2 : 1 premetallized dyes

The appearance of streaks with leveling or nonleveling acid and premetallized dye can be subdued by increasing the dye-bath pH from 5.5 to 6—7, at a sacrifice ia dye exhaust, by a dding chemical agents that retard the dye strike or, more effectively, by metering all or a portion of the dye ia a concentrated solution at or near the dyeiag temperature of the fiber (87.8—104.4°C) iastead of at the usual 26.7—48.9°C practiced by the trade (178). 

For end uses demanding high dye lightfastness such as automotive iaterior fabrics, select premetallized dyes and uv inhibitors are appHed through the dye bath (179—182). Nylon can also be codyed with polyurethane elastomeric fibers, wool, acryflcs, polyesters, and ceUulosics (183). 

The dyes used on wool can be divided into the following groups acid dyes, chrome dyes, premetallized dyes and reactive dyes (88,89,92—94,97—99). Strictly speaking, all types of wool dyestuffs can be described as acid dyes, but in practice this term is confined to leveling acid dyes, half-milling dyes, milling dyes, and supermilling dyes (94,97). This subclassification of acid dyes arises out of the methods used for their appHcation and their fastness properties on wool. 

There are three general classifications of acid dyes depending on their method of apphcation acid dyes that dye direcdy from the dyebath, mordant dyes that are capable of forming metallic lakes on the fiber when aftertreated with metallic salts, and premetallized dyes. 

Premetallized Dyes. Although discovered in 1912, the 1 1 chromium complexes known as Palatine Fast (BASF) and Neolan (Ciba) dyes had httie practical use as wool dyes until 1920 when it was found that a strongly acidic dyebath (pH ca 2.0) (51) was requited to obtain satisfactory dyeing and acceptable fastness properties. Dyes of this type exemplified by Neolan Blue 2G [6370-12-3] (57) (Cl Acid Blue 158A Cl 15050) are stiU in use despite the damage to the wool caused by the strong acid in the dyebath. 

Metallization of dyes was originally carried out during the mordanting process to help fix the dye to the substrate. Premetallized dyes ate now used widely in various oudets to improve the properties of the dye, particularly lightfastness. However, this is at the expense of brightness, since metallized azo dyes are duller than nonmetallized dyes. 

Dyeing is carried out by the method best suited to the fiber used as the outer sheath, eg, acid or premetallized dyes for nylon-based, reactive or direct dyes for cotton-based. 

Premetallized Dyes. This dye group is appHed to the same textile fibers and with the same procedures as those with acid dyes. The premetallized dyes offer better fastness properties, but lack brilliancy of shade. Except ia printing of carpeting, the neutral dyeiag types of premetallized dyes are appHed generally without acid or acid donor. 

Transfer of Acid and Premetallized Dyes in Nylon. A specimen of dyed nylon is placed in a dyebath with undyed nylon and the degree of transfer assessed at pH 4.5, 6.0, and 7.5 at 95°C. 

Premature ventricular complexes, 5 88—89 Premature ventricular contractions, 5 108 Premetallized dyes, 9 215-216, 399-401 29 758-759... 

Wool-Polyester Fibers. The wool-polyester blend is the most common liber combination in the worsted industry Disperse dyes for polyester and acid or neutral premetallized dyes for wool are employed in a one-hulh process. 

Complexes derived from medially metallizable, tridentate azo compounds represent the single most important class of metal complex dyestuffs in commercial terms. Some indication of this is afforded by the fact that in 1983 the world consumption of premetallized dyes of this type was of the order of 20 000 tons. 

Metallization of dyes was originally carried out during the mordanting process to help fix the dye to substrate. Premetallized dyes are now used widely in various... 

Besides the afterchrome dyes premetallized dyes became commercially important and remained so until to the present day. 

Another class of bidentate azo dyes are terminally metallizable dyes derived from bidentate coupling components such as salicylic acid, catechol, salicylaldox-ime and 8-hydroxy quinoline. They are mainly used as mordant dyes and rarely as premetallized dyes [3,4],... 

Efforts to overcome the drawbacks of mordant dyeing resulted in the manufacture of the so-called premetallized dyes, which are 1 1 chromium, 1 2 chromium, and 1 2 cobalt complexes. 

The use of both natural and synthetic mordant dyes has long passed its zenith. Synthetic mordant dyes are still listed as leather dyes in the Colour Index. These are chiefly monoazo dyes, which are used especially for prechromed wool. For leather, the operations involved in the metallization step are too complex and time-consuming. Nowadays, modem tanneries prefer premetallized dyes. 

A dyeing assistant used in printing and continuous dyeing of nylon and propylene with acid, disperse, and premetallized dyes to give level dye application with good penetration and color value. 

If a correction to the shade is necessary and the standard of fastness is to be maintained, the most convenient procedure is to cool the liquor to 60°C (140°F) and add sufficient sodium acetate to convert any free sulphuric to acetic acid, and then correct with an acid mordant or a premetallized dye. If the amount of dye required is not great the wool will already contain sufficient Cr Os to combine with the acid mordant dye. A few dyes suitable for shading are shown below. 

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