Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-09-20
2002-06-11
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S091000, C521S088000, C521S087000, C521S089000, C521S094000, C521S134000
Reexamination Certificate
active
06403663
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to methods of making foamed materials employing carbon dioxide.
BACKGROUND OF THE INVENTION
Methods for making conventional foamed materials, such as for example thermoplastic materials, have long been known. These methods have focused primarily on employing chemical blowing agents that include various volatile organic compounds (VOCs) and chlorofluorocarbons (CFCs). These blowing agents typically decompose at a critical temperature and release a gas such as nitrogen, carbon dioxide, or carbon monoxide. Conventional foaming processes are believed to be becoming increasingly undesirable. For example, the use of these organic compounds has received heightened scrutiny due to potential environmental risks associated with the same. Moreover, conventional foaming processes often disadvantageously produce voids or cells within the materials that are relatively large, for example approximately 100 microns or greater, along with relatively wide variances of void fraction percentages. The number of voids per unit volume of the polymeric material may be relatively low and the distribution of cells through out the polymeric material is often non-uniform.
In order to address the above possible shortcomings, efforts have been made at employing inert fluids to facilitate foaming of polymeric materials such as proposed, for example, in U.S. Pat. No. 5,334,356 to Baldwin et al.; and U.S. Pat. No. 5,158,986 to Cha et al. In particular, the '986 patent proposes providing a non-thermosetting, polymerized plastic material to be foamed, introducing a supercritical fluid into the polymerized plastic material to be foamed at a first temperature and a first pressure, and then externally changing the temperature and pressure from the first temperature and first pressure to a different selected second pressure to produce a supermicrocellular foamed material. The foamed material is disclosed to contain a plurality of voids or cells distributed substantially throughout the material. U.S. Pat. No. 5,160,674 to Colton et al. proposes a method of producing a foamed semi-crystalline polymeric material containing a uniform, closed cell microcellular void. The method involves saturating a melted polymeric material at an elevated pressure at or about the melting temperature with a uniform concentration of gas such as carbon dioxide. U.S. Pat. No. 5,120,559 to Rizvvi et al. proposes extruding dough using supercritical carbon dioxide.
Notwithstanding the above efforts, there remains a need in the art to provide foamed materials with improved properties relative to materials formed by prior art processes. In particular, it would be especially desirable to be able to manipulate conditions other than temperature and pressure so as to customize the physical properties of the final product. It would also be desirable to employ a foaming process that eliminates the need for using organic solvents as blowing agents. There is also a need to reduce the saturation time in embodiments involving batch processes, and to control the distribution and sizes of cells in the foamed materials.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method of producing a foamed material. The method comprises contacting a material with a fluid mixture comprising carbon dioxide and a surfactant. The surfactant facilitates dissolution of the carbon dioxide into the material to foam the material.
In another aspect, the invention relates to a method of extrusion processing a material. The method comprises introducing solid material into the barrel of an extruder, heating the material to melt the material, and thereafter contacting the molten material with a fluid mixture comprising carbon dioxide and a surfactant. The surfactant facilitates the dissolution of the carbon dioxide into the molten material to foam the material.
Other aspects and advantages of the invention are set forth in detail herein.
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International Search Report, PCT/US01/06558, mailed Sep. 19, 2001.
DeSimone Joseph M.
Khan Saad A.
Royer Joseph R.
Spontak Richard J.
Walker Teri Anne
Bagwell Melanie D.
Myers Bigel Sibley & Sajovec P.A.
North Carolina State University
Seidleck James J.
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