Why is nano-calcium carbonate added to photovoltaic adhesives? What are its characteristics and functions?
Silicone sealant https://www.useencalcium.com/industries/adhesives-and-sealants/ is a novel polymeric sealing material; by virtue of its "siloxane backbone" and "organic functional groups," it is endowed with excellent resistance to UV radiation, extreme temperatures, and high humidity. Furthermore, given its strong adhesion to substrates such as metals, glass, ceramics, and plastics, silicone sealant is widely utilized across industries including electronics and electrical appliances, lighting, photovoltaics, rail transit, and construction.
Applications of Silicone Sealants in the Photovoltaic Industry
Silicone sealants are one of the auxiliary materials used in solar photovoltaic modules, broadly categorized into two main types: bonding sealants and potting compounds. Within this context, silicone sealants in PV modules are primarily utilized for bonding solar cells to aluminum alloy frames, as well as for bonding junction boxes to backsheets; the predominant varieties employed are single-component, room-temperature-vulcanizing (RTV) silicone rubbers of the oxime-cure and alcohol-cure types.
Potting compounds are primarily used to encapsulate internal components within junction boxes, consisting predominantly of two-component, alcohol-releasing, room-temperature-vulcanizing (RTV) silicone rubber. Their primary function is to prevent moisture and oxygen from the air from penetrating the solar photovoltaic modules, thereby preventing a reduction in solar cell conversion efficiency caused by the oxidation of the silicon cells.
The performance characteristics of photovoltaic adhesives constitute the fundamental basis for their designation as "photovoltaic adhesives," while a series of performance metrics serve as the benchmarks for assessing their quality. Studies indicate that standard photovoltaic adhesives must exhibit an initial shear bond strength of no less than 1.5 MPa and a peel strength of no less than 9.5 kN/m. Regarding aging resistance, it is required that—following 1,000 hours of accelerated aging under "Double 85" conditions (85°C and 85% relative humidity)—the retention rate of all performance parameters (including both bonding and mechanical properties) remains above 75%; furthermore, the sealant must comply with relevant environmental protection standards.
Why is nano-calcium carbonate added to silicone sealants?
In practical applications, photovoltaic sealants are often applied to vertical surfaces; this necessitates a sealant that does not string, sag, or flow excessively. Consequently, the material must exhibit excellent thixotropy; otherwise, it risks contaminating the surface of the substrate and resulting in material waste. Thixotropy is a rheological phenomenon characteristic of dispersed systems, wherein viscosity and shear properties vary over time. Modified nano-calcium carbonate—featuring a surface coated with organic substances—demonstrates significantly enhanced compatibility and wettability with organic materials. When incorporated into silicone sealants, it effectively resolves issues such as excessive flow, low mechanical strength, and poor thixotropy.
Research Progress on Nano-Calcium Carbonate Reinforced Photovoltaic Adhesives
According to publicly available data, the primary functions of nano-calcium carbonate in photovoltaic adhesives are reinforcement and filling. The reinforcing effect of nano-calcium carbonate on photovoltaic adhesives encompasses aspects such as tensile strength, sag resistance, thixotropy, elastic recovery rate, aging resistance, and resistance to heat and humidity.
Studies indicate that when the formulation consists of 100 parts of base polymer, 100 parts of reinforcing fillers (comprising nano-calcium carbonate and fumed silica in a mass ratio of 10:2), 5 parts of crosslinking agent, 1 part of adhesion promoter (consisting of an aminosilane and an alkoxysilane polymer in a mass ratio of 2:1), and 2 parts of tetrabutyl titanate catalyst, the resulting sealant exhibits superior comprehensive performance; furthermore, after aging for 1000 hours at 85°C and 85% relative humidity, its performance retention rate exceeds 90%.
A concentrated slurry of nano-calcium carbonate is conveyed to a surface treatment tank. During the heating and stirring process, a first surface treatment agent—composed of beef tallow and ammonium polyphosphate—is added, followed by the addition of a second surface treatment agent, consisting of carboxyl-terminated polyester and phosphite. The temperature is maintained between 80°C and 90°C, and the mixture is subjected to high-speed stirring for 30 to 60 minutes to produce a nano-calcium carbonate product characterized by high dispersibility, low moisture absorption, and resistance to humid heat, high temperatures, and oxidation. When utilized as a filler in photovoltaic adhesives, this material enhances the mechanical properties of the adhesive and improves its resistance to both humid heat and high temperatures.
Conclusion
Over the past two years, the photovoltaic industry has demonstrated strong growth momentum, bringing widespread benefits to the entire industry chain market. Currently, my country's adhesives market is expanding rapidly, and both the number and scale of enterprises producing nano-calcium for photovoltaic adhesives are steadily increasing. It is worth noting that as production technologies for silicone sealants used in photovoltaics continue to evolve, the application and demand for nano-calcium carbonate within this sector remain dynamic and subject to ongoing development.