Three common drying methods

First, osmotic drying

This drying is mainly accomplished by the absorption of the paper and the permeation of the ink. The mechanism can be explained as follows: Since the paper is a porous material interwoven by fibers, the pore size is small. When the ink is transferred to the paper, the binder in the ink begins to absorb the binder due to the capillary action of the paper fiber voids. In the absorption process, the composition and rheological properties of the ink gradually change, the liquid composition of the ink gradually decreases, the cohesive force of the pigment particles gradually increases, and the ink gradually loses its fluid properties and assumes a solid state.

Second, the oxide film drying

This dry form utilizes oxidative polymerization to convert the ink from a liquid state to a solid state. The mechanism is that the dry vegetable oil in the ink contains an unsaturated double bond and polymerizes into a polymer film through a peroxy bridge. Dry vegetable oils absorb less oxygen due to the presence of traces of phospholipid organic antioxidants during the induction of drying and the oxidative polymerization reaction is slow. When the antioxidant is destroyed, the oxygen absorption of the dry vegetable oil causes the methylene group adjacent to the double bond to react with oxygen to generate a hydrogen peroxide. Since the hydrogen peroxide is very unstable, it will be separated into two radicals in the light, one of which is carboxyl-OH. Since the free radical chemistry is very reactive, when it attacks another oil molecule, it generates a new radical. The original radical will generate a stable compound. Small molecules of this oil are then polymerized into macromolecules until there are no double bonds. The ink becomes a dry solid film of a polymer network structure.

Third, volatile drying

This dry form is accomplished by volatilizing the solvent in the ink binder to hold the remaining resin and pigment forming solid film layer on the surface of the substrate. Used for gravure inks. The rate of volatile drying depends primarily on the latent heat of evaporation of the solvent, the proportion of pigment, the size of the particles' radius, and the type of resin.

Fourth, other dry forms

1) Radiation drying

Radiative drying refers to the dry form of the ink that changes from liquid to solid by polymerizing the molecules of the binder by the energy of the radiation. Includes:

a: UV drying.

b: The electron beam dries.

c: infrared drying.

d: Microwave drying.

e: wet coagulation drying, condensation drying, precipitation drying, filter drying and the like.