Title of Invention LUBRICATING OIL CONVOSITION Technical Field 5 [0001 ] The present invention relates to a lubricating oil composition with excellent lubricity, which is especially useful when using polar oxygen-containing compounds such as animal or vegetable oils, esters or ethers as base oils. Background Art 10 [0002] Environmental considerations have become important in a variety of fields in recent years . Reduction in carbon dioxide, in particular, has become an urgent issue, and efforts are being made to increase energy efficiency in domestic industrial fields and in transportation fields, including automobiles , as well as in styles of 15 consumption in general. [0003 ] For example, in systems of industrial machinery that require large work energy, such as injection molding machines , machine tools and press working machines , there are often employed hydraulic systems capable of converting the pressure energy of hydraulic pumps 20 to kinetic energy. The need for energy savings is also high in such hydraulic systems, and energy-efficiency countermeasures are being sought for hydraulic oils used as hydraulic system pressure media, with the aim of achieving lower viscosity and a higher viscosity index, but reduced viscosity has led to problems such as reduced abrasion 25 resistance and seizing at sliding parts. [0004] Recently, loads on sliding sections have been increasing due to FPIO-0654-00 trends toward smaller sizes, higher speeds and greater fuel efficiency and energy savings in mechanical systems, creating a demand for lubricant oils with more excellent lubricity, including wear resistance. The use of oxygen-containing synthetic oils such as esters and ethers 5 has been increasing to meet this demand. [0005] From the viewpoint of environmental pollution, on the other hand, biodegradable lubricant oils such as animal or vegetable oils or esters with specific structures are being increasingly employed as environmentally friendly base materials. It is therefore expected that 10 lubricant oils with oxygen-containing compounds as base oils, exhibiting characteristics not found in hydrocarbon oils such as mineral oils, will become even more prevalent in the future. [0006] The ideal characteristics for a lubricant oil are low frictional loss and low wear such as fretting wear, both at high speeds and at low 15 speeds. That is, a lubricant oil is desired to have low frictional loss and reduced wear. It is therefore desirable to have low frictional loss and minimal wear both during periods of high contact surface speeds such as during high-speed rotation, and during periods of high torque at low speeds. 20 [0007] In the case of polar oxygen-containing compound-based lubricant oils, however, wear-resistance agents used in common hydrocarbon-based lubricant oils such as mineral oils have affinity with polar base oils, and therefore the concentration of the wear-resistance agent at sliding sections is low resulting in a poor lubricity-improving 25 effect, such that further development of effective wear-resistance agents in oxygen-containing compound-based lubricant oils such as esters is 2 FP10-0654-00 desired. [0008] Polyol ester- and ether-based oxygen-containing compounds that exhibit compatibility with hydrofluorocarbon refrigerants are used as base oils in the field of refrigerating machine oils, and it has been 5 proposed to add 3,4,5-trihydroxybenzoic acid esters to such base oils, in order to inhibit elution of lead in refrigerating air conditioners that comprise lead-containing bearings (Patent document 1). Citation List Patent Literature 10 [0009] [Patent document 1] Japanese Unexamined Patent Application Publication No. 2006-169402 Summary of Invention Technical Problem [0010] It is an object of the present invention to provide a lubricating 15 oil composition that solves the problems associated with sliding sections, that are becoming more severe due to downsizing, increasing speeds, fuel efficiency and energy savings, exhibiting vastly reduced wear and a stable low frictional coefficient, and having high rust resistance for lubrication of iron-based sliding sections. 20 Solution to Problem [0011] The present inventors have pursued diligent research toward development of an oxygen-containing compound-based lubricant oil having low frictional loss and minimal wear including fretting wear, both at high speeds and low speeds. As a result, it was surprisingly 25 found that when a combination of a 3,4,5-trihydroxybenzoic acid ester and a phosphoric acid ester is used: 3 FPIO-0654-00 (i) the frictional coefficient is lowered and a function is exhibited that can inhibit wear, (ii) hematite, which is iron red rust, is reduced to hard, strong black rust (magnetite), thereby producing a high rust-preventing effect, and 5 (iii) the 3,4,5-trihydroxybenzoic acid ester sufficiently dissolves in oxygen-containing compound-based oils such as animal or vegetable oils and esters, so that its effect is adequately exhibited in combination with the phosphoric acid ester, and the invention was thereupon devised. 10 [0012] Specifically, the present invention provides the following. (1) A lubricating oil composition comprising a lubricant base oil, a 3,4,5-trihydroxybenzoic acid ester at 5-5000 ppm by mass, and a phosphorus compound at 0.001-10.0% by mass, based on the total mass of the lubricating oil composition. 15 (2) A lubricating oil composition according to (1), wherein the 3,4,5-trihydroxybenzoic acid ester is ethyl 3,4,5-trihydroxybenzoate or propyl 3 ,4, 5 -trihydroxybenzoate. (3) A lubricating oil composition according to (1) or (2), wherein the phosphorus compound is at least one compound selected from among 20 triphenyl phosphate and tricresyl phosphate. (4) A lubricating oil composition according to any one of (1) to (3), wherein the lubricant base oil is at least one compound selected from. among animal or vegetable oils, esters and ethers, and the 40°C kinematic viscosity of the lubricant base oil is 2-1000 mint/s. 25 (5)A lubricating oil composition according to any one of (1) to (4), which is used for lubrication of an iron-based sliding section. 4 I+P10-0654-00 (6) A lubricating oil composition according to any one of (1) to (5), having a biodegradation of 60% or greater. (7) A refrigerating machine oil comprising a lubricating oil composition according to any one of ( 1) to (6). 5 Advantageous Effects of Invention [0013] The lubricating oil composition of the invention significantly lowers wear, exhibits a stable low frictional coefficient, while having a high rust=preventing effect for iron-based sliding sections. The lubricating oil composition of the invention is therefore suitable for 10 prolonged use, and exhibits a notable effect for energy savings as well, due to its stable low frictional coefficient property. Description of Embodiments [0014] The lubricating oil composition of this embodiment comprises a lubricant base oil, a 3,4,5-trihydroxybenzoic acid ester at 5-5000 ppm 15 by mass, and a phosphorus compound at 0.001-10.0% by mass, based on the total mass of the lubricating oil composition. [0015] Incidentally, 3,4,5-trihydroxybenzoic acid esters have low solubility in hydrocarbon-based base oils such as mineral oilmba..sed base oils, and therefore, by themselves, cannot be added at concentrations 20 that allow improved lubricity to be exhibited; however, using a polar oxygen-containing compound as the base oil allows their use at concentrations that improve lubricity. In particular, C2 and C3 alkyl esters''of 3,4,5-trihydroxybenzoic acid , which have a suitable balance of solubility and lubricity-improving effect, exhibit exceptional 25 lubricity-improving effects in combination with phosphoric acid esters, [0016] 5 FP10-0654-00 [Lubricant base oil] According to the invention it is possible to use an oxygen-containing compound, such as an animal or vegetable oil or synthetic oil compound, as the lubricant base oil. Two or more of such lubricant 5 base oils may also be used in admixture. The physical properties of the lubricant base oil used for the invention are not particularly restricted, but it has a 40°C kinematic viscosity of preferably 2-1000 mm2/s, and for energy savings through viscosity reduction, more preferably 5-500 mm2/s and even more preferably 10 5-100 mm2/s. However, a high-viscosity base oil is preferably used for applications with high loads. [0017] The viscosity index is preferably 50 or greater, and more preferably 100250. The pour point, as a low-temperature characteristic, is preferably no higher than =10°C and more preferably 15 no higher than -15°C. Also, from a safety viewpoint, the flash point is preferably 70°C or higher and more preferably 150°C or higher. [0018] Suitable animal or vegetable oil-based lubricant base oils to be used include milk fat, beef tallow, lard, tallow, hoof oil, whale oil, salmon oil, bonito oil, herring oil, codfish oil, soybean oil, rapeseed oil, 20 sunflower oil, safflower oil, peanut oil, corn oil, cottonseed oil, rice bran oil, kapok oil, sesame oil, olive oil, linseed oil, castor oil, cocoa butter, shea butter, palm oil, palm kernel oil, coconut oil, hempseed oil, rice oil and tea seed oil, with no particular limitation to these. [0019] Synthetic oil-based lubricant base oils include esters, ethers, 25 glycols and the like. Esters and ethers are more preferably used. [0020] Compounds with various molecular structures are commercially 6 FP10-0654-00 available as esters, each having unique properties, and they have higher flash points compared to hydrocarbon-based base oils with similar viscosities. Although esters can be obtained by dehydrating condensation polymerization reaction between alcohols and fatty acids, 5 according to the invention, a diester of a dibasic acid and a monohydric alcohol or a polyol ester of a polyol and a monovalent fatty acid is preferably used as the base oil component, from the standpoint of chemical stability. [0021] Preferred as ethers are compounds represented by the following 10 formula (I). X[-0-(AO),,-R1]m (1) Formula (I) represents a compound wherein X is a hydrocarbon in the form of a hydroxyl group-removed mono-ol or polyol, A is a C2A alkylene, R1 is hydrogen or a C1-10 alkyl, m is the valency of X, and n 15 is an integer of 2 or greater. [0022] Preferred as glycols are polyoxyallcyleneglycol compounds represented by the following formula (II). R2-[(0R3)r0R4]g (II) Formula (II) represents a compound wherein R2 represents hydrogen, 20 C1,.10 alkyl, C2-10 acyl, or a residue of a compound having 2-8 hydroxyl groups, R3 represents C24 alkylene, R4 represents hydrogen, C1-10 alkyl or C2-10 acyl, f is an integer of 1-80, and g is an integer of 1-8. [0023] Normally, these synthetic oil-based and animal or vegetable 25 oil-based lubricant base oils may be combined as appropriate, and in suitable proportions to provide the performance required for different 7 FP10=0654-00 purposes. Multiple synthetic oil-based and animal or vegetable oil-based lubricant base oils may also be used. [0024] The base oil used for the invention may be a mineral oil or synthetic oil, or it may be a mixed base oil comprising a mineral oil and 5 a synthetic oil. Examples of mineral oils include paraffinic mineral oils or naphthenic mineral oils obtained by applying an appropriate combination of one or more refining means such as solvent deasphalting, solvent extraction, hydrotreatment, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing or white clay 10 treatment, on a tube-oil distillate obtained from atmospheric distillation and vacuum distillation of paraffinic crude oil, intermediate base crude oil or naphthenic crude oil. [0025 ] Of these mineral oils, it is preferred to use mineral oils that have been highly refined (hereunder referred to as "highly-refined mineral 15 oils"), from the viewpoint of excellent thermostability. Specific examples of highly-refined mineral oils include refined oils obtained by common refining of distilled oils obtained by atmospheric distillation of paraffinic crude oils, intermediate base crude oils or naphthenic crude oils, or by vacuum distillation of the residue oils of atmospheric 20 distillation; deep dewaxing oils obtained by further deep dewaxing treatment following refining; and hydrotreated oils obtained by hydrotreatment. [0026] There are no particular restrictions on the refining method in the refining step, and a conventionally known method may be employed, 25 such as (a) hydrotreatment, (b) dewaxing treatment (solvent dewaxing or hydrodewaxing), (c) solvent extraction , (d) alkaline cleaning or 8 FP10-0654-00 sulfuric acid cleaning or (e) white clay treatment, either alone, or 2 or more thereof in combination in an appropriate order. It is also effective to carry out any of the treatments (a) to (e) in a repetitive manner, divided into multiple stages. More specifically, this may be (i) 5 a method of hydrotreatment of distilled oil, or hydrotreatment followed by alkaline cleaning or sulfuric acid cleaning; (ii) a method of hydrotreatment of a distilled oil, followed by dewaxing treatment; (iii) a method of solvent extraction of a distilled oil, followed by hydrotreatment; (iv) a method of two or three stages of hydrotreatment 10 of a distilled oil, optionally followed by alkaline cleaning or sulfuric acid cleaning; or (v) a method of any of the above-mentioned treatments (i) to (iv), followed by further dewaxing treatment to obtain a deep dewaxing oil. [0027] Of the highly-refined mineral oils obtained by such refining 15 processes, naphthenic mineral oils and mineral oils obtained by deep dewaxing treatment are preferred from the viewpoint of low-temperature flow properties and avoiding wax deposition at ; low temperature. The deep dewaxing treatment may usually be carried out by solvent dewaxing treatment under harsh conditions, or by catalytic 20 dewaxing treatment using a zeolite catalyst. [0028] The non-aromatic unsaturated portion (degree of unsaturation) of the highly-refined mineral oil is preferably no greater than 10% by mass,' more preferably no greater than 5% by mass, even more preferably no greater than 1% by mass and most preferably no greater 25 than 0.1% by mass. If the non-aromatic unsaturated portion is greater than 10% by mass, sludge will tend to be generated, often resulting in 9 FP1O-0654-00 more obstruction of the expansion mechanisms such as capillaries composing the refrigerant circulation system. [0029] On the other hand, a synthetic oil used for the invention may be a hydrocarbon-based oil such as an olefin polymer, naphthalene 5 compound or alkylbenzene9 or an oxygen-containing synthetic oil such as an ester, polyalkylene glycol, polyvinyl ether, ketone, polyphenyl ether, silicone, polysiloxane or perfluoroether. [0030] Olefin polymers as hydrocarbon-based oils include those obtained by polymerization of 02-12 olefins, and hydrotreated forms of 10 those compounds obtained by polymerization, and there are preferably used polybutene, polyisobutene, C5-12 a-olefin oligomers (poly a-olefins), ethylene-propylene copolymers and their hydrotreated forms. [0031] There are no particular restrictions on the method for producing an olefin polymer, and it may be produced by any of various methods. 15 For example, a poly a-olefin is produced using an a-olefin produced from ethylene as starting material, and treating it by a known polymerization method such as a Ziegler catalyst method, radical polymerization method, aluminum chloride method or boron fluoride method. 20 [0032] There are no particular restrictions on naphthalene compounds as hydrocarbon-based oils, so long as they have a naphthalene skeleton, but from the viewpoint of excellent compatibility with refrigerants, they preferably have 1-4 C1-10 alkyl groups, with a total of 1-10 carbon atoms in the alkyl groups, and more preferably they have 1-3 C1-8 alkyl 25 groups, with a total of 3-8 carbon atoms in the alkyl groups. [0033] The C1-10 alkyl groups of a naphthalene compound may be, 10 FP1O-0654-00 specifically, methyl, ethyl, n-propyl, isopropyl, straight-chain or branched butyl, straight-chain or branched pentyl, straight-chain or branched hexyl, straight-chain or branched heptyl, straight-chain or branched octyl, straight-chain or branched nonyl, straight-chain or 5 branched decyl, and the like. [0034] When a naphthalene compound is used, it may be used alone as a compound with a single structure, or 2 or more compounds with different structures may be used in combination. [0035] Also, there are no particular restrictions on the method for 10 producing the naphthalene compound, and it may be produced by any of various known methods. Examples thereof include methods of adding halogenated 01-10 hydrocarbons, C2®10 olefins or C8-10 styrenes to naphthalene in the presence of acid catalysts including mineral acids such as sulfuric acid, phosphoric acid, silicotungstic acid or 15 hydrofluoric acid, solid acidic substances such as acidic white clay or active white clay, or Friedel-Crafts catalysts which are metal halides such as aluminum chloride or zinc chloride. [0036] There are no particular restrictions on alkylbenzenes as hydrocarbon-based oils, but from the viewpoint of excellent 20 compatibility with refrigerants, they preferably have 1-4 C1-40 alkyl groups, with a total of 1-40 carbon atoms in the alkyl groups, and more preferably they have 1-4 C1-30 alkyl groups, with a total of 3-30 carbon atoms 'in the alkyl groups. [0037] Specific C1-40 alkyl groups in alkylbenzenes include methyl, 25 ethyl, n-propyl, isopropyl, straight-chain or branched butyl, straight-chain or branched pentyl, straight-chain or branched hexyl, 11 FP10-0654-00 straight-chain or branched heptyl, straight-chain or branched octyl, straight-chain or branched nonyl, straight-chain or branched decyl, straight-chain or branched undecyl, straight-chain or branched dodecyl, straight-chain or branched tridecyl, straight-chain or branched 5 tetradecyl, straight-chain or branched pentadecyl, straight-chain or branched hexadecyl, straight-chain or branched heptadecyl, straight-chain or branched octadecyl, straight-chain or branched nonadecyl, straight-chain or branched eicosyl, straight-chain or branched heneicosyl, straight-chain or branched docosyl, straight-chain 10 or branched tricosyl, straight-chain or branched tetracosyl, straight-chain or branched pentacosyl, straight-chain or branched hexacosyl, straight-chain or branched heptacosyl, straight-chain or branched octacosyl, straight-chain or branched nonacosyl, straight-chain or branched triacontyl, straight-chain or branched hentriacontyl, 15 straight-chain or branched dotriacontyl, straight-chain or branched tritriacontyl, straight-chain or branched tetratriacontyl, straight-chain or branched pentatriacontyl, straight-chain or branched hexatriacontyl, straight-chain or branched heptatriacontyl, straight-chain or branched octatriacontyl, straight-chain or branched nonatriacontyl and 20 straight-chain or branched tetracontyl (including all isomers). [0038] These alkyl groups may be straight-chain or branched, but are preferably straight-chain alkyl groups from the viewpoint of compatibility with organic materials to be used in refrigerant circulation systems. From the viewpoint of refrigerant compatibility, 25 thermostability and lubricity, on the other hand, they are preferably branched alkyl groups, and from the viewpoint of availability, they are 12 F"PIO-0654-00 more preferably branched alkyl groups derived from olefin oligomers such as propylene , butene and isobutylene. [0039] When an alkylbenzene compound is used , it may be used alone as a compound with a single structure, or 2 or more compounds with 5 different structures may be used in combination. [0040] The method for producing the alkylbenzene may be any desired one without any restrictions, and it may be produced by the following synthesis method, for example. [0041] Specifically, benzene, toluene, xylene, ethylbenzene, 10 methylethylbenzene, diethylbenzene and mixtures thereof may be used as aromatic compounds for the starting material. As alkylating agents there may be used C6-40 straight-chain or branched olefins obtained by polymerization of lower monoolefins such as ethylene, propylene, butene or isobutylene (preferably propylene); C6-40 straight-chain or 15 branched olefins obtained by thermal decomposition of waxes, heavy oils, petroleum fractions, polyethylene, polypropylene or the like; and 0940 straight-chain olefins obtained by separating n-paraffins from petroleum fractions such as kerosene or light oil, and subjecting them to olefination with a catalyst, as well as mixtures of the foregoing. 20 [0042] When such an aromatic compound and an alkylating agent are to be reacted, there may be used a conventionally known alkylating catalyst, for example, a Friedel-Crafts catalyst such as aluminum chloride or zinc chloride or an acidic catalyst such as sulfuric acid, phosphoric acid, silicotungstic acid, hydrofluoric acid or active white 25 clay. [0043] Examples of esters as oxygen-containing synthetic oils include 13 FP10-0654-00 aromatic esters, dibasic acid esters, polyol esters, complex esters and carbonic acid esters, as well as mixtures of the foregoing. [0044] Such aromatic esters include esters of monovalent to hexavalent, preferably monovalent to tetravalent and more preferably monovalent to 5 trivalent aromatic carboxylic acids with C1-18 and preferably C1-12 aliphatic alcohols. Specific examples of monovalent to hexavalent aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid and pyromellitic acid, as well as mixtures of the foregoing. The C1-18 aliphatic alcohols 10 may be straight-chain or branched, and specifically they include methanol, ethanol, straight-chain or branched propanol, straight-chain or branched butanol, straight-chain or branched pentanol, straight-chain or branched hexanol, straight-chain or branched heptanol, straight-chain or branched octanol, straight-chain or branched nonanol, straight-chain or 15 branched decanol, straight-chain or branched undecanol, straight-chain or branched dodecanol, straight-chain or branched tridecanol, straight-chain or branched tetradecanol, straight-chain or branched pentadecanol, straight-chain or branched hexadecanol, straight, chain or branched heptadecanol and straight-chain or branched octadecanol, as 20 well as mixtures of the foregoing. [0045] Specific examples of aromatic esters obtained using aromatic compounds and aliphatic alcohols include dibutyl phthalate, di(2-ethylhexyl) phthalate, dinonyl phthalate, didecyl phthalate, didodecyl phthalate, ditridecyl phthalate, tributyl trimellitate, 25 tri(2-ethylhexyl) trimellitate, trinonyl trimellitate, tridecyl trimellitate, tridodecyl trimellitate and tritridecyl trimellitate. Naturally, when a 14 FP10-0654-00 dibasic or greater aromatic carboxylic acid has been used, the ester may be a simple ester comprising a single aliphatic alcohol, or a complex ester comprising 2 or more different aliphatic alcohols. Dibasic acid esters preferred for use include esters of C5-10 5 straight-chain or cyclic aliphatic dibasic acids such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,2-cyclohexanedicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic acid, and straight-chain or branched C1-15 monohydric alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, 10 octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol and pentadecanol, as well as mixtures of the foregoing. More specifically, they include diesters of ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate and 1,2-cyclohexanedicarboxylic acid with 15 C4-9 monohydric alcohols, and diesters of 4-cyclohexene-1,2-dicarboxylic acid with C4-9 monohydric alcohols, as well as mixtures of the foregoing. [0046] As polyol esters there may be used esters of diols or polyols with 3-20 hydroxyl groups, with C6-20 fatty acids. Specific examples 20 of diols include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 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-1,3-propanediol, 25 1,8=octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol and 1,12-dodecanediol. Specific examples of polyols include polyhydric 15 10-0654-00 alcohols such as trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol), tri-(pentaerythritol), glycerin, polyglycerins (2-20mers of glycerin), 1,3,5-pentanetriol, sorbitol, 5 sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol and mannitol, saccharides such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose and melezitose, and their partial etherified forms, and methylglucosides (glucosides). 10 Preferred among these as polyols are hindered alcohol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol) and tri-(pentaerythritol). [0047] There are no particular restrictions on the number of carbon 15 atoms in the fatty acid used for the polyol ester, but it will usually be C1-24. Among 01-24 fatty acids there are preferred those with 3 or more carbon atoms, more preferably 4 or more carbon atoms, even more preferably 5 or more carbon atoms and most preferably 10 or more carbon atoms, from the viewpoint of lubricity. From the viewpoint of 20 compatibility with refrigerants, the number of carbon atoms is preferably no greater than 18, more preferably no greater than 12 and even more preferably no greater than 9. [0048] The fatty acids may be straight-chain fatty acids or branched fatty acids, but from the viewpoint of lubricity they are preferably 25 straight-chain fatty acids, while from the viewpoint of hydrolytic stability they are preferably branched fatty acids. The fatty acids may 16 FP1O-0654-00 be either saturated fatty acids or unsaturated fatty acids. [0049] Specific fatty acids include pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, 5 pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid and oleic acid, and these fatty acids may be straight-chain fatty acids or branched fatty acids, and they may be fatty acids in which the a-carbon atom is a quaternary carbon atom (neo acids). Preferred for use among these are 10 valeric acid (n-pentanoic acid), caproic acid (n-hexanoic acid), enanthic acid (n-heptanoic acid), caprylic acid (n-octanoic acid), pelargonic acid (n-nonanoic acid), capric acid (n-decanoic acid), oleic acid (cis-9-octadecenoic acid), isopentanoic acid (3-methylbutanoic acid), 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid and 15 3,5,5-trimethylhexanoic acid. [0050] The polyol ester used for the invention may be a partial ester with a portion of the hydroxyl groups of the polyol remaining without esterification, a complete ester with all of the hydroxyl groups esterified, or a mixture of a partial ester and a complete ester, so long as 20 it has 2 or more ester groups, but it is preferably a complete ester. [0051] A complex ester is an ester of a fatty acid and a dibasic acid with a monohydric alcohol and a polyol, and the fatty acids, dibasic acids, monohydric alcohols and polyols used may be the fatty acids, dibasic acids, monohydric alcohols and polyols mentioned above for 25 explanation of dibasic acid esters and polyol esters. [0052] A carbonic acid ester is a compound having a carbonic acid ester 17 FF10-0654-00 bond represented by the following formula (III-1): -®-CO-®- (I1I-1) in the molecule. The number of carbonic acid ester bonds represented by formula (111-1) may be 1 or more per molecule. 5 [0053] As alcohols composing carbonic acid esters there may be used the monohydric alcohols and polyols mentioned above for explanation of dibasic acid esters and polyol esters, as well as polyglycols and polyglycol-added polyols. Compounds obtained from carbonic acid and fatty acids and/or dibasic acids may also be used. 10 [0054] When an ester is to be used, it may of course be used alone as a compound with a single structure, or 2 or more compounds with different structures may be used in combination. [0055] Preferred among these esters are dibasic acid esters, polyol esters and carbonic acid esters, from the viewpoint of compatibility with 15 refrigerants. [0056] Among dibasic acid esters there are more preferred alicyclic dicarboxylic acid esters such as 1,2-cyclohexanedicarboxylic acid; and 4-cyclohexene-1,2-dicarboxylic acid, from the viewpoint of compatibility with refrigerants and thermal and hydrolytic stability. 20 [0057] Specific examples of dibasic acid esters that may be preferably used for the invention include dibasic acid esters obtained from at least one monohydric alcohol selected from the group consisting of butanol, pentariol, hexanol, heptanol, octanol and nonanol, with at least one dibasic acid selected from the group consisting of 25 1,2-cyclohexanedicarboxylic acid and 4-cyclohexene-1,2-dicarboxylic acid, as well as mixtures of the foregoing. 18 FP10-0654-00 [0058] It is preferred for the dibasic acid ester of the invention to have 2 or more monohydric alcohols composing the dibasic acid ester, since this will improve the low-temperature characteristics of the refrigerating machine oil composition and its compatibility with refrigerants. A 5 dibasic acid ester composed of 2 or more monohydric alcohols is a mixture of 2 or more esters of dibasic acids and a single type of alcohol, or an ester of a dibasic acid and a mixture of 2 or more alcohols. [0059] More preferred among these polyol esters, for more excellent hydrolytic stability, are esters of hindered alcohols such as neopentyl 10 glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol) and tri-(pentaerythritol), more preferred are esters of neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane and pentaerythritol, and most preferred are esters of 15 pentaerythritol for particularly excellent compatibility with refrigerants and hydrolytic stability. [0060] Specific examples of polyol esters preferred for use according to the invention are diesters, triesters and tetraesters obtained from at least one fatty acid selected from the group consisting of valeric acid, caproic 20 acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, oleic acid, isopentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexaroic acid and 3,5,5-trimethylhexanoic acid, and at least one alcohol selected from the group consisting of neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane and 25 pentaerythritol, and mixtures of such esters. [0061] It is preferred for a polyol ester of the invention to have 2 or 19 FPI0-0654-00 more fatty acids composing the polyol ester, since this will improve the low-temperature characteristics of the refrigerating machine oil composition and its compatibility with refrigerants. Polyol esters composed of 2 or more different fatty acids include mixtures of 2 or 5 more esters of a polyol and one type of fatty acid, and esters of a polyol and mixtures of 2 or more different fatty acids. [0062] Preferred carbonic acid esters are those having a structure represented by the following formula (III-2): (X110)b-B-[0-(A"O)e-CO-0-(A 12®)d -Y111a (111-2) 10 [in formula (II1-2), X" represents hydrogen, alkyl, cycloalkyl or a group represented by the following formula (1I1-3): Y12-(OA13)e (1I1-3) (in formula (III-3), Y'2 represents hydrogen, alkyl or a cycloalkyl group, A13 represents a C2-4 alkylene group, and e represents an integer of 15 1-50), A" and A12 may be the same or different and each represents a C2=4 alkylene group, Y1' represents hydrogen, alkyl or cycloalkyl, B represents a residue of a compound with 3-20 hydroxyl groups, a represents an integer of 1-20 and b represents an integer of 0-19, such 20 that, a+b is 3-20, c represents an integer of 0-50 and d represents an integer of 1-50]. [0063] In formula (I11-2), X" represents hydrogen, alkyl, cycloalkyl or a group represented by formula (1II-3) above. There are no particular restrictions on the number of carbon atoms in the aforementioned alkyl 25 group, but it will usually be 1-24, preferably 1-18 and more preferably 1-12. The alkyl group maybe either straight-chain or branched. 20 FP10-0654-00 [0064] Specific C1-24 alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, straight-chain or branched pentyl, straight-chain or branched hexyl, straight-chain or branched heptyl, straight-chain or branched octyl, straight-chain or 5 branched nonyl, straight-chain or branched decyl, straight-chain or branched undecyl, straight-chain or branched dodecyl, straight-chain or branched tridecyl, straight-chain or branched tetradecyl, straight-chain or branched pentadecyl, straight-chain or branched hexadecyl, straight-chain or branched heptadecyl, straight-chain or branched 10 octadecyl, straight-chain or branched nonadecyl , straight-chain or branched eicosyl, straight-chain or branched heneicosyl, straight-chain or branched docosyl, straight-chain or branched tricosyl and straight-chain or branched tetracosyl. [0065] Specific cycloalkyl groups include cyclopentyl, cyclohexyl and 15 cycloheptyl groups. [0066] Specific C2-4 alkylene groups represented by A13 in formula (111-2) include ethylene, propylene, trimethylene, butylene, tetramethylene, 1-methyltrimethylene, 2-methyltrimethylene, 1,1-dimethylethylene and 1,2-dimethylethylene. 20 [0067] In formula (111-2). Y12 represents hydrogen, alkyl or cycloalkyl. There are no particular restrictions on the number of carbon atoms in the aforementioned alkyl group, but it will usually be 1-24, preferably 1-1g and more preferably 1-12. The alkyl group may be either straight-chain or branched. The C1-24 alkyl groups include the alkyl 25 groups mentioned above in the explanation for X. [0068] Specific cycloalkyl groups include cyclopentyl, cyclohexyl and 21 FP10-0654-00 cycloheptyl groups. [0069] Among groups represented by Y12 there are preferred hydrogen or CI-12 alkyl groups, and more preferably groups from among hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, 5 sec-butyl, tent-butyl, n-pentyl, iso-pentyl, neo-pentyl, n-hexyl, iso-hexyl, n-heptyl, iso-heptyl, n-octyl, iso-octyl, n-nonyl, iso-nonyl, n-decyl, iso-decyl, n-undecyl, iso-undecyl, n-dodecyl andiso-dodecyl groups. Also, e represents an integer of 1-50. [0070] The group represented by X11 is preferably hydrogen, C1-12 10 alkyl or a group represented by formula (III-3) above, and more preferably one from among hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, n-hexyl, iso-hexyl, n-heptyl, iso-heptyl, n-octyl, iso-octyl, n-nonyl, iso-nonyl, n-decyl, iso-decyl, n-undecyl, iso-undecyl, 15 n-dodecyl, iso-dodecyl and groups represented by formula (I1I-3). [0071] Compounds with B as a residue and having 3-20 hydroxyl groups include, specifically, the polyols mentioned above. i [0072] Also, All and A12 may be the same or different .tnd each represents a C2-4 alkylene group. Specific alkylene groups include 20 ethylene, propylene, trimethylene, butylene, tetramethylene, 1-methyltrimethylene, 2-methyltrimethylene, 1,1-dimethylethylene and 1,2-dimethylethylene. [0073] Aso, Y" represents hydrogen, alkyl or cycloalkyl. There are no particular restrictions on the number of carbon atoms in the 25 aforementioned alkyl group, but it will usually be 1-24, preferably 1-18 and more preferably 1-12. The alkyl group may be either 22 FPIO-0654-00 straight-chain or branched. The CI-24 alkyl groups include, specifically, the alkyl groups mentioned above in the explanation for X1 . [0074] Specific cycloalkyl groups include cyclopentyl, cyclohexyl and cycloheptyl groups. 5 [0075] Among these, the group represented by Y11 is preferably hydrogen or a CI-12 alkyl group, and more preferably a group from among hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, n-hexyl, iso-hexyl, n-heptyl, iso-heptyl, n-octyl, iso-octyl, n-nonyl, iso-nonyl, ti-decyl, 10 iso-decyl, n-undecyl, iso-undecyl, n-dodecyl and iso-dodecyl groups. [0076] In formulas (111-2) and (111-3), c, d and e represent the polymerization degree of the polyoxyalkylene chains, and the polyoxyalkylene chains in the molecule may be the same or different. When a carbonic acid ester represented by formula (111-2) has a plurality 15 of different polyoxyalkylene chains, there are no particular restrictions on the polymerization form of the oxyalkylene groups, and it may be random copolymerization or block copolymerization. j [0077] The method of producing a carbonic acid ester to be used for the invention may be any desired one, and for example, it may be obtained 20 by adding an alkylene oxide to a polyol compound to produce a polyalkyleneglycol polyol ether, and reacting this with chloroformate at 0-30°C, in the presence of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an alkali metal alkoxide such as sodium methoxide or sodium ethoxide, or an alkali such as metallic 25 sodium. Alternatively, it may be obtained by reacting a carbonic acid source such as a carbonic acid diester or phosgene with a 23 polyalkyleneglycol polyol ether at 80-150°C in the presence of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an alkali metal alkoxide such as sodium methoxide or sodium ethoxide, or an alkali such as metallic sodium. The free hydroxyl groups may then 5 be etherified if necessary. [0078] The product obtained from the starting materials may be purified to remove the by-products and unreacted substances, but there is no problem if small amounts of by-products or unreacted substances remain, so long as they do not interfere with the excellent performance 10 of the lubricant oil according to this embodiment. [0079] When a carbonic acid ester is used for the invention, it may be used alone as a compound with a single structure, or 2 or more compounds with different structures may be used in combination. There are no particular restrictions on the molecular weight of a 15 carbonic acid ester according to the invention, but from the viewpoint of further improving compressor sealability, the number-average molecular weight is preferably 200-4000 and more preferably 300-3000. The kinematic viscosity of the carbonic acid ester of the invention is preferably 2-150 mm2/s and more preferably 4-100 mine/s at 100°C. 20 [0080] Examples of polyoxyalkylene glycols to be used in a base oil for this embodiment include compounds represented by the following formula (111-4): R11-[(OR 12)rOR"]g (III-4) [in formula (111-4), R11 represents hydrogen, 01-10 alkyl, C2-10 acyl oY 25 a residue of a compound with 2-9 hydroxyl groups, R12 represents a C2-4 alkylene group, R'3 represents hydrogen, 01-10 alkyl or C2-1' 24 FPIO-0654-00 acyl, f represents an integer of 1-80 and g represents an integer of 1-8]. [0081] In formula (1II-4), alkyl groups represented by R11 and R13 may be straight-chain, branched or cyclic. Specific examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, straight-chain or 5 branched butyl, straight-chain or branched pentyl, straight-chain or branched hexyl, :straight-chain or branched heptyl, straight-chain or branched octyl, straight-chain or branched nonyl, straight-chain or branched decyl, cyclopentyl and cyclohexyl. If the alkyl group is greater than CIO, the compatibility with refrigerants will tend to be 10 reduced, and phase separation will tend to occur" more easily. The preferred number of carbon atoms of the alkyl group is 1-6. [0082] The alkyl group portions of acyl groups represented by R11 and R13 may also be straight-chain, branched or cyclic. Specific examples for the alkyl group portions of acyl groups include the alkyl groups 15 mentioned as examples of alkyl groups above, which have 1-9 carbon atoms. If the acyl group is greater than CIO, compatibility with refrigerants may be reduced and phase separation may occur. The preferred number of carbon atoms of the acyl group is 2-6. [0083] When the groups represented by R11 and R13 are both alkyl 20 groups, or when they are both acyl groups, the groups represented by R11 and R13 may be the same or different. When g is 2 or greater, the groups represented by Ru and R13 in the same molecule may be the same or different. [0084] When the group represented by Ru is a residue of a compound 25 having 2-8 hydroxyl groups, the compound may be either linear or cyclic. Specific examples of compounds with 2 hydroxyl groups 25 F'P10-0654-00 include ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, 2-methyl- 1,3 -propanediol, 1,5-peptanediol, neopentyl glycol, 1,6-hextnediol, 2-ethyl-2=methyl-1,3-propanediol, 1,7-heptanediol, 5 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl- 1,3 -propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol and 1,12-dndecanediol. [0085] Specific examples of compounds with 3-8 hydroxyl groups include polyhydric alcohols such as trimethyloleuhane, 10 trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, di-(pentaerythritol), tri-(pentaerythritol), glycerin, polyglycerins (2-6mers of glycerin), 1,3,5-pentanetriol, sorbitol, sorbitan, sorbitol-glycerin condensate, adonitol, arabitol, xylitol and mannitol, saccharides such as xylose, 15 arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, raffinose, gentianose and melezitose, and their partial etherified forms, and methylglucosides (glucosides). [0086] Of the polyoxyalkylene glycols represented by formula (1I1-4), 20 at least one of R11 and R13 is preferably an alkyl group (more preferably a C1-4 alkyl group), with methyl being especially preferred from the viewpoint of compatibility with refrigerants. From the viewpoint of thermal and chemical stability, both R11 and R13 are preferably alkyl groups (more preferably C1-4 alkyl groups), and most preferably both 25 are methyl groups. From the viewpoint of facilitating production and lowering cost, preferably one of R11 and R13 is an alkyl group (more 26 FPIO-0654-00 preferably a CI-4 alkyl group) while the other is hydrogen , and most preferably one is methyl and the other is hydrogen. [0087] In formula (I1I-4), R2 represents a C2-4 alkylene group, specific examples of alkylene groups including ethylene, propylene and 5 butylene. Oxyalkylene groups as repeating units represented by OR2 include oxyethylene, oxypropylene and oxybutylene groups. Multiple oxyalkylene groups in the same molecule may be the same, or they may include two different oxyalkylene groups. [0088] Among polyoxyallcylene glycols represented by formula (111-4) 10 there are preferred copolymers containing an oxyethylene group (EO) and an oxypropylene group (P®), from the viewpoint of refrigerant compatibility and the viscosity-temperature characteristic, in which case, from the viewpoint of the seizure load and the viscosity-temperature characteristic, the proportion of oxyethylene 15 groups of the total oxyethylene and oxypropylene groups (EO/(PO+E®)) is preferably in the range of 0.1-0.8 and more preferably in the range of 0.3-0.6. i [0089] From the viewpoint of hygroscopicity and heat and oxidation stability, the value of E®/(P0+BO) is preferably in the range of 0-0.5, 20 more preferably in the range of 0-0.2, and most preferably 0 (i.e. a propylene oxide homopolymer). [0090] In formula (III-4), f is an integer of 1-80 and g is an integer of 1-8. For example, when R11 is an alkyl group or acyl group, g is 1. When R11 is a residue of a compound having 2-8 hydroxyl groups, g is 25 the number of hydroxyl groups in the compound. [00911 There are no particular restrictions on the product off and g (f x 27 110-0654-00 g), but the average value of f x g is preferably 6-80, to provide a satisfactory balance for the required performance as a lubricant oil for a refrigerating machine. [0092] Preferred among polyoxyalkylene glycols having such a 5 structure, from the viewpoint of economy and the effect described above, are polyoxypropyleneglycol dimethyl ethers represented by the following formula (III-5): CH30-(C3H60)h-CH3 (111-5) (wherein h represents an integer of 6-80), 10 polyoxyethylene-polyoxypropyleneglycol dimethyl ethers represented by the following formula (I1I-6): CH3O-(C214O)1-(C3H6®)l CH3 (111-6) (wherein i and j are both 1 or greater, the total of i and j being an integer of 6-80), 15 and preferred from the viewpoint of economy are polyoxypropyleneglycol monobutyl ethers represented by the following formula (111-7): C4H90-(C3H6O)k-H (111-7) (wherein k represents an integer of 6-80), 20 as well as polyoxypropyleneglycol monomethyl ethers represented by the following formula (111-8): CH3O-(C3H O)1-H (111-8) (wherein 1 represents an integer of 6-80), polyoxyethylene®polyoxypropyleneglycol monomethyl ethers 25 represented by the following formula (11I-9): CH30-(C2H40)m (C3H60)nH (111-9) 28 FP10-0654-00 (wherein m and n are both 1 or greater, the total of m and n being an integer of 6-80), polyoxyethylene-polyoxypropyleneglycol monobutyl ethers represented by the following formula (III-10): 5 C4H9O-(C2H.4®)m-(C3H6®)n-H (III-10) (wherein m and n are both 1 or greater, the total of m and n being an integer of 640), and polyoxypropyleneglycol diacetates represented by the following formula (III-11): 10 CH3000-(C3II6®)1-COCH3 (III-11) (wherein 1 represents an integer of 6-80). Also, the polyoxyalkylene glycol used for the invention may be a polyoxyalkyleneglycol derivative having at least one structural unit represented by formula (111- 12): 15 [Chemical Formula 1] R14 R16 (111-12) I R15 R17 [in formula (I1I-12), R14-R17 may be the same or different and each represents hydrogen, a C1-10 monovalent hydrocarbon or a group represented by the following formula (111- 13): 20 [Chemical Formula 2] 29 FPIO-0654-00 18 ®.(R20O)r R21 (if913) R19 [in formula (III-13), R18 and R19 may be the same or different and each represents hydrogen, a C1-10 monovalent hydrocarbon or a C2-20 5 alkoxyalkyl group, R20 represents a C2-5 alkylene group, a total C2-5 substituted alkylene group having an alkyl group as a substituent or a total C4-10 substituted alkylene group having an alkoxyalkyl group as a substituent, r represents an integer of 0-20, and R21 represents a C1-10 monovalent hydrocarbon group], 10 at least one of R18-R21 being a group represented by formula (111-13)]. [0093] In formula (1I1-12), R14-R17 each represents hydrogen, a Cl-10 monovalent hydrocarbon group or a group represented by formula (III-13), and specific CI-10 monovalent hydrocarbon groups include Cl-10 straight-chain or branched alkyl, C2-10 straight-chain I or 15 branched alkenyl, C5-10 cycloalkyl or alkylcycloalkyl, C6-10 aryl or alkylaryl and C7-10 arylalkyl groups. Preferred among these monovalent hydrocarbon groups are