Sangeetha Pulapaka

Inks occupy an integral and versatile position in our daily lives. Our day begins on sleepy note with newspapers and toiletries to breakfast table which is replete with several ink-labelled, packaged consumer products such as tea or coffee, bread, butter and then gradually moving to ouir work places –schools or offices which have myriad ink laden products be it books, calendars, photocopies, computer prints, stamps or even money, ink is found everywhere. Generally, ink is an organic or inorganic pigment or dye dissolved or suspended in a solvent. However, chemically, it is viewed as a colloidal system of fine pigment particles, coloured or uncoloured, dispersed in an aqueous or organic solvent. 

There is a misconception that ink is harmless, however ink can be hazardous and can cause headaches, skin rashes and damage to the nervous system. Many chemicals used in inks can be dangerous to the environment, the ozone layer and ground water.

Today’s inks comprise two classes: printing and writing inks. The former is further broken down into two subclasses: ink for conventional printing, in which a mechanical plate comes in contact with or transfers an image to the paper or object being printed on; and ink for digital nonimpact printing, which includes ink-jet and electrophotographic technologies. Over 90 per cent of inks are printing inks, in which colour is imparted by pigments rather than the dyes used in writing inks.

Color printing inks primarily consist of linseed oil, soybean oil, or a heavy petroleum distillate as the solvent (called the vehicle) combined with organic pigments made up of salts of nitrogen-containing compounds (dyes), such as yellow lake, peacock blue, phthalocyanine green, and diarylide orange. Inorganic pigments (used to a lesser extent) in printing inks include chrome green, Prussian blue , cadmium yellow, and molybdate orange. White pigments, such as titanium dioxide, are used either by themselves or to adjust characteristics of color inks. Black ink is made using carbon black. Most red writing inks are a dilute solution of the red dye eosin. Blue colour can be obtained with substituted triphenylmethane dyes. Many permanent writing inks contain iron sulfate and gallic and tannic acids as well as dyes.

 Inks also contain additives such as waxes, lubricants, surfactants, preservatives, wetting and drying agents to aid printing and to impart any desired special characteristics. Other inorganic materials such as clays serve as fillers or extenders, which primarily reduces the cost of pigments, though some also improve ink properties. Metallic pigments like aluminium powder (aluminium bronze) and copper-zinc alloy powder (gold bronze) are used in novel silver and gold inks. Miscellaneous inorganic pigments provide luminescent and pearlescent effects. The major classes of printing processes are lithography or the offset process, flexography, gravure printing, screen-printing, letterpress and digital printing. The composition of printing inks depends on the type of printing process - specifically, how the ink distribution rollers are arranged in the printing press

Heavy metals that can be found in inks include lead, cadmium, chromium, mercury, antimony, barium, selenium, silver, nickel, copper and arsenic. Interestingly, small amounts of some of these metals are necessary for good health, but in larger amounts they can be poisonous.

 Chemicals: toluenetitanium acetylacetonate and phthalates in the printing of packaging materials used for food products.