Daimler-benz Ag

Jorg Zurn

Michele Melchiorre

Karsten Lohr

Bernd-Uwe Kettemann

Martin Guldenpfennig

A process for stripping of used parts or reject parts, in particular of polycarbonate (PC) or of a polycarbonate blend, preferably with polybutylene terephthalate (PBT/PC), for the purpose of recycling the plastic. In this process the plastics parts are first mechanically comminuted to a pourable size and then are circulated together with anhydrous alkalified diethylene glycol or propylene glycol in a mass with mutual abrasion of the plastics chips at elevated temperatures of at least 50.degree. C., preferably from 80.degree. to 100.degree. C., until complete removal of the paint. Thereafter the stripped plastics chips are separated from the stripping agent, flushed and then dried. The quantity of glycol added corresponds to from 1 to 10% of the volume of the mass to be treated, so that the circulated parts are only wetted by the glycol, but with stripping agent being circulated continuously through the treatment space of the mass from a relatively large reservoir. The circulation of the mass of parts is preferably carried out in a closable free-fall or positive mixer or in a rotary tube mixer. During the abrasive circulation the plastics parts are preferably admixed with abrasive particles whose specific apparent density corresponds roughly to the specific apparent density of the plastics parts.

Chemo-mechanical stripping of paint from plastic parts

A process is provided for disintegration and pure-sorted separation of different plastics of composite structural parts to be recycled, which parts consist of a support composed of thicker-walled hard plastic, an intermediate layer applied with firm adhesion to this support and composed of foam material, and a flexible foil adhering firmly to the outside of the intermediate layer and made thinner-walled than the support. The composite structural parts are first comminuted into approximately cuboid particles preferably of a granulation of approximately 20 mm and comprising still different plastics. Subsequently, the particles formed are disintegrated in a dry manner into their individual materials, and these are then separated in a pure-sorted manner. For this purpose, the less break-resistant foam material of the particles is selectively comminuted mechanically by an impact stressing of the particles to form substantially smaller crumbs than the remaining pieces of particles of more break-resistant plastic. The smaller foam crumbs are screened off from the coarser remaining particle pieces. These two operations are advantageously carried out in a batchwise operated hammer mill with an integrated screen plate. To produce cuboid particles, the composite structural parts are first cut into narrow strips in a twin-shaft cutter, and these are subsequently chopped into short parts in a knife mill. Where three-component structural parts are concerned, the initially remaining mixture of thick-walled hard-plastic fragments and of thin-walled foil chips is separated in a pure-sorted manner by a vertical low-turbulence wind sifter.

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Ulm, Germany

Jorg Zurn