JPH11170289A - Gas assisted molding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the intrusion of gas uniform and to stabilize the quality of a molding by installing a means for adjusting the pressure of introduced high pressure gas on a mold corresponding to a thick wall part. SOLUTION: A pressure valve 11 for adjusting the pressure of high pressure gas introduced into a gas channel 2 is installed on a mold corresponding to the channel 2 which is a thick wall part. A pressure sensitive pin which retreats to open the valve when the pressure of the gas becomes a prescribed pressure or above to keep the pressure at the prescribed pressure is set in the valve 11. After a resin being injected into a mold, the valve 11 is arranged to be actuated, and then the high pressure gas is injected into the channel 2 through a needle valve 4. The gas enters the position of the channel 2 in which the valve 11 is installed. In this way, the influence by the internal pressure distribution of the resin is minimized to make the intrusion of the gas uniform to stabilize the quality of a molding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas-assist molding apparatus for performing injection molding of plastics by using a gas-assist molding method, and more particularly to a gas-assist molding apparatus capable of controlling a range and a distance of a high-pressure gas to be introduced. About.

[0002]

2. Description of the Related Art In recent years, in plastic injection molding, a molding method called a gas assist molding method has been widely used, particularly for large molded products. In this molding method, at the time of injection molding, an inert gas is injected at a high pressure into a molded product in a mold after resin injection.

Conventionally, in order to ensure the transferability of the cavity and to suppress shrinkage of the resin, a pressure-holding step has been provided in which an injection pressure is further applied after filling the resin to maintain the inside of the cavity of the mold at a certain pressure. According to this pressure-holding step, there is a problem that the molding cycle becomes longer and there are places where it is difficult to apply the internal pressure. However, according to the gas assist molding method,
The molding cycle can be shortened by omitting the pressure-holding step, and gas can be pressurized to a location where the internal pressure is not easily applied by the injection pressure, thereby suppressing the shrinkage of the resin during solidification. As a result, it is possible to achieve the liberalization of the design shape by avoiding the thickness reduction and the partial thickening, and to save energy by reducing the injection pressure, and its application range is wide.

When performing injection molding of a molded product by gas assist molding, a thick gas introduction path called a gas channel is formed on the molded product, and a high-pressure gas is introduced into the molded product through the gas channel. Generally, a method of applying a gas pressure to a desired position is used. This is because the resin in the gas channel part is thicker than the resin in other parts, so the amount of resin shrinkage is large and solidification is slow, and the viscosity of the resin in this part immediately after injection is lower than that in other parts The purpose of this is to aim at the effect that high-pressure gas selectively penetrates into this part. The gas channel is often designed as a molded product as a portion having the effect of supporting the flow of resin as a flow leader.

However, since the resin is rapidly cooled after being injected into the mold and the viscosity increases, the pressure transmission in the resin during and after filling is significantly reduced, and as a result, the resin internal pressure becomes uneven. Is generated. It is very difficult to quantitatively grasp the distribution of the temperature, viscosity and internal pressure, because the amount of heat transfer depends on the state of the mold and the shape of the molded product. For this reason, it is difficult to control the quality of the molded product by the pressure holding process in general injection molding. Similarly, in gas assist molding, it is very difficult to control the gas introduction position in detail even if the gas channel is set for the above-mentioned purpose. For this reason, in some cases, gas is introduced into unexpected places, which may lead to poor appearance of the molded product and a significant decrease in strength due to generation of unnecessary hollow portions.

FIG. 9 is a top view schematically showing the structure of an example of a molded article formed by gas assist molding, and FIG. 10 is a side view of FIG. 9 and 10, the molded article 1 is formed in a cubic shape having a substantially rectangular cross section, and a gas channel 2 having a rectangular cross section is integrally formed in the center of the upper surface of the molded article 1 along the longitudinal direction. Is formed. A gate 3 for injecting a resin is connected to the center of the side surface of the molded article 1, and a gas injection needle 4 is connected to an upper surface near one end of the gas channel 2.
The gate 3 and the needle 4 are fixed to a mold (not shown).

FIG. 11 and FIG. 12 schematically show the gas mixing state in the molded article shown in FIG.
FIG. 13 shows a cross section EE in FIG.
Are cross sections FF and GG in FIG. 12, respectively. Reference numeral 5 shown in FIGS. 11 and 13 is a hollow portion formed in the gas channel 2 by gas intrusion. In the case of the molded article 1, it is desirable that the high-pressure gas injected from the needle 4 be uniformly injected into the gas channel 2 as shown in FIGS. Since there is a difference in the internal pressure distribution of the resin in the molded article 1 depending on the distance, molding conditions, and the like, the gas injection often becomes non-uniform as shown in FIGS. In particular, when gas enters a portion other than the gas channel 2 indicated by reference numeral 6 in FIGS. Further, when gas does not enter the thick portion of the gas channel 2 indicated by reference numeral 7 in FIGS. 12 and 15, appearance defects such as thinning are likely to occur in this portion. Such a tendency is remarkable in the case where the molded article 1 is large and the flow distance of the resin is large, or in a molded article having a complicated shape.

[0008]

As described above, according to the conventional gas-assist molding apparatus, there is a problem in that the distribution of the internal pressure of the resin in the mold causes uneven gas intrusion, thereby deteriorating the quality of the molded article. was there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a gas assist molding apparatus capable of uniformly injecting gas and stabilizing the quality of a molded article. I do.

[0010]

According to a first aspect of the present invention, there is provided a gas-assisted molding method in which a thick portion is formed on a molded product, and high-pressure gas is introduced into the thick portion to perform injection molding of plastic. The apparatus is characterized in that adjusting means for adjusting the pressure of the introduced high-pressure gas is provided on a mold corresponding to the thick portion.

According to a second aspect of the present invention, the adjusting means is a pressure valve which operates in response to the pressure of the high-pressure gas.

According to a third aspect of the present invention, the pressure valve includes a pressure-sensitive pin which moves forward and backward in response to the pressure of the high-pressure gas.

In the gas assist molding apparatus of the present invention configured as described above, by providing pressure adjusting means such as a pressure valve which operates in response to the gas pressure of the high-pressure gas to be introduced, the gas intrusion range Can be controlled, the influence of the internal pressure distribution of the resin can be minimized, and stable molding can be realized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the gas assist molding apparatus according to the present invention will be described below with reference to the drawings. 1 to 6 schematically show configuration examples of the embodiment of the present invention. 1 is a top view of the molded product, FIG. 2 is a side view of FIG. 1, and FIG.
FIG. 4 is a cross-sectional view taken along line AA of FIG. 1, FIG. 4 is a top view showing an example of gas intrusion of the molded article of FIG. 1, FIG. 5 is a cross-sectional view taken along line BB of FIG. It is sectional drawing. In these figures, parts corresponding to those of the conventional example shown in FIGS. 9 to 13 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

The feature of the present embodiment is that the pressure of the high-pressure gas introduced into the gas channel 2 is adjusted on a mold corresponding to the gas channel 2 which is a thick portion provided on the molded article 1. The point is that a pressure valve 11 is provided as a means. When the pressure of the high-pressure gas becomes equal to or higher than a set pressure, the pressure valve 11 has a built-in pressure sensing pin (not shown) which retreats and opens the valve to set a predetermined pressure. The structure of other parts is almost the same as the conventional example shown in FIGS.

According to the gas assist molding apparatus of the present invention configured as described above, the pressure valve 11 is operated after the resin is injected into the mold, and then the high pressure gas is supplied through the needle 4 to the gas. When the gas is injected into the channel 2, unlike the resin, the gas maintains a substantially uniform pressure even at the end of the gas channel 2, so that the gas selectively enters the position of the gas channel 2 where the pressure valve 11 is installed. As shown in FIGS. 4 to 6, this gas intrusion state becomes uniform in each part, and the influence of the internal pressure distribution of the resin is minimized, so that stable gas assist molding can be realized.

The means for adjusting the gas pressure is not limited to the pressure valve 11, but a hydraulic circuit or another structure may be used so that the operating pressure can be adjusted outside the mold. For simplicity, a spring or the like may be used.

FIGS. 7 and 8 show a configuration example of another embodiment of the present invention. FIG. 7 is a top view, and FIG.
FIG. 4 is a sectional view taken along line D. In this embodiment, a plurality of, for example, three pressure valves 11 shown in FIGS. 1 to 3 are provided on the gas channel 2. In this case, by changing the operating pressure of the pressure valve 11 depending on the position, the gas intrusion state can be more finely controlled.

[0019]

As described above, according to the gas assist molding apparatus of the present invention, the pressure of the introduced high-pressure gas is adjusted in accordance with the thickness of the gas channel formed on the molded product. Since the adjusting means is provided, it is possible to minimize the influence of the internal pressure distribution of the resin and to perform uniform gas intrusion, realize stable gas-assist molding, and stabilize the quality of molded products.

[Brief description of the drawings]

FIG. 1 is a top view schematically showing a molded product in a configuration example of an embodiment of a gas assist molding device of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 1;

FIG. 4 is a top view showing an example of a gas intrusion state into the molded article of FIG. 1;

FIG. 5 is a sectional view taken along line BB of FIG. 4;

FIG. 6 is a sectional view taken along line CC of FIG. 4;

FIG. 7 is a top view schematically showing a molded product in a configuration example of another embodiment of the gas assist molding device of the present invention.

FIG. 8 is a sectional view taken along line DD of FIG. 7;

FIG. 9 is a top view schematically showing a molded product in an example of a conventional gas assist molding device.

FIG. 10 is a side view of FIG. 9;

11 is a top view illustrating an example of a desirable gas intrusion state into the molded article of FIG. 9;

12 is a top view showing an example of an undesired gas intrusion into the molded article of FIG. 9;

FIG. 13 is a sectional view taken along line EE of FIG. 11;

FIG. 14 is a sectional view taken along line FF of FIG. 12;

FIG. 15 is a sectional view taken along line GG of FIG. 12;

[Explanation of symbols]

 1 molded product, 2 gas channel (thick part), 11 pressure valve (adjustment means),

Claims (3)

[Claims] 1. A gas-assist molding apparatus for forming a thick part on a molded product, and introducing a high-pressure gas into the thick part to perform injection molding of plastic, wherein a mold corresponding to the thick part is provided on a mold. A gas assist molding apparatus, further comprising adjusting means for adjusting the pressure of the introduced high-pressure gas. 2. The gas assist molding apparatus according to claim 1, wherein the adjusting means is a pressure valve that operates in response to the pressure of the high-pressure gas. 3. The gas assist molding apparatus according to claim 3, wherein the pressure valve includes a pressure-sensitive pin that moves forward and backward in response to the pressure of the high-pressure gas.