Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1998-04-24
2001-02-06
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S045800, C264S048000
Reexamination Certificate
active
06183673
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a process for the manufacture of a two-part foam product having a cellular body portion of one material and a thin integral ski n coating applied and fused to the outer surface of the body portion.
Extruded polyethylene foam products are commonly available and in many cases have a circular cross section. It is possible to manufacture other cross sections, however, these are more difficult, particularly when the size of the extruded product is large. Foam products produced by extrusion have an extrusion skin which is formed during cooling of the product and is of the same material as the body portion.
The density of extruded foam products is easily controlled and the nature of the product normally requires a certain density for the particular application or desired durability. For example, if the foam product is being used as a bumper for boats, the density would be relatively high.
There are some applications for extruded foam products where it would be desirable to provide a skin coating on the surface of the extruded product to impart to the exterior of the product, characteristics different from the material characteristics of the foam body. In some cases, it is desirable to impart a protective coating to form a sheath about the extruded foam product. Extruded sheath foam products are used as a protective wrap about structural members such as playground equipment, exercise equipment or structural members such as basketball poles or protective pads about exercise equipment. In such cases it is desirable to alter the surface characteristics of the extruded foam product by the application of an integral skin of a different material to provide different properties to the product or to make the product suitable for a particular application.
SUMMARY OF THE INVENTION
An apparatus for manufacture of a two-part extruded foam product according to the present invention comprises a co-extrusion apparatus having a main extruder and a secondary extruder. The main extruder extrudes the foam body portion of the product through a main die outlet for foaming to final shape after discharge from the main die outlet. The second extruder extrudes a coating on said body portion through a ring outlet as said body portion moves towards the main die outlet and coats the body portion prior to discharge through the main die outlet. This coating expands with the foam body portion after leaving the main die outlet.
According to an aspect of the invention the ring outlet includes a large reservoir about the ring outlet for feeding of the material to be extruded through the ring outlet.
According to yet a further aspect of the invention the co-extruder has a composite die for defining the main die outlet and the ring outlet. The composite die includes an adjustable part defining the size of the ring outlet and this adjustable part is movable, relative to the main die part for controlled adjustment of the ring outlet.
According to yet a further aspect of the invention, the adjustable part of the composite die is adjusted by a rotational movement of the adjustable part relative to the main die part.
According to yet a further aspect of the invention, the ring outlet is provided in an inwardly tapering wall leading to the main die outlet.
According to yet a further aspect of the invention, the inwardly tapering wall defines a conical passageway with the main die outlet located at the apex of the conical passageway.
A process for the manufacture of an extruded product having a foam body portion of a first material coated with an integral surface skin of a second material bonded to the foam body portion comprises preparing a mixture of the material of said body portion and a foaming agent, providing said mixture to a first extruder and extruding said mixture through a main die outlet causing foaming of the body portion and expansion of the cross-section of the body portion generally after extrusion through said main die outlet; preparing a second material in a second extruder, and forcing said second material through a ring outlet onto the first material immediately adjacent to the main die outlet, and in said first extruder, to form an integral surface coating on the first material prior to extrusion through the main die outlet.
According to yet a further aspect of the invention, the process includes adjusting the size of the ring outlet to achieve the continuous skin about the exterior of the foamed body portion.
According to yet a further aspect of the invention the process includes a mixture of the first material and a foaming agent which produces a dense foam body portion.
According to yet a further aspect of the invention the process includes using a second material having a melt index of at least 50% greater than the melt index of the first material.
According to yet a further aspect of the invention the process includes controlling the size of the extrusion product by controlling the first extruder and the mixture of the first extruder. With this process, the final size of the composite product can be accurately controlled.
According to yet a further aspect of the invention the process includes selecting the first material and the second material to have radically different characteristics with the second material selected to provide good air sealing characteristics.
According to yet a further aspect of the invention, the process includes controlling the size of the ring outlet to achieve in the extruded product a skin thickness of the second material of less than two thousandths of an inch.
According to yet a further aspect of the invention the process includes controlling the size of the ring outlet to produce an extruded product having a skin of the second material with a thickness of less than one thousandths of an inch.
According to yet a further aspect of the invention the process produces an initial thickness of a second material in the die of a first thickness which reduces in thickness by at least 50% as the body portion expands after extrusion through the main die outlet. With this arrangement, thinning of the skin is accomplished due to expansion of the body portion. This allows very thin skins to be produced on the final product and is advantageous in that less material may be used while still imparting the desirable characteristics to the surface of the product.
The present invention also is directed to this two-part foam product having a body portion of a first material and a thin skin coating of a second material where the skin coating is less than two thousandths of an inch.
The present invention is also directed to extruded foam products having a two-part composition of a body portion of one material and a skin of a different material where the tolerance variation with respect to the diameter of the product is maintained within 2%.
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Industrial Thermo Ploymers Limited
Kuhns Allan R.
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