Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-08-03
2003-03-11
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S140000, C427S142000, C427S258000, C427S261000, C427S264000, C427S287000, C427S385500, C427S386000, C427S388100, C427S397700, C427S407100, C427S409000, C427S410000, C427S435000, C427S443200, C427S500000, C427S504000, C427S510000, C427S514000, C427S551000, C427S552000, C427S554000, C427S555000, C427S556000, C427S557000, C427S558000, C427S559000
Reexamination Certificate
active
06531188
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. 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.
U.S. Pat. No. 4,668,529 thus describes a one-component surfacer coating compound for repair lacquering, which is curable by means of UV radiation. The only UV-curable components used are so-called reactive diluents. These are tripropylene glycol triacrylate and trimethyl propane triacrylate. A physically drying epoxy resin based on a bisphenol A-diglycidyl ether is contained additionally.
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.
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-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 or cross-linked 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.
The object of the invention was to provide a process for producing a multi-layer lacquer finish, in particular a repair lacquer finish, which enables environmentally acceptable surfacer coating compounds also to be applied without difficulty at high layer thicknesses and high pigmentation levels. The coatings obtained should show rapid and complete full curing and be fully sandable after a short drying time, as well as affording very good inter-layer adhesion, good top lacquer build and satisfactory resistance to chemicals, petrol and water.
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 the surfacer coating compound which is used is one which either contains binders which are curable exclusively by free radical and/or cationic polymerisation, wherein the said binders are cured by means of high-energy radiation, or is one which contains binders which are curable by free radical and/or cationic polymerisation, wherein the said binders are cured by means of high-energy radiation, and which additionally contains 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 show the same excellent properties demanded for a lacquer finish as have hitherto been obtained with the conventional highly regarded but solvent-based lacquers, in particular repair lacquers. This applies in particular to properties such as sandability, top lacquer build, resistance to water and chemicals. It was surprisingly found, furthermore, that as regards inter-layer adhesion as well as rapid and complete full curing the multi-layer structure according to the invention is even superior to a conventional repair lacquer structure, even at high layer thicknesses and high pigmentation levels.
The surfacer 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 high-solids aqueous or solvent-based systems, for example having a solids content of from 50 to 95 wt. % (in both aqueous and conventional, solvent-containing systems). The systems may, however, also be present as 100% coating compounds which can be applied without solvent and without water.
In the process according to the invention, 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 the cationic-curing systems irradiation causes Lewis acids to be formed from initiators, which in turn then trigger the cross-linking reaction.
The free radical-curing binders may be constituted, for example, by prepolymers such as polymers or oligomers having in the molecule olefinic double bonds which are polymerisable by free radical initiation. Examples of prepolymers and oligomers are (meth)acrylic-functional (meth)acrylic copolymers, epoxy resin (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, polyurethane (meth)acrylates, amino (meth)acrylates, silicone (meth)acrylates, melamine (meth)acrylates, unsaturated polyurethanes or unsaturated polyesters. The number average molar mass (Mn) of these compounds is preferably around 200 to 10 000. The molecule preferably contains on average 2 to 20 olefinic double bonds which are polymerisable by free radical initiation. Aliphatic and/or cycloaliphatic (meth)acrylates in each case are preferably used. (Cyclo)aliphatic polyurethane (meth)acrylates, polyester (meth)acrylates and epoxy (meth)acrylates are particularly preferred. The binders may be used singly or in mixture.
The prepolymers may be present in combination with reactive diluents, that is to say reactive polymerisabl
Lenhard Werner
Löffler Helmut
Maag Karin
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Pianalto Bernard
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