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
1997-11-21
2003-08-19
Hendrickson, Stuart L. (Department: 1754)
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
active
06608132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved carbon black for tire tread rubber. More particularly, the present invention relates to carbon black which imparts upon tire tread rubber improved treadwear, lower rolling resistance, lower heat buildup and improved tear resistance. The improved carbon black is in the N100 series and, when in rubber, combines the improved treadwear and low heat buildup advantages of N121 carbon black with the high tear resistance properties of N115. The present invention has particular application to truck and bus steel cord radial tire treads, especially for use in on/off highway conditions, and for high performance passenger car tires.
2. General Background
As worldwide dependence on truck transportation and other truck tire usage steadily increases, new designs in radial truck tire technology will have an increasingly significant impact on the many economies of the world. In recent years, many radial truck tire performance improvements have been made. However, further advances to resist both premature failure and accelerated treadwear in severe services are still needed in tire design and in compounding materials development. The art has recognized that there is a long felt but unresolved need for improved failure resistance and other performance improvements for tread compounds including longer treadwear, improved tear resistance, lower heat build-up and lower rolling resistance. (See, e.g., M. B. Rodgers and S. M. Mezynski, Kautschuk Gummi Kunst., 46, (9), 718 (1993); and, B. Lambillote and G. S. Eiber, Rubber World, 209, (1), 27 (October 1993)).
Carbon black, a form of elemental carbon, is widely used as a component of tire rubber, for both natural and synthetic rubbers and blends of natural rubber with synthetic polymers. The physical characteristics of carbon black, such as particle size and structure, affect various performance properties of rubber compounds, such as tire treadwear, rolling resistance, heat buildup and tear resistance.
The present invention relates to a new carbon black (herein referred to as “carbon black A”) designed to improve the qualities of tire tread rubber, including providing improved treadwear, lower rolling resistance, lower heat buildup and improved tear resistance. The improved carbon black is in the N100 series and, when in rubber, combines the long treadwear and low heat buildup advantages of N121 carbon black with the high tear resistance properties of N115. The carbon black of the present invention is particularly well suited for improving the qualities of tread for truck and bus steelcord radial tires (TBS/RT), and high performance passenger car tires. Medium or heavy-duty steelcord radial truck and bus tires (TBS/RT) encompass a number of market segments classified as over the highway truck and bus, construction/agricultural, mixed on/off road, city service and special fuel economy tires.
Currently, N100 and N200 series tread carbon blacks (as specified in ASTM D 1765) are used in TBS/RT and their retread compounds. These tread blacks are broadly characterized as having both high surface area and high structure levels.
The structure of a carbon black is the degree of particle aggregation, with a high structure carbon black having more particles aggregated into random structures than a low structure black. The structure of carbon black can be defined by the n-Dibutyl Phthalate Absorption number (DBPA). The larger the DBPA number, the higher the structure of the carbon black. Surface area can be measured by Iodine Adsorption number (Iodine No.). There is an inverse relationship between the iodine number surface area and particle size; the higher the number, the smaller the particle size.
The particle size and structure of carbon black affect various qualities of rubber containing carbon black, such as tire treadwear, tread rolling resistance, tread heat buildup and tread tear resistance. Accordingly, different carbon blacks are used in different treads depending on the specific service requirements of the tires.
For example, on-highway truck service exposes tires to high loads and high speeds over relatively smooth roads. For this application, in both Europe and North America, tread blacks such as N121, N110 and N234 are mainly used. Here, the performance concerns relate primarily to longer and more even treadwear.
However, rolling resistance is becoming a very important performance concern worldwide. In TBS/RT the tread plays the most important role in controlling rolling resistance.
The three aforementioned tread blacks (N121, N110 and N234), exhibit relatively high hysteresis characteristics (developing higher heat build-up temperatures and higher rolling resistance levels relative to coarser N200 and N300 series counterparts), with N110 being the most hysteretic followed by N121 and N234. Relative to each other, N121 develops the highest treadwear rating, followed by N234, and then N110. The applications for these tread blacks include new tread and retread compounds.
In on/off-highway truck service, the tires, when off the highway, generally experience rougher roads and sharper turns with high loads and at lower speeds than on-highway service. However, when they come back to the highway they experience the same high speeds and temperature conditions as on-highway tires.
For Europe and North America, the tread blacks commonly employed for this application include N110, N115 and N220. The performance concerns relate more to service life of the tread than to treadwear life. The greater the severity of tire service conditions the more important the resistance to failure becomes, particularly in the tread compound. These grades develop lower modulus levels and exhibit more resistance to tear than N121 or N234. N110 and N115 develop higher heat build-up temperatures and rolling resistance levels than N220 (or N121 and N234) and higher tear resistance levels.
While N115 and N110 are used in on/off highway treads in Europe, N115 is not used as much in this application in North America. These two tread blacks differ mainly in that N115 has higher tint, iodine number and nitrogen surface area levels than N110. Nevertheless, they perform similarly in rubber.
TBS/RT are often composed of carbon black reinforced polymer systems that are based mostly on natural rubber (NR) or blends of NR and synthetic polymers (emulsion styrene-butadiene copolymer, SBR, and polybutadiene, BR, rubber). (See, e.g., M. B. Rodgers and S. M. Mezynski, Kautschuk Gummi Kunst., 46, (9), 718 (1993), which is incorporated herein by reference)).
NR (natural rubber) is a natural product from latex-producing caoutchouc plants, of which the Hevea Brasiliensis is the most common, is a polyisoprene (methyl butadiene) elastomer.
BR (butadiene rubber) is a synthetic rubber produced from either an emulsion or solution polymerization of butadiene joined mostly linearly by 1,4 (preferred in cis-1,4 but, also in certain measure, trans-1,4 conformation) and by 1,2 additions.
SBR (styrene-butadiene rubber) is a synthetic rubber produced from either an emulsion or solution polymerization of butadiene and styrene in various ratios.
Among the rubbers suitable for use with the present invention are any natural rubbers, synthetic rubbers and blends of natural and synthetic rubbers. These include the so-called diene elastomers, i.e., for example oil-treated natural and synthetic rubbers, such as carboxyl rubbers, epoxy rubbers, transpolypentenamer, halogenated butyl rubbers, rubbers of 2-chlorobutadiene and polybutadiene rubbers. Typical of the synthetic rubbers are styrene-butadiene rubbers (SBR), whether clear or oil extended, emulsion SBR rubbers, high styrene SBR rubbers, solution SBR rubbers, starred solution SBR rubbers and functionalized solution SBR rubbers.
Further still, suitable rubbers are rubbers, plastics and mixtures thereof which can be crosslinked with sulfur and vulcanization accelerator(s) and also with peroxide to form elastomers. These include the so-called diene elastomers, i.e. for exampl
Bomo Francis G.
Swor Ronald A.
Columbian Chemicals Company
Garvey, Smith, Nehrbass & Doody, L.L.C.
Hendrickson Stuart L.
Smith Gregory C.
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