Cleaning and liquid contact with solids – Processes – Including distortion or deformation of work
Reexamination Certificate
2000-09-05
2002-08-20
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including distortion or deformation of work
C134S006000, C134S028000, C134S033000, C521S040000, C521S048000
Reexamination Certificate
active
06436197
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to removal of coatings (metallic, organic and/or inorganic based) from polymeric substrates. More particularly, the present invention relates to an optical media demetallization process. Most particularly the present invention relates to demetallizing optical media with high shear in the presence of an aqueous media. In a particularly preferred embodiment the present invention relates to demetallizing optical media in the presence of an organic acid at high shear conditions. The present invention also has application in removing lacquers and/or metals from a variety of other products, including, but not limited to, headlamp lenses or automotive trim components.
BACKGROUND OF THE INVENTION
Polymeric substrates are often used in a variety of applications in which a coating is applied to protect the underlying polymeric substrate while preserving optical clarity and/or improving impact resistance. Polymeric substrates are also known to be coated for decorative purposes, such as paints, and to impart a variety of other functional properties on the substrate. For example, polycarbonate sheets are often dipped into a silicone hardcoat solution, dried and then cured by known methods. Additional protective coatings commonly used on polycarbonate articles are acrylic hardcoats and hard coats based on formaldehyde-melamine resins. Other polymeric materials besides polycarbonates are known to be similarly coated such as a polymethacrylate sheet initially treated with a thermoset acrylic primer followed by the application of a silicone hardcoat.
Polycarbonates used for optical media, such as compact discs (CDs) and/or digital video discs (DVDs) present a particular problem. CDs are metallized with aluminum and then surface sealed with lacquers which may optionally be printed on. DVD halves are metallized with gold and aluminum, respectively. An adhesive is then used to bond the two halves together. The DVD is then optionally coated with an acrylic or lacquer and optionally printing is further applied thereon.
Polymeric material end users and manufacturers such as found in the polycarbonate industry have been faced with increasing environmental concerns due to the proliferation of CDs and DVDs which are becoming more and more commonplace in everyday life. The use of metals on the surfaces of these items raises significant environmental problems with their disposal. The lack of a suitable means for demetallizing the surfaces in an environmentally friendly manner have rendered the CDs and DVDs difficult to recycle. Thus landfilling has typically become the choice disposal method, which has significant environmental problems.
Current processes for the demetallization of optical media typically involve the use of a caustic solution such as sodium hydroxide. See for example, Eddy-Helenek et al., U.S. Pat. No. 5,817,183; Nee, U.S. Pat. No. 5,306,349; and Franci, U.S. Pat. No. 5,464,877. Although these processes have been shown to have some effect at demetallization, the caustic solution may cause appreciable damage to the polycarbonate polymer substrate by decreasing the molecular weight of the polycarbonate. There are additional environmental and OSHA issues associated with the use of caustic solutions on polycarbonates. One of these issues is the possible generation of bisphenol A monomer in the effluent process streams.
Mention is also made of Fennhoff et al., U.S. Pat. No. 5,151,452, which disclosed using acid media at reflux temperature and low shear conditions. Although this process would have some beneficial effect at demetallizing CDs the failure to recognize the need for high shear conditions to effect demetallization of the gold in DVDs renders this process ineffective in many applications. Furthermore, the lacquer removal process of Fennhoff et al. '452 is clearly dependent on chemical interaction between the acids and the target materials and thus fails to even remotely suggest the lacquer/metal removal by the high shear mechanical methods of the present invention.
Thus, it would represent a notable advance in the state of the art if a relatively environmentally benign process for removing coatings (optionally including metals) from a wide variety of metal surface treated polymeric scrap materials were developed.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an improved coating removal process which processes the polymeric substrate by flaking the polymeric substrate, intimately mixing the polymeric flakes at fluidized and relatively high shear conditions in order to effect the removal of the coating and any metal(s), adhesive and coating layers from the polymeric substrate, thereby creating a cleaned, undamaged polymeric flake suitable for recycling and allowing for recovery of the removed metals from the effluent through filtration or other separation or extraction techniques known to those of ordinary skill in the art. Optionally, the shearing may take place in the presence of a chemical accelerant such as one or more carboxylic acid esters, carboxylic acids or mixtures thereof.
In the case of DVDs, the present invention surprisingly also provides an effective process for recovering valuable gold content from the DVDs. Accordingly, the process of the present invention may also be performed in a closed-loop configuration to reduce environmental effects in which the release of fumes and effluent is kept relatively low and any active chemicals are conserved.
In one embodiment of the present invention there is provided a process for cleaning a polymeric substrate having a coating thereon, the process comprising the steps of: (a) mechanically flaking or granulating the polymeric substrate into relatively small particles; (b) delivering the particles of polymeric substrate to a mechanical shearing apparatus; (c) fluidizing the polymeric substrate particles; (d) shearing the fluidized particles at a relatively high rate of shear, optionally in the presence of an accelerant selected from the group consisting of carboxylic acids, carboxylic acid esters and mixtures thereof, to clean the polymeric substrate; and (e) recovering the cleaned polymeric particles. In especially preferred embodiments of the present invention, the coating on the polymeric particles includes a metallic substance, and the process of the present invention substantially completely demetallizes the polymeric particles, i.e., down to 20 ppmw of metal or less.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention provides a process for removing a coating from a coated polymeric substrate, the process comprising the steps of: (a) fragmenting the polymeric substrate into relatively small polymeric substrate particles; (b) delivering the particles of polymeric substrate to a mechanical shearing apparatus; (c) fluidizing the polymeric substrate particles; (d) shearing the particles at a relatively high rate of shear, optionally in the presence of an accelerant selected from the group consisting of carboxylic acids, carboxylic acid esters and mixtures thereof, to remove the coating from the polymeric substrate; and (e) recovering the cleaned polymeric particles.
Although polycarbonate substrates such as compact discs are used illustratively throughout the present specification, it is to be understood that the process of the present invention has application to a wide variety of polymeric substrates which have been surface coated, optionally where the surface coating also includes metals. For example the method of the present invention can also be used to clean aromatic polyester carbonates which accumulate in the production of lenses for spectacles or other optical applications, or lamp or headlight reflectors.
The polymeric substrate is first reduced into particles, fragments, flakes, granules, chips and the like by means well known to those of ordinary skill in the art. For example, the polymeric material may be cut or chopped, chipped, shredded, granulated, flaked, crushed or ground into relatively small individual particulates.
Grubb J. Michael
Heater Kenneth J.
Hodge R. Mark
Michaels Joshua R.
Sapienza Richard
Chaudhry Saeed
Gulakowski Randy
Hedman & Costigan ,P.C.
METSS Corporation
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