Polyester and natural fibre dyeing | Blebds Dye

Dyeing of polyester fibres

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Polyester fibres are hydrophobic, have a very low swelling capacity and, with the exception of copolymer fibres, have no reactive groups and no affinity for water-soluble dyes. Dye accessibility must be achieved by the addition of carriers or the use of high temperatures (Õ High-temperature dyeing). The heat-setting of polyester before dyeing has a considerable influence on dye affinity, especially in exhaust dyeing with carriers. Oligomers also have an effect on the dyeing results. Exhaust processes are of importance for disperse dyes and naphthol-based diazo combinations. In continuous dyeing processes, pigments are used for pastel shades whilst vat and vat leuco ester dyes are likewise only used for pale shades. In general, disperse dyes are applied by the heat-set thermofixation process. For dyeing polyester loose fibre and card sliver, HT circulating liquor dyeing machines with the material press-packed into cages are used; card sliver can also be dyed by continuous methods. Smooth yarns in the form of cross wound packages and textured yarns in the form of cross-wound muffs loaded on to spindles are likewise dyed in HT circulating liquor dyeing machines. For woven and knitted fabrics, HT winches or HT jet and HT beam dyeing machines are available. Thermosol plants are used for the continuous dyeing of woven fabrics. Polyester copolymer fibres (modified polyester) contain anionic groups and can therefore be dyed with cationic dyes as well. Optimal batchwise polyester dyeing processes are characterised by coordinated temperature control and liquor circulation. In this connection, it should be noted that an increased rate of liquor circulation leads to improved levelness. As a result, the critical rate of dyeing increases in proprtion to the rate of liquor circulation. However, an increased rate of liquor circulation through the textile material only leads to optimum levelness up to a certain limit. Moreover, with increased liquor throughput, increasingly unlevel results are observed. The conditions for this minimum unlevelness are to a large extent independent of the rate of heating.

Dyeing of acrylic polyester blends Single-bath and two-bath exhaust processes are used with disperse dyes for the polyester and cationic dyes for the acrylic fibres.

Dyeing of cotton or regenerated cellulose and polyester blends

These mixtures occupy a very large share of the market, and the blend ratio is nearly always 67% polyester and 33% cotton; with regenerated cellulose, the ratio is often 70 : 30 in many cases.

Disperse dyes are almost exclusively used for the polyester component and reactive, vat, vat leuco ester or sulphur dyes for the cellulosic component. Direct dyes are used only occasionally. In most cases, a tone-in-tone dyeing of both types of fibre is required, for which special ranges of pre-mixed dyes are available from different manufacturers. The formulation of these mixed dyes has been fine-tuned so that both fibre components can be dyed to the same shade by exhaust as well as continuous dyeing methods.

I. Exhaust method: for the dyeing of yarns this process is only of secondary importance. Dyeing is carried out on cross-wound yarn packages or warp beams by the single-bath single-stage or single-bath two-stage process. Direct dyes can be used for cotton in the single-bath single-stage process provided they have sufficient resistance to carriers. With the single-bath two stage process, the cellulosic component is dyed first in the case of reactive dyes whereas the polyester component is dyed first in the case of vat dyes. In two-bath processes, the polyester is likewise dyed first followed by the cellulose with appropriate dyes for each fibre.

Where the cellulosic fibres are too heavily stained with the disperse dyes, an intermediate reduction clear with dithionite must be given (as well as for processes involving the use of carriers in order to remove carrier residues). The exhaust method is also used for light weight woven fabrics as well as knitgoods. Dyeing equipment as for 100% polyester fabrics.

II. Continuous method: this process is used for all other qualities and offers numerous possibilities. Intermediate drying is critical as a certain amount of dye migration can take place at this stage. Most of the disperse dye on the cellulose is transferred by diffusion on to the polyester component during thermofixation.

Polyester natural silk blend Dye

The polyester component is dyed first with disperse dyes in a single-bath two-stage or two-bath process, followed by an intermediate reduction clear if necessary. Finally, the silk is dyed with acid dyes.

Polyester or polyester copolymer (cationic dyeable) Dyeing

This mixture is only seldom encountered. Disperse dyes are used for the polyester and cationic dyes for the modified polyester fibres in a single-bath two-stage or a two-bath process. For continuous dyeings, the modified polyester fibres are pre-dyed with cationic dyes on the pad-steam range, then disperse and vat dyes are applied on the padder followed by thermofixation and development on the pad-steam range. In the knitgoods sector, two-colour effects are produced as well as solid shades. Acid-modified polyester with a high rate of dyeing: carrier-free dyeing at the boil with suitable disperse and cationic dyes.

Dyeing of wool and polyester blends 

The blend ratio is mainly 55% polyester and 45% wool. For the highest quality it is recommended to dye each fibre separately.

Optimum fibre protection is not possible. As there is nothing to be gained by two-bath dyeing, it has been substituted by single-bath processes. A major disadvantage in dyeing this fibre blend is the fact that disperse dyes result in a more or less pronounced staining of the wool component and this staining has no colour fastness to speak of. A strict selection of those dyes which exhibit the least possible staining on wool is therefore necessary. Dyeing is carried out by the exhaust process at 105–107°C if possible, and with reduced amounts of carrier. Disperse dyes are used for the polyester and 1 : 2 metal-complex dyes for the wool. Pre-mixed dyes are also available from a few manufacturers.

Dyeing of polyvinylchloride (PVC)

 fibres Polyvinylchlorid fibres are mainly dyed with disperse dyes. Cationic or metal-complex dyes are also frequently used. Pigments are seldom and naphthol dyes only occasionally used. The dyes must be carefully selected and, depending on the type of fibre, are dyed with or without the addition of a swelling agent (carrier) or dyeing is carried out under HT conditions, whereby polyvinylchloride filament yarns have a considerably lower dye affinity than polyvinylchloride staple fibres.

Dyeing of regenerated cellulose fibres

(Viscose, cupro fibres, high wet modulus /polynosic fibres). In principle, all dyes used for dyeing cotton are suitable for dyeing regenerated cellulose fibres (Õ Dyeing of cotton). The most important dyes are substantive and reactive dyes, with preference being given to hot dyeing types. The affinities of fibres produced by various manufacturers differ and can even vary from batch to batch from the same manufacturer. Textiles made from these materials are sensitive to pressure, friction and tension and this must be taken into account during the dyeing process. A well-known fault is the streaky appearance of woven or knitted fabrics due to slight variations in fibre manufacture. This streakiness can be avoided to some extent by selection of suitable dyes. The pronounced swelling properties of these fibres must be taken into account from the dyeing kinetics point of view (exothermic swelling) so that a fibre specific processing sequence is necessary.


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