JPH06304953A - Gas injection molding method and its mold - Google Patents

Abstract

PURPOSE:To provide a gas injection molding method and its mold wherein molding property for a large-sized thin molded piece will be assuredly improved. CONSTITUTION:A mold 20 comprises a sprue 25 for connecting a filling opening 24, which supplies a melted resin 30, to an inside cavity 22, branched runners 26 which are branched off midway of the sprue 25 and to be connected to the cavity 22, and working pins 40 for opening/closing the branched runners 26. Filling of the melted resin 30 is performed by the sprue 25 and the branched runners 26. When gas is to be injected inside, the branched runners 26 are blocked by the working pins 40 and the gas is injected by only the sprue 25, so that collision of the gas in the cavity 22 is eliminated, a desired gas channel 32 can be formed assuredly, and molding property for a large-sized thin molded piece 31 will be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection molding method and a mold for the same, and relates to a large surface product such as an interior / exterior product such as a bumper or dashboard of an automobile or a casing of home electric appliances or a resin which is rapidly solidified by cooling. It can be used for product molding.

[0002]

2. Description of the Related Art Conventionally, as a mold for injection-molding a large-sized thin-walled molded article, a multi-point gate type in which a plurality of gates for injecting a molten resin are provided in one cavity is known. According to the multi-point gate type mold, the molten resin solidifies midway at one point because the mold cavity is large or the resin that is the molding material easily solidifies. Even when the filling becomes difficult, the molten resin is filled simultaneously from a plurality of gates dispersed in the cavity of the mold, so that the entire cavity can be filled with the molten resin.

On the other hand, a gas injection molding method is known as an injection molding method for obtaining a lightweight and highly rigid molded product. In this method, the main cavity in the mold is filled with molten resin, and then an inert gas such as pressurized nitrogen gas is injected into the cavity to perform injection molding. Since a gas flow path (hereinafter referred to as "gas channel") is formed in the filled molten resin by gas pressure, it is possible to obtain a good thin hollow molded product without sink marks. By applying this gas injection molding to a multi-point gate mold, it has been attempted to improve the moldability of a large-sized molded product used for the interior and exterior of automobile bumpers and dashboards.

[0004]

However, when gas injection molding is simply performed with a multi-point gate mold, the gas is injected into the molten resin from a plurality of gates at the same time. It becomes difficult to arrange the same, etc., and the way the gas enters is greatly different each time, and the quality of the molded product is not uniform. Also, since gas injection is performed at multiple locations,
The gas collides with the molten resin through the molten resin everywhere, and the collision part causes the resin to accumulate and sink, or the shock of collision causes the gas to flow into the general surface, resulting in poor appearance and poor strength. A so-called permeation phenomenon may occur. Therefore, there is a problem in that the moldability of a large-sized molded product or the like cannot be improved by simply applying gas injection molding to a multi-point gate type mold.

An object of the present invention is to provide a gas injection molding method and a mold for the same, which can surely improve the moldability of a large-sized thin-walled molded product or the like.

[0006]

A first aspect of the present invention is a gas injection molding method, which comprises a main runner as a cold runner for connecting a filling port for filling a molten resin to an internal cavity, and A mold provided with an auxiliary runner as a hot runner connected to and branched from the main runner and an opening / closing means for opening / closing the auxiliary runner is used, and the molten resin is introduced into the cavity through both the main runner and the auxiliary runner. And then closing the opening / closing means, and then injecting gas into the molten resin only through the main runner.

A second aspect of the present invention is a gas injection molding die, which is a main runner as a cold runner for connecting a filling port for filling a molten resin to an internal cavity, and is connected to this main runner. Moreover, the auxiliary runner as a branched hot runner and the opening / closing means for opening / closing the auxiliary runner are provided.

[0008]

In the present invention as described above, since the molten resin is filled using both the main runner and the auxiliary runner, the molten resin can be easily solidified even if the mold cavity is large. Also, it becomes possible to fill the entire cavity with the molten resin. Further, when injecting the gas into the molten resin, the gas is circulated only in the main runner of the main runner and the auxiliary runner by closing the opening / closing means, and the gas is injected in one place. Will be done. For this reason, the way in which the gas enters the molten resin is almost the same every time, the quality of the molded product is uniform, and the gas does not collide in the cavity of the mold, so sink marks, permeation, etc. Therefore, the above-mentioned object is achieved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an injection molding machine 1 according to the first embodiment of the present invention.
It is shown. The injection molding machine 1 is configured to include an injection device 10 that injects a synthetic resin and a mold 20 that is a mold for molding. The injection device 10 is one in which a molten resin 30 inside is kneaded with a screw 12 inside a cylindrical barrel 11. A nozzle 13 is provided at the tip of the barrel 11.
The injection molding machine 1 is configured to connect the nozzle 13 to the bush 21 of the mold 20 and fill the mold 20 with the molten resin 30 to mold a molded product 31. Inside the nozzle 13,
A blowing tube 14 for injecting a pressurized gas is inserted. An inert gas such as nitrogen gas is supplied to the blow-in pipe 14 from a supply source (not shown), and a gas channel is formed inside the molded product 31.
To form 32.

As shown in FIG. 2, the mold 20 has a cavity 22 inside, and this cavity 22 extends in an H-shape in a substantially rectangular thin plate portion 22A so as to extend in an H-shape. Is formed. The gas channel guide portion 23 is a portion in which the inner surface of the cavity 22 is carved further deeply, and the thickness thereof is thicker than the surroundings. A filling port 24 for filling the molten resin 30 is provided in the central portion of the bush 21 of the mold 20. The filling port 24 is connected to the cavity 22 by a sprue 25 as a main runner.

The sprue 25 is a conical passage that narrows toward the filling port 24, and is a so-called cold runner that is not heated by a heating device such as an electric heater. A plurality of branch runners 26 as auxiliary runners are branched from the middle portion of the sprue 25. The branch runner 26 is a heating device 26A such as an electric heater provided around the branch runner 26.
Is a hot runner capable of maintaining the molten state of the molten resin 30. The downstream end of the branch runner 26 is connected to the middle of the sprue 22 and the end edge 27 of the cavity 22. On the other hand, an operation pin 40 as an opening / closing means is provided near the upstream end of the branch runner 26. The operating pin 40 is
As shown in FIG. 3, the rod-shaped member is movable in the longitudinal direction. The tip portion 40A of the operating pin 40 closes the branch runner 26 in a state where it moves to the position A in the upper part of the drawing,
The branch runner 26 is opened in a state where the branch runner 26 is moved to a position B in the lower part of the figure. A hydraulic cylinder device 41 is arranged on the base end side of the operating pin 40, and the operating pin 40 is driven up and down by the hydraulic cylinder device 41. The hydraulic cylinder device 41 is controlled by the control device of the injection molding machine 1 or the like, and the operating pin 40 can be opened and closed in a timely manner.

In this embodiment, the operating pin 40 is pulled to the position B, the branch runner 26 is opened, and the molten resin 30 is filled in the cavity 22 through both the sprue 25 and the branch runner 26. Thereafter, the operating pin 40 is projected to the position A, the branch runner 26 is closed, and gas is injected into the molten resin 30 in the cavity 22 through only the sprue 25 of the sprue 25 and the branch runner 26. Here, by injecting the gas from only one place of the sprue 25, as shown in FIG. 2, one continuous gas channel is formed in the molten resin 30.
32 will be formed. As a result, when injection molding is performed a number of times in succession, the way gas is introduced is almost the same each time.

According to this embodiment as described above, the following effects can be obtained. That is, a plurality of branch runners 26 are provided in addition to the sprue 25 as the main runner, and the molten resin 30 is filled by using both the sprue 25 and the branch runners 26. Even if it is vast, the entire cavity 22 can be filled with the molten resin 30.

An operating pin 40 for opening and closing the branch runner 26
Since the branch runner 26 is closed by the operating pin 40 when the gas is injected, the sprue 25 and the branch runner are
Gas will flow only to the sprue 25 of the 26.
Therefore, when injection molding is repeated a number of times, the way in which the gas enters the molten resin 30 is almost the same each time.
Since the quality of 31 can be made uniform and the gas does not collide in the cavity 22 of the mold 20, it is possible to prevent occurrence of defective phenomena such as sink marks and permeation in the molded product 31.

Therefore, even in the case of a large-sized molded product or a molded product made of a resin which easily solidifies, it is possible to carry out injection molding with good moldability without causing defective phenomena such as sink marks and permeation.

Next, the effects of the present invention will be described based on concrete experimental examples. [Experimental Example] This experimental example is an experiment in which gas injection molding is performed using the mold according to the present invention. As the mold, the first
A mold having a structure basically the same as that of the mold 20 shown in the embodiment was adopted, and a large planar molded product 31 having an external shape shown in FIGS. 1 and 2 was molded as a test piece. [Comparative Example] This comparative example is an experimental example performed for comparison with the above experimental example, and injection molding is performed using a mold as shown in each of Comparative Examples 1 and 2 below. That is, Comparative Example 1 is one in which the test piece is injection-molded using a mold having a cavity 22 having the same shape as that of the experimental example and omitting the one corresponding to the branch runner 26 of the example. is there. Comparative example 2 is a cavity having the same shape as the experimental example.
The test piece is injection-molded by using a mold having 22 and a branch runner 26 and omitting the one corresponding to the operating pin 40. [Injection Conditions] In these Experimental Examples, Comparative Examples 1 and 2, a 2000-ton injection molding machine was used to perform injection molding under the same injection conditions as described below. Injection conditions Materials used: Polycarbonate Molding temperature: 280 ℃ Mold temperature: 80 ℃ Branch runner temperature: 260 ℃

[Experimental Results] In the experimental example, the capacity of the molding machine was set to 80%, and the gas pressure to be injected was 20 MPa.
As a result of performing the injection molding with setting to a, it was possible to obtain a good product having no defective portions such as sink marks on the surface of the molded product. In Comparative Example 1, when injection molding was performed under the same conditions as in the experimental example, a short shot resulted and injection molding could not be performed.
Here, even if the capacity of the molding machine was set to 99%, the required amount of resin could not be filled in the cavity. Further, in order to reduce the flow resistance of the resin, the resin temperature is set from 280 ° C to 30 ° C.
When the temperature was raised to 0 ° C and molding was performed, the resin deteriorated and molding could not be completed. Further, in Comparative Example 1, the filling time is 9
Since the time is long, the viscosity of the resin becomes high when the gas is injected, and at 20 MPa, the gas was not injected into the molded product. Therefore, sink marks were generated at the flow end of the resin. In Comparative Example 2, since the gas passes through the branch runner 26, the gas enters the branch runner 26 at the time of the next filling, so that the gas is mixed in the resin. As a result, a silver streak was generated on the surface of the molded product, and only a molded product having a defective portion was obtained. In Comparative Example 2, when the heating device for heating the branch runner was stopped and the runner was used as a so-called cold runner, injection molding was carried out. A molded product could not be obtained.

The present invention is not limited to the above-mentioned embodiments, but includes the following modifications. That is, the opening / closing means is not limited to one that opens and closes the auxiliary runner by providing a rod-shaped actuating pin so as to be movable in its longitudinal direction, and as shown in FIG. 4, it is bored in a direction orthogonal to the rotation axis. The valve body 43 having the through hole 42 may be used. In short, a specific structure can be appropriately selected as long as it is a valve mechanism that can block the flow of the injected gas.

Further, the auxiliary runners are not limited to the branch runners 26 formed on both sides of the sprue 25, but may be four branch runners 28 radially spreading around the sprue 25 as shown in FIG. .

Furthermore, the gas channel inside the molded product is not limited to the flat H-shaped gas channel shown in the above-mentioned embodiment, but a flat "D" -shaped gas channel 33 as shown in FIG. Well, in short, the shape of the gas channel may be any shape as long as it does not cause sink marks or the like on the surface of the molded product when formed inside.

[0021]

As described above, according to the present invention, even in the case of a large-sized thin-walled molded product or a resin-molded product that is easily solidified, a defective phenomenon such as sink mark or permeation does not occur.
Injection molding with good moldability can be reliably performed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line S2-S2 of FIG.

FIG. 3 is an enlarged sectional view showing the opening / closing means of the embodiment.

FIG. 4 is an enlarged sectional view showing a modified example of the present invention.

FIG. 5 is a diagram corresponding to FIG. 2 showing another modification of the present invention.

[Explanation of symbols]

 20 Mold 22 Cavity 24 Filling port 25 Sprue as main runner 26, 28 Branch runner as auxiliary runner 30 Molten resin 40 Actuating pin 43 as opening / closing means 43 Valve body as opening / closing means

Claims (2)

[Claims] 1. A main runner as a cold runner for connecting a filling port for filling a molten resin to an internal cavity, an auxiliary runner as a hot runner connected to this main runner and branched, and this auxiliary runner. A mold provided with opening / closing means for opening / closing is used to fill the molten resin into the cavity through both the main runner and the auxiliary runner, and after closing the opening / closing means, the gas is supplied through only the main runner. A method for gas injection molding, which comprises injecting into a molten resin. 2. A main runner as a cold runner for connecting a filling port for filling a molten resin to an internal cavity, an auxiliary runner as a hot runner connected to and branched from the main runner, and this auxiliary runner. A gas injection molding die, comprising: an opening and closing means for opening and closing.