Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2001-03-07
2002-08-13
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S385500, C427S407100, C427S508000, C427S553000, C427S557000, C427S559000, C427S595000
Reexamination Certificate
active
06432491
ABSTRACT:
The invention relates to a process for multilayer lacquering with, in particular, waterborne lacquers which finds application in particular in the field of vehicle refinishing.
For ecological reasons, attempts are being made to an increasing degree to replace solvent-based lacquers by waterborne lacquers, also in the field of vehicle refinishing. The waterborne lacquers developed have already achieved a quality level which makes them equal in quality to solvent-based lacquers in terms of a majority of properties. Some properties have not yet, however, reached the quality level of solvent-based lacquers. For example, when water-thinnable surfacers are used, inadequate sandability is observed. Moreover, it is difficult to guarantee a uniform quality of the coating, particularly with regard to surface properties and inter-layer adhesion, under different external conditions. Under conditions of greatly varying atmospheric humidity it is particularly difficult to obtain reproducible drying of waterborne lacquers and a resulting uniform surface quality of the lacquering.
The object of the invention was, therefore, to provide a process for multilayer lacquering, more particularly for vehicle refinishing, which makes it possible, even when waterborne surfacer coating compounds are used, to obtain surfacer layers with a high and uniform quality of the lacquering, particularly with regard to the surface properties and inter-layer adhesion. The uniform quality of the lacquering should also be guaranteed in particular under greatly varying ambient conditions during application, e.g., atmospheric humidity. A uniform quality of the lacquering should also be obtained at critical places such as beads or edges. Moreover, it should be possible to sand the surfacer layers obtained satisfactorily and rapidly.
It became apparent that this object may be achieved if a surfacer layer applied to an optionally precoated substrate is irradiated with NIR radiation. The invention therefore provides the use of NIR radiation for irradiating surfacer layers during the multilayer lacquering of substrates.
The NIR (near infra-red) radiation used according to the invention is short-wave infra-red radiation in the wave length range from about 760 to about 1500 nm, preferably 760 to 1200 nn.
The invention also provides a process for multilayer lacquering in which a surfacer coating compound is applied to an optionally precoated substrate and is then cured, a top coat layer of a colour-imparting and/or special effect-imparting base coat and a clear coat coating compound or of a pigmented one-coat top coat coating compound is applied to the surfacer layer obtained and cured, which is characterised in that, after application of the surfacer coating compound, the not yet cured surfacer layer is irradiated with NIR radiation in the wave length range from 800 to 1500 nm. According to a preferred embodiment of the invention, a waterborne surfacer coating compound is applied. It is also possible, however, to use solvent-containing surfacer coating compounds.
After application of the waterborne surfacer coating compound in particular, the not yet cured surfacer layer obtained may optionally undergo a flash-off phase. According to a preferred embodiment of the invention, irradiation with NIR radiation is carried out to dry the waterborne surfacer layer in particular.
Curing of the waterborne surfacer layer (final curing) may be carried out with a suitable curing process. It may be carried out, for example, at room temperature, by forced drying at relatively high temperatures, by irradiation with UV or IR or NIR radiation. Final curing with UV or NIR radiation is preferred.
It is also possible, however, to carry out curing of the surfacer layer after an optional flash-off phase only with a single NIR irradiation phase.
The use of NIR radiation in general for drying paints and lacquers is well known. Examples of potential applications include the following sectors: printing industry, film drying, pipe drying, wood coatings, powder coatings. Examples of particular advantages of NIR technology include the very rapid drying, particularly in the case of waterborne lacquers, and the gentle drying due to low heating of the substrate. Nothing is known about the potential applications of this technology in vehicle lacquering, particularly vehicle refinishing.
Surprisingly, it has now been found that the object of the present invention may be achieved by the use of NIR radiation for drying and curing waterborne surfacer layers in particular in a multilayer structure. It was also surprising that the surfacer could be dried directly with NIR radiation at all. Rather, in view of the great film thickness and the surfacer surface which coheres rapidly as a result of irradiation, it was to be expected that a considerable property gradient from the film surface to the interface with the substrate in terms of hardness, sandability and adhesion would be obtained.
The irradiation with NIR radiation carried out in the process according to the invention may be carried out with a conventional high-energy NIR radiator. NIR radiators of this kind are available commercially (for example, from Industrie SerVis). These are, for example, high output halogen radiators with a radiation density from generally more than 1 W/cm
2
, preferably more than 10 W/cm
2
to, for example, 15 MW/m
2
. The radiators reach a radiator surface temperature, for example, (coiled filament temperature) of more than 2000 K, e.g., from 2000 to 3000 K. For example, suitable radiators have an emission spectrum with a maximum between 750 and 1200 nm.
According to the invention, a flash-off phase may be included prior to irradiation with NIR radiation. The flash-off phase may be carried out in the usual way, for example, by leaving the article to stand in the air or by blowing on air, e.g., at temperatures from 10° C. to 80° C., for example, at room temperature.
Examples of surfacer coating compounds which may be used in the process according to the invention include conventional waterborne surfacers known to the skilled person, of the kind used in the field of vehicle lacquering, particularly vehicle refinishing. The surfacer coating compounds contain water-thinnable binders. The water-thinnable binders are the conventional binders known to the skilled person for this application. They may be, for example, one-pack or two-pack water-thinnable binder systems.
Examples of one-pack binder systems are those based on polyurethane, polyacrylic, polyester and/or epoxy resins. The one-pack binder systems may be, e.g., physically or oxidation drying.
Examples of two-pack crosslinkable binder systems are those based on hydroxy-functional binders such as, e.g., polyurethane, polyester urethane and/or polyacrylate polyols, and polyisocyanates based on epoxide/polyamine systems, based on acetoacetyl-functional and (meth)acryloyl-functional binders and based on acryloyl-functional or acryloyl- and glycidyl-functional binders and polyamines. Examples of the above-mentioned binder systems are described in more detail in DE-A-41 23 860, DE-A-42 26 243, DE-A-42 26 270, EP-A-542 209 and EP-A-476 388.
It is also possible to use water-thinnable binders which can be cured at least partially by high-energy radiation, preferably UV radiation. These are preferably binders which may be cured by free-radicals. Preferred binders which may be cured by free-radicals are prepolymers such as poly- or oligomers which have olefinic double bonds capable of free-radical polymerisation, particularly in the form of (meth)acryloyl groups in the molecule. The prepolymers may be present in combination with reactive thinners, i.e. reactive liquid monomers.
Examples of prepolymers or oligomers are (meth)acryloyl-functional (meth)acrylic copolymers, epoxy resin (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, polyurethane (meth)acrylates, unsaturated polyesters, unsaturated polyurethanes or silicone (meth)acrylates with number-average molecular masses (Mn) preferably in the range from 200 to 10,000,
Blatter Karsten
Lenhard Werner
Deshmukh Sudhir G.
E. I. du Pont de Nemours and Company
Pianalto Bernard
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