Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-04-10
2004-03-30
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S342000, C524S439000, C524S571000, C524S575500, C524S527000, C525S342000
Reexamination Certificate
active
06713534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing a rubber powder comprising a filler which has a silanol group and which has been modified using an organosilicon compound.
2. Discussion of the Background
A wide variety of publications has appeared concerning the purpose and benefits of using rubber powders, and also concerning possible processes for their preparation (U. Görl, K. H. Nordsiek, Kautsch. Gummi Kunstst. 51 (1998) 250; U. Görl, H. Lauer, Gummi, Fasern Kunstst. 53 (2000) 261; and R. Uphus, 0. Skibba, R. H. Schuster, U. Görl, Kautsch. Gummi Kunstst. 53 (2000) 276).
The interest in pulverulent rubbers probably stems from the processing technology used in the rubber industry, where rubber mixtures are prepared at high cost in terms of time, energy, and personnel. The main reason for this is that the raw rubber material is in the form of bales, and that the other constituents of the vulcanizable mixture have to be incorporated into the rubber phase.
Comminution of the bale and intimate mixing with fillers, mineral oil plasticizers, and vulcanization auxiliaries takes place on rolls or internal mixers in a number of process stages. Between the stages, the mixture is generally cooled on a batch-off system, laid out in milled sheet form on pallets, and put into intermediate storage. Downstream of the internal mixers or rolls there are appropriate extrusion or calendering processes.
Completely new processing technology is needed in order to avoid this very complicated method of rubber processing.
For some time there have been discussions on the use of free-flowing rubber powders which allow rubber mixtures to be processed as simply and rapidly as thermoplastic powders or pellets.
The preparation of the rubbers usually used in the rubber industry, via polymerization of various monomers, is generally divided into two fundamentally different processes: a) polymerization in water and b) polymerization in organic solvents.
a) Polymerization in Water (Emulsion Polymerization)
This process polymerizes the starting monomers (e.g. styrene, butadiene, or acrylonitrile) by a free-radical route in water to give high-molecular-weight units, with the aid of suitable initiator molecules. The factors determining the properties of the polymer, and also its molecular structure, and thus also the subsequent performance profile of the finished rubber mixture, include: the monomer units used, their respective percentage proportions, and also the reaction conditions selected (e.g. temperature, pressure). When emulsifiers are present, the rubber molecules are present as finely divided droplets in water after the polymerization. The terms latex or rubber emulsion are used in this context. This forms the raw rubber material for preparing rubber powder from the aqueous phase. This powder generally is produced by addition of fillers (e.g. industrial carbon blacks or precipitated silicatic fillers) followed by acid-catalyzed coprecipitation of rubber emulsion and filler.
Known rubbers present in or prepared in water are natural rubber (NR), emulsion styrene-butadiene rubber (ESBR), nitrite-butadiene rubber (NBR) and chloroprene rubber (CR). DE-C 28 22 148 describes a process for preparing a rubber powder from coprecipitation of rubber emulsion and a filler carried out in the aqueous phase.
Other versions of this process have been published in DE-C 37 23 213 and DE-C 37 23 214. They are aimed at eliminating the grain-size-dependent filler contents which result in the process.
More recent publications concerning the preparation of rubber powders by coprecipitation of filler and rubber emulsion in water have increasingly dealt separately with 1) the nature of each of the fillers used in the rubber industry, and 2) with the way in which each filler is used. The background to this is recognition that various classes of fillers also require a variety of processes for complying with specifications for the preparation of a rubber powder.
DE 198 16 972.8 describes for the first time the use of organosilanes and the way these compounds are used in the preparation of rubber powders.
The patent specification starts from what are known as presilanized fillers, the preparation of which is described in EP 0 442 143 131 and EPA 0 126 871, for example. This process begins with a mixing procedure which homogenizes the filler, e.g. a silica, with the organosilane, and this is followed by reaction of the filler at an elevated temperature. This homogenization process may take place using dried filler (dry process) or else in aqueous suspension (wet process). To prepare the rubber powder, this finished reaction product made from filler and organosilane is resuspended in water, and this suspension is combined with the rubber emulsion, and the latex/the rubber emulsion is coagulated with the aid of acids.
The many steps needed for pre-treatment of raw materials prior to preparation of a rubber powder make this a complicated and therefore expensive process. Furthermore, the dry silanization process mentioned is not applicable when the preliminary stages used for silica preparation are lower-cost methods, which are also of interest for application-related reasons, e.g. silica filtercake or indeed precipitation suspension. Any process for preparing rubber powder in these cases has to be one in which the organosilane is added directly during the process to prepare the rubber powder. DE 198 43 301.8 (starting from silica filtercake) and DE 100 56 696.0 (starting from silica precipitation suspension) describe these processes and the procedure needed for the same.
b) Polymerization in Organic Solvents
The second large group of rubbers is that of products polymerized in an organic solvent, in general by anionic methods, wherein the polymers are generally present in the organic solvent after the polymerization. Any process for preparing a rubber powder from solution polymers (dissolved in organic solvent) and fillers therefore has to consider the completely different nature of this form of rubber starting material.
Examples of important rubbers prepared in organic solvents are styrenebutadiene rubber based on solution polymerization (SSBR), butadiene rubber (BR), butyl rubbers, halobutyl rubbers, and also ethylene-propylene rubbers with (EPDM) or without (EPM) a copolymerized tercomponent.
The preparation of filled rubber powders from rubber solutions has also been described in detail in the patent literature, in principle using two different processes.
DE 21 35 266, DE 22 14 121, published patent applications 23 24 009, 23 25 554; 23 32 796; DE 26 54 358 and DE 24 39 237 describe processes in which the organic rubber solution is first converted into an aqueous emulsion, with the aid of large amounts of emulsifiers. The water moreover comprises some of the precipitating agent, generally sulfiric acid. The filler, generally carbon black, is suspended in water when added to this emulsion, and the entire emulsion is allowed to flow into a hot sodium waterglass solution. Coprecipitation of rubber and filler takes place with simultaneous removal of the solvent. The preparation process is therefore very closely related to the processes for preparing rubber powders using aqueous polymer systems, and is based on the principle of coagulation via acid addition. The use of large amounts of emulsifiers serves to raise the level of phase incompatibility between organic polymer solution and aqueous filler suspension. The patent specifications relate almost exclusively to carbon-black-filled systems. Silica-containing products are merely mentioned in passing, and the above patents do not include methods of using organosilanes, although these are of vital importance for the subsequent application of silica-filled systems, at least in high-performance rubber mixtures. In the light of experience (U. Görl, J. Müinzenberg, D. Luginsland, A. Müller, Kautsch. Gummi Kunstst. 52 (1999) 588) moreover, the organosilane would not survive the selected process and the extreme experimental conditions (sulfuri
Goerl Udo
Gouw Andreas
Schmitt Matthias
Stober Reinhard
PKU Pulverkautschuk Union GmbH
Sastri Saty{overscore (a)}
Wu David W.
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