Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-09-28
2002-10-22
Cameron, Erma (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S514000, C427S518000, C427S318000, C427S409000, C427S422000, C427S435000, C427S555000, C427S379000
Reexamination Certificate
active
06468597
ABSTRACT:
The invention relates to a method for producing a film of plastics or a plastics-containing material on a metal surface and a concentrate for producing a treatment liquid and a treatment liquid for producing the polymer film.
Polymer films on metal surfaces are used in many different ways. There are also all types of methods on an industrial scale for coating of metallic work pieces or work pieces having a metallic surface with a polymer film. According to the type of metal surface and the work pieces, it can be feasible for the application of a polymer film to be carried out without difficulties or it can have considerable disadvantages. As a result of the suitable chemical and physical adjustment of the polymer solution or dispersion to be applied, a polymer layer of the desired thickness can be generated in one operation by several methods. For example, with a roller application method such as roll coating, it is of particular significance to coordinate with each other the concentration of the plastics-containing treatment solution and the roller pressure of the application device, the roller speed and the running direction of the rollers with respect to the substrate. The treatment of small or relatively large-area, rounded work pieces, which are mostly coated by the electric immersion method or by the spraying method, also proves to be comparatively simple.
On the other hand, difficulties are often caused by the coating of single parts, in particular if they have a fairly large spatial extent, for example car body parts, bumpers, chassis, panellings, crash barriers.
With such substrates the roller application method has to be ruled out. Spraying methods are uneconomical in particular because of the costly industrial engineering and the high portion of treatment liquid being lost (over-spray). Dipping methods at ambient temperature without electrical deposition have the disadvantage that, due to the geometry of the parts, different layer thicknesses are generated, and that drops of the plastics-containing solution or dispersion remain on the run-off points, the drops being visible as a thickening after the subsequent drying. Even after a subsequent spray lacquering, these thickenings are clearly recognizable. In addition to the not very attractive appearance, the treated parts—in each case according to the purpose of use—are possibly also useless due to a lack of accuracy of fit.
DE-A-197 25 780 describes a method for applying plastics or plastics-containing layers to metallic single parts approximately at ambient temperature and its use as pretreatment of the single parts for the subsequent powder coating. In this respect, a solution or dispersion with a content of 5 to 50% by weight of an organic polymer is brought into contact with the metallic single part, the applied solution or dispersion is dried on, the coated single part is then brought into contact with a substantially identical, but greatly diluted, solution or dispersion, and its drying is completed. Drop-like areas of unevenness and fairly large thickenings are avoided by the double dipping treatment. Nevertheless, the layer thickness at the run-off edge is often larger than at the other surfaces of the single part by the factor 2 to 3. However, if dipping were to take place only once, the layer thickness at the run-off edge would be about 30 to 53 times thicker than at the other surfaces of the single part.
On the other hand, with a thin layer treatment the conventional chromating, for example on aluminium, zinc and their alloys, still provides the best protection against corrosion without subsequent lacquering. Hitherto it has been a very good and common pretreatment for a subsequent lacquering. As a result of chromium-containing solutions being harmful to the environment and being toxic, in particular from Cr
6+
-ions, for years there have been intensive efforts to develop economical coating methods suitable for line production, which enable protection against corrosion which is equivalent to chromating, also without the use of chromium.
WO 94/10244 describes several compositions for the pretreatment of substrates with polymer solutions or dispersions and a method for coating substrates with such treatment liquids. In this respect, it is mainly treatment liquids which are applied with the dipping method which are mentioned, with a polymer solution or dispersion being mixed with a so-called “compatible dispersion” and with water and the bath being heated to a temperature in the region of about 27 to 71° C., and the parts to be coated heated to a temperature in the region of about 104 to 927 C. The so-called compatible dispersion contains, according to the examples, for example graphite, aluminium, titanium oxide or a black pigment, with it being indicated that the mixtures with a compatible dispersion corresponding to the examples are pigment dispersions for inking protective films and for improving the sliding ability of the substrate surface (sliding lacquer) treated therewith. The examples describe in each case two synthetic resins with a pigment addition, but no content of corrosion inhibitors for improving the anti-corrosion properties. The synthetic resins used are acid-functional, physically drying acrylate resins which are not resistant to alkaline media (pH 6-14). For this reason, only slight protection against corrosion is to be expected. The dry film resulting from this formulation is not resistant to alkaline liquids, for example cutting oils, lubricants for cutting shaping or alkaline water lacquers for over-lacquering used for the further processing of the coated parts.
It was therefore an object of the present invention to provide a method for applying plastics or plastics-containing layers to substrates with metallic surface, which avoids the known, in particular the aforementioned, disadvantages, and also permits layers to arise at the run-off point of the coated substrates, which have a layer thickness which corresponds largely with the layer thickness of the other surface regions coated with plastics. This method should lead, as far as possible also without the use of chromate, to results which are equivalent to those of chromating.
The object is achieved with a method for producing a plastics film or a plastics-containing film on a metal surface, where a treatment liquid, which at the beginning of the wetting with the treatment liquid contains 0.1 to 50% by weight of a non-volatile film-forming mixture containing one or more resins, and 99.9 to 50% by weight of a water-miscible and/or water-soluble solvent and/or water, forms a film on the metal surface, with the volatile component escaping at least partially, with the treatment liquid at the beginning of the wetting, with the treatment liquid having a temperature in the region of 10 to 100° C., with the metal surface at the beginning of the wetting with the treatment liquid having a temperature higher than the treatment liquid by at least 20° C. and a temperature in the region of 30 to 700° C., and with the film being used for the treatment of the metal surface.
The temperature difference between the metal surface and the treatment liquid at the beginning of the wetting with the treatment liquid advantageously amounts to at least 25° C., preferably at least 32° C., particularly preferably at least 45° C., very particularly preferably at least 55° C. Moreover, the temperature of the substrate can advantageously lie at least 70° C., at least 100° C. or in many cases at least 150° C. above the temperature of the treatment liquid. The selected temperature difference can depend substantially on the type of heating of the substrates and optionally also on the integration into a line production, not only on the chemical and physical conditions of the film formation.
By the term “polymer film” in this application is to be understood a film of plastics or of a plastics-containing material. In the method in accordance with the invention, the treatment of the metal surface is understood to mean the application of a passivating layer to the su
Cameron Erma
Chemetall GmbH
Fulbright & Jaworski LLP
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