A
dye is a
colored substance that has an
affinity to the
substrate to which it is being applied. The dye is generally applied in an
aqueous solution, and requires a
mordant to improve the fastness of the dye on the fiber.Both dyes and pigments appear to be colored because they absorb some wavelengths of
light more than others. In contrast with a dye, a
pigment generally is insoluble, and has no affinity for the substrate. Some dyes can be
precipitated with an inert salt to produce a
lake pigment, and based on the salt used they could be aluminum lake, calcium lake or barium lake pigments.Dyed
flax fibers have been found in the
Republic of Georgia dated back in a prehistoric cave to 36,000
BP.
[1][2]Archaeological evidence shows that, particularly in
India and
Phoenicia,
dyeing has been widely carried out for over 5000 years. The dyes were obtained from
animal,
vegetable or
mineral origin, with no or very little processing. By far the greatest source of dyes has been from the
plant kingdom, notably
roots,
berries,
bark,
leaves and
wood, but only a few have ever been used on a commercial scale.
Natural dyeThe majority of natural dyes are from plant sources –
roots,
berries,
bark,
leaves, and
wood,
fungi, and
lichens.
Textile dyeing date back to the
Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes
Tyrian purple and crimson
kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as
woad,
indigo,
saffron, and
madder were raised commercially and were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using
resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes from the
New World such as
cochineal and
logwood were brought to Europe by the
Spanish treasure fleets, and the dyestuffs of Europe were carried by colonists to America.
The discovery of man-made synthetic dyes late in the 19th century ended the large-scale market for natural dyes.
Synthetic dyeThe first human-made (synthetic)
organic dye,
mauveine, was discovered
serendipitously by
William Henry Perkin in 1856. Many thousands of synthetic dyes have since been prepared.,
[3][4]Synthetic dyes quickly replaced the traditional natural dyes. They cost less, they offered a vast range of new colors, and they imparted better properties to the dyed materials.
[5] Dyes are now classified according to how they are used in the dyeing process.
Dye types
Acid dyes are
water-
solubleanionic dyes that are applied to
fibers such as
silk,
wool,
nylon and modified
acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and
cationic groups in the fiber. Acid dyes are not substantive to
cellulosic fibers. Most synthetic food colors fall in this category.
Basic dyes are water-soluble
cationic dyes that are mainly applied to
acrylic fibers, but find some use for wool and silk. Usually
acetic acid is added to the dyebath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of
paper.
Direct or
substantive dyeing is normally carried out in a neutral or slightly
alkaline dyebath, at or near
boiling point, with the addition of either
sodium chloride (NaCl) or
sodium sulfate (Na
2SO
4). Direct dyes are used on
cotton, paper,
leather, wool, silk and
nylon. They are also used as
pH indicators and as
biological stains.
Mordant dyes require a
mordant, which improves the fastness of the dye against water,
light and
perspiration. The choice of mordant is very important as different mordants can change the final color significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant,
potassium dichromate, is applied as an after-treatment. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.
Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in
alkaline liquor produces the water soluble
alkalimetalsalt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent
oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.
Reactive dyes utilize a
chromophore attached to a
substituent that is capable of directly
reacting with the fibre substrate. The
covalent bonds that attach reactive dye to natural fibers make them among the most permanent of dyes. "Cold" reactive dyes, such as
Procion MX,
Cibacron F, and
Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are by far the best choice for dyeing
cotton and other
cellulose fibers at home or in the art studio.
Disperse dyes were originally developed for the dyeing of
cellulose acetate, and are water insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to dye
polyester but they can also be used to dye nylon,
cellulose triacetate, and acrylic fibres. In some cases, a dyeing
temperature of 130 °C is required, and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.
Azoic dyeing is a technique in which an insoluble
azo dye is produced directly onto or within the fibre. This is achieved by treating a fibre with both diazoic and coupling
components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components. This method of dyeing cotton is declining in importance due to the toxic nature of the chemicals used.
Sulfur dyes are two part "developed" dyes used to dye cotton with dark colors. The initial bath imparts a yellow or pale
chartreuse color, This is aftertreated with a sulfur compound in place to produce the dark black we are familiar with in socks for instance. Sulfur Black 1 is the largest selling dye by volume.
Food dyesOne other class that describes the role of dyes, rather than their mode of use, is the
food dye. Because food dyes are classed as
food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by
legislation. Many are
azo dyes, although
anthraquinone and
triphenylmethane compounds are used for colors such as
green and
blue. Some naturally-occurring dyes are also used.
Other important dyes
A number of other classes have also been established, including:
- Oxidation bases, for mainly hair and fur
- Laser dyes: see, for example, rhodamine 6G and coumarin dyes.[6]
- Leather dyes, for leather
- Fluorescent brighteners, for textile fibres and paper
- Solvent dyes, for wood staining and producing colored lacquers, solvent inks, coloring oils, waxes.
- Carbene dyes, a recently developed method for coloring multiple substrates
- Contrast dyes, injected for magnetic resonance imaging, are essentially the same as clothing dye except they are coupled to an agent that has strong paramagnetic properties.[7]
Chemical classification
By the nature of their
chromophore, dyes are divided into:
[8]- Category:Acridine dyes, derivates of acridine
- Category:Anthraquinone dyes, derivates of anthraquinone
- Arylmethane dyes
- Category:Azo dyes, based on -N=N- azo structure
- Diazonium dyes, based on diazonium salts
- Nitro dyes, based on a -NO2nitro functional group
- Nitroso dyes, based on a -N=O nitroso functional group
- Phthalocyanine dyes, derivatives of phthalocyanine
- Quinone-imine dyes, derivativees of quinone
- Category:Thiazole dyes, derivatives of thiazole
- Xanthene dyes, derived from xanthene
See alsoReferences
- ^ Balter M. (2009). Clothes Make the (Hu) Man. Science,325(5946):1329.doi:10.1126/science.325_1329a
- ^ Kvavadze E, Bar-Yosef O, Belfer-Cohen A, Boaretto E,Jakeli N, Matskevich Z, Meshveliani T. (2009).30,000-Year-Old Wild Flax Fibers. Science, 325(5946):1359. doi:10.1126/science.1175404PMID 19745144Supporting Online Material
- ^ Hunger, K., ed. (2003). Industrial Dyes. Chemistry, Properties, Applications. Weinheim: Wiley-VCH.
- ^ Zollinger, H. (2003). Color Chemistry. Synthesis, Properties and Applications of Organic Dyes and Pigments, 3rd ed. Weinheim: Wiley-VCH.
- ^Simon Garfield (2000). Mauve: How One Man Invented a Color That Changed the World. Faber and Faber. ISBN 0-393-02005-3.
- ^F. J. Duarte and L. W. Hillman (Eds.), Dye Laser Principles (Academic, New York, 1990).
- ^patentstorm.us
- ^stainsfile.info
Further reading- Abelshauser, Werner. German History and Global Enterprise: BASF: The History of a Company (2004) covers 1865 to 2000
- Beer, John J. The Emergence of the German Dye Industry (1959)
External links
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