At a Glance
- 70°C Starting HSIT Window
- 120+ ppm VFFS Reference Speed
- Less Roll-Blocking Pressure
Collar drag and slip mattered as much as seal initiation because the coating still had to move cleanly through the forming set before any bag could be judged acceptable.
Lowering seal temperature exposed a second problem: the web still had to run cleanly on VFFS equipment
The converter was replacing a PE-based structure with an aqueous heat-seal route, but the first attempts treated HSIT as a single-variable target instead of a full process window.
- The original route still wanted too much thermal energy for the dwell window the VFFS line was actually using, which slowed qualification on the replacement structure.
- When the team pushed for lower activation temperature, blocking risk showed up in rewound rolls because the coating and cooling logic were not yet balanced for storage and unwinding.
- Collar friction created a third failure mode: if the COF drifted high, the web dragged and snapped; if it drifted too low, bag tracking and seal alignment became less stable.
An aqueous heat-seal route tuned around HSIT, collar COF, and blocking resistance
Senda treated the project as a process-fit problem, narrowing chemistry and trial logic together so seal initiation, rewind behavior, and VFFS travel could be qualified on the same structure instead of solved in isolation.
Products Used:
- Low-HSIT VFFS Heat-Seal Grade
Designed for lower activation temperature, anti-blocking behavior, and smoother passage across VFFS forming hardware.
- Repulpable Coating Platform
Supports broader PE-replacement qualification where repulpability, food-contact review, and coating-window control all stay in scope.
What made the program credible was that low HSIT was never treated as the finish line. The approved route still had to survive rewinding, unwind without blocking, travel with the right friction profile over the collar, and close the seal inside the real VFFS cycle.
Qualification path
Structure and seal-target review
The team first mapped substrate pair, seal target, dwell window, and whether the package needed a destructive permanent seal or a lighter opening profile before changing formulation.
Blocking and friction checks
Candidate grades were screened for rewind behavior, residual-heat sensitivity, and whether the collar-friction window stayed closer to the VFFS target instead of drifting into drag or slip.
Machine-side confirmation
Final approval stayed tied to line-speed behavior, sealing consistency, and roll stability together so a lower-temperature route did not create new web-handling failures upstream.
Collar drag and slip mattered as much as the seal itself because the coating still had to move cleanly through the forming set before any bag could be judged acceptable.
What changed on the converting program
- Lower usable seal initiation: The approved route moved the program closer to a lower HSIT window without asking the team to solve every sealing problem by simply adding heat.
- Steadier VFFS travel: COF tuning reduced the chance that the web would drag on the collar or slip out of alignment during high-speed bag formation.
- More stable rewind behavior: Blocking resistance remained part of qualification, so lower-temperature sealing did not come at the cost of hard-to-unwind or pickup-prone rolls later in the process.
Validated operating window
Validated operating window
Qualification stayed tied to the low-HSIT starting point already documented in the heat-seal evidence instead of defaulting back to PE-style temperature assumptions.
The friction range remained anchored to the repo-stated VFFS target band because machinability failure started at the collar before it showed up in finished bags.
Residual web temperature stayed part of approval because the repo evidence already ties blocking prevention to cooling the web below 35°C before rewinding.
Related resources
- Aqueous Heat-Seal Coatings: A Technical Guide for High-Performance Applications
HSIT, COF, Cobb, and VFFS machinability—the primary guide paired with this case study.
- Heat Seal Coatings: Optimizing HSIT and Blocking Resistance
Blocking resistance and seal-window tuning for aqueous heat-seal programs on flexible webs.
- Request a heat-seal coating trial
Prepaid sample for HSIT, collar COF, and rewind blocking screening on your substrate pair.
" We had several heat-seal options on the table, but the decision kept stalling once peel consistency, activation window, and substrate pairing had to work together on the actual pack. Senda helped us qualify a better-matched heat-seal route that stayed aligned with our sealing process, our package-opening target, and the approval work our team actually had to complete. "
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