Low-density flame-retardant silane modified sealant and preparation method thereof

Abstract

The invention relates to a low-density flame-retardant silane modified sealant and a preparation method thereof, and belongs to the technical field of high polymer materials. The sealant comprises the following components: an alkoxy-terminated silyl-organic phosphorus-silicon hybrid polyurethane prepolymer with a specific structure, a bis (triethoxysilylpropyl) phenyl phosphate reactive flame-retardant plasticizer, a flame-retardant filler, hollow glass beads, fumed silica, dipentaerythritol and the like. According to the invention, a phosphorus-based flame-retardant unit is embedded into a polymer main chain to realize intrinsic flame retardance, a terminal alkoxy silicon group of a reactive plasticizer is utilized to realize functional persistent bonding, and a composite filler system is constructed to realize synergistic interaction. The prepared sealant has a high flame-retardant grade, excellent mechanical properties, elastic recovery rate and long-term durability while the density is remarkably reduced, and the technical problems that a traditional flame-retardant sealant is large in density and poor in performance are solved.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, and relates to a low-density flame-retardant silane-modified sealant and its preparation method. Background Technology

[0002] Silane-modified sealants are high-performance sealing materials based on terminal alkoxysilane-based polyether resins or terminal alkoxysilane-based polyurethane prepolymers. They are moisture-cured to form an elastomer. Due to their excellent weather resistance, environmental friendliness, and adhesion to various substrates, they are widely used in construction, rail transportation, shipbuilding, and new energy fields. However, in applications with extremely high safety requirements, such as fireproofing of high-rise buildings and battery pack sealing, the sealant must have a high flame retardant rating, such as UL94 V-0.

[0003] Currently, commercially available flame-retardant silane-modified sealants mainly achieve their flame-retardant requirements by adding large amounts of inorganic flame-retardant fillers, such as aluminum hydroxide and magnesium hydroxide. However, the high density of these inorganic fillers leads to a significant increase in the density of the finished sealant, often exceeding 1.5 g / cm³. 3 Firstly, excessive filler increases structural load and construction burden. Secondly, high filler content severely impairs the sealant's key mechanical properties such as elasticity, elongation, and tensile strength, affecting its flexibility and long-term durability. Finally, excessive filler makes the paste stiff, difficult to extrude, and deteriorates its thixotropy, affecting construction efficiency and appearance.

[0004] Therefore, developing a silane-modified sealant that can achieve a high flame retardancy rating at low density while maintaining excellent mechanical and workability properties has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a low-density flame-retardant silane-modified sealant and its preparation method. This invention designs and synthesizes a polymer of structural formula (I), in which the flame-retardant element becomes part of the polymer backbone through chemical bonds, fundamentally eliminating migration, precipitation, and volatilization, ensuring the flame-retardant reliability of the product throughout its entire life cycle. Furthermore, it uses bis(triethoxysilylpropyl)phenyl phosphate of structural formula (II) as a reactive flame-retardant plasticizer. Its terminal silane groups can undergo a condensation reaction with the terminal alkoxysilane groups of the polymer, chemically bonding to the cross-linked network, fundamentally solving the migration and precipitation problems of small-molecule flame retardants, ensuring long-term flame-retardant stability, and constructing a composite filler system for synergistic effect, thereby achieving efficient utilization of flame-retardant components, effective density reduction, and overall performance optimization in the silane-modified sealant.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a low-density flame-retardant silane-modified sealant is provided, comprising the following components by weight: 30-50 parts of terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer; Reactive flame retardant plasticizer: 10-25 parts; Non-reactive flame retardant plasticizer: 5-20 parts; Flame retardant filler: 25-35 parts; Lightweight materials: 2-5 parts; Reinforcing filler: 1-3 parts; Carbon source precursor: 2-5 parts; Dehydrating agent: 2-5 parts; Adhesion promoter: 0.5~3 parts; Catalyst: 0.1~0.5 parts; Stabilizer: 1-3 parts.

[0007] Furthermore, the structure (I) of the terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer is as follows: R1 is the backbone of di(2-hydroxyethyl) phosphite after removing the hydroxyl groups at both ends. The molecular structure of di(2-hydroxyethyl) phosphite is as follows: Specifically, this polymer structure innovatively integrates flame-retardant groups on three levels: (1) Key flame-retardant units in the main chain: This is a flame-retardant functional unit embedded in the main chain, where P=O bond and phosphorus is the intrinsic flame-retardant source. During combustion, phosphorus compounds can promote polymer dehydration to form char, creating a dense and heat-insulating char layer (condensed phase flame retardant), which can significantly improve flame-retardant efficiency.

[0008] (2) Introducing a rigid benzene ring structure improves thermal stability and flame retardancy.

[0009] (3) Terminal silane functional groups (providing curing ability): Alkoxysilane groups located at both ends of the molecular chain. In the presence of moisture, alkoxy groups hydrolyze into silanol groups, which then condense to form a Si-O-Si three-dimensional network, allowing the sealant to cure from a paste to an elastomer. This is the basis for the sealant to obtain its final mechanical strength and adhesion.

[0010] Furthermore, the reactive flame retardant plasticizer is bis(triethoxysilylpropyl) phenyl phosphate, whose structural formula (II) is as follows: Specifically, this reactive flame-retardant plasticizer with a molecular structure is bis(triethoxysilylpropyl) phenyl phosphate, which has the following advantages, collectively constituting its unique performance advantages: (1) Core flame retardant center: phosphate ester unit, phosphorus element (P), provides efficient condensed phase flame retardancy. During combustion, it promotes the dehydration, cross-linking and charring of the polymer substrate, forming a heat-insulating and oxygen-barrier protective layer.

[0011] The benzene ring (-C6H5) introduces a rigid aromatic ring structure, bringing dual benefits: improved thermal stability and flame retardancy. The aromatic ring structure itself is difficult to burn, and at high temperatures, it helps to form a more stable aromatic char layer. It also reduces the migration of plasticizers, increases molecular volume and rigidity, and weakens their diffusion ability in sealant systems.

[0012] (2) Flexible connecting arm: propyl chain -CH2-CH2-CH2 The functional silane end groups are flexibly connected to the core flame-retardant center.

[0013] It provides the necessary molecular flexibility to ensure that the plasticizer can effectively perform its plasticizing function even at low temperatures, and to prevent the sealant from becoming brittle due to excessive molecular rigidity.

[0014] (3) Reactive or anchoring end group: Triethoxysilane-Si(OC2H5)3 Compared to the more reactive methoxy group (-OCH3), the hydrolysis rate of the ethoxy group is milder and more controllable. This helps ensure that the sealant has a longer pot life, allowing sufficient time for application while ensuring full curing. The alkoxysilane groups at both ends upgrade it from a traditional "physically mixed" plasticizer to a "reactively bonded" type.

[0015] Mechanism of action: During the curing process of the sealant, the alkoxysilane groups at both ends hydrolyze into silanol groups (-SiOH) under the action of moisture and catalyst, which then undergo a condensation reaction with the silanoxy groups at the polymer ends. This solves the problems of migration, exudation, and volatilization of traditional plasticizers, ensuring the durability of the flame retardant effect and the stability of the product during long-term use.

[0016] Furthermore, the non-reactive flame retardant plasticizer is selected from one or more of dimethyl methyl phosphate, tricresyl phosphate, and triisopropylphenyl phosphate.

[0017] Furthermore, the flame-retardant filler is one or more of ammonium polyphosphate (APP), melamine polyphosphate (MPP), and melamine cyanurate (MCA).

[0018] Furthermore, the lightweight material is hollow glass microspheres with a density of 0.2~0.6 g / cm³. 3 The reinforcing filler is hydrophobic fumed silica surface-treated with hexamethyldisilazane, with a specific surface area of ​​100-200 m² / g. 2 / g.

[0019] Furthermore, the carbon source precursor is dipentaerythritol, and the dehydrating agent is one or both of vinyltrimethoxysilane and methyl orthosilicate.

[0020] The char source precursor is dipentaerythritol, which, when combined with the flame-retardant filler system, makes it easier to form a rich, dense, and continuous expanded char layer during combustion, thereby improving flame-retardant performance.

[0021] Furthermore, the adhesion promoter is one or two of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and the catalyst is one or two of dibutyltin dilaurate and bis(acetylacetonate)dibutyltin.

[0022] Furthermore, the stabilizer is one or both of triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0023] Secondly, a method for preparing a low-density flame-retardant silane-modified sealant is provided, comprising the following steps: (1) The terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer, reactive flame retardant plasticizer, and non-reactive flame retardant plasticizer are added to a power mixer and stirred and mixed at 50~100r / min for 15~20min under a vacuum of -0.08MPa to -0.1MPa to obtain a premixed adhesive. (2) Add flame retardant filler and stabilizer to the premixed rubber compound. First, stir at 200~300r / min for 10~20min to make the filler completely wet. Then, increase the speed to 300~400r / min, turn on the equipment to heat, and heat and stir for 60~120min in a vacuum of -0.08MPa to -0.1MPa and a temperature of 100-110℃ until the moisture content drops below 500ppm. Then, stop heating, reduce the speed, and continue to evacuate and cool down to below 50℃. (3) Add reinforcing filler and carbon source precursor to the mixture in step (2) in batches and multiple times, turn on the stirring speed of 300~450r / min for 20~40min, control the temperature below 50℃, then add dehydrating agent, adhesion promoter and catalyst, stir at 300~450r / min for 25~35min under vacuum of -0.08MPa to -0.1MPa, and finally add light filler, stir at 300~400r / min for 10~20min under vacuum of -0.08MPa to -0.1MPa, degas and discharge into a can to obtain the low-density flame-retardant silane modified sealant.

[0024] The beneficial effects of this invention are: (1) In this invention, by designing and synthesizing a polymer with structural formula (I), the "phosphorus" flame retardant element is embedded in the polymer backbone. Phosphorus is an intrinsic flame retardant source. During combustion, phosphorus compounds can promote the dehydration of the polymer to form char, creating a dense and heat-insulating char layer (condensed phase flame retardant), which can significantly improve the flame retardant efficiency. The alkoxysilyl groups located at both ends of the molecular chain hydrolyze into silanol groups in the presence of moisture, and then condense with each other to form a Si-O-Si three-dimensional network, which makes the sealant solidify from a paste into an elastomer. This is the basis for the sealant to obtain the final mechanical strength and adhesion. In this invention, the flame retardant element becomes part of the polymer skeleton in the form of covalent bonds, which fundamentally eliminates the migration, precipitation and volatilization problems caused by physical blending of traditional flame retardants, ensuring the reliability of the flame retardant performance of the product throughout its entire life cycle. In addition, since the polymer itself has flame retardancy, the amount of high-density inorganic flame retardant fillers added in the formulation can be greatly reduced, making it easier to achieve the "low density" target, and also more conducive to maintaining the elasticity and durability of the sealant.

[0025] (2) In this invention, the traditional inert plasticizer, such as phthalates, is abandoned in its simple physical blending with flame retardants. Instead, a composite system of "crosslinkable reaction + flame retardancy" is adopted. Specifically, bis(triethoxysilylpropyl) phenyl phosphate with structural formula (II) is used as a reactive flame retardant plasticizer. This molecule has both a phenyl phosphate flame retardant center and a triethoxysilyl reactive end group. During the curing process of the sealant, its end group hydrolyzes and can undergo a co-condensation reaction with the terminal silane of polymer (I), thereby chemically bonding to the crosslinked network. This fundamentally solves the problem of easy migration and precipitation of small molecule flame retardant plasticizers, providing a long-lasting plasticizing effect while ensuring the long-term stability of the flame retardant function. The flexible propyl chain and benzene ring structure in its molecule contribute to good low-temperature plasticizing and thermal stability, respectively.

[0026] (3) This invention abandons the traditional reliance on high-density inorganic hydroxide fillers in flame-retardant sealants and innovatively constructs a composite filler of "lightweight material + flame-retardant functional material", which significantly reduces density while endowing multiple functions. Specifically, the lightweight filler (hollow glass microspheres) serves as the main weight-reduction unit, directly and effectively reducing product density while improving compressive strength and dimensional stability; the functionalized flame-retardant fillers (ammonium polyphosphate (APP), melamine polyphosphate (MPP), melamine cyanurate (MCA)) have a strong synergistic flame-retardant effect with the polymer and plasticizer due to the thermal decomposition and water absorption and char-promoting functions of the phosphorus-nitrogen system, achieving a high flame-retardant rating at a low addition amount; the reinforcing filler (fumed silica with hexamethyldisilazane surface treatment) and the char source precursor (dipentaerythritol) work together with the phosphorus-nitrogen flame-retardant system to promote the formation of a richer and denser expanded char layer. This system achieves lightweighting while improving flame-retardant efficiency through multiple mechanisms and reducing the negative impact on mechanical properties.

[0027] This invention successfully resolves the contradiction between "high flame retardancy" and "low density and high elasticity" through molecular design and system construction. The resulting sealant achieves a UL94 V-0 flame retardancy rating while significantly reducing density, and maintains high elasticity, high elongation, excellent adhesion, and workability. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with embodiments, is provided below.

[0029] Synthesis of terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymers (1) Synthesis of hydroxyl-terminated organophosphorus-silicon hybrid polyurethane prepolymer Reaction principle: Under anhydrous raw materials and nitrogen protection during the reaction process, di(2-hydroxyethyl) phosphite reacts with diphenylmethane diisocyanate to generate a hydroxyl-terminated prepolymer. Then, γ-isocyanate-propyltriethoxysilane reacts with the -OH at the end of the hydroxyl-terminated prepolymer to obtain a triethoxysilyl-organophosphorus-silicon hybrid polyurethane polymer.

[0030] Step 1: Di(2-hydroxyethyl) phosphite (DEHP) and diphenylmethane diisocyanate (MDI) are used to synthesize a hydroxyl-terminated prepolymer.

[0031] Reaction equation: nHO-R-OH + (n-1)OCN-R'-NCO → HO-[R-OOCNH-R'-NHCOO-R] (n-1) -OH In the formula, R represents the skeleton of di(2-hydroxyethyl) phosphite with the hydroxyl groups removed. R': Diphenylmethane diisocyanate with the skeleton of isocyanate groups removed at both ends. Reaction process: ① The raw material metering is set as n(-OH):n(-NCO)=1.2:1. High-purity nitrogen gas is introduced into a dry four-necked flask to maintain a slight positive pressure. The metered amount of di(2-hydroxyethyl) phosphite (1.2mol, 187.2g) is added. Stirring is started at 200~300r / min and the temperature is raised to 60℃.

[0032] ② Once the system temperature stabilizes at 60℃, add diphenylmethane diisocyanate (1 mol, 250 g) in 2-3 portions, with a 5-minute interval between each addition. After the addition is complete, continue stirring under nitrogen atmosphere for 10 minutes.

[0033] ③ Add 0.3g of dibutyltin dilaurate catalyst solution (0.07% of total material) dropwise using a constant pressure dropping funnel over a period of 5-10 minutes. After the addition is complete, raise the temperature to 70-75℃ and maintain the temperature for 2-3 hours.

[0034] ④ Take samples every 30 minutes and use di-n-butylamine titration to detect the free NCO content in the system until the NCO content drops to 0%, indicating that the reaction is complete and a pale yellow transparent terminal hydroxyl prepolymer is obtained. Keep the system temperature at 70℃ and carry out the second step of the end-capping reaction.

[0035] Step 2: End-capping by reacting the hydroxyl-terminated prepolymer with γ-isocyanate-propyltriethoxysilane. Reaction formula: HO-prepolymer-OH + 2OCN-(CH2)3-Si(OEt)3 →(EtO)3Si-(CH2)3-NHCOO-Prepolymer-OOCNH-(CH2)3-Si(OEt)3 In the formula, prepolymer is the main chain portion of the terminal hydroxyl prepolymer generated in the first step.

[0036] Reaction process: ① Maintain the reaction temperature at 70℃~75℃, nitrogen gas under slight positive pressure, and stir at 200~300r / min. Slowly add γ-isocyanate-propyltriethoxy (119.7g, 5% excess) through a constant pressure dropping funnel for 15~20min.

[0037] ② After the addition is complete, continue the reaction at a constant temperature of 70℃~75℃ for 1.5h~2h. During this period, take samples every 20min and use the acetylation method to detect the hydroxyl content of the system.

[0038] ③ When the hydroxyl content of the system drops below 0.1%, it indicates that the end-capping reaction is complete, and heating is stopped. Allow it to cool naturally to below 40℃, turn off the nitrogen gas, and keep stirring for 10 minutes to obtain the final triethoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer.

[0039] Example 1: Preparation of low-density flame-retardant silane-modified sealant 1. Formula (parts by weight): 35 parts of terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer; 15 parts of bis(triethoxysilylpropyl) phosphate; Dimethyl methyl phosphate: 10 parts Melamine cyanurate: 30 parts; Hollow glass microspheres: 3 parts; Hydrophobic fumed silica: 2 parts; Dipentaerythritol: 2 parts; Vinyltrimethoxysilane: 2 parts; N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane: 1 part; Dibutyltin bis(acetylacetonate): 0.2 parts; Diethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate]: 1 part.

[0040] 2. The preparation process is as follows: (1) The terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer, bis(triethoxysilylpropyl) phenyl phosphate and dimethyl methyl phosphate were added to a power mixer and stirred at 70 r / min for 17 min under a vacuum of -0.09 MPa to obtain a premixed adhesive. (2) Add melamine cyanurate and triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] to the premixed rubber compound. First, stir at 250 r / min for 15 min to completely impregnate the filler. Then, increase the speed to 350 r / min, turn on the equipment to heat, and heat and stir for 90 min under a vacuum of -0.09 MPa and a temperature of 105℃ until the moisture content drops below 500 ppm. Then, stop heating, reduce the speed, and continue to evacuate and cool down to below 50℃. (3) Add hydrophobic fumed silica and dipentaerythritol to the mixture in step (2) in batches and stir at 400 r / min for 30 min while keeping the temperature below 50 °C. Then add vinyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane and bis(acetylacetonate)dibutyltin. Stir at 400 r / min for 30 min under a vacuum of -0.09 MPa. Finally, add hollow glass microspheres and stir at 350 r / min for 15 min under a vacuum of -0.09 MPa. Degas and discharge the material into a container to obtain the low-density flame-retardant silane modified sealant.

[0041] Example 2: Preparation of low-density flame-retardant silane-modified sealant 1. Formula (parts by weight): 30 parts of terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer; 10 parts of bis(triethoxysilylpropyl) phenyl phosphate; Trimethylbenzene phosphate: 15 parts; Melamine polyphosphate: 35 parts; Hollow glass microspheres: 2 parts; Hydrophobic fumed silica: 1 part; Dipentaerythritol: 3 parts; Methyl orthosilicate: 2.5 parts; 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane: 1.5 parts; Dibutyltin dilaurate: 0.5 parts; Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]: 2 parts.

[0042] 2. The preparation process is as follows: (1) The terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer, bis(triethoxysilylpropyl) phenyl phosphate and tricresyl phosphate were added to a power mixer and stirred at 50 r / min for 20 min under a vacuum of -0.08 MPa to obtain a premixed adhesive. (2) Add melamine polyphosphate and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to the premixed rubber compound. First, stir at 200 r / min for 20 min to completely impregnate the filler. Then, increase the speed to 300 r / min, turn on the equipment to heat, and heat and stir for 120 min under a vacuum of -0.08 MPa and a temperature of 100℃ until the moisture content drops below 500 ppm. Then, stop heating, reduce the speed, and continue to evacuate and cool down to below 50℃.

[0043] (3) Add hydrophobic fumed silica and dipentaerythritol to the mixture in step (2) in batches and stir at 300 r / min for 40 min while keeping the temperature below 50 °C. Then add methyl orthosilicate, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and dibutyltin dilaurate. Stir at 300 r / min for 35 min under a vacuum of -0.08 MPa. Finally, add hollow glass microspheres and stir at 300 r / min for 20 min under a vacuum of -0.08 MPa. Degas and discharge the material into a container to obtain the low-density flame-retardant silane modified sealant.

[0044] Example 3: Preparation of low-density flame-retardant silane-modified sealant 1. Formula (parts by weight): Terminally alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer: 40 parts; bis(triethoxysilylpropyl) phenyl phosphate: 20 parts; Triisopropylphenyl phosphate: 5 parts; Ammonium polyphosphate: 30 parts; Hollow glass microspheres: 2 parts; Hydrophobic fumed silica: 1 part; Dipentaerythritol: 3 parts; Vinyltrimethoxysilane: 1.5 parts; Methyl orthosilicate: 1 part; 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane: 1 part; Dibutyltin bis(acetylacetonate): 0.1 parts; Dibutyltin dilaurate: 0.2 parts; Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]: 2 parts.

[0045] 2. The preparation process is as follows: (1) The terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer, bis(triethoxysilylpropyl) phenyl phosphate and triisopropylphenyl phosphate were added to a power mixer and stirred at 100 r / min for 15 min under a vacuum of -0.1 MPa to obtain a premixed adhesive. (2) Add ammonium polyphosphate and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] to the premixed rubber compound. First, stir at 300 r / min for 10 min to completely impregnate the filler. Then, increase the speed to 400 r / min, turn on the equipment to heat, and heat and stir for 60 min under a vacuum of -0.1 MPa and a temperature of 110°C until the moisture content drops below 500 ppm. Then, stop heating, reduce the speed, and continue to evacuate and cool down to below 50°C.

[0046] (3) Add hydrophobic fumed silica and dipentaerythritol to the mixture in step (2) in batches. Stir at 450 r / min for 20 min while keeping the temperature below 50 °C. Then add vinyltrimethoxysilane, methyl orthosilicate, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, bis(acetylacetonate) dibutyltin, and dibutyltin dilaurate. Stir at 450 r / min for 25 min under a vacuum of -0.1 MPa. Finally, add hollow glass microspheres and stir at 400 r / min for 10 min under a vacuum of -0.1 MPa. Degas and discharge the material into a container to obtain the low-density flame-retardant silane modified sealant.

[0047] Comparative Example 1 Based on Example 1, the terminal alkoxysilane-organophosphorus-silicon hybrid polyurethane prepolymer was replaced with a terminal alkoxysilane polyether polymer with the chemical formula: (CH3CH2O)2CH3Si-(CH2)3-(C3H6O)n-(CH2)3-SiCH3(OCH2CH3)2, such as Kaneka's S303H polymer, and other conditions remained the same as in Example 1.

[0048] Comparative Example 2 Based on Example 1, the reactive flame retardant plasticizer (bis(triethoxysilylpropyl)phenyl phosphate) and the non-reactive flame retardant plasticizer (dimethyl methyl phosphate) were replaced with diisononyl phthalate, while other conditions remained the same as in Example 1.

[0049] Comparative Example 3 Based on Example 1, melamine cyanurate was replaced with ordinary aluminum hydroxide, and hollow glass microspheres and hydrophobic fumed silica were not added, while other conditions remained the same as in Example 1.

[0050] Comparative Example 4 Based on Example 1, the terminal alkoxysilane-organophosphorus-silicon hybrid polyurethane prepolymer, reactive flame retardant plasticizer (bis(triethoxysilylpropyl)phenyl phosphate), and non-reactive flame retardant plasticizer (dimethyl methyl phosphate) and melamine cyanurate were replaced with ordinary silane-terminated polyether polymer, diisononyl phthalate, and ordinary aluminum hydroxide, respectively, and hollow glass microspheres and hydrophobic fumed silica were not added. Other conditions remained the same as in Example 1.

[0051] Comparative Example 5 Based on Example 1, dipentaerythritol was not added, and other conditions remained the same as in Example 1.

[0052] Performance testing The sealants prepared in the examples and comparative examples were subjected to performance tests according to the relevant national standards. The results are shown in Table 1. Density test method: Refer to GB / T 13477.2-2018; Test methods for tensile strength and elongation at break: Refer to GB / T 528-2009; Test method for extrudability: Refer to GB / T 13477.3-2017; Test methods for tensile modulus and elastic recovery rate: Refer to GB / T 13477.17-2017; Test methods for flame retardant performance: Refer to GB / T 2408-2021; Durability is the performance retention rate after accelerated aging. Here, the change rate of tensile strength and the change rate of elongation at break after thermal aging were tested, specifically referring to GB / T 3512-2014. Test method for tensile adhesion: Refer to GB / T 13477.8-2017.

[0053] The test results are shown in Table 1 below: Table 1. Performance test results of the silane-modified sealants in the examples and comparative examples. Note: In the changes in tensile strength and elongation at break after heat aging, "+" indicates improved performance and "-" indicates decreased performance; the smaller the absolute value, the higher the performance retention rate after aging.

[0054] According to the test results in Table 1, Examples 1-3 exhibited lower density and better workability. While achieving V-0 level flame retardancy, they maintained good tensile strength, elongation at break, and lower modulus, achieving "lightweight and high elasticity". Specifically, Comparative Examples 1-5 could not achieve V-0 level flame retardancy and had poor mechanical properties. This indicates that the terminal alkoxysilane-organophosphorus-silicon hybrid polyurethane prepolymer is a prerequisite for reducing reliance on high-addition flame retardant fillers and achieving lightweighting. The hollow glass microspheres and hydrophobic fumed silica in the composite filler system are key units for directly reducing density, and their good dispersibility, together with the flame retardant filler, ensures smoothness during construction. Comparative Examples 1 and 2 exhibit some mechanical properties similar to Example 1, but their performance deteriorates significantly after thermal aging and they fail to achieve V-0 flame retardancy. This indicates that the terminal alkoxysilane-organophosphorus-silicon hybrid polyurethane prepolymer, reactive plasticizer, and non-reactive plasticizer used in the examples possess certain flame retardancy. The phosphorus element in their molecular structure synergistically contributes to a good flame retardant effect with the fillers in the system, reducing the amount of flame-retardant fillers required to achieve the desired low density and high flame retardancy. Comparative Example 3 shows significant performance degradation, with high density, high modulus, and poor elasticity, and it also fails to achieve V-0 flame retardancy. This demonstrates that even with the core flame-retardant component, a poorly designed filler system cannot achieve a low-density flame retardant effect. Comparative Example 4 represents the traditional technical approach, with severe degradation. Its various properties are at a low level, especially in density, elasticity, and durability, exhibiting significant shortcomings. During combustion, it relies solely on the endothermic decomposition of aluminum hydroxide, resulting in poor flame retardancy. Comparative Examples 1-4 represent states where only a portion of the technology of this invention is used, and each of them reveals deficiencies in comprehensive performance such as sustained flame retardancy and lightweight high elasticity. In Comparative Example 5, lacking dipentaerythritol as a char source, the expanded char layer formed during combustion is not dense enough, leading to a decrease in flame retardant effect. Examples 1-3, based on terminal alkoxysilane-organophosphorus-silicon hybrid polyurethane prepolymers, laid the foundation for low filler requirements and high elasticity. Reactive flame retardants served as a bridge, permanently anchoring the flame retardant and plasticizing functions, ensuring long-term effectiveness. Optimization with composite fillers finely controlled density, mechanical properties, flame retardancy, and construction rheology, resulting in a significant positive synergistic effect. Ultimately, breakthroughs were achieved simultaneously in multiple key performance indicators, including low density, high elasticity, high flame retardancy, and excellent workability, achieving a balance of various performance aspects.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A low-density flame-retardant silane-modified sealant, characterized in that, Based on parts by weight, it includes the following components: Terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer: 30-50 parts; Reactive flame retardant plasticizer: 10-25 parts; Non-reactive flame retardant plasticizer: 5-20 parts; Flame retardant filler: 25-35 parts; Lightweight materials: 2-5 parts; Reinforcing filler: 1-3 parts; Carbon source precursor: 2-5 parts; Dehydrating agent: 2-5 parts; Adhesion promoter: 0.5~3 parts; Catalyst: 0.1~0.5 parts; Stabilizer: 1-3 parts.

2. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The structure of the terminal alkoxysilane-organophosphorus-silane hybrid polyurethane prepolymer is (I): R1 is the backbone of di(2-hydroxyethyl) phosphite after the removal of its two hydroxyl groups, and its molecular structure is as follows: .

3. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The reactive flame retardant plasticizer is bis(triethoxysilylpropyl) phenyl phosphate, and its structural formula (II) is as follows: 。 4. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The non-reactive flame retardant plasticizer is selected from one or more of dimethyl methyl phosphate, tricresyl phosphate, and triisopropylphenyl phosphate.

5. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The flame-retardant filler is one or more of ammonium polyphosphate, melamine polyphosphate, and melamine cyanurate.

6. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The lightweight material is hollow glass microspheres with a density of 0.2~0.6 g / cm³. 3 The reinforcing filler is hydrophobic fumed silica surface-treated with hexamethyldisilazane, with a specific surface area of ​​100-200 m² / g. 2 / g.

7. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The carbon source precursor is dipentaerythritol, and the dehydrating agent is one or both of vinyltrimethoxysilane and methyl orthosilicate.

8. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The adhesion promoter is one or two of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and the catalyst is one or two of dibutyltin dilaurate and bis(acetylacetonate)dibutyltin.

9. The low-density flame-retardant silane-modified sealant according to claim 1, characterized in that, The stabilizer is one or both of triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

10. A method for preparing the low-density flame-retardant silane-modified sealant according to any one of claims 1 to 9, characterized in that, Includes the following steps: (1) The terminal alkoxysilyl-organophosphorus-silicon hybrid polyurethane prepolymer, reactive flame retardant plasticizer and non-reactive flame retardant plasticizer are stirred and mixed at 50~100r / min for 15~20min under a vacuum of -0.08MPa to -0.1MPa to obtain a premixed adhesive. (2) Add flame retardant filler and stabilizer to the premixed rubber compound, stir at 200~300r / min for 10~20min to make the filler completely wet, then increase the speed to 300~400r / min, heat to 100-110℃, stir under vacuum of -0.08MPa to -0.1MPa for 60~120min until the moisture content drops below 500ppm, then reduce the speed and continue to evacuate and cool down to below 50℃; (3) Add reinforcing filler and carbon source precursor to the mixture in step (2), turn on the stirring speed of 300~450 r / min for 20~40 min, control the temperature below 50℃, then add dehydrating agent, adhesion promoter and catalyst, stir at 300~450 r / min for 25~35 min under vacuum of -0.08MPa to -0.1MPa, and finally add light filler, stir at 300~400 r / min for 10~20 min under vacuum of -0.08MPa to -0.1MPa, degas and discharge into a can to obtain the low-density flame-retardant silane modified sealant.

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