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
1999-09-10
2001-04-24
Gorr, Rachel (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...
C528S065000, C528S085000
Reexamination Certificate
active
06221999
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a cast polyurethane elastomer possessing both high resilience and high clarity.
Polyurethane elastomers are well known. See, e.g., U.S. Pat. Nos. 4,294,951, 4,555,562 and 5,599,874. In general, polyurethane elastomers can be formed by reacting an isocyanate, e.g., diphenyl methane diisocyanate (MDI), toluene diisocyanate, naphthalene diisocyanate, etc., with an organic polyol, e.g., polytetramethylene ether glycol, polyester diol, polyoxypropylene glycol, etc., and a chain extender, e.g., an aliphatic diol such as 1,4-butanediol. Additional components such as catalysts, surfactants and the like can also be added to the elastomer-forming reaction mixture in the usual amounts. The overall properties of the polyurethane will depend upon the type of polyol and isocyanate, the degree of crosslinking and cystallinity in the polyurethane, the molecular weight of the polyurethane and chemical structure of the polyurethane backbone.
U.S. Pat. No. 5,264,620 discloses liquid, low temperature stable prepolymers and quasi-prepolymers which are derived from MDI containing the 4,4′-MDI isomer and 2,4′-MDI isomer and a polytetramethylene ether glycol. To obtain the stable prepolymer, the '620 patent discloses that high amounts of the 2,4′-MDI isomer are highly desirable, e.g., in amounts up to about 90 percent.
Polyurethanes can be either thermoplastic or thermoset, i.e., cast, depending on the degree of crosslinking present. Thermoplastic polyurethanes do not have primary crosslinking while thermoset polyurethanes have a varying degree of crosslinking, depending on the functionality of the reactants.
For example, Japanese Patent Application No. 4,332,719 discloses a thermoplastic polyurethane resin free of fish eyes after the thermoplastic polyurethane resin solution is guided through a multiaxial extruder. The thermoplastic resin is obtained by employing a long chain polyol, a diisocyanate and a lower molecular weight diol having over 5 carbon atoms. The '719 application specifically discloses that by employing a diol having over 5 carbon atoms, e.g., 2-ethyl-1,3-hexanediol, 1,5-pentanediol, etc., instead of 1,4-butanediol, the thermoplastic resin will be free of fish eyes on the surface of the resulting resin after it has been sent through the extruder during the formation thereof.
The reaction to form polyurethane elastomers can be a prepolymer process wherein an excess of an isocyanate is first reacted with an organic polyol to form an intermediate isocyanate-terminated prepolymer. The intermediate prepolymer is then contacted with a diol chain extender such as the aforementioned 1,4-butanediol, which reacts with the residual terminated isocyanate groups to form the polyurethane elastomer. Alternatively, a quasi-prepolymer or one-shot process may be employed. In the quasi-prepolymer process, a portion of the polyol is first reacted with the isocyanate to form a quasi-prepolymer. The remainder of the polyol and the diol chain extender are then reacted simultaneously with the quasi-prepolymer to form the polyurethane elastomer. In the one-shot process, all of the reactants are combined simultaneously to form the polyurethane elastomer.
SUMMARY OF THE INVENTION
In accordance with the present invention, a polyurethane elastomer possessing a resilience of at least about 50 percent and a clarity index of at least about 80 percent is obtained by the process which comprises reacting under polyurethane elastomer-forming conditions a polyurethane elastomer-forming reaction mixture comprising:
a) an isocyanate selected from the group consisting of diphenyl methane diisocyanate (MDI), isocyanate obtained from the reaction of polyether diol with MDI and mixtures thereof wherein at least a major proportion by weight of the MDI is the 4,4′-MDI isomer;
b) at least one polyether diol; and,
c) at least one diol chain extender of the general formula
HO—CH
2
)
x
—OH
wherein x is an integer from 5 to about 16.
The foregoing components can be reacted by the prepolymer, quasi-prepolymer or one-shot process. The quasi-prepolymer process is preferred.
The cast polyurethane elastomer of this invention possesses greater resilience and greater clarity when employing MDI wherein at least a major proportion by weight of the MDI is the 4,4′-MDI isomer, e.g., in amounts greater than about 70 percent by weight, together with the foregoing diol chain extenders than known polyurethane elastomers, i.e., those obtained with MDI not containing the 4,4′-MDI isomer as a major proportion by weight thereof and diol chain extenders whose alkylene groups possess fewer than five carbon atoms such as 1,4-butanediol. Additionally, as the amount of the 4,4′-MDI isomer increases and the amount of any other isomer in the MDI, e.g., the 2,4′-MDI isomer, and/or 2,2′-MDI isomer, decreases the resiliency of the elastomer will increase. As such, the elastomer is especially well suited for applications where these properties are especially desirable, e.g., roller skate wheels.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polyurethane elastomers of this invention possess a resiliency of at least about 50 percent and a clarity index of at least about 80 percent and are obtained by reacting the following polyurethane elastomer-forming reaction mixture under polyurethane elastomer-forming conditions:
a) an isocyanate selected from the group consisting of MDI; isocyanate obtained from the reaction of polyether diol with MDI and mixture thereof wherein at least a major proportion by weight of the MDI is the 4,4′-MDI isomer;
b) at least one polyether diol; and,
c) at least one diol chain extender of the general formula:
HO—(CH
2
)
x
—OH
wherein x is an integer from 5 to about 16.
In general, MDI is an isomeric mixture composed of the 4,4′-MDI isomer and other isomers such as, for example, the 2,4′-MDI isomer and/or the 2,2′-MDI isomer. When employing MDI herein, it is particularly advantageous that MDI be made up of at least a major proportion by weight of the 4,4′-MDI isomer to obtain a polyurethane elastomer having a high resiliency. It has been found that the resiliency of the elastomer herein will increase as the amount of the 4,4′-MDI isomer increases and the amount of the other isomer(s) decreases. Accordingly, the MDI usable according to the instant invention can contain at least about 70 percent by weight of the 4,4′-MDI isomer, preferably at least about 85 percent by weight of the 4,4′-MDI isomer and more preferably at least about 95 percent by weight of the 4,4′-MDI isomer with the balance being other isomers such as the 2,4′-MDI isomer and/or 2,2′-MDI isomer of less than about 30 percent by weight of the isomer(s), preferably less than about 15% by weight of the isomer(s) and more preferably less than about 5 percent by weight of the isomer(s). It is particularly advantageous to employ MDI wherein substantially all of the MDI is the 4,4′-MDI isomer, i.e., in an amount of about 100 percent by weight of the MDI. The amount of MDI employed in the reaction mixture will ordinarily range from about 5 to about 50 weight percent, preferably from about 10 to about 40 weight percent and more preferably from about 15 to about 30 weight percent; by weight of the reaction mixture.
Useful polyether diols include polytetramethylene ether glycol, polyethylene ether glycol, polypropylene ether glycol, polypropylene ether glycol-polyethylene ether glycol copolymers, and the like with the preferred polyether diol being polytetramethylene ether glycol. The amount of polyether diol employed in the reaction mixture will ordinarily range from about 45 to about 95 weight percent, preferably from about 55 to about 90 weight percent and more preferably from about 65 to about 85 weight percent, by weight of the reaction mixture. The polyether diols employed in the reaction mixture herein can be in the form of a polyol mixture in which a polyether diol is the major component the
Carmen Michael E.
Gorr Rachel
Thompson Raymond D.
Uniroyal Chemical Company, Inc.
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