EP4680706A1

EP4680706A1 - Biodegradable grease composition

Info

Publication number: EP4680706A1
Application number: EP24709773.6A
Authority: EP
Inventors: Hiroto MIKAMI; Kazuya Watanabe; Keiji Tanaka
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2023-03-16
Filing date: 2024-03-12
Publication date: 2026-01-21
Also published as: CN121057806A; JP2026509507A; WO2024188995A1

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

BIODEGRADABLE GREASE COMPOSITION

Field of the Invention

The present invention relates to biodegradable grease compositions.

Background of the Invention

In recent years, due to the growing awareness of environmental issues, nature conservation on a global scale has begun to be emphasized in all industries. Most grease is used in a sealed state, and the impact on the natural environment is, therefore, considered to be small. However, accidental leakage into the natural environment such as soil, rivers, and the sea due to accidents or leaks can damage the natural environment. For this reason, in applications involving the possibility of external leakage of grease, the use of a biodegradable grease composition is desired. At the same time, with the advancement of mechanical technology, the lubrication environment is becoming harsher year by year, and the requirements for lubricity such as thermal oxidation stability and extreme pressure are also increasing.

In order to satisfy these requirements conventionally, biodegradable grease compositions using highly biodegradable vegetable oils and polyol esters, metal soap as a thickener, extreme pressure agents as additives, and the like as base oils have been disclosed, for example in JP11228983, JP2003171683 and JP2008208240.

However, it has been difficult to achieve both biodegradability and the performance required using conventional grease compositions. Therefore, an object of the present invention is to provide a grease composition having a heat resistance and a stable lubrication function while at the same time reducing the load on the environment.

Summary of the Invention

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. Detailed Description of the Invention

The present inventors have conducted intensive studies and found that a grease composition having a heat resistance and a stable lubrication function while at the same time reducing the load on the environment can be provided by the use of a grease composition comprising a polyol ester base oil thickened with a calcium complex soap and also containing an inorganic powder. Said biodegradable grease composition has excellent performance and can preferably be applied where there is a risk that the grease composition may leak to the outside such as an automobile, railway, construction machinery, or agricultural machinery.

One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual implementation may be described in the specification.

When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

The base oil comprises a polyol ester oil. Said polyol ester base oil may be synthetic or natural. Preferably, the polyol ester oil includes esters comprising one or more polyhydric alcohol component and one or more aliphatic monocarboxylic acid component. Preferable polyhydric alcohol components are one or more selected from the group consisting of neopentyl glycol, trimethylol ethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. Preferably, the aliphatic monocarboxylic acid components are one or more aliphatic monocarboxylic acid containing in the range of from 3 to 22, more preferably in the range of from 8 to 18, carbon atoms. More preferably, the aliphatic monocarboxylic acid components are one or more selected from those in the group consisting of caproic acid, caprylic acid, capric acid, undecanoic acid, lauric acid, palmitic acid, stearic acid and oleic acid.

The base oil may contain a base oil other than polyol ester oil. The base oil other than the polyol ester oil is preferably one or more base oils selected from mineral oil, GTL base oil, and poly-a-olefin base oil.

The kinematic viscosity of the base oils other than the polyol ester base oil at 100 °C is less than 13.00 mm²/s, and the %CP of said base oils by analysis according to ASTM D3238 is preferably 65% or more.

Poly-a-olefins are synthetic oils and may be a single polymer or copolymer of one or more a-olefin.

Mineral oils are base oils obtained by refining crude oil (paraffinic crude oil, naphthenic crude oil, intermediate crude oil, etc.). In a preferred embodiment, mineral oils for use herein are those to which a treatment step selected from one or more of solvent decontamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and white clay treatment, have been applied to the lubricating oil fraction obtained by distilling crude oil under normal pressure and vacuum distillation. Examples of suitable mineral oils include paraffinic and naphthenic mineral oils.

GTL (gas-to-liquid) base oil is a base oil synthesized by the Fischer Tropsch method, which is a liquid fuel technology for natural gas. Compared with mineral oil base oil refined from crude oil, GTL has an extremely low sulfur content and aromatic content, and an extremely high paraffin composition ratio, so it has excellent oxidation stability and very low evaporation loss.

The content of the polyol ester oil is preferably 30.0wt% or more, more preferably 35.Owt% by or more, even more preferably 40.0wtwt% or more and most preferably 45.0wt% or more, based on the overall weight of the biodegradable grease composition being 100.0wt%. Preferably, the polyol ester base oil is present in an amount of 75.0wt% or less based on the overall weight of the biodegradable grease composition.

The content of the base oil other than polyol ester oil is preferably at least 5.0wt%, more preferably at least 10.0wt%, most preferably at least 14.0wt% based on the overall weight of the biodegradable grease composition. The content of the base oil other than polyol ester oil is preferably at least at most 50.0wt%, more preferably at most 40.0wt% and most preferably at most

35.Owt%.

The thickener comprises a calcium complex soap. A calcium complex soap is the reaction product of basic calcium (typically 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 also include aromatic carboxylic acids in addition to the higher fatty acids and lower fatty acids. In addition to aromatic monocarboxylic acids, it is particularly preferable that the carboxylic acids in used in the calcium complex soap also include dicarboxylic acids. By formulating carboxylic acid in this way, the fibers of the soap become intricately and tightly intertwined. As a result, it is presumed that a biodegradable grease composition having excellent performance is obtained. In addition, as long as the effect of the present disclosure is not impaired, carboxylic acids other than these may be used.

The higher fatty acid is not particularly limited as long as calcium complex soap can be formed, but is preferably one or more linear higher fatty acid having a carbon number in the range of from 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 is preferably a saturated fatty acid.

Specific examples of the linear saturated higher fatty acid suitable for use in the calcium complex soap of the grease composition include stearic acid (octadecanoic acid, C18), tubercrostearic acid (nonadecanoic acid, C19), arachidic acid (eicosanoic acid, C20), henicosanoic acid (C21), behenic acid (C22, docosanoic acid), hydroxystearic acid (C18, castor curable fatty acid) and the like. Examples of the linear unsaturated higher fatty acid of C 18 ~ 22 include oleic acid, linoleic acid, linolenic acid (C18), gadoleic acid, eicosadienoic acid, mead acid (C20), erucic acid, docosadienoic acid (C22) and the like. Further, a hydrogenated oil can also be used instead of higher fatty acids. For example, a hydrogenated oil can be made by hydrogen addition using a catalyst such as nickel to fats and oils containing a large amount of unsaturated fatty acids such as castor oil.

The lower fatty acid is not particularly limited as long as calcium complex soap can be formed, but is preferably one or more linear saturated lower fatty acid having a carbon number in the range of from 2 to 4.

Specific examples of the linear saturated lower fatty acid include acetic acid, propionic acid, butyric acid and the like.

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 acid having a substituted or unsubstituted benzene ring. The aromatic monocarboxylic acid may have one or more substituents (eg, o-, m- or p- alkyl groups, hydroxy groups, alkoxy groups, etc.). In the present disclosure, the alkyl moieties of the "substituent" and the alkoxy are, for example, linear or branched alkyl having in the range of from 1 to 4 carbon atoms.

Specific examples of aromatic monocarboxylic acids include benzoic acid, methylbenzoic acid {toluic acid (p-, m-, o-)}, dimethylbenzoic acid (xylylic acid, hemeritic acid, mesitylenic acid), trimethylbenzoic acid {prenicylic acid, durylic acid, isoduryl acid (a-, p-, y-)}, 4- isopropylbenzoic acid (cumic acid), hydroxybenzoic acid (salicylic acid), Dihydroxybenzoic acid {pyrocatechic acid, resorcylic acid (a-, p-, y-), gentidic 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), hydroxydimethoxybenzoic acid (syringic acid) and the like.

The dicarboxylic acid is not particularly limited if calcium complex soap can be formed, but is preferably one or more substituted or unsubstituted saturated dicarboxylic acid. The saturated dicarboxylic acid may have one or more substituents (for example, a hydroxyl group) even if it is unsubstituted. The saturated dicarboxylic acid may be either linear or branched, but it 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 the side chain) is not particularly limited, but is preferably in the range of from 4 to 20, more preferably in the range of from 4 to 16, and particularly preferably in the range of from 4 to 10.

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

The calcium complex soap content is preferably 1.0wt% or more, more preferably 3.0wtwt%, even more preferably 5.0wt% or more based on the total weight of the biodegradable grease composition.

The total content of calcium complex soap and polyol ester oil is preferably 50.0wt% or more, more preferably 55.0wt% or more, most preferably 60.Owt% or more based on the weight of the biodegradable grease composition. Also preferably, Alternatively, preferably the total content of calcium complex soap and polyol ester oil is 85.0wt% or less.

The amount of higher fatty acids, based on the overall amount of carboxylic acid, is preferably in the range of from 20.0 to 70.0wt%, more preferably in the range of from 30.0 to 65.0wt%.

The amount of lower fatty acids, based on the overall amount of carboxylic acid, is preferably in the range of from 5.0 to 30.0wt%, more preferably in the range of from 10.0 to 25.0wt%.

The amount of aromatic monocarboxylic acid, based on the overall amount of carboxylic acid, is preferably in the range of from 1.0 to 10.0wt%, more preferably in the range of from 3.0 to 10.0wt%.

The amount of dicarboxylic acid, based on the overall amount of carboxylic acid, is preferably in the range of from 1.0 to 70.0wt%, more preferably in the range of from 5.0 to 55.0wt%.

The mass ratio of higher fatty acids to dicarboxylic acids is preferably in the range of from 20:80 to 95:5, more preferably in the range of from 30:70 to 85:15.

The mass ratio of aromatic monocarboxylic acid to dicarboxylic acid is preferably in the range of from 5:95 to 70:30, more preferably in the range of from 15:85 to 65:35.

The mass ratio of the lower fatty acid to the dicarboxylic acid is preferably in the range of from 5:95 to 85:15, more preferably in the range of from 15:85 to 80:20.

The thickener according to the present disclosure may contain one or more further thickener, other than the calcium complex soap. Examples of these other thickeners include alkali metal soap, alkali metal complex soap, alkaline earth metal soap, alkaline earth metal complex soap, alkali metal sulfonate, alkaline earth metal sulfonate, other metal soap, polytetrafluoroethylene and the like.

The content of the further thickener is suitably less than 50.0wt%, preferably 30.0wt% or less, more preferably 20.0wt% or less, even more preferably 10.0wt% or less, even more preferably 5.0wt% or less, and most preferably 1.0wt% or less, when the total amount of all thickeners in the entire biodegradable grease composition according to the present disclosure is 100.0wt%. The inorganic powder listed in another section may have an increasing effect. In consideration of this point, the "further thickener" in the present disclosure refers to an additive other than calcium complex soap and other than the inorganic powder. In a particularly preferred embodiment no further thickener is present in the grease composition and the thickener consists essentially of a calcium complex soap.

The inorganic powder is not particularly limited, Silicates such as aluminum silicate, magnesium silicate, calcium silicate, potassium silicate, zirconium silicate, etc.; phosphates such as dicalcium phosphate and tertiary calcium phosphate; carbonates such as calcium carbonate, barium carbonate, sodium carbonate, magnesium carbonate, lithium carbonate, strontium carbonate, etc.; borates such as aluminum borate, sodium borate, lithium borate, etc.; Titanate salts such as barium titanate, calcium titanate, strontium titanate, magnesium titanate; Zirconate such as calcium zirconate; aluminosilicates such as magnesium aluminosilicate; Sulfates such as calcium sulfate, barium sulfate, magnesium sulfate, etc.; Zinc oxide, aluminum oxide, yttrium oxide, magnesium oxide, vanadium oxide, bismuth oxide, gadolinium oxide, lanthanum oxide, titanium oxide, copper oxide, titanium dioxide, silicon dioxide oxide, etc.; Nitride such as aluminum nitride, silicon nitride, aluminum nitride, boron nitride; carbides such as silicon carbide, boron carbide, etc.; Chlorides such as barium chloride; sulfides such as zinc sulfide; Hydrotalcite, mica, talc, silica, zircon, silas, montmorinite, saponite, alumina, cholemanite, bentonite, zeolite, kaolinite, cerium, selicite, zirconia, feldspar, kaolin, sieklite, perlite, zirconia, halosite, petalite, calcia, magnesia, zirconia, barium ferrite Minerals such as or clay minerals; and the like.

The inorganic powder is preferably calcium carbonate or tertiary calcium phosphate.

The average particle diameter of the inorganic powder is not particularly limited, but is preferably 100 pm or less, more preferably 50 pm or less, and most preferably 10 pm or less. The lower limit of the average particle diameter 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 pm. The average particle size of the inorganic powder is measured as, for example, the volume average particle size using a laser diffraction method. The content of the inorganic powder is not particularly limited, but is preferably 1.0wt% or more, more preferably 1.5wt% or more, and preferably 20.0wt% or less, more preferably 15.0wt% or less, even more preferably 10.0wt% or less, even more preferably 5wt% or less, and most preferably 3wt% or less.

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

Other components including antioxidants, rust inhibitors, oil-based agents, extreme pressure agents, wear resistant agents, solid lubricants, metal inert agents, metal purifiers, non-metallic cleaners, corrosion inhibitors, polymers, additives such as colorants, may also be included in the grease composition.

The content of the other components is not particularly limited, but is preferably 20.0wt% or less, more preferably 15.0wt% or less, even more preferably 5.0wt% or less, even more preferably 3.0wt% or less, and most preferably 1.0wt% or less based on the overall weight of the grease composition.

It is known that sulfur-based extreme pressure agents are highly toxic to aquatic organisms depending on their chemical structure. According to the grease composition according to the present disclosure, the amount of the extreme pressure agent having low environmental compatibility should be relatively small. For example, the content of the sulfur-based extreme pressure agent with respect to the entire grease composition is preferably 1.0wt% or less, more preferably 0.lwt% or less.

The biodegradable grease composition according to the present disclosure has a miscibility measured in accordance with JIS K22207 "Grease Preference Test Method" (25 ° C., 60 W) that is preferably 210 to 475, more preferably 265 to 475, and particularly preferably 310 to 475.

The biodegradable grease composition according to the present disclosure preferably has a drop point of 200°C or higher measured in accordance with JIS K22208 "Grease drop point test method", more preferably 250°C or higher, and most preferably 260°C or higher. If the drop point of the grease composition is 200°C or higher, it is considered that lubrication problems, for example, loss of viscosity at high temperatures, associated leakage, baking, etc. can be suppressed.

The biodegradable grease composition according to the present disclosure preferably has an oxidation stability of 45kPa or less measured in accordance with JIS K2220 12 "Oxidation stability test method" (99°C, 100 hours), more preferably 40 kPa or less, and most preferably 35 kPa or less.

The biodegradable grease composition according to the present disclosure preferably has a fusion load of 1961N or more measured according to the following measurement method, and more preferably one that is 2452N or more. Under the following conditions, a high-speed four-sphere extreme pressure test is performed in accordance with ASTM D2596 to obtain a fusion load.

Speed 1770rpm

Time: 10 sec.

Temperature Room temperature

The biodegradable grease composition according to the present disclosure preferably has a friction coefficient measured according to the following measurement method of 0.105 or less, more preferably 0.100 or less, and most preferably 0.095 or less. Using a Bauden-type friction tester under the following conditions, a reciprocating test in which a longitudinal load is applied to the test material A and the test material B is reciprocated in the lateral direction is performed, and the force applied to the test material A is measured as a friction force. For the measurement of the friction force, the friction coefficient at the time of sliding is measured every round trip, and up to 20 round trips are performed, and the average value of the latter 10 round trips is calculated. The friction coefficient shown here is an average value of the dynamic friction coefficient and the static friction coefficient.

Test material A - Material SUJ2; Shape Steel ball with outer diameter 10.0mm

Test Material B - Material S45C; Plate-like body with length 120 mm, width 35 mm, thickness 4 mm Temperature 25°C Sliding speed 15.0mm/min Sliding distance 20.0mm Load 8.34N Surface pressure of contact surface 93MPa Number of slides: 20 round trips

The biodegradable grease composition according to the present disclosure preferably has a biodegradability of more than 60% according to the OECD301B method.

The biodegradable grease composition according to the present disclosure can be produced in the same manner as a conventionally known method for producing a grease composition except for changing the component to be blended. The biodegradable grease composition according to the present disclosure can be produced, for example, according to the following method.

A predetermined base oil and a predetermined carboxylic acid are mixed in a grease production kettle, and the contents are dissolved at a temperature of 60 to 90°C. Next, basic calcium (typically calcium hydroxide) dissolved and dispersed in a predetermined amount of distilled water in advance is placed in the kettle. The saponification reaction of carboxylic acid and basic calcium gradually produces soap in the base oil. Furthermore, by heating the inside of the kettle, dehydration is completed. After completion of dehydration, the mixture is heated to a temperature of 180 to 220°C, stirred and mixed sufficiently, and then cooled to room temperature. Thereafter, a disperser (e.g., a three-roll mill, etc.) is used to obtain a homogeneous grease composition.

In the case where dicarboxylic acid is used as the carboxylic acid, one carboxylic acid and another carboxylic acid may be put into the kettle at different timings. Furthermore, when carboxylic acids are put into the kettle at different timings, basic calcium may be injected into the kettle (at multiple timings) according to the timing of each carboxylic acid input.

Further, the timing of blending inorganic powder and other components is not limited. For example, in the above-described method, after producing a grease composition containing calcium complex soap, inorganic powder and other components may be separately blended, or inorganic powder and other components may be mixed in the kettle from the beginning together with the base oil or the like.

The biodegradable grease composition according to the present disclosure is excellent in biodegradability and excellent in various performances (for example, oxidation stability, extreme pressure, etc.). Therefore, the biodegradable grease composition according to the present disclosure can be preferably applied to applications where grease may flow out into the natural environment. More specifically, the biodegradable grease composition according to the present disclosure is a construction machinery such as an automobile, a power excavator, a bulldozer, and a crane truck, a steel industry, a paper industry, a forestry machine, an agricultural machinery, a chemical plant, a power generation facility, a drying furnace, a copier, a railway vehicle, It is also preferable to use in various high temperature / high load parts such as screw joints of seamless pipes. Examples

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The greases in Tables 1 to 3 were formulated with the following components:

Base oil A: Paraffinic mineral oil obtained by refining dewaxing solvent and belongs to group 1, with a kinematic viscosity of 40°C of 100.6 mm²/s, a kinematic viscosity of 100°C of 11.25 mm²/s, a viscosity index of 97, ASTM %CP for ring analysis by D3238 method; is 69.5.

Base oil B: GTL (gas-to-liquid) synthesized by the Fischer-Tropsch method, belongs to group 3, has a kinematic viscosity of 40 ° C. 43.88 mm²/ s, a 100°C kinematic viscosity of 7.77 mm²/s, and a viscosity index of 148, %CP for ring analysis by ASTM D3238 method; is 90.0 or higher.

Base oil C: Poly-a-olefin, belonging to group 4, with a kinematic viscosity of 46.6 mm²/s, a kinematic viscosity of 100°C of 7.90 mm²/s, a viscosity index of 138, ASTM %CP for ring analysis by D3238 method; is 90.0 or higher.

Base oil D: It is a polyol ester oil that is a triester of trimethylolpropane and monocarboxylic acid having 8 ~ 10 carbon atoms, belongs to group 5, and has a kinematic viscosity of 40°C. 20.00 mm²/s, a kinematic viscosity of 100°C. 4.40 mm²/s, and a viscosity index of 140.

Base oil E: A polyol ester oil that is a tetraester of pentaerythritol and monocarboxylic acids having 8 to 10 carbon atoms, belongs to group 5, and has a kinematic viscosity of 30.00 mm²/s at 40°C, a kinematic viscosity of 5.90 mm²/s at 100°C, and a viscosity index of 144.

Base oil F: Rapeseed oil with a kinematic viscosity of 36.0 mm²/s at 40°C.

Inorganic powder A: Calcium carbonate (average particle size: 2pm)

Inorganic powder B: Tertiary calcium phosphate (average particle size: 5 pm)

Organic liquid A: Olefin sulfide (sulfur content: 15.5% by weight)

Other additives: Mixtures 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 thickener in the table indicates the content of the thickener in the final grease composition.

For Examples 1 to 18 and Comparative Examples 1, 4, and 5, stearic acid, acetic acid, benzoic acid, and adipic acid were added in a base oil, heated to about 90°C, and then a calcium hydroxide aqueous solution was added to the reaction. The molar ratio of each component is [calcium hydroxide: stearic acid: acetic acid: benzoic acid: adipic acid] = [1.0: 0. 6:0.9:0.2:0.1]. Thereafter, the reaction solution was heated to about 200°C. while stirring, and then cooled to room temperature to complete the reaction. Thereafter, by adding other components to the obtained composition and mixing, the calcium complex soap- containing grease according to Examples 1 to 18 and Comparative Examples 1, 4, and 5 was obtained. The formulation of each component including other components is as described in Table 1 to 3.

For Comparative Examples 6 and 7, base oil was added to a heat-resistant container. After adding stearic acid and heating to about 90°C while stirring, a lithium hydroxide aqueous solution was added to the reaction. Thereafter, the reaction solution was heated to about 230°C while stirring, and then cooled to room temperature to complete the reaction. Thereafter, by adding other components to the obtained composition and mixing, the lithium soap-containing grease according to Comparative Examples 6 and 7 was obtained. The blending of each ingredient including other components is as shown in Table 3.

For Comparative Examples 2 and 3, base oil and 12- hydroxystearic acid were added to a heat-resistant container, heated to about 130°C while stirring, and then calcium hydroxide was added to react. Thereafter, the reaction solution was lowered to about 100°C while stirring, water was added, and the reaction mixture was cooled to room temperature to complete the reaction. Thereafter, by adding other components to the obtained composition and mixing, calcium soap-containing grease according to Comparative Examples 2 and 3 was obtained. The blending of each ingredient including other components is as shown in Table 3.

According to the above-described methods, the miscible degree, drop point, oxidation stability, fusion load by high-speed four-bulb extreme pressure test, friction coefficient by reciprocating test using a Bowden type tester, and biodegradability of the grease composition according to each Example and each comparative example were measured. The measurement results are shown in each table.

The grease composition of each example is different from the grease composition of each comparative example, has biodegradability of 60% or more, and excellent heat resistance shown from the test results of drop point and oxidation stability.

Claims

C L A I M S

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 comprises a base oil selected from the group of mineral oil, GTL, and poly-a-olefin base oils 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 acids comprises a higher fatty acid, a lower fatty acid, an aromatic carboxylic acid and a dicarboxylic acid.

4. The biodegradable grease composition according to any one of Claims 1 to 3, wherein the higher fatty acid is a substituted or unsubstituted carbon number 18 to 22 linear higher fatty acid and the lower fatty acid is a linear saturated lower fatty acid of carbon number in the range of from 2 to 4.

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 55.0wt% or more, based on the overall 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 from 10.0 to 40.0wt% based on the overall 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 tertiary calcium phosphate.

10. The biodegradable grease composition according to any one of claims 1 to 9, wherein the base oil has a kinematic viscosity of less than 13.00mm²/s at 100 °C and %CP ring analysis according to ASTM D3238 P of 65% or more.

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