WO2025062984A1 - Composition, coating film, and sliding member - Google Patents

Abstract

Provided are: a composition capable of improving friction characteristics, durability, and sealability by using a solid lubricant having a proper particle size and aspect ratio; a coating composition; a coating film thereof; and a sliding member. Specifically, the composition contains a solid lubricant (A). The solid lubricant (A) contains molybdenum disulfide particles (a1) in which the aspect ratio, which is the ratio of the median diameter D₅₀ (nm) and the thickness (nm) of the primary particles, is in the range of 2-110, and the median diameter D₅₀ is 50-500 nm.

Description

Composition, coating film and sliding member

The present invention relates to a composition, coating film, and sliding member containing a solid lubricant.

Molybdenum disulfide is used as a solid lubricant in a wide range of applications. For example, a sliding coating structure suitable for sliding parts such as the skirt, ring groove, and pin hole of an internal combustion engine piston in a gasoline engine or the like has been disclosed (Patent Document 1). This sliding coating structure has a lubricating coating that covers the surface of a metal substrate, and the lubricating coating is made of a heat-resistant resin containing a polyamide-imide resin and molybdenum disulfide particles, the weight percentage of the heat-resistant resin in the lubricating coating is 52 to 84 wt%, the weight percentage of the molybdenum disulfide particles is 48 to 16 wt%, and the average particle size of the molybdenum disulfide particles is in the range of 0.7 to 2.7 μm as measured by a laser diffraction scattering type particle size distribution measurement method.

Also, a resin composition for forming a lubricating film on the surface of a sliding member is disclosed, which contains a polyamideimide resin as a binder, a solid lubricant, and an organic solvent, the polyamideimide resin has a weight average molecular weight of 10,000 to 50,000, and the blending amounts of each component excluding the organic solvent are 89.0 to 97.5 volume % polyamideimide resin, 1 to 7 volume % fluorine-based solid lubricant, 1 to 5 volume % sulfur-containing compound-based solid lubricant, and 0.5 to 5 volume % carbon-based solid lubricant, with the total solid lubricant being 2.5 to 11 volume % (Patent Document 2).

Also, in a sealed sliding member that has a sliding surface that slides against another member and seals a fluid through the sliding surface, it has been disclosed that by providing the sliding surface with a sliding material that contains a solid lubricant and a thermosetting resin that fixes it, friction during sliding can be reduced and leakage from the seal surface can be prevented (Patent Document 3). Alternatively, a sliding member that combines sealing properties and sliding properties by using a liquid lubricant and a solid lubricant in combination has also been provided (Patent Document 4).

JP 2009-068584 A JP 2011-213761 A JP 2015-10689 A Japanese Patent Application Publication No. 8-100860 Patent No. 6614471

Molybdenum disulfide particles used to improve lubricity are generally obtained by cutting and crushing natural molybdenum disulfide ore. Inexpensive powders obtained by crushing natural molybdenum disulfide ore and then classifying it according to the application have a size of the order of μm as shown in the above Patent Document 1, and a very large specific gravity of about 5, so that the lubricating effect per added mass is small. In addition, when conventional molybdenum disulfide particles such as those described above are contained in a coating film, the surface of the coating film is rough due to the large particle size, and the molybdenum disulfide protruding from the surface of the coating film is easily broken or detached during sliding, resulting in low friction characteristics and durability. In particular, in sealed sliding components, when there are μm-order size molybdenum disulfide particles protruding from the surface, there is a problem that sealing properties are impaired, and there is also a problem that it is difficult to have sufficient molybdenum disulfide particles on the outermost surface of the lubricating layer due to their large specific gravity. In addition, when a liquid lubricant is applied onto the coating, the surface of the coating is rough, making it difficult to retain the liquid lubricant on the coating, and it is difficult to obtain the effect of reducing friction and wear that the liquid lubricant would provide. Furthermore, natural molybdenum disulfide minerals contain a large amount of impurities derived from mineral deposits, such as copper and lead, which reduces the lubricating effect.

The applicant holds a patent for a manufacturing method for synthesizing nm-sized molybdenum disulfide particles by heating molybdenum oxide in the presence of a sulfur source (Patent Document 5), and there is room for consideration and improvement as to whether the application of nm-sized molybdenum disulfide particles to coatings will contribute to improved friction properties and durability. In addition, the nm-sized molybdenum disulfide particles, which are a product uniquely developed by the applicant, have not only a 2H crystal structure but also a rare 3R (rhombohedral) structure. According to this technology, by manufacturing molybdenum disulfide particles using the applicant's technology ``nm-sized molybdenum trioxide fine particles'' as a raw material, it is possible to synthesize ``molybdenum disulfide that contains a 3R structure and has a lightweight property that is advantageous for nano-scale and large surface area,'' which is difficult to achieve by crushing mine products or synthesizing from general-purpose molybdenum trioxide.

The present invention aims to provide a composition, coating film, and sliding member that have appropriate particle size and aspect ratio and can improve friction characteristics, durability, and sealing properties.

As a result of intensive research, the present inventors have focused on the aspect ratio and particle size of molybdenum disulfide particles contained in a coating composition, etc., and have found that when the composition contains molybdenum disulfide particles having a proper aspect ratio and median diameter D ₅₀ of primary particles, the surface smoothness of the coating film, which is a cured product of the coating composition, or the lubricating layer made of the composition is improved, and defects that cause the coating film or lubricating layer to be destroyed by sliding between sliding surfaces are unlikely to occur, and when the amount added is the same as that of conventional molybdenum disulfide particles, the molybdenum disulfide particles have a small particle size and are distributed more uniformly within the surface, so that the load can be received by surface contact rather than point contact, and as a result, the friction characteristics and durability of the coating film or lubricating layer are improved. In addition, it has been found that when the molybdenum disulfide particles have a proper particle size and aspect ratio, the molybdenum disulfide particles are unlikely to protrude from the surface of the coating film or lubricating layer and therefore are unlikely to separate, thereby reducing the friction wear that occurs between the coating film or lubricating layer and the sliding target member. Furthermore, they found that when a liquid lubricant is applied onto the coating, the smoothing of the lubricating coating surface makes it easier to retain the liquid lubricant on the lubricating coating, making it easier to exert the effect of reducing friction and wear due to the liquid lubricant; and that in a lubricating layer used in combination with a liquid lubricant, molybdenum disulfide particles can be present uniformly within the layer, resulting in excellent homogeneity in the sliding parts.

Furthermore, it was found that if molybdenum disulfide particles have the appropriate particle size and aspect ratio, the gap between the coating film and the sliding member in the sliding part can be reduced, and therefore the sealing performance of the sliding part can be improved in addition to reducing friction and wear. Molybdenum disulfide particles generally have a layered crystal structure. Each layer is a single-layer two-dimensional sheet structure of molybdenum disulfide, and when an external force is applied in the two-dimensional in-plane direction, the layers are displaced. Due to this property, it is believed that molybdenum disulfide exerts an effect of reducing friction and wear. When an external force is applied to a molybdenum disulfide particle present in the sliding part by a sliding member, the surface layer of the molybdenum disulfide particle in particular is cleaved by the external force, and the cleaved molybdenum disulfide pieces intervene to better fill the gap between the coating film and the sliding member, and the labyrinth effect also works, resulting in good sealing performance. The applicant has discovered that molybdenum disulfide particles made using the technology he owns have a 3R crystal structure as described above, which makes this cleavage easier to occur than with molybdenum disulfide particles that have a 1H or 2H crystal structure, and therefore is more likely to produce the above-mentioned effects.

That is, the present invention provides the following configuration.
[1] Contains a solid lubricant (A),
The solid lubricant (A) comprises molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 (nm) to the thickness (nm) of the primary particles, in the range of 2 to 110, and the median diameter _D50 is 50 nm to 500 nm.

[2] A composition comprising a resin and a solid lubricant (A),
The solid lubricant (A) comprises molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 (nm) to the thickness (nm) of the primary particles, in the range of 2 to 110, and the median diameter _D50 is 50 nm to 500 nm.

[3] The solid lubricant (A) comprises the molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2) having a primary particle median diameter _D50 of 600 nm or more and 500 μm or less,
The composition according to [1] or [2], wherein a content ratio ((a1):(a2)) of the molybdenum disulfide particles (a1) to the molybdenum disulfide particles (a2) is 1:0 to 1:20 in terms of mass ratio.

[4] The composition according to [3], wherein the median diameter _D50 of the primary particles of the molybdenum disulfide particles (a2) is 1 μm or more and 50 μm or less.

[5] The composition according to [1] or [2], wherein the solid lubricant (A) is made of the molybdenum disulfide particles (a1).

[6] The composition according to any one of [1] to [5], in which the content of the solid lubricant (A) is 0.5% by mass or more and 30% by mass or less, when the total mass of the composition is 100% by mass.

[7] The composition according to any one of [2] to [5], wherein the resin comprises one or more resins selected from epoxy resins, phenolic resins, polyamide resins, polyimide resins, and polyamideimide resins.

[8] Further comprising a solid lubricant (B),
The composition according to any one of [1] to [7], wherein the solid lubricant (B) includes one or more types selected from a carbon-based solid lubricant and a fluorine-based solid lubricant.

[9] Further comprising a solvent,
The composition according to any one of [1] to [8], wherein the solvent includes one or more selected from the group consisting of N-methyl-2-pyrrolidone, γ-butyrolactone, cyclopentanone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, butyl cellosolve, and methyl ethyl ketone.

[10] The composition according to any one of [1] to [9], which contains antimony trioxide as an antioxidant.

[11] A composition according to any one of [2] to [10], which is a coating composition.

[12] A coating film that is a cured product of the composition described in any one of [1] to [11].

　[13] A sliding member having the coating film described in [10].

[14] A sliding member having, on at least a part of a sliding surface, a solid lubricant (A) containing molybdenum _disulfide particles (a1) having an aspect ratio, which is the ratio of a median diameter _D50 (nm) of primary particles to a thickness (nm), in the range of 2 to 110, and the median diameter D50 being 50 nm to 500 nm.

[15] The sliding member according to [13] or [14], which is a molded body.

The present invention provides a composition, coating film, and sliding member that have appropriate particle size and aspect ratio and can improve friction characteristics, durability, and sealing properties.

FIG. 2 is a cross-sectional view showing an example of the configuration of a coating film according to the present embodiment. FIG. 2 is a cross-sectional view showing an example of the configuration of a coating film according to the present embodiment. 1 is a graph showing the results of a paper vertical sliding test in the examples. 1 is a graph showing the results of a FALEX sliding test in an embodiment. 1 is a graph showing the results of a Kawamura type reciprocating friction test in an example.

The following describes in detail an embodiment of the present invention with reference to the drawings.

<Composition>
The composition according to the present embodiment includes a solid lubricant (A), and the solid lubricant (A) includes molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 of primary particles to the thickness, of 2 or more and 110 or less, and the median diameter _D50 is 50 nm or more and 500 nm or less.

The composition may contain resins, organic solvents, various additives, etc., as described below. In particular, due to the small particle size, it can be easily dispersed in liquid lubricants such as silicone oil, fluorine oil, polyalkylene glycol, white oil, mineral oil, white petrolatum (petrolatum), liquid paraffin, paraffin wax, olefin polymerized oil, alkylated aromatic oil, coal tar, hydrogenated oil, polyether oil, ester oil, and halogenated hydrocarbon oil, which are conventionally used as sliding members, and can improve lubricity and sliding properties without impairing sealing properties. It can also be easily dispersed in organic solvents, reactive monomers, and liquid resins. When dispersing in these media, various dispersants may be used in combination, or a method may be used in which the solid lubricant (A) containing the molybdenum disulfide particles (a1) is dispersed in a medium at a high concentration using various dispersants in advance, and then the solid lubricant (A) is dispersed in the same or different medium of interest at a desired concentration.

<Coating composition>
The coating composition according to the present embodiment comprises a resin and a solid lubricant (A), and the solid lubricant (A) comprises molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 of primary particles to the thickness, of 2 or more and 110 or less, and the median diameter _D50 is 50 nm or more and 500 nm or less.

[Molybdenum disulfide particles (a1)]
In this embodiment, the aspect ratio of the molybdenum disulfide particles (a1) is expressed by the ratio of the median diameter D ₅₀ (nm) to the thickness (nm) of the primary particle ((median diameter D ₅₀ )/thickness (height)), and is 2 to 110 on average for five particles. When the aspect ratio of the molybdenum disulfide particles (a1) is within the above range, the molybdenum disulfide particles (a1) are easily oriented so that their longitudinal direction is along the in-plane direction of the coating film or lubricating layer. This allows the surface of the coating film or lubricating layer to be efficiently covered, and wear and seizure due to rubbing can be sufficiently reduced. The larger the aspect ratio, the more the above-mentioned effects can be enjoyed. The aspect ratio is preferably 3 or more, more preferably 5 or more, and particularly preferably 8 or more. From the viewpoint of production, it is easy to obtain an aspect ratio of 80 or less, and even more easily to obtain an aspect ratio of 60 or less.

In addition, on the premise that the aspect ratio of the primary particle of the molybdenum disulfide particle (a1) is within the above range, the median diameter _D50 of the primary particle of the molybdenum disulfide particle (a1) is 50 nm or more and 500 nm or less. By having the median diameter _D50 of the molybdenum disulfide particle (a1) be 500 nm or less, the particle is less likely to protrude from the surface of the coating film or lubricating layer, and the surface of the coating film or lubricating layer is smoothed. Therefore, when an external force is applied by sliding, etc., the molybdenum disulfide particle (a1) is less likely to be detached, and the sealing property is also improved. In addition, even if the gap between the coating film or lubricating layer and the sliding material is small, less than 1000 nm, the molybdenum disulfide particle (a1) is likely to remain in the gap without being detached from the coating film or lubricating layer, and the lubricating property can be maintained for a long period of time.

From the viewpoint of the above-mentioned effects, the median diameter _D50 of the primary particles of the molybdenum disulfide particles (a1) is more preferably 400 nm or less, and even more preferably 300 nm or less. The median diameter _D50 of the primary particles of the molybdenum disulfide particles (a1) may be 100 nm or more, or may be 150 nm or more. The median diameter _D50 of the primary particles of the molybdenum disulfide particles (a1) is measured, for example, using a dynamic light scattering particle size distribution measuring device (Microtrackbell, Nanotrac WaveII) or a laser diffraction particle size distribution measuring device (Shimadzu Corporation, SALD-7000).

The shape of the primary particles of the molybdenum disulfide particles (a1) is not particularly limited, but it is preferable that the particles have a thin layer shape such as a disk shape, ribbon shape, or sheet shape. When the molybdenum disulfide particles (a1) have the above shape, they can cover the surface of the coating film or lubricating layer more efficiently even with a small content, and the friction and wear properties can be further improved.

The molybdenum disulfide (MoS ₂ ) particles (a1) may contain a 2H crystal structure and a 3R crystal structure. When the molybdenum disulfide particles (a1) having a molybdenum disulfide crystal phase with a ratio of 3R crystal structure of 10% or more are used as a coating material or a lubricating layer component, they not only prevent seizure even under high load, but also have excellent friction properties with a friction coefficient reduced by 20 to 30%. The ratio of 3R crystal structure in the molybdenum disulfide crystal phase is preferably 20% or more, more preferably 30% or more, even more preferably 50% or more, and particularly preferably 60% or more.

　The fact that the molybdenum disulfide particles (a1) have a 2H crystal structure and a 3R crystal structure can be confirmed, for example, by using an extended Rietveld analysis software (High Score Plus, manufactured by Malvern Panalytical) that can take into account the crystallite size. In this Rietveld analysis software, the entire XRD diffraction profile is simulated using a crystal structure model including the crystallite size, and compared with the XRD diffraction profile obtained in an experiment. The crystal lattice constants of the crystal structure model, crystal structure factors such as atomic coordinates, weight fraction (abundance ratio), etc. are optimized by the least squares method so that the residual between the diffraction profile obtained in the experiment and the diffraction profile obtained by calculation is minimized, and each phase of the 2H crystal structure and the 3R crystal structure is identified and quantified with high accuracy, so that the crystallite size can be calculated in addition to the crystal structure type and its ratio calculated by normal Rietveld analysis. Hereinafter, in this patent, the analysis method using the above-mentioned High Score Plus is referred to as "Extended Rietveld analysis".

In addition, in the molybdenum disulfide particles (a1) of this embodiment, the crystallite size of the 3R crystal structure calculated by extended Rietveld analysis based on the analytical formula L = Kλ / (β cosθ) using a profile obtained from powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source may be 1 nm or more and 150 nm or less. In the above formula, K is an apparatus constant depending on the XRD optical system (incident side and detector side) and setting, L is the crystallite size [m], λ is the measured X-ray wavelength [m], K is a constant, β is the half-width [rad], and θ is the Bragg angle [rad] of the diffraction line. If the crystallite size of the 3R crystal structure is 1 nm or more and 150 nm or less, slippage is likely to occur between layers when subjected to shear force, and the friction coefficient of the dispersion system can be reduced, thereby improving the friction characteristics. The crystallite size of the 3R crystal structure is preferably a value obtained by extended Rietveld analysis. The coefficient of friction can be measured, for example, from a Stribeck curve using a ball-on-disk tester or a four-ball tester.

From the viewpoint of the above-mentioned effects, the 3R crystal structure obtained by the extended Rietveld analysis is preferably composed of a crystalline phase composed of crystallites having a crystallite size calculated based on the analytical formula of 1 nm or more and 100 nm or less, more preferably the crystallite size is 1 nm or more and 50 nm or less, and even more preferably 1 nm or more and 40 nm or less.
In the molybdenum disulfide particles (a1) of this embodiment, the crystallite size of the 2H crystal structure is preferably 1 nm or more and 150 nm or less. When the crystallite size of the 2H crystal structure is 1 nm or more and 150 nm or less, the friction coefficient can be reduced and the friction characteristics can be improved.
The crystallite size of the 2H crystal structure is preferably a value obtained according to the extended Rietveld analysis. The 2H crystal structure obtained by the Rietveld analysis is preferably a crystalline phase composed of crystallites whose crystallite size calculated based on the analytical formula is 1 nm or more and 150 nm or less, and the crystallite size is more preferably 5 nm or more and 150 nm or less.

The 2H crystal structure obtained by extended Rietveld analysis is preferably composed of one crystal phase composed of crystallites having a predetermined crystallite size. In the manufacturing method described below, a 2H crystal structure composed of one crystal phase can be obtained by setting the heating temperature in the heat treatment to a relatively low temperature. In this case, the crystallite size of the 2H crystal structure is more preferably 1 nm or more and 20 nm or less, and more preferably 5 nm or more and 15 nm or less.

The crystallite size of the 2H crystal structure and the crystallite size of the 3R crystal structure can also be calculated, for example, using the peak half-width of the XRD diffraction profile.

The abundance ratio (2H:3R) of the 2H crystal structure and the 3R crystal structure in the crystal phase obtained by extended Rietveld analysis using the profile obtained from the above XRD is preferably 10:90 to 90:10. If the abundance ratio of the 3R crystal structure in the crystal phase is 10% to 90%, when the molybdenum disulfide particles (a1) are used as a coating material or a lubricating layer component, seizure is less likely to occur when a high load is applied, and the friction coefficient can be reduced by 20 to 30%.

The abundance ratio (2H:3R) of the 2H crystal structure and the 3R crystal structure in the crystal phase obtained by extended Rietveld analysis using the profile obtained from the XRD is more preferably 10:90 to 80:20, and even more preferably 40:60 to 80:20, from the viewpoint of the above-mentioned effects.

The 2H crystal structure obtained by the extended Rietveld analysis may be composed of a first crystal phase composed of crystallites having a predetermined crystallite size and a second crystal phase having a smaller crystallite size than the first crystal phase. In the manufacturing method described later, the molybdenum disulfide particles (a1) can be further heated as a post-treatment to obtain a 2H crystal structure composed of a first crystal phase and a second crystal phase. The crystallite size of the first crystal phase of the 2H crystal structure is, for example, greater than 20 nm and less than 150 nm, and may be 50 nm or more and 150 nm or less, or 100 nm or more and 150 nm or less. However, in order to reduce the friction coefficient, it is preferable that the first crystal phase does not exist in the crystal phase of the 2H crystal structure, or that the presence ratio of the first crystal phase is low. The crystallite size of the second crystal phase of the 2H crystal structure is preferably 1 nm or more and 20 nm or less, and may be 1 nm or more and 10 nm or less, or may be 5 nm or more and 15 nm or less.

The crystallite size of the first crystal phase of the 2H crystal structure, the crystallite size of the 3R crystal structure, and the crystallite size of the second crystal phase of the 2H crystal structure can also be calculated using, for example, the half-width of the peaks in the XRD diffraction profile, as described above.

The abundance ratio of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure in the crystal phase (2H (first crystal phase):3R:2H (second crystal phase)) obtained by extended Rietveld analysis using the profile obtained from the XRD is preferably 30-0:10-70:80-15. When the abundance ratio of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure in the crystal phase is 30-10:10-70:80-15, when the molybdenum disulfide particles (a1) are used as a coating material or lubricating layer component, seizure is less likely to occur when a high load is applied, and the friction coefficient can be reduced by 20-30%.

The abundance ratio of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure obtained by extended Rietveld analysis using the profile obtained from the XRD is more preferably 30-0:10-70:80-15, and even more preferably 25-0:20-60:75-20, from the viewpoint of the above effects.

In a profile obtained by powder X-ray diffraction (XRD) of the molybdenum disulfide particles (a1) using Cu-Kα radiation as an X-ray source, it is preferable that the peaks near 39.5° and 49.5° are due to the 2H crystal structure, and the peaks near 32.5°, 39.5°, and 49.5° are due to the 3R crystal structure, and the half-widths of the peaks near 39.5° and 49.5° are 1° or more. Furthermore, the molybdenum disulfide particles (a1) may contain a crystal structure other than the 2H crystal structure and 3R crystal structure of molybdenum disulfide, such as a 1H crystal structure.

The fact that the molybdenum disulfide particles (a1) contain a metastable 3R crystal structure can be distinguished by the fact that in a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source, the peaks near 39.5° and 49.5° are both composite peaks of the 2H crystal structure and the 3R crystal structure.

In practice, the abundance ratio of the 2H crystal structure is determined by the peak near 39.5° and the broad peak near 49.5° using the profile obtained from the powder X-ray diffraction (XRD). The abundance ratio of the 3R crystal structure is determined by optimizing the difference between the peak near 39.5° and the broad peak near 49.5° with two peaks near 32.5° and two peaks near 39.5°. In other words, both the peak near 39.5° and the peak near 49.5° are composite waves derived from the 2H crystal structure and the 3R crystal structure, and the abundance ratio of the 2H crystal structure and the 3R crystal structure in the molybdenum disulfide particle (a1) can be calculated by these composite waves.

Molybdenum disulfide particles (a1) may also contain an amorphous phase. The ratio of the amorphous phase in molybdenum disulfide particles (a1) is expressed as 100(%) - (degree of crystallinity (%)) and is preferably 5% or more, more preferably 15% or more, and even more preferably 20% or more. When the ratio of the amorphous phase in molybdenum disulfide particles (a1) is 5% or more, the friction coefficient is further reduced and the friction characteristics can be improved.

The specific surface area of the molybdenum disulfide particles (a1) measured by the BET method is preferably 10 m ² /g or more, more preferably 30 m ² /g or more, and even more preferably 40 m ² /g or more. The specific surface area of the molybdenum disulfide particles (a1) measured by the BET method may be 300 m ² /g or less, or may be 200 m ² /g or less.

The primary particles of the molybdenum disulfide particles (a1) have layers that are close to each other due to relatively weak interactions, and can be easily displaced by external forces such as friction. Therefore, when the primary particles of the molybdenum disulfide particles (a1) are sandwiched between metals as sliding materials, the layers that constitute the primary particles are displaced by the frictional force, reducing the apparent friction coefficient and preventing contact between sliding materials.
When the molybdenum disulfide particles (a1) have a specific surface area of 10 ^m2 /g or more as measured by the BET method, when the primary particles are present between sliding materials, the contact area between the sliding materials can be further reduced, which is thought to contribute to both improving the performance of the coating film or lubricating layer and preventing seizure.

In the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) profile of the molybdenum K-absorption edge of the molybdenum disulfide particles (a1), the ratio (I/II) of the peak intensity I due to Mo-S to the peak intensity II due to Mo-Mo is preferably greater than 1.0, more preferably 1.1 or more, and particularly preferably 1.2 or more.

Whether the crystal structure of molybdenum disulfide is a 2H crystal structure or a 3R crystal structure, the distance between Mo-S is approximately the same due to a covalent bond, and therefore the intensity of the peak due to Mo-S is the same in the extended X-ray absorption fine structure (EXAFS) profile at the K absorption edge of molybdenum. On the other hand, since the 2H crystal structure of molybdenum disulfide is hexagonal, the same hexagon is located 90° directly below the hexagon of Mo atoms, so the distance between Mo-Mo is closer and the peak intensity II due to Mo-Mo is stronger.
Conversely, since the 3R crystal structure of molybdenum disulfide is rhombohedral, the hexagon is not located 90° directly below the hexagon but is shifted by half an angle, which increases the distance between Mo-Mo and weakens the peak intensity II due to Mo-Mo.
In the pure 2H crystal structure of molybdenum disulfide, the ratio (I/II) is small, but as the 3R crystal structure is included, the ratio (I/II) becomes large.
In the 3R crystal structure, the hexagons of the Mo atoms in each of the three layers are offset from each other by half a hexagon. This is expected to result in smaller interactions between the layers and easier sliding, compared to the 2H crystal structure, in which the hexagons of the Mo atoms in two layers are regularly aligned perpendicular to each other.
Even in the case of a 2H crystal structure, if the crystallite size is small, it is expected that slippage will occur more easily at the contact surface.

The conversion rate R _C from the molybdenum oxide precursor compound to molybdenum disulfide particles (a1), which will be described later, is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more, because the presence of molybdenum trioxide is thought to adversely affect lubricating performance.
Since the conversion rate R _C to the molybdenum disulfide particles (a1) can be close to 100%, the molybdenum disulfide particles (a1) can have superior lubricating properties to other molybdenum disulfide materials or their precursors that may contain molybdenum trioxide or that are by-produced.

The conversion rate R _C to molybdenum disulfide particles (a1) can be determined by a RIR (reference intensity ratio) method from profile data obtained by subjecting the molybdenum disulfide particles (a1) to X-ray diffraction (XRD) measurement. The conversion rate R C to MoS ₂ can be calculated from the following formula (1) using the RIR value K _A of molybdenum disulfide (MoS _{2 )} and the integrated intensity I _A of the peak at about 2θ=14.4°±0.5° which is assigned to the (002) or ( ₀₀₃ ) plane of molybdenum disulfide (MoS ₂ ), as well as the RIR value K _B of each molybdenum oxide (the raw material _{MoO 3} , and the reaction intermediates Mo ₉ O ₂₅ , Mo ₄ O ₁₁ , MoO ₂ , etc.) and the integrated intensity I _B of the strongest peak of each molybdenum oxide (the raw material MoO 3 , and the reaction _{intermediates} Mo ₉ O ₂₅ , Mo 4 O 11 , MoO ₂ , etc.).
R _C (%)=(I _A /K _A )/(Σ(I _B /K _B ))×100...(1)
Here, the RIR value can be any value listed in the Inorganic Crystal Structure Database (ICSD) (manufactured by the Japan Chemical Information Association), and the analysis can be performed using integrated powder X-ray analysis software (PDXL2, manufactured by Rigaku Corporation).

The composition of the present embodiment only needs to contain the molybdenum disulfide particles (a1), which is an essential component, and may contain molybdenum sulfide particles represented by MoS _x (X = 1 to 3), or may contain one or more types of molybdenum sulfide particles represented by MoS _x (X = 1 to 3).

[Molybdenum disulfide particles (a2)]
The solid lubricant (A) may contain the molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2) having a primary particle median diameter _D50 larger than that of the molybdenum disulfide particles (a1). The molybdenum disulfide particles (a2) are, for example, crushed natural molybdenum disulfide ( _MoS2 ). Crushed natural molybdenum disulfide ( _MoS2 ) contains many particles with particle sizes exceeding 1 μm, and the use of only the molybdenum disulfide particles (a2) provides a small lubricating effect per added weight. However, by using molybdenum disulfide particles (a1) having a small median diameter _D50 of primary particle size in combination with molybdenum disulfide particles (a2) having a large median diameter _D50 of primary particle size, the small molybdenum disulfide particles (a1) enter between the relatively large molybdenum disulfide particles (a2), smoothing the surface of the coating film or sliding member. Therefore, when an external force is applied by sliding or the like, it is possible to suppress the detachment of the molybdenum disulfide particles (a1) and the molybdenum disulfide particles (a2).

The median diameter _D50 of the primary particles of the molybdenum disulfide particles (a2) is not particularly limited, and may be, for example, 600 nm or more and 500 μm or less, 1 μm or more and 50 μm or less, or 1 μm or more and 20 μm or less.

The shape of the primary particles of the molybdenum disulfide particles (a2) is not particularly limited, but may be, for example, spherical, polygonal, or amorphous. The primary particles of the molybdenum disulfide particles (a2) may have a different shape from the primary particles of the molybdenum disulfide particles (a1) which have a lamellar shape.

Molybdenum disulfide, which is generally used as a lubricant, is a hexagonal solid lubricant and has a crystal structure that is substantially composed of a 2H crystal structure. The molybdenum disulfide particles (a2) of this embodiment may differ from the molybdenum disulfide particles (a1) in that they do not contain a 3R crystal structure and are substantially composed of a 2H crystal structure.

When the solid lubricant (A) contains molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2), the content ratio of the molybdenum disulfide particles (a1) to the molybdenum disulfide particles (a2) ((a1):(a2)) is preferably 1:0 to 1:20 by mass, and more preferably 1:1 to 1:15. By making the content ratio of the molybdenum disulfide particles (a1) to the molybdenum disulfide particles (a2) 1:0 to 1:20, the surfaces of the coating film and the sliding parts are made smoother, and high lubricating properties and sealing properties can be obtained.

The solid lubricant (A) may contain molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2) as described above, or may consist of molybdenum disulfide particles (a1). When the solid lubricant (A) consists of molybdenum disulfide particles (a1), it is possible to maintain excellent lubricating properties and sealing properties over a long period of time while increasing the lubricating effect per added mass.

When the total mass of the composition is taken as 100 mass%, the content of the solid lubricant (A) is preferably 0.5 mass% or more and 30 mass% or less, more preferably 0.5 mass% or more and 20 mass% or less, and even more preferably 0.5 mass% or more and 10 mass% or less. By having the content of the solid lubricant (A) be 0.5 mass% or more and 30 mass% or less, it is possible to ensure good manufacturability of the coating film and sliding members while increasing the lubricating effect per added weight.

[resin]
The composition of this embodiment may contain a resin. The resin is not particularly limited as long as it has a binder function to disperse or fix the solid lubricant (A). For example, when the composition is used for a coating film, it is preferable to contain one or more resins selected from epoxy resins, phenol resins, polyamide resins, polyimide resins, and polyamideimide resins. Among these, from the viewpoints of heat resistance, chemical resistance, and adhesion to the coated member, it is more preferable to contain one or more resins selected from polyamide resins, polyimide resins, and polyamideimide resins, and polyamide resins and polyamideimide resins are even more preferable. In addition, in this embodiment, the resin used for the sliding member may be one or more resins selected from fluorine-based resins such as polyester resins, polyether resins, polyphenylene sulfide resins, and polytetrafluoroethylene, in addition to the above resins.

[Solid Lubricant (B)]
The composition of the present embodiment may further contain a solid lubricant (B). The solid lubricant (B) may contain, for example, one or more selected from carbon-based solid lubricants and fluorine-based solid lubricants. Examples of carbon-based solid lubricants include graphite, fullerene, carbon nanotubes, carbon nanofibers, graphite, and graphene, and one or more of these may be used. Examples of fluorine-based solid lubricants include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, and trichlorotrifluoroethylene, and one or more of these may be used. When the solid lubricant (B) further contains one or more selected from carbon-based solid lubricants and fluorine-based solid lubricants, the lubrication properties can be further improved.

[Antioxidant (C)]
The composition of the present embodiment may further contain an antioxidant (C). The antioxidant (C) may contain a metal oxide-based antioxidant. An example of the metal oxide-based antioxidant is antimony trioxide (Sb ₂ O ₃ ). By further containing a metal oxide-based antioxidant, particularly antimony trioxide, in the composition, oxidation of molybdenum disulfides (a1) and (a2) can be suppressed, and the friction coefficient can be stabilized even during long-term use.

[solvent]
The composition of the present embodiment may further contain a solvent. The solvent is not particularly limited, but preferably contains one or more selected from NMP (N-methyl-2-pyrrolidone), GBL (γ-butyrolactone), CPN (cyclopentanone), NEP (N-ethyl-2-pyrrolidone), 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, butyl cellosolve, and MEK (methyl ethyl ketone). By containing one or more of the specific compounds, the solubility of the resin, particularly the polyamideimide resin, can be improved, and the drying property can be controlled to ensure film-forming property.

When producing the composition, for example, the solid lubricant (a1) and various resins, solvents, liquid lubricants, and other media according to the application are stirred and mixed with a stirrer, and the resulting mixture is dispersed using a dispersing machine such as a bead mill or a three-roll mill. A solid lubricant (B) may be further added, and either or both of the solid lubricant (B) and the antioxidant (C) may be further added. Furthermore, various commonly used additives such as dispersants and antifoaming agents may be blended as necessary.

The composition can be diluted as necessary with a diluting solvent such as a nitrogen-containing solvent, a hydrocarbon solvent, or a ketone solvent, and applied or coated onto the surface of a sliding component to form a lubricating coating. The dilution ratio with the solvent can be adjusted to an appropriate viscosity depending on the method of application or coating to the part. Alternatively, a sliding component can be obtained by impregnating a fibrous or porous molded body with a composition containing a liquid medium.

<Coating film>
The coating film of the present embodiment is a cured product of the above composition. The coating film is formed on a sliding member, a slidable member disposed opposite the sliding member, or both of them.
Fig. 1 is a cross-sectional view showing an example of the structure of a coating film which is a cured product of a coating composition. As shown in Fig. 1, a coating film 100A has a base layer 10 formed on a substrate 101 and a solid lubricant 20 dispersed in the base layer 10. The base layer 10 corresponds to the resin in the coating composition, and the solid lubricant 20 corresponds to the solid lubricant (A) in the coating composition.
In this embodiment, the solid lubricant 20 includes a solid lubricant 21 and a solid lubricant 22. The solid lubricant 21 has an aspect ratio, which is the ratio of the median diameter _D50 of the primary particles to the thickness, of 2 or more and 110 or less, and the median diameter _D50 is 50 nm or more and 500 nm or less. The solid lubricant 22 has a primary particle median diameter _D50 of, for example, 600 nm or more and 500 μm or less. The solid lubricant 21 corresponds to the solid lubricant (a1) in the coating composition, and the solid lubricant 22 corresponds to the solid lubricant (a2).

In the coating film 100A, a part of the solid lubricant 21 and a part of the solid lubricant 22 protrude from the surface of the base layer 10. The small-particle-size solid lubricant 21 is inserted between the relatively large-particle-size solid lubricant 22, which forms minute irregularities on the surface of the base layer 10 and smoothes the surface of the coating film 100A. Therefore, when the sliding member 102 slides, the solid lubricant 21 protruding from the surface of the coating film 100A is unlikely to come off due to sliding, and frictional wear occurring between the coating film 100A and the sliding member 102 can be sufficiently reduced. In addition, when the liquid-based lubricant 103 is applied on the coating film 100A, since the surface of the coating film 100A is smoothed, the liquid-based lubricant 103 is easily retained on the coating film 100A, and the effect of reducing frictional wear due to the liquid-based lubricant 103 can be easily obtained.

The coating film 100A is obtained by applying or coating the above-mentioned coating composition to one or both sliding surfaces of members that slide against each other by relative movement. As the above-mentioned application or coating method, known methods such as spray application, roll application, application by pad method, dip coating, screen printing, offset printing, bar coating, and spin coating can be used, but from an industrial perspective, application by spray application or screen printing is preferred.

Fig. 2 is a cross-sectional view showing another example of the configuration of a coating film which is a cured product of a coating composition. As shown in Fig. 2, the coating film 100B has a base layer 10 formed on a substrate 101 and a solid lubricant 20 dispersed in the base layer 10. In this embodiment, the solid lubricant 20 contains a solid lubricant 21 but does not contain a solid lubricant 22. The configuration of the coating film 100B is the same as that of the coating film 100A, except for the solid lubricant 20.
In this way, when the solid lubricant 20 is composed of the solid lubricant 21, a part of the solid lubricant 21 protrudes from the surface of the base layer 10 in the coating film 100B. The small particle size solid lubricant 21 protrudes from the surface of the base layer 10, forming minute irregularities on the surface of the base layer 10, and the surface of the coating film 100B is smoothed. Therefore, when the sliding member 102 slides, the solid lubricant 21 protruding from the surface of the coating film 100B is unlikely to come off due to sliding, and the friction wear generated between the coating film 100B and the sliding member 102 can be sufficiently reduced. In addition, when the liquid lubricant 103 is applied on the coating film 100B, since the surface of the coating film 100B is smoothed, the liquid lubricant 103 is easily retained on the coating film 100B, and the effect of reducing friction wear by the liquid lubricant 103 can be easily obtained.

<Sliding Member>
The sliding member has the coating film at one or more parts. There is no particular limitation as long as the sliding member is a member that slides against each other by relative movement and has a part where the coating film can be formed on the sliding surface. The sliding member is typically a piston of an internal combustion engine such as a gasoline engine, a cylinder in an engine block, an intake/exhaust valve in a cylinder head, etc. When the sliding member is a piston, the part where the coating film is formed is, for example, a skirt part, a ring groove, a pin hole, etc. In addition, the sliding member may be a member other than an internal combustion engine member, for example, a mechanical element such as a bearing mechanism or a fastening member. When the sliding member is a bearing mechanism, the coating film can be provided on either or both of the shaft and the bearing. When the sliding member is a fastening member such as a bolt or a nut, the coating film can be provided on, for example, either or both of the male thread and the female thread of the screwing part.

The molybdenum disulfide particles (a1) can be prepared as a coating composition, applied to a sliding part, and used as a sliding member by forming a coating film, but can also be used as a sliding member that requires sealing properties at moving parts. The molybdenum disulfide particles (a1) have a characteristic shape that makes them difficult to protrude from the coating surface as described above, or have the effect of smoothing the coating surface, thereby reducing the gap between the coating film and the sliding member at the sliding part, thereby improving the sealing properties as well as the lubricity. Due to this characteristic, they can be suitably used as sliding members in moving parts where prevention of leakage of liquid or gas and pressure loss is required. In such a case, it is more preferable that such sliding members are not liquid or oily, but are molded bodies having a certain shape. Examples of such sliding members include shaft seal devices for rotating shafts, and more specifically, components and devices such as mechanical seals and gland packings. When the molybdenum disulfide particles (a1) are used in such a sliding member, a coating film may be formed on the surface of the sliding portion as described above, or the molybdenum disulfide particles (a1) may be used as a component uniformly present inside the sliding member. That is, in the sliding member of another embodiment of the present invention, at least a part of the sliding surface has a solid lubricant (A) containing molybdenum _disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter D50 (nm) of the primary particles to the thickness (nm), in the range of 2 to 110, and the median diameter _D50 being 50 nm to 500 nm.

When a solid lubricant (A) containing molybdenum disulfide particles (a1) is present inside the sliding member, lubrication and sealing properties can be maintained even if the sliding member wears out due to the presence of the molybdenum disulfide particles (a1) contained in the solid lubricant (A). The surface layer of the molybdenum disulfide (a1) present on the surface of the sliding part or in its vicinity is cleaved by the external force of the sliding part so that the cleavage plane is parallel to the sliding direction, and the cleaved molybdenum disulfide pieces bleed out and intervene to better fill the gap between the coating and the sliding member, and the labyrinth effect also works, providing good sealing properties. Such sliding members can be made by mixing the solid lubricant (A) of this application with the resin or the like that forms the molded body in advance, pelletizing it if necessary, and then injection molding it into the desired shape, or by immersing the molded body, if it is a fibrous or porous molded body that can be impregnated with a liquid component, in a liquid composition, entraining it in a liquid medium, and impregnating the molded body with the liquid medium to form a sliding member.

<Method of producing molybdenum disulfide particles>
Next, a method for producing the molybdenum disulfide particles (a1) in this embodiment will be described.
The molybdenum disulfide particles (a1) can be produced, for example, by heating molybdenum trioxide particles having an average primary particle size of 2 nm to 1000 nm in the presence of a sulfur source at a temperature of 200 to 1000° C.

The average particle size of primary particles of molybdenum trioxide particles refers to the average primary particle size of 50 randomly selected primary particles, when molybdenum trioxide particles are photographed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and the long axis (the Feret diameter of the longest observed part) and short axis (the short Feret diameter perpendicular to the Feret diameter of the longest part) of the smallest unit particle (i.e., primary particle) that constitutes the aggregate in the two-dimensional image are measured, and the average value is taken as the primary particle size.

In the method for producing molybdenum disulfide particles, the average particle size of the primary particles of the molybdenum trioxide particles is preferably 1 μm or less. From the viewpoint of reactivity with sulfur, it is more preferably 600 nm or less, even more preferably 400 nm or less, and particularly preferably 200 nm or less. The average particle size of the primary particles of the molybdenum trioxide particles may be 2 nm or more, 5 nm or more, or 10 nm or more.

The molybdenum trioxide particles used in the production of the molybdenum disulfide particles are preferably composed of an aggregate of primary particles containing a β crystal structure of molybdenum trioxide. The molybdenum trioxide particles have a better reactivity with sulfur than conventional molybdenum trioxide particles that are composed only of α crystals as a crystal structure, and since they contain the β crystal structure of molybdenum trioxide, they can increase the conversion rate R _C to _MoS2 in the reaction with a sulfur source.

The β-crystal structure of molybdenum trioxide can be confirmed by the presence of a peak (2θ: near 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) that belongs to the (011) plane of the β-crystal of _MoO3 in a profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source. The α-crystal structure of molybdenum trioxide can be confirmed by the presence of a peak (2θ: near 27.32°, No. 166363 (Inorganic Crystal Structure Database (ICSD)))) that belongs to the (021) plane of the α _- crystal of MoO3.

In the profile obtained by powder X-ray diffraction (XRD) using Cu-Kα radiation as an X-ray source, the molybdenum trioxide particles preferably have a ratio ( _β (011)/α(021) ₎ of the peak intensity attributable to the (011) plane of a β crystal of MoO3 to the peak intensity attributable to the (021) plane of an α crystal of MoO3 (2θ: near 27.32°_No. 166363 (Inorganic Crystal Structure Database (ICSD))) of 0.1 or more.

For the peak intensity attributable to the (011) plane of the β crystal of _MoO3 and the peak intensity attributable to the (021) plane of the α crystal of _MoO3 , the maximum intensity of the peak is read, and the ratio (β(011)/α(021)) is calculated.

In the molybdenum trioxide particles, the ratio (β(011)/α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

The β-crystalline structure of molybdenum trioxide can also be confirmed by the presence of peaks at wave numbers of 773, 848 cm ⁻¹ and 905 cm ⁻¹ in the Raman spectrum obtained from Raman spectroscopy. The α-crystalline structure of molybdenum trioxide can be confirmed by the presence of peaks at wave numbers of 663, 816 cm ⁻¹ and 991 cm ⁻¹ .

The average particle size of the primary particles of the molybdenum trioxide powder may be 5 nm or more and 2000 nm or less.

Sulfur sources include, for example, sulfur and hydrogen sulfide, which may be used alone or in combination.

The method for producing the molybdenum disulfide particles may include heating molybdenum trioxide particles consisting of an aggregate of primary particles containing the β crystal structure of molybdenum trioxide at a temperature of 100 to 800°C in the absence of a sulfur source, and then heating the molybdenum trioxide particles at a temperature of 200 to 1000°C in the presence of a sulfur source.

The heating time in the presence of the sulfur source may be any time that allows the sulfurization reaction to proceed sufficiently, and may be 1 to 20 hours, 2 to 15 hours, or 3 to 10 hours.

In the method for producing molybdenum disulfide particles, the ratio of the amount of S in the sulfur source to the amount of _MoO3 in the molybdenum trioxide particles is preferably such that the sulfurization reaction proceeds sufficiently. The amount of S in the sulfur source is preferably 450 mol% or more, more preferably 600 mol% or more, and even more preferably 700 mol% or more, relative to 100 mol% of the amount of MoO3 in the molybdenum _trioxide particles. The amount of S in the sulfur source may be 3000 mol% or less, 2000 mol% or less, or 1500 mol% or less, relative to 100 mol% of the amount of _MoO3 in the molybdenum trioxide particles.

In the method for producing molybdenum disulfide particles, the heating temperature in the presence of the sulfur source may be any temperature at which the sulfurization reaction proceeds sufficiently, and is preferably 320°C or higher, more preferably 340°C or higher, and even more preferably 360°C or higher. The heating temperature may be 320 to 1000°C, 340 to 1000°C, or 360 to 500°C. By lowering the heating temperature, the degree of crystallinity of the molybdenum disulfide particles decreases, and the proportion of amorphous phase can be increased.

In the method for producing molybdenum disulfide particles, the obtained molybdenum disulfide particles may be cooled and then heated as a post-treatment, if necessary. In this heat treatment, it is preferable to sinter the molybdenum disulfide particles, for example, in an inert atmosphere. By heating and sintering the obtained molybdenum disulfide particles, crystallization of the amorphous phase is promoted and the degree of crystallinity is improved. In addition, as the degree of crystallinity is improved, new 2H crystal structures and 3R crystal structures are generated, and the abundance ratio of the 2H crystal structure and the 3R crystal structure changes. When reheating is performed as a post-treatment in this manner, the crystallinity of the molybdenum disulfide particles is increased and the ease of peeling due to lubrication of each layer is reduced to a certain extent, but the abundance ratio of the 3R crystal structure, which contributes to improving the friction characteristics, increases, so that the friction characteristics can be improved compared to the case of only the 2H crystal structure. In addition, the abundance ratio of the 2H crystal structure and the 3R crystal structure can be adjusted by changing the temperature at which the obtained molybdenum disulfide particles are heated.

When the obtained molybdenum disulfide particles are heated and sintered at a predetermined temperature or higher, changing the amorphous phase into a 2H crystal structure, a second crystal phase composed of crystallites with a crystallite size of 20 nm or less, preferably 10 nm or less, is newly generated. In this case, if there are crystallites in the 2H crystal structure with a crystallite size of 10 nm or less before the molybdenum disulfide particles are heated, the crystallites grow to a crystallite size of 100 nm or more after the molybdenum disulfide particles are heated, and a first crystal phase composed of these grown crystallites is generated.

As described above, it is presumed that, among the crystal structures of molybdenum disulfide particles, the crystal phase constituting the 3R crystal structure contributes to improving frictional characteristics, while the first crystal phase constituting the 2H crystal structure does not contribute to frictional characteristics or may be a factor in reducing frictional characteristics. Therefore, from the viewpoint of increasing the abundance ratio of the crystal phase of the 3R crystal structure while keeping the abundance ratio of the first crystal phase of the 2H crystal structure as low as possible, the heating temperature of the molybdenum disulfide particles in the post-treatment is preferably 500 to 900°C, and more preferably 500 to 800°C.

In addition, the heating rate of the molybdenum disulfide particles in the post-treatment is preferably 1°C/min or more and 50°C/min or less, and more preferably 2°C/min or more and 10°C/min or less.

In the method for producing molybdenum disulfide particles, the molybdenum trioxide particles preferably have a content of _MoO3 of 99.5% or more as measured by X-ray fluorescence (XRF). This makes it possible to increase the conversion rate R _C to _MoS2 , and to obtain high-purity molybdenum disulfide with no risk of generating disulfides derived from impurities and with good storage stability.

The molybdenum trioxide particles preferably have a specific surface area, as measured by the BET method, of 10 m ² /g to 150 m ² /g.

In the molybdenum trioxide particles, the specific surface area is preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and even more preferably 30 m ² /g or more, in order to improve reactivity with sulfur. In the molybdenum trioxide particles, the specific surface area is preferably 150 m ² /g or less, in order to facilitate production, and may be 90 m ² /g or less, or may be 80 m ² /g or less.

The molybdenum trioxide particles preferably have a ratio (I/II) of the peak intensity I due to Mo-O to the peak intensity II due to Mo-Mo in the radial distribution function obtained from an extended X-ray absorption fine structure (EXAFS) profile at the molybdenum K absorption edge, greater than 1.1.

The maximum intensities of the peak intensity I due to Mo-O and the peak intensity II due to Mo-Mo are read, and the ratio (I/II) is calculated. The ratio (I/II) is considered to be an indicator of whether a β crystal structure of _MoO3 is obtained in the molybdenum trioxide particles, and the larger the ratio (I/II), the better the reactivity with sulfur.

In the molybdenum trioxide particles, the ratio (I/II) is preferably 1.1 to 5.0, may be 1.2 to 4.0, or may be 1.2 to 3.0.

(Method of producing molybdenum trioxide powder)
The method for producing the molybdenum trioxide powder used in the production method of the present embodiment includes vaporizing a molybdenum oxide precursor compound to form molybdenum trioxide vapor, and cooling the molybdenum trioxide vapor. For example, the production method disclosed in Patent Document A or Patent Document B below can be mentioned.
[Patent Document A] International Publication No. 2021/060375 [Patent Document B] International Publication No. 2022/202757

The molybdenum disulfide particles (a1) of this embodiment can be produced by the above-mentioned method for producing molybdenum disulfide particles.
Moreover, by the method for producing molybdenum trioxide powder, it is possible to produce molybdenum trioxide particles suitable for producing the molybdenum disulfide particles (a1) of this embodiment.

The following describes examples of the present invention. The present invention is not limited to the following examples.

[Synthesis Example 1]
A calcination furnace equivalent to a heat-resistant container, a cooling pipe provided with an outside air supply port, and a dust collector for recovering molybdenum oxide were prepared, a mixture of 1 kg of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) and 2 kg of aluminum hydroxide (manufactured by Wako Pharmaceutical Co., Ltd.) was charged into a sheath, the calcination furnace, the cooling pipe, and the dust collector were connected, and the temperature in the calcination furnace was raised to 1300°C and held for 10 hours to obtain α-alumina and to vaporize molybdenum trioxide in the calcination furnace. Next, air in a large excess compared to the amount of molybdenum trioxide was blown through the outside air supply port of the cooling pipe to the molybdenum trioxide vaporized from the exhaust port of the incinerator at a cooling rate of 2000°C/sec, and the molybdenum trioxide was rapidly cooled to 200°C or less to be powdered, and 890 g of molybdenum trioxide was obtained in the dust collector.

[Synthesis Example 2]
Into a magnetic crucible, 10.00 g (69.4 mmol) of molybdenum trioxide prepared in Synthesis Example 1 and 11.11 g (347 mmol) of sulfur powder (manufactured by Kanto Chemical) were added, and mixed with a stirring rod so that the powder was uniform. After mixing, the crucible was covered with a lid and placed in a high-temperature tubular furnace (manufactured by Yamada Denki, TSS type) for firing. The firing conditions were that the temperature was raised from room temperature of 25° C. at a rate of 5° C./min, and after reaching 500° C., the temperature was maintained for 4 hours. During the firing process, nitrogen gas was blown at 0.2 ml/min. After that, the temperature in the furnace was lowered by natural cooling to obtain molybdenum disulfide particles.

The specific surface area of the molybdenum disulfide particles obtained in Synthesis Example 2 was measured by the BET method using a high-precision gas adsorption measurement device (MICROTRAC, BELSORP-MINI), and was found to be 64.5 m ² /g. The particle size distribution of the molybdenum disulfide particles was measured using a nanoparticle size measurement device (MICROTRAC, MICROTRAC WAVE II) to determine the median diameter D ₅₀ , which was found to be 258 nm. Furthermore, the thickness was measured using an atomic force microscope (Oxford Instruments, Cypher-ES). The thickness measurement result was 2.7 nm. The aspect ratio was calculated to be 95.7 from the median diameter D 50 and the thickness.

[Example 1]
8.0% by mass of polyamideimide resin (Viromax HR11NN, manufactured by Toyobo Co., Ltd.) was added with 8.0% by mass of molybdenum disulfide particles (a1) obtained in Synthesis Example 2, 4.0% by mass of antimony trioxide (manufactured by Wako Pure Chemical Industries, Ltd.) reagent, 60.0% by mass of NMP (manufactured by Wako Pure Chemical Industries, Ltd.) reagent, and 20.0% by mass of MEK (manufactured by Wako Pure Chemical Industries, Ltd.) reagent, and then a dispersion treatment was performed to obtain a coating composition (1) containing molybdenum disulfide particles (a1). The obtained coating composition (1) was applied to a thickness of 1.0 mm on a steel plate by a spray method, and then sintered at 230 ° C. for 1 hour to obtain an evaluation coating film (1A).

[Example 2]
4.0% by mass of molybdenum disulfide particles (a1) obtained in Synthesis Example 2, 4.0% by mass of dry-ground molybdenum disulfide particles (a2) (manufactured by Climax, median diameter _D50 : 10.0 μm), 4.0% by mass of antimony trioxide, 60.0% by mass of NMP, and 20.0% by mass of MEK were added to 8.0% by mass of polyamideimide resin, and then a dispersion treatment was performed to obtain a coating composition (2) containing molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2). The obtained coating composition (2) was applied to a steel plate and dried in the same manner as in Example 1 to obtain an evaluation coating (2A).

[Example 3]
To 8.0 mass% of polyamideimide resin, 0.5 mass% of the molybdenum disulfide particles (a1) obtained in Synthesis Example 2, 7.5 mass% of the molybdenum disulfide particles (a2), 4.0 mass% of antimony trioxide, 60.0 mass% of NMP, and 20.0 mass% of MEK were added, and then a dispersion treatment was carried out to obtain a coating composition (3) containing the molybdenum disulfide particles (a1) and the molybdenum disulfide particles (a2). The obtained coating composition (3) was applied to a steel plate and dried in the same manner as in Example 1 to obtain an evaluation coating (3A).

[Comparative Example 1]
8.0% by mass of molybdenum disulfide particles (a2), 4.0% by mass of antimony trioxide, 60.0% by mass of NMP, and 20.0% by mass of MEK were added to 8.0% by mass of polyamideimide resin, and then a dispersion treatment was performed to obtain a coating composition (4) containing molybdenum disulfide particles (a2). The obtained coating composition (4) was spray-coated on a steel plate to a thickness of 1.0 mm, and then sintered at 230° C. for 1 hour to obtain an evaluation coating (4A).

[Example 4]
The steel plate on which the evaluation coating film (1A) obtained in Example 1 was formed was placed on the moving side of the ball-on-disk tester, and a SUJ2-7/32 inch ball was placed on the stationary side. The number of slides until the terminal friction reached μ=0.3 was measured at a sliding speed of 300 rpm in a normal temperature, dry atmosphere with a sliding speed of 300 rpm and a sliding diameter of 24.5 mm and a load of 1 kgf. The number of slides was 9670. The results are shown in Table 1 and FIG. 3.

[Example 5]
The number of sliding movements was measured in the same manner as in Example 4, except that the steel plate on which the evaluation coating film (2A) obtained in Example 2 was formed was placed on the moving side of the ball-on-disk tester. The number of sliding movements was 7260. The results are shown in Table 1 and FIG. 3.

[Example 6]
The number of sliding strokes was measured in the same manner as in Example 4, except that the steel plate on which the evaluation coating film (3A) obtained in Example 3 was formed was placed on the moving side of the ball-on-disk tester. The number of sliding strokes was 6908. The results are shown in Table 1 and FIG. 3.

[Comparative Example 2]
The number of sliding movements was measured in the same manner as in Example 4, except that the steel plate on which the evaluation coating film (4A) obtained in Comparative Example 1 was formed was placed on the moving side of the ball-on-disk tester. The number of sliding movements was 2227. The results are shown in Table 1 and FIG. 3.
The results of the paper vertical sliding test for Examples 4 to 6 and Comparative Example 2 are shown in Table 1 and FIG.

As shown in Table 1 and Figure 3, in all of Examples 4 to 6, when the solid lubricant (A) of the coating film (1A) to (3A) contains molybdenum disulfide particles (a1), and the aspect ratio of the molybdenum disulfide particles (a1), which is the ratio of the median diameter _D50 (nm) of the primary particles to the thickness (nm), is in the range of 2 to 110, and the median diameter _D50 is 50 nm to 500 nm, the number of slides until the terminal friction reaches μ = 0.3 in the paper vertical sliding test is 6500 times or more, and it is found that it shows excellent friction characteristics and durability. In particular, in Example 1, when the solid lubricant (A) of the coating film (1A) is made of molybdenum disulfide particles (a1), the number of slides until the terminal friction reaches μ = 0.3 in the paper vertical sliding test is 9500 times or more, and it is found that it shows extremely excellent friction characteristics and durability.

On the other hand, in Comparative Example 2, the solid lubricant (A) of the coating film (4A) was composed of molybdenum disulfide particles (a2) and did not contain molybdenum disulfide particles (a1). Therefore, in the paper vertical sliding test, the number of sliding cycles until the terminal friction reached μ = 0.3 was less than 2,500, and the friction characteristics and durability were inferior.

[Example 7]
A pin coated with the coating composition (1) prepared in Example 1 after SB#220 Mn phosphate treatment in the same manner as in Example 1 and dried to a thickness of 12 um and a block coated with the coating composition (1) prepared in Example 1 after SB#220 Mn phosphate treatment in the same manner as in Example 1 were attached to a FALEX sliding tester, and the time until the terminal friction reached μ = 0.2 was measured. The clamping load of the pin by the block was 1.2 kN for 180 seconds, then 1.8 kN for 60 seconds, and then 2.6 kN for 60 seconds, so that the final load was 765 lbs. The endurance time was 510 minutes. The results are shown in Table 2 and FIG. 4.

[Example 8]
The FALEX test was carried out in the same manner as in Example 7, except that the coating composition (2) prepared in Example 2 was used in the FALEX sliding tester. The durability time was 537 minutes. The results are shown in Table 2 and FIG. 4.

[Comparative Example 3]
A FALEX test was carried out in the same manner as in Example 7, except that the coating composition (4) prepared in Comparative Example 1 was used in the FALEX sliding tester. The durability time was 347 minutes. The results are shown in Table 2 and FIG. 4.

As shown in Table 2 and FIG. 4, in any of Examples 7 to 8, when the solid lubricant (A) of the coating films (1B) to (2B) contains molybdenum disulfide particles (a1), and the aspect ratio of the molybdenum disulfide particles (a1), which is the ratio of the median diameter D ₅₀ (nm) of the primary particles to the thickness (nm), is in the range of 2 to 110 and the median diameter D ₅₀ is 50 nm to 500 nm, the time until the terminal friction reaches μ = 0.2 in the FALEX sliding test is 500 minutes or more, and it is shown to exhibit excellent friction characteristics and durability.

On the other hand, in Comparative Example 3, the solid lubricant (A) of the coating film (4B) was composed of molybdenum disulfide particles (a2) and did not contain molybdenum disulfide particles (a1), so in the FALEX sliding test, the time until the terminal friction reached μ = 0.2 was less than 350 minutes, and the friction characteristics and durability were inferior.

[Example 9]
8.0% by mass of polyamideimide resin was mixed with 8.0% by mass of molybdenum disulfide particles (a1), 2.0% by mass of graphite (manufactured by Wako Pure Chemical Industries, Ltd.), 1.5% by mass of PTFE (manufactured by Daikin Corporation, Polyflon PTFE D-310), 0.5% by mass of antimony trioxide, 60% by mass of NMP, and 20% by mass of MEK, and then the mixture was subjected to a dispersion treatment to obtain a coating composition (5) containing molybdenum disulfide particles (a1). The obtained coating composition (5) was applied to a thickness of 1.0 mm on a steel plate by a spray method, and then sintered at 230° C. for 1 hour to obtain an evaluation coating (5A).

[Example 10]
4.0% by mass of molybdenum disulfide particles (a1), 4.0% by mass of molybdenum disulfide particles (a2), 2.0% by mass of graphite, 2.0% by mass of PTFE, 60% by mass of NMP, and 20% by mass of MEK solvent were added to 8.0% by mass of polyamideimide resin, and then the mixture was subjected to a dispersion treatment to obtain a coating composition (6) containing molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2). The obtained coating composition (6) was applied to a steel plate and dried in the same manner as in Example 9 to obtain an evaluation coating (6A).

[Example 11]
0.5% by mass of molybdenum disulfide particles (a1), 7.5% by mass of molybdenum disulfide particles (a2), 2.0% by mass of graphite, 1.5% by mass of PTFE, 0.5% by mass of antimony trioxide, 60% by mass of NMP, and 20% by mass of MEK were added to 8.0% by mass of polyamideimide resin, and then the mixture was subjected to a dispersion treatment to obtain a coating composition (7) containing molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2). The obtained coating composition (7) was applied to a steel plate and dried in the same manner as in Example 9 to obtain an evaluation coating (7A).

[Comparative Example 4]
8.0% by mass of molybdenum disulfide particles (a2), 2.0% by mass of graphite, 1.5% by mass of PTFE, 0.5% by mass of antimony trioxide, 60% by mass of NMP, and 20% by mass of MEK were added to 8.0% by mass of polyamideimide resin, and then the mixture was subjected to a dispersion treatment to obtain a coating composition (8) containing molybdenum disulfide particles (a2). The obtained solution was applied to a steel plate and dried in the same manner as in Example 9 to obtain an evaluation coating (8A).

[Example 12]
The steel plate with the evaluation coating film (5A) obtained in Example 9 formed thereon was placed on the moving side of a Kawamura type reciprocating friction tester, and a SUJ2-7/32 inch ball was placed on the stationary side. The number of slides until the terminal friction reached μ=0.3 was measured under conditions of initial speed of 9 rpm, sliding speed of 240 rpm, stroke of 10 mm, load of 3 kgf, and room temperature dry atmosphere. The number of slides was 1801. The results are shown in Table 3 and FIG. 5.

[Example 13]
The number of sliding strokes was measured in the same manner as in Example 12, except that the steel plate on which the evaluation coating film (6A) obtained in Example 10 was formed was placed on the moving side of the Kawamura-type reciprocating friction tester. The number of sliding strokes was 2789. The results are shown in Table 3 and FIG. 5.

[Example 14]
The number of sliding strokes was measured in the same manner as in Example 12, except that the evaluation coating film (7A) obtained in Example 11 was formed on the moving side of the Kawamura-type reciprocating friction tester and a steel plate was placed on it. The number of sliding strokes was 2513. The results are shown in Table 3 and FIG. 5.

[Comparative Example 5]
The number of sliding strokes was measured in the same manner as in Example 12, except that the steel plate coated with the evaluation coating film (8A) obtained in Comparative Example 4 was placed on the moving side of the Kawamura-type reciprocating friction tester. The number of sliding strokes was 1292. The results are shown in Table 3 and FIG. 5.

As shown in Table 3 and FIG. 5, in any of Examples 12 to 14, when the solid lubricant (A) of the coating films (5A) to (7A) contains molybdenum disulfide particles (a1), and the aspect ratio of the molybdenum disulfide particles (a1), which is the ratio of the median diameter D ₅₀ (nm) of the primary particles to the thickness (nm) of the molybdenum disulfide particles (a1), is in the range of 2 to 110 and the median diameter D ₅₀ is 50 nm to 500 nm, the number of sliding cycles until the terminal friction reached μ = 0.3 was 1,800 or more in the Kawamura type reciprocating friction test, and it was found that the coating films showed excellent friction characteristics and durability.

On the other hand, in Comparative Example 5, the solid lubricant (A) of the coating film (8A) was composed of molybdenum disulfide particles (a2) and did not contain molybdenum disulfide particles (a1). Therefore, in the Kawamura-type reciprocating friction test, the number of slides required to reach a terminal friction of μ = 0.3 was 1,300 or less, and the friction characteristics and durability were poor.

[Example 15]
A 50 mm x 90 mm x 2 mm plate was produced from 3 parts by mass of the molybdenum disulfide particles (a1) obtained in Synthesis Example 2 and 97 parts by mass of UBE NYLON POLYAMIDE6 1013NW8 manufactured by UBE Co., Ltd. under molding conditions of a kneading temperature of 280° C., a mold temperature of 70° C., a filling speed of 100 mm/s, and a pressure of 40 MPa using an injection molding machine PNX-603-5A manufactured by Nissei Plastic Industrial Co., Ltd. The obtained plate was sandwiched between a Separoth 55Z manufactured by Kiriyama Manufacturing Co., Ltd. connected to an aspirator, and the pressure was reduced. The aspirator was stopped at the lowest reduced pressure, and the pressure was measured after 1 minute and 2 minutes. Next, the plate was pressed against a bisque plate (surface roughness Ra = 7.2 μm, maximum 9.4 μm, minimum 4.4 μm, standard deviation 1.3 μm) made by firing high purity alumina, and rubbed 100 times in a circular motion (scratch treatment), and then sandwiched between a Kiriyama Seisakusho Separoth 55Z connected to an aspirator in the same manner as above, and the pressure was reduced. The aspirator was stopped at the lowest reduced pressure state, and the pressure was measured after 1 minute and 2 minutes. The results are shown in Table 4.

[Comparative Example 6]
The pressure was measured before and after the scratch treatment in the same manner as in Example 15, except that the molybdenum disulfide particles (a2) were used instead of the molybdenum disulfide particles (a1) in Example 15. The results are shown in Table 4.

As shown in Table 4, it can be seen that the plate of Example 15 maintains high airtightness even after scratching. On the other hand, it can be seen that the plate of Comparative Example 6 has poor airtightness after scratching. From this, it can be seen that the molded body using molybdenum disulfide particles (a1) is excellent as a sliding member that exhibits high sealing properties against pressure even when subjected to sliding motion.

10 Base layer 20 Solid lubricant 21 Solid lubricant 22 Solid lubricant 100A Coating film 100B Coating film 101 Substrate 102 Sliding member 103 Liquid lubricant

Claims (15)

Contains a solid lubricant (A),
The solid lubricant (A) comprises molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 (nm) to the thickness (nm) of the primary particles, in the range of 2 to 110, and the median diameter _D50 is 50 nm to 500 nm. Contains a resin and a solid lubricant (A),
The solid lubricant (A) comprises molybdenum disulfide particles (a1) having an aspect ratio, which is the ratio of the median diameter _D50 (nm) to the thickness (nm) of the primary particles, in the range of 2 to 110, and the median diameter _D50 is 50 nm to 500 nm. the solid lubricant (A) comprises the molybdenum disulfide particles (a1) and molybdenum disulfide particles (a2) having a primary particle median diameter _D50 of 600 nm or more and 500 μm or less,
The composition according to claim 1 or 2, wherein a content ratio ((a1):(a2)) of the molybdenum disulfide particles (a1) to the molybdenum disulfide particles (a2) is 1:0 to 1:20 in terms of mass ratio. The composition according to claim 3, wherein the molybdenum disulfide particles (a2) have a median particle diameter _D50 of 1 μm or more and 50 μm or less. The composition according to claim 1 or 2, wherein the solid lubricant (A) comprises the molybdenum disulfide particles (a1). The composition according to claim 1 or 2, wherein the content of the solid lubricant (A) is 0.5% by mass or more and 30% by mass or less when the total mass of the composition is 100% by mass. The composition according to claim 2, wherein the resin comprises one or more selected from the group consisting of epoxy resins, phenolic resins, polyamide resins, polyimide resins, and polyamideimide resins. Further comprising a solid lubricant (B),
The composition according to claim 1 or 2, wherein the solid lubricant (B) comprises one or more types selected from carbon-based solid lubricants and fluorine-based solid lubricants. Further comprising a solvent,
The composition according to claim 1 or 2, wherein the solvent comprises one or more selected from N-methyl-2-pyrrolidone, γ-butyrolactone, cyclopentanone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethylsulfoxide, butyl cellosolve, and methyl ethyl ketone. The composition according to claim 1 or 2, which contains antimony trioxide as an antioxidant. The composition according to claim 2, which is a coating composition. A coating film that is a cured product of the composition described in claim 11. A sliding member having the coating film according to claim 10. A sliding member having, on at least a part of a sliding surface, a solid lubricant (A) containing molybdenum _disulfide particles (a1) having an aspect ratio, which is the ratio of a median diameter D50 (nm) of primary particles to a thickness (nm), in the range of 2 to 110, and the median diameter _D50 being 50 nm to 500 nm. The sliding member according to claim 14, which is a molded body.

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