Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1993-04-05
1995-01-31
Kuhns, Allan R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 79, 521 94, 264 51, 264 54, 264 466, 296188, B29C 6722, C08J 906
Patent
active
053859510
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to processes for producing shaped foamable parts. The invention involves an improvement of the invention described in European Patent Application 89301406.6 (U.S. application Ser. No. 478,798 dated Feb. 13, 1989). The invention is particularly useful for making components for inserting into car bodies for blocking moisture or sound transmission in hollow cavities or in gaps between car components.
BACKGROUND OF THE INVENTION
The prior art referred to in the earlier Application is pertinent here also.
In order to permit industrial scale application, a foamable composition should be blendable and formable into processable material or parts on industrial scale equipment and retain a suitable foam structure during processing a vehicle on a production line.
SUMMARY OF THE INVENTION
The invention provides in a broad aspect a process for producing foamable pellets from a polymer composition containing polymer and a foaming and curative additive package which includes the steps of: additive package with a wax powder to produce a dry blend; and foaming and curing additive package at a temperature between the melting point and not more than 10.degree. C., preferably not more than 5.degree. C., above the melting point using a low shear condition to-produce a melt blend; and
Suitably the pellets may be formed into shaped foamable parts by: conditions of step (b) e.g. by injection molding, extruding or compression molding the melt blend material.
In a more particular aspect the invention provides a process for producing shaped foamable parts from a polymer composition containing polymer and a foaming and curing additive package which includes the steps of: additive package of the composition with a wax powder to produce a dry blend; at a temperature between the melting point and not more than 10.degree. C., preferably not more than 5.degree. C., above the melting point using a low shear condition to produce a melt blend; conditions of step (b).
The wax aids dispersion of the additive package and reduces shear resistance and hence local heating which might cause premature foaming. The wax may be cross-linked into the polymer matrix during foaming and so it is believed that it does not tend to migrate to the surface and reduce adhesion. The wax can be selected to have a low drop melting point, preferably of from 32.degree. to 90.degree. C.
The uniform additive dispersion and avoidance of local heating permits a relatively high melting point polymer to be foamed and cross-linked by a relatively mild curing step whilst the ingredients can still be blended and optionally additionally moulded in melt-form without triggering premature foaming.
The dry-blending needs to be performed with appropriately selected additives. The initial wax enhanced dry-blending step preferably also involves a blowing agent activator so that both blowing agent and activator are optimally dispersed.
The activator may be part of a proprietary blowing agent formulation or may be added separately from the blowing agent. References herein to the amount of blowing agent are to the combined amount of blowing agent and activator in a proprietary formulation used as starting material for the dry blending step.
Depending on the nature of the subsequent melt blending step, the additional additives used may include small amounts of paraffin preferably less than 1.5 wt %, especially less than 1 wt % to stick the wax powder to the blowing agent powder. This is particularly advantageous where a dry blended mixture is prepared for a one-feed melt blending step, which step then involves the simultaneous feeding of polymer pellet and blowing agent powder. The term dry-blending is used herein to include the blending also of small amounts of non-powderous components. The dry-blending may be performed with the additives only, without polymer pellets where polymer pellets are fed separately in a multiple-feed melt blending operation.
The polymer may be any suitable foamable polymer such as copolymer of ethylene and an eth
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Dialog accession No. 01424904, Furukawa Electric Co.: "Core-Sheath Foamable Polyethylene Pellets Prepn. by Extruding and Heating in the Mould" JP 49090364, A, 740829, 7545 (Basic) (Aug. 1974).
Patent Abstracts of Japan, vol. 11, No. 206, C433, abstract of JP 62-30132 publsihed 1987-02-09 (Toyoda Gosei Co., Ltd.).
Dew M. J.
Exxon Chemical Patents Inc.
Kuhns Allan R.
Miller D. W.
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