A lightweight noise-reducing foam component for automotive interior and its preparation method

Abstract

This invention relates to the field of polymer materials and discloses a lightweight noise-reducing foam component for automotive interiors and its preparation method. The invention aims to solve the technical problems of reduced sound insulation performance due to density reduction in existing automotive interior materials during the pursuit of lightweighting, as well as sound leakage caused by poor installation fit. This invention constructs a microscopic resonant sound-absorbing network by introducing coupling agent-grafted modified hollow glass microspheres, significantly improving noise blocking capability across the entire frequency band while significantly reducing density. Simultaneously, it utilizes the shape memory effect to achieve adaptive volume control, supporting high compression ratio storage and thermally induced in-situ expansion sealing, effectively eliminating the risk of sound leakage through gaps, and achieving a synergistic improvement in lightweighting, high noise reduction, and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and more specifically, to a lightweight noise-reducing foam for automotive interiors and its preparation method. Background Technology

[0002] As the automotive industry continues its pursuit of lightweighting, comfort, and NVH (noise, vibration, and harshness) quietness, automotive interior foam materials, as a key component of the vehicle's acoustic package, are no longer merely decorative elements. They now play irreplaceable roles in structural filling, sound insulation, noise reduction, and energy absorption. Especially in complex structural areas such as the A-pillar cavity, door panel gaps, carpet underlayer, and headliner interior, high-performance foam components not only provide essential mechanical support and sealing barriers but also directly determine the acoustic quality and ride comfort of the passenger space. They are crucial for blocking external wind noise, road noise, and engine noise from entering the vehicle.

[0003] However, in the industry's pursuit of ultimate lightweighting, traditional foam materials face a severe contradiction in their physical properties. On the one hand, to reduce vehicle weight and energy consumption, the density of foam materials is continuously compressed, directly leading to thinner cell walls, failure of the law of mass, and a significant reduction in sound insulation and noise reduction efficiency. On the other hand, low-density materials are often accompanied by decreased mechanical strength and insufficient resilience, making it difficult to maintain a tight fit to irregular gaps in the vehicle body during long-term service. This easily creates sound leakage channels due to installation tolerances or vibration displacement, resulting in severe deterioration of NVH performance. How to significantly reduce density while reconstructing an efficient sound energy dissipation mechanism and ensuring durable sealing has become a technical bottleneck restricting the development of next-generation high-performance automotive interior materials. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a lightweight noise-reducing foam component for automotive interiors and its preparation method, solving the technical problems of reduced sound insulation performance due to decreased density in existing automotive interior materials during the pursuit of lightweighting, and sound leakage caused by poor installation fit.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: The present invention provides a method for preparing lightweight noise-reducing foamed parts for automotive interiors, comprising the following steps: S1, grafting a coupling agent onto hollow glass microspheres to obtain modified noise-reducing filler; S2. Mix 40-70 parts by weight of poly(1,4-butanediol adipate) diol with 30-60 parts by weight of polycaprolactone diol and dehydrate under negative pressure. Then, add 15-25 parts by weight of modified noise-reducing filler, 1.0-1.75 parts by weight of 1,4-butanediol, 0.4-0.8 parts by weight of triethylenediamine, 1.25-2.0 parts by weight of modified polysiloxane and water in sequence. Mix evenly under high-speed shearing at a stirring speed of 1000-1400 rpm and a stirring time of 20-40 minutes to prepare a stable prepolymer emulsion. S3. The prepolymer emulsion at a constant temperature is mixed with 40-70 parts by weight of liquefied diphenylmethane diisocyanate by impact through the mixing head of a high-pressure foaming machine, and then rapidly injected into a mold for foaming and curing to obtain a primary foamed part. S4. The primary foamed part is mechanically broken through by a roller press with a roller gap of 30% to 50% of the original thickness of the part to connect the internal cell structure. Then, it is subjected to long-term heat treatment to eliminate internal stress and improve the cross-linking network. S5. Heat and compress the foamed part after secondary vulcanization, and then rapidly cool and solidify it while maintaining the compression state to obtain a finished foamed part with thermo-shaped shape memory function.

[0007] In a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S2, the mass fraction of the poly(1,4-butanediol adipate) is 55 parts, the mass fraction of the polycaprolactone diol is 45 parts, the mass fraction of the modified noise-reducing filler is 20 parts, the mass fraction of the 1,4-butanediol is 1.4 parts, the mass fraction of the triethylenediamine is 0.6 parts, and the mass fraction of the modified polysiloxane is 1.6 parts. The stirring speed is 1200 rpm and the stirring time is 30 minutes.

[0008] In a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S3, the mass fraction of the diphenylmethane diisocyanate is 55 parts.

[0009] As a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S4, the roller gap is 40% of the original thickness of the part.

[0010] As a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, wherein: in step S1, the coupling agent is γ-aminopropyltriethoxysilane, and the modification process specifically includes: dissolving the coupling agent in anhydrous ethanol to prepare a modified solution, spraying it onto the surface of the hollow glass microspheres, stirring and mixing at 400-600 rpm at 50-70°C for 20-40 minutes, and drying at 100-110°C for 1.5-2.5 hours, wherein the amount of the coupling agent is 1.2%-1.8% of the mass of the hollow glass microspheres.

[0011] As a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S2, the negative pressure dehydration conditions are a temperature of 100~120℃ and a pressure of -0.09~-0.10MPa, and the dehydration is carried out continuously for 1.5~2.5 hours until the moisture content is lower than 0.05%; the temperature during the preparation of the prepolymer emulsion is controlled at 40~50℃.

[0012] In a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S3, the temperature of the prepolymer emulsion is 40~50℃, the temperature of the liquefied diphenylmethane diisocyanate is 25~35℃, the injection pressure of the high-pressure foaming machine is 10~14MPa, the preheating temperature of the mold is 50~60℃, and the curing time is 6~10 minutes.

[0013] As a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S4, the temperature of the long-term heat treatment is 70~90℃ and the treatment time is 10~14 hours, so as to eliminate internal stress and improve the cross-linking network.

[0014] As a preferred embodiment of the method for preparing lightweight noise-reducing foamed parts for automotive interiors according to the present invention, in step S5, the heating temperature is 60~70℃, the compression ratio to the original volume is 15%~25%, the rapid cooling and shaping temperature is 5~15℃, and the cooling maintenance time is 3~7 minutes.

[0015] This invention also provides a lightweight noise-reducing foam for automotive interiors, wherein: the foam exhibits a multiphase composite structure in which modified hollow glass microspheres are uniformly dispersed in a polyurethane matrix network; the polyurethane matrix has soft and hard segment microphase separation characteristics, wherein the soft segment crystalline phase constitutes a reversible thermo-induced shape memory switch, and the hard segment phase and the modified hollow glass microspheres together constitute a rigid support skeleton; the foam has an internal interconnected open network formed by mechanical perforation, and the open network and the rigid cavity inside the microspheres together constitute multiple sound energy dissipation channels, giving the material comprehensive properties of being lightweight, high-strength, noise-reducing, and having thermo-induced shape memory.

[0016] The beneficial effects of this invention are as follows: By introducing hollow glass microspheres modified with coupling agents, a stable rigid cavity network is constructed in the polyurethane matrix. The thin-film resonance and multiple reflection effects significantly improve the blocking and dissipation capabilities across the entire frequency band, especially mid-to-high frequency noise, effectively resolving the physical contradiction of reduced sound insulation performance caused by decreased foam material density. Simultaneously, the shape memory effect enables adaptive volume control of the foamed component, allowing it to be compressed to 20% of its original volume at room temperature for efficient storage and transportation, and to rapidly return to its original shape after heating to tightly fill complex gaps in the vehicle body, eliminating the risk of sound leakage caused by poor installation fit. Furthermore, through systematic optimization of chain extenders, catalysts, and microstructure, the final product achieves both extreme lightweighting and excellent noise reduction characteristics while maintaining superior mechanical strength and dimensional stability, meeting the automotive industry's requirements for high-performance interior materials. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The figure shows the results of the screening experiment for the ratio of PBA to PCL.

[0019] Figure 2 The figure shows the experimental results of optimizing the amount of diphenylmethane diisocyanate.

[0020] Figure 3 The figure shows the experimental results of the synergistic screening and optimization of the ratio of diethanolamine to modified polysiloxane.

[0021] Figure 4 The figure shows the results of the screening experiment for catalyst dosage.

[0022] Figure 5 The figure shows the experimental results of screening and optimizing the dosage of surface modifiers.

[0023] Figure 6 The figure shows the results of the screening experiment for the amount of modified hollow glass microspheres.

[0024] Figure 7 The figure shows the experimental results for optimizing the dispersion process.

[0025] Figure 8 Figure showing the experimental results for optimizing the hole-breaking process.

[0026] Figure 9This is a flowchart illustrating the preparation process of a lightweight noise-reducing foam component for automotive interiors. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0030] Example 1 This embodiment aims to develop a polymer foam material that combines excellent shape memory properties with ultra-lightweight and high sound absorption characteristics, in order to solve the technical bottlenecks in automotive interior parts caused by reduced density, such as decreased sound insulation performance and poor installation fit, during the pursuit of ultimate lightweighting. Given that the target material needs to achieve efficient noise blocking across the entire frequency band while maintaining low density, and possess the ability to adaptively fill irregular gaps in the vehicle body upon heating, a robust experimental benchmark that balances lightweighting and high noise reduction efficiency needs to be established through deep matching of the material's intrinsic properties and microstructure. This will provide a material basis and technical path for the subsequent development of high-performance noise-reducing foam components.

[0031] 1.1 Selection of substrate materials To establish the core framework of foamed materials, it is necessary to screen polymer matrices that can balance excellent mechanical properties with good foaming characteristics. This matrix material not only needs to possess a well-defined micronetwork structure to provide long-term stable support, but also needs to have specific microphase states to achieve effective dissipation of sound energy.

[0032] Experimental groups: A1 Poly(1,4-butanediol adipate) diol (PBA, Mn=2000, f=2), A2 Polytetrahydrofuran ether diol (PTMG, Mn=2000, f=2), A3 Polycaprolactone diol (PCL, Mn=2000, f=2), A4 Polypropylene triol (PPG, Mn=3000, f=3), A5 Polycarbonate diol (PCDL, Mn= A6 Polyethylene oxide glycol (PEG, Mn=2000, f=2), A7 Polypropylene oxide glycol (PPG-2000, f=2), A8 Polycaprolactone triol (PCL-3000, f=3), A9 Polyethylene oxide-tetrahydrofuran coether glycol (EO / THF-2000), A10 Polycarbonate hexane glycol ester glycol (PCDL-1000).

[0033] To ensure that each component participates in the screening at its optimal performance, the most widely used and best-balanced industrial standard specifications in the foaming field were selected. Under uniform physical foaming conditions (using water as a chemical foaming agent, supplemented by a small amount of physical foaming agent, without introducing additional shape memory components or fillers), reaction molding tests were conducted with standard liquefied MDI (component B).

[0034] Tensile strength was tested according to GB / T6344-2008 standard. It characterizes the maximum stress that the foam matrix can withstand under external tensile force until fracture, reflecting the rigidity of molecular chain segments and the microscopic strength of the cell walls. It is a fundamental basis for evaluating whether a material can maintain structural integrity during long-term service.

[0035] The elongation at break was tested according to the GB / T6344-2008 standard. It characterizes the maximum deformation capacity of a material before fracture, directly reflecting the flexibility and mobility of the molecular chains. For shape memory materials, a higher elongation at break means that the material can withstand greater compressive deformation during the programming stage without brittle failure.

[0036] Referring to GB / T6669-2008 standard, the compression set was measured after 22 hours at 70℃ and 50% compression. This assesses the material's resilience under long-term pressure; a lower value indicates better dimensional stability, ensuring the foamed parts effectively fill gaps in the vehicle body after installation.

[0037] Differential scanning calorimetry (DSC) was used to determine the crystallization melting temperature. Characterizing the melting behavior of soft segment crystallites in the matrix material is a key parameter determining the shape memory transition temperature. Ideally, Tm should be located in the range of 40–60 °C to ensure that the material is in a crystalline hardened state (shape locked) at room temperature, and rapidly transforms into an amorphous softened state (triggered recovery) upon heating.

[0038] The sample is heated to above Tm and stretched by 100%. After cooling to room temperature, the load is unloaded, and its ability to retain the stretched shape is measured as the shape retention rate (Rf). This directly reflects the material's ability to remember a temporary shape. The higher the Rf value, the better the shape-locking effect of the material after cooling, which facilitates transportation and storage after volume compression.

[0039] The test results are as follows: Among them, polycarbonate diol (PCDL, A5) exhibits good tensile strength due to the high cohesive energy imparted by its rigid carbonate groups, but its elongation at break is relatively low due to the limited flexibility of its molecular chain segments, making it difficult to meet the toughness requirements under large deformation conditions. Polypropylene glycol (PPG, A7) achieves high elongation at break thanks to its highly flexible ether bond structure, but its lack of sufficient hard segment support and difficulty in forming an effective crystalline phase results in low tensile strength and shape retention, failing to provide the necessary structural support and shape locking function. Polytetrahydrofuran ether diol (PTMG, A2) exhibits good resilience and extremely low compression set, but its crystallization melting temperature is significantly low, indicating that it is difficult to maintain a crystalline state at room temperature and cannot be used as a base carrier for shape memory materials. Polycaprolactone diol (PCL, A3 / A8) has a high shape retention, but its excessive crystallinity makes the material too hard and brittle, which is not conducive to subsequent flexible processing and actual installation.

[0040] In contrast, poly(1,4-butanediol adipate) diol (PBA, Al) offers moderate tensile strength and elongation at break, ensuring sufficient support and deformation capacity. Its melting temperature also aligns with the usage environment and installation process of automotive interior parts. Furthermore, its good shape retention rate ensures excellent shape memory properties. Therefore, poly(1,4-butanediol adipate) diol (PBA-2000), with its superior overall performance, was selected as the matrix material.

[0041] 1.2 Screening of shape memory functional components To impart excellent shape memory effect to the matrix material, this experiment aims to screen for a switching component that can form a well-separated microstructure with the poly(1,4-butanediol adipate) matrix and possesses a suitable crystallization-melt transition temperature (Tm). This component needs to lock a temporary shape through crystalline phase at room temperature, and then rapidly melt upon heating to a specific temperature to release internal stress and drive the material to return to its initial shape.

[0042] Experimental groups (poly(1,4-butanediol adipate) diol in 50 parts): B1 polytetrahydrofuran ether diol (PTMG, Mn=2000, 50 parts), B2 polylactic acid diol (PLA, Mn=2000, 10 parts), B3 polycaprolactone diol (PCL, Mn=4000, 30 parts), B4 polyethylene oxide diol (PEG, Mn=6000, 20 parts), B5 polycarbonate diol (PCDL, Mn=2000, 30 parts), B6 ​​polypropylene oxide diol (PPG, Mn=2000, 60 parts), B7 polybutylene succinate diol (PBS, Mn=2000, 15 parts), B8 polycaprolactone diol (PCL, Mn=1000, 40 parts).

[0043] Measurements of elongation at break characterize the degree to which the toughness of the matrix material is retained after the introduction of functional components. Higher values ​​indicate that the material is less prone to brittle fracture under large deformations.

[0044] The temperature at which the spline begins to show obvious deformation during the heating process is recorded as the shape memory response temperature. The ideal response temperature should be in the range of 45~65℃, which avoids false triggering due to high summer temperatures and facilitates rapid activation using hot air.

[0045] A long strip of sample is bent into a 180° (U-shape) shape in hot water and then placed in cold water to hold it in place. After the external force is removed, the angle at which the sample automatically springs back is measured as the rebound angle after cooling. The smaller this angle, the stronger the material's ability to maintain its temporary shape.

[0046] The sample, now fixed in shape, is placed back into hot water, and its process of returning to its straight shape is observed. After stabilization, the residual angle that the sample failed to recover is measured. The smaller this angle, the stronger the material's ability to spring back to its initial shape.

[0047] The test results are as follows: Among them, polylactic acid glycol (PLA, B2) and polybutylene succinate diol (PBS, B7) have low rebound angles after cooling due to their good crystallinity and rigid chain segments; however, their rigidity leads to low elongation at break, and poor compatibility prevents the release of internal stress, resulting in a large residual bending angle after heating. This manifests as a locked but unyielding structure, making them extremely brittle and unable to meet the requirements for flexible foam components. Polypropylene glycol (PPG, B6) and polytetrahydrofuran ether glycol (PTMG, B1) have good elongation at break and low residual bending angles after heating, but due to the lack of an effective crystalline stationary phase (PPG is non-crystalline, and PTMG has a melting point <30℃), their rebound angles after cooling are too large.

[0048] Polycaprolactone diol (PCL-4000, B3) has excellent overall performance and a suitable temperature range, making it an ideal component for shape memory functions.

[0049] 1.3 Screening and Optimization of Chain Extenders To further improve the mechanical strength and thermal stability of foamed materials, this experiment aims to screen for a chain extender capable of molecular-level fusion with the PBA matrix and PCL switching phase. As the main source of polyurethane hard segments, the chemical structure of the chain extender directly determines the degree of microphase separation in the material. On the one hand, it needs to provide sufficient rigid hard segments to enhance the skeletal support of the material; on the other hand, it needs to possess suitable reactivity to match the gelation rate of the foaming system, avoiding foam bursting due to excessively rapid reaction or collapse due to excessively slow reaction.

[0050] Experimental groups: C1 is 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA, molten liquid feed), C2 is hydroquinone dihydroxyethyl ether (HQEE, solid slice feed), C3 is 1,4-butanediol (BDO, liquid feed), C4 is trimethylolpropane (TMP, liquid feed), C5 is ethylene glycol (EG, liquid feed), C6 is diethanolamine (DEA, liquid feed), C7 is 1,4-cyclohexanediethanol (CHDM, liquid feed), and C8 isophorone diamine (IPDA, liquid feed).

[0051] To ensure the impartiality of the screening process and its industrial guidance significance, each component adopted its standard industrial specifications in its corresponding system, and the formulation was designed according to its optimal chain extension coefficient (typically 0.95~1.05). While keeping the soft segment (PBA+PCL) content constant, polyurethane foam materials were prepared and their performance tested by adjusting the isocyanate index to 1.02.

[0052] In addition to testing tensile strength and elongation at break, tear strength should also be tested using right-angled specimens, in accordance with GB / T10808-2006 standard, to characterize the resistance of foamed materials to crack propagation under localized stress concentration. For foamed parts that require frequent bending and compression during installation, higher tear strength means that the material is less prone to macroscopic fracture due to microscopic defects, directly reflecting whether the hard segment phase constructed by the chain extender has sufficient toughness and cohesion.

[0053] The sample was heated to its shape memory response temperature (55°C) under 50% compression, and the restoring force generated when it attempted to return to its original shape was recorded. This indicator is directly related to the tightness of the foam filling the gaps in the car body after thermal expansion. The greater the restoring force, the stronger the elastic potential energy released by the material, which can more firmly hold against the gap walls, thereby effectively blocking the noise propagation path.

[0054] The test results are as follows: Among them, aromatic diamine chain extenders (MOCA, C1) and alicyclic diamines (IPDA, C8) endow the materials with high tensile strength and tear strength due to the extremely rigid benzene ring or alicyclic structure in their molecular chains; however, this also results in the materials being too hard, with a severely low elongation at break, exhibiting obvious brittle fracture characteristics, and in actual operation, due to the high reactivity of the amine groups, they are very prone to blistering, resulting in an extremely narrow process window; Trifunctional crosslinking agents (TMP, C4) significantly improve the modulus of materials by introducing chemical crosslinking points, but also limit the slippage ability of molecular chains, resulting in low elongation at break. Once the material is subjected to excessive stress, it will undergo irreversible damage. Although alkanolamine chain extenders (DEA, C6) endow materials with excellent flexibility (high elongation at break), the steric hindrance effect of their side groups disrupts the regular arrangement of hard segment crystallites, resulting in a tensile strength of only 3.24 MPa, which cannot meet the basic structural support requirements. Hydroquinone dihydroxyethyl ether (HQEE, C2) has good resilience, indicating excellent heat resistance. However, its high melting point makes it prone to precipitation and nozzle clogging during foaming, resulting in poor compatibility and unsatisfactory tear strength.

[0055] 1,4-Butanediol (BDO, C3) offers a good balance of tensile strength and elongation at break, combining rigidity and toughness. As a liquid additive, it exhibits excellent compatibility with the matrix, and the foaming process is stable and controllable. Therefore, 1,4-Butanediol was selected as a chain extender.

[0056] 1.4 Catalyst Screening To achieve precise kinetic matching between foaming and gelation reactions, this experiment aims to screen a catalyst system that can coordinate the bubble nucleation rate and the polymer skeleton growth rate. Catalyst selection is crucial in polyurethane foaming. If the foaming reaction is too rapid, gas will escape before the skeleton gains strength, leading to bubble collapse. If the gelation reaction is too rapid, the material will solidify prematurely, limiting bubble growth and causing closed-cell shrinkage or abnormally increased density.

[0057] Experimental groups: D1 Triethylenediamine (TEDA), D2 Bis(dimethylaminoethyl) ether (A-1), D3 Stannous octoate (T-9), D4 Dimethylethanolamine (DMEA), D5 1,8-diazabicycloundec-7-ene (DBU), and D6 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30).

[0058] In addition to detecting the density after free foaming without mold constraints, it is also necessary to evaluate the catalyst's ability to regulate foaming kinetics through milky time and gel time.

[0059] The milky white time is the point in time from the start of mixing until the material system begins to appear milky white and turbid due to gas generation, accompanied by volume expansion. It directly reflects the start-up rate of the foaming reaction (-NCO reacts with water to produce CO2). If the time is too short, it indicates that the initial foaming is too vigorous, which will not only lead to a very narrow operating window, but also cause co-occurrence and large bubbles due to excessively rapid bubble nucleation.

[0060] The gel time is the time from the start of mixing until the reactants lose their fluidity and can be drawn into fine filaments. This indicator precisely characterizes the rate of the gel reaction (crosslinking and curing of -NCO and -OH). If the time is too short, it indicates that the polymer skeleton cures too early, limiting the full expansion of the gas, leading to an abnormal increase in product density or internal stress cracking; if the time is too long, it means that the strength growth of the skeleton lags behind the gas expansion, making it unable to support the foam structure and easily leading to bubble collapse or closed-cell shrinkage.

[0061] The test results are as follows: Among them, the time parameters of triethylenediamine and 2,4,6-tris(dimethylaminomethyl)phenol both meet the requirements. However, the foam produced by 2,4,6-tris(dimethylaminomethyl)phenol is extremely brittle and breaks easily under light pressure. Therefore, triethylenediamine was selected as the best catalyst.

[0062] 1.5 Screening of Noise Reduction Fillers To endow foamed materials with excellent acoustic properties and lightweight characteristics, this experiment aims to screen a functional filler that combines low density, high strength, and high-efficiency sound absorption potential. This filler needs to construct a stable microscopic cavity structure within the foaming system to achieve noise reduction through the resonant dissipation mechanism of sound energy, while simultaneously serving as a rigid support point to improve the mechanical properties of the matrix and prevent structural collapse due to density reduction.

[0063] Experimental group: E1 expanded perlite powder (bulk density 0.08 g / cm³) 3 E2 thermoplastic organic hollow microspheres (Expancel, true density 0.03 g / cm³) 3 E3 fly ash cenospheres (industrial hollow glass microspheres, true density 0.7 g / cm³) 3 E4 hollow glass microspheres (HGM, true density 0.25 g / cm³) 3 E5 polyimide powder (PI, true density 1.4 g / cm³) 3 E6 chopped glass fiber (GF, true density 2.5 g / cm³) 3 ).

[0064] Polyurethane foam composite materials were prepared and their density was measured. The noise reduction coefficient was tested according to GB / T20247-2006 standard to evaluate the average sound absorption capacity of the foam material across the entire frequency range (125Hz-4000Hz). A higher value indicates a higher efficiency in dissipating sound energy, which is the core basis for evaluating whether the filler can effectively construct a noise reduction structure.

[0065] The compressive strength was tested at 10% deformation according to GB / T8813-2008 standard. This test assesses the resistance of foamed materials to collapse under continuous pressure. For interior components subjected to long-term vibration loads, higher compressive strength means that the filler not only contributes to weight reduction but also significantly enhances the rigidity of the matrix as a micro-skeleton.

[0066] The test results are as follows: Among them, thermoplastic organic hollow microspheres effectively reduce the apparent density of the material due to their extremely low true density, thus achieving effective weight reduction; however, due to the extremely poor temperature resistance of their polymer shell, they soften and collapse during the foaming and exothermic process, resulting in low compressive strength and the failure to form an effective resonant sound-absorbing cavity, thus exhibiting only average noise reduction performance. Although fly ash cenospheres and chopped glass fibers possess high compressive strength due to their high modulus inorganic material, they also significantly increase the density of the materials. Furthermore, the cenospheres have uneven wall thickness and high closed-cell rate, making it difficult for sound waves to penetrate and dissipate, resulting in a low noise reduction level. Expanded perlite powder has good noise reduction capabilities due to its rich porous structure, but its loose and brittle texture and easy moisture absorption and pulverization result in low compressive strength and inability to provide any effective structural support.

[0067] In contrast, hollow glass microspheres effectively reduce weight, dissipate sound energy through resonance, and provide good support strength. However, they have poor compatibility with materials and require surface modification before they can be used as noise-reducing fillers.

[0068] 1.6 Screening of Surface Modifiers To address the problems of weak interfacial bonding between hydrophilic inorganic microspheres and hydrophobic organic matrices, easy formation of microcracks, and high sound energy transmission loss, this experiment aims to screen for a surface modifier that can significantly improve the surface wettability of hollow glass microspheres and enhance their interfacial bonding strength with polyurethane matrix.

[0069] Experimental groups: F1 was γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), F2 was γ-methacryloyloxypropyltrimethoxysilane (KH-570), F3 was untreated hollow glass microspheres (blank control group), F4 was γ-aminopropyltriethoxysilane (KH-550, aminosilane), F5 was isopropyltris(dioctylpyrophosphate)titanate (NDZ-201), and F6 was stearic acid (octadecanoic acid).

[0070] In addition to testing tensile strength to quantify the contribution of the modifier to the interfacial bonding strength, a clean flat glass substrate of the same material as the hollow glass microspheres is selected as a simulated modification object, and the water contact angle is tested using the seated drop method. Each group of surface treatment agents is treated on the surface of the glass substrate using the same process parameters, and the static contact angle of deionized water droplets on the modified surface is measured. A larger angle indicates that the modified layer imparts stronger hydrophobicity to the inorganic surface, meaning that in the actual foaming system, the microspheres can be more easily wetted and encapsulated by the hydrophobic polyurethane matrix, thus significantly improving dispersibility and compatibility.

[0071] The test results are as follows: Stearic acid, with its long-chain alkyl group, possesses high hydrophobicity. However, this is merely a weak interaction based on physical adsorption, lacking chemical bonding. This leads to easy slippage and debonding at the interface under stress, resulting in reduced tensile strength. While KH-560 achieves the highest tensile strength due to the high reactivity of its epoxy groups, its small water contact angle indicates a less than ideal hydrophobic modification effect. This suggests that a significant number of hydrophilic hydroxyl groups remain on the microsphere surface, raising concerns about its long-term hydrolytic stability. KH-550 strikes a balance between mechanical reinforcement and hydrophobic compatibility, thus it was chosen as the surface modifier.

[0072] Example 2 Reference Figures 1-6 This is the second embodiment of the present invention. This embodiment aims to systematically and quantitatively optimize the basic formulation of the polyurethane foam material established in Example 1, in order to explore the nonlinear coupling effect of the addition amount of each core component on the material's microstructure, shape memory behavior, and macroscopic physical properties. The optimal formulation scheme that combines extreme lightweighting, efficient noise reduction, and excellent shape memory characteristics will be selected.

[0073] 2.1 Selection of PBA to PCL ratio To investigate the nonlinear coupling effect of the mass ratio of matrix component (PBA) to shape memory switch component (PCL) on the microstructure and macroscopic shape memory behavior of foamed materials, this experiment used a single-factor gradient analysis method. Under the premise of keeping the total amount of polyol at 100 parts by mass, the regulation law of the change of the ratio of the two components on the comprehensive performance of the material was systematically examined.

[0074] Using a 5-part-by-mass gradient, the addition of poly(1,4-butanediol adipate) (PBA) was gradually increased from 20 parts to 80 parts, while the addition of polycaprolactone diol (PCL) was gradually decreased from 80 parts to 20 parts, resulting in 13 experimental formulations. To ensure the stable progress of the foaming reaction and the consistency of the crosslinking network, 40 parts by mass of liquefied diphenylmethane diisocyanate (MDI) was introduced into each group of experiments to participate in the polymerization reaction. Polyurethane foam samples were prepared and their performance was tested.

[0075] In addition to quantitatively evaluating the mechanical toughness and shape memory performance of materials by detecting key indicators such as elongation at break, rebound angle after cooling, residual bending angle after heating, and compressive strength.

[0076] Test results are as follows Figure 1 As shown in the data fitting, the elongation at break increases non-linearly with increasing PBA content, and a significant inflection point appears at a PBA content of 68.34%, indicating that the material's toughness reaches the optimal level under matrix dominance at this point. The rebound angle after cooling gradually increases with increasing PBA content, but remains in the optimal range below 5° at a PBA content of 42.15%, indicating that the shape memory switching phase (PCL) can still dominate the shape locking function at this point. The residual bending angle after heating decreases rapidly with increasing PBA content, and drops below 1.5° at a PBA content of 58.67%, indicating that the material's recovery elasticity has become ideal at this point. The compressive strength decreases with increasing PBA content, but remains at a relatively high strength level at a PBA content of 45.89%, ensuring sufficient structural support.

[0077] Taking into account the marginal benefits and performance incompatibilities of various indicators, the coordinates of the four key points (68.34%, 42.15%, 58.67%, and 45.89%) were calculated using an equal-weighted averaging method, yielding a theoretical optimal PBA ratio of 53.76%. Considering the accuracy of raw material metering and the convenience of formula control in industrial production, the closest integer point was ultimately selected as the preferred ratio of this invention, namely, 55 parts of poly(1,4-butanediol adipate) (PBA) and 45 parts of polycaprolactone diol (PCL).

[0078] 2.2 Optimization of the dosage of diphenylmethane diisocyanate To investigate the dual function of isocyanate (MDI) as a hard segment donor and reactive source in foaming systems, insufficient MDI dosage leads to insufficient gas generation, thus limiting the foaming ratio; while excessive MDI may cause intense exothermic reactions leading to core burning or closed-cell shrinkage. With a fixed amount of polyol matrix (PBA:PCL=55:45) and other auxiliary components, the amount of liquefied diphenylmethane diisocyanate (MDI) was gradually increased from 30 parts to 70 parts in increments of 5 parts by mass.

[0079] Under uniform foaming process conditions, polyurethane foam specimens were prepared, and the structural rigidity and shape memory recovery effect of the material were quantitatively evaluated by measuring key mechanical indicators such as tensile strength, density, elongation at break and resilience.

[0080] Test results are as follows Figure 2 As shown in the data fitting, the density exhibits a typical U-shaped change with increasing MDI content, reaching a minimum value (approximately 53.89 kg / m³) at an MDI content of 48.56 parts. 3 The results indicate that the vaporization rate of the foaming agent and the growth rate of the polymer network have reached the optimal match, resulting in the maximum foaming ratio. The tensile strength shows a non-linear growth trend with the increase of MDI content, and a steep increase in slope occurs near 56.78 parts, indicating that the continuity of the hard segment phase is significantly enhanced at this point, becoming the main load-bearing skeleton. The elongation at break decreases sharply with the increase of MDI content, and falls below the 300% toughness threshold at 62.34 parts, indicating that the excessive crosslinking density has led to obvious brittleness in the material. The resilience first increases and then decreases with the increase of MDI content, reaching a peak at 58.45 parts (approximately 29.56 N), and then rapidly decays due to the brittleness of the material and the destruction of the closed-cell structure.

[0081] Taking into account the marginal benefits and performance incompatibilities of various indicators, the coordinates of the four key points (48.56, 56.78, 62.34, 58.45) were calculated using an equal-weighted averaging method, yielding a theoretical optimal MDI ratio of 56.53 parts. Considering the accuracy of raw material metering and the convenience of formula control in industrial production, the closest integer point was ultimately selected as the preferred ratio of this invention, namely, 55 parts of liquefied diphenylmethane diisocyanate (MDI).

[0082] 2.3 Synergistic screening and optimization of the ratio of diethanolamine to modified polysiloxane After establishing the optimal mass ratio of the polyurethane backbone (polyol + isocyanate), this experiment further focused on optimizing the synergistic ratio of the microstructure regulator chain extender (diethanolamine, DEA) and the foam stabilizer (modified polysiloxane). Diethanolamine not only acts as a crosslinking point to increase the hard segment content, but also profoundly affects the reaction kinetics due to the catalytic activity of its tertiary amine groups; while modified polysiloxane, as a surfactant, directly determines the uniformity of bubble nucleation and the stability of the cell walls. The two exhibit complex nonlinear interactions during foaming; excessively rapid chain extension leads to bubble breakage, while excessive foam stabilization leads to cell closure. Therefore, it is necessary to construct a structure-property relationship model between the amount of each additive and the microstructure and macroscopic mechanical properties of the foam.

[0083] Using 0.25 parts by mass as the increment, the addition amounts of diethanolamine and modified polysiloxane were gradually increased from 0.5 parts to 2.5 parts. Under uniform foaming process conditions, polyurethane foam samples were prepared and their performance was tested.

[0084] In addition to using the basic mechanical properties such as tensile strength and elongation at break established in Example 1, this experiment focuses on introducing the average cell diameter and closed-cell ratio as core microscopic evaluation parameters. The former directly reflects the effectiveness of the foam stabilizer in reducing surface tension; the smaller the diameter and the narrower the distribution, the finer the foam structure. The latter is related to the effect of the chain extender on the gelation rate; too high a closed-cell ratio will cause the foam to shrink and deform, while too low a closed-cell ratio will cause the foam to collapse.

[0085] Test results are as follows Figure 3 As shown in the data fitting analysis, the average cell diameter is extremely sensitive to the amount of silicone oil used, showing a decreasing trend. When the amount of silicone oil is less than 1.0 part, regardless of the change in DEA, the cell diameter remains at a high level of oscillation above 100 μm, indicating that the surface tension has not yet dropped to the nucleation critical point. When the amount of silicone oil increases to the range of 1.25~1.5 parts, the cell diameter converges to below 60 μm. After that, further increases in silicone oil lead to saturation of the refining effect. The closed-cell rate exhibits a climbing characteristic promoted by two factors, increasing monotonically with the increase of the amounts of both components. However, in the high-dose region (DEA>2.0, silicone oil>2.0), there is a risk of shrinkage due to excessively high closed-cell rate.

[0086] The tensile strength longitudinally increases significantly and monotonically with increasing DEA chain extender content, reflecting the decisive role of hard segment content. Transversely, it first increases and then decreases with increasing silicone oil content, reaching a peak in the 1.5–1.75 part range. This indicates that an appropriate amount of silicone oil can strengthen the material by improving the cell structure, but excessive amounts can lead to plasticization and strength degradation. Elongation at break is significantly negatively correlated with tensile strength, decreasing sharply with increasing DEA content. After DEA exceeds 1.5 parts, it falls below the 300% toughness threshold, indicating that the material has entered the brittle fracture zone.

[0087] To balance the dual requirements of high strength and high toughness, and to ensure the uniformity of the microcellular structure, the optimization target is set on the intersection region of various performance surfaces. To ensure an elongation at break >300% and tensile strength >4.5MPa, the amount of DEA added needs to be controlled between 1.25 and 1.5 parts; to ensure an average cell diameter <70μm and a moderate closed-cell rate (to avoid shrinkage), the amount of modified polysiloxane added needs to be controlled between 1.5 and 1.75 parts.

[0088] Within this overlapping range, a weighted scoring method was used to calculate the theoretical optimal ratio of DEA to modified polysiloxane, which was found to be 1.37 parts and 1.61 parts, respectively. Considering the weighing accuracy and formulation robustness in actual production, the preferred ratio was ultimately selected as 1.4 parts of diethanolamine (DEA) and 1.6 parts of modified polysiloxane.

[0089] 2.4 Screening of Triethylenediamine Catalyst Dosage To investigate the nonlinear regulatory effect of triethylenediamine (TEDA) catalyst on foaming reaction kinetics and polyurethane foam network structure formation, under the premise of fixed addition amounts of other components and process conditions, the addition amount of TEDA was gradually increased from 0.1 parts by mass to 2.0 parts by mass in increments of 0.1 parts by mass. Under uniform free foaming conditions, the milky white time, gel time, free foaming density, and resilience of each formulation were measured.

[0090] Test results are as follows Figure 4 As shown in the figure, through fitting analysis, both the milky whitening time and gelation time exhibit a monotonically decreasing exponential trend with increasing TEDA dosage, indicating that increasing the catalyst concentration significantly accelerates the foaming and gelation processes. When the TEDA dosage exceeds 0.8 parts, the milky whitening time is shortened to less than 10 seconds, and the gelation time is less than 50 seconds, resulting in an excessively narrow operating window, which easily leads to core burning or closed-cell shrinkage due to insufficient gas escape time. The foaming density gradually decreases with increasing TEDA dosage, and tends to plateau in the range of 0.6~0.7 parts (approximately 53 kg / m³). 3 The results indicate that the foaming efficiency is nearing its limit, and further increasing the catalyst will not significantly reduce the density. Instead, it may cause the cell walls to become too thin and collapse. The resilience shows a parabolic characteristic with the increase of TEDA dosage, and reaches a peak at 0.62 parts. This indicates that an appropriate amount of catalyst can promote the improvement and cross-linking of the polymer skeleton, but an excessive amount will cause the reaction to be too fast, resulting in micro-defects and internal stress, which will damage the elasticity of the foam.

[0091] Taking into account both the convenience of process operation (milky time > 10s) and the optimization of product performance (maximum resilience), a weighted scoring method was used to calculate the above key points, resulting in a theoretical optimal addition amount of TEDA of 0.63 parts. For ease of actual production formulation, 0.6 parts were ultimately selected as the preferred ratio.

[0092] 2.5 Screening and Optimization of Surface Modifier Dosage To investigate the effect of the grafting amount of surface modifier (KH-550) on the interfacial properties of hollow glass microspheres and the overall strength of the foamed composite material, this experiment employed a single-factor gradient analysis method. With a fixed microsphere addition amount (10 parts) and other components remaining constant, the dosage of γ-aminopropyltriethoxysilane (KH-550) was gradually increased from 0.3% to 3.0% in increments of 0.3 parts by mass (percentage relative to the microsphere mass). After surface treatment of the microspheres using an alcohol hydrolysis process, modified microsphere / polyurethane foam composite materials were prepared and their performance was tested.

[0093] The test results are shown in Figure 5. Through data fitting analysis, the water contact angle reaches a plateau when the dosage reaches about 1.53%, indicating that a dense hydrophobic monolayer has been basically formed on the surface of the microspheres at this time, and further increasing the modifier cannot significantly improve the hydrophobicity. The tensile strength first increases and then decreases with the increase of modifier dosage, and reaches a peak at 1.46%, indicating that an appropriate amount of coupling agent can effectively bridge the inorganic microspheres and the organic matrix, but an excessive amount of coupling agent will cause a self-condensation reaction at the interface to form a weak boundary layer, which will lead to a decrease in the interfacial bonding force.

[0094] Taking into account the saturation point of the modification effect and cost control, and for the convenience of actual production and batching, 1.5% was finally selected as the dosage ratio.

[0095] 2.6 Screening of the Dosage of Modified Hollow Glass Microspheres To investigate the maximum addition amount of modified hollow glass microspheres (a core functional filler) in foaming systems and its nonlinear effect on material lightweighting, acoustic performance, and mechanical strength, this experiment employed a single-factor gradient analysis method. With a fixed matrix formulation (PBA:PCL = 55:45, MDI = 55 parts, and optimal amounts of other additives), the addition amount of modified hollow glass microspheres was gradually increased from 5 parts to 40 parts in increments of 5 parts by mass, resulting in eight experimental formulations. Under uniform foaming conditions, polyurethane-microsphere composite foamed specimens were prepared, and their density, noise reduction coefficient, compressive strength, and elongation at break were measured.

[0096] Test results are as follows Figure 6 As shown in the data fitting analysis, the apparent density exhibits a U-shaped characteristic of first decreasing and then increasing with the increase of microsphere dosage, reaching a minimum value (approximately 33.89 kg / m³) at 24.32 parts. 3The results indicate that the physical occupancy effect of the microspheres and the foaming ratio have reached the optimal balance at this point. After exceeding this amount, the density actually increases due to the excessive thinning of the cell walls caused by the accumulation of microspheres (collapsed cells). The noise reduction coefficient and compressive strength both increase parabolically with the increase of microsphere content, reaching a peak at around 21.27 parts (NRC≈0.86, strength≈0.70MPa). This indicates that an appropriate amount of microspheres can effectively construct resonant sound-absorbing cavities and enhance the matrix skeleton, but excessive filling will destroy the continuity of the matrix, leading to obstructed sound energy transmission and decreased mechanical properties. The elongation at break decreases monotonically and linearly with the increase of microsphere content, and falls below the 200% toughness warning line at 32.4 parts, indicating that the material has shown obvious brittle characteristics.

[0097] Furthermore, during the experiment, it was observed that when the amount of microspheres exceeded 30 parts, the viscosity of the mixture increased sharply, leading to difficulties in mixing and a significant decrease in material flowability, which easily caused casting defects. Considering the marginal benefits of various indicators and the feasibility of the process operation, a weighted scoring method was used to calculate the coordinates of the above key points, resulting in a theoretical optimal addition amount of 22.6 parts of microspheres. Taking into account the convenience of powder feeding and the need for anti-clogging in industrial production, the final addition amount of modified hollow glass microspheres was determined to be 20 parts.

[0098] Example 3 Reference Figure 7 and Figure 8 This is the third embodiment of the present invention. This embodiment aims to optimize the process parameters for industrial-scale production of the polyurethane foam material laboratory formulations established in Examples 1 and 2. Given the significant differences between the laboratory pilot-scale environment and the actual industrial production line in terms of equipment size, mixing efficiency, and heat transfer rate, many minor factors that are negligible at the microscale (such as shear heat effect, mold flow resistance, and curing temperature gradient) are nonlinearly amplified during the scale-up process, thus significantly affecting the stability of the foaming system and the uniformity of the final product. Therefore, this experiment, based on a pilot-scale production line, systematically investigates the influence of key processing parameters on the foaming process and finished product quality, aiming to establish a stable and reliable industrial production control standard.

[0099] 3.1 Standardized Modification Treatment of Noise-Reducing Packing Material To ensure uniform dispersion and interfacial bonding strength of hollow glass microspheres in industrial-grade foaming systems, this step establishes a standardized surface grafting modification process based on the modified agent formulation (KH-550, 1.5%) optimized in Example 2.5.

[0100] Twenty portions of hollow glass microspheres were placed in a high-speed mixer equipped with a heating jacket and preheated to 50-70°C to activate the hydroxyl groups on the microsphere surface. Subsequently, γ-aminopropyltriethoxysilane (KH-550) was weighed at 1.5% of the microsphere mass and pre-dissolved in anhydrous ethanol at five times the mass of the microspheres to prepare a modification solution. This solution was then uniformly sprayed onto the microsphere surface through an atomizing nozzle. The mixing impeller was started, and the rotation speed was set to 500 rpm. High-speed shear mixing was continued for 30 minutes, utilizing mechanical force and the heat generated by solvent evaporation to drive the coupling agent molecules to form a monolayer graft on the microsphere surface.

[0101] After processing, the moistened microsphere powder was transferred to a forced-air drying oven and dried at a constant temperature of 105℃ for 2 hours to remove the ethanol medium and promote the dehydration condensation reaction of silanol groups. Finally, a hydrophobic modified noise-reducing filler with a surface rich in active amino groups was obtained and sealed for later use.

[0102] 3.2 Optimization of Premixing and Dispersion Processes for Shape Memory Polyurethane Matrix Component (Component A) After modifying the microsphere surface, the active components (poly(1,4-butanediol adipate), polycaprolactone diol, chain extender, catalyst, and foam stabilizer) and modified filler are homogenized and mixed to prepare a stable prepolymer emulsion. Vacuum dehydration is then performed continuously for 1.5–2.5 hours at 100–120 °C, 40–50 °C, and -0.09–-0.10 MPa to ensure the system moisture content is below 0.05%, thus preventing uncontrollable bubbles from forming during the subsequent isocyanate reaction.

[0103] Subsequently, the reactor temperature was lowered to 60°C, the vacuum was released, and modified hollow glass microspheres, diethanolamine, triethylenediamine, modified polysiloxane, and deionized water were added sequentially. At this point, the stirring speed and stirring time became the key process parameters determining the dispersion state and structural integrity of the microspheres. If the speed was too low or the time was too short, the microspheres could not overcome the viscous resistance of the matrix to form an effective dispersion, leading to agglomeration and sedimentation. If the speed was too high or the time was too long, the strong mechanical shear force could easily cause the brittle hollow glass microspheres to break, causing them to lose their lightweight and sound-absorbing functions. At the same time, excessive shear heat may also trigger local prepolymerization reactions, leading to an abnormal increase in the viscosity of the system.

[0104] The stirring speed was gradually increased from 800 rpm to 1600 rpm in increments of 100 rpm; the stirring time was gradually increased from 10 min to 50 min in increments of 5 min. Mixture A was prepared and samples were taken for performance testing under uniform feeding sequence and temperature control conditions.

[0105] In addition to testing the density after foaming to visually assess whether the microspheres have failed due to weight loss caused by breakage, it is also necessary to use a rotational viscometer to determine the viscosity of the mixture at a constant shear rate. This indicator directly reflects the degree of dispersion of the filler and the rheological properties of the system. Ideally, as stirring proceeds, the microsphere aggregates are broken up, the system exhibits shear thinning characteristics, and the viscosity should gradually decrease and tend to stabilize; if a large number of microspheres break down, the fragments not only increase the specific surface area, but also lead to increased thixotropy of the system due to changes in surface energy, resulting in an abnormally high viscosity.

[0106] Test results are as follows Figure 6 As shown, analysis using spatial surface plotting reveals that the viscosity of the mixture exhibits a typical dual-competitive mechanism of rheological shear thinning and fragmentation thickening. In the low-speed range, the shear force is insufficient to overcome the cohesive energy of the microsphere aggregates, and the system exhibits pseudoplastic fluid characteristics that decrease slowly over time, but the absolute viscosity remains high, indicating low dispersion efficiency. In the medium-speed range, the shear force is moderate, and the system quickly enters the optimal dispersion window for shear thinning, forming a stable low-viscosity plateau (<450 mPa·s) within the stirring range of 25–40 minutes. At this point, the microspheres are uniformly dispersed and structurally intact. In the high-speed range, intense mechanical shearing causes fatigue fragmentation of brittle hollow microspheres, and the sharp increase in the specific surface area of ​​the fragments triggers thixotropic thickening, resulting in a rapid rebound and surge in viscosity after a brief decrease, exhibiting a U-shaped deterioration curve.

[0107] The density change trend after foaming is highly coupled with the viscosity, reaching its lowest value (<48 kg / m³) in the medium speed range. 3 In the high-speed, long-duration stirring zone, the microspheres break down and lose their cavity structure, causing the density to significantly increase to 60 kg / m³. 3 The above verifies the destructive effect of excessive shearing on lightweight functionality.

[0108] To balance dispersion quality and industrial production efficiency, the optimization target was set on the overlapping region of the low viscosity plateau and high shear efficiency. Although higher rotational speeds can reach dispersion equilibrium very quickly, their operating window is extremely narrow, posing a significant risk to industrial control; while lower rotational speeds have a wider operating window, the time cost required to reach equilibrium is higher.

[0109] Taking all factors into consideration, at a stirring speed of 1200 rpm, the system maintained stable low viscosity and low density within the range of 25-40 minutes, demonstrating ideal process robustness. To minimize the processing time while ensuring dispersion quality, and to allow for a safety margin to prevent microsphere breakage, a stirring speed of 1200 rpm for 30 minutes was ultimately selected.

[0110] 3.3 Reaction Formation and Crystallization Kinetics Control The prepared stable mixture A (at a constant temperature of 40-50℃) and liquefied diphenylmethane diisocyanate (at a constant temperature of 25-35℃) are pumped into the mixing head of a high-pressure foaming machine and mixed at high speed under an injection pressure of 10-14 MPa. The mixed reaction stream must be rapidly injected into an aluminum mold preheated to 50-60℃ within 3 seconds.

[0111] The temperature of 55℃ is slightly higher than the crystallization melting temperature of the soft segment of polycaprolactone (PCL) (Tm≈52℃). This temperature range is designed to ensure that the molecular chains are in a fully extended amorphous molten state in the early stage of foaming expansion, eliminating the obstruction of molecular chain movement and internal stress concentration caused by premature crystallization, thereby promoting the free growth and uniformity of the cells. At the same time, this temperature range can also effectively balance the exothermic chemical reaction and the heat dissipation rate of the mold, avoiding skin shrinkage or core burning caused by excessive temperature difference.

[0112] After the mold is closed, the material undergoes chemical cross-linking and physical foaming reactions within the mold, rapidly expanding in volume and filling the cavity. The curing time is set to 6-10 minutes to ensure that the polyurethane network cross-linking degree reaches the demolding strength requirement and that a dense skin layer is formed on the surface. Then, the mold is opened and the part is removed to obtain the primary foamed part.

[0113] 3.4 Optimization of the pore-breaking treatment process To open up the sound energy propagation channels inside the foam and achieve efficient transformation from a closed-cell structure to an open-cell sound-absorbing network, this step introduces a forced mechanical pore-breaking process. The initial part, freshly demolded, has a high closed-cell rate, which not only hinders the entry and dissipation of sound waves but also leads to dimensional instability due to uneven internal gas pressure. By feeding the part into a precision roller pore-breaking machine, instantaneous high-pressure extrusion is applied to the part using upper and lower rollers, forcing the individual cell walls to rupture and connect, forming a three-dimensional network of open-cell structures.

[0114] Using a 10% increment, the percentage of the roller gap relative to the original thickness of the part was gradually increased from 10% to 90%. After the perforation treatment, all parts were placed in a vulcanizing oven at 70~90℃ for 10~14 hours to eliminate the internal stress caused by the rearrangement of polymer chain segments and to improve the cross-linking network. They were then removed and cooled to room temperature for testing of resilience and noise reduction coefficient.

[0115] Test results are as follows Figure 8As shown, to maximize sound absorption performance while retaining sufficient structural resilience, the optimization target is set at the inflection point where unit rebound loss yields maximum sound absorption gain. By calculating the ratio of the increase in noise reduction coefficient to the decrease in rebound rate, it was found that as the gap decreased from 50% to 40%, although the rebound rate only decreased slightly by 1.33%, the noise reduction coefficient significantly increased by 0.03, demonstrating extremely high cost-effectiveness. However, when further reduced to 30%, the rebound rate plummeted by more than 10%, and the noise reduction coefficient actually decreased. Therefore, a roller gap of 40% of the original thickness of the part was selected as the preferred process parameter.

[0116] 3.5 Morphology Programming (Enabling) and Shaping Process To endow the final product with thermo-shaped shape memory function and achieve adaptive volume control during transportation and installation, the finished foamed parts that have undergone secondary vulcanization and pore-breaking treatment need to be sent into a heating tunnel and heated to 60~70℃ (slightly higher than the crystallization melting temperature Tm of the switching phase PCL) so that the soft segment microcrystals inside the material are completely melted. At this time, the foam exhibits a soft and highly elastic rubber state.

[0117] Subsequently, the foamed part is compressed to 15%~25% of its original thickness using a precision servo press. While maintaining this compressed deformation state, high-speed cold air at 5~15℃ is immediately introduced for forced cooling, which is maintained for 3~7 minutes to induce the soft segment molecular chains to recrystallize and lock in a temporary shape.

[0118] After the external force is removed, the foamed parts are locked in a flat state due to the physical cross-linking effect of the crystalline phase, and the volume is reduced to 20% of the original value, which greatly reduces logistics and warehousing costs.

[0119] When assembled into automotive interiors (such as headliner cavities or irregularly shaped areas under carpets), the foam only needs to be heated to above 65°C by hot air or infrared. The frozen internal stress is released as the crystals melt, driving the foam to automatically rebound and expand, tightly filling the irregular gaps in the car body, creating a sealed noise reduction barrier without dead angles. At the same time, the hollow microspheres and open network inside efficiently dissipate noise energy across the entire frequency band.

[0120] Example 4 Reference Figure 9 This is the fourth embodiment of the present invention. This embodiment provides a preparation process for a lightweight noise-reducing foam component for automotive interiors, and the specific steps are as follows: S1. Standardized pretreatment (preparation of modified fillers): Weigh 200g of hollow glass microspheres (industrial grade, true density 0.25g / cm³). 3The microspheres were fed into a high-speed mixer. Separately, 3.0 g (1.5% of the microsphere mass) of γ-aminopropyltriethoxysilane (KH-550) was dissolved in 15 g of anhydrous ethanol to prepare a modification solution. The mixer was preheated to 60°C, and the stirring paddle was started at 500 rpm. The modification solution was evenly sprayed onto the surface of the microspheres through an atomizing nozzle, and the mixture was continuously stirred for 30 minutes. The moistened microspheres were then transferred to a forced-air drying oven and dried at 105°C for 2 hours to obtain a hydrophobic modified noise-reducing filler with active amino groups grafted onto its surface. This was then sealed and stored for later use.

[0121] S2. Premixing and Dispersion (Preparation of Component A): Add 550g of poly(1,4-butanediol adipate) diol (PBA-2000) and 450g of polycaprolactone diol (PCL-4000) to a reactor equipped with a heating jacket and vacuum system. Turn on the vacuum pump to evacuate the pressure inside the reactor to -0.095MPa, and simultaneously raise the temperature to 110℃. Continue dehydration for 2 hours until the moisture content is below 0.05%.

[0122] After cooling to 45℃, the vacuum was released, and 200g of the prepared modified noise-reducing filler, 14g of chain extender (1,4-butanediol), 6g of catalyst (triethylenediamine), 16g of foaming agent (modified polysiloxane), and an appropriate amount of deionized water (foaming agent) were added sequentially to the reactor. The stirring speed was set to 1200rpm, and high-speed shear dispersion was started for 30 minutes to ensure that the filler was uniformly suspended in the polyol system, thus obtaining a stable milky white prepolymer emulsion (component A), which was then kept at a constant temperature of 45℃ for later use.

[0123] S3, Reaction Molding (Fogging): A prepolymer emulsion (component A) at a constant temperature of 45°C and 550g of liquefied diphenylmethane diisocyanate (component B, MDI-100) at a constant temperature of 30°C were pumped into a high-pressure foaming machine, with the injection pressure set to 12MPa. The two components were mixed at high speed in the mixing head and then rapidly injected into an aluminum mold preheated to 55°C within 3 seconds. After mold closing, the material underwent chemical cross-linking and physical expansion within the mold. After curing for 8 minutes, the mold was opened to obtain the primary foamed part.

[0124] S4. Hole-breaking treatment and secondary vulcanization: The primary foamed part is fed into a precision roller press, with the roller gap set to 40% of the original thickness of the part, to perform mechanical de-pore treatment, which significantly reduces the closed-cell rate. Subsequently, the part is placed in an 80℃ vulcanizing oven for constant temperature heat treatment for 12 hours to eliminate internal stress during the foaming process and improve the cross-linking degree of the polyurethane network.

[0125] S5, Morphological Programming (Enabling): The part after secondary vulcanization is heated to 65℃ (softened state) and compressed to 20% of its original volume using a press (compression ratio 5:1). While maintaining the compressed state, it is forced to cool for 5 minutes with 10℃ cold air to set the shape. After the external force is removed, the part remains flat, thus obtaining a finished foamed part with thermotropic shape memory function.

[0126] The prepared foamed parts were subjected to performance testing (after recovery at 65℃), and their apparent density was 45.23 kg / m³. 3 Tensile strength: 7.89 MPa, elongation at break: 345.67%, noise reduction factor (NRC): 0.86, compression set: 4.12%, shape retention rate: 96.45%, shape recovery rate: 98.23%, response temperature: 54.56℃.

[0127] The method described in this invention can stably prepare high-performance automotive interior materials that combine lightweight, high strength, efficient noise reduction, and intelligent shape memory properties.

[0128] In summary, this invention, by introducing hollow glass microspheres modified with coupling agents, constructs a stable rigid cavity network within a polyurethane matrix. Utilizing thin-film resonance and multiple reflection effects, it significantly enhances the blocking and dissipation capabilities across the entire frequency range, especially mid-to-high frequency noise, effectively resolving the physical contradiction of reduced sound insulation performance due to decreased foam material density. Simultaneously, the shape memory effect enables adaptive volume control of the foamed component, allowing it to be compressed to 20% of its original volume at room temperature for efficient storage and transportation, and rapidly returning to its original shape after heating to tightly fill complex gaps in the vehicle body, eliminating the risk of sound leakage caused by poor installation fit. Furthermore, through systematic optimization of chain extenders, catalysts, and microstructure, the final product achieves extreme lightweighting and excellent noise reduction characteristics while maintaining superior mechanical strength and dimensional stability, meeting the automotive industry's requirements for high-performance interior materials.

[0129] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a lightweight noise-reducing foam component for automotive interiors, characterized in that... Includes the following steps: S1. The coupling agent is grafted onto hollow glass microspheres to obtain a modified noise-reducing filler. S2. Mix 40-70 parts by weight of poly(1,4-butanediol adipate) diol with 30-60 parts by weight of polycaprolactone diol and dehydrate under negative pressure. Then, add 15-25 parts by weight of modified noise-reducing filler, 1.0-1.75 parts by weight of 1,4-butanediol, 0.4-0.8 parts by weight of triethylenediamine, 1.25-2.0 parts by weight of modified polysiloxane and water in sequence. Mix evenly under high-speed shearing at a stirring speed of 1000-1400 rpm and a stirring time of 20-40 minutes to prepare a stable prepolymer emulsion. S3. The prepolymer emulsion at a constant temperature is mixed with 40-70 parts by weight of liquefied diphenylmethane diisocyanate by impact through the mixing head of a high-pressure foaming machine, and then rapidly injected into a mold for foaming and curing to obtain a primary foamed part. S4. The primary foamed part is mechanically broken through by a roller press with a roller gap of 30% to 50% of the original thickness of the part to connect the internal cell structure. Then, it is subjected to long-term heat treatment to eliminate internal stress and improve the cross-linking network. S5. Heat and compress the foamed part after secondary vulcanization, and then rapidly cool and solidify it while maintaining the compression state to obtain a finished foamed part with thermo-shaped shape memory function.

2. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S2, the mass fraction of the poly(1,4-butanediol adipate) diol is 55 parts, the mass fraction of the polycaprolactone diol is 45 parts, the mass fraction of the modified noise-reducing filler is 20 parts, the mass fraction of the 1,4-butanediol is 1.4 parts, the mass fraction of the triethylenediamine is 0.6 parts, and the mass fraction of the modified polysiloxane is 1.6 parts. The stirring speed is 1200 rpm and the stirring time is 30 minutes.

3. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S3, the mass fraction of the diphenylmethane diisocyanate is 55 parts.

4. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S4, the roller gap is 40% of the original thickness of the workpiece.

5. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S1, the coupling agent is γ-aminopropyltriethoxysilane. The modification process specifically includes: dissolving the coupling agent in anhydrous ethanol to prepare a modified solution, spraying it onto the surface of the hollow glass microspheres, stirring and mixing at 400-600 rpm for 20-40 minutes at 50-70°C, and drying at 100-110°C for 1.5-2.5 hours. The amount of the coupling agent used is 1.2%-1.8% of the mass of the hollow glass microspheres.

6. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S2, the negative pressure dehydration conditions are a temperature of 100~120℃ and a pressure of -0.09~-0.10MPa, with continuous dehydration for 1.5~2.5 hours until the moisture content is below 0.05%; the temperature during the preparation of the prepolymer emulsion is controlled at 40~50℃.

7. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S3, the temperature of the prepolymer emulsion is 40-50°C, the temperature of the liquefied diphenylmethane diisocyanate is 25-35°C, the injection pressure of the high-pressure foaming machine is 10-14 MPa, the preheating temperature of the mold is 50-60°C, and the curing time is 6-10 minutes.

8. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S4, the temperature of the long-term heat treatment is 70~90℃, and the treatment time is 10~14 hours, in order to eliminate internal stress and improve the cross-linking network.

9. The method for preparing lightweight noise-reducing foamed parts for automotive interiors according to claim 1, characterized in that, In step S5, the heating temperature is 60~70℃, the compression ratio to the original volume is 15%~25%, the rapid cooling and shaping temperature is 5~15℃, and the cooling maintenance time is 3~7 minutes.

10. A lightweight noise-reducing foam component for automotive interiors, characterized in that, The foamed component is prepared by the preparation method according to any one of claims 1 to 9; the foamed component is microscopically a multiphase composite structure in which modified hollow glass microspheres are uniformly dispersed in a polyurethane matrix network; the polyurethane matrix has soft and hard segment microphase separation characteristics, wherein the soft segment crystalline phase constitutes a reversible thermo-induced shape memory switch, and the hard segment phase and the modified hollow glass microspheres together constitute a rigid support skeleton; the inside of the foamed component has a network of interconnected open holes formed by mechanical puncture, and the open hole network and the rigid cavity inside the microspheres together constitute multiple sound energy dissipation channels, giving the material comprehensive properties of being lightweight, high-strength, noise-reducing and thermo-induced shape memory.

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