JPH0524062A - Hollow injection molding method - Google Patents

Abstract

(57) [Summary] [Structure] A hollow injection molding method characterized in that a cyclone filter is attached to the gas recovery pipe when recovering and reusing the gas press-fitted into the molten synthetic resin in the mold. [Effect] Most of the nitrogen gas used as the high-pressure injection gas for hollow injection molding can be recovered, so the cost of the nitrogen gas can be significantly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a hollow molded product by pressurizing a high-pressure gas into the molten synthetic resin in a mold in order to prevent the sink of the molded product when injection molding the molten synthetic resin. The present invention relates to a hollow injection molding method in which a gas recovered after a resin in a mold is cooled and solidified is used.

[0002]

2. Description of the Related Art Conventionally, it has been known to use an inert gas such as nitrogen gas as a high pressure gas used in hollow injection molding, and it is generally obtained by evaporating a nitrogen gas cylinder or liquid nitrogen. It was used by compressing nitrogen gas to high pressure with a compressor. However, when nitrogen gas was used, the cost of nitrogen gas required for each hollow injection-molded product was not negligible. In order to reduce this cost, it has been attempted to recover the pressurized nitrogen gas and reuse it.
Since the nitrogen gas recovered from the hollow portion of the synthetic resin molded product is accompanied by the waste of the synthetic resin, it is necessary to remove the resin waste in order to reuse the recovered nitrogen gas.

In order to remove this resin waste, it was necessary to attach a filter in the middle of the recovery pipe.

[0004]

In a normal filter using a general mesh type filter medium, the filter medium is clogged with resin waste, and nitrogen gas can be continuously collected for a long time and reused. could not. The present invention aims to solve the above problems.

[0005]

[Means for Solving the Problems] That is, in the present invention, in the hollow injection molding, when recovering and reusing the gas press-fitted into the molten synthetic resin in the mold, the gas recovery pipe is provided in the vicinity of the recovery gas outlet. A cyclone filter having an internal filter is attached to remove resin waste accompanying the recovered gas, and the high pressure gas obtained by recompressing the recovered gas is injected into the molten synthetic resin in the mold. This is a hollow injection molding method.

In the cyclone filter of the present invention, a filter is attached inside the vicinity of the outlet. The filter is preferably cylindrical. The material of the filter medium is not limited, but if strength is required, a sintered metal or ceramic filter medium is preferable. The average pore size of the filter medium is 10 to 200 depending on the conditions.
Effective in the μ range. It is preferably 50 to 150 μ.

By using the cyclone filter having such a structure, resin waste can be easily removed, and nitrogen gas can be continuously collected and reused. FIG. 1 shows an example of the structure of the cyclone filter ( 1 ), and FIG. 2 shows an example of a hollow injection molding (inert gas such as nitrogen gas) flow sheet using the cyclone filter.

A cross-sectional view of the structure of the cyclone filter shown in FIG. 1 will be described below. Figure (a) shows a plan view and Figure (b) shows a side view. (1) High-pressure nitrogen gas (2) containing resin scraps is blown from the gas inlet indicated by the arrow in FIG. 1 in the tangential direction of the circumference as shown in FIG. (2) The gas turns clockwise (clockwise) shown in FIG. 1A along the flow straightening tube (6), and the resin scraps are centrifugally moved along the side wall of the cyclone filter body by the centrifugal force. Collected at the bottom.

(3) The resin scraps (4) collected in the lower part are
The cyclone filter is discharged by occasionally opening the resin debris extraction valve (3) attached to the lower part of the body. (4) The gas from which the resin scraps have been removed passes through the sintered metal filter medium (5) and is exhausted from the gas outlet (7) at the upper part of the center of the cyclone filter. At this time, the fine resin scraps are not completely removed only by centrifugal force, but when passing through the sintered metal filter medium, the fine resin scraps are captured on the surface of the sintered metal filter medium,
Fine resin scraps are also completely removed.

(5) When the resin debris extraction valve attached to the lower part is opened to discharge the resin debris collected in the lower part of the cyclone filter, the gas flow in the cyclone filter is disturbed and the surface of the sintered metal filter medium is disturbed. The fine resin waste adhering to is also discharged from the resin waste extraction valve attached to the lower part. Next, the flow sheet shown in FIG. 2 will be described.

(1) The high-pressure nitrogen gas compressed by the nitrogen gas compressor (8) passes through the pipe shown by the solid line arrow in FIG. 2 from the nozzle 9 of the injection molding machine into the mold (not shown). Is pressed into the molten resin. At this time, since the check valve 10 is attached to the gas recovery pipe, the press-fitted gas does not flow toward the cyclone filter.

(2) After cooling and solidifying the molten resin in the mold, the nitrogen gas that has been press-fitted is recovered from the nozzle of the injection molding machine through the pipe shown by the dotted arrow in FIG. (3) The collected gas collected from the nozzle of the molding machine is accompanied by resin scraps. By passing this through the cyclone filter ( 1 ), the resin scraps are removed by the principle explained in FIG. Check valve (1
0) to the nitrogen gas tank (not shown) on the suction side of the nitrogen gas compressor.

(4) Since the recovered nitrogen gas does not contain resin waste, it is compressed to a high pressure by a nitrogen gas compressor and reused for blow molding.

[0014]

The present invention will be described in more detail with reference to the following examples.

[0015]

Example 1 Dimensions of the cyclone filter shown in FIG.
As, cylinder diameter = 80 mm, cylinder height = 80 m
m and the height of the conical portion = 60 mm. With a structure that can withstand high pressure
Thickness = 5mm^tAnd Cyclone filter
Of the sintered metal filter medium (SMC Co., Ltd.) to be installed inside
Dimensions are cylinder diameter = 30 mm, cylinder height = 50 m
m, thickness of sintered metal = 6 mm ^t, Average pore size of sintered metal =
It was set to 120μ. Average pore size is obtained by microscopic observation
The average pore size was calculated by arithmetic mean.

All materials were SUS304. This cyclone filter was installed in a gas recovery pipe for hollow injection molding, and hollow injection molding of ABS resin was performed. When nitrogen gas compressed to 180 kg / cm ² G was pressed into the molten resin in the mold for 5 seconds, about 30 liters (converted to the standard state) of nitrogen gas could be injected per molded product.

After the resin has been cooled and solidified, about 27 liters (converted to the standard state) of nitrogen gas per molded product can be recovered through the cyclone filter into the nitrogen gas tank on the suction side of the nitrogen gas compressor. It was 180 kg / cm ² G with nitrogen compressor It was recompressed and could be reused in hollow injection molding.

A shortage of about 3 liters (converted to the standard state) of nitrogen gas per molded product was supplied from a nitrogen gas cylinder. The resin debris accumulated in the cyclone filter can be removed once every approximately 3,000 molded products by opening the resin debris extraction valve attached to the bottom of the cyclone filter, and the nitrogen gas compressor and molding machine can be operated continuously. I had no trouble.

When only the sintered metal filter material attached to the inside of the outlet of this cyclone filter is used instead of the cyclone filter of the present invention, the filter is clogged with about 500 molded products and the filter of the nitrogen gas compressor is used. Continuous operation was not possible.

[0020]

As a high pressure injection gas for hollow injection molding, most of the used nitrogen gas can be recovered and recompressed by a compressor for reuse, so that the cost of nitrogen gas in the cost of the molded product can be greatly reduced. ..

[Brief description of drawings]

FIG. 1 shows a cross-sectional structure of a cyclone filter of the present invention.

FIG. 2 shows a flow sheet of the hollow injection molding method of the present invention.

[Explanation of symbols] 1 cyclone filter 2 inert gas containing resin waste 3 resin waste extraction valve 5 filter material 6 straightening cylinder 8 gas compressor 9 nozzle of injection molding machine

Claims (1)

Claims: 1. A resin for attaching a cyclone filter having an internal filter to a gas recovery pipe in the vicinity of a recovered gas outlet when recovering and reusing a gas pressed into a molten synthetic resin in a mold. A hollow injection molding method characterized by removing scraps.