Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-18
2002-10-01
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06458880
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyurethane compositions. In particular, the invention relates to polyurethane compositions that include a talc crystallization promoter.
BACKGROUND OF THE INVENTION
Polyurethanes are used in a variety of different products, including flexible or rigid foams, fibers, molded compositions, and adhesives. Polyurethanes are typically the reaction product of (a) one or more hydroxyl terminated polymers (e.g., polyols), such as hydroxyl terminated polyethers, polyesters, polycarbonates, and polycaprolactones, (b) one or more polyisocyanates, and, optionally, (c) one or more chain extenders. The properties of a particular polyurethane and its suitability for particular purposes depend, at least in part, on the reactants used to make the polyurethane.
One useful property for forming particular polyurethane products, including for example, many molded products, is the ability of some polyurethanes to crystallize. The crystallization of the polyurethane can result in a stronger, more stable, wear resistant, and/or solvent resistant product. Typically during product formation, a polyurethane must remain in a mold until the polyurethane starts to crystallize or is substantially crystallized. To have low molding cycle times, it is useful to find polyurethanes that crystallize quickly or at relatively high temperatures. Fast crystallization can also be advantageous in other processes where rapid set-up of the product is desirable including, for example, extrusion and film formation. In addition, other properties such as, for example, price, availability, color, stability, and strength should also be considered when selecting the proper polyurethane for a particular product.
SUMMARY OF THE INVENTION
Generally, the present invention relates to polyurethane compositions using talc as a crystallization promoter. One embodiment of the invention is a polyurethane composition containing polyurethane (e.g., a polyester-based polyurethane) and sufficient talc to provide a crystallization temperature of the polyurethane composition that is at least 10 degrees Celsius greater than the crystallization temperature of the polyurethane composition without talc, as measured by differential scanning calorimetry starting at a temperature of 270° C. and decreasing at a rate of 40° C. per minute. A suitable range for the amount of talc is, for example, about 0.2 to 4 wt. %, based on the total weight of the polyurethane composition.
Another embodiment is an article formed using this polyurethane composition. This article can be formed by, for example, molding or extruding the polyurethane composition.
Yet another embodiment is a method of forming the polyurethane composition described above. This method includes combining the polyurethane and the talc, typically in an extruder. The step of combining the polyurethane and the talc can include, for example, a) adding talc to a previously formed polyurethane, b) adding talc to the reactive components that are used to form the polyurethane, or c) adding talc to partially or substantially formed polyurethane in, for example, an extruder.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is directed to crystallizable polyurethane compositions that include talc as a crystallization promoter and the products made using these compositions.
The term “crystallizable” refers to compositions that are a) crystallized or b) uncrystallized, but capable of crystallization by a reduction in temperature of the composition. The crystallization temperature of the composition can typically be determined by differential scanning calorimetery. Generally, crystallized compositions can be melted, solvated, or otherwise amorphized and then recrystallized.
The term “polyurethane composition” refers to a composition, prior to extrusion, within the extruder, or after extrusion, that contains polyurethane or reagents used to make the polyurethane. 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 the polyurethane, reagents used to make the polyurethane, talc, and all other additives.
The polyurethane composition typically includes (i) at least one crystallizable thermoplastic polyurethane and (ii) talc which acts as a crystallization promoter. Other additives can also be provided in the polyurethane composition. The polyurethane and the talc can be combined in a variety of ways including mixing within an extruder that is also used for the reactive formation of the polyurethane, as described below. The addition of talc to polyurethanes (e.g., polyester-based polyurethanes) can yield a polyurethane composition with a crystallization temperature that is greater than the crystallization temperature of the same polyurethane composition without talc. For example, the crystallization temperature of the polyurethane composition can be at least 10 degrees Celsius greater than a crystallization temperature of the same polyurethane composition without the talc, as measured, for example, by differential scanning calorimetery (DSC) starting at a temperature of 270° C. and decreasing at a rate of 40° C. per minute.
Polyurethanes
Polyurethanes are generally prepared by combining and reacting a) at least one hydroxyl terminated intermediate (e.g., hydroxyl terminated polyester, polyether, polycarbonate, or polycaprolactone) with b) at least one polyisocyanate and, optionally, c) at least one chain extender. These reactants generate a polyurethane in, for example, an extruder or other reaction vessel. Suitable polyurethanes include thermoplastic polyurethanes, but can also include other polyurethanes, such as thermoset polyurethanes.
The reaction that forms the polyurethane can be complete before the polyurethane is introduced into the extruder and/or before combination with the talc. Suitable commercial polyurethanes include, for example, at least some of the Estane® series of polyurethanes available from BFGoodrich (Charlotte, N.C.), such as, for example, Estane® 58157, 58142, 58137, 58133, and 58134.
Alternatively, the reactants to produce the polyurethane can be added into the extruder or other reaction vessel and the reaction performed in situ. For example, the hydroxyl terminated polymer(s), the polyisocyanate(s), and the chain extender(s), if present, can be combined within the extruder and reacted as the material flows through the extruder. Talc can be added with the reactants or at another point along the extruder.
Based on the current experimental data, the crystallization promoting effect provided by the addition of talc is particularly apparent for polyurethanes derived from hydroxyl terminated polyesters (i.e., polyester-based polyurethanes). The addition of talc to certain hydroxyl terminated polyether-based polyurethanes, as illustrated in Examples 3-7, did not appear to result in any significant increase in crystallization temperature. It is thought that these polyether-based polyurethanes did not benefit from the addition of talc because the polyether portions of the polyurethane are phase separated from the urethane portions, allowing the urethane portions to more readily crystallize. In contrast, the polyester and urethane portions of the polyester-based polyurethanes are soluble in each other and allow for phase-mixing, which inhibits crystallization. Accordingly, the remainder of the discussion is generally directed to polyester-based polyurethanes. Other polyurethanes and methods for their formation are described in U.S. Pat. Nos. 5,110,850 and 5,959,059, incorporated herein by reference.
Hydroxyl Terminated Polyesters
Hydroxyl terminated polyesters can be used to form polyurethanes. Suitable hydroxyl terminated polyesters for forming polyurethanes are generally polyesters, often linear polyesters, having a number average molecular weight, M
n
, of at least 500 and often no more than 10,000 to provide the polyurethane with a distribution of hard and soft segments. The number
Loeber George Hunter
Onder Kemal
Black Bruce E.
Calloway Valerie L.
Noveon IP Holdings Corp.
Powell Joe A.
Rajguru U. K.
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