Layered composite noise reduction material for sound barrier and preparation method of layered composite noise reduction material

Abstract

The invention relates to the technical field of layered polymer composite materials, and discloses a layered composite noise reduction material for a sound barrier and a preparation method of the layered composite noise reduction material, and the noise reduction material is of an integrated composite structure with a functional skin and a sound absorption core material; the functional skin is prepared by reacting a first premix containing first polyether polyol, aliphatic polyol modified polyether amine and phosphate polyol; the sound absorption core material is prepared by reacting a second premix containing second polyether polyol and epoxy-terminated polysiloxane; according to the preparation method, an integrated forming process is adopted, the first premix is applied into a mold, and when the first premix reaches a gel state but is not completely cured, the second premix is injected to be jointly cured and formed; the problem of interlayer separation is solved, the aliphatic polyol modified polyether amine endows the skin with excellent toughness and weather resistance, the epoxy-terminated polysiloxane ensures the high aperture ratio and sound absorption performance of the core material, and the material is stable in structure, balanced in performance and suitable for the fields of metal sound barriers and the like.

Description

Technical Field

[0001] This invention relates to the field of layered polymer composite materials technology, and in particular to a layered composite noise reduction material for sound barriers and its preparation method. Background Technology

[0002] Noise barriers, as an important transportation infrastructure, are widely used along highways, railways, and urban rail transit lines to reduce the impact of traffic noise on the surrounding environment. Porous sound-absorbing materials, especially polyurethane foam, with its numerous interconnected pores, can effectively dissipate sound energy and are the core functional components of the sound-absorbing panels in noise barriers.

[0003] However, in practical applications, a single homogeneous polyurethane foam material cannot simultaneously meet the durability requirements and high-efficiency acoustic performance requirements in harsh outdoor environments. On the one hand, to achieve efficient sound absorption, the material needs to have a high porosity and low density, but this usually results in low mechanical strength and poor weather resistance. Under the influence of ultraviolet radiation, rainwater erosion, and temperature fluctuations, the material is prone to pulverization and aging, losing its sound absorption function. On the other hand, if a dense skin layer is formed on the material surface through process control to improve durability, this skin layer will reflect most of the incident sound waves due to its high acoustic impedance, rendering the internal sound-absorbing structure ineffective.

[0004] To address this contradiction, existing technologies typically employ multi-layered composite panel structures. These panels use pre-prepared open-cell polyurethane sound-absorbing foam as the core material, then bond a protective surface layer, such as non-woven fabric, fiberglass mat, or a functional coating, with an adhesive. This method, relying on post-processing physical bonding to manufacture layered products, leaves the interlayer interfaces as the weakest point in the entire panel structure. Under the repeated effects of traffic vibrations, wind loads, and thermal expansion and contraction that sound barriers endure over long periods, the bonding interfaces are prone to fatigue and aging, ultimately leading to delamination and separation between the surface layer and the core material. Once the protective surface layer fails, the fragile internal sound-absorbing core material is directly exposed to the environment and rapidly deteriorates, causing the entire sound barrier unit to lose its intended noise reduction function and significantly shortening its effective lifespan. Furthermore, this multi-step composite process increases production complexity and manufacturing costs. Therefore, developing a layered composite noise reduction panel that chemically bonds the protective surface layer and the sound-absorbing core layer to achieve a highly stable structure and excellent performance is a pressing technical problem in the current sound barrier and building sound insulation field. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a layered composite noise reduction material for sound barriers and its preparation method. It aims to overcome the technical defects of polyurethane sound-absorbing materials used as sound barrier components in the prior art, such as poor surface weather resistance and easy aging, as well as the weak bonding and easy delamination caused by the reliance on physical bonding between the protective surface layer and the sound-absorbing core material. At the same time, it solves the inherent contradiction that homogeneous materials cannot take into account both surface protection performance and internal sound absorption performance.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a layered composite noise reduction material for sound barriers, employing the following technical solution:

[0008] The layered composite noise reduction material is an integrally molded layered structure, comprising:

[0009] A functional skin layer formed by the reaction of a first premix with polymeric MDI; and a porous sound-absorbing core layer formed by the reaction of a second premix with polymeric MDI;

[0010] The functional skin layer and the porous sound-absorbing core material layer are bonded together by covalent bonds formed through in-situ chemical reactions at their interface.

[0011] The first premix comprises the following raw materials in parts by weight:

[0012] First polyether polyol: 35-40 parts;

[0013] Aliphatic polyol modified polyetheramine: 12-20 parts;

[0014] Phosphate ester polyols: 5-10 parts;

[0015] First silicone oil foam stabilizer: 0.8–1.2 parts;

[0016] First foaming catalyst: 0.15–0.3 parts;

[0017] First gel catalyst: 0.4–0.7 parts;

[0018] First deionized water: 0.2–0.4 parts;

[0019] The second premix comprises the following raw materials in parts by weight:

[0020] Second polyether polyol: 45-55 parts;

[0021] Polymer polyols: 22-25 parts;

[0022] Terminally epoxy-based polysiloxane: 1.0–2.5 parts;

[0023] Second silicone oil foam stabilizer: 1.2-1.8 parts;

[0024] Second foaming catalyst: 0.4–0.6 parts;

[0025] Second gel catalyst: 0.2–0.4 parts;

[0026] Second deionized water: 3.0 to 4.0 parts.

[0027] By adopting the above technical solution, this invention, through the synergistic design of the formulations of the functional skin layer and the porous sound-absorbing core layer, constructs a functional gradient within the same product, thereby obtaining a layered composite noise reduction board with highly stable structure and balanced performance. Its technical mechanism and advantages are reflected in the following three aspects:

[0028] First, the functional skin layer and the sound-absorbing core layer are integrated through chemical bonding.

[0029] In the formulation of the functional skin layer, the introduced phosphate ester polyol not only imparts flame retardancy to the material, but more importantly, the active hydroxyl groups contained in its molecular structure. When the functional skin layer reaches a gel state but is not completely cured using the subsequent preparation method of this invention, its inner surface is rich in unreacted active hydroxyl groups (-OH) provided by the polyol. At this time, the isocyanate groups (-NCO) in the injected sound-absorbing core material premix will undergo an in-situ addition reaction with these active hydroxyl groups to form urethane covalent bonds. The chemical cross-linking formed at the interface makes the two layers no longer a simple physical bond, but a continuous chemical gradient transition zone. Its bonding strength far exceeds the physical adhesion force, fundamentally solving the interlayer separation problem of traditional layered composite panels.

[0030] Second, a functional epidermal layer that combines durability and acoustic transparency was constructed.

[0031] The aliphatic polyol-modified polyetheramine introduced into the formulation of the functional skin contains flexible long aliphatic chains in its molecular structure. In the polyurethane curing network, these flexible segments act like molecular springs, which can effectively absorb and dissipate external stress, giving the skin layer excellent bending flexibility and high and low temperature impact resistance, so that it can serve as a tough outer protective layer to protect the internal porous structure.

[0032] The formula incorporates trace amounts of deionized water (0.2–0.4 parts) as a foaming agent, which reacts with isocyanate to generate trace amounts of carbon dioxide. During the rapid gelation of the outer layer, these gases are sufficient to form a permeable microporous network. The presence of this network gives the outer layer a certain degree of air permeability, resulting in low airflow resistance acoustically. This allows incident sound waves to penetrate smoothly into the inner sound-absorbing core layer, avoiding sound reflection caused by surface density and ensuring the sound absorption efficiency of the entire layered product.

[0033] Third, a porous sound-absorbing core material layer with high porosity was prepared.

[0034] The sound absorption performance of the sound-absorbing core layer mainly depends on its internal porosity. The terminal epoxy-based polysiloxane introduced into the formulation is an active pore-opening agent, and its mechanism of action is as follows: In the initial stage of polyurethane foaming reaction, the foam system has a low viscosity, and the role of conventional silicone oil foam stabilizers is mainly to form a uniform closed-cell structure.

[0035] As the reaction proceeds, the system temperature rises and the viscosity increases, entering the gel solidification stage. At this point, the reactivity of the epoxy groups at the ends of the epoxy-terminated polysiloxane molecular chains is activated.

[0036] The activated epoxy groups undergo a ring-opening reaction with the amine or hydroxyl groups in the polyurethane network. This reaction occurs on the curing cell wall film, disrupting the regularity of the polymer network and causing localized stress concentrations and structural weaknesses on the cell walls.

[0037] Under the pressure of the gas inside the foam cells, these structural weaknesses rupture, causing the originally closed foam cells to connect with each other, ultimately forming a foam structure with a high open-cell ratio. This porous structure provides ample channels for the incidence, reflection, and frictional dissipation of sound waves, and is the core functional layer for achieving high-efficiency sound absorption in this layered product.

[0038] Preferably, the aliphatic polyol modified polyetheramine is prepared by reacting an amino-terminated polyether with an aliphatic diepoxide at 95–110 °C.

[0039] More preferably, the terminal amino polyether is polypropylene glycol diamine with a number average molecular weight of 2000-4000 g / mol;

[0040] More preferably, the aliphatic diepoxide is 1,4-butanediol diglycidyl ether or 1,6-hexanediol diglycidyl ether.

[0041] By adopting the above technical solution, the synthesis route and raw material specifications of the key component are defined, which can ensure that the introduced flexible segments have appropriate molecular weight and structure, thereby precisely controlling the mechanical properties of the functional epidermis and maintaining sufficient strength and hardness while ensuring toughness.

[0042] Preferably, the first polyether polyol has an average functionality of 4.0 to 5.0, a number-average molecular weight of 500 to 600 g / mol, and a hydroxyl value of 380 to 420 mg KOH / g; the second polyether polyol has a functionality of 3, a number-average molecular weight of 4500 to 5500 g / mol, and a hydroxyl value of 30 to 40 mg KOH / g.

[0043] The first polyether polyol, characterized by high functionality and low molecular weight, is used to construct a functional skin layer with high cross-linking density, ensuring its rigidity and protective properties. The second polyether polyol, characterized by low functionality and high molecular weight, is used to form a soft and elastic sound-absorbing core layer matrix. This targeted selection is the basis for achieving the performance gradient within this layered product.

[0044] Preferably, the epoxy value of the terminal epoxy polysiloxane is 0.15 to 0.25 mol / 100g.

[0045] By adopting the above technical solution, the reactivity of the active pore-opening agent was quantitatively controlled. This epoxy value range ensured that the pore-opening reaction occurred in the gel stage in the later stage of foaming, which could effectively open the pores and avoid foam collapse caused by premature reaction, thus ensuring the macroscopic structural stability of the sound-absorbing core material layer.

[0046] Secondly, this invention provides a method for preparing a layered composite noise reduction material for sound barriers, employing the following technical solution:

[0047] (1) The first premix used to form the functional skin layer is mixed with polymeric MDI at an isocyanate index of 1.00 to 1.10 and then applied to the inner surface of the mold;

[0048] (2) When the functional skin layer reaches a gel state but is not completely cured, the second premix used to form the porous sound-absorbing core layer is mixed with polymeric MDI at an isocyanate index of 1.00 to 1.10 and then injected into the mold;

[0049] (3) Close the mold to solidify the functional skin layer and the porous sound-absorbing core layer into one piece, thereby forming a chemical bond between the two layers.

[0050] By adopting the above technical solution, the present invention establishes a "wet-on-wet" integrated molding process, the core of which lies in controlling the time window between the two casting steps to achieve in-situ chemical bonding between layers.

[0051] In polyurethane reaction kinetics, the "gel state" refers to a state where the polymer network has initially formed, the system has lost its fluidity, but the chemical reaction is far from over, and a large number of unreacted active functional groups (mainly hydroxyl and isocyanate groups) still exist in the gel matrix. This method utilizes this crucial intermediate state:

[0052] The operational node of step (2), namely, injecting the material of the sound-absorbing core layer when the functional skin layer reaches a gel state but is not completely cured, ensures that the inner surface of the functional skin layer maintains a high concentration of active chemical sites. When the mixture of the sound-absorbing core layer comes into contact with this active interface, the isocyanate groups in its components will undergo an in-situ polymerization reaction with the active functional groups (especially the hydroxyl groups from phosphate ester polyols) remaining on the surface of the skin layer.

[0053] This reaction crosses the physical boundary between the two material layers at the molecular level, forming a continuous network of urethane covalent bonds, thereby firmly bonding the functional skin layer and the sound-absorbing core layer into a single unit. The interface prepared by this method is a chemical gradient transition zone, rather than a physical adhesion interface formed by traditional processes, thus completely avoiding the risk of delamination failure caused by poor adhesion or aging in traditional layered composite panels.

[0054] Preferably, in step (2), the functional epidermal layer reaches a gel state after staying in the mold for 35 to 50 seconds.

[0055] By employing the above technical solution, the gelation time window was controlled. If the residence time is less than 35 seconds, the functional skin layer has not yet formed sufficient gel strength, and the mixing of the two layers may occur when the sound-absorbing core material is injected, disrupting the pre-designed layered gradient structure. If the residence time is longer than 50 seconds, the skin layer is over-cured, resulting in the consumption of a large number of surface-active groups and insufficient interfacial chemical bonding, leading to a decrease in interlayer bonding strength. This time range is the process guarantee for achieving optimal product structural integrity and interfacial bonding strength. A conventional stringing method (such as touching and pulling with a glass rod) can be used to determine if the material has reached a gel state but is not fully cured.

[0056] Preferably, in step (3), the temperature of the mold is controlled at 45-60°C, and the pressure holding and curing time is 5-8 minutes.

[0057] By adopting the above technical solution, suitable thermodynamic conditions are provided for the curing of the entire layered composite product. This temperature range can effectively promote the post-curing reaction of the functional skin layer and the sound-absorbing core layer, ensuring full cross-linking of the polymer network, while avoiding material burning or degradation due to excessive temperature. The pressure holding curing time ensures that the board achieves sufficient dimensional stability and mechanical strength before demolding.

[0058] Preferably, step (1) is applied using a low-pressure casting machine, and step (2) is injected using a high-pressure foaming machine.

[0059] By adopting the above technical solutions, the processing equipment was optimized for the characteristics of different material layers. The functional skin layer material has a relatively low viscosity, and low-pressure casting can achieve uniform and stable coating on the mold surface, ensuring the formation of a high-quality outer protective layer. The sound-absorbing core layer is a rapid foaming system. High-pressure foaming machines can achieve instantaneous and highly uniform mixing of raw materials, thereby ensuring the fineness and uniformity of the internal pore structure of the sound-absorbing core layer. This is a prerequisite for obtaining excellent and stable sound absorption performance.

[0060] In summary, the present invention has at least one of the following beneficial technical effects:

[0061] 1. This invention provides a layered composite noise reduction product with high interlayer bonding strength, which significantly improves the durability and reliability of the product as a building or facility component. By adopting a wet-on-wet integrated molding process, the sound-absorbing core material is injected when the functional skin layer reaches a gel state but is not completely cured. The active groups at the skin layer interface react in situ with the core material components to form a covalently bonded chemical gradient transition zone. This intrinsic chemical bonding fundamentally solves the risk of interlayer separation caused by physical adhesion or mechanical interlocking in traditional layered boards, enabling the product to maintain structural integrity even when subjected to long-term vibration, temperature cycling, and external impact.

[0062] 2. This invention achieves a highly efficient synergy between surface protection and internal sound absorption performance through an integrated layered structure design, overcoming the inherent contradiction between the two. The aliphatic polyol-modified polyetheramine introduced into the functional skin layer formulation endows this outer layer with excellent flexibility and weather resistance, serving as a robust protective layer against harsh outdoor environments. Simultaneously, the microporous structure formed by a trace amount of foaming agent ensures its acoustic transparency, preventing significant sound wave reflection. The epoxy-terminated polysiloxane introduced into the porous sound-absorbing core layer formulation acts as an active pore-opening agent, ensuring that this inner layer forms a high-open-ratio energy-dissipating structure, thereby achieving highly efficient sound energy absorption. The two layers have clearly defined functions and work synergistically, allowing a single product to meet all the performance requirements of a sound barrier.

[0063] 3. The manufacturing process of this invention is highly integrated, combining the construction of the functional skin layer and the foaming of the sound-absorbing core layer within a single molding cycle. This significantly improves production efficiency and reduces manufacturing costs. Compared to the traditional multi-step process of manufacturing layered sound-absorbing panels, which requires first manufacturing the core material and then bonding perforated panels or protective coatings, this invention directly generates an integrated layered product with both protective and sound-absorbing functions through formula design and process control. This avoids secondary processing or lamination steps, shortens the production cycle, and reduces equipment investment and potential process defects. Detailed Implementation

[0064] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0065] The first polyether polyol is specifically a branched polyether polyol obtained by ring-opening copolymerization of a polyol with propylene oxide and / or ethylene oxide. Its average functionality is 4.0–5.0, number-average molecular weight is 500–600 g / mol, hydroxyl value is 380–420 mg KOH / g, and viscosity at 25°C is 4000–5000 mPa·s.

[0066] The second polyether polyol is specifically a trifunctional polyether polyol obtained by ring-opening copolymerization of glycerol with propylene oxide and ethylene oxide. Its number-average molecular weight is 4500–5500 g / mol, its hydroxyl value is 30–40 mg KOH / g, and its viscosity at 25°C is 700–900 mPa·s.

[0067] Polymer polyol (POP) is a graft copolymer formed by in-situ free radical polymerization of styrene and acrylonitrile monomers in a second polyether polyol as the base polyether. Its polymer solids content is 40–50 wt%, hydroxyl value is 20–30 mg KOH / g, and viscosity at 25°C is 3500–4500 mPa·s.

[0068] Polymer MDI (PAPI), chemically known as polymethylene polyphenyl polyisocyanate, CAS number 9016-87-9, is a mixture of 4,4'-diphenylmethane diisocyanate (MDI) and polyfunctional isocyanates containing three or more benzene rings. It has a -NCO group content of 30.0–32.0% and a viscosity of 180–250 mPa·s at 25°C.

[0069] Phosphate ester polyols are reactive flame-retardant polyols containing phosphate ester groups. Their structure consists of an aliphatic polyol skeleton with phosphate ester groups and free hydroxyl groups attached. They contain 4–6 wt% phosphorus, have a hydroxyl value of 150–200 mg KOH / g, and an acid value of less than 1.0 mg KOH / g.

[0070] Conventional polyether polyols are trifunctional homopolymer polyether polyols obtained by ring-opening copolymerization of glycerol and propylene oxide. Their number-average molecular weight is 900–1000 g / mol, and their hydroxyl value is 175–185 mg KOH / g. This raw material is used in the comparative example to replace phosphate ester polyols.

[0071] Terminally epoxy-based polysiloxanes have a main molecular chain of polydimethylsiloxane, with epoxy functional groups linked to both ends via propylene groups. Their epoxy value is 0.15–0.25 mol / 100g, and their viscosity at 25°C is 30–60 mPa·s.

[0072] Conventional silicone oil foam stabilizers are non-hydrolyzable polyether-modified polydimethylsiloxanes, whose chemical structure consists of a polydimethylsiloxane backbone grafted with polyoxyethylene-polyoxypropylene copolymer segments. In this example, Evonik's Tegostab® B 8715 LF2 was selected.

[0073] Aliphatic polyol modified polyetheramine is a self-made substance of this invention. For details of its preparation method, please refer to Preparation Example 1 and Preparation Example 2.

[0074] The chain extender, chemically named 1,4-butanediol (BDO), CAS number 110-63-4, has a purity greater than 99.5%.

[0075] The foaming catalyst, chemically named triethylenediamine, CAS number 280-57-9, is used in this invention as a 33% (w / w) dipropylene glycol solution.

[0076] The gel catalyst, chemically named N,N-dimethylcyclohexylamine, CAS number: 98-94-2.

[0077] It should be understood that the silicone oil foam stabilizer, foaming catalyst, and gelling catalyst used in this invention are all commercially available products widely used in the polyurethane foam field. Those skilled in the art can select appropriate specific models and grades from commercially available products based on the formulation system and process requirements disclosed in this application; this is standard practice in the field.

[0078] Preparation Example 1:

[0079] This preparation example provides the preparation of a first aliphatic polyol modified polyetheramine, as detailed below:

[0080] In a 1000 mL four-necked flask equipped with a mechanical stirrer, a constant-pressure dropping funnel, a spherical condenser, and a nitrogen inlet tube, 400.0 g of amino-terminated polyether (polypropylene glycol diamine, number-average molecular weight approximately 2000 g / mol, amine value approximately 56 mg KOH / g) was added. Nitrogen protection was activated, and mechanical stirring was started, heating the reaction system to 95°C. 26.0 g of 1,4-butanediol diglycidyl ether was added dropwise at a uniform rate over 1.5 hours via the constant-pressure dropping funnel. During the addition, the temperature of the reaction system was maintained between 95 and 105°C by adjusting the heating device. After the addition was complete, the reaction was continued at this temperature for 3.5 hours. During the reaction, samples were taken every hour, and the amine value of the system was determined by acid-base titration. When the amine value reached 20.5 mg KOH / g, heating was stopped, and the mixture was cooled to room temperature while stirring. The material was discharged to obtain a colorless and transparent viscous liquid, which is the first aliphatic polyol modified polyetheramine, with a final amine value of 20.1 mg KOH / g. It was sealed and stored for later use.

[0081] Preparation Example 2:

[0082] This preparation example provides the preparation of a second aliphatic polyol-modified polyetheramine, as detailed below:

[0083] In the same reaction apparatus as in Preparation Example 1, 400.0 g of amino-terminated polyether (polypropylene glycol diamine, number-average molecular weight approximately 4000 g / mol, amine value approximately 28 mg KOH / g) was added. Nitrogen protection was activated, mechanical stirring was started, and the reaction system was heated to 100°C. 10.5 g of 1,6-hexanediol diglycidyl ether was added dropwise at a uniform rate over 1.0 hour using a constant-pressure dropping funnel. During the addition, the reaction system temperature was maintained at 100–110°C. After the addition was complete, the reaction was continued at this temperature for 4.0 hours. Process monitoring was performed using the same method as in Preparation Example 1. When the amine value reached 15.2 mg KOH / g, the reaction was stopped and post-processing was performed. A pale yellow, transparent, viscous liquid was finally obtained, which was the second aliphatic polyol-modified polyether amine with a final amine value of 15.0 mg KOH / g. It was sealed and stored for later use.

[0084] Example 1:

[0085] This embodiment provides a method for preparing a layered composite noise reduction material for sound barriers, specifically including the following steps:

[0086] (1) Preparation of premixes for each functional layer: Two premixes were prepared for forming the functional skin layer and the porous sound-absorbing core layer, respectively.

[0087] The formulation of the first premix for the functional skin layer, by weight, is as follows: 40 parts of a first polyether polyol, 15 parts of a first aliphatic polyol-modified polyether amine, 7 parts of a phosphate ester polyol, 1.0 part of a first silicone oil foam stabilizer, 0.2 parts of a first foaming catalyst, 0.5 parts of a first gel catalyst, and 0.3 parts of a first deionized water. The above components (except for the first gel catalyst and the first deionized water) are added to a mixing tank and stirred until homogeneous. Then, the first gel catalyst is added and stirred until homogeneous. Finally, the first deionized water is added and dispersed at high speed until homogeneous, thus obtaining the first premix.

[0088] The formulation of the second premix for the porous sound-absorbing core material layer, by weight, is as follows: 50 parts of second polyether polyol, 25 parts of polymer polyol (POP), 2.0 parts of terminal epoxy polysiloxane, 1.5 parts of second silicone oil foam stabilizer, 0.4 parts of second foaming catalyst, 0.3 parts of second gel catalyst, and 3.2 parts of second deionized water. The second premix for the porous sound-absorbing core material layer is prepared using the same method as the first premix for the functional skin layer.

[0089] (2) Integrated molding: The steel closed mold is preheated and kept constant at 50°C, and a release agent is evenly sprayed onto the inner wall of the mold. The functional skin layer is uniformly applied to the inner surface of the mold using a low-pressure casting machine, using the first premix and polymeric MDI (mixed at an isocyanate index of 1.05) to form a functional skin layer with a thickness of 2.0 mm. The skin layer is allowed to remain in the mold for 45 seconds to reach a gel state. Then, the porous sound-absorbing core layer is injected into the mold using a high-pressure foaming machine, using the second premix and polymeric MDI (mixed at an isocyanate index of 1.05), and the mold is quickly closed. The mold is demolded after being held under pressure at 50°C for 7 minutes. The product is then cured at room temperature for 24 hours to obtain the final layered composite noise reduction material with a total thickness of 5 cm.

[0090] Example 2:

[0091] This embodiment provides a method for preparing a layered composite noise reduction material for sound barriers, specifically including the following steps:

[0092] (1) Preparation of premixes for each functional layer:

[0093] The formulation of the first premix for the functional epidermis layer, by weight, is as follows: 35 parts of the first polyether polyol, 20 parts of the second aliphatic polyol modified polyether amine, 5 parts of phosphate ester polyol, 1.2 parts of the first silicone oil foam stabilizer, 0.3 parts of the first foaming catalyst, 0.7 parts of the first gel catalyst, and 0.2 parts of the first deionized water.

[0094] The formulation of the second premix for the porous sound-absorbing core material layer, by weight, is as follows: 55 parts of second polyether polyol, 22 parts of polymer polyol (POP), 1.0 part of terminal epoxy polysiloxane, 1.8 parts of second silicone oil foam stabilizer, 0.5 parts of second foaming catalyst, 0.4 parts of second gel catalyst, and 3.0 parts of second deionized water.

[0095] Both of the above premixes were prepared using the same method as in Example 1.

[0096] (2) Integrated molding: The mold is preheated and kept constant at 60°C. The functional skin layer is applied to the inner surface of the mold using a low-pressure casting machine with a first premix and polymeric MDI (mixed at an isocyanate index of 1.10) to form a functional skin layer with a thickness of 1.5 mm, and left to stand for 35 seconds. Then, the porous sound-absorbing core layer is injected into the mold using a high-pressure foaming machine with a second premix and polymeric MDI (mixed at an isocyanate index of 1.10), and the mold is closed. The mold is demolded after being held under pressure at 60°C for 5 minutes, and after being cured at room temperature for 24 hours, the final layered composite noise reduction material with a total thickness of 3 cm is obtained.

[0097] Example 3:

[0098] This embodiment provides a method for preparing a layered composite noise reduction material for sound barriers, specifically including the following steps:

[0099] (1) Preparation of premixes for each functional layer:

[0100] The formulation of the first premix for the functional epidermis layer, by weight, is as follows: 40 parts of the first polyether polyol, 12 parts of the first aliphatic polyol modified polyether amine, 10 parts of the phosphate ester polyol, 0.8 parts of the first silicone oil foam stabilizer, 0.15 parts of the first foaming catalyst, 0.4 parts of the first gel catalyst, and 0.4 parts of the first deionized water.

[0101] The formulation of the second premix for the porous sound-absorbing core layer is as follows (by weight): 45 parts of second polyether polyol, 25 parts of polymer polyol (POP), 2.5 parts of terminal epoxy polysiloxane, 1.2 parts of second silicone oil foam stabilizer, 0.6 parts of second foaming catalyst, 0.2 parts of second gel catalyst, and 4.0 parts of second deionized water.

[0102] Both of the above premixes were prepared using the same method as in Example 1.

[0103] (2) Integrated molding: The mold is preheated and kept constant at 45°C. The functional skin layer is applied to the inner surface of the mold using a low-pressure casting machine with a first premix and polymeric MDI (mixed at an isocyanate index of 1.00) to form a functional skin layer with a thickness of 2.5 mm, and left to stand for 50 seconds. Then, the porous sound-absorbing core layer is injected into the mold using a high-pressure foaming machine with a second premix and polymeric MDI (mixed at an isocyanate index of 1.00), and the mold is closed. The mold is demolded after being held under pressure at 45°C for 8 minutes, and after being cured at room temperature for 24 hours, the final layered composite noise reduction material with a total thickness of 10 cm is obtained.

[0104] Comparative Example 1:

[0105] Compared to Example 1, the difference lies in that, in the first premix of its functional skin layer, conventional polyether polyols with equal hydroxyl values ​​are used instead of phosphate ester polyols. The remaining components and preparation steps are the same as in Example 1.

[0106] Comparative Example 2:

[0107] Compared with Example 1, the difference is that the first aliphatic polyol modified polyetheramine in the first premix is ​​replaced with an equimolarly reactive chain extender (1,4-butanediol). The remaining components and preparation steps are the same as in Example 1.

[0108] Comparative Example 3:

[0109] Compared to Example 1, the difference lies in that an equal weight of conventional silicone oil foam stabilizer replaces the terminal epoxy polysiloxane in the second premix of the sound-absorbing core material layer. All other components and preparation steps are the same as in Example 1.

[0110] Comparative Example 4:

[0111] Compared with Example 1, the difference lies in the preparation process: in step (2) molding, after the functional skin layer is formed, it is completely cured in the mold at 50°C for 30 minutes, and after it cools to room temperature, the sound-absorbing core material is poured and foamed. The formulation of the first premix used is the same as that in Example 1.

[0112] Comparative Example 5:

[0113] This comparative example provides a method for preparing homogeneous polyurethane sound-absorbing foam. Its formulation uses only the second premix for the sound-absorbing core layer as described in Example 1. Under the molding conditions of Example 1, it is foamed in a single pour to form a board with the same dimensions as the final product of Example 1. This board does not have a functional skin layer.

[0114] Test Example 1:

[0115] This test case aims to verify whether the samples prepared by the methods of Examples 1 to 3 have an integrated composite structure, and whether the structure exhibits the expected density gradient in the thickness direction.

[0116] The testing steps are as follows:

[0117] (1) Structural integrity test:

[0118] Samples prepared in Examples 1, 2, and 3 were tested after curing at room temperature for 24 hours. First, the surface and cross-section of the samples were visually inspected, and the presence of defects such as delamination, blistering, or delamination was recorded. Then, using a thin-bladed tool, an attempt was made to insert it at the junction of the functional skin and the sound-absorbing core material on the sample cross-section, and a peeling force was applied along the interface direction. Whether the interface could be easily separated was observed and recorded; if separation was not possible, the location of the failure (interface separation or material failure) was recorded.

[0119] (2) Gradient density test:

[0120] 100mm × 100mm specimens were cut from the center of the samples prepared in Examples 1-3. Using a thin-film cutter, the functional skin and sound-absorbing core material were precisely separated at the interface to obtain separate functional skin layer samples and sound-absorbing core material samples. The length, width, and thickness of each sample were measured using a digital caliper with an accuracy of 0.01 mm. The average value of measurements at three different locations in each dimension was taken to calculate the volume V. The mass m was weighed using an electronic balance with an accuracy of 0.001 g. The density of each sample layer was calculated using the formula ρ = m / V.

[0121] The test results are shown in Table 1.

[0122] Table 1. Results of structural integrity and gradient density tests on the samples from the examples: sample Structural integrity observation Manual peeling results <![CDATA[Functional epidermal density (kg / m 3 )]]> <![CDATA[Absorption core material density (kg / m 3 )]]> Example 1 The interface is tightly integrated and has no layers. Unable to peel off, core material cohesion failure 812.5 42.6 Example 2 The interface is tightly integrated and has no layers. Unable to peel off, core material cohesion failure 855.2 46.1 Example 3 The interface is tightly integrated and has no layers. Unable to peel off, core material cohesion failure 789.8 33.8

[0123] The results of Test Example 1 show that the samples prepared in Examples 1-3 all exhibit an integrated composite structure. Visual observation and manual peel tests confirmed that there is no physical boundary between the functional skin layer and the sound-absorbing core layer; the two are firmly bonded, and the peeling attempt resulted in cohesive failure of the sound-absorbing core material rather than interfacial separation. This demonstrates that the interfacial bonding strength is higher than the cohesive strength of the sound-absorbing core material itself, forming a truly integral material. Density test data confirmed a significant density gradient along the thickness direction. The density of the functional skin layer is 789.8–855.2 kg / m³. 3 The density is much higher than that of sound-absorbing core materials (33.8–46.1 kg / m³). 3 This forms a gradient structure from dense to loose from the outside to the inside.

[0124] This integrated structure originates from the wet-on-wet two-step molding process employed in this invention. In the first step, when the functional skin layer reaches a gel state but is not fully cured, its inner surface still retains a large number of unreacted active groups, particularly the active hydroxyl groups derived from phosphate ester polyols. When the sound-absorbing core material mixture is injected and contacts this active interface in the second step, the isocyanate groups in the core material components undergo an in-situ chemical reaction with the active hydroxyl groups of the skin layer, forming covalent bonds across the interface. This interface layer, formed through chemical bonding, exhibits a bonding strength exceeding that of traditional physical adhesion or mechanical interlocking, thereby fundamentally eliminating the risk of interlayer delamination.

[0125] The density gradient of the material is directly attributed to the design of two premix formulations with distinct functions. The first premix, used for the functional skin layer, employs a high-functionality polyol and a very small amount of foaming agent to form a microporous protective layer with high cross-linking density and high mechanical strength. The second premix, used for the sound-absorbing core layer, uses a higher content of foaming agent to generate a low-density, high-porosity porous structure, thereby achieving efficient sound energy dissipation. The successful combination of the two formulations within a single molding cycle results in a gradient of physical properties in the material on a macroscopic scale.

[0126] In summary, the structural and density data of Test Example 1 macroscopically validate the feasibility of this invention in successfully preparing a gradient functional material that combines a dense protective skin with a low-density sound-absorbing core through a two-component formulation design and a wet-on-wet integrated molding process. The in-situ formed chemical bonding interface ensures the integrity and durability of the structure, while the precisely controlled density gradient is the foundation for achieving its comprehensive performance.

[0127] Test Example 2:

[0128] This test case indirectly verifies whether the functional skin prepared in Example 1 has a microporous structure that allows sound waves to pass through by measuring airflow resistance.

[0129] (1) Preparation of comparative samples:

[0130] To establish a valid control, a non-porous solid plate sample was prepared. This sample was prepared using the first premix for the functional skin layer in Example 1, with the only change being the omission of deionized water as a trace foaming agent. The remaining components, mixing process, and curing conditions were exactly the same as those for the functional skin layer preparation process in Example 1. The mixture was poured into a flat mold and cured to obtain a non-porous solid plate with a thickness of 2.0 mm.

[0131] (2) Test steps:

[0132] From the sample prepared in Example 1, the lower functional skin layer was separated along the interface, and circular specimens of the same size, each with a diameter of 100 mm, were cut from the non-porous solid plate prepared above. According to GB / T 18696.2-2002, using an airflow resistance tester, the static airflow resistance of the two samples was measured and recorded at a stable airflow rate.

[0133] The test results are shown in Table 2:

[0134] Table 2. Comparison of airflow resistance test results between functional skin layer and non-porous solid plate: Sample Description Sample thickness (mm) <![CDATA[Airflow resistance (Pa·s / m 3 )]]> Example 1: Sample Epidermis 2 1156.4 Non-perforated solid plate sample 2 3572900

[0135] The data from Test Example 2 show that the functional skin layer of Example 1 differs by orders of magnitude in airflow resistance from the non-porous solid plate prepared using the same chemical composition. The airflow resistance of the functional skin layer is 1156.4 Pa·s / m. 3 The airflow resistance of the solid plate is at a low level, while the airflow resistance of the non-perforated solid plate is extremely high, indicating that the former allows air to pass through with little resistance, while the latter is basically impermeable to airflow.

[0136] This result confirms the core mechanism of the invention. Although the functional skin layer contains only a trace amount (0.3 parts by weight) of deionized water as a foaming agent in the first premix, the carbon dioxide gas generated during the reaction with isocyanate is sufficient to form a through-hole microporous network in the rapidly gelling polymer matrix. This structure is not a foam in the macroscopic sense, but it is sufficient to build the channel required for sound wave propagation. Therefore, when the sound wave reaches the skin layer, the vibration of air as a medium can effectively penetrate the skin and enter the internal sound-absorbing core material, thereby avoiding the surface reflection of sound energy.

[0137] In contrast, non-porous solid panels, lacking foaming agents in their formulation, form a continuous, dense polymer material after curing. This material lacks interconnected channels, significantly hindering airflow and resulting in extremely high air resistance. In acoustic applications, such a dense surface creates a high acoustic impedance interface, causing most incident sound energy to be reflected, thus failing to achieve sound absorption.

[0138] The results of this test demonstrate the acoustic transparency of the functional skin from a fluid dynamics perspective. This invention, through precise control of micro-foaming, manufactures a functional surface layer in a single molding process that provides physical protection without negatively impacting acoustic performance. This design overcomes the technical shortcomings of traditional polyurethane foam surfaces with dense skins that reflect sound waves, and avoids the additional costs and process complexities associated with secondary protective structures such as perforated panels. This verifies the innovation of this invention in the integrated design of material structure and function.

[0139] Test Example 3:

[0140] This test example provides a comprehensive quantitative evaluation and comparison of the performance of samples prepared in Examples 1-3 and Comparative Examples 1-5. The test includes three aspects: a 180° peel test to evaluate the interlayer bonding strength, a flexibility and thermal shock resistance test to evaluate the durability of the functional skin, and a sound absorption coefficient test to evaluate the core acoustic performance of the material.

[0141] (1) Interlayer bond strength test (180° peel strength):

[0142] This test is only applicable to Examples 1-3 and Comparative Examples 1-4, which have layered structures. During the molding process of sample preparation, a 25mm wide flexible fabric strip was pre-embedded between the functional skin layer and the sound-absorbing core layer, with one end extending outside the mold. After the sample was fully cured, it was cut into 25mm wide specimens. According to ASTM D903, the specimens were fixed on a universal testing machine, and a tensile force in the 180° direction was applied to the embedded fabric strip at a speed of 50mm / min. The average force value during the stable peeling phase at the interface was recorded and calculated as the peel strength (N / m). If peeling did not occur at the interface, the failure mode was recorded.

[0143] (2) Functional skin durability test:

[0144] This test is only applicable to Examples 1-3 and Comparative Examples 1-4, which have functional skins.

[0145] Flexibility test (axial bending): According to the method of GB / T 11185-1989, the complete composite board sample is bent 180° around the shaft of different diameters in sequence, and the minimum bending diameter through which the functional skin layer can pass without cracks is recorded and compared.

[0146] Thermal shock cycle test: Place the complete composite board sample in a high and low temperature impact test chamber. Set the cycle conditions as follows: keep at 80℃ for 2 hours, then cool down to -30℃ within 30 minutes and keep for 2 hours. This is one cycle. After completing 100 cycles, take out the sample and visually inspect whether there are defects such as cracking, blistering or delamination from the core material on the functional skin.

[0147] (3) Sound absorption performance test:

[0148] This test applies to all examples and comparative samples. Circular specimens with a diameter of 100 mm were cut from each sample plate. For layered structures, it was ensured that they contained a complete functional skin. According to GB / T 18696.1-2002 standard, the perpendicular incident absorption coefficient of the samples in the frequency range of 100–6300 Hz was measured using an acoustic impedance tube (standing wave tube method). For ease of comparison, the arithmetic mean of the absorption coefficients of each sample at the center frequencies of the four octave bands of 250, 500, 1000, and 2000 Hz was calculated and recorded; this is the noise reduction coefficient (NRC).

[0149] The test results are shown in Table 3.

[0150] Table 3. Overall performance test data of the examples and comparative examples: sample Peel strength (N / m) Minimum bending diameter (mm) Post-thermal shock cycle state Noise Reduction Ratio (NRC) Example 1 Core material cohesive failure 18 intact 0.81 Example 2 Core material cohesive failure 15 intact 0.79 Example 3 Core material cohesive failure 22 intact 0.83 Comparative Example 1 8.7 18 intact 0.8 Comparative Example 2 Core material cohesive failure >80 (Surface cracking) Skin cracking 0.78 Comparative Example 3 Core material cohesive failure 19 intact 0.46 Comparative Example 4 5.3 19 Slight layering at the edges 0.8 Comparative Example 5 - - - 0.75

[0151] The results of this comprehensive test systematically verified the effectiveness of the technical solution of the present invention and revealed the contribution of each key technical element to the performance of the final product.

[0152] First, peel strength data showed that samples from Examples 1-3 did not experience interfacial separation during testing; instead, they exhibited cohesive failure of the sound-absorbing core material itself. This indicates that the bonding strength between the skin layer and the core layer exceeded the cohesive strength of the core material. The fundamental reason is that the wet-on-wet process ensured a large number of active groups at the gel interface of the skin layer, while the introduction of phosphate ester polyols provided sufficient reactive hydroxyl groups at this interface, promoting chemical cross-linking with the isocyanate component of the core material and forming a covalently bonded integrated structure. In contrast, Comparative Example 1 lacked phosphate ester polyols that provide key reaction sites, and Comparative Example 4 used a non-wet-on-wet cold bonding process, resulting in the deactivation of interfacial active groups. The interfaces of these two examples were only in physical contact, with weak bonding and extremely low peel strength, making it impossible to form a reliable integrated structure.

[0153] Secondly, the durability test of the functional skin highlighted the key role of the aliphatic polyol modified polyetheramine. The minimum bending diameter of the sample samples was small and they could withstand harsh thermal shock cycles, proving that their functional skin has both high toughness and excellent weather resistance. This is because the self-made modified polyetheramine introduces flexible long-chain aliphatic segments into the polymer network, which effectively buffers and dissipates the internal stress caused by mechanical bending or temperature difference. In contrast, Comparative Example 2 replaced this component with the conventional rigid small molecule chain extender 1,4-butanediol. Although chemical bonding was also formed, its skin layer exhibited high brittleness and cracked rapidly in bending and thermal shock tests, completely losing its durable function as a protective layer.

[0154] Finally, sound absorption performance tests confirmed the necessity of active guided opening technology for obtaining high sound absorption coefficients. Samples from Examples 1-3 all exhibited high noise reduction coefficients (NRC values ​​between 0.79 and 0.83). This is directly attributed to the use of terminal epoxy polysiloxane in the sound-absorbing core material formulation. This component, in the later stages of the foaming reaction, disrupts the solidifying cell walls through a ring-opening reaction, inducing a high proportion of interconnected pore structures, providing ample pathways for sound wave incident and dissipation. In contrast, Comparative Example 3 used a conventional foam stabilizer, resulting in a predominantly closed-cell foam structure where gas could not flow effectively between cells, leading to sound energy being primarily reflected rather than absorbed, resulting in an extremely low NRC value (0.46). While the homogeneous foam of Comparative Example 5 possessed some sound absorption capacity, its NRC value was slightly lower than that of the examples, and it lacked a weather-resistant protective skin, making it unsuitable for direct application in outdoor environments.

[0155] In summary, this invention utilizes the synergistic effect of three core elements—interlayer chemical bonding technology, stress-adaptive skin technology, and actively guided pore technology—to prepare a structurally integrated, performance-balanced graded functional material. This material achieves excellent sound absorption performance while ensuring strong interlayer bonding and skin durability, overcoming the inherent contradictions in these properties inherent in traditional materials.

[0156] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A layered composite noise reduction material for sound barriers, characterized in that, The layered composite noise reduction material is an integrally molded layered structure, comprising a functional skin layer and a porous sound-absorbing core layer; the functional skin layer and the porous sound-absorbing core layer are bonded together by covalent bonds formed through in-situ chemical reactions at their interface; The functional skin layer is formed by reacting a first premix containing phosphate ester polyols and aliphatic polyol-modified polyetheramines with polymeric MDI. The porous sound-absorbing core layer is formed by reacting a second premix containing terminal epoxy polysiloxane with polymeric MDI.

2. The layered composite noise reduction material for sound barriers according to claim 1, characterized in that, The aliphatic polyol modified polyetheramine is prepared by reacting terminal amino polyethers with aliphatic biepoxides at 95–110 °C.

3. The layered composite noise reduction material for sound barriers according to claim 2, characterized in that, The terminal amino polyether is polypropylene glycol diamine with a number average molecular weight of 2000-4000 g / mol; The aliphatic diepoxide is one of 1,4-butanediol diglycidyl ether or 1,6-hexanediol diglycidyl ether.

4. The layered composite noise reduction material for sound barriers according to claim 1, characterized in that, The first premix contains a first polyether polyol with an average functionality of 4.0 to 5.0, a number-average molecular weight of 500 to 600 g / mol, and a hydroxyl value of 380 to 420 mg KOH / g; the second premix contains a second polyether polyol with a functionality of 3, a number-average molecular weight of 4500 to 5500 g / mol, and a hydroxyl value of 30 to 40 mg KOH / g.

5. The layered composite noise reduction material for sound barriers according to claim 1, characterized in that, The epoxy value of the terminal epoxy polysiloxane is 0.15–0.25 mol / 100g.

6. The layered composite noise reduction material for sound barriers according to claim 1, characterized in that, The first premix comprises the following raw materials in parts by weight: First polyether polyol: 35-40 parts; Aliphatic polyol modified polyetheramine: 12-20 parts; Phosphate ester polyols: 5-10 parts; First silicone oil foam stabilizer: 0.8–1.2 parts; First foaming catalyst: 0.15–0.3 parts; First gel catalyst: 0.4–0.7 parts; First deionized water: 0.2–0.4 parts; The second premix comprises the following raw materials in parts by weight: Second polyether polyol: 45-55 parts; Polymer polyols: 22-25 parts; Terminally epoxy-based polysiloxane: 1.0–2.5 parts; Second silicone oil foam stabilizer: 1.2-1.8 parts; Second foaming catalyst: 0.4–0.6 parts; Second gel catalyst: 0.2–0.4 parts; Second deionized water: 3.0 to 4.0 parts.

7. A method for preparing a layered composite noise reduction material for a sound barrier according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The first premix and polymeric MDI are mixed at an isocyanate index of 1.00 to 1.10 and then applied to the inner surface of the mold to form a functional skin layer material; (2) When the functional skin layer reaches a gel state but is not completely cured, the second premix used to form the porous sound-absorbing core layer is mixed with polymeric MDI at an isocyanate index of 1.00 to 1.10 and then injected into the mold; (3) Close the mold to solidify the functional skin layer and the porous sound-absorbing core layer into one piece.

8. The preparation method according to claim 7, characterized in that, In step (2), the functional epidermal layer reaches a gel state after staying in the mold for 35 to 50 seconds.

9. The preparation method according to claim 7, characterized in that, In step (3), the temperature of the mold is controlled at 45-60°C, and the pressure curing time is 5-8 minutes.

10. The preparation method according to claim 7, characterized in that, Step (1) is applied using a low-pressure casting machine, and step (2) is injected using a high-pressure foaming machine.