3 Pre-tensioning unit, pull the paper roller in each part.

In order to achieve the best printing effect, the different parts of the entire printing production line have different requirements for the tension of the tape. Pulling rollers with independent driving capacity are installed in different parts of the machine to control the tension of the paper path to meet each Part of the tension requirement. The function of the pre-tension unit is similar to that of the paper-pass roller. The function is to further control the tension of the paper tape that enters each printing unit during the printing process, compensates for the influence of the paper-path change on the tension of the paper tape, and stabilizes the tension of the paper-sheet of the printing unit. For better printing results. However, the premise of normal work is that each drawing roller, especially the drawing roller before and after each printing unit, must be driven well, and the speed overshoot value is set correctly or it will inevitably affect the tension of the printing unit tapes, resulting in inaccurate overprinting. .

4 overprinting and set cut paper roller.

For a shaft driven printing press, the registration between the upper and lower units is mainly achieved by a paper roll. Overprinting and sleeve-cutting roller consists of a fixed roller and a cantilever roller. Under the control of the register motor, the cantilever roller can rotate horizontally around the axis of the roller. Therefore, the levelness of the cantilever roller and its stability during the printing process will directly affect the color registration between the upper and lower units. At the same time, the stability of the tape tension is also affected.

5 each part of the paper roller.

The paper-feeding roller is the guide roller of the printing paper path. Proper setting of the paper-passing roller in each part of the printing machine can achieve the best paper-feeding method, and is also conducive to the control of the paper-strip tension. Therefore, it must be ensured that the levels of the feed rollers are the same, especially the level of the transfer rollers of the upper and lower printing units must be the same, which is an important factor affecting the registration between the upper and lower units.

6 In addition, we must also carry out regular inspections on the rotating bearings of the above types of rollers. When necessary, new bearings should be replaced to prevent wear of the bearings, lack of oil, jamming, and the phenomenon of inner and outer races of the bearings to ensure that the bearings work well. Avoid overprinting errors due to bearing problems.

(2) Factors Affecting the Accurate Transfer of Graphic Texts

The printing unit is the direct printing processing part that realizes the precise transfer of the graphic from the printing plate to the paper. Therefore, any mechanical deviation of the printing unit will affect the accurate transfer of newspaper graphics. According to experience, there are several mechanical factors in the printing unit that affect the color registration:

1 version of oral sales. Version mouthpiece is a positioning component that enables the printing plate to be accurately positioned on the plate cylinder. If the plate pin of a certain color plate is worn, loosened, fallen off, or improperly mounted, the corresponding color image of the plate cannot be overprinted.

2 roller bearings. The roller bearing is the support body of the printing roller, and it is also the main mechanism for providing printing pressure for each printing roller and parallel to the axis of the roller. If the roller bearing wears out and the eccentric position of the bearing is deviated, the printing pressure of the roller will not be changed in parallel, making the overprinting of the roller newspaper inaccurate.

3 clutch pressure linkage. The clutch pressure linkage is a control operation mechanism that makes the printing cylinder clutch pressure, stabilize the bearing eccentricity, avoid damping vibration, and ensure that the axes of the printing cylinders are parallel. The gap accuracy between the connecting rod bearing and the copper sleeve and the bearing is very high. If the connecting rod bearing, the copper sleeve is worn badly or the bearing is loose, it will affect the accuracy of newspaper registration.

4 sets of adjustment mechanism. The registering mechanism is an adjusting mechanism for realizing precise overprinting of various colors and graphics. In the printing process, the registering mechanism axially and circumferentially registers by axially pulling the printing plate or the blanket cylinder, and keeps the axial position of the corresponding roller unchanged. of. Because the bearings of the register mechanism rotate at a high speed together with the drum, the lack of oil runs around the outer ring, resulting in wear of the bearing surface and the roller contact or formation of gaps. When the roller is pulled circumferentially, there is an empty path or axial position of the roller is uncertain. , resulting in inaccurate overprinting of color newspapers.

5 edition mouth. The occurrence of events such as web breaks, blankets, and high-speed emergency stops often causes deviations in the position of the platen in a certain printing platen during the printing process. In the case of a shaft driven high-speed transfer printer, axial and circumferential registrations occur. The adjustment scope is limited, so when the position of the edition mouth is deviated, the circumferential overprinting of the corresponding layout will be affected, and even the overprinting of the front and back surfaces will be inaccurate.

6 The main motor is also one of the mechanical factors that affect the color newspaper register. Because there is a gap between the printing roller gears, when the motor drive voltage fluctuates or fails, such as the failure of the speed motor caused by the speed of the main motor is not stable, the roller gear will lead to the phenomenon of preshoot, backlash, causing color newspaper overprint not Quasi-even ghosting and hair-flowering.

printing material:

The printing materials mentioned here mainly refer to newsprint, fountain solution, etc.

(1) Newsprint is affected by the temperature and humidity of the environment.

In the printing shop, the change of moisture content of the paper must not exceed ±0.1%, otherwise it will affect the accuracy of overprinting. When the humidity in the printing room is too high, the newsprint easily absorbs moisture and expands and contracts. This is indicated by the presence of “foliage” on both sides of the tape. When the humidity of the shop is lower than that of newsprint, tight edges may appear on the edges of the paper roll. Such a paper certainly cannot guarantee normal overprinting when it is printed on the machine, and it is easy to cause problems such as breakage of the paper tape or wrinkles.

Both shop temperature and shop humidity are closely related to the moisture content of the paper. Experiments have shown that when the relative humidity of the shop changes by 10%, the water content of the paper will change by 1%. If the relative humidity of the shop exceeds 80%, the moisture content of the paper will change when the humidity changes by 10%. 1.5～2%; When the temperature changes, the humidity of the workshop will also change correspondingly. For every 5°C change of the workshop temperature, the moisture content of the paper will change by 0.15%.

The moisture content of the paper is closely related to the surface shape stability of the paper. The stability of the overprint cannot be guaranteed unless the stability of the paper can not be guaranteed. Therefore, ensuring the stability and standardization of the temperature and humidity in the workshop is very important for the overprinting precision of the printing color newspaper. It is generally recommended that the temperature of the printing shop should be maintained at 18 to 24°C, the temperature change should not exceed ±3°C, and the relative humidity should be controlled within the range of 55 to 65%.

(2) The effect of fountain solution on overprinting.

Similar to the environmental temperature and humidity mentioned above, the effect of overprinting is similar to that of the color paper overlay. The dampening fluid also affects the surface area of ​​the paper by changing the humidity inside the paper, and thus has a certain influence on overprinting during the printing process. We can't always avoid this effect. In practical work, we always require the use of the minimum amount of water while ensuring the balance of ink and water. Minimize the overprint changes caused by this.

In summary, in the printing of color newspapers, the pre-press standardization operation is guaranteed; the stability of the machine's work is maintained; and the printability of printed materials is fully understood; these factors can help us to further guarantee the quality of overprinting for color newspapers.