Formulating Colours: More than just a “bit o’salt”
Dr Jim Bullock, iFormulate Ltd, takes a look at the wonderful world of formulating colours.
Longer ago than I care to remember, I was flattered to be asked to give a talk in Leeds to the SDC’s student section. The subject was the formulation of textile dyes, and after spending 45 minutes or so persuading the audience that formulation was a tricky task, and that plenty of science was involved, the organiser thanked me with the words “and I thought all you did was standardise wi’ a bit o’ salt”.
I shouldn’t have been surprised by the comment, because at the time formulation was seen as pretty empirical and one of the “dark arts” – and of course most of its practitioners didn’t do much to dispel that idea. However, a few years later the science and technology of formulation – in many sectors including pharmaceuticals, agrochemicals and cosmetic products – is acknowledged to be not just worthy of academic study but also something which can add huge commercial value. For instance, plans are afoot for the UK to set up a major collaborative R&D centre for formulation and skills and qualifications in the area are developing well in parallel to this.
Learning to formulate textile colours is actually an excellent way of gaining experience in science and technology which can be applied to other areas and industries. Disperse dye formulation teaches you about wetting, dispersion stabilisation and Ostwald ripening, pigment formulations provide dramatic examples of rheological variation due to variation in particle size and state of dispersion and reactive dye liquid formulations provide challenging examples of stabilising solutions at very high concentration.
In addition, there are great similarities between the products and techniques used in colorant formulation and those employed in agrochemical pesticides, pharmaceuticals and coatings. Indeed the trained eye can sometimes spot ideas popping up in the more “high-tech” industries which have their genesis many years previously in humble textile dye formulation. For instance, sub-micron particle dispersions (before they got the trendy nano name of course), co-crystal formulations and spray dried solid formulations were all established tricks in dye formulation before the pharma industry got around to having a look at them.
Recently I was particularly struck by the importance of a good grounding in formulation science and technology during a one-day course we presented in formulation for ink-jet printing. Whether in textile printing, reprographics, digital electronics or trendy 3D-printing, the use of ink-jet technology for digital design, imaging and patterning is experience a dramatic growth. Even those humble disperse dyes have been given a new lease of life outside the textile world by the growth of sublimation transfer printing Digital printing is used to apply disperse dyes to a transfer sheet, those dyes are then transferred by heating to a polymer substrate which can be used for displays and personalised articles from high value mobile phones through to humble coffee mugs.
But of course technology doesn’t stay still and the scientists and technologists of the ink-jet world have built on textile dye and pigment knowledge immensely over a period of years with the result that inks can be developed and used for extremely challenging materials and applications. For instance, printing electronic materials with solvent based inks can give rise to the appropriately named and somewhat undesirable “coffee stain effect” where solid is deposited from the ink droplet in a ring-like formation, rather than in a uniform circular disc. Clever formulation by understanding surface tension and evaporation of the solvents used can help solve the problem and enable uniform patterning and good quality devices to be printed.
Finally, no article of this sort would be complete without a mention of that wonder material, graphene. It’s a pretty tricky material to formulate as an ink but it seems that it can be done. In fact one look at the structure of graphene reminds me of polyaromatic conjugated vat dyes or pigments. Which makes me wonder whether some old dye formulators haven’t already been wheeled in to sort out graphene’s more critical formulation challenges, with or without recourse to “a bit o’ salt”!
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