Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1995-12-12
1998-04-28
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C08F 800
Patent
active
057445532
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is concerned with a method for the preparation of a crosslinked, extruded polymeric product whereby the polymer to be crosslinked is processed in the granulate or powder form with liquid additives while undergoing extrusion; the invention also concerns apparatus for carrying out the process.
A process and a device for the preparation of a crosslinked, extruded polymeric product is known from DE-OS 25 54 525, in which the polymer to be crosslinked is introduced through an extruder-feeding hopper of a screw extruder, and the other components necessary for further crosslinking are injected either into the lower part of the feeding hopper or directly into the neck part of the extruder.
For complete and uniform transverse crosslinking of the polymer, it is important to achieve sufficient mixing of all the components. However, this type of mixing has not yet been satisfactorily achieved with the devices available so far. Mere injection of certain components into the polymer located in the extruder-feeding hopper or in the neck of the extruder permits only achieving a high additive concentration in and around the injection point. Subsequently, the reaction mixture must be mixed in the extruder with the aid of an expensive extruder screw and even during homogenization. Thus, the conditions for good crosslinking are unfavorable and, moreover, an extruder screw is necessary, which is complicated and can be produced only at great expense.
Furthermore, it has been shown that when processing a conventional synthetic polymer granulate by injecting the additive necessary for crosslinking produces insufficient surface wetting of the granulate, which results in severe disadvantages. Although experiments were carried out to avoid these disadvantages, by providing a mixer before introducing the material into the extruder screw in order to achieve favorable mixing and wetting of the granulate, it was shown that the granulate commonly used is difficult to wet because of its smooth surface and because of its relatively large volume. The disadvantage resulting from this is that the liquid components are transported separately from the polymer granulate in the extruder screw all the way to the melting phase which will lead to local accumulation of liquid and thus to concentration differences, which finally has a strong adverse influence on the homogeneity of the material prepared from it.
A further developed process for the processing and crosslinking of a polymer with other substances is described in U.S. Pat. No. 4,703,093. Here, the polymer is finely ground and heated in order to increase the surface and to form gaps in the surface. As a result of this grinding and heating, the absorbing ability of the polymer for the crosslinking substances is increased. Cooling occurs after mixing the polymer granulate with the crosslinking substances.
In this further developed process, too, the mixing of the polymer with the additives or crosslinking substances is still insufficient, even though the material mixture is heated to increase reactivity in order to achieve better mixing of the substances.
SUMMARY OF THE INVENTION
Therefore, the task of the invention is to further develop a method and a device of the type mentioned at the outset so that better wetting of the granulate and thus better mixing is achieved before melting.
In order to solve this task, the method according to the present invention for the preparation of a crosslinked, extruded polymeric product, in which the polymer to be crosslinked is processed with liquid additives by extrusion, is characterized by the fact that a polymeric granulate or polymeric powder with a fissured, porous surface is used.
Preferably, polyethylene is used for crosslinking. It is especially favorable to use a polymer granulate/polymer powder, especially a polyethylene, with a density of about 0.89 to 1 g/cm.sup.3. The grain size of the polymer material is expediently about 10 .mu.m to 2 mm.
In carrying out the method, the polymer granulate/polymer pow
REFERENCES:
patent: 4703093 (1987-10-01), Thurman
Bernhard Rustige GmbH & Co. KG
Cain Edward J.
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