Plastic article or earthenware shaping or treating: apparatus – Distinct means to feed – support or manipulate preform stock... – And means to form or reshape preform
Reexamination Certificate
1999-08-25
2001-07-31
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Distinct means to feed, support or manipulate preform stock...
And means to form or reshape preform
C425S145000, C425S566000, C425S573000, C425S577000, C425S130000
Reexamination Certificate
active
06267576
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mold assembly suitable for making a multilayer molded article and a method of making the multilayer molded article using the same.
2. Related Background Art
Methods for making a thermoplastic resin molded article having protrusions such as ribs and bosses on its rear face by means of injection molding technique, injection compression molding technique, or the like have conventionally been well-known. In the thermoplastic resin molded article manufactured by such a method, a sink is likely to occur at a position on its base material surface corresponding to a protrusion, thereby making it difficult to yield a smooth surface.
Known as means for overcoming such a problem is a molding method using a foaming agent. In this method, however, it is difficult to control the state of foaming. Also, even in this method, a molded article having a smooth surface without sinks is hard to obtain. Further, the foaming agent is expensive in general, and its thermal stability upon heating may not be sufficient.
Known as another means is a method in which, from the viewpoint of form, the thickness of a protrusion such as rib or boss is made smaller than that of the base material in contact therewith, thereby preventing sinks from occurring. In this method, however, the form may lack adaptability. Also, since its strength decreases, the thickness of the base material surface has to be increased in order to maintain the strength. Therefore, this method is greatly restricted in terms of form and is hard to respond to the recent tendency of the molded article toward lighter weight and smaller thickness.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a mold assembly which can easily and efficiently make, in a series of steps without any restriction in terms of material and form, a molded article with a favorable appearance having no sinks generated on a surface of its base material opposite to a part where a protrusion such as rib or boss is attached.
It is another object of the present invention to provide a method of making a molded article, which enables making, efficiently and securely in a series of steps without any restriction in terms of material and form, of the molded article with a favorable appearance having no sinks generated on a surface of its base material opposite to a part where a protrusion such as rib or boss is attached.
The mold assembly for making a multilayer molded article in accordance with the present invention comprises:
a first mold having a cavity face, a resin-supplying gate open to the cavity face, and a resin passage communicating with the resin-supplying gate;
a second mold having a cavity face opposing the cavity face of the first mold;
a shut-off pin slidably received in the resin-supplying gate;
a pin-driving unit for moving the shut-off pin among an opening position where the shut-off pin is completely received in the first mold while the resin-supplying gate is maintained in an opening state, a closing position where the shut-off pin is completely received in the first mold while the resin-supplying gate is maintained in a closing state, and a projecting position where a part of the shut-off pin projects from the cavity face of the first mold while the resin-supplying gate is maintained in the closing state;
a resin-supplying unit for supplying a molten thermoplastic resin from the resin-supplying gate by way of the resin passage; and
a press unit, connected to the first and second molds, for moving at least one of these molds between an open position where the first and second molds are in an open state and a closed position where these molds are in a closed state.
In the above-mentioned mold assembly of the present invention, the shut-off pin can be projected from the cavity face of the first mold while the resin-supplying gate is maintained in the closing state. Accordingly, the first and second molds are closed so as to mold a resin in a state where the shut-off pin is thus projected. Thereafter, when the shut-off pin is returned into the first mold, a hole communicating with the resin-supplying gate is formed in the resulting resin molded article (first molded layer). Consequently, after the first and second molds are subsequently brought into an open state, a molten thermoplastic resin can be supplied between the first molded layer and the cavity face of the second mold by way of the hole in the first molded layer, whereby a multilayer molded article in which the front surface of the first molded layer (surface on the second mold side) is covered with another resin molded article (second molded layer) can be obtained. When a protrusion such as rib or boss is formed on the rear surface (surface on the first mold side) of the resulting multilayer molded article, though a sink may occur on the front surface of the first molded layer due to the protrusion, this surface is covered with the second molded layer as mentioned above. Accordingly, the front surface of the resulting multilayer molded article attains a favorable appearance without sinks. Also, since the molten thermoplastic resin for forming the second molded layer is supplied through the hole in the first molded layer, no irregularities occur on the front surface of the multilayer molded article due to the resin supplied.
Thus, the mold assembly of the present invention can easily and efficiently make, in a series of steps without any restriction in terms of material and form, a multilayer molded article with a favorable appearance having no sinks generated on a surface of its base material opposite to a part where a protrusion such as rib or boss is attached.
In the mold assembly of the present invention, the pin-driving unit may move the shut-off pin among the opening position, the closing position, and a plurality of projecting positions in which the projecting part of the shut-off pin projected from the cavity face of the first mold has respective lengths different from each other. When the projecting position of the shut-off pin is thus controllable in a plurality of steps, the projecting position of the shut-off pin can be adjusted in response to the thickness of the resin molded layer to be obtained. Accordingly, as will be explained later, a multilayer molded article comprising three or more layers can be obtained efficiently and securely.
Preferably, the mold assembly of the present invention further comprises a control unit, electrically connected to the pin-driving unit and the press unit, for controlling these units such that:
(a) while the resin-supplying gate is brought into the opening state by means of the shut-off pin, a molten thermoplastic resin is supplied, by way of the resin-supplying gate, between the cavity faces of the first and second molds that are in the open state;
(b) while the resin-supplying gate is brought into the closing state by means of the shut-off pin, a part of the shut-off pin is projected from the cavity face of the first mold;
(c) the first and second molds are closed so as to attain the closed state, thereby shaping the resin, and thus shaped resin is cooled so as to be solidified;
(d) the first and second molds are opened so as to attain the open state;
(e) the shut-off pin is returned into the first mold, so as to form a hole in the resin solidified in (c) and bring the resin-supplying gate into the opening state, and a molten thermoplastic resin is supplied between the resin solidified in (c) and the cavity face of the second mold by way of the resin-supplying gate and the hole;
(f) the resin-supplying gate is brought into the closing state by means of the shut-off pin;
(g) the first and second molds are closed so as to attain the closed state, thereby shaping the resin, and thus shaped resin is cooled so as to be solidified; and
(h) the first and second molds are opened.
When such a control unit is provided, the method of making a multilayer molded article in accordance with the present invention, which will be explained in the followin
Matsubara Shigeyoshi
Ohmura Yoshinori
Yamatsuta Kohji
Fitch Even Tabin & Flannery
Heckenberg Donald
Mackey James P.
Sumitomo Chemical Company Limited
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