High-temperature-resistant and high-pressure-resistant vacuum bag film

Abstract

The invention relates to the technical field of vacuum films, in particular to a high-temperature-resistant and high-pressure-resistant vacuum bag film which comprises an outer heat stabilizing layer, a gradient barrier layer, a self-adaptive sealing layer, 10-25% of polyether-ether-ketone, 60-75% of high-temperature-resistant thermoplastic polyurethane, 2-5% of silicon carbide whiskers and 0.5-1.5% of rare earth oxide which are sequentially stacked. The gradient barrier layer comprises a transition interface layer, an EVOH / SiO2 nanosheet composite layer and a boron nitride nanotube enhancement layer, the EVOH / SiO2 nanosheet composite layer and the boron nitride nanotube enhancement layer are alternately distributed, 0.1-0.3 wt% of hydroxylated carbon nanotubes are arranged in the transition interface layer, and the adaptive sealing layer is composed of 60-75% of metallocene catalyzed linear low density polyethylene, 20-30% of ultra-low density polyethylene, 1-2% of a lubricant and 1-2% of an anti-blocking agent. The pressure difference between the inside and the outside of the vacuum package can be effectively borne, the sealing performance and the integrity of the package are guaranteed, and particularly in severe environments such as high temperature and high pressure, package damage or leakage is prevented, and the vacuum effect is maintained.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum films, and more specifically, it relates to a high-temperature and high-pressure resistant vacuum bag film, which is applicable to the new energy field, such as the vacuum-assisted resin infusion or prepreg curing process of wind turbine blades. Background Art

[0002] As an indispensable material in modern industrial and consumer fields, the performance improvement of vacuum bag films is directly related to product quality, safety, and shelf life. Especially in fields such as food, medicine, chemical industry, and new energy manufacturing, the demand for high-performance vacuum bag films is increasing. In the manufacturing process of wind turbine blades, the commonly used vacuum-assisted resin infusion or prepreg curing process needs to be carried out in a high-temperature and high-pressure environment, which poses strict requirements on the temperature resistance, pressure resistance, barrier performance of the vacuum bag film, and the conformability and flexibility to complex molds. The multi-layer composite vacuum bag film technology has become a key technology in the field of high-performance packaging and manufacturing because it can combine the advantages of multiple materials according to different application requirements to achieve performance complementarity and optimization.

[0003] In the prior art, high-temperature resistant composite film materials mostly use matrix materials such as nylon (PA) and polypropylene (CPP) and are prepared by co-extrusion or biaxial stretching processes. For example, the patent with publication number CN105038204B discloses a PA6 / PA66 hybrid vacuum bag film, which shows good temperature resistance (tensile strength of 75 - 85 MPa) below 230°C, but the melting point of its PA-based material limits high-temperature application scenarios (it is prone to melting failure when > 250°C).

[0004] In addition, the patent with publication number CN117698258B improves the high-temperature resistance through the bonding design of the CPP composite film and the PET layer, but its CPP film layer still relies on traditional antioxidant and additive systems, and the barrier performance (oxygen transmission rate > 1.5 cc / m²·day) is difficult to meet the high requirements of food packaging.

[0005] Therefore, aiming at the limitations of the prior art high-temperature resistant vacuum bag films in the wind power manufacturing and other fields, such as insufficient temperature resistance, structural stability under high pressure, barrier performance, and conformability and flexibility to complex curved surface molds, it is urgent to develop a new type of high-performance composite vacuum bag film technology to meet the requirements of more stringent and complex application scenarios. Summary of the Invention

[0006] Therefore, the purpose of the present invention is to provide a high-temperature and high-pressure resistant vacuum bag film, which can not only effectively withstand the pressure difference inside and outside the vacuum packaging to ensure the sealing and integrity of the packaging, especially in high-temperature and high-pressure harsh environments such as wind turbine blade manufacturing, prevent packaging damage or leakage, maintain the vacuum effect, but also have good flexibility and can effectively conform to complex curved surface molds.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A high-temperature and high-pressure resistant vacuum bag film, the vacuum bag film includes a heat-stable outer layer, a gradient barrier layer, and an adaptive sealing layer stacked in sequence, wherein:

[0009] The heat-stable outer layer is composed of the following raw materials by mass percentage: 10-25% of polyether ether ketone, 60-75% of high-temperature resistant thermoplastic polyurethane, 2-5% of silicon carbide whiskers, and 0.5-1.5% of rare earth oxide, with a thickness of 15-20 μm;

[0010] The gradient barrier layer includes a transition interface layer and alternately distributed EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforced layers. The transition interface layer has 0.1-0.3 wt% of hydroxylated carbon nanotubes, wherein the mass ratio of EVOH to SiO2 nanosheets is 9:1, and the boron nitride nanotubes account for 3-5% of the volume of the reinforced layer in a vertically arranged manner, with a total thickness of 8-10 μm;

[0011] The adaptive sealing layer is composed of the following raw materials by mass percentage: 60-75% of metallocene-catalyzed linear low-density polyethylene, 20-30% of ultra-low density polyethylene, 1-2% of lubricant, and 1-2% of anti-blocking agent, with a thickness of 10-15 μm.

[0012] The present invention is further configured as: the high-temperature resistant thermoplastic polyurethane is polyether-based TPU, the glass transition temperature of the soft segment is ≤ -40°C, and the melting temperature of the hard segment is ≥ 200°C; the silicon carbide whiskers are high-purity, high aspect ratio β-SiC whiskers after surface modification treatment.

[0013] The present invention is further configured as: the SiO2 nanosheets are hexagonal single crystal wafers grown by chemical vapor deposition, with a thickness ≤ 5 nm, and the surface is modified by silane coupling agent KH-550.

[0014] The present invention is further configured as: the lubricant is erucamide, and the anti-blocking agent is silica.

[0015] The present invention is further configured as: the processing steps of the outer layer material are: mixing polyether ether ketone, high-temperature resistant thermoplastic polyurethane, silicon carbide whiskers, and rare earth oxide in proportion, performing segmented melt blending in a twin-screw extruder, the temperature of the first melting zone is 300-310°C, the temperature of the second melting zone is 310-320°C, the mixing time is 5-10 minutes, and after mixing, cooling and pelletizing to obtain the raw material of the heat-stable outer layer.

[0016] The present invention is further configured such that: the gradient barrier layer is formed by low-pressure plasma enhanced chemical vapor deposition, and an EVOH / SiO2 nanosheet composite layer and a boron nitride nanotube reinforcement layer are alternately deposited on the surface of the external heat stabilizing layer. Among them, EVOH / SiO2 is deposited in the form of a solution, the deposition temperature is 80-100 °C, and the working pressure is 50-100 Pa to form the gradient barrier layer.

[0017] The present invention is further configured such that: the treatment steps of the adaptive sealing layer material are as follows: metallocene-catalyzed linear low-density polyethylene, ultra-low density polyethylene, a lubricant, and an anti-blocking agent are mixed evenly in proportion, and are melt-extruded through a single-screw extruder. The extrusion temperature is controlled in sections as the first extrusion section at 170-180 °C, the second extrusion section at 180-190 °C, and the third extrusion section at 190-200 °C to prepare the raw material of the adaptive sealing layer.

[0018] The present invention is further configured such that: the forming steps of the vacuum bag film are as follows:

[0019] (a) After the raw material of the external heat stabilizing layer is granulated by a twin-screw extruder, it is extruded into a film through a single-screw extruder, and the extrusion temperature is 280-320 °C;

[0020] (c) On the surface of the external heat stabilizing layer, an EVOH / SiO2 nanosheet composite layer is alternately deposited by low-pressure plasma at a deposition rate of 5-8 nm / s and a boron nitride nanotube array layer with an orientation degree ≥ 85%; the raw material of the adaptive sealing layer and the semi-finished product obtained in step (b) are co-extruded and laminated, and the extrusion temperature is 170-200 °C;

[0021] (d) The composite film is subjected to primary mechanical stretching in sequence, with a stretching ratio of 2.0×2.0, a rate of 0.5-0.8 cm / s, and a temperature of 110-130 °C, and secondary gas expansion stretching, with a stretching ratio of 1.5×1.5, a rate of 0.3-0.5 cm / s, and a temperature of 150-170 °C;

[0022] (e) Microwave-assisted heat setting treatment, with a microwave frequency of 2450 MHz, a power density of 3-5 W / cm², and heating using a pulse mode. Each heating lasts for 100 milliseconds and then has an intermittent period of 50 milliseconds in a cycle, and the total duration is 120-180 seconds to obtain the finished vacuum bag film.

[0023] The present invention is further configured such that: the deposition rate of the EVOH / SiO2 nanosheet composite layer is 5-8 nm / s, and the orientation degree of the boron nitride nanotube reinforcement layer is ≥ 85%.

[0024] The present invention is further configured such that: the rate of primary mechanical stretching is 0.5-0.8 cm / s; the rate of secondary gas expansion stretching is 0.3-0.5 cm / s.

[0025] Compared with the deficiencies of the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. A composite outer heat-stable layer with high-temperature-resistant TPU as the main body and synergistic PEEK is constructed. On the premise of ensuring excellent high-temperature resistance, the flexibility of the film is significantly improved, enabling the composite vacuum bag film to effectively conform to complex curved surface molds, while still being able to withstand a long-term use temperature of up to about 280°C and a short-term high temperature of 300°C. It overcomes the deficiencies of insufficient temperature resistance of traditional matrix materials such as PA and CPP and the poor flexibility of high-PEEK materials, and is suitable for applications such as the manufacture of wind turbine blades that require high-temperature curing processes.

[0027] 2. A gradient barrier layer is constructed. This layer adopts an elaborate structure with alternating distribution of EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforcement layers. The vertical arrangement of boron nitride nanotubes effectively extends the diffusion path of gas molecules, significantly enhancing the barrier effect and ensuring the long-term maintenance of high vacuum in the vacuum infusion process such as the manufacture of wind turbine blades.

[0028] 3. The self-adaptive sealing layer uses a combination of mLLDPE and ULDPE, has good heat-sealing performance and low-temperature heat-sealing performance, and additives such as slip agents and anti-blocking agents are added to improve the processability and convenience of use of the film.

[0029] 4. The overall multi-layer composite structure and optimized preparation process enable the vacuum bag film to still maintain excellent mechanical strength, dimensional stability and vacuum retention in high-temperature and high-pressure environments, and are not prone to breakage or leakage, effectively ensuring the manufacturing quality of products such as wind turbine blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic structural diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Refer to Figure 1 To further illustrate a high-temperature and high-pressure resistant vacuum bag film of the present invention, specifically: The vacuum bag film includes an outer heat-stable layer, a gradient barrier layer and a self-adaptive sealing layer stacked in sequence, where:

[0032] The outer heat-stable layer is composed of raw materials in the following mass percentages:

[0033] Polyetheretherketone (PEEK) 10 - 25%: Use high-performance grade PEEK resin, and adopt VICTREX™ PEEK450G of Victrex Corporation.

[0034] High-temperature resistant thermoplastic polyurethane (TPU) 60 - 75%: Polyether-based TPU is used, and Estane® 58211 TPU is adopted. Polyether-based TPU has more excellent hydrolysis resistance and low-temperature performance compared with polyester-based TPU, and is more suitable for outdoor application environments such as wind power. The glass transition temperature of the soft segment ≤ -40 °C ensures the flexibility of TPU at low temperatures, and the melting temperature of the hard segment ≥ 200 °C ensures the heat resistance of TPU at high temperatures. As the main substrate of the outer layer, it endows the outer layer with good flexibility and high-temperature resistance. TPU and PEEK act synergistically to improve the comprehensive performance of the outer heat-stable layer, especially flexibility, so as to better fit the wind turbine blade.

[0035] Silicon carbide whiskers (SiC whiskers) 2 - 5%: High-purity, high aspect ratio β-SiC whiskers treated by surface modification are used. The diameter of the silicon carbide whiskers is controlled at 0.1 - 1 μm, and the length is 10 - 50 μm. Through surface modification treatment, the compatibility of SiC whiskers with the TPU and PEEK matrixes is improved, agglomeration is reduced, and the dispersion uniformity is enhanced, thereby effectively improving the mechanical strength, modulus, wear resistance and impact resistance of the composite layer, while reducing the adverse impact on flexibility.

[0036] Rare earth oxides 0.5 - 1.5%: Nano-scale rare earth oxides are used, and yttrium oxide (Y2O3) nano-powder or lanthanum oxide (La2O3) nano-powder is adopted. The particle size is controlled at 20 - 50 nm. As nano-fillers, rare earth oxides can improve the thermal oxidation resistance and thermal stability of the outer heat-stable layer in high-temperature environments and extend the service life of the material.

[0037] The gradient barrier layer includes:

[0038] Transition interface layer: The main function of this layer is to enhance the interfacial bonding strength between the outer heat-stable layer and the gradient barrier layer. Hydroxylated carbon nanotubes (CNTs-OH) 0.1 - 0.3 wt%: Multi-walled carbon nanotubes modified by surface hydroxylation are used, with a diameter of 8 - 15 nm and a length of 10 - 50 μm. Hydroxylation modification enhances the compatibility of carbon nanotubes with the polymer matrix. The addition of carbon nanotubes can improve the mechanical strength and thermal stability of the interface layer and act as a "bridge" to promote effective bonding between layers.

[0039] EVOH / SiO2 nanosheet composite layer: Ethylene-vinyl alcohol copolymer (EVOH), and EVOH resin with an ethylene content of 29 - 32 mol% is used.

[0040] SiO₂ Nanosheets: Hexagonal single-crystal SiO₂ nanosheets grown by chemical vapor deposition (CVD), using CVD-SiO₂ nanosheets provided by Suzhou Institute of Nano-Tech and Nano-Bionics. The thickness of the SiO₂ nanosheets is controlled to be ≤5 nm, and the width is 50 - 100 nm. [The ultra-thin nanosheet structure is beneficial to improving the flexibility and transparency of the composite material. The surface is modified with the silane coupling agent KH-550 to enhance the compatibility and dispersibility between the SiO₂ nanosheets and the EVOH matrix. The mass ratio of EVOH to SiO₂ nanosheets is 9:1. Optimizing the ratio can maintain the continuity of the EVOH matrix while ensuring the reinforcement effect of the SiO₂ nanosheets, thus ensuring the barrier performance.

[0041] Boron Nitride Nanotube (BNNTs) Reinforcement Layer: Using highly crystalline and high-purity boron nitride nanotubes, the boron nitride nanotubes are arranged perpendicular to the film surface and uniformly dispersed in the polymer matrix at a volume ratio of 3 - 5% to form a reinforcement layer. The perpendicular arrangement can more effectively block the diffusion path of gas molecules, improve the barrier effect, and enhance the puncture resistance of the film.

[0042] The self-adaptive sealing layer is composed of raw materials with the following mass percentages:

[0043] Metallocene-Catalyzed Linear Low-Density Polyethylene (mLLDPE) 60 - 75%: Using metallocene-catalyzed LLDPE resin with a density of 0.918 - 0.925 g / cm³ and a melt index (MI) of 1.0 - 2.0 g / 10 min, adopting DOWLEX™ 2045G.

[0044] Ultra-Low-Density Polyethylene (ULDPE) 20 - 30%: Using ULDPE resin with a density of 0.890 - 0.910 g / cm³ and a melt index (MI) of 2.0 - 4.0 g / 10 min, which can improve the low-temperature heat-sealing performance of the sealing layer and the overall flexibility of the film.

[0045] Slip Agent (Erucamide) 1 - 2%: Using high-purity erucamide. As a common polyolefin slip agent, erucamide can reduce the friction coefficient of the film surface, improve the opening and slipperiness of the film, and enhance the operating efficiency during high-speed packaging.

[0046] Anti-Adhesion Agent (Silica) 1 - 2%: Using nano-silica with a particle size controlled at 10 - 20 nm. As a common anti-adhesion agent, nano-silica can increase the surface roughness of the film, reduce the interlayer adhesion of the film, and prevent the film rolls from sticking during storage or use, affecting the smoothness of the high-speed packaging process.

[0047] The steps for preparing the film are as follows in detail:

[0048] (a) Preparation of the raw materials for the outer heat-stable layer:

[0049] Segmented melt blending: Melt blending is carried out using a twin-screw extruder.

[0050] Temperature of the first melting zone: 300 - 310 °C. Control the temperature of the first to the third zones of the extruder to be 300 - 310 °C. This temperature range is slightly higher than the melting point of PEEK (about 300 °C). The main purpose is to fully melt the PEEK resin and, using the shear force of the screw and the mixing elements, initially untangle the entangled PEEK molecular chains, reduce its melt viscosity, and create conditions for the subsequent uniform mixing and dispersion with other components.

[0051] Temperature of the second melting zone: 310 - 320 °C. Control the temperature of the fourth zone of the extruder to the die head to be 310 - 320 °C, further increasing the melt temperature and promoting the full mutual diffusion and uniform dispersion at the molecular level between the molten PEEK and components such as TPU, silicon carbide whiskers, and rare earth oxides. By adjusting parameters such as the screw speed, feeding speed, and temperature of each zone, optimize the melt blending effect, reduce component segregation, and improve the homogeneity of the outer layer material.

[0052] Mixing time: 5 - 10 minutes. Control the average residence time of the materials in the extruder to be 5 - 10 minutes to ensure that all components are fully and evenly mixed.

[0053] Cooling and pelletizing: Cool and pelletize the melt-blended materials through a water-cooled strand pelletizer to obtain granular raw materials for the outer heat-stable layer, which is convenient for subsequent film extrusion processing.

[0054] (b) Gradient barrier layer deposition:

[0055] Low-pressure plasma-enhanced chemical vapor deposition (PECVD): Use a radio-frequency capacitive-coupled plasma (RF-CCP) PECVD device.

[0056] Deposition gas precursors: EVOH / SiO2 composite layer: Use tetraethyl orthosilicate (TEOS) as the SiO2 precursor. Ethylene-vinyl alcohol copolymer (EVOH) is sprayed or spin-coated on the substrate surface in solution form. TEOS decomposes under the action of plasma to deposit a SiO2 thin film. The EVOH solution can use ethanol or isopropanol as the solvent to dissolve EVOH and uniformly disperse it with nano-SiO2 sheets to form a composite solution.

[0057] Boron nitride nanotube reinforcement layer: Boron trichloride (BCl3) and ammonia (NH3) are used as boron nitride precursors. BCl3 and NH3 react under the action of plasma to deposit a boron nitride thin film. At the same time, by applying an electric field or magnetic field assistance, the boron nitride nanotubes are controlled to be arranged perpendicular to the surface direction in the thin film, improving the degree of orientation. The substrate temperature is controlled at 80 - 100 °C. The lower deposition temperature protects the polymer substrate and avoids high-temperature damage. The working pressure of the vacuum chamber is controlled at 50 - 100 Pa. The low-pressure condition is beneficial to plasma discharge, improving the plasma density and uniformity, and obtaining a high-quality thin film.

[0058] Control the deposition rate of the EVOH / SiO2 composite layer at 5 - 8 nm / s. The lower deposition rate is beneficial to obtaining a dense and uniform barrier layer.

[0059] By adjusting the PECVD process parameters (such as radio frequency power, gas flow rate, bias voltage, magnetic field, etc.), control the perpendicular orientation degree of the boron nitride nanotubes in the thin film to reach ≥85%, improving the barrier performance and specific mechanical properties.

[0060] By precisely controlling the switching of gas precursors and deposition time, alternately deposit the EVOH / SiO2 composite layer and the boron nitride nanotube reinforcement layer to form a multi-layer gradient barrier structure. The deposition layers and thickness ratios of the two thin films can be adjusted according to actual needs to optimize the barrier performance.

[0061] (c) Preparation of raw materials for the adaptive sealing layer:

[0062] Melt extrusion: Use a single-screw extruder for melt extrusion, and adopt a three-stage stepped temperature rise to control the extrusion temperature:

[0063] Control the temperature from the feeding section to the compression section of the extruder at 170 - 180 °C. The lower temperature is beneficial to the stable transportation and preheating of solid materials.

[0064] Control the temperature from the compression section to the metering section of the extruder at 180 - 190 °C, gradually increasing the temperature to start melting the material.

[0065] Control the temperature from the metering section to the die head of the extruder at 190 - 200 °C, further increasing the temperature to fully melt and homogenize the material, ensuring that the extrusion temperature meets the processing requirements of mLLDPE and ULDPE, and at the same time avoiding thermal decomposition of polyethylene due to excessive temperature. The stepped temperature rise control can gradually reduce the melt viscosity of the sealing layer polyethylene along the extrusion direction, reduce the flow resistance of the melt in the die head, inhibit the occurrence of melt elastic instability, and finally improve the film layer thickness uniformity under high-speed extrusion.

[0066] Film formation: The molten polyethylene melt extruded by melt extrusion is extruded into a film through a casting die head and is cooled and shaped by a cooling roll to obtain an adaptive sealing layer film.

[0067] (d) Thin film forming step:

[0068] Melt and extrude the raw material of the outer heat-stable layer into a film again through a single-screw extruder. The extrusion temperature is controlled at 280 - 320 °C, and the specific temperature is adjusted according to the melting characteristics of PEEK and TPU to ensure the forming quality of the outer layer film. Use an annular die head to extrude a tubular film and carry out air ring cooling and shaping.

[0069] Transfer the single-layer film of the outer heat-stable layer to a PECVD device, and alternately deposit an EVOH / SiO2 nanosheet composite layer and a boron nitride nanotube reinforcement layer on its surface to prepare a semi-finished double-layer composite film. The deposition process parameters are as in the previous step (b).

[0070] Melt and extrude the raw material of the adaptive sealing layer through another extruder, and compound the melt of the adaptive sealing layer on the surface of the semi-finished double-layer composite film through a co-extrusion die head. Adopt a three-layer co-extrusion casting or blown film process to compound the outer heat-stable layer, the gradient barrier layer, and the adaptive sealing layer together to form a three-layer co-extrusion composite film. The extrusion temperature of the co-extrusion coating is controlled at 170 - 200 °C to ensure that the adaptive sealing layer can be well heat-sealed, while avoiding high-temperature damage to the gradient barrier layer and the outer heat-stable layer.

[0071] Biaxial stretching: Perform two-stage gradient biaxial stretching on the three-layer co-extrusion composite film, using a biaxial stretching test machine or industrial biaxial stretching equipment.

[0072] Fix the film with mechanical clamps and perform synchronous biaxial stretching of 2.0×2.0 within the temperature range of 110 - 130 °C, and control the stretching rate at 0.5 - 0.8 cm / s. The temperature of the preheating zone (110 - 120 °C) is lower than that of the stretching zone (120 - 130 °C), aiming to achieve temperature uniformity before the film enters the stretching zone and avoid uneven heating of the film caused by sudden temperature rise. The main purpose of the primary mechanical stretching is to initially stretch and orient, improving the strength and modulus of the film.

[0073] Put the film after the primary mechanical stretching into a gas expansion stretching device and perform biaxial stretching of 1.5×1.5 within the temperature range of 150 - 170 °C, and control the stretching rate at 0.3 - 0.5 cm / s. The temperature of the first expansion zone (150 - 160 °C) is lower than that of the second expansion zone (160 - 170 °C), aiming to gradually reduce the entanglement density of polymer molecular chains through staged temperature increase and regulate the orientation rate of molecular chains during biaxial stretching, so that the stress can be gradually released and evenly distributed along the film surface during the gas expansion stretching of the film. The main purpose of the secondary gas expansion stretching is to further increase the stretching ratio and uniformity of the film, and improve the mechanical properties and barrier properties of the film.

[0074] Microwave-assisted heat setting: The biaxially stretched film is subjected to microwave-assisted oscillating heating and heat setting treatment. A microwave frequency of 2450 MHz is used, and the power density is controlled at 3 - 5 W / cm². Synchronous heating and oscillation are carried out using a microwave heater and a mechanical oscillation device. The heat setting temperature is controlled in a segmented manner. The temperature in the heating-up stage is controlled at 140 - 150 °C, and the temperature in the constant-temperature stage is controlled at 150 - 160 °C. The temperature in the heating-up stage is relatively low to avoid excessive shrinkage or deformation of the film during rapid heating and maintain the dimensional stability of the film. The relatively high temperature in the constant-temperature stage enhances the thermal motion ability of polymer molecular chains, promotes the full relaxation and recrystallization of molecular chains in the stretched and oriented state, and eliminates internal stress. Microwave heating is carried out in a pulse mode, with each heating lasting for 100 milliseconds and then intermittent for 50 milliseconds in a cycle, and the total duration is controlled at 120 - 180 seconds. Pulse-mode microwave heating can better control the heating process and avoid local overheating or material damage. Oscillating heating can promote the relaxation and rearrangement of molecular chains and more effectively eliminate internal stress.

[0075] (e) Finished film: Through the above steps, the finished high-speed high-temperature resistant multi-layer composite vacuum bag film is finally obtained.

[0076] Based on the above content, the following are specific examples and comparative examples:

[0077] Example 1. The composition of the vacuum bag film in this example is as follows:

[0078] External heat-stable layer: The thickness is 15 μm. It is composed of the following raw materials by mass percentage: 10% polyether ether ketone, 75% high-temperature resistant thermoplastic polyurethane, 2% silicon carbide whiskers, and 0.5% rare earth oxide.

[0079] Gradient barrier layer: The total thickness is 8 μm. It includes a transition interface layer and an alternately distributed EVOH / SiO2 nanosheet composite layer and a boron nitride nanotube reinforced layer. The transition interface layer contains 0.1 wt% hydroxylated carbon nanotubes. The mass ratio of EVOH to SiO2 nanosheets is 9:1. The boron nitride nanotubes account for 3% of the volume of the reinforced layer in a vertically arranged manner.

[0080] Self-adaptive sealing layer: The thickness is 10 μm. It is composed of the following raw materials by mass percentage: 75% metallocene-catalyzed linear low-density polyethylene, 23% ultra-low density polyethylene, 1% lubricant, and 1% anti-blocking agent.

[0081] Film preparation steps:

[0082] Mix 10% polyether ether ketone, 75% high-temperature resistant thermoplastic polyurethane, 2% silicon carbide whiskers, and 0.5% rare earth oxide in proportion and carry out pre-dispersion treatment. Carry out segmented melt blending in a twin-screw extruder. The temperature in the first melting zone is 300 °C, the temperature in the second melting zone is 310 °C, and the mixing time is 5 minutes. After mixing, cool and pelletize.

[0083] On the surface of the external heat-stabilizing layer, a low-pressure plasma-enhanced chemical vapor deposition is used to alternately deposit a composite layer of EVOH / SiO2 nanosheets and a boron nitride nanotube reinforcement layer. 0.1 wt% of hydroxylated carbon nanotubes is deposited in the transition interface layer. EVOH / SiO2 is deposited in solution form, and the mass ratio of EVOH to SiO2 nanosheets is 9:1. The deposition temperature is 80 °C, the working pressure is 50 Pa, and the deposition rate is 5 nm / s. The boron nitride nanotubes are vertically arranged and account for 3% of the volume of the reinforcement layer, with an orientation degree ≥ 85%. The total thickness is 8 μm.

[0084] 75% of metallocene-catalyzed linear low-density polyethylene, 23% of ultra-low density polyethylene, 1% of lubricant, and 1% of anti-blocking agent are mixed evenly in proportion. They are melt-extruded through a single-screw extruder, and the extrusion temperature is controlled in sections: the first extrusion section is 170 °C, the second extrusion section is 180 °C, and the third extrusion section is 190 °C.

[0085] After the raw materials of the external heat-stabilizing layer are granulated by a twin-screw extruder, they are extruded into a film through a single-screw extruder, and the extrusion temperature is 280 °C; the film thickness is 15 μm.

[0086] On the surface of the external heat-stabilizing layer, a composite layer of EVOH / SiO2 nanosheets is alternately deposited by low-pressure plasma with a deposition rate of 5 nm / s and a boron nitride nanotube array layer with an orientation degree ≥ 85%; the raw materials of the adaptive sealing layer and the obtained semi-finished product are co-extruded and laminated, and a three-layer co-extrusion casting or blown film process is adopted to achieve tight bonding between layers through a multi-layer co-extrusion die head, and the extrusion temperature is 170 °C;

[0087] The composite film is subjected to primary mechanical stretching with a stretching ratio of 2.0×2.0, a rate of 0.5 cm / s, and a temperature of 110 °C, and secondary gas expansion stretching with a stretching ratio of 1.5×1.5, a rate of 0.3 cm / s, and a temperature of 150 °C.

[0088] Microwave-assisted heat setting treatment is carried out with a microwave frequency of 2450 MHz, a power density of 3 W / cm². The heating adopts a pulse mode, with each heating lasting for 100 milliseconds and then intermittent for 50 milliseconds in a cycle. The total duration is 120 seconds to obtain the finished vacuum bag film.

[0089] Example 2. The composition of the vacuum bag film in this example is as follows:

[0090] External heat-stabilizing layer: The thickness is 17.5 μm. It is composed of the following raw materials in mass percentages: 17.5% of polyether ether ketone, 67.5% of high-temperature-resistant thermoplastic polyurethane, 3.5% of silicon carbide whiskers, and 1.5% of rare earth oxides.

[0091] Gradient barrier layer: total thickness 9 μm. It includes a transition interface layer and an alternately distributed EVOH / SiO2 nanosheet composite layer and a boron nitride nanotube reinforcement layer. The transition interface layer contains 0.2 wt% of hydroxylated carbon nanotubes. The mass ratio of EVOH to SiO2 nanosheets is 9:1. The boron nitride nanotubes account for 4% of the volume of the reinforcement layer in a vertically arranged manner.

[0092] Adaptive sealing layer: thickness 12.5 μm. It is composed of the following raw materials by mass percentage: metallocene-catalyzed linear low-density polyethylene 68%, ultra-low-density polyethylene 29%, lubricant 1.5%, and anti-blocking agent 1.5%.

[0093] Steps for film preparation:

[0094] Mix 17.5% of polyether ether ketone, 67.5% of high-temperature resistant thermoplastic polyurethane, 3.5% of silicon carbide whiskers, and 1.5% of rare earth oxide in proportion and conduct pre-dispersion treatment. Perform segmented melt blending in a twin-screw extruder. The temperature of the first melting zone is 305°C, the temperature of the second melting zone is 315°C, and the mixing time is 7.5 minutes. After mixing, cool and pelletize.

[0095] On the surface of the external heat-stable layer, alternately deposit the EVOH / SiO2 nanosheet composite layer and the boron nitride nanotube reinforcement layer by low-pressure plasma enhanced chemical vapor deposition. Deposit 0.2 wt% of hydroxylated carbon nanotubes in the transition interface layer. EVOH / SiO2 is deposited in solution form. The mass ratio of EVOH to SiO2 nanosheets is 9:1. The deposition temperature is 90°C, the working pressure is 75 Pa, and the deposition rate is 6.5 nm / s. The boron nitride nanotubes account for 4% of the volume of the reinforcement layer in a vertically arranged manner, and the orientation degree is ≥85%. The total thickness is 9 μm.

[0096] Mix 68% of metallocene-catalyzed linear low-density polyethylene, 29% of ultra-low-density polyethylene, 1.5% of lubricant, and 1.5% of anti-blocking agent evenly. Melt and extrude through a single-screw extruder. The extrusion temperature is controlled in segments as 175°C for the first extrusion section, 185°C for the second extrusion section, and 195°C for the third extrusion section.

[0097] After the raw materials of the external heat-stable layer are pelletized by twin-screw extrusion, they are extruded into a film through a single-screw extruder. The extrusion temperature is 300°C; the film thickness is 17.5 μm.

[0098] On the surface of the external heat-stable layer, alternately deposit the EVOH / SiO2 nanosheet composite layer with a deposition rate of 6.5 nm / s and the boron nitride nanotube array layer with an orientation degree ≥85%; laminate the raw materials of the adaptive sealing layer and the obtained semi-finished product through co-extrusion coating. Adopt a three-layer co-extrusion casting or blown film process to achieve tight bonding between layers through a multi-layer co-extrusion die head. The extrusion temperature is 185°C;

[0099] The composite film is first subjected to mechanical stretching with a stretching ratio of 2.0×2.0, a rate of 0.65 cm / s, and a temperature of 120°C, and then to secondary gas expansion stretching with a stretching ratio of 1.5×1.5, a rate of 0.4 cm / s, and a temperature of 160°C.

[0100] Microwave-assisted heat setting treatment is carried out with a microwave frequency of 2450 MHz, a power density of 4 W / cm². The heating is carried out in a pulse mode, with each heating lasting for 100 milliseconds and then intermittent for 50 milliseconds in a cycle, and the total duration is 150 seconds, to obtain the finished vacuum bag film.

[0101] Example 3. The composition of the vacuum bag film in this example is as follows:

[0102] External heat-stable layer: thickness 20 μm. It is composed of the following raw materials by mass percentage: 25% polyether ether ketone, 60% high-temperature resistant thermoplastic polyurethane, 5% silicon carbide whiskers, and 1.5% rare earth oxide.

[0103] Gradient barrier layer: total thickness 10 μm. It includes a transition interface layer and alternating EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforced layers. The transition interface layer contains 0.3 wt% hydroxylated carbon nanotubes. The mass ratio of EVOH to SiO2 nanosheets is 9:1. The boron nitride nanotubes account for 5% of the volume of the reinforced layer in a vertically arranged manner.

[0104] Adaptive sealing layer: thickness 15 μm. It is composed of the following raw materials by mass percentage: 66% metallocene-catalyzed linear low-density polyethylene, 30% ultra-low density polyethylene, 2% lubricant, and 2% anti-blocking agent.

[0105] Film preparation steps:

[0106] Mix 25% polyether ether ketone, 60% high-temperature resistant thermoplastic polyurethane, 5% silicon carbide whiskers, and 1.5% rare earth oxide in proportion and carry out pre-dispersion treatment. Carry out segmented melt blending in a twin-screw extruder, with the temperature of the first melting zone being 310°C, the temperature of the second melting zone being 320°C, and the mixing time being 10 minutes. After mixing, cool and pelletize.

[0107] On the surface of the external heat-stable layer, alternately deposit EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforced layers by low-pressure plasma enhanced chemical vapor deposition. Deposit 0.3 wt% hydroxylated carbon nanotubes in the transition interface layer. EVOH / SiO2 is deposited in solution form, with the mass ratio of EVOH to SiO2 nanosheets being 9:1, the deposition temperature being 100°C, the working pressure being 100 Pa, and the deposition rate being 8 nm / s. The boron nitride nanotubes account for 5% of the volume of the reinforced layer in a vertically arranged manner, and the orientation degree is ≥85%. The total thickness is 10 μm.

[0108] Mix 66% of metallocene-catalyzed linear low-density polyethylene, 30% of ultra-low density polyethylene, 2% of lubricant and 2% of anti-blocking agent evenly. Melt and extrude through a single-screw extruder, and the extrusion temperature is controlled in sections: the first extrusion section is 180°C, the second extrusion section is 190°C, and the third extrusion section is 200°C.

[0109] After the raw materials of the external heat-stable layer are granulated by a twin-screw extruder, they are extruded into a film through a single-screw extruder, and the extrusion temperature is 320°C; the film thickness is 20μm.

[0110] Alternately deposit a composite layer of EVOH / SiO2 nanosheets and a boron nitride nanotube array layer on the surface of the external heat-stable layer by low-pressure plasma, with a deposition rate of 8nm / s and an orientation degree of ≥85%; co-extrude and laminate the raw materials of the adaptive sealing layer and the obtained semi-finished product, adopt a three-layer co-extrusion casting or blown film process, and achieve tight bonding between layers through a multi-layer co-extrusion die head, with an extrusion temperature of 200°C;

[0111] Perform primary mechanical stretching on the composite film successively, with a stretching ratio of 2.0×2.0, a rate of 0.8cm / s, and a temperature of 130°C, and secondary gas expansion stretching, with a stretching ratio of 1.5×1.5, a rate of 0.5cm / s, and a temperature of 170°C.

[0112] Perform microwave-assisted heat setting treatment, with a microwave frequency of 2450MHz, a power density of 5W / cm², heating in a pulse mode, heating for 100 milliseconds each time and then intermittent for 50 milliseconds in a cycle, and the total duration is 180 seconds to obtain the finished vacuum bag film.

[0113] Comparative Example 1 (based on CN105038204B):

[0114] Composition of the vacuum bag film: Main layer: PA6 / PA66 blend (e.g., 60% PA6, 40% PA66), with a thickness of about 60μm. Sealing layer: Polyethylene (PE) blend, with a thickness of about 40μm.

[0115] Comparative Example 2 (based on CN117698258B):

[0116] Composition of the vacuum bag film: Outer layer: PET (polyethylene terephthalate) film, with a thickness of about 25μm. Barrier / sealing layer: CPP (cast polypropylene) or modified CPP co-extruded film, with a thickness of about 75μm. The two layers are compounded through an adhesive.

[0117] Comparative Example 3:

[0118] Vacuum bag film composition: The outer heat-stable layer is composed of the following raw materials by mass percentage: 80% polyether ether ketone, 15% high-temperature resistant thermoplastic polyurethane, 4% silicon carbide whiskers, and 1% rare earth oxide, with a thickness of 17.5 μm; Gradient barrier layer: The composition and thickness are the same as in Example 2; Adaptive sealing layer: The composition and thickness are the same as in Example 2.

[0119] Comparative Example 4:

[0120] Vacuum bag film composition: The outer heat-stable layer is composed of the following raw materials by mass percentage: 20% polyether ether ketone, 80% high-temperature resistant thermoplastic polyurethane, with a thickness of 17.5 μm; Gradient barrier layer: The composition and thickness are the same as in Example 2; Adaptive sealing layer: The composition and thickness are the same as in Example 2.

[0121] Comparative Example 5: Vacuum bag film composition: Outer heat-stable layer: The composition and thickness are the same as in Example 2; Barrier layer: Single-layer EVOH film, with a thickness of 9 μm; Adaptive sealing layer: The composition and thickness are the same as in Example 2.

[0122] Comparative Example 6: Vacuum bag film composition: Outer heat-stable layer: The composition and thickness are the same as in the Example; Gradient barrier layer: The composition and thickness are the same as in Example 2; Adaptive sealing layer: It is composed of the following raw materials by mass percentage: 96% metallocene-catalyzed linear low-density polyethylene, 2% lubricant, 2% anti-blocking agent, with a thickness of 12.5 μm.

[0123] Based on the detection of the prepared vacuum bag film, Table 1 below is obtained.

[0124] Table 1

[0125]

[0126] Based on the data analysis in Table 1:

[0127] By comparing the performance data of the examples of the present invention (Examples 1 to 3) with those of the comparative examples (Comparative Examples 1 to 6), it can be clearly seen that the present invention has significant advantages in many key performance indicators, which benefits from its unique multi-layer composite structure and the optimized design of each layer component.

[0128] High temperature resistance and thermal stability:

[0129] The long-term tolerance temperature of the examples of the present invention can reach about 280 °C, and even can tolerate a high temperature of 300 °C in the short term. This is much higher than the temperature resistance upper limits of Comparative Example 1 (nylon-based, about 230 °C) and Comparative Example 2 (CPP / PET, about 250 °C). This is because the outer heat-stable layer of the present invention adopts a synergistic system of high-performance polyether ether ketone (PEEK) and high-temperature resistant thermoplastic polyurethane (TPU), which has higher thermal stability than traditional nylon or polypropylene.

[0130] The long-term heat tolerance temperature of Comparative Example 4 (without additive outer layer) is expected to be slightly lower than that of the examples of the present invention due to the lack of heat-resistant antioxidants such as rare earth oxides, and it is prone to aging and degradation at high temperatures.

[0131] The lower heat shrinkage rate (≤3.0%) also reflects the good dimensional stability of the present invention at high temperatures, which is superior to Comparative Examples 1 and 2.

[0132] Barrier performance and vacuum retention:

[0133] The examples of the present invention exhibit extremely low oxygen transmission rate (OTR≤0.35cc / m 2 ·day) and water vapor transmission rate (WVTR≤0.5g / m 2 ·day). This is far superior to Comparative Example 1 (nylon-based), Comparative Example 2 (CPP / PET), and Comparative Example 5 (single-layer EVOH barrier). These comparative examples have poor barrier performance, and gases / water vapor are easy to permeate, resulting in difficulty in maintaining the vacuum degree for a long time.

[0134] The excellent barrier performance of the present invention is directly converted into excellent vacuum retention (vacuum degree retention rate≥95% for 7 days), which is crucial for processes such as the manufacture of wind turbine blades that require maintaining a high vacuum degree for a long time to ensure sufficient resin infusion and curing. Due to poor barrier performance, the vacuum retention rate of Comparative Examples 1, 2, and 5 will decrease rapidly.

[0135] This excellent barrier effect stems from the unique gradient barrier layer structure of the present invention, especially the alternating distribution of the EVOH / SiO2 nanosheet composite layer and the vertically aligned boron nitride nanotube reinforcement layer. The synergistic effect of the nanoscale fillers and the special orientation of the nanotubes effectively extend the diffusion path of gas molecules.

[0136] Flexibility and mold fit:

[0137] The examples of the present invention have excellent flexibility and mold fit. This is mainly due to the contribution of the high-temperature resistant TPU as the main body in the outer heat-stable layer, and the combination of mLLDPE and ULDPE in the self-adaptive sealing layer. TPU endows the outer layer with good elasticity and flexibility that can still be maintained at high temperatures, enabling it to effectively fit complex curved surface molds such as wind turbine blades, reducing wrinkles and stress concentration.

[0138] In contrast, in Comparative Example 3 (with a high PEEK outer layer), due to the too high proportion of PEEK, its flexibility is significantly reduced, the elongation at break is low, it is difficult to fit complex molds, and defects are prone to occur.

[0139] The flexibility of Comparative Examples 1 and 2 is relatively average, and Comparative Example 6 (without the ULDPE sealing layer) may also be slightly inferior to the examples of the present invention in terms of low-temperature heat sealability and local mold fit to complex molds.

[0140] Mechanical Strength and Structural Stability:

[0141] In the embodiments of the present invention, while maintaining good flexibility, it still has a relatively high tensile strength (≥120 MPa), meeting the structural stability requirements under vacuum packaging and high-temperature and high-pressure environments. The SiC whiskers in the external heat-stable layer play an important strengthening role.

[0142] For Comparative Example 4 (without an additive outer layer), due to the lack of SiC whisker reinforcement, its tensile strength is expected to be lower than that of the embodiments of the present invention.

[0143] The overall composite structure of the present invention and the optimized interfacial bonding (through the transition interface layer and co-extrusion process) enable it to maintain structural integrity under harsh conditions such as autoclaving, and it is not prone to delamination or breakage, while Comparative Examples 1, 2, 3, and 4 have these risks.

[0144] Heat Sealing Performance and Operability:

[0145] The self-adaptive sealing layer of the present invention uses a combination of mLLDPE and ULDPE, providing reliable heat-sealing performance, including good low-temperature heat-sealing ability. The addition of slip agents and anti-blocking agents results in a relatively low surface friction coefficient of the film (≤0.2), improving the film's opening and slipperiness, which is convenient for high-speed packaging and laying on industrial production lines.

[0146] The low-temperature heat-sealing property of Comparative Example 6 (without a ULDPE sealing layer) may be inferior to that of the present invention. The surface friction coefficients of Comparative Examples 1 and 2 are relatively high, and the operability may be slightly worse.

[0147] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-temperature and high-pressure resistant vacuum bag film, characterized in that, The vacuum bag film includes an outer heat-stable layer, a gradient barrier layer, and an adaptive sealing layer that are stacked in sequence, where: The outer heat-stable layer is composed of raw materials in the following mass percentages: 10-25% polyether ether ketone, 60-75% high-temperature resistant thermoplastic polyurethane, 2-5% silicon carbide whiskers, and 0.5-1.5% rare earth oxide, with a thickness of 15-20 μm; The gradient barrier layer includes a transition interface layer and alternating EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforcement layers. The transition interface layer has 0.1-0.3 wt% hydroxylated carbon nanotubes. The mass ratio of EVOH to SiO2 nanosheets is 9:

1. The boron nitride nanotubes account for 3-5% of the volume of the reinforcement layer in a vertically arranged manner, with a total thickness of 8-10 μm; The adaptive sealing layer is composed of raw materials in the following mass percentages: 60-75% metallocene-catalyzed linear low-density polyethylene, 20-30% ultra-low density polyethylene, 1-2% lubricant, and 1-2% anti-blocking agent, with a thickness of 10-15 μm.

2. The high-temperature and high-pressure resistant vacuum bag film according to claim 1, wherein The high-temperature resistant thermoplastic polyurethane is polyether-based TPU, with a soft-segment glass transition temperature ≤ -40°C and a hard-segment melting temperature ≥ 200°C; the silicon carbide whiskers are high-purity, high aspect ratio β-SiC whiskers that have been surface-modified.

3. The high-temperature and high-pressure resistant vacuum bag film according to claim 1, wherein The SiO2 nanosheets are hexagonal single-crystal wafers grown by chemical vapor deposition, with a thickness ≤ 5 nm and a surface modified with the silane coupling agent KH-550.

4. The high-temperature and high-pressure resistant vacuum bag film according to claim 1, wherein The lubricant is erucamide, and the anti-blocking agent is silica.

5. The high-temperature and high-pressure resistant vacuum bag film according to claim 2, wherein The processing steps for the outer layer material are: mixing polyether ether ketone, high-temperature resistant thermoplastic polyurethane, silicon carbide whiskers, and rare earth oxide in proportion, and performing segmented melt blending in a twin-screw extruder. The temperature of the first melting zone is 300-310°C, the temperature of the second melting zone is 310-320°C, the mixing time is 5-10 minutes, and after mixing, it is cooled and pelletized to obtain the raw material for the outer heat-stable layer.

6. The high-temperature and high-pressure resistant vacuum bag film according to claim 5, wherein For the gradient barrier layer, low-pressure plasma-enhanced chemical vapor deposition is used to alternately deposit EVOH / SiO2 nanosheet composite layers and boron nitride nanotube reinforcement layers on the surface of the outer heat-stable layer. Among them, EVOH / SiO2 is deposited in solution form, the deposition temperature is 80-100°C, and the working pressure is 50-100 Pa to form the gradient barrier layer.

7. The high temperature and high pressure resistant vacuum bag film according to claim 6, characterized in that, The processing steps for the adaptive sealing layer material are: mixing metallocene-catalyzed linear low-density polyethylene, ultra-low density polyethylene, lubricant, and anti-blocking agent evenly, and melt-extruding through a single-screw extruder. The extrusion temperature is controlled in segments as the first extrusion segment at 170-180°C, the second extrusion segment at 180-190°C, and the third extrusion segment at 190-200°C to prepare the raw material for the adaptive sealing layer.

8. The high-temperature and high-pressure resistant vacuum bag film according to claim 7, wherein The forming steps of the vacuum bag film are: (a) After the raw material of the outer heat-stable layer is granulated by twin-screw extrusion, it is formed into a film by single-screw extrusion, and the extrusion temperature is 280-320°C; (c) Alternately deposit the EVOH / SiO2 nanosheet composite layer with a deposition rate of 5 - 8 nm / s and the boron nitride nanotube array layer on the surface of the outer heat-stable layer, with an orientation degree ≥ 85%; co-extrusion laminate the raw material of the adaptive sealing layer and the semi-finished product obtained in step (b), with an extrusion temperature of 170 - 200 °C; (d) Conduct primary mechanical stretching on the composite film successively, with a stretching ratio of 2.0×2.0, a rate of 0.5 - 0.8 cm / s, and a temperature of 110 - 130 °C, and secondary gas expansion stretching, with a stretching ratio of 1.5×1.5, a rate of 0.3 - 0.5 cm / s, and a temperature of 150 - 170 °C; (e) Conduct microwave-assisted heat setting treatment, with a microwave frequency of 2450 MHz, a power density of 3 - 5 W / cm², heating in a pulse mode, cycling with each heating lasting for 100 milliseconds and then intermittent for 50 milliseconds, and a total duration of 120 - 180 seconds to obtain the finished vacuum bag film.

9. The high-temperature and high-pressure resistant vacuum bag film according to claim 6, characterized in that, The deposition rate of the EVOH / SiO2 nanosheet composite layer is 5 - 8 nm / s, and the orientation degree of the boron nitride nanotube reinforced layer is ≥ 85%.

10. The high temperature and high pressure resistant vacuum bag film according to claim 8, wherein, The rate of primary mechanical stretching is 0.5 - 0.8 cm / s; the rate of secondary gas expansion stretching is 0.3 - 0.5 cm / s.

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