Liquid purification or separation – Processes – Using magnetic force
Patent
1996-09-09
2000-10-10
Reifsnyder, David A.
Liquid purification or separation
Processes
Using magnetic force
210744, 210767, 210772, 210800, 134 2, 134 10, 134 2217, 134 29, 510109, 510181, 510202, 510206, 510417, B08B 308, C23F 400, B01D 1102, B01D 3506
Patent
active
061298476
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for recovering raw materials from finely chopped wastes of magnetic recording media, consisting of a polymeric substrate and a magnetic layer present thereon, in which finely divided magnetic powder is dispersed in crosslinked or uncrosslinked polymeric binder, the magnetic powder and the substrate material being recovered by treatment in an alkaline medium.
In recent years, the rapid growth of the information industry has resulted in extensive consumption of large amounts of magnetic storage media, such as computer tapes, audio tapes, video tapes and diskettes. In particular, magnetic tapes and diskettes which have, for example, polyethylene terephthalate as the substrate have been produced in growing amounts in recent years, owing to their excellent magnetic and mechanical properties. In general, residues and wastes of such storage media occur in large amounts in the production and during use by the end users. At present, such wastes are disposed of by depositing them with the domestic waste in sanitary landfills or incinerating them in incineration furnaces. From the point of view of waste reduction and the recovery of useful materials, full utilization of such wastes is an outstanding requirement.
A process of the generic type stated at the outset is disclosed in German Offenlegungsschrift DOS 3,341,608. According to this publication, the magnetic tape wastes are finely shredded, after which the magnetic layer and the substrate are delaminated in aqueous alkaline solution and the magnetic powder is separated from the substrate by stirring at high speed. This process requires a very complicated bulky apparatus.
Further processes which are based on separation of the magnetic layer from the substrate by treatment with a base are described in Japanese Applications 112 979 (1978), 006 985 (1979), 070 404 (1978), 092 879 (1978) and 167 601 (1987) and Korean Application 89/03614. Japanese Applications 313 707 (1988), 112 413 (1989) and 146 624 (1982) describe separation by treatment with an acid. Japanese Application 054 050 (1983) describes the use of a solvent mixture comprising phenol and tetrachloroethane for delamination of the magnetic layer.
U.S. Pat. No. 5,246,503 discloses a delamination solution for coatings which consists of organic solvent, water, thickener and wetting agent, but where in addition the coating has to be removed mechanically by scratching.
If it is intended to delaminate the magnetic layer and the substrate and the aim is to recover the useful materials, in particular the magnetic powder and the polyethylene terephthalate, the PET film should as far as possible not be chemically degraded or attacked. If, on the other hand, polyurethanes crosslinked in the magnetic layer, are used as binders as described, for example, in European Patent 0,099,533, the processes described above are for the most part unsuccessful or give unsatisfactory results with regard to separation, delamination and recovery.
German Application P 43 30 839.9 discloses a process for recovering raw materials from magnetic recording media, in which these raw materials in finely chopped form are treated in organic solvents, an acid which is soluble therein and alcohols or thioalcohols and, if required, surfactants at elevated temperatures, the magnetic layer delaminated in this manner being separated from the substrate by a washing process, and thereafter both the finely shred substrate wastes and the magnetic powder being dried. That feature of this process which is essential for the invention is that the ester groups of the polyurethane binder are cleaved by hydrolysis by the stated treatment medium, whereas at the same time the ester groups of the polyethylene terephthalate substrate are not chemically destroyed. It has been found that it is difficult in this process to fulfill these boundary conditions; furthermore, the finely shred wastes must be treated for many hours in order to achieve complete separation.
It is an object of the present invention to provide a process of the ge
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WPI/Derwent; JP60223835 A (Abstract), Aug. 11, 1985.
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Eicher Jochen
Muller Norbert
Sartor Karl-Heinz
Schulze Axel-Rudiger
Stephan Oskar
BASF Magnetics GmbH
Reifsnyder David A.
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