Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1985-10-03
1987-10-06
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523307, 523309, C08J 322
Patent
active
046983783
DESCRIPTION:
BRIEF SUMMARY
The subject invention relates to a process for continuously converting PVC and additives, possibly with fillers, to a free flowing plastics pre-blend, and
refers to a procedure for the dispersion of granular or pulverized solids with liquid components, in particular for the continuous production of PVC-Dry-Blend in a vertical continuous blender provided with centrifugal disks rotating from a vertical shaft.
It is the task of the invention to propose a procedure capable of producing reactive and free flowing powders or agglomerates by means of blending and wetting granular or pulverized solids with liquids. In order to reduce the thermic stress to a minimum during the blending process and by maintaining the blending quality, that is, because either the solid particles and/or the liquid component are sensitive to a prolonged thermic exposure, the blending time is to be reduced to a few seconds.
This process enables a confectioning of granulated PVC materials in the sense of stabilizing the PVC in such a manner that it subsequently resists the high requirements at elevated temperatures in a kneading machine or other further processing apparatus. In this respect, the decomposition temperature is lower than the further processing temperature, so that the decomposition temperature need to be increased. This enables the prepared product to be processed further at high temperatures, without being decomposed thereby.
According to prevalent opinions, during a "dry blend", a PVC-Hot-Mixture must reach a blending temperature that is below the plasticization range of a PVC-mixture, e.g., depending on the preparation procedure, between 85.degree. and 150.degree. C.
For plasticized PVC a softening agent is added at 50.degree. to 60.degree. C. For unplasticized PVC the plastic raw material will be heated to the point of softening or melting in order to agglomerate with the admixed stabilizers and possibly fillers and to form a free flowing sintered powder. According to prior art, for this level of preparation, machines that proceed step by step are applied. They are either slow running and heatable ribbon flights or plough bar blenders or fast running turbomixers with a small chamber volume whereby a hot mixer is frequently combined, with a subsequent cooling mixer, in order to quickly cool the batch. Since the temperature increase depends on the size of the batch, the specific temperature of the product and the introduction of energy per time unit and since the first two parameters are set, the developments always concentrated upon introducing higher levels of energy per time unit into the blend.
During the hot mixing or dry blend, that is blending and simultaneous heating of the PVC to just below the plasticization temperature, that is approx. 130.degree. C., all additives are ground up, melted down and absorbed by the PVC-granulate. The product of the hot mixing process is called "dry blend". In order to produce "dry blend", energy introductions of 100-150 KJ/kg are deemed necessary.
Other plastic pre-blends are prepared in a similar manner.
Surprisingly, it has now been discovered that a high blending quality can be achieved even by a most gentle preparation process with minimal energy introduction, if the solids are vortexed at high revolutions and continuously dosaged into a continuous blender at room temperature and if the solids are simultaneously wetted by a highly heated liquid component. Hereby it is useful if the liquid component is heated acutely and immediately before dispersion.
For plasticized PVC it is advantageous if the liquid component is heated to 80.degree.-200.degree. C. and blown in. For unplasticized PVC, the passage slit between the inner wall of the housing and the continuous mixer and the rotors in form of centrifugal disks, is made smaller in an essentially known manner and high energies can thus be introduced kinematically into the penetrating material. The additives melt within a fraction of a second thus blending with the added solid admixtures. Cooling takes place in the process and a free
REFERENCES:
patent: 4252844 (1981-02-01), Nesgood et al.
patent: 4322170 (1982-03-01), Papenmeier
Franz Peter
Wehrli Werner
Buss AG
Michl Paul R.
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