In the can making process, one of the most important components are the packaging ends which comes in various kinds depending on the packaging variety as well as type of packages (food, beverages or others). Most common ends in the industry includes:
- Normal Ends
- Easy Open Ends
- Oval Ends or others Irregular Shape Ends
- Aerosol Ends
- Non-Metal Packaging Ends. For example: Crown caps, RO, ROPP, Lug Cap or Twist off
- Collapsible Tube
For Normal Ends, Easy Open Ends, Crown caps, or Lug Caps can be made from Tinplated Steel or Chrome Plated Metal. However nowadays, Chrome Plated Metal are more commonly used due to its strength and durability in withstanding higher pressure. The steps in the ends production process starts from using a sheet of metal that is precisely cut and sent into the pumping machine to bend into a form (Curling) so that the lid can expand when heated and shrink when cooled without breaking. In the case of easy open ends production, there is an additional step from normal ends which is notching a score line and drilling a ring to enable the lid to be opened by perforation of the score. Later, lacquer will be sprayed to repair the score line.
Next with Food Canning, high heat is used in the retort process to effectively sterilized microorganisms. However, it is still necessary to prevent microbes from seeping into the packaging again, therefore, food that has been sterilized must be packed in a well-sealed can in order to ensure no further contamination and hence secure longer shelf-life. The sealing of the cans is paramount because if leakage occurs, contaminations will be able to pass through and cause food spoilage. Generally, a can has three parts that need to be tightly sealed: the side seam, the bottom seam, and the top seam.
In this article we will discuss only Bottom seams and top seams where they are often made into hooks like double seam with a can seamer and using a roller to roll the seam shut.
The double seam is formed by the two-stage operation of the main component of the can seamer machinery, the ‘roller’.
Starting with the can body which has a protruding part at the can mouth called ‘flange’ and the can cover which has the protruding part called ‘curl’, two of which can be fit together. First operation of the roller will be rolling the protruding part of the curl to cover the flange and then second operation of the roller will be rolling to tightly squeeze the seams to form a layer and could be done up to 5 layers of metal folds. And under each layer, sealants compound will be dropped around the inner circumference to cause a hermetical seal of the curved edge of the lid (curl) in the amount of 60%-70% of bandwidth.
And above is the origin utilization of can sealing compound. The sealant that is inserted into the lid area to prevent leakage along the seam between the container and the lid. If it is a 3-piece can, sealant will be used for both the bottom lid seam and the top lid seam after packing food or products into the container to prevent contamination from outside to extend the shelf life of the product inside the can.
Water-based Sealing Compound
Furthermore, sealing compound will need to be able to withstand high temperatures from the retort sterilization process of canned food, in which these types of sealants will generally be water-based (water-based sealing compounds) which is a type of rubber that is accepted by US FDA to be used in food canning and have many distinctive points including being environmentally friendly and safe for consumer consumption under recommended amount. There are many varieties of compounds that depending on the utilization and the contents in the cans as different kinds of cans or packages would require varying degree of protection against leakages for example canned food and canned beverages, as well as general line cans which also used water-based sealing compounds in the seaming process, like gallons or drums for petroleum oil, aerosol cans, and collapsible tube for pharmaceutical or cosmetic products.
The quality of food cans is an important factor in the quality and safety of food products. An imperfect or defective cans could quickly deteriorate quality of food contents as a result of chemical reaction between the food constituents and the canning steel or microbial contamination into the food products thus causing spoilage. There are three level of defects with varying significance in cans and lids: 1. critical defects, 2. major defects and 3. minor or warning defects.
Another type of rubber sealant It is PVC Plastisol sealant, a vinyl compound obtained by mixing PVC Paste Resin, Plasticizer and various additives. It is a PVC particle that is dispersed in a plasticizer that looks like a thick liquid at normal temperature but when heated in plating or forming processes will fuse together to form a tough plastic film. Once solidified, it will not return to liquid form. PVC Plastisol’s advantages are its high scalability and good resistance to high temperature curing in the manufacturing process.
PVC Plastisol is used for sealing various metal packaging lids, such as 20 liter drums (Crimp Cap) to 200 liter drums such as gallon paint buckets, tanks for filling oil, etc. It is also used for non-metallic packaging such as Crown Cap of soft drink glass bottles, Screw cap sealant (RO) or twisted screw cap (ROPP) of energy drink bottles and rubber sealant for lug cap (Lug Cap or Twist -Off) of jam bottle caps as well.
Throughout the years, UBIS has consistently innovate and develop a variety of sealants, both water-based sealing compounds and PVC Plastisol and always strive to provide high quality products in order to meet our customers’ needs and has successfully expanded our presence both domestically and internationally, selling to countries all over the world whereby the majority of UBIS Customers are cans manufacturers for food cans, beverage cans as well as aerosol, gallons and many other lines of metal packaging manufacturers