Misregistration is one of the most common failures in lithographic offset printing. The reasons for overprinting failures are various. Here I will give a brief analysis of some methods and experiences summarized in long-term work practices.
Imprint can not be directly used to determine the printed sheet Normally printed on the crosshairs and the ruled lines such as the corner line and other rules against this rule line to determine whether overprinting accuracy.
There are two major causes of overprinting: one is caused by materials; the other is caused by printing machinery and operations.
Incorrect overprint caused by material
Water is involved in the offset printing process and the paper has strong water absorbency. The paper's telescopic deformation will affect the overlay accuracy. Due to the external environment or local overfeeding of the machine, local thermal deformation or localized expansion and contraction of the paper may cause overprinting.
The film also has characteristics similar to the paper shrinking after drying and drying. The plate is fastened to the plate cylinder with plate clamps. When the rules are applied, the PS plate will be stretched due to the tension, and it will form a cylindrical shape from the original plane, resulting in bending deformation. Bake plate processing to improve the resistance to printing If the baking time is too long or the temperature is not uniform, the plate is also easily stretched and deformed. More than a few of the above deformations can easily lead to overprint failure.
Remedy: No overprinting failure due to the paper telescopic deformation, the paper prepress humidity treatment. The temperature of the printing shop is controlled at 20-30°C and the humidity is controlled at 0-60% to close the doors and windows to prevent the convection between the workshop and the outside air. The printed semi-finished product is sealed from the air by wrapping paper or plastic film.
To maintain the stability of printing plate and printing plate to control the room temperature and humidity. When installing the plate, you should master the correct pull plate technique to prevent hard pulls and hard knocks from reducing the number of pull plates and to avoid abnormal deformation.
Overprinting due to printing machinery and operation is not allowed
The misprints caused by the printing machinery and operation mainly refer to improper adjustment of the paper feeding parts and positioning parts and overprinting due to improper roll lining.
1. Improper Overprinting Caused by Improper Paper Feeding Failure Analysis
Improper adjustment of the feeder and positioning parts can make the position of the printing plate graphic and text unable to be accurately transferred to the paper. In sheetfed offset printing, the improper adjustment of any part from the stacker's paper stack until the impression cylinder gripper will directly affect the accuracy of overprinting. The main factors that cause failure of overprinting of the sheet feeder are as follows.
(1) Part of the paper breakdown
1 It is too early or too late for the feeder to feed the rollers.
Remedy: Because the offset time of feeder's paper feeder is adjusted based on the pressure roller. Open the air pump to drive the paper feed feeder. When the paper feed nozzle sends the paper to stop the air suction and the air suction has not completely stopped yet, the two rollers on the pendulum axis of the paper feed roller should fall on the feed knurling shaft at the same time. The drive cam of the pendulum shaft of the platen press roller shall be at the lowest point, and the gap between the roller on the pendulum lever and the drive cam shall have a gap of approximately 0.1 mm so as to ensure a smooth paper reception. Adjust the relative position of the sprocket inside the transmission paper feeder to adjust the feeding time of the feeder.
2 The relative height of the presser foot and the separation nozzle is too small or the height of the paper stack is lower than the front paper stopper. The conveyed paper is blocked by the front paper stopper and slows the paper feeding. Presser foot and paper separation nozzle, pressure pedal to the already separated paper, can also cause paper failure.
Remedy: When the paper is flat, you can fine-tune the feeder screw, and properly raise the paper feeder to make the paper stack lower than the paper stopper tongue by 5 to 10 mm. When the paper is not even. The presser foot can easily step on the already separated paper. At this time, the paper can be leveled with a paper strip or a wedge. However, do not forget to remove the tape or wedge during the printing process to avoid squeezing the blanket and printing plate, causing quality accidents. In the use of paper tape and wedge at the same time can also be appropriate to adjust the presser eccentric cam, adjust the low pressure foot; increase the height of the paper nozzle, increase the distance between the presser foot and the paper nozzle.
The rubber band of the 3-minute paper suction nozzle and the delivery nozzle is too small or too thin. The paper blowing nozzle and the presser foot are too strong to blow the air and the paper cannot be sent out properly.
Remedy: Increase the suction volume of the paper nozzle and the delivery nozzle, and replace the rubber ring of the paper suction nozzle and the delivery nozzle according to the thickness of the paper. Appropriately reduce the amount of air blown by the loose paper mouthpiece and presser foot. Periodically clear the ventilation path, feed the paper to the suction chamber and the trachea, and regularly maintain the air pump to ensure the air path is smooth.
4 The paper feeder's feeding time and the timing of the front gauge fall time cause the paper to advance or lag behind the positioning time of the front gauge.
Remedy: The timing should be before the gauge to the position of the paper-feeding table. The position of the leading edge of the paper on the paper-feeder is approximately 3 to 5 mm from the front gauge. The Beiren series models can adjust the relative movement time by adjusting the flange below the conveying surface of the paper conveying board; the middle model series can adjust the paper feeder and the front gauge by changing the gear meshing relationship in the transmission box of the paper feeder. Handover time.
5 Line tension is too small or the pressure of the platen is too light. The pressure roller is worn. The pressure on both sides of the pressure roller is asymmetric and the paper does not reach the front gauge when it is positioned on the side.
Remedy: Loosen the tensioner pulley and check whether the tensioner and the tensioning shaft bearing operate smoothly and evenly. Tighten each belt properly to increase the pressure of the pressure roller, so that pressure on both sides of the pressure roller is replaced in time to replace the serious wear. Press roller.
6 Feeding table and paper feed The ball wear on the feeder shaft is severe. The breakage of the taper pin causes the timing of the registration of the printed sheet to become worse.
Remedy: Repeatedly give the universal ball to the ball which has been worn out with a large amount of oil on the ball every day and replace it in time. When replacing a broken taper pin, do not leave it too long to avoid injury.
When dealing with faults caused by poor sheet feeding, care should be taken to ensure that machinery and equipment are maintained and maintained at all times, and that Feida's suction chamber and gas path are promptly cleaned, and the air pump is maintained in time to maintain the constant temperature and humidity of the printing press for improved analysis and troubleshooting. ability.
Imprint can not be directly used to determine the printed sheet Normally printed on the crosshairs and the ruled lines such as the corner line and other rules against this rule line to determine whether overprinting accuracy.
There are two major causes of overprinting: one is caused by materials; the other is caused by printing machinery and operations.
Incorrect overprint caused by material
Water is involved in the offset printing process and the paper has strong water absorbency. The paper's telescopic deformation will affect the overlay accuracy. Due to the external environment or local overfeeding of the machine, local thermal deformation or localized expansion and contraction of the paper may cause overprinting.
The film also has characteristics similar to the paper shrinking after drying and drying. The plate is fastened to the plate cylinder with plate clamps. When the rules are applied, the PS plate will be stretched due to the tension, and it will form a cylindrical shape from the original plane, resulting in bending deformation. Bake plate processing to improve the resistance to printing If the baking time is too long or the temperature is not uniform, the plate is also easily stretched and deformed. More than a few of the above deformations can easily lead to overprint failure.
Remedy: No overprinting failure due to the paper telescopic deformation, the paper prepress humidity treatment. The temperature of the printing shop is controlled at 20-30°C and the humidity is controlled at 0-60% to close the doors and windows to prevent the convection between the workshop and the outside air. The printed semi-finished product is sealed from the air by wrapping paper or plastic film.
To maintain the stability of printing plate and printing plate to control the room temperature and humidity. When installing the plate, you should master the correct pull plate technique to prevent hard pulls and hard knocks from reducing the number of pull plates and to avoid abnormal deformation.
Overprinting due to printing machinery and operation is not allowed
The misprints caused by the printing machinery and operation mainly refer to improper adjustment of the paper feeding parts and positioning parts and overprinting due to improper roll lining.
1. Improper Overprinting Caused by Improper Paper Feeding Failure Analysis
Improper adjustment of the feeder and positioning parts can make the position of the printing plate graphic and text unable to be accurately transferred to the paper. In sheetfed offset printing, the improper adjustment of any part from the stacker's paper stack until the impression cylinder gripper will directly affect the accuracy of overprinting. The main factors that cause failure of overprinting of the sheet feeder are as follows.
(1) Part of the paper breakdown
1 It is too early or too late for the feeder to feed the rollers.
Remedy: Because the offset time of feeder's paper feeder is adjusted based on the pressure roller. Open the air pump to drive the paper feed feeder. When the paper feed nozzle sends the paper to stop the air suction and the air suction has not completely stopped yet, the two rollers on the pendulum axis of the paper feed roller should fall on the feed knurling shaft at the same time. The drive cam of the pendulum shaft of the platen press roller shall be at the lowest point, and the gap between the roller on the pendulum lever and the drive cam shall have a gap of approximately 0.1 mm so as to ensure a smooth paper reception. Adjust the relative position of the sprocket inside the transmission paper feeder to adjust the feeding time of the feeder.
2 The relative height of the presser foot and the separation nozzle is too small or the height of the paper stack is lower than the front paper stopper. The conveyed paper is blocked by the front paper stopper and slows the paper feeding. Presser foot and paper separation nozzle, pressure pedal to the already separated paper, can also cause paper failure.
Remedy: When the paper is flat, you can fine-tune the feeder screw, and properly raise the paper feeder to make the paper stack lower than the paper stopper tongue by 5 to 10 mm. When the paper is not even. The presser foot can easily step on the already separated paper. At this time, the paper can be leveled with a paper strip or a wedge. However, do not forget to remove the tape or wedge during the printing process to avoid squeezing the blanket and printing plate, causing quality accidents. In the use of paper tape and wedge at the same time can also be appropriate to adjust the presser eccentric cam, adjust the low pressure foot; increase the height of the paper nozzle, increase the distance between the presser foot and the paper nozzle.
The rubber band of the 3-minute paper suction nozzle and the delivery nozzle is too small or too thin. The paper blowing nozzle and the presser foot are too strong to blow the air and the paper cannot be sent out properly.
Remedy: Increase the suction volume of the paper nozzle and the delivery nozzle, and replace the rubber ring of the paper suction nozzle and the delivery nozzle according to the thickness of the paper. Appropriately reduce the amount of air blown by the loose paper mouthpiece and presser foot. Periodically clear the ventilation path, feed the paper to the suction chamber and the trachea, and regularly maintain the air pump to ensure the air path is smooth.
4 The paper feeder's feeding time and the timing of the front gauge fall time cause the paper to advance or lag behind the positioning time of the front gauge.
Remedy: The timing should be before the gauge to the position of the paper-feeding table. The position of the leading edge of the paper on the paper-feeder is approximately 3 to 5 mm from the front gauge. The Beiren series models can adjust the relative movement time by adjusting the flange below the conveying surface of the paper conveying board; the middle model series can adjust the paper feeder and the front gauge by changing the gear meshing relationship in the transmission box of the paper feeder. Handover time.
5 Line tension is too small or the pressure of the platen is too light. The pressure roller is worn. The pressure on both sides of the pressure roller is asymmetric and the paper does not reach the front gauge when it is positioned on the side.
Remedy: Loosen the tensioner pulley and check whether the tensioner and the tensioning shaft bearing operate smoothly and evenly. Tighten each belt properly to increase the pressure of the pressure roller, so that pressure on both sides of the pressure roller is replaced in time to replace the serious wear. Press roller.
6 Feeding table and paper feed The ball wear on the feeder shaft is severe. The breakage of the taper pin causes the timing of the registration of the printed sheet to become worse.
Remedy: Repeatedly give the universal ball to the ball which has been worn out with a large amount of oil on the ball every day and replace it in time. When replacing a broken taper pin, do not leave it too long to avoid injury.
When dealing with faults caused by poor sheet feeding, care should be taken to ensure that machinery and equipment are maintained and maintained at all times, and that Feida's suction chamber and gas path are promptly cleaned, and the air pump is maintained in time to maintain the constant temperature and humidity of the printing press for improved analysis and troubleshooting. ability.
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