Multi-layer molding nozzle

Details Multi-layer molding nozzle Multi-layer molding nozzle

1989-06-30

1991-07-09

Heitbrink, Timothy

Plastic article or earthenware shaping or treating: apparatus

Means feeding fluent stock from plural sources to common...

137114, 2643288, 26432813, 4251331, 425562, 425564, B29C 4522

Patent

active

050300776

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE ART

This invention relates to a multi-layer molding nozzle used when a synthetic resin molded product whose sectional construction is multilayered is injection molded.


BACKGROUND

A conventional multi-layer molding nozzle comprises a multiple nozzle in which a nozzle body having a central mouth portion at a tip thereof is provided interiorly with a plurality of concentric resin paths, and different molten resins in the respective resin paths can be cavity-injected from said mouth of the nozzle.
The formation of a synthetic resin molded product into a multi-layer causes the quality of a thin-wall molded product (such as a beverage container) to be further improved by the resin present as an intermediate layer. However, this poses a problem in that because of the provision of the intermediate layer, the shock resistance of the product is lowered or the cost of the product is lowered or the cost of the product increases, as compared with single layer products.
In view of the foregoing, an attempt has been made to use a conventional double or three-layer nozzle to control injection pressure, time, injection timing or the like of the molten resin which forms an intermediate layer so as to injection-mold a product partly having an intermediate layer. However, it has been very difficult to mold an intermediate layer within a predetermined range in terms of resin pressure.
Alternatively, a multiple nozzle is used in which a central path of a multiple resin path is made movable so that orifices of resin paths are selectively opened and closed to control molten resin, as disclosed in Japanese Patent Application Laid-Open No. 60-34819. However, in this case, a special valve device is required to control a flow of molten resin entering the central path passing through the orifice for injection, and in addition, the valve device is mechanically operated, and the nozzle has an extremely complicated construction.


DISCLOSURE OF THE INVENTION

This invention has been achieved in order to solve the above-described problems with respect to the conventional multiple nozzle. An object of this invention is to provide a new multi-layer molding nozzle which is simple in construction, and in which a flowpassage of molten resin which is to form an intermediate layer is opened and closed by a valve member to be operated by resin pressure to always accurately switch a multiple layer to a single layer and vice versa.
This invention having the aforesaid object overcomes the aforementioned problem encountered in the prior art by a three-layer nozzle in which a nozzle body is interiorly provided with a first resin path, a second resin path and a third resin path having the same injection opening in a concentric fashion, in which multiple nozzle, a mouth portion of the central third resin path located internally of a mouth portion of the second resin path is constituted by a valve member which is moved forward and backward by resin pressure of the third resin path and the second resin path to open and close the second resin path, and a mouth portion of the intermediate second resin path located internally of the first resin path is constituted by a valve member which is moved forward and backward by resin pressure of the second resin path and the first resin path to open and close the second resin path.
In the above-described structure, the molten resins of the respective resin paths applied with injection pressure are simultaneously injected from the mouth portion of the respective resin paths to cavities through the mouth portion of the nozzle. When the injection pressure of the second resin path is removed during the injection, the valve member is moved forward or backward by the resin pressure of the first or third resin path to close the second resin path to stop an outflow of the molten resin from the second resin path. Because of this, the molten resins of the first and third resin paths are merely injected to the cavity.
When injection pressure is applied to the second resin path, the valve member is moved backwa

REFERENCES:
patent: 4190409 (1980-02-01), Hehl
patent: 4511528 (1985-04-01), Kudert et al.
patent: 4863665 (1989-09-01), Schad et al.

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