JP2006007421A - Mold for molding hollow molded product and molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mold for molding a hollow molded product constituted so as not only to employ a different molding method of the hollow molded product because a silver streak or the like is easy to occur in the hollow molded product when the hollow molded product is molded by injecting gas in a cavity together with a molten resin through a runner and a gate but also to close the communication hole with the hollow part of the hollow molded product because a defective product is formed when plating or the like if there is the communication hole with the hollow part of the hollow molded product, and also to provide a molding method using the mold. <P>SOLUTION: In the molding method of the hollow molded product P by the injection of the gas G in the molten resin M, which is injected in the cavity 16 formed between a fixed mold 12 and a movable mold 13, from a gas passing port 18a, the gas G is directly injected in the molten resin M, which is injected in the cavity 16 from the gas passing port 18a to form the hollow part P1 and discharged from the gas passing port 18a with the advance of the cooling and solidification of the molten resin M and the communication of the gas passing port 18a and the hollow part P1 is closed by a part of the molten resin M injected in the cavity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molding die and a molding method for a hollow molded product in which a gas is injected into a molten resin injected into a cavity formed between a fixed mold and a movable mold, and particularly to a hollow portion of the hollow molded product. The present invention relates to a molding die and a molding method for a hollow molded product capable of closing a communicating hole.

  The molding method for hollow molded products, in which gas is injected into the molten resin injected into the cavity formed between the fixed mold and movable mold, prevents sinking of thick products, shortens molding time, and saves molding materials. It is widely performed for the purpose of. In the molding method of the hollow molded article, generally, a communication hole is left after molding after gas is injected to form a hollow portion. The communication hole not only leaves a problem in the appearance of the hollow molded product, but particularly when the hollow molded product is impregnated in a liquid tank in the subsequent process to perform plating or coating, a plating solution or the like is introduced into the hollow portion from the communication hole. There was a problem that the paint entered and defective products were generated.

Patent Documents 1 to 3 are known to solve the problem of communication holes remaining in a hollow molded product. None of the devices described in Patent Document 1 to Patent Document 3 are provided with a gas vent in the cavity, and inject molten resin and gas from the nozzle portion into the cavity via the runner and gate. . When the molten resin is cooled and solidified in the cavity, a part of the molten resin stored in the gate portion is extruded to close the communication hole of the hollow molded product. However, Patent Documents 1 to 3 have the following problems.
(1) Since the molten resin and gas are injected into the cavity through the runner and gate, the resin first injected into the cavity at the time of injection contains gas, and molding defects such as silver streaks and voids are likely to occur.
(2) The gas vent is separated from the cavity, and it is difficult for high-pressure gas to be exerted on the hollow portion formed in the cavity, and it is difficult to depressurize the gas.
(3) The cross-sectional area of the gate needs to be a predetermined cross-sectional area.

Japanese Patent Laid-Open No. 9-216246 (Claim 1, FIG. 5) JP-A-9-327840 (Claim 1, FIG. 5) Japanese Patent Laid-Open No. 7-100854 (Claim 1, FIG. 2)

  Therefore, in the present invention, when a hollow molded product is molded by injecting a gas together with a molten resin through a runner and a gate into a cavity formed between a fixed mold and a movable mold, the hollow molded product is silver. Since streaks and voids are likely to occur, it is possible to provide a molding die and a molding method for a hollow molded product different from the above, and if there is a communication hole communicating with the hollow portion of the hollow molded product, It is an object of the present invention to provide a mold for molding a hollow molded product and a molding method capable of closing a communication hole communicating with a hollow portion because defective products are generated when plating or painting is performed.

  According to a first aspect of the present invention, there is provided a molding die for a hollow molded product in which a gas is injected into a molten resin injected into a cavity formed between a fixed die and a movable die. A gas vent located in the cavity at least during gas injection, a resin reservoir formed in the vicinity of the gas vent, and an extrusion mechanism for extruding the molten resin in the resin reservoir into the cavity. It is characterized by that.

  According to a second aspect of the present invention, there is provided a molding die for a hollow molded article according to the first aspect, wherein the gas vent is formed at the tip of the gas nozzle pin, and is formed around the gas nozzle pin in a concave shape with respect to the cavity forming surface. The resin reservoir portion is provided, and at least a part of the resin reservoir portion is a surface of the extrusion mechanism.

  According to a third aspect of the present invention, there is provided a method for forming a hollow molded article, wherein a gas is injected from a gas vent into a molten resin injected into a cavity formed between a fixed mold and a movable mold. In the molding method, gas is directly injected from the gas vent into the molten resin injected into the cavity to form a hollow portion, and the gas is discharged from the gas vent with the progress of cooling and solidification of the molten resin, and injected into the cavity. Further, the communication between the gas vent and the hollow portion is blocked by a part of the molten resin.

  According to the method for molding a hollow molded product of the present invention, a gas is directly injected into a molten resin injected into a cavity from a gas vent to form a hollow portion, and the gas is vented from the gas vent with the progress of cooling and solidification of the molten resin. Since the gas vent and the hollow part are blocked by a part of the molten resin discharged and injected into the cavity, the runner and gate are formed in the cavity formed between the conventional fixed mold and the movable mold. Compared with a molding method in which a gas is injected together with molten resin to form a hollow molded product and the communication hole communicating with the hollow portion of the hollow molded product is closed, the hollow molded product has defects such as silver streaks and voids. Are less likely to occur, and the gas pressure exerted on the hollow molded article can be easily controlled. Also, the same effect is obtained with the molding die of the hollow molded product of the present invention.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a molding die for a hollow molded product in the present embodiment. 2 to 5 are cross-sectional views of a molding die showing a method for molding a hollow molded product in the present embodiment.

  The outline of the molding die 11 of the hollow molding product will be described with reference to FIGS. 1 to 5. The molding die 11 includes a stationary die 12 attached to a stationary platen of an injection molding machine (not shown) and a movable die attached to the movable platen. It consists of a mold 13. Cavity forming surfaces 14 and 15 are formed on the fixed mold 12 and the movable mold 13 to face each other. When the movable platen to which the movable mold 13 is attached is moved toward the fixed platen to which the fixed die 12 is attached and the die is closed, the cavity forming surface 14 of the fixed die 12 and the cavity of the movable die 13 are used. A cavity 16 is formed between the forming surfaces 15. Further, the fixed mold 12 is provided with a sprue bush 17 with which a nozzle of an injection device (not shown) is brought into contact. Therefore, the nozzle and the cavity 16 are communicated with each other through the sprue portion 17a and the gate portion 17b, which are inner holes of the sprue bush 17.

  A gas supply mechanism capable of directly injecting an inert gas into the cavity 16 without using the nozzle and the sprue bush 17 is disposed on the cavity forming surface 14 in the vicinity of the gate portion 17 b in the fixed mold 12. The gas nozzle pin 18 of the gas supply mechanism is fixed so as to protrude from the cavity forming surface 14 toward the movable mold 13 side. At the tip of the gas nozzle pin 18, a slit-like gas vent 18 a having a width direction of 20 μm to 40 μm having a longitudinal direction in a direction orthogonal to the flow direction of the molten resin M is formed. The gas vent 18 a is connected to a gas supply / discharge device 20 outside the mold through a communication hole 18 b inside the gas nozzle pin 18 and a communication hole 19 a in the stationary mold main body 19. The gas supply / discharge device 20 is composed of a valve, a compressor, a gas tank, and the like for injecting and discharging an inert gas into the cavity 16. The gas nozzle pin 18 can be vibrated by an ultrasonic vibration mechanism (not shown).

  A portion around the gas nozzle pin 18 in the cavity forming surface 14 is a concave resin reservoir 21 with respect to the other cavity forming surface 14, and the injected molten resin M is also filled in the resin reservoir 21. It has come to be. Around the gas nozzle pin 18, a sleeve 22 constituting an extrusion mechanism for extruding the molten resin M in the resin reservoir portion 21 into the cavity 16 is disposed. The outer diameter of the cavity side portion of the sleeve 22 is formed so as to be fitted to the inner diameter of the resin reservoir portion 21, and the inner diameter of the cavity side portion of the sleeve 22 is inserted through the gas nozzle pin 18 without a substantial gap. It is formed so that. The front end surface 22 a of the sleeve 22 forms the bottom surface of the resin reservoir 21. Further, the rear portion of the sleeve 22 is formed to have a larger diameter than the cavity-side portion inserted through the front resin reservoir portion 21 and is accommodated in a space in the fixed mold main body portion 19. Further, the rear end surface 22 b of the sleeve 22 is fixed to the rod of the hydraulic cylinder 23 of the extrusion mechanism that is also disposed in the fixed mold main body 19. Therefore, the sleeve 22 can move forward and backward by a predetermined distance with respect to the side surface 21 a forming the gas nozzle pin 18 and the resin reservoir portion 21 by driving the hydraulic cylinder 23.

  Next, a method for forming a hollow molded product according to the present embodiment will be described with reference to FIGS. First, when the movable mold 13 is brought into contact with the fixed mold 12 and a cavity 16 is formed between them, the resin reservoir is obtained from a nozzle of an injection device (not shown) through a sprue portion 17a and a gate portion 17b. Molten resin M not containing an inert gas is injected into the cavity 16 including the portion 21 (FIG. 2). The resin used in the present embodiment is a thermoplastic resin, and among them, polypropylene is preferably used. After the injected molten resin M passes through the portion of the gas nozzle pin 18 in the cavity 16, an inert gas (nitrogen gas G) is injected into the molten resin M through the gas vent 18a at a pressure of 15 MPa to 30 MPa. (FIG. 3). Therefore, in this embodiment, the molten resin M is hardly filled into the cavity 16 by the holding pressure from the injection device. Then, when the injected molten resin M comes into contact with the cavity forming surfaces 14 and 15 and the cooling and solidification progresses and the resin does not substantially contract, the nitrogen gas G is discharged from the gas vent 18a. In the present embodiment, the discharged nitrogen gas G is discharged into the atmosphere, but may be stored again in the tank of the gas supply / discharge device 20 and recycled. At this stage, the hollow portion P1 of the hollow molded product P that is being cooled and solidified in the cavity 16 is still in communication with the gas vent 18a (FIG. 4). In the present embodiment, since the gas vent 18a directly faces the cavity 16, it is easy to perform pressure increase control during inert gas injection and pressure decrease control during discharge as compared with the case where the gas vent is not in the cavity. Can be done.

  In parallel with the above, from the start of injection of the molten resin M into the cavity 16 until the cooling and solidification of the molten resin M in contact with the cavity forming surfaces 14 and 15 proceeds and the injected nitrogen gas G is discharged. The gas nozzle pin 18 vibrates by a vibration mechanism (not shown). Therefore, the molten resin M in the resin reservoir 21 is in a state where the vibration is applied from the gas nozzle pin 18 disposed in the resin reservoir 21 and the progress of solidification is delayed. When the nitrogen gas G is discharged from the gas vent 18a as shown in FIG. 4, the hydraulic cylinder 23 of the extrusion mechanism is operated and the sleeve 22 is advanced, so that the molten resin M in the resin reservoir 21 is transferred to the cavity 16. The gas nozzle pin 18 that faces it is pumped forward of the gas vent 18a. The molten resin M blocks the communication between the hollow portion P1 of the hollow molded product P and the gas vent 18a. Thereafter, when the cooling and solidification of the molten resin M with the communication closed is completed, the movable mold 13 is opened and protruded by an ejector (not shown) to take out a hollow molded product P having no communication hole with respect to the hollow portion P1. Is done. In addition, although the part which closed the communicating hole in the said hollow molded product P remains in the state which can be discriminate | determined from another part when visually observed, since it is a place where the back surface of a product is not conspicuous, there is almost no problem. The hollow molded product P is sent to the next plating step or the like.

  In the present embodiment, the gas supply mechanism including the gas nozzle pin 18 has been described as being disposed in the fixed mold 12. However, as long as it is disposed in at least one of the fixed mold and the movable mold. Good. Also, the number of gas supply mechanisms formed in one cavity is not limited. For example, in the case of a bumper mold, a plurality of gas supply mechanisms are provided. In this embodiment, in order to delay the solidification of the molten resin M in the resin reservoir portion 21, the gas nozzle pin 18 is vibrated by alternating vibration. However, the side surface of the resin reservoir portion and the sleeve (extrusion pin), etc. Any one of the surfaces may be vibrated. Further, the vibration mechanism applies vibrations ultrasonically or mechanically. Further, at least one of the side surfaces forming the gas nozzle pin and the resin reservoir is heated by a heater or heated by flowing a high-temperature fluid medium in the medium flow path to be heated to a temperature higher than the other cavity forming surface, and the molten resin in the resin reservoir You may make it delay cooling solidification of. Further, the gas nozzle pin may protrude into the cavity only at the time of gas injection / discharge, and retreat from the cavity forming surface when the communication between the hollow portion and the gas vent is closed. The shape of the gas vent may be circular as long as the molten resin does not enter and only gas flows, and the position of the gas vent may not be the tip of the gas nozzle pin.

  Furthermore, the resin reservoir only needs to be formed in the vicinity of the gas vent. For example, a gas nozzle pin having a gas vent is provided on the fixed mold side, and the cavity forming surface on the opposite movable mold side is disposed. A resin reservoir and an extrusion mechanism may be provided. The forward stroke of the sleeve 22 is not limited to the forward stroke of the front end surface 22a of the sleeve 22 up to substantially the same height as the cavity forming surface 14, and the forward stroke may be adjusted by the hydraulic cylinder 23. The bottom surface of the resin reservoir portion 21 is not limited to the front end surface 22a of the sleeve 22, and it is sufficient that at least a part of the resin reservoir portion constitutes the surface of the extrusion mechanism. And the part of the communicating hole in the molded product P may be closed by the molten resin M so that the hollow part P1 disappears as shown in FIG. 5, or only the communicating hole may be closed and the hollow part P1 may remain.

  The present invention is not enumerated one by one, but is not limited to the above-described embodiment, and it goes without saying that the present invention can be applied to those modified by a person skilled in the art based on the gist of the present invention.

It is sectional drawing of the shaping die of the hollow molded product in this embodiment. It is sectional drawing of the shaping die which shows the shaping | molding method of the hollow molded product in this embodiment, Comprising: The state which injected the molten resin in the cavity is shown. It is sectional drawing of the shaping die which shows the shaping | molding method of the hollow molded product in this embodiment, Comprising: The state which inject | poured gas into the molten resin in a cavity is shown. It is sectional drawing of the shaping die which shows the shaping | molding method of the hollow molded product in this embodiment, and shows the state which discharged | emitted gas. It is sectional drawing of the shaping die which shows the shaping | molding method of the hollow molded product in this embodiment, Comprising: The state which obstruct | occluded communication of a gas vent and a hollow part is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Molding die 12 Fixed die 13 Movable die 14,15 Cavity formation surface 16 Cavity 17 Sprue bush 17a Sprue part 17b Gate part 18 Gas nozzle pin 18a Gas ventilation port 18b, 19a Communication hole 19 Fixed mold body part 20 Gas supply -Discharge device 21 Resin reservoir 21a Side surface 22 Sleeve 22a Front end surface 22b Rear end surface 23 Hydraulic cylinder G Gas M Molten resin P Hollow molded product P1 Hollow portion

Claims (3)

In a mold for hollow molded products in which gas is injected into a molten resin injected into a cavity formed between a fixed mold and a movable mold,
A gas vent located in the cavity at least during gas injection;
A resin reservoir formed in the vicinity of the gas vent;
A molding die for a hollow molded product, comprising: an extrusion mechanism for extruding the molten resin in the resin reservoir portion into the cavity. The gas vent is formed at the tip of a gas nozzle pin,
The resin reservoir part formed in a concave shape with respect to the cavity forming surface is provided around the gas nozzle pin, and at least a part of the resin reservoir part is a surface of an extrusion mechanism. Mold for hollow molded products. In a molding method of a hollow molded product in which gas is injected from a gas vent into a molten resin injected into a cavity formed between a fixed mold and a movable mold,
A gas is directly injected from the gas vent into the molten resin injected into the cavity to form a hollow portion,
As the cooling and solidification of the molten resin proceeds, gas is discharged from the gas vent,
A method for molding a hollow molded article, wherein communication between the gas vent and the hollow portion is blocked by a part of the molten resin injected into the cavity.

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