Inside the base at the bottom of a normal gusseted box liner, you find four pockets that form naturally. When we manufacture the liners, we apply an additional 45 degree seal on each of the four gusset panels to close the pockets which result in leak proof square bottom bags. These bags are also sometimes referred to as cross corner seal bags.
When used in combination with grains or powders, without the mitre seal, these pockets can create product entrapment and therefore loss of product. Mitre seal bags and liners are not only designed to eliminate food waste or loss of product in the un-packing process, but the additional seals actually strengthen the bottom of the bag too. That’s why mitre seal bags and K-seal bags are very popular in the food processing industry as they prevent the bottom of gusset bags leaking. These bags are also available with a double bottom seal.
Some box liners are required to be lifted out of the box, with the contents still inside, sometimes reaching 20-25kg in weight. On a normal gusseted box liner without mitre seals, the stress points on the seal become holes and create leakage whereas the mitre seal bags prevent this, meaning reduced loss of product.
Other uses for the mitre seal and K-seal is in cross corner seal box covers. This is where the same seal is applied to U-fold sheets to create cross corner seal tray liners or dolav covers.