Thermofixing

Blends of polyester with cotton (qv) or viscose are first dyed with disperse dyes, then with sulfur dyes (see Fibers, polyester Fibers, regenerated CELLULOSics). Disperse and sulfur dyes can also be appHed simultaneously in a pad—dry—thermofix/chemical reduction pad—steam sequence. In this case, the sulfur dyes cannot be used in thein reduced form because of the effect of the sodium sulfide on the disperse dye. Therefore, this method is confined to the solubilized sulfur dyes or sulfur dyes in the dispersed form. 

After dyeing, the fabric is dried quickly to a moisture content below that at which migration can occur and then either steamed or baked (thermofixed), followed by a washing-off process. All the processes mn continuously and in tandem, the fabric passing from one process and machine to the next. 

These methods 2, J, and 4) are only used when applyiag fiber-reactive dyes. In all methods thermofixation conditions are 60—90 s at 190—220°C depending on the choice of disperse dye. In method (/) the chemical pad is caustic and hydrosulfite for vat dyes, and alkaU and salt for fiber reactives. This is the most popular method ia the United States. 

One-bath pad-thermofix One-bath pad-steam Two-bath pad-steam ... 

Disperse Dyes. There is a general correlation between heat fastness, the propensity to desorb under conditions of dry heat onto a white piece of polyester, and the dyeing properties of disperse dyes. Low energy dyes are not usually used in thermofixation. as their low heat fastness at the thermofixation temperatures used (200-210 C) results in the subliming of them from the hot fabric. 

From the above results, it can be concluded that PAN fibres resulted in the desired conductive behaviour and will be used further in this investigation. Microscope images of the cross-section of PAN fibres treated with NiCl2 show that after thermofixation of the fibre, no swelling is obtained. Therefore thermofixation will be an important step in the production process and will also be taken into account in the following steps of this investigation. Finally, it should be pointed out that similar absorption behaviour of PAN fibres for Co and CoS was observed but, contrary to Ni, this led to much weaker electroconductive properties of the metallised fibres. 

Freshly produced PAN fibres, obtained under optimal conditions for metallisation, were treated with NiCl2 and CoCl2 solutions for different immersion times. After treatment, an excess of liquor was removed and the fibres were dried, thermofixated at 413 K for 20min and washed until negative reaction against Ni and Co ions was observed. Finally, the physico-mechanical properties of the fibres were determined and are shown in Table... 

Table 11.4 Physico-mechanical properties of metallised PAN fibres as a function of metal content for thermofixated PAN fibres...

Changes in solution concentration of Ni(ll) and rongalite for an initial concentration ratio rongalite/Ni(ll) of 1.5/0.5 as a function of time containing (1) only Ni(ll) and rongalite, (2) thermofixated PAN fibre and (3) freshly formed PAN fibre. 

Disperse polyester, polyamide, acetate, acrylic and plastics fine aqueous dispersions often applied by high temperature/ pressure or lower temperature carrier methods dye may be padded on cloth and baked on or thermofixed azo, anthraquinone, styryl, nitro, and benzodifiiranone... 

In the case of PES-CEL fiber blends, the larger part of the liquor is absorbed by the CEL fiber during drying, because of its higher absorption capacity. Nevertheless, in the subsequent thermofixing step, disperse dyes are almost completely fixed to the PES fiber. Transfer from the CEL to the PES fiber occurs both by migration via direct fiber contact and through the gas phase. The type of transfer depends on the sublimation behavior of the dyes [120],... 

Another classification is based on covering up material differences in textured PES fibers. Dyes that have a low fastness to thermo fixing often hardly mark differences in texture they dye at relatively low temperature and are suited to carrier dyeing processes. Dyes that are very fast to thermofixing diffuse slowly into the fiber and must be dyed at high temperature they are not suited for carrier dyeing under atmospheric pressure they tend to mark texture and fixing differences in the fiber. 

In one formulation, dyes with similar rates of diffusion should be used. Very quickly diffusing dyes sublime easily, contaminate the fixing aggregate, and produce dyeings that have a low fastness to thermofixation. The color yield of very slowly diffusing dyes is sensitive to temperature variations. 

In terms of dyeing and finishing, CT is more similar to purely synthetic fibers than CA. It can be permanently pleated. For stress relaxation, articles made of CT, like those made of PES, are heat set (thermofixed) after dyeing [80, pp. 92-100], CT, like PES, can be dyed by the thermosol process (see Section 4.12.1). 

By using disperse dye liquid concentrates which have thermofixation of 95% or greater (26), polyester fabrics can be foam-dyed at very lew wet pick-ups (e.g., 15-20% for medium-deep shades) without need for afterwashing. The resultant annualized per-line energy and cost savings are estimated, using Wygand s data (24), to be 30 x 10 BIU and 75,000, respectively. 

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