In screen printing, the following points should be noted for the PET sheet itself:

1. Material selection:

1) Thickness uniformity: Choose PET sheets with uniform thickness, otherwise the ink layer thickness may be uneven during the printing process, affecting the printing quality. For example, if the thickness of the PET sheet is inconsistent, the adhesion effect of the ink layer in the thin and thick parts will be different during printing, which may make the clarity and color saturation of the pattern inconsistent in different parts.
2) Transparency and glossiness: According to the printing requirements, select PET sheets with high transparency and good glossiness. PET sheets with high transparency are conducive to showing the color and details of the printed pattern, and good glossiness can enhance the visual effect of the printed product. For example, for printed products that need to show high-definition and bright patterns, such as high-end packaging, display boards, etc., PET sheets with superior transparency and glossiness should be selected.
3) Surface flatness: Ensure that the surface of the PET sheet is flat, without bumps, wrinkles or scratches. Uneven surfaces can cause uneven contact between the screen and the sheet, resulting in uneven ink transfer, deformation, blurring or ink leakage of the printed pattern. For example, in the label printing of electronic products, if there are scratches on the surface of the PET sheet, the pattern on the label after printing may have defects at the scratches.

2. Surface treatment:

1) Cleaning: Before printing, the surface of the PET sheet needs to be thoroughly cleaned to remove impurities such as dust, oil, fingerprints, etc. These impurities will affect the adhesion of the ink, resulting in the printed pattern being weak and easy to fall off. For example, if there is oil on the surface of the PET sheet, it is difficult for the ink to adhere evenly, and some areas of the pattern may be missing or poorly adhered after printing.

2) Electrostatic treatment: PET sheets are prone to static electricity, which will absorb foreign matter such as dust, and will also affect the transfer and adhesion of ink. Therefore, static elimination treatment is required. The impact of static electricity can be reduced by using an electrostatic eliminator or increasing humidity in the environment. For example, when screen printing is performed in a dry environment, PET sheets are prone to static electricity and dust adsorption. Using an electrostatic eliminator to treat the sheet before printing can effectively improve the printing quality.
3) Surface activation: PET sheets are plastic film materials with medium and low surface energy. The surface energy is low and the ink is not easy to adhere. Surface pretreatment is usually required to increase the surface energy or wetting ability, such as chemical treatment, corona treatment, etc., to enhance the bonding force between the ink and the sheet, otherwise the ink is easy to fall off.

3. Storage conditions:

1) Temperature: PET sheets should be stored at a suitable temperature, generally recommended in an environment of 15℃ – 25℃. If the temperature is too high, the PET sheet may deform, soften, and affect its flatness and dimensional stability; if the temperature is too low, the sheet may become brittle and easily break during printing or processing. For example, in the hot summer, if the PET sheet is placed in a high temperature environment for a long time, it may deform, resulting in printing size deviation.
2) Humidity: The humidity of the storage environment should be moderate, avoiding excessive moisture or dryness. If the humidity is too high, the PET sheet will easily absorb moisture, which may affect its performance and printing quality; if the humidity is too low, the sheet will easily generate static electricity. It is usually more appropriate to control the relative humidity at 40% – 60%. For example, in the humid rainy season, attention should be paid to moisture-proofing of the PET sheet, otherwise it will cause problems such as ink smudge during printing due to water absorption.
3) Avoid extrusion and collision: During storage and transportation, PET sheets should be avoided from extrusion and collision to avoid deformation, damage or scratches of the sheets. PET sheets should be placed on flat, dry shelves or pallets and protected with suitable packaging materials. For example, during transportation, if the PET sheet is squeezed by heavy objects, it may cause the sheet to bend or crease, affecting the printing effect.