Phthalogen Dyes on Cellulosic Fibers

As with oxidation dyes, the actual dye in the Phthalogen process-the insoluble phthalocyanine pigment-is formed in the fiber itself. The dyeing is performed with precursors. There are two main processes. 

Polyisoindolenines, which are high-molecular Phthalogen developers and are complexes of heavy metals and indolenine, are developed with reducing agents in a wet treatment. The polyisoindolenine complexes are fiber-affinitive and can be applied by using the exhaustion process. Their substantivity is low but can be increased by pretreating the cellulose with anionic products. Reductive development is performed in an alkaline medium with hydrosulfite. For details, see [82, 83], 

Dyeings made with Phthalogen developers are characterized by high brilliance and excellent fastness. Thus, they are suitable for washfast and weatherproof articles. No danger of photochromism exists if a finishing operation is performed with synthetic resin products. 

For printing, the Phthalogen dye is mixed in a printing paste with solvents, and an ammoniacal solution of a copper or nickel complex. After printing, the fabric is dried immediately above 80°C, and fixation is accomplished by steaming for 8-5 min at 100-102°C or by hot-air treatment at 135-145°C for 3-5 min. Excess heavy metal is removed by an acid treatment, and thickener and loosely adhering dye pigment are washed off. 

Direct dyes (see Section 3.3) that contain aromatic amino groups can be diazo-tized on the fiber after dyeing and then coupled with a developer (a phenol, naphthol, or aromatic amine). Wetfastness, in particular, is improved by such an enlargement of the molecule, and the shade also changes (see Section 2.2). Conversely, water-soluble, substantive azo dyes which bear amino or hydroxyl groups capable of coupling can also be used, followed by aftertreatment with a diazo-nium compound. The resulting polyazo dye shows excellent wetfastness (see also Section 4.8). 

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