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
1999-10-25
2001-12-11
Wilson, Donald R. (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...
C524S392000, C524S332000, C524S493000, C524S305000, C524S419000, C152S209100
Reexamination Certificate
active
06329455
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rubber composition containing a disodium salt of 3,3′-dithiodipropionic acid and the processing of a sulfur-curable rubber composition containing a disodium salt of 3,3′-dithiodipropionic acid.
BACKGROUND OF THE INVENTION
Processing aids are commonly used in both natural and synthetic rubber compositions. Such processing aids are used during the mixing, permitting incorporation of fillers and other ingredients rapidly with lower power consumption. In instances where the filler is silica, well-known sulfur containing organosilicon compounds are used to further assist in compatibilizing the silica in the rubber composition.
SUMMARY OF THE INVENTION
The present invention relates to the use of a disodium salt of 3,3′-dithiodipropionic acid in a sulfur vulcanizable rubber.
DETAILED DESCRIPTION OF THE INVENTION
There is disclosed a method for processing a rubber composition which comprises mixing
(i) 100 parts by weight of at least one sulfur vulcanizable elastomer selected from conjugated diene homopolymers and copolymers and from copolymers of at least one conjugated diene and aromatic vinyl compound; with
(ii) 0.05 to 10 phr of a disodium salt of 3,3′-dithiodipropionic acid.
There is also disclosed a rubber composition comprising an elastomer containing olefinic unsaturation and a disodium salt of 3,3′-dithiodipropionic acid.
The present invention may be used to process sulfur vulcanizable rubbers or elastomers containing olefinic unsaturation. The phrase “rubber or elastomer containing olefinic unsaturation” is intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers. 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. 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. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile (which polymerize with butadiene to form NBR), methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. Specific examples of synthetic rubbers include polybutadiene (including cis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene), butyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/dicyclopentadiene terpolymers. The preferred rubber or elastomers are polybutadiene and SBR.
In one aspect, the rubber is preferably of at least two of diene-based rubbers. For example, a combination of two or more rubbers is preferred such as cis 1,4-polyisoprene rubber (natural or synthetic, although natural is preferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers.
In one aspect of this invention, an 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 E-SBR can be considered beneficial for a purpose of enhancing traction, or skid resistance, of the tire tread. The presence of the 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 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. In one aspect, the E-SBR may also contain acrylonitrile to form a terpolymer rubber, as E-SBAR, in amounts, for example, of about 2 to about 30 weight percent bound acrylonitrile in the terpolymer.
Emulsion polymerization prepared styrene/butadiene/acrylonitrile terpolymer rubbers containing about 2 to about 40 weight percent bound acrylonitrile in the terpolymer are also contemplated as diene-based rubbers for use in this invention.
The 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 S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.
A purpose of using S-SBR is for improved tire rolling resistance as a result of lower hysteresis when it is used in a tire tread composition.
The 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 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 100° C. per minute.
The cis 1,4-polybutadiene rubber (BR) is considered to be beneficial for a purpose of enhancing the tire tread's wear, or treadwear. Such 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 cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber are well known to those having skill in the rubber art.
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, 10 or elastomer.”
The disodium salt of 3,3′-dithiodipropionic acid used in the present invention may be prepared by adding 3,3′-dithiodipropionic acid to an aqueous solution of sodium hydrogen carbonate. Upon completion of the addition, the solid salt product is dried.
The disodium salt of 3,3′-dithiodipropionic acid used in the present invention may be added to the rubber by any conventional technique such as on a mill or in a Banbury. The amount of disodium salt of 3,3′-dithiodipropionic acid may vary widely depending on the type of rubber and other compounds present in the vulcanizable composition. Generally, the amount of disodium salt of 3,3′-dithiodipropionic acid is used in a range of from about 0.05 to about 10.0 phr with a range of 0.1 to about 5.0 phr being preferred. The disodium salt of 3,3′-dithiodipropionic acid may be added during the nonproductive stage or productive stage of mixing but is preferably added in the nonproductive stage.
For ease in handling, the disodium salt of 3,3′-dithiodipropionic acid may be used per se or may be deposited on suitable carriers. Examples of carriers which may be used in the present in
Sandstrom Paul Harry
Wideman Lawson Gibson
Harlan R.
Hendricks Bruce J.
The Goodyear Tire & Rubber Company
Wilson Donald R.
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