Study on the Application of High-speed Rotary Offset Fountain Solution (in Chinese)

1.2.2 Isopropyl alcohol

The main component of isopropyl alcohol fountain solution is isopropyl alcohol. The fountain solution is characterized by the obvious surface tension of the fountain solution, which increases with the concentration of isopropyl alcohol in the fountain solution, and at the same time reduces the amount of water supplied by the fountain solution and avoids the amount of water as much as possible. The inconsistency of the ink color caused by the size; because the boiling point of isopropanol is lower than the boiling point of water, and the vapor pressure of isopropyl alcohol is higher than the vapor pressure of water, so the isopropanol evaporates while also taking away the water, Makes the water easy to stay in the ink, thus reducing the degree of emulsification of the ink in a certain range, also plays a role in promoting the ink-water balance.

1.2.3 Hydrocolloids

Hydrocolloids used in fountain solutions are gum arabic and carboxymethyl cellulose.

The arabic gum reacts with the acid in the fountain solution to displace the arabinic acid, which can be firmly adsorbed on the non-graphic surface of the printing plate to form a tightly packed colloidal film. The carboxyl and hydroxyl groups in the film are relatively The strong hydrophilic group shows strong hydrophilic properties; in addition, this layer of film can also act as a good anti-oxidation barrier.

Carboxymethyl cellulose, also known as sodium glycol glycol, has the characteristics of strong hygroscopicity, dissolving in water, transparent and colorless sol, reversibility, and stable performance. The role of carboxymethyl cellulose is the same as that of gum arabic. Under the action of the acidic fountain solution, carboxymethyl cellulose is displaced and a hydrophilic film is formed on the non-graphic surface of the printing plate to make water molecules be good. Adsorption on it, play a role in repelling ink.

1.2.4 Phosphoric acid

The role of phosphoric acid in the fountain solution is as follows: displacement reaction with hydrophilic colloids, generation of hydrophilic groups, enhanced adsorption properties on the surface of the printing plate; chemical reaction with the bare metal on the non-graphic surface of the printing plate, resulting in the formation of A layer of inorganic salt layer, repair and enhance the hydrophilic properties of the plate; phosphoric acid has anti-oil properties, can remove the non-image part of the plate surface of the oil dirty, and the metal plate surface cleaning effect.

1.2.5 Buffer solution

The buffer solution is a solution that can control the change in the acidity of the fountain solution. It is configured using the principle of the same ion effect. The same ion effect means that if an identical ion is added to the solution during the ionization process, the ionization equilibrium will shift, resulting in a change in the ionization equilibrium due to the influence of the common ions. According to the influence of the same ion effect on the degree of ionization and acidity of the acidic solution, a buffer solution can be combined and configured. The buffer solution is usually composed of an aqueous solution of a weak acid and its salt, a weak base and its salt, and an acid salt having a different acidity. A dampening solution with a buffer solution can form a stable solution. If the acidity in the fountain solution is too large or too small, it will affect the printing process and the printing quality. In order to avoid or reduce the change in the acidity value of the fountain solution during the printing process, some buffer solution is used to maintain the pH of the fountain solution. Stability.

2 Application and control of high-speed web offset fountain solution

In the high-speed, multi-color web offset printing process, maintaining a stable relationship between the fountain solution and the ink is to ensure that the print job runs and obtains high-quality prints with rich tone, rich colors, and clear graphics. The essential.

The scientific, correct and reasonable use of fountain solution is to control the performance of the fountain solution according to different printing conditions, environments, and different printing materials, fully play the role of the fountain solution, and stabilize the non-graphic surface of the printing plate. Hydrophilic function, in the premise of stable printing quality, minimize the amount of fountain solution. However, if the amount of the fountain solution is too large or too small, it will affect the printing process and print quality.

1) The amount of fountain solution is too large and the amount of ink is not large: This phenomenon is the most prone to occur in printing production, due to the fact that water is not likely to cause stain defects. However, the large amount of water in the printing results in thickening of the water film on the surface of the printing plate, and the moisture turbulence, shearing and squeezing between the ink rollers accelerates the emulsification of the ink and is easily formed. The phenomenon of oil-in-water emulsification not only affects the ink transfer quality, but also the ink imprint after printing is poor in saturation, dull in ink, emptiness of dots, and lack of image layers; while large water can also cause moisture absorption and deformation of the paper and affect the quality of overprinting. (to be continued)