In-situ closed-cell foaming material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of thermal insulation foaming materials, and particularly relates to an in-situ closed-cell foaming material as well as a preparation method and application thereof. The in-situ closed-cell foaming material is prepared from the following raw materials through foaming and curing reactions: 40-60 parts by weight of a melamine prepolymer; 40 to 60 parts by weight of isocyanate; 1-5 parts by weight of a hydrolysable silane compound; 0.05 to 0.3 part by weight of a catalyst; 5-15 parts by weight of an inorganic cementing material; 1-10 parts by weight of a physical foaming agent; the content of bound water in the melamine prepolymer is 2.0 to 5.0 weight percent. The in-situ closed-cell foaming material provided by the invention has excellent thermal insulation performance, high specific strength and excellent waterproof, moisture-proof and anti-seepage performance, and the combustion performance grade is A2.

Description

Technical Field

[0001] This invention belongs to the field of thermal insulation foaming materials technology, specifically relating to an in-situ closed-cell foaming material, its preparation method, and its application. Background Technology

[0002] Thermal insulation foam, a type of lightweight functional material with a resin matrix and an internal cellular structure, has been widely applied in key fields such as building energy conservation, transportation, cold chain logistics, and electronic packaging due to its core advantages including light weight, low thermal conductivity, and simple molding process. In the construction sector, as an exterior wall and roof insulation layer, it can significantly reduce building energy consumption, contributing to the achievement of "dual carbon" goals. In cold chain transportation and refrigeration equipment, it can effectively maintain low-temperature environments, ensuring the quality stability of fresh products and pharmaceutical reagents. In the packaging and electronics sectors, it can provide both cushioning and thermal insulation, playing a vital role in protecting precision instruments and electronic components.

[0003] However, traditional thermal insulation foam materials have long faced performance bottlenecks and application limitations, making it difficult to meet the stringent requirements of high-end scenarios. Firstly, insufficient flame retardant performance is a core pain point. Mainstream expanded polystyrene (EPS) and expanded polyurethane (PU) materials are mostly classified as B3 (flammable) or B2 (combustible) in terms of fire rating. During combustion, they easily release large amounts of toxic fumes and molten drips, potentially causing secondary disasters. This severely restricts their application in scenarios with extremely high fire protection requirements, such as building exterior wall insulation and interiors of new energy vehicles (e.g., GB 50016-2014 "Code for Fire Protection Design of Buildings" explicitly requires that the fire rating of exterior wall insulation materials for high-rise buildings be no lower than B1). Firstly, the balance between strength and thermal insulation performance is a significant challenge. Most materials require increased pore size or reduced density to achieve lower thermal conductivity, which leads to a significant decrease in compressive strength and deformation resistance. Increasing strength often comes at the cost of sacrificing thermal insulation efficiency. Secondly, the waterproof and moisture-proof performance is poor. Traditional open or semi-open structures easily absorb moisture, which not only causes a sharp increase in thermal conductivity and failure of thermal insulation, but may also lead to problems such as material mold and substrate corrosion. In particular, the service life is greatly shortened in high humidity environments.

[0004] To address the aforementioned issues, the industry has undertaken extensive technological research and development and published relevant patents: Chinese patent CN108640295A discloses a flame-retardant polyurethane foam material, which improves flame retardant performance by adding inorganic flame retardants such as expanded graphite and aluminum hydroxide. However, the addition of a large amount of inorganic flame retardants leads to an increase in material density and a decrease in toughness. Furthermore, the cell structure is prone to interconnected pores due to uneven dispersion of flame retardants, which limits waterproof and heat insulation performance. Chinese patent CN110330842A discloses a melamine-formaldehyde resin foaming material that improves combustion performance by utilizing the flame-retardant properties of melamine itself. However, this material has the defects of high brittleness and poor water resistance. In addition, a large amount of free water needs to be introduced as a foaming medium during the foaming process, which can easily lead to interconnected cell structures and make it difficult to further reduce thermal conductivity. Chinese patent CN112143667A proposes a silane-modified polyurethane foam material, which improves the material's weather resistance through silane coupling agents, but does not precisely control the cell structure, resulting in a closed-cell rate of less than 85%, and there is still room for improvement in waterproof, moisture-proof, and heat-insulating performance. Chinese patent CN109776148A discloses an inorganic-organic composite foaming material that combines silicate cement and polyurethane resin to balance strength and flame retardancy. However, the composite system has poor compatibility, is prone to delamination, and has a long curing cycle and low production efficiency.

[0005] Although existing technologies have achieved some breakthroughs in single properties through flame-retardant modification and composite modification, they have not yet formed a technology that can simultaneously meet the requirements of "high flame retardant rating (B1 level or above) and excellent thermal insulation performance (thermal conductivity ≤0.030 W / (m²)". K), high specific strength (compressive strength / density ≥ 0.3 MPa / (g / cm³)). 3 This involves a comprehensive solution that offers superior waterproofing, moisture resistance, and seepage prevention (water absorption rate ≤1%). Especially in applications requiring extremely high comprehensive material performance, such as building exterior wall insulation, lightweighting of new energy vehicles, and high-end electronic packaging, existing materials still have significant shortcomings. Therefore, developing an in-situ closed-cell foam material that combines multiple excellent properties to address the core pain points of traditional materials has significant technological value and market application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide an in-situ closed-cell foam material, its preparation method and application. The foam of this in-situ closed-cell foam material has excellent thermal insulation performance, high specific strength and excellent waterproof, moisture-proof and seepage-proof performance, and its fire rating reaches A2 level.

[0007] Specifically, the present invention provides the following technical solutions: An in-situ closed-cell foam material is prepared by foaming and curing reaction of raw materials containing the following components: Component content (parts by weight) Melamine prepolymer 40-60; Isocyanate 40-60; Hydrolyzable silane compounds 1-5; Catalyst 0.05-0.3; Inorganic cementitious materials 5-15; Physical foaming agent 1-10; The bound water content in the melamine prepolymer is 2.0~5.0 wt%.

[0008] The raw materials used in this invention do not contain free water. The bound water remaining from the melamine prepolymer synthesis process (content of 2.0~5.0 wt%) and the water released during the foaming reaction of hydrolyzable silane compounds are used as in-situ foaming agents and closed-cell structure builders. This in-situ generated, trace, and uniform gas volatilization ensures that each bubble (cell) in the prepared foam material is independent and non-interconnected, completely encapsulated by the cell wall, thus exhibiting excellent thermal insulation performance, high specific strength, and superior waterproof, moisture-proof, and seepage-proof properties.

[0009] In this invention, the amount of hydrolyzable silane compound added is crucial. Without the addition of the hydrolyzable silane compound, the formation of closed-cell structures in the reaction system is limited, resulting in a low closed-cell rate and a significant decrease in thermal insulation and waterproofing performance. Conversely, excessive addition of the hydrolyzable silane compound leads to excessive water production during the reaction, causing interconnected pores and pore rupture in the cell structure, severely impacting material strength and closed-cell rate, while also increasing costs.

[0010] Preferably, the melamine prepolymer is a product of hydroxymethyl melamine modified by methanol or ethanol etherification, with a degree of hydroxymethylation of 2.0-2.8. While traditional hydroxymethylation ranges are relatively wide, this invention specifically selects a hydroxymethylation degree of 2.0-2.8 because research has found that: excessively low hydroxymethylation (<2.0) reduces reactive sites, hindering subsequent etherification and cross-linking curing with isocyanates; excessively high hydroxymethylation (>2.8) leads to excessively high resin viscosity, making it difficult to mix and flow uniformly during foaming, affecting the uniformity of the cell structure and the closed-cell rate. This range of hydroxymethylation ensures that the resin has suitable reactivity and viscosity, facilitating foaming and the formation of closed-cell structures.

[0011] More preferably, the method for preparing the melamine prepolymer includes the following steps: Step 1: Disperse melamine and formaldehyde in deionized water at a molar ratio of 2.5~3.0:1, and adjust the pH value to 8.0~9.0; Step 2: Stir the reaction at 60-80℃ for 1-2 hours to carry out the hydroxymethylation reaction and obtain a hydroxymethyl melamine solution; Step 3: Add methanol or ethanol (etherifying agent), adjust the pH value to 4.5~6.0, and carry out the etherification reaction at 50-65℃ for 1-3 hours to obtain the etherified modified melamine prepolymer; Step 4: Cooling, and control the water content through vacuum concentration to make the bound water content 2.0~5.0 wt% and the degree of hydroxymethylation 2.0-2.8.

[0012] In the above preparation method, the degree of hydroxymethylation is precisely controlled by adjusting the molar ratio of formaldehyde to melamine in step one (F:M = 2.5:1 to 3.0:1) and the reaction temperature (60-80℃) and time (1-2 hours) in step two. Subsequently, the bound water content is precisely controlled to be 2.0~5.0 wt% through vacuum concentration in step four.

[0013] Preferably, the hydrolyzable silane compound is a combination of 3-aminopropyltriethoxysilane and other silane compounds in a mass ratio of 1 to 1.5:2; the other silane compounds are selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, isobutyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, and hexadecyltrimethoxysilane.

[0014] This invention utilizes the hydrolyzable silane compound obtained by the above-mentioned compounding. Among them, 3-aminopropyltriethoxysilane contains an amino group, which can act as a synergistic catalyst to accelerate the reaction between isocyanate and hydroxyl groups and water in melamine prepolymer, thereby shortening the curing time. Its amino group can also form a stable urea bond structure with isocyanate, enhancing the mechanical strength of the material. Other silane compounds can improve the hydrophobicity of the material. After crosslinking with melamine prepolymer or isocyanate, they help to further improve the waterproof and moisture-proof performance.

[0015] Preferably, the isocyanate is at least one of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI).

[0016] Preferably, the catalyst is at least one of tertiary amine catalysts (such as triethylenediamine, N,N-dimethylcyclohexylamine) or organotin catalysts (such as dibutyltin dilaurate).

[0017] Preferably, the physical foaming agent is at least one of cyclopentane, dichlorofluoroethane, and carbon dioxide.

[0018] In this invention, adding an appropriate amount of physical foaming agent can bring more beneficial effects: Synergistic foaming: The rapid volatilization of physical foaming agents, combined with the gas generated by the hydrolysis of bound water and silanes, can quickly start the foaming process and ensure that the foam rises evenly. Reducing density: This helps to further reduce the overall density of foamed materials while ensuring the closed-cell ratio, thereby significantly improving specific strength and thermal insulation performance; Optimize cell structure: The addition of physical foaming agents helps to control the cell size distribution, forming a finer and more uniform closed-cell structure.

[0019] Preferably, the inorganic cementing material is at least one of water glass, silicate, and aluminate, which can undergo hydrolysis or cementation reaction in the reaction system.

[0020] The present invention also provides a method for preparing the above-mentioned in-situ closed-cell foam material, comprising the following steps: (1) Mix the raw materials containing the melamine prepolymer, isocyanate, hydrolyzable silane compound and catalyst evenly to form a reaction slurry; (2) Inject the reaction slurry into a mold or apply it to the surface of a substrate; (3) Perform foaming and curing reactions to obtain the product.

[0021] This invention controls the degree of hydroxymethylation (2.0-2.8) and bound water content (2.0~5.0 wt%) of melamine prepolymer, and adjusts the ratio of isocyanate to melamine prepolymer in the formulation, so that the viscosity of the reaction slurry formed after uniform mixing of raw materials is 500-2000 mPa·s (25℃). This viscosity range ensures that the slurry has good fluidity and wall adhesion during construction, and can uniformly fill the mold or cover the surface of the substrate, making it suitable for spraying or pouring processes.

[0022] Preferably, in step (3), the foaming and curing reaction includes the following two stages: First stage: Maintain at 50-60℃ for 2-5 minutes to complete foaming; Second stage: Heat in a microwave at 500W-900W for 3-5 minutes, or maintain at 90-120℃ for 3-8 minutes to complete rapid cross-linking and curing.

[0023] The present invention also provides the application of the above-mentioned in-situ closed-cell foam material in building exterior wall insulation, automotive lightweighting or electronic packaging.

[0024] The beneficial effects of this invention are at least as follows: (1) The in-situ closed-cell foam material provided by the present invention has excellent thermal insulation performance, and its thermal conductivity is not greater than 0.030 W / (m). K); (2) The in-situ closed-cell foam material provided by the present invention has a specific strength of not less than 4500 N. m / kg, providing excellent structural support; (3) The in-situ closed-cell foaming material provided by the present invention has a closed-cell rate of not less than 85%, excellent waterproof, moisture-proof and seepage-proof performance, and a volume water absorption rate of not more than 2%; (4) The in-situ closed-cell foaming material provided by the present invention has a combustion rating of A2. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product manual.

[0026] In the following examples, the melamine prepolymer was prepared using the following method: Melamine and formaldehyde (molar ratio F:M = 2.8:1) were dispersed in deionized water, and the pH was adjusted to 8.5. The reaction was stirred at 70°C for 1.5 hours to carry out the hydroxymethylation reaction, yielding a hydroxymethyl melamine solution; Add etherifying agent (methanol), adjust pH to 5.0, and carry out etherification reaction at 55℃ for 2 hours to obtain etherified modified melamine prepolymer; The reaction was stopped, cooled, and the water content was controlled by vacuum concentration to achieve a bound water content of 3.5 wt% and a degree of hydroxymethylation of 2.4.

[0027] Example 1 Example 1 provides an in-situ closed-cell foam material, prepared by the following method: (1) Mix 40 parts by weight of melamine prepolymer, 60 parts by weight of diphenylmethane diisocyanate, 1 part by weight of 3-aminopropyltriethoxysilane, 2 parts by weight of hexadecyltrimethoxysilane, 0.2 parts by weight of triethylenediamine, 10 parts by weight of water glass and 5 parts by weight of cyclopentane evenly to form a reaction slurry with a viscosity of 1200 mPa·s (25℃). (2) Inject the reaction slurry into the mold; (3) First stage: Keep at 55℃ for 4 minutes to complete foaming; Second stage: Keep at 90℃ for 6 minutes to complete cross-linking and curing, and you will get the product.

[0028] Example 2 Example 2 provides an in-situ closed-cell foam material, prepared by the following method: (1) Mix 40 parts by weight of melamine prepolymer, 40 parts by weight of toluene diisocyanate, 1.5 parts by weight of 3-aminopropyltriethoxysilane, 2 parts by weight of n-octyltriethoxysilane, 0.25 parts by weight of triethylenediamine, 5 parts by weight of water glass, and 1 part by weight of cyclopentane evenly to form a reaction slurry with a viscosity of 550 mPa·s (25℃). (2) Inject the reaction slurry into the mold; (3) First stage: Keep at 50℃ for 5 minutes to complete foaming; Second stage: Keep at 95℃ for 8 minutes to complete cross-linking and curing, and you will get the product.

[0029] Example 3 Example 3 provides an in-situ closed-cell foam material, prepared by the following method: (1) Mix 60 parts by weight of melamine prepolymer, 60 parts by weight of hexamethylene diisocyanate, 2 parts by weight of 3-aminopropyltriethoxysilane, 1 part by weight of methyltrimethoxysilane, 2 parts by weight of ethyltrimethoxysilane, 0.3 parts by weight of dibutyltin dilaurate, 15 parts by weight of sodium silicate, and 10 parts by weight of dichlorofluoroethane to form a reaction slurry with a viscosity of 1900 mPa·s (25℃). (2) Inject the reaction slurry into the mold; (3) First stage: Keep at 60℃ for 2 minutes to complete foaming; Second stage: Heat at 900W microwave for 3 minutes to complete cross-linking and curing, and you will get the product.

[0030] Comparative Example 1 Compared with Example 1, the only difference is that the hydrolyzable silane compounds 3-aminopropyltriethoxysilane and hexadecyltrimethoxysilane are replaced with 3 parts by weight of pure water.

[0031] Comparative Example 2 Compared with Example 1, the only difference is that the melamine prepolymer used does not contain bound water. The specific preparation method is as follows: in step four, the bound water is removed by further drying at 120°C under vacuum for 4 hours, so that the content of bound water is <0.1 wt%.

[0032] Test case The experimental examples are used to verify the effects of the implementation examples and comparative examples.

[0033] The performance test results of the examples and comparative examples are shown in Table 1.

[0034] Table 1

[0035] in conclusion: Examples 1-3 all exhibited excellent performance, with thermal conductivity ≤0.030W / (m²). K), flammability rating A2, specific strength > 4500 (N) m / kg), water absorption rate <1.0%.

[0036] Comparative Example 1 (using pure water instead of hydrolyzable silane compounds) showed a significant increase in thermal conductivity and high water absorption rate. This indicates that simply adding water cannot effectively form a stable closed-cell structure, and that water, as free water, participates in foaming, resulting in interconnected cells and extremely poor waterproof and moisture-proof performance.

[0037] The performance of Comparative Example 2 (melamine prepolymer without bound water) was also significantly lower than that of the Example, with both thermal conductivity and water absorption rate increasing. This indicates that an appropriate amount of bound water in the prepolymer is crucial for the construction of the in-situ closed-cell structure (low thermal conductivity, waterproof and moisture-proof).

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An in-situ closed-cell foam material, characterized in that, It is prepared from raw materials containing the following components through a foaming and curing reaction: 40-60 parts by weight of melamine prepolymer, 40-60 parts by weight of isocyanate, 1-5 parts by weight of hydrolyzable silane compound, 0.05-0.3 parts by weight of catalyst, 5-15 parts by weight of inorganic cementitious material, and 1-10 parts by weight of physical foaming agent. The bound water content in the melamine prepolymer is 2.0~5.0 wt%.

2. The in-situ closed-cell foam material according to claim 1, characterized in that, The melamine prepolymer is a product of hydroxymethyl melamine modified by methanol or ethanol etherification, and its degree of hydroxymethylation is 2.0-2.

8.

3. The in-situ closed-cell foam material according to claim 2, characterized in that, The method for preparing the melamine prepolymer includes the following steps: Step 1: Disperse melamine and formaldehyde in deionized water at a molar ratio of 2.5~3.0:1, and adjust the pH value to 8.0~9.0; Step 2: Stir the reaction at 60-80℃ for 1-2 hours to carry out the hydroxymethylation reaction and obtain a hydroxymethyl melamine solution; Step 3: Add methanol or ethanol, adjust the pH value to 4.5~6.0, and carry out the etherification reaction at 50-65℃ for 1-3 hours to obtain the etherified modified melamine prepolymer; Step 4: Cooling, and control the water content through vacuum concentration to make the bound water content 2.0~5.0 wt% and the degree of hydroxymethylation 2.0-2.

8.

4. The in-situ closed-cell foam material according to any one of claims 1-3, characterized in that, The hydrolyzable silane compound is a combination of 3-aminopropyltriethoxysilane and other silane compounds in a mass ratio of 1 to 1.5:2; the other silane compounds are selected from at least one of methyltrimethoxysilane, ethyltrimethoxysilane, isobutyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, and hexadecyltrimethoxysilane.

5. The in-situ closed-cell foam material according to any one of claims 1-3, characterized in that, The isocyanate is at least one of diphenylmethane diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate.

6. The in-situ closed-cell foam material according to any one of claims 1-3, characterized in that, The catalyst is at least one of tertiary amine catalysts or organotin catalysts.

7. The in-situ closed-cell foam material according to any one of claims 1-3, characterized in that, The physical foaming agent is at least one of cyclopentane, dichlorofluoroethane, and carbon dioxide.

8. The in-situ closed-cell foam material according to any one of claims 1-3, characterized in that, The inorganic cementing material is at least one of water glass, silicate, and aluminate.

9. A method for preparing the in-situ closed-cell foamed material according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Mix the raw materials containing the melamine prepolymer, isocyanate, hydrolyzable silane compound and catalyst evenly to form a reaction slurry; (2) Inject the reaction slurry into a mold or apply it to the surface of a substrate; (3) Perform foaming and curing reactions to obtain the product; Preferably, in step (3), the foaming and curing reaction includes the following two stages: First stage: Maintain at 50-60℃ for 2-5 minutes to complete foaming; Second stage: Heat in a microwave at 500W-900W for 3-5 minutes, or maintain at 90-120℃ for 3-8 minutes to complete rapid cross-linking and curing.

10. The application of the in-situ closed-cell foam material according to any one of claims 1-8, or the in-situ closed-cell foam material prepared by the preparation method according to claim 9, in building exterior wall insulation, automotive lightweighting, or electronic packaging.

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