Title of Invention REFRIGERANT OIL FOR FREEZERS AND OPERATING FLUID COMPOSITION FOR FREEZERS Technical Field [0001] The present invention relates to a refrigerating machine oil and to a working fluid composition for a refrigerating machine. Background Art [0002] In light of the problem of ozone layer depletion that is a focus of attention in recent years, the restrictions on CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons) that are used as refrigerants in conventional refrigerating machines have become more stringent, and HFCs (hydrofluorocarbons) are being used as substitute refrigerants. [0003] Mineral oils or hydrocarbon oils such as alkylbenzenes have been preferred for use as refrigerating machine oils when CFCs or HCFCs are the refrigerants, but since changing the refrigerant can cause the refrigerating machine oil used with it to exhibit unpredictable behavior in terms of its compatibility with the refrigerant, its lubricity, its viscosity when dissolved with refrigerants and its thermal and chemical stability, it has been necessary to develop different refrigerating machine oils for different refrigerants. Examples of refrigerating machine oils that have been developed for HFC refrigerants include polyalkylene glycols (see Patent document 1), esters (see Patent document 2), carbonic acid esters (see Patent document 3) and polyvinyl ethers (see Patent document 4). [0004] HFC-134a is an HFC refrigerant that is routinely used as a refrigerant for automobile air conditioners, and while it has an ozone depletion potential (ODP) of zero, its high global warming potential (GWP) has led to its restriction in Europe. It has therefore become an urgent issue to develop refrigerants that can be used as substitutes for HFC-134a. [0005] In light of this background it has been proposed to use, as substitute refrigerants for HFC-134a, unsaturated fluorinated hydrocarbon refrigerants which have very low ODP and GWP, are noncombustible and are comparable or superior to HFC-134a in terms of their thermodynamic properties, as a measure of refrigerant performance. There has also been proposed the use of refrigerant mixtures of unsaturated fluorinated hydrocarbons with saturated hydrofluorocarbons, C3-5 saturated hydrocarbons, dimethyl ether, carbon dioxide, bis(trifluoromethyl)sulfide or trifluoroiodomethane (see Patent document 5). [0006] In addition, there have been proposed refrigerating machine oils that employ mineral oils, alkylbenzenes, poly α-olefins, polyalkyleneglycols, monoesters, diesters, polyol esters, phthalic acid esters, alkyl ethers, ketones, carbonic acid esters, polyvinyl ethers and the like, as refrigerating machine oils that can be used with unsaturated fluorinated hydrocarbon refrigerants or refrigerant mixtures of unsaturated fluorinated hydrocarbons and saturated hydrofluorocarbons, C3-5 saturated hydrocarbons, dimethyl ether, carbon dioxide, bis(trifluoromethyl)sulfide or trifluoroiodomethane (see Patent documents 5-7). Citation List Patent literature [0007] [Patent document 1] Japanese Unexamined Patent Application Publication HEI No. 02-242888 [Patent document 2] Japanese Unexamined Patent Application Publication HEI No. 03-200895 [Patent document 3] Japanese Unexamined Patent Application Publication HEI No. 03-217495 [Patent document 4] Japanese Unexamined Patent Application Publication HEI No. 06-128578 [Patent document 5] International Patent Publication No. WO2006/094303 [Patent document 6] Japanese Patent Public Inspection No. 2006-512426 [Patent document 7] International Patent Publication No. WO2005/103190 Summary of Invention Technical Problem [0008] In refrigeration systems employing unsaturated fluorinated hydrocarbon refrigerants, as described in Patent documents 5, 6 and 7, the refrigerating machine oil employed may be a mineral oil or a hydrocarbon such as an alkylbenzene which is used in CFCs or HCFCs or a polyalkylene glycol, polyol ester or polyvinyl ether which is used in HFCs. Research by the present inventors, however, has shown that it is not possible to achieve a high level of the required performance simply by applying these conventional refrigerating machine oils in the systems mentioned above. Ether-based refrigerating machine oils with polyalkylene glycols or polyvinyl ethers, in particular, can cause problems in systems when the refrigerants or refrigerating machine oils decompose in the presence of unsaturated fluorinated hydrocarbon refrigerants. It has also been shown that, when anti-wear agents that have been commonly used in the prior art are added for improved wear resistance, their stability is further impaired in the presence of unsaturated fluorinated hydrocarbon refrigerants. [0009] The present invention has been accomplished in light of these circumstances, and its object is to provide a refrigerating machine oil and a working fluid composition for refrigerating machines, that can exhibit both stability in the presence of unsaturated fluorinated hydrocarbon refrigerants and a high level of wear resistance, in a refrigeration system that employs an unsaturated fluorinated hydrocarbon refrigerant. Solution to Problem [0010] In order to solve the problems described above, the invention provides a working fluid composition for a refrigerating machine comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, at least one compound selected from the group consisting of amine-based antioxidants, metal inactivating agents and alicyclic epoxy compounds, and an unsaturated fluorinated hydrocarbon refrigerant. [0011] The invention further provides a refrigerating machine oil to be used together with an unsaturated fluorinated hydrocarbon refrigerant, comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, and at least one compound selected from the group consisting of amine-based antioxidants, metal inactivating agents and alicyclic epoxy compounds. [0012] Working fluid compositions for a refrigerating machine according to the following (1) to (7) are preferred modes of the working fluid composition for a refrigerating machine according to the invention. (1) A working fluid composition for a refrigerating machine comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant and an unsaturated fluorinated hydrocarbon refrigerant. (2) A working fluid composition for a refrigerating machine comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, a metal inactivating agent and an unsaturated fluorinated hydrocarbon refrigerant. (3) A working fluid composition for a refrigerating machine comprising: a refrigerating machine oil comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil. (4) A working fluid composition for a refrigerating machine comprising: a refrigerating machine oil comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil. (5) A working fluid composition for a refrigerating machine comprising: a refrigerating machine oil comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil. (6) A working fluid composition for a refrigerating machine comprising: a refrigerating machine oil comprising a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil. (7) A working fluid composition for a refrigerating machine comprising: a refrigerating machine oil comprising a base oil containing an ether-based compound and an alicyclic epoxy compound, with a moisture content of 300-10,000 ppm by mass, and an unsaturated fluorinated hydrocarbon refrigerant. [0013] Refrigerating machine oils according to the following (8) to (14) are preferred modes of the refrigerating machine oil according to the invention. (8) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an amine-based antioxidant, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (9) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and a metal inactivating agent, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (10) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (11) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (12) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (13) A refrigerating machine oil comprising: a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil, the refrigerating machine oil being used together with an unsaturated fluorinated hydrocarbon refrigerant. (14) A refrigerating machine oil comprising: a base oil containing an ether-based compound and an alicyclic epoxy compound, the refrigerating machine oil having a moisture content of 300-10,000 ppm by mass and being used together with an unsaturated fluorinated hydrocarbon refrigerant. [0014] The working fluid composition for a refrigerating machine of the invention preferably contains at least one compound selected from among 1,2,3,3,3-pentafluoropropene, 1,3,3,3-tetrafluoropropene, 2,3,3,3-tetrafluoropropene, 1,2,3,3-tetrafluoropropene and 3,3,3-trifluoropropene, as an unsaturated fluorinated hydrocarbon refrigerant. [0015] The working fluid composition for a refrigerating machine of the invention may also comprise at least one unsaturated fluorinated hydrocarbon refrigerant (hereunder referred to as "refrigerant (A)") alone, or it may further comprise at least one component selected from among saturated hydrofluorocarbon, C3-5 hydrocarbon, dimethyl ether, carbon dioxide, bis(trifluoromethyl)sulfide and trifluoroiodomethane refrigerants (hereunder referred to as "refrigerant (B)"). [0016] In a refrigerant mixture comprising refrigerant (A) and refrigerant (B), the unsaturated fluorinated hydrocarbon refrigerant is preferably at least one selected from among 1,2,3,3,3 -pentafluoropropene (HFO-1225ye), 1,3,3,3 –tetrafluoropropene (HFO-1234ze), 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,2,3,3-tetrafluoropropene (HFO-1234ye) and 3,3,3-trifluoropropene (HFO-1243zf) refrigerants; the saturated hydrofluorocarbon is preferably one or more selected from among difluoromethane (HFC-32), pentafluoroethane (HFC-125), 1,1,2,2-tetrafluoroethane (HFC-134) 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1-difluoroethane (HDFC-152a), fluoroethane (HFC-161), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,1,3,3,3 –hexafluoropropane (HFC-23 6fa), 1,1,1,3,3 –pentafluoropropane (HFC-245 fa) and 1,1,1,3,3-pentafluorobutane (HFC-365mfc); and the C3-5 hydrocarbon is preferably at least one selected from among propane, normal-butane, isobutane, 2-methylbutane and normal-pentane. Advantageous Effects of Invention [0017] As mentioned above, the invention provides a refrigerating machine oil and a working fluid composition for a refrigerating machine, that can exhibit both stability in the presence of unsaturated fluorinated hydrocarbon refrigerants and a high level of wear resistance, in a refrigeration system that employs an unsaturated fluorinated hydrocarbon refrigerant. Description of Embodiments [0018] Preferred embodiments of the invention will now be described in detail. [0019] The refrigerating machine oil according to the first embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, and an amine-based antioxidant, and it is to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the first embodiment comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant and an unsaturated fluorinated hydrocarbon refrigerant. The working fluid composition for a refrigerating machine according to the first embodiment encompasses modes that contain the refrigerating machine oil of the first embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0020] The refrigerating machine oil according to the second embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and a metal inactivating agent, and it is to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the second embodiment comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, a metal inactivating agent, and an unsaturated fluorinated hydrocarbon refrigerant. The working fluid composition for a refrigerating machine according to the second embodiment encompasses modes that contain the refrigerating machine oil of the second embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0021] A refrigerating machine oil according to the third embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil, to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the third embodiment comprises a refrigerating machine oil that contains a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil. The working fluid composition for a refrigerating machine according to the third embodiment encompasses modes that contain the refrigerating machine oil of the third embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0022] A refrigerating machine oil according to the fourth embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil, to be used together with an unsaturated hydrocarbon-based refrigerant. A working fluid composition for a refrigerating machine according to the fourth embodiment comprises a refrigerating machine oil that contains a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil. The working fluid composition for a refrigerating machine according to the fourth embodiment encompasses modes that contain the refrigerating machine oil of the fourth embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0023] A refrigerating machine oil according to the fifth embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil, to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the fifth embodiment comprises a refrigerating machine oil that contains a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is greater than 0 and less than 400 ppm by mass based on the total amount of the refrigerating machine oil. The working fluid composition for a refrigerating machine according to the fifth embodiment encompasses modes that contain the refrigerating machine oil of the fifth embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0024] A refrigerating machine oil according to the sixth embodiment of the invention comprises a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil, to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the sixth embodiment comprises a refrigerating machine oil that contains a base oil containing an ether-based compound, an amine salt of an acidic phosphoric acid ester, an amine-based antioxidant, a metal inactivating agent and an alicyclic epoxy compound, and an unsaturated fluorinated hydrocarbon refrigerant, wherein the content of the amine salt of the acidic phosphoric acid ester is at least 400 ppm by mass based on the total amount of the refrigerating machine oil. The working fluid composition for a refrigerating machine according to the sixth embodiment encompasses modes that contain the refrigerating machine oil of the sixth embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0025] A refrigerating machine oil according to the seventh embodiment of the invention comprises a base oil containing an ether-based compound and an alicyclic epoxy compound, wherein the moisture content is 300-10,000 ppm by mass, to be used together with an unsaturated fluorinated hydrocarbon refrigerant. A working fluid composition for a refrigerating machine according to the seventh embodiment of the invention comprises a refrigerating machine oil that contains a base oil containing an ether-based compound and an alicyclic epoxy compound, wherein the moisture content is 300-10,000 ppm by mass, and an unsaturated fluorinated hydrocarbon refrigerant. The working fluid composition for a refrigerating machine according to the seventh embodiment encompasses modes that contain the refrigerating machine oil of the seventh embodiment and an unsaturated fluorinated hydrocarbon refrigerant. [0026] The components in the refrigerating machine oil and working fluid composition for a refrigerating machine according to the first to seventh embodiments will now be explained in detail. [0027] The ether-based compounds composing the base oils for the first to seventh embodiments are not particularly restricted so long as they are compounds having one or more ether bonds in the molecule. Specifically, this includes polyalkylene glycols, polyvinyl ethers, polyphenyl ethers, perfluoroethers and the like, among which polyalkylene glycols and polyvinyl ethers are preferably used. [0028] Examples of polyalkylene glycols include compounds represented by the following formula (1). R¹-[(OR²)f-OR³]g(1) [In formula (1), R1 represents hydrogen, CI-10 alkyl, C2-10 acyl, or a residue of a compound having 2-8 hydroxyl groups, R2 represents C2-4 alkylene, R3 represents hydrogen, C1-10 alkyl or C2-10 acyl, f represents an integer of 1-80, and g represents an integer of 1-8.] [0029] In formula (1), alkyl groups represented by R1 and R3 may be straight-chain, branched or cyclic. The number of carbon atoms in each alkyl group is preferably 1-10 and more preferably 1-6. If the alkyl group is greater than C10, compatibility with the working medium may be reduced. [0030] The alkyl group portions of acyl groups represented by R1 and RJ may also be straight-chain, branched or cyclic. The number of carbon atoms of the acyl group is preferably 2-10 and more preferably 2-6. If the acyl group is greater than C10, compatibility with the working medium may be reduced and phase separation may occur. [0031] When the groups represented by R and R are both alkyl groups, or when they are both acyl groups, the groups represented by R and R may be the same or different. When g is 2 or greater, the groups represented by R and R in the same molecule may be the same or different. [0032] When the group represented by R1 is a residue of a compound having 2-8 hydroxyl groups, the compound may be either linear or cyclic. [0033] Of the polyalkylene glycols represented by formula (1), at least one of R and R is preferably an alkyl group (more preferably a C1-4 alkyl group), with methyl being especially preferred from the viewpoint of compatibility with the working medium. [0034] From the viewpoint of thermal and chemical stability, both R1 and R3 are preferably alkyl groups (more preferably C1-4 alkyl groups), and most preferably both are methyl groups. [0035] From the viewpoint of facilitating production and lowering cost, one ofR!and R3 is an alkyl group (more preferably a C1-4 alkyl group) while the other is hydrogen, and most preferably one is methyl and the other is hydrogen. [0036] In formula (1), R represents a C2-4 alkylene group, specific examples of alkylene groups including ethylene, propylene and butylene. Oxyalkylene groups as repeating units represented by OR 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. [0037] Among polyalkylene glycols represented by formula (1) there are preferred copolymers containing an oxyethylene group (EO) and an oxypropylene group (PO), from the viewpoint of the viscosity-temperature characteristic, in which case, from the viewpoint of the seizure load and the viscosity-temperatur characteristic, the proportion of oxyethylene groups of the total oxyethylene and oxypropylene groups (EO/(PO+EO)) is preferably in the range of 0.1-0.8 and more preferably in the range of 0.3-0.6. [0038] From the viewpoint of compatibility with the working medium, hygroscopicity and heat and oxidation stability, the value of EO/(PO+EO) is preferably in the range of 0-0.5, more preferably in the range of 0-0.2, and most preferably 0 (i.e. a propylene oxide homopolymer). [0039] The symbol "f" in formula (1) represents the number of repeating units of oxyalkylene groups OR2 (polymerization degree), and it is an integer of 1-80. Also, g is an integer of 1-8. For example, when R1 is an alkyl group or acyl group, g is 1. When R1 is a residue of a compound having 2-8 hydroxyl groups, g is the number of hydroxyl groups in the compound. [0040] There are no particular restrictions on the product of f and g (f x 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. [0041] The number-average molecular weight of the polyalkylene glycol represented by formula (1) is preferably 500-3000, more preferably 600-2000 and even more preferably 600-1500, and n is preferably a number such that the number-average molecular weight of the polyalkylene glycol satisfies the condition mentioned above. If the number-average molecular weight of the polyalkylene glycol is too low, the lubricity may be insufficient in the copresence of an unsaturated fluorinated hydrocarbon refrigerant. If the number-average molecular weight is too high, on the other hand, the compositional range exhibiting compatibility with unsaturated fluorinated hydrocarbon refrigerants under low temperature conditions will be narrowed, potentially resulting in poor refrigerant compressor lubrication or hindered evaporator heat exchange. The ratio of the weight-average molecular weight (Mw) and number-average molecular weight (Mn) (Mw/Mn) in the polyalkylene glycol represented by formula (1) is preferably no greater than 1.00-1.20. If Mw/Mn is greater than 1.20, the compatibility between the unsaturated fluorinated hydrocarbon refrigerant and refrigerating machine oil will tend to be insufficient. [0042] Preferred among the aforementioned polyalkylene glycols, from the viewpoint of economy and the effect described above, are polypropyleneglycol dimethyl ethers represented by the following formula (2) and polyethylenepolypropyleneglycol dimethyl ethers represented by the following formula (3), while preferred from the viewpoint of economy are polypropyleneglycol monobutyl ethers represented by the following formula (4), polypropyleneglycol monomethyl ethers represented by the following formula (5), polyethylenepolypropyleneglycol monomethyl ethers represented by the following formula (6), polyethylenepolypropyleneglycol monobutyl ethers represented by the following formula (7), and polypropyleneglycol diacetates represented by the following formula (8). CH3O-(C3H6O)h-CH3 (2) (In the formula, h represents an integer of 6-80.) CH30-(C2H40)i-(C3H60)j-CH3 (3) (In the formula, i and j are each 1 or greater, and are numbers such that the total of i and j is 6-80.) C4H9O-(C3H6O)k-H (4) (In the formula, k represents an integer of 6-80.) CH30-(C3H60)I-H (5) (In the formula, 1 represents an integer of 6-80.) CH30-(C2H40)m-(C3H60)n-H (6) (In the formula, m and n are each 1 or greater, and are numbers such that the total of m and n is 6-80.) C4H90-(C2H40)m-(C3H60)n-H(7) (In the formula, m and n are each 1 or greater, and are numbers such that the total of m and n is 6-80.) CH3COO-(C3H60)i-COCH3 (8) (In the formula, 1 represents an integer of 6-80.) [0043] According to the first to seventh embodiments, the polyalkylene glycol used may be a polyalkyleneglycol derivative having at least one structural unit represented by formula (9). [Chemical Formula 1] (Formula Removed) [In formula (9), R4-R7 may be the same or different, and each represents hydrogen, a C1-10 monovalent hydrocarbon group or a group of the following formula (13): [Chemical Formula 2] (Formula Removed) (In formula (10), R and R may be the same or different and each represents hydrogen, a C1-10 monovalent hydrocarbon group or a C2-20 alkoxyalkyl group, R10 represents C2-5 alkylene, 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 R13 represents a C1-10 monovalent hydrocarbon group), and at least one of R8-Rn is a group represented by formula (13).] [0044] In formula (9), R4-R7 each represent hydrogen, a C1-10 monovalent hydrocarbon group or a group represented by formula (10), and specific C1-10 monovalent hydrocarbon groups include C1-10 straight-chain or branched alkyl, C2-10 straight-chain or branched alkenyl, C5-10 cycloalkyl or alkylcycloalkyl, C6-10 aryl or alkylaryl and C7-10 arylalkyl groups. Preferred among these monovalent hydrocarbon groups are