Patent ID: 7755759

Claim:
A system for evaluating a colorless or light color pigment dispersion, comprising: a data carrier for carrying computer readable instructions; a computer for executing the computer readable instructions; and a spectrophotometer adapted to communicate with the computer for evaluating a spectrum of a pigment dispersion over a predetermined wavelength range by collecting transmission intensity at a fixed angle, wherein the pigment dispersion is colorless or light color, and wherein the executed computer readable instructions cause the computer to receive the collected transmission intensity from the spectrophotometer for selecting a wavelength λ from the predetermined wavelength range based on the following characteristics: (i) 0.1<PS/λ<1, wherein PS is a particle size of interest, (ii) there is no absorption at or near the selected wavelength λ and apparent absorbance is due to light scattering of the pigment dispersion, (iii) the rate of apparent absorbance change with wavelength is not negligible at or near the selected wavelength λ, and (iv) a concentration of the pigment dispersion falls in a range for which apparent absorbance at the selected wavelength λ is from about 0.2 to about 2.0, calculate a particle size related scattering index of the pigment dispersion from the following equation: −(d log A/d log λ), wherein A is an absorbance value of the pigment dispersion at the selected wavelength λ, build a calibration curve to correlate the particle size related scattering index and relative particle size of the pigment dispersion, compare a particle size related scattering index of a sample of the pigment dispersion having an unknown particle size against the calibration curve to determine a relative particle size of the sample, and indicate the relative particle size of the sample.