Material having a marker, and method for sorting a mixture of materials

Abstract

The present invention relates to a material, preferably a plastic material, comprising foreign substances, characterised in that the material further comprises fluorescent compounds, and a process for sorting a mixture of materials.

Claims

1. A process for sorting a mixture of materials, wherein the mixture comprises at least one material comprising foreign substances or having a specific composition and quality and at least one Anti-Stokes fluorescent compound, the process comprising the steps of: i) optionally comminuting the materials; ii) exciting the at least one Anti-Stokes fluorescent compound in the at least one material; iii) detecting the at least one material fluorescing due to the exciting; and iv) separating the detected at least one material from other materials in the mixture of materials by screening out fluorescing material; characterized in that the detecting in step (iii) is by detection of fluorescence of the at least one Anti-Stokes fluorescent compound in the at least one material, wherein the Anti-Stokes fluorescent compound comprises Anti-Stokes-crystals or Anti-Stokes-pigments, wherein the Anti-Stokes fluorescent compound is blended into the at least one material homogeneously.

2. The process according to claim 1, characterised in that the process is carried out in several stages, wherein different excitation energies as used in each stage in order to excite different Anti-Stokes fluorescent compounds each time and to screen out the materials containing the respective Anti-Stokes fluorescent compound.

3. The process according to claim 1, characterised in that the at least one material is a plastic material.

4. The process according to claim 1, characterized in that the foreign substances are selected from the group consisting of glass fibres, silica and mixtures thereof.

5. The process according to claim 1, characterised in that the at least one material is selected from the group consisting of polyvinyl chloride (PVC) and vinyl chloride copolymers.

6. The process according to claim 5, characterised in that the at least one material comprises PVC window frames, PVC profiles, PVC production waste and mixtures thereof.

7. The process according to claim 1, characterized in that the foreign substances are fibrous or particulate.

8. The process according to claim 1, characterized in that the at least one material is comminuted in step i) to a size of 0.1-2.0 cm.

9. A process for sorting a mixture of materials, wherein the mixture comprises at least one material comprising foreign substances or having a specific composition and quality and at least one Anti-Stokes fluorescent compound, the process comprising the steps of: i) optionally comminuting the materials; ii) exciting the at least one Anti-Stokes fluorescent compound in the at least one material; iii) detecting the at least one material fluorescing due to the exciting; and iv) separating the detected at least one material from other materials in the mixture of materials by screening out fluorescing material; characterized in that the detecting in step (iii) is by detection of fluorescence of the at least one Anti-Stokes fluorescent compound in the at least one material, wherein the Anti-Stokes fluorescent compound comprises Anti-Stokes-crystals or Anti-Stokes-pigments, wherein the Anti-Stokes fluorescent compound is present in a concentration of 10-200 ppm based on the total weight of the material.

Description

DETAILED DESCRIPTION

(1) It has surprisingly been found that fluorescent materials, preferably Anti-Stokes-crystals, can be used in the invention material, especially plastic material, as optical markers which can, when excited accordingly, be caused to fluoresce, thus indicating in a simple and reliable manner that the material under examination, right down to small particle sizes, contains certain foreign substances or is of a specific composition and should therefore be screened out. If the material or the individual particle does not glow (for example fluoresce) in a corresponding detection step, the detected materials can be subjected to reprocessing in accordance with the state of the art.

(2) In addition, it has been found that the fluorescent materials used as optical markers, especially the Anti-Stokes-crystals, exhibit such chemical, thermal and UV stability that they can fulfil their function throughout the entire life cycle of the material, even if the material is processed in several recycling cycles.

(3) Nor does the addition of fluorescent materials to the plastic material lead to any change in colour or metamerism, neither in the recycling step nor in the products made from them, such as PVC window frames, which are in no way impaired with regard to their overall properties by the addition of the fluorescent materials.

(4) It should also be emphasised that the inventive material can be detected rapidly in a reprocessing process.

(5) Because of the narrow-band excitation, the invention offers advantages over the state of the art, especially in the case of multi-stage sorting processes, if different Anti-Stokes-crystals, which fluoresce at different excitation energies or react with fluorescence, are used for the different material compositions to be separated. The separation can then be carried out in several stages. Each time, only those particles which react to a particular excitation wavelength by fluorescing are screened out. All the other particles are transported to the next sorting stage, where a different excitation wavelength is used, so that different particles are screened out.

(6) The result is that with the process of the invention, it is not the usual case that a particular colour is used to screen the fluorescence or colour of particles to be screened, but rather the excitation wavelength and the fluorescence of particular particles, while all the other particles remain dark, or do not glow, respectively fluoresce. In order to detect and localise the particles, it is therefore always possible to use uniform and simple cameras.

(7) With the markings known in the state of the art based on colours, the camera has to detect not only luminescence, but also a particular colour. With the markings known in the state of the art based on UV pigments, these first have to be excited on a broad-band basis, whereupon all the pigments luminesce, luminescing at different wavelengths. The camera then not only has to detect luminescence, but also to differentiate by wavelength or colour. The requirements for the camera are more sophisticated. The cameras have to be set to a different wavelength at each sorting station.

(8) Further features and advantages of the inventive plastic material will become clear from the following detailed description of a preferred embodiment and its use in a recycling process.

(9) Plastic material in accordance with the invention in the form of PVC window frames is delivered to a recycling plant together with PVC material which is free of preferably fibrous or particulate foreign substances. The entire material is first coarsely comminuted, which can be done with a hammer mill, for example. A preferred particle size after the coarse comminution step is about 0.2 to 2.0 cm.

(10) The coarse comminution step can preferably be followed by a wet grinding step in order to achieve a better cleaning effect and thus better detection in a subsequent detection step.

(11) After comminution, the ground material is examined with an optical detector, which, after excitation with energy of a suitable wavelength, can detect the fluorescent materials added as markers, preferably Anti-Stokes-crystals, by their glowing, respectively fluorescence, and the parts marked and detected because of that are screened out. Equipment for separating/screening out unwanted plastic parts is well-known in the art and is already in industrial use.

(12) In the detection step, the fluorescent materials, preferably Anti-Stokes-crystals, are excited by a light source of a wavelength matched to the materials added, preferably using a laser with corresponding deflection optics.

(13) The fluorescent materials may be detected by means of a camera system which is already present in conventional sorting lines.

(14) The features of the invention disclosed in the above description and claims can be essential to implementing the invention in its various embodiments both individually and in any combination.