German Roland Company is one of the world's largest printing equipment suppliers. Its COLORMAN type printing machine is one of the most advanced printing machines in the newspaper industry. It is divided into 8-cylinder and 10-cylinder COLORMAN models. usage of. As the printing house with the strongest printing capacity in China, Guangzhou Daily Printing Center has a printing speed of 6.54 million pairs per hour. The Printing Center has 7 of the world's most advanced printing production lines, including two 8-cylinder and 10-cylinder COLORMAN printers from the German company Roland.
Although they are all COLORMAN printers, the printing quality of 8-roll and 10-roll COLORMAN is very different. For example, the problems of the 10-roll COLORMAN printing titles are false, the layout is uneven, and the 8-roll COLORMAN printing is difficult to register. I will combine the actual production practice to analyze the causes of these differences and discuss the solutions.
1. Analysis of the reasons for the difference
1. Structural differences
The 8-roller COLORMAN model is the most mature technology representative of the traditional mainstream shaft-driven wheel transfer newspaper machine of the 20th century of Man Roland. The maximum printing speed is 75,000 copies per hour.
The 10-roller COLORMAN model is Man Roland's top product, which represents the most mature technology and the best and most reliable product of the newspaper shaftless transmission printer. The 10-cylinder technology embodies the most advanced design concept of the world's newspaper rotary presses. At present, the same type of 10-cylinder equipment is mainly concentrated in developed countries in Europe and America. The maximum printing speed reaches 85,000 copies per hour. It has the characteristics of flexible Paper path, humanized maintenance interface, high registration accuracy, low scrap rate, and better printing quality.
The shaft transmission uses a main shaft to transmit power, and each part relies on the transmission gear to transmit the moving torque. Although the influence of torsional deformation is considered in the design, this deformation is inevitable. In the shaftless transmission mode, there is no distortion of the mechanical shaft and backlash of the gears. Therefore, there is no so-called transmission error, and the long-term running-in and squeezing between the gears will produce deformation and wear, which will affect the transmission accuracy of the power, and will cause overprint errors of the printed products, without shaft transmission. The system will not produce such defects. As a result, 8-cylinder COLORMAN printing is relatively difficult to register.
2. Printing paper path difference
The 8 cylinder COLORMAN is printed on both sides at the same time, while the 10 cylinder COLORMAN is not printed on both sides 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 colors of C, M, Y and K on the front are overprinted, the four colors of the back are embossed. In this case, the graphics and the ink on the front are embossed again in a very short time after the printing is completed Roller, then there will be a situation: in the case that the ink is not completely dry, it will be adhered to the impression roller to a certain extent, resulting in part of the picture and text is not strong, solid or even part of the missing, causing the layout is not Leveling and other phenomena.
Second, the solution
1.8 cylinder COLORMAN printing registration problem
The structure of the 8-drum shafted 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 transmission system, and try to minimize this transmission error.
The printing machine is equipped with an automatic registration system, and the color marks of the two colors printed in front are automatically tracked with an electric eye, and then fed back to the control center with a signal, and the control center automatically makes correct adjustments to achieve printing registration.
The reason for the 8-roller COLORMAN printing registration problem is also the paper and operation factors. During printing, the four-color separation on both sides of the paper is overprinted one after another. The paper is pressed with ink and the water is not dry. In the second wetting and embossing, the surface strength and tension are deformed and stretched. The transverse deformation is especially large. The heavier the compression, the stronger the transverse expansion and deformation. Therefore, the newsprint used for printing cannot be too absorbent. At the same time, during printing, the operator should pay attention to control the amount of water, try to use less water and less ink to achieve water and ink balance. Otherwise, it will not only cause deviation of registration, but also cause the paper to be rough.
In order to minimize the deformation and expansion of the paper after being compressed, we can consider slightly reducing the blanket pads of the two-color C and M (that is, the lower printing tower) printed first when C, M, Y, and K are overprinted. Can achieve a certain effect.
2.10 COLORMAN cylinder printing title is fuzzy and the layout is uneven
According to the reasons for the false title and uneven layout, we can make the following assumptions: Without reducing the printing pressure on the front side, that is, ensuring that the front image and the ink layer on the ground are not weakened, the pressure on the back side printing can be reduced, and the effect may be It will be better. In order to verify the above assumptions, the author once did an experiment. Without changing the layout, title, field, and ink volume, all the printing cylinders on the reverse side were disengaged, and only the front side was printed. Under the same conditions, double-sided printed newspapers printed after double-sided pressing are compared:
From Table 1, we can see that the headline and solid density of newspapers printed on one side are darker and more solid than those printed on both sides. This confirms the correctness of the above assumption, but normal newspaper printing cannot be printed on one side, so we can start adjusting from the blanket.
Reduce the cushion of the blanket cylinder of the reverse printing unit a little. Through this reduction, the graphics printed on the front will be less stressed when passing the platen roller, and the graphics printed on the front and the ground can be minimized. It is sticked out, so as to achieve the integrity of the title and graphics, and it looks more solid and smooth.
But if the blanket of the reverse printing unit is lightened (such as 0.18mm to 0.15mm), will it affect the quality of the reverse printing? Will not! Because the smoothness of the front side of newsprint paper is relatively higher than that of the reverse side, the front and back sides of newspaper printing are exactly opposite to the front and back sides of newsprint. The impact is not great. At the same time, the reduction of the printing pressure on the back side will cause the difference between the paper output speed of the printing section and the paper pulling speed of the front of the car to be changed. Because, according to experience, the lighter the pressure of the back color sequence, the tighter the paper is pulled, and the possibility of paper feed (the paper is not stable and not tight) is unlikely.
In addition, if the blanket is relatively hard, the deformation under compression will be small, which will help to improve the flatness of the layout, so it is recommended to print a black blanket with a slightly harder blanket to increase its hardness to achieve the title The sturdiness and smoothness of pictures and text.
If the printing time is too long every day, it is recommended that each machine has two sets of blankets used regularly alternately, because once the use time is too long, the elastic recovery of the blanket will continue to weaken. If used alternately, let it fully recover its elasticity, which can also extend the service 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.
There are many differences between 8-cylinder and 10-cylinder COLORMAN printing, and comparative research can better grasp the printing performance of 8-cylinder and 10-cylinder COLORMAN. Most of the above conclusions come from actual production. It can only be said that throwing bricks and introducing jade gives the printing industry peers a direction for exchange and discussion. As for the "degree" of adjustment and trial, it takes a long time of practice and experience.
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