Offset Troubleshooting Experience Highlights (1-9)

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.

Fifth, how to identify the size of water

To identify the major moisture, we must first look at the layout of moisture. This depends on the operator's experience. In general, the moisture content is large, and the amount of reflected light on the plate is strong, and the side view is bright. On the contrary, the amount of reflected light on the plate is weak and the side view is dark. If the water is too large, it can be observed from the following points:

(1) Scoop the ink on the ink roller with a paper jam. Small water drops will remain on the paper.
(2) Small water droplets on the string water roller, deinking or water droplets in the ink roller group;
(3) After the water is turned off or the machine has been shut down for a long time, the water in the layout still has not dried up;
(4) The imprinted dots are empty and the ink is dull and dull;
(5) There are shadows or drops of water on the tail end of the blanket cylinder.

Six, control the water balance

Ink and water are not absolutely incompatible. In the actual printing process, the ink and water are squeezed by the rubber roller and the rubber roller, and they fuse together to emulsify the ink. There are two types of ink emulsification: when the water is large in ink, the formation of "oil in water"; when the water is small in ink, the formation of "oil in water". In the offset printing process, the mastery of the ink-moisture balance has a close relationship with the normal transfer of imprinting, the depth of ink, the accuracy of color registration, and the drying and stickiness of the printed matter. In general, the water is large, the ink is emulsified, and the ink is light; the water is small, and the blank part of the layout will adhere to the ink and cause a stain. Therefore, it is the key to printing that offset control is a good balance between ink and water.

Seven, control the ink balance

To control the balance of ink and water, it is generally necessary to grasp the principle of less ink and thicker water. Less water means the premise that the blank part of the layout is not sticky; ink thick refers to the increase in the amount of ink that is built on the basis of less water. In the printing process, the most taboo is the big ink. When considering the amount of water, the area size and distribution of the layout, the thickness of the ink layer, the properties of the printing paper, the performance of the ink, the speed of the machine, the temperature and humidity of the workshop, the pH of the fountain solution, and the amount of ink added Supplements and other circumstances.

Eight, cleaning blanket, change the ink roller must be clean

After printing for a period of time, there will be paper, paper powder, ink and other dirt on the blanket, which will reduce the quality of the printed matter. Therefore, the blanket must be cleaned in time, especially when printing paper with low strength. The accumulation of paper powder is even more severe. Therefore, if the ink roller set is not cleaned when the color is changed frequently, the purity of the new ink color will be affected, especially when changing from dark ink to light ink. If black ink is replaced by yellow ink, if black ink is not cleaned, yellow ink will be black, which will affect the quality of printed matter. Therefore, the ink roller set must be cleaned when changing colors.

9. The main factors of overprinting

Before and after overprinting is not allowed:

(1) Printing press

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. gear wear;
f. The blanket is too loose and tight.

(2) Paper

a. Paper cutting accuracy is not high;
b. The amount of water during printing 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.

Left and right sets 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;