Use of carbon black in curable rubber compounds

Details Use of carbon black in curable rubber compounds Use of carbon black in curable rubber compounds

2000-09-28

2002-11-05

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S332100, C525S333100, C525S333200, C524S495000, C524S492000

Reexamination Certificate

active

06476154

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the use of non-conventional forms of carbon black in curable rubber compounds. The non-conventional carbon black generally includes particles in the shape open conical structures to enhance properties of rubber compounds, particularly for use in tires.
BACKGROUND OF THE INVENTION
Pneumatic rubber tires are conventionally prepared with at least one component, such as, for example, a rubber tread, which is often a blend of various rubbers and reinforced with conventional, granular carbon black. For example, a non-limiting list of such rubbers would include at least one, and more often two or more, of styrene/butadiene copolymer(s) (SBR), cis-1,4-polyisoprene including natural rubber, cis-1,4-polybutadiene and styrene/isoprene/butadiene terpolymer(s) as well as other elastomers. Further, such tires may, for example, have a tread composed of natural rubber, a tread composed of a blend of SBR and cis-1,4-polybutadiene rubbers, a tread composed of natural rubber and SBR as well as treads composed of tri-blends such as SBR (40 to 60 phr) with 20 to 45 percent styrene, cis-1,4-polyisoprene (20 to 30 phr) and cis-1,4-polybutadiene (20 to 30 phr). For example, see
The Vanderbilt Rubber Handbook
, 13
th
Edition (1990), Pages 603 and 604.
The characteristics of carbon black are a significant factor in determining various properties of a rubber composition with which the carbon black is compounded. Conventionally, for rubber reinforcement, tire tread rubber compositions use high surface area, elastomeric reinforcing granular carbon blacks for a purpose of providing tread rubber compositions with good traction and abrasion resistance. On the other hand, in order to enhance the fuel efficiency of a motorized vehicle, a decrease in the rolling resistance of the tire tread portion is desirable. There are some indications that this has been achieved, for example, by increasing the resilience of the rubber by using carbon blacks having a large particle diameter and a small surface area or granular carbon blacks having a wide range of aggregate size distribution per given particle diameter.
It is believed to be conventional wisdom that a tire tread composition designed to improve tread traction on the road usually results in a tire's increased tire rolling resistance. Similarly, modifying a tire tread composition to improve (reduce) a tire's rolling resistance usually results in a reduction in the tire tread traction and/or treadwear resistance. It is usually difficult to impart both high abrasion resistance and high resilience to the rubber at the same time, because the requirements have been thought to be somewhat contradictory with each other from the perspective of the properties of the granular carbon black in the rubber. These aspects involving a trade-off of tire, or tire tread, properties (traction, rolling resistance and treadwear) are well known to those having skill in such art. Thus, selection of various reinforcing carbon blacks tend to play a role in the ultimate properties of the rubber composition.
For some tire tread applications, silica is used for at least a portion of the rubber reinforcement, often in conjunction with the granular carbon black, and usually accompanied by a silica coupler.
The term “phr” as used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber elastomer”. In the description of this invention, the terms “rubber” and “elastomer” can be used interchangeably, unless otherwise distinguished. The terms “rubber composition”, “compounded rubber” and “rubber compound” can be 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 terms “granular carbon black” are used herein to refer to conventional carbon blacks, the use of which in rubber compositions is well known in the art. Generally, granular carbon black may be characterized as a multiplicity of elementary graphitic particles fused together to form grape-like aggregates familiar to those skilled in the art. Further description of conventional carbon black morphology can be found on Pages 398 through 410 of
The Vanderbilt Rubber Handbook
, 13
th
Edition.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with the present invention, a rubber compound is provided with an amount of conical carbon black for reinforcement, the conical carbon black comprising open conical carbon structures and flat plates.
The invention also relates to a tire having at least one portion composed of a rubber composition which contains, as reinforcement, a conical carbon black comprising open conical carbon structures which is useful as a reinforcement in rubber compounds in place of at least a portion thereof or in addition to, the normally used forms of granular carbon black reinforcement.
Such non-conventional, conical carbon black may be used as discrete particles and/or aggregates and agglomerates of such particles.
The term carbon black is herein used, unless otherwise indicated, in a broad sense to include any particulate graphitic material, including granular carbon blacks conventionally used as reinforcements in tires and rubber as well as other, nonconventional forms of particulate graphite. By carbon black comprising open conical structures, it is meant to be any carbon black comprising open conical carbon structures and flat plates, but may also comprise minor amounts of fullerenes, carbon nanotubes, and other graphitic structures. The terms “conical carbon”, “conical carbon black”, “open conical structures”, “cones and plates”, “cones and flat plates”, and “microcones” are herein used interchangeably to refer to the unconventional carbon black used in the rubber composition of the present invention.
According to this invention, a tire is provided having a tread of a rubber composition comprised of, based on 100 parts by weight rubber
(A) 100 parts by weight (phr) of at least one diene-based elastomer and
(B) about 10 to about 150, alternatively about 20 to about 100, phr of particulate elastomer reinforcement composed of about five to about 100, alternately about 10 to about 60, weight percent of at least one conical carbon black and from zero to about 95, alternately about 60 to about 10, weight percent of at least one of granular carbon black and, optionally, precipitated silica; wherein said conical carbon black has conical and flat plate shaped particles characterized by a topological disclination TD given by the general formula
TD=N
×60 degrees, where
N
=0, 1, 2, 3, 4, or 5
The structure of such conical particles and flat plates can be grossly described as stacks of graphitic sheets with flat (N=0) or conical structures (N=1 to 5), and holding cone angles of 180, 112.9, 83.6, 60.0, 38.9, and 19.2 degrees for each of N=0 to 5, respectively. The characteristic size, or longest dimension, of the particles is typically less that 5 micrometers and the thickness, measured as the wall thickness of the hollow cones or the thickness of the flat plate, is typically less than 100 nanometers. Cones of N=1 to 5, nanotubes, and fullerenes may make up about 20 percent of the conical carbon black, with the remaining about 80 percent being mainly flat plates of N=0. Alternatively, flat plates of N=0, TD=0 and a projected angle of 180° may be present as a major fraction of the conical carbon black, that is, in excess of 50 percent by weight. Cones of N=1, 2, 3, 4, or 5, fullerenes, or nanotubes may be present as a minor fraction of the conical carbon black, that is, less than 50 percent by weight.
Alternatively, the elastomer reinforcement may also be composed of (i) about 5 to about 90, alternatively about 10 to about 50, weight percent of said conical carbon black, and correspondingly (ii) about 95 to about 10, alternatively about 90 to about 50, weight pe

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