Basalt fiber reinforced non-heavy metal NAO friction material and preparation method thereof

Abstract

The application discloses a basalt fiber reinforced heavy metal-free NAO friction material and a preparation method thereof, and relates to the technical field of polymer compound composition friction-resistant and aging-resistant materials. The basalt fiber reinforced heavy metal-free NAO friction material is made of the following components in mass parts: 100 parts of phenolic resin, 10-30 parts of basalt fiber, 20-70 parts of mineral filler, 5-30 parts of friction performance regulator, 3-20 parts of organic fiber, 5-15 parts of polyether ether ketone, 3-7 parts of silane coupling agent and 1.5-1.5 parts of ultraviolet aging inhibitor. The application optimizes the formula and the process, utilizes the synergistic effect of the basalt fiber reinforced framework and the components, effectively improves the wear resistance of the friction material, and prolongs the service life. With the effect of absorbing ultraviolet rays and quenching free radicals of the new ultraviolet aging inhibitor, the aging resistance of the material is obviously improved, the performance of the material can be kept stable in long-term use, and the maintenance cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of friction-resistant and anti-aging materials of polymer compound compositions, specifically to a basalt fiber reinforced non-heavy metal NAO friction material and its preparation method. Background Technology

[0002] In today's industrial and transportation sectors, the demand for high-performance friction materials is growing. However, existing technologies have many shortcomings and urgently need improvement.

[0003] Currently, many friction materials need improvement in their friction resistance. Under high-intensity friction environments, such as automotive brakes and industrial braking systems, some materials are prone to accelerated wear and decreased braking performance. This not only shortens the service life of the friction materials but may also cause safety hazards, leading to longer braking distances or even brake failure, threatening people's lives and property.

[0004] Anti-aging performance is also a major shortcoming of existing friction materials. Long-term exposure to heat, oxygen, and ultraviolet radiation can easily cause friction materials to age. This alters their physical and chemical properties, leading to hardening, brittleness, and cracking, thus severely affecting the stability of their friction performance. Aging is more pronounced in outdoor use or high-temperature operating environments, resulting in increased maintenance costs and more frequent replacements. Preventing yellowing is also crucial. Some friction materials are prone to yellowing during use, which not only affects the product's appearance but may also indicate internal chemical changes. Yellowing may be due to oxidation and degradation reactions of certain components under heat and light, producing colored substances. This deterioration in appearance reduces user trust and satisfaction, especially in applications where aesthetics are critical, such as high-end automotive braking systems.

[0005] Furthermore, some existing friction materials contain heavy metals to improve performance. This can easily cause environmental pollution and harm human health during use and disposal, violating the requirements of modern society for environmental protection and sustainable development.

[0006] In conclusion, developing a friction-resistant, anti-aging, and yellowing-resistant heavy metal-free friction material has become an urgent need for industry development. This will not only improve the performance and service life of friction materials but also meet environmental protection requirements, promoting technological progress and industrial upgrading in related fields. Summary of the Invention

[0007] This invention addresses the problems of insufficient friction resistance and easy yellowing due to aging in existing friction materials, aiming to provide a basalt fiber-reinforced, heavy metal-free (NAO) (asbestos-free organic composition) friction material. This material, through a specific formulation and process, utilizes a basalt fiber-reinforced skeleton, a low-phenol environmentally friendly phenolic resin matrix, an optimized combination of mineral fillers, and the synergistic effect of UV antioxidants to achieve a comprehensive improvement in high wear resistance, anti-aging, anti-yellowing, and environmental friendliness.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a basalt fiber reinforced heavy metal-free NAO friction material, which is made of the following components in parts by weight: 100 parts phenolic resin, 10-30 parts basalt fiber, 20-70 parts mineral filler, 5-30 parts friction performance modifier, 3-20 parts organic fiber, 5-15 parts polyether ether ketone, 3-7 parts silane coupling agent, and 1.5-1.5 parts ultraviolet antioxidant;

[0009] The ultraviolet antioxidant is a compound represented by chemical formula 1;

[0010] Chemical Formula 1:

[0011] R1 in the chemical formula 1 is selected from: alkyl with 1-5 carbon atoms, alkoxy with 1-5 carbon atoms, nitro, cyano, and amino.

[0012] Furthermore, none of the components contain heavy metal compounds such as lead, cadmium, chromium, or antimony.

[0013] Furthermore, the free phenol content in the phenolic resin is ≤1%.

[0014] Furthermore, the basalt fibers have a length between 50 and 200 μm.

[0015] Furthermore, the mineral filler comprises the following raw material components in parts by weight: 10-40 parts barium sulfate, 5-25 parts vermiculite, and 5-20 parts alumina.

[0016] Furthermore, the friction performance modifier comprises the following raw materials in parts by weight: 5-15 parts tin sulfide, 10-25 parts ceramic powder, and 5-15 parts graphite.

[0017] Furthermore, the organic fiber is selected from aramid fiber or polyacrylonitrile fiber.

[0018] Furthermore, the silane coupling agent is selected from: silane coupling agent KH550 or silane coupling agent KH560.

[0019] Furthermore, R1 is selected from: methyl, ethyl, tert-butyl, methoxy, nitro, cyano.

[0020] Furthermore, the UV antioxidant is any one of the compounds shown in the following structures:

[0021]

[0022]

[0023] A method for preparing a basalt fiber-reinforced, heavy metal-free (NAO) friction material includes the following steps:

[0024] (1) The basalt fiber and silane coupling agent are stirred and mixed at 50-80℃ for 10-30 minutes to obtain modified basalt fiber;

[0025] (2) Add the modified basalt fiber, phenolic resin, mineral filler, friction performance modifier, organic fiber, polyether ether ketone and UV antioxidant into a mixer and mix for 10-30 minutes to obtain a uniform premix.

[0026] (3) The premixed material is loaded into a preheated mold and hot-pressed in a hot press.

[0027] (4) The hot-pressed blank is placed in an oven for heat treatment and cooled to room temperature to obtain a basalt fiber reinforced non-heavy metal NAO friction material.

[0028] Furthermore, the hot pressing conditions in step (3) are: molding temperature 160-190℃, molding pressure 20-40MPa, and holding time 10-30 minutes.

[0029] Furthermore, the heat treatment conditions in step (4) are: heat treatment temperature 180-220℃, heat treatment time 1.5-4 hours, and heating rate 2-5℃ / minute.

[0030] Furthermore, step (2) is performed under a nitrogen atmosphere.

[0031] In this invention, a novel UV antioxidant is used as a key component in a basalt fiber-reinforced, heavy metal-free NAO friction material. This antioxidant is specifically designed to address the problems of aging and yellowing that occur during long-term use. The core of this UV antioxidant is a compound represented by Chemical Formula 1, whose structural features include aromatic amino groups, ester groups, and a derived anthracene heteroaromatic conjugated structure. These structural elements work synergistically to significantly improve the material's anti-aging performance and anti-yellowing ability by absorbing ultraviolet light, quenching free radicals, and providing chemical stability. The aromatic amino group acts as an electron donor, providing strong nucleophilicity and easily capturing free radicals. The ester group increases molecular polarity through polar bonds, enhancing compatibility with the polymer matrix (phenolic resin). The anthracene ring of the derived anthracene heteroaromatic conjugated structure serves as the core framework, forming an extended π-π conjugated system that efficiently absorbs ultraviolet light energy and exhibits fluorescence. The derived anthracene heteroaromatic conjugated structure possesses a broad-domain conjugated system, enabling efficient absorption of ultraviolet radiation in the 290-400 nm wavelength range. Upon absorbing light energy, the molecule transitions from the ground state to an excited state, converting the energy into harmless heat through internal transformation rather than triggering polymer chain breakage. This directly prevents the photo-oxidative degradation of matrix materials such as phenolic resins (UV radiation is the main cause of yellowing and aging in materials). The aromatic amine group, as an active site, can capture free radicals (such as alkyl radicals R· or peroxy radicals ROO·) generated during frictional heating or oxidation. Through electron-donating effects, the aromatic amine group forms stable intermediates with the free radicals, interrupting the chain oxidation reaction. The ester group provides a polar protective layer, enhancing the dispersibility and thermal stability of the molecule in the polymer matrix. Simultaneously, the R1 substituent, through steric hindrance, prevents oxygen molecules or active species from approaching sensitive bonds (such as the phenolic hydroxyl groups in phenolic resins), thereby delaying oxidation and yellowing processes.

[0032] This invention discloses a basalt fiber-reinforced, heavy metal-free NAO friction material that addresses the problems of poor friction resistance, easy aging and yellowing, and heavy metal contamination through the proportioning of its components and multi-level synergistic effects. Phenolic resin, as a low-free-phenol (≤1%) matrix, reduces the oxidation starting point due to its high bonding stability. Combined with the high hardness and heat resistance (>300℃) of basalt fiber, it forms a reinforcing skeleton. Both are pretreated with a silane coupling agent at 50-80℃ to form a strong interfacial bond, resisting frictional stress delamination. Mineral fillers and friction performance modifiers synergistically construct the friction layer. Alumina and ceramic powder directly improve surface hardness and wear resistance, while tin sulfide and graphite optimize the coefficient of friction and lubricity. The thermal expansion characteristics of vermiculite, combined with the high thermal conductivity of graphite, rapidly dissipate frictional heat, preventing localized overheating and subsequent thermo-oxidative aging of the material. The core anti-aging component of the UV antioxidant utilizes its derived anthracene heteroaromatic conjugated structure to efficiently absorb 290-400nm UV light and convert it into heat energy through π-π conjugation. The aromatic amino groups capture alkyl / peroxide free radicals, synergistically enhancing the chemical inertness and high-temperature dimensional stability (>250℃) of polyether ether ketone, compensating for the thermal weaknesses of phenolic resins and inhibiting thermo-photooxidative degradation. This component also integrates with the resin matrix through its ester groups, forming a uniform protective layer during heat treatment. Organic fibers fill the voids in the composite material, improving toughness. Their aromatic ring structure assists the UV antioxidant in capturing free radicals, delaying the oxidative yellowing of the organic phase. Finally, through a completely heavy metal-free design, combined with hot pressing and nitrogen atmosphere processes, a highly wear-resistant, anti-aging, anti-yellowing, and environmentally friendly organic-inorganic synergistic system is achieved.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. Improved friction resistance: This invention effectively improves the wear resistance of friction materials and extends their service life by optimizing the formula and process, utilizing the basalt fiber reinforced skeleton and the synergistic effect of each component.

[0035] 2. Enhanced anti-aging properties: With the help of new UV antioxidants that absorb ultraviolet rays and quench free radicals, the anti-aging ability of the material is significantly improved, enabling it to maintain stable performance during long-term use and reduce maintenance costs.

[0036] 3. Significant anti-yellowing effect: The addition of a new type of UV antioxidant effectively prevents the yellowing of materials during use, improving the appearance quality of the product and user trust. Attached Figure Description

[0037] Figure 1 This is the NMR spectrum of the UV antioxidant 1 described in this invention. Detailed Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Preparation Example 1

[0040] Preparation of UV antioxidant 1:

[0041]

[0042] Step 1: Mix 10g of raw material 1, 8.66g of raw material 2, 1.33g of sodium hydroxide, and 150ml of toluene. Replace the air in the reaction system with nitrogen three times. Under nitrogen protection, add 0.9g of Pd(DBA)₂ and 0.35g of tri-tert-butylphosphine. Slowly heat to 100℃ and react for 4 hours under nitrogen protection. After the reaction, cool to room temperature, add 150mL of water, and extract twice with ethyl acetate (150mL). Combine the organic phases, dry with 10g of anhydrous sodium sulfate, and remove the solvent by rotary evaporation. Purify by column chromatography (silica gel column, eluent: n-heptane / ethyl acetate). Obtain 12.24g of intermediate 1.

[0043] Step 2: Mix 12.24 g of intermediate 1, 7.85 g of starting material 3, and 150 mL of tetrahydrofuran. Slowly add 1.37 g of concentrated sulfuric acid dropwise to the reaction system. Slowly heat to 80 °C and react for 4 hours under nitrogen protection. After the reaction, cool to room temperature, adjust the pH of the system to neutral with 0.1 mol / L sodium bicarbonate aqueous solution, add 150 mL of water, and extract three times with ethyl acetate (150 mL). Combine the organic phases and remove the solvent by rotary evaporation. Purify by column chromatography (silica gel column, eluent: n-heptane / ethyl acetate) to obtain 15.88 g of UV antioxidant 1.

[0044] Compound structure identification data:

[0045] Intermediate 1 mass spectrometry M / Z MS+H + :438;

[0046] UV antioxidant 1 Mass spectrometry M / Z MS+H + :675;

[0047] UV antioxidant 1 1 H NMR (Chloroform-d), Figure 1: δ8.87(s,1H),8.30(s,1H),8.13-8.00(m,4H),7.94-7.81(m,2H),7.70(m,2H),7.48-7.31(m,2H),7.20-7.11(m,2H),7.09(m,1H), 7.01(d,1H),6.81(dd,1H),5.57(m,1H),3.98(q,2H),2.50(t,3H),2.43(t,3H),2.00(d,3H),1.43(t,3H),1.37(d,3H),1.31(d,3H).

[0048] Preparation Examples 2-6

[0049] In Preparation Examples 2-6, UV antioxidants 2 and 6 were synthesized sequentially, following the same preparation method as in Preparation Example 1, except that raw material 1 was replaced, while the rest remained the same. The specific structures of raw material 1, UV antioxidants 2 and 6, and compound structure identification data are shown in Table 1.

[0050] Table 1.

[0051]

[0052]

[0053] Example 1

[0054] Preparation of a basalt fiber-reinforced NAO-free friction material:

[0055] 1. Raw material composition:

[0056] Phenolic resin: 100 parts, free phenol content ≤1%, purchased from: Shandong Chenghui New Material Co., Ltd., product number: PF-208;

[0057] Basalt fiber: 20 parts, length between 50-200μm, purchased from: Zhejiang Shijin Basalt Fiber Co., Ltd.

[0058] Mineral fillers: a total of 45 parts, including 25 parts barium sulfate, 15 parts vermiculite and 5 parts alumina. The barium sulfate and alumina were purchased from Shanghai Yuanye Biotechnology Co., Ltd., and the vermiculite was purchased from Shanghai Titan Technology Co., Ltd.

[0059] Friction performance modifier: a total of 20 parts, including 10 parts tin sulfide, 5 parts ceramic powder (200 mesh) and 5 parts graphite. Tin sulfide was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., ceramic powder was purchased from Asia Pacific (Shanghai) Trading Co., Ltd., and graphite was purchased from Zhejiang Yamei Nanotechnology Co., Ltd.

[0060] Organic fiber: 10 parts, selected from aramid fiber (powder, fiber diameter is 4-7μm, and the content of fineness less than 150μm is 99.9%), purchased from: Jiangsu Aierda Composite Materials Co., Ltd.

[0061] Polyetheretherketone (PEEK): 10 parts, purchased from: Wuhan Luhao New Materials Co., Ltd.

[0062] Silane coupling agent: 5 parts, using silane coupling agent KH550, purchased from: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0063] UV antioxidant: 1.5 parts, select UV antioxidant 1.

[0064] 2. Preparation method:

[0065] (1) Add 20 parts of basalt fiber and 5 parts of silane coupling agent to a reaction vessel, stir and mix at 500 rpm for 20 minutes at 70°C to obtain modified basalt fiber.

[0066] (2) Add the modified basalt fiber obtained in step (1), 100 parts of phenolic resin, mineral filler (25 parts of barium sulfate, 15 parts of vermiculite, 5 parts of alumina), friction performance modifier (10 parts of tin sulfide, 5 parts of ceramic powder, 5 parts of graphite), 10 parts of organic fiber, 10 parts of polyether ether ketone and 1.5 parts of UV antioxidant to a mixer and mix at 800 rpm for 15 minutes under nitrogen atmosphere protection to form a lumpy premix.

[0067] (3) The premixed material is loaded into a mold preheated to 170°C and placed in a hot press for molding. The molding conditions are set as follows: temperature 180°C, pressure 30MPa, and holding time 20 minutes.

[0068] (4) The hot-pressed blank is transferred to an oven for segmented heat treatment. The conditions are: heating to 200°C at 3°C / min, holding for 2 hours, and then naturally cooling to room temperature to obtain the basalt fiber reinforced non-heavy metal NAO friction material.

[0069] Examples 2-6

[0070] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out by referring to the preparation method of Example 1, except that the ultraviolet antioxidant is replaced sequentially with ultraviolet antioxidant 2-ultraviolet antioxidant 6 prepared in Preparation Examples 2-6, and the rest is the same as in Example 1.

[0071] Comparative Example 1

[0072] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material follows the preparation method of Example 1, except that the ultraviolet antioxidant is replaced with antioxidant AW. Everything else remains the same as in Example 1.

[0073] Comparative Example 2

[0074] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out by referring to the preparation method of Example 1, except that the ultraviolet antioxidant is replaced with antioxidant ODA (CAS: 101-67-7), and the rest is the same as in Example 1.

[0075] Comparative Example 3

[0076] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material, referring to the preparation method of Example 1, except that the ultraviolet antioxidant is replaced with: Everything else remains the same as in Example 1.

[0077] Comparative Example 4

[0078] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material, referring to the preparation method of Example 1, except that the ultraviolet antioxidant is replaced with: Everything else remains the same as in Example 1.

[0079] Comparative Example 5

[0080] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out according to the preparation method of Example 1, except that the ultraviolet antioxidant is not added, and the rest is the same as in Example 1.

[0081] Comparative Example 6

[0082] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out according to the preparation method of Example 1, except that the friction performance modifier is not added, and the rest is the same as in Example 1.

[0083] Comparative Example 7

[0084] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out according to the preparation method of Example 1, except that no organic fiber is added, and the rest is the same as in Example 1.

[0085] Comparative Example 8

[0086] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out according to the preparation method of Example 1, except that polyether ether ketone is not added, and the rest is the same as in Example 1.

[0087] Comparative Example 9

[0088] The preparation of a basalt fiber reinforced heavy metal-free NAO friction material is carried out according to the preparation method of Example 1, except that the silane coupling agent is not added, and the rest is the same as in Example 1.

[0089] Performance testing:

[0090] The test sample is a basalt fiber reinforced, heavy metal-free NAO friction material prepared in the examples and comparative examples;

[0091] 1. Impact strength: The test was conducted in accordance with the test method of GB / T 33835-2017 "Test Method for Impact Strength of Friction Materials", and the data are shown in Table 2;

[0092] 2.250℃ coefficient of friction: Tested according to GB 5763-2018 "Automotive Brake Liners", the data are shown in Table 2;

[0093] 3. Bending strength retention rate after aging: The sample was placed in a xenon lamp aging test chamber and exposed for 4800 hours, then its impact strength was tested, and the impact strength retention rate was calculated; the exposure conditions were: radiation intensity: 0.35 W / m 2 (At 340nm wavelength); Temperature cycling: 80℃ (light stage) to 15℃ (dark stage), 8 hours of light + 4 hours of condensation (simulated rain) per cycle; Relative humidity: 50%±5% (light stage), 95%±5% (condensation stage), data are shown in Table 2.

[0094] Table 2.

[0095] Example 1 133 0.32 97 Example 2 128 0.34 95 Example 3 131 0.30 98 Example 4 123 0.33 94 Example 5 134 0.31 93 Example 6 129 0.35 96 Comparative Example 1 110 0.36 79 Comparative Example 2 112 0.37 77 Comparative Example 3 116 0.35 82 Comparative Example 4 122 0.36 84 Comparative Example 5 107 0.40 50 Comparative Example 6 104 0.61 88 Comparative Example 7 73 0.48 86 Comparative Example 8 99 0.46 71 Comparative Example 9 83 0.59 79

[0096] Significant differences exist between the examples (formulations using the UV antioxidant of this invention) and the comparative examples (formulations using alternatives or omissions of key components). The examples exhibit a positive trend of performance improvement: generally higher impact strength, indicating enhanced toughness and impact resistance; a stable coefficient of friction at 250°C, reflecting consistent braking performance under high-temperature conditions; and a decreasing wear rate, highlighting optimized abrasion resistance. Furthermore, the flexural strength retention rate after aging remains high in the examples, indicating excellent anti-aging performance and effectively delaying performance degradation during long-term use. In contrast, the comparative examples show a negative trend: generally lower impact strength, especially when organic fibers or polyetheretherketone (PEEK) are missing; increased wear rate, indicating weakened abrasion resistance; and a significantly lower retention rate after aging, particularly when no UV antioxidant is added or alternative antioxidants are used, indicating significantly insufficient anti-aging ability. These trends collectively confirm the crucial role of the UV antioxidant and the synergistic system of the whole components in improving the overall performance of the material.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A basalt fiber reinforced, heavy metal-free NAO friction material, characterized in that, It is made from the following components in parts by weight: 100 parts phenolic resin, 10-30 parts basalt fiber, 20-70 parts mineral filler, 5-30 parts friction modifier, 3-20 parts organic fiber, 5-15 parts polyether ether ketone, 3-7 parts silane coupling agent, and 1.5-1.5 parts ultraviolet antioxidant. The ultraviolet antioxidant is a compound represented by chemical formula 1; Chemical Formula 1: R1 in the chemical formula 1 is selected from: alkyl with 1-5 carbon atoms, alkoxy with 1-5 carbon atoms, nitro, cyano, and amino.

2. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The free phenol content in the phenolic resin is ≤1%.

3. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The basalt fibers are between 50 and 200 μm in length.

4. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The mineral filler comprises the following raw materials in parts by weight: 10-40 parts barium sulfate, 5-25 parts vermiculite, and 5-20 parts alumina.

5. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The friction performance modifier comprises the following raw materials in parts by weight: 5-15 parts tin sulfide, 10-25 parts ceramic powder, and 5-15 parts graphite.

6. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The organic fiber is selected from: aramid fiber or polyacrylonitrile fiber; The silane coupling agent is selected from: silane coupling agent KH550 or silane coupling agent KH560.

7. The basalt fiber reinforced, heavy metal-free NAO friction material according to claim 1, characterized in that, The UV antioxidant is any one of the compounds shown in the following structures:

8. A method for preparing a basalt fiber reinforced, heavy metal-free NAO friction material according to any one of claims 1-7, characterized in that, Includes the following steps: (1) The basalt fiber and silane coupling agent are stirred and mixed at 50-80℃ for 10-30 minutes to obtain modified basalt fiber; (2) Add the modified basalt fiber, phenolic resin, mineral filler, friction performance modifier, organic fiber, polyether ether ketone and UV antioxidant into a mixer and mix for 10-30 minutes to obtain a uniform premix. (3) The premixed material is loaded into a preheated mold and hot-pressed in a hot press. (4) The hot-pressed blank is placed in an oven for heat treatment and cooled to room temperature to obtain a basalt fiber reinforced non-heavy metal NAO friction material.

9. The method for preparing a basalt fiber reinforced heavy metal-free NAO friction material according to claim 8, characterized in that, The conditions for hot pressing in step (3) are: molding temperature 160-190℃, molding pressure 20-40MPa, and holding time 10-30 minutes.

10. The method for preparing a basalt fiber reinforced heavy metal-free NAO friction material according to claim 8, characterized in that, The heat treatment conditions in step (4) are: heat treatment temperature 180-220℃, heat treatment time 1.5-4 hours, and heating rate 2-5℃ / minute.

Images