INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 19, No. 10
Automobile Finishes By H. C. Mougey GBNERALMOTORS CORPORATION, DETROIT, MICR
HE automobile industry has the reputation of asking
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for the impossible and then getting it. This changing of the “impossible” of yesterday to the ordinary routine of today is due to the cooperation of many people, and in this work the chemist has made very important contributions. In the early days of the automobile industry, manufacturers sometimes tried to offset a lack of horsepower or some other important factor by an additional pint or so of paint or varnish of the desired color. However, these early attempts to find the mechanical equivalent in horsepower of a pint of varnish were not entirely successful, and manufacturers soon settled down to the problem of developing to the highest degree all of the desirable properties of the automobile, both internal and external. In the field of automobile finishes the chemist has helped in several ways. By cooperation with paint and varnish makers he has helped put the industry on a scientific basis. On the material side he has produced by artificial means many of the paint and varnish raw materials which formerly were obtained from natural sources. By so doing he has increased the supply of raw materials, lowered costs, and improved and stabilized quality. In addition he has developed new artificial materials to replace those formerly obtained from natural sources. More recently he has developed entirely new products, with new properties, to replace the old-style finishes. This last achievement, which involves lacquer finishes, has been so revolutionary that, by comparison, it has dwarfed previous developments and has blinded us to many of the problems still awaiting solution. Under these conditions it may be desirable to study the factors involved in automobile finishes sometvhat in detail to see what really has been accomplished and what still remains to be done. Not many years ago the paint and varnish industry was on an empirical basis; the formulas of the different finishes were guarded as deep, mysterious secrets, handed down from a father on his death bed to his son, and together with products of merit most manufacturers also had many products of inferior quality, through lack of knowledge as to what was requi;ed and as to the composition and properties of the raw materials. Chemists, by the analysis of raw materials and by thousands of exposure and service tests, took much of the mystery out of paints and varnishes. Improvements were made in the composition and manufacture of the finishes. This was due more to the application of scientific methods than to a real knowledge of the chemical reactions involved, and it was only through the cooperation of the chemists, the paint and varnish makers, and the men who apply the finishes that these results were possible. These activities of the chemist related to his work with the paint and varnish industry as a whole, rather than to that part of the industry connected with automobile finishes. Automobile finishes may be divided into two general classes, those which require high temperatures for drying and those which may be dried a t ordinary temperatures. Black baking enamel, such as is now used almost universally on fenders, is an example of the first class. The paints and varnishes formerly used so generally on automobiles, as well as the present lacquer finishes, are examples of the second class.
Black Baking Enamel
Until the advent of the lacquer finish, black baking enamel was considered the standard of durability and the development of the modern conveyor enamel oven brought the use of black enamel to a high state of perfection. Strictly speaking, this is an engineering problem, but the chemist contributed to this work in many ways, as in developing insulating materials for the construction of the ovens, in developing enamels suitable for the process, and in heating and ventilating the ovens so that the proper temperatures and atmospheric conditions could be used to change chemically the liquid enamel to the hard, tough film on the fender. Black enamel is made by cooking together natural oils, such as linseed oil, with natural asphalts, such as gilsonite, and then thinning the mixture with a solvent that is volatile under the conditions of use of the enamel. Perhaps the part of the work on black enamels which has been most distinctly chemical is the development of the black enamel thinners from crude petroleum, with the resulting advantage of low cost. It is really the low cost of materials and labor to which black enamel owes its present place in the industry, for much remains to be desired in the resistance to rusting of blackenameled steel when subjected to conditions of high humidity. That this is due to a chemical action between the blackenamel film and the steel is shown in many ways. For example, if two pieces of steel are taken for a test and on one of these a flash of chromium plate is deposited while the other is simply cleaned in the best manner known, and if black enamel is then baked on these two pieces of steel and they are subjected to conditions of exposure a t high humidity, a remarkable difference will be found. The steel that is in direct contact with the blackenamel will rust under the enamel film and the enamel film itself will appear very brittle, but the enamel film that is insulated from the steel by the chromium plate will remain tough and the steel under the enamel film will not rust. A flash plate of the same thickness of nickel, copper, or zinc, between the steel and the enamel will not protect the steel from rusting or the enamel film from becoming brittle. The automobile industry is in great need of a finish which is as satisfactory as black enamel from the standpoints of cost and production, but which will offer more protection to the steel from rusting under conditions of high humidity. Another defect of black enamel is its tendency to lose its luster after a short exposure. This is due to microscopic cracks which develop in the surface, and which, as they cross and recross each other, soon change the high-luster finish to a dull, lifeless one. Since these cracks are only microscopic, polishing removes them and restores a new surface, which again may pass through the same cycle. It is possible to keep the black enamel surface looking well for a long time by the use of polish every few weeks, but it would be much better if the film would retain its luster longer, thus decreasing the necessity of frequent polishing. Paints and Varnishes The other class of automobile finishes is the one covering materials which may be dried a t normal temperatures, although it has long been known that many or all of these finishes may be dried more rapidly by the use of a moderate
October, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
increase in temperature. Paints and varnishes, such as were used before the advent of the lacquer finishes, were composed very largely of natural oils and resins, together with both natural and chemically prepared pigments. The contributions of the chemists to these older finishes lay mostly in applying scientific methods to paint manufacture and in chemically preparing pigments, although in recent years chemists have gone a long way in replacing turpentine with petroleum thinners, which involved more chemistry in their preparation, and in replacing natural resins with ester gum made from glycerol and rosin. L a c q u e r Finish
About six years ago a number of factors brought about the modern lacquer finish. The most important of these factors were : (1) The recognition by the automobile manufacturer of the need of a new type of finish more durable and better suited t o production than the old-type paints and varnishes. ( 2 ) The development of low-viscosity nitrocellulose. (3) The development of butyl alcohol in quantity production.
The modern lacquer finish is a good example of the work of the chemist. The nitrocellulose is a chemical product requiring very close chemical control and depending upon other chemical industries for nitric and sulfuric acids as well as other chemicals. The gums used in connection with the nitrocellulose may consist largely of chemically prepared ester gum. The plasticizers are definite artificial chemical products. Many of the pigments are artificial chemical products, and the solvents and thinners are chemical products. The proper combination of all these materials to produce the desired results of appearance, durability, ease of application, low cost, etc., requires chemical control, and the development of better combinations is a problem worthy of the best brains in the industry. Since the problems are so largely chemical, new solvents have been made to have the desired chemical properties, such as the monoethyl ether of ethylene glycol, the acetate of this ether, and an number of other ethers of similar composition. Some of these solvents, which a few years ago were classed as rare chemicals, are now being made on a tankcar basis. Other chemicals have been developed as solvents, such as butyl propionate, and more recently synthetic amyl alcohol and amyl acetate have appeared, prepared by chemical methods as distinct from fermentation processes. The development of toluene by chemists during the war for use in making T. N. T. was another chemical operation of great value, as about as much toluene is used in lacquer solvents and thinners as all other solvent ingredients combined. In the petroleum industry solvents are being developed for use in making blends to replace toluene and secondary alcohols are being made. These secondary alcohols are being used either in the manufacture of lacquer thinners or to replace other alcohols, and thus make them available as raw materials. In fact, a t the present time the problem is not one of obtaining solvents of the proper chemical properties, but of using these materials to the best advantage so that these chemical industries may continue in business as sources of supply. The list of materials available for solvents is very large, and changing commercial conditions may promote the use of certain materials not now in general use. For example, changes in the relative prices of acetone and of ethyl acetate may very greatly affect the use of these two materials in solvents. The chemists manufacturing pigments have helped greatly in the new lacquer finishes. It is the use of the proper kind and amount of pigment which gives lacquer its durability, and without the increase in durability brought about by the
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pigment the lacquers could not be used in automobile finishing. In the early days of the use of lacquers on automobiles there were some sad experiences due to the lack of appreciation of the work performed by the pigments, and even yet we occasionally have troubles due to the improper use of pigments or to the use of pigments with undesirable properties. Advantages of L a c q u e r s over Varnish Finishes These activities of the chemist in the lacquer field make it apparent that the chemist is necessary in the manufacture of lacquer, but the automobile industry is more interested in the advantages it obtains from lacquers as compared with the old-type varnish finishes. The advantages may be classified under the headings of greater durability and greater speed of application. Under greater durability is included the possibility of using a large variety of colors and still obtaining much greater durability than was possible with the most durable of the colors of varnish finishes. Greater speed of application, in itself, is of little value except as it is the cause of other advantages. In labor and material cost the lacquer finish does not offer much of an advantage over the paint and varnish finishes, but by decreasing the requirements of time of drying and of floor or oven space, great savings in cost are possible, and the manufacturer can finish and deliver cars when the public wants them. F u r t h e r Work f o r the C h e m i s t
Although lacquers have almost entirely replaced color and finishing varnishes in the automotive field, there still remains much for the chemist to do. Lacquer finishes for wood for outside exposure are not entirely satisfactory, and in many cases the oil varnishes must still be used. Lacquers are notoriously poor in adhesion to smooth metal, and although much has been done in lacquer primers and surfacers, most of the production plants in finishing automobiles use the oldstyle, oil-type primers and surfacers. In refinishing work or, in general, where the volume of business is not large enough to warrant the investment in ovens or drying space, lacquer primers and surfacers or oil-type primers followed by lacquer surfacers are finding use. The oil-type primers and surfacers require oxygen from the air to enable them to dry, and consequently they must be applied and dried in thin layers. Some other material for primers and surfacers, which will dry in thicker layers without requiring as much oxygen, is very badly needed in the automotive industry. This new material must not cost too much in money, time, or labor, or it cannot compete with the materials now available. Much work is being done on this subject and perhaps in a short time it will no longer be one of the important problems. Chemists have helped in other lines which are not so directly connected with the finish as the nitrocellulose, the solvents, or the pigments. I n order to get the proper luster the dried lacquer must be rubbed and polished. The development of waterproof sandpaper is an important factor, as well as the development of the proper polishes. Since the cost of hand rubbing and polishing is so high, it seems that a cheaper method of getting the smooth surface of high luster must be developed, but this is one of the unsolved problems a t the present time. Conclusion
It has been seen that the chemist has contributed greatly in developing the finishes used on automobiles, but the real secret of the progress in this work has been the cooperation of the men in all the different phases of the work, including those who have had the problem of applying the finishes to the automobiles. If this spirit of cooperation can be maintained, it is only reasonable to expect that in the future we may witness a continuation of this progress.
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INDUSTRIAL A N D ENGINEERILVGCHEMISTRY
Vd. 19. No. 10
Contribution of Leather to the Automobile By Norman Hertz M A X HERTZLEATHERCo.,
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EATHER has been acknowledged as the superior material for upholstery purposes since the days of the chariot. When carriages came into vogue, they were generally upholstered with leather, and the use of leather has continued down to the modern automobile. Some of the more expensive cars also have tooled-leather fittings and leather-covered accessories, such as vanity cases, smoking cases, and notebooks. During 1925, the latest year for which statistics are available, the production of upholstery leather in the United States was 64,000,000 square feet, of which 44,800,000, or 69 per cent, were used by automobile manufacturers. These figures include the splits underneath the grain surface, which are made available through the mechanical perfection of modern splitting machinery. It is now possible to split into layers, of any uniform thickness, the leather of cattle hides having a superficial area of from 50 to 75 square feet or more per skin. From a standpoint of wear, the split for upholstery leather is almost as good as the top surface. In order to keep pace with progress, science has greatly aided in the elimination of waste in manufacture, in the production of more uniform quality, and in attaining new and more beautiful finishes. For centuries the making of leather was a mystical art or craft, and even today scientific progress has been slow because the basic principles of the chemistry of the pelt and the substances used for tanning are veiy intricate. Leather manufacturers therefore decided that fundamental knowledge would be obtained more rapidly through the collaboration of specialists in the various branches of chemistry and its allied sciences. This method has been followed recently with promising results by the Tanners’ Council of America, the British Tanners Research Association in England, at the University of Cincinnati, and at the plants of a few tanners in this country and abroad. In most cases the collaborators are represented by a physical chemist, a pure organic chemist, a biological chemist, a microscopist, a histologist, and a bacteriologist, under the leadership of a man who understands the needs of the industry, and who has a broad enough knowledge of the various sciences to enable him to grasp the work of the separate scientists and derive therefrom basic scientific principles. Processes in Manufacture of Upholstery Leather
The processes involved in the manufacture of upholstery leather can be classified roughly as follows: (1) Conditioning of the animal skin or hide so that it may be preserved for a period of time before being converted into leather. (2) Conditioning of the pelt for unhairing. (3) Removal of the hair. (4) Conditioning of the pelt for the tanning process. ( 5 ) Tanning. (6) Sditting. (7) RetannLng. ( 8 ) Oiling of the skin to give the finished leather the proper pliability an8 strength. (9) Dyeing and dressing of leather to give it the desired appearance.
Tanning The three most important methods of tanning in vogue today are:
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(1) Vegetable tanning, which depends upon the action of the so-called tannins contained in the barks, wood, fruit, or root of various trees and plants, upon the pelt. (2) Mineral tanning, which utilizes the tanning properties of certain chromium or aluminum salts. (3) Oil tanning, where fish oils are employed to make chamois leather.
Each method produces leather with different physical and chemical properties. . The use of vegetable tannins produces leather having the most suitable properties for the upholstery of automobiles. T-egetable-tanned leather has the least stretch. Upholsterers can use it with little or no backing material, confident that their work will maintain its original shape after years of constant usage. Vegetable tannage produces more splits and greater area from a given hide. It also produces a leather which will better take and retain permanently the impressions with which it is embossed. Chemistry’s Contribution The process of tanning has been aided greatly by the increased physico-chemical knowledge of the proteins. Through the application of this new knowledge, the tanner has been able to shorten the time required to tan, to produce more uniformly tanned leather, and to reduce the tanning cost by (1) the use of more concentrated extracts, (2) the control of the hydrogen-ion concentration in the tanning baths, (3) the proper blending of the most suitable tanning materials, (4) temperature control of the tanning baths, and (5) control of the physico-chemical condition of the hide entering the tanning liquors. Oil, to soften and strengthen leather, was formerly applied by a brush in the hands of a workman, then by machine. The discovery of the emulsifying properties of sulfonated oils and certain proteins, which produce neutral or slightly acid emulsions, has made it possible to put oil into leather more uniformly and economically. Patent Leather Patent, or enameled, leather for harness and carriage upholstery was first produced in Kewark, N. J., by Seth Boyden. I n 1818 Boyden saw the enameled peak of a German military officer’s cap and, believing that similar material would be ornamental on harness. he set out to duplicate it. By analyzing the coating or varnish he discovered the process for making patent leather, an improvement over the original sample, as patent leather made in Europe was brittle and therefore had little commercial value. He then built the first shop in this country for the manufacture of patent leather. At first he dried the varnish on the leather in the sun, except the last coats, which were dried in a warm room. He made few articles of patent leather except for harness, for lack of proper ovens for drying the japan and because it was a novelty rather than a necessity. I n 1820 he made an oven which would hold sixteen skins, and he finished about seven a week. His sales increased rapidly, in 1829 totaling $20,341. At first the application of varnish to leather was the basis of practically all automobile leather finishes, although chemists now have changed the materials used. The slow process of drying in an oven and in,the sun has given way to more rapid methods of applying quick-drying coats of pyroxylin
