Pigments preparation

Iron oxide yellows can also be produced by the direct hydrolysis of various ferric solutions with alkahes such as NaOH, Ca(OH)2, and NH. To make this process economical, ferric solutions are prepared by the oxidation of ferrous salts, eg, ferrous chloride and sulfate, that are available as waste from metallurgical operations. The produced precipitate is washed, separated by sedimentation, and dried at about 120°C. Pigments prepared by this method have lower coverage, and because of their high surface area have a high oil absorption. 

Rutile pigments, prepared by dissolving chromophoric oxides in an oxidation state different from +4 in the mtile crystal lattice, have been described (25,26). To maintain the proper charge balance of the lattice, additional charge-compensating cations of different metal oxides also have to be dissolved in the mtile stmcture. Examples of such combinations are Ni " + Sb " in 1 2 ratio as NiO + Sb202, + Sb " in 1 1 ratio as Cr202 + Sb O, and Cr " +... 

In pigments, 2irconium sHicate serves as the host lattice for various chromophores, such as vanadium, praseodymium, iron, etc. Zirconium sHicate crystals are usuaHy formed in situ during pigment preparation by a high temperature reaction of Zr02 and Si02 ... 

Table 2.1 Typical pigments prepared from vat dyes...

A number of parameters change abruptly at the CPVC. Experimental data on the influence of binders, additives, and suitable pigment preparation are shown in Fig. 35, which is a plot of the viscosity versus PVC curves for three samples of one pigment, incorporated in three different offset varnishes [85],... 

The pigment industry today provides the user with a wide variety of pigment preparations to suit all purposes. In these pigment preparations, the pigment is in an already dispersed form. Purchasing a pigment in such a form considerably facilitates its application. Details regarding the composition, synthesis, and application of such preparations are described under the respective applications (Sec. 1.8.1, 1.8.2,1.8.3). 

Apart from pigment preparations which have been developed specifically for aqueous emulsion paints, there are also products known as multipurpose tinting pastes that show outstanding fastness. They have the advantage of being useful not only in emulsion paints but also in solvent containing architectural paints. 

In pigment preparations the pigment is present in dispersed form which, with appropriate choice of carrier material, enables the plastic to be colored uniformly, homogeneously and reproducibly under normal processing conditions. 

There are a number of mixing and processing techniques which have been used successfully to color granulated or powdered polyolefin with pigments or pigment preparations. Powders, for instance, are processed primarily with high-speed mixers, while granulated types respond better to slower mixers. 

Azomethine metal complex pigments replace the metal with tin stabilizers, resulting in a change in shade. In the case of manganese-laked pigments trouble can also be expected in the presence of epoxy compounds. Pigment preparations based on epoxidized soya bean oil are normally used instead of diisodecyl phthalate pastes in the automotive sector e.g. for coloring PVC roofs etc. 

Pigment preparations are frequently used in the PVC cable industry for coloration. The pigment content is often selected in such a way that one part by weight of the preparation is used to color 100 parts by weight of the polymer compound. The shades and color codes for cables and insulated lines are specified in standards in various European countries [35],... 

Pigment preparations are also marketed for coloring thermoplastic PUR. Their carrier materials range from vinyl chloride or vinyl acetate copolymers, such as are used for PVC, through low-molecular polyethylene to PUR itself. 

Rubber compounds are colored with powder pigments and increasingly with granulated pigment preparations, known in the rubber industry too as master-batches. 

As a rule, pigment preparations for this application are based on a carrier material which is identical or similar to the polymer which is to be extruded. 

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