What is the cause of uneven pressure when printing on the open rotary printer? In screen printing, proper and uniform printing pressure is an important guarantee for obtaining high-quality screen printing. If the printing pressure is uneven, more printing failures will occur. Therefore, controlling the factors that affect the printing pressure and improving the unevenness of the printing pressure has become the main problem to be solved in the screen printing process. So, what is the reason for the uneven pressure when printing on the open rotary printer?
1. The influence of ink viscosity on printing pressure
When printing a batch of screen-printed products, part of the solvent in the ink will evaporate over time, which will cause the color of the same batch of printed products to be inconsistent and affect the uniformity of the printed products. Generally speaking, the ink required for the same batch of printed products needs to be matched once, and the viscosity of the ink should be adjusted in time during the printing process to ensure the uniformity of the printed product.
2. The influence of screen elasticity on the uniformity of printing pressure
The printing pressure of screen printing is the result of the combination of the resilience generated by the deformation of the screen and the viscosity of the ink. In screen printing, due to the existence of the screen spacing, the screen will be stretched and deformed under the action of the squeegee pressure. With the position of the squeegee, the screen distortion is different due to the screen distortion. The screen flexibility is also different. Under the same squeegee pressure, the printing pressure will be uneven. For flat screen printing plates, the deformation of the screen can be divided into deformation along the stroke direction of the doctor blade and deformation along the length of the doctor blade.
Screen elasticity is the vertical component of the screen tension on the left and right sides of the squeegee. It can be seen from the above expression that when the squeegee moves on the screen, the screen deformation will follow the position of the squeegee. The screen flexibility produced by the screen is constantly changing. When the squeegee blade applies a constant scraping pressure to the screen during printing, the screen printing pressure will follow the position of the squeegee blade. The change is different, that is, the printing pressure is not uniform.
3. The influence of the screen frame on the uniformity of printing pressure
The screen is tightened on the screen frame. Due to the influence of the tension of the screen and the asymmetric connection between the screen and the screen frame, the screen frame is deformed, which results in uneven tension on the screen and adversely affects the uniformity of the influence of the printing pressure. In the printing process, to minimize the deformation of the screen frame after stretching, the screen frame can be pre-deformed. There are two pretreatment methods: one is to make the grid frame into a convex shape according to the strong principle of the arch structure.
4. The effect of screen spacing on the uniformity of printing pressure The screen spacing depends on the characteristics of the screen printing itself. Due to the difference in the screen spacing, the effect on the uniformity of the screen printing pressure is also different. From the screen tension formula introduced in the previous section, the larger the screen spacing, the larger the screen deformation range. This will increase the range of the screen printing pressure along the stroke of the squeegee, which will increase the unevenness of the printing pressure. However, if the screen pitch is too small, the separation of the screen and the substrate is not ideal, and the screen cannot rebound immediately, which will affect the clarity of the image. Therefore, to improve the uniformity of the screen printing pressure, the screen spacing should be as small as possible under the condition that the screen can rebound immediately.
Here are the reasons for the uneven pressure during the screen printing of the above-mentioned screen printer. The uneven pressure in the printing process needs to control the main factors that adversely affect the uniformity of the printing pressure according to the different products to be printed, to effectively improve the quality of screen printing.