Dispersion of pigments

Apart from displaying the desired physical properties, such as light and weather fastness, heat fasmess, solvent resistance etc., there is a prime requirement that the pigment be readily and evenly dispersible in the application medium. Most pigments are sold as solids and the ease of dispersion in the medium to be used in the application is very dependent on the size of the particles in these solids. 

For instance in azo pigment manufacture, the crude product is given some form of surface treatment, such as with rosin, to control crystal growth, control aggregation and to aid in dispersion. 

Another method, used particularly with phthalocyanine blues and greens, involves dissolving the pigment in a strong sulfuric acid (acid-pasting) and then controlling the particle size during precipitation into water. 

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A variety of additives are used to control the properties of wetting and dispersion of pigments, flow, Hthography, and mb-off of inks. These additives belong to classes of materials such as surfactants, bentonite clays, alkyds, functional resins, polymers, etc. 

FIGURE 11.3 One-way ANOVA (analysis of variance). One-way analysis of variance of basal rates of metabolism in melanophores (as measured by spontaneous dispersion of pigment due to G,.-protein activation) for four experiments. Cells were transiently transfected with cDNA for human calcitonin receptor (8 j-ig/ml) on four separate occasions to induce constitutive receptor activity. The means of the four basal readings for the cells for each experiment (see Table 11.4) are shown in the histogram (with standard errors). The one-way analysis of variance is used to determine whether there is a significant effect of test occasion (any one of the four experiments is different with respect to level of constitutive activity). 

Fig. 29 Dispersion of Pigment Violet 19, -modification, in PVC on a roll mill in relation to the plasticizer content (DOP) and the dispersion temperature.

Fig. 33 Effect of the dispersion temperature (roll temperature) and the pressure between the rolls during dispersing of Pigment Red 53 1 in a sheet offset varnish (pigment concentration 20%) in a three-roll mill on the degree of pigment dispersion. This correlation is illustrated by showing the viscosity of the printing inks at a shearing rate D = 220 s...

Fig. 36 Dispersion of Pigment Violet 19, (l-modification, in an alkyd-melamine resin baking enamel with a paint shaker. Reduction 1 2 with Ti02. Tinctorial strength-time curve.

Fig. 38 Dispersion of Pigment Blue 15 6 in an alkyd-melamine resin baking enamel. Effect of the dispersion time and the dispersion temperature on the coloristic properties (depth of shade). White reduction 1 50 Ti02.

Fig.84 Influence of different dispersing conditions on the degree of dispersion of Pigment Yellow 17 in a sheet offset varnish and on the gloss of prints which were produced from this system. Images of ultramicrotome-cut thin sections of the printed layers taken with a transmission electron microscope.

Fig. 88 Determination of the dispersibility of pigments in plastics by the Filter test method according to prEN 13900-5.

Ceramic coating Dispersion of pigments (cadmium, chromates, lead)... 

A pigment-binder dispersion is a suspension before it is dried after drying it is a solid sol. In pigment-binder systems, the concepts and laws of colloid chemistry therefore apply. The dispersing of pigments and extenders in binders is an extremely complex process of a series of steps that can be interlinked [1.63]. Dispersing involves the following steps ... 

The combined dispersion of pigments is only practical with colorants of similar dispersibility. Toning agents with a considerable higher resistance to dispersion than... 

A letterpress printing ink is a dispersion of pigment particles in a polymer solution. Deviation from ideality is assured by the presence of polymers of high molecular weight dissolved in solvents of differing polarity so as to disperse particles of differing polarity, shape, and size. 

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