Abstract: This article introduces the new technology of using powder coating for can coating in the production of food cans. Powder coating is a solid coating (no solvent), which is environmentally friendly, saves coatings, and has good coating quality. This technology has been widely used internationally. The equipment adopts a full automatic control system and uses corona coating method for continuous production. This article introduces the process method and equipment principle of this technology in detail, and explains the characteristics, uses and performance of the coating.
In the can-making process in my country, the inside of the can is often printed with iron in advance. The inner coating is food liquid paint. When printing iron, it is necessary to leave an edge for the seam weld. Generally, it is more difficult to leave an edge for the inner coating. , many factories need to carry out edge scraping before seam welding, so as not to affect the quality of seam welding.
However, the welding seam after seam welding needs to be repainted, which is a complicated process and the quality is not easy to guarantee. The powder coating process that has become increasingly popular in recent years is increasingly being used in the can-making industry. For the can-making industry, although the powder coating process is not a new technology, it is only recently that people have really begun to pay attention to it. A few years ago. As early as 20 years ago in the United States, the inside of the weld seam of three-piece cans was produced using the powder coating process. Since the coating of powder coating is thicker than that of liquid coating, the powder coating process can more effectively prevent the impact of iron odor on the taste and color of canned food. At present, there are at least 800 can-making production lines around the world using the technology of powder coating the inside of the weld seam.
Currently, the real applications of this process in the can-making industry are the repair of can coatings and the coating of the inside of three-piece cans. After a large number of scientific experiments, it has been proven that the coating effect of powder coating is very ideal. Products treated with powder coating can be used to can a variety of foods, beer, beverages and aerosols. Some people believe that within ten years, the powder coating process will be increasingly used in two-piece cans and beverage cans.
Why is the powder coating process so attractive? Because the use of powder coatings is more conducive to environmental protection, has highly reliable environmental performance, and has good economic benefits. Powder coating is 100% solid material. Compared with liquid coating, except that there is no solvent, the ingredients are exactly the same. When the can is placed in an oven and heated, the powder melts to form a continuous film.
Most powder coatings used in the can industry are modified with epoxy or polyester, varnish or pigments. The coating utilization rate is very high, so the loss is very small. Especially the recycling system can collect the overspray powder, adjust the overspray powder, and re-enter the system for recycling.
Because powder coating is in a solid state, it is in a solid state during use such as recycling, cleaning and purification, transportation and treatment. The powder coating process does not produce the losses that exist with liquid coatings, and the losses of liquid coatings are difficult to control and expensive. Powder coating is likely to become one of the most widely used coating technologies in the next few years. Because the powder is a dry coating and is 100% solid, it complies with the requirements of governments at all levels around the world to reduce or ban the use of volatile organic compound coatings.
For various can manufacturing plants, the use of this solvent-free powder coating is one of the effective methods to prevent the volatilization of organic compounds during the can surface treatment process.
Regarding environmental protection, the use of powder-coated can bodies and can lids is not only beneficial to can manufacturers, but also to food packaging manufacturers. In order to cater to customers' increasingly higher requirements for product packaging quality, food packaging factories have been looking for unique and innovative solutions. This kind of food canning container not only meets environmental protection and safety requirements, but is also easy to produce. If considered purely from a marketing perspective, canning containers treated with powder coating can help the canning factory establish an image of an environmentally friendly pacesetter. Just like the environmentally friendly products currently circulating in the market, they are very popular in the market. Coating equipment, China Painting Equipment Network's current new can sealing caps and three-piece can body coating repair equipment all adopt full-process automatic control systems. A typical system for powder coating is to suck the powder from the powder supply station by the feeder and transfer it to the recovery device. The recovery device mixes the original powder with the recovered powder, and then mixes it with air. At the same time, it is transferred to the friction spray gun by the pump system. . When the powder is transferred to the can body or can lid, the spray gun is electrified by friction, so that the powder particles are charged with electrostatic charge. The charge causes the powder to be adsorbed to the can body or can lid in a special and even spraying manner, and all overspray coatings are It has completely entered the recycling device to be recovered, adjusted and reused. This coating method causes the powder to pass through a positively charged electric field, making the powder particles negatively charged. In this case, the can body or lid is grounded, so that the powder particles can be absorbed.