Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-06-15
2001-07-10
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S131000, C521S056000
Reexamination Certificate
active
06258865
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to closed-cell polymer foams, particularly to such foams that include an insulation-enhancing amount of an oil-containing furnace black, and more particularly, to a method of making such foams.
Carbon black, well known in the art as an effective infrared radiation absorber and reflector, has a conventional use as an additive in insulative foam structures to reduce thermal conductivity. However, the addition of carbon black often results in dispersion problems when manufacturing the foams. Such processing problems include increased pressure drop, higher foam density, increased open cells, and poor skin quality.
An attempt to solve some of these problems uses thermal grade carbon black (thermal black). For example, U.S. Pat. No. 5,373,026 discloses that thermal black processes easier, incorporates into a foam structure more readily, induces a lower process pressure drop, and has a lesser impact on polymer foam skin quality, all relative to other forms of carbon black.
Other attempts use carbon black coated with small amounts of a compatibilizing agent, such as a fatty acid, a phthalic ester, an oil, or a polyalkylene glycol, to enhance carbon black dispersion in both foam formulation and a resulting end-product foam. See U.S. Pat. No. 5,461,098; 5,397,807; and 5,571,847. However, compatibilizing agent addition involves an extra manufacturing step that increases foam production expense.
U.S. Pat. No. 5,710,186 uses titanium dioxide (TiO
2
) particles surface treated with a small amount of a wetting agent to enhance insulation capability of foams. The surface treated TiO
2
grades cost more and provide less foam insulation performance improvement than carbon black.
Accordingly, a need remains for another cost-effective foam making method that provides enhanced insulation performance without adversely affecting foam processing or end product foam properties.
SUMMARY OF THE INVENTION
The present invention meets that need with a polymer foam that includes an oil-containing furnace black as an insulation enhancer. The use of oil-containing furnace black yields a foam with a lower thermal conductivity than comparable foams produced with thermal black and properties that compare favorably with those achieved with other conventional carbon blacks. The furnace black is also relatively low in cost.
One aspect of the present invention is a polymer foam prepared from a foamable polymeric material that contains a quantity of furnace black sufficient to reduce foam thermal conductivity to a level below that of a corresponding foam prepared from the same foamable polymeric material save for omission of the furnace black. The furnace black contains from 3 to 10 percent by weight oil (wt %), based on total furnace black weight. The oil preferably comprises a hydrotreated heavy naphthenic distillate. Preferably, the foam contains from 1 to 25 wt % more preferably from 2 to 10 wt %, based on total foam weight, furnace black.
The polymer foam may be made by an extrusion process that comprises the steps of: a) providing a foamable polymeric material; b) adding an amount of oil-containing furnace black to said foamable polymeric material sufficient to reduce the thermal conductivity of the foam below that of a foam without said furnace black, said furnace black having from 3-10 percent by weight oil, based on total furnace black weight, incorporated therein; c) adding a blowing agent to form a gel; d) cooling the foamable gel to an optimum foaming temperature; and e) extruding the gel through a die to form said foam. The use of an oil-containing furnace black in preparing foams of the present invention results in a foam with similar or better reduction in thermal conductivity than that achieved with the same loading of thermal black. In addition, the furnace black provides pressure drops and foam properties (cell sizes, densities, limiting oxygen index performance, heat distortion temperatures and/or open cell contents) similar to those obtained with thermal blacks. The furnace black is preferably added as a concentrate in the polymer.
The present invention also provides a method for making a thermoset polymer foam which comprises providing a first thermoset monomer; providing a second thermoset monomer the same or different than the first monomer and polymerizable with the first monomer; incorporating into either or both the first and second monomers an amount of furnace black sufficient to reduce the thermal conductivity of the foam below that of a foam without said furnace black, said furnace black having from 3-10 wt % oil, based on total furnace black weight, incorporated therein; incorporating a blowing agent into either or both the first and second monomers; and mixing the first and second monomers under polymerizing conditions to form the thermoset polymer foam.
An alternative embodiment of the invention provides a method for making expandable thermoplastic foam beads. The foam may be made by expanding such beads with or without an intermediate step of forming pre-expanded beads. This method comprises providing a first thermoplastic monomer; providing a second thermoplastic monomer the same or different than the first monomer and polymerizable with the first monomer; polymerizing the first and second monomers to form thermoplastic particles; incorporating, during polymerization, an amount of furnace black sufficient to reduce the thermal conductivity of the foam below that of a foam without said furnace black, said furnace black having from 3-10 percent by weight, based on total furnace black weight, of oil incorporated therein; incorporating a blowing agent into the thermoplastic particles during or after polymerization; and cooling the thermoplastic particles to form the expandable foam beads.
In another alternative embodiment, the invention is a process for making expandable thermoplastic foam beads, the process comprising: heating a thermoplastic polymer material to form a melt polymer material; incorporating into the melt polymer material an amount of furnace black sufficient to reduce the thermal conductivity of the foam below that of a foam without said furnace black, said furnace black having from 3-10 percent by weight, based on furnace black weight, of oil incorporated therein; further incorporating a blowing agent into the melt polymer material at an elevated temperature to form a foamable gel; cooling the foamable gel to form an essentially continuous expandable thermoplastic strand; and pelletizing the expandable thermoplastic strand to form expandable foam beads.
Accordingly, it is a feature of the present invention to provide a foam prepared using oil-containing furnace black. It is a further feature of the invention to provide a method of making such a foam. These, and other features and advantages of the present invention will become apparent from the following detailed description and the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The use of oil-containing furnace black unexpectedly provides effective insulation enhancement without substantially adversely affecting foam quality. This differs from carbon blacks that contain compatibilizing additives, which can plasticize the polymeric material and negatively impact heat distortion performance of the foam. The use of oil-containing furnace blacks also results in low manufacturing process pressure drops similar to those obtained with thermal black.
Furnace blacks that contain from 90 to 97 wt % carbon black and 3 to 10 wt % oil, based on furnace black weight, provide enhanced insulation without adversely affecting foam properties or causing unacceptably high pressure drops. An example of an oil-containing furnace black is PANTHER 18 (EC-261) available from Engineered Carbons, Inc. This furnace black has heretofore typically been used in printing applications, but has now been found to be beneficial in foam processing. The furnace black is in the form of oil-containing pellets having a nominal particle size of 30 nm and containing 7 wt % hydrotreat
Bagwell Melanie
Gorr Rachel
The Dow Chemical Company
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