The application of UV technology in the iron printing and can making industry is mainly marked by the introduction of KBA Metalprint's metalstar2 six color UV iron printing machine, which is currently the world's most advanced, by Shanghai Baoyin Metal Color Coating Co., Ltd. in 2004. Subsequently, Hangzhou COFCO Packaging Co., Ltd. also introduced the 5 color UV iron printing machine from the British company Quali. As a result, UV iron printing technology has entered a new development period in China. Due to the progressiveness of UV technology and its applicability to the iron printing and can making industry, since COFCO Packaging transformed the original traditional iron printing line into UV line in 2004, the development of UV technology in the iron printing and can making industry has entered a fast lane.
The Process and Technical Essentials of Traditional Iron Printing
coating
Before printing, it needs to be coated. Usually, the front of the sheet needs to be coated and printed, and the inner surface needs to be coated with paint to ensure that the printed iron product has good requirements for canning, canning, and exterior decoration. Coatings are classified by resin as oily, phenolic, epoxy, polyester, ethylene, acrylic, amino, etc. According to their use, they are divided into internal coatings, external coatings, color coatings, gloss coatings, special coatings, etc.
Plate making
The plate making process of printing iron is basically the same as that of ordinary offset printing, but due to the fact that printing iron products always require canning, printing iron plate making must meet the requirements of canning. When making plates, it is necessary to understand the basic characteristics of metal packaging containers. For example, when making oil cans, it is necessary to consider the requirement of leaving space for resistance welding. There is a certain spacing between the patterns to facilitate the cutting, high-frequency welding, and can making needs of the product after being printed with iron. For example, the battery casing should be arranged as many pieces as possible within the specified tin size range, and also to facilitate the cutting and punching of the battery casing. In addition, for candy boxes, it is necessary to understand the cutting edge size of the box cover and leave a certain amount of excess material based on this, otherwise it will cause trouble for the punching of the box cover. Only after the printing sheet is coated on the inside and outside can it be printed on the machine (except for special processes). Printing machines are divided into three types: monochrome machines, dual color machines, and multi color machines. At present, the main imported machines used in China are the dual color printing machines from the UK's Keli Company and the Japan's Fuji Company. The domestic machines mainly use the single color printing machines from Shanghai Gauss Printing Equipment Co., Ltd. The structural principle of a printing machine is similar to that of an offset printing machine. When printing, it is necessary to adjust the ink balance, printing pressure, and accurate overprinting. Due to the fact that the surface of the sheet is different from the paper and does not have the absorption of fine pores like paper, it is not possible to arrange large area wet pressing and multi-color overprinting when considering color sequence. Only wet pressing and wetting processes can be applied to mesh points below 50%. When arranging the color sequence, it is generally necessary to comprehensively consider the main color tone of the layout, the accuracy of overprinting, and the pros and cons of the operation, and analyze it specifically based on the characteristics of the product and machine performance.
polish
After completing all the color matching, a layer of bright oil needs to be applied to the printing iron surface to increase the glossiness of the printed product surface, while also improving the hardness of the product surface, making the printing ink layer have a certain degree of flexibility and corrosion resistance.
dry
Both paint and ink need to be dried in a tunnel oven. The drying conditions for iron printing ink are usually between 130 ℃ and 160 ℃, and the time is controlled within 10-12 minutes