Composite film with high hydrogen barrier property and preparation process

Abstract

The invention discloses a composite film with high hydrogen barrier property and a preparation process, and aims to provide a composite material suitable for ocean hydrogen transmission pipelines so as to ensure efficient and safe storage and transportation of hydrogen. The composite film structure is composed of multiple layers of structures, the number of layers can be changed according to needs, a material of a spherocrystal structure, a material of a medium draw ratio, a material of a high draw ratio and a material of a higher draw ratio are adopted from inside to outside, a biaxial drawing technology is combined, and the production process is accurately controlled, so that the composite film is obtained. And a gradient structure with gradually increased hydrogen permeation resistance is formed. The design is particularly suitable for being used as a winding layer of a hydrogen conveying pipeline, extra protection and blocking effects can be provided for the pipeline, hydrogen leakage is prevented, and the integrity and safety of a pipeline system are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine hydrogen transmission pipelines, and in particular relates to a composite film with high hydrogen barrier properties and a preparation process thereof. Background Art

[0002] With the transformation of the global energy structure and the development of the hydrogen economy, the storage and transportation safety of hydrogen, a clean and efficient energy carrier, is receiving increasing attention. In marine environments, hydrogen storage and transportation face even more stringent challenges, including high humidity, high salinity, and dynamic pressure fluctuations, all of which can accelerate hydrogen permeation and leakage, increasing safety risks. Therefore, the development of composite materials with high hydrogen barrier properties is crucial for ensuring the safety and reliability of marine hydrogen pipelines.

[0003] This high-hydrogen barrier composite film is specifically designed for use as a wrapping layer in marine hydrogen pipelines, providing additional protection and barrier properties. While traditional hydrogen barrier materials, such as polyethylene (PE) and polypropylene (PP), offer some barrier properties, their effectiveness often fails to meet the requirements of long-term, efficient storage and transportation in marine environments. Furthermore, these materials have limitations in mechanical properties, chemical resistance, and environmental adaptability, making them difficult to meet the demands of complex marine environments.

[0004] To improve hydrogen barrier performance, researchers have attempted to enhance the barrier properties of materials through multi-layer composite structures. However, these composite structures still face challenges in practical applications, such as insufficient interlayer bonding strength and poor environmental resistance, which limits their application in marine hydrogen pipelines.

[0005] Furthermore, existing composite film preparation processes often struggle to precisely control the film structure and properties, resulting in insufficient uniformity and stability. These processes also suffer from shortcomings in production efficiency, material utilization, and environmental adaptability, making them difficult to meet the requirements of large-scale, efficient, and environmentally friendly production. Summary of the Invention

[0006] To address the above-mentioned issues, the present invention discloses a composite film with high hydrogen barrier properties and its preparation process. By optimizing material selection, structural design, and preparation process, the film comprises a multilayer structure comprising an inner layer, an intermediate layer, and an outer layer. Each layer is effectively bonded using a specific adhesive or hot pressing. Biaxial stretching and heat treatment processes form a highly dense structure, significantly improving hydrogen barrier properties. A gradient structural design achieves efficient barrier to hydrogen permeation. The film also exhibits excellent mechanical properties, chemical resistance, and environmental adaptability, making it suitable for use in areas such as marine hydrogen pipelines. The wrapping layer design of this composite film not only significantly improves the hydrogen barrier properties of the pipeline, but also enhances the overall strength and durability of the pipeline, enabling it to better adapt to the challenges of the marine environment and ensuring the safe and efficient storage and transportation of hydrogen.

[0007] To achieve the above object, the technical solution of the present invention is as follows: A high hydrogen barrier composite film, comprising an inner layer, an intermediate layer and an outer layer structure, wherein: The inner layer is a spherulite structure material layer, the number of layers can be increased as needed, used to form the basic support structure and provide preliminary hydrogen barrier function; The middle layer is a material layer with a medium biaxial stretch ratio. The number of layers can be increased as needed to further improve the hydrogen barrier effect by adjusting the density of the molecular structure arrangement; The outer layer is a material layer with a high biaxial stretching ratio. The number of layers can be increased as needed to achieve high-density hydrogen barrier and significantly slow down the rate of hydrogen permeation.

[0008] Furthermore, the inner layer material is selected from polyethylene (PE), polypropylene (PP) or polyvinylidene chloride (PVDC) to provide basic support and preliminary hydrogen barrier; The middle layer material is made of polyimide (PI), polyethylene terephthalate (PET) or ethylene vinyl alcohol copolymer (EVOH) to further improve the barrier properties; The outer layer material is made of polyvinylidene fluoride (PVDC), nylon or polyester to form the outermost high-density barrier, which significantly reduces the hydrogen permeation rate.

[0009] A process for preparing a composite film with high hydrogen barrier properties comprises the following steps: S1. Measuring: Add all raw and auxiliary materials into the extruder hopper according to the measured weight. The inner layer accounts for 60-85% by weight; the middle layer accounts for 10-25% by weight; and the outer layer accounts for 5-15% by weight.

[0010] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is around 70-80°C and the drying time is 2-4 hours. The moisture content of the polymer chips after drying is required to be controlled below 20ppm.

[0011] S3. Feeding, Adding, and Extruding: After the respective extruders and die heads have met the insulation requirements, start each extruder and add a small amount of raw and auxiliary materials to the hopper. Initially, the screw rotates at a low speed. After the molten material passes through the die head and is blown into a tube bubble, the screw speed is gradually increased while the material is filled. After a certain period of time, the screw extruders are started and operated, and then the processed materials are extruded. At the same time, cooling water is used to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0012] S4. Filtration and impurity removal: In order to remove impurities, gel particles, fish eyes and other foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches, and the pore size of the filter is set at 10-30μm.

[0013] S5. Spherulite Generation and Shaping: The melted inner layer material is cooled by precisely controlling the cooling rate and adding a nucleating agent at a ratio of 0.1% to 2% to the inner layer material. This effectively regulates the formation of spherulites, thereby optimizing the film's physical properties and appearance. The melted intermediate and outer layer polymer raw materials are heated to a molten state in an extruder. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0014] S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine to divide the film into several groups of equal amounts.

[0015] S7. Inspection: The slit film is then inspected by a detection device. By observing the values ​​of the detection device, it is determined whether the production of the film meets the standards, and the film that does not meet the standards is then processed again.

[0016] S8, biaxial stretching and integrated molding: First, fix the outer film with the clamp of a small precision film biaxial stretching instrument in the laboratory, set the biaxial stretching ratio and oven temperature, the oven temperature is 30-40°C below the melting temperature of the material, send it into the first oven, stretch it after sufficient heating, stretch it to the medium stretching ratio, and send it into the second oven for heat setting. After the outer film is stretched, it is cut to the same size as the middle film, and then the two layers of film are overlapped and the above steps are repeated. In this way, a multilayer film with different stretching ratios in each layer can be obtained, and then the layers are connected with an adhesive. The biaxial stretching process includes synchronous biaxial stretching or asynchronous biaxial stretching. Preferably, synchronous biaxial stretching is selected to improve the gas barrier properties of the film.

[0017] S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0018] The beneficial effects of the present invention are: 1. Achieving Controllable Hydrogen Gradient Permeation: The composite film of this invention achieves progressively enhanced hydrogen barrier performance through the specific structural design of its inner, middle, and outer layers. The inner layer utilizes a spherulite structure, the middle layer utilizes a material with a medium biaxial stretch ratio, and the outer layer utilizes a material with a high biaxial stretch ratio. This creates a gradient structure with increasing hydrogen permeation resistance from the inside out. This effectively slows the hydrogen permeation rate, significantly improving the composite film's hydrogen barrier performance and enabling precise control of hydrogen permeation, allowing the film's barrier properties to be tailored to application requirements.

[0019] 2. Enhanced Mechanical Properties: The composite film's intermediate and outer layers are biaxially stretched, resulting in a denser and more ordered molecular structure. This process not only enhances the film's barrier properties but also significantly increases its mechanical strength and toughness, improving its tensile, puncture, and tear resistance. This ensures the composite film maintains excellent mechanical properties under a variety of operating conditions.

[0020] 3. In order to produce smaller, denser, and more uniform spherulites in the inner layer with better gas barrier properties, the present invention controls the cooling rate to regulate the size of the spherulites, and also adds a nucleating agent to promote heterogeneous nucleation, increase crystal growth points, improve crystallinity, produce more ribbon-like chain molecular structures between the spherulite grains, increase the interface strength between the spherulites, and refine the crystal particles, thereby improving the strength and gas barrier properties of the film.

[0021] 4. Improved Environmental Resistance: The composite film of this invention utilizes materials for its inner, middle, and outer layers that exhibit excellent chemical resistance and environmental adaptability, ensuring long-term stability and reliability in complex marine environments. The film's barrier and mechanical properties are effectively maintained, particularly in high-humidity and high-salinity marine environments.

[0022] 5. Ensured Safety: The composite film of this invention, through its highly dense structural design and strong interlayer bonding, effectively prevents hydrogen leakage and improves the safety of marine hydrogen pipelines. This design ensures that the composite film provides reliable hydrogen barrier and protection even in high-pressure and dynamically fluctuating marine environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the hydrogen gradient permeation path that gradually narrows from the inner layer to the outer layer; Figure 2 Schematic diagram of the inner spherulite structure; Figure 3 This is a schematic diagram of the biaxial stretching process; Figure 4 Schematic diagram of the microstructural changes of the middle and outer layers during biaxial stretching. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Example

[0025] This embodiment provides a process for preparing a composite film with high hydrogen barrier properties, comprising the following steps: S1. Metering: The inner PE layer, as the base support layer, must provide mechanical strength and accounts for 70% by weight. The middle PI layer, as the barrier reinforcement layer, must also consider processing performance and accounts for 20% by weight. The outer PVDF layer, as the high-barrier layer, must ensure density but avoid excessive thickness that may cause processing difficulties and accounts for 10% by weight. Add the three materials into the extruder hopper according to the dosage.

[0026] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is 75°C and the drying time is 3 hours. The moisture content of the polymer chips after drying is controlled at 18ppm.

[0027] S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements (among them, the temperature of the extruder for adding PE needs to reach 165°C, the temperature of the extruder for adding PI needs to reach 200°C, and the temperature of the extruder for adding PVDF needs to reach 210°C), start the extruders separately and add a small amount of raw and auxiliary materials (20% of the total amount) to the hopper. At the beginning, the screw rotates at a low speed. After the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the material at the same time. After 10 minutes, start the screw extruders separately, make the screw extruders work, and then extrude the processed materials. At the same time, use cooling water to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0028] S4. Filtration and impurity removal: In order to remove impurities, gel particles and other foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line usually uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches and the pore size of the filter is 20μm.

[0029] S5. Spherulite Generation and Shaping: The molten PE is treated with a nucleating agent at a ratio of 0.1% to the inner layer material, and the cooling rate is controlled at 10-15° / minute to effectively regulate the formation of spherulites, thereby optimizing the physical properties and appearance characteristics of the PE. The molten PI and PVDF are heated in an extruder until they are molten. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0030] S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine. After 30 minutes, the slitting machine will divide the film into several groups of equal amounts.

[0031] S7. Inspection: The slit film is then inspected using an existing inspection device. By observing the values ​​of the inspection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed.

[0032] S8. Biaxial Stretching and Integrated Molding: First, secure the outer film using the clamps of a small laboratory precision biaxial stretching apparatus. Set the biaxial stretch ratio to 2 and the oven temperature to 160°C. The film is then placed in the first oven, heated thoroughly, and stretched. After stretching, it is placed in the second oven for heat setting. After stretching, the outer film is cut to the same size as the middle film. The two films are then overlapped and the above steps repeated to create two multilayer films with different stretch ratios. The films composed of PE, PI, and PVDF are then preheated separately to appropriate temperatures to ensure uniform application and effective bonding of the adhesive. The adhesive must have excellent adhesion to PE, PI, and PVDF. During the coating process, the adhesive application amount must be precisely controlled to ensure the quality of the composite. The coated film is then dried in a drying oven to remove the solvent from the adhesive. The dried film is then laminated using hot pressing rollers. The laminated film is then cured at a specific temperature and time to allow the adhesive's base and curing agent to fully react and achieve optimal bonding strength. Finally, the composite film is cut into required specifications and subjected to necessary post-processing.

[0033] S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0034] Among them, in the S8 process, the adhesive is a polyurethane adhesive. Due to its outstanding low-temperature resistance, it is suitable for low-temperature marine environments. At the same time, it can form a soft-hard transition layer between different materials, providing buffering and shock absorption functions, thereby enhancing the overall strength of the structure. Example

[0035] The preparation process of a high hydrogen barrier composite film described in this embodiment includes the following steps: S1. Measurement: The inner layer of PP serves as the basic support layer, accounting for 85% by weight, providing mechanical strength and preliminary barrier properties. The middle layer of PET serves as the barrier reinforcement layer, accounting for 10% by weight, and must take into account both processability and barrier properties. The outer layer of nylon serves as the high barrier layer, accounting for 5% by weight, ensuring density but avoiding excessive thickness that may cause processing difficulties.

[0036] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is 70°C and the drying time is 4 hours. The moisture content of the polymer chips after drying is 15ppm.

[0037] S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements (among them, the temperature of the extruder for adding PP needs to reach 170°C, the temperature of the extruder for adding PET needs to reach 260°C, and the temperature of the extruder for adding nylon needs to reach 240°C), start the extruders separately and add a small amount of raw and auxiliary materials to the hopper. At the beginning, the screw rotates at a low speed. After the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the hopper with material. After 15 minutes, start the screw extruders separately and make them work, and then extrude the processed materials. At the same time, use cooling water to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0038] S4. Filtration and impurity removal: In order to remove impurities, gel particles and other foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line usually uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches, and the filter mesh aperture is set at 30μm.

[0039] S5. Spherulite Generation and Shaping: The molten PP is subjected to precise cooling rate control and the addition of a nucleating agent at a ratio of 1% to the inner layer material to effectively control the formation of spherulites, thereby optimizing the physical properties and appearance of the PP. The molten PET and nylon are heated in an extruder until molten. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0040] S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine. After 20 minutes, the slitting machine will divide the film into several equal groups.

[0041] S7. Inspection: The slit film is then inspected using an existing inspection device. By observing the values ​​of the inspection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed.

[0042] S8. Biaxial Stretching and Integrated Molding: First, the outer film is secured in the clamps of a small laboratory precision biaxial stretching apparatus. The biaxial stretch ratio is set to 3 and the oven temperature is set to 170°C. The film is then placed in the first oven, heated thoroughly, and stretched. After stretching, it is placed in the second oven for heat setting. After stretching, the outer film is cut to the same size as the middle film. The two films are then overlapped and the above steps are repeated to produce two multilayer films with different stretch ratios. The films made of PP, PET, and nylon are then preheated to appropriate temperatures to ensure uniform application and effective bonding of the adhesive. The adhesive must have excellent adhesion to PP, PET, and nylon. During the coating process, the adhesive application amount must be precisely controlled to ensure the quality of the composite. The coated film is then dried in a drying oven to remove the solvent from the adhesive. The dried film is then laminated using hot pressing rollers. The laminated film is then aged at a specific temperature and time to allow the adhesive base and curing agent to fully react and achieve optimal bonding strength. Finally, the composite film is cut into required specifications and subjected to necessary post-processing.

[0043] S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0044] Among them, in the S8 process, the adhesives selected are modified polyurethane glue (PU-AM ​​series) and epoxy-polyamide copolymer (EP-PA). Due to their outstanding low-temperature resistance, they are suitable for low-temperature marine environments, have long service life under dynamic loads, and are compatible with existing biaxial stretching-hot pressing composite production lines. Example

[0045] The preparation process of a high hydrogen barrier composite film described in this embodiment includes the following steps: S1. Measurement: The inner layer of PVDC serves as the basic support layer, accounting for 60% by weight. It needs to be thick enough to provide a hydrogen barrier foundation, while avoiding excessive processing degradation. The middle layer of EVOH serves as a barrier reinforcement layer, accounting for 25% by weight. Its performance decreases after moisture absorption, and it needs to be isolated from moisture by the outer layer of polyester. The proportion needs to balance the barrier properties and interlayer bonding strength. The outer layer of polyester serves as a high barrier layer, accounting for 15% by weight. As the outer layer, it can resist erosion in the marine environment, but the thickness needs to be controlled to avoid the impact of high-temperature processing on other layers.

[0046] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is 80°C and the drying time is 2 hours. The moisture content of the polymer chips after drying is 19ppm.

[0047] S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements (among them, the extruder temperature for adding PVDC is 200°C, the extruder temperature for adding EVOH is 210°C, and the extruder temperature for adding polyester is 280°C), start the extruders separately and add a small amount of raw and auxiliary materials into the hopper. At the beginning, the screw rotates at a low speed. When the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the hopper with material. After 20 minutes, start the screw extruders separately and make them work, and then extrude the processed materials. At the same time, use cooling water to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0048] S4. Filtration and impurity removal: In order to remove impurities, gel particles and other foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line usually uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches, and the pore size of the filter is generally set at 10μm.

[0049] S5. Spherulite Generation and Shaping: The melted PVDC is subjected to precise cooling rate control and the addition of a nucleating agent at a 2% ratio of nucleating agent to inner layer material to effectively regulate the formation of spherulites, thereby optimizing the physical properties and appearance characteristics of the PVDC. The melted EVOH and polyester are heated in an extruder until molten. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0050] S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine. After 30 minutes, the slitting machine will divide the film into several equal groups.

[0051] S7. Inspection: The slit film is then inspected using an existing inspection device. By observing the values ​​of the inspection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed.

[0052] S8. Biaxial Stretching and Integrated Molding: First, the outer film is secured in the clamps of a small laboratory precision biaxial stretching apparatus. The biaxial stretch ratio is set to 4 and the oven temperature is set to 190°C. The film is then placed in the first oven, heated thoroughly, and stretched. After stretching, it is placed in the second oven for heat setting. After stretching, the outer film is cut to the same size as the middle film. The two films are then overlapped and the above steps repeated to produce two multilayer films with different stretch ratios. The films composed of PVDC, EVOH, and polyester are then preheated to appropriate temperatures to ensure uniform application and effective bonding of the adhesive. The adhesive must have excellent adhesion to PVDC, EVOH, and polyester. During the coating process, the adhesive application amount must be precisely controlled to ensure the quality of the composite. The coated film is then dried in a drying oven to remove the solvent from the adhesive. The dried film is then laminated using hot pressing rollers. The laminated film is then cured at a specific temperature and time to allow the adhesive base and curing agent to fully react and achieve optimal bonding strength. Finally, the composite film is cut into required specifications and subjected to necessary post-processing.

[0053] S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0054] Among them, in the S8 process, the adhesive is selected from maleic anhydride grafted polyethylene (MAH-g-PE) and polyurethane adhesives, which are suitable for low-temperature marine environments due to their outstanding low-temperature resistance. Compared with traditional materials, the hydrogen permeability of the film of Example 1 is reduced by 80% to 90%, the hydrogen permeability of the film of Example 2 is reduced by 60% to 70%, and the hydrogen permeability of the film of Example 3 is reduced by 65% ​​to 75%. The gradient structure design adopts the inner layer spherulites to provide dynamic pressure buffering, the middle layer enhances the barrier property, and the outer layer has a high stretching ratio to form a dense barrier; the biaxial stretching process is adopted, and the simultaneous biaxial stretching makes the molecular chains highly oriented, reduces grain boundary defects, and significantly extends the hydrogen permeation path; the adhesive is optimized to enhance the interlayer bonding strength and avoid leakage caused by interface delamination. Comparative Example 1 The preparation process of a high hydrogen barrier composite film described in this comparative example lacks the filtration and impurity removal steps compared to the embodiment, and specifically includes the following steps: S1. Metering: The inner PE layer, as the base support layer, must provide mechanical strength and accounts for 70% by weight. The middle PI layer, as the barrier reinforcement layer, must also consider processing performance and accounts for 20% by weight. The outer PVDF layer, as the high-barrier layer, must ensure density but avoid excessive thickness that may cause processing difficulties and accounts for 10% by weight. Add the three materials into the extruder hopper according to the dosage.

[0055] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is around 70°C and the drying time is 4 hours. The moisture content of the polymer chips after drying is required to be controlled below 20ppm.

[0056] S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements (among them, the extruder temperature for adding PE is 160°C, the extruder temperature for adding PI is 200°C, and the extruder temperature for adding PVDF is 220°C), start the extruders separately and add a small amount of raw and auxiliary materials into the hopper. At the beginning, the screw rotates at a low speed. After the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the hopper with material. After 30 minutes, start the screw extruders separately and make them work, and then extrude the processed materials. At the same time, use cooling water to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0057] S4. Spherulite Generation and Shaping: The molten PE is subjected to precise control of the cooling rate and the addition of a nucleating agent at a ratio of 0.1% to the inner layer material to effectively regulate the formation of spherulites, thereby optimizing the physical properties and appearance characteristics of the PE. The molten PI and PVDF are heated in an extruder until they are molten. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0058] S5. Slitting: Place the shaped film on the slitting machine, then start the slitting machine. After 30 minutes, the slitting machine will divide the film into several equal groups.

[0059] S6. Inspection: The slit film is then inspected using an existing inspection device. By observing the values ​​of the inspection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed.

[0060] S7. Biaxial Stretching and Integrated Molding: First, the outer film is secured in the clamps of a small laboratory precision biaxial stretching apparatus. The biaxial stretch ratio is set to 2 and the oven temperature is set to 170°C. The film is then placed in the first oven, heated thoroughly, and stretched. After stretching, it is placed in the second oven for heat setting. After stretching, the outer film is cut to the same size as the middle film. The two films are then overlapped and the above steps are repeated to produce two multilayer films with different stretch ratios. The films made of PE, PI, and PVDF are then preheated to appropriate temperatures to ensure uniform application and effective bonding of the adhesive. The adhesive must have excellent adhesion to PE, PI, and PVDF. During the coating process, the adhesive application amount must be precisely controlled to ensure the quality of the composite. The coated film is then dried in a drying oven to remove the solvent from the adhesive. The dried film is then laminated using hot pressing rollers. The laminated film is then cured at a specific temperature and time to allow the adhesive base and curing agent to fully react and achieve optimal bonding strength. Finally, the composite film is cut into required specifications and subjected to necessary post-processing.

[0061] S8. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0062] Among them, in the S7 process, the adhesive is a polyurethane adhesive, which is suitable for low-temperature marine environments. At the same time, it can form a soft-hard transition layer between different materials, provide buffering and shock absorption functions, and thus enhance the overall strength of the structure. Comparative Example 2 The preparation process of a high hydrogen barrier composite film described in this comparative example lacks the biaxial stretching process compared with the embodiment, and specifically includes the following steps: S1. Metering: The inner PE layer, as the base support layer, must provide mechanical strength and accounts for 80% by weight. The middle PI layer, as the barrier reinforcement layer, must also consider processing performance and accounts for 15% by weight. The outer PVDF layer, as the high-barrier layer, must ensure density but avoid excessive thickness that may cause processing difficulties and accounts for 5% by weight. Add the three materials into the extruder hopper according to the dosage.

[0063] S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is around 70°C and the drying time is 3 hours. The moisture content of the polymer chips after drying is 18ppm.

[0064] S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements (among them, the temperature of the extruder for adding PE needs to reach 165°C, the temperature of the extruder for adding PI needs to reach 210°C, and the temperature of the extruder for adding PVDF needs to reach 210°C), start the extruders separately and add a small amount of raw and auxiliary materials to the hopper. At the beginning, the screw rotates at a low speed. When the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the material at the same time. After 20 minutes, start the screw extruders separately, make the screw extruders work, and then extrude the processed materials. At the same time, use cooling water to continuously circulate and cool the extruder motor to ensure that the extruder motor is within a safe temperature range.

[0065] S4. Filtration and impurity removal: In order to remove impurities, gel particles and other foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line usually uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches, and the pore size of the filter is set at 15μm.

[0066] S5. Spherulite Generation and Shaping: The molten PE is subjected to precise control of the cooling rate and the addition of a nucleating agent, with the ratio of nucleating agent to inner layer material being approximately 0.1%, to effectively regulate the formation of spherulites, thereby optimizing the physical properties and appearance characteristics of PE. The molten PI and PVDF are heated to a molten state in an extruder. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled in a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a pulling device to reduce thickness and increase strength.

[0067] S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine. After 20 minutes, the slitting machine will divide the film into several equal groups.

[0068] S7. Inspection: The slit film is then inspected using an existing inspection device. By observing the values ​​of the inspection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed.

[0069] S8, integrated molding: Preheat the films formed by the three materials PE, PI, and PVDF to appropriate temperatures to ensure that the adhesive can be evenly coated and effectively bonded. The adhesive needs to have good bonding properties to PE, PI, and PVDF. During the coating process, the amount of adhesive applied needs to be precisely controlled to ensure the quality of the composite material. The coated film needs to be dried in a drying tunnel to remove the solvent in the adhesive. The dried film is compounded by hot pressing rollers. The compounded film needs to be aged at a certain temperature and time to allow the main agent and curing agent of the adhesive to fully react and achieve the best bonding strength. Finally, the compounded film is cut into the required specifications and subjected to necessary post-processing.

[0070] S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

[0071] Among them, in the S8 process, the adhesive is selected as a polyurethane adhesive, which is suitable for low-temperature marine environments. At the same time, it can form a soft-hard transition layer between different materials, provide buffering and shock absorption functions, and thus enhance the overall strength of the structure. Compared with the raw materials and preparation methods of the present invention, the hydrogen permeability of the film of Comparative Example 1 is only reduced by 30% to 40%, and the hydrogen permeability of the film of Comparative Example 2 is only reduced by 20% to 30%. Without filtration and impurity removal, the impurities in the melt lead to the formation of micropores and defects inside the film, and the hydrogen permeation paths increase; without biaxial stretching, the molecular chains are disordered, the grain boundary defects are significant, the density is insufficient, and an effective barrier cannot be formed. Therefore, after comparison, the steps S1 to S9 and parameters in Example 1 are adopted, and through the gradient polarity structure design and synchronous biaxial stretching process, its comprehensive performance makes it an ideal choice for marine hydrogen pipelines, with long-term barrier, mechanical stability and environmental adaptability, meeting the requirements of high-pressure dynamic working conditions.

[0072] It should be noted that the above content merely illustrates the technical idea of ​​the present invention and cannot be used to limit the scope of protection of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications all fall within the scope of protection of the claims of the present invention.

Claims

1. A composite film with high hydrogen barrier properties, characterized by: It includes inner layer, middle layer and outer layer structure, among which: The inner layer is a spherulite structure material layer, and the number of layers is increased as needed to form the basic support structure and provide preliminary hydrogen barrier function; The middle layer is a material layer with a medium biaxial stretch ratio. The number of layers can be increased as needed to further improve the hydrogen barrier effect by adjusting the density of the molecular structure arrangement. The outer layer is a material layer with a high biaxial stretch ratio. The number of layers is increased as needed to achieve high-density hydrogen barrier and significantly slow down the rate of hydrogen permeation. The inner layer, middle layer and outer layer regulate the crystal size of each layer through different orientations, realizing a gradient structure design in which the hydrogen permeation path gradually narrows from the inner layer to the outer layer, forming a controllable hydrogen permeation channel, and making the hydrogen permeability gradually decrease in a gradient, thereby achieving precise control of hydrogen permeation.

2. The high hydrogen barrier composite film according to claim 1, characterized in that: The inner layer material is made of polyethylene (PE), polypropylene (PP) or polyvinylidene chloride (PVDC), which provides basic support and initial hydrogen barrier; The middle layer material is made of polyimide (PI), polyethylene terephthalate (PET) or ethylene vinyl alcohol copolymer (EVOH) to further improve the barrier properties; The outer layer material is made of polyvinylidene fluoride (PVDC), nylon or polyester to form the outermost high-density barrier, which significantly reduces the hydrogen permeation rate.

3. The process for preparing a composite film with high hydrogen barrier properties according to claim 1, wherein: The following steps are included: S1. Measuring: Add all raw and auxiliary materials into the hopper of the extruder according to the metering method; S2. Drying: For polymers with a tendency to absorb moisture, they need to be dried before processing. The drying temperature is around 70-80°C and the drying time is 2-4 hours. The moisture content of the polymer chips after drying is required to be controlled below 20ppm. S3, feeding, adding and extruding: When the respective extruders and die heads meet the insulation requirements, start the extruders respectively, add a small amount of raw and auxiliary materials into the hopper, and rotate the screw at a low speed at the beginning. When the molten material passes through the die head and is blown into a tube bubble, gradually increase the screw speed and fill the material at the same time; after 15 to 30 minutes, start the screw extruders respectively, make the screw extruders work, and then extrude the processed materials; at the same time, use cooling water to circulate the extruder motor continuously to ensure that the extruder motor is within a safe temperature range; S4. Filtration and impurity removal: In order to remove impurities, gel particles and foreign matter that may exist in the melt, a filter is installed before and after the metering pump on the melt pipeline. The film production line uses a disc filter, which is made of a combination of stainless steel mesh and stainless steel sintered felt. The size of the stainless steel disc is Φ12 inches, and the filter mesh pore size is set at 10-30μm; S5. Spherulite formation and shaping: The melted inner layer material is effectively regulated by precisely controlling the cooling rate and adding a nucleating agent to optimize the physical properties and appearance characteristics of the film. The melted intermediate and outer layer polymer raw materials are heated to a molten state in an extruder. The melt passes through a filter to remove impurities and is then extruded through a die to form a film. The extruded film is rapidly cooled by a water bath or air cooling system to solidify the polymer and form a solid film. The cooled film is initially stretched by a traction device to reduce thickness and increase strength. S6. Slitting: Place the shaped film on the slitting machine, then start the slitting machine to divide the film into several equal groups; S7, inspection: The slit film is then inspected by a detection device. By observing the values ​​of the detection device, it is determined whether the film production meets the standards, and the film that does not meet the standards is then reprocessed; S8. Biaxial stretching and integrated molding: First, the outer film is fixed with the fixture of a small laboratory precision film biaxial stretching instrument, and the biaxial stretch ratio and oven temperature are set. The oven temperature is 30-40°C below the melting temperature of the material. The film is placed in the first oven and stretched after being fully heated. After being stretched to a medium stretch ratio, it is placed in the second oven for heat setting. After the outer film is stretched, it is cut to the same size as the middle film, and the two layers are overlapped and the above steps are repeated. In this way, a multilayer film with different stretch ratios is obtained, and the layers are then connected by hot pressing or adhesive. S9. Packaging and warehousing: After inspection, the multi-layer composite films that meet the relevant requirements and those that do not meet the relevant requirements will be labeled. The films that meet the relevant requirements will be packaged and placed in the finished product raw material area; the films that do not meet the relevant requirements will be labeled and placed in the finished product raw material area for independent storage.

4. The process for preparing a composite film with high hydrogen barrier properties according to claim 3, wherein: The inner layer accounts for 60-85% of the mass; the middle layer accounts for 10-25% of the mass; and the outer layer accounts for 5-15% of the mass.

5. The process for preparing a composite film with high hydrogen barrier properties according to claim 3, wherein: The ratio of the nucleating agent to the inner layer material in step S5 is 0.1% to 2%.

6. The process for preparing a composite film with high hydrogen barrier properties according to claim 3, wherein: The adhesive described in step S8 is one or more of silicone pressure-sensitive adhesive, UV curing adhesive, hot melt adhesive film, epoxy resin adhesive and polyurethane adhesive.

7. The process for preparing a composite film with high hydrogen barrier properties according to claim 3, wherein: The biaxial stretching process described in step S8 is simultaneous biaxial stretching.

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