A polyvinylidene fluoride composition for a wind turbine blade vortex generator, a wind turbine blade vortex generator, and a preparation method and application thereof

Abstract

The application discloses a polyvinyl fluoride composition for a wind power blade vortex generator, the wind power blade vortex generator and a preparation method and application thereof. The polyvinyl fluoride composition for the wind power blade vortex generator comprises a PVDF resin, a toughening agent, an ultraviolet-resistant main agent, nano titanium dioxide, an interface bonding improver, a fluorine-based processing lubricant and an antioxidant. The molecular weight of the PVDF resin is 200,000-1,100,000. The ultraviolet-resistant main agent is a compound of a benzophenone ultraviolet absorber and a hindered amine light stabilizer. The material realizes all-round long-acting light stabilization protection of the PVDF material outdoors through three-level synergy of physical reflection-chemical absorption-radical capture, the aging rate of the material in a strong ultraviolet, humid heat and salt spray environment is reduced by more than one order of magnitude, the long-term mechanical property retention rate is significantly improved, and the wind power blade vortex generator is ensured not to be brittle, not to be deformed and not to be shed in a 20-30 year service cycle.

Description

Technical Field

[0001] This invention belongs to the technical field of wind power generation equipment, specifically relating to a polyvinylidene fluoride composition for a wind turbine blade eddy current generator, a wind turbine blade eddy current generator, its preparation method, and its application. Background Technology

[0002] Vortex generators (VGs) are miniature vortex elements mounted on the blade surface. They typically consist of a row of small plates arranged radially along the blade and vertically fixed within the blade's boundary layer at a given installation angle. Their primary function is to control boundary layer separation by inducing eddies, thereby improving the wind turbine's power generation efficiency by 1.5-3% and reducing blade vibration risk. However, wind turbine blades need to operate outdoors for 20-30 years, which places stringent requirements on VG materials: they must possess excellent resistance to UV aging, good mechanical strength and impact resistance, and excellent interfacial adhesion strength with fiberglass blades.

[0003] The mainstream materials for existing wind turbine blade eddy current generators include aluminum alloy, epoxy fiberglass, PC / ASA plastic alloy, ASA, and PVC plastic, but the following technical problems still exist:

[0004] 1) Poor weather resistance and short service life: Ordinary plastics (ASA plastics, PC / ASA plastic alloys, etc.) have insufficient resistance to outdoor ultraviolet rays, damp heat, and salt spray, and will powder, crack, and peel off after 5-10 years; aluminum alloys are prone to corrosion and oxidation; fiberglass will powder and peel off its protective coating after long-term outdoor exposure, and the fiberglass substrate is prone to aging and delamination. None of these can meet the design life of 20-25 years for wind turbine blades. Generally, on-site maintenance is required 3-4 times during the service life.

[0005] 2) High maintenance costs: Current VG turbines require multiple maintenance cycles throughout their blade lifespan, resulting in costs for materials, equipment, and personnel. This is especially true for offshore wind turbine blades, where each maintenance requires chartering a vessel to operate at sea, making maintenance extremely expensive. According to industry statistics, the cost of a single maintenance cycle for an offshore wind turbine VG is approximately 80,000 to 150,000 yuan, and the cumulative maintenance cost over its entire lifespan can reach 3 to 5 times the initial purchase cost.

[0006] 3) Limited functionality: Ordinary VG only has aerodynamic performance optimization function and cannot achieve additional functions such as anti-icing and self-cleaning.

[0007] 4) Weight and drag issues: Both metal and fiberglass VG are too heavy, increasing the load on the blades; fiberglass VG lacks toughness, requiring a thicker design, which increases aerodynamic drag.

[0008] While existing patent CN105556114B mentions that PVDF can be used as a material for eddy current generators, it does not disclose a specific modified formula for PVDF materials suitable for wind turbine blades, nor does it mention meeting the requirement of a 30-year long service life, nor does it disclose the matching low-stress injection molding process, interface-strengthened bonding process, and fluorocarbon coating protection system. Patent CN105556114B only discloses that PVDF can be used for VG, but it does not address the three core pain points: "high internal stress and easy cracking in injection molding of highly crystalline PVDF, low surface energy of fluorinated materials making adhesion difficult, and poor dispersion and easy failure of weather-resistant systems."

[0009] Existing VG technology cannot simultaneously solve the four core problems of PVDF eddy current generators: toughness, weather resistance, formability, and bonding reliability. With the wind power industry's requirements for cost reduction and efficiency improvement, there is a trend to gradually extend the life of wind turbine units to 30 years or more. Therefore, there will be an urgent need for a wind turbine blade eddy current generator that meets the requirements of long life and its preparation and bonding methods. Summary of the Invention

[0010] To address the technical problems of poor weather resistance, short service life, and frequent maintenance in eddy current generators commonly used in wind turbine blades, the primary objective of this invention is to provide a polyvinylidene fluoride (PVDF) composition for wind turbine blade eddy current generators. This material exhibits excellent weather resistance, enabling wind turbine blade eddy current generators to achieve long service life, high reliability, and low maintenance, thereby significantly reducing the total life cycle cost of wind turbine units.

[0011] Another object of the present invention is to provide a polyvinylidene fluoride wind turbine blade eddy current generator.

[0012] Another object of the present invention is to provide the application of the above-mentioned polyvinylidene fluoride wind turbine blade eddy current generator.

[0013] The objective of this invention is achieved through the following technical solution:

[0014] A polyvinylidene fluoride composition for wind turbine blade eddy current generators, comprising the following components by weight: 75-88 parts by weight of PVDF resin, 3-20 parts by weight of toughening agent, 0.5-4.5 parts by weight of UV-resistant main agent, 2-10 parts by weight of nano-titanium dioxide, 1-10 parts by weight of interfacial adhesion improver, 0.3-1.5 parts by weight of fluorine-based processing lubricant, and 0.2-1.2 parts by weight of antioxidant.

[0015] Furthermore, the molecular weight of the PVDF resin is 200,000 to 1,100,000.

[0016] Furthermore, the toughening agent is selected from at least one of fluoropolymers, fluoroelastomers, and weather-resistant core-shell toughening agents.

[0017] More preferably, the toughening agent is specifically selected from at least one of ethylene-tetrafluoroethylene copolymer (ETFE), ternary fluoropolymer (THV), fluororubber (FKM), perfluoroethylene-propylene copolymer (FEP), ethylene-trifluorochloroethylene copolymer (ECTFE), weather-resistant acrylate core-shell toughening agent (ACR), and silicone-modified acrylate toughening agent (Si-ACR).

[0018] Furthermore, the content of the toughening agent is preferably 5 to 12 parts by weight.

[0019] Furthermore, the UV-resistant main agent is a combination of benzophenone-based UV absorbers (e.g., UV-531) and hindered amine light stabilizers (e.g., HALS).

[0020] Furthermore, the nano-titanium dioxide is rutile type with a particle size of 20~50nm.

[0021] Furthermore, the interfacial adhesion improver is at least one of the following: silane coupling agent, anhydride-grafted fluoropolymer, GMA-grafted fluoropolymer, carboxyl-modified PVDF, epoxy-modified fluoropolymer, amino-modified fluoropolymer, fluorinated alkyl coupling agent, and phosphate ester coupling agent.

[0022] More preferably, the interfacial adhesion improver is a compound system of silane coupling agent and acid anhydride grafted fluoropolymer.

[0023] The silane coupling agent is selected from at least one of KH550, KH560, KH570, and A-171 (vinyltrimethoxysilane); the anhydride-grafted fluoropolymer is selected from at least one of MAH-g-PVDF, GMA-g-PVDF, MAH-g-ETFE, and MAH-g-THV.

[0024] In the most preferred embodiment, the interfacial adhesion improver is a compound of silane coupling agent (KH-550, γ-aminopropyltriethoxysilane) and maleic anhydride-grafted PVDF (MAH-g-PVDF, grafting rate 1.2-1.8%).

[0025] Furthermore, the fluorine-based processing lubricant is preferably PTFE micro powder with a particle size of 1~5μm.

[0026] Furthermore, the antioxidant is prepared by compounding hindered phenolic antioxidant (1010) and phosphite auxiliary antioxidant (168).

[0027] The above-mentioned polyvinylidene fluoride composition for wind turbine blade eddy current generators can be used to prepare wind turbine blade eddy current generators.

[0028] The present invention also provides a polyvinylidene fluoride (PVDF) wind turbine blade eddy current generator, which is prepared from the above-mentioned PVDF composition for wind turbine blade eddy current generators.

[0029] Specifically, the polyvinylidene fluoride wind turbine blade eddy current generator is manufactured through the following steps:

[0030] (1) Prepare raw materials according to the ratio, first mix PVDF resin with toughening agent, then add UV resistant main agent, nano titanium dioxide, interface adhesion improver, fluorine processing lubricant and antioxidant and mix. After mixing evenly, PVDF granules are produced by extrusion granulation through an extruder. The length-to-diameter ratio of the extruder is L / D≥40:1 and the extrusion vacuum degree is -0.06~-0.08MPa.

[0031] (2) Dry the PVDF granules to remove water, so that the moisture content is ≤0.015%;

[0032] (3) The dried PVDF granules are prepared into a polyvinylidene fluoride wind turbine blade eddy current generator by injection molding process; the barrel temperature and injection mold temperature are set, preheated for 30 min, the temperatures of the front, middle and rear sections of the barrel are 210~220℃, 205~215℃ and 190~200℃ respectively, the nozzle temperature is 205~215℃, and the injection mold temperature is ≥80℃.

[0033] Furthermore, the drying and dehydration temperature in step (2) is 80~90℃, and the time is 4~6 hours.

[0034] Furthermore, the temperature of the injection mold in step (3) is 80~100℃.

[0035] Furthermore, in step (3), the injection mold has venting grooves at the sharp corner, the wall thickness change point and the wingtip of the corresponding vortex generator. The venting grooves have a depth of 0.02~0.04mm, a width of 3~5mm and a length of 8~12mm.

[0036] Further, the conditions of the injection molding process in step (3) include: injection rate: medium to high speed 20~40mm / s; injection pressure: 50~110MPa; holding pressure: 50~60MPa; holding time: 10~25s (preferably 10~15s); cooling time: 15~40s; screw back pressure: 3~5MPa.

[0037] Furthermore, the polyvinylidene fluoride wind turbine blade eddy current generator described in step (3) is naturally cooled after molding.

[0038] The polyvinylidene fluoride wind turbine blade eddy current generator described in this invention can be used to manufacture wind turbine blades for wind power generation equipment.

[0039] In the fabrication of wind turbine blades, the eddy current generator of the wind turbine blade is first subjected to surface activation treatment, and then bonded to the fiberglass reinforced plastic (FRP) blade using acrylic structural adhesive to finally obtain the wind turbine blade. This method enhances the bonding strength between PVDF and FRP, increasing the bonding strength to 3.5-5.0 MPa, breaking through the technical bottleneck of weak bonding between traditional PVDF and FRP, and solving the risk of detachment of the eddy current generator during long-term service of the wind turbine blade.

[0040] Furthermore, the surface activation treatment includes one or more of mechanical roughening, PVDF interface chemical activation, and silane coupling agent primer treatment; the PVDF interface chemical activation includes plasma activation treatment, chemical etching, coating with a fluorine-specific CPO primer, ozone oxidation treatment, or surface grafting with a phosphate ester coupling agent.

[0041] Furthermore, after the surface activation treatment of the wind turbine blade eddy current generator is completed, it also includes a coating protection treatment before being bonded to the fiberglass blade.

[0042] Compared with the prior art, the polyvinylidene fluoride wind turbine blade eddy current generator of the present invention has the following advantages:

[0043] 1. Ultra-weather-resistant and long-life: The high bond energy structure of PVDF makes it highly resistant to ultraviolet rays, damp heat, salt spray, and acid rain. The wind turbine blade eddy current generator described in this invention has an outdoor service life of ≥30 years, matching the design life of wind turbine blades and solving the problem of frequent replacement of traditional VG. It is suitable for offshore wind turbine blades, meeting the requirement of maintenance-free operation of offshore blades throughout their 25-30 year life cycle, greatly reducing the cost of VG replacement and maintenance.

[0044] 2. Stable aerodynamic performance: The wind turbine blade eddy current generator of the present invention has low surface energy (hydrophobic contact angle ≥90°), which can realize self-cleaning function, reduce the adhesion of sand, insects and ice, and maintain the aerodynamic shape accuracy for a long time;

[0045] 3. Lightweight and low drag: The PVDF VG structure of the wind turbine blade eddy current generator described in this invention is 30-50% lighter than traditional metal VG and 10-20% lighter than fiberglass VG, reducing blade load;

[0046] 4. Significant cost reduction and efficiency improvement: The power generation gain remains stable at 1.5-3% over the long term, and the total cost of ownership (LCOE) is reduced by 5-8% due to the reduction in maintenance frequency, demonstrating clear industrial application value.

[0047] The method for preparing the polyvinylidene fluoride wind turbine blade eddy current generator described in this invention has the following advantages:

[0048] 1) This invention solves the technical challenge of "the contradiction between PVDF toughening and processability". By selecting a fluoroethylene-tetrafluoroethylene copolymer (ETFE) toughening agent (which, like PVDF, is a fluoropolymer with excellent compatibility); optimizing the mixing sequence (mixing PVDF resin and toughening agent first, then adding fillers and additives); and controlling the extrusion temperature range (185-215℃) and screw speed (280-320 r / min), this invention achieves "synergistic optimization of PVDF toughening and processability".

[0049] 2) This invention solves the problem of uneven dispersion and failure of UV-resistant additives. In traditional PVDF molding, nano-sized UV-resistant fillers are prone to agglomeration, and UV absorbers / light stabilizers are prone to migration or high-temperature volatilization, leading to a decline in weather resistance. The process of this invention avoids additive volatilization and agglomeration by using raw material pretreatment (drying and dehydrating nano-TiO2) and stepwise mixing (first dispersing the filler at high speed, then adding the additive at low speed), and vacuum degassing (-0.06 to -0.08 MPa) during extrusion.

[0050] 3) The "PVDF injection molding process window" has been optimized, reducing the difficulty of industrialization. Traditional PVDF injection molding processes have a narrow temperature range (prone to degradation or insufficient flowability), high equipment requirements, and are difficult to industrialize. This invention addresses these issues by: a) precisely controlling the barrel temperature gradient to avoid overheating and degradation; b) setting appropriate mold temperature and injection speed to solve the problems of insufficient mold filling and internal stress during the molding of thin-walled parts; and c) optimizing drying parameters to avoid defects such as bubbles and silver streaks. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0052] The first objective of this invention is to provide a polyvinylidene fluoride composition for wind turbine blade eddy current generators, comprising, by weight, the following components: 75-88 parts by weight of PVDF resin, 3-20 parts by weight of toughening agent, 0.5-4.5 parts by weight of UV-resistant main agent, 2-10 parts by weight of nano-titanium dioxide, 1-10 parts by weight of interfacial adhesion improver, 0.3-1.5 parts by weight of fluorine-based processing lubricant, and 0.2-1.2 parts by weight of antioxidant.

[0053] The main resin, PVDF, primarily provides long-term weather resistance, hydrophobicity, and structural integrity. The PVDF resin used in this invention has a molecular weight of 200,000 to 1,100,000, more preferably 400,000 to 600,000. The melt index of PVDF ranges from 6 to 15 g / 10 min at 230℃ / 5 kg. PVDF exists in various crystal forms, including α, β, γ, and δ, with the β phase exhibiting higher polarity and superior mechanical properties, which is beneficial for improving interfacial bonding strength and long-term fatigue resistance. This invention, by selecting high-molecular-weight PVDF resin, combined with the heterogeneous nucleation effect of polar interfacial modifiers and nano-inorganic fillers, and by controlling temperature, shear, and orientation during injection molding, effectively increases the proportion of the β phase in the system, thereby significantly enhancing the strength, toughness, and structural stability of the composite material, ensuring that the blade vortex generator does not crack or debond under long-term outdoor conditions.

[0054] Furthermore, the toughening agent is selected from at least one of fluoropolymers, fluoroelastomers, and weather-resistant core-shell toughening agents. The toughening agent improves fracture toughness, impact resistance, and fatigue resistance, but does not affect UV aging resistance.

[0055] More preferably, the toughening agent is specifically selected from at least one of ethylene-tetrafluoroethylene copolymer (ETFE), ternary fluoropolymer (THV), fluororubber (FKM), perfluoroethylene-propylene copolymer (FEP), ethylene-trifluorochloroethylene copolymer (ECTFE), weather-resistant acrylate core-shell toughening agent (ACR), and silicone-modified acrylate toughening agent (Si-ACR); most preferably, ETFE.

[0056] Furthermore, the content of the toughening agent is preferably 5 to 12 parts by weight.

[0057] Furthermore, the UV-resistant main agent is a compound of benzophenone-based UV absorber (UV-531) and hindered amine light stabilizer (HALS). The function of the UV-resistant main agent is to absorb ultraviolet light and capture free radicals, thereby extending the weather resistance life.

[0058] Furthermore, the nano-titanium dioxide is rutile type with a particle size of 20-50 nm. The nano-titanium dioxide serves as a UV-resistant filler, reflecting ultraviolet light and synergistically enhancing weather resistance.

[0059] Furthermore, the interfacial adhesion improver is one or more of the following: silane coupling agent, anhydride-grafted fluoropolymer, GMA-grafted fluoropolymer, carboxyl-modified PVDF, epoxy-modified fluoropolymer, amino-modified fluoropolymer, fluorinated alkyl coupling agent, and phosphate ester coupling agent. The function of the interfacial adhesion improver is to enhance the bonding strength between VG and FRP blades and improve interfacial compatibility.

[0060] More preferably, the interfacial adhesion improver is a compound system of silane coupling agent and acid anhydride grafted fluoropolymer.

[0061] The silane coupling agent is selected from at least one of KH550, KH560, KH570, and A-171 (vinyltrimethoxysilane); the anhydride-grafted fluoropolymer is selected from at least one of MAH-g-PVDF (maleic anhydride-grafted polyvinylidene fluoride), GMA-g-PVDF (glycidyl methacrylate-grafted polyvinylidene fluoride), MAH-g-ETFE (maleic anhydride-grafted ethylene-tetrafluoroethylene copolymer), and MAH-g-THV. For example, the interfacial adhesion improver can be one or a combination of the following: KH570+MAH-g-PVDF, KH560+GMA-g-PVDF, KH550+KH570+MAH-g-ETFE, KH-550+MAH-g-PVDF, etc.

[0062] In the most preferred embodiment, the interfacial adhesion improver is a compound of silane coupling agent (KH-550, γ-aminopropyltriethoxysilane) and maleic anhydride-grafted PVDF (MAH-g-PVDF, grafting rate 1.2-1.8%).

[0063] Furthermore, the fluorine-based processing lubricant is preferably PTFE micro powder with a particle size of 1~5μm. The function of the processing aid is to reduce melt viscosity, improve mold release properties, and not affect surface hydrophobicity.

[0064] Furthermore, the antioxidant is a combination of hindered phenolic antioxidant (1010) and phosphite auxiliary antioxidant (168), with a combination ratio of antioxidant (1010:168=1:1~1:2).

[0065] The polyvinylidene fluoride (PVDF) used in the eddy current generator of wind turbine blades described in this invention features a UV protection system in its raw material formulation that achieves comprehensive and long-lasting light stability protection for PVDF materials outdoors through a three-level synergistic effect of physical reflection, chemical absorption, and free radical capture—namely, "UV absorption + free radical capture + UV reflection." Testing shows that the UV shielding efficiency of this invention's system is more than 40% higher than that of a single component, while reducing the light stabilizer migration rate by 60%.

[0066] Nano-TiO2 (rutile type) first strongly reflects and scatters ultraviolet light, significantly reducing the ultraviolet energy entering the material's interior and weakening the driving force of photoaging from the outside. The ultraviolet light that is not completely reflected is efficiently absorbed by UV-531, and the light energy is converted into heat energy and dissipated through intramolecular proton transfer, preventing the PVDF molecular chain from being excited. For a small amount of free radicals induced by light, heat, and stress, HALS quickly captures and blocks the chain reaction of oxidative degradation, while realizing its own recycling and regeneration. UV-531 and HALS work synergistically to reduce mutual consumption and improve migration resistance. The physical shielding of nano-TiO2 further reduces the chemical stabilizer load. The combined effect of these three factors reduces the aging rate of the material in strong ultraviolet, humid heat, and salt spray environments by more than an order of magnitude, significantly improving the long-term mechanical property retention rate and ensuring that the eddy current generator does not crack, deform, or fall off during its 20-30 year service life. This ternary composite system is not a simple superposition of components, but rather a multi-level, multi-mechanism, complementary and synergistic light-stabilizing system that achieves unexpected long-term weather resistance and plays a key role in realizing long life and maintenance-free operation of wind turbine blade eddy current generators.

[0067] The second objective of this invention is to provide a polyvinylidene fluoride (PVDF) wind turbine blade eddy current generator.

[0068] Specifically, the polyvinylidene fluoride wind turbine blade eddy current generator is manufactured through the following steps:

[0069] (1) Prepare raw materials according to the ratio, first mix PVDF resin with toughening agent, and then add UV resistant main agent, nano titanium dioxide, interface adhesion improver, fluorine processing lubricant and antioxidant to make PVDF granules;

[0070] (2) Dry the PVDF granules to remove water, so that the moisture content is ≤0.015%;

[0071] (3) The dried PVDF granules are prepared into polyvinylidene fluoride wind turbine blade eddy current generators by injection molding process; Injection molding process parameters: set the barrel temperature and injection mold temperature, preheat for 30 min, the temperatures of the front, middle and rear sections of the barrel are 210~220℃, 205~215℃ and 190~200℃ respectively, the nozzle temperature is 205~215℃, and the injection mold temperature is ≥80℃.

[0072] In step (1), the mixture is made into PVDF granules using conventional methods in the art (e.g., screw extrusion granulation). The specific operation includes: first, adding PVDF resin and toughening agent to a high-speed mixer and premixing for 3 min at 800~1000 r / min; then adding UV-resistant main agent, nano titanium dioxide, interface adhesion improver, fluorine-based processing lubricant and antioxidant, and mixing for 2 min at 500 r / min, for a total mixing time of 5~6 min; after uniform mixing, extruding and granulating through a parallel twin-screw extruder (L / D≥40:1), with an extrusion temperature of 185~215℃, screw speed of 280~320 r / min, vacuum degree of -0.06~-0.08MPa, water-cooled strip cutting, and drying at 80℃ for 2 h to obtain PVDF granules.

[0073] Furthermore, the drying and dehydration temperature in step (2) is 80~90℃, and the time is 4~6 hours.

[0074] PVDF compositions need to be thoroughly dried before injection molding to avoid bubbles, silver streaks, and interface defects. This invention investigated the effects of different drying temperatures and times on the moisture content of PVDF granules, and the results are shown in Table 1. Based on the experimental results, the preferred PVDF drying conditions selected in this invention are drying at 80-90°C for 4-6 hours.

[0075] Furthermore, the temperature of the injection mold in step (3) is 80~100℃. The mold must be heated to above 80℃, otherwise the VG surface will have poor gloss, be prone to internal stress, and be prone to cracking. The injection mold temperature in this invention is preferably 80~100℃ to promote the relaxation of PVDF molecular chains, reduce internal stress, induce the formation of β crystal phase, and improve the crystallinity and dimensional stability of the product.

[0076] Furthermore, in step (3), the injection mold has venting grooves at the sharp corners, abrupt changes in wall thickness, and wingtips corresponding to the eddy current generator. This ensures smooth venting during the filling process, reduces trapped air, scorching, porosity, and weld lines, and improves the density, structural uniformity, and long-term fatigue crack resistance of the product. The venting grooves have a depth of 0.02~0.04 mm, a width of 3~5 mm, and a length of 8~12 mm.

[0077] This invention employs a gradually increasing barrel temperature gradient from the feeding section to the nozzle (temperatures in the front, middle, and rear sections of the barrel are 210~220℃, 205~215℃, and 190~200℃, respectively, with the nozzle temperature at 205~215℃). This allows for control of the PVDF granule melt viscosity within the range of 1100~1400 Pa·s, achieving excellent mold filling flowability and melt stability. Appropriate shear and temperature conditions reduce internal stress, improve surface quality, promote the regular arrangement of PVDF molecular chains, and increase the β-phase proportion. Simultaneously, high-temperature degradation is avoided, ensuring the composite material's mechanical strength, aging resistance, and structural stability under long-term outdoor conditions, meeting the durability requirements of wind turbine blade eddy current generators. When the β-phase proportion is ≥60%, the notched impact strength of the material is increased by more than 50% compared to materials dominated by the α-phase, and the long-term fatigue resistance is improved by more than 2 times.

[0078] In addition, since PVDF is corrosive, the preferred solution is to use nozzles and barrels made of corrosion-resistant materials such as Ni-based alloys.

[0079] Further, the conditions of the injection molding process in step (3) include: injection rate of medium to high speed 20~40mm / s; injection pressure of 50~110MPa; holding pressure of 50~60MPa; holding time of 10~25s (preferably 10~15s); cooling time of 15~40s; and screw back pressure of 3~5MPa.

[0080] In injection molding, the trial molding method employs a gradual increase in speed and pressure, starting with low speed and pressure, and adjusting the holding pressure to eliminate shrinkage marks. This invention preferably uses an injection rate of 20–40 mm / s (medium-high speed range). This rate range ensures sufficient melt filling while achieving a balance between melt flow stability and shear orientation, significantly optimizing internal stress reduction, surface quality improvement, and crystal phase structure control. Injection rates <20 mm / s result in slow filling, uneven cooling, high internal stress, and noticeable surface defects; injection rates >40 mm / s lead to shear overheating, excessive molecular chain orientation, and increased stress concentration, easily causing product warping and potentially localized degradation. A medium-high speed injection rate of 20–40 mm / s achieves optimal overall performance in terms of filling efficiency, flow stability, internal stress control, surface quality, and β-phase development.

[0081] This invention controls the injection molding holding pressure at 50-60 MPa and the holding time at 10-25 s. This range of process parameters effectively compensates for melt cooling shrinkage and improves the density and dimensional consistency of the product. Holding pressure < 50 MPa or holding time < 10 s results in insufficient shrinkage compensation, obvious shrinkage marks, large dimensional deviations, and low density. Holding pressure > 60 MPa or holding time > 25 s easily leads to over-pressurization, stress accumulation, difficulty in demolding, and gate sticking, while also increasing internal stress and negatively impacting long-term fatigue resistance. A holding pressure of 50-60 MPa and a holding time of 10-25 s achieves an optimal balance between shrinkage compensation, dimensional accuracy, internal stress levels, and production stability, ensuring that the parts meet the requirements of high precision, high consistency, and long-term reliable service for wind turbine blade eddy current generators. The impact of the core injection molding process parameters on performance is shown in Table 3.

[0082] After stabilization, continuous production will be carried out. The wind turbine blade eddy current generator described in step (3) will be naturally cooled after molding to avoid internal stress cracking caused by rapid cooling.

[0083] This invention preferably employs a natural slow cooling process (internal mold cooling + room temperature resting, cooling time ≥ 20 min). Compared with rapid cooling, this process can reduce internal stress in the product by more than 60%, significantly increase the proportion of β-crystal phase, significantly reduce warpage, and greatly improve crack resistance and long-term fatigue resistance, making it more suitable for the harsh service environment of wind turbine blade eddy current generators. Experimental results show that if rapid cooling (water cooling / forced air cooling, cooling time ≈ 1~3 min) is used, the following problems will occur: 1) Large temperature difference between the surface and interior of the product, and rapid cooling rate; 2) Internal stress test value: 22~28 MPa; 3) Molecular chains do not have time to relax, and orientation is severely frozen; 4) β-crystal phase proportion of PVDF: only 45%~52%; 5) Warpage of the product: 0.6~1.0 mm; 6) After thermal shock (-40℃~80℃ cycle), obvious cracking occurs at the edges and sharp corners, with a high tendency to crack; 7) Stress whitening and microcrack propagation are prone to occur under long-term wind vibration conditions.

[0084] As can be seen from the above, the preparation method of this invention addresses the industry pain points of PVDF's high crystallinity, which easily leads to internal stress and cracking, through a four-pronged approach of temperature control, pressure holding, slow cooling, and forced degassing. This invention provides solutions to common problems encountered in VG manufacturing, as detailed below:

[0085] a) Surface silver streaks: The cause is excessive moisture and temperature. This invention solves this problem by enhancing drying and reducing nozzle temperature. Trace amounts of moisture rapidly vaporize at high temperatures in the barrel, forming tiny bubbles. When the melt fills the mold, these bubbles burst and stretch, forming continuous, thread-like silver streaks on the surface of the part. Simultaneously, moisture weakens the intermolecular forces of PVDF, reducing melt strength and exacerbating surface defects. Excessively high nozzle temperature leads to localized thermo-oxidative degradation of PVDF, causing molecular chain breakage and decreased melt strength. Under shear flow, this easily results in melt fracture and surface silver streaks. Furthermore, high temperatures intensify the vaporization of residual moisture, further worsening surface quality. By enhancing drying to ensure a moisture content ≤150 ppm and controlling the nozzle temperature within the range of 205~215℃, the causes of moisture bubbling and thermal degradation can be eliminated at the source, essentially completely suppressing surface silver streaks.

[0086] b) Wingtip material shortage: The cause is poor venting and low mold temperature. This invention solves this problem by increasing the mold temperature through venting. Increasing the mold temperature to ≥80℃ and setting appropriate venting grooves at the wingtip can reduce the wingtip material shortage rate from over 40% to below 1%, significantly improving mold filling integrity and structural uniformity, ensuring sufficient strength and fatigue resistance at the wingtip of the eddy current generator, and meeting the requirements for long-term reliable service.

[0087] c) Cracking and brittle fracture: The cause is high internal stress and excessively rapid cooling. This invention solves this problem by increasing the mold temperature and extending the cooling time. Extending the cooling time allows the PVDF molecular chains to fully deorient and rearrange near the glass transition temperature, avoiding stress freezing and significantly reducing stress concentration at sharp corners and weak points. Under slow cooling conditions, crystal development is more complete, the crystal form is more stable, and the material has higher toughness, making it less prone to microcracks under external loads and environmental changes. Slow and uniform cooling can reduce the internal and external temperature difference and shrinkage gradient, reduce warping and additional stress, and improve long-term dimensional stability and fatigue resistance. By increasing the mold temperature to ≥80℃ and adopting a slow cooling process (cooling time ≥20 min), the internal stress of the product can be controlled at 6~12MPa, reducing the microcrack rate to below 5% and the brittle fracture rate to 0%, significantly reducing the tendency of the eddy current generator to crack and brittle fracture during long-term service, and ensuring durability and reliability.

[0088] d) Discoloration and yellowing: This is caused by degradation at high temperatures. This invention solves this problem by lowering the temperature and increasing vacuum exhaust. By controlling the processing temperature at 190~220℃ and using high vacuum exhaust (-0.09 ~ -0.10MPa), the yellowness value (YI) of the PVDF composite material can be controlled within the range of 1.5~3.8, with volatile residue ≤200ppm, completely suppressing discoloration and yellowing defects while ensuring melt flowability and molding quality. This optimized solution allows the material to maintain its original color while retaining long-term UV resistance and anti-aging properties, meeting the appearance stability and performance reliability requirements of wind turbine blade eddy current generators for long-term outdoor service.

[0089] A third objective of this invention is to provide the application of the wind turbine blade eddy current generator in the manufacture of wind turbine blades for wind power generation equipment.

[0090] To ensure a strong bond between the VG and the fiberglass blade, the eddy current generator of the wind turbine blade needs to undergo surface activation treatment before bonding to the wind turbine blade. This process breaks the CF2 bonds, introduces polar groups, and improves the adhesion of the coating. Finally, acrylic structural adhesive is used for bonding. The surface activation treatment includes one or more of the following: mechanical roughening, chemical activation of the PVDF interface, and silane coupling agent primer treatment.

[0091] a) Mechanical roughening: After gently sanding the lower surface (bonding surface) of the VG base with 400-600 grit sandpaper, the interface can be microscopically roughened, forming mechanical interlocking and greatly increasing the adhesive wetting area; then wipe with acetone, isopropanol or anhydrous ethanol or ultrasonic cleaning; finally blow clean compressed air and wipe the VG surface with a lint-free cloth to remove mold release agent, oil, and dust.

[0092] b) PVDF interfacial chemical activation:

[0093] The mechanically roughened VG base surface is subjected to interfacial chemical activation. Specific methods include plasma activation treatment, chemical etching, coating with a fluorine-specific CPO primer (or a commercially available fluorine-specific primer), ozone oxidation treatment, or surface grafting with a phosphate ester coupling agent.

[0094] The plasma activation treatment was conducted with an Ar / O2 volume ratio of 1:1, a vacuum of 30–50 Pa, and a power density of 1.0–3.0 W / cm³. 2The process involves a power of 200-300W and a time of 10-40s. After plasma surface treatment, the material surface transforms from a non-polar CF structure into an activated surface rich in polar functional groups such as -OH, -C=O, and -COOH. The surface energy increases from 29 mN / m to 45-50 mN / m, and the roughness Ra is controlled at 70-90 nm. The bonding strength with the fiberglass blade increases from 1.8 MPa in the untreated case to 3.7-4.0 MPa, and the strength retention rate is ≥85% after 1000 hours of damp heat aging, meeting the requirement of long-term service without detachment of wind turbine blades.

[0095] The chemical etching process involves using a sodium-naphthalene complex etching solution, immersing the sample in the solution for 10-30 seconds at room temperature, rinsing it with running water, and finally drying it.

[0096] Apply a CPO primer specifically for fluorine materials: improves wettability and adhesion strength.

[0097] Ozone oxidation treatment: introducing polar groups such as hydroxyl and carboxyl groups onto the surface of PVDF.

[0098] Surface grafting with phosphate ester coupling agents improves hydrolysis and salt spray resistance.

[0099] c) Silane coupling agent primer treatment:

[0100] A silane coupling agent (one or more of KH550, KH560, and KH570) is added to a mixed solvent of ethanol and water (ethanol:water = 90:10, volume ratio) to make the concentration of the silane coupling agent 0.5wt%~3.0wt%. The mixture is stirred at room temperature for 10~15 min to completely hydrolyze the silane. The pH is then adjusted to 4.0~5.5 with acetic acid to obtain a hydrolysate. The hydrolysate is then used to spray or impregnate the bonding surface of the plasma-treated PVDF eddy current generator. Subsequently, it is dried with hot air at 60℃ for 10 min to form uniform and dense coupling monomolecules.

[0101] Furthermore, after the surface activation treatment of the wind turbine blade eddy current generator is completed, a protective coating treatment is also applied before bonding it to the fiberglass blade. This additional protective coating treatment provides better triple protection: weather resistance of the blade itself, interface strengthening, and surface protection, thus better meeting the design life of wind turbine blades for outdoor use of 30 years or more.

[0102] The coating protection treatment includes: after VG undergoes surface activation treatment, a primer and a topcoat are sequentially applied to its surface.

[0103] The primer is selected from fluorocarbon-specific primers (containing hydroxyl / epoxy groups) or chlorinated polyolefin (CPO) primers, with a coating thickness of 5-20 μm. The primer serves as a transition layer, resolving the issue of non-wetting between PVDF and the fluorocarbon topcoat.

[0104] The topcoat is FEVE fluorocarbon topcoat, with a coating thickness of 30-60μm. The function of FEVE fluorocarbon topcoat is to ensure weather resistance ≥30 years, prevent chalking and fading, and provide hydrophobic self-cleaning properties. It can be applied by spraying, brushing, etc. FEVE fluorocarbon topcoat cures at room temperature and is fully cured after 7 days.

[0105] The eddy current generator of the wind turbine blade is preferably bonded to the wind turbine blade at room temperature using acrylic adhesive, which typically achieves complete curing after 7 days, ensuring complete cross-linking, aging resistance, fatigue resistance, and hydrolysis resistance.

[0106] In the preferred embodiment of this invention, a four-level interface strengthening system of "mechanical roughening + plasma activation + silane coupling + coating protection" is adopted to achieve a 30-year long-life bonding between PVDF-VG and the blade shell.

[0107] The sources of the raw materials used in the following examples and comparative examples are as follows:

[0108] Ethylene-tetrafluoroethylene copolymer (ETFE), Shandong Huafu Chemical Co., Ltd.;

[0109] Benzophenone-based ultraviolet absorber (UV-531), Nanjing Milan Chemical Co., Ltd.;

[0110] Hindered amine light stabilizer (HALS), RIASORB® UV-944, Lialon Corporation;

[0111] Nano titanium dioxide (particle size 20-50nm, rutile type), Jiangsu Hehai Nanotechnology Co., Ltd.

[0112] KH550 (γ-aminopropyltriethoxysilane), Anhui Sibao Organosilicon New Materials Co., Ltd.;

[0113] Maleic anhydride-grafted PVDF (MAH-g-PVDF, grafting rate 1.2-1.8%), Arkema, France;

[0114] Processed lubricant PTFE micro powder, particle size 1-5μm, Nanjing Tianshi New Material Technology Co., Ltd.

[0115] Hindered phenolic antioxidant (1010), BASF, Germany;

[0116] Phosphite-based auxiliary antioxidant (168), Shanghai Kaiyin Chemical Co., Ltd.;

[0117] The PVDF resin used in Example 1 has a molecular weight of 450,000, a melt index of 6-15 g / 10 min (230℃ / 5Kg, ASTM D1238), and is from Solvay Corporation, USA, grade 6010.

[0118] The PVDF resin used in Example 2 had a molecular weight of 600,000 and a melt index of 6-15 g / 10 min (230℃ / 5Kg, ASTM D1238) and was Arkema Kynar 720.

[0119] The PVDF resin used in Example 3 has a molecular weight of 400,000 and a melt index of 6-15 g / 10 min (230℃ / 5Kg, ASTM D1238), Shandong Dongyue Shenzhou DS206.

[0120] The 1000h dual 85 / QUV mentioned in the examples and comparative examples refers to performing 1000h each of dual 85 damp heat aging and QUV ultraviolet aging. The test conditions for dual 85 damp heat aging are 1000h at 85°C and 85% RH (ISO4611); the test conditions for QUV ultraviolet aging are 1000h of UVB-313nm ultraviolet aging (ISO4892).

[0121] Example 1

[0122] Step 1, Raw material preparation:

[0123] Prepare PVDF granules for injection molding according to the following formula (parts by weight): 84 parts by weight of PVDF resin, 8 parts by weight of ETFE, 0.5 parts by weight of UV-531, 0.5 parts by weight of HALS, 4.1 parts by weight of nano titanium dioxide, 0.7 parts by weight of KH550, 1.3 parts by weight of MAH-g-PVDF, 0.5 parts by weight of PTFE micro powder, 0.2 parts by weight of hindered phenolic antioxidant (1010), and 0.2 parts by weight of phosphite auxiliary antioxidant (168).

[0124] First, PVDF resin and toughening agent are added to a high-speed mixer and premixed for 3 min at 900 r / min. Then, UV-resistant main agent, nano titanium dioxide, interfacial adhesion improver, fluorine-based processing lubricant and antioxidant are added and mixed for 2 min at 500 r / min, for a total mixing time of 5 min. After uniform mixing, the mixture is extruded and granulated through a parallel twin-screw extruder (L / D≥40:1) at an extrusion temperature of 200℃, a screw speed of 300 r / min, and a vacuum degree of -0.07MPa. The granules are then water-cooled, drawn into strips, and dried at 80℃ for 2 h to obtain PVDF granules.

[0125] Step 2, Drying process: Dry the PVDF granules at 90℃ for 4 hours to remove water, so that the moisture content is ≤0.015%.

[0126] Step 3, Injection Molding: The dried PVDF granules are injection molded into a wind turbine blade eddy current generator, which is then allowed to cool naturally after molding. The mold temperature is set at 90℃, and the temperatures of the front, middle, and rear sections of the barrel are 215℃, 210℃, and 195℃, respectively; the nozzle temperature is 207℃. The injection pressure is 95MPa; the holding pressure is 55MPa; the holding time is 12s; the cooling time is 25s; and the screw back pressure is 4MPa. The surface contact angle of the eddy current generator is measured to be 95°, indicating self-cleaning capability.

[0127] Step 4, Performance Testing:

[0128] 1. This experiment involves preparing tensile, bending, and notched impact test specimens from the PVDF granules dried in step 2 using the injection molding process described in step 3, and then conducting UV aging tests. The test results are as follows:

[0129] According to ISO 527 testing, the tensile strength is 42 MPa and the elongation at break is 42%; according to ISO 178 testing, the flexural strength is 56 MPa and the flexural modulus is 1.4 GPa; according to GB / T 1043 testing, its notched impact strength is 240 J / m. The β-phase ratio of PVDF, determined by DSC method, is 65%–72%.

[0130] After UVB aging for 3000 hours (according to ISO 4892), the retention rates of tensile strength and notched impact strength both exceeded 85%.

[0131] 2. In this experiment, the PVDF granules prepared in step 1 were dried at different temperatures and times, and the moisture content of the dried PVDF granules was measured. The specific experiments and moisture content results are shown in Table 1:

[0132] Table 1. Effects of different drying temperatures and times on the moisture content of PVDF granules.

[0133]

[0134] 3. Based on step 3, this experiment changed the nozzle temperature and PVDF particle moisture content to investigate the effects of nozzle temperature and moisture on VG surface quality. The results are shown in Table 2:

[0135] Table 2. Effects of moisture and nozzle temperature on VG surface quality

[0136]

[0137] 4. Based on step 3, this experiment changed the core injection molding process parameters and then tested the key performance of the product. The results are shown in Table 3:

[0138] Table 3. Impact of core injection molding process parameters on key product performance.

[0139]

[0140] 5. This experiment, based on step 3, changed the cooling method after VG molding to examine the comparison of crystal phase and microstructure parameters of PVDF composite materials under different process conditions. The results are shown in Table 4:

[0141] Table 4 Comparison of crystal phase and microstructure parameters of PVDF composite materials under different processing conditions

[0142]

[0143] 6. This experiment tests the relevant properties after bonding the VG obtained in step 3 with fiberglass (FRP) blades. The effects of different interface treatments on the bonding performance of VG and blades are shown in Table 5.

[0144] Bonding Method 1: After lightly sanding the bonding surfaces of the VG chassis and blades with 500-grit sandpaper, the surfaces are cleaned with acetone. Then, Ar / O2 (volume ratio 1:1) plasma activation treatment is performed at a vacuum of 30~50Pa, power density of 1.0 W / cm², and time of 30 s. Next, a silane coupling agent KH-550 ethanol dilute solution is used as a primer (drying at 60℃ for 10 min). Acrylic adhesive (Beijing Tianshan GI9633 or commercially available similar acrylic structural adhesive) is used for bonding. After 7 days at room temperature, complete curing is achieved. According to ISO4587, the single lap tensile shear strength is 4.2MPa (adhesive film thickness 1mm).

[0145] Bonding method 2: Without pretreatment, the VG obtained in step 3 is directly bonded to the fiberglass (FRP) blade using acrylic adhesive (adhesive film thickness 1mm).

[0146] Bonding Method 3: Lightly sand the bonding surfaces of the VG chassis and blades with 500-grit sandpaper, and then use acrylic adhesive to bond the sanded VG to the fiberglass (FRP) blades (adhesive film thickness 1mm).

[0147] Bonding Method 4: After lightly sanding the bonding surfaces of the VG chassis and blades with 500-grit sandpaper, clean the surface with acetone; then use acrylic adhesive to bond the treated VG to the fiberglass (FRP) blades (adhesive film thickness 1mm).

[0148] After bonding according to bonding method 1, relevant performance tests were conducted. The test results showed that the initial tensile shear bond strength was 4.2 MPa; after 200 cycles of high and low temperature cycling test from -40℃ to 85℃, the bond strength was 3.6 MPa, with a strength retention rate of 86%; while the strength retention rate of the untreated sample (bonding method 2) was only 39%, and the strength retention rate of the plasma-treated sample was only about 65%.

[0149] Table 5. Effects of different interface treatments on adhesive performance

[0150]

[0151] 7. The performance of the PVDF VG prepared in step 3 above was compared with that of the VG of traditional materials. The results are shown in Table 6. The PVDF VG of the present invention has the characteristics of long life, self-cleaning and strong adhesion.

[0152] Table 6. Comparison of main properties of the PVDF VG of the present invention with those of VG made from traditional materials.

[0153]

[0154] Note: Service life is assessed using QUV ultraviolet light + dual 85 damp heat accelerated aging equivalent evaluation: 1000h ≈ 10 years outdoors, 3000h ≈ 30 years outdoors. The accelerated aging conditions comply with ISO 4892-3 UVB cycle test + ISO 4611 dual 85 damp heat test. The aging factors are matched with the actual irradiance, temperature and humidity data of wind power scenarios in Northwest / Southeast coastal my country, and the equivalent conversion factor has been verified by a third-party testing agency.

[0155] Example 2

[0156] Step 1: Prepare PVDF granules for injection molding according to the following formula (parts by weight): 86.2 parts by weight PVDF resin, 5 parts by weight ETFE, 0.6 parts by weight UV-531, 0.6 parts by weight HALS, 5 parts by weight nano titanium dioxide, 0.6 parts by weight KH560, 1.2 parts by weight GMA-g-PVDF, 0.4 parts by weight PTFE micro powder, 0.2 parts by weight hindered phenolic antioxidant (1010), 0.2 parts by weight phosphite auxiliary antioxidant (168).

[0157] First, PVDF resin and toughening agent are added to a high-speed mixer and premixed for 3 min at 900 r / min. Then, UV-resistant main agent, nano titanium dioxide, interfacial adhesion improver, fluorine-based processing lubricant and antioxidant are added and mixed for 2 min at 500 r / min, for a total mixing time of 5 min. After uniform mixing, the mixture is extruded and granulated through a parallel twin-screw extruder (L / D≥40:1) at an extrusion temperature of 200℃, a screw speed of 300 r / min and a vacuum degree of -0.07 MPa. The granules are then water-cooled, drawn into strips, and dried at 80℃ for 2 h to obtain PVDF granules.

[0158] Step 2: Dry the PVDF granules at 80℃ for 5 hours to remove water, so that the moisture content is ≤0.015%.

[0159] Step 3: The dried PVDF granules are molded into vortex generators for PVC wind turbine blades using an injection molding process. After molding, the granules are allowed to cool naturally. The mold temperature is set to 100℃, and the temperatures of the rear, middle, and front sections of the barrel are 198℃, 210℃, and 215℃, respectively. The nozzle temperature is 206℃. The injection pressure is 100MPa; the holding pressure is 60MPa; the holding time is 12s; the cooling time is 30s; and the screw back pressure is 4MPa.

[0160] The PVDF granules dried in step 2 were processed into tensile, flexural, and notched impact test specimens using the injection molding process in step 3. Following the performance testing methods described in Example 1, the tensile strength of the specimens prepared in Example 2 was measured to be 38 MPa, and the elongation at break was 30%. The β-phase ratio of PVDF was determined to be 70%–78% using the DSC method.

[0161] The VG surface treatment and bonding were performed according to bonding method 1 as described in Example 1.

[0162] Tensile shear strength of a single lap joint after PVDF / FRP bonding (film thickness 1mm): 3.8MPa; Strength retention rate of double 85 / QUV 1000h ≥85%.

[0163] Example 3

[0164] Step 1 Raw material preparation: Prepare PVDF granules for injection molding according to the following formula (parts by weight): 81 parts by weight PVDF resin, 12 parts by weight ETFE, 0.4 parts by weight UV-531, 0.4 parts by weight HALS, 3 parts by weight nano titanium dioxide, 0.8 parts by weight KH570, 1.4 parts by weight MAH-g-ETFE, 0.6 parts by weight PTFE micro powder, 0.2 parts by weight hindered phenolic antioxidant (1010), and 0.2 parts by weight phosphite auxiliary antioxidant (168).

[0165] First, PVDF resin and toughening agent are added to a high-speed mixer and premixed for 3 min at 900 r / min. Then, UV-resistant main agent, nano titanium dioxide, interfacial adhesion improver, fluorine-based processing lubricant and antioxidant are added and mixed for 2 min at 500 r / min, for a total mixing time of 5 min. After uniform mixing, the mixture is extruded and granulated through a parallel twin-screw extruder (L / D≥40:1) at an extrusion temperature of 200℃, a screw speed of 300 r / min and a vacuum degree of -0.07 MPa. The granules are then water-cooled, drawn into strips, and dried at 80℃ for 2 h to obtain PVDF granules.

[0166] Step 2 Drying process: Dry the PVDF granules at 92℃ for 4 hours to remove water, so that the moisture content is ≤0.015%.

[0167] Step 3: Injection Molding: The dried PVDF granules are molded into vortex generators for PVC wind turbine blades using injection molding. The mold temperature is set to 100℃, and the temperatures of the rear, middle, and front sections of the barrel are 198℃, 210℃, and 215℃, respectively; the nozzle temperature is 206℃. The injection pressure is 100MPa; the holding pressure is 60MPa; the holding time is 12s; the cooling time is 30s; and the screw back pressure is 4MPa.

[0168] Step 4 Performance Testing:

[0169] The PVDF granules dried in step 2 were processed into material through the injection molding process in step 3. Tensile, bending, and notched impact test specimens were prepared. Referring to the performance testing method in Example 1, the tensile strength of the specimen prepared in Example 3 was measured to be 47 MPa, and the elongation at break was 60%. The PVDF β-phase ratio was determined to be 60%–68% by DSC method.

[0170] The VG surface treatment and bonding were performed according to bonding method 1 of Example 1.

[0171] The tensile shear strength of a single lap joint after PVDF / FRP bonding (film thickness 1mm) is 4.9MPa; the strength retention rate is ≥85% after 1000h of double 85 damp heat aging + 1000h of QUV ultraviolet aging. It has excellent impact resistance and fatigue resistance, and is suitable for coastal and high-vibration working conditions.

[0172] Comparative Example 1:

[0173] PVDF granule composition: PVDF resin (molecular weight 1.5 million): 100 parts by weight

[0174] It does not contain ETFE toughening agent, UV absorber, light stabilizer, nano TiO2, KH550 and other silane coupling agents, MAH-g-PVDF, PTFE micro powder, antioxidants, etc.

[0175] Manufacturing process:

[0176] Step 1: Prepare PVDF granules by twin-screw extrusion granulation and dry at 80℃ for 3.5 hours;

[0177] Step 2: The dried PVDF granules are then molded into eddy current generators for wind turbine blades using an injection molding process. Injection molding process: mold temperature 90℃, barrel temperature 190-220℃, injection pressure 95MPa, holding pressure 55MPa, cooling for 25s.

[0178] The lower surface of the VG base was wiped with acetone only, without plasma activation or KH550 coupling agent. Acrylic structural adhesive was used for bonding at room temperature and cured for 7 days.

[0179] Results (refer to the performance testing method in Example 1):

[0180] 1) Poor mechanical properties

[0181] With a fracture elongation of 12% and a notched impact strength of 110 J / m, it is brittle and prone to brittle fracture, making it unable to withstand long-term aerodynamic vibration and alternating loads on wind turbine blades.

[0182] 2) Severely insufficient weather resistance life.

[0183] The system without UV absorption and light stabilization showed obvious powdering, yellowing, and cracking on the surface after 1000 hours of UVB aging, with a tensile strength retention rate of only 48%.

[0184] 3) Extremely low bonding strength and easy to detach.

[0185] Without interface modification and activation treatment, PVDF has low surface energy and poor wettability. Its bonding shear strength with FRP is 1.4 MPa, which further decreases after aging. During use, interface debonding and VG detachment are prone to occur.

[0186] 4) Difficult molding and processing

[0187] Without processing aids and toughening modifications, the melt viscosity is high and the fluidity is poor. The injection molded parts have high internal stress, are prone to cracking, have many silver streaks on the surface, and have a low finished product qualification rate, making it impossible to achieve stable industrial production.

[0188] Comparative Example 2

[0189] Step 1: Raw Material Preparation: Prepare PVDF granules for injection molding according to the following formula (parts by weight): 86.1 parts by weight of PVDF resin (molecular weight 1.5 million), 8 parts by weight of ETFE, 0.5 parts by weight of UV-531, 0.5 parts by weight of HALS, 4 parts by weight of nano titanium dioxide, 0.5 parts by weight of PTFE micro powder, 0.2 parts by weight of hindered phenolic antioxidant (1010), and 0.2 parts by weight of phosphite auxiliary antioxidant (168). Mix all raw materials at high speed for 10 minutes, then granulate by twin-screw extrusion at a temperature of 190-220℃.

[0190] Step 2 Drying process: Dry the PVDF granules obtained in Step 1 at 80℃ for 3.5 hours to remove water, so that the moisture content is ≤0.015%.

[0191] Step 3 Injection Molding Process: The dried PVDF granules are prepared into wind turbine blade eddy current generators through injection molding, and then naturally cooled after molding; the injection molding process conditions are the same as in Example 1.

[0192] The surface of the wind turbine blade eddy current generator prepared in Comparative Example 2 was only degreased with acetone, without plasma treatment or application of silane coupling agent KH550 surface treatment. After bonding with acrylic structural adhesive, it was cured at room temperature for 7 days.

[0193] Effect:

[0194] 1) Poor interfacial compatibility and insufficient adhesive wetting.

[0195] Due to the lack of silane coupling agents and interface modifiers, the PVDF matrix and the adhesive layer cannot form an effective chemical bond, resulting in weak interfacial adhesion.

[0196] 2) Bond strength is significantly lower than expected.

[0197] The tensile shear strength of PVDF / FRP is only 2.3 MPa, which is far lower than the 4.2 MPa of Example 1, and cannot meet the structural bonding requirements.

[0198] 3) Poor resistance to aging and fatigue, prone to premature failure.

[0199] After aging for 1000 hours with double 85 (according to ISO4611), the bonding strength retention rate is 57%. Under long-term wind vibration and hot and cold cycling, interface debonding and VG loosening and falling off are prone to occur, and the 30-year service life cannot be guaranteed.

[0200] 4) The packing dispersion deteriorated, and the mechanical properties decreased slightly.

[0201] Without an interface modifier, the nano-TiO2 is unevenly dispersed, resulting in a slight decrease in the material's toughness and impact resistance. Long-term use may lead to the propagation of microcracks.

[0202] The experimental data from the above embodiments and comparative examples show that the PVDF composition formulation and process of the present invention can meet the durability requirements of wind turbine blade eddy current generators for outdoor use for 30 years.

[0203] Comparative Example 3 (TiO2 only, without UV-531 / HALS):

[0204] This comparative example prepared VG according to the method of Example 1, except that the only difference from Example 1 was the formulation of PVDF granules (parts by weight), while other conditions remained unchanged. The PVDF granule formulation of this comparative example was as follows: 85 parts by weight of PVDF, 8 parts by weight of ETFE, 5 parts by weight of nano-TiO2, 0.7 parts by weight of KH550, 1.3 parts by weight of MAH-g-PVDF, 0.5 parts by weight of PTFE, and 0.4 parts by weight of antioxidant; without UV-531 and HALS.

[0205] Results: After 1000 hours of QUV treatment, the strength retention rate was 62%, which is much lower than the 85% in Example 1, and the surface was noticeably yellowed.

[0206] Comparative Example 4 (UV-531 / HALS only, without TiO2):

[0207] This comparative example prepared VG according to the method of Example 1, except that the only difference from Example 1 was the formulation of PVDF granules (parts by weight), while other conditions remained unchanged. The PVDF granule formulation of this comparative example was as follows: 89 parts by weight of PVDF, 8 parts by weight of ETFE, 0.5 parts by weight of UV-531, 0.5 parts by weight of HALS, 0.7 parts by weight of KH550, 1.3 parts by weight of MAH-g-PVDF, 0.5 parts by weight of PTFE, and 0.4 parts by weight of antioxidant; no nano-TiO2 was included.

[0208] Results: After 1000 hours of QUV treatment, the strength retention rate was 70%, which is insufficient for weather resistance and cannot meet the 30-year requirement.

[0209] Comparative Example 5 (Ordinary anatase TiO2 replacing rutile):

[0210] This comparative example prepares VG according to the method of Example 1. The only difference from Example 1 is that rutile TiO2 is replaced with anatase TiO2, while other conditions remain the same.

[0211] Results: After 1000 hours of QUV protection, the strength retention rate was 68%, indicating low UV protection efficiency and easy aging.

[0212] The experimental results from Comparative Examples 3-5 and Example 1 show that only the ternary synergy of rutile nano-TiO2 + UV-531 + HALS can achieve a weather resistance retention rate of ≥85%. Single or non-matching combinations cannot achieve the effect of this invention, proving that the system is not obvious.

[0213] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A polyvinylidene fluoride composition for a wind turbine blade eddy current generator, characterized in that, By weight, it contains the following components: 75-88 parts by weight of PVDF resin, 3-20 parts by weight of toughening agent, 0.5-4.5 parts by weight of UV resistant main agent, 2-10 parts by weight of nano titanium dioxide, 1-10 parts by weight of interfacial adhesion improver, 0.3-1.5 parts by weight of fluorine-based processing lubricant, and 0.2-1.2 parts by weight of antioxidant; The PVDF resin has a molecular weight of 200,000 to 1,100,000; the UV-resistant main agent is a compound of benzophenone-based UV absorbers and hindered amine light stabilizers. The toughening agent is one or more of the following: fluorine-based toughening agents, weather-resistant acrylate core-shell toughening agents, and organosilicon-modified acrylate toughening agents.

2. The polyvinylidene fluoride composition for a wind turbine blade eddy current generator according to claim 1, characterized in that, The toughening agent is selected from at least one of ethylene-tetrafluoroethylene copolymer, ternary fluoropolymer, fluororubber, perfluoroethylene-propylene copolymer, ethylene-trifluorochloroethylene copolymer, weather-resistant acrylate core-shell toughening agent, and organosilicon-modified acrylate toughening agent.

3. The polyvinylidene fluoride composition for a wind turbine blade eddy current generator according to claim 1, characterized in that, The UV-resistant main agent is a compound of benzophenone-based UV absorber UV-531 and hindered amine light stabilizer HALS. The nano-titanium dioxide is rutile type with a particle size of 20~50nm.

4. The polyvinylidene fluoride composition for a wind turbine blade eddy current generator according to claim 1, characterized in that, The interface adhesion improver is at least one of the following: silane coupling agent, anhydride-grafted fluoropolymer, GMA-grafted fluoropolymer, carboxyl-modified PVDF, epoxy-modified fluoropolymer, amino-modified fluoropolymer, fluorinated alkyl coupling agent, and phosphate ester coupling agent.

5. A polyvinylidene fluoride composition for a wind turbine blade eddy current generator according to claim 4, characterized in that, The interfacial adhesion improver is a compound system of silane coupling agent and acid anhydride grafted fluoropolymer. The silane coupling agent is selected from at least one of KH550, KH560, KH570, and A-171; the anhydride-grafted fluoropolymer is selected from at least one of MAH-g-PVDF, GMA-g-PVDF, MAH-g-ETFE, and MAH-g-THV.

6. A polyvinylidene fluoride (PVDF) wind turbine blade eddy current generator, characterized in that, The raw material for its preparation is the polyvinylidene fluoride composition for wind turbine blade eddy current generators as described in any one of claims 1-5.

7. The polyvinylidene fluoride wind turbine blade eddy current generator according to claim 6, characterized in that, It is prepared through the following steps: (1) Prepare the raw material components according to the proportion of the polyvinylidene fluoride composition for wind turbine blade eddy current generator according to any one of claims 1-5; first mix PVDF resin with toughening agent, then add UV resistant main agent, nano titanium dioxide, interface adhesion improver, fluorine processing lubricant and antioxidant and mix evenly, then extrude and granulate through an extruder to produce PVDF granules, wherein the length-to-diameter ratio of the extruder is L / D≥40:1 and the extrusion vacuum degree is -0.06~-0.08MPa; (2) Dry the PVDF granules to remove water, so that the moisture content is ≤0.015%; (3) The dried PVDF granules are prepared into polyvinylidene fluoride wind turbine blade eddy current generators by injection molding process, and then naturally cooled after molding; Set the barrel temperature and injection mold temperature, preheat for 30 minutes, with the barrel front, middle and rear temperatures at 210~220℃, 205~215℃ and 190~200℃ respectively, the nozzle temperature at 205~215℃, and the injection mold temperature at ≥80℃; injection rate at 20~40mm / s; injection pressure at 50~110MPa; holding pressure at 50~60MPa, holding time at 10~25s; cooling time at 15~40s; and screw back pressure at 3~5MPa.

8. The polyvinylidene fluoride wind turbine blade eddy current generator according to claim 7, characterized in that, The drying and dehydration process in step (2) is carried out at a temperature of 80-90°C for 4-6 hours. The temperature of the injection mold in step (3) is 80~100℃; In step (3), the injection mold has venting grooves at the sharp corner, the wall thickness change and the wing tip of the corresponding vortex generator. The venting grooves are 0.02~0.04mm deep, 3~5mm wide and 8~12mm long.

9. The application of the polyvinylidene fluoride wind turbine blade eddy current generator as described in claim 7 or 8 in the manufacture of wind turbine blades for wind power generation equipment.

10. The application according to claim 9, characterized in that, In the process of preparing wind turbine blades, the polyvinylidene fluoride wind turbine blade eddy current generator described in claim 7 or 8 is first subjected to surface activation treatment, and then it is finally bonded to the fiberglass blade with acrylic structural adhesive to obtain the wind turbine blade. The surface activation treatment includes one or more of mechanical roughening, PVDF interface chemical activation, and silane coupling agent primer treatment; the PVDF interface chemical activation includes one or more of plasma activation treatment, chemical etching, coating with a fluorine-specific CPO primer, ozone oxidation treatment, or surface grafting with a phosphate ester coupling agent. Before bonding, the polyvinylidene fluoride wind turbine blade eddy current generator is also subjected to a coating protection treatment: a 5~20μm fluorocarbon special primer and a 30~60μm FEVE fluorocarbon topcoat are applied in sequence.

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