The overprint accuracy of letterpress prints is one of the important factors to measure the quality of letterpress products. However, due to improper operation and technological measures, there are many failures such as unstable positioning and overprinting in the printing process, which are more harmful and must be paid attention to. There are many reasons for the inaccurate printing of relief printing products:
1. Keep the lining process technology close to prevent the printing from being deformed and causing overprinting to be inaccurate
The lining is a bridge to realize the imprint transfer of the layout, which has a certain influence on the printing accuracy. Due to the difference in equipment structure, the requirements for the thickness of the lining are also different. Only by strictly controlling the thickness of the lining of the machine in accordance with the specifications of the printing machine can the printing plate be guaranteed not to be out of shape. If the thickness of the liner is not enough, the longitudinal size of the printed plate is often less than the corresponding plate length; if the thickness of the liner exceeds the specified parameters of the device, the printed plate is larger than the actual format of the plate, which is another factor that affects the printing accuracy. In addition, if the lining is not tight enough, there are loose, bulging and large-scale digging and repairing of the outer lining, or only the side of the gritted area is pasted when the paper is lined, and the trailing position is not pasted in one case. This will also cause large deformation of the printing plate, resulting in printing misalignment. In order to ensure the accuracy of letterpress printing, it is advisable to use neutral and hard packing materials and tightly pack them.
2. The adjustment of printing pressure has an impact on printing quality
Printing pressure is an important factor to achieve uniform transfer of imprints. The ideal printing ink layer comes from a moderately balanced printing pressure. In general, when the surface of the substrate is rough and the printing area is large, the printing pressure should be increased accordingly. However, in actual operation, the printing pressure cannot be increased blindly to meet the visual effect of the printed ink layer. If the printing pressure is adjusted too much, it will not only accelerate the wear of the machine and the printing plate, but also lead to misregistration. This is because when the printing pressure is too high, on the one hand, the printed sheet will be deformed, causing the printing plate to appear large, causing overprinting to be inaccurate; on the other hand, the printing pressure is too large, and the printing sheet on the cylinder will inevitably be pressed during printing Sexual pulling force causes the printed sheet to slide outward from the gripper, which will make the predetermined position of the printed sheet unstable and appear small. In order to avoid such undesirable consequences, the pressure adjustment of relief printing should be gradually increased from light to heavy under the condition that the ink supply on the plate is normal, so that the appropriate printing pressure can be accurately adjusted to ensure the printing quality.
3. The bottom of the printing plate is not solid, and the flatness and compressive strength are poor, which causes the printing to be inaccurate.
The hardness and precision of the plate support (sticky plate support) used in letterpress printing greatly affects the printing accuracy of the product.
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