Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-04-19
2002-01-22
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S200000, C523S203000, C523S204000, C523S209000, C523S212000, C523S216000, C524S492000, C524S493000, C524S494000, C524S495000, C524S496000
Reexamination Certificate
active
06340724
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on German Patent Application DE 19816972.8 filed Apr. 17, 1998, the disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to powdered rubbers containing fillers modified with organosilicon compounds, to a process for the production thereof and to the use thereof.
BACKGROUND OF THE INVENTION
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 powdered 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 plasticizers and vulcanization 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/pelletizers 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 powdered thermoplastics.
DE-PS 2822 148 discloses a process for the production of a powered rubber containing fillers.
According to this patent, an aqueous filler emulsion is added to a rubber latex, rubber solution or an aqueous 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, Calif., 6-9 May 1997 (GAK 6/1997 (50) 456-464)), despite the bright future predicted in the Delphi Report (Delphi Report, “Künftige Herstellverfahren in der Gummiindustrie”,
Rubber Journal
, volume 154, no. 11, 20-34 (1972)) for powdered and pelletized rubbers and numerous attempts made by well-known polymer manufacturers from the mid 1970's until the early 1980's to produce powdered NBR, SBR/carbon black masterbatches and pelletized NR, the rubber bale remains the standard form in which rubber is 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&mgr;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.
The object of the invention is accordingly to provide a powdered rubber containing filler which is easily handled, together with a process for the production thereof.
SUMMARY OF THE INVENTION
The present invention provides a powdered rubber in which a filler, at least a proportion of which is modified by organosilicon compounds, is solidly bonded to the rubber matrix by a precipitation process. No confusion is thus possible with only superficially or adhesively coated rubber particles.
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 powdered 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 surfaced-modified using organosilicon compounds of the formula (I) known in the rubber art. 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 a solution polymerization process, having styrene contents of 10 to 25%, as well as 1,2-vinyl constituent contents of 20 to 55% oand isoprene rubbers, in particular 3,4-polyisoprene.
In addition to these 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-chlorobutadiene, ethylene/vinyl acetate copolymers, epichlorohydrins, optionally also chemically modified natural rubber, such as for example epoxidized 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 m
2
/g, a CTAB value of 15 to 600 m
2
/g, a DBP absorption 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, per 100 parts of rubber, preferably 20 to 150 parts, per 100 parts of rubber, more preferably 40 to 100 parts, per 100 parts of rubber.
Precipitated silicas known from the rubber art are also suitable.
These generally have an N
2
surface area, determined using the known BET method, of 35 to 700 m
2
/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, preferably 20 to 100 parts, relative to 100 parts of rubber.
If white natural fillers are used, such as clays or siliceous chalks having an N
2
surface area of 2 to 35 m
2
/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.
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
[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
B
1
: means —SCN, —SH, —Cl, —NH
2
(if q=1) or —SX— (if q=2)
R and R
1
: mean an alkyl group having 1 to 4 carbon atoms, branched or unbranched, a phenyl residue, wherein all residues R and R
1
may each have the same or a different meaning, preferably an alkyl group,
R: means C
1
-C
4
alkyl, C
1
-C
4
alkoxy group, branche
Ernst Uwe
Görl Udo
Lauer Hartmut
Stober Reinhard
Niland Patrick D.
PKU Pulverkautschuk Union GmbH
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