Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-07-14
2002-04-02
Cameron, Erma (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S496000, C427S388100
Reexamination Certificate
active
06365234
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polymerizable compositions for the organic coating of metallic materials, to a process for their production and to a process for the coil coating of steel.
BACKGROUND OF THE INVENTION
In the metal-processing industry, particularly in the assembly of motor vehicles and in machine construction, the metallic components of the products have to be protected against corrosion. At present, the metal plates are first coated with corrosion-inhibiting oils at the rolling mill and are optionally coated with drawing oils before forming and die-stamping. In vehicle assembly or in machine construction, the metal plates shaped for bodywork, bodywork parts or machinery are stamped out and are formed by deep drawing using the drawing oils mentioned above. This is generally followed by assembly by welding and/or flanging and/or bonding and—after complicated cleaning steps—by a corrosion-inhibiting surface pretreatment. This corrosion-inhibiting surface pretreatment consists of phosphating and, generally, chromating, after which the first coating of paint is applied to the parts in question, often by electrodeposition. This initial electrodeposition step is generally followed by the application of several other layers of paint, particularly in the case of car bodies.
Recently, so-called coil coating processes have been increasingly used for the pretreatment of steel plates because coil coating simplifies many process steps. In coil coating, steel strip is continuously pretreated and, optionally, organically coated at the rolling mill. Coil coating can save considerably on energy. In addition, it uses fewer chemicals and less fresh water and reduces the accumulation of wastewater. Nowadays, a range of steel strip surfaces, for example hot-dip-galvanized, electrolytically galvanized, galvannealed, aluminized surfaces, is available for improving the protection of the steel plates against corrosion. The steel strip thus treated is protected against corrosion immediately after production. Key standards for the quality of the vehicles or machinery produced from these steel plates are good paint adhesion and effective protection against corrosion. In conventional pretreatment processes based on coil coating, the use of chromium-containing products has hitherto been essential for increasing corrosion prevention and paint adhesion. Thus, even where such processes as alkaline passivation and the zinc or iron phosphating of steel or galvanized steel strip are used, after-passivation products containing chromic acid have to be used in order to obtain the required protection against corrosion. The wastewaters which accumulate where these processes are used have to be treated and disposed of at considerable cost. In addition, special safety measures have to be taken for handling chemicals containing chromium(VI) in the production of the pretreatment products, their transportation and their use.
A first step towards cleaner wastewater was the development of products based on chromic acid which were applied by a new process where no rinsing baths were used. This process came to be known as the no-rinse process.
Chromium-free no-rinse pretreatment processes have recently been developed on the basis of aqueous acidic solutions of fluoride-containing titanium salts and organic polymers as principal components. In addition, metal ions, such as manganese, cobalt, nickel or zinc, and phosphate and silicates may also be present. The organic constituents used are chelating polymers, such as polyacrylates or polyvinyl phenol derivatives. A key function of these chelating polymers is to form with the metal ions complexes which are stable in the aqueous phase. These chromium-free systems are described, for example, in EP 178020, in EP 469034 and in EP 555383. Although the processes just mentioned enable chromium-free systems to be used without any adverse effect on corrosion prevention, their disadvantage is that these chromium-free systems can only be applied from strongly acidic solutions and require a very high concentration of fluoride ions.
Accordingly, there is a need to develop pretreatment chemicals and pretreatment processes for chromium-free pretreatment which enable effective corrosion control to be obtained without having to use strong acids or high fluoride concentrations. The various constituents should preferably be uniformly distributed throughout the composition in order to avoid separation during production, transportation, storage and use.
SUMMARY OF THE INVENTION
The solution provided by the present invention is defined in the claims and essentially comprises providing polymerizable compositions for the organic coating of metallic materials which contain at least one titanium, manganese and/or zirconium salt of an olefinically unsaturated polymerizable carboxylic acid, at least one other olefinically unsaturated comonomer and at least one radical polymerization initiator in a non-aqueous system.
The present invention also relates to a process for the production of the organic coating compositions mentioned above and to a process for the coil coating of steel strip.
DETAILED DISCUSSION OF THE INVENTION
Suitable olefinically unsaturated polymerizable carboxylic acids for producing the corresponding titanium, manganese or zirconium salts are any homopolymerizable and/or copolymerizable olefinically unsaturated carboxylic acids known perse, namely: acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, maleic acid semiesters, i.e. esters of maleic acid in which a carboxyl group is esterified with an alkyl group, fumaric acid or fumaric acid semiesters, reactive carboxyfunctional macromonomers or mixtures of the acids mentioned above. “Macromonomers” in the context of the present invention are understood to be oligomers or polymers containing functional terminal groups through which the polymerization reactions can take place. In principle, therefore, they are macromolecular monomers. In general, these macromonomers contain unsaturated C,C-bonds, i.e. vinyl, acryl, methacryl or styryl groups, as terminal groups.
The composition may additionally contain other copolymerizable comonomers, such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, C
1—8
alkyl acrylates or methacrylates and one or more of the olefinically unsaturated carboxylic acids mentioned above in free form, i.e. not in salt form. The hydroxyfunctional comonomers mentioned above may even be partly replaced by polyethylene glycol semiesters of the olefinically unsaturated polymerizable carboxylic acids.
In addition, the compositions according to the invention contain at least one initiator for initiating the radical polymerization. The coating is cured by thermal polymerization, photopolymerization and/or electron-beam polymerization. Photopolymerization is particularly preferred so that the coating compositions suitable for photopolymerization contain a photoinitiator. Various commercially available photoinitiators are suitable. The compositions contain photoinitiators in quantities of 0.1 to 20% by weight, preferably in quantities of 2 to 12% by weight and more preferably in quantities of 3 to 8% by weight.
Examples of suitable photoinitiators are benzoins, benzoin alkyl ethers, benzil ketals such as, for example, benzil dimethyl ketal, acetophenone derivatives, for example dialkyl acetophenones, or even dichloro- and trichloroacetophenones. Examples of commercially available photoinitiators of the above-mentioned type are Irgacure 651 or 907 (Ciba Geigy).
In addition to or instead of the photoinitiators mentioned above, the compositions according to the invention may also contain free radical initiators of the peroxide type, for example benzyl peroxide, or azo compounds, for example 2,2′-azo-bis-isobutyronitrile. In cases where the polymerization is carried out solely as a thermal polymerization, the compositions do not of course contain a photoinitiator.
The poly
Fischer Herbert
Gorzinski Manfred
Kuepper Stefan
Schieferstein Ludwig
Cameron Erma
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
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