Analysis of the difference in COLORMAN printing quality between 8 rollers and 10 rollers
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Germany Manroland is one of the world's largest suppliers of printing equipment. Its COLORMAN model is one of the most advanced printing machines in the newspaper industry. It is divided into 8 rollers and 10 rollers COLORMAN. It has different degrees in China. usage of. Guangzhou Daily Printing Center is China's printing industry with the strongest printing capacity. The printing speed per hour can reach 6.54 million pairs. The Printing Center has seven of the world's most advanced printing lines, including two from Germany's Manroland's 8-roller and 10-roller COLORMAN models.
Although the COLORMAN model is also the same, the 8 roller and 10 roller COLORMAN print quality is very different. For example, the 10 roller COLORMAN print title is imaginary, the layout is uneven, 8 roller COLORMAN printing is difficult to register, etc. The author will combine the actual production practice, analyze the causes of these differences and explore solutions.
First, the analysis of the reasons for the difference
1. Structural differences
The 8-roller COLORMAN model is the most mature technical representative of Man Roland's 20th century traditional mainstream shaft drive wheel transfer machine, with a maximum printing speed of 75,000 copies per hour.
The 10 roller COLORMAN model is the top product of Manroland, which represents the most mature technology and the best and most reliable product of the newspaper shaftless printing printer. 10 drum technology reflects the most advanced design concept of the world newspaper rotary printing machine. At present, the same type of 10 roller equipment is mainly concentrated in developed countries in Europe and America. The maximum printing speed is 85,000 copies per hour. It has the characteristics of flexible paper path, humanized maintenance interface, high registration accuracy, low waste reporting rate and better printing quality.
The shaft transmission uses a main shaft to transmit power, and each part transmits the moving torque by the transmission gear. Although the influence of torsional deformation is considered in the design, such deformation is inevitable. In the shaftless transmission mode, there is no distortion of the mechanical shaft and backlash between the gears. Therefore, there is no so-called transmission error, and the long-term running-in and compression between the gears will cause deformation and wear, which will affect the transmission precision of the power, which will cause the overprinting error of the printed product, and the shaftless transmission. The system will not produce such defects. Therefore, 8 cylinder COLORMAN printing is relatively difficult to register.
2. Printing paper path difference
Figure 1 shows the 8 roller and 10 roller COLORMAN four-color printing paper road maps.
Figure 1 8 roller COLORMAN four-color printing paper road map 10 roller COLORMAN four-color printing paper road map
As can be seen from Figure 1, the 8 rollers COLORMAN are printed on both sides at the same time, while the 10 rollers COLORMAN are not printed at the same time. The four-color overprint on the front side is printed first, and then the four-color overprint on the reverse side is printed. After the four-color overprinting of the front C, M, Y, and K is completed, the four-color embossing on the reverse side is performed. In this way, the front graphic and the ink in the field are embossed again in a very short time after the printing is completed. Roll, then there will be a situation: in the case that the ink is not completely dry, it will be adhered to the embossing roller to a certain extent, resulting in the image is not strong, the field is imaginary or even partially missing, resulting in the layout is not Leveling and other phenomena.
Second, the solution to the discussion
1. 8 roller COLORMAN printing registration problem
The structure of the 8-roller type shaft drive cannot be changed, and the transmission error is inevitable. Only in actual production, pay special attention to the maintenance and repair work of the machine drive system, and try to minimize this transmission error.
The printing machine is equipped with an automatic registration system, which automatically tracks the color code of the first two colors printed by the electric eye, and then feeds back to the control center with the signal, and the control center automatically makes the correct adjustment to achieve the printing registration.
The cause of the 8-roller COLORMAN printing registration problem is paper and operation factors. When printing, the four colors of the paper are overprinted one after another, the paper is pressed with ink, and the paper passes through when the ink is not dry. The second wetting and embossing, the surface strength and tension of the surface deformation and expansion, the lateral stretching deformation is particularly large, and the heavier the pressure, the more the lateral stretching deformation, so the water absorption of the newsprint used for printing can not be too strong. At the same time, during printing, the operator pays attention to controlling the amount of water, and tries to achieve ink and water balance with less water and less ink. Otherwise, it will not only cause registration deviation, but also cause paper to be pulled.
In order to minimize deformation and expansion after pressing the paper, we can consider slightly reducing the two-color C and M (ie, lower printing tower) blanket pads that are printed first when C, M, Y, and K are overprinted. Can achieve a certain effect.
2. 10 Roller COLORMAN print headline imaginary, layout unevenness problem
According to the reason that the title is imaginary and the layout is uneven, we can make the following assumptions: under the premise of not reducing the front printing pressure, that is, ensuring that the front image and the ink layer in the field are not weakened, the pressure on the reverse printing is reduced, and the effect may be It will be better. In order to verify the above ideas, the author once conducted a test, in the case of the layout, title, field, and the same amount of ink, the entire printing cylinder was removed, only the front page was printed, and the single-sided printed newspaper was printed. Comparison of double-sided printed newspapers printed on both sides under the same conditions:
Table 1 Under the same printing conditions, single-sided printed newspaper and double-sided printed newspaper title, field comparison table
From Table 1, we can see that the title and solid density of single-sided printed newspapers are darker and more solid than when printing on both sides. This confirms the correctness of the above assumptions, but normal newspaper printing cannot be single-sided printing, so we can adjust from the blanket.
The cushion of the blanket cylinder of the reverse printing unit is lightened a little. By such relief, the front printed image is less stressed when passing through the embossing roller, and the front printed image and the field can be minimized. It is glued off, thus achieving the completeness of the title and graphics, which is more solid and smooth.
However, if the blanket of the reverse printing unit reduces the padding (such as 0.18mm to 0.15mm), will it affect the printing quality of the reverse side? Will not! Because the smoothness of the front side of newsprint paper is relatively high, the front and back of newspaper printing is just the opposite of the front and back of newsprint, that is, the reverse side of newspaper is the front side of newsprint, the smoother side, slightly reducing the printing pressure on newspaper printing quality. The impact is not great. At the same time, the reduction of the printing pressure on the reverse side will cause the difference between the paper exiting speed of the printing section and the drawing speed of the front end, which needs to be re-adjusted, and the tension between the rollers in the printing tower is relatively unaffected. Because, according to experience, the lighter the pressure of the back color sequence, the tighter the paper is pulled, which makes it less likely that the paper will be fed (the paper is not stable or tight).
In addition, if the blanket is relatively hard, the compression deformation is small, which helps to improve the flatness of the layout. Therefore, it is recommended to print a black blanket using a blanket with a slightly higher hardness to increase the hardness to achieve the title. The sturdiness and the flatness of the picture and the text.
If the printing time is too long per day, it is recommended that two sets of blankets be used alternately on each machine at regular intervals, because once the use time is too long, the elastic recovery of the blanket will continue to weaken. If it is used alternately, let it fully restore its elasticity, which will also extend the life of the blanket to a certain extent, and at the same time improve the printing quality of the newspaper and the flatness of the layout.
The printing difference between the 8 roller and the 10 roller COLORMAN still has a lot of places that we need to pay attention to. The comparative study can better grasp the printing performance of the 8 roller and 10 roller COLORMAN. Most of the above conclusions come from actual production. It can only be said that the bricks and jade are used to give the printing industry a direction of exchange and discussion. As for the "degree" of adjustment and experiment, it takes a long time of practice and experience.