Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1994-08-09
1998-02-03
Drodge, Joseph W.
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
134 10, 134 26, 210774, 210805, 210806, 264 37, 264DIG69, B01D 1104
Patent
active
057140707
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for cleaning polyolefin, in particular polyethylene recyclate shreds, as well as to devices for carrying out the process.
2. The Prior Art
Polyethylene is a polyolefin, which is processed in large quantities for the manufacture of foils for packaging purposes. For example, shrink hoods, bags and the like are manufactured from the foils.
Polyethylene, as a thermoplastic material, is fusible and formable repeatedly because of its molecular structure. It is basically suitable for being reused several times. However, reprocessing to high-quality recycling products, preferably to polyethylene foils with defined properties, is opposed by the fact that the used articles, particularly foils, are equipped during their manufacture with application-oriented additives such as antistatic agents, lubricants, thermal or UV-stabilizers, which are then present in unknown amounts and combinations in the recycling product manufactured from such articles. Sorting of the used articles according to ingredient substances is hardly possible technically and economically speaking.
Recycling products, in particular foils loaded with such ingredient substances lead to problems during further processing, for example during gluing, welding or imprinting. Often, the connecting seams, which initially show good properties, come apart only at the user.
Furthermore, the used foils contain degradation products of the polyethylene such as polyethylene waxes, as well as decomposition products of the additives. Such products develop during the life span in the course of processing processes, as well as due to the action of heat, light and weathering. They effect to some extent a considerable reduction of the properties of use of the recycling product.
Finally, the used foils, in particular packaging foils, are more or less heavily imprinted. During the extrusion of recycled materials, such printing inks lead to polyethylene foils with a strong undefined discoloration, so that only refuse bags dyed in dark colors can be manufactured from such materials. With very high proportions of imprinted areas in relation to the amount of polymer, even unusable regranulates foamed by decomposition gases can be obtained.
For removing the foil additives, the nonpolar polyethylene waxes and the adhering printing inks from the used foils, DE-OS 4 122 277 discloses a known method. It specifies a process in which the used foils are shredded and, under intensive motion, subjected to an extraction in a solvent bath containing an organic solvent.
The shreds treated under heat with an organic solvent, following mechanical separation of the solvent, still contain about 50 to 60% by weight solvent, for example in the case of ethyl acetate. The solvent can be found both on the surfaces of the shreds and diffused into the interior of the shreds. In addition, on the surface, the shreds contain residues of nitrocellulose, the preferred vehicle for flexographic printing inks. Such residual amounts of nitrocellulose, even though low, lead to carbonization during regranulation, and thus to black spots in the recyclate foil.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide processes by which polyolefin, preferably in the form of polyethylene shreds, can be cleaned.
According to the invention, this object is achieved by a process for the removal of solvent and/or nitrocellulose residues from precleaned polyolefin, particularly from precleaned polyethylene recyclate shreds, said process being characterized in that the polyolefin is mixed with water, the solvent is either expelled or separated by extraction, and the residues of nitrocellulose are at the same time washed off from the surfaces of the polyolefin shreds.
In the process according to the invention, expelling and/or extraction can take place continuously or discontinuously.
In a special implementation of the process, ethyl acetate is used as the solvent.
In a discontinuous procedure, for example in an
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Drodge Joseph W.
Nordenia Verpackungswerke GmbH
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