Grease composition

Abstract

Provided is a grease composition which contains a base oil (A), hydrophilic nanofibers (B) having a diameter (d) of 1-500 nm, and particles (C). The hydrophilic nanofibers (B) are one or more selected from among cellulose nanofibers (B1) and modified cellulose nanofibers (B2), the particles (C) have a structure that has a hydrophobic group on the outermost surface of a hydrophilic base structure, and the average particle diameter of the particles (C) is 1-500 nm in this grease composition. This grease composition has an appropriate degree of oil separation and excellent water resistance, while using hydrophilic nanofibers.

Description

Grease composition

[0001] The present invention relates to a grease composition.

[0002] Grease is easier to seal than lubricating oils, allowing for the miniaturization and weight reduction of machines to which it is applied. Therefore, grease has been widely used to lubricate various sliding parts of automobiles, electrical equipment, industrial machinery, and other machinery. In recent years, grease compositions using biodegradable thickeners have been proposed to provide grease compositions with low environmental impact. For example, Patent Document 1 proposes a grease composition using cellulose nanofibers (hereinafter also referred to as "CNF") as a thickener.

[0003] Japanese Patent Application Laid-Open No. 2017-210612

[0004] However, grease compositions using hydrophilic nanofibers such as CNF as a thickener have problems such as being prone to oil separation and having insufficient water resistance. Therefore, there is a need for a grease composition that uses such hydrophilic nanofibers and yet has an appropriate degree of oil separation and excellent water resistance.

[0005] Therefore, an object of the present invention is to provide a grease composition that uses hydrophilic nanofibers, yet has an appropriate degree of oil separation and excellent water resistance.

[0006] The present inventors have discovered that a grease composition containing a base oil, specific hydrophilic nanofibers, and specific particles can solve the above-mentioned problems, and have completed the present invention.

[0007] That is, the present invention provides the following [1]: [1] A grease composition containing a base oil (A), hydrophilic nanofibers (B) having a thickness (d) of 1 nm to 500 nm, and particles (C), wherein the hydrophilic nanofibers (B) are one or more types selected from cellulose nanofibers (B1) and modified cellulose nanofibers (B2), and the particles (C) have a structure having hydrophobic groups on the outermost surface of a hydrophilic matrix structure, and the average particle diameter of the particles (C) in the grease composition is 1 nm to 500 nm.

[0008] According to the present invention, it is possible to provide a grease composition that uses hydrophilic nanofibers and yet has an appropriate degree of oil separation and excellent water resistance.

[0009] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0010] [Grease composition] The grease composition of the present embodiment is a grease composition containing a base oil (A), hydrophilic nanofibers (B) having a thickness (d) of 1 nm to 500 nm, and particles (C), wherein the hydrophilic nanofibers (B) are one or more types selected from cellulose nanofibers (B1) and modified cellulose nanofibers (B2), and the particles (C) have a structure having hydrophobic groups on the outermost surface of a hydrophilic matrix structure, and the particles (C) have an average particle size of 1 nm to 500 nm in the grease composition.

[0011] The present inventors have conducted extensive research to solve the above problems. It has been found that using cellulose nanofibers as a thickener is useful as a base material for a biodegradable grease composition that has excellent lubricity and heat resistance. However, cellulose nanofibers have the problem of being easily absorbed by moisture due to their high hydrophilicity, making them less likely to remain on sliding surfaces when washed away by water. Another problem is that they are prone to oil separation. As a result of extensive research conducted by the present inventors to solve these problems, it has been found that a grease composition containing particles (C) with a specific particle size and having a structure that has hydrophobic groups on the outermost surface of a hydrophilic matrix structure can solve these problems.

[0012] Here, in the base oil (A), the hydrophilic nanofibers (B) are likely to form a higher-order structure. Furthermore, the hydrophilic nanofibers (B) are likely to be uniformly dispersed in the base oil (A). Furthermore, the grease composition of this embodiment contains particles (C) as an essential component. The particles (C) have a structure in which hydrophobic groups are present on the outermost surface of a hydrophilic matrix structure, and in the grease composition, the particles (C) have an average particle size of 1 nm to 500 nm.

[0013] The particles (C) impart an appropriate degree of oil separation to the grease composition and also impart water resistance. Although the detailed mechanism is unknown, it is presumed, for example, as follows. It is presumed that the hydrophilic nanofibers (B) and the particles (C) form some kind of higher-order structure, which gives the grease composition an appropriate degree of oil separation and excellent water resistance. Furthermore, as a result of the formation of this higher-order structure, it is thought that the grease composition is likely to have an appropriate worked penetration even when the content of the formed hydrophilic nanofibers (B) is small and the content of the particles (C) is small.

[0014] In the following description, the "base oil (A)," the "hydrophilic nanofibers (B)," and the "particles (C)" will also be referred to as "component (A)," "component (B)," and "component (C)," respectively. In the grease composition of this embodiment, the total content of components (A), (B), and (C) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount (100% by mass) of the grease composition. Furthermore, the total content is usually 100% by mass or less, preferably less than 100% by mass, more preferably 99% by mass or less, and even more preferably 98% by mass or less. The grease composition of this embodiment may contain components other than components (A), (B), and (C) as long as the effects of the present invention are not impaired.

[0015] As will be described later, the "antioxidant (D)," "rust inhibitor (E)," and "additive (F)" that may be contained in the grease composition of this embodiment are also referred to as "component (D)," "component (E)," and "component (F)," respectively. In the grease composition of this embodiment, the total content of components (A), (B), (C), (D), (E), and (F) is preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, and still more preferably 90 mass% or more, based on the total amount (100 mass%) of the grease composition. Furthermore, the total content is usually 100 mass% or less, preferably less than 100 mass%, more preferably 99 mass% or less, and even more preferably 98 mass% or less. The grease composition of this embodiment may contain components other than components (A), (B), (C), (D), (E), and (F) within a range that does not impair the effects of the present invention.

[0016] <Base Oil (A)> The grease composition of the present embodiment contains a base oil (A). Examples of the base oil (A) include one or more oils selected from the group consisting of mineral oils, synthetic oils, and vegetable oils.

[0017] Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; mineral oils obtained by subjecting the distillates to one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; wax isomerized mineral oil, etc. Note that one mineral oil may be used alone, or two or more mineral oils may be used in combination.

[0018] Examples of synthetic oils include hydrocarbon oils, aromatic oils, ester oils, ether oils, and fatty acid esters. One type of synthetic oil may be used alone, or two or more types may be used in combination.

[0019] Examples of hydrocarbon oils include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, 1-decene and ethylene co-oligomer and other poly-α-olefins (PAO), and hydrogenated products thereof.

[0020] Examples of aromatic oils include alkylbenzenes such as monoalkylbenzenes and dialkylbenzenes; alkylnaphthalenes such as monoalkylnaphthalenes, dialkylnaphthalenes, and polyalkylnaphthalenes; and the like.

[0021] Examples of ester oils include diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, and methyl acetyl ricinoleate; aromatic ester oils such as trioctyl trimellitate, tridecyl trimellitate, and tetraoctyl pyromellitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane bellargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol bellargonate; and complex ester oils such as oligoesters of polyhydric alcohols and mixed fatty acids of dibasic and monobasic acids.

[0022] Examples of ether-based oils include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether; and phenyl ether-based oils such as monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyl tetraphenyl ether, and dialkyl tetraphenyl ether.

[0023] The fatty acid constituting the fatty acid ester is preferably a fatty acid having 8 to 22 carbon atoms, and specific examples thereof include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, erucic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, isostearic acid, arachic acid, ricinoleic acid, 12-hydroxystearic acid, etc. Specific examples of the fatty acid ester include glycerin fatty acid ester, polyglycerin fatty acid ester, and propylene glycol fatty acid ester.

[0024] Examples of glycerin fatty acid esters include glycerin monooleate, glycerin monostearate, glycerin monocaprylate, glycerin dioleate, glycerin distearate, and glycerin dicaprylate.

[0025] Examples of polyglycerol fatty acid esters include diglycerol monooleate, diglycerol monoisostearate, diglycerol dioleate, diglycerol trioleate, diglycerol monostearate, diglycerol distearate, diglycerol tristearate, diglycerol triisostearate, diglycerol monocaprylate, diglycerol dicaprylate, diglycerol tricaprylate, triglycerol monooleate, and triglycerol dioleate. , Triglycerol trioleate, Triglycerol tetraoleate, Triglycerol monostearate, Triglycerol distearate, Triglycerol tristearate, Triglycerol tetrastearate, Triglycerol monocaprylate, Triglycerol dicaprylate, Triglycerol tricaprylate, Triglycerol tetracaprylate, Diglycerol monooleate monostearate, Diglycerol monooleate distearate, Diglycerol monocaprylate monostearate, Triglycerol monooleate monostearate, Triglycerol dioleate distearate, Triglycerol dioleate monostearate, Triglycerol monooleate monostearate monocaprylate, Diglycerol monolaurylate, Diglycerol dilaurylate, Triglycerol monolaurylate, Triglycerol trilaurylate, Triglycerol trilaurylate, Diglycerol Examples of such glycerin include glycerin monomyristate, diglycerin dimyristate, triglycerin monomyristate, triglycerin dimyristate, triglycerin trimyristate, diglycerin monolinoleate, diglycerin dilinoleate, triglycerin monolinoleate, triglycerin dilinoleate, triglycerin trilinoleate, decaglycerin monooleate, decaglycerin monostearate, and decaglycerin monocaprylic acid monooleate.

[0026] Examples of propylene glycol fatty acid esters include propylene glycol monooleate, propylene glycol monostearate, propylene glycol monocaprylate, and propylene glycol monolaurate.

[0027] <<Vegetable Oil (A1)>> The base oil (A) preferably contains a vegetable oil (A1). By including the vegetable oil (A1) in the base oil (A), it is possible to reduce the environmental load and improve the safety of the grease composition.

[0028] Examples of the vegetable oil (A1) include crude oil obtained by squeezing and extracting natural vegetable oil raw materials; refined oil that has been subjected to various refining treatments such as filtration to remove suspended impurities contained in the crude oil, degumming to remove phospholipids and the like, deacidification to remove free fatty acids, bleaching to remove pigments, and dewaxing to remove wax; and processed oil that has been further subjected to treatments such as hardening, fractionation, transesterification, and hydrogenation.

[0029] Specific examples of the vegetable oil (A1) include oils derived from plants, such as rapeseed oil, peanut oil, corn oil, cottonseed oil, canola oil, soybean oil, camellia oil, olive oil, peanut oil, sunflower oil (preferably high oleic type), safflower oil (preferably high oleic type), safflower oil (preferably high oleic type), palm oil, palm kernel oil, coconut oil, rice bran oil, sesame oil, perilla oil, linseed oil, grape seed oil, and plant-derived base oils such as estolide esters. The vegetable oil (A1) may be composed of only one type of vegetable oil, or may be a mixed vegetable oil composed of two or more types of vegetable oils.

[0030] Examples of fatty acids constituting the vegetable oil (A1) include one or more selected from oleic acid, linoleic acid, linolenic acid, palmitic acid, stearic acid, palmitoleic acid, arachidic acid, eicosenoic acid, behenic acid, erucic acid, lignoceric acid, lauric acid, myristic acid, etc., and a particularly representative example is oleic acid. Note that "fatty acids constituting the vegetable oil (A1)" refers to fatty acids in compounds constituting the vegetable oil, in which fatty acids and glycerin are ester-bonded.

[0031] From the viewpoint of further improving the oxidation stability of the grease composition, the content of oleic acid among the fatty acids constituting the vegetable oil (A1) is preferably 50 mass% or more, based on the total amount of constituent fatty acids in the vegetable oil (A1). From the same viewpoint, the content of oleic acid is more preferably 55 mass% or more, and even more preferably 60 mass% or more, based on the total amount of constituent fatty acids in the vegetable oil (A1). Furthermore, the content of oleic acid is typically less than 85 mass% based on the total amount of constituent fatty acids in the vegetable oil (A1). Examples of methods for measuring the fatty acid composition of the vegetable oil (A1) include a method in which lipids are extracted from the vegetable oil (A1) with an organic solvent, the organic solvent is then distilled off, and fatty acid methyl esters are then prepared from the obtained lipids and subjected to gas chromatography mass spectrometry (GC-MS analysis).

[0032] From the viewpoint of making it easier to improve the oxidation stability of the grease composition, the content of saturated fatty acids among the fatty acids constituting the vegetable oil (A1) is preferably 3 mass% or more, more preferably 4 mass% or more, and even more preferably 5 mass% or more, based on the total amount of constituent fatty acids in the vegetable oil (A1).

[0033] Of the fatty acids constituting the vegetable oil (A1), the total content of oleic acid, linoleic acid, and linolenic acid is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on the total amount of constituent fatty acids in the vegetable oil (A1).

[0034] Among the fatty acids constituting the vegetable oil (A1), the content of erucic acid is preferably 0% by mass to 45% by mass, more preferably 1% by mass to 35% by mass, and even more preferably 2% by mass to 20% by mass, based on the total amount of constituent fatty acids in the vegetable oil (A1).

[0035] The content of the vegetable oil (A1) is appropriately adjusted depending on the composition of the vegetable oil (A1). For example, the content of the vegetable oil (A1) is 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, 90 mass% or more, or 100 mass% based on the total amount of the base oil (A).

[0036] The kinematic viscosity at 40°C of the base oil (A) used in this embodiment is preferably 10 mm ２ / s or more, more preferably 20 mm ２ / s or more, more preferably 30 mm ２ / s or more, and even more preferably 35 mm ２ In addition, the base oil (A) of this embodiment preferably has a kinematic viscosity at 40°C of 120 mm / s or more, from the viewpoint of making it easier to exhibit the effects of the present invention. ２ / s or less, more preferably 100 mm ２ / s or less, more preferably 90 mm ２ / s or less, and even more preferably 80 mm ２ The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 10 to 120 mm ２ / s, more preferably 20 to 100 mm ２ / s, more preferably 30 to 90 mm ２ / s, and even more preferably 35 to 80 mm ２ / s.

[0037] The kinematic viscosity at 100°C of the base oil (A) used in this embodiment is preferably 2.0 mmHg, from the viewpoint of easily exhibiting the effects of the present invention. ２ / s or more, more preferably 3.0 mm ２ / s or more, more preferably 4.0 mm ２In addition, the base oil (A) of this embodiment preferably has a 100°C kinematic viscosity of 20 mm / s or more, from the viewpoint of making it easier to exhibit the effects of the present invention. ２ / s or less, more preferably 18 mm ２ / s or less, more preferably 16 mm ２ The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 2.0 to 20 mm ２ / s, more preferably 3.0 to 18 mm ２ / s, more preferably 4.0 to 16 mm ２ The base oil (A) used in this embodiment may be a mixed base oil prepared by combining a high-viscosity base oil and a low-viscosity base oil to have a kinematic viscosity within the above range.

[0038] From the viewpoint of making it easier to exert the effects of the present invention, the viscosity index of the base oil (A) used in this embodiment is preferably at least 90, more preferably at least 110, and even more preferably at least 130. In this specification, the kinematic viscosity and viscosity index of the base oil (A) refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0039] In the grease composition of this embodiment, the content of base oil (A) is, based on the total amount (100 mass%) of the grease composition, preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, and still more preferably 80 mass% or more. The content of base oil (A) is, based on the total amount (100 mass%) of the grease composition, preferably 100 mass% or less, more preferably 98 mass% or less, even more preferably 97 mass% or less, and still more preferably 95 mass% or less.

[0040] <Hydrophilic nanofibers (B)> Hydrophilic nanofibers refer to fibrous materials having a thickness of 500 nm or less that are composed of a forming material containing a hydrophilic compound, and are distinguished from particulate materials. Hydrophilic nanofibers (B) have a low environmental impact and are safe for the human body. Therefore, by including hydrophilic nanofibers (B), it is possible to reduce the environmental impact and improve the safety of the grease composition.

[0041] (Criteria for determining "hydrophilicity") Whether a nanofiber is "hydrophilic" or not is determined as follows: The target nanofiber (fibrous material) is formed into a sheet-like material, and a water droplet is dropped onto the surface of the sheet-like material. The nanofiber is determined to be "hydrophilic" if (1) the contact angle with water is 90° or less, or (2) the dropped water droplet is quickly absorbed into the sheet-like material.

[0042] ("Thickness" of Hydrophilic Nanofibers) Furthermore, the definition of the "thickness" of a hydrophilic nanofiber is the same as the definition of the thickness of a general fibrous material. Specifically, when a hydrophilic nanofiber is cut perpendicular to the tangent direction at any point on its side surface, if the cut surface is a circle or an ellipse, the diameter or major axis of the hydrophilic nanofiber is the "thickness" of the hydrophilic nanofiber. If the cut surface is a polygon, the diameter of the circumscribing circle of the polygon is the "thickness" of the hydrophilic nanofiber.

[0043] When a flake-like, powder-like, or particulate hydrophilic compound having a size of several microns or more is blended with a base oil as a thickener, the hydrophilic compound tends to aggregate in the base oil, forming so-called "lumps." As a result, aggregates of the hydrophilic compound precipitate on the surface of the resulting grease composition, making the dispersion state uneven. In this case, adding a large amount of the hydrophilic compound is necessary to increase the worked penetration of the resulting grease composition. However, since the grease composition contains particles larger than the oil film thickness, it results in a grease composition with poor wear resistance. On the other hand, the grease composition of the present invention blends hydrophilic nanofibers having a thickness (d) of 1 nm to 500 nm with the base oil, and therefore the hydrophilic nanofibers do not aggregate in the base oil, allowing the hydrophilic nanofibers to be uniformly dispersed, while forming a high-order structure due to the hydrophilic nanofibers. As a result, a grease composition with an appropriate worked penetration can be obtained despite the small amount of hydrophilic nanofiber content.

[0044] (Thickness (d) and aspect ratio of hydrophilic nanofibers) In the present invention, the "thickness (d) of hydrophilic nanofibers" refers to the thickness of the hydrophilic nanofibers dispersed in the base oil, and is distinguished from the "thickness (d') of the hydrophilic nanofibers" as a raw material before being blended into the base oil, which will be described later. However, there is almost no difference between the "thickness (d) of the hydrophilic nanofibers" dispersed in the base oil and the "thickness (d') of the hydrophilic nanofibers" as a raw material before being blended into the base oil. Therefore, the "thickness (d) of the hydrophilic nanofibers" dispersed in the base oil and the "thickness (d') of the hydrophilic nanofibers" as a raw material before being blended into the base oil can be considered to be substantially the same. The thickness (d) of the hydrophilic nanofibers dispersed in the base oil is 1 nm to 500 nm, but from the viewpoint of forming a higher-order structure of the hydrophilic nanofibers in the base oil and dispersing the hydrophilic nanofibers more uniformly, the thickness is preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm.

[0045] It is sufficient that the hydrophilic nanofibers contained in the grease composition of the present invention are dispersed with at least hydrophilic nanofibers having a thickness (d) within the above range, and hydrophilic nanofibers having a thickness (d) outside the above range may also be dispersed. However, in the grease composition of one embodiment of the present invention, from the viewpoint of forming a higher-order structure of the hydrophilic nanofibers in the base oil and from the viewpoint of dispersing the hydrophilic nanofibers more uniformly, the average thickness (d) of 10 hydrophilic nanofibers arbitrarily selected from the hydrophilic nanofibers dispersed in the base oil is 1 nm to 500 nm, preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm. Furthermore, from the above viewpoint, it is preferable that, among 10 arbitrarily selected hydrophilic nanofibers contained in the grease composition of the present invention, the number of hydrophilic nanofibers having a thickness (d) within the above range is 1 or more (more preferably 5 or more, and even more preferably 7 or more), and it is even more preferable that all of the selected 10 hydrophilic nanofibers have a thickness (d) within the above range.

[0046] In the grease composition of one embodiment of the present invention, the aspect ratio of the hydrophilic nanofiber is preferably 5 or greater, more preferably 10 or greater, even more preferably 15 or greater, even more preferably 30 or greater, and even more preferably 50 or greater. In this specification, "aspect ratio" refers to the ratio of the length to the thickness (length / thickness) of the hydrophilic nanofiber being observed, and the "length" of the hydrophilic nanofiber refers to the distance between the two most distant points on the hydrophilic nanofiber. Furthermore, if a portion of the hydrophilic nanofiber being observed is in contact with other hydrophilic nanofibers, making it difficult to determine its "length," the length of only the portion of the hydrophilic nanofiber being observed whose thickness can be measured can be measured, and the aspect ratio of that portion should be within the above-mentioned range. Furthermore, the average aspect ratio (hereinafter also referred to as the "average aspect ratio") of 10 arbitrarily selected hydrophilic nanofibers contained in the grease composition of the present invention is preferably 5 or greater, more preferably 10 or greater, even more preferably 15 or greater, even more preferably 30 or greater, and even more preferably 50 or greater.

[0047] (Thickness (d') and aspect ratio of hydrophilic nanofibers) The thickness (d') of the hydrophilic nanofibers as a raw material before mixing with the base oil is 1 nm to 500 nm, preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm. Furthermore, the average aspect ratio of the hydrophilic nanofibers as a raw material before mixing with the base oil is preferably 5 or more, more preferably 10 or more, even more preferably 15 or more, still more preferably 30 or more, and even more preferably 50 or more.

[0048] In this specification, the "thickness (d)" of the hydrophilic nanofibers dispersed in the base oil, the "thickness (d')" of the hydrophilic nanofibers as raw materials before being blended into the base oil, and the aspect ratios of these hydrophilic nanofibers are values ​​measured using an electron microscope or the like.

[0049] (Materials for forming hydrophilic nanofibers) The hydrophilic nanofibers used in one embodiment of the present invention may be made from a material containing a compound having hydrophilicity. Examples of hydrophilic compounds include compounds having a functional group with a hydrogen-bonding hydroxyl group, such as a hydroxyl group or an amino group, and metal oxides. However, from the viewpoint of providing a grease composition that has a low environmental impact and excellent safety for the human body, and from the viewpoint of improving affinity with the base oil, the hydrophilic nanofibers used in one embodiment of the present invention preferably contain a polysaccharide, more preferably contain one or more polysaccharides selected from cellulose, carboxymethylcellulose, chitin, and chitosan, even more preferably contain cellulose, and even more preferably are cellulose nanofibers.

[0050] Lignocellulose can also be used as a raw material for cellulose nanofibers. Lignocellulose is a complex hydrocarbon polymer that constitutes the cell walls of plants and is known to be composed mainly of the polysaccharides cellulose and hemicellulose and the aromatic polymer lignin. The cellulose that constitutes the cellulose nanofibers may be one or more types selected from lignocellulose and acetylated lignocellulose. Furthermore, the cellulose nanofibers may contain one or more types selected from hemicellulose and lignin. Furthermore, the cellulose that constitutes the cellulose nanofibers may be chemically bonded to one or more types selected from hemicellulose and lignin.

[0051] The hydrophilic nanofibers used in one embodiment of the present invention may be those whose surfaces have been subjected to a modification treatment. More specifically, hydrophilic nanofibers whose surfaces have been subjected to one or more modification treatments selected from esterification such as acetylation, phosphorylation, urethanation, carbamidation, etherification, carboxymethylation, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation, and periodate oxidation may also be used.

[0052] In the hydrophilic nanofiber used in one embodiment of the present invention, the polysaccharide content is preferably 60% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass to 100% by mass, based on the total amount (100% by mass) of the hydrophilic nanofiber.

[0053] The degree of polymerization of the polysaccharide is preferably 50 to 3,000, more preferably 100 to 1,500, even more preferably 150 to 1,000, and still more preferably 200 to 800. In the present invention, the degree of polymerization of the polysaccharide polymer means a value measured by a viscosity method.

[0054] (Hydrophilic Nanofiber Content) In the grease composition of one embodiment of the present invention, the content of the hydrophilic nanofibers (B) is preferably 0.1 to 15 mass%, more preferably 0.5 to 13 mass%, even more preferably 0.7 to 10 mass%, still more preferably 1.0 to 8.0 mass%, and even more preferably 1.5 to 6.0 mass%, based on the total amount (100 mass%) of the grease composition. When the content of the hydrophilic nanofibers (B) is 0.1 mass% or more, it is easy to prepare a grease composition having an appropriate worked penetration. Furthermore, when the content of the hydrophilic nanofibers (B) is 20 mass% or less, it is easy to prepare a grease composition.

[0055] <Particles (C)> The grease composition of this embodiment contains particles (C). The particles (C) have a structure having hydrophobic groups on the outermost surface of a hydrophilic matrix structure, and the average particle diameter of the particles (C) in the grease composition is 1 nm to 500 nm. By containing particles (C) in the grease composition of this embodiment, it is possible to provide a grease composition that has an appropriate degree of oil separation and excellent water resistance, even while using hydrophilic nanofibers. The average particle diameter of the particles (C) (average particle diameter of primary particles) is preferably 3 nm to 400 nm, and more preferably 5 nm to 300 nm. The average particle diameter of the particles (C) can be measured, for example, from an image of the primary particles obtained by observing the grease composition with an electron microscope.

[0056] The hydrophilic matrix structure of particles (C) is not particularly limited as long as it can control particles (C) to have an average particle size within the above range, and the constituent material thereof is also not particularly limited as long as it is a hydrophilic material. From the viewpoint of satisfying the requirement of an "average particle size of 1 nm to 500 nm," examples of hydrophilic materials that constitute the hydrophilic matrix structure of particles (C) include mineral-based materials such as bentonite, and metal oxide-based materials such as silica and alumina. Among these, silica is preferred, and fumed silica is more preferred, from the viewpoint of improving the effects of the present invention.

[0057] The hydrophobic group of the particles (C) is not particularly limited as long as it is a hydrophobic group that can be bonded to the outermost surface of the hydrophilic matrix structure. For example, when the material constituting the hydrophilic matrix structure is silica, the silica preferably has one or more hydrophobic groups selected from the group consisting of dimethylsilyl groups, trimethylsilyl groups, and dimethylpolysiloxanes. These hydrophobic groups can be formed on the silica surface by surface-treating the silica with one or more surface-treating agents selected from the group consisting of dimethyldicyclosilane, hexamethyldisilazane, and silicone oils.

[0058] In a more preferred embodiment of the particles (C), the fumed silica has one or more hydrophobic groups (preferably dimethylsilyl groups) selected from the group consisting of dimethylsilyl groups, trimethylsilyl groups, and dimethylpolysiloxanes. These substituents can be formed on the surface of the fumed silica by surface-treating the fumed silica with one or more surface-treating agents (preferably dimethyldicyclosilane) selected from the group consisting of dimethyldicyclosilane, hexamethyldisilazane, and silicone oils.

[0059] Suitable examples of particles (C) include the Aerosil (registered trademark) series manufactured by EVONIK (Aerosil (registered trademark) R972, R974, R9200, R976, R976S, NX130, RY200S, R202, RX200, R8200, RY200, RY200L, RX300, R812, R812S, RY300) and the HDK (registered trademark) series manufactured by Wacker Asahi Kasei Silicone Co., Ltd. (HDK (registered trademark) H15, H15P, H17, H18, H20, H30, H2000). One type of particle (C) may be used alone, or two or more types may be used in combination.

[0060] The content of particles (C) is, based on the total amount (100 mass%) of the grease composition, preferably 6.0 mass% or more, more preferably 6.5 mass% or more, even more preferably 7.0 mass% or more, and even more preferably 10.0 mass% or more, and is preferably 20.0 mass% or less, more preferably 18.0 mass% or less, and even more preferably 16.0 mass% or less.

[0061] <Antioxidant (D)> The grease composition of the present embodiment may contain an antioxidant (D). When the base oil (A) in the grease composition of the present embodiment contains the vegetable oil (A1), the grease composition may also contain the antioxidant (D), thereby improving the oxidation stability of the grease composition.

[0062] Examples of the antioxidant (D) include a phenol-based antioxidant (D1), a naphthylamine-based antioxidant (D2), a diphenylamine-based antioxidant (D3), etc. Among these, the phenol-based antioxidant (D1) and the naphthylamine-based antioxidant (D2) are preferred from the viewpoint of improving the oxidation suppression effect.

[0063] <<Phenol-based antioxidant (D1)>> The phenol-based antioxidant (D1) may be a phosphorus-free phenol-based antioxidant that is generally used as an antioxidant for lubricating oil compositions. The phenol-based antioxidant (D1) may be used alone or in combination of two or more.

[0064] From the viewpoint of further improving the effects of the present invention, the phenolic antioxidant (D1) preferably contains a compound (D1-1) represented by the following general formula (d1-1): From the same viewpoint, the content of the compound (D1-1) in the phenolic antioxidant (D1) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the phenolic antioxidant (D1).

[0065]

[0066] In the above general formula (d1-1), R ｄ１ is an alkylene group having 1 to 5 carbon atoms. ｄ１ The number of carbon atoms in the alkylene group that can be selected as R is preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2, from the viewpoint of further improving the effects of the present invention. ｄ１ Specific examples of the alkylene group that can be selected as aryl include linear alkylene groups such as a methylene group, an ethylene group, an n-propylene group, an n-butylene group, and an n-pentylene group; and branched alkylene groups such as an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, and a neopentylene group.

[0067] In the above general formula (d1-1), R ｄ２ is an alkyl group having 1 to 25 carbon atoms. ｄ２ The number of carbon atoms in the alkyl group that can be selected as R is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, from the viewpoint of making it easier to improve the effects of the present invention. It is also preferably 22 or less, more preferably 21 or less, and even more preferably 20 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 2 to 20, more preferably 4 to 15, and even more preferably 6 to 10. R ｄ２Specific examples of alkyl groups that can be selected as include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, heniicosyl, docosyl, tricosyl, tetracosyl, and pentacosyl groups. These may be linear or branched.

[0068] The compound (D1-1) may be used alone or in combination of two or more.

[0069] <<Naphthylamine-Based Antioxidant (D2)>> As the naphthylamine-based antioxidant (D2), any naphthylamine-based antioxidant commonly used as an antioxidant for lubricating oil compositions can be used. The naphthylamine-based antioxidant (D2) may be used alone or in combination of two or more.

[0070] The naphthylamine-based antioxidant (D2) may be unsubstituted or may have a substituent such as an alkyl group.

[0071] From the viewpoint of further improving the effects of the present invention, the naphthylamine antioxidant (D2) preferably contains a compound (D2-1) represented by the following general formula (d2-1): From the same viewpoint, the content of the compound (D2-1) in the naphthylamine antioxidant (D2) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the naphthylamine antioxidant (D2).

[0072]

[0073] In the above general formula (d2-1), R ｂ１is an alkyl group having 1 to 30 carbon atoms. When the alkyl group has 1 to 30 carbon atoms, the effects of the present invention are more likely to be improved. ｂ１ The number of carbon atoms in the alkyl groups that can be selected as R is preferably 1 to 20, more preferably 4 to 16, and even more preferably 4 to 14, from the viewpoint of further improving the effects of the present invention. ｂ１ Specific examples of alkyl groups that can be selected as R ａ１ and R ａ２ Examples of the alkyl group that can be selected from include those exemplified above. The alkyl group may be linear or branched.

[0074] In the above general formula (d2-1), nb1 is an integer of 0 to 5. From the viewpoint of making it easier to improve the effects of the present invention, nb1 is preferably 0 or 1.

[0075] The compound (D2-1) may be used alone or in combination of two or more.

[0076] <<Diphenylamine-Based Antioxidant (D3)>> As the diphenylamine-based antioxidant (D3), diphenylamine-based antioxidants generally used as antioxidants for lubricating oil compositions can be used. The diphenylamine-based antioxidants (D3) may be used alone or in combination of two or more.

[0077] From the viewpoint of further improving the effects of the present invention, the diphenylamine antioxidant (D3) preferably contains a compound (D3-1) represented by the following general formula (d3-1): From the same viewpoint, the content of the compound (D3-1) in the diphenylamine antioxidant (D3) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the diphenylamine antioxidant (D3).

[0078]

[0079] In the above general formula (d3-1), R ａ１ and R ａ２ are each independently an alkyl group having 1 to 30 carbon atoms. When the alkyl group has 1 to 30 carbon atoms, the effects of the present invention are more likely to be improved. ａ１ and R ａ２ The number of carbon atoms in the alkyl groups that can be selected as R is preferably 1 to 20, more preferably 4 to 16, and even more preferably 4 to 14, from the viewpoint of further improving the effects of the present invention. ａ１ and R ａ２ Specific examples of alkyl groups that can be selected as include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, triacontyl, etc. These may be linear or branched.

[0080] In the general formula (d3-1), na1 and na2 each independently represent an integer of 1 to 5. From the viewpoint of making it easier to improve the effects of the present invention, na1 and na2 each independently represent preferably an integer of 1 to 3, more preferably 1 or 2, and even more preferably 1.

[0081] The compound (D3-1) may be used alone or in combination of two or more.

[0082] The content of the antioxidant (D) is, based on the total amount (100 mass%) of the grease composition, preferably 0.8 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, still more preferably 3.0 mass% or more, even more preferably 5.0 mass% or more, and is preferably 10 mass% or less, more preferably 9.0 mass% or less, and even more preferably 8.0 mass% or less.

[0083] <Rust inhibitor (E)> The grease composition of this embodiment may contain a rust inhibitor (E). The grease composition of this embodiment contains the hydrophilic nanofibers (B). However, the hydrophilic nanofibers (B) are highly hydrophilic and therefore prone to moisture absorption, which may cause rust. Therefore, by including the rust inhibitor (E) in the grease composition of this embodiment, the rust prevention properties of the grease composition can be improved.

[0084] Examples of the rust inhibitor (E) include fatty acid soap, carboxylic acid-based rust inhibitor, carboxylate-based rust inhibitor, sulfonic acid metal salt, organic phosphite ester, organic phosphate ester, amine salt of organic phosphate ester, organic phosphate metal salt, alkenyl succinate ester, alkenyl succinic acid polyhydric alcohol ester, amine-based rust inhibitor, fatty acid amine, thiadiazole and its derivative, benzotriazole and its derivative, etc. The rust inhibitor (E) may be used alone or in combination of two or more. Among these, fatty acid soap, amine salt of organic phosphate ester, and sulfonic acid metal salt are preferred.

[0085] The fatty acid soap is not particularly limited, and examples thereof include fatty acid zinc salts, fatty acid aluminum salts, fatty acid calcium salts, and fatty acid magnesium salts. Among these, fatty acid zinc salts are preferred. The number of carbon atoms in the fatty acid zinc salts is preferably 4 to 30, more preferably 6 to 24, and even more preferably 8 to 20. Examples of fatty acid zinc salts include zinc stearate and zinc neodecanoate.

[0086] The amine salt of an organic phosphate is not particularly limited, and examples thereof include an organic phosphate amine salt having a hydrocarbon group having 1 to 30 carbon atoms. The number of carbon atoms in the organic phosphate amine salt is preferably 4 to 24, and more preferably 8 to 18.

[0087] Metal sulfonates are metal salts of various sulfonic acids. Examples of sulfonic acids that form metal sulfonates include aromatic petroleum sulfonic acids, alkyl sulfonic acids, aryl sulfonic acids, and alkylaryl sulfonic acids. More specifically, preferred examples include dodecylbenzenesulfonic acid, dilauryl cetylbenzenesulfonic acid, paraffin wax-substituted benzenesulfonic acid, polyolefin-substituted benzenesulfonic acid, polyisobutylene-substituted benzenesulfonic acid, naphthalenesulfonic acid, and dinonylnaphthalenesulfonic acid. Preferred examples of metals that form metal sulfonates include sodium, magnesium, calcium, zinc, and barium. There are no particular limitations on the base number of these metals, and they may be neutral or overbased.

[0088] The rust inhibitor (E) preferably contains a fatty acid zinc salt and an organic phosphate amine salt in combination. Examples of the fatty acid zinc salt used in combination with the organic phosphate amine salt include zinc stearate and zinc neodecanoate.

[0089] When a fatty acid zinc salt and an organic phosphate amine salt are used in combination, the total content of the fatty acid zinc salt and the organic phosphate amine salt is, from the viewpoint of rust prevention, preferably 0.1% by mass to 10.0% by mass, more preferably 0.3% by mass to 8.0% by mass, even more preferably 0.4% by mass to 5.0% by mass, still more preferably 0.5% by mass to 3.0% by mass, and even more preferably 0.8% by mass to 1.5% by mass.

[0090] When a fatty acid zinc salt and an organic phosphate amine salt are used in combination, the ratio of (fatty acid zinc salt / organic phosphate amine salt) is preferably 1 / 9 to 9 / 1, more preferably 3 / 7 to 8 / 2, and even more preferably 5 / 5 to 7 / 3.

[0091] The content of the rust inhibitor (E) is, based on the total amount (100 mass%) of the grease composition, preferably 0.1 mass% to 10.0 mass%, more preferably 0.3 mass% to 8.0 mass%, even more preferably 0.4 mass% to 5.0 mass%, still more preferably 0.5 mass% to 3.0 mass%, and even more preferably 0.8 mass% to 2.0 mass%.

[0092] <Additive (F)> The grease composition of this embodiment may further contain additive (F) that is blended into a general grease composition, as long as the effects of the present invention are not impaired. Examples of additive (F) include dispersants, lubricity improvers, thickeners, detergent dispersants, corrosion inhibitors, extreme pressure agents, and metal deactivators. These various additives may be used alone or in combination of two or more.

[0093] (Dispersant) The dispersant may be any solvent that is compatible with both water and oil, and examples thereof include one or more selected from aprotic polar solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as propanol, ethylene glycol, propylene glycol, and hexylene glycol; and surfactants such as polyglycerin fatty acid esters, sucrose fatty acid esters, citric acid monoglycerides, diacetyltartaric acid monoglycerides, polyoxyethylene sorbitan acid esters, and sorbitan acid esters. Specific examples include sorbitan trioleate, succinic acid half esters, urea, and various surfactants.

[0094] When the grease composition of one embodiment of the present invention contains a dispersant, the content of the dispersant is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.2% by mass to 5% by mass, based on the total amount (100% by mass) of the grease composition.

[0095] (Lubricity Improver) Examples of lubricity improvers include sulfur compounds (sulfurized fats and oils, sulfurized olefins, polysulfides, sulfurized mineral oils, thiophosphates such as triphenyl phosphorothioate, thiocarbamic acids, thioterpenes, dialkylthiodipropionates, etc.), phosphate esters, phosphites (tricresyl phosphate, triphenyl phosphite, etc.), etc. When the grease composition of this embodiment contains a lubricity improver, the content of the lubricity improver is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.2% by mass to 5% by mass, based on the total amount (100% by mass) of the grease composition.

[0096] (Thickener) A thickener increases the viscosity of the base oil as needed and is blended to adjust the base oil containing the thickener to an appropriate kinematic viscosity. Examples of thickeners include polymethacrylate (PMA), olefin copolymer (OCP), polyalkylstyrene (PAS), and styrene-diene copolymer (SCP). When the grease composition of this embodiment contains a thickener, the content of the thickener is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.2% by mass to 5% by mass, based on the total amount (100% by mass) of the grease composition.

[0097] (Detergent-dispersant, corrosion inhibitor, extreme pressure agent, metal deactivator) Examples of detergent-dispersants include succinimide and boron-based succinimide. Examples of corrosion inhibitors include benzotriazole-based compounds and thiazole-based compounds. Examples of extreme pressure agents include phosphorus-based compounds, zinc dithiophosphate, and organic molybdenum. Examples of metal deactivators include benzotriazole. When the grease composition of this embodiment contains these additives, the content of each of these additives is preferably 0.01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass, and even more preferably 0.2% by mass to 5% by mass, based on the total amount (100% by mass) of the grease composition.

[0098] [Characteristics of the Grease Composition] In the grease composition of this embodiment, the hydrophilic groups of the hydrophilic nanofibers (B) are protected by the particles (C), so the hydrophilic nanofibers (B) are pseudo-hydrophobic. Therefore, the grease composition of this embodiment has an appropriate degree of oil separation and excellent water resistance. Furthermore, in the grease composition of this embodiment, a higher-order structure is easily formed by the hydrophilic nanofibers (B), and the hydrophilic nanofibers (B) are uniformly dispersed in the base oil (A). Furthermore, the particles (C) are also uniformly dispersed in the base oil (A). Therefore, the grease composition of this embodiment is likely to have an appropriate worked consistency even when the contents of the hydrophilic nanofibers (B) and particles (C) are small.

[0099] [Physical Properties of Grease Composition] <Worked Penetration> From the viewpoint of pumpability and oil leakage prevention, the worked penetration of the grease composition of this embodiment at 25°C is preferably 220 to 430, more preferably 240 to 400, even more preferably 250 to 345, still more preferably 255 to 300, and even more preferably 265 to 295. In this specification, the worked penetration of the grease composition means a value measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0100] <Oil Separation Rate> The oil separation rate of the grease composition of this embodiment can be evaluated by the method described in the Examples below. From the viewpoint of suppressing oil leakage during use, the oil separation rate of the grease composition of this embodiment is preferably 10% by mass or less, more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, and preferably 0.5% by mass or more, more preferably 0.8% by mass or more, even more preferably 1.0% by mass or more. In this specification, the oil separation rate of the grease composition means a value measured in accordance with the oil separation rate test method of JIS K2220:2013 (Clause 11) under conditions of a temperature of 100°C and a time of 24 hours.

[0101] <Water-washing resistance> The water resistance of the grease composition of this embodiment can be evaluated by measuring the water-washing resistance by the method described in the Examples below. From the viewpoint of water resistance, the water-washing resistance of the grease composition of this embodiment is preferably 10% by mass or less, more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less. In this specification, the water-washing resistance of the grease composition means a value measured using water at 79°C in accordance with the water-washing durability test of JIS K2220:2013 (Clause 16).

[0102] <Oxidation Stability> The oxidation stability of the grease composition of this embodiment can be evaluated by measuring the oxidation stability using the method described in the Examples below. From the viewpoint of oxidation stability, the oxidation stability of the grease composition of this embodiment is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. In this specification, the oxidation stability of the grease composition means a value measured in accordance with the oxidation stability test of JIS K2220:2013 (Clause 12) under the conditions of a temperature of 99°C, a time of 100 hours, and an oxygen pressure of 750 kPa.

[0103] <Bearing Rust Prevention Test> The rust prevention properties of the grease composition of this embodiment can be evaluated by performing a bearing rust prevention test using the method described in the Examples below. From the perspective of rust prevention, it is preferable that the grease composition of this embodiment does not show reddish-brown or black discoloration (rust) on the surface when evaluated using the method described in the Examples below. In this specification, the rust prevention properties of the grease composition refer to a value evaluated in accordance with the bearing rust prevention test of ASTM D 1743, under conditions of a temperature of 52°C and a time of 48 hours.

[0104] [Method for Producing Grease Composition] The method for producing the grease composition of this embodiment preferably includes the following steps (1) to (3). Step (1): A step of preparing a mixed solution by mixing a base oil and a dispersant with an aqueous dispersion obtained by blending hydrophilic nanofibers in water, the nanofibers having a thickness (d') of 1 nm to 500 nm, preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm. Step (2): A step of removing water from the mixed solution to prepare a grease. Step (3): A step of blending particles (C) into the grease. Note that step (2) may also be a step of removing water and the dispersant from the mixed solution. The grease composition obtained through these steps can be dispersed in the base oil with hydrophilic nanofibers in a state where aggregation of the hydrophilic nanofibers is suppressed and the fibrous shape is maintained, with the hydrophilic nanofibers having a thickness (d) of 1 nm to 500 nm, preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm. As a result, it is presumed that the hydrophilic nanofibers and particles (C) form some kind of higher-order structure in the base oil, resulting in the preparation of a grease composition with an appropriate degree of oil separation and excellent water resistance. Steps (1) to (3) are described below.

[0105] <Step (1)> Step (1) is a step of preparing a mixed solution by mixing an aqueous dispersion of hydrophilic nanofibers in water, the hydrophilic nanofibers having a thickness (d') of 1 nm to 500 nm, preferably 3 nm to 300 nm, more preferably 5 nm to 200 nm, even more preferably 10 nm to 100 nm, still more preferably 15 nm to 70 nm, and even more preferably 20 nm to 50 nm, with a base oil and a dispersant. Details of the hydrophilic nanofibers and base oil used in step (1) are as described above. Note that, as described above, the "thickness (d')" here refers to the thickness of the hydrophilic nanofibers as a raw material before being blended into the base oil or water, and the preferred range of the "thickness (d')" is the same as described above.

[0106] The solids concentration of the aqueous dispersion containing hydrophilic nanofibers is typically 0.1% by mass to 70% by mass, preferably 0.1% by mass to 65% by mass, more preferably 0.1% by mass to 60% by mass, even more preferably 0.5% by mass to 55% by mass, and even more preferably 1.0% by mass to 50% by mass, based on the total amount (100% by mass) of the aqueous dispersion. The aqueous dispersion can be prepared by blending the hydrophilic nanofibers, and optionally a surfactant, into water, and stirring thoroughly either manually or with a stirrer. Powdered hydrophilic nanofibers may also be used as the hydrophilic nanofibers, and this may be added to water to form the aqueous dispersion.

[0107] The amount of the dispersant in the mixed liquid prepared in step (1) is, based on the total amount (100 mass%) of the mixed liquid, preferably 0.1 mass% to 50 mass%, more preferably 0.5 mass% to 40 mass%, even more preferably 1.0 mass% to 30 mass%, still more preferably 1.0 mass% to 20 mass%, and even more preferably 1.0 mass% to 10 mass%.

[0108] The amount of water in the mixed solution prepared in step (1) is preferably 1% by mass to 60% by mass, more preferably 3% by mass to 50% by mass, and even more preferably 5% by mass to 40% by mass, based on the total amount (100% by mass) of the mixed solution.

[0109] The blending ratio of water to dispersant (water / dispersant) in the mixed liquid prepared in step (1) is preferably 0.01 to 600, more preferably 0.05 to 400, even more preferably 0.1 to 300, and still more preferably 0.2 to 200, by mass.

[0110] The mixture may contain the aqueous dispersion containing hydrophilic nanofibers, the base oil, and the dispersant, as well as the various additives typically used in grease compositions.The mixture can be prepared by mixing these components and thoroughly stirring them manually or with a stirrer.

[0111] <Step (2)> Step (2) is a step of removing at least water from the mixed liquid prepared in step (1). In this step, the dispersant may be removed from the mixed liquid along with the water. A preferred method for removing the water and dispersant is to heat the mixed liquid to evaporate and remove the water and dispersant. The preferred conditions for evaporating and removing the water are to heat the mixed liquid at a temperature range of 0°C to 100°C under a pressure of 0.001 MPa to 0.1 MPa. The preferred conditions for evaporating and removing the dispersant are to heat the mixed liquid at a temperature range of [the boiling point of the dispersant (°C)] - 120°C to [the boiling point of the dispersant (°C)] - 0°C under a pressure of 0.001 MPa to 0.1 MPa. The evaporative removal of the water and dispersant may be performed by atmospheric distillation. A grease is prepared in step (2).

[0112] <Step (3)> Step (3) is a step of blending particles (C) with the grease prepared in step (2). Specifically, for example, the grease prepared in step (2) and particles (C) are mixed, and then homogenized using a homogenizer, a roll mill, or the like, to prepare the grease composition of this embodiment. If necessary, an antioxidant (D), a rust inhibitor (E), and an additive (F) may be blended at the same time as the particles (C) are mixed.

[0113] [Uses of the Grease Composition] The grease composition of the present embodiment uses hydrophilic nanofibers, yet has an appropriate degree of oil separation and excellent water resistance, and therefore can exhibit excellent lubricating performance even in hygroscopic environments.

[0114] Examples of mechanical parts to which the grease composition of the present embodiment can be applied include bearings and gears, and more specifically include various bearings such as sliding bearings and rolling bearings, gears, internal combustion engines, brakes, torque transmission device parts, fluid couplings, compression device parts, chains, hydraulic device parts, vacuum pump device parts, watch parts, hard disk drive parts, refrigeration machine parts, cutting machine parts, rolling mill parts, drawing and drawing machine parts, rolling machine parts, forging machine parts, heat treatment device parts, heat exchanger parts, washing machine parts, shock absorber parts, sealing device parts, etc. The grease of the present embodiment is also suitable for lubricating the sliding parts of general bearings, construction machinery bearings, etc.

[0115] According to one aspect of the present invention, the following items [1] to

[13] are provided. [1] A grease composition containing a base oil (A), hydrophilic nanofibers (B) having a thickness (d) of 1 nm to 500 nm, and particles (C), wherein the hydrophilic nanofibers (B) are one or more types selected from cellulose nanofibers (B1) and modified cellulose nanofibers (B2), and the particles (C) have a structure having hydrophobic groups on the outermost surface of a hydrophilic matrix structure, and the average particle diameter of the particles (C) in the grease composition is 1 nm to 500 nm. [2] The grease composition according to item [1], wherein the base oil (A) contains a vegetable oil (A1). [3] The grease composition according to item [1] or [2], wherein the content of the hydrophilic nanofibers (B) is 0.1 mass % to 20 mass % based on the total amount of the grease composition. [4] The grease composition according to any one of [1] to [3], wherein the hydrophilic matrix structure comprises silica particles. [5] The grease composition according to any one of [1] to [4], wherein the content of the particles (C) is 6.0 mass % or more, based on the total amount of the grease composition. [6] The grease composition according to any one of [1] to [5], further comprising an antioxidant (D). [7] The grease composition according to [6], wherein the antioxidant (D) comprises one or more selected from the group consisting of phenol-based antioxidants and naphthylamine-based antioxidants. [8] The grease composition according to [6] or [7], wherein the content of the antioxidant (D) is 0.8 mass % or more, based on the total amount of the grease composition. [9] The grease composition according to any one of [1] to [8], further comprising a rust inhibitor (E).

[10] The grease composition according to [9] above, wherein the rust inhibitor (E) comprises a zinc salt of a fatty acid and an organic phosphate ester amine salt.

[11] The grease composition according to [9] or

[10] above, wherein the content of the rust inhibitor (E) is 0.5% by mass to 3.0% by mass based on the total amount of the grease composition.

[12] The grease composition according to any one of [1] to

[11] above, wherein the worked penetration at 25°C is 220 to 430.

[13] A lubrication method, comprising lubricating a lubrication site with the grease composition according to any one of [1] to

[12] .

[0116] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0117] [Various physical properties] The various physical properties were measured as follows. (1) 40°C kinematic viscosity and viscosity index of base oil (A): Measured and calculated in accordance with JIS K2283:2000. (2) Thickness and aspect ratio of hydrophilic nanofibers of thickener (B): Using a transmission electron microscope (TEM), the thickness and length of 10 arbitrarily selected hydrophilic nanofibers were measured, and the value calculated from "length" / "thickness" was used as the "aspect ratio" of the hydrophilic nanofibers. (3) Worked penetration (1 / 2) of grease composition: Measured at 25°C in accordance with JIS K2220:2013 (Clause 7).

[0118] [Raw Materials] In Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-6, the base oil (A), hydrophilic nanofiber dispersion, particles (C), and dispersant used as raw materials for preparing the grease compositions were as follows.

[0119] <Base oil (A)> Base oil (A1): vegetable oil (rapeseed oil, product name: Fumi Sawayaka Oil, manufactured by Showa Sangyo Co., Ltd., kinematic viscosity at 40°C: 37.71, viscosity index: 208) Base oil (A2): poly-α-olefin (PAO) (kinematic viscosity at 40°C: 57.14, viscosity index: 146)

[0120] <Hydrophilic nanofiber (B)> Hydrophilic nanofiber dispersion (product name: nanoforest-S, manufactured by Chuetsu Pulp Co., Ltd., aqueous dispersion containing cellulose nanofiber (CNF) having a degree of polymerization of 600 (thickness (d'): 20 nm to 50 nm (average value: 35 nm), aspect ratio: 100 or more (average value: 100 or more))

[0121] <Particles (C)> Particle (C1): Hydrophobic silica gel (fumed silica surface treated with dimethyldichlorosilane, product name: Aerosil (registered trademark) R972, manufactured by EVONIK, average primary particle diameter: approximately 16 nm) Particle (C2): Organic bentonite (product name: Baragel 3000, manufactured by ELEMENTIS) Particle (C3): Organic bentonite (product name: Bentone (registered trademark) 27, manufactured by ELEMENTIS) Particle (C4): Organically modified mineral (product name: GARAMITE (registered trademark) 7303, manufactured by BYK) Comparative component (C'1): Polybutene Comparative component (C'2): Polymethacrylate (PMA)

[0122] <Antioxidants (D)> Antioxidant (D1): Phenolic antioxidant (n-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate) Antioxidant (D2): Phenolic antioxidant (n-octadecyl 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate) Antioxidant (D3): Naphthylamine Antioxidant (D4): Dinonyldiphenylamine

[0123] <Rust inhibitors (E)> Rust inhibitor (E1): A mixture of zinc stearate and an organic phosphate amine salt (mass ratio of zinc stearate / organic phosphate amine salt = 7 / 3, number of carbon atoms in the organic phosphate amine salt: 10 to 12) Rust inhibitor (E2): A mixture of zinc neodecanoate and an organic phosphate amine salt (product name: G-1340, manufactured by KING INDUSTRIES, number of carbon atoms in the organic phosphate amine salt: 10 to 12) Rust inhibitor (E3): Zinc stearate Rust inhibitor (E4): Organic phosphate amine salt Rust inhibitor (E5): A mixture of calcium sulfonate and sodium sulfonate Rust inhibitor (E6): Barium sulfonate (overbased) Rust inhibitor (E7): Sodium sulfonate (neutral) Rust inhibitor (E8): Sodium sulfonate (overbased)

[0124] <Additives (F)> Dispersant: sorbitan trioleate

[0125] Example 1-1 200 g of hydrophilic nanofiber dispersion (B) (containing 20.0 g of CNF), 438 g of base oil (A1), and 2.0 g of dispersant (F) were mixed and thoroughly stirred at 25°C to prepare a mixed solution. The mixed solution was then heated to 90°C under normal pressure (atmospheric pressure), and water was evaporated from the mixed solution. After cooling to room temperature (25°C), 40.0 g of particles (C1) was added to the mixed solution and thoroughly stirred. A homogenization treatment was then performed using a three-roll mill to prepare the grease composition of Example 1-1.

[0126] (Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-6) Grease compositions of Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-6 were prepared in the same manner as the grease composition of Example 1-1, except that the components and contents were changed as shown in Tables 1 and 2.

[0127] Next, the oil separation rate and water resistance of the grease compositions of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-6 were evaluated.

[0128] [Evaluation of oil separation rate] The mass percentage of oil separated from the grease composition was measured at a temperature of 100°C for 24 hours in accordance with the oil separation rate test of JIS K2220:2013 (Clause 11). An oil separation rate of 10% by mass or less was determined to be appropriate.

[0129] [Evaluation of Water Resistance] Using water at 79°C, the mass of the grease composition washed away with water (water resistance after washing) relative to the mass of the grease composition before the test (100 mass%) was measured in accordance with the water washing durability test of JIS K2220:2013 (Clause 16). If the water resistance after washing was 10 mass% or less, the water resistance was determined to be good.

[0130] The compositions, physical properties, and evaluation results of the grease compositions of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-6 are shown in Tables 1 and 2.

[0131]

[0132]

[0133] As shown in Table 1, it was found that the grease compositions of Examples 1-1 to 1-4 had an appropriate degree of oil separation and were also excellent in water resistance.

[0134] Example 2-1 Next, a grease composition of Example 2-1 was prepared in the same manner as in Example 1-1, except that 25 g of antioxidant (D1) was added to the mixed liquid together with 40.0 g of particles (C1).

[0135] Examples 2-2 to 2-13 Grease compositions of Examples 2-2 to 2-13 were prepared in the same manner as the grease composition of Example 2-1, except that the components and amounts thereof were changed as shown in Tables 3 and 4.

[0136] Next, the oil separation rate, water resistance, and oxidation stability of the grease compositions of Examples 2-1 to 2-13 are evaluated.

[0137] [Evaluation of oil separation degree] Measurement was performed in the same manner as in the above-mentioned "Evaluation of oil separation degree." Note that an oil separation degree of 10% by mass or less was determined to be an appropriate oil separation degree.

[0138] [Evaluation of Water Resistance] The degree of water resistance after washing was measured in the same manner as in the above-mentioned "Evaluation of Water Resistance." If the degree of water resistance after washing was 10% by mass or less, the water resistance was determined to be good.

[0139] [Evaluation of oxidation stability] In accordance with the oxidation stability test of JIS K2220:2013 (Clause 12), the pressure drop was measured under the conditions of a temperature of 99°C, a time of 100 hours, and an oxygen pressure of 750 kPa. If the oxidation stability was 80 or less, the oxidation stability was determined to be good.

[0140] The compositions, physical properties, and evaluation results of the grease compositions of Examples 2-1 to 2-13 are shown in Tables 3 and 4.

[0141]

[0142]

[0143] As shown in Tables 3 and 4, the grease compositions of Examples 2-1 to 2-13 were found to have an appropriate degree of oil separation and excellent water resistance. Furthermore, the grease compositions of Examples 2-1 to 2-6, 2-8, and 2-11 also had excellent oxidation stability.

[0144] Example 3-1 Next, a grease composition of Example 3-1 was prepared in the same manner as in Example 1-1, except that 25 g of an antioxidant (D1) and 5.0 g of a rust inhibitor (E1) were added to the mixed solution together with 20.0 g of particles (C1).

[0145] Examples 3-2 to 3-8 Grease compositions of Examples 3-2 to 3-8 were prepared in the same manner as the grease composition of Example 3-1, except that the components and amounts thereof were changed as shown in Table 5.

[0146] Next, the oil separation rate, water resistance, and rust prevention properties of the grease compositions of Examples 3-1 to 3-8 are evaluated.

[0147] [Evaluation of oil separation degree] Measurement was performed in the same manner as in the above-mentioned "Evaluation of oil separation degree." Note that an oil separation degree of 10% by mass or less was determined to be an appropriate oil separation degree.

[0148] [Evaluation of Water Resistance] The degree of water resistance after washing was measured in the same manner as in the above-mentioned "Evaluation of Water Resistance." If the degree of water resistance after washing was 10% by mass or less, the water resistance was determined to be good.

[0149] [Evaluation of Rust Prevention] In accordance with the bearing rust prevention test of ASTM D 1743, each grease composition was placed in a high-humidity thermostatic chamber at a temperature of 52°C for 48 hours, and visually observed for rust formation. The rust prevention was judged to be good if the rating was "A" in the following evaluation criteria. - Evaluation criteria - A: No reddish-brown or black discoloration (rust) was observed on the surface. B: Reddish-brown or black discoloration (rust) was observed on the surface.

[0150] The compositions, physical properties, and evaluation results of the grease compositions of Examples 3-1 to 3-8 are shown in Table 5.

[0151]

[0152] As shown in Table 5, the grease compositions of Examples 3-1 to 3-8 were found to have an appropriate degree of oil separation and excellent water resistance. Furthermore, the grease compositions of Examples 3-1 and 3-2 also had excellent rust prevention properties.

Claims

1. A grease composition containing a base oil (A), hydrophilic nanofibers (B) having a thickness (d) of 1 nm to 500 nm, and particles (C), The hydrophilic nanofiber (B) is one or more selected from cellulose nanofiber (B1) and modified cellulose nanofiber (B2). A grease composition in which the particles (C) have a structure in which hydrophobic groups are present on the outermost surface of a hydrophilic matrix structure, and the average particle diameter of the particles (C) in the grease composition is 1 nm to 500 nm.

2. The grease composition according to claim 1, wherein the base oil (A) comprises a vegetable oil (A1).

3. The grease composition according to claim 1 or 2, wherein the content of the hydrophilic nanofiber (B) is 0.1% by mass to 20% by mass on a basis of the total amount of the grease composition.

4. The grease composition according to claim 1 or 2, wherein the hydrophilic matrix structure includes silica particles.

5. The grease composition according to claim 1 or 2, wherein the content of the particles (C) is 6.0% by mass or more based on the total amount of the grease composition.

6. Furthermore, the grease composition according to claim 1 or 2, further containing an antioxidant (D).

7. The grease composition according to claim 6, wherein the antioxidant (D) comprises one or more selected from phenolic antioxidants and naphthylamine antioxidants.

8. The grease composition according to claim 6, wherein the content of the antioxidant (D) is 0.8% by mass or more based on the total amount of the grease composition.

9. Furthermore, the grease composition according to claim 1 or 2 contains a rust inhibitor (E).

10. The grease composition according to claim 9, wherein the rust inhibitor (E) comprises a fatty acid zinc salt and an organophosphate ester amine salt.

11. The grease composition according to claim 9, wherein the content of the rust inhibitor (E) is 0.5% by mass to 3.0% by mass on a basis of the total amount of the grease composition.

12. The grease composition according to claim 1 or 2, wherein the miscible consistency at 25°C is 220 to 430.

13. A lubrication method for lubricating a lubrication part using the grease composition described in claim 1 or 2.