Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
1999-03-23
2001-08-28
Knable, Geoffrey L. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C152S524000
Reexamination Certificate
active
06279633
ABSTRACT:
FIELD
The invention relates to a tire having a sidewall component of an EPDM-based rubber composition prepared with specified precipitated silica reinforcement and an organosilane disulfide material. In one aspect, such rubber composition may be exclusive of carbon black and may thereby be of color other than black.
BACKGROUND
It is often desired to use an EPDM rubber (ethylene/propylene
on-conjugated diene-based rubber) for various tire components, such as a sidewall component, primarily because it typically has superior resistance to ozone degradation. However, EPDM elastomers are of limited usefulness for such purposes, primarily because of their typically low resistance to cut growth propagation.
The problem is compounded where it may be desired to provide a tire component of a non-black colored rubber composition so that, therefore, carbon black is not suitable for the rubber reinforcement.
Accordingly, it is desired to prepare a tire component which has the desirable age resistant properties of EPDM yet with acceptable cut growth resistance, particularly for EPDM-based rubber compositions which do not contain carbon black reinforcement.
In practice, it is recognized that precipitated silica typically has only a limited ability for reinforcing elastomers, as compared to carbon black, without a presence of a silica coupling agent such as, for example, an organosilane polysulfide which contains at least about 3.5 sulfur atoms in its polysulfidic bridge
While, in practice, it is recognized that precipitated silica, in combination with an organosilane disulfide, has been used for reinforcement of diene-based elastomers for use as tire components, it is usually accompanied by adding free sulfur, or at least additional free sulfur, at some place in the rubber composition formulation. It is believed that this is well known to those having skill in such art.
It is to be appreciated that an organosilane disulfide, with its relatively strong sulfur-to-sulfur bonds, is not a good sulfur donor for rubber processing purposes, particularly as compared to an organosilane polysulfide which has at least 3.5 sulfur atoms in its polysulfidic bridge.
Accordingly, by itself, an organosilane disulfide would not ordinarily be considered a silica coupling agent for coupling a precipitated silica to a diene-based elastomer.
Further, a utility of an organosilane disulfide would considered to be very limited, if at all, in an EPDM rubber composition because of (1) its relative ineffectiveness as a sulfur source for coupling to carbon-to-carbon double bonds of an elastomer and, further (2) the relatively small amount of carbon-to-carbon double bonds available in an EPDM elastomer.
In practice, it is sometimes desired to color a portion of a sidewall to add some color other than black, albeit primarily for cosmetic reasons.
An inherent difficulty in providing such colored components for a tire is providing a non-carbon reinforced rubber composition with suitable properties for a tread sidewall.
In the description of this invention, the term “phr” is used to specify amounts of materials or ingredients in a rubber, or elastomer, composition in terms of parts by weight of such ingredient per 100 parts by weight of elastomer(s).
Also, in the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably as well as rubber composition and rubber compound unless otherwise indicated.
STATEMENT AND PRACTICE OF THE INVENTION
In accordance with this invention, a tire is provided having a sidewall component of a rubber composition which is comprised of, based on 100 parts (phr) by weight elastomer, (A) about 30 to about 50 phr of EPDM, about 20 to about 40 phr of natural cis 1,4-polyisoprene rubber and about 20 to about 40 phr of cis 1,4-polybutadiene (B) about 30 to about 50 phr of reinforcing filler selected from precipitated silica and carbon black which contains from about 80 to about 98, alternately about 100 percent of said silica; wherein said precipitated silica has a BET surface area in a range of about 110 to about 130 m
2
/g and (C) a liquid organosilane disulfide having from 2 to 4, with an average of from 2 to 2.6, sulfur atoms in its polysulfidic bridge.
Accordingly, in one aspect of the invention, the reinforcing filler for the sidewall component is precipitated silica in absence of, or exclusive of, carbon black.
In further accordance with this invention, a tire is provided with at least one component of a non-black colored rubber composition which contains a non-black colorant pigment; wherein said reinforcing filler for said rubber composition is precipitated silica exclusive of carbon black.
In additional accordance with this invention, a tire is provided with a sidewall having at least a portion of said sidewall comprised of said rubber composition which preferably contains reinforcing filler as a precipitated silica exclusive of carbon black. In practice, such tire's sidewall component portion contains an inorganic coloring pigment of a color other than black.
A significant aspect of this invention, for said tire component and particularly for said sidewall component, is considered herein to be an innovative combination of (1) an EPDM-based rubber composition (2) a specified precipitated silica and (3) a liquid organosilane disulfide material, and alternatively (4) such component containing filler reinforcement exclusive of carbon black.
It is considered herein that a precipitated silica for use in this invention is limited to a BET surface area in a range of about 110 to about 130 m
2
/g.
It is considered herein that a liquid organosilane disulfide material with an average of from 2 to about 2.6 sulfur atoms in its polysulfidic bridge is to be used in the rubber composition for this invention because it tends to cause less modulus increase and, also creates less processing viscosity increase during mixing of the rubber composition than an organosilane polysulfide with an average of at least 3.5 sulfur atoms in its polysulfidic bridge
Examples of such organosilane disulfide materials are, for example, bis-(3-alkoxy-silyl-alkyl) polysulfide having an average of from 2 to 2.6 sulfur atoms in its polysulfidic bridge.
Representative of such disulfides are, for example, bis-(3-ethoxysilylpropyl) disulfide and bis-(3-methoxysilylpropyl) disulfide.
Various colorant pigments can be used in the practice of this invention. In one aspect, such pigments should be chemically inert insofar as typical ingredients for the rubber composition are concerned. Typically, such ingredients are inorganic materials. Representative of such pigments are, for example, titanium dioxide as a typical white colorant, as well as other colorants as, for example, diarylide yellow pigment as a yellow colorant.
The EPDM terpolymers are polymerized from ethylene, propylene, and a small percentage of a non-conjugated diene which provides unsaturation in side chains pendent from the saturated “backbone”. EPDM can be vulcanized with peroxides, but the small amount of unsaturation also permits conventional sulfur vulcanization. EPDM's with larger amounts of carbon-to-carbon unsaturation provide generally faster curing terpolymer elastomers, and they can be blended with other rubbers to impart resistance to weathering and other degradation
Typical non-conjugated dienes are, for example, dicyclopentadiene, 1,4-hexadiene and ethylidene norbornene.
The non-conjugated diene contents of EPDM's vary with the individual grades of the terpolymer. It is usually in the range of about 2 to about 5 weight percent and faster curing EPDM's may have a slightly higher content of the non-conjugated diene.
The composition of commercial EPDM elastomers typically contain about 60 to 85, usually about 65 to 75, mole percent units derived from ethylene. Higher molecular weight grades are sometimes preferred.
EPDM terpolymer elastomers′ and their preparation are well known to those having skill in such art and they are usually simply referred to as “EPDM's”.
As hereinbefore presented, the side
Knable Geoffrey L.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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