Pigment dispersion problems

The following economic losses caused by pigment dispersion problems were described by Smith as follows [8] ... 

For pigments, counting is the most suitable method for several reasons. The counting operation is carried out in the binder medium of interest, whereas with sedimentation analysis or the Coulter counter the medium cannot be freely chosen. Furthermore, counting can be carried out under the dispersion conditions used for examination (in contrast to methods in which a specified binder medium must be used that can lead to a different state of dispersion). Problems associated with concentration are much less frequent than in other methods, which sometimes require extremely dilute suspensions (especially optical analysis and the Coulter coun-... 

Many of the problems associated with color reproducibility have been eliminated entirely. The finished tablet color has been predetermined by color matching the pigment dispersion before coating. 

Mottling Uneven colour distribution in film. Inadequate pigment dispersion. Colour migration, a problem with dyes and lakes rather than pigments. Alter suspension prepartion to ensure pigment aggregates are dispersed. Replace dyes with pigments. 

The problems and advantages associated with the mixing of cohesive powders have been highlighted by those industries which demand a very high degree of uniformity within the bulk mixture. The pharmaceutical and pigment dispersion industries are good examples of industries with this requirement. 

When incorporating metallic pigments into plastics care needs to be taken as not to damage the flake during the dispersing process which would result in reduced brilliance. Since aluminum and bronze pigments disperse very easy, this represents no problem. 

Uses Pigment dispersant/wetting agent for water-reducible paints such as alkyds defoamer in food-contact paper/paperboard Features Designed to minimize problems of blistering and adhesion loss Regulatory FDA 21 CFR 176.210... 

Uses Pigment dispersant, color enhancer improving color acceptance in water-based coatings, latexes, esp. in tint toses FeatiMes Does not generate foaming problems Properties Nonionic... 

This type of finish is an extension of the one-pack moisture-curing type. It is virtually the same finish, to which a small quantity of catalyst is added just before use. Tertiary amines, such as N,N-dimethylethanolamine [HO CH2 CH2 N(CH3)2], are most frequently used as catalysts. Even if the moisture content of the air is low, the finish will harden rapidly, but the more reliable drying performance is obtained at the expense of a limited pot-life. Unfortunately, the activator is non-polymeric and so cannot be used for pigment dispersion. Pigments are dispersed in pre-polymer and must be free from moisture, as in the one-pack composition. The uncatalysed finish is water-sensitive, presenting a shelf-life storage problem as before. 

---