The so-called out-of-print refers to the decrease in the fat-sensitivity of the graphics on the printing plate, which weakens the ink affinity of the layout, and the dot area becomes smaller or even lost; the paste version refers to the expansion and deformation of the dot area of ​​the layout. It sticks to the blank part and the printed image is blurry. Looking at the lithographic printing process, there are many reasons for the off-set and paste-up. It must be carefully analyzed and the necessary preventive measures must be taken in production to reduce or avoid the occurrence of off-set and paste-up phenomena to ensure the quality of product printing.
1 Excessive pressure
1) The pressure of plate cylinder and rubber cylinder is too heavy. Pressure is a necessary condition to achieve imprint transfer. Only moderate pressure can effectively guarantee the imprint transfer effect. If the pressure is too light, the imprint transfer is uneven and incomplete, which is easy to cause the ink color of the printing plate to be unclear; on the contrary, if the pressure is too heavy, the friction of the blanket on the surface of the printing plate increases, and the printing will inevitably increase the printing time. The abrasion of the ink-receptive film layer on the surface of the plate is easy to produce a plate-off phenomenon, making the imprint lighter, or even making the graphic printing unclear or the phenomenon of missing pens and broken strokes. In addition, if the pressure between the plate cylinder and the rubber cylinder is too high, it is also easy to cause the expansion and denaturation of the imprint during the transfer process due to the squeezing phenomenon, resulting in the occurrence of paste plate defects.
2) The pressure of the impression cylinder and rubber cylinder is too heavy. When the pressure between the impression cylinder and the rubber cylinder is too heavy, the imprint on the surface of the blanket is bound to be squeezed and spread, and it is easy to form a paste phenomenon.
3) The contact pressure between the inking roller and the inking roller and the printing plate. If the pressure of the inking roller or the water roller and the printing plate is too heavy, excessive squeezing friction will be generated on the surface of the printing plate, and the ink-loving and hydrophilic foundation of the printing plate will be destroyed, resulting in the phenomenon of plate-off or paste-up.
2 Inking roller and water roller
1) The heads of the inking roller and inking roller are worn or deformed or the bearings are damaged. When the shaft head of the inking roller or inking roller is worn due to poor lubrication and the bearing is damaged, on the one hand, due to the occurrence of beating and sliding phenomena, it forms an abnormal friction on the plate surface, thereby destroying the ink-friendly and hydrophilic foundation of the plate surface ; On the other hand, the uneven rotation of the rollers affects the layout to obtain uniform and sufficient ink supply and water supply, and it is also easy to cause the phenomenon of off-set and paste.
2) The ink roller colloid is hard or aging. If the colloid of the inking roller is hard or the surface is cracked and aging, one will increase the friction against the plate surface; the other is that it will easily slip during the ink application; the third is that the adsorption performance of the ink is reduced and it cannot be maintained The effect of inking will inevitably affect the uniform and normal supply of ink on the layout, thereby increasing the chance of the occurrence of offset.
3) There is an eccentric phenomenon on the inking roller or water roller. When the roller body of the inking roller or water roller is eccentric, during the roller rolling process, the friction force on the plate surface of the plate with a large radius increases, which causes damage to the plate film layer, and it is easy to cause plate loss. Gluing phenomenon occurs.
4) The water roller is aging. When the water roller uses aging or the fleece of the fleece is worn, and the water roller is attached with ink stains and impurities, etc., it will affect the normal water absorption and water transfer performance of the water roller. Then, in the case of abnormal water supply, the hydrophilic membrane layer of the layout is easy to absorb ink, so that the ink on the edges of text, lines or dots expands to form a paste phenomenon.
3 Paper quality
As the printing material, the quality of paper directly affects the printing quality and the printing durability of the printing plate. If the paper quality is not good, the surface strength of the paper is poor, and powdering and fluffing are easy to occur during the printing process. After the paper powder and paper wool adhere to the ink roller or water roller, on the one hand, it will affect the normal ink absorption, ink and water absorption. And the water transfer effect, on the other hand, the impurities attached to the ink roller or water roller will increase the friction against the printing plate, and even adhere to the printing plate, resulting in the occurrence of plate-off and pasting defects.
4 Equipment aging
When the equipment is aging, some key components are poorly lubricated, causing wear and loosening, such as roller shaft heads, bushes, gear components, eccentric sleeves, etc. Then, during the pressing process of the cylinder, a slight amount of vibration or sliding phenomenon is likely to occur, which intensifies the friction and wear on the printing plate surface, resulting in the phenomenon of squeezing and pasting indirectly caused by the extrusion deformation during the imprint transfer process.
5 Blanket
1) The blanket is uneven. When the cushion of the blanket is uneven or loose, the surface is bulged, and abnormal friction occurs during imprinting to damage the printing plate film layer, resulting in the phenomenon of plate-off and paste-up. At the same time, due to the looseness of the blanket, it is also likely to cause printing ghosting failures that look like paste.
2) Rubber blankets become harder with aging. If the blanket is used for a long time, the material will be hardened, and the friction force on the plate surface during printing will increase, which will damage the plate film layer, and it will also cause the phenomenon of plate-off and paste-up.
3) The wrong direction of the blanket thread is used? The horizontal thread of the blanket is easily stretched and deformed. If it is used to wrap the cylinder in the circumferential direction, it is easy to appear loose due to extrusion during printing , The raised part of the blanket is not in close contact with the roller, and it is easy to produce sliding friction and squeezing during imprinting, resulting in off-page? Pasting and ghosting failures?
6 Improper adjustment and control of fountain solution
1) Improper adjustment of acidity and alkalinity of fountain solution. If the acidity of the fountain solution is too weak, not enough inorganic salt can be formed to supplement the hydrophilic base layer that is constantly worn away by the plate, so that the oil resistance of the blank part of the plate will gradually weaken, making the dots of the graphic part outward Extend to form a paste phenomenon. On the contrary, when the acidity of the fountain solution is too strong, it will easily corrode the graphic parts of the printing plate and its plate sand, which will weaken the ink absorption of the dots and the graphic, reduce the fat-sensing ability, and damage the lipophilic foundation, resulting in Off-page phenomenon.
2) Improper control of the moisture content of the layout. If the water content on the plate surface is too large, it will make the plate surface and the ink roller have a thicker water film, which will affect the normal uniform transfer and coating of the ink, which will easily cause the plate-off phenomenon; and the plate surface moisture will also make the printing ink color Faint, if you blindly increase the amount of ink to increase the ink color density, it will cause excessive emulsification due to large water and ink. If the water content of the plate surface is too small, it can not compete with the ink, so that the ink layer of the plate surface spreads, and it can also cause the phenomenon of paste.
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