The overprint accuracy of letterpress prints is one of the important factors in measuring the quality of letterpress products. However, due to improper operation and process measures, there is no lack of faults such as unstable positioning, overprinting, and misalignment during the printing process. The hazards are serious and must be taken seriously. The reasons for the inaccurate printing of embossed products are many:
First, improper ink transfer, ink viscosity is too large, the position of the front sheet is not stable
Practice has shown that maintaining the proper viscosity of ink is an important condition for ensuring the quality of printed products. Ink lacking a certain viscosity cannot print solid, saturated, and bright ink layers. However, there is no uniform standard for ink viscosity, and the viscosity of the ink can be adjusted empirically based on the characteristics of the printed material (substrate) and the layout of the printing plate. If the viscosity is adjusted too low, slipping of the rubber roller will occur, so that the ink transfer and ink distribution will be uneven, and "oily" will appear on the printing plate surface. If the viscosity of the ink is too high, the printed sheets in the imprinting are liable to be pulled by the ink to slip with the roller, resulting in a failure of the predetermined position. Such as DT4OO type four automatic platform printing machine in the printing of a large area of ​​the field version, if the ink viscosity is too large, will have a strong pull on the roller sheet pull effect, so that the sheet slides out from the bite of paper teeth, the former regulatory position The error can reach about 3mm, and the adverse consequences are very serious. To prevent this kind of failure from happening, when printing a letterpress product with a large ink-absorption capacity, an appropriate amount of a de-bonding agent or varnish may be added according to the viscosity of the ink as appropriate to reduce the stickiness of the ink to the printed sheets and ensure the printing accuracy. .
Second, the printing pressure over the ambassador slipped from the position of paper teeth, resulting in inaccurate printing
Printing pressure is an important factor in the uniform transfer of prints. The ideal printing ink layer is derived from moderately balanced printing pressure. In general, when the surface of the substrate is rough and the printing surface is large, the printing pressure should be increased accordingly. However, in actual operation, the printing pressure cannot be increased blindly to satisfy the visual effect of the printed ink layer. The printing pressure is too heavy, which not only speeds up the wear of the machine and printing plate, but also causes overprinting misalignment. This is because when the printing pressure is too high, on the one hand, the printed sheets may be deformed, causing the printed sheets to be enlarged, resulting in inaccurate overprinting; on the Other hand, the printing pressure is too high, and the imprints on the rollers are bound to be oppressed during the imprinting. Sexual pull force causes the slippage of the printed sheet to slide outwards from the gripper teeth, which will make the prescribed position before the printed sheet unstable and appear to be too small. In order to avoid this undesirable effect, the pressure adjustment of letterpress printing should be gradually light and heavy under the condition that the page ink supply is normal, so as to accurately adjust the printing pressure to ensure the printing quality.
Third, the printing plate base is not solid, flatness, poor compressive strength caused by printing is not allowed
The hardness and precision of the plate support used in letterpress printing (viscous platen) largely affect the printing accuracy of the product. If a traditional gluing plate is used as a large-size relief printing plate, the plywood will be deformed due to its poor flatness, fastness and compression resistance, and will be added during the printing process due to uneven pressure or emptiness. With large printing pressure, it is easy to cause distortion of the printing plate layout, so that the printing surface is larger than the actual printing plate. In addition, due to the bowing of the wood tray, the impression of the stamp on the cylinder during the imprinting will inevitably slip due to the slight vibration or movement of the printing plate, resulting in inaccurate overprinting of the product. Therefore, in the printing of large-format, high-pressure printing plate should be used magnetic version of Taiwan or aluminum version of sticky version, which can better guarantee product overprint accuracy.
Fourth, the good lining process technology to prevent the printing product deformation caused by overprinting is not allowed
Lining is a bridge that realizes transfer of layout printing and has a certain influence on printing accuracy. Due to the differences in equipment structure, the requirements for the thickness of the lining are also different. Only by strictly controlling the lining thickness of the machine according to the specification parameters of the printer, can we ensure that the printing plate surface is not deformed. If the thickness of the lining is not enough, the longitudinal dimension of the printed layout is often smaller than the corresponding length of the printing plate; if the lining thickness exceeds the equipment specified parameters, the printed surface is larger than the actual size of the printing plate, which is another factor that affects the printing accuracy. In addition, if the lining is not tight enough, there are phenomena such as looseness, bulging, and large areas of the outer lining, etc., or only the side of the occlusal part is stuck on the upper pad, and one example of the tip is not affixed and allowed to flutter. , This will also cause the printing plate layout to be distorted, resulting in print misalignment. In order to ensure the accuracy of letterpress printing, it is better to use a neutral, harder packing material and to pack the packing material tightly.
Fifth, roller paper teeth misalignment caused by the positioning of printed pages are not allowed
When printing the field version, if the pressure of the roller teeth is insufficient, since the ink viscosity of the layout will produce a certain degree of anti-peeling resistance to the printed sheets, the printed sheets in the printing can easily slip out of the teeth. Such as the DT400 type four open automatic platform printing machine, printing large area of ​​field Toppan products is prone to the above drawbacks. The main reason for the study is that the pressure of the spring steel of the original drum teeth is not enough, so that the bite is not tight. The author once added steel to the teeth of the roller to achieve a tight grip on the printed sheet to prevent the sheet from slipping and shifting during imprinting, thus ensuring better printing accuracy. In addition, there are still other drawbacks affecting the positioning of printed sheets that are worthy of attention. That is, after the sheet enters the teeth of the roller, there is sometimes a slight retreat at one end of the sheet when the jaws are closed by the teeth, thus causing a printing skew. The main reason is that there is ink or agglomerated paper dust accumulating in the corresponding teeth of the skewed edge. When the teeth are closed, the raised dust in the teeth just touches the edge of the paper, causing the former position to be inaccurate. As long as the dust in the teeth is cleaned, the fault can be eliminated.
To sum up, the good operation and process technology are not only effective in ensuring the printing quality of letterpress printing and improving the precision of product printing, but also can improve the production efficiency of enterprises.
First, improper ink transfer, ink viscosity is too large, the position of the front sheet is not stable
Practice has shown that maintaining the proper viscosity of ink is an important condition for ensuring the quality of printed products. Ink lacking a certain viscosity cannot print solid, saturated, and bright ink layers. However, there is no uniform standard for ink viscosity, and the viscosity of the ink can be adjusted empirically based on the characteristics of the printed material (substrate) and the layout of the printing plate. If the viscosity is adjusted too low, slipping of the rubber roller will occur, so that the ink transfer and ink distribution will be uneven, and "oily" will appear on the printing plate surface. If the viscosity of the ink is too high, the printed sheets in the imprinting are liable to be pulled by the ink to slip with the roller, resulting in a failure of the predetermined position. Such as DT4OO type four automatic platform printing machine in the printing of a large area of ​​the field version, if the ink viscosity is too large, will have a strong pull on the roller sheet pull effect, so that the sheet slides out from the bite of paper teeth, the former regulatory position The error can reach about 3mm, and the adverse consequences are very serious. To prevent this kind of failure from happening, when printing a letterpress product with a large ink-absorption capacity, an appropriate amount of a de-bonding agent or varnish may be added according to the viscosity of the ink as appropriate to reduce the stickiness of the ink to the printed sheets and ensure the printing accuracy. .
Second, the printing pressure over the ambassador slipped from the position of paper teeth, resulting in inaccurate printing
Printing pressure is an important factor in the uniform transfer of prints. The ideal printing ink layer is derived from moderately balanced printing pressure. In general, when the surface of the substrate is rough and the printing surface is large, the printing pressure should be increased accordingly. However, in actual operation, the printing pressure cannot be increased blindly to satisfy the visual effect of the printed ink layer. The printing pressure is too heavy, which not only speeds up the wear of the machine and printing plate, but also causes overprinting misalignment. This is because when the printing pressure is too high, on the one hand, the printed sheets may be deformed, causing the printed sheets to be enlarged, resulting in inaccurate overprinting; on the Other hand, the printing pressure is too high, and the imprints on the rollers are bound to be oppressed during the imprinting. Sexual pull force causes the slippage of the printed sheet to slide outwards from the gripper teeth, which will make the prescribed position before the printed sheet unstable and appear to be too small. In order to avoid this undesirable effect, the pressure adjustment of letterpress printing should be gradually light and heavy under the condition that the page ink supply is normal, so as to accurately adjust the printing pressure to ensure the printing quality.
Third, the printing plate base is not solid, flatness, poor compressive strength caused by printing is not allowed
The hardness and precision of the plate support used in letterpress printing (viscous platen) largely affect the printing accuracy of the product. If a traditional gluing plate is used as a large-size relief printing plate, the plywood will be deformed due to its poor flatness, fastness and compression resistance, and will be added during the printing process due to uneven pressure or emptiness. With large printing pressure, it is easy to cause distortion of the printing plate layout, so that the printing surface is larger than the actual printing plate. In addition, due to the bowing of the wood tray, the impression of the stamp on the cylinder during the imprinting will inevitably slip due to the slight vibration or movement of the printing plate, resulting in inaccurate overprinting of the product. Therefore, in the printing of large-format, high-pressure printing plate should be used magnetic version of Taiwan or aluminum version of sticky version, which can better guarantee product overprint accuracy.
Fourth, the good lining process technology to prevent the printing product deformation caused by overprinting is not allowed
Lining is a bridge that realizes transfer of layout printing and has a certain influence on printing accuracy. Due to the differences in equipment structure, the requirements for the thickness of the lining are also different. Only by strictly controlling the lining thickness of the machine according to the specification parameters of the printer, can we ensure that the printing plate surface is not deformed. If the thickness of the lining is not enough, the longitudinal dimension of the printed layout is often smaller than the corresponding length of the printing plate; if the lining thickness exceeds the equipment specified parameters, the printed surface is larger than the actual size of the printing plate, which is another factor that affects the printing accuracy. In addition, if the lining is not tight enough, there are phenomena such as looseness, bulging, and large areas of the outer lining, etc., or only the side of the occlusal part is stuck on the upper pad, and one example of the tip is not affixed and allowed to flutter. , This will also cause the printing plate layout to be distorted, resulting in print misalignment. In order to ensure the accuracy of letterpress printing, it is better to use a neutral, harder packing material and to pack the packing material tightly.
Fifth, roller paper teeth misalignment caused by the positioning of printed pages are not allowed
When printing the field version, if the pressure of the roller teeth is insufficient, since the ink viscosity of the layout will produce a certain degree of anti-peeling resistance to the printed sheets, the printed sheets in the printing can easily slip out of the teeth. Such as the DT400 type four open automatic platform printing machine, printing large area of ​​field Toppan products is prone to the above drawbacks. The main reason for the study is that the pressure of the spring steel of the original drum teeth is not enough, so that the bite is not tight. The author once added steel to the teeth of the roller to achieve a tight grip on the printed sheet to prevent the sheet from slipping and shifting during imprinting, thus ensuring better printing accuracy. In addition, there are still other drawbacks affecting the positioning of printed sheets that are worthy of attention. That is, after the sheet enters the teeth of the roller, there is sometimes a slight retreat at one end of the sheet when the jaws are closed by the teeth, thus causing a printing skew. The main reason is that there is ink or agglomerated paper dust accumulating in the corresponding teeth of the skewed edge. When the teeth are closed, the raised dust in the teeth just touches the edge of the paper, causing the former position to be inaccurate. As long as the dust in the teeth is cleaned, the fault can be eliminated.
To sum up, the good operation and process technology are not only effective in ensuring the printing quality of letterpress printing and improving the precision of product printing, but also can improve the production efficiency of enterprises.
Together Vacuum Flasks Manufactory Co., Ltd. , http://www.togethercontainer.com