A method for recycling photovoltaic backsheets

Abstract

This invention discloses a method for recycling photovoltaic backsheets, belonging to the field of polymer material recycling. This method employs a specific two-stage separation process to treat the photovoltaic backsheet, which can effectively separate and recover the adhesive components in the raw material, as well as recover the outer layer material and recycled PET material with a high recovery rate. Furthermore, the obtained recycled PET material has high purity and can be used directly, resulting in high overall economic benefits from recycling.

Description

Technical Field

[0001] This invention relates to the field of polymer material recycling technology, specifically to a method for recycling photovoltaic backsheets. Background Technology

[0002] Existing photovoltaic backsheets mainly feature a TPT structure, which is a composite interlayer structure of PVF (or PP) / adhesive / PET / adhesive / PVF (or PP). After long-term use, some polymer chains in this material have undergone fusion or cross-linking, making separation difficult. Current recycling processes typically involve first soaking and dissolving the layers in organic solvents to peel them off, followed by specific removal of the adhesive to achieve layered recycling. However, the main recycled products, PVF / PP and PET, often have insufficient purity due to adhesive residues. Using strong solvents for recycling could cause the recycled materials (PVF / PP and PET) to dissolve as well, leading to recycling losses. Furthermore, existing recycling technologies do not consider adhesive recovery. However, adhesives in photovoltaic backsheets, such as EVA and acrylates, can be recycled into various products such as adhesives and fillers. The products after recycling PET are generally PET dissociation oligomers, but these oligomers have lower practicality than PET, affecting the overall recycling efficiency. Summary of the Invention

[0003] Based on the shortcomings of existing technologies, the purpose of this invention is to provide a method for recycling photovoltaic backsheets. This method uses a specific two-stage separation process to process the photovoltaic backsheets, which can not only effectively separate and recover the adhesive components in the raw materials, but also recover the outer layer materials and PET recycled materials with a high recovery rate. Furthermore, the recovered PET recycled materials have high purity and can be used directly, resulting in high economic benefits from comprehensive recycling.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for recycling photovoltaic backsheets includes the following steps:

[0006] (1) After the photovoltaic backsheet is cut and broken, it is placed in the first solvent and heated to 168~222℃ for heat preservation treatment. It is filtered while hot to obtain filtrate I and insoluble matter; the first solvent is a lactone solvent.

[0007] (2) After cooling and crystallizing the filtrate I, filter it to obtain recycled PET (polyethylene terephthalate);

[0008] (3) The insoluble material is placed in the second solvent and heated and kept warm. The mixture is filtered while hot to obtain the outer layer recovery material and filtrate II. The second solvent is at least one of toluene, dichloromethane, xylene, chloroform and tetrahydrofuran.

[0009] (4) The organic solvent in filtrate II is recovered by heating and condensing to obtain adhesive recovery material.

[0010] Preferably, in step (1), the size of the photovoltaic backsheet after cutting and breaking is 1×1cm. 2 The cut and broken fragments include PET, outer layer, and adhesive.

[0011] It should be noted that the dimensions of the photovoltaic backsheet after cutting described in this application are not limited to the above range. Depending on the actual processing and handling conditions, it can also be cut to a larger size, such as 2×2 cm. 2 Or smaller, such as 0.5 × 0.5 cm. 2 However, no specific restrictions are imposed on this.

[0012] In existing photovoltaic backsheets, besides PVF (polyvinyl chloride) and PP (polypropylene), the material with significant recycling value is PET, which is located in the middle of the sheet. However, since the various sheet structures are mostly bonded with adhesives such as EVA and acrylate, it is impossible to separate them using weakly polar solvents. If strongly polar solvents are used, PET itself has low chemical stability and is prone to hydrolysis. In addition, some molecules have degraded after long-term use, which may cause PET and even the outer layer materials to dissolve in the solvent, reducing the recycling rate. Furthermore, highly polar solvents can also dissolve impurities contained in the photovoltaic backsheet to a certain extent, further reducing the purity of the recycled materials. Therefore, in this invention, to balance PET recycling efficiency and purity, a specific lactone solvent is creatively used to immerse and separate the photovoltaic backsheet at a specific temperature of 168-222°C. During this process, the solvent exhibits high selectivity, allowing the PET in the photovoltaic backsheet to be separated in liquid phase without dissociating or degrading it. High-purity recycled PET can then be obtained simply through cooling and crystallization, resulting in minimal PET loss and an extremely high recovery rate, while the outer layer material is virtually unaffected. Furthermore, the filtered insoluble matter contains outer layer recycled material such as PV... For F or PP and adhesive EVA or acrylate, in order to ensure maximum separation and effective recovery of the adhesive, the present invention further heats the insoluble matter with specific organic solvents such as toluene, dichloromethane, xylene, chloroform, and tetrahydrofuran at a specific temperature, so that the adhesive components are completely separated from the insoluble matter. Only simple organic solvent removal is needed to obtain the adhesive recovery material, and there is almost no adhesive residue in the outer layer of recovery material, resulting in high separation efficiency. In addition, the first and second solvents obtained from the separation and recovery can be recycled, resulting in high economic benefits from recycling.

[0013] Furthermore, if the outer layer of the photovoltaic backsheet contains fillers (such as glass fiber), they will eventually be separated into insoluble material I as the components are separated in the solution described in this invention. At this time, those skilled in the art can further process the insoluble material I according to actual needs, or separate these fillers separately after obtaining the recycled material of the outer layer to improve the overall recycling rate of the photovoltaic backsheet. No specific limitation is made in this regard.

[0014] Preferably, the heat preservation time in step (1) is 40~90 min.

[0015] In some embodiments, the heat preservation time in step (1) is one or any two of the following: 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 85 min, and 90 min.

[0016] In some embodiments, the temperature of the heat preservation treatment in step (1) can be a range of one or any two of 168°C, 170°C, 175°C, 180°C, 190°C, 195°C, 200°C, 210°C, 220°C, and 222°C.

[0017] More preferably, the temperature of the heat preservation treatment in step (1) is 190~200℃.

[0018] As mentioned above, after the photovoltaic backsheet is crushed and placed in the first solvent, highly selective separation of PET can be achieved. When the temperature is further preferably within the above range under the heating conditions, higher PET recycling efficiency can be achieved, and the recycling purity of the recycled material is also higher.

[0019] Preferably, in step (1), the filter screen used for hot filtration has a pore size of 80~120 μm.

[0020] Preferably, the lactone solvent has 4 to 8 carbon atoms per mole.

[0021] More preferably, the lactone solvent includes at least one of γ-valerolactone, δ-valerolactone, γ-heptyllactone, and γ-caprolactone.

[0022] In the technical solution of this invention, γ-valerolactone, δ-valerolactone, γ-hepterolactone, and γ-caprolactone can be precisely separated from PET at a specific reaction temperature without damaging the outer layer and adhesive. If the temperature is too high, it may lead to the loss of the outer layer material, but if the temperature is too low, the degree of separation of PET cannot reach the ideal level.

[0023] Preferably, the first solvent is γ-valerolactone.

[0024] Among the specific lactone solvents, their solubility selectivity for PET varies to some extent. When γ-valerol is selected as the first solvent, its solubility selectivity is higher, further improving the PET recycling efficiency.

[0025] Preferably, in step (1), the ratio of the mass of the photovoltaic backsheet to the volume of the first solvent is 5g:(80~120)mL.

[0026] Preferably, in step (1), the ratio of the mass of the photovoltaic backsheet to the volume of the first solvent is one or any two of the following: 5g:80mL, 5g:90mL, 5g:100mL, 5g:110mL, 5g:120mL.

[0027] Preferably, in step (2), the cooling can be natural cooling or temperature-controlled cooling, the temperature after cooling is 20~30℃, and the cooling time is 10~60h.

[0028] Preferably, in step (3), the temperature of the heating and heat preservation treatment is 58~102℃ and the time is 30~80min.

[0029] In some embodiments, the temperature of the heat preservation treatment in step (3) can be one or any two of the following: 58°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 100°C, and 102°C.

[0030] More preferably, the temperature of the heat preservation treatment in step (3) is 80~90℃.

[0031] When using specific organic solvents to separate the outer layer recycled material PVF and adhesives, the separation temperature is crucial and needs to be strictly controlled within the range of 60~100℃. Furthermore, when the temperature is preferably between 80~90℃, the recovery rate of the adhesive can be even higher.

[0032] Preferably, the second solvent is toluene.

[0033] After separating PET, the main components of the insoluble matter are the outer layer PP or PVF and adhesive components. When toluene is selected as the organic solvent for separation, the adhesive can be recovered more effectively, and the adhesive recovery rate is higher.

[0034] Preferably, in step (3), the ratio of the mass of the insoluble matter to the volume of the second solvent is 5g:(40~60)mL.

[0035] In some embodiments, the mass ratio of the insoluble substance to the volume of the second solvent is a range of one or both of the following: 5g:40mL, 5g:42mL, 5g:45mL, 5g:48mL, 5g:50mL, 5g:52mL, 5g:55mL, 5g:58mL, and 5g:60mL.

[0036] Preferably, in step (4), the heating temperature of filtrate II is greater than or equal to the boiling point of the second solvent.

[0037] Preferably, the photovoltaic backsheet includes an outer layer and a PET layer, and the outer layer and the PET layer are bonded together with an adhesive.

[0038] Preferably, the outer layer comprises at least one of PVF, PP, PE (polyethylene), and PA (polyamide).

[0039] Preferably, the outer layer may further include fillers, the fillers including at least one of talc, glass fiber, and mica powder.

[0040] The recycling method for photovoltaic backsheets described in this invention is not limited to common types of recycling systems. It can be implemented for other types of peripheral layer systems, such as those containing other functional plastics like PE and PA, or those containing reinforcing materials like fillers. No special limitations are imposed on these types.

[0041] More preferably, the outer layer includes at least one of PVF and PP; more preferably, the adhesive includes at least one of EVA and acrylate.

[0042] More preferably, the outer layer recycled material includes at least one of PP recycled material and PVF recycled material, and the adhesive recycled material includes at least one of EVA and acrylate.

[0043] Preferably, the number average molecular weight of the recycled PET material is 30,000 to 40,000.

[0044] It should be noted that the number-average molecular weight of the recycled PET material can be confirmed in the following way:

[0045] Referring to ISO 16014-5:2021, gel permeation chromatography was employed, using o-dichlorobenzene (ODCB) + phenol (volume ratio 1:1) as the mobile phase. The test temperature was 135℃, the mobile phase flow rate was 1.0 mL / min, and a PLgel 10 μm MIXED-B column was used with a differential refractive index detector (RI). The number-average molecular weight of the sample was confirmed by normalization fitting based on the standard curve and the curve obtained from the test. Compared with the low molecular weight oligomers or solvents of free PET molecules obtained by traditional PET recycling methods, the recycling method described in this invention can directly obtain PET finished products with high purity, which can be directly applied in various PET material fields and is comparable to virgin PET, thus having high application value.

[0046] The beneficial effects of this invention are that it provides a method for recycling photovoltaic backsheets. This method uses a specific two-stage separation process to process the photovoltaic backsheets, which can not only effectively separate and recover the adhesive components in the raw materials, but also recover the outer layer materials and PET recycled materials with a high recovery rate. Furthermore, the recovered PET recycled materials have high purity and can be used directly, resulting in high economic benefits from comprehensive recycling. Attached Figure Description

[0047] Figure 1 This is a schematic flowchart of the photovoltaic backsheet recycling method described in this invention.

[0048] Figure 2 Infrared schematic diagram of PVF recycled material in the method described in Example 1.

[0049] Figure 3 Infrared schematic diagram of PET recycled material and adhesive recycled material in the method described in Example 1.

[0050] Figure 4 Infrared schematic diagram of the PP recycled material in the method described in Example 2.

[0051] Figure 5 Infrared schematic diagram of PET recycled material and adhesive recycled material in the method described in Example 2. Detailed Implementation

[0052] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this invention are commonly used reagents and instruments.

[0053] The photovoltaic backsheet 1 described in this invention is a recycled PVF / EVA / PET / EVA / PVF structure product recovered by Trina Solar Co., Ltd.

[0054] Photovoltaic backsheet 2 is a recycled PP / acrylate / PET / acrylate / PP structure product recovered by Trina Solar Co., Ltd.

[0055] Example 1

[0056] An embodiment of the photovoltaic backsheet recycling method of the present invention includes the following specific steps: Figure 1 As shown, it includes the following steps:

[0057] (1) Cut 5g of photovoltaic backsheet 1 into pieces of 1×1 cm. 2 After the fragments were removed, they were placed in 100 mL of the first solvent and heated to 190 °C for 60 min. While still hot, they were filtered through a 100 μm pore size filter to obtain filtrate I and insoluble matter. The first solvent was γ-valerolactone. The filtrate I contained PET liquid phase, and the insoluble matter included the outer layer material PVF and adhesive.

[0058] (2) Let filtrate I stand and cool naturally to 25°C and crystallize for 24 hours until crystallization is complete. Then filter to obtain recycled PET material; at the same time, recover the first solvent for the next batch of recycling process;

[0059] (3) Place 5g of insoluble matter into 60mL of the second solvent and heat it in an oil bath to 80℃ for 60min. Filter it while it is still hot to obtain the outer layer recovered material and filtrate II. The second solvent is toluene. The outer layer recovered material mainly includes PVF recovered material.

[0060] (4) The filtrate II is heated to 112°C (above the boiling point of toluene) and the second solvent is recovered by condensation using a condenser. After the organic solvent is completely separated, the adhesive recovery material is obtained. The adhesive recovery material mainly includes EVA.

[0061] The purity of the PET recycled material was determined using high-performance liquid chromatography (HPLC) with a Waters HPLC system (E2695-2998) and a DAD detector. The PET recycled material was dissolved in a methanol / dichloromethane (1:1 mass ratio) solution for testing. Test conditions: A Discovery C-18 column (4.6 mm × 250 mm, 5 μm) was used, with acetonitrile and water as the mobile phase and isocratic elution. The results showed that the purity of the obtained PET recycled material reached 99.5%.

[0062] Simultaneously, infrared spectroscopy was used to detect the EVA content in the PVF recycled material, and the results were as follows: Figure 2 The results showed that no characteristic peaks of EVA (C=O stretching vibration, CO stretching vibration) were detected in the PVF recycled material, and the adhesive in the PVF recycled material was completely separated. When the PET recycled material and the adhesive recycled material were subjected to the same tests, the product also showed no obvious impurity characteristic peaks. Figure 3 As shown.

[0063] Example 2

[0064] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that it includes the following steps:

[0065] (1) Cut 5g of photovoltaic backsheet 2 into pieces of 1×1 cm. 2 After the fragments were removed, they were placed in 100 mL of the first solvent and heated to 190 °C for 80 min. While still hot, they were filtered through a 100 μm pore size filter to obtain filtrate I and insoluble matter. The first solvent was γ-valerolactone. The filtrate I contained PET liquid phase, and the insoluble matter included outer layer material and adhesive.

[0066] (2) Let filtrate I stand and cool naturally to 25°C and crystallize for 24 hours until crystallization is complete. Then filter to obtain recycled PET material.

[0067] (3) Place 5g of insoluble matter into 40mL of the second solvent and heat it in an oil bath to 80℃ for 80min. Filter it while it is still hot to obtain the outer layer recovered material and filtrate II. The second solvent is toluene. The outer layer recovered material mainly includes PP recovered material.

[0068] (4) The filtrate II is heated to 112°C and the second solvent is recovered by condensation using a condenser. After the second solvent is completely separated, the adhesive recovery material is obtained. The adhesive recovery material mainly includes acrylate.

[0069] The product was subjected to a similar infrared test as in Example 1, and the results were as follows: Figure 4 and Figure 5 As shown, the test results are similar to those in Example 1.

[0070] Example 3

[0071] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that the heating temperature in step (1) is 200°C.

[0072] Example 4

[0073] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that the heating temperature in step (1) is 170°C.

[0074] Example 5

[0075] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that the heating temperature in step (1) is 220°C.

[0076] Example 6

[0077] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that the first solvent used in step (1) is replaced with an equal mass of δ-valerolactone.

[0078] Example 7

[0079] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that the first solvent used in step (1) is replaced with an equal mass of γ-heptanolactone.

[0080] Example 8

[0081] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from embodiment 1 only in that the heating and heat preservation temperature in step (3) is 90°C.

[0082] Example 9

[0083] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from embodiment 1 only in that the heating and heat preservation temperature in step (3) is 60°C.

[0084] Example 10

[0085] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from embodiment 1 only in that the heating and heat preservation temperature in step (3) is 100°C.

[0086] Example 11

[0087] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from Embodiment 1 only in that, in step (3), the second solvent is replaced with an equal mass of dichloromethane.

[0088] Example 12

[0089] An embodiment of the photovoltaic backsheet recycling method of the present invention differs from embodiment 1 only in that, in step (3), the second solvent is replaced with an equal mass of tetrahydrofuran.

[0090] Comparative Example 1

[0091] A method for recycling photovoltaic backsheets differs from Example 1 only in that, in step (1), the first solvent is replaced with an equal mass of dimethyl sulfoxide.

[0092] Comparative Example 2

[0093] A method for recycling photovoltaic backsheets differs from Example 1 only in that, in step (1), the first solvent is replaced with an equal mass of m-cresol.

[0094] Comparative Example 3

[0095] A method for recycling photovoltaic backsheets differs from Example 1 only in that, in step (1), the first solvent is replaced with an equal mass mixture of γ-valerolactone and acetone, with a mass ratio of 7:3.

[0096] Comparative Example 4

[0097] A method for recycling photovoltaic backsheets differs from Example 1 only in that the heating temperature in step (1) is 150°C.

[0098] Comparative Example 5

[0099] A method for recycling photovoltaic backsheets differs from Example 1 only in that the heating temperature in step (1) is 250°C.

[0100] Comparative Example 6

[0101] A method for recycling photovoltaic backsheets differs from Example 1 only in that, in step (3), the second solvent is replaced with an equal mass of ethyl acetate.

[0102] Comparative Example 7

[0103] A method for recycling photovoltaic backsheets differs from Example 1 only in that, in step (3), the second solvent is replaced with an equal mass of acetone.

[0104] Comparative Example 8

[0105] A method for recycling photovoltaic backsheets differs from Example 1 only in that the heating and heat preservation temperature in step (3) is 45°C.

[0106] Comparative Example 9

[0107] A method for recycling photovoltaic backsheets differs from Example 1 only in that the heating and heat preservation temperature in step (3) is 130°C.

[0108] Example 1

[0109] To verify the recycling efficiency of the photovoltaic backsheet described in this invention, in addition to purity testing of the PET recycled material, the recycling rates of the PET recycled material, outer layer recycled material, and adhesive recycled material obtained in each embodiment and comparative example were statistically analyzed, wherein:

[0110] The method for calculating the recovery rate of the PET recycled material is as follows:

[0111] PET recycled material mass / theoretical PET mass × 100%

[0112] Theoretical PET mass: The thickness of the PET layer and its proportion are determined by taking pictures of the cross-section of the photovoltaic backsheet with a microscope or scanning electron microscope (SEM) (the thickness is measured at 3 random locations on the cross-section and the average of the three results is taken). The theoretical PET mass in the photovoltaic is calculated by combining the density of each material.

[0113] The method for calculating the recovery rate of the outer layer recycled material is as follows:

[0114] Mass of recycled material in the outer layer / theoretical mass of the outer layer × 100%

[0115] Theoretical outer layer recovery quality: The thickness of the outer layer and its proportion are determined by taking pictures of the photovoltaic backsheet cross section with a microscope or scanning electron microscope (SEM) (the thickness is measured at 3 random locations on the cross section and the average of the three results is taken). The quality of the theoretical outer layer in the photovoltaic backsheet is calculated by combining the density of each material.

[0116] The method for calculating the recovery rate of the recycled adhesive material is as follows:

[0117] Mass of recycled adhesive / theoretical mass of adhesive × 100%

[0118] The theoretical adhesive recovery rate and quality are determined by photographing the cross-section of the photovoltaic backsheet using a microscope or scanning electron microscope (SEM) to determine the thickness of the adhesive (the thickness is measured at 3 random locations on the cross-section, and the average of the three results is taken) and its proportion. The theoretical adhesive quality in the photovoltaic backsheet is then calculated by combining the density of each material.

[0119] The test results are shown in Table 1.

[0120] Table 1. Test Results

[0121]

[0122] As shown in Table 1, the photovoltaic backsheet recycling method described in this invention achieves excellent recycling results regardless of whether the outer layer material of the TPT structure backsheet is PVF-based or PP-based. In each embodiment, the recycled PET material not only has a high recovery rate (over 94%), but also a high purity (over 97%), making it perfectly usable without interference from adhesives. Furthermore, during this process, there is no significant loss of adhesives or outer layer materials due to dissolution. The recovery rate of the outer layer material can reach over 94% (with a purity of over 97% after similar testing of the PET material), while the adhesive can achieve a recovery rate of over 88%. This is mainly due to the design concept of this invention: in the initial stage, a specific polar solvent is used at a specific heating temperature to first separate PET from the material, based on lactone solvents such as γ-... The high selectivity of valproic acid, δ-valproic acid, γ-heptyl lactone, and γ-caprolactone allows PET to achieve efficient separation. However, if other types of solvents are used, as shown in Comparative Examples 1 and 2, it will not only reduce the recovery efficiency and purity of PET (unsuitable solvents will cause other materials to be dissolved in filtrate I in step (1) and precipitate with PET, affecting purity, or make it difficult to achieve ideal precipitation efficiency during precipitation, resulting in low recovery rate), but will also affect the recovery loss of other materials (unsuitable solvents may cause non-target substances to be dissolved in filtrate I in step (1), but they cannot be re-precipitated in subsequent recovery steps, resulting in the loss of non-target substances). Furthermore, even if the above-mentioned limited types of polar solvents are selected, if other types of solvents are introduced during the dissolution process, it will also affect the separation and recovery effect, as shown in Comparative Example 3. In the first solvent, when γ-valerol is further preferred, as shown in Examples 1 and 6-7, its solubility selectivity is better, which can further improve the PET recovery efficiency. On the other hand, as can be seen from Examples 1, 3-5 and Comparative Examples 4-5, the specific selectivity of this lactone solvent in the dissolution and separation process needs to be established within a specific temperature range. When the heating temperature is below 170°C, the reaction rate of PET dissolution and separation slows down significantly, and the purity also decreases. When the temperature is above 220°C, the reaction rate does not increase significantly, and there is also some dissolution competition. Both the recovery of PET in the front stage and the recovery of the outer layer and adhesive in the back stage will be affected (the separation and recovery stage in the back stage also has high selectivity). Therefore, it is necessary to strictly limit the range. When the temperature is further preferred to be 190-200°C, the overall recovery effect is better.After the PET recycled material is separated, step (3) of the method of the present invention uses a specific organic solvent for heat preservation and dissolution treatment. In this process, similar to step (1), the selection of organic solvent and heat preservation temperature are equally critical. As can be seen from the comparison of Examples 1, 8-12 and Comparative Examples 6-9, only when at least one of toluene, dichloromethane, xylene, chloroform and tetrahydrofuran is selected as the dissolution and separation solvent, and the heat preservation temperature is between 60 and 100°C, can the scheme take into account the recovery rate of the outer layer recycled material and the adhesive. Otherwise, it may lead to incomplete separation of the two (for example, in Comparative Examples 8 and 9, the outer layer recycled material still contains...). The material contains a large amount of adhesive, resulting in a high calculated yield of the outer layer recycled material, but the purity is less than 95%. Due to the initial loss of adhesive, the subsequent adhesive recycled material recovery rate is low. Alternatively, it may be impossible to re-condense and recover the precipitated material (for example, in Comparative Examples 6 and 7, when an unsuitable solvent is used, some outer layer components may be dissolved, but they cannot be precipitated in the subsequent condensation process, and the adhesive precipitation efficiency is also low, ultimately resulting in not only a low yield of adhesive recycled material, but also a lower recovery rate of outer layer recycled material than in the example scheme). Under the aforementioned conditions, using toluene as a solvent and treating at 80~90°C yields the best results.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for recycling photovoltaic backsheets, characterized in that, Includes the following steps: (1) After the photovoltaic backsheet is cut and broken, it is placed in the first solvent and heated to 168~222℃ for heat preservation treatment. It is filtered while hot to obtain filtrate I and insoluble matter; the first solvent is a lactone solvent; the lactone solvent includes at least one of γ-valerolactone, δ-valerolactone, γ-heptanelactone, and γ-caprolactone. (2) After cooling and crystallizing the filtrate I, filter it to obtain recycled PET material; (3) The insoluble material is placed in the second solvent and heated and kept warm, and then filtered while hot to obtain the outer layer recovery material and filtrate II; the second solvent is at least one of toluene, dichloromethane, xylene, and tetrahydrofuran; the temperature of the heating and keeping warm treatment is 58~102℃; (4) The organic solvent in filtrate II is recovered by heating and condensing to obtain adhesive recovery material.

2. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, The outer layer recycled material includes at least one of PP recycled material and PVF recycled material, and / or the adhesive recycled material includes at least one of EVA and acrylate.

3. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, The heat preservation time in step (1) is 40~90 minutes.

4. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, In step (1), the ratio of the mass of the photovoltaic backsheet to the volume of the first solvent is 5g: (80~120)mL.

5. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, In step (3), the heating and heat preservation treatment time is 30~80 minutes.

6. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, The second solvent is toluene.

7. The method for recycling photovoltaic backsheets as described in claim 1, characterized in that, In step (3), the mass ratio of the insoluble matter to the volume of the organic solvent is 5g:(40~60)mL.

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