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.