Alkaline dye bath

In 1958, Hoechst introduced the vinyl sulfone reactive dyes, offered as the sulfatoester from which the reactive vinyl sulfone group was generated in the alkaline dye bath. 

Direct dyes provide the simplest means of coloring cellulosic fibers, normally being applied from neutral or slightly alkaline dye baths, with the addition of sodium chloride or sodium sulfate salts. The purpose of the salt is to counteract the slight negative charge that cellulosics have in aqueous conditions because it would repel an anionic dye. 

As opposed to the use of acid-based dye baths, water-soluble direct dyeing processes utilize a more alkaline dye bath with sodium chloride or sodium sulfate added to promote dye wlckability or uptake. The mixture is heated to near 100 prior to introducing cellulosic, natural, and polymeric fiber structures. 

Speciai dyes have been developed to react directly with the substrate. Such dyes are reactive dyes applied within an alkaline dye bath. These dyes contain a reactive group, such as a haloheterocycle, which covalently bonds to hydroxyl groups on cellulosic fibers in particular. 

Sulfur Dyes. These dyes ate appHed to cottoa from an alkaline-teduciag bath with sodium sulfide as the reduciag ageat. NumeticaUy this is a relatively smaU group. However, the low cost and good washfastness properties of the dyeiags make this class important from an economic standpoiat (see SULFURDYES). 

Preparation for Dyeing. A hot alkaline scour with a synthetic surfactant and with 1% soda ash or caustic soda is used to remove size, lubricants, and oils. Sodium hypochlorite is sometimes included in the alkaline scouring bath when bleaching is requked. After bleaching, the polyester fabric is given a bisulfite rinse and, when requked, a further scouring in a formulated oxahc acid bath to remove mst stains and mill dkt which is resistant to alkaline scouring. 

Cotton and wool, even non-mordanted, are dyed in a dye bath containing sodium sulphate dyed natural wool gives up its Substantive colour in a slightly alkaline medium to white cotton. . . colouring matters... 

Currently, a wide range of reactive dyes of varying constitution is available which are suitable for many different applications [33], [6, p. 510-516], In most cases, dye is fixed to the substrate under alkaline conditions. However, dyes with phos-phonate groups are applied in an acid dyeing bath, and quaternary nicotinic acid derivatives require neutral conditions. These dyes are used mainly for dyeing PES-CEL blends. 

In the hydrosulfite process, the dye bath is discharged after dyeing and hydrosulfite is added in an alkaline solution. After reductive cleaning two rinsing steps are necessary. A neutralizing step finishes the process. 

Dipotassium tin trioxide EINECS 236-255-9 Potassium stannate Potassium stannate(IV) Stannate (SnOa ), dipotassium. Textile dyeing and printing, alkaline tinplating bath, [trihydrate] d = 3.197 soluble in H2O (100 g/100 ml), insoluble in EtOH. Allchem Ind Blythe, Williams Ltd. Elf Atochem N. Am. M T Harshaw Nihon Kagaku Sangyo. 

Substantive Dyes.—The dyes of this class are absorbed from solution by the fiber, and combine with it in such a way that the fiber is dyed by simply immersing it in the solution of the dye. With certain coloring matters dyeing is effected more readily in weakly acidic solution, and with others in weakly alkaline solution. Acid sodium sulphate, acetic acid, and tartaric acid are often added to the dye-bath. Silk is usually dyed in a weak soap-solution, or in a bath containing sodium phosphate. Salts are frequently added to the bath to reduce the solubility of the dye and to obtain faster or more even colors sodium sulphate, sodium chloride, and magnesium sulphate are used for this purpose. 

The following procedure, based on the interaction between cuprous thiocyanate and alkaline l,2-diaminoanthraquinone-3-sulfonic acid, is recommended when considerable quantities of accompanying materials, particularly cobalt and nickel salts, are present. A drop of the test solution is placed on filter paper and dried (oven). The spot is then treated with a drop of potassium thiocyanate solution containing sulfur dioxide, and dried again. This treatment produces insoluble white cuprous thiocyanate, which remains fixed in the capillaries of the paper. Manganese, cobalt, nickel, or other heavy metal salts can be removed by bathing the paper repeatedly in potassium thiocyanate solution and finally in distilled water. The dried paper is then spotted with the alkaline dye solution. 

Vat Dyes. These water-iasoluble dyes ate appHed mainly to ceUulosic fibers as soluble leuco-salts after teductioa ia an alkaline bath, usuaUy with sodium hydrosulfite. FoUowiag exhaustion onto the fiber, the leuco forms ate reoxidized to the iasoluble keto forms and aftertreated, usuaUy by soapiag, to redevelop the crystal stmcture. The principal chemical classes of vat dyes ate anthraquiaone and iadigoid. 

The phosphonic acid reactive dyes were appHed to cellulose under slightly acid pH rather than alkaline pH required for other ceUulosic reactive dyes. This feature made them especially attractive for one bath appHcation with disperse dyes to cotton/polyester blends. A review of these dyes appears ia Refereace 5. 

Cl Sulphur Black 1, which is produced from the relatively simple intermediate 2,4-dinitrophenol and aqueous sodium polysulphide. A similar product (Cl Sulphur Black 2) is obtained from a mixture of 2,4-dinitrophenol and either picric acid (6.148 X = N02) or picramic acid (6.148 X = NH2). A black dye possessing superior fastness to chlorine when on the fibre (Cl Sulphur Black 11) can be made from the naphthalene intermediate 6.149 by heating it in a solution of sodium polysulphide in butanol. An equivalent reaction using the carbazole intermediate 6.150 gives rise to the reddish blue Cl Vat Blue 43 (Hydron blue). This important compound, which also possesses superior fastness properties, is classified as a sulphurised vat dye because it is normally applied from an alkaline sodium dithionite bath. Interestingly, inclusion of copper(II) sulphate in the sulphurisation of intermediate 6.150 leads to the formation of the bluish black Cl Sulphur Black 4. 

Adjustment of pH by neutralization. Cellulose dyeing and finishing companies mainly release alkaline baths, which can be neutralized by introduction of C02-containing waste gas from the power/steam generation plant [76]. 

In two-bath processes either the cotton or the acry lic can be dyed first. Heavy shades are best dyed by first dyeing the acrylic and then dyeing the cotton under alkaline conditions. In order to prevent desorption of the cationic dye the dyeing temperature for the cotton dyeing must be below ihe glass-transition temperature for the acrylic of 80V. 

Dyes cotton direct from alkaline or neutral bath primrose-yellow (see Preparation 302). (D.R.P., 56606.)... 

If the wool is intensely coloured, tin presence of artificial organic dye or of indigo carmine is probable. In this case the operation is nqn-.ited in an add or alkaline bath according to which gives the more intensely coloured wool the colouring matter is then extracted from the w(x> and identified by the methods describ d for artificial organic dyes (.see Chapter XV). 

Direct or substantive colouring matters dye vegetable and animal fibres directly in a bath with a little soap, soda or alkaline salt, without need of a mordant. The benzidine colouring matters, for instance, belong to this group. 

Mordant colouring matters dye wool or cotton in neither a neutral, nor an add, nor an alkaline bath, but act only in presence of a metallic mordant. 

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