After degreasing, metal is treated by known green chroming process during less than 10 secs. at temp. of 50 degrees C. Coating with max. thickness of 0.2 and preferably between 0.05 and 0.1 mm. is formed. Advantages are that:- Al alloys can be used as well as pure aluminium. Other varnishes can replace phenolic varnishes and thus colourless varnishes can be used. Increased formability . Better corrosion resistance and durability when sterilized. Better printing surface. White pigmented printing colours can be used. No discoloration when outside of container must not be varnished. Improved adherence of metal with varnishes, adhesives and dispersions of synthetic materials, fritted synthetic powders and extruded thermoplastics. No mechanical means such as brushes needed for pre-treatment. Hygienic and conforms to legal stipulations. Simpler and cheaper.
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