Net distance and quality in printing (below)

In addition, it should be noted that in screen printing, because the increase of the net pitch has the same effect as the increase of screen tension, some people want to increase the squeegee pressure by increasing the net pitch, so that the screen gets a higher tension, but This method has a lot of negative effects (especially the dot increase), so the screen tension should be increased in the printing instead of increasing the pitch.
The effect of small net distance on the print quality In most cases, the net distance should be as small as possible, but too small net distance will cause the screen and the substrate to be separated from the ideal, so that the screen can not be immediately ejected from the workpiece The separation speed of the screen and the substrate is slower than that of the squeegee, leaving a net mark and causing the pattern to become dirty. In addition, if the mesh distance is too small, the ink will adhere unevenly, and the squeegee will ripple on the screen when printing, which will affect the registration and cause image ghosting. The correct net distance should be under the condition that the screen plate has a certain tension, which ensures that the scraping pressure of the squeegee during the screen printing process is minimized and the screen can be ejected from the workpiece immediately. The choice of net spacing is related to the screen tension. High tension screens can choose a relatively small screen pitch, and low tension screens should choose a relatively large screen pitch. The adjustment range of the general network distance is 0.1-12.7mm, but 1.5-3.0mm is more common and more feasible. When the quality of the printed product is required to be high, the size of the net distance will be limited by the range of deformation that the screen can allow. In the printing of electronic products, stainless steel nets are often used, and the net pitch is relatively small, 0.1-0.2 mm.
Registering problems In multi-color printing, the accuracy of overprinting is an important factor to measure the quality of the printing, and the net distance plays a decisive role in the stable printing and registering. The screen is deformed due to its elasticity. The larger the distance, the more the squeegee forces the screen to extend, causing the image to be deformed on the printing material, and the peeling will make the problem worse. In order to reduce this distortion, the network spacing should be as small as possible. For products with higher printing precision, the net distance should be less than 3.0mm. Practice has proved that using 1.5mm is more ideal. In addition, many problems will arise. For example, in order to make the screen and the substrate contact with each other, the good transfer of the ink is achieved, the pressure to increase the squeegee must be increased, and excessive force is exerted on the screen plate in the squeegee. The cutting edge will multiply, and the longer size of the squeegee will bring more problems. The result is not only an increase in image edge distortion but also a significant reduction in print quality. The increase in grid distance also tends to skew and lengthen the entire image. This effect will vary depending on the position of the image, the length of the squeegee relative to the frame, and the direction of travel of the squeegee. The uniformity of the mesh distance is also an important factor affecting the registration. If the screen pitches of the screen before and after printing are inconsistent, partial overprinting of the printed matter will occur. In this case, the next color is printed, and it is difficult to register with the first color in any case. In addition, the impact of registration and shrinkage and expansion of the substrate. When multi-color printing, the net distance used must be the same, otherwise it will cause deviation in printing accuracy.
How to adjust the optimal network spacing Since the determination of the network spacing is related to a variety of factors, it is necessary to consider different materials and printing equipment to adjust the optimal network spacing. To use the smallest possible network distance, consider the following aspects:
(1) Improve screen tension. The screen tension is high, so that the network distance can be reduced and the printing speed can be increased. Therefore, according to the actual level of equipment, materials, and stretch netting, try to obtain a screen with higher tension. However, it should be noted that it is difficult to stretch the large-size screen to a higher tension. Therefore, when determining the screen pitch, the size and tension of the screen must be taken into consideration. In general, screen tension can choose 18 ~ 25N/cm. Multi-color printing also needs to be consistent with the tension of each screen, so as to ensure that the screen pitch of each screen is the same. In this way, not only can the print registration between color and color be guaranteed, but the relative printing pressure can also remain the same.
(2) Reduce the ink viscosity. The viscosity of the ink is determined by factors such as thixotropy, ink composition, size and amount of pigment particles, surface tension, storage time, and the like. To reduce the viscosity of the ink, you can improve the ink, or find another good printing ink. The lower viscosity of the ink will also reduce the requirements for web spacing and stretch tension.
(3) Select the appropriate screen. The geometry of the screen is also an element that affects the ability of the ink to transfer. Using a screen with a small surface area (eg, a wire with a wire diameter of 27 to 31 mm), the force required to separate the ink from the printing material will be smaller, the required force is small, and the mesh distance may be small.
(4) The characteristics of the substrate. Substrate also has a great influence on ink transfer and peeling. Absorbent materials are more easily peeled than non-porous materials. The tension on the surface of the substrate is related to the surface energy of the ink. Therefore, it also affects the peeling of the ink. Taking a textile substrate as an example, textiles have water absorption, and there is no problem of peeling from the screen. This is the reason why the net distance of textile printing is smaller than that of other graphics. Smaller net distances for printed textiles can minimize the deposition of ink underneath the screen. Because textiles are generally printed with multiple table tops and print heads, ensuring consistent web spacing at each print station is the key to achieving good overprinting and ink uniformity. Textile printing sometimes requires several garments to print the same pattern. The thickness of these garments is different, and the net pitch must be adjusted accordingly.
In a word, as one of the five major variables in screen printing, the screen pitch has a great influence on the quality of screen printing. Therefore, the best screen distance should be debugged according to various factors such as equipment, materials, and substrates. In this way, you can print beautiful products.