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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. I n 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. I n 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 a n oven and in,the sun has given way to more rapid methods of applying quick-drying coats of pyroxylin
October, 1927
ILVDUSTRIALAKD ENGINEERIA’G CHEMISTRY
as the base coats, with two or more japan coats to make the surface more durable and gire it a better appearance. Specifications f o r Automobile L e a t h e r
Leather manufact’ure consists of a series of processes which convert raw animal tissue into many kinds of leather. Each variety, whether used for the sole or upper of a shoe, for belting, for traveling goods, or for upholstery, must have physical, chemical, and artistic properties essential to those demands required by its destined use. Such properties are inherent in automobile leather. They are responsible, together with its price, for its value as upholstery material in the automobile. For a long time the properties of automobile leather were vaguely agreed upon between the buyer and seller; but the Society of Automotive Engineers in conjunction with the manufacturers of automobile leather and their chemists, has drawn up a set of specifications which were adopted in February, 1924, and revised in March, 1926. The salient features of these specifications are as follows:
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thickness of a hide obtained after either a full-grain or machinebuffed split has been removed. Test specimens shall show no evidence of tearing under a load of 200 pounds. Advantages of L e a t h e r f o r Automobile Upholstery
Automobile manufacturers, realizing more fully than ever before that beauty is essential in selling their products, find in the soft and artistic finishes now made available on leather through the tanners’ skill a crowning touch representing genuine luxury in the combined appearance and indisputable utility of this material. Leather possesses low frictional resistance, clothes are not readily wrinkled or drawn out of place or shape. From the standpoint of cleanliness, automobile leather has a relatively smooth and waterproof surface into which dirt, grease, and bacteria cannot penetrate, and from the surface of which they can be removed by soapy water without undue expenditure of time and labor. Dr. Allen Rogers, of Pratt Institute, in a n address delivered April 17, 1925, at the Chemists’ Club, showed that a square foot of fabric taken from a sedan which had been run for two years with constant vacuum SPECIFICATIOXS FOR FCLL-GRAIN (SNUFFED) UPHOLSTERY cleaning and very good care contained a large amount of dirt LEATHER in the wash water subsequently used to remove it from the These specifications are intended t o cover the first split from a hide containing the full grain of the leather, the surface of wrhich vacuum cleaner, and twice as much when the same fabric was then cleaned with naphtha. On the other hand, a square is shaved either by hand or machine, removing shavings of no appreciable size or thickness. foot of Spanish leather removed from a four-year-old car which A vertical section of full-grain leather shall show t h a t approxi- had received good care showed practically no dirt. mately one-third of the thickness is made up of the fine fibers. Leather is resistant to the ravages of the moth. The thickness shall be inch with tolerance of plus and So long as the car lasts its leather upholstery iemains as minus inch as measured with a Woburn gage or the equivalent. fresh and beautiful as the day it was made. I n the case of Hides shall show no defect or surface blemish affecting the imitation leather only the pyroxylin surface wears, once this appearance of the material, such as brush marks or stops and is gone, the cotton fabric goes to pieces in a short time. For bad flows. this reason leather is used for the seat, back, and arm-rests Leather must show no evidence of surface cracking when doubled and creased a t 32 F. of taxicabs. The rest of the cab is lined with imitation leather From each 500 hides received a sample measuring 6 by 9 which is cheaper but which serves its purpose in those parts inches shall be cut from a location in the hide representative of of the interior where wear is not essential but where harmony the leather that is t o be cut into upholstery. The tearing properties of three 3 by 6-inch test specimens cut from each sample of appearance and cleanliness are desired. shall be determined by gripping the test specimens 3 inches apart There would not be enough cattle in the world to supply between jaws t h a t are 1 inch wide on the upper side and 3 inches the hides needed if all automobiles were upholstered and wide on the under side and pulling in a tensile testing machine a t lined with leather alone. Imitation leather has, therefore, the rate of 12 inches per minute. Test specimens shall show no evidence of tearing under a load of 100 pounds. The elongation filled an economic need as a cheap lining. at the above load shall not be over 33 per cent. It will be noted that the word “imitation” has been used SPECIRICATIONS FOR MACHINE-BUFFED UPHOLSTERY LEATHER instead of “artificial,” because there is no such a material These are the same as for full grained leather with the follow- as artificial leather in the sense that there is artificial ice, ing exceptions : or artificial indigo. The adjective “artificial” is applicable These specifications are intended to cover the first split from only where man has reproduced a natural product by artifice. a hide after a thin layer of the grain thickness, called a buffing I n other words, the artificial product has all the properties inch thick, has been removed. a n d approximately A vertical section of machine-buffed leather shall show some of the natural one, whereas the imitation has not. There is, therefore, no artificial leather and imitation leather is of the thickness is made up of the fine fibers. Test specimens shall show no evidence of tearing under a load not leather a t all. of 150 pounds. There is nothing like upholstery leather. Impervious to SPECIFICATIONS FOR KO. 1 SPLITUPHOLSTERY LEATHER dust and moisture, likewise to heat and cold, exposure to These are the same as for machine-buffed leather with the the elements detracts neither from its appearance nor life, following exceptions: because this material merely represents a successful effort to These specifications are intended to cover the second split or go Nature one better in her own answer to sun and storm.
Europe, Our Best Chemical Market Europe affords the best market for American chemicals despite t h e fact t h a t i t also offers the keenest competition in other countries. I n 1926 chemicals and related products worth $62,000,000-representing 36 per cent of our total chemical exports-were shipped t o European countries. Of the 25 best markets in the world, according to values, 8 are in Europe. England leads, taking 17 per cent of our exports, and Germany holds fcurth place with 7 per cent. The other 6 countries are France, the Netherlands, Belgium, Spain, Italy, and Sweden. The three largest consumers, England, Germany, and France, all purchased considerably more last year than in 1922, Spain being t h e only European country t o import less than formerly,
The United States leads in the world markets for several important crude and semi-manufactured products such as rosin, turpentine, and sulfur, and in addition to t h e crudes annually ships to European markets finished products such as prepared medicines, dentifrices, toilet preparations, paints, lacquers, plastics, etc., valued at millions of dollars. The increase from 1922 for crude and semi-manufactured products is attributable t o a greater industrial activity, while the gain in finished goods is explainable by the increased purchasing power of a large population which, as their earning powers increase, spend more for the type of commodities we export.
