JP2008068606A - Molding method of synthetic resin molded article and molding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method and a molding apparatus for molding a synthetic resin product capable of making a surface quality of a molded article high under keeping a molding cycle short and homogenizing a size of a foamed cell of the foamed molded article as a whole and stabilizing its physical properties all over the molded article. <P>SOLUTION: A molten synthetic resin containing a foaming agent 16 is injected into a cavity 41 at a state that a gas flow layer 42 flowing to an opposite side of an injection opening 40 along a cavity face of a mold 8 is formed, then the gas is discharged into the out side, then by making the surface part of the synthetic resin in the cavity 41 contact to the cavity face and making cool it. The molding apparatus 1 includes a gas flow layer forming apparatus 5 and a gas suction apparatus 6 to attain the molding method described above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a molding method and a molding apparatus for molding a synthetic resin molded product by injecting a molten synthetic resin or a molten synthetic resin containing a foaming agent into a cavity of a molding die.

  Conventionally, in the molding method of synthetic resin, when the molten synthetic resin is injected into the mold cavity, the mold is generally cooled, and the molten synthetic resin injected into the cavity is molded. It is rapidly cooled and solidified by the mold. Therefore, in this molding method, there is a problem that the transfer to the mold is insufficient, or a weld line is generated on the surface of the molded product, and a molded product having a poor appearance is molded. Therefore, as a countermeasure for preventing these appearance defects, a method of increasing the temperature of the mold surface is proposed and put into practical use.

  For example, in the method of injection compression molding of a conductive thermoplastic resin in Patent Document 1, a thin heat insulating layer is provided on the cavity surface of the mold, and the mold is heated before filling with the molten synthetic resin. The cavity surface of the mold is kept at a high temperature by the heat insulating layer, the surface layer portion of the injected molten synthetic resin flows while in contact with the cavity surface of the mold, the mold is cooled after filling, The molten synthetic resin is cooled by the mold and solidified to form a synthetic resin molded product.

  Further, in the molding method of the foamed resin molded article of Patent Document 2, the temperature of the mold surface is maintained at a temperature equal to or higher than the thermal deformation temperature of the synthetic resin when the molten synthetic resin is injected, and the molten synthetic resin is injected into the mold cavity. The resin surface layer flows while in contact with the cavity surface. Upon completion of filling, the mold is rapidly cooled by the cooling medium, and the molten synthetic resin is cooled and solidified by the mold to form a synthetic resin molded product. .

Here, in the molding methods of Patent Documents 1 and 2, a foamed synthetic resin molded product is molded by injecting a molten synthetic resin containing a foaming agent. In the method of molding a foamed synthetic resin molded product, a synthetic resin is melted in an injection cylinder, and a supercritical fluid (SCF) such as nitrogen or carbon dioxide in a supercritical state is injected as a physical foaming agent. A molten synthetic resin mixed with SCF is injected into a cavity of a molding die and finely foamed by releasing the pressure to form a foamed synthetic resin molded product. The synthetic resin is foamed, and the foaming pressure suppresses the shrinkage of the synthetic resin, thereby preventing the occurrence of sink marks on the surface of the molded product.
JP 2005-297486 A JP-A-2005-7589

  In the molding method of Patent Document 1, a heat insulating layer is provided on the cavity surface of a mold, and a synthetic resin molded product is molded by injecting a molten synthetic resin containing a foaming agent, thereby preventing the occurrence of sink marks and weld lines. can do. However, in this molding method, since it takes time to cool and solidify the molten synthetic resin injected into the mold in a high temperature state, the molding cycle time becomes long. In addition, since the foam cells in the inner layer portion of the synthetic resin are likely to be enlarged before the mold in the high temperature state is cooled, it is difficult to form a fine foam foam molded product.

  In the molding method of Patent Document 2, since the mold is cooled by the cooling medium after the filling of the synthetic resin into the cavity is completed, foam breakage at the surface portion of the foamed cell foamed in the vicinity of the cavity surface is prevented. . However, strictly speaking, since the foaming of the molten synthetic resin has already started in the flow process until the filling into the cavity is completed, the cooling start timing for switching the mold to the cooling state before foaming is appropriately set. It is difficult to set. Further, since it takes time to inject and fill the molten synthetic resin into a mold maintained at a temperature higher than the heat distortion temperature of the synthetic resin and to cool and solidify it, the molding cycle time becomes longer.

  In the conventional general synthetic foam molding method, as shown in FIG. 9, since the mold is always cooled, if the synthetic resin 101 comes into contact with the cavity surface 100 of the mold, the fluidity of the synthetic resin decreases. Then, the contact resistance acts on the surface layer portion of the synthetic resin from the cavity surface 100 and flows so as to blow out from the central portion of the flow of the synthetic resin toward the flow end portion to the cavity surface 100 (fountain flow state), so the flow of the synthetic resin The large foam cells 102 generated on the tip side of the liquid flow toward the cavity surface 100, and many foam cells 102 are generated on the surface layer portion of the molded product, the surface quality of the molded product is deteriorated, and the surface layer portion of the molded product is deteriorated. Since the size of the foamed cell varies between the inner layer portion and the inner layer portion, there is a problem that the physical characteristics of the molded product cannot be stabilized over the entire molded product.

  The object of the present invention is to improve the surface quality of the molded product while keeping the molding cycle short, to make the foam cell size of the foam molded product uniform throughout the molded product, and to improve the physical characteristics. It is an object to provide a molding method and a molding apparatus for molding a synthetic resin molded product that can be stabilized over the entire molded product.

  The method for molding a synthetic resin molded article according to claim 1 is a molding method in which a molten synthetic resin is injected into a mold and the synthetic resin molded article is molded, and flows to the opposite side of the injection port along the cavity surface of the mold. With the gas flow layer formed, a first step of injecting a molten synthetic resin into the cavity, a second step of discharging the gas in the cavity to the outside, and then a synthesis filled in the cavity And a third step of bringing the surface layer portion of the resin into contact with the cavity surface and cooling with a mold.

  In the first step, the gas flow layer is formed so as to flow along the cavity surface to the opposite side of the injection port of the molten synthetic resin in the cavity of the mold, and the molten synthetic resin is injected in a state where the gas flow layer is formed. Is done. At this time, the molten synthetic resin does not easily come into contact with the cavity surface due to the gas flow layer, and since the molten synthetic resin is not cooled on the cavity surface, the fluidity of the molten synthetic resin is maintained, and the frictional resistance hardly acts on the synthetic resin from the cavity surface. Flow formation is suppressed.

  Next, in the second step, the gas in the gas flow layer formed between the molten synthetic resin and the cavity surface is discharged to the outside. Next, in the third step, when the gas is discharged to the outside, the surface layer portion of the filled molten synthetic resin comes into contact with the cavity surface, the molten synthetic resin is cooled by the mold, and the synthetic resin molded product is molded. The Molding can be performed while the mold is maintained in a cooled state, and the molten synthetic resin can be cooled after the gas is discharged, so that it is not necessary to lengthen the molding cycle time.

  The method for molding a synthetic resin molded article according to claim 2 is a molding method in which a molten synthetic resin is injected into a mold and the synthetic resin molded article is molded, and flows to the opposite side of the injection port along the cavity surface of the mold. With the gas flow layer formed, a first step of injecting a molten synthetic resin containing a foaming agent in the cavity, a second step of discharging the gas in the cavity to the outside, and then in the cavity And a third step of bringing the surface layer portion of the filled synthetic resin into contact with the cavity surface and cooling with a mold.

  In this molding method, the same synthetic method as in claim 1 is used, and a molten synthetic resin containing a foaming agent is injected to form a foamed synthetic resin molded product. In particular, when filled with molten synthetic resin, the formation of fountain flow in the molding cavity is suppressed, so that many foam cells are not generated in the surface layer of the molded product, and the entire molded product is fine. A foam cell is formed.

  The method for molding a synthetic resin molded product according to claim 3 is the method according to claim 1 or 2, wherein, in the first step, formed in a portion of the cavity surface of the mold other than the flow end portion where the injected synthetic resin flows. The gas flow layer is formed by ejecting gas from the numerous pores and discharging the gas from the numerous pores formed in the portion of the cavity surface on the flow end side. is there.

  According to a fourth aspect of the present invention, there is provided a method for molding a synthetic resin molded product according to any one of the first to third aspects, wherein in the second step, the gas in the cavity is discharged by suction. The method for molding a synthetic resin molded article according to claim 5 is characterized in that, in the invention of any one of claims 1 to 4, the gas forming the gas flow layer is an inert gas.

According to a sixth aspect of the present invention, there is provided a method for molding a synthetic resin molded product according to the second aspect of the present invention, wherein the foaming agent is a physical foaming agent.
According to a seventh aspect of the present invention, there is provided a method for molding a synthetic resin molded product, wherein the physical foaming agent is a fluid in a supercritical state or a subcritical state.

  The molding apparatus according to claim 8 is a molding apparatus for injecting a molten synthetic resin into a mold and molding a synthetic resin molded product, and at least during the injection of the molten synthetic resin into the cavity of the mold. A gas flow layer forming means for forming a gas flow layer flowing to the opposite side of the injection port, and a first gas discharge means for discharging the gas in the cavity to the outside after injecting the molten synthetic resin into the cavity It is.

  The gas flow layer forming means forms a gas flow layer that flows along the cavity surface to the opposite side of the molten synthetic resin injection port in the cavity of the mold. After injecting the molten synthetic resin into the cavity, the gas in the gas flow layer is discharged out of the cavity by the first gas discharge means. The effect similar to that of the first aspect is obtained.

  The molding apparatus according to claim 9 is a molding apparatus for molding a synthetic resin molded product by injecting a molten synthetic resin containing a foaming agent into a mold, and at least a melt synthesis containing the foaming agent in a cavity of the molding die. A gas flow layer forming means for forming a gas flow layer that flows to the opposite side of the injection port along the cavity surface during the injection of the resin, and a second method for discharging the gas in the cavity to the outside after injecting the molten synthetic resin into the cavity. 2 gas discharge means. This molding apparatus is an apparatus for injecting a molten synthetic resin containing a foaming agent to mold a foamed synthetic resin molded product, and basically exhibits the same operation as that of the second aspect.

  According to a tenth aspect of the present invention, there is provided the molding apparatus according to the eighth or ninth aspect, wherein the gas flow layer forming means molds a portion of the cavity surface of the mold other than the flow end portion through which the injected synthetic resin flows. A porous body, a gas supply means for supplying pressurized gas to the outer surface side of the first porous body, a second porous body forming a portion of the cavity surface on the flow end side, and a second porous body And a third gas discharging means for discharging gas from the outer surface side.

  A molding apparatus according to an eleventh aspect of the present invention is the molding apparatus according to any one of the eighth to tenth aspects, wherein the gas discharge means is constituted by a gas suction means for sucking the gas in the cavity and discharging it to the outside. It is.

According to the invention of claim 1, since the molten synthetic resin is injected in a state where the gas flow layer along the cavity surface is formed in the cavity in the first step, the molten synthetic resin is less likely to contact the cavity surface, Since it is not cooled at the cavity surface, the fluidity of the molten synthetic resin is maintained, and friction resistance from the cavity surface is less likely to act on the molten synthetic resin, so the formation of fountain flow is suppressed and the synthetic resin is surely secured to every corner of the molding cavity. Can be filled.
In the second step, gas in the gas flow layer is discharged, and in the third step, the molten synthetic resin filled in the cavity is brought into contact with the cavity surface and the surface layer portion of the molten synthetic resin is cooled by the molding die. Therefore, it is possible to mold a synthetic resin molded product excellent in appearance and surface quality without significantly increasing the molding cycle time, without generating a weld line on the outer surface of the molded product.

According to the invention of claim 2, the molding method is almost the same as that of claim 1, but basically, when a molten synthetic resin containing a foaming agent is injected to form a foamed synthetic resin molded product, it is basically claimed. In addition to the same effect as 1, the following effect is also obtained.
As mentioned above, since the formation of fountain flow is suppressed when filling with molten synthetic resin, many foamed cells are not generated on the surface layer of the molded product, and fine foamed cells are formed throughout the molded product. Can be generated uniformly, and a foamed synthetic resin molded product with stable physical characteristics can be molded over the entire molded product.

  According to the invention of claim 3, in the first step, gas is ejected from a large number of pores formed in a portion other than the flow end portion where the injected synthetic resin flows in the cavity surface of the mold, and the cavity surface Since the gas is discharged from a large number of pores formed in the flow end portion side of the gas, a gas flow layer can be formed along the flow of the molten synthetic resin flowing in the cavity. Since there are only a large number of pores appearing on the surface of the cavity surface without obstructing the flow of the cavity, the quality of the cavity surface can be almost ensured, and the surface quality of the molded product can be almost ensured. .

  According to the invention of claim 4, in the second step, the gas in the cavity is discharged by suction, so that the gas in the gas flow layer can be rapidly discharged. Therefore, the molten synthetic resin can be uniformly cooled at an early stage after filling, and the close adhesion of the surface layer of the synthetic resin to the cavity surface can be promoted to improve the transferability.

According to the invention of claim 5, since the gas forming the gas flow layer is an inert gas, there is no adverse effect such as changing the physical properties of the synthetic resin.
According to the invention of claim 6, since the foaming agent is a physical foaming agent, a molded product having fine foam cells can be formed. A synthetic resin molded article having a fine foam cell structure that is excellent in physical properties and uniformized over the surface layer portion and the inner layer portion of the molded product can be formed.
According to the invention of claim 7, since it is a fluid in a supercritical state or a subcritical state, a molded product having a high foaming density can be formed with fine foamed cells.

  According to the invention of claim 8, since the gas flow layer forming means and the gas discharge means are provided in the molding apparatus for molding the synthetic resin molded product, the molding method of claim 1 can be realized. The same effect as 1 is obtained. In addition, like a normal shaping | molding apparatus, it shall shape | mold in the state cooled by circulating the cooling fluid to a metal mold | die.

  According to the invention of claim 9, since the gas flow layer forming means and the gas discharge means are provided in the molding apparatus for molding the foamed synthetic resin molded product, the molding method of claim 2 can be realized, so The same effect as in item 2 can be obtained. In addition, like a normal shaping | molding apparatus, it shall shape | mold in the state cooled by circulating the cooling fluid to a metal mold | die.

  According to the invention of claim 10, the gas flow layer forming means includes a first porous body that molds a portion of the cavity surface of the mold other than the flow end portion through which the injected synthetic resin flows, and the first porous body. Gas supply means for supplying pressurized gas to the outer surface side of the body, a second porous body forming a portion of the cavity surface on the fluid end side, and gas is discharged from the outer surface side of the second porous body Therefore, a gas flow layer that flows in the same direction as the flow of the molten synthetic resin flowing in the cavity can be formed, and the flow of the molten synthetic resin is not hindered.

  According to the eleventh aspect of the present invention, since the gas discharge means is constituted by the gas suction means for sucking the gas in the cavity and discharging it to the outside, the gas in the gas flow layer can be discharged rapidly. Therefore, it is not necessary to lengthen the molding cycle time significantly, adhesion of the surface layer of the synthetic resin to the cavity surface is promoted, transferability is improved, and the quality of the molded product can be ensured.

The method for molding a synthetic resin molded article of the present invention is to inject a molten synthetic resin containing a foaming agent into a cavity in a state where a gas flow layer that flows to the opposite side of the injection port along the cavity surface of the mold is formed. Thereafter, the gas is discharged to the outside, and then the surface layer portion of the synthetic resin in the cavity is brought into contact with the cavity surface and cooled by a molding die.
The molding apparatus for a synthetic resin molded product of the present invention is a molding apparatus that achieves the molding method described above.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, a synthetic resin molded product molding apparatus 1 includes an injection molding machine 2, a fluid injection device 3, a gas flow layer forming device 5, a gas suction device 6, a control unit 46, and the like. ing. The injection molding machine 2 includes an injection unit 7 that heats, melts, and injects synthetic resin, a mold clamping unit 9 that opens and closes a molding die 8, and holds a high pressure.

  The injection unit 7 includes an injection cylinder 11 that injects a molten synthetic resin such as polypropylene from the nozzle portion 10 at the front end into the molding die 8, a screw 12 that is rotatable and can be moved forward and backward, and the screw 12 is rotated. It has a drive device 25 that drives in the front-rear direction while driving. A band heater for heating the synthetic resin introduced into the injection cylinder 11 from the hopper 14 is provided on the outer peripheral portion of the injection cylinder 11.

  The injection cylinder 11 is formed of a cylindrical cylinder, and a chamber 13 is formed in the front end side portion of the injection cylinder 11 for containing a molten synthetic resin just before injection containing a foaming agent. At the rear part of the cylinder 11, there is a hopper 14 for feeding the pellet-shaped synthetic resin raw material into the inside thereof, and a measuring unit for measuring the amount of the synthetic resin injected into the molding die 8 from the rotational speed of the screw 12 for each injection cycle. 15 are provided.

  A foaming agent injection nozzle 17 for injecting a physical foaming agent 16 supplied from the fluid injection device 3 to the molten synthetic resin conveyed from the rear part of the cylinder to the front part of the cylinder is provided in the middle part in the length direction of the injection cylinder 11. A kneading part 18 for kneading the foaming agent 16 injected from the foaming agent injection nozzle 17 into the molten synthetic resin is provided. In this embodiment, as the physical foaming agent 16, supercritical carbon dioxide gas is employed, but supercritical nitrogen gas and other gases can also be employed.

  The screw 12 is disposed in the injection cylinder 11, a conical head portion 19 is formed at the tip of the screw 12, and a first backflow prevention portion with a check valve in the vicinity of the rear side of the head portion 19. 20 is provided, and a second backflow prevention portion 21 with a check valve is formed in the middle in the length direction. Two spiral members 22 and 23 are attached to the outer peripheral portion of the screw 12. A backflow prevention mechanism 24 that prevents the foaming agent 16 from flowing backward is formed at the rear end portion of the spiral member 22. The backflow prevention mechanism 24 has a labyrinth structure in which a flow path of the synthetic resin is formed in a labyrinth shape at a portion behind the foaming agent injection nozzle 17 of the cylinder 11.

  The drive device 25 is provided with a rotation device 26 having a hydraulic or electric screw rotation motor for rotating the screw 12 and a hydraulic or electric pressure unit 27 for moving the screw 12 forward and backward in the forward and backward movement direction. It has been.

Next, the fluid injection device 3 will be described.
As shown in FIG. 1, the fluid injection device 3 is an SCF device 29 that generates a physical foaming agent 16 in which an inert gas (carbon dioxide or nitrogen gas) supplied from a cylinder 28 is brought to a high temperature and high pressure to be in a supercritical state. And a foaming agent injection part 31 to which the physical foaming agent 16 is supplied from the SCF device 29 via the supply passage 30.

Next, the mold clamping unit 9 will be described.
As shown in FIG. 1, the mold clamping unit 9 includes a molding die 8 (comprising a fixed die 32 and a movable die 33 that can be opened), and a stationary platen 34 to which the stationary die 32 is fixed. A movable platen 35 to which the movable mold 33 is fixed, and a driving device 36 are provided. An inflow hole 38 for molten synthetic resin is formed in the central wall portion 37 of the fixed mold 32, and this inflow hole 38 is connected to the nozzle portion 10 at the front end of the injection cylinder 11 through the inflow hole 39 of the stationary platen 34. An injection port 40 that faces the cavity 41 is formed at the downstream end of the inflow hole 38.

In the state in which the molding die 8 is clamped, a cavity 41 is formed in the molding die 8 to mold the molten synthetic resin injected and filled from the injection port 40 of the fixed die 32 into a molded product having a predetermined shape. While the molten synthetic resin is injected into the cavity 41 in the molding die 8 by the gas flow layer forming device 5, the gas flow layer 42 flows along the inner wall surface 41 a of the cavity 41 to the side opposite to the injection port 40 (see FIG. 2) is formed. The fixed plate 34, the movable plate 35, and the molding die 8 are provided with a guide pin, an ejector pin, a mold cooling system for cooling the molding die 8, and the like. The drive device 36 has a hydraulic cylinder for opening and closing the mold, and the piston rod 62 is connected to the rear end of the movable platen 35.

Next, the gas flow layer forming apparatus 5 will be described.
As shown in FIG. 1, the gas flow layer forming device 5 supplies pressurized gas to the first and second porous bodies 43 and 44 mounted in the molding die 8 and the outer surface side of the first porous body 43. A gas supply device 45 for discharging the gas from the outer surface side of the first and second porous bodies 43 and 44 to the outside of the molding die 8.

  The first porous body 43 is composed of a sintered metal porous body having a large number of pores, and other than the flow end portion where the molten synthetic resin injected from the injection port 40 flows out of the cavity surface of the molding die 8. It is provided so as to form the inner wall surface 41a of the cavity 41 which is a part. An annular gas channel 47 is provided on the outer surface side of the porous body 43. The porous body 43 is configured so that a molding pressure acting from a molten synthetic resin to be filled can be transmitted to the molding die 8. A gas supply path 48 and a gas discharge path 49 are connected to the gas flow path 47.

  The second porous body 44 is formed in the same manner as the porous body 43, and is provided so as to form an inner wall surface 41 b of the cavity 41 on the flow end side side of the cavity surface of the cavity 41. A gas flow path 50 is provided on the outer surface side of the porous body 44. The porous body 44 is configured to transmit a molding pressure acting from a molten synthetic resin to be filled to the molding die 8. A gas discharge path 51 is connected to the gas flow path portion 50.

The gas supply device 45 includes a nitrogen gas cylinder (not shown) that is a supply source of an inert gas (for example, nitrogen gas), a compressor 52 that pressurizes the inert gas, and an inert gas that is pressurized by the compressor 52. And an accumulator 53 having a predetermined capacity.
The inert gas accumulated in the accumulator 53 can be supplied to the gas flow path 47 on the outer surface side of the porous body 43 through the gas supply path 48, and the gas supply path 48 is provided with an electromagnetic opening / closing valve 54. Yes. The on-off valve 54 is opened / closed by a solenoid 54a.

  The gas suction device 6 is configured such that the inert gas supplied into the cavity 41 can be sucked and discharged to the outside of the molding die 8. The gas suction device 6 is a gas discharge means of the gas flow layer forming device 5. It also serves as. The gas suction device 6 includes a gas suction pump 56 and a gas storage tank 57 that stores an inert gas sucked by the gas suction pump 56.

  The gas flow path 47 is connected to a gas suction pump 56 through a gas discharge path 49. An electromagnetic open / close valve 58 is interposed in the gas discharge path 49, and the open / close valve 58 is opened / closed by a solenoid 58a. The gas flow path 50 on the outer surface side of the porous body 44 is connected to a gas discharge path 49 by a gas discharge path 51, and an electromagnetic open / close valve 59 is interposed in the gas discharge path 49. The open / close valve 59 is connected to a solenoid 59a. Open and close operation. The gas storage tank 57 is connected to the suction port of the compressor 52 by a gas passage 60. An electromagnetic opening / closing valve 61 is interposed in the gas passage 60, and the opening / closing valve 61 is opened / closed by a solenoid 61a.

  When the gas flow layer forming device 5 is operated to form the gas flow layer 42 in the cavity 41, the pressurized inert gas is supplied from the accumulator 53 to the gas flow path 47, while the gas flow path 50 is By sucking the inert gas, a gas flow layer 42 along the inner wall surface of the cavity 41 and flowing to the opposite side of the injection port 40 is formed. After filling with the molten synthetic resin, the supply of the inert gas is stopped, and the inert gas is sucked from the gas flow paths 47 and 50.

Next, the control unit 46 will be described.
The control unit 46 controls the entire molding apparatus 1 of this embodiment, but at least the drive unit 25 for the injection cylinder 11, the drive unit 36 for the mold clamping unit 9, the SCF unit 29, the compressor 52, and the like. The gas suction pump 56 and solenoids 54a, 58a, 59a, 61a of the on-off valves 54, 58, 59, 61 are connected to and controlled.
The control unit 46 drives the drive devices 25 and 36 to supply the physical foaming agent 16 supplied from the SCF device 29 to the foaming agent injecting section 31 at a predetermined time in each injection cycle. The compressor 45 is driven, the gas suction pump 56 is driven, and the solenoids 54a, 58a, 59a, 61a of the on-off valves 54, 58, 59, 61 are driven.

Next, a molding method for molding a synthetic resin molded product using the above-described synthetic resin molded product molding apparatus 1 will be described with reference to a molding process diagram shown in FIG. In FIG. 8, Pi (i =
1, 2,... Indicate each step.
As shown in FIG. 8, at P1, granular synthetic resin (for example, polypropylene resin) charged into the hopper 14 is charged into the rear part of the cylinder, and the synthetic resin injected into the molding die 8 by the measuring unit 15 is measured. The synthetic resin is heated and melted to about 200 to 300 ° C. by the heater.

At P2, the injection screw 12 starts rotating by the screw rotation motor of the rotating device 26, and the measured resin of the next cycle is moved forward while the screw 12 is driven backward from the advanced state where the injection has been completed in the previous cycle. Be transported. At P3, in the front side of the cylinder 11, the supercritical CO ₂ fluid supplied from the fluid injection device 3 to the blowing agent injection unit 31 is injected from the blowing agent injection nozzle 17, and the CO ₂ fluid is mixed. The molten synthetic resin is transferred to the kneading section 18 at the front of the cylinder, and one shot of the molten synthetic resin is transferred to the chamber 13 by the rotating screw 12. At P4, the rotation and backward movement of the screw 12 are stopped.

  Next, after the molding die 8 is clamped in P5, the open / close valve 54 of the gas supply path 48 and the open / close valve 59 of the gas discharge path 51 are opened in P6 as shown in FIG. In P 6, a necessary amount of inert gas (for example, temperature 40 to 80 ° C.) passes through the gas supply path 48 from the accumulator 53 in which the pressurized inert gas generated by the gas supply device 45 is accumulated. The porous body 44 is supplied to the flow path 47 and ejected from the numerous pores of the porous body 43 into the cavity 41, while the inert gas is sucked and discharged from the gas flow path 50 through the gas discharge path 51. The inert gas in the cavity 41 is sucked through the gas and the gas flow layer 42 that flows to the opposite side of the injection port 40 along the inner wall surface 41a of the cavity 41 is formed.

  Next, in P7, the pressure unit 27 drives the screw 12 forward at high speed and forcefully, and as shown in FIG. 3, the physical foaming agent 16 is introduced into the cavity 41 in the state where the gas flow layer 42 is formed. The contained molten synthetic resin is injected. The molten synthetic resin is less likely to contact the inner wall surface 41 a of the cavity 41 due to the gas flow layer 42, and flows in a state where it hardly contacts the inner wall surface 41 a of the cavity 41. As shown in FIG. 4, when the flow end portion side of the molten synthetic resin in contact with the inner wall surface 41b of the cavity 41 is detected by the pressure sensor, the on-off valve 59 of the gas discharge passage 51 is switched to the closed state. Then, the discharge of the inert gas through the porous body 44 is stopped.

  In P8, immediately after the detection by the pressure sensor, the on-off valve 54 of the gas supply path 48 is switched to the closed state, the on-off valve 58 of the gas discharge path 49 is switched to the open state, and the gas suction pump 56 is driven. As shown in FIG. 5, the inert gas in the cavity 41 in which the gas flow layer 42 is formed in the cavity 41 is rapidly sucked by the gas suction pump 56 and discharged to the outside of the molding die 8. As a result, as shown in FIG. 6, the surface layer portion of the melted synthetic resin comes into contact with the inner wall surface 41 a of the cavity 41 and comes into close contact.

Next, at P9, the on-off valve 58 of the gas discharge passage 49 is switched to the closed state, and as shown in FIG. 7, the molten synthetic resin is cooled by the cooling mold 8 and solidified to some extent. Next, in P10, the molded product in the cavity 41 is opened after solidification, and in P11, the molded product is taken out from the mold 8 via the ejector mechanism. This molded product is a foamed synthetic resin synthetic resin molded product in which fine foam cells of CO ₂ gas are uniformly formed in the entire interior.

The function and effect of the molding method and molding apparatus of the synthetic resin molded product described above will be described.
In the cavity 41, a gas flow layer 42 that flows to the opposite side of the injection port 40 along the inner wall surface 41 a of the cavity 41 by the inert gas ejected from the porous body 43 into the cavity 41 is formed to a predetermined thickness. In this state, when a molten synthetic resin containing a supercritical CO ₂ fluid is injected, the surface layer portion of the molten synthetic resin becomes difficult to contact the inner wall surface 41a of the cavity 41, and the gas flow layer 42 functions as a heat insulating layer. In addition, since the surface layer portion is not cooled by the inner wall surface 41a, the fluidity of the molten synthetic resin is maintained, and the frictional resistance hardly acts on the surface layer portion of the molten synthetic resin from the inner wall surface 41a. It flows to the end side while the formation of is suppressed.

  When the melted synthetic resin for one cycle is filled in the cavity 41, the inert gas that forms the gas flow layer 42 is discharged from a large number of pores of the porous body 43 by suction with the gas suction pump 56. By discharging the inert gas, the surface layer portion of the molten synthetic resin comes into contact with the inner wall surface 41a of the cavity 41 and the surface layer portion of the molten synthetic resin is cooled by the molding die 8. Can cool rapidly.

  As described above, since the molten synthetic resin is injected in a state where the gas flow layer 42 along the inner wall surface 41a and flowing to the opposite side of the injection port 40 is formed in the cavity 41, the molten synthetic resin is injected. The synthetic resin is less likely to come into contact with the inner wall surface 41a, the gas flow layer 42 has a heat insulation effect, and since it is not cooled by the inner wall surface 41a, the fluidity of the molten synthetic resin is maintained, and the friction resistance acts on the molten synthetic resin from the cavity surface. Therefore, the formation of the fountain flow is suppressed, and the synthetic resin can be reliably filled to every corner of the molding cavity 41.

  After filling with the synthetic resin, the gas in the gas flow layer 42 is discharged. Next, by discharging the gas, the molten synthetic resin filled in the cavity 41 is brought into contact with the cavity surface, and the surface layer of the molten synthetic resin is cooled by the mold 8. Therefore, it is possible to mold a synthetic resin molded product excellent in appearance and surface quality without significantly increasing the molding cycle time, without generating a weld line on the outer surface of the molded product.

As mentioned above, since the formation of fountain flow is suppressed during filling with the melted synthetic resin, many large foam cells are not generated on the surface layer of the molded product, and the entire molded product is fine. Foamed cells can be generated uniformly, and a foamed synthetic resin molded product having stable physical characteristics over the entire molded product can be molded.

  During the formation of the gas flow layer 42, the gas is ejected from a large number of pores formed in the inner wall surface 41 a of the cavity 41 of the mold 8 other than the flow end portion where the injected synthetic resin flows, and the cavity 41. Since the gas is discharged from a large number of pores formed in the flow end portion side portion of the inner wall surface 41a, the gas flow layer 42 along the flow of the molten synthetic resin flowing in the cavity 41 can be formed. Since the flow of the molten synthetic resin is not hindered and only a large number of pores appear on the surface of the cavity surface, the wall surface quality of the cavity 41 can be almost ensured, and the surface quality of the molded product can be ensured. Can be almost secured.

  After filling with the molten synthetic resin, the inert gas in the cavity 41 is discharged by the gas suction pump 56, so that the gas in the gas flow layer 42 can be discharged rapidly. Therefore, the molten synthetic resin can be uniformly cooled at an early stage after filling, and the close adhesion of the surface layer of the synthetic resin to the cavity surface can be promoted to improve the transferability.

  Since the gas forming the gas flow layer 42 is an inert gas, there is no adverse effect such as changing the physical properties of the synthetic resin. Further, since the foaming agent 16 is a physical foaming agent, a molded product having fine foam cells can be formed. A synthetic resin molded article having a fine foam cell structure that is excellent in physical properties and uniformized over the surface layer portion and the inner layer portion of the molded product can be formed.

Here, a modified example in which the embodiment is partially modified will be described.
1] In the example, the molding method for injecting the molten synthetic resin containing the foaming agent 16 into the molding die 8 and molding the synthetic resin molded product has been described. Using the same molding apparatus as in the example, A synthetic synthetic resin article may be formed by injecting a molten synthetic resin not containing the foaming agent 16 into the molding die 8 and using the same molding method as in the example. In this case as well, there is no formation of fine foam cells, but almost the same effect as in the above embodiment can be obtained.

2] In the examples, polypropylene resin is taken as an example of the synthetic resin, but other various synthetic resins (polyethylene, polystyrene, polycarbonate, etc.) and synthetic resins mixed with reinforcing fibers (carbon fiber, glass fiber, etc.) are used. It may be adopted.

3] In the examples, supercritical CO ₂ fluid is used as the physical foaming agent, but supercritical N ₂ fluid may be used, and subcritical CO ₂ fluid or N ₂ fluid may be used. Also good.
4] Although the physical foaming agent 16 is employed as the foaming agent 16 in the embodiments, a chemical foaming agent may be employed.

5] In addition, the present invention can be implemented in a form in which the above-described embodiment is partially changed without departing from the spirit of the present invention, and the present invention includes such a modified form.

It is a schematic block diagram of the shaping | molding apparatus of the synthetic resin molded product which concerns on the Example of this invention. It is a principal part enlarged view which shows the state which has formed the gas flow layer in the cavity. It is a principal part enlarged view which shows the state by which the molten synthetic resin was inject | poured in the state in which the gas flow layer was formed in the cavity. It is a principal part enlarged view which shows the flow state of the molten synthetic resin in a cavity. It is a principal part enlarged view which shows the state from which the gas of the gas flow layer in a cavity is discharged | emitted. It is a principal part enlarged view which shows the state of the fusion | melting synthetic resin by gas discharge | emission. It is a principal part enlarged view which shows the state by which the molten synthetic resin with which it filled is cooled with a shaping | molding die. It is a shaping | molding process figure of the shaping | molding method of a synthetic resin molded product. It is a figure which shows the flow state of the molten synthetic resin in the conventional cavity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molding apparatus 5 of a synthetic resin molded product 5 Gas flow layer forming apparatus 6 Gas suction apparatus 8 Mold 16 Foaming agent 40 Injection port 41 Cavity 42 Gas flow layer 43 First porous body 44 Second porous body 45 Gas supply apparatus

Claims (11)

In a molding method for injecting molten synthetic resin into a mold and molding a synthetic resin molded product,
A first step of injecting a molten synthetic resin into the cavity in a state where a gas flow layer flowing to the opposite side of the injection port along the cavity surface of the mold is formed;
Next, a second step of discharging the gas in the cavity to the outside,
Next, a third step of bringing the surface layer portion of the synthetic resin filled in the cavity into contact with the cavity surface and cooling with a molding die,
A method for molding a synthetic resin molded product, comprising: In a molding method for injecting molten synthetic resin into a mold and molding a synthetic resin molded product,
A first step of injecting a molten synthetic resin containing a foaming agent into the cavity in a state where a gas flow layer flowing to the opposite side of the injection port along the cavity surface of the mold is formed, and then in the cavity A second step of discharging gas to the outside;
Next, a third step of bringing the surface layer portion of the synthetic resin filled in the cavity into contact with the cavity surface and cooling with a molding die,
A method for molding a synthetic resin molded product, comprising:   In the first step, gas is ejected from a large number of pores formed in a portion other than the flow end portion where the injected synthetic resin flows in the cavity surface of the mold, and the flow end portion side of the cavity surface The method for molding a synthetic resin molded article according to claim 1 or 2, wherein the gas flow layer is formed by discharging gas from a large number of pores formed in the portion.   The method for molding a synthetic resin molded product according to any one of claims 1 to 3, wherein in the second step, the gas in the cavity is discharged by suction.   The method for molding a synthetic resin molded article according to any one of claims 1 to 4, wherein the gas forming the gas flow layer is an inert gas.   The method for molding a synthetic resin molded product according to claim 2, wherein the foaming agent is a physical foaming agent.   The method for molding a synthetic resin molded article according to claim 6, wherein the physical foaming agent is a fluid in a supercritical state or a subcritical state. In a molding apparatus for molding a synthetic resin molded product by injecting a molten synthetic resin into a mold,
A gas flow layer forming means for forming a gas flow layer that flows to the opposite side of the injection port along the cavity surface while injecting the molten synthetic resin into the cavity of the mold at least;
First gas discharge means for discharging the gas in the cavity to the outside after injecting the molten synthetic resin into the cavity;
A molding apparatus comprising: In a molding apparatus for molding a synthetic resin molded product by injecting a molten synthetic resin into a mold,
A gas flow layer forming means for forming a gas flow layer that flows to the opposite side of the injection port along the cavity surface while injecting at least the molten synthetic resin containing the foaming agent into the cavity of the mold;
Second gas discharge means for discharging the gas in the cavity to the outside after injecting the molten synthetic resin into the cavity;
A molding apparatus comprising:   The gas flow layer forming means includes a first porous body for forming a portion other than a flow end portion through which the injected synthetic resin flows in a cavity surface of a mold, and a pressurized gas on an outer surface side of the first porous body. Gas supply means for supplying gas, a second porous body forming a portion of the cavity surface on the flow end side, and a third gas discharge means for discharging gas from the outer surface side of the second porous body. The molding apparatus according to claim 8, wherein the molding apparatus is provided. The molding apparatus according to any one of claims 8 to 10, wherein the gas discharge means is constituted by a gas suction means for sucking the gas in the cavity and discharging it to the outside.

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