Disperse Thermosol Process

Antlblaze 19. Antiblaze 19 (Mobil), a flame retardant for polyester fibers (134), is a nontoxic mixture of cycHc phosphonate esters. Antiblaze 19 is 100% active, whereas Antiblaze 19T is a 93% active, low viscosity formulation for textile use. Both are miscible with water and are compatible with wetting agents, thickeners, buffers, and most disperse dye formulations. Antiblaze 19 or 19T can be diffused into 100% polyester fabrics by the Thermosol process for disperse dyeing and printing. This requires heating at 170—220°C for 30—60 s. 

Although polyester is always brightened with disperse-type products, the methods of application vary. FBAs are marketed for incorporation in the polymer mass, for exhaust application with or without carrier and for use in the pad-thermosol process at a temperature within the range 160-220 °C. Most products are applicable by more than one method, although none can he applied satisfactorily by all methods and cost-effective products introduced in the 1950s still remain important today. 

Many other compounds have been marketed as polyester brighteners for application by exhaustion or in the pad-thermosol process. No account would be complete without mention of the important class of coumarin disperse FBAs, of which structure 11.39 is a typical example. Many commercial brighteners for polyester contain one or two benzoxazole groups, including compounds 11.31, 11.35, 11.36, 11.40 and 11.41. 

Fixation is performed by steaming under various conditions, depending on the fibers and dyes involved. Generally, saturated steam at ca. 100°C is applied. Pressure steamers permit a reduction of the steaming time. Disperse dyes are fixed in polyester fibers by the Thermosol process the fabric is heated in a infrared unit by radiation, by hot air, or with contact heat to 210-220°C for 30-60 s. Superheated steam facilitates rapid fixation at lower temperatures. 

PES fibers are almost exclusively colored with disperse dyes. For some time, dia-zotization dyes were used for dark shades. They are coupled in the fiber with suitable components (e.g., 2-hydroxynaphthoic acid). Although fast colors are obtained, the dyeing process is time-consuming and susceptible to failure, and dyeing reproducibility is poor. Vat dyes are also occasionally used for PES dyeing. Small molecular thioindigo derivatives, in particular, diffuse into PES fibers if they are applied in the thermosol process. 

In the thermosol pad batch process, a semicontinuous process, alkali-sensitive disperse dyes can be used if the alkali is applied after the thermosol process. Conversely, if the thermosol process is carried out after the pad batch step, the pH must be lowered before the thermosol process so that the disperse dye is not destroyed. 

Application Techniques, Structural Variations, and Fastness Properties. When appHed to polyester fiber, many of the disperse dyes originally developed for ceUulose acetate were found to be deficient in Hghtfastness, build-up properties, and especially fastness to the high temperatures employed in the newer dyeing and finishing, printing, and Thermosol (dry heat) processes. 

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. 

The thermosol pad steam process is especially important. Disperse and reactive dyes are padded together, and alkali and salt are padded after the thermosol passage. If a steamer is not available, the reactive dye can be fixed continuously by means of alkali shock in a roller vat with a relatively high alkali concentration. 

Disperseand Sulfur Dyes (see also Section 4.7.3). The thermosol pad steam process is the primary method for application of disperse and sulfur dyes. The sulfur dyes that are used preferentially in the ready-for-dyeing soluble form, and are especially inexpensive for muted shades, must be applied after the thermosol step because of their incompatibility with disperse dyes. 

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