Ⅰ. Poor ink adhesion
1. Reasons:
1) PET sheet has low surface energy, and ink is difficult to adhere well;
2) The compatibility of ink and PET sheet is poor;
3) The humidity in the printing workshop is high, affecting the ink’s drying and adhesion.
2. Solutions:
1) Surface treatment of PET sheet, such as corona treatment, coating treatment agent, etc., to improve surface energy;
2) Select ink with good compatibility with PET sheet, and add adhesion promoter to the ink;
3) Control the humidity in the printing workshop to ensure the ink is fully dried.

Ⅱ. Inaccurate overprinting
1. Reasons: Insufficient precision of printing equipment, deformation of PET sheet during printing, improper operation, etc.
2. Solutions:
1) Regularly check and maintain printing equipment to ensure equipment accuracy;
2) Select a PET sheet with good dimensional stability, and pre-treat the sheet appropriately before printing;
3) Strengthen operator training, improve operating skills, and ensure accurate overprinting.

Ⅲ. Plate blocking
1. Reasons: Ink dries too fast, impurities in the ink clog the plate mesh, improper scraper pressure, etc.
2. Solutions:
1) Adjust the drying speed of the ink, add an appropriate amount of slow-drying agent; filter the ink to remove impurities; 2) Adjust the scraper pressure and angle to ensure good contact between the scraper and the plate, so that the excess ink can be scraped off without damaging the plate.

Ⅳ. Color difference
1. Reasons: Inaccurate ink mixing, changes in ink viscosity during printing, uneven printing pressure, etc.
2. Solutions:
1) Strictly mix the ink according to the standard formula;
2) Control the viscosity of the ink, which can be adjusted by adding diluents or thickeners;
3) Adjust the printing pressure to ensure uniform and stable pressure.

Ⅴ. Ink bar
1. Reasons: Uneven pressure between the plate cylinder and the impression cylinder, wear on the plate surface, poor ink fluidity, etc.
2. Solution:
1) Adjust the pressure between the plate cylinder and the impression cylinder to make it evenly distributed;
2) Check the surface of the plate and replace it in time if it is worn;
3) Optimize the ink formula to improve the fluidity of the ink.