Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
1999-11-22
2001-12-25
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C106S285000, C252S600000, C427S385500, C427S407100, C427S508000, C427S514000, C427S551000, C427S558000, C427S559000
Reexamination Certificate
active
06333077
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for lacquer coating substrates with a coloured and/or effect base lacquer and a clear lacquer topcoat and to clear lacquer coating compositions usable in this process.
BACKGROUND OF THE INVENTION
Modern automotive original lacquer coatings generally consist of a base lacquer/clear lacquer topcoat, which is applied onto a body which has been electrophoretically primed and coated with surfacer. In such coating processes, the coloured and/or effect base lacquer and the clear lacquer are preferably applied wet-on-wet, i.e. the base lacquer and subsequently applied clear lacquer are jointly stoved.
The optical/aesthetic qualities of such base lacquer/clear lacquer two layer lacquer coatings are substantially influenced by the quality of the clear lacquer layer. ideally, the texture of the clear lacquer layer is identical on the horizontal and vertical surfaces of a three-dimensional substrate, for example an automotive body, which may be ascertained, for example, by determining the long- and short-wave components of the surface texture of the clear lacquer surface. This ideal situation is, however, not straightforward to achieve in practice. For example, differences in surface texture or leveling of the outer clear lacquer layer may occur as, once applied and in particular during the heating phase of the stoving process, the clear lacquers have a tendency to run or sag on non-horizontal surfaces due to a temperature-determined reduction in viscosity. There are various ways of counteracting unwanted running phenomena in clear lacquers. For example, additives having a favourable effect on running behaviour are added to the stoving clear lacquers.
However, this frequently results in reduced gloss of the clear lacquer layer, if the clear lacquer layer is compared with a clear lacquer layer produced from a corresponding, additive-free stoving clear lacquer. Another possibility for counteracting unwanted running phenomena in clear lacquers involves rotating the substrate around an axis after application of the stoving lacquer during the flashing-off and/or stoving operations, an approach which is disclosed, for example, in EP-B-0 261 644.
Longer term retention of the optical/aesthetic qualities of base lacquer/clear lacquer two coat lacquer coatings, in particular in automotive applications, is substantially determined by the clear lacquer layer's resistance to chemicals and scratching, which is in particular manifested over a relatively long period of service by a greater or lesser resistance to acid rain and washing scratches.
EP-A-0 000 407 describes a radiation-curing coating composition based on a hydroxy-functional polyester resin esterified with acrylic acid, a vinyl compound, a photoinitiator and a polyisocyanate. In a first curing stage, the coating is radiation-cured by UV light and in a second curing stage hydroxyl/isocyanate crosslinking imparts the final hardness to the coating composition. The second curing stage may proceed at elevated temperature.
EP-A-0 247 563 describes a radiation-curable coating composition based on a poly(meth)acryloyl-functional compound, a polyol mono(meth)acrylate, a polyisocyanate, a light stabiliser and a photoinitiator. Radiation curing proceeds by UV light. The hydroxyl functions in one part of the radiation-curing binder provide an additional possibility for curing the polyisocyanate, for example in shaded areas.
EP-A-0 540 884 describes a process for the production of a multilayer lacquer coating by applying a clear lacquer coating onto a dried or crosslinked coloured and/or effect base lacquer layer, wherein the clear lacquer coating is applied from a coating composition which is curable solely by free-radical and/or cationic polymerisation and curing is initiated and/or performed by high-energy radiation.
SUMMARY OF THE INVENTION
The object of the invention is to provide a process which may be performed wet-on-wet for lacquer coating substrates with a coloured and/or effect base lacquer and a clear lacquer topcoat with outstanding optical/aesthetic qualities. The process to be provided should prevent running of the clear lacquer on vertical surfaces and clear lacquer layers should be formed which have reduced susceptibility to chemicals and scratching, in particular to acid and washing scratches. In particular, it should be possible to perform the process using clear lacquer coating compositions of a simple composition, preferably such compositions which may be formulated from conventional, for example commercially available components, i.e. any constituents of the clear lacquer coating composition which are not commercially available should be simple to synthesis.
It has been found that this object may surprisingly be achieved by a process for the production of a multilayer lacquer coating, in which a coloured and/or effect base lacquer layer of a base lacquer coating composition is applied onto a substrate and is provided in a wet-on-wet process with the clear lacquer coating, wherein, before being jointly stoved or jointly cured with the base lacquer layer, the uncured clear lacquer layer is exposed to high-energy radiation, characterised in that the clear lacquer coating composition used is one, the resin solids content of which consists of 50 to 98 wt. % of a system A) thermally curable by addition and/or condensation reactions, which system contains substantially no free-radically polymerisable double bonds and substantially no groups capable of reacting in another way with free-radically polymerisable double bonds of system B), and of 2 to 50 wt. % of a system B) which is curable under the action of high-energy radiation by free-radical polymerisation of olefinic double bonds, wherein the weight percentages add up to 100 wt. % and wherein the C═C equivalent weight of the total resin solids content from A) and B) is between 300 and 10000.
The weight percentages here and below relate in each case to the composition of the resin solids content (=total of all film-forming constituents of the clear lacquer coating composition=sum of all constituents of systems A) and B)). Resin solids content here and below means the theoretical resin solids content, which takes account neither of any evaporative losses nor of stoving losses during application and curing of the clear lacquer coating composition. This resin solids content, together with any further non-volatile constituents optionally present in the clear lacquer coating composition, constitutes the solids content thereof.
The phrase “contains substantially no free-radically polymerisable double bonds and substantially no groups capable of reacting with free-radically polymerisable double bonds of system B)” means here and below that, apart from a possible content arising from industrial contamination, system A) contains no free-radically polymerisable double bonds nor any groups capable of reacting in another way with free-radically polymerisable double bonds of system B).
This invention furthermore relates to the clear lacquer coating compositions usable in the process according to the invention, which are characterised in that the resin solids content thereof consists of 50 to 98 wt. % of a system A) thermally curable by addition and/or condensation reactions, which system contains substantially no free radically polymerisable double bonds and substantially no groups capable of reacting in another way with free radically polymerisable double bonds of system B), and of 2 to 50 wt. % of a system B) which is curable under the action of high-energy radiation by free-radical polymerisation of olefinic double bonds, wherein the weight percentages add up to 100 wt. % and wherein the C═C equivalent weight of the total resin solids content from A) and B) is between 300 and 10000.
The coloured and/or effect base lacquer coating layer may be produced in the process according to the invention using per se known coloured and/or effect base lacquer coating compositions applicable by spraying, as are used for the
Dossel Karl-Friedrich
Maag Karin
Herberts GmbH & Co. KG
Pianalto Bernard
Pillsbury & Winthrop LLP
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