Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-12-09
2001-10-02
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S131000
Reexamination Certificate
active
06297321
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyurethane compositions and methods of forming the compositions. In particular, the invention relates to polyurethane compositions that include at least one fluoropolymer and methods of making and using the compositions.
BACKGROUND OF THE INVENTION
Extruded polyurethane compositions, particularly extruded thermoplastic polyurethane compositions, are used in a variety of products. A portion of the thermoplastic polyurethane, however, tends to stick to the metal surfaces of the extruder and can crystallize. The crystallized polyurethane can build up within the extruder, particularly at points where the polymer resides for an extended period of time. Such build-up of the crystallized polyurethane can hinder the flow of the remainder of the polymer through the extruder. This crystallized polyurethane must be periodically removed from the interior of the extruder to reduce the pressure needed to maintain adequate throughput of the polyurethane composition. To remove the crystallized polyurethane, the extruder typically must be taken off-line and cleaned. This reduces the efficiency of the extrusion process and results in longer production times.
Additives, such as waxes, have been used to reduce build-up of crystallized polyurethane in the extruder. Waxes, however, tend to negatively alter the properties of the polyurethane, such as decreasing the strength and reducing the heat and chemical resistance of the polyurethane. In addition, the waxes tend to migrate to the surface of the extruded object, thereby modifying the surface properties of the extruded polyurethane composition.
SUMMARY OF THE INVENTION
Generally, the present invention relates to polyurethane compositions including at least one fluoropolymer. The fluoropolymer is typically added to enhance processability of the polyurethane composition. In particular, a fluoropolymer composition containing at least one fluoropolymer is combined with polyurethane, or the reactants that form the polyurethane, to facilitate extrusion of the polyurethane composition from an extruder. The addition of the fluoropolymer composition to the polyurethane composition typically results in less build up in the extruder than would be produced without the addition of the fluoropolymer composition.
One embodiment of the invention is a polyurethane composition that includes (a) polyurethane and (b) a fluoropolymer composition having at least one fluoropolymer. The fluoropolymer composition is present in the polyurethane composition in an amount that is effective to produce less build-up of polyurethane within an extruder than would be produced using the same polyurethane composition without the fluoropolymer composition. The polyurethane composition optionally includes a carrier for the fluoropolymer composition. In one embodiment, the fluoropolymer composition is at least 0.002 wt. % of the total polyurethane composition.
Another embodiment of the invention is a polyurethane article formed using this polyurethane composition. The polyurethane article can also include other components made from different materials.
A further embodiment of the invention is a method of making a polyurethane article by extruding the polyurethane composition described above. The method can optionally include other process steps such as, blowing or molding the polyurethane composition after extruding. When extruding the polyurethane composition, the polyurethane can be introduced into the extruder, or the reactants can be introduced into the extruder to form the polyurethane within the extruder. The fluoropolymer composition can be added to the polyurethane composition (e.g., the polyurethane or the components that are reacted to form the polyurethane) prior to introduction of the polyurethane into the extruder or through a port positioned at a point along the length of the extruder. Typically, the fluoropolymer composition is added prior to a position in the extruder where significant build-up of material occurs without the fluoropolymer composition.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is applicable to extrudable and extruded polyurethane compositions. In particular, the present invention is directed to extrudable polyurethane compositions, including extrudable thermoplastic polyurethane compositions, and products made from the compositions, as well as methods of extruding the compositions.
A polyurethane composition for extruding includes polyurethane (or reagents used to form the polyurethane or a combination of polyurethane and reagents), a fluoropolymer composition, and, optionally, a carrier for the fluoropolymer composition. The polyurethane is typically a thermoplastic polyurethane and the carrier is usually a polymer carrier that can facilitate the accurate addition and uniform dispersion of relatively small amounts of the fluoropolymer composition. When extruded, the polyurethane composition can be used to form polyurethane articles, either as extruded or by further processing, such as, for example, cutting, blowing, or molding. These polyurethane articles can be composite articles and include portions formed by other methods or using other materials.
The term “polyurethane composition” refers to a composition containing polyurethane, reagents used to form the polyurethane, or a combination thereof and can refer to this composition prior to extrusion, within the extruder, or after extrusion. When referring to the weight percentage of a particular material in the polyurethane composition based on the total weight of the polyurethane composition, the polyurethane composition includes any polyurethane, any unreacted reagents used to make the polyurethane, the fluoropolymer composition, optional carrier, and all other additives.
The components of the polyurethane composition can be combined to form the polyurethane composition prior to introduction into the extruder or they can be combined in situ within the extruder. The fluoropolymer composition is typically provided in an amount sufficient to produce less build-up of polyurethane (e.g., crystallized polyurethane) in the extruder (e.g., along the metal surface of the extruder) than would be found using the same polyurethane composition without the fluoropolymer composition. For purposes of this comparison, the amount of build-up for a given amount of material that has been extruded can be determined in a variety of ways including, for example, comparing the thickness of the build-up, the surface area of the extruder covered by the build-up, and/or the weight of the build-up for a given amount of polyurethane composition extruded at the same conditions. For example, for a given extruder, extruder configuration, extrusion conditions (e.g., extrusion temperature(s), pressure(s), and speed(s)), and period of time, the addition of a fluoropolymer composition can reduce the build-up by at least 10%. Extrusion conditions and amounts of fluoropolymer composition can be chosen so that build-up can be reduced by at least 50%, and even by at least 80% or more. In at least some instances, the addition of a fluoropolymer composition can prevent (e.g., reduce by about 100%), what would otherwise be significant, build-up for a given set of conditions and period of time. Reduction in build-up can be measured using one or more measurement criteria (e.g., the thickness, weight, or surface area of the build-up described above). The specified percentage of reduction in build-up is achieved if there is the appropriate reduction in build-up according to at least one measurement criterion, even if that reduction percentage is not met when using another measurement criteria.
For example,, a polyurethane composition without a fluoropolymer composition can be extruded through a 2½″ Killion single screw extruder (Killion Extruder, Inc., Cedar Grove, N.J.) fitted with a barrier screw at a 30:1 length/diameter ratio, a temperature setting of about 200 to 225° C., a screw speed of about 30 to 40 rpm (revolutions per minute), and an extrusion pressure
Loeber George Hunter
Onder Kemal
Vontorcik Joseph J.
Calloway Valerie L.
Dunlap Thoburn T.
Hudak Daniel J.
The B. F. Goodrich Company
Woodward Ana
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