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INDUSTRIAL AND ENGINEERING CHEMISTRY
deficiency of potash in the phosphoric acid made by volatilization, in the manufacture of monopotassium phosphate. A simple process for effecting the combination between phosphoric acid and potassium chloride has been developed which produces an almost pure grade of monopotassium phosphate containing over 80 per cent total available plant food. It is believed that this salt can be profitably marketed in the Middle West, on the Pacific Coast, in the export trade and possibly under favorable conditions throughout the entire United States. It would also seem that the growing demand
Vol. 25, No. 4
for fertilizers from the Middle West is a factor which favorably affects the prospects of the proposed industry a t Green River. LITERATURE CITED (1) Ross, IT. H., and Haaen, T.,U. S. Patent 1,486,851 (1923). (2) Ross, W.H., hlehring, A. L., and Merz, .4. R., IND.ENQ.CHEX., 19, 211 (1927). (3) Strickler, U. S. Patent 1,037,837 (1912).
RECEIVED August 3, 1932
Manufacture of Printing Ink WOODFORD F. HARRISON The California Ink Company, Inc., San Francisco, Calif.
T
HE printing ink industry, small and almost unknown, is entirely dependent on its parent, the printing industry. Rapid developments in printing machinery have necessitated like progress in ink making, such machinery modifications often having been devised with little regard to ink problems. Originally, pressmen made their own inksconcoctions of pigments and oils, which were simple in comparison with the carefully controlled products of today which are formulated with the precision that is essential for the modern high-production press. The many kinds of printing presses and paper and the innumerable uses for printed materials have made ink manufacture a variety business as well as largely a specialty business. Printing processes can in general be classified under three headings: typographic, or printing from surfaces in relief; lithographic, or printing from plane surfaces; and intaglio, including gravure processes and engraving, steel die, etc. This seems simple for the ink maker, and would be so, were it not true that each of the above classifications is extremely general and includes printing by numerous processes using many kinds of press mechanisms. Again calling attention to the huge variety of papers and other materials on which printing is done, and to the many purposes for which printed materials are to be used, it becomes clear that these factors, coupled with the many printing processes, necessitate a multiplicity of modifications in ink formulation. It is not within the scope of this paper to explain in detail the various printing processes, but a cursory description of the principal ones will aid in providing a clear understanding of the printing ink manufacturer’s problems. Printing from surfaces in relief is so common that it need only be mentioned. Practically all small job printing is so done. There is a great variety of printing presses using this principle, and it is adaptable for almost any printing purpose. Under printing from plane surfaces comes the important lithograph process. Modern lithography is usually done from specially grained zinc or aluminum plates. The design on the plate is not in relief but is simply prepared to make it accept ink while the surrounding area of grained plate is wettable by water and not by ink. Thus the inking process applies ink to the design but not to the surrounding area, whereas this specially grained and water-adsorptive surrounding area is wet with water from damping rolls that have no power to wet the design. In general there are two types of lithography: direct, in which printing is directly from plates to paper; and offset, in which a rubber blanket first contacts the plate and then the paper. Offset lithography has practically displaced direct. Under printing from below the surface, come the
popular rotogravure processes. The design is etched into a copper cylinder. The cylinder revolves in a fountain of ink, and the excess is scraped off. The paper literally absorbs ink from depressions in the cylinder, as i t is brought into close contact by the impression cylinder. The ink sets initially by absorption. and is finally dried by evaporation of solvents as the paper passes over a steam-heated drum. XEEDFOR RESEARCH IN INKMAKIKG Although printing ink manufacture is essentially a chemical industry, it is only recently that the chemist has had an opportunity to organize properly the ink experience of many years past and to build a scientific foundation of fundamental information. The ink maker of today still employs many materials simply by rule-of-thumb; good scientific reasons for their uses are not always known. To be more explicit, lithographic inks have practically always been made of pigment, oxidizable oils (chiefly linseed oils), driers, and possibly waxy materials. The pigment is ground into heatpolymerized oils to obtain an ink of proper consistency which is considerably more viscous and plastic than an enamel paint. It is known by experience that the correct combination of pigment, viscous polymerized oils, and drier will work reasonably well on a lithographic press; that is, it will distribute properly on inking rolls, take readily on the lithographic plate without adhering to the dampened portion of the plate, transfer sharply to the rubber blanket and then likewise to the paper or other material being printed. After being so printed it must dry with the desired finish in proper time, and perhaps take well over other colors, or accept other inks afterwards, or both. The adjustment of the ink to do all of these things was a t one time accomplished by purely rule-of-thumb methods. It may always have been common sense to avoid use of a vehicle that can emulsify readily with water or the water solutions used on lithographic damping rolls. The ink chemist, however, is thinking of the picture as one largely influenced by surface tension of vehicle and interfacial tension between vehicle and water, between pigment and water, and between pigment and vehicle. Exploration of such fields not only provides a better understanding of the functions of the materials used, but also brings to light untried materials having more favorable properties than those now in use. Methods developed in the past few years for measurement of preferential wetting of pigments by liquids and of adhesion tension are of great value in contributing toward a better understanding of ink formulation. These are tools with which the printing-ink research chemist must become more familiar.
April, 1933
I N D U S T H I A I,
A N 1)
E ”i (iI ?; E 13 II I
i n spite OS pronounced differences betwen vnrieties of printing inks, they are nearly all siniilar in priricipic of makc-up. Most printing inks consist principally of a suspended pigment or color in an oil which may vary from air oily Huid to a sticky and viscous or plastic material. The color is usually in~olubleboth in wnter and in the oil iii whiclr it is snspended, and it may be either orgnnio or inorganic!. The hinding material or vehicle, altliougli nearly d l oil, is supplenrentcd by varions gurns, resina, \vext:s. and water-insoluiilti soaps. It s h o u l d be clcar that thc matrufact,ure uf printing ink is a subject ~nvolving the p r o d u c t i o n a n d use of far too marry clrenricals to Ije more than LriPHs o u t l i n e d here. The ink m a k e r thinks OS the temi “ p r i n t i n g ink” as a very general one, conveying littie meaning until it is further modified by terms ruclr as ,!ffset, litho, or n e w s , but requirements go far beyond the kind of press on which it is tu be used. Speed of the press, c l i m a t i c eonditions, k i n d of p a p e r , and thc purpose for which the p r i n t e d niatt.er is t o b e used-all aid in determining specifications to which an ink rnuat c o n f o r m . Fur instance, hiRh-speed presses like t h o s e used for newsprint reqnire a rather tackless ink of semi-p1ast.k fiiiid consistency. It niust dry entirely by pcnetratioii in order to permit handling of a newsvrint as soon as it comes &om the folder of the p e w . S e w s inks consist largely of pigments ground in luhriea,ting petroleum oils with various resinous materials to obtain pigment dispersion, proper consistency, and other necessary properties. It. is sufficient to say that tlie properties of inkh w e suited to any ret of printing conditions: (1) by c!lianges in eonsistency to obtain good working proi~ertiesfor particiiiar job and press conditinns; and (2) by selectirnr and coinpanndinp of resins, oils, pigments, wases, driers, antioxidants, and insoluhle soaps to provide desired color, method of drying (i. e., hy penetration ur oxidation), drying spced, finish (i. e., Hat or glossy), uiinimum of offset and sticking of printed materials, and other propertie8 of minor importance. Therc are also certain requirenients that depend largcly on thr: nature of pigments used, such as color pertnanency boward light, heat, alkali, acids, water, hot paraffin, foodstuffs, various adhesives, ctc. Ihxtunately all these ti~irigsneed not he considered for any one ink. A careful classifieatioii of all materials used in ink making, aecording to their properties, makes correct fonnuiatioii simpler than it seems to the layman. INK VEHICLE8
Ink vehicle has mure influence 011 working properties of inks then niost. idher ingredients. The way in which its consistency and wetting power for pigrnents affect ink properties has alrrsdy been explained. Snks that dry by absorption usnally contain vehicles consisting of petroleum oils,
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resins, a r i d ~iossiblywaxefi. Hald-dryirig inks that do ,rot entirely iieperrd OII nbrorptiori for dryiirg usually contain pdyrocrizi~d linseed oil that, may vary in consistency from that of tlir raw oil to a lung sticky inaterial that will barely Bo\v. (:ruobinabions of resins arid drying Oils are wed for glos.: inks, and other cornliinatiotw frir special requirements. l’rimwrs i’ri~rtingink pigments are too numerous to list. It is tiecessary t,o use approximately eighty to ninety pignicnts, including whites and blacks, in urder to obtaiu desired color, perin a n e n c y , and price, and to m e e t o t h e r specifications listed shove. Xearly ail the colors and w h i t e p i g m e n t s used in paint are also used in inks, altlrongli the paint. pigm e n t ~conaisting of largesized p a r t i c l e s , such as n a t u r a l iron o x i d e s and liarytes, are too gritty for ink m a k i n g . Lead clrromates, iron bhies, insoluble dyes (especially azo), plrosphrmolyhdic and phmphot u n g s t i c l a k e s of b a s i c dyes, and t h e calcium, Irarium, and a l u m i n u m lakes of acid dyes are the general classifications which
