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| Issue date:01/12/2007 |
| ATA Journal for Asia on Textile & Apparel - Dec 2007 Issue |
| Source:Journal for Asia on Textile & Apparel |
| by Chen Rongqi |
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| In face of growing popularity of environmental protection around the world, textile dye manufacturers are quickly responding to develop new environment-friendly dye products for the textile and apparel supply chain. |
In 1994, Germany approved the revised "Act on Food and Consumer Goods", leading to the research and development of environmentally friendly dyes in the textile and apparel business community to substitute the banned dyes.
New eco-friendly dyes are being developed to replace banned dyes (Photo: Clariant)
Generally speaking, newly developed dyes should be free of arylamine, which is banned for its carcinogenic characteristics that can cause cancer.
They should be non-carcinogenic, non-allergic and non-toxic. Extractable heavy metals, if available, should be kept in the level of acceptable minimum, as well as formaldehyde. They should be environmentally friendly, containing as little pollutants, especially polluting chemical substances, as possible.
There are currently four major groups of eco-friendly dyes, namely reactive dyes, disperse dyes, acid dyes and direct dyes.
Reactive dyes are free of heavy metal
Reactive dyes are characterized by an improved fixation rate, reduced use of salt, heavy-metal-free property and improved colorfastness.
Sumitomo launched Sumifix Supra NF and Sumifix HF reactive dyes in 1998, featuring a high fixation rate of 85%-95% and good fastness to sunlight, sweat, light and chlorine. These reactive dyes are suitable for exhaust dyeing and pad dyeing under high temperature between 70℃-80℃.
Ciba's Cibacron LS (low-salt) range has been expanded from eight products to currently 12 products. It requires as low as one-fourth of salt (sodium sulfate) in the dyeing process, resulting in a drastic reduction of industrial wastewater. Additionally, Cibacron S reactive dyes, used for warm exhaust dyeing of cellulose fibers, are able to achieve cost-effective deep shades.
Disperse dyes replace anthraquinone
Previously more than 10 disperse dyes, including C.I. disperse yellow (RGFL), were suspected to release carcinogenic arylamine in the process of reductive cleavage. As a consequence, a number of substitutes were developed, such as C.I. disperse yellow 54, 64, 104, 119 and 211, as well as disperse orange 29.
Some disperse dyes, like C.I disperse orange 76 and C.I disperse orange 37, were found to be potentially allergic. The International Oeko-Tex Standard Association pointed out in its official publication that these two dyes shared the same molecular structure. Currently, substitutes used in the market include C.I disperse orange 29, 30, 44 and 61.
In addition, azo disperse dyes are used to replace anthraquinone disperse dyes that cause environmental pollution in recent years.
Azo dyes give high-intensity colors brighter than anthraquinones. They have fair to good fastness properties, but not so good as the carbonyl and phthalocyanine classes.
An azo dye usually requires two organic compounds: one is a coupling component and the other a diazo component. They can be altered considerably to give possibly a wide range of dyes. The environmental impact is reduced as the required reactions can be carried out in water, which is easy and cheap to obtain, clean and dispose of. Given the favorable environmental and economic reasons, azo dyes have become a more attractive choice for users.
When using disperse dyes for fine-denier polyester fibers, users may find that uneven dyeing often occurs though it usually take a short time to finish the dyeing process. This gets more obvious when the polyester fiber has a finer denier, because it has a larger surface area per unit weight. As a result, ideal disperse dyes for fine-denier polyester fibers are characterized by such properties as high strength, high color fastness, good dye mobility, stable thermal dispersion and dyeing uniformity. These are criteria for users to choose suitable high-performance disperse dyes available on the market.
Wool-dyeing by acid dyes
Acid dyes are highly water soluble, and have better light fastness than basic dyes. They can be divided into two sub-groups: acid-leveling or acid-milling.
Acid-leveling dyes show moderate inter-molecular attractions for wool fibers. Hence, they are able to achieve an even color as dye molecules can move quite easily through the fibers. However, these dyes can be sometimes washed out.
Acid-milling dyes, meanwhile, are larger than acid-leveling dyes, and show a much stronger affinity for wool fibers. Though the color may be less even, they are more resistant to washing.
Other than wool, acid dyes are used for silk and nylon as well as leather, paper and ink.
New products of acidic dyes on market are environmentally friendly, including dyes of weak acid content, and free from carcinogenic arylamine and heavy metal. These acid dyes offer bright color with excellent color fastness in wet treatment and milling.
As weak-acid dye for wool dyeing, Clariant's Sandolan MF ranges is free from metal and features high exhaustion rate, complete chromatogram, good color matching performance and fastness in wet treatment and under sunlight.
Telon K ranges from DyStar are mainly used for nylon and acetate fiber dyeing or nylon printing, showing good color fastness.
Latest products of black acid dyes are free from heavy metal and carcinogenic arylamine. They are often DASA-based trisazo dyes.
As a metal-free acid dye for polyamide fiber dyeing, Erionyl A ranges originally from Ciba Specialty Chemicals feature good dyeing levelness, building-up property, light fastness, wet fastness and compatibility. When used in metal-free weak-acid dye for polyamide fiber, the Tectilon ranges are easy to dye with good uniformity. They also provide good dyeing fastness.
Direct dyes for cellulose fibers
Direct dyes are mainly used to dye and print cellulose fibers such as cotton, as well as viscose and silk textiles.
All environmentally friendly direct dyes are based on diamino compounds as ingredients. Of which, C.I acid black 210 and 234 with DASA as intermediate are black acid dyes with good color fastness. They may also directly dye cellulose fiber. As environmentally friendly black dyes, they are used for cotton and viscose dyeing and can also be used as substitution for C.I direct black 38.
Chen Rongqi is a senior consultant for China Dyestuff Technical Experts and Shanghai Dope Dyestuff Trade Association.
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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