One of offset printing fault collection

First, the ink's performance:

1) Concentration: The ink with high concentration has less use of ink in printing, and the ink is better; the ink with smaller concentration uses more ink in printing, and the ink is light;

2) Fineness: It is the size of ink particles, high ink fineness, high ink density, clear and full of printing points, low ink fineness, easily printed hairs, and low printing rate.

3) Viscosity, high viscosity, easy to cause uneven ink transfer, netting and flower pattern, etc.; small viscosity, easy to cause ink emulsification and layout floating phenomenon;

4) Fluidity: The fluidity is large, which will make the level of the graphic and text unclear, and the ink color is not full; the fluidity is small, so that the ink is not spread smoothly and unevenly. Deep phenomenon;

5) Lightfastness: The ink with good lightfastness can be printed with brilliant color, full and solid, rich in three-dimensional, and can be stored for a long time. The light with poor lightfastness can easily become lighter and darker.

6) Water resistance, acid resistance, alkali resistance: For offset printing inks, special attention should be paid to the inks with water resistance, acid resistance, alkali resistance, water resistance, acid resistance, and alkali resistance. The printed products have bright colors, distinct layers, and clear dots. Water-resistant, acid-resistant, alkali-resistant, and poor inks, the printed products are gray and weak, the level is unknown, and the outlets are not clean.

Second, dampening water

The pH plant of the dampening water is generally between 3.8-4.6. In the actual production, it is necessary to verify according to the specific conditions of the printing conditions. If the dampening water is too acidic, the blisters and the oleophilic basis of the graphics are blank. The corrosiveness will increase again, which will cause the phenomenon of stencil printing, which will reduce the printing resistance of the printing plate; at the same time, the ink will be easily emulsified, the ink roller will be de-inked, and the printing will be dark and dull.

If the dampening water is too weak, the hydrophilicity and oil-repellent properties of the blank part of the printing plate will be weakened, and the layout will be easy to get dirty and the stencil printing phenomenon will be caused by the expansion of the printed dot. (If the UV ink is printed, if the dampening water is acidic, The layout is easy to get dirty

Third, the color sequence

Color sequence refers to the sequential printing sequence of various printing plates in multi-color printing. Different color sequences will produce a variety of different printing effects. It is important to arrange the color sequence properly. However, the color sequence is not absolute. The general arrangement of the color sequence is:

Monochromatic machine: yellow → magenta → blue → black color machine: black → yellow, magenta → blue (print landscape) or blue → red (print characters); gold, silver, full version of the field printing, generally First gold, silver, full version of the field, wait until the ink is dry and then set four colors of ink.

Fourth, batch printing

1) Check whether the four-color film specifications are the same (whether four films are complete);
2) Check the proofs and check whether the pictures are complete.
3) Stabilize water and ink levels to achieve ink-jet ink consistency to ensure consistency in the inks of the same batch of printed materials;
4) Clean the blanket as little or as little as possible (it is possible to put some overprint paper)

In the formal printing, the operator should concentrate on:

(1) Look at: Look at the operation of the machine, look at the sample ink, register and network quality;
(2) Hear: if there is any abnormality in the sound of the machine, whether there is noise in the sensitive area of ​​the machine or not;
(3) Touch: Touch the parts of the machine that are prone to increase in temperature due to wear. Is there a significant temperature change?
(4) Smell: There is no scorching of electrical appliances and other abnormal smells. (UV ink should pay more attention to the UV power cord);
(5) Inspection: Check the condition of the printed product and the abnormal condition of the machine. If any problem is found, remove it promptly.

Source: Guangdong Printing