Where Does Ink Come From?

Mixtures of vehicles and coloring matter, transferred by a mechanical printing press from a bulk state to form an image on a surface, are considered printing inks. Their basic composition varies according to the transfer or printing process used. 

Today, practically all printing falls into one of three process classifications: typography or letterpress; lithographic, also known as planographic or offset, gravure, which may be called intaglio, photogravure, or rotogravure. 

In typographic printing, ink is applied to a raised and designed surface of the metal or a raised rubber surface in the separate kind of letterpress designated as aniline or flexographic printing. An impression is made, most commonly on paper, from this raised surface. 

Lithographic printing applies ink to a plane-metal or stone surface that has been previously treated to accept the ink only in certain desired areas; an impression is made from those ink areas on another surface.

This gravure process employs an etched or engraved depression below the printing plate’s surface; only the depression is filled with ink, which is subsequently transferred to another surface by contact, making an impression of the engraving.

The primary consideration of the formulator of printing inks is the method or printing employed. Highspeed rotogravure magazine presses use a thin fluid of low viscosity. The process calls for an ink easily applied to miniature, etched cells below the printing-plate cylinder’s surface that can be wiped from the unetched portion efficiently and transferred to the printing surface instantly upon contact.

Since gravure ink dries mostly by evaporation and only partly due to absorption by the paper, highly volatile solvents are used in the vehicle. The resin or binder in the vehicle dissolves thoroughly in the solvent and, after mixing the pigments, leaves an impression upon transmission that dries rapidly and is not sticky.

A gravure ink is another type, one for steel – or copper-plate engravings, employs an entirely different vehicle of a short, butterflylike consistency. It is greaseless because, after the line engraving has been filled with ink, the excess must be thoroughly wiped off the plate’s unengraved surface without distributing the ink in the engraving. 

Since hard papers are the usual printing surface for this slow, exacting process, absorption is responsible for minimal drying. Slower drying solvents are used so that the ink will not dry up in the engraving. However, the solvent is volatile enough and the binder hard enough for the ink to dry thoroughly without stickiness. 

Except for flexographic inks used with a rubber type and “Vaporin” inks, dried with controlled gas flames, typographic and lithographic inks rely little upon evaporation for drying. Generally, typographic inks have a high viscosity and a long or “stringy” body, with tack or stickiness when on the press. 

Lithographic inks are even heavier, but shorter or less stringy, and possess considerable tack. The vehicles for these inks seldom contain volatile solvents. Bodied oils or resinous varnishes with driers are used as vehicles. They dry primarily by oxidation. Linseed oil, linseed-oil-bodied varnishes, tung oil, and soybean oil are typical ingredients in such inks. 

Flexographic and flame-drying vehicles are more like gravure; they contain some volatile solvents. The viscosity of these vehicles is controlled by the amount of solvent and kind of binder used. The end use of the printed product also plays a part in determining the composition of the vehicle. 

A magazine ink, for example, would not be suitable for printing cellophane candy wraps as the vehicle would not adhere satisfactorily and might be softened by the ingredients of the candy. Such characteristics as gloss, flexibility, odor, clarity, resistance to scratch, rub, abrasion, and chemical action dictate a vehicle’s components.

The pigment is the coloring matter of ink. This is a solid portion which remains undissolved unless dyes are used. It is ground into extremely fine particles as it is thoroughly dispersed within the vehicle. Some inorganic pigments, including hydrated oxides of iron, chalk, white, and China clay, occur in nature and require only crushing, washing, and cleaning to be used in inks. 

Important manufactured inorganic pigments are chrome yellows, iron blues, molybdate orange, cadmium reds, and titanium dioxide. Organic pigments are insoluble colors manufactured from natural or synthetic dyestuffs. Hansa and benzidine yellows, methyl violet and peacock blue, eosin, phloxine, and lithol- reds are common pigments of this type. 

The blacks used in printing inks are carbonaceous, carbon black, furnace black, and lampblack, with few exceptions. A bronze powder of aluminum, copper, or alloy bronze is used to produce a metallic effect. A pigment’s presence affects the ink’s properties, such as gloss, opacity, consistency, resistance to fading, durability, and the impact of grease or soap. The use of printed material limits the choice of pigments.

Click here for more information about printing ink.