Indian Patents. 206362:RUBBER POWDERS WHICH CONTAIN LARGE AMOUNTS OF FILLERS, A PROCESS FOR PREPARING THEM AND THEIR USE

Title of Invention	RUBBER POWDERS WHICH CONTAIN LARGE AMOUNTS OF FILLERS, A PROCESS FOR PREPARING THEM AND THEIR USE
Abstract	The invention provides rubber powders with a high degree of 5 filling which are obtained by precipitating water-containing suspensions which contain fillers and rubber emulsions or rubber solutions and their use to prepare vulcanisable rubber mixtures.

Full Text	1A Rubber powders which contain large amounts of fillers, a process for preparing them and their use 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 that way and their use. The production of powdered rubbers containing small amounts of filler (rubber powders) is already known in principle (DE-PS 37 23 213, still unpublished DE-198 43 301.8).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 (inter alia 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 these powdered products of this type is produced by the processing technique in the rubber industry. There, rubber mixtures are produced with high time, energy and staffing requirements. The main reason for this is that the raw material rubber is present in the form of bales and the other constituents of the vulcanisable mixtures have to be admixed in several process stages on rollers or internal mixers. The rolling resistance (savings in petrol) and wet-sliding behaviour have been improved since the start of the 90s by the use of highly active precipitated silicas combined with bifunctional organosilanes in the tread mixtures. [DE-OS 43 34 201.9 and DE-OS 44 27 137.9], 2 Bis-(triethoxysilylpropyl)tetrasulfane (TESPT) is the most important representative 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 silanisation 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 comprises the raw materials suppliers performing the silanisation 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 and primarily for technical reasons. EP 0 442 1433 Bl 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 in- the rubber-engineering characteristics. 3 Another possibility for preparing pre-modified silicas is wet silanisation. EP 0 177 674 provides a process in which silica and silane are homogenised with the aid of a special emulsifier and then the reaction is performed at elevated temperature with simultaneous drying of the product. In US-PS 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-polymerise during the course of 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 silanisation in water, in accordance with EP 0 177 67 4, is so happens that silica particles agglomerate strongly in water and therefore that particle sizes suitable for the silanisation 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 fact that unreacted proportions of silane are one reason for the ageing behaviour of silanised silicas, especially those silanised with TESPT, makes a new approach to the preparation of pre-modified products understandable. 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 lowering the pH to a region between 2 and 5. A Rapid and comprehensive reaction of the silane with the silica takes place_ in this pH region. As shown in practice, the silane tends to self-polymerise 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 summarise, the following problems in particular need to be avoided in their entirety or solved. Reducing the agglomeration behaviour of silica during silanisation Avoiding self-polymerisation of the silane Complete reaction of the silane with the siliceous surface 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, this powder and the use thereof. The invention provides a process for preparing finely divided rubbers (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 chosen from groups II a, II b, III a and VIII in the Periodic System of Elements, which is characterised in that 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 5 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 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 the polymer latex, polymer emulsion or polymer solution, the pH of this mixture is lowered with an acid or 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 using methods known per se and e) the filler-containing rubber is dried. It is also possible to use siliceous fillers already pre-modified with the organosilicon compounds mentioned above. Hexanetriol, glycol, diethylene glycol, triethylene glycol or polywax 4000 {a long-chain hydrocarbon) are preferably 6 used as polyols. o-toluyl-biguanidine, hexa-K, DOTG (di-o-toluylguanidine), DPG (diphenylguanidine) or TEA (triethanolamine), for example, are suitable as polyvalent amines. In a special embodiment, an aqueous plastics emulsion containing polystyrene, polystyrene/butadiene copolymers of different compositions, polyethylenes, polypropylenes or polyvinyl acetate of different chemical constitutions is also added to the powdered rubber found in the aqueous medium, prior to separating and drying, in amounts of 0.5 -10 phr, in particular 1-4 phr. These form a coating during the drying process which prevents the absorption of water. The ratios by weight in the suspension are adjusted so that a powdered rubber with a filler content of > 250 phr, preferably = 400 phr precipitates out. The drying process is advantageously performed in a dryer with a gas inlet temperature of 130 to 170°C and a gas outlet temperature of 50 to 70°C. The temperature of the product should not exceed 40 to 80°C. The duration and extent of the precipitation process, which depends on the pH and the concentration of filler, may readily be established by a series of measurements. The products are produced as a free-flowing powder without further additional measures to prevent adhesion. Quantitative determination of the sulfur atoms contained in the silane in accordance with formula (I) before and after extraction of the powdered rubber with hot ether show, for example, that the silane used for modification purposes is present virtually fully chemically bonded to the silica. As further fillers, carbon blacks known from the rubber industry are optionally used, preferably in a finely divided (fluffy) form, which generally have an average particle 7 diameter, without mechanical treatment, of 1 to 9 m, preferably 1 to 8 m, before they are suspended. Precipitated silicas may advantageously be used in the form of a salt-free washed filter cake. Suitable metal salts are those which arise from elements in groups IIa, IIb, IIIa, and VIII in the Periodic System of Elements. This group classification corresponds to that in the old IUPAC recommendation (see: Periodisches System der Elemente, Verlag Chemie, Weinheim, 1985). Typical representatives are magnesium chloride, zinc sulfate, aluminium chloride, aluminium sulfate, iron chloride, iron sulfate, cobalt nitrate and nickel sulfate, wherein salts of aluminium are preferred. Aluminium sulfate and other Lewis acids are particularly preferred. The salts are used in an amount of 0.1 to 6.5 parts by weight per 100 parts by weight of rubber. Additional mineral acids such as e.g. sulfuric acid, phosphoric acid and hydrochloric acid are optionally used to adjust to the desired pH, wherein sulfuric acid is particularly preferred. However, carboxylic acids such as e.g. formic acid and acetic acid may also be used. The amount of acid is governed by the type and amount of water-soluble metal salt, the filler, the organosilane used and the optionally present alkali metal silicate. It can readily be determined by some orienting trial runs. The solids content of the latices used is generally 20 to 25 wt.%. The solids content of rubber solutions is generally 3 to 20 wt.% and that of rubber emulsions is generally 5 to 60 wt.%. The process according to the invention may be performed either batchwise or continuously. The precipitated rubber powder is advantageously first separated from the majority 8 of the water. This can be achieved, for example, by using a centrifuge, a filter press or a decanter. Then the product is dried to a residual moisture content of Rubber powders according to the invention, which are also provided by the invention, are generally prepared, if siliceous or oxidic fillers, in particular precipitated silicas, are used, by using one or more organosilicon compounds of the general formulae in which B: represents -SCN, -SH -Cl, NH2 (when q = 1) or -Sx- (when q = 2) R and R1: represent an alkyl group with 1 to 4 carbon atoms, which is branched or unbranched, or a phenyl group, wherein all the groups R and R are identical or different and preferably represent an alkyl group, R: represent a C1-C4-alkyl or -C1-C4-alkoxy group, which is branched or unbranched n: is 0, 1 or 2, 9 Alk: represents a divalent straight or branched hydrocarbon group with 1 to 6 carbon atoms, m: 0 or 1 Ar: represents an arylene group with 6 to 12 carbon atoms p: is 0 or 1, with the proviso that p, m and n are not simultaneously 0, x: a number from 2 to 8, Alkyl: represents a monovalent straight or branched saturated hydrocarbon group with 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms, Alkenyl: represents a monovalent straight or branched unsaturated hydrocarbon group with 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms. These compounds are generally used in the form of solutions, if they are water-soluble, or emulsions, wherein the solutions or emulsions may also be formed in the presence of the suspension of siliceous fillers or their mixtures with carbon black. The emulsions or solutions are preferably prepared at room temperature. However, temperatures of 10 to 60°C are also suitable. The concentration of the organosilicon compound(s) in the solutions or suspension used is 0.5 to 20 wt.%, preferably 5 to 12 wt.%, with respect to the total amount of siliceous filler used. The pH of the emulsion or solution, like the pH of the filler suspension after admixing the emulsion, is in the weakly acid or weakly alkaline region, but is preferably about 7. 10 The expression water-insoluble used is understood to mean that: after mixing the organosilicon compound (without a surface active substance) with the suspension of the filler, clear solution is not formed around the filler particles in the desired pH and concentration region. Rather, the separate phases remain, these consisting of water, solid and organosilicon compound(s). The oligosulfidic organosilanes in accordance with general formula (I) cited above are known per se and can be prepared by known processes. Examples of preferably used organosilanes are e.g. bis(trialkoxysilyl-alkyl)oligosulfides which can be prepared according to US-PS 3 842 111 such as bis (trimethoxy-, triethoxy-, trimethoxy- ethoxy-, tripropoxy-, tributoxy-, tri-i-propoxy and tri-i-butoxy-silyl-methyl)-oligosulfides, to be precise in particular the di-, tri-, tetra-, penta-, hexasulfides etc., also bis-(2-trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy- and -tri-n- and -i-butoxy-ethyl)-oligosulfides, to be precise in particular the di-, tri-, tetra-, penta-, hexasulfide etc., furthermore bis-(3-trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy-, tri-n-butoxy- and tri-i-butoxysilyl-propyl)-oligosulfides, to be precise again the di-, tri-, tetrasulfides etc. up to octasulfides, there again the corresponding bis-(3-trialkoxy-silylisobutyl)-oligosulfides and the corresponding bis-(4-trialkoxysilylbutyl)-oligosulfides. Of these selected, relatively simply constructed organosilanes of the general formula I, preferred compounds are again the bis-(3-trimethoxy-, triethoxy- and tripropoxysilylpropyl)-oligosulfides, to be precise the di-, tri-, tetra- and pentasuIfides, in particular triethoxy compounds with 2, 3 or 4 sulfur atoms and their mixtures. Alk in general formula I represents a divalent, straight or branched hydrocarbon group with 1 to 6 carbon atoms, preferably a saturated 11 alkylene group with a straight carbon chain with 1 to 4 carbon atoms. Silanes with the following structural formula are also especially suitable: and their methoxy analogues, which can be prepared in accordance with DE-AS 25 58191. These compounds are not water-soluble. Surface active substances which are generally used, and in this case are preferred, are non-ionogenic, cationic and anionic surfactants, the concentration of these in the emulsion is 1 to 15 wt.%, preferably 2 to 10 wt.%, with respect to the amount of organosilane compounds. Examples of these types of surfactants are alkylphenol polyglycol ethers, alkyl polyglycol ethers, polyglycols, alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyltrimethylammonium salts, alkylbenzene sulfonates, alkyl hydrogen sulfates, alkyl sulfates. 12 The natural or precipitated oxidic or siliceous fillers to be modified, also used as a mixture of two or more of these fillers, are fillers known per se in rubber technology. An essential prerequisite for their suitability is the presence of OH groups at the surface of the filler particles which can react with alkoxy groups in the organosilicon compounds. They are oxidic and siliceous fillers which are compatible with rubbers and have the degree of fineness demanded and known for this use. Suitable natural silicates are in particular kaolin or clays. However, kieselguhr or diatomaceous earths may also be used. Oxidic fillers which may be mentioned by way of example are aluminium oxide, aluminium hydroxide or trihydrate and titanium dioxide. "Modified fillers" in this connection means that the organosilicon compounds are bonded either by chemical reaction (OH groups) or adsorptively at the surface. Adsorptively bonded groups are converted into chemically bonded groups at the latest during the drying stage. The emulsion or solution is mixed with the filler suspension in amounts such that the concentration of organosilicon compound is 0.5 to 20 wt.%, preferably 5 to 12 wt.%, with respect to the amount of filler. The modified filler contains 0.5 to 20 wt.%, preferably 0.5 to 12 wt.% of organosilicon compound, with respect to the dry filler. They are particularly suitable for use in vulcanisable and mouldable rubber mixtures. A salt-free washed filter cake obtained from silica precipitation is advantageously used for the process according to the invention. 13 Also suitable are suspensions such as are obtained during the working up of natural fillers such as clays.- An energy-consuming drying step is saved in this way, as compared with the prior art. The silicas used are known from the rubber sector. They generally have a N2 surface area, determined by the well-known BET method, of 35 to 700 m2/g, a CTAB surface area of 30 to 500 m2/g and a DBP index of 150 to 400 ml/lOOg. The product according to the invention contains these silicas in an amount of > 250 to 5000 parts, in particular 400 to 1000 parts, with respect to 100 parts of rubber. If they are white, natural fillers, such as clays or silica chalks with a N2 surface area of 2 to 35 m2/g, they are preferably used in an amount of 400 to 1250 parts, with respect to 100 parts of rubber. Filler-containing rubber powders may also be prepared which contain siliceous fillers, in particular silicas, and carbon black as a mixture or which contain only carbon black. The total amount of filler may then be between > 250 and 5000 phr, in particular up to 2000 phr. The proportion of silica, if present, is generally > 250 phr to 1250 phr. For degrees of filling of > 1000 phr, carbon black is chosen in particular as the filler; carbon black is generally used at a rate of > 250 to 1000 phr. Carbon blacks which are generally used in rubber processing are especially suitable. These include furnace blacks, channel blacks and lamp blacks with an iodine absorption index of 5 to 1000 m2/g, a CTAB 14 index of 15 to 600 m2/g, a DBP adsorption of 30 to 400 ml/100 g and a 24 M4 DBP index of 50 to 370 ml/100 g. The following species have proved useable as types of rubber and can be prepared as aqueous emulsions, separately or as mixtures with each other: Natural rubber, emulsion SBR with a styrene proportion of 10 to 50 %, butyl/acrylonitrile rubber. Butyl rubber, terpolymers of ethylene, propylene (EPM) and non-conjugated dienes (EPDM), butadiene rubbers, SBR, prepared by the solution polymerisation process, with styrene contents of 10 to 25 %, and also concentrations of 1,2-vinyl constituents of 20 to 55 % and isoprene rubber, in particular 3,4-polyisoprene. Emulsion and solution SBR are particularly suitable. In the case of polymers prepared by the solution process, special precautions have to be taken during processing due to the presence of solvent. Apart from the rubbers mentioned above, the following elastomers are suitable, individually or as a mixture: Carboxyl rubber, epoxide rubber, trans-polypentenamers, halogenated butyl rubber, rubbers made from 2-chloro-butadiene, ethylene/vinyl acetate copolymers, epichlorohydrins, optionally also modified natural rubber such as e.g. epoxidised species. Rubber powders according to the invention generally have a particle size of 25 m to 3000 m, in particular 500 m to 1000 urn, and may optionally contain, in addition to the fillers already mentioned, processing or vulcanising aids known in the rubber processing industry such as zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticisers, anti-ageing agents which protect against heat, light or oxygen 15 and ozone, reinforcing resins, flame retardants such as e.g. Al(OH)3 and Mg(OH)2, pigments, various cross-linking chemicals and optionally sulfur, in concentrations which are conventionally used in the rubber industry. These are preferably added to the suspensions which contain fillers before precipitating the rubber powder, naturally taking account of their pH stability. According to the invention, finely divided rubber powders which contain siliceous fillers which are modified with organosilicon compounds and/or carbon black can be prepared which can be used in this form in combination with any common types of rubber as a reinforcing filler. Powdered rubbers which contain silanised silicas are characterised in particular by high storage stability, are easy to process without the noticeable emission of alcohol and lead to exceptional rubber-engineering characteristics for the vulcanisates prepared when they are used. Using the present invention, a new development has been produced which includes the provision of a polymer-bonded, optionally modified, filler in the rubber processing industry. In contrast to classical mixing processes, degrees of filling with highly active silica fillers of > 250 phr, in particular between 4 00 and 1250 phr, can be achieved only with the aid of powdered rubber technology. This means that after precipitation each filler particle is still surrounded by a thin layer of rubber, despite the high degree of filling. In this case, we can refer to coating the filler with the polymer. A non-dusty filler is obtained in this way, and this is optionally provided with a water repellent coating and can be used in the classical mixing process and can be incorporated into any rubber. 16 In the following examples, the ability to perform the invention and the advantages of the present invention are explained without restricting it to the features described there. Raw materials used during preparation E - SBR Emulsion styrene/butadiene latex with a 23.5 % styrene concentration (BSL) Si 69 Bis(triethoxysilylpropyl)tetrasulfane (Degussa-Huls AG) Si 7 5 Bis(triethoxysilylpropyl)disulfane (Degussa-Hiils AG) Ultrasil 7000 precipitated sulfur with a N2 surface area (BET) of 175 m2/g and improved dispersion properties (Degussa-Hiils AG) , dried or as filter cakes Marlipal Emulsifier: fatty alcohol polyethylene 1618/25 glycol ether 17 Example I Preparing a rubber powder using E - SBR, Ultrasil 7000 and Si 69 (EPB I) A stable suspension is prepared from 22.5 kg of 7000 filter cakes, 1.8 kg of Si 69 and 0.225 kg of Marlipal 1618/25 in 272 1 of water, with stirring. Then this suspension is mixed with 13.62 kg of a 21 % strength E-SBR latex emulsion, E - SBR - 1500, with vigorous stirring and then the pH is lowered to a value of 5.0 by adding a 10 % strength A12(SO4)3 solution. After the precipitation process, mechanical separation of the greater amount of the water is performed, followed by a drying stage down to a residual moisture content of Example II Preparing a powdered rubber using E - SBR, Ultrasil 7000 filter cakes and Si 7 5 A stable suspension of 103 kg of 7000 filter cakes, 1.8 kg of Si 75 and 0.225 kg of Marlipal 1618/25 in 272 1 water is prepared, with stirring. Then the suspension is mixed with 13.71 kg of a 21 % strength E-SBR latex emulsion with vigorous stirring and then the pH is lowered to a final value of 5.0 by adding a 10 % strength A12(SO4)3 solution. After the precipitation process, mechanical separation of the water is performed, followed by a drying stage down to a residual moisture content of 18 The powdered product contains 100 parts of E-SBR, 750 parts of silica, 8 parts of Si 75, with respect to 100 parts of silica. The reaction is performed in such a way that the silane is fully bonded to the silica. The following products were used in a rubber-engineering application: Chemicals E-SBR 1500 styrene/butadiene rubber with a concentration of 23.5 % of styrene 10 Naftolen ZD arom. mineral oil plasticiser EPB I powdered rubber, consisting of 100 parts of E-SBR 1500, 750 parts of Ultrasil 7000 reacted with 8 parts of Si 69 with respect to 100 parts of silica 15 6 PPD N-(l,3-dimethylbutyl)N-phenyl-p- phenylene diamine CBS benzothiazyl-2-cyclohexylsulfenamide DPG diphenylguanidine TBZTD tetrabenzylthiuram disulfide 20 Buna VSL 5025-1 oil-extended solution-SBR with 50 % of 1,2-vinyl units and 25 (sic) styrene (Bayer AG) Buna CB 24 butadiene rubber (cis > 96 %) {Bayer AG} The following rubber engineering test methods were used: 19 Mooney viscosity DIN 53 523/3 Tensile trial DIN 53 504 Modulus, 300 % DIN 53 504 Modulus, 300/100 % Shore hardness DIN 53 505 Dispersion (Philips) ISO/DIS 11 345 (sic) Extension at break DIN 53 504 Vulcameter curve DIN 53 529 Ball rebound ASTM D 5308 Viscoelastic DIN 53 513 properties Example A A comparison of the rubber engineering characteristics of the product according to the invention (manufacturing example 1) against a standard mixture Formulation 20 Mixing process Stage Internal mixer : GK 1.5 E; volume 1.5 1; friction 1 : 1; punch 5.5 bar 21 Stage Internal mixer: GK 1.5 E; volume 1.5 1; Friction 1: 1 punch 5.5 bar; RPM 40; degree of filling 0.53; Throughput temperature 60 % (sic) Both mixtures 0 - 3' Mix batch from stage 1 and discharge Discharge temperature: ~ 135°C Stage Internal mixer : GK 1.5 E; volume 1.5 1; Friction 1 : 1; Punch 5.5 bar; RPM 30; degree of filling 0.52; Throughput temperature 60°C Both mixtures 0 - 1.5 Batch from stage 2, accelerator, sulfur 1.5' Discharge and draw out a sheet Rubber engineering data Vulcanisation: 165 °C, 15 22 23 WE CLAIM: 1. A process for preparing rubber powder containing one or more oxidic or silicatic fillers, in particular a precipitated silica, in an amount of > 250 phr to 5000 phr in the case of a synthetic filler of this kind, or in an amount of > 350 phr to 5000 phr in the case of a natural filler, the surface thereof being modified, during preparation, with one or more organosilicon compounds of the general formulae in which B is -SCN, -SH, -Cl or NH2 (if q = 1} or Sx (if q = 2) R and R1 are each an alkyl group having from 1 to 4 carbon atoms, branched or not branched, or the phenyl radical, it being possible for all radicals R and R1 to have in each case the same definition or a different definition, preferably an alkyl group, n is 0, 1 or 2, Alk is a divalent straight or branched hydrocarbon radical having from 1 to 6 carbon atoms, m is 0 or 1, Ar is an arylene radical having from 6 to 12 carbon atoms, p is 0 or 1, with the proviso that p, m and n are not simultaneously 0, x is a number from 2 to 8, - 24 - Alkyl is a monovalent straight or branched saturated hydrocarbon radical having from 1 to 20 carbon atoms, preferably from 2 to 8 carbon atoms, Alkenyl is a monovalent straight or branched unsaturated hydrocarbon radical having from 2 to 20 carbon atoms, preferably from 2 to 8 carbon atoms, alone or in combination with carbon black in an amount of > 250 phr to 5000 phr, the total amount of the fillers not exceeding 5000 phr. 2. A process for preparing a finely divided, filler-containing rubber (rubber powder) according to claim 1 by precipitation from a water-containing mixture containing filler in suspension form, 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 Table, characterized in that a) first a filler suspension having a suspension density of from 0.5% to 10%, in particular from 5% to 7%, based on the solids, is prepared from a silicatic compound, alone or in combination with carbon black and water, with stirring, the solids particles being ground down (deagglomerated), if desired, beforehand, by means of a suitable mill, additionally, if desired, a compound which forms hydrogen bonds, such as a polyalcohol or polyvalent amine, is added in an amount of from 0.5 to 10 parts, based on 100 parts of the filler, to the suspension, and, if desired, the suspension is heated to a temperature within the range from 2 5 to 95°C; b) subsequently one or more organosilicon compounds of the formulae (I) to (III) containing at least one alkoxy group are mixed, in solution in water or emulsified directly or, if desired, in the presence of a surface-active substance in water, - 25 - with the stated aqueous suspension of this filler or a mixture thereof with a carbon black, at a temperature from 10 to 60°C, preferably at room o temperature, with stirring, c) this suspension thus prepared is mixed with the polymer latex, the polymer emulsion or the polymer solution, the pH of this mixture is lowered to a pH of from 7 to 4, preferably, from 6.5 to 4.5, using an acid or the aqueous solution of one of the abovementioned salts, in particular a Lewis acid, and the rubber present in the mixture is precipitated together with the filler modified, if desired, by means of the stated organosilicon compound, d) the precipitated, filler-containing rubber powder is separated off by measures which are known per se, and, if desired, is washed free of acid, and e) the filler thus obtained is dried and, if desired, granulated. 3. A process according to claim 2, characterized in that following step c) an aqueous polymer emulsion containing polystyrene, polystyrene-butadiene copolymers of various composition, polyethylene, polypropylene or polyvinyl acetate of various chemical constitution is added in an amount of from 0.5 to 10 phr, in particular from 1 to 4 phr, to the reaction mixture. 4. A process according to claim 2, characterized in that the filler concentration in the reaction mixture is adjusted to: a) > 250 phr, in particular from 400 phr to 5000 phr, when using synthetic silica and/or the filter cake obtained during its preparation, b) > 350 phr, in particular from 400 phr to 1250 phr, when using a natural silicatic filler, as it is or in the form of the slurry obtained during work-up, or - 26 - c) for carbon black, individually or in a mixture with the aforementioned fillers, > 250 to 5000 phr. 5. A process according to any of claims 2 to 4, characterized in that a nonionic, cationic or anionic surfactant is used as a surface-active substance. 6. A process - according to one or more of the preceding claims, characterized in that prior to the precipitation step up to 5 parts by weight of an alkali metal silicate solution, preferably waterglass with an Na2O:SiO2 ratio of from 2:1 to 1:4, based on 100 parts of rubber, are added to the suspension. 7. A process according to one or more of the preceding claims, characterized in that precipitated silica is used in the form of the filter cake obtained during its preparation. 8. A process according to one or more of the preceding claims, characterized in that the suspension according to claim 2, section a) is prepared using a silicatic filler premodif ied with one or more organosilicon compounds according to the formulae (I) to (III). 9. A process according to claim 2, characterized in that one or more of the following processing aids or vulcanizing aids are added to the suspension of the filler, if desired after it has been mixed with the polymer (rubber) but prior to the precipitation operation (section c): zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticizers, - 27 - anti-ageing heat or light stabilizers or reinforcing resins, flame retardants (Al(OH)3, Mg(OH)2) , if desired, sulphur, at a concentration customary in the rubber industry. 10. A rubber prepared according to one or more of the preceding claims, having a particle spectrum from 25 m to 3000 m or, in granulated form, from 2 to 10 mm. 11. A process for preparing a vulcanizable rubber mixture, characterized in that rubber prepared according to one or more of the present claims is incorporated as a filler, in an amount customary for fillers, into the corresponding rubber, with the addition, if desired, of further necessary, known processing aids and vulcanizing aids. The invention provides rubber powders with a high degree of 5 filling which are obtained by precipitating water-containing suspensions which contain fillers and rubber emulsions or rubber solutions and their use to prepare vulcanisable rubber mixtures.

Full Text

1A
Rubber powders which contain large amounts of fillers, a process for preparing them and their use
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 that way and their use.
The production of powdered rubbers containing small amounts of filler (rubber powders) 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 (inter alia 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 these powdered products of this type is produced by the processing technique in the rubber industry. There, rubber mixtures are produced with high time, energy and staffing requirements. The main reason for this is that the raw material rubber is present in the form of bales and the other constituents of the vulcanisable mixtures have to be admixed in several process stages on rollers or internal mixers.
The rolling resistance (savings in petrol) and wet-sliding
behaviour have been improved since the start of the 90s by the use of highly active precipitated silicas combined with bifunctional organosilanes in the tread mixtures. [DE-OS 43 34 201.9 and DE-OS 44 27 137.9],

2
Bis-(triethoxysilylpropyl)tetrasulfane (TESPT) is the most important representative 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 silanisation 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 comprises the raw materials suppliers performing the silanisation 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 and primarily for technical reasons.
EP 0 442 1433 Bl 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 in- the rubber-engineering characteristics.

3
Another possibility for preparing pre-modified silicas is wet silanisation. EP 0 177 674 provides a process in which silica and silane are homogenised with the aid of a special emulsifier and then the reaction is performed at elevated temperature with simultaneous drying of the product. In US-PS 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-polymerise during the course of 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 silanisation in water, in accordance with EP 0 177 67 4, is so happens that silica particles agglomerate strongly in water and therefore that particle sizes suitable for the silanisation 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 fact that unreacted proportions of silane are one reason for the ageing behaviour of silanised silicas, especially those silanised with TESPT, makes a new approach to the preparation of pre-modified products understandable. 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 lowering the pH to a region between 2 and 5.

A
Rapid and comprehensive reaction of the silane with the silica takes place_ in this pH region.
As shown in practice, the silane tends to self-polymerise 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 summarise, the following problems in particular need to be avoided in their entirety or solved.
Reducing the agglomeration behaviour of silica during silanisation
Avoiding self-polymerisation of the silane
Complete reaction of the silane with the siliceous
surface
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, this powder and the use thereof.
The invention provides a process for preparing finely
divided rubbers (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 chosen from groups II a, II b, III a and
VIII in the Periodic System of Elements, which is
characterised in that
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

5
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 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 the
polymer latex, polymer emulsion or polymer solution, the
pH of this mixture is lowered with an acid or 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 using methods known
per se and
e) the filler-containing rubber is dried.
It is also possible to use siliceous fillers already pre-modified with the organosilicon compounds mentioned above.
Hexanetriol, glycol, diethylene glycol, triethylene glycol or polywax 4000 {a long-chain hydrocarbon) are preferably

6
used as polyols. o-toluyl-biguanidine, hexa-K, DOTG (di-o-toluylguanidine), DPG (diphenylguanidine) or TEA (triethanolamine), for example, are suitable as polyvalent amines.
In a special embodiment, an aqueous plastics emulsion containing polystyrene, polystyrene/butadiene copolymers of different compositions, polyethylenes, polypropylenes or polyvinyl acetate of different chemical constitutions is also added to the powdered rubber found in the aqueous medium, prior to separating and drying, in amounts of 0.5 -10 phr, in particular 1-4 phr. These form a coating during the drying process which prevents the absorption of water.
The ratios by weight in the suspension are adjusted so that a powdered rubber with a filler content of > 250 phr, preferably = 400 phr precipitates out.
The drying process is advantageously performed in a dryer with a gas inlet temperature of 130 to 170°C and a gas outlet temperature of 50 to 70°C. The temperature of the product should not exceed 40 to 80°C. The duration and extent of the precipitation process, which depends on the pH and the concentration of filler, may readily be established by a series of measurements.
The products are produced as a free-flowing powder without further additional measures to prevent adhesion. Quantitative determination of the sulfur atoms contained in the silane in accordance with formula (I) before and after extraction of the powdered rubber with hot ether show, for example, that the silane used for modification purposes is present virtually fully chemically bonded to the silica.
As further fillers, carbon blacks known from the rubber industry are optionally used, preferably in a finely divided (fluffy) form, which generally have an average particle

7
diameter, without mechanical treatment, of 1 to 9 m, preferably 1 to 8 m, before they are suspended.
Precipitated silicas may advantageously be used in the form of a salt-free washed filter cake.
Suitable metal salts are those which arise from elements in groups IIa, IIb, IIIa, and VIII in the Periodic System of Elements. This group classification corresponds to that in the old IUPAC recommendation (see: Periodisches System der Elemente, Verlag Chemie, Weinheim, 1985). Typical representatives are magnesium chloride, zinc sulfate, aluminium chloride, aluminium sulfate, iron chloride, iron sulfate, cobalt nitrate and nickel sulfate, wherein salts of aluminium are preferred. Aluminium sulfate and other Lewis acids are particularly preferred. The salts are used in an amount of 0.1 to 6.5 parts by weight per 100 parts by weight of rubber.
Additional mineral acids such as e.g. sulfuric acid, phosphoric acid and hydrochloric acid are optionally used to adjust to the desired pH, wherein sulfuric acid is particularly preferred. However, carboxylic acids such as e.g. formic acid and acetic acid may also be used.
The amount of acid is governed by the type and amount of water-soluble metal salt, the filler, the organosilane used and the optionally present alkali metal silicate. It can readily be determined by some orienting trial runs. The solids content of the latices used is generally 20 to 25 wt.%. The solids content of rubber solutions is generally 3 to 20 wt.% and that of rubber emulsions is generally 5 to 60 wt.%.
The process according to the invention may be performed either batchwise or continuously. The precipitated rubber powder is advantageously first separated from the majority

8
of the water. This can be achieved, for example, by using a centrifuge, a filter press or a decanter. Then the product is dried to a residual moisture content of Rubber powders according to the invention, which are also provided by the invention, are generally prepared, if siliceous or oxidic fillers, in particular precipitated silicas, are used, by using one or more organosilicon compounds of the general formulae

in which
B: represents -SCN, -SH -Cl, NH2 (when q = 1) or -Sx- (when q = 2)
R and R1: represent an alkyl group with 1 to 4 carbon atoms, which is branched or unbranched, or a phenyl group, wherein all the groups R and R are identical or different and preferably represent an alkyl group,
R: represent a C1-C4-alkyl or -C1-C4-alkoxy group,
which is branched or unbranched

n:

is 0, 1 or 2,

9
Alk: represents a divalent straight or branched hydrocarbon group with 1 to 6 carbon atoms,
m: 0 or 1
Ar: represents an arylene group with 6 to 12 carbon atoms
p: is 0 or 1, with the proviso that p, m and n
are not simultaneously 0,
x: a number from 2 to 8,
Alkyl: represents a monovalent straight or branched
saturated hydrocarbon group with 1 to 20 carbon atoms, preferably 2 to 8 carbon atoms,
Alkenyl: represents a monovalent straight or branched unsaturated hydrocarbon group with 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms.
These compounds are generally used in the form of solutions, if they are water-soluble, or emulsions, wherein the solutions or emulsions may also be formed in the presence of the suspension of siliceous fillers or their mixtures with carbon black.
The emulsions or solutions are preferably prepared at room temperature. However, temperatures of 10 to 60°C are also suitable. The concentration of the organosilicon compound(s) in the solutions or suspension used is 0.5 to 20 wt.%, preferably 5 to 12 wt.%, with respect to the total amount of siliceous filler used.
The pH of the emulsion or solution, like the pH of the filler suspension after admixing the emulsion, is in the weakly acid or weakly alkaline region, but is preferably about 7.

10
The expression water-insoluble used is understood to mean that:
after mixing the organosilicon compound (without a surface active substance) with the suspension of the filler, clear solution is not formed around the filler particles in the desired pH and concentration region. Rather, the separate phases remain, these consisting of water, solid and organosilicon compound(s). The oligosulfidic organosilanes in accordance with general formula (I) cited above are known per se and can be prepared by known processes. Examples of preferably used organosilanes are e.g. bis(trialkoxysilyl-alkyl)oligosulfides which can be prepared according to US-PS 3 842 111 such as bis (trimethoxy-, triethoxy-, trimethoxy- ethoxy-, tripropoxy-, tributoxy-, tri-i-propoxy and tri-i-butoxy-silyl-methyl)-oligosulfides, to be precise in particular the di-, tri-, tetra-, penta-, hexasulfides etc., also bis-(2-trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy- and -tri-n- and -i-butoxy-ethyl)-oligosulfides, to be precise in particular the di-, tri-, tetra-, penta-, hexasulfide etc., furthermore bis-(3-trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy-, tri-n-butoxy- and tri-i-butoxysilyl-propyl)-oligosulfides, to be precise again the di-, tri-, tetrasulfides etc. up to octasulfides, there again the corresponding bis-(3-trialkoxy-silylisobutyl)-oligosulfides and the corresponding bis-(4-trialkoxysilylbutyl)-oligosulfides. Of these selected, relatively simply constructed organosilanes of the general formula I, preferred compounds are again the bis-(3-trimethoxy-, triethoxy- and tripropoxysilylpropyl)-oligosulfides, to be precise the di-, tri-, tetra- and pentasuIfides, in particular triethoxy compounds with 2, 3 or 4 sulfur atoms and their mixtures. Alk in general formula I represents a divalent, straight or branched hydrocarbon group with 1 to 6 carbon atoms, preferably a saturated

11
alkylene group with a straight carbon chain with 1 to 4 carbon atoms.
Silanes with the following structural formula are also especially suitable:

and their methoxy analogues, which can be prepared in accordance with DE-AS 25 58191. These compounds are not water-soluble.
Surface active substances which are generally used, and in this case are preferred, are non-ionogenic, cationic and anionic surfactants, the concentration of these in the emulsion is 1 to 15 wt.%, preferably 2 to 10 wt.%, with respect to the amount of organosilane compounds.
Examples of these types of surfactants are alkylphenol polyglycol ethers,
alkyl polyglycol ethers, polyglycols,
alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyltrimethylammonium salts, alkylbenzene sulfonates, alkyl hydrogen sulfates, alkyl sulfates.

12
The natural or precipitated oxidic or siliceous fillers to be modified, also used as a mixture of two or more of these fillers, are fillers known per se in rubber technology. An essential prerequisite for their suitability is the presence of OH groups at the surface of the filler particles which can react with alkoxy groups in the organosilicon compounds. They are oxidic and siliceous fillers which are compatible with rubbers and have the degree of fineness demanded and known for this use.
Suitable natural silicates are in particular kaolin or clays. However, kieselguhr or diatomaceous earths may also be used.
Oxidic fillers which may be mentioned by way of example are aluminium oxide, aluminium hydroxide or trihydrate and titanium dioxide.
"Modified fillers" in this connection means that the organosilicon compounds are bonded either by chemical reaction (OH groups) or adsorptively at the surface.
Adsorptively bonded groups are converted into chemically bonded groups at the latest during the drying stage.
The emulsion or solution is mixed with the filler suspension in amounts such that the concentration of organosilicon compound is 0.5 to 20 wt.%, preferably 5 to 12 wt.%, with respect to the amount of filler. The modified filler contains 0.5 to 20 wt.%, preferably 0.5 to 12 wt.% of organosilicon compound, with respect to the dry filler.
They are particularly suitable for use in vulcanisable and mouldable rubber mixtures.
A salt-free washed filter cake obtained from silica precipitation is advantageously used for the process according to the invention.

13
Also suitable are suspensions such as are obtained during the working up of natural fillers such as clays.-
An energy-consuming drying step is saved in this way, as compared with the prior art.
The silicas used are known from the rubber sector.
They generally have a N2 surface area, determined by the well-known BET method, of 35 to 700 m2/g, a CTAB surface area of 30 to 500 m2/g and a DBP index of 150 to 400 ml/lOOg.
The product according to the invention contains these silicas in an amount of > 250 to 5000 parts, in particular 400 to 1000 parts, with respect to 100 parts of rubber.
If they are white, natural fillers, such as clays or silica chalks with a N2 surface area of 2 to 35 m2/g, they are preferably used in an amount of 400 to 1250 parts, with respect to 100 parts of rubber.
Filler-containing rubber powders may also be prepared which contain siliceous fillers, in particular silicas, and carbon black as a mixture or which contain only carbon black. The total amount of filler may then be between > 250 and 5000 phr, in particular up to 2000 phr. The proportion of silica, if present, is generally > 250 phr to 1250 phr.
For degrees of filling of > 1000 phr, carbon black is chosen in particular as the filler; carbon black is generally used at a rate of > 250 to 1000 phr.
Carbon blacks which are generally used in rubber processing are especially suitable.
These include furnace blacks, channel blacks and lamp blacks with an iodine absorption index of 5 to 1000 m2/g, a CTAB

14
index of 15 to 600 m2/g, a DBP adsorption of 30 to
400 ml/100 g and a 24 M4 DBP index of 50 to 370 ml/100 g.
The following species have proved useable as types of rubber and can be prepared as aqueous emulsions, separately or as mixtures with each other:
Natural rubber, emulsion SBR with a styrene proportion of 10 to 50 %, butyl/acrylonitrile rubber.
Butyl rubber, terpolymers of ethylene, propylene (EPM) and non-conjugated dienes (EPDM), butadiene rubbers, SBR, prepared by the solution polymerisation process, with styrene contents of 10 to 25 %, and also concentrations of 1,2-vinyl constituents of 20 to 55 % and isoprene rubber, in particular 3,4-polyisoprene.
Emulsion and solution SBR are particularly suitable.
In the case of polymers prepared by the solution process,
special precautions have to be taken during processing due to the presence of solvent.
Apart from the rubbers mentioned above, the following elastomers are suitable, individually or as a mixture:
Carboxyl rubber, epoxide rubber, trans-polypentenamers, halogenated butyl rubber, rubbers made from 2-chloro-butadiene, ethylene/vinyl acetate copolymers, epichlorohydrins, optionally also modified natural rubber such as e.g. epoxidised species. Rubber powders according to the invention generally have a particle size of 25 m to 3000 m, in particular 500 m to 1000 urn, and may optionally contain, in addition to the fillers already mentioned, processing or vulcanising aids known in the rubber processing industry such as zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticisers, anti-ageing agents which protect against heat, light or oxygen

15
and ozone, reinforcing resins, flame retardants such as e.g. Al(OH)3 and Mg(OH)2, pigments, various cross-linking chemicals and optionally sulfur, in concentrations which are conventionally used in the rubber industry. These are preferably added to the suspensions which contain fillers before precipitating the rubber powder, naturally taking account of their pH stability.
According to the invention, finely divided rubber powders which contain siliceous fillers which are modified with organosilicon compounds and/or carbon black can be prepared which can be used in this form in combination with any common types of rubber as a reinforcing filler. Powdered rubbers which contain silanised silicas are characterised in particular by high storage stability, are easy to process without the noticeable emission of alcohol and lead to exceptional rubber-engineering characteristics for the vulcanisates prepared when they are used.
Using the present invention, a new development has been produced which includes the provision of a polymer-bonded, optionally modified, filler in the rubber processing industry.
In contrast to classical mixing processes, degrees of filling with highly active silica fillers of > 250 phr, in particular between 4 00 and 1250 phr, can be achieved only with the aid of powdered rubber technology. This means that after precipitation each filler particle is still surrounded by a thin layer of rubber, despite the high degree of filling. In this case, we can refer to coating the filler with the polymer. A non-dusty filler is obtained in this way, and this is optionally provided with a water repellent coating and can be used in the classical mixing process and can be incorporated into any rubber.

16
In the following examples, the ability to perform the invention and the advantages of the present invention are explained without restricting it to the features described there.
Raw materials used during preparation
E - SBR Emulsion styrene/butadiene latex with a 23.5 % styrene concentration (BSL)
Si 69 Bis(triethoxysilylpropyl)tetrasulfane
(Degussa-Huls AG)
Si 7 5 Bis(triethoxysilylpropyl)disulfane
(Degussa-Hiils AG)
Ultrasil 7000 precipitated sulfur with a N2 surface area
(BET) of 175 m2/g and improved dispersion properties (Degussa-Hiils AG) , dried or as filter cakes
Marlipal Emulsifier: fatty alcohol polyethylene 1618/25 glycol ether

17 Example I
Preparing a rubber powder using E - SBR, Ultrasil 7000 and Si 69 (EPB I)
A stable suspension is prepared from 22.5 kg of 7000 filter cakes, 1.8 kg of Si 69 and 0.225 kg of Marlipal 1618/25 in 272 1 of water, with stirring.
Then this suspension is mixed with 13.62 kg of a 21 % strength E-SBR latex emulsion, E - SBR - 1500, with vigorous stirring and then the pH is lowered to a value of 5.0 by adding a 10 % strength A12(SO4)3 solution.
After the precipitation process, mechanical separation of the greater amount of the water is performed, followed by a drying stage down to a residual moisture content of Example II
Preparing a powdered rubber using E - SBR, Ultrasil 7000 filter cakes and Si 7 5
A stable suspension of 103 kg of 7000 filter cakes, 1.8 kg of Si 75 and 0.225 kg of Marlipal 1618/25 in 272 1 water is prepared, with stirring.
Then the suspension is mixed with 13.71 kg of a 21 % strength E-SBR latex emulsion with vigorous stirring and then the pH is lowered to a final value of 5.0 by adding a 10 % strength A12(SO4)3 solution. After the precipitation process, mechanical separation of the water is performed, followed by a drying stage down to a residual moisture content of
18
The powdered product contains 100 parts of E-SBR, 750 parts of silica, 8 parts of Si 75, with respect to 100 parts of silica. The reaction is performed in such a way that the silane is fully bonded to the silica.
The following products were used in a rubber-engineering
application:
Chemicals
E-SBR 1500 styrene/butadiene rubber with a
concentration of 23.5 % of styrene
10 Naftolen ZD arom. mineral oil plasticiser
EPB I powdered rubber, consisting of 100
parts of E-SBR 1500, 750 parts of Ultrasil 7000 reacted with 8 parts of Si 69 with respect to 100 parts of silica
15 6 PPD N-(l,3-dimethylbutyl)N-phenyl-p-
phenylene diamine
CBS benzothiazyl-2-cyclohexylsulfenamide
DPG diphenylguanidine
TBZTD tetrabenzylthiuram disulfide
20 Buna VSL 5025-1 oil-extended solution-SBR with 50 % of
1,2-vinyl units and 25 (sic) styrene (Bayer AG)
Buna CB 24 butadiene rubber (cis > 96 %)
{Bayer AG}
The following rubber engineering test methods were used:

19
Mooney viscosity DIN 53 523/3
Tensile trial DIN 53 504
Modulus, 300 % DIN 53 504
Modulus, 300/100 %
Shore hardness DIN 53 505
Dispersion (Philips) ISO/DIS 11 345 (sic)
Extension at break DIN 53 504
Vulcameter curve DIN 53 529
Ball rebound ASTM D 5308
Viscoelastic DIN 53 513
properties
Example A
A comparison of the rubber engineering characteristics of
the product according to the invention (manufacturing
example 1) against a standard mixture
Formulation

20
Mixing process
Stage
Internal mixer : GK 1.5 E; volume 1.5 1; friction 1 : 1; punch 5.5 bar

21
Stage
Internal mixer: GK 1.5 E; volume 1.5 1; Friction 1: 1 punch 5.5 bar; RPM 40; degree of filling 0.53;
Throughput temperature 60 % (sic) Both mixtures
0 - 3' Mix batch from stage 1 and discharge Discharge temperature: ~ 135°C
Stage
Internal mixer : GK 1.5 E; volume 1.5 1; Friction 1 : 1; Punch 5.5 bar; RPM 30; degree of filling 0.52; Throughput temperature 60°C
Both mixtures
0 - 1.5 Batch from stage 2, accelerator, sulfur
1.5' Discharge and draw out a sheet

Rubber engineering data
Vulcanisation: 165 °C, 15

22

23
WE CLAIM:
1. A process for preparing rubber powder containing one or more oxidic or silicatic fillers, in particular a precipitated silica, in an amount of > 250 phr to 5000 phr in the case of a synthetic filler of this kind, or in an amount of > 350 phr to 5000 phr in the case of a natural filler, the surface thereof being modified, during preparation, with one or more organosilicon compounds of the general formulae

in which
B is -SCN, -SH, -Cl or NH2 (if q = 1} or Sx (if
q = 2) R and R1 are each an alkyl group having from 1 to 4
carbon atoms, branched or not branched, or
the phenyl radical, it being possible for all
radicals R and R1 to have in each case the
same definition or a different definition,
preferably an alkyl group, n is 0, 1 or 2, Alk is a divalent straight or branched
hydrocarbon radical having from 1 to 6 carbon
atoms,
m is 0 or 1, Ar is an arylene radical having from 6 to 12
carbon atoms, p is 0 or 1, with the proviso that p, m and n
are not simultaneously 0, x is a number from 2 to 8,

- 24 -
Alkyl is a monovalent straight or branched saturated hydrocarbon radical having from 1 to 20 carbon atoms, preferably from 2 to 8 carbon atoms,
Alkenyl is a monovalent straight or branched unsaturated hydrocarbon radical having from 2 to 20 carbon atoms, preferably from 2 to 8 carbon atoms,
alone or in combination with carbon black in an amount
of > 250 phr to 5000 phr, the total amount of the
fillers not exceeding 5000 phr.
2. A process for preparing a finely divided, filler-containing rubber (rubber powder) according to claim 1 by precipitation from a water-containing mixture containing filler in suspension form, 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 Table, characterized in that
a) first a filler suspension having a suspension
density of from 0.5% to 10%, in particular from 5%
to 7%, based on the solids, is prepared from a
silicatic compound, alone or in combination with
carbon black and water, with stirring, the solids
particles being ground down (deagglomerated), if
desired, beforehand, by means of a suitable mill,
additionally, if desired, a compound which forms
hydrogen bonds, such as a polyalcohol or
polyvalent amine, is added in an amount of from
0.5 to 10 parts, based on 100 parts of the filler,
to the suspension, and, if desired, the suspension
is heated to a temperature within the range from
2 5 to 95°C;
b) subsequently one or more organosilicon compounds
of the formulae (I) to (III) containing at least
one alkoxy group are mixed, in solution in water
or emulsified directly or, if desired, in the
presence of a surface-active substance in water,

- 25 -
with the stated aqueous suspension of this filler or a mixture thereof with a carbon black, at a temperature from 10 to 60°C, preferably at room o temperature, with stirring,
c) this suspension thus prepared is mixed with the
polymer latex, the polymer emulsion or the polymer
solution, the pH of this mixture is lowered to a
pH of from 7 to 4, preferably, from 6.5 to 4.5,
using an acid or the aqueous solution of one of
the abovementioned salts, in particular a Lewis
acid, and the rubber present in the mixture is
precipitated together with the filler modified, if
desired, by means of the stated organosilicon
compound,
d) the precipitated, filler-containing rubber powder
is separated off by measures which are known per
se, and, if desired, is washed free of acid, and
e) the filler thus obtained is dried and, if desired,
granulated.
3. A process according to claim 2, characterized in
that following step c) an aqueous polymer emulsion containing polystyrene, polystyrene-butadiene copolymers of various composition, polyethylene, polypropylene or polyvinyl acetate of various chemical constitution is added in an amount of from 0.5 to 10 phr, in particular from 1 to 4 phr, to the reaction mixture.
4. A process according to claim 2, characterized in
that the filler concentration in the reaction mixture
is adjusted to:
a) > 250 phr, in particular from 400 phr to 5000 phr,
when using synthetic silica and/or the filter cake
obtained during its preparation,
b) > 350 phr, in particular from 400 phr to 1250 phr,
when using a natural silicatic filler, as it is or
in the form of the slurry obtained during work-up,
or

- 26 -
c) for carbon black, individually or in a mixture with the aforementioned fillers, > 250 to 5000 phr.
5. A process according to any of claims 2 to 4,
characterized in that a nonionic, cationic or anionic
surfactant is used as a surface-active substance.
6. A process - according to one or more of the
preceding claims, characterized in that prior to the
precipitation step up to 5 parts by weight of an alkali
metal silicate solution, preferably waterglass with an
Na2O:SiO2 ratio of from 2:1 to 1:4, based on 100 parts
of rubber, are added to the suspension.
7. A process according to one or more of the
preceding claims, characterized in that precipitated
silica is used in the form of the filter cake obtained
during its preparation.
8. A process according to one or more of the
preceding claims, characterized in that the suspension
according to claim 2, section a) is prepared using a
silicatic filler premodif ied with one or more
organosilicon compounds according to the formulae (I)
to (III).
9. A process according to claim 2, characterized in
that one or more of the following processing aids or
vulcanizing aids are added to the suspension of the
filler, if desired after it has been mixed with the
polymer (rubber) but prior to the precipitation
operation (section c):
zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticizers,

- 27 -
anti-ageing heat or light stabilizers or
reinforcing resins,
flame retardants (Al(OH)3, Mg(OH)2) ,
if desired, sulphur, at a concentration customary in
the rubber industry.
10. A rubber prepared according to one or more of the
preceding claims, having a particle spectrum from 25 m
to 3000 m or, in granulated form, from 2 to 10 mm.
11. A process for preparing a vulcanizable rubber
mixture, characterized in that rubber prepared
according to one or more of the present claims is
incorporated as a filler, in an amount customary for
fillers, into the corresponding rubber, with the
addition, if desired, of further necessary, known
processing aids and vulcanizing aids.
The invention provides rubber powders with a high degree of 5 filling which are obtained by precipitating water-containing suspensions which contain fillers and rubber emulsions or rubber solutions and their use to prepare vulcanisable rubber mixtures.

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Patent Number

206362

Indian Patent Application Number

00295/CAL/2000

PG Journal Number

17/2007

Publication Date

27-Apr-2007

Grant Date

27-Apr-2007

Date of Filing

22-May-2000

Name of Patentee

PKU PULVERKAUTSCHUK UNION GMBH

Applicant Address

PAUL-BAUMANN-STRASSE 1, DE-45764 MARL,

Inventors:

#	Inventor's Name	Inventor's Address
1	GORL UDO	DORSTENER STRASSE 15A, DE -45657 RECKLINGHAUSEN,
2	TREMPLER THOMAS	BURGSTRASSE 17, DE-63477 MAINTAL,
3	STOBER REINHARD	BORNWIESENWEG 22, DE-63594 HASSELROTH,
4	ERNST UWE	OPHOFFSTRASSE 22B, DE-45768 MAR1,

PCT International Classification Number

C08 J 3/215

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19924366.2	1999-05-27	Germany