Pigments are used in various fields, such as paints, inks, cosmetics, foodstuffs, and so on. Among them,
pigment ink has been used as the color component of inkjet printer ink for a long time because of its
characteristics of high color stability, lightfastness, and gradation etc. Properties of pigment ink depend on the
primary particle size. Pigment ink with small particle size has high transparency, high optical density, and
stable dispersion, but it suffers from a decrease in light fastness, and clogging of the printer head due to
aggregation between particles. Therefore, determining the primary particle size and size distribution of
pigment ink is one of the most important processes in the pigment ink industry. Small-Angle X-ray Scattering
(SAXS) and Ultra-Small-Angle X-ray Scattering (USAXS) observe the particle size and the size distribution,
ranging from nanometer to several hundred nanometers in size. Since both methods are non-destructive,
carried out with dispersion solutions without dilution, the particle size and the size distribution can be
investigated irrespective of the state of materials. In this application note, we illustrate the particle sizes and
the size distributions of pigment inks analyzed from scattering profiles obtained by USAXS.
