Injection molding method

Details Injection molding method Injection molding method

1999-05-11

2001-05-15

Heitbrink, Jill L. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

C264S572000, C264S297200, C264S328800

Reexamination Certificate

active

06231805

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a molding method using a hot-runner mold with multiple cavities of the same or different shape having a plurality of valve gates.
BACKGROUND OF THE INVENTION
In a conventional injection molding method in which injection molding is performed for each cavity in succession by using a multi-cavity hot-runner mold having a plurality of valve gates, a valve for a first cavity is closed after the filling into the first cavity is finished, and at the same time a valve for a second cavity is opened to perform the filling into the second cavity. For a third and the succeeding cavities, injection molding is performed in the same way.
However, the aforementioned molding method has a problem in that a surface sink mark and the like are produced in the appearance of a product. Also, it has a problem in that a large mold clamping force is needed to completely fill each cavity.
Accordingly, an object of the present invention is to provide an injection molding method for performing injection molding for each cavity in succession by using a multi-cavity hot-runner mold, wherein a surface sink mark or the like is not produced in the appearance of a product.
SUMMARY OF THE INVENTION
The injection molding method in accordance with the present invention is characterized in that a gas is injected into a cavity into which a molding material has been filled to carry out a pressure holding step, thereby to effect injection for each cavity in succession.
An object of the present invention is to provide an injection molding method in which a surface sink mark or the like is not produced in the appearance of a product.
According to a first mode of the invention, the injection molding method for performing molding by using a multi-cavity hot-runner mold having a hot runner valve gate for each cavity, comprises: a molding material filling step in which the valve gate for a cavity into which a molding material has been filled is closed and the valve gate for a cavity into which the molding material is to be filled next is opened, so that injection is effected into each cavity in succession; and a pressure holding step in which a gas is injected into the molding material having been filled. Also, the injection molding method is characterized in that a pressure holding operation in which a gas is injected into each molding material having been filled is repeated successively in the order of the filling of the molding material into each cavity, and in that a gas having an injection pressure set for each cavity is injected thereby to hold a pressure in the molding material in each cavity.
By this method in which after a cavity has been filled, the filling into the next cavity is started, a plurality of products having an appearance free from such a defect as a surface sink mark or the like can be obtained. Also, the pressure in the cavity can be reduced by the gas pressure, so that a required mold clamping force can be reduced.
According to a second mode of the invention, the injection molding method for performing molding by using a multi-cavity hot-runner mold having a hot runner valve gate for each cavity, comprises: a step of starting filling another cavity with a molding material, while a particular cavity is being filled with the molding material; and a step of carrying out the molding by repeating an operation in which the valve gate to the cavity having been filled with the molding material is closed and a gas is injected into the mold material having been filled, thereby to hold a pressure therein.
In addition to the effects of the first mode of the present invention, this method, in which the filling of the next cavity is started while a particular cavity is being filled, enables it to shorten the time taken to complete the molding of all products because the filling of the molding material into a plurality of cavities can be performed in parallel.


REFERENCES:
patent: 5135703 (1992-08-01), Hunerberg et al.
patent: 5707659 (1998-01-01), Erikson
patent: 5773038 (1998-06-01), Hettinga
patent: 5882693 (1999-03-01), Silkowski et al.
patent: 5919492 (1999-07-01), Tarr et al.
patent: 5922363 (1999-07-01), Beck et al.

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