Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-22
2001-12-11
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S213000, C524S446000, C524S571000, C524S572000, C528S014000
Reexamination Certificate
active
06329449
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to German Application DE 198 43 301.8, filed Sep. 22, 1998, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a process for the preparation of rubber powders comprising fillers modified with organosilicon compounds, and the powders thus prepared.
BACKGROUND INFORMATION
A large number of publications have appeared relating to the aim and purpose of the use of powdered rubbers and possible processes for their preparation.
The explanation for the interest in pulverulent rubbers can readily be found from the processing techniques of the rubber industry. There, rubber mixtures are prepared with a high expenditure of time, energy and personnel. The main reason for this is that the raw material rubber takes the form of balls, and the other constituents of the vulcanizable mixture must be incorporated.
Comminution of the balls and intimate mixing with fillers, mineral oil plasticizers and vulcanization auxiliaries takes place on mills in internal mixers in several process stages. Between the stages, the mixture is generally cooled on a batch off-line, deposited on pallets as rolled sheets and intermediately stored. The internal mixers or mills are followed by appropriate extruders or calendering processes.
Only a completely new processing technology can lead away from this very involved technique of rubber processing.
The use of free-flowing rubber powders has therefore been considered for some time, because of the possibility of being able to process rubber mixtures easily and quickly in the same way as thermoplastic powders.
DE-PS 2822 148 discloses a process for the preparation of a pulverulent, filler-containing rubber.
According to this patent specification, an aqueous filler emulsion is added to a rubber latex (e.g. natural rubber) a rubber solution (e. g. BR) or an aqueous emulsion of a synthetic rubber (e. g. SBR) and the desired rubber powder is precipitated out.
To avoid the particle size-dependent filler contents obtained by this process, patents have been applied for relating to variants, for example DE-PS 15 3723 213 and DE-PS 3723 214.
DE-PS 3723213, discloses a process which proceeds in two stages. In the first step, an amount of ≧50% of the filler is integrated into the rubber powder particles. In the second step, the remainder of the filler is absorbed on to the so-called rubber base particles. This can be regarded as a variant of powdering, since no bond is formed between the filler and rubber.
As E. T.
Italiaander
(Paper 151. Technische Tagung der Rubber Div der ACS [Technical Conference of the Rubber Div. of the ACS], Anaheim, Calif. May 6-9 , 1997 (GAK 6/1997 (50) 456-464) found, however, regardless of the great future predicted in the Delphi Report (Delphi Report “Künftige Herstellverfahren in der Gummiindustrie [Future Production Processes in the Rubber Industry]” Rubber Journal, vol. 154, no. 11, 20-(1972)) for pulverulent and granulated rubber, and despite numerous attempts undertaken by well-known polymer producers from the mid 1970's into the early 1980's to prepare pulverulent NBR, SBR-carbon black masterbatches and granulated NR, the standard delivery form of polymers has remained rubber balls.
One disadvantage of the known processes lies in the fact that a grinding operation is required in order to establish the particle diameter of the filler particles of 10 &mgr;m regarded as necessary for the quality of the end product. This not only results in a high expenditure of energy, but also causes damage to the filler structure, which, along with the active surface area, is an important characteristic parameter for the effectiveness in use in rubbers.
Another disadvantage is that the ease of handling of the products according to the prior art suffers due to the particles sticking to one another during storage.
A precipitation process in which suspensions of fillers modified with organosilicon compounds are prepared and stirred into the rubber emulsion is the subject of German Patent application P 198 16 972.8. The rubber powder is then precipitated out of this mixture.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process with few process stages which yields a rubber powder which comprises modified fillers and can be advantageously employed.
The invention provides a process for the preparation of finely divided rubbers (rubber powders) by precipitation from aqueous mixtures. The rubber composition so obtained comprises filler in the form of suspensions, water-soluble salts of a metal of groups IIa, IIb, IIIa and VIII of the periodic table of the elements and a rubber latex, an aqueous emulsion of a rubber or a rubber solution, which is characterized in that
a) one or more organosilicon compound(s) containing at least one alkoxy group is or are dissolved or emulsified, optionally in the presence of a surface-active substance, in water, or the compounds mentioned are mixed directly, optionally with a surface-active substance, with an aqueous suspension of an oxidic or silicatic finely divided filler or a mixture of these fillers at a temperature of 10 to 60 ° C., preferably at room temperature, while stirring, the amount of this mixture envisaged for incoporation in the rubber, based on the filler content, in general being divided into two batches, and
b) a first batch is mixed with the polymer latex, the polymer emulsion or the polymer solution, the pH of this mixture is lowered to 6.0 to 4.5 with an acid, in particular a Lewis acid (first batch, first stage),
c) the remaining content (second batch, splitting amount) is added with further lowering of the pH to 4.5 to 2.6, in particular to approximately 3.2 (second stage), so that the rubber in the mixture precipitates out together with the filler modified by organosilicon compound(s)
d) the solid which has precipitated out is separated off by means known in the art,
e) the product is then preferably washed, in order to adjust the pH to a value of approx. 6 to 7 which is more compatible with the further processing, and
f) the filler-containing rubber is dried.
Drying is advantageously carried out in a drier at a gas intake temperature of 140 to 160° C. and a gas discharge temperature of 50 to 70° C. The temperature of the product should not exceed 40 to 50 ° C.
The duration, which depends on the pH and the filler content, and the extent of the precipitating operation can easily be determined by a measurement series using routine experimentation.
In the case of powdered rubber with a high filler content (≧80 parts of filler phr), 1 to 10 parts of this amount will in general be employed as the remaining content in the second stage in the precipitation of the powdered rubber.
If the powdered rubber comprises less than 80 parts of filler phr, for example only 50 parts phr in total, >10 to 20 parts of this amount is further introduced into the mixture in the form of a suspension before the conclusion of the precipitating operation.
The fillers are bonded into the outer particle region (margin region) of the rubber powders in this manner.
These contents of the filler are therefore not absorbed externally on to the individual rubber particles (see DE-PS 37 23213), but are integrated into the rubber surface.
This distribution of the filler and the nature of the bonding of the fillers in the rubber composition cause the high flowability of the powders according to the invention and prevent agglutination during storage of the powders, without these properties being lost due to mechanical stresses during conveying, silation etc.
Further fillers which are optionally employed are the carbon blacks known from the rubber industry, preferably in finely divided form (fluffy), which in general have an average particle diameter of 1 to 9 &mgr;m, preferably 1 to 8 &mgr;m, without mechanical treatment, before they are suspended.
This facilitates dispersion, so that aqueous suspensions with filler particles having an average particle diam
Ernst Uwe
Gorl Udo
Lauer Hartmut
Stober Reinhard
Dawson Robert
Peng Kuo-Liang
Pillsbury & Winthrop LLP
PKU Pulverkautschuk Union GmbH
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