Background

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, light fastness, 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.