Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-01-25
2001-05-15
Cooney, Jr., John M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S082000, C264S051000
Reexamination Certificate
active
06232354
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microcellular polymer foams and methods for their production and more specifically to microcellular crystalline and semi-crystalline polymer foams produced by a similar method. Filled polymer foams and methods for their manufacture are also described.
BACKGROUND OF THE INVENTION
The production of polymeric foams is well known in the art. For example, foams of amorphous polymers such as polystyrene have been manufactured for decades. Most commercial foam production processes involve the use of chemical blowing agents (CBAs) which decompose during processing or blowing gases like CFCs or carbon monoxide, which are toxic or polluting. Such foaming techniques generally produce foams whose cell sizes are on the order of millimeters and have mechanical properties much weaker than those of the solid form of the parent polymer material.
Structural foams have more recently been processed from polymers such as polymethacrylic imide and polyvinyl urea-amides. The production of such foams poses several problems. In the case of the former material, for example, the foam is manufactured by hot foaming methacrylic acid and methacrylonitrile monomers using carbon monoxide, a toxin, as the blowing agent. Additionally, such foams remain “macrocellular” and do not demonstrate mechanical properties anywhere near those of the parent polymer material.
To overcome the mechanical property deficiencies of macrocellular foams, the production of microcellular foams has been proposed. In these cases, microcellular foams were defined as having cell sizes on the order of tens of microns and cell densities on the order of 10
8
-10
9
/cc. Such a process was developed for the production of amorphous polymeric foams. This process involved saturation of the polymer sample with a non-reactive gas such as nitrogen at elevated pressure and a temperature below the T
g
(glass transition temperature) of the polymer. The pressure was then released and the temperature raised above the T
g
of the polymer. These techniques required soaking times on the order of 24 hours to allow the gas to dissolve in the polymer. These efforts to produce microcellular foams have been conducted primarily with amorphous polymers, although some more recent efforts have been made to use the process to foam semi-crystalline polymers such as PET.
High temperature polymers such as liquid crystalline polymers (LCPs) are more difficult to foam. In fact, to our knowledge, there are currently no LCP foams available because of the lack of a high temperature blowing agent as required by conventional “blowing” or foam manufacturing techniques.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an environmentally friendly process for the production of microcellular foams.
It is another object of the present invention to provide a commercially practicable process for the production of microcellular foams.
It is yet another object of the present invention to provide a process for the manufacture of microcellular foams from crystalline and semi-crystalline polymers.
Still a further object of the present invention is to provide a method for the so-called “loaded” or filled microcellular foams, which have been reinforced with particulate or fibrous material to enhance their mechanical, electrical, thermal, etc. properties.
SUMMARY OF THE INVENTION
The present invention provides an environmentally friendly and commercially practicable process for the production of microcellular polymer foams from amorphous, semi-crystalline and crystalline polymers which involves consolidating the polymer, saturating the polymer with an inert gas at elevated temperature and under elevated pressure, and cooling, i.e. quenching the saturated polymer under a variety of temperature and pressure conditions to produce either a closed or open celled microcellular foam or a high density microcellular foam, as defined hereinafter. Microcellular foams of amorphous, semi-crystalline and crystalline polymers that demonstrate unusually high mechanical properties can be made using the techniques of the present invention and are also described. Additionally the manufacturing processes described herein are equally applicable to the production of reinforced or filled microcellular polymer foam materials, which demonstrate exceptional mechanical, electrical or other properties.
REFERENCES:
patent: 5340841 (1994-08-01), Tokoro et al.
patent: 5391581 (1995-02-01), Kuwabara et al.
patent: 5424336 (1995-06-01), Taniguchi
patent: 5830922 (1998-11-01), Wirobski et al.
patent: 5917011 (1999-06-01), Duda et al.
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