How to control the uniformity of screen printing pressure?

The screen printing process is very common in the manufacture of cosmetic packaging materials. The process of screen printing is relatively simple. However, there are many changing factors that affect product quality in the entire screen printing process. This article shares how to control the uniformity of the printing pressure of the screen printing. The content is for your reference:

The influence of screen printing uniformity

In screen printing, proper and uniform printing pressure is an important guarantee for obtaining high-quality screen prints. If the printing pressure is too low, the printing plate cannot touch the substrate and cannot be printed, resulting in incomplete printing graphics and uneven ink thickness; when the printing pressure is too high, the screen will be deformed too much and the printed graphics will be blurred. Printing failures such as severe abrasion of the screen and squeegee. If the printing pressure is uneven, more printed product failures will occur. Therefore, controlling the factors that affect the printing pressure and improving the unevenness of the printing pressure have become the primary problem to be solved by the screen printing process.

There are many factors that affect the uniformity of screen printing pressure. The following focuses on the analysis of the influence of the uniformity of printing pressure from the aspects of screen resilience, screen spacing, screen frame deformation and screen printing machine.

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Wire mesh resilience
The printing pressure of screen printing is the result of the combined effect of the squeegee pressure applied by the squeegee, the resilience caused by the deformation of the screen, and the ink viscosity. In screen printing, due to the presence of the screen distance, the screen will be elongated and deformed under the pressure of the squeegee. With the position of the squeegee, the amount of deformation of the screen is also different, due to the deformation of the screen. The resilience of the screen is also different. Under the same squeegee pressure, the printing pressure will appear uneven. For flat screen printing plates, the deformation of the screen can be divided into deformation along the stroke direction of the squeegee and deformation in the length direction of the squeegee.

The unevenness of the printing pressure along the stroke direction of the squeegee is different from the length direction of the squeegee. If compensation is made for these two kinds of pressure unevenness, the squeegee can be positioned in the center of the printing plate along the length of the squeegee to ensure The distance between the two sides of the squeegee and both sides of the screen is equal, so that the printing pressure along the length of the squeegee can be kept uniform; and in the direction of the squeegee movement, the relationship between the printing pressure and the position of the squeegee needs to be calculated, and then Corresponding measures are compensated.

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Net distance
The screen distance is determined by the characteristics of the screen printing itself. Due to the difference of the screen distance, the influence on the uniformity of the screen printing pressure is also different. From the screen tension formula introduced in the previous section, it can be seen that the larger the screen distance, the larger the range of screen deformation, which will increase the range of screen printing pressure along the stroke direction of the squeegee, thereby increasing The unevenness of printing pressure. However, if the screen distance is too small, the separation between the screen and the substrate is not ideal, and the screen cannot rebound immediately, which affects the clarity of the image. Therefore, in order to improve the uniformity of the screen printing pressure, the screen distance should be as small as possible while ensuring that the screen can rebound immediately.

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Ink viscosity
When printing a batch of screen-printed products, part of the solvent in the ink will evaporate over time, making the colors of the same batch of printed products inconsistent and affecting the uniformity of the printed products. Generally speaking, the ink required for the same batch of printed products needs to be fully prepared at one time, and the viscosity of the ink should be adjusted in time during the printing process to ensure the uniformity of the printed product.

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Screen frame
The screen is tight on the screen frame. Due to the tension of the screen and the asymmetric connection of the screen to the frame, the screen frame is deformed, resulting in uneven tension on the screen, which is unfavorable to the uniformity of the printing pressure. influences.

In the printing process, in order to minimize the deformation of the screen frame after stretching the screen, the screen frame can be pre-deformed. There are two pretreatment methods: one is to make the screen frame into a convex shape according to the strength principle of the arch structure.

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Screen printing machine
There are many machine factors that affect the uniformity of screen printing pressure, mainly including the parallelism of the guide rail and the uniformity of the force applied by the squeegee assembly.

①The parallelism of the guide rail. In the screen printing machine, the guide rail plays a key role in the uniformity of the printing pressure. Generally, the screen printing machine has two cylindrical or rectangular guide rails. The squeegee assembly slides back and forth on the guide rail through the slider to realize the squeegee movement. The parallelism of the guide rail and the printing platen is the uniformity of the squeegee pressure. It is ensured that if the guide rail is inclined, the squeegee pressure applied by the squeegee assembly will change, which will cause uneven printing pressure. To improve the parallelism of the guide rails, when the guide rails are installed, the guide rails can be measured by a parallelism meter, and adjustments should be made continuously to minimize the influence of the parallelism of the guide rails on the uniformity of printing.

②The uniformity of force applied by the squeegee assembly. The squeegee is the force applying mechanism for the squeegee pressure. It is the key to ensure the uniformity of the printing pressure to ensure the uniformity of the squeegee force and the straightness of the squeegee surface during work. If the squeegee is worn, it will affect the uniformity of the printing pressure. Therefore, it is necessary to check the wear of the squeegee surface frequently and scrape in time. The uniformity of the squeegee pressure of the screen printer can be ensured by the structure of the squeegee assembly. At present, the screen printer often uses two cylinders of the same specification to control the squeegee.

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other factors
The uniformity of screen printing pressure is a comprehensive problem. In addition to printing materials and printing machinery, there are also human and environmental factors, such as the technical level of the operators, operating methods, and working attitudes. This requires constantly improving the technical level of operators, accumulating operating experience, and reducing the impact of man-made causes on uneven printing pressure; in addition, maintaining a clean environment, stable temperature, humidity, voltage, and air pressure is also the key to ensuring uniform printing pressure. In the actual printing process, it is necessary to control the main factors that adversely affect the uniformity of the printing pressure according to the different products to be printed, so as to effectively improve the quality of the screen printing.