Pigment dispersion process

The process of dispersing pigment particies in a vehicie involves a combination of three distinct phenomena caiied wetting, grinding and dispersion. 

The pigment used in the coating is suppiied in the form of agglomerates (Section 3.2.2.3). The process ofwetting involves displacement of air and moisture from the surface of the pigment by the vehicle, followed by penetration of the vehicie in the spaces between the 

---

The pigment dispersion process can be viewed as being composed of three stages, although the stages overlap in any actual grinding process ... 

Printing Inks. Printing ink preparation is similar to many coating systems. The resin is dissolved in the solvent, followed by pigment dispersion to produce the ink. In most printing operations, the solvent must evaporate fast for best production speed. Alcohol—hydrocarbon solvent combinations are used with polyamide resins for some printing processes (see Inks). 

The process of textile print coloration can be divided into three steps. First, the colorant is appHed as pigment dispersion, dye dispersion, or dye solution from a vehicle caUed print paste or printing ink, containing in addition to the colorant such solutions or dispersions of chemicals as may be required by the colorant or textile substrate to improve and assist in dye solubUity, dispersion stabUity, pH, lubricity, hygroscopicity, rate of dye fixation to the substrate, and colorant-fiber bonding. The required viscosity characteristics of a print paste are achieved by addition of natural or synthetic thickening agents or by use of emulsions. 

Pretreatment of the pigment prior to the dispersion process, including time, temperature, wetting, and other parameters connected with incorporation of the pigment in the vehicle. 

Sometimes the dispersion process may inadvertently result in destruction of the aggregates and the primary particles, which happens particularly with pigment powders consisting of coarse or acicular particles - not to forget the effect of intensive shear [59]. 

Wetting out a pigment for several days by simply storing the manually prepared pigmented PVC paste (DOP content 39%) makes for almost optimum dispersion, which requires very little shear (see Fig. 88, p. 162). The wetting of the surface of the pigment particles by the plasticizer molecules thus determines the outcome of the dispersion process. 

---