JP2010201696A - Method and device for injection molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for injection molding capable of maintaining or shortening a cycle time for molding while preventing the performance of a molded article from deteriorating by residual gas. <P>SOLUTION: In the method for injection molding, a molten resin is injected into a molding space CV of a molding mold 40 to fill the molding space CV in such a state that the inside of the molding space CV is made to be comparatively low vacuum degree P2 by a lessening step (S14) for lowering the inside of the molding space CV than the vacuum degree P1 attained by a decompression step (S13). The molding space CV can be quickly depressurized thereby, and gas melted in a molten resin by the higher vacuum degree than necessary can be prevented from being separated from the molten resin. The cycle time for injection molding can be shortened by quickly depressurizing the molding space CV like this. Furthermore, a flow mark or the like can be prevented from being formed on the surface of a lens LE of the molded article by preventing gas from separating from the molten resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an injection molding method and apparatus for injection molding optical elements and the like, and more particularly to an injection molding method and apparatus for performing molding by injecting an injection melt into a decompressed mold.

  As a known injection molding apparatus, there is one in which a mold clamping cylinder, a mold clamping position detection device, and a communication switching valve are provided in a mold clamping device for clamping an upper mold and a lower mold (Patent Document 1). . In this device, the communication switching valve communicates a cavity formed between the upper die and the lower die with a tank-like vacuum device connected to and driven by the clamping cylinder by a signal from the position detection device. The pressure of the cavity is reduced during resin injection.

  As a mold for an injection molding device, with an on-off valve inserted in a gas vent provided on the opposite side of the pouring port open, an injection melt is injected into the cavity through the pouring port and a plunger There is a thing to extrude at (Patent Document 2). In this device, after a predetermined time has elapsed after the pouring port has been closed by the plunger, the degassing path is switched from the open state to evacuation, and then the evacuation is stopped by closing the on-off valve when the cavity is completely filled. And block the venting path.

  As another mold for an injection molding apparatus, there is one in which a vacuum tank is provided in the vicinity of a cavity and air in the cavity is sucked and exhausted by opening / closing control of the vacuum valve (Patent Document 3). In this apparatus, the vacuum valve is turned on to allow the cavity and the vacuum tank to communicate with each other before injection, and the vacuum valve is turned off to shut off the exhaust flow path before holding pressure after completion of injection.

JP-A-62-50105 JP-A-4-123858 JP 2002-166448 A

  However, in the devices of Patent Documents 1 to 3, a vacuum tank is used for pressure reduction in the cavity, and even if the vacuum degree of the vacuum tank is easy to adjust, the degree of vacuum in the cavity before resin injection is adjusted. It is not easy to manage precisely. Moreover, the vacuum tank for decompression requires a certain volume, and the apparatus becomes large.

  Although it is possible to directly depressurize the cavity before resin injection by a vacuum pump without using a vacuum tank, the following problems arise. That is, if the exhaust flow rate for cavity depressurization is large, the degree of vacuum in the cavity increases, so that a small amount of gas dissolved in the molten resin tends to separate and accumulate in a deep depression in the cavity. Conceivable. For example, when the required accuracy of the surface shape is high as in optical parts, the residual gas as described above may cause a wavy appearance defect (hereinafter referred to as a flow mark), which may deteriorate the performance of the molded product. The present inventors have confirmed experimentally. On the other hand, if the exhaust flow rate for reducing the cavity pressure is small, the degree of vacuum in the cavity is considered to be low enough to suppress the generation of gas, but the time to reach the target degree of vacuum becomes longer, and the molding cycle time Will increase.

  Therefore, an object of the present invention is to provide an injection molding method and apparatus capable of maintaining or shortening the molding cycle time while preventing the performance of the molded product from being deteriorated by the residual gas.

  In order to solve the above-described problems, an injection molding method according to the present invention includes (a) closing a first mold and a second mold constituting a molding mold to form a molding space in the molding mold. A mold closing step to be formed; and (b) a pressure reducing step in which the inside of the molding space is evacuated from the molding space through a pressure reducing path formed in the molding die and communicated with the molding space; (C) a relaxation step of reducing the inside of the molding space below a predetermined degree of vacuum by suppressing or stopping the decompression operation, and (d) a state where the reduction of the degree of vacuum of the molding space is allowed by the relaxation step. And an injection step of filling the molding space by injecting the injection melt into the molding space.

  In the above injection molding method, the molding space is placed in the molding space of the molding die in a state in which the molding space is made to have a relatively low vacuum level by a relaxation process that lowers the molding space from a predetermined vacuum level achieved by the decompression step. Since the injection melt is injected to fill the molding space, a high vacuum level corresponding to the vacuuming flow rate suitable for rapid decompression of the molding space and a low vacuum when filling the molding space with the injected melt It can be used properly with the state of the degree. Accordingly, the molding space can be quickly decompressed, and the gas dissolved in the injection melt can be prevented from being separated from the injection melt due to an unnecessarily high degree of vacuum. Thus, the cycle time of injection molding can be shortened by rapidly depressurizing the molding space. Further, by preventing the gas dissolved in the injection melt from being separated from the injection melt, it is possible to prevent such gas from being trapped between the molding space and the injection melt, and molding. It is possible to prevent the formation of a flow mark (deteriorating appearance of wave pattern) or the like on the surface of the product.

  In a specific aspect or aspect of the present invention, in the injection molding method, in the decompression step, the decompression path communicating with the molding space is evacuated at a first flow rate, and in the relaxation process, the decompression path is directed to the decompression path. By either evacuating at a second flow rate smaller than the first flow rate or stopping evacuation to the decompression path, a reduction in the degree of vacuum in the molding space is allowed. In this case, the degree of vacuum when filling the forming space with the injection melt can be easily set to an appropriate range by adjusting the flow rate such as reduction or cancellation of the flow rate when evacuating.

  In another aspect of the present invention, the flow path connected to the pressure reducing path in the pressure reducing process and the flow path connected to the pressure reducing path in the relaxation process are switched at a predetermined timing using a flow path switching device. In this case, the adjustment of the switching timing is simple and reliable.

  In yet another aspect of the present invention, switching from the decompression step to the relaxation step is performed based on a timing signal generated by the molding machine body that operates the molding die. In this case, it is possible to accurately synchronize the timing of mold closing, mold clamping, and the like by using an operation signal at the time of mold opening and closing performed by the molding machine body.

  In still another aspect of the present invention, the step of cooling the melt to be injected in the molding space and the mold opening by separating the first mold and the second mold in a state where the decompression path is returned to the atmospheric pressure. And the step of performing. In this case, it is possible to prevent a vacuum break when the mold is opened. Accordingly, it is possible to keep the inner surface of the molding die such as the transfer surface clean by suppressing dust around the molding die from entering the die when the die is opened.

  In yet another aspect of the present invention, the molding space has a larger thickness in the central portion than in the peripheral portion, and the injection melt is injected into the molding space via an inlet provided at a predetermined position in the peripheral portion. To do. In this case, air easily collects on the transfer surface of the mold corresponding to the central portion, but as described above, the injection melt can be injected in a state of an appropriate degree of vacuum by the relaxation process. Generation of desorbed gas from the melt to be injected is reduced, and formation of flow marks can be suppressed.

  In yet another aspect of the present invention, the optical element is formed by curing the injection melt in the molding space by cooling. In this case, the surface including the optical functional surface of the optical element as a molded product can be processed into a highly accurate state without a flow mark due to desorbed gas.

  An injection molding apparatus according to the present invention includes (a) a first mold and a second mold, and communicates with a molding space formed by closing the first mold and the second mold. A molding die provided with a decompression path; (b) a vacuum pump for decompressing the molding space via the decompression path; and (c) a first flow that provides a predetermined degree of vacuum by decompressing the molding space. A flow path switching device that selectively switches the path and the second flow path that lowers the inside of the molding space below a predetermined degree of vacuum by suppressing or stopping the pressure reduction operation, and (c) the flow path. After the switching device switches from the state where the first flow path is selectively communicated with the pressure reducing path to the state where the first flow path is selectively communicated with the pressure reducing path, the injection melt is injected into the molding space from the injection device. And a control device for injecting.

[First Embodiment]
Hereinafter, an injection molding method and apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram illustrating an injection molding apparatus for carrying out the method of the present embodiment. The injection molding apparatus 100 includes an injection molding machine 10 that is a mechanical mechanism for injection molding a molded product MP, a temperature adjustment apparatus 18 that adjusts the temperature of a molding die 40 provided in the injection molding machine 10, and the like. A pressure adjusting device 19 that adjusts the pressure inside the mold such as the molding die 40 and a control device 30 that comprehensively controls the operating state of each part of the injection molding device 100 are provided. The control device 30 constitutes a molding machine main body that performs the basic operation of injection molding together with the injection molding machine 10.

  The injection molding machine 10 includes a molding die 40, a fixed platen 11, a movable platen 12, a mold clamping plate 13, an opening / closing drive device 15, and an injection device 16. The injection molding machine 10 enables molding by sandwiching a fixed mold 41 and a movable mold 42 between the movable platen 12 and the fixed platen 11 and clamping both the molds 41 and 42. Here, in the injection molding machine 10, mold opening and mold closing are in the horizontal direction. The injection molding machine 10 is not limited to the type that opens and closes the mold in the horizontal direction, but can be an injection molding machine that opens and closes the mold in the vertical direction.

  FIG. 2 is a view for explaining a side sectional structure and the like of the molding die 40. As illustrated, the molding die 40 includes a fixed die 41 that is a first die and a movable die 42 that is a second die. The fixed mold 41 and the movable mold 42 can be opened and closed with the parting line PL as a boundary. For example, a groove 42c is formed around the mold surface 42a side of the movable mold 42, and a sealing O-ring 43 is embedded in the groove 42c. When the fixed mold 41 and the movable mold 42 are brought close to each other, first, both the molds 41 and 42 are in contact with each other, that is, the initial sealing state in which the O-ring 43 is in contact with the mold surface 41a of the fixed mold 41 (per die contact). State). When the fixed mold 41 and the movable mold 42 are tightened so as to be closer to each other, the mold surfaces 41a and 42a of both the molds 41 and 42 are brought into a clamped state in which they are in close contact with each other with a necessary pressure.

  A plurality of molding spaces CV for molding a lens are formed by performing the above-described mold clamping on the fixed mold 41 and the movable mold 42, and a molten resin is supplied to each molding space CV. A flow path portion FC is formed as a resin circulation space for this purpose. The molding space CV and the flow path portion FC are resin filling spaces corresponding to the molded product MP. Among these, the molding space CV is, as shown in FIG. 3A, a main body space CV1 sandwiched between a pair of optical transfer surfaces S1 and S2, and a flange space CV2 surrounded by a pair of peripheral transfer surfaces S3 and S4. With. In this case, the molding space CV has an inner surface shape corresponding to the outer surface shape of the convex lens, and the thickness of the main body space CV1 that is the central portion is larger than the thickness of the flange space CV2 that is the peripheral portion. Further, as shown in FIG. 2, the flow path portion FC has a sprue portion SP at the center, has a plurality of runner portions RP branched from the sprue portion SP, and is provided at the tip of each branched runner portion RP. It has a gate portion GP. The flow path portion FC has a structure communicating with the molding space CV through the gate portion GP. The gate portion GP is connected to the side surface portion of the flange space CV2 in the molding space CV. That is, the boundary between the molding space CV and the gate portion GP serves as an introduction port IL for injecting the molten resin that has passed through the flow path portion FC into the disk-shaped molding space CV having a particularly thick center from the side surface direction. .

  A molding space CV, which is a space between both molds 41 and 42, corresponds to the shape of a lens LE (see FIG. 3B) as an optical element constituting a part of the molded product MP. Yes. The lens LE is made of plastic and includes a center portion OLa as an optical function portion having an optical function, and an annular flange portion OLb extending from the center portion OLa in the outer diameter direction. The center portion OLa corresponds to the main body space CV1 in FIG. 3A, and the flange portion OLb corresponds to the flange space CV2 in FIG. This lens LE is, for example, an imaging lens built in a portable terminal device or an objective lens for an optical pickup device. In the example shown in the figure, the deviation ratio (the state in which the thickness of the optical element has changed abruptly) becomes high. Yes. Thus, when the inclination angle α around the center portion OLa is 50 ° or more, the prospective angle β of the corresponding main body space CV1 in the molding space CV is also 50 ° or more, and the main body space CV1. It becomes easy for gas to accumulate around the apex of and to be confined. Such gas removal will be described later.

  As shown in FIG. 3A, a shallow ventilation groove 46 extending outward from the flange space CV2 of the molding space CV is formed on the mold surface 42a of the movable mold 42. The molds 41 and 42 are connected to a vent pipe 47 extending into the fixed mold 41 with the molds 41 and 42 in contact with each other. The other end of the vent pipe 47 extends to the side surface of the fixed mold 41. The ventilation groove 46 and the ventilation pipe 47 communicate with the molding space CV to form a decompression path 49 that enables decompression, that is, exhaustion, in the molding space CV and the flow path portion FC. The exhaust port OL, which is the boundary between the ventilation pipe 47 and the molding space CV, is provided at a position facing the introduction port IL across the central main body space CV1 in the side surface portion of the flange space CV2. That is, the exhaust port OL for evacuation and the introduction port IL for resin injection are arranged at the farthest positions across the molding space CV in consideration of the reliability of exhaust of the molding space CV.

  Returning to FIG. 1, the fixed platen 11 of the injection molding machine 10 is fixed to the center of the support frame 14 so as to face the movable platen 12. The fixed platen 11 detachably supports a fixed mold 41. Note that the fixed platen 11 is fixed to the mold clamping plate 13 via a tie bar so that it can withstand the pressure of mold clamping during molding.

  The movable platen 12 is supported by a slide guide 15a so as to be movable back and forth with respect to the fixed platen 11. The movable platen 12 detachably supports the movable mold 42. An ejector device 50 is incorporated in the movable platen 12. The ejector device 50 operates the eject pin 55 to push out the molded product MP in the movable mold 42 to the opposite fixed mold 41 side, and the molded product MP can be gripped and carried out by a take-out device (not shown). To.

  The mold clamping machine 13 supports the movable board 12 from the back via the power transmission part 15d of the opening / closing drive device 15 when clamping the molds 41 and 42 with a necessary pressure.

  The opening / closing drive device 15 includes a slide guide 15a, a power transmission unit 15d, and an actuator 15e. The slide guide 15a supports the movable platen 12 and enables a smooth reciprocating movement in the advancing / retreating direction of the movable platen 12 with respect to the fixed platen 11. The power transmission unit 15 d expands and contracts by receiving a driving force from an actuator 15 e that operates under the control of the control device 30. As a result, the movable platen 12 approaches and moves away from the fixed platen 11 and moves freely, and as a result, the fixed platen 11 and the movable platen 12 move close to and away from each other and move with the fixed mold 41. Mold clamping and mold opening with the mold 42 are performed.

  The injection device 16 includes a cylinder 16a, a raw material reservoir 16b, a screw 16c, and a resin injection end 16d. The injection device 16 is a part that operates at an appropriate timing under the control of the control device 30, and can discharge the molten resin from the resin injection end 16d in a temperature-controlled and pressure-controlled state. The injection device 16 can detachably connect the resin injection end 16d of the cylinder 16a to a sprue portion SP (see FIG. 2) that opens on the back surface of the fixed mold 41 through an opening provided in the fixed platen 11. it can. That is, the injection device 16 has a flow path portion FC (see FIG. 2) communicating with a molding space CV (see FIG. 2) formed in a state where the fixed mold 41 and the movable mold 42 are clamped. The molten resin as the injection melt can be supplied at a desired timing.

  The temperature adjusting device 18 is a part that adjusts the temperature of the molds 41 and 42 of the injection molding machine 10. The temperature adjustment device 18 has a temperature adjustment circuit, and the temperature of the fixed mold 41 and the movable mold 42 can be adjusted. Specifically, for example, by supplying a temperature adjusting medium to a fluid circulation path provided in the fixed platen 11 and the movable platen 12, the fixed die 41 and the movable die 42 are heated to a necessary temperature or cooled. To do. The temperature may be adjusted using a heater or the like without using a medium.

  The pressure adjusting device 19 can adjust the pressure in the molding space CV formed with the fixed mold 41 and the movable mold 42 being clamped. As shown in detail in FIG. 2, the pressure adjusting device 19 includes a branching unit 61, a first channel switching device 62, a second channel switching device 63, a vacuum pump 64, and a control pressure supply unit 65. A digital pressure switch 71, a flow meter 72, a vacuum gauge 73, and a pressure control device 79. When the pressure adjusting device 19 depressurizes the molding space CV in the molding die 40, the pipe 81a, the branching portion 61, the first flow path switching device 62, the pipe 81b, and the second flow path switching device 63 are used. And the flow path which connected the piping 81c and the vacuum pump 64 in order is formed. Further, when the reduced pressure state of the molding space CV in the molding die 40 is relaxed, the state of the first flow path switching device 62 is changed to switch the flow path in the branch portion 61 and suppress evacuation. Or stop. Further, when the molding space CV in the molding die 40 is opened to the atmosphere, the pipe 81a, the branch portion 61, and the first channel switching device are changed by changing the state of the second channel switching device 63. 62, a pipe 81b, a second flow path switching device 63, and an air introduction part 82 are connected in order. The digital pressure switch 71 is connected to a pipe 81 a between the molding die 40 and the branch part 61, and the flow meter 72 is connected between the first flow path switching device 62 and the second flow path switching device 63. The vacuum gauge 73 is connected to a pipe 81 c between the second flow path switching device 63 and the vacuum pump 64.

  The branch part 61 is branched into two from the pipe 81a, and includes a first tube 61a corresponding to the first flow path and a second tube 61b corresponding to the second flow path. The first tube 61a is provided so as to connect the branch point 61c and the first switching port 62a of the first flow path switching device 62, and the second tube 61b is connected to the branch point 61c and the first flow path switching device 62. The second switching port 62b is connected. Among these, on the 2nd tube 61b as a 2nd flow path, the flow regulating valve 61d is inserted, and the flow volume of the 2nd tube 61b is restrict | limited to a desired grade by control from the pressure control apparatus 79. Be able to. Specifically, for example, when the flow rate adjustment valve 61d is opened, the flow rate of the air in the second tube 61b is changed to the standard first flow rate achieved by the first tube 61a when the first tube 61a is used. Can be equal. Further, when the flow rate adjusting valve 61d is partially opened, the flow rate of the air in the second tube 61b is set to a desired flow rate (second flow rate) smaller than the standard first flow rate of the first tube 61a. be able to. Furthermore, when the flow rate adjusting valve 61d is partially closed, the air flow in the second tube 61b can be blocked.

  The first flow path switching device 62 is an electromagnetic switching valve for selectively communicating one of the first tube 61 a and the second tube 61 b with the pipe 81 b extending from the third flow path switching device 63. is there. The first flow path switching device 62 has a switching valve main body 62d and a gas driving unit 62e, and electromagnetically switches the direction of operation of the external pilot pressure supplied to the gas driving unit 62e, thereby switching the main body of the switching valve. The function of 62d, that is, the circuit connection state can be switched. For example, when the first flow path switching device 62 is in the first circuit connection state, the first tube 61a that can relatively increase the flow rate, and the pipe that extends from the second flow path switching device 63 and can be connected to the vacuum pump 64 81b is connected. Further, when the first flow path switching device 62 is in the second circuit connection state, the second tube 61 b that can relatively reduce the flow rate and the pipe 81 b that extends from the second flow path switching device 63 are connected. In the first flow path switching device 62, the basic port 62c is connected to the pipe 81b.

  The second flow path switching device 63 selectively connects the pipe 81b extending from the first flow path switching device 62 to one of the pipe 81c extending from the vacuum pump 64 and the air introduction part 82 for opening to the atmosphere. This is an electromagnetic switching valve. The second flow path switching device 63 has a switching valve main body 63d and a gas driving unit 63e, and electromagnetically switches the direction of operation of the external pilot pressure supplied to the gas driving unit 63e, thereby switching the main body of the switching valve. The function of 63d, that is, the circuit connection state can be switched. For example, when the second flow path switching device 63 is in the first circuit connection state, a pipe 81b connected to the molding die 40 via the first flow path switching device 62 and a pipe 81c extending from the vacuum pump 64 are connected. Is done. Moreover, when the 2nd flow-path switching apparatus 63 exists in a 2nd circuit connection state, the piping 81b extended from the 1st flow-path switching apparatus 62 and the air introduction part 82 provided with a silencer are connected. In the second flow path switching device 63, the basic port 63a is connected to the pipe 81b. The first switching port 63 b of the second flow path switching device 63 is connected to the pipe 81 c, and the second switching port 63 c of the second flow path switching device 63 is connected to the air introduction part 82.

  The vacuum pump 64 is a decompression device configured by, for example, a rotary pump, and a filter 64b for protecting the vacuum pump 64 is provided on a pipe 81c extending therefrom.

  The control pressure supply unit 65 generates an external pilot pressure to be supplied to the gas drive unit 62e of the first flow path switching device 62 and the gas drive unit 63e of the second flow path switching device 63.

  The digital pressure switch 71 is a sensor that measures the pressure in the pipe 81a extending from the decompression path 49 of the molding die 40, and generates an output corresponding to the pressure in the pipe 81a (pressure in the molding space CV when the mold is clamped). To do. The output of the digital pressure switch 71 is monitored by a pressure control device 79. For example, based on the output of the digital pressure switch 71, it is determined whether or not the molding space CV of the molding die 40 has a sufficiently low pressure as a pre-stage of molten resin injection, and the molding space CV returns to atmospheric pressure. It is then determined whether the mold 40 is ready for mold opening or mold release.

  The flow meter 72 is a sensor that measures the flow rate of the gas in the pipe 81a connecting the first flow path switching device 62 and the second flow path switching device 63, and generates an output corresponding to the gas flow rate in the pipe 81a. To do. The output of the flow meter 72 is monitored by the pressure control device 79 and is used when monitoring the switching operation of the flow path in the branching section 61 by the first flow path switching device 62. The output of the flow meter 72 can also be used as a feedback signal for adjusting the degree of opening of the flow rate adjusting valve 61d provided in the branching portion 61 in the pressure control device 79.

  The vacuum gauge 73 is a sensor that measures the degree of vacuum in the pipe 81c extending from the vacuum pump 64, and generates an output corresponding to the degree of vacuum in the pipe 81c. The output of the vacuum gauge 73 is monitored by the pressure control device 79 and is used when monitoring the operation of the vacuum pump 64.

  The pressure control device 79 controls operations of the first flow path switching device 62, the second flow path switching device 63, and the vacuum pump 64, and includes a digital pressure switch 71, a flow meter 72, and a vacuum gauge 73. The output is monitored. Thereby, the state of the 2nd flow-path switching apparatus 63 is switched via the control pressure supply part 65 at a required timing. Specifically, by switching the second flow path switching device 63 from the second circuit connection state to the first circuit connection state, the pipe 81a extending from the molding die 40 is connected to the vacuum pump 64 to thereby form the molding die. The inside of 40 can be evacuated. Thereby, pressure reduction of the molding space CV in the molding die 40 can be started. Further, by switching the second flow path switching device 63 from the first circuit connection state to the second circuit connection state, the pipe 81a extending from the molding die 40 is connected to the air introduction part 82 to be in the atmosphere open state. be able to. Thereby, the mold opening of the molding die 40 can be started easily. On the other hand, when the second flow path switching device 63 is in the first circuit connection state, the first tube 61a is selected by setting the first flow path switching device 62 to the first circuit connection state. With the first flow rate, the decompression path 49 and thus the molding space CV in the molding die 40 are decompressed. Further, when the second flow path switching device 63 is in the first circuit connection state, the second tube 61b is selected by setting the first flow path switching device 62 to the second circuit connection state. The decompression path 49 in the molding die 40 and thus the molding space CV are decompressed at a second flow rate smaller than the first flow rate, and the decompression operation is suppressed. In this case, the degree of vacuum in the forming space CV gradually increases. When the first channel switching device 62 is set to the second circuit connection state and the second tube 61b is selected, the decompression path 49 in the molding die 40 and thus the molding space CV are disconnected from the outside, and the decompression is reduced. The operation is stopped. In this case as well, the degree of vacuum in the molding space CV gradually increases slightly due to leakage or gas from the molten resin.

  The pressure control device 79 has a built-in timer for controlling the operation timing of the first flow path switching device 62 and the second flow path switching device 63, and this timer is a timer built in the control device 30. The time has been adjusted to match. Such a timer can be replaced with a synchronizer for synchronizing with a timing signal output from the control device 30 described later.

  Returning to FIG. 1, the control device 30 includes an opening / closing control unit 31, an injection device control unit 32, and an ejector control unit 33. The opening / closing control unit 31 enables the molds 41 and 42 to be clamped and opened by operating the actuator 15e. The injection device controller 32 causes the molten resin to be injected at a desired pressure into the molding space CV formed between the molds 41 and 42 by operating the screw 16c and the like. The ejector control unit 33 operates the ejector device 50 to push out the molded product MP remaining in the movable mold 42 from the inside of the movable mold 42 when the mold is opened. The control device 30 outputs a command signal and a timing signal for instructing the operation to the opening / closing drive device 15, the injection device 16, the temperature adjusting device 18, the pressure adjusting device 19, and the like.

  The operation of the injection molding apparatus 100 shown in FIGS. 1 and 2 will be described below with reference to the flowchart of FIG. FIG. 5 is a timing chart for supplementarily explaining the operation of the injection molding device 100 in relation to the operation of the pressure adjusting device 19.

  First, the temperature adjusting device 18 of the injection molding device 100 is operated under the control of the control device 30 to heat both molds 41 and 42 to a temperature suitable for molding (step S10). At this time, the pressure adjusting device 19 is set to the initial state by the control device 30, holds the first flow path switching device 62 in the first circuit connection state, and sets the second flow path switching device 63 in the second circuit connection state. Hold on. That is, the decompression pipe 81a extending from the molding die 40 is connected to the air introduction part 82 via the first and second flow path switching devices 62 and 63, and the pipe 81c extending from the vacuum pump 64 is kept airtight. Be drunk. As a result, the decompression path 49 and the like formed in the molding die 40 can be opened to the atmospheric pressure, that is, the atmosphere.

  Next, the opening / closing drive device 15 is operated under the control of the control device 30, and the movable platen 12 is moved forward to start mold closing (step S11). In FIG. 5, the mold closing start timing is T0. Immediately before the mold clamping operation starts from the mold closing step, the pressure adjusting device 19 is switched to the rapid exhaust state under the control of the control device 30, and the first flow path switching device 62 is maintained in the first circuit connection state. Thus, the second flow path switching device 63 is switched to the first circuit connection state (step S12). In other words, in a state where the first tube 61a is selected as the flow path by the first flow path switching device 62, the vacuum pump 64 exhausts at a relatively large first flow rate (for example, 10 L / min). In FIG. 5, the start timing of this rapid exhaust is T1.

  In parallel with this, by continuing the mold closing operation, that is, the closing operation of the opening / closing drive device 15, the movable platen 12 moves to the fixed platen 11 side to the die contact position where the fixed die 41 and the movable die 42 come into contact with each other. Then, the mold closing is completed, and the closing operation of the opening / closing drive device 15 is further continued, whereby the mold clamping for clamping the fixed mold 41 and the movable mold 42 with a necessary pressure is started (step S13). In FIG. 5, the timing of the mold clamping start is T2. At this time, a molding space CV is formed between the clamped fixed mold 41 and the movable mold 42, and the pipe 81a is formed from the molding space CV at the above-described relatively large first flow rate (for example, 10 L / min). Exhaust is performed through That is, it is possible to execute a depressurization process that rapidly depressurizes the forming space CV to the target value. Note that the degree of vacuum P1 in the forming space CV achieved by the above-described decompression step or decompression operation is, for example, about 0.1 MPa, with the atmospheric release state being 0 MPa.

  Next, the pressure adjustment device 19 is switched to the reduced pressure relaxation state under the control of the control device 30, and the first flow path switching device 62 is maintained while maintaining the second flow path switching device 63 in the first circuit connection state. Is switched to the second circuit connection state (step S14). In other words, the second tube 61b is selected as the flow path by the first flow path switching device 62, and from the molding space CV through the pipe 81a at a relatively small second flow rate (for example, greater than 0 and 1.0 L / min or less). Exhaust is performed. Thereby, the decompression of the molding space CV is relieved, and the degree of vacuum in the molding space CV can be lowered relatively slowly compared to the decompression operation of step S12. Such suppression of the decompression of the molding space CV is referred to as a relaxation operation. In FIG. 5, the start timing of this relaxation operation is T3. As described above, by providing the relaxation process for switching from the rapid exhaust state to the reduced pressure relaxation state, not only can the molding space CV be rapidly changed to the target vacuum degree, but the vacuum degree in the molding space CV is excessive. The pressure environment suitable for filling the molten resin can be realized by preventing the increase. In addition, when the degree of vacuum in the molding space CV becomes excessively high, as will be described later, the gas dissolved in the molten resin injected into the molding space CV is easily separated from the molten resin, causing a problem.

  Next, the injection molding machine 10 waits for the completion of mold clamping to operate the injection device 16, so that a flow path is formed in the molding space CV between the clamped fixed mold 41 and the movable mold 42. The molten resin heated through the portion FC is injected at a necessary pressure (step S15). In FIG. 5, the start timing of this injection process is T4. At this time, the degree of vacuum in the forming space CV is lowered to the target value due to the pressure reducing operation started in step S13. The target degree of vacuum P2 is, for example, about 0.04 MPa or more. Thus, by keeping the inside of the molding space CV at an appropriate degree of vacuum P2, it is possible to prevent the desorbed gas separated from the molten resin from being trapped between the molding space CV and the molten resin. By continuing the injection of the molten resin, a filling process, that is, an injection process is performed in which the molding resin C is filled into the molding space CV between the fixed mold 41 and the movable mold 42 that are clamped. In addition, after completing the injection | pouring process which fills this molding space CV, the injection molding machine 10 performs the holding pressure which maintains the molten resin pressure in the molding space CV for a fixed period (for example, 10 seconds).

  In the above injection process, the degree of vacuum in the molding space CV is kept at P2 or less, so that the desorbed gas separated from the molten resin can be prevented from being trapped between the molding space CV and the molten resin, and after the curing It is possible to prevent a flow mark from being formed on the surface of the molded product. That is, even with a lens LE having a high thickness deviation ratio and having a diffractive structure or the like, it is possible to prevent surface transfer failure and increase the transfer accuracy of the optical surface.

  With respect to the molding die 40, the molding space CV and the flow path portion FC are appropriately heated by the temperature adjusting device 18, and the molten resin supplied from the injection device 16 and filled in the molding space CV or the like is molded metal. The mold 40 is gradually cooled, and gradually hardens with the cooling (step S16).

  Before the molten resin is cured in the molding die 40 and at a stage where the molten resin is cooled to some extent in the molding die 40, the pressure adjusting device 19 is switched to the air release preparation state under the control of the control device 30. It is done. That is, the first flow path switching device 62 is switched from the second circuit connection state to the first circuit connection state and returned to the normal state. In FIG. 5, the start timing of this air release preparation is T5.

  After that, when the molten resin is sufficiently cooled in the molding die 40, the pressure adjusting device 19 is switched to the atmosphere open state under the control of the control device 30 (step S17). That is, the second flow path switching device 63 is switched from the first circuit connection state to the second circuit connection state, the pipe 81a extending from the molding die 40 is connected to the gas introduction path 82, and the molding space CV and the pressure reduction path 49 or the like is in an open state to atmospheric pressure, that is, air.

  Next, the opening / closing drive device 15 is operated to open the mold to retract the movable platen 12 (step S18). Along with this, the movable mold 42 moves backward, and the fixed mold 41 and the movable mold 42 are separated. As a result, the molded product MP, that is, the lens LE is released from the fixed mold 41 while being held by the movable mold 42. In FIG. 5, the start timing of the mold opening operation is T7. When the mold is opened, the decompression path 49 returns to the atmospheric pressure, and a phenomenon in which outside air is strongly sucked into the decompression path 49 does not occur.

  Next, in the injection molding machine 10, the ejector device 50 is operated to cause the molded product MP to be ejected (step S19). Specifically, the eject pin 55 is advanced to the opposing fixed mold 41 side, and the molded product MP is pushed out to the fixed mold 41 side. As a result, the molded product MP is released from the movable mold 42.

  When the molded product MP is released from the movable mold 42, a take-out device (not shown) is operated to grasp a proper position of the projected molded product MP and carry it out (step S20). The lens LE is separated from the molded product MP to be a finished product.

  Thereafter, returning to step S11, the processing described above is repeated, and continuous production of the molded product MP becomes possible. Such a cycle of continuous production is shown as a cycle time T in the chart of FIG.

  In the above injection molding, the values of the vacuum degrees P1 and P2 are exemplifications, and the number, size and shape of the molding space CV, the type of the molten resin that is the molding material, the molding temperature and humidity, the capacity of the piping system It can adjust suitably according to etc.

  The timing T1 for starting the pressure reducing operation, the timing T3 for starting the pressure reducing relaxation operation, the timing T4 for injecting the molten resin, etc. depend on the size of the molding space CV, the performance of the vacuum pump 64, the capacity of the piping system, etc. The output can be adjusted as appropriate by using the outputs of the digital pressure switch 71, the flow meter 72, and the like.

  Further, the steps such as air release preparation performed in step S16 and air release performed in step S17 are not essential. That is, it is not necessary to switch the state of the flow path switching devices 62 and 63 for mold opening.

  According to the injection molding method of the present embodiment described above, the interior of the molding space CV is relatively moved by the relaxation process (step S14) that lowers the interior of the molding space CV below the degree of vacuum P1 achieved by the decompression process (step S13). In a state where the degree of vacuum P2 is low, molten resin is injected into the molding space CV of the molding die 40 to fill the molding space CV. Therefore, a state of a high degree of vacuum P1 (for example, about 0.1 MPa) corresponding to a vacuuming flow rate suitable for rapid decompression of the molding space CV and a low degree of vacuum P2 (for example, when filling the molding space CV with molten resin) And a state of about 0.04 MPa or more). Thereby, the molding space CV can be quickly decompressed, and the gas dissolved in the molten resin due to a higher degree of vacuum than necessary can be prevented from being separated from the molten resin. Thus, the cycle time of injection molding can be shortened by rapidly depressurizing the molding space CV. Further, by preventing the gas from separating from the molten resin, it is possible to prevent such gas from being trapped between the molding space CV and the molten resin, and a flow mark or the like is formed on the surface of the lens LE. Can be prevented.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications are possible. For example, the flow path switching devices 62 and 63 are not limited to electromagnetic switching valves using pilot pressure, but can be other types of electromagnetic switching valves, and are composed of other types of valves and valves that do not operate electromagnetically. Can be.

  Further, the shape of the molding space CV provided in the molding die 40 composed of the fixed die 41 and the movable die 42 is not limited to that shown in the figure, and can be various shapes. That is, the shape of the molding space CV is merely an example, and can be appropriately changed according to the use of the lens LE or other molded product MP. That is, the molded product MP obtained by the injection molding machine 10 is not limited to the imaging lens, the optical objective lens, and the like, but may be a light guide plate having a fine structure.

  In the above embodiment, the injection molding machine 10 may be, for example, a hydraulic type or an electric type as long as it can open and close the molding die 40 and the like.

It is a front view explaining the injection molding device of an embodiment. It is a block diagram explaining the side cross-section structure of a shaping die, and a pressure regulator. (A) is the elements on larger scale of the molding die of Drawing 1, and (B) is a sectional side view of a lens. It is a flowchart explaining operation | movement of the injection molding apparatus of FIG. 5 is a timing chart for supplementarily explaining the operation of the injection molding apparatus in FIG. 4.

  DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 11 ... Fixed board, 12 ... Movable board, 15 ... Opening / closing drive device, 16 ... Injection device, 18 ... Temperature adjusting device, 19 ... Pressure adjusting device, 30 ... Control device, 31 ... Opening / closing control part, 32 ... Injection device control unit, 33 ... Ejector control unit, 40 ... Molding die, 41, 42 ... Mold, 46 ... Ventilation groove, 47 ... Ventilation pipe, 49 ... Pressure reducing path, 50 ... Ejector device, 61 ... Branching unit 61a ... first tube, 61b ... second tube, 61d ... flow rate adjusting valve, 62 ... first flow path switching device, 63 ... second flow path switching device, 64 ... vacuum pump, 65 ... control pressure supply unit, 71 ... Digital pressure switch, 72 ... Flow meter, 73 ... Vacuum gauge, 79 ... Pressure control device, 82 ... Air introduction part, 100 ... Injection molding device, CV ... Molding space, FC ... Flow path part, GP ... Over root section, IL ... inlet, MP ... moldings, OL ... exhaust port

Claims (8)

A mold closing step of forming a molding space in the molding die by closing the first die and the second die constituting the molding die;
A depressurization step of evacuating the molding space to a predetermined degree of vacuum by exhausting from the molding space through a decompression path formed in the molding die and communicating with the molding space;
A relaxation step of reducing the inside of the molding space below the predetermined degree of vacuum by suppressing or stopping the decompression operation;
An injection step of injecting an injection melt into the molding space of the molding die and filling the molding space in a state in which a reduction in the vacuum degree of the molding space is allowed by the relaxation step. A featured injection molding method. In the decompression step, evacuation is performed at a first flow rate with respect to the decompression path communicating with the molding space;
In the relaxation step, the molding is performed by either evacuating the decompression path at a second flow rate smaller than the first flow rate or stopping evacuation of the decompression path. The injection molding method according to claim 1, wherein a reduction in the degree of vacuum in the space is allowed.   The flow path connected to the pressure reduction path in the pressure reduction step and the flow path connected to the pressure reduction path in the relaxation step are switched at a predetermined timing using a flow path switching device. The injection molding method according to claim 2.   The switching from the decompression step to the relaxation step is performed based on a timing signal generated by a molding machine main body that operates a molding die. Injection molding method.   A step of cooling the injection melt in the molding space, and a step of opening the mold by separating the first mold and the second mold in a state where the decompression path is returned to the atmospheric pressure, The injection molding method according to any one of claims 1 to 4, further comprising: The molding space has a shape in which the thickness of the central part is larger than the thickness of the peripheral part,
The injection molding according to any one of claims 1 to 5, wherein the melt to be injected is injected into the molding space through an introduction port provided at a predetermined position in the peripheral portion. Method.   The injection molding method according to any one of claims 1 to 6, wherein the optical element is formed by curing an injection melt in the molding space by cooling. A molding die having a first die and a second die, and having a decompression path communicating with a molding space formed by closing the first die and the second die;
A vacuum pump for decompressing the inside of the molding space via the decompression path;
Switching between a first flow path that reduces the pressure in the molding space to a predetermined degree of vacuum and a second flow path that reduces the pressure in the molding space below the predetermined level of vacuum by suppressing or stopping the pressure reduction operation. A flow path switching device that selectively communicates with the decompression path;
After switching from the state where the first flow path is selectively communicated with the pressure reducing path by the flow path switching device to the state where the first flow path is selectively communicated with the pressure reducing path, An injection molding apparatus comprising: a control device that injects an injection melt into a molding space.

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