Abstract


Colour fastness is of considerable interest to all consumers of home textiles and clothing, and therefore to all fashion houses, retailers and branding companies.


Our featured question this article comes from a Turkish producer;


The rinsing and washing processes in my dyehouse are too long. Is there any way that we can utilise our existing machinery to improve the efficiency and reduce the rinsing time without compromising fastness properties? Our machine supplier is telling us that the latest Jet dyeing machines automatically reduce the washing off time. Is this true?


In summary, we emphasise that our comments are related to the exhaust dyeing of cellulosic fibres with reactive dyes. Having said that, anyone can shorten a rinsing process. Various people (machinery suppliers or chemical suppliers for example) will try to convince you that it is simple, and that only one approach holds the key. It is for you to decide whether or not that opinion derives from a vested interest. In our experience, the objective should be not only to shorten the rinsing process time, reduce the number of rinse baths, but to do so without any compromise to the safety of the process or to the level of Right First Time production.


Thus, many chemical suppliers will seek to convince you that the number of rinses after bleaching and before dyeing can be reduced by the use of a peroxide killer. But this is only true if the modified rinsing process leaves the substrate Fit for Dyeing. Peroxide is only one of the potentially harmful residual chemicals which must not be carried forward into the dyebath. If the use of a peroxide killer leads to a reduced number of rinse baths, will that reduced number still be sufficient to remove residual alkali ? In our experience not necessarily so. Thus also, the number of rinse baths after dyeing can easily be reduced. But what is the effect on critical wash-fastness? There is no doubt whatsoever that machinery suppliers have made great strides in the last decade to shorten rinsing process times considerably with such techniques as CCR (Combined Cooling & Rinsing) and Smart Rinsing.


But we would urge readers not to place too much reliance on machinery hardware developments without taking full consideration of a full understanding of all the critical success factors involved. So far as machinery developments are concerned, we attempt in this article to give an independent review without any vested interest of any kind.


2. Full Article : Rinsing Cellulosic fibres


2.1. Background to Machinery Hardware Developments.


This area of wet processing tends to get the least attention yet it has been estimated that 80% of the water consumption, 90% of the energy and 70% of the time of the total wet process is consumed in bleaching, washing and rinsing. General improvements in production efficiency via the dyeing (colouration) stage have been realised through a more widespread adoption of Controlled Coloration principles that lead to higher Right-First-Time (RFT) performance and reductions in costly and wasteful reprocessing. When RFT performance has been optimised the focus should change to increasing productivity by utilising the latest generation of textile machinery and machine controllers, in order to reduce the fixed costs per unit of production. We have emphasised frequently that such drives should follow, and never precede, optimisation of the basics.


The introduction of newer elements of application technology has already led to significant productivity gains in the exhaust dyeing of cellulosic substrates in pre-treatment and dyeing.


The essential machinery developments in this respect have been:


- Low liquor ratio machines

- Multi- tasking controllers

- And heat recovery systems and hot water supplies.


The increasing costs of water and waste-water treatment, coupled with the need to drive down production cycle times and costs, forced the industry to re-evaluate the way in which this vital commodity was utilised.


ITMA 1995 thus saw the unveiling of a range of machines from the major manufacturers with smart rinsing systems in which fresh hot water could be metered into the dyeing machine to dilute and remove fabric contaminants, dyes and processing chemicals. In addition to significant time savings and much more