Imprinting is not one of the most common failures in sheetfed offset printing. It directly affects the printing quality and production efficiency. It also has a certain degree of influence on the company’s image. Therefore, in practical work, how to effectively eliminate it becomes a The required technology of each machine worker. Here are some of the methods and experiences I have summarized in my work practice. I hope that my colleagues will criticize and correct me!
Prepress section 1. When the film is output, if overprinting of the four-color film is not allowed, it must be re-produced.
2. When making a printing plate, it must be ensured that the perforation is upright; the printing should be carried out in accordance with normal operating procedures to prevent sun drying and sun drying; at an appropriate time. The baking version is performed according to the process requirements under temperature conditions.
3. When cutting paper, ensure that the paper is flat, straight, and clean.
Printing section 1. When using a monochrome machine for multi-color printing, the paper is brought into contact with the fountain solution before printing, which increases the moisture content inside the paper, and there is a certain time difference after the printing, which causes the paper to deform to a different degree, resulting in a One-color images and overcolor images are overprinted. So usually the printing house stores the paper. The printing shop conducts temperature and humidity control. In order to prevent overprinting, some large companies also perform temperature and humidity control on high-precision semi-finished products.
2. Since a multi-color printer performs printing of a plurality of colors instantaneously, there is basically no problem of deformation of the paper caused by the time difference of the monochrome machine. However, due to the action of the fountain solution and a certain printing pressure, the paper will also have a constant deformation. This deformation is usually overcome by increasing the 0.02mm increment from the first color to the last color when the film is produced. Therefore, once the printing color sequence is determined, it should not be arbitrarily changed.
Although multicolor printing presses have a lower probability of overprinting than monochromatic printing presses, multicolor overprinting is generally used for high-end exquisite packaging products. Therefore, high precision is required for overprinting, and overprinting in multicolor printing machines is not The quasi-exclusion is also much more complex than monochromatic machines, which should be eliminated one by one according to different situations. In addition, there is still a problem of misalignment in the multicolor printing machine, which is generally caused by mechanical reasons. According to the requirements of the printing products, they should be thoroughly considered and solved one by one.
Operation section 1. If the amount of fountain solution is too much, it is very unfavorable for printing overprinting, so the amount of fountain solution should be as little as possible without affecting the smooth progress of printing.
2. The paper did not come into place, causing the needle to jump, causing overprinting and ghosting.
3. Aging blankets and loss of elasticity can cause overprinting.
4. Loose blankets or plates can cause misprints. Among them, when the folder is loose, there are also phenomena such as ink bars and water bars.
5. Plate lining, improper blanket lining, or lining with folds or defects may cause overprinting.
6. When the printing plate is installed, if the plate is mounted too obliquely and the twisted version is too large, overprinting may occur, and the printing plate needs to be replaced.
7. Printing pressure is the most critical factor in printing. If the printing pressure is not adjusted properly, the most important effect is the transfer of ink and the printing effect. At the same time, it also has a certain impact on overprinting.
8. The difference in line speed between the surface of the printing plate and the surface of the blanket is too large, resulting in a certain slippage of the two surfaces within the embossing arc, thus affecting overprinting. By increasing or decreasing the blanket lining and the lining of the printing plate, the longitudinal overprint due to the deformation of the paper can be solved, but this method is not conducive to the transfer of the ink.
9. During the maintenance of the machine, always check the cleaning to prevent paper powder, paper hairs from entering, and plugging the front gauge. Side regulations. Correctly adjusting the height of the front gauge and the lateral gauge can prevent overprinting.
10. If there is oil contamination between the three pillows, there will be too much residual ink, which will also result in overprinting. Therefore, the three-rollers should be cleaned frequently.
Mechanical part 1. There is a close connection between the transfer tooth, the delivery of paper teeth, the pressure on the impression cylinder, and the pressure on the row. The pressure requirements of the cavities are uniform and even. If a single or a few cavities are loose, partial image overprinting will be inaccurate. If the entire row of teeth is loose, the entire image will be overprinted. Therefore, it is necessary to prevent the cavities from springing. Aging screw and loosening.
2. Another mechanical cause of misprinting is the plate cylinder gears, the impression cylinder gears, the transfer bar row shaft, the bearings, the transfer bar row shaft, the bearings, the impression cylinder row bar, the bearings and other related to the transfer. Damaged mechanical parts, excessive oil or excessive clearance.
In short, there are many unstable factors in the offset printing process, such as equipment factors, environmental factors, and human factors. Therefore, when overprinting is found to be inaccurate, it should be based on the actual situation, specific analysis, and one by one.
Prepress section 1. When the film is output, if overprinting of the four-color film is not allowed, it must be re-produced.
2. When making a printing plate, it must be ensured that the perforation is upright; the printing should be carried out in accordance with normal operating procedures to prevent sun drying and sun drying; at an appropriate time. The baking version is performed according to the process requirements under temperature conditions.
3. When cutting paper, ensure that the paper is flat, straight, and clean.
Printing section 1. When using a monochrome machine for multi-color printing, the paper is brought into contact with the fountain solution before printing, which increases the moisture content inside the paper, and there is a certain time difference after the printing, which causes the paper to deform to a different degree, resulting in a One-color images and overcolor images are overprinted. So usually the printing house stores the paper. The printing shop conducts temperature and humidity control. In order to prevent overprinting, some large companies also perform temperature and humidity control on high-precision semi-finished products.
2. Since a multi-color printer performs printing of a plurality of colors instantaneously, there is basically no problem of deformation of the paper caused by the time difference of the monochrome machine. However, due to the action of the fountain solution and a certain printing pressure, the paper will also have a constant deformation. This deformation is usually overcome by increasing the 0.02mm increment from the first color to the last color when the film is produced. Therefore, once the printing color sequence is determined, it should not be arbitrarily changed.
Although multicolor printing presses have a lower probability of overprinting than monochromatic printing presses, multicolor overprinting is generally used for high-end exquisite packaging products. Therefore, high precision is required for overprinting, and overprinting in multicolor printing machines is not The quasi-exclusion is also much more complex than monochromatic machines, which should be eliminated one by one according to different situations. In addition, there is still a problem of misalignment in the multicolor printing machine, which is generally caused by mechanical reasons. According to the requirements of the printing products, they should be thoroughly considered and solved one by one.
Operation section 1. If the amount of fountain solution is too much, it is very unfavorable for printing overprinting, so the amount of fountain solution should be as little as possible without affecting the smooth progress of printing.
2. The paper did not come into place, causing the needle to jump, causing overprinting and ghosting.
3. Aging blankets and loss of elasticity can cause overprinting.
4. Loose blankets or plates can cause misprints. Among them, when the folder is loose, there are also phenomena such as ink bars and water bars.
5. Plate lining, improper blanket lining, or lining with folds or defects may cause overprinting.
6. When the printing plate is installed, if the plate is mounted too obliquely and the twisted version is too large, overprinting may occur, and the printing plate needs to be replaced.
7. Printing pressure is the most critical factor in printing. If the printing pressure is not adjusted properly, the most important effect is the transfer of ink and the printing effect. At the same time, it also has a certain impact on overprinting.
8. The difference in line speed between the surface of the printing plate and the surface of the blanket is too large, resulting in a certain slippage of the two surfaces within the embossing arc, thus affecting overprinting. By increasing or decreasing the blanket lining and the lining of the printing plate, the longitudinal overprint due to the deformation of the paper can be solved, but this method is not conducive to the transfer of the ink.
9. During the maintenance of the machine, always check the cleaning to prevent paper powder, paper hairs from entering, and plugging the front gauge. Side regulations. Correctly adjusting the height of the front gauge and the lateral gauge can prevent overprinting.
10. If there is oil contamination between the three pillows, there will be too much residual ink, which will also result in overprinting. Therefore, the three-rollers should be cleaned frequently.
Mechanical part 1. There is a close connection between the transfer tooth, the delivery of paper teeth, the pressure on the impression cylinder, and the pressure on the row. The pressure requirements of the cavities are uniform and even. If a single or a few cavities are loose, partial image overprinting will be inaccurate. If the entire row of teeth is loose, the entire image will be overprinted. Therefore, it is necessary to prevent the cavities from springing. Aging screw and loosening.
2. Another mechanical cause of misprinting is the plate cylinder gears, the impression cylinder gears, the transfer bar row shaft, the bearings, the transfer bar row shaft, the bearings, the impression cylinder row bar, the bearings and other related to the transfer. Damaged mechanical parts, excessive oil or excessive clearance.
In short, there are many unstable factors in the offset printing process, such as equipment factors, environmental factors, and human factors. Therefore, when overprinting is found to be inaccurate, it should be based on the actual situation, specific analysis, and one by one.