Highly reflective uv resistant photovoltaic module gap film and method of making same

Abstract

The application discloses a high-reflection ultraviolet-resistant photovoltaic module gap film and a preparation method thereof, wherein the thickness is 30-100 mu m, the average reflectivity of 400-1200 nm is greater than or equal to 88%, the structure is ABA three-layer structure, the raw material of the A layer comprises 5-15 parts of mixed UV-resistant agent and 85-95 parts of PET resin, the raw material of the B layer comprises 3-5 parts of hydrolysis-resistant polyester chip, 15-20 parts of reflective particle, 0.05-0.1 part of fluorescent whitening agent and 65-75 parts of PET resin. Through improvement on the raw material of the gap film and the preparation process, the gap film has good hydrolysis resistance under the condition of less hydrolysis-resistant agent, meanwhile, the gap film can obtain higher reflectivity under the condition of no need of aluminum plating and smaller thickness, and is convenient for application in the photovoltaic module.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic module technology, and in particular to a high-reflectivity, ultraviolet-resistant photovoltaic module gap film and its preparation method. Background Technology

[0002] Solar energy is a renewable and clean energy source with enormous development potential. Solar cells are devices that directly convert solar energy into electrical energy through the photoelectric effect or photochemical effect. To ensure the proper use and protection of solar cells, solar photovoltaic (PV) modules have been developed. In PV modules, there are generally gaps between the cells. This is because copper strips are welded between the cells; if they are too close together, the cells will short-circuit. Furthermore, the spacing within the solar panel is to accommodate different voltage requirements; the spacing between the cells is determined by the power of the solar panel—the higher the power, the larger the spacing. Light passing through these gaps cannot be utilized by the cells, reducing the effective area of ​​the solar PV module and lowering its photoelectric efficiency.

[0003] To improve photoelectric efficiency, many photovoltaic (PV) modules use reflective gap films between the cells. Currently, these gap films typically employ a multi-layer structure, achieving good light reflection by depositing an aluminum-coated layer on the surface of a PET base film. For example, patent CN219085989U discloses a gap film for PV modules comprising a base film layer, a concave prism structure layer, a white high-reflectivity coating, and an EVA resin adhesive layer. In existing gap films, reflection relies primarily on the aluminum-coated layer, with the PET base film mainly providing support. The aluminum-coating process for this multi-layer structure is complex and costly. Furthermore, aluminum-containing gap films are highly conductive, potentially causing short circuits when applied to the welding strips between PV cells. Additionally, the small spacing between PV cells and the back glass or backsheet leaves even less space for the gap film, requiring it to be as thin as possible. However, existing prism-coated aluminum gap films are generally quite thick, easily causing different cells to be strung together, affecting cell power generation efficiency and even damaging the cells.

[0004] Meanwhile, photovoltaic modules typically operate in environments ranging from -40℃ to 85℃ and from 0% to 100% RH, facing working conditions that can range from scorching, dry deserts to cold, snowy plains. This places higher demands on photovoltaic modules. Existing interlayer membranes generally use PET as their supporting substrate. While PET has low permeability to gases and water vapor, it is prone to hydrolysis under high temperature and humidity. Currently, photovoltaic modules use double-glass or single-glass structures, which offer some moisture protection, but for high-performance photovoltaic modules, the photovoltaic reflective film also needs to possess a certain degree of hydrolysis resistance. To improve the hydrolysis resistance of the photovoltaic reflective film, the most common method is to add a hydrolysis-resistant agent, polycarbodiimide, to the PET matrix. This acts as a stabilizer; polycarbodiimide reacts with carboxyl-containing substances in the system to generate stable acylurea, thereby inhibiting hydrolysis and improving the hydrolysis resistance of the polyester material, as described in patent CN103627150A. However, polycarbodiimide is expensive, which is not conducive to the current cost reduction requirements of photovoltaic modules. Summary of the Invention

[0005] The present invention aims to overcome the aforementioned problems existing in the gap films of photovoltaic modules in the prior art, and provides a high-reflectivity, UV-resistant photovoltaic module gap film and its preparation method. By improving the gap film raw materials and preparation process, the gap film can have good hydrolysis resistance with a smaller amount of hydrolysis resistant agent added; at the same time, the gap film can achieve high reflectivity without aluminum plating and with a smaller thickness, which facilitates its application in photovoltaic modules.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-reflectivity, UV-resistant photovoltaic module gap film with a thickness of 30–100 μm and an average reflectivity of ≥88% at 400–1200 nm; the structure is an ABA three-layer structure.

[0008] Layer A is a weather-resistant layer, which, by weight, consists of 5 to 15 parts of mixed UV-resistant agent and 85 to 95 parts of PET resin; Layer B is a high-performance reflective layer, which, by weight, consists of 3 to 5 parts of hydrolysis-resistant polyester chips, 15 to 20 parts of reflective particles, 0.05 to 0.1 parts of fluorescent whitening agent, and 65 to 75 parts of PET resin.

[0009] The intrinsic viscosity of the PET resin is 0.72-0.80 dL / g, and the end carboxyl group content is less than 12 mol / t; the content of carbodiamine in the hydrolysis-resistant polyester chips is 13-14 wt%; the reflective particles are rutile TiO2 with a particle size of 200 nm.

[0010] This invention uses an ABA three-layer PET film as a gap film for photovoltaic modules. A mixed UV-resistant agent is added to the surface layer A to give the film good weather resistance and improve its service life. Rutile TiO2 is added to layer B as reflective particles, along with a small amount of fluorescent whitening agent. This allows the film to achieve good reflectivity without a surface aluminum plating layer, avoiding the short circuits that can easily occur with aluminum plating and simplifying the gap film preparation process. Furthermore, by controlling the intrinsic viscosity of the PET resin and the particle size and dosage of the reflective particles, this invention allows the resulting gap film to meet performance requirements even at a relatively thin thickness, facilitating its application in photovoltaic modules. The gap film of this invention achieves an average reflectivity of over 88% at a thickness of 30–100 μm and a wavelength of 400–1200 nm, exhibiting excellent reflectivity. Furthermore, this invention strictly controls the end carboxyl group content of PET resin to improve its hydrolysis resistance, so that the gap membrane can have good water resistance with a small amount of hydrolysis-resistant polyester chips added, which greatly reduces the amount of hydrolysis-resistant agent carbodiamine used and helps to meet the cost reduction requirements of photovoltaic modules.

[0011] Preferably, the thickness is 35–75 μm.

[0012] Preferably, the total thickness of layer B is 80-90% of the total thickness of the gap film in the high-reflectivity, UV-resistant photovoltaic module.

[0013] Preferably, the mixed UV absorber comprises benzotriazole UV absorbers and hindered amine UV absorbers in a mass ratio of 1-2:1-2.

[0014] Preferably, the fluorescent whitening agent is OB-1. Adding a small amount of fluorescent whitening agent to the B layer is beneficial for its coordination with reflective particles, enabling the gap membrane to have good reflective properties at a relatively thin thickness, without affecting the mechanical properties and hydrolysis resistance of the gap membrane or other properties.

[0015] The present invention also provides a method for preparing the above-mentioned high-reflectivity, UV-resistant photovoltaic module gap film, comprising the following steps:

[0016] (1) Mix the raw materials in layer A and layer B respectively, add them to the extruder, and obtain a cast sheet after three-layer co-extrusion and cooling casting.

[0017] (2) The casting is stretched longitudinally with a stretching ratio of 2.7 to 3.2;

[0018] (3) The casting is stretched laterally with a stretching ratio of 3.3 to 3.7;

[0019] (4) After heat setting the casting, the high-reflection UV-resistant photovoltaic module gap film is obtained by winding. The heat setting includes four stages: the first stage temperature is 200-205℃ and the time is 3-20s; the second stage temperature is 205-210℃ and the time is 3-20s; the third stage temperature is 180-185℃ and the time is 1-10s; the fourth stage temperature is 140-145℃ and the time is 1-10s.

[0020] During the research process, this invention discovered that in addition to the raw material composition affecting the hydrolysis resistance of the gap membrane, the process conditions during preparation also have a significant impact. Based on the raw material composition of the gap membrane, this invention has also made corresponding improvements to the process conditions during its preparation, limiting the stretching ratio of longitudinal and transverse stretching and optimizing the heat setting process, further improving the hydrolysis resistance of the gap membrane, and ensuring that the gap membrane can still possess good hydrolysis resistance even with a reduced amount of hydrolysis-resistant agent added.

[0021] Preferably, in step (1), the raw materials are mixed and dried before being added to an extruder for extrusion; the drying temperature is 140-150℃ and the drying time is 1-5h.

[0022] Preferably, the extruder temperature during the three-layer co-extrusion in step (1) is 260-280°C, and the temperature during the cooling of the cast sheet is 15-25°C.

[0023] Preferably, the temperature during longitudinal stretching in step (2) is 70-80°C, and the longitudinal stretching cooling temperature is 20-30°C.

[0024] Preferably, the temperature during transverse stretching in step (3) is 70–90°C.

[0025] Therefore, the present invention has the following beneficial effects:

[0026] (1) Adding rutile TiO2 as reflective particles to layer B and adding a small amount of fluorescent whitening agent can enable the film to obtain better reflective performance without setting an aluminum coating layer on the surface, avoiding the battery short circuit that is easily caused by the aluminum coating layer, and simplifying the preparation process of the gap film.

[0027] (2) By controlling the intrinsic viscosity of PET resin and the particle size and dosage of reflective particles, the performance of the resulting gap membrane can meet the requirements of use even with a relatively thin thickness of 30 to 100 μm.

[0028] (3) The end carboxyl group content of PET resin is strictly controlled and the process conditions during preparation are optimized so that the gap membrane can have good hydrolysis resistance with a small amount of hydrolysis resistant polyester chips added, which greatly reduces the amount of hydrolysis resistant agent carbodiamine and helps to meet the cost reduction requirements of photovoltaic modules. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments.

[0030] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0031] The benzotriazole UV absorber used in this embodiment of the invention was purchased from Tianjin Lianlong New Material Co., Ltd., brand name UV-1577; the hindered amine UV absorber was purchased from Tianjin Lianlong New Material Co., Ltd., brand name UV-944; and the hydrolysis-resistant polyester chips were purchased from Shanghai Langyi Functional Materials Co., Ltd., with a carbodiamine content of 13.5 wt% in the chips.

[0032] Example 1:

[0033] A high-reflectivity, UV-resistant photovoltaic module gap film has an ABA three-layer structure with a total thickness of 50 μm, wherein the two A layers each account for 7% of the total thickness and the B layer accounts for 86% of the total thickness.

[0034] Layer A is a weather-resistant layer. By weight, the raw materials include 5 parts of benzotriazole UV absorber, 5 parts of hindered amine UV absorber, and 90 parts of PET resin (intrinsic viscosity of 0.75 dL / g, end carboxyl content of 8 mol / t).

[0035] Layer B is a high-performance reflective layer. By weight, the raw materials include 5 parts hydrolysis-resistant polyester chips, 20 parts rutile TiO2 with a particle size of 200 nm, 0.1 parts fluorescent whitening agent OB-1, and 74.9 parts PET resin (intrinsic viscosity of 0.75 dL / g and end carboxyl content of 8 mol / t).

[0036] The preparation steps of the above-mentioned high-reflectivity, UV-resistant photovoltaic module gap film are as follows:

[0037] (1) Mix the raw materials in layer A and layer B in proportion and dry them at 150°C for 3 hours.

[0038] (2) The dried raw material is added to the main extruder and the auxiliary extruder respectively, and after three-layer co-extrusion and cooling casting, a casting sheet is obtained; the extruder temperature is 260-280℃, and the cooling casting sheet temperature is 20℃.

[0039] (2) The casting sheet is stretched longitudinally at a temperature of 70-80℃ and a stretching ratio of 2.95; after longitudinal stretching, it is cooled to 20℃; (3) The casting sheet is stretched transversely at a temperature of 70-90℃ and a stretching ratio of 3.7.

[0040] (4) After heat setting the casting, the high-reflection UV-resistant photovoltaic module gap film is obtained by winding. The heat setting includes four stages: the first stage temperature is 200℃ and the time is 6s; the second stage temperature is 205℃ and the time is 6s; the third stage temperature is 180℃ and the time is 3s; the fourth stage temperature is 140℃ and the time is 3s.

[0041] Example 2:

[0042] The difference between Example 2 and Example 1 is that PET resin with an intrinsic viscosity of 0.72 dL / g and a terminal carboxyl group content of 12 mol / t is used in layers A and B, while the rest are the same as in Example 1.

[0043] Example 3:

[0044] The difference between Example 3 and Example 1 is that PET resin with an intrinsic viscosity of 0.80 dL / g and a terminal carboxyl group content of 8 mol / t is used in layers A and B, while the rest are the same as in Example 1.

[0045] Example 4:

[0046] The difference between Example 4 and Example 1 is that the raw materials of layer B, by weight, include 3 parts of hydrolysis-resistant polyester chips, 15 parts of rutile TiO2 with a particle size of 200 nm, 0.05 parts of fluorescent whitening agent OB-1, and 65 parts of PET resin (intrinsic viscosity of 0.75 dL / g and end carboxyl content of 8 mol / t); the rest are the same as in Example 1.

[0047] Example 5:

[0048] The difference between Example 5 and Example 1 is that the temperatures of the four stages of heat setting are 200℃, 210℃, 180℃ and 140℃, respectively; the rest are the same as in Example 1.

[0049] Comparative Example 1:

[0050] The difference between Comparative Example 1 and Example 1 is that the temperatures of the four stages of heat setting are 200°C, 230°C, 180°C and 140°C, respectively; the rest are the same as in Example 1.

[0051] Comparative Example 2:

[0052] The difference between Comparative Example 2 and Example 1 is that the temperatures of the four stages of heat setting are 200°C, 190°C, 180°C and 140°C, respectively; the rest are the same as in Example 1.

[0053] Comparative Example 3:

[0054] The difference between Comparative Example 3 and Example 1 is that the temperatures of the four stages of heat setting are 210°C, 200°C, 180°C and 140°C, respectively; the rest are the same as in Example 1.

[0055] Comparative Example 4:

[0056] The difference between Comparative Example 4 and Example 1 is that the stretching ratio during transverse stretching is adjusted to 3.0; all other aspects are the same as in Example 1.

[0057] Comparative Example 5:

[0058] The difference between Comparative Example 5 and Example 1 is that the stretching ratio during transverse stretching is adjusted to 4.5; all other aspects are the same as in Example 1.

[0059] Comparative Example 6:

[0060] The difference between Comparative Example 6 and Example 1 is that PET resin with an intrinsic viscosity of 0.68 dL / g and a terminal carboxyl group content of 8 mol / t is used in layers A and B, while the rest are the same as in Example 1.

[0061] Comparative Example 7:

[0062] The difference between Comparative Example 7 and Example 1 is that PET resin with an intrinsic viscosity of 0.75 dL / g and a terminal carboxyl group content of 30 mol / t was used in layers A and B, while the rest were the same as in Example 1.

[0063] Comparative Example 8:

[0064] The difference between Comparative Example 8 and Example 1 is that PET resin with an intrinsic viscosity of 0.90 dL / g and a terminal carboxyl group content of 8 mol / t is used in layers A and B, while the rest are the same as in Example 1.

[0065] Comparative Example 9:

[0066] The difference between Comparative Example 9 and Example 1 is that the raw materials for layer B, by weight, include 5 parts of hydrolysis-resistant polyester chips, 10 parts of rutile TiO2 with a particle size of 200 nm, 0.1 parts of fluorescent whitening agent OB-1, and 84.9 parts of PET resin (intrinsic viscosity of 0.75 dL / g and end carboxyl content of 8 mol / t); the rest are the same as in Example 1.

[0067] Comparative Example 10:

[0068] The difference between Comparative Example 10 and Example 1 is that the raw materials for layer B, by weight, include 5 parts of hydrolysis-resistant polyester chips, 30 parts of rutile TiO2 with a particle size of 200 nm, 0.1 parts of fluorescent whitening agent OB-1, and 64.9 parts of PET resin (intrinsic viscosity of 0.75 dL / g and end carboxyl content of 8 mol / t); the rest are the same as in Example 1.

[0069] Comparative Example 11:

[0070] The difference between Comparative Example 11 and Example 1 is that hydrolysis-resistant polyester chips are not added to the raw materials of layer B, while the rest are the same as in Example 1.

[0071] Comparative Example 12:

[0072] The difference between Comparative Example 12 and Example 1 is that 400nm rutile TiO2 is used as the reflective particle in layer B, while the rest are the same as in Example 1.

[0073] Comparative Example 13:

[0074] The difference between Comparative Example 13 and Example 1 is that no fluorescent whitening agent OB-1 is added to layer B, while the rest are the same as in Example 1.

[0075] The performance of the gap membranes prepared in the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0076] The test method for reflectance refers to the GB / T 3979-2008 standard. The reflectance is tested by a spectrophotometer, and the average value of the test results in the range of 400 to 1200 nm is taken as the average reflectance.

[0077] The peel strength test method for EVA is as follows: peel samples are prepared in the order of glass-EVA-gap film, and then the samples are laminated. After lamination, the peel strength test is carried out in accordance with the peel strength test conditions GB / T31034-2014.

[0078] Hydrolysis resistance was reflected by the PCT48h elongation at break, with PCT48h test conditions of 121℃ and 100% RH; the tensile test method was in accordance with GB / T 13542.4-2009.

[0079] The UV reflectance attenuation rate and yellowing test methods are as follows: cut the gap membrane into 5*5cm samples, place them in an accelerated UV aging chamber, irradiate with UV for 300kwh, and the aging conditions are: 60℃ and dry environment; the sample b-value and reflectance are tested according to GB / T 3979-2008, the reflectance attenuation rate = (initial reflectance - UV-induced reflectance) / initial reflectance * 100%, and the yellowing Δb = UV-induced b-value - initial b-value.

[0080] The battery gain test method is as follows: the gap film is attached to the welding strip between the cells in the photovoltaic module, and the same photovoltaic module without the gap film is placed under sunlight for 7 days. The power generation of each photovoltaic module is measured. The power generation improvement rate of the photovoltaic module with the gap film and the photovoltaic module without the gap film is calculated.

[0081] Table 1: Test results of gap membrane performance.

[0082]

[0083] As can be seen from Table 1, the gap membranes prepared using the raw material formulation and method of the present invention in Examples 1 to 5 have good reflectivity, hydrolysis resistance, and UV resistance, and can significantly improve power generation when used in photovoltaic modules.

[0084] In Comparative Example 1, the temperature in the second stage of heat setting was too high, exceeding the temperature range of this invention. This resulted in a significant decrease in the peel strength between the gap membrane and EVA, as well as the PCT48h elongation at break compared to Example 1, and a deterioration in hydrolysis resistance. In Comparative Example 2, the temperature in the second stage of heat setting was too low. Similarly, in Comparative Example 3, changing the temperatures of the first and second stages of heat setting also led to a decrease in the peel strength between the gap membrane and EVA, and in its hydrolysis resistance. This demonstrates that the process conditions during the heat setting stage have a significant impact on the performance of the gap membrane.

[0085] In Comparative Examples 4 and 5, the peel force between the gap membrane and EVA and the elongation at break of PCT48h decreased compared to Example 1 when the stretching ratio was reduced or increased during transverse stretching, indicating that the stretching process also affects the hydrolysis resistance of the gap membrane.

[0086] In Comparative Example 6, the intrinsic viscosity of the PET resin was too low, resulting in a decrease in the peel strength, hydrolysis resistance, and UV resistance of the interstitial membrane to EVA compared to Example 1. In Comparative Example 7, the end carboxyl group content of the PET resin was too high, which also reduced the peel strength, hydrolysis resistance, and UV resistance of the interstitial membrane to EVA. In Comparative Example 8, the intrinsic viscosity of the PET resin was too high. Although the hydrolysis resistance and peel strength to EVA were not significantly different from those in the examples, the interstitial membrane was difficult to form, prone to breakage, and had a low yield, which was detrimental to production.

[0087] In Comparative Example 9, fewer reflective particles were added, which improved the hydrolysis resistance of the gap film, but the reflectivity was insufficient, the reflectivity decay was increased, and the cell gain was reduced. In Comparative Example 10, too many reflective particles were added. Although the reflectivity was improved, the hydrolysis resistance of the gap film was poor, which was not conducive to the use of photovoltaic modules.

[0088] In Comparative Example 11, without the addition of hydrolysis-resistant polyester chips in layer B, the interstitial membrane exhibits poor hydrolysis resistance, making it difficult to meet the requirements for use in photovoltaic modules.

[0089] In Comparative Example 12, rutile TiO2 with a larger particle size was used as the reflective particles. The reflectivity of the interstitial membrane to light of a small wavelength decreased, and its hydrolysis resistance was reduced compared to Example 1.

[0090] In Comparative Example 13, no fluorescent whitening agent was added to layer B, and the reflectivity of the gap membrane could not achieve the effect of this invention.

Claims

1. A method for preparing a high-reflectivity, UV-resistant photovoltaic module gap film, characterized in that the steps include... include: (1) Mix the raw materials in layer A and layer B respectively, add them to the extruder, and obtain the cast sheet after three-layer co-extrusion and cooling casting. By weight, layer A comprises 5-15 parts of a mixed UV-resistant agent and 85-95 parts of PET resin; layer B comprises 3-5 parts of hydrolysis-resistant polyester chips, 15-20 parts of reflective particles, 0.05-0.1 parts of fluorescent whitening agent, and 65-75 parts of PET resin; the intrinsic viscosity of the PET resin is 0.72-0.80 dL / g, and the end carboxyl group content is less than 12 mol / t; the content of carbodiamine in the hydrolysis-resistant polyester chips is 13-14 wt%; the reflective particles are rutile TiO2 with a particle size of 200 nm. (2) The casting is stretched longitudinally with a stretching ratio of 2.7 to 3.2; (3) The casting is stretched laterally with a stretching ratio of 3.3 to 3.7; (4) After heat setting, the cast film is wound up to obtain a high-reflectivity, UV-resistant photovoltaic module gap film with an average reflectivity ≥88% and a thickness of 30~100μm and 400~1200nm. The structure is an ABA three-layer structure. The heat setting includes four stages: the first stage temperature is 200~205℃ and the time is 3~20s; the second stage temperature is 205~210℃ and the time is 3~20s; the third stage temperature is 180~185℃ and the time is 1~10s; the fourth stage temperature is 140~145℃ and the time is 1~10s.

2. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, The thickness of the gap film for the high-reflectivity, UV-resistant photovoltaic module is 35~75μm.

3. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, The total thickness of layer B is 80-90% of the total thickness of the spacer film in high-reflectivity, UV-resistant photovoltaic modules.

4. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1 or 3, characterized in that, The aforementioned mixed UV absorber comprises benzotriazole UV absorbers and hindered amine UV absorbers in a mass ratio of 1~2:1~2.

5. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, The fluorescent whitening agent mentioned is OB-1.

6. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, In step (1), the raw materials are mixed and dried before being added to the extruder for extrusion; the drying temperature is 140~150℃ and the drying time is 1~5h.

7. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1 or 6, characterized in that, In step (1), the extruder temperature during the three-layer co-extrusion is 260~280℃, and the temperature during the cooling of the cast sheet is 15~25℃.

8. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, The temperature during longitudinal stretching in step (2) is 70~80℃, and the longitudinal stretching cooling temperature is 20~30℃.

9. The method for preparing the high-reflectivity, UV-resistant photovoltaic module gap film according to claim 1, characterized in that, The temperature during transverse stretching in step (3) is 70~90℃.

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