FLAME RETARDANT HYDRAULIC OIL COMPOSITION

Technical Field

[1] The present invention relates to a flame retardant hydraulic oil composition, more specifically to such a flame retardant hydraulic oil composition that is most suitably used for applications where it is used under high temperature and pressure conditions with the high risk of fire breakout, such as for use in aluminum die-cast extruding machines or operations in iron mill facilities and that is applicable to a high-pressure pump, has excellent long life, sludge suppressing, antiwear, and ant i - seizure properties , is hardly hydrolyzed, and thus can be used for a long period of time.

Background Art

[2] Conventionally, as a hydraulic oil that is used at sites with the high risk of fire breakout such as use in aluminum die-cast extruding machines or operations in iron mill facilities, a frame retardant hydraulic oil (fluid) such as water-glycol or a fatty acid ester has been used to maintain safety at the sites. Particularly in sites subject to the regulations of Petroleum No. 4 of the Fire Service Act, a water-glycol fluid has been mainly used but has drawbacks regarding cumbersome storage of the used oil and antiwear properties. However, a revision of the Fire Service Act in 2002 makes the hydraulic oil containing a base oil, which is a fatty acid ester having a flash point of 250°C or higher inapplicable within the scope of the Fire Service Act, resulting in the widened applications of the hydraulic oil.

[3] The properties of an fatty acid ester vary depending on the composition of the fatty acid constituting the ester. A saturated fatty acid is excellent in oxidation stability. However, the saturated fatty acid is produced by synthesizing a petroleum raw material or hydrogenating an unsaturated fatty acid derived from an animal or vegetable oil, and thus an expensive raw material that is not environment friendly. Currently, an natural synthetic ester or a fat has also been used, which contains a fatty acid containing an unsaturated fatty acid, derived from an animal or vegetable oil that is environment friendly and advantageous in cost (see Patent Literatures 1 to 3 below).

[4] Meanwhile, since recent hydraulic systems have been used under higher pressures and become more free in maintenance than ever before, a hydraulic oil used under these circumstances has been required to have long-life properties and excellent antiwear properties, but esters are hydrolyzed in the presence of moisture, which is the biggest disadvantage. The acid produced as the result of hydrolysis facilitates the corrosion of various metals and wears of sliding parts and thus affect not only the working life of the hydraulic oil but also the antiwear properties thereof . Some metals acts as a catalyst for this hydrolysis, but the acid produced by the hydrolysis itself can also be a catalyst. As the result, once hydrolysis is generated, it proceeds at an accelerated pace. It is thus extremely important to capture acids generating at the initial stage, quickly and render them harmless.

A natural synthetic ester produced from a natural, material as the raw material contains mainly unsaturated fatty acids and thus is environment friendly and advantageous in cost. However, it has a drawback that it is extremely inferior in oxidation stability to synthetic esters of saturated fatty acids or synthetic hydrocarbon oils.

When a synthetic ester or an animal or vegetable fat is fresh, acids that are impurities are present therein and causes hydrolysis or oxidation deterioration. The use of an acid scavenger capturing these acids can extend the deterioration life significantly. Examples of known acid scavengers include carbodiimide compounds and epoxy compounds (see, for example, Patent Literature 4 below).

[5] However, it is known that the single use of the acid scavenger adversely affect the antiwear properties of a hydraulic oil, which was not improved by adding a phosphorus antiwear agent typically used for a hydraulic oil, such as tricresyl phosphate.
An ester containing an unsaturated fatty acid is poor in oxidation stability. The single use of a phenolic or aminic antioxidant that has been used for a hydrocarbon hydraulic oil failed to obtain a sufficient antioxidation effect for such an ester. Citation List Patent Literature

[6] Patent Literature 1: Japanese Patent Laid-Open Publication No. 2001-214187
Patent Literature 2: Japanese Patent Publication No. 3548591
Patent Literature 3: Japanese Patent Publication No. 2888747
Patent Literature 4: Japanese Patent Laid-Open Publication No. 2001-316687 Summary of Invention

Technical Problem

[7] A natural synthetic ester-based hydraulic oil produced using a fatty acid composed of mainly an unsaturated fatty acid, derived from an animal or vegetable oil that is environment friendly and advantageous in cost is poor in hydrolytic stability, oxidation stability and antiwear properties. It is thus necessary to capture quickly acids initially generating and render them harmless. However, the single use of an acid scavenger adversely affects the antiwear properties of the hydraulic oil. The use of a new excellent antiwear agent in combination is thus required. Furthermore, since an ester comprising an unsaturated fatty acid is poor in oxidation stability, the combination of additives that can provide better antioxidation effect than the conventional ones is required.

Solution to Problem

[8] The present invention was made under these circumstances and accomplished on the basis of the finding as the result of extensive studies intended to provide a long-lasting flame retardant hydraulic oil which comprises a synthetic ester derived from a raw material containing mainly an unsaturated fatty acid or an animal or vegetable fat and has sufficient antioxidation and antiwear properties and long life corresponding to the tendency of the recent hydraulic systems that are operated under high pressure and free of maintenance, the above problems were able to be solved by blending a hydrocarbon oil, an synthetic ester and/or a fat, particularly a synthetic ester containing mainly an unsaturated fatty acid derived from a natural raw material with a specific acid scavenger and a specific phosphorus compound. [0009] That is, the present invention provides a
flame retardant hydraulic oil composition comprising: (A) at least one base oil selected from hydrocarbon oils, synthetic esters, and fats; (B) an epoxy compound and/or a carbodiimide compound represented by formula (1) below in an amount of 0.01 to 2 percent by mass on the basis of the total mass of the composition; and (C) at least one antiwear agent selected from sulfur-containing phosphoric acid esters, acidic phosphoric acid esters, acidic phosphoric acid ester amine salts and phosphorus acid esters in an amount of 0.001 to 5 percent by mass on the basis of the total mass of the composition:
wherein R1 and R2 are each independently an alkyl group having 4 to 26 carbon atoms, an (a1kyl)phenyl group, an aralkyl group or an (alkyl)cycloalkyl group and may be the same or different from each other.

[9] The present invention also relates to the foregoing flame retardant hydraulic oil composition, wherein the carbodiimide compound represented by formula (1) is a compound represented by following formula (2):

wherein R3 to R8 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms and may be the same or different from each other.

[11] The present invention also relates to the foregoing flame retardant hydraulic oil composition further comprising an amine and/or phenolic ant ioxidant in an amount of 0.01 to 5 percent by mass on the basis of the total mass of the composition.

Advantageous Effects of Invention

[12] The present invention can provide a flame retardant hydraulic oil composition comprising a fatty acid ester oil containing mainly an unsaturated fatty acid, which is excellent in oxidation stability and antiwear properties. Furthermore, the present invention can provide a flame retardant hydraulic oil composition whose failure stage in FZG gear test is 10 or higher.

Best Mode for Carrying Out the Invention

[13] Preferable embodiments of the present invention will be described in more detail below.

The base oil used in the flame retardant oil composition of the present invention may be at least one type of base oil selected from the group consisting of hydrocarbon oils, synthetic esters and fats. Specific examples of such base oils include polyol esters, diesters, various vegetable fats, and various animal fats. In particular, the base oil is preferably a polyol ester or an ester of rapeseed oil, sunflower oil or soybean oil, which is high in the ratio of oleic acid, and particularly preferably a base oil whose kinematic viscosity at 40°C is from 10 to 200 mm2/s.

[14] Examples of the hydrocarbon oils include mineral oils and synthetic hydrocarbon oils. Specific examples include naphthenic and paraffinic mineral oils, synthetic hydrocarbon oils such as olefin copolymers, naphthalene compounds, alkylbenzens, and mixtures thereof.

[15] Examples of the mineral oils include paraffinic or naphthenic mineral oils produced by subjecting a lubricating oil fraction resulting from atmospheric and vacuum distillation of paraffinic crude oil, intermediate base crude oil or naphthenic crude oil to any one or more refining techniques selected from solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid treatment, and clay treatment.

[16] Among these mineral oils, highly refined mineral oils are preferably used because of their more excellent stability. A highly refined mineral oil used in the present invention preferably has a %CA of 2 or less, a %CP/%CN of 6 or greater, and an iodine value of 2.5 or greater. The %CP, %CN, and %CA used herein denote the percentage of paraffin carbon number in the total carbon number , the percentage of naphthene carbon number in the total carbon number, and the percentages of the aromatic carbon number in the total carbon number, respectively, determined by a method (n-d-M ring
analysis) in accordance with ASTM D 3238-85.

The non-aromatic unsaturate content (unsaturate degree) is preferably 10 percent or less. A unsaturate degree of 10 percent or greater may possibly cause sludge formation. From the viewpoint of this, the unsaturate degree in the present invention is preferably 5 percent or less, more preferably 1 percent or less, most preferably 0.1 percent or less. Specific examples of such highly refined mineral oils include refined oil produced by refining distilled oil resulting from atmospheric distillation of paraffinic crude oil, intermediate base crude oil or naphthenic crude oil or from vacuum distillation of residual oil resulting from atmospheric distillation, in accordance with a conventional method; deep-dewaxed oil produced by deep-dewaxing the refined oil; and hydrogenated oil produced by hydrogenating the deep-dewaxed oil. No particular limitation is imposed on the method of refining. Various methods may be used.

[17] Examples of the olefin copolymer include those produced by copolymerizing olefins having 2 to 12 carbon atoms and those produced by further hydrogenating these copolymers. Specific examples include polybutene, polyisobutene, oligomers of a-olefins having 5 to 12 carbon atoms (poly-α -olefins), ethylene-propylene copolymers; and hydrogenated compounds of these copolymmers.

[18] No particular limitation is imposed on the naphthalene compound as long as it has a naphthalene skeleton. However, the naphthalene compound is preferably a compound represented by formula (3):

[19] In formula (3) , R9, R10, R11 and R12 may be the same or different from each other and are each independently hydrogen or a hydrocarbon group having 1 to 10, preferably 1 to 8 carbon atoms. Examples of the hydrocarbon group include alkyl, alkenyl, aryl, alkylaryl, and aralkyl groups. The total carbon number of R9, R10, R11 and R12 is preferably from 1 to 10.

The naphthalene compound may be not only a compound with a single structure but also a mixture of two or more compounds having different structures.

No particular limitation is imposed on the method of producing the above-described naphthalene compound. It may be produced by any of various known methods. A naphthalene compound having a sulfur content of 500 ppm by mass or less is preferably used because its excellent thermal and oxidation stabilities.

[20] With regard to the alkylbenzene, any alkylbenzene may be used as long as it does not impair the properties of the resulting hydraulic oil. Preferred examples include alkylbenzenes that have 1 to 4 alkyl groups having 1 to 30 carbon atoms, the total carbon number of which alkyl groups is from 20 to 30.

The alkyl groups may be straight - chain or branched but are preferably branched alkyl groups in view of stability and viscosity characteristics, more preferably branched alkyl groups derived from oligomers of olefins such as propylene, butene, and isobutylene in view of availability.

[21] The number of alkyl groups in the alkylbenzene is 1 to 4. Alkylbenzenes having 1 or 2 alkyl groups, i.e., monoalkylbenzenes, dialkylbenzenes or mixtures thereof are most preferably used in view of stability and availability.

The alkylbenzene may be not only an alkylbenzene with a single structure but also a mixture of two or more alkylbenzenes having different structures.

No particular limitation is imposed on the method of producing the alkylbenzene.

[22] Examples of the synthetic esters include fatty acid esters, dibasic acid esters, polyol esters, complex esters, aromatic esters, carbonic acid esters, and mixture thereof.

[23] Examples of the fatty acid esters include esters of unsaturated fatty acids such as palmitoleic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, and 8,11-eicosadienoic acid or saturated fatty acids having a straight-chain or branched alkyl group having 5 to 19 carbon atoms, such as pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, and nonadecanoic acid and monohydric alcohols having a straight-chain or branched alkyl group having 1 to 19 carbon atoms, such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, and nonadecanol; and mixtures thereof. Specific preferred examples include fatty acid esters such as oleylstearate and oleyllaurate.

[24] Examples of the dibasic acid esters include esters of dibasic acids having 5 to 10 carbon atoms, such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid and the monohydlic alcohols having a straight - chain or branched alkyl group having 1 to 15 carbon atoms as described with respect to the fatty acid esters; and mixtures thereof. Specific examples include ditridecyl glutarate, di-2-ethylhexyl adipate, disodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, and mixtures thereof.

[25] The polyol esters are preferably esters of diols or polyols having 3 to 20 hydroxyl groups and fatty acids having 1 to 24 carbon atoms.

Specific examples of the diols include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanedioil, 1,2-butanediol,

2-methyl-1,3-propanediol, 1, 5-pentanediol, neopentyl glycol, 1,6-hexanediol,

2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol, 2-methyl- 2-propyl-1,3-propanediol,

2,2-diethyl-l,3-propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol.

[26] Specific examples of the polyols include polyhydric alcohols such as trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane) , tri- (trimethylolpropane) , pentaerythritol, di-(pentaerythritol), tri-(pentaerythritol), glycerin, polyglycerins (dimmer to eicosamer of glycerin), 1,3,5-pentanetriol, sorbitol, sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol, and mannitol; saccharide such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose, and melezitose; partially eterified products thereof; and methyl glucoside (glycoside).
Among these, preferred polyols are hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, and di - (pentaerythritol) because of their excellent hydrolysis stability.

[27] Examples of the fatty acids of the polyol esters include the unsaturated fatty acids exemplified with respect to the above - described fatty acid esters and saturated fatty acids having a straight - chain or branched alkyl group having 5 to 19 carbon atoms. The unsaturated fatty acids exemplified with respect to the above-described fatty acid esters are particularly preferably used. Neo acid whose α carbon atom is quaternary may also be used. Specific examples of the branched saturated fatty acids include isopentanoic acid (3-methylbutanoic acid), 2-methylhexanoic acid, 2 -ethy1pentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethy1hexanoic acid.

[28] Specific examples of preferred polyol esters include diesters, triesters and tetraesters of one or more fatty acids selected from the group consisting of valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid,

2-ethylpentanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid and polyols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, and pentaerythritol.

Esters of two or more fatty acids and a polyol may be a mixture of two or more esters of one fatty acid and a polyol or an ester of two or more mixed fatty acids and a polyol.

[29] Among these polyol esters, preferred are esters of hindered alcohols such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol), and tri-(pentaerythritol) and still more preferred are esters of neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, and pentaerythritol because of their excellent hydrolysis stability. Most preferred are esters of trimethylolpropane and pentaerythritol because of their particularly excellent hydrolysis stability. Specific examples include trimethylolpropane oleate and pentaerythritol oleate.

[30] The polyol ester may be a partial ester wherein a part of the hydroxyl groups remains unesterif ied or a full ester wherein all of the hydroxyl groups are esterified. Further, the polyol ester may be a mixture of a partial ester and a full ester but is preferably a full ester.

[31] The complex ester is an ester of a fatty acid and a dibasic acid with a monohydric alcohol and a polyol. The fatty acid, dibasic acid, monohydric alcohol, and polyol may be those exemplified with respect to the above-mentioned dibasic acid ester and polyol esters.

[32] Examples of the aromatic esters include esters of monovalent to hexavalent, preferably monovalent to tetravalent, more preferably monovalent to trivalent aromatic carboxylic acids and aliphatic alcohols having 1 to 18, preferably 1 to 12 carbon atoms . Specific examples of the monovalent to hexavalent aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, and mixtures thereof. The aliphatic alcohols having 1 to 18 carbon atoms may be monohydlic alcohols having a straight-chain or branched alkyl group having 1 to 15 carbon atoms exemplified with respect to the above-described fatty acid ester, straight - chain or branched hexadecanol, straight - chain or branched heptadecanol, strai ght- chain or branched octadecanol, and mixtures thereof.

Specific examples of the aromatic ester include dibutyl phthalate, di (2-ethylhexyl) phthalate, dinonyl phthalate, didecyl phthalate, didodecyl phthalate, ditridecyl phthalate, tributyl trimellitate, tri(2-ethylhexyl) trimel1itate, trinonyl trimellitate, tridecyl trimellitate, tridodecyl trimellitate, and tritridecyl trimellitate. It is understood that when an aromatic carboxylic acid of divalent or more is used, the ester may be a simple ester composed of one type of aliphatic alcohol or a complex ester composed of two or more types of aliphatic alcohols.

[33] Carbonic acid ester refers to a compound having a carbonic acid ester structure per molecule. The carbonic acid ester may have one or more carbonic acid ester structures per molecule.

The alcohol constituting the carbonic acid ester may be any of the aforesaid aliphatic alcohols or polyols, polyglycols, or polyols to which a polyglycol is added. Alternatively, compounds produced using carbonic acid and fatty acids and/or dibasic acids may be used.

[34] Needless to mention, the ester referred herein may be a compound of a single structure or a mixture of two or more compounds with different structures.

Among the above-exemplified ester-based base oils, preferred are polyol esters because of their excellent hydrolysis stability.

In the present invention, the above-described ester-based base oils may be used alone or in combination.

[35] Examples of the fats used as the base oil of the flame retardant hydraulic oil composition of the present invention include natural animal or vegetable fats, such as rapeseed oil, sunflower oil, soybean oil, castor oil, coconuts oil, corn oil, cotton seed oil,
olive oil, rice bran oil, palm oil, palm kernel oil, peanut oil, tall oil, beef tallow, lard, and hydrogenated products thereof. Among these fats, preferred are high oleic acid type fats wherein the ratio of the unsaturated fatty acids, particularly oleic acid in the fatty acid constituting an ester is high, more preferred are high oleic vegetable oils that are further increased in oleic acid ratio.

[36] The base oil of the flame retardant hydraulic oil composition of the present invention may be one or more types selected from the group consisting of the above-described mineral oils, synthetic hydrocarbons, synthetic esters and fats.

[37] The synthetic esters and/or fats may contain any of a saturated fatty acid, an unsaturated fatty acid, a straight-chain fatty acid and a branched fatty acid as the constituent fatty acid but preferably contains an unsaturated fatty acid from the viewpoint of advantageous effects achieved by addition of Component (B) that is an acid scavenger such as a carbodiimide compound represented by formula (1) or an epoxy compound.
The ratio of the unsaturated fatty acid in the fatty acid constituting an ester is 30 percent by mole or more, preferably 50 percent by mole or more, more preferably 70 percent by mole or more.

If the ratio of the unsaturated fatty acid in the fatty acid constituting an ester is less than 30 percent by mole or less, blending of Component (B) is effective in suppressing the viscosity and acid value from increasing at the initial stage of use of the hydraulic oil but after- further progress of the use, deteriorated product tends to become sludge rapidly and cause troubles in a hydraulic system.

[38] No particular limitation is imposed on the kinematic viscosity of these base oils. However, the kinematic viscosity at 40°C is preferably from 10 to 200 mm2/s, more preferably from 15 to 150 mm2/s, more preferably from 20 to 100 mm2/s because the resulting) hydraulic composition would be excellent in flame retardant properties, antiwear properties and anti-seizure properties and less in friction loss by stirring resistance. No particular limitation is imposed on the viscosity index of the base oils, either. However, the viscosity index is preferably from 80 to 500 , more preferably from 100 to 300 with the objective of maintaining oil film at high temperatures. Furthermore, the pour point is also optional but is preferably -5°C or lower, more preferably -15°C or lower with the viewpoint of pump startability during winter.

[39] In formula (1) below representing a carbodiimide compound that is Component (B) of the flame retardant hydraulic oil composition, R1 and R2 are each independently an alkyl group, a phenyl group, an alkylphenyl group, an aralkyl group, a cycloparaffin group or an al kylcyclopara f f in group and may be the same or different from one another.

[40]
(1)

[41] Preferred alkyl groups are straight-chain or branched alkyl groups having 4 to 26 carbon atoms, and more preferred are straight-chain or branched alkyl groups having 4 to 12 carbon atoms, such as butyl, pentyl, hexyl, and octyl groups.

Examples of compounds represented by formula (1) wherein R1 and R2 are alkylphenyl groups include diphenylearbodiimides and dialkylphenylcarbodiimides represented by formula (2) below. In formula (2), R3, R4, R5, R6, R7 and R8 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms and may be the same or different from each other.

Examples of the cycloparaffin and a1ky1cyc1oparaffin groups includes the phenyl groups of the dialkylphenylcarbodiimide substituted to cyclohexyl group.

[43] In formula (1), R1 and R2 are preferably alkylphenyl groups, particularly preferably phenyl groups to which ethyl or a branched alkyl group having 3 or 4 carbon atoms is attached, such as diisopropylpheny1 and ditertiarybutylphenyl, and specific example of the compound of formula (1) includes bis(2,6-di-tert- butylphenol)carbodiimide.

The carbon number of each R1, R2 is preferably 4 to 26, more preferably 4 to 20, more preferably 4 to 12. If the carbon number of R1 or R2 is 3 or fewer, it is not preferable because the resulting composition would be increased in reactivity and become unstable.
If the carbon number is more than 27, it is not preferable either because the ratio of functional groups in the molecule would be less and thus an acid scavenging effect would be adversely affected.

[44] The epoxy compound of Component (B) may be at least one epoxy compound selected from the group consisting of alkyloxirane compounds, aryloxirane compounds, phenylglycidylether type epoxy compounds, alkylglycidylether type epoxy compounds, glycidylester type epoxy compounds, alicyclic epoxy compounds, epoxidized fatty acid monoesters, and epoxidized vegetable oils.

[45] The alkyl group of the alkyloxirane compounds is a straight-chain or branched alkyl group having 4 to 20 carbon atoms, preferably an alkyl group having 8 to 20 carbon atoms, more preferably an alkyl group having 10 to 18 carbon atoms. If the carbon number of the alkyl group is fewer than 3 . , the resulting composition would likely evaporate and thus be poor in stability. If the carbon number is greater than 21, the resulting composition would be poor in low temperature performances and solubility, in particular solubility after capturing acids.

[46] Specific examples of the alkyloxirane compound include 1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, 1,2-epoxytridecane,
1,2 -epoxytetradecane, 1,2 - epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,1,2-epoxyoctadecane , 2-epoxynonadecane and 1,2 -epoxyeicosane.

[47] Specific examples of the aryloxirane compound include 1,2-epoxystyrene and
alkyl-1,2-epoxystyrene.

[48] Specific examples of the phenylglycidyl ether type epoxy compounds include phenylglycidyl ethers and alkylphenylglycidyl ethers. The alkylphenylglycidyl ether referred herein may be any of those having 1 to 3 alkyl groups each having 1 to 13 carbon atoms, preferably those having one alky group having 4 to 10 carbon atoms . Preferred examples of such alkylphenylglycidyl ethers include n-butylphenylglycidyl ether, i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether, tert-butylphenylglycidyl ether, pentylphenylglycidyl ether, hexylphenylglycidyl ether, heptylphenylglycidylether, octylphenylglycidylether, nonylphenylglycidyl ether and decylphenylglycidyl ether.

[49] Specific examples of the alkylglycidyl ether type epoxy compounds include decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, 2 -e thylhexy1glyc i dy1 ether, neopentylglycoldiglycidyl ether, trimethylolpropane triglycidyl ehter, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, polyalkyleneglycol monoglycidyl ethers and polyalkyleneglycol diglycidyl ethers.

[50] Specific examples of the glycidyl ester type epoxy compounds include phenylglycidyl esters, alkylglycidyl esters and alkenylglycidyl esters. Preferred are glycidyl-2,2-dimethyloctanoate, glycidyl benzoate, glycidyl acrylate and glycidyl methacrylate.
[51] Specific examples of the alicyclic epoxy compounds include 1,2- epoxycyclohexane,
1,2 -epoxycyc1opentane,
3,4 -epoxycyclohexylmethyl-3,4 -epoxycyc1ohexane carboxylate,
bis(3,4-epoxycyclohexylmetyl) adipate, exo-2,3-epoxynorbornane, bis(3,4 -epoxy-6-methycyclohexylmetyl) adipate, 2 - (7-oxabicyclo[4.1.0]
hept-3-yl) -spiro(l,3-dioxane- 5, 3'-[7]oxabicyclo[4.1.0]) heptane,
4 - (1'-metylepoxyethyl)-1,2-epoxy-2 - methylcyclohexane and 4 -epoxyethyl-1,
2-epoxycyclohexane.

[52] Specific examples of the epoxidized fatty monoesters include esters of epoxidized fatty acids having 12 to 20 carbon atoms with alcohols having 1 to 8 carbon atoms, phenols or alkylphenols. Particularly preferred are epoxystearic acid butyl, hexyl, benzyl, cyclohexyl, me thoxyethyl, phenyl and butylphenyl esters.

[53] Specific examples of the epoxidized vegetable oils include epoxidized compounds of vegetable oils such as soybean oil, linseed oil and cottonseed oil .

[54] Among these epoxy compounds, preferred are alkyloxirane compounds, phenylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds and epoxidized fatty acid monoesters. More preferred are alkyloxirane compounds, phenylglycidyl ether type epoxy compounds and glycidyl ester type epoxy compounds. Particularly preferred are 1,2-epoxytetradecane, phenylglycidyl ether, butylphenylglycidy1 ether, alkylglycidyl esters and mixtures thereof.

[55] The upper limit content of Component (B) in the flame retardant hydraulic oil composition of the present invention is 2 percent by mass, preferably 1.5 percent by mass, more preferably 1.0 percent by mass on the basis of the total mass of the composition. A content of more than 2 percent by mass would result in a composition that is poor in solubility after acid scavenging, causing sludge formation. The lower limit content of Component (B) is 0.01 percent by mass, preferably 0.05 percent by mass, more preferably 0.1 percent by mass. A content of less than 0.01 percent by mass would result in a composition that is insufficient in a scavenging effect.

[56] The flame retardant hydraulic oil composition of the present invention contains Component (C) that is at least one antiwear agent selected from sulfur-containing phosphoric acid esters, acidic phosphoric acid esters, acidic phosphoric acid ester amine salts and phosphorus acid esters.

[57] Specific examples of the sulfur-containing phosphoric acid esters include trialkyl phosphorothionates whose alkyl group has 4 to 18 carbon atoms, trioleyl phosphorothionate, triphenyl phosphorothionate, tricresyl phosphorothionate, trixylenyl phosphorothionate, cresyldiphenyl phosphorothionate, xylenyldiphenyl phosphorothionate, tris(n-propylphenyl) phosphorothionate, tris ( isopropylphenyl) phosphorothionate, tris(n-butylphenyl) phosphorothionate, tris(isobutylphenyl) phosphorothionate, tris(s-butylphenyl) phosphorothionate, and tris(t-butylphenyl) phosphorothionate.

[58] Specific examples of the acidic phosphoric acid esters include alkyl acid phosphates whose alkyl group has 4 to 22 carbon atoms and dioleyl acid phosphates, and diphenyl acid phosphates and dicresyl ester acid phosphates that are aromatic acidic phosphates. Among these, preferred are dialkyl acid phosphates that contain no aromatic and have an alkyl group of 4 to 22 carbon atoms. More preferred are dialkyl acid phosphates having an alkyl group of 6 to 18 carbon atoms.

[59] Specific examples of the acidic phosphorus acid ester amine salts include salts of the aforesaid acidic phosphorus acid esters with an amine selected from the group consisting of amines having an alkyl group of 1 to 8 carbon atoms, amines having two alkyl groups of 1 to 8 carbon atoms, and amines having three alkyl groups of 1 to 8 carbon atoms.

[60] Specific examples of the phosphorus acid esters include dialkyl phosphites having two alkyl groups of 4 to 12 carbon atoms, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, trialkyl phosphites having three alkyl groups of 4 to 12 carbon atoms, trioleyl phosphite, triphenyl phosphite, and tricresyl phosphite.

[61] Sulfur-containing phosphorus acid esters, acidic phosphorus acid esters, acidic phosphorus acid ester amine salts are preferably used as Component (C) in the present invention because they exhibit superior effects in combination with a synthetic ester or fats.

[62] The upper limit content of Component (C) in the flame retardant hydraulic oil composition of the present invention is 5 percent by mass, preferably 2 percent by mass, more preferably 1.5 percent by mass on the basis of the total mass of the composition. A content of more than 5 percent by mass is not preferable because the resulting composition would be poor in thermal stability and thus cause sludge formation. The lower limit content of Component (C) is 0.001 percent by mass, preferably 0.005 percent by mass, more preferably 0 . 01 percent by mass on the basis of the total mass of the composition. A content of less than 0.001 percent by mass is not preferable because the resulting composition would be insufficient in antiwear properties and anti-seizure properties.

[63] Preferably, the flame retardant hydraulic oil composition of the present invention contains further an amine and/or phenolic antioxidant. The use of the antioxidant in combination can add superior antioxiation properties and sludge suppressing properties. No particular limitation is imposed on the antioxidant since any conventional aminic or phenolic compound that has been used as an antioxidant for lubricants may be used.

[64] Typical examples of the amine antioxidant include phenyl-a-naphthylamines represented by formula (4) and p , p '-dial kyldiphenylamines represented by formula (5).

[65]

[66] In formula (4), R13 is hydrogen or an alkyl group having 1 to 16 carbon atoms.

In formula (5), R14 and R15 are each independently an alkyl group having 1 to 16 carbon atoms.

[67] Compounds represented by formula (4) wherein R13 is an alkyl group can provide an excellent sludge suppressing effect, and thus R13 is preferably a branched alkyl group having 8 to 16 carbon atoms, more preferably a branched alkyl group having 8 to 16 carbon atoms derived from an oligomer of an olefin having 3 or 4 carbon atoms.
Specific examples of the olefin having 3 or 4 carbon atoms include propylene, 1-butene, 2-butene and isobutylene, but preferred are propylene and isobutylene with the objective of attaining a more excellent sludge suppressing effect. In order to attain a more excellent sludge suppressing effect, R13 is more preferably branched octyl derived from isobutylene dimmer, branched nonyl derived from propylene trimer, branched dodecyl derived from isobutylene trimer, branched dodecyl derived from propylene tetramer or branched pentadecyl derived from propylene pentamer, more preferably branched octyl derived from isobutylene dimmer, branched dodecyl derived from isobutylene trimer, or branched dodecyl derived from propylene tetramer, most preferably branched dodecyl.

[68] In formula (5) representing p,p'-dialkyldiphenylamines, R14 and R15 are each independently preferably a branched alkyl group having 3 to 16 carbon atoms, more preferably a branched alkyl group having 3 to 16 carbon atoms derived from an olefin having 3 or 4 carbon atoms or an oligomer thereof in order to obtain a more excellent sludge suppressing effect. Specific examples of the olefin having 3 or 4 carbon atoms include propylene, 1-butene, 2-butene and isobutylene, but preferred are propylene and isobutylene with the objective of attaining a more excellent sludge suppressing effect.

R14 and R15 are each independently most preferably tert-butyl derived from isobutylene or branched octyl derived from isobutylene dimmer.

[69] As p,p1-dialkyldiphenylamines represented by formula (5) , any commercially available or synthetic product may be used. The synthetic product may be synthesized easily by reacting a halogenated alkyl compound having 1 to 16 carbon atoms with diphenyl amine or reacting an olefin having 1 to 16 carbon atoms or an oligomer thereof with diphenylamine, both using a Friedel Crafts catalyst, similarly to
phenyl-α -naphthylamine represented by formula (4). However, any synthesis method may be used.

[70] The upper limit content of the amine antioxidant is preferably 2 percent by mass, more preferably 1.5 percent by mass, more preferably 1 percent by mass or less on the basis of the total mass of the composition. A content of more than 2 percent by mass is not preferable because it would cause sludge formation. The lower limit content is preferably 0 . 001 percent by mass, more preferably 0.05 percent by mass or less, more preferably 0. 1 percent by mass on the basis of the total mass of the composition. A content of less than 0.001 percent by mass is not preferable because the resulting composition would be insufficient in an anti-oxidation effect.

[71] No particular limitation is imposed on the phenolic antioxidant since any alkylphenolic compound that has been used as an antioxidant for lubricants. However, the phenolic antioxidant is preferably one or more alkylphenolic compound selected from those represented by formulas (6) and (7) below.

[72]
(6)

[73] In formula (6), R16 is an alkyl group having 1 to 4 carbon atoms, R17 is hydrogen or an alkyl group having 1 to 4 carbon atoms, R18 is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a group represented by formula (i) or (ii) below.

[74]

[75] In formula (i) , R19 is an alkylen group having 1 to 6 carbon atoms, R20 is an alkyl or alkenyl group having 1 to 24 carbon atoms.

In formula (ii), R21 is an alkylene group having 1 to 6 carbon atoms, R22 is an alkyl group having 1 to 4 carbon atoms, R23 is hydrogen or an alkyl group having 1 to 4 carbon atoms, and n is an integer of 0 or 1.

[76] In formula (7), R24 and R28 are each independently an alkyl group having 1 to 4 carbon atoms, R25 and R29 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, R26 and R27 are each independently an alkylene group having 1 to 6 carbon atoms, and Y is an alkylene group having 1 to 18 carbon atoms or a group represented by formula (iii) - R30- S - R31- (iii) .

In formula (iii), R30 and R31 are each independently an alkylen group having 1 to 6 carbon atoms.

[77] In formula (6), R16 is an alkyl group having 1 to 4 carbon atoms. R16 is particularly preferably tert-butyl in view of excellent anti-sludge properties. R17 is hydrogen or an alkyl group having 1 to 4 carbon atoms. R17 is particularly preferably hydrogen, methyl or tert-butyl in view of excellent anti-sludge properties. R18 is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a group represented by formula (i) or (ii) above. The alkyl group for R18 is preferably methyl or ethyl in view of excellent anti-sludge properties.

[78] Examples of the compound represented by formula (6) include various compounds as described above. Preferred examples of compounds where R18 is an alkyl group having 1 to 4 carbon atoms include

2,6-di-tert-butyl-p-cresol and

2,6-di-1ert-butyl - 4-ethylphenol. Preferred examples of compounds where R18 is a group represented by formula (i) include n-hexyl

(3-methyl-5-tert-butyl-4-hydroxyphenyl) succinate,

iso-hexyl (3-methyl - 5 -tert-butyl- 4-hydroxyphenyl) propionate,

n-heptyl(3,5-di-tert-butyl-4 -hydroxyphenyl) acetate, 2 -ethylhexyl (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and

isodecyl(3,5-di-tert-butyl-4-hydroxyphenyl) propionate. Preferable examples of compounds where R18 is a group represented by formula (ii) include bis(3,5-di-tert-butyl-4-hydroxyphenyl), bis (3, 5-di-tert'-butyl-4 - hydroxyphenyl) methane . Mixtures of these compounds are also preferred.

[79] In formula (7) , Y is an alkylene group having 1 to 18 carbon atoms or a group represented by formula (iii) above. The alkylene group for Y may be straight - chain or branched. In view of easy availability of the raw material, Y is preferably an alkylene group having 1 to 6 carbon atoms, particularly preferably a straight - chain alkylene group having 2 to 6 carbon atoms, such as ethylene (dimemthy1ene), trimethylene, straight-chain butylene (tetramethylene) , straight - chain pentylene (pentamethylene) , or straight - chain hexylene (hexamethylene).

[80] The upper limit content of the phenolic antioxidant is preferably 5 percent by mass, more preferably 2 percent by mass, more preferably 1.5 percent by mass on the basis of the total mass of the composition. A content of more than 5 percent by mass is not preferable because it causes sludge generation. The lower limit content is preferably 0.01 percent by mass, more preferably 0.05 percent by mass, more preferably 0 . 1 percent by mass on the basis of the total mass of the composition. A content of less than 0.01 percent by mass is not also preferable because the resulting composition would be insufficient in an antioxidation effect.

[81] As described above, in the present invention, at least one base oil selected from hydrocarbon oils, synthetic esters, and fats is blended with Components (B) and (C) and furthermore an amine and/or phenolic antioxidant thereby producing a flame retardant hydraulic oil composition that is excellent in antioxidation and antiwear properties. However, in order to further enhance these properties, the oil composition may be blended with any one or suitable combinations of various additives such as other antioxidants, rust inhibitors, metal deactivators, antiwear agents, viscosity index improvers, pour point depressants, anti-foaming agents, demulsifiers, stickslip preventive agents, and oiliness improvers.

[82] Specific examples of the rust inhibitors include amino acid derivatives; partial esters of polyhydric alcohols; esters such as lanolin fatty acid ester, alkyl succinic acid esters and alkenyl succinic acid esters; sarcosine; polyhydric alcohol partial esters such as sorbitan fatty acid esters; metal soaps such as fatty acid metal salts, lanolin fatty acid metal salts and oxidized wax metal salts; sulfonates such as calcium sulfonate and barium sulfonate; oxidized waxes; amines; phosphorus acid; and phosphorus acid salts. Among these rust inhibitors, amino acid derivatives are preferably used because of their superior rust inhibiting effect.

[83] Examples of the above-mentioned amino acid derivatives include compounds represented by formula (8) below:

[84] In formula (8), A is a group represented by formula (9) or (10), B is an alkyl group having 1 to 12 carbon atoms or a residue of a monohydric carboxylic acid ester represented by formula (11) below, R32 is an alkyl group having 4 to 12 carbon atoms, and R33 is an alkyl group having 1 to 10 carbon atoms:

R 350 - C O - R34- ( 9 )
R 370 - C O - R36-C O - (10)
-C-CO-O-R38 (11)

wherein R34 is an alkylene group having 1 to 12 carbon atoms, R36 is an alkylene group having 1 to 10 carbon atoms, R35 and R37 are each independently hydrogen or an alkyl group having 1 to 10 carbon atoms, and R38 is an alkyl group having 1 to 10 carbon atoms.

[85] R32 is an alkyl group having 4 to 12, preferably 4 to 10, more preferably 6 to 10 carbon atoms . R33 and R38 are each independently an alkyl group having 1 to 10, preferably 1 to 8, more preferably 1 to 6 carbon atoms. R37 is hydrogen or an alkyl group having 1 to 10, preferably 1 to 8, more preferably 1 to 6 carbon atoms.

[86] In the present invention, the hydraulic oil composition may be blended with any one or more of these rust inhibitors in any amount. However, in general the content is preferably from 0.001 to 2.0 percent by mass, more preferably from 0.01 to 1.5 percent by mass, more preferably from 0.05 to 1 percent by mass on the basis of the total mass of the composition.

[87] Specific examples of the metal deactivators include benzotriazole-, thiaziazole-, and imidazole-based compounds. In the present invention, the hydraulic oil composition may be blended with any one or more of these metal deactivators in any amount.
However, in general the content is preferably from 0.001 to 1 percent by mass on the basis of the total mass of the composition.

[88] Specific examples of the viscosity index improvers include non-dispersant type viscosity index improvers such as copolymers of one or more monomers selected from various methacrylic acid esters or hydrogenated compounds thereof, ethylene-a-olefin copolymers (a -olefin may be propylene, 1-butene, or 1-pentene) or hydrogenated compounds thereof, polyisobutylenes or hydrogenated compounds thereof; hydrogenated compounds of styrene-diene, and polyalkylstyrenes. In the present invention, the hydraulic oil composition may be blended with any one or more of these viscosity index improvers in any amount . However, in general the content is preferably from 0.001 to 10 percent by mass on the basis of the total mass of the composition.

[89] Specific examples of the pour point depressants include copolymers of one or more monomers selected from various acrylic acid esters and methacrylic acid esters or hydrogenated compounds thereof. In the present invention, the hydraulic oil composition may be blended with any one or more of these pour point depressants in any amount. However, in general the content is preferably from 0.01 to 5 percent by mass on the basis of the total mass of the composition.

[90] Specific examples of the anti-foaming agents include silicones such as dimethylsilicone and fluorosilicone. In the present invention, the hydraulic oil composition may be blended with any one or more of these anti-foaming agents in any amount. However, in general the content is preferably from 0.001 to 0.05 percent by mass on the basis of t'he total mass of the composition.

Examples of the demulsifiers include polyoxyalkyleneglycols, polyoxyalkylenealkylethers, polyoxyalkylenealkylmides, and polyoxyalkylene fatty acid esters.

Specific examples of the stickslip preventive agents include polyhydric alcohol esters (full esters and partial esters) .

Specific examples of the oiliness improvers include fatty acids, esters, and alcohols.
Ingeneral, the content is preferably from 0.01 to 0.5 percent by mass on the basis of the total mass of the hydraulic oil composition.

Examples

[91] The present invention will be described in more details with reference to the following examples but is not limited thereto.

[92] (Examples 1 to 17, Comparative Examples 1 to 3)

As set forth in Tables 1 to 4, hydraulic oil compositions were prepared by blending a base oil with additives. The base oils and additives that were used in Examples and Comparative Examples are as follows.

[93]

A1 : oleic acid ester of trimethylol propane (kinematic viscosity at 40°C: 47.2 mm2/s, viscosity index: 190)

A2: rapeseed oil containing oleic acid in a higher ratio (kinematic viscosity at 40°C: 35 mm2/s, viscosity index: 190, ratio of oleic acid in all the fatty acids constituting the ester: 75 percent by mole, ratio of unsaturated fatty acid in all the fatty acids constituting the ester: 90 percent by mole)

A3: poly-α -olefin oligomer (kinematic viscosity at 40°C: 44.5 mm2/s, viscosity index: 145)

[94] < Component (B) (Acid Scavenger)> Bl: bis(2 ,6-di-tert-butylphenyl) carbodiimide represented by the following formula:

(R3 and R4 are each hydrogen, R4, R5, R6 and R7 are each tert-butyl.)
B2: 1,2-epoxytetradecane

[95] CI: triphenylthiophosphate

C2: 2-ethylhexyl acid phosphate C3: tricresylphosphate

[96]

DI: N-p-isododecylphenyl-a-naphtylamine D2: p,p'-dioctyldiphenylamine D3 :
bis(3,5-di-tert-butyl-4-hydroxyphenyl) methane

[97]

El: amino acid derivative compound represented by the following formula

wherein R1 is octyl, R2 is butyl, and R3 is butylene.
E2 : sorbitan monooleate

[98]

F1: N-methylbenzotriazole
F2: polymethacrylate (molecular weight:
50,000)

[99] Each of the hydraulic oil compositions thus produced were subjected to flash point measurement, RPVOT test, Four-ball test, FZG gear test, V104C vane pump test and rust inhibiting test. The results are set forth in Tables 1 to 4 below. The properties were determined as follows and the tests were carried out as follows .

[100] [Flash Point]

The flash point of each composition was measured in accordance with JIS J 2265 "Crude Oil and Petroleum Products-Determination of flash point".

[101] [RPVOT Test]

In accordance with JIS K 2514 "Rotating Pressure Vessel Oxidation Test", 50 g of a sample, a coil-shaped copper catalyst, and 10 ml of water were charged into a test vessel with a lid, which was then placed into a vessel equipped with a pressure gauge, into which was then filled with oxygen with a pressure of 620 kPa. The vessel was placed into a thermostat bath. The vessel was rotated at 100 rpm at an angle of 30 degrees. The sample was evaluated in this test by time spent till the maximum pressure dropped by 175 kPa .

[102] [Four-Ball Test]

This test was carried out at 1200 rpm, a load of 294 N, an oil temperature of room temperature for 30 minutes in accordance with ASTM D 2783-88 "Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Four-Ball Method)" to measure the average of scar diameters (mm) of fixed three balls.

[103] [FZG Gear test]

This is a gear test defined in ASTM D 5182. This test was started at 1500 rpm and at an oil temperature of 90°C, and a gear is loaded by applying a certain weight defined in each stage for 15 minute. The anti-seizure properties of each oil was evaluated with the stage where seizure occurs. The stage of load at which the gear seizes is defined as failure.

[104] [Vane Pump Test (V104C Test)]

The vane pump test defined in ASTM D 2882 was carried out. The weights of a vane and a rings were measured before and after the test to determine the wear amount. The test time was 100 hours.

[105] [Rust Inhibiting Test]

This is a test for rust inhibition using a rolled carbon steel for cold-finished steel bars, defined in JIS K 2510. There are two types of methods depending on water to be used, that are a method using distilled water and a method using artificial seawater. For these examples, the test was carried out using artificial sea water, which is severer. The test was carried out for 24 hours, and the test oil temperature was 600 C.

[0106] [Acid Value]

The acid value is determined by the titration amount of potassium hydroxide required to neutralize acidic components contained in a certain amount of sample as defined in JIS K 2501. That is, 1 (KOH/mg) indicates the amount of acidic components in 1 mg of sample that can be measured with a KOH solution.

[107] TO [110] TABLES

Industrial Applicability

[111] The present invention can provide a flame retardant hydraulic oil composition that is excellent in long life, sludge suppressing, antiwear, and anti-seizure properties, is hardly hydrolyzed, and thus can be used for a long period of time.

Claims

[Claim 1] A flame retardant hydraulic oil composition comprising:

(A) at least one base oil selected from the group consisting of hydrocarbon oils, synthetic esters, and fats;

(B) an epoxy compound and/or a carbodiimide compound represented by formula (1) below in an amount of 0.01 to 2 percent by mass on the basis of the total mass of the composition; and

(C) at least one antiwear agent selected from the group consisting of sulfur-containing phosphoric acid esters, acidic phosphoric acid esters, acidic phosphoric acid ester amine salts and phosphorus acid esters in an amount of 0.001 to 5 percent by mass on the basis of the total mass of the composition:

(1)

wherein R1 and R2 are each independently an alkyl group having 4 to 26 carbon atoms, an (alkyl)phenyl group, an aralkyl group or an (alkyl)cycloalkyl group and is the same or different from each other.

[Claim 2] The flame retardant hydraulic oil composition according to claim 1, wherein the carbodiimide compound represented by formula (1) is a compound represented by formula (2):

wherein R3 to R8 are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms and is the same or different from each other.

[claim 3] The flame retardant hydraulic oil composition according to claim 1 or 2 further comprising an amine and/or phenolic antioxidant in an amount of 0.01 to 5 percent by mass on the basis of the total mass of the composition.