JPS62294515A - Reactive injection molding method - Google Patents

Abstract

PURPOSE:To improve a quality by preventing generation of voids of an injection molded product, by performing injection molding by depressurizing the inside of a cavity of a molding tool through suction of air of the same and the same is filled with gas of high solubility prior to injection of raw materials. CONSTITUTION:A vacuum pump 5 for depressurization in a cavity 3 formed by a molding bottom force 1 and molding top force 2 through suction of air of the same is connected with the cavity 3 through a valve 6 and a gas cylinder 7 is connected with the cavity 3 through a valve 8. To perform molding, valves 8, 9, 10 are closed, to begin with, and the inside of the cavity is depressurized by sucking the air of the same into a vacuum tank 4 through a vacuum pump 5 by opening the valve 6. Then the valve 6 is closed by opening the valve 8. With this construction, the cavity 3 is filled with gas of high solubility to raw materials in the gas cylinder 7 or that liquefied by pressure at the time of the molding. Then the raw materials are injected by opening the valves 9, 10 connecting with vent holes 9a, 10a.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to reaction injection molding, and relates to a reaction injection molding method that takes measures to prevent the generation of air voids.

(Prior Art) Molding of plastic materials and the like by reaction injection molding is widely practiced. However, since there is air in the mold before the raw material is completely injected, the air remains on the instep of the molded product, causing air bonding defects. To prevent this,
A sealing member is installed between the upper and lower molds of the mold, and after the mold is closed, the air in the cavity is removed to reduce the pressure, and then the molding material is injected to perform molding. .

(Problems to be Solved by the Invention) When the air in the cavity of the mold is removed by reducing the pressure, a difference in air pressure from the outside air is created, and a sealing member is therefore required. Furthermore, since the molding material must be injected into the mold while maintaining a pressure difference, advanced techniques are required to maintain airtightness. Further, there is no sealing member that can withstand repeated molding over a long period of time while maintaining airtightness, and the number of man-hours increases because the sealing member must be replaced frequently. The present invention was made in order to obtain a molded product that does not require advanced sealing technology and is free of air voids.

(Means for Solving the Problems) The present invention provides, as a means for solving the above-mentioned problems, that when reaction injection molding is performed, suction of air in the mold cavity is performed before cool injection for each molding. The pressure is reduced, and then injection molding is performed after filling with a gas that has a higher solubility in the raw material than air or a gas that condenses and liquefies at the pressure during molding.

(Function) In this way, the inside of the cavity is immediately filled with gas at atmospheric pressure after the suction pressure is reduced. Therefore, there is no need to strictly seal the inside of the cavity and maintain airtightness until the injection molding is completed. In addition, even if the gas inside the cavity is drawn into the molding material, it has a high solubility in the raw material and is under great pressure, so it dissolves in the raw material and liquefies, increasing its volume. As it decreases, it dissolves in the raw material in a liquid state before injection and solidification. Therefore, air void defects do not occur, and defective products do not occur.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In the figure, the lower mold 1. Cavity 3 formed by upper mold 2
is formed. A vacuum tank 4 and a vacuum pump 5, which are used to suck and decompress the air in the cavity 3, are connected to the cavity 3 via a pulp 6, and a gas cylinder 7 is connected to the cavity 3 via a pulp 8. Further, in the cavity 3, an openable pulp 9 is provided in connection with the vent hole 9a, and an openable pulp 10 is provided in connection with the vent hole 9a.
It is connected to a.

To perform molding, first pulp 8. 9. 10 is closed, the pulp 6 is opened, and the air in the cavity 3 is sucked and depressurized into the vacuum tank 4 by the vacuum pump 5. Then pulp 8 is opened and pulp 6 is closed. As a result, the cavity 3 is filled with a gas that is highly soluble in the raw material in the gas cylinder 7 or a gas that liquefies under the pressure during molding. Next, the pulp 9 connected to the vent hole 91.10m,
10 and inject the raw material.

The molded product in this case is an automobile bumper, and the finished flap of the molded product has an average density of 4.15ρf1 and 1.06 P/
cm”.The gas in gas cylinder 7 was CO,
Using gas. Then, the air in the cavity 3 was removed, COt gas was filled into the cavity 3, and the pulp 9.10 in the vent hole was opened to bring the inside of the cavity to atmospheric pressure and the raw material was injected. Twenty identical bumpers were molded for each of the bumpers molded in this manner and those molded with air left in the cavity 3.

The state of void defects in that case was investigated, and the results are shown in the table below. If the void diameter is 2 mm or more, the commercial value of the molded product will be impaired and it will become a substantial defect, so the table shows only cases where the void diameter is 2 mm or more.

As shown in the table, in this example, the actual void defects were greatly reduced and the quality was improved, but the reason for this was that the pressure inside the mold at the time of raw material injection was 300 to 1000 kP.

and the CO caught up in the flow of raw material under this pressure,
It is thought that this is because the gas is dissolved in the raw material.

(Effects of the Invention) Since the present invention has the above-described structure and operation, voids are not generated in the injection molded product, and the quality is improved. Also, like when creating a true chamber and injecting,
There is no need for advanced technology to maintain airtightness or sealing materials, and the number of man-hours is also increased by 2.

[Brief explanation of drawings]

The figure is a configuration diagram of a molding apparatus that performs injection molding according to the method of the present invention. 1...Lower die 2...Upper die 3...Cavity 4... True tank 5...Odor pump 7・Old・・Gas cylinder

Claims (1)

[Claims] (1) In reaction injection molding, before raw material injection for each molding,
The air inside the mold cavity is suctioned and decompressed, and then,
A reaction injection molding method characterized by performing injection molding by filling the material with a gas that has a higher solubility in raw materials than air or a gas that condenses and liquefies under the pressure during molding.