Mute cotton as well as preparation method and application thereof

Abstract

The invention discloses mute cotton and a preparation method and application thereof, and relates to the field of foam materials.The preparation method of the mute cotton comprises the steps that after polyhydric alcohol, octavinyl polyhedral oligomeric silsesquioxane, steric hindrance type alkyl diamine, a catalyst, a foaming agent, a foam stabilizer and a surfactant are mixed, isocyanate is added for mixing, and the mute cotton is obtained. The mold is provided with a high-temperature side and a low-temperature side, and the alpha-carbon atom of the amino group of the steric hindrance type alkyl diamine is provided with a straight chain, branched chain or cyclic aliphatic diamine with C1-C4 alkyl substituent groups. The mute cotton with the gradient pore structure prepared by the method is used on a rubber tire, medium-high frequency noise generated by friction between the tire and a road surface is absorbed through smaller pores, low-frequency cavity resonance noise is dissipated through larger pores, and full-band noise reduction can be realized.

Description

Technical Field

[0001] This invention relates to the field of foam materials, and more specifically to a sound-absorbing cotton, its preparation method, and its application. Background Technology

[0002] With the rapid development of the automotive industry, especially electric vehicles, unprecedentedly high standards have been set for the NVH (noise, vibration, and harshness) performance of vehicles. As the only component of a vehicle in contact with the road surface, tires generate rolling noise, particularly low-frequency noise caused by resonance within the tire's internal cavities, which has become one of the main noise sources affecting ride comfort. To address this issue, applying polyurethane foam sound-absorbing material to the inner wall of the tire has become an industry-recognized and effective solution.

[0003] Currently, most tire noise reduction materials on the market use traditional polyurethane foam. However, these materials generally face two major bottlenecks: First, the material itself has insufficient damping loss factor and mechanical strength. Under the long-term effects of centrifugal force generated by the high-speed rolling of the tire, periodic deformation, and thermal aging, it is prone to fatigue damage, increased permanent compression deformation, and even detachment from the tire sidewall, resulting in a decrease in noise reduction effect over time. Second, the cell structure of traditional foam is simple and random, which cannot achieve wide-band efficient absorption of tire noise with complex frequency spectrum, thus limiting the noise reduction effect.

[0004] To improve the sound absorption spectrum width, several sound-absorbing cotton designs with gradient pore structures have emerged in existing technologies. For example, CN108859362B uses multi-layer composites of foam layers with different pore sizes, CN103146016A adds special pore-forming agents during the foaming process, and CN118027336A uses complex pressure conditions to attempt to construct pore size variations. However, these methods generally suffer from problems such as complex processes, high costs, weak interlayer bonding, or uncontrollable and discontinuous gradient structures, making it difficult to meet the stringent requirements of efficiency, cost, and consistency for large-scale industrial production. More importantly, these methods do not involve deep synergistic design with the chemical composition and reaction processes of the material itself. The formation of the gradient structure depends on external physical intervention rather than the control of the essential foaming kinetics, thus resulting in limited and unstable performance improvements.

[0005] Therefore, further improvements and development are still needed. Summary of the Invention

[0006] To address the shortcomings of existing technologies and solve the aforementioned problems, a sound-absorbing cotton, its preparation method, and its application are proposed, and the following technical solution is provided: A method for preparing sound-absorbing cotton, characterized in that polyol, octavinyl cage-type polysilsesquioxane, sterically hindered alkyl diamine, catalyst, foaming agent, foam stabilizer, and surfactant are mixed, and then isocyanate is added and mixed again. The mixture is then injected into a mold for foaming to obtain sound-absorbing cotton. The mold is a mold-closing mold, which has a high-temperature side and a low-temperature side. The temperature of the high-temperature side of the mold-closing mold is 5-15°C higher than that of the low-temperature side, so as to induce the sound-absorbing cotton to form pores with a gradually increasing pore size from the low-temperature side to the high-temperature side. The structure is a gradient, wherein the sterically hindered alkyl diamine is a straight-chain, branched, or cyclic aliphatic diamine with C1-C4 alkyl substituents on the α-carbon atom of the amino group; by mass, the polyol is 90-120 parts, the isocyanate is 100-140 parts, the octavinyl cage-type polysilsesquioxane is 5-10 parts, the sterically hindered alkyl diamine is 5-10 parts, the catalyst is 0.1-0.5 parts, the blowing agent is 1-3 parts, and the foam stabilizer is 1-3 parts.

[0007] Furthermore, the high-temperature side temperature of the mold is 50-70℃, and the low-temperature side temperature is 40-60℃.

[0008] Furthermore, after the foaming step, there is a curing step, which is to cure at 80-120°C for 1-3 hours.

[0009] Furthermore, the mass ratio of the polyol to the octavinyl cage-type polysilsesquioxane is 1:(0.05-0.1).

[0010] Furthermore, the polyol is a polyether polyol, the isocyanate is diphenylmethane diisocyanate, the sterically hindered alkyl diamine is isophorone diamine, the catalyst is one or more of amine catalysts and organotin catalysts, the foaming agent is water, and the foam stabilizer is silicone oil.

[0011] The present invention also provides a sound-absorbing cotton obtained according to the above-described method for preparing sound-absorbing cotton.

[0012] Furthermore, the sound-absorbing cotton has pores of varying sizes in the thickness direction.

[0013] The present invention also provides an application of the sound-absorbing cotton prepared according to the above-described sound-absorbing cotton method, characterized in that the sound-absorbing cotton is applied to a rubber tire, wherein the sound-absorbing cotton is adhered to the tread area on the inner side of the tire.

[0014] Furthermore, the side of the sound-absorbing cotton with the larger pore size is fitted to the inner tread area of ​​the tire.

[0015] Due to the adoption of the above technical solutions, the beneficial technical effects of the present invention are as follows: 1. The sound-absorbing cotton of the present invention uses a strong and tough polyurea network formed by sterically hindered alkyl diamine and octavinyl cage-type polysilsesquioxane as reinforcement points. Its resistance to deformation is significantly higher than that of ordinary sound-absorbing cotton. It can withstand the centrifugal force, deformation and heat load under the high speed of tire rolling for a long time, ensuring durability.

[0016] 2. The addition of octavinyl cage-type polysilsesquioxane in this invention can cause the pores of the sound-absorbing cotton to form gradient pores under the influence of temperature. The gradient pore structure prepared by the method can absorb the mid-to-high frequency noise generated by the friction between the tire and the road surface by smaller pores, while larger pores can specifically dissipate low-frequency cavity resonance noise, thereby achieving noise reduction across the entire frequency band.

[0017] 3. In this invention, the side with larger pores of the sound-absorbing cotton is attached to the inner wall of the tire crown, which allows the sound-absorbing cotton to preferentially and efficiently dissipate low-frequency noise such as tire cavity resonance noise. At the same time, this structure achieves an optimized distribution of material mechanical properties. The side with larger pore diameter ensures a tight fit with the curved tire wall, while the side with smaller pore diameter provides overall support to resist centrifugal force, thus ensuring the durability and reliability of the product. Attached Figure Description

[0018] Figure 1 The sound absorption curves of the sound-absorbing cotton in Example 1 and Comparative Example 1 are shown. Figure 2 This is a schematic diagram of the structure of the sound-absorbing cotton in Example 1; Figure 3 The infrared spectrum of the sound-absorbing cotton in Example 1 is shown. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application.

[0020] A method for preparing sound-absorbing cotton includes mixing a polyol, an octavinyl cage-type polysilsesquioxane, a sterically hindered alkyl diamine, a catalyst, a foaming agent, a foam stabilizer, and a surfactant; then adding isocyanate and mixing the mixture before injecting it into a mold for foaming to obtain sound-absorbing cotton. The mold is a mold-closing mold, which has a high-temperature side and a low-temperature side. The temperature of the high-temperature side of the mold is 5-15°C higher than that of the low-temperature side, to induce the sound-absorbing cotton to form pores with a gradually increasing pore size from the low-temperature side to the high-temperature side. The structure is a gradient, wherein the sterically hindered alkyl diamine is a straight-chain, branched, or cyclic aliphatic diamine with C1-C4 alkyl substituents on the α-carbon atom of the amino group; by mass, the polyol is 90-120 parts, the isocyanate is 100-140 parts, the octavinyl cage-type polysilsesquioxane is 5-10 parts, the sterically hindered alkyl diamine is 5-10 parts, the catalyst is 0.1-0.5 parts, the blowing agent is 1-3 parts, and the foam stabilizer is 1-3 parts.

[0021] The addition of octavinyl-vinyl cage-type polysilsesquioxane in this invention allows the pores of the sound-absorbing cotton to form a gradient pore structure affected by temperature. The gradient pore structure prepared by this method allows smaller pores to absorb mid-to-high frequency noise generated by tire-road friction, while larger pores can specifically dissipate low-frequency cavity resonance noise, achieving noise reduction across the entire frequency range. The long chains attached to the outer side of the octavinyl cage-type polysilsesquioxane act as thermosensitive chains. At high temperatures, these chains contract, and molecules tend to aggregate, acting as ultra-large heterogeneous nucleation sites, inducing the formation of larger and more uniform pores. At low temperatures, the chain segments extend, and molecules disperse more evenly, acting as fine nucleation sites, inducing the formation of smaller and denser pores. The addition of octavinyl-vinyl cage-type polysilsesquioxane in this application significantly enhances and stabilizes the pore size gradient, making the gradient transition more natural—something that cannot be achieved with a single chemical foaming agent or ordinary filler.

[0022] This application also provides a sound-absorbing cotton, the raw materials of which include isocyanate, polyol, octavinyl cage-type polysilsesquioxane, and sterically hindered alkyl diamine. The sterically hindered alkyl diamine has a straight-chain, branched, or cyclic aliphatic diamine with C1-C4 alkyl substituents on the α-carbon atom of its amino group. The sound-absorbing cotton forms a gradient pore structure under temperature influence. The sound-absorbing cotton of this invention, through the strong and tough polyurea network formed by the sterically hindered alkyl diamine and the octavinyl cage-type polysilsesquioxane as reinforcement, has significantly higher resistance to deformation than ordinary sound-absorbing cotton, and can withstand the centrifugal force, deformation, and heat load under high-speed tire rolling for a long time, ensuring durability. The eight vinyl groups (-CH=CH2) of octavinyl cage-type polysilsesquioxane can chemically bond to the three-dimensional network of polyurethane through free radical copolymerization with the active hydrogen from -OH of polyols, H-OH of water, or -NH2 of sterically hindered alkyl diamines in the polyurethane foam system under the action of a catalyst. This avoids the aggregation of nanoparticles and achieves molecular-level organic-inorganic hybridization.

[0023] This application also provides an application of sound-absorbing cotton, which is applied to a rubber tire and adheres to the inner crown area of ​​the tire. The side of the sound-absorbing cotton with larger pores adheres to the inner crown area of ​​the tire. The larger pores of the sound-absorbing cotton adhere to the inner wall of the tire crown, allowing it to preferentially and efficiently dissipate low-frequency noise such as tire cavity resonance noise. Simultaneously, this structure achieves an optimized distribution of material mechanical properties. The side with larger pores ensures a tight fit with the curved tire sidewall, while the side with smaller pores provides overall support to resist centrifugal force, ensuring the product's durability and reliability.

[0024] Example 1 100 parts of polypropylene glycol, 8 parts of octavinyl cage polysilsesquioxane, 8 parts of isophorone diamine (IPDA), 0.3 parts of triethanolamine, 2 parts of water, and 2 parts of silicone oil were added to a mixing vessel and stirred at 60°C and 200 rpm for 30 minutes to fully disperse the octavinyl cage polysilsesquioxane and obtain a uniform mixture of material A.

[0025] Pour the mixture of component A into the mixing cup of a high-speed mixer at room temperature. Adjust the speed to 3000 rpm. Within 5 seconds of starting mixing, rapidly pour 120 parts of diphenylmethane diisocyanate (MDI) into the mixing cup and mix at high speed for 10 seconds to obtain a mixture. When milky white foam begins to rise from the mixture, immediately pour the mixture into a preheated flat mold. The mold is an aluminum flat mold with a temperature difference. Set one side of the mold temperature to 65°C (high temperature side) and the other side temperature to 55°C (low temperature side), with a temperature difference of 10°C. After pouring the mixture, close the mold and allow the foam to freely expand and fill the cavity. The foaming time is 3 minutes. After foaming, transfer the mold with the foam to an oven at 110°C and cure for 2 hours. After curing, demold the foam and place it at room temperature for at least 24 hours for post-curing. Then cut it into the required size to obtain the sound-absorbing cotton.

[0026] Example 2 120 parts of polypropylene glycol, 10 parts of octavinyl cage polysilsesquioxane, 10 parts of isophorone diamine (IPDA), 0.5 parts of triethanolamine, 3 parts of water, and 3 parts of silicone oil were added to a mixing vessel and stirred at 60°C and 200 rpm for 30 minutes to fully disperse the octavinyl cage polysilsesquioxane and obtain a uniform mixture of material A.

[0027] Pour the mixture of component A into the mixing cup of a high-speed mixer at room temperature. Adjust the speed to 3000 rpm. Within 5 seconds of starting mixing, rapidly pour 140 parts of diphenylmethane diisocyanate (MDI) into the mixing cup and mix at high speed for 10 seconds to obtain a mixture. When milky white foam begins to rise from the mixture, immediately pour the mixture into a preheated flat mold. The mold is an aluminum flat mold with a temperature difference. Set one side of the mold temperature to 65°C (high temperature side) and the other side temperature to 55°C (low temperature side), with a temperature difference of 10°C. After pouring the mixture, close the mold and allow the foam to freely expand and fill the cavity. The foaming time is 3 minutes. After foaming, transfer the mold with the foam to an oven at 110°C and cure for 2 hours. After curing, demold the foam and leave it at room temperature for at least 24 hours for post-curing. Then cut it into the required size to obtain the sound-absorbing cotton.

[0028] Example 3 Add 90 parts of polypropylene glycol, 5 parts of octavinyl cage polysilsesquioxane, 5 parts of isophorone diamine, 0.1 parts of dibutyltin dilaurate, 1 part of water, and 1 part of silicone oil to a mixing vessel, and stir at 60°C and 200 rpm for 30 minutes to fully disperse the octavinyl cage polysilsesquioxane and obtain a uniform mixture of material A.

[0029] Pour the mixture of component A into the mixing cup of a high-speed mixer at room temperature. Adjust the speed to 3000 rpm. Within 5 seconds of starting mixing, quickly pour 100 parts of diphenylmethane diisocyanate (MDI) into the mixing cup and mix at high speed for 10 seconds to obtain a mixture. When milky white foam begins to rise from the mixture, immediately pour the mixture into a preheated flat mold. The mold is an aluminum flat mold with a temperature difference. Set one side of the mold temperature to 65°C (high temperature side) and the other side temperature to 55°C (low temperature side), with a temperature difference of 10°C. After pouring the mixture, close the mold and allow the foam to freely expand and fill the cavity. The foaming time is 3 minutes. After foaming, transfer the mold with the foam to an oven at 110°C and cure for 2 hours. After curing, demold the foam and place it at room temperature for at least 24 hours for post-curing. Then cut it into the required size to obtain the sound-absorbing cotton.

[0030] Example 4 100 parts of polytetrahydrofuran diol, 8 parts of octavinyl cage polysilsesquioxane, 8 parts of isophorone diamine (IPDA), 0.3 parts of triethylenediamine, 2 parts of water, and 2 parts of silicone oil were added to a mixing vessel and stirred at 60°C and 200 rpm for 30 minutes to fully disperse the octavinyl cage polysilsesquioxane and obtain a uniform mixture of material A.

[0031] Pour the mixture of component A into the mixing cup of a high-speed mixer at room temperature. Adjust the speed to 3000 rpm. Within 5 seconds of starting mixing, rapidly pour 120 parts of diphenylmethane diisocyanate into the mixing cup and mix at high speed for 10 seconds to obtain a mixture. When milky white foam begins to rise from the mixture, immediately pour the mixture into a preheated flat mold. The mold is an aluminum flat mold with a temperature difference. Set one side of the mold temperature to 70°C (high temperature side) and the other side temperature to 55°C (low temperature side), with a temperature difference of 15°C. After pouring the mixture, close the mold and allow the foam to freely expand and fill the cavity. The foaming time is 3 minutes. After foaming, transfer the mold with the foam to an 80°C oven for curing for 2 hours. After curing, demold the foam and place it at room temperature for at least 24 hours for post-curing. Then cut it into the required size to obtain the sound-absorbing cotton.

[0032] Example 5 100 parts of polytetrahydrofuran diol, 8 parts of octavinyl cage polysilsesquioxane, 8 parts of isophorone diamine (IPDA), 0.2 parts of dibutyltin dilaurate, 0.2 parts of triethylenediamine, 2 parts of water, and 2 parts of silicone oil were added to a mixing vessel and stirred at 60°C and 200 rpm for 30 minutes to fully disperse the octavinyl cage polysilsesquioxane and obtain a uniform mixture of material A.

[0033] Pour the mixture of component A into the mixing cup of a high-speed mixer at room temperature. Adjust the speed to 3000 rpm. Within 5 seconds of starting mixing, rapidly pour 120 parts of diphenylmethane diisocyanate into the mixing cup and mix at high speed for 10 seconds to obtain a mixture. When milky white foam begins to rise from the mixture, immediately pour the mixture into a preheated flat mold. The mold is an aluminum flat mold with a temperature difference. Set the temperature of one side of the mold to 50°C (high temperature side) and the temperature of the other side to 45°C (high temperature side), with a temperature difference of 5°C. After pouring the mixture, close the mold and allow the foam to freely expand and fill the cavity. The foaming time is 3 minutes. After foaming, transfer the mold with the foam to an oven at 120°C and cure for 2 hours. After curing, demold the foam and place it at room temperature for at least 24 hours for post-curing. Then cut it into the required size to obtain the sound-absorbing cotton.

[0034] Comparative Example 1 The sound-absorbing cotton used in this comparative example is prepared using the technical solution described in CN120718598A, a type of tire-specific sound-absorbing cotton.

[0035] A tire-specific sound-absorbing cotton includes a sound-absorbing layer and an adhesive strip. The adhesive strip is composed of the following substances: 90 parts of styrene-butadiene-styrene block copolymer, 27.5 parts of epoxidized soybean oil acrylate, 27.5 parts of terpene resin, 25 parts of naphthenic oil, 5 parts of nano-montmorillonite, 5 parts of silica aerogel, 2 parts of antioxidant 1520, and 2 parts of 1,3,5-tris(4-boronic acid phenyl)benzene. The sound-absorbing layer is composed of the following substances in parts by weight: 50 parts of graphene-polyurethane composite foam, 25 parts of polyester fiber, 8 parts of aluminum hydroxide, 5 parts of mica powder, and 4 parts of epoxy resin binder.

[0036] The preparation method of the adhesive strip is as follows: S21. Styrene-butadiene-styrene block copolymer, epoxidized soybean oil acrylate, terpene resin, naphthenic oil, nano-montmorillonite, silica aerogel and antioxidant 1520 are added to a high-speed mixer in proportion and stirred and mixed evenly at room temperature to obtain mixture A; S22. 1,3,5-tris(4-boronic acid phenyl)benzene is added to mixture A obtained in step S21 and stirred and mixed evenly to obtain mixture B; S23. Mixture B is added to a twin-screw extruder and extruded to obtain the adhesive strip.

[0037] The method for preparing the sound-absorbing layer is as follows: S31. Graphene-polyurethane composite foam is crushed into fine particles and added to a high-speed mixer along with polyester fiber, aluminum hydroxide, and mica powder and stirred evenly to obtain mixture C; S32. Epoxy resin binder is added to mixture C obtained in step S31 and stirred evenly to obtain mixture D; S33. Mixture D obtained in step S32 is placed in a mold and hot-pressed, then removed, trimmed, and inspected to obtain the sound-absorbing layer.

[0038] The method for preparing the sound-absorbing cotton is as follows: cut the adhesive strip to the required width and length, paste it onto the sound-absorbing layer, and package it to obtain the sound-absorbing cotton.

[0039] Comparative Example 2 The only difference between this comparative example and Example 1 is that octavinyl cage-type polysilsesquioxane is not added; otherwise, they are the same as in Example 1.

[0040] Comparative Example 3 The only difference between this comparative example and Example 1 is that no sterically hindered alkyl diamine is added; all other aspects are the same as in Example 1.

[0041] Comparative Example 4 Compared with Example 1, the only difference is that there is no temperature difference between the two sides of the mold in this comparative example; otherwise, they are the same as in Example 1.

[0042] The sound-absorbing cotton obtained in Examples 1-5 and Comparative Examples 1-4 were subjected to the following tests, and the test results are shown in Tables 1-2 below.

[0043] Density: According to national standard GB / T 6343-2009; Compression permanent deformation: Refer to international standard ISO 1856-2018; Sound absorption coefficient: based on national standard GB / T 20247-2006.

[0044] Table 1. Test results of sound-absorbing cotton in Examples 1-5 and Comparative Examples 1-4 Table 2 Test results of sound absorption coefficients for Examples 1-5 and Comparative Examples 1-4 The sound-absorbing cotton obtained in Example 1 of this application has a moderate density, low permanent compressibility, and good low deformation capability. The structure of the sound-absorbing cotton obtained in Example 1 is as follows: Figure 2 As shown, Figure 2 Side A represents the side with smaller pores, corresponding to the low-temperature side of the mold; side B represents the side with larger pores, corresponding to the high-temperature side of the mold. Their infrared spectra are as follows: Figure 3 As shown. Examples 2-5 adjusted the corresponding process parameters. Although their performance was not as good as Example 1, it was still better than the comparative examples. From the sound absorption coefficient, the sound-absorbing cotton of Examples 1-5 can effectively reduce noise in all frequency bands, thanks to the gradient pore design of the sound-absorbing cotton of this invention. Comparative Examples 2-3 lacked the necessary components of this invention, making the sound-absorbing cotton significantly inferior to the examples in terms of compression set. In terms of acoustic performance, the sound absorption effect in the low frequency band was poor. This is because the lack of octavinyl cage-type polysilsesquioxane or sterically hindered alkyl diamine prevents the formation of an effective temperature response and gradient structure. Although the porosity may be maintained, the optimization ability for the most critical low-frequency noise of tires is lost. This strongly proves that octavinyl cage-type polysilsesquioxane or sterically hindered alkyl diamine is the key material basis for achieving the temperature-affected gradient pore formation, which cannot be replaced by ordinary fillers. Comparative Example 4 did not use a mold with a temperature difference, and its low-frequency absorption was extremely poor, indicating that a sufficient temperature difference (5-15℃) is a necessary process condition for obtaining significant performance improvement.

[0045] The sound absorption curves of the sound-absorbing cotton in Example 1 and Comparative Example 1 are shown below. Figure 1 (Curve 1 represents Example 1, and Curve 2 represents Comparative Example 1). In the low-frequency range of 125-250 Hz, the sound absorption coefficient of Example 1 is much greater than that of Comparative Example 1. Throughout the entire test frequency range of 125-4000 Hz, the sound absorption curve of Example 1 remains high and smooth, while the curve of Comparative Example 1 is generally low. This directly demonstrates that the gradient pore structure of the present invention achieves noise reduction across the entire frequency range.

[0046] Test Example 1 The side with the larger pores of the sound-absorbing cotton obtained in Example 1 was attached to the inner wall of the tire crown for sound absorption testing.

[0047] Test Example 2 The side with smaller pores of the sound-absorbing cotton obtained in Example 1 was attached to the inner wall of the tire crown for sound absorption testing.

[0048] The test results obtained from Test Examples 1-2 above are recorded in Table 3.

[0049] Table 3 Sound absorption coefficients of test examples 1-2 The sound absorption capacity of Test Example 2 in the low frequency range of 125-250Hz is inferior to that of Test Example 1. This is because the side with the larger hole is attached to the inner wall of the tire crown, which allows the sound-absorbing cotton to dissipate low-frequency noise such as tire cavity resonance noise preferentially and efficiently.

[0050] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing sound-absorbing cotton, characterized in that, A mixture of polyol, octavinyl cage-type polysilsesquioxane, sterically hindered alkyl diamine, catalyst, blowing agent, foam stabilizer, and surfactant is prepared. Isocyanate is then added and the mixture is injected into a mold to foam and obtain sound-absorbing cotton. The mold is a mold-closing mold with a high-temperature side and a low-temperature side. The high-temperature side of the mold is 5-15°C higher than the low-temperature side to induce the sound-absorbing cotton to form a gradient structure with pore sizes gradually increasing from the low-temperature side to the high-temperature side. The sterically hindered alkyl diamine is a straight-chain, branched, or cyclic aliphatic diamine with C1-C4 alkyl substituents on the α-carbon atom of its amino group. By mass, the polyol is 90-120 parts, the isocyanate is 100-140 parts, the octavinyl cage-type polysilsesquioxane is 5-10 parts, the sterically hindered alkyl diamine is 5-10 parts, the catalyst is 0.1-0.5 parts, the blowing agent is 1-3 parts, and the foam stabilizer is 1-3 parts.

2. The method for preparing sound-absorbing cotton according to claim 1, characterized in that, The high-temperature side temperature of the mold is 50-70℃, and the low-temperature side temperature is 40-60℃.

3. The method for preparing sound-absorbing cotton according to claim 1, characterized in that, The foaming step is followed by a curing step, which involves curing at 80-120℃ for 1-3 hours.

4. The method for preparing sound-absorbing cotton according to claim 1, characterized in that, The mass ratio of the polyol to the octavinyl cage-type polysilsesquioxane is 1:(0.05-0.1).

5. The method for preparing sound-absorbing cotton according to claim 1, characterized in that, The polyol is a polyether polyol, the isocyanate is diphenylmethane diisocyanate, the sterically hindered alkyl diamine is isophorone diamine, the catalyst is one or more of amine catalysts and organotin catalysts, the foaming agent is water, and the foam stabilizer is silicone oil.

6. A method for preparing a sound-absorbing cotton according to any one of claims 1-5.

7. The sound-absorbing cotton according to claim 6, characterized in that, The sound-absorbing cotton has pores of varying sizes in the thickness direction.

8. The application of a sound-absorbing cotton prepared by the method according to any one of claims 1-5, characterized in that, The sound-absorbing cotton is used on rubber tires and is attached to the tread area on the inside of the tire.

9. The application of sound-absorbing cotton according to claim 8, characterized in that, The side of the sound-absorbing cotton with the larger pore size is attached to the inner crown area of ​​the tire.

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