Metal-Complex Dyes on Wool

45 min. If the exhaustion of the bath is too low, more formic acid is added toward the end. For subsequent chroming the bath is cooled to 70 °C, followed by the addition of potassium dichromate and heating. The temperature is maintained at 90-100°C for 30-45 min, then sodium sulfate is added to detach the saltlike bound chromate from the wool and make it accessible to complex formation. Other variants use reducing and complexing agents to support the chemical reactions [93], Finally, the bath is neutralized with ammonia (pH 8). 

In the one-bath chroming method (metachrome process), complex formation must be preceded by dye diffusion. For this reason, the release of CrVI must be delayed. The dye liquor is prepared with metachrome mordant (a mixture of sodium chromate and ammonium sulfate) and sodium sulfate. After a prerun at 40-50 °C, the system is heated slowly and dyed at boiling temperature for 45-90 min. Shortly before dyeing is completed, the bath is exhausted by the addition of acetic acid. 

The boiling time is shortest in the afterchroming method, and the most level and fast colors are produced. Poor shading possibilities represent a disadvantage. The one-bath chroming method is most important. 

Metal-complex dyes (Sections 2.10 and 3.11) are chemically similar to chrome dyes. The risk of fiber damage during dyeing is reduced because the complex is formed during dye production. 

In the dyeing process, the pH is adjusted with sulfuric acid to 1.9-2.2 (pH 2.5 in the presence of auxiliary agents). After addition of sodium sulfate, the dyebath is heated to 40-50°C then the dissolved dye is added. Dyeing is carried out at boiling temperature for 90 min. The material is then cooled and rinsed ammonia or sodium acetate can be added to the last rinsing bath. A lowering of the dyeing temperature to 80 °C is possible in the presence of an ethoxylated fatty amine (pH 1.9-2.2). 

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The dye-fibre systems of obvious interest for approach (b) are milling acid and 1 2 metal-complex dyes on wool or nylon, basic dyes on acrylic fibres and disperse dyes on various fibres. With wool and nylon there is often some overlap with approach (c) (section 12.2). 

Acid and Metal-Complex Dyes on Wool and Silk... 

Table 5.2 Dyeing and fastness properties of 1 2 metal-complex dyes on nylon 6 and wool [20]... 

Levelling acid dyes and particularly 1 1 metal-complex types generally require an exceptionally low pH in order to promote exhaustion and levelling up to 3% o.w.f. sulphuric acid is most commonly used for levelling acid dyes, although hydrochloric, formic and phosphoric acids are also effective. In the case of conventional 1 1 metal-complex dyes it is essential to use a sufficient excess of acid over and above the typical 4% o.w.f. sulphuric acid normally absorbed by the wool, otherwise there may be a tendency towards tippy dyeings and lower wet fastness. The actual excess required depends on applied depth and liquor ratio [2] typical recommendations are given in Table 12.2. 

Both 2 1 chromium and cobalt complex azo dyestuffs have little or no affinity for cellulosic fibres and until the early 1960s their use was restricted to wool and nylon. With the introduction by ICI of their Procion range of fibre-reactive dyes, however, their use was extended to cellulosic fibres on which they give prints having excellent fastness to light and wet treatments. Before that time the development of metal complex dyes for cellulose had followed a similar pattern to that of the development of such dyes for wool but, in this case, the most important metal was copper. Early work in this field has been reviewed by several authors.1 The after-treatment of dyeings on cotton obtained from dyestuffs such as (11) with copper salts was used for many years to improve fastness... 

Much more important commercially are the 2 1 chromium(III) and 2 1 cobalt(III) complexes of tridentate azo compounds, which find a wider application, particularly as dyestuffs for wool, polyamide fibres and leather. These have been the subject of reviews23 24 which discuss their dyeing properties in detail. The patent literature on metal complex dyes of these types is vast but since this relates principally to the achievement of specific, desirable technical effects by appropriate substitution of the azo compounds it will not be considered in detail here. Rather will the emphasis be placed upon those aspects of dyestuffs of this type which are of general interest in the context of their coordination chemistry and, more particularly, on those areas where uncertainties exist or conflicting results have been reported. 

Metal complexes of tetradentate azomethines, e.g. (199), are reported136 to have very high light-fastness but to be tinctorially weak and dull in hue. Despite this they are of technical interest as very fast yellow to brown pigments. They find no application as dyestuffs, however, because of these deficiencies for example, the chromium complex of (200) gives dull, tinctorially weak dyeings on wool possessing poor wet-fastness properties. 

Forerunners of the preformed metal-complex dyes are the chrome or mordant dyes, which can be applied only on wool fibers. 

Dyes. In dyeing PES-wool mixtures, disperse dyes are used for the PES component, and acid or metal-complex dyes for the wool. Disperse dyes can soil wool to a great extent. Since they produce poorly fast dyeings on wool, the dyes selected must stain wool as slightly as possible or must be easily removable by a washing step, which may be reductive if necessary. Frequently used dyes are C.I. Disperse Yellow 23, 54, 64 C.I. Disperse Orange 30, 33 C.I. Disperse Red 50, 60, 73, 91, 167, 179 and C.I. DisperseBlue 56, 73, 87. Premixed dyes consisting of disperse and wool dyes are occasionally available. 

An investigation carried out by Rattee y.S.D.C., 1953, 69, 288) showed that the 1 1 metal complex dyes could be applied satisfactorily from a dyebath containing only 5 per cent of sulphuric acid on the weight of the goods. It was suggested that there are three factors involved in the adsorption of these dyes by wool ... 

Metal complex dye based on Cu, Cr, and Ni for dyeing of wool, polyamide, and blends with manmade cellulosic fiber should only be permitted in dyeing, and provided MSDS of such dyes is supplied for verification. 

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