A modified functionalized cycloolefin copolymer transparent photovoltaic backsheet and preparation method thereof

Abstract

The present invention relates to the technical field of a cycloolefin copolymer transparent photovoltaic backplane, in particular to a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof: in order to solve the problems of poor weather resistance, toxic fluorine elements, and low interlayer peeling strength of the existing coated fluorine-containing transparent backplane, the present invention provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. The transparent photovoltaic backplane comprises, from the battery end to the air end, a transparent inner layer, a transparent copolymer base layer, and a weather-resistant layer. The backplane has excellent light transmittance, weather resistance, and interlayer peeling strength, does not require adhesives, and is low in cost. The backplane is suitable for double-sided photovoltaic modules, has a simple preparation process, high cost-effectiveness, and broad market prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic backplane preparation methods, and in particular, relates to a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. Background Art

[0002] The photovoltaic backplane is one of the key components of photovoltaic modules. Because it is located on the outermost layer on the back of the photovoltaic module and is directly exposed to the external environment, it must have excellent weather resistance (resistance to ultraviolet radiation, anti-aging, etc.), water vapor barrier and electrical insulation properties to ensure the long-term stable operation of photovoltaic modules in the changing outdoor environment. Transparent photovoltaic backplanes are mainly used for the back packaging of double-glass photovoltaic modules, and double-glass modules are one of the mainstream technologies for high-efficiency modules and are widely used at home and abroad. Transparent photovoltaic backplanes not only need to meet high light transmittance (higher than 90%) and sufficient mechanical strength, but also need to meet the requirements of 25 years of outdoor use of photovoltaic modules. Current research on transparent backplanes includes: Patent CN209000937 U mentions a high-resistance water-transparent backplane with a water vapor transmittance of less than 1g / m2·day and a light transmittance of more than 90%, but it is a fluorine-containing backplane and has certain potential risks to the environment;

[0003] Patent CN110271254A mentions a polyolefin-based transparent photovoltaic backplane and its application, comprising a transparent polyolefin inner layer, a first glue layer, a transparent PET substrate layer, a second glue layer and a transparent fluorine-containing polymer weather-resistant layer. This structure is also a common transparent backplane structure in the photovoltaic industry. Patent CN105428445A also proposes a transparent backplane including a weather-resistant layer, two transparent coating layers and a fluorine film layer, which also contains UV-resistant glue. Although this structure is easy to mass produce and has a low production cost, this type of multi-layer structure has the potential to cause stratification and accelerated aging during long-term outdoor use.

[0004] At the same time, in order to prevent the transparency of the back of the component from decreasing due to scratches and wear during long-term outdoor use, the patent CN209641671U mentions a wear-resistant transparent backplane, which is based on the KPC or EPC structure transparent backplane, and a fluorine-containing friction-resistant coating or a silicon-containing friction-resistant coating is coated on the air side. Patent CN112786724A discloses a transparent photovoltaic backplane with high weather resistance and low water vapor permeability, including a PET main substrate, the surface of the PET is compounded with a fluorine film including a PVDF base film through an adhesive layer, and a UV cut-off coating is applied to the surface of the transparent PVDF base film after surface treatment, and then an adhesive layer is applied to the surface of the PET, and then the PVDF base film coated with the UV cut-off coating is bonded to the PET, and the finished transparent photovoltaic backplane is obtained after ripening, standing and cutting. A functional protective layer is formed on the inner surface of the fluorine film and the outer surface of the PET by the combined use of the UV cut-off coating and the water vapor shielding coating. Similar to the above-mentioned backplane structures, all coatings have a potential risk, namely the problem of bonding firmness with the substrate and the risk of accelerated aging of the coating itself.

[0005] In the photovoltaic backplane preparation technology, we have to mention a non-adhesive technology - that is, a three-layer co-extruded backplane. For example, the three-layer co-extruded adhesive-free transparent solar photovoltaic backplane mentioned in patent CN112928176A includes a transparent inner layer, a transparent middle layer and a transparent outer layer. The raw materials for the preparation of the inner layer and the middle layer at least include polyolefins; the raw materials for the preparation of the outer layer at least include polyolefins and ethylene methacrylate ionomers. This is a typical polyolefin backplane. Although the production process is simple, there is no adhesive, and the interlayer peeling strength is increased, there are still environmental aging problems such as UV resistance. Summary of the invention

[0006] In view of the above potential risks and problems existing in the existing transparent backplane technology, the present invention provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. The technical solution adopted by the present invention is:

[0007] A modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof, comprising, from the battery side to the air side (from top to bottom), a transparent inner layer, a transparent copolymer base layer, and a transparent weather-resistant layer; the transparent copolymer base layer is located between the transparent inner layer and the transparent weather-resistant layer; the raw materials for preparing the transparent inner layer at least include polyolefin; the raw materials for preparing the transparent copolymer base layer at least include one polyolefin and one cycloolefin polymer; the raw materials for preparing the weather-resistant layer at least include a copolymer of polyolefin and cycloolefin.

[0008] Preferably, the polyolefin includes one or more of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polypropylene (PP), and poly-4-methyl-1-pentene (TPX).

[0009] Preferably, the raw materials for preparing the transparent inner layer include, by weight, 50-90 parts of PP, 1-20 parts of cycloolefin polymer (COC), and 1-10 parts of TPX.

[0010] Preferably, the raw materials for preparing the transparent copolymer base layer include, by weight, 50-80 parts of PP, 1-50 parts of cycloolefin polymer (COC), and 1-20 parts of TPX.

[0011] Preferably, the functionalized cyclic olefin copolymer (COC) comprises one or both of ethylene-norbornene copolymer and ethylidene-norbornene copolymer.

[0012] Preferably, the main structure of the transparent photovoltaic backsheet described above is formed by co-extruding the inner layer and the base layer through an extruder.

[0013] Preferably, the transparent weather-resistant layer is on the surface of the transparent polymer base layer close to the air side, and free radicals are generated on the back surface of the substrate by online gamma ray irradiation, and then these free radicals are re-grafted and copolymerized to form a stable surface weather-resistant layer.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] Through the two-layer co-extrusion molding process, the inner layer and the base layer with almost the same main raw material components but different raw material ratios can be combined into a whole. On the one hand, it can increase the compatibility of the inner layer with the packaging material, and on the other hand, the base material has good transparency, heat resistance, water vapor airtightness and rigidity. The most core technical feature is that the mature gamma ray grafting polymerization process is used to form a weather-resistant layer with stable performance on the outermost surface. No adhesive is required, the structure is simple, and the process time is short. It not only enhances the outdoor weather resistance of the backplane, but also maintains good transparency and overall firmness. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the attached picture:

[0017] Figure 1 Schematic diagram of the modified functionalized cycloolefin copolymer transparent photovoltaic backsheet of the present invention;

[0018] In the figure, 1 is a transparent inner layer, 2 is a transparent copolymer base layer, and 3 is a transparent weather-resistant layer. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0020] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0021] In addition, when describing embodiments of the present invention, the use of "preferred", "preferably", "more preferably", etc. refers to embodiments of the present invention that may provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0022] The first aspect of the present invention provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof, wherein the transparent photovoltaic backplane comprises a transparent inner layer, a transparent copolymer base layer, and a transparent weather-resistant layer; the transparent copolymer base layer is located between the transparent inner layer and the transparent weather-resistant layer; the raw materials for preparing the transparent inner layer at least include polyolefins; the raw materials for preparing the transparent copolymer base layer include at least one polyolefin and one cycloolefin polymer; the raw materials for preparing the weather-resistant layer include at least a copolymer of polyolefins and cycloolefins.

[0023] In some preferred embodiments, the polyolefin includes one or more of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polypropylene (PP), and poly-4-methyl-1-pentene (TPX).

[0024] In some preferred embodiments, the polyolefin includes a mixture of PP and TPX. PP is a very representative polyolefin elastomer, with low cost and side chain methyl groups for subsequent grafting reactions; TPX has good insulation, a volume resistivity similar to that of polytetrafluoroethylene, and corrosion resistance, and is a good backsheet material to replace fluororesins; at the same time, TPX has a melting point of up to 240°C, and after blending, it can combine the advantages of both to improve the impact resistance and high temperature resistance of the backsheet.

[0025] For a photovoltaic backsheet with a multi-layer structure, if the main components of each layer are not the same or the content of the main components is too different, it will increase the difficulty of combining the layers during the co-extrusion molding process. On the other hand, due to the different thermal expansion coefficients of different components, different layers will easily cause interlayer stress concentration during use, resulting in delamination or even cracking, reducing the service life. In order to avoid these problems, in some preferred embodiments, the main raw material components used in the inner layer and the base layer of the transparent photovoltaic backsheet of the present invention are basically the same, all of which are a mixture of PP, COC and TPX.

[0026] In some preferred embodiments, the raw materials for preparing the transparent inner layer include 50-90 parts of PP, 1-20 parts of cycloolefin polymer (COC), and 1-10 parts of TPX by weight. The PP content is increased to make it more compatible with packaging materials such as EVA or POE, to make the combination more firm, and to prevent the back sheet from delaminating.

[0027] In some preferred embodiments, the raw materials for preparing the transparent copolymer base layer include 50-80 parts of PP, 1-50 parts of cycloolefin polymer (COC), and 1-20 parts of TPX by weight. The base layer mainly needs to have good light transmittance, insulation, and dimensional stability. Increasing the proportion of COC is conducive to utilizing its excellent properties such as low birefringence, low water absorption, and high rigidity; increasing the proportion of TPX is helpful to improve the insulation and corrosion resistance of the backplane; it can improve its aging resistance and product stability.

[0028] In order to improve the transparency of the photovoltaic backsheet, in some preferred embodiments, the PP is a highly transparent PP. In order to be more conducive to extrusion molding, in some preferred embodiments, the melt flow rate of the PP 235°C / 1.85kg is 10-20g / 10min.

[0029] In some preferred embodiments, the functionalized cyclic olefin copolymer (COC) includes one or both of ethylene-norbornene copolymer and ethylidene-norbornene copolymer.

[0030] In order to improve or achieve some specific properties, in some preferred embodiments, some additives can be added in trace amounts to the raw materials for preparing any layer, and in order not to affect the transparency of the photovoltaic backsheet, the additives are all transparent additives. For example, in order to improve the weather resistance of the backsheet, in some preferred embodiments, some antioxidants such as TPP are added to the surface of the transparent polymer base layer close to the air side, and free radicals are generated on the back surface of the substrate by online gamma ray irradiation, and then these free radicals are re-grafted and copolymerized to form a stable surface weather-resistant layer.

[0031] The present invention also provides a method for preparing a two-layer co-extruded adhesive-free transparent photovoltaic backsheet, wherein the two-layer co-extruded adhesive-free transparent photovoltaic backsheet is extruded by an extruder. During the high-temperature extrusion process, molecules between layers interpenetrate each other to form an adhesive layer, so that the layers can be tightly combined without glue. Compared with interlayer bonding methods such as UV-resistant glue, the co-extrusion molding process can significantly improve the bonding strength between layers and increase the service life of the photovoltaic backsheet.

[0032] In some preferred embodiments, the main structure of the transparent photovoltaic backsheet described above is formed by co-extruding the inner layer and the base layer through an extruder.

[0033] The method for preparing the transparent photovoltaic backsheet comprises the following steps:

[0034] 1. According to the formula, PP, TPX, COC and some additives are mixed evenly and mixed multiple times by a twin-screw extruder to obtain a transparent inner layer material and a transparent copolymer base material;

[0035] 2. Add the transparent inner layer material and the transparent copolymer base material into the screw of the extruder respectively, and then melt and extrude them in the screw extruder at the same time, and the extruded two layers of molten material enter the composite mold;

[0036] 3. In the composite mold, the two layers of molten materials are cooled down to the same temperature and then co-extruded to obtain a composite film, which is then subjected to an online gamma ray irradiation graft polymerization process, cooling, pulling, and winding to obtain the transparent photovoltaic backplane.

[0037] The present invention is specifically described below by way of examples. In addition, if not otherwise specified, all raw materials used are from industry market sales channels.

[0038] Example 1

[0039] Example 1 provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. The transparent photovoltaic backplane comprises a transparent inner layer, a transparent copolymer base layer, and a transparent weather-resistant layer; the transparent copolymer base layer is located between the transparent inner layer and the transparent weather-resistant layer.

[0040] The raw materials for preparing the transparent inner layer include, by weight, 80 parts of PP, 15 parts of cycloolefin polymer (COC), and 5 parts of TPX.

[0041] The raw materials for preparing the transparent copolymer base layer include 50 parts of PP, 50 parts of cycloolefin polymer (COC), and 5 parts of TPX, calculated by weight.

[0042] In order to improve the transparency of the photovoltaic backsheet, in some preferred embodiments, the PP is a highly transparent PP. In order to be more conducive to extrusion molding, in some preferred embodiments, the PP 235°C / 1.85kg has a melt flow rate of 10-20g / 10min and is purchased from Ningbo Formosa Plastics with a brand number of 5250T.

[0043] The functionalized cycloolefin copolymer (COC) was purchased from Hongcheng Plastics, with the brand name Topas 8007F-600. The TPX was purchased from Mitsui Chemicals, Japan, with the brand name MLL411.

[0044] Example 1 also provides a method for preparing a modified functionalized cycloolefin copolymer transparent photovoltaic backsheet, comprising the following steps:

[0045] 1. According to the formula, PP, TPX, COC and some additives are mixed evenly and mixed multiple times by a twin-screw extruder to obtain a transparent inner layer material and a transparent copolymer base material;

[0046] 2. Add the transparent inner layer material and the transparent copolymer base material into the screw of the extruder respectively, and then melt and extrude them in the screw extruder at the same time, and the temperature is controlled at 260°C; the extruded two layers of molten material enter the composite mold;

[0047] 3. In the composite mold, the two layers of molten materials are cooled down, and when the molten materials are cooled to 190° C., a composite film is obtained by co-extrusion, and then the transparent photovoltaic backplane is obtained by an online gamma ray irradiation graft polymerization process, cooling, pulling, and winding.

[0048] Example 2

[0049] Example 1 provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. The transparent photovoltaic backplane comprises a transparent inner layer, a transparent copolymer base layer, and a transparent weather-resistant layer; the transparent copolymer base layer is located between the transparent inner layer and the transparent weather-resistant layer.

[0050] The raw materials for preparing the transparent inner layer include, by weight, 70 parts of PP, 20 parts of cycloolefin polymer (COC), and 5 parts of TPX.

[0051] The raw materials for preparing the transparent copolymer base layer include 55 parts of PP, 45 parts of cycloolefin polymer (COC), and 7 parts of TPX, calculated by weight.

[0052] In order to improve the transparency of the photovoltaic backsheet, in some preferred embodiments, the PP is a highly transparent PP. In order to be more conducive to extrusion molding, in some preferred embodiments, the PP 235°C / 1.85kg has a melt flow rate of 10-20g / 10min and is purchased from Ningbo Formosa Plastics with a brand number of 5250T.

[0053] The functionalized cycloolefin copolymer (COC) was purchased from Hongcheng Plastics, with the brand name Topas 8007F-600. The TPX was purchased from Mitsui Chemicals, Japan, with the brand name MLL411.

[0054] Example 1 also provides a method for preparing a modified functionalized cycloolefin copolymer transparent photovoltaic backsheet, comprising the following steps:

[0055] 1. According to the formula, PP, TPX, COC and some additives are mixed evenly and mixed multiple times by a twin-screw extruder to obtain a transparent inner layer material and a transparent copolymer base material;

[0056] 2. Add the transparent inner layer material and the transparent copolymer base material into the screw of the extruder respectively, and then melt and extrude them in the screw extruder at the same time, and the temperature is controlled at 255°C; the extruded two layers of molten material enter the composite mold;

[0057] 3. In the composite mold, the two layers of molten materials are cooled down, and when the molten materials are cooled to 185° C., a composite film is obtained by co-extrusion, and then the transparent photovoltaic backplane is obtained by an online gamma ray irradiation graft polymerization process, cooling, pulling, and winding.

[0058] Performance Evaluation

[0059] 1. Light transmittance test

[0060] The transparent photovoltaic backsheet prepared in the above embodiment was tested using a spectrophotometer UV-3600i-Plus to see if its transmittance was higher than 90%. The results are shown in Table 1.

[0061] 2. Interlayer peeling force test

[0062] The transparent photovoltaic backsheet prepared in the above embodiment was tested for interlayer peeling force using a plastic tensile testing machine GL6502. The results are shown in Table 1.

[0063] 3. Anti-ultraviolet performance

[0064] The transparent photovoltaic backsheet prepared in the above embodiment was tested for reliability, quality and safety according to IEC61215: 2005 standard, with an ultraviolet radiation of 15 kwh / m 2 , the results are shown in Table 1.

[0065] Example Transmittance / % Interlayer peel strength (N / cm) Anti-ultraviolet aging ability Example 1 92 15 Meet the Standard Example 2 91 18 Meet the Standard

[0066] It can be seen from the above embodiments that the present invention provides a modified functionalized cycloolefin copolymer transparent photovoltaic backplane and a preparation method thereof. The transparent photovoltaic backplane has high light transmittance, strong interlayer bonding force, and anti-ultraviolet aging performance.

[0067] It is particularly pointed out that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A modified functionalized cycloolefin copolymer transparent photovoltaic backsheet, characterized in that: The transparent inner layer, the transparent copolymer base layer, and the transparent weather-resistant layer are sequentially included from the battery side to the air side; the raw materials for preparing the transparent inner layer at least include polyolefin; the raw materials for preparing the transparent copolymer base layer at least include one polyolefin and one cycloolefin copolymer; The polyolefin includes one or more of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polypropylene (PP), and poly-4-methyl-1-pentene (TPX); the cyclic olefin copolymer includes one or two of ethylene-norbornene copolymer and ethylidene norbornene copolymer; The transparent weather-resistant layer is on the surface of the transparent copolymer base layer close to the air side. Free radicals are generated on the surface of the transparent copolymer base layer by online gamma ray irradiation, and then these free radicals are re-grafted and copolymerized to form a stable surface weather-resistant layer.

2. The modified functionalized cycloolefin copolymer transparent photovoltaic backsheet according to claim 1, characterized in that: The raw materials for preparing the transparent inner layer include, by weight, 50-90 parts of PP, 1-20 parts of cycloolefin copolymer, and 1-10 parts of TPX.

3. The modified functionalized cycloolefin copolymer transparent photovoltaic backsheet according to claim 1, characterized in that: The raw materials for preparing the transparent copolymer base layer include 50-80 parts of PP, 1-50 parts of cycloolefin copolymer and 1-20 parts of TPX, calculated by weight.

4. A modified functionalized cycloolefin copolymer transparent photovoltaic backsheet according to any one of claims 1 to 3, characterized in that: The main structure of the transparent photovoltaic back sheet is formed by co-extruding an inner layer and a base layer through an extruder.

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