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
2001-11-28
2004-11-16
Wyrozebski, Katarzyna (Department: 1714)
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...
C524S447000, C524S186000, C524S493000
Reexamination Certificate
active
06818693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a sulfur-curable rubber compound for tire tread rubber, in particular, tire tread rubber of racing tires, which comprises at least one diene rubber, at least one filler, plasticizer, as well as additional common additives. Furthermore, it relates to vehicle tires, in particular, racing tires, the tread rubbers of which contain this rubber compound.
2. Discussion of Background Information
Various fillers, such as carbon black, silica, alumosilicates, kaolin, metal oxides, or chalk, for example, are added to rubber compounds for tire tread rubbers. Due to their specific effect on the rubber the fillers not only help to lower the cost of the rubber compounds but also influence the characteristics of the uncured rubber compound and the tires made therefrom. Active fillers, also called reinforcing fillers, including the majority of carbon blacks, silicas, and the majority of silicates of small particle size, generally improve a number of characteristics of the vulcanized material, such as strength, (tensile) modulus, and tear strength, while other characteristics such as elongation at tear and rebound elasticity are adversely affected. Here, the activity of the filler depends on the particle size, the specific surface area, the geometric shape of the surface, and the chemical composition.
In the past, the known fillers were tested, altered, and modified in multiple ways in order to optimize the characteristics of tires containing these fillers. Additionally, new classes of fillers were developed for this purpose.
Layered silicates from one of these classes of fillers; layered silicates pose the problem that, due to their polar surface they are not compatible with conventional rubber compounds, i.e., they must be modified prior to introducing them into a rubber compound such that they are organophilic and compatible with the surrounding rubber matrix. This is the only way the layered silicate can be well distributed in the rubber matrix. To achieve this, it has been known for a long time to modify the normally hydrophilic surface of the layered silicates by cation exchange using alkyl-ammonium ions in order to render it organophilic. Then the individual organically modified layers are stacked parallel and form small stacks in which organic and inorganic layers alternate regularly.
An overview of nanocomposites based on polymers and layered silicates, their production, characterization, and use can be found, e.g., in the article “Polymer layered silicate nanocomposites” by M. Zanetti, S. Lomakin, and G. Camino in Macromol. Mater. Eng. 279, pp. 1-9 (2000), which is expressly incorporated herein by reference in its entirety.
Four methods for producing nanocomposites based on polymers and layered silicates are described in this article: in-situ polymerization, intercalation of the polymer from a solution, direct intercalation of molten polymer, and sol/gel technology. These processes cause the individual layers of the silicate to be expanded and sometimes even be completely unfoiled (exfoliated). The individual layers have a thickness of approximately 1 nm and are surrounded by polymer. The presence of nanocomposites in polymer materials renders it possible to endow the polymer products made therefrom with new and improved characteristics. The concept of nanocomposites based on layered silicates is used primarily in the area of thermoplasts, in order to improve their characteristics, for example, with respect to tensile strength. The four above-mentioned processes for producing nanocomposites can be used for thermoplasts, while for rubber compounds the direct intercalation of the molten polymer is impossible due to the high viscosity in the conventional processing temperature range. The other three processes can also be used for rubber compounds, however, these processes are technically very cumbersome and invariably involve the use of solvents, which have to be removed entirely in the further course of the processing of such nanocomposites, e.g., for the incorporation into a curable rubber compound.
From WO 97/00910, expressly incorporated herein by reference in its entirety, it is known to produce a latex that contains layered silicate having intercalated emulsion polymer. For the production of such a latex, initially the layered silicate is rendered organophilic by an ion exchange using onium salts and, subsequently, a rubber is emulsion polymerized from its monomers in the presence of the organophilic layered silicate into the layers of the silicate. Thus nanocomposites are formed. After coagulation and drying, such nanocomposites can be used in rubber compounds, e.g., for rubbers of tire innerliners having reduced gas permeability.
U.S. Pat. No. 5,576,372, expressly incorporated herein by reference in its entirety, describes the use of layered silicates in the rubbers of tire innerliners of reduced gas permeability, with the layered silicates being provided with a reactive rubber having positively charged groups. To this end, the layered silicates are treated with a solution containing the reactive rubber, generally a solution having an organic solvent such as toluene. The reactive rubber swells into and between the layers. Subsequently, all solvents must be removed prior to further processing, e.g., the incorporation into a lubber compound of a tire innerliner. Additionally, many organic solvents must be considered ecologically and toxicologically questionable.
Specially treated layered silicates for rubber compounds with improved mechanical characteristics and reduced gas permeability are also known from U.S. Pat. No. 6,103,817, which is expressly incorporated herein by reference in its entirety. Prior to the incorporation into the rubber compounds, the special layered silicates are rendered organophilic by ion exchange using onium salts and, subsequently, additional organic guest molecules are introduced/swelled from organic solvents or by treating the organophilic layered silicates with liquid guest molecules (with substances of low melting point), in order to increase the distance between the layers in the layered silicate and to facilitate and improve the distribution in the rubber compound. One or two different substances may be introduced into the layered silicate, and at least one substance must have polar groups.
The three processes described have in common that prior to the incorporation into a rubber compound, the layered silicates are modified by expensive processes such that prior to incorporation the separate silicate layers have already been separated from one another by lubber molecules so that nanocomposites are present.
From U.S. Pat. No. 6,034,164, expressly incorporated herein by reference in its entirety, it is known to incorporate layered silicates modified with alkylammonium ions directly into a rubber compound made from two special rubbers without any prior swelling or polymerization of rubber or guest molecules. The rubbers in question are, on the one hand, a non-ionic polymer having a molecular weight >50,000 g/mol and, on the other hand, a non-ionic polymer compatible with the first polymer and with a molecular weight lower than that of the first polymer. The forces acting during the mixing process result in layered packages of modified layered silicate having a thickness of more than 10 nm. This is to avoid complete exfoliation. Such rubber compounds may be used for the production of gas impermeable elastomer membranes, such as tire innerliners or bladders.
Rubber compounds used for tire innerliners (main purpose: gas impermeability) are generally insufficient to meet the requirements of rubber compounds of tire tread rubber. For example, the rubber compounds used for tire tread rubber must render the tires optimized with respect to abrasion, skid resistance, rolling resistance, heat build up, tear propagation resistance, and low temperature flexibility. Tread rubber of racing tires for, e.g., race cars or race karts is primarily required to have high skid resistance and
Heinrich Gert
Herrmann Wolfram
Kendziorra Norbert
Pietag Thomas
Recker Carla
Continental Aktiengesellschaft
Greenblum & Bernstein P.L.C.
Wyrozebski Katarzyna
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