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
2000-03-29
2003-02-25
Wu, David W. (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...
C524S442000, C524S495000, C524S426000, C524S427000, C524S274000, C152S209100
Reexamination Certificate
active
06525133
ABSTRACT:
FIELD
This invention relates to a pneumatic tire with a rubber tread which utilizes an alpha-methyl styrene oligomer.
BACKGROUND OF THE INVENTION
Pneumatic rubber tires are sometimes intended to be used for purposes where traction (skid resistance) is a primary consideration. For example, it may be desired for a high performance tire tread rubber to have good initial grip, or traction, while also having good durability and, also, good overall traction or grip. Often for such tires, resistance to tread wear is less of a consideration.
Historically, for emphasizing tread rubber traction, the tread may, for example, be compounded to have a relatively high ratio of resin and processing oils to rubber (e.g. a range of about 15 to about 40 weight percent in the rubber composition) which may be more conventionally expressed in terms of parts by weight per 100 parts by weight rubber (phr) as being, for example, in a range of about 45 to about 120 phr.
The purpose of the resin, among other purposes, is to enhance traction of the tread due, at least in part, to a choice of resin with an appropriate softening point.
For example, a resin with a softening point of about 30° C. would be expected to soften and become very hysteretic at a tread temperature of about 20° C. to about 50° C. and, thus, aid in providing tire traction at such tread temperatures.
A considerably higher softening point resin would be desirable to enhance tread traction at a higher tread temperature (e.g. at least 100° C.) associated with the higher vehicular speed.
However, the resin may become too incompatible with the rubber and lose the tire traction properties.
Therefore, it is desirable to use a resin that is at least semi-compatible with the rubber.
Various examples of such resins which, as it is understood, are or may be used to aid in tire tread traction are hydrocarbon-derived synthetic resins, coumarone-indene resins, rosin, rosin derivatives and dicyclopentadiene based resins such as, for example, dicyclopentadiene/diene resins.
Such resins may typically have softening points (Ring and Ball) within the aforesaid range of about 20° C. to about 110° C. and even up to about 170° C.
In another aspect of tire tread rubber considerations, it should be pointed out that viscoelastic properties of a rubber, or a rubber blend, for tire tread applications, are important. For example, a tangent delta viscoelastic property is the ratio of the viscous contribution to the elastic contribution for a viscoelastic rubber article subjected to a cyclic deformation. The term “tangent delta” is often referred to herein as “tan. delta”. Its characterization of viscoelastic properties of rubber is well known to those skilled in such art. Such property is typically represented in the form of a curve as a temperature sweep plot of tangent delta values on a y, or vertical, axis versus temperature on an x, or horizontal, axis.
Although various rubber compositions are taught to provide various benefits, some for tire treads, it is desired to provide a pneumatic tire having a rubber tread having enhanced traction qualities over a relatively wide temperature range and, thus, a tan. delta characteristic which maintains a high tan. delta as the temperature increases.
In the description of this invention, rubber compound, sulfur-cured rubber compound, rubber composition, rubber blend and compounded rubber are used somewhat interchangeable to refer to rubber which has been mixed with rubber compounding ingredients. Such terms are well known to those having skill in such art.
In the description of this invention, the term “phr” is an abbreviation for “parts (of an indicated material) by weight per 100 parts by weight rubber”.
DISCLOSURE AND PRACTICE OF INVENTION
In accordance with this invention, a pneumatic tire is provided having an outer circumferential tread where said tread is comprised of, based upon 100 parts by weight rubber (phr),
(A) 100 parts by weight of at least one diene hydrocarbon based elastomer;
(B) from about 1 to about 40, alternately about 3 to about 10, phr of a liquid alpha-methyl styrene oligomer;
(C) about 20 to about 150, alternately about 60 to about 100 phr of reinforcing filler selected from at least one of carbon black, precipitated silica and silica modified carbon black; and
(D) a coupling agent for said silica and/or silica modified carbon black, as the case may be, having a moiety reactive with said silica, (usually hydroxyl groups on the surface of the silica such as silanol groups) and carbon black and another moiety interactive with at least one of said diene-based elastomers.
It is to be appreciated that said tread rubber composition may also contain
(E) about one to about 50 phr of at least one resin having a softening point within a range of about 65° C. to about 165° C. (Ring and Ball softening point) selected from at least one of:
(i) coumarone-indene resin(s);
(ii) alkylated hydrocarbon resin(s);
(iii) aromatic petroleum hydrocarbon resin(s); and
(iv) dicyclopentadiene/diene resin(s).
A significant aspect of this invention is that the liquid resin greatly reduces the dynamic low-strain stiffness (G′ at one percent strain), and gives a comparable high strain loss compliance (J″ at fifty percent strain) to the control resin.
This is considered herein to be important because it tends to give tire traction at lower temperatures (G′ at one percent strain) before tread heat-up can occur in the tread and, subsequent, improved cornering traction (J″ at 50 percent strain) at higher tread temperatures.
The alpha-methyl styrene oligomer for use in this invention may be characterized as coupled alpha-methyl styrene moieties that tend to form in a head-to-tail fashion and may have a residual olefinic character.
The oligomer is composed primarily of dimers as may be represented by the following Formula (I)
wherein n is a value from zero to 100, alternatively an average of from 2 to 10.
Such oligomers may be prepared, for example, by free radical, cationic or anionic polymerization as would be understood by one having skill in such art.
By tread traction it is meant handling, grip and cornering performance of the tire and particularly the tire's resistance to skidding on a road surface.
As hereinbefore discussed, where traction is to be emphasized for a tire tread, various resins may be desired to be included in its rubber composition.
The term “softening point” for the resins, as hereinbefore observed, refers to Ring and Ball softening point as determined by ASTM No. E28.
Representative examples of such contemplated resins are petroleum hydrocarbon resins, coumarone-indene resins, alkylated petroleum hydrocarbon resins, aromatic hydrocarbon resins, dicyclopentadiene/diene resins, and rosin and rosin derivatives.
Preferred contemplated resins are of the coumarone-indene type, dicyclopentadiene/diene type, and aromatic petroleum resins.
For example, for a coumarone-indene resin in a softening point range of about 20° C. to 40° C., a resin such as Cumar R-29 from Neville Chemical Co. is contemplated. Coumarone-indene resins are a class of resins recognized by those having skill in such resin art. They are typically derived from the polymerization of coumarone and indene.
For example, for an alkylated petroleum hydrocarbon resin in about a 120° C. to 150° C. softening point range, primarily saturated alkylated resins are contemplated such as, for example, Nevchem 150 by Neville Chemical Co. Such resins might be prepared, for example, by the alkylation of aromatic hydrocarbons with dicyclopentadiene (see U.S. Pat. No. 3,023,200).
For example, for an aromatic petroleum hydrocarbon resin in an intermediate softening point range of about 90° C. to about 110° C. a resin such as LX-782 by Neville is contemplated. In one aspect, such resins contain carbon-to-carbon unsaturation (double bonds) and may conventionally be a mixture of aromatic and acyclic polymer moieties, although they may be referred to as ‘aromatic petroleum resins”. The aromatic component of the resin is preferably selected fro
Blok Edward John
Kralevich, Jr. Mark Leslie
Sandstrom Paul Harry
Wideman Lawson Gibson
Lee Rip A
The Goodyear Tire & Rubber Company
Wu David W.
Young, Jr. Henry C.
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