The reasons and exclusion of offset printing before and after the appearance of offset printing
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In the process of offset printing, sometimes the inconsistency of the ink color is inconsistent on the same printed sheet, that is, the printed sheet is deep in front of the blotting ink at the two positions of the bite and the tip, and the back is shallow, and most of the ink is deep before the ink. After the light, a very small number of cases are dark and deep, especially when printing products in the field, the inconsistency of the ink on the same sheet will affect the quality of the printed product. Now the cause and treatment of this fault The analysis is as follows:
1. The cause of smooth aging of the surface of the inking roller is deep and dark before the imprinting
The inking roller of the offset printing machine generally has four branches, and the surface of the inking roller is smooth and aged, which will affect the adsorption performance and transfer ability of the ink. The surface of the inking roller can not absorb enough ink. When it is transferred for the first time on the printing plate, due to the small amount of ink stored, the dark portion of the image or the ground has absorbed the transfer ink on its surface. Going mostly, and at the same time, it is impossible to get enough ink to replenish immediately on the ink roller, so when the second transfer is performed, the ink obtained in the dark portion of the image or in the field is already at the first turn. When the ink is much less, although there are four ink rollers that pass the ink, there will still be a phenomenon in which the ink is dark before and after.
Solution: Remove the ink roller of the offset press. Under the premise of the diameter of the ink roller, it can be ground to make the surface rougher to increase the adsorption and transfer performance of the ink. Ink roller with too small diameter, only replace the new ink roller, at the end of normal work, wipe the four ink rollers to prevent the ink roller from being smooth and aging.
2. The diameter of the inking roller is too small
The diameter of the offset roller of the offset printing machine is too small, and some of them are design problems. When the printing machine is printed on the whole version, it is easy to produce a phenomenon of deep front and back light. This is a defect in the design of the offset printing machine. It can't be changed. Some ink rollers have a small diameter. The ink roller is too small to be used during the grinding process. It can barely be used. Therefore, the pressure between the ink roller and the ink roller is too small, which affects the ink transmission. There is no problem when printing a product with a small amount of ink. However, when printing a product with a large amount of ink, the drawbacks of inconsistent ink color will be revealed.
Solution: Replace the ink roller of the appropriate diameter.
3. The aging of the ink roller affects the effect of ink transfer
The surface of the offset ink roller is composed of nitrile rubber. The aging of rubber for a long time has two forms: first, the photoaging of rubber will affect the ink transfer performance of the ink roller; second, the thermal aging of rubber affects the rubber. The surface becomes soft, sticky, and even cracked. It is required that the printing ink roller can absorb and transfer ink to the maximum extent, and at the same time, it can absorb moisture to a minimum, and also has good oil resistance and certain acid resistance. Since the printing process often has continuous contact with moisture, ink, paper, etc., it may be Adsorption with the surface of the rubber ink roller forms a state of the film layer, thereby weakening its lipophilicity and enhancing hydrophilicity.
Solution: The aging of the ink roller is always a phenomenon. The ink roller should be stored in a place where there is no direct sunlight, dry and clean, and avoid excessive humidity or overheating. The ink roller should be straight at the journal end, and The surfaces between the ink roller and the ink roller should not touch each other or be in contact with other surfaces to deform and stick.
4. The number of ink rollers is too small
In the offset printing, sometimes the operator removes some of the ink rollers for convenience. For example, taking the first inking roller and the small ink roller on the upper side, the ink storage amount of the ink roller is insufficient to cause an abnormal phenomenon such as shortening and accelerating the ink delivery period.
Solution: All the ink rollers on the offset printing machine are required to be placed to ensure the ink storage capacity of the ink transfer system. This will have a certain effect on solving the problem of dark and dark before the ink color.
5. The pressure between the rubber ink roller and the ink roller is too light
The rubber ink roller acts as a transfer ink, and the pressure between the rubber ink roller and the ink roller is too light, which affects the normal transmission of the ink amount. Sometimes the upper half of the ink roller is filled with the ink amount, and the ink roller is piled up. The amount of ink on the half of the ink roller is still too small, which is because the pressure of the leveling roller and the roller are too light. In particular, when the pressure of the four inking rollers and the inking roller is too light, it is easy to cause a dark and dark fault before the ink color.
Solution: Low-speed offset printing machine can adjust the eccentricity to adjust the pressure between the ink rollers. The high-speed machine roller is not eccentrically adjusted, and can be replaced with a thicker rubber roller. The pressure of the four inking rollers and the inking roller can be adjusted in order from front to back depending on the mutual contact width.
6. The effect of the drum on the deep and dark before the imprint
Since the three cylinders of the printing plate, the rubber and the embossing do not reach the static balance, in the printing process, the center of gravity on the circumference is often darker than the segment, and the radius of the printing surface of the roller is inconsistent, which may result in darkness before and after the ink color, and may also be Produce the ink before it is dark and deep.
Solution: The above is a drawback in the design and manufacture of offset printing machinery. The printing operator is difficult to solve in the process of normal printing. Only when it is overhauled, the re-processing of the drum that does not reach the static balance will be remedied. Operators sometimes add pressure to lighter areas of the ink, but these are temporary measures and are not very effective.
7. The rubber has poor lipophilicity
Printing blankets require maximum adsorption and transfer of ink while minimizing moisture absorption and good oil and acid resistance. Since the printing process often has continuous contact with moisture, ink, paper, etc., it may adhere to the surface of the blanket to form a film state, which changes their wetting properties, that is, the lipophilic ink transfer performance is weakened, and the hydrophilicity Sexual enhancement. This is also prone to the drawbacks of deep before and after. At the same time, the blanket light and heat aging will make the surface of the blanket soft, sticky, and even crack, which will reduce the ink transfer performance, and it is easy to appear inconsistencies in the ink color of the print.
8. The ink is not suitable for mixing, the viscosity is large, and the fluidity is small.
Solution: In order to make the ink have good printing adaptability, it is often necessary to add some auxiliary materials according to the requirements of the printing. The ink is very viscous, and it is necessary to add varnish. Printing companies often use 0-6 and 05-01 resin varnish to improve the viscosity and fluidity of the ink. No. 0 varnish has a large viscosity. When the ink binder does not have sufficient adhesive force, and there are often drawbacks such as floating ink and greasy on the flower plate or printing plate, an appropriate amount of varnish can be added to improve the performance.
No. 6 varnish is a yellowish color obtained by heating and refining dry vegetable oil, and has a certain viscous oily fluid. No. 6 varnish has two functions: 1 to dilute in the ink and also to reduce the viscosity of the ink; 2 to reduce the concentration of the ink, increase the fluidity of the ink, the brushability, and enhance the printing of the ink. Sex.