Ink is a colored liquid, powder, or paste used for writing, drawing, or printing. There are thousands of kinds of inks, many of which are used for printing newspapers, magazines, and cartons and other packaging, or for writing with ballpoint pens and fountain pens. The printing industry uses more ink and more kinds of ink than any other industry.
Most inks consist of a colorant and a liquid or paste vehicle. The colorant provides the ink’s color. Colorants are made from dyes, which dissolve completely in the vehicle, or from pigments, which remain suspended in the vehicle. Among the most widely used pigments are black pigments called carbon blacks. Carbon blacks are made from the soot that is produced by burning petroleum or similar fuels in limited supplies of air. Other commonly used dyes and pigments include phthalocyanine (blue or green), ultramarine (blue), iron oxide (red), lead chromate (yellow or orange), and titanium dioxide (white).
The vehicle carries the colorant and helps bind it to the paper or other substrate (base material). Vehicles consist of colorless solids or semisolids called resins dissolved in liquids called solvents. Most of the resins used in inks are synthetic substances. Alcohol, petroleum, and water are popular solvents. Oils used as solvents include mineral oils and such vegetable oils as tung or linseed oil.
Writing inks
include those used in ballpoint pens, fountain pens, and special pens used by artists. Most writing inks consist of dyes and resins dissolved in a solvent that has little odor. The most commonly used solvents are water and glycols or similar alcohols. Most writing inks dry when the solvent has evaporated and the paper has absorbed the colorant and resins.
Different kinds of pens use different kinds of inks. For example, ballpoint pens use a thick, sticky ink. This ink is designed so that it does not leak around the tiny, rotating ball that transfers the ink from the pen onto the paper. Certain ballpoint pens use inks that may be easily erased. Such inks contain pigments and, unlike most writing inks, are not readily absorbed by the paper. Instead, the resin at first binds the pigment only to the surface of the paper. The resin and pigment can then be erased without damage to the paper.
Most pens other than ballpoints use highly fluid inks. Ink for a fountain pen, for example, must flow easily through a system of thin tubes leading from the ink reservoir to the nib (point). Most fountain pen inks consist of iron compounds mixed with tannic acid in water.
Printing inks
generally contain pigments instead of dyes. Vehicles used in printing vary greatly. Printing inks differ depending upon the method of printing. Some printing presses, such as those used to print books and magazines, require thick, sticky inks. Other presses use ink that is much more fluid.
Different printing inks dry by different processes. Some are passed through heated rollers or dryers that evaporate the solvent. Some inks are heated and then chilled to dry in a process called solidification. In absorption, the vehicle seeps into the paper and leaves the pigment trapped by fibers at the paper’s surface. In oxidation, resins and oils in an ink react chemically with oxygen in the air to form a solid.
Computer inkjet printers use highly fluid inks that contain pigments or dyes. Most inkjet printers use small droplets of ink to reproduce text and illustrations. The computer instructs nozzles in the printer to spray the proper pattern of ink droplets on the substrate. Once the ink reaches the paper, it dries by absorption or evaporation. Laser printers use an electrically charged ink powder or liquid called toner. This type of ink sticks to magnetized areas of a cylinder inside the printer. The ink is transferred to paper, which then passes through heated rollers. The heat causes the ink to adhere permanently to the substrate.
History.
The ancient Egyptians and Chinese used inks at least as early as the 2500’s B.C. They made their inks from various natural materials, such as berries, bark, linseed oil, and soot. Other early inks were made from galls (abnormal growths) on oak trees. Through the centuries, thousands of different formulas have been developed for inks. Today, most inks are made from synthetic chemicals.
See also Eraser ; Inkjet printer ; Invisible ink ; Pen ; Printer (Laser printers) .
