Pigment surface

Incorporation of less than a stoichiometric amount of alkyl sulfonamides of copper phthalocyanines into copper phthalocyanine improves the pigment s properties in rotogravure inks (67). Monomeric and polymeric phthalocyanine derivatives with basic substituents adsorb strongly to the pigment surface and promote the adsorption of binder molecules (68—72). 

In some cases, a pigment s thermal and chemical resistance can be improved by the encapsulation of the pigment particles by an iasoluble, colorless layer of metal oxide or oxide—hydroxide, eg, siUca, Si02. The function of such a shell is to prevent direct contact and reaction between the pigment surface and the organic matrix ia which the pigment is dispersed (11). 

Loss of Dry. When the initial dry time of a solvent-based coating becomes substantially longer after aging, it is said to lose dry. The primary cause of this problem has been identified as adsorption of the drier on the pigment surface. Pigments with large surface areas are the worst offenders. 

The crystal structure of the OCP from Arthrospira maxima has been solved to 2.1 A resolution (Kerfeld et al. 2003). It is composed of two domains and the carotenoid, 3 -hydroxyechinenone, spans both. The carotenoid is almost completely buried within the protein only 3.4% of the pigment surface is accessible to solvent (see Figure 1.3a). The OCP is a dimer in solution the intermolecular interactions are largely mediated by hydrogen bonding among the N-terminal 30 amino acids, as shown in Figure 1.3b... 

The effectiveness of zinc is related to its associated anion (Table 7) the chloride, acetate, or benzoate salts were the most effective. The maximum effectiveness of the metal would be expected if the exchange reaction with the pigment surface was... 

Certain metal salts effectively reduce the photoactivity of titanium dioxide pigments. Combination of these salts with an appropriate antioxidant and/or ultraviolet stabilizer provided highly efficient stabilization of polypropylene. The deactivation/ stabilization performance of the metal salts is adequately explained on the basis of their decomposition of hydrogen peroxide at the pigment surface and by annihilation of positive holes in the pigment crystal lattice. 

It is interesting to note that in spite of equal composition and equal pigment surface concentration, two samples may respond differently to light, depending on... 

Fig. 44 Influence of the pigment volume concentration on the lightfastness at constant pigment surface concentration of the resulting letterpress proof prints (different thickness of layers). Pigment concentration in the printing ink ...

However, the transparency number is not only a function of pigment and vehicle it usually changes with the thickness of the layer (e.g., the pigment surface concentration). The transparency number of a sample which is applied at a thickness somewhere in the interval between two limits hi and h2 is calculated as follows ... 

Adsorption of e.g. rosin (abietic acid) at the pigment surface may - depending on the concentration of the rosin - reduce or accelerate the crystal growth. The presence of an excess amount of rosin during the production of diarylide yellow pigments of the Pigment Yellow 13 type affords an additional crystal modification, which can be identified by X-ray diffraction spectroscopy [4],... 

The specific surface areas mentioned in this context are frequently minimum values pigment preparation tends to increase the surface area, so that the actual value may be much higher. A resinated P.Y.83 type, which is washed repeatedly with petrol ether, for instance, will slowly increase the measured specific surface area from 70 m2/g to more than 100 m2/g (Sec. 1.5.1). It should be noted that considerable amounts of resin remain on the pigment surface, even after repeated washing. 

The 1982 Swedish ban on the use of cadmium as a pigment, surface treatment and stabiliser, backs up this conclusion. 

Deposition from the gas phase by hydrolysis or decomposition of volatile substances such as chlorides or organometallic compounds. Precipitation onto the pigment surface is brought about by adding water vapor. This method is especially applicable to chloride pigments, which are formed under dry conditions. 

Addition of oxides, hydroxides, or substances that can be adsorbed onto the surface during pigment grinding. This can produce partial coating of the pigment surface. 

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