In recent years, the number of color prints with negative text on the layout has increased, and the failure of offset printing text paste has also occurred from time to time. If you encounter this fault, if you do not analyze it correctly, find out the cause of the fault and eliminate it as soon as possible, you will inevitably make detours and increase consumption. Today, the editor will share with you the causes and solutions of the offset problem.

01

After the text is blurred, the first thing to check is whether there is a problem with the printing plate .

The smearing phenomenon mostly occurs in small strokes and lines. Because of the contrast between "on the spot" and the blank words, if you don't observe carefully, you can't see the problem of plate making, and it's easy to be ignored. 

In addition to the original version factors, the reasons for the plate-making aspect to cause the paste version: 

PS plate manufacturing quality

The PS version has too shallow, too thin, and low water storage; 

Some PS plates do not have enough time to seal holes, and the extremely tiny holes on the plate are not sealed, which makes the plate have too much adsorption capacity; 

Recycled PS plate has uneven sand mesh and sensation layer.

Printing aspect

Insufficient exposure time or low developer concentration; 

Because the indoor light is not paid attention to during the printing process, the PS plate will produce fog under natural light, which will bring difficulties to the development and cause the negative characters to be grease sensitive. In order to achieve the thickness of the ink film, the amount of ink under the ink fountain must be increased, which is more likely to cause Negative text paste version. 

Solution:

Adopt PS plate with high quality standardization to print the printing plate; 

The exposure must be sufficient during the printing operation, and the development must be thorough; 

The indoor lighting during the printing process should not use strong light sources, the windows should be covered with ink cloth, and the doors should be double doors separated by colored ribbons.  

02

In addition to the plate making factor, the ink film is too thick when printing is also the main reason

Because of the high smoothness of the surface for color printing, the absorption is not strong, the ink film is slightly thicker, it is easy to spread into the negative text, resulting in paste failure.

There are two situations when the ink film is too thick

The ink film caused by "small water and large ink" is too thick. After the formal printing, it is found that the ink film is too thick. Increase the amount of water and adjust the amount of ink to eliminate it; 

"Big water and ink" cause the ink film to be too thick. This is because the ink volume of the ink fountain is adjusted excessively before the formal printing, the water supply volume is incorrectly increased after continuous printing, or the water is large at the beginning of the printing, the ink film is thinned, and the ink volume is increased by mistake, resulting in "large water and large ink. "Vicious circle, the ink is emulsified seriously, the viscosity is reduced, and it is very easy to paste.

Solution

① In daily operation, we should always sum up experience and improve the technical level. The ink volume should be calculated correctly in the ink fountain before the formal printing. The thickness of the film is appropriate to avoid smearing;

② Because the water supply volume of the “on-the-spot” layout cannot be small, in order to avoid the ink film being too thick due to the “big water and large ink”, the PH value of the syrup (increasing the acid value) can be reduced, or an appropriate amount of surfactant can be added to reduce the water supply. If there is a large amount of ink and ink emulsification, clean the emulsified ink on the ink cleaning roller in time, and then reduce the amount of ink, and re-ink and print; 

③ The color of the multi-color and light-colored inks should be slightly darker than the original color when the ink is adjusted. The three primary colors should also be selected with strong coloring power. The dark ink thin printing measures can also avoid the ink film being too thick. 

03

In addition to the above two main reasons, the following factors will also cause the negative text to be blurred during printing.

• Too much printing pressure; 

• The fluidity of the ink is too large; 

• Ink particle group or pigment is poor in water resistance; 

• Excessive amount of dry oil added during ink adjustment; 

• The inking roller is aging; 

• The inking roller is too soft and curved, and it slips relative to the plate cylinder during operation; 

• The pressure of the inking roller and the printing plate is too large; 

• The water on the page is too small or the water roller is too dirty, the pressure between the water roller and the printing plate is too light or too heavy; 

• The blanket is not tight; 

• The drum lining is not suitable; 

• The paper has serious powder off; 

• In the summer room temperature, due to the quick drying of the moisture of the PS plate, the plate is not coated with protective glue when the machine is stopped, and the re-printing will cause the paste.