Coating processes – Restoring or repairing – Metal article
Reexamination Certificate
2001-09-27
2002-12-17
Beck, Schrive P. (Department: 1762)
Coating processes
Restoring or repairing
Metal article
C427S140000, C427S256000, C427S258000, C427S265000, C427S286000, C427S287000, C427S407100, C427S409000, C427S421100
Reexamination Certificate
active
06495201
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the multi-layer repair coating of substrates with colour- and/or special effect-imparting water-based base coats and with transparent clear coats. The process may find application in particular in vehicle repair coating.
For ecological reasons, water-based coatings are also being used to an increasing extent in vehicle repair coating. However, the coatings obtained with water-based coatings do not yet achieve the high level of quality of conventional solvent-based coatings in terms of all the properties. For example, wetting faults in respect of the substrate may occur during the application of water-based base coats. Further disadvantages are the visual appearance of the coating layers applied which is still unsatisfactory at times, such as, for example, the clouding tendency, inadequate clear coat stability during coating over with clear coats and, in the case of special effect water-based base coats, an insufficient special effect development. The relatively long flash-off and drying times are generally a disadvantage when water-based coatings are used.
There has been no lack of attempts hitherto to overcome or at least mitigate the disadvantages of the prior art, for example, by appropriate binder developments and adapted coating composition formulations. The application parameters such as atomization parameters (nozzle parameters) or sequence of application and method of application of the coating material also have a substantial effect on the visual appearance of a coating. For the application of water-based base coats, for example, it has been proposed in the past to apply the coating compositions in one operation comprising a preceding thin spray pass and a subsequent normal spray pass (“Anwendungstechnische Information” Spies Hecker; Permahyd® Base coat series 280, water-dilutable; A-data sheet no. 100.0/03/97-D).
In the same way, it is possible to operate with two normal spray passes followed, in the case of special effect coatings, by an additional over-spraying spray pass (Technical Data Sheet Chromax® “Basislacksystem auf Wasserbasis”; REF Chromax-3-D of 09.12.1998).
Moreover, a process for repair coating with aqueous metallic and special effect base coats is described in EP-A-729 390, for example, wherein the water-based base coat is applied to the prepared surface of an existing coating in a first spray pass until a boundary is reached and the surface thus coated is then coated with the water-based base coat in a second spray pass. Said process stages are then repeated, again until a boundary is reached, until the entire object to be coated is provided with the base coat layer.
A process for repair coating by means of a blend-in-system is described in EP-A-719 185 wherein an aqueous base coat is applied in a covering finish to the damaged part in one spray pass, and whilst the base coat is applied to the zones of the existing coating adjacent to the defect the spray gun is inclined towards the defect such that the spray gun forms an angle between 25 and 65° with the surface of the existing coating.
It has not yet been possible, however, to improve the above-mentioned disadvantages satisfactorily with the application methods known in the prior art, so there is still a need for further improved processes for multi-layer repair coating with water-based base coats.
The object of the invention was, therefore, to provide a process for the multi-layer repair coating of substrates, particularly of vehicles, which makes it possible to apply water-based base coats of good quality similar to that of conventional solvent-based base coats. The water-based base coats, particularly special effect water-based base coats, should have a low clouding tendency during application and good special effect development. No wetting faults in respect of the substrate should occur. The water-based base coat layers should exhibit good clear coat gloss and flow when coated over with clear coats. Moreover, shorter flash-off times are required. The relatively high build-up of coating material at critical places such as corners, edges or flanges should also be improved.
SUMMARY OF THE INVENTION
The object of the invention is achieved by a process for the multi-layer repair coating of substrates wherein a base coat layer of a colour- and/or special effect-imparting water-based base coat coating composition is applied to a precoated substrate and a clear coat layer of a transparent clear coat coating composition is applied to the base coat layer thus obtained, which is characterised in that the base coat layer of the water-based base coat coating composition is applied in three successive spray passes and each spray pass is executed such that uniform, adjacent and substantially non-overlapping coating strips are applied to the substrate surface to be coated.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The application of the water-based base coats takes place according to the invention in three successive spray passes, i.e., the water-based base coats are applied in three successive layers. The spray passes to be executed are not normal full spray passes but so-called half spray passes (0.5 spray pass). The peculiarity of these in comparison with a normal full spray pass (1 spray pass) is that no uniformly continuous coating film is formed on the substrate surface by the coating applied in an individual half spray pass, when considered by itself. Effectively, an incompletely and non-uniformly covering coating layer with an incomplete covering capacity is applied with a half spray pass. The term covering capacity in this context means the ability to cover up the colour or the colour differences of the substrate (see DIN 55 987: 1981-02). Only by virtue of the combination of the three coating layers to be applied in the three half spray passes is a covering coating layer obtained with a uniformly continuous coating surface. A half spray pass is also described in coating terminology as a thin, open spray pass. A half spray pass is not, however, an over-spraying spray pass. The coatings expert is familiar with the terms “normal full” spray pass and “half” spray pass and with the equivalent terms that may be used and is able to translate these terminological definitions into practice without difficulty.
A spray pass is generally executed in such a way that uniform coating strips are applied on the surface to be coated, i.e., the coating material is applied in uniform parallel strips with the spray gun until the entire surface is coated. The spray gun is passed evenly over the spray surface at an angle of approximately 90°. One applied coating strip has a layer thickness gradient over the width of the coating strip such that a decrease in layer thickness to as little as 0 &mgr;m towards the edges of the coating strip is obtained and a layer thickness maximum is present in the central zone of the coating strip which approximately corresponds to the desired layer thickness to be applied. In order to produce a covering coating film with a uniformly continuous film surface on the substrate to be coated with one spray pass, each coating strip applied on the surface should therefore usually overlap by about half with the preceding applied coating strip, within one spray pass (see, e.g., “Das Fachwissen für den Maler und Lackierer”, Stam-Verlag Cologne, Munich, 2nd edition 1989, p. 169, 170). According to the invention, however, not withstanding this, each spray pass is executed in such a way that adjacent, substantially non-overlapping coating strips are applied. Substantially non-overlapping in this context means non-overlapping or only slightly overlapping, whereby the zones of overspray between two adjacent coating stripes may quite overlap. In this way, an incompletely and non-uniformly covering coating film with a non-uniformly continuous surface is produced with one spray pass. The next spray pass in each case is then advantageously applied such as to be at least partially offset in relation to the preceding spray pass, i.e., the coating st
Berschel Guenter
Duda Andrew
Feyrer Wolfgang
Beck Schrive P.
Deshmukh Sudhir G.
E. I. du Pont de Nemours and Company
Kolb Michener Jennifer
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