The so-called off-page refers to the reduction of the graphic sensory fat on the printing plate, which weakens the printing plate's ink receptivity, and the dot area becomes smaller or even lost. The pasting plate refers to the enlargement and deformation of the screen dot area, and the blank area is covered with ink to make the printing mark thicker. Adhesion to the blank part, the printed image is blurred. Looking at the lithography process, there are many reasons for the loss of printing and stencil printing. It is necessary to carefully analyze and take necessary preventive measures in production to reduce or avoid the appearance of stencil and stencil printing and ensure the quality of product printing.
1 Overstressed
1) The pressure of the plate cylinder and the blanket cylinder is too heavy. Pressure is a necessary condition for the imprinting transfer. Only moderate pressure can effectively guarantee the transfer effect of imprinting. If the pressure is too light, the imprinting is uneven and incomplete, and the ink on the layout of the printed product may not be clear. On the other hand, if the pressure is too heavy, the friction of the blanket against the surface of the printing plate will increase, and printing will inevitably exacerbate printing. The wear of the ink-film layer on the surface of the plate is prone to produce plate-off phenomenon, lightens the printing of the printing, and even makes the printing of the picture and text unclear or the phenomenon of lack of writing and scratching. In addition, if the pressure between the plate cylinder and the blanket cylinder is too large, it is also easy for the imprint to expand and degenerate due to the extrusion phenomenon in the transfer process, resulting in the occurrence of paste plate defects.
2) The pressure of the impression cylinder and the blanket cylinder is too heavy. When the pressure between the impression cylinder and the blanket 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) Contact pressure between the ink roller and the water roller and the plate. If the pressure of the ink roller or the water roller and the printing plate is too heavy, excessive press friction will be generated on the surface of the printing plate, so that the pro-inking and hydrophilic basis of the printing plate will be damaged, resulting in off-plate or stencil printing.
2 Ink roller and water roller
1) Inker roller and water roller roller head wear deformation or bearing damage. When the shaft head of the ink roller or the water roller is worn due to poor lubrication, and the bearing is damaged, on the one hand, due to the occurrence of a jumping and sliding phenomenon, the plate surface constitutes an abnormal friction, thereby destroying the ink-receptive and hydrophilic basis of the plate. On the other hand, due to the uneven rotation of the rollers, the uniform layout, sufficient ink supply, and water supply are affected, which can easily result in the occurrence of stencil and stencil printing.
2) Applicator roller colloid is hard or aging. If the roller is colloidally stiff or the surface is cracked and aged, one will increase the friction on the plate surface; the other is that the ink will slide easily during the inking process; and the third is the decrease of the ink's adsorption performance, and it cannot maintain good The effect of inking will inevitably affect the uniform and normal ink supply on the layout, thereby increasing the chance of missing the version.
3) The ink roller or the water roller has eccentricity. When the roller body of the ink roller or the water roller appears eccentricity, during the rolling process, the frictional force of the large radius facing the printing plate layout increases, so that the printing plate film layer is damaged, and it is easy to cause the plate off, Paste phenomenon occurs.
4) Water roller aging. When the water roller is used for aging or pile fluff wear, and the water roller with ink, impurities, etc., will affect the water roller's normal water absorption and water transfer performance. Then, under the condition that the water supply is not normal, the hydrophilic film on the plate easily absorbs the ink and expands the ink on the edges of the characters, lines or dots to form a paste phenomenon.
3 Paper quality
Paper as a printing material, its quality has a direct impact on the quality of printing and printing plate printing rate. If the paper quality is not good, the surface strength of the paper is poor, and the phenomenon of powder dropping and pulling is liable to occur during the printing process. After the paper powder and paper hair adhere to the ink roller or the water roller, the normal ink absorption, ink application, and water absorption are affected on the one hand. And the effect of water transfer, on the other hand, attached to the ink roller or water roller on the impurities will increase the friction of the printing plate, and even adhere to the printing plate, resulting in off plate and paste the ills.
4 Equipment aging
When the equipment is used for aging, poor lubrication of some key components causes wear and looseness, such as roller shaft heads, bushings, gear parts, and eccentric sleeves. Then, during the process of pressurizing the roller, it is easy to produce a slight amount of chattering or sliding phenomenon, which intensifies the friction and wear on the printing plate layout, resulting in the phenomenon of inversion and stencil printing caused by the extrusion deformation in the transfer process of the printing.
5 Blanket
1) The blanket is uneven. When the blanket of the blanket is not flat or the looseness occurs, the surface of the blanket is bulged. When the embossing occurs, abnormal friction occurs and the printing plate layer is destroyed, resulting in the occurrence of plate-off and paste-off phenomena. At the same time, due to the virtual looseness of the blanket, it is also easy to cause ghosting-like ghosting problems.
2) The blanket is hardened by aging. If the blanket is used for a long time, the material will harden, and the friction on the plate will increase when the plate is imprinted, which will cause the plate film layer to be damaged, and it will also cause the plate-off and paste plate phenomenon.
3) The direction of the blanket silkworm is misaligned. The cross direction wire of the blanket is easily stretched and deformed. If it is used to circumferentially pack the drum body, it will be prone to looseness due to extrusion during the printing process. The uplifted area of ​​the blanket is not in close contact with the drum. Sliding friction and squeezing are likely to occur during embossing, resulting in the occurrence of plate-off and ghosting failures.
6 Fountain solution adjustment, improper control
1) The pH of the dampening solution is not properly adjusted. If the dampening solution's acidity is too weak, it will not be able to form enough inorganic salts to supplement the hydrophilic base layer on which the plate surface is continuously worn out. As a result, the oil resistance of the blank part of the plate will be gradually weakened and the dots of the graphic part will be outward. Extend and form a paste phenomenon. On the contrary, when the acidity of the fountain solution is too strong, the graphic part of the plate and its plateau are easily eroded, so that the ink absorption of the dot and the graphic text is weakened, the sense fat capacity is reduced, and the lipophilic basis is destroyed, resulting in the generation of Off edition phenomenon.
2) Improper control of the size of the surface moisture. If the layout of water is too large, it will make the layout and ink roller with a thick layer of water film, thereby affecting the normal and uniform transfer of ink and coating, which can easily lead to plate-off phenomenon; and the layout of water is too large will make the printing ink color Too light, if blindly increase the amount of ink to increase the ink concentration, it will cause excessive emulsification due to water and large ink. If the layout of the water is too small, it will not be able to compete with the ink, so that the layout of the ink layer spread, it will also cause paste version.
6 Fountain solution adjustment, improper control
1) The pH of the dampening solution is not properly adjusted. If the dampening solution's acidity is too weak, it will not be able to form enough inorganic salts to supplement the hydrophilic base layer on which the plate surface is continuously worn out. As a result, the oil resistance of the blank part of the plate will be gradually weakened and the dots of the graphic part will be outward. Extend and form a paste phenomenon. On the contrary, when the acidity of the fountain solution is too strong, the graphic part of the plate and its plateau are easily eroded, so that the ink absorption of the dot and the graphic text is weakened, the sense fat capacity is reduced, and the lipophilic basis is destroyed, resulting in the generation of Off edition phenomenon.
2) Improper control of the size of the surface moisture. If the layout of water is too large, it will make the layout and ink roller with a thick layer of water film, thereby affecting the normal and uniform transfer of ink and coating, which can easily lead to plate-off phenomenon; and the layout of water is too large will make the printing ink color Too light, if blindly increase the amount of ink to increase the ink concentration, it will cause excessive emulsification due to water and large ink. If the layout of the water is too small, it will not be able to compete with the ink, so that the layout of the ink layer spread, it will also cause paste version.
Source: Print World
