Deep before and after shallow failure and ink structure analysis

When a sheet-fed offset printing machine prints a large area of ​​a graphic or a printed matter with a field version, the phenomenon of darkness and darkness of the same ink before printing often occurs. This phenomenon occurs in addition to the improper operation and adjustment, and the more direct reason comes from Influence on the layout and structure of the machine itself. 1. Effect of the roller structure When the ink roller is inked to the printing plate, when the ink roller is in the idle position of the plate cylinder, the ink roller does not ink, the ink volume accumulated on the ink roller is large, and then the roller rolls forward Each ink fountain roller is inked to the front plate position of the plate with the largest amount of ink. As the ink roller continues to roll ink, the amount of ink on the ink roller gradually decreases, and when it is rolled to the plate tip portion, the ink roller The amount of ink is already very small. This can easily cause darkness and lightness.

2. Influencing the arrangement of the ink roller The ink roller of the ink inking device is generally divided into two groups, ink inking and ink insulting. Different machines have different arrangement of the ink roller in the two groups. The evenly distributed ink roller is arranged in two halves. The four ink rollers are evenly inked. For the ink roller arrangement, if the ink roller is not properly adjusted, the last two ink rollers will not be able to refill the ink, even the ink, and recover excess ink. The role of the ink layer, the print is very easy to appear before the phenomenon of shallow depth. In addition, the ink roller has less ink before and after the ink roller. The first two ink rollers account for 90%, and the second two are 10%. Such distribution generally does not produce the deep and shallow phenomenon of printed ink.

3. Process remedies and precautions in operation

(1) The over-smooth aging ink roller should be replaced in time to ensure good ink transfer performance of the ink roller and sufficient ink storage on the surface of the ink roller, so that the ratio of the ink consumed in printing to the ink storage volume of the ink roller is as small as possible. This will enhance the ability of the ink roller itself to adjust the amount of ink and make the print ink uniform.

(2) Grasp the fluidity and viscosity of the ink, because the fluidity and viscosity of the ink directly affect the ink transfer speed and ink storage volume.

(3) Strictly control the layout moisture, prevent the ink from emulsifying excessively, and ensure the normal transmission and adhesion performance of the ink.

(4) For the even distribution type ink channel layout, when adjusting the pressure of the printing roller, the first two pieces should be heavier, the latter two pieces should be lighter, and the contact width between each Other should be generally adjusted from front to back to 6mm, 6mm and 4mm. , 4mm. The pressure between the ink roller and the ink roller should be equal to the contact pressure between the ink roller and the plate surface. Because the rotation of the ink roller should depend on the bilaterally equivalent friction force, if the pressure difference between the two sides is too great, the rotation of the ink roller on the surface of the ink roller or printing plate will become frictional sliding rather than pure frictional rotation, which will not only affect the ink The normal transmission also affects the even application of the ink roller to the plate.

(5) Increase the printing pressure by inserting paper in shallow ink, which can also play a certain remedial role.