| For reasons such as energy and resource efficiency, dyeing and finishing houses have been more interested in multi-purpose auxiliaries that fulfil more than one wish at a time, writes Ian Holme |
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| Prote-Sperse RD-BF multifunctional auxiliary from Protex can be used with reactive dyes |
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The textile dyeing and finishing sector provides a service to the rest of the textile and apparel industries by converting harsh and unattractive loomstate fabrics into products with enhanced colour, appearance, handle and performance that are appropriate for the end use. Textile dyeing companies are now constantly striving to improve their market competitiveness in the face of global competition, and to streamline their dyeing operations to improve the bottom line.
Right-first-time dyeing is now essential to maintain cost-competitiveness and to maximise machine utilisation and production output. While modern dyestuff formulations are highly sophisticated and are structured to provide high performance both in dyeing and on the subsequent dyed fabric, the requirement to obtain right-first-time dyeing places greater demands that the dyestuff formulation alone cannot provide. Modern dyers are fortunate to be able to rely upon a broad spectrum of dyeing chemicals, generally termed auxiliaries or dyeing assistants, that boost exhaust and continuous dyeing operations and create the optimum dyebath conditions for right-first-time dyeing.
Increasingly highly automated low liquor ratio exhaust dyeing machinery requires the use of one-shot multifunctional liquid auxiliaries that can be poured or pumped into the machine. Multifunctionality decreases the number of products that need to be purchased, stored and either weighed or dispensed, and decreases the liquor volume that must be added into the machine. Concentrated liquid auxiliaries can also be transported and stored in less space with advantages to both the chemical supplier and the textile dyer. The multifunctionality of the auxiliaries is optimised for use in the dyebath by the chemical supplier based upon much research and development. Thus one-shot multifunctional auxiliaries offer many technical and practical advantages to textile dyehouses.
In the exhaust dyeing of polyester and polyester / cellulosic yarns and fabrics it is important to use auxiliaries that do not foam, especially in jet dyeing. In addition the high temperature dyeing conditions used place many demands upon the dispersion performance of disperse dyestuffs in the dye liquor. A multifunctional non-foaming dyebath auxiliary, Eganal PLM liq, has been introduced by Clariant that combines not only dispersing and diffusion-accelerating properties, but also migration-promoting properties. The improved dyebath dispersion stability is essential to prevent aggregation of disperse dyes and their physical deposition on fibre surfaces which can subsequently lead to poor rub fastness. Eganal PLM liq ensures good penetration and increased colour yield. The better dye coverage afforded to materials in which different dye affinities may be present can also be obtained with a reduction in the dyeing time and / or the dyeing temperature.
Eganal PLM liq can also be utilised for the levelling or partial stripping of faulty dyeings should these occur. Important benefits to the polyester dyer are that Eganal PLM liq exerts no adverse effects upon wet fastness and has minimal or no impact on the colour fastness to light. In addition, and in contrast to some other products used commercially, there are no unpleasant odours generated during dyeing or thermal drying.
Softening water for improved dyeing
Rucogal ERQ is a phthalate-free PES-leveller from Rudolf Chemie |
Modern dyehouses are heavily dependent upon the use of softened water, from which metal ions such as calcium and magnesium have been removed. This is essential to prevent changes of shade occurring on the dyed material through the formation of dye-metal complexes in the dyebath that are then absorbed by the fibre. One approach to solving this problem, as well as overcoming the problem of residual bicarbonate that can create pH control problems in the water from an ion-exchange softening plant is to use an auxiliary that combines pH buffering, metal sequestering and dye levelling properties.
One such multifunctional auxiliary is Prote-Sperse RD-BF from Protex (France) which is designed for use in dyeing cellulosic / synthetic and cellulosic / viscose blends with reactive dyes. Prote-Sperse RD-BF is uniquely formulated to provide process control to ensure shade accuracy, levelness and reproducibility in repeat dyeings. This auxiliary sequesters calcium and magnesium effectively without any effect upon the reactive dye structures and also prevents the premature fixation of reactive dyestuffs during the migration phase of reactive dyeing by optimising pH control. Prote-Sperse RD-BF is also claimed to provide clearer, cleaner dyebaths for exhaust dyeings.
Testing the fogging behaviour of materials for automotive interiors according to DIN 75201, draft of February 2008 (Source: Rudolf Chemie) |
Any auxiliary used in the dyeing of polyester materials for automotive fabrics must not give rise to the problem of fogging in the vehicle. This occurs when the vehicle interior becomes hot in direct sunlight and any auxiliary residues evaporate and deposit on the interior surfaces, generating fogging of the windscreen etc. Rucogal ERQ (Rudolf Chemie, Germany) is a nonionic low foaming levelling agent / dyeing accelerator for high temperature dyeing of polyester that has no negative impact upon the fogging value of the subsequent dyed fabric. The strong diffusion-promoting properties of Rucogal ERQ ensures improved dyestuff yield and this multipurpose levelling agent is suitable for very short liquor ratio dyeing and moreover can be automatically metered, both important factors for cost-effective polyester dyeing.
Rucogal ERQ is effective for obtaining uniform dye distribution across parallel-sided yarn packages e.g. cheese form packages. It is also particularly suited for use in carrier dyeing as well as in high temperature polyester dyeing and in the critical dye application method of fabric beam dyeing. Rucogal ERQ is ecofriendly in that it is free of APEO (alkyl phenol ethylene oxide) or APEO derivatives and also of any phthalic acid ester. This multifunctional auxiliary is compatible with nonionic and anionic products and formulated to be stable to the acids, alkalis and electrolytes used in common application amounts.
A novel dyebath softener that is formulated to avoid the precipitation of calcium and magnesium salts is Albatex DBS (Huntsman). This dyebath softener also promotes the dyebath levelling process to achieve shade uniformity throughout the textile material and improves the appearance of the material. Albatex DBS provides excellent sequestering properties for heavy metal ions.
Processing temperature-sensitive fibres
For temperature-sensitive fibres such as wool and other animal protein fibres e.g. cashmere it is important, wherever possible to operate low temperature dyeing in order to preserve the initial properties of the fibres and prevent fibre damage by hydrolysis during dyeing. This is especially important in the dyeing of wool as loose stock or slubbing, because fibre damage is manifested by inferior spinning efficiency and lower yields through the loss of broken / damaged short fibres that then necessitate greater downtime for cleaning the spinning machinery to prevent fibre contamination of the next yarn to be spun on the equipment.
The Miralan LTD-Lanasol low temperature dyeing process for wool fibres and slubbing utilises Huntsman's Lanasol and Lanasol CE dyes and Miralan LTD. The latter is a unique auxiliary formulation that ensures high quality dyeing for wool and cashmere fibres. Microlan LTD is engineered to achieve excellent shade levelness combined with the highest standards of colour fastness to satisfy the consumer demands in this specialist sector of the market.
When dyeing cellulosic fibres and their blends with reactive dyes one of the major problems is the prevention of the uptake of hydrolysed reactive dyestuffs because this leads to inferior wet and rub fastness. Eriopon WFE (Huntsman) has been introduced as a wash fastness enhancer and as an afterclearing agent for reactive dyeings and prints. This auxiliary prevents the renewed uptake of dye hydrolysates and is formulated to ensure optimum effectiveness irrespective of the water hardness or the presence of residual salt in the bath.
Dyeing of polyester and polyester blends, especially polyester / elastane blends, benefits from dyeing at lower dyeing temperatures, saving on energy and restricting the uptake of disperse dyes by the elastane. Univadine DFM from Huntsman is an auxiliary that acts both as a dye diffusion accelerant as well as an effective migration agent to ensure level dyeing. Univadine DFM can thus be used to allow disperse dyeing to take place at a lower temperature than 130°C and alternatively is also capable of shortening the dye cycle time when dyeing at high temperature.
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