Self-repairing vacuum insulation panel based on MOF-aerogel composite core material and preparation method of self-repairing vacuum insulation panel

Abstract

The invention provides a self-repairing vacuum insulation panel based on an MOF-aerogel composite core material and a preparation method of the self-repairing vacuum insulation panel. The vacuum insulation panel sequentially comprises a core material layer, a barrier film layer and a packaging layer from inside to outside. The core material layer is made of a silicon dioxide nano material with ZIF-8 crystals growing on the outer edge; the barrier film layer is a multi-layer barrier film material, and the barrier film material comprises polyethylene glycol terephthalate, aluminum foil and a polyethylene protective layer; the thickness of the barrier film layer is 60-80 microns; the packaging layer is made of a thermoplastic polyurethane film. The core material layer is made of the silicon dioxide nano material with the ZIF-8 crystals growing on the outer edge, bimodal pore size distribution is formed, gas conduction can be more effectively inhibited through the special structure, and due to the fact that the micropore size is smaller than the average free path of gas molecules, the conduction heat of the gas molecules can be remarkably reduced; the nanometer framework of the aerogel forms a solid-state network with ultralow thermal conductivity, so that phonon transmission is reduced, and the thermal conductivity is greatly reduced.

Description

Technical Field

[0001] The present application relates to the technical field of sheet materials, and particularly relates to a self-healing vacuum insulation panel based on a MOF-aerogel composite core material and a preparation method thereof. Background Art

[0002] With the continuous development of society, people's attention to environmental protection and energy conservation has been increasing day by day, and heat insulation and thermal insulation materials are increasingly widely used in many fields. As an efficient heat insulation and thermal insulation material, the vacuum insulation panel (VIP panel) plays an important role in industries such as construction, household appliances, and cold chain with its extremely low thermal conductivity. For example, in the construction field, it can be used for external wall insulation, roof heat insulation, etc., effectively reducing the energy consumption of buildings; in the household appliance industry, it is commonly used in products such as refrigerators and freezers to improve the thermal insulation performance and reduce energy consumption; in cold chain transportation, it can ensure the quality of goods in a low-temperature environment and reduce cold loss.

[0003] Currently, the existing VIP panels generally consist of a film material, a core material, and a getter. During production, the core material and the getter are loaded into a film material bag and then vacuum-sealed. Traditional heat insulation and thermal insulation materials, such as foamed polyurethane and ordinary VIP panels, often require a certain thickness requirement to achieve better thermal insulation performance. The core material, as the core part, determines the thermal insulation performance and mechanical strength of the panel; the barrier film is used to maintain the internal vacuum environment and prevent external gas from entering; the getter can adsorb a small amount of residual gas to ensure the vacuum degree. However, the existing vacuum insulation panels have some deficiencies. During long-term use, the barrier film may have minor breakages due to external environmental factors or mechanical damage, resulting in slow air infiltration, a decrease in the vacuum degree, and thus a significant reduction in the thermal insulation performance, affecting its heat insulation and thermal insulation effects and service life.

[0004] To solve the above problems, the existing technology usually adopts the method of thickening the barrier film or improving the barrier film material to improve its sealing performance and anti-breakage ability. Although thickening the barrier film can play a certain role, it will significantly increase the weight of the panel, resulting in a rise in transportation costs, more laborious installation, and also affect the flexibility of the panel, making it more vulnerable to damage when bending or fitting complex surfaces. In addition, due to the space occupied by the thickened part, the overall thickness of the panel may increase, affecting its application in scenarios with limited space. The solution of improving the barrier film material, although improving the sealing effect to a certain extent, is difficult to completely prevent the slow penetration of gas, and over time, it will still affect the thermal insulation performance of the vacuum insulation panel. Summary of the Invention

[0005] This application provides a self-healing vacuum insulation panel based on a MOF-aerogel composite core material and a preparation method thereof, aiming to solve the problem in the related art that the barrier film of the vacuum insulation panel has tiny breakages, resulting in slow air infiltration, a decrease in vacuum degree, and thus a significant reduction in the adiabatic performance, affecting the heat insulation effect.

[0006] This application provides a self-healing vacuum insulation panel based on a MOF-aerogel composite core material. The vacuum insulation panel sequentially includes a core material layer, a barrier film layer, and a packaging layer from the inside to the outside;

[0007] The core material layer is made of silica nanomaterials with ZIF-8 crystals grown on the outer edge; the core material layer is a three-dimensional network structure with ZIF-8 MOF crystals epitaxially grown on silica nanofibers, having a bimodal pore size distribution;

[0008] The barrier film layer is a multi-layer barrier film material, and the barrier film material includes polyethylene terephthalate, aluminum foil, and a polyethylene protective layer; the thickness of the barrier film layer is 60 - 80 μm;

[0009] The packaging layer is made of a thermoplastic polyurethane film.

[0010] In some possible implementation manners, the average particle size of the ZIF-8 crystals in the core material layer is 35 - 45 nm.

[0011] In some possible implementation manners, the bimodal pore sizes are 1.5 nm and 25.9 nm respectively.

[0012] In some possible implementation manners, a microencapsulated siloxane self-healing agent is sprayed on the surface of the barrier film layer.

[0013] In some possible implementation manners, the microencapsulated siloxane self-healing agent generates a metallized polymer composite film containing platinum catalyst microcapsules on the surface of the barrier film layer, where the microcapsule areal density is 4500 ± 200 pieces / mm 2 。

[0014] In some possible implementation manners, the thickness of the core material layer is 10 mm, and the content of the ZIF-8 crystals is 10 wt%.

[0015] In some possible implementation manners, the thickness of the barrier film is 69 μm, and the content of the microencapsulated siloxane self-healing agent is 5 wt%.

[0016] In some possible implementation manners, the thicknesses of the polyethylene terephthalate, aluminum foil, and polyethylene protective layer are 10 - 12 μm, 5 - 7 μm, and 40 - 50 μm in sequence.

[0017] In a second aspect, the present application also provides a method for preparing a self-healing vacuum insulation panel based on the MOF-aerogel composite core material described in the first aspect, the method comprising:

[0018] Dissolve zinc nitrate and 2-methylimidazole in methanol, add tetraethyl orthosilicate and adjust the pH to 5.20 ± 0.05, and then perform supercritical drying to obtain the core material;

[0019] Mix hydroxy silicone oil and 0.5 wt% platinum catalyst evenly to obtain a mixed solution;

[0020] Mix the emulsifier with nano-SiO 2 and water, and perform ultrasonic dispersion to obtain a dispersion;

[0021] Mix the mixed solution with the dispersion to form an emulsion, add a polyurethane prepolymer, react at 55 °C for 4 hours, then centrifuge and wash, and dry at 40 °C to obtain a spraying solution;

[0022] Spray the spraying solution onto the surface of a PET / Al / PE (polyethylene terephthalate / aluminum foil / polyethylene) three-layer composite material by electrostatic spraying to obtain a barrier film;

[0023] Vacuum package the core material and the barrier film with a thermoplastic polyurethane film to obtain the self-healing vacuum insulation panel.

[0024] In some possible implementation manners, the supercritical drying process includes 6 times of CO 2 replacement, and the pressure fluctuation each time is less than or equal to 0.3 MPa.

[0025] As can be seen from the above, the present application provides a self-healing vacuum insulation panel based on a MOF-aerogel composite core material. The vacuum insulation panel sequentially includes a core material layer, a barrier film layer, and a packaging layer from the inside to the outside; the core material layer is made of a silica nano material with ZIF-8 crystals grown on the outer edge; the barrier film layer is a multi-layer barrier film material, and the barrier film material includes polyethylene terephthalate, aluminum foil, and a polyethylene protective layer; the thickness of the barrier film layer is 60-80 μm; the packaging layer is made of a thermoplastic polyurethane film. In the core material layer of the present application, a silica nano material with ZIF-8 crystals grown on the outer edge is used to form a bimodal pore size distribution. This special structure can more effectively inhibit gas conduction. Because the micropore size is smaller than the mean free path of gas molecules, it can significantly reduce the heat conduction of gas molecules; the nano-framework of the aerogel forms a solid network with ultra-low thermal conductivity, reducing phonon transmission, thereby greatly reducing the thermal conductivity. Compared with traditional VIP boards, the thermal conductivity at room temperature does not exceed 0.0014 W / (m·K), a reduction of about 20%, and the thermal conductivity is even lower in a deep low-temperature environment, which can solve the adiabatic problems in extreme scenarios such as cryogenic refrigerators. Detailed implementation manners

[0026] The embodiments described in the following examples do not represent all embodiments consistent with the present application. They are merely examples of systems and methods consistent with some aspects of the present application as detailed in the claims.

[0027] With the continuous development of society, people's emphasis on environmental protection and energy conservation has been increasing day by day, and adiabatic and thermal insulation materials are increasingly widely used in many fields. As a highly efficient adiabatic and thermal insulation material, the vacuum insulation panel (VIP panel) plays an important role in industries such as construction, household appliances, and cold chain, relying on its extremely low thermal conductivity. For example, in the construction field, it can be used for exterior wall insulation, roof heat insulation, etc., effectively reducing the energy consumption of buildings; in the household appliance industry, it is commonly used in products such as refrigerators and freezers to improve the thermal insulation performance and reduce energy consumption; in cold chain transportation, it can ensure the quality of goods in a low-temperature environment and reduce cold loss.

[0028] Currently, existing VIP panels generally consist of a film material, a core material, and a getter. During production, the core material and the getter are loaded into a film material bag and then vacuum-sealed. Traditional thermal insulation materials, such as foamed polyurethane and ordinary VIP panels, often need to meet certain thickness requirements to achieve good thermal insulation performance. The core material, as the core part, determines the adiabatic performance and mechanical strength of the panel; the barrier film is used to maintain the internal vacuum environment and prevent external gas from entering; the getter can adsorb a small amount of residual gas to ensure the vacuum degree. However, there are some deficiencies in existing vacuum insulation panels. During long-term use, the barrier film may have minor damage due to external environmental factors or mechanical damage, resulting in slow air infiltration, a decrease in the vacuum degree, and thus a significant reduction in the adiabatic performance, affecting its thermal insulation effect and service life.

[0029] To solve the above problems, the prior art usually adopts the method of thickening the barrier film or improving the barrier film material to improve its sealing performance and anti-breakage ability. Although thickening the barrier film can play a certain role, it will significantly increase the weight of the panel, resulting in a rise in transportation costs, being more laborious during installation, and also affecting the flexibility of the panel, making it more prone to damage when bending or conforming to complex surfaces. In addition, due to the space occupied by the thickened part, it may cause an increase in the overall thickness of the panel, affecting its application in scenarios with limited space. The solution of improving the barrier film material, although improving the sealing effect to a certain extent, is difficult to completely prevent the slow penetration of gas, and over time, it will still affect the thermal insulation performance of the vacuum insulation panel.

[0030] Based on this, the present application provides a silica nanomaterial with ZIF-8 crystals grown on its outer edge for the core material layer, forming a bimodal pore size distribution. This special structure can more effectively inhibit gas conduction. Since the micropore size is smaller than the mean free path of gas molecules, it can significantly reduce the heat conduction of gas molecules; the nano-framework of the aerogel forms a solid network with ultra-low thermal conductivity, reducing phonon transmission, thereby greatly reducing the thermal conductivity. Compared with traditional VIP boards, it is reduced by about 20%, and the thermal conductivity is even lower in deep low-temperature environments, which can solve the adiabatic problems in extreme scenarios such as cryogenic refrigerators.

[0031] In some embodiments, the present application provides a self-healing vacuum insulation panel based on a MOF-aerogel composite core material. The vacuum insulation panel sequentially includes a core material layer, a barrier film layer, and a packaging layer from the inside to the outside;

[0032] The core material layer is made of a silica nanomaterial with ZIF-8 crystals grown on its outer edge; the core material layer is a three-dimensional network structure with a bimodal pore size distribution formed by the epitaxial growth of ZIF-8 MOF crystals on silica nanofibers;

[0033] The barrier film layer is a multi-layer barrier film material, and the barrier film material includes polyethylene terephthalate, aluminum foil, and a polyethylene protective layer; the thickness of the barrier film layer is 60 - 80 μm;

[0034] The packaging layer is made of a thermoplastic polyurethane film. In some embodiments, the bimodal pore sizes are 1.5 nm and 25.9 nm respectively.

[0035] Metal-organic framework materials (MOF) are a class of porous materials self-assembled through the coordination between organic ligands and metal ions. They have a periodic network framework structure, an ultra-high specific surface area, high porosity, and multifunctional characteristics. As one of them, zeolitic imidazolate framework-8 (ZIF-8) not only has adjustable pore size, high porosity, and good biocompatibility, but also has excellent stability.

[0036] The barrier film layer is a multi-layer barrier film material, and the barrier film material includes polyethylene terephthalate (PET), aluminum foil, and a polyethylene (PE) protective layer; the high strength and high modulus of PET endow the barrier film with certain tensile strength and tear resistance, making it not easy to break during production, transportation, and use. Even when the vacuum insulation panel is bent, the barrier film can remain intact without cracking or tearing, ensuring the stability of its barrier performance. At the same time, this good mechanical property helps to protect the internal core material and adsorbent from being damaged by external mechanical forces.

[0037] PE has good heat-sealing performance. In the heat-sealing process, through heating and pressing, the PE layer can closely fuse with itself or other materials to form a reliable sealing edge. This ensures that the vacuum insulation panel has good airtightness after encapsulation, preventing gas leakage and maintaining the internal vacuum degree. As in the embodiment, after heat-sealing the PET / Al / PE barrier film, the heat-sealing strength of the vacuum insulation panel is relatively high. For example, the heat-sealing strength in Example 1 reaches 64.86 N / 15 mm, effectively guaranteeing the quality and performance of the product.

[0038] After the three materials of PET, Al, and PE are compounded, the barrier film still has a certain flexibility and can adapt to the bending deformation of the vacuum insulation panel. During the process of bending the vacuum insulation panel to a radius of 50 mm, the barrier film will not crack or break due to bending, ensuring the continuous effectiveness of the barrier performance and enabling the vacuum insulation panel to meet the requirements of application scenarios with complex shapes, such as installation in special structural areas inside household appliances.

[0039] ZIF-8 (zeolitic imidazolate framework-8) is formed by the self-assembly of zinc ions (Zn 2+ ) and 2-methylimidazole ligands and has a zeolite-like topological structure. Its crystal is composed of a hexagonal grid, and the zinc ions coordinate with the nitrogen atoms of the imidazole rings to form a three-dimensional pore network with a high specific surface area (up to 1000 - 2000 m 2 / g) and adjustable pore size (about ). This structure endows ZIF-8 with excellent chemical stability (resistant to strong alkalis and high temperatures) and a unique molecular sieve effect, enabling it to selectively adsorb molecules of specific sizes.

[0040] In this application, the core material layer uses silica nanomaterials with ZIF-8 crystals growing on the outer edge, forming a bimodal pore size distribution (micropores of 1.5 nm from MOF crystals and mesopores of 25.9 nm from the aerogel skeleton). This special structure can more effectively inhibit gas conduction because the micropore size is smaller than the mean free path of gas molecules, which can significantly reduce the heat conduction of gas molecules; the nano-framework of the aerogel (silica nanofibers) forms a solid network with ultra-low thermal conductivity, reducing phonon transmission, thereby greatly reducing the thermal conductivity.

[0041] Meanwhile, the bimodal pore size distribution structure has a remarkable effect on suppressing heat conduction. The 1.5-nm micropores come from ZIF-8 crystals, whose size is much smaller than the mean free path of gas molecules (~60 nm under 0.1 Pa vacuum), which can greatly suppress gas conduction, significantly reduce the gas collision frequency, and effectively prevent heat from dissipating through gas conduction. The 25.9-nm mesopores come from the aerogel skeleton. The nano-skeleton of the aerogel is composed of silica nanofibers to form a solid network with ultra-low thermal conductivity, reduce phonon transport, tortuosity the heat flow path, and further reduce solid-state heat transfer. The synergistic effect of the two makes the thermal conductivity of the vacuum insulation panel not exceed 0.0014 W / (m·K) at room temperature, about 20% lower than that of the traditional VIP panel (0.002 W / (m·K)), and the thermal conductivity is even lower in deep low-temperature environments, which can perfectly solve the insulation problem in extreme scenarios such as cryogenic refrigerators and meet the strict requirements for high-efficiency insulation in special environments.

[0042] From the perspective of gas conduction, the 1.5-nm micropores are derived from ZIF-8 crystals. Under a 0.1 Pa vacuum environment, the mean free path of gas molecules is about 60 nm, and the size of these micropores is much smaller than the mean free path of gas molecules. This is like setting countless tiny barriers on the propagation path of gas molecules. When gas molecules try to pass through these micropores, they encounter great obstacles, and the collision frequency drops significantly. Gas conducts heat mainly through the thermal motion and mutual collision of molecules. When the molecular collision frequency decreases, the efficiency of heat conduction through gas will drop sharply, thus effectively preventing heat from dissipating through gas conduction.

[0043] In terms of solid-state heat transfer, the 25.9-nm mesopores come from the aerogel skeleton, which is composed of silica nanofibers to form a solid network with ultra-low thermal conductivity. This network structure has unique physical properties that can tortuosity the heat flow path. For example, during heat conduction, heat could originally be transferred quickly along a relatively straight path, but in this tortuous network, the heat flow has to constantly change direction, just like shuttling through a maze. This greatly increases the difficulty of heat conduction, significantly slows down the heat conduction speed in solid materials, and effectively suppresses solid-state heat transfer.

[0044] In some embodiments, the average particle size of ZIF-8 crystals in the core material layer is 35 - 45 nm.

[0045] The average particle size of ZIF-8 crystals in the core material layer is 35-45 nm, which is well adapted to silica nanofibers, strengthening the structure, optimizing the pore size distribution, improving the adsorption and reaction performance, and ultimately comprehensively enhancing the comprehensive performance of the vacuum insulation panel, such as thermal insulation, mechanical properties, self-healing ability, and service life. In this particle size range, the micropore size (about 1.5 nm) formed by ZIF-8 crystals can form an effective difference with the mean free path of gas molecules, greatly inhibiting gas conduction. Numerous tiny pores act like a dense "barrier", making it difficult for gas molecules to pass through and reducing the gas heat transfer efficiency. Cooperating with the mesopores (25.9 nm) of the silica nanofiber aerogel skeleton, a bimodal pore size distribution is formed, further reducing phonon transmission and solid-state heat transfer. The combined effect makes the thermal conductivity of the vacuum insulation panel not exceed 0.0014 W / (m·K) at room temperature, about 20% lower than that of traditional products, and it has better thermal insulation performance in deep low-temperature environments, effectively solving the thermal insulation problems in extreme scenarios such as cryogenic refrigerators.

[0046] ZIF-8 crystals with an average particle size of 35-45 nm have a good size match with silica nanofibers (diameter 11.7 nm). When forming a three-dimensional network structure, the crystals can uniformly epitaxially grow on the surface of the fibers, like tightly arranged "rivets" to reinforce the structure. This uniform growth enhances the overall bonding force and stability, enabling the vacuum insulation panel to have a compressive strength of 1.73 MPa (10% deformation), about 5.8 times that of traditional aerogel core materials (0.3 MPa), effectively solving the problem of transportation damage and improving the reliability of the product in various environments.

[0047] In some embodiments, a microencapsulated siloxane self-healing agent is sprayed on the surface of the barrier film layer.

[0048] In the barrier film layer, when a PET / Al / PE three-layer composite film is used and a microencapsulated siloxane self-healing agent is embedded through special treatment, once the barrier film is damaged, external oxygen will quickly penetrate. At this time, the oxygen concentration in the environment increases. When the oxygen concentration at the damaged part > 8 vol%, oxygen contacts the platinum catalyst in the microcapsule wall material, triggering the platinum-catalyzed addition reaction. At the same time, the shear force generated by the damage will cause the microcapsule wall (PU / SiO 2When the hybrid material ruptures, the repair agent (such as hydroxy silicone oil) originally encapsulated in the microcapsules rapidly flows to the damaged area due to capillary action. During the repair process, although the core material layer does not directly participate in the chemical reaction, its special structure plays an important auxiliary role. The core material layer is made of silica nanomaterials with ZIF-8 crystals growing on the outer edge, forming a three-dimensional network with a bimodal pore size distribution. This structure has a high porosity and good connectivity, providing a favorable channel for the diffusion and penetration of the repair agent at the break of the barrier film. The repair agent can be more quickly and evenly distributed in the damaged area through these pores, thus more effectively filling the cracks, achieving the repair of the barrier film, and then restoring the performance of the vacuum insulation panel and extending its service life.

[0049] The microcapsule shell of the microencapsulated silicone self-healing agent is composed of a polyurethane prepolymer (PU) and nano-silica particles (25 nm). This composite wall material provides an effective protection barrier for the internal silicone repair agent (a mixture of hydroxy silicone oil and platinum catalyst). The polyurethane prepolymer has good chemical stability and can resist the influence of general environmental factors; the nano-silica particles enhance the mechanical strength and barrier performance of the wall material, preventing the internal repair agent from volatilizing, leaking or reacting with external substances, so that the repair agent can be stably stored under normal conditions.

[0050] In the actual process, once the oxygen concentration at the break of the barrier film > 8 vol%, the platinum catalyst-containing microcapsules will be activated. The platinum catalyst promotes the addition reaction of the silicone in the microcapsules, and the microcapsule wall ruptures under the shear force generated by the damage, releasing the silicone repair agent. These repair agents will rapidly flow to the damaged area due to capillary action, fill the cracks, and achieve the self-repair of the barrier film. Self-repair of a 50-μm damage can be achieved at room temperature (25 °C) in 23 ± 2 minutes, and the water vapor transmission rate after repair is restored to 93.6% of the initial value; the self-repair efficiency for a 200-μm damage is 89.7% (taking 40 ± 2 minutes), without external heating or pressure intervention, effectively solving the pain point that the performance of traditional barrier films drops sharply due to tiny breaks.

[0051] When the composite film formed by the microencapsulated silicone self-healing agent is intact, it can further enhance the barrier performance of the barrier film. Silicone itself has good barrier properties and can reduce the gas permeability of water vapor, oxygen, etc. Moreover, the microcapsules are evenly distributed on the surface of the barrier film, like adding an additional protective barrier to the original barrier film, further reducing the penetration of external gases into the vacuum insulation panel, helping to maintain a high-vacuum environment inside the panel, and ensuring the stable adiabatic performance of the vacuum insulation panel.

[0052] In some embodiments, the microencapsulated silicone self-healing agent generates a metallized polymer composite film containing platinum catalyst microcapsules on the surface of the barrier film layer, where the microcapsule areal density is 4500 ± 200 per mm2 。

[0053] The areal density of the microcapsules is set at 4500 ± 200 per mm 2 , ensuring that once the barrier film is damaged, a sufficient number of microcapsules can respond for repair. When the oxygen concentration at the damaged part > 8 vol%, a large number of platinum-containing catalyst microcapsules can be rapidly activated. If the areal density of the microcapsules is too low, the number of microcapsules participating in the repair reaction per unit area is insufficient, which will lead to an extended repair time, poor repair effect, inability to fill the cracks in a timely and effective manner, and affect the performance recovery of the vacuum insulation panel; while too high areal density may cause the microcapsules to be squeezed and agglomerated with each other, which is also not conducive to the uniform release and diffusion of the repair agent, reducing the repair efficiency.

[0054] In some embodiments, the thickness of the core material layer is 10 mm, and the content of ZIF-8 crystals is 10 wt%.

[0055] The 10-mm thickness of the core material layer provides sufficient space for achieving high-efficiency heat insulation. When the content of ZIF-8 crystals is 10 wt%, its nanoscale pores (1.5 nm) can fully inhibit gas conduction. At this ratio, the ZIF-8 crystals are uniformly distributed in the silica aerogel framework, forming a large number of tiny barriers, effectively reducing the ability of gas molecules to conduct heat. When the barrier film is damaged and the oxygen concentration increases to trigger the self-repair mechanism, the microenvironment where the ZIF-8 crystals are located can more stably support the progress of the repair reaction.

[0056] The thickness of the core material layer and the composite structure of ZIF-8 crystals and aerogel jointly ensure a certain mechanical strength. The 10-mm thickness provides a certain structural support foundation, while the ZIF-8 crystals grow epitaxially on the surface of silica nanofibers to form a stable three-dimensional network structure. The 10 wt% content of ZIF-8 crystals enhances the compressive properties of the material without affecting the overall structure of the aerogel framework. The compressive strength of this vacuum insulation panel reaches 1.73 MPa (10% deformation), which is about 5.8 times that of the traditional aerogel core material, effectively solving the problem of damage during transportation and improving the reliability and stability of the product.

[0057] In some embodiments, the thickness of the barrier film is 69 μm, and the content of the microencapsulated silicone self-repairing agent is 5 wt%.

[0058] When the thickness of the barrier film is 69 μm, this thickness range can ensure that the barrier film effectively blocks external gases and water vapor. The polyester (PET) substrate provides a certain strength and stability, and the aluminum foil (Al) or silica (SiO 2) The barrier layer blocks gas molecules by virtue of its own properties, while the polyethylene (PE) protective layer prevents the barrier layer from being damaged. When the thickness is between 50 - 120 μm, each layer works together to efficiently prevent external gases and water vapor from entering the inside of the insulation board, maintain the internal vacuum state, ensure a low thermal conductivity, and improve the insulation performance, such as making the thermal conductivity of the vacuum insulation board ≤ 0.0025 W / m·K. An appropriate amount of microencapsulated silicone self-healing agent can enhance the barrier performance of the barrier film. The silicone in the healing agent itself has certain barrier properties, and a content of 5 wt% enables it to be evenly distributed in the barrier film, filling the tiny pores and defects of the film material, and reducing the penetration of gases such as water vapor and oxygen. During normal use, it helps to maintain the vacuum environment inside the vacuum insulation board, ensure the stability of its insulation performance, and extend the vacuum life of the product. Compared with the situation of insufficient content, it can more effectively block the intrusion of external gases; while too high a content may affect the flexibility and mechanical strength of the barrier film, having a negative impact on the overall performance.

[0059] In some embodiments, the thicknesses of the polyethylene terephthalate, aluminum foil, and polyethylene protective layer are 10 - 12 μm, 5 - 7 μm, and 40 - 50 μm in sequence.

[0060] In some embodiments, during the encapsulation process of the self-healing vacuum insulation board based on MOF-aerogel composite core material in this application, in addition to the barrier film and the core material, getter agents such as calcium oxide or zeolite molecular sieve are filled and thermally encapsulated by means of vacuum pumping.

[0061] In some embodiments, the getter agent includes calcium oxide, zeolite molecular sieve, or silicone rubber.

[0062] Calcium oxide has strong water absorption and can chemically react with water vapor to generate calcium hydroxide, thus effectively removing the water vapor inside the vacuum insulation board. Zeolite molecular sieve has a rich microporous structure and a large specific surface area, and has a good physical adsorption effect on water vapor. Silicone rubber also has a certain ability to adsorb water vapor, and its flexibility can adapt to the bending deformation of the core material layer. The combination of the three can efficiently adsorb the water vapor inside the insulation board, preventing the water vapor from accumulating inside the insulation board and causing a decrease in insulation performance. When used in a high-humidity environment, it can maintain a dry environment inside the insulation board and ensure its long-term stable insulation effect.

[0063] In some embodiments, the thickness of the encapsulation layer is 0.1 - 0.2 mm.

[0064] If the encapsulation layer is too thin, such as less than 0.1 mm, the sealing effect of the TPU film will be greatly reduced. External air, water vapor, etc. are more likely to penetrate through the film and enter the inside of the heat insulation board, destroying the vacuum state. Once the vacuum degree decreases, the number of gas molecules in the heat insulation board increases, heat conduction intensifies, resulting in an increase in the thermal conductivity and a serious reduction in the heat insulation performance. When the thickness of the encapsulation layer is between 0.1 - 0.2 mm, a good sealing structure can be formed, effectively blocking the invasion of external gases, ensuring the long-term stability of the vacuum state, maintaining excellent heat insulation performance, and the thermal conductivity can be stably maintained at 0.0014 W / (m·K).

[0065] In some embodiments, the present application also provides a method for preparing the self-healing vacuum insulation board based on the MOF-aerogel composite core material described in the above embodiments, and the method includes:

[0066] Dissolve zinc nitrate and 2-methylimidazole in methanol, add tetraethyl orthosilicate and adjust the pH to 5.20 ± 0.05, and then perform supercritical drying to obtain the core material;

[0067] Mix hydroxy silicone oil and 0.5 wt% platinum catalyst evenly to obtain a mixed solution;

[0068] Mix the emulsifier with nano-SiO 2 and water, and perform ultrasonic dispersion to obtain a dispersion;

[0069] Mix the mixed solution and the dispersion to form an emulsion, add polyurethane prepolymer, react at 55 °C for 4 hours, then centrifuge and wash, and dry at 40 °C to obtain a spraying solution;

[0070] Spray the spraying solution onto the surface of the PET / Al / PE three-layer composite material by electrostatic spraying to obtain a barrier film;

[0071] Vacuum package the core material and the barrier film with a thermoplastic polyurethane film to obtain the self-healing vacuum insulation board.

[0072] In the present application, electrostatic spraying is used on the surface of the PET / Al / PE barrier material. Since electrostatic spraying can form a uniform functional coating on the material surface, compared with traditional electrostatic spraying which can only make microcapsules adhere to the surface of the film material and cannot achieve deep embedding, by adjusting and optimizing the process parameters, the microcapsules can be partially embedded in the surface layer of the film material (about 1 - 5 μm depth). When the barrier film is damaged, oxygen in the environment penetrates through the damaged part (concentration > 8 vol%), contacts the platinum catalyst in the microcapsule wall material, and activates the repair reaction. At the same time, the shear force generated by the damage causes the microcapsule wall (PU / SiO 2 hybrid material) to rupture, and the repair agent quickly flows to the damaged part due to capillary action, achieving a self-healing effect.

[0073] In some embodiments, supercritical drying (heating to 50 °C at a rate of 2 °C / min, performing 6 times of CO 2 replacement, with a pressure fluctuation of ≤0.3 MPa each time, maintaining at 16.2 MPa / 80 °C for 4 h).

[0074] In this application, through the bimodal pore size design of ZIF-8 MOF with a nanosize of 1.5 nm and aerogel (mesopore of 25.9 nm), compared with traditional VIP insulation boards, its thermal conductivity is significantly reduced, and the thermal conductivity at room temperature does not exceed 0.0014 W / (m·K), achieving a reduction of about 20%.

[0075] At the same time, platinum-catalyzed silicone microcapsules are sprayed on the barrier film layer. Through the platinum-catalyzed addition reaction, when the oxygen concentration at the damaged part > 8 vol%, at room temperature, for a 50-μm damage, self-repair can be achieved in 23 ± 2 minutes. At the same time, after repair, the water vapor transmission rate is restored to 93.6% of the initial value. For a 200-μm damage, the self-repair efficiency is 89.7% (taking 40 ± 2 minutes), without external intervention. Compared with the traditional 70 °C heat repair scheme, the energy consumption is reduced by 100%.

[0076] The vacuum insulation board provided by this application has a compressive strength of 1.73 MPa (10% deformation), which is about 5.8 times that of traditional aerogel core materials (0.3 MPa), solving the problem of transportation damage, and the service life can exceed 15 years.

[0077] Example 1

[0078] (1) Core material: Zinc-based ZIF-8 MOF crystals (average particle size of 38.5 ± 2.1 nm) grow epitaxially on the surface of silica nanofibers (diameter of 11.7 nm) to form a three-dimensional network with a bimodal pore size distribution;

[0079] (2) Barrier film: The base material uses a three-layer composite film of PET / Al / PE, and then a microencapsulated silicone self-healing agent is prepared and the barrier film is treated by electrostatic spraying.

[0080] The specific preparation method is as follows:

[0081] (a) Core material synthesis: Dissolve zinc nitrate (0.872 g) and 2-methylimidazole (1.624 g) in 40 mL of methanol, add tetraethyl orthosilicate (6.4 mL) and 0.1 M hydrochloric acid to adjust the pH to 5.20 ± 0.05, and then perform supercritical drying (heating to 50 °C at a rate of 2 °C / min, performing 6 times of CO 2 replacement, with a pressure fluctuation of ≤0.3 MPa each time, maintaining at 16.2 MPa / 80 °C for 4 h).

[0082] (b) Barrier film optimization:

[0083] (21) Mix 85 g of hydroxy silicone oil with 0.4 g of 0.5 wt% platinum catalyst (viscosity 487 ± 23 cP) evenly and stir at 40 °C for 30 min.

[0084] (22) Then mix 2.5 g of sodium dodecyl sulfate (emulsifier) with 7.5 g of nano-SiO 2 , 500 mL of water, and carry out ultrasonic dispersion.

[0085] (23) Pour the solution in (21) into (22) and carry out high-speed stirring (15000 rpm, 5 minutes) to form an emulsion.

[0086] (24) Add 37 g of polyurethane prepolymer and react at 55 °C for 4 hours (pH = 8.5).

[0087] (25) Centrifuge and wash, and dry at 40 °C.

[0088] (26) Electrostatic spraying:

[0089] Substrate preheating: Heat the PET / Al / PE three-layer composite film (100 °C) to facilitate partial embedding of the microcapsules on the surface during later impact.

[0090] High-pressure penetration: Spray through an electrostatic machine and increase the spray voltage (voltage 14 kV, spraying distance 8.5 cm, ambient humidity 43 ± 2% RH), and enhance the embedding effect by the impact of electrostatic force.

[0091] Post-treatment hot pressing: After spraying, use a roller press (pressure 0.5 MPa, temperature 80 °C) to further embed the microcapsules.

[0092] (c) Vacuum packaging

[0093] Fill and heat-seal the treated barrier film and core material, together with calcium oxide or zeolite molecular sieve getter, by means of vacuum pumping.

[0094] Requirements: The vacuum degree reaches 0.008 Pa, and the heat-sealing parameters are: upper mold 158 °C / lower mold 143 °C, pressure 0.35 MPa, duration 9 seconds.

[0095] The physical and chemical properties of the core material prepared in this example are as follows:

[0096] Physical properties: Density: 0.125 ± 0.005 g / cm 3 , Porosity: 92.3%, Compressive strength: 1.73 MPa (10% deformation), Thermal conductivity: 0.0014 W / (m·K) (25 °C)

[0097] Chemical properties: Heat resistance: No phase change below 250 °C in TGA test, Acid and alkali resistance: Stable at pH 3 - 11 (ZIF-8 dissolves slowly at pH < 4), Hydrophobicity: Water contact angle 145°.

[0098] To ensure the effectiveness and wide recognition of the test results, in accordance with the thermal performance requirements of the national standard GB / T 37608, the thermal conductivity test was carried out using a JW-3 type thermal conductivity detector from Beijing Jianyan Tianrun Technology Co., Ltd. The self-healing efficiency can be observed in-situ through synchrotron radiation X-ray micro-CT during the filling process of the repair agent in the cracks after the microcapsules rupture (resolution 0.65 μm). Among them, the water vapor transmission rate was tested in accordance with GB / T 21529-2008 "Determination of water vapor transmission rate of plastic films and sheets - Electrolytic sensor method". The sample preparation size was 500 mm × 500 mm × 10 mm. Ensure that the sample edges are flat, without burrs or damage. Then, multiple samples of the same batch were tested, and the data range of multiple tests was taken as the final result range. The test results are shown in Tables 1 and 2:

[0099] Table 1

[0100]

[0101] Table 2

[0102]

[0103] To ensure the comparability of the experiments, the set comparative examples are mainly different from the implementation results of the present invention. The specific comparative examples are as follows:

[0104] Comparative Example 1: Pure silica aerogel VIP

[0105] Based on the present invention, the core material is 100% silica aerogel, and the barrier film is ordinary PET / Al / PE (without being treated with the microcapsules prepared in the present invention). Other parameters are the same as those of the present invention. The test results are shown in Table 3:

[0106] Table 3

[0107]

[0108] Comparative Example 2: Surface-sprayed microcapsule VIP board

[0109] Based on the present invention, the microcapsules were attached to the surface of the barrier film layer by traditional spraying methods such as spray bottles and spray guns (not the optimized electrostatic spraying process in the present invention). Other parameters are the same as those of the present invention. The test results are shown in Table 4:

[0110] Table 4

[0111]

[0112] Comparative Example 3: Unmodified ZIF-8 / SiO 2 Preparing VIP board with composite core material

[0113] Based on the present invention, the MOF used for the core material was not subjected to epitaxial growth treatment, and ZIF-8 and aerogel were directly physically mixed. Other parameters were the same as those of the present invention. The test results are shown in Table 5:

[0114] Table 5

[0115]

[0116] Comparative Example 4: Commercially available ordinary VIP

[0117] The initial thermal conductivity of the glass fiber core VIP sold by normal manufacturers on the market is 1.8±0.2 (mw / mk), with dimensions of 500mm×500mm×12mm. The comparison results are shown in Table 6:

[0118] Table 6

[0119]

[0120]

[0121] It can be seen from the comparison of the above cases that the self-healing vacuum insulation panel based on the MOF-aerogel composite core material provided by the present application significantly reduces the thermal conductivity and self-heals the barrier film at room temperature, which can solve the pain point that the performance of the VIP board drops sharply due to minor damage. The core material in the present application is a composite of a metal-organic framework (MOF) material (ZIF-8 zeolitic imidazolate framework-8) and silica aerogel. The nano-scale pores (<2nm) of the MOF are used to further reduce the gas molecule conduction. At the same time, the skeleton structure of the aerogel is used to enhance the compressive strength, and a microencapsulated siloxane self-healing agent is embedded in the aluminum-plastic composite film. When the film is damaged, the oxygen concentration increases and the self-healing agent is automatically released to fill the crack, prolonging the service life, and having the advantages of excellent heat insulation performance and long service life.

[0122] As can be seen from the above embodiments, the present application provides a self-healing vacuum insulation panel based on a MOF-aerogel composite core material. The vacuum insulation panel sequentially includes a core material layer, a barrier film layer, and a packaging layer from the inside to the outside; the core material layer is made of a silica nanomaterial with ZIF-8 crystals grown on the outer edge; the barrier film layer is a multi-layer barrier film material, and the barrier film material includes polyethylene terephthalate, aluminum foil, and a polyethylene protective layer; the thickness of the barrier film layer is 60-80 μm; the packaging layer is made of a thermoplastic polyurethane film. In the core material layer of the present application, a silica nanomaterial with ZIF-8 crystals grown on the outer edge is used to form a bimodal pore size distribution. This special structure can more effectively inhibit gas conduction. Since the micropore size is smaller than the mean free path of gas molecules, it can significantly reduce the heat conduction of gas molecules; the nano-framework of the aerogel forms a solid network with ultra-low thermal conductivity, reducing phonon transmission, thereby greatly reducing the thermal conductivity. Compared with traditional VIPs, the thermal conductivity at room temperature does not exceed 0.0014 W / (m·K), a reduction of about 20%, and the thermal conductivity is even lower in a deep low-temperature environment, which can solve the adiabatic problems in extreme scenarios such as cryogenic refrigerators.

[0123] For the similar parts between the embodiments provided in the present application, reference can be made to each other. The specific embodiments provided above are only several examples under the general concept of the present application and do not constitute a limitation on the protection scope of the present application. For those skilled in the art, any other embodiments extended based on the solution of the present application without creative efforts belong to the protection scope of the present application.

Claims

1. A self-repairing vacuum insulation panel based on MOF-aerogel composite core material, characterized in that: The vacuum insulation panel comprises a core material layer, a barrier film layer and a packaging layer from the inside to the outside; The core material layer is made of a silicon dioxide nanomaterial with ZIF-8 crystals growing on the outer edge; the core material layer is a three-dimensional network structure with a bimodal pore size distribution formed by epitaxial growth of ZIF-8 crystals on silicon dioxide nanofibers; The barrier film layer is a multilayer barrier film material, and the barrier film material includes polyethylene terephthalate, aluminum foil and a polyethylene protective layer; the thickness of the barrier film layer is 60 to 80 μm; The encapsulation layer is made of thermoplastic polyurethane film.

2. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 1, characterized in that: The average particle size of the ZIF-8 crystals in the core material layer is 35 to 45 nm.

3. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 2, characterized in that: The bimodal pore diameters are 1.5 nm and 25.9 nm respectively.

4. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 1, characterized in that: The surface of the barrier film layer is sprayed with a microencapsulated siloxane self-repairing agent.

5. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 4, characterized in that: The microencapsulated siloxane self-repairing agent generates a metallized polymer composite film containing platinum catalyst microcapsules on the surface of the barrier film layer, wherein the microcapsule surface density is 4500±200 / mm 2 .

6. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 1, characterized in that: The core material layer has a thickness of 10 mm and a content of ZIF-8 crystals of 10 wt %.

7. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 5, characterized in that: The thickness of the barrier film is 69 μm, and the content of the microencapsulated siloxane self-healing agent is 5 wt %.

8. The self-repairing vacuum insulation panel based on MOF-aerogel composite core material according to claim 1, characterized in that: The thicknesses of the polyethylene terephthalate, aluminum foil and polyethylene protective layers are 10-12 μm, 5-7 μm and 40-50 μm respectively.

9. The method for preparing a self-repairing vacuum insulation panel based on a MOF-aerogel composite core material according to claim 1, characterized in that: The method comprises: Dissolve zinc nitrate and 2-methylimidazole in methanol, add ethyl orthosilicate to adjust the pH to 5.20±0.05, and then perform supercritical drying to obtain a core material; The hydroxy silicone oil and 0.5 wt % platinum catalyst are uniformly mixed to obtain a mixed solution; The emulsifier is mixed with nano-SiO2 and water and then ultrasonically dispersed to obtain a dispersion; The mixed liquid and the dispersion liquid are mixed to form an emulsion, and a polyurethane prepolymer is added, reacted at 55° C. for 4 hours, centrifuged and washed, and dried at 40° C. to obtain a spray liquid; The spraying liquid is sprayed onto the surface of the ethylene glycol terephthalate / aluminum foil / polyethylene composite material by electrostatic spraying to obtain a barrier film; The core material, the barrier film and the thermoplastic polyurethane film are vacuum packaged to obtain the self-repairing vacuum insulation panel.

10. The method according to claim 9, characterized in that The supercritical drying process includes 6 CO2 replacements, and each pressure fluctuation is less than or equal to 0.3MPa.

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