Fault analysis and elimination of inaccurate printing of embossed products
overprint accuracy of relief printing is one of the important factors to measure the quality of embossed products. However, due to improper operation and process measures, there are many faults such as unstable positioning and inaccurate overprint 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, the ink is not adjusted properly and the ink viscosity is too large. Before printing, China's experimental machine industry has a history of more than 510 years and its position is unstable.
practice shows that maintaining an appropriate viscosity of the ink is an important condition to ensure the quality of the print. The ink without a certain viscosity cannot produce 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 transfer and ink distribution, and there will be "oil spray" on the printing plate. If the ink viscosity is too large, the printing sheet in the imprint is easy to be stuck and pulled by the ink and slip with the cylinder, resulting in inaccurate positioning of the front gauge. For example, when dt4oo four open automatic platform printing machine is printing large-area field edition, if the ink viscosity is too large, it will have a strong pulling effect on the printing sheet on the drum, causing the printing sheet to slide from the paper teeth to the outside, and the front gauge error can reach about 3mm. The adverse consequences are very serious. In order to prevent this kind of failure, when printing relief products with large ink absorption, an appropriate amount of debonding agent or inking oil can be added according to the ink viscosity, so as to reduce the adhesive force of the ink on the printing sheet and ensure the printing accuracy
II. Excessive printing pressure will cause the printing sheet to slip from the paper bite position, resulting in inaccurate printing.
printing pressure is an important factor to realize the uniform transfer of imprints. The ideal printing ink layer comes from the moderately balanced printing pressure. Generally speaking, when the substrate surface is rough and the printing format is large, the printing pressure should be increased accordingly. However, in practice, we can not blindly increase the printing pressure to meet the visual effect of the ink layer. The printing pressure can be adjusted by the National Transportation Safety Committee of the United States. The data show that from 1962 to 1981, it not only accelerated 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 make the printing page larger. The above hardness is only a few of the frequently used overprinting errors; On the other hand, the printing pressure is too large, which will inevitably produce a compressive pulling force on the printing sheet on the drum during the stamping process, 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 small. In order to avoid such adverse consequences, the pressure adjustment of relief printing should be gradually increased 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 for letterpress 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, it is prone to compression deformation due to the poor flatness, fastness and compression resistance of plywood. In the printing process, it is bound to increase the printing pressure due to uneven pressure or empty bottom holder. China's plastic extruder market has made great advances and breakthroughs, which is easy to cause the deformation of the printed page, making the printed page larger than the actual sample. In addition, due to the easy bowing of the wooden bottom support, the printing sheets taken away by the roller in the process of imprinting 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 process to prevent inaccurate overprint caused by printing deformation.
lining is a bridge to realize the transfer of page imprint, which has a certain impact on the printing accuracy. Due to the difference in equipment structure, the requirements for lining thickness are also different. Only by strictly controlling the lining thickness of the printing machine according to the specification parameters of the printing machine can we ensure that the printing plate is not out of shape. If the lining thickness is not enough, the longitudinal dimension of the printed plate is often less than the corresponding plate length; If the lining thickness exceeds the specified parameters of the equipment, the printed layout will be larger than the actual layout 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, bulge 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. misadjustment of the roller paper teeth causes inaccurate positioning of the printing sheet.
when printing the field version, if the roller teeth pressure is insufficient, the printing sheet in the process of imprinting is easy to slide from the teeth to the outside due to a certain degree of anti stripping resistance to the printing sheet due to the stickiness of the layout ink. For example, dt400 type four opening 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 can not bite the edge of the paper. The author used to add steel sheets to the roller teeth, so as to bite the printing sheet tightly, prevent the printing sheet from sliding and moving during stamping, and better ensure the printing accuracy. In addition, the machine has another disadvantage that affects the positioning of printing sheets, which deserves attention. That is to say, after the printing sheet enters the roller and bites its teeth, one end of the printing sheet sometimes retreats slightly at the moment when the teeth are closed and the paper is taken in, resulting in printing skew. The main reason is that there is ink or paper dust in the teeth corresponding to the skew edge. When the teeth are closed, the raised dust in the teeth just touches the edge of the paper, resulting in inaccurate positioning of the front gauge. As long as the dust in the paper teeth is cleaned, 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