Rotary screen printing process
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When screen printing is performed by a rotary screen, a screen printing cylinder with a mesh is internally covered with ink, and when the web substrate is in contact with the rotating plate cylinder, the ink is pressed by a squeegee located inside the drum. The ink is passed through a mesh in the screen plate and transferred to the substrate material. We can control the thickness of the ink layer transferred to the substrate by selecting a screen version of a different mesh (which can now be done above 400 mesh/inch) and adjusting the print pressure.
The screen making process of the screen plate is also relatively simple: firstly, the screen plate is coated with a liquid water-based emulsion to block all the meshes, and then the screen plate is dried in a dry box; The positive film with the printed image is wound on a screen-coated cylinder coated with an emulsion and exposed to it with a UV light source (since the screen plate is generally roll-shaped, a screen cylinder is required). After the exposure is completed, the screen plate is rinsed in an automatic plate processor, and the unexposed emulsion is washed away, leaving the mesh of the graphic portion.
After the above steps, the plate cylinder can be printed on the machine. Different from flat screen printing, the squeegee in the rotary screen printing is fixed in the plate cylinder. Before printing, the inside of the drum is filled with ink. When printing, it depends on the rotation of the screen cylinder, in the squeegee. The ink is printed on the printing material under pressure; after printing, the printing plate can be cleaned and stored with the corresponding finishing equipment for use in printing again. Some of the screen layers (such as some of Stork's screen-based versions) can be completely stripped and then used for coating and imaging. The number of reuses can be as high as 10 to 20 times. Obviously this is very Important cost effectiveness. We can do a small calculation. If the price of a plate cylinder is 3,000 yuan, the cost of the screen version can be reduced to 150 yuan per print by repeated use.
Rotary screen printing usually runs at speeds from 75 ft/min to 150 ft/min, but if you print a thicker ink layer, the speed will be slower; if the intermediate drying time is longer, the speed of the rotary screen can reach 150. Feet/minute to 350 ft/min. In fact, the speed of the rotary screen printer itself is not limited (the speed can be as high as 600 feet / minute), the real limiting factor is the ink and its drying performance.
The inks used in rotary screen printing are mostly UV-curable inks, which are cured by UV light sources. However, there are also solvent-based inks that are dried by hot air. For example, the conductive silver ink used for printing the "antenna" of RFID tags is solvent type. Ink, which uses a hot air drying method.
In order to strengthen the position of rotary screen printing in UV flexographic printing, ink manufacturers have not stopped researching and developing new inks. In foreign countries, many ink companies such as SunChemical, AkzoNobel and FlintInk and Deco-Chem in Mashawaka, Indonesia are working hard to research and develop UV inks for flexographic and rotary screen printing. Nowadays, a kind of UV ink has been developed. Rotary screen printing RSF silicone-free ink. Domestic ink manufacturing enterprises should learn from foreign companies, strengthen technical exchanges and cooperation with foreign companies, and consider increasing research and development in this area to lay the foundation for their superior position in the fierce market competition.