Ink is transferred from a plate or stencil to paper some other material during the printing process. The ink forms the image on the printed product. Over two thousand years ago, the Chinese made and used inks to print from wood blocks.
Most printing inks consist of pigments, vehicles, and modifiers. Pigment is theingredient that provides the color of the ink. Many pigment colors are produced from rocks and clays. Others can be traced to plants, sea life, or even insects. Several pigments may be blendedtogether to obtain adesired color ink.
The vehicle is the fluid that carries the pignent. Oil, lacquer, alcohol, and water are all used as ink vehicles.
Modifiers may added to ink for certain desired characteristics. For example, driers are added to speed up the drying process. Waxes used to minimize setoff. Setoff refers to the transfer of ink from a freshly printed sheet to the back of the sheet above.
Figure 9-4 shows the key steps in the manufacture of printing inks. Ingredient preparation includes selecting and processing the required pigments, modifiers, and vehicle prior to mixing.
Ink is usually mixed in batches. The required quantities of all ingredients are blended in an ink mixer.
The blended ink mixture is then transferred to a mill or grinder. Here the size of the solid particles in the mixture is reduced for better distribution throughout the vehicle.
Testing follows grinding. The ink is tested to insure that the batch of ink will behave as it is supposed to under actual printing conditions.
Packing is the final step in the manufacture of printing inks. Inks may be packaged in tubes, cans, or drums. Where a large quantity of ink is required, such as in newspaper produciton, tank trucks may be used to deliver the ink to the customer.
MIXING INKS IN THE SHOP
Two or more inks can be mixed together to obtain a desied sade or color of printing ink. Mixing is generally done on a slab of glass with an ink knife or spatula.
Several manufacturers now offer a kit containing six to eight different colors of ink, a color chart,and instructions. With such a kit it is possible to mix more than 400 different colors of printing ink.
SELECTING THE RIGHT INK FOR THE JOB
Each printing process requires the use of an ink developed specifically for that process. Letterpress, gravure, lithographic, and screen-process inks are specially formulated to match the requirements of the printing process. For example, letterpress inks are designed to distribute evenly over and well to raised plate surfaces. Gravure inks are quite fluite fluid and dry rapidly. Lithographic inks are formulated so as not to absorb or combine with the fountain solution in the press. And inks used for screen-process printing will have the consistency of thick paint, which is usually required in this process.
Another consideration when selecting an ink is the eventual use of the printed item. For example, ink on items used outdoors must be able to witthstand the weather. Ink printed on fabrics should hold up under repeated washings. Food packages should be printed with an odorless ink. And products that will be handled by young children must be printed with non-toxic inks.