Commercially Available Naphthol AS Pigments

The number of Naphthol AS pigments that have gained commercial recognition is comparatively large (Table 18). There is a dual classification system according to the substitution pattern (Sec. 2.6.2). 

Somewhat of an intermediate position is assumed by a compound which may be considered both a disazo and a Naphthol AS pigment. Pigment Blue 25 is an interesting example of a cross compound, derived from coupling bisdiazotized 3,3 -dimethoxy-4,4 -diaminodiphenyl with Naphthol AS. 

5 12490 och3 H S02N(C2H5)2 OCHj OCHj Cl carmine 

187 12486 och3 H CONHC6H4-(p)CONH2 OCHj OCHj Cl bluish red 

2 provides a medium red shade, which is somewhat yellower than the Naphthol AS pigment P.R.112. Its main area of application is the printing inks field. In some systems, P.R.2 is even slightly stronger than P.R.112, although it does not quite achieve the same lightfastness. 1/1 SD letterpress proof prints equal step 5 

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Commercially available Naphthol AS pigments afford a variety of shades ranging from yellowish to very bluish red including all possible intermediate shades, such as bordeaux, maroon, violet, and brown. Most are tinctorially very strong compared to other pigments that cover the same range of shades. 

Commercially Available Naphthol AS Pigment Lakes General... 

There is no common structural principle to these pigments beyond the basic Naphthol AS pigment skeleton. Table 21 lists the commercially available Naphthol AS pigment lakes. 

Table 21 Commercially available Naphthol AS pigment lakes.

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. 

The pigment affords very bluish shades of red, which are too much on the blue side to match the standard magenta for three and four color printing. The commercially available type is considerably opaque but not very lightfast compared to other Naphthol AS pigments. 1/3 SD letterpress proof prints, for instance, equal only step 3 1 on the Blue Scale for lightfastness while 1/25 SD specimens match step 3. 

Only very few (3-naphthol pigments continue to play an important role in today s pigment industry. The list of important products includes Toluidine Red (P.R.3) and Dinitroaniline Orange (P.O.5). Other compounds, such as P.R.6, Parachlor Red, which is the positional isomer of P.R.4 P.O.2, Orthonitroaniline Orange, which is the positional isomer of the para toner P.R.l are only of regional importance. Table 16 lists the commercially available (3-naphthol pigments. The Colour Index numbers are listed along with the common names, since older products are frequently referred to by these names. 

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