Correct use and maintenance of blankets

Blanket plays a very 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 of several blankets for the reader's reference.

Blanket cutting

When the blanket is cut, it should be noted to identify the direction of the filament (warp and weft), and the shape should be rectangular. The latitude and longitude direction of the blanket can be judged from the direction of the weaving line of the dark color on the back of the blanket (warp direction), and the rubber roller should be wrapped to withstand greater tension, so that the elongation is small and the imprinting deformation is small. Whether the shape is rectangular or not can be measured with right triangles or diagonals equal. A non-rectangular blanket will produce torsional deformation when printed.

Blanket installation

When the blanket is loaded into the plate clamp, a 2 cm long mark line can be drawn with a stroke on the mouth of the blanket and the tip of the blanket to check whether the depth of the blanket inserted into the plate clamp is the same. The amount of the two clamps on the opposite side of the blanket should be the same. When tightening the plate clamp screws, tighten them one by one from the center to the sides. Note that the degree of tightness of the screws should be the same.

I have encountered an example of a partial ghosting failure because the apprentice worker twists the rubber plate clamps, and the screws are not tightened one by one from the center to the sides, so that the two sides of the blanket are not telescopic and cause ghost.

After the board clamps are installed, the parallelism of the board clamps should be re-measured. Then put the rubber blanket into the groove of the rubber roller tensioning shaft, and note that the clamping screw has a turbulent amount in the blinking hole in the tensioning shaft slot. Therefore, the blanket opening and the dragging plate clamping screw are in the blink of an eye. Move to the operating side or drive side at the same time to prevent torsional deformation, and then tighten the blanket. Note that the new blanket should be re-tensioned after it has been pressed for a while. The degree of tightness of the blanket can be identified by the sound of the sticking on the blanket.

Blanket cleaning

The surface of the blanket is mainly composed of non-polar synthetic rubber and observed under a 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, during the printing process, pigment particles in the paint particles, vegetable fibers, and ink in the paper tend to stay in the pores of the glue layer on the surface of the blanket due to physical adsorption, thereby forming a covering layer. Since most substances of the cover layer are polar substances, the oleophilicity of the blanket is reduced, and the hydrophilicity is enhanced, so that the small dots on the printing plate cannot be transferred to the paper by the blanket. The appearance of fine powder spots in the field partially affected the printing quality. On the other hand, the hydrophilicity of the blanket is enhanced, and the dampening fluid absorbed by the non-graphical part of the printing plate is transmitted to the paper more through the blanket, causing the paper to stretch, the overprinting to be inaccurate, and printing failures such as feathering and powder falling. . If the cover layer is gradually thickened and hardened, even an “aurora” phenomenon occurs, the rubber layout part will have a larger plastic deformation, and the uniformity of the thickness of the blanket will be damaged. When the other products are changed, partial pressure will be insufficient.

Therefore, always thoroughly scrub the blanket so that the surface is always fluffy. Because the blanket cover layer contains polar substances (paper powder, paper hair, etc.) and non-polar linking materials, according to the principle of similar dissolving, when cleaning the blanket, it is washed with water first and then the volatile organic solvent ( Such as gasoline, etc.) for cleaning.

The internal friction of the blanket

The blanket has a good elasticity, which is different from general materials. The blanket has a low elastic modulus, a large deformation rate, and heat release during the compression. Because the blanket is deformed by periodic alternating stress during the printing process, and always lags behind the change of stress, some elastic potential energy inside the rubber is too late to be released and converted into heat energy. This phenomenon is called internal friction. The internal friction of the blanket cannot 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 press, a good elasticity and low internal friction air cushion rubber can be selected. cloth.

Blanket maintenance

The correct use and maintenance of the blanket can improve its printability, prolong its service life, and improve printing quality. To prevent blanket aging, you can start from the following aspects.

(1) Clean the blanket, remove the paper dust, paper dust and other dirt on it. Pay attention to the cleaning agent.
(2) If the downtime is long, loosen the blanket to allow it to relax and rub the surface with talcum powder, which is conducive to restoring internal stress.
(3) The blanket of the blanket should be flat.
(4) Store the blanket to avoid strong light, it is best covered with black paper.