Plastic and nonmetallic article shaping or treating: processes – Treating shaped or solid article – To remove entrained material from article
Patent
1992-07-22
1994-03-01
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Treating shaped or solid article
To remove entrained material from article
134 13, 159 23, 264 37, 26421123, 264349, 264DIG69, 425209, B29B 1702
Patent
active
052905055
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The instant invention relates to a method of recycling plastic sheet material coated with adhesive and available in chopped form by separating the plastic from the adhesive.
BACKGROUND, OBJECTS AND SUMMARY OF THE INVENTION
The underlying problem in the first place pertains to the art of manufacturing adhesive tapes from plastics but it is transferable equally well to any kind of plastic material which is coated with adhesive. The manufacture of plastic adhesive tapes and of the other materials mentioned involves the production of waste, for instance, in the form of marginal strips cut off from the material in the manufacturing process. In a more general sense the term "plastic waste coated with adhesive" preferably is understood as relating to waste of thermoplastic materials, especially polyethylene, polypropylene, polystyrene, polyester, and polyvinyl chloride (PVC). Even in optimized manufacturing processes the proportion of this waste--among others also due to rejects--still accounts for some 10% of the production and, as a rule, results in the form of chopped sheet material of varying size, preferably between 1 and 10 mm long, at the manufacturer's of plastic film or sheet material. It is not only economic for reasons but also under environmental aspects that renewed use is aimed at of this adhesive coated plastic sheet material waste in the form of its separated components.
An economically operating process of the kind mentioned initially is unknown. True, DE-OS 38 31 023 discloses a beneficiation method for reuse of soiled plastic products wherein the chopped sheet material is agitated in a washing solution of organic solvents and subsequently removed from the washing solution in a turbulence-free zone, then predried mechanically by centrifugal force, and thereafter redried thermally by hot gas, the solvent being recycled from the drying stage into the washing stage. However, this known method is not suited to achieve the aim of the instant invention, namely the sustained separation of the adhesive from the plastic sheet material, or not so in an economic manner. Rather, the known method is directed at cleaning the plastic waste mentioned from contamination; the method steps in that case are not adapted to bring about sufficient separation of adhesives from the chopped sheet material, which adhesives stick quite firmly to the chopped sheet material, such as rubber-based adhesives which are not soluble in water and glycol.
It is the object of the invention to indicate a method of the kind mentioned initially for separating the adhesive from the chopped sheet material by means of a solvent in an economic and reliable way.
This object is met, in accordance with the invention, in that time while the solvent is being added so that the adhesive will become dispersed in the solvent; chopped sheet material by the action of mechanical force and discharged.
The kneading of the adhesive-coated chopped sheet material in the presence of the solvent in method step (a) turns the adhesive and the solvent into a pasty, honey-like dispersion which can be separated from the chopped sheet material in the subsequent method step (b), for example by squeezing or shearing forces. It is an advantage of the novel process that reliable separation is achieved and that it is economical because the residence time of the chopped material is short and little solvent is used as compared to the amount of adhesive to be separated. In addition, the adhesive is yielded in the form of a solvent-adhesive dispersion which also permits direct renewed used of the adhesive, such as by applying it on sheet material.
To obtain particularly clean chopped sheet material, the novel method preferably is carried out in two stages, or best in three stages, where method steps (a) and (b) present one first stage of the process which is followed by a second stage or by second and third stages, each comprising steps (a) and (b). Here the chopped sheet material being treated always comes from the preceding stage, the solvent-ad
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Patent Abstracts of Japan-vol. 10, No. 78 (C-335) (2135) 27. Marz 1986 & JP,A,60 212 434 (Takeda Yakuhin Kogyo K.K.) 24. Oktober 1985 siehe Zusammenfassung.
Patent Abstracts of Japan-vol. 11, No. 282 (C-446) (2729) 11. Sep. 1987 & JP,A,67 079 241 (Mitsumaru Kagaku K.K.) 11. Apr. 1987 siehe Zusammenfassung.
Huber Gerhard
Pichl Karl
Thurlow Jeffery
WNC-Nitrochemie GmbH
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