Canning and Fish Packaging Technology

Unit 11 - Heat Sealing

11.1.3.Criteria for proper heat sealing and to produce a reliable seal

• Fusion is a necessary requirement for formation of an acceptable heat seal. It occurs when the opposing seal surfaces are welded together so that is not possible to distinguish visually sealing surfaces at the inner seal junction.
• Fusion sometimes does not occur as a result of contamination of the sealing area with water, grease or particulate matter. Hence contamination of seal area should be avoided.
• Clouding due to decrease in time of sealing. This is due to structural reorganization of polymers.
• Wrinkles in the sealing are occur due to slightly differing amounts of plastic material on the two sides of the seal. This can also be due to slippage of sealing bars.
• Blisters in the heat seal area are due to entrapment of water, grease or food particles.