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A case history in right-first-time (RFT) dyeing

Summary

The advantages (and indeed the necessity) of achieving right-first-time (RFT) dyeing production have been well documented. However, the percentage of exhaust, batch dyeing operations worldwide achieving this philosophy is still believed to be relatively low. This is perhaps because few real-life examples have been published to describe successful installations.  It is hoped that this case study, accomplished by the authors some time ago, will encourage a renewed interest in the philosophy which the authors continue to assist in achieving.

Introduction

In the early 1980s, the opportunity arose to modernise a yarn package dyeing facility in Leicester (UK). In this project, a modern plant layout was developed with the installation of modern dye-pack preparation, with control technology for dye and chemical weighing and dispensing together with dyeing machine control and automation. Up-dated, state-of-the-art quality control facilities together with support laboratories for dyeing technology, physical and chemical evaluation and testing were provided. The details of this installation were described in some detail [1]. In addition, this project, which was completed in about eighteen months, has been a useful case history and template in the stages of achieving right-first-time (RFT) dyeing, allied to computer colour matching and instrumental quality control of colour [2].

Costing studies

In what must be considered as an early and unique paper in the development of right-first-time dyeing [3], Boyd and his co-workers, which included an accountant, gave detailed costs of dyeing processes, indicating the savings that could be obtained by the use of optimised dyeing procedures and the elimination of colour corrections. The considerable savings obtained by blind-dyeing techniques were quantified in this study [3-5], to which can be added further savings and benefit [2]. This team were amongst others that continued to progress towards RFT dyeing and from the mid-1980s, the important factors to obtain dyeing reproducibility were being identified, fifteen factors [5] and seventeen factors having been listed [6] respectively. By 2004, it had been possible to identify approximately twenty factors which must be monitored by laboratory evaluation or controlled by standard operating procedures (SOP) to achieve RFT processing in the dyeing process [7]. These factors have been discussed in earlier papers [2, 8] and are given in Table 1.

Table 1 – Important factors influencing RFT production

Factor

Monitor by
lab check
Control by SOP
Starting materials
Purity of water          X
Dyeability of textile substrate          X
Preparation of textile substrate       X
Standardisation of dye supply          X
Moisture content of dye supply          X
Moisture content of substrate          X
Dyeing process control
Weighing of substrate batch to be dyed       X
Weighing and dispensing of dyes       X
Weighing and dispensing of chemicals       X
Control of liquor ratio       X
Control of pH       X
Time/temperature profile       X
Control of liquor flow or       X
Control of substrate circulation       X

Colour control

Selection of dyes and dyebath additions       X
Behaviour of dyes in combination       X
Accuracy of laboratory dyeing recipe       X
Accuracy of transfer to bulk-scale dyeing       X
Batch to batch reproducibility in bulk-
scale dyeing
      X
Method of colour assessment       X
Determination of metamerism index          X

Technology and control

At the beginning of the capital installation project, rationalised ranges of dyes had been selected based on dye screening projects carried out in the company’s laboratories. Accordingly, short ranges of not more than 10 to 15 dyes were required for each substrate and end-use requirement to be processed. Standard operating procedures (SOP) were also established in a standard methods manual, using best available technology. These were readily loaded into the control systems for the dispensary and dyeing operations, so that SOPs were consistently and accurately followed. Monitored weighing was provided by the dispensary system.

Computer colour measurement (CCM)

Database was prepared accurately in the laboratory since the installation of a computer colour matching (CCM) system could be justified on the basis of cost savings and improved colour quality by the elimination of visual colour assessment. This system provided:

  • a match prediction program, including the possibility of recipe correction and dye evaluation
  • a perpetual inventory program, interfaced into the recorded-weighing system
  • recipe storage and retrieval
  • a colour-difference program.

Regarding recipe storage, the formulation for a colour that had been successfully ‘blind-dyed’ at least twice was added to the recipe storage program. The colour library created could often be used, together with the match prediction program, to achieve rapid colour matching for new shades. In addition, the colour library allowed the concept of non-physical standards (NPS) – so-called matching by numbers – to be successfully developed and exploited. Further studies [9] have led to the widespread acceptance of NPS and the concept of electronic textile colour standards (ETCS) [10]. A long-term relationship with the research department of J&P Coats gave access to the JPC 79 colour difference equation. An in-house project to compare visual and instrumental assessments using this equation enabled single number shade passing (SNSP) [11] to be successfully employed both for internal quality purposes and for customer colour acceptance. The practical details of the installation and operation of this CCM technology together with the benefits obtained have been discussed [12].

Major financial benefits

Typical benefits and cost savings obtained from the use of colour physics technology have been well documented [13], as has the use of RFT [2]. The project described in this paper gave the following major financial benefits:

  • right-first-time production of 98.5% was consistently and continuously achieved
  • savings in dye purchases of 10 to 30%, depending on the substrate, by using least-cost formulations from a  rationalised dye selection.

Major improvements in quality and customer satisfaction are also obtained but these are more difficult to accurately define in financial terms [2].

figure_2

Figure 1 – Total colour control

Conclusions

RFT production can be successfully achieved by a progressive and technically-competent management team which appreciates the major cost savings and quality benefits that can be achieved. Processes must be based on a rationalised selection of technically satisfactory dyes, applied by rationalised and optimised processes which are documented in standard operating procedures (SOP) which must be followed. Adequate laboratory support is necessary whilst control systems ensure that weighing, dispensing and dye application methods are followed. Computer colour measurement (CCM) can give significant savings in dye costs and improvements in quality.

The initial achievement and success of the concept of right-first-time processing was obtained by net-working over a number of years by a relatively small number of organisations in the dye- and machinery-making and –using industries [2]. The concept of total colour control based on RFT processing was developed which is the basis of modern techniques of dyehouse management (Figure 1).

References

[1] International Dyer, 162 (1979) 170
[2] J. Park and J. Shore, Color. Technol., 125 (2009) 133
[3] W.M. Boyd, J. Park, T.M.Thompson and T. Warbis, J, Soc, Dyers & Col., 96 (1980) 497
[4] J. Park, Textile Today, 4, March/April 2011
[5] J. Park, AATCC Int. Conf. Exhib., USA, 1985, 103; Text, Month, May 1986, 17
[6] J. Park, J. Soc. Dyers & Col., 103 (1987) 199
[7] J. Park and J. Shore, Practical Dyeing (Bradford: SDC, 2004)
[8] J. Park, Textile Today, 6 (March 2013)
[9] R. I. Fenn and J. Park, J. Soc. Dyers & Col., 113 (1997) 56
[10] J. Park, Color. Technol., 123 (2007) 1
[11] J. Park and T. M. Thompson, J. Soc. Dyers & Col., 97 (1981) 523
[12] J. Park and T. M. Thompson, J. Soc. Dyers & Col., 98 (1982) 74
[13] J. Park, Colour Science, Vol. 3, 218 (Leeds University, 2001)

Further reading

The following recent books may be useful and are available from:
http://www.park-associates.com

The Practical Application of Colour Measurement, J. Park and J. Shore (Nottingham: J. Park,  2013)

Modern Dyehouse Management, J. Park and J. Shore (Nottingham: J, Park, 2013)

The Dyehouse Support Laboratory, J. Park and K. Park (Nottingham: J. Park, 2013)

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