The function of the adhesive film in the photovoltaic module is to stick the photovoltaic glass, the cell and the backplane together, and at the same time, it plays the role of protecting the cell and isolating the air,accounting for 3%-4% of the cost in the module.
The types of photovoltaic film include two categories: EVA film material film and POE film, EVA film includes traditional transparent EVA film, white EVA film and others (such as anti-PID film, etc.), POE film Including cross-linked, thermoplastic, white, co-extrusion and other types. Among them, EVA photovoltaic film occupies more than 80% of the market and is a well-deserved mainstream product.
Analysis of bonding packaging principle
The raw materials of EVA photovoltaic film are EVA resin, cross-linking agent, silane coupling agent and other modifiers.
After stirring evenly in the mixer, mix it in a closed container and let it stand for a period of time, extract the mixed material and put it in the film production line, and cast and extrude it into a molten film. After the molten adhesive film is cooled by multiple cooling rollers, it is trimmed and harvested into rolls; it is non-sticky at room temperature and easy to operate. When the components are laminated, the EVA is heated to a certain temperature and is in a molten state to achieve bonding.
High liquidity
Good fluidity can ensure that the EVA film is laid on the substrate, increase the contact area with the substrate, and rely on its own polarity and the intermolecular force between the properties of the substrate to form a physical bond point to achieve bonding;
Silane coupling agent
Since photovoltaic glass is an inorganic material with a smooth surface, and the photovoltaic backsheet is a fluorine-containing material with a surface that is difficult to bond. Thersfore silane coupling agent is usually contained in the EVA film to modify the EVA to enhance its polarity. During the heating and curing process, the silane coupling agent reacts with water to form a covalent bond with the substrate and EVA, the inorganic glass and the polymer EVA are connected together like a bridge, so as to realize the bonding effect. The specific principle is as follows:
Factors influencing bond strength
1. EVA's own performance effects
If the VA content of the raw material EVA is small, the heat resistance is good, but the polarity is poor, resulting in poor film adhesion and low-temperature flexibility. In addition, the larger the melt index, the better the fluidity of EVA, the better the tiling, the more physical bonding points, the greater the peel strength; but if the melt index is large to a certain extent, the EVA will have a lower degree of polymerization, resulting in its own strength decreases, and the cohesive force decreases. In order to maintain good adhesion, resins with VA content of 28-33% and MI 10-400 are generally selected.
2. Effect of EVA crosslinking degree
The degree of cross-linking refers to the mass ratio of linear molecules cross-linked into network molecules when the EVA film is heated. When the components are laminated, while the heating temperature of the laminator reaches the decomposition temperature of the cross-linking agent, the peroxy bond in the cross-linking agent is broken to form a peroxy radical RO-, which is easily combined with the H of the alkyl group on the EVA branch chain, and the two alkyl active groups are combined to form a crosslink EVA. The specific mechanism is as follows:
The degree of crosslinking determines the cohesion strength of the EVA film, which affects the peeling strength of the EVA film and the backsheet and glass, also determines the quality of the photovoltaic cell module.
Too much cross-linking agent is added, and the degree of cross-linking is high, but too much will cause aging yellowing. If the cross-linking agent is too small, the cross-linking is too low, and the bond strength and anti-aging are also affected. The experimental analysis proves that the degree of cross-linking is the best at 75%-80%.
In addition, the curing temperature, curing time,cross-linking agent content, compatibility of the entire formulation system, and surface properties of the glass and backsheet will directly or indirectly affect the peel strength of the EVA film.
Epilogue
Therefore, the photovoltaic film seems simple it hides a lot of university questions, and China's photovoltaic film has developed rapidly in recent years, in 2021, three of the top four companies in the market share of the photovoltaic film industry are from China. In addition to the first-ranked Foster, the second, third, and fourth ranks of Swick, Haiyou New Material, and Saiwu Technology have market shares of 13.54%, 10.36%, and 10.36% respectively 4.37%。 China's photovoltaic film manufacturers have now become the leading force in the global photovoltaic film market.
Therefore, photovoltaic film seems to be simple, but it actually hides a lot of university questions. China's photovoltaic film has developed rapidly in recent years. In 2021, three of the top four companies in the photovoltaic film industry will be from China. Excluding the No. 1 Foster, the No. 2, No. 3, and No. 4 Swick, Haiyou New Materials, and Saiwu Technology have market shares of 13.54%, 10.36%, and 4.37%, respectively. China's photovoltaic film manufacturers have now become the leading force in the global photovoltaic film market.
