Briefly introduce the knowledge about lithographic printing ink

Because lithographic printing is based on the principle of immiscibility of oil and water, and it is a typical indirect printing, the lithographic offset printing ink matched with it has some different properties from the relief printing ink. In principle of formula design of ink, first of all, it must be considered that lithographic ink will frequently contact with water during the printing process, and the ink should have strong water resistance to prevent excessive emulsification of the ink. This requires that the pigments in the ink must be strong water-resistant pigments, that is, insoluble in water and solvents, otherwise the pigments will break away from the binder under the action of mechanical friction during the printing process and dissolve in the fountain solution, resulting in non-graphic prints Partial coloring affects quality; due to indirect printing, the transferred ink layer is relatively thin, so the coloring power of the pigment is required to be strong, and the proportion of pigment in the ink is appropriately higher (not higher is better, in many cases, the pigment content exists (Critical value); In addition, the dispersibility of the pigment is also required to ensure the fluidity of the ink. The link material is the heart of the ink, especially for the offset ink link material. If the water resistance of the binder is not good, it will cause serious emulsification, cause poor ink transfer, and will also affect the drying performance of the ink. In addition, the color, viscosity, and pH of the binder will have a significant impact on the properties of the ink. Generally speaking, the greater the molecular weight of the binder, the better the water resistance. The oil-based binder used in the past was mainly linseed oil, which has poor water resistance and slow drying, and has been rarely used. Today's offset inks use a variety of resin binders.

Lithographic printing inks can be divided into sheet-fed offset printing inks, web offset printing inks, iron printing inks, tube printing inks and special lithographic printing inks according to the types of substrates.