Abstract
Anodizing of aluminium is widely applied when a controllable morphology and properties of the surface are required. Anodic oxide films may be developed by appropriate selection of electrolyte and film-forming conditions for various applications in the fields of architecture, aerospace, electronics, packaging and printing. In the present study, the printability of aluminium with respect to anodizing conditions is discussed. In particular, AA1050 alloy specimens were anodized in either sulfuric acid or phosphoric acid at temperatures ranging from 10?C to 40?C, thereby affecting the porosity and anodic layer thickness. Both the porosity and oxide thickness increase with the temperature, whereas anodization in phosphoric acid produces thinner and more porous layer than that in sulfuric acid. After the anodization step, two different printing techniques were used (i.e. digital printing and screen printing). Printed specimens were characterized by means of colour parameters, microscopy, adhesion and light fastness test. Colour parameters and ink adhesion measurements indicate that both digital and screen printing techniques give a better print quality when the anodization step is conducted in the range of 20?C - 30?C.
Highlights
The anodic oxide films formed on AA1050 specimens in P.A. and S.A. at 20oC are shown as SEM micrographs in Figure 2(a) and Figure 2(b), respectively, where the differences in the thickness and morphology of these films are evident
As can be seen the anodic oxide film formed in S.A. is thicker and well-defined compared to the one formed in P.A. which is thinner and very porous, with formations resembling protrusions or whiskers on its surface, in accordance to Wernick et al [1]
Since differences in the structure and porosity or roughness of the surface of anodic oxide films influence their optical properties [15] [16], the reflectance spectra obtained from specimens that have been anodized in P.A. at various anodizing temperatures and printed by digital printing were recorded
Summary
Among the various types of printing substrates for special or external applications (panels, signage, barcodes, awards, labels, etc.), aluminium has gain a great interest due to its superior decorative and fashionable design appearance; it is a light weighting, long-lasting, recyclable material that ensures contemporary aesthetic, durability, light. Anodizing of aluminium surface has received significant attention due to its diverse applications in various fields such as architecture, aerospace, electronics and packaging, but only a few special references are known in the field of printing and graphic arts. Among the various types of electrolytes used for anodizing, sulphuric (S.A.) and phosphoric acid (P.A.) solutions form porous anodic films on the aluminium surface. Equal anodizing time and applied potential will induce the formation of thicker oxide layers as the electrolyte temperature is increased, given that the maximum film thickness under the considered conditions is not reached. The relation of the characteristics (thickness and morphology) of the oxide layers formed under specific anodizing conditions with the printing quality of the anodized specimens, as well as the light fastness and adhesion of the imprint was investigated. Current transients during anodizing were recorded via a multimeter (Keithley 2000) connected with a PC
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