Fine white particles comprising polymer-encapsulated titanium oxide

Abstract

The present invention relates to white fine particles from which a white ink that is capable of satisfying both of high hiding power and good bending resistance in a printed material can be obtained, and further relates to white fine particles from which an ink that is capable of satisfying not only excellent fixing properties even when printed on a non-liquid absorbing printing medium such as a resin film, but also suppression of increase in viscosity of the ink and at the same time good deinking properties at a high level can be obtained. The present invention provides [1] white fine particles containing titanium oxide and a polymer component with which the titanium oxide is encapsulated, in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy (XPS) is not more than 7 atomic %, [2] a water-based ink containing the aforementioned white fine particles, in which the titanium atomic fraction of the surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by XPS is not more than 5 atomic %, and [3] a process for producing a dispersion of white fine particles, including step 1 of mixing titanium oxide and a polymer dispersant to obtain a titanium oxide dispersion and step 2 of adding a polymerizable monomer to the thus obtained titanium oxide dispersion to subject the polymerizable monomer to polymerization reaction, thereby obtaining the dispersion of the white fine particles, in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by XPS is not more than 7 atomic %.