Film Heat Seal Tester: Map Optimal Seal Windows for PE, PP, EVOH, and BOPP Films
For flexible film manufacturers and R&D labs, heat seal window mapping is the critical first step in any new film qualification. The KHT STH-3A 5-position gradient heat seal tester generates a complete temperature-seal curve per ASTM F2029 in a single test session — replacing hours of sequential single-point testing.
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Why Film Heat Seal Window Mapping Is Critical for R&D and QC
Every new flexible film formulation, co-extrusion structure, or surface treatment changes the heat seal window — the temperature range where the film bonds acceptably without delaminating or burning through. Characterizing this window is the first task in any film qualification. It also guides production line setup: jaw temperature must be within the optimal window at all production speeds. A narrow seal window means production is more sensitive to temperature variation; a wide window provides process robustness. Without quantitative heat seal data, film qualification is incomplete and production quality control lacks an objective benchmark.
5-Position Gradient Testing: Generating a Full Heat Seal Curve in One Session
The STH-3A's 5 independently controlled heating zones apply 5 different temperatures across one film specimen simultaneously. After conditioning per ASTM F2029, you peel all 5 sections in sequence on a tensile tester, recording the seal strength (N/15mm) at each temperature. The resulting curve shows: (1) cold seal region below SIT; (2) rising strength to optimal plateau; (3) degradation at excessive temperature. The whole process — sealing, conditioning, peeling — takes 30–45 minutes for a complete 5-point curve. For labs qualifying 10–20 film grades per year, this efficiency is substantial.
Temperature, Time, and Pressure (3T) Optimization for Flexible Films
ASTM F2029 is explicit that heat sealing involves three variables — temperature (T), dwell time (t), and jaw pressure (P) — which must all be documented and controlled. The standard practice is to fix two variables and vary the third. The STH-3A makes temperature variation the most efficient: fix force and dwell time, then test 5 temperatures in one gradient run. For subsequent optimization of dwell time, run a series of gradient tests at fixed temperature and force, varying dwell time per run. This systematic 3T approach yields a documented design space for the film's optimal sealing conditions.
ASTM F2029: Standard Procedure for Laboratory Heat Seal Evaluation of Flexible Films
ASTM F2029 ('Standard Practices for Making and Testing Lap Seals and Peel Seals of Flexible Barrier Materials') defines: (1) sealing equipment requirements (temperature uniformity ≤±1°C, jaw force calibration); (2) specimen preparation and orientation; (3) parameter recording (temperature, force, dwell, date); (4) conditioning before peel testing (23°C, 50% RH, minimum 1 hour per ASTM D882 or as specified). All KHT STH models meet F2029 equipment requirements. The STH-3A's digital temperature display per zone makes the ±1°C uniformity requirement verifiable.
Recommended KHT Models for Film R&D Laboratories
For flexible film R&D labs, the STH-3A is the standard recommendation. The 5-position gradient capability directly supports the systematic characterization workflow required for new film qualification and process development. The STH-3 is adequate for spot-check QC at a known production parameter, but does not provide the gradient efficiency needed for R&D. For film manufacturers with production-line monitoring requirements and IoT integration needs, the STH-5 touchscreen model adds data logging and remote access.
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