Gold leaf have been colored with organic or inorganic pigments for use in various applications. Alternatively, metal leaf such as silver- or copper-based leaf which exhibit different colors from gold leaf have also been utilized as colored leaf. However, those colored leaf have much room to improve in color saturation and durability. In this study, we utilized gold (Au) nanoparticles as coloring materials and porous titanium dioxide (TiO₂) thin film as a binder. The Au/TiO₂ composite film exhibited excellent chemical stability and coating adhesion. In addition, it was demonstrated that the patterning of the Au/TiO₂ composite film on a gold leaf is easily achieved by using conventional printing techniques.

Colloidal stability of oil-in-water (O/W) emulsions in the absence of any emulsifiers such as surfactants (named as emulsifier-free O/W emulsions) has been investigated to understand the metastable state of O/W emulsions. Colloidal stability (metastable state) of emulsifier-free O/W emulsions depends on the physical properties of oil as a dispersed phase. In particular, the solubility of oil to water is an important physical property to determine the colloidal stability (metastable state) of emulsifier-free O/W emulsions because the solubility of oil to water enhances the Ostwald ripening which is the diffusion of oil molecules through the water (continuous phase) from smaller oil droplets to larger oil droplets. So, if the reversible molecular diffusion among oil droplets (from smaller oil droplets to larger oil droplets and vice versa) was achieved in emulsifier-free O/W emulsions, the metastable state of emulsifier-free O/W emulsions should be retained in the long term. Then, we considered that the reversible diffusion of oil molecules among oil droplets in the emulsifier-free O/W emulsion would be achieved by oils blending because of the diffusion of oil molecules from smaller oil droplets to larger oil droplets driven by different sizes of oil droplets (Ostwald ripening) (that is described by Kelvin's law) and the diffusion of oil molecules from larger oil droplets to smaller oil droplets driven by difference concentrations of another oil in oil droplets (that is described by Raoult's law). Indeed, the long-term colloidal stabilization of emulsifier-free O/W emulsions was achieved by oils blending.

Among various inkjet inks for industrial use, UV curable inks are characterized by high coating strength and quick drying, and are widely used for printing on non-permeable substrates such as plastics, metals, and glass. When formulating UV inks cured by radical photopolymerization method, an acrylate compound is generally used as a monomer material as a main component. In order to have a viscosity low enough to be compatible with the ink jet system, monomer materials need to have a low molecular weight. However, low molecular weight acrylate compounds exhibit toxicity including skin sensitization in most cases. Ricoh has been developing UV curable inkjet inks that exhibit lower than ever toxicity from the viewpoint of reducing the physical burden on manufacturing site workers. In this paper, we introduce application examples of UV curable inkjet inks using methacrylate compounds and also introduce newly discovered acrylamide compounds.

When preparing carbon black aqueous inks in relatively low pigment concentration, such as inkjet inks, various difficulties rise originated from carbon black’s hydrophobic nature. For this reason, control of the initial wetting is extremely important because it greatly affects the productivity of the subsequent processes, phase separation during the storage, and so on. In this report, initial wetting of carbon black is discussed and instructions for earning controlled dispersion is summarized.

NMR is a powerful method to analyze the structures and dynamics of the materials. To develop new materials, it is necessary to analyze the chemical structures and interactions of the constituents. In this review article, we introduce the basic NMR methods and research examples. The topics are: the interaction between resins and inorganic particles (such as pigments); the interaction between resins (such as thickeners); phase separation structures and dynamics in polymer films; reaction process of resins; degradation of coating films.