Polyesters continuous dyeing

The majority of vat dyes used worldwide are appHed by continuous dyeing polyester—cotton blends are the most important substrate. The fabric is padded with vat dye dispersion, dried, padded with sodium hydrosulfite, caustic soda, and salt, steamed for 30—60 s at 102°C, rinsed, and dried. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

Thermosol dyeing. The characteristics of low-molecular-weight polyester dyes can be utilized in thermosol dyeing processes. In this continuous dyeing process the material is impregnated with the dispersed dye, dried, and heated to a temperature of approximately 200-210°C. The dyestuff is fixed by sublimation into the fiber. 

Blends of polyesterand cellulosic fibers are printed with disperse and reactive dyes only in cases, when pigment printing is unsatisfactory. Dye selection follows basically the rules given for continuous dyeing polyester and cellulose fibers. 

Natural gum antimigrant for continuous dyeing of cotton and polyester/cotton with disperse, reactive, vat, naphthol and sulfur dyes as well as pigments. 

A softener to be used in the dyebath or after-rinse to give softness to nylon or polyester fibers. Excellent for use in the continuous dyeing and printing of carpet. 

The Thermosol process of Du Pont, or similar thermofix methods, are used extensively for continuous dyeing of materials made of polyester alone or when mixed with other fibres. The process, see Fig. 23.11, is... 

The Thermosol process (Chapter 23) is applied extensively to the continuous dyeing of cloth made of blends of polyester and cellulosic fibres. 

Chemtherm AM. [Chem-Tex Labs] Pdlymeric antimigrator fix use in continuous dyeing of cotton and polyester with vats, sulftir, direct, and disperse dyes. 

Uses Wetting agenL scouring agent, penetrant for continuous dyeing of nylon and polyester... 

Eor printing on polyester, the fixation conditions are more rigorous than on other disperse dyeable fibers, owing to the slower diffusion of disperse dyes in polyester. Eor continuous fixation the prints are exposed at atmospheric pressure to superheated steam of 170—180°C for 6—8 min. A carrier may be added to the print paste for accelerated and fliU fixation. Dry-heat fixation conditions of 170—215°C for 1—8 min are less popular for printed fabrics, but are sometimes employed because of lack of other equipment. 

Printing on triacetate follows the same general rules as for polyester. For batch-type pressure steaming, the steam pressure is reduced to 7—10 kPa (50—75 mm Hg) at 115—120°C. Acetate requires a steam pressure of ca 3.5 kPa (25 mm Hg), 108°C for full fixation of disperse dyes. With selected disperse dyes of a higher rate of diffusion ia acetate, ia combination with a suitable carrier, continuous steam fixation under atmospheric pressure at 100—105°C duting 20—30 min is also possible. A light scouting at 40—50°C completes the operation. 

Steps in conventional continuous pad-thermosol dyeing, e.g., for polyester fabrics, are (a) pad application of dyes and auxiliaries (b) infrared predrying to about 30% moisture ... 

Hoechst A. G., "Process and Device for the Continuous Fixation of Prints and Pad-Dyeings on Polyester Fibers and Their Mixtures With Cellulose Fibers", U.S. Patent 3,973,902 (Aug. 10, 1976). 

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