Composite material for brake pad and preparation method thereof

Abstract

The invention discloses a composite material for a brake pad and a preparation method of the composite material. Comprising the following raw materials: 15-20 parts of modified phenolic resin, 12-16 parts of modified composite fiber, 4-7 parts of aramid fiber, 5-8 parts of rubber powder, 3-5 parts of steel fiber, 6-9 parts of graphite, 4-6 parts of modified sepiolite, 3-5 parts of aluminum oxide, 2-3 parts of silicon carbide, 4-6 parts of vermiculite, 9-13 parts of potassium titanate whisker and 8-11 parts of barium sulfate. The modified composite fiber is prepared by the following steps: mixing basalt fiber and carbon fiber, coating lanthanum gadolinium oxide on the surface through hydrothermal reaction, modifying with silane, and finally reacting with 4, 5-diamino-2, 6-dimercaptopyrimidine. The composite material for the brake pad has the advantages of being good in high temperature resistance and friction performance, excellent in abrasion resistance and low in noise, and the service life of the brake pad is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to a composite material for brake pads and a preparation method thereof. Background Art

[0002] Brake pads are also called brake linings. In the braking system of an automobile, brake pads are the most critical safety components. The braking effect depends entirely on the brake pads, which generally consist of a steel plate, an adhesive heat insulation layer, and a friction block. Among them, the friction block is composed of a friction material and an adhesive. During braking, it is pressed against the brake disc or brake drum to generate friction, thereby achieving the purpose of vehicle deceleration and braking. Due to the friction, the friction block will gradually wear. Generally speaking, the lower the cost of the brake pads, the faster they wear. During emergency braking of an automobile, there is intense friction between the brake pads and the brake disc / brake drum, which not only generates a large amount of heat and wear debris. If the generated heat cannot be cooled in time, it will cause the local temperature of the brake pads to be too high and oxidize, greatly reducing the braking performance of the brake pads and affecting driving safety. In addition, under the action of contact stress, cracks are likely to occur due to material fatigue, further damaging the surfaces of the brake pads / brake drum.

[0003] Traditional automotive brake pad friction blocks usually use asbestos friction materials, semi-metallic friction materials, or non-asbestos organic friction materials, etc. Due to the unstable high-temperature friction performance, high braking noise, short service life, and strong carcinogenicity of asbestos brake pads, they have been replaced by semi-metallic and non-asbestos organic friction materials. However, most current semi-metallic and non-asbestos brake pads still cannot fully adapt to complex and harsh braking conditions and higher environmental protection requirements, especially in braking conditions such as high speed and heavy load. Semi-metallic brake pads have high braking noise, are prone to damage the mating parts, are prone to rust, and are prone to cause friction performance degradation; non-asbestos brake pads will release harmful gases after high-temperature friction and are prone to thermal fade, resulting in braking failure and causing major safety accidents, bringing huge economic losses to people. Existing friction materials for brake pads have gradually achieved excellent performance in some brake pads through changes and additions of various components. However, they inevitably have one or more poor performances, affecting people's use experience and safety performance. Compared with traditional organic friction materials, ceramic materials have great advantages in terms of lifespan, environment, and stability, thus becoming an important research direction.

[0004] Chinese Patent CN107489717A discloses a brake pad with heat fade resistance and composite fiber reinforcement, which is made of the following components by weight: 7-23 parts of phenolic resin, 5-15 parts of reinforced composite fiber, 3-17 parts of mineral fiber, 2-8 parts of glass fiber, 3-8 parts of montmorillonite nanopowder, 0.3-0.9 parts of 2,4,6-tris(dimethylaminomethyl)phenol, 5-15 parts of barium sulfate, 3-12 parts of nitrile powder, 4-11 parts of coke powder, 5-15 parts of friction powder, 5-15 parts of graphite, 5-15 parts of tire powder, 3-7 parts of carbon black, 4-10 parts of nano-fluorite powder, 2-7 parts of sepiolite, 3-9 parts of nano-silica aerogel powder, 2-6 parts of heavy calcium carbonate, and 5-15 parts of silane coupling agent. The metal-free brake pad of the invention has high thermal stability and thermal decomposition resistance, strong heat fade resistance, stable friction coefficient, high wear resistance, and low braking noise. However, the silica aerogel in this patent is added in the form of powder, which is prone to uneven mixing, resulting in very unstable product performance.

[0005] Therefore, it is of great significance to develop a composite material for brake pads with strong thermal stability, excellent friction performance, and low noise in the art. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a composite material for brake pads and its preparation method. The composite material has good high-temperature resistance and friction performance, and also has excellent wear resistance and low noise characteristics, improving the service life of brake pads.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: A composite material for brake pads, by weight, includes the following raw materials: 15-20 parts of modified phenolic resin, 12-16 parts of modified composite fiber, 4-7 parts of aramid fiber, 5-8 parts of rubber powder, 3-5 parts of steel fiber, 6-9 parts of graphite, 4-6 parts of modified sepiolite, 3-5 parts of alumina, 2-3 parts of silicon carbide, 4-6 parts of vermiculite, 9-13 parts of potassium titanate whiskers, 8-11 parts of barium sulfate; The modified composite fiber is prepared by mixing basalt fiber and carbon fiber, coating lanthanum gadolinium oxide on the surface through hydrothermal reaction, then modifying with silane, and finally reacting with 4,5-diamino-2,6-dimercaptopyrimidine.

[0008] Preferably, the modified phenolic resin is boron-cashew oil double-modified phenolic resin.

[0009] In the present invention, through the synergistic effect of various raw materials, the comprehensive performance balance required for the composite material for brake pads is achieved. Using modified phenolic resin as the matrix material, other components are bonded together. Aramid fiber improves the overall strength and impact toughness of the material, preventing the material from brittle fracture; steel fiber provides excellent structural strength and stiffness, while improving the thermal conductivity of the material, helping to dissipate frictional heat and reducing thermal fade; potassium titanate whiskers can effectively stabilize the friction coefficient and improve the wear resistance of the material; alumina and silicon carbide are hard abrasives used to provide basic frictional force, clean the surface of the mating disc, and maintain effective frictional contact; graphite, as a solid lubricant, can form a lubricating film at the friction interface, stabilize the friction coefficient, reduce wear, and contribute to heat conduction and noise reduction; rubber powder, vermiculite, and modified sepiolite are used to absorb vibration and reduce braking noise.

[0010] Preferably, a composite material for brake pads, by weight, comprises the following raw materials: 17 - 20 parts of modified phenolic resin, 14 - 16 parts of modified composite fiber, 5 - 7 parts of aramid fiber, 6 - 8 parts of rubber powder, 3 - 4 parts of steel fiber, 6 - 8 parts of graphite, 5 - 6 parts of modified sepiolite, 3 - 4 parts of alumina, 2 - 3 parts of silicon carbide, 5 - 6 parts of vermiculite, 11 - 13 parts of potassium titanate whiskers, and 8 - 10 parts of barium sulfate.

[0011] Preferably, the preparation method of the modified composite fiber comprises the following steps: S1. Mix basalt fiber and carbon fiber evenly, then add them to an acidic potassium permanganate solution for impregnation treatment. After the treatment is completed, filter, wash, and dry to obtain mixed fiber. S2. Add the mixed fiber obtained in step S1 to deionized water, then add lanthanum nitrate and gadolinium nitrate, and then add ammonia water for hydrothermal reaction. After the reaction is completed, filter, wash, dry, and calcine to obtain composite fiber. S3. Add the composite fiber obtained in step S2 to an ethanol aqueous solution, then add vinyltriethoxysilane and stir for reaction. After the reaction is completed, filter, wash, and dry to obtain organic composite fiber. S4. Add the organic composite fiber obtained in step S3 to DMF, then add 4,5 - diamino - 2,6 - dimercaptopyrimidine and benzophenone, and carry out a constant - temperature reaction under ultraviolet irradiation. After the reaction is completed, filter, wash, and dry to obtain the modified composite fiber.

[0012] Preferably, in step S1, the mass ratio of the basalt fiber to the carbon fiber is 8 - 9:1 - 2, the mass concentration of the acidic potassium permanganate solution is 3 - 5%, and the pH is 2 - 3; the temperature of the impregnation treatment is 30 - 40°C, and the time is 2 - 3 h.

[0013] In the present invention, a mixture of basalt fiber and carbon fiber is used as the basic framework, combining the good mechanical properties, chemical corrosion resistance, and relatively low cost of basalt fiber, as well as the high modulus, high strength, excellent thermal conductivity, and inherent good tribological properties of carbon fiber. Through acid potassium permanganate pretreatment, more binding sites are generated on the fiber surface.

[0014] Preferably, in step S2, the mass fraction of the ammonia water is 15 - 20%, and the ratio of the mixed fiber, deionized water, lanthanum nitrate, gadolinium nitrate, ammonia water is 40 - 50:600 - 700:15 - 25:5 - 10:30 - 40; the temperature of the hydrothermal reaction is 150 - 170 °C, and the time is 6 - 8 h; the temperature of the calcination is 400 - 500 °C, and the time is 2 - 3 h.

[0015] In the present invention, during the hydrothermal reaction and subsequent calcination, lanthanum / gadolinium composite oxides are in-situ generated on the surface of the mixed fiber. The formation of a solid solution between the two has better comprehensive thermodynamic stability than a single oxide, which endows the fiber surface with better high-temperature resistance and anti-wear performance.

[0016] Preferably, in step S3, the mass ratio of the composite fiber to vinyltriethoxysilane is 50 - 60:6 - 9, the temperature of the stirring reaction is 60 - 70 °C, and the time is 2 - 3 h.

[0017] Preferably, in step S4, the mass ratio of the organic composite fiber, 4,5-diamino-2,6-dimercaptopyrimidine, and benzophenone is 60 - 70:5 - 7:0.3 - 0.5; the intensity of the ultraviolet irradiation is 10 - 20 mW / cm², the temperature of the constant-temperature reaction is 70 - 80 °C, and the time is 1 - 2 h.

[0018] In the present invention, the composite fiber is treated with a silane coupling agent to introduce double bond groups on its surface. Subsequently, through a thiol-ene click chemical reaction, one thiol group of the 4,5-diamino-2,6-dimercaptopyrimidine molecule undergoes an addition reaction with the vinyl group on the fiber surface to form a stable thioether bond. The pyrimidine heterocyclic structure in the 4,5-diamino-2,6-dimercaptopyrimidine molecule itself has good thermal stability, which helps to improve the stability of the interface region at high temperatures. Moreover, the 4,5-diamino-2,6-dimercaptopyrimidine molecule has two active amino groups, which can undergo a chemical reaction with the active groups (such as hydroxymethyl) in the modified phenolic resin during the hot pressing and curing process of the composite material to form strong covalent bonds, greatly enhancing the interfacial bonding strength between the modified composite fiber and the resin matrix, far superior to traditional physical adsorption or weak hydrogen bond interactions.

[0019] Preferably, the preparation method of the modified sepiolite is as follows: Add 50 g of sepiolite into a nitric acid solution with a mass fraction of 5 - 10%, impregnate for 1 - 2 h, then filter, wash, and dry. Add it into 800 mL of an ethanol - water solution (the volume ratio of ethanol to water is 3:1), then add 6 - 8 g of γ - aminopropyltrimethoxysilane, and react at 60 - 65 °C for 2 - 3 h. After the reaction is completed, filter, wash, and dry to obtain organic sepiolite. Subsequently, add 50 g of organic sepiolite into toluene, then add 7 - 10 g of 1,4 - butanediol diglycidyl ether, and react at 50 - 60 °C for 1 - 2 h. After the reaction is completed, filter, wash, and dry to obtain modified sepiolite.

[0020] In the present invention, the sepiolite is first acid - treated to remove impurities, increase the specific surface area, and activate the surface hydroxyl groups. Subsequently, it is modified with a silane coupling agent to obtain sepiolite with amino groups on the surface. Finally, the amino groups grafted on the surface react with the epoxy groups in 1,4 - butanediol diglycidyl ether, introducing a modified sepiolite on the surface of sepiolite that contains a flexible chain segment (butanediol chain segment) and has a reactive epoxy group at the end. This not only enhances its chemical bonding force with the phenolic resin matrix and improves the interfacial compatibility, but also the flexible butanediol chain segment can play a certain toughening role and help dissipate vibration energy, reducing the noise and vibration generated during the friction process of the composite material.

[0021] The present invention also protects a preparation method of the composite material for brake pads as described above, which includes the following steps: Weigh the raw materials according to the formula, add each raw material into a high - speed mixer and mix evenly to obtain a blend. Subsequently, add the blend into a mold for pressing and then perform heat treatment to obtain the composite material for brake pads.

[0022] Preferably, the pressing conditions are pressing at 160 - 180 °C and 30 - 40 MPa for 6 - 8 min, and the heat treatment is heat - preservation at 170 - 190 °C for 4 - 6 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1)The composite material for brake pads provided by the present invention uses modified phenolic resin as the matrix resin, and at the same time introduces composite fibers that have undergone multiple steps of surface chemical modification as the core reinforcing phase, and is scientifically proportioned with other traditional but effective reinforcing fibers, friction modifiers and fillers. Under the synergistic effect of multiple components, the mechanical properties, wear resistance, thermal stability and friction stability of the composite material are significantly improved; the modified composite fibers are based on basalt / carbon fiber, and are successively coated with lanthanum / gadolinium rare earth oxide coatings and 4,5-diamino-2,6-dimercaptopyrimidine organic layers grafted by silane and thiol-ene click chemistry, which can simultaneously improve the mechanical strength, wear resistance and high-temperature stability of the material, and significantly modify the interfacial bonding force between the composite fiber and the resin matrix by introducing rare earth oxides and amino groups; at the same time, the formula also includes diversified auxiliary reinforcing fibers such as aramid fibers, steel fibers and potassium titanate whiskers, which can further improve the toughness, thermal conductivity and friction stability of the composite material; and adding rubber powder, vermiculite and modified sepiolite can be used to absorb vibration, reduce braking noise and improve the comprehensive performance of the brake pads.

[0024] (2)For the composite material for brake pads provided by the present invention, the added modified composite fibers use a mixture of basalt fiber and carbon fiber as the basic skeleton, and are impregnated under acidic potassium permanganate to make the fiber surface have more binding sites. Subsequently, through hydrothermal reaction and subsequent calcination, a uniform lanthanum / gadolinium composite oxide is in-situ generated on the surface of the mixed fibers. This composite oxide can play multiple roles during the friction process. At the low-temperature stage, it helps to promote the formation of a stable friction film and transfer film, reduce the surface roughness of the contact surface, and change the wear mechanism from the more destructive adhesive wear part to the milder abrasive wear, thereby improving the wear resistance. At the high-temperature friction stage, the lanthanum / gadolinium composite oxide can effectively inhibit the thermal degradation of the phenolic resin matrix, improve the overall heat resistance and thermal fade resistance of the composite material, and lanthanum oxide can also react with alumina in the formula at high temperature to generate a LaAlO3 phase with better thermal stability, further improving the high-temperature friction and wear performance of the composite material under severe braking conditions; then 4,5-diamino-2,6-dimercaptopyrimidine is grafted onto the composite fibers through a chemical reaction. The amino groups carried on the 4,5-diamino-2,6-dimercaptopyrimidine molecule can chemically react with the modified phenolic resin during the curing process to form strong interfacial chemical bonds, greatly enhancing the interfacial bonding strength between the modified composite fiber and the resin matrix, facilitating the effective transfer of stress between the matrix and the reinforcing phase, improving the overall mechanical properties of the composite material, and at the same time, the grafted pyrimidine heterocyclic aromatic structure itself has good thermal stability, which helps to improve the stability of the interfacial region at high temperature and improve the wear resistance of the composite material at high temperature.

[0025] (3) The composite material for brake pads provided by the present invention, with the addition of modified sepiolite, through the double surface treatment of silane coupling agent and 1,4-butanediol diglycidyl ether, not only improves the compatibility between sepiolite and phenolic resin matrix, promotes its uniform dispersion in the matrix, but also the flexible butanediol chain segment in 1,4-butanediol diglycidyl ether helps sepiolite to more effectively exert its structural characteristics to absorb the vibration energy generated during braking, thus significantly reducing brake noise. Specific Embodiments

[0026] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0027] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased through market channels or synthesized from raw materials purchased through market channels.

[0028] The boron-cashew oil double-modified phenolic resin is purchased from Jining Tangyi Chemical Co., Ltd., with the model of FBY double-modified high-temperature and high-carbon resin; the basalt fiber has a length of 6-8 mm and a diameter of 10-15 μm; the carbon fiber has a length of 3-6 mm and a diameter of 7-12 μm; the aramid fiber has a length of 6-8 mm and a diameter of 10-15 μm; the rubber powder is nitrile rubber powder with a particle size of 100 mesh; the steel fiber has a length of 10 mm and a diameter of 8 μm; the graphite is expandable graphite with a particle size of 325 mesh; the sepiolite has a particle size of 325 mesh; the alumina has a particle size of 325 mesh, the silicon carbide has a particle size of 400 mesh, the vermiculite has a particle size of 300 mesh, the potassium titanate whisker has a length of 30-40 μm and a diameter of 0.3-0.5 μm; the barium sulfate has a particle size of 325 mesh.

[0029] Example 1

[0030] A composite material for brake pads, by weight, comprises the following raw materials: 18 parts of modified phenolic resin, 14 parts of modified composite fiber, 6 parts of aramid fiber, 7 parts of rubber powder, 4 parts of steel fiber, 8 parts of graphite, 5 parts of modified sepiolite, 4 parts of alumina, 2.5 parts of silicon carbide, 5 parts of vermiculite, 11 parts of potassium titanate whisker, 10 parts of barium sulfate.

[0031] The preparation method of the modified composite fiber comprises the following steps: S1. Mix 85 g of basalt fibers and 15 g of carbon fibers evenly, then add them into an acidic potassium permanganate solution with a pH of 2.5 (the mass concentration of potassium permanganate is 4%), immerse and treat at 35 °C for 2.5 h. After the treatment, filter, wash and dry to obtain mixed fibers; S2. Add 45 g of the mixed fibers obtained in step S1 into 650 g of deionized water, then add 20 g of lanthanum nitrate and 8 g of gadolinium nitrate. Subsequently, add 35 g of ammonia water with a mass concentration of 20%, carry out hydrothermal reaction at 160 °C for 7 h. After the reaction, filter, wash and dry, and calcine at 450 °C for 2.5 h to obtain composite fibers; S3. Add 55 g of the composite fibers obtained in step S2 into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 8 g of vinyltriethoxysilane, stir and react at 65 °C for 2.5 h. After the reaction, filter, wash and dry to obtain organic composite fibers; S4. Add 65 g of the organic composite fibers obtained in step S3 into 900 mL of DMF, then add 6 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.4 g of benzophenone, carry out a constant temperature reaction under ultraviolet irradiation. The intensity of ultraviolet irradiation is 15 mW / cm², the temperature of the constant temperature reaction is 75 °C, and the time is 1.5 h. After the reaction, filter, wash and dry to obtain the modified composite fibers.

[0032] The preparation method of the modified sepiolite is as follows: Add 50 g of sepiolite into a nitric acid solution with a mass fraction of 8%, immerse for 1.5 h, then filter, wash and dry. Add it into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 7 g of γ-aminopropyltrimethoxysilane, react at 63 °C for 2.5 h. After the reaction, filter, wash and dry to obtain organic sepiolite. Subsequently, add 50 g of organic sepiolite into 800 mL of toluene, then add 9 g of 1,4-butanediol diglycidyl ether, react at 55 °C for 1.5 h. After the reaction, filter, wash and dry to obtain the modified sepiolite.

[0033] A preparation method of a composite material for brake pads includes the following steps: Weigh the raw materials according to the formula, add each raw material into a high-speed mixer and mix evenly to obtain a blend. Subsequently, add the blend into a mold and press it. The pressing conditions are pressing at 170 °C and 35 MPa for 7 min, and then carry out heat treatment. The heat treatment process is to keep warm at 180 °C for 5 h to obtain the composite material for brake pads.

[0034] Example 2

[0035] A composite material for brake pads, by weight, includes the following raw materials: 15 parts of modified phenolic resin, 12 parts of modified composite fiber, 4 parts of aramid fiber, 5 parts of rubber powder, 3 parts of steel fiber, 6 parts of graphite, 4 parts of modified sepiolite, 3 parts of alumina, 2 parts of silicon carbide, 4 parts of vermiculite, 9 parts of potassium titanate whiskers, 8 parts of barium sulfate.

[0036] The preparation method of the modified composite fiber comprises the following steps: S1. Mix 80 g of basalt fiber and 20 g of carbon fiber evenly, then add them into an acidic potassium permanganate solution with a pH of 3 (the mass concentration of potassium permanganate is 3%), impregnate at 30 °C for 3 h, filter, wash and dry after the treatment to obtain mixed fiber; S2. Add 40 g of the mixed fiber in step S1 into 600 g of deionized water, then add 15 g of lanthanum nitrate and 5 g of gadolinium nitrate, then add 30 g of ammonia water with a mass concentration of 20%, carry out hydrothermal reaction at 150 °C for 8 h, filter, wash and dry after the reaction, and calcine at 400 °C for 3 h to obtain composite fiber; S3. Add 50 g of the composite fiber in step S2 into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 6 g of vinyltriethoxysilane, stir and react at 60 °C for 3 h, filter, wash and dry after the reaction to obtain organic composite fiber; S4. Add 60 g of the organic composite fiber in step S3 into 900 mL of DMF, then add 5 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.3 g of benzophenone, carry out a constant-temperature reaction under ultraviolet irradiation, the intensity of ultraviolet irradiation is 10 mW / cm², the temperature of the constant-temperature reaction is 70 °C, and the time is 2 h, filter, wash and dry after the reaction to obtain the modified composite fiber.

[0037] The preparation method of the modified sepiolite is as follows: Add 50 g of sepiolite into a nitric acid solution with a mass fraction of 5%, impregnate for 1 h, then filter, wash and dry, add it into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 6 g of γ-aminopropyltrimethoxysilane, react at 60 °C for 3 h, filter, wash and dry after the reaction to obtain organic sepiolite, then add 50 g of organic sepiolite into 800 mL of toluene, then add 7 g of 1,4-butanediol diglycidyl ether, react at 50 °C for 2 h, filter, wash and dry after the reaction to obtain the modified sepiolite.

[0038] A preparation method of a composite material for brake pads comprises the following steps: Weigh the raw materials according to the formula, add each raw material into a high-speed mixer and mix evenly to obtain a blend. Subsequently, add the blend into a mold and press it. The pressing conditions are pressing at 160 °C and 30 MPa for 8 minutes, and then conduct heat treatment. The heat treatment process is to keep the temperature at 170 °C for 6 hours to obtain the composite material for brake pads.

[0039] Example 3

[0040] A composite material for brake pads, by weight, comprises the following raw materials: 20 parts of modified phenolic resin, 6 parts of modified composite fiber, 7 parts of aramid fiber, 8 parts of rubber powder, 5 parts of steel fiber, 9 parts of graphite, 6 parts of modified sepiolite, 5 parts of alumina, 3 parts of silicon carbide, 6 parts of vermiculite, 13 parts of potassium titanate whiskers, 11 parts of barium sulfate.

[0041] The preparation method of the modified composite fiber comprises the following steps: S1. Mix 90 g of basalt fiber and 10 g of carbon fiber evenly, then add them into an acidic potassium permanganate solution with a pH of 2 (the mass concentration of potassium permanganate is 5%), and soak and treat at 40 °C for 2 hours. After the treatment, filter, wash, and dry to obtain mixed fiber; S2. Add 50 g of the mixed fiber in step S1 into 700 g of deionized water, then add 25 g of lanthanum nitrate and 10 g of gadolinium nitrate, and then add 40 g of ammonia water with a mass concentration of 20%. Conduct hydrothermal reaction at 170 °C for 6 hours. After the reaction, filter, wash, and dry, and calcine at 500 °C for 2 hours to obtain composite fiber; S3. Add 60 g of the composite fiber in step S2 into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 9 g of vinyltriethoxysilane, and stir and react at 70 °C for 2 hours. After the reaction, filter, wash, and dry to obtain organic composite fiber; S4. Add 70 g of the organic composite fiber in step S3 into 900 mL of DMF, then add 7 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.5 g of benzophenone, and conduct a constant-temperature reaction under ultraviolet irradiation. The intensity of ultraviolet irradiation is 20 mW / cm², the temperature of the constant-temperature reaction is 80 °C, and the time is 1 hour. After the reaction, filter, wash, and dry to obtain the modified composite fiber.

[0042] The preparation method of the modified sepiolite is as follows: Add 50 g of sepiolite to a nitric acid solution with a mass fraction of 10%, impregnate for 2 h, then filter, wash, and dry. Add it to 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 8 g of γ-aminopropyltrimethoxysilane, and react at 65 °C for 2 h. After the reaction is completed, filter, wash, and dry to obtain organic sepiolite. Subsequently, add 50 g of organic sepiolite to 800 mL of toluene, then add 10 g of 1,4-butanediol diglycidyl ether, and react at 60 °C for 1 h. After the reaction is completed, filter, wash, and dry to obtain modified sepiolite.

[0043] A preparation method of a composite material for brake pads includes the following steps: Weigh the raw materials according to the formula, add each raw material to a high-speed mixer and mix evenly to obtain a blend. Subsequently, add the blend to a mold for pressing. The pressing conditions are pressing at 180 °C and 40 MPa for 6 min, and then perform heat treatment. The heat treatment process is to keep the temperature at 190 °C for 4 h to obtain the composite material for brake pads.

[0044] Comparative Example 1

[0045] A composite material for brake pads, by weight, includes the following raw materials: 18 parts of modified phenolic resin, 14 parts of modified composite fiber, 6 parts of aramid fiber, 7 parts of rubber powder, 4 parts of steel fiber, 8 parts of graphite, 5 parts of modified sepiolite, 4 parts of alumina, 2.5 parts of silicon carbide, 5 parts of vermiculite, 11 parts of potassium titanate whiskers, and 10 parts of barium sulfate.

[0046] The preparation method of the modified composite fiber includes the following steps: S1. Mix 85 g of basalt fiber and 15 g of carbon fiber evenly, then add them to an acidic potassium permanganate solution with a pH of 2.5 (the mass concentration of potassium permanganate is 4%), and impregnate at 35 °C for 2.5 h. After the treatment is completed, filter, wash, and dry to obtain mixed fiber; S2. Add 45 g of the mixed fiber in step S1 to 650 g of deionized water, then add 20 g of lanthanum nitrate and 8 g of gadolinium nitrate, and then add 35 g of ammonia water with a mass concentration of 20%. Perform hydrothermal reaction at 160 °C for 7 h. After the reaction is completed, filter, wash, and dry, and calcine at 450 °C for 2.5 h to obtain composite fiber; S3. Add 55 g of the composite fiber in step S2 to 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 8 g of vinyltriethoxysilane, and stir and react at 65 °C for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain modified composite fiber.

[0047] The preparation method of the modified sepiolite is as follows: 50 g of sepiolite was added to a nitric acid solution with a mass fraction of 8%, impregnated for 1.5 h, then filtered, washed, and dried. It was added to 800 mL of an ethanol aqueous solution (volume ratio of ethanol to water is 3:1), then 7 g of γ-aminopropyltrimethoxysilane was added, and the reaction was carried out at 63 °C for 2.5 h. After the reaction was completed, it was filtered, washed, and dried to obtain organic sepiolite. Subsequently, 50 g of organic sepiolite was added to 800 mL of toluene, then 9 g of 1,4-butanediol diglycidyl ether was added, and the reaction was carried out at 55 °C for 1.5 h. After the reaction was completed, it was filtered, washed, and dried to obtain modified sepiolite.

[0048] A preparation method of a composite material for brake pads includes the following steps: Weigh the raw materials according to the formula, add each raw material into a high-speed mixer and mix evenly to obtain a blend. Subsequently, the blend was added into a mold for pressing. The pressing conditions were pressing at 170 °C and 35 MPa for 7 min, and then heat treatment was carried out. The heat treatment process was to keep the temperature at 180 °C for 5 h to obtain the composite material for brake pads.

[0049] Compared with Example 1, 4,5-diamino-2,6-dimercaptopyrimidine was not introduced onto the modified composite fiber in this comparative example.

[0050] Comparative Example 2

[0051] A composite material for brake pads, by weight, includes the following raw materials: 18 parts of modified phenolic resin, 14 parts of modified composite fiber, 6 parts of aramid fiber, 7 parts of rubber powder, 4 parts of steel fiber, 8 parts of graphite, 5 parts of modified sepiolite, 4 parts of alumina, 2.5 parts of silicon carbide, 5 parts of vermiculite, 11 parts of potassium titanate whiskers, 10 parts of barium sulfate.

[0052] The preparation method of the modified composite fiber includes the following steps: S1. Mix 85 g of basalt fiber and 15 g of carbon fiber evenly, then add it into an acidic potassium permanganate solution with a pH of 2.5 (mass concentration of potassium permanganate is 4%), and impregnate and treat it at 35 °C for 2.5 h. After the treatment is completed, filter, wash, and dry to obtain mixed fiber; S2. Add 55 g of the mixed fiber in step S1 into 800 mL of an ethanol aqueous solution (volume ratio of ethanol to water is 3:1), then add 8 g of vinyltriethoxysilane, and stir and react at 65 °C for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain organic composite fiber; S3. Add 65 g of organic composite fiber in step S3 into 900 mL of DMF, then add 6 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.4 g of benzophenone, and carry out a constant-temperature reaction under ultraviolet irradiation. The intensity of the ultraviolet irradiation is 15 mW / cm², the temperature of the constant-temperature reaction is 75 °C, and the time is 1.5 h. After the reaction is completed, filter, wash, and dry to obtain the modified composite fiber.

[0053] The preparation method of the modified sepiolite is as follows: Add 50 g of sepiolite into a nitric acid solution with a mass fraction of 8%, impregnate for 1.5 h, then filter, wash, and dry. Add it into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 7 g of γ-aminopropyltrimethoxysilane, and react at 63 °C for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain organic sepiolite. Subsequently, add 50 g of organic sepiolite into 800 mL of toluene, then add 9 g of 1,4-butanediol diglycidyl ether, and react at 55 °C for 1.5 h. After the reaction is completed, filter, wash, and dry to obtain the modified sepiolite.

[0054] A preparation method of a composite material for brake pads includes the following steps: Weigh the raw materials according to the formula, add each raw material into a high-speed mixer and mix evenly to obtain a blend. Subsequently, add the blend into a mold for pressing. The pressing conditions are pressing at 170 °C and 35 MPa for 7 min, and then carry out heat treatment. The heat treatment process is to keep warm at 180 °C for 5 h to obtain the composite material for brake pads.

[0055] Compared with Example 1, lanthanum gadolinium oxide was not introduced onto the modified composite fiber in this comparative example.

[0056] Comparative Example 3

[0057] A composite material for brake pads, by weight, includes the following raw materials: 18 parts of modified phenolic resin, 14 parts of modified composite fiber, 6 parts of aramid fiber, 7 parts of rubber powder, 4 parts of steel fiber, 8 parts of graphite, 5 parts of sepiolite, 4 parts of alumina, 2.5 parts of silicon carbide, 5 parts of vermiculite, 11 parts of potassium titanate whiskers, and 10 parts of barium sulfate.

[0058] The preparation method of the modified composite fiber includes the following steps: S1. Mix 85 g of basalt fiber and 15 g of carbon fiber evenly, then add them into an acidic potassium permanganate solution with a pH of 2.5 (the mass concentration of potassium permanganate is 4%), and impregnate at 35 °C for 2.5 h. After the treatment is completed, filter, wash, and dry to obtain the mixed fiber; S2. Add 45 g of the mixed fibers in step S1 into 650 g of deionized water, then add 20 g of lanthanum nitrate and 8 g of gadolinium nitrate. Subsequently, add 35 g of ammonia water with a mass concentration of 20%. Carry out hydrothermal reaction at 160 °C for 7 h. After the reaction is completed, filter, wash, and dry, and then calcine at 450 °C for 2.5 h to obtain composite fibers; S3. Add 55 g of the composite fibers in step S2 into 800 mL of an ethanol aqueous solution (the volume ratio of ethanol to water is 3:1), then add 8 g of vinyltriethoxysilane. Stir and react at 65 °C for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain organic composite fibers; S4. Add 65 g of the organic composite fibers in step S3 into 900 mL of DMF, then add 6 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.4 g of benzophenone. Carry out a constant-temperature reaction under ultraviolet irradiation. The intensity of the ultraviolet irradiation is 15 mW / cm², the temperature of the constant-temperature reaction is 75 °C, and the time is 1.5 h. After the reaction is completed, filter, wash, and dry to obtain the modified composite fibers.

[0059] A preparation method of a composite material for brake pads, comprising the following steps: Weigh the raw materials according to the formula, add the raw materials into a high-speed mixer and mix them evenly to obtain a blend. Subsequently, add the blend into a mold for pressing. The pressing conditions are pressing at 170 °C and 35 MPa for 7 min, and then carry out heat treatment. The heat treatment process is to keep the temperature at 180 °C for 5 h to obtain the composite material for brake pads.

[0060] Compared with Example 1, sepiolite was not modified in this comparative example.

[0061] Perform performance tests on the composite materials for brake pads prepared in Examples 1-3 and Comparative Examples 1-3. Among them, the impact strength is tested according to the standard GB / T 33835-2017 "Test Method for Impact Strength of Friction Materials"; the flexural strength is tested according to the standard GB / T 9341-2008, and the friction coefficient and wear amount are tested according to the standard GB 5763-2018 "Automotive Brake Linings". The test results are shown in Table 1 below: Table 1 Performance test results of each group of composite materials for brake pads

[0062] As can be seen from Table 1 above, the composite material for brake pads prepared by the present invention has good mechanical properties, a stable friction coefficient, and also has good heat resistance and sound absorption properties, and has good application prospects.

[0063] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite material for brake pads, characterized in that, By weight, it includes the following raw materials: 15-20 parts of modified phenolic resin, 12-16 parts of modified composite fiber, 4-7 parts of aramid fiber, 5-8 parts of rubber powder, 3-5 parts of steel fiber, 6-9 parts of graphite, 4-6 parts of modified sepiolite, 3-5 parts of alumina, 2-3 parts of silicon carbide, 4-6 parts of vermiculite, 9-13 parts of potassium titanate whiskers, 8-11 parts of barium sulfate.

2. The composite material for brake pads according to claim 1, characterized in that, By weight, it includes the following raw materials: 17-20 parts of modified phenolic resin, 14-16 parts of modified composite fiber, 5-7 parts of aramid fiber, 6-8 parts of rubber powder, 3-4 parts of steel fiber, 6-8 parts of graphite, 5-6 parts of modified sepiolite, 3-4 parts of alumina, 2-3 parts of silicon carbide, 5-6 parts of vermiculite, 11-13 parts of potassium titanate whiskers, 8-10 parts of barium sulfate.

3. The composite material for brake pads according to claim 1, wherein, The preparation method of the modified composite fiber includes the following steps: S1. Mix basalt fiber and carbon fiber evenly, then add them into an acidic potassium permanganate solution for impregnation treatment to obtain mixed fiber; S2. Add the mixed fiber into deionized water, then add lanthanum nitrate and gadolinium nitrate, and then add ammonia water for hydrothermal reaction to obtain composite fiber; S3. Add the composite fiber into an ethanol aqueous solution, then add vinyltriethoxysilane and carry out a stirring reaction to obtain an organic composite fiber; S4. Add the organic composite fiber into DMF, then add 4,5-diamino-2,6-dimercaptopyrimidine and benzophenone, and carry out a constant-temperature reaction under ultraviolet irradiation to obtain the modified composite fiber.

4. The composite material for brake pads according to claim 3, characterized in that, In step S1, the mass ratio of the basalt fiber to the carbon fiber is 8-9:1-2, the mass concentration of the acidic potassium permanganate solution is 3-5%, and the pH is 2-3; the temperature of the impregnation treatment is 30-40°C, and the time is 2-3 h.

5. The composite material for brake pads according to claim 3, characterized in that, In step S2, the mass fraction of the ammonia water is 15-20%, and the ratio of the mixed fiber, deionized water, lanthanum nitrate, gadolinium nitrate, and ammonia water is 40-50:600-700:15-25:5-10:30-40; the temperature of the hydrothermal reaction is 150-170°C, and the time is 6-8 h; the temperature of the calcination is 400-500°C, and the time is 2-3 h.

6. The composite material for brake pads according to claim 3, characterized in that In step S3, the mass ratio of the composite fiber to vinyltriethoxysilane is 50-60:6-9, the temperature of the stirring reaction is 60-70°C, and the time is 2-3 h.

7. The composite material for brake pads according to claim 3, wherein, In step S4, the mass ratio of the organic composite fiber, 4,5-diamino-2,6-dimercaptopyrimidine, and benzophenone is 60-70:5-7:0.3-0.5; the intensity of the ultraviolet irradiation is 10-20 mW / cm², the temperature of the constant-temperature reaction is 70-80°C, and the time is 1-2 h.

8. The composite material for brake pads according to claim 1, wherein, The preparation method of the modified sepiolite is as follows: After treating 50 g of sepiolite with acid, it was added to an ethanol aqueous solution, and then 6 - 8 g of γ-aminopropyltrimethoxysilane was added. The reaction was carried out at 60 - 65 °C for 2 - 3 h. After the reaction was completed, organic sepiolite was obtained. Subsequently, 50 g of organic sepiolite was added to toluene, and then 7 - 10 g of 1,4-butanediol diglycidyl ether was added. The reaction was carried out at 50 - 60 °C for 1 - 2 h. After the reaction was completed, modified sepiolite was obtained.

9. A preparation method of the composite material for brake pads according to any one of claims 1-8, characterized in that, It includes the following steps: Weigh the raw materials according to the formula, add each raw material to a high-speed mixer and mix evenly to obtain a blend. Subsequently, the blend was added to a mold for pressing and then heat-treated to obtain the composite material for brake pads.

10. The preparation method according to claim 9, wherein, The conditions for the pressing were pressing at 160 - 180 °C and 30 - 40 MPa for 6 - 8 min, and the heat treatment was heat preservation at 170 - 190 °C for 4 - 6 h.

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