Quinone diimine as a rubber additive

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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Reexamination Certificate

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06184276

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for improving the processing qualities of vulcanized rubber by high temperature mixing of quinone diimines in the presence of natural rubber or its synthetic derivatives and carbon black.
BACKGROUND OF THE INVENTION
Quinone diimines show multiple functional activities useful to the rubber industry. A commonly used quinone-diimine, N-1,3-Dimethylbutyl-N′-phenyl-p-quinone diimine, is derived from the corresponding N-1,3-dimethylbutyl-N′-p-phenylene diamine via an oxidation reaction as follows:
Activities of quinone diimines which have been demonstrated as useful to the rubber and polymer industry include:
1.) Bound antioxidant,
2.) Diffusable antiozonant,
3.) PVI—process safety—delays scorch in new and reprocessed rubber,
4.) Antioxidant for polymers and hydrocarbon liquids,
5.) Polymerization Inhibitor for vinyl monomers.
Quinone diimines have been studied for use in various rubber technologies. In early studies, it was shown that after vulcanization of natural rubber or general-purpose elastomers in the presence of quinone diimines, a portion of the antidegradant is no longer extractable from the rubber. In addition, the remainder of the quinone diimine antidegradant is reduced to the commonly used p-phenylene diamine antiozonant. Corresponding experiments conducted with p-phenylene diamine antidegradants return nearly all of the antidegradant in its original form.
That the antioxidant is polymer bound has been demonstrated independently in experiments at the NRPA and at Voronezh Subsidiary of the All-Union Scientific Research Institute of Synthetic Rubber. (Raevsky et al.,
Kauch. Rezina
, 29(3), pp. 9-10 (1970)). Raevsky et al. showed by ESR experiments that at least a portion the antidegradant becomes polymer bound and forms somewhat stable radicals. Synthetic poly(isoprene) was oxidized in the presence of quinone diimines. ESR signals were observed which correspond to those expected for the quinone diimine antidegradant. Even after re-precipitation in alcohol three times from solution in benzene, a reduced but persistent ESR signal was still observed. Since the polymer was re-precipitated, the authors concluded that the radicals must be chemically bonded to the polymer.
Perhaps Cain et al. (
Rubber Industry
, p. 216-226, 1975) gave better proof of the polymer bound nature of the antidegradant by demonstrating antioxidant activity that persisted even after solvent extraction. Cain tested vulcanizates protected with quinone imines or quinone diimines before and after hot methanol-acetone-chloroform azeotropic extraction. These vulcanizates showed antioxidant activity 2-30 times that of a control compound (unprotected azeotrope extracted vulcanizate).
Cain et al. compared the vulcanizate extraction experiments to monoalkene model studies. The results indicate that the additional products formed would indeed be bound to the polymer. Rubber parts are generally exposed to environmental factors such as heat, water, oils, and detergents causing losses of antidegradant through volatilization, and extraction or leaching mechanisms. Polymer-bound antidegradant will not be susceptible to these loss mechanisms. This persistent antioxidant activity demonstrated above should readily translate into long lasting antioxidant performance in rubber articles.
In order to observe the same level of antiozonant protection, the quinone diimine antidegradants require a higher loading than that of p-phenylene diamine antidegradants. This is to be expected when a portion of the antidegradant becomes bound to the polymer and is no longer diffusionally mobile. Ozone degradation occurs at the surface of the rubber. The antiozonant must be capable of migrating to the surface of the rubber in order to provide chemical or barrier protection.
Thus, prior to the present invention, quinone diimines were known as possessing antioxidant as well as antiozonant activity in the rubber polymer industry.
SUMMARY OF THE INVENTION
The present invention relates to the use of quinone diimines as an additive in the processing of rubber to provide the rubber with enhanced handling and processability properties.
In accordance with the practice of the present invention, it has been found that the high temperature mixing of carbon black and natural rubber or synthetic derivatives in the presence of quinone diimines provides for a variety of processing advantages without negative effects on the dynamic properties of the vulcanizate.
A first advantage according to the present invention relates to the ability of the quinone diimine to reduce the Mooney viscosity of the vulcanized rubber.
Another advantage realized when practicing the present invention relates to the production of vulcanized rubber which has a faster relaxation rate.
An additional advantage realized when practicing the present invention involves a higher uncured tangent delta as well as a lower cured tangent delta for vulcanized rubber produced according to the process of the invention compared to vulcanized rubber produced by conventional processes. A further advantage obtained when practicing the present invention concerns production of vulcanized rubber having lower Payne effect compared to vulcanized rubber produced by a conventional process.
These and other advantages will be readily recognized to those skilled in the art upon a reading and understanding of the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a process for improving the processing qualities of vulcanized rubber by early addition of quinone diimines into the initial rubber/carbon black mix at a high temperature.
In accordance with the practice of the present invention, a quinone diimine antidegradant is added to a conventional mixer along with an elastomeric material and mixing is initiated. Carbon black may be added along with the quinone diimine or may be added after initial mixing of the quinone diimine. The quinone diimine, elastomer and carbon black are then mixed at a higher than normal mixing temperature(at or above about 140° C) along with other conventional compounding adjuvants.
The above composition is then dumped after appropriate mixing with curatives and accelerators and subsequently vulcanized via conventional techniques such as by heating with a sulfur vulcanizing agent and a thiazole vulcanization accelerator.
The vulcanized rubber composition prepared in accordance with the process set forth above possesses enhanced handling and processing qualities compared to vulcanized rubber compositions prepared by conventional processes which incorporate antidegradants, such as p-phenylene diamines, after the initial mixing of carbon black with the elastomer.
In accordance with a more detailed description of the process according to the invention, the process comprises the steps of:
a) adding one or more elastomeric materials to a mixer;
b) adding at least one quinone diimine antidegradant to the elastomeric material (s);
c) mixing the combination of steps (a) and (b) for a period of about zero to about two minutes at an initial temperature of from about 60° C. to about 100° C.;
d) adding carbon black, zinc oxide and stearic acid to the mixture of step (c) and continue mixing for about two to eight minutes or until the temperature reaches about 140° C. to about 180° C.;
e) discharging the mixture of step (d) from the mixer;
f) adding curatives, accelerators, processing aids, modifiers, tackifiers and conventional rubber processing aids;
wherein the composition of step (f) is subsequently vulcanized thereby producing a vulcanized rubber composition having enhanced handling and processing properties.
In accordance with the process according to the present invention, quinone diimines having antidegradant properties are mixed with the elastomeric material prior to or in conjunction with the carbon black addition. Quinone diimines which may be used in accordance with the practice of the present invention include, but are not limite

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