Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-03-01
2004-09-14
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...
C521S134000, C521S135000, C521S136000, C521S137000, C521S138000, C521S139000, C521S140000, C264S050000, C264S051000
Reexamination Certificate
active
06790870
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to methods of making foamed materials from a blend of thermoplastic polymer materials employing various blowing agents.
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 and physical blowing agents that include, for example, azos, various volatile organic compounds (VOCs), and chlorofluorocarbons (CFCs). The chemical blowing agents typically decompose at a critical temperature and release a gas such as nitrogen, carbon dioxide, or carbon monoxide. The physical blowing agents typically are dissolved in the polymer material and then precipitated to form a foamed structure. 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. The typical embodiment of an improved foaming process would be to use carbon dioxide as a physical blowing agent to generate a polymeric foam which contains a uniform distribution of cells (with sizes ranging from about 10 microns to submicron size) defined herein as microcellular.
Semicrystalline polymers present various processing challenges, particularly with respect to producing microcellular foams via a continuous processing. Structural foams, along with other conventional foams, typically proceed commercially with physical blowing agents and semicrystalline polymers. Nonetheless, problems with these foams tend to stem from the small size of the cell walls, and a small defect in the cell wall is often a significant weak point in the structure leading to the observed problems. Producing various foamed semicrystalline thermoplastic polymers such as (poly)vinylidene fluoride in a continuous process has often been observed to be problematic. It has been observed that as the material exits the nozzle of a foaming system, the extrudate often becomes brittle and breaks up into fine powder. Although not wishing to be bound by theory, it is believed that the semicrystalline nature of polymer causes the extrudate to break into small particles when the blowing agent is released. This tends to be most significant in the formation of a microcellular foams, where the large number of small well-distributed cells creates a situation in which the cell walls of the foamed material are significantly thinner that those of conventional foams.
There is a need in the art to provide foamed polymers which avoid the problems stated above, particularly with respect to semicrystalline polymers.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method of producing a foamed material. The method comprises contacting a mixture comprising a first thermoplastic polymer and a second thermoplastic polymer with a blowing agent. The first thermoplastic polymer has a higher percent crystallinity than the second thermoplastic polymer. The mixture of thermoplastic polymers is then subjected to conditions sufficient to create a thermodynamic instability in the blend to foam the mixture. The mixture comprising the first and second thermoplastic polymers has a percent crystallinity lower than the first thermoplastic polymer.
In another aspect, the invention provides a method of extrusion processing a blend of thermoplastic materials. The method comprises introducing at least two thermoplastic polymers into an extruder barrel. The at least two thermoplastic polymers comprise a first thermoplastic polymer and a second thermoplastic polymer. The first thermoplastic polymer has a higher percent crystallinity that the second thermoplastic polymer. The blend of thermoplastic materials is then heated to provide a molten blend thereof. The molten blend is then contacted with a blowing agent, and the blend is subjected to conditions sufficient to create a thermodynamic instability in the blend to foam the blend. The blend has a percent crystallinity lower than the first thermoplastic polymer.
Other aspects and advantages of the invention are set forth in detail herein.
REFERENCES:
patent: 3879505 (1975-04-01), Boutillier et al.
patent: 4424287 (1984-01-01), Johnson et al.
patent: 4466933 (1984-08-01), Huggard
patent: 4473665 (1984-09-01), Martini-Vvedensky et al.
patent: 4482582 (1984-11-01), Weisman
patent: 4673695 (1987-06-01), Aubert et al.
patent: 4692381 (1987-09-01), Pecsok
patent: 4906672 (1990-03-01), Stone et al.
patent: 4940733 (1990-07-01), Kuphal et al.
patent: 4945119 (1990-07-01), Smits et al.
patent: 5037859 (1991-08-01), Williams, Jr. et al.
patent: 5066684 (1991-11-01), LeMay
patent: 5084486 (1992-01-01), Patten et al.
patent: 5120559 (1992-06-01), Rizvi et al.
patent: 5120770 (1992-06-01), Doyle et al.
patent: 5158986 (1992-10-01), Cha et al.
patent: 5160674 (1992-11-01), Colton et al.
patent: 5180751 (1993-01-01), Park et al.
patent: 5252620 (1993-10-01), Elliott, Jr. et al.
patent: 5269987 (1993-12-01), Reedy et al.
patent: 5286429 (1994-02-01), Blythe et al.
patent: 5288740 (1994-02-01), Park et al.
patent: 5302624 (1994-04-01), Reedy et al.
patent: 5312846 (1994-05-01), Smits et al.
patent: 5334356 (1994-08-01), Baldwin et al.
patent: 5411683 (1995-05-01), Shah
patent: 5411687 (1995-05-01), Imeokparia et al.
patent: 5422378 (1995-06-01), Vo
patent: 5424014 (1995-06-01), Glorioso et al.
patent: 5451633 (1995-09-01), DeSimone et al.
patent: 5525640 (1996-06-01), Gerkin et al.
patent: 5589105 (1996-12-01), DeSimone et al.
patent: 5639836 (1997-06-01), DeSimone et al.
patent: 5670102 (1997-09-01), Perman et al.
patent: 5670552 (1997-09-01), Gusavage et al.
patent: 5674916 (1997-10-01), Shmidt et al.
patent: 5674957 (1997-10-01), DeSimone et al.
patent: 5676705 (1997-10-01), Jureller et al.
patent: 5683977 (1997-11-01), Jureller et al.
patent: 5684055 (1997-11-01), Kumar et al.
patent: 5698665 (1997-12-01), Odell
patent: 5707573 (1998-01-01), Biesenberger et al.
patent: 5780521 (1998-07-01), Shmidt et al.
patent: 5783082 (1998-07-01), DeSimone et al.
patent: 5789454 (1998-08-01), McVey
patent: 5801210 (1998-09-01), Radovich et al.
patent: 5821273 (1998-10-01), Venkataraman et al.
patent: 5830393 (1998-11-01), Nishikawa et al.
patent: 5833930 (1998-11-01), Sulzbach et al.
patent: 5883197 (1999-03-01), Barbieri et al.
patent: 5889069 (1999-03-01), Suh et al.
patent: 5922493 (1999-07-01), Humphrey, Jr. et al.
patent: 6169139 (2001-01-01), van Cleeff
patent: 6284412 (2001-09-01), Minakata et al.
patent: 11140210 (1999-05-01), None
patent: WO9947603 (1999-09-01), None
Gupta, C. “Fluoropolymer Foams”, Handbook of Polymeric Foams and Foam Technology, Klempner and Frisch, eds., Hanser Publishers, New York: 1991, pp. 339-354.*
CAPCE Newsletter, The Ohio State University vol. 1, Iss. 2, pp. 1-8, Winter/Spring 1999.
Arora et al.;Preparation and Characterization of Microcellular Polystyrene Foams, Macromolecules 31:4614-4620 (1998).
Baldwin et al.;An Extrusion System for the Processing of Microcellular Polymer Sheets: Shaping and Cell Growth Control, Polymer Engineering and Science, 36:10 1425-1435 (1996).
Baldwin et al.;A Microcellular Processing Study of Poly(Ethylene Terephthalate)in the Amorphous and Semicrystalline States. Part II: Cell Growth and Process Design, Polymer Engineering and Science, 36:11 1446-1453, (1996).
Behravesh et al.;Approach to the Production of Low-Density, Microcellular Foams in Extrusion, Antec '98, 1958-1967, (1998).
Burke;Rheological Properties of Polyvinylidene, Journal of VinylTechnology 15:3 177-187 (Sep. 1993).
Chiou et al.;Plasticization of Glassy P
DeSimone Joseph M.
Gay Yvon J.
Khan Saad A.
Royer Joseph R.
Siripurapu Srinivas
Bissett Melanie
Myers Bigel Sibley & Sajovet, PA
North Carolina State University
LandOfFree
Methods of making foamed materials of blended thermoplastic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods of making foamed materials of blended thermoplastic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods of making foamed materials of blended thermoplastic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3245987