Some Opinions of Screen Printing Tower Combination Four Color Registration

In the following, some issues that arise in the production of the tower B-B combination structure printing group are discussed. The phenomenon and solution of the overprint error caused by the unstable running of the tape in the rotary printing are discussed.

The web of paper is fed into the first group of rollers of the printing group after passing through the tension roller and the paper roll has a tension control device to bring proper tension to the paper. In this position, the web is moderately tensioned. And smooth. After the first color printing cylinder is imprinted, the tape enters the second color printing cylinder through a short distance. In the distance between the paper supply section and the second color roller, the paper tape does not easily undergo any major change. The first and second color registrations basically meet the requirements of the standard. After the tape has been subjected to the adsorption of the dampening water and the ink of the two sets of rollers, a total of four pages, the physical properties of the tape itself have begun to change, and there is no compactness just after pulling out from the paper roll. The paper body becomes soft and becomes sticky because of the ink sticking to the surface of the tape. Therefore, when the tape enters the third color printing cylinder from the second color printing cylinder or enters the fourth color printing cylinder from the third color printing cylinder, it is easy to cause the paper strip to run unstably, the tension is not enough, and the paper swings. In other cases, overprinting is inaccurate or takes place; in severe cases, irregular twisting and wrinkling can occur, and the final two colors cannot be printed at all.

For this type of situation, if the printing can be done successfully, it is necessary to solve the problem of how the four-layer BB printing group can maintain enough tension on the paper. When the tape passes through the first two sets of printing cylinders, the tension can basically be obtained from the web tension control system. However, when the tape enters the latter two sets of printing rollers, the paper roll tension control system cannot provide sufficient tension to the paper tape because the tape is affected by the printing pressure of the first two sets of printing cylinders. At this time, the speed of the surface of the blanket cylinder of the four-layer printing group must be taken into consideration. The surface speed of the blanket cylinder of the four-layer printing group is basically the same or the surface speed of the blanket cylinder of the third and fourth layer printing groups is slightly larger than the first and second. The surface speed of the blanket cylinder of the layer printing group enables the tape to maintain proper tension during the entire printing process to maintain the smoothness of the ribbon.

Based on the above considerations, solutions to the problem can be found in the deformation characteristics of the blanket, the principle of rolling of the blanket cylinder, and the center distance of the blanket cylinder.

Each printing cylinder of the rotary printing press is relatively rolled against each other. Although the rotary printing presses used today are basically air-cushioned blankets, due to the elasticity of the air-cushion layer during embossing, the adjacent sides of the rubber surface-pressing lines are theoretically no longer bulging convex bulges. However, in the practical use of the rotary printing press, the elasticity of the rubber blankets of the two blanket cylinders in the relative rolling and pressing eyebrows immediately restores its original shape. During the compression deformation of the printing plate cylinder and the other blanket cylinder at tens of thousands times per hour, The elasticity of the blanket quickly returns to its original shape because the rubber unit body in the blanket enters into the embossing zone to cause compression deformation, and the rubber unit body returns to the pressure disappearing from the embossing area and recovers. Due to the high elasticity of the rubber county, the development of high elastic deformation always lags behind stress. When the previous deformation of the rubber unit body has not yet disappeared due to springback, the next stress is applied again. This continues to circulate, and the elastic energy stored in the rubber is too late to be released into heat. The more heat is released, the greater the internal friction of the rubber. The higher the frequency of stress applied to the rubber blanket, the less elastic the blanket will be, resulting in a slight similarity between the air-cushion blanket and the adjacent sides of the rubber imprinting line. Hysteresis of deformation of convex hulls. Therefore, when the two blanket cylinders are being rolled, the length of the circumference actually rotated by the blanket due to the effect of diameter increase is greater than the length of the blanket when the blanket is not pressed. In addition, the higher the pressure and the higher the convex bulge, the longer the circumference of the blanket is. This theory is a theory developed by Miller of the UK through experiments and is the result of a multiplier effect.

This theory is combined with the working mode of the blanket cylinder of the rotary printing press, and the two blanket cylinders are regarded as the interaction cylinders. After the blanket cylinder is pressed, the rolling radius will increase, and the blanking radius of the blanket cylinder will be increased. The ratio of the free radius to the roll-to-roll ratio, which directly affects the running speed of the paper, is a great help for the proper tension and accuracy of the print.

The factors that affect the rolling ratio are the following:

1. The characteristics of the blanket, different types, different characteristics of the blanket have different rolling ratio. The blanket is mainly selected from the following characteristics:

(1) Hardness: The ability of rubber to resist the pressing of other substances onto its surface. Take into account the quality of the printed matter, the printing rate of the printing plate, the precision of the printing press, and the flatness of the blanket itself.

(2) Elasticity: The ability of the blanket to restore its original shape immediately after removing the external force that deforms it. During the printing process, the blanket is deformed by the pressure of another blanket cylinder. When the pressure is turned away from the surface of the blanket cylinder, the blanket is required to recover quickly to accept the ink on the printing plate. Then it quickly returns to its original state and transfers the carried ink to the paper by the pressure of another blanket cylinder.

(3) Compression deformation: The strength of rubber deformation after the blanket has been compressed several times. When the blanket is printed, it undergoes numerous compression recovery processes, resulting in compression fatigue and permanent deformation. At this time, the blanket thickness will decrease and the elasticity will decrease.

2. Blanket compression: The same blanket has different roll ratios at different compression levels. When the two blanket cylinders are being rolled, the length of the circumference actually rotated by the blanket is greater than the length of the circumference when the blanket is not pressed. The greater the pressure, the longer the circumference of the blanket that it turns. This shows that by changing the center distance between the blanket cylinder and the blanket cylinder, different rolling ratios can be obtained and the surface speed of the blanket cylinder can be changed. In the actual use of adjustment, the center distance between the rollers as long as there is a difference of about 0.01mm-0.02mm, different effects can already be obtained.

The tightness of the blanket: The amount of blanket beyond the original length under a certain tension. The length of the blanket is generally expressed in terms of elongation, the smaller the elongation of the blanket, the better, the elongation is high, the eraser Easy to be stretched, the adhesive layer will be thinned and the elasticity will be reduced. The tighter the blanket is stretched, the thinner it is, and the smaller the free radius of the blanket cylinder, the greater the roll ratio, because the roll ratio will increase and the blanking radius of the blanket cylinder will be greater. The blanket must be tight on the blanket cylinder with proper tension. If the blanket is too loose, when the blanket is imprinted, it will be displaced under the action of the pressing force and cannot be reset in time. This may cause ghosting and other malfunctions to occur. The rubber blanket is too tight and the blanket rubber layer is thinned and the elasticity is reduced. In particular, the air-cushion blanket basically used on the rotary FH~iJ machine may cause the microbubble sponge layer to fail if it is stretched too tightly and loses the air cushion rubber. Due to the good performance of the cloth, the synchronous roll-to-roll ratio of the blanket cylinder relative to the plate cylinder and the impression cylinder will rise, destroying the state of rolling with less.

From the actual production test, we can see that the above adjustments have a very good effect on improving the operation of paper. The tape running from the second color FFJ~U cylinder into the third color FICHU cylinder or from the third color printing cylinder into the fourth color printing cylinder can basically be solved by the above theory. | Method.

printing art

1. In the case of various mechanical parameters of the machine and equipment, the blanket with higher hardness can produce enough printing pressure with a small amount of deformation. At this point, the thickness of the blanket is reduced, the free radius is smaller, and the synchronous rolling ratio is larger; on the contrary, when the blanket having a lower hardness is to reach the same FIchU pressure, the thickness of the blanket needs to be increased. The free radius of the drum increases and the amount of compression increases. At this time, the synchronous rolling ratio becomes smaller, which will cause the dot deformation and affect the register effect. Therefore, by using a same-size blanket with a hardness higher than that of the preceding three-color printing cylinders in the fourth color printing cylinder, a moderate tension of the tape can be achieved.

2. In the case of unified specifications and sizes of four-color printing cylinder blankets and liners, by adjusting the distance between the centers of the two blanket cylinders in the third and the P11 color printing cylinders, the compression of the blanket is subject to the theory of the increase in diameter effect. The change achieves the effect of increasing the speed of the third and fourth color printing rollers. However, if the size of the blanket and the pad are unified, simply changing the compression amount of the blanket will cause four-color dot distortion to affect the registration. At this time, it is necessary to balance the relationship between the center distance adjustment of the roller, the pad size adjustment, the tape running, and the print registration, and the technical properties of the printing material such as the hardness of the blanket, the pad hardness, and the weight of the paper. Have a close relationship. In actual production, it is attempted to reduce the center distance of the drum while achieving a desired effect on the original size of the liner.

Reprinted from: Guangdong Printing