Black-and-white structured high-reflection black EVA adhesive film, preparation method and application thereof

Abstract

A black and white high-reflectivity EVA film, its preparation method and application, belongs to the field of EVA film technology. This invention relates to a black and white high-reflectivity EVA film, comprising a black high-reflectivity layer and a white high-reflectivity layer sequentially stacked and co-extruded. The black high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix and contains 0.8–3.0 wt% infrared-reflective black pigment, 0.3–1.0 wt% crosslinking agent, 0.3–1.5 wt% coupling agent, 0.1–0.5 wt% antioxidant, 0.1–0.8 wt% light stabilizer, 0–0.5 wt% carbon black, and 0–3 wt% processing aids. The white high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix and contains 8–25 wt% titanium dioxide, 0.3–1.0 wt% crosslinking agent, 0.3–1.5 wt% coupling agent, 0.1–0.5 wt% antioxidant, 0.1–0.8 wt% light stabilizer, and 0–15 wt% inorganic filler and processing aids. The EVA film of this invention has a reflectivity of over 85% in the 760-1100nm infrared band, which reduces the temperature during module use, increases module power generation efficiency, greatly improves PID performance, and extends the module's service life.

Description

Technical Field

[0001] This invention belongs to the field of EVA film technology, specifically relating to a black and white structured high-reflectivity EVA film, its preparation method, and its application. Background Technology

[0002] As the core unit of a solar power generation system, the photovoltaic module's photoelectric conversion efficiency and long-term operational stability directly determine the investment return and energy utilization level of the power generation system. Meanwhile, the encapsulation material, as the "protective barrier" and "performance link" of the photovoltaic module, has a significant impact on the overall performance of the module.

[0003] Ethylene-vinyl acetate copolymer (EVA) film, due to its excellent flexibility, optical transparency, adhesion, and processing adaptability, has become the mainstream material for photovoltaic module encapsulation since the 1980s. After decades of technological iteration, it has formed a mature product system. In a typical photovoltaic module encapsulation structure, EVA film needs to achieve reliable adhesion between the solar cells and the glass, backsheet (or other substrates), while forming a stable adhesive layer through cross-linking and curing. This ensures the mechanical strength of the module and reduces the erosion of the solar cells by environmental factors. Its performance is directly related to the module's power generation efficiency and service life.

[0004] As photovoltaic modules upgrade towards higher efficiency and longer lifespan, the market is placing higher demands on the performance of EVA encapsulant films. Currently, one of the core bottlenecks restricting the improvement of module power generation efficiency lies in the synergistic problem of insufficient utilization of the solar spectrum and excessively high operating temperatures. Specifically, about 30% of the infrared light in the solar spectrum irradiating the module surface cannot be absorbed and utilized by the cells and is converted into heat energy, causing the module temperature to rise. For every 1°C increase in module temperature, its power generation efficiency typically decreases by 0.4%-0.5%, severely impacting power generation revenue. Simultaneously, in high-temperature and high-humidity outdoor environments, modules are prone to potential-induced degradation (PID), where metal ions in the glass migrate through the encapsulant film to the cell surface, resulting in a power degradation of up to 20%, becoming a key factor restricting the long-term stability of modules.

[0005] To address the aforementioned issues, the industry has developed two types of EVA film improvement solutions focusing on infrared light management and PID protection performance. However, significant technical limitations remain, making it difficult to simultaneously meet efficiency improvement and reliability requirements. One type is conventional transparent EVA film. These products are designed primarily for high light transmittance, with mainstream products achieving visible light transmittance exceeding 92%. However, their reflectivity in the infrared band is weak (typically below 10%), making it difficult to effectively block the infrared photothermal effect, which is detrimental to power generation. This results in higher module operating temperatures and significant efficiency losses. Simultaneously, their low volume resistivity limits their ability to block metal ions, leading to insufficient PID protection performance and making them prone to significant module power degradation in harsh environments such as high temperature and high humidity.

[0006] Another type is a single-color high-reflectivity EVA film (such as white EVA film). This type of product increases reflectivity by adding fillers such as titanium dioxide. Although it can reduce heat accumulation to some extent, it has three major defects: First, the reflection spectrum is concentrated, and the reflection efficiency of the full-band infrared light is insufficient, resulting in limited cooling effect; Second, the surface of titanium dioxide contains water-absorbing functional groups, which easily leads to increased water absorption of the film and accelerates the hydrolysis of silane additives. This not only reduces the bonding reliability with the backsheet and glass, but also leads to a further decrease in volume resistivity after aging, making the PID protection performance inferior to that of conventional transparent films; Third, the single white structure provides poor shielding of the circuitry on the back of the component, which is not conducive to the installation, commissioning, and troubleshooting of the component.

[0007] It is worth noting that with the rapid development of photovoltaic power generation technology and the continuous expansion of application scenarios, photovoltaic modules are increasingly widely used in the field of building-integrated photovoltaics (BIPV). Traditional photovoltaic modules mostly adopt the aforementioned white design scheme, usually by pairing them with white backsheets or white EVA films to enhance light reflection, thereby improving solar energy utilization and thus increasing module power generation efficiency. However, in addition to the aforementioned performance defects, this design also has obvious application compatibility issues: on the one hand, the color difference between white modules and crystalline silicon cells is significant, seriously affecting the overall aesthetics of buildings; on the other hand, in application scenarios such as rooftop distributed power stations, the light reflection generated by white modules can easily cause light pollution, and this issue is already subject to relevant regulations.

[0008] To address the aforementioned issues of aesthetic compatibility and light pollution, the market demand for black photovoltaic modules is gradually emerging. Black modules can better integrate with the building environment while effectively reducing light pollution. Currently, the mainstream approach to achieving black modules is primarily through the use of black backsheets or black aluminum frames.

[0009] To improve the overall performance of black modules, researchers have conducted various attempts, such as adding thermally conductive fillers to the encapsulant film to enhance heat dissipation and using a black high-reflectivity backsheet. However, these methods generally have limitations: for example, adding thermally conductive fillers may cause the black film to turn white, disrupting the appearance consistency of the black module; and the high UV cutoff encapsulant film placed between the backsheet and the cells will reduce the effective light utilization rate. Therefore, developing a black encapsulant film that can simultaneously solve multiple problems such as appearance compatibility, light pollution, infrared heat dissipation, PID protection, and light utilization rate has become a key research focus in the photovoltaic field to meet the development needs of BIPV.

[0010] Several invention patents have been developed to address the issues of improving the reflectivity of photovoltaic modules, reducing their operating temperature, enhancing PID performance, and extending their lifespan.

[0011] In addition, patent application CN117467363A discloses a high-reflectivity black photovoltaic encapsulant film and its preparation method. The encapsulant film includes a white high-reflectivity encapsulant film layer, a black heat-resistant base layer, and a transparent EVA encapsulant film layer arranged sequentially from bottom to top. However, this structure is actually closer to a composite sheet with a black heat-resistant base film as the core and EVA coated on both sides, rather than a traditional all-EVA encapsulation film. On the one hand, the high-melting-point, rigid black heat-resistant base layer such as PET / PVDF has a large difference in thermal expansion coefficient and modulus compared to flexible EVA. Under long-term temperature cycling, the interface is prone to large shear stress, which may lead to reliability issues such as delamination and warping. On the other hand, the patent does not limit the infrared optical performance of the black heat-resistant base layer. Its "black" layer may still have strong absorption in the near-infrared band. Some of the light reflected back from the white high-reflectivity layer is absorbed again when passing through the black layer, making it difficult to effectively reduce the infrared absorption and operating temperature of the module in a timely manner.

[0012] The existing technology has the following drawbacks: 1. The color difference between traditional white photovoltaic modules and crystalline silicon cells is significant, affecting aesthetics. Furthermore, light pollution caused by white light reflection in locations such as rooftops of distributed power stations is subject to regulatory restrictions. 2. Existing black modules mainly use black backsheets or black aluminum frames. Issues include the possibility of thermally conductive fillers causing the black film to turn white, affecting aesthetics, and the UV high-cutoff film affecting light utilization. 3. Currently used black high-reflectivity films have strong absorption in the infrared band, causing the module temperature to rise by 5-10℃, reducing power generation efficiency and shortening lifespan. 4. In existing technologies, the raw material ratio between the black and white high-reflectivity layers is not yet optimal, requiring further research to find a better ratio. 5. While improving reflectivity, existing black encapsulation films often neglect optimizing film thickness, resulting in a thicker film that affects the overall performance and aesthetics of the module.

[0013] In summary, existing EVA films generally suffer from insufficient reflectivity, leading to poor module cooling performance, weak PID protection, and low spectral utilization efficiency, failing to meet the upgrade requirements of high-efficiency photovoltaic modules for encapsulation materials. Therefore, developing a novel EVA film that combines high reflectivity, excellent heat dissipation performance, and strong PID suppression capability is of significant practical importance and industrial value for promoting the improvement of photovoltaic module efficiency and the extension of its lifespan. Summary of the Invention

[0014] To address the problems existing in the prior art, the present invention aims to design and provide a black and white high-reflectivity EVA film. The present invention constructs an EVA film by sequentially layering a black high-reflectivity layer and a white high-reflectivity layer, co-extruded together, and then pre-crosslinking the white film surface by irradiation. The black high-reflectivity layer, through the addition of specific infrared-reflective pigments to the EVA resin, possesses high infrared reflectivity. The synergistic effect of the black and white high-reflectivity layers results in a high reflectivity for the high-reflectivity black film, improving module power, reducing module temperature, and significantly reducing module power loss due to heat generation, making it particularly suitable for BIPV (Building Integrated Photovoltaics) scenarios.

[0015] The present invention adopts the following technical solution:

[0016] On the one hand, the present invention provides a black and white high-reflectivity EVA film, comprising a black high-reflectivity layer and a white high-reflectivity layer that are sequentially stacked and co-extruded.

[0017] The black high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix, and by weight of the matrix, the black high-reflectivity layer further comprises: 0.8–3.0 wt% infrared-reflective black pigment, 0.3–1.0 wt% crosslinking agent, 0.3–1.5 wt% coupling agent, 0.1–0.5 wt% antioxidant, 0.1–0.8 wt% light stabilizer, 0–0.5 wt% carbon black, and 0–3 wt% processing aids;

[0018] The white high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix. Based on the mass of the matrix, the white high-reflectivity layer further comprises: 8–25 wt% rutile titanium dioxide, 0.3–1.0 wt% crosslinking agent, 0.3–1.5 wt% coupling agent, 0.1–0.5 wt% antioxidant, 0.1–0.8 wt% light stabilizer, and 0–15 wt% inorganic filler and processing aids. The titanium dioxide is rutile or anatase titanium dioxide, with a D50 particle size of 0.1–0.5 μm in flake or nano-sized particles.

[0019] A small amount of carbon black is used only to adjust the blackness, and its mass fraction does not exceed 0.3 wt%.

[0020] The black and white high-reflection EVA film has an ethylene-vinyl acetate copolymer with a vinyl acetate content of 28-33 wt%.

[0021] The black and white high-reflectivity EVA film has a thickness ratio of 1:(0.9~1.1) between the black high-reflectivity layer and the white high-reflectivity layer.

[0022] Preferably, the total thickness of the black and white high-reflectivity EVA film is 0.45–0.55 mm, the thickness of the black high-reflectivity layer is 0.18–0.22 mm, and the thickness of the white high-reflectivity layer is 0.27–0.33 mm.

[0023] The aforementioned black and white high-reflectivity EVA film has a thickness ratio of 1:1 between the black high-reflectivity layer and the white high-reflectivity layer.

[0024] The black and white high-reflection EVA film is described above, wherein the light stabilizer is selected from at least one of ultraviolet absorbers or hindered amine light stabilizers;

[0025] The infrared reflective black pigment is selected from one or more of inorganic near-infrared reflective black pigments or perylene imide-based organic near-infrared reflective black pigments;

[0026] The crosslinking agent is selected from at least one of dicumyl peroxide, 1,1-di-tert-butylperoxide-3,3,5-trimethylcyclohexane, tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxide, trimethylolpropane triacrylate, triallyl isocyanurate, or pentaerythritol triacrylate.

[0027] The coupling agent is selected from at least one of vinyl silane coupling agents, methacryloxysilane coupling agents, amino silane coupling agents, epoxy silane coupling agents, and titanate coupling agents;

[0028] The antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, antioxidant 2246, antioxidant 168, antioxidant 626, and antioxidant DSTP;

[0029] The inorganic filler is selected from at least one of fumed silica, nano-calcium carbonate, talc, titanium dioxide, carbon black, mica powder, aluminum hydroxide, magnesium hydroxide, barium sulfate, or montmorillonite.

[0030] The processing aid is selected from at least one of lubricants, plasticizers, anti-blocking agents, and heat stabilizers.

[0031] The black and white structured high-reflectivity EVA film uses rutile titanium dioxide in the form of flakes or nano-sized particles with a D50 particle size of 0.1–0.5 μm. This structure can significantly increase the multiple reflection and scattering paths of light, improve diffuse reflectance, and endow the high-reflectivity EVA with a high reflectance in the infrared band.

[0032] The infrared reflective black pigment is selected from at least one of iron chromium black, copper chromium black, cobalt black, iron manganese black, nickel iron black, spinel-type inorganic IR black, non-spinel CICP, perylene black 32 or perylene black 31;

[0033] The light stabilizer is at least one of benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers.

[0034] Secondly, the present invention provides a method for preparing a black-and-white high-reflectivity EVA film according to any one of the claims, comprising the following steps:

[0035] Weigh out ethylene-vinyl acetate copolymer, infrared reflective black pigment, crosslinking agent, coupling agent, antioxidant, light stabilizer, carbon black and processing aid, premix them, melt blend and extrude them, cool them, stretch them into strips and cut them into pellets to obtain black high reflective EVA masterbatch;

[0036] Weigh out ethylene-vinyl acetate copolymer, rutile titanium dioxide, crosslinking agent, coupling agent, antioxidant, light stabilizer, inorganic filler and processing aid, premix them, melt blend and extrude them, cool them, stretch them into strips and cut them into pellets to obtain white high reflectance EVA masterbatch.

[0037] The aforementioned black high-reflectivity EVA masterbatch and white high-reflectivity EVA masterbatch are fed into the two extrusion channels of a co-extrusion die, respectively. The extrusion rate of the two extrusion channels is adjusted, and the film is extruded, cooled, and fixed in thickness to obtain a double-layer EVA film with black and white high-reflectivity layers. The white high-reflectivity layer side is used as the irradiation surface for irradiation pre-crosslinking, so that the pre-crosslinking degree of the white high-reflectivity layer is 25-35% and the melt flow index (ML) value is 0.35-0.45, thus obtaining a black-and-white high-reflectivity EVA film.

[0038] With the white high-reflectivity layer side as the outer side of the component, the reflectivity of the film in the 760-1100 nm band is not less than 85%, and the laminated appearance of the component is free from black overflow, white overflow, greening, and redding.

[0039] In the preparation method described above, the premixing time is 30–50 min;

[0040] The conditions for melt blending are: temperature 80~85℃;

[0041] The extrusion conditions are: temperature 30~50℃;

[0042] The conditions for the irradiation pre-crosslinking are: irradiation energy of 300–500 keV and irradiation dose of 15–23 kGy.

[0043] Thirdly, the present invention provides the use of the aforementioned black and white structured high-reflectivity EVA film in the preparation of building-integrated photovoltaic (BIPV) equipment.

[0044] Fourthly, the present invention provides a photovoltaic module comprising, in sequence from the light incident side, tempered glass, a transparent encapsulating film, a solar cell, a black and white high-reflective EVA film as described in any one of the claims, a backsheet or a second glass, wherein the black high-reflective layer faces the solar cell.

[0045] When in use, the black high-reflectivity layer of the photovoltaic module faces outwards.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. When the mass fraction of titanium dioxide in the white high-reflectivity layer of this invention is increased from 10 wt% to 20 wt%, the reflectivity of the white film layer in the 760–1100 nm wavelength band increases by at least 90 percentage points. Under the same battery cell and circuit design conditions, the output power of the black component encapsulated with the aforementioned film is increased by at least 5W compared to the component encapsulated with ordinary black EVA film.

[0048] 2. This invention irradiates the black film surface to achieve a pre-crosslinking degree of 25-35% between the black film and the white film layer. The laminated appearance is free of black overflow and green or red tinge. The fluidity ML value is 0.35-0.45, and the finishing fluidity is appropriate, ensuring a normal appearance and guaranteeing that the laminated component has no white overflow or green tinge.

[0049] 3. This invention optimizes the ratio of black and white structures by using specific raw material ratios in the black and white high-reflectivity layers respectively. The reflectivity of the EVA film in the 760-1100nm infrared band can reach more than 85%, thereby reducing the temperature of the module during use and improving the module power generation efficiency. This effectively solves the problem of module temperature rise caused by strong absorption in the infrared band of black modules in the prior art.

[0050] 4. The black and white high-reflectivity EVA film of the present invention can reduce the temperature of the module during use by 5-10℃, significantly improve the power generation efficiency of the module, extend the service life of the module, overcome the short service life of traditional black modules, and greatly improve PID performance.

[0051] 5. By rationally designing the thickness ratio of the black high-reflectivity layer to the white high-reflectivity layer (1:0.9 to 1:1.1), this invention enables the film to have good mechanical and optical properties, while ensuring the overall performance and aesthetics of the component.

[0052] 6. This invention uses a specific light stabilizer, which effectively improves the UV stability of the film, reduces performance degradation caused by UV light, and extends the service life of the component.

[0053] 7. This invention further improves the depth and purity of black by adding infrared reflective black pigment to the black high reflective layer, making the components better match the building environment, reducing light pollution, and solving the problem of color mismatch between traditional white components and crystalline silicon cells. Attached Figure Description

[0054] Figure 1 This is a schematic diagram illustrating the reflection principle of the product of the present invention;

[0055] Figure 2 The graph shows the reflectance data of the black film layer in Example 1 and Comparative Example 1.

[0056] Figure 3 The diagram shows the client verification results for Example 7 and Comparative Example 1. Detailed Implementation

[0057] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0058] Example 1:

[0059] A method for preparing a black-and-white high-reflectivity EVA film includes the following steps:

[0060] 1) Black layer granulation: Weigh ethylene-vinyl acetate copolymer (with vinyl acetate content of 30wt%), and add spinel-type inorganic IR black 2.0 wt%, dicumyl peroxide 0.6 wt%, titanate coupling agent 1.0 wt%, antioxidant 1010 0.3 wt%, benzotriazole UV absorber 0.5 wt%, carbon black 0.2 wt%, lubricant and plasticizer 1 wt% in total, premix in a high-speed mixer for 30 min, melt blend in an extruder at 85℃, extrude at 30℃, cool, draw into strands, and granulate to obtain black high-reflectivity EVA masterbatch;

[0061] 2) White layer granulation: Weigh ethylene-vinyl acetate copolymer, and add 10 wt% of flaky rutile titanium dioxide with a D50 particle size of 0.1-0.5 μm, 0.6 wt% of trimethylolpropane triacrylate, 1.0 wt% of titanate coupling agent, 0.3 wt% of antioxidant 168, 0.5 wt% of benzophenone-based ultraviolet absorber, and 10 wt% of fumed silica, lubricant and plasticizer, based on the mass of ethylene-vinyl acetate copolymer. After premixing, melt blend at 85℃ and granulate to obtain white high-reflectivity EVA masterbatch.

[0062] 3) Black and white co-extrusion film formation: Black high-reflectivity EVA masterbatch and white high-reflectivity EVA masterbatch are fed into the two extrusion channels of the co-extrusion die head respectively. The extrusion amount of each channel is adjusted so that the thickness ratio of black and white layers is black:white = 1:1. After forming, cooling and thickness fixing by the co-extrusion die head, a black and white double-layer structure EVA film is obtained.

[0063] 4) White surface irradiation pre-crosslinking: Using one side of the white high-reflectivity layer as the irradiation surface, irradiation treatment is performed under a 400 keV electron beam with an irradiation dose of 20 kGy, resulting in a pre-crosslinking degree of 38% and an ML value of 0.38 for the white high-reflectivity layer. A schematic diagram of the reflection principle of the product of this invention is shown below. Figure 1 As shown.

[0064] Comparative Example 1: Ordinary Black Component

[0065] Purchase a common black component from the market as the product for comparison example 1.

[0066] A comparison of the results of Example 1 and Comparative Example 1 shows that Comparative Example 1 uses an irradiated white film surface. In contrast, Example 1 uses an irradiated black film surface, which increases the pre-crosslinking degree to 38%. The laminated appearance shows no black overflow, no greening, and no reddish tinge. The flowability ML value is 0.38, indicating appropriate flowability and ensuring a normal appearance, thus preventing white overflow and greening in the laminated module. Furthermore, the reflectivity performance of the products from Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 2 As shown, the black film reflectance of the product in Example 1 of this invention is about 90% at a wavelength of 760-1100nm; while the black film reflectance of the product in Comparative Example 1 is 72-85% at a wavelength of 760-1100nm. The advantages of the product of this invention are significant.

[0067] Example 2:

[0068] The experiment was conducted following the same steps as in Example 1, except that the 10 wt% rutile titanium dioxide raw material used in white layer granulation was changed to 20 wt% rutile titanium dioxide.

[0069] Example 3:

[0070] The experiment was conducted following the same steps as in Example 1, except that the raw material rutile titanium dioxide was changed from 10 wt% to 10 wt% anatase titanium dioxide during white layer granulation.

[0071] The reflectivity was tested at wavelengths of 760-1100nm, and the results are shown in Table 1 below.

[0072] Table 1. Results of reflectance data of the white film layer of the products prepared in Examples 1-3

[0073]

[0074] Based on the results of Examples 1-3, it is shown that by adjusting the amount of titanium dioxide added, the present invention increases the content of rutile titanium dioxide by half, thereby increasing the reflectivity of the white film layer by about 4%. Furthermore, compared to anatase titanium dioxide (Example 3), rutile titanium dioxide (Example 1) has a higher refractive index, making it more effective at reflecting visible light.

[0075] Example 4:

[0076] A method for preparing a black-and-white high-reflectivity EVA film includes the following steps:

[0077] 1) Black layer granulation: Weigh ethylene-vinyl acetate copolymer (with vinyl acetate content of 28wt%), and add perylene black 32 0.8 wt%, pentaerythritol triacrylate 0.3 wt%, vinyl silane coupling agent 0.3 wt%, antioxidant 626 0.1 wt%, and triazine UV absorber 0.1 wt% based on the mass of ethylene-vinyl acetate copolymer. After premixing in a high-speed mixer for 30 min, melt blend in an extruder at 80℃, extrude at 35℃, cool, stretch, and granulate to obtain black high-reflectivity EVA masterbatch;

[0078] 2) White layer granulation: Weigh ethylene-vinyl acetate copolymer (of which vinyl acetate content is 28wt%), and add 8wt% nano-sized rutile titanium dioxide, 0.3wt% trimethylolpropane triacrylate, 0.3wt% epoxy silane coupling agent, 0.1wt% antioxidant DSTP, and 0.1wt% benzotriazole UV absorber based on the mass of ethylene-vinyl acetate copolymer. After premixing, melt blend and granulate at 80℃ to obtain white high reflectance EVA masterbatch;

[0079] 3) Black and white co-extrusion film formation: Black high-reflection EVA masterbatch and white high-reflection EVA masterbatch are fed into the two extrusion channels of the co-extrusion die, and the extrusion amount of each channel is adjusted so that the thickness ratio of black and white layers is black:white = 1:1.1. After forming, cooling and thickness fixing by the co-extrusion die, a black and white double-layer EVA film is obtained.

[0080] 4) White surface irradiation pre-crosslinking: Using one side of the white high reflectivity layer as the irradiation surface, the white high reflectivity layer is irradiated with an electron beam of 300 keV and an irradiation dose of 15 kGy to achieve a pre-crosslinking degree of 27% and an ML value of 0.36.

[0081] Example 5:

[0082] A method for preparing a black-and-white high-reflectivity EVA film includes the following steps:

[0083] 1) Black layer granulation: Weigh ethylene-vinyl acetate copolymer (with vinyl acetate content of 28wt%), and add perylene black 32 0.8 wt%, pentaerythritol triacrylate 0.3 wt%, vinyl silane coupling agent 0.3 wt%, antioxidant 626 0.1 wt%, and triazine UV absorber 0.1 wt% based on the mass of ethylene-vinyl acetate copolymer. After premixing in a high-speed mixer for 30 min, melt blend in an extruder at 80℃, cool, draw into strands, and granulate to obtain black high-reflectivity EVA masterbatch;

[0084] 2) White layer granulation: Weigh ethylene-vinyl acetate copolymer (of which vinyl acetate content is 28wt%), and add 8wt% nano-sized rutile titanium dioxide, 0.3wt% trimethylolpropane triacrylate, 0.3wt% epoxy silane coupling agent, 0.1wt% antioxidant DSTP, and 0.1wt% benzotriazole UV absorber based on the mass of ethylene-vinyl acetate copolymer. After premixing, melt blend and granulate at 80℃ to obtain white high reflectance EVA masterbatch;

[0085] 3) Black and white co-extrusion film formation: Black high-reflectivity EVA masterbatch and white high-reflectivity EVA masterbatch are fed into the two extrusion channels of the co-extrusion die, and the extrusion amount of each channel is adjusted so that the thickness ratio of black and white layers is black:white = 1:0.9. After forming, cooling and thickness fixing by the co-extrusion die, a black and white double-layer EVA film is obtained.

[0086] 4) White surface irradiation pre-crosslinking: Using the white high reflectivity layer side as the irradiation surface, irradiate it with an electron beam of 300 keV and an irradiation dose of 15 kGy.

[0087] Comparative Example 2:

[0088] The experiment was conducted following the same steps as in Example 4, except that the black-white layer thickness ratio was changed from black:white = 1:1 to black:white = 1:1.22.

[0089] Comparative Example 3:

[0090] The experiment was conducted following the same steps as in Example 4, except that the black-white layer thickness ratio was changed from black:white = 1:1 to black:white = 1:1.50.

[0091] The reflectance of the black film layer at wavelengths of 760-1100 nm was tested on the products prepared in Example 4, Comparative Examples 2 and 3, and the results are shown in Table 2 below.

[0092] Table 2. Reflectance results of the black film layer of products with different black and white film structure thickness ratios prepared in Example 4 and Comparative Examples 2 and 3.

[0093]

[0094] As can be seen from Table 2, the best effect is achieved when the thickness ratio of the black and white layers in this invention is 1:1. The effect is not as good as when the thickness ratio is 1:1.22 and 1:1.5, but it is still much higher than the reflectivity of the prior art (such as Comparative Example 1).

[0095] Comparative Example 4:

[0096] The experiment was conducted using the same procedures as in Example 1, with the only changes being: white granulation was omitted, and the product did not contain a white reflective layer. The resulting EVA film had a pre-crosslinking degree of 22%, an ML value of 0.47, and a reflectance of 0.4% at wavelengths of 760-1100 nm.

[0097] Comparative Example 5:

[0098] The experiment was conducted using the same steps as in Example 1, with the only changes being: black granulation was omitted, and the product did not contain a black reflective layer. The resulting EVA film had a pre-crosslinking degree of 25%, an ML value of 0.46, and a reflectance of 58% at wavelengths of 760-1100 nm.

[0099] Comparative Example 6:

[0100] A black and white bilayer EVA film was prepared using the same method as in Example 1; the difference lies in the irradiation crosslinking method. In this invention, the black side is pre-crosslinked by irradiation: the black high-reflectivity layer side is used as the irradiation surface, and irradiation is performed under a 400 keV electron beam with an irradiation dose of 20 kGy, resulting in a pre-crosslinking degree of 18% for the black high-reflectivity layer, an ML value of 0.52, and a reflectivity of 78.5% at wavelengths of 760-1100 nm. The laminated appearance exhibits black overflow, green tinge, and reddish tinge.

[0101] Example 6: Photovoltaic Module

[0102] Photovoltaic modules were fabricated using the EVA films obtained in Examples 1-5 and Comparative Examples 1-5, respectively. The fabrication method included: sequentially stacking tempered glass, transparent encapsulating film, solar cells, black-and-white high-reflective EVA film, and backsheet from the light incident side to obtain photovoltaic modules.

[0103] Perform client-side verification results, such as Figure 3 As shown, the photovoltaic modules prepared using the EVA films obtained in Comparative Example 1 and Example 1 exhibit significant power differences. The power output of the module of the present invention is approximately 5W higher than that of the ordinary black module. The PID performance of the photovoltaic modules prepared using the EVA films obtained in Examples 1-5 and Comparative Examples 1-5 was also tested, and the results are shown in Table 3 below.

[0104] Table 3 PID performance results data

[0105]

[0106] As can be seen, the photovoltaic modules (Examples 1-5) prepared using the black and white structure high reflective EVA film of the present invention, after being tested for 192H and 288H in a high temperature and high humidity environment, have better open circuit voltage (Uoc), short circuit current (Isc), maximum output power (Pmpp) and fill factor (FF) than the modules prepared using the existing encapsulant film (Comparative Examples 1-4). Comparative Example 6 shows a module encapsulated with a film made using an irradiated black high-reflectivity layer. In the 192H and 288H PID tests, its open-circuit voltage, short-circuit current, maximum output power, and fill factor were significantly lower than those of Examples 1-5 of this application, and inferior to the ordinary black module of Comparative Example 1. This is mainly because the black high-reflectivity layer contains infrared-reflecting black pigment and a small amount of carbon black. These dark fillers have strong absorption, shielding, and scattering effects on electron beams, making it difficult for electron beam energy to penetrate the black layer and reach the white high-reflectivity layer. Simultaneously, the black layer itself is locally over-cured, while the white layer is almost not effectively irradiated, ultimately resulting in severely uneven cross-linking between the two layers and a significantly insufficient overall effective cross-linking degree. This leads to severely insufficient cross-linking degree of the encapsulated film, fluidity imbalance, a significant decrease in infrared reflection performance and volume resistivity, and an inability to effectively block metal ion migration, resulting in accelerated PID degradation and a significant reduction in long-term reliability. This indicates that compared with existing technologies, the photovoltaic module of this invention has significantly improved PID performance, effectively suppressing power degradation under high temperature and high humidity environments and significantly extending the module's service life.

Claims

1. A black-and-white high-reflectivity EVA film, characterized in that, It comprises a black high-reflection layer and a white high-reflection layer that are sequentially stacked and co-extruded; The black high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix, and by weight of the matrix, the black high-reflectivity layer further comprises: 0.8–3.0 wt% infrared-reflective black pigment, 0.3–1.0 wt% crosslinking agent, 0.3–1.5 wt% coupling agent, 0.1–0.5 wt% antioxidant, 0.1–0.8 wt% light stabilizer, 0–0.5 wt% carbon black, and 0–3 wt% processing aids; The white high-reflectivity layer uses ethylene-vinyl acetate copolymer as a matrix, and by weight of the matrix, the white high-reflectivity layer further comprises: 8-25 wt% titanium dioxide, 0.3-1.0 wt% crosslinking agent, 0.3-1.5 wt% coupling agent, 0.1-0.5 wt% antioxidant, 0.1-0.8 wt% light stabilizer, and 0-15 wt% inorganic filler and processing aid.

2. The black and white high-reflectivity EVA film as described in claim 1, characterized in that, The vinyl acetate content of the ethylene-vinyl acetate copolymer is 28–33 wt%. The titanium dioxide is rutile titanium dioxide or anatase titanium dioxide.

3. The black and white high-reflectivity EVA film as described in claim 1, characterized in that, The thickness ratio of the black high-reflectivity layer to the white high-reflectivity layer is 1:(0.9~1.1).

4. The black and white high-reflectivity EVA film as described in claim 1, characterized in that, The thickness ratio of the black high-reflectivity layer to the white high-reflectivity layer is 1:

1.

5. The black and white high-reflectivity EVA film as described in claim 1, characterized in that, The light stabilizer is selected from at least one of ultraviolet absorbers or hindered amine light stabilizers; The infrared reflective black pigment is selected from one or more of inorganic near-infrared reflective black pigments or perylene imide-based organic near-infrared reflective black pigments; The crosslinking agent is selected from at least one of dicumyl peroxide, 1,1-di-tert-butylperoxide-3,3,5-trimethylcyclohexane, tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxide, trimethylolpropane triacrylate, triallyl isocyanurate, or pentaerythritol triacrylate. The coupling agent is selected from at least one of vinyl silane coupling agents, methacryloxysilane coupling agents, amino silane coupling agents, epoxy silane coupling agents, and titanate coupling agents; The antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, antioxidant 2246, antioxidant 168, antioxidant 626, and antioxidant DSTP; The inorganic filler is selected from at least one of fumed silica, nano-calcium carbonate, talc, titanium dioxide, carbon black, mica powder, aluminum hydroxide, magnesium hydroxide, barium sulfate, or montmorillonite. The processing aid is selected from at least one of lubricants, plasticizers, anti-blocking agents, and heat stabilizers.

6. The black and white high-reflectivity EVA film as described in claim 1, characterized in that, The titanium dioxide is rutile titanium dioxide in the form of flakes or nano-sized particles with a D50 particle size of 0.1 to 0.5 μm. The infrared reflective black pigment is selected from at least one of iron chromium black, copper chromium black, cobalt black, iron manganese black, nickel iron black, spinel-type inorganic IR black, non-spinel CICP, perylene black 32 or perylene black 31; The light stabilizer is at least one of benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers.

7. A method for preparing a black-and-white high-reflectivity EVA film according to any one of claims 1-6, characterized in that, Includes the following steps: Weigh out ethylene-vinyl acetate copolymer, infrared reflective black pigment, crosslinking agent, coupling agent, antioxidant, light stabilizer, carbon black and processing aid, premix them, melt blend them, extrude them, cool them, stretch them into strips and granulate them to obtain black high reflective EVA masterbatch. Weigh out ethylene-vinyl acetate copolymer, rutile titanium dioxide, crosslinking agent, coupling agent, antioxidant, light stabilizer, inorganic filler and processing aid, premix them, melt blend them, extrude them, cool them, stretch them into strips and granulate them to obtain white high reflectance EVA masterbatch. The black high-reflectivity EVA masterbatch and the white high-reflectivity EVA masterbatch are fed into the two extrusion channels of the co-extrusion die, respectively. The extrusion amount of the two extrusion channels is adjusted, and the film is extruded, cooled, and fixed in thickness to obtain a double-layer EVA film with black and white high-reflectivity layers. The white high-reflectivity layer side is used as the irradiation surface for irradiation pre-crosslinking to obtain a black and white high-reflectivity black EVA film.

8. The preparation method according to claim 7, characterized in that, The premixing time is 30–50 min; The conditions for melt blending are: temperature 80~85℃; The extrusion conditions are: temperature 30~50℃; The conditions for the irradiation pre-crosslinking are: irradiation energy of 300–500 keV and irradiation dose of 15–23 kGy.

9. The use of the black and white high-reflectivity EVA film as described in claim 1 in the preparation of building-integrated photovoltaic equipment.

10. A photovoltaic module, characterized in that, It includes tempered glass, transparent encapsulating film, battery cell, black and white high-reflective EVA film as described in any one of claims 1-6, back sheet or second glass, which are stacked sequentially from the light incident side. When in use, the black high-reflectivity layer of the photovoltaic module faces outwards.

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