The process of pressure printing is essentially to transfer the pattern formed by the ink attached to the printing plate to the printed material. During the ink transfer process, a certain amount of pressure must be applied, known as printing pressure. When other conditions remain constant, the transfer rate increases with the increase of printing pressure. When the printing pressure is increased to a certain level, the ink transfer rate no longer increases, and further increasing the printing pressure is actually harmful. Therefore, from the perspective of ink transfer, the transition point from an elevated state to a balanced state is the appropriate printing pressure, which is the necessary minimum pressure.
The transfer of hot and cold air, as well as temperature and humidity, ink onto plastic film is dried through the convective and diffusion evaporation of solvents. In order to improve the drying speed, hot air should be combined with cold air to accelerate the diffusion, penetration, and convection of solvents between ink films. That is to say, the drying speed should be adapted to the release of solvents, changes in vehicle speed, and color matching requirements. When printing multiple sets of stacked color patterns, the ink thickness and drying speed requirements for each set of colors are different. For example, the viscosity of the ink between the first set of colors and subsequent sets should be gradually reduced, and the first set of colors should be controlled in a state where the ink is dry but not dry. If the ink dries too quickly or too slowly, the phenomenon of the back printing roller sticking to the front printing roller will occur.
The temperature and humidity of the working environment affect the dryness and drying speed of ink, and therefore have a significant impact on the quality of the finished product. According to reports, a doubling of humidity will delay the drying speed by nearly two times, which will cause adhesion problems. Moreover, in polyamide ink, when the humidity is high, the evaporation latent heat of some alcohol solvents is high. When the ink film cools, the condensation of surrounding moisture can also cause whitening of the product. On the contrary, low environmental humidity can cause problems such as printing. The temperature in the printing workshop should be between 18-22C and the humidity should be between 65-75%.
