Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-07-27
2003-04-29
Lee, John R. (Department: 2881)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C356S300000
Reexamination Certificate
active
06555822
ABSTRACT:
The present invention relates to a method for identification of different plastic materials by spectroscopy measurements.
Plastics industry has experienced a permanent 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. The total plastic waste generated by the E&E sector was estimated to have reached 830.000 tons and is expected to increase up to 1.400.000 t in the year 2005.
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. One of the main problems occur in the use of flame retardant additives in plastic products to meet specific safety specifications. The percentage of plastics treated with flame retardants in “brown products” like TV sets is about 50%, whereas in the data processing equipment 100% of external parts of monitors are treated with flame retardants. These additives may be hazardous and therefore require specific environmental consideration and treatment for waste recovery.
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.
Especially with carbon filled (black) plastics, the identification of materials is very difficult and the identification rate is insufficiently low.
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 modem 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.
Especially for plastic materials containing flame retardants or additives, e. g. for coatings, the identification procedure of the state of art is not sufficiently reliable.
It is therefore an object of the present invention, to provide a method 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 achieved by a method according to claim
1
. Claims
2
to
21
show preferred features of the inventive method of independent claim
1
.
According to the invention a multi-level measurement is conducted, wherein in each level the number of possible materials is further limited. At least in the first level, there are defined at least two sub-group of possible materials, wherein one sub-group comprises all possible materials that are easily distinguishable from each other and at least one further group comprises materials that are difficult to distinguish from each other. To each sub-group there is at least one identification frequency range associated. This at least one identification frequency range is dependent on the possible materials of interest contained in the respective group. The spectral distances are only determined within said at least one identification frequency range and with respect only to the reference spectra of the materials being comprised in the respective sub-group.
By selecting and grouping possible materials of interest according to this invention, the spectral distances between sample spectra and reference spectra, necessary to be determined with a high resolution in order to reliably identify the sample material, can be determined, dependent on specific selected materials in a sub-group, only in frequency ranges, where spectral distances are present. Furthermore, spectral distances in “different directions” (plus/minus value), possibly leading to a nullification of the determinable spectral distance over the respective frequency range, can be avoided, thereby leading to extremely reliable identification results. Furthermore, the processing time for comparing sample spectra and reference spectra can be decreased, as only limited frequency ranges have to be taken into account.
The grouping and the association of specific identification frequency ranges to the respective sub-groups therefore leads both to a very high reliability and to very short identification times. Measurements with common plastic materials being used in most consumer products, including plastics with flame retardants and additives, did show identification results with a reliability of over 99% within a identification time of less than 1 second.
Preferably, the identification frequency ranges of each sub-group in one level have no frequency overlap. In addition, spectra appear only once in the respective sub-group. A clear distinction between frequency ranges, where spectral distances are relevant and measurable, taking into account the ratio between signal value and value differences and also taking into account noise of the measurements, from frequency ranges not showing a remarkable spectral distance, having an insufficient noise/signal or noise/signal-difference ratio, is achieved, thereby supporting reliability of the measurements.
With respect to mostly used and common plastic materials in consumer products, i. e.,the most important plastic materials of interest according to the invention, in the following there are given preferred groupings and identification frequency ranges as preferred realizations of the inventive method as claimed in claim
1
of the present invention.
For the sake of clarity, in the following there are given some short definitions for the terms used in the specification and in the claims: A “polymer” in the sense of this invention consists of an elementary (monomeric) unit and a chain. Such an elementary unit can be, for example, a styrene, wherein the chain can be an ali
Kalivoda Christoher M.
Lee John R.
Smid Dennis M.
Sony International (Europe) GmbH
LandOfFree
Method for identification of plastic materials by optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for identification of plastic materials by optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for identification of plastic materials by optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3091262