A high-density closed-cell structured polyurethane and its use in earplugs or earmuffs

Abstract

This invention discloses a high-density closed-cell polyurethane structure and its application in earplugs or earmuffs, belonging to the field of polymer materials technology. By weight, it comprises the following components: 30-40 parts of polyether polyol I, 10-20 parts of polyether polyol II, 5-15 parts of chain extender, 1-3 parts of organosilicon surfactant, 1-3 parts of hydrophobic silica, 8-15 parts of foaming agent, 19-42 parts of polymethylene polyphenyl polyisocyanate, 8-12 parts of pyridine-amide-terminated diisocyanate, and 6-10 parts of ureidopyrimidinone diisocyanate. Compared with existing technologies, the polyurethane earplugs of this invention have excellent overall performance; the self-healing network and rigid closed-cell foam wall structure work synergistically, exhibiting good repeatability and suitability for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a high-density closed-cell polyurethane and its application in earplugs or earmuffs. Background Technology

[0002] Polyurethane materials are widely used in the manufacture of personal protective equipment such as earplugs and earmuffs, as well as consumer electronics products, due to their good mechanical properties, adjustable hardness and elasticity, good biocompatibility and convenient processing and molding characteristics. There are three main methods for preparing traditional polyurethane earplugs: Cast polyurethane preparation uses a two-step or prepolymer method, mixing liquefied diisocyanate with polyols and chain extenders, followed by injection molding and heating to cure, resulting in dense, highly elastic products. However, this method suffers from high density, poor wearing comfort, and often features open or interconnected pore structures, leading to insufficient sound wave blocking at specific frequencies. Compression molding foaming involves adding one or more chemical or physical foaming agents, utilizing their thermal decomposition or vaporization to form pores and prepare low-density foam earplugs. However, the pore structure is difficult to control precisely, easily leading to poor product resilience and insufficient durability. Introducing functional fillers can also damage the pore walls, causing uneven performance or failure. Water-based foaming uses the reaction of isocyanate with water to generate carbon dioxide as the foaming source. This process is environmentally friendly, but the reaction is violent and difficult to control. The resulting products often have a hydrophilic open-pore structure, poor hydrolysis resistance and dimensional stability, making them unsuitable for long-term use in humid environments.

[0003] Traditional preparation methods have significant technical bottlenecks: First, it is difficult to balance performance, making it hard to simultaneously achieve synergistic optimization of low density, high resilience, high closed-cell ratio, and sufficient structural strength. High closed-cell structures are often accompanied by increased hardness and decreased resilience. Second, functional integration is difficult. Functional fillers are prone to migration and detachment, interfering with foaming and matrix mechanical properties. Self-healing components have poor compatibility with the polyurethane matrix, and some require external stimulation to achieve repair, making them unsuitable for everyday earplugs and reducing the initial strength of the material. Third, the process controllability is poor. The multi-step synthesis and post-processing are complex, which is not conducive to large-scale production. Precise control of the cell structure and dispersion of functional components is difficult, resulting in a low product yield. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a high-density closed-cell polyurethane and its application in earplugs or earmuffs. The high-density closed-cell polyurethane of the present invention has a density of 130~200 kg / m³.

[0005] The technical solution for achieving the objective of this invention is as follows: A high-density closed-cell polyurethane, comprising the following components by weight: 30-40 parts of polyether polyol I, 10-20 parts of polyether polyol II, 5-15 parts of chain extender, 1-3 parts of organosilicon surfactant, 1-3 parts of hydrophobic silica, 8-15 parts of foaming agent, 19-42 parts of polymethylene polyphenyl polyisocyanate, 8-12 parts of pyridine-amide-terminated diisocyanate, and 6-10 parts of ureidopyrimidinone diisocyanate.

[0006] Specifically, the polyether polyol I is selected from one or more of polytetrahydrofuran ether diol, polypropylene glycol, and polypropylene triol; the polyether polyol II is selected from one or two of polypropylene glycol and polyethylene glycol; the chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, diethylene glycol, and neopentyl glycol; the foaming agent is selected from one or more of cyclopentane, cyclohexane, and isopentane; the organosilicon surfactant is selected from organosilicon-polyether copolymer surfactants; the hydrophobic silica is treated with a silane coupling agent before use; and the silane coupling agent is selected from one or two of hydroxysilane coupling agents and aminosilane coupling agents.

[0007] The method for preparing the pyridine-amide-terminated diisocyanate includes the following steps: 4-Aminomethylbenzyl alcohol and pyridine-2,6-dicarboxylic acid were mixed and reacted in the presence of a condensing agent and a catalyst to obtain a diol product. The diol product was then dissolved in a dry organic solvent and slowly added dropwise to a diisocyanate. Subsequently, dibutyltin dilaurate was added, and after the reaction was completed, the product was purified to obtain a pyridine-amide-terminated diisocyanate.

[0008] Specifically, the condensing agent is selected from 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; the catalyst is selected from 4-dimethylaminopyridine; the molar ratio of 4-aminomethylbenzyl alcohol to pyridine-2,6-dicarboxylic acid is (2.05~2.2):1; the amount of diisocyanate used is 2.0~2.5 times relative to the amount of 5-diol product; the diisocyanate is selected from one or more of 1,6-hexyl diisocyanate, 1,5-pentyl diisocyanate, and 1,4-butane diisocyanate; and the amount of dibutyltin dilaurate used is 0.1%~0.5% of the total mass of the reaction system.

[0009] The preparation method of the ureidopyrimidinone diisocyanate includes the following steps: 2-Acetylbutyrolactone and guanidine carbonate were dissolved in anhydrous ethanol to prepare a 1.0 mol / L solution. An alkaline catalyst was added, and the mixture was heated under reflux. After the reaction was completed, the solution was purified to obtain 5-(2-hydroxyethyl)-6-methyl-2-aminouracil, which was then mixed with diisocyanate and pyridine. The reaction mixture was heated and stirred, and after the reaction was completed, the solution was purified to obtain ureidylpyrimidinone diisocyanate.

[0010] Specifically, the base catalyst is selected from triethylamine, and the amount of the base catalyst is twice the amount of 2-acetylbutyrolactone; the diisocyanate is selected from one or more of 1,6-hexyl diisocyanate, 1,5-pentyl diisocyanate, and 1,4-butane diisocyanate; the amount of hexyl diisocyanate is 2.0 to 3.0 times the amount of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil; and the amount of pyridine is 10% of the volume of the diisocyanate.

[0011] A method for preparing a high-density closed-cell polyurethane earplug includes the following steps: Preparation of S1.A component: Mix 30-40 parts of polyether polyol I and 10-20 parts of polyether polyol II and dehydrate. Under stirring, add 5-15 parts of chain extender, 1-3 parts of organosilicon surfactant, 1-3 parts of hydrophobic silica, and 8-15 parts of foaming agent in sequence. After mixing evenly, seal and preheat for later use. Preparation of S2.B component: Preheat 19-42 parts of polymethylene polyphenyl polyisocyanate; grind 6-10 parts of ureidinone diisocyanate and pass through a 200-mesh sieve, then slowly add it to the polymethylene polyphenyl polyisocyanate while simultaneously shearing at high speed; preheat 8-12 parts of pyridine-amide-terminated diisocyanate; mix the preheated pyridine-amide-terminated diisocyanate with the mixture of polymethylene polyphenyl polyisocyanate and ureidinone diisocyanate from the previous step, and form a homogeneous component B at 35-45°C; maintain component B at 35-45°C and immediately proceed to the next foaming step; S3. Foaming and Molding: Ensure that the temperature of component A is 30~40℃ and the temperature of component B is 35~45℃. Quickly pour component B into component A. Immediately use a high-speed mixer to vigorously stir at a speed of 4500~5000 rpm for 20~30 seconds. Stop stirring when the liquid turns white and begins to expand in volume. Quickly pour the mixture into an earplug mold preheated to 50~60℃ and close the mold. Immediately transfer the mold to an oven at 65~75℃ for normal pressure curing. S4. Post-processing: After curing, demold the polyurethane foam earplugs and remove the initial product; place the product in a vacuum oven; close the oven and allow it to cool naturally to room temperature to obtain high-density closed-cell polyurethane earplugs.

[0012] Specifically, the vacuum oven conditions in step S4 are set to 70~80℃ and vacuum degree ≤1 mbar.

[0013] Another object of the present invention is to protect the use of polyurethane earplugs made from polyurethane with the above-mentioned high-density closed-cell structure as raw material, or polyurethane earplugs with the high-density closed-cell structure prepared by the above-mentioned method for preparing polyurethane earplugs with the above-mentioned high-density closed-cell structure in earplugs or earmuffs.

[0014] The core mechanism behind the superior performance of the material in this invention lies in the synergy of its structure: 1. Construction of a dynamic reversible crosslinking network: Uriidine pyrimidinone diisocyanate and pyridine-amide-terminated diisocyanate were used as functionalized isocyanate components and reacted with a polyol system. In the formed polyurethane hard segments, the uridine pyrimidinone units form physical crosslinking points through extremely strong quadruple hydrogen bonds, providing good toughness, elasticity, and self-healing driving force; the pyridine-amide units can contribute to the dynamic network through coordination or π-π stacking.

[0015] 2. Stable Closed-Cell Structure and Functional Locking: During the one-step foaming process, the cells formed by the vaporization of the physical blowing agent are encapsulated by the rapidly gelling polyurethane melt. The presence of the dynamic network increases the melt strength, effectively preventing cell merging or collapse, and facilitating the formation of a uniform, stable, and highly closed-cell structure. Simultaneously, all functional groups are chemically bonded to the cell walls, preventing migration and leakage.

[0016] 3. Performance synergy and enhancement: (1) Self-repair: When the material is damaged, the non-covalent interaction of the ureidopyrimidinone quadruple hydrogen bond and the pyridine-amide unit in the damaged area can undergo reversible dissociation and recombination, thereby reshaping the microstructure and repairing the macroscopic damage.

[0017] (2) Sound insulation and resilience: The high closed-cell structure can effectively dissipate sound wave energy and provide good sound insulation performance. The dynamic network gives the material high resilience and fatigue resistance.

[0018] In summary, by resolving the technical contradictions in performance balance, functional integration, and process controllability of traditional polyurethane earplug materials, this invention provides a novel preparation method for high-density closed-cell functionalized polyurethane earplugs.

[0019] Beneficial effects

[0020] The high-density closed-cell functionalized polyurethane and its preparation method provided by this invention have the following advantages compared with the prior art: 1. Excellent overall performance: Through a one-step foaming process and specific formulation design, a polyurethane material with a dense, uniform cell structure and high closed-cell rate is obtained. This structure allows it to maintain a low density to ensure a lightweight feel while possessing good resilience, resistance to compression set, and good acoustic isolation and damping performance, making it suitable for products such as earplugs and earmuffs.

[0021] 2. Inherently integrates multiple advanced functions: (1) High efficiency self-healing: The material itself has a dynamic reversible network based on the quadruple hydrogen bonds, π-π stacking and coordination of ureidopyrimidinone, which gives the product a high efficiency self-healing ability. Scratches and indentations can be repaired at room temperature or with moderate heating, thus extending the service life.

[0022] (2) Synergy between function and structure: The self-healing network and the rigid closed-cell bubble wall structure work together to ensure that functionalization does not sacrifice mechanical strength; the function originates from the chemical structure of the polymer backbone, and the performance is durable and stable.

[0023] 3. Simple and controllable process: The optimized one-step foaming process is adopted, in which all functional components directly participate in the construction of polyurethane network through chemical bonding, resulting in uniform dispersion, wide process window, good repeatability, and suitability for large-scale production. Attached Figure Description

[0024] Figure 1 The specific implementation details the synthetic route for pyridine-amide-terminated diisocyanate.

[0025] Figure 2 The specific implementation details the synthetic route for ureidopyrimidinone diisocyanate.

[0026] Figure 3 The image shows the 1H NMR spectrum of N2,N6-bis[(4-hydroxymethyl)benzyl]pyridine-2,6-dicarboxamide in a specific embodiment.

[0027] Figure 4 The image shows the 1H NMR spectrum of ureidopyrimidinone diisocyanate in a specific embodiment. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0030] The raw materials and equipment used in the examples and comparative examples are described below, where eq represents molar equivalent: PTMG-1000: Polytetrahydrofuran ether diol, molecular weight 980~1000, hydroxyl value 112.20~114.50 mg KOH / g, purchased from Xinjiang Lanshan Tunhe Technology Co., Ltd.

[0031] PPG-400: Polypropylene glycol, molecular weight 360~440, hydroxyl value 255~312 mg KOH / g, purchased from Haian County Guoli Chemical Co., Ltd.

[0032] Polymethylene polyphenyl polyisocyanate: NCO content 30%, viscosity 200 mPa·s, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0033] Chain extender: 1,4-Butanediol, hydroxyl value 626 mg KOH / g, commercially available.

[0034] Organosilicon surfactant: Model B-8002, brand Evonik.

[0035] Hydrophobic silica: Particle size 30~50 nm, purchased from Hangzhou Jikang New Materials Co., Ltd. The pretreatment method was as follows: The hydrophobic silica powder was vacuum dried at 120℃ for 3 h to remove adsorbed water, then dispersed in anhydrous toluene and ultrasonically treated to form a uniform suspension; under nitrogen protection and stirring, the suspension in a three-necked flask was heated, and 10% (by weight of silica) of aminosilane coupling agent KH-550 was slowly added dropwise, reacting at 100℃ for 5 h; after the reaction was completed, the mixture was cooled, centrifuged, the supernatant was discarded, and the mixture was repeatedly ultrasonically dispersed and centrifuged with anhydrous ethanol to remove physically adsorbed impurities. Finally, the solid was vacuum dried at 70℃ for 12 h to obtain the treated hydrophobic silica.

[0036] Pyridine-amide-terminated diisocyanate: prepared in-house, as follows: At room temperature, 2.2 eq of 4-aminomethylbenzyl alcohol, 3.0 eq of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and 2.0 eq of 4-dimethylaminopyridine were dissolved in anhydrous dichloromethane. 1.0 eq of pyridine-2,6-dicarboxylic acid was added to this mixture with stirring. The reaction mixture was stirred continuously at room temperature for approximately 12 h under an inert atmosphere. After confirming the completeness of the reaction by thin-layer chromatography, the reaction solution was washed with water and saturated brine. The organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to remove the solvent. The solution was then purified by silica gel column chromatography to obtain N2,N6-bis[(4-hydroxymethyl)benzyl]pyridine-2,6-dicarboxamide. Under a dry nitrogen atmosphere, 1.0 eq of pyridine-2,6-dicarboxylic acid was added to the mixture. N2,N6-bis[(4-hydroxymethyl)benzyl]pyridine-2,6-dicarboxamide was completely dissolved in anhydrous toluene dried with molecular sieves. Under ice-water bath cooling, this solution was slowly added dropwise to a toluene solution of 2.2 eq 1,6-hexamethylene diisocyanate. Subsequently, dibutyltin dilaurate catalyst was added at 0.5% of the total mass of the reaction system. The ice bath was removed, and the reaction mixture was heated to 65°C and stirred continuously at this temperature. The reaction progress was monitored in real time using Fourier transform infrared spectroscopy. When the hydroxyl groups were completely consumed, heating was stopped, and the reaction solution was cooled to room temperature. The cooled reaction solution was then transferred to a rotary thin-film evaporator. Under a high vacuum of <0.1 mbar, the apparatus was immersed in an oil bath, and the oil bath temperature was controlled at 80°C. Under these conditions, excess 1,6-hexamethylene diisocyanate and toluene solvent were distilled off. Distillation continued until no more fractions were distilled off, yielding a pyridine-amide-terminated diisocyanate with the following structure: .

[0037] Uriazinone diisocyanate: Prepared in-house, as follows: In a dry round-bottom flask equipped with a reflux apparatus, 1.0 eq of 2-acetylbutyrolactone and 1.0 eq of guanidine carbonate were dissolved in anhydrous ethanol to prepare a 1.0 mol / L solution. Under stirring, 2.0 eq of triethylamine was added to this mixture as a base catalyst. The reaction mixture was heated to reflux and maintained for 1 h, during which time the solution gradually became clear. The reflux reaction was then continued for another 3 h. After the reaction was complete, the mixture was cooled to room temperature, and the resulting product precipitated from the solution. The resulting pale yellow solid was collected by filtration and thoroughly washed three times with cold ethanol for purification. Finally, the product was dried under vacuum to obtain a white powdery solid, namely 5-(2-hydroxyethyl)-6-methyl-2-aminouracil. Under a nitrogen atmosphere, 1.0 eq of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil synthesized in the above steps was dissolved in 2.5 eq of triethylamine. A mixture of 1,6-hexyl diisocyanate and pyridine (10% by volume of 1,6-hexyl diisocyanate) was prepared. The reaction mixture was stirred at 65°C for 6 h. After the reaction was complete, the solution was cooled and slowly poured into a ten-fold excess of petroleum ether to precipitate the product. The solid was then collected by filtration and washed with pentane to remove residual reactants and catalyst. Finally, the product was dried under vacuum to give ureidylpyrimidinone diisocyanate, with the structure shown below: .

[0038] Example

[0039] Example 1

[0040] High-density closed-cell polyurethane earplugs 1: Homemade, preparation method as follows: Preparation of Component S1.A: 35 parts PTMG-1000 and 15 parts PPG-400 were added to a dry three-necked flask; the mixture was stirred and dehydrated for 2 h at 80 °C and a vacuum degree ≤5 mbar; the vacuum was released, heating was stopped, and the mixture was cooled to 40 °C; 10 parts 1,4-butanediol, 2 parts organosilicon surfactant, and 2 parts hydrophobic silica were added sequentially while stirring at 500 rpm; the stirring speed was increased to 2000 rpm, and stirring was continued at 40 °C for 30 min until the system was homogeneous; the mixture was cooled to 30 °C; 12 parts cyclopentane were added in a well-ventilated area, and the mixture was stirred at 1000 rpm for 5 min until homogeneous and then sealed; the prepared Component A was preheated and stabilized at 35 °C for later use. Preparation of Component S2.B: Preheat 31 parts of polymethylene polyphenyl polyisocyanate to 40°C; grind 8 parts of ureidinone diisocyanate and pass through a 200-mesh sieve, then slowly add it to the polymethylene polyphenyl polyisocyanate while simultaneously applying high-speed shear at 8000 rpm for 5 min; preheat 10 parts of pyridine-amide-terminated diisocyanate to 50°C; mix the preheated pyridine-amide-terminated diisocyanate with the mixture of polymethylene polyphenyl polyisocyanate and ureidinone diisocyanate from the previous step, and stir at 3000 rpm for 5 min at 40°C under nitrogen protection until a homogeneous Component B is formed; keep Component B at 40°C and immediately proceed to the next foaming step; S3. Foaming and Molding: Ensure that the temperature of component A is 35℃ and the temperature of component B is 40℃. Quickly pour component B into component A. Immediately use a high-speed mixer to vigorously stir at 4500 rpm for 25 seconds. Stop stirring when the liquid turns white and begins to expand in volume. Quickly pour the mixture into an earplug mold preheated to 55℃ and close the mold. Immediately transfer the mold to a 70℃ oven for normal pressure curing for 50 minutes. S4. Post-processing: After curing, demold the polyurethane foam earplugs and remove the initial product; place the product in a vacuum oven and cure for 6 hours at 75℃ and a vacuum degree ≤1 mbar; close the oven and allow it to cool naturally to room temperature to obtain high-density closed-cell polyurethane earplug 1.

[0041] Example 2

[0042] High-density closed-cell polyurethane earplug 2: self-made. The preparation method is the same as that of high-density closed-cell polyurethane earplug 1, except that PTMG-1000 is replaced with 30 parts, PPG-400 is replaced with 10 parts, 1,4-butanediol is replaced with 5 parts, organosilicon surfactant is replaced with 1 part, hydrophobic silica is replaced with 1 part, cyclopentane is replaced with 8 parts, polymethylene polyphenyl polyisocyanate is replaced with 19 parts, pyridine-amide-terminated diisocyanate is replaced with 8 parts, and ureidopyrimidinone diisocyanate is replaced with 6 parts. All other conditions remain unchanged to obtain high-density closed-cell polyurethane earplug 2.

[0043] Example 3

[0044] High-density closed-cell polyurethane earplug 3: self-made. The preparation method is the same as that of high-density closed-cell polyurethane earplug 1, except that PTMG-1000 is replaced with 40 parts, PPG-400 is replaced with 20 parts, 1,4-butanediol is replaced with 15 parts, organosilicon surfactant is replaced with 3 parts, hydrophobic silica is replaced with 3 parts, cyclopentane is replaced with 15 parts, polymethylene polyphenyl polyisocyanate is replaced with 42 parts, pyridine-amide-terminated diisocyanate is replaced with 12 parts, and ureidopyrimidinone diisocyanate is replaced with 10 parts. All other conditions remain unchanged to obtain high-density closed-cell polyurethane earplug 3.

[0045] Comparative Example 1 High-density closed-cell polyurethane earplug 4: self-made. The preparation method is the same as that of high-density closed-cell polyurethane earplug 1, except that polymethylene polyphenyl polyisocyanate is replaced with 35 parts and ureidopyrimidinone diisocyanate is replaced with 0 parts, while other conditions remain unchanged, thus obtaining high-density closed-cell polyurethane earplug 4.

[0046] Comparative Example 2 High-density closed-cell polyurethane earplug 5: self-made. The preparation method is the same as that of high-density closed-cell polyurethane earplug 1, except that the polymethylene polyphenyl polyisocyanate is replaced with 35 parts and the pyridine-amide-terminated diisocyanate is replaced with 0 parts, while other conditions remain unchanged, thus obtaining high-density closed-cell polyurethane earplug 5.

[0047] Comparative Example 3 High-density closed-cell polyurethane earplug 6: self-made. The preparation method is the same as that of high-density closed-cell polyurethane earplug 1, except that polymethylene polyphenyl polyisocyanate is replaced with 39 parts, pyridine-amide-terminated diisocyanate is replaced with 0 parts, and ureidopyrimidinone diisocyanate is replaced with 0 parts. All other conditions remain unchanged to obtain high-density closed-cell polyurethane earplug 6.

[0048] Table 1. Formulations of Examples 1-3 and Comparative Examples 1-3 (by weight)

[0049] The following are the test methods for performance parameters involved in this invention: 1. Nuclear magnetic resonance hydrogen spectrum test: Characterization was performed using a nuclear magnetic resonance spectrometer (Bruker AM-600, Advance 600).

[0050] 2. Density: The test method is based on ISO 845-2006.

[0051] 3. Rebound time: The test method is in accordance with GB / T 26392-2011.

[0052] 4. Noise level: The test method is in accordance with T / CAIACN 006-2021.

[0053] 5. Tensile strength and elongation at break: Test methods refer to GB / T 6344-2008.

[0054] 6. Tear strength, tear strength after washing: Test method refers to ISO 8067-2018.

[0055] Table 2 Performance test results of Examples 1-3 and Comparative Examples 1-3

[0056] As shown in Table 2, the polyurethane earplugs prepared in Examples 1-3 of this invention exhibit good overall performance. Example 1, while maintaining suitable density and softness, demonstrates good tensile strength, resilience, and sound insulation properties. Furthermore, it possesses self-healing capabilities and maintains a high tear strength retention rate after washing. Comparative analysis clearly reveals the indispensability and synergistic effect of each functional component: Comparative Example 1 completely loses its self-healing function, and its strength retention rate decreases after washing, confirming that the ureidopyrimidinone quadruple hydrogen bond network is the core of self-healing; Comparative Example 2 shows a significant decrease in mechanical strength, indicating that this rigid structure is crucial for reinforcing the network; while Comparative Example 3 exhibits low performance across all aspects, fully demonstrating that the multifunctional characteristics of this invention cannot be obtained solely through conventional components. The above experimental results fully demonstrate that polymethylene polyphenyl polyisocyanate, pyridine-amide-terminated diisocyanate, and ureidopyrimidinone diisocyanate, through synergistic effects, jointly endow the material with a high-density closed-cell structure, good mechanical properties, acoustic properties, and self-healing characteristics, effectively solving the technical bottleneck of the single performance of traditional polyurethane earplugs.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-density closed-cell polyurethane, characterized in that, By weight, it includes the following components: 30-40 parts of polyether polyol I, 10-20 parts of polyether polyol II, 5-15 parts of chain extender, 1-3 parts of organosilicon surfactant, 1-3 parts of hydrophobic silica, 8-15 parts of foaming agent, 19-42 parts of polymethylene polyphenyl polyisocyanate, 8-12 parts of pyridine-amide-terminated diisocyanate, and 6-10 parts of ureidopyrimidinone diisocyanate.

2. The high-density closed-cell polyurethane structure as described in claim 1, characterized in that, The polyether polyol I is selected from one or more of polytetrahydrofuran ether diol, polypropylene glycol, and polypropylene triol; the polyether polyol II is selected from one or two of polypropylene glycol and polyethylene glycol; the chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, diethylene glycol, and neopentyl glycol; the foaming agent is selected from one or more of cyclopentane, cyclohexane, and isopentane; the organosilicon surfactant is selected from organosilicon-polyether copolymer surfactants; the hydrophobic silica needs to be treated with a silane coupling agent before use; the silane coupling agent is selected from one or two of hydroxysilane coupling agents and aminosilane coupling agents.

3. The high-density closed-cell polyurethane structure as described in claim 1, characterized in that, The method for preparing the pyridine-amide-terminated diisocyanate includes the following steps: 4-Aminomethylbenzyl alcohol and pyridine-2,6-dicarboxylic acid were mixed and reacted in the presence of a condensing agent and a catalyst to obtain a diol product. The diol product was dissolved in a dry organic solvent and then slowly added dropwise to a diisocyanate. Subsequently, dibutyltin dilaurate was added, and after the reaction was completed, the product was purified to obtain a pyridine-amide-terminated diisocyanate.

4. The high-density closed-cell polyurethane structure as described in claim 3, characterized in that, The condensing agent is selected from 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; the catalyst is selected from 4-dimethylaminopyridine; the molar ratio of 4-aminomethylbenzyl alcohol to pyridine-2,6-dicarboxylic acid is (2.05~2.2):1; the amount of diisocyanate used is 2.0~2.5 times relative to the amount of diol product; the diisocyanate is selected from one or more of 1,6-hexyl diisocyanate, 1,5-pentyl diisocyanate, and 1,4-butane diisocyanate; the amount of dibutyltin dilaurate used is 0.1%~0.5% of the total mass of the reaction system.

5. The high-density closed-cell polyurethane structure as described in claim 1, characterized in that, The preparation method of the ureidopyrimidinone diisocyanate includes the following steps: 2-Acetylbutyrolactone and guanidine carbonate were dissolved in anhydrous ethanol, an alkaline catalyst was added, and the mixture was heated under reflux. After the reaction was completed, the mixture was purified to obtain 5-(2-hydroxyethyl)-6-methyl-2-aminouracil. Then, it was mixed with diisocyanate and pyridine, heated and stirred, and purified after the reaction was completed to obtain ureidylpyrimidinone diisocyanate.

6. The high-density closed-cell polyurethane structure as described in claim 5, characterized in that, The base catalyst is selected from triethylamine, and the amount of the base catalyst is twice the amount of 2-acetylbutyrolactone; the diisocyanate is selected from one or more of 1,6-hexyl diisocyanate, 1,5-pentyl diisocyanate, and 1,4-butane diisocyanate; the amount of the diisocyanate is 2.0 to 3.0 times the amount of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil; and the amount of pyridine is 10% of the volume of the diisocyanate.

7. A method for preparing a high-density closed-cell polyurethane earplug as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Preparation of S1.A component: Mix 30-40 parts of polyether polyol I and 10-20 parts of polyether polyol II and dehydrate. Under stirring, add 5-15 parts of chain extender, 1-3 parts of organosilicon surfactant, 1-3 parts of hydrophobic silica, and 8-15 parts of foaming agent in sequence. After mixing evenly, seal and preheat for later use. Preparation of S2.B component: Preheat 19-42 parts of polymethylene polyphenyl polyisocyanate; grind 6-10 parts of ureidinone diisocyanate and pass through a 200-mesh sieve, then slowly add it to the polymethylene polyphenyl polyisocyanate while simultaneously shearing at high speed; preheat 8-12 parts of pyridine-amide-terminated diisocyanate; mix the preheated pyridine-amide-terminated diisocyanate with the mixture of polymethylene polyphenyl polyisocyanate and ureidinone diisocyanate from the previous step, and form a homogeneous component B at 35-45°C; maintain component B at 35-45°C and immediately proceed to the next foaming step; S3. Foaming and molding: Ensure that the temperature of component A is 30~40℃ and the temperature of component B is 35~45℃, and quickly pour component B into component A; Immediately use a high-speed mixer to vigorously stir at 4500~5000 rpm for 20~30 seconds, and stop when the liquid turns white and begins to expand in volume; quickly pour the mixture into earplug molds preheated to 50~60℃ and close the molds; immediately transfer the molds into an oven at 65~75℃ for normal pressure curing; S4. Post-processing: After curing, demold the polyurethane foam earplugs and remove the initial product; place the product in a vacuum oven; close the oven and allow it to cool naturally to room temperature to obtain high-density closed-cell polyurethane earplugs.

8. The method for preparing a high-density closed-cell polyurethane earplug as described in claim 7, characterized in that, The vacuum oven conditions in step S4 are set to 70~80℃ and vacuum degree ≤1 mbar.

9. The use of polyurethane earplugs made from high-density closed-cell polyurethane as described in any one of claims 1 to 6, or high-density closed-cell polyurethane earplugs prepared by the method of preparing high-density closed-cell polyurethane earplugs as described in any one of claims 7 to 8, in earplugs or earmuffs.

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