Dyeing

When dyeing textile material by applying colorants in dyeing or printing processes colored ( "colored" ).

In order to influence the color and especially the brilliance of the natural color of the fabric during the dyeing process as little as possible, be bleached textiles from natural fibers. If the ink is removed from the fabric, preferably at faulty dyeings, one speaks of pulling off the fabric.

The dyer being has a millennia-old tradition and a private profession with numerous specializations emerged. Today it is - if not technically executed - the chemical industry attributed.

The term " color" is also used to vary other material in their color.

Historical

The few knowledge about the staining of antiquity are mainly based on grave finds and records of Greek and Roman writers and their technological descriptions. More details you can not say about the dyes. Millennia was one case rely on natural dyes from minerals ( ocher, cinnabar ), from plants such as indigo, Redwood, (see also dye plants ) or animal ( cochineal, purple snail ). Already in ancient Egypt, there are finds of dyed with madder textiles. After the discovery of America, the dyers Europe got another new lift, which was mainly due to the imported color woods.

In the Middle Ages were the dyers wage workers of the other cloth manufacturing guilds. Only later emerged own dyers guilds. There have been since the Middle Ages, the distinction between different dyers:

• Black dyers, dyeing a deep black was considered as a special art.
• Canvas dyer, dyer bad, the guild of dyers who dyed generally coarse fabrics.
• Cloth dyers, who specialized in dyeing wool.
• Dyer, Waidfärber, originally the native Waid, and later used exclusively for the much more expensive imported indigo.
• Schönfärber, a later arisen designation for the use of foreign dyes in the application and in particular fine fabrics ( here occurs because the metaphor of " whitewashing ) ".
• Turkish Rotfärber who were dedicated to the coloring of a beautiful red tone with elaborate method.
• Silk dyer
• Smoke and Zobelfärber dyers, leather and skins ( furs ) colored
• Garnfärber
• Bogolanfärber in the African- Asian

The specialization has been locally and at different times referred to or summarized to various professional groups or guilds.

The dyeing was in the Middle Ages as a dirty business. So dyers were often considered unclean because they dealt with foul- smelling substances ( such as urine ). With the cruises, however, began in Europe an increased interest in consuming colored materials. In the 13th century the European market for colored fabrics and trained dyer expanded were in great demand. So own guilds who promoted the dyer professional and protected their interests were. One of the most famous dyers guilds of the late Middle Ages was the "Arte di Calimala " in Florence, which made ​​higher demands on the products of their craft that they all towels that were not colored in accordance with the quality standards, burned and the responsible Dyer finished with fines.

Developed in the 19th century, synthetic dyes have increasingly replaced the natural dyes. Today, the reactive dyes, followed by the dispersion and direct dyes have attained the greatest importance. The dyestuff solution is referred to as the "color " or " dye bath " or a " dye bath ". " Textile printing " can be regarded as localized dyeing.

Dyeing process

Can dyeing in the textile processing chain almost done anywhere.

• Individual fibers or whole wool fleece can be dyed before spinning.
• Finished spun yarn can be dyed.
• A finished woven or knitted fabric can be dyed.

Depending previously dyed in the manufacturing process, the more irregularities may be compensated for in the final product. For the production of patterns in weaving dyed yarns are required. Extensive textiles are dyed to a uniform surface ( evenness ) and to have individual colors in small quantities to be able to generate.

The dyeing is possible according to three different technologies.

• In the exhaust ( discontinuous dyeing process ), the dyes are dissolved or dispersed in water. During a defined time / temperature curve as well as a controlled movement of the material and / or the fleet of the dye takes evenly on the material, and is usually in the same dye bath - rare in a second treatment bath - fixed on the fiber. Depending on the substrate / dye system textile auxiliaries can simplify the process by, for example provide for better wettability of the substrate. May also be a need to add chemicals to the process, in order to enable the fixation of the dye to the fiber or in the fiber (for example, salt and soda on cotton for reactive dyes or hydrosulfite on vat dyes for cotton). The proportion of unfixed dye is removed in subsequent treatment baths.
• In continuous processes, the dye solution (also called a padding ) is applied to the substrate by padding. In Foulard the dye liquor is padded onto the fabric. Here, there is a uniform wetting of the material with dye liquor and over the fabric width uniform squeezing between usually two or three hard rubber rollers on defined liquor intake. Thereafter, the dyes are fixed on the fiber, which can be done either by treatment with steam ( saturated steam at about 100 ° C ( PadSteam process) or superheated steam at about 180 ° C) or dry heat up to 220 ° C in a few seconds to minutes. After a washing process follows, in order to remove the unfixed dye from the fiber and to obtain good fastness properties.
• Semikontinueverfahren the impregnation of the product by padding the fixation of the dye at a later stage is carried out continuously, also continuously or intermittently. An example of the Semikontinueverfahren is called block - cold batch process is dyed at the cotton with reactive dyes. After padding, the cotton with the liquor, the fabric is wound onto a roll and stored for several hours at room temperature, rotating. Then, the washing out of the unfixed dye is done on a wide washing machine or a tree apparatus.

As to the chemical and physical processes involved in dyeing, four types of dyeing processes in the modern textile dyeing can be distinguished.

• Direktfärbeverfahren
• Development coloring
• Reactive dyeing
• Dispersion staining

Dye classes

The appropriate class of dye is selected primarily on the substrate to be dyed and the required / necessary fastness level (strength of staining against influences during processing and the use of textile finishing material).

Depending on the item, such as composition ( mixture of fiber types or sheer fabric form), type of yarn, knitted or woven fabric, binding of the dye on the fiber requirement of the handle of the finished product, the decision whether a dyeing machine, an apparatus or a dyeing apparatus necessary is done is. The conditional of the fiber influences the class of dyes suitable for the dyeing process conditions.

For cellulosic fibers dyes are used, either by physical forces (ionic or dispersion forces) are bound to the fiber or the fiber undergo a chemical bond ( reactive dyes ).

• Dyeing with vat dyes, to a method that the surface of the fibers to be bound with water-insoluble dye molecules by adsorption. Advantage is the high color fastness. The most famous vat dye is indigo.
• Dyeing with dyes, development, a method wherein the dye is formed only on the fibers (for example, by azo coupling ). The first water-soluble component is added to the fiber by adsorption, the second component then forms a water-insoluble azo dye. The color then adheres to the fiber through the formation of van der Waals forces and hydrogen bonding. In addition, still forces between polarized groups of molecules act.
• Dyeing with direct dyes ( substantive dyes ), a process in which raise the dyes directly from the dye liquor to the fibers. It is most often used in agents for self dyeing at home.

For wool and polyamide ( such as nylon) with the basic amino groups are acid dyes suitable. For polyacrylonitrile fibers (such as polyacryl ) and similar with their acid groups basic dyes are suitable. For the stable molecule of the polyester fibers disperse dyes are preferably used, in which the molecular structure is " expanded " by high temperatures in the dyeing and remains involved when using temperature in the molecular structure. The poor rub fastness of indigo and vat dyes on cotton fibers by the physical binding only superficial has been the hallmark of genuine dyed "Blue Jeans" and must be achieved by treatment with modern dyes.

Dyeing / dyeing machines / dyeing machines

When dyeing by the (discontinuous) exhaust ( the fiber absorbs the dye from the fleet ) one distinguishes different types of dyeing machines, depending on the transport mechanism of the substrate and of the fleet:

• Dyeing machine: moving fleet, resting goods; The liquor is pumped through the stationary goods (eg dyeing beam, yarn dyeing )
• Dyeing: moving goods, dormant fleet; the goods are moved through a stationary fleet (eg winch ). Some modern machines often used today in addition to goods movement also targeted liquor circulation occurs, however.
• Dyeing machine: for the ( continuous ) continuous process is the historic structure on the basis of the revised technology irrelevant.

The dyeing machines for the exhaust in turn are divided into those for temperatures below 100 ° C and those for high temperature.

• Natural fibers can usually be dyed at moderate temperatures, the dyeing is carried out under atmospheric pressure in ( economically ) competitive (open) machines.
• Synthetic fibers ( polyester in particular ) usually take dyes only at temperatures above 100 ° C on. Since the water would evaporate at ambient pressure, dyeing must take place under pressure. Are usual temperatures up to 135 ° C at a static pressure to 4.0 bar. This requires pressure-tight and therefore more expensive machines.
• Particularly problematic is the dyeing of fiber blends of synthetic and natural fibers. It is usually colored with two different dye classes, the different fibers are, however, to give color to the same. ( Tone-in- tone dyeing ).

For the different forms of presentation of different machines are available.

• In jigger the dyed material is fed into tense and wrinkle-free state by the dye liquor. This guarantees a uniform color distribution over the whole width.
• In the winch, the tissue is performed without voltage is wide or skeins by the fleet, thus the goods are not warped.
• In the Düsenfärbmaschine the fabric and the fleet to be moved.

Environmental aspects

The dyeing of textiles takes place since the 19th century in industrial production. The aqueous dye solutions or dye dispersions are added to other chemicals (salts, acids, alkalis ), and textile auxiliaries. If left untreated into the environment, this is sometimes heavily loaded. Previously, the residual liquors and effluents were pumped directly into rivers, which could then also colored. Today, it is regarded in many parts of Europe and the United States by making substantial investments in sewage treatment plants and in the use of modern dyes and the prohibition problematic products as solved. In many other parts of the world, as in some Asian and Eastern European countries this level has not been reached in environmental protection.