Лако-красочные материалы — производство

The money value of world dye production is actually extremely small, corresponding in 1913 ( 500 million francs) to less than one-tenth of the value of wool production, less than one-fifth of cotton production, and about one-fifth of rubber production. Dye manufacturing was a highly competitive business, requiring expensive factories, and the ener­gy, intelligence, and perseverance put into this industry is without paral­lel.

The development of the dye industry had the result that many closely guarded secrets were made available for the general good of the various interests. Ulmann’s great encyclopedia of technical science has shown that many of the processes have been known for a long time by a majority of the manufacturers. Also, the freedom of workers to move from place to place had the result that every important improvement became known, in a relatively short time, to all competitors. The success of the large dye firms is not based on secret processes, therefore, but depends on long tradition, good organization, and specialties protected by patent.

It would be a grave error to believe that specialties alone could keep a dye plant in business although this view has been stated not only by young, inexperienced chemists, but by established technical and business people. Specialties are, in most cases, only profitable additions to the line of regular products, and in order for a firm to attain a large size at all, it must produce the large-volume items. Chief among such large-volume, staple articles are the blue-blacks, such as direct deep black EW, for example, chrome blacks of various composition, such as diamond black PV, eriochrome black T, etc. After the black dyes, which make up more than 50 per cent of the total demand, come the blue dyes, chief among which are indigo, indanthrene, direct blue, and sul­phur blue. Next are the red dyes and finally the yellows such as chryso — phenine and naphthamine yellow NN.

These mass production articles enable the manufacturer to carry his specialties to the public, and, on the other hand, to keep his general factory costs at a minimum. It has been pointed out repeatedly how important it is in the preparations of intermediates to recover all by­products. With this in mind, the different dye manufacturers have formed combined interests in order to work out production costs of the more important intermediates to their mutual benefit, and to share their experience in manufacturing operations. This concentration makes it possible to prepare each intermediate on a very large scale and to recover all by-products, such as nitrous and sulfurous acids, hydrogen sulfide, thiosulfate, and Glauber salt. Such a combine must, of course, also manufacture the necessary inorganic intermediates so that it has an independent supply of caustic soda, sulfuric acid, hydrochloric acid, soda, chlorine, and, if possible, also common salt and coal.

The arrangement of a dye plant must be modem; the greatest mis­take, which unfortunately often appears, lies in the use of old, inefficient apparatus. Sometimes it is necessary to change a plant overnight for a new process, and it is the duty of the plant manager to provide the most suitable equipment. A thoroughgoing alteration is almost always less expensive than the continued use of an impractical arrangement re­quiring many workers and much space. It generally turns out that such an alteration, irrespective of cost, is actually the cheapest way out Estimates are made by the accounting department, based on facts sup­plied by the engineer and plant chemist.

In order that a plant of so complicated a nature as a dye factory may function correctly, it must be well organized. The management U always composed of business men and chemists, operating in their own spheres, but remaining in contact on all questions. An intermediate group has the responsibility of arranging current affairs, such as re­clamation, investigation of new and foreign dyes, preparation of pat­tern cards, etc.

The position of the chemist in the dye factory is quite different de­pending on whether he is employed in the dye house, the research laboratory, the plant, the patent department, or elsewhere. The duties of the research chemist consist in working on new and scientific prob­lems, with constant reference to the literature. It might be emphasized that it is senseless to attack any problem before obtaining all available published information about it. Well run dye factories, therefore, have a literary division which collects all the references, on request, from a carefully prepared index, thus providing a rapid and complete sur­vey of the literature. Frequently, it is necessary to extend a certain reaction to several fields and to prepare, systematically, hundreds of dye and other compounds because it is known that only a very few of the compounds, at the most, will have any value (Ehrlich 606). After the management, in combination with the various subdivision* such as the dye house, pharmaceutical laboratory, or other departments^ finds a new compound or a new process sufficiently interesting, larger scale tests must usually be carried out. These are conducted in the industrial division, a connecting link between laboratory and plant, using apparatus which is larger than that in the laboratory but much smaller than plant equipment. These tests give an indication of how the reaction will probably behave in large scale operation, and often save large sums of money.

At this stage it is also decided whether a patent application should be filed on the reaction or compound. It is the duty of the patent depart­ment to decide whether patent protection can probably be obtained, or whether it appears best to keep the observation secret until the whole field has been investigated so that there will be no possibility of avoiding the patent when it is granted. Only in rare cases is it decided to attempt keeping a discovery secret. This is an unsafe practice, and therefore is resorted to only in necessary cases.

The chemist is obliged to submit to the management at regular intervals a report on his activities so that the management is completely informed of current happenings. These reports are submitted once a month, or at longer, but regular, intervals, and are prepared under the supervision of the laboratory director.

Before a product goes into plant production, it is submitted for cost analysis by the accounting department. The necessary data are supplied by the laboratory director and the plant engineer. An example is given later in Section P, showing how the price of a dye is arrived at.

The plant proper is divided into three sections: chemical-technical, analytical and dyeing, and engineering.

The corrosive action of chemicals results in rather rapid destruction of apparatus, and furthermore, changes are frequently necessary, so that the ratio of chemical workers to hand workers (locksmiths, tube makers, cabinet makers, painters, masons, etc.) remains at about 2 to 1. Chief among the workshops are the repair shops which are under the direction of the plant engineer. Repairs, or a change in the arrangement of the equipment, are carried out under the direction of the plant chem­ist, with approval of the management, or if gross alterations are involved, under the supervision of the engineer. All work orders are entered on forms which go to the accounting division when the work is completed.

Large dye plants have their own construction shops, but even these have large pieces made by outside machine firms with whom agree­ments are made as to price and delivery. It is desirable to use as few different models as possible so that replacements can be made from stock. In this way, few replacement parts need be stocked for several apparatus if the parts are interchangeable.

Charges. Besides the costs associated with wearing out and re­placing equipment, other plant costs of various kinds must be con­sidered. Some of these are accurately determined, and some of them are lumped together and calculated as general costs. Wages are among the costs which can be determined relatively easily, being calculated on the basis of work sheets and records of the plant chemist. Further, steam consumption is calculated from the readings of regular steam gauges, as are also compressed air and vacuum.

Steam Consumption. The steam consumption in a dye plant is an important factor, large quantities being used, especially in the evapora­tion of reduction reaction mixtures. Multiple evaporators (double and triple stage) are coming into increasing use. In this kind of apparatus, the steam is used two or three times by passing the exhaust steam from one vessel into a second vessel where it evaporates a further quantity of liquid under reduced pressure. These apparatus are modeled in part after the multiple evaporators of the sugar beet industry, except that here the liquid to be evaporated is circulated rapidly from a heating vessel through a tube evaporator. One advantage lies in the fact that the boiler scale (mostly gypsum) is deposited solely in the side-vessel in which the tubes can be replaced in a few hours. Fuel consumption is reduced very considerably by this multiple use of the steam, and the large dye plants now use triple-stage evaporators almost exclusively. The use of steam is carried still further by heating the steam originally to 60 to 100 atmospheres pressure instead of only 5. This high pressure steam is used to drive a steam turbine, and the exhaust steam, at about 5 atmospheres, is lead into the plant lines. The pressure drop from 60 or 100 atmospheres to 5 yields so much energy that the dye plant may even produce an excess of electrical power. It has been proposed to reduce the steam pressure to only 2 atmospheres, but then conduction of the steam is difficult if excessive losses by radiation are to be avoided, particularly in winter. More recently, a new method has been intro­duced for better utilization of steam, although the principles upon which the method is based are quite old. The steam from the evaporating liquid is drawn out from the hermetically sealed evaporator by a turbo blower and led under a pressure of about % atmosphere into a tube system built into the same vessel. Compression of the steam results in significant heating, and up to 80 per cent of the fuel may be saved. Apparatus of this type is apparently being adopted rapidly, and deserves the most serious consideration for use under the conditions prevailing in Switzer­land.

Compressed Air and Vacuum. The amount of compressed air re­quired must also be considered along with the quantity of steam. Air is usually employed at a pressure of 2 to 3 atmospheres, obtained with either reciprocating or rotatory pumps. The amount required depends chiefly on the number of filter presses in use, since these use air for the most part. Every precipitate, before being removed from the press, is subjected to a stream of air for some time to blow out most of the mother liquor. One press having 40 chambers uses, for example, up to 100 cubic meters of air (at 2 atmospheres) per hour, costing 3 to 5 rappen depending on the unit cost.

Thus, the air cost for a dye plant is an important factor and must be calculated exactly. The compressor-vacuum pump shown in Figure 39 has proved very satisfactory (see also page 344).

The cost of water must also be determined accurately, since large amounts of it are used, especially as cooling water for condensers.

Function of the Plant Chemist. The work of the plant chemist is among the most interesting in the whole industry because the chemical reactions do not permit of simple control and must be followed closely and often be corrected. The chemist should always be alert and he should know each step in the manufacture in detail.

Manufacturing. The necessary raw materials are ordered a day or so in advance on order forms which are sent to the store room or, in some cases, to another plant. The chemicals are brought to the manufacturing section on the evening before they are to be used so that all of the materials are at hand when the process is begun. The chemist is respon­sible for seeing that the products are dry. Since many dyes are sensitive

to higher temperature and therefore require careful handling, the driers should be carefully supervised by the chemist who is always aware of the effect of drying on the color strength and tint of a dye. Representative cases have been mentioned in connection with methylene green and azo yellow.

Sample Dyeing. The finished dye goes directly from the driers to the dye house where a small representative sample is tested against the standard. The results are reported immediately to the management, the accounting department, and the chemist so that everyone is kept in­formed of the progress of the process. Frequently, a dyeing test is made with a small sample removed when the filter press is emptied so that any possible errors can be discovered at that stage.

Drying in recent years has been carried out to an increasing extent in vacuum drying ovens since it has been shown that this system uses less steam and leads to products of greater strength. Figure 52 shows a modern vacuum (hying oven, many models of which are in use. Stable intermediates, such as sodium /З-naphthalenesulfonate and simple azo dyes, can also be dried on simple steam plates or in drying tunnels using the counter-current principle. Even with these systems, however, va-

cuum drying is being used more and more since it saves both time and space. About 6 to 6.5 kilograms of steam are required to dry 1 kilo­gram of a dye in a vacuum drying oven, whereas 9 kilograms are needed in a tunnel kiln without vacuum.

A product, to be dried rapidly, must be broken up at least once during drying. Since considerable dust is formed in this operation, the drying room is often provided with dust removing equipment.

The vapors from the drying ovens are condensed in moisture con­densers so that the pumps are not exposed to acid or alkaline fumes.

When a number of batches of a dye have been dried, they are ground up and adjusted to a desired standard strength. The grinding and mix­ing is usually carried out in a separate blending plant which is under the direction of the factory dye house.

Grinding. The dyes are ground in modern disintegrators such as the one shown schematically in Figures 53 and 54. The efficiency of these machines exceeds by 10 to 15 times that of the old edge mills or grinding drums with steel balls, and in addition, they give much smaller particle size. Many rejections of a product because of insufficient solubility are the result of improper grinding since the older apparatus often press the material together in very hard, slate-like tablets which dissolve with difficulty.

Whenever possible, approximately the necessary quantity of dilu­ent is milled together with the dye so that the milling time is shortened. The concentrated dye is mixed with the diluent (Glauber salt, com­mon salt, soda, dextrin, etc.) and the mixture is then put through the mill. The mffi pictured gives automatic screening and has a magnet for removing iron particles which are always present in a product. The tlye is crushed by hammers of a special type and whirled around until it passes through the screen (Fig. 53). Air is drawn into the apparatus by centrifugal action — and must be permitted to escape. Tubular filter bags (G) permit the air to escape but retain all the dust. Most of the dust, however, is caught in the air chamber (F) into which the air stream is directed tangentially to the chamber wall. If very soft materials, such as /J-naphthol or naphthalene are to be ground, it is better to remove the screen because it clogs so easily. The material is carried by a short screw conveyor directly into the mixing drum where it is mixed for several hours. Figure 55 shows a modern mixing drum equipped with a reversible spiral gear which permits automatic filling and emptying. Such apparatus is designed to handle quantities up to 4000 kilograms and is gradually replacing the old, uneconomical mix­

ing equipment, especially for use with large-volume preparations. Use is also made of simpler mixing apparatus operated with compressed air or vacuum. Some dyes must be pulverized outside of the grinding room, either because they are inflammable or because they are unpleasant to handle (Bengal blue or methylene blue, page 311).

After the dye house has found a dye correct for tint and color strength, the dye goes to the package store from which it is withdrawn for the market. The management, accounting department, and plant chemist are informed and attention is directed to any special facts, such as good or bad yield and tint, etc. When these data are filed on a prod­uct, either a dye or an intermediate, the function of the industrial chem­ist comes to an end.