Immersion, peel and damp heat testing is a combined reliability evaluation used to assess the adhesion strength and moisture resistance of laminated glass, photovoltaic encapsulants, adhesive tapes, composite films and coated assemblies. By subjecting specimens to water immersion, boiling, and elevated temperature–humidity conditioning followed by peel strength measurement, this test sequence reveals interfacial degradation that single-condition testing may miss. This article explains the applicable standards, sample types, test methods, typical parameters and acceptance criteria for immersion peel damp heat testing.
Technical Overview
Immersion, peel and damp heat testing is a sequential evaluation method that combines environmental conditioning with mechanical adhesion measurement. It is widely applied to laminated and bonded products whose long-term performance depends on the stability of interfaces between substrates, interlayers, adhesives and coatings. Moisture is one of the most aggressive agents for adhesive joints and polymer interlayers: it can diffuse through the edge of a laminate, hydrolyze coupling agents, plasticize the interlayer, and drastically reduce interfacial bond strength.
The test sequence typically involves three stages. First, immersion testing exposes specimens to water at ambient or elevated temperature (including boiling water for laminated glass) to accelerate moisture ingress. Second, damp heat testing holds specimens under controlled high temperature and high relative humidity conditions, such as 85 °C / 85 % RH, in an environmental chamber. Third, peel testing quantifies the adhesion strength of the interface after conditioning, allowing engineers to calculate strength retention relative to unconditioned control specimens and to detect delamination, blistering, whitening or corrosion.
The method is referenced by numerous international and national standards, including IEC 60068-2-78 (damp heat, steady state), IEC 60068-2-30 (damp heat, cyclic), GB/T 2423.3 and GB/T 2423.4, ISO 12543 series for laminated glass, GB/T 5137.3 for automotive safety glass, ASTM D3330, ASTM D903, ASTM D1876 and ISO 8510 for peel adhesion, ASTM D870 and ISO 2812 for water immersion, ASTM D2247 for coated specimens at 100 % RH, and IEC 61215 and IEC 61730 for photovoltaic modules.
Testing Samples
Laminated Safety Glass and Interlayer Materials
Laminated glass specimens bonded with polyvinyl butyral (PVB), ionoplast (SG-type) or EVA interlayers are tested for boiling water resistance, humidity durability and interlayer-to-glass adhesion. These samples are common in automotive windshields and architectural glazing.
Photovoltaic Encapsulants and Module Laminates
EVA and POE encapsulant films, module mini-laminates and full-size photovoltaic modules are evaluated for encapsulant-to-glass and encapsulant-to-backsheet peel strength before and after damp heat aging at 85 °C / 85 % RH.
Adhesive Tapes, Labels and Flexible Packaging Films
Pressure-sensitive adhesive tapes, labels, and multi-layer flexible packaging laminates are tested for peel adhesion retention after immersion and humidity exposure, using specimen strips cut to a defined width.
Coated and Bonded Assemblies
Painted metal panels, coated plastics, bonded joints in electronic assemblies, sealing materials and conformal coatings are conditioned and then assessed for adhesion loss, blistering and substrate corrosion.
Testing Items
- Water immersion resistance at ambient and elevated temperature
- Boiling water immersion test (typically 2 hours) for laminated glass
- Chemical and liquid immersion resistance for coatings and plastics
- 90° peel strength (flexible-to-rigid bonding)
- 180° peel strength (flexible-to-rigid bonding, adhesive tapes)
- T-peel strength (flexible-to-flexible laminated films)
- Peel strength retention after damp heat conditioning
- Damp heat steady-state testing (e.g., 40 °C / 93 % RH; 85 °C / 85 % RH)
- Damp heat cyclic testing (e.g., 25 °C to 55 °C, 12 h + 12 h cycles)
- Visual and microscopic evaluation of delamination, bubbles, whitening, haze and corrosion
Testing Methods
Immersion Testing
Specimens of specified size are fully immersed in deionized water or a defined test liquid. For laminated glass, the boiling test requires specimens to be boiled for 2 hours followed by cooling and immediate visual inspection for bubbles, delamination or interlayer opacity, in accordance with the ISO 12543 series and GB/T 5137.3. For coatings and adhesives, immersion durations and temperatures are selected with reference to ASTM D870, ASTM D543 and ISO 2812, after which the specimens are inspected and transferred directly to peel strength measurement.
Peel Adhesion Testing
Peel tests are performed on a universal testing machine equipped with suitable grips and a peel fixture. Standard configurations include 180° peel per ASTM D3330, ASTM D903 and ISO 8510-2, 90° peel per ASTM D6862 and ISO 8510-1, and T-peel per ASTM D1876 and GB/T 8808 for flexible laminates. Specimen strips, typically 25 mm in width, are peeled at a constant crosshead speed in the range of 100–300 mm/min, and the average and peak peel forces are recorded and expressed as force per unit width (N/mm or N/25 mm). Testing may be conducted on dry specimens, on wet specimens immediately after removal from water, or after a defined recovery period.
Damp Heat Testing
Specimens are placed in a climate chamber under steady-state conditions such as 85 °C ± 2 °C with 85 % ± 5 % relative humidity for a common duration of 1000 hours, as used for photovoltaic modules in IEC 61215 and IEC 61730. Alternative conditions include 40 °C / 93 % RH per IEC 60068-2-78 and GB/T 2423.3, or cyclic damp heat per IEC 60068-2-30 and GB/T 2423.4. After conditioning, specimens are inspected for appearance changes and then subjected to peel testing to determine adhesion retention.
Combined Sequential Evaluation
In a full evaluation program, baseline peel strength is first measured on unconditioned control specimens. Identical specimens then undergo immersion and damp heat conditioning, followed by repeat peel testing. The strength retention rate is calculated as the ratio of conditioned to unconditioned peel strength, providing a quantitative durability index for material qualification, supplier comparison and failure analysis.
Applications
- Qualification of automotive laminated windshields and safety glazing
- Certification and reliability testing of photovoltaic modules and encapsulant materials
- Incoming inspection and process validation of adhesive tapes, labels and laminating adhesives
- Quality control of flexible packaging multilayer films for food and pharmaceutical products
- Durability assessment of architectural laminated glass and window films
- Reliability screening of adhesives, sealants, conformal coatings and bonded electronic assemblies
- Failure analysis of delamination, blistering and edge corrosion complaints in field-returned parts
FAQ
What is the difference between immersion testing and damp heat testing?
Immersion testing places the specimen directly in liquid water, producing the most aggressive moisture exposure and liquid-phase chemical attack at exposed edges. Damp heat testing exposes the specimen to a controlled humid atmosphere at elevated temperature, which better simulates long-term service in tropical or humid climates. The two methods complement each other and are frequently combined with peel testing in one evaluation program.
Why is peel strength measured after humidity conditioning?
Many adhesive interfaces show acceptable strength in the dry state but degrade rapidly once moisture penetrates the interface. Measuring peel strength before and after immersion or damp heat aging quantifies this degradation and provides a safety margin for real-world humidity exposure that a dry-state test alone cannot reveal.
How long does a typical damp heat test take?
The most common photovoltaic damp heat test is 1000 hours at 85 °C / 85 % RH. Depending on the product standard, durations of 96, 240, 500 or 2000 hours may also be specified. Boiling immersion tests for laminated glass are much shorter, typically 2 hours of boiling.
What specimens and dimensions are required?
Peel specimens are usually strips with a width of 25 mm and sufficient bonded length, typically at least 150–200 mm, to obtain a stable peel plateau. Laminated glass boiling and humidity specimens are commonly squares of 300 mm × 300 mm prepared with production-edge or ground-edge conditions as required by the applicable standard.
What are typical acceptance criteria?
Criteria depend on the product specification. Laminated glass must show no bubbles or delamination extending from the edge beyond the limit defined in the ISO 12543 series after boiling and humidity exposure. For encapsulants and adhesives, a minimum peel strength value or a minimum retention percentage, for example no more than a defined strength loss after damp heat aging, is typically required by the customer specification.
Can the test be performed on finished products rather than laboratory coupons?
Yes. Accredited third-party laboratories can test finished items such as complete glazing units, photovoltaic modules, tape rolls and bonded assemblies where destructive sampling is permitted. Testing finished products provides the most realistic assessment of edge sealing, real production interfaces and overall moisture durability.