Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-06-18
2001-09-04
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S236000
Reexamination Certificate
active
06284178
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to manufacturing methods and, in an embodiment described herein, more particularly provides a method of producing crosslinked polyethylene products.
It is well known to produce crosslinked polyethylene products using a process conventionally known as the “monosil” process. Unfortunately, however, the monosil process is generally considered to be unsuitable for producing products which are to be used in potable water applications in the United States where it is generally used for wire insulation products. This is due to the fact that regulated extractants, such as methanol, may be released as a by-product of the crosslinking process.
Additionally, there exists a need for methods of conveniently and economically producing reformed products which are made of highly crosslinked material. However, products which are highly crosslinked are typically not easily reformed. For example, forming an enlarged sealing surface on a highly crosslinked tubular product usually results in an objectionable fold or other anomaly on the seal surface.
From the foregoing, it can be seen that it would be quite desirable to provide methods of producing crosslinked polyethylene products, which use the monosil process for crosslinking the polyethylene, but which produce products satisfactory for use in potable water applications. In addition, it would be desirable to provide methods for conveniently and economically producing highly crosslinked reformed products. It is accordingly an object of the present invention to provide such methods.
SUMMARY OF THE INVENTION
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method is provided which economically reduces the amount of silane used in the monosil process, produces conveniently reformable products, and which produces products satisfactory for use in potable water applications.
In one embodiment of the invention, the method includes the steps of preheating base polyethylene to approximately 160° F., blending the base polyethylene with a master batch of additives, introducing silane, peroxide and a catalyst in the feed throat of an extruder, extruding a product, reforming the product, and then curing the reformed product.
In one aspect of the present invention, a reduced quantity of silane is utilized in the described monosil process. For example, the combined silane, peroxide and catalyst may be 1.6-1.8% of the mixture extruded.
In another aspect of the present invention, an extruded product produced by the monosil process is reformed, after the extrusion step, but before the product is cured to an elevated crosslinked percentage. In this manner, the extruded product is reformed to its final shape before elevated crosslinking prevents convenient and effective reforming.
In still another aspect of the present invention, a product produced by the monosil process is treated to reduce levels of regulated extractants. The product may then be used in potable water applications.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings.
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Bancroft Patrick A.
Runyan Gary L.
Russell Robert G.
Stachowiak Robert S.
Konneker & Smith P.C.
Tentoni Leo B.
United States Brass Corporation
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