Corona treatment and its importance in flexo printing
Authors:   Marmara University, Vocational School of Technical Sciences Audiovisual Techniques and Media Productions, Istanbul, Turkey, Acar Büyükpehlivan Gülhan , Oktav Mehmet ,   Marmara University, Faculty of Applied Sciences, Printing Technologies Department, Istanbul, Turkey
Published: November 2022

With the increasing importance of flexible packaging in recent years, the trend of packaging printing in the printing industry has increased. The most widely used printing systems in flexible packaging printing are flexo and rotogravure printing. Although rotogravure printing is as high quality and fast as flexo printing, it has made flexo printing more preferable because the printing preparation processes take longer and are more costly. Flexo printing is a high printing system, and it is a printing system that is widely used especially in corrugated cardboard and flexible packaging printing. In flexo printing, the main factors affecting quality are the material to be printed and its physical properties. In flexo printing, the main factors affecting quality are the material to be printed and its physical properties. In particular, the surface structure of plastic film and metallized packaging substrates with low surface energy is expected to be ink-retaining. Because the surfaces of synthetic plastic films and metallized foils have a smooth and slippery structure, preventing printing inks from sticking. Because the binder in the structure of the ink does not have a rough surface to penetrate. In order for plastic films to be printed, their surfaces must have certain properties. For this, surface improvement process called corona is applied to these material surfaces. With this process, the film material surfaces are made micro-rough and the ink adheres to the surface better and is more resistant to external factors. It should be borne in mind that the surface of a film material that has undergone a corona treatment may deteriorate over time unless it is printed on. Because the effectiveness of the corona treatment is time-limited and the surface energy inevitably decreases after a while. They are also affected by environmental conditions such as temperature and humidity. In this study, to show the importance of corona surface coating, test prints were made with flexo printing on corona treated film materials whose corona became insufficient due to time. In the examination of the microscopic images of the test prints, it was observed that the ink adhered very well and was resistant to external factors on the surfaces where the corona treatment was adequately applied. On the other hand, it was determined that the ink color intensity decreased and the print quality deteriorated in the material with insufficient corona after the corona period. As a result, in printing systems, the surface energies of the plastic films must be approximately 10 mN/m higher than the surface tension of the ink during the printing process, in order to maintain good printing quality and unchanged throughout the printing, and for this, the surface energies of the plastic films must be increased by corona surface treatment. demonstrated on test prints and microscopic images of prints.