Maintaining colour5 February 2020
Richard Neale highlights that the linen rental sector is still beset by problems of maintaining the original colour of the fabrics used until the end of the contract. Here he offers some solutions to a comprehensive selection of problems
Despite the UK’s proud history of weaving and dyeing workwear fabrics, the sector is still beset by problems of maintaining the original colour of the fabrics used until the end of the rental contract. Users are frequently surprised to learn how straightforward it is to eliminate complaints relating to colour maintenance, simply by following a few simple steps.
The problems range from simple greying of white food industry cottons and polycottons, through to the yellow stripes on blue garage overalls turning green, right onto entire loads of all white garments suddenly turning pale blue or pale pink after 20 or more washes.
The workwear rental sector is not renowned for being gullible, with some of the shrewdest, hard-nosed operators in the business and yet there are those who are still prepared to believe the unbelievable when faced with non-credible assurances from some of the less scrupulous garment sales teams regarding colourfastness of a new range.
This month we take a look at current problems and consider how to prevent the worst of these and even to recover tinted white garments and rescue a contract.
Classification of each colour separately is still a requirement in most rental laundries. We are not yet at the stage where colours can be confidently mixed, whatever the garment salesman might have said. If a batch of whites suddenly changes from white to off-white then the cause is probably the accidental inclusion of a blue or a green one.
If the change is a more pronounced change to say pastel blue, this is unlikely to be the consequence of a single garment getting into the wrong batch. A more credible solution is the opening of a large marker pen in the damaged load, which a more thorough pocket search might have revealed.
Using a tunnel washer to process both white and coloured garments is usually going to result in greying of all the white ones. This can always be minimised but not avoided.
Long term progressive greying of white cottons or polycottons is usually the result of incorrect washing. Detergent suppliers are now well able to solve this problem, although they might still struggle to recover the grey garments. The keys are to incorporate enough suspending agent in the detergent mix to prevent greying caused by redeposition and to include enough non-ionic detergent to clean and keep clean the polyester fibres.
The causes of colour change
- Dyeing quality: the primary cause of colour change and colour transfer is use of a dye recipe with poor fastness to washing (usually to achieve a low first-cost for the garment), or failing to fix the dyes properly onto the cloth, or both. There is no point in simply specifying vat dyes for a batch of cotton towels or cotton table linen (which should achieve improved colourfastness to washing), if the specification does not also include fixing these so that they do not come off in the first few washes.
Close on the heels of poor colourfastness to washing is failure to wash-off properly after dyeing. The rental laundry can usually cope with imperfect wash-off if the garment is genuinely single colour, but if it is white trimmed with red piping say, then it is surprising just how far a tiny bit of loose red dye can go in a whites load. This applies even if the piping is polyester and the garment is polycotton. The term ‘washing off’ should not really be applied to polyester, because it implies that washing off is sufficient. To be suitable for workwear garment rental, polyester yarn needs a ‘reduction clear’, which is washing-off assisted chemically by a reducing agent, designed to pull unfixed dye molecules of the fabric. Only this will prevent colour transfer in the first few washes.
- Incompatible OBAs: of increasing importance in recent batches of fabric has been the incidence of troublesome optical brightening agents (OBAs) on white fabric. An optical brightener acts like a colourless dye and bonds securely to the textile. It reacts with the ultraviolet portion of the daylight to create brilliant white light, making the colour look both whiter and brighter. A little of the OBA is lost in washing and some white-work detergents then replace the lost OBA with a slightly different one (usually of better quality). The result can be a distinct tint (blue, pink or pale green) caused not by colour transfer but by the interaction of two non-compatible OBAs. The problem is made worse by appearing of different severity in different lights. The lights in the customer’s restaurant often seem to display it at its worst!
- Processing mixed work in a CBTW: uprating the washhouse from washer-extractors to a tunnel washer should deliver very significant productivity and wash-cost benefits. However, the internal water recycling that accompanies these benefits means that any loose dye from garment batches will contaminate every recycle tank, every pocket and every internal water flow. It has been standard practice for workwear plants to tackle this by ensuring that two empty pockets are left after a run of coloured work, before switching to white work. The result has not been satisfactory; any improvement made by the two empty pockets has been largely illusory – more a sop to the conscience than a scientific solution.
A better technique is to empty and drain down the CBTW at the end of the working day and then to start afresh with white-work in the morning. If all of the whites can be processed in one continuous run, the machine can then be switched to colours with just two empty pockets in between. This minimises production losses and it also virtually eliminates the risk of colour transfer. Of course, this does demand careful scheduling, which is often easier with garments then with flatwork, but the improvement in the colour of the whites can make it worth making the effort.
- Greying in the tumble dryer: the correct drying of terry towels in flatwork plants is a sadly neglected art, which is widely responsible for long term greying of this classification (when compared with sheets and pillowcases, for example). The source of the greying of towels can be identified using a special test piece. This consists of two brand new towels and a small net bag. One towel is folded tightly into the net bag, which is pinned closed. The other is attached to the net bag and allowed to float freely. The test piece is then washed 25 times and disassembled.
Any greying of the towel in the net bag could only have happened in the wash, because this towel will never have become dry. This greying can be assessed by comparing it with another new towel from the same batch. Greying of the towel which was floating freely will have occurred both in washing and drying, the difference in colour between this and the towel in the net bag indicates the degree of greying in the dryer. It is usually found that in a modern laundry, greying in the drying greatly exceeds greying in washing.
Greying in drying occurs at the end of the drying cycle, when the bone-dry terry loops brush against the rotating metal cage, creating a tiny static charge on each loop. This is sufficient to attract every dirt particle from the drying airstream and create progressive greying which is exceptionally difficult to reverse in the next wash. Greying in drying can be avoided by fitting cycle terminators to the dryers, programmed to halt drying when the moisture content is around 2%, Some trial and error might be needed to strike the happy medium between avoiding tangible dampness and greying when bone-dry, but the effort will be found to be well worthwhile.
Recovering a tinted batch
Bleaching a batch of white textiles that has been turned pale pink or another pastel shade rarely works, especially if the problem stems from a marker pen or similar. However, if bleaching by chemical oxidation fails (using sodium hypochlorite or hydrogen peroxide), then it is worth trying chemical reduction. Dyers used sodium dithionite as a dye stripping agent with considerable success. The main reasons why this is not now widely used in the laundry sector are twofold:
a. The process gives off a strong odour of bad eggs, so the recovery process needs a well-ventilated area. The bad egg odour is poisonous, so local extraction may be needed.
b. Special storage precautions are needed when keeping sodium dithionite, for safety reasons. It can be explosive if stored incorrectly.
For these reasons, the process should be designed in conjunction with a reputable chemicals supplier and carried out when there are only essential washroom staff present.
Maintaining the correct colour of items in the rental contract calls for professional laundering skills, but it is not an expensive or impossible task. By applying the principles described here it is possible to avoid the worst problems, even if workwear of different shades and whites have to be processed in a single CBTW. Avoiding the long-term greying of white towels does involve some investment (typically up to £5,000 per dryer), but this is usually recoverable in the first 12 months in energy saved. It also carries with it an increase in towel productivity which is sometimes worth even more than the quality improvement achieved.
- If you have problem that you think LTC Worldwide can help with, or that you feel would make a good subject for Material Solutions, please call T: 00 44 (0) 816545