Co-extruded EVA Film for PV Module Lamination
1Key Takeaways
This standard specifies the technical requirements, testing methods, and inspection rules for the materials used in the encapsulation of photovoltaic components. It covers the composition, performance characteristics, and application conditions of the co-extruded film. The standard also outlines the procedures for samp…
2Expert Interpretation
An in-depth interpretation of the national standard GB/T 45939-2025 for co-extruded films for photovoltaic module encapsulation, covering the technical requirements, physical performance indicators, aging test methods and inspection rules for co-extruded films, providing an authoritative technical basis for the selection of photovoltaic module encapsulation materials.
In-depth interpretation of the national standard for co-extruded adhesive films for photovoltaic module encapsulation
GB/T 45939-2025 "Co-extruded adhesive films for photovoltaic module encapsulation" is an important technical standard jointly issued by the State Administration for Market Regulation and the Standardization Administration of China. This standard will be officially implemented in 2025 and provides unified technical specifications and quality requirements for photovoltaic module encapsulation materials.
Background of standard formulation and technological evolution
With the rapid development of photovoltaic technology, traditional single-layer EVA film is gradually unable to meet the needs of high-efficiency modules in terms of weather resistance and anti-PID performance. Co-extruded film technology achieves complementary performance through the compounding of EVA and POE materials, becoming a key material for improving module reliability. This standard was proposed by the National Technical Committee for Standardization of Semiconductor Equipment and Materials (SAC/TC203) and jointly drafted by 23 industry-leading companies such as Hangzhou Foster, reflecting industry consensus and technological advancement.
Term Definition and Scope Definition
The standard clearly defines co-extruded film as a multi-layer encapsulation film formed by melt extrusion and composite molding using ethylene-vinyl acetate copolymer (EVA) resin and polyolefin elastomer (POE) resin as the main raw materials. Polyolefin elastomers mainly refer to copolymers of ethylene and α-olefins (1-butene, 1-hexene, 1-octene, etc.).
The scope of application includes co-extruded film for crystalline silicon photovoltaic module encapsulation, and films for thin-film module encapsulation can be used as a reference. This scope definition takes into account both mainstream technical routes and leaves room for emerging technologies.
Technical Requirements System Analysis
Appearance Quality Requirements
The surface of co-extruded film products should be flat, free of creases, stains, visible impurities, bubbles, and clear embossing. These appearance indicators directly affect the quality and aesthetics of module encapsulation.
Specifications and Deviation Control
| Item | Scope | Allowance | Test Method |
|---|---|---|---|
| Area Density/(g/m²) | ≥250～≤600 | ±5% | Sampling Device + Analytical Balance |
| POE Layer Thickness/μm | >120～≤300 | ±25% | Scanning Electron Microscope/Microscope |
| POE Layer Thickness/μm | >50～≤120 | Agreed by Both Parties | Scanning Electron Microscope/Microscope |
Physical Performance Index System
| Performance Category | Test Items | Technical Requirements | Test Standards |
|---|---|---|---|
| Optical Performance | Light Transmittance (380-1100nm) | ≥90.0% | GB/T 2410 |
| Light Transmittance (290-380nm) | UV High Transmittance ≥70% UV Cut-off ≤30% | GB/T 2410 | |
| Yellowness Index △YI | ≤5.0 | GB/T 39822 | |
| Mechanical properties | Crosslinking degree | 75%-95% | GB/T 29848-2018 |
| POE mass ratio | 15%-75% | TGA thermogravimetric analysis | |
| Peel strength with glass | ≥60N/cm | GB/T 2790 | |
| Shrinkage | Longitudinal ≤4.0% Transverse ≤2.0% | Heat shrinkage test | |
| Electrical properties | Volume resistivity | ≥1.0×10¹⁵Ω·cm | GB/T 31838.2 |
| Electrical Strength | ≥28.0kV/mm | GB/T 1408.1 | |
| Relative Tracking Index | ≥400V | GB/T 4207 |
Aging Performance Requirements and Test Methods
The standard specifies four aging test items to comprehensively evaluate the long-term reliability of co-extruded film:
UV Aging Performance (120kWh/m²)
Simulates outdoor UV radiation environment, requiring that after aging, the peel strength from glass must be ≥30N/cm and the yellowing index △YI must be ≤5.0.
Wet Heat Aging Performance (1000h)
Tested at 85°C/85%RH for 1000 hours to evaluate performance retention in high temperature and high humidity environments.
Autoclaving Aging Performance (48h)
Tested under harsh conditions of 121°C/100%RH, this is an optional item suitable for more demanding applications.
UV High Temperature and High Humidity Aging Performance (300h)
A comprehensive aging test that simultaneously applies UV, high temperature, and high humidity stresses to more realistically simulate actual usage environments.
Test methods and instrument requirements
The standard specifies the test methods for various properties in detail, including:
Crosslinking degree test: Using the xylene extraction method, perform in accordance with GB/T 29848-2018
POE mass proportion test: Using a thermogravimetric analyzer (TGA), the EVA and POE components are distinguished by the characteristic thermal decomposition temperature
Peel strength test: Using a tensile testing machine, test according to the 180° peel method of GB/T 2790
All tests are carried out under standard environmental conditions (23±2℃, 50±5%RH) to ensure the comparability of the results.
Inspection Rules and Quality Control
A complete quality control system has been established in the standard, including:
Inspection Classification
- Factory Inspection: Each batch of products must be inspected, including appearance, surface density, etc.
- Periodic Inspection: Conducted once every quarter, covering more comprehensive performance indicators
- Identification Inspection: Conducted when new products are finalized or when major process changes occur
Sampling Plan
Special inspection level S-2 is adopted in accordance with GB/T 2828.1, and a single sampling plan is used for normal inspection, with an AQL value of 6.5.
Packaging, Transportation and Storage Requirements
The standard sets clear requirements for product packaging, labeling, transportation and storage:
- Storage temperature: 0-30°C
- Relative humidity: below 60%
- Store away from light and heat
- Use within 8 hours after opening
- Shelf life: at least 120 days from the date of production
Implementation Recommendations and Technology Outlook
Implementation Recommendations for Manufacturers
1. Establish a comprehensive raw material inspection system to ensure the stable quality of EVA and POE raw materials
2. Optimize co-extrusion process parameters to control the thickness uniformity of the POE layer
3. Strengthen online testing capabilities to monitor surface density and appearance quality in real time
4. Establish an aging test laboratory to regularly verify the long-term reliability of the product
Selection Recommendations for Component Manufacturers
1. Select the appropriate test methods and acceptance criteria based on the module type (single-glass/double-glass)
2. Pay attention to the correlation between POE content and module anti-PID performance
3. Consider the requirements for film aging performance under different climatic conditions
4. Establish supplier quality files and conduct regular third-party verification tests
Technological development trends
With the popularization of high-efficiency battery technologies such as n-type technology and heterojunction, higher requirements are placed on encapsulation films:
- Higher volume resistivity requirements (≥1.0×10¹⁶Ω·cm)
- Better resistance to moisture and heat aging
- Better light transmittance and UV resistance
- Compatibility with new battery materials
The implementation of GB/T 45939-2025 will promote the upgrading of photovoltaic encapsulation material technology, promote high-quality development of the industry, and provide technical support for the realization of carbon peak and carbon neutrality goals.