Migration fastness

Countercurrent electrophoresis can be nsed to split a mixtnre of mobile species into two fractions by the electrical analog of elntria-tion. In such countercurrent electrophoresis, sometimes termed an ion still, a flow of the suspending flnid is maintained parallel to the direction of the voltage gradient. Species which do not migrate fast enough in the applied electric field will be physically swept out of the apparatus. An apparatus based mainly on this principle bnt nsing also natural convection currents has been developed (Bier, Electrophoresis, vol. II, Academic, New York, 1967). 

Incorporation of the dyes into host matrices raises concerns about achievable concentration, aggregate formation, and migration fastness. 

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. 

PVC is processed by all methods suitable for thermoplastics. Consequently the required heat resistance and migration fastness of the organic pigments differ greatly. 

The pigment also lends itself to application in elastomers, such as natural rubber blends. It is migration fast enough to satisfy most specifications. P.R.53 1 is also completely bleed resistant in natural rubber, although some color is transferred into the wet cotton cloth liner, the wrapper (Sec. 1.8.3.6). P.R.53 1 is lightfast enough for most applications. Products containing P.R.53 1 are not always entirely fast to hot water or alcohol. 

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. 

Naphthol AS pigment series. Excellent fastness to solvents and chemicals is accompanied by good migration fastness. Benzimidazolone pigments do not bloom, and most of them show good and some even excellent bleed fastness and fastness to overcoating. All benzimidazolone pigments, with one exception (P.Y.151), are inert to alkali and acid. Most of them disperse easily in the common application media. 

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. 

P.R.209 is a specialty product. It is used in much less volume than the 3- and y-modifications of unsubstituted quinacridone and also than 2,9-dimethylquinacri-done. P.R.209 has stimulated a certain amount of interest, not only for its excellent lightfastness and weatherfastness, migration fastness and heat stability, which are comparable to those of P.R.122, but also for its very yellowish shade of red, which is unusual for a quinacridone pigment. 

Depending on the substituent R1 (CH3, CF3, Cl, Br, N(CH3)2), the resulting reddish yellow to bluish violet pigments show excellent lightfastness and weatherfastness and very good migration fastness. If two differently substituted benzoni-triles are used, the product is a mixture of the symmetrically substituted and the two unsymmetrically substituted diphenyl-DDP pigments (mixed synthesis). 

Acylation of 1-aminoanthraquinone affords 1-acylaminoanthraquinones. The carbonamide function renders these compounds very fast to migration. The migration fastness may be improved further by introducing substituents which carry additional carbonamide groups, or by molecular dimerization using aromatic dichlorides. 

While P. V.23 is used in considerable volume, P.V.37 is a specialty product. Pigments of the P.V.34 and 35 type, which are much inferior in terms of tinctorial strength and sometimes also migration fastness, especially in plastics, have been discontinued several years ago. These compounds typically contained ethoxyani-line with acetylamino or benzoylamino moieties instead of the carbazole group of P.V.23 [7-9],... 

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