Blanket is the most popular key to improve the qua

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The key to improve the quality of offset printing -- blanket

blanket is an indispensable indirect transfer in offset printing. Offset printing belongs to indirect printing, which is the process of transferring the pictures and texts of the printing plate to the blanket, and then printing the pictures and texts on the substrate under the pressure of the blanket and the embossing cylinder. Therefore, the selection and use of the clutch angle measurement range of the blanket: 30o directly affects the printing quality of offset printing products. At a recent seminar, I interviewed the relevant technical personnel of Beijing jinyinlian company, the domestic designated agent of German ContiTech blanket, and made an in-depth understanding of the selection, use and maintenance of blanket

if printing enterprises want to achieve a higher profit margin, they usually need to work from two aspects: one is to increase the added value of products, the other is to reduce production costs. Therefore, to measure the quality of a blanket, we can mainly consider the printing quality and service life. Among them, the main parameters that affect the printing quality of blanket are elasticity, flatness and stretch. Because the blanket relies on elasticity to generate pressure to transfer the ink carried to the substrate, the stronger the instant resilience of the blanket, the better the point reduction, and the more the original can be truly restored; If the surface smoothness of the blanket is high, and the work of the printing machine to overcome the surface smoothness of the blanket is relatively small, the printing pressure will be reduced accordingly, and many printing problems can be fundamentally avoided; In sheet fed offset printing, the blanket is stretched on the drum, and there will be circumferential stretching in the printing direction. The deformation of the blanket with good stretching property is small, and the image and text deformation of the transfer of the printing plate is small, so the reducibility is higher

there are also two important parameters of blanket, namely, resilience and oxidation resistance, which are closely related to the service life of blanket. After being used, the thickness of the rubber blanket will change due to the effect of pressure. If the rubber blanket has good recovery, the thickness change is small, and it can withstand long-term use and changes of different printing areas. Secondly, the blanket will be cleaned frequently in the process of use. Substances such as car washing water will contact its edge to penetrate, causing uneven edges, especially when using kerosene, gasoline and other materials to clean the blanket, it will cause greater damage to the blanket, so oxidation resistance is also a decisive factor for the service life of the blanket

at present, the commonly used offset blanket is divided into air cushion blanket and ordinary blanket. The main difference between these two types of products is that compared with ordinary rubber blanket, air cushion rubber blanket adds a micro foam sponge layer under the surface adhesive layer in addition to the base cloth, elastic rubber adhesive and surface adhesive layer. This layer of microbubble sponge layer consists of countless tiny, closed air spheres dispersed in the adhesive layer, which is constructed in strict accordance with the requirements of Shandong University and the standards of the State Key Laboratory; 12 enterprises formed in the establishment of cooperative relations with Shandong South University. After the rubber layer on the surface of the air cushion rubber blanket is compressed, the air sphere reduces its volume under the action of pressure, causing the rubber blanket to produce vertical compression, avoiding the bulge around the compression area of the ordinary rubber blanket due to the incompressible volume of the rubber itself, resulting in the increase of the slip between the rubber drum and the printing plate drum, and between the rubber drum and the printing drum, resulting in the expansion of the point, The correctness of image and text transfer decreases

for color products with high number of lines, the use of air cushion blanket reduces the dot expansion rate, reduces the loss of layers, improves the clarity of products, and improves the accuracy of gradation and color reproduction. In addition, due to the existence of micro foam sponge layer, air cushion blanket has better sensitivity, elasticity, resilience and impact resistance than ordinary blanket. For high-speed printing machines, when the frequency of alternating response is very high, the use of air cushion blanket can not make the internal friction of blanket too large. In addition to maintaining the stability of printing pressure, it can also reduce the aging speed and prolong the service life of blanket. The "Kangdi" blanket represented by Jinyin union is the third generation blanket invented in the 1990s. It has a number of technical patents, and the theoretical design has reached 4million pieces. Compared with other brands, the subsidence coefficient is 0.05mm ~ 0.1mm less, which has an excellent performance in high-end printing products

however, the price of air cushion blanket is much higher than that of ordinary blanket, which increases the production cost. Only when air cushion blanket is used on high-speed printing machines and when high-end products are printed with hard lining or neutral hard lining, can the advantages of air cushion blanket with high graphic transfer accuracy and good sensitivity and elasticity be brought into full play. If ordinary products are printed with soft lining, it is not worth using air cushion blanket because of its large compression, wide embossing surface and easy spreading and expansion, which offsets the advantages of high graphic transfer accuracy of air cushion blanket

choosing high-quality blanket is only the basis for enterprises to improve product quality. As for how to ensure the stable and efficient operation of printing machinery, today's printing union technicians suggest that enterprises in the industry should pay attention to installation, use, maintenance and other details

during the installation of rubber blanket, it must be tightened on the rubber drum under the action of appropriate tightening force. If the blanket is stretched too loosely, the blanket will shift under the action of extrusion pressure and cannot be reset in time, which will lead to ghosting failure. If the blanket is too tight, it will affect the synchronous rolling state due to the thinning of the adhesive layer and the reduction of elasticity, resulting in uneven printing pressure, which will make the original uniform field or flat background color become uneven, the hue of the color image will shift, and accelerate the creep and aging of the blanket

during the embossing process of blanket, if the axial positions of the surface are affected by forces of different directions or sizes, the shape of the blanket will be twisted and deformed, resulting in adverse effects on the graphic shape, ink transfer, overprint accuracy and the service life of the blanket. In the production process, in addition to avoiding carelessness in adjusting the center distance between the rollers or the uneven center distance at both ends of the rollers caused by the self movement of the pressure regulator during the long-term use of the printing machine, attention should also be paid to the correct cutting and installation according to the usage specifications of the blanket. At the same time, it should also be noted that the weft direction of the blanket should be parallel to the plate clip, especially when cutting the split or full blanket discarded due to hard damage as 4-split blanket, it should pay attention to the direction of warp and weft

the rubber blanket fastened on the rubber drum will produce internal stress by itself to compete with the tension of tightening it, but the internal stress will gradually decay with the extension of time, so that the competitiveness of the market will further improve and the tension will decline, which is called the stress relaxation of rubber blanket. The stress relaxation phenomenon is most likely to occur on the newly replaced blanket. Therefore, on the one hand, the newly replaced blanket cannot be too tight at one time. On the other hand, fine chemical industry must be tightened again after a period of pressure printing. Fine chemical industry is one of the most dynamic fields in the chemical industry today. In this way, after repeated three or four times, the stress relaxation phenomenon can be weakened, and the tightness of the blanket will remain stable for a long time

due to the different pressures on the rubber blanket in use, the plastic deformation of the thickness of the rubber blanket is different, which will also lead to the uneven thickness of the rubber blanket. Because this lack of pressure is caused by the local depression of the blanket, even if the overall pressure between the rollers is increased, it cannot be significantly improved. If this phenomenon occurs in the blanket selected by the enterprise, it can only be remedied by filling the rubber, and this blanket cannot be used to print products with high quality requirements

if you want to ensure that the blanket is always in good running condition and prolong its service life, enterprises in the industry should also pay attention to the maintenance of the blanket. As the rubber blanket has the shortcomings of light aging and heat aging, the rubber blanket to be used after purchase should be wrapped in black paper and stored in a cool place

in daily maintenance, attention should also be paid to the cleaning of rubber blanket. Before cleaning, use warm water to wipe away the substances dissolved in water, and then use organic solvent with fast volatility as detergent. If there is calcium and magnesium ion deposition on the surface, you can use car washing water containing citric acid or weak acid substances such as vinegar for cleaning. When washing, clean and dry the blanket without leaving any residue. On the one hand, the remnants are easy to oxidize and dry up, which makes the blanket age in advance; On the other hand, when printing other products at the residue, the ink color is easy to be uneven at the beginning. After a product is printed, if the downtime is long, the tightening device of the blanket can be loosened to relax the blanket, get the opportunity of internal stress recovery, and play an active role in preventing stress relaxation

due to the various types of printing machines, different chemical compositions of inks and pharmaceutical solutions, and different printability of substrates, the characteristics of blanket, as an important intermediary, play an important role in the offset printing process. At the end of the interview, the technicians of Jinyin union suggested that enterprises should base their selection and use of blanket on their own printing methods, substrates and other relevant materials. For enterprises, there is no best blanket, only the most suitable blanket

reprinted from: China Packaging News

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