The printing plate is mainly rubbed arabic glue.
Gum arabic is a solid crystalline object that absorbs water when it is soaked in water and eventually becomes a viscous colloidal solution. After the liquid colloid rubs on the printing plate and the water evaporates, the glue liquid returns from the liquid state to the original solid state and is adsorbed on the plate surface. Its function is that after the glue is dry, it is covered with a hardened film on the plate, and the plate is isolated from the air so as to prevent oxidation from becoming dirty.
Gum arabic contains arabic acid (X-COOH). This acid is a good cleanser for removing greasy stains on the plate. The effect of the glue on the plate is greater after drying.
After the plate is rubbed with gum arabic, the glue solution is in contact with the plate inorganic salt layer to form a layer of a better hydrophilic film and improve the hydrophilicity of the plate.