STH-5 Gradient Heat Seal Tester: 5-Point Testing for Faster Process Optimization

Traditional heat seal testing requires running one test per temperature point. To generate a 5-point temperature curve — standard practice for film qualification per ASTM F2029 — you would run 5 separate sealing cycles, each with its own heating/cooling cycle. Total time: 2–4 hours. The STH-5 has 5 jaws (40 × 10 mm each), each held at its own temperature. One press seals 5 specimens at 5 different temperatures simultaneously. After one cooling/conditioning period, you test all 5 on a tensile tester. Total time: 30–45 minutes. For labs running multiple film grades or developing new packaging formats, this represents 70–80% time savings per seal curve.

The STH-5 controls temperature independently on each of its 5 jaws, from room temperature +10°C to 250°C, each accurate to ±1°C. Sealing pressure (0.1–0.7 MPa) is the same on all 5 jaws and dwell time is synchronized for all jaws within a single run — ensuring that pressure and time are held constant while only temperature varies, which is the correct experimental design for temperature-seal curve generation per ASTM F2029. The digital display shows the current temperature of each jaw, allowing operators to verify gradient settings before sealing.

A heat seal curve typically shows three regions: (1) Cold Seal Zone — below SIT, where bond strength is insufficient; (2) Optimal Window — where strength plateaus at or above the minimum specification; (3) Degradation Zone — where excessive heat causes film distortion, delamination, or burn-through. The STH-5's 5-point gradient captures all three regions in one test, allowing QC managers to verify that their production temperature is within the optimal window, not drifting toward cold seal or degradation. This is essential for film qualification, incoming material inspection, and process change validation.

The STH-5's gradient capability makes it the preferred model for: (1) Food packaging labs mapping Seal Initiation Temperature for dairy lidstock and snack bag films; (2) Pharmaceutical packaging labs qualifying new blister foil grades per ISO 11607; (3) Flexible film R&D labs characterizing PE, PP, EVOH, BOPP, and aluminum laminate films; (4) Lithium battery manufacturers qualifying aluminum laminate pouch films at the 200°C range required for pouch cell top and side seals.

Labthink, RDM, and Cell Instruments all offer heat seal testers, but gradient (multi-zone) capability is typically found only on their premium models. The KHT STH-5 delivers 5-point gradient testing at a price point 30–60% below Western equivalents — factory direct from Shandong, China, with full ASTM F88/F2029/ISO 11607 compliance and English-language documentation.