Offset common fault analysis

The main factors of misregistration

Before and after overprinting is not allowed:

1) Printing machine

a. The heavenly adjusting plate locking screw is not fixed, or the M5 hexagonal screw on the feed rocker arm is tightly fixed;

b. Push paper seat copper sleeve is worn out;

c. Paper feed wear;

d. Printing pressure is too small;

e. The gears are worn, the blanket is too loose and there is no tightness.

2) Paper

a. Paper cutting accuracy is not high;

b. The amount of printing water is too large and the paper is stretched.

3) Others

a. There is a problem with the plate or manuscript itself;

b. The stack of paper jams is too high or the pressure of the platen is too heavy, causing paper jams.

4) Left and right overprints are not allowed:

a. The left and right baffles are too tight or the left and right baffle screws are fixed;

b. The length of cardboard is different;

c. The drum moves around.

The cause of dirty oil

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 " Milk."

The causes of dirty oil are:

1) Printing plate

a. The printed version is not of high quality (bad or reprinted version);

b. Insufficient exposure time during printing and the developer concentration is too low;

c. The printing plate surface protection glue is not clean;

d. The blank part of the plate is oxidized;

2) Printing machine

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 rubber surface;

e. paper powder and paper wool wear plate;

f. Fountain solution pH is not proper.

Before and after ink shades

In the actual printing, sometimes the ink on the same screen is found to have different shades of darkness, but often the ink is darker and darker, and the ink is lighter and darker. The reasons for the different ink shades are:

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 its surface area is ink, which causes it to be unable to ink.

c. The viscosity of the ink is too high.