Title of Invention

"PRODUCTION OF FILLED RUBBER POWDER"

Abstract

Finely divided powdered rubbers containing filter which remain free-flowing even after exposure to mechanical stresses and to a process for the production thereof, in which the rubber powder is obtained in two precipitation steps, and to the use of these powdersfor the production of vulcanizable rubber compounds. The fillers used, which are both precipitated silicas and carbon blacks known in the rubber art, are surface-modifed by organosilicon compounds.

Full Text

1A- Pulverulent rubber powder containing modified fillers, process for the production thereof and use thereof This invention relates to pulverulent rubbers containing fillers modified with organosilicon compounds, to a process for the production thereof and to the use thereof. Numerous publications have appeared relating to the aim and purpose of using powdered rubbers as well as to possible processes for the production thereof. The explanation for the interest in pulverulent rubbers is readily evident from the processing techniques used in the rubber industry, where rubber compounds are produced in time-consuming processes with elevated inputs of energy and labour. The principal reason for this is that the rubber raw material is in bale form. Comminuting the bale, intimate mixing with fillers, mineral oil plasticisers and vulcanisation auxiliaries proceeds in 'roll mills or in internal mixers in two or more processing stages. The compound is generally stored between the stages. Downstream from the internal mixers or roll mills are extruder/pelletisers or extruder/roller dies. The only way out of this highly complex rubber processing method is to use an entirely novel processing technology. The use of free-flowing rubber powders has accordingly long been discussed as such powders would make it possible to process rubber compounds simply and rapidly in the same manner as pulverulent thermoplastics. DE-PS 2822 148 discloses a process for the production of a pulverulent rubber containing fillers. According to this patent, an aqueous filler emulsion is added to a rubber latex, rubber solution or an aqueous 2 emulsion of a rubber and the desired rubber powder is precipitated. Variants for preventing the resultant filler contents being determined by grain size, as occurs when this process is used, have been filed and, as DE-PS 3723 213 and DE-PS 3723 214, are part of the prior art. According to DE-PS 3723213, in a two-stage process, a quantity of >50% of the filler is initially incorporated into the rubber powder particles. In the second stage, the remainder of the filler is applied onto the so-called basic rubber grains. This may be considered a variant of dusting as no bond is created between the filler and rubber. However, as E.T. Italiaander has pointed out (presentation 151, technical conference of the Rubber Division of the ACS, Anaheim, California, 6-9 May 1997 (GAK 6/1997 (50) 456-464)), despite the bright future predicted in the Delphi Report (Delphi Report, "Kunftige Herstellverfahren in der Gummiindustrie", Rubber Journal, volume 154, no. 11, 20-34 (1972)) for pulverulent and pelletised rubbers and numerous attempts made by well-known polymer manufacturers from the mid 1970's until the early 1980's to produce pulverulent NBR, SBR/carbon black masterbatches and pelletised NR, the rubber bale remains the standard form in which polymers are supplied. One disadvantage of known processes is firstly that a grinding operation is necessary in order to achieve a grain diameter of the filler particles of 10 m, which is considered essential to the quality of the final product. However, this requires not only elevated energy input but also results in damage to the filler structure which, together with the active surface area, is a significant parameter for its effectiveness in rubber applications. Secondly, the handling properties of prior art products suffer in that the particles stick together during storage. 3 The object of the invention is accordingly to provide a pulverulent rubber containing filler which is easily handled, together with a process for the production thereof. The present invention provides a pulverulent rubber (rubber powder) which [sic] a filler, at least a proportion of which are [sic] modified by organosilicon compounds, solidly bonded to the rubber matrix by the precipitation process. No confusion is thus possible with only superficially (adhesively) coated rubber particles (keyword: dusting, surface precipitation). The powders according to the invention exhibit a narrow size distribution which is shifted towards smaller particle sizes as is known from the prior art {Kautschuk + Gummi + Kunststoffe 7, 28. (1975) 397-402) . This fact facilitates processing of the powders. Moreover, due to the production process, the filler content of the individual particles is not determined by grain size. The pulverulent rubbers contain from 20 to 250 phr, in particular from 50 to 100 phr, of filler (phr: parts per hundred parts of rubber), of which at least a proportion has been surface-modified using organosilicon compounds of the formula (I) known in the rubber sector. The following, individually or as mixtures, have proved to be suitable types of rubber: natural rubber, emulsion SBR having a styrene fraction of 10 to 50%, butyl/acrylonitrile rubber, butyl rubbers, terpolymers prepared from ethylene, propylene (EPM) and unconjugated dienes (EPDM), butadiene rubbers, SBR, produced using the solution polymerisation process, having styrene contents of 10 to 2 5%, as well as 1,2-vinyl constituent contents of 20 to 55% and isoprene rubbers, in particular 3,4-polyisoprene. In addition to the stated rubbers, the following elastomers may be considered, individually or as mixtures: carboxyl rubbers, epoxy rubbers, trans-polypentenamer, halogenated butyl rubbers, rubbers prepared from 2-chloro-butadiene, ethylene/vinyl acetate copolymers, epichlorohydrins, optionally also chemically modified natural rubber, such as for example epoxidised grades. Fillers which may be mentioned are the carbon blacks known from rubber processing and white fillers of a synthetic nature, such as for example precipitated silicas or natural fillers, such as for example siliceous chalk, clays etc.. Carbon blacks, as are generally used in rubber processing, are particularly suitable. Such carbon blacks include furnace blacks, gas blacks and lamp backs having an iodine absorption value of 5 to 1000 m2/g, a CTAB value of 15 to 600 m2/g, a DBP adsorption of 30 to 400 ml/100 g and a 24 M4 DBP value of 50 to 370 ml/100 g in a quantity of 5 to 250 parts, in particular of 20 to 150 parts, per 100 parts of rubber, in particular of 40 to 100 parts. Precipitated silicas known from the rubber sector are also suitable. These generally have an N2 surface area, determined using the known BET method, of 35 to 700 m2/g, a CTAB surface area of 30 to 500 m2/g, a DBP value of 150 to 400 ml/100 g. The product according to the invention contains these silicas in a quantity of 5 to 250 parts, in particular of 20 to 100 parts, relative to 100 parts of rubber. If white natural fillers are used, such as clays or siliceous chalks having an N2 surface area of 2 to 35 m2/g, they are used in a quantity of 5 to 350 parts, relative to 100 parts of rubber. Filled rubber powders containing a mixture of silicas and carbon black are also suitable. 5 Unmodified fillers of the stated type are present in the rubber compounds claimed here only in addition to the fillers modified according to the invention. The proportion of the unmodified fillers depends upon the particular compound to be produced. In any event, the total filler content amounts to 20 to 250 phr. This quantity generally consists of 30 to 100%, preferably from 60 to 100%, of the modified fillers: silica and/or optionally carbon black. Surface-modification is generally performed using organosilicon compounds of the general formula [R1n-(RO)3-n Si- (Alk)m -(Ar)p] q[B] R1n (RO)3-n Si-(Alk) (II) , or R1n (RO)3-n Si-(Alkenyl) (III) in which B: means -SCN, -SH, -Cl, -NH2 (if q = 1) or -Sx-(if q = 2) R and R : mean an alkyl group having 1 to 4 carbon atoms, branched or unbranched, the phenyl residue, wherein all residues R and R may each have the same or a different meaning, preferably an alkyl group, R: means C1-C4 alkyl, -C1-C4 alkoxy group, branched or unbranched, n: means 0; 1 or 2, Alk: means a divalent linear or branched carbon residue [sic] having 1 to 6 carbon atoms, m: means 0 or 1 Ar: means an arylene residue having 6 to 12 C atoms p: means 0 or 1, providing that p and n do not simultaneously mean 0, x: means a number from 2 to 8, Alkyl: means a monovalent linear or branched unsaturated hydrocarbon residue having 1 to 2 0 carbon atoms, preferably 2 to 8 carbon atoms, Alkenyl: means a monovalent linear or branched unsaturated hydrocarbon residue having 2 to 2 0 carbon atoms, preferably 2 to 8 carbon atoms. Examples of preferably used organosilanes are the bis(trialkoxysilyl-alkyl) oligosulfides which may be produced, for example, according to BE-PS 787 691, such as bis-(trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy-, tributoxy-, tri-i-propoxy- and tri-i-butoxy-silyl-methyl) oligosulfides and specifically the di-, tri-, tetra-, penta-, hexasulfides etc., as well as bis-(2-trimethoxy-, triethoxy-, trimethoxyethoxy-, tripropoxy- and tri-n- and i-butoxy-ethyl) oligosulfides and in particular the di-, tri-, tetra-, penta-, hexasulfides etc., furthermore the bis-(3-trimethoxy-, triethoxy-, trimethoxyethoxy- , tripropoxy-, tri-n-butoxy- and tri-i-butoxysilyl-propyl) oligosulfides and again specifically the di-, tri-, tetrasulfides etc. up to octasulfides, moreover the corresponding bis-(3-trialkoxysilylisobutyl) oligosulfides, the corresponding bis-(4-trialkoxysilylbutyl) oligosulf ides. Of these selected organosilanes of a relatively simple structure of the general formula I, those which are preferred are again the bis-(3-trimethoxy-, triethoxy- and tripropoxysilylpropyl) oligosulfides and specifically the di-, tri-, tetra- and pentasulfides, in particular the triethoxy compounds having 2, 3 or 4 sulfur atoms and mixtures thereof. In the general formula I, Alk means a divalent, linear or branched hydrocarbon residue, 7 preferably a saturated alkylene residue having a linear carbon chain with 1 to 4 carbon atoms. The silanes of the following structural formula are also particularly suitable and the methoxy analogues thereof, which may be produced according to DE AS 25 58191 Nonionic, cationic and anionic surfactants are preferably used as surface-active substances. The concentration thereof in the suspension is 0.5 to 15 wt.%, preferably 0.5 to 5 wt.%, relative to the quantity of filler. Examples of such surfactants are alkylphenol polyglycol ethers, alkyl polyglycol ethers, polyglycols, alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyltrimethylammomium salts, alkylbenzene sulfonates, alkyl hydrogen sulfates, alkyl sulfates. In this manner, the entire quantity of organosilicon compounds necessarv for the production of advantaqeous rubber compounds and vulcanisates may be incorporated by means of the modified filler. It is, however, possible to perform processes in which only a proportion of the organosilicon compounds are introduced in this manner and the other proportion is added to the rubber compound in the conventional manner. Such modified fillers are described, for example, in EP-B 0442 143, EP-B 0177 674 and in particular in pellet form in 8 EP-A 0795-579. (white fillers) and in EP-B 0519 188 (carbon black). Suitable bis(alkoxysilylalkyl)oligosulfanes have in particular proved to be those of the type of bis(trialkoxysilylalkyl)tetrasulfane and -disulfane. The modified fillers known from the stated applications and patents and the organosilicon compounds mentioned therein are explicitly included in the present application as a constituent of the claimed compositions. Apart from the above-stated fillers, the rubber powders according to the invention optionally contain known processing or vulcanisation auxiliaries such as zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticisers, anti-ageing agents to counter the action of heat, light or oxygen and ozone, reinforcing resins, flame retardants, such as for example Al(OH)3 and Mg(OH)2, pigments, various crosslinking chemicals and optionally sulfur in concentrations conventional in rubber processing. The cross-section of the rubber powders according to the invention differs distinctly from that of products known from the prior art. Depending upon the filler loading, filler particles are incorporated into the surface, such that the particles do not stick together, even under pressure, such as when several sacks are stacked. This "inertisation" of the surface should not be confused with the known technique of dusting tacky powders with fillers. These only superficially adhering fillers are rapidly detached when exposed to mechanical stress, for example in conveying plant or on transfer into silos. The sticking and agglomeration of the finely divided powders, which it is the intention to avoid, then occurs despite the dusting. 9 Unlike the tacky particles superficially coated with fillers as flow auxiliaries as are known from the prior art, according to the invention, filler particles are incorporated into the surface during the precipitation process for the production of the pulverulent rubber. Depending upon the filler loading with one or more of the above-stated fillers, the advisable distribution between the interior of the particles and an outer zone associated therewith is established. In a product having an elevated filler loading (>80 parts of filler per hundred parts of rubber), only 1 to 10 parts of this quantity of filler are incorporated in the outer grain zone. However, if the pulverulent rubber contains a total of The distributions of the filler within the particles and in the so-called peripheral zone-generally vary between these contents. The greater is the total filler content, the less is the need to suppress the tackiness of the powder by an increased concentration of filler in the peripheral zone. The present invention also provides a process for the production of finely divided, pulverulent rubbers containing filler (rubber powders) by precipitation from mixtures containing water which contain filler in the form of suspensions, water-soluble salts of a metal of groups IIa, IIb, IIIa and VIII of the periodic system of elements and a rubber latex or aqueous emulsions of a rubber solution by addition of an acid, which process is characterised in that >50 wt.% of the finely divided filler, at least a proportion of which has been surface-modified with an organosilicon compound according to the 10 formulae (I), (II) or (III), are mixed with 0.1 to 6.5 parts by weiqht per 100 parts by weight of rubber of the stated water-soluble salts and a rubber latex or an aqueous emulsion of a rubber solution, the pH value of the mixture is reduced to a value in the range from 5.5 to 4.5 (first stage) , the remainder of the finely divided filler in the form of a suspension is added and the pH value is reduced to approx. 3.2 (second stage), such that the rubber in the mixture is completely-precipitated-together with the filler. The duration of the precipitation operation, which is determined by the pH value and the filler content, and the extent thereof may readily be determined by means of a series of measurements. In the case of a powder rubber having an elevated filler loading (>80 parts of filler phr), 1 to 10 parts of this quantity will generally be used as the remaining proportion in the second stage on precipitation of the powder rubber. If the powder rubber contains less than 80 parts of filler phr, for example a total of only 50 parts phr, >10 to 20 parts of this quantity will be introduced into the mixture in the form of a suspension before conclusion of the precipitation operation. In this manner, the fillers are incorporated into the outer grain zone (peripheral zone) of the rubber powder. These proportions of the filler are thus not applied externally onto the individual rubber particles (c.f. DE-PS 37 23213), but are integrated into the surface of the rubber. This distribution of the filler and the manner in which the fillers are bonded to the rubber composition bring about the elevated flowability of the powders according to the invention and prevent sticking during storage of the powder, without these properties being lost on exposure to 11 mechanical stresses during conveying, transfer into silos etc. . The above-stated carbon blacks are used as fillers in finely divided (fluffy) form, the carbon blacks generally having an average grain diameter of 1 to 9 m, preferably of 1 to 8 m, before they are suspended. This facilitates dispersion, such that aqueous suspensions containing filler particles of an average particle diameter of distinctly less than 10 m are obtained without elevated energy input. Precipitated silica may advantageously be used in the form of a filter cake which has been washed until salt-free. Metal salts which may be considered are those originating from elements of groups IIa, IIb, IIIa and VIII of the periodic system of elements. This division into groups corresponds to the former IUPAC recommendation (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 the salts of aluminium are preferred. Aluminium sulfate is particularly preferred. The salts are used in a quantity of 0.1 to 6.5 parts by weight per 100 parts by weight of rubber. Acids suitable for establishing the defined pH values are primarily mineral acids, such as for example sulfuric acid, phosphoric acid and hydrochloric acid, wherein sulfuric acid is particularly preferred. However, carboxylic acids, such as for example formic and acetic acid, may also be used. The quantity of acid is determined by the nature and quantity of the water-soluble metal salt, the filler, the rubber and the optionally present alkali metal silicate. 12 This quantity may readily be determined by initial investigatory testing. According to a preferred embodiment of the process according to the invention, up to 5 parts by weight per 100 parts by weight of rubber of silica (SiO2) are additionally used in the form of an alkali metal silicate solution, preferably as water glass having an Na2O:SiO2 molar ratio of 2:1 to 1:4. The alkali metal silicate solution may here be added both to the rubber component and to the filler suspension. It is preferably added to the rubber component, especially when the process is performed continuously. The process according to the invention is generally performed as follows: first of all, a filler suspension is produced by dispersing a proportion, preferably >50%, of the filler present in the final product in water together with the metal salt and optionally the alkali metal silicate solution. The overall quantity of water is determined by the nature of the filler and the degree of digestion. In general, the water-insoluble constituents of the filler amount to approx. 6 wt.%. This value is not a binding restriction and both lower and higher quantities may be encountered. The maximum content is limited by the pumpability of the suspension. The filler suspension produced in this manner is then intimately mixed, preferably in the presence of an emulsifier, with the rubber latex optionally containing alkali metal silicate solution or the aqueous emulsion of a rubber solution optionally containing alkali metal silicate solution. Known stirrers, such as for example propeller stirrers, are suitable for this purpose. After mixing, a pH value in the range from 5.5 to 4.5 is first established while stirring is continued. This results in basic rubber grains having a constant filler content. The size of these basic grains is controlled by the selected quantity of metal salt in the range from 0.1 to 13 6.5 phr. Control is effected by the largest grain size being obtained with the lowest quantity of metal salt. The remainder of the finely divided, optionally also modified white filler is added in the form of a suspension and the pH value is lowered to approx. 3.2. The solids content of the latex used generally amounts to 20 to 25 wt.%. The solids content of the rubber solutions is generally 3 to 35 wt.%, that of the rubber emulsions generally from 5 to 30 wt.%. These mixtures and the production thereof are known from the prior art. When working up rubber powders having filler contents of >100 phr, it is advantageous to reduce the pH value down to 2.5 before phase separation. An acid from the above-stated group of acids is advantageously used for this purpose. The process according to the invention may be performed both discontinuously and continuously. The precipitated rubber powder is advantageously separated by means of a centrifuge and then dried to a residual water content of generally During the production process, further processing and/or vulcanisation auxiliaries may be added to the rubber powder according to the invention in a quantity conventional for vulcanisable rubber compounds or also a smaller quantity. The rubber powders according to the invention are used for the production of vulcanisable rubber compounds. The constituents necessary for producing the compound may all be present in the rubber powder. Preferably, however, the powders contain rubber of the above-stated types and fillers. They may, however, also be mixed in a conventional manner 14 with other rubbers and fillers, if this is necessary for the desired rubber compound. It is possible according to the invention to produce a finely divided rubber powder which is free-flowing and also remains free-flowing after exposure to mechanical stresses (for example conveying, packaging). By virtue of the finely divided nature thereof, no grinding or other comminution measures are required to obtain finely divided dispersions. These then give rise to the finely divided rubber powders, which may readily be processed/ and to vulcanisates having improved properties. 15 Examples A. The Examples describe the production and properties of vulcanisable rubber compounds which have been produced 1. using a rubber powder produced according to the invention (containing silica premodified with TESPT) and, in comparison thereto 2. using a rubber compound produced using silica premodified with TESPT. B. Test standards used in the Examples: Unit Standard Tensile strength Mpa DIN 53504 Elongation at break % DIN 53504 Fracture energy [J] C. Chemicals used in the Examples: TESPT bis(triethoxysilylpropyl)tetrasulfane (Si69) Degussa AG Naftolen ZD plasticiser, aromatic hydrocarbons 6PPD N-l,3-dimethylbutyl-N'-phenylenediamine CBS N-cyclohexyl-2-benzothiazolesulfenamide Coupsil 8113 precipitated silica surface-modified with 11.3 wt.%, relative to the silica Vulkanox 4020 antioxidant based on phenylenediamine Vulkacit CZ benzothiazyl-2-cyclohexylsulfenamide Vulkazit D diphenylguanidine 16 Protektor G35P ozone protection wax Example 1 Comparison of a vulcanisate produced from powder rubber with a prior art vulcanisate a) Formulation (E-SBR base stock, TESPT content, (phr) relative to silica : 11.3%) (1) (2) Powder rubber 156 Coupsil 8113 56 Buna SB 1500 100 Naftolen ZD 3 3 ZnO 2 2 Stearic acid 2 2 Vulkanox 4020 1 1 Protektor G35P 1 1 Sulfur 1.5 1.5 Vulkacit CZ 1.7 1.7 Vulkacit D 2 2 17 b) Scorching behaviour (130°C) (1) (2) Scorch time (min) 32.07 21.13 Scorch time (min) 41.57 26.3 c) Tensile test on annular test piece (DIN 53504) (1) (2) Tensile strength (MPa) 21 19.1 Elongation at break (%) 590 530 Fracture energy (I)[sic] 161.7 135.6 d) Dispersion test (1) (2) Surface roughness 1940 2750 -18-We claim : 1. A process for producing a filled rubber powder, characterized in that the filled rubber powder contains, firmly bonded to the rubber matrix, a filler modified with an organosilicon compound of the formula (I), (II) or (III) [R1n-(RO)3-nSi-(Alk)m-(Ar)p]q [B] (I), R1n(RO)3-nSi-(Alk) (II), or R1n(RO) 3-nSi-(Alkenyl) (III) where B is -SCN, -SH, -Cl, -NH2 (if q = 1) or -Sx-(if q = 2). R and R1 are an alkyl group having from 1 to 4 carbon atoms, branched or unbranched, or the phenyl radical, where each radical R and R1 may be identical or different, R is a C1-C4-alkyl or C1-C4-alkoxy group, branched or unbranched, n is 0,1 or 2, Alk is a bivalent, straight-chain or branched carbon 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 and n are not simultaneously 0, 19- x is a number from 2 to 8, Alkyl is a monovalent, straight-chain or branched, saturated hydrocarbon Radical having from 1 to 20 carbon atoms, Alkenyl is a monovalent, straight-chain or branched, unsaturated hydrocarbon radeiical having from 2 to 20 carbon atoms, or a filter modified with bis (trialkoxysilylpropyl) tetrasuifane or with bis (trialkoxysilylpropyl) disulfane, by additing an acid to bring about precipitation from an aqueous mixture which contains filler in the form a suspension, contains a water-soluble salt of a metal of group IIa,IIb, IIIa or vIII of the Periodic Table of the Elements, and contains a rubber latex or contains or aqueous emulsion of a rubber solution, characterized in that >50% by weight of the fine-particle filler, which has been at least to some extent modified on its surface with an organosilicon compound as in formula (I), (II) or (III), is mixed with from 0.1 to 6.5 parts by weight of the water soluble salts mentioned per 100 parts by weight of rubber and with a rubber latex or with an aqueous emulsion of a rubber solution, the pH of the mixture is lowered to a value within the range from 5.5 to 4.5 (first stage), the remainder of the fine-particle, if appropriate likewise modified, white or, if appropriate black filler, in the form or a suspension, is added, and the pH is lowered to about 3.2 (second stage), so that the rubber present in the mixture is completely precipitated together with the filler. 20 2. A process for producing a filled rubber powder as claimed in claim 1, wherein the filled rubber powder has from 20 to 250 phr content of modified and unmodified fillers. 3. A process for producing a filled rubber powder as claimed in claim 1 or 2, wherein the filled rubber powder contains, as filler, from 5 to 200 phr of a precipitated silica modified with an organosilicon compound according to claim 1. 4. A process for producing a filled rubber powder as claimed in claim 1 or 2, wherein the filled rubber powder contains, as filler, from 20 to 250 phr or an organosilicon-modified or unmodified carbon black. 5. A process for producing a filled rubber powder as claimed in claim one or more of the preceding claims, wherein the filled rubber powder contains, as filler, from 5 to 250 phr in total of modified silica, carbon black and unmodified silica, 6. A process as claimed in claim 1 wherein when the total proportion of filler used is >_ 30 parts phr, from 1 to 10 parts from this amount are added as remainder in the second state. 7. A process as claimed in claim 1 wherein when the total proportion of filler used is 10 to 20 parts from this amount are added as remainder in the second stage. 8. A process as claimed in any of the preceding claims wherein use is made of a carbon black with an average particle size of from 1 to 9 urn. 9. A process as claimed in any of the preceding claims, wherein use is additionally made of silica in the form of a filter cake washed until free from salts. -21- 10.A process as claimed in any of the preceding claims, wherein during the precipitation of the rubber powders other customary processing aids or other customary vulcanization auxiliaries are added. 11. A process as claimed in any of the preceding claims, wherein aluminium sulphate is used as water-soluble salt. 12.A process as claimed in any of the preceding claims, wherein operations are carried out in the presence of alkali metal silicate. 13.A process as claimed in claim 12, wherein up to 5 phr of SiO2 are added in the form of alkali metal silicate solution. 14.A process as claimed in any of the preceding claims, wherein during preparation of a rubber powder with filler level > 100 phr, the pH is lowered to 2.5 prior to phase separation. Finely divided powdered rubbers containing filter which remain free-flowing even after exposure to mechanical stresses and to a process for the production thereof, in which the rubber powder is obtained in two precipitation steps, and to the use of these powdersfor the production of vulcanizable rubber compounds. The fillers used, which are both precipitated silicas and carbon blacks known in the rubber art, are surface-modifed by organosilicon compounds.

Documents:

00337-cal-1999 abstract.pdf

00337-cal-1999 claims.pdf

00337-cal-1999 correspondence.pdf

00337-cal-1999 description(complete).pdf

00337-cal-1999 form-1.pdf

00337-cal-1999 form-18.pdf

00337-cal-1999 form-2.pdf

00337-cal-1999 form-3.pdf

00337-cal-1999 form-5.pdf

00337-cal-1999 g.p.a.pdf

00337-cal-1999 letters patent.pdf

00337-cal-1999 priority document others.pdf

00337-cal-1999 priority document.pdf

337-CAL-1999-CORRESPONDENCE 1.1.pdf

337-CAL-1999-CORRESPONDENCE-1.2.pdf

337-CAL-1999-CORRESPONDENCE-1.3.pdf

337-CAL-1999-FOR ALTERATION OF ENTRY.pdf

337-CAL-1999-FORM 27-1.1.pdf

337-CAL-1999-FORM 27.pdf

337-CAL-1999-FORM-27.pdf

337-CAL-1999-OTHERS.pdf

337-CAL-1999-PA-1.1.pdf

337-CAL-1999-PA.pdf