A layered composite noise reduction material for a sound barrier and a preparation method thereof

Abstract

The present application relates to the technical field of layered polymer composite material, and discloses a layered composite noise reduction material for sound barrier and a preparation method thereof, the noise reduction material is an integrated composite structure with a functional skin and a sound absorption core material; the functional skin is prepared by reaction of a first premix containing a first polyether polyol, an aliphatic polyol modified polyether amine and a phosphate ester polyol; the sound absorption core material is prepared by reaction of a second premix containing a second polyether polyol and an epoxy-terminated polysiloxane; the preparation method adopts an integrated forming process, the first premix is applied in a mold, and when it reaches a gel state but has not completely solidified, the second premix is injected for co-solidification forming; the present application solves the problem of interlayer separation, the aliphatic polyol modified polyether amine endows the skin with excellent toughness and weather resistance, and the epoxy-terminated polysiloxane ensures high porosity and sound absorption performance of the core material, the material has stable structure and balanced performance, and is suitable for fields such as metal sound barrier.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of layered polymer composite materials, in particular to a layered composite noise reduction material for sound barriers and a preparation method thereof. BACKGROUND

[0002] Sound barriers, as an important transportation infrastructure, are widely used along highways, railways and urban rail transit to reduce the impact of traffic noise on the surrounding environment. Porous sound-absorbing materials, especially polyurethane foams, can effectively dissipate sound energy due to the presence of a large number of interconnected pore structures inside, and are the core functional components of sound barrier sound-absorbing panels.

[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 high-efficiency sound absorption, the material needs to have a high open porosity and low density, but this usually results in low mechanical strength and poor weather resistance, which easily leads to powdering and aging under the action of ultraviolet light, rain erosion and temperature alternation, and the loss of sound absorption function. On the other hand, if a dense skin layer is formed on the surface of the material through process control to improve durability, the skin layer will reflect most of the incident sound waves due to its high acoustic impedance, so that the internal sound-absorbing structure cannot function.

[0004] To solve this contradiction, the existing technology usually adopts a multi-layer composite panel structure, i.e., using a pre-prepared open-cell polyurethane sound-absorbing foam as the core material, and then covering a protective surface layer such as non-woven fabric, glass fiber mat or functional coating through an adhesive. This way of manufacturing layered products by relying on post-processing physical adhesion makes the interfacial bonding between the layers the weak link of the entire panel structure. Under the repeated action of traffic vibration, wind load and thermal expansion and contraction that the sound barrier bears for a long time, the adhesive interface is prone to fatigue and aging, eventually leading to peeling and delamination of the surface layer and the core material. Once the protective surface layer fails, the fragile sound-absorbing core material will be directly exposed to the environment and quickly deteriorate, thus causing the entire sound barrier unit to lose its preset noise reduction function and significantly shortening its effective service life; in addition, this multi-step composite process also increases the complexity of production and manufacturing costs. Therefore, developing a layered composite noise reduction panel that integrates the protective surface layer and the sound-absorbing core layer by chemical bonding to obtain a highly stable structure with excellent performance is a technical problem that needs to be solved in the field of sound barriers and building sound insulation. SUMMARY

[0005] The technical problem solved by the present application is to provide a layered composite noise reduction material for sound barriers and a preparation method thereof, which aims to overcome the technical defects of poor surface weather resistance and easy aging of the polyurethane sound absorption material as a sound barrier component in the prior art, and the combination of the protective surface layer and the sound absorption core material is not firm and easy to delaminate due to the dependence on physical bonding.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] In the first aspect, the present application provides a layered composite noise reduction material for sound barriers, which adopts the following technical solutions:

[0008] The layered composite noise reduction material is an integrated and formed layered structure, comprising:

[0009] a functional skin layer formed by the reaction of the first premix and polymeric MDI, and a porous sound absorption core material layer formed by the reaction of the second premix and polymeric MDI;

[0010] The functional skin layer and the porous sound absorption core material layer are bonded through the covalent bond formed by the in-situ chemical reaction at the interface therebetween.

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

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

[0013] Fatty polyol modified polyether amine: 12-20 parts;

[0014] Phosphate ester polyol: 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 by weight:

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

[0021] Polymer polyol: 22-25 parts;

[0022] Epoxy-terminated 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: 3.0-4.0 parts.

[0027] By adopting the technical scheme, the functional gradient is constructed in the same product by the synergistic design of the formula of the functional skin layer and the porous sound-absorbing core material layer, so that the layered composite noise reduction board with high structural stability and balanced performance is obtained. The technical mechanism and advantages are reflected in the following three aspects:

[0028] First, the integration of the functional skin layer and the sound-absorbing core material layer is realized by chemical bonding.

[0029] In the formula of the functional skin layer, the introduced phosphate polyol not only gives the material flame retardancy, but more importantly, the active hydroxyl group contained in its molecular structure. When the functional skin layer reaches the gel state but is not completely cured by using the subsequent preparation method of the application, the inner surface is rich in active hydroxyl groups (-OH) provided by the polyol which do not participate in the reaction. At this time, the isocyanate groups (-NCO) in the sound-absorbing core material pre-mixed material injected will react with these active hydroxyl groups in situ to form urethane covalent bonds, and chemical cross-linking is formed at the interface. The combination strength between the two layers is far beyond the physical adhesion, which fundamentally solves the problem of interlayer separation of traditional layered composite board.

[0030] Second, the functional skin layer with durability and acoustic transparency is constructed.

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

[0032] The trace amount of deionized water (0.2-0.4 parts) added in the formula as a foaming agent reacts with isocyanate to generate a trace amount of carbon dioxide. In the process of rapid gelation of the skin layer, these gases are sufficient to form a network of micro-pores. The existence of the network makes the skin layer have certain air permeability, which is manifested as low airflow resistance in acoustics, allowing the incident sound wave to penetrate the skin layer into the internal sound-absorbing core material layer, avoiding sound reflection caused by the dense surface, and ensuring the sound absorption efficiency of the entire layered product.

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

[0034] The sound-absorbing performance of the sound-absorbing core material layer mainly depends on the open porosity inside it. The terminal epoxy group-containing polysiloxane introduced in the formula is a positive open porosity agent, and its action mechanism is as follows:

[0035] In the initial stage of the polyurethane foaming reaction, the viscosity of the foaming system is low, and the action of the conventional silicone oil foaming stabilizer is dominant, forming a uniform closed cell structure.

[0036] As the reaction proceeds, the system temperature rises and the viscosity increases, entering the gel curing stage. At this time, the reactivity of the epoxy groups at the chain ends of the terminal epoxy group-containing polysiloxane is activated.

[0037] The activated epoxy groups undergo ring-opening reaction with amine groups or hydroxyl groups in the polyurethane network. This reaction occurs on the thin film of the bubble wall that is being cured, destroying the regularity of the polymer network and causing local stress concentration and structural weakness on the bubble wall.

[0038] Under the action of the gas pressure inside the bubble, rupture occurs at these structural weaknesses, thereby connecting the originally closed cells to each other, and finally forming a foam structure with high open porosity. This porous structure layer provides sufficient channels for the incidence, reflection and friction dissipation of sound waves, and is the core functional layer for realizing high-efficiency sound absorption of the layered product.

[0039] Preferably, the aliphatic polyol-modified polyether amine is prepared by reacting a terminal amino polyether with an aliphatic diepoxy compound at 95-110°C;

[0040] More preferably, the terminal amino polyether is a polypropylene glycol diamine with a number average molecular weight of 2000-4000 g / mol;

[0041] More preferably, the aliphatic diepoxy compound is 1,4-butanediol diglycidyl ether or 1,6-hexanediol diglycidyl ether.

[0042] By adopting the above technical solution, the synthesis path and raw material specifications of the key component are limited, which can ensure that the introduced flexible chain segment has a suitable molecular weight and structure, thereby accurately regulating the mechanical properties of the functional skin layer, while ensuring toughness, maintaining sufficient strength and hardness.

[0043] Preferably, the average functionality of the first polyether polyol is 4.0-5.0, the number average molecular weight is 500-600 g / mol, and the hydroxyl value is 380-420 mg KOH / g; the functionality of the second polyether polyol is 3, the number average molecular weight is 4500-5500 g / mol, and the hydroxyl value is 30-40 mg KOH / g.

[0044] The first polyether polyol has high functionality and low molecular weight, and is used to build a functional skin layer with high crosslinking density, ensuring its hardness and protection. The second polyether polyol has low functionality and high molecular weight, and is used to form a soft and elastic sound-absorbing core layer matrix. This targeted selection is the basis for achieving the internal performance gradient of the layered product.

[0045] Preferably, the epoxy value of the terminal epoxy group-containing polysiloxane is 0.15-0.25 mol / 100g.

[0046] By using the above technical solution, the reactivity of the active cell opener is quantitatively controlled, and the epoxy value range ensures that the cell opening reaction occurs in the gel stage in the late foaming stage, which can effectively open the cells and avoid foam collapse due to premature reaction, ensuring the stability of the macrostructure of the sound-absorbing core layer.

[0047] In the second aspect, the present application provides a method for preparing a layered composite noise reduction material for sound barriers, which uses the following technical solution:

[0048] (1) The first premix for forming a functional skin layer is mixed with polymeric MDI at an isocyanate index of 1.00-1.10, and then applied to the inner surface of the mold;

[0049] (2) When the functional skin layer reaches the gel state but has not completely cured, the second premix for forming a porous sound-absorbing core layer is mixed with polymeric MDI at an isocyanate index of 1.00-1.10, and then injected into the mold;

[0050] (3) Close the mold, and integrally cure the functional skin layer and the porous sound-absorbing core layer to form a chemical bond between the two layers.

[0051] By using the above technical solution, the present application establishes a "wet-on-wet" integrated molding process, the core of which is to control the time window between the two pouring steps to achieve in-situ chemical bonding between the layers.

[0052] In the kinetics of polyurethane reaction, "gel state" refers to the state in which the polymer network is initially formed, the system loses fluidity, but the chemical reaction is far from complete, and there are still a large number of unreacted active functional groups (mainly hydroxyl and isocyanate groups) in the gel matrix. This method takes advantage of this key intermediate state:

[0053] The operating node of step (2), namely the injection of the sound-absorbing core material layer when the functional skin layer reaches the 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 material layer contacts this active interface, the isocyanate groups in its components will undergo in-situ polymerization reaction with the active functional groups (especially the hydroxyl groups from phosphate-based polyols) remaining on the surface of the skin layer.

[0054] This reaction crosses the physical boundary between the two material layers at the molecular level, forming a continuous urethane covalent bond network, thereby firmly bonding the functional skin layer and the sound-absorbing core material layer into a whole. The interface prepared by this method is a chemical gradient transition zone, rather than a physically adhered interface formed by traditional processes, thus completely avoiding the risk of delamination failure due to poor adhesion or aging of traditional layered composite boards.

[0055] Preferably, in step (2), the functional skin layer reaches the gel state after staying in the mold for 35-50 seconds.

[0056] By adopting the above technical solution, the gel time window is controlled. If the residence time is less than 35 seconds, the functional skin layer has not formed sufficient gel strength, and the mixture of the two materials may occur when the sound-absorbing core material layer is injected, destroying the preset layered gradient structure. If the residence time is longer than 50 seconds, the skin layer is too high in curing degree, and the surface active groups are largely consumed, which cannot form sufficient interface chemical bonding, resulting in a decrease in interlayer bonding strength. This time range is a process guarantee for optimizing the structural integrity and interface bonding strength of the product. The gel state but not completely cured can be determined by a conventional pulling method (such as touching and pulling up with a glass rod).

[0057] 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.

[0058] 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 material layer, ensuring that the polymer network is fully crosslinked, while avoiding material burning or degradation due to excessively high temperature. The pressure holding and curing time ensures that the board reaches sufficient dimensional stability and mechanical strength before demolding.

[0059] Preferably, step (1) is applied by a low-pressure casting machine, and step (2) is injected by a high-pressure foaming machine.

[0060] By adopting the technical scheme, the processing equipment is optimized according to the characteristics of different material layers, the viscosity of the functional skin layer material is relatively low, low-pressure pouring can be adopted to realize uniform and smooth coating on the surface of the mold, and the high-quality outer protective layer is ensured. The sound-absorbing core material layer is a rapid foaming system, and a high-pressure foaming machine can realize instantaneous and highly uniform mixing of raw materials, thereby ensuring the fineness and uniformity of the bubble structure inside the sound-absorbing core material layer, which is a prerequisite for obtaining excellent and stable sound-absorbing performance.

[0061] In summary, the present application includes at least one of the following beneficial technical effects:

[0062] 1. The present application provides a layered composite noise reduction product with high interlayer bonding strength, significantly improving the durability and reliability as a building or facility component, by adopting a wet-on-wet integrated molding process, injecting sound-absorbing core material into the functional skin layer when it reaches the gel state but has not fully solidified, utilizing the active groups on the skin layer interface to react with the core material components in situ, forming a covalently bonded chemical gradient transition zone. This inherent chemical bonding fundamentally solves the risk of interlayer separation caused by physical adhesion or mechanical engagement in traditional layered boards, enabling the product to maintain structural integrity when subjected to long-term vibration, temperature cycling, and external impact.

[0063] 2. The present application realizes efficient synergy between surface protection performance and internal sound-absorbing performance through integrated layered structure design, overcoming the inherent contradiction between the two. The aliphatic polyol modified polyether amine introduced in the functional skin layer formula gives the outer layer excellent flexibility and weather resistance, which can serve as a strong protective layer against harsh outdoor environments; at the same time, the micro-porous structure formed by the trace foaming agent ensures its acoustic transparency, which does not significantly reflect sound waves. The epoxy-terminated polysiloxane introduced in the porous sound-absorbing core material layer formula as a positive pore opener ensures that the inner layer forms a high-porosity energy-consuming structure, thereby achieving efficient sound energy absorption. The two layers have clear functions and synergistic effects, making a single product meet all performance requirements of a sound barrier.

[0064] 3. The preparation process of the present application is highly integrated, integrating the construction of the functional skin layer and the foaming of the sound-absorbing core material layer in one molding cycle, significantly improving production efficiency and reducing manufacturing cost. Compared with the traditional layered sound-absorbing board, which requires multiple processes of manufacturing the core material and then combining the perforated board or protective coating through adhesion, the present application directly generates an integrated layered product with both protection and sound-absorbing functions through formula design and process control. This avoids secondary processing or compounding processes, shortens the production cycle, reduces equipment investment and potential process defects. DETAILED DESCRIPTION

[0065] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically explained are commercially available analytical pure or higher grade products.

[0066] The first polyether polyol is specifically branched polyether polyol obtained by ring-opening copolymerization of polyol as starter 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℃ is 4000-5000 mPa·s.

[0067] The second polyether polyol is specifically trifunctional polyether polyol obtained by ring-opening copolymerization of glycerol as starter with propylene oxide and ethylene oxide. Its number average molecular weight is 4500-5500 g / mol, hydroxyl value is 30-40 mg KOH / g, and viscosity at 25℃ is 700-900 mPa·s.

[0068] The polymeric polyol (POP) is a graft copolymer obtained by in-situ radical polymerization of styrene and acrylonitrile monomers in the second polyether polyol. Its polymer solid content is 40-50wt%, hydroxyl value is 20-30 mg KOH / g, and viscosity at 25℃ is 3500-4500 mPa·s.

[0069] The polymeric MDI (PAPI) is a chemical name for poly-methylene poly-phenyl poly-isocyanate, and its CAS number is 9016-87-9. It is a mixture of 4,4'-diphenyl methane diisocyanate (MDI) and polyfunctional isocyanate containing three or more benzene rings, -NCO group content is 30.0-32.0%, and viscosity at 25℃ is 180-250 mPa·s.

[0070] The phosphate ester polyol is a reactive flame-retardant polyol containing phosphate ester groups, and its structure is that the phosphate ester groups and free hydroxyl groups are connected to the aliphatic polyol skeleton. Its phosphorus content is 4-6wt%, hydroxyl value is 150-200 mg KOH / g, and acid value is less than 1.0 mg KOH / g.

[0071] The conventional polyether polyol is a trifunctional homopolymer polyether polyol obtained by ring-opening copolymerization of glycerol as starter with propylene oxide. Its number average molecular weight is 900-1000 g / mol, and hydroxyl value is 175-185 mg KOH / g. This raw material is used to replace the phosphate ester polyol in the comparative examples.

[0072] End epoxy polydimethylsiloxane, the molecular structure of which is a polydimethylsiloxane main chain, and the two ends of which are connected with epoxy functional groups through propylene. The epoxy value thereof is 0.15-0.25 mol / 100g, and the viscosity thereof at 25°C is 30-60 mPa·s.

[0073] The conventional silicone oil foam stabilizer is a non-hydrolyzed polyether modified polydimethylsiloxane, and the chemical structure thereof is a graft copolymer in which polyoxyethylene-polyoxypropylene copolymer segments are grafted on a polydimethylsiloxane main chain. In this embodiment, Tegostab® B 8715 LF2 from Wacker is selected.

[0074] The aliphatic polyol modified polyether amine is a self-made substance in the present application, and the specific preparation method thereof is shown in Preparation Example 1 and Preparation Example 2.

[0075] The chain extender is 1,4-butanediol (BDO) with a CAS number of 110-63-4 and a purity of greater than 99.5%.

[0076] The foaming catalyst is triethylenediamine with a CAS number of 280-57-9. A dipropylene glycol solution with a mass fraction of 33% of the foaming catalyst is used in the present application.

[0077] The gelation catalyst is N,N-dimethylcyclohexylamine with a CAS number of 98-94-2.

[0078] It should be understood that the silicone oil foam stabilizer, the foaming catalyst and the gelation catalyst used in the present application are all commercialized products widely used in the field of polyurethane foam. Those skilled in the art can select appropriate specific models and brands from commercially available products according to the formula system and process requirements disclosed in the present application, which is a routine technical practice in the art.

[0079] Preparation Example 1:

[0080] The present preparation example provides preparation of the first aliphatic polyol modified polyether amine, which is as follows:

[0081] Into 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 an amino-terminated polyether (polypropylene glycol diamine, number average molecular weight about 2000 g / mol, amine value about 56 mg KOH / g) was charged. The nitrogen protection was started and the mechanical stirring was started. The reaction system was heated to 95°C. 26.0 g of 1,4-butanediol diglycidyl ether was added at a constant speed through the constant pressure dropping funnel within 1.5 hours. During the addition, the temperature of the reaction system was maintained at 95-105°C by adjusting the heating device. After the addition was completed, the reaction was continued at this temperature for 3.5 hours. During the reaction, samples were taken every 1 hour and the amine value of the system was determined by acid-base titration. When the amine value reached 20.5 mg KOH / g, the heating was stopped and the temperature was lowered to room temperature under stirring. The product was discharged and a colorless transparent viscous liquid was obtained, which was the first aliphatic polyol modified polyether amine with an amine value of 20.1 mg KOH / g. The product was sealed and stored for use.

[0082] Preparation Example 2:

[0083] The present preparation example provides the preparation of a second aliphatic polyol modified polyether amine, which is specifically as follows:

[0084] Into the same reaction device as in Preparation Example 1, 400.0 g of an amino-terminated polyether (polypropylene glycol diamine, number average molecular weight about 4000 g / mol, amine value about 28 mg KOH / g) was charged. The nitrogen protection was started and the mechanical stirring was started. The reaction system was heated to 100°C. 10.5 g of 1,6-hexanediol diglycidyl ether was added at a constant speed through the constant pressure dropping funnel within 1.0 hour. During the addition, the temperature of the reaction system was maintained at 100-110°C. After the addition was completed, the reaction was continued at this temperature for 4.0 hours. The same method as in Preparation Example 1 was used for process monitoring. When the amine value reached 15.2 mg KOH / g, the reaction was stopped and the post-treatment was performed. Finally, a light yellow transparent viscous liquid was obtained, which was the second aliphatic polyol modified polyether amine with an amine value of 15.0 mg KOH / g. The product was sealed and stored for use.

[0085] Example 1:

[0086] The present example provides a method for preparing a layered composite noise reduction material for sound barriers, which specifically comprises the following steps:

[0087] (1) Preparation of each functional layer premix: two kinds of premixes for forming the functional skin layer and the porous sound-absorbing core material layer were prepared respectively.

[0088] The formulation of the first premix for the functional skin layer is 40 parts by weight 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 part of a first foaming catalyst, 0.5 part of a first gelation catalyst, and 0.3 part of deionized water. The above components (except the first gelation catalyst and the deionized water) are added to a stirred tank and stirred uniformly, then the first gelation catalyst is added and stirred uniformly, and finally the deionized water is added and dispersed uniformly at high speed to prepare the first premix.

[0089] The formulation of the second premix for the porous sound-absorbing core layer is 50 parts by weight of a second polyether polyol, 25 parts of a polymeric polyol (POP), 2.0 parts of an epoxy-terminated polysiloxane, 1.5 parts of a second silicone oil foam stabilizer, 0.4 part of a second foaming catalyst, 0.3 part of a second gelation catalyst, and 3.2 parts of deionized water. The second premix for the porous sound-absorbing core layer is prepared by the same method as that for the first premix for the functional skin layer.

[0090] (2) Integrated molding: The steel closed mold is preheated and kept at 50°C, and the inner wall of the mold is uniformly sprayed with a release agent. The first premix for the functional skin layer and polymeric MDI (mixed at an isocyanate index of 1.05) are uniformly applied to the inner surface of the mold by a low-pressure pouring machine to form a functional skin layer with a thickness of 2.0 mm, and the functional skin layer is allowed to gel in the mold for 45 seconds. Then, the second premix for the porous sound-absorbing core layer and polymeric MDI (mixed at an isocyanate index of 1.05) are injected into the mold by a high-pressure foaming machine, and the mold is quickly closed. After the mold is kept at 50°C for 7 minutes, the product is demolded and cured at room temperature for 24 hours to obtain the final layered composite noise reduction material with a total thickness of 5 cm.

[0091] Example 2:

[0092] The present embodiment provides a method for preparing a layered composite noise reduction material for a sound barrier, which specifically comprises the following steps:

[0093] (1) Preparation of premixes for each functional layer:

[0094] The formulation of the first premix for the functional skin layer is 40 parts by weight 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 part of a first foaming catalyst, 0.5 part of a first gelation catalyst, and 0.3 part of deionized water. The above components (except the first gelation catalyst and the deionized water) are added to a stirred tank and stirred uniformly, then the first gelation catalyst is added and stirred uniformly, and finally the deionized water is added and dispersed uniformly at high speed to prepare the first premix.

[0095] The formulation of the second premix for the porous sound-absorbing core layer is as follows in parts by weight: second polyether polyol 55 parts, polymeric polyol (POP) 22 parts, second silicone oil foam stabilizer 1.8 parts, second foaming catalyst 0.5 parts, second gelation catalyst 0.4 parts, and second deionized water 3.0 parts.

[0096] Both of the above-mentioned premixes are prepared by the same method as in Example 1.

[0097] (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 by a low-pressure casting machine using the 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 it is left for 35 seconds. Then, the porous sound-absorbing core layer is injected into the mold by a high-pressure foaming machine using the second premix and polymeric MDI (mixed at an isocyanate index of 1.10) and the mold is closed. After the mold is kept at 60°C for 5 minutes, it is demolded, and after room temperature curing for 24 hours, the final layered composite noise reduction material with a total thickness of 3 cm is obtained.

[0098] Example 3:

[0099] The present embodiment provides a method for preparing a layered composite noise reduction material for sound barriers, which specifically comprises the following steps:

[0100] (1) Preparation of premixes for each functional layer:

[0101] The formulation of the first premix for the functional skin layer is as follows in parts by weight: first polyether polyol 40 parts, first aliphatic polyol modified polyether amine 12 parts, phosphate ester polyol 10 parts, first silicone oil foam stabilizer 0.8 parts, first foaming catalyst 0.15 parts, first gelation catalyst 0.4 parts, and first deionized water 0.4 parts.

[0102] The formulation of the second premix for the porous sound-absorbing core layer is as follows in parts by weight: second polyether polyol 45 parts, polymeric polyol (POP) 25 parts, epoxy-terminated polysiloxane 2.5 parts, second silicone oil foam stabilizer 1.2 parts, second foaming catalyst 0.6 parts, second gelation catalyst 0.2 parts, and second deionized water 4.0 parts.

[0103] Both of the above-mentioned premixes are prepared by the same method as in Example 1.

[0104] (2) Integrated molding: Preheat the mold and keep it at 45 °C. Apply the functional skin layer with the first premix and polymeric MDI (mixed at isocyanate index 1.00) into the inner surface of the mold by a low-pressure casting machine to form a functional skin layer with a thickness of 2.5 mm, and let it stay for 50 seconds. Then, inject the porous sound-absorbing core material layer with the second premix and polymeric MDI (mixed at isocyanate index 1.00) into the mold by a high-pressure foaming machine and close the mold. After keeping the mold at 45 °C for 8 minutes, demold and keep it at room temperature for 24 hours to obtain the final layered composite noise-reducing material with a total thickness of 10 cm.

[0105] Comparative Example 1:

[0106] Compared with Example 1, the difference is that the functional skin layer uses the first premix in which the phosphonate polyol is replaced by a conventional polyether polyol with the same hydroxyl value. The remaining components and preparation steps are the same as those of Example 1.

[0107] Comparative Example 2:

[0108] Compared with Example 1, the difference is that the functional skin layer uses the first premix in which the first aliphatic polyol-modified polyether amine is replaced by a chain extender (1,4-butanediol) with the same molar reactivity. The remaining components and preparation steps are the same as those of Example 1.

[0109] Comparative Example 3:

[0110] Compared with Example 1, the difference is that the sound-absorbing core material layer uses the second premix in which the terminal epoxy group-containing polysiloxane is replaced by an equal weight of a conventional silicone foam stabilizer. The remaining components and preparation steps are the same as those of Example 1.

[0111] Comparative Example 4:

[0112] Compared with Example 1, the difference is the preparation process: in step (2) of molding, after the formation of the functional skin layer, it is completely cured in the mold at 50 °C for 30 minutes, and then the casting and foaming of the sound-absorbing core material are carried out after it is cooled to room temperature. The first premix used is the same as that of Example 1.

[0113] Comparative Example 5:

[0114] This comparative example provides a method for preparing a homogeneous polyurethane sound-absorbing foam. It only uses the second premix for the sound-absorbing core material layer in Example 1, and is formed by one-time casting and foaming under the molding conditions of Example 1 to form a plate with the same size as the final product of Example 1, which does not have a functional skin layer.

[0115] Test Example 1:

[0116] This test example aims to verify whether the samples prepared by the methods of Examples 1-3 have an integrated composite structure, and whether the structure presents the expected density gradient in the thickness direction.

[0117] The test procedure is as follows:

[0118] (1) Structural integrity test:

[0119] The samples prepared in Examples 1, 2 and 3 were tested after maturation at room temperature for 24 hours. First, visual inspection was performed on the surface and cross-section of the samples to record whether there were defects such as delamination, blistering or delamination. Then, using a thin-bladed tool, an attempt was made to insert it from the functional skin to the sound-absorbing core at the junction of the cross-section of the sample, and to apply a peeling force along the interface direction. It was observed and recorded whether the interface could be easily separated, and if not, the location of the damage (interface separation or material body damage) was recorded.

[0120] (2) Gradient density test:

[0121] A sample of size 100 mm x 100 mm was cut from the center of the sample prepared in Examples 1-3. Using a sheet cutting machine, the functional skin layer sample and the sound-absorbing core sample were obtained by accurately separating along the interface between the functional skin and the sound-absorbing core. Using a digital caliper with a precision of 0.01 mm, the length, width and thickness of each sample were measured, and the average value of three different positions in each dimension was taken to calculate the volume V. Using an electronic balance with a precision of 0.001 g, the mass m was measured. According to the formula p = m / V, the density of each layer sample was calculated.

[0122] The test results are shown in Table 1.

[0123] Table 1: Results of structural integrity and gradient density tests of example samples:

[0124] Sample Structural Integrity Observations Manual Peel Results Functional epidermal density (kg / m 3 )]]> Sound absorbing core material density (kg / m 3 )]]> Example 1 Tight interface, no delamination Failed to peel, core material cohesive failure 812.5 42.6 Example 2 Tight interface, no delamination Failed to peel, core material cohesive failure 855.2 46.1 Example 3 Tight interface, no delamination Failed to peel, core material cohesive failure 789.8 33.8

[0125] The results of Test Example 1 show that the samples prepared in Examples 1-3 all present an integrated composite structure. Visual observation and manual peeling test confirm that there is no physical boundary between the functional skin layer and the sound-absorbing core layer, and the two are firmly combined. When attempting to peel, cohesive failure of the sound-absorbing core occurs rather than interface separation. This proves that the interface bonding strength is higher than the cohesive strength of the sound-absorbing core itself, forming a truly integrated material. The density test data confirm that there is a significant density gradient along the thickness direction of the material. The density of the functional skin layer (789.8-855.2 kg / m 3 ) is much higher than that of the sound-absorbing core (33.8-46.1 kg / m 3 ), forming a gradient structure from dense to loose from the outside to the inside.

[0126] This integrated structure is a result of the two-step wet-on-wet molding process adopted in the present application. At the gel state but not fully cured stage of the first step functional skin layer, its inner surface still retains a large amount of unreacted active groups, especially the active hydroxyl groups from the phosphate-based polyol. When the second step sound absorbing core material mixture is injected and contacts the active interface, the isocyanate groups in the core material components chemically react with the active hydroxyl groups of the skin layer in situ, forming covalent bonds across the interface. This interface layer formed by chemical bonding has a bonding strength that surpasses the traditional physical adhesion or mechanical engagement, thus fundamentally eliminating the risk of interlayer separation.

[0127] The density gradient of the material is directly attributed to the two different functional pre-mix formulation designs. The functional skin layer uses a high-functionality polyol and a small amount of blowing agent in the first pre-mix to form a high-crosslinking-density, high-mechanical-strength microporous protective layer; the sound absorbing core material layer uses a second pre-mix to generate a low-density, high-openness porous structure by using a higher content of blowing agent, in order to achieve efficient dissipation of sound energy. The successful compounding of the two formulations in one molding cycle makes the material have a macroscopically gradient-changing physical property.

[0128] In summary, the structure and density data of Test Example 1 verify the feasibility of the present application in successfully preparing a gradient functional material with a dense protective skin and a low-density sound absorbing core through a two-component formulation design and a wet-on-wet integrated molding process from the macroscopic performance. The in-situ formed chemically bonded interface ensures the integrity and durability of the structure, and the precisely controlled density gradient is the basis for achieving its comprehensive performance.

[0129] Test Example 2:

[0130] This test example indirectly verifies whether the functional skin prepared in Example 1 has a micro-porous structure that allows sound waves to penetrate by measuring airflow resistance.

[0131] (1) Preparation of comparative sample:

[0132] To establish an effective control, a non-porous solid plate sample needs to be prepared. The sample is prepared using the first pre-mix of the functional skin layer in Example 1, but with the only modification that no deionized water is added as a trace blowing agent. The remaining components, mixing process and curing conditions are exactly the same as the preparation process of the functional skin layer in Example 1. Pour the mixture into a flat plate mold, and after curing, a non-porous solid plate with a thickness of 2.0 mm is obtained.

[0133] (2) Test steps:

[0134] From the sample prepared in Example 1, the lower functional skin layer was separated along the interface, and a circular sample of the same size was cut from the non-porous solid slab prepared above, with a diameter of 100 mm. According to the provisions of GB / T 18696.2-2002, the static air flow resistance of the two samples was measured and recorded respectively using an air flow resistance tester at a stable air flow rate.

[0135] The test results are shown in Table 2:

[0136] Table 2: Comparison of air flow resistance test results of functional skin layer and non-porous solid slab:

[0137] Sample Description Test Specimen Thickness (mm) Airflow resistance (Pa-s / m 3 ) Example 1 Sample Skin Layer 2 1156.4 No-Hole Solid Panel Sample 2 3572900

[0138] The data of Test Example 2 shows that there is an order of magnitude difference in air flow resistance between the functional skin layer of Example 1 and the non-porous solid slab prepared with the same chemical composition. The air flow resistance value of the functional skin layer (1156.4 Pa·s / m 3 ) is at a low level, while the air flow resistance of the non-porous solid slab is extremely high, indicating that the former allows air to pass through with small resistance, while the latter is basically impermeable to air flow.

[0139] This result confirms the core mechanism of the present application. Although only a small amount (0.3 parts by weight) of deionized water as a foaming agent is contained in the first premix of the functional skin layer, during the reaction with isocyanate, the generated carbon dioxide gas is sufficient to form a network of interconnected micro-pores in the rapidly gelled polymer matrix. This structure is not a macroscopic foam, but it is sufficient to build the channels 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.

[0140] On the contrary, the non-porous solid slab, due to the absence of a foaming agent in the formulation, forms a continuous and dense polymer material after curing. This material lacks interconnected channels inside, which poses a huge obstacle to air flow, thus showing extremely high air flow resistance. In acoustic applications, such a dense skin layer forms a high acoustic impedance interface, resulting in the reflection of most of the incident sound energy and failing to play a sound-absorbing role.

[0141] The results of this test example prove the acoustic transparency of the functional skin from the perspective of fluid mechanics. The present application precisely controls the trace foaming to manufacture a functional skin layer that can provide physical protection without negatively affecting the acoustic performance in one molding process. This design solves the technical defect of the dense skin layer of traditional polyurethane foam reflecting sound waves, and avoids the additional cost and process complexity brought by the secondary protective structure such as perforated plate, verifying the innovation of the present application in the design of material structure and function integration.

[0142] Test Example 3:

[0143] This test example quantitatively evaluates and compares the comprehensive performance of the samples prepared in Examples 1-3 and Comparative Examples 1-5. The test content includes three aspects: 180° peeling test to evaluate interlayer bonding strength, flexibility and heat shock resistance test to evaluate the durability of the functional skin, and sound absorption coefficient test to evaluate the acoustic performance of the material core.

[0144] (1) Interlayer bonding strength test (180° peeling strength):

[0145] This test is only applicable to Examples 1-3 and Comparative Examples 1-4 with a layered structure. In the molding step of sample preparation, a flexible fabric strip with a width of 25 mm is pre-embedded between the functional skin layer and the sound-absorbing core layer, with one end of the strip extending out of the mold. After the sample is fully cured, it is cut into a test sample with a width of 25 mm. According to the ASTM D903 standard, the test sample is fixed on a universal material testing machine, and a 180° tensile force is applied to the pre-embedded fabric strip at a speed of 50 mm / min. The average force value during the stable peeling stage is recorded and calculated as the peeling strength (N / m), and if the peeling does not occur at the interface, the failure mode is recorded.

[0146] (2) Functional skin durability test:

[0147] This test is only applicable to Examples 1-3 and Comparative Examples 1-4 with a functional skin.

[0148] Flexibility test (axial bending): According to the method of GB / T 11185-1989, the complete composite board sample is successively bent by 180° around different diameter shafts, and the minimum bending diameter that the functional skin layer can pass without cracking is recorded and compared.

[0149] Heat shock cycle test: Place the complete composite board sample in a high-low temperature shock test chamber, and set the cycle conditions as follows: maintain at 80°C for 2 hours, then reduce the temperature to -30°C within 30 minutes and maintain for 2 hours, which is one cycle. After completing 100 cycles, take out the sample and visually inspect for defects such as cracking, blistering, or delamination of the core material.

[0150] (3) Sound absorption performance test:

[0151] The test is applicable to all the example and comparative sample, cut out a circular sample with a diameter of 100 mm from each sample, for the layered structure sample, make sure it contains a complete functional skin. According to GB / T 18696.1-2002 standard, use the acoustic impedance tube (standing wave tube method) to measure the normal incidence sound absorption coefficient of the sample in the frequency range of 100-6300 Hz. For comparison, calculate and record the arithmetic mean value of the sound absorption coefficient of each sample at the four center frequencies of 250, 500, 1000 and 2000 Hz, that is, the noise reduction coefficient (NRC).

[0152] The test results are shown in Table 3.

[0153] Table 3: Comprehensive performance test data of examples and comparative examples

[0154] Sample Peel Strength (N / m) Minimum Bend Diameter (mm) Condition After Thermal Shock Cycling Noise Reduction Coefficient (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 Edge slight delamination 0.8 Comparative Example 5 Core material cohesive failure Intact - - - 0.75

[0155] The results of this comprehensive test systematically verify the effectiveness of the technical solutions of the present application, and reveal the contribution of each key technical element to the performance of the final product.

[0156] Firstly, the peel strength data shows that the samples of examples 1-3 do not separate at the interface in the test, but show cohesive failure of the sound absorption core itself. This indicates that the bonding strength between the skin layer and the core layer exceeds the cohesive strength of the core material. The fundamental reason is that the wet-on-wet process ensures that there are a large number of active groups at the gel interface of the skin layer, and the introduction of phosphate polyols provides sufficient reactive hydroxyl groups for the chemical crosslinking with the isocyanate component of the core material, forming a covalently bonded integrated structure. In contrast, comparative example 1 lacks phosphate polyols, which provide key reaction sites, and comparative example 4 uses a non-wet-on-wet cold bonding process, which causes the inactivation of the active groups at the interface. The interface of the two is only physical contact, the bonding force is weak, and the peel strength is extremely low, so it cannot form a reliable integrated structure.

[0157] Secondly, the durability test of the functional skin highlights the key role of the aliphatic polyol modified polyetheramine. The minimum bending diameter of the example samples is small, and they can withstand severe thermal shock cycles, proving that the functional skin has high toughness and excellent weather resistance. This is because the self-made modified polyetheramine introduces flexible long-chain aliphatic segments into the polymer network, effectively buffering and dissipating internal stress caused by mechanical bending or temperature difference; comparative example 2 uses a conventional rigid small molecule chain extender, 1,4-butanediol, to replace this component, although a chemical bond is formed, the skin layer is highly brittle and quickly cracks in the bending and thermal shock tests, completely losing the durability function as a protective layer.

[0158] Finally, sound absorption performance tests confirmed the necessity of the active open-cell technology for achieving high sound absorption coefficients. Samples of 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 the terminal epoxy-based polysiloxane in the sound absorption core formulation. This component, through ring-opening reactions at the later stage of the foaming reaction, destroys the walls of the curing cells, inducing the formation of a high proportion of connected channel structures, providing sufficient paths for the incidence and dissipation of sound waves; Comparative Example 3 uses a conventional foam stabilizer, and its foam structure is mainly closed-cell, and the gas cannot flow effectively between the cells, resulting in that the sound energy is mainly reflected rather than absorbed, and the NRC value is very low (0.46); Comparative Example 5, although having a certain sound absorption capacity, has a slightly lower NRC value than the examples, and lacks a weather-resistant protective skin, and cannot be directly applied to outdoor environments.

[0159] In summary, the present application, through the synergistic effect of the three core elements of interlayer chemical bonding technology, stress self-adaptive skin technology and active open-cell technology, prepares a gradient functional material with integrated structure and balanced performance. Under the premise of ensuring firm interlayer bonding and skin durability, the material achieves excellent sound absorption performance, overcoming the inherent contradictions of traditional materials in these properties.

[0160] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application 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 material layer is formed by reacting a second premix containing terminal epoxy polysiloxane with polymeric MDI. The first premix is ​​mixed with polymeric MDI at an isocyanate index of 1.00 to 1.10 to form the functional skin layer; The second premix is ​​mixed with polymeric MDI at an isocyanate index of 1.00 to 1.10 to form the porous sound-absorbing core material layer.

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.