Common offset ink failure analysis - dirty

One, dirty

Generally refers to the non-graphic area to produce dirt. It also includes the phenomenon of imprinting auxiliary, paste, and even dot network. However, the dirt can be divided into two kinds of situations: floating dirt and oil dirt. The breakdown is as follows:

1, floating dirty phenomenon

Dirty stains are produced in non-graphic areas and are not easily stained off because they are not printed on the plate.

Reasons: (1) The main reason is that the ink is relatively soft, some of the inks are emulsified into the fountain solution after the action of the fountain solution, forming an oil-type emulsion in water. (2) Chemicals and wetting agents in the paper promote ink emulsification. (3) The fountain solution contains soaps or detergents to cause ink emulsification.

Treatment methods: (1) Replace the hard-emulsified ink with high viscosity and thick, or add high-viscosity varnish to the original ink. (2) Change paper. (3) Adjust dampening fluid composition and pH.

2. Dirty phenomenon

The non-graphic area of ​​the printing plate becomes fat-sensitive, and the ink adheres to it, contaminating the printed matter.

Reasons: (1) ink is soft and lean. (2) Too much ink. (3) Free fatty acids, resin acids, and surfactants are present in the ink. (4) The effect of the treatment agent in the pigment. (5) The pressure of the ink roller dampening roller and the blanket is too large, and the surface structure of the printing plate is damaged. (6) Dissolve lipids from the paper coating.

Treatment methods: (1) Replace the ink or add high-viscosity resin oil (or No. 0 oil) and gum oil to the original ink to make the ink sticky and elastic. (2) Adjust the ink supply. (3) Adjust the appropriate amount of fountain solution. (4) Use a fountain solution with a higher surface tension. (5) Adjust the pressure. When (6) replace the paper.

(to be continued)