Chemistry in the Printing Industry B. L. W E H M H O F F , 1 West Virginia Pulp a n d P a p e r C o . , 230 Park Ave., New York, N . Y. Early H i s t o r y Some people in the printing industry still regard a chemist as an unworldly creature, dealing with test tubes, smells, and various concoctions in some secret recess, and feel that he is a sort of expensive luxury, hobby, or, at the best, a new form of advertising to which his employer can point with pride when the occasion demands. This situation, as regards the larger printing plants, is far from the truth. One of the first printers to employ chemists was J. Lyons and Co. of England, who installed a laboratory in 1919. There is no record of the first printing plant laboratory in this country, but some of the larger plants have had one or more chemists in their employ for over ten years. The largest and best equipped printing laboratory is in the Government Printing Office in Washington. Technical research and control in that office was initiated by the then Public Printer of the United States, George H. Carter, who has been one of the most consistent advocates of research in printing. Some plants employ chemists, others chemical engineers as well. As a rule the chemists deal with processes and materials, while the chemical engineer deals also with equipment. Modern Printing Modern printing is divided into three main branches—letterpress, intaglio, and planographic—each o f which has certain inherent characteristics which yield widely different final results. These terms are derived from the character of the printing surfaces used. Letterpress is done from relief type or plates, all printing areas being raised above the remainder of the form or plate. Ink is transferred direct from the printing surface to the paper. INDUSTRIAL AND ENGINEERING CHEMISTRY
is a good example of quality letterpress work in one color. Intaglio printing, of which rotogravure is the most common example, is done from a cylinder in which all the printing areas are recessed. The cylinder revolves in a trough of thin ink which fills all the recesses. Any ink adhering to the surfaces of the cylinder is removed as the cylinder passes under a "doctor" blade just before coming into contact with the paper. The ink is absorbed by the paper in much the same manner as a blotter picks up writing ink. Planographic printing, as indicated by the name, is done from a plane surface, both the printing and non-printing areas being in the same or practically the same plane. This kind of printing is done in two ways—direct and indirect, or ''offset." Direct lithography is confined mainly to posters and similar products for billboards. "Offset" printing derives its name from the fact that the inked image is transferred from the plate to a rubber blanket and then again transferred or "offset" on the paper. In both cases the printing plate is a sheet of aluminum or zinc, usually the latter, on which the matter to be printed is applied by photographic methods. B y means of chemical treatment the non-printing portions of the plate are made ink-repellent and are kept so during the operation of printing by the use of a weak solution of gum arabic and acid. The printing areas, on the other hand, are ink-receptive. When the inking rollers pass over the plate only the print» Chemical engineer, formerly technical director, U. S. Government Printing Office, Washington, D. C . and \V. F. Hall Printing Co., Chicago. 111.
Plates Foreword RINTING is as closely allied to chemistry and chemical engineering as any other industry, yet for some unknown reason the presence of a chemist in a printing plant almost invariably brings forth the query, "But what is there for a chemist to do in a printing plant?" I have been asked this question many times, not only b y printers, but by chemists and engineers, so in what follows I have attempted to tell the chemists, at least, a few of the reasons why a chemist and a printing plant fit together as well as some other combinations, such as moonlight and roses, Scotch and soda, bam and eggs, or what have you.
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ing areas take ink, the non-printing areas having been previously wet by water rollers. A recent development in offset printing is the "deep-etch" plate, in which the printing areas are recessed a few tenthousandths of an inch. This process adds t o the sharpness of the printing and permits longer runs before the plates wear out. All three processes are based on chemical reactions. A chemist has the background of chemical knowledge necessary in overcoming the various problems that arise and also is able to help control many variables that affect both the quantity and quality of the finished product. Type Type is necessary at present in all three printing processes, although the actual printing is not done from the original type except in the case of short runs by the letterpress method. The metal from which type is cast is a lead-tin-antimony alloy, the proportions varying according to the characteristics of the casting machine used. In addition to being used for type, these lead-tin-antimony alloys are also employed in the manufacture of stereotype plates and for the backs of electrotype plates. The proportions of the three metals must be kept within certain well-defined limits for each of the various requirements, if both quality and Quantity production are to be obtained. Attempts have been made from time to time to substitute a single alloy for the four or five ordinarily used. These efforts have invariably resulted in lessened production and inferior quality of work. The maintenance of the alloys in their proper proportions requires chemical analysis, followed by the addition of the amounts of whatever constituents are required. In addition to maintenance of standard formulas, it is often necessary to remove small quantities of other metals, such as zinc and copper. The presence of these metals is undesirable, as small percentages have an adverse effect on the operation of casting machines, as well as on the quality of the type produced. Small printing plants depend on the metal supply company to keep their type alloys in good condition, but large plants frequently find it economical to have their own chemists maintain the required control, since it can be done in connection with other control processes in the plant. 417
Most letterpress printing is done from plates rather than type. Type metal is soft and can be used tor only a few thousand impressions before being so badly worn as to produce poor printing. Furthermore, type can be used only when held in a steel "chase," or form. This limits its use in actual printing to fiatbed presses, which are too slow and costly to operate on long runs. Plates may be curved to fit the cylinders of rotary presses, which run at high speeds and consequent low cost. A page in the average magazine or catalog usually contains some illustrated matter in the form of halftones or line cuts. In addition to the illustrations there is also some reading matter. The transition from the original type and halftones grouped together in a steel chase to the finished curved or flat electrotype or stereotype plate comprises a series of chemical reactions, particularly in the case of electrotypes. The "form/"' composed of type and halftones, the surface of which is all at practically the same level, may be used to make any number of duplicate plates. Most magazines and catalogs are printed on two or more sets of such plates in order to speed up production. Electrotype plates are made by first molding the form in wax or lead, according to the character of the form. Lead gives fine detail but cannot be used on type as the pressure employed in molding is sufficient to crush the type. Wax, therefore, is the usual molding medium. The mold, after being released from the form, is rendered electrically conductive by means of graphite, following which a copper * 'shell" is deposited on it by the usual means. For long runs a thin facing of nickel, seldom over 0.0015 inch thick, is first deposited on the mold. In either case copper is deposited until the shell has a thickness of approximately 0.0010 inch. This deposit, after being removed from the mold, is backed with lead-tin-antimony alloy, shaved to the required thickness, and'all points on the surface are brought to the proper printing height. The finished plates may be either curved or fiat, depending on the particular press on which they are to be used. The wax employed for molding must have certain well-defined characteristics, and laboratory control will ensure a more uniform material than can be had by guesswork methods. The qualities of materials used—wax, graphite, nickel, copper, nickel and copper salts, acids, etc.—affect the character of the finished plate. Laboratory control of the quality of these materials has proved t o be of as definite value in the manufacture of printing plates as in any other industry. Electrodeposit ion, whether of copper, nickel, or chromium, is essentially a chemical process. Installation of technical control over the composition and operating conditions of the plating tanks has been found to yield good dividends wherever tried. In one case the time required for the deposition of the copper shell was reduced to one-third of that originally needed. The percentage of defective shells dropped to negligible proportions at the same time. Stereotype plates are used for letterpress printing where the highest quality of printing is not required. High quality work can be and is being done in certain cases from stereotypes, but these are the
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exception rather than the rule. As in the case of electrotypes, .·. nold is made from the type and halftones, but the molding medium for stereotype plates is a paper and paste "flung." After l>eing molded, the matrix is dried and trimmed and is ready for use in making the plate. This is done by inserting in a casting box or mold, which is then filled with molten stereotype metal, another lead-tin-antimony alloy. As soon as the metal has solidified it is removed from the box, shaved on the back, trimmed, and beveled. It is then ready for the press, unless intended for a long run, in which case a thin deposit of nickel is put on the face. Chemical control in stereotyping is applied on materials and in the plating bath. Intaglio "plates" are elect rolytically deposited sheaths of copper on metal cylinders. The deposition of the sheath involves the same reactions and control as the copper shells of electrotype plates. The subsequent treatment of the copper to produce a printing surface is a combination of photography with subsequent etching of the image by chemical means. The reactions are the same as those described later in the manufacture of halftones. The offset process is even more of a chemical nature than the other two classes of printing. Practically every operation, from the graining of the plate through photographing and printing the image, development, etching, and even the final printing, involves one or more chemical reactions. This process, being comparatively recent in general application, is a fertile field for research. For instance, the action of gum arabic and similar materials, used generally in offset printing, is not yet definitely understood, despite the research that has already been conducted. Line C u t s Mention has been made of halftones and line cuts used for illustrations. The latter are employed for coarse work, such as graphs, pen and ink sketches, etc., and as the name indicates, are composed of a series of lines. These may be connected or separated according to the area to be printed. The reactions taking place in their manufacture are essentially the same as in the manufacture of halftones. Halftones Halftones get their name from the fact that of the original or fulltone picture, approximately half the effective area is lost. This is not as serious as it sounds, as is evidenced by the high quality of the illustrations in even low-priced publications. This loss of effective area is necessary in order to obtain a series of printing areas of different density. The first step in the manufacture of a halftone is the photographing of the original through a halftone screen. This screen consists of two glass plates with precision black lines ruled parallel. The number of lines used varies from 55 to 175 per inch. The two plates are cemented together with the lines at right angles, forming a "screen." The resultant image is printed on sensitized copper or zinc, and the print etched with ferric chloride or acid, or by electrolytic means. The process of making halftones is essentially a series of chemical reactions, all of which require close control if the best re suits are to be obtained. A chemist is not a photoengraver, but all photoengravers are of necessity rule-of-thumb chemists. The services of a chemist are of value in any photoengraving plant, since by working in cooperation with the engravers he can determine the most
desirable characteristics of the various materials and control them within predetermined limits. This relieves the engraver from attempting cut-and-try methods when variables are encountered, leaving him free to exercise to the fullest extent bis skill in producing halftones which will reproduce the original with great fidelity. Ink and Paper The basis of all printing, once the plates are made, is ink and paper. If these two items are not suited to each other or to the particular job inferior work inevitably results. Ink manufacture, like papermaking, is a separate industry from printing, although some of the larger printing firms make part or all of their own ink. Even in such cases, the ink plant is operated as a separate unit. It is the function of the printing plant chemist to make such tests a s may be necessary to ensure t hat t he ink furnished for each job is of the correct shade, consistency, and quality, and that it possesses the desired drying characteristics. All this should be done before the job is sent to the press, as otherwise valuable press time is wasted with consequent danger of delaying the job, in addition to increasing the cost. Until recently there were no laboratory methods for evaluating the printing quality of paper. Printers ordered '•English finish," "antique," **supor," or whatever trade designation they wanted. Tests for printing quality were limited to "•feel" and appearance, and often wide variations in the printed work were in evidence. Within the past few years, through research conducted in printing plants, it has become possible t o measure at least some of the most desirable printing characteristics of paper, such as ink receptivity and smoothness. The desirable range for these characteristics must, of course, be determined for each of the various kinds of work. This involves a knowledge of the different printing processes, plates, inks, presses, etc., and naturally can be done only by technically trained men familiar with printing. The next logical step is cooperative study with paper manufacturers in an effort to standardize the printing quality of the different grades and finishes of paper. At least one large paper manufacturer is actively engaged in such standardization work. Since a considerable amount of paper is used by the smaller printing houses, whose volume of work is not sufficient to warrant employing a chemist, the problem of determining the permissible limits for printing quality has naturally fallen to the lot of the paper makers and the larger printers. However, once the limits are denned, the paper produced under such specifications will work as well in small plants as in large ones. The main value of testing paper in printing plants is to ensure the uniformity of successive deliveries of the same paper and to provide accurate data for the use of the paper maker in overcoming troubles and in standardizing the quality of his product. Specifications for paper, developed only from the standpoint of the printer, are likely to cause trouble, since the normal variations in papier manufacture may not be considered. For this reason any specification should be the result of cooperative work between the printer and the paper manufacturer. Binding Materials Binding materials, such a s binder's board for book covers, book cloth, thread, wire, and glue can now all be purchased
on definite technical specificat ions. St udy is frequently necessary to determine the most economical grade of each material, and of course all deliveries should be subjected to routine laboratory test to ensure that they comply with the specifications under which they are purchased. Glue and glycerol have long been used as the basic ingredients in flexible glues .used in binding books, magazines, and catalogs. Owing to the hvgroscopic nature of glycerol, the percentage is usually reduced during the summer months, even though the products bound with the glue may, as in the case of mail order catalogs, be intended for use during the winter. As a result, the backs of such publications tend to crack and sometimes open up during the winter. The only real improvement in flexible glues in recent years was the result of a technical study in the laboratory of a large producer of catalogs and magazines. Research was conducted for several months before sufficient progress was made to warrant a test in the bindery. Practical tests and further research alternated until finally a flexible glue was produced which contained a higher jiercentage of glycerol than had previously i>een possible. The production of books, even during the summer when both temperature and relative humidity conditions equaled the records, was maintained at the maximum. No glue troubles were encountered, and the hooks had a degree of flexibility which had not been approached in previous editions. The percentage of poorly bound books, particularly in the summer, was reduced to a mere fraction of that formerly experienced. This one research job alone has brought a considerable financial reward to the firm in question. Opportunities for t h e Chemist The possibilities for savings through research in printing plants have not been exhausted. On the contrary, the surface has only been scratched. There is as much, if not more, opportunity for the chemist in printing than in almost any other industry. A chemist or chemical engineer in a printing plant is of little or no value until he has obtained some training in the rudiments of printing. It is advisable that, instead of going directly into the laboratory, a !>eginner spend several mont lis as helper or apprentice in each of the various departments in the plant. This will by no means make him a printer or engraver, but will give him an opportunity to learn the fundamentals underlying the different steps and processes as well as the basic chemical facts on which they are founded. A few months of experience in hunting for "type lice," "quad splitters," and other non-existent printing plant equipment, getting ink in his hair, washing rollers, etc., should reduce the recent graduate to the point where he is ready to begin his education in printing from a chemical standpoint.
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