Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2001-04-06
2003-01-14
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S385500, C427S421100, C427S508000, C427S510000, C427S512000, C427S514000, C427S521000, C427S557000, C427S558000, C427S559000
Reexamination Certificate
active
06506458
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of lacquering, in particular of multi-coat lacquering motor-vehicle bodies or parts thereof using, in particular, water-based lacquers, in particular in the field of motor-vehicle repair lacquering.
For ecological reasons, attempts are being made to replace solvent-based lacquers by water-based lacquers to an increasing extent, even in the field of motor-vehicle repair lacquering. The water-based lacquers developed have already reached a quality level that makes them equal to the solvent-based lacquers in a plurality of properties. Some properties have, however, not yet reached the quality level of solvent-based lacquers. For example, the use of water-thinnable undercoat, clear and one-coat top lacquers still presents problems in ensuring.uniform lacquering quality, in particular with regard to surface properties and interlayer adhesion under varying external conditions. It is particularly difficult to achieve a reproducible drying of water-based lacquers and a uniform surface lacquering quality resulting therefrom under ambient conditions involving widely varying atmospheric humidity.
The object of the invention was therefore to provide a method of multi-coat lacquering, in particular for motor-vehicle repair lacquering, which makes it possible to achieve coatings having a high and uniform lacquering quality, in particular with regard to surface properties and interlayer adhesion, when water-based undercoat, clear and one-coat top lacquers are used. The uniform quality of the lacquering should be ensured, in particular even under widely varying ambient conditions during application, such as, for example, atmospheric humidity. The lacquering quality should likewise be uniform at critical points, such as corrugations or edges. Furthermore, hard and scratch-resistant coatings should be obtained by the method according to the invention. Associated therewith is the requirement for a good coating polishing capability and, in particular, for a good polishing capability relatively quickly after application and drying.
It has been found that this object can be achieved by the use, to which the invention relates, of NIR radiation for curing clear-lacquer coats or one-coat top lacquers on motor-vehicle bodies or parts thereof, in particular in the case of repair lacquering.
The NIR (near-infrared) radiation used according to the invention is short-wave infrared radiation having the wavelength range from about 760 to about 1500 nm, preferably 760 to 1200 nm.
SUMMARY OF THE INVENTION
The invention furthermore provides a method of lacquering a substrate by applying a clear-lacquer coating compound to a precoated substrate or a one-coat top lacquer coating compound to an optionally precoated substrate, followed by curing, the substrate being a motor-vehicle body or parts thereof, which is characterized in that the substrate is subjected, after the application of the clear-lacquer coating compound or one-coat top lacquer coating compound, optionally to a drying phase and the curing is then performed by irradiation with NIR radiation having the wavelength range from 760 to 1500 nm.
DETAILED DESCRIPTION OF THE INVENTION
The clear-lacquer coating compound or one-coat top lacquer coating compound used according to the invention may preferably be water-based. It is, however, also possible to use solvent-based coating compounds.
The method according to the invention may be, in particular, a method of multi-coat lacquering. In this case, a top lacquer coating is applied, for example, to the substrate, optionally coated with filler compounds and/or further coating compounds. Said top lacquer coating may be composed, for example, of a colouring and/or special effect producing solvent-based or water-based undercoat coating compound and a water-based clear-lacquer coating compound. The top lacquer coating may also be composed of a water-based pigmented one-coat top lacquer-coating compound. For example, the procedure may be such that, in the case of application of the top-lacquer coating compound in the form of a pigmented one-coat top lacquer, the top-lacquer coat is first subjected optionally to a drying phase and then cured by irradiation with NIR radiation and that, in the case of application of the top-lacquer coating compound in the form of an lacquer undercoat/clear-lacquer structure, a lacquer undercoat is first applied, after curing of the lacquer undercoat or in the wet-on-wet form, optionally after a drying phase, the clear-lacquer coating is applied, optionally subjected to a drying phase and then cured by irradiation with NIR radiation.
The use of NIR radiation generally to dry paints and lacquers is known. As possible applications, for example, the following fields are mentioned: the printing sector, film drying, pipe drying, wood coatings, and powder coatings. As particular advantages of the NIR technology, mention is made of the very rapid drying, in particular in the case of water-based lacquers, and the gentle drying as a result of low heating of the substrate. Nothing is known of the possible applications of this technology in motor vehicle lacquering, in particular motor-vehicle repair lacquering.
Surprisingly, it has now been found that the object of the present invention can be achieved by using NIR radiation to cure clear-lacquer and one-coat top lacquer coatings in a multi-coat structure.
The irradiation performed in the method according to the invention with NIR radiation can be performed with a conventional, high-energy NIR source. Such NIR sources are available commercially (for example from the Industrie SerVis company). These are, for example, high-power halogen sources having a radiation density of generally more than 1 W/cm
2
, preferably more than 10 W/cm
2
, up to, for example, 15 MW/m
2
. The sources reach, for example, a source surface temperature (incandescent filament temperature) of over 2500 K, for example of 2500 to 3000 K. Suitable sources have, for example, an emission spectrum with a maximum between 750 and 1200 nm.
Preferably, a drying phase is included, according to the invention, before the irradiation with NIR radiation. The drying phase is performed conventionally, for example in air or by blasting with air, for example at temperatures of 10 to 80° C., in particular at room temperature. The air blasted may optionally also be heated. Various blasting systems may be used, for example hand-held blasting guns, rack-mounted or wall-mounted blasting systems. In the simplest case, drying can be achieved by standing at room temperature.
As a result of including a drying phase, it is possible to avoid blister formation on the lacquer surface that sometimes occurs with NIR irradiation in the case of direct irradiation after application.
Clear-lacquer coating compounds and one-coat top lacquer coating compounds that can be used in the method according to the invention are, for example, conventional water-based clear lacquers and one-coat top lacquers known to the person skilled in the art, such as those used in the field of motor-vehicle lacquering, in particular of motor-vehicle repair lacquering. The clear-lacquer coating compounds and one-coat top lacquer coating compounds contain water-thinnable binders. The water-thinnable binders are the conventional binders known to the person skilled in the art for this application purpose. They may, for example, be one-component or two-component water-thinnable binder systems. Preferred, however, are two-component binder systems.
Examples of one-component binder systems are those based on water-thinnable polyurethane, polyacrylate, polyester and/or alkyd resins. The one-component binder systems may, for example, be physically or oxidatively drying.
Examples of water-thinnable two-component, crosslinkable binder systems are those based on hydroxyl-functional binders, such as, for example, polyurethane polyols, polyesterurethane polyols and/or polyacrylate polyols and polyisocyanates, based on acetoacetyl-functional and (meth)acryloyl-functional binders, and based
Blatter Karsten
Lenhard Werner
Deshmukh Sudhir G.
Pianalto Bernard
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