Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-06-26
2001-08-21
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S205000, C523S207000, C523S210000, C523S215000, C523S216000, C523S217000
Reexamination Certificate
active
06277901
ABSTRACT:
The invention relates to a rubber additive granulate, to a process for its preparation by means of fluidized-bed technology, to its use in the preparation of rubber mixtures and to rubber mixtures and products created using it.
In the preparation of rubber mixtures for rubber production, liquid and solid substances are mixed with the rubber or the rubbers. The solids are on the one hand substances having melting or softening points below the processing temperature and on the other hand substances which are not present in molten or softened form at the processing temperature. From the point of view of solubility, the solids to be mixed in can be divided into those which are well soluble in rubber, those which are not soluble in rubber and various intermediate forms.
The more poorly soluble the substances and in particular the solids are, and the higher the melting point or the less the softening at the processing temperature, the more difficult is their dispersion.
The incorporation and the distribution, i.e. the dissemination of the solids is decisively determined by the form in which they are supplied as a commercial product to the rubber-processing industry: fine powders form clouds of dust which are often also frequently electrostatically charged, so that mixing-in losses, unhealthy dust formations and workplace contamination result. Fine powders also often form agglomerations upon incorporation, which cannot be broken up again with the forces occurring in the rubber mixture, so that deficient distribution and dispersion qualities result.
Coarse powders or substance granulates are more likely to have small dust contents and in most cases can be better incorporated into the rubber. However, it must be guaranteed that the forces occurring in the mixture are capable of mechanically reducing and distributing the coarse particles to an adequate degree.
It is the state of the art to store solid substances for rubber production in silos or at least place them in day silos. They are removed from such silos by screws, conveyor belts and/or pneumatic conveyance to the automatic weighing station and onward from there to be fed into the mixing unit. While in storage and also when being transported by the producer to the rubber-processing plant, powders, in particular fine powders, tend to cake depending on the stacking height or layer thickness, as a result of which an automatic further processing is ruled out.
While in storage, powders are also exposed, unprotected, to environmental influences such as for example humidity, oxygen, carbon dioxide and nitric oxides, as a result of which caking or even chemical reactions result. The consequence is that they cannot be transported and/or there is a diminution of the effect of the additive in the rubber mixture.
When powders are being transported from the silo to the mixing unit, other possible occurrences are caking, incrustation, bridging in pipes, an increase in the dust content as a result of mechanical reduction of coarser constituents in the powders and wear in the transport apparatus caused by abrasive, i.e. grinding solids or constituents of solids.
Solutions described hitherto in the state of the art to the problems listed above follow various routes, which are briefly explained in the following:
1. The powdery substances are bound with various oils, in most cases mineral oil, and/or other non-polymeric ingredients, optionally subjected to a special physical treatment and then marketed as a non-dust-forming, easy-flowing powder, as a paste or in the form of small rods measuring several millimetres, cylinders, flakes, scales, lozenges or balls. These forms offer various advantages compared with the original finely powdered form: some lie in the weighing and feeding steps, some in the smaller dust content and in a reduced electrostatic charge, others in more rapid incorporation and distribution, and yet others in protection against humidity and carbon dioxide. However, it is rare for more than two of the said possible advantages to be obtained at the same time, with the result that these forms of product can be described as technically satisfactory only in special cases.
2. The rubber-processing industry itself produces pre-mixtures, so-called batches. A rubber which is also used in the main mixtures is mixed with powdery chemicals or chemicals bound in accordance with point 1 and optionally with other constituents customary in rubber processing such as oils and processing additives and then added to the main mixtures. However, problems often result during storage and feeding, as such batches do not permit automatic feeding with customary processes. Moreover, there remain the problems of finely powdered substances or those treated in accordance with point 1 during processing, albeit in the preparation of the pre-mixture, instead of the main mixture.
3. The chemicals are bound into a matrix comprising higher-molecular-weight cross-linked materials such as factices or epoxidized fatty acid triglycerides which have been cross-linked by means of dicarboxylic acids, as is described in DE 39 20 411, and the like. The matrix is firm and as dust-free as possible under the transport conditions. Under incorporation conditions, it melts or undergoes mechanical decomposition. The remaining problems are in this case stability of the transport form, silo storage plus automatic transport, weighing and feeding. Moreover, compatibility with the rubber mixture does not always obtain. The homogeneity of the distribution with this product form is decisively determined by the particulate fineness of the powdery chemicals upon incorporation into the matrix.
4. The chemicals are bound in a matrix comprising elastomeric polymerizates with thermoplastic properties and supplied to the rubber-processing industry in the form of cylinders or cubes having diameters measuring a few millimetres. In most cases the matrix consists of ethylene/vinyl acetate copolymer and/or ethylene/propylene co- or terpolymer together with oil and dispersants based on fatty acids, as is described in DE 21 23 214. The problems of dust generation and of automatic feedability are thus solved. However, there are still dispersion problems. These result either from the fact that the polymers using for binding are compatible with only some of the rubbers used in the rubber-processing industry, and/or the fact that the created particles are too hard for the rubber mixture into which they are to be incorporated. In addition, a longer incorporation time is necessary, because of the particle size.
5. It is merely a further development of the method according to point 3 to disperse the substance in a polymerizable liquid and then polymerize this, as described in EP-A-0 625 543, especially if, as is described in the patent, the solid powdery substance is mixed together with a so-called ester plasticizer into natural or epoxidized natural fatty acid triglyceride, and polybasic acid is then added in the form of phosphoric acid and the composition is thus cross-linked to give a product which is somewhat plastic but can be made to crumble. Although this form is dust-free and can be obtained for a smaller energy outlay and with a better homogeneity, relative to the chemicals preparation that is to be mixed in, compared with the method according to point 4, it also has the disadvantages listed in point 3.
The object of the present invention is accordingly to provide rubber additives in a composition which is suitable for use in rubber or rubber mixtures. The additives are to be capable of being readily incorporated into the rubber and display a high degree of effectiveness in the rubber or in the rubber mixture. The compositions are also to be characterized by good a dispersability in the rubber and good compatibility with customary rubbers and with one another. In addition, the formulation of the composition is to guarantee stability during transportation and storage and be processing-friendly (no dust formation, rapid processability).
A further object of the invention is to provide a process for the
Cain Edward J.
Collard & Roe P.C.
Schill & Seilacher (GmbH & Co.)
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