Composite friction material and its preparation and use in brake pads

Abstract

The application discloses a kind of composite friction material and preparation and application in brake pad, the composite friction material with phenolic resin as matrix, modified barium sulfate and red copper fiber are dispersed in matrix;The modified barium sulfate is composed of barium sulfate particles and the coating on its surface, that is, it has core-shell structure, wherein the coating includes UiO-66 metal organic framework material.Compared with existing pure phenolic resin and only adding ordinary barium sulfate particle composite material, the composite friction material provided by the application shows significant advantages in friction coefficient, thermal stability and wear resistance by introducing modified barium sulfate, and can reduce friction noise, suitable as brake pad material application.

Description

Technical Field

[0001] This invention belongs to the technical field of composite materials and motor vehicle braking components, and specifically relates to a composite friction material, its preparation, and its application in brake pads. Background Technology

[0002] Brake pads, as a core safety component of a vehicle's braking system, directly impact driving safety. However, existing brake pad material systems often suffer from insufficient wear resistance, high braking noise, and poor thermal stability, making it difficult to meet increasingly stringent driving conditions and environmental requirements. Specifically, commonly used particulate fillers in traditional brake pads, such as calcium carbonate, are prone to decomposition at high temperatures, leading to the formation of a porous structure in the friction layer and causing braking vibration. Meanwhile, natural barite, due to its impurities, has weak interfacial bonding with the resin matrix, exacerbating wear and generating high-frequency noise.

[0003] To address these issues, the industry has attempted to improve performance through composite filler systems, such as ternary reinforcement schemes like copper fiber / graphite / alumina. While these can increase the coefficient of friction, they significantly increase costs and complicate the process. Furthermore, modification with wollastonite or mica, although improving thermal stability, may sacrifice material density, affecting braking response sensitivity. Therefore, developing a novel material system that can significantly improve the overall performance of brake pads while maintaining controllable costs has become an urgent need.

[0004] In recent years, barium sulfate has shown great potential in the fields of high-end engineering plastics and sound insulation coatings due to its controllable high purity (≥99.5%) and excellent physicochemical properties. Its unique crystal structure and high-temperature stability (decomposition temperature far exceeding the working temperature range of brake pads) make it an ideal candidate for functional fillers in brake pads. However, due to the use of ultra-fine particle size and high purity, barium sulfate powder is prone to agglomeration, making it difficult to distribute directionally in the resin matrix, especially when the addition amount is >4%. Therefore, the amount of barium sulfate powder added is strictly controlled, which limits the friction performance, toughness, and other mechanical properties of friction pads when high-purity barium sulfate is used directly. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a composite friction material, its preparation, and its application in brake pads. This invention addresses the limitations in improving the friction performance and toughness of brake pad materials due to the direct use of high-purity barium sulfate caused by agglomeration and other factors in the prior art. Furthermore, it solves problems such as low thermal stability and high noise levels. By optimizing the filler composition, the invention improves the friction performance, thermal stability, wear resistance, and physical hardness of brake pads, while simultaneously reducing noise and lowering costs, thus meeting the demands of the modern automotive industry for high-performance brake pads.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a composite friction material, wherein the composite friction material uses phenolic resin as a matrix, and modified barium sulfate and copper fibers are dispersed in the matrix; the modified barium sulfate is composed of barium sulfate particles and a coating layer on its surface, that is, it has a core-shell structure, wherein the coating layer includes UiO-66 metal-organic framework material.

[0007] In one embodiment, the coating layer further includes a structure-directing agent, which in this invention may be selected as polyethylene glycol (PEG), and phenolic resin typically 2123. UiO-66 metal-organic framework material and PEG are co-coated onto the surface of barium sulfate particles to form modified barium sulfate with a core-shell structure. The amount of polyethylene glycol (PEG) used is generally about 1:1 or 1:0.8 of the mass of ZrCl4, the raw material for Uio-66 synthesis.

[0008] In one embodiment, the coating layer further includes graphene oxide (GO). UiO-66 metal-organic framework material is co-coated with GO, or with PEG and GO, onto the surface of barium sulfate particles to form modified barium sulfate with a core-shell structure. The amount of graphene oxide (GO) used is typically about 1% of the mass of ZrCl4, the raw material for Uio-66 synthesis.

[0009] In one embodiment, the ratio of the matrix, modified barium sulfate, and copper fiber by weight is (0.7-0.8):(0.15-0.25):(0.04-0.05). More preferably, it is 0.75:0.20:0.05.

[0010] Secondly, the present invention provides a method for preparing the composite friction material described in the first aspect, which is prepared by chemical modification and mainly includes the following steps: Step 1: Using zirconium tetrachloride (ZrCl4), terephthalic acid (H2BDC) and barium sulfate particles as raw materials, a solvothermal method is used to react at 110℃-130℃ for 12-36 hours to generate UiO-66 metal-organic framework material on the surface of barium sulfate particles, thus obtaining modified barium sulfate with a core-shell structure. Step 2: Mix the modified barium sulfate, copper fiber and phenolic resin powder evenly, put them into a mold sprayed with silicone release agent, press and demold to obtain the composite friction material.

[0011] In one embodiment, the barium sulfate particles are prepared by the following method: Barite is reduced and calcined with coal powder to produce barium sulfide. The barium sulfide is then leached with water and filtered to obtain a barium sulfide solution. This solution is reacted with sodium sulfate solution to produce barium sulfate precipitate. The precipitate is purified, dried, and pulverized to obtain barium sulfate particles with a content ≥99.5%. These particles meet the following requirements: volatile matter ≤0.13% at 105℃, water-soluble matter ≤0.20%, pH 8-10 (preferably 9.13), fineness ≤0.05%, whiteness ≥97.0%, oil absorption 13-18% (typically 14.2%), Fe content ≤0.10%, and particle size range 0.75-0.85 micrometers (approximately 0.83 micrometers).

[0012] In one embodiment, in step 1, when preparing modified barium sulfate, UiO-66 is synthesized in situ, and the ratio of zirconium tetrachloride, terephthalic acid and barium sulfate particles by weight is 1:1:(10-16), more preferably 1:1:16.

[0013] In one embodiment, the solvothermal method further involves adding polyethylene glycol (PEG) and / or graphene oxide (GO) to the solvent for reaction, wherein the molar ratio of zirconium tetrachloride, PEG, and graphene oxide is 100:(100-80):1. PEG acts as a structure-directing agent, promoting the uniform growth of Uio-66 on the surface of barium sulfate particles and forming a smaller-sized coating layer. The introduction of GO enhances the interfacial bonding between the coating layer and the barium sulfate particles.

[0014] In one embodiment, step 2, pressing, employs a hot pressing process, including: Initial pressure stage: Maintain pressure at 3-5 MPa for 5-10 minutes to expel gas voids, then simultaneously heat to 150-160℃ at 7-10 MPa, preferably at a heating rate of 3℃ / min, and maintain pressure for 60-120 minutes. Preferably, at 160℃... o Hot-pressed at C for 90 minutes, the composite friction material is obtained after demolding.

[0015] Thirdly, the present invention provides typical applications of the composite friction material described in the first aspect, which can be used to prepare brake pads, especially automotive brake pads. It can be prepared using only the composite friction material, or with the addition of other auxiliary components known in the art.

[0016] Compared with existing pure phenolic resins and composite materials with only ordinary barium sulfate particles, the composite friction material provided by this invention, by introducing modified barium sulfate and coating the surface of barium sulfate particles with UiO-66 metal-organic framework material, improves dispersion uniformity, surface smoothness and interfacial bonding, and achieves its directional distribution and interfacial strengthening in thermosetting resin. It shows significant advantages in terms of friction coefficient, thermal stability and wear resistance, and can reduce friction noise, making it suitable for use as a brake pad material.

[0017] Especially in terms of thermal stability, the introduction of PEG promotes the smaller size of Uio-66 encapsulation on barium sulfate particles, effectively increasing the initial thermal decomposition temperature of the material, thereby extending the service life of brake pads and improving driving safety. Attached Figure Description

[0018] Figure 1 These are SEM cross-sectional images of the composite friction material of Comparative Example 1 of this invention, with the upper image showing a scale of 20 μm and the lower image showing a scale of 5 μm.

[0019] Figure 2 These are EDS mapping images of the composite friction material of Comparative Example 1 of the present invention, where (a) is a SEM cross-sectional image of the composite friction material of Comparative Example 1, (b) is the corresponding C element distribution, (c) is the corresponding O element distribution, and (d) is the corresponding Ba element distribution.

[0020] Figure 3 This is a SEM cross-sectional image of the friction material in Comparative Example 2 of this invention.

[0021] Figure 4 This is a SEM image of the Uio-66 / BaSO4 / PEG / GO filler particles in Example 1 of this invention.

[0022] Figure 5 This is a SEM image of the Uio-66 / BaSO4 / GO filler particles in Example 2 of the present invention.

[0023] Figure 6 This is a SEM image of the Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction material in Example 1 of this invention.

[0024] Figure 7 This is a SEM image of the Uio-66 / BaSO4 / GO / phenolic resin composite friction material in Example 2 of the present invention.

[0025] Figure 8 This is a SEM cross-sectional image of the Uio-66 / BaSO4 / phenolic resin friction material in Example 3 of the present invention.

[0026] Figure 9This is a comparison of infrared spectra of Uio-66 / BaSO4 / PEG / GO filler particles, Uio-66 / BaSO4 / GO filler particles, barium sulfate particles, and Uio-66 particles according to embodiments of the present invention.

[0027] Figure 10 This is the thermogravimetric curve of the friction material in Comparative Example 2 of this invention.

[0028] Figure 11 This is the thermogravimetric curve of the composite friction material of Comparative Example 1 of the present invention.

[0029] Figure 12 This is the thermogravimetric curve of the composite friction material in Embodiment 1 of the present invention.

[0030] Figure 13 This is the thermogravimetric curve of the composite friction material in Embodiment 2 of the present invention.

[0031] Figure 14 This is the thermogravimetric curve of the composite friction material in Example 3 of the present invention.

[0032] Figure 15 This refers to the coefficient of friction of the Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction material of Example 1 of the present invention at different temperatures.

[0033] Figure 16 This refers to the coefficient of friction of the Uio-66 / BaSO4 / GO / phenolic resin composite friction material in Example 2 of the present invention at different temperatures.

[0034] Figure 17 This refers to the coefficient of friction of the Uio-66 / BaSO4 / phenolic resin composite friction material in Example 3 of the present invention at different temperatures.

[0035] Figure 18 Comparative Example 1 of this invention: the coefficient of friction of BaSO4 / phenolic resin composite friction material at different temperatures.

[0036] Figure 19 Comparative Example 2 of this invention shows the coefficient of friction of pure phenolic resin friction material at different temperatures. Detailed Implementation

[0037] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0038] Example 1 In this embodiment, the composite friction material is a Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction material, and its preparation method mainly includes the following steps: 1) Preparation of high-purity barium sulfate.

[0039] Barite (BaSO4) is reduced and calcined with pulverized coal to produce barium sulfide (BaS). The BaS is then leached with water, and the resulting solution is filtered. The BaS solution reacts with sodium sulfate solution to form BaSO4 precipitate. This precipitate is then purified by acid washing, water washing, centrifugal filtration, and other steps to remove impurities. Finally, it is dried and pulverized to obtain a functional filler with a precipitated barium sulfate content ≥99.5% (XRF detection). It meets the following requirements: volatile matter (105℃) ≤0.13%, water-soluble matter content ≤0.20%, pH value 8-10 (9.13 in this example), fineness ≤0.05%, whiteness ≥97.0%, oil absorption 13-18% (14.2% in this example), Fe content ≤0.10%, and particle size range 0.75-0.85 micrometers (0.83 micrometers in this example).

[0040] 2) Preparation of Uio-66 / BaSO4 / PEG / GO metal-organic framework modified barium sulfate High-purity barium sulfate (≥99.5%) was selected as the basic functional filler, and zirconium tetrachloride (ZrCl4) and terephthalic acid (H2BDC) were used as raw materials. Polyethylene glycol (PEG) and graphene oxide (GO) were also introduced, and the mixture was reacted with high-purity barium sulfate in DMF solvent for 120 minutes. o A reaction at C for 24 hours resulted in the reaction of zirconium tetrachloride and terephthalic acid on the surface of barium sulfate to generate Uio-66 metal-organic framework material. During this process, PEG, acting as a structure-directing agent, promoted the uniform growth of Uio-66 on the surface of barium sulfate particles, forming a smaller encapsulation layer. Simultaneously, the introduction of GO enhanced the interfacial bonding between the encapsulation layer and the barium sulfate particles.

[0041] 3) Preparation of composite friction materials Modified barium sulfate filler (20% by mass) and copper fiber (5% by mass) were mixed uniformly to form a composite filler. The components were placed in a double-cone mixer and mixed at 30 rpm for 60 minutes to obtain a premix. The premix was then loaded into a mold coated with silicone release agent and pressed using a four-column hydraulic press. Initial pressing stage: 3 MPa pressure was maintained for 5 minutes to expel gas voids; then, the temperature was simultaneously raised to 160℃ at 7 MPa pressure (heating rate 3℃ / min) and maintained for 90 minutes. After cooling, the Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction material sample was demolded and removed.

[0042] To compare performance, this invention also prepared Uio-66 / BaSO4 / GO / phenolic resin composite friction materials, BaSO4 / phenolic resin composite friction materials, and pure phenolic resin materials as comparisons. The specific synthesis methods are described below.

[0043] Example 2 The composite friction material in this embodiment is a Uio-66 / BaSO4 / GO / phenolic resin composite friction material, and its preparation method mainly includes the following steps: High-purity barium sulfate (≥99.5%) was selected as the base filler, and zirconium tetrachloride (ZrCl4) and terephthalic acid (H2BDC) were used as raw materials. Graphene oxide (GO) was introduced and reacted with high-purity barium sulfate in DMF solvent for 120 minutes. o The reaction was carried out at C for 24 hours, allowing zirconium tetrachloride and terephthalic acid to react on the surface of barium sulfate to generate Uio-66 metal-organic framework material. The difference between this and the material in Example 1 is that PEG was not added during the synthesis process.

[0044] Modified barium sulfate filler (20% by mass) and copper fiber (5% by mass) were mixed uniformly to form a composite filler. The components were placed in a double-cone mixer and mixed at 30 rpm for 60 minutes to obtain a premix. The premix was then loaded into a mold coated with silicone release agent and pressed using a four-column hydraulic press. Initial pressing stage: 3 MPa pressure was maintained for 5 minutes to expel gas voids; then, the temperature was simultaneously raised to 160℃ at 7 MPa pressure (heating rate 3℃ / min) and maintained for 90 minutes. After cooling, the Uio-66 / BaSO4 / GO / phenolic resin composite friction material sample was demolded and removed.

[0045] Example 3 In this embodiment, the composite friction material is a Uio-66 / BaSO4 / phenolic resin composite friction material, and its preparation method mainly includes the following steps: High-purity barium sulfate (≥99.5%) was selected as the base filler, and zirconium tetrachloride (ZrCl4) and terephthalic acid (H2BDC) were used as raw materials. The mixture was reacted with high-purity barium sulfate in DMF solvent for 120 minutes. o The reaction was carried out at C for 24 hours, allowing zirconium tetrachloride to react with terephthalic acid on a barium sulfate surface to generate Uio-66 metal-organic framework material. The difference between this and the material in Example 1 is that PEG and GO were not added during the synthesis process.

[0046] Modified barium sulfate filler (20% by mass) and copper fiber (5% by mass) were mixed uniformly to form a composite filler. The components were placed in a double-cone mixer and mixed at 30 rpm for 60 minutes to obtain a premix. The premix was then loaded into a mold coated with silicone release agent and pressed using a four-column hydraulic press. Initial pressing stage: 3 MPa pressure was maintained for 5 minutes to expel gas voids; then, the temperature was simultaneously raised to 160℃ at 7 MPa pressure (heating rate 3℃ / min) and maintained for 90 minutes. After cooling, the Uio-66 / BaSO4 / phenolic resin composite friction material sample was demolded and removed.

[0047] Comparative Example 1 The comparative example composite friction material is a BaSO4 / phenolic resin composite friction material, and its preparation method mainly includes the following steps: Using phenolic resin 2123 as the matrix and high-purity barium sulfate (4 wt%) as the composite filler, the components were placed in a double-cone mixer and mixed at 30 rpm for 60 minutes to obtain a premix. The premix was then loaded into a mold coated with silicone release agent and processed using a four-column hydraulic press. Initial pressing stage: 3 MPa pressure was maintained for 5 minutes to expel gas voids, followed by simultaneous heating to 160℃ at 7 MPa pressure (heating rate 3℃ / min) and maintaining the pressure for 90 minutes. After cooling, the BaSO4 / phenolic resin composite friction material sample was demolded and removed.

[0048] Comparative Example 2 This comparative example uses pure phenolic resin friction material, i.e., a blank sample. Its preparation method mainly includes the following steps: Phenolic resin 2123 powder was loaded into a mold coated with silicone release agent and pressed using a four-column hydraulic press. Initial pressing stage: 3 MPa pressure was maintained for 5 minutes to expel gas voids; then, the temperature was simultaneously raised to 160℃ at 7 MPa pressure (heating rate 3℃ / min) and maintained for 90 minutes. After cooling, the pure phenolic resin friction material sample was demolded and removed.

[0049] The performance of the above-mentioned composite friction materials was verified as follows: SEM morphology and EDS analysis: The BaSO4 / phenolic resin composite friction material obtained in Comparative Example 1 was observed by scanning electron microscopy (SEM). Figure 1 and Figure 2 As shown, the barium sulfate particles in the composite friction material after the addition of barium sulfate are relatively uniformly distributed and dispersed, with no obvious interface separation. The surface structure shows no obvious defects (such as large particles, cracks, or irregularities), but some pores are present. EDS data shows that the composite friction material is mainly composed of four elements: carbon (C), oxygen (O), sulfur (S), and barium (Ba). Carbon has the highest apparent concentration, reaching 31.65%, accounting for 53.48% of the total sample mass (Wt%) and 83.49% of the atomic percentage (At%). Barium accounts for 36.71% of the total mass and 5.01% of the atomic percentage. This analysis is consistent with the sample composition being a low-content barium sulfate filler and a phenolic resin matrix.

[0050] The pure phenolic resin friction material sample (i.e., the blank sample) obtained in Comparative Example 2 was observed using a scanning electron microscope (SEM). Figure 3As shown, the resin matrix surface exhibits a uniform morphology, with no inorganic filler particles or second-phase components, exhibiting typical characteristics of a pure resin continuous phase. The material contains a relatively regularly distributed pore structure with consistent pore morphology and uniform density. There are no obvious cracks or large particle aggregations; the resin matrix microstructure is continuous and dense, with a high degree of surface smoothness, exhibiting only micron-level irregular undulations, and no interlayer separation or interface defects.

[0051] The Uio-66 / BaSO4 / PEG / GO filler particles obtained in Example 1 and the Uio-66 / BaSO4 / GO filler particles obtained in Example 2 were analyzed by scanning electron microscopy (SEM). Figure 4 and Figure 5 As shown, the results indicate that successful composite formation of Uio-66 particles was observed in both types of particles, but the introduction of PEG promoted smaller Uio-66 size and more effective encapsulation on barium sulfate particles. Furthermore, without the structure-directing agent PEG, exposed spindle-shaped, hexagonal sheet-like, and irregularly shaped barium sulfate particles were visible in many areas of the electron microscope images, with octahedral UiO-66 particles also visible locally, indicating uneven encapsulation. With only the structure-directing agent PEG, the particles obtained were noticeably finer than those without the agent, and the size of the encapsulation layer could be preliminarily estimated to be 200 nm - 1 μm. With both PEG and graphene oxide present, the situation was largely the same as with only PEG; most of the electron microscope images showed octahedral UiO-66 particles with a size of 200-300 nm, and the size of the encapsulation layer could be preliminarily estimated to be 200 nm - 1 μm, with a small amount of sheet-like graphene oxide also visible.

[0052] The Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction materials obtained in Example 1, Example 2, and Example 3 were subjected to scanning electron microscopy (SEM) tests. Figure 6 , Figure 7 and Figure 8As shown, the results indicate that the microstructures of the three composite materials exhibit significant differences: In Example 1 (Uio-66 / BaSO4 / PEG / GO / phenolic resin), the inorganic particles are relatively uniformly distributed, with GO sheets completely encapsulating the particles and embedding them into the dense phenolic resin matrix. The introduction of PEG effectively reduces particle agglomeration, resulting in tight interfacial bonding. In Example 2 (without PEG), although the encapsulation effect of GO is retained, slight agglomeration of inorganic particles occurs locally, and the matrix density decreases. In Example 3 (without PEG and GO), obvious structural defects are observed, with large-area agglomeration of inorganic particles, a loose phenolic resin matrix, and significant interfacial gaps between the matrix and the particles. This morphological evolution suggests that the two-dimensional layered structure of GO enhances stress transmission at the inorganic-organic interface through physical encapsulation, while the dispersion effect of PEG further optimizes the particle distribution. The synergistic effect of both results in the composite material of Example 1 possessing superior microstructural integrity, thereby achieving a comprehensive improvement in both frictional and mechanical properties.

[0053] Infrared spectroscopy was performed on the Uio-66 / BaSO4 / PEG / GO filler particles obtained in Example 1 and Example 2, respectively. Barium sulfate particles and Uio-66 particles were also tested as a comparison. Figure 9 As shown, the results indicate that infrared peaks corresponding to Uio-66 particles and barium sulfate particles were observed in both Uio-66 / BaSO4 / PEG / GO and Uio-66 / BaSO4 / GO filler particles, proving the successful composite of Uio-66.

[0054] Thermal stability test: Thermogravimetric analysis (TGA) was performed on each sample under a nitrogen atmosphere at a heating rate of 10℃ / min. The initial thermal decomposition temperature was recorded to assess its thermal stability. (Reference) Figure 10 , Figure 11 , Figure 12 , Figure 13 , Figure 14 As shown, the initial thermal decomposition temperature of the Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction material in Example 1 was significantly higher than that of the blank sample in Comparative Example 2, and comparable to that of the BaSO4 / phenolic resin composite friction material sample in Comparative Example 1, indicating that it has better thermal stability. After the addition of PEG, Uio-66 is encapsulated in smaller sizes on the barium sulfate particles, effectively increasing the initial thermal decomposition temperature of the material. The initial thermal decomposition temperature of the Uio-66 / BaSO4 / GO / phenolic resin composite friction material in Example 2 was lower than that of the blank sample in Comparative Example 2, further confirming the role of PEG in improving thermal stability.

[0055] Friction coefficient test: Using a friction testing machine, under the same test conditions (such as temperature, pressure, speed, etc.), the friction coefficient of each sample is measured to evaluate its frictional performance. (Reference) Figure 15 , Figure 16 , Figure 17 , Figure 18 , Figure 19 As shown in Table 1, the friction coefficients of the modified composite friction material samples (i.e., Examples 1, 2, and 3 of this invention) were significantly higher than those of the blank sample in Comparative Example 2 and the BaSO4 / phenolic resin composite friction material sample in Comparative Example 1, indicating that the addition of modified barium sulfate and copper fiber effectively improved the friction performance of the material. Meanwhile, the friction coefficients of the non-PEG modified composite friction material samples (i.e., Examples 2 and 3 of this invention) were slightly lower than those of the modified composite friction material sample (i.e., Example 1 of this invention), indicating that the introduction of PEG has a positive effect on improving friction performance.

[0056] Table 1. Average friction coefficient data of each comparative example at different temperatures.

[0057] Impact strength test: at an initial angle of 150° o Under conditions of an impact velocity of 2.9 m / s and an impact energy of 7.5 J, the sample dimensions (length × width × height) were 120 mm × 15 mm × 10 mm. The impact strength of the blank sample in Comparative Example 2 and the composite friction material sample containing barium sulfate were measured using a simply supported beam impact testing machine. The impact strength of the modified composite friction material samples in Examples 1-2 was significantly higher than that of the blank sample in Comparative Example 2 and the BaSO4 / phenolic resin composite friction material sample in Comparative Example 1, indicating that the addition of modified barium sulfate and copper fiber effectively improved the impact strength of the material. Although the Vickers hardness of the Uio-66 / BaSO4 / phenolic resin composite friction material in Example 3 was relatively high, its impact strength decreased.

[0058] Vickers hardness: The Vickers hardness of the composite friction material samples with added barium sulfate and the blank sample of Comparative Example 2 were measured using a TMSV-1 microhardness tester. The results showed that the Vickers hardness of the modified composite friction material samples of Examples 1-3 and the BaSO4 / phenolic resin composite friction material sample with added 4% barium sulfate in Comparative Example 1 were all higher than that of the phenolic resin blank sample. The results of the above tests are shown in Table 2: Table 2. Test results data of key items for each comparative example.

[0059] Through the comparative experiments described above, the Uio-66 / BaSO4 / PEG / GO / phenolic resin composite friction materials and the Uio-66 / BaSO4 / GO / phenolic resin composite friction materials prepared in this invention exhibit significant advantages in terms of friction coefficient, thermal stability, and impact strength. In particular, the introduction of PEG promotes the smaller size encapsulation of Uio-66 on barium sulfate particles, effectively improving the initial thermal decomposition temperature and overall performance of the material. Therefore, the high-performance composite friction materials prepared in this invention have broad market application prospects and significant practical value.

[0060] In summary, the high-performance composite friction material prepared by the present invention through innovative chemical modification not only solves many problems existing in traditional brake pad materials, but also provides a brand-new solution for the development of a new generation of high-performance brake pads, demonstrating significant technological progress and broad market application prospects.

Claims

1. A composite friction material, comprising a phenolic resin matrix, wherein modified barium sulfate and copper fibers are dispersed in the matrix; characterized in that, The modified barium sulfate consists of barium sulfate particles and a coating layer on their surface, the coating layer comprising UiO-66 metal-organic framework material, polyethylene glycol and graphene oxide; By weight, the ratio of the matrix, modified barium sulfate, and copper fiber is (0.7-0.8):(0.15-0.25):(0.04-0.05). The modified barium sulfate is prepared by the following method: using zirconium tetrachloride, terephthalic acid, and barium sulfate particles as raw materials, a solvothermal method is used to react at 110℃-130℃ for 12-36 hours, so that zirconium tetrachloride and terephthalic acid react on the surface of barium sulfate particles to generate UiO-66 metal-organic framework material, thus obtaining modified barium sulfate; wherein, by molar amount, the ratio of zirconium tetrachloride, terephthalic acid, and barium sulfate particles is 1:1:(10-16); in the solvothermal method, polyethylene glycol and graphene oxide are also added to the solvent for reaction, and by weight, the ratio of zirconium tetrachloride, polyethylene glycol, and graphene oxide is 100:(100-80):

1.

2. The method for preparing the composite friction material according to claim 1, characterized in that, Includes the following steps: Step 1: Using zirconium tetrachloride, terephthalic acid and barium sulfate particles as raw materials, the reaction is carried out at 110℃-130℃ for 12-36 hours using a solvothermal method, so that zirconium tetrachloride and terephthalic acid react on the surface of barium sulfate particles to generate UiO-66 metal-organic framework material, thus obtaining modified barium sulfate. Step 2: Mix the modified barium sulfate, copper fiber and phenolic resin powder evenly, put them into a mold sprayed with silicone release agent, press and demold to obtain the composite friction material.

3. The method for preparing the composite friction material according to claim 2, characterized in that, The barium sulfate particles are prepared by the following method: Barite is reduced and calcined with coal powder to produce barium sulfide. The barium sulfide is then leached with water and filtered to obtain a barium sulfide solution. The barium sulfide solution is reacted with sodium sulfate solution to produce barium sulfate precipitate. After impurity removal, purification, drying, and pulverization, barium sulfate particles with a precipitate barium sulfate content ≥99.5% are obtained, which meet the following requirements: volatile matter ≤0.13% at 105℃, water-soluble matter content ≤0.20%, pH value 8-10, fineness ≤0.05%, whiteness ≥97.0%, oil absorption 13-18%, Fe content ≤0.10%, and particle size range 0.75-0.85 micrometers.

4. The method for preparing the composite friction material according to claim 2, characterized in that, Step 2, pressing, includes: Initial pressure stage: Hold pressure at 3-5 MPa for 5-10 minutes to expel gas gaps, then simultaneously heat to 150-160℃ at 7-10 MPa pressure and hold pressure for 60-120 minutes.

5. The application of the composite friction material of claim 1 in the preparation of brake pads.

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