Study on the adhesion between the adhesive coating and the packaging film of photovoltaic back panel

The photovoltaic backplane is located at the outermost layer of the photovoltaic module, which protects and supports the battery With the rapid development of photovoltaic industry, photovoltaic backplane, as an important packaging material for modules, has attracted more and more attention The backboard is mainly composed of three layers, from the outside to the inside are weatherproof layer, insulating layer and bonding layer In recent years, the bonding layer of backplane is mostly fluorocarbon coating (fluorocarbon bonding layer / bonding coating) In recent years, the delamination of bonding coating and packaging film EVA from power plant feedback components is the main problem of component failure The bonding performance of fluorocarbon coating and EVA is the key factor to determine the packaging effect of backplane and EVA Some component manufacturers even increased the bonding force standard of fluorocarbon coating and EVA from the original 40n / cm to 60N / cm It has become an important research topic for many backplane manufacturers to determine the factors that affect the adhesion between the coating and EVA, and to effectively use them to improve the adhesion between the coating and EVA Because both the fluorocarbon coating and the EVA adhesive film can affect the adhesion, this paper studies the factors that affect the adhesion between the coating and the EVA from the two aspects of the formulation of the EVA adhesive film and the fluorocarbon coating, so as to provide a useful reference for the preparation of the fluorocarbon coating with excellent adhesion with the EVA adhesive film 1 experiment 1.1 fluorocarbon resin: trifluorochloroethylene vinyl ether copolymer, Changxing Chemical Co., Ltd.; acrylic resin: Deqian chemical; titanium dioxide: DuPont; extinction powder: 5 μ m, degusse; anionic dispersant: bicker chemical; acrylic leveling agent: Evonik; curing agent: HDI Trimer: Kosnik EVA film a: transparent, general type, provided by a company in China; EVA film B: transparent, snail resistant, provided by a company in China; EVA film C: transparent, PID resistant, provided by a company in China; film a, film B, film C placed for a period of time for standby 1.2 preparation of coating and coating samples The fluorocarbon resin, acrylic resin, solvent, dispersant and titanium dioxide are added to the beaker in a certain proportion in turn After the dispersion is uniform, they are led into the grinder for grinding After the fineness of the coating is controlled below 5 μ m, the material is discharged to obtain the premix of fluorocarbon coating Then a certain amount of extinction powder and leveling agent are added into the premix for secondary dispersion, and the fluorocarbon coating is obtained after the dispersion is uniform Pour the fluorocarbon coating, curing agent and solvent into the beaker according to a certain proportion, mix them evenly, and then obtain the fluorocarbon coating for the bonding layer of the back plate Apply the coating on the pet base material after corona with a wire rod, dry and mature, and then obtain the bonding layer for the solar back plate 1.3 performance test the adhesion between backplane and EVA shall be tested in accordance with the provisions of GB / t2790-1995 The crosslinking degree of EVA film was tested by extraction method [6] Results and discussion 2.1 the influence of EVA film on the adhesion between coating and EVA the EVA film is an important packaging material for battery components In recent years, there are more and more functional requirements for EVA film In addition to the conventional film a, there are also anti snail film B and anti PID film C Therefore, this paper studies these three kinds of packaging film 2.1.1 the influence of the type of EVA adhesive film on the adhesion between the coating and EVA under different laminating time, the adhesion between the three adhesive films and the coating is shown in Figure 1 Fig 1 the change of adhesive force of three kinds of adhesive films at different lamination time It can be seen from Fig 1 that under different lamination time, the adhesive force of three kinds of adhesive films and coating increases first and then decreases The optimal lamination time of three kinds of adhesive films is 11min, and under this condition, the adhesive force of a and B adhesive films and coating is better than that of C Under different laminating time, the crosslinking degree of three kinds of films is shown in Figure 2 Fig 2 change of crosslinking degree of three kinds of films at different laminating time It can be seen from Figure 2 that when laminating for 7min, the crosslinking degree of film C is higher than that of a and B, and the time is extended to 11min, the reaction rate of film a and B increases rapidly, and the crosslinking degree exceeds the crosslinking degree of C This change trend corresponds to the adhesive force of film and coating, that is, the greater the crosslinking degree is, the greater the adhesive force of film and coating is Therefore, when the optimal laminating time is 11min, the crosslinking degree of film a and B is higher than that of coating The adhesion is better than C 2.1.2 the influence of different time on the adhesion between the coating and EVA under the condition of poor sealing, after a period of time, the adhesion between the coating and EVA film is as shown in Figure 3 Fig 3 Effect of adhesive film placement time on adhesive force between coating and adhesive film It can be seen from Fig 3 that with the extension of EVA adhesive film placement time, the adhesive force of three EVA adhesive films and coating presents a trend of vibration and decline Because the adhesive properties of film a and film B are equal and better than that of film C, the vulcanization curve of film a is selected to study the influence of different time of EVA film placement on the adhesive force between the coating and EVA, and the reason of adhesive force attenuation of film is analyzed The vulcanization curve of the film is shown in Figure 4 Fig 4 vulcanization curve of new and old rubber film It can be seen from Fig 4 that the maximum torque of rubber film is smaller and smaller with the extension of placing time, and the maximum torque of rubber film after 6 months has little change, but after 9 months, the torque of rubber film is significantly reduced, that is to say, the crosslinking degree of old rubber film is significantly reduced, so the adhesion between coating and EVA decreases after placing rubber film for a period of time New plastic film should be used up within 6 months if it is not stored tightly 2.2 the influence of coating formulation on the adhesion between coating and EVA the coating formulation mainly contains resin and pigments and fillers, and the difference of each component and content will affect the adhesion between coating and EVA 2.2.1 the influence of the mass ratio of fluorocarbon and acrylic resin on the adhesion between the coating and EVA there is fluorocarbon resin in the bonding coating, but the surface energy of fluorocarbon resin is low In order to improve the adhesion between the coating and EVA, acrylic resin is often added to modify The effect of the mass ratio of fluorocarbon resin and acrylic resin on the adhesion between the coating and EVA is shown in Figure 5 Fig 5 Effect of resin quality ratio on adhesion between coating and EVA It can be seen from Fig 5 that with the increase of the proportion of acrylic resin, the adhesion between the coating and EVA adhesive film increases gradually, which is mainly because the acrylic resin contains polar groups with good adhesion to Eva When the content of acrylic resin increases, the number of polar groups in the coating increases, thus increasing the adhesion between the coating and EVA However, when the ratio of acrylic resin increases to 1:2, the increase of adhesive force slows down In addition, with the increase of acrylic resin, the weatherability of the coating will decrease Therefore, the mass ratio of fluorocarbon to acrylic acid is 1:1 2.2.2 the influence of the type and content of extinction powder on the adhesion between the coating and EVA the extinction powder is often added to the fluorocarbon coating to adjust the gloss of the coating, but the existing extinction powder has been treated or not In order to improve the adhesion between the coating and EVA, the influence of the amount of these two extinction powder on the adhesion between the coating and EVA is investigated, as shown in Figure 6 Fig 6 Effect of extinction powder on adhesion between coating and EVA It can be seen from Figure 6 that with the increase of extinction powder content, the adhesion between the coating and EVA decreases Compared with the two kinds of extinction powder, the adhesion between the surface treated extinction powder and EVA decreases faster than that of the non surface treated extinction powder The reason is that there is polyethylene wax on the surface of the surface treated extinction powder, which will form a weak interface layer with EVA during lamination and reduce the adhesion between the coating and ev A In order to ensure the adhesion between the coating and EVA, it is necessary to select the polishing powder which is not treated on the surface, and the content of the polishing powder should be less than 3% 2.3 effect of coating thickness on adhesion between coating and EVA the effect of thickness of fluorocarbon coating on adhesion between coating and EVA is shown in Figure 7 Fig 7 Effect of coating thickness on adhesion between coating and EVA It can be seen from Fig 7 that the thicker the coating is, the greater the adhesion between coating and EVA When the thickness of coating is greater than 6.5 μ m, the increase of adhesion between coating and EVA slows down The surface morphology of the coating with different thickness is shown in Figure 8 Fig 8 surface morphology of coating with different thickness it can be seen from Fig 8 that the thicker the coating is, the less inorganic particles are exposed Therefore, the more sufficient the contact between the resin and EVA, the greater the adhesion between the coating and EVA When the thickness of the coating increases to 6.5 μ m, which is larger than the particle size of extinction powder 5 μ m, the contact area between the resin and EVA tends to saturated state, and then continues to increase the thickness of the coating, the increase of the adhesion between the coating and EVA slows down Considering the influence of the size of pigments and fillers, the thickness of the coating is 6.5-7.5 μ M Conclusion (1) the degree of crosslinking of three kinds of film (Universal a, anti PID function B, anti snail function c) is different from that of the same coating after lamination, resulting in different adhesive force The adhesive performance of film a and B is equivalent, which is superior to film C (2) The adhesive force between the coating and the adhesive film will be reduced during the placement of the adhesive film In this experiment, the adhesive film should be used up within 6 months in case of poor sealing (3) In this experiment, the mass ratio of fluorocarbon and acrylic acid is 1:1, and the adhesion value tends to be stable (4) When the extinction powder is added to the coating, it is better to select the silicon dioxide without organic wax surface treatment, and its content should be less than 3% (5) The thickness of the coating should be larger than the particle size of the pigments and fillers in the coating If the particle size of the pigments and fillers is 5 μ m, the preferred thickness of the coating is 6.5-7.5 μ M.