Analysis of the control of printing pressure uniformity in screen printing
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 will not be able to contact the substrate and cannot be printed, resulting in incomplete printing graphics and uneven ink thickness; when the printing pressure is too high, it will cause excessive deformation of the screen and blurred printing graphics. Printing failures such as severe wear of screen and doctor blades. If the printing pressure is not uniform, there will be more print failures. Therefore, controlling the factors that affect the printing pressure and improving the unevenness of the printing pressure has become the primary problem to be solved in the screen printing process. There are many factors that affect the uniformity of screen printing pressure. This article focuses on the analysis of the influence of screen resilience, screen pitch, screen frame deformation and screen printing machine on the uniformity of printing pressure, and explores the technology to improve the uniformity of printing pressure. Measures. 1. The influence of screen springback force on the uniformity of printing pressure The printing pressure of screen printing is the result of the combination of the scraping pressure applied by the doctor blade, the resilience generated by the deformation of the screen and the ink viscosity. In the screen printing, due to the existence of the screen pitch, the screen will be elongated and deformed under the pressure of the doctor blade. With the position of the doctor blade, the deformation of the screen will be different. The resilience of the screen produced is also different. Under the same scraping pressure, the printing pressure will be uneven. For a flat screen printing plate, the deformation of the screen can be divided into the deformation along the stroke direction of the doctor blade and the deformation along the length of the blade. The resilience of the screen is the vertical component of the screen tension on the left and right sides of the doctor blade. When the blade moves on the screen, the deformation of the screen will vary with the position of the doctor blade. The resilience of the screen thus generated changes constantly. When the doctor blade applies a constant scraping pressure to the screen during the scraping process, the screen printing pressure will change with the position of the scraper, that is, Uneven printing pressure has occurred. The deformation of the screen in the longitudinal direction of the squeegee is the same whether it is a fixed or variable pitch. It can be seen from the above expression: when the doctor blade is deflected to the side of the screen frame in the longitudinal direction, the deformation of the left and right sides of the screen is different, and the resulting return force is also different, resulting in uneven printing pressure along the length of the blade . Based on the above analysis, the uneven printing pressure in the stroke direction and length direction of the squeegee is different. If the compensation work is done for these two types of pressure unevenness, the squeegee can be placed in the printing plate along the length of the squeegee. The central position ensures that the distance between the two sides of the blade and the screen is equal, so that the printing pressure along the length of the blade can be kept uniform; and in the direction of the blade movement, the printing pressure and the position of the ink blade need to be calculated Relationship, and then take corresponding measures to compensate. [next] 2. The effect of screen pitch on the uniformity of printing pressure The screen pitch is determined by the characteristics of the screen printing itself. Due to the difference in screen pitch, the influence on the uniformity of the screen printing pressure is also different. According to the formula of screen tension introduced in the previous section, 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 blade and thus increase Non-uniformity of printing pressure. However, if the screen distance is too small, the separation between the screen and the substrate is not ideal, which prevents the screen from rebounding immediately and affects the image clarity. Therefore, in order to improve the uniformity of the screen printing pressure, the screen distance should be selected as much as possible while ensuring that the screen can rebound immediately. 3. The effect 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, 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 matched 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 products. 4. The influence of screen frame on the uniformity of printing pressure The screen is tight on the screen frame. Due to the tension of the screen and the asymmetric connection of the screen to the screen frame, the screen frame is deformed, resulting in uneven tension on the screen, which is detrimental 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 methods of pretreatment: one is to make the frame into a convex shape according to the strength principle of the arch structure, or the already made frame is stretched into this shape with special tools; the other is to stretch the net At the same time, pre-deformation treatment is carried out, that is, the screen frame is deformed by pulling the front baffle of the net device, so that the screen frame is deformed. After the network is fixed, the force and direction of the screen frame are basically the same. After the pre-deformed screen frame is made into a printing plate, the tension distribution on the printing plate is uniform, which can improve the uniformity of the printing pressure during the printing process. [next] 5. The effect of screen printing machine on the uniformity of printing pressure The machine factors that affect the uniformity of screen printing pressure are many, mainly including the parallelism of the guide rail and the uniformity of the force applied by the doctor blade assembly. â‘ Parallelism of the guide rail. In the screen printing machine, the guide rail plays a key role in the uniformity of the printing pressure. The general screen printing machine has two cylindrical or rectangular parallelepiped guide rails. The doctor blade assembly slides back and forth on the guide rails through the slider to realize the ink scraping movement. The parallelism of the guide rail and the printing platen is uniform in applying the ink scraping pressure. Ensure that if the guide rail is tilted, it will cause the scraping pressure applied by the scraping assembly to change, which will cause uneven printing pressure. To improve the parallelism of the guide rail, the guide rail can be measured by the parallelism meter when the guide rail is installed, and continuously debugged to minimize the influence of the parallelism of the guide rail on the printing uniformity. â‘¡ Uniformity of force application of the doctor blade assembly. The doctor blade is the force applying mechanism of the printing pressure, ensuring the uniformity of the application force of the doctor blade and the straightness of the doctor blade surface during work are the keys to ensuring the uniformity of the printing pressure. If the doctor blade wears, it will affect the uniformity of the printing pressure, so it is necessary to frequently check the doctor blade surface wear and timely scrape. The uniformity of the squeegee pressure application of the screen printing machine can be guaranteed by the structure of the squeegee assembly. At present, the screen printing machine often uses two cylinders of the same specification to control the squeegee. The air source supplies air, so the forces acting on both ends of the doctor blade are equal. During the entire printing process, ensuring the cylinder pressure is constant also ensures that the doctor pressure is uniform. The problem of uniformity of screen printing pressure is a comprehensive problem. In addition to printing materials and printing machinery, there are human factors and environmental factors, such as the operator's technical level, operating method, and work attitude. This requires constantly improving the technical level of the operator, accumulating operating experience, and reducing the influence of human factors on the uneven printing pressure. In addition, keeping the environment clean and stable, stable temperature and 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 printed products, so as to effectively improve the quality of the screen printed matter. Leather Corner Sofa is normally put into the corner of the room. The leather corner sofa is a kind of combination sofa which make the room more beautiful. There are many kinds of combinations for the leather corner sofa. 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