M. S. Siddiqui
Printing ink is a liquid, semi liquid or solid material containing pigments or dyes and used to colour the surface to produce an image, text, or design. They are broadly categorised based on their application into three main segments: publication, graphics, and packaging. Ink designed for use in different writing instruments or printing methods have quite dissimilar components recipes for formulation of ink have been modified over the years.
Ink, for writing and printing, dates to 3200 B.C. when the Egyptians used lampblack suspended in vegetable gum. Egyptians and the Greeks used iron oxide to make ink from about 2800 B.C. Ancient, Chinese were making red ink (from mercury sulphate) and black ink (form iron oxide). Combinations with resins, preservatives and wetting agents are also used. Throughout history, ink has been made many different coloured juices and extracts of plants and animals as well as synthetic materials. Modern ink contains many substances aiming to improve ink characteristics. Chemical inks are a mixture and composed of colourants, vehicles and additives.
The requirements of good printing ink should consist of a viscous liquid which will easily transfer to the paper and not spread. It should dry quickly to avoid offsetting and it should be wiped easily from the plate or block. The Chinese, in the third century, made printing inks for woodblock printing on silk or paper. That ink was virtually identical to the writing inks of the time, a thin water-based fluid with gum Arabic as the binder.
Various types of printing ink are used in Bangladesh. The major printing processes are classified by the method of image transfer and by the general type of image carrier employed. Depending upon the process, the printed image is transferred to the substrate either directly or indirectly. In direct printing, the image is transferred directly from the image carrier to the substrate. Printing inks are also broadly distinguished by the printing process in which they are used. Flexographic and Gravure inks are called liquid inks and have lower viscosity. Letterpress and Lithographic inks are known as paste inks and have higher viscosity than liquid inks.
Traditional ink making involved labour-intensive processes, often passed down across generations. Ancient ink included ingredients like soot, honey, vinegar, and binders. The very first ink used charcoal or soot from the fire as the main pigment, hence why most of the early written works found were written in black ink. The black pigment used from earlier times would have remained relatively unchanged since the beginning of printmaking.
Changes in ink chemistry over the years closely reflect developments in the instruments for ink coating, the pen and the printing machine. At present inks are available in different categories slow drying ink, wax-free inks, transparent ink, and many others.
The ink is made of different coolants (dye or pigment) and additives. Some standard ink ingredients are pigments, dispersants, resin or polymers, and so on.
Based on a colourant used, inks are classified as dye and pigmented inks. Similarly, vehicle (water or solvent) used to manufacture inks also categorised the inks as aqua based and solvent based inks. Other additives ensure adhesion of the pigment to the surface and prevent it from being removed by mechanical abrasion. These materials are typically referred to as resin (in solvent-based inks) or binding agent (in aqua based inks). Pigmented inks have an advantage that less ink need to be used to create a high intensity of color as pigment stays on the surface of paper. Dye based inks are generally much stronger than pigmented ink and can produce much more color of a given density per unit of mass.
Oils, once used as a binder during the early fourteenth century, was purified by leaving it to stand for at least one year, so that impurities would settle out. In the nineteenth century, manufacture moved towards reducing costs and manual labour, and to the use of new technology. An elaborate filter was devised, and chemical methods were used to speed up the purification process.
Regarding resins and other additives, turpentine or rosin was added from earliest times. It prevented the ink from spreading and causing haloes to form around the lines of the printed image. It also improved the drying time. The use of turpentine and sandarac would also have greatly increased the viscosity of the ink.
When introduced to oil it is liquefied by the heat, but returns to a solid on cooling, thus producing suitable viscosity with less burning. The excessive use of rosin to reduce the production time and cost. Other additives such as driers were added to the oil such as litharge (lead oxide) to make the oil dry more quickly and that it made it thicker.
Ink is one of the essential materials of printing, and printmakers paid much attention to the quality of their inks, carefully guarding their recipes and handing them down through generations. Today’s ink industry uses highly developed technology, constantly having to adapt to new applications. This is very dynamic product with the changed technology and application of printing ink.
The writer is the CEO of Bangla Chemical
