Low and medium frequency sound absorption and insulation EVA double-layer foam material and preparation method thereof

Abstract

The invention relates to the field of polymer composite materials, and particularly discloses a low and medium frequency sound absorption and insulation EVA double-layer foam material and a preparation method thereof. The low and medium frequency sound absorption and insulation EVA double-layer foam material comprises a sound absorption layer and a sound insulation layer which are fixedly connected, and the thickness of each layer is 1.5 mm. The preparation method comprises the following steps: mixing the raw materials in the sound-absorbing layer material according to the ratio, mixing the raw materials in the sound-insulating layer material according to the ratio, carrying out a composite extrusion foaming process, controlling the thickness of a single-layer material to be 1.5 mm, and controlling the total thickness to be 3mm, thereby obtaining the double-layer foam material. The low and medium frequency sound absorption and insulation EVA double-layer foam material has the advantages that the process is simplified, the thickness is reduced, and the applicability of the material in solving low and medium frequency sound noise of automobiles is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of high polymer composite materials, in particular to a medium-low frequency sound-absorbing and sound-insulating EVA double-layer foam material and a preparation method thereof. BACKGROUND

[0002] Foamed materials are a kind of lightweight materials with a porous structure formed inside the materials by physical or chemical methods. The main advantages of foamed materials are low density and high strength, which can replace traditional metals or solid plastics, reduce the weight of the whole vehicle, and improve fuel efficiency or the endurance of electric vehicles. The application of foamed materials in automobiles not only effectively reduces the weight of the whole vehicle, but also provides excellent heat insulation, sound insulation, cushioning and energy absorption performance, thereby ensuring the comfort and safety of the automobile.

[0003] With automobile manufacturers striving to reduce the noise, vibration and comfort (NVH) level inside the vehicle, the demand for effective sound insulation materials is crucial. NVH (Noise, Vibration, Harshness) control is an important indicator for measuring the comfort of an automobile, which directly affects the comfort of driving and riding. Foamed materials, with excellent sound absorption, vibration reduction and sealing performance, have become one of the core materials for NVH optimization of passenger cars and commercial vehicles.

[0004] However, to solve the incompatibility of sound absorption and sound insulation, the existing technology mostly uses different materials to design multiple layers (three layers and above) of structures, which has the problems of poor interlayer compatibility, complex process, and high thickness. Moreover, the low-frequency sound absorption coefficient of traditional EVA foamed materials is low (less than 2000 Hz, sound absorption coefficient less than 0.3), which cannot meet the demand of solving the medium-low frequency sound noise in automobiles. SUMMARY

[0005] In order to simplify the process, reduce the thickness, and improve the applicability of the material in solving the medium-low frequency sound noise in automobiles, the application provides a medium-low frequency sound-absorbing and sound-insulating EVA double-layer foam material and a preparation method thereof.

[0006] In the first aspect, the application provides a medium-low frequency sound-absorbing and sound-insulating EVA double-layer foam material, which adopts the following technical scheme:

[0007] A medium-low frequency sound-absorbing and sound-insulating EVA double-layer foam material, comprising a sound-absorbing layer and a sound-insulating layer fixedly connected, and the thickness of each layer is 1.5 mm;

[0008] The sound-absorbing layer material comprises the following raw materials by weight: EVA 92-98 parts; PBAT 2-8 parts; AC foaming agent 8 parts; 461WU microsphere foaming agent 1-5 parts; ZnO foaming aid 1.5 parts; DCP crosslinking agent 1.2 parts; TAIC crosslinking aid 0.5 parts; calcium carbonate 20 parts; white carbon black 10 parts;

[0009] The sound insulation layer material comprises the following raw materials by weight: EVA 100 parts; AC foaming agent 5 parts; 461WU microsphere foaming agent 1-4 parts; ZnO foaming aid 1.2 parts; DCP crosslinking agent 1.2 parts; TAIC auxiliary crosslinking agent 0.8 parts; calcium carbonate 0-15 parts; white carbon black 10 parts; modified montmorillonite 5-20 parts.

[0010] By adopting the above technical scheme, the sound absorption layer and the sound insulation layer with a thickness of 1.5 mm are prepared, PBAT is introduced into the sound absorption layer material, the acoustic impedance of the material is changed through the flexibility of the molecular chain of PBAT, and the sound absorption spectrum is moved to low frequency; the modified montmorillonite is added in the sound insulation layer, the sound wave barrier is formed by using the lamellar structure of the modified montmorillonite, the compatibility with EVA is improved through surface modification, the cell structure is stabilized, fine and closed pores are formed, and thus the sound insulation volume of the material is improved. By improving the sound absorption coefficient of the sound absorption layer and the sound insulation volume of the sound insulation layer, the structure is simplified, and the double-layer material is prepared by composite extrusion. Therefore, the effects of simplifying the process, reducing the thickness, and improving the applicability of the material in solving the low-frequency sound and noise in the automobile are achieved.

[0011] In addition, the fine and closed pore structure induced by the modified montmorillonite enables the double-layer foam material to effectively block the penetration of water, improves the sound absorption and insulation performance, ensures the water tightness of the material, and makes the material have waterproof performance.

[0012] Optionally, the modified montmorillonite is obtained by modifying montmorillonite with didodecyldimethylammonium chloride.

[0013] By adopting the above technical scheme, the compatibility of the modified montmorillonite with EVA is improved by modifying the montmorillonite with didodecyldimethylammonium chloride, so as to stabilize the cell structure, form fine and closed pores, and thus improve the sound insulation volume of the sound insulation layer material.

[0014] Optionally, the particle size of the modified montmorillonite is 500 mesh.

[0015] Optionally, the weight of the modified montmorillonite is 15 parts.

[0016] By adopting the above technical scheme, the increase in the amount of the modified montmorillonite helps to form more sound wave scattering centers and a more dense closed pore structure, so that the sound insulation volume and the water pressure resistance performance are simultaneously improved. When the amount is 15 parts, the best balance is achieved, and when the amount continues to increase to 20 parts, the performance may slightly decrease due to uneven dispersion.

[0017] Optionally, the weight of the PBAT is 6 parts.

[0018] By adopting the above technical scheme, with the increase of PBAT from 2 parts to 6 parts, the material flexibility is enhanced, and the low-frequency sound absorption coefficient is significantly improved. However, an excessive amount (8 parts) may cause a slight decrease in system compatibility and a slight drop in performance. 6 parts is the optimal value.

[0019] Optionally, the weight parts of the 461WU microsphere foaming agent in the sound absorption layer material is 4-5 parts, and the weight parts of the 461WU microsphere foaming agent in the sound insulation layer material is 3-4 parts.

[0020] Currently, the EVA foaming system is mostly foamed above 150℃, and the use of activators is required to reduce the decomposition temperature of the foaming agent to realize foaming below 140℃, but the activators are not stable for the overall EVA foaming. The two-layer structure material introduces the microsphere foaming agent 461WU, and the initial foaming temperature gradually decreases. After adding 4 parts of 461WU microsphere foaming agent to the sound absorption layer material, the initial foaming temperature is reduced to below 140℃, and after adding 3 parts of 461WU microsphere foaming agent to the sound insulation layer material, the initial foaming temperature is reduced to below 140℃, meeting the low-temperature foaming performance of 140℃. Therefore, on the basis of ensuring the stability of EVA foaming, the introduction of microsphere foaming agent 461WU can realize low-temperature stable foaming.

[0021] Optionally, the sound absorption layer material further comprises 2-6 parts by weight of floating beads, 0.2-0.5 parts by weight of polyanionic cellulose, and 2-4 parts by weight of short-cut polyester fiber.

[0022] By adopting the above technical scheme, the floating beads as "hard" hollow balls dissipate energy by internal cavity resonance and increase sound wave reflection and scattering paths in the matrix. The polyanionic cellulose can stabilize and refine the cells, act as "heterogeneous nucleation points", and promote the formation of more uniform and dense cell nuclei, so that the final cell structure can be more uniform and delicate. The addition of polyanionic cellulose can also slightly change the rheological properties of the polymer melt, which can help the dispersion of other fillers (such as floating beads, calcium carbonate, and white carbon black). The short-cut polyester fiber has good compatibility with EVA / PBAT, is easy to disperse, is soft itself, and acts as a damping enhancement skeleton. Through the interface friction between the fiber and the matrix and the vibration damping of the fiber itself, the material internal friction can be increased without significantly increasing the stiffness, which helps to form more micropores, generate strong interface friction during vibration, and stabilize the overall porous structure of the material. The combination of the three can systematically cover various sound absorption mechanisms such as scattering, friction, and damping, further improving the sound absorption performance of the material.

[0023] Optionally, the particle size specifications of the floating beads are 0.01mm, 0.5mm, and 2.5mm, and the weight ratio of each specification of the floating beads is 1:2:1.

[0024] By adopting the technical scheme, the three particle size specifications of the floating beads are compounded, which is helpful to form multi-scale scattering and further improve the middle and low frequency sound absorption capacity.

[0025] In a second aspect, the application provides a preparation method of a middle and low frequency sound absorption and insulation EVA double-layer foam material, which adopts the following technical scheme:

[0026] The preparation method of the middle and low frequency sound absorption and insulation EVA double-layer foam material comprises the following steps: mixing each raw material in the sound absorption layer material according to the proportion, mixing each raw material in the sound insulation layer material according to the proportion, and performing a composite extrusion foaming process, wherein the thickness of the single-layer material is controlled to be 1.5 mm, and the total thickness is controlled to be 3 mm, so as to obtain the double-layer foam material.

[0027] By adopting the technical scheme, the double-layer foam material prepared has simple process, small thickness, and improved applicability in solving the middle and low frequency sound noise of the automobile, and has excellent water tightness.

[0028] In summary, the application has the following beneficial effects:

[0029] 1. Since the sound absorption layer and the sound insulation layer prepared in the application have a thickness of 1.5 mm, the sound absorption coefficient of the sound absorption layer and the sound insulation volume of the sound insulation layer are improved by improving the formula of the sound absorption layer material and the sound insulation layer material, thereby simplifying the structure and obtaining the double-layer material by composite extrusion. Therefore, the effect of simplifying the process, reducing the thickness, and improving the applicability of the material in solving the middle and low frequency sound noise of the automobile is obtained.

[0030] 2. In the application, the microsphere foaming agent 461WU is introduced, the initial foaming temperature gradually decreases, and stable foaming at low temperature is realized on the basis of ensuring stable foaming of EVA.

[0031] 3. The method of the application, the double-layer foam material prepared has simple process, small thickness, and improved applicability in solving the middle and low frequency sound noise of the automobile, and has excellent water tightness. DETAILED DESCRIPTION

[0032] The application will be further described in detail below in combination with examples. It should be specially noted that: in the following examples, the specific conditions not noted are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the raw materials used in the following examples can be sourced from the ordinary market unless specially noted.

[0033] The floating beads are purchased from Shijiazhuang Qiantong Mineral Products Co., Ltd., and the particle sizes are 0.01 mm, 0.5 mm and 2.5 mm.

[0034] The polyanionic cellulose (PAC) is an industrial grade, the viscosity is less than or equal to 40 mPa·s, and the brand is Chao Yannian New Material.

[0035] Chopped polyester fiber, length 3-6mm, brand Haosong.

[0036] EVA, industrial grade, melt index 25 g / 10min, brand Jiangsu Suerban.

[0037] PBAT, industrial grade, melt index 3-5 g / 10min, brand Wanhua Chemical.

[0038] AC foaming agent, brand Yado Chemical.

[0039] 461WU microsphere foaming agent, 6-9 microns, brand Nuorion.

[0040] ZnO foaming aid, industrial grade, brand Dalian Zinc Oxide.

[0041] DCP crosslinking agent, brand Nuorion.

[0042] TAIC co-crosslinking agent, TAIC-70, brand Plimac New.

[0043] Calcium carbonate, industrial grade, 1250 mesh, brand Jinghua Calcium Industry.

[0044] White carbon black, 1500 mesh, brand Shandong Xibaihe Chemical Industry.

[0045] Distearyl dimethyl ammonium chloride, brand Jinan Ausley Chemical Industry.

[0046] Montmorillonite, industrial grade, brand Hebei Mingzhe Mineral.

[0047] Preparation Example

[0048] Preparation Example 1

[0049] The preparation method of the modified montmorillonite is as follows:

[0050] Weigh 7.0g of distearyl dimethyl ammonium chloride (DODMAC) into 200mL of 60℃ water and stir until completely dissolved and clear. Slowly add 10g of dry montmorillonite into 1000mL of 70℃ deionized water. Stir at high speed (600rpm) for 2 hours at 70℃ to ensure that the montmorillonite is fully hydrated and dispersed into a uniform slurry. Slowly add (about 30 minutes to drop) the DODMAC solution into the montmorillonite slurry at 70℃ under vigorous stirring (800rpm). After the addition is complete, maintain the temperature at 70℃ and continue to stir vigorously for 4 hours to allow the reaction to proceed fully. After the reaction is complete, centrifuge or suction filter the reaction mixture to obtain a filter cake which is dried in a vacuum drying oven at 80℃ for 48 hours until completely dry. Grind the dried hard block with a grinder or ball mill, sieve through a 500 mesh sieve to obtain the modified montmorillonite.

[0051] Example

[0052] Example 1

[0053] A low-frequency sound-absorbing and sound-insulating EVA double-layer foam material, comprising a sound-absorbing layer and a sound-insulating layer fixedly connected, and the thickness of each layer is 1.5 mm.

[0054] The sound-absorbing layer material comprises the following raw materials: EVA; PBAT; AC foaming agent; 461WU microsphere foaming agent; ZnO foaming aid; DCP crosslinking agent; TAIC auxiliary crosslinking agent; calcium carbonate; white carbon black. The specific amount is shown in Table 1.

[0055] The sound-insulating layer material comprises the following raw materials: EVA; AC foaming agent; 461WU microsphere foaming agent; ZnO foaming aid; DCP crosslinking agent; TAIC auxiliary crosslinking agent; calcium carbonate; white carbon black; modified montmorillonite prepared in Preparation Example 1. The specific amount is shown in Table 2.

[0056] The preparation method of the low-frequency sound-absorbing and sound-insulating EVA double-layer foam material comprises the following steps: mixing the raw materials in the sound-absorbing layer material according to the proportion, mixing the raw materials in the sound-insulating layer material according to the proportion, and performing a composite extrusion foaming process. The temperature setting of the heating section of the extruder is 70℃ (first section), 75℃ (second section), 75℃ (third section), and 78℃ (die head), respectively. When the total output is 100 kg / h, the pulling speed is set to 3.5 m / min, the thickness of the single-layer material is controlled to be 1.5 mm, the total thickness is 3 mm, the foaming requirement is 150℃, and the foaming time is 10 min. The double-layer foam material is prepared.

[0057] Example 2

[0058] The difference between this embodiment and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials in the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials in the sound-insulating layer material are shown in Table 2.

[0059] Example 3

[0060] The difference between this embodiment and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials in the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials in the sound-insulating layer material are shown in Table 2.

[0061] Example 4

[0062] The difference between this embodiment and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials in the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials in the sound-insulating layer material are shown in Table 2.

[0063] Example 5

[0064] The difference between this embodiment and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials in the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials in the sound-insulating layer material are shown in Table 2.

[0065] Example 6

[0066] The difference between this example and Example 1 is that the amounts of the raw materials are different, and the amounts of the raw materials of the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer material are shown in Table 2.

[0067] Example 7

[0068] The difference between this example and Example 1 is that the amounts of the raw materials are different, and the amounts of the raw materials of the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer material are shown in Table 2.

[0069] Example 8

[0070] The difference between this example and Example 3 is that the sound-absorbing layer material further comprises floating beads, polyanionic cellulose and short-cut polyester fibers, and the amounts of the raw materials of the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer material are shown in Table 2.

[0071] The particle size specifications of the floating beads are 0.01 mm, 0.5 mm and 2.5 mm, and the weight ratio of the floating beads of each specification is 1:2:1.

[0072] Example 9

[0073] The difference between this example and Example 8 is that the amounts of the floating beads, polyanionic cellulose and short-cut polyester fibers are different, and the amounts of the raw materials of the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer material are shown in Table 2.

[0074] Example 10

[0075] The difference between this example and Example 8 is that the amounts of the floating beads, polyanionic cellulose and short-cut polyester fibers are different, and the amounts of the raw materials of the sound-absorbing layer material are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer material are shown in Table 2.

[0076] Example 11

[0077] The difference between this example and Example 9 is that the sound-absorbing layer material does not contain floating beads.

[0078] Example 12

[0079] The difference between this example and Example 9 is that the sound-absorbing layer material does not contain polyanionic cellulose.

[0080] Example 13

[0081] The difference between this example and Example 9 is that the sound-absorbing layer material does not contain short-cut polyester fibers.

[0082] Comparative Example

[0083] Comparative Example 1

[0084] The difference between the present comparative example and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials of the sound-absorbing layer are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer are shown in Table 2.

[0085] PBAT and modified montmorillonite are not used in the present comparative example.

[0086] Comparative Example 2

[0087] The difference between the present comparative example and Example 1 is that the amounts of the raw materials are different. The amounts of the raw materials of the sound-absorbing layer are shown in Table 1, and the amounts of the raw materials of the sound-insulating layer are shown in Table 2.

[0088] PBAT, modified montmorillonite and 461WU microsphere foaming agent are not used in the present comparative example.

[0089] Table 1 Amounts of Raw Materials of Sound-Absorbing Layer

[0090]

[0091] Table 2 Amounts of Raw Materials of Sound-Insulating Layer

[0092]

[0093] Performance Test

[0094] Test Method

[0095] 1. Sound absorption coefficient: The double-layer foam materials prepared in Examples 1 to 4 and 8 to 13 and Comparative Example 1 were made into cylinders with a diameter of 100 mm and 30 mm, and then put into an impedance tube to test the sound absorption coefficient, with a wavelength of 500 Hz and a microphone model of TYPE 3160A. The test results are shown in Table 3.

[0096] 2. Sound insulation volume: The double-layer foam materials prepared in Examples 1 to 4 and Comparative Example 1 were made into cylinders with a diameter of 100 mm and 30 mm, and then put into an impedance tube to test the sound insulation volume, with a wavelength of 0 to 2000 Hz and a microphone model of TYPE 3160A. The test results are shown in Table 4.

[0097] 3. Water tightness: The double-layer foam materials prepared in Examples 1 to 4 and Comparative Example 1 were made into circular samples with an inner diameter of 10 mm and an outer diameter of 18 mm, clamped in a 150 mm X 120 mm X 1.6 mm metal plate, with a hole with a diameter of 10 mm in the middle of the upper metal plate. After going through 170℃ X 20 min, room temperature for 1 h, 160℃ X 20 min, room temperature for 1 h, 140℃ X 20 min, room temperature for 1 h, the upper part was connected with a transparent water storage cylinder with an outer diameter of 75 mm and a wall thickness of 2 mm and a stainless steel connecting body by butyl rubber, and water was injected to 500 mm, and observed for 60 minutes without water leakage. The test results are shown in Table 4.

[0098] 4. The initial foaming temperature in the preparation process of the low-frequency sound-absorbing and sound-insulating EVA double-layer foam material of Example 4 to Example 7 and Comparative Example 2 is shown in Table 5.

[0099] Table 3. Detection results of sound absorption coefficient

[0100]

[0101] Table 4. Detection results of sound insulation volume and water tightness

[0102]

[0103] Table 5. Initial foaming temperature detection results

[0104]

[0105] In combination with Example 1 to Example 4, Example 8 to Example 13 and Comparative Example 1 and in combination with Table 3, it can be seen that as the PBAT increases from 2 parts to 6 parts, the material flexibility is enhanced, the low-frequency sound absorption coefficient is significantly improved, but an excessive amount (8 parts) can cause a slight decrease in system compatibility and a slight decline in performance, and 6 parts is the optimal value. After adding floating beads, polyanionic cellulose and short-cut polyester fibers to the sound-absorbing layer material, the sound absorption coefficient is further improved.

[0106] In combination with Example 1 to Example 4 and Comparative Example 1 and in combination with Table 4, it can be seen that the increase in the amount of modified montmorillonite helps to form more sound wave scattering centers and a more dense closed-cell structure, so the sound insulation volume and water pressure resistance performance are simultaneously improved, and the best balance is reached at 15 parts (45 dB, 32 cm). Continue to increase to 20 parts, which can cause a small decline in performance due to uneven dispersion.

[0107] In combination with Example 4 to Example 7 and Comparative Example 2 and in combination with Table 5, it can be seen that as the 461WU microsphere foaming agent is introduced, the initial foaming temperature gradually decreases, the sound-absorbing layer is added with 4 parts of 461WU microsphere foaming agent, and the initial foaming temperature is reduced to 134℃, the sound-insulating layer is added with 3 parts of 461WU microsphere foaming agent, and the initial foaming temperature is reduced to 138℃, which can meet the low-temperature foaming performance of 140℃.

[0108] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A mid-to-low frequency sound-absorbing and sound-insulating EVA double-layer foam material, characterized in that, It includes a fixedly connected sound-absorbing layer and a sound-insulating layer, both with a thickness of 1.5mm; The sound-absorbing layer material comprises the following raw materials in parts by weight: EVA 92-98 parts; PBAT 2-8 parts; AC foaming agent 8 parts; 461WU microsphere foaming agent 1-5 parts; ZnO foaming agent 1.5 parts; DCP crosslinking agent 1.2 parts; 0.5 parts TAIC crosslinking agent; 20 parts calcium carbonate; 10 parts silica; The sound insulation layer material comprises the following raw materials in parts by weight: 100 parts EVA; 5 parts AC foaming agent; 1-4 parts 461WU microsphere foaming agent; ZnO foaming agent 1.2 parts; DCP crosslinking agent 1.2 parts; 0.8 parts of TAIC crosslinking agent; 0-15 parts of calcium carbonate; 10 parts of silica; 5-20 parts of modified montmorillonite.

2. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 1, characterized in that: The modified montmorillonite was obtained by modifying montmorillonite with dioctadecyl dimethylammonium chloride.

3. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 2, characterized in that: The modified montmorillonite has a particle size of 500 mesh.

4. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 3, characterized in that: The modified montmorillonite is 15 parts by weight.

5. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 1, characterized in that: The PBAT is in the form of 6 parts by weight.

6. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 1, characterized in that: The 461WU microsphere foaming agent in the sound-absorbing layer material is 4 to 5 parts by weight, and the 461WU microsphere foaming agent in the sound-insulating layer material is 3 to 4 parts by weight.

7. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 1, characterized in that: The sound-absorbing layer material also includes 2-6 parts by weight of cenospheres, 0.2-0.5 parts by weight of polyanionic cellulose, and 2-4 parts by weight of chopped polyester fibers.

8. The low-frequency sound-absorbing and sound-insulating EVA double-layer foam material according to claim 1, characterized in that: The particle size specifications of the cenospheres are 0.01mm, 0.5mm and 2.5mm, and the weight ratio of each specification of cenospheres is 1:2:

1.

9. The method for preparing the low-to-medium frequency sound-absorbing and insulating EVA double-layer foam material according to any one of claims 1 to 8, characterized in that, Includes the following steps: The raw materials for the sound-absorbing layer are mixed according to the formula, and the raw materials for the sound-insulating layer are mixed according to the formula. A composite extrusion foaming process is carried out, with the thickness of a single layer material controlled at 1.5 mm and the total thickness controlled at 3 mm, to obtain a double-layer foam material.

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