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
1997-09-04
2001-05-29
Mulcahy, Peter D. (Department: 1713)
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
06239203
ABSTRACT:
BACKGROUND OF THE INVENTION
The abrasion resistance of a rubber compound may be an extremely important property depending on its application. This is especially the case where the application is in a tire tread. The greater the abrasion resistance, the greater the treadlife of the tire.
A common method to improve the abrasion resistance is to use increasing levels of low particle-size carbon blacks. Unfortunately, with increasing levels of carbon black, there is a concomitant reduction in rebound properties. Since the rolling resistance of a tire is correlated to rebound properties, one does not want to sacrifice one beneficial property (rolling resistance) for another (treadwear). Therefore, there exists a need for increasing the abrasion resistance of a rubber compound without a significant reduction in rebound properties.
SUMMARY OF THE INVENTION
The present invention relates to a method for improving the abrasion resistance of a cured rubber composition that is particularly suited for a tire tread compound comprising (a) dispersing from 1.0 phr to 30 phr of a C
12
-C
36
alcohol and from 0.5 to 2.0 phr of sulfur throughout a dry isolated sulfur-vulcanizable rubber and (b) curing the rubber.
DETAILED DESCRIPTION OF THE INVENTION
There is disclosed a method of improving the abrasion resistance of a cured rubber composition that is particularly suited for a tire tread compound comprising
(a) adding from 1.0 to 30 phr of a C
12
-C
36
alcohol and from 0.5 to 2.0 phr of a sulfur vulcanizing agent to 100 parts by weight of at least one dry isolated sulfur-vulcanizable rubber selected from the group consisting of natural rubber, conjugated diene homopolymers and copolymers and from copolymers of at least one conjugated diene and aromatic vinyl compound;
(b) dispersing the C
12
-C
36
alcohol and sulfur throughout the rubber; and
(c) curing the rubber.
The present invention may be used to improve the physical properties of dry, isolated sulfur-vulcanizable synthetic rubbers or elastomers containing olefinic unsaturation. The terms “dry and isolated” are intended to only include those elastomers which have been recovered from a natural latex and an emulsion or solution after polymerization, isolated and dried. Therefore, dry and isolated specifically excludes rubbers in cement or latex. In the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The term “treated rubber” means a dry and isolated synthetic rubber which has had a C
12
-C
36
alcohol added to it and thereafter the C
12
-C
36
alcohol is dispersed throughout the rubber. Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers.
Specific examples of rubbers for use in the tread rubber composition are natural rubber, synthetic cis 1,4-polyisoprene, 3,4-polyisoprene rubber, styrene/butadiene copolymer rubbers, isoprene/butadiene copolymer rubbers, styrene/isoprene copolymer rubbers, styrene/isoprene/butadiene terpolymer rubbers, cis 1,4-polybutadiene rubber, trans 1,4-polybutadiene rubber (70-95 percent trans), low vinyl polybutadiene rubber (10-30 percent vinyl), medium vinyl polybutadiene rubber (30-50 percent vinyl), high vinyl polybutadiene rubber (50-90 percent vinyl) and mixtures thereof.
In one aspect, the treated rubber is combined with untreated diene-based rubbers. In another aspect, two or more treated rubbers may be combined. For example, a combination of two or more treated rubbers that is preferred includes treated cis 1,4-polyisoprene rubber, treated 3,4-polyisoprene rubber, treated styrene/isoprene/butadiene rubber, treated emulsion and solution polymerization derived styrene/butadiene rubbers, treated cis 1,4-polybutadiene rubbers and treated emulsion polymerization prepared butadiene/acrylonitrile copolymers.
In one aspect of this invention, a treated emulsion polymerization derived styrene/butadiene (E-SBR) might be used having a relatively conventional styrene content of about 20 to about 28 percent bound styrene or, for some applications, an E-SBR having a medium to relatively high bound styrene content; namely, a bound styrene content of about 30 to about 45 percent.
The relatively high styrene content of about 30 to about 45 for the treated E-SBR can be considered beneficial for a purpose of enhancing traction, or skid resistance, of the tire tread. The presence of the treated E-SBR itself is considered beneficial for a purpose of enhancing processability of the uncured elastomer composition mixture, especially in comparison to a utilization of a treated solution polymerization prepared SBR (S-SBR).
By emulsion polymerization prepared E-SBR, it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art. The bound styrene content can vary, for example, from about 5 to about 50 percent.
The treated solution polymerization prepared SBR (S-SBR) typically has a bound styrene content in a range of about 5 to about 50, preferably about 9 to about 36, percent. The treated S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.
A purpose of using treated S-SBR is for improved tire rolling resistance as a result of lower hysteresis when it is used in a tire tread composition.
The treated 3,4-polyisoprene rubber (3,4-PI) is considered beneficial for a purpose of enhancing the tire's traction when it is used in a tire tread composition. The untreated 3,4-PI and use thereof is more fully described in U.S. Pat. No. 5,087,668 which is incorporated herein by reference. The Tg refers to the glass transition temperature which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10° C. per minute.
The treated cis 1,4-polybutadiene rubber (BR) is considered to be beneficial for a purpose of enhancing the tire tread's wear, or treadwear. The untreated BR can be prepared, for example, by organic solution polymerization of 1, 3-butadiene. The BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.
The term “phr” as used herein, and according to conventional practice, refers to “parts by weight of a respective material per 100 parts by weight of rubber, or elastomer.”
The alcohols for use in the present invention are primary, straight chain, saturated monoalcohols having from 12 to 36 carbon atoms. Representative examples of such alcohols include 1-dodecanol (lauryl alcohol), 1-tetradecanol (myristyl alcohol), 1-hexadecanol (cetyl alcohol), 1-octadecanol (stearyl alcohol), 1-eicosanol (arachidyl alcohol), 1-docosanol (behenyl alcohol), 1-tetracosanol, 1-hexacosanol, 1-octaconsanol, 1-triacontanol (melissyl alcohol), 1-dotriacontanol, 1-tetratriacontanol and mixtures thereof. The preferred alcohol is 1-octadecanol.
The present invention relates to the use of the above alcohols to improve the abrasion resistance of a tire tread rubber. The C
12
-C
36
alcohol that is used in the present invention may be added to the isolated dry rubber by any conventional technique such as on a mill, extruder or in a Banbury. The amount of C
12
-C
36
alcohol may vary widely depending on the type of rubber and other compounds present in the vulcanizable composition. Generally, the amount of C
12
-C
36
alcohol is used in a range of from about 1.0 to about 30.0 phr with a range of 2 to about 15 phr being preferred. The C
12
-C
36
alcohol may be added during the nonproductive stage or productive stage of mixing
Marsh Harold Allen
Sandstrom Paul Harry
Hendricks Bruce J
Mulcahy Peter D.
The Goodyear Tire & Rubber Company
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