Friction

Abstract

In a friction pair that generates braking force through the frictional force between a friction material and a nitrided mating material, the present invention provides a friction pair in which the friction material has a high coefficient of friction. [Solution] In a friction pair that generates braking force by the frictional force generated between a friction material and a nitrided mating material, the composition formula K x Mg 0.4 Ti 1.6 O 4-y A friction pair comprising a friction material composed of a molded body of a friction material composition containing magnesium potassium titanate and a binder, represented by the formula [wherein x is 0.1 ≤ x ≤ 0.6, y = (0.8 - x) / 2], and a mating material having an iron-based substrate and a nitrided layer provided on the iron-based substrate, wherein the nitrided layer is positioned on the friction surface side with the friction material, and the magnesium potassium titanate has a pseudo-tunnel crystal structure.

Description

Technical Field

[0001] The present invention relates to a friction pair that generates braking force by the frictional force generated between a friction material and a mating material.

Background Art

[0002] In vehicles such as automobiles, friction materials such as disc brake pads and brake linings are used for braking. These friction materials obtain braking force by friction with a mating material such as a disc rotor or a brake drum. Therefore, the friction material is required not only to have an appropriate friction coefficient according to the use conditions, but also to have a long life (wear resistance) and low aggressiveness to the mating material.

[0003] In the friction material composition used for forming the friction material, titanates have attracted attention as components that carry a transfer film other than copper and as components that can reduce fine wear dust. Examples of titanates include titanates having a tunnel crystal structure (for example, potassium hexatitanate) and titanates having a layered crystal structure (for example, lithium potassium titanate, magnesium potassium titanate), and they are used alone or in combination according to the application of the friction material. For example, Patent Document 1 proposes a friction material composition containing a titanate and barium sulfate having an average particle diameter of 0.1 μm to 20 μm.

[0004] On the other hand, as the mating material of the friction material, a disc rotor or the like generally made of an iron-based material (cast iron, martensitic stainless steel, etc.) is used. However, an iron-based disc rotor may rust when the vehicle is left outdoors for a long time or when a vehicle damaged by salt damage is driven. As a countermeasure, not only the countermeasure by rust removal on the mating material side by brake braking but also the countermeasure from the friction material side has been studied. For example, Patent Document 2 proposes a method of blending a pH adjuster such as an alkali metal salt or an alkaline earth metal salt into the friction material composition as a method of suppressing rusting by the friction material.

[0005] Furthermore, with the increasing adoption of regenerative braking systems in electric and hybrid vehicles in recent years, the number of braking cycles decreases compared to conventional hydraulic brakes, which can lead to insufficient rust removal. Therefore, methods to suppress rust formation by applying nitriding treatment to the mating material, which is made of iron-based material, are also being considered. For example, Patent Document 3 proposes a method for uniformly and densely forming an iron oxide layer mainly composed of Fe3O4 on the surface of a mating material that has undergone soft nitriding treatment. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 164028 [Patent Document 2] Japanese Patent Publication No. 2017-025286 [Patent Document 3] Japanese Patent Publication No. 2014-118583 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As described in Patent Document 3, when a nitrided mating material is used, rust suppression can be expected. However, when a friction material that was conventionally used in combination with a mating material that has not been nitrided is used in combination with a nitrided mating material, the coefficient of friction may decrease compared to when the mating material has not been nitrided.

[0008] The object of the present invention is to provide a friction pair in which a friction material has a high coefficient of friction, in which a braking force is generated by the frictional force generated between the friction material and the nitrided mating material. [Means for solving the problem]

[0009] The present invention provides the following friction pairs.

[0010] Item 1. A friction pair that generates braking force by the frictional force generated between a friction material and a mating material subjected to nitriding treatment, the friction pair being composed of a molded body of a friction material composition containing potassium magnesium titanate represented by the compositional formula K x Mg 0.4 Ti 1.6 O 4-y 〔where x satisfies 0.1 ≤ x ≤ 0.6, and y = (0.8 - x) / 2〕, and a mating material having an iron-based substrate and a nitriding treatment layer provided on the iron-based substrate, the nitriding treatment layer being disposed on the friction surface side with respect to the friction material, characterized in that the potassium magnesium titanate has a pseudo-tunnel crystal structure.

[0011] Item 2. In the Raman spectrum of the potassium magnesium titanate, the ratio (Ia / Ib) of the peak area (Ia) at 100 cm -1 ~165 cm -1 to the peak area (Ib) at 215 cm -1 ~325 cm -1 is 0.03 or more, and the ratio (Ic / Ib) of the peak area (Ic) at 785 cm -1 ~900 cm -1 to the peak area (Ib) at 215 cm -1 ~325 cm -1 is 0.40 or less. The friction pair according to Item 1.

[0012] Item 3. The friction pair according to Item 1 or Item 2, wherein the iron-based substrate is cast iron.

[0013] Item 4. The friction pair according to any one of Items 1 to 3, wherein the thickness of the nitriding treatment layer is 20 μm to 500 μm.

[0014] Item 5. The friction pair according to any one of Items 1 to 4, wherein the nitriding treatment layer has a nitrogen diffusion layer provided on the iron-based substrate and a nitrogen compound layer provided on the nitrogen diffusion layer.

[0015] Item 6 The friction pair according to item 5, wherein the nitrided layer further comprises an iron oxide layer provided on the nitrogen compound layer.

[0016] Item 7 The friction pair according to any one of items 1 to 6, wherein the magnesium potassium titanate substantially does not contain anatase-type titanium dioxide.

[0017] Item 8 The friction pair according to any one of items 1 to 7, wherein the magnesium potassium titanate is in the form of plate-like particles.

[0018] Item 9 The friction pair according to any one of items 1 to 8, wherein the average particle size of the magnesium potassium titanate is 0.1 μm to 100 μm.

[0019] Item 10 The specific surface area of ​​the magnesium potassium titanate is 0.1 m² 2 / g~10m 2 A friction pair as described in any one of items 1 to 9, where the value is / g.

[0020] Item 11 The friction pair according to any one of items 1 to 10, wherein the alkali metal ion elution rate of magnesium potassium titanate is 0.01% by mass to 15% by mass.

[0021] Item 12 The friction pair according to any one of items 1 to 11, wherein the content of copper components is less than 0.5% by mass as copper element per 100% by mass of the total amount of the friction material composition.

[0022] Item 13 The friction pair according to any one of items 1 to 12, wherein the content of magnesium potassium titanate is 1% to 40% by mass based on 100% by mass of the total amount of the friction material composition. [Effects of the Invention]

[0023] According to the present invention, a friction pair is provided in which a braking force is generated by the frictional force generated between a friction material and a mating material that has undergone nitriding treatment, and in which the friction material has a high coefficient of friction. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a mating material used in the present invention. [Figure 2] Figure 2 shows a scanning transmission electron microscope (STEM) image of magnesium potassium titanate 1 obtained in manufacturing example 2. [Figure 3] Figure 3 shows the Raman spectral spectra of magnesium potassium titanate and potassium hexatinate obtained in Production Example 1 and Production Example 2. [Figure 4] Figure 4 shows a scanning transmission electron microscope (STEM) image of magnesium potassium A titanate obtained in Production Example 1. [Modes for carrying out the invention]

[0025] The following describes an example of a preferred embodiment of the present invention. However, the following embodiments are merely illustrative. The present invention is not limited in any way to the following embodiments. In this specification, "~" is used to mean that the numerical values ​​described before and after it are included as the lower limit and upper limit.

[0026] [friction vs.] The friction pair of the present invention is a friction pair that generates braking force by the frictional force generated between the friction material and the nitrided mating material. In particular, the friction pair of the present invention has compositional formula K x Mg 0.4 Ti 1.6 O 4-y The friction material comprises a molded body of a friction material composition containing magnesium potassium titanate and a binder, represented by the formula [wherein x is 0.1 ≤ x ≤ 0.6, y = (0.8 - x) / 2], and a mating material having an iron-based substrate and a nitrided layer provided on the iron-based substrate, with the nitrided layer positioned on the friction surface side with the friction material, and characterized in that the magnesium potassium titanate has a pseudo-tunnel crystal structure.

[0027] Furthermore, when a nitrided mating material is used, rust formation can be expected to be suppressed. However, when a friction material that was conventionally used in combination with a mating material that had not been nitrided is used in combination with a nitrided mating material, the coefficient of friction sometimes decreases compared to when the mating material has not been nitrided.

[0028] In response to this, the inventors focused on the friction material composition that constitutes the friction material, and in particular found that magnesium potassium titanate contained in the friction material composition has a pseudo-tunnel-shaped crystalline structure, which can suppress the decrease in the coefficient of friction of the friction material in a friction pair where braking force is generated by the frictional force generated between the friction material and the nitrided mating material.

[0029] Therefore, according to the present invention, it is possible to provide a friction pair in which the friction material has a high coefficient of friction while suppressing rust formation.

[0030] Furthermore, since the friction pair of the present invention uses a friction material composed of a molded body of a friction material composition containing magnesium potassium titanate, it is also expected to suppress the generation of fine wear dust such as PM10 and PM2.5 during braking.

[0031] <Friction material> The friction material used in this invention is composed of a molded body of a friction material composition. The friction material composition contains magnesium potassium titanate, a binder, and other materials as needed.

[0032] (1. Magnesium potassium titanate) The magnesium potassium titanate used in this invention has a pseudo-tunnel crystal structure. In this specification, "pseudo-tunnel crystal structure" means that although it is magnesium potassium titanate, its crystal structure does not have a layered crystal structure, but rather a crystal structure that is close to a tunnel crystal structure.

[0033] Furthermore, potassium magnesium titanate, which has a pseudo-tunnel crystal structure, exhibits a Raman spectrum at 100 cm⁻¹. -1~165cm -1 Peak area (Ia) at 215 cm² -1 ~325cm -1 The ratio (Ia / Ib) to the peak area (Ib) at 785 cm² is 0.03 or greater, and the value is 785 cm². -1 ~900cm -1 Peak area (Ic) at 215 cm² -1 ~325cm -1 The ratio (Ic / Ib) to the peak area (Ib) at 0.40 or less.

[0034] Raman spectroscopy is a technique that utilizes the fact that each crystal lattice has its own unique lattice vibration. When laser light of a specific wavelength is shone onto a crystal, light that has lost energy equal to the phonon energy is scattered (this is called Raman scattering). By detecting this scattering with a spectrometer, insights into phonon energy can be obtained.

[0035] Here, composition formula K is known to have a layered crystalline structure. 0.8 Mg 0.4 Ti 1.6 In the Raman spectrum of conventional lepidocrocite-type potassium magnesium titanate, represented as O4, the following value is observed: 835 cm⁻¹ -1 The presence of a peak in the vicinity suggests that this peak originates from a layered crystal structure.

[0036] Furthermore, the composition formula K2Ti6O is known to have a tunnel-like crystal structure. 13 The Raman spectrum of potassium hexatinate, represented by [formula], shows 110 cm⁻¹. -1 Nearby and 140cm -1 Nearby and 860cm -1 The presence of peaks in the vicinity suggests that these peaks originate from the tunnel-like crystal structure of potassium hexatinate.

[0037] In the Raman spectrum of magnesium potassium titanate used in this invention, a peak of 835 cm² is observed, which is thought to originate from the layered crystal structure. -1No peaks were observed in the vicinity, and the peak at 140 cm is thought to originate from a tunnel-like crystal structure. -1 Nearby and 860cm -1 The presence of peaks in the vicinity suggests that the spectrum is close to that of a tunnel-shaped crystal structure. Furthermore, scanning transmission electron microscopy (STEM) images suggest that the magnesium potassium titanate contained in the above friction material composition has a structure close to that of a tunnel-shaped crystal structure.

[0038] Thus, it can be seen that the magnesium potassium titanate used in the present invention, while being magnesium potassium titanate, does not have a layered crystalline structure, but rather a pseudo-tunnel crystalline structure that is close to a tunnel crystalline structure. From these viewpoints, it is clear that the magnesium potassium titanate used in the present invention and conventional magnesium potassium titanate are different inorganic substances.

[0039] The magnesium potassium titanate used in this invention has a pseudo-tunnel crystal structure, and it is believed that when used as a friction modifier in friction materials, it can increase the coefficient of friction of the friction material. Furthermore, the magnesium potassium titanate used in this invention is presumed to be in a more distorted state compared to the tunnel crystal structure of potassium hexatinate. Therefore, when this magnesium potassium titanate is used, it is believed that the crystals will collapse under high load, thereby improving the stability of the coefficient of friction in the friction material.

[0040] The Raman spectrum of magnesium potassium titanate can be obtained, for example, using a Raman spectrometer with an excitation wavelength of 785 nm and a wavenumber of 100 cm⁻¹. -1 ~3200cm -1 Measurements can be taken under conditions of an exposure time of 1 second and 10 scans. Furthermore, the peak area in each wavelength range can be calculated, for example, by removing the background from the Raman spectroscopic spectrum using the asymmetric least squares method (ASLS method) and then performing numerical integration using the Simpson method.

[0041] In the Raman spectroscopy spectrum of magnesium potassium titanate used in the present invention, the ratio (Ia / Ib) is preferably 0.03 or higher, more preferably 0.10 or higher, even more preferably 0.15 or higher, preferably 2.00 or lower, more preferably 1.00 or lower, and even more preferably 0.40 or lower. By setting the ratio (Ia / Ib) within the above range, the coefficient of friction of the friction material can be made larger.

[0042] Furthermore, in the Raman spectroscopy spectrum of magnesium potassium titanate used in the present invention, the ratio (Ic / Ib) is preferably 0.40 or less, more preferably 0.35 or less, even more preferably 0.26 or less, preferably 0.20 or more, and more preferably 0.22 or more. By setting the ratio (Ic / Ib) within the above range, the coefficient of friction of the friction material can be further stabilized.

[0043] The chemical formula of magnesium potassium titanate used in this invention is K x Mg 0.4 Ti 1.6 O 4-y [In the formula, x is 0.1 ≤ x ≤ 0.6, and y = (0.8 - x) / 2]. In particular, in magnesium potassium titanate, from the viewpoint of making it easier to form a pseudo-tunnel-like crystal structure, x is preferably 0.2 or more, more preferably 0.25 or more, preferably 0.5 or less, and more preferably 0.35 or less.

[0044] In the magnesium potassium titanate used in the present invention, from the viewpoint of further improving the stability of the coefficient of friction when used as a friction material, the content of anatase-type titanium dioxide is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably substantially free of anatase-type titanium dioxide. In this specification, "substantially free of anatase-type titanium dioxide" means that the content of anatase-type titanium dioxide is less than 1.0% by mass, which is the detection limit of the XRD method described later. Furthermore, the magnesium potassium titanate used in the present invention may, of course, have an anatase-type titanium dioxide content of 0% by mass.

[0045] The crystallite size of magnesium potassium titanate used in this invention is preferably 20 Å to 200 Å, more preferably 30 Å to 150 Å, and even more preferably 35 Å to 100 Å. When the crystallite size of magnesium potassium titanate is within the above range, the friction coefficient can be stabilized more efficiently when used as a friction material. The crystallite size can be determined by the Halder-Wagner method using an X-ray diffraction analyzer.

[0046] The average particle size of magnesium potassium titanate used in this invention is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm, and even more preferably 3 μm to 30 μm. When the average particle size of magnesium potassium titanate is within the above range, the frictional properties when used as a friction material can be further improved. In this specification, "average particle size" refers to the particle size D at 50% volume-based cumulative particle size distribution measured by laser diffraction. 50 This refers to the particle size D at 50% cumulative volume. 50 This is the particle diameter at the point where the cumulative value reaches 50%, obtained by counting the number of particles from smallest to largest on a cumulative curve where the total volume is set to 100% after determining the particle size distribution based on volume.

[0047] The specific surface area of ​​the magnesium potassium titanate used in this invention is preferably 0.1 m². 2 / g~10m 2 / g, more preferably 0.3m 2 / g~6m 2 / g, more preferably 0.4m 2 / g~5m 2 The value is / g. When the specific surface area of ​​magnesium potassium titanate falls within the above range, the frictional properties when used as a friction material can be further improved. The specific surface area can be measured in accordance with JIS Z8830.

[0048] The alkali metal ion elution rate of magnesium potassium titanate used in the present invention is preferably 0.01% to 15% by mass, more preferably 0.05% to 6% by mass, and even more preferably 0.1% to 3% by mass. In this specification, "alkali metal ion elution rate" refers to the mass percentage of alkali metal ions eluted into water from a measurement sample such as magnesium potassium titanate in water at 80°C.

[0049] Incidentally, friction material compositions generally use binders, and in the curing reaction of a novolac-type phenolic resin, for example, hexamethylenetetramine, used as a curing accelerator, opens its ring and bonds with the hydroxyl groups in the novolac-type phenolic resin, initiating the curing reaction. However, if alkali metal ions are present at this time, these alkali metal ions and the hydrogen ions in the hydroxyl groups of the novolac-type phenolic resin undergo an ion exchange reaction, which can inhibit the bonding (curing inhibition) between hexamethylenetetramine (curing accelerator) and the novolac-type phenolic resin (thermosetting resin).

[0050] On the other hand, if the friction material composition constituting the friction material contains magnesium potassium titanate, it is thought that alkaline components derived from magnesium potassium titanate will leach out to the friction surface due to the wear and failure of the friction material caused by braking. Therefore, by keeping the alkali metal ion leaching rate of magnesium potassium titanate below the above upper limit, it is possible to prevent inhibition of curing of the thermosetting resin during heat and pressure molding, and as a result, the crack resistance of the friction material under high temperature and high load conditions can be further improved. Furthermore, by keeping the alkali metal ion leaching rate of magnesium potassium titanate above the above lower limit, rust formation of the rotor when the friction material is left unused for a long period of time after braking can be more reliably suppressed. In other words, by keeping the alkali metal ion leaching rate of magnesium potassium titanate within the above range, it is possible to achieve an even higher level of balance between the crack resistance of the friction material and the suppression of rotor rust formation.

[0051] The magnesium potassium titanate used in this invention is preferably non-fibrous particles from the viewpoint of the working environment. Non-fibrous particles include, for example, spherical particles (including those with slight irregularities on the surface or those with an elliptical cross-section or other shapes that are roughly spherical), columnar particles (including those with an overall roughly columnar shape such as rod-shaped, cylindrical, prismatic, rectangular, rectangular, roughly cylindrical, and roughly rectangular shapes), plate-shaped, block-shaped, shapes with multiple protrusions (amoeba-shaped, boomerang-shaped, cross-shaped, konpeito-shaped, etc.), and irregular shapes, and these can be used in combination. Among these, magnesium potassium titanate is preferably plate-shaped particles. Furthermore, magnesium potassium titanate may also be porous particles. These various particle shapes can be arbitrarily controlled by manufacturing conditions, and in particular by raw material composition and firing conditions. Furthermore, the particle shape can be analyzed, for example, by scanning electron microscopy (SEM) observation.

[0052] In this specification, "non-fibrous particles" refer to particles in which the longest side of the smallest rectangular parallelepiped (circumscribed rectangular parallelepiped) circumscribing the particle is the major axis L, the next longest side is the minor axis B, and the shortest side is the thickness T (B > T), and L / B is 5 or less. Furthermore, "having multiple protrusions" refers to a shape whose projected shape onto a plane differs from at least ordinary polygons, circles, ellipses, etc., and can have protrusions in two or more directions. Specifically, these protrusions refer to parts that protrude when a polygon, circle, ellipse, etc. (basic shape) is superimposed onto a photograph (projection image) taken with a scanning electron microscope (SEM).

[0053] In the present invention, from the viewpoint of further improving adhesion with the binder used in the friction material composition, a treatment layer consisting of a surface treatment agent may be formed on the surface of magnesium potassium titanate. Known surface treatment agents such as silane coupling agents and titanium coupling agents can be used as the surface treatment agent. Among these, silane coupling agents are preferably used as the surface treatment agent, and amino-based silane coupling agents, epoxy-based silane coupling agents, and alkyl-based silane coupling agents are more preferably used. The above surface treatment agents may be used individually or in mixtures of two or more types.

[0054] As a method for forming a treatment layer consisting of a surface treatment agent on the surface of magnesium potassium titanate, known surface treatment methods can be used. For example, a wet method can be used in which the surface treatment agent is dissolved in a solvent that promotes hydrolysis (e.g., water, alcohol, or a mixture thereof) to make a solution, and this solution is sprayed onto the magnesium potassium titanate.

[0055] The amount of surface treatment agent used when treating the surface of magnesium potassium titanate is not particularly limited, but in the case of a wet method, for example, a solution of the surface treatment agent can be sprayed so that the content of the surface treatment agent is 0.1 to 20 parts by mass per 100 parts by mass of magnesium potassium titanate.

[0056] As magnesium potassium titanate, it is also possible to use magnesium potassium titanate that has been treated with the above-mentioned surface treatment agent or the binder described later to form granules. The average particle size of the granular magnesium potassium titanate is preferably 100 μm to 200 μm.

[0057] The magnesium potassium titanate content used in this invention is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of the total amount of the friction material composition. By setting the magnesium potassium titanate content within the above range, even better frictional properties can be obtained when used as a friction material.

[0058] The method for producing magnesium potassium titanate used in the present invention is not particularly limited, but for example, it can be produced by the following method.

[0059] First, the raw material, magnesium potassium titanate (hereinafter sometimes referred to as "raw material KTMO"), is prepared. Next, the raw material KTMO is mixed with an acid (acid treatment), and the compound obtained by the acid treatment is calcined to produce the product.

[0060] As for the raw material KTMO, K 0.8 Mg 0.4 Ti 1.6 O4, K 0.7 Mg 0.4 Ti 1.6 O 3.95 It is preferable to use magnesium potassium titanate with a layered crystalline structure. By forming a pseudo-tunnel-shaped crystalline structure using a layered crystalline structure as a raw material, excellent frictional properties can be obtained when used as a friction material. Furthermore, this can suppress the formation of WHO fibers.

[0061] The raw material KTMO can be obtained, for example, by calcining a mixture of titanium dioxide or compounds that produce titanium dioxide upon heating (collectively referred to as "titanium compounds"), potassium oxide or compounds that produce potassium oxide upon heating (collectively referred to as "potassium compounds"), and magnesium oxide or compounds that produce magnesium oxide upon heating (collectively referred to as "magnesium compounds").

[0062] In conventional methods for producing magnesium potassium titanate, potassium chloride, potassium fluoride, potassium molybdate, potassium tungstate, etc., are used as fluxes to facilitate the specification of crystal orientation, as crystals are formed at temperatures below the melting point and the crystals grow with a shape surrounded by flat crystal faces that reflect the crystal structure.

[0063] In the production of the raw material KTMO used in the present invention, suppressing the crystal growth of the raw material KTMO makes it easier to form a pseudo-tunnel-shaped crystal structure in subsequent processes. Therefore, from this viewpoint, the amount of flux used is preferably less than 10 parts by mass, and more preferably 0 parts by mass, per 100 parts by mass of the total amount of titanium compound, potassium compound, and magnesium compound. Furthermore, from the viewpoint of eluting potassium from the intercrystalline layers of the layered crystal structure of the raw material KTMO and facilitating the formation of the desired composition and pseudo-tunnel-shaped crystal structure, it is preferable to control the amount of chloride ions on the particle surface or within the crystals of the raw material KTMO to below a certain level. Specifically, the chloride ion elution rate of the raw material KTMO is preferably 400 ppm or less, and more preferably 200 ppm or less.

[0064] In this specification, "chloride ion elution rate" refers to the mass percentage of chloride ions eluted into water from a measurement sample such as titanate or titanium compound in water at 25°C.

[0065] As the titanium compound, lower titanium dioxide, hydrated titanium dioxide, titanium dioxide hydrate, titanium hydroxide, etc., can be used. Among these, titanium dioxide is preferred as the titanium compound. The crystalline system of the titanium dioxide is preferably rutile or anatase. One type of titanium compound may be used alone, or two or more types may be used in combination. From the viewpoint of further reducing the chloride ion elution rate of the raw material KTMO, the chloride ion elution rate of the titanium compound is preferably 100 ppm or less, and more preferably 50 ppm or less.

[0066] Examples of potassium compounds include potassium oxide, potassium carbonate, potassium hydroxide, and potassium nitrate. Among these, potassium carbonate or potassium hydroxide are preferred. The potassium compound may be used individually or in combination of two or more.

[0067] Examples of magnesium compounds include magnesium oxide, magnesium hydroxide, magnesium carbonate, and magnesium fluoride. Among these, magnesium hydroxide is preferred as the magnesium compound. The magnesium compound may be used individually or in combination of two or more.

[0068] The mixing ratio of titanium compounds, potassium compounds, and magnesium compounds can be appropriately adjusted according to the composition formula of the target raw material KTMO. For example, if K is used as the raw material KTMO... 0.8 Mg 0.4 Ti 1.6 When producing O4, the molar ratio of Ti:K:Mg should be 1.6:0.8:0.4.

[0069] The calcination process for the raw material KTMO can be carried out using an electric furnace or the like. Furthermore, the calcination reaction can be completed by maintaining a temperature range of 800°C to 1100°C for 1 to 24 hours. After calcination, the resulting powder may be crushed to the desired size or sieved to loosen it.

[0070] The acid used in the acid treatment is not particularly limited, and any known acid can be used. Examples of acids used in the acid treatment include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, or organic acids such as acetic acid. Two or more acids may be used in combination as needed.

[0071] Furthermore, the acid treatment can be carried out by mixing acid with an aqueous slurry of the raw material KTMO. The concentration of the aqueous slurry is not particularly limited and can be appropriately selected from a wide range. Considering workability, the concentration of the aqueous slurry should be about 1% to 30% by mass. In addition, since a pseudo-tunnel-shaped crystalline structure is formed by firing in a crystalline state in which some potassium is missing due to the acid treatment, the amount of acid mixed with the aqueous slurry is preferably 0.10 to 0.40 equivalents, and more preferably 0.20 to 0.30 equivalents, relative to the intercalation elements of the raw material KTMO. After the acid treatment, the solids are separated from the aqueous slurry by filtration, centrifugation, etc. The separated solids can be washed with water and dried as needed.

[0072] The firing can be carried out using an electric furnace or the like. Furthermore, from the viewpoint of suppressing crystallization transitions to anatase-type titanium dioxide or other crystal structures while forming a pseudo-tunnel-shaped crystalline structure, the firing temperature is preferably in the range of 350°C to 600°C, more preferably 400°C to 550°C, and it is desirable to hold the temperature in that range for preferably 0.5 hours to 12 hours, more preferably 0.5 hours to 10 hours, and even more preferably 0.5 hours to 5 hours. After firing, the obtained powder may be crushed to a desired size or loosened by passing it through a sieve. In this way, magnesium potassium titanate used in the present invention can be obtained.

[0073] Furthermore, in the method for producing magnesium potassium titanate used in the present invention, as described above, by reducing the amount of flux used during the production of the raw material KTMO, lowering the chloride ion elution rate of the raw material KTMO, and applying thermal energy to unstable crystals in which some of the potassium in the raw material KTMO is missing through calcination, it is possible to easily form a pseudo-tunnel crystal structure in the obtained magnesium potassium titanate, and to adjust the above ratio (Ia / Ib) and above ratio (Ic / Ib) to the desired range.

[0074] (2.Binding material) The binder used in the present invention is not particularly limited, and thermosetting resins and the like, which are commonly used as binders for friction materials, can be used.

[0075] Examples of thermosetting resins include phenolic resins; elastomer-dispersed phenolic resins such as acrylic elastomer-dispersed phenolic resins and silicone elastomer-dispersed phenolic resins; modified phenolic resins such as acrylic-modified phenolic resins, silicone-modified phenolic resins, cashew-modified phenolic resins, epoxy-modified phenolic resins, and alkylbenzene-modified phenolic resins; formaldehyde resins; melamine resins; epoxy resins; acrylic resins; aromatic polyester resins; and urea resins. Thermosetting resins may be used individually or in combination of two or more. Among these, from the viewpoint of further improving heat resistance, moldability, and frictional properties when used as a friction material, phenolic resins (straight phenolic resins) or modified phenolic resins are preferred as thermosetting resins. As phenolic resins, either resol-type phenolic resins or novolac-type phenolic resins can be used, but novolac-type phenolic resins are preferred from the viewpoint of manufacturing stability and cost. Furthermore, novolac-type phenolic resins may contain additives such as curing agents and curing accelerators (e.g., hexamethylenetetramine) as needed.

[0076] The binder content is preferably 5% to 30% by mass, more preferably 8% to 20% by mass, based on 100% by mass of the total amount of the friction material composition. By setting the binder content within the above range, an appropriate amount of binder is filled into the gaps between the compound materials, resulting in even better frictional properties when used as a friction material.

[0077] (3. Other materials) The friction material composition used in the present invention may, in addition to the magnesium potassium titanate and binder described above, optionally contain other materials commonly used in friction material compositions. These other materials may include steel fibers, fiber base materials, organic friction modifiers, inorganic friction modifiers, lubricants, pH adjusters, or fillers.

[0078] The content of other materials in the friction material composition is preferably 30% to 94% by mass, and more preferably 45% to 87% by mass, based on 100% by mass of the total amount of the friction material composition.

[0079] (3-1. Steel-based fibers) As the steel fibers, steel fibers commonly used in friction material compositions can be used. More specifically, examples of steel fibers include steel fibers, stainless steel fibers, etc., and steel fibers are preferably used.

[0080] Examples of steel fibers include straight fibers obtained by methods such as chatter vibration cutting, and curled fibers obtained by cutting long fibers. Straight fibers have a linear fiber shape. On the other hand, curled fibers have a curved shape and include simple arc-shaped fibers, wavy fibers, spiral-shaped fibers, or spiral-shaped fibers.

[0081] In particular, among the steel fibers, curled fibers are preferred from the viewpoint of minimizing shedding from the friction material on the friction surface and more reliably maintaining the frictional properties of the friction material during high-temperature braking. Furthermore, it is even more preferable that the curled fibers include portions with a radius of curvature of 100 μm or less. In this case, adhesion to the friction material becomes stronger, and shedding of the friction material on the friction surface is further reduced.

[0082] The average fiber length of the steel fibers is preferably 5 mm or less, more preferably 2.5 mm or less, from the viewpoint of further improving the wear resistance of the friction material at high temperatures. Furthermore, the average fiber length of the steel fibers is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.1 mm or more, from the viewpoint of further improving the reinforcing properties of the steel fibers.

[0083] The average fiber diameter of the steel fibers is preferably 300 μm or less, more preferably 100 μm or less, from the viewpoint of further suppressing brake vibration at high temperatures when used as a friction material. Furthermore, the average fiber diameter of the steel fibers is preferably 10 μm or more, more preferably 30 μm or more, from the viewpoint of further preventing the shedding of steel fibers.

[0084] The average fiber length and average fiber diameter of steel fibers can be confirmed using a microscope. For example, the average values ​​of the average fiber length and average fiber diameter of 30 steel fibers observed with a microscope can be used.

[0085] When using NAO material in which the steel fiber content is less than 10% by mass (preferably 0% by mass) of the total amount of the friction material composition, the coefficient of friction in the high-load region can be increased, and the stability of the coefficient of friction can also be further improved.

[0086] In the case of low-steel materials where the steel fiber content is 10% to 30% by mass relative to 100% by mass of the total amount of the friction material composition, the coefficient of friction in the high-load range can be increased when used as a friction material.

[0087] (3-2. Fiber base material) Examples of fiber base materials include inorganic fibers, metal fibers, organic fibers, or carbon-based fibers commonly used in friction material compositions. The fiber base material may be used individually or in combination of two or more types.

[0088] When the friction material composition contains a fibrous base material, the content of the fibrous base material is not particularly limited, but is preferably 0.1% to 40% by mass, more preferably 0.1% to 20% by mass, and even more preferably 0.1% to 10% by mass, based on 100% by mass of the total amount of the friction material composition.

[0089] Examples of inorganic fibers include glass fibers, rock wool, ceramic fibers, biodegradable ceramic fibers, biodegradable mineral fibers, biosoluble fibers (SiO2-CaO-SrO-based fibers, etc.), wollastonite fibers, silicate fibers, and mineral fibers. Rock wool is preferred as the inorganic fiber.

[0090] When the friction material composition contains rock wool, the rock wool content is preferably 1% to 10% by mass, more preferably 1% to 7% by mass, based on 100% by mass of the total amount of the friction material composition. When the rock wool content is within the above range, the coefficient of friction during high-load braking can be increased when used as a friction material.

[0091] Examples of metal fibers include straight or curled metal fibers whose main component is metal, such as aluminum, iron, zinc, tin, titanium, nickel, magnesium, silicon, and other metals in elemental or alloy form (excluding steel fibers).

[0092] Examples of organic fibers include aromatic polyamide (aramid) fibers, fibrillated aramid fibers (also called aramid pulp), acrylic fibers (fibers of monopolymers or copolymers mainly composed of acrylonitrile), fibrillated acrylic fibers, cellulose fibers, fibrillated cellulose fibers, and phenolic resin fibers.

[0093] As for the organic fibers, aramid fibers or fibrillated aramid fibers are preferred. In this case, the friction material is given appropriate water absorption, making it easier for moisture from the atmosphere to be absorbed into the friction material, and the alkaline component of magnesium potassium titanate is more easily leached out, thus providing a rust-preventive effect on the rotor and steel fibers.

[0094] As for the organic fiber, from the viewpoint of further improving heat resistance, para-aramid fibers, such as poly-p-phenylene terephthalamide, are preferred. Furthermore, as for the organic fiber, fibrillated aramid fibers are preferred from the viewpoint of further improving the moldability of the friction material and further improving the retention of fillers. The specific surface area of ​​the fibrillated aramid fiber is preferably 5 m². 2 / g~25m 2 / g, comfortably 5m 2 / g~15m 2 The value is / g. The fiber length of the fibrillated aramid fiber is preferably 0.5 mm to 1.2 mm.

[0095] When the friction material composition contains fibrillated aramid fibers, the content of fibrillated aramid fibers is preferably 1% to 10% by mass, more preferably 1% to 8% by mass, and even more preferably 1% to 6% by mass, based on 100% by mass of the total amount of the friction material composition. When the content of fibrillated aramid fibers is above the lower limit, the crack resistance and wear resistance of the friction material can be further improved. Furthermore, when the content of fibrillated aramid fibers is below the upper limit, deterioration of the crack resistance and wear resistance of the friction material due to uneven distribution of fibrillated aramid fibers and other materials can be more reliably prevented.

[0096] Examples of carbon-based fibers include flame-resistant fibers, PAN-based carbon fibers, pitch-based carbon fibers, and activated carbon fibers.

[0097] (3-3.Organic friction modifier) Organic friction modifiers are friction modifiers that are compounded to further improve the sound and vibration performance and wear resistance of friction materials. Examples of organic friction modifiers include unvulcanized or vulcanized rubber powders such as tire rubber, acrylic rubber, isoprene rubber, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), chlorinated butyl rubber, butyl rubber, and silicone rubber; cashew dust; rubber-coated cashew dust; and melamine dust. Organic friction modifiers may be used individually or in combination of two or more types.

[0098] When the friction material composition contains an organic friction modifier, the content of the organic friction modifier is preferably 0.1% to 30% by mass, more preferably 0.1% to 20% by mass, and even more preferably 0.1% to 10% by mass, based on 100% by mass of the total amount of the friction material composition.

[0099] (3-4.Inorganic friction modifier) Inorganic friction modifiers (excluding magnesium potassium titanate mentioned above) are friction modifiers that are added to friction materials to prevent deterioration of heat resistance or to improve wear resistance and further increase the coefficient of friction. Examples of inorganic friction modifiers include abrasives, metal powders, and other inorganic fillers. Inorganic friction modifiers may be used individually or in combination of two or more types.

[0100] The abrasive material can be appropriately selected based on the material of the mating material, such that it acts as an abrasive and improves the coefficient of friction, and can be selected based on the Mohs hardness of the mating material. From the viewpoint of more effectively exhibiting the coefficient of friction by the abrasive material, the Mohs hardness of the abrasive material is preferably 6 to 9, more preferably 6 to 8.

[0101] Examples of abrasive materials include silicon carbide, titanium dioxide, α-alumina, γ-alumina, silica, magnesia, zirconia (zirconium oxide), zircon (zirconium silicate), chromium oxide, iron oxide (triiron tetroxide, etc.), chromite, quartz, and iron sulfide. Among these, the abrasive material is preferably zirconia (zirconium oxide) or zircon (zirconium silicate). The average particle size of zirconia (zirconium oxide) is preferably 1 μm to 14 μm. The average particle size of zircon (zirconium silicate) is preferably 0.2 μm to 2 μm.

[0102] Furthermore, in the case of abrasive materials, abrasive materials with a large average particle size and abrasive materials with a small average particle size may be used in combination. Specifically, abrasive materials with an average particle size of 0.5 μm to 15 μm may be used in combination with abrasive materials with an average particle size of 20 μm to 200 μm. In addition, the mass ratio of abrasive materials with a small average particle size to abrasive materials with a large average particle size (abrasive material with a small average particle size / abrasive material with a large average particle size) is preferably 0.1 to 10, more preferably 2 to 8, from the viewpoint of further reducing wear dust when used as a friction material. In this case, in the friction material, the coefficient of friction can be increased during high-load braking while further improving the stability of the coefficient of friction during light-load braking.

[0103] If the friction material composition contains an abrasive, the abrasive content is preferably 0.1% to 30% by mass, more preferably 5% to 25% by mass, and even more preferably 5% to 18% by mass, based on 100% by mass of the total amount of the friction material composition.

[0104] Examples of metal powders include powders of individual metals or alloys such as aluminum, zinc, iron, and tin.

[0105] Other inorganic fillers include vermiculite, clay, mica, talc, dolomite, chromite, mullite, calcium silicate, and titanates other than magnesium potassium titanate (hereinafter referred to as "other titanates").

[0106] Other titanates that can be used include potassium hexatinate such as TERRACESS JSL, TERRACESS JSL-R, TERRACESS DP-R, TERRACESS DP-A, TERRACESS DP-AS from Otsuka Chemical Co., Ltd., TXAX-MA, TXAX-A from Kubota Corporation, and TOFIX-S, TOFIX-SNR from Toho Titanium Co., Ltd.; sodium hexatinate such as TERRACESS DSR from Otsuka Chemical Co., Ltd.; potassium octatinate such as TERRACESS TF-SS, TERRACESS TF-S, TERRACESS TF-L, TERRACESS JP from Otsuka Chemical Co., Ltd.; magnesium potassium titanate such as TERRACESS PM, TERRACESS PS from Otsuka Chemical Co., Ltd.; and lithium potassium titanate such as TERRACESS L, TERRACESS L-SS, TERRACESS JSM-M from Otsuka Chemical Co., Ltd. Other titanates that can be used are preferably sodium hexatinate and potassium octatinate with a tunnel-like crystalline structure; and magnesium potassium titanate and lithium potassium titanate with a layered crystalline structure, and more preferably magnesium potassium titanate with a layered crystalline structure. In addition, other titanates, such as those with a tunnel-shaped crystal structure or a layered crystal structure, may be used individually, or both may be used in combination.

[0107] When the friction material composition contains other titanates, the mass ratio of the other titanates to the above-mentioned magnesium potassium titanate (other titanates / above-mentioned magnesium potassium titanate) is preferably 0.1 to 3, more preferably 0.1 to 0.8, from the viewpoint of increasing the coefficient of friction in the high-load region when used as a friction material.

[0108] (3-5. Lubricants) As a lubricant, a solid lubricant is preferable. Examples of lubricants include carbon-based solid lubricants, sulfide-based solid lubricants, and polytetrafluoroethylene (PTFE). The lubricant may be used alone or in combination of two or more types. The solid lubricant is preferably at least one of carbon-based solid lubricants and sulfide-based solid lubricants. From the viewpoint of further reducing harmful effects on the human body, the solid lubricant is more preferably a carbon-based solid lubricant.

[0109] If the friction material composition contains a lubricant, the lubricant content is preferably 0.1% to 20% by mass, more preferably 1% to 10% by mass, and even more preferably 1% to 5% by mass, based on 100% by mass of the total amount of the friction material composition.

[0110] Examples of carbon-based solid lubricants include synthetic or natural graphite, flake graphite, phosphate-coated graphite, carbon black, petroleum coke, coal coke, activated carbon, and elastographitized carbon. From the viewpoint of more reliably imparting thermal conductivity to the friction material, synthetic graphite or natural graphite is preferred as the carbon-based solid lubricant.

[0111] When the friction material composition contains a carbon-based solid lubricant, the content of the carbon-based solid lubricant is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably 8% by mass or less, based on 100% by mass of the total amount of the friction material composition. When the content of the carbon-based solid lubricant is above the lower limit, wear of the friction material at high temperatures can be further reduced when used as a friction material. Also, when the content of the carbon-based solid lubricant is below or below the upper limit, the decrease in the friction coefficient of the friction material can be further suppressed.

[0112] The average particle size of the carbon-based solid lubricant is not particularly limited, but is preferably 10 μm to 1000 μm. One type of carbon-based solid lubricant may be used alone, or two or more types of carbon-based solid lubricants having different average particle sizes may be used in combination. When the average particle size of the carbon-based solid lubricant is above the lower limit, it is possible to suppress an excessive increase in thermal conductivity when used as a friction material, and the occurrence of vapor lock due to heat transfer from friction to the backplate side can be further suppressed. Furthermore, when the average particle size of the carbon-based solid lubricant is below the upper limit, the thermal conductivity of the friction material is improved, the hardening of the binder during friction material molding is promoted, and the strength of the friction material can be further improved.

[0113] Examples of sulfide-based solid lubricants include antimony trisulfide, molybdenum disulfide, tin sulfide, iron sulfide, zinc sulfide, bismuth sulfide, and tungsten disulfide. From the viewpoint of further reducing the harmful effects of sulfide-based solid lubricants on the human body, tin sulfide or molybdenum disulfide are preferred as the sulfide-based solid lubricant.

[0114] When the friction material composition contains a sulfide-based solid lubricant, the content of the sulfide-based solid lubricant is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, preferably less than 15% by mass, more preferably less than 10% by mass, and even more preferably 8% by mass or less, based on 100% by mass of the total amount of the friction material composition. When the content of the sulfide-based solid lubricant is above the lower limit, rotor wear can be further suppressed when used as a friction material. Also, when the content of the sulfide-based solid lubricant is below or below the upper limit, the decrease in the friction coefficient of the friction material can be further suppressed.

[0115] However, it is preferable that the friction material composition substantially does not contain sulfide-based solid lubricants such as metal sulfides. "Substantially free of sulfide-based solid lubricants" means that sulfide-based solid lubricants are not intentionally blended into the friction material composition, and that the friction material composition does not contain sulfide-based solid lubricants except in cases where trace amounts of sulfide-based solid lubricants are mixed in as impurities. In particular, it is preferable that the content of sulfide-based solid lubricants is less than 0.1% by mass per 100% by mass of the total amount of the friction material composition, and it is even more preferable that the friction material composition does not contain sulfide-based solid lubricants at all. When sulfide-based solid lubricants are substantially absent, the harmful effects on the human body can be further reduced.

[0116] In friction material compositions, it is preferable that the copper content is less than 0.5% by mass as copper element relative to 100% by mass of the total amount of the friction material composition, and it is more preferable that the friction material composition does not contain any copper component. In this case, the environmental burden can be reduced compared to conventional friction material compositions. In this specification, "does not contain copper component" means that copper fibers, copper powder, copper-containing alloys (brass, bronze, etc.), and compounds are not blended as raw materials for the friction material composition.

[0117] In particular, in the friction material composition, it is preferable that the copper component content is less than 0.5% by mass as copper element relative to 100% by mass of the total amount of the friction material composition, and that it substantially does not contain sulfide-based solid lubricants.

[0118] (3-6.pH adjustment material) Examples of pH adjusting agents include inorganic bases such as calcium hydroxide (slaked lime), sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and dipotassium hydrogen phosphate, as well as organic bases such as imidazole, histidine, and hexamethylenediamine. From the viewpoint of reducing costs and further enhancing hygroscopicity, inorganic bases are preferred as pH adjusting agents. One type of pH adjusting agent may be used alone, or two or more types may be used in combination. pH adjusting agents are also sometimes used to prevent rust adhesion between the friction material and the mating material (rotor).

[0119] When the friction material composition contains a pH adjusting agent, the content of the pH adjusting agent is preferably 0.1% to 8% by mass, relative to 100% by mass of the total amount of the friction material composition.

[0120] (3-7. Filler) Examples of fillers include barium sulfate and calcium carbonate. Barium sulfate is preferably used as the filler. The filler may be used individually or in combination of two or more types.

[0121] Barium sulfate can be obtained as elutriated barium sulfate (barite powder), which is produced by crushing a mineral called barite, washing it to remove iron, and elutriating it, or as precipitated barium sulfate, which is artificially synthesized. With precipitated barium sulfate, the particle size can be controlled by the conditions during synthesis, making it possible to produce fine barium sulfate with a low content of coarse particles. From the viewpoint of further reducing impurities and making the particle size distribution of barium sulfate particles more uniform, it is preferable to use precipitated barium sulfate.

[0122] (4. Method for manufacturing friction material composition) The friction material composition used in the present invention can be manufactured by (1) mixing each component in a mixer such as a Redigge mixer ("Redigge" is a registered trademark), a pressure kneader, or an Eich mixer ("Eich" is a registered trademark); or by (2) preparing granules of the desired components and mixing other components as necessary using a mixer such as a Redigge mixer, a pressure kneader, or an Eich mixer.

[0123] The content of each component in the friction material composition used in the present invention can be appropriately set according to the desired friction characteristics. Alternatively, the friction material composition may be prepared by creating a masterbatch containing specific components at a high concentration, and then adding and mixing a thermosetting resin or the like to this masterbatch.

[0124] (5.Friction material) The friction material used in the present invention is a molded body of the above-mentioned friction material composition. In the present invention, the friction material composition is pre-molded at room temperature (20°C), the resulting pre-molded body is heated and pressurized, the resulting molded body is heat-treated in a heating furnace as needed, and then the molded body is machined or polished to produce a friction material having a predetermined shape. The molding pressure during heating and pressurizing can be, for example, 10 MPa to 40 MPa. The molding temperature during heating and pressurizing can be, for example, 150°C to 200°C. The heat treatment temperature can be, for example, 150°C to 220°C. The holding time during heat treatment can be, for example, 1 hour to 12 hours.

[0125] The friction material used in the present invention includes not only a configuration consisting solely of the friction material, but also configurations such as one having a base material such as a backing plate and a friction material provided on the base material to provide a friction surface.

[0126] The base material is used to further improve the mechanical strength of the friction material. Examples of base material materials include metals such as iron and stainless steel, and fiber-reinforced resins such as glass fiber reinforced resin and carbon fiber reinforced resin.

[0127] Furthermore, friction materials typically have numerous fine pores formed inside. These pores serve as escape routes for decomposition products (gases and liquids) at high temperatures, preventing a decrease in frictional properties. They also reduce the rigidity of the friction material, improving damping and thus preventing squeaking. In friction materials, the material composition and molding conditions are usually determined so that the porosity of the friction material is preferably 5% to 30%, more preferably 10% to 25%.

[0128] <Opponent material> The mating material used in this invention is made of an iron-based material. Specifically, the mating material has an iron-based substrate and a nitrided layer provided on the iron-based substrate. Because the mating material has a hard nitrided layer on the iron-based substrate, when used as a friction pair, not only is corrosion resistance (rust suppression) improved, but wear resistance can also be improved.

[0129] Figure 1 is a schematic cross-sectional view showing an example of a mating material used in the present invention.

[0130] As shown in Figure 1, the mating material 10 comprises an iron-based substrate 20 and a nitrided layer 30. The nitrided layer 30 is provided on the main surface 20a of the iron-based substrate 20.

[0131] In this embodiment, the nitrided layer 30 has a nitrogen diffusion layer 40, a nitrogen compound layer 50, and an iron oxide layer 60. The nitrogen diffusion layer 40 is provided on the main surface 20a of the iron-based substrate 20. The nitrogen compound layer 50 is provided on the nitrogen diffusion layer 40. Furthermore, the iron oxide layer 60 is provided on the nitrogen compound layer 50.

[0132] Examples of iron-based substrates 20 include iron (pure iron), cast iron, stainless steel, or carbon steel. Among these, cast iron is preferred for the iron-based substrate 20.

[0133] If the iron-based base material 20 is cast iron, for example, a cast material formed by a casting method such as sand casting can be used. As such an iron-based base material 20, for example, gray cast iron or ductile cast iron such as FC200, FC250, or FCD450 can be used.

[0134] If the iron-based substrate 20 is stainless steel, for example, austenitic, austenitic-ferritic, ferritic, martensitic, etc., can be used.

[0135] The nitrogen diffusion layer 40 is a layer formed by the supersaturation of nitrogen in solid solution during the nitriding treatment described later. The thickness of the nitrogen diffusion layer 40 is preferably 15 μm to 450 μm, more preferably 50 μm to 300 μm.

[0136] The nitrogen compound layer 50 is a layer formed on the nitrogen diffusion layer 40. The nitrogen compound layer 50 can be made of, for example, Fe3N. The thickness of the nitrogen compound layer 50 is preferably 3 μm to 70 μm, more preferably 5 μm to 50 μm.

[0137] The iron oxide layer 60 is a layer formed on the nitrogen compound layer 50. The iron oxide layer 60 can be made of, for example, Fe3O4. The thickness of the iron oxide layer 60 is preferably 0.5 μm to 30 μm, more preferably 1 μm to 20 μm.

[0138] The overall thickness of the nitrided layer 30 is preferably 20 μm to 500 μm, more preferably 50 μm to 300 μm.

[0139] Examples of methods for forming a nitrided layer 30 on an iron-based substrate 20 include gas nitriding, gas soft nitriding, gas carbonitriding, salt bath nitriding, salt bath soft nitriding, salt bath carbonitriding, ion nitriding, ion sulfiding, and plasma soft nitriding. Among these, the method for forming the nitrided layer 30 on the iron-based substrate 20 is preferably a soft nitriding method such as gas soft nitriding, salt bath soft nitriding, or plasma soft nitriding, and more preferably a gas soft nitriding method.

[0140] Soft nitriding is a surface treatment method that typically involves the penetration and diffusion of nitrogen and carbon at temperatures ranging from 550°C to 590°C.

[0141] Gas nitriding is a soft nitriding treatment method performed under a carbon dioxide or ammonia gas atmosphere. In gas nitriding, a gas nitriding furnace can be used to perform soft nitriding on iron-based materials. Pit furnaces, batch furnaces, and continuous furnaces can be used as gas nitriding furnaces. These furnaces can be supplied with ammonia gas, nitrogen gas, carbon dioxide gas, etc. The flow rate of these gases into the furnace can be controlled, for example, by a mass flow controller.

[0142] Salt bath nitriding is a soft nitriding treatment method performed in a salt bath containing sodium chloride or the like.

[0143] Plasma soft nitriding is a soft nitriding method that utilizes glow discharge to ionize nitrogen gas and uses the decomposed nitrogen ions.

[0144] When forming the nitrided layer 30 on the iron-based substrate 20, oils, greases, iron powder, and other harmful oxide films adhering to the surface of the iron-based material to be treated may be removed by pretreatment such as washing, if necessary. Furthermore, when forming the nitrided layer 30 on the iron-based substrate 20, partial nitriding prevention treatment (such as nitrogen-preventive paste or electroplating) may be applied as necessary.

[0145] In the mating material 10, the nitrided layer 30 is positioned on the friction surface side with the friction material. In particular, in this embodiment, the iron oxide layer 60 is positioned on the friction surface with the friction material. However, the iron oxide layer 60 is not required to be provided in the nitrided layer 30, in which case the nitrogen compound layer 50 may be positioned on the friction surface with the friction material. Alternatively, a protective film, such as a coating or film application, may be formed on the nitrided layer 30, which is quickly removed by friction with the friction material immediately after use, and this protective film may be positioned on the friction surface with the friction material. Furthermore, an adhesive film (transfer film) may be formed on the friction surface between the nitrided layer 30 and the friction material.

[0146] <Friction> The friction pair of the present invention generates braking force through the frictional force generated between a friction material and a nitrided mating material. In particular, the friction pair of the present invention comprises a friction material composed of a molded body of a friction material composition containing magnesium potassium titanate and a binder, and a mating material having an iron-based substrate and a nitrided layer provided on the iron-based substrate, with the nitrided layer positioned on the friction surface side with respect to the friction material, and is characterized in that the magnesium potassium titanate has a pseudo-tunnel-shaped crystalline structure.

[0147] The friction pair of the present invention can be suitably used in brake systems of various vehicles and industrial machinery, etc., that use a mating material having a nitrided layer on an iron-based substrate. [Examples]

[0148] The present invention will be described in more detail below based on specific examples.

[0149] The present invention is not limited in any way to the following embodiments, and can be implemented with appropriate modifications without altering its essence.

[0150] <Manufacturing of magnesium potassium titanate> (Manufacturing example 1: Magnesium potassium A titanate) 496.9 g of anatase-type titanium dioxide (chloride ion elution rate: 20 ppm), 213.7 g of potassium carbonate, and 89.4 g of magnesium hydroxide were mixed by conventional methods to obtain a raw material mixture. The raw material mixture was filled into a vibratory mill and ground for 30 minutes under conditions of vibration frequency 1200 cpm and amplitude 6.0 mm to obtain a ground mixture. 48 ml of water was added to the ground mixture and mixed, and 15 g of the ground mixture was formed into pellets using a hydraulic press at a pressure of 10 MPa. These pellets were calcined in an electric furnace at 1000°C for 4 hours, then slowly cooled, and the resulting calcined material was crushed and passed through a 20-mesh sieve to obtain the target magnesium potassium titanate A. Note that magnesium potassium titanate A did not contain anatase-type titanium dioxide.

[0151] Table 1 shows the chemical composition (composition formula), crystal structure (including peak area ratio from Raman spectroscopy), crystallite size, average particle diameter, specific surface area, particle shape, alkali metal ion elution rate, and chloride ion elution rate of the obtained magnesium potassium A titanate.

[0152] (Manufacturing example 2: Magnesium potassium titanate 1) A 20% by mass aqueous slurry of magnesium potassium titanate A, produced in Production Example 1, was prepared. 0.27 equivalents of sulfuric acid relative to the potassium content of magnesium potassium titanate were mixed into this aqueous slurry and stirred at room temperature (20°C) for 2 hours. This aqueous slurry was filtered by suction, washed with deionized water, and the separated cake (solid content) was dried at 110°C for 12 hours. After firing in an electric furnace at 500°C for 1 hour, it was slowly cooled, and the resulting fired product was passed through a 20-mesh sieve to obtain the target magnesium potassium titanate 1. Note that magnesium potassium titanate 1 did not contain anatase-type titanium dioxide.

[0153] Table 1 shows the compositional formula, crystal structure (including peak area ratio from Raman spectroscopy), crystallite size, average particle diameter, specific surface area, particle shape, alkali metal ion elution rate, and chloride ion elution rate of the obtained magnesium potassium titanate 1.

[0154] <Measurement of physical properties of magnesium potassium titanate> The physical properties of magnesium potassium titanate 1 and magnesium potassium titanate A were measured as follows.

[0155] (composition formula) This was confirmed using an ICP-AES analyzer (manufactured by SII Nanotechnologies, model number "SPS5100").

[0156] (Crystal structure) The findings were confirmed using a scanning transmission electron microscope (STEM, JEOL Ltd., model number "JEM-ARM200F") and a Raman spectrometer (METTLER TOLEDO, model number "React Raman 785"). For STEM observation, TEM samples were prepared by argon ion milling using an ion slicer. Raman spectrometer measurements were performed at an excitation wavelength of 785 nm and wavenumber of 100 cm⁻¹. -1 ~3200cm -1 The procedure was performed under the conditions of an exposure time of 1 second and 10 scans. Specifically, the crystal structure was confirmed as follows.

[0157] Figure 2 shows a scanning transmission electron microscope (STEM) image of magnesium potassium titanate 1 obtained in manufacturing example 2. Figure 4 shows a scanning transmission electron microscope (STEM) image of magnesium potassium titanate A obtained in manufacturing example 1.

[0158] As shown in Figure 2, magnesium potassium titanate 1 obtained in Production Example 2 had a pseudo-tunnel crystal structure, which was close to a tunnel crystal structure. On the other hand, as shown in Figure 4, magnesium potassium titanate A obtained in Production Example 1 had a layered crystal structure.

[0159] Figure 3 shows the Raman spectral spectra of magnesium potassium titanate and potassium hexatinate obtained in Production Example 1 and Production Example 2.

[0160] As shown in Figure 3, magnesium potassium titanate 1 obtained in Production Example 2 exhibits a peak at 835 cm², which is thought to originate from the layered crystal structure, similar to magnesium potassium titanate A in Production Example 1. -1 No peaks were observed in the vicinity. On the other hand, magnesium potassium titanate 1 obtained in production example 2 showed a peak at 140 cm, which is thought to originate from a tunnel-like crystal structure, similar to potassium hexa-titanate. -1 Nearby and 860cm -1 Since peaks are observed in the vicinity, the spectrum of magnesium potassium titanate 1 obtained in production example 2 can be said to be similar to the spectrum of potassium hexa-titanate.

[0161] Furthermore, from the Raman spectroscopy spectra of magnesium potassium titanate 1 and magnesium potassium titanate A, 100 cm⁻¹ -1 ~165cm -1 Peak area (Ia) at 215 cm² -1 ~325cm -1 The ratio (Ia / Ib) to the peak area (Ib) at 785cm² -1 ~900cm -1 Peak area (Ic) at 215 cm² -1 ~325cm -1 The ratio (Ic / Ib) to the peak area (Ib) was calculated.

[0162] The peak area in each wavelength range was calculated by first removing the background from the Raman spectroscopic spectrum using the asymmetric least squares method (ASLS method), and then performing numerical integration using the Simpson method.

[0163] (crystallite size) X-ray diffraction measurements were performed using the wide-angle X-ray diffraction method. CuKα rays (wavelength 1.5418 Å) were used as the X-ray source. The X-ray diffraction apparatus used was a Rigaku Ultima IV. X-ray diffraction measurements were performed in the range of 2θ from 5° to 60°, and the crystallite size was calculated using the Halder-Wagner method.

[0164] (Average particle size) The particle size distribution was measured using a laser diffraction particle size analyzer (Shimadzu Corporation, model number "SALD-2300"), and the average particle size was defined as the particle diameter at which the volume-based cumulative volume reached 50% in the obtained particle size distribution.

[0165] (specific surface area) The measurement was performed using an automatic specific surface area measuring device (manufactured by micromeritics, model number "TriStarII3020").

[0166] (particle shape) This was confirmed using a field emission scanning electron microscope (Hitachi High-Tech Corporation, model number "S-4800").

[0167] (Alkali metal ion elution rate) The mass (X) g of the sample was measured, and then the sample was added to ultrapure water to prepare a 1% by mass slurry. After stirring at 80°C for 4 hours, the solids were removed using a 0.2 μm pore size membrane filter to obtain an extract. The mass (Y) g of alkali metal ions in the obtained extract was measured using an ion chromatograph (Dionex, product number "ICS-1100"). Then, using the above mass (X) g and mass (Y) g values, the alkali metal ion elution rate (mass%) was calculated based on the formula [(Y) / (X)] × 100.

[0168] (Chloride ion elution rate) The mass (X) g of the sample was measured, and then the sample was added to ultrapure water to prepare a 1% by mass slurry. After stirring at 25°C for 10 minutes, the solids were removed using a 0.2 μm pore size membrane filter to obtain an extract. The mass (Y) g of chloride ions in the obtained extract was measured using an ion chromatograph (Dionex, part number "ICS-1100"). Then, using the above values ​​of mass (X) g and mass (Y) g, the formula [(Y) / (X)] × 10⁻¹⁰ was used. 6 Based on this, the chloride ion elution rate (ppm) was calculated.

[0169] [Table 1]

[0170] As shown in Table 1, scanning transmission electron microscope (STEM) images and Raman spectroscopy confirmed that magnesium potassium titanate 1 obtained in Production Example 2 had a pseudo-tunneling crystal structure, with a ratio (Ia / Ib) of 0.03 or greater and a ratio (Ic / Ib) of 0.40 or less in the Raman spectroscopy spectrum. On the other hand, magnesium potassium titanate A obtained in Production Example 1 had a layered crystal structure, with a ratio (Ia / Ib) of less than 0.03 and a ratio (Ic / Ib) greater than 0.40 in the Raman spectroscopy spectrum.

[0171] <Manufacturing of friction materials> For the manufacture of the friction material, magnesium potassium titanate 1, magnesium potassium titanate A, and the following materials were used.

[0172] Thermosetting resin: Hexamethylenetetramine-containing novolac-type phenolic resin powder Barium sulfate: Precipitating barium sulfate powder, average particle size 1.6 μm Mica: Natural mica, average particle size 180 μm Cashew dust: Average particle size 200 μm Iron oxide: Average particle size 0.3 μm, Mohs hardness 6 Zirconium silicate: Zirconium silicate powder, average particle size 1.1 μm, Mohs hardness 7.5 Antimony trisulfide: Average particle size 1.5 μm Graphite: Synthetic graphite, average particle size 730 μm Aramid fiber: Fibrilized para-aramid fiber (aramid pulp), fiber length 0.89 mm, specific surface area 9.8 m² 2 / g Slaked lime: Average particle size 0.2 μm Rock wool: Average fiber length 125 μm, maximum shot content (125 μm or more) 5.0% Potassium hexa-titanate A: Potassium hexa-titanate, tunnel-shaped crystalline structure, columnar particles, average particle size 36 μm, manufactured by Otsuka Chemical Co., Ltd. (product name: TERRACESS JSL) Potassium hexatinate B: Potassium hexatinate, tunnel-shaped crystalline structure, porous spherical particles, average particle size 60.1 μm, manufactured by Otsuka Chemical Co., Ltd. (product name: TERRACESS DP-AS)

[0173] (Example 1 and Comparative Examples 1-3) Each material was mixed according to the mixing ratios listed in Table 2 and mixed for 3 minutes using an Eich mixer. The resulting mixture was pressurized at room temperature (20°C) at a pressure of 15 MPa for 5 seconds to produce a temporary molded body. The temporary molded body was placed in the cavity of a heat-molding mold heated to 150°C, and with a back plate (material: steel) placed on top, the molded body was pressurized at a pressure of 10 MPa to 40 MPa for 300 seconds to achieve a porosity of 15%. Five degassing processes were performed between 5 and 70 seconds from the start of pressurization. The resulting molded body was placed in a constant-temperature dryer heated to 220°C and held for 2 hours to allow for complete curing, thereby obtaining a friction material.

[0174] <Evaluation of friction materials> The friction tests of the friction materials prepared as described above were carried out as follows. The rotors used were cast iron rotors and cast iron rotors that had been nitrided (nitrided rotors) belonging to ASTM standard numbers A48 / A48M.

[0175] The nitriding treatment was carried out using a gas soft nitriding method, which resulted in the layering of a nitrogen diffusion layer, a nitrogen compound layer, and an iron oxide layer on the cast iron rotor in that order. The thickness of the nitrogen diffusion layer was 0.1 mm, the thickness of the nitrogen compound layer was 17 μm, and the thickness of the iron oxide layer was 6 μm. The Vickers hardness of the surface (friction surface) of the nitrided rotor was 897 HV.

[0176] (Friction test) The surface (friction surface) of the friction material was polished to 1.0 mm, and a friction test was performed according to JASO C406 to determine the average coefficient of friction (average μ) and the amount of wear on the mating material.

[0177] The difference in average friction coefficient (average μ) was calculated from the difference between the average friction coefficient (average μ) obtained using a cast iron rotor and the average friction coefficient (average μ) obtained using a nitrided rotor.

[0178] The results are shown in Table 2 below.

[0179] [Table 2]

[0180] The average μ of Example 1, a friction pair using magnesium potassium titanate 1 with a pseudo-tunnel crystal structure, was high regardless of whether the rotor was nitrided or not, demonstrating excellent performance as a friction pair. In contrast, the average μ of Comparative Examples 1 to 3, friction pairs that did not use magnesium potassium titanate 1 with a pseudo-tunnel crystal structure, decreased after nitriding the surface of the cast iron rotor.

[0181] Furthermore, the amount of wear on the nitrided rotor of the friction pair in Example 1 was less than that of the friction pairs in Comparative Examples 2 and 3, which used potassium hexatinate A and potassium hexatinate B, respectively. This indicates that magnesium potassium titanate 1, which has a pseudo-tunnel crystal structure, has low aggressiveness towards the nitrided rotor. [Explanation of symbols]

[0182] 10... Opposing material 20… Iron-based base material 20a…main surface 30…Nitrided layer 40… Nitrogen diffusion layer 50…Nitrogen compound layer 60…Iron oxide layer

Claims

1. A friction pair that generates braking force through the frictional force between a friction material and a nitrided mating material, Composition formula K ｘ Mg ０．４ Ti １．６ O ４－ｙ A friction material comprising a molded body of a friction material composition containing magnesium potassium titanate and a binder, represented by the formula [wherein x is 0.1 ≤ x ≤ 0.6, y = (0.8 - x) / 2], A mating material having an iron-based substrate and a nitrided layer provided on the iron-based substrate, wherein the nitrided layer is positioned on the friction surface side with the friction material, Equipped with, A friction pair characterized in that the magnesium potassium titanate has a pseudo-tunnel-shaped crystalline structure.

2. In the Raman spectrum of the magnesium potassium titanate, the ratio (Ia / Ib) of the peak area (Ia) at 100 cm －１ to 165 cm －１ to the peak area (Ib) at 215 cm －１ to 325 cm －１ is 0.03 or more, and the ratio (Ic / Ib) of the peak area (Ic) at 785 cm －１ to 900 cm －１ to the peak area (Ib) at 215 cm －１ to 325 cm －１ is 0.40 or less. The friction pair according to claim 1.

3. The friction pair according to claim 1 or 2, wherein the iron-based substrate is cast iron.

4. The friction pair according to claim 1 or 2, wherein the thickness of the nitrided layer is 20 μm to 500 μm.

5. The friction pair according to claim 1 or 2, wherein the nitrided layer comprises a nitrogen diffusion layer provided on the iron-based substrate and a nitrogen compound layer provided on the nitrogen diffusion layer.

6. The friction pair according to claim 5, wherein the nitrided layer further comprises an iron oxide layer provided on the nitrogen compound layer.

7. The friction pair according to claim 1 or 2, wherein the magnesium potassium titanate substantially does not contain anatase-type titanium dioxide.

8. The friction pair according to claim 1 or 2, wherein the magnesium potassium titanate is in the form of plate-like particles.

9. The friction pair according to claim 1 or 2, wherein the average particle size of magnesium potassium titanate is 0.1 μm to 100 μm.

10. The specific surface area of ​​the aforementioned magnesium potassium titanate is 0.1 m². ２ / g to 10m ２ The friction pair according to claim 1 or 2, wherein the coefficient of friction is / g.

11. The friction pair according to claim 1 or 2, wherein the alkali metal ion elution rate of magnesium potassium titanate is 0.01% by mass to 15% by mass.

12. The friction pair according to claim 1 or 2, wherein the content of copper components is less than 0.5% by mass as copper element relative to 100% by mass of the total amount of the friction material composition.

13. The friction pair according to claim 1 or 2, wherein the content of magnesium potassium titanate is 1% to 40% by mass based on 100% by mass of the total amount of the friction material composition.

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