Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-06-21
2002-10-29
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S258000, C427S287000, C427S385500, C427S386000, C427S388100, C427S393500, C427S407100, C427S407300, C427S409000, C427S410000, C427S435000, C427S443200, C427S496000, C427S500000, C427S508000, C427S510000, C427S514000, C427S551000, C427S552000, C427S553000, C427S554000, C427S555000, C427S558000, C427S559000, C427S595000, C427S596000
Reexamination Certificate
active
06472026
ABSTRACT:
The invention relates to a process for the multi-layer lacquering, in particular repair lacquering, of substrates, with a surfacer layer and a top lacquer layer, which in particular has uses in the automotive lacquering and automotive parts lacquering field.
Multi-layer automotive repair lacquer finishes generally consist of a surfacer layer applied to optionally pre-coated substrates and a top coating comprising a colour-imparting and/or special effect-imparting base lacquer layer and a transparent clear lacquer layer. However, it may also be a case of a top coating comprising a pigmented one-layer top lacquer.
Ecological considerations are behind a drive to reduce solvent emissions also from coating compounds in automotive repair lacquering. Thus, aqueous coating compounds or so-called high-solids coating compounds have already been developed for virtually all the lacquer layers. For example, two-component waterborne lacquers based on hydroxy-functional binders and polyisocyanate curing agents and on epoxy/polyamine systems are known for the surfacer and primer sector. On a number of points, however, coatings obtained with these lacquers still fail to match the properties of conventional solvent-based surfacers and primers. For example, the sandability of waterborne surfacers is still inadequate, and there are difficulties in achieving blister-free application at higher layer thicknesses.
In particular, reduction of the solvent content of base lacquers, especially in special-effect base lacquers which at approximately 80 wt. % have a high organic solvent content, makes an effective contribution towards the lowering of overall lacquering solvent emission. Waterborne base lacquers have already been developed for use in automotive repair lacquering. However, the coatings obtained with these waterborne base lacquers still fail to match the properties of conventional base lacquers on some points. For example, water resistance, hardness and inter-layer adhesion are still inadequate.
The same is also true of waterborne clear lacquers. For example, resistance to petrol and water still need improvement, as do hardness and appearance.
When waterborne lacquers are used a prolonged drying time must furthermore generally be accepted, thus compromising productivity, for example in a lacquering workshop.
It is already known to use coating compounds which are curable by means of high-energy radiation in automotive lacquering.
EP-A-540 884 describes a process for producing a multi-layer lacquer finish for automotive production line lacquering by the application of a clear lacquer layer to a dried and cured base lacquer layer, with the clear lacquer coating compound containing binders which are curable by free radical and/or cationic polymerisation, and with curing being carried out by means of high-energy radiation. Irradiation of the clear lacquer layer is followed by the stoving process, with the base lacquer and the clear lacquer being stoved together at, for example, from 80 to 160° C.
EP-A-247 563 describes UV-curable clear lacquers based on a poly(meth)acryloyl-functional compound, a polyol mono(meth)acrylate, a polyisocyanate, a light stabiliser and a photoinitiator. Here, some of the radiation-curable binders still contain hydroxy functions which are able to react with the available polyisocyanate, and afford additional curing potential.
EP-A-000 407 describes radiation-curable coating compounds based on an OH-functional polyester resin esterified with acrylic acid, a vinyl compound, a photoinitiator and a polyisocyanate. In a first curing step the irradiation curing is effected by means of UV light, and in a second curing step the coating obtains its final hardness as a result of OH/NCO cross-linking.
The second curing step can take place at from 130 to 200° C. or over a period of days at room temperature. The final hardness is achieved only after a number of days.
U.S. Pat. No. 4,668,529 thus describes a UV-curable one-component surfacer coating compound for repair lacquering. Tripropylene glycol triacrylate and trimethyl propane triacrylate are used as UV-curable binder components. It additionally contains an epoxy resin based on a bisphenol A-diglycidyl ether.
The object of the invention was to provide a process for producing a multi-layer lacquer finish, which enables environmentally acceptable coating compounds to be used in all the lacquer layers of a multi-layer structure, in order consequently to lower overall lacquering solvent emission to a minimum, and which simultaneously substantially shortens the total curing operation. The coatings obtained should have very good hardness, inter-layer adhesion and very good resistance to water, petrol and chemicals. Resistance to tree resin and pancreatine should furthermore be improved, and the lacquer finishes should achieve an impeccable optical appearance. The process should in particular be suitable for repair lacquering, for example of automotive bodies or parts thereof.
The object is achieved by a process for producing a multi-layer lacquer finish, in which a surfacer coating compound is applied to a substrate optionally pre-coated with a priming compound and/or further coating compounds, after which a top coating comprising a colour-imparting and/or special-effect-imparting base lacquer layer and a transparent clear lacquer layer, or a top coating comprising a pigmented one-layer top lacquer, are applied, characterised in that coating compounds which contain binders which are curable by free radical and/or cationic polymerisation are used as the surfacer, the base lacquer and the clear lacquer as well as the one-layer top lacquer, and wherein the said binders are cured by means of high-energy radiation.
The coating compounds for the individual lacquer layers may in each case additionally contain physically drying and further chemically cross-linking binders.
It was surprising and not deducible from the prior art that the multi-layer lacquer finishes obtained by the process according to the invention, in which each of the aforementioned lacquer layers is cured by means of high-energy radiation, show the same excellent properties demanded for repair lacquering, as have hitherto been obtained with the conventional highly regarded but solvent-based repair lacquers. This applies in particular to properties such as sandability, adhesion, hardness, resistance to water and chemicals, and appearance. Further properties were even able to be improved. Thus, the curing of the overall structure can be effected very rapidly, for example within the region of a few minutes. Problem-free application and rapid and complete full curing are possible even at high layer thicknesses and high pigmentation levels. It was further surprisingly found that resistance to petrol, tree resin and pancreatine can also be improved with the multi-layer lacquer finish according to the invention, by comparison with a solvent-based multi-layer structure.
The surfacer, base lacquer, clear lacquer and one-layer top lacquer coating compounds which are usable in the process according to the invention are constituted by coating compounds which cross-link by means of high-energy radiation by way of free radical and/or cationic polymerisation. They may here be aqueous, solvent-based or 100% coating compounds which can be applied without solvent and without water. High-solids water-based or solvent-based coating compounds are preferably formulated. The coating compounds then contain only small quantities of organic solvents.
In the process according to the invention, in all the named coating compounds any conventional radiation-curable binders or mixtures thereof, which are known to those skilled in the art and are described in the literature may be used as binders which are curable by means of high-energy radiation. These are binders which are cross-linkable either by free radical or cationic polymerisation. In the case of the former, as a result of the high-energy radiation acting on the photoinitiators, radicals arise which then trigger the cross-linking reaction. In th
Lenhard Werner
Loffler Helmut
Maag Karin
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Pianalto Bernard
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