Molding Method

The present invention relates to the manufacture of electrical connectors by injection molding of thermoplastic materials in which a highly elastic, stretchy, squeezable material is utilized as an insulating sheath for an electrical conducting wire.

In the past, thermoplastic materials were used to form electrical connectors and these materials have encased wires that were sheathed in insulators. Injection molding techniques for manufacturing such connectors were not wholly satisfactory because the thermoplastic material had to be injected into the mold under high pressures to form the connector. Because the insulated wire had to extend from the mold at an opening, the thermoplastic material squeezed by the insulator and oozed outside of the mold. Such leakage made a product which was less desirable and wasted the thermoplastic material. The use of castable, and/or low pressure plastics was quite time consuming and inefficient because of the molding time, although leakage was avoided.

According to the present invention, we have discovered that if the insulated wire is first fitted with a heat shrinkable sleeve at the point where the wire will extend through a port in the mold and the sleeve is shrunk tightly about the insulated material, then plastic will not ooze from the mold when it is injected. Such oozing is caused by the fact that most dielectric insulators are highly elastic, stretchy, squeezable and subject to deformation. We have found that leakage will occur at the place where the wire extends outside of the mold when the thermoplastic material is injected under high pressure, generally in the order of 2000 to 7000 pounds per square inch. The insulator will deform slightly and allow the thermoplastic material to flow by. The shrunk sleeve on the insulated wire will form a rigid plug-like cover which prevents leakage of the thermoplastic material, even under high injection pressures. The shrunk sleeve conforms to the shape of the insulated wire and tends to confine it somewhat while the insulator is urging it outwardly. Then when the sleeve is disposed within the thermoplastic material, the insulator urges the sleeve outwardly towards the thermoplastic material and forms a mechanical seal which is relatively impervious to the permeation of water and other contaminants.

The present invention may be better understood by reference to the detailed description of a specific embodiment thereof when taken in conjunction with the drawings, in which the Figures show various stages of manufacture of an electrical connector formed of an insulated wire embedded in a thermoplastic material.

Referring now to FIG. 1, a pin 2 is shown having an axial bore 6. A wire 8 is affixed within axial bore 6 and will conduct current from an external source to the connector 2. The wire 8 is sheathed in an insulating material formed of a low durometer composition, generally less than 60 durometers and is stretchy, squeezable and highly elastic, preferably silicone rubber or synthetic carbon based rubbers.

As shown in FIG. 2, connector is fitted with a sleeve 12 of thin wall, tough, heat shrinkable plastic such as PVF2 [Irradiated Polyvinylidene Fluoride (Kynar) manufactured by Roychem Corporation], which when heated, will shrink to conform to the shape of the sheath 10 and form a rigid sleeve around the sheath 10. The sleeve 12 is then heated to between about 200.degree. to 500.degree. F. so as to shrink it about the external surfaces of sheath 10 as shown in FIG. 3 and exert a pressure which will slightly deform the sheath 10 to form a rigid construction. Since the sheath 10 is quite resilient, the heat shrinkable sleeve 12 forms an O-ring-like seal which squeezes the sheath 10 causing the sheath 10 to exert outward force because of its natural tendency to regain its original shape. Only a mechanical bond is formed between the sheath 10 and the sleeve 12 and there is no chemical interaction between the materials. The constant expanding force of the sheath 10 will provide a rigid internal seal as will be apparent in subsequent Figures.

In FIG. 4, the pin 2 is disposed within mold 14 through opening 18 and extending partially external thereof. The insulated wire 10 extends through an opening 16 in the other side. The heat shrunk sleeve 12 is disposed within the opening 16 and rigidly held by notched edges (not shown) disposed therein. The notched edges of the opening 16 will grasp the sleeve 12 and the opening 18 will grasp the pin 2 of the assembly. With this configuration, the insulating sheath 10 will force against the inside of the sleeve 12 and form the equivalent of an O-ring seal with the opening 16. Because the sleeve 12 is rigid after shrinking, it will be firmly grasped by the notches in the opening 16 and form the plug.

Referring now to FIG. 5, the thermoplastic material is injected through a port 19 with a conventional nozzle 20 under pressures in the order of 2000 to 7000 pounds per square inch. Thermoplastic materials used for such injection molding include polypropylene, nylon, polyethylene and polyesters. The thermoplastic material then fills the mold cavity and encases the sleeve 12, the sheath 10 and part of the pin 2. The thermoplastic material cools and shrinks down tightly on sleeve 12 which in turn compresses further the resilient sheath 10 forming an impervious seal of one to the other. Because the sleeve 12 forms a plug in the mold, leakage of the thermoplastic material, even under pressures in the order of 2000 to 7000 pounds per square inch, does not occur. In this embodiment, the thermoplastic material is injected into one port while the other two ports in the mold are sealed off, one by the pin 2 and the other by the sleeve 12. If desired, the mold may be provided with an egress port which can be unblocked during injection of the thermoplastic material to flush entrapped air from the interior of the mold and to insure the complete filling of the chamber with the thermoplastic material.

In FIG. 6, the mold 4 is separated and the formed electrical connector shown in FIG. 6 can be removed. Mating notchings from the opening 16 appear on the sleeve 12 when the connector is removed from the mold. Since thermoplastic material is used, the connector is ready to use when it is removed from the mold and curing is not required for the process.

As shown in FIG. 7, the pin 2 is partially encased within the molded thermoplastic material 3 to form the insulated connector. The thermoplastic material 3 is rigidly formed about a portion of the pin 2 and also encases an inward extension of sheath 10. The sleeve 12 preferably extends outwardly from the body of the thermoplastic material 3 and forms a mechanical bond between the sheath 10 and the thermoplastic material 3.

While the embodiment described relates to the manufacture of male connectors, it is apparent that female connectors can be fabricated using similar techniques in which case there will be no male pin extending externally of the mold. Other devices can also be molded in which there is a need to join a highly elastic material to a thermoplastic material and form a water impervious joint.

It is apparent that modifications and changes can be made within the spirit and scope of the present invention, but it is our intention, however, only to be limited by the scope of the appended claims.