Blanket: Indispensable indirect transfer material for offset printing

July 14, 2019

Blanket is an indispensable indirect transfer material in offset printing. Offset printing belongs to indirect printing. It is the process of transferring the graphics of the printing plate to the blanket, and the pressure of the blanket and the impression cylinder is used to print the graphic on the substrate. Therefore, the selection and use of the blanket directly affects the printing process. To print quality of offset printing products. At a recent symposium, the reporter interviewed the relevant technical personnel of the domestic designated agent of the ContiTech blanket in China, Beijing Yinlian Printing Company, and made an in-depth understanding of the selection, use, and maintenance of the blanket.

If a printing company wants to obtain a higher profit rate, it usually uses two aspects, one is to increase the added value of products, and the other is to reduce the production cost. Thus, the quality of a blanket can be measured primarily in terms of print quality and service life. Among them, the main parameters affecting the printing quality of the blanket are elasticity, flatness and stretchability. Because the blanket is relying on the elasticity to generate pressure to transfer the carried ink onto the substrate, the stronger the instantaneous rebound force of the blanket, the better the reduction of the dot, and the more the original can be truly restored; and if the blanket The surface roughness is high, and the work done by the printing press to overcome the flatness of the blanket surface is relatively small, the printing pressure is accordingly reduced, and many printing problems can be fundamentally avoided; in sheet-fed offset printing, the blanket is stretched On the roller, there will be a circumferential stretch in the printing direction, the deformation of the blanket with good stretchability will be small, and the graphic deformation of the printing plate will be small and the reduction will be even higher.

The blanket also has two important parameters, namely resilience and oxidation resistance, both of which are closely related to the service life of the blanket. After the blanket is used, the thickness of the blanket will change due to the effect of pressure. If the blanket has good recovery, the thickness of the blanket will change little, and it can withstand long-term use and changes in different printing areas. Second, the blankets are often cleaned during use. Car wash water and other substances will contact the edge to infiltrate, resulting in uneven edges, especially when kerosene, gasoline and other cleaning blankets are used to damage the rubber blanket, so the oxidation resistance is also a decisive factor in the service life of the blanket.

The commonly used offset blankets are classified into air-cushion blankets and ordinary blankets. The main difference between these two types of products is that the air-cushion blanket has a micro-foam sponge layer under the surface adhesive layer in addition to the base cloth, the elastic rubber adhesive, and the surface adhesive layer. This layer of microbubble sponge is formed by numerous tiny, closed air spheres dispersed in the gel layer. After the surface of the air-cushion blanket is under pressure, the air sphere reduces its volume under pressure, so that the blanket can be vertically compressed, avoiding the common blanket. Because the rubber itself is incompressible, the surface layer will be under pressure after being pressed. The area around the area from the convex bulge, causing the rubber roller and the plate cylinder between and between the blanket and the impression roller imprinting increased slippage, resulting in the expansion of the network, the correctness of the transfer of graphics and textual defects.

For color products with a high number of screen printing lines, the use of air-cushioned blankets reduces the expansion rate of the dots, reduces the loss of gradation, improves the definition of the product, and improves the accuracy of tone adjustment and color reproduction. In addition, due to the presence of the microbubble sponge layer, the air-cushion blanket has better sensitivity, elasticity, resilience, and impact resistance than the conventional blanket. For high-speed printing presses, the use of an air-cushioned blanket can make the internal consumption of the blanket not too high in the case of high alternation frequency response. In addition to maintaining the stability of printing pressure, it can also reduce the speed of aging and prolong its use. The life of the blanket. The "Candique" blanket acted by Jinyin is the third-generation blanket invented in the 1990s. It has a number of technical patents and the theoretical design reaches 4 million pieces. Compared with other brands, the dip coefficient is less than 0.05mm. 0.1mm, has excellent performance in high-end printing products.

However, the price of air-cushioned blankets is much higher than that of ordinary blankets, which increases the production cost. Air-cushion blankets are used only on high-speed printing presses and when rigid liners or neutral over-hard liners are used to print high-end products. The superiority of the transfer rate of the Bu Tuwen's high accuracy and sensitivity is well exerted. If soft liners are used to print common products, because of the large amount of compression of the soft liners, the wide embossing area, and the easy spread of the outlets, which offsets the advantage of high precision of the graphic transfer of the air-cushion blanket, it is not worth using the air-cushioned eraser. Cloth up.

Choosing high-quality rubber blankets is just the basis for companies to improve product quality. For how to ensure the stable and efficient operation of printing machinery, the technical staff of Printing Press today recommends that companies in the industry pay attention to details such as installation, use, and maintenance.

During the installation of the blanket, it must be tightened on the blanket cylinder with proper tension. If the blanket is too loose, when the blanket is imprinted, displacement occurs under the action of the pressing force and cannot be reset in time. This can cause ghosting failure. If the blanket is stretched too tightly, the adhesive layer will be thinned and the elasticity will be reduced, affecting the state of simultaneous rolling, resulting in non-uniform printing pressure, so that the background color of the solid or flat net that should have been evenly uniform becomes uneven. The color tone shifts and accelerates the creep and aging of the blanket.

During the imprinting process, if the surface of the blanket is subjected to different directions or forces of different sizes in different axial positions, the shape of the blanket will be torsionally deformed, resulting in graphic shape, ink transfer, overprinting, and blankets. The adverse effects of the service life etc. In the production process, in addition to avoiding carelessness in the adjustment of the center distance between the rollers or during the long-term use of the printing press during the long-term use, the center distance between the two ends of the drum is not equal, and care should be taken to properly follow the specification of the blanket. Cut, install. At the same time, attention should also be paid to making the blanket parallel to the weft and the plate clamp, especially when using a split or full-length blanket that has been scrapped due to a rigid damage and used as a 4-open blanket. Attention should be paid to the warp and weft directions. Sex.

The rubber blanket fastened to the blanket cylinder will inherently contend with the internal stress and the tension that tightens it, but the internal stress will gradually decay with time, causing the tightness to decrease, which is called the stress relaxation of the blanket. The phenomenon of stress relaxation is most likely to occur on newly replaced rubber blankets. Therefore, on the one hand, the newly replaced blanket cannot be stretched too tightly. On the other hand, after printing for a certain period of time, it must be tightened again. This will be repeated three or four times. After that, the stress relaxation phenomenon can be weakened and the tightness of the blanket can be kept stable for a long time.

Due to the different pressures of the blanket in use, the plastic deformation of the blanket may be different, which may lead to uneven thickness of the blanket. Since this lack of pressure is caused by the partial depression of the blanket, even if the overall pressure between the rollers is increased, there can be no obvious improvement. If the blankets selected by the company show such phenomena, only the rubber can be used. Remedy, and this blanket cannot be used to print products with high quality requirements.

If you want to ensure that the blanket is always in a good state of operation and extend its service life, companies in the industry should also pay attention to the maintenance and maintenance of the blanket. Due to the shortcomings of photo aging and heat aging, blankets used by businesses after purchase are wrapped in black paper and stored in a cool place.

In daily maintenance, you should also pay attention to the cleaning of the blanket. Before cleaning, you should use warm water to wipe off the water-soluble substances, and then use a more volatile organic solvent as a detergent, such as the surface of calcium and magnesium ion deposition can use citric acid-containing car wash water or weak acid substances such as vinegar Cleaning. Wash and dry the blanket when washing, leaving no residue. On the one hand, the residue is easily oxidized and dried, which will cause the blanket to age prematurely. On the other hand, when the residue is printed on other products, the unevenness of ink is likely to occur at the beginning. After a certain product is printed, if the downtime is long, the tensioning device of the blanket can be loosened, the blanket can be relaxed, the internal stress can be restored, and the effect of stress relaxation can be actively prevented.

Due to the variety of types of printing presses, the chemical composition of inks and liquids are different, and the printability of the substrates is not the same. The characteristics of blankets, which are important intermediaries, play an important role in the offset printing process. At the end of the interview, the technical staff of the Printing Press today advised companies to base their selection and use of blankets on their own printing methods, substrates, and other related materials. For the enterprise, there is no best blanket, only the most suitable blanket.

Author: Zhiyuan pay Reprinted from: China Packaging

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