Talking about the Application of Powder Coating in Can Making

In our country's can making process, the inside of the can body is pre-printed with iron in advance. The inner coating is a food liquid coating. When printing iron, it is necessary to leave seams at the seam welding position. Generally, it is difficult to apply the edge coating. Many factory seams must be welded before welding. Scraping is done so as not to affect the quality of seam welding. However, after the seam welding, the weld seam must be additionally coated, the process is more complicated, and the quality is not easy to guarantee. In recent years, the powder coating coating technology, which is becoming more and more popular, is increasingly used in the can manufacturing industry. For the can manufacturing industry, the powder coating technology is not a new technology, but people really begin to pay attention to it. A few years. As early as 20 years ago in the United States, the inner side of the weld in the three-piece can was already produced by the powder coating process. Since the powder coating has a thicker coating than the liquid coating, the powder coating process can more effectively prevent the influence of iron odor on the taste and color of the canned food. At present, there are at least 800 canning lines in the world that use powder coating to weld the inside of the welder.

Currently, the real application of this process in the canning industry is the repair of cans and the coating on the inside of three cans. After a lot of scientific experiments have proved that the coating effect of powder coating is very satisfactory, and the powder coated product can be used to canned a variety of foods, beer, beverages and aerosols. Some people think that in a decade the powder coating process will be increasingly applied to 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, with highly reliable environmental performance, but also has a good economic benefit. Powder coating is 100% solid material. Compared with liquid coating, the ingredients are completely identical except no solvent. When the can is heated in the oven, the powder melts to form a continuous film.

Most powder coatings used in the canning industry are modified with epoxy or polyester, varnish or pigments. Paint coating utilization is very high, so the loss is very small, especially the recovery system can collect overspray powder and adjust the overspray powder to re-enter the system for recycling.

Because the powder coating is in the solid state, the recycling, cleaning and purifying, transportation and processing are all in solid state during use. The powder coating process does not cause the loss of the liquid paint, and the loss of the liquid paint is not easily controlled and is expensive.

Powder coatings may become one of the most widely used coating technologies in the coming years. Because the powder is a dry coating, it is 100% solid, and thus meets the requirements of all levels of governments around the world to reduce or prohibit the use of volatile organic compound coatings. For each can manufacturing plant, the use of this solvent-free powder coating is one of the effective methods for tank surface treatment to eliminate volatilization of organic compounds.

For environmental protection, the use of powder coated cans and lids is not only beneficial to can makers but also to food packaging manufacturers. In order to meet the increasing demands of customers on product packaging, food packaging plants have been seeking unique and innovative solutions. This kind of food canned container meets environmental safety requirements and is easy to produce. If purely from the point of view of market sales, the use of powder coating cans can set the image of an environmental model. Just as the environment-friendly products that are currently circulating on the market are very popular in the market.

The current new can lids and three-piece cans are all equipped with automatic control systems. A typical system for powder coating is to draw the powder from the powder supply station from the feeder and transfer it to the recovery unit. The recovery unit mixes the original powder with the recycled powder, then mixes with the air, and the pump system transfers the friction type spray gun. . When the powder is delivered to the can body or can lid, the spray gun is electrified by friction so that the powder particles are electrostatically charged so that the powder is adsorbed onto the can body or the can lid in a special uniform spray manner, and all the overspray coating is The recirculation system is completely recycled, adjusted and reused. This method of painting causes the powder to pass through a positively charged electric field, causing the powder particles to be negatively charged. In this case, the can body or can lid is grounded so that the powder particles can be adsorbed.

This corona coating method removes the charged particles by frictional electrification. This friction electrification method reduces the electrostatic shielding effect and allows the powder particles to migrate to the corners and gaps of the can body or can lid. This is especially suitable for painting cans and can lids.

Currently, there are two kinds of coating technologies, including continuous spraying technology and intermittent spraying technology, which are widely used. The former is applicable to the outer side of a coating can. When the can enters the painting area, the spray gun starts. In the painting area, various sprays can be applied. In the method, the powder particles are directly coated on a portion to be coated of the can; the latter is a coating method of the spray gun when the can body or the can lid enters the spraying area. In order to control the opening and closing of the gun, the adjustment of the gas or powder is controlled in a control tube. The gas flow is readjusted by a diverter to control the amount of coating and rapid flow cut off of the workpiece when the gun is stopped.

This process is achieved through a series of solenoid valve controls. The powder pump solenoid control valve controls the amount of powder required for the part to be coated. When the powder pump sends the powder out of the powder hose to the control tube, the powder is accelerated by the amplifier while the uniformity of the powder or gas is optimized through an atomizing nozzle. After entering the control tube, the powder particles in the tube are brought into contact with the control tube wall to be electrostatically charged. The charged powder passes through the nozzle of the spray gun and is applied to the can body or the lid of the lid. The pump is shut down and the air flow diverter is opened. Shut off the spray gun and repeat this cycle for each can body or lid.

The operating cycle speed of a single piece depends on the amount of powder to be coated for each part. For example, for the post-repair of epoxy coating can lids, each gun can handle 300 to 350 per minute. When the lid of the can is placed in front of the spray gun by a set of positioning mechanism, the friction-type spray gun sprays electrostatic charged powder onto the can lid. All the over spray powder will collect and re-enter the supply hose to enter the system. Recirculation, then coated can lids are conveyed through a curing oven with a conveyor belt where the powder melts into the scratches and weld areas of the workpiece.

This process can be applied to both the outside and the inside of the lid, and the amount of coating is typically 60 to 80 milligrams. In order to increase the appearance of the outside of the can lid, a larger amount of powder is required. For the inner powder coating of the three-piece can body, a new powder coating process has been developed. The maximum coating speed of this coating process is about 75 pieces per minute per spray gun. The open end of the can body is conveyed by a positioning and transport mechanism to the front of the friction-electrifying type spray gun, charged powder is injected into the can, and any overspray powder is recovered by the apparatus and re-entered into the system for recycling. The cans were then sent to a flat belt conveyor oven where they were fired, cured, and fired at a temperature of 425F for about 2 minutes. For general international standards, coatings generally use modified epoxy powders with an average accuracy rating of 10 to 15 microns, while hygienic-grade canned coating films are approximately 15 to 20 microns. This canning manufacturer can obtain excellent coating quality, eliminate the volatilization of organic compounds on the workpiece, and the utilization rate of the material can reach as high as 99%. Due to the clean and effective coating process, the cleaning and maintenance costs of the workpiece can be greatly reduced.

Like the can plant, the food package can benefit from the end of the coating process

Manufacturers, due to the excellent quality of the improved can coatings, and the powder coatings improve the shelf life of foods, minimize leakage, corrosion, and iron odor effects on canned foods, that is, powder coating An excellent protective film is provided between the food and the packaging container, thereby improving the quality and life of the canning product.

Powder-coated canned products have a longer shelf life. The use of powder coated metal cans in a variety of food products and canned products of different sizes can completely replace the canning method using liquid coating.

For the powder coating materials and processes required for food canning, currently the relevant manufacturers are gradually improving and striving for excellence to meet the requirements of food canning.

Now, powder and raw material production plants need to develop more types of resin products. There are not many studies currently available on many resins and additives that can be used to improve powder properties and help overcome powder coating defects.

Powder manufacturers also need to understand the entire potential of metal coating, and determine which coating technology is more practical, whether it is three-piece cans, spray cans, cans, cans, cans or coils, each material Different resin-modified powders are required for coating to obtain the best performance.

Spray cans require inner wall coatings that have antifogging capabilities, and three food cans must have the ability to resist erosion of certain foods while also having the ability to resist cooking. Changes in performance depend on changes in the composition of the metal raw material. For example, powders that perform well on tin cans may not be accepted in aluminum cans.

The clean, high-gloss polished surface formed by the powder coating technology makes the quality, hygiene, and appearance of can containers more noticeable. These are selling points that attract the attention of customers at the time of purchase, or open cans and rinses. The convenience of recycling again.

Packers will greatly improve the quality of their food products by adopting new and improved powder-coated containers that meet environmental requirements.