Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-03-15
2003-06-24
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
Reexamination Certificate
active
06581660
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a tire with rubber tread of cap/base construction. The tread base underlies the tread cap. The tread base is relatively thick, namely at least 50 percent of the thickness of the tread cap. It is desired that the tread base rubber composition contains a significant amount of sulfur to enhance physical properties of the tread base. The tread base rubber composition contains a combination of anti-reversion agents to counteract a tendency for reversion of physical properties of the tread base which is relatively thick as compared to the tread cap. The combination of anti-reversion co-agents is 1,3-bis-(citraconimidomethyl)benzene and hexamethylene 1,6-bis(thiosulfate), disodium salt, dihydrate. By thereby substantially maintaining the integrity of physical properties of the tread base, reduced tire operating temperature, as well as retarded or eliminated groove cracking in the tread cap has been observed.
BACKGROUND OF THE INVENTION
Tires, particularly light and medium duty truck tires, are often manufactured with a tread of a cap/base construction in which the tread base has a relatively thick cross-section which may be sometimes be greater than 50 percent of the thickness of the tread cap. Such cap/base construction of tire treads is well known to those having skill in such art as are truck tire treads with treads which contain a relatively thick tread base as compared to the thickness of the tread cap.
Conventionally, a tread cap, of a tread cap/base construction, is designed to be ground-contacting and thus is conventionally configured with lugs and grooves and/or ribs and grooves and is usually comprised of a rubber composition intended to provide suitable traction, rolling resistance and treadwear for the tire.
The associated tread base, which is conventionally co-extruded with and underlies the tread cap is not normally intended to be ground-contacting. The tread base is usually designed to be a buffer between the tread cap and tire carcass and is usually of a rubber composition which has adequate heat durability and physical properties such as modulus and rebound, a hysteretic property.
For some truck tire treads, particularly for tire carcasses of a bias ply construction, the tread base is relatively thick, as compared to the thickness of the tread cap, and is often of a thickness of at least 50 percent of the thickness of the associated tread cap, instead of being a relatively thin tread base of a thickness less than about 30 percent of the thickness of the associated tread cap as may be found, for example, in passenger tires. This is in contrast to radial ply tires, such as example passenger tires and light truck tires, which often have a tread of a cap/base construction where such tread base is often relatively thin, such as being less than 30 percent of the thickness of the associated tread cap.
Relatively thick tread bases present unique problems insofar as reversion of rubber properties due to, for example, endurance of relatively high tire cure temperatures as well as relatively high operational temperatures at vehicular loads and speeds. Such rubber properties of concern are, for example, reduction of 300 percent modulus and reduction in rebound (100° C.) values
For example, upon shaping and curing the tire in a suitable mold at cure temperatures in a range of about 140° C. to 150° C., for example, the relatively thick tread base, because of its relatively large rubber mass, might remain hot for a period of time so that it may sometimes tend to over cure to an extent that a degree of cure reversion, or degradation of the sulfur bond, may occur and rubber properties such as, for example, 300 percent modulus and rebound, may be adversely reduced, insofar as their desirable properties for a tread base, are concerned.
Conventionally, then, relatively low levels of sulfur content may be conventionally used for such relatively thick tread base rubber compositions to minimize cure reversion, usually in a range, for example, of about 0.75 to about 1.5 phr of sulfur curative.
However, if enhanced 300 percent modulus and/or rebound property for the tread base rubber composition is desired, increased sulfur curative for content of the rubber composition is usually used, in a range, for example, of about 2.5 to about 5 phr.
Accordingly, it is desired to minimize a reversion of physical properties such as 300 percent modulus and/or rebound due to exposure of the tread base rubber composition to elevated temperatures whether during cure or under service conditions, particularly where it is desired to use from 2.5 to 5 phr of sulfur curative in the tread base rubber composition to enhance its 300 percent modulus and/or rebound physical properties.
It is therefore appreciated that the phenomenon of reversion of physical properties in the accelerated sulfur vulcanization of cis 1,4-polyisoprene (natural or synthetic) or other diene-based elastomers is undesirable. Reversion occurs when polysulfidic crosslinks deteriorate with time and temperature. Subsequently, this can lead to a reduction in crosslink density and a deterioration of physical properties (lower modulus and higher hysteresis).
In the description of this invention, the term “phr,” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer,” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound,” if used herein, 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 terms “cure” and “vulcanize” may also be used interchangeably unless otherwise noted.
In the description of this invention, portions of tire treads designed to be ground contacting are described as being configured with lugs and grooves. Such tread lugs are intended herein to mean individual tread lugs as well as somewhat continuous lugs in a form of circumferential ribs which are often simply referred to as being ribs or tread ribs.
SUMMARY AND DESCRIPTION OF THE INVENTION
In accordance with this invention, a tire is provided which a rubber tread of a co-extruded cap/base construction wherein said tread base underlies said tread cap, is of a thickness of at least 50 percent of the thickness of said tread cap and is of a sulfur vulcanizable rubber comprised of, based upon parts by weight per 100 parts by weight rubber (phr)
(A) 100 phr by weight of at least one diene-based elastomer of which a major portion, or at least 55 weight percent, of the elastomer(s) is cis 1,4-polyisoprene natural rubber,
(B) about 2.5 to about 5 phr of sulfur,
(C) about 0.5 to about 10 phr of 1,3-bis-(citraconimidomethyl)benzene and hexamethylene 1,6-bis(thiosulfate), disodium salt, dihydrate in a weight ratio of said benzene and said disodium salt materials in a range of from about 0.2/1 to about 0.5/1, and
(D) to about 60 phr of reinforcing filler as
(1) about 5 to about 50 phr of rubber reinforcing carbon black by having an Iodine value in a range of about 38 to about 48 g/kg (ASTM D1510) and dibutyl phthalate DBP) value in a range of about 110 to about 130 cm
3
/100 g (ASTM D2414), and
(2) about 10 to about 20 phr of aggregates of precipitated silica,
wherein said precipitated silica contains hydroxyl groups (e.g. silanol groups) in its surface.
Preferably such tread base rubber composition is exclusive of a coupling agent for said precipitated silica and particularly exclusive of coupling agents such as bis(3-triethoxysilylpropyl) polysulfides, which contain from 2 to 8 with an average of from 2 to 2.6 or from 3.5 to 4, connecting sulfur atoms in their polysulfidic bridge.
The practice of this invention is considered to be particularly applicable where it is desired to provide a relatively thick tread base, of a t
Golden James Joseph
Meza Roberto Cerrato
Maki Steven D.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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