The concept of screen printing

What is screen printing？

Screen printing refers to a printing method in which the ink is evenly coated on the substrate so that the ink is evenly attached to the surface of the substrate. The common screen printing includes screen printing, offset printing and plastic printing. Silk screen printing, also known as offset printing, is famous for its special screen printing method, fastness and low cost. Screen printing is widely welcomed by the industry due to its high process value, high printing precision, fast printing speed, etc; Offset printing uses coating printing, but it is widely used because of its slow printing speed, high cost and strict requirements for the substrate; Plastic printing mostly adopts glue coating printing; Screen printing uses a combination of gluing, coating and printing to control the ink evaporation rate by adjusting the pressure (especially the printing pressure) during the printing process, so as to achieve rich colors in concave and convex layers and clear and transparent printing. The screen printing process mainly includes four links: screen setting and printing preparation, screen printing plate and printing tool preparation, printing process cleaning, plate making after printing, and final printing effect inspection.

How to set and prepare for Screen printing？

Screen setting refers to taking the printing plate or printing tool out of the screen and performing relevant operations. Generally speaking, printing with ink in silk screen is to cut the screen into a certain shape from the middle part, and then paint the ink evenly on the surface of the workpiece, and after ink treatment, form a smooth network structure; The offset printing and plastic printing press the ink on the screen to the printing pressure, so that the ink is evenly attached to the surface of the substrate. Therefore, in the process of silk thread setting,what should be noticed is transferring the ink to the dot or screen surface to avoid stains or uneven mesh size on the surface of the printed matter, leaving air holes between the meshes, thus affecting the final effect. However, due to the volatile ink during screen printing, attention should be paid to cleaning the dot during printing, otherwise the mesh size may be uneven or the mesh may be blocked, thus affecting the final effect. The network shall be cleaned first; Remove the residual oil, dirt and other foreign matters from the dot, and then repaint the remaining ink into the mesh. If there is too much residual ink at the dot, it will affect the flow rate of the ink (especially in the drying process), and the color will become darker and the transparency will decline; If the dot is not cleaned and there is too much residual ink, the color will change (for example, black will turn red and show spots); In addition, a large number of stains on the screen may lead to poor screen printing effect. Therefore, the screen should be cleaned and dedusted before printing.

How to prepare Screen printing plate？

The setting of printing plate is closely related to the precision of screen printing machine. The printing plates of different sizes and complexity shall meet different requirements. The common diameter is 80-120 μ m. The ordinary plate with a length of about 10 mm shall be made. At the same time, the plate making machine needs to be modified during the production process. Before printing, the printing quality can be guaranteed by adjusting the pressure, ink amount, ink evaporation rate and drying time. The printing plate is made of special ink, which is especially suitable for flexible printing screen, bronzing, post embossing coating and other substrates with high technical requirements, especially for water-based coatings. The printing machine generally needs to be equipped with high-speed screen printing mechanism.

How to clean the silk screen printing

As there are many polar substances in silk screen printing ink, if the content of polar substances in offset printing and plastic printing ink is too much during the printing process, it will cause excessive solvent volatilization in the ink and uneven pollution of the printed matter, which will affect the printing quality, and even cause ink film cracking, mesh plugging, and even make the printing not solid (inaccurate overprint and screen leakage may occur in serious cases). Therefore, when making plates before printing, most of the solvent in the ink layer should be volatilized first. At the same time, the solvent should be minimized to volatilize into the ink during the screen printing process (and the porosity of the screen should also be reduced). This can prevent the ink layer from forming poor ink jet due to the cracking of the ink layer and blocking of the mesh during printing. If the printing ink is effectively controlled by adjusting the pressure of the high pressure roller of the screen printing machine, the ink quality can be guaranteed to meet the printing requirements; However, if the regulating pressure is too small, the ink-jet effect cannot be controlled. Therefore, plate making and cleaning shall be carried out in strict accordance with the production process specifications.