Structure and printing characteristics of the hott

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The structure and printing characteristics of offset blanket

offset blanket is a product of high molecular compounds. Understanding and mastering the structure and printing characteristics of offset blanket is of great significance for rational use. This article makes a brief discussion on this knowledge, throwing a brick to attract jade, with a view to our common discussion and research

I. types of printing blanket

there are many types of printing blanket, which can be divided into rubber blanket for impression cylinder and rubber blanket for transfer according to their functions. Gravure printing blanket and lead printing blanket belong to the blanket for embossing cylinder (this kind of blanket printing process is not in contact with the ingenious woman of ink, making bricks without straw), sheet fed offset press blanket, web offset press blanket and iron printing blanket belong to transfer printing blanket. From raw materials to products, offset blanket should not only be composed of special synthetic rubber and excellent compounding agents, but also have special rubber processing equipment and advanced processing technology. With the continuous development of the printing industry, the variety and quality of printing blanket have also been greatly developed and improved. At present, in addition to ordinary rubber blanket, air cushion rubber blanket has also been widely used

second, the structure of offset blanket

these are issues that need to be focused on.

the structure of offset blanket is designed according to the distance between the rollers of the printing machine and the thickness of the outer lining of the rubber roller, combined with the requirements of printing technology (such as ink, solvent, printing pressure and other factors). The structure of offset blanket is shown in Figure L

l, total thickness: the thickness of domestic blanket is the same as that of foreign similar products, with a total thickness of l.80~1.90 mm. There is also a small amount of blanket with a total thickness of 160~1.7o mm, which is composed of three layers of bottom cloth

2. Thickness of surface glue: the thickness of surface glue should be appropriate, generally 0.6~0.7 mm. If it is too thin, the elasticity is low and the hardness is high, which will wear the printing plate, reduce the printing resistance of the printing plate, and also make the point not full. The ink bar (i.e. the strip head of the picture) and the black depth are different; If the surface glue is too thick, the printing points will be deformed (such as point expansion, elongation, etc.), resulting in the movement of the imprint, inaccurate overprint, and blurred picture

3. Thickness of cloth layer glue; Cloth layer glue is mainly used to bond the base cloth and increase elasticity. Its thickness is generally controlled at 1.2~1.3 mm (including four layers of base cloth) due to the limitation of surface glue thickness and total thickness. The thickness of the adhesive layer between the four layers of base cloth is also different, as shown in Figure 2. The thickness and performance design of the adhesive layer between 1~2 layers of base cloth mainly takes into account the compressibility and softness of the adhesive layer close to the printing surface. The thickness and performance of the adhesive layer between 3~4 layers of base cloth only play the role of bonding the base cloth

4. The number and thickness of the base cloth: the radial force on the blanket during printing is very large, nearly 100o kg. Therefore, the blanket should choose the high-strength plush cotton cloth as the skeleton material

5. Structure of air cushion blanket: there is no obvious difference between the shape of air cushion blanket and ordinary blanket. Its thickness is roughly 1.65~1.9 mm, which is divided into several specifications. The main difference between air cushion blanket and ordinary blanket is that there are not only different fabric layers and rubber layers, but also an inflatable layer in the middle, which constitutes an elastic layer. The inflatable layer is mainly divided into micro bubble and air groove

III. characteristics of offset rubber

offset blanket is different from ordinary rubber products. It is responsible for transferring the ink on the printing plate to the paper. In order to make the printing ink uniform, clear and rich in layers, offset blanket must have the characteristics of moderate hardness, small compression deformation, good ink transfer performance and small elongation. In terms of chemical properties, it must not only have the function of adsorbing ink and fountain solution, but also have the performance of not reacting with oil and potion and being eroded by oil and potion. And because it is lithographic printing, it requires high flatness of blanket. The technical requirements for offset blanket are as follows:

1. Hardness: refers to the ability of rubber to resist other substances pressing into its surface. In terms of printing requirements, too high or too low hardness is not enough. Three aspects should be considered: the quality of printed matter, the service life of printing plate, and the accuracy of printing machine and blanket itself. 2. After all the bomb projects are put into production, it refers to the ability of the rubber blanket to return to its original state immediately after removing the external force of its deformation. During the printing process, when the rubber drum contacts with the embossing drum, the rubber blanket will be deformed under certain pressure. When the surface of the embossing drum turns away from the surface of the rubber drum, the rubber blanket is required to quickly restore to the original state and then accept the ink on the printing plate. Therefore, the rubber blanket must have high elasticity. 3. Compression deformation: refers to the strength of rubber deformation of rubber blanket after repeated compression. When the blanket is printed, it will be compressed thousands of times per hour. Countless compression recovery processes will produce compression fatigue and permanent deformation. At this time, the thickness of the blanket will be thinner and the elasticity will be reduced, so that the blanket cannot be used anymore. Therefore, the smaller the compression deformation of the blanket, the better. 4. Breaking force: refers to the force used when the blanket is broken. The tension of the blanket during printing is nearly 1000 kg. Therefore, when considering the framework material, the warp yarn of the base cloth should have quite high strength, because the blanket mainly relies on the base cloth to bear these forces when under tension; In addition, the surface rubber layer must also have a certain strength, so that the surface rubber will not be crushed by the sand in the paper or folded paper. 5. Ink transmissibility: refers to the ability of the blanket to transfer ink. Blanket should not only have a strong ability to accept ink (that is, the ability to absorb), but also have the ability to transfer ink appropriately. 6. Oil resistance and solvent resistance of surface glue: refers to the ability of rubber cloth surface glue to resist the penetration of oil or some solvents. Without this resistance, the part of the blanket that contacts the ink and solvent will expand, affecting the printing. 7. Flatness: when processing blanket, there are requirements for the thickness uniformity of each point, that is, the processing thickness must have a certain accuracy. Offset blanket is used for offset lithography. During printing, the compression between the rubber cylinder and the impression cylinder is only 0.1~0.2 mm. Therefore, the flatness of the blanket must be properly determined. The flatness error generally should not exceed 0.04 mm. If it exceeds 0.04 mm, the ink color of the print will be uneven, and the dot shape will change, etc. Sometimes you have to stick paper on the back of the blanket to make it flat before using it. Therefore, flatness is particularly important for offset blanket. 8. Elongation: refers to the amount that the rubber blanket exceeds the original length under a certain tension. The elongation of the rubber blanket is generally expressed by elongation. The smaller the elongation of the rubber blanket is, the better. When the elongation is larger, the rubber is easy to be stretched, the rubber layer will be thinner, and the elasticity will be reduced. The elongation of rubber blanket mainly depends on the strength of the four layer base cloth. 9. Appearance quality: if there are pores on the weld of the blanket, the surface should be treated like the printing plate, so that the surface is evenly distributed with countless small sand holes, and the surface is fine, clean and smooth, without small impurities. If the surface is not treated, the surface of the blanket is too smooth, and its ink absorption is poor. On the other hand, experiments have proved that the rubber blanket with high smoothness (also known as smoothness) has much greater force in absorbing paper wool impurities than the rubber blanket with rough surface

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