Dyeing

DYEING, an operation—by means of which in the textile industry all fibers are given a uniform color, in other words, the entire fabric or yarn or raw material (cotton, wool) is dyed in a solid color. The operation, by which multi-colored patterns are applied to fabric, is called 'printing'; the latter is especially widely developed in the cotton industry. There, dyeing is often combined with printing, i.e., patterns are applied to fabric dyed in a uniform color ('reserve' and 'discharge'). The most complex and of greatest sanitary-hygienic interest is dyeing in the cotton industry. Paper is most often dyed in the form of fabric, much less frequently—in the form of yarn and fiber. For dyeing, so-called 'dyes' are used, i.e., 'colored substances for which there are methods of fixing them on the fiber and which at the same time possess sufficient permanence in relation to the action of various external influences' (Petrov-Viktorov). The number of dyes used in dyeing is very large. Previously, dyes of mineral, animal and vegetable origin were used; since the mid-19th century, artificial dyes have gradually displaced natural ones, and the use of the latter is currently limited. By the method of fixation on cotton fabrics, dyes are divided into the following groups. 1. Substantive (diamine) dyes, direct-dyeing, fixing on cotton fibers without any preliminary or subsequent treatment. 2. Basic or tannin dyes, fixed on the fabric by tannin and potassium alum. 3. Mordant (alizarin) dyes, as well as natural dyes, fixed on the fiber after preliminary treatment with metal compounds called 'mordants'. 4. Mineral dyes. 5. Aniline black, resulting from the oxidation of aniline on the fabric. 6. Sulfur and vat dyes, requiring special substances for their dissolution. 7. Ice or diazo dyes, requiring preliminary preparation of the goods by impregnating them with naphthol (or phenol).—Besides dyes themselves, other chemical materials are also used in dyeing: acids, alkalis, salts, soaps, various organic substances. The following apparatus are used for dyeing: vats, jiggers, kier boilers, continuous dyeing machines. In vats, the goods are impregnated with a dye solution, immediately squeezed, and sent to a drying apparatus. A jigger is a wooden or iron box inside which there are several rollers; the goods moves from a roll over the rollers through the dye solution and is wound onto a roller, this passing through the dye being repeated several times. A kier boiler consists of a large trough over which a 'beam' (a four-sided beam) is mounted in a frame, set in rotational motion; the goods hangs on the beam in the form of separate loops, the lower ends of which are immersed in the kier boiler with the dye solution. When the 'beam' rotates, there is a gradual movement of the goods from one side of the boiler to the other, which promotes even dyeing. Continuous dyeing machines consist of a series of iron basins equipped with rollers, along which the goods moves; on these machines 'continuous' dyeing is carried out, i.e., the goods is dyed, immediately washed, soaped, etc. Usually, the dye is first prepared; the appropriate ingredients are taken from the warehouse and mixed in a certain order; then the dye is dissolved, water is added to the apparatus, and it is started. The dyed fabric then goes to washing, and some fabrics are first passed through various solutions (in various apparatuses) to fix the dye; then the goods goes to drying in drying apparatuses (after aniline or naphthol padding) or in drying, so-called 'red' drums (for drying bleached goods, the same drums are used, which are called 'white' there). From the professional-hygienic point of view, dyeing is of special interest, since here there are specific professional hazards. These should primarily include high temperature and high humidity, which occur either together (during dyeing itself) or separately (high temperature for dryers). The main mass of workers in the dyeing industry suffers from these hazards. Some types of dyeing are also of professional-toxicological interest: they involve working with poisonous substances, or harmful gases and vapors are released into the air. Here, special attention is deserved by black aniline, sulfur, vat and cold dyeing. Despite the presence of specific and moreover sharply expressed hazards in dyeing, this production has been almost completely unstudied until recently. Only in the last few years in the USSR a number of research works have been carried out, which made it possible to identify the main hazards of dyeing and outline ways to improve its health conditions. The overwhelming majority of dyeing processes, as well as subsequent (or preliminary) treatment and washing, are carried out in water heated to a temperature of 60-80° (in sulfur dyeing even up to 100°). At the same time, a huge amount of heat and water vapor is released into the surrounding air.—Observations conducted by the Institute of Labor Protection and the Sanitary Inspection of the People's Commissariat of Labor showed _g that the temperature in various dye houses (depending on various factors) ranges from 24° to 30-32°, and sometimes higher, with very high relative humidity [80-90% and very often 100% (formation of fog)]. The same observations by the Institute of Labor Protection revealed that these conditions are unstable and undergo constant fluctuations depending on the type of apparatus in operation, time of year, hour of work, day of the week, etc. (see fig.). Monday Tuesday Wednesday Thursday Friday hours 12 4- 1_t2 б 12 4 1-2 12 4-1-2 -12 4-1-2 and -12 4 1-2 Yabs ylaэь . /7 // ~" * ⁺ / \ \ / >' / и chesy -9 10-11 11 12 1 lllll -2 2-3 4-5 8-9 10 -11 11 -12-1-2 2-3 4-Б I -"7" li / »4_V / 1 Г ^J ( / -~- 11 III- fab V February 1026 year 1 13 May 1925 year ____ temperature absolute humidity They are different in different places in the dye house; they are also different vertically: the higher the level, the higher the temperature and absolute humidity (e.g. at the 1st Moscow Calico Printing Factory, b. Tsindel: 25 cm from the floor temperature 20°, absolute humidity 17.3; at chest level—the corresponding figures 26° and 25; under the ceiling -30° and 31); conditions are worse in winter than in summer (humidity is less in summer, since open windows allow exchange with outside air); the closer to the end of the day, the worse the conditions become; the same as the end of the week approaches. The figure shows examples of temperature and absolute humidity curves determined in the dye house of the above factory in 1925-26. Due to this combination of high temperature and high humidity, working conditions in dye houses must be considered very unfavorable. Physiological observations conducted by the Institute of Labor Protection on workers of the dye house of the same factory showed that the effect of these factors leads to a number of changes in pulse, blood pressure, respiration; especially sharp changes were noted in body temperature: it was often elevated (37-37.5° and higher), and this increase went parallel with the increase in room temperature and humidity.—At drying drums, the humidity is not so high (relative humidity here usually does not exceed 50%), but the temperature here is much higher than in the dye house: it reaches 32-36-38° and even more. In some types of dyeing, harmful gases and vapors are released. (Black aniline and cold dyeing—see Aniline-aniline production, Azo dyes.) Sulfur dyeing is harmful because when boiling the dyes (which is usually done in tanks standing on a platform in the dye house) and during dyeing itself, H₂S and other, still unstudied sulfur compounds are released into the air; sulfur dyeing itself is carried out in jigers at 100° ('on the boil'), and the release of heat and moisture here is especially intense: working conditions here are most unfavorable (temperature—35° and higher, relative humidity 90-100%).'For vat dyeing, the process of preparing hydrosulfite is unfavorable (in the presence of hydrosulfite and caustic soda, indigo dye becomes soluble in water); during this preparation (from bisulfite and sulfuric acid), sulfur dioxide is released into the air.—Further, contact with substances causing irritation and various skin lesions should be noted: with chromium, alkalis, acids, etc. Wool dyeing (woolen and worsted production) in terms of working conditions to a large extent resembles dyeing in paper production; here dyeing is often the first process—the fiber itself is dyed. Dyeing is carried out in kier boilers (fabric) and round apparatuses—'essers' (wool); mainly substantive and acid dyes are used (release of acetic acid vapors); dyeing is carried out exclusively 'on the boil', i.e., at a water temperature of 100°.

The temperature and humidity of the room are very high—not lower than in paper dye houses, while the work here, especially with vats, is physically harder (handling heavy goods). Silk is dyed (in the form of yarn and fabric) in vats, mainly with substantive dyes, in hot solutions. The working conditions are generally the same. Data on morbidity and mortality among dyers are extremely scarce, or rather—there are almost none at all, as materials in statistics are not given separately for dyers; they are included in the general category of 'textile workers', 'workers of calico factories', etc. When deciding on improving working conditions in dye houses, the general sanitary-hygienic working conditions in them should be taken into account. With rare exceptions, dye houses are arranged extremely unsanitary; they are located in unimproved, sometimes low (below 4 m) premises, the equipment is arranged very tightly: a huge number of steaming apparatuses are placed almost directly next to each other; there is either no ventilation at all or it is arranged irrationally. In some factories, to combat fog formation, hot (50-60°) air is let into the room, which further increases the temperature; or above the apparatuses emitting steam, hoods with exhaust to the outside are installed, which helps little, as a significant amount of steam still enters the room. The fight against high temperature and humidity in dye production is by no means an easy task, and a number of attempts at this fight have led to failures. For example, an investigation of four wool dye houses by the Moscow Labor Sanitary Inspectorate showed that despite the powerful (18-20 times per hour) inflow of heated dry air created in them, the meteorological conditions did not improve significantly—evaporation of moisture from open vats proceeds so intensively that even the supply of huge amounts of warm dry air cannot improve the situation. The most radical solution to the problem should be considered the removal of steam and heat from the place of formation, which is achieved by completely closing the apparatuses with strong exhaust from them ( and with an inflow of fresh air into the room). If the equipment cannot be completely closed, then supply-exhaust ventilation is built according to a different method. The supply of air into the room is done in two ways: large amounts of warm (18-20°) dry air are supplied to the working zone, and hot air (50-60°) is supplied to the upper zone at a level of 4-5 m from the floor, which dissolves the water vapor and leaves with them under the ceiling, from where exhaust is carried out. Successful implementations of such installations already exist, for example, at the 'Osobozhdenny trud' (Liberated Labor) woolen factory (Moscow), where the vats for dyeing wool are completely closed. The principle of double air supply with exhaust from above has also been very successfully applied at the Ustin silk-winding factory (Moscow), where working conditions are the same as in dye houses; the same has been done in some Leningrad factories, etc. The height of the dyeing room (not less than 5-6 m), the arrangement of the equipment, its proper closure, etc., are of very great importance. Drying drums must be well insulated (double-walled, as for example at the Sverdlov factory); they also require powerful exhaust from the chamber where the drums are located and an inflow of fresh warm air into the room. A number of processes should be mechanized, mainly the preparation and dissolution of dyes, especially poisonous ones (aniline, diazo, sulfur, etc.). Further attention should be paid to the workers' special clothing, washbasins with cold and hot water and solutions for washing off dyes, showers, changing rooms, ventilation of the premises during breaks, etc.