| 摘要 |
An apparatus and a method are disclosed, for use to sort objects such as bottles, made of different transparent or translucent plastic materials according to the kind of plastic material of which these objects are made. The method consists in producing a beam of U.V. light and subjecting each object to be sorted to this beam in a detection zone, and detecting the intensity of the beam transmitted by the object at different wavelengths selected within a range encompassing the "cut-off wavelengths" of the different plastic materials to be sorted, the cut-off wavelength being the wavelength known per se and specific to each plastic material, above which the coefficient of light transmission through the plastic material, dramatically increases. By comparing with each other the values of the intensity detected at said different wavelengths, one can determine the cut-off wavelength of the plastic material of which the object subjected to the beam is made, and thus identify this plastic material. This method makes it possible to industrially recycle reject objects made of different plastic materials, which has proved to be very difficult to do up to now.
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