The thermal sublimation ink between two rolling rollers is in a state of flow relative to the roller. An elastic roll and a rigid roll to roll situation, the outer edge of the two rollers form a two-way flare gap. After passing through the narrowest part of the gap, a tiny gap (nucleus) begins to appear inside the ink layer, and the nucleus gradually grows into the gap. In the process of the gap growing, the offset printing thermal sublimation ink between the holes is drawn, the ink wire grows and breaks in one or several places, and most of the ink is adhered to the two rollers respectively. A small amount of ink may come out and form an ink mist. This is a brief description of the flow of ink between rollers.
The ink pressure change between the two rollers is: between the confluence, each is atmospheric pressure; After the convergence, the pressure begins to increase, reaches the maximum not far in front of the center of the roll gap, and then begins to decline until the minimum value (less than atmospheric pressure) is known. At the lowest pressure, a hollow core begins to appear, and then the pressure returns to atmospheric pressure.
The speed of the flow of ink on the surface of the roller is ideally equal to the linear speed of the outer edge of the roller. Inside the ink flow, the velocity distribution of each section is symmetrical up and down, reaching the maximum or minimum value at the midpoint. Before reaching the maximum pressure, the velocity of each point inside the ink flow is smaller than that of the outer edge of the ink roller. When the maximum pressure is exceeded, the velocity of each point inside the ink flow is greater than that of the outer edge of the ink roller. As for the average velocity, along the direction of the ink flow, it gradually decreases before reaching the maximum pressure. After exceeding the maximum pressure, it gradually rises until it reaches the lowest pressure. The velocity gradient on each section is the result of ink viscous shear flow.
Ink as a viscoelastic material, both fluid viscosity and solid elastic characteristics. If the tension time is longer, the ink is more viscous, the ink will be pulled for a long time, and the rebound after fracture is slower; If the tension action time is very short, the ink is more elastic characteristics, the ink is broken in a very short time, and the rebound faster.
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