Friction material, brake pad and preparation method thereof

Abstract

The invention discloses a friction material, a brake pad and a preparation method of the brake pad. Comprising the following raw materials: 14-18 parts of modified phenolic resin, 10-15 parts of modified composite fiber, 4-7 parts of aramid fiber, 3-5 parts of rubber powder, 5-8 parts of steel fiber, 7-11 parts of graphite, 3-6 parts of aluminum oxide, 3-5 parts of silicon carbide, 4-6 parts of mica powder, 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 friction material has the advantages of good mechanical properties, low wear rate, high thermal stability and stable friction coefficient, and is suitable for automobile brake pads.

Description

Technical Field

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

[0002] Friction materials are functional materials used in many moving machines and equipment to play roles such as transmission, steering, braking, deceleration, and parking. Taking the friction material of brake pads as an example, the quality of its performance directly affects the safety of braking.

[0003] In recent years, the automotive manufacturing has gradually developed towards the directions of safety, environmental protection, high speed and long life, which puts forward higher requirements for the comprehensive performance of the automotive braking system and the high-temperature stability and reliability of brake pad materials. As an important material for the friction drive braking system, friction materials need to have high compressive strength, large friction coefficient, low wear rate, and excellent stability, etc.

[0004] Traditional automotive brake pads usually adopt asbestos friction materials, semi-metallic friction materials or non-asbestos organic friction materials, etc. Since asbestos brake pads have unstable high-temperature friction performance, large braking noise, and short service life, they have been replaced by semi-metallic and non-asbestos organic friction materials.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 large braking noise, are easy to damage the mating parts, are easy to rust and are easy to cause friction performance degradation; non-asbestos brake pads will release harmful gases after high-temperature friction and are prone to thermal degradation, causing braking failure and resulting in major safety accidents, bringing huge economic losses to people. The existing friction materials for brake pads have gradually achieved excellent performance of some brake pads through the change and addition of various components. However, at the same time, 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 life, environment and stability, thus becoming an important research direction.

[0005] Chinese Patent CN107489717A discloses a brake pad with composite fiber reinforcement for heat fade resistance, 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 nanometer powder, 0.3-0.9 part 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 this invention has good 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 the problem of uneven mixing, resulting in very unstable product performance. Chinese Patent Application CN101077912A discloses a friction material reinforced by hybrid of aramid fiber and inorganic mineral fiber and its preparation method. The novel asbestos-free non-metallic friction material consists of aramid fiber, LAPINUS inorganic mineral fiber, phenolic resin, nitrile rubber powder, inorganic filler, and friction modifier. This invention uses an organic-inorganic composite material as the reinforcing agent of the friction material to improve the comprehensive performance of the friction material. The friction performance of the product is stable, and with the change of temperature, the deviation of the friction coefficient is within 10%. Although this novel graphite-free non-metallic friction material is heat-resistant, the friction coefficient of this friction material is unstable at high temperatures.

[0006] Therefore, it is of great significance to develop a friction material with good mechanical properties, low wear rate, and excellent stability in this field. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a friction material, a brake pad, and its preparation method. The friction material has good mechanical properties, low wear rate, high thermal stability, stable friction coefficient, and is suitable for automotive brake pads.

[0008] To achieve the above purpose, the present invention provides the following technical solutions: A friction material, by weight, includes the following raw materials: 14-18 parts of modified phenolic resin, 10-15 parts of modified composite fiber, 4-7 parts of aramid fiber, 3-5 parts of rubber powder, 5-8 parts of steel fiber, 7-11 parts of graphite, 3-6 parts of alumina, 3-5 parts of silicon carbide, 4-6 parts of mica powder, 9-13 parts of potassium titanate whisker, 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.

[0009] Preferably, the modified phenolic resin is a boron-cashew oil double-modified phenolic resin.

[0010] In the present invention, through the synergistic effect of various raw materials, the comprehensive performance balance required for friction materials is achieved. Using the modified phenolic resin as the matrix material to bond other components together, aramid fiber improves the overall strength and impact toughness of the material, preventing the material from brittle cracking; steel fiber provides excellent structural strength and stiffness, while improving the thermal conductivity of the material, helping to dissipate frictional heat and reducing heat 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 counter disk, 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 is used to absorb vibration and reduce braking noise; mica powder, as a flaky filler, helps to improve the dimensional stability of the material, fill voids, and to a certain extent, stabilize the friction coefficient and reduce noise.

[0011] Preferably, a friction material comprises the following raw materials in parts by weight: 16-18 parts of modified phenolic resin, 12-15 parts of modified composite fiber, 4-6 parts of aramid fiber, 4-5 parts of rubber powder, 5-7 parts of steel fiber, 9-11 parts of graphite, 4-6 parts of alumina, 4-5 parts of silicon carbide, 4-5 parts of mica powder, 11-13 parts of potassium titanate whiskers, and 8-10 parts of barium sulfate.

[0012] Preferably, the preparation method of the modified composite fiber comprises the following steps: S1. Mix basalt fiber and carbon fiber evenly, then add them into 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 in step S1 into 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 in step S2 into an ethanol aqueous solution, then add vinyltriethoxysilane and carry out a stirring reaction. After the reaction is completed, filter, wash, and dry to obtain organic composite fiber; S4. Add the organic composite fiber in step S3 into 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.

[0013] 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.

[0014] In the present invention, a mixture of basalt fiber and carbon fiber is used as the basic skeleton, 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 acidic potassium permanganate pretreatment, more binding sites are generated on the fiber surface.

[0015] Preferably, in step S2, the mass fraction of the ammonia water is 15-20%, and the mass 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.

[0016] In the present invention, through hydrothermal reaction and subsequent calcination, lanthanum / gadolinium composite oxide is in-situ generated on the surface of the mixed fiber. The formation of a solid solution between the two has more excellent comprehensive thermodynamic stability than a single oxide, which endows the fiber surface with better high-temperature resistance and anti-wear performance.

[0017] 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.

[0018] 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.

[0019] 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, a 4,5-diamino-2,6-dimercaptopyrimidine molecule undergoes an addition reaction with the vinyl group on the fiber surface through one of its mercapto groups 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 friction 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.

[0020] The present invention also protects a method for preparing the friction material as described above, comprising 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 conduct heat treatment to obtain the friction material.

[0021] 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.

[0022] The present invention also protects a brake pad, comprising the friction material as described above and a steel back.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1)The friction material provided by the present invention uses modified phenolic resin as the matrix resin, and at the same time introduces composite fibers that have undergone multi-step 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 action of multiple components, the mechanical properties, wear resistance, thermal stability and friction stability of the friction 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 fibers and the resin matrix by introducing rare earth oxides and amino groups; at the same time, the formula also contains 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 friction material; and carefully proportioned hard abrasives such as alumina and silicon carbide, solid lubricants such as graphite, and fillers and stabilizers such as rubber powder, mica powder and barium sulfate are used to precisely control the friction coefficient, wear rate, noise and thermal performance, so that the prepared friction material has the characteristics of good mechanical properties, low wear rate, high thermal stability and stable friction coefficient.

[0024] (2)For the friction material 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 friction material under harsh 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 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 fibers and the resin matrix, which is beneficial to the effective transfer of stress between the matrix and the reinforcing phase, improving the overall mechanical properties of the friction material. 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 friction material at high temperature. Detailed implementation mode

[0025] 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 the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0026] Unless otherwise specified, the chemical reagents and materials in the present invention are all purchased through market channels or synthesized from raw materials purchased through market channels.

[0027] The boron-cashew oil double-modified phenolic resin is purchased from Jining Tangyi Chemical Co., Ltd., and the model is FBY double-modified high-temperature and high-carbon resin; the length of the basalt fiber is 6-8 mm, and the diameter is 10-15 μm; the length of the carbon fiber is 3-6 mm, and the diameter is 7-12 μm; the length of the aramid fiber is 6-8 mm, and the diameter is 10-15 μm; the rubber powder is nitrile rubber powder with a particle size of 100 mesh; the length of the steel fiber is 10 mm, and the diameter is 8 μm; the graphite is expandable graphite with a particle size of 325 mesh; the particle size of the alumina is 325 mesh, the particle size of the silicon carbide is 400 mesh, the particle size of the mica powder is 300 mesh, the length of the potassium titanate whisker is 30-40 μm, and the diameter is 0.3-0.5 μm; the particle size of the barium sulfate is 325 mesh.

[0028] Example 1

[0029] A friction material, by weight, comprises the following raw materials: 16 parts of modified phenolic resin, 13 parts of modified composite fiber, 6 parts of aramid fiber, 4 parts of rubber powder, 7 parts of steel fiber, 9 parts of graphite, 5 parts of alumina, 4 parts of silicon carbide, 5 parts of mica powder, 11 parts of potassium titanate whisker, and 10 parts of barium sulfate.

[0030] Among them, the preparation method of the modified composite fiber comprises 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%), impregnate at 35 °C for 2.5 h, filter, wash, and dry after the treatment to obtain mixed fiber; S2. Add 45 g of the mixed fiber in step S1 into 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%, carry out hydrothermal reaction at 160 °C for 7 h, filter, wash, and dry after the reaction, and calcine at 450 °C for 2.5 h to obtain composite fiber; S3. Add 55 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 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 the organic composite fiber; S4. Add 65 g of the 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.

[0031] A preparation method of a friction material, comprising the following steps: Weigh the raw materials according to the formula, add the raw materials 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 the temperature at 180 °C for 5 h to obtain the friction material.

[0032] Example 2

[0033] A friction material, by weight, comprises the following raw materials: 16 parts of modified phenolic resin, 12 parts of modified composite fiber, 6 parts of aramid fiber, 4 parts of rubber powder, 6 parts of steel fiber, 8 parts of graphite, 4 parts of alumina, 4 parts of silicon carbide, 5 parts of mica powder, 10 parts of potassium titanate whiskers, 9 parts of barium sulfate.

[0034] Among them, the preparation method of the modified composite fiber comprises 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 carry out impregnation treatment 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 fiber in step S1 into 650 g of deionized water, then add 20 g of lanthanum nitrate and 7 g of gadolinium nitrate, and then add 35 g of ammonia water with a mass concentration of 15%. Carry out 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 the composite fiber; S3. Add 55 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 7 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 the organic composite fiber; S4. Add 65 g of the 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.

[0035] A preparation method of a friction material, comprising 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 the temperature at 180 °C for 5 h to obtain the friction material.

[0036] Example 3

[0037] A friction material, by weight, comprises the following raw materials: 14 parts of modified phenolic resin, 10 parts of modified composite fiber, 4 parts of aramid fiber, 3 parts of rubber powder, 5 parts of steel fiber, 7 parts of graphite, 3 parts of alumina, 3 parts of silicon carbide, 4 parts of mica powder, 9 parts of potassium titanate whiskers, 8 parts of barium sulfate.

[0038] Among them, 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%), and carry out impregnation treatment at 30 °C for 3 h. After the treatment is completed, filter, wash, and dry to obtain the 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, and then add 30 g of ammonia water with a mass concentration of 15%. Carry out hydrothermal reaction at 150 °C for 8 h. After the reaction is completed, filter, wash, and dry, and calcine at 400 °C for 3 h to obtain the 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, and carry out stirring reaction at 60 °C for 3 h. After the reaction is completed, filter, wash, and dry to obtain the organic composite fiber; S4. Add 60 g of the organic composite fiber in step S3 to 900 mL of DMF, then add 5 g of 4,5-diamino-2,6-dimercaptopyrimidine and 0.3 g of benzophenone, and carry out a constant-temperature reaction under ultraviolet irradiation. The intensity of the ultraviolet irradiation is 10 mW / cm², the temperature of the constant-temperature reaction is 70 °C, and the time is 2 h. After the reaction is completed, filter, wash, and dry to obtain the modified composite fiber.

[0039] A preparation method of a friction material, 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 and press it. The pressing conditions are pressing at 160 °C and 30 MPa for 8 min, and then carry out heat treatment. The heat treatment process is to keep the temperature at 170 °C for 6 h to obtain the friction material.

[0040] Example 4

[0041] A friction material, by weight, comprises the following raw materials: 18 parts of modified phenolic resin, 15 parts of modified composite fiber, 7 parts of aramid fiber, 5 parts of rubber powder, 8 parts of steel fiber, 11 parts of graphite, 6 parts of alumina, 5 parts of silicon carbide, 6 parts of mica powder, 13 parts of potassium titanate whiskers, 11 parts of barium sulfate.

[0042] Among them, 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 carry out impregnation treatment at 40 °C for 2 h. After the treatment is completed, filter, wash, and dry to obtain the mixed fiber; S2. Add 50 g of the mixed fiber in step S1 to 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%. Carry out hydrothermal reaction at 170 °C for 6 h. After the reaction is completed, filter, wash, and dry, and calcine at 500 °C for 2 h to obtain the composite fiber; S3. Add 60 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 9 g of vinyltriethoxysilane, and carry out stirring reaction at 70 °C for 2 h. After the reaction is completed, filter, wash, and dry to obtain the 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 carry out a constant-temperature reaction under ultraviolet irradiation. The intensity of the ultraviolet irradiation is 20 mW / cm², the temperature of the constant-temperature reaction is 80 °C, and the time is 1 h. After the reaction is completed, filter, wash, and dry to obtain the modified composite fiber.

[0043] A preparation method of a friction material, comprising the following steps: Weigh the raw materials according to the formula, add the raw materials 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 180 °C and 40 MPa for 6 min, and then carry out heat treatment. The heat treatment process is to keep the temperature at 190 °C for 4 h to obtain the friction material.

[0044] Comparative Example 1

[0045] A friction material, by weight, comprises the following raw materials: 16 parts of modified phenolic resin, 13 parts of modified composite fiber, 6 parts of aramid fiber, 4 parts of rubber powder, 7 parts of steel fiber, 9 parts of graphite, 5 parts of alumina, 4 parts of silicon carbide, 5 parts of mica powder, 11 parts of potassium titanate whiskers, 10 parts of barium sulfate.

[0046] Among them, the preparation method of the modified composite fiber comprises 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 carry out impregnation treatment at 35 °C for 2.5 h. After the treatment is completed, filter, wash, and dry to obtain a mixed fiber; S2. Add 45 g of the mixed fiber in step S1 into 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%. Carry out a 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 a composite fiber; S3. Add 55 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 8 g of vinyltriethoxysilane, and carry out a stirring reaction at 65 °C for 2.5 h. After the reaction is completed, filter, wash, and dry to obtain a modified composite fiber.

[0047] A preparation method of a friction material, comprising 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 minutes, followed by heat treatment. The heat treatment process is to keep warm at 180 °C for 5 hours to obtain the friction material.

[0048] Compared with Example 1, 4,5-diamino-2,6-dimercaptopyrimidine was not introduced onto the modified composite fiber in this comparative example.

[0049] Comparative Example 2

[0050] A friction material, by weight, comprises the following raw materials: 16 parts of modified phenolic resin, 13 parts of modified composite fiber, 6 parts of aramid fiber, 4 parts of rubber powder, 7 parts of steel fiber, 9 parts of graphite, 5 parts of alumina, 4 parts of silicon carbide, 5 parts of mica powder, 11 parts of potassium titanate whiskers, 10 parts of barium sulfate.

[0051] Among them, the preparation method of the modified composite fiber comprises 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%), impregnate at 35 °C for 2.5 h, filter, wash, and dry after the treatment to obtain mixed fibers; S2. Add 55 g of the mixed fibers in step S1 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, filter, wash, and dry after the reaction to obtain organic composite fibers; S3. Add 65 g of the organic composite fibers in step S2 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. Filter, wash, and dry after the reaction to obtain the modified composite fiber.

[0052] A preparation method of a friction material 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 for pressing. The pressing conditions are pressing at 170 °C and 35 MPa for 7 minutes, followed by heat treatment. The heat treatment process is to keep warm at 180 °C for 5 hours to obtain the friction material.

[0053] Compared with Example 1, lanthanum gadolinium oxide was not introduced onto the modified composite fiber in this comparative example.

[0054] Comparative Example 3

[0055] A friction material, by weight, comprises the following raw materials: 16 parts of modified phenolic resin, 13 parts of modified composite fiber, 6 parts of aramid fiber, 4 parts of rubber powder, 7 parts of steel fiber, 9 parts of graphite, 5 parts of alumina, 4 parts of silicon carbide, 5 parts of mica powder, 11 parts of potassium titanate whiskers, 10 parts of barium sulfate.

[0056] Among them, the preparation method of the modified composite fiber comprises 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%), impregnate at 35 °C for 2.5 h, filter, wash and dry after the treatment to obtain mixed fibers; S2. Add 55 g of the mixed fibers in step S1 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, filter, wash and dry after the reaction to obtain the modified composite fiber.

[0057] A preparation method of a friction material 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. Then add the blend into a mold for pressing. The pressing conditions are pressing at 170 °C and 35 MPa for 7 min, and then perform heat treatment. The heat treatment process is to keep the temperature at 180 °C for 5 h to obtain the friction material.

[0058] Compared with Example 1, lanthanum gadolinium oxide and 4,5-diamino-2,6-dimercaptopyrimidine are not introduced onto the modified composite fiber in this comparative example.

[0059] Perform performance tests on the friction materials prepared in Examples 1-4 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 / T9341-2008, and the friction coefficient and wear amount are tested according to the standard GB 5763-2018 "Brake Linings for Motor Vehicles". The test results are shown in Table 1 below: Table 1 Performance test results of each group of friction materials

[0060] It can be seen from Table 1 above that the friction material prepared by the present invention has good mechanical properties, a suitable friction coefficient, a stable friction coefficient, and also has good heat resistance. It still has a low wear rate at a relatively high temperature and has good application prospects.

[0061] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A friction material, characterized in that, By weight, it includes the following raw materials: 14-18 parts of modified phenolic resin, 10-15 parts of modified composite fiber, 4-7 parts of aramid fiber, 3-5 parts of rubber powder, 5-8 parts of steel fiber, 7-11 parts of graphite, 3-6 parts of alumina, 3-5 parts of silicon carbide, 4-6 parts of mica powder, 9-13 parts of potassium titanate whiskers, 8-11 parts of barium sulfate.

2. The friction material according to claim 1, characterized in that, By weight, it includes the following raw materials: 16-18 parts of modified phenolic resin, 12-15 parts of modified composite fiber, 4-6 parts of aramid fiber, 4-5 parts of rubber powder, 5-7 parts of steel fiber, 9-11 parts of graphite, 4-6 parts of alumina, 4-5 parts of silicon carbide, 4-5 parts of mica powder, 11-13 parts of potassium titanate whiskers, 8-10 parts of barium sulfate.

3. The friction material according to claim 1, characterized in that, 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 friction material 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 friction material 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 friction material 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 friction material according to claim 3, characterized in that 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. A method for preparing a friction material according to any one of claims 1-7, characterized in that, It 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. Then, add the blend into a mold for pressing and then conduct heat treatment to obtain the friction material.

9. The preparation method according to claim 8, characterized in that, 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 170-19 °C for 4-6 h.

10. A brake pad, characterized in that, It includes the friction material as described in any one of claims 1-7 and a steel backing.

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