The surfaces of tinplate and tin free steel (TFS) are traditionally coated with lacquers for applications to can stock. Recently, replacement of lacquers with thermosetting resins, films of thermoplastic resins have been attempted to can ends, drawn cans, stretch-drawn cans, 18 liter cans, aerosol parts and other containers. These laminated materials for can containers fundamentally require formability, corrosion resistance and adhesive property with polyethylene terephthalate/isophthalate co-polimerized (PET/I) film.
The typical laminated material consists of the bottom layer of metallic chromium, middle layer of hydrated chromium oxide and surface layer of PET/ I film (12 to 25 micrometers thick) on steel substrates. A base steel, TFS, was prepared by cathodic electrolysis in a chromic acid (CrO3) solution containing either a fluoride compound or a sulfuric acid. A proper quantity of hydrated chromium oxide is necessary for sufficient adhesion, depending on its composition and microstructure. Laminated TFS with about 100mg/m2 metallic chromium and about 5 to 20mg/m2 hydrated chromium oxide satisfies the adhesivity.
