Proper use and maintenance of the blanket
Time:2023-08-22
Views:1622
The cutting of rubber sheets
When cutting the rubber cloth, attention should be paid to identifying the direction of its thread (warp and weft), and the shape should be rectangular. The warp and weft direction of the rubber cloth can be judged from the direction of the dark woven thread on the back of the rubber cloth (warp direction), and the warp direction should be wrapped in the rubber drum to withstand the larger tensile strength, so that the elongation is small and the imprint deformation is small. Whether the shape is rectangular can be measured with a right triangle or diagonal equality. Rubber sheets that are not rectangular will produce torsion deformation when printed.
Installation of rubber blanket
To check whether the rubber cloth is inserted into the clip at the same depth, draw a 2cm marker at the mouth of the rubber cloth and at the trailing tip. The amount of excess blanket on the opposite side of the two plates should be the same. When tightening the plate clamp screws, it should be tightened one by one from the middle to both sides, paying attention to the same degree of screw tightness.
Originally encountered a case of local ghosting fault, the reason is that when the apprentices screw the rubber sheet clamp, the screws are not tightened from the middle to both sides one by one, so that the two sides of the rubber sheet do not expand and cause ghosting.
After the plate is installed, the parallelism of the plate should be re-measured. Then put the rubber cloth into the groove of the tensioning shaft of the rubber drum, and note that the plate clamp screw in the tensioning shaft groove to have a open momentum in the mortise, so the rubber cloth mouth and drag pin plate clamp screw in the mortise should move to the operating side or transmission side at the same time, to prevent torsion deformation, and then tensioning the rubber cloth. Note that the new rubber cloth should be re-tensioned after a short rotation, and the tightness of the rubber cloth can be identified by the sound of tapping the rubber cloth with a snap of the finger.
Cleaning of rubber sheets
The surface of the rubber blanket is mainly composed of non-polar synthetic rubber. When observed under a magnifying glass, the smooth surface of the rubber blanket is fluff-like. As a result, moisture can be absorbed and transferred to a maximum extent during the printing process.
However, in the printing process, due to physical adsorption, the paint particles in the paper, plant fibers and pigment particles in the ink are easy to stay in the villous pores of the rubber layer on the surface of the rubber blanket, forming a covering layer. Because the substance of the covering layer is mostly polar substances, the lipophilicity of the rubber blanket decreases, and the hydrophilicity increases, resulting in small dots on the printing plate that cannot be transferred to the paper through the rubber blanket. There are powdery fine spots in the field, which seriously affects the printing quality. On the other hand, the hydrophilicity of the rubber blanket is enhanced, and the moistening liquid adsorbed by the non-graphic part of the printing plate is more transferred to the paper through the rubber sheet, resulting in paper elongation, inaccurate overprinting, and printing failures such as hair drawing and powder dropping. If the covering layer gradually thickens and hardens, and even produces the "aurora" phenomenon, the rubber layout part produces a large plastic deformation, destroys the uniformity of the thickness of the rubber blanket, and is prone to the phenomenon of insufficient local pressure when changing other products.
Therefore, it is necessary to scrub the blanket thoroughly and often, so that its surface is always fluffy. Since the blanket covering layer contains polar substances (paper powder, paper wool, etc.) and non-polar linkers, according to the principle of similar solubility, the rubber blanket is cleaned with water first, and then with volatile organic solvents (such as gasoline, etc.) for cleaning.
Internal friction of the rubber cloth
Rubber blanket has good elasticity, different from general materials, rubber blanket elastic modulus is low, deformation rate is large, tensile compression will release heat. Because the rubber blanket is deformed by the action of periodic alternating stress in the printing process, and always lags behind the change of stress, part of the elastic potential energy inside the rubber is too late to release, converted into heat energy release, which is called internal friction. The internal friction of the rubber blanket can not be avoided, so the temperature and humidity of the offset printing workshop and the temperature of the moistening solution should be controlled to reduce the temperature of the rubber blanket, reduce the thermal aging of the rubber blanket, and the air cushion rubber blanket with good elasticity and low internal friction can be selected for the high-speed offset press.
Maintenance of rubber blanket
The correct use and maintenance of the rubber blanket can improve its printability, extend its service life and improve the printing quality. To prevent the aging of rubber blanket, you can start from the following aspects.
(1) Clean the blanket frequently, remove the paper powder, paper wool and other dirt on it, and pay attention to the cleaning agent to be suitable.
(2) If the downtime is long, loosen the rubber blanket, make it in a relaxed state, and apply talcum powder on the surface, which is conducive to restoring the internal stress.
(3) The padding of the rubber blanket should be smooth.
(4) To avoid strong light, it is best to cover with black paper.
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Anna Zhang