Process for reducing adhesive property of photovoltaic EVA (Ethylene Vinyl Acetate) by utilizing supercritical fluid

Abstract

The invention discloses a process for reducing the adhesive property of a photovoltaic EVA (Ethylene Vinyl Acetate) adhesive film by utilizing supercritical fluid, which comprises the following steps of: (1) cutting a photovoltaic module into small blocks of 20mm * 20mm, and putting an assistant cross-linking agent and a green cosolvent into a reaction kettle together through formula engineering; (2) heating the reaction kettle, introducing CO2 and pressurizing; (3) carrying out heat preservation treatment for 0.5-1 hour under the condition of stable temperature and pressure; (4) quickly releasing pressure and cooling to form a porous structure at the interface of the EVA adhesive film; and (5) taking out the treated photovoltaic module, and stripping the EVA adhesive film foam for recycling. Through the synergistic effect of supercritical CO2 and a cosolvent, an EVA adhesive film interface processing aid migrates inwards, the crosslinking degree of the EVA adhesive film is further increased to 98.6%, the interaction with a back plate is reduced by forming a porous structure on the EVA adhesive film interface, the porosity reaches 85%, the contact area is reduced, the bonding strength of the EVA adhesive film is remarkably reduced, and the peel strength is reduced by 70% or above.

Description

Technical Field

[0001] The present invention relates to a processing technology of photovoltaic adhesive films, and more specifically to a technology for reducing the bonding performance of photovoltaic EVA adhesive films by using supercritical fluids. Background Art

[0002] With the rapid development and continuous technological upgrading of the photovoltaic industry, the problem of recycling and reusing retired photovoltaic modules has become increasingly prominent and has become the key to promoting the sustainable development of the photovoltaic industry. However, in the process of recycling and reusing photovoltaic modules, the primary technical problem faced is how to efficiently disassemble photovoltaic modules, and the core challenge in module disassembly lies in removing the bonding performance of photovoltaic adhesive films.

[0003] The lamination structure of a photovoltaic module usually consists of five layers of materials: glass, organic adhesive film, solar cells, organic adhesive film, and backsheet. The photovoltaic EVA adhesive film among them forms a stable three-dimensional network structure through cross-linking reactions during the module encapsulation process. This cross-linked structure endows the EVA adhesive film with excellent durability and mechanical properties, but at the same time, it tightly binds to the glass and the backsheet, with extremely high and irreversible bonding strength, thus greatly increasing the difficulty of module disassembly. In addition, since both the adhesive film and the backsheet are polymer materials, their strong bonding performance has become the main obstacle restricting the disassembly and recycling efficiency of photovoltaic modules.

[0004] Currently, the mainstream technologies for disassembling photovoltaic modules can be divided into the following three methods:

[0005] ① Physical method: mainly mechanical crushing, separating the photovoltaic module by external force. However, the physical method fails to effectively process the EVA adhesive film, and it is difficult to obtain high-purity recycled materials even through subsequent sorting processes.

[0006] ② Pyrolysis method: using high temperature to thermally degrade the photovoltaic adhesive film to weaken its bonding performance. Although the pyrolysis method can achieve module disassembly to a certain extent, a large amount of waste gas is generated during its operation, posing a potential risk of environmental pollution.

[0007] ③ Chemical solvent method: chemically dissolving the EVA adhesive film with an organic solvent to separate the adhesive film from other materials. However, this method inevitably generates waste liquid during the processing, bringing certain risks to the ecological environment and industrial safety.

[0008] In summary, although the above methods can achieve the disassembly of photovoltaic modules to a certain extent, they all have problems such as low efficiency, high cost, and serious environmental pollution, and are difficult to meet the green and efficient requirements of the recycling of the photovoltaic industry. Therefore, it is urgent to develop a green and environmentally friendly technology for efficiently reducing the bonding performance of adhesive films, which is crucial for the sustainable development of the recycling of retired photovoltaic modules. Summary of the Invention

[0009] In order to solve the problem of difficult peeling between the EVA film and the backsheet of photovoltaic modules in the prior art, by utilizing the high-efficiency permeability of supercritical CO2 fluid and the synergistic effect of green co-solvents, combined with crosslinking aid formulation engineering and process flow, the bonding performance between the EVA film and the backsheet is significantly reduced, thereby realizing the efficient recycling and environmental protection treatment of photovoltaic modules. Specifically, it includes the following steps:

[0010] A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid, characterized in that the process includes the following steps:

[0011] S1. Sample preparation: Use a cutting device to cut the photovoltaic module into small pieces of 20mm×20mm, and place the cut photovoltaic module sample together with 5 - 10 mL of green co-solvent in a reaction kettle;

[0012] S2. Temperature and pressure setting: Heat the reaction kettle to 30℃ - 150℃. After the kettle temperature is stable, introduce CO2 gas to pressurize the reaction kettle, and the pressurization range is 10MPa - 12 MPa;

[0013] S3. Heat preservation and saturation treatment: Under the conditions of stable kettle temperature and pressure, perform heat preservation and saturation treatment to ensure the synergistic effect of CO2 and co-solvent to modify the EVA film;

[0014] S4. Pressure relief and cooling: After the saturation treatment is completed, perform a pressure relief operation, and at the same time cool the reaction kettle to form a porous structure at the EVA film interface;

[0015] S5. Sample separation: After cooling is completed, remove the reaction kettle, take out the photovoltaic module sample, and separate the modified EVA foam layer.

[0016] Furthermore, the green co-solvent in S1 is one or a combination of two of ethanol or butanol, and the addition amount of the green co-solvent is 1% - 5% of the volume of the reaction kettle.

[0017] Furthermore, the heating temperature of the reaction kettle in S2 is 80 - 120℃ to ensure that supercritical CO2 is in a highly effective state.

[0018] Furthermore, the time for heat preservation and saturation treatment in S3 is 0.5 - 1h to ensure that the interfacial modification aid migrates sufficiently and reaches the best treatment effect.

[0019] Furthermore, the pressure relief time in S4 is 3 - 5s. By quickly relieving the pressure, a porous structure is formed, thereby significantly reducing the peeling strength between the film and the backsheet.

[0020] Furthermore, the cooling time in S4 is 2min to ensure the integrity of the sample structure and facilitate subsequent separation operations.

[0021] Furthermore, when the green co-solvent is ethanol, the formulation engineering of the co-crosslinking agent added is trimethylolpropane triacrylate C 15 H 20 O6, trimethylolpropane trimethacrylate C 18 H 26 O6, ethoxylated trimethylolpropane triacrylate C 21 H 32 O9 or propoxylated trimethylolpropane triacrylate [H2C=CHCO2(C3H6O) n CH2]3CC2H5, or a combination of one or more thereof.

[0022] Furthermore, the weight of the EVA film is 100 parts, the weight of the green co-solvent is 5 - 10 parts, and the weight of the co-crosslinking agent is 0.1 - 5 parts.

[0023] Furthermore, the pressure in S2 is 11 MPa, and CO2 under this pressure condition can enter the supercritical state to achieve the best permeability.

[0024] Beneficial effects:

[0025] The present invention provides a process for reducing the bonding performance of photovoltaic EVA using supercritical fluids, which specifically includes the following advantages:

[0026] (1) This method uses the synergistic effect of supercritical CO2 and green co-solvents (such as ethanol, butanol, etc.), avoiding the generation of waste gas and waste liquid in the pyrolysis method and chemical solvent method, and meeting the requirements of green environmental protection.

[0027] (2) After detection: Infrared spectroscopy analysis shows that after supercritical CO2 treatment, the main components of the EVA matrix have not changed significantly, but the surface VA content has decreased, and aromatic rings and groups such as N and Cl have migrated, which is caused by the migration of processing aids. This migration weakens the bonding strength on the surface of the film, laying a foundation for subsequent performance optimization. The water contact angle and diiodomethane contact angle have increased from 84° to 103° and from 34° to 52° respectively, and the surface of the material has changed from hydrophilic to hydrophobic, significantly reducing the surface adhesion. The interfacial tension results show that the interfacial tension of the film after foaming has increased from 5.32 mN / m to 10.18 mN / m, weakening the bonding strength. Enthalpy testing and crosslinking degree calculation show that the crosslinking degree of the EVA film has increased from 80.74% to 98.6%, and the material properties have changed from plastic to rigid, effectively reducing the viscosity, providing guarantee for the stability and lifespan of the photovoltaic film in complex environments. SEM observation and particle size distribution testing show that supercritical CO2 treatment significantly increases the average pore diameter of the bubbles (from 92.33 μm to 249.26 μm), the foam expansion ratio has increased to 15 times, and the porosity exceeds 85%. This effective regulation of the porous morphology endows the EVA film with more excellent lightweight and breathability characteristics. Due to the synergistic effects of multiple factors such as the migration of processing aids, the increase in crosslinking degree, the reduction of the interaction between the film and the backsheet, and the increase in porosity, the bonding strength between the film and the backsheet has been significantly reduced by more than 70%, and the optimization of this bonding strength improves the dismountability and reprocessing performance of the film.

[0028] (3) It can be widely applied to photovoltaic modules with EVA as the main component of the film, which has universality and strong adaptability to the component materials.

[0029] (4) The process is simple, can be promoted industrially, has a low operation cost, and meets the disassembly and recycling requirements of large-scale retired photovoltaic modules.

[0030] (5) By precisely controlling parameters such as temperature, pressure, and the amount of co-solvent, this method has excellent repeatability and controllability, ensuring stable treatment effects. Description of the Drawings

[0031] Figure 1 (a) is the infrared spectrum of the example, Figure 1 (b), (c) are the partial enlarged views of the infrared spectrum of the example, Figure 1 (d) is the thermogravimetric TGA graph.

[0032] Figure 2 is the DSC curve graph of the example.

[0033] Figure 3 (a), (b), (c) are the water contact angles of the example, and (a1), (b1), (c1) are the diiodomethane contact angles.

[0034] Figure 4 It is a diagram for regulating the porous morphology of the embodiment.

[0035] Figure 5 It is a diagram showing the change of the peel strength of the embodiment with the foam porosity.

[0036] Figure 6 It is a comparison table for the crosslinking degree test of the embodiment.

[0037] Figure 7 It is a comparison table for the solution contact angle test of the embodiment.

[0038] Figure 8 It is a comparison table between the embodiment and the comparative example.

[0039] Figure 9 It is a schematic diagram of the whole application. Detailed implementation manners

[0040] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in combination with embodiments. These embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0041] The present invention provides a process for reducing the bonding performance of photovoltaic EVA film by using supercritical fluid. The following are specific embodiments:

[0042] Step 1: Sample preparation

[0043] Use a cutting device to cut the retired photovoltaic module into small pieces with a size of 20 mm × 20 mm for easy processing in the reaction kettle.

[0044] Put the cut photovoltaic module sample into the reaction kettle, and at the same time add 8 mL of ethanol as a green co-solvent. The addition amount of ethanol is about 3% of the volume of the reaction kettle, which can effectively enhance the dissolution ability of supercritical CO2 and the modification effect on the EVA film.

[0045] Step 2: Temperature and pressure setting

[0046] Heat the reaction kettle and set the target temperature to 100 °C to make the temperature in the kettle stable in the optimal temperature range (80 °C - 120 °C) for the efficient action of supercritical CO2.

[0047] When the temperature in the kettle reaches the set value, introduce CO2 gas and pressurize the reaction kettle.

[0048] The pressure range is set to 11 MPa to ensure that CO2 is in a supercritical state and acts synergistically with the green co-solvent to significantly improve the bonding performance of the EVA film.

[0049] After the temperature and pressure are stable, start the next operation.

[0050] Step 3: Heat preservation and saturation treatment

[0051] Maintain the temperature in the reactor at 100 °C and the pressure at 11 MPa for heat preservation and saturation treatment.

[0052] Set the heat preservation time to 0.75 hours to ensure that supercritical CO2 and ethanol can fully penetrate into the interface between the EVA film and the backplane and effectively migrate the modifying additives at the interface.

[0053] Step 4: Pressure relief and cooling

[0054] After the heat preservation treatment, quickly perform the pressure relief operation.

[0055] The pressure relief duration is 4 seconds to form a porous structure at the interface and reduce the adhesive force of the film.

[0056] At the same time, cool the reactor. The cooling duration is 2 minutes. Quickly cool the reactor temperature to room temperature through a water cooling or air cooling system to ensure the stability of the sample structure.

[0057] Step 5: Sample separation

[0058] After cooling, open the reactor and take out the photovoltaic module sample.

[0059] Perform a separation operation on the treated sample. It is observed that the adhesive force between the EVA film and the backplane is significantly reduced, and the EVA film shows a porous foamed structure and can be easily peeled off and recycled.

[0060] Analysis of treatment effect

[0061] The embodiments of the present invention are based on supercritical CO2 foaming technology, combined with a green co-solvent (such as ethanol), and significantly reduce the adhesion performance of the EVA film through multiple action mechanisms. The specific effect analysis is as follows, and the result diagrams are shown in Figure 1 , 2 , 3, 4, 5, 6, 7 as follows:[[]]END]]

[0062] Figure 1 (a) is the infrared spectrum diagram of the embodiment. All the main characteristic peaks of the embodiment are consistent with those of the blank sample, indicating that the matrix material of the embodiment is EVA and the basic components have not changed significantly after supercritical treatment. Figure 1(b)-(c) are the partial enlarged infrared spectrograms of the examples. Compared with the untreated samples, the peak intensities of the examples decrease at 1610⁻¹ - 1620⁻¹, 1580⁻¹, 1540⁻¹, 1125⁻¹, 935⁻¹, 875⁻¹, etc., corresponding to the stretching vibration of C═C double bonds, the C═C vibration of aromatic rings, the bending vibration of N-H, the stretching vibration of C–O, the C-C═O stretching in vinyl acetate, the stretching vibration of C-Cl, etc. On the one hand, the VA content on the surface of the examples is lower than that of the untreated samples, which may weaken the plasticity of the examples; on the other hand, since the EVA pure sample does not contain aromatic ring structures and elements such as N and Cl, these groups can only come from the modification additives of the photovoltaic film. Thermogravimetric tests show that the composition of the samples before and after supercritical CO₂ treatment has not changed significantly. Combining the results of the two tests indicates that this method causes the migration of modification additive ions on the surface of the EVA film, weakening the bonding strength of the film surface.

[0063] Figure 2 Figure 4 is the DSC curve of the example. The crosslinking degree of the prepared samples was tested by the DSC method. The crosslinking degree is obtained from Equation (1):

[0064]

[0065] where G is the crosslinking degree of EVA (%), H1 is the enthalpy value of the uncrosslinked sample (J / g), and H2 is the remaining enthalpy value of the crosslinked sample (J / g). The test data are as Figure 6 shown in the table:

[0066] The above DSC test results show that this method further improves the crosslinking degree of the EVA film. Before and after supercritical CO₂ treatment, the crosslinking degree of the photovoltaic film increases from 80.74% to 98.6%, making it transform from plasticity to rigidity and effectively reducing the viscosity of the film.

[0067] Figure 3 Figures 5(a)-(c) are the water contact angles and Figures 5(a1)-(c1) are the diiodomethane contact angles of the examples. Among them, the test material for (a)-(a1) is the photovoltaic backplane (adhesive film side), the test material for (b)-(b1) is the photovoltaic film (adhesive backplane side), and the test material for (c)-(c1) is the photovoltaic film foam after supercritical foaming treatment (adhesive backplane side). For the water contact angle, before and after supercritical foaming treatment, the water contact angle increases from 84° to 103°, and the material changes from hydrophilic to hydrophobic. For the diiodomethane contact angle, before and after supercritical foaming treatment, the contact angle increases from 34° to 52°. The surface energy of the material is calculated from the test results of the contact angles of the two solutions, and then the interfacial tension is calculated. The results show that before and after supercritical foaming treatment, the interfacial tension at the backplane-film interface increases from 5.32 mN / m to 10.18 mN / m, indicating that the interfacial bonding effect is weakened. The relevant experimental results are as Figure 7 shown in the table.

[0068] Figure 4 are the SEM images, particle size distribution diagrams, and nano-profile diagrams of EVA foams after being treated by different processes for photovoltaic encapsulant films. Under specific process treatments, the average pore diameter of the EVA foam pores increases from 92.33 μm to 249.26 μm, the foam expansion ratio can be increased to 15 times, and the porosity is increased to more than 85%, indicating that supercritical CO2 foaming treatment can effectively regulate the porous morphology of the EVA encapsulant film.

[0069] Figure 5 are the changes in the peel strength between the backsheet and the encapsulant film after different processes for photovoltaic encapsulant films with respect to the foam porosity. The synergistic effects of surface ion migration, increased crosslinking degree and interfacial tension, and changes in the porous morphology and porosity effectively reduce the adhesion strength at the backsheet-encapsulant film interface by more than 70%.

[0070] Example 1 is the treatment process of this application. The experimental temperature is 85 °C, the test pressure is 10 MPa, the saturation time is 45 min, the co-solvent is 2%, the co-crosslinking agent is 0.1%, and the peel strength is 29.97 N / cm.

[0071] Example 2 is the treatment process of this application. The experimental temperature is 80 °C, the test pressure is 11 MPa, the saturation time is 60 min, the co-solvent is 4%, the co-crosslinking agent is 1%, and the peel strength is 27.42 N / cm.

[0072] Example 3 is the treatment process of this application. The experimental temperature is 90 °C, the test pressure is 10 MPa, the saturation time is 45 min, the co-solvent is 10%, the co-crosslinking agent is 2%, and the peel strength is 22.38 N / cm.

[0073] Example 4 is the treatment process of this application. The experimental temperature is 105 °C, the test pressure is 12 MPa, the saturation time is 45 min, the co-solvent is 8%, the co-crosslinking agent is 5%, and the peel strength is 19.73 N / cm.

[0074] Comparative Example 1 is the existing chemical solvent method. The experimental temperature is 80 °C, the test pressure is 10 MPa, the saturation time is 45 min, the co-solvent is 2%, the co-crosslinking agent is 2%, and the peel strength is 38.57 N / cm.

[0075] Comparative Example 2 is the existing chemical solvent method. The experimental temperature is 80 °C, the test pressure is 11 MPa, the saturation time is 30 min, the co-solvent is 4%, the co-crosslinking agent is 3%, and the peel strength is 30.26 N / cm.

[0076] Comparative Example 3 is the existing chemical solvent method. The experimental temperature is 90 °C, the test pressure is 10 MPa, the saturation time is 45 min, the co-solvent is 2%, there is no co-crosslinking agent, and the peel strength is 44.92 N / cm.

[0077] Comparative Example 4 is the existing chemical solvent method. The experimental temperature is 105 °C, the test pressure is 12 MPa, the saturation time is 45 min, the co-solvent is 4%, there is no co-crosslinking agent, and the peel strength is 39.42 N / cm.

[0078] As a further improvement, the above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid, characterized in that, The process described above includes the following steps: S1. Sample preparation: Use a cutting device to cut the photovoltaic module into small pieces of 20mm×20mm, and place the cut photovoltaic module sample together with 5 - 10 mL of green co - solvent and co - crosslinking agent in a reaction kettle; S2. Temperature and pressure setting: Heat the reaction kettle to 30℃ - 150℃. After the kettle temperature is stable, introduce CO2 gas to pressurize the reaction kettle, and the pressure range is 10MPa - 12 MPa; S3. Heat preservation and saturation treatment: Under the conditions of stable kettle temperature and pressure, conduct heat preservation and saturation treatment to ensure that CO2 and co - solvent act synergistically to modify the EVA film; S4. Pressure relief and cooling: After the saturation treatment is completed, perform a pressure relief operation, and at the same time cool the reaction kettle to form a porous structure at the interface of the EVA film; S5. Sample separation: After cooling is completed, remove the reaction kettle, take out the photovoltaic module sample, and separate the modified EVA foam layer.

2. The process for reducing the bonding performance of photovoltaic EVA by using supercritical fluid according to claim 1, characterized in that, The green co - solvent in S1 is one or a combination of two of ethanol or butanol, and the addition amount of the green co - solvent is 1% - 5% of the volume of the reaction kettle.

3. A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid according to claim 1, characterized in that, The heating temperature of the reaction kettle in S2 is 80 - 120℃.

4. A process for reducing the bonding performance of photovoltaic EVA by using supercritical fluid according to claim 1, characterized in that, The time for heat preservation and saturation treatment in S3 is 0.5 - 1h.

5. A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid according to claim 1, characterized in that, The pressure relief time in S4 is 3 - 5s.

6. A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid according to claim 1, characterized in that, The cooling time in S4 is 2min.

7. A process for reducing the bonding performance of photovoltaic EVA using supercritical fluid according to claim 2, characterized in that, When the green co-solvent is ethanol, the formulation engineering of the co-crosslinking agent added is trimethylolpropane triacrylate C 15 H 20 O6, trimethylolpropane trimethacrylate C 18 H 26 O6, ethoxylated trimethylolpropane triacrylate C 21 H 32 O9 or propoxylated trimethylolpropane triacrylate [H2C=CHCO2(C3H6O) n CH2]3CC2H5, or a combination of one or more thereof.

8. A process for reducing the adhesion performance of photovoltaic EVA by using supercritical fluid according to claim 7, characterized in that The weight of the EVA film is 100 parts, the weight of the green co - solvent is 5 - 10 parts, and the weight of the co - crosslinking agent is 0.1 - 5 parts.

9. A process for reducing the bonding performance of photovoltaic EVA by using supercritical fluid according to claim 1, characterized in that, The pressure in S2 is 11MPa.

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