JP7464039B2 - Friction member, friction material composition, friction material and vehicle - Google Patents

Description

The present invention relates to a friction member, a friction material composition, a friction material and a vehicle.

Friction materials such as disc brake pads and brake linings are used in automobiles and other vehicles for braking. These friction materials generate braking force by rubbing against mating materials such as disc rotors and brake drums. For this reason, friction materials are required to not only have an appropriate friction coefficient (effectiveness characteristics) according to the conditions of use, but also to be less likely to cause brake squeal over a wide frequency range from low to high frequencies (squeal characteristics) and to have a long lifespan (wear resistance).

Friction materials are broadly classified into semi-metallic materials that contain 30-60% by mass of steel fibers as a fiber base material, low-steel materials that contain less than 30% by mass of steel fibers, and NAO (Non-Asbestos Organic) materials that contain no steel fibers. However, friction materials that contain only trace amounts of steel fibers are sometimes classified as NAO materials.

NAO materials generally contain copper in the form of powder or fibers. However, friction materials containing copper, copper alloys, etc., contain copper in the wear powder generated during braking, and it has been suggested that they may pollute rivers and lakes. For this reason, in the US states of California and Washington, etc., a bill has been passed to prohibit the sale and installation of friction materials containing 5% or more by mass of copper from 2021 onwards and 0.5% or more by mass of copper from 2023 onwards. In response to this, there is an urgent need to develop NAO materials that do not contain copper or have a low copper content.

One of the main functions of copper is its thermal conductivity. Copper has high thermal conductivity, so it can diffuse heat generated during braking from the friction interface, suppressing wear caused by excessive temperature rise.
The second major function of copper is to protect the friction interface during high-temperature braking.
Copper has high ductility and malleability, so it spreads on the surface of the friction material and forms a coating when braking. As a result, it reduces wear on the friction material during high-speed, high-temperature braking and allows for a stable friction coefficient to be achieved. In addition, the copper spreading film makes it easier to hold the abrasive, so it is possible to achieve a good friction coefficient even during low-speed, low-temperature braking.
Therefore, in order to develop an NAO material that does not contain copper or has a low copper content, a copper replacement technology is required from the standpoints of improving thermal conductivity, protecting the interface, and retaining the abrasive material as described above.

In particular, when a stable friction coefficient is not obtained, brake squeal and abnormal noise tend to occur, so that NAO materials that do not contain copper or have a low copper content are required to have (1) a stable friction coefficient in a wide frequency range from low to high frequencies, making brake squeal and abnormal noise unlikely to occur [characteristic (1)], and (2) a high friction coefficient [characteristic (2)]. However, in order to obtain an NAO material with a high friction coefficient, it is necessary to contain an abrasive material with a high Mohs hardness, such as a metal oxide such as aluminum oxide, and on the other hand, the inclusion of such an abrasive material with a high Mohs hardness tends to cause brake squeal and abnormal noise, that is, a stable friction coefficient tends not to be obtained in a wide frequency range from low to high frequencies, so the characteristics (1) and (2) are in a trade-off relationship, and it is difficult to achieve both in NAO materials that do not contain copper or have a low copper content.

So far, several friction materials that do not contain copper or have a low copper content have been proposed. For example, in Patent Document 1, an NAO material containing stabilized or partially stabilized zirconia with a purity of 99.0% by weight or more is invented with the objective of providing an NAO material that can stabilize the friction coefficient even under severe conditions such as fading, and in paragraph [0028] it is taught that by not containing inorganic substances with a Mohs hardness of 7 or more, brake vibration and increased wear caused by grinding the rotor can be avoided.
In addition, in Patent Document 2, the objective of the invention is to provide a friction material that provides stable effectiveness over a long period of time and does not deteriorate the coefficient of friction or brake squeal, and the friction material contains an organic material containing a carbon element and inorganic fibers, in which the total content of the organic material is 30 mass% or less of the entire friction material composition, and the inorganic fibers are defibrated biosoluble inorganic fibers that have a Mohs hardness of 5 or more and 7 or less, a heat-resistant temperature of 1,000°C or more, and a fiber length of 1 mm or more, and does not contain a hard inorganic powder material with a Mohs hardness of 8 or more.

JP 2016-216696 A JP 2016-132702 A

However, the NAO material described in Patent Document 1 requires the use of special zirconia to stabilize the friction coefficient, which has the problem of greatly restricting the composition design of the NAO material. In addition, the NAO material described in Patent Document 1 does not sufficiently suppress brake squeal and abnormal noise. The friction material described in Patent Document 2 is indeed described as having excellent stability of the friction coefficient and a high friction coefficient, but this is the result of a composition containing aluminum powder, which is a metal material. If there was an NAO material that could achieve both the above characteristics (1) and (2) even if it did not contain metal powder, it would be preferable because it would broaden the scope of composition design in the development of the NAO material.

Therefore, the object of the present invention is to provide a friction member having a friction material with a high friction coefficient, a friction material composition capable of providing said friction material, said friction material, and a vehicle equipped with said friction member or friction material, which (1) has a stable friction coefficient over a wide frequency band from low to high frequencies, thereby making brake squeal and abnormal noise less likely to occur, even if it does not contain copper or, if it does contain copper, the copper content is less than 0.5 mass % in terms of elemental copper, and (2) has a high friction coefficient.

As a result of intensive research, the inventors have found that the above problems can be solved by a friction material that does not substantially contain any substance having a Mohs hardness of more than 6.4 and contains wollastonite as mineral fiber, and have thus completed the present invention. That is, the present invention relates to the following [1] to [27].

[1] A friction member having a friction material and a backing metal,
The friction material does not contain copper, or if it contains copper, the copper content is less than 0.5 mass% in terms of copper element, and does not substantially contain any substance having a Mohs hardness of more than 6.4, and contains wollastonite as mineral fibers.
[2] The friction member according to the above [1], wherein the friction material contains one or more types of mineral fibers other than the wollastonite.
[3] The friction member according to the above [1] or [2], wherein the friction material contains two or more kinds of mineral fibers other than the wollastonite.
[4] The friction member according to the above [2] or [3], wherein the mineral fibers other than wollastonite contain two types of mineral fibers: those having a fiber length of 200 μm or less and those having a fiber length of more than 200 μm.
[5] The friction member according to any one of the above [2] to [4], containing at least rock wool as the mineral fiber other than the wollastonite.
[6] The friction member according to any one of the above [1] to [5], wherein the wollastonite content in the friction material is 3 to 10 mass % based on the total amount of the friction material.
[7] The friction member according to any one of the above [2] to [6], wherein the total content of the mineral fibers in the friction material is 3 to 35 mass % based on the total amount of the friction material.
[8] The friction member according to any one of the above [1] to [7], wherein the friction material further contains magnesium oxide.
[9] The friction member according to any one of the above [1] to [8], wherein the friction material further contains mica.
[10] The friction member according to any one of the above [1] to [9], wherein the friction material further contains organic fibers.
[11] The friction member according to any one of the above [1] to [10], wherein the friction material further contains graphite.
[12] The friction member according to any one of the above [1] to [11], wherein the friction material contains at least one selected from the group consisting of an inorganic filler, an organic filler, a fibrous base material, and a binder.
[13] A vehicle equipped with the friction member according to any one of [1] to [12] above.
[14] A friction material composition which does not contain copper, or if it contains copper, the copper content is less than 0.5 mass% in terms of elemental copper, and which is substantially free of any substance having a Mohs hardness of more than 6.4, and which contains wollastonite as mineral fibers.
[15] The friction material composition according to the above [14], which contains one or more types of mineral fibers other than the wollastonite.
[16] The friction material composition according to the above [14] or [15], which contains two or more types of mineral fibers other than the wollastonite.
[17] The friction material composition according to the above [15] or [16], wherein the mineral fibers other than wollastonite contain [I] mineral fibers having an average fiber length of more than 200 μm and [II] mineral fibers having an average fiber length of 200 μm or less.
[18] The friction material composition according to any one of the above [15] to [17], containing at least rock wool as the mineral fiber other than the wollastonite.
[19] The friction material composition according to any one of [14] to [18] above, wherein the content of wollastonite is 3 to 10 mass % based on the total amount of the friction material composition.
[20] The friction material composition according to any one of [14] to [19] above, wherein the total content of the mineral fibers is 3 to 35 mass % based on the total amount of the friction material composition.
[21] The friction material composition according to any one of the above [14] to [20], further comprising magnesium oxide.
[22] The friction material composition according to any one of [14] to [21] above, further comprising mica.
[23] The friction material composition according to any one of the above [14] to [22], further comprising organic fibers.
[24] The friction material composition according to any one of [14] to [23] above, further comprising graphite.
[25] The friction material composition according to any one of the above [14] to [24], further comprising at least one selected from the group consisting of an inorganic filler, an organic filler, a fibrous base material, and a binder.
[26] A friction material comprising the friction material composition according to any one of [14] to [25] above.
[27] A vehicle equipped with the friction material described in [26] above.

According to the present invention, even if the friction material does not contain copper or contains copper in an amount of less than 0.5 mass % in terms of elemental copper, it is possible to provide a friction member having a friction material that (1) has a stable friction coefficient over a wide frequency band from low frequency to high frequency, thereby making it difficult for brake squeal and abnormal noise to occur, and (2) has a high friction coefficient, a friction material composition that can provide the friction material, the friction material, and a vehicle equipped with the friction member or friction material.
The friction member, friction material, and friction material composition of the present invention do not contain copper, or even if they contain copper, the copper content is less than 0.5 mass% in terms of copper element, that is, they are substantially free of copper, and therefore are environmentally friendly.

1 is a schematic diagram of a cross section of a friction member (disc brake pad) in which a friction material (upper layer) is disposed on one surface of a back plate via a lower layer.

Hereinafter, a friction member, a friction material composition, a friction material, and a vehicle according to an embodiment of the present invention will be described in detail. However, in the following embodiments, the components are not essential unless otherwise specified. The same applies to the numerical values and their ranges, and they do not limit the present invention.
In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the Examples. Furthermore, in this specification, when there are multiple substances corresponding to each component, the content of each component in the friction material composition means the total content of the multiple substances present in the friction material composition, unless otherwise specified.
In the present invention, "normal braking" refers to a state in which braking is performed with a hydraulic pressure of 2 to 4 MPa when traveling at a speed of 20 to 50 km/h, and "high-speed braking" refers to a state in which braking is performed with a hydraulic pressure of 2 to 4 MPa when traveling at a speed of 100 to 200 km/h.
Additionally, any combination of the descriptions in this specification is also included in the present invention.

[Friction materials and friction members]
The friction member according to the present embodiment is a friction member having a friction material and a backing metal, the friction material does not contain copper, or if it contains copper, the copper content is less than 0.5 mass % in terms of elemental copper, and the friction member does not substantially contain any substance having a Mohs hardness of more than 6.4, and contains wollastonite as mineral fibers.

The friction material of the present embodiment does not contain copper, or even if it does contain copper, the copper content is less than 0.5 mass % in terms of elemental copper, and therefore is environmentally friendly.
The above "copper" refers to copper in the form of fibers, powder, etc.; copper element contained in copper alloys, copper compounds, etc., and the "copper content" refers to the content relative to the total amount of the friction material.
From the viewpoint of preventing environmental pollution, the copper content is preferably 0.4 mass % or less, more preferably 0.2 mass % or less, and even more preferably 0.1 mass % or less, based on the total amount of the friction material. It is particularly preferable that the friction material does not contain copper.

(Materials with a Mohs hardness of over 6.4)
Furthermore, the friction material of the present embodiment does not substantially contain any material having a Mohs hardness of more than 6.4, such as metal oxides having a Mohs hardness of more than 6.4, such as zirconium oxide (Mohs hardness 7) and aluminum oxide (Mohs hardness 9), and metal silicates having a Mohs hardness of more than 6.4, such as zirconium silicate (Mohs hardness 7.5).
As described above, materials having a Mohs hardness of more than 6.4 include abrasives having a Mohs hardness of more than 6.4 (or 6.5 or more).
In this specification, "substantially not contained" means not contained at all, that is, 0 mass%, but also means, for example, 0.05 mass% or less (in some cases, it may be 0.03 mass% or less, or 0.01 mass% or less), and also includes a case where the content is so low that it is hardly meaningful to include it.

(Wollastonite [mineral fiber])
The friction material of the present embodiment satisfies the above conditions and contains wollastonite as mineral fibers. In other words, the wollastonite is fibrous wollastonite. The fibrous wollastonite refers to a naturally occurring silicate mineral mainly composed of _CaSiO3 that is pulverized, classified, and processed into fibers.
The average fiber length of the fibrous wollastonite is preferably 20 to 1,000 μm, more preferably 40 to 850 μm, even more preferably 100 to 850 μm, particularly preferably 100 to 400 μm, and most preferably 100 to 200 μm, from the viewpoint of suppressing the occurrence of brake squeal and abnormal noise and from the viewpoint of obtaining a high coefficient of friction. The average fiber diameter of the fibrous wollastonite is preferably 70 μm or less, more preferably 60 μm or less, from the viewpoint of suppressing the occurrence of brake squeal and abnormal noise and from the viewpoint of obtaining a high coefficient of friction. There is no particular restriction on the lower limit of the average fiber diameter, but it is preferably 5 μm or more, more preferably 8 μm or more.
In this specification, the average fiber length and the average fiber diameter are respectively average values obtained by randomly selecting 50 inorganic fibers to be used and measuring the fiber length and fiber diameter under an optical microscope, but for commercially available products, the catalog values can be referred to. In this specification, the fiber diameter refers to the diameter of the fiber.

The average aspect ratio (average fiber length/average fiber diameter) of the fibrous wollastonite is not particularly limited, but is preferably 8 or more, more preferably 8 to 20, even more preferably 9 to 20, and particularly preferably 10 to 16. By setting the average aspect ratio to 8 or more, it is possible to suppress the generation of brake squeal and abnormal noise, and to obtain a high friction coefficient. Here, the average aspect ratio means the d50 value (cumulative median value of volume distribution).
In order to enhance the affinity with the binder, the fibrous wollastonite may be surface-treated with aminosilane, epoxysilane, or the like.

The content of the wollastonite in the friction material is not particularly limited, but from the viewpoint of suppressing the generation of brake squeal and abnormal noise and from the viewpoint of obtaining a high friction coefficient, the content is preferably 3 to 10 mass %, more preferably 4 to 10 mass %, further preferably 5 to 9 mass %, and particularly preferably 6.0 to 8.5 mass %, based on the total amount of the friction material.
The wollastonite may be used alone or in combination of two or more kinds.

[Components of friction materials]
The friction material of the present embodiment preferably contains at least one selected from the group consisting of inorganic fillers, organic fillers, fibrous base materials, and binders. In the present invention, since the material does not substantially contain any substance having a Mohs hardness of more than 6.4, it goes without saying that the inorganic fillers, organic fillers, fibrous base materials, and binders do not contain any substance having a Mohs hardness of more than 6.4, and the same applies hereinafter even if not specified. For example, even when simply referred to as "inorganic fillers" in this specification, it refers to inorganic fillers with a Mohs hardness of 6.4 or less (preferably a Mohs hardness of 6 or less, as described below).
Hereinafter, each of the components contained in the friction material of the present embodiment, other than the wollastonite, will be described in detail.

<Inorganic filler>
The friction material of the present embodiment preferably contains an inorganic filler. The inorganic filler can function as a friction modifier to prevent deterioration of the heat resistance, wear resistance, stability of the friction coefficient, etc. of the friction material. Here, in the present invention, the inorganic filler does not include fibrous ones (i.e., inorganic fibers described later).
The mating material, the disk rotor, is generally cast iron with a Mohs hardness of about 4.5, so an inorganic filler with a Mohs hardness of 5 or more acts as an abrasive and has the effect of increasing the coefficient of friction.
From the viewpoint of suppressing brake squeal and abnormal noise and obtaining a high coefficient of friction, the inorganic filler is an inorganic filler having a Mohs hardness of 6.4 or less, and preferably an inorganic filler having a Mohs hardness of 6 or less.
The inorganic fillers may be used alone or in combination of two or more kinds.

Examples of the inorganic filler include titanates such as potassium titanate, lithium potassium titanate, sodium titanate, and magnesium potassium titanate; metal sulfides such as bismuth sulfide, antimony trisulfide, tin sulfide, molybdenum disulfide, iron sulfide, zinc sulfide, tungsten sulfide, and manganese sulfide; magnesium oxide, mica, graphite, coke, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, vermiculite, calcium sulfate, talc, clay, zeolite, chromite, triiron tetroxide, and zinc oxide; and metal powders such as iron powder, cast iron powder, aluminum powder, nickel powder, tin powder, zinc powder, and alloy powders containing at least one of the above metals. It is preferable that the inorganic filler contains at least one type selected from these, and from the viewpoint of suppressing the occurrence of brake squeal and abnormal noise and obtaining a high friction coefficient, it is more preferable that the inorganic filler contains at least one type selected from the group consisting of magnesium oxide, graphite, titanate, metal sulfide, mica, calcium carbonate, calcium hydroxide, and barium sulfate, it is even more preferable that the inorganic filler contains at least one type selected from the group consisting of magnesium oxide, graphite, potassium titanate, tin sulfide, mica, calcium carbonate, calcium hydroxide, and barium sulfate, it is particularly preferable that the inorganic filler contains at least magnesium oxide, graphite, metal sulfide, mica, calcium hydroxide, and barium sulfate, and it is most preferable that the inorganic filler contains at least magnesium oxide, graphite, tin sulfide, mica, calcium hydroxide, and barium sulfate.
Although there is no particular limitation, it is preferable that the inorganic filler does not contain copper or iron-based metals.

The total content of the inorganic filler in the friction material of the present embodiment is preferably 40 to 85 mass %, more preferably 45 to 80 mass %, and even more preferably 50 to 70 mass %, based on the total amount of the friction material, from the viewpoints of the heat resistance, wear resistance, and stability of the friction coefficient of the friction material.
Preferred inorganic fillers will be described in detail below.

(graphite)
The friction material of the present embodiment preferably contains graphite as an inorganic filler. By containing graphite, the friction material can be given superior thermal conductivity. The graphite is not particularly limited, and any known graphite, that is, either natural graphite or artificial graphite, can be used.
The average particle size of the graphite is not particularly limited, but is preferably 1 to 50 μm, more preferably 2 to 40 μm, even more preferably 5 to 30 μm, and particularly preferably 5 to 20 μm. Two or more types of graphite having different average particle sizes may be used in combination. If the average particle size of the graphite is equal to or greater than the lower limit, the thermal conductivity is prevented from increasing excessively, and the frictional heat tends to be transferred to the back plate side and the occurrence of vapor lock is easily prevented. If the average particle size of the graphite is equal to or less than the upper limit, the thermal conductivity is improved, the hardening of the binder during molding is promoted, and excellent strength is exhibited. Note that graphite having an average particle size outside the range may be used.
In this specification, the average particle size means the d50 value (median size of volume distribution, cumulative median value) measured using a laser diffraction particle size distribution measurement method, and the same applies hereinafter. The average particle size can be measured, for example, by a laser diffraction/scattering type particle size distribution measurement device, product name: LA-920 (manufactured by Horiba, Ltd.).

When the friction material of this embodiment contains graphite, the content is preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %, even more preferably 2 to 10 mass %, and particularly preferably 3 to 8 mass %, based on the total amount of the friction material. If the graphite content is equal to or greater than the lower limit, there is a tendency for the thermal conductivity to be easily improved, and if it is equal to or less than the upper limit, there is a tendency for an excessive increase in the thermal conductivity to be suppressed and a decrease in the friction coefficient to be easily suppressed.

(Titanate)
The titanate preferably includes at least one selected from the group consisting of potassium titanate (potassium 6-titanate, potassium 8-titanate), lithium potassium titanate, magnesium potassium titanate, and sodium titanate, and more preferably includes potassium titanate.
The shape of the titanate is not particularly limited, but is preferably non-acicular from the viewpoint of avoiding harmfulness to the human body. Non-acicular titanate refers to plate-like titanate having a shape such as a polygon, circle, or ellipse, or titanate having an irregular shape. The shape of the titanate can be analyzed, for example, by observation with a scanning electron microscope (SEM).
Titanate has a low Mohs hardness of about 4 and a relatively high melting point of 1,000° C. or higher, so its presence at the friction interface during high-speed, high-temperature braking can reduce increased wear of the friction material.

When the friction material of this embodiment contains titanate, the content is preferably 2 to 25 mass % of the total amount of the friction material, more preferably 3 to 20 mass %, even more preferably 3 to 15 mass %, and particularly preferably 5 to 12 mass %. If the titanate content is equal to or greater than the lower limit, the friction coefficient during high-speed, high-temperature braking tends to be good, and if it is equal to or less than the upper limit, the decrease in the friction coefficient during low-speed, low-temperature braking tends to be suppressed.

(Metal sulfides)
Examples of the metal sulfide include bismuth sulfide, antimony trisulfide, tin sulfide, molybdenum disulfide, iron sulfide, zinc sulfide, tungsten sulfide, and manganese sulfide, and at least one selected from the group consisting of these is preferable. Among these, from the viewpoint of less harmfulness to the human body, it is preferable to contain at least one selected from the group consisting of bismuth sulfide, tin sulfide, molybdenum disulfide, iron sulfide, zinc sulfide, tungsten sulfide, and manganese sulfide, and from the viewpoint of stability of the friction coefficient during normal braking, it is more preferable to contain tin sulfide.
The metal sulfides may be used alone or in combination of two or more kinds.

When the friction material of this embodiment contains metal sulfide, the content is preferably 0.1 to 10 mass % of the total amount of the friction material, more preferably 0.5 to 6 mass %, even more preferably 1 to 5 mass %, and particularly preferably 1 to 4 mass %. If the content of metal sulfide is equal to or greater than the lower limit, rotor wear tends to be suppressed, and if it is equal to or less than the upper limit, a decrease in the coefficient of friction tends to be suppressed.

(Mica)
Examples of mica include phlogopite, biotite, muscovite, and synthetic mica. One type of mica may be used alone, or two or more types may be used in combination.
Phlogopite is known as soft mica, and has the composition formula KMg ₃ AlSi ₃ O ₁₀ (OH) _2. Furthermore, biotite (composition formula: K(Mg,Fe) ₃ AlSi ₃ O ₁₀ (OH) ₂ ) is phlogopite in which part of the Mg is replaced with Fe, and is a continuous solid solution of phlogopite and annite (iron mica, composition formula: KFe ₃ AlSi ₃ O ₁₀ (OH) ₂ ). Phlogopite and biotite have a Mohs hardness of 2.0 to 2.5, and are characterized as being relatively soft among micas.
The molar ratio of Mg to Fe (Mg/Fe) in biotite is not particularly limited, but is preferably 50/50 or more, more preferably 60/40 or more, and even more preferably 80/20 or more. Note that, since phlogopite is obtained when the molar ratio (Mg/Fe) is 100/0, the upper limit of the preferred range of the molar ratio (Mg/Fe) is less than 100/0.
Muscovite (white mica, composition formula: KAl ₂ AlSi ₃ O ₁₀ (OH) ₂ ), known as hard mica, has a Mohs hardness of 2.5 to 3.5, and synthetic mica (one example is synthetic mica, composition formula: KMg ₃ (AlSi ₃ )O ₁₀ F ₂ ), has a Mohs hardness of 3.4, making these types of mica hard.
There is no particular restriction on the average particle size of the mica, but from the viewpoint of suppressing low-frequency abnormal noise and further reducing the occurrence of wear and cracks, it is preferably 340 to 1,500 μm, more preferably 450 to 1,300 μm, and even more preferably 600 to 1,100 μm.

When the friction material of this embodiment contains mica, the content is preferably 1 to 10 mass % of the total amount of the friction material, more preferably 2 to 8 mass %, even more preferably 3 to 8 mass %, and particularly preferably 4 to 7 mass %. If the mica content is equal to or greater than the lower limit, rotor wear tends to be improved, and if it is equal to or less than the upper limit, a decrease in the friction coefficient tends to be suppressed.

(Calcium Carbonate)
By including calcium carbonate in the friction material of the present embodiment, the strength of the friction material can be improved. As the calcium carbonate, commercially available calcium carbonate can be used as it is. As the calcium carbonate, it may be either surface-treated or not.
The calcium carbonate is not particularly limited, but calcium carbonate having a specific surface area of 1.0 to 60 m ² /g as measured by the BET method may be used.

When the friction material of this embodiment contains calcium carbonate, the content is preferably 1 to 10 mass % relative to the total amount of the friction material, more preferably 2 to 8 mass %, even more preferably 2 to 6 mass %, and particularly preferably 3 to 7 mass %.

(Calcium hydroxide)
Since calcium hydroxide increases the pH of the friction material and tends to make the aramid fibers more easily decomposed, it is preferable to pay attention to the amount used when using calcium hydroxide together with the aramid fibers so that the pH does not become too high. When the friction material of the present embodiment contains calcium hydroxide, the content of calcium hydroxide is preferably 0.5 to 10 mass %, more preferably 1 to 8 mass %, and even more preferably 2 to 5 mass %, based on the total amount of the friction material.

(Barium Sulfate)
The average particle size of barium sulfate is not particularly limited, but is preferably 1 to 100 μm, more preferably 5 to 75 μm, and even more preferably 10 to 50 μm.
The barium sulfate acts simply as a filler to adjust the volume of the friction material, i.e., the amount of barium sulfate depends on the amount of other ingredients, and the barium sulfate can be used to make up the remainder to make up the desired amount of friction material.

<Organic filler>
The friction material of the present embodiment preferably contains an organic filler. The organic filler is contained as a friction modifier for improving the noise and vibration performance, wear resistance, etc. of the friction material. Here, in the present invention, the organic filler does not include fibrous fillers (i.e., organic fibers described later).
The organic fillers may be used alone or in combination of two or more kinds.
Examples of the organic filler include cashew particles and rubber components.

(Cashew particles)
The cashew particles are obtained, for example, by pulverizing polymerized and hardened cashew nut shell oil, and are generally called cashew dust. Note that the cashew particles are preferably unmodified cashew particles.
Cashew particles are generally classified into brown, brown-black, black, etc., depending on the type of curing agent used in the curing reaction. By adjusting the molecular weight, etc., it is possible to easily control the heat resistance, sound vibration, and further the film forming property on the rotor, which is the mating material. From the viewpoint of dispersibility, the average particle size of the cashew particles is preferably 850 μm or less, more preferably 750 μm or less, and even more preferably 600 μm or less. There is no particular restriction on the lower limit of the average particle size of the cashew particles, and it may be 200 μm or more, 300 μm or more, or 400 μm or more. Needless to say, a numerical range obtained by arbitrarily combining the upper limit value and the lower limit value is also included in a preferred embodiment of the average particle size of the cashew particles.
As the cashew particles, commercially available products can be used.
The cashew particles may be used alone or in combination of two or more kinds.

When the friction material of this embodiment contains cashew particles, the content is preferably 1 to 16 mass % of the total amount of the friction material, more preferably 1.5 to 10 mass %, even more preferably 2 to 7 mass %, and particularly preferably 2 to 5 mass %. When the content of cashew particles is within the above range, there is a tendency for the noise and vibration performance, such as squeal caused by the low elasticity of the friction material, to be easily improved.

(Rubber component)
The rubber component may be any known rubber component used in friction materials, such as natural rubber and synthetic rubber. Examples of synthetic rubber include acrylonitrile-butadiene rubber (NBR), acrylic rubber, isoprene rubber, polybutadiene rubber (BR), styrene butadiene rubber (SBR), silicone rubber, and crushed powder of tire tread rubber (sometimes referred to as rubber powder). Among these, acrylonitrile-butadiene rubber (NBR) and crushed powder of tire tread rubber (rubber powder) are preferred from the viewpoint of the balance between heat resistance, flexibility, and manufacturing costs.
When the friction material of the present embodiment contains a rubber component, the content is preferably 0.2 to 15 mass%, more preferably 0.2 to 10 mass%, even more preferably 0.3 to 6 mass%, and particularly preferably 0.3 to 5 mass%, based on the total amount of the friction material. Furthermore, the upper limit of the above-mentioned numerical range of the content of the rubber component may be 3 mass% or less, 2 mass% or less, or 1.5 mass% or less. By setting the content of the rubber component within the above-mentioned range, it is possible to avoid an increase in the elastic modulus of the friction material, and it is possible to avoid deterioration of vibration damping properties such as squealing, and it is also possible to avoid deterioration of heat resistance and reduction in strength due to thermal history.

The friction material of this embodiment preferably contains one or more selected from the group consisting of cashew particles and rubber components, and more preferably uses cashew particles and a rubber component in combination. When using cashew particles and a rubber component in combination, cashew particles coated with a rubber component may be used, or from the viewpoint of sound vibration performance, cashew particles and a rubber component may be blended separately.

When the friction material of the present embodiment contains an organic filler, the total content thereof is preferably 1.2 to 20 mass %, more preferably 2 to 10 mass %, and even more preferably 2 to 8 mass %, based on the total amount of the friction material. Furthermore, the upper limit of the numerical range of the organic filler content may be 5 mass % or less, or may be 4 mass % or less.
When the content of the organic filler is within the above range, the elasticity of the friction material is reduced, which tends to improve noise and vibration performance such as squeal, and also tends to prevent deterioration of heat resistance and reduction in strength due to thermal history.

<Fiber base material: organic fibers and inorganic fibers>
The fiber substrate exhibits a reinforcing effect. Examples of the fiber substrate include organic fibers and inorganic fibers. The fiber substrate may be used alone or in combination of two or more kinds.
In the friction material of this embodiment, the aforementioned mineral fiber wollastonite is essentially contained as the inorganic fiber, so hereinafter, a fiber base material other than wollastonite will be described.

- Organic fiber -
The friction material of the present embodiment preferably contains organic fibers, which are fibrous materials whose main component is an organic substance.
Examples of the organic fibers include hemp, cotton, aramid fibers, cellulose fibers, acrylic fibers, phenolic resin fibers (having a cross-linked structure), etc. The organic fibers may be used alone or in combination of two or more kinds.
As the organic fiber, from the viewpoint of heat resistance, aramid fiber is preferable. Also, from the viewpoint of improving the strength of the friction material, it is preferable that the organic fiber contains fibrillated organic fiber, and more preferably contains fibrillated aramid fiber. Fibrillated organic fiber is an organic fiber that has been split and has fluff, and is commercially available.

When the friction material of this embodiment contains organic fibers, the content is not particularly limited, but is preferably 1 to 15 mass%, more preferably 1 to 10 mass%, even more preferably 1.5 to 6 mass%, and particularly preferably 1.5 to 4 mass% of the total amount of the friction material. If the content is equal to or greater than the lower limit, good shear strength, crack resistance, and abrasion resistance tend to be exhibited, and if the content is equal to or less than the upper limit, deterioration of shear strength and crack resistance due to uneven distribution of organic fibers (fibrillated organic fibers) and other materials in the friction material composition tends to be effectively suppressed.

- Inorganic fiber -
The friction material of the present embodiment may contain only the wollastonite as the inorganic fiber, but it is also preferable that the friction material contains inorganic fibers other than the wollastonite. The inorganic fibers can exhibit the effect of improving the mechanical strength and wear resistance of the friction material.
Examples of inorganic fibers include mineral fibers (excluding the above-mentioned wollastonite, the same applies below), glass fibers, metal fibers, carbon fibers, ceramic fibers, biodegradable ceramic fibers, sepiolite (α-type sepiolite and β-type sepiolite), attapulgite, potassium titanate fibers, silica alumina fibers, and flame-resistant fibers.
The inorganic fibers are preferably fibrous materials mainly composed of inorganic substances other than metals and metal alloys, more preferably mineral fibers and glass fibers, and even more preferably mineral fibers.
The inorganic fibers may be used alone or in combination of two or more kinds.

(Mineral Fibers)
The mineral fibers are man-made inorganic fibers melt-spun mainly from blast furnace slag such as slag wool, basalt such as basalt fiber, other natural rocks, etc. Examples of the mineral fibers include mineral fibers containing SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na ₂ O, etc., or mineral fibers containing one or more of these compounds. As the mineral fibers, mineral fibers containing aluminum element are preferred, mineral fibers containing Al ₂ O ₃ are more preferred, and mineral fibers containing Al ₂ O ₃ and SiO ₂ are even more preferred.

From the viewpoint of suppressing brake squeal and abnormal noise and obtaining a high friction coefficient, the friction material of the present embodiment preferably contains one or more types of mineral fibers other than the wollastonite, more preferably contains two or more types of mineral fibers other than the wollastonite, and even more preferably contains two types of mineral fibers other than the wollastonite.
From the viewpoint of suppressing the generation of brake squeal and abnormal noise and from the viewpoint of obtaining a high coefficient of friction, rock wool is preferred as the mineral fiber. In other words, the friction material of the present embodiment preferably contains at least rock wool as the mineral fiber other than the wollastonite.
Furthermore, the mineral fibers may be surface-treated or may not be surface-treated, and a preferred embodiment is one in which surface-treated mineral fibers and non-surface-treated mineral fibers are used in combination.

The longer the average fiber length of the mineral fibers contained in the friction material, the lower the shear strength tends to be. Therefore, the average fiber length of the mineral fibers is preferably 500 μm or less, more preferably 100 to 400 μm, and even more preferably 120 to 340 μm.

On the other hand, from the viewpoint of the stability of the friction coefficient, it is also preferable to use in combination [I] mineral fibers having an average fiber length of more than 200 μm (hereinafter referred to as mineral fibers [I]) and [II] mineral fibers having an average fiber length of 200 μm or less (hereinafter referred to as mineral fibers [II]). Mineral fibers [I] are also called wool-like mineral fibers, and their average fiber length is preferably more than 200 to 500 μm, more preferably more than 200 to 400 μm, even more preferably more than 200 to 300 μm, and particularly preferably 210 to 250 μm. Mineral fibers [II] are also called cut-like mineral fibers, and their average fiber length is preferably 50 to 200 μm, more preferably 100 to 200 μm, even more preferably 100 to 180 μm, and particularly preferably 120 to 180 μm.
When the mineral fiber [I] and the mineral fiber [II] are used in combination, the content ratio of the mineral fiber [I] to the mineral fiber [II] in the friction material ([I]/[II]) is preferably 5/95 to 50/50, more preferably 10/90 to 45/55, further preferably 15/85 to 40/60, and particularly preferably 20/80 to 40/60, by mass ratio.
The average fiber diameter of the mineral fibers is not particularly limited, but is usually from 1 to 20 μm, and may be from 2 to 15 μm, or may be from 2 to 8 μm.

From the viewpoint of toxicity to the human body, the mineral fiber is preferably biosoluble. The biosoluble mineral fiber referred to here is a mineral fiber that has the characteristic that even if it is taken into the human body, it is partially decomposed in a short time and discharged from the body. Specifically, it refers to a fiber (see Nota Q (carcinogenicity exemption) of EU Directive 97/69/EC) that satisfies any of the following chemical composition: the total amount of alkali oxides and alkaline earth oxides (total amount of oxides of sodium, potassium, calcium, magnesium and barium) is 18% by mass or more, and (a) in a short-term inhalation exposure in vivo durability test, the half-life of fibers with a length of more than 20 μm is less than 10 days, (b) in a short-term intratracheal infusion in vivo durability test, the half-life of fibers with a length of more than 20 μm is less than 40 days, (c) in an intraperitoneal administration test, or (d) in a long-term inhalation exposure test, the pathological findings or tumor formation associated with carcinogenicity are not observed. Examples of such biodegradable mineral fibers include _SiO2 - _{Al2O3 -} CaO-MgO-FeO ( _-K2O - _Na2O ) based fibers, and include mineral fibers containing at least two types selected from _SiO2 , _{Al2O3 ,} CaO, MgO, FeO, _K2O , _Na2O , etc., in any combination.

(Glass fiber)
Glass fiber refers to a fiber produced by melting and spinning glass. Glass fibers can be made from E-glass, C-glass, S-glass, D-glass, etc., and among these, glass fibers containing E-glass or S-glass are preferably used from the viewpoint of particularly high strength. In addition, in order to improve the affinity with the binder, glass fibers whose surfaces are treated with aminosilane or epoxysilane are preferred. In addition, from the viewpoint of improving the handleability of the raw material and the friction material composition, glass fibers bundled with urethane resin, acrylic resin, phenol resin, etc. can be used, and the number of bundles is preferably 50 to 1,000, and more preferably 50 to 500 from the viewpoint of the balance between dispersibility and handleability.

The average fiber length of the glass fibers is not particularly limited, but is preferably 80 to 6,000 μm, more preferably 150 to 5,000 μm, even more preferably 300 to 5,000 μm, particularly preferably 1,000 to 5,000 μm, and most preferably 2,000 to 4,000 μm. If the average fiber length is 80 μm or more, the strength of the friction material tends to improve, and if it is 6,000 μm or less, the decrease in dispersibility tends to be suppressed. In addition, the average fiber diameter of the glass fibers is preferably 5 to 20 μm, more preferably 7 to 15 μm. If the average fiber diameter is 5 μm or more, it is possible to suppress the glass fibers from breaking during mixing of the friction material composition, and if it is 20 μm or less, the strength of the friction material tends to improve.

When the friction material of the present embodiment contains glass fibers, the content is not particularly limited, but is preferably 0.5 to 10 mass %, and more preferably 2 to 6 mass %, based on the total amount of the friction material. By setting the glass fiber content within this range, toughness can be imparted without impairing the handleability of the friction material composition after mixing, and there is a tendency that the strength of the friction material can be easily improved.
On the other hand, the friction material of the present embodiment does not necessarily need to contain glass fibers.

When the friction material of this embodiment contains inorganic fibers other than the wollastonite, the total content of the inorganic fibers including the wollastonite is preferably 3 to 35 mass % relative to the total amount of the friction material, more preferably 4 to 30 mass %, even more preferably 10 to 30 mass %, and particularly preferably 15 to 30 mass %.

(Metal Fiber)
Examples of the metal fibers include fibers of a single metal such as aluminum, iron, zinc, tin, titanium, nickel, magnesium, or an alloy thereof, and fibers mainly composed of a metal such as cast iron. Examples of the alloy fibers (alloy fibers) include iron alloy fibers and aluminum alloy fibers. The metal fibers may be used alone or in combination of two or more kinds. In the present invention, the friction material may not contain metal fibers.
From the viewpoint of improving crack resistance and wear resistance, generally, copper fiber, copper alloy fiber, iron fiber and iron alloy fiber are preferred. However, when copper or copper alloy fiber is contained, it may cause pollution of rivers and the like when it is released into the environment as wear powder, so the copper content in the friction material is less than 0.5 mass% as copper element, more preferably 0.3 mass% or less, even more preferably 0.1 mass% or less, and particularly preferably substantially free of copper. Incidentally, examples of copper alloy fiber include copper fiber, brass fiber, bronze fiber, etc.
Furthermore, when iron fibers or iron alloy fibers are contained, the aggressiveness to a cast iron disc rotor increases. Therefore, the iron content in the friction material is preferably less than 0.5 mass % in terms of iron element, more preferably 0.2 mass % or less, even more preferably 0.1 mass % or less, and particularly preferably an embodiment in which the friction material contains substantially no iron.

<Binding material>
The friction material of the present embodiment preferably further contains a binder, which binds together the organic filler, fibrous base material, and other components contained in the friction material to provide strength to the material.
The binder may be used alone or in combination of two or more kinds.
As the binder, a thermosetting resin that is usually used for friction materials can be used.
Examples of the thermosetting resin include various modified phenolic resins such as phenolic resins (e.g., straight novolac phenolic resins), acrylic rubber modified phenolic resins, silicone modified phenolic resins, cashew modified phenolic resins, epoxy modified phenolic resins, alkylbenzene modified phenolic resins, etc. Among these, phenolic resins (e.g., straight novolac phenolic resins) and acrylic rubber modified phenolic resins are preferred, and acrylic rubber modified phenolic resins may be selected from the viewpoint of flexibility.

When the friction material of the present embodiment contains a binder, the content thereof is preferably 4 to 14 mass %, more preferably 6 to 12 mass %, and further preferably 8 to 10 mass %, based on the total amount of the friction material.
When the content of the binder is within the above range, there is a tendency that the decrease in strength of the friction material can be further suppressed, and also that the porosity of the friction material is reduced and the elastic modulus is increased, thereby suppressing the deterioration of sound vibration performance such as squeal.

<Other ingredients>
The friction material of the present embodiment may contain materials other than the above-mentioned components, if necessary.
Other materials include, for example, metal powders such as zinc powder and aluminum powder; and organic additives such as fluorine-based polymers such as polytetrafluoroethylene (PTFE).
In the case where the friction material of the present embodiment contains the above-mentioned other materials, the content of each of them is preferably 5 mass % or less, more preferably 3 mass % or less, based on the total amount of the friction material, and the friction material may not contain other materials. In particular, in the present invention, even if the friction material does not contain metal powder, it is advantageous in that (1) it has a stable friction coefficient over a wide frequency range from low frequency to high frequency, making it difficult for brake squeal and abnormal noise to occur, and (2) it has a high friction coefficient.

<Method of manufacturing friction material>
The friction material of the present embodiment can be produced by a commonly used method.
As a method for producing the friction material of this embodiment, for example, a method of producing the friction material composition satisfying the composition of the friction material of this embodiment by hot and pressure molding can be mentioned. In detail, for example, the friction material composition of this embodiment described later is mixed uniformly using a mixer such as a Lödige (registered trademark) mixer, a pressure kneader, or an Eirich (registered trademark) mixer, the mixture is preformed in a molding die, the preform obtained is molded under conditions of a molding temperature of 130 to 160 ° C, a molding pressure of 20 to 50 MPa, and a molding time of 3 to 10 minutes, and the obtained molded product is heat-treated at 180 to 230 ° C for 3 to 5 hours. In addition, painting, scorching treatment, polishing treatment, etc. may be performed as necessary.

<Uses of friction materials>
The friction material of the present embodiment is used, for example, in the following aspects (1) to (3).
(1) Composition consisting of friction material only.
(2) A friction member having a backing metal and the friction material of the present embodiment formed on the backing metal to form a friction surface.
(3) In the above configuration (2), a primer layer for surface modification to enhance the adhesive effect of the back metal and an adhesive layer for bonding the back metal and the friction member are further interposed between the back metal and the friction member.
Among these, it is preferable to use the friction material of the present embodiment and a backing metal as a friction member, as in the above (2) or (3).
The back metal is used to improve the mechanical strength of the friction member, and examples of the material thereof include metals such as iron and stainless steel; and fiber-reinforced plastics such as inorganic fiber-reinforced plastics and carbon fiber-reinforced plastics.
The primer layer and adhesive layer may be any layer that is normally used for friction members such as brake shoes.

The friction material of the present embodiment is useful as a friction member such as a disc brake pad or brake lining.
A specific embodiment of a friction member using the friction material of this embodiment will be described with reference to Fig. 1. The friction member is composed of a back plate 1, a friction material (also referred to as an upper layer in Fig. 1) 2, and an underlayer 3, and the friction material (upper layer) 2 is fixed to a surface 11 (here, the upper surface of the back plate 1) on which the friction material of the back plate 1 is arranged, via the underlayer 3. The friction material of the present invention can be used as the "upper layer" or the "underlayer", but is preferably used as the "upper layer". The "upper layer" is a friction material that becomes the friction surface of the friction member, and the "underlayer" is a layer that is interposed between the friction material that becomes the friction surface of the friction member and the back metal, and is intended to improve the shear strength and crack resistance near the adhesive portion between the friction material and the back metal.

The friction material of this embodiment is suitable as a friction material for disc brake pads, brake linings, etc. for automobiles, etc. In addition, the friction material of this embodiment can also be used as a friction material for clutch facings, electromagnetic brakes, holding brakes, etc. by subjecting it to processes such as molding, processing, and attachment into the desired shape.

[Friction material composition]
The friction material composition according to the present embodiment does not contain copper, or if it does contain copper, the copper content is less than 0.5 mass % in terms of elemental copper, and does not substantially contain any substance having a Mohs hardness of more than 6.4. The friction material composition contains wollastonite as mineral fibers.
The types of components contained in the friction material composition of this embodiment and the manufacturing method thereof are the same as those of the friction material of this embodiment, and the preferred embodiments are also the same. The preferred ranges of the contents of the components in the friction material composition are the same as those described for the friction material of this embodiment, but the content standard is "the total amount of the friction material composition."
Furthermore, the present invention also provides a friction material containing the friction material composition of this embodiment. The friction material containing the friction material composition of this embodiment can be produced, for example, by a method of thermocompression molding a preform obtained by preforming the friction material composition of this embodiment, or a method of directly thermocompressing the friction material composition of this embodiment and, if necessary, subjecting it to heat treatment to heat-cure the binder. The specific production method is as described in the above-mentioned method for producing the friction material of this embodiment and in the examples described later.

[vehicle]
The present invention also provides a vehicle equipped with the friction member of the present embodiment. For example, the vehicle may use the friction member of the present invention in a disc brake pad, a brake lining, a clutch facing, an electromagnetic brake, a holding brake, etc. Examples of the vehicle include various automobiles including four-wheeled automobiles and motorcycles, such as large automobiles, medium-sized automobiles, standard automobiles, large special-purpose automobiles, small special-purpose automobiles, large motorcycles, and standard motorcycles.

The friction material and friction material composition of this embodiment will be described in more detail below with reference to examples, but the present invention is not limited to these in any way.

<Examples 1 to 5 and Comparative Examples 1 to 2>
[Making disc brake pads]
The materials were mixed according to the mixing ratios shown in Table 1 to obtain each friction material composition.
Next, this friction material composition was mixed in a Lödige (registered trademark) mixer (manufactured by Matsubo Co., Ltd., product name: Lödige (registered trademark) mixer M20), and this mixture was preformed in a molding press (manufactured by Morita Hydraulics Co., Ltd.). Next, the obtained preform was heated and pressurized together with a backing metal (made of iron) manufactured by Sugawa Kogyo Co., Ltd. using a molding press (manufactured by Morita Hydraulics Co., Ltd.) under conditions of a molding temperature of 145°C, a molding pressure of 30 MPa, and a molding time of 5 minutes. Next, the obtained molded product was heat-treated at 210°C for 4.5 hours, polished using a rotary polisher, and scorched at 500°C to obtain a disc brake pad (friction material thickness: 12 mm, friction material projected area: 61 ^cm2 ).
The details of the various materials used in the examples and comparative examples are as follows: The various materials used in the examples and comparative examples were the same.

[Binding material]
・Phenol resin

[Organic filler]
・Cashew particles ・Rubber component: Rubber powder

[Fiber base material]
(Organic Fiber)
・Aramid fiber (inorganic fiber)
・Glass fiber (average fiber length 3,000 μm, average fiber diameter 13 μm, aspect ratio 230)
Mineral fiber A: fibrous wollastonite (average fiber length 150 μm, average fiber diameter 12 μm, aspect ratio 13)
Mineral fiber B: Rock wool (average fiber length 230 μm, average fiber diameter 5.5 μm, wool-like)
Mineral fiber C: Rock wool (average fiber length 150 μm, average fiber diameter 5.0 μm, cut form)

[Inorganic filler]
・Graphite ・Abrasive A: Magnesium oxide (Mohs hardness 6)
Abrasive B: Aluminum oxide (Mohs hardness 9)
Titanates: Potassium titanate Metal sulfides: Tin sulfide Mica Calcium carbonate Calcium hydroxide Barium sulfate

[Evaluation test]
The disc brake pads obtained in each example were subjected to the following performance evaluation using a brake dynamo tester (manufactured by Shin Nippon Tokki Co., Ltd.).
In the performance evaluation test, a general pin-slide collet type caliper and a ventilated disc rotor (FC250 (gray cast iron)) manufactured by KIRIU CORPORATION were used.

(1. Evaluation of the coefficient of friction (μ))
An effectiveness test based on AK-Master was carried out, and the average coefficient of friction generated when braking with a hydraulic pressure of 20 to 40 bar (2 to 4 MPa) during normal driving (40 km/h) and high-speed driving (120 km/h) was calculated and evaluated according to the following criteria.
A: μ is 0.39 or more (excellent)
B: μ is greater than 0.34 and less than 0.39 (good)
C: μ is 0.34 or less (unsuitable)

(2. Evaluation of the Stability of the Friction Coefficient (μ))
The rate of change in the coefficient of friction during high speed braking relative to the coefficient of friction during normal braking was calculated and judged based on the following criteria.
A: 95% or more and 105% or less (excellent)
B: More than 90% and less than 95%, or more than 105% and less than 110% (good)
C: 90% or less or more than 110% (unsuitable)

In Examples 1 to 5, the friction coefficients during normal braking and high-speed braking were good, and the rate of change in the friction coefficient during high-speed braking relative to the friction coefficient during normal braking was small, and the stability of the friction coefficient was excellent. In other words, in Examples 1 to 5, friction materials having a high friction coefficient and a stable friction coefficient over a wide frequency band from low frequency to high frequency were obtained. In particular, Examples 2 to 5, which contained two other mineral fibers in addition to wollastonite as the fiber base material, showed a superior friction coefficient during high-speed braking and an even more superior stability of the friction coefficient than Example 1, which contained one type of mineral fiber other than wollastonite.
On the other hand, in Comparative Examples 1 and 2 in which the friction material contained an abrasive having a Mohs hardness of more than 6.4, the friction coefficient was insufficient or the stability of the friction coefficient was insufficient.

Compared to conventional products, the friction material, friction material composition, and friction member of the present invention do not use copper, which is likely to pollute the environment, and (1) have a stable friction coefficient over a wide frequency range from low to high frequencies, making them less likely to cause brake squeal and other abnormal noises, and (2) have a high friction coefficient, making them suitable for use in various automobiles and other vehicles.

1 Back plate 11 Surface of the back plate on which the friction material is arranged 12 Other surface of the back plate 2 Friction material (upholstery material)
3 Underlayment

Claims (25)

A friction member having a friction material and a backing metal, the friction material containing at least one selected from the group consisting of an inorganic filler, an organic filler, a fibrous base material, and a binder,
The friction material does not contain copper, or if it contains copper, the copper content is less than 0.5 mass% as copper element, and does not contain any substance having a Mohs hardness of more than 6.4 or the content of such substance is 0.05 mass% or less, and contains wollastonite as a mineral fiber,
The friction member further comprises the friction material containing two or more kinds of mineral fibers other than the wollastonite (provided that the mineral fibers do not include ceramic fibers) . The friction member according to claim 1, wherein the mineral fibers other than wollastonite contain two types of mineral fibers: those with a fiber length of 200 μm or less and those with a fiber length of more than 200 μm. The friction member according to claim 1 or 2, which contains at least rock wool as the mineral fiber other than wollastonite. The friction member according to any one of claims 1 to 3, wherein the wollastonite content in the friction material is 3 to 10 mass % relative to the total amount of the friction material. The friction member according to any one of claims 1 to 4, wherein the total content of mineral fibers in the friction material is 3 to 35 mass% based on the total amount of the friction material. The friction member according to any one of claims 1 to 5, wherein the friction material further contains magnesium oxide. The friction member according to any one of claims 1 to 6, wherein the friction material further contains mica. The friction member according to any one of claims 1 to 7, wherein the friction material further contains organic fibers. The friction member according to any one of claims 1 to 8, wherein the friction material further contains graphite. The friction member according to any one of claims 1 to 9, wherein the friction material further contains a metal sulfide. The friction member according to any one of claims 1 to 10, wherein the friction material further contains calcium hydroxide. A vehicle equipped with the friction member according to any one of claims 1 to 11. A friction material composition comprising at least one material selected from the group consisting of an inorganic filler, an organic filler, a fibrous base material, and a binder, which does not contain copper or, if it contains copper, the copper content is less than 0.5 mass% as elemental copper, and which does not contain a substance having a Mohs hardness of more than 6.4 or the content of such substance is 0.05 mass% or less, and which contains wollastonite as a mineral fiber, and further comprises two or more types of mineral fibers other than the wollastonite (with the proviso that the mineral fibers do not include ceramic fibers) . The friction material composition according to claim 13, wherein the mineral fibers other than wollastonite contain [I] mineral fibers having an average fiber length of more than 200 μm and [II] mineral fibers having an average fiber length of 200 μm or less. The friction material composition according to claim 13 or 14, which contains at least rock wool as the mineral fiber other than wollastonite. The friction material composition according to any one of claims 13 to 15, wherein the wollastonite content is 3 to 10 mass% based on the total amount of the friction material composition. The friction material composition according to any one of claims 13 to 16, wherein the total content of the mineral fibers is 3 to 35 mass% based on the total amount of the friction material composition. The friction material composition according to any one of claims 13 to 17, further comprising magnesium oxide. The friction material composition according to any one of claims 13 to 18, further comprising mica. The friction material composition according to any one of claims 13 to 19, further comprising organic fibers. The friction material composition according to any one of claims 13 to 20, further comprising graphite. The friction material composition according to any one of claims 13 to 21, further comprising a metal sulfide. The friction material composition according to any one of claims 13 to 22, further comprising calcium hydroxide. A friction material containing the friction material composition according to any one of claims 13 to 23. A vehicle equipped with the friction material described in claim 24.

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