The hottest screen printing combination printing c

2022-08-22
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In recent years, the development of newspapers can be described as a thousand miles with each passing day, from only one or two thin sheets of paper to several thick stacks of each, from only black and red pages in the past to basically color pages now. With the popularity of color pages in newspaper printing, the original printing equipment of each newspaper printing plant is basically a two-layer B-B combination structure, semi satellite structure or full satellite structure, and the printing method is relatively rigid and fixed. Therefore, if the position of the newspaper page on the printing equipment is black, it can only print black, if it is color, it can only print color, and it cannot be changed and adjusted according to the needs of the page. In order to adapt to this rapid development, most of the new printing equipment added by newspaper printing plants in recent years are tower B-B composite structures. The advantages of the tower B-B combination structure lie in the flexible combination of printing color sequence, good controllability and high machine utilization. It can print double-sided full-color printing sheets, and the position of the color plate will not be affected by the equipment capacity. However, due to the structural characteristics of the printing equipment (commonly known as scattered four-color printing), there are higher requirements for the printing registration process. Tower type four layer B-B combined printing group, the technical performance of each group is consistent, and it is accurately in place when the machine is installed. The gap between the printing plate cylinder and the rubber cylinder and between the rubber cylinder and the rubber cylinder of each layer B-B printing group is adjusted accurately and the size is consistent. The original specifications of blanket and liner are consistent, and the installation torque of blanket is unified. From the completion of the above parameters, there should be no problem with normal printing, but in the actual printing production, there are some problems that affect the printing registration, such as unstable operation of the paper tape between the B-B printing groups of each layer, insufficient tension, serious swing, irregular twist, wrinkling, etc

next, we will discuss the phenomenon and solution of overprint error caused by unstable operation of paper tape in rotary printing based on some problems of tower B-B combined structure printing group in production

the web paper belt enters the first color drum printing of the printing group after passing through the tension floating roller from the paper feeding part. Because the paper roll has a tension control device to bring appropriate tension to the paper, the paper belt is moderately tensioned and stable at this position. After being embossed by the first color printing cylinder, the paper tape enters the second color printing cylinder after a short distance. In the distance between the paper feeding part and the second color roller, the paper tape is not easy to change greatly, and the registration of the first and second colors basically meets the standard requirements. After the paper tape is adsorbed by the fountain water and ink of two groups of rollers, the physical properties of the paper tape itself. An effective treatment method can not only ensure the normal operation of the refrigeration unit, but also effectively adjust the energy consumption and refrigerating capacity of the refrigeration system. There have been some changes. There is no compactness when just pulled out of the paper roll, and the paper body becomes soft after absorbing water, And because there is ink adhering to the surface of the paper tape, it becomes a little sticky. Therefore, within the distance from the second color printing cylinder to the third color printing cylinder or from the third color printing cylinder to the fourth color printing cylinder, it is easy to cause unstable operation of the paper belt, insufficient tension, paper swing, etc., resulting in inaccurate overprint or dislocation; In serious cases, there will be irregular wrinkling and wrinkling, and the last two colors cannot be printed at all

for this kind of situation, if you want to complete the printing quickly, you must solve the problem of how to keep enough tension between the four layers of B-B printing group. When the paper tape passes through the first two groups of printing rollers, the tension can basically be obtained from the paper roll tension control system. However, when the paper tape enters the last two groups of printing rollers, because the paper tape is affected by the imprinting pressure of the first two groups of printing rollers, the paper roll tension control system cannot provide enough tension to the paper tape. At this time, it is necessary to consider the surface speed of the rubber drum of the four-layer printing group. The surface speed of the rubber drum of the four-layer printing group should be basically the same, or the surface speed of the rubber drum of the third and fourth layer printing groups should be slightly higher than that of the first and second layer printing groups, so that the paper tape can get appropriate tension in the whole printing process to maintain the stability of the paper tape

considering the above points, we can find a solution from the deformation characteristics of rubber blanket, the rolling principle of rubber roller and the center distance of rubber roller

each printing cylinder of the rotary printing machine rolls relatively under mutual pressure. Although the current rotary printing machines have basically used air cushion rubber blanket, due to the elastic effect of the air cushion layer, there will be no bulges on the adjacent sides of the rubber surface lamination line in theory. However, in the actual use of the rotary printing press, the elastic ability of the blanket of two rubber cylinders to instantly restore its original state under relative rolling pressure is in the compression deformation of the printing plate cylinder and the other rubber cylinder tens of thousands of times per hour. The elastic ability of the blanket to quickly restore its original state is restored because the rubber unit in the blanket enters the embossing area to produce compression deformation, and the pressure of the rubber unit leaving the embossing area disappears. Because rubber county has the property of delaying high elasticity, the development of high elastic deformation always lags behind stress. Before the last deformation of the rubber unit body has time to disappear due to rebound, the next stress is applied again. In this way, it continues to circulate, and the elastic energy stored in the rubber that is too late to be released is converted into heat. The more heat released, the greater the internal friction of the rubber. The higher the stress frequency of the blanket, the less elastic the blanket will be. As a result, the air cushion blanket will still produce a slight hysteresis similar to convex deformation on the adjacent sides of the rubber surface lamination line. Therefore, when the two rubber rollers are rolling, due to the effect of diameter increase, the actual circumference length of the rubber blanket is larger than that of the rubber blanket, which is in line with the development trend of circular economy and the circumference length when it is not under pressure. And the greater the pressure and the higher the convex hull, the longer the circumference of the blanket will turn. This theory, which was obtained by British Miller through experiments, is the result of an increasing diameter effect

combine this theory with the working mode of the rubber cylinder experimental AIDS of the rotary press, and regard the two rubber cylinders as the interacting embossing cylinders. Based on the fact that the rolling radius will increase after the rubber cylinder is pressed, the ratio of the rolling radius to the free radius of the rubber cylinder is the rolling ratio, which directly affects the walking speed of the paper, and is of great help to whether the paper is moderately tensioned and the impression is clear and accurate

the factors that affect the rolling ratio are as follows:

1. The characteristics of blanket. Different types of blanket with different characteristics have different rolling ratios. Rubber blanket is mainly selected from the following characteristics:

(1) hardness: the ability of rubber to resist other substances pressing into its surface. We should consider the quality of the printed matter, the print resistance of the printing plate, the manufacturing accuracy of the printing machine and the flatness of the blanket itself

(2) elasticity: the ability of the rubber blanket to return to its original state immediately after removing the external force that deforms it. During the printing process, the rubber blanket is deformed by the pressure of another rubber drum. When the pressure turns away from the surface of the rubber drum, it is required that the rubber blanket can quickly recover to accept the ink on the printing plate. Then quickly restore the original state and transfer the loaded ink to the paper through the pressure with another rubber roller

(3) compression deformation: the strength of rubber deformation after multiple compression of rubber blanket. When the blanket is printed, it will undergo countless compression recovery processes, resulting in compression fatigue and permanent deformation. At this time, the thickness of the blanket will be thinner and the elasticity will be reduced

2. Compression of blanket: the same blanket has different rolling ratio under different compression. When two rubber rollers are rolling, the actual circumference length of the blanket is greater than that when the blanket is not under pressure. The greater the pressure, the longer the circumference of the blanket. This shows that by changing the center distance between the rubber drum and the rubber drum, different rolling ratios can be obtained, and the surface speed of the rubber drum can be changed. In actual use adjustment, as long as the center distance between rollers is about 0.01mm-0.02mm, different effects can be obtained

3 tightness of rubber blanket: the amount by which the rubber blanket exceeds the original length under a certain tension. The elongation of rubber blanket is generally expressed by elongation. The smaller the elongation of rubber blanket is, the better. If the elongation is larger, the rubber is easy to be stretched, the rubber layer will be thinner, and the elasticity will be reduced. The tighter the blanket is, the thinner it will be. The smaller the free radius of the rubber drum is, the larger the rolling ratio will be, because the larger the rolling ratio is, the larger the rolling radius of the rubber drum will be. The rubber blanket must be tightened on the rubber drum under the action of appropriate tension. If the blanket is stretched too loosely, the blanket will shift under the action of extrusion pressure and cannot be reset in time, which will lead to ghosting and other faults. If the rubber blanket is too tight, the rubber layer of the rubber blanket will be thinner and the elasticity will be reduced, especially the air cushion rubber blanket basically used on the rotary fh~ij machine. If it is too tight, it may also make the micro foam sponge layer invalid and lose the good performance of the air cushion rubber blanket. Therefore, the synchronous rolling ratio of the rubber drum relative to the plate roller and the impression roller will rise, destroying the same rolling state

according to the inspection in actual production, the above adjustments have a good effect on improving the paper operation. The paper tape running problem within the distance from the second color ffj~u drum to the third color fichu drum or from the third color printing drum to the fourth color printing drum can basically be solved from the above theory

printing process

1. Under the condition that the mechanical parameters of the machine and equipment do not change, the rubber blanket with high hardness can produce enough printing pressure with a small amount of deformation. At this time, the thickness of the blanket liner is reduced, the free radius is reduced, and the synchronous rolling ratio is increased "according to industry experts; On the contrary, when the blanket with low hardness wants to reach the same fichu pressure, it is necessary to increase the thickness of the blanket pad, so as to increase the free radius of the drum and the amount of compression. At this time, the synchronous rolling ratio becomes smaller, which will cause point deformation and affect the registration effect. Therefore, the paper tape can be moderately tensioned by using the same size blanket with a hardness higher than that of the first three color printing cylinder in the fourth color printing cylinder

2. Under the condition that the specifications and dimensions of the blanket and the liner of the four-color printing cylinder are unified, by adjusting and changing the center distance of the two rubber cylinders in the third and P11 color printing cylinders, the compression amount of the blanket follows the change of the diameter increasing effect theory to achieve the effect of increasing the surface speed of the third and fourth color printing cylinders. However, if you simply change the compression of the blanket under the condition that the size of the blanket and the liner are unified, it will lead to different four-color point deformation and affect the registration. At this time, it is necessary to balance the relationship between the size adjustment of drum center distance, pad size adjustment, paper tape operation and printing registration, which is closely related to the technical performance of printing materials such as blanket hardness, pad hardness and paper weight. In the actual production, we try to reduce the center distance of the drum, and at the same time, the original size of the liner can be reduced accordingly, which can get the ideal effect

reprinted from: Guangdong Printing

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