A review of dye screening and selection – some case histories in networking

Introduction

It has been claimed [1] that new entrants into dyeing laboratories in the 1950s and 1960s, particularly in the traditional textile-producing countries of the western hemisphere, were given the important task of undertaking extensive dye screening projects, as part of their training programme and to fulfil a major need. A major reason for this need was that a large number of both small and large dye manufacturers worldwide were entering the existing markets with dyes for the major fibres which were then principally natural in origin, namely wool and cellulosics [2]. A new class of dyes, 1:2 metal complex dyes, was launched for wool in 1953. In addition, the truely-synthetic fibres had been developed [3]; polyamides being launched in 1939, polyesters in the late 1940s and polyacrylonitriles in 1953. Early dyeing techniques for these new fibres depended initially on the use of available dye ranges from existing dye classes, until dye R&D could ‘catch up’ and develop dye ranges specifically tailored for these fibres [2, 3], with each major dye manufacturer producing independent ranges.

Indeed, it took some time for R&D to catch up with the new requirements. As an example, it was the early 1960s before it was decided that the newer modified cationic (basic) dyes would be the dyes preferred for dyeing polyacrylonitrile substrates rather than disperse dyes.

These were thus the reasons for major dye-screening exercises, especially since this was before the concept of dye rationalisation became common practice which was later assisted by optimised dyeing methods based on calculation techniques. Dye screening and selection was therefore necessary to restrict purchases to a limited number of products, not only for financial reasons, but so that end-product specifications could be met, level dyeing achieved and practical dyers could become familiar with the colour and other properties of a limited range of dyes selected for use in bulk processing.

Early dye screening exercises

Further evidence of this claim [1] can be gained from the author’s personal experience as indicated in Table 1. In several of these projects (*), between 300 and 600 dyes were included in screening programmes. Parallel studies were undoubtedly carried out in dye application laboratories well into the 1980s, by which time systemised dyeing processes were being developed, dye manufacturers were rationalising their ranges and a reduction in laboratory staffing in harsh economic climates made dye screening a casualty, thereby removing a useful training aid [1]. Perhaps unsurprisingly but in common with most workers in this area of technology, the results from the period 1 evaluations (Table 1) were never officially published but those from period 2 were discussed [4], whilst those from period 4 were also published [6].  Only a limited amount of information from period 5 and virtually none of the results from dye screening exercises in periods 1, 3 and 6 were published at the time the work was carried out, the information being disseminated by networking through student/lecturer relationships in educational establishments and by the representatives of dye suppliers. It was not until much later that the results from these early studies were published. These are listed in chronological order of publication in Table 2, with the references being given in both Tables 1 and 2.

Table 1 – Dye screening exercises

Levelling agents for wool dyeing

By the late 1950s, a number of workers, but notably Peryman [13], had confirmed that minimum wool damage during dyeing occurred in the iso-electric region of wool, (pH 4.0 to 4.5). Suitable levelling agents were developed which formed complexes with the dye thus allowing dyes of higher fastness and poorer levelling properties to be dyed at this optimum pH to minimise fibre damage, thereby giving level dyeing and optimum exhaustion. During period 1, an extensive evaluation of these levelling agents for wool was carried out. Although this was a limited publication [14], Ciba had sponsored the project and the thesis had been successfully entered in a Worshipful Company of Woolmen competition. Thus some exposure had been given. This work also proved a useful starting point for that on felt (period 2), nylon (periods 3 and 4) and wool (period 5).

It is therefore perhaps surprising that it took over twenty years for major dye manufacturers to exploit this technology when Ciba-Geigy (later becoming Huntsman) launched the Lanaset dyes [15] and Sandoz (now Clariant) developed the Optilan concept [16]. These developments have enabled the Woolmark standard to be achieved using these concepts, as discussed later.

 Table 2 – Publication of results

        (*) – fast to cross-dyeing with nylon
(**) – the same dye selection was used for dyeing and printing
(***) – selected for various end-uses
(****) – double jersey end-use
(*****) – automotive fabric end-use

In addition, a rationalised range of twelve vat dyes for cellulose was given [5] whilst Clarke [12] listed ranges of rationalised dyes for dyeing acrylic, polyester, nylon and wool in fibrous form by both exhaust and continuous methods.

Early networking

In addition to the above, it is thus worth discussing three further major achievements of early networking, namely, the development of Woolmark standards, the exploitation of fibre-reactive dyes and the evolution of right-first-time processing.

Achieving Woolmark fastness standards – history and development

Until the late 1960’s, no basic specification existed for piece-dyed 100% woollen cloth except that it must be dyed to an acceptable standard of levelness and be of reasonable light fastness. Bulk dyeing of such fabrics was usually carried out on winch dyeing machines which were often relatively primitive, without control or dispensing equipment and ancient. Even when jet-dyeing machines became available in the early 1970s, few traditional woollen piece-dyers installed these due to a combination of high capital cost, the long life expectancy of winches, the decline in the popularity of the wool fibre and an increasing use of other forms for dyeing wool. From 1951until currently, worldwide wool consumption has declined from 9.4 to 2% of total fibre usage.

Historically, level-dyeing acid dyes were widely used since these dyes would also give coverage of irregularities in the fabric, for example, from previous carbonising processes. Woolmark was a brand established in 1964 by the (then) International Wool Secretariat (IWS – now WDI) to improve the quality and performance of wool textiles by creating standards for all stages of processing, including dyeing and finishing. This included a specification for piece-dyed ladies’ dress-goods for fastness to light and water. Although the light fastness specification could readily be obtained with dyes then in use, meeting the fastness to water specification was more problematical.

An initial dye screening project was commenced in 1968 which included more than 300 dyes for wool.  The candidate dyes were dyed at a range of appropriate depths on carbonised woollen fabric to assess level-dyeing characteristics and to evaluate fastness to light and water. In addition to dyes with relatively superior level-dyeing properties, acid milling and 1:2 metal-complex dyes with higher fastness properties were evaluated, these being applied by an adjusted technique as regards pH and levelling agent.

For dye selection, a triangulation approach was developed. The initial dye screening work indicated that mode (mixture) colours could be achieved in terms of satisfactory levelness and fastness to Woolmark specifications for light and water by using a tertiary mixture (of yellow, red and blue dyes) of monosulphonated acid levelling dyes. Brighter and/or darker colours were achieved to these standards by replacing one or more components of the trio with alternative dyes such as an orange, red, violet or navy component. A total of twelve dyes could achieve a wide colour gamut, although this could result in an increase in dye cost. A large gamut of colours could be produced with a small number of dyes. The results of this work was published [8] and a colour atlas exhibiting 250 popular colours based on this dye selection and identified by Munsell numbers was produced and used commercially [17]. This joint project resulted in a further rationalised dye selection, enlarged with a small number of metal-complex dyes [7]. This document was used by IWS in industry for a number of years to give guidance on dye selection.

Although wool piece-dyers were perhaps slow to adopt jet-dyeing technology, jets being installed for the first time as late as the 1980s by some companies, these machines allowed higher-fastness dyes to be employed. As a result of evaluation of costs, rationalisation and major changes in the dye manufacturing industry [2], most of the dyes listed in the early studies [7-9] will have been renamed or have disappeared. However, as discussed above, new or rationalised ranges of dyes for wool, suitable for piece-dyeing on jets were introduced [15, 16]. A common factor within these dye ranges was application in the iso-electric region of the wool fibre where minimum fibre damage occurs, dyeing being carried out in the presence of a suitable levelling agent.

Neolan P (Ciba, now Huntsman) are 1:1 metal-complex dyes and are applied at pH 3.5 to 4.0. A number of these dyes will meet the Woolmark specification for light and water fastness up to depths of 2.0 to 2,5% [18]. The Optilan concept (Sandoz, now Clariant) [16] contains two ranges of dyes, both designed to give improved fibre quality. The Sandolan MF dyes from this package [19] are level-dyeing dyes and this range (and similar ranges) will give satisfactory Woolmark fastness up to depths of 1.0 to 1.5%. Applying Sandolan MF dyes to woollen pieces by a modified method in which formic acid is added after 30 minutes at the boil to lower the pH to about 3.0, gives a greater solidity of shade than the conventional method at pH 4.0 to 4.5 [18].

The Lanaset (Ciba, now Huntsman) dyes [15] are a compatible range of fifteen dyes from the milling acid, 1:2 metal-complex and reactive ranges which have been selected to enable a wide colour gamut to be obtained whilst giving high levels of reproducibility, fastness and levelness when applied using a levelling agent (Albegal SET) at pH 4.0 to 4.5. The dyes are applied by a standardised method, at all depths and colour areas. Albegal SET has been used as a satisfactory levelling agent with other dye ranges. For dark colours on wool, chrome dyes, once a major dye range for dark colours on protein fibres, have virtually been replaced by reactive dyes for ecological reasons. A major use for reactive dyes on  wool has been for dyeing shrink-resistant materials suitable for machine washing. Lanasol (β-bromoacrylamido) dyes developed in 1966 by Ciba-Geigy (now Huntsman) have probably been the market leaders and the most commercially successful range. This is a rationalised range of eight dyes which will provide a wide gamut of dark colours, meeting the necessary fastness properties. Fibre damage is minimised using this dyeing method thereby preserving fibre quality giving significant positive implications and financial benefits in the spinning process [20].

Fibre-reactive dyes for cellulosic fibres

Reactive dyes have the unique property that they are designed to bond covalently with the substrate on application. They are principally used for dyeing and printing of cellulose, have been used to a lesser extent on polyamides but are used for important outlets in the coloration of wool and silk. Their brilliance of shade and high fastness to washing makes this class of dye ideal for materials that are subjected to frequent wash-wear cycles, which has become increasingly important with changes in fashion and washing practices. Since their discovery and the launch of the first ranges of reactive dyes by ICI in 1956, fibre-reactive dyes have increased enormously in their importance and application. Exhaust application methods still account for over 50% of reactive dye consumption with continuous dyeing and printing accounting for about a further 30%. The importance of reactive dyes is further indicated in that at least fourteen commercial dye ranges based on eleven reactive systems were developed [21]. Currently, reactive dyes account for 36% of total dye sales worldwide [22].

A recent paper [23] has reviewed the history, development and exploitation of reactive dyes. Much networking has taken place with reactive dyes and as a result many other developments and improvements to which they have contributed must include:

1. impetus for the improvement of continuous dyeing techniques
2. replacement of ecologically unfriendly dyes
3. a high level of right-first-time processing on cotton
4. improvement of jet dyeing machines
5. the ability to produce master standards and developments such as electronic textile colour standards [24].

Dye evaluation and RFT processing

It was pointed out in 1982 [25] that many parameters must be considered in the selection of dyes and methods for dye evaluation were published [26, 27]. Dye selection was discussed [21] when it was noted that so-called ‘identical’ dyes were not identical in reality but only equivalent as regards the major coloured component but not necessarily in terms of application properties. A selection of rationalised dyes must be based on a significant number of parameters. The more extensive dye screening procedures and the selection of a rationalised range of dyes has made a major contribution to right-first-time (RFT) processing [28] which makes a major contribution to cost saving and profitability. Since this concept was achieved by the combined efforts of the technical and laboratory staff of a relatively small number of manufacturers and users of fibres, dyes and equipment, no formal R&D programme ever having been organised, much networking must have occurred before publication.

As a result of evaluation of costs, rationalisation, renaming of dyes and the demise of dye manufacturing companies [2], many of the dyes selected from early dye screening work will have disappeared. These, however, will have been replaced by modern, rationalised dye ranges applicable by optimised dyeing procedures [28]. A major element in the success of RFT processing is the production of standard operating procedures (SOPs) and procedures manuals.

Conclusion

Early dye screening programmes were carried out on the traditional dye/fibre combinations, a major objective being to obtain cost-effective dye ranges and this resulted in a number of rationalised dye ranges. The results from this work were seldom published at the time, perhaps containing data on only a few parameters and communicated by networking. As perhaps indicated above, relationships and good communications were established with dye suppliers by which information was exchanged in both directions by networking through regular seminars and meetings. Joint projects, some resulting in joint publications, were undertaken.

With the migration of textile manufacture, wet processing and dye manufacture to the eastern hemisphere, much current, valid and useful information is still available by networking which still exists between dye makers and users, technical support organisations, technical publications and consultants.

References

  [1] R. McDonald (J.P. Coats), private communication
[2] Dye manufacture – a history, J. Park and J. Shore (Nottingham: J. Park, 2013)
[3] J. Park and J. Shore, J. Soc. Dyers & Col., 115 (1999) 157, 207, 255, 298
[4] J. Park, J. Soc. Dyers & Col., 80 (1964) 588
[5] A practical introduction to yarn dyeing, J. Park (Bradford: SDC, 1981)
[6] J. Park, J. Soc. Dyers & Col., 84 (1968) 601
[7] Attainment of Woolmark Specification 4, Colour fastness to water on women’s woven
piece-dyed fabrics, J. Park (J. Crowther) and P. J. Smith (IWS), IWS Project W109
(October 1969)
[8] J. Park, Dyer, 147 (7/1/72) 27
[9] A practical introduction to the dyeing and finishing of wool fabrics,
I. Bearpark, F. W. Marriott and J. Park (Bradford: SDC, 1986)
[10] J. Park, Text. Chem. & Col., 11 (1979) 156
[11] J. Park, Dyer, 158 (11/11/77) 481
[12] A practical introduction to fibre and tow coloration, G. Clarke (Bradford: SDC, 1982)
[13] R. V. Peryman, J. Soc. Dyers & Col., 73 (1957) 455
[14] The effectiveness of certain levelling agents in wool dyeing, J. Park,
Scottish Woollen Technical College (now Heriot Watt University), Thesis, 1960
[15] H. Flensberg, W. Mossiman and H. Salathé, Dyer, 169 (1984) 9, 37
[16] A. Welham, Wool Record, April 1988, 72
[17] K. M. Lewis and J. Park, J. Soc. Dyers & Col., 105 (1989) 152
[18] Private communication
[19] A. Welham, Dyer, 169 (1984) 5, 38
[20] P. Duffield, M. Rushforth, K. Lordan, A. Ng, F. Gruener and Y. C. Kim,
Dyer, 195, Dec 2010, 15
[21] Practical Dyeing, J. Park and J. Shore (Bradford: SDC, 2004)
[22] E. Fernandes, N. Pingale and V. K. Sai Ganesh, Dyer, 196, (April 2011) 27
[23] J. Park, Textile Today, April 2013
[24] J. Park, Color. Technol., 123 (2007) 1
[25] J. Park and J. Shore, Rev. Prog. Col., 12 (1982) 1
[26] Dyeing laboratory manual, J. Park and J. Shore
(Upperhulme, Roaches International, 1999)
[27] Getting results from your coloration laboratory, J. Park and J. Shore
(Bradford: SDC, 2006)
[28] J. Park and J. Shore, Color. Technol., 125 (2009) 133; J. Park, Textile Today,
March/April 2011 and March 2013