Melamine foam for high temperature insulation and a method for preparing the same

Abstract

This invention relates to the field of melamine foam technology, specifically providing a high-temperature insulation melamine foam and its preparation method. The preparation method includes the following steps: S1, melamine, paraformaldehyde, and water are subjected to a hydroxymethylation reaction to obtain a melamine prepolymer; S2, hollow inorganic microspheres are surface-modified with silanization, and after solid-liquid separation and washing, they are dispersed in water to obtain a modified hollow inorganic microsphere dispersion; S3, the modified hollow inorganic microsphere dispersion and a foam stabilizer are added to the melamine prepolymer for dispersion and mixing, and then a foaming agent and an acid catalyst are added to form a foaming liquid; S4, the foaming liquid is foamed and simultaneously cured to obtain a wet foam body; S5, the wet foam body is subjected to drying and curing treatments in sequence to obtain melamine foam. This application improves the high-temperature insulation and structural stability of the foam by silanizing hollow inorganic microspheres and in-situ integrating them into the foam pore skeleton.

Description

Technical Field

[0001] This invention relates to the field of melamine foam technology, and more specifically, to a melamine foam for high-temperature insulation and its preparation method. Background Technology

[0002] Melamine foam is a type of thermosetting porous material formed by the foaming and curing of melamine-formaldehyde resin. It is characterized by its lightweight, high porosity, good flame retardancy, and excellent sound absorption properties, and has been widely used in building insulation, transportation, industrial insulation, and acoustic noise reduction. With the increasing demand for high-temperature equipment, pipeline insulation, vehicle thermal protection, and heat-resistant sound insulation materials, melamine foam not only needs to maintain its lightweight porous structure but also requires lower heat transfer capacity and more stable structural retention under high-temperature environments.

[0003] Existing melamine foam primarily relies on the resin cell structure itself for insulation. However, its pore walls are still composed of a continuous organic resin skeleton, allowing heat to be transferred along this skeleton at high temperatures. Furthermore, the melamine resin skeleton may shrink, become brittle, or experience a decrease in structural strength under prolonged thermal exposure, leading to reduced insulation performance and dimensional stability. To improve insulation, existing technologies typically incorporate inorganic fillers, aerogel particles, or hollow microspheres to reduce the overall thermal conductivity of the material.

[0004] However, when hollow inorganic microspheres and other insulation units are directly added to melamine prepolymer, they are prone to agglomeration, floating, or settling due to differences in surface polarity, density, and insufficient interfacial compatibility, making it difficult to disperse them uniformly and stably in the foam skeleton. At the same time, the unmodified inorganic microspheres have a weak interfacial bond with melamine resin, which can easily disrupt the cell formation process during foaming, curing, and subsequent use, leading to uneven cell formation, cell collapse, pore wall defects, or loss of inorganic components, which in turn affects the lightweight porous structure and mechanical stability of the foam.

[0005] Therefore, how to stably introduce hollow inorganic insulation units into the foam skeleton without damaging the foam pore structure of melamine foam, so as to improve the insulation performance and structural stability of foam in high-temperature environments, has become an urgent technical problem to be solved. Summary of the Invention

[0006] The present invention aims to provide a melamine foam for high-temperature insulation and its preparation method.

[0007] To address the above problems, this invention provides a method for preparing melamine foam for high-temperature insulation, comprising the following steps: S1. Melamine, paraformaldehyde and water are subjected to a hydroxymethylation reaction to obtain melamine prepolymer; S2. The hollow inorganic microspheres were surface-modified with silanization, and after solid-liquid separation and washing, they were dispersed in water to obtain a modified hollow inorganic microsphere dispersion. S3. The modified hollow inorganic microsphere dispersion and foam stabilizer are added to the melamine prepolymer for dispersion and mixing, and then the foaming agent and acid catalyst are added to form a foaming liquid. S4. The foaming liquid is foamed and simultaneously cured to obtain a wet foam body; S5. The wet foam is subjected to drying and curing treatments in sequence to obtain high-temperature heat-insulating melamine foam.

[0008] In the above technical solution, in S1, the pH of the hydroxymethylation reaction is 10.5~11.5, the temperature is 85~95℃, and the time is 60~180min; and / or the mass ratio of melamine to paraformaldehyde is 100:(40~70).

[0009] In the above technical solution, in S2, the hollow inorganic microspheres include hollow silica microspheres.

[0010] The above technical solution specifically includes S2 as follows: S21. Disperse hollow inorganic microspheres in an ethanol / water mixed solution to obtain the first dispersion; S22. Add a silane coupling agent to the first dispersion and perform surface silanization modification under ultrasonic conditions to obtain a second dispersion; S23. The second dispersion is subjected to solid-liquid separation to obtain a wet filter cake of modified hollow inorganic microspheres; S24. The modified hollow inorganic microsphere wet filter cake is washed to obtain a washed wet filter cake. S25. Disperse the washed wet filter cake in water to obtain a modified hollow inorganic microsphere dispersion.

[0011] In the above technical solution, the pH of the surface silanization modification is 4.5~5.5, and the time is 30~60 min; and / or the silane coupling agent is at least one of KH550 and KH560.

[0012] In the above technical solution, the average particle size of the hollow inorganic microspheres is 5~30μm; and / or the amount of hollow inorganic microspheres added is 3~10% of the solid content of melamine prepolymer.

[0013] In the above technical solution, in S3, the foam stabilizer includes at least one of SDS, AES, AEO-9, Tween80, and polyether-modified silicone oil; and the amount of foam stabilizer added is 0.1-3% of the solid content of melamine prepolymer; and / or the acid catalyst includes at least one of formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid; and / or the foaming agent includes at least one of cyclopentane, isopentane, and n-hexane; and / or the pH of the foaming liquid is 4.0-6.0.

[0014] In the above technical solution, in S4, the foaming molding adopts hot air foaming, microwave foaming, or a combination of hot air and microwave foaming; and / or the curing temperature is 60~100℃ and the time is 5~30min.

[0015] In the above technical solution, in S5, the drying temperature is 60~90℃ and the time is 0.5~2h; and / or the aging temperature is 120~160℃ and the time is 1~4h.

[0016] The present invention also provides a melamine foam for high-temperature insulation, which is prepared by any of the above preparation methods.

[0017] Beneficial effects (1) The present invention improves the interfacial compatibility between hollow inorganic microspheres and melamine prepolymer by silanization modification, so that hollow inorganic microspheres can be more uniformly dispersed in foaming liquid, reducing the problems of agglomeration, floating or settling that are easy to occur when unmodified inorganic microspheres are added directly. (2) In this invention, the modified hollow inorganic microspheres are foamed together with the melamine prepolymer and cured simultaneously, so that the hollow inorganic microspheres are in situ bonded to the pore walls and skeleton nodes of the melamine resin during the formation of the foam, thereby reducing the damage of the microspheres to the foam structure and maintaining the lightweight porous structure of the foam. (3) Hollow inorganic microspheres have a closed cavity structure. After they are distributed in the melamine resin foam skeleton, they can form dispersed low thermal conductivity insulation units, weaken the solid phase heat transfer path of the pore wall, and improve the insulation performance and structural stability of the foam in high temperature environment. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention will be provided below.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available. Experimental methods in the following examples that do not specify particular conditions should be performed according to conventional methods and conditions, or as selected in the product instructions.

[0020] This invention provides a melamine foam for high-temperature insulation and its preparation method. The preparation method of this invention allows modified hollow inorganic microspheres to be stably dispersed in a foaming liquid and embedded or combined in situ within the melamine resin cell framework during the foaming and curing process. The specific preparation method is as follows: S1. Melamine, paraformaldehyde and water are subjected to a hydroxymethylation reaction to obtain melamine prepolymer; S2. The hollow inorganic microspheres were surface-modified with silanization, and after solid-liquid separation and washing, they were dispersed in water to obtain a modified hollow inorganic microsphere dispersion. S3. The modified hollow inorganic microsphere dispersion and foam stabilizer are added to the melamine prepolymer for dispersion and mixing, and then the foaming agent and acid catalyst are added to form a foaming liquid. S4. The foaming liquid is foamed and simultaneously cured to obtain a wet foam body; S5. The wet foam is subjected to drying and curing treatments in sequence to obtain high-temperature heat-insulating melamine foam.

[0021] In S1, melamine, paraformaldehyde and water are subjected to a hydroxymethylation reaction to obtain melamine prepolymer. The melamine prepolymer has a flowability suitable for subsequent dispersion modification of hollow inorganic microspheres and contains hydroxymethyl active groups that can continue to polycondense and crosslink under acid catalysis, thereby enabling simultaneous curing and fixation of the cell structure during subsequent foaming.

[0022] Preferably, the pH of the hydroxymethylation reaction is 10.5~11.5, the temperature is 85~95℃, and the time is 60~180min; the mass ratio of melamine to paraformaldehyde is 100:(40~70); under the above conditions, a melamine prepolymer with suitable viscosity and reactivity can be obtained, avoiding the difficulty of subsequent dispersion and foaming caused by premature polycondensation of the prepolymer, and also avoiding the influence of insufficient hydroxymethylation on the curing strength of the cell skeleton.

[0023] In S2, the hollow inorganic microspheres undergo surface silanization modification to improve the wettability, dispersibility, and interfacial bonding stability between the hollow inorganic microspheres and the aqueous melamine prepolymer. The hollow inorganic microspheres themselves have a closed-cavity structure, which can be introduced into the melamine foam skeleton as low thermal conductivity insulation units. However, when directly added to the melamine prepolymer, they are prone to agglomeration, floating, settling, or local enrichment due to differences in surface properties, density, and insufficient interfacial compatibility, thereby disrupting the foaming liquid stability and the cell formation process. Through silanization modification, a silane-modified layer can be formed on the surface of the hollow inorganic microspheres. This silane-modified layer can improve the dispersion stability of the hollow inorganic microspheres in the aqueous system and enhance the interfacial bonding between them and the melamine resin-cured skeleton. This allows the modified hollow inorganic microspheres to be in situ fixed in the cell walls, ribs, and / or skeleton nodes during subsequent foaming and simultaneous curing.

[0024] Furthermore, the hollow inorganic microspheres include hollow silica microspheres. These microspheres have a closed or semi-closed cavity structure, enabling them to form dispersed low-thermal-conductivity insulating units within the melamine resin foam framework. This prolongs the heat transfer path within the foam framework and weakens solid-phase heat transfer in the continuous resin phase of the pore walls. Hollow silica microspheres possess low thermal conductivity, good thermal stability, and abundant surface hydroxyl groups, making them easy to modify with silanization, and suitable for improving the thermal insulation performance and interfacial bonding stability of foam.

[0025] Furthermore, S2 specifically includes: S21. Disperse hollow inorganic microspheres in an ethanol / water mixed solution to obtain the first dispersion; S22. Add a silane coupling agent to the first dispersion and perform surface silanization modification under ultrasonic conditions to obtain a second dispersion; S23. The second dispersion is subjected to solid-liquid separation to obtain a wet filter cake of modified hollow inorganic microspheres; S24. The modified hollow inorganic microsphere wet filter cake is washed to obtain a washed wet filter cake. S25. Disperse the washed wet filter cake in water to obtain a modified hollow inorganic microsphere dispersion.

[0026] In step S21, the ethanol / water mixture wets the surface of the hollow inorganic microspheres, reducing microsphere aggregation and resulting in a more uniform suspension dispersion. In step S22, the silane coupling agent hydrolyzes in the ethanol / water system, forming hydrolysis products containing silanol structures. These hydrolysis products can condense or adsorb onto the hydroxyl groups or active sites on the surface of the hollow inorganic microspheres, thus forming a silane-modified layer on the surface. In step S23, the surface-silanized hollow inorganic microspheres are separated from the reaction medium, reducing the amount of unreacted silane coupling agent, alcohol solvents, and small molecule byproducts remaining in the system, thereby avoiding their adverse effects on subsequent melamine prepolymer foaming, emulsification, and acid-catalyzed curing. In step S24, washing further removes unbound silane coupling agent, free alcohols, and byproducts, reducing the interference of residues on the stability of the subsequent foaming system. In S25, the modified hollow inorganic microsphere wet filter cake can be converted back into an aqueous dispersion system suitable for adding melamine prepolymer. Since the melamine prepolymer itself is an aqueous system, pre-dispersing the modified hollow inorganic microspheres in water is beneficial for their rapid and uniform dispersion when the prepolymer is added later, reducing local agglomeration and cell defects caused by direct addition of dry powder.

[0027] Preferably, the pH of the surface silanization modification is controlled at 4.5-5.5 to allow the silane coupling agent to undergo relatively stable hydrolysis and form an effective bond with the surface of the hollow inorganic microspheres. Within this weakly acidic range, the alkoxy groups in the silane coupling agent are more easily hydrolyzed to generate silanol structures. The formed silanol structures can further condense with the hydroxyl groups or active sites on the surface of the hollow inorganic microspheres to form a relatively stable interface modification layer. The surface silanization modification time is controlled at 30-60 minutes to ensure that the silane coupling agent can be fully hydrolyzed and interact with the surface of the hollow inorganic microspheres, while avoiding excessive self-condensation of the silane coupling agent due to excessively long reaction time.

[0028] Preferably, at least one of KH550 and KH560 is selected as the silane coupling agent because both contain hydrolyzable silane groups, which can combine with hydroxyl groups or active sites on the surface of hollow inorganic microspheres after hydrolysis in an ethanol / water system, thereby forming a silane-modified layer on the surface of the microspheres. Preferably, the amount of silane coupling agent added is 1-5% of the mass of the hollow inorganic microspheres.

[0029] Furthermore, controlling the average particle size of the hollow inorganic microspheres to 5–30 μm is to balance thermal insulation performance, dispersion stability, and foam pore structure stability. If the particle size of the hollow inorganic microspheres is too small, their specific surface area is large, making them prone to aggregation and significantly increasing the viscosity of the foaming liquid, affecting the emulsification and dispersion of the foaming agent and the uniform formation of foam pores; simultaneously, the contribution of excessively small particle size to cavity insulation is limited. If the particle size of the hollow inorganic microspheres is too large, the microspheres are prone to mechanically disturbing the foam pore liquid film during the foaming process, leading to pore wall defects, uneven pore size, or localized bubble collapse, and may reduce the compression resilience and structural integrity of the foam.

[0030] Furthermore, controlling the addition amount of hollow inorganic microspheres to 3-10% of the melamine prepolymer solid content is to maintain the stability of the foaming system and the integrity of the cell structure while improving thermal insulation performance. When the addition amount of hollow inorganic microspheres is too low, the number of low thermal conductivity insulation units formed in the cell skeleton is insufficient, making it difficult to significantly weaken the solid-phase heat transfer path in the continuous skeleton of melamine resin, resulting in limited improvement in thermal insulation performance. When the addition amount of hollow inorganic microspheres is too high, the viscosity of the foaming liquid increases, and the probability of contact and aggregation between microspheres increases, which can easily affect the emulsification of the foaming agent and the cell growth process, leading to uneven cell structure, pore wall defects, or decreased cell strength.

[0031] In S3, modified hollow inorganic microsphere dispersion and foam stabilizer are added to melamine prepolymer for dispersion and mixing, and then foaming agent and acid catalyst are added to form foaming liquid. This allows the modified hollow inorganic microspheres to form a relatively uniform dispersion in the melamine prepolymer. At the same time, the foam stabilizer improves the emulsification stability of the foaming agent in the aqueous prepolymer system, and the acid catalyst adjusts the polycondensation and curing rate of the melamine prepolymer, so that the process of foaming agent vaporization to form cells matches the curing and shaping process of melamine prepolymer.

[0032] Specifically, modified hollow inorganic microspheres are pre-added to the melamine prepolymer in the form of an aqueous dispersion. This reduces agglomeration and localized enrichment caused by direct addition of dry powder, making it easier for the hollow inorganic microspheres to distribute within the subsequently formed cell walls and skeletal nodes. The foam stabilizer reduces the interfacial tension of the foaming liquid, improves the dispersion uniformity of the foaming agent in the aqueous melamine prepolymer, and stabilizes the cell liquid film during foaming, reducing problems such as bubble formation, collapse, and uneven cell size. The acid catalyst enables the melamine prepolymer to undergo condensation crosslinking during foaming, ensuring that the cell structure is promptly solidified and fixed after formation.

[0033] Furthermore, the foam stabilizer includes at least one of SDS, AES, AEO-9, Tween80, and polyether-modified silicone oil. These foam stabilizers can improve the uniformity of the foaming liquid and the stability of cell formation, thereby reducing the disturbance of the cell structure by the modified hollow inorganic microspheres. The amount of foam stabilizer added is 0.1-3% of the solid content of the melamine prepolymer. When the amount of foam stabilizer added is too low, the emulsification and dispersion effect of the foaming agent in the aqueous prepolymer is insufficient, and large cells, bubble coalescence, or localized bubble collapse are likely to occur during the foaming process. When the amount of foam stabilizer added is too high, it may lead to excessive foam stability in the system, difficulty in drainage, or affect the acid-catalyzed curing process of the melamine prepolymer, thereby reducing the strength of the cell skeleton.

[0034] Furthermore, the acid catalyst includes at least one of formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid. The role of the acid catalyst is to lower the pH of the foaming liquid and promote the condensation and cross-linking of the hydroxymethyl structure in the melamine prepolymer, allowing the foamed cell structure to solidify and solidify simultaneously during the foaming process. The foaming agent includes at least one of cyclopentane, isopentane, and n-hexane. These are all low-boiling-point organic foaming agents that can vaporize and generate bubbles under heating conditions, thereby promoting the formation of porous foam from the melamine prepolymer. After adding the acid catalyst, the pH of the foaming liquid is controlled at 4.0~6.0. This pH range allows the melamine prepolymer to have an appropriate condensation and solidification rate, enabling it to gradually solidify and solidify while the foaming agent vaporizes to form cells. If the pH of the foaming liquid is too high, the melamine prepolymer will solidify too slowly, making it difficult to fix the cells in time after they are formed, which can easily lead to cell collapse or shrinkage. If the pH of the foaming liquid is too low, the prepolymer will condense too quickly, and the foaming liquid may gel prematurely before the foaming agent is fully vaporized, resulting in insufficient foaming ratio, rough cells, or uneven internal structure.

[0035] In this invention, modified hollow inorganic microsphere dispersion and foam stabilizer are first added to melamine prepolymer, followed by foaming agent and acid catalyst. This is to first complete the dispersion of hollow microspheres and stabilize the foaming system, avoiding premature condensation of the prepolymer by the acid catalyst and shortening the dispersion operation window, thereby improving the uniformity of the distribution of modified hollow inorganic microspheres in the foaming liquid.

[0036] In step S4, the foaming liquid is foamed and simultaneously cured to obtain a wet foam body. During the foaming process, the foaming agent is heated and vaporized to form bubbles, which drive the melamine prepolymer to form a cell structure; at the same time, the melamine prepolymer undergoes condensation crosslinking under acid catalysis, causing the cell walls and skeleton to gradually solidify and take shape.

[0037] Preferably, the foaming process employs hot air foaming, microwave foaming, or a combination of hot air and microwave foaming; the curing temperature is 60~100℃, and the time is 5~30min. These conditions help to match the vaporization of the foaming agent, cell growth, and resin curing, avoiding insufficient foaming, large cells, bubble aggregation, or bubble collapse.

[0038] In step S5, the wet foam is sequentially subjected to drying and curing treatments to obtain high-temperature insulating melamine foam. The drying treatment is used to gradually remove moisture, residual foaming agent, and low-boiling-point components from the wet foam, reduce the volatilization pressure inside the foam, and reduce cell shrinkage, cell wall cracking, or localized cell collapse. The curing treatment is used to promote further post-curing of the melamine resin cell skeleton, improving the dimensional stability, skeleton strength, and heat resistance of the foam.

[0039] Preferably, the drying temperature is 60~90℃ and the time is 0.5~2h; the curing temperature is 120~160℃ and the time is 1~4h. By using a segmented treatment method of drying first and then curing, the bonding stability between the modified hollow inorganic microspheres and the melamine resin skeleton can be improved while maintaining the integrity of the cell structure.

[0040] The present invention also provides a melamine foam for high-temperature insulation. The melamine foam is prepared by any of the above preparation methods, and therefore will not be described in detail.

[0041] Example 1

[0042] This embodiment provides a melamine foam for high-temperature insulation and its preparation method, including the following steps: S1. Add 100g of melamine, 50g of paraformaldehyde and 180g of deionized water to a reaction vessel. Under stirring, adjust the pH of the system to 11.0 with a 10% sodium hydroxide solution. Then, carry out a hydroxymethylation reaction at 90℃ for 120min to obtain melamine prepolymer. S21. Hollow silica microspheres with an average particle size of 15 μm were selected as hollow inorganic microspheres. 9.0 g of hollow silica microspheres were weighed, based on the addition amount being 6% of the melamine prepolymer solid content. The hollow silica microspheres were added to an ethanol / water mixed solution with a volume ratio of 80:20, and stirred for 10 min to obtain the first dispersion. S22. The pH of the first dispersion was adjusted to 5.0 using glacial acetic acid. 0.27g of KH550 silane coupling agent was added to the first dispersion, and the surface was silanized by ultrasonic water bath at 150W for 45min to obtain the second dispersion. S23. The second dispersion is vacuum filtered to obtain a wet filter cake of modified hollow silica microspheres. S24. The wet filter cake is washed sequentially with an ethanol / water mixed solution and deionized water to obtain a washed wet filter cake. S25. Add the washed wet filter cake to 90g of deionized water and disperse it for 15min under stirring at 800rpm to obtain a modified hollow silica microsphere dispersion. S3. Add the modified hollow silica microsphere dispersion to the melamine prepolymer, then add 0.6g of SDS and 0.6g of AEO-9 as foam stabilizers, stir and disperse for 15min, then add 18g of cyclopentane as a foaming agent, and continue stirring and emulsifying for 5min; then add 20% formic acid solution dropwise to adjust the pH of the foaming solution to 5.0 to obtain the foaming solution; S4. Pour the foaming liquid into the mold, place the mold in an 80℃ hot air environment for foaming and simultaneous curing, and the processing time is 15 minutes to obtain a wet foam body. S5. Place the wet foam in a 75℃ hot air drying oven for 1 hour, then heat it to 140℃ for 2 hours to obtain high-temperature heat-insulating melamine foam.

[0043] Example 2

[0044] This embodiment provides a melamine foam for high-temperature insulation and its preparation method. The preparation method is the same as in Embodiment 1, except that: In S1, melamine is 100g, paraformaldehyde is 40g, the pH of the hydroxymethylation reaction is 10.5, the reaction temperature is 85℃, and the reaction time is 180min. In S21, the average particle size of the hollow silica microspheres is 8 μm, and the amount of hollow silica microspheres added is 3% of the melamine prepolymer solid content; In S22, KH560 was selected as the silane coupling agent, and the amount of KH560 added was 2% of the mass of the hollow silica microspheres; the pH for surface silanization modification was 4.5, and the modification time was 60 min. In S3, the foam stabilizer used is Tween80 and polyether-modified silicone oil, with Tween80 added at 0.4% of the melamine prepolymer solids content and polyether-modified silicone oil added at 0.2% of the melamine prepolymer solids content; the blowing agent used isopentane, added at 10% of the melamine prepolymer solids content; and acetic acid is used as the acid catalyst to adjust the pH of the foaming liquid to 5.5. In S4, hot air foaming is used for foaming, and the curing temperature is 70℃ for 20 minutes. In S5, the drying temperature is 60℃ and the time is 2h; the curing temperature is 120℃ and the time is 4h, to obtain high-temperature heat-insulating melamine foam.

[0045] Example 3

[0046] This embodiment provides a melamine foam for high-temperature insulation and its preparation method. The preparation method is the same as in Embodiment 1, except that: In S1, melamine is 100g, paraformaldehyde is 70g, the hydroxymethylation reaction pH is 11.5, the reaction temperature is 95℃, and the reaction time is 60min. In S21, the average particle size of the hollow silica microspheres is 25 μm, and the amount of hollow silica microspheres added is 10% of the solid content of the melamine prepolymer. In S22, the silane coupling agent is a mixture of KH550 and KH560, with a mass ratio of KH550 to KH560 of 1:1. The total amount of silane coupling agent added is 3% of the mass of the hollow silica microspheres. The pH for surface silanization modification is 5.5, and the modification time is 30 min. In S3, the foam stabilizer is a mixture of SDS, AES and polyether-modified silicone oil, with the total amount of foam stabilizer added being 2.0% of the melamine prepolymer solid content; the blowing agent is n-hexane, with an addition amount of 15% of the melamine prepolymer solid content; and the acid catalyst is oxalic acid, which is used to adjust the pH of the foaming liquid to 4.5. In S4, the foaming molding process uses a combination of microwave and hot air foaming. First, the foaming liquid is treated under microwave conditions for 3 minutes to make it foam quickly, and then it is cured and molded in a 90°C hot air environment for 10 minutes to obtain a wet foam body. In S5, the drying temperature is 90℃ and the time is 0.5h; the curing temperature is 160℃ and the time is 1h, to obtain high-temperature heat-insulating melamine foam.

[0047] Comparative Example 1 This comparative example provides a melamine foam for high-temperature insulation and its preparation method. The preparation method is the same as that in Example 1, except that hollow silica microspheres are not added, and the surface silanization modification step in S2 is not performed; in S3, an equal amount of deionized water is used to replace the modified hollow silica microsphere dispersion in Example 1.

[0048] Comparative Example 2 This comparative example provides a melamine foam for high-temperature insulation and its preparation method. The preparation method is the same as in Example 1, except that the hollow silica microspheres are not surface-silanized. Instead, unmodified hollow silica microspheres with an average particle size of 15 μm are directly dispersed in deionized water to obtain an unmodified hollow silica microsphere dispersion. Subsequently, the unmodified hollow silica microsphere dispersion is added to the melamine prepolymer, and the amount of hollow silica microspheres added is the same as in Example 1.

[0049] Comparative Example 3 This comparative example provides a high-temperature insulation melamine foam and its preparation method. The preparation method is the same as in Example 1, except that: after surface silanization modification, solid-liquid separation, and washing, the hollow silica microspheres are dried at 80°C for 2 hours to obtain modified hollow silica microsphere powder; subsequently, the modified hollow silica microsphere powder is directly added to the melamine prepolymer for dispersion. The amount of hollow silica microspheres added is the same as in Example 1, and other conditions are the same as in Example 1.

[0050] Performance testing The following performance tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the results are shown in Table 1. Apparent density test: Calculate the apparent density based on the mass and volume of the foam sample; Thermal conductivity test: Cut the foam sample into specimens of uniform size and test the thermal conductivity at 25℃. Thermal conductivity test after high temperature treatment: The foam sample was placed in an environment of 200℃ for 2 hours and then cooled to room temperature to test the thermal conductivity. Dimensional shrinkage test: Cut the foam sample into regular size and measure the initial length, width and thickness; after being treated at 200℃ for 2 hours and cooled to room temperature, measure the size again and calculate the dimensional shrinkage rate; Compression strength test: The foam sample is cut into a specified size and the compressive stress is tested under a specified compression deformation to evaluate the stability of the foam skeleton structure; Table 1

[0051] The test results above show that, compared to Comparative Example 1 without hollow inorganic microspheres, Examples 1-3, by introducing silanized modified hollow silica microspheres into the melamine foam framework, can form dispersed low thermal conductivity insulation units, weaken the solid-phase heat transfer path in the foam framework, thereby reducing the thermal conductivity of the foam and improving the insulation retention capacity after high-temperature treatment. Compared to Comparative Example 2 using unmodified hollow silica microspheres, the surface silanized modification of the hollow silica microspheres in Examples 1-3 improves the wettability, dispersibility, and interfacial bonding stability between them and the melamine prepolymer. Compared to Comparative Example 3, where modified hollow silica microsphere powder was directly added, the modified hollow silica microspheres in Examples 1-3 had already formed a stable aqueous dispersion state before the addition of the melamine prepolymer, reducing secondary agglomeration and local enrichment caused by the addition of dry powder, which is beneficial for maintaining the uniformity of the foam structure and the stability of the foam structure.

[0052] In summary, this invention modifies the surface of hollow inorganic microspheres by silanization and adds them to melamine prepolymer in the form of wet filter cake aqueous dispersion. Then, through foaming and simultaneous curing, the modified hollow inorganic microspheres can be in situ incorporated into the melamine foam pore skeleton. This improves the high-temperature insulation performance and structural stability of the foam without significantly damaging its lightweight porous structure.

[0053] Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing melamine foam for high-temperature insulation, characterized in that, Includes the following steps: S1. Melamine, paraformaldehyde and water are subjected to a hydroxymethylation reaction to obtain melamine prepolymer; S2. The hollow inorganic microspheres were surface-modified with silanization, and after solid-liquid separation and washing, they were dispersed in water to obtain a modified hollow inorganic microsphere dispersion. S3. The modified hollow inorganic microsphere dispersion and foam stabilizer are added to the melamine prepolymer for dispersion and mixing, and then a foaming agent and an acid catalyst are added to form a foaming liquid; S4. The foaming liquid is foamed and simultaneously cured to obtain a wet foam body; S5. The wet foam is subjected to drying and curing treatments in sequence to obtain high-temperature heat-insulating melamine foam.

2. The preparation method according to claim 1, characterized in that, In S1, The hydroxymethylation reaction is performed at a pH of 10.5–11.5, a temperature of 85–95°C, and a time of 60–180 min; and / or The mass ratio of melamine to paraformaldehyde is 100:(40~70).

3. The preparation method according to claim 1, characterized in that, In S2, the hollow inorganic microspheres include hollow silica microspheres.

4. The preparation method according to claim 3, characterized in that, Specifically, S2 includes: S21. The hollow inorganic microspheres are dispersed in an ethanol / water mixed solution to obtain a first dispersion; S22. Add a silane coupling agent to the first dispersion and perform the surface silanization modification under ultrasonic conditions to obtain a second dispersion; S23. The second dispersion is subjected to the solid-liquid separation to obtain a modified hollow inorganic microsphere wet filter cake; S24. The modified hollow inorganic microsphere wet filter cake is washed to obtain a washed wet filter cake. S25. Disperse the washed wet filter cake in water to obtain the modified hollow inorganic microsphere dispersion.

5. The preparation method according to claim 4, characterized in that, The surface silanization modification is performed at a pH of 4.5–5.5 for 30–60 min; and / or The silane coupling agent includes at least one of KH550 and KH560.

6. The preparation method according to claim 1, characterized in that, The hollow inorganic microspheres have an average particle size of 5~30μm; and / or The amount of hollow inorganic microspheres added is 3 to 10% of the solid content of the melamine prepolymer.

7. The preparation method according to claim 1, characterized in that, In S3, The foam stabilizer includes at least one of SDS, AES, AEO-9, Tween 80, and polyether-modified silicone oil; and the amount of the foam stabilizer added is 0.1-3% of the solid content of the melamine prepolymer; and / or The acid catalyst includes at least one of formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid; and / or The foaming agent includes at least one of cyclopentane, isopentane, and n-hexane; and / or The pH of the foaming solution is 4.0~6.

0.

8. The preparation method according to claim 1, characterized in that, In S4, The foaming process employs hot air foaming, microwave foaming, or a combination of hot air and microwave foaming; and / or The curing temperature is 60~100℃ and the time is 5~30min.

9. The preparation method according to claim 1, characterized in that, In S5, The drying process is carried out at a temperature of 60-90°C for a time of 0.5-2 hours; and / or The aging process is carried out at a temperature of 120-160°C for 1-4 hours.

10. A type of melamine foam for high-temperature insulation, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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