fixed mold 13 are formed. From the glass transition temperature Tg of polycarbonate, which is a resin to be molded, to the cooling medium flow path 50 for cooling the surface 42a, the cooling medium flow path 51 for cooling the vicinity of the sprue bush 44 and the runner formation surface 54 by a temperature controller. A cooling medium (cooling water) whose temperature is controlled to about 80 to 120 ° C., which is about 70 ° C. lower, is flowing.

  The temperature of the front zone (zone closest to the nozzle 2b) of the heating cylinder 2a of the injection apparatus 3 is set to 360 ° C., and a molten resin of polycarbonate is measured as a molding material. Then, the mold clamping cylinder 10 is actuated to move the movable mold 12 attached to the movable plate 9 closer to the fixed mold 13 attached to the fixed plate 6. Then, when it is detected by a sensor such as a linear scale (not shown) that the movable mold 12 is in a stop position where the mold opening amount at the start of injection is secured, the movement of the movable mold 12 is controlled to stop. That is, from the start of mold clamping until it is stopped at a position where the predetermined mold opening amount is reached, the position of the movable mold 12 is detected, and position control for controlling the movement of the movable mold 12 is performed based on the result. At that time, the position A (FIG. 7) at the start of injection of the movable plate 9 and the core portion 16 of the movable mold 12 is such that the distance between the cavity forming surface 16a of the movable mold 12 and the cavity forming surface 42a of the fixed mold 13 is the same. Stop control is performed at a position obtained by adding a predetermined mold opening amount to the thickness of the light guide plate P to be molded. When the movable platen 9 and the core portion 16 of the movable mold 12 are stopped at the position A at the start of injection, the movable plate 9 and the core portion 16 of the movable die 12 are moved by the mold clamping cylinder 10 of the mold clamping device 5. It is sealed in the main mold clamping drive cylinder chamber 114a and the booster cylinder ram chamber 114b so that the position does not retreat by receiving the injection pressure of the molding material (retraction amount 0 mm) or the retraction amount is at most 0.05 mm. The pressure detectors 121a, 121b, 121c, so that the force for moving the ram 10a forward by the hydraulic oil introduced and the force for moving the ram 10a backward by the hydraulic oil sealed in the mold opening drive cylinder chamber 115 are balanced. The servo valve 118 and the control device 300 are controlled.

  At this time, the core portion 16 is once advanced to the most advanced position (the fixed mold 13 side further than the light guide plate thickness), the spring 18 is contracted, and the movable frame portion 19 and the mold main body portion 15 are brought into contact with each other. The movable platen 9 and the like are moved forward to the mold closing completion position (0 position) to be contacted, and then the movable platen 9 and the like are moved back by a small amount again by the mold clamping cylinder 10 to control the position to the position A at the start of injection in FIG. May be stopped. 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.

  Further, the inside of the cavity 14 may be decompressed before the start of injection. When the inside of the cavity 14 is depressurized before the start of injection, the molten resin can flow quickly to the end on the light incident surface forming block 20 side without receiving air resistance in the cavity 14 at the time of injection. Therefore, this is particularly effective when a thin light guide plate P having a thickness of 0.2 to 0.3 mm is formed. Furthermore, for the same purpose, the parting surface may be slightly opened at the start of injection without making the inside of the cavity 14 decompressed, so that the air in the cavity 14 can be easily released.

  Next, when a predetermined injection delay time elapses, an injection mechanism (not shown) of the injection device 3 is operated to advance the screw in the heating cylinder 2a to inject the molten resin. In the present embodiment, the injection speed is set to about 200 to 550 mm / sec, preferably 300 to 400 mm / sec at the peak, and the screw advance speed is controlled by an injection servo motor (not shown) of the injection apparatus 3. . In the prior art, the injection speed was set to 600 to 1000 mm / sec as a countermeasure against insufficient filling, whereas in the present invention, injection filling can be performed in the cavity 14 at such a relatively low injection speed. The internal stress in the vicinity of the gate of the light guide plate P can be reduced. FIG. 8 shows a light guide plate P formed by the injection press molding method of this embodiment. FIG. 13 shows a light guide plate formed by a conventional method, and the internal stress in the vicinity of the gate is large.

FIG. 9 shows that when the light guide plate P having a plate thickness of 0.3 mm and a diagonal dimension of 3 inches is formed, the mold opening amount at the start of injection (the stop position of the movable mold 12 at the start of injection) is indicated as the light guide plate. It is a test result which shows the relationship between an injection speed and resin temperature in the case of carrying out injection press molding in the state which opened the plus 0.3 mm mold | die from P board thickness. In FIG. 9, the resin temperature indicates the set temperature of the front zone of the heating cylinder 2a. The injection speed indicates the set injection speed. The resin used throughout the test is polycarbonate (Teflon LC1500 from Idemitsu Kosan Co., Ltd .: molecular weight 10,000 to 12,000). According to the test, when the resin temperature was 330 ° C., the defect of the plate and the unevenness of the plate thickness due to insufficient filling (thin the portion farther from the gate) occurred at any injection speed. When the resin temperature is 340 ° C., the injection speed is 300 mm / sec or less, the resin temperature is 350 ° C., 360 ° C., the injection speed is 200 mm / sec or less, and the resin temperature is 370 ° C., the injection speed is 150 mm / sec or less. A defect due to insufficient filling occurred. When the resin temperature was 390 ° C. or higher, the resin deteriorated and yellowing occurred at any injection speed. Even in the range of 340 to 380 ° C., when the injection speed was 600 mm / sec, the injection speed was too high, yellowing or burring of the resin occurred due to shear heat generation, and the internal stress distribution was unfavorable. In contrast, when the resin temperature is 340 to 380 ° C., the injection speed is 350 to 550 mm / sec, when the resin temperature is 350 to 380 ° C., the injection speed is 300 to 550 mm / sec, and when the resin temperature is 370 to 380 ° C., the injection speed is 200 to 550 mm / sec. It was found that good products can be molded with Therefore, the molding by the injection press method of the light guide plate P having a plate thickness of 0.3 mm and a diagonal size of 3 inches is an injection speed of 200 to 550 mm / sec (preferably 300 to 450 mm / sec, more preferably 300 to 400 mm / sec), It is preferable to mold at a resin temperature (set temperature at the front of the heating cylinder 2a) of 350 to 380 ° C. Although molding is possible even when the injection speed exceeds 400 mm / sec and up to 550 mm / sec, the injection apparatus is increased in size and wasteful in terms of energy efficiency. In addition, when the plate | board thickness of the light-guide plate P to shape | mold is 0.3 mm, when an injection speed shall be 200 mm / sec, in order to ensure the fluidity | liquidity of the molten resin in a cavity, resin temperature (setting of the front part of the heating cylinder 2a) Good products cannot be molded unless the temperature is set to 370 to 380 ° C. Accordingly, 0.3 mm is the limit as the thickness of the light guide plate P having a diagonal size of 3 inches that can be molded at an injection speed of 200 mm / sec.
If possible, the resin temperature should not be raised too much from the viewpoints of burrs, optical characteristics, and economy. Regarding this condition, a light guide plate having a thickness of 0.3 to 0.7 mm can be similarly formed. The temperature of the cooling medium sent to the cooling medium channels 17 and 50 for cooling the cavity 14 is set to 110 ° C. The higher the temperature of the cooling medium, the better the flow of the molten resin in the cavity 14, but there is a problem that the molding cycle becomes longer.

  Next, FIG. 10 shows that when the light guide plate P having a thickness of 0.2 mm and a diagonal size of 3 inches is formed, the mold opening amount at the start of injection (the stop position of the movable mold at the start of injection) is determined by the plate. It is a test result which shows the relationship between the injection speed and the resin temperature when injection press molding is performed in a state where the mold is opened by plus 0.3 mm from the thickness. According to the test, when the resin temperature was 350 ° C., the defect of the plate due to insufficient filling and the uneven thickness of the plate (thin the portion farther from the gate) occurred at any injection speed. Further, even when the resin temperature was 360 to 380 ° C., defects due to insufficient filling occurred when the injection speed was 200 mm / sec or less. The reason for this is that when the plate thickness is less than 0.3 mm, the flowable cross-sectional area other than the skin layer formed by cooling and solidifying the molten resin in the cavity becomes small. This is because the resin becomes difficult to flow. As a countermeasure, it is effective to widen the cavity interval before injection, but the effect is limited when the plate thickness is less than 0.3 mm. The reason is that when the plate thickness is less than 0.3 mm, the injection filling amount of the molten resin itself is small, and the molten resin in the cavity is compressed by the mold clamping device and sent to the vicinity of the cavity end. This is because the distance between the cavities is narrowed to near the plate thickness of the molded product, and the molten resin cannot be injected and filled in a state where the distance between the cavities is widened to the end of the cavity. When the resin temperature was 390 ° C. or higher, the resin deteriorated and yellowing occurred at any injection speed. Even at 360 to 380 ° C., when the injection speed was 600 mm / sec, yellowing of the resin or burrs occurred due to shear heat generation, and the distribution of internal stress was not preferable. Therefore, molding of the light guide plate P having a thickness of 0.2 mm and a diagonal size of 3 inches by the injection press method is performed when the injection speed is 300 to 550 mm / sec and the set temperature of the front zone of the heating cylinder 2a is 360 to 380 ° C. Was found to be able to mold good products. In particular, when the plate thickness is less than 0.2 to 0.3 mm, the injection speed is more preferably 350 to 550 mm / sec. In addition, it is more desirable to set the temperature of the cooling medium sent to the cooling medium flow paths 17 and 50 for cooling the cavities as high as 100 to 120 ° C. in order to promote the flow of the molten resin. When the temperature of the molten resin is increased and the injection speed is increased, burrs are likely to occur in the gap between the core portion 16 and the movable frame portion 19 of the mold. Therefore, when the plate thickness is less than 0.2 to 0.3 mm, it is even more desirable to prevent the occurrence of burrs that require post-treatment, particularly by setting the gap of the gap portion to 5 to 10 μm.

Next, FIG. 11 shows the injection speed when the light guide plate P having a plate thickness of 0.3 mm and a diagonal dimension of 3 inches is injection press molded at a resin temperature (set temperature at the front of the heating cylinder) of 360 ° C. It is a test result about the relationship of the mold opening amount at the start of injection (the stop position of the movable mold at the start of injection). According to this test, when the mold opening amount at the start of injection is 0.1 mm, insufficient filling occurs at any injection speed, and when the mold opening amount is 0.6 mm or more, injection is performed at any injection speed. The formed resin could not be crushed completely, or a defect called a press mark was generated. Therefore, in this embodiment, the thickness of the light guide plate P to be molded is 0.3 mm, and the ratio of 0.2 mm, which is the minimum mold opening amount at the start of injection when a non-defective product can be molded, to the plate thickness of 0.3 mm Is 66.7%. The ratio of the maximum mold opening amount 0.5 mm at the start of injection at which a good product could be formed without generating a press mark to the plate thickness 0.3 mm was 166.7%.
Moreover, the mold opening amount at the start of injection required for the light guide plate P may be almost the same mold opening amount at the start of injection when the thickness of the light guide plate P is between 0.2 and 0.7 mm. It was found that the plate thickness of the light guide plate P and the mold opening amount at the start of injection are not proportional (however, when the diagonal dimension is 5 to 7 inches, the thickness less than 0.3 mm is excluded. (If the square dimension is 7 inches or more, the thickness less than 0.5 mm is excluded.) In the case of a diagonal size of 5 to 7 inches and a plate thickness of 0.3 to 0.5 mm, the injection speed is set to 350 similarly to the molding conditions of the light guide plate having a diagonal size of 3 inches and a plate thickness of 0.2 mm. ˜550 mm / sec. It is more preferable to mold at a resin temperature (set temperature at the front of the heating cylinder 2a) of 360 to 380 ° C.
The reason for this is that when the plate thickness is relatively small, the cross-sectional area of the cavity through which the molten resin can flow becomes smaller due to the formation of a skin layer on the cavity forming surface. This is because the mold opening amount needs to be higher. On the other hand, if the plate thickness is relatively thick, even if the skin layer is formed, the end of the cavity can be injected and filled relatively easily, so that the mold opening amount at the start of injection is not so much required. In addition, as the mold opening amount at the start of injection is increased with respect to the light guide plate P having a relatively thin plate thickness, the injection amount itself is smaller, and therefore it is necessary to speed up the mold clamping start timing after the start of injection. In this way, the mold opening amount at the start of injection is set to a ratio (wide interval) that cannot be assumed in the prior art, and the sheet thickness is extremely 0.2 mm to 0.7 mm by rapidly closing and increasing the pressure during or after injection. Even a thin light guide plate P can be injected and filled at a relatively low injection speed.

  When the injection is performed, the mold clamping force is held by position control so that the retraction amount from the stop position is 0 to a maximum of 0.05 mm as described above. As a result, the set mold opening amount is maintained, so that a light guide plate with good optical characteristics can be formed. After injection (substantially at the same time as injection completion) or immediately before injection completion, the mold clamping cylinder 10 of the mold clamping device 5 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 surface 16a of the movable mold 12 from the cavity forming surface 42a of the fixed mold 13 of the cavity 14 is shortened. The molten resin in 14 is compressed. In this embodiment, as shown in FIGS. 6 and 7, the mold clamping cylinder 10 is operated when the screw of the injection mechanism reaches 80 to 100%, preferably 85 to 95%, at the position with respect to the total forward travel. To start compression. Thereby, the injection of the molding material into the cavity and the compression of the molding material in the cavity can be appropriately performed. Therefore, the relatively thin light guide plate P has a good yield and good optical characteristics. Can be molded. At this time, the pressure of hydraulic fluid supplied to the clamping cylinder 10 is detected as the clamping force by the clamping cylinder 10 by the pressure detectors 121a, 121b, and 121c (FIG. 2). Based on this, the pressure of the mold clamping cylinder 10 is controlled, and the supply pressure of the hydraulic oil is controlled so that the setting is 130 kN (when converted into a single die). The mold clamping force is controlled so that this value is 25 to 80 MPa, more preferably 35 to 60 MPa in terms of the pressure exerted on the resin that is the molding material in the cavity 14. And when the said pressure exceeds 80 Mpa, it will become easy to generate | occur | produce a burr | flash in the light-guide plate shape | molded.

  FIG. 12 shows the relationship between the pressurization time during which the pressure is increased to the set pressure by mold clamping (see B in FIG. 7) and the transferability. For example, when a light guide plate P having a plate thickness of 0.3 mm and a diagonal size of 3 inches is boosted at a mold opening amount of 0.3 mm at the start of injection, a resin temperature (set temperature at the front of the heating cylinder) of 360 ° C., and a cavity temperature of 110 ° C. In the time of 0.040 seconds or more, insufficient transfer occurred. In 0.035 seconds, good transfer molding was possible. The pressurization time is preferably short, but in the mold clamping apparatus 5 of this embodiment, the pressurization time is limited to 0.020 seconds. The pressurization time means the time required for the mold clamping force to reach a set value after the mold clamping is started with a predetermined mold opening amount.

Here, when the mold opening amount at the start of injection is 0.2 mm which is the lower limit of the settable range, 0.2 mm ÷ 0.020 sec = 10 mm / sec when the pressurizing time is 0.020 seconds (clamping the mold) Speed 1)
Similarly, when the mold opening amount at the start of injection is 0.2 mm and the pressurizing time is 0.035 seconds, 0.2 mm ÷ 0.035 sec = 5.7 mm / sec (clamping speed 2)
It becomes. That is, when the mold opening amount at the start of injection is 0.2 mm, the mold clamping speed can be set to 5.7 to 10 mm / sec. However, a faster pressurization time is desirable from the viewpoint of transferability with respect to optical products, and more desirably 0.020 seconds to 0.025 seconds. And when the pressurization time is 0.025 seconds,
0.2 mm / 0.025 sec = 8 mm / sec (clamping speed 3)
It becomes. Therefore, when the light guide plate P having a plate thickness of 0.3 mm is molded with a mold opening amount of 0.2 mm at the start of injection, the mold clamping speed is preferably set to 8 to 10 mm / sec.

On the other hand, when the mold opening amount at the start of injection is 0.5 mm, which is the upper limit that can be set, and when the pressurization time is 0.020 seconds, 0.5 mm ÷ 0.020 sec = 25 mm / sec (clamping speed 4)
Similarly, when the mold opening amount at the start of injection is 0.5 mm and the pressurization time is 0.035 seconds, 0.5 mm ÷ 0.035 sec = 14.3 mm / sec (clamping speed 5)
It becomes. That is, when the mold opening amount at the start of injection is 0.5 mm, the mold clamping speed is preferably set to 14.3 to 25 mm / sec.

  Therefore, in the present embodiment, the mold opening amount is 5.7 mm / sec (the mold clamping speed 2) when the lower limit is 0.2 mm, and the mold opening amount is 25 mm / sec (the mold clamping speed) when the mold opening amount is 0.5 mm. A range of speed 4) is desirable. However, if the mold clamping speed is too high, defects that occur during compression called press marks are likely to occur. Therefore, it is desirable to keep the mold clamping speed at 20 mm / sec (mold clamping speed 6). Moreover, if the mold clamping speed exceeds 20 mm / sec, burrs are likely to occur in the gap between the core 16 and the movable frame 19 of the mold. Therefore, it is necessary to manufacture a more precise mold. Therefore, the mold clamping speed performed according to the present invention is most preferably in the range of 8 mm / sec (mold clamping speed 3) to 20 mm / sec (mold clamping speed 6).

  In addition, when the mold opening amount at the start of injection of the movable mold 12 is set to 0.3 mm, for example, when the mold opening amount is moved, the pressure is rapidly increased to about 130 kN. In the mold clamping device 5, the mechanism using the mold clamping cylinder 10 using the accumulator is faster in the case of substantially the same scale than the mechanism using the servo motor, and a high mold clamping speed is achieved. can do. In the example of the single-piece molding of the light guide plate P having a diagonal size of 3 inches according to this embodiment, the mold clamping is performed at 130 kN, and the mold clamping is performed at 150 to 400 kN even in the case of the two-cavity mold. Is called. In some cases, the mold clamping may be started at the same time as the injection start or after the injection, not during the injection. In the present embodiment, mold clamping is performed by pressure control from the start of operation of the mold clamping device 5, but when the servo motor is used for the mold clamping mechanism, the position is maintained until a predetermined mold clamping force (or detected resin pressure) is reached. The movable platen may be moved by control, and then changed to pressure control.

  When the screw position reaches a predetermined holding pressure switching position by the injection device 3, 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, the gate cutter member driving device (not shown) is moved forward by 0.45 to 0.8 mm by a gate cutter member driving device (not shown) almost simultaneously with switching to the holding pressure control, and the gate P3 is cut. At this time, the gate P3 is cut between the gate cutter 24b, which is the blade of the gate cutter member 24 of the movable mold 12, and the gate cutter 45b, which is the blade of the gate cutter member 45 of the fixed mold 13. 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. As a result, the holding pressure does not reach the molten resin in the cavity 14 from the injection device side, but the core portion 16 of the movable mold 12 is advanced by driving the clamping cylinder 10 of the clamping device 5. Since the molten resin in the cavity 14 can be compressed, even if there is shrinkage due to cooling, sink does 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 (see FIG. 5) of the light guide plate P. In the meantime, the molten resin used for the next molding is measured on the injection device side. When a predetermined time elapses, the mold clamping force is reduced and the air passage 34 between the movable frame portion 19 and the core portion 16 of the movable mold 12, the cavity forming block 42 and the insert block 43 of the fixed mold 13, Release air is applied to the cavity 14 from the air passage 53 between the contact block 46 and the like. Next, the mold clamping device is operated to perform pressure release and mold opening in order. At that time, the light guide plate P, the sprue P1 and the runner P2 are each taken out while being held on the movable mold 12 side. Note that the mold clamping force may be detected at a crosshead position of a tie bar sensor or a toggle mechanism, and may be controlled in multiple stages, for example, by lowering at a gate cut timing.

  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 suck the light guide plate P separately. At the time of the removal, the gate cutter member 24 is stopped at the advanced position. As shown in FIG. 8, the light guide plate P molded by the injection press molding method of this embodiment has substantially uniform internal stress in the vicinity of the gate, and was molded by the conventional method shown in FIG. The light guide plate has a significant difference compared to the non-uniform internal stress in the vicinity of the gate. 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 can be recycled and used separately.

Next, the relationship between the diagonal dimension and thickness of the light guide plate P and the molding conditions will be described. The relationship between the diagonal dimension and thickness of the light guide plate P and the molding conditions includes a portion that can be covered depending on the resin and the molding conditions. The light guide plate P less than the plate thickness 0.2mm~0.3mm the range of diagonal dimension from 1.5 to 5 inches or area 7.5cm ² ~75cm ² is particularly desirable, diagonal dimension 5-7 inches (150 cm ^{In the} light guide plate P of ² ), the plate thickness is particularly preferably 0.3 mm to 0.5 mm. Furthermore, a thickness of 0.5 to 0.7 mm is particularly desirable for a diagonal size of 7 to 13 inches. For example, in a 7-inch light guide plate P, the distance from the gate to the farthest corner from the gate is about 15 cm. Therefore, a larger light guide plate P requires higher injection speed and higher mold clamping speed. Become. In order to improve the flow of the resin as the light guide plate P is larger, it is desirable that the temperature of the molten resin is higher. In addition, the clamping force is 200 to 700 kN in the case of two or four pieces having a diagonal size of 1.5 to 3 inches or one or two pieces having a diagonal size of 2.5 to 5 inches. In the case of taking a single light guide plate P having an angular dimension of 6 inches or more, the mold clamping force is set according to the projected area. The mold clamping force is determined so that the pressurization time to the set maximum pressure can be 0.02 to 0.035 seconds. Accordingly, the light guide plate P can be a larger one, but a diagonal size of 1.5 to 13 inches (520 cm ² ) is primarily assumed, and the corners are arcuate and each side is This includes arcs. In that case, the intersecting point on the extension line of the two sides of the light guide plate P is set as a diagonal measurement reference point. Or 7.5cm ² ~520cm ² of the light guide plate P is assumed in area terms.

  The molding cycle time of the light guide plate P requires the following time. For the light guide plate P having a diagonal size of 1.5 to 5 inches and a plate thickness of 0.2 to 0.5 mm, the time (molding time) from the completion of mold closing to the start of mold opening is 2.5 to 4. The time from the start of mold opening to the completion of mold closing (mold opening / closing time) is 0.75 to 2.2 seconds, and the total molding cycle time is within 6.2 seconds. It is possible. In the light guide plate P having a thickness of 0.4 mm to 0.5 mm and a diagonal size of 5 to 7 inches, the molding time from mold closing to injection to mold opening (excluding mold opening and closing time) is 5 to 6 seconds. The mold opening and closing time is almost the same, so the total molding cycle time can be performed within 8 seconds. In the light guide plate P having a diagonal dimension exceeding 7 inches and a plate thickness of 0.5 mm to 0.7 mm, the molding cycle time can be performed within 20 seconds.

  Further, in the present invention, injection press molding may be performed using a light guide plate molding die 71 of another embodiment as shown in FIG. In this example of another embodiment, the main change is that the number of cavities 72 in the molding die (injection press molding die) 71 is increased to two. It doesn't matter. In the movable mold 73, a core part 75 on which a cavity forming surface 75a is formed is fixed to the mold main body 74. A movable frame portion 76 is attached to the mold main body portion 74 by a spring 82, and the movable frame portion 76 is provided so as to be movable relative to the core portion 75. Further, a gate cutter member 77 is disposed on the movable mold 73. A runner forming member 83 having a protruding pin is disposed adjacent to the movable gate cutter member 77 at the approximate center of the movable mold 73. The runner forming member may be provided integrally with the movable frame portion so that the distance between the runner and the gate is constant. In this case, the distance between the runner and the gate is made thicker than the thickness of the light guide plate. It is desirable. On the other hand, in the fixed mold 78, a contact block 81 is disposed around the cavity forming block 80 where the cavity forming surface 80a is formed, and the movable frame portion 76 and the contact block 81 are contacted to form the cavity 72. It has come to be. The distance between the cavity forming surface 75a of the movable mold 73 and the cavity forming surface 80a of the fixed mold 78 of the cavity 72 is provided to be variable after the mold contact, and the molten resin in the cavity 72 can be compressed. Yes.

  Furthermore, the present invention may be injection press molded by a light guide plate molding die 91 of still another embodiment as shown in FIG. The molding die 91 is a so-called inlay die. Specifically, a cavity forming block 94 having a cavity forming surface 94a on the front surface and a fitting surface formed on the side surface is fixed to the mold main body 93 of the movable mold 92. Further, a runner forming block 95 on which an ejector ejecting pin or the like is disposed is fixed to the mold main body 93, and the side surface of the runner forming block 95 is also a fitting surface. A convex portion is formed by the cavity forming block 94 and the runner forming block 95.

  On the other hand, the fixed mold 96 is provided with a nozzle abutting portion 98 on the fixed plate side of the mold main body 97 and is connected to a manifold block 99 of a hot runner. The manifold block 99 is connected to a hot runner nozzle 100, and a valve gate 102 that is opened and closed by a cylinder 101 is disposed in the hot runner nozzle 100. A runner forming block 103 is disposed around the hot runner nozzle 100. A cavity forming block 104 that forms a cavity forming surface 104a is fixed at the approximate center of the mold main body 97 on the movable mold 92 side. A frame forming block 105 is fixed to the periphery of the mold main body 97 on the movable mold 92 side so as to surround the cavity forming block 104. An inner side of the frame forming block 105 on the movable mold 92 side is a cavity side surface forming surface 105a. A recess is formed by the cavity forming surface 104 a of the cavity forming block 104 and the cavity side surface forming surface 105 a of the frame forming block 105.

  Even when the convex part of the movable mold 92 is fitted into the concave part of the fixed mold 96, the fitting surface and the cavity side surface forming surface 105a form a slight gap where the molten resin does not leak. , 96 is formed in the cavity 106. The frame forming block 105 of the fixed mold 96 and the mold main body 93 of the movable mold 92 are not in contact with each other, and between the cavity forming surface 104a of the fixed mold 96 and the cavity forming surface 94a of the movable mold 92. The distance and the volume of the cavity 106 are variable.

  Therefore, at the time of injection press molding, first, the distance between the cavity forming surface 94a of the movable mold 92 and the cavity forming surface 104a of the fixed mold 96 is 0.2 to the thickness of the light guide plate P to be molded. The movable mold 92 is stopped so that the position where 0.5 mm is added, and then the injection is started and the molten resin in the cavity 106 is compressed. As a result, it is possible to form a light guide plate having a thickness of 0.2 to 0.7 mm and a diagonal size of 1.5 to 13 inches with good optical characteristics.

  Although the present invention is not enumerated one by one, it is not limited to that of the above-described embodiment, and it goes without saying that the present invention is applied to those modified by a person skilled in the art based on the gist of the present invention. is there. In the present embodiment, the light guide plate molding die (injection press molding die) for a mobile phone having a diagonal size of 3 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-type light guide plate includes a gate formed in a portion other than the light incident surface, and the thin-wall portion having a thickness of 0.2 to 0.7 mm is included in the injection press molding method of the present invention. Alternatively, a backlight type light guide plate (including a light diffusing plate) that enters from the back surface and exits from the front surface or a device that reflects external light may be used. 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 also envisaged that the present invention performs lenses and other optical thin plates with incident and outgoing light. In any case, at least one of the transfer surfaces is more effective for the injection press molding method of the present invention.

  In the above embodiment, one mold provided with a fixed gate cutter is a fixed mold, and the other mold provided with a movable gate cutter has been described as an example of a movable mold. That is, the movable gate cutter may be disposed in the fixed mold, and the fixed gate cutter may be disposed in the movable mold. The light guide plate molding die (injection press molding die) may be one that does not perform gate cutting. In general, the light guide plate is taken out by the movable mold, but may be held by the fixed mold side. In the present embodiment, the molding die (injection press molding die) attached to the injection molding machine that 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 case in which the molten resin is compressed by changing the distance between the cavity forming surface of the stationary mold and the cavity forming surface of the movable mold by the mold clamping device of the injection molding machine. A hydraulic cylinder for injection press may be provided in the mold, and the core may be moved by the hydraulic cylinder to compress the molten resin.

  Furthermore, as for the resin that is a molding material used for molding, examples of polycarbonate have been described, but other resins may be used as long as they have excellent optical performance and fluidity. Examples include methacrylic resins and cycloolefin polymer resins. Is mentioned. Since the temperature of the molten resin and the glass transition temperature differ depending on the resin, it goes without saying that the timing of gate cut, the temperature of the cooling medium, the molding cycle time, and the like are also different.

  As described above, in the injection press molding, the distance between the cavity forming surface 42a of the fixed mold 13 and the cavity forming surface 16a of the movable mold 12 adds a predetermined amount to the plate thickness B of the light guide plate P before the start of injection. The movable mold 12 is stopped at a position A that is a value (a position at which the mold opening amount at the start of injection is kept constant), and the molten resin in the cavity 14 is compressed after the start of injection (during or after injection). This is a method of forming. In the injection press molding, since the injection is performed with the cavity 14 and the gate slightly opened with respect to the completion of the molding, the flow loss is small. Therefore, there is no need for an injection device having an ultra-high speed injection capability, and the molten resin can be injected at a relatively low speed and low pressure. In addition, because the gate has a large cross-sectional area and a low injection speed, the pressurization time by the mold clamping device can be shortened, and a light guide plate P having a thin plate thickness can be formed with the residual stress near the gate P3 being minimized It is. 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 in 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 after the start of injection (during injection or after injection), the molten resin is compressed, so that the flow of the molten resin is accelerated at a position far from the gate portion of the cavity 14. In addition to eliminating insufficient filling, there are also advantages that fine transfer can be performed satisfactorily. In addition, after the gate P3 is cut, a normal injection mold cannot apply pressure from the injection device, but 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 in an injection compression molding method in which the cavity 14 is slightly opened and compressed again by injection from the mold clamping completion position.

It is a front view of the injection molding machine used for the injection press molding method of the thin plate-shaped optical molded product of this embodiment. It is the conceptual diagram shown in order to demonstrate the mold clamping apparatus of the injection molding machine used for the injection press molding method of the thin plate-shaped optical molded article of this embodiment. It is sectional drawing of the shaping | molding die used for the injection press molding method of the thin plate-shaped optical molded article of this embodiment, Comprising: It is a figure which shows the state which the movable mold stopped in the position before the injection start. It is sectional drawing of the shaping die used for the injection press molding method of the thin plate-shaped optical molded article of this embodiment, Comprising: It is a figure which shows the state which compressed resin in the cavity. It is sectional drawing of the shaping die used for the injection press molding method of the thin plate-shaped optical molded article of this embodiment, and is a figure which shows the state by which the gate cut was carried out. It is a chart figure which shows the injection press molding method of the thin plate-shaped optical molded article of this embodiment. It is a graph which shows the change of the mold opening amount of a movable metal mold | die by a mold clamping apparatus, and the change of mold clamping pressure. It is the light-guide plate shape | molded with the injection press molding method of this embodiment. It is a test result which shows the relationship between the injection speed at the time of injection press molding the light guide plate of 0.3 mm in plate thickness, and resin temperature. It is a test result which shows the relationship between the injection speed at the time of carrying out injection press molding of the light-guide plate of plate | board thickness 0.2mm, and resin temperature. It is a test result which shows the relationship between the injection speed and the mold opening amount at the start of injection. It is a test result showing the relationship between the pressurization time at the start of mold clamping and transferability. It is the light-guide plate shape | molded by the conventional method. It is sectional drawing of the shaping die used for the injection press molding method of the thin plate-shaped optical molded article of another embodiment. It is a horizontal sectional view of the molding die used for the injection press molding method of the thin plate-like optical molded product of still another embodiment.

Explanation of symbols

1: Injection molding machine 3: Injection device 5: Clamping device 6: Fixed platen 9: Movable platen 10: Clamping cylinder 11: Molding die 12: Movable die 13: Fixed die 14: Cavity 15, 41: Gold Mold body portion 16: Core portion 16a, 42a: Cavity forming surface 19: Movable frame portion 24, 45: Gate cutter member P: Light guide plate P1: Sprue P2: Runner P3: Gate

Claims (5)

A mold is injected into the cavity with a predetermined amount of mold open and filled, and the mold is clamped by a mold-clamping device to compress the molding material injected into the cavity. An injection press molding method for molding an optical molded article,
A thin plate-like optical system characterized in that mold clamping is performed at a mold clamping speed set based on a pressurization time from the start of compression of a molding material until reaching a set mold clamping force and the amount of mold opening at the start of injection. Injection molding method for molded products.   2. The injection press molding method for a thin plate-like optical molded article according to claim 1, wherein the mold clamping is performed at a mold clamping speed of 5.7 to 25.0 mm / sec.   3. The method for injection press molding of a thin plate-like optical molded product according to claim 1, wherein the thickness of the thin plate-shaped optical molded product is formed to 0.2 to 0.7 mm.   The mold clamping device is stopped at a position where the mold is opened by a predetermined amount by detecting the position of the mold before starting the compression, and detecting the mold clamping force after starting the compression. The mold clamping force is controlled, and the injection press molding method for a thin plate-like optical molded article according to any one of claims 1 to 3. The injection press molding of a thin plate-like optical molded article according to any one of claims 1 to 4, wherein the clamping force is controlled so that the pressure exerted on the molding material in the cavity is 25 to 80 MPa. Method.