JP2007210163A - Method for controlling temperature of hot runner and injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the thermal degradation of a resin left in a hot runner by lowering the temperature of the hot runner efficiently after molding is stopped. <P>SOLUTION: In a method for controlling the temperature of the hot runner 53 set in an injection molding machine 1, the hot runner 53 is cooled to make the hot runner 53 have a prescribed temperature to be interlocked with the change-over of the operation mode of the injection molding machine 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a hot runner temperature control method and an injection molding apparatus, and more specifically, a hot runner temperature control method used for resin molding of an optical component that transmits light such as a light guide plate, a lens, or a prism. And an injection molding apparatus provided with such a hot runner.

  In recent years, transparent resins having stable characteristics have been developed, and molding techniques for such resins have been developed. Accordingly, a plastic lens is used as a lens of an optical device such as an optical head of a CD player, a video camera, or a camera-equipped mobile phone.

  For example, plastic lenses used for camera mechanisms of camera-equipped mobile phones are often small in size. When such a plastic lens is molded by an injection molding machine, it is common to form a large number of molds. For example, four to six plastic lenses are formed with one mold. (For example, see Patent Document 1). In addition, a light guide plate that plays a role of reflecting light from a peripheral light source in the screen direction is used in mobile phones and liquid crystal displays.

A plurality of plastic lenses molded in one molding cycle are connected by a runner. The runner is a resin solidified in a passage for guiding the molten resin from the resin injection port of the mold to the gate which is the entrance of the cavity, and is an unnecessary part as a molded product. Therefore, after the plastic lens connected by the runner is taken out from the mold, it is separated from the runner at the gate portion to become individual plastic lenses.
JP 7-266391 A

  In such a conventional molding method, a runner is always formed on a molded product such as a plastic lens, and it is necessary to separate the runner. When the size of the plastic lens is small, the resin amount of the runner portion is larger than the resin amount of the plastic lens. That is, in the entire resin solidified in the mold, the ratio of the resin amount in the runner portion becomes large, and the resin amount in the discarded portion becomes larger than the resin amount in the portion that actually becomes a molded product.

  In addition, since the resin used for optical parts such as plastic lenses needs to be highly transparent and stable, there are many expensive resins, and if there are many parts to be discarded as described above, the manufacturing cost of plastic lenses is increased accordingly. Will pull up.

  In addition, a step of separating the runner after the molded product is taken out from the mold is necessary, and the manufacturing cost is excessive due to this step.

  From this point of view, when the runner portion is constantly heated so that the runner portion in the mold is maintained in a molten state, and the molten resin filled in the mold cavity is cooled and solidified, the mold is solidified with the runner. There has been proposed a hot runner type resin molding in which a product part (inside the cavity) is shut off using a gate shut-off pin. In the hot runner type resin molding, the solidified runner portion is not formed, and it is possible to prevent the expensive resin for optical components from being discarded as the runner portion.

  However, in such a hot runner type resin molding, especially in the ultra-compact hot runner type resin molding for manufacturing a small plastic lens, when a molded product is not produced, the inside of a heating cylinder or hot run is used. In order to prevent the residual resin from burning, it is necessary to change the temperature setting of the heater from the molding temperature to a warming temperature that is lower than the molding temperature when the molding operation is stopped. .

  However, since the hot runner is made of a material having low thermal conductivity, it takes a very long time to drop the temperature from the molding temperature to the heat retention temperature. For this reason, the resin remaining in the hot runner when molding is stopped is subjected to a large heat load. Therefore, the physical properties of the molded product of the first shot are greatly reduced (thermal degradation) when molding is started next time, and such thermal degradation cannot be completely removed in subsequent molding, resulting in burn defects. However, a good product could not be molded. Further, such a heat-degraded resin may remain in the hot runner, and it has been necessary to disassemble and clean them to remove them.

  The present invention has been made in view of the above-described problems, and after the molding is stopped, the temperature of the hot runner can be efficiently lowered, and the thermal deterioration of the resin remaining in the hot runner can be prevented. It is an object of the present invention to provide a control method and an injection molding apparatus provided with such a hot runner.

  According to one aspect of the present invention, there is provided a temperature control method for a hot runner provided in an injection molding machine so that the hot runner reaches a predetermined temperature in conjunction with switching of the operation mode of the injection molding machine. The hot runner temperature control method is characterized in that the hot runner is cooled.

  In the method, the hot runner may be cooled by causing a cooling medium to flow in the hot runner cooling section in conjunction with switching of the operation mode of the injection molding machine. Moreover, it is good also as cooling so that the said hot runner may become predetermined | prescribed temperature by adjusting the flow volume of the said cooling medium. Furthermore, the operation mode of the injection molding machine may be switched from the molding mode to the heat retention mode after the molding operation of the injection molding machine is completed. The operation mode of the injection molding machine may be automatically switched to the heat retention mode when a predetermined time has elapsed after the molding operation of the injection molding machine is completed. Further, the predetermined temperature may be a high temperature within about 50 ° C. from the glass transition temperature of the resin used in the injection molding machine. Further, when the hot runner reaches a predetermined temperature, the cooling of the hot runner may be stopped.

  According to another aspect of the present invention, the injection molding machine includes a hot runner, and further includes a control unit that controls a molding operation of the injection molding machine, and the operation mode of the injection molding machine is controlled by the control unit. In conjunction with the switching, an injection molding apparatus is provided in which cooling of the hot runner is controlled so that the hot runner reaches a predetermined temperature.

  According to the present invention, a hot runner temperature control method capable of efficiently lowering the temperature of a hot runner after molding is stopped and preventing thermal deterioration of the resin remaining in the hot runner, and such a hot runner. The injection molding apparatus provided with can be provided.

  Embodiments of the present invention will be described below.

  An injection molding of a molded product such as a plastic lens according to an embodiment of the present invention will be described with reference to the drawings.

  First, an outline of an injection molding machine that performs injection molding according to the present embodiment will be described. FIG. 1 is a side view of an injection molding machine that performs injection molding according to an embodiment of the present invention.

  The electric injection molding machine 1 shown in FIG. 1 includes an injection device 10 and a mold clamping device 20.

  The injection device 10 includes a heating cylinder 11, and the heating cylinder 11 is provided with a hopper 12. A screw 13 is provided in the heating cylinder 11 so as to be movable forward and backward and rotatable. Inside the heating cylinder 11 and around the screw 13, a temperature sensor 300 such as a thermocouple is provided to detect the temperature inside the heating cylinder 11. The rear end of the screw 13 is rotatably supported by the support member 14. A weighing motor 15 such as a servo motor is attached to the support member 14 as a drive unit. The rotation of the metering motor 15 is transmitted to the screw 13 of the driven part via a timing belt attached to the output shaft.

  The injection device 10 has a screw shaft 17 parallel to the screw 13. The rear end of the screw shaft 17 is connected to the output shaft of the injection motor 19 via a timing belt. Therefore, the screw shaft 17 can be rotated by the injection motor 19. The front end of the screw shaft 17 is engaged with a nut fixed to the support member 14. When the injection motor 19 is driven and the screw shaft 17 is rotated via the timing belt, the support member 14 can move forward and backward, and as a result, the screw 13 of the driven part can be moved back and forth.

  The mold clamping device 20 includes a movable platen 22 to which a movable mold 21A is attached, and a fixed platen 24 to which a fixed mold 21B is attached. The movable mold 21A and the fixed mold 21B constitute a mold apparatus 23 according to the present embodiment described later. The movable platen 22 and the fixed platen 24 are connected by a tie bar 25. The movable platen 22 is slidable along the tie bar 25. Further, the mold clamping device 20 includes a toggle mechanism 27 having one end connected to the movable platen 22 and the other end connected to the toggle support 26. A ball screw shaft 29 is rotatably supported at the center portion of the toggle support 26. A nut 31 formed on a cross head 30 provided in the toggle mechanism 27 is engaged with the ball screw shaft 29. A pulley 32 is provided at the rear end of the ball screw shaft 29, and a timing belt is provided between the output shaft 33 of the mold clamping motor 28 such as a servo motor and the pulley 32.

  In the mold clamping device 20, when the mold clamping motor 28 that is a driving unit is driven, the rotation of the mold clamping motor 28 is transmitted to the ball screw shaft 29 via the timing belt 34. Then, the ball screw shaft 29 and the nut 31 convert the rotational motion into a linear motion, and the toggle mechanism 27 operates. By the operation of the toggle mechanism 27, the movable platen 22 moves along the tie bar 25, and mold closing, mold clamping, and mold opening are performed. A position detector 35 is connected to the rear end of the output shaft 33 of the mold clamping motor 28. The position detector 35 detects the number of rotations or the amount of rotation of the mold clamping motor 28, thereby moving the movable platen connected to the crosshead 30 by the crosshead 30 or the toggle mechanism 27 that moves as the ball screw shaft 29 rotates. 22 position is detected.

  In the present embodiment, the electric injection molding machine 1 is provided with a control unit 40. The control unit 40 controls the metering motor 15 and the injection motor 19 of the injection apparatus, and controls the mold clamping motor 28 of the mold clamping apparatus 20. The control unit 40 further controls opening and closing of a pneumatic valve 220 (see FIG. 3) connected to an air pressure source 225 described later. This will be described in detail later.

  Next, the mold apparatus 23 according to the present embodiment will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the mold apparatus 23 attached to the movable platen 22 and the fixed platen 24.

  The mold apparatus 23 of the present embodiment is a mold apparatus that can be used for molding various optical components such as a plastic convex lens, concave lens, and prism.

  The mold device 23 is a so-called hot runner type mold device, and a runner portion (solidified resin portion) formed by attaching to a molded product in a normal cold runner method is not formed.

  In the hot runner method, the runner portion is constantly heated so that the runner portion in the mold is maintained in a molten state. Therefore, when the molten resin filled in the cavity of the mold is cooled and solidified, it is necessary to provide a mechanism for shutting off the runner and the molded product portion (in the cavity) to be solidified. This mechanism for blocking corresponds to the gate valve mechanism 60 in FIG.

  In FIG. 2, the boundary (so-called parting line) between the movable mold 21A and the fixed mold 21B is indicated by a thick line PL. The left side of the thick line PL is the movable mold 21A, and the right side is the fixed mold 21B. The state shown in FIG. 2 is a state in which the mold apparatus 23 is closed, and when the mold is opened, the movable mold 21A moves leftward in FIG.

  The movable mold 21A includes a movable mold middle plate portion 82 between a movable mold mounting plate portion 81 attached to the movable platen 22 and a movable mold plate portion 83 whose end surface forms the parting line. It has a provided structure. In addition, ejector spacer blocks 87 (not shown) are formed on the upper and lower portions between the movable mold mounting plate portion 81 and the movable mold middle plate portion 82, respectively. A space is formed in a portion surrounded by the spacer block 87, and a molded product ejecting rod 86 connected to a rear end portion of a core 21Aa, which will be described later, and a rear end of the take-out rod 86 are formed in the space. A first protrusion plate 84 and a second protrusion plate 85 that sandwich the portion are provided movably.

  The fixed mold 21B includes a fixed mold middle plate portion 92 between a fixed mold attachment plate portion 91 attached to the fixed platen 24 and a fixed mold plate portion 93 whose end surface forms the parting line. It has a provided structure.

  The fixed mold 21B is provided with a core 21Ba for forming the outer shape of the molded product. The mold 21A is provided with a core 21Aa for forming the outer shape of the molded product. A cavity 52 is formed when the mold apparatus 23 is closed by the core 21Aa and the core 21Ba.

  The molded product 50 is formed by filling the cavity 52 with a molten resin and cooling and solidifying. After the molten resin is solidified in the mold apparatus 23 and the molded product 50 is molded, when the movable mold 21A moves (opens), the core 21Aa is linked with the movement of the movable mold 21A in FIG. Although it moves to the left side, by moving the core 21Aa to the right side via the molded product ejecting rod 86, the molded product 50 solidified in the cavity 52 can be separated and taken out from the movable mold 21A.

  A molten resin is supplied to the fixed mold 21B from the injection apparatus 10 shown in FIG. A connecting pipe 94 is provided inside the fixed mold 21 </ b> B, and a passage (runner) 53 for flowing molten resin and guiding it to the cavity 52 is formed in the connecting pipe 94.

  One end of the runner 53 is connected to a nozzle touch portion 54 formed on the side surface of the fixed mold 21B. A nozzle 99 at the tip of the heating cylinder 11 is connected to the nozzle touch portion 54, and the resin melted and measured by the heating cylinder 11 is supplied to the runner 53.

  The other end of the runner 53 is connected to the gate passage 55, and the gate passage 55 is connected to the cavity 52 via a gate 56 surrounded by the gate bush 100. Accordingly, the molten resin supplied to the runner 53 is filled into the cavity 52 through the gate passage 55 and the gate 56. The gate passage 55 is provided with the gate valve mechanism 60 as described above, and the gate 56 can be opened or closed. The gate valve mechanism 60 includes a valve 61 serving as shut-off means that is movably positioned in the gate passage 55 and a drive mechanism 62 that drives the valve 61.

  A plurality of heaters 96 for heating the runner 53 are arranged inside the connecting pipe 94 and around the runner 53.

  In order to maintain the molten state of the resin in the runner 53, the temperature control of the heater 96 is performed based on the detection value of the temperature sensor 200 embedded in each arbitrary area in the fixed mold 21B. Yes.

  In addition, a gas heat insulating portion 95 that is a flow path for the cooling medium and functions as a runner cooling portion is disposed on the outer peripheral portion of the connecting tube 94 so as to surround the connecting tube 94. The gas heat insulating portion 95 is further inserted through the inside of the fixed mold middle plate portion 92 and the fixed mold plate portion 93, and the air inlet 210 is formed on the upper surface of the fixed mold plate portion 93 to fix the gas. An air outlet 215 is formed on the lower surface of the mold middle plate portion 92.

  Compressed air enters from the inlet 210 as a cooling medium, flows through the gas heat insulating portion 95, and is discharged from the outlet 215, thereby preventing heat conduction from the heater 96 to the stationary mold 21B.

  However, the cooling medium described above is not limited to air, and may be, for example, nitrogen. In addition, a liquid such as water may be used as the cooling medium. In this case, a sleeve or the like is formed as a flow path for the cooling medium so that the liquid can flow instead of the gas heat insulating portion 95. For convenience of explanation, the gas heat insulating portion 95 is drawn large in FIG. 2, but is actually formed around the connecting pipe 94 as a small gap.

  The temperature of the runner 95 cooled by the gas heat insulating part 95 is detected by the temperature sensor 200 described above.

  FIG. 3 is a block diagram showing the concept of temperature control of the runner 95 shown in FIG.

  Referring to FIGS. 2 and 3, an air nozzle (not shown) is disposed near the inlet 210 (see FIG. 2) of the gas heat insulating portion 95. The air nozzle is connected to an air pressure source 225 (see FIG. 3) via a pneumatic valve (valve) 220 (see FIG. 3). By opening the pneumatic valve 220, compressed air is blown from the air pressure source 225 through the air nozzle 210 through the inlet 210 (see FIG. 2) and into the gas heat insulating portion 95. The surface of the enclosed runner 53 is cooled.

  Opening and closing of the pneumatic valve 220 is controlled by a runner control unit 230 (see FIG. 3) connected to the pneumatic valve 220. The runner control unit 230 is connected to the control unit 40 (see FIGS. 1 and 3) of the molding machine 1 through communication or I / O (Input / Output), so that the pneumatic valve 220 can be opened and closed. This can be performed by one control unit 40.

  Next, a method of controlling the temperature of the runner 95 in such a structure will be described with reference to FIG. Here, FIG. 4 is a flowchart showing a method of temperature control of the runner 53.

  The control unit 40 of the molding machine 1 interlocks the switching of two operation modes described later with the inflow of compressed air into the gas heat insulating unit 95.

  Referring to FIGS. 3 and 4, when the normal molding operation is completed (step S1), the operator of the molding machine 1 switches the molding machine 1 from the molding mode to the heat retention mode (step S2 (1)). That is, the mode setting displayed on the screen of the control unit 40 of the molding machine 1 is switched, and the molding cylinder 1 is heated from the molding mode in which the molding operation is performed on the heating cylinder 11 and the like. 11 and the runner 53 and the like are switched to a heat insulation mode for keeping them at a predetermined temperature.

  Here, in the molding mode, full-automatic operation for mass production of molded products, semi-automatic operation for taking out the conditions while taking out the molded products every shot before mass production of the molded products, and replacement of the resin in the heating cylinder 11 are performed. The operation such as purging is performed, and the operation state is accompanied by the injection operation and the rotation operation of the screw 13.

  On the other hand, the heat retention mode is a mode used in a state where the molding machine is temporarily stopped without performing the injection operation or the rotation operation of the screw 13. In the heat retaining mode, since the resin is kept in the heating cylinder 11, the temperature is set lower than that at the time of molding in order to prevent resin burn.

  In the molding mode, the heating cylinder 11 and the runner 53 are about 100 ° C. higher than the temperature at which the resin provided for molding changes from a glassy hard state to a rubbery state, that is, the glass transition temperature Tg. It is in a temperature state. In the molding mode, it is usually set to a temperature at which molding can be performed continuously.

  On the other hand, in the heat retention mode, the heating cylinder 11 and the runner 53 are in a high predetermined temperature (heat retention temperature) within about 50 ° C. from the glass transition temperature Tg. If the temperature is higher than about 50 ° C. from the glass transition temperature Tg, the resin remaining in the runner 53 can be prevented from being burned. In the heat retention mode, the temperature is usually set to a temperature that does not cause a problem even if the molding material stays in the heating cylinder 11 for a long time.

  Further, the purging operation may be a mode independent of the molding mode. In the purge mode in which the purging operation is performed, the glass transition temperature Tg is set as the lower limit of the set temperature. In the purge mode, as an upper limit of the set temperature, a temperature at which the torque necessary for the rotation of the screw 13 can be maintained or a temperature at which the screw 13 is not broken even when the screw 13 is rotated is set experimentally or empirically.

  In conjunction with the switching from the molding mode to the heat retention mode, the control unit 40 of the molding machine 1 outputs an ON signal to the runner control unit 230 and is connected to the air pressure source 255 via the runner control unit 230. The pressure valve 220 is opened (step S2 (2)). Then, the compressed air flows from the air pressure source 225 through the air nozzle through the inlet 210 (see FIG. 2), flows in the gas heat insulating portion 95, and the surface of the runner 53 surrounded by the gas heat insulating portion 95 is cooled. Is done.

  The temperature of the runner 53 is detected by a temperature sensor 200 provided around the runner 53, and it is confirmed whether or not the detected temperature of the runner 53 has reached the above-described heat retention temperature (step 3).

  Until the temperature of the runner 53 detected by the temperature sensor 200 reaches the above-described temperature keeping temperature, the pneumatic valve 220 continues to be opened (step 4-1), and the compressed air continues to flow into the gas heat insulating portion 95. The surface of 53 continues to be cooled.

  When the temperature of the runner 53 detected by the temperature sensor 200 reaches the above-described temperature keeping temperature, the control unit 40 of the molding machine 1 outputs an OFF signal to the runner control unit 230 and the air pressure source 255 via the runner control unit 230. The connected pneumatic valve 220 is closed (step S4-2). If it does so, inflow of the compressed air from the air pressure source 225 to the gas heat insulation part 95 will be stopped, and cooling of the runner 53 will be stopped.

  Thus, according to the present embodiment, after the molding operation is stopped, the pneumatic valve 220 connected to the air pressure source 255 is opened in conjunction with the switching from the molding mode to the heat retention mode. Therefore, the temperature of the hot runner can be efficiently lowered until reaching the heat retention temperature, which is a temperature that can prevent the resin remaining in the runner 53 from being burned, and the hot runner remains in the hot runner. It is possible to prevent thermal degradation of the resin that is present.

  In addition, as soon as the temperature of the runner 53 detected by the temperature sensor 200 reaches the heat retention temperature, the pneumatic valve 220 is not completely closed immediately, but the opening and closing of the pneumatic valve 220 is appropriately controlled to control the temperature of the runner 53. May be. That is, even if the compressed air flows in the gas heat insulating portion 95 and the surface of the runner 53 is cooled, the inside of the runner 53 may actually be higher than the heat retaining temperature. Accordingly, the temperature detected by the temperature sensor 200 may rise as soon as the flow of the compressed air is stopped. Therefore, in this case, the pneumatic valve 200 is opened again to allow the compressed air to flow again to the gas heat insulating portion 93, thereby cooling the runner 53. In this way, the temperature of the runner 53 may be controlled by repeatedly opening and closing the pneumatic valve 200 until the temperature of the runner 53 detected by the temperature sensor 200 reliably reaches the preset temperature.

  Further, a flow rate detector of the compressed air may be provided at an arbitrary position in the flow path of the compressed air between the air pressure source 225 and the gas heat insulating portion 95. Based on the detected value of the flow rate of the compressed air by the flow rate detector, the amount of compressed air flowing through the gas heat insulating portion 95 is adjusted, so that the temperature of the runner 53 reliably reaches the preset temperature. The temperature can be finely adjusted.

  Furthermore, when the operator forgets to switch from the molding mode to the heat retention mode, etc., when the molding machine 1 stops operation and a predetermined time elapses, it automatically switches to the above heat retention mode. In conjunction with the automatic switching, the pneumatic valve 220 is opened to flow the compressed air into the gas heat insulating portion 95 until the temperature of the runner 53 detected by the temperature sensor 200 reaches the above-described heat retention temperature. The surface of the runner 53 may be continuously cooled. Also in this case, the temperature of the hot runner can be lowered efficiently until reaching the heat retaining temperature that is a temperature that can prevent the resin remaining in the runner 53 from being burned. It is possible to prevent thermal degradation of the resin that is being used.

  Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and various modifications and changes are within the scope of the gist of the present invention described in the claims. It can be changed.

It is a side view of the injection molding machine which performs the injection molding by embodiment of this invention. It is sectional drawing which shows the metal mold apparatus attached to the movable platen and the fixed platen. It is the block diagram which showed the concept of the temperature control of a runner. It is the flowchart which showed the method of temperature control of a runner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding machine 21A Movable metal mold 21B Fixed mold 23 Mold apparatus 40 Control part 50 Molded product 52 Cavity 53 Runner 56 Gate 61a Pin 61 Valve 95 Air insulation part 220 Pneumatic valve 225 Air pressure source 230 Runner control part

Claims (8)

A temperature control method for a hot runner provided in an injection molding machine,
A hot runner temperature control method, wherein the hot runner is cooled so that the hot runner reaches a predetermined temperature in conjunction with switching of the operation mode of the injection molding machine. A temperature control method for a hot runner according to claim 1,
A method for controlling the temperature of a hot runner, wherein the hot runner is cooled by causing a cooling medium to flow in a hot runner cooling section in conjunction with switching of the operation mode of the injection molding machine. A temperature control method for a hot runner according to claim 2,
A hot runner temperature control method, wherein the hot runner is cooled to a predetermined temperature by adjusting a flow rate of the cooling medium. A temperature control method for a hot runner according to any one of claims 1 to 3,
The method of controlling a temperature of a hot runner, wherein the switching of the operation mode of the injection molding machine is switching from a molding mode to a heat retention mode after completion of the molding operation of the injection molding machine. A temperature control method for a hot runner according to claim 4,
The temperature control of the hot runner, wherein the operation mode of the injection molding machine is automatically switched to the heat retaining mode when a predetermined time elapses after the molding operation of the injection molding machine is completed. Method. A temperature control method for a hot runner according to any one of claims 1 to 5,
The temperature control method for a hot runner, wherein the predetermined temperature is a high temperature within about 50 ° C. from a glass transition temperature of a resin used in the injection molding machine. A temperature control method for a hot runner according to any one of claims 1 to 6,
The hot runner temperature control method, wherein when the hot runner reaches a predetermined temperature, cooling of the hot runner is stopped. An injection molding machine equipped with a hot runner,
A control unit for controlling the molding operation of the injection molding machine;
The injection molding apparatus, wherein the controller controls cooling of the hot runner so that the hot runner reaches a predetermined temperature in conjunction with switching of the operation mode of the injection molding machine.

Images