Precautions and difficult issues in the printing process

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. Aging roller surface aging

b. The ink roller has not been cleaned for a long time, and the surface area of ​​the ink is too low for ink

c. Too much ink viscosity

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.

XIV. Why is the flower version eliminated?

The flower version refers to the narrowing and emptiness of the dots on the printing plate, the weakening of the sense of fat, the loss of fine ideas, and the dullness of color. The cause of the floral version and its elimination methods are:

(1) The pressure between the plate cylinder and the blanket cylinder is too large and the thickness of the cylinder liner should be reduced;

(2) The pressure between the water roller and the upper water roller is too small (water volume), and the pressure of the water roller and the water roller should be properly adjusted;

(3) The dampening water is too acidic, and it should dilute dampening water to reduce its acidity;

(4) When the amount of water is too large, the amount of water supply should be reduced;

(5) The viscosity of the ink is too high, a certain amount of ink should be added to the ink to reduce the viscosity of the ink;

(6) The printed version is already printed in the process of plate making and printing, and it should be replaced with a new one.

15. What are the reasons for the paste version? How to eliminate?

The reasons for eliminating stencils and eliminating them are:

(1) The pressure between the plate cylinder and the blanket cylinder is too large, and the pressure between the plate cylinder and the blanket cylinder should be reduced;

(2) Relying on the plate roller and plate pressure is too light, the pressure should be readjusted (2.5-3mm);

(3) The pressure on the plate roller and plate should be reduced;

(4) The dampening water is too acidic and the acidity of dampening water should be properly reduced;

(5) Ink is too thin. Add "0#" ink to the ink;

(6) Too much ink should reduce the amount of ink supply;

(7) Add excessive amount of desiccant in the ink, the ink roller should be cleaned to reduce the amount of desiccant in the ink;

(8) The printed body is too fine and should be replaced with a new one.

XVI. Causes of back stains and remedies

Back scumming refers to the fact that the newly printed sheets are stacked together. The ink on the bottom of the sheet is rubbed against the back of one of the sheets, resulting in contamination of the printed sheets.

The reason for removing the back of the back and how to remove it is:

(1) Ink drying is not good or the amount of ink is too large, appropriate amount of desiccant and anti-sticking agent should be added to the ink or reduce the amount of ink;

(2) Stacking the paper too high should reduce the stacking height of the paper;

(3) The ink is not dry and the paper is too heavy;

XVII. Causes of ghosting

Ghosting, commonly known as double printing, ghosting, has two kinds: axial ghosting, in which the footprint of the ghosted part is approximately parallel to the axis of the drum; the circumferential ghosting, that is, the marking of the ghosted part is perpendicular to the axis of the drum.

Causes of axial ghosting:

(1) Poor machine accuracy and bearing wear.

(2) Axial displacement of the plate cylinder or blanket cylinder occurs.

(3) Axial movement of the ink roller (or the plate roller is not compatible with the original machine)

(4) Paper "Ruffle"

The reasons for the weekly ghosting are:

(1) The blanket is not tight

(2) The drum pressure is not in place

(3) The machine is used for many years, the roller gear, bearing wear, or clearance between the three rollers is too large