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
1999-04-07
2003-04-15
Mulcahy, Peter D. (Department: 1713)
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...
C524S423000, C524S428000, C524S429000, C524S436000, C524S492000, C524S496000, C524S571000, C524S575000
Reexamination Certificate
active
06548584
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on German Application No. 19815453.4, the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to pulverulent rubbers containing fillers, 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 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 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 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 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., May 6-9, 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 pulverulent and pelletized 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 pelletized 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 &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.
SUMMARY OF THE INVENTION
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 or rubber powder having a filler content solidly bonded to the rubber matrix by the precipitation process. No confusion is thus possible with only superficially surface coated 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 pulverulent rubbers contain from 20 to 250 phr, in particular from 50 to 100 phr, of filler (phr: parts per hundred parts of rubber).
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% and isoprene rubbers, in particular 3,4-polyisoprene.
In addition to these 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 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 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 m
2
/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 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, which contain a mixture of silicas and carbon black are also suitable. In this case, the total quantity of filler amounts to 20 to 250 parts of filler per 100 parts of rubber.
Apart from the above-stated fillers, the rubber powders according to the invention optionally contain known processing or vulcanization auxiliaries such as zinc oxide, zinc stearate, stearic acid, polyalcohols, polyamines, plasticizers, anti-aging 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. While these latter products ideally exhibit a homogeneous distribution of the filler in the rubber composition or vice versa and have a shell of filler particles, according to the invention there is a homogeneous distribution of filler and rubber component within the pulverulent products and in the associated peripheral zone.
Depending upon the filler loading of the particles, 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 “inertization” of the surfac
Ernst Uwe
Görl Udo
Lauer Hartmut
Stober Reinhard
Mulcahy Peter D.
Pillsbury & Winthrop LLP
PKU Pulverkautschuk Union GmbH
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