Antistatic modified carbon fiber reinforced paper-based friction material and method for manufacturing the same

Abstract

The present application relates to a kind of anti-static modified carbon fiber reinforced paper-based friction material and its preparation method, belongs to high-performance friction material technical field, paper-based friction material includes reinforcing fiber system, binder system, friction performance regulator and anti-static modifier composition.The preparation method includes the following operating steps: first step: modified carbon fiber is treated with anti-static modification.The second step: paper forming.The third step: using paper page former or wet papermaking equipment, filter water forming, obtains wet paper blank.The fourth step: wet paper blank is dried in drying oven.The fifth step: after drying, paper blank is immersed in modified phenolic resin solution.The sixth step: after impregnation, material is placed in hot press and is heat pressed, finally, after the step-by-step temperature rise in oven, solidification treatment is carried out.The anti-static function of polyaniline is combined with the surface modification technology of carbon fiber, and the key problems of traditional carbon fiber reinforced paper-based friction material in interface bonding, dispersibility and static accumulation are solved.

Description

Technical Field

[0001] This invention relates to the field of high-performance friction materials technology, specifically to an antistatic modified carbon fiber reinforced paper-based friction material and its preparation method. Background Technology

[0002] Traditional paper-based friction materials typically consist of fibers (such as cellulose, aramid, and carbon fiber), binders (such as phenolic resin), and fillers. While carbon fiber has excellent thermal conductivity and reinforcing properties, high carbon fiber content can lead to static electricity buildup under certain operating conditions, or result in weak bonding with the resin due to its surface chemical properties.

[0003] Paper-based friction materials rely on their porous structure to store lubricating oil, forming an oil film during friction to achieve power transmission. Carbon fiber, due to its high strength, high modulus, and excellent thermal conductivity, is an ideal reinforcing material. However, unmodified carbon fiber has the following problems: 1. Surface inertness: Carbon fiber has a smooth surface, low chemical activity, poor adhesion to the resin matrix, and is prone to interfacial delamination.

[0004] 2. Static electricity accumulation: Although carbon fiber itself is conductive, under certain fiber arrangements or low content, isolated conductive islands may be formed inside the material. Static electricity generated during friction is difficult to discharge, which may interfere with electronic equipment or attract dust.

[0005] 3. Brittleness: Excessive addition will lead to a decrease in the toughness of the material.

[0006] Paper-based friction materials are widely used in automotive automatic transmissions (wet clutches) and construction machinery, operating in environments where they are immersed in and circulated with transmission fluid (ATF / CVT Fluid). However, with the development of modern transmission systems towards high speed, heavy load, and compactness, traditional paper-based friction materials have revealed the following fatal problems: I. Safety Hazards and Failure Risks Caused by Static Electricity Accumulation: During the high-speed slippage and engagement / disengagement of the clutch, intense frictional shearing occurs between the friction material and the mating steel plates, resulting in a strong triboelectric effect. Traditional paper-based materials are mostly insulators (relying on insulating components such as phenolic resin and cellulose), which cannot effectively dissipate the generated static electricity. Static electricity accumulation not only easily breaks down the oil film, causing electrochemical corrosion, but under certain operating conditions, it can even generate electric sparks, leading to localized oil deterioration or safety hazards. Simultaneously, static electricity causes excessive sludge and wear debris to adhere to the friction surfaces, altering the coefficient of friction and causing clutch engagement jerking or slippage.

[0007] II. Limitations of Traditional Reinforcing Fibers: Early paper-based friction materials mostly used asbestos or pure plant fibers. Asbestos is banned due to its carcinogenicity; although pure plant fibers have good papermaking properties, they have poor heat resistance and are prone to carbonization and degradation under high-temperature friction, resulting in a sharp drop in material strength, powdering, and brittleness.

[0008] III. Interfacial Challenges of Direct Carbon Fiber Applications: While carbon fiber possesses ultra-high strength, excellent heat resistance, and thermal conductivity, making it an ideal alternative to asbestos, untreated carbon fiber surfaces are chemically inert (lacking active functional groups), smooth, and hydrophobic. When directly used in wet-process papermaking and impregnated with phenolic resin, the interfacial bonding between the fiber and the resin matrix is ​​extremely weak. Under shear forces, "fiber pull-out" rather than "fiber breakage" easily occurs, leading to a sharp decrease in material wear resistance and a shortened service life.

[0009] IV. Disadvantages of Existing Antistatic Solutions: To address conductivity issues, existing technologies often employ the addition of large amounts of carbon black, graphite, or metal powder to achieve antistatic properties. However, fillers such as carbon black often act as "solid lubricants" at friction interfaces, and excessive addition can significantly reduce the dynamic / static friction coefficients of the material, failing to meet the stringent torque transmission requirements of the clutch. Simultaneously, metal powders have high density and are prone to sedimentation during wet papermaking, resulting in uneven distribution of material components. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by providing an antistatic modified carbon fiber reinforced paper-based friction material and its preparation method. It combines the antistatic function of polyaniline with the surface modification technology of carbon fiber, solving the key problems of interfacial bonding, dispersion and electrostatic accumulation in traditional carbon fiber reinforced paper-based friction materials.

[0011] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: An antistatic modified carbon fiber reinforced paper-based friction material comprises a reinforcing fiber system, a binder system, a friction performance modifier, and an antistatic modifier; the reinforcing fiber system consists of modified carbon fiber and auxiliary fibers; the binder system uses modified phenolic resin; the friction performance modifier uses graphite, molybdenum disulfide, wollastonite, alumina, or barium sulfate; and the antistatic modifier is polyaniline.

[0012] Preferably, the auxiliary fiber is aramid pulp or cellulose fiber, or the auxiliary fiber is a mixture of aramid pulp and cellulose fiber.

[0013] Preferably, the paper-based friction material formulation is mixed in parts by weight, comprising 14-18 parts modified carbon fiber, 8-12 parts aramid pulp, 8-12 parts cellulose fiber, 20-25 parts friction performance modifier, 37-43 parts modified phenolic resin, and 2-4 parts polyaniline.

[0014] A method for preparing an antistatic modified carbon fiber reinforced paper-based friction material includes the following steps: Step 1: Modify the carbon fiber by performing antistatic modification treatment, using liquid phase oxidation, surface coating / coating, or gas phase oxidation.

[0015] Step 2: Papermaking and forming. Modified carbon fiber, auxiliary fiber, friction modifier and polyaniline are dispersed in water, and a dispersant is added and stirred evenly to form a suspension slurry.

[0016] Polyaniline is added at this step to ensure it is uniformly dispersed in the fiber network. The dispersant is polyethylene oxide (PEO) or cationic polyacrylamide (CPAM) to prevent agglomeration and sedimentation, ensuring a uniform paper blank. The dispersant helps break up fiber entanglement, forming a uniform suspension.

[0017] Step 3: Use a paper forming machine or wet papermaking equipment to filter water and form paper blanks to obtain wet paper blanks.

[0018] Step 4: Dry the wet paper blank in a drying oven at a temperature of 110-130℃ to remove moisture.

[0019] Step 5: Immerse the dried paper blank in a modified phenolic resin solution.

[0020] Step 6: Place the impregnated material into a hot press for hot pressing, and finally cure it in an oven with stepped heating.

[0021] Stepwise heating can effectively eliminate low-molecular-weight volatiles (such as water vapor and free phenols) generated during the curing process, prevent bubbles or delamination from forming inside the material, and completely complete the cross-linking and curing of the resin.

[0022] Preferably, the short-cut carbon fibers are immersed in concentrated nitric acid or mixed acid and refluxed at a temperature of 38–45°C to complete the liquid-phase oxidation method.

[0023] Strong oxidizing agents such as concentrated nitric acid or mixed acids can etch the surface of carbon fibers, introducing polar functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH), significantly improving surface energy and chemical activity. This improves dispersibility and enhances wettability and adhesion to phenolic resins.

[0024] Preferably, the concentration of concentrated nitric acid is 65% to 68%, which is 100% by mass.

[0025] Preferably, a surface plating / coating method is used to deposit metal layers such as nickel and copper on the carbon fiber surface by chemical plating or electroplating, or to coat it with conductive polymer.

[0026] Metallic coatings can significantly improve the electrical conductivity of carbon fibers, fundamentally constructing highly efficient electron conduction channels, making it a powerful means of antistatic modification. Simultaneously, the metallic layer can also enhance the mechanical bonding between the fiber and the matrix, endowing the material with excellent antistatic properties and potentially improving thermal conductivity.

[0027] Preferably, carbon fibers are treated at high temperatures in an air or oxygen atmosphere to remove the weak boundary layer on the surface, thus completing the gas-phase oxidation method.

[0028] High-temperature oxidation removes the weak boundary layer and impurities on the surface of carbon fibers, while introducing a small number of oxygen-containing functional groups to improve surface activity.

[0029] Preferably, the temperature for hot pressing in the hot press is 165–175°C, and the pressing pressure is 9–10 MPa.

[0030] The present invention can achieve the following effects: This invention provides an antistatic modified carbon fiber reinforced paper-based friction material and its preparation method. Compared with existing technologies, it combines the antistatic function of polyaniline with the surface modification technology of carbon fiber, systematically solving the key problems of interfacial bonding, dispersion, and electrostatic accumulation in traditional carbon fiber reinforced paper-based friction materials. It has the following significant beneficial effects: I. Constructing a "dual / multiple conductive network" to achieve efficient and stable antistatic function. Instead of using carbon black, which would damage the coefficient of friction, an innovative approach was taken to introduce three parts of polyaniline, combined with modified carbon fiber.

[0031] Synergistic effect: Modified carbon fibers construct a one-dimensional "microscopic conductive framework" within the material, while polyaniline particles dispersed in the phenolic resin matrix construct a three-dimensional "macroscopic conductive pathway." The two interlock within the matrix, forming a three-dimensional antistatic network.

[0032] Uncompromising performance: Polyaniline itself has excellent tribological properties and will not significantly reduce the coefficient of friction like carbon black. Adding only 3 parts can drastically reduce the volume resistivity of the material, achieving antistatic levels and completely solving the problem of static electricity buildup during high-speed sliding.

[0033] II. Completely solves the problem of "difficult interface bonding" in carbon fiber, resulting in a leap in mechanical properties and wear resistance. Strict surface modification of the carbon fiber brings three major benefits: Increased physical anchoring: Oxidation etching roughens the surface of carbon fiber, increasing the mechanical interlocking force of the resin.

[0034] Introducing chemical bonding: Oxygen-containing functional groups such as carboxyl and hydroxyl groups are introduced into the surface of carbon fibers. These groups can react chemically with modified phenolic resin (or form strong hydrogen bonds), turning the original "physical contact" into "chemical bonding".

[0035] Improved dispersibility: The introduction of hydrophilic groups enables the hydrophobic carbon fibers to be better and more uniformly dispersed with water and cellulose fibers in the second step of wet papermaking, thus avoiding fiber clumping.

[0036] Results: The tensile strength and shear strength of the material were significantly improved, the "fiber pull-out" phenomenon during the friction process was effectively suppressed, and the wear rate of the material was significantly reduced.

[0037] Third, the hybrid fiber system brings excellent comprehensive physical and mechanical properties. 16 parts modified carbon fiber provide rigidity, thermal conductivity, and electrical conductivity; 9 parts aramid pulp provide extremely high toughness, impact resistance, and noise reduction; 11 parts cellulose fiber provide excellent wet papermaking water-filtering and molding properties, and maintain the basic pore skeleton of the material. The "rigid-flexible-tough" hybrid reinforcement system formed by these three components makes the final hot-pressed paper-based material both strong and tough without becoming brittle, and fully capable of withstanding the severe mechanical impacts caused by frequent clutch engagement and disengagement.

[0038] IV. Impregnation and stepped curing processes ensure consistent high quality throughout the material. Precise control of 30%–50% solids content ensures that the 39 parts of modified phenolic resin can smoothly penetrate deep into the micropores of the paper blank without floating on the surface, avoiding the defect of "burnt on the outside and tender on the inside" and guaranteeing the uniformity of internal bonding strength.

[0039] Stepped curing from 140℃ to 160℃ to 180℃ to 200℃: The temperature profile design allows the resin ample time for "flow-penetration-initial crosslinking-deep curing". This effectively releases internal stress during the curing process, completely eliminates internal volatiles, avoids material warping, delamination, or bulging, and significantly improves product yield and dimensional stability.

[0040] V. Stable coefficient of friction and minimal thermal degradation. Due to the rational combination of 22 friction performance modifiers (graphite, molybdenum disulfide, wollastonite, etc.) and the excellent thermal conductivity of carbon fiber (which can quickly dissipate heat from the friction surface), this material exhibits a high and stable coefficient of dynamic friction in the transmission oil environment. Even under high temperature and high load conditions, it is not prone to "thermal degradation" caused by resin degradation, ensuring the accuracy and smoothness of power transmission in the transmission. Detailed Implementation

[0041] The technical solution of the invention will be further described in detail below through examples.

[0042] Example: An antistatic modified carbon fiber reinforced paper-based friction material, comprising a reinforcing fiber system, a binder system, a friction performance modifier, and an antistatic modifier. The reinforcing fiber system consists of modified carbon fibers and auxiliary fibers, wherein the auxiliary fibers are aramid pulp or cellulose fibers, or a mixture of aramid pulp and cellulose fibers. The binder system uses modified phenolic resin. The friction performance modifier uses graphite, molybdenum disulfide, wollastonite, alumina, or barium sulfate. The antistatic modifier is polyaniline.

[0043] The paper-based friction material formulation is mixed according to the following parts by weight: 16 parts modified carbon fiber, 9 parts aramid pulp, 11 parts cellulose fiber, 22 parts friction performance modifier, 39 parts modified phenolic resin, and 3 parts polyaniline.

[0044] A loose skeleton is formed by 16% modified carbon fiber and 20% auxiliary fiber, 22% filler occupies part of the space, and 39% resin is impregnated through a 30-50% solids content. This combination can still retain about 15%-25% microporosity after final hot pressing, which is beneficial for paper-based friction materials when working in transmission fluid (the fluid needs to be stored in the pores for cooling and lubrication).

[0045] A method for preparing an antistatic modified carbon fiber reinforced paper-based friction material includes the following steps: Step 1: Modify the carbon fiber by performing antistatic modification treatment, using liquid phase oxidation, surface coating / coating, or gas phase oxidation.

[0046] Short-cut carbon fibers are immersed in concentrated nitric acid or a mixed acid at an oxidation temperature of 80°C. The concentration of the concentrated nitric acid is 65%–68% by mass, and the oxidation time is 2–4 hours. Then, reflux treatment is performed at 42°C to complete the liquid-phase oxidation method.

[0047] The surface plating / coating method involves depositing metal layers such as nickel and copper on the surface of carbon fibers using chemical plating or electroplating, or coating them with conductive polymers.

[0048] Carbon fibers are treated at high temperatures in an air or oxygen atmosphere to remove the weak boundary layer on the surface, thus completing the gas-phase oxidation process.

[0049] Step 2: Papermaking and forming. Modified carbon fiber, auxiliary fiber, friction modifier and polyaniline are dispersed in water, and a dispersant is added and stirred evenly to form a suspension slurry.

[0050] Step 3: Use a paper forming machine or wet papermaking equipment to filter water and form paper blanks to obtain wet paper blanks.

[0051] Step 4: Dry the wet paper blank in a drying oven at a temperature of 115℃ to remove moisture.

[0052] Step 5: Immerse the dried paper blank in a modified phenolic resin solution. The solid content of the modified phenolic resin solution is 30%–50%, ensuring that the resin fully penetrates into the pore structure of the material.

[0053] Step 6: Place the impregnated material into a hot press for hot pressing at a temperature of 170℃ and a pressing pressure of 10MPa. Finally, perform a stepped temperature increase curing treatment in an oven. The stepped temperature increases are 140℃, 160℃, 180℃, and 200℃, with each stage held for 1-2 hours.

[0054] 140℃ / 160℃: This is the initial stage of the cross-linking reaction of phenolic resin. At this time, the resin's melt viscosity decreases, allowing it to penetrate deeper into the fiber gaps and begin to form a network structure. Slow heating can prevent the formation of internal bubbles and internal stress.

[0055] 180℃ / 200℃: This is the deep curing period, during which the resin forms a highly cross-linked three-dimensional network structure, giving the material its final heat resistance, hardness, and mechanical strength. If the material is directly placed into a 200℃ oven without a gradual heating process, the surface resin will instantly solidify and form a shell, preventing the internal solvents from evaporating. This will cause the material to bulge, crack, and become unusable.

[0056] In summary, this antistatic modified carbon fiber reinforced paper-based friction material and its preparation method combine the antistatic function of polyaniline with the surface modification technology of carbon fiber, systematically solving the key problems of interfacial bonding, dispersion, and electrostatic accumulation in traditional carbon fiber reinforced paper-based friction materials. Introducing polyaniline into the paper-based friction material system solves the problem of easy static electricity accumulation in traditional materials.

[0057] A dual strategy of "carbon fiber surface modification + polyaniline addition" is adopted. Surface modification strengthens the "point-to-point" bonding between the fiber and the resin, while polyaniline forms a "surface-to-surface" conductive network in the matrix. The two work together to achieve efficient antistatic properties without significantly sacrificing other material properties.

[0058] By chemically modifying or physically coating carbon fibers, not only is the mechanical strength of the material improved, but it is also endowed with excellent antistatic properties, making it suitable for high-end heavy-duty clutches and precision transmission devices that are sensitive to static electricity.

[0059] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. An antistatic modified carbon fiber reinforced paper-based friction material, characterized in that: It comprises a reinforcing fiber system, a binder system, a friction modifier, and an antistatic modifier; the reinforcing fiber system consists of modified carbon fiber and auxiliary fibers; the binder system uses modified phenolic resin; the friction modifier uses graphite, molybdenum disulfide, wollastonite, alumina, or barium sulfate; and the antistatic modifier is polyaniline.

2. The antistatic modified carbon fiber reinforced paper-based friction material according to claim 1, characterized in that: The auxiliary fiber is aramid pulp or cellulose fiber, or the auxiliary fiber is a mixture of aramid pulp and cellulose fiber.

3. The antistatic modified carbon fiber reinforced paper-based friction material according to claim 2, characterized in that: The paper-based friction material formulation is mixed in parts by weight, comprising 14-18 parts modified carbon fiber, 8-12 parts aramid pulp, 8-12 parts cellulose fiber, 20-25 parts friction performance modifier, 37-43 parts modified phenolic resin, and 2-4 parts polyaniline.

4. A method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 3, characterized in that... The following steps are included: Step 1: Modify the carbon fiber by performing antistatic modification treatment, using liquid phase oxidation, surface coating / coating, or gas phase oxidation. Step 2: Papermaking and forming. Modified carbon fiber, auxiliary fiber, friction modifier and polyaniline are dispersed in water, dispersant is added and stirred evenly to form a suspension slurry; Step 3: Use a paper forming machine or wet papermaking equipment to filter water and form a wet paper blank; Step 4: Dry the wet paper blank in a drying oven at a temperature of 110-130℃ to remove moisture; Step 5: Immerse the dried paper blank in a modified phenolic resin solution; Step 6: Place the impregnated material into a hot press for hot pressing, and finally cure it in an oven with stepped heating.

5. The method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 4, characterized in that: Short-cut carbon fibers are immersed in concentrated nitric acid or mixed acid at an oxidation temperature of 75–85°C, followed by reflux treatment at a temperature of 38–45°C to complete the liquid-phase oxidation method.

6. The method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 5, characterized in that: The concentration of concentrated nitric acid is 65%–68%, which is 100% by mass, and the oxidation time is 2–4 hours.

7. The method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 4, characterized in that: The surface plating / coating method involves depositing metal layers such as nickel and copper on the surface of carbon fibers using chemical plating or electroplating, or coating them with conductive polymers.

8. The method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 4, characterized in that: Carbon fibers are treated at high temperatures in an air or oxygen atmosphere to remove the weak boundary layer on the surface, thus completing the gas-phase oxidation process.

9. The method for preparing the antistatic modified carbon fiber reinforced paper-based friction material according to claim 4, characterized in that: The hot pressing temperature in the hot press is 165-175℃, and the pressing pressure is 9-12 MPa.