Friction material with excellent moldability and method for producing the same

Abstract

The application relates to the technical field of friction materials, in particular to a friction material with excellent formability and a preparation method thereof. Raw materials of the friction material include allyl phenolic resin, bismaleimide, a photoinitiator, thiol-modified fillers and an auxiliary agent; the fillers include reinforcing fillers, friction-increasing fillers and friction-reducing fillers. The application grafts bismaleimide on the surface of thiol-modified reinforcing fillers, effectively improves the compatibility of the fillers and the resin, reduces the viscosity of the mixture, and significantly improves the fluidity during hot pressing. The application constructs a three-dimensional interfacial interpenetrating network with the fillers as nodes by using the bifunctional group characteristics of bismaleimide, so that the resin consumption is less than 15 wt%, and the interfacial bonding strength is higher than that of a traditional coupling agent treatment. In the interfacial interpenetrating network formed by the application, the imide ring structure of bismaleimide endows the material with excellent thermal stability, the interface does not debond at high temperatures, the friction coefficient is stable, and the anti-thermal decay capacity is excellent.

Description

Technical Field

[0001] This invention relates to the field of friction materials technology, specifically a friction material with excellent formability and its preparation method. Background Technology

[0002] Currently, friction materials used in electromagnetic brakes are generally annular, internally square, internally hexagonal, or internally splined, with relatively small overall dimensions and thin thickness. Therefore, due to the shape, to improve the yield rate and reduce rejects during the pressing of electromagnetic brake friction materials, the binder content and pressing pressure are generally increased to improve formability. However, this has many adverse effects, such as blistering, delamination during pressing, poor thermal stability of the product, and energy waste. Furthermore, excessively high binder content significantly increases product cost. In addition, the binder is generally a resin material, which is easily degraded by heat; excessive binder content is one of the main causes of thermal degradation in friction materials. Therefore, the industry is currently working to reduce the amount of binder used in friction materials.

[0003] However, reducing the binder content can also decrease the compatibility between fillers and reduce the moldability of friction materials. Generally, when the resin content drops below 15%, if the formulation lacks an effective plasticizer or reinforcing skeleton, it can easily lead to pressing difficulties, incomplete mold filling, material shortages, loose corners, and uneven density, and can also cause a decrease in the strength of the friction material. Currently, to obtain low-binder friction materials, the general approach is to reduce the amount of binder used while maintaining a certain level of moldability, but the effectiveness of this method is limited. In existing technologies, there are schemes that directly modify the surface of fillers to increase the chemical bonding with binders, thereby improving compatibility and adhesion, and thus reducing the amount of binder used. For example, Chinese patent CN112228483A uses silane modification, and the amount of binder used is <15%. However, the silane coupling agent forms a monolayer chemical bond between the filler and the binder. This two-dimensional interface structure is prone to stress concentration when subjected to thermal and mechanical stress, leading to interface debonding. At the same time, it may reduce the fluidity of the mixture, resulting in problems such as uneven density and cracking during hot pressing, and the improvement in formability is limited.

[0004] In summary, developing a compression molding compound with low binder content but good flowability is of great significance for improving the formability of friction materials, reducing scrap rate, lowering production costs, and enhancing thermal stability, thus impacting the production and use of friction materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a friction material with low adhesive content to at least achieve good formability and excellent thermal stability.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A friction material with excellent formability, comprising allyl phenolic resin, bismaleimide, photoinitiator, mercapto-modified reinforcing filler, friction-increasing filler, friction-reducing filler, and additives, and prepared by means of the following steps:

[0008] S1: Bismaleimide and mercapto-modified reinforcing filler are dispersed in an organic solvent, then a photoinitiator is added, and ultraviolet light is used to irradiate and carry out a photocrosslinking reaction. After the reaction is completed, the filler is washed to obtain bismaleimide-modified reinforcing filler.

[0009] S2: Allyl phenolic resin, bismaleimide modified reinforcing filler, friction-increasing filler, friction-reducing filler and additives are mixed and kneaded, then crushed and sieved to obtain granules;

[0010] S3: The granules are subjected to cold pressing and hot pressing in sequence, and then placed in an oven for heat treatment to obtain the final product.

[0011] In some embodiments, the raw materials, by weight, include 6-8 parts of allyl phenolic resin, 15-25 parts of the reinforcing filler, 40-45 parts of the friction-increasing filler, 8-15 parts of the friction-reducing filler, and 0.8-2 parts of the additives.

[0012] The amount of bismaleimide used is 5-8% of the mass of the mercapto-modified reinforcing filler, and the amount of photoinitiator used is 1-3% of the mass of bismaleimide. In practical applications, the bismaleimide and photoinitiator can be added in excess, preferably in excess of 1.5-2 times.

[0013] In some embodiments, the method of thiol modification is: to perform a silane reaction using a thiol silane coupling agent.

[0014] In some examples, the mercaptosilane coupling agent includes KH-590.

[0015] In some embodiments, the reinforcing filler includes at least one of carbon fiber powder, aramid pulp, mineral fiber, and calcium sulfate whiskers.

[0016] It is worth noting that the reinforcing fillers provide mechanical strength to the friction material and are the main load-bearing components. They are mostly fibrous or needle-like, and their reinforcing effect is highly dependent on the effective transfer of interfacial shear stress. Poor interfacial bonding makes them prone to pull-out and failure under external force, thus being most affected by the binder content. Among them, carbon fiber powder has high-temperature resistance, maintaining high mechanical strength even at high temperatures, resisting tension and bending, and preventing material cracking; aramid pulp has a branched structure, forming physical entanglement with other raw materials, which can improve the toughness of the friction material; mineral fibers, including sepiolite and wollastonite fibers, are low-cost, can fill spaces, and provide moderate mechanical support; calcium sulfate whiskers have a needle-like structure, which can fill tiny pores, maintain material integrity, and prevent high-temperature collapse.

[0017] In some embodiments, the friction-enhancing filler includes at least one of sapphire, nano-silicon carbide, kaolin, precipitated barium sulfate, wollastonite powder, and silicon nitride.

[0018] It is worth noting that the friction-enhancing filler provides a stable coefficient of friction for the friction material; sapphire has high hardness and does not soften at high temperatures, thus providing stable basic friction; nano-silicon carbide can form a uniform friction film on the friction surface, providing wear resistance and remaining stable at high temperatures; kaolin, after calcination, has a layered structure, which, when combined with other hard particles, can disperse stress; precipitated barium sulfate has high density and chemical pores, which can fill pores and stabilize friction; wollastonite powder has low cost, and its fibrous structure has a certain mechanical strength, also providing friction enhancement and wear resistance; silicon nitride has extremely high hardness, almost no wear, and can cope with emergency braking situations.

[0019] In some embodiments, the friction-reducing filler includes at least one of flake graphite, polytetrafluoroethylene micro powder, antimony sulfide, molybdenum disulfide, and organosilicone powder.

[0020] It is worth noting that the friction-reducing material provides lubrication for the friction material, protects the mating disc, and reduces wear; the flake graphite has a sheet-like structure, which can form a lubricating film, help dissipate heat, and reduce grinding disc wear; the polytetrafluoroethylene micro powder has good temperature resistance and can provide continuous lubrication at high temperatures; antimony sulfide and molybdenum disulfide are layered sulfides that can maintain lubrication under high pressure and can cope with emergency braking situations; and organosilicone powder is a commonly used lubricant.

[0021] In some embodiments, the photoinitiator includes at least one of photoinitiator 1173, photoinitiator 754, and TPO.

[0022] In some embodiments, the additives include toughening agents and release agents;

[0023] The toughening agent includes 2,2'-diallylbisphenol A;

[0024] The release agent includes at least one of stearamide and erucamide.

[0025] In some examples, in step S1, the wavelength of the ultraviolet light is 365 nm;

[0026] In step S1, the photocrosslinking reaction is carried out in a dark environment;

[0027] In step S2, the mixing temperature is 50~80℃ and the mixing time is 10~15min;

[0028] In step S3, the cold pressing temperature is 50~60℃, the cold pressing pressure is 40-60MPa, and the cold pressing time is 8~15s;

[0029] In step S3, the hot pressing includes molding hot pressing and cross-linking hot pressing; the temperature of molding hot pressing is 150~160℃, the pressure of hot pressing is 20~30MPa, and the time of hot pressing is 2~3min; the temperature of cross-linking hot pressing is 180~200℃, the pressure of hot pressing is 20~30MPa, and the time of hot pressing is 30~60min.

[0030] In actual production, the blank is first cold-pressed in a cold pressing mold to obtain a cold blank, then transferred to a hot pressing mold for hot pressing, and finally transferred to an oven for heat treatment. In mass production, cold pressing, hot pressing, and heat treatment can be performed simultaneously to improve production efficiency.

[0031] In step S3, the purpose of the heat treatment is to improve production efficiency. The temperature of the heat treatment is 180~200℃, and it is carried out at normal pressure for 2~4 hours.

[0032] It is worth noting that the present invention sequentially grafts mercapto groups and bismaleimide onto the surface of the reinforcing filler, and utilizes bismaleimide (BMI) and allyl phenolic resin to form an interpenetrating polymer network, forming an interfacial IPN with the reinforcing filler as the node, thus forming a three-layer gradient structure of mercapto-BMI-allyl groups. This simultaneously improves the adhesion and flowability between fillers, enhances moldability, and the amount of resin (allyl phenolic resin + BMI) does not exceed 15 wt%, and significantly improves the heat resistance of the friction material.

[0033] Specifically, reinforcing fillers are most affected by interfacial bonding forces. Although their proportion in the total filler is not high, they are the main component affected by binder content. In contrast, while friction-increasing and friction-reducing fillers have a higher overall proportion, their impact on interfacial bonding forces is not significant. Therefore, this invention chooses to modify the reinforcing filler. BMI is a resin material with two active maleimide end groups. The C=C double bond in its molecular structure has high reactivity and can react with allyl double bonds to form a three-dimensional interpenetrating polymer network (IPN). This network structure combines rigidity, heat resistance, and a certain degree of flexibility, providing the material with good thermal stability and mechanical properties. Therefore, if BMI can be successfully introduced between the filler and the resin, acting as a "molecular bridge" connecting the filler surface at one end and crosslinking with the resin network at the other, a gradient transition interfacial layer can be constructed between the filler and the resin. This can effectively buffer the internal stress caused by the difference in thermal expansion coefficients during hot pressing, while providing sufficient space for molecular chain movement during hot pressing deformation. This overcomes the problems of decreased fluidity and stress concentration caused by the formation of rigid monolayer connections in traditional silane coupling modification. However, BMI exhibits extremely high reactivity at high temperatures (>150℃), with the reaction windows of its two maleimide double bonds being similar. Whether BMI is first crosslinked with allylphenol resin or reacted with surface-modified fillers, both end groups of BMI are easily consumed simultaneously, resulting in a crosslinked structure where both ends have reacted. Once both end groups have participated in the reaction, BMI loses its ability to react further and cannot be linked to another component.

[0034] Therefore, this invention employs a method of photocrosslinking followed by thermal curing. First, highly reactive thiol groups are introduced onto the surface of the reinforcing filler using a thiol silane coupling agent. Under mild conditions, utilizing the high selectivity and efficiency of the thiol-alkene click reaction, one maleimide double bond of BMI preferentially undergoes a Michael addition reaction with the thiol groups on the filler surface, achieving single-end chemical anchoring of BMI on the filler surface. This reaction is carried out at low temperature, effectively preventing premature activation of the other double bond of BMI. After the reaction is complete, unreacted free BMI is removed by thorough washing, ensuring that only single-end anchored BMI molecules remain on the filler surface, with the other end of the maleimide double bond intact for crosslinking with allyl groups.

[0035] In addition, allyl phenolic resin has a better wetting effect on non-polar fillers compared with ordinary phenolic resin adhesives. Although it does not form chemical bonds with friction-increasing and friction-reducing fillers, it has a physical adsorption effect, resulting in better adhesion and dispersibility than phenolic resin.

[0036] The beneficial effects of this invention are:

[0037] 1. This invention enhances the surface of the filler by grafting bismaleimide onto the filler surface with thiol-modified filler, introducing organic long chains into the filler surface, effectively improving the compatibility between the filler and the resin, reducing the viscosity of the mixture, significantly improving the fluidity during hot pressing, making the filling of complex shapes more complete, and achieving a hot pressing pass rate of over 86%.

[0038] 2. This invention utilizes the bifunctional characteristics of bismaleimide, with one end chemically bonded to the filler and the other end crosslinked with allylphenol resin, to construct a three-dimensional interfacial interpenetrating network with the filler as nodes. While using less than 15wt% of resin, the interfacial bonding strength is higher than that of traditional coupling agent treatment.

[0039] 3. In the interpenetrating network formed by the present invention, the imide ring structure of bismaleimide endows the material with excellent thermal stability. The thermal decomposition temperature is expected to be above 400℃. The interface does not debond at high temperature, the friction coefficient is stable, and the resistance to thermal degradation is excellent. Detailed Implementation

[0040] The technical solution of the present invention will be described in further detail below, but the scope of protection of the present invention is not limited to the following description.

[0041] Example 1

[0042] This embodiment provides a friction material with excellent formability, and the preparation method is as follows:

[0043] 1) Preparation of mercapto-modified reinforced fillers:

[0044] A total of 25 parts of reinforcing materials were taken, including 1 part of carbon fiber powder, 1 part of aramid pulp, 13 parts of sepiolite fiber and 10 parts of calcium sulfate whiskers.

[0045] The above-mentioned reinforcing filler was mixed evenly, and then 3 wt% KH-590 solution (solvent is 5 wt% ethanol solution, adjusted to pH=5 with glacial acetic acid) was added. The mixture was stirred and reacted at 70℃ for 2 h, filtered, and the filter residue was washed three times with ethanol and dried at 80℃ for 2 h to obtain the mercapto-modified reinforcing filler.

[0046] 2) Preparation of BMI-modified reinforced fillers:

[0047] In a dark room, 4 parts of BMI were dissolved in acetone (solid-liquid ratio 1:20 g / mL), and then 0.08 parts of photoinitiator 1173 and the above-mentioned mercapto-modified reinforcing filler were added. The mixture was ultrasonically dispersed for 5 min, and then irradiated with a 365 nm UV lamp (200 W) while stirring slowly. After 20 min, the irradiation was stopped, the acetone was removed by filtration, the mixture was washed, and then dried at 60 °C for 2 h to obtain the BMI-modified reinforcing filler.

[0048] The grafting rate was determined using thermogravimetric analysis (TGA) on parallel samples, with unmodified reinforced filler mixture and thiol-modified reinforced material as controls. The unmodified reinforced filler mixture showed almost no weight loss in the 300–500℃ range, with only a small amount of adsorbed water evaporating, indicating good thermal stability of the filler itself in this temperature range. The weight loss curve of the thiol-modified reinforced filler basically overlapped with that of the unmodified filler, and there was no obvious weight loss step in the 300–500℃ range. This may be because the thiol silane coupling agent graft layer is thin, and its thermal decomposition contributes negligibly to the total weight loss. However, the BMI-modified reinforced filler showed a significant weight loss step in the 300–500℃ range, with a weight loss rate of approximately 3.5–4.2%. This weight loss originated from the thermal decomposition of the bismaleimide molecules grafted onto the filler surface, indicating that the method of this invention successfully grafted BMI onto the surface of the reinforced material. Based on the weight loss rate at this stage, the grafting rate of BMI was calculated to be approximately 3.7–4.0%.

[0049] 3) Secret refining:

[0050] BMI modified reinforcing filler and 45 parts of friction-increasing materials (10 parts of calcined sapphire, 3 parts of nano-silicon carbide, 15 parts of calcined kaolin, 8 parts of precipitated barium sulfate, 8 parts of wollastonite powder and 1 part of silicon nitride), 12 parts of friction-reducing materials (6 parts of flake graphite, 1 part of polytetrafluoroethylene micro powder, 0.2 parts of organosilicon powder and 4.8 parts of antimony sulfide), 1.6 parts of 2,2'-diallyl bisphenol A, 0.2 parts of stearamide and 8 parts of allyl phenolic resin (etherification degree 50%) were added to a mixer and mixed. The mixture was then mixed at 60°C for 12 minutes, then removed and cooled. After being crushed by a crusher, the mixture was passed through an 18-mesh sieve to obtain granules with a particle size of less than 1 mm.

[0051] 4) Suppression:

[0052] The granules are loaded into a mold (internal spline shape, 3.2 mm thick) and pre-formed by cold pressing at 55°C and 50 MPa for 10 seconds. Then, the temperature is raised to 155°C and the pressure is 25 MPa for hot pressing for 3 minutes to allow the resin to melt and flow. Without releasing the pressure, the temperature is raised to 190°C, at which point the crosslinking reaction between BMI and allyl phenolic resin is triggered to form IPN. The temperature is maintained for 40 minutes, and then the mixture is placed in an oven and further treated at 200°C for 2 hours to obtain the friction material.

[0053] Example 2

[0054] This embodiment provides a friction material with excellent formability. The preparation method is the same as in Embodiment 1, except that the composition of the filler is adjusted, that is, step 1) is replaced with:

[0055] 1) Preparation of mercapto-modified reinforcing filler: Take a total of 20 parts of reinforcing materials, including 2 parts of carbon fiber powder, 2 parts of aramid pulp and 20 parts of calcium sulfate whiskers.

[0056] The above materials were mixed evenly, and then 3 wt% KH-590 solution (solvent is 5 wt% ethanol solution, adjusted to pH=5 with glacial acetic acid) was added. The mixture was stirred and reacted at 70℃ for 2 h, filtered, and the filter residue was washed three times with ethanol and dried at 80℃ for 2 h to obtain the mercapto-modified reinforced filler.

[0057] Example 3

[0058] This embodiment provides a friction material with excellent formability. The preparation method is the same as in Embodiment 1, except that the amount of allyl phenolic resin added is reduced, that is, step 3) is replaced with:

[0059] 3) Internal mixing: Add BMI modified reinforcing filler, 45 parts of friction-increasing material (formulation same as in Example 1), 12 parts of friction-reducing material (formulation same as in Example 1), 1.2 parts of 2,2'-diallyl bisphenol A, 0.2 parts of stearamide, and 6 parts of allyl phenolic resin (etherification degree 50%) to an internal mixer and mix. Mix at 60°C for 12 minutes, then remove and cool. After crushing, pass through an 18-mesh sieve to obtain granules with a particle size of less than 1 mm.

[0060] Comparative Example 1

[0061] This comparative example provides a friction material, using the same method as Example 1, except that BMI modification is not performed. Instead, mercapto-modified reinforcing filler is directly mixed and kneaded with friction-increasing filler, friction-reducing filler, allyl phenolic resin, and additives. The specific steps are as follows:

[0062] 1) Preparation of thiol-modified reinforced filler: Same as in Example 1.

[0063] 2) Internal mixing: The mercapto-modified reinforcing filler, 45 parts of friction-increasing material (formulation same as in Example 1), 12 parts of friction-reducing material (formulation same as in Example 1), 1.6 parts of 2,2'-diallyl bisphenol A, 0.2 parts of stearamide and 8 parts of allyl phenolic resin (etherification degree 50%) were added to an internal mixer and mixed. The mixture was then internally mixed at 60°C for 12 minutes, then removed and cooled, and ball-milled through an 18-mesh sieve to obtain granules with a particle size of less than 1 mm.

[0064] 3) Pressing: Same as in Example 1.

[0065] Comparative Example 2

[0066] This comparative example provides a friction material, using the same method as in Example 1, except that the reinforcing filler is modified with amino groups instead of thiol groups. Since the reaction between amino groups and BMI is extremely slow at low temperatures and does not undergo photocrosslinking, the reaction temperature is increased to employ a thermal crosslinking synthesis method, and the reaction time is extended to 4 hours to ensure the degree of reaction. The details are as follows:

[0067] 1) Preparation of amino-modified reinforced fillers:

[0068] A total of 25 parts of reinforcing material were taken, including 1 part carbon fiber powder, 1 part aramid pulp, 13 parts sepiolite fiber, and 10 parts calcium sulfate whiskers. The above materials were mixed evenly, and then 3 wt% KH-550 solution (solvent is 5 wt% ethanol solution, adjusted to pH=5 with glacial acetic acid) was added. The mixture was stirred at 70℃ for 2 h. After the reaction was completed, the mixture was filtered, washed three times with ethanol, and dried at 80℃ for 2 h to obtain amino-modified reinforcing filler.

[0069] 2) Preparation of BMI-modified reinforced fillers:

[0070] Four parts of BMI were dissolved in acetone (solid-liquid ratio 1:20 g / mL), and then the above-mentioned amino-modified reinforcing filler was added. The mixture was ultrasonically dispersed for 5 min, heated to 90 °C, and 0.5% of the mass of BMI in triethylamine was added as a catalyst. The mixture was stirred and reacted for 4 h. The acetone was removed by filtration, and the mixture was washed and then dried at 60 °C for 2 h to obtain the BMI-modified reinforcing filler.

[0071] 3) Intensive mixing: Same as Example 1.

[0072] 4) Pressing: Same as in Example 1.

[0073] Comparative Example 3

[0074] This comparative example provides a friction material, using the same method as in Example 1, except that photocrosslinking is not performed; instead, the materials are directly mixed, as detailed below:

[0075] 1) Preparation of thiol-modified reinforced filler: Same as in Example 1.

[0076] 2) Preparation of BMI modified reinforcing filler: Dissolve 4 parts of BMI in acetone (solid-liquid ratio 1:20 g / mL), then add mercapto-modified reinforcing filler, ultrasonically disperse for 5 min, stir for 15 min, and obtain BMI mixed reinforcing filler.

[0077] 3) Internal mixing: Add BMI mixed reinforcing filler, 45 parts of friction-increasing material (formulation same as in Example 1), 12 parts of friction-reducing material (formulation same as in Example 1), 1.6 parts of 2,2'-diallyl bisphenol A, 0.2 parts of stearamide, and 8 parts of allyl phenolic resin (etherification degree 50%, purchased from Puyang Weilin Technology Development Co., Ltd.) to an internal mixer and mix. Mix at 60°C for 12 minutes, then remove and cool, ball mill through an 18-mesh sieve to obtain granules with a particle size of less than 1 mm.

[0078] 4) Pressing: Same as in Example 1.

[0079] Comparative Example 4

[0080] This comparative example provides a friction material using a traditional direct mixing method, as detailed below:

[0081] 1) Filler preparation: Take a total of 25 parts of reinforcing materials, including 1 part of carbon fiber powder, 1 part of aramid pulp, 13 parts of sepiolite fiber and 10 parts of calcium sulfate whiskers; take a total of 45 parts of friction-increasing fillers, including 10 parts of calcined sapphire, 3 parts of nano silicon carbide, 15 parts of calcined kaolin, 8 parts of precipitated barium sulfate, 8 parts of wollastonite powder and 1 part of silicon nitride; take a total of 12 parts of friction-reducing materials, including 6 parts of flake graphite, 1 part of polytetrafluoroethylene micro powder, 0.2 parts of organosilicon powder and 4.8 parts of antimony sulfide.

[0082] 2) Internal mixing: Add the above filler and 1.6 parts of 2,2'-diallylbisphenol A, 0.2 parts of stearamide and 8 parts of allylphenol resin (etherification degree 50%) to an internal mixer and mix. Mix at 60°C for 12 minutes, then remove and cool, ball mill and pass through an 18-mesh sieve to obtain granules with a particle size of less than 1 mm.

[0083] 3) Pressing: Same as in Example 1.

[0084] Experimental Example 1

[0085] This experimental example is used to test the hot pressing pass rate of the friction materials in Examples 1-3 and Comparative Examples 1-4. The specific method is as follows:

[0086] The granules from Examples 1-3 and Comparative Examples 1-4 were subjected to the same pressing process 100 times each. The pressing die was spline-shaped and 3.2 mm thick. After hot pressing, the appearance and dimensions of each friction pad were visually inspected and measured. The following conditions were considered unqualified:

[0087] 1) Obvious cracks, missing material, loose texture, and bubbles on the surface; 2) Large color deviation; 3) Incomplete internal spline shape. The number of qualified parts in each group was counted, and the hot-pressing pass rate was calculated (pass rate = number of qualified parts / 100 × 100%). The average value was taken, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] The hot-pressing pass rates of Examples 1-3 were all higher than 86%, significantly better than those of the comparative examples. Among them, Example 1 had the highest pass rate (91%), indicating that the present invention effectively improved the forming pass rate of complex-shaped friction materials through thiol modification-photografting BMI and stepwise hot-pressing process. In contrast, the forming rate of Comparative Example 4 was only 74%, indicating that the formability of the friction material was extremely poor at this binder dosage.

[0091] Experiment Example 2

[0092] This experiment was used to test the coefficient of friction and wear rate of Examples 1-3 and Comparative Examples 1-4 at different temperatures. The specific methods are as follows:

[0093] Ten spline-shaped friction materials from Examples 1-3 and Comparative Examples 1-4 were respectively processed into ten constant-speed friction test specimens, which were then tested using a constant-speed friction testing machine (such as the XM type). The mating disc was made of HT250 gray cast iron with a Brinell hardness of 180-220 HB, and was polished with 240 grit sandpaper; the rotational speed was 480-500 r / min, and the pressure was 0.98 MPa.

[0094] The test temperatures were 100℃, 150℃, 200℃, 250℃, and 300℃. After grinding the test block for 3000 revolutions per minute, the test was performed at each temperature point for 5000 revolutions per minute. The coefficient of friction and wear rate were recorded, and the average value was taken. The wear rate was calculated using the following formula:

[0095] Wear rate (10) -7 cm 3 / N·m) = Volumetric wear / (pressure × total revolutions × friction radius)

[0096] The test results are shown in Table 2 (coefficient of friction) and Table 3 (wear rate):

[0097] Table 2

[0098]

[0099] Table 3

[0100]

[0101] As can be seen, the coefficients of friction of Examples 1-3 are significantly higher than those of the comparative examples, and remain above 0.45 at different temperatures, while the wear rates are significantly lower than those of the comparative examples. Specifically, Example 1 has a coefficient of friction of 0.49 at 200℃, and a wear rate of only 0.08 × 10⁻⁶. -7 cm 3 The coefficient of friction remains at 0.47 at 300℃, with a wear rate of only 0.12 × 10⁻⁶ N·m. -7 cm 3 With a temperature fading rate of / N·m and excellent wear resistance, it exhibits good overall performance.

[0102] Comparative Example 4, serving as a blank control, exhibited the lowest friction coefficient and the highest wear rate, indicating that the performance of the unmodified friction material was poor under low binder dosage. Comparative Example 1 showed a decrease in friction coefficient and an increase in wear rate at high temperatures, suggesting insufficient interfacial bonding and easy debonding failure at high temperatures in the absence of a BMI bridging layer. Comparative Example 2 exhibited poor wear resistance, possibly related to its low amine reactivity and selectivity, and insufficient grafting efficiency. Comparative Example 3 had the highest wear rate, indicating that ungrafted BMI could not form a stable interfacial network, resulting in significant interfacial failure at high temperatures.

[0103] In summary, the interfacial interpenetrating network constructed by thiol modification-photografting BMI-step hot pressing in this invention achieves excellent comprehensive performance with high friction coefficient and low wear rate while significantly reducing resin usage, and has good prospects for industrial application.

[0104] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a friction material with excellent formability, characterized in that, Includes the following steps: S1: Bismaleimide and mercapto-modified reinforcing filler are dispersed in an organic solvent, then a photoinitiator is added, and ultraviolet light is used to irradiate and carry out a photocrosslinking reaction. After the reaction is completed, the filler is washed to obtain bismaleimide-modified reinforcing filler. S2: Allyl phenolic resin, bismaleimide modified reinforcing filler, friction-increasing filler, friction-reducing filler and additives are mixed and kneaded, then crushed and sieved to obtain granules; S3: The granules are subjected to cold pressing and hot pressing in sequence, and then placed in an oven for heat treatment to obtain the final product.

2. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: By weight, the mixture comprises 6-8 parts of allyl phenolic resin, 15-25 parts of reinforcing filler, 40-45 parts of friction-increasing filler, 8-15 parts of friction-reducing filler, and 0.8-2 parts of the aforementioned additives.

3. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The reinforcing filler includes at least one of carbon fiber powder, aramid pulp, mineral fiber, and calcium sulfate whiskers.

4. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The friction-enhancing filler includes at least one of the following: sapphire, nano-silicon carbide, kaolin, precipitated barium sulfate, wollastonite powder, and silicon nitride. The friction-reducing filler includes at least one of flake graphite, polytetrafluoroethylene micro powder, antimony sulfide, molybdenum disulfide, and organosilicone powder.

5. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The additives include toughening agents and release agents; the toughening agent includes 2,2'-diallylbisphenol A; the release agent includes at least one of stearamide and erucamide.

6. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The photoinitiator includes at least one of photoinitiator 1173, photoinitiator 754, and TPO.

7. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The amount of bismaleimide used is 5-8% of the mass of the thiol-modified reinforcing filler, and the amount of photoinitiator used is 1-3% of the mass of bismaleimide.

8. The method for preparing the friction material with excellent formability according to claim 1, characterized in that: The method for thiol modification is as follows: a silane reaction is carried out using a thiol silane coupling agent.

9. The preparation method according to claim 1, characterized in that: In step S1, the wavelength of the ultraviolet light is 365 nm; the time of the photocrosslinking reaction is 10~60 min; In step S2, the mixing temperature is 50~80℃ and the mixing time is 10~15min; In step S3, the cold pressing temperature is 50~60℃, the cold pressing pressure is 40-60MPa, and the cold pressing time is 8~15s; In step S3, the hot pressing includes molding hot pressing and cross-linking hot pressing; the temperature of molding hot pressing is 150~160℃, the pressure of hot pressing is 20~30MPa, and the time of hot pressing is 2~3min; the temperature of cross-linking hot pressing is 180~200℃, the pressure of hot pressing is 20~30MPa, and the time of hot pressing is 30~60min.

10. A friction material prepared by the method for preparing a friction material with excellent formability as described in any one of claims 1-9.

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