The printing plate printing rate usually refers to the number of times the printing plate completes the printing transfer from the beginning of printing to the printing plate failure. The form of printing plate failure usually includes the wear failure of the printing plate photosensitive layer, the wear failure of the printing plate blank layer and the failure of the printing plate. three conditions. The factors affecting the printing durability of CTP plates in the printing production process are various. It is mainly related to the two major aspects of plate making and printing. This article analyzes the factors affecting the printing durability of the plates from these two aspects. Provide useful ideas and solutions for encountering such problems in your production.
First, CTP platemaking
1. If the optical path of the CTP platesetter is not cleaned for a long time or the focus is not correct, the laser energy output on the surface of the plate will be lower than the laser energy required for the photopolymerization of the plate. The photosensitive layer on the surface of the plate cannot be The photopolymerization photochemical reaction is completely carried out, so that the photosensitive layer in the image portion cannot be completely crosslinked, thereby causing a decrease in the printing durability. Therefore, the plate light path is cleaned and calibrated regularly to ensure that the laser energy on the surface of the plate is correct, so as to ensure the normal printing durability.
2. The plate can not be properly attached to the drum surface in the CTP plate making machine, which will cause the laser energy on the surface of the plate to be incorrect, which will also lead to a decrease in the printing durability.
3. The pre-heating function of the plate-making machine plays an important role in further curing the photosensitive layer on the surface of the plate material which has been photochemically reacted on the aluminum substrate of the plate material, thereby improving the printing durability. If the preheating temperature is too low, the photosensitive material does not cure well on the surface of the plate, resulting in a decrease in the printing durability.
4. During the printing process, the developer concentration, temperature is too high or the development time is too long, and the corrosion of the photosensitive layer causes the printing durability to decrease.
5. If the amount of water washed in the post-printing process is insufficient, the residual developer will continue to erode the photosensitive layer and cause the printing rate to drop.
6. Some protective glue will react with the photosensitive layer. If there is no protective glue that can properly use CTP plate (original protective glue is recommended), it may also lead to insufficient printing durability.
7. If the temperature and humidity of the CTP room are extremely extreme, it will also affect the printing durability of the board.
8. If the temperature is too high or too low in the baking plate, the time is too long or too short, which will lead to a decrease in the printing durability.
Second, the printing link
(1) The influence of the state of the printing press on the printing durability of the printing plate
The state of the printing press during printing is one of the main factors affecting the printing durability of the printing plate. The three main forms of failure of the plates are mostly related to press pressure adjustment.
1. Each type of offset printing machine is designed to have a reasonable printing pressure according to the selection of the blanket lining. For example, a hard-lined machine usually has an rubber compression of about 0.1 mm. When the imprinting is not real in the production, the operator sometimes chooses to increase the printing pressure to improve, which will lead to excessive printing pressure. During the printing process, the sliding friction of the embossing surface will greatly increase the wear of the printing plate and seriously reduce the printing durability of the printing plate. Generally, the printing machine should strive to make the embossing surface purely rolling, but when embossing, the compression amount of the blanket is different. The corresponding actual rotation radius is inconsistent, and there is inevitably sliding friction on the embossed surface. Therefore, when the printing machine is designed for the drum, the relationship between the radius of the roller and the lining should be considered to minimize the sliding of the embossed surface. When printing and printing, the data and pressure of the lining should not be arbitrarily changed. Otherwise, it is easy to increase the sliding friction of the embossed surface, resulting in a decrease in the printing durability of the printing plate.
2. The contact pressure between the inking roller and the lower ink roller is too large, and the line speed of the inking roller may be inconsistent with the linear speed of the plate cylinder, resulting in a speed difference and a large wear on the printing plate, thereby reducing the printing durability.
3. If the contact pressure between the inking roller and the printing plate is too large, the imprinting dot will not be clear and smooth, or the dot will be enlarged; if the impact jumps at the biting mouth, the ink bar will appear; the blank part or the graphic basis of the layout is accelerated. Wear and reduce the printing durability of the plate.
4. The machine structure is different, which also has a great influence on the printing durability of the printing plate. The sheet-fed press cylinder has a neutral angle. When the inking roller and the water-feeding roller turn over the neutral angle to contact the printing plate, there is an impact on the plate mouth, and the hydrophilic layer at the bite of the printing plate is more likely to wear the upper dirt. The surface of the web offset press roller is basically continuous, and the impact of the water roller and the ink roller on the plate mouth is relatively small. Therefore, the same type of paper, usually the printing plate on the web offset press will have a significantly higher printing yield than the single. Sheet of paper offset press.
5. If the pressure between the inking roller and the printing plate is too light, the ink cannot be supplied to the printing plate sufficiently. If the pressure is too light, the impression will be emptied. If it can not be found in time, the graphic basis of the surface of the printing plate can not be protected by the ink layer, and it is eroded by the dampening liquid, which eventually leads to the elimination of the plate and reduces the printing durability of the printing plate.
(2) Printing materials
1. Adjust the viscosity of the ink and control the thickness of the ink layer of the printing plate to meet the protection effect of the remaining ink layer on the printing plate. If the remaining ink layer is too thin after the printing, the abrasion of the printing plate will be aggravated. As a result, the printing durability of the printing plate is reduced. Sometimes when printing a spot color, if the color of the spot color ink is too deep, the spot color can only be printed lightly by reducing the amount of ink. When the amount of ink is too small, the ink layer of the plate is too thin. The plate printing rate is reduced.
2. Paper lint and powder drop will reduce the printing durability of the printing plate. Paper and paper powder will play the role of abrasive, which will increase the wear on the printing plate.
3. The hardness of the rubber layer on the surface of the blanket will also affect the printing durability of the printing plate. Generally, the surface hardness of the blanket is larger, which is good for the quality of the dot reduction, and the durability of the blanket is also higher, so the company tends to choose A blanket with a higher hardness, but the wear on the plate and blanket embossed surface will be heavier. We recommend that when the precision of the printing press is good and the substrate is coated paper, a blanket with a higher hardness can be selected, and vice versa, a blanket with a smaller hardness is selected.
4. The aluminum plate of the plate is rolled into an aluminum plate by calendering. The calendering process will break up and lengthen the grain of the aluminum, so that the mechanical strength of the plate rolling direction will be better than its vertical direction. For the sheet-fed machine, in order to improve the overprinting accuracy by using the stretched printing plate, the rolling direction of the plate base is usually parallel to the axial direction of the drum; and the web printing machine has a high printing speed, a large printing number, and is easy to produce a plate in the imprinting process. The tail fracture causes the printing plate to fail. Therefore, the rolling direction of the web printing press plate is usually the vertical roller axial direction, so that the mechanical strength of the plate base rolling direction can be utilized to improve the printing durability of the printing plate.
5. The use of harder calcium carbonate powder for dusting will reduce the printing durability of the printing plate.
(3) Printing process control
1. When the printing plate is bent on the upper plate, the size of the curved plate is not suitable. When printing, the printing plate cannot be evenly and closely attached to the plate cylinder, resulting in uneven force, which will accelerate the wear of the printing plate. In addition, the plate should be placed with no foreign matter on the front side of the plate, and the plate pad should be kept at the proper thickness.
2. The blanket should not be stretched too tightly. The data of the synchronous rolling ratio will increase with the increase of the tightness. If the tension is excessive, the sliding between the rollers will be increased. If the blanket is stretched too tightly, the surface of the blanket will lack the retracting space. It is inevitable that there is a speed difference between the rubber and the printing plate. If the surface layer has a retreating space, the blanket may move along with the printing plate. Otherwise, it is easier to produce a relative sliding between the eraser and the printing plate, which tends to increase the grinding plate.
3. The pH of the dampening solution is usually controlled between 4.8 and 5.3. When the acidity is too weak, it may cause printing defects such as emulsion and ink emulsification, but the acidity is too strong, which will increase the corrosion of the hydrophilic layer by the fountain solution. If it is excessively corroded the layer basis, it will cause the plate to fail and cause the plate to fail. If the hydrophilic layer of the blank area is excessively corroded, the surface of the new metal is exposed, which will cause the smear and cause the plate to fail. Therefore, when the acidity of the fountain solution is too strong, the printing durability of the printing plate is also lowered.
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