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
2000-05-23
2004-11-23
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...
C524S495000, C524S442000, C524S437000, C524S436000, C524S261000, C524S262000, C524S263000, C524S264000, C524S265000, C524S267000, C523S333000, C523S334000, C523S206000, C428S403000, C428S407000
Reexamination Certificate
active
06822036
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 199 24 366.2, filed May 27, 1999, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The invention provides a process for preparing rubber powders which contain large amounts of siliceous fillers modified with organosilicon compounds and/or carbon black, the rubber powders prepared in this way and use thereof.
BACKGROUND OF THE INVENTION
The production of rubber powders containing small amounts of filler is already known in principle (DE-PS 37 23 213, still unpublished DE-198 43 301.8). These products are generally obtained via stepwise precipitation of an aqueous emulsion which contains a filler (e.g., precipitated silica) and a rubber latex.
In these products the rubber is intended to form the main proportion or at least the essential proportion as compared with the filler (e.g. silica and/or carbon black). The amount of filler is preferably chosen so that it corresponds to the concentration in a conventional rubber mixture.
Interest in the processing technique for these powdered products has been shown by the rubber industry as such rubber mixtures are produced with high time, energy and manpower requirements. The main reason for this is that the rubber raw material is present in the form of bales and the other constituents of the vulcanizable mixtures have to be admixed in several process stages using rollers or internal mixers.
Rolling resistance of vehicle tires (which produces savings in gas consumption) and wet-sliding behavior have been improved since the start of the 1990s by the use of highly active precipitated silicas combined with bifunctional organosilanes in tire mixtures. See DE-OS 43 34 201.9 and DE-OS 44 27 137.9.
Bis-(triethoxysilylpropyl)tetrasulfane (TESPT) is the most important compound used for this application.
TESPT reacts with the silanol groups in the silica via its triethoxysilyl groups during preparation of the mixtures.
During this so-called silanization or modification reaction, ethanol is released in stoichiometric amounts, which may require considerable safety precautions in the workplace if this reaction does not take place until the rubber mixtures are being prepared.
The rubber industry is therefore making an effort to find a remedy in the near future. One possibility comprises the installation of plants for suction and post-incineration or the incorporation of biofilters. Since this has to be done for each compounding line, however, the costs are correspondingly high. A second possibility requires the raw materials suppliers to perform the silanization reaction, i.e. the reaction between silica and silane, collecting the alcohol being released and disposing of it or recycling it.
Processes for the modification of siliceous fillers, including precipitated highly active silicas, are known from the literature. None of these products has penetrated the market, however, for economic reasons and, primarily, for technical reasons.
EP 0 442 1433 B1 provides a process in which the silane is applied to dry silica and then reacted at elevated temperature with the release of ethanol. Apart from the economic disadvantage of using pre-dried silica as starting material, an additional disadvantage is due to the inadequate storage stability of the products prepared in this way and thus the ongoing deterioration of the rubber-engineering characteristics.
Another possibility for preparing pre-modified silicas is wet silanization. EP 0 177 674 provides a process in which silica and silane are homogenized with the aid of a special emulsifier and then the reaction is performed at elevated temperature with simultaneous drying of the product. In U.S. Pat. No. 3,567,680, special water-soluble mercaptosilanes are described as suitable for the reaction.
As shown in practice, however, products prepared by this process are also not very storage stable. Tests have shown, in both processes, that it is difficult for TESPT, in particular when used in large amounts, to fully react with the OH groups on the silica surface. This unreacted portion of silane tends to self-polymerize during storage and cannot then be used for the desired modification of the silica. As a result, the rubber-engineering characteristics are reduced. In the case of silanization in water, in accordance with EP 0 177 674, silica particles agglomerate strongly in water and therefore particle sizes suitable for the silanization process are not present, especially at high suspension densities. If this type of pre-modified product is incorporated, mechanical degradation of the particles takes place and silica particles which have not been modified or are insufficiently modified are released. The result is a distinct decrease in the properties relating to rubber-engineering characteristics.
The unreacted proportions of silane are one reason for the aging behavior of silanized silicas, especially those silanized with TESPT. This makes a new approach to the preparation of pre-modified products desirable. DE 196 09 619.7 undertakes the task of clearly increasing the degree of reaction of the silane, inter alia TESPT, i.e. reacting as many of the ethoxy groups as possible. This is possible by reducing the pH to a range of pH between 2 and 5. Rapid and comprehensive reaction of the silane with the silica takes place in this pH range.
As shown in practice, the silane tends to self-polymerize at a low pH. That means that the silica is not modified in the desired manner and furthermore that the rubber-engineering characteristics are unsatisfactory.
To summarize, the following problems in particular need to be avoided in their entirety or solved.
Reducing the agglomeration behavior of silica during silanization;
Avoiding self-polymerization of the silane; and
Complete reaction of the silane with the siliceous surface.
SUMMARY OF THE INVENTION
The object of the invention is to provide a process for preparing a rubber powder which contains a large amount of filler, in particular precipitated silica and/or carbon black, these rubber powders and the use thereof.
The invention provides a process for preparing finely divided rubber or rubber powders by precipitation from a water-containing mixture which contains oxidic, in particular siliceous, fillers and/or carbon black in the form of suspensions, an aqueous emulsion of a rubber (polymer) or a rubber solution, by adding water-soluble salts of a metal selected from groups IIa, IIb, IIIa and VIII of the Periodic System of Elements, in which:
a) first, a filler suspension with a suspension density between 0.5 and 10%, in particular between 5 and 7%, with respect to the solids, is prepared from a siliceous compound and/or carbon black by stirring, the solid particles optionally having been previously milled down (deagglomerated) by means of a suitable mill. Additional hydrogen bridge-forming compounds such as polyalcohols or polyvalent amines are optionally added to the suspension in amounts of 0.5 to 10 parts, with respect to 100 parts of filler, and the suspension is optionally heated to within the range from 25° to 95° C.,
b) then, if the suspension contains siliceous fillers, one or more organosilicon compound(s) in accordance with formulae (I) to (III) which contain at least one alkoxy group are dissolved in water or optionally emulsified in water in the presence of a surface active substance, and mixed with the aqueous suspension of filler mentioned above or its mixture with a carbon black, at a temperature of 10° to 60° C., preferably at room temperature, with stirring,
c) this suspension, prepared in this way, is mixed with a polymer latex, polymer emulsion or polymer solution. The pH of this mixture is reduced with an acid or with the aqueous solution of one of the salts mentioned above, in particular a Lewis acid, to a value between 7 and 4, preferably between 5.5 and 4.5, and the rubber in the mixture is precipitated together with the fillers optionally modified by the organosilicon compounds mentioned above,
d) the precipitated solid is separated
Ernst Uwe
Görl Udo
Stober Reinhard
Trempler Thomas
Lee Rip A.
Pillsbury & Winthrop LLP
PKU Pulverkautschuk Union GmbH
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