Biodegradable grease composition

Abstract

The present invention provides a biodegradable grease composition comprising a base oil, a thickener, and an inorganic powder, wherein the base oil comprises a polyol ester oil and the thickener comprises a calcium complex soap.

Description

[Technical Field]

[0001] This invention relates to a biodegradable grease composition. [Background technology]

[0002] In recent years, with growing awareness of environmental issues, global environmental protection has begun to be emphasized in all industries. Most greases are used in sealed conditions and are therefore considered to have little impact on the natural environment. However, accidental leaks into the natural environment, such as soil, rivers, and seas, due to accidents or spills, can damage the natural environment. For this reason, the use of biodegradable grease compositions is desirable in applications where there is a possibility of grease leaking to the outside. At the same time, with advances in mechanical technology, lubrication environments are becoming more severe year by year, and the requirements for lubricity, such as thermal oxidation stability and extreme pressure, are also increasing.

[0003] Conventionally, biodegradable grease compositions that use highly biodegradable vegetable oils and polyol esters, metal soaps as thickeners, and extreme pressure agents as additives as base oils to satisfy these requirements have been disclosed, for example, in JP11228983, JP2003171683, and JP2008208240. [Overview of the project]

[0004] The present invention provides a biodegradable grease composition comprising a base oil, a thickener, and an inorganic powder, wherein the base oil comprises a polyol ester oil and the thickener comprises a calcium complex soap. [Modes for carrying out the invention]

[0005] However, it has been difficult to achieve both biodegradability and the required performance using conventional grease compositions. Therefore, the object of the present invention is to provide a grease composition that has heat resistance and stable lubrication function while simultaneously reducing the burden on the environment.

[0006] The inventors have conducted extensive studies and found that by using a grease composition containing a polyol ester base oil thickened with calcium complex soap and similarly containing inorganic powder, it is possible to obtain a grease composition that has heat resistance and stable lubrication function while simultaneously reducing environmental impact. This biodegradable grease composition has excellent performance and can be preferably applied to locations in automobiles, railways, construction machinery, or agricultural machinery where there is a risk of leakage.

[0007] One or more specific embodiments of this disclosure are described below. These embodiments described are examples of the technology of this disclosure. Furthermore, in order to provide a concise description of these embodiments, not all features of actual implementations may be described herein.

[0008] When describing elements of the various embodiments of this disclosure, the articles “a,” “an,” and “the” are intended to indicate that one or more of the elements exist. The terms “equip,” “include,” and “have” are intended to be inclusive and mean that additional elements other than those listed may exist. In addition, it should be understood that any reference in this disclosure to “one embodiment” or “embodiment” is not intended to be construed as excluding the existence of additional embodiments that also incorporate the listed features.

[0009] The base oil contains a polyol ester oil. The polyol ester base oil may be synthetic or natural. Preferably, the polyol ester oil contains an ester comprising one or more polyhydric alcohol components and one or more aliphatic monocarboxylic acid components. The preferred polyhydric alcohol components are one or more selected from the group consisting of neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. Preferably, the aliphatic monocarboxylic acid component is one or more aliphatic monocarboxylic acids containing 3 to 22 carbon atoms, more preferably 8 to 18 carbon atoms. More preferably, the aliphatic monocarboxylic acid component is one or more selected from the group consisting of caproic acid, caprylic acid, capric acid, undecanoic acid, lauric acid, palmitic acid, stearic acid, and oleic acid.

[0010] The base oil may contain base oils other than polyol ester oil. Preferably, the base oil other than polyol ester oil is one or more base oils selected from mineral oil, GTL base oil, and poly-α-olefin base oil.

[0011] The kinematic viscosity at 100°C for base oils other than polyol ester base oils is 13.00 mm². 2 The %CP of the base oil is less than / s, and the %CP of the base oil, as determined by analysis in accordance with ASTM D3238, is preferably 65% ​​or higher.

[0012] Poly-α-olefins are synthetic oils and may be monopolymers or copolymers composed of one or more α-olefins. Mineral oil is a base oil obtained by refining crude oil (such as paraffinic crude oil, naphthenic crude oil, or intermediate crude oil). In preferred embodiments, the mineral oil used in the present invention is obtained by distilling crude oil under atmospheric pressure and reduced pressure to obtain a lubricating oil fraction, to which one or more treatment processes selected from solvent decontamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment are applied. Examples of suitable mineral oils include paraffinic and naphthenic mineral oils.

[0013] GTL (Glass Liquefied) base oil is a base oil synthesized using the Fischer-Tropsch process, a liquid fuel technology for natural gas. Compared to mineral oil-based base oils refined from crude oil, GTL has extremely low sulfur and aromatic content, an extremely high paraffin composition ratio, and therefore excellent oxidation stability and extremely low evaporation loss.

[0014] The polyol ester oil content is preferably 30.0% by weight or more, more preferably 35.0% by weight or more, even more preferably 40.0% by weight or more, and most preferably 45.0% by weight or more, based on a total weight of 100.0% by weight of the biodegradable grease composition. Preferably, the polyol ester base oil is present in an amount of 75.0% by weight or less, based on the total weight of the biodegradable grease composition.

[0015] The content of base oils other than polyol ester oil is preferably at least 5.0% by weight, more preferably at least 10.0% by weight, and most preferably at least 14.0% by weight, relative to the total weight of the biodegradable grease composition. The content of base oils other than polyol ester oil is preferably at least at a maximum of 50.0% by weight, more preferably at a maximum of 40.0% by weight, and most preferably at a maximum of 35.0% by weight.

[0016] The thickener includes calcium complex soap. Calcium complex soap is a reaction product of basic calcium (usually calcium hydroxide) and two or more carboxylic acids. The carboxylic acids used to form the calcium complex soap preferably include higher fatty acids and lower fatty acids. More preferably, the carboxylic acids used to form the calcium complex soap include aromatic carboxylic acids in addition to higher fatty acids and lower fatty acids. It is particularly preferable that the carboxylic acids used in the calcium complex soap include dicarboxylic acids in addition to aromatic monocarboxylic acids. By incorporating carboxylic acids in this way, the soap fibers become intricately and densely intertwined. As a result, it is presumed that a biodegradable grease composition with excellent performance can be obtained. Furthermore, other carboxylic acids may be used as long as the effects of this disclosure are not impaired.

[0017] The higher fatty acid is not particularly limited as long as a calcium complex soap can be formed, but preferably one or more linear higher fatty acids having carbon atoms in the range of 18 to 22 carbon atoms. The linear higher fatty acid may have one or more substituents. The linear higher fatty acid may be a saturated fatty acid or an unsaturated fatty acid, but it is preferably a saturated fatty acid.

[0018] Specific examples of linear higher saturated fatty acids suitable for use in calcium complex soaps of this grease composition include stearic acid (octadecanoic acid, C18), tuberculous stearic acid (nonadecanoic acid, C19), arachidic acid (eicosanoic acid, C20), henicosanoic acid (C21), behenic acid (docosanoic acid, C22), and hydroxystearic acid (C18, castor oil hydrogenated fatty acid).

[0019] Examples of C18-C22 straight-chain unsaturated higher fatty acids include oleic acid, linoleic acid, linolenic acid (C18), gadaleic acid, eicosadienoic acid, meadic acid (C20), erucic acid, and docosadienoic acid (C22). Furthermore, hydrogenated oils can also be used instead of higher fatty acids. For example, hydrogenated oils can be produced by hydrogenating oils and fats containing a large amount of unsaturated fatty acids, such as castor oil, using a catalyst such as nickel.

[0020] The lower fatty acid is not particularly limited as long as a calcium complex soap can be formed, but is preferably one or more linear saturated lower fatty acids having 2 to 4 carbon atoms. Specific examples of the linear saturated lower fatty acids include acetic acid, propionic acid, butyric acid and the like.

[0021] The aromatic carboxylic acid is not particularly limited as long as a calcium complex soap can be formed, but is preferably one or more aromatic monocarboxylic acids having a substituted or unsubstituted benzene ring. The aromatic monocarboxylic acid may have one or more substituents (for example, o-, m- or p-alkyl group, hydroxy group, alkoxy group, etc.). In the present disclosure, the "substituent" and the alkyl moiety of the alkoxy are, for example, linear or branched alkyl having 1 to 4 carbon atoms in the range.

[0022] Specific examples of the aromatic monocarboxylic acids include benzoic acid, methylbenzoic acid {toluic acid (p-, m-, o-)}, dimethylbenzoic acid (xylilyl acid, hemeritic acid, mesitylic acid), trimethylbenzoic acid {prenicylic acid, zuric acid, isoduryl acid (α-, β-, γ-)}, 4-isopropylbenzoic acid (cumic acid), hydroxybenzoic acid (salicylic acid), dihydroxybenzoic acid {pyrocatechic acid, resorcylic acid (α-, β-, γ-), gentisic acid, protocatechuic acid}, trihydroxybenzoic acid (gallic acid), hydroxy-methylbenzoic acid {kresotinic acid (p-, m-, o-)}, dihydroxy-methylbenzoic acid (orcelinic acid), methoxybenzoic acid {anisic acid (p-, m-, o-)}, dimethoxybenzoic acid (veratoric acid), trimethoxybenzoic acid (asalonic acid), hydroxy-methoxybenzoic acid (vanillic acid, isovanillic acid), hydroxy-dimethoxybenzoic acid (syringic acid) and the like.

[0023] The dicarboxylic acid is not particularly limited as long as it can form a calcium complex soap, but is preferably one or more substituted or unsubstituted saturated dicarboxylic acids. The saturated dicarboxylic acid may be unsubstituted or may have one or more substituents (e.g., a hydroxyl group). The saturated dicarboxylic acid may be either linear or branched, but is preferably linear. The number of carbon atoms of the saturated dicarboxylic acid (in the case of a branched chain, the total number of carbon atoms in the main chain and side chains) is not particularly limited, but is preferably in the range of 4 to 20, more preferably in the range of 4 to 16, and particularly preferably in the range of 4 to 10.

[0024] Specific examples of the saturated dicarboxylic acid include oxalic acid (C2), malonic acid (C3), succinic acid (C4), 2-methylsuccinic acid, pentanedioic acids such as glutaric acid (C5), hexanedioic acids such as adipic acid (C6), heptanedioic acids such as pimelic acid (C7), octanedioic acids such as suberic acid (C8), nonanedioic acids such as azelaic acid (C9), decanedioic acids such as sebacic acid (C10), and examples thereof include undecanedioic acid (C11), dodecanedioic acid (C11), tridecanedioic acids such as brasyl acid (C13), tetradecanedioic acid (C14), pentadecanedioic acid (C15), hexadecanedioic acid (C16), heptadecanedioic acid (C17), octadecanedioic acid (C18), nonadecanedioic acid (C19), icosanedioic acid (C20), and the like.

[0025] The content of the calcium complex soap is preferably 1.0% by weight or more, more preferably 3.0% by weight, and even more preferably 5.0% by weight or more based on the total weight of the biodegradable grease composition.

[0026] The total content of the calcium complex soap and the polyol ester oil is preferably 50.0% by weight or more, more preferably 55.0% by weight or more, and most preferably 60.0% by weight or more based on the weight of the biodegradable grease composition. Similarly, preferably, the total content of the calcium complex soap and the polyol ester oil is 85.0% by weight or less.

[0027] The amount of higher fatty acids relative to the total amount of carboxylic acids is preferably in the range of 20.0 to 70.0% by weight, and more preferably in the range of 30.0 to 65.0% by weight. The amount of lower fatty acids, relative to the total amount of carboxylic acids, is preferably in the range of 5.0 to 30.0% by weight, and more preferably in the range of 10.0 to 25.0% by weight.

[0028] The amount of aromatic monocarboxylic acid relative to the total amount of carboxylic acid is preferably in the range of 1.0 to 10.0% by weight, and more preferably in the range of 3.0 to 10.0% by weight. The amount of dicarboxylic acid relative to the total amount of carboxylic acid is preferably in the range of 1.0 to 70.0% by weight, and more preferably in the range of 5.0 to 55.0% by weight.

[0029] The mass ratio of higher fatty acids to dicarboxylic acids is preferably in the range of 20:80 to 95:5, and more preferably in the range of 30:70 to 85:15. The mass ratio of aromatic monocarboxylic acid to dicarboxylic acid is preferably in the range of 5:95 to 70:30, and more preferably in the range of 15:85 to 65:35.

[0030] The mass ratio of lower fatty acids to dicarboxylic acids is preferably in the range of 5:95 to 85:15, and more preferably in the range of 15:85 to 80:20. The thickeners according to this disclosure may contain one or more additional thickeners other than calcium complex soaps. Examples of these other thickeners include alkali metal soaps, alkali metal complex soaps, alkaline earth metal soaps, alkaline earth metal complex soaps, alkali metal sulfonates, alkaline earth metal sulfonates, other metal soaps, and polytetrafluoroethylene.

[0031] When the total amount of thickeners in the biodegradable grease composition according to this disclosure is 100.0% by weight, the content of further thickeners is preferably less than 50.0% by weight, preferably 30.0% by weight or less, more preferably 20.0% by weight or less, even more preferably 10.0% by weight or less, even more preferably 5.0% by weight or less, and most preferably 1.0% by weight or less. Inorganic powders listed in another section may have an increasing effect. In consideration of this, “further thickeners” in this disclosure refers to additives other than calcium complex soaps and inorganic powders. In a particularly preferred embodiment, there are no further thickeners in the grease composition, and the thickener is essentially composed of calcium complex soaps.

[0032] The inorganic powder is not particularly limited, Silicates such as aluminum silicate, magnesium silicate, calcium silicate, potassium silicate, and zirconium silicate; phosphates such as dicalcium phosphate and tricalcium phosphate; carbonates such as calcium carbonate, barium carbonate, sodium carbonate, magnesium carbonate, lithium carbonate, and strontium carbonate; borates such as aluminum borate, sodium borate, and lithium borate; Titanates such as barium titanate, calcium titanate, strontium titanate, and magnesium titanate; zirconates such as calcium zirconate; aluminosilicates such as magnesium aluminosilicate; sulfates such as calcium sulfate, barium sulfate, and magnesium sulfate; oxides of zinc oxide, aluminum oxide, yttrium oxide, magnesium oxide, vanadium oxide, bismuth oxide, gadolinium oxide, lanthanum oxide, titanium oxide, copper oxide, titanium dioxide, and silicon dioxide; nitrides such as aluminum nitride, silicon nitride, aluminum nitride, and boron nitride. Carbides such as silicon carbide and boron carbide; chlorides such as barium chloride; sulfides such as zinc sulfide; hydrotalcite, mica, talc, silica, zircon, shirasu, montmorillonite, saponite, alumina, colemanite, benite, zeolite, kaolinite, cerium, sericite, zirconia, feldspar, kaolin, sieklite, perlite, zirconia, halosite, petalite, calcia, magnesia, zirconia, barium ferrite minerals (clay minerals, etc.).

[0033] The inorganic powder is preferably calcium carbonate or tricalcium phosphate. The average particle size of the inorganic powder is not particularly limited, but is preferably 100 μm or less, more preferably 50 μm or less, and most preferably 10 μm or less. The lower limit of the average particle size of the inorganic powder is not particularly limited, but is preferably at least 100 nm, more preferably at least 500 nm, and most preferably at least 1 μm. The average particle size of the inorganic powder is measured as the volume-average particle size, for example, using laser diffraction.

[0034] The inorganic powder content is not particularly limited, but is preferably 1.0% by weight or more, more preferably 1.5% by weight or more, preferably 20.0% by weight or less, more preferably 15.0% by weight or less, even more preferably 10.0% by weight or less, even more preferably 5% by weight or less, and most preferably 3% by weight or less.

[0035] The ratio of calcium complex soap to inorganic powder content (calcium complex soap / inorganic powder) in the biodegradable grease composition is preferably 0.5:1 or higher, more preferably 0.6:1 or higher, most preferably 0.8:1 or higher, preferably 20.0:1 or lower, more preferably 18.0:1 or lower, and most preferably 15.0:1 or lower.

[0036] Other components, including antioxidants, rust inhibitors, lubricants, extreme pressure agents, wear inhibitors, solid lubricants, metal deactivators, metal detergents, non-metal detergents, corrosion inhibitors, polymers, and additives (such as colorants), may also be included in this grease composition.

[0037] The content of other components is not particularly limited, but is preferably 20.0% by weight or less, more preferably 15.0% by weight or less, even more preferably 5.0% by weight or less, even more preferably 3.0% by weight or less, and most preferably 1.0% by weight or less, relative to the total weight of the grease composition.

[0038] Sulfur-based extreme pressure additives are known to be highly toxic to aquatic organisms depending on their chemical structure. The grease compositions according to this disclosure should contain relatively small amounts of environmentally unsuitable extreme pressure additives. For example, the content of sulfur-based extreme pressure additives in the total grease composition is preferably 1.0% by weight or less, more preferably 0.1% by weight or less.

[0039] The biodegradable grease composition according to this disclosure has a mixing degree, as measured in accordance with JIS K2220 7 "Grease Preference Test method" (25°C, 60W), preferably 210 to 475, more preferably 265 to 475, and particularly preferably 310 to 475.

[0040] The biodegradable grease composition according to this disclosure, when measured in accordance with JIS K2220 8 "Grease Dropping Point Test Method," preferably has a dropping point of 200°C or higher, more preferably 250°C or higher, and most preferably 260°C or higher. When the dropping point of this grease composition is 200°C or higher, it is believed that lubrication problems, such as viscosity reduction at high temperatures, associated leaks, and seizure, can be suppressed.

[0041] The biodegradable grease composition according to this disclosure preferably has an oxidation stability of 45 kPa or less, more preferably 40 kPa or less, and most preferably 35 kPa or less, as measured in accordance with JIS K2220 12 "Oxidation Stability Test Method" (99°C, 100 hours).

[0042] The biodegradable grease composition according to this disclosure preferably has a fusion load of 1961 N or more, more preferably 2452 N or more, when measured according to the measurement method described below. The fusion load is obtained by performing a high-speed four-ball extreme pressure test in accordance with ASTM D2596 under the following conditions.

[0043] Speed ​​1770rpm Time: 10 seconds temperature room temperature The biodegradable grease composition according to this disclosure preferably has a coefficient of friction of 0.105 or less, more preferably 0.100 or less, and most preferably 0.095 or less, when measured according to the following measurement method. Using a Bowden friction tester, a longitudinal load is applied to test material A, and a reciprocating test is performed by moving test material B back and forth in the lateral direction under the following conditions, and the force applied to test material A is measured as the friction force. Regarding the measurement of the friction force, the coefficient of friction during sliding is measured for each reciprocation, up to a maximum of 20 reciprocations, and the average value of the last 10 reciprocations is calculated. The coefficient of friction shown here is the average value of the dynamic coefficient of friction and the static coefficient of friction.

[0044] Test material A - Material SUJ2; Shaped steel ball with outer diameter 10.0 mm Test material B - Material S45C; plate-like body with length 120 mm, width 35 mm, and thickness 4 mm. Temperature 25℃ Sliding speed: 15.0 mm / min Sliding distance: 20.0 mm Load 8.34N Contact surface pressure: 93 MPa Number of slides: 20 back and forth The biodegradable grease compositions according to this disclosure preferably have a biodegradability of more than 60% in accordance with the OECD 301B method.

[0045] The biodegradable grease compositions according to this disclosure can be manufactured in the same manner as conventionally known methods for manufacturing grease compositions, except for changing the blended components. The biodegradable grease compositions according to this disclosure can be manufactured, for example, in accordance with the following method.

[0046] In a grease manufacturing kettle, a predetermined base oil and a predetermined carboxylic acid are mixed, and the contents are dissolved at a temperature of 60-90°C. Next, basic calcium (usually calcium hydroxide), which has been pre-dissolved and dispersed in a predetermined amount of distilled water, is added to the kettle. Soap is gradually formed in the base oil by the saponification reaction between the carboxylic acid and basic calcium. Dehydration is completed by further heating the inside of the kettle. After dehydration is complete, this mixture is heated to 180-220°C, thoroughly stirred and mixed, and then cooled to room temperature. After that, a uniform grease composition is obtained using a disperser (e.g., a three-roll mill).

[0047] When dicarboxylic acids are used as carboxylic acids, one type of carboxylic acid and another type of carboxylic acid may be added to the vessel at different times. Furthermore, if the carboxylic acids are added to the vessel at different times, basic calcium may be added to the vessel (at multiple times) according to the timing of each carboxylic acid's addition.

[0048] Furthermore, the timing of blending the inorganic powder with other components is not limited. For example, in the above method, the inorganic powder and other components may be blended individually after the grease composition containing calcium complex soap is produced, or the inorganic powder and other components may be mixed together with the base oil, etc., in the kettle from the beginning.

[0049] The biodegradable grease compositions according to this disclosure exhibit excellent biodegradability and various performance characteristics (e.g., oxidation stability, extreme pressure resistance, etc.). Therefore, the biodegradable grease compositions according to this disclosure can be preferably applied to applications where there is a risk of the grease being released into the natural environment. More specifically, the biodegradable grease compositions according to this disclosure are suitable for use in automobiles, construction machinery such as power shovels, bulldozers and cranes, the steel industry, the paper industry, forestry machinery, agricultural machinery, chemical plants, power generation equipment, drying ovens, photocopiers, and railway vehicles, and are also suitable for use in various high-temperature / high-load components such as threaded joints of seamless pipes. [Examples]

[0050] The present invention will be described hereafter with reference to examples and comparative examples, but the present invention is not limited thereto. The greases in Tables 1-3 were formulated using the following components: Base oil A: A paraffinic mineral oil obtained by refining a dewaxing solvent, belonging to Group 1, with a kinematic viscosity of 100.6 mm at 40°C. 2 kinematic viscosity at 100°C is 11.25 mm² / s. 2 The viscosity index is 97, and in the case of ring analysis by the D3238 method, the ASTM %CP is 69.5.

[0051] Base oil B: This is a GTL (gas-liquefied) synthesized by the Fischer-Tropsch process, belonging to Group 3, with a kinematic viscosity of 43.88 mmHg at 40°C. 2 kinematic viscosity at 100°C is 7.77 mm² / s. 2 It has a viscosity index of 148, and in ring analysis by ASTM D3238, it has a %CP of 90.0 or higher.

[0052] Base oil C: A poly-α-olefin belonging to Group 4, with a kinematic viscosity of 46.6 mmHg. 2 kinematic viscosity at 100°C is 7.90 mm² / s. 2 The viscosity index is 138, and in the case of ring analysis by the D3238 method, the ASTM %CP is 90.0 or higher.

[0053] Base oil D: A polyol ester oil which is a triester of trimethylolpropane and a monocarboxylic acid having 8 to 10 carbon atoms, belongs to Group 5, and has a kinematic viscosity at 40 °C of 20.00 mm 2 / s, a kinematic viscosity at 100 °C of 4.40 mm 2 / s and a viscosity index of 140.

[0054] Base oil E: A polyol ester oil which is a tetraester of pentaerythritol and a monocarboxylic acid having 8 to 10 carbon atoms, belongs to Group 5, and has a kinematic viscosity of 30.00 mm at 40 °C 2 / s, a kinematic viscosity of 5.90 mm at 100 °C 2 / s and a viscosity index of 144.

[0055] Base oil F: Rapeseed oil having a kinematic viscosity of 36.0 mm at 40 °C 2 / s. Inorganic powder A: Calcium carbonate (average particle size: 2 μm) Inorganic powder B: Tricalcium phosphate (average particle size: 5 μm) Organic liquid A: Olefin sulfide (sulfur content: 15.5 wt%) Other additives: A mixture of rust inhibitors, corrosion inhibitors, etc. According to the following method, a thickener was formed in the base oil to produce a grease composition. The amount of the thickener in the table indicates the content of the thickener in the final grease composition.

[0056] In Examples 1-18 and Comparative Examples 1, 4, and 5, stearic acid, acetic acid, benzoic acid, and adipic acid were added to the base oil and heated to approximately 90°C. Next, an aqueous calcium hydroxide solution was added to the reaction product. The molar ratio of each component was [calcium hydroxide:stearic acid:acetic acid:benzoic acid:adipic acid] = [1.0:0.6:0.9:0.2:0.1]. The reaction solution was then heated to approximately 200°C while stirring, and then cooled to room temperature to complete the reaction. After that, the calcium complex soap-containing greases according to Examples 1-18 and Comparative Examples 1, 4, and 5 were obtained by adding and mixing the other components to the resulting composition. The formulations of each component, including the other components, are shown in Tables 1-3.

[0057] For Comparative Examples 6 and 7, the base oil was added to a heat-resistant container. Stearic acid was added, and the mixture was heated to approximately 90°C while stirring. Then, an aqueous lithium hydroxide solution was added to the reactant. The reaction solution was then heated to approximately 230°C while stirring, and then cooled to room temperature to complete the reaction. After that, the lithium soap-containing greases of Comparative Examples 6 and 7 were obtained by adding and mixing other components to the resulting compositions. The blends of each component, including the other components, are shown in Table 3.

[0058] In Comparative Examples 2 and 3, a base oil and 12-hydroxystearic acid were added to a heat-resistant container and heated to approximately 130°C while stirring. Calcium hydroxide was then added and the reaction was allowed to proceed. Subsequently, the reaction solution was cooled to approximately 100°C while stirring, water was added, and the reaction mixture was cooled to room temperature to complete the reaction. The calcium soap-containing greases of Comparative Examples 2 and 3 were then obtained by adding and mixing other components to the resulting compositions. The blends of each component, including the other components, are shown in Table 3.

[0059] In accordance with the above method, the degree of mixing, dropping point, oxidation stability, fusion load by high-speed four-ball extreme pressure test, coefficient of friction by reciprocating test using a Bowden-type tester, and biodegradability of the grease compositions for each example and comparative example were measured. The measurement results are shown in the respective tables.

[0060] The grease compositions of each example differ from those of each comparative example, exhibiting biodegradability of 60% or more and possessing excellent heat resistance as indicated by the results of dropping point and oxidation stability tests.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Table 3]

Claims

1. A biodegradable grease composition comprising a base oil, a thickener, and an inorganic powder, wherein the base oil comprises a polyol ester oil and the thickener comprises a calcium complex soap.

2. The biodegradable grease composition according to claim 1, wherein the base oil also includes a base oil selected from the group consisting of mineral oil, GTL, poly-α-olefin base oil, and mixtures thereof.

3. The biodegradable grease composition according to claim 1 or 2, wherein the calcium complex soap is a reaction product of one or more carboxylic acids and calcium hydroxide, and the carboxylic acid includes higher fatty acids, lower fatty acids, aromatic carboxylic acids and dicarboxylic acids.

4. The biodegradable grease composition according to any one of claims 1 to 3, wherein the higher fatty acid is a substituted or unsubstituted straight-chain higher fatty acid having 18 to 22 carbon atoms, and the lower fatty acid is a straight-chain saturated lower fatty acid having 2 to 4 carbon atoms.

5. The biodegradable grease composition according to claim 3 or claim 4, wherein the aromatic carboxylic acid is an aromatic monocarboxylic acid having a substituted or unsubstituted benzene ring.

6. The biodegradable grease composition according to any one of claims 3 to 5, wherein the dicarboxylic acid is a substituted or unsubstituted saturated dicarboxylic acid.

7. The biodegradable grease composition according to any one of claims 1 to 6, wherein the total content of the calcium complex soap and the polyol ester oil is 55.0% by weight or more based on the total weight of the biodegradable grease composition.

8. The biodegradable grease composition according to any one of claims 2 to 7, wherein the content of the base oil other than polyol ester oil is in the range of 10.0 to 40.0% by weight relative to the total weight of the biodegradable grease composition.

9. The biodegradable grease composition according to any one of claims 1 to 8, wherein the inorganic powder is calcium carbonate or tricalcium phosphate.

10. The base oil is 13.00 mm at 100°C. ２ A biodegradable grease composition according to any one of claims 1 to 9, having a kinematic viscosity of less than 0.0 / s and a %CP ring analysis value of 65% or more in accordance with ASTM D3238P.

11. The biodegradable grease composition according to any one of claims 1 to 10, wherein the thickening agent substantially consists of a calcium complex soap.

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