Flexible thermal insulation composite and method for its production

Abstract

The application discloses a flexible heat-insulating composite material and a preparation method thereof. The heat-insulating composite material comprises at least one microporous membrane layer and at least one non-woven layer, the microporous membrane layer and the non-woven layer are arranged in sequence and are spaced, and the microporous membrane layer and the non-woven layer are filled with aerogel fillers in the pores. The microporous membrane layer is an ePTFE membrane layer, and the non-woven layer is a bicomponent non-woven fabric layer or an inorganic microfiber layer. The porosity of the ePTFE membrane layer is greater than or equal to 85%, and the thickness is 0.5-20 um. The average fiber diameter of the non-woven layer is 0.1-12 um, and the thickness of the non-woven layer is 0.1-0.5 mm. The thickness of the flexible heat-insulating composite material is 0.1-1.5 mm. The heat-insulating composite material is flexible, can be extruded and deformed, has excellent processability, and can be used in the fields of electronic heat preservation and the like. After the modification step, the powder dropping rate of the composite material is greatly reduced, and meanwhile, the composite material still has a good thermal conductivity and excellent heat-insulating performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal insulation materials, in particular to a flexible thermal insulation composite material and a preparation method thereof. BACKGROUND

[0002] Modern life is increasingly dependent on digital products, such as smart phones, laptops, wearable smart devices, digital cameras, etc. However, almost all digital products have a problem that the internal temperature gradually rises with the extension of the use time, among which laptops and smart phones are the most serious. Improving the thermal conductivity of the shell material can effectively dissipate heat, but it reduces the user experience and interferes with the function of the heat-sensitive components. Maintaining a pore between the shell material and the body and uniformly externalizing the lead can improve the problem, but it limits the further miniaturization of the device.

[0003] Silica aerogel is a lightweight nanoporous amorphous solid material with excellent thermal insulation performance, which has a high specific surface area, nanoscale pores, low density and other special microstructures. Based on these structures, it exhibits excellent performance in thermal and acoustic aspects. The nanoporous structure of silica aerogel can effectively suppress solid-state heat conduction and gas heat transfer, and it is currently recognized as the solid material with the lowest thermal conductivity. The low density of aerogel leads to poor mechanical properties and easy fragmentation, which limits its application.

[0004] Expanded PTFE (ePTFE) membrane is a porous, low-density and high-toughness material obtained by expanding dispersed PTFE (polytetrafluoroethylene) resin through certain production and processing processes. It has air permeability, hydrophobicity and excellent flexibility. The combination of aerogel and ePTFE membrane can integrate the advantages of both materials. However, the physical properties of the two materials differ greatly, and both have nanopores, making it difficult to combine them.

[0005] Patent application CN108778707A describes an insulating material containing at least one microporous layer (expanded fluoropolymer membrane, expanded polyethylene membrane, or expanded polypropylene membrane) and at least one porous layer (aerogel) adjacent to the microporous layer. The porous layer is the base layer, and the microporous layer is the surface layer. The microporous layer has fine pores that can intercept aerogel particles, solving the problem of powder. The product embodiment has a thickness of 1.61 mm and 2.29 mm.

[0006] Patent application CN107641213A describes an aerogel-polytetrafluoroethylene composite heat insulation and sound insulation breathable film, which comprises a breathable film layer and a sol film layer, the sol film layer is compounded on one side or multiple sides of the breathable film layer, and the thickness of the sol film layer is 10-100 μm. Its preparation method is to uniformly coat a proper amount of aerogel precursor, i.e. solution, on the cleaned breathable film by different methods, and then put the breathable film coated with the sol film into an oven for drying, so that the sol is gelled and converted into aerogel. Since the aerogel is a rigid particulate matter and the ePTFE film is flexible, the aerogel is easy to break and cause powder loss when it is bent.

[0007] Patent application CN206501539A describes a composite material of a heat-insulating and sound-insulating aerogel layer composite breathable film, which contains a breathable film layer, a bonding connection layer and an aerogel layer, and the breathable film layer and the aerogel layer are bonded through the bonding connection layer. The bonding connection layer is a flame-retardant polyurethane adhesive or a coating containing aerogel. The bonding effect of the adhesive is only on the contact surface, and the bonding effect of the thicker aerogel layer is poor.

[0008] Patent application CN113527760A describes a ePTFE-silica aerogel composite heat insulation film material. The ePTFE film is treated by ultrasonic in deionized water, ethanol and acetone respectively, and then coated with an aerogel precursor (sol) on the surface for drying, so that the sol is gelled and converted into aerogel, and finally the ePTFE-silica aerogel composite heat insulation film material is prepared. The pretreatment can increase the bonding degree of ePTFE and the aerogel precursor solution, but its function is limited, the formed aerogel layer is thin, and it is not easy to be uniform.

[0009] Patent application CN114132034A describes an electronic-grade flexible polytetrafluoroethylene heat insulation film. An aerogel slurry layer is formed on the surface of the ePTFE film to make an ePTFE-SiO2 composite film, and then two or more ePTFE-SiO2 composite films are stacked and hot-pressed to make the electronic-grade flexible polytetrafluoroethylene heat insulation film. The process is complex, the cost is high, and it is not easy to realize mass production.

[0010] The composite material of aerogel and ePTFE film needs to be further developed and researched. SUMMARY

[0011] The purpose of the present application is to provide a flexible heat insulation composite material with excellent heat insulation performance and not easy to lose powder and a preparation method thereof.

[0012] In order to achieve the purpose, the technical scheme adopted by the present application is:

[0013] A flexible thermal insulation composite material, the thermal insulation composite material comprising at least one microporous membrane layer and at least one non-woven layer, the microporous membrane layer and the non-woven layer being arranged in sequence and spaced apart, and the pores of the microporous membrane layer and the non-woven layer being filled with aerogel filler; the microporous membrane layer is an ePTFE membrane layer, and the non-woven layer is a bicomponent non-woven layer or an inorganic microfiber layer.

[0014] The porosity of the ePTFE membrane layer is greater than or equal to 85%, and the thickness is 0.5-20um.

[0015] The average fiber diameter of the non-woven layer is 0.1-12um, and the thickness of the non-woven layer is 0.1-0.5mm.

[0016] The thickness of the flexible thermal insulation composite material is 0.1-1.5mm.

[0017] Preferably, the number of layers of the ePTFE membrane layer is 1-15 layers, and the number of layers of the non-woven layer is 1-15 layers.

[0018] Preferably, the number of layers of the ePTFE membrane layer is 1-10 layers or 1-5 layers or 1-3 layers or 1-2 layers, and the number of layers of the non-woven layer is 1-10 layers or 1-5 layers or 1-4 layers or 1-3 layers.

[0019] Preferably, the thickness of the non-woven layer is 0.1-0.4mm; the thickness of the flexible thermal insulation composite material is 0.1-1.2mm or 0.1-1.0mm or 0.1-0.9mm, and the thermal conductivity is less than or equal to 22mW / M·K.

[0020] Preferably, the non-woven layer is a bicomponent non-woven layer, the low melting point component of the bicomponent non-woven layer has a melting point lower than 327℃, the average fiber diameter of the bicomponent non-woven layer is between 6-12um, and the bicomponent non-woven layer presents 90% normal distribution or uniform distribution; the bicomponent non-woven layer and the ePTFE membrane layer are compounded by hot pressing.

[0021] Preferably, the bicomponent non-woven layer is a flame-retardant non-woven layer, including side-by-side type, core-sheath type and split type bicomponent non-woven layers.

[0022] The material of the bicomponent non-woven layer is polyolefin, thermoplastic polyester or PA(polyamide), the polyolefin includes PP(polypropylene) and PE(polyethylene), and the thermoplastic polyester includes PET(polyethylene terephthalate).

[0023] The aerogel is a silica aerogel.

[0024] In the above technical solution, the non-woven layer is an inorganic microfiber layer, and the raw fiber of the inorganic microfiber layer is selected from one or more of glass microfiber, ceramic microfiber, high-silica microfiber and basalt microfiber.

[0025] The average fiber diameter of the inorganic microfiber layer is between 0.1-10um or 0.3-7um or 0.4-6um, with 90% normal distribution or uniform distribution;

[0026] The inorganic microfiber layer is bonded with the ePTFE membrane layer by an adhesive.

[0027] Preferably, the adhesive is EVA, PA, PES, HDPE or TPU, and the amount of adhesive between each inorganic microfiber layer and the ePTFE membrane layer is 0.8-1.5g / m 2 ;

[0028] The aerogel is a silica aerogel.

[0029] Preferably, the adhesive contains a flame retardant.

[0030] The method for preparing the flexible thermal insulation composite material according to any one of the preceding, comprising the following steps:

[0031] 1) Preparation of ePTFE membrane / non-woven layer composite substrate

[0032] When the non-woven layer is a bicomponent non-woven layer, the ePTFE membrane and the bicomponent non-woven layer are compounded together by a hot pressing process to form an ePTFE / non-woven composite substrate;

[0033] When the non-woven layer is an inorganic microfiber layer, the ePTFE membrane and the inorganic microfiber layer are compounded together by an adhesive spraying compounding process to form an ePTFE / inorganic microfiber layer composite substrate;

[0034] 2) Modification of ePTFE membrane / non-woven layer composite substrate

[0035] Solid polyvinyl alcohol is added to ethanol to prepare a polyvinyl alcohol ethanol solution, with a polyvinyl alcohol concentration of 5-25g / L, the PH of the polyvinyl alcohol ethanol solution is adjusted to ≥8, after mixing uniformly, it is left to stand for 20-30min, the PH of the solution is adjusted to 3-4 with citric acid, and an aqueous glutaraldehyde solution is added, so that the mass ratio of glutaraldehyde to polyvinyl alcohol in the mixed solution is 1:8-16, the ePTFE membrane / non-woven layer composite substrate is soaked in the above solution for more than 15min, the excess solution is drained by hanging, and drying is performed to obtain a modified ePTFE membrane / non-woven layer composite substrate;

[0036] 3) Preparation of silica aerogel-ePTFE membrane / non-woven layer composite material

[0037] The silica aerogel precursor solution is prepared, the silica aerogel precursor solution is uniformly coated on the modified ePTFE composite substrate, and the silica sol-ePTFE membrane / non-woven layer composite material is formed by standing, and the silica aerogel-ePTFE membrane / non-woven layer composite material, i.e., the flexible thermal insulation composite material, is obtained after supercritical drying.

[0038] Preferably, the PH value of the polyvinyl alcohol ethanol solution is adjusted by using sodium hydroxide ethanol solution in step 2).

[0039] The drying in step 2) is drying the material in an oven at 60-80℃.

[0040] Preferably, the silicon source raw material for preparing the silica aerogel precursor solution in step 3) is water glass, silicon tetrachloride, methyl orthosilicate, ethyl orthosilicate or alkoxysilane.

[0041] Preferably, the preparation method for preparing the silica aerogel precursor solution in step 3) is: the raw materials ethyl orthosilicate, acetone, anhydrous ethanol and water are fully mixed and stirred uniformly according to a molar ratio of 1:4:4:4 to obtain a sol, the PH value of the sol is adjusted to 3-4 by using dilute hydrochloric acid, the PH value of the sol is adjusted to ≥6 by adding dilute ammonia water, and the silica aerogel precursor solution is obtained after fully mixing and uniformity.

[0042] The present application has the following beneficial effects:

[0043] The expanded PTFE membrane has good flexibility and high porosity, the aerogel is filled in the pores, a relatively uniform aerogel thermal insulation layer is formed, and the aerogel particles are not easy to fall off. However, the expanded PTFE material has good waterproof performance and poor compatibility with the silica aerogel precursor solution. After the modification step in the present application, the expanded PTFE has good wettability with the silica aerogel precursor solution, which ensures that the aerogel is uniformly and firmly distributed in the pores of the expanded PTFE membrane, and greatly reduces the powder falling rate of the material.

[0044] The non-woven fabric / inorganic fiber has a certain strength, mainly plays a supporting and reinforcing role in the tensile strength of the composite material. The improvement of the material strength is beneficial to batch processing and increases the service life of the material. After being combined with the aerogel, the non-woven fabric / inorganic fiber protects the ePTFE layer and can further reduce the falling of the aerogel. In addition, the porous structure formed by the non-woven fabric / inorganic fiber is also beneficial to maintaining the filling amount of the aerogel. The flexibility of the composite material also depends on the performance of the non-woven fabric / inorganic fiber, so the best non-woven fabric / inorganic fiber and its number of layers can be selected according to the stiffness and softness of the final material.

[0045] The flexible heat insulation composite material prepared by the method of the present application is a material that can be extruded and deformed, and has excellent processability, and can be used in the field of electronic heat preservation, etc. After the modification step, the powder dropping rate of the composite material is greatly reduced, and the composite material also maintains a good thermal conductivity and good heat insulation performance. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a cross-sectional SEM image of the composite material prepared in experimental group 2 in Example 1.

[0047] Figure 2 is an SEM image of the surface of the ePTFE film layer of the composite material prepared in experimental group 3 in Example 1. DETAILED DESCRIPTION

[0048] The present application will be further described in conjunction with the examples below, but the present application is not limited by the examples.

[0049] In the following examples, the experimental methods are conventional methods unless otherwise specified; and the chemical reagents and materials used are conventional reagents and materials in the art unless otherwise specified, and are commercially available.

[0050] I. Preparation method

[0051] The flexible heat insulation composite material in the examples of the present application is prepared according to the following steps:

[0052] 1) Preparation of ePTFE film / non-woven layer composite substrate

[0053] When the non-woven layer is a bicomponent non-woven fabric layer, the ePTFE film and the bicomponent non-woven fabric layer are compounded together by a hot pressing process to form an ePTFE / non-woven fabric composite substrate.

[0054] When the non-woven layer is an inorganic microfiber layer, the ePTFE film and the inorganic microfiber layer are compounded together by a glue spraying compounding process to form an ePTFE / inorganic microfiber layer composite substrate.

[0055] 2) Modification of ePTFE film / non-woven layer composite substrate

[0056] The solid polyvinyl alcohol is added into ethanol to prepare a polyvinyl alcohol ethanol solution, the polyvinyl alcohol concentration is 5-25 g / L, the polyvinyl alcohol ethanol solution is adjusted to PH≥8 (adjusting to PH between 8-14) by using sodium hydroxide ethanol solution, after being mixed uniformly, standing for 20-30 min (letting the polyvinyl alcohol be partially alcoholized, if the alcoholization time exceeds 30 min, white precipitate will be produced, which is not conducive to the next experimental step), adjusting the solution PH value to 3-4 by using citric acid, adding glutaraldehyde aqueous solution, so that the mass ratio of glutaraldehyde to polyvinyl alcohol in the mixed solution is 1:8-16, immersing the ePTFE membrane / non-woven layer composite substrate in the above solution for more than 15 min, hanging and draining the excess solution, and drying in a 60-80℃ oven to obtain the modified ePTFE membrane / non-woven layer composite substrate.

[0057] 3) Preparation of silica aerogel-ePTFE membrane / non-woven layer composite material

[0058] The silica aerogel precursor solution is uniformly coated on the modified ePTFE composite substrate, standing to form a silica sol-ePTFE membrane / non-woven layer composite material, and after supercritical drying, a silica aerogel-ePTFE membrane / non-woven layer composite material, i.e. a flexible thermal insulation composite material, is obtained.

[0059] The silica aerogel precursor solution is uniformly coated on the modified ePTFE composite substrate, which can be achieved by spraying the substrate or immersing the substrate in the aerogel precursor solution. In actual production, in order to save cost, the spraying method is usually adopted. The coating amount is the saturation state of the substrate absorbing the aerogel precursor solution.

[0060] The silicon source raw material for preparing the silica aerogel precursor solution can be water glass, silicon tetrachloride, methyl orthosilicate, ethyl orthosilicate or alkoxysilane, which is prepared by using the prior art. Compared with inorganic silicon sources, organic silicon sources are more expensive, but have high purity and good process adaptability, and can adapt to supercritical drying and atmospheric drying. Although inorganic silicon sources are relatively low in price, they have more impurities and are currently mainly used in atmospheric drying.

[0061] The silica aerogel precursor solution in the embodiment of the present application is prepared by using ethyl orthosilicate: the raw materials ethyl orthosilicate, acetone, anhydrous ethanol and water are fully mixed and stirred uniformly according to a molar ratio of 1:4:4:4 to obtain a sol, the PH value of the sol is adjusted to 3-4 by using dilute hydrochloric acid, the reaction is carried out, dilute ammonia water is added to adjust the PH value of the sol to≥6, and after being fully mixed and uniformly mixed, the silica aerogel precursor solution is obtained.

[0062] II. Performance detection

[0063] In the embodiment of the present application, the prepared thermal insulation composite material is detected for the following performance indexes:

[0064] 1. Thermal conductivity refers to the heat transferred through 1 square meter area in one hour under the condition of stable heat transfer, with the temperature difference of 1 degree (K, ℃) between the two sides of 1m thick material, and the unit is watt per meter degree (W / (m·K), sometimes K can be replaced by ℃.

[0065] The thermal conductivity test method refers to the national standard GB / T 10294-2008 "Determination of Steady-state Thermal Resistance and Related Properties of Thermal Insulation Materials by Guarded Hot Plate Method", the test temperature is 25℃, the thinner sample is tested by multiple layers of samples, usually 5 layers. The thicker sample can be tested by single layer. The thicker the thickness, the closer to the true thermal insulation performance. The test sample is thin, which may have test deviation. Since the thermal conductivity refers to the heat transfer amount in unit thickness and unit temperature difference, it is not related to the test thickness.

[0066] 2. Test method of powder dropping rate: after the critical drying is completed, the thermal insulation composite material sample is weighed, and the weight m1 is recorded. The sample is placed in a sealed transparent plastic bag, bent on a roller with a diameter of 20 cm for 10 times on the front and back surfaces respectively, and the sample is taken out from the sealed transparent plastic bag, weighed and recorded as weight m2, and the powder dropping rate is calculated.

[0067]

[0068] 3. Test method of flame retardant performance: according to the following standard: DIN 53438-2-1984: Test for the determination of the flame retardant properties of flammable materials: surface flame method.

[0069] 4. Flexible material: flexible material is a material that can be extruded and deformed, and rigid material will be broken. Rigid material and flexible material are defined according to the deformation ability of the material, and rigid material refers to weak deformation ability. The present application prepares a flexible ultrathin thermal insulation composite material with low powder dropping rate and excellent processing performance, which can be used in the field of electronic heat preservation.

[0070] Example 1, silica aerogel-ePTFE membrane / non-woven fabric flexible thermal insulation composite material

[0071] The bicomponent non-woven fabric is divided into parallel type (mainstream), skin-core type and split type, and the main materials are PET, PP, PE, PA and other polyolefins, which can be directly purchased.

[0072] The ePTFE film and the bicomponent nonwoven material in the embodiment are directly commercially available. The low-melting-point component in the bicomponent nonwoven material has a melting point lower than 327℃, and the average fiber diameter of the bicomponent nonwoven material is between 6-12um, showing 90% normal distribution or uniform distribution. The parameters of the ePTFE film and the bicomponent nonwoven material used in the embodiment are shown in Tables 1 and 2.

[0073] Table 1. Raw material parameters of ePTFE film

[0074] ePTFE film raw material Thickness um Porosity ePTFE film raw material 1 0.5 98％ ePTFE film raw material 2 5 96％ ePTFE film raw material 3 10 95％ ePTFE film raw material 4 15 92％ ePTFE film raw material 5 20 85％

[0075] Table 2. Parameters of bicomponent nonwoven material

[0076]

[0077] The materials in Table 3 are prepared by using the foregoing method steps:

[0078] Table 3. Composition of thermal insulation composite material

[0079]

[0080] The specific process parameters in the preparation method are shown in Table 4, and the performance indicators of the prepared composite material are shown in Table 4:

[0081] Table 4. Process parameters and performance indicators

[0082]

[0083] Comparing the comparative group 1 and the experimental group 2, the materials used in each layer are the same, but the comparative group 1 is not treated by the modification step 2), and the final obtained composite material has a more serious powder dropping problem; the SEM image of the cross section of the composite material prepared in the experimental group 2 is shown in Figure 1 The SEM image of the surface of the ePTFE film layer of the composite material prepared in the experimental group 3 is shown in Figure 2

[0084] The comparative groups 2-4 only use single-layer materials, and the thermal conductivity of the thermal insulation material is high, and the thermal insulation performance is obviously poorer than that of the experimental group, and the powder dropping problem is also more serious. Comparing the comparative groups 2 and 3, the materials used are the same, but the comparative group 2 is not treated by the modification step 2), and the comparative group 3 is treated by the modification step 2). The product performance test results show that after the modification step 2) treatment, the thermal conductivity of the material is significantly reduced, the thermal insulation performance is better, and the product powder dropping rate is also significantly reduced. The composite material prepared by the method of the present application has obviously better thermal insulation performance compared with the single-layer material or the composite material without modification step, and the powder dropping problem is solved, and the powder dropping rate is significantly reduced.

[0085] ​Example 2. Flexible thermal insulation composite material of silica aerogel-ePTFE film / inorganic micro-fiber layer

[0086] The ePTFE film and inorganic micro-fiber layer material used in this example were directly commercially available, and the parameters of the ePTFE film and inorganic micro-fiber layer material used in this example are shown in Table 1 and Table 5:

[0087] Table 5. Inorganic micro-fiber layer material

[0088]

[0089]

[0090] The materials in Table 6 were prepared using the aforementioned method steps:

[0091] Table 6. Thermal insulation composite material composition

[0092]

[0093] The specific process parameters in the preparation method are shown in Table 7, and the performance indicators of the prepared composite material are shown in Table 7:

[0094] Table 7. Main process parameters and performance indicators

[0095]

[0096]

[0097] Comparative Group 1 and Experimental Group 2 were compared, and the same material was used for each layer, but Comparative Group 1 was not treated by modification step 2), and the final composite material had a more serious problem of powder falling.

[0098] Comparative Groups 2-4 only used single-layer materials, and the thermal insulation performance and powder falling rate of the thermal insulation material were significantly poorer than the experimental group. Comparative Groups 2 and 3 used the same material, but Comparative Group 2 was not treated by modification step 2), and Comparative Group 3 was treated by modification step 2). The product performance test results showed that after modification step 2), the thermal conductivity of the material decreased significantly, the thermal insulation performance was better, and the product powder falling rate also decreased significantly.

[0099] Comparative Group 5, Experimental Group 2, and Comparative Group 1 were compared, and the amount of adhesive between each layer of inorganic micro-fiber layer and ePTFE film layer was 1.6 g / m 2 The final product did not meet the F1 requirement for flame retardant performance, and after repeated experiments by the inventors, it was found that when the amount of adhesive between each layer of inorganic micro-fiber layer and ePTFE film layer was more than 1.5 g / m 2At that time, the flame retardant performance of the final product did not meet the F1 requirement. In comparison group 6, the amount of adhesive used between each inorganic microfiber layer and the ePTFE membrane layer was 0.7 g / m². 2 The bonding strength between different layers is poor, making delamination easy. Through numerous experiments, the inventors discovered that when the amount of single-layer adhesive is less than 0.8 g / m²... 2 In such cases, there is often a problem of poor composite strength between different layers.

[0100] The composite material prepared by the method of the present invention has significantly better thermal insulation performance than single-layer materials or composite materials without modification steps, and the problem of powder shedding is also solved, with a significant reduction in powder shedding rate.

Claims

1. A flexible thermal insulation composite material, characterized in that: The flexible thermal insulation composite material includes at least one microporous membrane layer and at least one nonwoven layer, wherein the microporous membrane layer and the nonwoven layer are arranged alternately, and the pores of both the microporous membrane layer and the nonwoven layer are filled with aerogel filler; the microporous membrane layer is an ePTFE membrane layer, the nonwoven layer is a bicomponent nonwoven fabric layer or an inorganic microfiber layer, and the aerogel is silica aerogel; the number of ePTFE membrane layers is 1-15, and the number of nonwoven layers is 1-15. The porosity of the ePTFE membrane is ≥85%, and the thickness is 0.5-20 μm; The average fiber diameter of the nonwoven layer is 0.1-12 μm, and the thickness of the nonwoven layer is 0.1-0.5 mm; The thickness of the flexible thermal insulation composite material is 0.11-1.5 mm; The preparation method of flexible thermal insulation composite material includes the following steps: 1) Preparation of ePTFE film / nonwoven composite substrate When the nonwoven layer is a two-component nonwoven fabric layer, the ePTFE film and the two-component nonwoven fabric layer are combined together by hot pressing to form an ePTFE / nonwoven fabric composite substrate. When the nonwoven layer is an inorganic microfiber layer, the ePTFE membrane and the inorganic microfiber layer are bonded together by an adhesive spraying process to form an ePTFE / inorganic microfiber layer composite substrate. 2) Modified ePTFE membrane / nonwoven composite substrate Solid polyvinyl alcohol is added to ethanol to prepare a polyvinyl alcohol ethanol solution with a polyvinyl alcohol concentration of 5-25 g / L. The pH of the polyvinyl alcohol ethanol solution is adjusted to ≥8. After mixing evenly, the solution is allowed to stand for 20-30 min. Citric acid is used to adjust the pH of the solution to 3-4. Glutaraldehyde aqueous solution is added so that the mass ratio of glutaraldehyde to polyvinyl alcohol in the mixed solution is 1:8-16. The ePTFE membrane / nonwoven layer composite substrate is immersed in the above solution for more than 15 min, hung to drain excess solution, and dried to obtain the modified ePTFE membrane / nonwoven layer composite substrate. 3) Preparation of silica aerogel-ePTFE membrane / nonwoven layer composite material A silica aerogel precursor solution was prepared and uniformly coated onto a modified ePTFE membrane / nonwoven composite substrate. After standing, a silica sol-ePTFE membrane / nonwoven composite material was formed. After supercritical drying, the silica aerogel-ePTFE membrane / nonwoven composite material, i.e., a flexible thermal insulation composite material, was obtained.

2. The flexible thermal insulation composite material according to claim 1, characterized in that: The number of layers of the ePTFE membrane is 1-10, and the number of layers of the nonwoven layer is 1-10; The thickness of the nonwoven layer is 0.1-0.4 mm; the thickness of the flexible thermal insulation composite material is 0.11-1.2 mm, and the thermal conductivity is ≤22 mW / (M×K).

3. The flexible thermal insulation composite material according to claim 1, characterized in that: The nonwoven layer is a bicomponent nonwoven fabric layer, in which the low-melting-point component has a melting point below 327°C. The average fiber diameter of the bicomponent nonwoven fabric is between 6 and 12 μm, exhibiting a 90% normal or uniform distribution. The two-component nonwoven fabric layer and the ePTFE membrane layer are composited by hot pressing.

4. The flexible thermal insulation composite material according to claim 3, characterized in that: The bicomponent nonwoven fabric is made of polyolefin, thermoplastic polyester, or PA. The polyolefin includes PP and PE, and the thermoplastic polyester includes PET.

5. The flexible thermal insulation composite material according to claim 1, characterized in that: The nonwoven layer is an inorganic microfiber layer, and the raw material fibers of the inorganic microfiber layer are selected from one or more of glass microfibers, ceramic microfibers, high silica microfibers, and basalt microfibers. The average fiber diameter of the inorganic microfiber layer is 0.1-10 μm, exhibiting a 90% normal or uniform distribution; The inorganic microfiber layer is bonded to the ePTFE membrane layer with an adhesive.

6. The flexible thermal insulation composite material according to claim 5, characterized in that: The adhesive is EVA, PA, PES, HDPE, or TPU, and the amount of adhesive used between each inorganic microfiber layer and the ePTFE membrane layer is 0.8-1.5 g / m³. 2 .

7. The flexible thermal insulation composite material according to claim 6, characterized in that: The adhesive contains a flame retardant.

8. A method for preparing the flexible thermal insulation composite material according to any one of claims 1 to 7, characterized in that, Includes the following steps: 1) Preparation of ePTFE film / nonwoven composite substrate When the nonwoven layer is a two-component nonwoven fabric layer, the ePTFE film and the two-component nonwoven fabric layer are combined together by hot pressing to form an ePTFE / nonwoven fabric composite substrate. When the nonwoven layer is an inorganic microfiber layer, the ePTFE membrane and the inorganic microfiber layer are bonded together by an adhesive spraying process to form an ePTFE / inorganic microfiber layer composite substrate. 2) Modified ePTFE membrane / nonwoven composite substrate Solid polyvinyl alcohol is added to ethanol to prepare a polyvinyl alcohol ethanol solution with a polyvinyl alcohol concentration of 5-25 g / L. The pH of the polyvinyl alcohol ethanol solution is adjusted to ≥8. After mixing evenly, the solution is allowed to stand for 20-30 min. Citric acid is used to adjust the pH of the solution to 3-4. Glutaraldehyde aqueous solution is added so that the mass ratio of glutaraldehyde to polyvinyl alcohol in the mixed solution is 1:8-16. The ePTFE membrane / nonwoven layer composite substrate is immersed in the above solution for more than 15 min, hung to drain excess solution, and dried to obtain the modified ePTFE membrane / nonwoven layer composite substrate. 3) Preparation of silica aerogel-ePTFE membrane / nonwoven layer composite material A silica aerogel precursor solution was prepared and uniformly coated onto a modified ePTFE membrane / nonwoven composite substrate. After standing, a silica sol-ePTFE membrane / nonwoven composite material was formed. After supercritical drying, the silica aerogel-ePTFE membrane / nonwoven composite material, i.e., a flexible thermal insulation composite material, was obtained.

9. The preparation method according to claim 8, characterized in that: In step 2), the pH value of the polyvinyl alcohol ethanol solution is adjusted using sodium hydroxide ethanol solution; The drying described in step 2) involves placing the material in an oven at 60-80℃ to dry it.

10. The preparation method according to claim 8 or 9, characterized in that: In step 3), the silicon source material for preparing the silica aerogel precursor solution is water glass, silicon tetrachloride, methyl orthosilicate, ethyl orthosilicate, or alkoxysilane.

11. The preparation method according to claim 10, characterized in that: The preparation method for the silica aerogel precursor solution in step 3) is as follows: Ethyl orthosilicate, acetone, anhydrous ethanol and water are mixed thoroughly in a molar ratio of 1:4:4:4 to obtain a sol. The pH value of the sol is adjusted to 3-4 with dilute hydrochloric acid and the reaction is carried out. Dilute ammonia is added to adjust the pH value of the sol to ≥6. After thorough mixing, the silica aerogel precursor solution is obtained.

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