Red Azo Pigment Lakes

Violet, P.V.50 is redder at greater depth of shade, while samples which are further reduced with TiOz appear bluer and considerably duller. P.V.50 is tinctorially weaker than P.V.23, which in some media is as much as twice as strong as the former. 

50 is used in printing inks and in office articles. Poor lightfastness and a strong tendency to migrate makes it an inadequate product for most plastics materials. Lack of lightfastness also precludes its use in paints (see also P.V.44). 

25 is only produced in small volume in Europe, Japan, and the USA. It is used for the spin dyeing of secondary acetate, lends color to rubber, and is found in inks for packaging purposes. 

Its hue is a somewhat reddish navy blue, which varies considerably if the pigment is chemically modified. 

25 is very fast in application it is fast to fats, oils, soap, and paraffin, which makes it a suitable candidate for packaging inks. Its lightfastness, however, is not excellent. In natural rubber, P.B1.25 tolerates curing very well, and it bleeds neither into the rubber nor into the fabric backing (Sec. 1.8.3.6). In rubber, the pigment is fast to cold and hot water, to soap, soda, and alkali solutions, and to acetic acid. 

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The hue of a red azo pigment lake carrying sulfonic acid functions is determined to a considerable extent by the metal ion. In the series Na->-Ba->Sr->Ca->Mn the shift of hue from yellowish to bluish red increases in the order in which they are listed. The complex correlation between chemical constitution and color in pigment molecules poses a quantum mechanical challenge. This is complicated by interactions within the crystal lattice and by the contribution of intermolecular and... 

Red azo pigment lakes may be classified according to the coupling component. There are four industrially important groups. Pigments are based on the following coupling components ... 

In contrast to red azo pigment lakes, which have stimulated considerable technical interest, the corresponding yellow pigments are much less important (Sec. 2.3.1.2 2.3.4.1 Table 13). 

The development of azo pigment lakes was initiated by the discovery of Lithol Red by Julius (BASF) in 1899. Lithol Red, which is synthesized by an indirect diazotization procedure using 2-naphthylamine-l-sulfonic acid as a diazonium compound, was initially employed in the form of its calcium and barium salts, which were precipitated onto inorganic carrier materials. The pigment was used in its pure form after it became apparent that the carriers contribute very little to the application properties of the product. Lithol Red is one of the earliest colorant developed specifically for application as pigment. 

Lake red 4R 1-((4-Methyl-2-nitrophenyl) azo)-2-naphthalenol 2-Naphthalenol, 1-((4-methyl-2-nitrophenyl) azo)- Permanent red 4R Pigment scarlet... 

Claret red n. Azo pigment produced by coupling Tobias acid (2-naphthylamine-l-sulfonic acid) with 3-oxynaphthoic acid, followed by conversion to the calcium lake. 

Red lake C n. Family of organic acid azo pigments prepared by coupling the diazo-nium salt of ortho-chloro-meta-toluidine-para-sulfonic acid with /i-naphthol. 

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