Wet paper-based friction material as well as coating preparation method and application thereof

Abstract

The invention belongs to the field of friction material preparation, and discloses a wet-type paper-based friction material and a coating preparation method and application thereof. The method comprises the following steps: coating raw paper of a paper-based friction material with a carbon-based micro-nano material dispersion liquid to obtain carbon-based micro-nano material coated paper; the carbon-based micro-nano material coated paper is placed in a thermosetting resin solution to be soaked, pre-curing, hot pressing and curing are carried out, the wet-type paper-based friction material with the carbon-based micro-nano material coating is obtained, and the carbon-based micro-nano material is at least one of carbon nano tubes, nano carbon fibers, graphene, graphite or micron carbon fibers. A novel coating process is adopted, and a series of wet-type paper-based friction materials with controllable pore structures, mechanical properties and heat-conducting properties are obtained by regulating and controlling the coating amount and the coating thickness change. Compared with a traditional papermaking technology, the technology is efficient and simple, and the problems of low retention rate, long forming time, low energy efficiency ratio, low friction coefficient and the like of a carbon-based material in wet forming are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of friction materials, and particularly relates to a wet type paper-based friction material and a coating preparation method and application thereof. BACKGROUND

[0002] The wet type paper-based friction material is a porous friction material suitable for oil environment, which is prepared by a papermaking forming method with high-performance fibers as a skeleton, resin as a matrix, and friction performance regulators and fillers as aids, and has the advantages of light weight, high strength, resistance to sliding wear, and large energy load, and is widely used in clutches of passenger cars, commercial vehicles, and military equipment. With the expansion of the market scale of military vehicles, engineering vehicles, and civilian vehicles in China, the paper-based friction material is experiencing a replacement process from light load working conditions to heavy load working conditions. However, the current paper-based friction material has defects such as thermal elastic instability and unstable friction coefficient under high pressure, which limits the application of the wet type paper-based friction material.

[0003] In order to improve the comprehensive performance of the paper-based friction material, many scholars have carried out a large amount of research on formula design and process control, including the addition of high-performance fibers and resin as reinforcing phases, but the cost of the two is high, and the formula optimization design among the mixed fibers is complex and difficult. CN102864678B discloses a carbon fiber powder modified paper-based friction material and a preparation method thereof. The method introduces 50-60% carbon-based powder as a reinforcing body into the formula system, and the aramid fiber and the filler are uniformly mixed in water, a slurry addition method is used to prepare a friction material preform, then the preform is immersed in a modified phenolic resin solution for treatment, and a wet type paper-based friction material is prepared through processes such as hot pressing and curing. Although the method has a narrow pore size distribution range and good uniformity, the average dynamic friction coefficient is between 0.125-0.137, but the addition amount of the carbon-based powder is much larger than that of the prior art, the cost is high, the preparation process is complex, and the friction performance is limited.

[0004] The wet type paper-based friction material reinforced by carbon-based micro-nano materials is prepared by a traditional papermaking method. In the papermaking process, the raw materials are not uniformly dispersed, the retention rate is poor, and the large surface area fillers are easy to block the screen in the vacuum filtration process, which increases the forming time, causes the loss of carbon-based micro-nano materials to be high, and the energy efficiency ratio to be low, and seriously affects the comprehensive performance of the paper-based friction material. Therefore, it is of great significance to develop a wet type paper-based friction material preparation method with low cost, simple preparation process, and stable friction performance. SUMMARY

[0005] To overcome the shortcomings and deficiencies of the prior art, the primary object of the present application is to provide a coating preparation method of a wet type paper-based friction material.

[0006] Another object of the present application is to provide a wet type paper-based friction material.

[0007] Still another object of the present application is to provide an application of the wet paper-based friction material.

[0008] The object of the present application is achieved by the following technical solutions:

[0009] A coating preparation method of the wet paper-based friction material, comprising the following steps:

[0010] (1) coating the paper-based friction material base paper with a carbon-based micro-nano material dispersion liquid to obtain a carbon-based micro-nano material coated paper;

[0011] (2) immersing the carbon-based micro-nano material coated paper in a thermosetting resin solution, and then pre-curing, hot pressing and curing to obtain a carbon-based micro-nano material coated wet paper-based friction material.

[0012] Preferably, the carbon-based micro-nano material in step (1) is at least one of carbon nanotubes (CNTs), nano-carbon fibers (CNFs), graphene (GNPs), graphite (Gr) or micro-carbon fibers (CF).

[0013] Preferably, the carbon-based micro-nano material in step (1) is any two of carbon nanotubes, nano-carbon fibers, graphene, graphite or micro-carbon fibers, and the mass ratio of the two carbon-based micro-nano materials is 1:9 to 9:1.

[0014] Preferably, the carbon-based micro-nano material in step (1) is graphene and micro-carbon fibers (GNPs@CF), graphene and nano-carbon fibers (GNPs@CNFs), or nano-carbon fibers and micro-carbon fibers (CNFs@CF).

[0015] Preferably, the carbon-based micro-nano material dispersion liquid in step (1) is a single water dispersion liquid or a mixed water dispersion liquid.

[0016] The preparation method of the single water dispersion liquid is as follows:

[0017] The carbon-based micro-nano material is added to a polymer dispersant aqueous solution, and ultrasonic treatment is performed to obtain a single water dispersion liquid.

[0018] The concentration of the carbon-based micro-nano material in the single water dispersion liquid is 0.3 to 0.7 wt%.

[0019] The polymer dispersant is polyvinylpyrrolidone and sodium carboxymethyl cellulose, and the addition amount is 10 to 20% of the mass of the carbon-based micro-nano material, more preferably 10 to 15%.

[0020] The preparation method of the mixed water dispersion liquid is as follows:

[0021] Any two of the above single water dispersion liquids are selected, a certain amount of polymer dispersant aqueous solution is added for dilution, and shear homogenization treatment is performed to obtain a mixed dispersion liquid.

[0022] Preferably, the concentration of any carbon-based micro-nano material in the mixed aqueous dispersion is 0.15-0.45wt%.

[0023] Preferably, the shearing homogenization conditions are: rotation speed 10000-30000rpm, and processing time 10min-50min.

[0024] Preferably, the coating in step (1) is performed using an automatic feeding coating experiment machine, and the coating method is a combination of roll coating and blade coating, more preferably roll coating followed by blade coating.

[0025] The process parameters for the coating are: dispersion liquid flow rate 3-10mL / s, coating speed 2-6mm / s, coating stroke 150-250mm, coating times 1-3 times, and coating amount 3-10g / m 2 .

[0026] Preferably, the paper-based friction material base paper in step (1) is prepared by wet forming, and the specific steps are as follows:

[0027] A certain amount of raw material is weighed according to the formula, and mixed slurry is obtained by defibrating with water, and is prepared by vacuum filtration and wet forming;

[0028] The paper-based friction material base paper has a basis weight of 200-400g / m 2 , and a thickness of 0.5-1.2mm.

[0029] Preferably, the raw material includes carbon fiber, aramid fiber, natural fiber and filler.

[0030] Preferably, the raw material includes 5-40wt% carbon fiber, 5-40wt% aramid fiber, 5-40wt% natural fiber and 40-60wt% filler, and the sum of the above raw materials is 100wt%.

[0031] More preferably, the raw material includes 10-20wt% carbon fiber, 10-20wt% aramid fiber, 10-20wt% natural fiber and 50wt% filler.

[0032] Preferably, 0.5-2wt% of the dry weight of the fiber is added to the dispersion agent, and the dispersion agent is polyethylene oxide for defibrillation, and then the filler is added to form a uniform mixed slurry with water.

[0033] Preferably, the carbon fiber is one or more of polyacrylonitrile carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber and vapor-phase grown carbon fiber; and the natural fiber is cotton fiber.

[0034] The filler is one or more of graphite, diatomite and silicon dioxide.

[0035] The vacuum filtration condition is that the vacuum degree is 0.01-0.1 Mpa, and the filtration time is 1-5 min.

[0036] Preferably, the thermosetting resin in step (2) is one or more than two of phenolic resin, cashew nut shell oil modified phenolic resin, boron modified phenolic resin, melamine-cashew nut shell oil modified phenolic resin, and the impregnation time is 5-10 min.

[0037] The pre-curing temperature is 150-180℃, and the pre-curing time is 30-60 min.

[0038] The hot-pressing temperature is 150-180℃, the hot-pressing pressure is 2-8 Mpa, and the hot-pressing time is 1-5 min.

[0039] The curing temperature is 150-180℃, and the curing time is 1-2 h.

[0040] A wet type paper-based friction material prepared by the above method.

[0041] Application of the above wet type paper-based friction material in clutch and brake devices of engineering machinery, heavy load vehicles, cars, motorcycles or ships.

[0042] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0043] (1) The present application proposes a wet type paper-based friction material prepared based on a coating method, the above single / mixed carbon-based micro-nano material water dispersion liquid is placed in a sample tank, and the original paper is coated by using an automatic feeding coating experiment machine, a series of wet type paper-based friction materials with controllable pore structure, mechanical properties and thermal conductivity are obtained by adjusting the coating amount and coating thickness.

[0044] (2) The present application can make the retention rate of carbon-based micro-nano materials reach more than 90%, which is beneficial to improve the utilization efficiency ratio of CNTs, CNFs and GNPs in the wet type paper-based friction material.

[0045] (3) The present application improves the thermal conductivity of the paper-based friction material by the method of coating the carbon-based micro-nano material dispersion liquid, when the coating amount of the GNPs dispersion liquid is 5 g / m 2 , the thermal conductivity coefficient in X / Y direction can reach 1.7 W / (m·K), which is improved by 35.9% compared with the traditional papermaking method.

[0046] (4) The present application improves the friction performance of paper-based friction materials by multi-scale mixed micro-nano carbon particle coating formula. When GNPs and CNFs are 1:9, the average dynamic friction coefficient of the prepared paper-based friction material is 0.131, 0.138 and 0.143 under brake pressures of 0.775 MPa, 1.94 MPa and 2.96 MPa, respectively. Compared with the traditional papermaking method, the friction coefficient is increased by 9.4%, 40.7% and 52.9%, respectively. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Preparation flow chart of carbon-based micro-nano material coated composite wet paper-based friction material.

[0048] Figure 2 Retention rate comparison of carbon-based micro-nano material under different preparation methods.

[0049] Figure 3 Thermal conductivity comparison of carbon-based micro-nano material under different preparation methods.

[0050] Figure 4 Average dynamic friction coefficient and coefficient of variation of carbon-based micro-nano material coated enhanced paper-based friction material.

[0051] Figure 5 Wear rate of carbon-based micro-nano material coated enhanced paper-based friction material. DETAILED DESCRIPTION

[0052] The present application will be further specifically and in detail described below in combination with specific examples, but the embodiments of the present application are not limited thereto. For process parameters not specifically mentioned, conventional techniques can be referred to.

[0053] Example 1

[0054] Example 1 is to illustrate the influence of single carbon-based micro-nano material direct addition method on the performance of paper-based friction material.

[0055] Step 1: PVP and CMC are added to water to obtain a PVP / CMC aqueous solution, and then CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano materials are added to the PVP / CMC aqueous solution, the addition amount of PVP and CMC is 10% of the mass of the carbon-based micro-nano material, to prepare a 4wt% water dispersion, then ultrasonic treatment is performed by using an ultrasonic cell crusher, and then the high-shear homogenizer is treated for 10 min at a speed of 20000 rpm, to prepare five different single carbon-based micro-nano material dispersions for standby.

[0056] Step 2: According to the formula in Table 1, the corresponding mass fraction of raw materials was weighed, and the carbon fiber, aramid fiber, cotton fiber were added in sequence, then 1wt% of polyethylene oxide (accounting for the absolute dry mass of the fiber) was added for defibration, and then graphite, diatomite, silicon dioxide and water were added for defibration to form a uniform mixed slurry, and then the CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano material water dispersions prepared in step 1 were added, wherein the addition amount of the above five kinds of carbon-based micro-nano materials was 2wt% (carbon-based micro-nano materials accounted for 2wt% of the absolute dry mass of the fiber and filler), and finally poured into a former, vacuum filtration, and wet forming technology was used to prepare a wet paper-based friction material with a basis weight of 272.3g / m 2 , and a thickness of 1.008mm.

[0057] Step 3: The raw paper obtained in step 2 was placed in a cashew shell oil modified phenolic resin solution and immersed under vacuum conditions (immersion for 5min), and the glue amount was controlled at 30%, and after the ethanol was volatilized, the sample was pre-cured at 160℃ for 20min.

[0058] Step 4: The sample after pre-curing was placed in a flat plate hot press, and hot pressing was carried out at 12MPa and 170℃, and then post-curing was carried out to obtain a paper-based friction material containing a direct addition method.

[0059] Step 5: The carbon-based micro-nano material friction material obtained in step 4 was subjected to retention rate test and thermal conductivity performance test, and the retention rate test standard referred to GB / T 24328.1-2009, and the thermal conductivity performance test standard referred to ASTM E 1461-2011 "Standard Test Method for Thermal Diffusivity by Flash Method".

[0060] Example 1 shows that among the above five kinds of carbon-based micro-nano material direct addition method for preparing wet paper-based friction material, the retention rate of CNTs is 70.7%, and the X / Y thermal conductivity coefficient is 0.7W / (m·K); the retention rate of CNFs is 47.3%, and the X / Y thermal conductivity coefficient is 0.8W / (m·K); the retention rate of GNPs is 77.8%, and the X / Y thermal conductivity coefficient is 1.3W / (m·K); the retention rate of Gr is 64.5%, and the X / Y thermal conductivity coefficient is 0.8W / (m·K); the retention rate of CF is 41.9%, and the X / Y thermal conductivity coefficient is 0.9W / (m·K).

[0061] Table 1 Raw material formula of paper-based friction material in direct addition method

[0062]

[0063] Example 2

[0064] The paper-based friction materials of Examples 2-4 are prepared by the method of coating single carbon-based micro-nano materials. The formulations of the paper-based friction materials of Examples 2-4 are shown in Table 2.

[0065] Table 2 Formulation of raw materials of paper-based friction materials

[0066]

[0067] Step 1: PVP and CMC are added to water to obtain a PVP / CMC aqueous solution. CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano materials are then added to the PVP / CMC aqueous solution, respectively. The addition amount of PVP and CMC is 10% of the mass of the carbon-based micro-nano materials. CNTs water dispersion with a concentration of 0.3wt%, CNFs water dispersion with a concentration of 0.7wt%, GNPs water dispersion with a concentration of 0.5wt%, Gr water dispersion with a concentration of 0.5wt% and CF water dispersion with a concentration of 0.5wt% are prepared. The dispersions are then treated by an ultrasonic cell crusher for ultrasonic treatment. The dispersions are then treated by a high-shear homogenizer for 10 minutes at a speed of 20000 rpm to obtain five different single carbon-based micro-nano material dispersions for standby.

[0068] Step 2: The corresponding mass fraction of raw materials is weighed according to Table 2. Carbon fiber, aramid fiber and cotton fiber are added in sequence. 1wt% of polyethylene oxide (based on the absolute dry weight of the fibers) is then added for defibration. Graphite, diatomite and silicon dioxide are then added for defibration to form a uniform mixed slurry. The slurry is then poured into a former. The paper-based friction material raw paper with a basis weight of 270.1g / m 2 and a thickness of 1.062mm is prepared by vacuum filtration and wet forming technology.

[0069] Step 3: The raw paper obtained in Step 2 is placed on the plane of an automatic feeding and coating testing machine. The CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano material dispersions prepared in Step 1 are placed in sample tanks. After connecting the air source, the pressure switch is adjusted to control the flow rate of the dispersions at 6ml / s. The coating speed is 2mm / s, and the coating stroke is 210mm. The coating is carried out by a combination of roller coating and blade coating (first roller coating and then blade coating). After the feeding is completed, the paper is vacuum filtered for 1 minute, dried, and the carbon-based micro-nano material coated paper is obtained. The coating is carried out twice, and the coating amount is controlled at 5g / m 2 .

[0070] Step 4: The single carbon-based micro-nano material coated paper obtained in Step 3 is vacuum impregnated in cashew shell oil modified phenolic resin solution. The glue amount is controlled at 30%. After the ethanol is volatilized, the sample is pre-cured at 160℃ for 10 minutes. Finally, the sample is hot-pressed at 10MPa and 160℃ for post-curing to obtain five paper-based friction materials with single carbon-based micro-nano material coatings.

[0071] The paper-based friction material of the five single carbon-based micro-nano material coatings was tested for retention rate and thermal conductivity. The results showed that in the paper-based friction material of the five carbon-based micro-nano material coatings of Example 2, the retention rate of CNTs was 83.6%, the X / Y thermal conductivity coefficient was 0.8 W / (m·K); the retention rate of CNFs was 81.0%, the X / Y thermal conductivity coefficient was 0.9 W / (m·K); the retention rate of GNPs was 84.3%, the X / Y thermal conductivity coefficient was 1.4 W / (m·K); the retention rate of Gr was 84.7%, the X / Y thermal conductivity coefficient was 0.9 W / (m·K); the retention rate of CF was 85.8%, the X / Y thermal conductivity coefficient was 0.7 W / (m·K).

[0072] Example 3

[0073] Step 1: PVP and CMC were added to water to obtain a PVP / CMC aqueous solution, and then CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano materials were added to the PVP / CMC aqueous solution, respectively, and the addition amount of PVP and CMC was 10% of the mass of the carbon-based micro-nano material. A CNTs water dispersion with a concentration of 0.3wt%, a CNFs water dispersion with a concentration of 0.7wt%, a GNPs water dispersion with a concentration of 0.5wt%, a Gr water dispersion with a concentration of 0.5wt% and a CF water dispersion with a concentration of 0.5wt% were prepared, and then ultrasonic treatment was performed using an ultrasonic cell crusher. The dispersion was treated by a high-shear homogenizer for 10 min at a speed of 20,000 rpm to obtain five different single carbon-based micro-nano material dispersions for standby.

[0074] Step 2: The raw materials with corresponding mass fractions were weighed according to Table 2, and then carbon fibers, aramid fibers, cotton fibers were added in sequence, followed by 1wt% polyethylene oxide (based on the absolute dry weight of the fibers) for defibration, and then graphite, diatomite and silicon dioxide were added for defibration to form a uniform mixed slurry, which was then poured into a former, and a paper-based friction material base paper with a basis weight of 277.9g / m 2 and a thickness of 1.111mm was prepared by vacuum filtration and wet forming technology.

[0075] Step 3: The base paper obtained in Step 2 was placed on the plane of an automatic feeding and coating test machine, and the CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano material dispersions prepared in Step 1 were placed in sample tanks. After connecting the gas source, the pressure switch was adjusted to control the dispersion flow rate at 6ml / s, the coating speed at 2mm / s, and the coating stroke at 210mm. The coating was combined with roll coating and blade coating. After the feeding was completed, vacuum filtration was performed for 1min, and then drying was performed to obtain carbon-based micro-nano material coated paper. The coating times were 2 times, and the coating amount was controlled at 5g / m 2 .

[0076] Step 4: The paper coated with different single carbon-based micro-nano materials obtained in step 3 was placed in a cashew nut shell oil modified phenolic resin solution, vacuum impregnated, and the glue amount was controlled to be 30%. After the ethanol was volatilized, the sample was pre-cured at 170°C for 20 min. Finally, the sample was hot-pressed at 12 MPa and 170°C for post-curing to obtain a paper-based friction material coated with single carbon-based micro-nano materials.

[0077] The retention rate and thermal conductivity of the paper-based friction materials coated with the five kinds of single carbon-based micro-nano materials were tested. The results showed that in the paper-based friction material coated with the five kinds of carbon-based micro-nano materials of Example 3, the retention rate of CNTs was 88.6%, the X / Y thermal conductivity was 0.9 W / (m·K); the retention rate of CNFs was 87.0%, the X / Y thermal conductivity was 0.8 W / (m·K); the retention rate of GNPs was 89.3%, the X / Y thermal conductivity was 1.6 W / (m·K); the retention rate of Gr was 89.7%, the X / Y thermal conductivity was 0.7 W / (m·K); and the retention rate of CF was 95.8%, the X / Y thermal conductivity was 0.7 W / (m·K).

[0078] Example 4

[0079] Step 1: PVP and CMC were added to water to obtain a PVP / CMC aqueous solution, and then CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano materials were added to the PVP / CMC aqueous solution, and the addition amount of PVP and CMC was 10% of the mass of the carbon-based micro-nano materials. A CNTs water dispersion with a concentration of 0.3wt%, a CNFs water dispersion with a concentration of 0.7wt%, a GNPs water dispersion with a concentration of 0.5wt%, a Gr water dispersion with a concentration of 0.5wt%, and a CF water dispersion with a concentration of 0.5wt% were prepared, and then ultrasonic treatment was performed using an ultrasonic cell disruptor. The dispersion was treated by a high-shear homogenizer for 10 min at a speed of 20000 rpm to obtain different single carbon-based micro-nano material dispersions for standby.

[0080] Step 2: The raw materials with corresponding mass fractions were weighed according to Table 2, and then carbon fibers, aramid fibers, cotton fibers, 1wt% polyethylene oxide (based on the absolute dry mass of the fibers) were added in sequence for defibration, and then graphite, diatomite, silicon dioxide and water were added for defibration to form a uniform mixed slurry. The slurry was poured into a former, and a paper-based friction material base paper with a basis weight of 279.5g / m 2 and a thickness of 1.025mm was prepared by vacuum filtration and wet forming technology.

[0081] Step 3: The base paper obtained in step 2 was placed on the automatic feeding coating tester plane, and the CNTs, CNFs, GNPs, Gr and CF carbon-based micro-nano material dispersion liquid prepared in step 1 was placed in the sample tank. After connecting the gas source, the pressure switch was adjusted to control the dispersion liquid flow rate to be 6 ml / s, the coating speed was 2 mm / s, the coating stroke was 210 mm, and the coating was combined with roll coating and blade coating. After the feeding was completed, vacuum filtration was performed for 1 min, and drying was performed to prepare the carbon-based micro-nano material coated paper, wherein the coating times were 2 times, and the coating amount was controlled to be 5 g / m 2 .

[0082] Step 4: The different single carbon-based micro-nano material coated paper obtained in step 3 was placed in the cashew shell oil modified phenolic resin solution, vacuum impregnated, and the sizing amount was controlled to be 30%. After the ethanol was volatilized, the sample was pre-cured at 170°C for 30 min. Finally, the sample was hot-pressed at 15 MPa and 170°C for post-curing to prepare the single carbon-based micro-nano material coated paper-based friction material.

[0083] The retention rate test and the thermal conductivity test were performed on the five kinds of single carbon-based micro-nano material coated paper-based friction materials. The results showed that in the five kinds of carbon-based micro-nano material coated paper-based friction materials of example 4, the retention rate of CNTs was 93.6%, the X / Y thermal conductivity coefficient was 0.9 W / (m·K); the retention rate of CNFs was 91.0%, the X / Y thermal conductivity coefficient was 0.9 W / (m·K); the retention rate of GNPs was 94.3%, the X / Y thermal conductivity coefficient was 1.7 W / (m·K); the retention rate of Gr was 94.7%, the X / Y thermal conductivity coefficient was 0.7 W / (m·K); and the retention rate of CF was 95.8%, the X / Y thermal conductivity coefficient was 0.7 W / (m·K).

[0084] The retention rates of the five kinds of carbon-based micro-nano materials in example 1 were all lower than 80%, and the retention rates of CF and CNF were the lowest. The retention rates of the five kinds of carbon-based micro-nano materials in examples 2-4 were all above 90%, which was 14.9%-53.9% higher than that of the direct addition method. In the coating method, the X / Y thermal conductivity coefficient of the carbon-based micro-nano material paper-based friction material containing CNTs, CNFs and GNPs was improved, and the X / Y thermal conductivity coefficient of the carbon-based micro-nano material paper-based friction material containing Gr and CF was basically unchanged.

[0085] Example 5

[0086] Examples 5-6 illustrate the influence of coating process parameters on the performance of mixed carbon-based micro-nano material coated paper-based friction materials.

[0087] Step 1: First, the above method was used to prepare 0.5wt% GNPs and 0.7wt% CF water dispersions, respectively, then mixed according to the carbon material concentration corresponding to the mass of the water dispersion in Table 2, the volume of the added single dispersion was controlled to adjust the mass ratio of GNPs to CF to be 1:9, 3:7, 5:5, 7:3 and 9:1, respectively. Finally, the mixed carbon-based micro-nano material dispersion was obtained by high shear homogenization treatment for 20 min at a speed of 10000 rpm.

[0088] Step 2: According to the formulation of Example 4 in Table 2, a certain mass fraction of raw materials was weighed, and then carbon fibers, aramid fibers, cotton fibers were added in turn, followed by 1wt% polyethylene oxide (based on the absolute dry mass of the fibers) for defibration, and then graphite, diatomite, silicon dioxide and water were added to form a uniform mixed slurry, which was then poured into a former and prepared into a paper-based friction material raw paper with a basis weight of 281.2g / m 2 , and a thickness of 1.029mm by vacuum filtration and wet forming technology.

[0089] Step 3: The raw paper obtained in Step 2 was placed on the plane of the automatic feeding and coating tester, and different mass ratios of mixed carbon-based micro-nano material dispersion were placed in the sample tank. After connecting the gas source, the pressure switch was adjusted to control the flow rate of the dispersion to be 8ml / s, the coating speed was 1mm / s, the coating stroke was 220mm, and the coating was combined with roll coating and blade coating. After the feeding was completed, vacuum filtration was carried out for 1min, and drying was carried out to obtain mixed carbon-based micro-nano material coated paper, wherein the coating times were 1 times and the coating amount was controlled to be 10g / m 2 .

[0090] Step 4: The mixed carbon-based micro-nano material coated paper obtained in Step 3 was placed in the cashew shell oil modified phenolic resin solution and vacuum impregnated, and the sizing amount was controlled to be 30%. After the ethanol was volatilized, the sample was pre-cured at 170℃ for 30min. Finally, the sample was hot-pressed at 15MPa and 170℃ for post-curing to obtain a mixed carbon-based micro-nano material coated paper-based friction material. The mixed carbon-based micro-nano material coated paper-based friction materials with GNPs to CF mass ratios of 1:9, 3:7, 5:5, 7:3 and 9:1 were respectively marked as GC-19, GC-37, GC-55, GC-19, GC-73 and GC-91.

[0091] Step 5: The mixed carbon-based micro-nano material coated paper-based friction material obtained in Step 4 was tested for friction performance. The friction performance test method was tested by Bruker UMT friction and wear tester clutch module. The friction coefficient curve of each sample was tested at an oil temperature of 120℃, a load pressure of 0.775MPa, 1.94MPa and 2.96MPa, respectively, and a test speed from 0m / s to 1.65m / s, and the friction coefficient value was recorded.

[0092] Example 5 shows that the average dynamic friction coefficient of all the mixed carbon-based micro-nano material coated paper-based friction materials is basically maintained above 0.12 at 0.775 MPa, among which GC-19 has the highest average dynamic friction coefficient at 0.775 MPa, 1.94 MPa and 2.96 MPa braking pressure, which are 0.120, 0.129 and 0.133 respectively, and the relative A0 is increased by 8.6%, 33.7% and 45.9% respectively. And when the mass ratio of GNPs to CF is 1:9, the wear rate of the paper-based friction material prepared is as low as 0.6*10 -7 (m 3 / N·m).

[0093] Example 6

[0094] Step 1: First, the above method is used to prepare 0.5wt% GNPs and 0.7wt% CF water dispersions respectively, then the water dispersions corresponding to the mass of the carbon material concentration in Table 3 are mixed, the mass ratio of GNPs to CF is controlled to be 1:9, 3:7, 5:5, 7:3 and 9:1 respectively, a certain amount of PVP / CMC aqueous solution is added for dilution, and finally the mixed carbon-based micro-nano material dispersion is obtained by high shear homogenization treatment for 20 min at a speed of 10000 rpm.

[0095] Step 2: According to the formula of Example 4 in Table 2, a certain mass fraction of raw materials is weighed, carbon fibers, aramid fibers, cotton fibers are added in turn, 1wt% polyethylene oxide (based on the absolute dry mass of fibers) is added for defibration, then graphite, diatomite, silicon dioxide and water are added for defibration to form a uniform mixed slurry, which is poured into a former, and a paper-based friction material base paper with a basis weight of 284.2g / m 2 and a thickness of 1.031mm is prepared by vacuum filtration and wet forming technology.

[0096] Step 3: The base paper obtained in step 2 is placed on the plane of the automatic feeding and coating test machine, and the mixed carbon-based micro-nano material dispersion with different mass ratios is placed in the sample tank. After connecting the gas source, the pressure switch is adjusted to control the dispersion flow rate to be 6ml / s, the coating speed is 2mm / s, the coating stroke is 210mm, the coating is combined with roll coating and blade coating, and after the feeding is completed, vacuum filtration is carried out for 1min, and drying is carried out to prepare a mixed carbon-based micro-nano material coated paper, wherein the coating times are 2 times and the coating amount is controlled to be 5g / m 2 .

[0097] Step 4: The paper coated with the mixed carbon-based micro-nano materials of different mass ratios obtained in step 3 was placed in a cashew nut shell oil modified phenolic resin solution and vacuum impregnated, with the glue amount controlled at 30%. After the ethanol was volatilized, the sample was pre-cured at 170°C for 30 min. Finally, the sample was hot-pressed at 15 MPa and 170°C for post-curing, to obtain the paper-based friction material coated with the mixed carbon-based micro-nano materials. The paper-based friction materials coated with the mixed carbon-based micro-nano materials with the ratio of CF to GNPs being 1:9, 3:7, 5:5, 7:3 and 9:1 were respectively marked as GC-19, GC-37, GC-55, GC-19, GC-73 and GC-91.

[0098] Example 6 shows that at 0.775 MPa, the average dynamic friction coefficients of all the paper-based friction materials coated with the mixed carbon-based micro-nano materials substantially maintained above 0.12, among which the average dynamic friction coefficients of GC-19 were the highest at 0.775 MPa, 1.94 MPa and 2.96 MPa braking pressures, being 0.123, 0.133 and 0.137 respectively, which were respectively increased by 8.8%, 35.7% and 48.9% compared with A0. And when the mass ratio of GNPs to CF was 1:9, the wear rate of the prepared paper-based friction material was as low as 0.6*10 -7 (m 3 / N·m).

[0099] Based on Examples 5-6, it is concluded that the optimization of the coating process parameters can improve the uniformity of the coating liquid, the bonding force between the coating and the paper-based friction material, and thus the friction performance of the paper-based friction material. It is proved that when the flow rate of the dispersion liquid is 6 ml / s, the coating speed is 2 mm / s, the coating stroke is 210 mm, the coating times are 2 and the coating amount is 5 g / m 2 , the coating process is the best.

[0100] Table 3 Preparation conditions of GNPs@CF water dispersion liquid and coating amount of paper-based friction material

[0101]

[0102] Note: All the concentrations in the table are the concentrations of carbon materials in 1000 ml of mixed water dispersion liquid.

[0103] A0 is the wet paper-based friction material prepared according to the formula of Example 4 by adding method in pulp, without adding any carbon-based micro-nano materials, which is used as a blank control group; CF-2 is the sample prepared by coating method with the CF concentration being 0.5 wt% and the coating amount being 5 g / m 2 .

[0104] Example 7

[0105] Step 1: First, the above method was used to prepare 0.7wt% CNFs and 0.7wt% CF water dispersions, respectively, then the water dispersions were mixed according to the mass corresponding to the material concentration in Table 3, and the mass ratio of CNFs to CF was controlled to be 1:9, 3:7, 5:5, 7:3 and 9:1, respectively, a certain amount of PVP / CMC aqueous solution was added for dilution, and finally the mixed carbon-based micro-nano material dispersion was obtained by high shear homogenization treatment for 20 min at a speed of 10000 rpm.

[0106] Step 2: According to the formula of Example 4, a certain mass fraction of raw materials was weighed and mixed with water to form a uniform mixed slurry, which was poured into a former and then vacuum filtered to prepare a paper-based friction material with a mass of 282.6g / m 2 and a thickness of 1.026mm.

[0107] Step 3: The original paper obtained in Step 2 was placed on the plane of the automatic feeding and coating test machine, and different mass ratios of mixed carbon-based micro-nano material dispersion were placed in the sample tank. After connecting the gas source and adjusting the pressure switch, the flow rate of the dispersion was controlled to be 6ml / s, the coating speed was 2mm / s, the coating stroke was 210mm, and the coating was carried out by combining roller coating and blade coating. After the feeding was completed, vacuum filtration was carried out for 1min, and then drying was carried out to obtain a mixed carbon-based micro-nano material coated paper, wherein the coating times were 2 times and the coating amount was controlled to be 5g / m 2 .

[0108] Step 4: The mixed carbon-based micro-nano material coated paper obtained in Step 3 was placed in a cashew shell oil modified phenolic resin solution and vacuum impregnated, and the glue amount was controlled to be 30%. After the ethanol was volatilized, the sample was pre-cured at 170℃ for 30min. Finally, the sample was hot-pressed at 15MPa and 170℃ for post-curing to obtain a mixed carbon-based micro-nano material coated paper-based friction material. The mixed carbon-based micro-nano material coated paper-based friction materials with CNFs to CF mass ratios of 1:9, 3:7, 5:5, 7:3 and 9:1 were denoted as VC-19, VC-37, VC-55, VC-73 and VC-91, respectively.

[0109] Example 7 shows that at 0.775MPa, the average dynamic friction coefficients of all the mixed carbon-based micro-nano material coated paper-based friction materials basically maintained above 0.125, among which the average dynamic friction coefficients of VC-19 were the highest at 0.775MPa, 1.94MPa and 2.96MPa, which were 0.127, 0.135 and 0.138, respectively, and the relative A0 was increased by 8.9%, 38.7% and 49.9%, respectively. When the mass ratio of CNFs to CF was 1:9, the wear rate of the prepared paper-based friction material was as low as 0.4×10 -7 (m 3 / N·m).

[0110] Table 4 CNFs@CF aqueous dispersion preparation conditions and paper-based friction material coating amount

[0111]

[0112] Note: CNFs-2 is a CNFs dispersion with a concentration of 0.5wt%, and the coating amount is 5g / m 2 .

[0113] Example 8

[0114] Step 1: First, 0.7wt% CNFs and 0.5wt% GNPs dispersions were prepared according to the above method, respectively, then the water dispersions with the corresponding mass of material concentration were mixed according to Table 5, and the mass ratio of GNPs to CNFs was controlled to be 1:9, 3:7, 5:5, 3:7 and 9:1, respectively, a certain amount of PVP / CMC aqueous solution was added for dilution, and finally the mixed carbon-based micro-nano material dispersion was obtained by high shear homogenization treatment for 20min at a speed of 10000rpm.

[0115] Step 2: According to the formula of Example 4, a certain mass fraction of raw materials was weighed, and carbon fibers, aramid fibers, cotton fibers were added in turn, then 1wt% polyethylene oxide (based on the absolute dry mass of fibers) was added for defibration, then graphite, diatomite, silicon dioxide and water were added for defibration to form a uniform mixed slurry, which was then poured into a former, and a paper-based friction material with a basis weight of 285.2g / m 2 and a thickness of 1.034mm was prepared by vacuum filtration and wet forming technology.

[0116] Step 3: The original paper obtained in Step 2 was placed on the plane of the automatic feeding and coating test machine, and the mixed carbon-based micro-nano material dispersion with different mass ratios was placed in the sample tank. After connecting the air source, the pressure switch was adjusted to control the dispersion flow rate to be 6ml / s, the coating speed was 2mm / s, the coating stroke was 210mm, and the coating was carried out by combining roller coating and blade coating. After the feeding was completed, vacuum filtration was carried out for 1min, and the mixed carbon-based micro-nano material coated paper was obtained by drying, wherein the coating times were 2 times and the coating amount was controlled to be 5g / m 2 .

[0117] Step 4: The paper coated with the mixed carbon-based micro-nano materials of different mass ratios obtained in step 3 was placed in a cashew nut shell oil modified phenol formaldehyde resin solution, vacuum impregnated, and the glue amount was controlled to be 30%. After the ethanol was volatilized, the sample was pre-cured at 170°C for 30 min. Finally, the sample was hot-pressed at 15 MPa and 170°C for post-curing to obtain the paper-based friction material coated with the mixed carbon-based micro-nano materials. The paper-based friction materials coated with the mixed carbon-based micro-nano materials with the mass ratio of CNFs to GNPs being 1:9, 3:7, 5:5, 3:7 and 9:1 were denoted as VG-19, VG-37, VG-55, VG-73 and VG-91, respectively.

[0118] Example 8 shows that at 0.775 MPa, the average dynamic friction coefficients of all the paper-based friction materials coated with the mixed carbon-based micro-nano materials substantially maintained above 0.130. Among them, the average dynamic friction coefficients of VG-19 were the highest at 0.131, 0.138 and 0.143 under the braking pressures of 0.775 MPa, 1.94 MPa and 2.96 MPa, respectively, which were increased by 9.4%, 40.7% and 52.9% compared with A0, respectively. When the mass ratio of CNFs to GNPs was 1:9, the wear rate of the prepared paper-based friction material was as low as 0.3*10 -7 (m 3 / N·m). It is indicated that the synergistic effect of GNPs and CNFs promotes the reduction of the wear rate of the material.

[0119] Table 5: Preparation conditions of GNPs@CNFs aqueous dispersion and coating amount of paper-based friction material

[0120]

[0121] Note: GNPs-2 is GNPs with a concentration of 0.5wt%, which is coated by using a coating method, and the coating amount is 5g / m 2 .

[0122] Examples 7-8 prove that the mixed micro-nano carbon particle coated wet paper-based friction material can make up for the defects of single carbon particle coating while retaining the advantages of enhanced friction performance, and greatly improve the energy efficiency ratio of each carbon material.

[0123] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be included in the protection scope of the present application.

Claims

1. A method for preparing a wet paper-based friction material by coating, characterized in that, Includes the following steps: (1) A carbon-based micro-nano material dispersion was used to coat the paper base paper of the paper-based friction material to obtain carbon-based micro-nano material coated paper; (2) The carbon-based micro-nano material coated paper is immersed in a thermosetting resin solution, and then pre-cured, hot-pressed and cured to obtain a wet paper-based friction material with carbon-based micro-nano material coating.

2. The method for preparing wet paper-based friction material by coating according to claim 1, characterized in that, The carbon-based micro / nano material mentioned in step (1) is at least one of carbon nanotubes, carbon nanofibers, graphene, graphite, or micron-sized carbon fibers.

3. The method for preparing wet paper-based friction material according to claim 2, characterized in that, The carbon-based micro / nano material mentioned in step (1) is any two of carbon nanotubes, carbon nanofibers, graphene, graphite, or micron-sized carbon fibers, and the mass ratio of the two carbon-based micro / nano materials is 1:9 to 9:

1.

4. The method for preparing wet paper-based friction material by coating according to claim 1, characterized in that, The carbon-based micro / nano material dispersion in step (1) is a single aqueous dispersion or a mixed aqueous dispersion; The method for preparing the single-aqueous dispersion is as follows: Carbon-based micro / nano materials were added to an aqueous solution of a polymer dispersant and sonicated to obtain a single aqueous dispersion; the concentration of carbon-based micro / nano materials in the single aqueous dispersion was 0.3–0.7 wt%. The method for preparing the mixed aqueous dispersion is as follows: Select any two of the above single aqueous dispersions, dilute them, and perform shearing and homogenization to obtain a mixed aqueous dispersion, wherein the concentration of any carbon-based micro / nano material in the mixed aqueous dispersion is 0.15–0.45 wt%.

5. The method for preparing wet paper-based friction material according to claim 1, characterized in that, The coating method described in step (1) is a combination of roller coating and blade coating; The coating process parameters are as follows: dispersion flow rate of 3-10 mL / s, coating speed of 2-6 mm / s, coating stroke of 150-250 mm, coating times of 1-3 times, and coating amount of 3-10 g / m³. 2 .

6. The method for preparing wet paper-based friction material according to claim 1, characterized in that, The paper-based friction material base paper described in step (1) is prepared by wet forming, and the specific steps are as follows: A certain amount of raw materials are weighed according to the formula, dissolved with water to obtain a mixed slurry, which is then vacuum filtered and wet-formed to obtain the final product. The basis weight of the paper-based friction material is 200-400 g / m³. 2 The thickness is 0.5-1.2mm.

7. The method for preparing wet paper-based friction material according to claim 6, characterized in that, The raw materials include carbon fiber, aramid fiber, natural fiber, and filler; The vacuum filtration conditions are: vacuum degree of 0.01-0.1 MPa, filtration time of 1-5 min.

8. The method for preparing wet paper-based friction material according to claim 1, characterized in that, The thermosetting resin in step (2) is one or more of the following: phenolic resin, cashew nut shell oil modified phenolic resin, boron modified phenolic resin, and melamine-cashew nut shell oil modified phenolic resin, and the impregnation time is 5-10 min. The pre-curing temperature is 150-180℃, and the pre-curing time is 30-60 min; The hot pressing temperature is 150-180℃, the hot pressing pressure is 2-8 MPa, and the hot pressing time is 1-5 min; The curing temperature is 150–180℃, and the curing time is 1–2 hours.

9. A wet paper-based friction material, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the wet paper-based friction material of claim 9 in the clutch and braking devices of engineering machinery, heavy-duty vehicles, automobiles, motorcycles or ships.

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