In offset printing, the following common printing failures and solutions may occur when using PET sheets:

I. Poor ink adhesion
1. Manifestation: The printed pattern is easy to fall off and fade, and the ink will fall off when it is gently wiped by hand.
2. Reason: The surface energy of PET sheets is low, making it difficult for ink to adhere well; the compatibility of ink and PET sheets is poor; and the humidity in the printing workshop environment is high, affecting the drying and adhesion of ink.
3. Solution:
1) Surface treatment of PET sheets, such as corona treatment, coating treatment agent, etc., to improve surface energy and enhance ink adhesion.
2) Choose ink compatible with PET sheets, and add an adhesion promoter to the ink.
3) Control the humidity of the printing workshop, keep the environment dry, and ensure that the ink is fully dried.

II. Inaccurate overprinting
1. Manifestation: Patterns of different colors are misaligned and cannot be accurately aligned.
2. Reason: Insufficient precision of printing equipment, deformation of paper or PET sheets during printing, improper operation, etc.
3. Solution:
1) Regularly check and maintain printing equipment to ensure equipment accuracy.
2) Select PET sheets with good dimensional stability, and perform appropriate pretreatment of the sheets before printing, such as preheating, moisturizing, etc.
3) Strengthen operator training, improve operating skills, and ensure accurate overprinting.
Ⅲ. Loss or expansion of dots
1. Performance: Part of the dots in the printed pattern are missing, or the dots become larger, resulting in blurred images and reduced layering.
2. Causes: Improper offset pressure, inappropriate ink viscosity, aging of the rubber blanket, etc.
3. Solution:
1) Adjust the offset pressure and find the appropriate pressure value through testing.
2) Adjust the ink viscosity and add an appropriate amount of diluent or thickener.
3) Replace the aging rubber blanket in time to ensure uniform ink transfer.
Ⅳ. Wrinkling or curling
1. Performance: PET sheets have wrinkles or edge curling, which affects printing quality and subsequent processing.
2. Causes: Stress of the PET sheet itself, changes in temperature and humidity during printing, uneven ink drying, etc.
3. Solution:
1) Choose PET sheets with good quality and low stress.
2) Control the temperature and humidity during the printing process to avoid large changes.
3) Adjust the ink drying speed to ensure uniform drying. Auxiliary drying methods such as hot air drying can be used.
Ⅴ. Ghosting phenomenon
1. Performance: faint repetitive patterns appear on one or both sides of the printed pattern, affecting the beauty of the picture.
2. Cause: uneven pressure between the plate cylinder and the rubber cylinder, poor ink transfer, etc.
3.Solution:
1) Adjust the pressure between the plate cylinder and the rubber cylinder to make it evenly distributed.
2) Optimize the ink formula to improve ink transfer.
3) Check each component of the printing equipment to ensure normal operation without looseness or wear.