Professional knowledge of aluminum foil composite packaging bags 1． First of all, the style and size of the design and production of the printing plate should be combined with the requirements of overprinting accuracy, and the depth of the color mark dots of the printing plate should be adjusted according to many factors such as the speed of the overprinting machine, printing pressure, and several colors of overprinting.2． Establish standard requirements for the installation and cleaning of printing plate rollers, and achieve standardized operations for plate loading and unloading.3． Focus on monitoring the change of tension during machine operation, and adjust it reasonably to avoid breaking and cracking of the substrate during the overprinting process. 4． In the process of overprinting, it is necessary to do: the pressure angle of the squeegee is correct, which can reduce the pollution and scratches of the printing layer and color mark ink; properly adjust the tension of the aluminum foil, which can avoid inaccurate color registration, dot loss and printing streak defects; master ink viscosity and Solvent affinity, can solve problems such as sticking back, poor color mark registration, and thin gloss.5． To enhance the sense of responsibility of operators, strengthen training and enhance quality awareness at ordinary times. During the process of overprinting, frequent sampling and inspection should be carried out. When overprinting errors are found to be large, timely adjustments should be made.Problems and solutions in overprinting aluminum foil bags1． In terms of equipment, the problem of mechanical wear is prone to occur: the taper heads at both ends of the sleeve shaft are worn; the traction roller is unbalanced; the bearing is damaged. Solution: replace the cone head; adjust the traction roller to make it balanced.2． In terms of printing plate rollers, the problem is that the rubber rollers of the printing plate have uneven pressure on the left and right ends during overprinting; the printing plate roller shaft is loose. Solution: adjust the pressure of the printing plate rubber roller to balance the pressure at both ends; re-tighten the printing plate roller shaft.3． Problems are prone to occur in terms of process technology: unbalanced tension control for unwinding and winding; tension imbalance caused by misoperation. Solution: In terms of technical management, process management points should be established to monitor the tension of rewinding and unwinding, and have records; perform reasonable operations according to the operation method.4． Problems with the plate-making color scale: the layout color scale exceeds the normal error range. Solution: re-plate to achieve standard error.5． Problems with raw materials: The thickness of the aluminum foil is uneven, which affects the tension and causes inaccurate registration. Solution: Change the aluminum foil; the viscosity of the ink is high, which affects the overprinting accuracy, and the viscosity of the ink should be readjusted.6． Subjective reasons: the poor sense of responsibility of the operator leads to poor overprinting accuracy. The sense of responsibility of the operator should be strengthened to find problems and solve them in time.