STH-3A Gradient Heat Seal Tester: 5-Position Digital Testing for Faster Process Optimization
The STH-3A is KHT Instrument's flagship heat seal tester. Its 5-position gradient capability tests five temperature points simultaneously, generating a complete temperature-seal strength curve in a single 30-minute session — replacing what would otherwise require 5 separate test runs.
How 5-Position Gradient Testing Works
- 1
Set a temperature gradient across 5 zones (e.g., 130°C / 140°C / 150°C / 160°C / 170°C)
- 2
Apply film specimen across all 5 positions with identical force and dwell time in one press
- 3
After cooling, test each of the 5 sealed sections on your tensile tester
- 4
Plot the 5 peel strength values to generate your complete temperature-seal curve
- 5
Identify SIT (Seal Initiation Temperature), optimal window, and burn-through threshold — in one session
What Is a 5-Position Gradient Heat Seal Tester and Why It Saves Hours
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-3A's gradient jaw divides into 5 independently temperature-controlled zones. 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.
STH-3A Technical Specifications: Temperature Gradient, Force Control, Digital Display
The STH-3A controls temperature in 5 independent zones across the sealing jaw, each accurate to ±0.5°C. Sealing force is uniform across all 5 positions (0–600N) and dwell time is synchronized for all zones within a single run — ensuring that force 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 LED display shows current temperature at each zone, allowing operators to verify gradient settings before sealing.
How Gradient Testing Maps Your Optimal Heat Seal Window
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-3A's 5-position 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.
Applications: Food Lidstock SIT, Pharma Blister, Film R&D, Battery Pouch
The STH-3A'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.
STH-3A vs Competitors: Why Gradient Testing Is Rare on Budget Models
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-3A delivers 5-position 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.
STH-3A Specifications
Temperature Range
0–300°C
Gradient across 5 zones
Temperature Accuracy
±0.5°C
Per zone, independently controlled
Gradient Step
Configurable
E.g., 10°C steps: 130/140/150/160/170°C
Sealing Force
0–600N
Uniform across all 5 positions
Dwell Time
0–60 seconds
Same for all positions in one run
Seal Width
10mm × 5 positions
Standard; custom widths available
Display
Digital LED readout
Per-zone temperature display
Standards
ASTM F88 / F2029 / ISO 11607
Full compliance
Power
220V / 110V
Dual voltage
Dimensions
~450 × 220 × 300mm
Benchtop
Frequently Asked Questions
Get the STH-3A Gradient Tester — Factory Direct
Request a quote for the STH-3A with your required seal width, gradient configuration, and delivery address. Response within 24 hours.
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