Offset press processing highlights

Ten, the cause of oil dirty

Dirty oil can be divided into two categories: one is due to the blank part of the layout of the ink fat, greasy state, commonly known as "greasy"; the other is due to the ink emulsified with fine particles evenly distributed in the layout, commonly known as " Dirty."

The causes of dirty oil are:

(1) Plate

a. The printed version is not of high quality (bad edition or recycled version);
b. Insufficient exposure time during exposure and developer concentration too low;
c. The printing plate surface protection glue is not clean;
d. The blank part of the plate is oxidized;

(2) Printing presses

a. Pressure on the plate is too light;
b. The pressure between the rollers is too light;
c. The viscosity of the ink is too low;
d. Aging of the blanket surface;
e. paper powder and paper wool wear plate;
f. Fountain solution pH is not proper.

XI. Causes of different shades of ink before and after

In actual printing, we sometimes find that the ink on the same screen is different in depth before and after, and often the ink is darker and lighter than before, and the ink is lighter and darker. The reasons for the inconsistency of ink color before and after are as follows:

(1) Roller section

a. Roller gear or bearing journal wear for a long time.
b. The drum journal is not the same as the drum shell.
c. Relying on the plate roller and plate pressure is too heavy, which causes a jump.

(2) Ink roller section

a. The use of aging old ink roller surface b. Ink roller can not be cleaned for a long time, the surface area of ​​ink, can not be inked c. Ink viscosity is too high.

XII. What is the production of ink bars and how can they be eliminated?

The ink stick refers to the appearance of a deep stripe mark in the plate layout and on the print when printed on the flat screen or in the field, commonly known as "black bar" or "black bar".

The causes of ink sticks and their solutions are:

(1) The roller gears wear out for a long time and a new set of new gears should be replaced;

(2) The printing pressure is too high or the pressure between the plate cylinder and the blanket cylinder is too high. Should adjust the appropriate pressure;

(3) Paper, ink, and other dirt are embedded between the gears. Should remove all kinds of dirt between the gears, add new gear lubricants, and strengthen the cleaning and maintenance of the machine;

(4) The pressure between the printing plate and the printing roller is too large, and the pressure of the printing roller and printing plate should be adjusted;

(5) If the surface of the reversing roller is uneven or the roller core is bent or not straight, a new ink roller should be replaced;

(6) If the ink is too thin, an appropriate amount of 0# varnish should be added to enhance the viscosity of the ink;

(7) Paper is rough and surface strength is poor. Should wash the blanket, and add 6 # ink in the ink to reduce the viscosity of the ink, reduce the degree of paper powder, hair loss.

XIII. How to solve the problem of water plumbing?

The water bar refers to the appearance of a thin strip in the axial direction of the printing plate and the printed part when printing plain or solid prints, commonly known as "white bars" or "white bars".

The water bar is generally caused by the water delivery section. The causes and solutions are:

(1) The pressure between the upper roller and the main uniform ink is too high, and the pressure between them should be readjusted to make it appropriate to relieve some of the pressure;

(2) ink emulsification, water roller surface too much ink;

(3) If the layout is too large, reduce the amount of water supply, clean the blanket, and clean the ink roller when it is severe;

(4) The dampening water is too acidic and the dampening water's acidity should be reduced.

Source: Guangdong Printing