Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
1999-08-06
2002-07-02
Copenheaver, Blaine (Department: 1773)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C428S414000, C427S407100, C427S409000, C427S412100, C523S414000
Reexamination Certificate
active
06413642
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of coating substrates, preferably of metal.
Many of the nowadays customary methods of producing surface-treated strip and metal sheet had already been developed by the beginning of this century. The key breakthrough then came in the 1930s in Europe, with the electrogalvanizing (tinplate) and hot-dip galvanizing of wide strips. Since 1959, when the first hot-dip galvanizing plant was put into operation, there has been an increasing supply of surface-treated thin metal sheet in Germany, beginning with the standard products and numerous other variants in the 1970s and 80s.
In recent years, the metal sheet processing industry has made increasing use of such flat products with metallic coverings and/or organic coatings. Advances in plant technology, in the materials field and in the processing method have advanced the changeover from piece treatment to the pretreated metal sheet or a combination of the two. The evermore complex requirements made of the materials have led to a need to combine the advantages of the substrate material, steel—for example, strength, shapability and weldability—with the specific new properties, such as corrosion resistance and decorative appearance.
The fields of use of the metal sheets coated by means of these methods (so-called coil coating) are very diverse. For the architectural sector there are numerous applications. Coated metal sheets are also used in the interior construction sector for walls, furniture, lamps and domestic electrical appliances. There is also an increasing range of applications in automotive construction. Truck bodies and “bolt-on” automotive parts are often manufactured from precoated materials. Caravans and motor home bodies are produced almost without exception from coated metal sheets.
On the basis of the areas of application indicated, diverse requirements are made of the coatings of the metal sheets. In particular, great flexibility and shapability must be combined with outstanding adhesion by the coating. This is required in particular when the coated material has to be arched at small radii, as when producing car bodies, for example.
At the same time it is necessary to offer a material for further processing which meets the most stringent requirements: thickness, shade, surface quality, and behavior under load. These properties must also be retained when bending and cutting the materials.
Coating materials which can be used for coil coating are known, for example, from the U.S. Pat. Nos. 4,692,382 and 4,692,383. These patents relate to mixtures based on isocyanates and phosphated polyepoxides. In terms of the abovementioned requirements, the properties of these coatings are still not fully satisfactory. This applies in particular to the subfilm corrosion at the scribe mark and at edges. There are also continual adhesion problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method—devoid of the abovementioned disadvantages—of coating substrates, preferably of metal, by cleaning the substrate surface, applying, if desired, an organic or inorganic pretreatment composition, applying a primer coat, applying, if desired, a topcoat by spraying, dipping, knife coating, roller coating or brushing, and subsequent baking.
This object is surprisingly achieved by the provision of primers which comprise an amine-modified epoxy resin.
The present invention additionally provides substrates, preferably of metal, which are coated with one or more coats and can be produced by cleaning the metal surface, applying, if desired, an organic or inorganic pretreatment composition, applying a primer coat, applying a topcoat by spraying, dipping, knife coating, roller coating or brushing, then baking the coating system, and, if desired, layering a removable sheet over the coating film.
The advantages achieved by virtue of the invention are to be seen essentially in that the primer of the invention exhibits minimal surface defects, if any, and that no adhesion problems occur. The primer of the invention surprisingly exhibits excellent contamination resistance; i.e., the good surface properties of the baked coat are retained even when substances causing surface defects are present.
It is also advantageous that the substrates coated in accordance with the invention are of high and uniform quality and are notable for outstanding properties in terms of shapability, durability, chemical resistance, corrosion resistance and weathering stability. The coated material is therefore particularly suitable for segments requiring small-radius bending. Accordingly, the coated material lends itself particularly well to the production of car bodies. The same applies to the flexibility and adhesion of the coating. Furthermore, the coated substrate meets every requirement in respect of the thickness of the primer, the color shade, the surface quality, and the behavior under load. A particular advantage is the resistance to subfilm corrosion (creep) at the scribe mark and at edges.
Substrates
DETAILED DESCRIPTION OF THE INVENTION
Because of the diverse uses, a very wide variety of substrate materials are used in coil coating. As the first criterion for selection, the subsequent machining steps must be taken into account. Chamfering, bending and deep-drawing require certain qualities and strengths which are ensured by way of the steel alloy or aluminum alloy in question. A further important selection criterion is the subsequent field of use.
In many cases the substrates are pretreated, especially when they are metallic substrates. Suitable pretreatment compositions are all of the organic and inorganic products known to the person skilled in the art. One example is the application of a phosphate coat to the substrate. Steel products not subject to massive corrosion attacks can be processed by coil coating without further pretreatment. In the case of higher humidity and climatic stress, electrogalvanized or hot-dip galvanized material is employed. Even in these treatment stages, different quality standards are produced depending on the intended application. Apart from steel, aluminum is also an important substrate material.
In the case of the metal coverings, zinc and aluminum and their alloys are predominant. The one or two-character symbols correspond to the European standard: Z stands for zinc (Zn), A for aluminum (Al), F for iron (Fe), N for nickel (Ni), S for silicon (Si), E for electrolytic and OC for organic coated. Alloy coverings have gained in importance owing to the possibilities that there are. In addition to standard galvanization, the high-aluminum variants Galfan and Galvalume play an important part here.
The most important coating methods are:
1. Melt dipping, an immersion of the strip into the molten coating metal (which can be used with metals having a relatively low melting point). In this method the strip runs from the annealing furnace under inert gas directly into the hot melt which depending on the metal is at between about 420 and 660° C. Directly thereafter excess metal is blown off on the ascending strip in order to establish the desired add-on both sides, the surface formation is controlled, and the coated strip is cooled. Small additions of aluminum, of around 0.2%, restrict the formation of an alloy layer at the boundary between steel and zinc coating. The additions of silicon in the case of the high-aluminum coatings of hot-dip aluminized metal sheet have a similar effect. Furthermore, the formerly customary small amount of lead (around 0.1%) has been very greatly reduced owing to the formation of the known large zinc bloom in the case of hot-dip galvanized metal sheet, or, indeed, a lead-free procedure is adopted.
Thermal aftertreatment of the freshly galvanized strip at about 520° C. leads, if desired, to a “galvannealed” embodiment, in which the pure zinc coating is converted totally into a zinc/iron alloy (corresponding to the delta phase=FeZn
7
) with a matt gray appearance. Occasionally, one of the two sides of the strip is fr
Bremser Wolfgang
Bürstinghaus Rainer
Clausen-Meiring Ulrike
Drescher Dorothe
Grobe Brinkhaus Karl-Heinz
BASF Coatings AG
Copenheaver Blaine
Paulraj Christopher
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