A method for preparing a polyurethane sealant

Abstract

This invention relates to the field of polymer material preparation technology, specifically a method for preparing a polyurethane sealant. The method involves first preparing an IPDI-g-KH-550@MTMS / TEOS@modified flame retardant, then mixing it with modified expandable graphite, polyether polyol, isocyanate, a catalytic system, functional additives, etc., and finally filling the mixture with a propellant. Specifically, IPDI grafting achieves chemical anchoring of the flame retardant, and the MTMS / TEOS hybrid shell and modified expandable graphite form a synergistic flame-retardant carbon layer. DMDEE, organic bismuth, and organic zinc constitute a ternary catalytic system, which, combined with a latent curing agent, achieves stable curing over a wide temperature range. This invention solves the problem of simultaneously achieving flame retardancy and application adaptability at -10℃ to 40℃ in existing polyurethane sealants, meeting the engineering requirements for high flame retardancy and wide climate adaptability in building sealant materials.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation technology, specifically a method for preparing a polyurethane sealant. Background Technology

[0002] Polyurethane sealant (usually in aerosol cans) is widely used in building decoration projects such as door and window installation, wall crack repair, and pipe sealing. It cures through moisture to form a foam sealant with a certain degree of elasticity and adhesive strength, offering advantages such as convenient application, high foaming ratio, and good sealing and sound insulation effects. Currently, commercially available single-component polyurethane sealants mainly consist of polyether polyols and isocyanate prepolymers, combined with catalysts, foaming agents, and foam stabilizers, and packaged in aerosol cans.

[0003] However, in actual building applications, polyurethane sealants often face the dual contradiction of insufficient flame retardancy and poor adaptability to all seasons. Ordinary polyurethane sealants have a low oxygen index (usually 18%~21%), are easily flammable and produce molten droplets when exposed to fire, and cannot meet the flame retardancy requirements for sealants in curtain walls, pipe shafts and other parts of the "Code for Fire Protection Design of Buildings" (GB 50016) (usually requiring a B1 or B2 rating). To improve flame retardant performance, existing technologies often directly add halogen-free flame retardants, such as melamine cyanurate, expandable graphite, and ammonium polyphosphate, to the formulation. However, the direct physical blending method has the following prominent problems: poor compatibility between the flame retardant and the polyurethane matrix, resulting in decreased storage stability of the sealant system (easy settling and valve blockage in aerosol cans), and a significant reduction in the mechanical properties of the foam after curing (such as compressive strength and resilience); although expandable graphite has excellent expansion flame retardant effect, its surface is hydrophilic and oleophobic, resulting in poor dispersibility in polyurethane prepolymers, and it is prone to moisture absorption and failure during long-term storage; while the effective flame retardant content of melamine cyanurate flame retardants often reaches 15% to 20%, and at this filling amount, the foaming ratio of the sealant is unstable and the surface powdering is severe.

[0004] Meanwhile, the moisture curing reaction of polyurethane sealant is highly sensitive to ambient temperature and humidity: at low temperatures (≤5℃), the reactivity decreases significantly, curing time is prolonged, and it may even fail to cure completely; at high temperatures (≥35℃), the reaction rate is too fast, heat release is concentrated, which can easily cause cell collapse and surface cracking, while the increased pressure inside the can also pose a safety hazard; humidity fluctuations also lead to unstable curing quality. Existing technologies attempt to broaden the application window by compounding catalysts or introducing latent curing agents, but conventional catalyst systems are difficult to achieve across a wide temperature range—insufficient activity at low temperatures, and a tendency for reaction to runaway at high temperatures; the compatibility of latent curing agents with isocyanates is limited, and excessive use can damage the mechanical properties of the foam; most existing products can only be stably applied within a narrow temperature window of 15℃ to 30℃.

[0005] To address these issues, existing technologies attempt to improve the compatibility of flame retardants with the polyurethane matrix through surface modification. For example, wet surface treatment of expandable graphite or melamine cyanurate is performed using silane coupling agents (such as KH-550 and KH-560), or a silica layer is coated onto the flame retardant surface. However, flame retardant treated with ordinary silane coupling agents only forms a monolayer. Under long-term humid and hot conditions (such as temperature differences and rainwater penetration at building joints), the coupling layer is prone to hydrolysis and detachment, and the flame retardant still migrates and aggregates. While a single silica coating can improve thermal stability, it lacks functional groups that can react with isocyanates, failing to achieve chemical bonding between the flame retardant and the polyurethane matrix, resulting in insufficient interfacial bonding strength. In terms of construction adaptability, some technologies use end-capped latent catalysts or microencapsulated isocyanates to delay high-temperature reactions, but these are costly and have limited improvement on low-temperature curing. Other technologies use water-absorbing agents (such as molecular sieves and oxazolidines) to cope with humidity fluctuations, but these often sacrifice the adhesion of the foam.

[0006] Therefore, existing technologies still cannot simultaneously achieve the comprehensive requirements of long-term storage stability, excellent flame retardant properties, and construction adaptability of polyurethane sealant in aerosol cans, making it difficult to meet the engineering needs of building sealant materials for high flame retardant safety and wide climate adaptability. Summary of the Invention

[0007] To address the above problems, the present invention provides a method for preparing a polyurethane sealant, comprising the following steps:

[0008] S1. Methyltrimethoxysilane (MTMS) and tetraethyl orthosilicate (TEOS) are dissolved in an ethanol solvent at a mass ratio of (1~2):1, wherein the mass ratio of anhydrous ethanol to deionized water in the ethanol solvent is 4:1, and the mass ratio of the ethanol solvent to the total mass of MTMS and TEOS is (2~3):1. The pH is adjusted to 5.5~6.5 with 5%~10% dilute nitric acid, and hydrolyzed for 30~45 min at 45~55℃ and 200~400 rpm to form an MTMS / TEOS hybrid sol. The modified flame retardant is dispersed in 2~3 times its mass of ethanol solvent, wherein the modified flame retardant and MTM... The mass ratio of S to TEOS is 1:(1.5~2.5). The above MTMS / TEOS hybrid sol is slowly added dropwise at 30~40℃ and 200~300rpm with stirring. The addition time is controlled at 25~30min. The temperature is raised to 60~70℃ and stirring is continued at 300~500rpm for 3~4h. After the reaction is completed, the mixture is centrifuged at 4000~6000rpm for 10~15min at room temperature and washed 2~3 times with anhydrous ethanol. The mixture is then dried at 50~70℃ and vacuum degree -0.09~-0.1MPa for 8~10h to obtain MTMS / TEOS@modified flame retardant.

[0009] S2. The MTMS / TEOS@ modified flame retardant prepared in S1 is redispersed in 5-10 times its mass of ethanol solvent. 4%-8% (by mass) of KH-550 (MTMS / TEOS@ modified flame retardant) is added, and the pH is adjusted to 4-5 with 5%-10% (by mass) dilute acetic acid. The mixture is stirred at 40-50℃ and 200-400 rpm for 1.5-2.5 h. After the reaction, the mixture is centrifuged, washed 2-3 times with anhydrous ethanol, and dried to constant weight at 50-60℃ and a vacuum of -0.09 to -0.1 MPa to obtain KH-550@MTMS / TEOS@ modified flame retardant. The above KH-550@MTMS / TEOS@ modified flame retardant is dispersed... In anhydrous toluene, the mass ratio of anhydrous to KH-550@MTMS / TEOS@ modified flame retardant is (4~6):1. Under nitrogen protection, the temperature is raised to 60~70℃, and 5%~10% of isophorone diisocyanate (IPDI) and 0.1%~0.3% of bismuth octanoate catalyst are added. The mixture is stirred at 200~400 rpm for 2~3 h. After the reaction is completed, the mixture is filtered, washed 3~4 times with ethyl acetate, and vacuum dried at 50~60℃ and a vacuum degree of -0.09~-0.1 MPa for 6~8 h to obtain IPDI-g-KH-550@MTMS / TEOS@ modified flame retardant.

[0010] S3. By weight, dehydrate 100 parts of polyether polyol, 5-8 parts of halogen-free phosphorus-containing polyol, and 1-3 parts of resorcinol di(2-hydroxyethyl) ether at 110-120℃ and a vacuum of -0.09 to -0.1 MPa for 2-3 hours until the moisture content is below 0.05%. Cool to 60-70℃ and add 55-65 parts of isocyanate in 3-4 batches. Heat to 70-75℃ and react for 2-3 hours to obtain the prepolymer. Cool the prepolymer system to 50-60℃ and add each component in two batches under vacuum: add 8-14 parts of IPDI-g-KH... -550@MTMS / TEOS@ modified flame retardant and 6-8 parts modified expandable graphite are pre-dry mixed evenly and added to the prepolymer. Stir at 200-400 rpm for 15-20 min until evenly dispersed. Mix 8-12 parts plasticizer and 5.5-8.5 parts functional additives and add them to the mixture. Stir at a vacuum of -0.09--0.1 MPa and 200-400 rpm for 15-20 min until uniform. Add 0.5-1.0 parts catalytic system and stir at 200-300 rpm for 10-15 min until uniform to obtain the mixed component.

[0011] S4. Pour the mixed components into an aerosol can, seal it, add 50-60 parts of propellant, install the nozzle, check for leaks, and vertically cure in a constant temperature chamber at 20-25℃ for 24-48 hours to allow the system inside the can to fully react and stabilize the pressure, thus obtaining the polyurethane sealant. It should be noted that this curing step is a standard post-processing procedure for preparing aerosol can-type polyurethane sealants in this field; refer to JC / T 936-2004 "Single-component polyurethane foam sealant". Its purpose is to ensure that the components in the system inside the can are fully miscible and to balance the vapor pressure inside the can.

[0012] Preferably, the modified flame retardant is prepared by the following method: melamine cyanurate and zinc borate are atomized and sprayed into a silane coupling agent hydrolysate under stirring at 300-500 rpm. The mass ratio of melamine cyanurate, zinc borate, and silane coupling agent hydrolysate is (2.5-3):1:(2-6), and the mass ratio of KH-550:anhydrous ethanol:deionized water in the silane coupling agent hydrolysate is 1:(4-6):(1-2). The spraying time is 8-12 min. After spraying, the speed is increased to 1200-1500 rpm and stirred for 15-25 min. After the reaction is completed, the mixture is cooled to room temperature, centrifuged at 2500-3500 rpm for 10-15 min, washed 2-3 times with anhydrous ethanol, and dried at 50-70℃ and a vacuum of -0.09 to -0.1 MPa for 8-10 h to obtain the modified flame retardant.

[0013] Preferably, the polyether polyol comprises 60-70 parts PPG and 30-40 parts PTMG; the halogen-free phosphorus-containing polyol is Exolit OP 550; the isocyanate is PM-200; the catalytic system comprises 0.2-0.4 parts 2,2'-dimorpholinodiethyl ether (DMDEE), 0.2-0.4 parts organobismuth catalyst and 0.1-0.2 parts organozinc catalyst; the plasticizer is alkyl sulfonate phenyl ester; the functional additives comprise 3-4 parts latent curing agent, 1-1.5 parts foam stabilizer, 1-2 parts antioxidant and 0.5-1 part ultraviolet absorber; the propellant comprises 10-14 parts dimethyl ether and 36-46 parts propane-butane.

[0014] Preferably, the organobismuth catalyst is one or more of bismuth neodecanoate or bismuth isooctanoate; the organozinc catalyst is one or two of zinc isooctanoate or zinc neodecanoate.

[0015] Preferably, the latent curing agent is one or both of ketimine latent curing agents (ALT-403) or oxazolidine latent curing agents (ALT-101).

[0016] Preferably, the foam stabilizer is an organosilicon foam stabilizer, and is selected from one or more of the following: polyether modified polysiloxane foam stabilizer (TEGOSTAB B 8462), polyether modified polysiloxane organosilicon surfactant (IOTA 13086), and organosilicon foam stabilizer (CGY-6885).

[0017] Preferably, the antioxidant is a hindered phenolic antioxidant, and is selected from one or both of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate isooctyl ester (antioxidant 1135) or β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate octadecyl ester (antioxidant 1076).

[0018] Preferably, the ultraviolet absorber is one or both of 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (UV-571) or 2-hydroxy-4-methoxybenzophenone (UV-1).

[0019] Preferably, the modified expandable graphite is prepared by the following method: 8-12 parts of expandable graphite are preheated to 60-70°C at 500-800 rpm; KH-550 and anhydrous ethanol are mixed at a mass ratio of 1:2 to form a spray solution, wherein the mass of the spray solution is 8%-10% of the mass of the expandable graphite; the spray solution is atomized and sprayed for 5-10 minutes; after spraying, the rotation speed is increased to 1200-1500 rpm, and stirring is continued for 20-30 minutes; the material is discharged and dried at 50-70°C and a vacuum degree of -0.09 to -0.1 MPa for 4-6 hours to obtain the modified expandable graphite.

[0020] The present invention has at least one of the following technical effects: 1. The present invention forms a heat-insulating carbon layer during combustion through the synergistic condensation phase charring effect of flame retardant and modified expandable graphite, which significantly reduces the heat release rate and reduces the generation of molten droplets; at the same time, the flame retardant is anchored in the matrix by chemical bonds, which effectively delays the decay of flame retardant performance after wet heat or thermo-oxidative aging and maintains a high flame retardant level.

[0021] 2. This invention regulates the isocyanate-water reaction rate by compounding the catalytic system and introducing a latent curing agent, enabling the sealant to cure rapidly and form a uniform and stable foam structure in a wide temperature range of -10℃ to 40℃ and under different humidity conditions, thus avoiding the problems of slow curing in winter and cell collapse in summer.

[0022] 3. This invention improves the compatibility between flame retardant and polyurethane matrix through interface modification, improves its dispersion uniformity, and avoids agglomeration and sedimentation. After curing, the flame retardant is anchored in the cross-linked network, effectively solving the problems of uneven foaming and performance degradation caused by flame retardant migration and agglomeration, thereby maintaining good foaming ratio and cell uniformity in different construction seasons. Attached Figure Description

[0023] Figure 1 TEM image of IPDI-g-KH-550@MTMS / TEOS@modified flame retardant prepared in Example 1 of this invention;

[0024] Figure 2 This is a SEM image of the MTMS / TEOS@modified flame retardant prepared in Example 1 of this invention. Detailed Implementation

[0025] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for the purpose of illustrating the invention only and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0026] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0027] The triethoxysilane at one end of the KH-550 molecule hydrolyzes to generate silanol groups (Si-OH), which form hydrogen bonds / condensations with water molecules or amino groups adsorbed on the supramolecular surface of melamine cyanurate, anchoring the silane chain to the flame retardant surface. The amino group (-NH2) at the other end participates in the reaction during the subsequent MTMS / TEOS hybrid coating process, achieving stable adhesion of the silane layer. Simultaneously, the introduction of zinc borate can synergistically catalyze char formation with melamine cyanurate during combustion, improving the density of the char layer.

[0028] Using MTMS and TEOS as precursors, a hybrid sol containing a Si-O-Si network structure is formed by hydrolysis and condensation under acidic conditions. A surface-modified flame retardant is dispersed in an ethanol / water system. After the hybrid sol is added dropwise, the sol particles are deposited on the flame retardant surface through electrostatic adsorption and hydrogen bonding, and further condense during subsequent heating to form a dense MTMS / TEOS organic-inorganic hybrid shell. MTMS provides organic methyl groups (-CH3), imparting hydrophobicity and flexibility to the shell; TEOS provides more silanol crosslinking sites, enhancing the thermal stability and structural strength of the shell. The modified flame retardant surface is exposed with amino groups (-NH2) due to the KH-550 treatment in step S1. These amino groups can undergo condensation reactions with the silanol groups (Si-OH) in the MTMS / TEOS hybrid sol, thereby guiding the sol particles to preferentially deposit on the flame retardant surface and inhibiting the self-nucleation phenomenon of the sol particles.

[0029] The MTMS / TEOS hybrid shell, formed by the hydrolysis of KH-550 and the residual silanol groups on its surface, undergoes a condensation reaction with the silanol groups on the shell surface, thereby introducing amino groups into the shell surface. The MTMS / TEOS hybrid shell is an organic-inorganic hybrid network structure formed by the sol-gel polymerization of MTMS and TEOS, containing numerous uncondensed silanol (Si-OH) active sites on its surface. During the secondary KH-550 treatment, the silanol groups generated by KH-550 hydrolysis condense with the residual Si-OH groups on the hybrid shell surface, introducing amino groups into the shell surface, achieving secondary amino modification and increasing the surface amino density. Simultaneously, in the alcohol-water-acid system, the shell surface may undergo slight swelling or etching, exposing more reactive sites in the inner layer, further promoting the introduction of amino groups. Under combustion conditions, this hybrid network undergoes thermal condensation. After the methyl side groups oxidize and decompose at high temperatures, the silanol groups in the network further cross-link and condense, forming a dense silicon-oxygen network layer that provides thermal insulation and flame retardancy. The molecular-level permeability of the shell at room temperature and the densification transformation at high temperature are not contradictory—the former serves secondary modification during the preparation process, while the latter serves flame-retardant functionality under combustion conditions. The two isocyanate groups (-NCO) in the isophorone diisocyanate (IPDI) molecule have different reactivity. Under the action of an organobismuth catalyst, the primary -NCO of IPDI preferentially reacts with the -NH2 introduced by KH-550 to form a urea bond. This reaction is a classic nucleophilic addition reaction between isocyanate and primary amine, and under the aforementioned reaction conditions (60~70℃, organobismuth catalysis), it is a necessary chemical transformation, thereby anchoring IPDI to the flame retardant surface. The less reactive secondary -NCO (isocyanate group attached to cyclohexane) in the IPDI molecule is not consumed due to steric hindrance and remains on the flame retardant surface as a free isocyanate group. During subsequent moisture curing, the secondary -NCO participates in the cross-linking reaction in the presence of moisture, achieving chemical bonding between the flame retardant and the polyurethane matrix.

[0030] It should be noted that although the reaction rate of the remaining secondary-NCO after IPDI grafting with the polyol hydroxyl groups is extremely low during the prepolymer mixing stage (50~60℃), in order to avoid potential urethane ester side reactions between the large amount of free-NCO and secondary-NCO in the system under long-term heating or local overheating conditions, this application strictly controls the addition of the organic bismuth catalyst after the flame retardant and filler are evenly dispersed, and the prepolymer mixing temperature never exceeds 60℃. This ensures the feasibility of the process while suppressing the occurrence of side reactions to the greatest extent and ensuring the chemical stability of the grafted structure during storage in the tank.

[0031] After hydrolysis, KH-550 reacts with a small number of oxygen-containing functional groups (-OH, -COOH) on the graphite surface, introducing amino groups into the graphite flakes, improving its compatibility with non-polar polyurethane prepolymers, while reducing the hygroscopicity of the graphite surface and improving long-term storage stability.

[0032] Polyether polyols (PPG / PTMG) react with isocyanates (PM-200) to form prepolymers with terminal isocyanate groups, providing reactivity for subsequent moisture curing. IPDI-g-KH-550@MTMS / TEOS@modified flame retardant is pre-dry-mixed with modified expandable graphite to ensure uniform contact between the two powders with different morphologies and flame-retardant mechanisms, facilitating the formation of a gradient char layer with a dense inner layer and an expanded outer layer during combustion. DMDEE, a sterically hindered tertiary amine catalyst, exhibits high catalytic activity at low temperatures, effectively promoting curing reactions under low-temperature conditions. Organobismuth primarily catalyzes the reaction between hydroxyl groups and isocyanates, exhibiting mid-temperature equilibrium catalytic characteristics. Organozinc, as a slower gel and crosslinking catalyst, reduces the acidity of the system and promotes the crosslinking reaction. The three components synergistically maintain a suitable curing rate over a wide temperature range of -10℃ to 40℃. The latent curing agent preferentially reacts with water to generate active amines under low-temperature, high-humidity conditions, promoting isocyanate curing.

[0033] In the IPDI-g-KH-550@MTMS / TEOS@ modified flame retardant, the remaining -NCO groups after IPDI molecule grafting are secondary -NCO, whose reactivity is significantly lower than primary -NCO, and their steric hindrance effect is more pronounced. During the prepolymer mixing step, the system temperature is controlled at 50~60℃, and the polyol has been pre-dehydrated to a moisture content below 0.05%. Under these conditions, the reaction rate between free secondary -NCO and the polyol hydroxyl groups is extremely low, maintaining chemical stability during processing. Simultaneously, organic bismuth is added only after the flame retardant and modified expandable graphite are uniformly dispersed, avoiding direct contact with -NCO during the prepolymer mixing stage, further preventing side reactions. When the sealant is sprayed from the aerosol can and comes into contact with moisture, the secondary -NCO participates in the crosslinking reaction in the presence of moisture, anchoring the flame retardant within the polyurethane crosslinking network.

[0034] Example

[0035] Example 1

[0036] S1. Preheat 15g of melamine cyanurate and 5g of zinc borate to 35℃ with stirring at 400rpm to obtain a mixed powder. Prepare a silane coupling agent hydrolysate: take 2.0g of KH-550, 10.0g of anhydrous ethanol, and 3.0g of deionized water, mix them evenly, and adjust the pH to 4.5 with 8% dilute acetic acid. Atomize the silane coupling hydrolysate into the above mixed powder and spray for 10min. After spraying, increase the speed to 1300rpm and stir for 20min. After the reaction is complete, cool to room temperature, centrifuge at 3000rpm for 12min, wash three times with anhydrous ethanol, and dry at 60℃ and vacuum degree -0.095MPa for 9h to obtain the modified flame retardant.

[0037] S2. Take 10g of modified flame retardant and disperse it in 25g of 80% ethanol solvent to obtain a modified flame retardant dispersion. Dissolve 9g of MTMS and 6g of TEOS in 37.5g of the same ethanol solvent, adjust the pH to 6.0 with 8% dilute nitric acid, and hydrolyze for 40min at 50℃ and 300rpm to form an MTMS / TEOS hybrid sol. Add the above modified flame retardant dispersion dropwise to the above MTMS / TEOS hybrid sol at 35℃ and 250rpm with stirring for 30min. Raise the temperature to 65℃ and continue stirring at 400rpm for 3.5h. After the reaction is complete, centrifuge at 5000rpm for 12min at room temperature and wash three times with anhydrous ethanol. Dry at 60℃ and vacuum degree -0.095MPa for 9h to obtain MTMS / TEOS@modified flame retardant.

[0038] S3. Disperse 10g of MTMS / TEOS@ modified flame retardant in 50g of 80% ethanol solvent, add 0.6g of KH-550, adjust the pH to 4.5 with 8% dilute acetic acid, and stir the mixture at 45℃ and 300rpm for 2h. After the reaction, centrifuge, wash three times with anhydrous ethanol, and dry to constant weight at 55℃ and -0.095MPa vacuum to obtain KH-550@MTMS / TEOS@ modified flame retardant. Disperse 9g of the above KH-550@MTMS / TEOS@ modified flame retardant in 45g of anhydrous toluene, heat to 65℃ under nitrogen protection, and add 0.9g of... IPDI and 0.0225 g of bismuth octanoate catalyst were stirred at 300 rpm for 2.5 h. After the reaction was completed, the mixture was filtered, washed four times with ethyl acetate, and vacuum dried at 55 °C and -0.095 MPa for 7 h to obtain IPDI-g-KH-550@MTMS / TEOS@modified flame retardant.

[0039] S4. Preheat 10g of expandable graphite to 65℃ at 600rpm. Prepare a spray solution: mix 0.3g of KH-550 and 0.6g of anhydrous ethanol evenly. Atomize the spray solution and spray it into the expandable graphite for 8min. After spraying, increase the speed to 1300rpm and continue stirring for 25min. Discharge the material and dry it at 60℃ and vacuum degree -0.095MPa for 5h to obtain modified expandable graphite.

[0040] S5. By weight, 100 parts of polyether polyol, 6.5 parts of halogen-free phosphorus-containing polyol, and 2 parts of resorcinol di(2-hydroxyethyl) ether are dehydrated at 115°C and a vacuum of -0.095 MPa for 2.5 hours until the moisture content is below 0.05%. The temperature is then lowered to 65°C, and 60 parts of isocyanate are added in four batches. The mixture is then heated to 72°C and reacted for 2.5 hours to obtain the prepolymer. In this embodiment, the NCO mass fraction of the prepolymer is controlled to be 18%~22%, and the NCO / OH molar ratio is 1.2~1.5:1 to ensure complete subsequent moisture curing and sufficient formation. The crosslinking density was determined. The prepolymer system was cooled to 55°C, and each component was added in two batches under vacuum: 14 parts of IPDI-g-KH-550@MTMS / TEOS@modified flame retardant and 8 parts of modified expandable graphite were pre-dry mixed evenly. The dry mixing operation was carried out in an environment with relative humidity ≤30% and the mixing time did not exceed 5 min. The mixture was added to the prepolymer and stirred for 18 min under vacuum of -0.095 MPa and 300 rpm until evenly dispersed. 10 parts of alkyl sulfonate, 4 parts of ALT-403, 1.2 parts of TEGOSTAB B 8462, 1.5 parts of antioxidant 1135 and 0.8 parts of UV-571 were mixed and added, and stirred at 300 rpm for 18 min until uniform. 0.35 parts of DMDEE, 0.35 parts of bismuth neodecanoate and 0.2 parts of zinc isooctanoate were added and stirred at 250 rpm for 12 min until uniform to obtain the mixed component.

[0041] S6. Pour the mixed components into an aerosol can, seal it, add 14 parts dimethyl ether and 46 parts propane and butane, install the nozzle, check for leaks, and vertically stand in a constant temperature chamber at 23°C for 36 hours to allow the system inside the can to fully react and stabilize the pressure, thus obtaining polyurethane sealant.

[0042] Example 2

[0043] The difference from Example 1 is that in S5, the modified flame retardant IPDI-g-KH-550@MTMS / TEOS@ is 11 parts and the modified expandable graphite is 7 parts, while the rest of the preparation steps are the same as in Example 1.

[0044] Example 3

[0045] The difference from Example 1 is that in S5, the amount of IPDI-g-KH-550@MTMS / TEOS@modified flame retardant is 8 parts, the amount of modified expandable graphite is 6 parts, and the rest of the preparation steps are the same as in Example 1.

[0046] Example 4

[0047] The difference from Example 1 is that in S2, MTMS is 7.5g and TEOS is 7.5g, while the rest of the preparation steps are the same as in Example 1.

[0048] Example 5

[0049] The difference from Example 1 is that in S2, MTMS is 10g and TEOS is 5g, while the rest of the preparation steps are the same as in Example 1.

[0050] Example 6

[0051] The difference from Example 1 is that in S1, melamine cyanurate is 14.3g and zinc borate is 5.7g, while the rest of the preparation steps are the same as in Example 1.

[0052] Example 7

[0053] The difference from Example 1 is that the amount of IPDI added in S3 is 0.72g, and the rest of the preparation steps are the same as in Example 1.

[0054] Example 8

[0055] The difference from Example 1 is that the amount of IPDI added in S3 is 0.45g, and the rest of the preparation steps are the same as in Example 1.

[0056] Example 9

[0057] The difference from Example 1 is that: in S5, DMDEE is 0.2 parts, bismuth neodecanoate is 0.4 parts, and zinc isooctanoate is 0.2 parts; in S6, dimethyl ether is 15 parts and propane is 45 parts; the remaining preparation steps are the same as in Example 1.

[0058] Example 10

[0059] The difference from Example 1 is that: in S5, DMDEE is 0.4 parts, bismuth neodecanoate is 0.2 parts, and zinc isooctanoate is 0.2 parts; in S6, dimethyl ether is 12 parts and propane is 43 parts; the remaining preparation steps are the same as in Example 1.

[0060] Comparative Example

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the IPDI-g-KH-550@MTMS / TEOS@modified flame retardant in S5 is replaced with an equal mass of modified flame retardant, and the remaining preparation steps are the same as in Example 1.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that the IPDI-g-KH-550@MTMS / TEOS@ modified flame retardant in S5 is replaced with an equal mass of MTMS / TEOS@ modified flame retardant, and the remaining preparation steps are the same as in Example 1.

[0065] Comparative Example 3

[0066] The difference from Example 1 is that the IPDI-g-KH-550@MTMS / TEOS@modified flame retardant in S5 is replaced with an equal mass of IPDI-g-KH-550@modified flame retardant, that is, the modified flame retardant is directly grafted with KH-550 and IPDI, and the remaining preparation steps are the same as in Example 1.

[0067] Comparative Example 4

[0068] The difference from Example 1 is that the IPDI-g-KH-550@MTMS / TEOS@modified flame retardant in S5 is replaced with an equal mass of IPDI-g-KH-550@MTMS@modified flame retardant, that is, only MTMS is used to coat the modified flame retardant, and the rest of the preparation steps are the same as in Example 1.

[0069] Comparative Example 5

[0070] The difference from Example 1 is that the IPDI-g-KH-550@MTMS / TEOS@modified flame retardant in S5 is replaced with an equal mass of IPDI-g-KH-550@TEOS@modified flame retardant, that is, only TEOS is used to coat the modified flame retardant, and the rest of the preparation steps are the same as in Example 1.

[0071] Comparative Example 6

[0072] The difference from Example 1 is that only 0.45 parts of DMDEE and 0.45 parts of bismuth neodecanoate are added in S5, and the rest of the preparation steps are the same as in Example 1.

[0073] Comparative Example 7

[0074] The difference from Example 1 is that only 0.9 parts of DMDEE are added in S5, and the rest of the preparation steps are the same as in Example 1.

[0075] Comparative Example 8

[0076] The difference from Example 1 is that the modified expandable graphite in S5 is replaced with an equal mass of IPDI-g-KH-550@MTMS / TEOS@modified flame retardant, and the remaining preparation steps are the same as in Example 1.

[0077] Comparative Example 9

[0078] The difference from Example 1 is that IPDI-g-KH-550@MTMS / TEOS@modified flame retardant and modified expandable graphite are not added in step S5, while the rest of the preparation steps are the same as in Example 1.

[0079] The polyurethane sealants prepared in Examples 1-10 and Comparative Examples 1-9 were tested for oxygen index, wide temperature range (-10℃, 5℃, 23℃, 40℃) curing time, volume water absorption, tensile strength, compressive strength, bond strength, closed cell ratio, thermo-oxidative aging, and ultraviolet aging performance. The results are shown in Tables 1 and 2.

[0080] Performance Test 1

[0081] The oxygen index was determined according to GB / T 2406.2-2009. After the sealant was cured, it was cut into strips of 80mm×10mm×10mm. The oxygen concentration was adjusted step by step in an oxygen-nitrogen mixed gas flow using the "rise-fall method". The combustion behavior of the samples was observed and the oxygen index was calculated to an accuracy of 0.1%.

[0082] Performance Test 2

[0083] Curing time (total drying time) is determined according to the test principle of GB / T 13477.22-2022 (steel needle indentation method). Taking into account the characteristics of foamed sealant, the sealant is sprayed onto the substrate to form a strip (uniform size Φ20mm×20mm). It is then immediately placed in a constant temperature and humidity chamber with a set temperature (-10℃, 5℃, 23℃ or 40℃) and (50±5)%RH. The time required for the surface to become non-sticky and the interior to be completely hardened is determined by the steel needle indentation method.

[0084] Performance Test 3

[0085] The volumetric water absorption rate was determined according to GB / T 8810-2005. The cured foam was cut into 50mm×50mm×25mm samples, dried and weighed, and then immersed in distilled water at (23±2)℃ for 96h. After draining the surface moisture, the samples were weighed and the water absorption rate was calculated.

[0086] Performance Test 4

[0087] The tensile strength was determined according to GB / T 9641-2025. The cured foam was cut into dumbbell-shaped specimens and stretched at a rate of (5±1) mm / min until fracture. The maximum load was recorded and the tensile strength was calculated.

[0088] Performance Test 5

[0089] The compressive strength was determined according to GB / T 8813-2020. The cured foam was cut into 50mm×50mm×50mm cubic specimens and compressed at a rate of (5±1)mm / min until yield or relative deformation ≥10%. The maximum load was recorded and the compressive strength was calculated.

[0090] Performance Test 6

[0091] The bonding strength was determined according to GB / T 13477.8-2017. The sealant was injected between two parallel substrates to form a bonding specimen. After curing for 7 days under standard conditions, the specimen was stretched at a rate of (5±1) mm / min until failure. The maximum load was recorded and the bonding strength was calculated.

[0092] Performance Test 7

[0093] The closed-cell ratio was determined according to GB / T 10799-2008, using the helium expansion method and a true density analyzer to measure the closed-cell volume, and then calculated based on the apparent volume.

[0094] Performance Test 8

[0095] Thermo-oxidative aging (humid heat aging) is performed according to ISO 2440:2019. The sample is placed at 70℃±2℃ and 95%RH±5% for 22h. After adjustment, the tensile strength and oxygen index are measured. The retention rate (%) = (performance value after humid heat aging / performance value before humid heat aging) × 100%.

[0096] Performance Test 9

[0097] UV aging was performed according to GB / T 16422.3-2022, using UVB-313 lamps (irradiance 0.6W / m²). 2 @310nm), 8h of light exposure / 4h of condensation cycle, total 72h of aging, after which tensile strength and oxygen index were measured. Retention rate (%) = (performance value after UV aging / performance value before UV aging) × 100%.

[0098] Performance Test 10

[0099] Storage stability (settling rate) is determined according to Appendix B of JC / T 936-2004. After standing vertically for 24 hours, the complete aerosol can is shaken thoroughly and the initial solid content is measured. After standing vertically for 30 days, a sample is taken from the bottom of the can to measure the solid content. The sedimentation rate is calculated as (initial solid content - solid content after sedimentation) / initial solid content × 100%.

[0100] Table 1 Performance test results of Examples 1-10

[0101]

[0102] Table 2 Performance test results of Comparative Examples 1-9

[0103]

[0104] As can be seen from Examples 1-3, when the total amount of IPDI-g-KH-550@MTMS / TEOS@modified flame retardant and modified expandable graphite decreases sequentially, the initial oxygen index, the oxygen index after thermo-oxidative aging, and the oxygen index after UV aging all show a decreasing trend; the tensile strength shows an increasing trend, while the compressive strength, bond strength, and closed-cell rate all show a decreasing trend; the storage stability deteriorates; the curing time at -10℃ and 5℃ shows a shortening trend, while the curing time at 40℃ shows a lengthening trend, and the curing time at 23℃ does not show an obvious monotonic change pattern (first shortening and then lengthening).

[0105] A comparison of Examples 4, 1, and 5 shows that when the MTMS:TEOS mass ratio increases from 1:1 to 1.5:1, the oxygen index increases; when it continues to increase to 2:1, the oxygen index decreases. This indicates that when the MTMS:TEOS ratio is 1.5:1, the hybrid network exhibits both good compatibility and thermal stability, resulting in better flame retardant efficiency.

[0106] A comparison of Example 6 and Example 1 shows that when the mass ratio of MCA to zinc borate decreases from 3:1 to 2.5:1, the oxygen index decreases, the compressive strength, bond strength, and closed-cell rate decrease slightly, while the tensile strength increases slightly.

[0107] A comparison of Examples 7 and 8 with Example 1 shows that as the IPDI grafting amount decreased from 10% to 8% and then to 5%, the oxygen index (including after aging) decreased, as did the compressive strength, bond strength, and closed-cell rate; storage stability deteriorated; curing time at each test temperature increased; while tensile strength increased. This indicates that a higher grafting amount results in a stronger chemical anchoring effect and superior flame retardant migration resistance and overall performance.

[0108] The comparison between Example 9 and Example 1, and between Example 10 and Example 1, shows that by adjusting the ratio of the catalytic system and the composition of the propellant, the curing speed at different temperatures can be directionally controlled: the curing time of Example 9 at each test temperature was longer than that of Example 1, indicating that reducing the amount of DMDEE can slow down the overall reaction rate, which is suitable for construction in high-temperature seasons or scenarios where long operation time is required; the curing time of Example 10 at each test temperature was shorter than that of Example 1, indicating that increasing the amount of DMDEE can significantly accelerate curing, which is suitable for construction in low-temperature seasons or scenarios where rapid shaping is required; the oxygen index of the three examples did not have obvious abrupt changes, and the tensile strength, compressive strength, and aging retention rate were basically the same.

[0109] A comparison of Examples 1-10 with Comparative Examples 1-9 shows that: omitting any step in the MTMS / TEOS hybrid coating and IPDI grafting, using only a single-component shell, lacking the organozinc or organobismuth catalyst in the ternary catalytic system, or not using modified expandable graphite, will not simultaneously achieve the comprehensive level of this invention in terms of flame retardancy rating, flame retardancy retention rate after thermo-oxidative / ultraviolet aging, wide-temperature-range curing speed, storage stability, and mechanical properties.

[0110] TEM images of the prepared IPDI-g-KH-550@MTMS / TEOS@modified flame retardant are shown below. Figure 1 As shown, the core-shell structure is clear; the SEM image of the prepared MTMS / TEOS@modified flame retardant is shown below. Figure 2 As shown, the surface coating layer is complete and dense.

[0111] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0112] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a polyurethane sealant, characterized in that, Includes the following steps: S1. Dissolve MTMS and TEOS in an ethanol solvent at a mass ratio of (1~2):1, wherein the mass ratio of anhydrous ethanol to deionized water in the ethanol solvent is 4:1, and the mass ratio of the ethanol solvent to the total mass of MTMS and TEOS is (2~3):

1. Adjust the pH to 5.5~6.5 and stir for 30~45 min to form an MTMS / TEOS hybrid sol. Disperse the modified flame retardant in an ethanol solvent of 2~3 times its mass, wherein the mass ratio of the modified flame retardant to the total mass of MTMS and TEOS is 1:(1.5~2.5). Slowly add the above MTMS / TEOS hybrid sol dropwise while stirring, and continue stirring with the temperature increased. After the reaction is complete, centrifuge, wash, and dry to obtain MTMS / TEOS@modified flame retardant. S2. The MTMS / TEOS@ modified flame retardant prepared in S1 is redispersed in 5-10 times its mass of ethanol solvent. 4%-8% of KH-550 (by mass of MTMS / TEOS@ modified flame retardant) is added, the pH is adjusted to 4-5, and the mixture is stirred for 1.5-2.5 hours. After the reaction is complete, the mixture is centrifuged, washed, and dried to constant weight to obtain KH-550@MTMS / TEOS@ modified flame retardant. KH-550@MTMS / TEOS@ modified flame retardant was dispersed in 4-6 times its mass of anhydrous toluene. Under nitrogen protection, the temperature was raised to 60-70℃, and 5%-10% of IPDI and 0.1%-0.3% of bismuth octanoate catalyst by mass of KH-550@MTMS / TEOS@ modified flame retardant were added. The mixture was stirred and reacted for 2-3 hours. After the reaction was completed, the mixture was filtered, washed, and dried to obtain IPDI-g-KH-550@MTMS / TEOS@ modified flame retardant. S3. By weight, 100 parts of polyether polyol, 5-8 parts of halogen-free phosphorus-containing polyol, and 1-3 parts of resorcinol di(2-hydroxyethyl) ether are dehydrated to a moisture content of less than 0.05% at 110-120℃ and a vacuum of -0.09 to -0.1 MPa. The mixture is then cooled to 60-70℃, and 55-65 parts of isocyanate are added. The mixture is heated to 70-75℃ and reacted for 2-3 hours to obtain a prepolymer. The prepolymer system is cooled to 50-60℃, and 8-14 parts of IPDI-g-KH-550@MTMS / TEOS@ modified flame retardant and 6-8 parts of modified expandable graphite are added under vacuum and stirred until uniformly dispersed. 8-12 parts of plasticizer and 5.5-8.5 parts of functional additives are mixed and added, and stirred until uniform. 0.5-1.0 parts of catalytic system are added and stirred until uniform to obtain a mixed component. S4. Pour the mixed components into an aerosol can, seal it, add 50-60 parts of propellant, install the nozzle, check for leaks, and allow it to mature to obtain polyurethane sealant.

2. The method for preparing a polyurethane sealant according to claim 1, characterized in that, The modified flame retardant is prepared by the following method: melamine cyanurate and zinc borate are atomized and sprayed into a silane coupling agent hydrolysate under stirring. The mass ratio of melamine cyanurate, zinc borate and silane coupling agent hydrolysate is (2.5~3):1:(2~6). The mass ratio of KH-550, anhydrous ethanol and deionized water in the silane coupling agent hydrolysate is 1:(4~6):(1~2). After spraying, the rotation speed is increased to 1200~1500 rpm and stirred for 15~25 min. After the reaction is completed, the mixture is cooled to room temperature, centrifuged, washed and dried to obtain the modified flame retardant.

3. The method for preparing a polyurethane sealant according to claim 1, characterized in that, The polyether polyol comprises 60-70 parts PPG and 30-40 parts PTMG; the halogen-free phosphorus-containing polyol is Exolit OP 550; the isocyanate is PM-200; the catalytic system comprises 0.2-0.4 parts DMDEE, 0.2-0.4 parts organic bismuth catalyst, and 0.1-0.2 parts organic zinc catalyst; the plasticizer is alkyl sulfonate phenyl ester; the functional additives comprise 3-4 parts latent curing agent, 1-1.5 parts foam stabilizer, 1-2 parts antioxidant, and 0.5-1 part ultraviolet absorber; the propellant comprises 10-14 parts dimethyl ether and 36-46 parts propane-butane.

4. The method for preparing a polyurethane sealant according to claim 3, characterized in that, The organobismuth catalyst is one or both of bismuth neodecanoate and bismuth isooctanoate; the organozinc catalyst is one or both of zinc isooctanoate and zinc neodecanoate.

5. The method for preparing a polyurethane sealant according to claim 3, characterized in that, The latent curing agent is one or both of ALT-403 or ALT-101.

6. The method for preparing a polyurethane sealant according to claim 3, characterized in that, The foam stabilizer is an organosilicon foam stabilizer, specifically one or more of TEGOSTAB B 8462, IOTA 13086, and CGY-6885.

7. The method for preparing a polyurethane sealant according to claim 3, characterized in that, The antioxidant is one or both of antioxidant 1135 and antioxidant 1076.

8. The method for preparing a polyurethane sealant according to claim 3, characterized in that, The ultraviolet absorber is one or both of UV-1 or UV-571.

9. The method for preparing a polyurethane sealant according to claim 1, characterized in that, The modified expandable graphite is prepared by the following method: 8-12 parts of expandable graphite are preheated to 60-70°C at 500-800 rpm, KH-550 and anhydrous ethanol are mixed at a mass ratio of 1:2 to form a spray solution, the mass of which is 8%-10% of the mass of expandable graphite, and sprayed into the solution. After spraying, the rotation speed is increased to 1200-1500 rpm, stirring is continued, and the solution is discharged and dried to obtain the modified expandable graphite.

Images