Printing Ink Continued…

The vehicle for printing inks is generally linseed oil, soybean oil, or a heavy petroleum distillate. The colorants are either organic pigments such as phthalocyanine green and diarylide orange, or inorganic pigments such as cadmium yellow and chrome green. Black ink is colored with carbon.

Conventional Printing

There are several methods of conventional printing, and each type uses specialized inks.

Lithography – Lithography is also known as offset printing. Offset inks are generally oil-based and highly viscous. Offset printing is used for newspapers, commercial packaging, and many other applications.

Flexography – This type of printing is used on paper and some types of plastic. The inks used are either water or solvent based.

Gravure – In gravure printing, engraved cylinders press solvent-based liquid inks onto a substrate.

Letterpress – Letterpress printing uses oil-based inks that are highly viscous.

There are a number of specialty inks for specific purposes. Currency inks are highly pigmented and very viscous. Screen printing inks are used for many tasks, including packaging and labeling. Metallic inks are used in packaging to catch the consumer's eye with their sparkle. Thermochromic and photochromic inks change color when exposed to heat or light. These are used for packaging and for printing sensitive documents.

Soy inks were introduced in 1987 and have become popular for certain printing tasks. The vehicle for these inks is soybean oil. Soy inks are competitively priced and much more environmentally friendly than petroleum-based inks. A large percentage of the nation's newspapers are now printed with soy inks.

Digital Printing

An inkjet printer uses three colors of ink: yellow, magenta, and cyan. The printer creates an image by using a series of small nozzles to spray tiny droplets of ink onto paper.

Laser printers and copy machines use a dry ink called toner. A positively charged photosensitive drum is exposed to the laser or light source. This creates a negatively charged electrostatic image of the document on the drum. Then the drum is coated with the positively charged toner. The toner sticks to the electrostatic image, but not to the background. The drum then rolls over a sheet of paper and the toner is transferred to the paper. Finally, the paper is fed through a set of heated rollers that melt and fuse the dry toner to the paper.

By Carla Wakeman