Solvent and Migration Fastness

Lightfastness and weatherfastness of quinacridone pigments (Sec. 3.2) deteriorate in the order 2,9 - 3,10 - 4,11 substitution. It is assumed that decreasing the distance between substituents and NH function disturbs the formation of hydrogen bonds [14] a tendency which culminates in the very poor light and weather resistance of 5,12-N,N -dimethyl quinacridone. 

Metal complex formation considerably improves both lightfastness and weatherfastness in o,o -dihydroxyazo and o,o -dihydroxy azomethine pigments, usually compromised by distinctly dull color. 

Likewise, the lightfastness of an azo pigment lake is controlled to a certain extent by the metal cation manganese salts are usually most lightfast. 

The influence of the chemical constitution as related to solvent and migration resistance opens up a number of options to improve pigment performance  

Substituents such as long-chain alkyl, alkoxy, or alkylamino groups and also sulfonic acid functions tend to increase solubility. 

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Basically, there are two ways of improving the solvent and migration fastness of an organic pigment ... 

The excellent solvent and migration fastness which is typical of all benzimid-azolone pigments probably results from this singular structural principle, which has not yet been discovered in any other azo pigment class. 

The technical applicability of (J-naphthol pigments is severely limited by poor fastness to organic solvents and migration. 

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. 

There are a number of advantages to complexation. It imparts better weatherfastness and lightfastness, as well as enhanced solvent resistance and migration fastness compared with the metal free compound. 

Most of them have good light and weather fastness combined with good solvent and migration resistance. 

These pigments are obtained by coupling substituted aryl diazonium salts with ary-lides of 2-hydroxy-3-naphthoic acid (2-hydroxy-3-naphthoic acid anilide = Naph-tol AS). They provide a broad range of colors from yellowish and medium red to bordeaux, carmine, brown, and violet their solvent fastness and migration resistance are only marginal. Naphthol AS pigments are used mainly in printing inks and paints. 

There is no precise definition for the frequently used term application fastness of a pigment. It usually refers to the behavior exhibited by a finished product used in accordance with the specifications. The term may thus refer to a print, a coated object, or a plastic product, and the list of features ranges from properties such as lightfastness and weatherfastness to migration fastness and fastness to solvents. In this context, there is a certain amount of emphasis on features which play a role in connection with packaging materials and packed articles. 

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