Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-04-04
2002-07-30
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S323000, C428S418000, C428S500000
Reexamination Certificate
active
06426147
ABSTRACT:
The invention relates to a substrate provided with a multilayer coating which exhibits a surfacer layer, a colour and/or effect decorative layer and a protective layer, the surfacer layer being closest to the substrate and the protective layer furthest from the substrate, the decorative coating material used for the decorative layer comprising a binder from the group “acrylate resins, carboxyl-, epoxy-, and/or hydroxyl-containing binders” or mixtures thereof and comprising a crosslinker from the group “isocyanates, amino resins or TACT” or mixtures thereof and the protective coating material used for the protective layer being from the group “one-component clearcoats, two-component clearcoats, transparent powder coating materials”, and to a process for preparing such a substrate provided with a multilayer coating.
A surfacer layer is prepared from a so-called surfacer. A surfacer is in essence a coating material but one having particular properties and being applied with a comparatively high layer thickness. The function of a surface layer is to even out disruptive unevennesses (in the micrometer range) on the surface of a substrate, so that the surface of the substrate need not be subjected to a levelling pretreatment prior to coating. The abovementioned comparatively high layer thickness of the surfacer is, inter alia, employed for this purpose. The surfacer may be applied to the material of the substrate directly or with interposition of a primer and/or adhesion promoter. In the former case, when applying the surfacer to a metallic material, it is advisable to use a surfacer having an anti-corrosive action. In the case of certain surfacers, which have now been surpassed technologically, it was necessary to subject the surfacer layer obtained following application and drying or curing of a surfacer to a levelling surface treatment, such as sanding. This involved making use of the fact that a surfacer layer is generally less hard and/or easier to work than the material of the substrate. Modern surfacers, by contrast, have a self-levelling function. This means that, following application of the surfacer to a substrate with surface defects, (initial) drying and (initial) crosslinking of the surfacer are all that is required to produce a surfacer layer whose outer surface is virtually level even in the micrometer range. In other words, the substrate-side boundary surface of the resulting surfacer layer forms a complement to the surface of the substrate, in terms of surface structures in the micrometer range. A decorative layer is formed from a decorative coating material. A decorative coating material has not only customary coatings binders and crosslinkers but also, in particular, colour and/or special-effect pigments. Examples of special-effect pigments are metallic pigments and mica pigments. The decorative layer is essentially responsible for the visual impression to a viewer of the substrate provided with the multilayer coating. A protective layer is generally formed from a clearcoat. This clearcoat must have particular properties in terms of its behaviour relative to mechanical stress, chemical stress and light stability and in terms of its transmission behaviour, since the protective layer is exposed to the environment and is intended, in particular, to protect the decorative layer. Multilayer coatings of the type described are used in particular for coating motor vehicle bodies or parts thereof made from sheet steel or sheet aluminum, but also for coating plastic mouldings that are employed in the motor vehicle sector.
The document FR 2 511 617 discloses the application of subsequent layers to a primer/surfacer layer and only thereafter the curing of the multilayer coating thus formed. This procedure is dubbed “wet on wet” technology. With the processes known to this extent, as far as the primer/surfacer layer is concerned, a customary aqueous primer/surfacer is employed. It has been found, however, that above certain applied layer thicknesses (which are necessary for levelling out substrate defects if in-between sanding is to be avoided) there are instances of matting and impaired flow. A substrate provided with a multilayer coating and a process for its preparation, of the type specified at the outset, are known from the document EP 0 238 037 B1. In this case, an electrodeposition coating material is used for the primer/surfacer layer. This electro-deposition coating material is initially baked. The decorative layer and the protective layer are then applied “wet on wet”, it being possible for the coating materials used for this purpose to be aqueous coating materials. Especially in the case of decorative layers comprising an effect coating material, however, it has been found in accordance with this document that it is absolutely necessary to interpose a separating layer between primer and surfacer layer in order that the effect of the coating on the finished product satisfies the visual requirements. The need for a separating layer is a nuisance because of the effort required. On grounds of energy consumption, the separate process step of baking required for the primer/surfacer layer is a nuisance. A further factor is that satisfactory results are only achieved when the separating layer is based on organic solvents. This is a nuisance for environmental reasons. If an aqueous coating material is used for the separating layer it is disadvantageous, moreover, that rapid initial drying of the separating layer prior to applying the subsequent layers cannot easily be achieved. As a result, the effort and/or the production time is increased to an undesirable extent.
Against this background, the technical problem on which the invention is based is to specify a substrate provided with a multilayer coating that can be prepared with little effort and unproblematic environmental characteristics, and a process for its preparation.
To solve this technical problem the invention teaches that the surfacer layer is formed from a precrosslinkable powder coating material, the powder—coating surfacer layer having a layer thickness in the range from 30 &mgr;m to 250 &mgr;m.—The particular advantages of the use of a powder coating material for preparing a surfacer layer are, inter alia, that it can be done without solvent and that the losses that occur due to overspray with customary surfacers are avoided since virtually all of the non-adhering powder coating material can be recycled. All customary prior art methods are suitable for the application of the powder coating material. Particular preference is given to application by means of electrostatic adhesion, preferably by applying a high voltage or by frictional charging.
The coating of substances with powder coating materials is per se a common process. The pulverulent dry coating material is applied uniformly to the substrate to be coated and then the coating material is melted and baked by heating the substrate. In the context of the invention, however, and in departure from this customary procedure, the powder coating material is first of all precrosslinked by heating and is only baked together with the layers applied subsequently. Therefore, relative to the prior art, a separate process step of baking for the surfacer layer is omitted. Instead, all layers of coating material are baked in a common step, leading, surprisingly, to a multilayer coating which satisfies all the requirements. This approach implies a considerable simplification of the coating process. The abandonment of an intermediate baking operation reduces both the capital and operating costs. Only a single baking oven need be made available and operated. As a result, there is also a saving on heating energy. In addition, the overall operating time for the coating operation is shorter, and so the productivity of the unit is increased.
Suitable formulations for the powder coating material are all known coating-material formulations: for example, those described in EP-509 392, EP-509 393, EP-322 827, EP-517 536, U.S. Pat. No. 5,055,524 and U.S. Pat. No. 4,849,283. The pow
Holzapfel Klaus
Wonnemann Heinrich
BASF Coatings AG
Dixon Merrick
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