The history of printing, which by its very nature is the most thoroughly documented of any history, is practically identical with that of relief or letterpress printing (printing from a raised surface). Historically, the bulk of all printing has been produced by this entirely mechanical method. Modern printing, however, increasingly relies on photomechanical and chemical processes. The enabler for all the processes are binder systems carrying colorants, which are able to transfer from a subject to a substrate.

Printing in the East

The earliest surviving examples of Chinese printing, produced before A.D. 200, were printed from letters and pictures cut in relief on wood blocks. In 972, the Tripitaka, the sacred Buddhist scriptures comprising more than 130,000 pages, was printed entirely from wood blocks. The blocks were inked with water soluble inks which had been used for writing the original manuscripts.

Printing in the West

Movable metal type was first cast in Europe and printed with a printing press on paper by the middle of the 15th century. The invention appears to have been unrelated to earlier developments in the Far East, and the techniques differed considerably in detail. Whereas Eastern printers had used watersoluble inks, Western printers used oilbased inks from the beginning. In the East, printers made impressions simply by pressing the paper against the wood block with a flat piece of wood. The earliest Western printers in the Rhine River valley used mechanical presses derived in design from winepresses and made of wood. The Eastern printers who had used movable type held the letters together with clay or with rods pushed between the type. Western printers developed a technique of casting types with such precision that the letters could be held together by pressure applied to the edges of the tray containing the type for the page. In this system, a single letter a fraction of a millimeter too big could cause the letters surrounding it to fall out of the page. The development of a method of casting letters to precise dimensions was the essential contribution of the Western invention. The principals involved in printing had been used by European textile workers, in printing designs on cloth, for at least a century before printing on paper was invented.

Johann Gutenberg, of the German city of Mainz, is traditionally considered the inventor of Western printing. The date associated with the invention is 1450. Both Dutch and French historians of printing have attributed the invention to people in their own countries and have produced considerable supporting evidence. The books of the first Mainz printer, however, particularly the book known as the Gutenberg Bible, far surpass in beauty and artisanship all the books that reputedly preceded them. The ink played a considerable part in this success. The blackness of the print made from wooden blocks using water-type inks being brown and washy by comparison. An entirely new ink preparation had been used. The water-based inks where totally unsuitable for wetting the new metallic type and due to the low viscosity resulted in poor reproduction. Gutenberg and later Caxton with others, examined alternative materials and developed their own inks. The precise details of the composition of theses inks remains a mystery to this day, although their basic formulation is known.

Until the 15th century, the medium that artists were using for painting pictures was tempera. The pigments were ground with water and yolk of egg was added to provide a binder. The paint was usually applied to an absorbent surface, such as plaster or wood. Drying oils helped to overcome some of the restrictions. The processing of linseed and walnut oil by heat allowed to produce oils with various viscosities. Gutenberg found a great basis in those oils and developed his own inks. His inks mainly included linseed oil, walnut oil, turpentine, rosin, pitch, Venice turps, lamp-black and vermillion.

In the 16th century the refinement of linseed oil by heat was a well-established process to produce inks. Raw linseed oil on heating could be clarified. Mucilage separated and was removed by throwing bread into the hot oil which mucilage adhered. Litharge was added producing a quick drying unbodied oil. Longer processing time increased the body of the so-called varnish. These varnishes could be modified by adding rosin.

By the beginning of the 17th century water-based printing inks were obsolete, and all inks were being made from drying oils and resins, the formulation of which changed little for the next 300 years.

By the end of the 1700s the demand for print in all forms had increased to such an extent that the printer found ink making an irksome, time-wasting time. This encourage the start of independent inkmakers. This also opened the way to a much greater use of colors. Colored inks had been little used since the printer found them more difficult to make. Colored pigments were minerals as used by the artist painter. Not only were these difficult to grind to a fine enough powder, but each color required its own proportion of varnish.

Lithography

By far the most important and versatile printing process today is offset lithography. The underlying principles were established at the end of the 18th century by a German map inspector, Alois Senefelder, who was experimenting with methods of producing limestone relief printing surfaces using an acid etching process. Senefelder found that a wet limestone surface would repel an oilbased printing ink, and that an image drawn on the surface with a grease pencil would repel water and attract ink. Any drawing on the stone surface could be reproduced by bringing a damp sheet of paper into contact with the freshly inked image. This cycle could be repeated several hundred times before the drawing could no longer be faithfully reproduced.

The process, called chemical printing by Senefelder, quickly became a popular art medium because it enabled artists to produce multiple copies of freehand drawings. Inks had to be modified and more carefully formulated to resist the water successfully. They continued however, to be based on linseed oil and rosin with the addition of waxes and other additives to improve printing qualities. Emulsion properties and water release of the inks became very important.

Offset Lithography Today

The function of the original stone printing surfaces is now served by thin aluminum plates, although other materials, such as stainless steel and plastic, can also be used. The plates are wrapped around the circumference of the printing cylinder and make direct contact with the rubber blanket cylinder. Rubber rollers carry ink and water to the plate surface. The ink is transferred first to the blanket cylinder and then to the paper.

With today’s printing techniques, there are several different ways in which printing may be accomplished, such as lithography, letterpress, flexography, gravure, and screen printing. All these printing techniques use simple mechanisms for rapidly applying colorants to substrates such as paper or plastic to form multiple reproductions of original images for mass distribution.

Multiple colors can be printed in one pass through the press. Spot color printing uses custom mixed inks to reproduce specific colors and is widely used in package printing, where large areas of uniform color are common. Process color printing uses four transparent inks-cyan (bluegreen), magenta (red), yellow, and black-printed one on top of another in varying amounts. Color photographs and other artwork can be faithfully reproduced by this method.

Modern Printing Ink Composition

Printing Ink is a complex mixture of ingredients that are combined in a specific formulation to meet desired characteristics of the printing application. Ingredients in no-heat inks (Coldset or newsprint) fall into four classifications: pigments, resins, oils or carriers and additives.

Historically newsprint inks are based on petroleum derivatives, however with rising prices in the 1980th alternative oils were explored. Soybean oil was successfully tested in 1987 at The Gazetta from Iowa/USA. The SoySeal is now regulated by the America Soybean Association. Todays ink manufactucturer are using both technologies, depending on cost structure, paper qualities and customer requirements.

Black Newsink

The function of the pigment is to provide the coloristic properties of the inks. The resin is added as a dispersion aid and as a binder to affix the pigment to the paper. The oil or carrier is the medium for transferring the pigment and resin through the press to the paper. Additives are used in no-heat inks to control pigment wetting and dispersion, viscosity and flow characteristics, as well as to provide a proper ink/water balance.

To review these ingredients in more detail, a comparison between Letterpress and Web Offset is provided:

Typical Black Formulation

The table shows typical black formulations for both printing techniques. The ingredients used in these types of formulations are both similar, however they are different in concentration.

The pigment used in new black is carbon black. Carbon black is produced by cracking oil in a continuous furnace. The furnaces are highly controlled in order to produce a specific grade of pigment varying in particle size and structure. The oil used is also of a specific grade so that certain requirements can be met. The ink film thickness applied by the printing application dictates the concentration of pigment needed to meet the required print density. Therefore, the web offset formulation has a higher concentration than the letterpress. This is because the letterpress printing process applies a much thicker film of ink than web offset.

Resins for news inks vary depending on the rub off quality that an ink requires. The resins are the most expensive part in news ink black, so their selection and concentration are limited by economic constraints. The chemistry is mainly based on modified rosin and hydrocarbons. The oil or carriers used mainly in today´s news black are threated petroleum oils. These oils are non-drying. The drying process of a news ink is by absorption of this oil into the paper stock. Changes in the absorption characteristics of a newsprint can drastically affect the run off quality of the finished products also.

Typically, newspaper presses are not temperature controlled nor are the rollers washed up at the end of the run. If any volatile material was used, the ink would tend to dry on the roller train and cause problems.

Additives used in news black are form a variety of different materials. News ink black will require different viscosity or flow characteristics depending on the type of press used. The ink is also required to provide a proper emulsification rate so that the web offset printing process will work. If a formulation did nor accept any fountain solution, the ink would not transfer to the plate and stripping would result. If an ink emulsified too much fountain solution, high dot gain / tone value increase and poor print quality would result. In extreme cases, ink would tend to go to the non-image area of a plat and scum.

Colored Newsink

The pigments used in news inks colors are classified as organic pigments. These are organic materials that are formed under specific conditions to produce the desired characteristic of color and crystal size. The typical pigments used are phthalocyanine blue for cyan, lithol rubine for magenta, and diarylide yellow for yellow. Pigments for the printing ink industry are supplied in form of dry powder or in the form of heavy concentrated bases or “Flushes”.

The resins used for colors tend to be much cleaner in color than those used for black inks, so that the printed color can reflect its truer color. The oils used by the newspaper market today are from petroleum oil or from the vegetable family.

Color printing inks also use extender pigments. The pigments are typically kaolin type clays and provide functional properties to a given formulation. The additives used will be like in black inks.

In modern printing processes and high-speed production processes, inks are undergoing a significant shear stress. They must maintain their designed properties during the delivery process from the manufacturing process to press, from the ink duct to the plate, and finally from the blanket to the paper substrate.

This graphic illustrates a typical process flow from bulk delivery to finished printed product.

Literature

R.H. Leach, R.J. Pierce, The Printing Ink Manual, fifth edition, published by Blueprint, an imprint of Chapman & Hall, 2–6 Boundary Row, London SE1 8HN, UK, ISBN 0 948905 81 6

Dennis Cheeseman, US Ink’s Press Doctor, SunChemical Corporation, 35 Waterview Boulevard, Parsippany NJ, 07054-1285, U.S.A.