Fermentation or enzyme-using processes to synthesise a desired chemical compound

C12P

Colouring of foods; food colour per se

A23L 5/40

Cosmetics or similar toilet preparations; Preparations for permanently dyeing the hair

A61K 8/00, A61Q 5/10

Coating compositions, e.g. paints, varnishes or lacquers; inks

C09D

Duplicating or marking methods using dyes

B41M 5/00

Preparation of mordant compounds

C01, C07

Acyclic, carbocyclic, or heterocyclic compounds containing elements other than carbon, hydrogen, halogen, oxygen, nitrogen, sulfur selenium, or tellurium

C07F

Use of inorganic or non-macromolecular organic substances as compounding ingredients

C08K

Using dyes in detergent compositions

C11D 3/40

Using dyes during the manufacture of artificial filaments or the like

D01F

Dyeing textiles, leather, furs, or solid macromolecular substances

D06P

Using dyes in paper or pulp

D21H

Acid dyes are water-soluble anionic dyes that are applied to fibres such as silk, wool, nylon and modified acrylic fibres using neutral to acid dye baths. Attachment to the fibre is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fibre. Acid dyes are not substantive to cellulosic fibres. Most synthetic food colours fall in this category.

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 colour 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.

Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibres, 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 fibre. Basic dyes are also used in the colouration 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 (Na2SO4). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

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.

Dye is a coloured 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 fibre.

Both dyes and pigments appear to be coloured 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.

Dyestuffs are substances that can be used as a dye or from which a dye can be obtained.

Indigoid dyes are a group of vat dyes closely resembling indigo in structure and used to dye cellulose and protein fibres as well as for cotton printing. These dyes cover a broad range of the colour spectrum, from orange to black. Their resistance to light and water are rather high but inferior to that of polycyclic dyes. Indigo and thioindigo are characteristic indigoid dyes. The range of indigoid dyes was considerably extended at the beginning of the 20th century. Subsequently some of them were replaced by other classes of dyes; 15-20 indigoid dyes are still used. The manufacture of indigoid dyes is a complex, multistage process. The starting compounds are various derivatives of aniline, naphthalene, and other substances.

Lake is an insoluble pigment formed by the reaction between an organic dye and a mordant. The colour of a lake depends upon the mordant as well as the dye used. Generally, lakes are not as colourfast as many inorganic dyes, but their colours are more brilliant

Mordant is a substance used in dyeing to fix certain dyes (mordant dyes) in cloth. Either the mordant (if it is colloidal) or a colloid produced by the mordant adheres to the fibre, attracting and fixing the colloidal mordant dye. The chemical compounds used as mordants are either acidic or basic. Acid mordants (e.g., tannic acid) are employed with basic dyes; basic mordants (e.g., alum, chrome alum, and certain salts of aluminum, chromium, copper, iron, potassium, and tin) are employed with acid dyes. Cloth to be dyed may be treated first with the mordant and then with the dye, or the mordant and dye may be applied together. The vividness of certain dyes that ordinarily do not require the use of a mordant may be markedly increased when one is employed.

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 colour 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.

Sulfur dyes are two part "developed" dyes used to dye cotton with dark colours. The initial bath imparts a yellow or pale chartreuse colour, 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.

Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. The colour of denim is due to indigo, the original vat dye.

Colour Index