High porosity wet paper-based friction material and its preparation method and application

Abstract

The application provides a high-porosity wet paper-based friction material and a preparation method and application thereof, and relates to the technical field of friction materials.The natural fiber, synthetic fiber, friction performance regulator and water are mixed, and are sequentially subjected to dewatering forming, drying, glue dipping, drying, hot pressing vulcanization to obtain a wet paper-based friction material glue-dipped paper, wherein the slurry or glue-dipping liquid contains a pore-forming agent.Under the condition that the main raw materials and production process remain unchanged, the application adds the low-cost inorganic pore-forming agent in the slurry or glue-dipping liquid, the inorganic pore-forming agent reacts to release small molecule gas during hot pressing vulcanization, the porosity of the wet paper-based friction material is improved, the friction coefficient is also improved, and the friction and wear performance of the wet paper-based friction material is improved.Further, the preparation method provided by the application uses raw materials which are environmentally friendly, easy to obtain and low in price, the production process is simple and easy to operate, no organic toxic and harmful gas is discharged, no additional equipment and process are needed, and the operation process is simple.

Description

Technical Field

[0001] This invention relates to the field of friction materials technology, specifically to a high-porosity wet paper-based friction material, its preparation method, and its application. Background Technology

[0002] Wet paper-based friction materials are fiber composite materials that operate in oil media. They are made by using cellulose fibers or synthetic fibers as reinforcing fibers, adding friction modifiers and fillers, forming the material through a papermaking process, impregnating it with a binder resin, and then hot-pressing and curing it. Compared with other wet friction materials such as cork rubber-based friction materials, powder metallurgy friction materials, and carbon / carbon-based friction materials, wet paper-based friction materials have advantages such as a high dynamic friction coefficient, a static / dynamic friction coefficient ratio close to 1, strong torque transmission capability, low friction noise, a smooth and stable bonding process, good wear resistance, and customizable structural shapes. They are widely used in the transmission and braking devices of various vehicles and engineering machinery, such as wet clutches in automotive automatic transmissions, motorcycle clutches, and wet braking systems for heavy vehicles.

[0003] Tribological performance is a key indicator of wet paper-based friction materials, which depends on the proportion of raw materials, manufacturing method, and morphology of the friction surface. When the types and proportions of raw materials are constant, tribological performance is greatly affected by the overall material structure, especially the porosity. Higher porosity allows oil on the sliding contact surface to penetrate more easily, more effectively removing the oil film. Simultaneously, the oil flows better within the material, the surface temperature is relatively lower, and thermal decay is less, resulting in a higher coefficient of friction.

[0004] Chinese patent CN110965385A discloses a method for preparing a paper-based friction material with optimized pore structure. The method involves immersing a preform of the paper-based friction material in a binder solution formed by a surfactant, thickener, and physical foaming agent, followed by physical foaming. After foaming, the material is cured by hot pressing. However, the physical foaming agent used in this patent is flammable and volatile; its vapor mixes with air to form an explosive mixture, most of which can cause poisoning and environmental pollution, resulting in poor safety and making practical operation very difficult.

[0005] Chinese patent CN114197250A discloses a method for preparing wet paper-based friction materials based on foam molding. The method uses foam molding to adjust the pore structure of the wet paper-based friction material. A surfactant is added to an aqueous dispersion system of natural fibers, synthetic fibers, fillers, and dispersants to induce foaming. After the foam slurry is dried, a paper-based friction material base paper is obtained. Then, the base paper is impregnated with glue, hot-pressed, and cured to obtain the foam-molded wet paper-based friction material. This patent uses micron-sized water-based bubbles (water + surfactant + air) as the dispersion medium, which can improve the bulk and porosity of the base paper, achieving control over the porosity and pore structure of the base paper. However, slurry containing a large number of bubbles can cause difficulties in pulp flow and wire forming, and the amount and size of the bubbles are difficult to control.

[0006] Chinese patent CN112064404A discloses a method for preparing a high-porosity paper-based friction material. By introducing chemical foaming technology into the traditional paper-based friction material preparation process, the pore structure of the material is effectively controlled, significantly improving the average pore size and porosity after the hot-pressing process. The organic chemical foaming agent used is one or more of N,N'-dinitrospentamethylenetetramine, N,N'-dimethyl-N,N'-dinitrosterephthalamide, diazoaminobenzene, azodicarbonamide, azobisisobutyronitrile, azodicarbonate, barium azodicarbonate, benzenesulfonyl hydrazine, p-toluenesulfonyl hydrazine, 4,4'-oxobisbenzenesulfonyl hydrazine, 1,3-benzenedisulfonyl hydrazine, or 3,3'-disulfonyl hydrazine diphenyl sulfone; the foaming aid is one or more of urea, diethylene glycol, stearic acid, lauric acid, salicylic acid, zinc stearate, glycerin, or sorbitol. However, most of the aforementioned organic chemical foaming agents are toxic and carcinogenic, and some have very strict requirements for storage and use. For example, N,N'-dinitrospentamethylenetetramine is listed as a Group 3 carcinogen by the International Agency for Research on Cancer of the World Health Organization; diazoaminobenzene is toxic and polluting; and pure N,N'-dimethyl-N,N'-dinitrosterephthalamide is an explosive, sensitive to impact and friction, and poses a safety hazard.

[0007] Chinese patent CN108978346A discloses a method for preparing a foamed phenolic resin impregnated paper-based friction material. The method involves mixing low molecular weight phenolic resin, polyimide resin, water, anhydrous ethanol, emulsifier, thickener, polyacrylamide, chromium salt, and additives, followed by constant-temperature stirring and continuous introduction of carbon dioxide gas during the reaction to obtain a foamed phenolic resin solution. This foamed phenolic resin solution is then used to impregnate a wet-process paper-based friction material base paper, followed by hot pressing to obtain the foamed phenolic resin impregnated paper-based friction material. This method requires additional equipment, continuous introduction of carbon dioxide gas, and effective control of the gas distribution within the material.

[0008] Chinese patent CN107326721A discloses a method for preparing a paper-based friction material with uniform pores. First, alumina, potassium feldspar, etc., are mixed and ball-milled. The resulting ball-milled powder is then filled into a mold and melted at high temperature to obtain mixed short-cut fibers. Next, aluminum isopropoxide powder is mixed and dispersed with glacial acetic acid solution. Silica sol is added, followed by mixing with tetraethylammonium hydroxide to obtain a modified mixture. The mixed short-cut fibers are then added to the modified mixture, dispersed, dried, and mixed with bamboo fiber and water. After loosening treatment, the mixture is placed on a paper forming device with a screen, dried, and then immersed in a phenolic resin ethanol solution. After immersion, it is removed and vulcanized to obtain a paper-based friction material with uniform pores. The high-temperature melting and drawing process requires preheating at 250–300°C for 25–30 minutes under a nitrogen protective atmosphere, followed by heating at 15°C / min to 1750–1800°C and holding for melting for 1–2 hours. After melting, a glass rod is used to guide the fibers at the crucible spout. The paper-based friction material prepared by this patent has the characteristics of high friction coefficient and good controllability of pore structure, making it an ideal friction material. However, the preparation steps of this patented paper-based friction material are complex, and the high-temperature melting and drawing step requires a special high-temperature resistant device, resulting in high energy consumption and high production costs. Therefore, there is an urgent need to provide a method for preparing high-porosity wet paper-based friction materials that uses safe reagents, has simple steps, and low cost. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a high-porosity wet paper-based friction material, its preparation method, and its application. The preparation method provided by this invention is simple in steps, uses an inorganic pore-forming agent, is safe and environmentally friendly, has low energy consumption, and low production cost.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for preparing a high-porosity wet paper-based friction material, comprising the following steps:

[0012] Natural fibers, synthetic fibers, friction modifiers, fillers, and water are mixed to obtain a slurry;

[0013] The slurry is dehydrated, shaped, and then dried to obtain wet paper-based friction material base paper;

[0014] The wet paper-based friction material base paper is impregnated in a phenolic resin impregnation solution and then dried to obtain wet paper-based friction material impregnated paper.

[0015] The wet paper-based friction material is hot-pressed and vulcanized to obtain a high-porosity wet paper-based friction material.

[0016] The slurry or the phenolic resin impregnation solution also includes a pore-forming agent;

[0017] The pore-forming agent in the slurry includes a water-soluble pore-forming agent and an inorganic strong base, or an insoluble pore-forming agent; the water-soluble pore-forming agent includes aluminum sulfate, or alum and sulfuric acid; the insoluble pore-forming agent includes aluminum hydroxide particles and / or calcium oxalate powder, and the pH value of the slurry containing the inorganic strong base is 6 to 8.

[0018] The pore-forming agent in the phenolic resin impregnation solution includes one or more of aluminum hydroxide particles, alum, and calcium oxalate powder.

[0019] Preferably, when the slurry also includes aluminum sulfate and an inorganic strong base, the method for preparing the slurry containing the pore-forming agent includes the following steps: adding aluminum sulfate to the slurry until the pH value is 0.1 to 5, and then adding an inorganic strong base to adjust the pH value to 6 to 8;

[0020] When the slurry also includes alum, sulfuric acid and inorganic strong alkali, the preparation method of the slurry containing the pore-forming agent includes the following steps: adding alum to the slurry, adding sulfuric acid to adjust the pH value to 0.1-5, and then adding inorganic strong alkali to adjust the pH value to 6-8; the mass of alum in the slurry accounts for 0.1-5% of the dry weight of the slurry without the addition of insoluble pore-forming agent;

[0021] When the slurry also includes an insoluble pore-forming agent, the method for preparing the slurry containing the pore-forming agent includes the following steps: adding an insoluble pore-forming agent to the slurry; the mass of the insoluble pore-forming agent accounts for 0.001 to 10% of the mass of the slurry without the addition of the insoluble pore-forming agent.

[0022] Preferably, when the phenolic resin impregnation solution also includes a pore-forming agent, the mass of the pore-forming agent accounts for 0.1% to 5% of the dry weight of the phenolic resin; the particle size of the pore-forming agent is 1 to 1000 nm.

[0023] Preferably, the phenolic resin in the phenolic resin impregnation solution includes one or more of the following: unmodified phenolic resin, cashew nut shell oil modified phenolic resin, melamine modified phenolic resin, latex modified phenolic resin, and boron modified phenolic resin.

[0024] The solid content of the phenolic resin impregnation solution is 20-50%.

[0025] Preferably, the natural fiber includes one or more of hemp fiber, cotton fiber, bamboo fiber, and wood pulp fiber;

[0026] The synthetic fibers include one or more of aramid fibers, carbon fibers, glass fibers, ceramic fibers, and polyimide fibers;

[0027] The friction performance modifier filler includes one or more of diatomaceous earth, silica, feldspar, barium sulfate, graphite, alumina, and organic friction powder.

[0028] The mass ratio of the natural fiber to the synthetic fiber is 1:0.1 to 8;

[0029] The mass ratio of the natural fiber to the friction modifier filler is 1:0.1 to 12;

[0030] The solid content of the slurry is 0.5% to 3%.

[0031] Preferably, the impregnation time is 3 to 20 minutes.

[0032] Preferably, the hot-press vulcanization temperature is 180–230°C, the pressure is 1–30 MPa, and the time is 1–30 min.

[0033] The present invention also provides a high-porosity wet paper-based friction material prepared by the preparation method described in the above technical solution.

[0034] Preferably, the basis weight of the high-porosity wet paper-based friction material is 100–2000 g / m³. 2 The thickness is 0.2 to 5 mm.

[0035] The present invention also provides the application of the high porosity wet paper-based friction material described in the above technical solution in wet clutches or wet braking devices.

[0036] This invention mixes natural fibers, synthetic fibers, friction modifiers, fillers, and water, and then dehydrates, shapes, dries, impregnates, and dries the resulting slurry. By adding a pore-forming agent to the slurry or phenolic resin impregnation solution, thermal decomposition occurs during hot-pressing vulcanization, thus obtaining a porous wet-type paper-based friction material impregnated paper.

[0037] When water-soluble pore-forming agents and inorganic strong bases are added to the slurry, a multi-step chemical reaction method using inorganic substances is employed to control the porosity of wet paper-based friction materials. Aluminum sulfate and alum are both strong acid-weak base salts; in the presence of an inorganic strong base, they undergo hydrolysis in aqueous solution, generating colloidal aluminum hydroxide precipitate and H+ precipitate on the fiber surface and within the system. + The solution is acidic. Adding alkaline solution to the slurry system to adjust the pH to 6-8 will generate a large amount of aluminum hydroxide precipitate. Aluminum hydroxide is easily decomposed by heat, generating aluminum oxide and water during hot-press vulcanization. When the water vapor escapes, it forms pores inside the material, which can significantly increase the porosity and pore size of the material. The reaction equation is as follows: 2Al(OH)3=Al2O3+3H2O↑. Moreover, this invention can control the amount of aluminum hydroxide generated by the reaction by adjusting the amount of aluminum sulfate and / or alum and inorganic strong alkali in the slurry, thereby controlling the amount of water vapor generated during hot-press vulcanization and achieving porosity control of wet paper-based friction materials.

[0038] When aluminum hydroxide particles and / or calcium oxalate powder are added to the slurry, or when one or more of aluminum hydroxide particles, alum, and calcium oxalate powder are added to the phenolic resin impregnation solution, the aforementioned pore-forming agents readily decompose upon heating. During hot-press vulcanization, aluminum hydroxide generates alumina and water vapor, alum dehydrates to generate anhydrous alum and water vapor, and calcium oxalate monohydrate begins to lose water at approximately 180°C, decomposing into anhydrous calcium oxalate and water vapor. Anhydrous calcium oxalate begins to decompose at approximately 200°C, generating calcium carbonate and carbon monoxide. The escape of water vapor and carbon monoxide forms pores within the material, significantly increasing its porosity and pore size. This invention, by controlling the amount of the aforementioned pore-forming agent added, can control the gases (water vapor and / or carbon monoxide) generated during hot-press vulcanization, thereby achieving porosity control of wet paper-based friction materials.

[0039] This invention, while keeping the main raw materials and production process unchanged, increases the porosity of wet paper-based friction materials by adding a low-cost inorganic pore-forming agent to the slurry or impregnation solution. This agent reacts during hot-press vulcanization, releasing small-molecule gases, thereby improving the friction coefficient and the tribological properties of the wet paper-based friction material. The pore-forming agent used in this invention is inorganic, which, compared to organic agents, does not emit toxic or harmful organic gases, is more environmentally friendly, and is also cheaper and easier to operate. By adjusting the amount of pore-forming agent added, different amounts of small-molecule gases can be generated during hot-press vulcanization, thus controlling the porosity and pore size of the wet paper-based friction material, overcoming the shortcomings of existing technologies such as environmental unfriendliness and operational difficulties. By adding a low-cost inorganic agent and undergoing a composite chemical reaction, a high-porosity wet paper-based friction material is obtained while maintaining the main raw materials unchanged. This method is low-cost, increases porosity, and improves tribological properties. Furthermore, the preparation method provided by this invention uses environmentally friendly, readily available, and inexpensive raw materials, is simple and easy to operate, does not emit toxic organic gases, requires no additional equipment or processes, and is simple to operate. Attached Figure Description

[0040] Figure 1 The pore size distribution diagram of the wet paper-based friction material prepared in Comparative Example 1;

[0041] Figure 2 The pore size distribution diagram of the wet paper-based friction material prepared in Comparative Example 2;

[0042] Figure 3 The pore size distribution diagram is shown for the wet paper-based friction material prepared in Example 1.

[0043] Figure 4 The pore size distribution diagram is shown for the wet paper-based friction material prepared in Example 2.

[0044] Figure 5 The pore size distribution diagram is shown for the wet paper-based friction material prepared in Example 3.

[0045] Figure 6 The pore size distribution diagram is shown for the wet paper-based friction material prepared in Example 4.

[0046] Figure 7 The pore size distribution diagram of the wet paper-based friction material prepared in Comparative Example 3;

[0047] Figure 8 The pore size distribution diagram is shown for the wet paper-based friction material prepared in Example 5.

[0048] Figure 9 The image shows the pore size distribution of the wet paper-based friction material prepared in Example 6. Detailed Implementation

[0049] This invention provides a method for preparing a high-porosity wet paper-based friction material, comprising the following steps:

[0050] Natural fibers, synthetic fibers, friction modifiers, fillers, and water are mixed to obtain a slurry;

[0051] The pulp is dehydrated, shaped, and then dried to obtain the base paper;

[0052] The base paper is impregnated with phenolic resin solution and then dried to obtain impregnated paper.

[0053] The impregnated paper is subjected to hot-press vulcanization to obtain a high-porosity wet paper-based friction material.

[0054] The slurry or the phenolic resin impregnation solution also includes a pore-forming agent;

[0055] The pore-forming agent in the slurry includes a water-soluble pore-forming agent and an inorganic strong base, or an insoluble pore-forming agent; the water-soluble pore-forming agent includes aluminum sulfate, or alum and sulfuric acid; the insoluble pore-forming agent includes aluminum hydroxide particles and / or calcium oxalate powder, and the pH value of the slurry containing the inorganic strong base is 6 to 8.

[0056] The pore-forming agent in the phenolic resin impregnation solution includes one or more of aluminum hydroxide particles, alum, and calcium oxalate powder.

[0057] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0058] This invention mixes natural fibers, synthetic fibers, friction modifiers, fillers, and water to obtain a slurry.

[0059] In this invention, the natural fiber preferably includes one or more of hemp fiber, cotton fiber, bamboo fiber, and wood pulp fiber, more preferably cotton fiber or a hemp-cotton fiber mixture, wherein the mass ratio of hemp fiber to cotton fiber in the hemp-cotton fiber mixture is preferably 1:1. In this invention, the diameter of the natural fiber is preferably 1–50 μm, more preferably 10–40 μm; the length of the natural fiber is preferably 0.2–10 mm, more preferably 0.5–5 mm.

[0060] In this invention, the synthetic fiber preferably includes one or more of aramid fiber, carbon fiber, glass fiber, ceramic fiber, and polyimide fiber. In this invention, the diameter of the synthetic fiber is preferably 1–30 μm, more preferably 3–20 μm; the length of the synthetic fiber is preferably 0.1–10 mm, more preferably 0.3–5 mm. In this invention, the synthetic fiber preferably includes an aramid fiber-carbon fiber mixture, wherein the mass ratio of aramid fiber to carbon fiber in the aramid fiber-carbon fiber mixture is preferably 8–13:7–8, more preferably 1:1 or 13:7.

[0061] In this invention, the mass ratio of natural fiber to synthetic fiber is preferably 1:0.1 to 8, more preferably 1:1 to 6, and even more preferably 1:2 to 4. Specifically, it is preferably 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, or 1:8.

[0062] In this invention, the friction performance modifier filler preferably comprises one or more of diatomaceous earth, silica, feldspar, barium sulfate, graphite, alumina, and organic friction powder; the feldspar preferably comprises one or more of sodium feldspar, calcium feldspar, potassium feldspar, and barium feldspar; the organic friction powder preferably comprises one or more of rubber powder, cashew nutshell oil friction powder, tire powder, and amino ester powder. In this invention, by mass parts, the friction performance modifier filler is more preferably a first composite friction performance modifier filler or a second composite friction performance modifier filler; the first composite friction performance modifier filler preferably comprises a mixture of diatomaceous earth, feldspar, graphite, rubber powder, and cashew nutshell oil friction powder in a mass ratio of 15:5:6:30:20; the second composite friction performance modifier filler preferably comprises a mixture of diatomaceous earth, feldspar, alumina, graphite, and rubber powder in a mass ratio of 23:10:2:15:10. In this invention, alumina is dispersed in the material, and may partially cover the surface of natural and synthetic fibers, which can improve the friction coefficient of the material. In this invention, the particle size of the friction performance modifier filler is preferably 10-800 mesh, more preferably 20-350 mesh.

[0063] In this invention, the mass ratio of the natural fiber to the friction modifier filler is preferably 1:0.1 to 12, more preferably 1:1 to 10, and even more preferably 1:2 to 8. Specifically, it is preferably 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10, 1:10.5, 1:11, 1:11.5, or 1:12.

[0064] In this invention, when the slurry also includes aluminum sulfate and an inorganic strong alkali, the preparation method of the slurry containing the pore-forming agent preferably includes the following steps: adding aluminum sulfate to the slurry to a pH value of 0.1-5 (preferably), and then adding an inorganic strong alkali to adjust the pH value to 6-8, thereby obtaining a slurry containing the pore-forming agent. In this invention, the aluminum sulfate is preferably used in the form of an aqueous solution of aluminum sulfate, and the concentration of the aqueous solution of aluminum sulfate is preferably 0.5-25 wt%, more preferably 1-25 wt%, further preferably 5-20 wt%, and most preferably 10-15 wt%. In this invention, after adding aluminum sulfate, the pH value of the system is more preferably 0.5-4, further preferably 1-3, and specifically preferably 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. After adding aluminum sulfate to the slurry, stirring is preferably also performed, the stirring temperature is preferably room temperature, and the stirring time is preferably 5-30 min, more preferably 10-20 min. In this invention, the pH value of the system (i.e., the slurry containing the pore-forming agent) after adding the inorganic strong base is more preferably 6.5-7.5, and even more preferably 7. In this invention, the inorganic strong base is preferably used in the form of an aqueous solution of the inorganic strong base, and the solid content of the aqueous solution of the inorganic strong base is preferably 1-30%, more preferably 3-25%, even more preferably 5-20%, and most preferably 10-15%; the inorganic strong base preferably includes one or more of sodium hydroxide, potassium hydroxide, and barium hydroxide.

[0065] Aluminum sulfate and alum are both salts of strong acid and weak base. In the presence of a strong inorganic base, they undergo hydrolysis in aqueous solution, forming a colloidal precipitate of aluminum hydroxide and H₂O on the fiber surface and within the system. + The solution is acidic. Taking aluminum sulfate as an example, the reaction equation is Al 3+ +3H₂O=Al(OH)₃+3H + When the pH of the system is <3.0, it mainly consists of Al(H2O)6. 3+It exists in the form of Al(OH)3; when the pH value is >5.8, it exists entirely in the form of Al(OH)3. Adding alkali to the slurry system and adjusting the pH value to 6-8 will generate a large amount of aluminum hydroxide precipitate, with the reaction equation being Al2(SO4)3 + 6NaOH = 2Al(OH)3↓ + 3Na2SO4. Aluminum hydroxide is easily decomposed by heat, generating alumina and water during hot-press vulcanization. When the water vapor escapes, it forms pores inside the material, which can significantly increase the porosity and pore size of the material, as shown in the reaction equation: 2Al(OH)3 = Al2O3 + 3H2O↑. Moreover, this invention can control the amount of aluminum hydroxide generated by the reaction by controlling the amount of aluminum sulfate and / or alum and inorganic strong alkali in the slurry, thereby controlling the amount of water vapor generated during hot-press vulcanization and achieving the control of the porosity of wet paper-based friction materials.

[0066] In this invention, when the slurry further includes alum, sulfuric acid, and an inorganic strong alkali, the preparation method of the slurry containing the pore-forming agent preferably includes the following steps: adding alum to the slurry, adding sulfuric acid to adjust the pH value to 0.1-5, and then adding an inorganic strong alkali to adjust the pH value to 6-8; the amount of alum in the slurry accounts for 0.1-5% of the dry weight of the slurry without the addition of the insoluble pore-forming agent. In this invention, the alum is preferably used in the form of an alum aqueous solution, and the concentration of the alum solution is preferably 0.5-25 wt%, more preferably 1-25 wt%, further preferably 5-20 wt%, and most preferably 10-15 wt%. In this invention, the mass of alum (KAl(SO4)2·12H2O) in the slurry preferably accounts for 0.1-5% of the dry weight of the slurry without the addition of insoluble pore-forming agent, more preferably 0.5-4%, further preferably 1-3%, and specifically preferably 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. In this invention, the pH value after adjustment with sulfuric acid is more preferably 0.5-4, more preferably 1-3, and specifically preferably 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. In this invention, after adding alum and sulfuric acid to the slurry, stirring is preferably performed, preferably at room temperature, and preferably for 5-30 minutes, more preferably 10-20 minutes. In this invention, the pH value of the system (i.e., the slurry containing the pore-forming agent) after adding the inorganic strong base is more preferably 6.5-7.5, and even more preferably 7. In this invention, the inorganic strong base is preferably used in the form of an aqueous solution of the inorganic strong base, and the solid content of the aqueous solution of the inorganic strong base is preferably 1-30%, more preferably 3-25%, even more preferably 5-20%, and most preferably 10-15%; the inorganic strong base preferably includes one or more of sodium hydroxide, potassium hydroxide, and barium hydroxide.

[0067] In this invention, when the slurry also includes an insoluble pore-forming agent, the preparation method of the slurry containing the pore-forming agent includes the following steps: adding an insoluble pore-forming agent to the slurry to obtain a slurry containing the pore-forming agent; the insoluble pore-forming agent includes one or more of aluminum hydroxide microparticles, calcium oxalate powder, and magnesium hydroxide. In this invention, the particle size of the insoluble pore-forming agent is preferably 100-800 mesh, more preferably 200-500 mesh; the purity of the aluminum hydroxide microparticles is preferably chemically pure or analytically pure; the aluminum hydroxide microparticles are preferably obtained by grinding aluminum hydroxide; the equipment used for grinding preferably includes at least one of a ball mill, a sand mill, and a bead mill; this invention does not have special limitations on the diameter of the grinding beads, the ball-to-particle ratio, and the grinding time used for grinding, as long as aluminum hydroxide microparticles with a particle size of [specific value missing] are obtained. In this invention, the water-insoluble pore-forming agent preferably accounts for 0.001 to 10% of the mass of the slurry without added insoluble pore-forming agent, more preferably 0.1 to 8%, and even more preferably 1 to 5%, specifically preferably 0.001%, 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0068] When aluminum hydroxide particles and / or calcium oxalate powder are added to the slurry, or when one or more of aluminum hydroxide particles, alum, and calcium oxalate powder are added to the phenolic resin impregnation solution, the aforementioned insoluble pore-forming agents readily decompose upon heating. During hot-press vulcanization, aluminum hydroxide generates alumina and water vapor, alum dehydrates to generate anhydrous alum and water vapor, and calcium oxalate monohydrate begins to lose water at approximately 180°C, decomposing into anhydrous calcium oxalate and water vapor. Anhydrous calcium oxalate begins to decompose at approximately 200°C, generating calcium carbonate and carbon monoxide. The escape of water vapor and carbon monoxide forms pores within the material, significantly increasing its porosity and pore size. This invention, by controlling the amount of the aforementioned pore-forming agent added, can control the gases (water vapor and / or carbon monoxide) generated during hot-press vulcanization, thereby achieving porosity control of wet paper-based friction materials.

[0069] The present invention does not have any special limitations on the mixing method, and any mixing method known to those skilled in the art can be used, such as stirring.

[0070] In this invention, the solid content of the slurry is preferably 0.5-3%, more preferably 0.5-2.5%, further preferably 1-2%, and most preferably 1.5%.

[0071] After obtaining the pulp, the present invention dehydrates and shapes the pulp and then dries it to obtain the base paper.

[0072] In this invention, the dewatering and forming process preferably includes: pouring the pulp into a forming machine or a sheet forming machine, and after the pulp is evenly dispersed, vacuum dewatering to obtain a first wet paper web, and pressing the first wet paper web to dewater it to obtain a second wet paper web.

[0073] In this invention, the vacuum degree of the vacuum dehydration is preferably 0.01-0.06 MPa, more preferably 0.02-0.05 MPa, and even more preferably 0.03-0.04 MPa; the present invention does not have a special limitation on the vacuum dehydration time, so that the solid content of the first wet paper web is 10-25%, the solid content is more preferably 15-20%, and the vacuum dehydration time is specifically 3-300s.

[0074] In this invention, the pressing and dewatering are preferably carried out on a press. In this invention, the moisture content of the second wet paper web is preferably 25-50%, more preferably 30-45%, and even more preferably 35-40%.

[0075] In this invention, the drying temperature is preferably 70-110°C, more preferably 80-100°C, and even more preferably 90-95°C; the drying time is preferably 3-600s, more preferably 50-500s, and even more preferably 100-300s; the drying is preferably carried out in a drying cylinder, a vacuum dryer, or an oven.

[0076] After obtaining the base paper, the present invention impregnates the base paper in a phenolic resin impregnation solution and then dries it to obtain impregnated paper.

[0077] In this invention, when the slurry does not contain a pore-forming agent, the phenolic resin impregnation solution further includes a pore-forming agent; the pore-forming agent in the phenolic resin impregnation solution includes one or more of aluminum hydroxide particles, alum, and calcium oxalate powder.

[0078] In this invention, the particle size of the pore-forming agent is preferably 1–1000 nm, more preferably 50–950 nm, and even more preferably 100–500 nm; the purity of the aluminum hydroxide particles is preferably chemically pure or analytically pure; the aluminum hydroxide particles are preferably obtained by grinding aluminum hydroxide; the grinding equipment preferably includes at least one of a ball mill, a sand mill, and a bead mill; this invention does not have special limitations on the diameter of the grinding beads, the ball-to-material ratio, and the grinding time, as long as aluminum hydroxide particles with a particle size of 1–1000 nm can be obtained. In this invention, the mass of the pore-forming agent is preferably 0.1–5% of the dry weight of the phenolic resin, more preferably 0.5–4.5%, and even more preferably 1–2%, specifically preferably 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0079] In this invention, the phenolic resin in the phenolic resin impregnation solution preferably includes one or more of the following: unmodified phenolic resin (pure phenolic resin), cashew nut shell oil-modified phenolic resin, melamine-modified phenolic resin, latex-modified phenolic resin, and boron-modified phenolic resin. This invention does not specifically limit the type of phenolic resin; it can be prepared using commercially available products or preparation methods well-known to those skilled in the art. In a specific embodiment of this invention, the phenolic resin was purchased from Shengquan Group. In this invention, the solvent in the phenolic resin impregnation solution preferably includes ethanol. In this invention, the solid content of the phenolic resin impregnation solution is preferably 20-50%, more preferably 25-45%, further preferably 30-40%, and most preferably 35%.

[0080] In this invention, the solid content of the phenolic resin impregnation solution is preferably 20-50%, more preferably 25-45%, further preferably 30-40%, and most preferably 35%. When the phenolic resin impregnation solution contains no pore-forming agent, the solid content is the mass fraction of the dry weight of the phenolic resin. When it contains a pore-forming agent, the solid content is the total mass fraction of the dry weight of the phenolic resin and the pore-forming agent.

[0081] In this invention, when the phenolic resin impregnation solution also contains a pore-forming agent, the phenolic resin impregnation solution is preferably obtained by mixing phenolic resin, aluminum hydroxide particles, and ethanol. In this invention, the mixing temperature is preferably room temperature, and the mixing time is preferably 1–60 min, more preferably 5–50 min, and even more preferably 10–30 min; the mixing method preferably includes stirring and / or ultrasonic mixing, more preferably stirring, or ultrasonic mixing followed by stirring.

[0082] In this invention, the impregnation temperature is preferably room temperature, and the impregnation time is preferably 3 to 20 minutes, more preferably 3 to 20 minutes, and even more preferably 3 to 20 minutes.

[0083] In this invention, the glue content of the impregnation is preferably 20-40%, more preferably 30-35%, and specifically preferably 30.3%, 30.5%, 32.3% or 32.4%; wherein, the glue content = (mass of wet paper-based friction material - mass of base paper) / mass of wet paper-based friction material × 100%.

[0084] After obtaining the impregnated paper, the present invention performs hot-press vulcanization on the impregnated paper to obtain a high-porosity wet paper-based friction material.

[0085] In this invention, the temperature of the hot-press vulcanization is preferably 180–230°C, more preferably 190–220°C, and even more preferably 200–210°C; the pressure of the hot-press vulcanization is preferably 1–30 MPa, more preferably 1.5–10 MPa, and even more preferably 2–5 MPa; the time of the hot-press vulcanization is preferably 1–30 min, more preferably 3–20 min, and even more preferably 5–10 min; the hot-press vulcanization is preferably carried out in a vulcanizing machine.

[0086] This invention provides a high-porosity wet paper-based friction material prepared by the preparation method described in the above technical solution.

[0087] In this invention, the preferred basis weight of the high-porosity wet paper-based friction material is 100–2000 g / m³. 2 More preferably, it is 200–1500 g / m 2 More preferably, it is 300–1000 g / m 2 Specifically, the preferred value is 341g / m 2 345g / m 2 366g / m 2 398g / m 2 400g / m 2 401g / m 2 409g / m 2 410g / m 2The thickness of the high-porosity wet paper-based friction material is preferably 0.2–5 mm, more preferably 0.25–2 mm, further preferably 0.3–1 mm, and most preferably 0.35–0.5 mm. Specifically, it is preferably 0.379 mm, 0.386 mm, 0.398 mm, 0.400 mm, 0.412 mm, 0.414 mm, or 0.416 mm. The porosity of the high-wear-resistant wet paper-based friction material is preferably 25.1%, 26.9%, 27%, 29.9%, 44.3%, 46.1%, or 46.8%. The average pore size of the high-wear-resistant wet paper-based friction material is preferably 2.1721 μm, 2.3524 μm, or 2.3325 μm. The micrometer diameters are 3.1700 μm, 3.4131 μm, 3.4178 μm, or 4.0456 μm; the dynamic friction coefficient of the high wear-resistant wet paper-based friction material is preferably ≥0.094, more preferably 0.094~0.121, specifically preferably 0.094, 0.096, 0.102, 0.108, 0.110, 0.119, or 0.121; the static friction coefficient of the high wear-resistant wet paper-based friction material is preferably ≥0.108, more preferably 0.108~0.134, specifically preferably 0.108, 0.110, 0.113, 0.128, 0.130, or 0.134; the wear rate of the high wear-resistant wet paper-based friction material is preferably ≤4.5×10⁻⁶. -7 cm 2 / J, preferably 2×10 -7 cm 2 / J、3×10 -7 cm 2 / J、4×10 -7 cm 2 / J or 4.5×10 -7 cm 2 / J.

[0088] This invention provides the application of the high-porosity wet paper-based friction material described above in wet clutches or wet braking devices. In this invention, the high-porosity wet paper-based friction material is preferably applied to wet clutches or wet braking devices of various vehicles or engineering machinery, and more preferably to wet clutches of automotive automatic transmissions, motorcycle clutches, or wet braking devices of heavy vehicles; the high-porosity wet paper-based friction material preferably operates in an oil medium.

[0089] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a high-porosity wet paper-based friction material, its preparation method, and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0090] In the following examples and comparative examples, the feldspar is potassium feldspar; the phenolic resin is the phenolic resin for friction materials from Shengquan Group; and the rubber powder was purchased from Cardlä Company.

[0091] Comparative Example 1

[0092] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber powder, and 20 parts cashew nut shell oil friction powder were evenly dispersed with water to obtain a slurry with a solid content of 1.5%. The slurry was poured into a sheeter and evenly dispersed. It was then dehydrated under a vacuum of 0.01–0.06 MPa to a solid content of 10–25%. The slurry was then further dehydrated using a press to obtain a wet paper web with a moisture content of 40%. This wet web was dried in a vacuum dryer at 95°C to obtain the base paper. The base paper was then immersed in a 30% phenolic resin ethanol solution at room temperature for 10 minutes, removed, and dried at 105°C for 10 minutes to obtain glazed paper with a glaze content of 29.7%. The glazed paper was then placed on a vulcanizing machine and hot-pressed at 200°C and 2 MPa for 5 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material is 408 g / m³. 2 The thickness is 389μm.

[0093] The porosity of this high-porosity wet paper-based friction material was measured to be 23.0% using a fully automated true density analyzer. The average pore size of the material was measured to be 3.0078 μm using a Capillary Flow Porometer. The pore size distribution is shown below. Figure 1 As shown.

[0094] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of a rotational speed of 2000 r / min and a pressure of 0.4 MPa, the dynamic friction coefficient of the wet paper-based friction material was 0.084, and the static friction coefficient was 0.095. After 2000 tests, the wear rate was 5 × 10⁻⁶. -7 cm² / J. Meets the requirements for Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0095] Comparative Example 2

[0096] By weight, 10 parts cotton fiber, 10 parts hemp fiber, 13 parts aramid fiber, 7 parts carbon fiber, 23 parts diatomaceous earth, 10 parts feldspar, 2 parts alumina, 15 parts graphite, and 10 parts rubber powder were uniformly dispersed with water to obtain a slurry with a solid content of 1.7%. The slurry was poured into a sheeter and, after uniform dispersion, dehydrated under a vacuum of 0.01–0.06 MPa to a solid content of 10–25%. Then, a press was used to further remove moisture, resulting in a wet paper web with a moisture content of 41%. This web was dried in a 105°C drying oven to obtain the base paper. The base paper was immersed in a 34% phenolic resin ethanol solution at room temperature for 15 minutes, then removed and dried at 100°C for 30 minutes to obtain glazed paper with a glaze content of 32.3%. The glazed paper was placed on a vulcanizing machine and hot-pressed at 200°C and 4 MPa for 3 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material is 338 g / m³. 2 The thickness is 391μm.

[0097] The porosity of this high-porosity wet paper-based friction material was measured to be 44.1% using a fully automated true density analyzer. The average pore size of the material was measured to be 1.9732 μm using a Capillary Flow Porometer. The pore size distribution is shown below. Figure 2 As shown.

[0098] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of a rotational speed of 2000 r / min and a pressure of 0.4 MPa, the dynamic friction coefficient of the wet paper-based friction material was 0.095, and the static friction coefficient was 0.106. This meets the requirements for Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0099] Example 1

[0100] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber powder, and 20 parts cashew nut shell oil friction powder were evenly dispersed with water to obtain a slurry with a solid content of 1.5%. The slurry was poured into a sheet-making machine, and after it was evenly dispersed, it was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01-0.06 MPa. Then, it was further dehydrated using a press to obtain a wet paper web with a moisture content of 40%, which was then dried in a vacuum dryer at 95℃ to obtain the base paper. Chemically pure aluminum hydroxide was ground in a ball mill for 55 minutes with a ball diameter of 5-10 mm and a ball-to-particle ratio of 15:1 to obtain aluminum hydroxide particles with an average particle size of 930 nm. These aluminum hydroxide particles were added to a 30% phenolic resin ethanol solution and mechanically stirred at room temperature for 20 minutes to obtain a phenolic resin impregnation solution. The base paper was immersed in the above-mentioned phenolic resin impregnation solution at room temperature for 10 minutes, then removed and dried at 105°C for 10 minutes to obtain impregnated paper with a resin content of 30.1%. The impregnated paper was placed on a vulcanizing machine and hot-pressed at 200°C and 2MPa for 5 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material was 401 g / m³. 2 The thickness is 400 μm. The aluminum hydroxide particles account for 1.5% of the dry weight of the phenolic resin.

[0101] The porosity of this high-porosity wet paper-based friction material was measured to be 27.0% using a fully automated true density analyzer. The average pore size of the material was measured to be 3.4178 μm using a capillary flow pore size analyzer. The pore size distribution is as follows: Figure 3 As shown.

[0102] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the high-porosity wet paper-based friction material was 0.102, which was 7.4% higher than that of Comparative Example 1; the static friction coefficient was 0.110, which was 3.8% higher than that of Comparative Example 1. It meets the requirements of Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0103] Example 2

[0104] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber powder, and 20 parts cashew nut shell oil friction powder were evenly dispersed with water to obtain a slurry with a solid content of 1.5%. The slurry was poured into a paper machine and, after being evenly dispersed, was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01-0.06 MPa. Then, the water was further removed using a press to obtain a wet paper web with a moisture content of 40%, which was dried in an oven at 105℃ to obtain the base paper. Chemically pure aluminum hydroxide was ground in a bead mill for 45 minutes, with bead diameters of 3-5 mm and a bead-to-particle ratio of 20:1, to obtain aluminum hydroxide particles with an average particle size of 200 nm. These aluminum hydroxide particles were added to a 29% phenolic resin ethanol solution and mechanically stirred at room temperature for 30 minutes to obtain a phenolic resin impregnation solution. The base paper was immersed in the above-mentioned phenolic resin impregnation solution at room temperature for 10 minutes, then removed and dried at 105°C for 20 minutes to obtain impregnated paper with a resin content of 29.5%. The impregnated paper was then placed on a vulcanizing machine and hot-pressed at 200°C and 2MPa for 5 minutes to obtain a high-porosity wet-based paper friction material. The basis weight of the high-porosity wet-based paper friction material was 398 g / m³. 2 The thickness is 414 μm. The aluminum hydroxide particles account for 2% of the dry weight of the phenolic resin.

[0105] The porosity of this high-porosity wet paper-based friction material was measured to be 29.9% using a fully automated true density analyzer. The average pore size of the material was measured to be 4.0456 μm using a Capillary Flow Porometer. The pore size distribution is shown below. Figure 4 As shown.

[0106] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the high-porosity wet paper-based friction material was 0.110, which was 15.8% higher than that of Comparative Example 1; the static friction coefficient was 0.128, which was 20.8% higher than that of Comparative Example 1. It meets the requirements of Class 2 and Class 3 products in the national standard GB / T37208-2018 for non-metallic paper-based wet friction materials.

[0107] Example 3

[0108] By weight, 10 parts cotton fiber, 10 parts hemp fiber, 13 parts aramid fiber, 7 parts carbon fiber, 23 parts diatomaceous earth, 10 parts feldspar, 2 parts alumina, 15 parts graphite, and 10 parts rubber powder were uniformly dispersed with water to obtain a slurry with a solid content of 1.9%. The slurry was poured into a paper machine and, after uniform dispersion, vacuum-dehydrated to a solid content of 10-25% under a vacuum of 0.01-0.06 MPa. Then, the water was further removed using a press to obtain a wet paper web with a moisture content of 41%. This wet paper was dried in a 105℃ drying cylinder to obtain the base paper. Aluminum hydroxide was ground in a ball mill for 55 minutes with a bead diameter of 1-2 mm and a ball-to-material ratio of 20:1 to obtain aluminum hydroxide microparticles with an average particle size of 100 nm. These aluminum hydroxide microparticles were added to a 30% phenolic resin ethanol solution and mechanically stirred at room temperature for 30 minutes to obtain a phenolic resin impregnation solution. The base paper was immersed in the above-mentioned phenolic resin impregnation solution at room temperature for 10 minutes, then removed and dried at 80°C for 40 minutes to obtain impregnated paper with a resin content of 28.9%. The impregnated paper was then placed on a vulcanizing machine and hot-pressed at 200°C and 4MPa for 3 minutes to obtain a high-porosity wet-based paper friction material. The basis weight of the high-porosity wet-based paper friction material was 366 g / m³. 2 The thickness is 414 μm. The aluminum hydroxide particles account for 1% of the dry weight of the phenolic resin.

[0109] The porosity of this high-porosity wet paper-based friction material was measured to be 46.1% using a fully automated true density analyzer. The average pore size of the material was measured to be 2.1721 μm using a Capillary Flow Porometer. The pore size distribution is as follows: Figure 5 As shown.

[0110] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the high-porosity wet paper-based friction material was 0.119, which was 25.3% higher than that of Comparative Example 2; the static friction coefficient was 0.134, which was 26.4% higher than that of Comparative Example 2. It meets the requirements of Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0111] Example 4

[0112] By weight, 10 parts cotton fiber, 10 parts hemp fiber, 13 parts aramid fiber, 7 parts carbon fiber, 23 parts diatomaceous earth, 10 parts feldspar, 2 parts alumina, 15 parts graphite, and 10 parts rubber powder were uniformly dispersed with water to obtain a slurry with a solid content of 1.9%. The slurry was poured into a paper machine and, after uniform dispersion, was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01-0.06 MPa. Then, the water was further removed using a press to obtain a wet paper web with a moisture content of 43%, which was dried in a 105℃ drying cylinder to obtain the base paper. Aluminum hydroxide was ground in a ball mill for 30 minutes with a ball diameter of 1-2 mm and a ball-to-material ratio of 25:1 to obtain aluminum hydroxide microparticles with an average particle size of 90 nm. These aluminum hydroxide microparticles were added to a 34% solid content phenolic resin ethanol solution, ultrasonically treated for 15 minutes, and then mechanically stirred for 30 minutes to obtain a phenolic resin impregnation solution. The base paper was immersed in the above-mentioned phenolic resin impregnation solution at room temperature for 10 minutes, then removed and dried at 80°C for 40 minutes to obtain impregnated paper with a resin content of 33.1%. The impregnated paper was then placed on a vulcanizing machine and hot-pressed at 200°C and 4MPa for 3 minutes to obtain a high-porosity wet-based paper friction material. The basis weight of the high-porosity wet-based paper friction material was 345 g / m³. 2 The thickness is 416 μm. The aluminum hydroxide particles account for 3% of the dry weight of the phenolic resin.

[0113] The porosity of this high-porosity wet paper-based friction material was measured to be 46.8% using a fully automated true density analyzer. The average pore size of the material was measured to be 2.3325 μm using a Capillary Flow Porometer. The pore size distribution is as follows: Figure 6 As shown.

[0114] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of a rotational speed of 2000 r / min and a pressure of 0.4 MPa, the dynamic friction coefficient of the high-porosity wet paper-based friction material was 0.121, which was 27.4% higher than that of Comparative Example 2; the static friction coefficient was 0.134, which was 26.4% higher than that of Comparative Example 2. It meets the requirements for Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0115] Comparative Example 3

[0116] By weight, 20 parts cotton fiber, 10 parts aramid fiber, 10 parts carbon fiber, 30 parts diatomaceous earth, 5 parts feldspar, 5 parts barium sulfate, 10 parts graphite, and 10 parts rubber powder were uniformly dispersed with water to obtain a slurry with a solid content of 2%. The slurry was poured into a sheeter and, after uniform dispersion, vacuum-dehydrated to a solid content of 10-25% under a vacuum of 0.01–0.06 MPa. Then, a press was used to further remove moisture, resulting in a wet paper web with a moisture content of 43%. This web was dried in a 105°C drying cylinder to obtain the base paper. The base paper was immersed in a 27% phenolic resin ethanol solution at room temperature for 10 minutes, then removed and dried at 85°C for 30 minutes to obtain glazed paper with a glaze content of 28.9%. The glazed paper was placed on a vulcanizing machine and hot-pressed at 210°C and 3 MPa for 5 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material is 345 g / m³. 2 The thickness is 380μm.

[0117] The porosity of this high-porosity wet paper-based friction material was measured to be 41.7% using a fully automated true density analyzer. The average pore size of the material was measured to be 1.8635 μm using a capillary flow pore size analyzer. The pore size distribution is as follows: Figure 7 As shown.

[0118] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of a rotational speed of 2000 r / min and a pressure of 0.4 MPa, the dynamic friction coefficient of the wet paper-based friction material was 0.106, and the static friction coefficient was 0.112. After 2000 tests, the wear rate was 3 × 10⁻⁶. -7 cm 2 / J. Meets the requirements for Class 2 and Class 3 products in the national standard GB / T37208-2018 Non-metallic Paper-based Wet Friction Materials.

[0119] Example 5

[0120] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber, and 20 parts friction powder were evenly dispersed with water to obtain a pulp with a solid content of 1.7%. A 3wt% aluminum sulfate aqueous solution was added to the pulp to adjust the pH of the system to 3.0, and the mixture was stirred for 10 minutes. A 5wt% sodium hydroxide aqueous solution was then added to adjust the pH of the system to 7.0, and the mixture was stirred for 10 minutes. The prepared pulp was poured into a paper machine, and after the pulp was evenly dispersed, it was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01–0.06 MPa. The pulp was then further dehydrated using a press to obtain a wet paper web with a moisture content of 42%. This wet paper web was then dried in a 95℃ vacuum dryer for 5 minutes to obtain the base paper. The base paper was immersed in a phenolic resin ethanol solution with a solid content of 30% for 10 minutes, then removed and dried at 105℃ for 10 minutes to obtain impregnated paper with a resin content of 29.2%. This impregnated paper was then hot-pressed on a vulcanizing machine at 200℃ and 2MPa for 5 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material was 410 g / m³. 2 The thickness is 386μm.

[0121] The porosity of this high-porosity wet paper-based friction material was measured to be 25.1% using a fully automated true density analyzer. The average pore size of the material was measured to be 3.1700 μm using a Capillary Flow Porometer. The pore size distribution is shown below. Figure 8 As shown.

[0122] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the material was 0.094, which was 11.9% higher than that of Comparative Example 1; the static friction coefficient was 0.113, which was 18.9% higher than that of Comparative Example 1; and the wear rate was 4 × 10⁻⁶. -7 The ratio of cm² / J is 20% lower than that of Comparative Example 1; it meets the requirements of Class 2 and Class 3 products in the national standard GB / T37208-2018 for non-metallic paper-based wet friction materials.

[0123] Example 6

[0124] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber, and 20 parts friction powder were evenly dispersed with water to obtain a slurry with a solid content of 1.7%. A 15wt% aluminum sulfate aqueous solution was added to the slurry to adjust the pH to 1.0, and the mixture was stirred for 5 minutes. A 20wt% sodium hydroxide aqueous solution was then added to adjust the pH to 7.3, and the mixture was stirred for 15 minutes. The prepared slurry was poured into a paper machine, and after it was evenly dispersed, it was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01–0.06 MPa. The paper was then further dehydrated using a press to obtain a wet paper web with a moisture content of 42%. This wet paper web was then dried in an oven at 105℃ for 5 minutes to obtain the base paper. The base paper was immersed in a phenolic resin ethanol solution with a solid content of 33% for 15 minutes, then removed and dried at 105℃ for 10 minutes to obtain impregnated paper with a resin content of 32.4%. This impregnated paper was then placed on a vulcanizing machine and vulcanized and hot-pressed at 210℃ and 2.2MPa for 10 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material was 400 g / m³. 2 The thickness is 398μm.

[0125] The porosity of this high-porosity wet paper-based friction material was measured to be 26.9% using a fully automated true density analyzer. The average pore size of the material was measured to be 3.4131 μm using a Capillary Flow Porometer. The pore size distribution is as follows: Figure 9 As shown.

[0126] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the material was 0.108, which was 28.6% higher than that of Comparative Example 1; the static friction coefficient was 0.109, which was 14.7% higher than that of Comparative Example 1; and the wear rate was 3 × 10⁻⁶. -7 cm 2 / J, which is 40% lower than Comparative Example 1.

[0127] Example 7

[0128] By weight, 8 parts cotton fiber, 8 parts aramid fiber, 8 parts carbon fiber, 15 parts diatomaceous earth, 5 parts feldspar, 6 parts graphite, 30 parts rubber, and 20 parts friction powder were evenly dispersed with water to obtain a slurry with a solid content of 1.8%. 2 parts 800-mesh aluminum hydroxide were added to the slurry and stirred for 20 minutes. The prepared slurry was poured into a sheeter, and after it was evenly dispersed, it was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01-0.06 MPa. Then, the water was further removed using a press to obtain a wet paper web with a moisture content of 42%. This web was dried in a 105℃ drying cylinder for 5 minutes to obtain the base paper. The base paper was then immersed in a phenolic resin ethanol solution with a solid content of 34% for 15 minutes, removed, and dried at 90℃ for 30 minutes to obtain sized paper with a sizing content of 31.7%. The impregnated paper was placed on a vulcanizing machine and vulcanized and hot-pressed at 210℃ and 3MPa for 3 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material was 409 g / m³. 2 The thickness is 412μm.

[0129] The porosity of this high-porosity wet paper-based friction material was measured to be 24.5% using a fully automated true density analyzer, which is 6.5% higher than that of Comparative Example 1; the average pore size was 3.1879 μm, which is 6% higher than that of Comparative Example 1.

[0130] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of a rotational speed of 2000 r / min and a pressure of 0.4 MPa, the dynamic friction coefficient of the material was 0.096, which was 14.3% higher than that of Comparative Example 1; the static friction coefficient was 0.108, which was 13.7% higher than that of Comparative Example 1; and the wear rate was 4.5 × 10⁻⁶. -7 cm2 / J, a decrease of 10% compared to Comparative Example 1.

[0131] Example 8

[0132] By weight, 20 parts cotton fiber, 10 parts aramid fiber, 10 parts carbon fiber, 30 parts diatomaceous earth, 5 parts feldspar, 5 parts barium sulfate, 10 parts graphite, and 10 parts rubber were uniformly dispersed with water to obtain a pulp with a solid content of 1.8%. A 25wt% aluminum sulfate aqueous solution was added to the pulp to adjust the pH of the system to 0.7, and the mixture was stirred for 15 minutes. A 30wt% sodium hydroxide aqueous solution was then added to adjust the pH of the system to 7.2, and the mixture was stirred for 15 minutes. The prepared pulp was poured into a paper machine, and after the pulp was uniformly dispersed, it was vacuum dehydrated to a solid content of 10-25% under a vacuum of 0.01–0.06 MPa. The pulp was then further dehydrated using a press to obtain a wet paper web with a moisture content of 43%. This wet paper web was then dried in a 105℃ drying cylinder for 6 minutes to obtain the base paper. The base paper was immersed in a phenolic resin ethanol solution with a solid content of 27% for 10 minutes, then removed and dried at 85°C for 30 minutes to obtain impregnated paper with a resin content of 28.6%. This impregnated paper was then placed on a vulcanizing machine and vulcanized and hot-pressed at 210°C and 3MPa for 5 minutes to obtain a high-porosity wet paper-based friction material. The basis weight of the high-porosity wet paper-based friction material was 341 g / m³. 2 The thickness is 379μm.

[0133] The porosity of this high-porosity wet paper-based friction material was measured to be 44.3% using a fully automated true density analyzer, which is 6.2% higher than that of Comparative Example 3; the average pore size was 2.3524 μm, which is 26.2% higher than that of Comparative Example 3.

[0134] The tribological properties of this high-porosity wet paper-based friction material were tested using an MM2000 tribological testing machine. Under the conditions of 2000 r / min rotation speed and 0.4 MPa pressure, the dynamic friction coefficient of the material was 0.108, which was 1.9% higher than that of Comparative Example 3; the static friction coefficient was 0.130, which was 16.1% higher than that of Comparative Example 3; and the wear rate was 2×10⁻⁶. -7 cm2 / J, a 50% reduction compared to Comparative Example 3.

[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-porosity wet paper-based friction material, comprising the following steps: Natural fibers, synthetic fibers, friction modifiers, fillers, and water are mixed to obtain a slurry; The pulp is dehydrated, shaped, and then dried to obtain the base paper; The base paper is impregnated with phenolic resin solution and then dried to obtain impregnated paper. The impregnated paper is subjected to hot-press vulcanization to obtain a high-porosity wet paper-based friction material. The slurry or the phenolic resin impregnation solution also includes a pore-forming agent; The pore-forming agent in the slurry includes a water-soluble pore-forming agent and an inorganic strong base, or an insoluble pore-forming agent; the water-soluble pore-forming agent is aluminum sulfate, or alum and sulfuric acid; the insoluble pore-forming agent is aluminum hydroxide particles and / or calcium oxalate powder, and the pH value of the slurry containing the inorganic strong base is 6-8; the mass of alum in the slurry accounts for 0.1-5% of the dry weight of the slurry without the addition of insoluble pore-forming agent; the mass of the insoluble pore-forming agent accounts for 0.001-10% of the mass of the slurry without the addition of insoluble pore-forming agent. The pore-forming agent in the phenolic resin impregnation solution is one or more of aluminum hydroxide microparticles, alum, and calcium oxalate powder. The particle size of the pore-forming agent in the phenolic resin impregnation solution is 1~1000nm, and the mass of the pore-forming agent accounts for 0.1~5% of the dry weight of the phenolic resin. The hot-press vulcanization temperature is 200~230℃.

2. The preparation method according to claim 1, characterized in that, When the slurry also includes aluminum sulfate and an inorganic strong base, the preparation method of the slurry containing the pore-forming agent includes the following steps: adding aluminum sulfate to the slurry until the pH value is 0.1~5, and then adding an inorganic strong base to adjust the pH value to 6~8; When the slurry also includes alum, sulfuric acid and inorganic strong base, the preparation method of the slurry containing pore-forming agent includes the following steps: adding alum to the slurry, adding sulfuric acid to adjust the pH value to 0.1~5, and then adding inorganic strong base to adjust the pH value to 6~8; When the slurry also includes an insoluble pore-forming agent, the method for preparing the slurry containing the pore-forming agent includes the following steps: adding an insoluble pore-forming agent to the slurry.

3. The preparation method according to claim 1, characterized in that, The phenolic resin in the phenolic resin impregnation solution includes one or more of the following: unmodified phenolic resin, cashew nut shell oil modified phenolic resin, melamine modified phenolic resin, latex modified phenolic resin, and boron modified phenolic resin. The solid content of the phenolic resin impregnation solution is 20-50%.

4. The preparation method according to claim 1 or 2, characterized in that, The natural fibers include one or more of hemp fiber, cotton fiber, bamboo fiber, and wood pulp fiber; The synthetic fibers include one or more of aramid fibers, carbon fibers, glass fibers, ceramic fibers, and polyimide fibers; The friction performance modifier filler includes one or more of diatomaceous earth, silica, feldspar, barium sulfate, graphite, alumina, and organic friction powder. The mass ratio of the natural fiber to the synthetic fiber is 1:0.1~8; The mass ratio of the natural fiber to the friction modifier filler is 1:0.1~12; The solid content of the slurry is 0.5-3%.

5. The preparation method according to claim 1, characterized in that, The impregnation time is 3 to 20 minutes.

6. The preparation method according to claim 1, characterized in that, The hot-press vulcanization pressure is 1~30MPa, and the time is 1~30min.

7. The high-porosity wet paper-based friction material prepared by the preparation method according to any one of claims 1 to 6.

8. The high-porosity wet paper-based friction material according to claim 7, characterized in that, The quantitative amount of the high-porosity wet paper-based friction material is 100~2000 g / m³. 2 The thickness is 0.2~5mm.

9. The application of the high-porosity wet paper-based friction material as described in claim 7 or 8 in a wet clutch or wet braking device.

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