In China canning process, use of pre-printed inside the tank iron approach within the liquid coating composition for the food coatings, printing iron when welding seam at the left side to give generally more difficult to stay within the coated side, a lot plant seam welded to the front scraping edge treatment, so as not to affect the quality of the welding seam.
But in the weld seam after welding but also for painted up, process more complex, but also in quality assurance is not easy. In recent years, the growing popularity of Powder Coating processes are increasingly being used in canning industry for the canning industry, the powder coating process, while not any new technology, but it really started to pay attention to it is near a few years ago.
As early as 20 years ago, the United States, the inside seam of three-piece cans have been using powder coating technology of production. Since the powder paint coating is thicker than the coating liquid coating technology, so the use of powder coating process can more effectively prevent the influence of the iron smell of canned food taste and color. At present, the world has at least 800 canning production line using powder coating technology for the production of weld inside.
Currently, the process in the field of canning industry in the application is true cans coating repair and three cans inside coating. After a number of scientific tests proved that the effect of the coating powder coatings are ideal, by powder coating products can be used to deal with a variety of canned food, beer, soft drinks and aerosols. Some people think that, within a decade, powder coating process will increasingly be applied to the two-piece cans and beverage cans.
Why powder coating process so attractive? Because the use of more environmentally friendly powder coating, highly reliable environmental performance, but also has good economic benefits. Powder coating is 100% solid material and liquid coatings compared, in addition to the absence of solvent, the composition exactly the same. When the tank is placed inside the oven is heated, the powder melted to form a continuous film.
Most powder coatings are used in canning industry epoxy or polyester, varnish or paint modification treatment. Coating utilization is very high, so the loss is very small, especially recovery system can collect overspray powder, and the powder overspray is adjusted to re-enter the system recycling.
Because powder coatings are solid, so the use of the process such as recycling and cleaning purification, transportation and processing are in a solid state. By powder coating process does not produce liquid coating exist loss, but the loss of the liquid coating is difficult to be controlled, and expensive. Powder Coatings in the next few years, may become one of the large-scale application of coating technology. Because of the dry powder coating is 100% solids, and therefore in line with the global levels of government to reduce or prohibit the use of volatile organic compounds paint requirements.
For each canning production plant, the use of solvent-free powder coating surface treatment process tank is one of the effective methods to eliminate volatile organic compounds.
For environmental protection, the use of powder coating process cans and lids, not only beneficial for canning plant, also advantageous for food packaging manufacturers. In order to meet customers' increasingly high quality of the product packaging requirements, food packaging plant has been seeking different, unconventional means of settlement. This canned food containers in line with environmental safety requirements, but also easy to produce. If just from the marketing point of view, the use of powder coating process can canned cans container plant to establish a model of environmentally friendly image. As circulation on the market of environmentally friendly products in the market is very strong sales.
New cans and closures currently three cans of coating repair equipment are based on full automatic control system. Typical powder coating system is the powder from the powder supply from the feeder station sucked out, transferred to the recovery by the recovery and recycling of the original powder mixed powder, then mixed with air, and transferred by the pump system to friction gun . When the powder is transferred to the tank lid or the body, the spray gun by friction electrification, electrostatic charge to bring the powder particles, the powder charge in a special way is adsorbed onto a uniform spray cans or lids, and all the paint overspray full access to the recirculating means is recycled, reused and adjusted. This method of coating powder from a positive charge through the field, the powder particles with a negative charge, in this case, cans or lids are grounded, so that you can absorb the powder particles.
This corona coating method is removed from the electric charge on the powder particles by friction, this triboelectric way to reduce the electrostatic shielding effect, the powder particles can move cans or lids corners and crannies site site this is especially applicable for paint cans and lids.
There are two continuous coating techniques include spraying technology and batch spray technology is widely used, the former suitable for coating the outside of the tank when the tank parts into the paint gun start area, can be used in a variety of spray painting area ways to make the powder particles directly coating member to be coated in a tank parts; the latter is a switch of the gun when spraying cans or lids enter a zone coating method. To control gun switch, adjust the control of gas or powder in a controlled, air flow through a shunt re-adjustment and control is the amount of coating the workpiece when the gun is shut off and the fast flow.
This process is realized through a series of solenoid valve control, powder pump solenoid control valve portion of the workpiece to be coated powder dose required. When the powder sent powder lose powder pump hose blowing control tube, the powder is accelerated amplifier, while optimizing the uniformity of powder or gas through an atomizing nozzle. After entering the control tube, the tube is put in contact with the powder particles by electrostatic charge and control of the wall, powder charged through the gun nozzle, paint cans or lids on the workpiece, stop the pump at the same time open the airflow splitter, shut down the gun, each workpiece cans or lids are repeating this loop. Operating cycle speed depends on every single piece of the work required amount of powder coating. For example, the epoxy coating after the repair can lid, each gun can handle per minute at 300-350. When the lid is placed before the gun through a positioning mechanism, this triboelectric spray guns can lids to be electrostatically charged powder, re-enter the supply hose after all overspray powder will enter the collection system recycling, then paint can lids to good conveyor belt through a curing oven in the oven to melt the powder flow into the workpiece location and scratch pads.
This process regardless of the outside and inside of the lid can be coated, the coating amount is generally at 60 to 80 mg. In order to increase the quality of the appearance of the outside of the lid, the amount of powder needed to be bigger. For powder coating the inside of jars three-piece body, now there is a new powder coating process, the maximum coating speed of this process is that each painting spray gun per minute about 75 single piece. Open end of the body by the positioning transfer mechanism will be sent to the front triboelectric guns, charged powder is sprayed into the tank, while any over spray apparatus are recycled back into the system after recycling. Then the tank is supplied to the flat belt conveyor oven, baking, curing, firing holding time at 425 ℉ temperature for about 2 minutes. In terms of general international standards, the coating is generally used an average accuracy rating for modified epoxy powder 10-15 microns, and meet the health level of canned coating film of about 15 to 20 microns. Can manufacturers thus obtained excellent coating quality, eliminate volatile organic compounds workpiece, material utilization can be up to 99%, due to the effective cleaning and painting technology, can greatly reduce the cost of cleaning and maintenance of the workpiece.
And manufacturing plant, as powder coating process can benefit from food packaging manufacturers, canned coating because of its excellent quality improved, as well as powder coating increases the shelf life of food, leakage, corrosion and iron smell of pot reduce the impact of food loaded to a minimum, that is, powder coating between food and packaging containers provide superior protection film layer, thereby improving the quality of the canned products plant life. By powder coating canned products have a longer shelf life. In a variety of different specifications of canned food and products in the field using the powder coating of metal cans can completely replace the use of liquid coating method for processing canned. For the use of powder coating performance of the coating and the shelf life further technical information, many users of packaging tests confirmed available.
For the powder coating materials and processes required for canned food, is gradually improving, strive to achieve more suitable for canned food requirement.
Currently, powder and raw materials manufacturers need to have developed more types of resins. Currently available on a variety of powder used to improve performance and to help overcome deficiencies powder coating resins and additives complete test, still few, and even less to obtain the relevant certification.
Powder manufacturers also need to understand the whole potential metal coating, while determining what kind of coating technology more practical value, whether it is three cans, aerosol cans, cans closures, canning plate or sheet, each material are It requires different resin-modified powders by spray coating, to get the best performance.
Spray cans is required to have anti-fog capabilities inner coating, and three-piece food cans must have certain anti-erosion ability of food, while having resistance to cooking. Changes in performance, depending on changes in the composition of the metal material. For example, the coating in tin cans on a good performance in aluminum cans powder may not be accepted.
Powder coating technology using clean form, with high gloss polished surface of the quality of the tank container is more excellent health, look more eye-catching, these are caused by the customer's attention when buying a selling point, or open metal cans and rinse or to re-convenient recycling later.
Packaging manufacturers due to use of new and improved powder-coated packaging meets the requirements of environmental protection, improve the storage quality of food, which will greatly improve the quality of their products.