Lacquers

LACQUERS, liquids that form after drying in the air a thin, hard or elastic film and serve to protect the coated materials from the destructive action of the atmosphere (temperature, humidity, gases, vapors, etc.), as well as to give colored objects an attractive appearance. There is a large number of different varieties of lacquers, very diverse in composition, which however can be divided into several main groups; of these, the most important are oil-based, alcohol-based, nitrocellulose (or shellac), asphalt, and enamel lacquers. - Oil-based lacquers are solutions of natural (copal, dammar, etc.) or artificial (coumarone, bakelite) resins in vegetable oil with the addition of special metallic compounds and volatile solvents (turpentine, gasoline, etc.) that serve to thin the lacquers. These lacquers are most widely used and are used for lacquering railway cars, carriages, automobiles, furniture, machines, for various decorative works, as well as an insulating layer in products of the electrical industry. - Alcohol-based lacquers belong to the so-called volatile lacquers and consist of plant (gum lac, shellac, harpax, etc.) resins dissolved in alcohols (ethyl, methyl, propyl, allyl, etc.). - As solvents in these lacquers, many other toxic substances are often encountered: benzene, acetone, trichloroethylene, carbon tetrachloride, carbon disulfide, etc. Alcohol-based lacquers are used mainly for polishing and lacquering objects not exposed to strong external atmospheric influences (leather, paper, baskets, hats, musical instruments). This group of lacquers also includes polishes, widely used for polishing wooden products. - Nitrocellulose, or shellac lacquers, have become widely used in painting, recently mainly due to the introduction of new methods of coloring (spraying, or so-called pneumatic painting), which require fast-drying lacquers. These lacquers are solutions of nitrocellulose or acetatecellulose in volatile solvents (acetone, amyl acetate, benzene, tetrachloroethane, gasoline, etc.), to which various coloring substances (pigments) are often added. - Asphalt lacquers consist of natural or artificial asphalt, fused with resins (harpax, etc.) or vegetable oil and dissolved in volatile substances (turpentine, gasoline, benzene, etc.). These lacquers are black in color and possess resistance to acids and alkalis, as well as the ability to protect iron parts from rust for a long time - for which reason they have become widely used in lacquering various metal products. - Enamel lacquers represent a mixture of alcohol-based lacquers with some covering paint (lead or zinc white, lithopone, chrome yellow, ochre, ultramarine, coal-tar pigments, etc.). - Due to their rapid drying, attractive appearance, and great strength, enamel lacquers have found significant and diverse application in technology. The production of lacquers in a factory setting is schematically reduced to the following basic processes: 1) crushing and sifting (in mills, crushers, and sifters of various systems) of solid substances that make up the lacquers, mainly resins; 2) melting resins in special metal kettles, heated either on fire furnaces or by gas, superheated steam, or superheated water; 3) cooking the melted resins with vegetable oils in the same kettles; 4) adding drier to the cooled (to 200-220°) cooked lacquer with vigorous stirring of the mixture; 5) diluting the lacquer in solvents at various temperatures depending on the boiling point of the solvent used; 6) settling, filtering, or centrifuging the finished lacquers with the help of special devices and apparatus (tanks, filter presses, centrifuges) for the purpose of purifying them from various impurities and contaminants; 7) filling the finished product into containers. -- Each of the listed production processes has its own special professional hazards. The processes of grinding and sifting products are accompanied by dust emission from the apparatus. The melting of resins proceeds with constant formation of gaseous products of dry distillation, extremely harmful to health and very dangerous from a fire point of view, and the use of fire furnaces can in addition promote the release of carbon monoxide. The use of various volatile substances as solvents is accompanied by constant release of very harmful, toxic vapors. These same phenomena also occur in the final processes related to the production of lacquers (settling, filtering), as well as when filling finished products into containers. The degree of air pollution in the indicated lacquer production processes depends on the equipment of the plant, the condition of its apparatus, and the degree of perfection of the sanitary-technical installations (ventilation, gas traps, etc.). Not all the listed harmful factors have the same professional-hygienic significance; the most serious attention deserves the gases released during the melting of resins and various vapors formed when using one or another volatile solvents. The presence of the latter in lacquers also determines the harmfulness and danger of these products when used by painters in painting and lacquering various objects. The degree of toxicity of different solvents depends not only on the poisonousness of these substances, but also on their volatility ("two-phase toxicity" of Lehmann). The rate of evaporation of the liquid part of the lacquer depends on the boiling point of the solvent, external meteorological conditions (temperature and air movement speed), as well as on the concentration of solid substances contained in the liquid. Experiments conducted on the volatility of various lacquers showed quite significant and rapid volatility of their liquid components. Thus, for example, when studying some aerosol lacquers, it turned out that the main mass of the solvent passes into a vapor state already after 15-20 minutes after applying the lacquer to the surface to be painted. - Due to such significant volatility of lacquers in their production and use in painting, there is quite a large content of volatile vapors in the air of work premises even in enterprises equipped with " hermetic apparatus, mechanical devices for servicing it and good ventilation installations. Thus, for example, at the Leningrad lacquer production plant with a large volume and supply-exhaust ventilation with hourly exchanges of 2.6 times for exhaust and 7 times for intake, the concentration of benzene vapor in the air at workplaces fluctuated from 0.135 mg/m³ (during operations of mixing and dissolving the components of the lacquer) to 1 mg/m³ (when filling the finished product into containers). Such a content of benzene in the room air can undoubtedly cause chronic poisoning in workers. Meanwhile, it is benzene that has become most widespread as a lacquer solvent, and according to data from the lacquer industry of Leningrad, its content in these products fluctuates on average within the range from 13% to 35%, reaching in some varieties of lacquer an even higher concentration. When examining (1923) the health status of workers at Moscow chemical plants, it turned out that for 100 workers in the lacquer-boiling department of the Presnya paint and varnish plant, there are 131.6 diseases, and in the filling department of the same plant this morbidity coefficient reaches 160 with average indicators of 155.1 for all worker groups of the "Aniltrest" and "Lakokraska" plants and 133.5 for workers of the "Zhirkost" plants. These figures indicate that workers in lacquer plants are undoubtedly exposed to the harmful effects on their bodies of unfavorable production factors that cause them increased morbidity, little different in intensity from the morbidity of workers in other harmful chemical industries. Measures to combat hazards in lacquer production. To eliminate dust formed during crushing and sifting of materials, maximum sealing of the apparatus and installation of local dust collectors are needed, if possible structurally connected with the apparatus itself. The installation of ordinary hoods over the kettles, connected with exhaust pipes for removing gases formed during the melting of resins and cooking of oil, is not expedient due to the very slight hygienic effectiveness of these devices, as well as the impossibility of capturing with their help the distillation products of resins, which also have purely production value.

Of the various installations proposed for the removal of gases (passing them through fans via moistened pipes or pits with coke and then diverting the non-condensed vapors into the atmosphere or boiler furnaces), the Sommer system is the most rational from both hygienic and production standpoints. This system, widely used in Germany, consists of gases and vapors from boilers being drawn into a system of hermetically sealed pipes, specially designed shower nozzles by means of which all emissions from the boilers are completely cooled, condensed, and collected in liquid form in special reservoirs and utilized.-The fight against the danger of poisoning from vapors of volatile solvents and toxic pigments (lead, etc.) should be conducted mainly along the line of replacing toxic substances with other harmless products. In addition, factories should be equipped with technically perfect apparatus with various mechanical devices (mixers, pneumatic measures, centrifuges, pumps, etc.) that eliminate the need for manual labor and reduce to a minimum the possibility of harmful substances entering the air of work premises.-Among measures of personal prevention, special attention should be paid to protecting the hands when working with substances that dissolve the fatty lubrication of the skin (benzene, etc.) and are easily absorbed into the body at the same time. The strong local action of solvents on the skin is especially frequently observed in polishers and varnishers of wooden products when using various varnishes. The epidemic outbreaks of eczematous diseases often observed in these cases on individual enterprises are mostly due to a sudden deterioration in the quality of individual components of varnishes or the inclusion of substances that strongly irritate the skin (poor-quality shellac-Blaschko, pyridine-Koelsch, turpentine-Weyl, methyl alcohol-White).

D. Kagan. In microscopy and technology, lacs are insoluble in water colored precipitates of natural (alizarin, hematoxylin, etc.) and artificial dyes (derivatives of anthraquinone and naphthoquinone, etc.) with metal salts and tannin, possessing high coloring power.The color of the lac differs from the original color of the pigment and varies considerably depending on the metal taken. Alizarin with lime or baryta gives a blue lac, with salts of iron oxide gives a violet-black lac, with chrome salts gives a violet-brown lac, with aluminum salts gives a bright red lac. Carmine acid with aluminum salts gives a violet-red lac, with tin salts gives a bright red lac, with lead salts gives a violet-blue lac, with uranium salts gives a green lac. Hematoxylin (see) gives weakly colored or colorless lacs; its oxidation product, hematein, gives blue lacs, and the stronger the oxidation, the darker the color of the lac; thus, hematein-chrome lac is sky-blue, dihydroxyhematein-chrome lac is dark blue, di- and trihydroxyhematein-iron lac is black. Products of greater oxidation (tetra and penta) of hematein already give a brown tone and lose their coloring power. Gallocyanin, a coloring pigment in the form of a powder or paste of green color, insoluble in water, gives with aluminum salts a blue lac, with chrome and iron salts a dark blue lac.--Lacs are used for so-called substantive dyeing, where the coloring pigment is not absorbed by the fabric directly from the solution, but the dyeing is obtained due to the combination of the dye with the mordant, and the resulting lac enters into combination with the fabric. In this case, the object is either subjected to the action of the mordant first, and then the dye (e.g., staining nuclei by Heidenhain's iron hematoxylin), or is dyed with the dye mixed with the mordant, i.e., a dye-lac (e.g., staining with iron hematoxylin by Weigert, carmine by Ehrlich, etc.). For acid dyes, metallic salts, especially Al, Fe, O, Zn, are mainly used as mordants; for basic dyes, tannin as such or in mixture with iron salts (iron gall ink), for example in staining bacterial flagella by Löffler.