Mutual dependence between parameters and material
Heat sealing is not defined by a single setting, but by the mutual dependence between temperature,
sealing force, time, cooling and material properties.
The five factors are inseparably linked. Changing one parameter will affect the entire sealing process:
- A change in material often requires adjustment of all process parameters
- Increasing temperature may allow shorter sealing time, but increases the
risk of shrinkage and material degradation - Reducing cooling time improves cycle speed, but demands tighter control
of material behaviour
A stable and repeatable sealing process is achieved only when material characteristics and process parameters are matched and controlled together.
- Temperature
Temperature activates the sealing layer and allows the material surfaces to fuse.
- Must be high enough to soften or melt the sealing layer
- Too low temperature results in weak or incomplete seals
- Excessive temperature can cause material degradation, shrinkage or burn-through
Each material has a defined sealing temperature window. Operating outside this window reduces process stability and seal quality.
- Sealing Force (Pressure)
Sealing force ensures intimate contact between the material layers during heating.
- Compensates for material thickness variations and surface irregularities
- Enables efficient heat transfer into the sealing interface
- Directly affects seal strength and visual appearance
Dense materials often require moderate force, while woven, non-woven or structured materials require higher force to compress the layers and achieve proper fusion.
Excessive force may thin or distort the seal area, while insufficient force can prevent proper bonding.
- Time
Time defines how long heat and pressure are applied to the material.
- Determines how deeply heat penetrates the sealing layers
- Strongly linked to temperature, material thickness and machine speed
- Has a direct impact on productivity and cycle time
If sealing time is too short, the material does not fully fuse.
If sealing time is too long, unnecessary thermal stress is introduced, increasing wear and reducing efficiency.
- Cooling
Cooling stabilizes the seal after heating and before mechanical load is applied.
- The seal must cool below its softening temperature to retain shape and strength
Insufficient cooling can lead to:
- shrinkage
- puckering or deformation
- reduced seal strength
Cooling may occur naturally or be actively supported, depending on process speed and material sensitivity.
Reducing cooling time increases production speed but also increases the risk of seal distortion.
Eliminating cooling entirely often results in unstable seals that change shape after release.
- Material
Material properties define the usable process window for all other parameters.
Key material characteristics include:
- Polymer type and melting behaviour
- Film thickness and layer structure
- Coatings, laminates and surface finishes
- Thermal conductivity and shrink characteristics
Some materials tolerate wide variations in temperature and time, while others have very narrow sealing windows and require precise control. Multi-layer laminates may require different energy input than single-layer films, even at the same thickness.
Material variability directly affects seal consistency. For this reason, stable heat sealing depends not only on machine parameters, but also on consistent and well-defined material specifications.
Vinther & Strand perspective
High-quality heat sealing is achieved through precise control of temperature, sealing force, time and cooling, combined with a thorough understanding of the material being sealed.
Because even small material variations can significantly affect the sealing window, we always recommend performing practical sealing tests as part of the process design.
Sealing tests make it possible to:
- Confirm optimal parameter settings
- Verify seal strength and visual appearance
- Identify cooling- or shrink-related issues before production start-up
This ensures consistent seal quality, reduced scrap and a reliable, cost-effective sealing process from the outset.