Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-08-21
2003-03-18
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S256000, C427S287000, C427S385500, C427S388100, C427S407100, C427S409000, C427S500000, C427S504000, C427S508000, C427S514000, C427S551000, C427S552000, C427S555000, C427S558000, C427S559000
Reexamination Certificate
active
06534130
ABSTRACT:
The invention relates to a process for the multi-layer coating of substrates with a colour-and/or special effect-imparting base lacquer and a clear lacquer layer, which finds application in particular in the field of vehicle and vehicle part coating and more particularly repair coating.
Multi-layer vehicle refinishing generally comprises a base lacquer/clear lacquer top coating, which may be applied to substrates optionally precoated with primers, primer surfacers or further coating compounds.
For ecological reasons, attempts are also being made to reduce the solvent emission of coating compounds in vehicle refinishing. More particularly, a reduction in the solvent content in base lacquers, particularly in special effect base lacquers which, with about 80 wt. %, have a high proportion of organic solvents, makes an effective contribution to lowering the solvent emission of the coating as a whole. Waterborne base lacquers for use in vehicle refinishing have already been developed. The coatings obtained with said waterborne base lacquers do not yet correspond, however, with the level of properties of conventional base lacquers in all respects. For example, water resistance, hardness and inter-layer adhesion are still insufficiently well developed. Moreover, a longer drying time has to be accepted when waterborne base lacquers are used, which impairs the efficiency, for example, in a paint shop.
It is already known to use coating compounds which can be cured by high-energy radiation in vehicle coating.
EP-A-000 407 describes radiation-curing 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, radiation curing takes place by means of UV light and in a second curing step the coating receives its final hardness as a result of OH/NCO crosslinking. The second curing step may be carried out at 130° C. to 200° C. or over several days at room temperature.
EP-A-540 884 describes a process for the preparation of a multi-layer coating for motor vehicle production line coating by application of a clear lacquer layer to a dried or cured base lacquer layer, wherein the clear lacquer coating compound contains binders which can be cured by free-radical and/or cationic polymerisation, and curing is carried out by means of high-energy radiation. After irradiation of the clear lacquer layer, the stoving process takes place, wherein base lacquer and clear lacquer are stoved together at, e.g., 80° C. to 160° C.
EP-A-247 563 describes clear lacquers which can be cured by UV radiation based on a poly(meth)acryloyl-functional compound, a polyol mono(meth)acrylate, a polyisocyanate, a light stabiliser and a photoinitiator. A part of the radiation-curing binders still contains hydroxyl functions here which may react with the polyisocyanate present and offer an additional curing option.
U.S. Pat. No. 4,668,529 describes a 1-pack primer surfacer coating compound for refinishing which can be cured by UV radiation. The binder is based on tripropylene glycol triacrylate and trimethylpropane triacrylate. In addition, an epoxy resin based on a bisphenol A diglycidyl ether is also present.
The object of the invention was to provide a process for the preparation of a multi-layer coating, more particularly refinishing which, in its overall composition, permits a substantial reduction in solvent emission and has short drying times. Moreover, very good water resistance and hardness and very good inter-layer adhesion and resistance of the base lacquer to partial dissolution by underlying and overlying lacquer layers are to be guaranteed.
The object is achieved by a process for the preparation of a multi-layer coating wherein a colour- and/or special effect-imparting base lacquer coating compound is applied to a substrate optionally precoated with a primer and/or primer surfacer coating compound and/or further coating compounds and a clear lacquer is then applied to the colour- and/or special effect-imparting base lacquer layer, characterised in that the colour- and/or special effect-imparting base lacquer coating compound used is one which contains binders which can be cured by free-radical and/or cationic polymerisation under the action of high-energy radiation.
It was surprising and could not have been derived from the prior art that the multi-layer coatings obtained with the process according to the invention exhibit the same high level of properties required for a coating, particularly refinishing, in terms of such properties as hardness, scratch resistance, resistance to water and chemicals, as multi-layer coatings which were prepared with conventional base lacquer/clear lacquer layers for vehicle (repair) coating. It was also surprising that various properties such as, e.g., inter-layer adhesion, resistance to partial dissolution by underlying or overlying lacquer layers, resistance to fuel, tree resin and pancreatin, could be substantially improved.
The colour- and/or special effect-imparting base lacquers that may be used in the process according to the invention are coating compounds which are crosslinked by free-radical and/or cationic polymerisation by means of high-energy radiation. The systems may be high-solids waterborne systems, for example, with a solids content from 50 to 95 wt. % which are present as an emulsion, but the systems may also be present in the solvent-based form. The systems may also, however, be 100% coating compounds which may be applied without solvents and without water.
The binders which can be cured by high-energy radiation which may be used in the base lacquers which can be used in the process according to the invention are all the conventional radiation-curing binders or mixtures thereof which are known to the skilled person and described in the literature. These are binders which can be crosslinked either by free-radical or by cationic polymerisation. In the case of the former, radicals are formed by the action of high-energy radiation on the photoinitiators, which radicals then initiate the crosslinking reaction. In the cationically curing systems, Lewis acids are formed from initiators by irradiation, which acids then in turn initiate the crosslinking reaction.
The free radical-curing binders may be, e.g., prepolymers or oligomers having olefinic double bonds in the molecule capable of undergoing free-radical polymerisation. Examples of prepolymers or oligomers are (meth)acrylic-functional (meth)acrylate 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 molecular mass (Mn) of said compounds is preferably 200 to 10000. The binders may be used individually or in mixture.
The prepolymers may be present in combination with reactive thinners, i.e. reactive polymerisable liquid monomers. The reactive thinners are generally used in amounts from 1 to 50 wt. %, preferably 5 to 30 wt. %, based on the total weight of prepolymer and reactive thinner. The reactive thinners may be mono-, di- or polyunsaturated. Examples of monounsaturated reactive thinners are: (meth)acrylic acid and esters thereof, maleic acid and half esters thereof, vinyl acetate, vinyl ether, substituted vinyl ureas, styrene, vinyl toluene. Examples of diunsaturated reactive thinners are: di(meth)acrylates such as alkylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butane diol di(meth)acrylate, vinyl (meth)acrylate, allyl (meth)acrylate, divinyl benzene, dipropylene glycol di(meth)acrylate, hexane diol di(meth)acrylate. Examples of polyunsaturated reactive thinners are: glycerine tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythitol tetra(meth)acrylate. The reactive thinners may be used individually or in mixture. Reactive thinners used in preference are diacrylates such as, e.g., dipropylene glycol diacrylate,
Krumpolt Frank-Jürgen
Kurz Christine
Lenhard Werner
Löffler Helmut
Maag Karin
E. I. du Pont de Nemours and Company
Pianalto Bernard
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