Plastic and nonmetallic article shaping or treating: processes – With printing or coating of workpiece – Coating or impregnating workpiece before molding or shaping...
Reexamination Certificate
2002-07-01
2004-08-10
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With printing or coating of workpiece
Coating or impregnating workpiece before molding or shaping...
C264S259000, C264S265000, C264S271100, C264S275000
Reexamination Certificate
active
06773645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection molding method of a molded article of a polyamide resin represented by Nylon (under trade name).
2. Description of the Related Art
Ordinarily, a linear polymer having an amide bond as a repeating unit in a molecule is called a polyamide and, among other things, the polyamide mainly comprising an aliphatic chain is widely distributed as a resin under a trade name of ‘Nylon’ represented by Nylon 66, Nylon 6 and the like. Since a polyamide resin comprises an amide group having a large polarity, the polyamide resin has an excellent resistance to hydrocarbon type solvents such as gasoline, oil and the like. Further, since the polyamide resin has a relatively high heat resistance, it has been used as a favorable material for components of automotive vehicles, components of machinery and the like. Meanwhile, an integrally molding method that comprises the steps of continuously fabricating molded articles by an extrusion molding process and the like which has a high productivity to prepare an already-molded article, setting the thus-prepared already-molded article in a metallic mold and separately injection-molding only a complicated part which can not be molded by extrusion molding to the thus-set already-molded article is effective, since it can save cost and labor required for injection-molding a final molded article as an entire body.
However, even when, for aiming at performing molding by using the polyamide resin by means of the above-described method, a molten polyamide resin is injection-filled against a predetermined integral molding part of the already-molded article comprising the polyamide resin which has already been molded by using extrusion molding or the like, the molten polyamide resin and the already-molded article are not integrally bonded to each other such that they separate from each other as they are cooled. It has ordinarily been known that, even when a molten resin, of a crystalline polymer such as the polyamide resin, which has a same composition as that of the already-molded article is filled against the already-molded article in a metallic die for injection molding, there occurs no integral bonding therebetween. The reason is surmised as described below. It is required for heating the metallic die to hold a predetermined temperature when the already-molded article is set in the metallic die and, then, the molten resin is filled for an addition molding part. On this occasion, since crystallization of the already-molded article in the metallic die is promoted, bonding strength thereof against an amorphous molten resin to be used for the additional molding part is decreased. This is because it is considered that, when the crystalline polymer is heated, partial melting occurs therein at a considerably lower temperature than a melting point thereof and, subsequently, recrystallization occurs therein. Therefore, the already-molded part and the molten resin part become each individually crystallized where upon they are not bonded to each other. Since a crystal structure of the polyamide resin is firm with an involvement of a hydrogen bond between amide bonds, it has been difficult to perform integration.
It has been known that, in the case described above, particularly in a case of a polyethylene resin molded article or the like which is a crystalline polymer similar to the polyamide resin, when, after an acetone type primer is applied to a predetermined integral molding part of the already-molded article, the above-described injection-addition molding operation is performed, the already-molded article and the resultant molded part are bonded to each other. The primer on this occasion denotes an organic solvent to be applied in advance as a pretreatment agent to the predetermined bonding part of the already-molded article and, for this application, the primer mainly comprising acetone has conventionally been distributed in the market. However, when, in the case of the polyamide resin, the present inventor performed such a molding operation by applying the acetone type primer to the polyamide resin, a molded article having a sufficient boding strength was unable to be obtained.
Further, as an integral injection molding method of a polyamide resin molded article having a sufficient bonding strength at a bonded part between the already-molded article and the additional molding part, a resistance welding method has been known. It is a method in which an electrically conductive wire is incorporated into the already-molded article along a periphery of the predetermined integral molding part of the already-molded article and, then, heated by an introduction of electric current to a hot wire whereby the above-described predetermined integral molding part is allowed to be slightly melted to be in an amorphous state and, then, the polyamide molten resin for the additional parts injection-filled in the metallic die such that the polyamide molten resin covers the predetermined integral molding part to perform molding. In a case of this method, there are mentioned problems described below. (1) Working efficiency in performing incorporation of the electrically conductive wire is extremely low whereupon, particularly, incorporation work against a small-sized molded article becomes difficult. (2) Since it takes time to melt the already-molded article comprising the polyamide resin by the hot wire, production efficiency at the time of injection molding is low. (3) Since the electrically conductive wire remains in the polyamide resin after the injection molding has been executed, when the resin molded article is recovered for the purpose of reuse after a product comprising such a resin molded article has been used, it is impossible to reuse the part thereof incorporated with the electrically conductive wire. (4) Since a part of the molten resin corresponding to a volume of the electrically conductive wire is squeezed out to be a burr when the molded article is released from the metallic die whereupon there is a need for a finishing treatment.
OBJECTS OF THE INVENTION
An object, therefore, of the present invention is to provide a method in which, when an additional molding part comprising a same resin as that of an already-molded article which comprises a polyamide resin is injection-molded against the already-molded article, they are integrated while securing a sufficient bonding strength therebetween only by an application of a primer.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a method in which an already-molded article comprising a polyamide resin is set in a molding die and, then, the polyamide resin that has been heated to be in a molten state is injection-filled in a cavity to which a part of the already-molded article faces thereby integrally molding an additional molding part onto the part of the already-molded article, characterized in that a primer comprising an alcohol solution containing the polyamide resin and a chemical that is capable of dissolving the polyamide resin is applied to a predetermined integral molding part of the already-molded article with the additional molding part and, then, the thus primer-applied already-molded article is set in a molding die.
According to the first aspect of the present invention, at the time of molding the polyamide resin, when a molded article having an intended shape is molded by firstly molding in advance a part having a shape suitable for continuous molding such as extrusion molding, blow molding or the like to prepare an already-molded article and, then, injection-molding a only part having a complicated shape which is incapable of being continuously molded in an additional manner against the thus-prepared already-molded article thereby integrally bonding them, it is possible to integrate an additional molding part while having a sufficient bonding strength by injection molding only by adding such a simple operation as to apply the above-described primer to the predetermined integral molding part of t
IOI Limited Company
Ortiz Angela
Wenderoth , Lind & Ponack, L.L.P.
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