JP2009113257A - Injection molding method and injection molding mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding method and an injection molding mold for turning a molding defective of the first shot at the beginning of starting molding production into a conforming article in regard to the injection molding mold having a hot runner structure. <P>SOLUTION: The injection molding mold includes: a back flow prevention valve 7 disposed on a resin flowing-in port 6 of a hot runner of a stationary mold 1; and a valve gate 9 or a back flow prevention valve disposed on a resin flowing-out port 8 of the hot runner, whereby, before a resin extruder is separated from an injection mold when injection molding production is ended, all of the resin flowing-in port 6 of the hot runner of the stationary mold 1 is closed, thereafter, all of the resin flowing-in port 6 is closed by the back flow prevention valve 7, thereby, a resin pressure in the hot runner is retained in 40 Mpa to 80 Mpa by the resin extruder, the resin extruder is separated from the injection molding mold, the injection molding mold is cooled, thereby, the pressure in the hot runner is reduced and, as the result, the degree of volume contraction of the resin in process remaining in the hot runner is reduced to minimize a clearance developed in the hot runner. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an injection molding method and an injection mold in which molding defects are eliminated.

  For example, resin bumpers for automobiles are manufactured by injection molding. As shown in FIG. 3, the conventional general injection molding includes a fixed mold 1 including a hot runner block 4 and a hot runner nozzle 5 having a valve gate 9 that opens and closes a resin outlet 8 with a valve pin 10, and the fixed mold. 1 is molded by an injection mold comprising a movable mold 2 that forms a cavity 3 corresponding to the shape of the molded product.

  The above-described conventional injection mold has a problem in that streaky non-air is entrained in the first molded product at the beginning of molding production. The cause is that at the end of injection molding production, the resin extruder is separated from the injection mold, and the injection mold is ejected from the machine and cooled. The hanging resin shrinks in volume, and a gap is formed as indicated by symbol G in FIG. Since air from the gap G is entrained, a stripe-like defect is generated in the molded product due to the influence of the air. Therefore, the first molded product at the beginning of molding production was wasted as a defective product. In the second and subsequent molded products, the hot runner is filled with the resin without any gaps in the hot runner, so air is not involved and no streak-like defects occur.

In order to solve this problem, the volume of the in-process resin remaining in the hot runner does not shrink by supplying electricity to the injection mold carried out of the machine after the end of injection molding production and continuing heating. Therefore, although the above-mentioned defective products do not occur, it is practically impossible from the viewpoint of other safety that it is wasteful use of electricity to continue heating by supplying electricity to the injection mold carried out of the machine. is there. Also, the hot runner block has a structure that can be disassembled, and the hot runner block of the injection mold that has been taken out of the machine after the completion of injection molding production is disassembled to remove the in-process resin remaining in the hot runner and clean it. However, this is not something that can be handled on a daily basis, and it is inadequate as a production site mechanism and has not yet been put into practical use.
JP-A-6-143356 JP 2002-307493 A JP 2004-160899 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an injection molding method for making a molding defect in the first shot at the beginning of molding production that occurs chronically in an injection mold having a hot runner structure into a non-defective product by a safe and simple method. And providing an injection mold.

  The injection molding method of the present invention for achieving the above object is, as described in claim 1, a fixed mold having a hot runner block and a hot runner nozzle, and a shape of a molded product in combination with the fixed mold. In the injection mold consisting of a movable mold that forms a corresponding cavity, all the hot runner resin inlet and resin outlet of the fixed mold are equipped with opening and closing means, and the resin extruder is injection molded at the end of injection molding production Before separating from the mold, all of the fixed mold hot runner resin inlets are closed, and then the resin extruder is used to apply pressure into the hot runner to close all of the fixed mold hot runner resin inlets. It includes a step of maintaining the resin pressure in the runner at 40 Mpa to 80 Mpa.

  The injection molding method according to the present invention includes a fixed mold having a hot runner block and a hot runner nozzle, and a movable mold that forms a cavity corresponding to the shape of the molded product in accordance with the fixed mold. In the injection mold comprising the above, the fixed mold hot runner resin inlet and the resin outlet are provided with opening and closing means, and before the resin extruder is separated from the injection mold at the end of injection molding production, After all the fixed-type hot runner resin inlets are closed, pressure is applied to the hot runner by the resin extruder, and all the fixed-type hot runner resin inlets are closed to reduce the resin pressure in the hot runner to 40 MPa. The temperature of the fixed mold is lowered, and then the temperature of the fixed mold is increased, and then used for the next injection molding. It is an.

  The injection mold according to the present invention includes a fixed mold having a hot runner block and a hot runner nozzle, and a movable mold that forms a cavity corresponding to the shape of the molded product together with the fixed mold. In the injection mold comprising the above, the fixed mold hot runner resin inlet and the resin outlet are provided with opening and closing means, and before the resin extruder is separated from the injection mold at the end of injection molding production, After all the fixed-type hot runner resin inlets are closed, pressure is applied to the hot runner by the resin extruder, and by closing all the fixed-type hot runner resin inlets, the resin pressure in the hot runner is reduced to 40 MPa. Including a step of holding at 80 Mpa.

  According to the present invention, there is no need to heat the injection mold separated from the resin extruder and carried out of the machine at the end of injection molding production, and it remains in a hot runner with an impractical decomposition structure. Without removing the in-process resin and cleaning it, the volume shrinkage of the in-process resin remaining in the hot runner is reduced, the gap generated in the hot runner is reduced, and air is generated by the clearance to produce the product. This eliminates the occurrence of defective products in the first molded product at the beginning of the process, and has the effect of always producing good products.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a fixed mold, and 2 is a movable mold that forms a cavity 3 corresponding to the shape of a molded product together with the fixed mold 1. The fixed mold 1 includes a hot runner block 4 and a hot runner nozzle 5.

  Therefore, the present invention is provided with opening and closing means at the resin inlet 6 and the resin outlet 8 of the hot runner of the fixed mold 1, and before separating the resin extruder from the injection mold at the end of injection molding production, After all the fixed-type hot runner resin inlets 6 are closed, pressure is applied to the hot runner by the resin extruder, and all the fixed-type hot runner resin inlets 6 are closed to reduce the resin pressure in the hot runner. The pressure in the hot runner is reduced by holding the pressure at 40 Mpa to 80 Mpa, separating the resin extruder from the injection mold and cooling the injection mold (natural cooling is appropriate), and the in-process resin remaining in the hot runner The volume shrinkage is reduced, and the gap generated in the hot runner is reduced. Further, by closing all the hot runner resin inlets 6 of the fixed mold 1 to maintain the resin pressure in the hot runner at 40 Mpa to 80 Mpa, the temperature of the fixed mold 1 is lowered, and then the temperature of the fixed mold 1 is increased. And it is characterized by preparing for the next injection molding.

  A specific structural example of the opening / closing means for the resin inlet 6 and the resin outlet 8 of the hot runner will be described. The hot runner resin inlet 6 is provided with a check valve 7 as shown in FIG. The backflow prevention valve 7 has a structure in which a piston valve body 13 is urged forward by a streamline-shaped holding member 11 forming a resin flow passage 12 so that the piston valve body 13 can move forward and backward, and the resin inlet 6 is always closed by a spring 14. .

  In the backflow prevention valve 7, when the pressure flows into the resin inlet 6 from the resin extruder, the piston valve body 13 moves backward against the pressing force of the spring 14, so that the resin flows from the resin inlet 6 into the streamlined holding member 11. It flows into the hot runner from the resin flow passage 12 formed on the outer periphery of the hot runner. When the resin extruder does not flow to the resin inlet 6, the piston valve body 13 moves forward by the pressing force of the spring 14 to close the resin inlet 6.

  With respect to the hot runner and the resin outlet 8, the resin outlet 8 is opened and closed by a valve pin 10 that moves forward and backward by a valve gate 9. The valve gate 9 may also be provided with the backflow prevention valve 7 at the resin outlet 8.

  Since the present invention is configured as described above, before the resin extruder is separated from the injection mold at the end of injection molding production, all the hot runner resin inlets 6 of the fixed mold 1 are closed, and then the resin A resin pressure of 40 Mpa to 80 Mpa is applied to the hot runner by an extruder, the resin extruder is separated from an injection mold, the resin inlet 6 is closed by a backflow prevention valve 7, and the resin outlet is valved. It closes by the gate 9 or the backflow prevention valve 7 to hold the inside of the hot runner. And the inside of a hot runner is pressure-reduced by cooling the injection molding die carried out of the apparatus. Thereby, the volume shrinkage of the in-process resin remaining in the hot runner is reduced, and the gap generated in the hot runner is reduced.

  Before the resin extruder is separated from the injection mold at the end of the injection molding production, all the hot runner resin inlets 6 of the fixed mold 1 are closed, and then the resin pressure in the hot runner is set to 40 Mpa by the resin extruder. As for the numerical value held at -80 Mpa, as a result of molding experiments, the appearance of the first molded product is poor at 40 Mpa or lower and 80 Mpa or higher, and the first molded product does not have a defective appearance when the resin pressure in the hot runner is in the range of 40 Mpa to 80 Mpa. Since a good molded product was obtained, the resin pressure in the hot runner was specified as a numerical value in the range of 40 Mpa to 80 Mpa.

  Incidentally, FIG. 4 explains a comparison between an injection molding method using a conventional injection mold and an injection molding method using an injection mold according to the present invention. As shown by A at the time of heating (molding), the resin volume in the hot runner is the same as the hot runner volume D in both the conventional injection molding method using the injection mold and the injection molding method using the injection mold according to the present invention. As shown, in a conventional injection molding method using an injection mold, the resin in the hot runner contracts as shown by B when the resin is solidified (the mold is outside the machine), and a gap G is generated in the hot runner. However, in the injection molding method using the injection mold according to the present invention, as shown by C, the volume shrinkage of the resin inside the hot runner is reduced, and the gap generated in the hot runner is reduced.

  As described above, the fact that the clearance generated in the hot runner is reduced means that the air due to the clearance G is not involved, and the occurrence of streaky defective products in the molded product due to the influence of air is eliminated. .

  In this way, the present invention eliminates the occurrence of defects in the first molded product at the beginning of molding production by adding a simple structure to an injection mold that has been generally used in the past. Is solved. In addition, it is practical because it eliminates the troublesome cleaning work of disassembling the hot runner block of the injection mold carried out of the machine after the completion of injection molding production and removing the in-process resin remaining in the hot runner. In addition, there is an advantage that the cost of mold equipment can be reduced.

  It should be noted that the present invention is not limited to injection molding of automobile bumpers but can be applied to various resin molded products.

Cross section of an injection mold according to the present invention Cross section of check valve Sectional view showing a conventional general injection mold Comparison diagram of resin volume in hot runner between conventional injection mold and injection mold according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed type 2 Movable type 3 Cavity 4 Hot runner block 5 Hot runner nozzle 6 Resin inflow port 7 Backflow prevention valve 8 Resin outflow port 9 Valve gate 10 Valve pin 11 Holding member 12 Resin flow path 13 Piston valve body 14 Spring

Claims (3)

  In an injection mold comprising a fixed mold having a hot runner block and a hot runner nozzle, and a movable mold that forms a cavity corresponding to the shape of the molded product together with the fixed mold, the hot runner resin flow of the fixed mold Opening and closing means are provided at all of the inlet and the resin outlet, and before the resin extruder is separated from the injection mold at the end of injection molding production, all the hot runner resin inlets of the fixed mold are closed, and then the resin An injection molding method comprising a step of applying a pressure in a hot runner by an extruder and maintaining a resin pressure in the hot runner at 40 to 80 Mpa by closing all of the fixed hot runner resin inlets.   In an injection mold comprising a fixed mold having a hot runner block and a hot runner nozzle, and a movable mold that forms a cavity corresponding to the shape of the molded product together with the fixed mold, the hot runner resin flow of the fixed mold Opening and closing means are provided at all of the inlet and the resin outlet, and before the resin extruder is separated from the injection mold at the end of injection molding production, all the hot runner resin inlets of the fixed mold are closed, and then the resin A pressure is applied to the hot runner by an extruder, and the resin pressure in the hot runner is maintained at 40 Mpa to 80 Mpa by closing all the hot runner resin inlets of the fixed mold. An injection molding method comprising a step of heating a fixed mold and using it for next injection molding.   In an injection mold comprising a fixed mold having a hot runner block and a hot runner nozzle, and a movable mold that forms a cavity corresponding to the shape of the molded product together with the fixed mold, the hot runner resin flow of the fixed mold Opening and closing means are provided at all of the inlet and the resin outlet, and before the resin extruder is separated from the injection mold at the end of injection molding production, all the hot runner resin inlets of the fixed mold are closed, and then the resin An injection mold comprising a step of applying a pressure in a hot runner by an extruder and maintaining a resin pressure in the hot runner at 40 to 80 Mpa by closing all the hot runner resin inlets of the fixed mold.

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