Sealing and causes of leaks
Each packaging user has their own defined reason for keeping their product sealed, some use Nitrogen as an inert gas to keep oxygen out, others such as red meats are packed in an Oxygen rich environment to keep the meat looking red and appetising, and carbon dioxide to restrict bacterial growth. All these packs are only then successful if the internal environment is maintained and the gas is contained and external contaminants kept out. In a normal working environment it is impossible to control every element that could affect the seal quality, contamination, material quality, sealing parameters and normal packaging issues such as creasing in the formed packaging materials.The following sealing conditions affect packaging:
1. Contamination Each sealing process has the potential of seal contamination issues. Horizontal Flow Wrap can have issues were particles of the product have fallen on to the material and land in the seal area, or can be blown into the seal area with the purge pipe. Vertical Form Fill and Seal where some of the product is either stuck to the side on the formed tube, or is still falling through when the sealing jaws close on the material. Thermoformed and tray sealers can also have product particles landing on the flat seal face prior to sealing, or thinning of the material at corners. A range of measures can be introduced to minimise this contamination including particle removal using air knives, anti-static measures and better control over the filling process.
2. Packaging Film Quality There are probably 2 main issues in this area at present, one is price, quite simply the better the seal ability and robustness of the material the more expensive it is. The second is the drive to reduce and minimise the packaging material used. As most packaging materials are a combination of at least two materials and an adhesive layer to hold them together, the quality and control of this manufacturing process can have a big influence on the quality and reliability of the final packaging. Therefore poor process control can obviously affect the quality of each layer in the film, the thickness and uniformity of each layer, the strength of the bond between them and finally how they are wound on to a core ready for delivery to you the customer.
3. Sealing Parameters For seal testing purposes, to create a seal between two pieces of material and ensure there are three parameters at work, Time, Pressure and Temperature. Time is normally controlled by the throughput of the machine and can normally only be adjusted by slowing the speed of the packaging machine, so it is usually the last resort when trying to improve seal quality. Pressure is adjustable and can play a vital part in the quality of the seal, too little pressure and the material is not well bonded, too much pressure and the material can be damaged. This is also complicated by high points in the seal at overlaps in Vertical Form Fill and Seal or Horizontal Flow Wrap where the longitudinal or fin seal is sealed in the end seal. Regarding temperature, the heat required to melt the sealing layers so that they are totally melted and fused together, comes from the seal tool. Due to the small amount of time the seal tools are closed on the packaging material and the fact that plastics are poor heat conductors, the tool temperature is usually much higher than the melting temperature of the sealing layer. This temperature issue combined with the constraints of time and pressure often lead to seal failure when using substandard products. Only by tackling all of these parameters together can one ensure packaging is 100% free of any leaks and remain completely sealed from any outside contamination.
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