The following brief review is intended to draw attention to some of the newer developments in textile dyeing machinery which are designed to minimize energy and water consumption, and minimize effluent loading during textile processing. DyStar collaborates with the leading machinery suppliers to develop new application technology and optimism dye selection and process parameters in order to fully exploit the features of the latest machines.

Exhaust piece dyeing

A combination of advantages of long tube machine design with aerodynamic fabric transportation principle has been developed by THEN with their new development the THEN AIRFLOW® LOTUS machine which is the world’s first long tube machine to operate using to the original aerodynamic principle. The objective of the development was to create a system that would be especially suitable for the wet processing of delicate, easily creased, cellulose and synthetic fibre knits and wovens with a high percentage of elastane fibre, which are used in the lingerie, sport, leisure and swimwear segments.

Resource benefits focus on ultra low liquor ratio 1:2 to 1:5 with associated reduction in water demand, effluent volume and loading from reduced salt consumption when reactive dyeing, and a reduced energy requirement.

The successful THEN-AIRFLOW SYNERGY® machine based on the round autoclave design has been refined to permit high temperature drain to a closed collection tank for heat recovery whilst the fabric is running, which increases productivity and prevents redeposition of impurities and oligomers when dyeing polyester based fabrics.

A new highly productive process for polyester/cotton blends has been developed in conjunction with DyStar showing efficiencies of up to 8% chemical, 35% water, 6% steam, and 50% electrical energy consumption versus a conventional machine and process.

FONG’S have further refined their JUMBOFLOW machine with Advanced Intelligent Rinsing (AIR) with the option of a conductivity measurement to detect when the concentration of electrolyte has reduced after reactive dye processing to a concentration where the rinsing is transferred to the soaping stage…thereby optimising water consumption.

THIES have further developed their ecoMaster machine incorporating Multi Contact Dyeing from the double liquor: fabric interchange design to permit reduced dyeing times and low liquor ratios from 1:3 for synthetics to 1: 4.5 for cotton fabrics, and an auto control of the rinsing procedure using RINSEtronic software to further reduce process times and water consumption.

The development of the pneumatic/hydraulic exhaust dyeing machine as a collaboration project between THIES and DyStar resulted in the high technology Luft-roto plus which demonstrates market leading application process flexibility.

A new rapid dyeing process for dyeing black reactive shades particularly suited to vertical operations has been developed in conjunction with DyStar which delivers up to 30% higher productivity with up to 60% reduction in water consumption and 40% less energy usage.

Cold pad batch dyeing

For vertical knitted fabric operations there is a renewed interest in reactive dye application by cold pad batch application due to the lower consumption of water and reduced effluent loading, with a claimed reduction in variable costs of between 15 and 30%. The resultant fabric has a much cleaner stitch definition due to no surface abrasion, and to produce a similar g/sq.m fabric as exhaust dyeing, an increase in stitch density should be considered at the knitting stage if the cpb application route is intended.

Developments in machine design are mostly for open width processing using sophisticated auto-centre and edge uncurling devices but also include dosing pumps, low-liquor troughs and configurations to allow dye application in the nip as well as in the low-liquor trough. Also on modern pad rollers the pressure can be adjusted across the full width to allow uniform liquor pick-up to eliminate side-centre-side variation.

Integrated heating and cooling systems have also been developed to ensure constant temperature in the pad trough regardless of the time of day/season and thus improve the reliability of the process re liquor stability/batching time. For dark shades DyStar has developed the high strength and high fixation value Remazol® Ultra RGB reactive dye range which allows deep shades to be achieved with reduced physical quantities of dye to be dissolved and reduced dye hydrolysate to be washed off thereby lowering colour in effluent loading. In addition a concentrated silicate free alkali has been introduced Sera® Fix C-SF which simplifies handling and dissolution and prevents deposits on pad rollers and fabric, reduces the electrolytic effect causing increase in substantivity of hydrolysed dye, and facilitates wash-off. For earth-tone shades such as beige, khaki, and grey on emerised woven fabrics with the highest fastness performance requirements, DyStar has developed a dye combination which minimises the face to back shade difference in both hue and depth. The preferred combination is based on Levafix® Amber CA, Levafix® Fast Red CA, and Levafix® Blue CA which delivers high light fastness with no photochromism.

As part of the DyStar ColorXPT® software programmes, the Optidye® CR calculates the optimum conditions for liquor stability and fixation time for Remazol® and Levafix® dyes taking into account the substrate and production/machinery parameters.

Continuous Dyeing

Econtrol® Process

The Econtrol® process utilises the innovation of the Thermex Hot Flue from MONFORTS combined with reactive dye technology from DyStar.  The innovation exploits the thermodynamics of water evaporation from cellulose to provide the optimum temperature and moisture conditions within the Hot Flue dryer ideal for the efficient fixation of the specially selected reactive dyes.

The most recent development from DyStar sees the heterobifunctional Levafix® CA dyes introduced into the process. An important feature of these dyes is a very high fixation level in the Econtrol® process which brings added benefits in terms reduced colour load to the effluent and easier wash-off of dye hydrolysate, aided by the fact that there is no salt or silicate to remove when using the Econtrol® process.

MONFORTS have in conjunction with DyStar further developed the successful Econtrol® process and at ITMA Munich in 2007 launched the new Econtrol T-CA process for the coloration of polyester/cellulose blends. This development combines the humidity control for reactive dyes with a Thermosol unit for application of new Dianix® T-CA disperse dyes and a new auxiliary package which obviates the need for an intermediate reduction clear process.

The savings in chemicals, water, and energy are significant as indicated in the following diagram:

Conclusion

Newest machine technology places high demands on modern dye combinations

To maximise the synergy between innovative machinery design and application process to deliver productivity, cost efficiency, and environmental benefits, it is critical to optimism dye selection. For exhaust application of reactive dyes the selected combination should feature similar rates of substantivity in both the neutral exhaust/migration phase and alkaline fixation phase resulting in an on-tone build-up which exhibits minimum sensitivity to small production variables. A further requirement is a high degree of fixation on the fibre with no dye-dye interaction causing so called ‘blocking’ which is typical in many commodity reactive dye combinations based on a golden yellow, red and black reactive dye ternary.

For pad application the selected combinations should exhibit no tendency towards tailing throughout the entire production run, and for difficult fabrics such as emerised woven fabrics a similar hue on the sanded face and nonemerised reverse.

Dye selection is therefore critical for the specific application and substrate using Best Available Technology through the use of higher strength and build-up Remazol® Ultra RGB reactive dyes particularly for deep shades, and Levafix® CA dyes for pale to medium shades, which will also contribute to reduced effluent loading compared with commodity reactive dyes and represents the preferred technology in markets where environmental restrictions are required to be met.

An example of such a homogeneous Levafix® CA trichromat with a good on-tone build up by exhaust application is illustrated on the next column:

For all advanced coloration processes to deliver the full synergy of developments in both machinery and dye application processes, DyStar has engineered dye combinations which display such homogeneous dyeing performance to deliver customer benefits in productivity, cost efficiency and minimised environmental impact.

Further information regarrding DyStar efforts in this area, can be obtained from its website at www.dystar.com.