Refrigerating machine oil

Abstract

 Refrigerating machine oils for use with a dimethyl ether refrigerant comprises a hydrocarbon oil. The refrigerating machine oil has an excellent lubricity, miscibility with a refrigerant, electric insulation, hydrolysis resistance and kinematic viscosity, all of which are well-balanced.

Description

[0001] This invention relates to refrigerating machine oils, and more particularly to refrigerating machine oils for refrigerating machines using dimethyl ether (DME) as a refrigerant.

Description of the Prior Art

[0002] Due to the recent issues concerning with the ozone shield depletion, conventional refrigerants for refrigerating machine such as CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) have become targets of regulation. In place of these refrigerants, HFC (hydrofluorocarbon) has been used as such a refrigerant. However, since the HFC refrigerants also has a problem that it is highly capable of earth warming, the search of alternative refrigerants for the fluorocarbon type refrigerants has been proceeded. In such a situation, the application of dimethyl ether (DME: CH₃-O-CH₃) has been drawn considerable attention because of its harmlessness to the environments, safety and availability.

[0003] Characteristics required for refrigerating machine oils are lubricity, miscibility with refrigerants and safety, but these characteristics significantly vary depending on types of the coexisting refrigerants. Because DME is different in chemical structure from those of the conventional fluorocarbon type refrigerants, the conventional refrigerating machine oils having been used therewith are not applicable to refrigerating machines using the DME refrigerant, as they are. A refrigerating machine oil having excellent characteristics required for a refrigerating machine using the DME refrigerant has not been developed yet.

[0004] In view of the foregoing, an object of the present invention is to provide a refrigerating machine oil which can be used with a DME refrigerant and has excellent lubricity, miscibility with the refrigerant and safety.

[0005] It has now been found after extensive research that use of hydrocarbon oil makes it possible to produce a refrigerating machine oil which can be used with a DME refrigerant and be superior in the aforesaid characteristics.

BRIEF SUMMARY OF THE INVENTION

[0006] According to the present invention, there is provided a refrigerating machine oil containing a hydrocarbon oil for a refrigerating machine using a DME refrigerant.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention will now be further described in more detail.

[0008] Eligible hydrocarbon oils for the inventive refrigerating machine oil may be naphthenic- or paraffinic mineral oils, olefin polymers, naphthalene compounds, alkylbenzene oils and mixtures thereof.

[0009] Specific examples of the mineral oils are paraffinic- or naphthenic-mineral oils produced by subjecting the refrigerating machine oil fraction resulting from the atmospheric or vacuum distillation of a paraffinic- or naphthenic- crude oil or an intermediate base crude oil to one or more than two of refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrofinishing, sulfuric acid washing or clay treatment.

[0010] Among these mineral oils, it is preferred to use highly refined mineral oils because of their excellent stability. The highly refined mineral oils used for the present invention preferably contain unsaturates (degree of unsaturation) in non-aromatics of less than 10 percent. Unsaturates greater than 10 percent would cause the formation of sludge and the clogging of capillaries. Therefore, in the present invention, the unsaturation degree should be preferably less than 5 percent, more preferably less than 1 percent and most preferably 0.1 percent. Specific examples of such highly refined mineral oils are refined oils obtained by refining the distillate resulting from the atmospheric distillation of a paraffinic- or naphthenic- crude oil or an intermediate base crude oil or the distillate resulting from the vacuum distillation of the residue obtained by this atmospheric distillation, in accordance with a conventional manner; deep-dewaxed oils obtained by further deep-dewaxing the refined oils; and hydrogenated oils obtained by further hydrogenating the refined oils. No particular limitation is imposed on the refining process upon the production of these mineral oils.

[0011] Generally, there may be employed (a) hydrogenation, (b) dewaxing (solvent dewaxing or hydrodewaxing), (c) solvent extraction, (d) alkali or sulfuric acid washing and (e) day treatment processes, singularly or in combination. Alternatively, it is advantageous to repeat the same refining process multi-stepwise. For example, the refining process may be conducted as follows:

i) hydrogenating distillate or alkali or sulfur acid washing the distillate after being hydrogenated;

ii) dewaxing the distillate which has been hydrogenated;

iii) hydrogenating the distillate which has been subjected to solvent extraction;

iv) hydrogenating the distillate in two or three stages or alkali or sulfur washing the distillate which have been subjected to this hydrogenation; and

v) dewaxing after the aforesaid processes to obtain a deep-dewaxed oil.

[0012] Preferred highly refined minerals obtained by the above processes are naphthenic mineral oils and mineral oils obtained by the deep-dewaxing process because of fluidity at low temperatures and no wax precipitation at low temperatures. The deep-dewaxing process may be conducted by solvent dewaxing under sever conditions or by catalytic dewaxing using a zeolite catalyst.

[0013] The olefin polymers may be those obtained by polymerizing an olefin having 2 to 12 carbon atoms, and the products obtained by hydrogenating the polymerized olefin. Specific examples of such olefin polymers are polybutene, polyisobutene, the oligomers of α-olefin (poly-α-olefin) having 5 to 12 carbon atoms, ethylene-propylene copolymer, and the hydrogenates thereof.

[0014] The olefin polymers can be produced by any suitable conventional methods. A poly-α-olefin may be produced by employing the conventional polymerization processes such as a Ziegler catalysis process, a radical polymerization process, an aluminum chloride process and a boron fluoride process wherein an α-olefin derived from ethylene is used as a raw material.

[0015] No particular limitation is imposed on the naphthalene compounds as long as they have naphthalene skeleton, but preferred are compounds represented by the following formula because of their excellent miscibility with a DME refrigerant;

wherein R¹, R², R³ and R⁴ may be the same or different and are each independently a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, provided that the total number of carbon atoms of R¹ through R⁴ is within a range of 1 to 10.

[0016] In Formula (1), R¹, R², R³ and R⁴ may be the same or different and are each independently a hydrogen atom or a hydrocarbon group having 1 to 10, preferably 1 to 8 carbon atoms. The hydrocarbon group may be an alkyl, alkenyl, aryl, alkylaryl or aralkyl group.

[0017] Preferred hydrocarbon groups for R¹, R², R³ and R⁴ include a C₁ - C₈ alkyl group such as methyl, ethyl, n-propyl, isopropyl, straight or branched butyl, straight or branched pentyl, straight or branched hexyl, straight or branched heptyl and straight or branched octyl; a C₂ - C₈ alkenyl group such as ethenyl (vinyl), 1-propenyl, 2-propenyl (allyl), 1-methylethenyl (isopropenyl), straight or branched butenyl, straight or branched pentenyl, straight or branched hexenyl, straight or branched heptenyl and straight or branched octenyl; a C₆ - C₈ aryl or alkylaryl group such as phenyl, tolyl, xylyl, ethylphenyl and vinylphenyl; and a C₇ - C₈ aralkyl group such as benzyl, 1-phenylethyl and 2-phenylethyl (phenethyl). Among these hydrocarbon groups, particularly preferred are a C₁ - C₈ alkyl group and a C₂ - C₈ alkenyl group and most preferred are branched chain type thereof.

[0018] A total number of carbon atoms of R¹, R², R³ and R⁴ in Formula (1) should be in the range of 1 to 10, preferably 1 to 8. If the total number of carbon atoms is within this range, then R¹, R², R³ and R⁴ may be the same or different. In other words, all of R¹, R², R³ and R⁴ may be a hydrocarbon group, or at least one of R¹, R², R³ and R⁴ may be a hydrocarbon group while the rest thereof may be a hydrogen atom. In view of miscibility with a refrigerant, it is preferred that 1 to 3 of R¹, R², R³ and R⁴ are a hydrocarbon group while the rest thereof are a hydrogen atom and that the total number of carbon atoms of R¹, R², R³ and R⁴ is within the range of 3 to 8.

[0019] When two of R¹, R², R³ and R⁴ are each a hydrocarbon group, the combination thereof is not particularly restricted. A pair of hydrocarbon groups may be attached to the same condensed ring (a benzene ring) as in the case where R¹ and R² are each hydrocarbon groups. Alternatively, a single hydrocarbon group may be attached to each of different condensed rings (benzene rings) as in the case where R¹ and R³ are each hydrocarbon groups.

[0020] Preferred naphthalene compounds of Formula (1) include (n-propyl) naphthalene, isopropylnaphthalene, (n-butyl) naphthalene, isobutylnaphthalene, (sec-butyl) naphthalene, (tert-butyl) naphthalene, (sec-pentyl) naphthalene, (1-ethylpropyl) naphthalene, (tart-pentyl) naphthalene, (1-methylpentyl) naphthalene, (1-ethylbutyl) naphthalene, (1,1-dimethylbutyl) naphthalene, (1-ethyl-1-methylpropyl) naphthalene, (1-methylhexyl) naphthalene, (1-ethylpentyl) naphthalene, (1-propylbutyl) naphthalene, (1,1-dimethylpentyl) naphthalene, (1-ethyl-1-methylbutyl) naphthalene, (1,1-diethylpropyl) naphthalene, (1-methylheptyl) naphthalene, (1-ethylhexyl) naphthalene, (1-propylpentyl) naphthalene, (1,1-dimethylhexyl) naphthalene, (1-ethyl-1-methylpentyl) naphthalene, (1-methyl-1-propylbutyl) naphthalene, (1,1-diethylbutyl) naphthalene, ethylmethyl naphthalene, diethyl naphthalene methyl (n-propyl) naphthalene, methyl isopropylnaphthalene, di(n-propyl) naphthalene, diisopropylnaphthalene, (n-butyl) methylnaphthalene, isobutylmethylnaphthalene, (sec-butyl) methylnaphthalene, (tert-butyl) methylnaphthalene, di(n-butyl) naphthalene, diisobutylnaphthalene, di(sec-butyl) naphthalene, di(tert-butyl) naphthalene, trimethylnaphthalene, triethylnaphthal ene, ethyldimethylnaphthalene, diethylmethylnaphthalene, dimethyl (n-propyl) naphthalene, dimethylisopropyl naphthalene, methyl di(n-propyl) naphthalene, n-methyldiisopropylnaphthalene, (n-butyl) dimethyl naphthalene, isobutyldimethylnaphthalene, (sec-butyl) dimethylnaphthalene, (tert-butyl) dimethyl naphthalene, phenylnaphthalene, tolylnaphthalene, xylyl naphthalene, (ethylphenyl) naphthalene, (vinylphenyl) naphthalene, benzylnaphthalene, phenethylnaphthalene and (1-phenylethyl) naphthalene.

[0021] The naphthalene compounds may be compounds having a single structure or may be a mixture of compounds having different structures as long as these compounds are each represented by Formula (1).

[0022] No particular limitation is imposed on the production method of the naphthalene compounds and thus any of suitable conventional methods can be used. For instance, they can be obtained by attaching (or addition of reacting) compounds selected from the group consisting of halides of hydrocarbon compounds having 1 to 10 carbon atoms, olefins having 2 to 10 carbon atoms and styrenes having 8 to 10 carbon atoms to naphthalene in the presence of a mineral acid such as sulfuric acid, phosphoric acid, silicotungstic acid or hydrofluoric acid; a solid acidic substance such as acid clay or activated clay; or a Friedel-Crafts catalyst which is a metal halide such as aluminum chloride or zinc chloride.

[0023] Any type of the alkylbenzene oils are eligible for the purpose of the present invention, but it is preferred to use the alkylbenzene oils containing more than 60 mass percent, preferably more than 65 mass percent, more preferably more than 70 mass percent, further more preferably more than 80 mass percent, most preferably 100 mass percent of alkylbenzene components having a molecular weight of 200 to 350 in view of little possibility of the occurrence of seizure of a refrigerating compressor during a long period of its operation.

[0024] Furthermore, in view of the capability of preventing the occurrence of seizure of the refrigerating compressor during its prolonged operation, the alkylbenzene oils may desirably contain preferably more than 30 mass percent, more preferably more than 35 mass percent, most preferably more than 40 mass percent of alkylbenzene components having a molecular weight of 200 to 300.

[0025] No particular limitation is imposed on the alkylbenzene components having a molecular weight of 200 to 350 as long as their molecular weight falls within the range. However, in view of improving a long-term reliability of a refrigerating system, it is preferred to use an alkylbenzene oil (hereinafter referred to as an alkylbenzene oil (A)) composed of alkylbenzenes having 1 to 4 alkyl groups each having 1 to 19 carbon atoms, the total number of carbon atoms of these alkyl groups being 9 to 19. It is more preferred to use alkylbenzenes having 1 to 4 alkyl groups having each 1 to 15 carbon atoms, the total number of carbon atoms in the alkyl groups being 9 to 15

[0026] Specific examples of alkyl groups having 1 to 19 carbon atoms are methyl, ethyl, propyl (including all isomers), butyl (including all isomers), pentyl (including all isomers), hexyl (including all isomers), heptyl (including all isomers), octyl (including all isomers), nonyl (including all isomers), decyl (including all isomers), undecyl (induding al isomers), dodecyl (including all isomers), tridecyl (including all isomers), tetradecyl (including all isomers), pentadecyl (including all isomers), hexadecyl (induding all isomers), heptadecyl (including all isomers), octadecyl (induding all isomers) and nonadecyl (induding all isomers).

[0027] These alkyl groups may be of straight chain or branched chain. However, in view of the stability and viscosity characteristics, branched alkyl groups are preferred. Furthermore, in view of availability, more preferred are branched alkyl groups derived from oligomers of olefins such as propylene, butene and isobutylene.

[0028] The number of alkyl groups in the alkylbenzene oils (A) is confined to 1 to 4. However, in view of the stability and availability, it is the most preferred to use alkylbenzenes having one or two alkyl groups, such as a monoalkylbenzene, a dialkylbenzene or a mixture thereof.

[0029] The alkylbenzenes (A) may be not only those having the same molecular structure, but also a mixture of those having different molecular structures as long as they satisfy the conditions that they contain 1 to 4 alkyl groups each having 1 to 19 carbon atoms, the total number thereof being 9 to 19.

[0030] The alkylbenzene oils used for the present invention may preferably contain less than 40 mass percent, preferably less than 35 mass percent, more preferably less than 30 mass percent, of the alkylbenzenes having a molecular weight of less than 200 or more than 350. However, in view of the capability of retaining reliability of a compressor to be used during a long period operation thereof, it is preferred that the molecular weight of such alkylbenzenes be confined to a range of more than 350 to 450, preferably 350 to 430.

[0031] No particular limitation is imposed on the molecular structure of the alkylbenzenes having a molecular weight of less than 200 or more than 350 as long as their molecular weight falls within this range. However, in view of the stability and availability, preferred alkylbenzenes are those having 1 to 4 alkyl groups having each 1 to 40 carbon atoms, the total number of carbon atoms in the alkyl groups being 20 to 40 (hereinafter referred to as alkylbenzenes (B)), and more preferred are those having 1 to 4 alkyl groups having each 1 to 30 carbon atoms, the total number of thereof being 20 to 30.

[0032] Specific examples of alkyl groups having 1 to 40 carbon atoms are methyl, ethyl, propyl (including all isomers), butyl (including all isomers), pentyl (including all isomers), hexyl (including all isomers), heptyl (induding all isomers),octyl (including all isomers), nonyl (including all isomers), decyl (including all isomers), undecyl (including al isomers), dodecyl (including all isomers), tridecyl (including all isomers), tetradecyl (including all isomers), pentadecyl (induding all isomers), hexadecyl (including all isomers), heptadecyl (including all isomers), octadecyl (including all isomers), nonadecyl (induding all isomers), icosyl (including all isomers), heneicosyl (induding all isomers), docosyl (induding all isomers), tricosyl (including all isomers), tetracosyl (including all isomers), heptacosyl (induding all isomers), hexacosyl (including all isomers), octacosyl (including all isomers), nonacosyl (including all isomers), triacontyl (including all isomers), hentriacontyl (induding all isomers), dotrlacontyl (including all isomers), tritriacontyl (including all isomers), tetratriacontyl (including all isomers), pentatriacontyl (including all isomers), hexatriacontyl (including all isomers), heptatriacontyl (including all isomers), octatriacontyl (including all isomers), nonatriacontyl (including all isomers) and tetracontyl (including all isomers).

[0033] These alkyl groups may be of straight chain or branched chain. However, in view of the stability and viscosity characteristics, branched alkyl groups are preferred. Furthermore, in view of availability, more preferred are branched alkyl groups derived from oligomers of olefins such as propylene, butene and isobutylene.

[0034] The number of alkyl groups in the alkylbenzene oils (B) is confined to 1 to 4. However, in view of the stability and availability, it is the most preferred to use alkylbenzenes having one or two alkyl groups, such as a monoalkylbenzene, a dialkylbenzene or a mixture thereof.

[0035] The alkylbenzenes (B) may be not only those having the same molecular structure, but also a mixture of those having different molecular structures as long as they satisfy the conditions that they contain 1 to 4 alkyl groups each having 1 to 40 carbon atoms, the total number thereof being 20 to 40.

[0036] The above-described alkylbenzenes can be produced by any suitable method such as the following synthesizing method.

[0037] Eligible aromatic compounds as a raw material include benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene and a mixture thereof. Eligible alkylating agents include a straight or branched olefin obtained by polymerizing a lower-olefin having 6 to 40 carbon atoms, such as ethylene, propylene, butene and isobutylene, among which propylene is preferred or obtained by thermally decomposing wax, heavy oils, a petroleum fraction, polyethylene and polypropylene; a straight olefin having 9 to 40 carbon atoms obtained by separating n-paraffin from a petroleum fraction such as kerosene or gas oil and then catalytically transforming the n-paraffin into an olefin; and a mixture thereof.

[0038] An alkylating catalyst used for the alkylation may be a conventional catalyst exemplified by a Friedel-Crafts catalyst such as aluminum chloride and zinc chloride; and an acidic catalyst such as sulfuric acid, phosphoric acid, silicotungstic acid, hydrofluoric acid or activated clay.

[0039] The alkylbenzene oil may be obtained by mixing separately prepared alkylbenzenes having a molecular weight of 200 to 350 with alkylbenzenes having a molecular weight of less than 200 or more than 350 within a ratio as defined by the present invention. Alternatively, it is advantageous in practice to obtain a distillate containing at least 60 mass percent of alkylbenzenes having a molecular weight of 200 to 350 through distillation or separation with chromatography from a mixture of alkylbenzenes which is produced in accordance with the method described above or is commercially available.

[0040] There is no particular restriction on the content of the hydrocarbon oil in the inventive refrigerating machine oil. However, in view of the capability of improving lubricity, miscibility with a refrigerant, thermal and chemical stabilities and electric insulation. The inventive refrigerating machine oil may contain the hydrocarbon oil in an amount of preferably more than 50 mass percent, more preferably more than 70 mass percent, further more preferably more than 80 mass percent, most preferably more than 90 mass percent, based on the total mass of the refrigerating machine oil.

[0041] The refrigerating machine oil according to the present invention contains the above-mentioned hydrocarbon oil but in addition to this, may further contain an oxygen-containing synthetic oil such as an ester, polyglycol, polyvinyl ether, ketone, polyphenyl ether, silicone, polysiloxane and perfluoro ether. Among these oxygen-containing synthetic oils, preferred are an ester, polyglycol, ketone, polyvinyl ether and a mixture thereof.

[0042] The refrigerating machine oil according to the present invention may contain the hydrocarbon oil alternatively with the oxygen-containing synthetic oil as a base oil. The refrigerating machine oil of the present invention can be put in use without being incorporated with an additive. However, the refrigerating machine oil may contain any of various additives as required.

[0043] In order to further improve the wear resistance and load resistance of the inventive refrigerating machine oil, it may be blended with at least one phosphorus compound selected from the group consisting of phosphoric esters, acidic phosphoric esters, amine salts of acidic phosphoric esters, chlorinated phosphoric esters and phosphorous esters. These phosphorus compounds are esters obtained by a reaction between phosphoric acid or phosphorous acid and an alkanol or polyether type alcohol, and are also derivatives of these esters.

[0044] Specific examples of phosphoric esters are tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, triundecyl phosphate, tridodecyl phosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentradecyl phosphate, trihexadecyl phosphate, triheptadecyl phosphite, trioctadecyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylyl phosphate, cresyldiphenyi phosphate and xylyldiphenyl phosphate.

[0045] Specific examples of acidic phosphoric esters are monobutyl acid phosphate, monopentyl acid phosphate, monohexyl acid phosphate, monoheptyl acid phosphate, monooctyl acid phosphate, monononyl acid phosphate, monodecyl acid phosphate, monoundecyl acid phosphate, monododecyl acid phosphate, monotridecyl acid phosphate, monotetradecyl acid phosphate, monopentadecyl acid phosphate, monohexadecyl acid phosphate, monoheptadecyl acid phosphate, monooctadecyl acid phospahte, monooleyl acid phosphate, dibutyl acid phosphate, dipentyl acid phospahte, dihexyl acid phospahte, diheptyl acid phospahte, dioctyl acid phosphate, dinonyl acid phosphate, didecyl acid phosphate, diundecyl acid phosphate, didodecyl acid phophate, dirtridecyl acid phosphate, ditetradecyl acid phospahte, dipentadecyl acid phosphate, dihexadecyl acid phosphate, diheptadecyl acid phosphate, dioctadecyl acid phosphate and dioleyl acid phosphate.

[0046] Specific examples of amine salts of acidic phosphoric esters are methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine and trioctylamine of the acidic phosphoric ester.

[0047] Specific examples of chlorinated phosphoric esters are tris-dichloropropyl phosphate, tris-chloroethyl phosphate, tris-chlorophenyl phosphate and polyoxyalkylene bis[di(chloroalkyl)] phosphate.

[0048] Specific examples of phosphorous esters are dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, dioleyl phosphite, diphenyl phosphite, dicresyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphite, trioctyl phophite, trinonyl phosphite, tridecyl phosphite, triundecyl phosphite, tridodecyl phosphite, trioleyl phosphite, triphenyl phosphite and tricresyl phosphite.

[0049] Although these phosphorus compounds may be blended with the inventive refrigerating machine oil in any suitable ratio, their content may be within the range of 0.01 to 5.0 mass percent, preferably 0.02 to 3.0 mass percent, based on the total mass of the refrigerating machine oil (based on the total mass of the base oil and the Whole additives).

[0050] Furthermore, in order to improve the stability of the refrigerating machine oil according to the present invention, it may be blended with at least one kind of an epoxy compound selected from the group consisting of:
(1) phenylglycidyl ether type epoxy compounds, (2) alkylglycidyl ether type compounds, (3) glycidyl ester type epoxy compounds, (4) aryl oxirane compounds, (5) alkyl oxirane compounds, (6) alicyclic epoxy compounds, (7) epoxidized fatty monoesters and (8) epoxidized vegetable oils.

[0051] Specific examples of phenylglycidyl ether type epoxy compounds (1) are phenylglycidyl ether and alkylphenylglycidyl ether. The alkylphenylglycidyl ether may be 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 are n-butylphenylglyddyl ether, i-butylphenylglycidyl ether, sec-butyl phenylglycidyl ether, tert-butyl phenylglycidyl ether, pentylphenylglycidyl ehter, hexylphenylglycidyl ether, heptylphenylglycidyl ehter, octylphenylglycidyl ether, nonylphenylglycidyl ehter and decylphenylglycidyl ehter.

[0052] Specific examples of alkylglycidyl ether type compounds (2) are decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, 2-ethylhexylglycidyl ether, neopentylglycoldiglycidyl ether, trimethylolpropane triglycidyl ehter, pentaerythritol tetraglycidyl ether, 1,6-hexanediol diglycidyl ether, sorbitol polyglycidyl ether, polyalkyleneglycol monoglycidyl ether and polyalkyleneglycol diglycidyl ether.

[0053] Specific examples of glycidyl ester type epoxy compounds (3) are phenylglycidyl ester, alkylglycidyl ester and alkenylglycidyl ester. Preferred are glycidyl-2,2-dimethyloctanoate, glycidyl benzoate, glycidyl acrylate and glycidyl methacrylate.

[0054] Specific examples of aryl oxirane compounds (4) are 1,2-epoxystyrene and alkyl-1 ,2-epoxystyrene.

[0055] Specific examples of alkyl oxirane compounds (5) are 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, 1,2-epoxyoctadecane, 1,2-epoxynonadecane and 1,2-epoxyeicosane.

[0056] Specific examples of alicydic epoxy compounds (6) are 1,2-epoxycyclohexane7 1,2-epoxycyclopentane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane 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(1,3-dioxane-5,3'-[7]oxabicyclo[4.1.0]) heptane, 4-(1'-metylepoxyethyl)-1,2-epoxy-2-methylcyclohexane and 4-epoxyethyl-1,2-epoxycyclohexane.

[0057] Specific examples of epoxidized fatty monoesters (7) are an ester formed by reacting an epoxidized fatty acid having 12 to 20 carbon atoms with an alcohol having 1 to 8 carbon atoms, phenol or alkylphenol. Particularly preferred are epoxystearates such as butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, phenyl and butylphenyl esters of epoxystearic acid.

[0058] Specific examples of epoxidized vegetable oils (8) epoxy compounds of vegetable oils such as soybean oil, linseed oil and cottonseed oil.

[0059] Among these epoxy compounds, preferred are phenylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds and epoxidized fatty monoesters. More preferred are phenylglycidyl ether type epoxy compounds and glycidyl ester type epoxy compounds. Particularly preferred are phenylglycidyl ether, butylphenylglycidyl ether, alkylglycidyl ester and mixtures thereof.

[0060] The inventive refrigerating machine oil may be blended with these epoxy compounds in any suitable blending ratio. The epoxy compound is generally blended in an amount of 0.1 to 5.0 mass percent, preferably 0.2 to 2.0 mass percent, based on the total mass of the refrigerating machine oil (based on the total mass of the base oil and the whole additives).

[0061] Needless to mention, more two kinds of each of the phosphorus compounds and the epoxy compounds may be used in combination.

[0062] If necessary, in order to further enhance the properties of the refrigerating machine oil of the present invention, it may be blended with suitable conventional additive singly or in combination. The suitable additives may be anti-oxidants of a phenol type such as di-tett-butyl-p-cresol and bisphenol A or of an amide type such as phenyl- α-naphthyl amine and N,N-di(2-naphthyl)-p-phenylenediamine; anti-wear additives such as zinc dithiophosphate; extreme pressure agents such as chlorinated paraffin and sulfur compounds; oiliness improvers such as fatty acid; silicone-type antiforming agents; metal inactivators such as benzotriazole; viscosity index improvers; pour point depressants; and detergent-dispersants. These additives may be added in an amount of less than 10 mass percent, preferably less than 5 mass percent, based on the total mass of the refrigerating machine oil (based on the total mass of the base oil and the whole additives).

[0063] Although there is no particular restriction imposed on the kinematic viscosity of the refrigerating machine oil of the present invention, it preferably has a kinematic viscosity at 40 °C of preferably 3 to 100 mm²/s, more preferably 4 to 50 mm²/s, most preferably 5 to 40 mm²/s and a kinematic viscosity at 100 °C of preferably 1 to 20 mm²/s, more preferably 2 to 10 mm²/s.

[0064] Although not restricted, the refrigerating machine oil of the present invention preferably has a volume resistivity of greater than 1.0 x 10¹² Ω · cm, preferably greater than 1.0 x 10¹³ Ω · cm, more preferably greater than 1.0 x 10¹⁴ Ω · cm. When refrigerating machine oils are used in a sealed type refrigerating machine, such volume resistivity is required to be high. The volume resistivity used herein designates a value measured at a temperature of 40 °C in accordance with JIS C 2101 "Testing methods of electrical insulating oils".

[0065] The water content of the refrigerating machine oil of the present invention is not particularly restricted, but may be present within the range of preferably less than 200 ppm, more preferably less than 100 ppm, most preferably less than 50 ppm. When refrigerating machine oils are used in a sealed type refrigerating machine, less water contents are preferred in view of the stability and electric insulation of the oils.

[0066] The total acid value of the refrigerating machine oil of the present invention is not particularly restricted, but may be preferably less than 0.1 mgKOH/g, more preferably 0.05 mgKOH/g in order to prevent the corrosion of metals used in a refrigerating machine or pipes thereof. The total acid value used herein designates a total acid value measured in accordance with JIS K 2501 "Petroleum products and lubricants-Determination of neutralization number".

[0067] The ash content of the refrigerating machine oil of the present invention is not particularly restricted, but may be preferably less than 100 ppm, more preferably 50 ppm. The ash content used herein designates a value of ash content measured in accordance with JIS K 2272 "Testing Methods for Ash and Sulfated Ash of Crude Oil and Petroleum Products".

[0068] The refrigerant used in a refrigerating machine together with the refrigerating machine oil is dimethyl ether (DME) or alternatively a mixture of DME and other refrigerants such as hydrofluorocarbon, hydrocarbon, carbon dioxide and ammonia.

[0069] The hydrofluorocarbon refrigerants may be hydrofluorocarbon having 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms. Specific examples of the hydrofluorocarbon refrigerants are difluoromethane (HFC-32), trifluoromethane (HFC-23), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1-trifluoroethane (HFC-143a), 1,1-difluoroethane (HFC-152a) and a mixture of at least two kinds of thereof.

[0070] These refrigerants are suitably selected in accordance with use and performances to be required. Preferred refrigerants are HFC-32 alone; HFC-23 alone; HFC-134a alone; HFC-125 alone; a mixture of HFC-134a / HFC-32 in a ratio of 60-80 mass % / 40-20 mass %; a mixture of HFC-32 / HFC-125 in a ratio of 40-70 mass % / 60-30 mass %; a mixture of HFC-125 / HFC-143a in a ratio of 40-60 mass % / 60-40 mass %; a mixture of HFC-134a / HFC-32 / HFC-125 in a ratio of 60 mass % / 30 mass % / 10 mass %; a mixture of HFC-134a / HFC-32 / HFC-125 in a ratio of 40-70 mass % / 15-35 mass % / 5-40 mass % and a mixture of HFC-125 / HFC134a / HFC-143a in a ratio of 35-55 mass % / 1-15 mass % / 40-60 mass %. More specifically, the HFC refrigerant mixtures include a mixture of HFC-134a / HFC-32 in a ratio of 70 mass % / 30 mass %; a mixture of HFC-32 / HFC-125 in a ratio of 60 mass % / 40 mass %; a mixture of HFC-32 / HFC-125 in a ratio of 50 mass % / 50 mass % (R410A); a mixture of HFC-32 / HFC-125 in a ratio of 45 mass % / 55 mass % (R410B) ; a mixture of HFC-125 / HFC-143a in a ratio of 50 mass % / 50 mass % (R507C); a mixture of HFC-32 / HFC-125 / HFC-134a in a ratio of 30 mass % / 10 mass % 60 mass %; a mixture of HFC-32 / HFC-125 / HFC-134a in a ratio of 23 mass %/ 25 mass % / 52 mass % (R407C); a mixture of HFC-32 / HFC-125 / HFC-134a in the ratio of 25 mass % / 15 mass % / 60 mass % (R407E) and a mixture of HFC-125 / HFC-134a/HFC-143a in a ratio of 44 mass % / 4 mass % / 52 mass % (R404A).

[0071] The hydrocarbon refrigerants may be those which are gaseous at 25 °C and one atmospheric pressure. Specific examples of the hydrocarbon refrigerants are alkanes, cycloalkanes and alkenes each having 1 to 5 carbon atoms, preferably 1 to 4 carbon atoms, such as methane, ethylene, ethane, propylene, propane, cyclopropane, butane, isobutane, cyclobutane, methylcyclopropane and a mixture of at least two kinds thereof.

[0072] The blending ratio of DME to hydrofluorocarbon and/or hydrocarbon refrigerants is not particularly restricted. The total amount of hydrofluorocarbon and/or hydrocarbon may be within the range of preferably 1 to 200 parts by weight, more preferably 10 to 100 parts by weight per 100 parts by weight of DME.

[0073] The refrigerating machine oil according to the present invention is generally present in the form of a fluid composition admixed with DME alone or with other refrigerants in a refrigerating machine. The mixing ratio of the inventive refrigerating machine oil to the refrigerants are not particularly restricted, but the refrigerating machine oil may be present in a ratio of 1 to 500 parts by weight, more preferably 2 to 400 parts by weight per 100 parts by weight of the refrigerant.

[0074] The refrigerating machine oil according to the present invention can be used as a refrigerating machine oil for the refrigerant compressors of any types of refrigerating machine. Refrigerating machines to which the inventive refrigerating machine oil is applicable are room air conditioners, packaged air conditioning systems, refrigerators, automobile air conditioners, dehumidifiers, freezers, refrigerating chambers, vending machines, show-cases and cooling systems for chemical plants. Furthermore, the inventive refrigerating machine oil is preferably used in refrigerating machines having sealed compressors. The inventive refrigerating machine oil is also eligible for use in a reciprocating, rotary, or centrifugal type compressor.

[0075] This invention will be further described by way of the following examples which are provided for illustration purposes only.

Examples 1 -14

[0076] A sample oil of each of Examples 1 to 14 was prepared by blending the following base oils and additives in accordance with the formulations indicated in Tables 1 - 3. Tables 1 - 3 shows the properties (kinematic viscosity at 40 °C and 100 °C and total acid value) of each sample oils.

Base oil A :

Highly refined paraffinic mineral oil (Pour point : - 50 °C, Aniline point : 110 °C, C_A : 0.0%, C_N : 36.5%, C_P : 63.5%)

Base oil B :

Highly refined paraffinic mineral oil (Pour point : - 40 °C, Aniline point : 115 °C, C_A : 0.0%, C_N : 37.0%, C_P : 63.0%)

Base oil C :

Naphthenic mineral oil (Pour point : - 42.5 °C, Aniline point: 80 °C, C_A : 10.0%, C_N : 43.0%, C_P : 47.0%)

Base oil D :

Naphthenic mineral oil (Pour point : - 40.0 °C, Aniline point : 85 °C, C_A : 12,0%, C_N : 44.0%, C_P : 44.0%)

Base oil E :

Poly-α-olefin (Oligomer of 1-decene, Number-average molecular weight : 370)

Base oil F :

Poly-α-olefin (Oligomer of 1-decene, Number-average molecular weight : 510)

Base oil G :

Alkylnaphthalene (Number-average molecular weight : 200)

Base oil H :

Alkylnaphthalene (Number-average molecular weight : 360)

Base oil I :

alkylbenzene (Number-average molecular weight : 210)

Base oil J :

Alkylbenzene (Number-average molecular weight : 270)

Additive A:

Phenylglycidyl ether

Additive B :

Tricresylphosphate

[0077] The sample oils thus obtained were each subjected to the following tests.

Miscibility Test

[0078] 27 grams of each of the sample oils were blended with 3 grams of a DME refrigerant and then subjected to a test in accordance with "Testing method of evaluating miscibility with a refrigerant" prescribed in JIS K 2211 "Refrigerating machine oils" to observe if the refrigerant ant the sample oil would dissolve in each other or if they would be separated from each other or turned into a white-turbid liquid. The results are shown in Tables 1 - 3.

Insulation Test

[0079] In accordance with JIS C 2101 "Testing method of electrical insulating oils", a test was conducted to measure the volume resistivity at 25 °C of each of the sample oils. The results are shown in Tables 1 - 3.

Thermal Stability Test

[0080] 90 grams of each of the sample oils, 10 grams of a DME refrigerant and a catalyst (wire-shaped iron, copper and aluminum) were charged into an autoclave and heated at 175 °C. After two weeks, a test was conducted so as to observe the appearance of both of the sample oils and the catalyst and measure the volume resistivity and total acid value of each of the sample oils. The results are shown in Tables 1 - 3.

Evaluation Test for Lubricity

[0081] In accordance with ASTM D 2670 "Falex Wear Test", each of the sample oils was subjected to a friction test in which a test machine was run under a load of 250 lb for two hours after being warmed up at an oil temperature of 100 °C under a load of 150 lb for a period of one minute. With respect to each of the sample oils, the level of abrasion of the test journal (pin) was measured. The results are shown in Tables 1 - 3.

Evaluation Test for Hydrolysis Stability

[0082] 90 grams of each of the sample oils, 0.1 gram of water and 10 grams of a DME refrigerant were taken into a 300 ml glass test tube and then subjected to thermal deterioration at 175 °C for 168 hours in a stainless steel autoclave in which wires made of copper, iron and aluminum were placed as a deterioration accelerating catalyst. After this procedure, the total acid value of each of the sample oils was measured. The results are shown with the total acid value prior to the procedure, in Tables 1 - 3.

Table 1

		Example 1	Example 2	Example 3	Example 4	Example 5
Base oil		A	B	C	D	E
(mass %)		100	100	100	100	100
Additive		- -	-	-	-	-
(mass %)
Kinematic	(40°C(mm2/s)	21.6	68.6	29.5	55.2	16.9
Viscosity	100°C(mm2/s)	4.09	8.60	4.35	5 90	3.91
Total acid value (mgKOH/g)		0.00	0.00	0.00	0.00	0.00
Miscibility		Miscible	Miscible	Miscible	Miscible	Miscible
Volume resistivity (Ω·cm)		6.7 × 1015	4.1 × 1015	5.3 × 1015	2.3 × 1015	2.1 × 1015
Thermal stability test	Sample oil appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Catalyst appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Volume resistivity (Ω · cm)	1.1 × 1015	9.2 × 1014	4.6 × 1013	7.8 × 1014	3.3 × 1014
	Total acid value (mgKOH/g)	0.01	0.01	0.01	0.01	0.01
FALEX test	Abrasion wear of pin (mg)	17	15	18	16	19
Hydrolysis stability test	Total acid value (mgKOH/g)	0.02	0.02	0.02	0.02	0.02

Table 2

		Example 6	Example 7	Example 8	Example 9	Example 10
Base oil		F	G	H	I	J
(mass %)		100	100	100	100	100
Additive		-	-	-	-	-
(mass %)
Kinematic	40°C(mm2/s)	30.5	5.14	31.1	15.1	65.7
Viscosity	100°C(mm2/s)	5.93	1.53	5.12	2.05	6.34
Total acid value (mgKOH/g)		0.00	0.00	0.00	0.00	0.00
Miscibility		Miscible	Miscible	Miscible	Miscible	Miscible
Volume resistivity (Ω · cm)		2.1 × 1015	5.7 × 1015	6.3 × 1015	2.9 × 1015	2.8 × 1015
Thermal stability test	Sample oil appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Catalyst appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Volume resistivity (Ω · cm)	5.0 × 1014	8.9 × 1014	1.5 × 1015	7.2 × 1014	5.7 × 1014
	Total acid value (mgKOH/g)	0.01	0.01	0.01	0.01	0.01
FALEX test	Abrasion wear of pin (mg)	18	19	16	17	15
Hydrolysis stability test	Total acid value (mgKOH/g)	0.02	0.02	0.02	0.02	0.02

Table 3

		Example 11	Example 12	Example 12	Example 13	Example 14
Base oil		A(50)	A	A	E	E
		E(50)
(mass %)		100	99.9	99	99.9	99
Additive		-	A	B	A	B
(mass %)			0.1	1.0	0.1	1.0
Kinematic	40°C(mm2/s)	19.2	21.6	21.6	16.9	16.9
Viscosity	100°C(mm2/s)	4.01	4.09	4.09	3.91	3.91
Total acid value (mgKOH/g)		0.00	0.00	0.00	0.00	0.00
Miscibility		Miscible	Miscible	Miscible	Miscible	Miscible
Volume resistivity (Ω · cm)		1.9 × 1015	3.1 × 1015	2.1 × 1015	1.5 × 1015	1.0 × 1015
Thermal stability test	Sample oil appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Catalyst appearance	Not changed	Not changed	Not changed	Not changed	Not changed
	Volume resistivity (Ω · cm)	7.2 × 1014	1.1 × 1014	1.1 × 1015	1.0 × 1014	1.7 × 1014
	Total acid value (mgKOH/g)	0.01	0.01	0.01	0.00	0.01
FALEX test	Abrasion wear of pin (mg)	16	17	11	19	9
Hydrolysis stability test	Total acid value (mgKOH/g)	0.02	0.02	0.02	0.00	0.02

[0083] As apparent from the results shown in Tables 1 - 3, the sample oils of Examples 1 to 14 according to the present invention had an excellent lubricity, miscibility with refrigerants, electric isolation, resistance to hydrolysis and kinematic viscosities, all of which were well-balanced when used in combination with a dimethyl ether refrigerant.

Claims

1. A refrigerating machine oil for use with a dimethylether refrigerant, which comprises a hydrocarbon oil.

2. The refrigerating machine oil according to claim 1 wherein said hydrocarbon oil is selected from the groups consisting of a mineral oil, an olefin polymer, a naphthalene compound and alkylbenzene.

3. The refrigerating machine oil according to claim 1 or 2, further comprising a phosphorus compound.

4. The refrigerating machine oil according to claim 1, 2 or 3 further comprising an epoxy compound.

5. A fluid composition for a refrigerating machine which comprises the refrigerating machine oil as defined in 1, 2, 3, 4 or 5 and dimethylether.