WO2019093142A1 - Lubrication system and liquid agent set for lubrication system - Google Patents

Abstract

The present invention provides a lubrication system and liquid agent set for the lubrication system, which are suitable for achieving low friction and low wear on a DLC sliding surface. The lubrication system according to the present invention uses a lubricant, which contains a relatively low concentration of nanodiamond particles, to lubricate the DLC sliding surface, which is made low-friction using an initial conformability agent containing a relatively high concentration of nanodiamond particles. The concentration of the nanodiamond particles in the initial conformability agent is preferably 0.01-2 mass%. The concentration of the nanodiamond particles in the lubricant is preferably 0.001 mass% or less.

Description

Lubrication system and fluid system set for lubrication system

The present invention relates to a lubrication system and a liquid agent set for the lubrication system. This application claims the priority based on Japanese Patent Application No. 2017-216443 which is a Japanese application dated November 9, 2017, and uses all the contents described in these applications.

Since hard carbon (diamond like carbon; DLC) films have high hardness and chemical stability, their application to the surface (sliding surface) of a sliding member is expected. The use of the DLC film as the sliding surface as described above is described, for example, in Patent Document 1 below.

The DLC film is a material which is chemically stable and high in hardness, but is disadvantageous for forming a surface with low friction and low wear. There is a need for a technique for forming a low friction and low wear surface on a sliding surface using a DLC film, and for reducing friction and wear for a long time.

JP 2012-246545 A

The present invention has been conceived under the above circumstances, and provides a lubrication system suitable for achieving low friction and low wear on a DLC sliding surface, and a liquid agent set for the lubrication system. Do.

According to a first aspect of the present invention, a lubrication system is provided. This lubrication system is a low friction diamond-like carbon (DLC) slide using an initial conformant containing relatively high concentrations of nanodiamond particles (hereinafter sometimes referred to as "ND particles"). For lubrication of the surface, a lubricant containing relatively low concentration of nanodiamond particles is used.

According to the findings of the present inventors, when water (pure) is used as a lubricant solution for the DLC sliding surface, a significant decrease is seen in the friction coefficient of the DLC sliding surface, so-called initial fit-in period and subsequent period Although wear on the sliding surface tends to be suppressed, the sliding surface friction coefficient tends to gradually increase after passing through the initial fitting period as described above. On the other hand, when a relatively high concentration ND particle water dispersion is used as the lubricating liquid agent for the DLC sliding surface, the sliding surface after the initial fitting period in which a significant drop is seen in the friction coefficient of the DLC sliding surface. Although the increase in the coefficient of friction tends to be suppressed, the wear on the sliding surface tends to progress. The higher the frequency of contact of the high-hardness ND particles with the DLC sliding surface, as with bulk diamond, the easier the wear progresses.

Unlike the above, in the above-described lubrication system according to the first aspect of the present invention, as the lubricating fluid agent for the DLC sliding surface, the initial sliding-adjusting agent having a relatively high concentration of ND particles is first used to Low surface friction can be achieved (initial contact period). Then, a lubricant having a relatively low concentration of ND particles is used as a lubricant for lubricating the DLC sliding surface, whereby the lubricating system of the DLC sliding surface is established and maintained. During the period of use of the above-mentioned initial conformity agent, ND particles and water in which carbon atoms are similarly arranged on the surface and are present at a relatively high concentration with respect to the DLC sliding surface on which carbon atoms are arranged on the surface It is thought that the wettability improvement and smoothing of the DLC sliding surface will advance at an early stage by the tribochemical reaction in the system where T and T act in a superimposed manner, and the DLC sliding surface tends to reduce the friction early. The present inventors have obtained the knowledge that During the period of use of the lubricant after the initial fitting period, the physical concentration of the ND particles on the DLC sliding surface is reduced because the concentration of the ND particles in the lubricant is relatively low. It is considered that the wettability and smoothness of the DLC sliding surface are maintained by the tribochemical reaction in a system in which water and relatively low concentration ND particles act on the DLC sliding surface in an overlapping manner. The inventors of the present invention have obtained the finding that the low friction property tends to be maintained while the wear of the DLC sliding surface is suppressed. The above findings are, for example, as shown in the following Examples and Comparative Examples.

As described above, the lubrication system according to the first aspect of the present invention is suitable for achieving low friction and low wear on the DLC sliding surface.

In the present invention, it is preferable that the ND particle concentration of the initial conformant is 0.01 to 2% by mass. The configuration is suitable for early formation of a surface having both smoothness and wettability by tribochemical reaction in a system in which ND particles are present on a DLC sliding surface.

In the present invention, the ND particle concentration of the lubricant is preferably 0.001% by mass or less. The composition is suitable for maintaining the smoothness and wettability of the DLC sliding surface formed by the initial bonding agent, and reducing friction and wear on the sliding surface.

In the present invention, the friction coefficient of the sliding surface measured in the following friction test is 0.05 or less, and the ball wear volume determined by the following wear amount calculation method after the friction test is 1.0 × 10 ^-4 mm It is preferable that it is ³ or less.
Friction test: First, a disk with a diameter of 30 mm and a thickness of 4 mm having a DLC sliding surface formed by a 3 μm thick DLC film on the surface and a 8 mm diameter with a DLC sliding surface formed by a 3 μm thick DLC film on the surface Using a ball-on-disk type sliding friction tester fitted with a ball, drop 1 mL of the initial bonding agent onto the DLC sliding surface of the disk, and place the ball in a load of 10 N While sliding 10 m relatively at a velocity of 10 mm / s in the circumferential direction of the disk, the coefficient of friction between the DLC sliding surfaces of the disk and the ball is measured during the sliding with a sliding distance of 0 to 10 m. The disc and ball are then removed from the sliding friction tester and ultrasonic cleaned. After washing, the ball may be wiped with acetone to remove nanodiamonds attached to the ball. Next, using a sliding friction tester fitted with a disc and a ball, 1 mL of a lubricant is dropped onto the DLC sliding surface of the disc, and then the ball is abutted with a load of 10 N while the disc circumference The sliding is carried out for a further 90 m at a speed of 10 mm / s relative to the direction, and the friction coefficient between the DLC sliding surface of the disc and the ball is measured during the sliding with a sliding distance of 10 to 100 m.
Wear amount calculation method: A circular wear mark formed on the ball subjected to the friction test is observed using a confocal microscope, and from the observation image, a uniformly smooth plane is obtained for the circular wear mark. Assuming that there is a diameter r (mm) is determined. And ball wear volume V (mm < ³ >) is computed by following formula (1) and Formula (2). H in Formula (1) is height (mm) of the ball crown of the said circular shaped abrasion mark, and is calculated | required from following formula (2). R in Formula (2) is a radius of the said ball, and is 4 (mm).

In the present invention, the ND particles may be an oxygen oxidation treatment of detonation nano diamond particles. According to the detonation method, it is possible to appropriately generate an ND having a primary particle size of 10 nm or less.

In the present invention, the zeta potential of ND may be negative.

In the present invention, the peak position attributed to the C = O stretching vibration in the FT-IR of the ND particles may be 1750 cm ⁻¹ or more.

In the present invention, the ND particles may be a hydrogen reduction treatment product of the detonation nano diamond particles. According to the detonation method, it is possible to appropriately generate an ND having a primary particle size of 10 nm or less.

In the present invention, the zeta potential of ND may be positive.

In the present invention, the peak position attributed to the C = O stretching vibration in the FT-IR of the ND particles may be less than 1750 cm ⁻¹ .

In the present invention, it is preferable that the lubricant base in the initial adjustor and lubricant is water.

According to a second aspect of the present invention, there is provided a fluid system set for a lubrication system. The liquid lubricant set for lubricating system comprises an initial blender containing nanodiamond particles with a concentration of 0.01 to 2% by mass, and a lubricant containing nanodiamond particles with a concentration of 0.001% by mass or less. The fluid system set for lubrication system according to the second aspect can be used for the lubrication system according to the first aspect. Using the liquid lubricant set for the lubricating system can form a low friction surface early on the DLC sliding surface, maintain the low friction surface, and is suitable for reducing wear on the sliding surface. That is, the lubricant system solution set is suitable for achieving low friction and low wear on the DLC sliding surface.

It is process drawing of an example of the manufacturing method of ND dispersion liquid which concerns on one Embodiment of this invention. It is a graph which shows the relationship between a sliding distance and a friction coefficient by the friction test of the comparative example 1. FIG. It is a graph which shows the relationship between a sliding distance and a friction coefficient by the friction test of Example 1. FIG. It is a graph which shows the relationship of a sliding distance and abrasion loss by the friction test of Example 1 and Comparative Example 1. It is a FT-IR spectrum of the ND particle manufactured in the example.

The lubrication system of the present invention comprises a relatively low concentration of ND particles in the lubrication of a low friction DLC sliding surface using an initial conformant containing a relatively high concentration of ND particles. Use the agent. The liquid agent set for lubricating system of the present invention is used for the lubricating system, and includes the above-mentioned initial conformant and lubricant. The sliding surface means, for example, a surface that rubs against and slides due to relative movement, such as a contact surface of a shaft and a bearing in a machine.

The initial adhesion agent is a solution (dispersion liquid) in which the ND particles are dispersed in a lubricant base. The ND particle concentration of the initial conformant is, for example, 0.01 to 2% by mass, preferably 0.03 to 1.0% by mass, more preferably 0.05 to 0.8% by mass, more preferably 0.07 to It is 0.6% by mass, more preferably 0.08 to 0.4% by mass. It is suitable for early formation of a surface having both smoothness and wettability by tribochemical reaction in a system in which ND particles exist on the sliding surface of the DLC, when the ND particle concentration of the initial conformant is in the above range .

The lubricant is a solution (dispersion liquid) in which ND particles are dispersed in a lubricant base. The ND particle concentration of the lubricant is, for example, 0.001 mass% or less (1.0 × 10 ⁻⁵ to 1.0 × 10 ⁻³ mass%), preferably 3.0 × 10 ⁻⁵ to 5.0 × 10 ^{It is -4} % by mass, more preferably 5.0 × 10 ^-5 to 3.0 × 10 ^-4 % by mass, more preferably 8.0 × 10 ^-5 to 2.0 × 10 ^-4 % by mass. When the ND particle concentration of the lubricant is in the above range, it is suitable for maintaining the smoothness and the wettability on the DLC sliding surface formed by the initial bonding agent, and reducing the friction and the wear on the sliding surface.

The ND particles contained in the initial conformant and lubricant are dispersed as primary particles in the initial conformant and lubricant separately from each other. The particle size of the ND primary particles is, for example, 10 nm or less. The lower limit of the particle size of primary particles of ND is, for example, 1 nm. The particle diameter D50 (median diameter) of the ND primary particles is, for example, 10 nm or less, preferably 9 nm or less, more preferably 8 nm or less, more preferably 7 nm or less, more preferably 6 nm or less. The particle size D50 of the ND primary particles can be measured, for example, by dynamic light scattering.

The ND particles are preferably detonation method ND particles (ND particles produced by detonation method). According to the detonation method, it is possible to appropriately generate an ND having a primary particle size of 10 nm or less.

The ND particles may be an oxygen oxidation treatment of detonation method ND particles. In the case of the oxidized oxidized product, the peak position attributed to CCO stretching vibration in the FT-IR of the ND particles tends to be 1750 cm ^-1 or more, and the zeta potential of the ND particles tends to be negative at this time. There is. The oxygen oxidation treatment of the detonation method ND particles is as described in the oxygen oxidation step in the production process described later.

Further, the ND particles may be a hydrogen reduction treatment product of the detonation method ND particles. In the case of the hydrogen reduction product, the peak position attributed to the C = O stretching vibration in the FT-IR of the ND particles tends to be less than 1750 cm ^−1, and the zeta potential of the ND particles at this time becomes positive. Tend. The hydrogen reduction treatment of the detonation method ND particles is as described in the hydrogen reduction treatment step in the production process described later.

The value when the so-called zeta potential of the ND particles is negative is, for example, -60 to -30 mV. For example, in the production process, as described later, by setting the temperature condition of the oxygen oxidation treatment to a relatively high temperature (for example, 400 to 450 ° C.), the negative zeta potential can be obtained for the ND particles. The value when the zeta potential is positive is, for example, 30 to 60 mV. For example, by performing a hydrogen reduction treatment step after an oxygen oxidation step as described later in the manufacturing process, it is possible to obtain a positive zeta potential for the ND particles.

The initial conformant and lubricant can be produced by mixing the ND dispersion obtained by the method described later with a desired component such as a lubricant base. The ND dispersion can be produced, for example, through a process including the following production process S1, purification process S2, oxygen oxidation process S3, and crushing process S4.

In the production step S1, nanodiamonds are produced, for example, by detonation. Specifically, first, a shaped explosive provided with an electric detonator is installed inside a pressure-resistant container for detonation, and in a state in which a predetermined gas and the used explosive coexist in the container, the container Seal the The container is, for example, made of iron, and the volume of the container is, for example, 0.5 to 40 m ³ . As an explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylene trinitroamine or hexogen (RDX) can be used. The mass ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40/60 to 60/40. The amount of explosive used is, for example, 0.05 to 2.0 kg. The above-mentioned gas sealed in the container together with the explosive used may have an atmospheric composition or may be an inert gas. From the viewpoint of producing nanodiamonds having a small amount of functional groups on the primary particle surface, the above-mentioned gas sealed in the container together with the used explosive is preferably an inert gas. That is, from the viewpoint of producing nanodiamond having a small amount of functional groups on the primary particle surface, detonation for producing nanodiamond is preferably carried out under an inert gas atmosphere. As the inert gas, for example, at least one selected from nitrogen, argon, carbon dioxide, and helium can be used.

Next, in the generation step S1, the electric detonator is detonated and the explosive is detonated in the container. A detonation refers to an explosion associated with a chemical reaction in which the flame surface on which the reaction occurs travels at a high speed beyond the speed of sound. At the time of detonation, the used explosive partially burns incompletely and liberated carbon is used as a raw material to generate nano diamond by the action of pressure and energy of shock wave generated by explosion. According to the detonation method, as described above, it is possible to appropriately generate nanodiamonds having a primary particle size of 10 nm or less. The nano diamond is a product obtained by the detonation method, which is very strongly due to the Coulomb interaction between the adjacent primary particles or crystallites in addition to the action of van der Waals force. Assemble and form a cohesive body.

Next, in the production step S1, the container and the inside thereof are cooled by leaving at room temperature, for example, for 24 hours. After this cooling, the nanodiamond crude product is recovered. For example, the nanodiamond crude product is recovered by scraping off the nanodiamond crude product adhering to the inner wall of the container (including the agglomerates and wrinkles of the nanodiamond produced as described above) with a spatula be able to. By the detonation method as described above, a crude product of nanodiamond particles can be obtained. Moreover, it is possible to acquire a desired amount of nano diamond crude products by performing the above production processes S1 as many times as necessary.

In the present embodiment, the purification step S2 includes an acid treatment in which a crude acid, which is a raw material of the raw nanodiamond material, is reacted with a strong acid in an aqueous solvent, for example. A crude nanodiamond product obtained by the detonation method is likely to contain metal oxides, and this metal oxide is an oxide such as Fe, Co, Ni, etc. derived from the container etc. used for the detonation method. is there. For example, the metal oxide can be dissolved and removed from the crude nanodiamond product by reacting with a predetermined strong acid in an aqueous solvent (acid treatment). The strong acid used for the acid treatment is preferably a mineral acid, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. In the acid treatment, one strong acid may be used, or two or more strong acids may be used. The concentration of the strong acid used in the acid treatment is, for example, 1 to 50% by mass. The acid treatment temperature is, for example, 70 to 150.degree. The acid treatment time is, for example, 0.1 to 24 hours. In addition, the acid treatment can be performed under reduced pressure, normal pressure, or increased pressure. After such acid treatment, washing with water (including nano-diamond aggregates) of the solid content is performed by, for example, decantation. It is preferable to repeat the washing of the solid content by decantation repeatedly until the pH of the precipitate reaches, for example, 2 to 3. When the content of the metal oxide in the nanodiamond crude product obtained by the detonation method is small, the above acid treatment may be omitted.

In the purification step S2, in the present embodiment, a solution oxidation treatment for removing non-diamond carbon such as graphite and amorphous carbon from a nanodiamond crude product (nanodiamond adhesion body before completion of purification) using an oxidizing agent is used. Including. The crude diamond product obtained by the detonation method contains non-diamond carbon such as graphite (graphite) and amorphous carbon. This non-diamond carbon causes partial burnout of the used explosive partially. It originates in carbon which did not form nano diamond crystals among the liberated carbon. For example, after the above-mentioned acid treatment, non-diamond carbon can be removed from the nanodiamond crude product by acting a predetermined oxidizing agent or the like in an aqueous solvent (solution oxidation treatment). Examples of oxidizing agents used for this solution oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, salts thereof, nitric acid, and mixed acids (a mixture of sulfuric acid and nitric acid). It can be mentioned. In the solution oxidation treatment, one type of oxidizing agent may be used, or two or more types of oxidizing agents may be used. The concentration of the oxidizing agent used in the solution oxidation treatment is, for example, 3 to 50% by mass. The amount of the oxidizing agent used in the solution oxidation treatment is, for example, 300 to 2000 parts by mass with respect to 100 parts by mass of the nanodiamond crude product subjected to the solution oxidation treatment. The solution oxidation treatment temperature is, for example, 50 to 250.degree. The solution oxidation treatment time is, for example, 1 to 72 hours. Solution oxidation treatment can be performed under reduced pressure, normal pressure or increased pressure. After such solution oxidation treatment, washing with solids (including nano-diamond aggregates) is performed, for example, by decantation. It is preferable to repeatedly carry out washing of the solid content by decantation until the supernatant liquid is colored at the beginning of washing until the supernatant liquid is visually clear.

After the supernatant is removed from the nanodiamond-containing solution subjected to this treatment, for example, by decantation, the remaining fraction is subjected to a drying treatment to obtain a dry powder. Examples of the drying treatment include spray drying using a spray drying apparatus and evaporation to dryness using an evaporator.

In the next oxygen oxidation step S3, the nanodiamond powder that has undergone the purification step S2 is heated in a gas atmosphere of a predetermined composition containing oxygen, using a gas atmosphere furnace. Specifically, nanodiamond powder is disposed in a gas atmosphere furnace, oxygen-containing gas is supplied or flowed to the furnace, and the temperature in the furnace is raised to the temperature condition set as the heating temperature. , Oxygen oxidation treatment is carried out. The temperature condition of this oxygen oxidation treatment is, for example, 250 to 500.degree. In order to realize a negative zeta potential for the ND particles contained in the ND dispersion to be produced, the temperature conditions of this oxygen oxidation treatment are preferably relatively high, for example, 400 to 450 ° C. . Further, the oxygen-containing gas used in the present embodiment is a mixed gas containing an inert gas in addition to oxygen. Inert gases include, for example, nitrogen, argon, carbon dioxide, and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35% by volume.

In order to realize a positive zeta potential for the ND particles contained in the ND dispersion to be produced, preferably, a hydrogen reduction treatment step S3 'is performed after the above-described oxygen oxidation step S3. In the hydrogen reduction treatment step S3 ', the nanodiamond powder that has undergone the oxygen oxidation step S3 is heated in a gas atmosphere of a predetermined composition containing hydrogen using a gas atmosphere furnace. Specifically, a hydrogen-containing gas is supplied or flowed to a gas atmosphere furnace in which nanodiamond powder is disposed inside, and the temperature in the furnace is raised to the temperature condition set as the heating temperature, Hydrogen reduction treatment is performed. The temperature conditions of this hydrogen reduction treatment are, for example, 400 to 800.degree. The hydrogen-containing gas used in the present embodiment is a mixed gas containing an inert gas in addition to hydrogen. Inert gases include, for example, nitrogen, argon, carbon dioxide, and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50% by volume. In order to realize a negative zeta potential for the ND particles contained in the ND dispersion to be produced, the following crushing step S4 may be performed without performing such a hydrogen reduction treatment step.

Even after purification through a series of processes as described above, detonation nanodiamonds may take the form of an aggregate (secondary particles), and further primary particles from the aggregate. Next, a crushing step S4 is performed to separate. Specifically, first, nanodiamonds that have undergone the oxygen oxidation step S3 or the subsequent hydrogen reduction treatment step S3 'are suspended in pure water to prepare a slurry containing nanodiamonds. In preparing the slurry, centrifugation may be performed to remove relatively large assemblies from the nanodiamond suspension, or the nanodiamond suspension may be subjected to ultrasonication. Then, the slurry is subjected to a wet crushing process. The crushing process can be performed using, for example, a high shear mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high pressure homogenizer, an ultrasonic homogenizer, or a colloid mill. The crushing process may be performed by combining these. From the viewpoint of efficiency, it is preferable to use a bead mill.

The bead mill, which is a pulverizer or disperser, includes, for example, a cylindrical mill container, a rotor pin, a centrifugal separator, a raw material tank, and a pump. The rotor pin has a common axis with the mill container and is configured to be rotatable at high speed inside the mill container. The centrifuge system is disposed at the top in the mill vessel. In bead milling using a bead mill in the crushing step, as a predetermined amount of beads is filled in the mill container and the rotor pins are stirring the beads, the action of the pump acts as a raw material from the raw material tank to the lower part of the mill container. The above-mentioned slurry (including nano-diamond aggregates) is introduced. The slurry passes through the rapidly stirred beads in the mill vessel to reach the top in the mill vessel. In this process, the nano-diamond aggregates contained in the slurry are subjected to the action of crushing or dispersion by contact with the vigorously moving beads. As a result, the disintegration of the nano-diamond agglomerates (secondary particles) into primary particles proceeds. The slurry and the beads that reached the upper centrifuge in the mill vessel are centrifuged using the specific gravity difference by the operating centrifuge, the beads remain in the mill vessel, and the slurry It is discharged out of the mill container via a hollow line slidably connected. The discharged slurry is returned to the raw material tank and then introduced again into the mill container by the action of the pump (circulation operation). In such bead milling, the crushing media used is, for example, zirconia beads, and the diameter of the beads is, for example, 15 to 500 μm. The amount (apparent volume) of beads packed in the mill vessel is, for example, 50 to 80% of the volume of the mill vessel. The circumferential speed of the rotor pin is, for example, 8 to 12 m / min. The amount of slurry to be circulated is, for example, 200 to 600 mL, and the flow rate of the slurry is, for example, 5 to 15 L / hour. Further, the processing time (circulation operation time) is, for example, 30 to 300 minutes. In the present embodiment, a batch-type bead mill may be used instead of the continuous-type bead mill as described above.

Through such a crushing step S4, an ND dispersion containing nanodiamond primary particles can be obtained. The dispersion obtained through the crushing step S4 may be subjected to classification operation for removing coarse particles. For example, using a classifier, coarse particles can be removed from the dispersion by classification using centrifugation. Thereby, for example, a black transparent ND dispersion in which primary particles of nanodiamond are dispersed as colloidal particles is obtained.

Lubricants in initial conformers and lubricants include polar solvents or nonpolar solvents. Examples of the polar solvent include water, methanol, ethanol, propanol, butanol, polyfunctional alcohols (ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol and the like), mixed solvents thereof and the like. Moreover, as nonpolar solvents, synthetic oils (poly-α-olefin, alkyl naphthalene, polybuden etc.), mineral oils, synthetic hydrocarbon oils, ester oils (polyol esters, diesters, complex esters etc), silicone oils, fluorine oils And castor oil and mixed solvents thereof. Among them, water is preferred as a lubricant for the initial adjustor and lubricant.

In the embodiment, the content of the lubricant base in the initial fitting agent is, for example, 98% by mass or more, preferably 99% by mass or more, more preferably 99.5% by mass or more, and more preferably 99.9% by mass or more It is.

In the embodiment, the content of the lubricant base in the lubricant is, for example, 99.9% by mass or more, preferably 99.95% by mass or more, more preferably 99.99% by mass or more, and more preferably 99.999%. It is mass% or more.

Initial conformers and lubricants may contain other components in addition to the ND particles and lubricant base. Other components include, for example, surfactants, thickeners, coupling agents, rust inhibitors for rusting of metal members to be lubricated, and corrosion prevention for suppressing corrosion of non-metal members to be lubricated. Agents, freezing point depressants, antifoam agents, antiwear additives, preservatives, colorants, and solid lubricants other than ND particles.

In the lubrication system of the present invention, a suitable amount of initial welding agent is added to the DLC sliding surface, and friction (pre-slip) is performed in advance. Thereafter, the DLC sliding surface is further slid (sliding) in the presence of the lubricant. The lubrication system of the present invention is suitable, for example, to reduce the coefficient of friction and wear on sliding surfaces such as sliding bearings in machines. In the lubrication system of the present invention, it is considered that the wettability improvement and the smoothing of the DLC sliding surface proceed at an early stage due to the tribochemical reaction in the system where the ND particles act when the initial conformant is used. The sliding surface tends to reduce friction early. In addition, the use of a lubricant tends to maintain low friction while suppressing wear of the DLC sliding surface. Thus, the lubrication system of the present invention is suitable for achieving low friction and low wear on the DLC sliding surface. The particle concentration in the initial habituation agent containing relatively high concentration of nanodiamond particles is preferably 0.01 to 2% by mass, and the particle concentration in the lubricant containing relatively low concentration of nanodiamond particles is , Preferably 0.001 mass% or less.

The following friction test is, for example, a test imitating a slide bearing having a DLC sliding surface in a machine. The coefficient of friction of the sliding surface measured in the following friction test is 0.05 or less (more preferably 0.03 or less), and the ball wear volume determined by the following method for calculating the amount of wear after the friction test is 1.0 × It is preferably 10 ⁻⁴ mm ³ or less (more preferably 7.0 × 10 ⁻⁵ mm ³ or less).
Friction test: First, a disk with a diameter of 30 mm and a thickness of 4 mm having a DLC sliding surface formed by a 3 μm thick DLC film on the surface and a 8 mm diameter with a DLC sliding surface formed by a 3 μm thick DLC film on the surface Using a ball-on-disk sliding friction tester fitted with a ball, 1 mL of the initial bonding agent is dropped onto the DLC sliding surface of the disk and then the ball is brought into contact with a load of 10 N The disk is slid 10 m relatively at a velocity of 10 mm / s in the circumferential direction of the disk, and the coefficient of friction between the DLC sliding surface of the disk and the ball is measured during the sliding at a sliding distance of 0-10 m. The disc and ball are then removed from the sliding friction tester and ultrasonic cleaned. After washing, the ball may be wiped with acetone to remove nanodiamonds attached to the ball. Next, using a sliding friction tester fitted with a disk and a ball, 1 mL of the lubricant is dropped onto the DLC sliding surface of the disk and then the ball is abutted with a load of 10 N The sliding is further performed 90 m in the circumferential direction relatively at a speed of 10 mm / s, and the coefficient of friction between the disk and the DLC sliding surface of the ball is measured during the sliding at a sliding distance of 10 to 100 m.
Wear amount calculation method: A circular wear mark formed on the ball subjected to the friction test is observed using a confocal microscope, and from the observation image, it is a plane that is uniformly smooth about the circular wear mark. Assuming that the diameter r (mm) is determined. And ball wear volume V (mm < ³ >) is computed by following formula (1) and Formula (2). H in Formula (1) is height (mm) of the ball crown of the said circular shaped abrasion mark, and is calculated | required from following formula (2). R in Formula (2) is a radius of the said ball, and is 4 (mm).

The diamond like carbon (DLC) film on the DLC sliding surface is an amorphous (amorphous) hard film mainly composed of a hydrocarbon or an allotrope of carbon. DLC can distinguish its properties depending on the hydrogen content and whether the crystalline electron orbits contained are close to diamond or close to graphite. As DLC, for example, amorphous hydrogenated carbon aC: H, amorphous carbon aC, tetrahedral amorphous carbon ta-C: H, and hydrogenated tetrahedral amorphous carbon ta -C is mentioned.

[Preparation of nano diamond aqueous dispersion]
A nanodiamond aqueous dispersion X1 (ND aqueous dispersion) was produced through the following production steps, purification steps, oxygen oxidation steps, and crushing steps.

In the production step, first, a shaped explosive provided with an electric detonator was installed inside a pressure-resistant container for detonation to seal the container. The container is made of iron and the volume of the container is 15 m ³ . As an explosive, 0.50 kg of a mixture of trinitrotoluene (TNT) and cyclotrimethylene trinitroamine or hexogen (RDX) was used. The mass ratio of TNT to RDX (TNT / RDX) in the explosive is 50/50. Next, the electric detonator was detonated and the explosive was detonated in the container. Next, the container and its inside were cooled by leaving at room temperature for 24 hours. After this cooling, a crude nanodiamond product (including the agglomerates and wrinkles of nanodiamond particles produced by the above detonation method) attached to the inner wall of the vessel was recovered. The nanodiamond crude product was obtained by performing the above-mentioned production process a plurality of times.

Next, acid treatment of the purification step was performed on the nanodiamond crude product obtained in the above generation step. Specifically, the slurry obtained by adding 6 L of 10% by mass hydrochloric acid to 200 g of the crude nanodiamond product was subjected to heat treatment under reflux under normal pressure conditions for 1 hour. The heating temperature in this acid treatment is 85 to 100.degree. Next, after cooling, decantation was performed to wash the solid content (including nano-diamond aggregates and soot) with water. The solid was repeatedly washed with water by decantation until the pH of the precipitate reached 2 from the low pH side. Next, mixed acid treatment was performed as solution oxidation treatment in the purification step. Specifically, 6 L of a 98 mass% aqueous sulfuric acid solution and a 1 L of 69 mass% aqueous nitric acid solution were added to a precipitation solution (including nanodiamond agglutinate) obtained through decantation after acid treatment to form a slurry Thereafter, the slurry was subjected to heat treatment for 48 hours under reflux under normal pressure conditions. The heating temperature in this oxidation treatment is 140 to 160.degree. Next, after cooling, the solid content (including nano-diamond aggregates) was washed with water by decantation. The supernatant liquid at the beginning of washing with water was colored, and the washing of the solid content by decantation was repeated until the supernatant was visually clear. Next, a drying step was performed. Specifically, 1000 mL of the nanodiamond-containing liquid obtained through the above-mentioned water washing treatment was subjected to spray drying using a spray dryer (trade name "SPRAY DRYER B-290, manufactured by Nippon Buchi Co., Ltd.) . This gave 50 g of nanodiamond powder.

Next, an oxygen oxidation step was performed using a gas atmosphere furnace (trade name “gas atmosphere tube furnace KTF045N1” manufactured by Koyo Thermo System Co., Ltd.). Specifically, 4.5 g of nano diamond powder obtained as described above was allowed to stand still in the core tube of a gas atmosphere furnace, and nitrogen gas was allowed to flow through the core tube at a flow rate of 1 L / min for 30 minutes. Thereafter, the flow gas was switched from nitrogen to a mixed gas of oxygen and nitrogen, and the mixed gas was allowed to flow through the core tube at a flow rate of 1 L / min. The oxygen concentration in the mixed gas is 4% by volume. After switching to the mixed gas, the temperature in the furnace was raised to 400 ° C., which is the heating set temperature. The temperature rising rate was 10 ° C./min up to 380 ° C., which is 20 ° C. lower than the heating set temperature, and then 1 ° C./min from 380 ° C. to 400 ° C. Then, while maintaining the temperature condition in the furnace at 400 ° C., the oxygen oxidation treatment was performed on the nano diamond powder in the furnace. The processing time was 3 hours.

After the oxygen oxidation treatment, evaluation of an oxygen-containing functional group such as a carboxy group in the ND particles was carried out by FT-IR analysis by the method described later. The spectrum obtained by this analysis is shown in FIG. From FIG. 5, C = O stretching absorption near 1780 cm ^-1 attributable to the vibration P ₁ has been detected as a main peak. When the peak position is 1750 cm ⁻¹ or more, the zeta potential can be a raw material of the nanodiamond dispersion having a negative.

Next, the crushing process was performed. Specifically, first, 1.8 g of nanodiamond powder that had undergone an oxygen oxidation step and 28.2 mL of pure water were mixed in a 50 mL sample bottle to obtain about 30 mL of a slurry. Next, the pH of the slurry was adjusted by the addition of a 1 M aqueous solution of sodium hydroxide, and then ultrasonication was applied. In the ultrasonic treatment, the slurry was subjected to ultrasonic irradiation for 2 hours using an ultrasonic irradiator (trade name “ultrasonic cleaner AS-3”, manufactured by AS ONE) . Thereafter, bead milling was performed using a bead milling apparatus (trade name “parallel four-cylinder sand grinder LSG-4U-2L type”, manufactured by Imex Co., Ltd.). Specifically, 30 mL of the slurry after ultrasonic wave irradiation and zirconia beads with a diameter of 30 μm are charged into 100 mL of a mill container, vessel (manufactured by IMEX Co., Ltd.), and sealed, and the device is driven to execute bead milling. did. In this bead milling, the input amount of zirconia beads is about 33% of the volume of the mill vessel, the rotation speed of the mill vessel is 2570 rpm, and the milling time is 2 hours. Next, the slurry or suspension subjected to such a crushing step was subjected to centrifugation using a centrifugal separator (classification operation). The centrifugal force in this centrifugation was 20000 × g, and the centrifugation time was 10 minutes. Next, 10 mL of the supernatant of the nanodiamond-containing solution subjected to the centrifugation treatment was collected. In this way, an ND aqueous dispersion in which nanodiamonds are dispersed in pure water, which is a stock solution of the initial adjustability composition and the lubricant, was obtained. With respect to this ND aqueous dispersion, the solid content concentration to the nanodiamond concentration was 59.1 g / L, and the pH was 9.33. The particle diameter D50 (median diameter) was 3.97 nm, the particle diameter D90 was 7.20 nm, and the zeta potential was -42 mV.

<Nano diamond concentration>
The nanodiamond content (ND concentration) of the obtained ND aqueous dispersion is the weighing value of 3 to 5 g of the weighed dispersion, and the dried product remaining after evaporation of the water from the weighing dispersion by heating (powder Body) was calculated based on the value measured by a precision balance.

<Particle size>
The particle diameter (median diameter, D50 to D90) of the nanodiamond particles contained in the obtained ND aqueous dispersion is determined by dynamic light scattering using an apparatus manufactured by Malvern (trade name "Zetasizer Nano ZS"). It was measured by the method (noncontact backscattering method). The ND aqueous dispersion subjected to measurement was subjected to ultrasonic irradiation by an ultrasonic cleaner after being diluted with ultrapure water so that the solid content concentration or nano diamond concentration would be 0.5 to 2.0 mass%. It is a thing.

<PH>
The pH of the obtained ND aqueous dispersion was measured using pH test paper (trade name "Sleeve Band pH test paper", manufactured by As One Corporation).

<Zeta potential>
The zeta potential of the nano diamond particles contained in the obtained ND aqueous dispersion was measured by a laser Doppler electrophoresis method using a device manufactured by Malvern (trade name "Zeta Sizer Nano ZS"). The ND aqueous dispersions X1 and Y1 subjected to the measurement were subjected to ultrasonic irradiation by an ultrasonic cleaner after being diluted with ultrapure water so that the solid content concentration to nano diamond concentration would be 0.2 mass%. And the zeta potential measurement temperature is 25.degree.

<FT-IR Analysis>
Fourier transform infrared spectroscopy (FT-IR) (FT-IR apparatus (trade name "Spectrum 400 type FT-IR", manufactured by PerkinElmer Japan Co., Ltd.) for each of the above-described oxygen-oxidized nano diamond samples using Fourier transform infrared spectroscopy (FT- IR) was done. In this measurement, the infrared absorption spectrum was measured while heating a sample to be measured at 150 ° C. in a vacuum atmosphere. Heating under a vacuum atmosphere was realized by using ST-Japan Japan Model-HC900 Heat Chamber and TC-100WA Thermo Controller in combination.

[Preparation of initial conformant and lubricant]
The ND aqueous dispersion obtained above and the ultrapure water are mixed to adjust the concentration, whereby an initial conformant containing 0.1% by mass of ND particles and a lubricant containing 0.0001% by mass of ND particles are mixed. Made.

Example 1: Friction Test
For the friction test, a ball-on-disk sliding friction tester was used. Using a SUJ2 ball of 8 mm in diameter and a SUJ2 disk of 30 mm in diameter and 4 mm in thickness as a base material, a DLC film of about 3 μm was formed on the surface of the ball and the disk. At the start of the test, 1 mL of the initial adhesion agent was dropped on the disc surface, and the ball was allowed to slide 10 m at a speed of 10 mm / s while applying a load of 10 N on the disc. The ball and disc were then removed from the friction tester and subjected to ultrasonic cleaning in purified water for 15 minutes. After washing, the nano diamond attached to the ball was removed by wiping the ball with acetone. After that, the ball and the disc were attached to a friction tester, and the above lubricant was used to slide 90 m at a speed of 10 mm / s. Friction test of Example 1, the horizontal axis sliding distance [m], a graph in which the ordinate the coefficient of friction in Figure 3, the horizontal axis sliding distance [m], Ball Wear volume (amount of wear) [mm ^3] The graph which made y vertical axis | shaft is shown in FIG. In FIG. 3, the line with the lower end of the coefficient of friction 0 seen at a sliding distance of 10 m and the upper end near 0.10 is the noise when sliding is resumed using a lubricant and is measured in this test It shall not be included in the coefficient of friction.

Comparative Example 1: Friction Test
The friction test was conducted in the same manner as in Example 1 except that water containing no nanodiamond particles was used instead of the above-mentioned initial conformant and lubricant. In the friction test of Comparative Example 1, a graph in which the sliding distance [m] is taken along the horizontal axis and the friction coefficient is taken along the vertical axis is shown in FIG. 2; the sliding distance [m] is taken along the horizontal axis; The graph which made the vertical axis | shaft the ball | bowl wear volume (wear amount) [mm < ³ >] calculated | required from these is shown in FIG.

In the friction test of Comparative Example 1 (FIG. 2), it can be seen that the coefficient of friction gradually increases as the sliding distance increases. On the other hand, in the friction test of Example 1 (FIG. 3) using the initial conformant and lubricant, no increase in the coefficient of friction as in Comparative Example 1 was observed at a sliding distance of 100 m, and low friction was maintained. I understand. In other words, the use of the initial conformer enables the early formation of a low friction surface with a short pre-slip of 10 m, and the use of a lubricant maintains the low friction surface in the subsequent 90 m of sliding motion. I know that I was able to do it. Further, according to FIG. 4, in Comparative Example 1 in which only water is used, the amount of wear does not increase so much and wear can be suppressed, but even in Example 1 in which ND particles are used, the sliding distance is 10 to 90 m. It can be seen that the wear can be suppressed to the same extent as 1.

As a summary of the above, the configuration of the present invention and the variations thereof are listed below as a supplementary note.

[Supplementary Note 1]
Use a lubricant containing a relatively low concentration of nanodiamond particles for the lubrication of a low friction DLC sliding surface using an initial fluxing agent containing a relatively high concentration of nanodiamond particles Lubrication system.
[Supplementary Note 2]
The lubrication system according to any of the preceding claims, wherein the concentration of nano diamond particles of said initial conformant is 0.01-2 wt%.
[Supplementary Note 3]
The lubrication system according to claim 1 or 2, wherein the concentration of nano diamond particles in the lubricant is 0.001 mass% or less.
[Supplementary Note 4]
The friction coefficient of the DLC sliding surface measured by the following friction test is 0.05 or less, and the ball wear volume determined by the wear amount calculation method after the following friction test is 1.0 × 10 ^-4 mm ³ or less The lubricating system according to any one of appendices 1 to 3 (the method of calculating the amount of wear is as described in the present specification).
[Supplementary Note 5]
The lubrication system according to any one of Appendices 1 to 4, wherein the primary particle size of the nano diamond particles is 10 nm or less.
The lubrication system according to any one of Appendices 1 to 5, wherein the nanodiamond particles are an oxygen-oxidized product of detonation nanodiamond particles.
[Supplementary Note 7]
The lubrication system according to any one of claims 1 to 6, wherein the zeta potential of the nanodiamond particles is negative.
[Supplementary Note 8]
8. The lubrication system of clause 7, wherein the zeta potential of the nanodiamond particles is -60 to -30 mV.
[Supplementary Note 9]
11. The lubrication system according to any one of appendices 1 to 8, wherein a peak position attributed to C = O stretching vibration in FT-IR of the nanodiamond particles is 1750 cm ⁻¹ or more.
[Supplementary Note 10]
The lubrication system according to any one of claims 1 to 5, wherein the nano diamond particles are a hydrogen reduction treatment product of detonation nano diamond particles.
[Supplementary Note 11]
10. The lubrication system according to any one of appendices 1 to 5 and 10, wherein the zeta potential of the nanodiamond particles is positive.
[Supplementary Note 12]
15. The lubrication system of clause 11, wherein the zeta potential of the nanodiamond particles is 30 to 60 mV.
[Supplementary Note 13]
10. The lubrication system according to any one of appendices 1 to 5 and 10 to 12, wherein the peak position attributed to C = O stretching vibration in FT-IR of the nanodiamond particles is less than 1750 cm ⁻¹ .
[Supplementary Note 14]
15. A lubrication system according to any one of the preceding claims, wherein the lubricant in the initial conformant and the lubricant is water.
[Supplementary Note 15]
A liquid agent set for a lubrication system comprising: an initial blender containing nanodiamond particles in a concentration of 0.01 to 2% by mass; and a lubricant containing nanodiamond particles in a concentration of 0.001% by mass or less.

S1 generation process S2 purification process S3 oxygen oxidation process S3 'hydrogen reduction treatment process S4 crushing process

Claims (12)

Use a lubricant containing a relatively low concentration of nanodiamond particles for the lubrication of a low friction DLC sliding surface using an initial fluxing agent containing a relatively high concentration of nanodiamond particles Lubrication system. The lubrication system according to claim 1, wherein the concentration of nano diamond particles in the initial adhesion agent is 0.01 to 2% by mass. The lubrication system according to claim 1, wherein the concentration of nano diamond particles in the lubricant is 0.001% by mass or less. The friction coefficient of the DLC sliding surface measured by the following friction test is 0.05 or less, and the ball wear volume determined by the following wear amount calculation method after the following friction test is 1.0 × 10 ^-4 mm ³ or less The lubrication system according to any one of claims 1 to 3, which is
Friction test: First, a disk with a diameter of 30 mm and a thickness of 4 mm having a DLC sliding surface formed by a 3 μm thick DLC film on the surface and a 8 mm diameter with a DLC sliding surface formed by a 3 μm thick DLC film on the surface Using a ball-on-disk sliding friction tester equipped with a ball, 1 mL of the initial bonding agent was dropped onto the DLC sliding surface of the disk, and then the ball was loaded with a load of 10 N. The disc is slid 10 m relatively at a velocity of 10 mm / s in the circumferential direction of the disc while in contact with the disc, and the coefficient of friction between the disc and the DLC sliding surface of the ball is measured during the sliding of 0-10 m. The disc and the ball are then removed from the sliding friction tester and ultrasonic cleaned. Next, 1 mL of the lubricant is dropped onto the DLC sliding surface of the disk using the sliding friction tester with the cleaned disk and ball attached, and then the ball is loaded with a load of 10 N While making contact, slide 90 m relatively at a velocity of 10 mm / s in the circumferential direction of the disk, and measure the coefficient of friction between the DLC sliding surface of the disk and the ball during the sliding with a sliding distance of 10 to 100 m.
Wear amount calculation method: A circular wear mark formed on the ball subjected to the friction test is observed using a confocal microscope, and from the observation image, a uniformly smooth plane is obtained for the circular wear mark. Assuming that there is a diameter r (mm) is determined. And ball wear volume V (mm < ³ >) is computed by following formula (1) and Formula (2). H in Formula (1) is height (mm) of the ball crown of the said circular shaped abrasion mark, and is calculated | required from following formula (2). R in Formula (2) is a radius of the said ball, and is 4 (mm).

The lubrication system according to any one of claims 1 to 4, wherein the nano diamond particles are an oxygen oxidation treatment of detonation nano diamond particles. The lubrication system according to any one of claims 1 to 5, wherein the zeta potential of the nanodiamond particles is negative. The lubrication system according to any one of claims 1 to 6, wherein a peak position attributed to C = O stretching vibration in FT-IR of the nanodiamond particles is 1750 cm ^-1 or more. The lubrication system according to any one of claims 1 to 4, wherein the nano diamond particles are hydrogen reduction products of detonation nano diamond particles. The lubrication system according to any one of claims 1 to 4 and 8, wherein the zeta potential of the nanodiamond particles is positive. The lubrication system according to any one of claims 1 to 4, 8 and 9, wherein a peak position attributed to C = O stretching vibration in FT-IR of the nanodiamond particles is less than 1750 cm ^-1 . The lubrication system according to any one of claims 1 to 10, wherein a lubricant base in the initial conformant and the lubricant is water. An initial adjustor containing nanodiamond particles having a concentration of 0.01 to 2% by mass;
A liquid agent set for a lubrication system, comprising: a lubricant containing nanodiamond particles having a concentration of 0.001% by mass or less.

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