Polyurethane foaming material for motor noise reduction and preparation method thereof

Abstract

The invention relates to the technical field of foaming materials, in particular to a polyurethane foaming material for motor noise reduction and a preparation method thereof.The preparation method comprises the steps that part of an amine catalyst and polyol mixture, a foaming agent, a metal catalyst, a surfactant, expanded graphite, an anti-aging agent and the like are mixed, and a first component is obtained; isocyanate and the first component are subjected to high-pressure mixing according to a preset proportion, and a mixed system is obtained; and injecting the mixed system into a mold, carrying out gradient foaming to obtain a foaming body, carrying out surface hot pressing twice, and carrying out product curing and cutting to obtain a finished product of the motor wrapping part. The polyurethane foam material provided by the invention simultaneously meets the requirements of medium-high frequency sound absorption, vibration damping and oil stain protection.

Description

Technical Field

[0001] The present invention relates to the technical field of foam materials, and in particular to a polyurethane foam material for motor noise reduction and a preparation method thereof. Background Art

[0002] The acoustic performance of polyurethane sound-insulating foam plastics primarily depends on structural characteristics such as its density, thickness, porosity, and pore morphology. Open-cell polyurethane foam exhibits excellent sound absorption due to its unique microporous structure: the material contains a large number of interconnected tiny pores, and these open channels allow sound waves to penetrate deeply into the material. When sound waves act on the surface of the material, they cause the air within the micropores to vibrate. The friction between the air and the pore walls creates viscous resistance, converting sound energy into heat energy. Simultaneously, heat conduction occurs during the adiabatic compression / expansion process, further dissipating sound energy. Furthermore, the entangled structure of the polyurethane molecular chains undergoes a conformational transition under the action of sound waves, and the internal friction generated by chain segment slippage creates additional energy loss, enhancing the sound absorption effect.

[0003] Existing materials used in automotive motor noise reduction suffer from the following drawbacks: First, the closed-cell structure of rubber and conventional polyurethane foam results in low mid- and high-frequency sound absorption efficiency (the 2000Hz sound absorption coefficient is generally <0.6). Second, the harsh operating environment of motors (oil penetration and constant vibration) makes it difficult for existing materials to address the degradation of acoustic performance caused by oil intrusion and clogging of micropores, while vibration conditions accelerate structural fatigue cracking. Third, traditional processes struggle to reconcile performance conflicts; increasing the porosity sacrifices mechanical strength. Particularly for confined installations such as automotive window lift motors, the wrapping material must be both ultra-thin (<15mm) and capable of mid- and high-frequency sound absorption. A more prominent contradiction is that while a high porosity improves sound absorption, it also increases the risk of oil penetration. Existing technical solutions cannot meet this comprehensive requirement.

[0004] Chinese Patent Publication No. CN113174028A discloses a fully water-blown polyurethane foam, its preparation method, and uses. The polyurethane foam is prepared from the following components in the following weight ratios: 80-120 parts polyol, 3-10 parts chain extender, 1-5 parts blowing agent, 1-6 parts amine catalyst, 0.1-1.5 parts gel catalyst, 2-8 parts surfactant, 1-10 parts cross-linking agent, and 40-150 parts isocyanate. The polyurethane foam prepared by the present invention utilizes fully water-blown foaming, making it environmentally friendly. Furthermore, the foam exhibits a good internal pore structure, low apparent density, low deadweight, and excellent tear and compressive resistance. While improving compressive strength, the polyurethane foam overcomes the problems of decreased tear strength and increased apparent density, achieving high compressive strength, high tear strength, and low apparent density, enhancing the overall performance of the polyurethane foam. It can be used to prepare materials for automotive interiors, shock absorption, sound absorption, packaging, and other applications, and has broad application prospects.

[0005] It can be seen that the above-mentioned all-water-blown polyurethane foam and its preparation method and use have the following problems: the polyurethane foam is difficult to meet the requirements of vibration reduction and noise reduction at the same time, and cannot solve the problem of motor oil intrusion and clogging of micropores. Summary of the Invention

[0006] To this end, the present invention provides a polyurethane foam material for motor noise reduction and a preparation method thereof, so as to overcome the problem in the prior art of lacking absorption of broadband noise of the motor.

[0007] To achieve the above object, the present invention provides a polyurethane foam material for motor noise reduction, comprising:

[0008] Step S1, mixing part of the amine catalyst with a polyol mixture, a foaming agent, a metal catalyst, a surfactant, expanded graphite, and an anti-aging agent to obtain a premixed first component;

[0009] Step S2, determining a delay time according to the dynamic viscosity value of the premixed first component;

[0010] Step S3, adding the remaining amine catalyst based on the delay time to obtain a second component, and recording the time of adding the remaining amine catalyst as the start time;

[0011] Step S4, mixing isocyanate as the third component with the second component at a preset volume ratio under high pressure to obtain a mixed system;

[0012] Step S5, injecting the mixed system into a mold and adjusting the foaming temperature according to the motor operating parameters and the amount of metal catalyst added to perform gradient foaming molding to obtain a foamed body with a gradient structure in which the inner layer density is higher than the outer layer density;

[0013] Step S6, hot pressing the surface of the foam to form a surface dense layer to obtain a hot pressed foam;

[0014] Step S7, cutting the hot-pressed foam after curing to obtain a finished motor wrapping component;

[0015] Among them, the preset ratio is third component: second component = 1:1.2 to 1:1.5.

[0016] Furthermore, the step S5 includes:

[0017] Step S51, obtaining motor operating parameters, and determining the thickness of the acoustic resistance layer of the foam material based on the motor operating parameters, wherein the motor operating parameters include an average vibration frequency and an average noise decibel;

[0018] Step S52, determining the foaming temperature of the acoustic resistance layer according to the amount of the metal catalyst added and the thickness of the acoustic resistance layer;

[0019] Step S53, monitoring the expansion rate change of the mixed system in real time, and determining the temperature adjustment amount according to the expansion rate change;

[0020] Step S54, when the expansion height of the mixed system meets the thickness of the acoustic resistance layer, adjusting the mold temperature according to the temperature adjustment amount;

[0021] Step S55 , when the total thickness of the mixed system meets the target thickness of the polyurethane foam material, the foaming is stopped to obtain the foamed body.

[0022] Furthermore, in step S53, the expansion height increment of the mixed system per unit time is continuously recorded.

[0023] The expansion rate change is determined based on a rate of change of the expansion height increment.

[0024] Furthermore, in step S54, the foaming time is determined based on the start time.

[0025] Furthermore, step S6 includes:

[0026] Step S61, hot pressing the surface of the foam body with a first pressure, wherein the first pressure is determined according to the remaining volume of the mold cavity and the thickness of the shock-absorbing layer;

[0027] Step S62, obtaining the thickness and density of the dense layer of the foam surface after step S61 to determine the second pressure, and performing secondary hot pressing on the foam surface with the second pressure to obtain the hot-pressed foam.

[0028] Furthermore, in step S61 , the thickness of the shock-absorbing layer is determined according to the target thickness of the polyurethane foam material and the thickness of the acoustic resistance layer.

[0029] Furthermore, the delay time is negatively correlated with the dynamic viscosity value.

[0030] Furthermore, the temperature adjustment amount is positively correlated with the expansion rate change amount.

[0031] Furthermore, the foaming time of the acoustic resistance layer is inversely proportional to the added amount of the metal catalyst.

[0032] Furthermore, the present invention also provides a polyurethane foam material for motor noise reduction, the polyurethane foam material is composed of a second component and a third component, wherein the second component is composed, by weight, of 100 parts of a polyol mixture, 1 to 3 parts of a foaming agent, 0.5 to 2 parts of an amine catalyst, 0.1 to 0.5 parts of a metal catalyst, 2 to 5 parts of nano-silicon dioxide, 5 to 10 parts of expanded graphite, and 0.5 to 1 part of an anti-aging agent; the third component is composed of an isocyanate;

[0033] The polyol mixture is prepared by compounding polyether polyol and polyester polyol, the hydroxyl value of which is 120 mgKOH / g to 180 mgKOH / g, and the mass ratio of polyether polyol to polyester polyol is 7:3; the isocyanate is modified MDI, and the NCO content of which is 25% to 31%; the foaming agent is deionized water; and the anti-aging agent is UV-328.

[0034] Compared with the existing technology, the present invention controls the foaming reaction kinetics by synergistically adding amine catalysts and metal catalysts in steps, combines gradient foaming molding technology to construct a density gradient structure with high inside and low outside, and uses surface hot pressing technology to form a dense protective layer, so that the polyurethane foam material has the triple functions of broadband sound absorption, high-efficiency vibration damping and oil pollution barrier. It effectively solves the technical contradiction in the field of motor noise reduction that high-porosity sound-absorbing materials are difficult to be compatible with oil pollution resistance and vibration resistance, and significantly improves the long-term acoustic stability of motor packages in high-temperature oil pollution environments.

[0035] Furthermore, the present invention constructs a gradient structure of an internal high-density acoustic resistance layer and an external low-density shock-absorbing layer, utilizing the high acoustic impedance characteristics of the acoustic resistance layer to achieve broadband absorption of medium and high-frequency noise. At the same time, the porous open structure of the shock-absorbing layer effectively dissipates low-frequency sound wave energy, allowing the material to maintain excellent sound absorption performance within the entire operating frequency band of the motor.

[0036] Furthermore, the present invention forms a cellular skeleton with a continuous density gradient by regulating the foaming process, uses a high-density acoustic resistance layer to disperse mechanical vibration stress, and a low-density shock-absorbing layer absorbs vibration energy through viscoelastic deformation of molecular chains, thereby achieving multi-stage damping attenuation of the motor's broadband vibration and significantly reducing the vibration transmission efficiency.

[0037] Furthermore, the present invention forms a dense crystalline layer on the surface of the foam through a two-stage hot pressing process. This layer constructs a continuous physical barrier through the oriented arrangement of polyurethane molecular chains and the stacking of expanded graphite layers, effectively preventing oil from penetrating into the internal pore structure of the material and avoiding the attenuation of acoustic performance caused by oil blockage.

[0038] Furthermore, the present invention ensures that the foam maintains the mechanical strength of the foam skeleton while forming a high-opening-porosity structure by real-time monitoring of the expansion rate changes and dynamically adjusting the mold temperature. Combined with the reinforcing effect of the surface dense layer, the material maintains structural integrity and acoustic functional stability under long-term vibration conditions.

[0039] Furthermore, the present invention achieves controllable preparation of gradient density structures through the coordinated control of the step-by-step catalyst addition sequence and expansion state feedback, accurately matching the rate balance of the foaming reaction and the gelation reaction, significantly improving the consistency between product batches and the adaptation accuracy to complex motor surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a method for preparing a polyurethane foam material for motor noise reduction according to an embodiment of the present invention;

[0041] Figure 2 This is a flow chart of step S5 of the method for preparing a polyurethane foam material for motor noise reduction according to an embodiment of the present invention;

[0042] Figure 3 This is a logic judgment diagram of step S5 of the method for preparing a polyurethane foam material for motor noise reduction according to an embodiment of the present invention;

[0043] Figure 4 This is a flow chart of step S6 of the method for preparing a polyurethane foam material for motor noise reduction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0045] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0046] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0047] An embodiment of the present invention provides a polyurethane foam material for motor noise reduction. The polyurethane foam material is composed of a second component and a third component. The second component is composed, by weight, of 100 parts of a polyol mixture, 1 to 3 parts of a foaming agent, 0.5 to 2 parts of an amine catalyst, 0.1 to 0.5 parts of a metal catalyst, 2 to 5 parts of nano-silicon dioxide, 5 to 10 parts of expanded graphite, and 0.5 to 1 part of an anti-aging agent. The third component is composed of isocyanate.

[0048] The polyol mixture is prepared by compounding polyether polyol and polyester polyol, the hydroxyl value of which is 120 mgKOH / g to 180 mgKOH / g, and the mass ratio of polyether polyol to polyester polyol is 7:3; the isocyanate is modified MDI, and the NCO content of which is 25% to 31%; the foaming agent is deionized water; and the anti-aging agent is UV-328.

[0049] In a specific embodiment, preferably, the amine catalyst may be a combination of one or more of N,N-dimethylcyclohexylamine, N,N-diethylethanolamine and N,N-dimethylbenzylamine.

[0050] In a specific embodiment, preferably, the metal catalyst is dibutyltin dilaurate.

[0051] In a specific embodiment, preferably, the expanded graphite is 300 mesh and has an expansion volume of 100 ml / g.

[0052] In a specific embodiment, preferably, the nano-silica is a combination of one or more of SP15 nano-silica, SP30 nano-silica and SP50 nano-silica.

[0053] In a specific embodiment, preferably, the polyether polyol includes trihydroxy polyoxypropylene ether, and the polyester polyol includes polyhexamethylene adipate.

[0054] Specifically, see Figure 1 , which are respectively flow charts of a polyurethane foam material for motor noise reduction and a preparation method thereof according to an embodiment of the present invention; the present invention also provides a method for preparing a polyurethane foam material for motor noise reduction, which is used to prepare the polyurethane foam material, comprising:

[0055] Step S1, mixing part of the amine catalyst with a polyol mixture, a foaming agent, a metal catalyst, a surfactant, expanded graphite, and an anti-aging agent to obtain a premixed first component;

[0056] In a specific embodiment, polyether polyol and polyester polyol are weighed in a mass ratio of 7:3, and mixed and stirred at a constant temperature of 25° C. for 10 minutes to obtain a polyol mixture; deionized water, dibutyltin dilaurate, nano-silica, expanded graphite, UV-328, and a portion of N,N-dimethylcyclohexylamine are added to the polyol mixture, where the first portion of N,N-dimethylcyclohexylamine added is 60% to 70% of the total mass of N,N-dimethylcyclohexylamine; the mixture is stirred at a high speed of 1200 rpm for 10 to 15 minutes;

[0057] Step S2, determining a delay time according to the dynamic viscosity value of the premixed first component;

[0058] Specifically, the delay time is negatively correlated with the dynamic viscosity value.

[0059] In a specific embodiment, the dynamic viscosity of the premixed first component is measured by a rotational viscometer at a constant temperature of 25° C., which is recorded as η in Pascal seconds (Pa·s). The calculation formula for the delay time is specifically:

[0060] ,

[0061] Where t is the delay time, in seconds (s); f is the delay coefficient, in Pa·s 2 , the value range is 1000Pa·s 2 ~1500Pa·s 2 , preferably, f is 1500Pa·s 2 .

[0062] It is understandable that the dynamic viscosity η directly affects the molecular diffusion rate and reaction activity of the premixed components. A high η value indicates poor system fluidity and a reduced frequency of molecular collisions, leading to a delayed reaction start-up. Adding the remaining catalyst at a fixed time can easily cause uneven foaming or insufficient open porosity, while a low η value indicates that the reaction is too fast, which may cause premature gelation and sacrifice mechanical strength. The compensation effect of viscosity on reaction delay is quantified by the delay coefficient f. The f value is calibrated based on several historical experiments and can better balance the reaction start-up speed (avoiding too fast gelation at high temperatures) and process stability (ensuring uniform cell growth).

[0063] The present invention optimizes the foaming reaction kinetics and microstructure formation by precisely controlling the timing of adding the amine catalyst.

[0064] Step S3, adding the remaining amine catalyst based on the delay time to obtain a second component, and recording the time of adding the remaining amine catalyst as the start time;

[0065] In a specific embodiment, the remaining N,N-dimethylcyclohexylamine is added to the mixed system, and this moment is recorded as the starting time; the stirring is maintained at 800 rpm until the third component is injected, thereby completing the preparation of the second component.

[0066] As you can understand, polyurethane foaming systems typically utilize a two-component reaction: a polyol (material A) and a polyisocyanate (material B) react in the presence of a catalyst to form urethane and urea bonds. The foaming reaction is the reaction between water and isocyanate to produce carbon dioxide gas, while the gelation reaction is the cross-linking reaction between the polyol and isocyanate. A balance between these two reactions is crucial to achieving an ideal foam structure. Premature foaming can lead to foam collapse or coarse cells, while slow gelation can result in an uneven surface or insufficient strength. In the staged catalyst addition process, the initial addition of 60% to 70% by weight of an amine catalyst is intended to initiate the basic foaming reaction. This minimum amount ensures sufficient initiation of the polyol-isocyanate reaction, while the upper limit prevents premature gelation, which could lead to a closed-cell structure. The remaining 30% to 40% of the catalyst is added at the initial stage to create an inflection point for the reaction acceleration. This staged addition mechanism regulates the foaming / gelation rate ratio, causing the cell walls to expand and thin mid-foaming before rupturing directionally, ultimately achieving a three-dimensional, interconnected structure with a high open porosity.

[0067] Step S4, mixing isocyanate as the third component with the second component at a preset volume ratio under high pressure to obtain a mixed system;

[0068] Among them, the preset ratio is third component: second component = 1:1.2 to 1:1.5.

[0069] In a specific embodiment, the second component is maintained at a constant temperature of 40±2°C and transported to a high-pressure mixing head through a gear pump; modified MDI is preheated to 45±1°C as the third component and synchronously injected into the mixing chamber through a plunger pump; the volume ratio of the two components is controlled to be 1:1.2 to 1:1.5, and the two components are mixed in a static mixer at a mixing pressure of 10MPa to 12MPa, and the outlet material temperature is controlled to be ≤48°C, and then injected into a mold to obtain a mixed system.

[0070] Step S5, injecting the mixed system into a mold and adjusting the foaming temperature according to the motor operating parameters and the amount of metal catalyst added to perform gradient foaming molding to obtain a foamed body with a gradient structure in which the inner layer density is higher than the outer layer density;

[0071] For more details, please refer to Figure 2 and Figure 3As shown in FIG. 1 , they are respectively a flow chart of step S5 of the polyurethane foam material for motor noise reduction and the preparation method thereof according to an embodiment of the present invention and a logic judgment diagram of step S5 of the preparation method of the polyurethane foam material for motor noise reduction according to an embodiment of the present invention, wherein step S5 includes:

[0072] Step S51, obtaining motor operating parameters, and determining the thickness of the acoustic resistance layer of the foam material based on the motor operating parameters, wherein the motor operating parameters include an average vibration frequency and an average noise decibel;

[0073] In a specific embodiment, the average vibration frequency f (unit: Hz) and the average noise decibel value L (unit: dB) of the target motor are collected by a motor test bench. The calculation formula of the thickness of the acoustic resistance layer is specifically:

[0074] ,

[0075] Wherein, d1 is the thickness of the acoustic resistance layer, in millimeters (mm); f r is the reference vibration frequency, in Hertz (Hz), preferably, f r Take 100Hz; L r is the reference noise value, in decibels (dB), preferably, L r Take 70dB; k1 is the frequency influence coefficient, the value range is -0.3 to -0.2mm / Hz, preferably, k1 is -0.25mm / Hz; k2 is the noise influence coefficient, the value range is 0.8 to 1mm / dB, preferably, k2 is 0.8mm / dB.

[0076] Understandably, based on the principles of acoustic impedance matching and vibration energy transfer, the thickness of the acoustic resistance layer must be determined based on both the mechanical vibration attenuation requirements and the sound wave absorption efficiency. As the motor's vibration frequency increases, the relaxation time of the polymer chain segments deteriorates in alignment with the vibration period. This necessitates increasing the thickness of the damping layer to extend the vibration wave propagation path and fully dissipate mechanical energy through multi-stage friction within the molecular chains. In other words, while maintaining the overall thickness of the material, the thickness of the impedance layer must be reduced accordingly. As the noise decibel level increases, the energy density of the sound wave increases, requiring an increase in the physical thickness of the acoustic resistance layer to allow the sound wave to undergo longer, multiple reflections and mode conversions within the material, converting the sound energy into heat. The vibration damping mechanism of polyurethane foam material essentially converts mechanical vibration energy into frictional heat within the molecular chains, and its efficiency depends on the matching of the material's loss factor with the vibration frequency. Under high-frequency vibration, the motion of the molecular chains lags behind the stress changes. Increasing the thickness of the material prolongs the vibration wave propagation path within the material, allowing more mechanical energy to be converted into heat through the viscoelastic hysteresis effect. Regarding acoustic performance, according to the law of mass action, the surface density of a material is positively correlated with its sound insulation.

[0077] The present invention optimizes the thickness of the acoustic resistance layer and the shock absorption layer for specific motor models through collaborative analysis of vibration and noise parameters, thereby ensuring effective attenuation of high-frequency vibrations while meeting the absorption requirements of broadband noise, avoiding insufficient vibration reduction caused by an overly thick acoustic resistance layer or insufficient noise reduction caused by an overly thin acoustic resistance layer.

[0078] Step S52, determining the foaming temperature of the acoustic resistance layer according to the amount of the metal catalyst added and the thickness of the acoustic resistance layer;

[0079] In a specific embodiment, the foaming temperature of the acoustic resistance layer is determined according to the actual addition amount of the metal catalyst m (unit: parts) and the thickness of the shock-absorbing layer d (unit: mm). The calculation formula of the foaming temperature of the acoustic resistance layer is specifically:

[0080] ,

[0081] Among them, T g T is the foaming temperature of the acoustic resistance layer, in degrees Celsius (℃); b is the reference foaming temperature, in degrees Celsius (°C), ranging from 70°C to 80°C. Preferably, T b Take 70℃; mr is the catalyst standard addition amount, preferably, m r Take 0.3 parts; a is the thickness influence index, the unit is ℃ / mm, the value range is 0.2~0.3, preferably, a is 0.3℃ / mm.

[0082] It is understood that the optimal temperature conditions for the formation of the acoustic resistance layer are determined by evaluating the system's reactivity based on the amount of metal catalyst added, combined with the structural characteristics required to characterize the thickness of the acoustic resistance layer. As a gel reaction accelerator, increasing the amount of metal catalyst added significantly increases the system's cross-linking reaction rate. In this case, the foaming temperature should be appropriately lowered to slow the reaction process and prevent premature solidification of the bubble walls, which would affect the formation of an open-pore structure. Conversely, when the catalyst addition is reduced, the temperature should be increased to compensate for insufficient reactivity. Furthermore, increasing the thickness of the acoustic resistance layer leads to an enhanced heat accumulation effect and a wider internal temperature gradient. In this case, the set temperature should be lowered to prevent overheating and solidification of the surface layer. Thinner acoustic resistance layers dissipate heat more quickly, requiring higher temperatures to maintain sufficient reactivity. By establishing a dynamic equilibrium model of catalyst concentration, thickness, and temperature, the foaming process is carried out within the optimal temperature window, ensuring the formation of an ideal open-pore structure and high-density properties in the acoustic resistance layer.

[0083] The present invention effectively solves the contradiction between high open porosity and structural stability, ensuring that the acoustic resistance layer forms a uniform open cell network and 80kg / m 3 ~100kg / m 3 high-density structure.

[0084] Step S53, monitoring the expansion rate change of the mixed system in real time, and determining the temperature adjustment amount according to the expansion rate change;

[0085] Specifically, the temperature adjustment amount is positively correlated with the expansion rate change amount.

[0086] In a specific embodiment, a laser displacement sensor is used to collect expansion height data of the mixed system in real time, and the expansion height increment Δh per unit time Δt is calculated to obtain the expansion rate v = Δh / Δt (unit: mm / s). Based on the expansion rate change Δv (i.e., the difference in v within adjacent Δt periods), the temperature adjustment amount ΔT is determined. The calculation formula for the temperature adjustment amount ΔT is specifically:

[0087] ,

[0088] Where ΔT is the temperature adjustment in degrees Celsius (°C), with negative values ​​indicating a temperature drop. s is the conversion coefficient in °C·s / mm, ranging from 8 to 12, preferably 10. Δv is the rate of change in expansion rate in mm / s. The conversion coefficient s is calibrated using the PU-2000 foaming instrument.

[0089] It's understandable that the change in expansion rate directly reflects the intensity of the foaming reaction. Accelerated expansion indicates that the gas generation rate exceeds the cell wall's load-bearing capacity, necessitating timely cooling to suppress the foaming reaction and transition the system from the high-density acoustic resistance layer to the low-density damping layer. This temperature regulation mechanism, by altering the molecular chain's kinematic activity, regulates the balance between cell growth and solidification, ensuring a closed-cell to open-cell transition in the acoustic resistance layer while leaving ample room for the damping layer to expand.

[0090] Step S54, when the foaming time meets the foaming time of the acoustic resistance layer, adjusting the mold temperature according to the temperature adjustment amount;

[0091] Specifically, the foaming time of the acoustic resistance layer is inversely proportional to the added amount of the metal catalyst.

[0092] In a specific embodiment, the acoustic resistance layer foaming time t c (unit: h) is determined by the amount of metal catalyst added m (unit: part), and the foaming time of the acoustic resistance layer t c The calculation formula is as follows:

[0093] ,

[0094] Where r is the catalyst activity constant, in parts·h, with a value range of 3 to 5, preferably, r is 4 parts·h; β is the time offset, in hours (h), with a value range of 3 to 5, preferably, β is 4h; m is the actual amount of metal catalyst added, in parts. When the foaming time measured from the starting time reaches t c When the temperature is adjusted, the ΔT calculated in step S53 is immediately executed to realize the conversion from generating the acoustic resistance layer to generating the shock absorbing layer.

[0095] It is understandable that the concentration of the metal catalyst determines the gel reaction rate, and its inverse relationship with the conversion time ensures that the interlayer conversion is started at the optimal time when the acoustic resistance layer structure is stable. Premature conversion leads to insufficient density of the acoustic resistance layer, while too late conversion results in limited expansion space of the shock-absorbing layer. By precisely matching the catalyst activity with the timing, the temperature is lowered when the pore wall of the acoustic resistance layer completes the initial cross-linking but is not fully solidified, so that the shock-absorbing layer forms a large-sized open-pore structure under low reaction activity, and finally constructs 80kg / m 3 ~100kg / m 3 Sound resistance layer and 30kg / m 3 ~50kg / m 3 Gradient density system of shock-absorbing layer.

[0096] Step S55 , when the total thickness of the mixed system meets the target thickness of the polyurethane foam material, the foaming is stopped to obtain the foamed body.

[0097] In a specific embodiment, when the total thickness of the mixed system meets the target thickness of the polyurethane foam material, the mixed system is determined to have completed foaming, the mold temperature is maintained for 10 seconds to allow the foam to set, and the foaming is stopped to obtain the foam;

[0098] Step S6, hot pressing the surface of the foam to form a surface dense layer to obtain a hot pressed foam;

[0099] For more details, please refer to Figure 4 As shown, it is a flow chart of step S6 of the polyurethane foam material for motor noise reduction and the preparation method thereof according to an embodiment of the present invention, wherein step S6 includes:

[0100] Step S61, hot pressing the surface of the foam body with a first pressure, wherein the first pressure is determined according to the remaining volume of the mold cavity and the thickness of the shock-absorbing layer;

[0101] Specifically, in step S61 , the thickness of the shock-absorbing layer is determined according to the target thickness of the polyurethane foam material and the thickness of the acoustic resistance layer.

[0102] In a specific embodiment, according to the residual volume V of the mold cavity rThe first pressure P1 is calculated based on the thickness of the shock-absorbing layer d2 (unit: cm³) and the thickness of the shock-absorbing layer d2 (unit: mm). The calculation formula of the first pressure P1 is specifically as follows:

[0103] ,

[0104] Among them, k v k is the volume compensation coefficient, the unit is MPa·cm³, the value range is 0.05~0.08, and the preferred value is 0.065; d is the thickness compensation coefficient, the unit is MPa / mm, the value range is 0.02~0.03, and the preferred value is 0.025;

[0105] d2=D t −d1, D t is the target thickness of the polyurethane foam material, and d1 is the thickness of the acoustic resistance layer.

[0106] Place the foam on a hot press, set the hot press plate temperature to 150°C ± 5°C, and apply pressure at P1 for 10 to 15 seconds.

[0107] It's understandable that the residual volume of the mold cavity reflects the density of the foam's internal structure. A smaller volume indicates a denser cell network, requiring lower pressure to avoid over-compression and damage to the skeleton structure. The thickness of the shock-absorbing layer represents the compressible space in the material; increasing thickness requires higher pressure to drive the rearrangement of the surface molecular chains. This pressure-setting mechanism, by matching the material's internal stress state with the external load, promotes oriented crystallization of the surface polyurethane molecules under thermal activation conditions, forming an initial dense layer without damaging the internal gradient structure.

[0108] Step S62, obtaining the thickness and density of the dense layer of the foam surface after step S61 to determine the second pressure, and performing secondary hot pressing on the foam surface with the second pressure to obtain the hot-pressed foam.

[0109] In a specific embodiment, the thickness d3 (unit: mm) and density ρ of the dense layer after the first hot pressing are measured. c (Unit: kg / m³), calculate the second pressure P2, the calculation formula of the second pressure P2 is specifically:

[0110]

[0111] Among them, P r is the basic second pressure, in MPa, with a value range of 1 to 1.2. Preferably, P r Take 1Mpa; ρ r is the target density in kg / m 3 , the value range is 200~220; i is the density response coefficient, the unit is MPa·m 3 / kg, the value range is 0.005~0.008, and the preferred value is 0.0065MPa·m 3 / kg.

[0112] At 160℃±3℃, apply pressure twice at P2 pressure for 15s to 20s.

[0113] It is understandable that the state of the dense layer formed by the first hot pressing is the core basis for setting the secondary pressure. If the thickness of the dense layer is too small, it indicates that the molecular chain orientation is insufficient, and the pressure needs to be increased to drive the deep molecules to migrate to the surface; if the density is too low, it reflects that the crystallinity is insufficient, and the pressure needs to be increased to promote the close stacking of the molecular chains; the generation of the density response coefficient i is derived from the structural state feedback of the material after the first hot pressing. When the actual density of the dense layer is detected to be lower than the target value, it indicates that the molecular chain orientation is insufficient or the filler is unevenly dispersed. At this time, the pressure compensation strength required for the unit density deviation needs to be calibrated experimentally. The density response coefficient i is essentially a comprehensive characterization of the molecular chain segment rearrangement energy barrier and filler migration resistance of the polyurethane system in a thermodynamically non-equilibrium state. It is calibrated by systematically testing the density change gradient under different pressure-temperature combinations and establishing a linear response relationship between the pressure increment and the density correction value. This will not be repeated here.

[0114] The present invention uses a staged pressure loading mechanism and the viscoelastic relaxation characteristics of the polyurethane material. After the basic orientation structure is established by the first hot pressing, the entanglement density of the surface molecular chain is strengthened by the secondary pressure to form a 0.2mm to 0.4mm thick and 220kg / m 3 A continuous dense layer of ~250kg / m³ achieves dual optimization of oil and dirt barrier and acoustic impedance.

[0115] Step S7: cutting the hot-pressed foam after curing to obtain a finished motor wrapping part.

[0116] In a specific embodiment, the hot-pressed foam is moved to a constant temperature and humidity curing room and left to stand for 24 hours at an ambient temperature of 23°C ± 2°C and a relative humidity of 50% ± 5% to complete curing; a CNC cutting machine is used to program according to the three-dimensional drawing of the motor housing; the cured foam is fixed on a cutting platform, and a special-shaped contour is cut along a preset path to obtain a finished motor package. It can be understood by those skilled in the art that the above implementation is a prior art and will not be repeated here.

[0117] Example 1

[0118] The formula of polyurethane foam material is:

[0119] The second component: polyol mixture (polyether polyol: polyester polyol = 7:3, hydroxyl value 150mgKOH / g) 10kg, deionized water 0.1kg, N,N-dimethylcyclohexylamine 0.05kg (70% added for the first time, i.e. 0.035kg), dibutyltin dilaurate 0.01kg, SP30 nano-silica 0.2kg, expanded graphite (300 mesh, 100ml / g) 0.5kg, UV-328 anti-aging agent 0.05kg;

[0120] The volume ratio of the third component: modified MDI (NCO content 28%) to the above-mentioned second component is 1:1.5.

[0121] The target thickness of the polyurethane foam material is 12 mm.

[0122] The preparation process is as follows: the polyol mixture is stirred at 25° C. for 10 minutes, deionized water, N,N-dimethylcyclohexylamine, dibutyltin dilaurate, nano-silica, expanded graphite, and UV-328 are added, and stirred at 1200 rpm for 10 minutes to prepare a premixed first component.

[0123] The measured dynamic viscosity η = 12 Pa·s, and the calculated delay time t = 125s.

[0124] After a delay of 125 seconds, the remaining 0.015 kg of N,N-dimethylcyclohexylamine catalyst was added, and the mixture was slowly stirred at 800 rpm to prepare the second component.

[0125] The second component is maintained at a constant temperature of 40±2°C and transported to a high-pressure mixing head via a gear pump; the modified MDI as the third component is preheated to 45±1°C and synchronously injected into the mixing chamber via a plunger pump; the volume ratio of the two components is controlled to be 1:1.2 to 1:1.5, and the two components are mixed in a static mixer at a mixing pressure of 10MPa to 12MPa. The outlet material temperature is controlled to be ≤48°C and injected into the mold for gradient foaming;

[0126] The thickness of the acoustic resistance layer is d1 = 6.35 mm (f = 122 Hz, L = 78 dB);

[0127] Acoustic resistance layer foaming temperature T g =71.9℃;

[0128] When the expansion rate changes Δv=0.8mm / s, ΔT=-8℃;

[0129] Acoustic resistance layer foaming time t c =17.3h, when the anti-foaming time meets the foaming time of the acoustic resistance layer, the temperature is lowered by 8°C and foaming is continued. When the total thickness of the mixed system meets the target thickness of the polyurethane foam material, the mixed system is determined to have completed foaming. The mold temperature is maintained for 10 seconds to allow the foam to set, and then foaming is stopped to obtain the foam.

[0130] Hot pressing the surface of the foam body at a first pressure, wherein the first pressure P1=0.12 MPa;

[0131] Obtain the thickness and density of the dense layer on the surface of the foam to determine the second pressure, and perform secondary hot pressing on the surface of the foam at the second pressure, where the second pressure P2 = 1.03 MPa;

[0132] Curing and cutting: Curing at 23℃ / 50%RH for 24 hours, CNC cutting and shaping to obtain the finished motor package.

[0133] Example 2

[0134] The formula composition of the polyurethane foam material is adjusted to:

[0135] The second component: polyol mixture (polyether polyol: polyester polyol = 7:3, hydroxyl value 150mgKOH / g) 10kg, deionized water 0.3kg, N,N-dimethylcyclohexylamine 0.2kg (70% added for the first time, i.e. 0.14kg), dibutyltin dilaurate 0.05kg, SP30 nano-silica 0.5kg, expanded graphite (300 mesh, 100ml / g) 1kg, UV-328 anti-aging agent 0.1kg;

[0136] The volume ratio of the third component: modified MDI (NCO content 28%) to the above-mentioned second component is 1:1.2, and the rest is the same as Example 1.

[0137] Example 3

[0138] The volume ratio of the modified MDI to the second component was adjusted to 1:1, and the rest was the same as in Example 1.

[0139] Example 4

[0140] The ratio of polyether polyol to polyester polyol was adjusted to 6:4, and the rest was the same as in Example 1.

[0141] Example 5

[0142] The amount of N,N-dimethylcyclohexylamine was adjusted to 0.02 kg, and the rest was the same as in Example 1.

[0143] Example 6

[0144] The calculation of the acoustic resistance layer foaming temperature in step S52 is omitted, and the acoustic resistance layer foaming temperature is fixed at 70° C. The rest is the same as in Example 1.

[0145] Example 7

[0146] The first pressure hot pressing in step S61 is omitted, and hot pressing is directly performed at a fixed pressure of 1 MPa. The rest is the same as in Example 1.

[0147] Example 8

[0148] The stepwise addition of the amine catalyst in steps S1 to S3 is omitted, and all the amine catalyst is directly added in step S1 to obtain the second component. The rest is the same as in Example 1.

[0149] Example 9

[0150] The volume ratio of the modified MDI to the second component was adjusted to 1:1.4, and the rest was the same as in Example 1.

[0151] Example 10

[0152] The volume ratio of the modified MDI to the second component was adjusted to 1:1.3, and the rest was the same as in Example 1.

[0153] Example 11

[0154] The amount of N,N-dimethylcyclohexylamine was adjusted to 0.1 kg, and the rest was the same as in Example 1.

[0155] Example 12

[0156] The amount of N,N-dimethylcyclohexylamine was adjusted to 0.15 kg, and the rest was the same as in Example 1.

[0157] The motor packaging products of Examples 1 to 12 were subjected to performance tests according to the following standard methods:

[0158] Noise reduction performance is measured in an anechoic chamber at 2000 Hz using a B&K 4206 impedance tube system in accordance with GB / T 18696.2-2002, “Measurement of Sound Absorption Coefficient by Impedance Tube Method.”

[0159] The vibration damping performance is tested by simulating the motor's operating vibration (122Hz / 78dB) on an electromagnetic vibration table and measuring the material's vibration attenuation rate. The equipment used is an LDS V900 vibration table and a PCB 352C03 accelerometer.

[0160] Oil pollution protection is based on GB / T 1690-2010 "Rubber liquid resistance test method": immerse the rubber in 15W-40 engine oil at 85℃ for 72 hours, measure the mass change rate and penetration depth, and the oil bath circulation flow rate is 0.5m / s.

[0161] The compression strength was tested according to GB / T 8813-2008 “Determination of compression properties of rigid foam plastics” with a 50% deformation compression strength test and a loading rate of 10 mm / min using an Instron 3365 universal testing machine.

[0162] The experimental results are shown in Tables 1 and 2.

[0163] Table 1 Experimental results of the finished motor packaging parts of Examples 1 to 8

[0164]

[0165] Table 2 Experimental results of the finished motor packaging parts of Examples 9 to 12

[0166]

[0167] Table 1 shows that the formulation ratios and process steps defined in the claims of the present invention have a decisive influence on material performance. Both Examples 1 (lower formulation limit) and 2 (upper formulation limit) meet the core sound absorption coefficient requirements, validating the claim scope. In Example 2, the increased expanded graphite content enhances the connectivity of the pore structure, further improving sound absorption performance. Examples 3-5, which exceed the formulation limits, experience significant performance degradation: Example 3 suffers from an incomplete crosslinking network due to an imbalanced volume ratio, significantly reducing the sound absorption coefficient. Example 4 suffers from a significant decrease in vibration attenuation due to a shift in the polyol ratio, disrupting the gradient pore structure. Example 5 suffers from an insufficient catalyst, resulting in an incomplete reaction and increased oil penetration. Examples 6-8, which omit process steps, also experience systematic attenuation. In Example 6, the fixed foaming temperature weakens the acoustic resistance layer and reduces sound absorption performance. In Example 7, the omission of the primary hot pressing results in the loss of the dense surface layer, significantly reducing oil protection. In Example 8, the one-time addition of catalyst disrupts the gradient foaming process, resulting in a comprehensive deterioration in all performance characteristics.

[0168] As can be seen from Table 2, component optimization based on the lower limit of the formula can further improve material performance. Examples 9 to 12 all meet the core indicators of the sound absorption coefficient, proving that it is feasible to adjust the component ratio within the scope of the claims. Volume ratio optimization (Examples 9 to 10) significantly improves the vibration attenuation efficiency by improving the uniformity of isocyanate distribution; the catalyst increment (Examples 11 to 12) enhances the stability of the cross-linked network and improves the oil pollution protection performance. It is worth noting that Example 10 achieves simultaneous optimization of sound absorption performance, mechanical strength and protective effectiveness under specific volume ratio conditions. This ratio forms a more complete gradient structure inside the material by precisely controlling the matching relationship between the molecular chain assembly dynamics and the pore development rate.

[0169] In summary, the present invention comprises an indivisible technical system comprised of step-by-step catalytic timing control, expansion rate feedback temperature control, and two-stage pressure dynamic adaptation. By precisely regulating the self-assembly behavior of molecular chains, this system enables the polyurethane foam material to simultaneously achieve the triple functions of broadband noise absorption, mechanical vibration damping, and dielectric penetration resistance under high-temperature, oil-contaminated, and vibrating motor conditions. This provides a lightweight and long-life solution for high-end motor packaging.

[0170] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a polyurethane foam material for motor noise reduction, characterized in that: include: Step S1, mixing part of the amine catalyst with a polyol mixture, a foaming agent, a metal catalyst, a surfactant, expanded graphite, and an anti-aging agent to obtain a premixed first component; Step S2, determining a delay time according to the dynamic viscosity value of the premixed first component; Step S3, adding the remaining amine catalyst based on the delay time to obtain a second component, and recording the time of adding the remaining amine catalyst as the start time; Step S4, mixing isocyanate as the third component with the second component at a preset volume ratio under high pressure to obtain a mixed system; Step S5, injecting the mixed system into a mold and adjusting the foaming temperature according to the motor operating parameters and the amount of metal catalyst added to perform gradient foaming molding to obtain a foamed body with a gradient structure in which the inner layer density is higher than the outer layer density; Step S6, hot pressing the surface of the foam to form a surface dense layer to obtain a hot pressed foam; Step S7, cutting the hot-pressed foam after curing to obtain a finished motor wrapping component; Among them, the preset ratio is third component: second component = 1:1.2 to 1:1.

5.

2. The method for preparing a polyurethane foam material for motor noise reduction according to claim 1, characterized in that: The step S5 comprises: Step S51, obtaining motor operating parameters, and determining the thickness of the acoustic resistance layer of the foam material based on the motor operating parameters, wherein the motor operating parameters include an average vibration frequency and an average noise decibel; Step S52, determining the foaming temperature of the acoustic resistance layer according to the amount of the metal catalyst added and the thickness of the acoustic resistance layer; Step S53, monitoring the expansion rate change of the mixed system in real time, and determining the temperature adjustment amount according to the expansion rate change; Step S54, when the foaming time meets the foaming time of the acoustic resistance layer, adjusting the mold temperature according to the temperature adjustment amount; Step S55 , when the total thickness of the mixed system meets the target thickness of the polyurethane foam material, the foaming is stopped to obtain the foamed body.

3. The method for preparing a polyurethane foam material for motor noise reduction according to claim 2, characterized in that: In step S53, the expansion height increment of the mixed system per unit time is continuously recorded. The expansion rate change is determined based on a rate of change of the expansion height increment.

4. The method for preparing a polyurethane foam material for motor noise reduction according to claim 2, characterized in that: In the step S54, the foaming time of the acoustic resistance layer is determined based on the starting time.

5. The method for preparing a polyurethane foam material for motor noise reduction according to claim 2, characterized in that: The step S6 comprises: Step S61, hot pressing the surface of the foam body with a first pressure, wherein the first pressure is determined according to the remaining volume of the mold cavity and the thickness of the shock-absorbing layer; Step S62, obtaining the thickness and density of the dense layer of the foam surface after step S61 to determine the second pressure, and performing secondary hot pressing on the foam surface with the second pressure to obtain the hot-pressed foam.

6. The method for preparing a polyurethane foam material for motor noise reduction according to claim 5, characterized in that: In the step S61 , the thickness of the shock-absorbing layer is determined according to the target thickness of the polyurethane foam material and the thickness of the acoustic resistance layer.

7. The method for preparing a polyurethane foam material for motor noise reduction according to claim 1, characterized in that: The delay time is negatively correlated with the dynamic viscosity value.

8. The method for preparing a polyurethane foam material for motor noise reduction according to claim 2, characterized in that: The temperature adjustment amount is positively correlated with the expansion rate change amount.

9. The method for preparing a polyurethane foam material for motor noise reduction according to claim 2, characterized in that: The foaming time of the acoustic resistance layer is inversely proportional to the added amount of the metal catalyst.

10. A polyurethane foam material for motor noise reduction, which is manufactured using the method for preparing a polyurethane foam material for motor noise reduction according to any one of claims 1 to 9, characterized in that: The polyurethane foam material is composed of a second component and a third component, wherein the second component is composed, by weight, of 100 parts of a polyol mixture, 1 to 3 parts of a foaming agent, 0.5 to 2 parts of an amine catalyst, 0.1 to 0.5 parts of a metal catalyst, 2 to 5 parts of nano-silicon dioxide, 5 to 10 parts of expanded graphite, and 0.5 to 1 part of an anti-aging agent; and the third component is composed of isocyanate. The polyol mixture is prepared by compounding polyether polyol and polyester polyol, the hydroxyl value of which is 120 mgKOH / g to 180 mgKOH / g, and the mass ratio of polyether polyol to polyester polyol is 7:3; the isocyanate is modified MDI, and the NCO content of which is 25% to 31%; the foaming agent is deionized water; and the anti-aging agent is UV-328.

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