Grease composition, and method for improving and evaluating torque performance of grease composition

Abstract

To provide a grease composition capable of improving torque performance in a rolling bearing.SOLUTION: Provided is a grease composition in which an existence ratio of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more in fluidity analysis using Particle Image Velocimetry, and which comprises a base oil and a thickener. The tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less as measured by a laser diffraction / scattering method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a grease composition. The present invention also relates to a method for improving and evaluating the torque performance of a grease composition.

[0002] Grease is a semi-solid lubricant made by dispersing a solid, highly lipophilic thickener in a base oil. Grease adheres more easily to the lubricated parts and is less likely to leak out than lubricating oil. Therefore, using grease makes it possible to simplify the structure of the lubrication system. Grease is mainly used to lubricate machine elements such as rolling bearings, plain bearings, ball screws, linear guides, and gears. Rolling bearings are widely used in machine tool spindles, railroad car carriages, engine accessories such as automobile alternators, constant velocity joints, and wheels. From the viewpoint of energy conservation, low torque rolling bearings are desirable.

[0003] Various studies have been conducted to reduce the torque of rolling bearings filled with grease. For example, Patent Document 1 discloses a grease composition that can reduce torque by adding a specific component as a friction modifier. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-16687 A Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 requires the addition of specific components as friction modifiers, which can impose restrictions on product design. When it comes to reducing the torque of rolling bearings filled with grease, the addition of specific components, as in Patent Document 1, has been the mainstream approach, resulting in restrictions on formulation. On the other hand, there has been little research into reducing the torque of rolling bearings by focusing on the fluidity of grease at the contact point between the rolling bearing and the grease. An object of the present invention is to provide a grease that can reduce the torque of a rolling bearing, that is, can improve the torque performance, by focusing on the fluidity of the grease. [Means for solving the problem]

[0006] The present inventors have focused on the fluidity of grease and conducted extensive research into whether it is possible to improve the torque performance of rolling bearings. As a result, they have surprisingly found that the above object can be achieved by adjusting the proportion of tracer particles having a velocity of 1.0 mm / s or more to 5.0% or more in a grease composition containing a base oil and a thickener in a fluidity analysis using Particle Image Velocimetry (sometimes referred to as PIV in this specification), and have thus completed the present invention. The present invention is as follows.

[0007] <1> A grease composition comprising a base oil and a thickener, wherein a proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more in a flowability analysis using Particle Image Velocimetry, The grease composition as described above, wherein the tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less as measured by a laser diffraction / scattering method. <2> In the measurement conditions of the velocity of the tracer particle in the ball-on-disk type device, the peripheral speed of the disk is 210 mm / s, and the maximum Hertzian surface pressure between the ball and the disk is 0.51 GPa. <1> The grease composition according to claim 1. <3> Using Particle Image Velocimetry, measure the velocity distribution of tracer particles added to a grease composition. A method for evaluating torque performance of a grease composition containing a base oil and a thickener, comprising: <4> The measured proportion of tracer particles with a velocity above a certain velocity is compared to a threshold value. further comprising: <3> A method for evaluating the torque performance of the grease composition according to claim 1. <5> The abundance ratio is the abundance ratio of tracer particles having a velocity of 1.0 mm / s or more, The tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less. <3> or <4> A method for evaluating the torque performance of the grease composition according to claim 1. <6> In Particle Image Velocimetry, the proportion of tracer particles with a velocity of 1.0 mm / s or more must be adjusted to 5.0% or more. A method for improving torque performance of a grease composition, comprising: The method, wherein the tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a grease composition that can improve the torque performance of a rolling bearing. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows a schematic diagram of a ball-on-disk experimental setup that can be used as a measurement device for the velocity of tracer particles. [Figure 2] This is a photograph of a ballistic mark on a grease composition analyzed by PIV. The trajectory of the tracer particles is shown by countless lines, and the mark left by the ball is shown by a tree branch-like pattern (branch pattern). The squares represent unit areas, which will be described later. [Figure 3] FIG. 1 is a diagram showing the relationship between the proportion of tracer particles having a velocity of 1.0 mm / s or more and bearing torque in the evaluations carried out in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] (base oil) The base oil used in the grease composition of the present invention may be either a mineral oil or a synthetic base oil, as long as the proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more based on the total amount of the composition. In the grease composition of the present invention, it is preferable to use a synthetic base oil as the base oil.

[0011] Examples of synthetic base oils include polyolefins such as poly-α-olefins, ester base oils such as diesters and polyol esters, polyalkylene glycols, alkylbenzenes, alkylnaphthalenes, GTL base oils, etc. Among the synthetic base oils, poly-α-olefins are preferred in terms of availability, cost, viscosity characteristics, and oxidation stability.

[0012] Mineral oils can be distillates obtained by atmospheric distillation of crude oil. Lubricating oil fractions obtained by further vacuum distillation of the distillates and then refining them through various refining processes can also be used. Refining processes can include hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, and clay treatment, and can be combined as appropriate. Base oils that can be used in the present invention can be obtained by combining these refining processes in an appropriate order. Mixtures of refined oils with different properties, obtained by subjecting different crude oils or distillates to a combination of different refining processes, can also be used.

[0013] In the grease composition of the present invention, mineral oils or synthetic base oils can be used alone or in combination of two or more.

[0014] The kinematic viscosity at 40°C of the base oil used in the grease composition of the present invention is preferably 15 mm 2 / s or more, preferably 30 mm 2 / s or more, preferably 100 mm 2 / s or less, preferably 70 mm 2 In one embodiment, the kinematic viscosity of the base oil at 40°C is preferably 15 mm / s or less. 2 / s or more 100mm 2 / s or less, preferably 30 mm 2 / s or more 70mm 2 / s or less. In this specification, the kinematic viscosity at 40°C means the kinematic viscosity at 40°C measured in accordance with JIS K2283:2000.

[0015] In the grease composition of the present invention, the content of the base oil is preferably 50% by mass or more, more preferably 60% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, based on the total amount of the grease composition. In one embodiment, the content of the base oil is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 90% by mass or less. When the content of the base oil is within the above range, a grease composition having a desired consistency can be easily prepared.

[0016] (thickener) The grease composition of the present invention may contain any thickener as long as the proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more based on the total amount of the composition. Preferably, the grease composition contains at least one thickener selected from the group consisting of metal soap thickeners and urea thickeners.

[0017] [Metal soap-based thickener] Metal soap thickeners include simple soaps and complex soaps. Simple soaps are metal soaps in which fatty acids or fats are saponified with alkali metal hydroxides or alkaline earth metal hydroxides. Complex soaps are complexes in which an organic acid with a different molecular structure is combined with the fatty acid used in simple soaps. The fatty acid may be a fatty acid derivative having a hydroxy group or the like. As the fatty acid, monovalent or divalent aliphatic carboxylic acids are preferred. As the fatty acid, aliphatic carboxylic acids having 6 to 20 carbon atoms are preferred, and monovalent aliphatic carboxylic acids having 12 to 20 carbon atoms or divalent aliphatic carboxylic acids having 6 to 14 carbon atoms are more preferred. As the fatty acid, monovalent aliphatic carboxylic acids having one hydroxy group are preferred. As the organic acid to be combined with the fatty acid in complex soaps, dibasic acids such as acetic acid, azelaic acid, or sebacic acid, or benzoic acid are preferred. The metal for the metal soap thickener may be an alkali metal such as lithium or sodium, an alkaline earth metal such as calcium, or an amphoteric metal such as aluminum. In the present invention, "having 6 to 20 carbon atoms" means having 6 or more and 20 or less carbon atoms.

[0018] [Urea-based thickener] As the urea-based thickener, for example, a diurea compound obtained by the reaction of a diisocyanate with a monoamine, or a polyurea compound obtained by the reaction of a diisocyanate with a monoamine or diamine can be used.

[0019] Diisocyanates are compounds in which two hydrogen atoms of a hydrocarbon are substituted with isocyanate groups. The hydrocarbon may be an acyclic hydrocarbon or a cyclic hydrocarbon, and may be any of an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon. The number of carbon atoms in these hydrocarbons is preferably 4 to 20, more preferably 8 to 18. Preferred specific examples of diisocyanates include phenylene diisocyanate, tolylene diisocyanate, biphenyl diisocyanate (diphenyl diisocyanate), diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. One type of diisocyanate may be used alone, or two or more types may be used in combination.

[0020] A monoamine is a compound having one amino group per molecule. Preferred monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine (octadecylamine), oleylamine, aniline, p-toluidine, and cyclohexylamine. A diamine is a compound having two amino groups per molecule. Preferred diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane. The hydrocarbon group of the monoamine or diamine may be an acyclic hydrocarbon group or a cyclic hydrocarbon group, or may be an aromatic hydrocarbon group, an alicyclic hydrocarbon group, or an aliphatic hydrocarbon group. The number of carbon atoms is preferably 2 to 20, and more preferably 4 to 18.

[0021] As the urea-based thickener, a diurea compound is preferred, and as the diisocyanate, one having an aromatic hydrocarbon group is more preferred. Furthermore, as the monoamine, an aromatic amine, an alicyclic amine, or an aliphatic amine can be used. A mixed amine of these can also be used.

[0022] The thickener may be used alone or in combination of two or more. The content of the thickener is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the grease composition of the present invention, and is preferably 30% by mass or less, and more preferably 20% by mass or less. In one embodiment, the content of the urea-based thickener is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 20% by mass or less.

[0023] (Tracer particles with a velocity of 1.0 mm / s or more) In the grease composition of the present invention, the proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more in a flowability analysis using PIV.

[0024] The velocity of tracer particles can be measured by analyzing the fluidity of a grease composition using PIV. PIV is a fluid visualization technique that measures direction and velocity by irradiating tracer particles in space with laser light twice in succession and analyzing the brightness distribution of the tracer particles in two consecutive images of a group of tracer particles taken at the same time. In other words, the velocity of tracer particles means the speed at which tracer particles contained in a grease composition move in a given direction. In the analysis of the fluidity of a grease composition using PIV, the high velocity of tracer particles in the grease composition means that the flow of the grease composition inside the bearing is not hindered. Therefore, it is thought that the torque of the rolling bearing is reduced because the balls inside the bearing do not encounter resistance when passing over the rolling surface.

[0025] A ball-on-disk type experimental device, as shown in Figure 1, can be used to measure the velocity of tracer particles. A grease composition containing dispersed tracer particles for PIV is applied to the disk, and the velocity of the tracer particles is analyzed after the ball and disk are rotated. A ball-on-disk type experimental apparatus such as that shown in Figure 1 can be designed by a person skilled in the field of lubricants. The configuration of the experimental apparatus is similar to that used for measuring the thickness of an oil film made of grease or lubricating oil, and a person skilled in the field of lubricants can make the necessary modifications and use it to measure the velocity of tracer particles. The configuration of an experimental apparatus used for measuring the thickness of an oil film made of grease or lubricating oil is exemplified, for example, in the following documents:

[0026] Measurement of Nanometer-Scale Oil Film Thickness and Wear in Pure Sliding Contact by Ultrathin Film Optical Interferometry, Journal of Japanese Society of Tribologists, Vol. 52, No. 11, pp. 818-826, Published: November 15, 2007 ·Effects of a thickener structure on grease elastohydrodynamic lubrication films, Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology Volume:214 Issue:4,page(s):327-336

[0027] In the grease composition of the present invention, in a flow analysis using PIV, the proportion of tracer particles having a velocity of 1.0 mm / s or greater is 5.0% or greater, preferably 5.5% or greater, and more preferably 6.0% or greater. The measurement conditions for measuring the velocity of the tracer particles are a disk peripheral speed of 210 mm / s and a maximum Hertzian surface pressure between the ball and disk of 0.51 GPa. The load, disk diameter, and ball and disk materials can be appropriately selected or adjusted so that the disk peripheral speed is 210 mm / s and the maximum Hertzian surface pressure is 0.51 GPa. It is preferable to use sapphire glass as the disk material and SUJ2 (high carbon chromium bearing steel) as the ball material. The peripheral speed of the ball is preferably set to 210 mm / s, the same as the peripheral speed of the disk. The diameter of the ball is preferably 20 mm or greater and 22 mm or less, more preferably 20 mm. It is preferable to use a load of 3 N when measuring the velocity of the tracer particles.

[0028] Tracer particles are substances that emit fluorescence when irradiated with laser light. For example, fluorescent pigments with an average particle size of 3.5 μm to 4.5 μm can be used as tracer particles. The average particle size can be measured by laser diffraction and scattering. SINLOIHI FA-207 is preferably used as the tracer particles. The amount of tracer particles added to the grease composition when measuring the velocity may be, for example, 0.01% by mass or more and 1% by mass or less, or 0.1% by mass or more and 0.5% by mass or less.

[0029] Figure 2 shows a photograph of the ballistic marks on the grease composition analyzed by PIV. The numerous small arrows in Figure 2 represent the trajectories of the tracer particles. The speed of the tracer particles can be analyzed by dividing the length of this line by the difference in the time between the capture of the two images. When measuring the velocity of tracer particles, the velocity of the tracer particles in a unit area on the ballistic mark of the grease composition is analyzed. "The proportion of tracer particles having a velocity of 1.0 mm / s or more is 5% or more" means that the proportion of tracer particles having a velocity of 1.0 mm / s or more in a unit area on the ballistic mark of the grease composition at the time of velocity measurement is 5.0% or more (for example, if there are 100 tracer particles in a unit area on the ballistic mark, 5 or more have a velocity of 1.0 mm / s or more). In this specification, in a photograph of a ballistic mark analysis, the direction perpendicular to the ball's rotation direction is called the horizontal direction, and the direction parallel to the ball's rotation direction is called the vertical direction. The horizontal length of a unit area (horizontal side) is the maximum width of the ballistic mark. The vertical length of a unit area (vertical side) is not particularly limited, but is preferably 0.5 to 1.5 times the length of the horizontal side. The ballistic mark refers to a mark left by the ball on the surface of the grease composition, formed when a grease composition containing dispersed tracer particles for PIV is applied to the disk of a ball-on-disk experimental device and the ball and disk are rotated. The ball scoops up the grease composition on the sliding surface, forming a ballistic mark. The ballistic mark appears as a branch pattern as shown in Figure 2.

[0030] In the grease composition of the present invention, the proportion of tracer particles having a velocity of 0.5 mm / s or more and less than 1.0 mm / s is preferably 9.5% or more and 15% or less, and more preferably 10% or more and 13% or less. In the grease composition of the present invention, the proportion of tracer particles having a velocity of less than 0.5 mm / s is preferably 86% or less, and more preferably 85% or less.

[0031] To increase the proportion of tracer particles with a velocity of 1.0 mm / s or more, homogenization using, for example, a triple-roll mill can be performed for a long period of time. Alternatively, a thickener with pre-fine particles can be added.

[0032] [Other additives] In addition to the above components, the grease composition of the present invention may contain additives generally used in greases, such as solid lubricants, anti-wear or extreme pressure agents, antioxidants, rust inhibitors, and corrosion inhibitors.

[0033] [Grease composition] The consistency of the grease composition of the present invention is preferably 150 or more and 350 or less, and more preferably 200 or more and 350 or less. In this specification, the consistency refers to worked consistency measured in accordance with JIS K2220:2013.

[0034] [Method for evaluating torque performance of grease composition] The method for evaluating the torque performance of a grease composition of the present invention includes determining the proportion of tracer particles having a velocity in the grease composition. In this specification, "determining the proportion of tracer particles having a velocity equal to or greater than a certain velocity" means measuring the proportion of tracer particles having a velocity equal to or greater than a certain velocity. An example of a procedure for determining the proportion of the velocity of tracer particles in a grease composition will be described below.

[0035] Tracer particles are dispersed in the grease composition. The grease composition is applied to the surface of the disk. The thickness of the applied grease composition can be adjusted appropriately depending on the consistency of the grease composition and the measurement conditions for the speed of the tracer particles, but it is preferably 5 μm or more and 15 μm or less (for example, 10 μm). Then, the grease composition applied to the surface of the disk is brought into contact with a ball, and a load is applied. The ball and disk are driven, and the disk is stopped after a certain time or a certain number of revolutions. Then, the sliding surface (trajectory mark) immediately after the ball passes is photographed with a high-speed camera. The photographing position is 180° from the contact position between the ball and the disk.

[0036] The method for evaluating the torque performance of a grease composition of the present invention preferably includes comparing the proportion of tracer particles having a velocity equal to or greater than a specific velocity with a threshold value, with respect to the proportion of tracer particles in the measured grease composition. The threshold value is, for example, 5.0% of the total amount of the composition for the proportion of tracer particles having a velocity equal to or greater than 1.0 mm / s. When the proportion of tracer particles having a velocity equal to or greater than 1.0 mm / s is 5.0% or greater, the torque can be evaluated as being reduced compared to when the proportion is less than 5.0%. [Example]

[0037] The present invention will be described below using examples that are embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0038] <Formulation of grease composition> Test grease compositions were prepared by blending thickeners and base oils in the blending ratios shown in Table 1 for each of Examples 1 to 4 and Comparative Examples 1 and 2. The test grease compositions obtained were evaluated as follows. The evaluation results are shown in Table 1 and Figure 2. The evaluation results are the average of n=3.

[0039] (1) Base oil Base oil 1 Poly-α-olefin (40℃ kinematic viscosity = 47.5mm 2 / s)

[0040] (2) Thickener Thickener 1: Lithium complex thickener (lithium complex soap obtained by reacting lithium hydroxide, 12-hydroxystearic acid and azelaic acid) Thickener 2: Urea thickener (a diurea compound obtained by reacting octadecylamine with diisocyanate) Thickener 3: Urea thickener (diurea compound obtained by reacting octylamine with diisocyanate) Thickener 4: Urea-based thickener (diurea compound obtained by reacting cyclohexylamine with diisocyanate, no coarse particles of thickener (10 μm or more when observed under an optical microscope)) Thickener 5: Urea thickener (diurea compound obtained by reacting cyclohexylamine with diisocyanate)

[0041] <Production of grease composition> Example 1 The base oils were placed in stainless steel containers in the blending ratios shown in Table 1. 12-Hydroxystearic acid was added to the base oil in the container, heated to 70°C, and while stirring with a magnetic stirrer, an aqueous lithium hydroxide solution was added, followed by thermal dehydration. Azelaic acid was then added and dissolved at 100°C. Lithium hydroxide was added again, followed by thermal dehydration and cooling to room temperature, yielding semisolid compositions. Each of the resulting semisolid compositions was then dispersed using a three-roll mill to obtain grease compositions having the compositions shown in Table 1. Examples 2 and 3, Comparative Example 1 The raw materials, amine and isocyanate, were added to the base oil in separate containers in the proportions shown in Table 1, heated to 60-65°C, and mixed while stirring with a magnetic stirrer to react the amine and diisocyanate. The mixture was then cooled to room temperature to obtain a semi-solid composition. Each of the resulting semi-solid compositions was then dispersed using a three-roll mill to obtain the grease compositions shown in Table 1. Example 4 A grease composition having the composition shown in Table 1 was obtained by manufacturing in the same manner as in Comparative Example 1, except that the three-roll dispersion treatment step was carried out at a higher pressure and rotation speed to refine the thickener particles.

[0042] <Evaluation> (1) Measurement of the velocity of tracer particles PIV tracer particles were dispersed in a grease composition formulated as shown in Table 1 at a concentration of 0.2 mass% based on the total mass of the grease composition. SINLOIHI FA-207 tracer particles with an average particle size of 3.5 μm to 4.5 μm were used as the tracer particles. The grease with the dispersed tracer particles was then applied to a disk to a thickness of 10 μm using a ball-on-disk device. The disk peripheral speed was adjusted to 210 mm / s, and the maximum Hertzian contact pressure between the ball and disk was adjusted to 0.51 GPa. Sapphire glass was used as the disk material, and SUJ2 (high-carbon chromium bearing steel) was used as the ball material. The ball peripheral speed was set to 210 mm / s, the same as the disk peripheral speed, and the ball diameter was 20 mm. The load used for measuring the tracer particle velocity was set to 3 N. The ball and disk were driven, and the disk was stopped after a certain time or a certain number of revolutions. The sliding surface immediately after the ball passed was photographed with a high-speed camera. The photograph was taken at a position 180° from the contact point between the ball and disk. Under the above conditions, the ball and disk were rotated, and the velocity distribution of tracer particles within a unit area on the ballistic mark of the grease composition was analyzed. The horizontal length of the unit area (horizontal side) was taken as the maximum width of the ballistic mark. The vertical length of the unit area (vertical side) was set to 0.5 to 1.5 times the length of the horizontal side.

[0043] (2) Torque measurement A deep groove ball bearing with a non-contact seal and a crown-type resin cage was fitted with 2 g of the grease composition and evaluated. An axial load of 50 N and a radial load of 50 N were applied, and the inner ring was rotated at 200 rpm at room temperature. The tangential force acting on the housing was measured with a load cell, and the rotational torque was calculated. The evaluation time was 10 minutes.

[0044] [Table 1]

[0045] In the test grease compositions of Examples 1 to 4, in which the proportion of tracer particles having a velocity of 1.0 mm / s or more was 5.0% or more, the torque was reduced to 20 mN·m or less in all cases. The test grease compositions of Comparative Example 1, in which the proportion of tracer particles having a speed of 1.0 mm / s or more was less than 5.0%, all had torques exceeding 20 mN·m, which was a deterioration. [Industrial Applicability]

[0046] According to the present invention, it is possible to provide a grease composition that can improve the torque performance of a rolling bearing.

Claims

1. measuring the proportion of the velocity of tracer particles added to the grease composition using Particle Image Velocimetry; and In a flowability analysis using Particle Image Velocity, if the proportion of tracer particles having a velocity of 1.0 mm / s or more is 5.0% or more, the torque of the grease composition is evaluated as being reduced, and if the proportion of tracer particles having a velocity of 1.0 mm / s or more is less than 5.0%, the torque of the grease composition is evaluated as being increased. Including, the abundance ratio is the abundance ratio of tracer particles having a velocity of 1.0 mm / s or more, A method for evaluating torque performance of a grease composition containing a base oil and a thickener, wherein the tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less.

2. In Particle Image Velocity, the proportion of tracer particles having a velocity of 1.0 mm / s or more is adjusted to 5.0% or more. A method for improving torque performance of a grease composition, comprising: The method, wherein the tracer particles are fluorescent pigments having an average particle size of 3.5 μm or more and 4.5 μm or less.

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