Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2002-11-07
2004-09-21
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C134S016000, C521S040000
Reexamination Certificate
active
06793709
ABSTRACT:
The present invention relates to a process for recycling electronic scrap material such as optical recording media, for instance CDs and DVDs. In part the process involves delamination of electronic scrap material in order to recover the constituent components of it.
The use of optical recording media such as CDs and DVDs has increased enormously in recent years with applications in the computer and audio/visual entertainment industries. These media typically include a metal, such as aluminium and/or precious metals (typically gold or a mixture containing gold) provided on a polymeric substrate such as a polycarbonate. Typically the metal is provided on the polymeric substrate as a thin metallic film. A protective layer is usually formed on the outer surfaces, and acrylates such as polymethyl (meth)acrylates are commonly used in this respect. These optical recording media have a relatively short life of only a few years as they may become superseded or outdated. This leads to a considerable waste stream. Furthermore, there is a waste stream generated at the time of manufacture due to strict quality control standards: typically up to 20% of manufactured product is rejected. Disposal of such waste is an increasing concern and recycling techniques are being investigated. Similarly other electronic scrap materials including precious metals and plastics are becoming increasingly available, and disposal of them is an important consideration also. In this specification the term “electronic scrap material” is used to embrace all such materials, including optical recording media such as CDs and DVDs.
Known processes for recycling electronic scrap material include smelting and chemical dissolution treatments that are primarily directed at recovering precious metals. Such methods tend to be damaging to any associated plastic material and, furthermore, the disposal of the plastic material can lead to environmental problems. Accordingly, chemical recycling methods tend not to be sympathetic to the environment.
U.S. Pat. No. 5,306,349 assigned to Sony Music Entertainment Inc discloses a method for removing lacquer and aluminium coatings from the polycarbonate substrate of compact discs. This method uses an alkaline solution and the application of ultrasonic energy to compact discs immersed in this solution. Such treatments are not satisfactory when gold is present. Furthermore, the treatment could degrade the polycarbonate plastic.
Recycling methods which rely on physical rather than chemical mechanisms have also been applied. For example, attempts have been made to remove a metallic layer from a polymeric substrate by slicing or shaving techniques. However, with such techniques the throughput can be relatively low and thus uneconomic where a large number of articles are to be recycled. Additionally, for security reasons, manufacturers sometimes choose to cut articles to be recycled (e.g. CDs and, DVDs) into pieces prior to transportation to a recycling facility. Techniques such as slicing and shaving cannot be applied practically to the articles in cut form.
With this background in mind, the present invention seeks to provide a process for recycling an electronic scrap material which does not involve hazardous or potentially harmful chemicals and which is thus environmentally friendly, has high throughput and does not rely on the material to be recycled being in unitary form. The method is easy to perform and economic in practice. Moreover, it has been found that the polymer component it is desired to recover does not significantly degrade during the recycling process so that production of a high grade recycled product may be achieved.
Accordingly, the present invention provides a process for recycling an electronic scrap material comprising a metal provided on a polymeric substrate, which method comprises:
milling flaked electronic scrap material with a bead impact material in the presence of water to produce flakes of cleaned polymeric substrate;
adding water to the milled material and separating the flakes of cleaned polymeric substrate from metal-containing material;
dewatering and drying the flakes of cleaned polymeric substrate; and
treating the metal-containing material to recover the metal.
In the present specification the term milling is used to denote any process by which attrition of the surface of the flakes of scrap material by contact with the bead impact material may be achieved. Such attrition removes of surface layer(s) of the scrap material and is a fundamental aspect of the present invention. In the context of the present invention the terms milling and attrition may be used interchangeably in addition to their usual meanings in the particle science industry.
The scrap material to be milled is in flake form. This means that the scrap material, for example a CD or DVD, is cut into individual flakes. This may be achieved using a conventional shredding machine or granulator. Ideally shredding/granulation cuts the material cleanly without any bending or distortion so that the resultant flakes are planar (assuming the original unitary material is planar). Bending or distortion of the scrap material during shredding/granulation can lead to metal smearing of the polymeric substrate material and/or may reduce the efficiency of the subsequent milling operation due to shielding effects.
The scrap material may be cut into flakes at the intended site of recycling or it may be supplied to the site in flake form. Thus, the process of the invention may include as preliminary steps the transportation of electronic scrap material to a flaking station followed by cutting the material into flakes. The flakes may then be transported to a recycling station where subsequent processing is carried out in accordance with the steps of the invention already described. If the scrap material is provided as is to the site where recycling is to take place, flake preparation will obviously be required prior to the subsequent processing. It is envisaged that in practice the scrap material would be supplied to a recycling facility in flake form. Depending on the flake size, further cutting of the flakes may be required prior to processing.
In an embodiment of the invention the flake size prior to milling is usually in the range 1 to 20 mm, for example 1 to 15 mm, preferably 4 to 8 mm and more preferably 4 to 6 mm. The optimum flake size will depend upon such factors as the size of the bead impact material used in the milling step. If the flake size is too small, valuable polymeric material may be lost as fines in downstream process steps.
The flake size has implications with respect to the size of bead impact material used in the milling step. Thus, for relatively large flakes, milling may be optimised using a different size bead impact material when compared with the size of bead impact material most suitable for attrition of smaller flakes.
In a preferred embodiment, the flake size falls within a narrow distribution so that a correspondingly narrow distribution of size of bead impact material may be used in the milling step. For example, it is preferred that at least 50 wt %, for instance at least 75 wt % of flakes have a size of 4-8 mm, and preferably 4-6 mm. It will be appreciated however that a given batch of flakes to be treated may well have a broad distribution of flake size, and to optimise the milling step, bead impact material having a range of particle sizes may be used.
In an embodiment of the invention the flakes to be processed may include a distribution of flake size such that it will be most efficient to mill flakes above a predetermined size with a first size of diameter bead impact material and to mill flakes at or below the predetermined size with a second size diameter of bead impact material. This embodiment of the present invention would thus comprise the following steps:
milling flaked electronic scrap material that is above a predetermined flake size with a first size diameter of bead impact material in the presence of water to produce flakes of cleaned polymeric substrate;
mill
Hall John S
Heater Kenneth James
Hodge Robert Mark
McRae-Williams Michael Scott
Andrews Melvyn
Hedman & Costigan ,P.C.
METSS.org, LLC
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