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Assignee3M Innovative Properties Company
InventorsChristopher K. Haas, Mark D. Gehlsen, Sara B. Mortenson, Joan M. Strobel, Ravi K. Sura, David L. Vall
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The present invention is directed to a process for producing a polypropylene foam by mixing a high melt strength polypropylene and a blowing agent to form a melt mixture, reducing the temperature of the melt mixture at the exit of the apparatus to an exit temperature that is no more than 30° C. above the melt temperature of the neat polypropylene while maintaining the melt mixture at a pressure sufficient to prevent foaming; passing the mixture through said exit shaping orifice and exposing the mixture to atmospheric pressure, whereby the blowing agent expands causing cell formation resulting in foam formation, and orienting said foam. The foam is useful as tape backings, thermal and acoustical insulation and as a diffuse reflector for use in optical applications such as computer displays.
A multilayer article comprising at least one oriented high melt strength polypropylene foam layer wherein the foam has an average cell size of 50 micrometers or less prior to orientation, wherein the high melt strength polypropylene has a melt strength in the range of 25 to 60 cN at 190° C.
An oriented high melt strength polypropylene foam having an average cell size prior to orientation of 50 micrometers or less wherein the tensile strength of the foam in the cross direction is within 30% of the tensile strength in the machine direction.
Dependencies are inferred from the claim text.