Friction material containing graphite, method for producing the friction material, and use thereof

Abstract

The present invention relates to a friction material comprising graphite having a c / 2 of 0.3358 nm or less and a springback of 40% or more, such as 41% or more. The present invention further relates to a method for making and a use of such a friction material.

Description

Technical Field

[0001] Field of the Invention The present invention relates to a friction material containing an elastic graphite material. The present invention further relates to a method for manufacturing such a friction material and its use.

Background Art

[0002] Background of the Invention Friction materials are used in various applications, for example, for disk brakes, drum brakes, or clutches, and for end use in vehicles such as automobiles, heavy vehicles, wind turbines, railways, etc. Friction materials must meet various requirements depending on their intended use. Some of the desired properties include good heat dissipation obtained by high thermal conductivity, a well-defined and stable coefficient of friction, good lubricity, high compressibility, vibration damping properties, noise reduction, and low disk brake resistance. The use of asbestos in friction materials has been clearly phased out over the past few decades due to workplace safety, health, and environmental concerns. Furthermore, the use of copper in friction materials with good thermal conductivity having a good and stable coefficient of friction has been phased out considering long-standing environmental regulations. Previously, graphite and graphite-like carbon have been used in friction materials. In particular, elastic graphite materials provide the spring-back properties required for use in friction materials. For example, EP 3 088 764 A1 discloses the use of an elastic graphite material in non-asbestos organic (NAO) brake pads. Elastic graphite carbon particles are formed by expanding carbonaceous mesophase or coke and subsequently graphitizing at 1900 - 2700 °C to obtain a graphitization degree of 80 - 95% as measured by X-ray analysis. This results in an improved volume recovery rate when the applied compressive load is removed. Furthermore, the formation of cracks is reduced, thereby reducing chipping.

[0003] One drawback of using a graphite material in a friction material results from conflicting requirements for the graphite material in terms of springback characteristics and thermal conductivity. The springback of graphite generally correlates with crystallinity. Without being bound by theory, carbon springback tends to increase with a decrease in crystallinity. For example, amorphous cokes with a c / 2 value higher than about 0.34 nm and an Lc value less than about 50 nm will have a springback value of 50% or more. Also, graphitized carbon with a c / 2 less than about 0.3356 nm and an Lc value between about 100 and about 200 nm will have a lower springback. Typical flake type natural graphite with a c / 2 value less than about 0.3358 nm and an Lc value greater than about 200 nm will have a very low springback value, for example, of about 10% or less. High crystallinity results in high thermal conductivity for heat dissipation, good lubricity for stabilizing the friction coefficient, all of which are desirable properties for a friction material. On the other hand, high springback results in high compressibility of the friction material for good vibration damping, reduced noise, and low disc brake resistance. Thus, the use of a graphite material in a friction material results in an action that balances the opposing properties of the material and requires a compromise in one or more of the properties of this friction material. Thus, the state of the art poses a problem. SUMMARY OF THE INVENTION

[0004] Brief Description of the Invention The above problems are solved by the present invention as defined in the appended claims. More particularly, the present invention provides a material having good thermal conductivity, and / or a sufficient friction coefficient and / or sufficient lubricity. Further, the material of the present invention provides a sufficiently high springback. In particular, the present invention is embodied by a friction material comprising graphite having a c / 2 of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and a springback of 40% or more, for example 40.5% or more, or 41% or more. As is known to those skilled in the art, graphitization of 95.3% or more corresponds to a c / 2 of 0.3358 nm or less. It has been found that graphite having these parameters can be obtained and can impart good properties in the friction material. According to one embodiment, the graphite used in the friction material according to the present invention can have a springback of 45% or more, for example 50% or more, or 60% or more. Such materials have been found to be particularly advantageous for use in friction pad applications.

[0005] According to one embodiment of the present invention, the graphite contained in the friction material has a graphitization degree of 95.3% or more, for example 96% or more, for example 97% or more. According to one embodiment of the present invention, the graphite contained in the friction material has a xylene density of 2.0 g / cm 3 or more. According to one embodiment of the present invention, the graphite contained in the friction material has a crystallinity (L c ) of 50 nm or more. According to one embodiment of the present invention, the graphite contained in the friction material has a BET surface area of 9 m 2 / g or less. According to one embodiment of the present invention, the graphite contained in the friction material is surface-modified graphite. For example, the graphite contained in the friction material may be surface-modified natural graphite or surface-modified synthetic graphite, or may be a mixture of surface-modified natural graphite and surface-modified synthetic graphite, for example surface-modified graphite by heat treatment and coated graphite by surface coating treatment. According to one embodiment of the present invention, the surface modification of graphite includes surface modification by heat treatment. According to one embodiment of the present invention, the surface modification includes an additional coating on the surface of the graphite particles, and the above surface coating can be carried out simultaneously with or separately from the heat treatment, for example following the heat treatment.

[0006] According to a further embodiment of the present invention, the surface modification of graphite includes surface coatings that can be obtained by a chemical vapor deposition (CVD) process, such as a carbon coating obtained by a CVD process. According to yet another embodiment of the present invention, the surface modification of graphite includes surface modification by heat treatment, and further, for example, by a CVD process, the obtained surface coating, coating the graphite surface with amorphous carbon or a coating of a carbon precursor, and then carbonizing by heat treatment in an inert gas atmosphere. Also, after the CVD process, the material is typically hydrophobic. Further treatment of the material after the CVD process may improve the wettability with water and, if desired, help make the material more hydrophilic or more hydrophobic. Thus, a further oxidation treatment may form part of the present invention. The degree of oxidation makes it possible to control the hydrophilicity of the graphite surface and thus its wettability by humidity. The same oxidation can be applied to a graphite material having a surface coating of amorphous carbon.

[0007] According to one specific embodiment of the present invention, the friction material includes 0.1% to 30% by mass of graphite having the characteristics defined above, based on the total mass of the friction material. According to one specific embodiment of the present invention, the friction material has a copper content of 5% by mass or less, for example, a copper content of 0.5% by mass or less. According to one embodiment of the present invention, the friction material is essentially free of copper. According to one specific embodiment of the present invention, the friction material has an in-plane thermal conductivity of 1.5 W / mK or more, as measured according to ASTM E1461 using a laser flash by NETZSCH LFA447. According to one specific embodiment of the present invention, the friction material has a coefficient of friction of 0.5 or less. According to yet another embodiment of the present invention, the friction material can include one or more additional components selected from the group consisting of a resin or cement binder, antimony trisulfide, copper, barium sulfate, metal powder, metal fiber, mineral fiber, iron sulfide, coke, other natural, synthetic, expanded graphite, calcium carbonate, mica, talc, zirconia, and mixtures thereof, and additional components typically used in friction materials known to those skilled in the art.

[0008] Also, a part of the present invention is a method for manufacturing a friction material, comprising: (a) preparing graphite; (b) subjecting the graphite prepared in step (a) to heat treatment at 600 °C or higher for 30 minutes or more; (c) mixing the treated graphite obtained at the end of step (b) with additional components and processing to form a friction material, for example, by compression molding, or hot compression molding, or curing by heat treatment, or any combination thereof. According to one embodiment, the prepared graphite may be natural graphite, or synthetic graphite, or a mixture of natural graphite and synthetic graphite. According to one further embodiment, the treatment in step (b) may further include a surface coating treatment, such as a CVD treatment, or an amorphous carbon surface coating treatment. According to one further embodiment, the treatment step (b) of the above method includes a first heat treatment that is part of a surface coating treatment such as a CVD coating or a pitch coating with subsequent carbonization, and a second heat treatment that is not part of the surface coating treatment and may be performed before or after the surface coating treatment. According to one further embodiment, the second heat treatment is a post-treatment (i.e., performed after the first treatment such as a surface coating treatment). According to one further embodiment, the treatment step (b) may not include a surface coating treatment such as a CVD treatment.

[0009] Also, a part of the present invention is the use of the friction material according to the present invention in the manufacture of brake pads, for example, in the manufacture of low-copper brake pads, or in the manufacture of copper-free brake pads. Also, a part of the present invention is a brake pad including a friction material according to the present invention, which may be for use in an electric vehicle. It should be understood that the following description and drawings relate to exemplary embodiments of the present invention and do not limit the scope of the claims.

Mode for Carrying Out the Invention

[0010] Detailed Description of the Invention The present invention according to the appended claims is a friction material containing graphite, wherein the graphite has a c / 2 value of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and a springback of 40% or more, for example 40.5% or more, or 41% or more, and provides a friction material. The core of the present invention lies in enabling the coexistence of the essentially conflicting properties of graphitization and springback of graphite for effective use in a friction material. Those skilled in the art will recognize that the springback of graphite generally depends on its crystallinity. Graphite with low crystallinity generally has high springback properties, and vice versa. High springback results in low compressibility, and the compression density of graphite powder decreases. A friction material containing a graphite material having a combination of physical parameters according to the present invention has not been shown previously.

[0011] Graphite Material According to the present invention, the graphite contained in the friction material has a c / 2 value of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and a springback of 40% or more, for example 40.5% or more, or 41% or more, for example 45% or more, for example 50% or more, for example 55% or more, for example 60% or more, for example 65% or more, for example 70% or more, for example 75% or more. According to the present invention, the graphite contained in the friction material has a c / 2 value of 0.3358 nm or less, for example, a c / 2 value of 0.3357 nm or less, or a c / 2 value of 0.3356 nm or less. It will be apparent to those skilled in the art that it is most advantageous to have a high degree of graphitization and a high springback. Accordingly, a friction material containing graphite having a c / 2 value of 0.3358 nm or less and a springback of more than 40%, for example 41% or more, and a friction material containing graphite having a c / 2 value of 0.3358 nm or less and a springback of 50% or more, and a friction material containing graphite having a c / 2 value of 0.3358 nm or less and a springback of 60% or more, and even a friction material containing graphite having a degree of graphitization of 95.3% or more and a springback of 70% or more, and even a friction material containing graphite having a c / 2 value of 0.3356 nm or less (degree of graphitization of 98% or more) and a springback of 75% or more are considered to be part of the present invention.

[0012] As described in the introduction section above, a high degree of graphitization results in good thermal conductivity of the graphite, and thus causes good heat dissipation in the friction material containing this graphite. Also, good springback results in good compressibility of this material, thereby bringing about an improvement in vibration damping and noise reduction. According to one embodiment of the present invention, the graphite contained in the friction material has a degree of graphitization of 95.3% or more and a springback of more than 40%, for example 41% or more, for example, a degree of graphitization of 96% or more, or a degree of graphitization of 97% or more, or even a degree of graphitization of 98% or more. According to one embodiment of the present invention, the friction material contains graphite having a crystallinity L of 50 nm or more c For example, this friction material contains graphite having a crystallinity L of 100 nm or more c or a crystallinity L of 150 nm or more c or a crystallinity L of 200 nm or more c or a crystallinity L of 250 nm or more c Even contains graphite having. As used herein, this crystallinity L c represents the average crystallite size of the graphite.

[0013] According to one embodiment of the present invention, the friction material has a xylene density of 2.0 g / cm 3 or more, for example, a xylene density of 2.1 g / cm 3 or more, for example, a xylene density of 2.2 g / cm 3 or more, for example, a xylene density of 2.23 g / cm 3 or more, for example, a xylene density of 2.24 g / cm 3 or more, for example, a xylene density of 2.25 g / cm 3 or more, or a xylene density of 2.26 g / cm 3 or more, and includes graphite having such a xylene density. For example, the graphite contained in the friction material according to one embodiment of the present invention does not have a xylene density higher than 2.26 g / cm 3 Higher xylene density generally indicates higher crystallinity of graphite without directly providing information on the numerical value of the crystallite size of the c / 2 distance, and thus indicates an improved thermal diffusivity of the material, giving improved properties for use in friction materials. Higher xylene density generally indicates higher crystallinity of graphite without directly providing information on the numerical value of the crystallite size of the c / 2 distance, and thus indicates an improved thermal diffusivity of the material, giving improved properties for use in friction materials. According to one embodiment of the present invention, the above friction material includes graphite having a BET surface area of 9 m 2 / g or less. For example, the graphite contained in the friction material according to the present invention has a BET surface area of 8 m 2 / g or less, a BET surface area of 8.0 m 2 / g or less, or a BET surface area of 7.0 m 2 / g or less, or a BET surface area of 6.0 m 2 / g or less, or a BET surface area of 5.0 m 2 / g or less, or a BET surface area of 4.5 m 2 / g or less, or a BET surface area of 4.0 m 2 / g or less. One advantage of a lower BET surface area is generally a lower resin consumption.

[0014] Preparation of a Graphitic Material Having Desired Properties by Surface Treatment According to some embodiments of the present invention, the graphite material for use in the friction material may be natural graphite, or synthetic graphite, or a mixture thereof. For example, the graphite material may be surface-treated natural graphite, or surface-treated synthetic graphite. According to one embodiment, the graphite can be selected from expanded graphite and / or non-expanded graphite. According to a further embodiment, the graphite is selected from non-expanded graphite. According to an embodiment of the present invention, the surface treatment of the graphite material may be a heat treatment. For example, the heat treatment may be a heat treatment at a temperature of 600 °C or higher, for example 800 °C or higher, or 1000 °C or higher, or 1200 °C or higher, for example 1400 °C. According to an embodiment of the present invention, the surface treatment of the graphite material may be a surface coating treatment such as a chemical vapor deposition (CVD) treatment, or coating graphite particles with a carbon precursor and then carbonizing in an inert gas atmosphere.

[0015] Typical surface coating processes are based on coating a carbon precursor such as coal tar or petroleum pitch (typically called pitch coating), or an organic polymer such as phenolic resin or polystyrene, polyvinyl alcohol, furan resin, or furfuryl alcohol (known to give a high carbon yield upon carbonization) onto the graphite surface by a dry or wet mixing process and then carbonizing at a high temperature in an inert gas atmosphere [Wan et al., Journal of Applied Electrochemistry, 2009, 39, 1081; Yoon et al. Journal of Power Sources, 2001, 94, 68]. Another known process described in the art involves coating of pyrolytic carbon on the graphite surface achieved by treating graphite particles in hydrocarbon gas or vapor at a high temperature (chemical vapor deposition), typically called CVD coating. The surface coatings described form a coating of amorphous carbon on the surface of the graphite particles. Examples of these surface modifications include heat treatment and surface coating treatments, which are simultaneous in the case of CVD coatings, for example, and independent in the case of pitch coatings of carbon precursors with subsequent carbonization.

[0016] During the CVD process, the carbon source in the gas phase, which is usually a hydrocarbon, is decomposed at high temperature, and the carbon particles are deposited as so-called pyrolytic carbon on the graphite surface. The hardening effect of pyrolytic carbon, especially isotropic carbon, has been shown in the literature (see, for example, Handbook Of Carbon, Graphite, Diamond And Fullerenes, Properties, Processing and Applications, Hugh O. Pierson, published in 1993 by Noyes Publications, ISBN: O-8155-1339-9, Printed in the United States, Published in the United States of America by Noyes Publications Mill Road, Park Ridge, New Jersey 07656). In its random structure, the deposited isotropic pyrolytic carbon lacks orientation and as a result is very hard. According to one embodiment, the CVD process can be carried out using, for example, a rotary kiln, a fluidized bed furnace or a fixed bed furnace, as known from the prior art applications WO 2016 / 008951 or EP 0 977 292. According to the methods disclosed in these publications, hydrocarbon gases such as propane, methane or toluene and benzene vapors are decomposed at temperatures between 600 °C and 1200 °C. The resulting final material is coated with a continuous layer of amorphous carbon from 10 nm to 100 nm, and 0.5 to 30% by mass can be hydrophobic or hydrophilic. Any other known CVD process for depositing pyrolytic carbon, such as thermal CVD, plasma enhanced CVD, hot filament CVD, low pressure CVD, liquid injection CVD, etc., can also be used.

[0017] A more detailed method for manufacturing a graphite material surface-treated for use in a friction material will be further described below. According to the present invention, the carbon-coated graphite material prepared as described above was analyzed, and an increase in springback was actually observed. In addition to the effect of the pyrolytic carbon acting as a hardening agent as described above, heat treatment in an inert atmosphere has the effect of increasing springback. At temperatures higher than 500 °C with a fairly long residence time, it is presumed that a small amount of non-graphitic carbon inside the graphite particles undergoes a structural change leading to an increase in springback. For these reasons, it is part of the present invention to provide a friction material containing a graphite material derived from a surface-treated synthetic or natural graphite, wherein the surface treatment can be carried out by heat treatment in an inert atmosphere, or a surface coating treatment such as CVD treatment, or both of these simultaneously or subsequently.

[0018] Friction material According to one embodiment of the present invention, there is provided a friction material containing the above-described graphite material, wherein the graphite material is contained in the friction material in an amount of 0.1% to 30% by mass based on the total amount of the friction material. For example, the graphite material may be present in the friction material in an amount of 0.1% by mass or more, for example, 0.1% by mass or more, or 0.5% by mass or more, or 1% by mass or more, or 5% by mass or more, or 10% by mass or more, or 15% by mass or more, or 20% by mass or more, or 25% by mass or more, for example, in an amount of about 30% by weight. For example, the graphite material may be present in the friction material in an amount of 30% by mass or less, for example, 25% by mass or less, or 20% by mass or less, or 15% by mass or less, or 10% by mass or less, or 5% by mass or less, or 1% by mass or less, or 0.5% by mass or less, or in an amount of about 0.1% by mass. For example, the graphite-based material according to the present invention may be present in the friction material in an amount of 0.5% to 30% by mass, for example 1% to 25% by mass, or for example 2% to 10% by mass, based on the total amount of the friction material.

[0019] The friction material can further include other materials suitable for use in friction materials known to those skilled in the art, such as resin or cement binders, antimony trisulfide, copper, barium sulfate, metal powders, metal fibers, mineral fibers, iron sulfide, coke, other natural, synthetic, or expanded graphite, calcium carbonate, mica, talc, and zirconia. For example, the friction material may further include expanded graphite (e.g., TIMREX, C-THERM) in the case of a high thermal conductivity friction material. According to certain embodiments, the friction material includes less than 5% by mass of copper, for example less than 1% by mass of copper, or less than 0.5% by mass of copper, or less than 0.1% by mass of copper. According to certain embodiments, the friction material does not contain copper. As used herein, a friction material is considered to be copper-free if it contains less than 0.05% by mass of copper or no detectable copper. The friction material may further include expanded graphite (e.g., TIMREX C-THERM), for example, when there is a high need for thermal conductivity. The friction material according to the present invention can have an in-plane thermal conductivity of 1.5 W / mK or more, for example 5 W / mK or more, as measured according to ASTM E1461 using a laser flash by NETZSCH LFA 447. The friction material according to the present invention can have a coefficient of friction of 0.5 or less, for example between 0.2 and 0.5, or between 0.3 and 0.5.

[0020] Method for manufacturing a friction material According to one embodiment of the present invention, the friction material can be formed by preparing a graphite material having a springback of 40% or more, or 41% or more, and a c / 2 value of 0.3358 nm or less, for example, 0.3357 nm or less, or 0.3356 nm or less. Such graphite can be obtained using a method as described above, including steps of heat treatment and / or surface coating treatment, such as CVD treatment, of synthetic or natural particulate graphite. According to the present invention, the friction material can be formed by preparing graphite, heat-treating the prepared graphite at 600 °C or higher for 30 minutes or longer, and mixing and treating the obtained treated graphite with further components to form the friction material. Such further components can be selected from the group consisting of resin or cement binders, antimony trisulfide, copper, barium sulfate, metal powders, metal fibers, mineral fibers, iron sulfide, coke, other natural, synthetic, expanded graphite, calcium carbonate, mica, talc and zirconia, and / or other components typically used in friction materials and mixtures thereof. After mixing with these further components, the mixture can be treated by compression molding, for example, cold compression molding, or hot compression molding, or curing by heat treatment, or a combination thereof.

[0021] The graphite prepared by the method according to the present invention can be selected from natural graphite, synthetic graphite and mixtures thereof. For example, the graphite may be pulverized natural graphite or pulverized synthetic graphite, or a combination of pulverized natural graphite and synthetic graphite. The heat treatment can be performed at a temperature of 700 °C or higher, or 800 °C or higher, or 850 °C or higher. The heat treatment can be performed for a time of 30 minutes or longer, preferably 60 minutes or longer, or 120 minutes or longer. According to one embodiment, the heat treatment can be performed for a time of 120 minutes or longer at a temperature including between 600 °C and 850 °C. According to one embodiment, the heat treatment is performed at about 1000 °C or higher for at least 30 minutes. According to one embodiment, the heat treatment is performed at about 1000 °C or higher for at least 60 minutes. According to one embodiment, the heat treatment is performed at about 1200 °C or higher for at least 30 minutes. According to one embodiment, the heat treatment is performed at about 1200 °C or higher for at least 60 minutes. According to one embodiment, the heat treatment is performed at about 1300 °C or higher for at least 30 minutes. According to one embodiment, the heat treatment is performed at about 1300 °C or higher for at least 60 minutes. According to one embodiment, the heat treatment is performed at about 1500 °C or higher for at least 30 minutes. According to one embodiment, the heat treatment is performed at about 1500 °C or higher for at least 60 minutes.

[0022] According to one embodiment of the present invention, step (b) of the method for manufacturing a friction material may include a surface coating, for example, a CVD treatment, and the heat treatment can be performed simultaneously with the coating treatment, or the surface coating treatment can be performed before the heat treatment. For example, the graphite surface can be coated with a carbon precursor and then carbonized under an inert gas. In this case, the above carbonization is a heat treatment. According to some embodiments of the present invention, such a CVD treatment uses an amorphous hydrocarbon gas such as methane, ethane, propane, butane, benzene, or toluene in the presence of a carrier gas such as nitrogen or argon. According to another embodiment, step (b) includes a separate CVD treatment (including a heat treatment and a surface coating treatment) and a separate heat treatment (not part of the CVD treatment) as described above. In this embodiment, the heat treatment is independent of the CVD treatment, and both treatments may be performed sequentially with or without other intermediate steps such as cooling, quenching, or chemical treatment. According to one embodiment of the present invention, the prepared graphite includes natural graphite, and step (b) includes a heat treatment and a surface coating treatment.

[0023] According to yet another embodiment, step (b) of the above method may include a first heat treatment and a second heat treatment (not part of the surface coating treatment) that are part of a surface coating treatment (e.g., CVD coating or pitch coating followed by carbonization), and the second heat treatment can be carried out before or after the surface coating treatment. According to yet another embodiment, such a second heat treatment is a post-treatment. According to yet another embodiment, step (b) of the above method may not include a surface coating treatment. According to one embodiment of the present invention, the prepared graphite includes synthetic graphite, and method step (b) may or may not include a surface coating treatment such as CVD treatment. Furthermore, according to the present invention, various other materials for forming a friction material are provided, such as resin or cement binders, antimony trisulfide, copper, barium sulfate, metal powders, metal fibers, mineral fibers, iron sulfide, coke, other natural, synthetic, or expanded graphite, calcium carbonate, mica, talc, and zirconia.

[0024] Also, a part of the present invention is the use of the graphite material disclosed herein in the formation of a friction material, and in the formation of brake pads for disk brakes, drum brakes, or clutches, and the use of such friction materials for applications in vehicles such as automobiles including electric vehicles, large vehicles, and railways. In electric vehicles, since there is no noise from the engine, it is even more advantageous to use brake pads that generate reduced noise. The friction material according to the present invention can also be used, for example, in carbon brushes and bipolar plates for fuel cells, or for disk brakes, drum brakes, or clutches, and for applications in vehicles such as automobiles, large vehicles, wind turbines, and railways. According to one embodiment of the present invention, the prepared graphite can be used, for example, in carbon brushes and bipolar plates for fuel cells, for self-lubricating polymer compounds. Also, a part of the present invention is a method for improving the performance of a brake pad, which includes using a friction material according to the present invention, the friction material containing graphite having a c / 2 value of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and a springback of 40% or more, for example 41% or more. The performance of this brake pad can be evaluated from viewpoints such as noise reduction, durability, vibration attenuation, braking power, and friction coefficient stabilization. Also, a part of the present invention is a brake pad including a friction material according to the present invention.

[0025] Graphite springback Springback is an information source regarding the elasticity of compressed graphite powder. A predetermined amount of powder is injected into a 20 mm diameter die. After inserting a punch and sealing the die, air is evacuated from the die. A compressive force of 1.5 metric tons is applied, resulting in a pressure of 0.477 t / cm 2 and the height of the powder is recorded. This height is recorded again after the pressure is released. Springback is the percentage of the difference in height with respect to the height under pressure.

[0026] Interlayer spacing c / 2 and graphitization degree The interlayer space c / 2 was measured by X-ray diffraction method. By determining the angular position of the peak maximum of the

[0002] reflection profile and applying Bragg's equation, the interlayer spacing was calculated (Klug and Alexander, Xray diffraction Procedures, John Wiley & Sons Inc., New York, London (1967)). To avoid problems caused by the low absorption coefficient of carbon, the instrument alignment of the sample, and non-planarity, an internal standard, silicon powder, was added to the sample, and the graphite peak position was recalculated based on the position of the silicon peak. The graphite sample was mixed with the silicon standard powder by adding a mixture of polyglycol and ethanol. Then, the resulting slurry was applied onto a glass plate with a blade at 150 pm intervals and dried. The interlayer spacing (d 002 ) and the graphitization degree (g) are directly related by the following formula:

[0027]

Number

[0028] Graphite crystallite size L c Crystallite size L c is determined by the analysis of the (002) and ((004) diffraction profiles. In the present invention, the method proposed by Iwashita (N. Iwashita, C. Rae Park, H. Fujimoto, M. Shiraishi and M. Inagaki, Carbon 42, 701-714 (2004)) is used. The algorithm proposed by Iwashita has been specifically developed for carbon materials. Measure the width of the line profile at half of the maximum value of the sample and the reference. The width of the pure diffraction profile can be determined by a correction function. Then, this crystallite size is calculated by applying the Scherrer's equation (P. Scherrer, Goettinger-Nachrichten 2 (1918) p. 98).

[0029] Xylene density The analysis is based on the principle of liquid exclusion as defined in DIN 51901. Weigh about 2.5 g (accuracy 0.1 mg) of powder with a 25 mL pycnometer. Add xylene in vacuum (15 Torr (20 mbar)). After a residence time of several hours under normal pressure, adjust and weigh the pycnometer. Density represents the ratio of mass to volume. The mass is indicated by the mass of the sample, and the volume is calculated from the difference in the mass of the pycnometer filled with xylene with and without the sample powder.

[0030] BET specific surface area The method is based on registering the adsorption isotherm of liquid nitrogen in the range of p / p0 = 0.04 to 0.26 at 77K. The monolayer capacity can be determined according to the procedure proposed by Brunauer, Emmett, and Teller (Adsorption of Gases in Multimolecular Layers, J. Am. Chem. Soc., 1938, 60, 309-319). The specific surface area can be calculated based on the cross-sectional area of nitrogen molecules, the monolayer capacity, and the mass of the sample. It should be noted that the present invention can include any combination of features and / or limitations referred to herein, except combinations of features that are mutually exclusive. The above description is directed to specific embodiments of the present invention and is for the purpose of explaining specific embodiments of the present invention. However, it will be apparent to those skilled in the art that many changes and modifications can be made to the embodiments described herein. All such changes and modifications are intended to be within the scope of the present invention as defined by the appended claims.

Example

[0031] Example 1: Hydrophobic CVD-coated synthetic graphite using a rotary furnace D 10 = 5μm and D 90The ground synthetic graphite "GRAPHITE SGA" with a particle size distribution of =73 μm was used as a starting material to improve its springback characteristics and other properties as a friction material containing graphite. This starting material was continuously fed for 2 hours into a rotary kiln reactor heated to 1050 °C using a single screw, producing approximately 2000 g of material. Chemical vapor deposition (CVD) treatment was carried out using a mixture of hydrocarbon and inert gas (amorphous carbon precursor: C3H8 (3 L / min) and carrier gas: N2 (1 L / min)), and the reactor was fed so as to maintain the pressure in this reactor at 0 to 8 mbar higher than atmospheric pressure. The inclination of this tube was set at 4°, the rotation speed was set at 6 rpm, and the residence time in the kiln was set at approximately 30 minutes. To eliminate the amount of polycyclic aromatic hydrocarbons (PAHs), further treatment in a muffle furnace or further treatment in a rotary furnace at 700 °C in an inert atmosphere (N2) was added. The ground synthetic graphite "GRAPHITE SGA" was again used as a starting material to improve its springback characteristics and other properties as a friction material containing graphite. This starting material was charged into a fluidized bed reactor and heated to approximately 900 °C under an inert gas. Chemical vapor deposition (CVD) was carried out using a mixture of an organic solvent and an inert gas (nitrogen flow of 4 L / min) while maintaining the atmospheric pressure in the reactor. The total time required for the treatment was 7 hours (including heating and cooling). The discharged material SG HSB B was then sieved through a 150 μm sieve to a controlled sieve. Table 1 shows the properties of the untreated starting material "GRAPHITE SGA" and the properties of the obtained high springback materials "GRAPHITE SG HSB A" and "GRAPHITE SG HSB B":

[0032]

Table 1

[0033] Example 2: Hydrophilic CVD-coated natural graphite with additional heat treatment using a rotary furnace As a starting material for a hydrophilic graphite friction material based on treated natural graphite having high springback, D 10 = 6 μm and D 90 = 42 μm flaky natural graphite "GRAPHITE NGB" with a particle size distribution was used. This starting material was continuously fed into a rotary kiln reactor externally heated to 1050 °C for 2 hours, producing approximately 700 g of material. Chemical vapor deposition (CVD) treatment was carried out using a mixture of hydrocarbon and inert gas (amorphous carbon precursor: C3H8 (3 L / min) and carrier gas: N2 (1 L / min)), and fed into the reactor to maintain the pressure in the reactor at 0 - 8 mbar higher than atmospheric pressure. The inclination of this tube was set at 4°, the rotation speed was set at 6 rpm, and the residence time in the kiln was about 30 minutes. To improve the wettability of the obtained CVD-modified "GRAPHITE NGB", an additional process step was added to Example 1. The obtained CVD-modified "GRAPHITE NGB" was fed into a rotary furnace heated to 650 °C filled with an oxygen-containing atmosphere (a flow of 2 L / min of synthetic air), and the inclination was set at 6° and the rotation speed at 6 rom. 350 g of the material was fed over about 30 minutes. The properties of the untreated starting material "GRAPHITE NGB" and the characteristics of the obtained high springback material "GRAPHITE NG HSB B" are shown in Table 2:

[0034]

Table 2

[0035] Example 3: CVD-treated synthetic graphite using a fluidized bed As a starting material for the fluidized bed batch process, D 10 = 7 μm and D 90Graphite in the shape of potatoes "GRAPHITE PSG" with a particle size distribution of = 36 μm was used. This starting material (8500 g) was charged into a fluidized bed reactor and then heated to 920 °C under a nitrogen atmosphere. CVD treatment was carried out for 260 minutes using a mixture of hydrocarbon and inert gas (amorphous carbon precursor: toluene C7H8 and carrier gas: N2). Thereafter, the reactor and the treated graphite were cooled under a nitrogen atmosphere. When this material reached ambient temperature, it was discharged from the fluidized bed. The properties of the untreated starting material "GRAPHITE PSG" and the characteristics of the obtained high springback material "GRAPHITE PSG HSB C" are shown in Table 3:

[0036] [Table 3]

[0037] Example 4: Heat-treated synthetic graphite using a box furnace Approximately 450 g of crushed synthetic graphite "GRAPHITE PSG" (see Example 3) was placed in a crucible and put into a high-temperature gas-tight box furnace. The starting material with a 12% springback was heated to 1500 °C at a rate of 10 °C / min. This was carried out with a constant nitrogen flow rate of 10 L / min. When 1500 °C was reached, this temperature was maintained for a residence time of 60 minutes. Thereafter, the sample was cooled in a nitrogen atmosphere (still at a flow rate of 10 L / min), discharged, and analyzed once it reached ambient temperature. The properties of the untreated starting material "GRAPHITE PSG" and the characteristics of the obtained heat-treated high springback material "GRAPHITE PSG HSB HT" are shown in Table 4:

[0038] [Table 4]

[0039] Example 5: Preparation of brake pads Brake pads having the following components were manufactured according to Table 5.

[0040]

Table 5

[0041] These components were dry mixed, cold pressed with a 140 bar press, cured by compression molding at 160°C for 9 minutes, post-cured in an oven (2 hours at 120°C and then 5 hours at 160°C), and then ground to finish as brake pads. Four types of brake pads were prepared according to the above procedure. BP1 contains "GRAPHITE NGB" as the graphite type, and BP2 contains "GRAPHITE" SGA " as the graphite type. BP3 contains "GRAPHITE SG HSB A" as the graphite type, and BP4 contains "GRAPHITE SG HSB B" as the graphite type. The properties of these graphite types can be found in Table 1 and Table 2 above. The density and porosity of brake pads BP1 to BP4 were measured. The density was measured using standard SAE 9380. The porosity was measured using standard JIS D4418:1996 using either water or oil. The physical properties of these brake pads are shown in Table 6 below.

[0042]

Table 6

[0043] It was found that the brake pads BP3 and BP4 of the present invention have a lower density and a higher porosity than the brake pads BP1 and BP2 of the comparative examples. The higher porosity of the brake pads is considered to reduce the generation of noise during use. Next, the brake pads BP1 to BP4 were tested for these performances by testing the coefficient of friction and mass loss in a standard procedure. The brake pads were installed and bedded by applying 100 brakes at 30 bar at a speed of 80 km / h on the brake pads. After bedding, the brake disc was replaced with a test disc having a surface roughness of Ra = 3 to 4 μm. The following test cycles were applied to each test brake pad: · Cycle 1: Apply 25 brakes at 20 bar at a speed of 60 km / h on the brake pad, then apply 25 brakes at 30 bar, and then apply 25 brakes at 40 bar; · Cycle 2: Apply 25 brakes at 20 bar at a speed of 80 km / h on the brake pad, then apply 25 brakes at 30 bar, and then apply 25 brakes at 40 bar; · Cycle 3: Apply 25 brakes at 20 bar at a speed of 100 km / h on the brake pad, then apply 25 brakes at 30 bar, and then apply 25 brakes at 40 bar. Therefore, each of these test brake pads was subjected to 75 braking actions at 60 km / h, 80 km / h, and 100 km / h respectively, for a total of 225 braking actions. The coefficient of friction was measured for each pressure / speed combination. At the end of Cycle 3, the mass loss of the brake pad was measured by determining the mass difference of the brake pad before Test Cycle 1 and after Test Cycle 3. The measured values of the coefficient of friction are summarized in Table 7.

[0044]

Table 7

[0045] All of the results shown are average values obtained after two test runs using equivalent brake pads. The mass losses measured for the brake pads BP3 and BP4 of the present invention were 58 mg and 55 mg, respectively, while the mass losses measured for the brake pads BP1 and BP2 of the comparative examples were 50 mg and 66 mg, respectively. Except for the low stress test at 20 bar / 60 km / h, it can be seen that the brake pads BP3 and BP4 of the present invention achieve a higher coefficient of friction compared to the brake pads BP1 and BP2 of the comparative examples. In any case, the coefficient of friction of BP4 (varying between 0.33 and 0.44) is more stable than the coefficients of friction of BP1 (varying between 0.30 and 0.43) and BP2 (varying between 0.30 and 0.46). Another aspect of the present invention may be as follows. 〔1〕A friction material containing graphite having c / 2 of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and springback of 40% or more, for example 41% or more. 〔2〕The friction material according to 〔1〕 above, wherein the graphite has a graphitization degree of 95.3% or more, for example 96% or more, for example 97% or more. 〔3〕The friction material according to 〔1〕 or 〔2〕 above, wherein the graphite has a springback of 45% or more, or 50% or more, or 60% or more. 〔4〕The graphite has a xylene density of 2.0 g / cm 3 or more, for example 2.1 g / cm 3 or more, for example 2.2 g / cm 3 or more, for example 2.23 g / cm 3 or more, and the friction material according to any one of 〔1〕 to 〔3〕 above. 〔5〕The friction material according to any one of 〔1〕 to 〔4〕 above, wherein the graphite has a crystallinity (L c ) of 50 nm or more. 〔6〕The graphite has a BET surface area of 9 m 2 / g or less, for example 8.0 m 2 / g or less, or 7.0 m 2 / g or less, or 6.0 m 2 / g or less, or 5.0 m 2 / g or less, or 4.5 m 2 / g or less, or 4.0 m 2 / g or less, and the friction material according to any one of 〔1〕 to 〔5〕 above. 〔7〕The friction material according to any one of 〔1〕 to 〔6〕 above, wherein the graphite is surface-modified graphite, for example surface-modified natural graphite or surface-modified synthetic graphite, or a mixture thereof, for example surface-modified graphite by heat treatment and coated graphite that may be by surface coating treatment. 〔8〕The surface modification of the graphite includes surface modification by heat treatment and / or surface coating treatment, for example a surface coating obtained by a chemical vapor deposition (CVD) process. The surface modification may include a further treatment to increase wettability, for example oxidation treatment. The surface coating may be performed simultaneously with or separately from the heat treatment, for example subsequent to the heat treatment. The friction material according to 〔7〕 above. 〔9〕The friction material according to any one of 〔1〕 to 〔8〕 above, containing 0.1% by mass to 30% by mass of the graphite according to any one of 〔1〕 to 〔8〕 above with respect to the total mass of the friction material. 〔10〕The friction material according to any one of 〔1〕 to 〔9〕 above, having a copper content of 5% by mass or less, for example 0.5% by mass or less. 〔11〕The friction material according to any one of 〔1〕to 〔10〕above, which has an in-plane thermal conductivity of 1.5 W / mK or more when measured according to ASTM E1461 using a laser flash by NETZSCH LFA447. 〔12〕The friction material according to any one of 〔1〕to 〔11〕above, which has a coefficient of friction of 0.5 or less. 〔13〕The friction material according to any one of 〔1〕to 〔12〕above, further comprising at least one selected from the group consisting of a resin or cement binder, antimony trisulfide, copper, barium sulfate, metal powder, metal fiber, mineral fiber, iron sulfide, coke, other natural, synthetic, expanded graphite, calcium carbonate, mica, talc, and zirconia. 〔14〕A method for manufacturing the friction material according to any one of 〔1〕to 〔13〕above, (a) A step of preparing graphite, (b) A step of subjecting the graphite prepared in step (a) to heat treatment at 600 °C or higher for 30 minutes or more, (c) A step of mixing the treated graphite obtained at the end of step (b) with further components and treating it by compression molding, or hot compression molding or curing by heat treatment, or a combination thereof, etc. to form a friction material including. 〔15〕The method according to 〔14〕above, wherein the graphite prepared in step (a) is selected from natural graphite, synthetic graphite, or a mixture thereof. 〔16〕The method according to 〔14〕or 〔15〕above, wherein the heat treatment in step (b) includes a surface coating treatment, such as a CVD treatment or an amorphous carbon coating treatment. 〔17〕The heat treatment is a first heat treatment which is a part of the surface coating treatment, such as CVD coating or pitch coating and subsequent carbonization, and a second heat treatment which is not a part of the surface coating treatment and can be carried out, for example, as a post-treatment before or after the first heat treatment including. 〔18〕The method according to 〔17〕above, wherein the second heat treatment does not include a surface coating treatment, such as a CVD treatment. 〔19〕Use of the friction material according to any one of 〔1〕to 〔13〕above in the manufacture of brake pads, for example, in the manufacture of low-copper brake pads, or in the manufacture of copper-free brake pads. Use of the friction material according to any one of items [1] to

[13] for applications in automobiles, large vehicles, wind turbines, or railways in a carbon brush, bipolar plate for a fuel cell, disk brake, drum brake, or clutch. A brake pad comprising the friction material according to any one of items [1] to

[13] , which may also be for use in an electric vehicle.

Claims

1. A friction material containing graphite having a c / 2 of 0.3358 nm or less, for example 0.3357 nm or less, or 0.3356 nm or less, and a springback of 65% or more, wherein the graphite is amorphous carbon-coated synthetic graphite.

2. The friction material according to claim 1, wherein the graphite has a graphitization degree of 95.3% or more, for example 96% or more, for example 97% or more.

3. The graphite has a xylene density of 2.0 g / cm 3 or more, for example 2.1 g / cm 3 or more, for example 2.2 g / cm 3 or more, for example 2.23 g / cm 3 or more. The friction material according to claim 1 or 2.

4. The graphite has a crystallinity (L c ) of 50 nm or more. The friction material according to any one of claims 1 to 3.

5. The graphite has a BET surface area of 9 m 2 / g or less, for example 8.0 m 2 / g or less, or 7.0 m 2 / g or less, or 6.0 m 2 / g or less, or 5.0 m 2 / g or less, or 4.5 m 2 / g or less, or 4.0 m 2 / g or less. The friction material according to any one of claims 1 to 4.

6. The friction material according to any one of claims 1 to 5, containing 0.1% to 30% by mass of the graphite according to any one of claims 1 to 5 based on the total mass of the friction material.

7. The friction material according to any one of claims 1 to 6, having a copper content of 5% by mass or less, for example 0.5% by mass or less.

8. The friction material according to any one of claims 1 to 7, having an in-plane thermal conductivity of 1.5 W / mK or more when measured according to ASTM E1461 using a laser flash by NETZSCH LFA447.

9. The friction material according to any one of claims 1 to 8, having a coefficient of friction of 0.5 or less.

10. The friction material according to any one of claims 1 to 9, further comprising at least one selected from the group consisting of a resin or cement binder, antimony trisulfide, copper, barium sulfate, metal powder, metal fiber, mineral fiber, iron sulfide, coke, other natural, synthetic, expanded graphite, calcium carbonate, mica, talc, and zirconia.

11. A method for manufacturing the friction material according to any one of claims 1 to 10, comprising: (a) preparing graphite; (b) subjecting the graphite prepared in step (a) to heat treatment at 600 °C or higher for 30 minutes or more; (c) mixing the treated graphite obtained at the end of step (b) with further components and treating it by compression molding, or hot compression molding or curing by heat treatment, or a combination thereof, to form a friction material. The method comprising.

12. The method according to claim 11, wherein the graphite prepared in step (a) is synthetic graphite.

13. The method according to claim 11 or 12, wherein the heat treatment in step (b) includes a surface coating treatment including an amorphous carbon coating treatment.

14. The heat treatment includes a first heat treatment which is a part of the surface coating treatment, for example, CVD coating or pitch coating and subsequent carbonization, and a second heat treatment which is not a part of the surface coating treatment and can be carried out, for example, as a post-treatment, before or after the first heat treatment. The method according to claim 13, including.

15. The method according to claim 14, wherein the second heat treatment does not include a surface coating treatment, such as a CVD treatment.

16. Use of the friction material according to any one of claims 1 to 10 in the manufacture of brake pads, for example in the manufacture of low-copper brake pads or in the manufacture of copper-free brake pads.

17. Use of the friction material according to any one of claims 1 to 10 for applications in automobiles, large vehicles, wind turbines or railways, in carbon brushes, bipolar plates for fuel cells, disc brakes, drum brakes or clutches.

18. A brake pad comprising the friction material according to any one of claims 1 to 10, which may also be for use in an electric vehicle.

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