Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
2001-08-03
2004-06-01
Beck, Shrive P. (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S508000, C427S516000, C427S521000, C427S140000, C427S142000, C427S146000, C427S147000, C427S148000, C427S149000, C427S150000, C427S152000, C427S154000, C427S155000, C427S156000, C427S407100, C427S409000
Reexamination Certificate
active
06743466
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for repairing coated substrate surfaces by means of radiation-curable coating compositions. The process may find application particular for repairing small coating blemishes in automotive and industrial coating.
DESCRIPTION OF RELATED ART
It is known to use coating compositions curable by high-energy radiation in automotive coating and likewise in automotive repair coating. Coating compositions based on free-radically polymerizable binders are in particular used in such applications. This application also utilizes the advantages of radiation-curable coating compositions, such as, the very short curing times, the low solvent emission of the coating compositions and the good hardness and scratch resistance of the resulting coatings.
When repairing coating blemishes, it is often unnecessary to completely recoat an entire vehicle or vehicle part, for example, a bonnet. In the case of small coating blemishes, it is usually sufficient to recoat the area immediately surrounding the blemished area (spot repair). The preparation, coating and clean-up effort expended by the finisher is here largely independent of the size of the coating blemish to be repaired. For example, operations, such as, preparing the coating material and spray gun, putting on the breathing mask, applying the coating with a spray gun, cleaning the spray gun and other equipment or containers must always be carried out.
There is accordingly a requirement in repair coating for a simplified processes to repair small coating blemishes, in particular also in those cases in which only a top coat is to be repaired.
Prior art processes are known in which, as an alternative to conventional spray application, coated films are applied onto the substrate to be treated, for example, an automotive body. The films may here be provided on one side with one or more coating layers and may have on the same or the other side an adhesive layer so that the film can be fixed to the substrate. Where appropriate binders are used, the coating and/or adhesive layers may also be cured by ultraviolet light (UV) radiation. Such films and corresponding application processes have often been described in the literature, for example in WO-A-00/08094, WO-A-00/63015, EP-A-251 546 and EP-A-361 351. In general, the film is laminated onto the substrate, where it remains. DE-A-196 54 918 describes coating film usable for decorative purposes that comprises a “free coating film”. The coating film comprises an adhesive layer and at least one coating layer. It is possible to dispense with a stabilizing backing film in this case.
SUMMARY OF THE INVENTION
The process according to the invention provides a process for repairing coated substrate surfaces by means of radiation-curable coating compositions, which process is in particular suitable for repairing small blemished areas, for example, in the context of repair coating in automotive original coating or in a repair bodyshop and permits the performance of the repair to the required quality quickly and straightforwardly without major preparation and clean-up effort.
The present invention relates to a process for repairing coated substrate surfaces comprising the following successive steps:
a) optionally preparing a blemished area to be repaired,
b) providing a backing film coated on one side with an uncured or at least partially cured coating layer of a coating composition curable by means of high energy radiation,
c) applying the backing film with its coated side onto the blemished area to be repaired,
d) irradiating the coating applied in this manner onto the blemished area to be repaired with high energy radiation and
e) removing the backing film, wherein
the coating is irradiated through the backing film and/or after removing the backing film.
DETAILED DESCRIPTION OF THE EMBODIMENTS
It has surprisingly been found that, using the process according to the invention, it is possible quickly and straightforwardly to repair in particular small coating blemishes without any reduction in quality in comparison with conventional processes. Smooth, optically faultless surfaces are obtained which have the good hardness and solvent resistance typical of UV cross-linking systems.
Steps d) and e) are preferably performed in such a manner that irradiation proceeds through the backing film, the backing film is removed after irradiation and irradiation is optionally performed again after removal of the backing film. It is also possible, but less preferred, to irradiate the coating only after removal of the backing film.
The individual steps of the process according to the invention are explained in greater detail below.
In general, the blemished area to be repaired is prepared prior to the repair. In this case, the process according to the invention begins with step a), namely preparation of the blemished area to be repaired. This involves preparing the damaged coating in accordance with the requirements of the repair. Normally, the coating is initially thoroughly cleaned, for example, with a silicone remover. The surface may then be sanded lightly with rubbing compound or sandpaper and optionally cleaned once again. If necessary, a putty composition, for example, may be applied and appropriately post-treated. Alternatively, the blemished area may also be prepared by laser treatment.
Step b) of the process according to the invention comprises the provision of a backing film coated on one side with an uncured or at least partially cured coating layer of a coating composition curable by means of high energy radiation. The backing film comprises films made from any desired, in particular thermoplastic, plastics that meet certain requirements with regard to UV transmittance and heat resistance. In the case of the preferred embodiment of irradiation in which high energy radiation is passed through the backing film, the films must transmit UV radiation and be resistant to the temperatures that arise in the film material on irradiation with UV radiation. The films must also be resistant to the temperatures optionally required for partially gelling/tackifying the applied coating layer. Suitable film materials are, for example, polyolefins, such as, polyethylene, polypropylene, polyurethane, polyamide and polyesters, such as, polyethylene terephthalate and polybutylene terephthalate. Films may also consist of polymer blends and also may be optionally surface-treated. It is also possible for the films to have a textured surface, for example, a micro- and/or macrotextured surface. The thickness of the films may, for example, be between 10 and 1000 &mgr;m, preferably, between 10 and 500 &mgr;m, particularly preferably, between 20 and 250 &mgr;m and is determined by practical considerations of processability. The films selected should preferably be those that are elastic and extensible and cling effectively to the substrate by electrostatic forces.
The backing films are coated on one side with liquid or pasty coating compositions curable by means of high energy radiation. The coating compositions may be aqueous, diluted with solvents or contain neither solvents nor water. The coating compositions curable by irradiation with high energy radiation are cationically and/or free-radically curable coating compositions known to the person skilled in the art, wherein free-radically curable coating compositions are preferred.
Cationically curable coating compositions that are to be applied onto the backing film in the process according to the invention contain one or more cationically polymerizable binders. These may comprise conventional binders known to the person skilled in the art, such as, polyfunctional epoxy oligomers containing more than two epoxy groups per molecule. These comprise, for example, polyalkylene glycol diglycidyl ethers, hydrogenated bisphenol A glycidyl ethers, epoxyurethane resins, glycerol triglycidyl ether, diglycidyl hexahydrophthalate, diglycidyl esters of dimer acids, epoxidised derivatives of (methyl)cyclohexene, such as, for example 3,4-epoxycyclohexylmeth
Doessel Karl-Friedrich
Fey Thomas
Flosbach Carmen
Lenhard Werner
Reis Oliver
Beck Shrive P.
E. I. du Pont de Nemours and Company
Kolb Michener Jennifer
Lerman Bart E.
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