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
2000-02-14
2002-10-15
Mulcahy, Peter D. (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...
C524S496000, C524S515000, C524S237000, C525S333300
Reexamination Certificate
active
06465560
ABSTRACT:
FIELD
Pneumatic rubber tire with an outer, circumferential tread comprised of a cis 1,4-polybutadiene-rich and silica-rich rubber composition which contains specified elastomers with spatially defined glass transition temperatures, in conjunction with silica and specified carbon black reinforcement.
BACKGROUND OF THE INVENTION
Pneumatic rubber tires, particularly high performance tires, are desired to have treads of a rubber composition which will provide good traction on the road.
Resistance to treadwear of such tires is often sacrificed in order to achieve such good traction.
Indeed rubber compositions designed to specifically emphasize very good traction for a tire tread often have relatively low abrasion resistance and associated relatively poor treadwear and typically exhibit a relatively high, single, glass transition temperature (Tg) of above −50° C. and usually within a range of about zero to about −50° C.
Conversely, rubber compositions designed to specifically emphasize very good resistance to abrasion for a tire tread often have relatively poor traction and also typically exhibit a single low Tg below −50° C.
Therefore, a tread rubber composition exhibiting a balance between traction and treadwear is difficult to achieve where the rubber composition exhibits only a single Tg.
In U.S. Pat. No. 5,723,530, a tire is presented with a tread where good traction is desired yet still having an acceptable treadwear.
In U.S. Pat. No. 5,723,530, a tire is provided with a tread which is composed of four elastomers, of which two of the elastomers are spatially defined, namely, (1) 25 to 60 phr of styrene/butadiene rubber with Tg in a range of −15° C. to −45° C.; (2) 5 to 40 phr of medium vinyl polybutadiene rubber with vinyl content of 40 to 65 and a Tg in a range of −45° C. to −65° C.; (3) 20 to 40 phr of cis 1,4-polybutadiene rubber with a Tg in a range of −95° C. to −105° C.; and (4) 5 to 30 phr of cis 1,4-polyisoprene rubber having a Tg in a range of −65° C. to −70° C.; wherein the Tg of the cis 1,4-polybutadiene rubber is at least 50° C. lower than the Tg of the styrene/butadiene rubber. A specified carbon black is also specified. It is readily seen in this patent disclosure that a tire tread rubber composition is provided which exhibits dual Tgs but is comprised of carbon black as reinforcement and less than 45 phr of cis 1,4-polybutadiene.
In the description of this invention, terms such as “compounded rubber”, “rubber compound” and “compound”, if used herein, refer to rubber compositions composed of one or more elastomers blended with various ingredients, including curatives such as sulfur and cure accelerators. The terms “elastomer” and “rubber” might be used herein interchangeably. It is believed that all of such terms are well known to those having skill in such art.
A reference to glass transition temperature, or Tg, of an elastomer or elastomer composition, where referred to herein, represents the glass transition temperature(s) of the respective elastomer or elastomer composition in its uncured state or possibly a cured state in a case of an elastomer composition. A Tg can be suitably determined by a differential scanning calorimeter (DSC) at a temperature rate of increase of 10° C. per minute.
The existence of more than one glass transition temperature of a cured rubber composition can be determined by dynamic mechanical testing and demonstrated, for example, as a graphical representation, or plot, of tangent delta, or of loss modulus (i.e. E″) as a function of temperature. The existence of more than one glass transition temperature for the rubber composition is evident when at least two humps, or peaks, are present in the plot between the temperatures of −90° C. and 10° C.
DISCLOSURE AND PRACTICE OF THE INVENTION
In accordance with this invention, a pneumatic rubber tire is provided having a circumferential rubber tread where said tread is a rubber composition comprised of, based on 100 parts by weight of the tread rubber,
(A) conjugated diene-based elastomers comprised of
(1) at least 45 to about 85, alternatively at least 50 to about 85, or even from a threshold of at least 55 to about 85, phr of cis 1,4-polybutadiene rubber having a Tg within a range of about −956° C. to about −105° C.;
(2) about 15 to about 55, alternatively about 15 to about 50, phr of at least one elastomeric styrene/butadiene copolymer rubber having a bound styrene content in a range of about 30 to about 55 percent selected from one of
(i) emulsion polymerization prepared styrene/butadiene copolymer having a Tg within a range of −15° C. to −45° C.; or
(ii) organic solution polymerization prepared tin coupled styrene/butadiene copolymer having a Tg within a range of −55° C. to −25° C.;
(3) about 0 to about 15, alternatively about 5 to about 15 phr of a medium vinyl polybutadiene having a vinyl content in a range of about 45 to about 70 and a Tg in a range of about −55° C. to about −35° C.;
wherein the Tg of the cis 1,4-polybutadiene Tg elastomer is at least 50° C. lower than the Tg of the styrene/butadiene elastomer; and
(4) about zero to about 15, alternatively about 5 to about 15, phr of cis 1,4-polyisoprene having a Tg in a range of about −65° C. to about −70° C.
(B) about 60 to about 110, alternatively about 60 to about 90, phr of reinforcing filler comprised of amorphous silica which alternately includes a high structure carbon black reinforcing filler characterized by having an Iodine adsorption value in a range of about 116 to about 135, g/kg together with a DBP number in a range of about 125.to about 140, cm
3
/100 g; wherein the weight ratio of said silica to said carbon black is at least 1/1, alternatively at least 5/1 and alternatively in a range of about 1/1 to 20/1 whereas in one aspect, such filler is composed entirely of silica; and
(C) a coupling agent having a moiety (e.g.: a silane moiety) reactive with hydroxyl groups (e.g.: silanol groups) contained on the surface of said silica and another moiety interactive with at least one of said diene-based elastomers; wherein said coupling agent is preferably an organosilane polysulfide and more preferably a bis (trialkoxysilylalkyl) polysulfide.
It is an important aspect of this invention that the tread rubber composition is both cis 1,4-polybutadiene rubber-rich and, also silica-rich, together with an organosilane polysulfide coupling agent.
Another important aspect of the invention is a requirement that at least two elastomer phases are present in the tread rubber composition as being generated by a requirement that the combination of cis 1,4-polybutadiene and styrene/butadiene elastomers are in the clear majority insofar as elastomers in the tread rubber are concerned and, moreover, that the Tg of the cis 1,4-polybutadiene rubber is at least 50° C. lower than the Tg of the styrene/butadiene copolymer rubber.
More specifically, it is required that at least 45, preferably at least 50, and even up to a threshold of at least 55, weight percent of the elastomers have a Tg lower than −95° C., namely the cis 1,4-polybutadiene, and at least 15 weight percent of the elastomers have a Tg of higher than −55° C., namely the styrene/butadiene copolymer.
In this manner, it is considered herein that the relatively low Tg cis 1,4-polybutadiene elastomer is relatively incompatible with the high Tg styrene/butadiene copolymer elastomer as evidenced by their individual Tan. delta peaks on a graphical presentation, or plot, of Tan. delta versus temperature cured of the rubber composition within a temperature range of about −90° C. to about 10° C.
Accordingly, the elastomers of said tread rubber are present in at least two phases, comprised of a cis 1,4 polybutadiene phase and an additional phase comprised of said styrene/butadiene and/or tin coupled styrene/butadiene phase.
In particular, and as one aspect of this invention, a graphical plot of Tan. delta versus temperature curve within a bro
Puhala Aaron Scott
Zanzig David John
Mulcahy Peter D.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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