Now You Know Control of Tailing and Listing Problems in Continuous Dyeing – a Systematic and Practical Approach

Control of tailing and listing problems in continuous dyeing – a systematic and practical approach

Dr. Eng. Zeeshan Khatri
Associate Professor
Dept. of Textile Engineering,
Mehran University of Engineering & Technology, Pakistan

Introduction

The increasing requirement for dyeing larger batches, the demand for minimum shade variation throughout the length and the shift from batch dyeing to continuous dyeing has led the textile coloration industries to consider all aspects that affect tailing and listing. Water consumption has to be reduced as well as the liquor-to-goods ratio.

Control of tailing and listing problems in continuous dyeing Now You Know Control of Tailing and Listing Problems in Continuous Dyeing – a Systematic and Practical Approach

Fig: Problems in dyeing

Shade consistency is an additional advantage of continuous dyeing and longer runs are possible with minimum shade variation. There is the need for, and increasing possibility of, automation and control of all the different aspects of the dyeing processes.

Market trends force dyers to be fully abreast of the latest requirements demanded by a buyers’ retail market with much shorter fashion seasons. Two of the major problems encountered by dyers are tailing and listing. The dyer must consider all factors influencing listing and tailing right from greige to finished fabric.

This is a comprehensive article identifying the factors influencing colour variation, factors which can cause listing and tailing. A systematic and practical approach is adopted in a manner which can be used as a practical guide for dyers and colourists.

Research and Development
It is necessary to review the past research into colour variations such as listing and tailing and developments.

Dye makers and machinery manufacturers have been involved in research and development for many years, advancements in weaving have occurred to produce more consistent fabric properties.

Dye, fibre and chemical manufacturers have made contributions in fibre and dye chemistry including improvements in dye substantivity and affinity, ionic characteristics, fastness properties, mechanical and thermal behavior and with the introduction of more fibre reactive dyes with stronger dye–fibre interactions.

Machine manufacturers have produced more control systems that are robust in a works situation as well. Indirect heating in chambers, radiation drying, engineered padders and troughs, dye dispensing and online colour measurement are a few examples of recent advancements.

The role of the dyeing team has a tremendous influence in producing quality fabric and is only possible when qualified and skilled team members are there.

Tailing and listing
Tailing is shade variation along the length of the fabric and is determined by a series of comparisons of the colour from the first metre to the last, checked and measured during the dyeing process. For example, if 10000 m of fabric is to be dyed in a continuous dyeing range, the dyeing is started and the shade being matched is sampled and agreed and this sampling is continued up to the end of the 10 000 m at intervals.These intervals depend on past history of the dyes and fabric being dyed. The term ‘ending’ has also been used as well as listing.

Listing is shade variation across the width of the fabric and it is also checked during dyeing. Variation can be from side-to-side or side-to-centre. When the fabric runs in open width this parameter should not be ignored and must be checked in a similar manner as the tailing. When dyeing in jet machines where the fabric is in a rope form, listing is rarely a dyeing machine problem.

Testing staff should be made aware of the phenomena of thermochromic effects as certain chromophores can exhibit vast temporary colour changes. The effect of moisture on shade should be considered especially when urgent orders are being processed. Shade varations can occur in finishing but these effects should have been checked in the laboratory.

Continuous dyeing processes
Most fabrics are treated and run continuously on machines for treatments such as bleaching, pad application such as thermosol dyeing and pad–steam and the many washing off procedures used at all processing stages.

Greige fabric is received by the greige department where full details of the fabric,the job/lot numbers and the full processing route are issued. The fabric may need to be tested to determine size content, grams per square meter (GSM), width and, if necessary, suspect foreign impurities are checked. See Appendix 1 for the range of tests needed.

All fabrics to be processed have to be checked against the fabric standard, especially with repeat orders. Fabric is passed for the singeing and desizing process where it is normally singed at high speed and padded with the liquor containing desizing agent The desized fabric is then washed and/or dried before passing to the continuous bleaching range for scouring and/or bleaching. Correct scouring and bleaching with fully controlled washing is necessary. An optional mercerising process may be carried out either before or after bleaching depending on the end use.

General factors influencing listing and tailing
An assumption has to be made that for large dyeing orders the fabric is fully suitable for purpose and has consistent properties. Factors influencing tailing and listing include variation in yarn count, yarn twist, fabric density and width GSM of the greige fabric. Sizing agents should be water soluble. Uneven size application affects the degree of desizing.

Tailing and listing problems can be caused by two controlling factors, namely:

Equipment parameter changes or variations or
Eye properties.

Equipment control parameters
Correct singeing/desizing: this has a major influence on listing, if singeing or desizing varies across the width. Where pad batch processing is used, batching equipment alignment is very important.

Uneven padder pressure at any stage in desizing, washing, scouring, bleaching, dye application and washing off can cause variations and thus listing can occur. Faulty padder equipment is the most likely cause of listing. The individual padder pressures from left, centre and right play a dominant role and have a direct effect on listing and tailing. Padder diameter variation across the width may also producing listing. Variation of air of hydraulic pressures can lead to variable padding expression. A long run of smaller width fabric will leave an impression across the width on the padder, which will leave an impression on wider fabric that will show up during dyeing.

Some companies invest in keeping two dyeing padders operative in one dyeing range where wider and small width changeover is frequent, one for narrow fabric width and the second for wider width fabric, in order to avoid any variation caused by the padder and also to increase the life of the padder.

Mercerising: variations in the degree of mercerizing across the width cause listing and should be controlled. The washing process needs careful control.

The drying or dye fixation of fabric must be controlled and even, in order to ensure a consistent moisture content. A stenter must be fully controlled in terms of temperature and recycling. Even temperature is needed when there are different temperature zones. Over- or under-drying can cause listing later in the dyeing process where there is steam injection for thermosol processes; control is paramount.

A major control problem that is caused by dye properties can be corrected by good padder design.

Control of washing off: this is vital for both quality and effluent and environmental considerations. Water flow in each tank must be controlled throughout the production run; the padder pressures and the condition of the padders in each washing chamber should regularly be checked. Variation in washing temperature, feeding rate of soap and neutralizing acid can also account for listing and tailing.

The volume of dye liquor for long runs has to be established and mixing tanks provided for shade continuity. The padding expressions for the fabric to be padded have to be decided. The padding trough volume has to be sufficient to stop tailing due to variable ‘strike’ in a bath containing a mixture of dyes of differing dye properties.

Dyeing properties and the effect on tailing and listing
Different dyes can have vastly different dyeing properties and it is of paramount concern that the dye manufacturers’ recommendations be followed. Dyes that have been matched with other dyes are more likely to give similar dyeing characteristics. Colours have different substantivity and affinities, often at different temperatures and in the presence of added electrolytes commonly used in dyeing procedures. For example, a mixture of three dyes in a padding bath might have differing substantivities. If the pad bath is large or the liquor feed control poor and the machine is running more slowly because of a heavy fabric, one of the dyes might be removed from the bath more quickly – hence the start of a tailing situation. This problem was given a name in the very early days of dyeing, the problem of ‘strike’.

It is essential that good records of dyeing problems be kept so that certain mixtures of dyes for certain fabrics can be avoided if possible or special care taken.

The dye manufacturers have spent time and money on developing efficient dyeing systems and their efforts should be used to create a viable and prosperous industry.

Shade evaluation and quantifying listing and tailing
Visual assessment is carried out in a standard light bo x. For listing, width-wise fabric is stitched to accommodate three areas marked as left, centre and right; this article is then assessed in a standard light box with specified light such as D65, TL84, Inca or CWF. For tailing, a number of fabric samples are collected at 500 m intervals and assessed against the customer’s standard in a light box. The number of samples and intervals vary according to the total length being dyed in bulk.

Spectrophotometric and computer colour matching systems can be used instead of the visual assessment procedure, but this needs to be done against defined standards. The customer standard is taken as a reference for measurement in a spectrophotometer and then compared to the production run.

Where there are problems, a checklist can be used and a list for both listing and tailing is given in Appendix 2.

All of these factors have different impacts depending on the fabric, the fibre and the dyeing system. Herein lies the skill of the colourist.

Conclusions
Dyeing with consistent shade is the key to success, regardless of whether shorter or longer runs are being employed. The global market is constantly changing and this rapid change of shades is now common as the retail lifespan of fashion is drastically reducing. Dyeing shorter runs in continuous processes keeps dyers on a tightrope and achieving consistent shades with the minimum amount of rejections has become a gigantic task.

Since large investments in continuous dyeing could be decreasing due to the emerging trend of doing shorter runs, the pressure now is on dyers to achieve consistent shades with minimum variations. Under these circumstances, the dyer should be technically sound using all the information available to him so that the pressures to produce quality shades with the available resources is achieved consistently. This will be for his own, and the company’s, survival in the market.

Appendix 1: Predyeing tests for control of tailing and listing

Suggested test	Method	Reason for test	Result
Fabric GSM width/ length	GSM cutter with weighing scale.	To ensure no fabric variations in weights	Uniform result avoids listing and tailing problems in subsequent dyeing process
Fabric pilling	ICI pilling tester or NuMartindale	In order to check the fabric pills	Shows singeing efficiency
Degree of desize	Iodine drop test for degree of desize.	To assess the extent of starch removal from fabric during desizing.	Variation will be more apparent in case of dyeing reactive and vat dyes
Absorbency	Capillary method with either time constant or level constant. Drop test method with sink-in time and spreading diameter	To check the fabric absorbency left, centre and right; and with 1000 m intervals along the length.	Gives an idea of fabric pick-up variation and can then be controlled accordingly during dyeing. A lot can be segregated prior to dyeing if any major variation is observed.
Fabric pH	Drop test and pH by extraction method	To check pH of fabric left, centre and right – must be neutral	Measures the fabric pH which can cause listing and tailing problems if this varies within the lot
Degree of mercerising	Barium number	To check the degree of mercerising; sampling at 2000–3000 m intervals.	Shows the absorbency variation across the width and along the length
Degree of whiteness	Spectrophotometer	To check the fabric degree of whiteness	Consistent whiteness along the length ensures shade consistency and puts the focus of variation on other causes