Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1995-12-21
2002-05-28
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S137000, C521S174000, C521S176000, C525S127000, C525S131000, C525S453000, C525S460000, C528S065000, C528S076000
Reexamination Certificate
active
06395798
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to the field of microcellular polyurethane elastomers. More particularly, the present invention pertains to microcellular elastomers suitable for athletic midsoles prepared by the diol chain extension of an isocyanate-terminated prepolymer having an NCO group content in the range of 6-16 weight percent, prepared from a high functionality, high molecular weight polyoxyalkylene diol in the presence of water as a reactive blowing agent.
BACKGROUND ART
Microcellular polyurethane elastomers have become increasingly important in the athletic shoe and other markets. The midsoles of athletic shoes in particular require high resiliency and low compression set while maintaining suitable hardness. The density of the microcellular midsoles is also important, as shoes of light weight are generally desired. The method currently used by the industry to prepare microcellular midsoles and other products of similar density is to chain extend an 18% NCO content, isocyanate-terminated prepolymer with an aliphatic diol. The Shore A hardness may be adjusted within the range of Shore A 30 to Shore A 50 by varying the type and amount of chain extenders and cross-linkers.
The prior art products have several defects which can be improved upon, however. For example, midsoles and other microcellular components are normally molded to a density of from 0.35 to 0.50 g/cm
3
to overcome problems with respect to shrinkage. If the microcellular foam product shrinks appreciably following demold, it will not possess the desired design dimensions. As a result, the mold must be designed, largely by trial and error, to produce a dimensionally larger part which, upon shrinking, has the desired final dimensions. It would be advantageous to produce microcellular elastomers of lower density without undue shrinkage. The microcellular foam product must also possess the necessary tensile strength, elongation, and tear strength necessary to maintain integrity not only during use, but in manufacturing processes including demolding and insertion into fabric surrounds, etc. Finally, the compression set must be low, otherwise a great deal of the cushioning will be lost after the first few periods of use.
Of the raw material components used in the preparation of microcellular elastomers, the isocyanate component of the isocyanate-terminated prepolymer is generally the most expensive. However, lowering the % NCO content of the isocyanate-terminated prepolymers used to prepare the elastomers has not been successful heretofore, as lower NCO content prepolymers produced a softer elastomer which does not provide sufficient support. Thus, the industry standard for microcellular elastomer isocyanate-terminated prepolymers has remained at 18% NCO.
The use of higher molecular weight polyoxyalkylene polyols during the preparation of the isocyanate-terminated prepolymers would allow the preparation of lower NCO content prepolymers and the use of less isocyanate relative to polyol weight. However, until recently, higher molecular weight polyols of suitable functionality have not been available. Moreover, the use of a higher molecular weight polyol should increase the soft segment content of the elastomer, which would be expected to produce an elastomer of insufficient hardness.
Polyoxypropylene diols used in prepolymer preparation have been limited to molecular weights of c.a. 2000 Da (Daltons) or less due to the rearrangement of propylene oxide to allyl alcohol during base-catalyzed oxypropylation, and the subsequent oxypropylation of this monohydric species. As a result of this phenomenon, during continued oxyalkylation, the mol percentage of monomeric oligomers steadily increases until the gain in average molecular ceases to increase further. At this point, the monofunctional oligomers may comprise 50 mol percent of the product, and the theoretical, or “nominal” functionality of two will be lowered to c.a. 1.6 to 1.7 or less. Thus, the preparation of high molecular weight polyoxypropylene diols having actual functionalities close to two has been impossible.
Numerous attempts have been made to lower the monol content of polyoxyalkylene polyols, but few have been successful. Use of more expensive and less commonly used basic catalysts such as cesium or rubidium hydroxides, and barium or strontium oxides or hydroxides have resulted in some improvement, as has lowering catalyst level and oxyalkylation temperatures, the latter two measures at the expense of greatly increased process time. Moreover, the improvement, as measured by the amount of unsaturation by ASTM D-2849-69, “Testing Urethane Foam Polyol Raw Materials,” has been marginal at best.
Use of metal naphthenates, alone or in conjunction with tertiary amine co-catalysts, has resulted in lowering the unsaturation from the normal range of 0.06-0.12 meq/g to about 0.03-0.04 meq/g. However, at the latter level, a 4000 Da polyoxypropylene diol still contains c.a. 15% monol, and has an actual average functionality of only about 1.85.
The use of double metal cyanide complex catalysts as oxyalkylation catalysts was proposed in the decade of the 1960's and improved catalysts, such as those disclosed in U.S. Pat. No. 5,158,922 have lowered unsaturation to the range of 0.015 to 0.018 meq/g. However, the polyol products still contain from 5 to 10% monol, and commercialization has been problematic due to the cost/activity ratio of the catalyst as well as the difficulty of removing catalyst residues from the polyol product. Most recently, the ARCO Chemical Company has introduced double metal cyanide complex catalysts of much higher activity. In addition, these catalysts allow easy removal of catalyst residues from the polyol product by simple filtration. As a result, polyoxyalkylene polyols of exceptionally low unsaturation, in the range of 0.003 to 0.007 meq/g have now been commercialized. Although the exceptionally low but measurable unsaturation implies a finite monol concentration, conventional gel permeation chromatography fails to detect a low molecular weight component which would correspond to monofunctional species. The content of monol is believed to be less than 2 mol percent. Moreover, the product polyols have very low polydispersities, generally in the range of Mw/Mn=1.10, thus being virtually “monodisperse”.
Despite long standing efforts to lower unsaturation in polyoxyalkylene polyols, exceptionally low unsaturation polyols are not generally “drop in” replacements for conventional, base-catalyzed polyols. For example, R. L. Mascioli, “Urethane Applications For Novel High Molecular Weight Polyols”, 32nd Annual Polyurethane Technical/Marketing Conference, Oct. 1-4, 1989, disclosed that substitution of a 11,000 Da molecular weight triol having an unsaturation of about 0.007 meq/g for a conventional, base-catalyzed triol having a calculated molecular weight of c.a. 6000 and an unsaturation of 0.084 meq/g, resulted in a stiff and boardy foam product, whereas a softer product would be expected in view of the higher polyol molecular weight.
C. P. Smith et al., “Thermoplastic Polyurethane Elastomers Made From High Molecular Weight Poly-L™ Polyols”, Polyurethanes World Congress—Sep. 24-26, pp. 313-318, disclosed one-shot polyurethane elastomers prepared from high molecular weight, high primary hydroxyl, polyoxyethylene-capped diols having measured unsaturations in the range of 0.012 to 0.016 meq/g. As expected, cast elastomers prepared from a 6600 Da molecular weight diol were softer than those prepared from a 4000 Da diol, and of similar hardness to those prepared from a conventional base-catalyzed diol, although having improved elongation and tensile strength.
In U.S. Pat. No. 4,985,491 are disclosed moisture cured polyurethane sealants containing very low NCO group content prepolymers prepared from high molecular weight triols. Sealants prepared from high molecular weight polyoxyethylene capped (10,000 Da) triols had significantly lower hardness than those prepared from 5800 Da triols. Both triols had unsaturations in the range
Bayer Antwerp N.V.
Gil Joseph C.
Sergent Rabon
Whalen Lyndanne M.
LandOfFree
Low density microcellular elastomers based on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low density microcellular elastomers based on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low density microcellular elastomers based on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2863349