Talking about the use and maintenance of blanket
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Simply put, the role of the blanket in the offset printing process is to transfer the graphic from the printing plate to the substrate (paper) by the elastic pressure generated by the compression deformation between the roller and the rubber. Most blankets are made up of three layers of long-fiber cotton felt and special rubber. And it is coated with a mixed rubber layer on one side. There are some subtle differences between different blankets. In order to ensure the quality, the thickness deviation of the blanket must not exceed ±O.01mm; many printing houses currently use more advanced air cushion blankets, which add a lot of tiny closed air spheres in the structure and are dispersed in the glue layer. Therefore, it can be compressed when it comes into contact with the plate cylinder and the impression cylinder, and the air cushion rubber cloth has stronger impact resistance, crush resistance and elasticity. Its compression capacity is 0.10mm larger than that of ordinary blankets. Its elasticity, ink transmission performance, and service life are much stronger than the latter. It is mainly used in high-speed machines and printing presses that use rigid or neutral lining and high-grade products.
Before the new blanket is placed on the machine, it must be cut according to the size required by the printer. In theory, all four sides are right angles. If the blanket is skewed, the force will be uneven, and it will be easy to creep or twist. The dot is deformed during printing. When the upper plate is clamped, the position in the warp and weft direction should be distinguished. Generally, there is a mark on the rubber, and the red or green line on the back base cloth is the direction of the blanket. It is also possible to use a hand to force the stretch test. The one that can feel the obvious elongation is the latitudinal position, that is, the direction of the upper rubber band, and the one that is not easy to stretch is the warp position. If the direction is wrong, the blanket will not be pulled up longer after the machine is on the machine, and the printed matter will have a ghost phenomenon, and the rubber will be scrapped. After determining the direction, when the upper rubber clamp screw should be measured on both sides and the longitudinal distance is the same, tighten the middle bolt first, and tighten the screws in the order of the two sides. If the upper two sides are first, the blanket is easy to be wavy, which affects the EN, J effect and blanket life. After all the screws are tightened, check with a ruler to ensure that the two rubber clips are parallel and the distance is the same. If the two sides of the loaded clip are not parallel, the tension of the rubber in the axial direction is not uniform, so that the side of the blanket is loose and the side is tight. The blanket will thus be twisted and deformed. When the rubber blanket is put on the machine, the rubber clip must be stuck in place, otherwise the plate will not be in place, and the machine will be damaged when the high-speed printing is damaged. The blanket and liner should be tightly wrapped around the drum to maintain sufficient tension to prevent slippage under the printing pressure. Since the upper blanket is manually controlled, the error may be very large: in general: the tension is controlled between 50-70 kg force, the elasticity is harder when pressed by hand, and the finger bullet has a distinct "click" sound. It is appropriate. If the tension is too loose, the blanket will be displaced under the action of the pressing force and cannot be reset in time, causing the ghosting failure, and the tension is too tight, which will lead to the thinning of the rubber layer, the decrease of the elasticity, and the uneven plastic deformation.
After the new blanket is installed on the machine, it can be cleaned with pumice powder and then cleaned with a cleaning agent to effectively remove foreign particles on the surface due to production or transportation. The blanket will stretch under tension and roller pressure, so it must be re-tightened over time to make it suitable. Therefore, the new blanket should be pressed and printed for 10 minutes, then tighten the rubber again. Otherwise, the print will have a ghost image, and the overprint will not be allowed to wait for production failure. In particular, it should be noted that the rubber lining must be added according to the parameters of the printing machine. If the lining is not suitable, it is too thick and too soft. During the printing process, the diameter of the blanket cylinder is not equal with the roller pressing, which affects the inconsistent line speed. The speed difference, the rubber and the printing plate and the surface of the substrate are rubbed, so that the plate image points are irregularly enlarged, reduced and ghosted, resulting in a wide and narrow position, the position is not fixed, and the serious feeling of the machine is obviously dull. Sound, accelerate machine wear, damage machine gear and other phenomena. Of course, after a certain period of use, the blanket will also be plastically deformed in the thickness direction under the action of the tension and the roller pressure, resulting in a reduction in the thickness of the blanket. Therefore, the printing pressure is weakened, resulting in the illusion of the printed matter, the unclear text, and the incompatibility of the ink color; the thickness of the blanket is also reduced by the measurement of the dry scale, and it is necessary to consider appropriately increasing the thickness of the liner, the thickness or adjusting the machine pressure. make up. In order to ensure the quality of normal printing products.
In the printing process, paper wool, paper powder, and ink are accumulated on the blanket to form an indentation; the operator should develop the cleaning habit in time, otherwise the local printing pressure will be increased, so that more plastic deformation occurs locally in the rubber. Or a layer of white paste paper powder is deposited on the rubber, which is difficult to clean. At the same time, quick-drying ink, dry oil and other additions of Dl:i-N will also harden the rubber layer, cause crystallization, reduce its elasticity and ink absorption, and affect the normal ink transfer of the blanket. In this case, remove the blanket, clean the blanket with gasoline or reducing agent, and then wipe it repeatedly with pumice powder and detergent until the crystal or paper powder is completely removed. The rubber is placed in the shade for a while, so that it slowly returns to elasticity and then used. When cleaning the blanket, you should use an organic solvent that evaporates faster. Slowly volcanic kerosene or other solvent cleaning blanket will swell, wash and wipe the blanket when cleaning, leaving no residue. Especially when the two shifts are handed over, the blanket must be thoroughly cleaned. Otherwise, the paper wool, paper powder and ink residue will accumulate on the blanket for a long time. Accelerating the aging of the blanket will greatly reduce the function of the blanket transfer. The ink and paper powder on the impression cylinder must also be cleaned in time. If it is accumulated for a long time, the blanket will be damaged and its service life will be affected.
During the production process, it is inevitable that wood strips, screws, rotten paper strips, and excessively thick cardboard will fall into the printing press to break the rubber. If the surface of the blanket is damaged, it must be replaced with a new one. If it is only partially pressed into a dent, it can be reduced with a rubber reducing agent, and then the paper is padded at the back indentation to raise the concave portion to achieve the printing effect. The repaired blanket can still be used for a long period of time.