When printing PET sheets, controlling process parameters is crucial to ensure quality, which can be done from the following aspects:

1. Printing pressure control

Printing pressure directly affects ink’s transfer effect and PET sheets’ degree of deformation.

Offset printing: The printing pressure during offset printing should be moderate, generally between 0.15-0.25mm. If the pressure is too high, it will cause excessive deformation of PET sheets, and problems such as dot enlargement and plate smudging will occur; if the pressure is too low, the ink transfer will be insufficient, and the pattern color will be light and unclear. For example, when printing fine patterns, excessive pressure may make fine lines thicker or even smushed together, affecting the printing quality.
Gravure printing: The printing pressure of gravure printing is relatively large, usually around 0.2-0.3mm. However, it also needs to be adjusted according to the thickness and hardness of the PET sheet. For thinner PET sheets, the pressure should be appropriately reduced to avoid sheet rupture; for harder PET sheets, the pressure can be appropriately increased to ensure sufficient ink transfer.
Flexo printing: The pressure of flexo printing is relatively gentle, generally between 0.1-0.2mm. Since flexo printing uses an elastic printing plate, excessive pressure can easily cause the printing plate to deform, affecting printing accuracy.

2. Printing speed control

The printing speed affects the drying effect and production efficiency of the ink.

Speed ​​selection: The printing speed should be determined according to the drying performance of the ink, the material of the PET sheet, and the complexity of the printed pattern. Generally speaking, for ordinary PET sheet printing, the speed can be controlled at 50-100 meters/minute. If the ink dries slowly, the printing speed should be appropriately reduced to ensure that the ink is fully dried to avoid problems such as adhesion and smearing. For example, when using water-based ink, the printing speed is usually not too fast due to its relatively slow drying speed.
Stability control: During the printing process, the printing speed should be kept stable. Excessive speed fluctuations can easily lead to problems such as inconsistent printing colors and inaccurate overprinting. The precise control and stability of the printing speed can be ensured by using advanced printing equipment and control systems.

3. Ink drying temperature control

The appropriate drying temperature can ensure that the ink dries quickly without affecting the performance of the PET sheet.

Hot air drying: For hot air drying, the temperature is generally controlled between 50-80℃. If the temperature is too low, the ink will not dry sufficiently, which will affect the next process; if the temperature is too high, the PET sheet may deform and shrink, and even affect the color and adhesion of the ink. For example, during the printing process, if the drying temperature is too high, wrinkles may appear on the surface of the PET sheet, affecting the printing quality.
Infrared drying: The temperature of infrared drying is relatively high, which can be between 80-120℃. But it also needs to be adjusted according to the heat resistance of the PET sheet. For PET sheets with poor heat resistance, the temperature of infrared drying should be lowered to avoid damage to the sheet. At the same time, attention should be paid to the uniformity of infrared drying to avoid local temperatures being too high or too low.
UV drying: UV drying is an efficient drying method that instantly cures the ink through ultraviolet irradiation. The temperature of UV drying is relatively low, but attention should be paid to the control of ultraviolet intensity. Generally speaking, the intensity of ultraviolet light is between 80-120mW/cm². If the intensity is too low, the ink will not be cured completely; if the intensity is too high, it may have adverse effects on the PET sheet, such as yellowing and brittleness.

4. Control of other process parameters

Ink viscosity control: The viscosity of the ink should be adjusted according to the printing method and the surface characteristics of the PET sheet. Generally speaking, the viscosity is more suitable between 15-30 seconds (apply 4 cups). Too high viscosity will lead to poor ink fluidity, unsmooth printing, blockage, and hair pulling; too low viscosity will cause excessive ink transfer, resulting in blurred patterns and dull colors. The viscosity can be controlled by adding diluents or adjusting the ink formula.
Anilox roller parameter control: In gravure and flexographic printing, the number of lines and depth of the anilox roller have an important influence on the amount of ink transfer. For the printing of PET sheets, an anilox roller with a line number of 150-300 lines/inch is generally selected. The depth of the anilox roller should be adjusted according to the viscosity of the ink and the printing requirements to ensure uniform and stable ink transfer.
Environmental humidity control: The humidity of the printing environment also has a certain impact on the drying of the ink and the performance of the PET sheet. Generally speaking, the humidity in the printing workshop should be controlled between 50%-60%. Too high humidity will slow down the drying of the ink and even cause problems such as ink emulsification; too low humidity may cause static electricity on the PET sheet, affecting the printing quality. The environmental humidity can be adjusted by installing a humidifier or dehumidifier.