Coating processes – With pretreatment of the base – Metal base
Patent
1997-09-24
2000-05-09
Pianalto, Bernard
Coating processes
With pretreatment of the base
Metal base
106 1405, 106 1413, 106 1414, 106 1421, 106 1444, 427409, 427435, 4274432, B05D 300
Patent
active
060601221
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to the cleaning and corrosion-proofing of tin-plated steel, more particularly food or beverage cans of this material, so-called "tin cans", between the forming and lacquering steps of the can manufacturing process.
TECHNICAL BACKGROUND AND RELATED ART
Tin cans are normally produced by preliminary forming, deep drawing and smoothing. They have a desirable bright surface so that, after coating with a clear or opaque organic lacquer or printing of the outer surface, they are suitable as an attractive pack. The sequence of process steps involved in the production of tin cans normally comprises offwinding the strip of tin plate provided with a layer of protective oil from the coil, applying drawing lubricants, preliminary forming into a cup and deep drawing and smoothing to the final shape. In the deep drawing and smoothing steps, cooling lubricants, such as water or aqueous emulsions, are normally also used to facilitate the deep drawing process. After forming, residues of the protective oil and deep drawing lubricants and also metal dust are removed in a cleaning steep. After the cleaning step, the containers pass through one or more water rinsing stages and are then dried in a drying oven. This is followed by lacquering in one or more stages and by decorative printing of the outer surface. Accordingly, the metal surface has to be of such quality that the lacquer has sufficient adhesion and affords reliable protection against corrosion.
In the production of such cans, however, it has been found that rust spots can develop during or before drying, particularly if the cans are cleaned with an acidic medium (pH 3-5), too much water is retained in certain areas or if, during stoppage of the production line, the individual process steps are not completed sufficiently quickly. Rust spots can thus develop. They are visible through the lacquer and promote poor lacquer adhesion, so that the product packed in such a container soon becomes unfit for consumption.
According to the teaching of EP-B-161 667, this problem can be solved in non-tinned steel cans, so-called black plate cans, by treating the cans after the actual cleaning step with an aqueous corrosion-inhibiting solution which contains 10 to 5,000 ppm of aluminum ions, 10 to 200 ppm of fluoride ions and up to 1,000 ppm of ions of at least one of the metals titanium, zirconium and/or hafnium and which has a pH value of 2 to 5.5.
The problem addressed by the present invention was to provide a treatment solution, a concentrate for its preparation and a treatment process with which tin cans could be cleaned and provided with a surface protected against corrosion in a single treatment step so that corrosion of the surface before lacquering would be prevented and firm lacquer adhesion would be promoted.
BRIEF SUMMARY OF THE INVENTION
In a first embodiment, the present invention relates to an aqueous treatment solution for tin-plated steel which contains: zirconium and/or hafnium; ingredients or auxiliaries and which has a pH value in the range from 3 to 6.
DETAILED DESCRIPTION OF THE INVENTION
The following concentration ranges are particularly preferred for the individual active ingredients: zirconium and/or hafnium;
The addition of aluminum ions to the cleaning solution in a concentration of about 50 to 300 ppm and, preferably, about 80 to about 200 ppm has been found to have positive effects.
An aluminum salt soluble in the concentration range mentioned is preferably used as the source of aluminum ions. For example, aluminum nitrate and, in particular, aluminum sulfate are suitable for this purpose, aluminum chloride being less preferred in the interests of corrosion control.
Depending on the surface condition of the cans before cleaning, the additional presence in the cleaning solution of one or more monobasic, dibasic or tribasic hydroxycarboxylic acids containing 4 to 7 carbon atoms in the molecule (the sum total of hydroxyl and carboxyl groups being at least 3) as a further active ingredient or
REFERENCES:
patent: 3888778 (1975-06-01), Beckwith et al.
patent: 4313769 (1982-02-01), Frelin et al.
patent: 4370177 (1983-01-01), Frelin et al.
patent: 4496404 (1985-01-01), King
patent: 4617068 (1986-10-01), King
patent: 5391239 (1995-02-01), Boulos
Metal Finishing, 78(7):78 (Jul. 1980).
Henkel Kommanditgesellschaft aut Aktien
Jaeschke Wayne C.
Pianalto Bernard
Szoke Ernest G.
Wisdom, Jr. Norvell E.
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