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
2002-05-08
2004-09-28
Cain, Edward J. (Department: 1714)
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...
C521S043000, C521S043500, C523S215000, C524S295000, C524S302000, C524S526000, C525S332600
Reexamination Certificate
active
06797757
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to articles of manufacture, such as for example, tires and industrial products, which have at least one component comprised of a rubber composition which contains particles of pre-sulfur vulcanized rubber (e.g. ground recycled rubber) and impure tetrathiodipropionic acid, namely a blend comprised primarily of tetrathiodipropionic acid and trithiodipropionic acids of a weight ratio thereof in a range of about 80/20 to about 30/70. Said blend is referred to herein as an S4/S3 blend. The S4/S3 blend may be introduced directly to a rubber composition or may be provided as particles of a composite of said S4/S3 blend and a particulate support therefor for a purpose of aiding the dispersion of the S4 and S3 within the elastomer host. Representative of such support, or carrier, may be, for example, silica, particularly amorphous precipitated silica, carbon black, clay, starch, calcium carbonate, calcium silicate, titanium dioxide and the like, wherein carbon black is preferred. It is considered herein that an advantageous nature of the invention is to provide such an S4/S3 blend, for example, in a manner to somewhat depress the melting point of the trithiodipropionic acid and therefore promote its processability and incorporation with particles of pre-vulcanized rubber without substantially degrading any beneficial effect thereof. Thus, the invention is intended to be exclusive of use of 100 percent pure tetrathiodipropionic acid and exclusive of relatively high purity trithiodipropionic acid which contains at least 80 percent trithiodipropionic acid.
BACKGROUND OF THE INVENTION
Tetrathiodipropionic acid has been suggested for use in treating sulfur pre-vulcanized scrap rubber which has been ground to a fine particle size for a purpose of recycling such rubber in its vulcanized form by blending such particles with unvulcanized elastomers to form a rubber composition which may be fabricated into various articles of manufacture. For example, see U.S. Pat. No. 5,883,139.
Generally, such particulate recycled sulfur pre-vulcanized rubber is a complex mixture of largely unknown diene-based elastomers and various rubber compounding ingredients, and may contain a small quantity of textile fiber, and the like.
It has been observed that, after adding sulfur and accelerator to recycled sulfur pre-vulcanized rubber, followed by its revulcanization, the resulting physical properties, such as tensile and elongation, are usually lower than the corresponding properties of the original vulcanized rubber from which it was derived.
A process, for example, of improving properties of ground recycled sulfur vulcanized rubber is disclosed in said U.S. Pat. No. 5,883,139 which teaches the use of tetrathiodipropionic acid (referred to herein as S4) to improve properties of rubber compositions which contain particles of ground recycle, sulfur cured diene-based rubber while the use of dithiodipropionic acid (S2) is not considered herein to improve the properties of rubber compositions which contain particles of ground recycle, sulfur cured diene-based rubber in a manner similar to the use of the S4 and is therefore more as a diluent for the rubber composition.
In the description of this invention, the term “phr” relates to parts by weight in a rubber composition of an ingredient therein per 100 parts of elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “rubber composition” and “compound” may be use interchangeably unless otherwise indicated. The terms “vulcanize” and “cure” may also be used interchangeably unless otherwise indicated.
SUMMARY OF THE INVENTION
The present invention relates to a process for improving the properties of ground recycled sulfur-vulcanized rubber and particularly improving sulfur curable diene-based rubber compositions which contain particulate pre-sulfur vulcanized diene-based rubber.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention, a process of preparing sulfur vulcanizable rubber composition which comprises:
(A) preparing a pre-blend by homogeneously blending
(1) particles of a sulfur vulcanized, diene-based rubber composition, together with
(2) a blend of tetrathiodipropionic acid and trithiodipropionic acid in a weight ratio thereof in a range of from about 80/20 to about 30/70, alternately in a range of from about 80/20 to about 35/65, and particles of carbon black; or
(3) particles of a composite comprised of tetrathiodipropionic acid and trithiodipropionic acid in a weight ratio thereof in a range of from about 80/20 to about 30/70, alternately in a range of from about 80/20 to about 35/65, having a weight ratio of said polythiodipropionic acids and a particulate support selected from at least one of carbon black, precipitated silica, starch, clay, calcium carbonate, calcium silicate and titanium dioxide, preferably carbon black, in a range of from about 1/10 to about 10/1;
wherein said polythiodipropionic acids have the general Formula (I):
HO
2
CCH
2
CH
2
—S
n
—CH
2
CH
2
CO
2
H (I)
wherein n is a value of from 4 for said tetrathiodipropionic acid and a value of 3 for said trithiodipropionic acid,
wherein about 0.18 to about 10, alternately from 1 to about 5, parts by weight of said polythiodipropionic acids are provided per 100 parts by weight of diene-based rubber contained in said sulfur vulcanizable rubber composition, and wherein said particles of sulfur vulcanized rubber composition is of a particle size of less than 420 microns;
(B) mixing about one to about 40, alternately about 15 to about 20, parts by weight of said pre-blend with 100 parts by weight of at least one unvulcanized hydrocarbon diene-based, sulfur vulcanizable rubber to form a rubber composition comprised of said unvulcanized rubber and said pre-blend.
Accordingly, in practice, said blend of tetrathiodipropionic acid and trithiodipropionic acid may be added directly to the particulate pre-vulcanized rubber or as said carbon black composite.
In further accordance with this invention, a rubber composition is provided which is comprised of said pre-blend and said unvulcanized rubber.
In additional accordance with this invention, sulfur (referred to herein as free sulfur) is blended with said rubber composition in an amount in a range of about 1 to about 5 parts by weight thereof per 100 parts by weight of said unvulcanized diene-based rubber (usually together with conventional sulfur cure accelerators and other conventional rubber compounding ingredients in conventional amounts) to form a free sulfur-containing rubber composition.
In further accordance with this invention, said free sulfur-containing rubber composition is sulfur vulcanized in a suitable mold under conditions of elevated temperature (e.g. in a range of about 140° C. to about 180° C.) and pressure to form a sulfur vulcanized article of manufacture.
In further accordance with this invention a sulfur vulcanized, pre-vulcanized rubber-containing, rubber composition is provided.
In additional accordance with this invention, an article of manufacture is provided which contains at least one component of a said sulfur vulcanized, pre-vulcanized rubber-containing, rubber composition.
In further accordance with this invention, a tire is provided which contains at least one component of a rubber composition comprised of said sulfur vulcanized, pre-vulcanized rubber-containing, rubber composition.
In additional accordance with this invention, a tire is provided having a tread of a rubber composition which is comprised of said sulfur vulcanized, pre-vulcanized rubber-containing, rubber composition.
It is considered herein to be significant that a trithiodipropionic acid (S3) is substantially diluted with a tetrathiodipropionic (S4) acid in a manner that a melting of one of the polythiodipropionic acids is lowered somewhat to thereby promote a processing of the blend with the particulate pre-vulcanized rubber at the associated elevated rubber mixing temperature be using similar polythiodipropionic acids but witho
Balogh George Frank
Wideman Lawson Gibson
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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