Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1998-09-21
2001-07-10
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C264S176100, C528S061000, C528S063000, C528S076000
Reexamination Certificate
active
06258917
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved extrudable, thermoplastic, elastomeric polyurethane for use in efficiently manufacturing products such as air bags with excellent properties, and a process for making the same.
BACKGROUND OF THE INVENTION
Urethane elastomers are an important segment of the urethane industry. Urethane elastomers have many potential uses, including cast systems, adhesives, spray coatings, millable gums, and injection molding systems for commercial, automotive and military applications. However unsatisfactory thermal aging characteristics as well as poor hydrolysis and microbial resistance has limited the use of urethane elastomers particularly in applications which require the urethane product to undergo long term environmental exposure before or during its intended use. For example, new air bag technology demands a polyurethane elastomer which combines high-temperature resistance with excellent physical properties, processing parameters, and resistance to hydrolysis, oxygen, and ozone. In particular, for air bag use or any other related use, some of the most important properties are extrudability, high-temperature resistance, low temperature flex, high strength, elongation, low to moderate tensile modulus, good environmental resistance, excellent tear resistance, with an “A” durometer of about 80.
The extrudable urethane elastomers currently commercially available are typically hydroxyl-extended and do not have the thermal resistance necessary to resist the temperature of the gas generator during air bag deployment.
It is believed that there are currently no thermoplastic urethane elastomer compositions available that are urea-extended and that can be extruded with a combination of excellent temperature resistance, physical, and environmental properties. It has been believed in the art that a processable thermoplastic urethane could not be obtained using a diamine chain extender because the resulting urea segments gave the urethane a very high melting point. As such, the polyurethanes could not be processed by typical methods used in processing thermoplastic elastomeric materials, such as extrusion, without decomposition of the urethane.
Extrusion of thermoplastic polyurethane elastomers would be desirable to allow flexibility in the formation of various product shapes and sizes, including air bag bladders and the like. Extrusion also is a less expensive and faster processing method compared to other formation processes such as liquid casting.
Taub, U.S. Pat. No. 3,600,358, discloses a polyurethane elastomer prepared from a 4,4′-methylene bis(cyclohexylisocyanate), neopentyl adipate and aromatic diamine. Following addition of the aromatic diamine to the urethane prepolymer, the mixture is heated and poured into a mold for curing. Taub does not indicate that the urethane can be extruded. Taub also does not disclose or suggest the inclusion of a mixture of diamine materials to improve the extrudability of a urea-extended urethane.
Slagel, U.S. Pat. No. 3,866,242, discloses a protective shield comprising a polyurethane made from a polyester or polyether glycol, a diisocyanatodicyclohexylmethane isocyanate material, and a primary amine such as 4,4′-methylenebis(2-chloroaniline). The polyurethanes are cast between glass plates and cured to form the protective shield. The polyurethane disclosed by Slagel is not elastomeric, as evidenced by the disclosure that the material has a hardness on the “D” scale of 77-80 (col. 3, line 30). Slagel does not indicate that the polyurethane can be extruded. Slagel also does not disclose or suggest the inclusion of a mixture of diamine materials to improve the extrudability of a urea-extended urethane.
Accordingly, it is an object of the present invention to provide a thermoplastic polyurethane elastomer that is extrudable, that has high temperature resistance, and that is strong and durable for use in manufacturing urethane products such as air bags and the like. It is a further object of the present invention to provide a process for making such polyurethanes, as well as a process for extruding such polyurethanes.
Novel features of the invention, together with advantages thereof, will be better understood from the following descriptions in which embodiments of the invention are illustrated by way of examples.
SUMMARY OF THE INVENTION
Polyurethanes of the present invention comprise an extrudable reaction product of at least one aliphatic diisocyanate with at least one hydroxy-containing intermediate selected from polyester glycols, polyether glycols, and mixtures thereof, and at least one diamine curing agent. The polyurethanes may also include an extrusion processing aid. A process of the present invention comprises reacting at least one aliphatic diisocyanate with at least one hydroxy-containing intermediate to form a prepolymer, and then reacting the prepolymer with at least one diamine curing agent to form a thermoplastic polyurethane elastomer. Alternatively, at least one aliphatic diisocyanate may be reacted with less than one equivalent of the hydroxy-containing intermediate to form a prepolymer, and then the remaining equivalents of the hydroxy-containing intermediate may be added along with at least one diamine curing agent to form a cured elastomer. In addition, the present invention relates to a process of extruding polyurethanes of the invention, as well as extruded polyurethane products.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Polyurethanes of the present invention comprise a reaction product of at least one aliphatic diisocyanate with at least one hydroxy-containing intermediate selected from polyester glycols, polyether glycols, and mixtures thereof, and at least one diamine curing agent. Preferably, the diamine curing agent system is a mixture of at least one first diamine curing agent and at least one second diamine curing agent. However, the polyurethane may be cured with only the at least one first diamine curing agent. At least one extrusion processing aid may also be included in the polyurethane. The polyurethanes of the present invention are thermoplastic elastomers that can be readily extruded into various urethane products.
The present polyurethanes are extrudable due to possessing an excellent melt flow property while at the same time having high thermal stability. Compared to commercially available thermoplastic urethane elastomers having a Shore A hardness of about 80, polyurethanes according to the invention having a similar Shore A hardness have a lower melt flow temperature on the order of 10 to 70° C. lower, when measured according to the ASTM D-1238 method. The melt flow index of the polyurethanes of the present invention ranges from about 5 to 40 inches per minute, more preferably from about 8 to 25 inches per minute, when measured in accordance with the modified ASTM D-1238 method described in Example 9. Thus, embodiments of the inventive polyurethanes are extrudable within the range of about 215° C. to 310° C., preferably about 235° C. to 260° C. Commercially available polyurethanes, on the other hand, liquify at such processing temperatures. Typically, commercially available polyurethanes, such as Pellethane (a hydroxyl-extended extrudable grade polyurethane commercially available from Dow), are extruded through a melt flow indexer at temperatures of about 224° C., using a load of 2 to 6 kg of pressure. Higher extrusion temperatures cannot be used because these commercially available polyurethanes destabilize and liquify at higher temperatures. The polyurethanes of the present invention, however, can be extruded at very high temperatures without degradation.
Without wishing to be bound by theory, the inventor believes that the present urea extended polyurethanes possess such superior properties and are extrudable due to the polyurethane including an aliphatic diisocyanate, preferably a saturated aliphatic diisocyanate. As such, the polyurethane exhibits thermoplastic properties and does not form any side reactions, e.g. does not form biurets,
Pittman Shaw
Sergent Rabon
Simula Inc.
LandOfFree
Extrudable thermoplastic elastomeric urea-extended polyurethane does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Extrudable thermoplastic elastomeric urea-extended polyurethane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Extrudable thermoplastic elastomeric urea-extended polyurethane will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2515460