In the printing process, the phenomenon of dirt on the blank part of the printing plate often occurs, which not only reduces the printing resistance of the printing plate, but also affects the printing quality, and brings unnecessary waste to manpower and material resources. The causes of the blankness of the blank part of the printing plate are "congenital" and "acquired" as well as the nature of raw materials.
First, the dirt caused by the printing version (used as "congenital")
1. Underexposure results in incomplete decomposition of the photosensitive layer, incomplete removal of the development, and dirtiness in the blank area. Minor can be rescued by the second development method, and only severely scrapped. Determining the proper exposure time is the key to determining the quality of the printing plate. Different types, manufacturers of PS version have different exposure times, we can use the gray radiography or Bruner test strip to determine the exposure time for later use, usually the proof version in the 3.5-4.5 class white, The machine is transparent at 4.5-5.5 level. Different manuscripts also have different exposure times. For example, text and line versions are longer than fine dot image versions. We must use them flexibly according to actual conditions.
2. Underdeveloped. The causes of underdevelopment are: 1 the concentration of the developer is not enough; 2 the temperature of the developer is low; 3 the development time is insufficient. It is best to refer to the information provided by the manufacturer of the PS plate about the alkali resistance, chemical stability, and recommended formulation of the photosensitive layer in the developer solution, and make the PH value between 7.5-9. The temperature of the developer should be kept between 20-24°C. The development time should be measured with a printing plate, and it should be periodically replaced and replenished with new developer.
3. Baking version. Bakeware is a technique used by manufacturers to improve the printing plate's resistance to printing and reduce the loss of raw materials, but it has its own disadvantages. After baking, the blank part of PS plate is easy to get dirty, so we must Carefully clean the plate, completely remove dirt, and apply baking solution, then bake it in an oven at 230-250°C for 5-8min, take out the product and then perform secondary development with natural cooling to minimize dirt.
4. Others. In addition to the dirty method is not enough dirty dose, the time is not enough, in addition to the dirty agent on the printing plate; improper ink; wipe the protective rubber when there is a leak; the printing plate, the base, the plate glass on the dirty Traces, dust, etc. will cause the blank part of the plate to "congenitally dirty."
Second, the improper adjustment caused by printing dirty
1. The pressure between the printing plate and the blanket is too high, so that the oxide film of the blank part is damaged, and the sand becomes lighter and dirtier. Therefore, under the premise of ensuring the quality of printed products, try to use the minimum pressure that is the pressure can make the prints solid without spreading.
2. The pressure between the water roller and the plate, between the ink roller and the printing plate is too large, which causes chemical damage and large friction, which damages the dirt on the grain. Generally, the indentation between the water roller and the printing plate is between 6 and 7 mm, and the indentation between the ink roller and the printing plate is between 5 and 6 mm.
3. The fountain solution has a low pH. A low pH results in corrosion of the plate's hydrophilic oxide film, resulting in less water on the plate and dirtiness. Generally, the pH is controlled between 5-6.
4. Others. In printing, artificially damaged plates, thick ink on the layout, long downtime and no sealing can cause dingy. We not only need to take good care of the printing plate, but also need to keep the printing quality under the premise of small water, small ink and low pressure. In order to save time, peach gum can be added to the dampening solution, and it is not necessary to seal at 1-2 hours of shutdown.
2, the impact of the nature of raw materials
1. The nature of the PS version. 1 The transparency is not good, thus hindering the light from passing through due to underexposure; 2 uneven coating of the photosensitive adhesive, causing insufficient decomposition during exposure; 3 having a large degree of fog and so on.
2. The nature of the paper. 1 The paper's PH value is generally around 7; when it is greater than 7, it will neutralize the fountain solution and affect the hydrophilicity of the printing plate; 2 the paper loses powder, loses wool, has sand, and sticks to the printing plate or blanket during printing. It increased friction.
3. The nature of the ink. If the particle size is large and the friction is large, the dirt on the grain is damaged.
Therefore, we must not only regulate the machine, control the printing plate, but also can not ignore the choice of raw materials.
First, the dirt caused by the printing version (used as "congenital")
1. Underexposure results in incomplete decomposition of the photosensitive layer, incomplete removal of the development, and dirtiness in the blank area. Minor can be rescued by the second development method, and only severely scrapped. Determining the proper exposure time is the key to determining the quality of the printing plate. Different types, manufacturers of PS version have different exposure times, we can use the gray radiography or Bruner test strip to determine the exposure time for later use, usually the proof version in the 3.5-4.5 class white, The machine is transparent at 4.5-5.5 level. Different manuscripts also have different exposure times. For example, text and line versions are longer than fine dot image versions. We must use them flexibly according to actual conditions.
2. Underdeveloped. The causes of underdevelopment are: 1 the concentration of the developer is not enough; 2 the temperature of the developer is low; 3 the development time is insufficient. It is best to refer to the information provided by the manufacturer of the PS plate about the alkali resistance, chemical stability, and recommended formulation of the photosensitive layer in the developer solution, and make the PH value between 7.5-9. The temperature of the developer should be kept between 20-24°C. The development time should be measured with a printing plate, and it should be periodically replaced and replenished with new developer.
3. Baking version. Bakeware is a technique used by manufacturers to improve the printing plate's resistance to printing and reduce the loss of raw materials, but it has its own disadvantages. After baking, the blank part of PS plate is easy to get dirty, so we must Carefully clean the plate, completely remove dirt, and apply baking solution, then bake it in an oven at 230-250°C for 5-8min, take out the product and then perform secondary development with natural cooling to minimize dirt.
4. Others. In addition to the dirty method is not enough dirty dose, the time is not enough, in addition to the dirty agent on the printing plate; improper ink; wipe the protective rubber when there is a leak; the printing plate, the base, the plate glass on the dirty Traces, dust, etc. will cause the blank part of the plate to "congenitally dirty."
Second, the improper adjustment caused by printing dirty
1. The pressure between the printing plate and the blanket is too high, so that the oxide film of the blank part is damaged, and the sand becomes lighter and dirtier. Therefore, under the premise of ensuring the quality of printed products, try to use the minimum pressure that is the pressure can make the prints solid without spreading.
2. The pressure between the water roller and the plate, between the ink roller and the printing plate is too large, which causes chemical damage and large friction, which damages the dirt on the grain. Generally, the indentation between the water roller and the printing plate is between 6 and 7 mm, and the indentation between the ink roller and the printing plate is between 5 and 6 mm.
3. The fountain solution has a low pH. A low pH results in corrosion of the plate's hydrophilic oxide film, resulting in less water on the plate and dirtiness. Generally, the pH is controlled between 5-6.
4. Others. In printing, artificially damaged plates, thick ink on the layout, long downtime and no sealing can cause dingy. We not only need to take good care of the printing plate, but also need to keep the printing quality under the premise of small water, small ink and low pressure. In order to save time, peach gum can be added to the dampening solution, and it is not necessary to seal at 1-2 hours of shutdown.
2, the impact of the nature of raw materials
1. The nature of the PS version. 1 The transparency is not good, thus hindering the light from passing through due to underexposure; 2 uneven coating of the photosensitive adhesive, causing insufficient decomposition during exposure; 3 having a large degree of fog and so on.
2. The nature of the paper. 1 The paper's PH value is generally around 7; when it is greater than 7, it will neutralize the fountain solution and affect the hydrophilicity of the printing plate; 2 the paper loses powder, loses wool, has sand, and sticks to the printing plate or blanket during printing. It increased friction.
3. The nature of the ink. If the particle size is large and the friction is large, the dirt on the grain is damaged.
Therefore, we must not only regulate the machine, control the printing plate, but also can not ignore the choice of raw materials.
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