Analysis of the dirty and dirty of offset printing fault (2)

Three paste version

Paste printing refers to the lines and lines of printed graphics, between dot and dot, and highlights should not be dirty with ink, but sometimes it belongs to the category of dirty, and sometimes belongs to the dirty category.

In the printing process, often judged according to the following conditions:

(1) The position with dirt is determined, but the darker ink is definitely dirty.
(2) Dirty positions often change, but the ink is lighter and definitely dirty.

If the types of dirt on the layout are sorted out, then the fault can be handled accordingly.

Four dirty, paste, flower version failure analysis

During the printing process, the dirty, paste, and floral prints had the exception of the ink factor. Most of the rest, however, were of varying degrees of damage to the blank part of the printing plate and helped to separate the hydrophilic layer, but the form was different. The specific factors are;

(1) The strength of the wetting fluid is too weak. The wetting fluid is too weak in acidity, and the hydrophilic salt layer is generated slowly. The inorganic salt layer in the blank portion cannot be supplied and replenished in time, so that the hydrophilicity and oleophobicity of the blank portion is reduced. Acidity is too strong, there is corrosion on the printing plateau, destroy the hydrophilic salt layer, easy to make the plate under the pressure friction shine, resulting in dirty, sometimes flower version.

(2) The aging of the ink roller makes the printing plate greasy and the printing plate ink roller aging, the hydrophilic property is strong, and the ink transmission performance is poor. In the mechanical rolling, the water is dispersed in the ink in the form of fine droplets, due to water and ink. The immiscible principle makes the ink on the ink roller emulsified, the viscosity of the ink is reduced, and the adhesive force is reduced. The ink can easily fall from the ink roller onto the blank part of the printing plate, so that the hydrophilic salt layer produces lipophilicity, resulting in the greasy printing plate and Graphic part of the flower version.

(3) The pressure between the water roller and the printing plate is too large, which causes the printing plate to produce dirty oil and the stencil containing the acid wetting liquid. The driving force of the water roller is under the effect of pressure and depends on the surface friction force during the transmission process. Due to the compression and deformation of the water roller and the plate cylinder, there is a certain linear velocity difference, so that the surface of the water roller and the printing plate is rubbed, the sand mesh is destroyed, and the stability of the inorganic salt layer is also destroyed, so that the blank part is easy to feel fat. Produce a dirty version. Therefore, the contact pressure between the water roller and the printing plate must be properly adjusted.

(4) The pressure between the ink roller and the printing plate is so large that the blank part is dirty. The graphic part of the ink roller has a large number of friction with the printing plate, and the roller has ink on it. Some of the ink filler particles act as abrasives, resulting in printing. Part of the blank part of the dirty, graphic part of the flowers.

(5) The ink pressure on the printing plate is too small. When the ink pressure on the printing plate is too low, the ink transferred to the printing plate is reduced accordingly. The ink on the plate graphics part is less, and the printing plate does not get enough ink. In the case of layers, the graphic part is subject to wear and tear, and over time the pattern is created.

(6) Excessive pressure between the plate cylinder and the blanket cylinder will cause the plate to be dirty, and increase the pressure between the plate and the plate cylinder and the blanket cylinder when the pressure between the plate cylinder and the blanket cylinder exceeds the specified value. Extrusion force, plate sand gradually flattened to reduce water storage capacity, began to produce stencil, after printing to a certain number, sand polished, the printing plate shines, the foundation of the outlet was also destroyed, and the emergence of the flower version . The shortcomings from the initial paste version to the final version seriously affected the printing quality. At this time, the printing pressure and lining must be readjusted.