Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-13
2002-02-19
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S318000, C523S324000
Reexamination Certificate
active
06348522
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the continuous preparation of filler-containing rubber powders, in which a filler suspension and rubber suspension are mixed in the aqueous phase, the mixture is passed through a tube, at least a coagulant is added in the tube and filler-containing rubber particles are precipitated.
BACKGROUND OF THE INVENTION
According to the prior art, rubber mixtures are prepared from crude rubber in the form of balls with a high expenditure of time, energy and personnel. The comminution of the balls and mixing with additives are expensive and cost-intensive. On the other hand, the use of free-flowing rubber powders offers the possibility of preparing and processing rubber mixtures simply and quickly. U.S. Pat. 4,265,939 discloses a process for the continuous preparation of rubber powders, but no coagulant is mixed in a tube of relatively narrow cross-section. Effective mixing of the two components is said to take place in the narrow tube on the basis of the turbulent flow. The coagulated rubber material is then passed into a tube of widened cross-section. A polymer, as a coating composition, is fed to the liquid mixture in this tube. This known process leaves something to be desired with respect to effectively mixing the components. Furthermore, troublesome deposits or caking on the walls occur, especially in the tube section of narrowed cross-section, and these change the flow conditions. The properties of the products prepared by this process are therefore not reproducible and, because of the varying flow circumstances during the preparation these products also have disadvantageous undesirable properties. The fact that, in the context of a process for the continuous preparation of filler-containing rubber powders, the rubber material can be mixed continuously with the filler in a tube is also known in principle from DE 37 23 213 C2 and DE 37 23 214 C2. However, no fixed methodology for carrying out the process can be obtained from the two documents.
Processes for the preparation of filler-containing rubber powders which are operated batchwise or carried out discontinuously are furthermore known. In these, as a rule a filler-containing suspension is brought together with a suitable latex in the presence of a precipitant and the mixture is then allowed to react in a container. These known processes disadvantageously require a relatively high expenditure of apparatus and time. Such a discontinuous process is described, for example, in DE 28 22 148 C2.
SUMMARY OF THE INVENTION
In contrast, the invention is based on the object of providing a process for preparing a filler-containing rubber powder with reproducible properties, without problems and with a low expenditure, and to avoid the disadvantages described above.
The invention provides a process for the continuous preparation of a filler-containing rubber powder, in which
a) filler dispersions and rubber suspensions are mixed
b) the liquid mixture is passed through a tube, at least one coagulant is added and the filler-containing rubber powder is precipitated,
c) the liquid mixture is passed through a tube with at least one throttle position of variable throttle cross-section, and
d) the throttle cross-section is adjusted, with the proviso that the drop in pressure in the liquid mixture achieved with the throttle position is greater than 0.5 bar.
It lies within the context of the invention that the liquid mixture comprises at least one liquid medium, in particular water. Preferably, a suspension, expediently an aqueous suspension of the filler, is employed or added to the rubber material. A rubber latex and/or a rubber solution and/or an aqueous emulsion of a rubber solution is expediently employed as the rubber material. The rubber material may be a synthetic and/or naturally occurring rubber. According to a preferred embodiment of the invention, a styrene-butadiene copolymer is used as the rubber latex. Further, according to the invention, one or more fillers may be used. Carbon black, for example, may be used as the filler. In one embodiment of the invention, an aqueous suspension of carbon black is added to the rubber material, in particular a 2 to 7 wt. % aqueous suspension of carbon black is added to the rubber material.
The particle size range of the rubber powders obtained according to the invention is in general between 0.05 and 10 mm, in particular between 0.5 and 2 mm.
The pulverulent rubbers comprise 20 to 250 phr, in particular 50 to 100 phr of filler (phr: parts per hundred parts of rubber), and have optionally been modified partly or completely on the surface before the process according to the invention takes place, using the organosilicon compounds according to the formulae (I), (II) or (III), shown below, known in the rubber art. The following species, individually or as a mixture with one another, have been found to be suitable types of rubber for use in the invention: natural rubber, emulsion SBR with a styrene content of 10 to 50%, butyl-acrylonitrile rubber. Butyl rubbers, terpolymers of ethylene, propylene (EPM) and non-conjugated dienes (EPDM), butadiene rubbers, SBR, prepared by the solution polymerization process, with styrene contents of 10 to 25%, and contents of 1,2-vinyl constituents of 20 to 55% and isoprene rubbers, in particular 3,4-polyisoprene are useful in the invention.
In addition to the rubbers mentioned, the following elastomers may be used, individually or as a mixture: carboxyl rubbers, epoxide rubbers, trans-polypentenamer, halogenated butyl rubbers, rubbers of 2-chloro-butadiene, ethylene/vinyl acetate copolymers, epichlorohydrins, optionally also chemically modified natural rubber, such as, for example, epoxidized types. Fillers which are additionally used are in general the carbon blacks and white fillers of a synthetic nature, such as e. g. precipitated silicas, or naturally occurring fillers, such as e. g. siliceous chalk, clays etc., known from rubber processing.
Carbon blacks such as are generally employed in rubber processing are particularly suitable.
These include furnace blacks, gas and flame blacks with an iodine adsorption number of 5 to 1000 m
2
/g, a CTAB number of 15 to 600 M
2
/g, a DBP adsorption of 30 to 400 ml/100 g and a DBP number of 50 to 370 ml/100 g, in an amount of 5 to 250 parts, in particular 20 to 150 parts per 100 parts of rubber, in particular 40 to 100 parts.
The silicate fillers of synthetic or natural origin known from the rubber art, in particular precipitated silicas, are likewise suitable.
In general, these have an N
2
surface area, determined by the known BET method, of 35 to 700 m
2
/g, a CTAB surface area of 30 to 500 m
2
/g, and a DBP number of 150 to 400 ml/100 g. The product according to the invention comprises these silicas in an amount of 5 to 250 parts, in particular 20 to 100 parts, based on 100 parts of rubber.
If the fillers are white, naturally occurring fillers, such as clays or siliceous chalks with an N
2
surface area of 2 to 35 m
2
/g, these are employed in an amount of 5 to 350 parts, based on 100 parts of rubber.
Powders which comprise one or more of the abovementioned fillers in a mixture are also suitable.
In addition to the non-modified fillers of the type mentioned, modified fillers are optionally additionally employed in the preparation of the rubber powders described herein. The content of non-modified fillers depends on the mixture specifically to be prepared. In all cases, the total amount of filler amounts to 20 to 250 phr. This in general comprises the non-modified fillers: silica and/or carbon black to the extent of 100% in particular to the extent of 30 to 100%, preferably 60 to 100%. Organosilicon compounds which are employed for the modification of the surfaces are in general those of the general formulae
[R
1
n−
(RO)
3−n
Si—(Alk)
m
—(Ar)
p
]
q
[B
1
] (I),
R
1
n
(RO)
3−n
Si—(Alk) (II),
or
R
1
n
(RO)
3−n
Si—(alkenyl) (III),
in which the symbols denote
B
1
: —SCN, —SH, —Cl, —NH
2
(if q&equ
Ernst Uwe
Smigerski Hans-Jürgen
Michl Paul R.
PKU Pulver Kautschuk Union GmbH
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