Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Patent
1997-02-27
1998-04-07
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
521 54, 521 59, 521 60, 521134, 521143, 264DIG7, C08J 9232, C08J 924, C08J 933, C08J 935
Patent
active
057365857
DESCRIPTION:
BRIEF SUMMARY
The application relates to polyethylene and/or polypropylene foam moldings for packaging which consist of more than 50% of recycled material.
Polyethylene and in particular polypropylene foam moldings for packaging are enjoying increasing popularity and proliferation owing to their very good material properties, for example good impact absorption and resistance to solvents. Compared with polystyrene foam, their higher costs are disadvantageous for widespread use.
Under these circumstances and also in order to improve disposal of used packaging moldings, it is desirable to process the latter and to re-use them for the production of packaging moldings. Indeed, this is already done to a small extent. However, the fact that the material properties of recycled material are drastically reduced means that recycled material can only be used in maximum amounts of 20-30%.
The object was therefore to improve the processing and recycling of used polyethylene and/or polypropylene foam moldings in such a way that moldings having good material properties, even when they contain high proportions of recycled material, can be produced.
This object is achieved by the present invention.
The invention therefore relates to a process for the production of polyethylene and/or polypropylene foam moldings for packaging, which is characterized in that the starting material consists of more than 50% of recycled material.
The invention also relates to polyethylene and/or polypropylene foam moldings for packaging which are characterized in that they comprise more than 50% of recycled material.
Crucial factors for these possibilities, which are surprising to the person skilled in the art, are both novel and modified process steps in the processing of the used material to give beads which can be employed in molding, and also in the production of the moldings themselves.
The used material is generally processed in such a way that a material with the highest possible type purity is obtained by removal of foreign substances. This material is first subjected to coarse comminution, for example in a shredder, and then ground under gentle conditions in a mill with interchangeable screens, so that the polymer foam beads which have been fused to form the moldings are removed from the composite with as little damage as possible and are recovered.
In spite of this gentle grinding, it is impossible to prevent the primary particles (polymer foam beads) from being attacked and suffering damaged surfaces. The irregular and rough surface formed seems to be partially responsible for the poor quality of moldings produced from recycled material. Surprisingly, it has now been found that thermal aftertreatment of the polymer foam beads obtained from recycling allows a significant improvement to be achieved. To this end, the material is agitated at an elevated temperature of about 40.degree.-90.degree. C. in a tank with rotating internals, resulting in smoothing of the bead surfaces.
The aim of this aftertreatment is to approximate the surface structure of the recycled material to that of virgin material. The result of the treatment is a significant improvement in the quality of moldings obtained from this material.
However, in order to obtain high-quality moldings, the bead processing conditions are preferably also modified. The processing of virgin material generally commences with impregnation, i.e. charging with air at superatmospheric pressure, usually of from 2.5 to 3.5 bar. The material is then blown into the mold, where it is compressed mechanically, and finally fused by heat treatment, for example by the action of superheated steam.
The process conditions to be observed here, for example the pressures and temperatures to be used, depend on the materials to be processed, but are known to the person skilled in the art both for polyethylene and for polypropylene foam and can be obtained from relevant publications, for example the processing guidelines published by the raw material manufacturers, for example BASF AG (Ludwigshafen), Kaneka (Belgium) or JS
REFERENCES:
patent: 4013616 (1977-03-01), Wallace
patent: 4104206 (1978-08-01), Hachiu et al.
patent: 4123584 (1978-10-01), Brewton
Bossler Hans
Meyer Harald
Scherer Josef
Foelak Morton
Merck Patent Gesellschaft mit beschrankter Haftung
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