Acid dyes wash fastness

New water-insol. naphthalic acid imide dyestuffs - used to dye blends of polyamide or urethane- and polyester or tri acetate fibres having good light and washing fastness C91-110.342 RICH DE GB LI) ... 

The increase in affinity for wool imparted to acid dye structures by the inclusion of long-chain alkyl groups has a noteworthy effect on wet fastness. Thus the incorporation of such a group into the levelling acid dye Cl Acid Red 1 (3.129 R = H) to form the super-milling acid dye Red 138 (3.129 R = n-dodecyl) raises the fastness to washing at 50 °C (effect on pattern) from 2-3 to 4-5. Similar effects for a series of alkylated phenylazo-2-naphthol-6-sulphonate dyes are recorded in Table 3.41. 

This wash-fastness mechanism of acid dyes on polyamide fibres may be a model for the uptake of nutritive substances, of drugs and so on by the organism or the uptake of K+ by complexes in cells too. 

An important discovery was the realization that diaminodiphenyls substituted in the 2,2 -positions are outstandingly suitable for the manufacture of very wash-fast and millingfast wool dyes, while the substantivity toward cellulosic fibers is reduced. A number of important acid wool dyes have been developed on this basis, for example, C.I. Acid Yellow 44, 23900 [2429-76-7] (15). 

Aftertreatment. Frequently, textiles manufactured from polyamide fibers (hosiery, underwear) come into close contact with the skin. Therefore, the material has to be carefully rinsed or washed after dyeing. For the treatment with synthetic tanning agents to improve the wet fastness, see above (Acid Dyes). 

For best fastness to light and washing, nylon 66 is dyed with acid dyes, and nylon dye variants thus are based on manipulation of the level of acid dye uptake. By adding a monobasic acid such as acetic acid to the reaction mix near the end of the polymerization process, the amino end groups are converted to amide groups which have no affinity for acid dyes under normal dyeing conditions. 

One of the oldest known methods of producing wash-fast colors involves the use of metallic hydroxides, which form a link, or mordant (L. mordere, to bite), between the fabric and the dye. Other substances, such as tannic acid, also function as mordants. The color of the final product depends on both the dye used and the mordant. For instance, the dye Turkey Red (alizarin) is red with an aluminum mordant, violet with an iron mordant, and brownish-red with a chromium mordant. Some important mordant dyes possess a structure based on triphenylmethane, as do Crystal Violet and Malachite Green. 

In another method [30] fabrics treated with several concentrations of NaOH are immersed in a mixture of 1.3 g/1 Telon Fast Red AF-3G 150% (BAY), a low molecular weight acid dye, C.I Acid Red 151 and 1.4 g/1 Benzo New Blue GS 140% (BAY), a large molecular weight direct dye, C.I. Direct Blue 10, liquor ratio 70 1 at pH 2 using H SO for 10 min cold followed by washing off. Untreated cotton is stained red and becomes progressively bluer with increase in NaOH concentration. 

The washing test applied to the first five was that of the I.S.O. (Mechanical Mild Wash at 40°C (104°F) for 30 minutes) and for the remainder the S.D.C. No. 2 test (50°C (122°F) for 45 minutes. The figures show that there is a loss of fastness of 1 to 2 gradings with the level-dyeing acid dyes, but none with the premetallized or fast acid dyes. Different unshrinkable finishes would not give exactly the same results but they could be expected to be of the same order. Shrink-resisting processes are usually applied to goods which are washed frequently, and it follows that the use of the molecularly-dispersed acid dyes is undesirable. 

There are direct dyes the wash-fastnesses of which are improved by after-treatment with potassium bichromate in the following maimer. Immerse for 20 to 30 minutes at 60° to 80°C (140° to 180°F) in a solution containing 1 to 3 per cent of potassium or sodium bichromate and 1 to 2 per cent of acetic acid (30 per cent). Fastness to light as well as washing is sometimes improved by substituting 1 to 2 per cent of bichromate, 1-2 per cent of copper sulphate, and 2-4 per cent of 30 per cent acetic acid. 

Sulphur dyes are after-treated with copper sulphate or, more commonly, with copper sulphate together with potassium or sodium dichromate and acetic acid. The treatment improves light-fastness and, in some cases, wash-fastness, to a small extent. When copper sulphate alone is used the process consists of running, after rinsing, at 70°C (160°F) for 20 to 30 minutes in a liquor containing... 

The light fastness is of the order of 5 to 6 and washing fastness when tested by the ISO Washing Test No. 2 is between 4 and 5. It is recommended that, in order to achieve the best wet fastness, dyeing should be followed by back tanning, in the manner which will be described when dealing with the application of acid dyes to polyamides. 

As an illustration the light and washing fastnesses of a few acid dyes are quoted below ... 

When wash-fastness is not important the molecularly dispersed acid dyes can be used. The normal method of dyeing with acid and Glauber s salt gives a good reserve provided dyes are selected which are known to be suitable for the purpose. 

The molecularly dispersed acid dyes have poor wash-fastness and are not suitable for goods like men s socks which have usually had an unshrinkable treatment with the resultant adverse effect upon wet-fastness. 

Incorporation of an arylazo substituent at the para position of phenol gives a dye that can react with methanal into polymeric dyes. Such polymeric dyes are prepared from substituted 4-Arylazo-3-aminophenolic compounds and methanal in the presence of aqueous oxylic acid (equation 40). The polymerization of the monomeric dyes on nylon and polyester leads to brilliant shades and excellent dye fixation on both materials. Furthermore, the light and wash fastness can be increased by polymerization of the monomeric dyes on the fibers [127],... 

---