Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-07-27
2003-05-13
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339060, C250S339120
Reexamination Certificate
active
06563119
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for identification of different plastic materials by optical measurements, especially by spectroscopy analysis.
BACKGROUND OF THE INVENTION
The plastics industry has experienced global growth in the past decades and this tendency will be continued in the future, as plastic products are used for a lot of products, being sold in increasing numbers. Especially casings for computers, laptops, screens, televisions, packaging materials, interior elements and devices in cars as well as external automotive parts, furniture, casings for electronic devices, etc. are manufactured from different plastic materials or even combinations thereof.
With the increasing manufacturing of plastic and plastic products, disposal and recycling of such plastic products have become a problem for the environment. Therefore, it is desired to recycle most of the plastic materials. For an effective recycling it is necessary that these plastic materials are identified and separated, as different materials require different and separated further treatments.
As sorting and identification techniques, different methods are known in the art, using e.g. properties such as density, electrical, magnetical, tripological or chemical separation. But, there are similar polymers, like co-polymers or polymer blends, as well as materials with different additives that cannot be separated by these methods.
Therefore, optical measurements, especially spectroscopic techniques have been developed. Different techniques are known in the art, as e.g. Near Infrared Reflection (NIR), Mid-Infrared Reflection (MIR), MIR Pyrolysis, MIR Acousto-Optic Tunable Filters (AOTF), RAMAN Scattering, or others. Among the above mentioned techniques, NIR, MIR and RAMAN are the techniques with the best reliability for identification of plastic materials, as used in modern products.
With the above mentioned or other spectroscopic measurements, samples are measured and sample spectra as well as reference spectra for specific plastic materials are provided. Normally, the raw data, achieved by the spectroscopic measurement, are further prepared and/or processed, e.g. by performing a Fourier Transformation, a base line correction, a vector normalization, etc., in order to make a further comparison of reference spectra and sample spectra easier and more reliable. These preparations of raw data can be performed e.g. by means of a computer together with respective computer programs.
After a sample spectrum has been measured and prepared or processed, it will be compared to reference data of all plastic materials of interest. Spectral distances between the sample spectrum and between each reference spectrum is determined, whereas the sample is supposed to be of the material with the reference spectrum that shows the minimum spectral distance, ideally the spectral distance is equal to 0.
Because the number of plastic materials of interest is possibly very large, a lot of comparing steps of the sample spectra with each reference spectra over the whole frequency range, e.g. in MIR between 400 and 4000 cm
−1
, is necessary. Such a procedure is very time consuming, and the correct identification ratio is unsufficiently low, as the measured and achieved spectral distances do not clearly distinguish for some possible materials of interest.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and an apparatus for identification of plastic materials of interest, wherein the procedure can be conducted in a less time consuming way and wherein more reliable results and therefore a higher correct identification rate can be achieved.
This object is solved by a method according to claim
1
and an apparatus according to claim
24
. Claims
2
to
23
show preferred features of the inventive method of independent claim
1
and claims
25
to
26
show preferred embodiments of the apparatus according to claim
24
.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, at least one identification range having a high absolute deviation ratio D and/or a high smoothed deviation ratio D′ between all pairs of possible plastic materials of interest is determined and a spectral distance, i.e. the added distance between two spectra to be compared over the relevant region, is only determined within said at least one identification ratio. A “high” ratio in this sense covers both high plus and minus values.
The absolute deviation ratio reflects a ratio between the absolute signal distances of the spectra of two materials to be compared and the consistency or noise and is therefore an indicator for the reliability of the measurement at the respective frequency for these materials. The identification frequency ranges are therefore those areas, where the distance between the absolute signals of the respective spectra to be compared is very high on the one hand and the noise is very low on the other hand, thereby leading to a high reliability. The noise may be measured by means of a standard deviation, when measuring a certain number of samples with the same molecular origin, but also any other value for the noise or consistency of the measurements can be used.
With the inventive method, only the frequency ranges, where spectral differences are present, will be investigated. Thereby a processing of areas, where the still remaining possible plastic materials of interest do not show remarkable or measurable differences, is omitted, thereby saving valuable measurement time.
Furthermore, and even more important, the reliability of a measurement results can be increased by comparing spectra only within limited ranges, as measurement noise will add up over a wide measurement range and may probably eliminate signal or spectra differences, making an identification impossible. Further, spectral distances that can be measured in a certain frequency range may add up to 0 with spectral distances in another frequency range, when measuring over the whole possible range, i.e. over more than the identification frequency range, as it is done according to the known methods of the state of art. The method according to the invention therefore avoids erroneous identification decisions.
The method according to the present invention has especially advantages, when polymers, containing additives, and similar plastic materials, having similar spectra over a wide frequency range, have to be identified.
It has been shown that with the present invention a reliability, i.e. a correct identification rate, of over 95 to 98% can be achieved within less than 2 seconds when identifying the standard main stream plastics.
Depending on the materials that have to be identified and separated, the reliability factor of the identification results is therefore up to 3 times better in comparison with a method according to the state of art.
When determining more than one identification frequency range and simply adding the spectral differences in all identification frequency ranges, it should be cross checked that there is no nullification or remarkable decreasing of the overall spectral difference (and therefore of the sum or integral of the deviation ratio over all identification frequency ranges) between all pairs of possible materials, as this might decrease measurement reliability. No problems will arise, when each identification frequency range is first considered separately and the overall spectral difference over all frequency ranges is determined by adding only absolute values |x|, i.e. positive values, of each identification frequency range, as spectral differences in each identification range can then only add up, when not taking into account different signs (plus/minus).
According to another aspect of the present invention, the method comprises at least two process or method levels, being conducted subsequently, wherein in each level the number of possible materials of interest is further limited. Within each level, the sample spectra, achieved by
Frommer William S.
Frommer & Lawrence & Haug LLP
Hannaher Constantine
Megerditchian Samuel H.
Moran Timothy
LandOfFree
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