JP5855951B2 - Manufacturing method of injection molded body - Google Patents

Description

  The present invention relates to a method for manufacturing an injection molded body capable of manufacturing an injection molded body having a shape closer to a design value while suppressing an increase in the cooling period.

  Generally, an injection-molded body is molded by injecting molten resin into a mold and then cooled, but there are cases where a space is provided inside the injection-molded body for reasons such as suppressing an increase in the cooling period. For an injection molded body having such a hollow portion, for example, an injection molding method described in the following patent document has been proposed.

  In this injection molding method, molten resin is injected into a cavity formed by clamping a first mold and a second mold, and a pressurized fluid is injected into the cavity after the injection. By this injection, after a hollow portion is formed in the molten resin, the molten resin is pushed forward with the inner wall of the mold through the hollow portion, and is finally broken through at the end portion of the cavity. After the molten resin is pierced in this manner, the injection of the pressurized fluid is continued, and the molten resin is cooled and solidified by the pressurized fluid, whereby an injection molded body having a hollow portion is obtained. In addition, it is more preferable to cool such a pressurized fluid itself from the viewpoint of suppressing a prolonged cooling period.

JP 2005-96329 A

  However, the molten resin continues to be cooled by the pressurized gas until it is pierced by the pressurized fluid. For this reason, compared with the injection | pouring site | part of pressurized gas, it becomes the tendency for the cooling nonuniformity that the cooling degree of the pierced site | part becomes low to produce easily. This tendency becomes more prominent as the distance between the pressurized gas injection site and the site where the molten resin is broken is longer. And when this cooling nonuniformity arises, the problem that a cooling period becomes long will arise compared with the case where the said cooling nonuniformity does not exist.

  On the other hand, when the pressurized gas itself is cooled, compared to the case where the pressurized gas itself is not cooled, the lengthening of the cooling period due to uneven cooling can be slightly suppressed, but the inner wall of the resin forming the hollow portion Tends to solidify before the outer wall. And when the inner wall of the resin that forms the hollow portion is solidified before the outer wall, the pressure applied by the pressurized fluid to the inner wall is difficult to be transmitted to the outer wall, causing a sink on the outer wall, and a shape different from the design value There arises a problem that an injection molded body of the above is obtained.

  The present invention has been made in consideration of the above points, and intends to propose an injection molded body manufacturing method capable of manufacturing an injection molded body having a shape closer to the design value while suppressing an increase in the cooling period. It is.

  In order to solve such a problem, the present invention is a method for manufacturing an injection-molded body, and includes a resin injection step of injecting a molten resin into a cavity formed by a first mold and a second mold in a clamped state. Injecting pressurized gas into the cavity, forming a hollow portion in the molten resin with the pressurized gas, then flowing the molten resin along the cavity through the hollow portion, and at the flow end of the molten resin A pressurized gas injection step of breaking through the molten resin, and a cooling step of opening the path connected to the flow end of the molten resin after the molten resin is broken through and passing the cooling medium through the hollow portion And in the cooling step, the cooling medium is injected into the hollow portion through a portion where the molten resin is pierced from a path connected to the flow end of the molten resin, and the pressurized gas Injection It is characterized in that for discharging the cooling medium from the position.

  In the pressurized gas injection step of such a manufacturing method, when the molten resin flows along the cavity through the hollow portion, the molten resin starts to be cooled by the pressurized fluid along the flow direction. On the other hand, in the cooling step, the cooling medium is injected into the hollow portion through the portion where the molten resin is pierced from the path connected to the flow end of the molten resin, and the cooling medium is the injection portion of the pressurized gas. Discharged from. That is, the molten resin is cooled by the cooling medium that flows in the direction opposite to the flow direction of the molten resin. For this reason, the cooling nonuniformity of the injection | pouring site | part of a pressurized gas and the site | part by which the molten resin was pierced can be reduced irrespective of the distance between these site | parts. Therefore, even if the pressurized fluid itself or the cooling medium itself is not cooled, the lengthening of the cooling period due to the cooling unevenness can be suppressed. That is, by cooling the pressurized fluid itself or the cooling medium itself, it is possible to avoid the occurrence of sink marks on the outer wall due to the solidification of the inner side of the outer side of the molten resin. Thus, there is provided an injection molded body manufacturing method capable of manufacturing an injection molded body having a shape closer to the design value while suppressing an increase in the cooling period.

  In addition, at least one of the first mold and the second mold is provided with a concave portion that forms the cavity, and the surface of the concave portion or the vicinity of the surface is provided with the first mold and the second mold. It is preferable that a heat insulating member having a heat penetration rate lower than the heat penetration rate is provided.

  In this case, solidification of the molten resin injected into the cavity through the resin injection process can be delayed as compared with the case where the heat insulating member is not provided on the surface of the mold recess. Therefore, the fluidity of the molten resin in the pressurized gas injection process can be improved, and as a result, the cooling unevenness can be further reduced. In addition, the transferability of the molten resin to the surface of the mold recess can be improved.

And a pressure holding step of waiting for injection of the cooling medium in a state in which a path connected to the flow end of the molten resin is closed until a predetermined period has elapsed since the molten resin was pierced. And in the cooling step, after the period has elapsed, the injection of the pressurized gas is stopped, the path connected to the flow end of the molten resin is opened, and the cooling medium is passed through the hollow portion. It is preferable.

  In this case, the flow (passage) of the pressurized gas in the cavity is suppressed for a certain period after the molten resin is pierced, and during this period, the molten resin is melted mainly by heat conduction to the mold. The outside of the resin is cooled. For this reason, although the pressurized fluid itself or the cooling medium itself is not cooled, it is possible to prevent the inside of the molten resin fat from solidifying earlier than the outside. Moreover, it can also prevent that an inner side solidifies earlier than the outer side of the said molten resin irrespective of the thickness between the inner wall and outer wall of the molten resin in which a hollow part is formed. On the other hand, after the period has elapsed, the molten resin is rapidly cooled by the flow (passage) of the cooling medium, so that it is possible to suppress an increase in the cooling period.

  As described above, according to the present invention, there is provided an injection molded body manufacturing method capable of manufacturing an injection molded body capable of manufacturing an injection molded body having a shape closer to a design value while suppressing an increase in the cooling period. The

It is a conceptual diagram which shows an injection molding apparatus. It is sectional drawing which shows the metal mold | die assembly in a mold clamping state. It is a flowchart which shows the manufacturing method of the injection molded body which concerns on this embodiment. It is sectional drawing which shows the mode after a resin injection process. It is sectional drawing which shows a mode immediately after the start of pressurized gas injection | pouring. It is sectional drawing which shows the mode in the middle of pressurized gas injection | pouring. It is sectional drawing which shows a mode just before a molten resin is pierced. It is sectional drawing which shows a mode after molten resin was pierced.

  Hereinafter, a preferred embodiment of a method for producing an injection-molded body according to the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, an injection molding apparatus 1 using the method of manufacturing an injection molded body according to this embodiment includes a control unit 10, a molten resin injection unit 20, a pressurized gas injection unit 30, and a cooling air injection unit 40. And a die assembly 50 as a main component.

  The control unit 10 is a unit that performs overall control of the entire injection molding apparatus 1. The control unit 10 appropriately gives commands to the molten resin injection unit 20, the pressurized gas injection unit 30, the cooling air injection unit 40, or the mold assembly 50 to execute various control processes.

  The molten resin injection unit 20 is a unit that injects a molten resin (hereinafter referred to as a molten resin) into the mold assembly 50 based on a command from the control unit 10.

  The type of resin to be used in the molten resin injection unit 20 is not particularly limited, but specifically, polyolefin resins such as polyethylene resin and polypropylene resin; polyamide resins such as polyamide 6, polyamide 66, and polyamide MXD6 Resin; Polyoxymethylene (polyacetal, POM) resin; Polyester resin such as polyethylene terephthalate (PET) resin and polybutylene terephthalate (PBT) resin; Polyphenylene sulfide resin; Styrene resin such as polystyrene resin, ABS resin, AES resin, AS resin Resin; Methacrylic resin; Polycarbonate resin; Modified polyphenylene ether (PPE) resin; Polysulfone resin; Polyethersulfone resin; Polyarylate resin; Bromide resin; polyimide resins; polyether ketone resins; polyether ether ketone resins; polyester carbonate resin; can be exemplified a liquid crystal polymer.

  The resin to be used in the molten resin injection unit 20 includes a plasticizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a fungicide, a lubricant, a colorant, a crosslinking agent, an impact resistance enhancer, and a filler. Any one or a plurality of agents may be mixed.

  The pressurized gas injection unit 30 is a unit that injects a gas to which a predetermined value of pressure is applied (hereinafter referred to as a pressurized gas) into the mold assembly 50 based on a command from the control unit 10. The pressurized gas injection unit 30 has an opening / closing valve 31 in the path with the mold assembly 50. When the opening / closing valve 31 is in an open state, the pressurized gas is injected into the mold assembly 50. The

  The gas to be used in the pressurized gas injection unit 30 is not particularly limited as long as it is a gas at normal temperature and normal pressure, but is preferably one that does not react or mix with the resin used in the molten resin injection unit 20. Specific examples include nitrogen gas, carbon dioxide gas, helium gas, and air. Nitrogen gas or helium gas is preferable in consideration of safety and economy.

  The cooling air injection unit 40 is a unit that injects cooling air, to which a pressure in a range of, for example, 0.2 MPa or more and 5 MPa or less is applied, to the mold assembly 50 based on a command from the control unit 10.

  The cooling air injection unit 40 includes a three-way valve 41 that can be switched to a route to the mold assembly 50 or a route to an air communication port (not shown). The three-way valve 41 is the cooling air injection unit 40. And the mold assembly 50 are connected to each other, cooling air is injected into the mold assembly 50. When the three-way valve 41 connects the mold assembly 50 and the atmosphere communication port, the pressurized gas injected from the pressurized gas injection unit 30 is discharged into the atmosphere through the mold assembly 50. The

  As shown in FIG. 2, the mold assembly 50 includes a first mold 51 and a second mold 52. The first mold 51 and the second mold 52 are separated from each other (hereinafter referred to as mold open state), one surface of the first mold 51, and the second mold 52 based on a command from the control unit 10. It is possible to shift between a state in which the first surface and the other surface are overlapped with each other with a predetermined pressure (hereinafter referred to as a mold clamping state). FIG. 2 shows the mold assembly 50 in a clamped state.

  A concave portion is formed on the surfaces of the first mold 51 and the second mold 52, and the surface of the concave portion is covered with a heat insulating member 53. The heat insulating member 53 has a heat permeability lower than that of the first mold 51 and the second mold 52, and can withstand a resin filling pressure and a pressurized gas pressure.

  Examples of the material of the heat insulating member 53 include ceramics such as alumina and zirconia, engineering plastics, and the like. Further, as a method of providing the heat insulating member 53 on the concave surface, for example, a method of coating the heat insulating member 53 by a thermal spraying method such as a plasma powder spray method or HVOF (High Velocity Oxygen Fuel), or a heat insulating member 53 is installed as a nest The method etc. are mentioned.

  When the first mold 51 and the second mold 52 of the mold assembly 50 are in the clamped state, a space (hereinafter referred to as a space) is formed by the recess of the first mold 51 and the recess of the second mold 52. , Referred to as a cavity). Specifically, a cavity (hereinafter referred to as a molding cavity) SPC1 that represents a molded product to be molded, a cavity (hereinafter referred to as an overflow cavity) SPC2 that stores excess molten resin, and a molding cavity SPC1 and an overflow cavity SPC2 A cavity (hereinafter referred to as “communication cavity”) SPC3 is formed.

  In the molding cavity SPC1, a gate (hereinafter referred to as a resin injection gate) GT for injecting molten resin is formed, and the resin injection gate GT communicates with the outside of the mold. Further, a hole (hereinafter referred to as a nozzle insertion hole) HL for inserting a nozzle (hereinafter referred to as gas injection nozzle) NL for injecting pressurized gas is formed, and this nozzle insertion hole HL is also communicated with the outside of the mold. In the case of this embodiment, the resin injection gate GT and the nozzle insertion hole HL are formed in the vicinity of the end side opposite to the end side where the communication cavity SPC3 is formed in the molding cavity SPC1.

  Based on the command of the control unit 10, the gas injection nozzle NL has a position where the nozzle tip is in the cavity (hereinafter referred to as a start position) PX and a position where the nozzle tip is outside the cavity (hereinafter referred to as a retracted position) PY. It is movable through the nozzle insertion hole HL.

  On the other hand, in the overflow cavity SPC2, a recess 60 that is recessed toward the outside of the mold is formed on the inner wall of the mold that is the end in the flow direction of the molten resin flowing from the communication cavity SPC3. The outer shape of the recess 60 is, for example, a truncated cone, and the recess space is tapered toward the bottom of the recess (outside the mold). A tube (hereinafter referred to as a communication tube) 61 is connected to the recess bottom of the recess 60, and the overflow cavity SPC 2 and the outside of the mold are connected by the communication tube 61.

  Next, the manufacturing method of the injection molded body according to the present embodiment will be described. As shown in FIG. 3, the manufacturing method of the injection molded body according to the present embodiment includes a mold clamping step P1, a resin injection step P2, a pressurized gas injection step P3, a pressure holding step P4, and a pressurized gas discharge step P5. The cooling process P6 and the mold opening process P7 are provided as main processes.

<Mold clamping process P1>
In this mold clamping step P1, the first mold 51 and the second mold 52 are clamped, and as shown in FIG. 2, a molding cavity SPC1, an overflow cavity SPC2, and a communication cavity SPC3 are formed. The Further, as shown in FIG. 2, the gas injection nozzle NL is moved from the retracted position PY to the start position PX through the nozzle insertion hole HL, and a part of the gas injection nozzle NL is inserted into the molding cavity.

<Resin injection process P2>
In the resin injection process P2, the on-off valve 31 (FIG. 1) is closed, and the three-way valve 41 (FIG. 1) is connected to the mold assembly 50 and the atmosphere communication port. In this state, the molten resin starts to be injected into the cavity from the molten resin injection unit 20 (FIG. 1) via the resin injection gate GT (FIG. 2). The injection of the molten resin is stopped when the specified injection amount of the molten resin is injected. In this way, as shown in FIG. 4, the molten resin is filled into the cavity.

  The three-way valve 41 may be closed. However, when the three-way valve 41 is in the closed state, the amount of atmospheric emissions per unit time in each of the cavities SPC1 to SPC3 is higher than when the three-way valve 41 is in a state of connecting the mold assembly 50 and the atmosphere communication port. There is a possibility that the cavity internal pressure may hinder injection of the molten resin. Therefore, from the viewpoint of preventing such a possibility, it is preferable that the three-way valve 41 is in a state of connecting the mold assembly 50 and the air communication port.

<Pressurized gas injection process P3>
In this pressurized gas injection process P3, the three-way valve 41 (FIG. 1) is closed. In this state, the on-off valve 31 (FIG. 1) is opened after the molten resin injection stops, and pressurized gas begins to be injected into the cavity via the gas injection nozzle NL (FIG. 2). As a result, as shown in FIG. 5, a hollow portion HW is formed in the molten resin injected into the molding cavity SPC1 by the pressurized gas flowing into the cavity. Then, as shown in FIG. 6, the hollow portion HW advances by pushing the molten resin forward with the mold inner wall. As a result, the molten resin flows in the order of the molding cavity SPC1, the communication cavity SPC3, and the overflow cavity SPC2 along the inner wall of the mold, and as shown in FIG. 7, starts to flow into the recess 60 that is the end portion of the overflow cavity. . Subsequently, as shown in FIG. 8, the molten resin that has flowed into the recess 60 of the overflow cavity is broken through to the bottom of the recess (hereinafter referred to as blowout), and the hollow portion HW and the communication pipe 61 are in communication with each other. It becomes. In this way, in the pressurized gas injection process P3, the molten resin is transferred to the cavity surface through the hollow portion HW, and the hollow portion HW and the communication pipe 61 connected to the concave portion 60 at the end portion of the cavity are communicated. The

  By the way, when the three-way valve 41 is in a state of connecting the mold assembly 50 and the atmosphere communication port at the time of blowout, the pressure in each of the cavities SPC1 to SPC3 is likely to drop rapidly, and due to the pressure fluctuation, The molten resin tends to peel from the inner wall surface of the first mold 51 or the second mold 52 and the pressurized gas injection nozzle. And when molten resin peels from a pressurized gas injection | pouring nozzle, pressurized gas may leak from the peeling part, and control of a cavity internal pressure may become difficult, and sink will arise in this case. However, in this pressurized gas injection process P3, since the three-way valve 41 is in a closed state at the time of blowout, it is possible to suppress the variation of the internal pressure of the cavity caused by the blowout, and as a result, leakage of the pressurized gas, Can prevent sink marks.

  Moreover, it is possible to prevent the communication pipe 61 from being blocked by blowing out the molten resin flowing into the recess 60 until the molten resin reaches the bottom of the recess. Note that the blowout of the molten resin that has flowed into the recess 60 before reaching the bottom of the recess adjusts the injection amount of the molten resin, the injection timing of the pressurized gas, and the like according to the volumes of the cavities SPC1 to SPC3. It is feasible. This has already been confirmed by experiments of the present inventors.

<Pressure holding process P4>
In this pressure-holding step P4, the pressurized gas is injected while the three-way valve 41 is closed until a predetermined period (hereinafter referred to as a standby period) that should be waited without injecting the cooling air from the blowout time. Is continued, and the injection of the pressurized gas is stopped when the standby period elapses. Therefore, the pressure in the cavity is kept constant without the pressurized gas flowing (passing) through the cavity. In this pressure holding process P4, since the pressurized gas is prevented from flowing (passing) through the cavity, the molten resin is cooled mainly by heat conduction to the first mold 51 and the second mold 52. .

  As a waiting period, it is desirable to secure a period in which the outside of the molten resin is solidified and starts to have sufficient rigidity. Mainly, the thickness of the molten resin in the molding cavity SPC1 (the inner wall of the mold and the hollow portion HW ), The temperature of the molten resin, and the temperature of the mold. Specifically, the waiting period becomes longer as the thickness of the molten resin is larger and the temperature of the molten resin or mold is higher. For example, the thickness of the molten resin in the molding cavity SPC1 is 3 mm, and the temperature of the molten resin is When the temperature is 300 ° C. and the mold temperature is 80 ° C., the standby period is 40 seconds.

<Pressurized gas discharge process P5>
In this pressurized gas discharge process P5, the three-way valve 41 is brought into a state of connecting the mold assembly 50 and the air communication port after the standby period has elapsed. Thereby, the pressurized gas in each cavity SPC1-SPC3 is discharged | emitted in air | atmosphere.

<Cooling process P6>
In the cooling process P6, the gas injection nozzle NL is moved from the start position PX (FIG. 2) to the retracted position PY (FIG. 2). Further, the three-way valve 41 (FIG. 1) connects the cooling air injection unit 40 and the mold assembly 50. Thereby, the cooling air flows in from the communication pipe 61 and is discharged from the nozzle insertion hole HL through the overflow cavity SPC2, the communication cavity SPC3, and the molding cavity SPC1 in this order. As the cooling air flows in the cavity, the molten resin is quickly cooled.

<Mold mold opening process P7>
In this mold opening process P7, the first mold 51 and the second mold 52 are brought into the mold open-clamped state, and the molded bodies molded in the cavities SPC1 to SPC3 are taken out. And an unnecessary part (communication cavity SPC3 and overflow cavity SPC2 part) is parted from this molded object, and the molded article (molding cavity SPC1 part) for the shaping | molding objective is obtained.

  As described above, in the pressurized gas injection step P3 of the manufacturing method of the injection molded body of the present embodiment, the pressurized gas is injected from the gas injection nozzle NL into the molding cavity SPC1, and the molten resin is hollowed by the pressurized gas. After forming the part HW, the molten resin is caused to flow along the cavity through the hollow part HW, and the molten resin is blown out at the flow end of the molten resin.

  In the pressurized gas injection step P3, when the molten resin flows along the cavity through the hollow portion HW, the molten resin starts to be cooled by the pressurized fluid along the flow direction.

  On the other hand, in the cooling process P6, the path (communication pipe 61) connected to the flow end of the molten resin is opened after blowout, and cooling air is passed through the hollow portion HW. Specifically, cooling air is injected from the communication pipe 61 into the hollow portion HW via the blowout portion (recess 60), and the cooling air is discharged from the pressurized gas injection portion (nozzle insertion hole HL).

  That is, in this cooling process P6, the molten resin is cooled by the cooling air flowing in the direction opposite to the flowing direction of the molten resin. For this reason, the cooling nonuniformity of the injection site | part (nozzle insertion hole HL) of pressurized gas and a blowout site | part (recessed part 60) is reduced irrespective of the distance between these parts. Therefore, even if the pressurized fluid itself or the cooling air itself is not cooled, it is possible to suppress an increase in the cooling period due to uneven cooling. That is, by cooling the pressurized fluid itself or the cooling air itself, it is possible to avoid the occurrence of sink marks on the outer wall due to the solidification of the inner side of the outer side of the molten resin.

  Thus, there is provided an injection molded body manufacturing method capable of manufacturing an injection molded body having a shape closer to the design value while suppressing an increase in the cooling period.

  Moreover, in this embodiment, the heat insulation member which becomes a heat | fever permeability lower than the heat | fever permeability in the said 1st metal mold | die 51 and the 2nd metal mold | die 52 on the surface of the recessed part in the 1st metal mold | die 51 and the 2nd metal mold | die 52. 53 is provided.

  When the heat insulating member 53 is provided, solidification of the molten resin injected into the molding cavity SPC1 through the resin injection step P2 can be delayed as compared with the case where the heat insulating member 53 is not provided. Therefore, the fluidity of the molten resin in the pressurized gas injection step P3 can be improved, and as a result, the cooling unevenness can be further reduced. Moreover, the transfer property of the molten resin to the surface of the concave portion in the first mold 51 and the second mold 52 can be improved.

  Further, in the present embodiment, the pressure holding step P4 for waiting for the injection of cooling air while the communication pipe 61 is closed by the three-way valve 41 until a predetermined period (standby period) elapses from the blowout time of the molten resin. Is provided. In the cooling step P6, after the waiting period has elapsed, the injection of the pressurized gas is stopped, the communication pipe 61 is opened by the three-way valve 41, and the cooling air is passed through the hollow portion HW.

  In this pressure-holding step P4, the flow (passage) of the pressurized gas in the cavity is suppressed for a certain period after the molten resin is pierced, and in this period, mainly by heat conduction to the mold, The outside of the molten resin is cooled.

  Therefore, it is possible to prevent the inside of the molten resin from solidifying earlier than the outside of the molten resin, although the pressurized fluid itself or the cooling medium itself is not cooled. Moreover, it can also prevent that an inner side solidifies earlier than the outer side of the said molten resin irrespective of the thickness between the inner wall and outer wall of the molten resin which form the hollow part HW. On the other hand, after the standby period elapses, the molten resin is rapidly cooled by the flow (passage) of the cooling medium, so that it is possible to suppress an increase in the cooling period.

  The above embodiment is merely an example, and the present invention is not limited to the above embodiment.

  For example, in the above embodiment, air is applied as the cooling medium used in the cooling process P6. However, the cooling medium is not limited to air. For example, a gas such as nitrogen gas, carbon dioxide gas or helium gas, a liquid such as water, or a gas containing mist-like water can be used as the cooling medium. However, those that do not react with or mix with the molten resin are desirable, and air, nitrogen gas, helium gas, water, or the like is preferable in view of safety and economy. The cooling medium may be injected in a high pressure state. However, from the viewpoint of simplifying the configuration, it is preferable to inject in a state where the pressure is not high, for example, in the range of 0.2 MPa to 5 MPa because the compressor and the like can be simplified.

  Further, in the above embodiment, the injection of the pressurized gas is stopped when the standby period elapses. However, the injection of the pressurized gas may be stopped before the standby period elapses. However, it is preferable that the pressurized gas is continuously injected until the standby period elapses. Even if the pressurized gas leaks from the boundary between the molds 51 and 52 in the mold-clamped state (the mold 51 and 52), the molten resin is caused by the pressure of the pressurized gas. Can continue to be pushed into the molds 51 and 52. For this reason, it is because the heat transfer efficiency from molten resin to the metal mold | dies 51 and 52 can be improved.

  Moreover, in the said embodiment, although the discharge destination of the pressurized gas inject | poured in the cavity was made into the communicating pipe 61, it is good also as the nozzle insertion hole HL. Specifically, the gas injection nozzle NL is moved from the start position PX (FIG. 2) to the retracted position PY (FIG. 2) while the three-way valve 41 (FIG. 1) is closed, and the nozzle obtained by the movement is moved. The pressurized gas is discharged from the insertion hole HL. In this way, since the pressurized gas can be discharged without using the communication pipe 61 as the pressurized gas discharge path, the communication pipe 61 is used exclusively as the cooling air injection path. Is possible. Therefore, the three-way valve 41 (FIG. 1) can be replaced with the same one as the on-off valve 21, the path switching step can be omitted, and the mold assembly 50 (communication pipe 61) and the atmosphere communication port are connected. The route can be omitted. In addition, by supplying cooling air in the cooling process P6, the pressurized gas can be discharged into the atmosphere. For this reason, as in the above embodiment, after the three-way valve 41 is opened and the pressurized gas is discharged in the pressurized gas discharge step P5, the cooling air is flowed in the cooling step P6. The air can be shared not only for cooling the molten resin but also for discharging the pressurized gas, and the process can be simplified. As a result, it is possible to simplify the method for manufacturing the injection-molded body and to reduce the size of the injection molding apparatus 1. In addition, compared with the case where the cooling medium injected from the communication pipe 61 is discharged from the boundary between the molds 51 and 52 (division of the molds 51 and 52), the discharge area can be secured larger. A large amount of the cooling medium can be passed through the hollow portion of the molten resin.

  In the above embodiment, the three-way valve 41 is closed before the pressurized gas is injected. However, the time when the three-way valve 41 is closed is not limited to the above embodiment. For example, it may be any time point in the period from the time when the pressurized gas is injected to immediately before the time when the molten resin is blown out. In short, if the three-way valve 41 is in a closed state before blowout, the pressure fluctuation due to blowout can be suppressed as in the above embodiment.

  Moreover, in the said embodiment, injection | pouring of pressurized gas was started after the time of injection | pouring of molten resin being stopped. However, the injection timing of the pressurized gas is not limited to the above embodiment, and can be any point in the period from the start of the injection of the molten resin to the stop.

  Moreover, in the said embodiment, the external shape of the recessed part 60 formed in the 2nd metal mold | die 52 was made into truncated cone shape. However, the outer shape of the recess 60 is not limited to this embodiment, and may be, for example, a cylindrical shape. However, from the viewpoint of improving the release of the molded product, it is desirable that the recessed space is tapered toward the outside of the mold. Further, from the viewpoint of avoiding the arrival of the molten resin to the bottom of the recess, the value of H / D is 1.2 or more, preferably 2 or more, more preferably 5 or more when the diameter of the opening of the recess is D depth H. Good to be. In addition, the site | part in which the recessed part 60 is formed is so preferable that the distance of the split (boundary) of the 1st metal mold | die 51 and the 2nd metal mold | die 52 is long. This is because if the portion where the recess 60 is formed is close to the split, the pressurized gas may leak from the split.

  In the above embodiment, the cavities SPC1 to SPC3 are formed by the recesses formed in both the first mold 51 and the second mold 52 in the mold-clamped state, but the first in the mold-clamped state. The cavity may be formed by a recess formed in one of the mold and the second mold. Further, the cavity SPC2 or SPC3 may be omitted.

  In the above embodiment, the heat insulating member 53 is provided on the surface of the recess formed in the first mold 51 and the second mold 52, but the heat insulating member may be provided inside the vicinity of the surface. Further, the heat insulating member 53 may be omitted. However, it is preferable to provide the heat insulating member 53 from the viewpoint of delaying the solidification of the molten resin injected into the molding cavity SPC1 through the resin injection step P2 or improving the transferability of the molten resin.

  In the above embodiment, the control unit 10 controls the molten resin injection unit 20, the pressurized gas injection unit 30, and the cooling air injection unit 40. However, a plurality of units that control these units separately are used. A control unit may be applied. Further, the unit that controls the molten resin injection unit 20 may control the pressurized gas injection unit 30 and the cooling air injection unit 40, respectively.

  The present invention can be used in the field of handling articles having hollow portions.

DESCRIPTION OF SYMBOLS 1 ... Injection molding apparatus 10 ... Control unit 20 ... Molten resin injection unit 30 ... Pressurized gas injection unit 31 ... On-off valve 40 ... Pressurized gas injection unit 41 ... Three-way Valve 50 ... Mold assembly 51 ... First mold 52 ... Second mold 60 ... Recess 61 ... Communication pipe 70 ... Cooling air injection unit SPC1 ... Molding Cavity SPC2 ... Overflow cavity SPC3 ... Communication cavity GT ... Resin injection gate HL ... Nozzle insertion hole HW ... Hollow part NL ... Gas injection nozzle PX ... Start position PY ... Retraction position P1 ... Mold clamping process P2 ... Resin injection process P3 ... Pressurized gas injection process P4 ... Holding pressure process P5 ... Pressurized gas discharge process P6 ... Cooling process P7 ... Die mold opening Process

Claims (1)

A resin injection step of injecting a molten resin into a cavity formed by the first mold and the second mold in a clamped state;
A pressurized gas is injected into the cavity, and after the hollow portion is formed in the molten resin by the pressurized gas, the molten resin is flowed along the cavity through the hollow portion, and the molten resin is melted at the flow end of the molten resin. A pressurized gas injection process for breaking through the resin;
A pressure-holding step of stopping the flow of the pressurized gas until a predetermined period has elapsed from the time when the molten resin is pierced, and solidifying the outside of the molten resin;
A path that communicates with the flow end of the molten resin is opened after the period has elapsed , and includes a cooling step of passing a cooling medium through the hollow portion,
In the cooling step, the cooling medium is injected into the hollow portion through a portion where the molten resin is pierced from a path connected to the flow end of the molten resin, and the pressurized gas is injected from the injection portion. Drain the cooling medium ,
At least one of the first mold and the second mold is provided with a recess that forms the cavity,
Near the surface or surfaces of said recess, leaving morphism you wherein the <br/> heat insulating member made of a low thermal effusivity than the thermal effusivity of the first mold and the second mold is provided Manufacturing method of a molded object.

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