1. Introduction
With the growing demand for clean energy, the number of solar power plants has surged in recent years. Solar cell modules are essential power generation components in solar power plants. Solar cell modules primarily consist of tempered glass, EVA film, silicon cells, and a composite backsheet. The backsheet, located on the back of the solar cell module, protects the cells and provides reliable insulation, sealing, waterproofing, and aging resistance. Solar cell backsheets typically employ a three-layer structure, such as PVDF/PET/PE. PVDF, a fluorinated film, serves as the outer protective layer and offers excellent resistance to environmental corrosion. The middle PET film offers excellent insulation, while the PE film provides excellent bonding properties. Composite solar cell backsheets are constructed by bonding these three layers using a two-component composite adhesive. However, due to the low surface tension of fluorinated films like PVDF, lamination and bonding of PVDF to PET film is challenging. Furthermore, composite solar panel backsheets must withstand 2.000 to 3.000 hours of the "Double 85" test—an accelerated aging test at 85°C and 85% humidity, or PCT (121°C steam cooking for 50 hours). This places high demands on the adhesive's heat and hydrolysis resistance.
2. Classification
Polyurethane adhesives are generally classified as one-component and two-component. Two-component polyurethane adhesives are a widely used solvent-free polyurethane adhesive composed of a base and a curing agent in a specific ratio. The main components of two-component polyurethane adhesives typically include one or more of polyester polyols, polyether polyols, and polyether polyol prepolymers modified with isocyanates or polyester polyols. Polyester polyols readily form hydrogen bonds, resulting in stronger intermolecular forces. Therefore, polyester-based two-component polyurethane adhesives exhibit superior mechanical properties and heat resistance compared to other adhesives. However, polyester-based two-component polyurethane adhesives suffer from issues such as high viscosity and poor compatibility with other additives, resulting in insufficient performance enhancement from the addition of additives.
3. Summary
In summary, through the design of the main agent formula and the use of a hydrolysis-resistant additive, the heat resistance and hydrolysis resistance of the polyurethane composite adhesive have been significantly improved, meeting the technical requirements of composite backsheets for solar cell modules and possessing significant application value.
