A method for preparing a fully inorganic alumina fiber / aerogel composite heat-insulating paper

Abstract

The application discloses a preparation method of full-inorganic alumina fiber / aerogel composite heat insulation paper, and the method comprises the following steps: alumina fiber web is pretreated by inorganic glue and a network roller to obtain alumina fiber base paper; a silica sol and an alkali catalytic liquid are prepared; the silica sol and the alkali catalytic liquid are mixed and then combined with the alumina fiber base paper; the obtained alumina fiber base / wet gel paper is subjected to solvent replacement and aging treatment; and the alumina fiber base / wet gel paper after aging is dried to complete the preparation. The alumina fiber / aerogel composite heat insulation paper prepared by the method has good mechanical strength, adjustable hardness, excellent heat insulation performance, high-temperature resistance (above 900 DEG C) and low burning loss, and can meet the application scene requirements of high-temperature closed environment heat insulation material coating and ring punching.

Description

Technical Field

[0001] This invention belongs to the field of nano-insulation materials technology, specifically relating to a method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper. Background Technology

[0002] Aerogel materials are a new type of material with a special microstructure, such as high specific surface area, nanoscale pores, and low density. Based on this special microstructure, they exhibit excellent thermal insulation performance. However, due to their special microstructure, they also have poor mechanical strength. To realize the practical application of aerogel materials, they are usually compounded with various fiber substrates to retain the excellent thermal insulation performance of aerogel while increasing its mechanical strength.

[0003] A thermal battery is a highly efficient and stable storage chemical power source used in spacecraft and missiles. It boasts advantages such as high energy density, high stability, rapid response, small size, and light weight. Its working principle involves a single thermal activation, using an inorganic molten salt as the electrolyte to continuously provide electrical energy through an electrochemical reaction within a certain timeframe. During discharge, the solidification of the electrolyte signifies the end of the thermal battery's lifespan. Thermal insulation materials effectively slow down the temperature drop of the electrolyte, extending its molten state time and preventing the thermal battery from being affected by external temperatures. Therefore, the performance of thermal insulation materials directly determines the discharge performance and lifespan of the thermal battery, making them a key component.

[0004] Existing aerogel insulation materials used in thermal batteries, such as ZL200910154313.1, disclose a method for preparing a silica aerogel composite insulation sleeve with glass fiber as the substrate. This aerogel, using glass fiber as the substrate, has a maximum operating temperature of 600℃. However, with the increasing lifespan of new thermal batteries, the high-temperature resistance of traditional silica aerogel composite insulation materials with glass fiber as the substrate is no longer sufficient. Existing fiber substrates resistant to temperatures above 900℃, such as quartz glass fiber, alumina fiber, mullite fiber, and carbon fiber, all require reinforcement with organic adhesives before use. Thermal batteries have a closed internal structure, and the insulation material cannot generate gas at high temperatures; the loss on ignition must be less than 3.5%. Therefore, there are currently no commercially available fiber substrates that can be directly used to withstand temperatures above 900℃. On the other hand, the thermal insulation materials used inside thermal batteries are limited by the battery volume, and the thickness is generally less than 1mm. Sometimes they need to be punched, and sometimes they need to be wound and wrapped. Therefore, the thermal insulation materials are required to have good mechanical strength and adjustable softness and hardness. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an all-inorganic alumina fiber / aerogel composite thermal insulation paper. This method produces a thermal insulation material with good mechanical strength, adjustable hardness, excellent thermal insulation performance, resistance to temperatures above 900℃, and low loss on ignition, in order to meet the needs of applications such as winding, wrapping, and punching of thermal insulation materials for new thermal batteries and other high-temperature enclosed environments.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper includes the following steps: (1) Pretreatment of alumina fiber mesh with inorganic adhesive / anilox roller reinforcement: After soaking the alumina fiber mesh with a certain concentration of alumina adhesive, it is squeezed by an anilox roller to remove excess alumina adhesive and physically reinforce the alumina fiber mesh. Then, the alumina fiber mesh is placed in an oven to dry and remove excess moisture, thus obtaining alumina fiber base paper reinforced with alumina inorganic adhesive and anilox roller.

[0007] (2) Preparation of silica sol and alkaline catalyst: Disperse the silicon source in a certain amount of solvent, add water and acid catalyst and stir evenly, then hydrolyze at 40-60℃ for 2-3 h to obtain silica sol; dissolve the alkaline catalyst in water to obtain alkaline catalyst.

[0008] (3) Alumina fiber base paper and silica sol composite: After mixing silica sol and alkaline catalyst in a certain proportion, the mixture is sprayed onto the alumina fiber base paper obtained in step (1) at a certain flow rate, so that the mixture can fully penetrate into the alumina fiber base paper. The sprayed alumina fiber base paper is heated at 40-60℃ for a certain time until the silica sol gels and alumina fiber base / wet gel paper is obtained.

[0009] (4) Solvent replacement and aging of alumina fiber-based / wet gel paper: The alumina fiber-based / wet gel paper was soaked in ethanol solution and heated to replace the solvent, and aged alumina fiber-based / wet gel paper was obtained.

[0010] (5) Drying of aged alumina fiber-based / wet gel paper: The aged alumina fiber-based / wet gel paper is placed in a supercritical drying device and dried under certain drying conditions to finally obtain an inorganic alumina fiber / aerogel composite insulation paper.

[0011] Preferably, the alumina fiber mesh in step (1) is made by a combination of blow spinning and electrospinning (commercially available), with a basis weight of 30-400 g / m². 2 The alumina adhesive concentration is 3-20 wt%, the anilox roller mesh count is 10-300 mesh, the extrusion pressure is 0.1-0.5 MPa, and the extrusion line speed is 1-20 m / min.

[0012] Preferably, in step (2), the silicon source includes any one or a combination of two or more of methyl orthosilicate, tetraethyl orthosilicate, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, and water-soluble silica gel; the solvent includes any one or a combination of two or more of methanol, ethanol, acetone, tetrahydrofuran, dimethylformamide, pyrrolidone, and dimethyl sulfoxide; the mass ratio of the silicon source to the solvent is 1:0.5-5, preferably 1:1-2.

[0013] Preferably, in step (2), the acid catalyst is any one or a combination of two or more of sulfuric acid, hydrochloric acid, nitric acid, 85% phosphoric acid, boric acid, and acetic acid, and the mass ratio of silicon source to acid catalyst is 1:0.0005-0.05, preferably 1:0.005-0.01; in step S2, during the preparation of silica sol, the mass ratio of silicon source to water is 1:0.05-2, preferably 1:0.5-0.8.

[0014] Preferably, the alkaline catalyst in step (2) is any one or a combination of two or more of sodium bicarbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, calcium hydroxide and ammonia water, and the concentration of the alkaline catalyst solution is 0.01 wt%-1 wt%, preferably 0.5 wt%-0.8 wt%.

[0015] Preferably, in step (3), the volume ratio of silica sol to alkaline catalyst is 1:0.1-10, preferably 1:1-1.5, the spray flow rate of the mixture is 1-200 L / h, and the heating time of the sprayed alumina fiber base paper at 40-60℃ is 1-30 min, preferably 10-20 min.

[0016] Preferably, in step (4), the alumina fiber-based / wet gel paper is repeatedly soaked in ethanol solution and heated to perform solvent replacement. The number of solvent replacements is 3-6 times, and the concentration of the ethanol solution in each subsequent replacement is greater than or equal to the concentration of the previous replacement. The concentration of the first ethanol solution is 50-95 wt%, the concentration of the ethanol solutions in each intermediate replacement is 80-99 wt%, and the concentration of the last ethanol solution is 98-100 wt%.

[0017] Furthermore, when the solvent is replaced three times, the concentration of the ethanol solution in the first replacement is 90-95 wt%, the concentration of the ethanol solution in the middle replacement is 95-99 wt%, and the concentration of the ethanol solution in the last replacement is 98-99 wt%.

[0018] Furthermore, when the solvent is replaced 4-6 times, the concentration of the ethanol solution in the first replacement is 50-60 wt%, the concentration of the ethanol solution in the second replacement is 80 wt%-90 wt%, and the concentration of the ethanol solution in each of the remaining intermediate replacements is 95-99 wt%. For example, when the solvent is replaced 4 times, each of the intermediate replacements except the second is the third; when the solvent is replaced 5 times, each of the intermediate replacements except the second is the third and fourth, and so on; the concentration of the ethanol solution in the last replacement is 98-99 wt%.

[0019] Furthermore, in step (4), the solvent replacement temperature is 40-60℃ and the time is 6-12 h.

[0020] Preferably, in step (5), the supercritical drying temperature is 250-300℃, the pressure is 7-10 MPa, and the heat and pressure holding time is 1-5 h.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper provides a method that reinforces the fiber substrate through physical extrusion using inorganic adhesives and anilox rollers, without using any organic adhesives. The silica sol and alkaline catalyst are prepared separately, and the density and hardness of the aerogel can be easily adjusted by modifying the ratio of silicon source solvent in the sol and the ratio of sol to alkaline catalyst. A multi-level gradient displacement strategy ensures that the pores do not collapse and the thermal conductivity does not increase after adjusting the aerogel's hardness. The resulting alumina fiber / aerogel composite insulation paper exhibits good mechanical strength, adjustable hardness, excellent thermal insulation performance, resistance to temperatures above 900℃, and low loss on ignition. Furthermore, this preparation method is also applicable to other high-temperature resistant inorganic fiber substrates that require reinforcement with organic adhesives, facilitating the diversification of applications for high-temperature resistant thermal insulation aerogel composite insulation materials. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, and the beneficial effects of the present invention will be illustrated by two comparative examples.

[0023] In a specific embodiment of the present invention, the fiber-based paper prepared using wet papermaking technology (commercially available) is sourced from Changzhou Kaibo Fiberglass Co., Ltd., with product number S-KFM40.

[0024] The commercially available alumina fiber mesh (made by a combination of blown and electrospinning) is from Shanghai Rongrong New Material Technology Co., Ltd., product number NW-F-1600.

[0025] In a specific embodiment of the present invention, the ethanol solution used for solvent replacement is an ethanol-water mixture.

[0026] Comparative Example 1: A method for preparing composite thermal insulation paper (1) Fiber-based paper is prepared using wet papermaking technology (commercially available), 0.3 mm thick, with a basis weight of 40 g / m². 2 Glass fiber paper with a tensile strength of 0.2 KN / m is used as the base material, and no reinforcement treatment is required; (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:1. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as the alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain glass fiber-based / wet gel paper. (4) The glass fiber-based / wet gel paper was placed in a 95 wt% ethanol solution and kept at 50℃ for 12 h; the glass fiber-based / wet gel paper was then removed and placed in a 99 wt% ethanol solution and kept at 50℃ for 12 h; the glass fiber-based / wet gel paper was then removed and placed in a 99 wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged glass fiber-based / wet gel paper. (5) Place the aged glass fiber-based / wet gel paper into a supercritical drying device, set the supercritical drying temperature to 255℃, the pressure to 7 MPa, and the heat and pressure holding time to 1 h. Then depressurize and cool, and take out to obtain glass fiber-based / aerogel composite insulation paper. The relevant physical properties are shown in Table 1.

[0027] Comparative Example 2: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the substrate, soaked in 3wt% acrylic emulsion, and then extruded through a smooth roller (without mesh) at a pressure of 0.3MPa and an extrusion speed of 5 m / min. After drying, alumina fiber base paper reinforced with organic glue is obtained. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:1. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet coagulation paper. (4) The alumina fiber-based / wet gel paper was placed in a 95wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then removed and placed in a 99wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then removed and placed in a 99wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0028] Comparative Example 3: A method for preparing composite thermal insulation paper (1) Fiber-based paper is prepared using wet papermaking technology (commercially available), 0.3 mm thick, with a basis weight of 40 g / m². 2 Glass fiber paper with a tensile strength of 0.2 KN / m is used as the base material, and no reinforcement treatment is required; (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:1. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as the alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain glass fiber-based / wet gel paper. (4) The glass fiber-based / wet gel paper was placed in a 95 wt% ethanol solution and kept at 50℃ for 12 h; the glass fiber-based / wet gel paper was removed and placed in a 95 wt% ethanol solution again and kept at 50℃ for 12 h; the glass fiber-based / wet gel paper was removed and placed in a 95 wt% ethanol solution again and kept at 50℃ for 6 h to obtain the aged glass fiber-based / wet gel paper. (5) Place the aged glass fiber-based / wet gel paper into a supercritical drying device, set the supercritical drying temperature to 255℃, the pressure to 7 MPa, and the heat and pressure holding time to 1 h. Then depressurize and cool, and take out to obtain glass fiber-based / aerogel composite insulation paper. The relevant physical properties are shown in Table 1.

[0029] Example 1: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 5wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 80, a pressure of 0.3 MPa, an extrusion speed of 5 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:1. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The glass fiber-based / wet gel paper was placed in a 95wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0030] Example 2: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 10wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 150, a pressure of 0.4 MPa, an extrusion speed of 3 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:1. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The glass fiber-based / wet gel paper was placed in a 95wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0031] Example 3: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 10wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 150, a pressure of 0.4 MPa, an extrusion speed of 3 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:2. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1.5. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The glass fiber-based / wet gel paper was placed in a 95wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0032] Example 4: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 10wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 150, a pressure of 0.4 MPa, an extrusion speed of 3 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:2. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1.5. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The alumina fiber-based / wet gel paper was placed in a 50wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in an 80wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 95wt% ethanol solution and kept at 50℃ for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99wt% ethanol solution and kept at 50℃ for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0033] Example 5: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 40 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 10wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 150, a pressure of 0.4 MPa, an extrusion speed of 3 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:2. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1.5. The mixture is sprayed on the base paper in step (1) with a flow rate of 100 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The alumina fiber-based / wet gel paper was placed in a 50 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in an 80 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 95 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99 wt% ethanol solution and kept at 50 °C for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0034] Example 6: A method for preparing composite thermal insulation paper (1) Commercially available fiber-based paper with a basis weight of 80 g / m² is used. 2 Alumina fiber mesh (made by a combination of blown and electrospinning) is used as the base material, soaked in 5wt% alumina adhesive, and then extruded by an anilox roller with a mesh count of 150, a pressure of 0.4 MPa, an extrusion speed of 3 m / min, and dried to obtain inorganic adhesive-reinforced alumina fiber base paper. (2) Methyl orthosilicate was used as the silicon source and mixed with acetone solvent at a mass ratio of 1:2. Then water and 85% phosphoric acid were added. The mass ratio of silicon source to water was 1:0.5 and the mass ratio of silicon source to 85% phosphoric acid was 1:0.005. After mixing evenly, the mixture was hydrolyzed at 50°C for 2 h to obtain silica sol. Potassium hydroxide was dissolved into a 0.5 wt% solution as an alkaline catalyst. (3) The volume ratio of silica sol to alkaline catalyst is 1:1.5. The mixture is sprayed on the base paper in step (1) with a flow rate of 150 L / h. The base paper after spraying is heated at 50°C for 15 min to obtain alumina fiber-based / wet gel paper. (4) The alumina fiber-based / wet gel paper was placed in a 50 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in an 80 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 95 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99 wt% ethanol solution and kept at 50 °C for 12 h; the alumina fiber-based / wet gel paper was then placed in a 99 wt% ethanol solution and kept at 50 °C for 6 h to obtain the aged alumina fiber-based / wet gel paper. (5) The aged alumina fiber-based / wet gel paper was placed in a supercritical drying device, the supercritical drying temperature was set to 255℃, the pressure was 7 MPa, the heat preservation and pressure holding time was 1 h, and then the pressure was released and cooled. The alumina fiber-based / aerogel composite insulation paper was obtained. The relevant physical properties are shown in Table 1.

[0035] Table 1. Physical properties of fiber-based / aerogel composite thermal insulation paper prepared in Comparative Examples 1-2 and Examples 1-6 .

[0036] In Table 1, the test standard for the highest operating temperature is GB / T 17430-2015. The highest operating temperature usually refers to the dimensional stability and thermal insulation performance stability at high temperatures (no melting, sintering, degradation, etc. occur after treatment at high temperatures for a certain period of time, and the thermal conductivity does not decrease significantly).

[0037] The loss on ignition in Table 1 refers to the mass change after ignition at 600±20℃ for 60 minutes, at which temperature all organic matter will decompose.

[0038] The above embodiments achieve the all-inorganic alumina fiber-based / aerogel composite insulation paper of the present invention by selecting specific fiber-based paper and fiber-based paper reinforcement processes, silicon source and solvent ratios, hydrolysate and alkaline catalyst ratios, mixed solution spray flow rates, displacement aging strategies, and supercritical drying parameters. Furthermore, the above embodiments are only for illustrating the present invention and are not intended to limit the invention. Those skilled in the art can make different changes and improvements without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing an all-inorganic alumina fiber / aerogel composite thermal insulation paper, characterized in that, Includes the following steps: S1: After the alumina fiber mesh is fully soaked in alumina adhesive, it is squeezed by an anilox roller to remove excess alumina adhesive and physically reinforce the mesh. After drying, alumina inorganic adhesive and anilox roller-reinforced alumina fiber base paper are obtained. S2: Disperse the silicon source in a solvent, add water and acid catalyst, stir evenly, and then heat to hydrolyze to obtain silica sol; dissolve the alkaline catalyst in water to obtain alkaline catalyst solution; S3: After mixing silica sol with alkaline catalyst solution, spray it onto the alumina fiber base paper obtained in step S1 to allow the mixture to fully penetrate into the alumina fiber base paper. Heat the sprayed alumina fiber base paper until the silica sol gels to obtain alumina fiber base / wet gel paper. S4: Alumina fiber-based / wet gel paper is soaked in ethanol solution and heated to replace the solvent, and aged alumina fiber-based / wet gel paper is obtained. Finally, it is dried by supercritical drying to obtain an all-inorganic alumina fiber / aerogel composite insulation paper. In step S1, the alumina fiber web is made by a combination of blowing and electrospinning, with a grammage of 30-400 g / m 2 , and an alumina glue concentration of 3-20 wt%; In step S2, the silicon source includes any one or a combination of two or more of methyl orthosilicate, tetraethyl orthosilicate, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, and water-soluble silica gel; the solvent includes any one or a combination of two or more of methanol, ethanol, acetone, tetrahydrofuran, dimethylformamide, pyrrolidone, and dimethyl sulfoxide; the mass ratio of the silicon source to the solvent is 1:1-2. In step S4, the alumina fiber-based / wet gel paper is repeatedly immersed in ethanol solution and heated to perform solvent replacement. The number of solvent replacements is 3-6 times, and the concentration of the ethanol solution in each subsequent immersion is greater than or equal to the concentration of the previous immersion. The concentration of the ethanol solution in the first immersion is 50-95 wt%, the concentration of the ethanol solution in each of the intermediate immersions is 80-99 wt%, and the concentration of the ethanol solution in the final immersion is 98-100 wt%. The alkaline catalyst is any one or a combination of two or more of sodium bicarbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, calcium hydroxide, and ammonia water, and the concentration of the alkaline catalyst solution is 0.5 wt%-0.8 wt%. In step S3, the volume ratio of the silica sol to the alkaline catalyst is 1:1-1.

5.

2. The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper according to claim 1, characterized in that: In step S1, the anilox roller has a mesh size of 10-300, the extrusion pressure is 0.1-0.5 MPa, and the extrusion speed is 1-20 m / min.

3. The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper according to claim 1, characterized in that: In step S2, the acid catalyst is any one or a combination of two or more of sulfuric acid, hydrochloric acid, nitric acid, 85% phosphoric acid, boric acid, and acetic acid, and the mass ratio of silicon source to acid catalyst is 1:0.0005-0.05; in the process of preparing silica sol in step S2, the mass ratio of silicon source to water is 1:0.05-2.

4. The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper according to claim 1, characterized in that: In step S2, the temperature for heating the hydrolysis reaction is 40-60℃, and the hydrolysis reaction time is 2-3 h.

5. The method for preparing an all-inorganic alumina fiber / aerogel composite thermal insulation paper according to claim 1, characterized in that: In step S3, the spray flow rate of the mixed solution is 1-200 L / h, and the base paper after spraying is heated at 40-60℃ for 1-30 min.

6. The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper according to claim 1, characterized in that: In step S4, the solvent replacement temperature is 40-60℃ and the time is 6-12 h.

7. The method for preparing an all-inorganic alumina fiber / aerogel composite insulation paper according to claim 1, characterized in that: The supercritical drying temperature is 250-300℃, the pressure is 7-10 MPa, and the heat and pressure holding time is 1-10h.