Commercially Available Pigments

Application of P.O.13 in polyolefins is limited. It is recommended for use at temperatures up to 200°C (Sec. 2.4.1.3). This is equally true for polystyrene and other plastic materials which are processed above 200°C, such as polymethacrylate, in which P.O.13 is used. P.O.13 is one of the pigments which do not affect the extrusion shrinkage of HDPE, but it is nevertheless rarely employed to color such materials. In LDPE, there is some danger of blooming. 

13 is extensively used in the rubber industry. It is fast to vulcanization and bleeding in natural rubber. Due to its excellent fastness to water the pigment can be applied for bathing articles, sponges and sealing rubbers for preservation glasses. 

13 shows less stability in paints than P.O.34 types of similar particle size. This includes both fastness to overpainting in baking enamels and lightfastness in air drying paints. The volume of trade sales for this purpose is accordingly limited. 

34 is supplied in a variety of types, which differ considerably in their particle size distributions. Specific surface areas range from 15 m2/g in highly opaque versions to about 75 m2/g in transparent types. It is these physical characteristics that determine the coloristic and fastness properties of each type. Even varieties of P.O.34 with fine particle sizes are generally not resinated. 

34 shows good solvent resistance to a number of organic solvents. Its prints are more stable in this respect than those made from P.O.13, which is also true for the standard DIN 16 524 solvent mixture (Sec. 1.6.2.1). In spite of these comparatively good fastness properties, P.O.34 may recrystallize in various printing inks, depending on the processing conditions. P.O.34 prints are fast to paraffin and dioctyl phthalate likewise, they tolerate clear lacquer coatings and may be sterilized. 

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Table 17 lists a number of commercially available pigments, along with their chemical structures, in order to illustrate the different structural types of Naphthol AS pigments. Fastness to solvents and migration resistance improve from top to bottom, i.e., with increasing number of CONH groups in the molecule. The first example, a simple (3-naphthol pigment, is the skeleton from which all other species are derived. 

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