Reference Book
Ink - Ingredients, Properties and Manufacturing
Ink is a coloured coating used to place a printed image on a substrate. Ink has
several properties that can affect print quality. Ink is formed by a mixture of
three ingredients- pigment, vehicle and additives.
Ingredients in Ink
Pigment:- It provides the colour of an ink. Pigments are of 4 types - Black
pigment, white pigment, organic colour pigment, inorganic colour pigment.
Black pigments are produced by burning natural gas and oil on to a collecting
device. The by-products from the burning process are called thermal black and
furnace black.
White pigments are sub divided into two groups - opaque and transparent
pigments. White ink containing ‘opaque pigments’ (through which light can
not pass) is used when transferring an image to cover a substrate or when
overprinting another colour. Opaque whites are also used for mixing with
other inks to lighten the colour or hue.
‘Transparent’ white pigments (through which light can pass) are used to allow
the background material or ink to be seen.
Organic pigments are derived from living organisms. All organic pigments
contain carbon and hydrogen, and most are made from petroleum; however,
coal, wood, animal fats and vegetable oils are also used in organic pigment
manufacture. The major advantages of organic pigments over inorganic
pigments are that organic pigments provide a wider selection of colours, tend
to be richer in colour, brighter, more transparent and purer than inorganic
pigments. These qualities are important for four-colour printing.
Inorganic pigments are made from minerals and are classified according to
their chemical make up - chromes, cadmiums, irons and earth colours.
Vehicle:- Vehicle is a binding agent that holds the ink together. It also carries
the pigment. Vehicle is often a solvent resin or oil resin combination. Now-a-
days soya based paste inks are widely used.
Additives:- Ingredients such as drier, lubricant, wax or starch are added to the
ink to impart special charactristics such as tack, workablility and drying time.
Properties of Ink
Viscosity:- is the resistance to flow under applied force. Lithographic and
letterpress inks have high viscosity because they are paste like. Flexo and
gravure inks are less viscous. Viscometers are used to measure the viscosity
of liquids.