Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-26
2003-05-13
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...
C523S200000, C523S204000, C523S210000, C523S201000, C524S495000, C524S432000, C524S422000, C524S492000
Reexamination Certificate
active
06562883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing fine-particle rubber powders from rubber-latex emulsions by precipitation from an aqueous mixture having a filler. Further, the invention relates to the resulting powders.
2. Discussion of the Background
A wide variety of publications has dealt with the purpose and reasons for the use of rubber powders, and also with processes for the preparation of rubber powders.
The interest in pulverulent rubber/filler masterbatches can be explained as a necessary result of the processing technology used in the rubber industry, where rubber mixtures are prepared with high costs for energy, time and personnel. A main reason for this is that the rubber raw material is in bale form and its processing requires incorporation and dispersion of large amounts of active fillers (industrial carbon blacks, silicas, etc.) into the rubber phase.
This mechanical kneading process generally takes place industrially in large internal mixers or on roll mills, generally in two or more stages. The mixture is placed in intermediate storage between the individual mixing stages, and finally, after addition of the crosslinking chemicals the ready-to-use raw mixture is further processed in extruder systems or on calenders to give semifinished products (e.g. tire treads).
Only a completely new process technology can overcome this complicated method of rubber processing.
Rubber powder technology has long been regarded as the most suitable candidate. [Delphi Report “Künftige Herstellverfahren in der Gummiindustrie” [Production processes for the future in the rubber industry] Rubber Journal, Vol. 154, No. 11, 20-34 (1942)]. This technology combines the need for incorporating a filler at an early stage of the process with presentation of the material specifically in the form of a free-flowing rubber powder suitable for use in continuous mixing processes which have been state of the art for many years in the plastics industry.
The rubber powder is prepared as in the prior art by precipitation from a mixture of a filler suspension (e.g. carbon black or silica) and a rubber-latex emulsion, by lowering the pH with the aid of appropriate Brönsted or Lewis acids (DE-C 37 23 213, DE-C 37 23 214 and DE-C 28 22 148).
All of these patents regard it as essential to add water-soluble salts of a metal of Groups IIa, IIb, IIIa or VIII of the Periodic Table of the Elements, in amounts of from 0.5 to 6.5 phr. In more recent patents, DE 198 15 453.4 and DE 198 16 972.8, the addition of 10 phr of water-soluble salts of a metal of groups IIa, IIb, IIIa or VIII to the filler suspension is described.
This Group classification corresponds to the IUPAC recommendation (see Periodisches System der Elemente [Periodic Table of the Elements], Verlag Chemie, Weinheim, 1985). Typical examples for water-soluble salts of the above metals are magnesium chloride, zinc sulfate, aluminum chloride, aluminum sulfate, iron chloride, iron sulfate, cobalt nitrate and nickel sulfate. Aluminum salts are preferably used and more preferably aluminum sulfate.
The presence of an alkali metal silicate in amounts of up to 5 phr is also indispensable according to the prior art.
However, all of these non rubber-specific substances that are added in large amounts during preparation of the rubber powder have to be regarded as unnecessary and in some cases even as injurious constituents of the product. These non rubber-specific substances are partially incorporated into the product and a large part remains in the precipitation water. Thus, they are potential environmental pollutants. Complicated treatment of the wastewater is needed in some instances. The aim is therefore to prepare rubber/filler masterbatches by using, as far as possible, only substances which are desirable in rubber technology and/or improve vulcanizate performance, or which at least have no adverse effect (Cabot patent, PCT/US98/20279).
SUMMARY OF THE INVENTION
The object of the present invention is to develop a precipitation and preparation process for a fine-particle, pulverulent, filled rubber which is free from the undesirable ancillary constituents mentioned above and at the same time fulfills the other requirements placed upon the rubber powder, such as control of tack, and excellent vulcanizate properties.
This and other objects have been achieved according to the invention, the first embodiment of which includes a process for preparing a fine-particle, pulverulent, filled rubber, comprising:
precipitating said fine-particle, pulverulent, filled rubber from an aqueous mixture of a filler suspension and a rubber-latex emulsion in the absence of a water-soluble salt of a metal of Groups IIa, IIb, IIIa or VIII of the Periodic Table of the Elements, and in the absence of an alkali metal silicate.
DETAILED DESCRIPTION OF THE INVENTION
The invention describes a novel process for preparing pulverulent, free-flowing rubber/filler masterbatches. The process is characterized by the following procedure.
At the start of preparation of the novel rubber powders, the entirety of the filler is divided into three portions: core black, splitting black 1 and splitting black 2. The core black, which makes up from about 30 to 60% of the entirety of the carbon black in the final product, is dispersed in water. The total amount of water depends on the nature of the filler and on its degree of disaggregation. The amount of water-insoluble constituents in the filler is generally from 1 to 10%, preferably from 4 to 7%. The amount of water-insoluble constituents includes all values and subvalues therebetween, especially including 2, 3, 4, 5, 6, 7, 8 and 9%. The filler content of the suspension acts in the absence of the abovementioned bivalent salts as a regulator for the particle size distribution that is desired in the final product. Generally, higher solids content in the suspension gives a coarser product, and lower solids content yields a finer product.
Two different precipitation procedures can then follow the preparation of these filler suspensions.
1. Precipitation using a Precipitation Tube (Semicontinuous Precipitation)
For this, a Bronsted acid, preferably sulfuric acid, is used to adjust the filler suspension described above which is composed of the core black at an early stage to the final pH value for the precipitation of from 2.5 to 6, preferably from 3.8 to 5.5. The suspension is then run through a tubular reactor together with the rubber-latex emulsion. This initiates coagulation of the latex and formation of the rubber powder grains, and the grains formed are collected in a tank. The pH value of the precipitation includes all values and subvalues therebetween, especially including 3, 3.5, 4, 4.5, 5 and 5.5.
At the same time, an aqueous suspension with a pH of from 7 to 9.5, preferably from 7.5 to 8.5, made from the second portion of the carbon black (splitting black 1) composed of from 30 to 60% of the entirety of the carbon black is fed continuously to the rubber powder grains formed in the collector. Again in parallel with this, continuous addition of 10% sulfuric acid is used to maintain the pH of the rubber powder suspension at the desired final pH for the precipitation, i.e. from 2.5 to 6, preferably from 3.8 to 5.5, and the precipitation is completed under these conditions. The grain size of the rubber powder is controlled via the continuous feed of the splitting black 1.
Once the precipitation has ended, the third portion of the carbon black (splitting black 2), consisting of from 5 to 15% of the entirety of the carbon black, is added, in the form of a filler suspension, to the aqueous rubber powder suspension. Optionally, sulfuric acid is again used to adjust the final pH value within the above-mentioned range.
2. Premix Precipitation
First, a filler suspension is prepared by dispersing a portion of the filler present in the final product preferably from 50 to 98%, in water. The portion of the filler includes all values and subvalues therebetween, especially includ
Goerl Udo
Schmitt Matthias
Stober Reinhard
Lee Rip A.
PKU Pulverkautschuk Union GmbH
Wu David W.
LandOfFree
Process for preparing carbon-black-filled rubber powders... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing carbon-black-filled rubber powders..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing carbon-black-filled rubber powders... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3081429