Inkjet technology for ceramic products. Influence of some process variables on ink penetration

Abstract

Digital printing is nowadays widely used for decorating ceramic products. Noble metal-free, metal-like, tile decoration was developed in the first decade of the 21st century. These glazes are still used in traditional applications, mainly by the bell/waterfall method, which requires application of a large amount of glaze per unit surface area (200-300 g/m 2 ) for the above effect to develop appropriately. Studies 1-6 indicate that, in these glazes, which have a high phosphorus and iron content, during fast firing of the tiles in a typical single-firing process, surface crystallization occurs of iron phosphates, mixed alkali and alkaline-earth phosphates, and hematite nanocrystals, which together determine the surface appearance of the fired coating.As digital printing hardly allows such large amounts of glaze to be applied as those required to obtain the metallic effect, Color Esmalt, S.A., has developed and patented a method for obtaining a metallic effect on ceramic bases by inkjet printing. 7 The method yields a metallic effect by a superimposed application of glaze and ink with an appropriate chemical composition. The set of oxides required to obtain the metallic gloss is distributed between both applications: the iron oxide is introduced in the ink, whereas the other oxides make up the glaze on to which the ink is applied. AbstractInkjet technology has become very popular in recent years and is nowadays widely used for decorating ceramic products. This has led to in-depth study of the operating principles and process variables involved. These notably influence the properties of the deposited ink layers, as do the physicochemical properties of the applied inks and of the glazes on which the inks are deposited. The problems associated with

Improvement of the mechanical and aesthetic properties of a coating by inkjet technology

“…The following results were obtained: ε * = 0.21 and (d 50 ) pore /(D 50 ) ink = 1.23. These values were very similar to those obtained for the G4 glaze particle size distribution in the previous study 4 the composition profile of the ink applied at 400, 600, and 800 dpi, respectively, X versus z, on the G4 glaze particle size distribution, 4 were fitted to Equation 4 using the same values obtained for the fitting parameters for this glaze and this ink (n = 0.8 and k = 0.16 µm −0.8 ). The results were observed to fit the model quite well (Figure 10).…”

“…The penetration distance at which the SrO content was substantial (e.g., X = 0.5%) was verified to increase with ink application (dpi). The penetration curves were fitted to the model 4 :…”

“…Indeed, inkjet technology enables the obtainment of a surface layer, about 50 µm thick, whose composition varies from the surface inwards, depending on the relative size of the pigment and open pores of the unfired glaze substrate (directly related to glaze particle size distribution). 4 Therefore, a priori, coatings can be obtained whose mechanical characteristics and surface textures differ highly from those of the glaze substrate onto which they are applied, without excessive stresses being generated between the top layer and the glaze substrate, in inkjet coatings as a function of the applied amount of ink and pore size and volume in the unfired glaze substrate relative to average ink particle size. Microhardness and indentation modulus of the fired glaze substrate without an ink application and of the fired ink-containing coatings were determined.…”

“…However, this technology has hardly been used to enhance ceramic tile surface properties and hence technical performance, which represents a research area of the greatest interest given the microstructural characteristics of the resulting layers. Indeed, inkjet technology enables the obtainment of a surface layer, about 50 µm thick, whose composition varies from the surface inwards, depending on the relative size of the pigment and open pores of the unfired glaze substrate (directly related to glaze particle size distribution) 4 . Therefore, a priori, coatings can be obtained whose mechanical characteristics and surface textures differ highly from those of the glaze substrate onto which they are applied, without excessive stresses being generated between the top layer and the glaze substrate, owing to the gradual variation of the composition.…”

“…The effect of the applied amount of ink (dpi), made up of the above Sr frit, on the depth profile of the resulting fired coating, its microstructure, surface roughness, and mechanical characteristics was determined. It was also sought to verify the suitability of the penetration model, developed in a previous study, 4 to satisfactorily describe the ink depth profile, X = f ( z ), in the glaze layer, and the quantity of ink retained in the glaze surface as a function of the applied amount of ink, dpi, and of an ink retention coefficient, K, the latter depending solely on the porous texture of the unfired glaze substrate. No studies were found in the literature on the application of inkjet technology to obtain glaze surfaces with improved aesthetic and mechanical properties.…”