How to use and maintain the blanket properly
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The blanket plays an important role in the printing process. Proper use and maintenance of the blanket can extend its service life. The following describes the use and maintenance methods of several blankets for the reader's reference.
Blanking of the blanket
When the blanket is cut, care should be taken to identify the direction of the thread (latitude and longitude), and the shape should be rectangular. The warp and weft direction of the blanket can be judged from the direction of the deep color of the back of the blanket (warp direction), and the rubber cylinder should be wrapped in the warp direction to withstand a large tensile strength, so that the elongation is small and the deformation of the print is small. Whether the shape is rectangular or not, it can be measured with a right triangle or a diagonal. A blanket that is not rectangular will produce torsional deformation during printing.
Blanket installation
When the blanket is loaded into the plate holder, a 2cm long mark line can be drawn on the placket and the tip of the blanket to check whether the depth of the blanket insertion plate holder is the same. The amount of the opposite sides of the two plate clamps should be consistent. When tightening the plate clamp screws, tighten them one by one from the middle to the sides. Note that the screws are the same.
I have encountered a partial ghosting fault. The reason is that when the apprentice worker twists the blanket plate clamp, the screws are not tightened one by one from the middle to the two sides, so that the two sides of the blanket are not retractable and cause ghosting.
After the plate clamp is installed, the parallelism of the plate clamp should be re-measured. Then insert the blanket into the groove of the rubber roller tensioning shaft, and pay attention to the amount of sway in the mortise in the tensioning shaft groove of the plate clamp screw, so the rubber squeegee and the trailing plate clamp screw are in the blink of an eye. It should be moved to the operating side or the drive side at the same time to prevent torsional deformation and then tension the blanket. Note that the new blanket should be re-tensioned after being rotated for a while, and the tightness of the blanket can be identified by the sound of the finger rubbing the blanket.
Blanket cleaning
The surface of the blanket is mainly composed of non-polar synthetic rubber. Under the magnifying glass, the surface of the smooth blanket is fluffy. Therefore, it is possible to maximize the adsorption and transfer of moisture during the printing process.
However, in the printing process, due to the physical adsorption, the paint particles in the paper, the plant fibers and the pigment particles in the ink tend to stay in the pores of the rubber layer on the surface of the blanket to form a covering layer. Since the material of the covering layer is mostly a polar substance, the oleophilicity of the blanket is lowered and the hydrophilicity is enhanced, so that small dots on the printing plate cannot be transferred to the paper through the blanket. Powdery fine spots appear in the field, which seriously affects the printing quality. On the other hand, the hydrophilicity of the blanket is enhanced, and the dampening solution adsorbed by the non-image part of the printing plate is more transmitted to the paper through the blanket, causing the paper to elongate, the overprinting is not allowed, and the printing failures such as pulling and falling powder are caused. . If the covering layer is gradually thickened and hardened, even the phenomenon of "Aurora" is generated, which causes large plastic deformation of the rubber layout portion, and the uniformity of the thickness of the blanket is destroyed, and partial pressure shortage is likely to occur when printing other products.
Therefore, always wipe the blanket thoroughly and keep its surface in a fluffy shape. Since the blanket cover layer contains polar substances (paper powder, paper wool, etc.) and non-polar binders, according to the principle of similar compatibility, the rubber blanket is washed once with water, and then the organic solvent is evaporated. Such as gasoline, etc. for cleaning.
Internal friction of the blanket
The blanket has good elasticity. Different from the general material, the blanket has low elastic modulus, large deformation rate, and exotherm when stretched and compressed. Since the blanket is deformed by the cyclic alternating stress during the printing process, and always lags behind the change of the stress, part of the elastic potential energy inside the rubber is not released, and is converted into heat energy, which is called internal friction. The internal friction of the blanket can not be avoided. Therefore, the temperature and humidity of the offset printing workshop and the temperature of the fountain solution should be controlled to reduce the temperature of the blanket and reduce the heat aging of the blanket. For the high-speed offset printing machine, an air cushion rubber with good elasticity and small internal consumption can be selected. cloth.
Blanket maintenance
Proper use and maintenance of the blanket can improve its printability, extend the service life and improve the printing quality. To prevent the aging of the blanket, you can start from the following aspects.
(1) Wash the blanket frequently, remove the paper powder, paper hair and other dirt on it, and pay attention to the cleaning agent.
(2) If the downtime is long, loosen the blanket to make it loose and apply talcum powder on the surface to help restore internal stress.
(3) The blanket of the blanket should be flat.
(4) To store the blanket to avoid strong light, it is best to cover it with black paper.