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Reasons for poor ink transfer in flexographic printing

Date:2024-05-13  From:Star Color   

Flexographic ink transfer issues can be caused by various factors. 

  1. Ink viscosity: The viscosity of the ink is an important factor affecting ink transfer. If the ink viscosity is too high, due to increased surface tension, it is difficult for the ink to enter the mesh holes of the printing anilox roller, resulting in reduced ink transfer. Conversely, if the ink viscosity is too low, with excessive solvent, the number of ink particles per unit volume decreases, which can also lead to reduced ink transfer and even cause significant color deviation and quality issues.

  2. Blade angle, pressure, and the distance between the blade contact point and the impression point: The larger the blade angle and pressure, the more ink is scraped from the anilox roller, resulting in reduced ink transfer. Additionally, the greater the distance between the blade contact point and the impression point (the contact point between the printing plate roller and the impression roller), the longer the drying time before ink contact with the substrate, leading to increased viscosity and transfer difficulties.

  3. Printing speed: Printing speed has an impact on ink transfer. Faster printing speeds increase ink transfer as there is less time for the ink to dry before transfer, resulting in less viscosity change. Therefore, increasing the printing speed while maintaining printing quality can help improve ink transfer.

  4. Electrostatic ink assist devices: Actual ink transfer rates are only around 60%. Small mesh holes in the anilox roller can be difficult to fill with ink because it's not easy to form a capillary action. Electrostatic ink assist devices can help improve ink transfer rates, but if these devices are not functioning properly, they can cause ink transfer issues.

  5. Environmental factors: Temperature and humidity have a direct impact on ink fluidity and drying speed. Temperatures between 20-25°C typically result in good ink fluidity and printing quality. Too high or too low humidity can affect ink drying speed and transfer effectiveness.

  6. Insufficient or incomplete cleaning of the printing plate: The height of the raised dots on the flexographic plate should be appropriate. Excessively high dots can cause ink accumulation, while too low dots can affect ink adhesion, resulting in poor transfer. Incomplete cleaning of the plate can reduce adhesion with the ink, affecting ink transfer.

  7. Printing machine issues: Uneven or insufficient printing pressure can not only lead to poor flexographic ink transfer but also cause equipment malfunction and damage. Additionally, if the printing machine is not cleaned thoroughly, residual ink or printing debris can affect ink transfer and print quality.