When printing a composite sheet with a flexographic printing plate, a sheet material roll having a total thickness of about 300 μ is often printed on a group flexo printing machine, a table printing process, a Uv ink, and a layer of Uv light is printed on the last color group after printing. oil. The process of printing composite materials is basically the same as the process of printing pressplate paper, offset paper, and paperboard with the unit type flexo press. However, due to the thicker sheets and the higher grammage, the accuracy of overprinting is a very interesting issue compared with the general paper printing. Several key processes that cause overprint errors, such as tension control, automatic color tracking, plate adjustment, etc., are several joint points to solve this problem.
1. Tension control
The tension system of the unit type flexo press is similar to the tension system of the unit type gravure press introduced from Japan and other countries in the 1980s. The entire production line is divided into three parts: unwinding, printing and winding. Since the unit type flexo printing generally has a post-processing unit, some of the winding units are changed into functional units such as die cutting and singulation, and there is no longer a separate winding mechanism. The tension control system of the entire production line acts as a tension portion of the unwinding before the rubber roller of the paper feeding unit. The tension adjustment mechanism in this part mainly uses the magnetic powder brake mounted on the discharge reel in order to maintain the constant tension of unwinding as the unwinding diameter is gradually reduced. This is the same principle as the unwinding mechanism of the gravure printing machine. The magnetic powder brake control principle is based on the first-order linear control characteristics of the automatic control theory, which automatically adjusts the force of the reel to avoid inconsistency in the entire range of unwinding diameter from maximum to minimum. After the rubber roller from the paper feed unit, printing is completed until the printing is completed. The tension control of this unit is the core of the multicolor printing unit. Multi-color printing units, whether equipped with a color registration tracker to automatically adjust the color registration accuracy, or do not install trapping color trackers, use manual adjustment methods to calibrate the accuracy of the overlay, and their common basic parts all require a constant tension. The variable feed unit and its variable feed force alignment system are dedicated to this important task. In the printing of composite sheets, due to the thickness of about 300μ, and the inner and outer surfaces are all PE, the thickness is larger than the paper, and the surface friction coefficient is small. Although the feed roller surface of the paper feeding mechanism has a certain roughness, In order to generate enough friction, the pressure of the rubber platen roller should be adjusted slightly larger. The tension setting of this part is also larger than when printing paper. Especially in the composite sheet can not achieve the desired uniformity of thickness, unwinding can be found when the opposite ends of the roll material is not the same elastic, sometimes even the so-called "foliar edge", the tension setting value is even greater. Tighten the sheet and straighten it to follow the subsequent offset printing. Since aluminum foil is used as a skeleton in the composite sheet, even if the tension is set to be larger, the sheet will not be excessively stretched and deformed due to excessive tension, which must be strictly controlled when the EPE film is printed on the printed sheet. .
2 automatic color tracking
A complete unit type printing press is generally equipped with an automatic color registration tracker. The gravure press of the unit type is the same, and so is the unit type flexo press. According to the principle of automatic registration, there is a cursor on each set of plates, and a constant size is set between the cursors of each color group. At the time of stencil printing, the photoelectric head of a printing unit sends the photo marks on the printing plate of this group to the microprocessor, and the microprocessor compares the distance between the previous group of photo marks and the group of photo marks and then sends a signal fine-tuning. The position of the plate roller makes it registerable. The automatic registration system of the flexographic printing press is similar to that of the gravure printing machine's registration system, and its accuracy is generally around 0.1-0.15 mm.
Due to the manufacturing cost of printing machinery, many batch printers do not have an automatic color registration tracker, so they can only be adjusted by operators based on the error values ​​displayed on screens after various colors are printed, or by directly taking product samples with certain errors. The accuracy of the layout, which depends on the staff's strong work responsibilities and skilled operating skills, replaces machinery with labor. of course. Unlike the group-type gravure printing machine, which uses plastic film as the main printing raw material, the group-type printing machine uses paper as the main printing material. After the preheating, the paper's expansion and contraction rate is smaller than that of the plastic film. Therefore, automatic tracking is not required. Dumpling 嵊 îŒ„å‘ îŒ„å‘ ç²• 粕 粕 呛芷 摹 摹 摹 摹 鞵 5 摹 M 鞵 E sheet Although the inside and outside layers are PE film, but it is relatively thick, and the middle and composite aluminum foil, tensile deformation is relatively small, with manual adjustment of color Accuracy is also completely guaranteed.
3. Plate adjustment
In flexographic printing, erroneous overlays are not possible. Therefore, how to use some plate-making techniques to make plates is a common method to mask the lack of overprinting. When validating an artwork, try not to make it as clear as possible before and after, and often call it “zero touch zeroâ€. At this time, there is a slight error, either white or a dark shadow after the phasor. The first impression is that overprinting is not allowed. The conventional approach is to prefer more leaks instead of stacking more.
For example, the two colors in a drawing may have a gap between the two colors. At this time, even if there are some errors in the version, the human eye is not able to distinguish between the narrow and the narrow, and the defects of overprinting errors cover the past. . For the two colors to be docked, it is best to use the overprint method and try to avoid overprinting. The clasp method in the plate is also one of the methods used to hide overprinting. Set the size of the deduction set, it depends on the specific details in the view draft. In short, the deduction sleeve itself is to mask the overlay error. When the flexible plate is printed on the composite sheet, the main process points are not very different from the printed one. . It is necessary to remind that when the last coating is done, since the coating is under full pressure, and the varnish itself is colorless, it is necessary to judge whether the varnish is printed in place or not. The varnish is often seen obliquely from a 45° angle. Reflective to determine. Therefore, it is recommended that the coating pressure (the pressure of the anilox roller on the printing plate roller) can be larger when coating, but the printing pressure (ie the pressure of the printing plate roller on the platen roller) should not be too great, due to the excessive printing pressure, from the optical oil layer The surface is not visible, but it tends to shift the material roll. I have seen a sample, and the overprinting of the previous color is fairly accurate, but the last time the coating is found to be offset, which may be the same as the printing pressure. Too big about it.
1. Tension control
The tension system of the unit type flexo press is similar to the tension system of the unit type gravure press introduced from Japan and other countries in the 1980s. The entire production line is divided into three parts: unwinding, printing and winding. Since the unit type flexo printing generally has a post-processing unit, some of the winding units are changed into functional units such as die cutting and singulation, and there is no longer a separate winding mechanism. The tension control system of the entire production line acts as a tension portion of the unwinding before the rubber roller of the paper feeding unit. The tension adjustment mechanism in this part mainly uses the magnetic powder brake mounted on the discharge reel in order to maintain the constant tension of unwinding as the unwinding diameter is gradually reduced. This is the same principle as the unwinding mechanism of the gravure printing machine. The magnetic powder brake control principle is based on the first-order linear control characteristics of the automatic control theory, which automatically adjusts the force of the reel to avoid inconsistency in the entire range of unwinding diameter from maximum to minimum. After the rubber roller from the paper feed unit, printing is completed until the printing is completed. The tension control of this unit is the core of the multicolor printing unit. Multi-color printing units, whether equipped with a color registration tracker to automatically adjust the color registration accuracy, or do not install trapping color trackers, use manual adjustment methods to calibrate the accuracy of the overlay, and their common basic parts all require a constant tension. The variable feed unit and its variable feed force alignment system are dedicated to this important task. In the printing of composite sheets, due to the thickness of about 300μ, and the inner and outer surfaces are all PE, the thickness is larger than the paper, and the surface friction coefficient is small. Although the feed roller surface of the paper feeding mechanism has a certain roughness, In order to generate enough friction, the pressure of the rubber platen roller should be adjusted slightly larger. The tension setting of this part is also larger than when printing paper. Especially in the composite sheet can not achieve the desired uniformity of thickness, unwinding can be found when the opposite ends of the roll material is not the same elastic, sometimes even the so-called "foliar edge", the tension setting value is even greater. Tighten the sheet and straighten it to follow the subsequent offset printing. Since aluminum foil is used as a skeleton in the composite sheet, even if the tension is set to be larger, the sheet will not be excessively stretched and deformed due to excessive tension, which must be strictly controlled when the EPE film is printed on the printed sheet. .
2 automatic color tracking
A complete unit type printing press is generally equipped with an automatic color registration tracker. The gravure press of the unit type is the same, and so is the unit type flexo press. According to the principle of automatic registration, there is a cursor on each set of plates, and a constant size is set between the cursors of each color group. At the time of stencil printing, the photoelectric head of a printing unit sends the photo marks on the printing plate of this group to the microprocessor, and the microprocessor compares the distance between the previous group of photo marks and the group of photo marks and then sends a signal fine-tuning. The position of the plate roller makes it registerable. The automatic registration system of the flexographic printing press is similar to that of the gravure printing machine's registration system, and its accuracy is generally around 0.1-0.15 mm.
Due to the manufacturing cost of printing machinery, many batch printers do not have an automatic color registration tracker, so they can only be adjusted by operators based on the error values ​​displayed on screens after various colors are printed, or by directly taking product samples with certain errors. The accuracy of the layout, which depends on the staff's strong work responsibilities and skilled operating skills, replaces machinery with labor. of course. Unlike the group-type gravure printing machine, which uses plastic film as the main printing raw material, the group-type printing machine uses paper as the main printing material. After the preheating, the paper's expansion and contraction rate is smaller than that of the plastic film. Therefore, automatic tracking is not required. Dumpling 嵊 îŒ„å‘ îŒ„å‘ ç²• 粕 粕 呛芷 摹 摹 摹 摹 鞵 5 摹 M 鞵 E sheet Although the inside and outside layers are PE film, but it is relatively thick, and the middle and composite aluminum foil, tensile deformation is relatively small, with manual adjustment of color Accuracy is also completely guaranteed.
3. Plate adjustment
In flexographic printing, erroneous overlays are not possible. Therefore, how to use some plate-making techniques to make plates is a common method to mask the lack of overprinting. When validating an artwork, try not to make it as clear as possible before and after, and often call it “zero touch zeroâ€. At this time, there is a slight error, either white or a dark shadow after the phasor. The first impression is that overprinting is not allowed. The conventional approach is to prefer more leaks instead of stacking more.
For example, the two colors in a drawing may have a gap between the two colors. At this time, even if there are some errors in the version, the human eye is not able to distinguish between the narrow and the narrow, and the defects of overprinting errors cover the past. . For the two colors to be docked, it is best to use the overprint method and try to avoid overprinting. The clasp method in the plate is also one of the methods used to hide overprinting. Set the size of the deduction set, it depends on the specific details in the view draft. In short, the deduction sleeve itself is to mask the overlay error. When the flexible plate is printed on the composite sheet, the main process points are not very different from the printed one. . It is necessary to remind that when the last coating is done, since the coating is under full pressure, and the varnish itself is colorless, it is necessary to judge whether the varnish is printed in place or not. The varnish is often seen obliquely from a 45° angle. Reflective to determine. Therefore, it is recommended that the coating pressure (the pressure of the anilox roller on the printing plate roller) can be larger when coating, but the printing pressure (ie the pressure of the printing plate roller on the platen roller) should not be too great, due to the excessive printing pressure, from the optical oil layer The surface is not visible, but it tends to shift the material roll. I have seen a sample, and the overprinting of the previous color is fairly accurate, but the last time the coating is found to be offset, which may be the same as the printing pressure. Too big about it.
Reprinted from: Printed in China
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