Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1996-09-27
2001-05-15
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S328700, C264S328800, C264S328140, C264S328160, C425S130000, C425S573000
Reexamination Certificate
active
06231798
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a multi-layer molded product of thermoplastic resins.
2. Description of the Related Art
Multi-layer molded products as combinations of thermoplastic resins are conventionally well known, and the following methods are known as processes for producing them.
(1) A method for bonding sheets of thermoplastic resins preliminarily produced to each other (for example, as described in the Japanese Patent Application Laid-open Gazette No. Sho
63-104805
), or a method for bonding such sheets at the same time as molding of the thermoplastic resins (for example, as described in the Japanese Patent Application Laid-open Gazette No. Sho
49-23261
).
(2) A method by sandwich injection molding (for example, as described in the Japanese Patent Application Laid-open Gazette No. Sho
62-268618
corresponding to U.S. Ser. No. 862269 or in the Japanese Patent Application Laid-open Gazette No. Sho 63-309417 corresponding to U.S. Ser. No. 050680).
In addition, an example of a process for producing a multi-layer molded product consisting of a resin molded body and a skin material is the process as described in U.S. Pat. No. 5,154,872.
However, the methods in (1) described above need a lot of steps because they include molding of members preliminarily processed in the sheet form. The method in (2) described above needs high injection pressure and needs two mold-closing steps in order to obtain a two-layer molded product. Further, in the process described in above U.S. Pat. No. 5,154,872, supply pressure of resin is low and there are many losses of edges of the skin material.
SUMMARY OF THE INVENTION
Under such circumstances, an object of the present invention is to provide a process for producing a multi-layer molded product having a plurality of resin layers, which can solve the above problems. More specifically, an object of the present invention is to provide a process capable of producing a high-quality multi-layer molded product having a plurality of resin layers with good repeatability under relatively low resin supply pressure and by single mold closing. A further object of the present invention is to provide a process capable of producing a high-quality multi-layer molded product, even if the thermoplastic resins employed have suitable molding temperatures or melt temperatures (temperatures of supply resins) largely different from each other, without so much time or cost for production of molded product and without restrictions on the thermoplastic resins used.
DETAILED DESCRIPTION OF THE DISCLOSURE
The present invention provides a process for producing a multi-layer molded product, comprising:
a step of supplying first and second molten thermoplastic resins through first and second resin-supplying gates to between female and male molds kept in an open state with a time difference being provided between supply starts of the first and second resins, the first and second resin-supplying gates being temperature-controllable independently of each other; and
a step of closing the female and male molds after completion of supply of said first and second resins.
Further, the present invention provides a process for producing a multi-layer molded product, comprising:
a step of closing female and male molds from a first open state in which the female and male molds are positioned with such a space that the multi-layer molded product can be taken out through between the female and male molds to a second open state in which a space between the female and male molds is smaller than the space in the first open state and a cavity clearance between the female and male molds is greater than a thickness of the desired multi-layer molded product;
a step of supplying a first thermoplastic resin in a molten state to between the female and male molds kept in the open state while controlling the first thermoplastic resin at a predetermined temperature higher than a melting point of the first resin and lower than a decomposition temperature thereof:
a step of supplying a second thermoplastic resin in a molten state to between the female and male molds while controlling the second thermoplastic resin at a predetermined temperature higher than a melting point of the second resin and lower than a decomposition temperature thereof separately and independently of the supply temperature of the first resin, after a lapse of a predetermined period of time from a supply start of the first thermoplastic resin;
a step of closing the molds from the open state to a closed state in which a cavity clearance between the female and male molds is substantially coincident with a thickness of the desired multi-layer molded product, and thereafter holding the molds in the closed state for a predetermined period of time to solidify the first and second thermoplastic resins; and
a step of opening the space between the female and male molds to take the multi-layer molded product out through between the molds.
In one aspect of the present invention, supply of the second molten thermoplastic resin is started after completion of supply of the first molten thermoplastic resin. In another aspect of the present invention, supply of the second molten thermoplastic resin is started after start of supply of the first molten thermoplastic resin and before completion of supply of the first resin.
In the process of the present invention, supply of the second thermoplastic resin is preferably started after a surface solid layer is formed in the first thermoplastic resin supplied to between the female and male molds and, in one aspect of the present invention, the second thermoplastic resin is supplied without breaking through the surface solid layer of the first thermoplastic resin. In another aspect of the present invention, the second thermoplastic resin is supplied with breaking through a portion near the second resin supplying gate in the surface solid layer of the first thermoplastic resin and without breaking through the other portions.
In such a process of the present invention, because the first and second molten thermoplastic resins are supplied to between the female and male molds kept in the open state through the first and second resin supplying gates temperature-controllable independently of each other, the temperatures of the respective supply resins can be accurately controlled at suitable temperatures of the respective resins, so that repeatability can be greatly improved for a forming speed of the solid layer formed in the resin surface after each resin is supplied to between the molds. Therefore, the process of the present invention is effective to obtain the desired multi-layer molded product having at least one layer for each of the resins with good repeatability by setting the time difference between the supply starts of the first and second molten thermoplastic resins and properly selecting the time difference.
Namely, with poor repeatability of forming speed of surface solid layer, even if the period of time is constant between the supply start of the first molten thermoplastic resin and the supply start of the second molten thermoplastic resin, there is such a possibility that the resins are mixed with each other or that the resins are solidified more than necessary before closing of molds, which makes it difficult to produce good multi-layer molded products with good repeatability. In contrast with it, the process of the present invention assures high repeatability of forming speed of surface solid layer, and is thus free of the above problems.
Further, since the process of the present invention assures such high repeatability of forming speed of surface solid layer, it permits a control of whether the second resin breaks through the surface solid layer of the first resin or not to be effected in accordance with the period from the supply start of the first molten thermoplastic resin to the supply start of the second molten thermoplastic resin, which permits the structure of multi-layer molded product obtained thereby
Funakoshi Satoru
Matsubara Shigeyoshi
Matsumoto Masahito
Murotani Hitoshi
McDowell Suzanne E.
Pillsbury Madison & Sutro LLP
Silbaugh Jan H.
Sumitomo Chemical Company Ltd.
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