Polymer-based low-frequency sound absorption structure and manufacturing method

Abstract

This application provides a polymer-based low-frequency sound-absorbing structure and its manufacturing method. The structure includes a backplate, a transition composite layer, and a structural resonant layer that are sequentially and tightly bonded together. The backplate is the side furthest from the sound source during use; the structural resonant layer is the side closest to the sound source during use; the transition composite layer is disposed between the backplate and the structural resonant layer; the backplate material is melamine foam; the structural resonant layer material is a hollow sphere polymer-based composite material; and the transition composite layer material is a polyurethane-melamine foam interpenetrating blend. This invention uses an impregnation method to combine hollow spheres and two lightweight polymer materials with excellent sound absorption properties to prepare a composite structure with good sound absorption and insulation performance in the low-frequency range. Furthermore, by changing the structural parameters, the sound absorption performance of the composite structure can be controlled to meet different application environments.

Description

Technical Field

[0001] This application relates to the field of polymer-based acoustic structures, and more particularly to a polymer-based low-frequency sound-absorbing structure and its fabrication method. Background Technology

[0002] With the rapid development of industrial technology, the application of high-power power devices in fields such as ships, aerospace, and ground transportation has gradually increased. As a result, mechanical vibration and noise have become more and more significant. In particular, low-frequency vibration has led to a decrease in the accuracy of instruments and meters, which has become an issue that cannot be ignored in equipment applications.

[0003] Low-frequency noise can significantly impact people's working and living environments, seriously endangering human health. Therefore, the need for vibration reduction and noise reduction structures in fields such as shipbuilding and aerospace is becoming increasingly urgent.

[0004] Traditional sound absorption methods mainly include porous media (such as sponge, foam, fiber felt, etc.) and perforated and micro-perforated plates. They absorb sound based on damping dissipation and heat conduction mechanisms, and have good sound absorption effects for mid-to-high frequency noise. However, they are very weak in the loss of low frequency sound waves. They require structures or materials with wavelength dimensions to have certain sound absorption performance, and have defects such as large size and low efficiency. Summary of the Invention

[0005] To address the problem that the existing technology has very weak loss for low-frequency sound waves, requiring structures or materials with wavelength dimensions to achieve certain sound absorption performance, resulting in defects such as large size and low efficiency, this application provides a polymer-based low-frequency sound absorption structure, including a back plate, a transition composite layer, and a structural resonant layer.

[0006] The back panel is the side furthest from the sound source during use; the structural resonance layer is the side closest to the sound source during use; and the transition composite layer is located between the back panel and the structural resonance layer.

[0007] The backsheet is made of melamine foam, the structural resonance layer is made of hollow sphere polymer-based composite material, and the transition composite layer is made of a blend of polyurethane-melamine foam structures that interpenetrate.

[0008] In one feasible implementation, the polyurethane in the transition composite layer material is a flexible elastic polyurethane with a density of 0.99 g / cm³. 3 ~1.04g / cm 3 .

[0009] In one feasible implementation, the melamine foam density in both the backsheet and the transition composite layer material is in the range of 4 × 10⁻⁶. -3 g / cm 3 ~1.2×10-2 g / cm 3 .

[0010] In one feasible implementation, the hollow spheres in the structural resonant layer material are stainless steel hollow spheres.

[0011] In one feasible implementation, the diameter of the stainless steel hollow sphere ranges from 2mm to 3mm, and the average density is 0.5g / cm³. 3 ~1g / cm 3 .

[0012] In one feasible implementation, the backplate and the structural resonant layer are closely attached to the two sides of the transition composite layer.

[0013] In one feasible implementation, the thickness of the backplate ranges from 0.45cm to 3cm.

[0014] In one feasible implementation, the thickness of the transition composite layer ranges from 0.5 cm to 2 cm.

[0015] Another aspect of this application provides a method for fabricating a polymer-based low-frequency sound-absorbing structure, comprising:

[0016] Hollow spheres were modified by hydrolysis of silanol;

[0017] The hollow spheres modified by silanol hydrolysis were placed at the bottom of the mold;

[0018] Liquid polyurethane is added above the hollow sphere until it is submerged, so as to form a hollow sphere polymer-based composite material layer at the bottom of the mold, and the hollow sphere polymer-based composite material layer is used as a structural resonance layer.

[0019] Melamine foam is added above liquid polyurethane, and a portion of the melamine foam is in contact with a portion of the liquid polyurethane to form a polyurethane-melamine foam interpenetrating blend material layer in the middle layer of the mold, and the polyurethane-melamine foam interpenetrating blend material layer is used as a transition composite layer.

[0020] The mold with the structural resonance layer and the transition composite layer is placed in a vacuum oven and left to stand for a preset time until the polyurethane on the surface of the transition composite layer is completely cured. A cured melamine foam layer is formed on the top layer of the mold, and the melamine foam layer is used as the backing plate.

[0021] In one feasible implementation, the density of melamine foam is in the range of 4 × 10⁻⁶. -3 g / cm 3 ~1.2×10 - 2 g / cm 3 .

[0022] The polymer-based low-frequency sound-absorbing structure provided in this application includes a backplate, a transition composite layer, and a structural resonant layer. The backplate is the side furthest from the sound source during use; the structural resonant layer is the side closest to the sound source during use; the transition composite layer is disposed between the backplate and the structural resonant layer; the backplate is made of melamine foam, the structural resonant layer is made of hollow sphere polymer-based composite material, and the transition composite layer is made of a polyurethane-melamine foam interpenetrating blend. The low-frequency sound-absorbing structure of this application can form a stable, strong resonant sound absorption peak in the low-frequency range of 0-1000Hz. The frequency band of the absorption peak can be changed by altering the thickness of the exposed foam. As the thickness of the backplate foam decreases, the sound absorption performance of the material gradually shifts towards broadband characteristics. Furthermore, the introduction of hollow spheres significantly improves the sound insulation performance of the composite acoustic structure, giving the composite structure both excellent sound absorption and insulation properties. This excellent low-frequency sound absorption and insulation characteristic, along with its adjustable characteristics, is of great significance for the research and development of hollow sphere polymer-based composite structures in vibration reduction and noise reduction. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the embodiments of the present invention. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0024] Figure 1 This is a schematic diagram of a polymer-based low-frequency sound-absorbing structure shown in an exemplary embodiment of this application;

[0025] Figure 2 This is a schematic flowchart of the method for fabricating the polymer-based low-frequency sound-absorbing structure of this application;

[0026] Figure 3 This is the first curve showing the adjustable sound absorption coefficient of the polymer-based low-frequency sound-absorbing structure of this application.

[0027] Figure 4 This is a second curve showing the adjustable sound absorption coefficient of the polymer-based low-frequency sound-absorbing structure of this application;

[0028] Figure 5 This is a graph showing the low-frequency sound transmission loss of the polymer-based low-frequency sound-absorbing structure of this application.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-Backplate; 2-Transition composite layer; 3-Structural resonance layer. Detailed Implementation

[0031] Example embodiments will now be described more fully with reference to the accompanying drawings. In the following description, numerous specific details are provided to give a full understanding of how embodiments of the invention are implemented. However, those skilled in the art will recognize that the technical solutions of the embodiments of the invention may be practiced with one or more of these specific details omitted, or other methods, steps, etc., may be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring aspects of the embodiments of the invention.

[0032] Low-frequency noise can significantly impact people's working and living environments, seriously endangering human health. Therefore, the demand for vibration reduction and noise reduction structures in fields such as shipbuilding and aerospace is becoming increasingly urgent. Traditional sound absorption methods mainly include porous media (such as sponges, foams, and fiber felts) and perforated and micro-perforated plates, relying on damping dissipation and heat conduction mechanisms for sound absorption. While these methods are effective for mid-to-high frequency noise, they are very weak at low-frequency sound waves, requiring structures or materials with wavelengths comparable to achieve adequate sound absorption. These methods suffer from drawbacks such as large size and low efficiency. This application provides a polymer-based low-frequency sound absorption structure to address the problem of low-frequency sound absorption and insulation, referring to... Figure 1 As shown, Figure 1 This is a schematic diagram of a polymer-based low-frequency sound-absorbing structure shown in an exemplary embodiment of this application; it includes a backplate 1, a transition composite layer 2, and a structural resonant layer 3.

[0033] Among them, the back plate 1 is the side away from the sound source when in use; the structural resonance layer 3 is the side close to the sound source when in use; and the transition composite layer 2 is located between the back plate 1 and the structural resonance layer 3.

[0034] The material of the backing plate 1 is melamine foam, the material of the structural resonance layer 3 is hollow sphere polymer-based composite material, and the material of the transition composite layer 2 is a blend of polyurethane-melamine foam structure interpenetration.

[0035] The backing plate 1 is made of melamine foam, a soft thermosetting foam plastic with a nanoscale three-dimensional network cross-linked structure, produced by microwave foaming of alkaline melamine-formaldehyde resin using a special process. Due to the three-dimensional network open-cell structure and high open-cell ratio (up to 99.9%), sound waves can easily and effectively penetrate deep into the foam, transforming into vibrations within the network and being consumed and absorbed, while effectively eliminating reflected waves. Melamine foam exhibits superior sound absorption performance over a wide frequency range, particularly excelling in absorbing low-frequency noise.

[0036] The polyurethane mixed with the transition composite layer 2 is an elastic polymer material. Due to its unique viscoelasticity, it has a high equivalent damping ratio and is simple to prepare, making it widely used in the research and application of damping materials. It also has good vibration reduction and noise reduction functions. For example, polyurethane flexible foam is mostly open-cell and usually has the characteristics of low density, air permeability, sound absorption, heat insulation, and good resilience.

[0037] Furthermore, the numerous pores contained within porous materials have wide applications in the field of sound-absorbing materials. Whether it is an interconnected open-cell structure or a closed-cell material with independent pores, both exhibit good sound dissipation capabilities. Common open-cell foams are mostly used in high-frequency sound absorption environments above 1000Hz, while existing research shows that closed-cell structures, due to their independent pore structure, have good sound energy dissipation performance in the low-frequency range below 1000Hz.

[0038] Therefore, by incorporating uniformly sized hollow metal spheres into polymer materials, a novel composite structure combining open and closed pores can be formed. The closed-pore structure created by the hollow spheres within this composite structure induces resonance at low frequencies, thereby improving the sound absorption performance of the composite structure and simultaneously increasing the density of the composite material, thus enhancing its sound insulation performance. This invention employs a composite of stainless steel hollow spheres, melamine foam, and a polyurethane matrix. Benefiting from the uniformly distributed closed-pore structure within the hollow spheres, the resulting structural resonance causes significant sound energy loss. The foam portion on the back of the composite structure further enhances the resonance effect, resulting in a substantial improvement in the overall sound absorption performance of the structure.

[0039] In one feasible implementation, the backplate 1 and the structural resonance layer 3 are tightly bonded to both sides of the transition composite layer 2. The polyurethane in the transition composite layer 2 is a soft elastic polyurethane, which is a flexible polyurethane foam with a certain degree of elasticity. In this embodiment, the density of the soft elastic polyurethane is 0.99 g / cm³. 3 ~1.04g / cm 3 It can have a multi-pore structure, low density and good resilience, which can enhance the sound insulation effect; the melamine foam in the back panel 1 and the transition composite layer 2 materials both have a density range of 4×10 -3 g / cm 3 ~1.2×10 -2 g / cm 3 This lower density range allows for more open pores in the melamine foam, resulting in better sound insulation. Within this density range, the sound absorption coefficient of the melamine foam gradually increases with frequency up to 1000Hz, reaching 0.75 at 1000Hz. The hollow spheres in structural resonant layer 3 are made of stainless steel; the diameter of the stainless steel hollow spheres ranges from 2mm to 3mm, with an average density of 0.5g / cm³.3 ~1g / cm 3 The stainless steel hollow spheres mixed with polyurethane can stably contain the polyurethane without deterioration. Specifically, 316L stainless steel material can be selected, and a smaller diameter can be chosen to place more hollow spheres in the structural resonance layer 3, and the number of holes in the structural resonance layer 3 structure can also be increased.

[0040] In one feasible implementation, the thickness of the backplate 1 ranges from 0.45 cm to 3 cm; the thickness of the transition composite layer 2 ranges from 0.5 cm to 2 cm. The polymer-based low-frequency sound-absorbing structure of this application allows for adjustment of the resonance peak position and amplitude of the overall structure by changing the thickness of the melamine foam in the backplate 1. Increasing the thickness of the backplate 1 can shift the material's resonance peak to lower frequencies, while decreasing the thickness of the backplate 1 can shift the material's resonance peak to higher frequencies.

[0041] This application provides two experiments and their results in the embodiments. The first experiment in this embodiment illustrates the effect of the thickness of the backplate 1 on sound absorption. Figure 3 As shown, Figure 3 The curve shows the adjustable sound absorption coefficient of the polymer-based low-frequency sound-absorbing structure of this application. In Experiment 1 of this embodiment, three groups of polymer-based low-frequency sound-absorbing structures with different structural thicknesses were compared.

[0042] The samples were all 3 cm thick, with the overall thickness of the transition composite layer 2 being 1.25 cm. In the first group, the melamine foam thickness of the back panel 1 was 1.65 cm, and curve a1 represents the adjustable sound absorption coefficient curve for the first group. In the second group, the melamine foam thickness of both the back panel 1 and the transition composite layer 2 was 1.05 cm, and curve a2 represents the first curve of the adjustable sound absorption coefficient for the second group. In the third group, the melamine foam thickness of the back panel 1 was 0.45 cm, and the melamine foam thickness of the transition composite layer 2 was 1.2 cm, and curve a3 represents the adjustable sound absorption coefficient curve for the second group. Figure 3 The experimental results show that as the thickness of the melamine foam in the backplate 1 decreases, the resonant absorption peak frequency of the composite acoustic structure gradually shifts from low frequency to higher frequency.

[0043] The second experiment in this embodiment illustrates the effect of the melamine foam thickness in the transition composite layer 2 on the peak intensity of the acoustic absorption peak. For example... Figure 4 As shown, Figure 4 This is the second curve of the adjustable sound absorption coefficient of the polymer-based low-frequency sound-absorbing structure of this application; Experiment 2 of this embodiment involves four groups of polymer-based low-frequency sound-absorbing structures with different structural thicknesses for comparison.

[0044] In the first group, the melamine foam thickness of the back panel 1 is 3cm; curve b1 is the adjustable sound absorption coefficient curve corresponding to the first group. In the second group, the melamine foam thickness of the back panel 1 is 3cm, and the melamine foam thickness in the transition composite layer 2 is 0.35cm; curve b2 is the adjustable sound absorption coefficient curve corresponding to the second group. In the third group, the melamine foam thickness of the back panel 1 is 1.2cm, and the melamine foam thickness in the transition composite layer 2 is 0.45cm; curve b3 is the adjustable sound absorption coefficient curve corresponding to the third group. In the fourth group, the melamine foam thickness of the back panel 1 is 1.7cm, and the melamine foam thickness in the transition composite layer 2 is 0.45cm; curve b4 is the adjustable sound absorption coefficient curve corresponding to the second group. Figure 4 The experimental results show that adding the transition composite layer 2 melamine foam can reduce the material resonance intensity and regulate the peak intensity of the absorption peak.

[0045] The experimental results show that the absorption peak decreases as the thickness of the melamine foam in the backing plate 1 decreases. The thickness of the melamine foam in the transition composite layer 2 can reduce the material resonance intensity and regulate the peak intensity of the absorption peak. The thickness of the melamine foam in the backing plate 1 can change the frequency of the absorption peak. As the thickness of the melamine foam in the backing plate 1 increases, the absorption peak of the composite structure shifts to lower frequencies, and the sound absorption coefficient can reach up to 0.75. The sound absorption performance of the structure can be controlled by changing the foam thickness of the backing plate 1 and the transition composite layer 2 in the polymer-based low-frequency sound absorption structure.

[0046] Furthermore, in this application, adding hollow spheres to polyurethane to form a composite structure can improve low-frequency sound transmission loss. An embodiment is provided in this application to illustrate the function of the hollow sphere structure, such as... Figure 5 As shown, Figure 5 This is a low-frequency sound transmission loss curve of the polymer-based low-frequency sound-absorbing structure of this application. Five sets of structural resonant layers 3 with different thicknesses are provided for comparison in this embodiment.

[0047] Among them, the polyester-amino acid content and thickness are the same in groups one, two, three, and five. In group one, it is a pure polyurethane structure, and curve c1 is the low-frequency sound transmission loss curve corresponding to group one. In group two, a small amount of melamine foam is added to polyurethane, and curve c2 is the low-frequency sound transmission loss curve corresponding to group two. In group three, a large amount of melamine foam is added to polyurethane, and curve c3 is the low-frequency sound transmission loss curve corresponding to group three. In group four, a thickened polyurethane is mixed with the same amount of melamine foam as group two, and curve c4 is the low-frequency sound transmission loss curve corresponding to group four. In group five, it is a hollow sphere polymer-based open and closed acoustic structure of polyurethane and hollow spheres, and curve c5 is the low-frequency sound transmission loss curve corresponding to group five. According to Figure 5Comparing the sound transmission loss curves, it can be seen that with the addition of hollow spheres, the sound transmission loss of the acoustic structure is improved by 20% compared to the polyurethane matrix.

[0048] As can be seen from the above embodiments, the polymer-based low-frequency sound-absorbing structure provided in this application includes a backplate, a transition composite layer, and a structural resonant layer; the backplate is made of melamine foam, the structural resonant layer is made of hollow sphere polymer-based composite material, and the transition composite layer is made of a polyurethane-melamine foam interpenetrating blend. The low-frequency sound-absorbing structure of this application can form a stable, strong resonant sound absorption peak in the low-frequency range of 0-1000Hz. The frequency band of the absorption peak can be changed by altering the thickness of the exposed foam. As the thickness of the backplate foam decreases, the sound absorption performance of the material gradually shifts towards broadband characteristics. Furthermore, the introduction of hollow spheres significantly improves the sound insulation performance of the composite acoustic structure, giving the composite structure both excellent sound absorption and insulation properties.

[0049] The second aspect of this application provides a method for fabricating a polymer-based low-frequency sound-absorbing structure, such as... Figure 2 As shown, Figure 2 This is a schematic flowchart of the method for fabricating the polymer-based low-frequency sound-absorbing structure of this application; the steps include:

[0050] S100: Hollow spheres are modified by hydrolysis of silanol.

[0051] S200: The hollow spheres modified by silanol hydrolysis are placed at the bottom of the mold; the mold can be designed according to the actual required area and thickness, and the mold material can be carbon tool steel or other materials, which are not limited in this application; the bottom, middle and top layers of the mold can be designed with scales according to the required thickness, so that it is convenient to confirm whether the amount of material put in is insufficient or overflowing when placing the material.

[0052] S300: Add liquid polyurethane above the hollow sphere until it is submerged, so as to form a hollow sphere polymer-based composite material layer at the bottom of the mold, and use the hollow sphere polymer-based composite material layer as the structural resonance layer 3; the liquid polyurethane added above the hollow sphere should completely cover the hollow sphere, and can be higher than the hollow sphere by a certain height, which can be adjusted according to the required thickness of the transition composite layer 2.

[0053] S400: Melamine foam is added above liquid polyurethane, and a portion of the melamine foam is in contact with a portion of the liquid polyurethane to form a polyurethane-melamine foam interpenetrating blend material layer in the middle layer of the mold, and the polyurethane-melamine foam interpenetrating blend material layer is used as transition composite layer 2.

[0054] S500: Place the mold with the structural resonance layer 3 and the transition composite layer 2 into a vacuum oven and let it stand for a preset time until the polyurethane on the surface of the transition composite layer 2 is completely cured, forming a cured melamine foam layer on the top layer of the mold, and using the melamine foam layer as the back plate 1.

[0055] Specifically, the polyurethane on the surface of the transition composite layer 2 can be fully cured by placing it in a vacuum oven for 12 hours, or by adding a catalyst or heating to shorten the curing time. The choice can be made based on actual curing requirements, and this application does not impose any restrictions.

[0056] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. The embodiments of this application are intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0057] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A polymer-based low-frequency sound-absorbing structure, characterized in that, It includes a backplate (1), a transition composite layer (2), and a structural resonance layer (3). Wherein, the back plate (1) is the side away from the sound source when in use; the structural resonance layer (3) is the side close to the sound source when in use; the transition composite layer (2) is disposed between the back plate (1) and the structural resonance layer (3); The material of the back plate (1) is melamine foam, the material of the structural resonance layer (3) is hollow sphere polymer-based composite material, and the material of the transition composite layer (2) is a blend of polyurethane-melamine foam structure interpenetration. The method for fabricating the polymer-based low-frequency sound-absorbing structure includes: Hollow spheres were modified by hydrolysis of silanol; The hollow spheres modified by silanol hydrolysis were placed at the bottom of the mold; Liquid polyurethane is added above the hollow sphere until it is submerged, so as to form a hollow sphere polymer-based composite material layer at the bottom of the mold, and the hollow sphere polymer-based composite material layer is used as a structural resonance layer (3). Melamine foam is added above the liquid polyurethane, and a portion of the melamine foam is in contact with a portion of the liquid polyurethane to form a polyurethane-melamine foam interpenetrating blend material layer in the middle layer of the mold, and the polyurethane-melamine foam interpenetrating blend material layer is used as a transition composite layer (2). The mold with the structural resonance layer (3) and the transition composite layer (2) is placed in a vacuum oven and left to stand for a preset time until the polyurethane on the surface of the transition composite layer (2) is completely cured. A cured melamine foam layer is formed on the top layer of the mold, and the melamine foam layer is used as the back plate (1).

2. The polymer-based low-frequency sound-absorbing structure according to claim 1, characterized in that, The polyurethane in the transition composite layer (2) is a soft elastic polyurethane with a density of 0.99 g / cm³. 3 ~1.04g / cm 3 .

3. The polymer-based low-frequency sound-absorbing structure according to claim 1, characterized in that, The melamine foam density in both the backplate (1) and the transition composite layer (2) is in the range of 4 × 10⁻⁶. -3 g / cm 3 ~1.2×10 -2 g / cm 3 .

4. The polymer-based low-frequency sound-absorbing structure according to claim 1, characterized in that, The hollow spheres in the structural resonance layer (3) are stainless steel hollow spheres.

5. The polymer-based low-frequency sound-absorbing structure according to claim 4, characterized in that, The diameter of the stainless steel hollow spheres ranges from 2mm to 3mm, and the average density is 0.5g / cm³. 3 ~1g / cm 3 .

6. The polymer-based low-frequency sound-absorbing structure according to claim 5, characterized in that, The back plate (1) and the structural resonance layer (3) are closely attached to both sides of the transition composite layer (2).

7. The polymer-based low-frequency sound-absorbing structure according to claim 6, characterized in that, The thickness of the back plate (1) ranges from 0.45cm to 3cm.

8. The polymer-based low-frequency sound-absorbing structure according to claim 6, characterized in that, The thickness of the transition composite layer (2) ranges from 0.5cm to 2cm.

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