Sealing Parameters for Three-Side Seal Vacuum Bags
Sealing is one of the most critical processes in three-side seal vacuum bag production. A reliable seal must withstand vacuum pressure, handling, transportation, and product loading without leakage or separation. Proper control of temperature, pressure, dwell time, and film compatibility is essential.
Heat-Sealing Temperature
The appropriate sealing temperature depends primarily on the inner sealant layer and film structure. PE, CPP, and other heat-sealable materials have different sealing characteristics.
Insufficient temperature may result in weak or incomplete seals, while excessive temperature can cause film deformation, shrinkage, sticking, or seal-through. The recommended sealing range should therefore be established through material trials rather than using a universal temperature.
Sealing Pressure
Sealing pressure must provide sufficient contact between the film layers across the entire sealing width. Uniform pressure distribution is particularly important at corners and multi-layer areas.
Excessive pressure may squeeze molten sealant away from the sealing area, while insufficient pressure can produce inconsistent bonding. Sealing jaws should be regularly checked for alignment and surface condition.
Dwell Time
Dwell time determines how long heat and pressure are applied to the sealing area. Temperature and dwell time should be optimized together to achieve adequate seal strength without damaging the film.
High-speed production may require careful adjustment of sealing temperature and pressure to compensate for shorter dwell times.
Seal Width and Position
The seal width should provide sufficient bonding area for the intended vacuum level and product weight. Consistent seal width and accurate positioning help prevent weak points and improve package appearance.
The sealing area should remain free of product contamination, especially when packaging powders, liquids, oils, or foods with irregular particles.
Vacuum Compatibility
Vacuum packaging creates negative pressure inside the bag, placing additional stress on the seals. The film structure should provide adequate puncture resistance, flexibility, and seal strength.
After vacuuming, the package should be inspected for seal opening, wrinkles, channels, pinholes, and leakage.
Quality Testing
Finished bags should undergo seal-strength and leak testing. ASTM F88/F88M can be used to evaluate seal strength, while ASTM F2096 or ASTM D3078 may be used for appropriate leak-detection applications.
Vacuum retention testing and filled-bag trials can provide additional confirmation of real-world performance.
Process Control
Production parameters should be monitored continuously, including sealing temperature, pressure, dwell time, jaw alignment, film tension, and sealing-surface cleanliness. Regular sampling helps identify process drift before defective bags are produced in large quantities.
References
ASTM F88/F88M – Standard Test Method for Seal Strength of Flexible Barrier Materials
ASTM F2096 – Standard Test Method for Detecting Gross Leaks in Packaging by Internal Pressurization
ASTM D3078 – Standard Test Method for Determination of Leaks in Flexible Packaging by Bubble Emission
ASTM D3985 – Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting
ISO 9001 – Quality Management Systems
