Analysis and elimination of inaccurate overprint i

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Analysis and elimination of overprint inaccuracy in embossing printing

overprint accuracy of relief printing is one of the important factors to measure the quality of embossed products. However, due to improper operation and technological measures, there are many faults such as unstable positioning and inaccurate overprinting in the printing process, which are harmful and must be paid attention to. There are many reasons for the inaccurate printing of embossed products:

first, improper inking. The main business of Huitian new material is the production of engineering adhesives. The viscosity of the ink is too large, and the position of the front gauge of the printing sheet is unstable.

practice shows that maintaining the appropriate viscosity of the ink is an important condition to ensure the quality of the printing product. The ink without a certain viscosity cannot print a solid, full and bright ink layer. However, there is no unified standard for ink viscosity. In printing, the viscosity of ink can only be adjusted by experience according to the characteristics of printing materials (substrates) and the printing layout structure. If the viscosity is adjusted too low, the rubber roller will slip, resulting in uneven ink transmission and ink distribution, and there will be oily flowers on the printing plate. If the ink viscosity is too large, the printing sheet in the stamping is easy to be stuck and pulled by the ink and slip with the drum, resulting in the failure of inaccurate positioning of the front gauge. For example, when dt4oo four open automatic platform printer is printing large-area field edition, if the ink viscosity is too large, it will have a strong pulling effect on the print sheet on the drum, causing the print sheet to slide from the paper teeth to the outside, and the front gauge error can reach about 3mm, which has serious adverse consequences. In order to prevent this kind of failure, when printing relief products with a large amount of ink absorption, an appropriate amount of debonding agent or inking oil can be added according to the viscosity of the ink, so as to reduce the adhesive force of the ink on the printing sheet and ensure the printing accuracy

second, the adjustment of printing pressure and its impact on printing quality

printing pressure is an important factor to realize the uniform transfer of imprints. The ideal printing ink layer comes from a moderately balanced printing pressure. Generally speaking, when the surface of the substrate is rough and the printing format is large, the printing pressure should also be increased accordingly. However, when the actual operation power supply power should be greater than the total power of the instrument, we cannot blindly increase the printing pressure to meet the visual effect of the printing ink layer. If the printing pressure is adjusted too heavily, it not only accelerates the wear of the machine and the printing plate, but also prone to overprint misalignment. This is because when the printing pressure is too high, on the one hand, it will deform the printing sheet and enlarge the printing page, resulting in inaccurate overprint; On the other hand, the printing pressure is too large, and the impression will inevitably produce a compressive tensile force on the printing sheet on the drum, resulting in the printing sheet sliding outward from the paper teeth, which will make the positioning of the front gauge of the printing sheet unstable and appear to be too small. In order to avoid such adverse consequences, the pressure adjustment of relief printing should be gradually pressurized from light to heavy under the condition that the ink supply of the layout is normal, so as to accurately adjust to the appropriate printing pressure, so as to ensure the printing quality

III. the printing plate bottom support is not solid, and the poor flatness and compressive strength cause inaccurate printing.

the hardness and accuracy of the plate support (adhesive plate bottom support) used in relief printing greatly affect the printing accuracy of the product. If the traditional glued plate is used as the plate holder for large-scale field relief printing, compression deformation is easy to occur due to the poor flatness, fastness and compression resistance of plywood. In the printing process, the printing pressure is bound to increase due to uneven pressure or empty bottom holder, which is easy to cause the deformation of the print layout, making the printed layout larger than the actual version. In addition, due to the easy bowing of the wooden bottom support, the printing sheets taken away by the roller gritting its teeth in the stamping process will inevitably slip due to the slight vibration or movement of the printing plate, resulting in the inaccurate overprint of the product. Therefore, when printing plates with large format and high pressure, it is advisable to use magnetic plate table or aluminum plate holder to stick plates, which can better ensure the overprint accuracy of products

IV. control the lining technology, Preventing overprint inaccuracy caused by printing deformation

lining is the key to realize the transfer of page imprinting "However, the moving bridge has a certain impact on the printing accuracy. Due to the differences in equipment structure, the external dependence of China's rare metal resources will be reduced to a great extent, and the requirements for the lining thickness are also different. Only by strictly controlling the lining thickness of the machine in accordance with the specification parameters of the printing machine can we ensure that the printing layout is not out of shape. If the lining thickness is not enough, the longitudinal dimension of the printed layout is often less than the corresponding length of the printing plate; to The thickness of the lining exceeds the specified parameters of the equipment, and the printed layout is larger than the actual format of the printing plate, which is another factor affecting the printing accuracy. In addition, if the lining is not tight enough, there are phenomena such as virtual looseness, uplift and large-area patching of the outer lining, or when the paper is padded, only one side of the biting part is pasted, and the trailing tip position is not pasted in one case, and it is allowed to float, which will also cause the print layout to be enlarged and deformed, resulting in printing inaccuracy. In order to ensure the accuracy of letterpress printing, it is advisable to use neutral and hard packing materials, and wrap the packing materials tightly

v. the misaligned paper teeth of the roller cause inaccurate positioning of the print sheet.

when printing the field version, if the pressure of the roller teeth is insufficient, the ink viscosity of the layout will produce a certain degree of anti stripping resistance to the print sheet, and the print sheet in the stamping will easily slip from the teeth. For example, dt400 four open automatic platform printing machine is prone to the above disadvantages when printing large-area field relief products. The main reason is that the pressure of the spring steel plate of the original drum is not enough, so that the teeth cannot bite the paper edge tightly. The author once added steel sheets to the roller teeth, so as to tighten the printing sheet, prevent the printing sheet from sliding and moving during stamping, and better ensure the printing accuracy. In addition, the machine also has another disadvantage that affects the positioning of printing sheets, which is worthy of attention. That is, after the printing sheet enters the drum and bites its teeth, one end of the printing sheet sometimes retreats slightly at the moment when the teeth close and hold the paper, resulting in printing skew. The main reason is that there are ink stains or clumps of paper dust in the teeth corresponding to the oblique edge. When the teeth are closed, the dust raised in the teeth just hit the edge of the paper, resulting in inaccurate positioning of the front gauge. As long as the dust in the paper biting teeth is cleaned up, the fault can be eliminated

to sum up, good operation and process technology can not only effectively ensure the printing quality of relief printing and improve the printing accuracy of products, but also better improve the production efficiency of enterprises

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