Ester for refrigerator oil, base oil for refrigerator oil, refrigerator oil, and working fluid composition

Abstract

An ester for refrigerator oil, which contains a first ester that is an ester of a polyhydric alcohol and a C6-9 fatty acid, a second ester that is an ester of pentaerythritol and a fatty acid, and a third ester that is an ester of pentaerythritol, a dicarboxylic acid and a fatty acid, the fatty acid constituting the second ester and the fatty acid constituting the third ester are both mixed fatty acids of at least one selected from the group consisting of branched butyric acid, branched pentanoic acid, and linear pentanoic acid, and any one selected from branched caprylic acid and branched nonanoic acid.

Description

Technical Field

[0001] The present invention relates to an ester for refrigeration oil, a base oil for refrigeration oil, refrigeration oil and a working fluid composition. Background Art

[0002] Refrigerator, car air conditioner, room air conditioner, vending machine and other freezers are equipped with a compressor for circulating refrigerant in a refrigeration cycle. In addition, the compressor is filled with refrigeration oil for lubricating sliding parts.

[0003] Refrigeration oil contains a base oil and additives. The base oil in the refrigeration oil is appropriately selected based on properties such as compatibility with the refrigerant. For example, Patent Document 1 discloses a tetraester of pentaerythritol for use in refrigeration oils, etc., which has excellent compatibility with difluoromethane refrigerants.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2012 / 026212 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] If the refrigerant dissolves in the refrigeration oil, the kinetic viscosity of the refrigeration oil (the refrigerant dissolving viscosity) decreases, causing problems such as poor lubrication of sliding parts, sintering, and increased wear. Alternatively, increasing the kinetic viscosity of the refrigeration oil itself (the kinetic viscosity of the refrigeration oil when the refrigerant is not dissolved) can be considered. However, if the kinetic viscosity of the refrigeration oil itself is too high, the refrigeration oil is likely to remain in the evaporator or evaporation tube within the refrigeration cycle, or the start-up performance of the refrigerator is reduced, which may worsen the efficiency of the refrigerator. Therefore, it is necessary to increase the refrigerant dissolving viscosity of the refrigeration oil without excessively increasing the kinetic viscosity of the refrigeration oil itself.

[0009] Therefore, one aspect of the present invention is to provide a refrigeration oil ester capable of increasing the refrigerant solution viscosity of difluoromethane when dissolved in refrigeration oil without excessively increasing the kinematic viscosity of the refrigeration oil itself, a refrigeration oil base oil, and a refrigeration oil.

[0010] Solutions for solving problems

[0011] The present inventors have found that a mixed ester of two polyol esters and a complex ester is suitable as a refrigeration oil ester. This refrigeration oil ester can increase the refrigerant solution viscosity when difluoromethane is dissolved in the refrigeration oil without increasing the kinematic viscosity of the refrigeration oil itself.

[0012] The present invention includes the following aspects.

[0013] [1] An ester for refrigeration oil, comprising a first ester being an ester of a polyol and a fatty acid having 6 to 9 carbon atoms, a second ester being an ester of pentaerythritol and a fatty acid, and a third ester being an ester of pentaerythritol, a dicarboxylic acid, and a fatty acid, wherein the fatty acid constituting the second ester and the fatty acid constituting the third ester are both mixed fatty acids selected from at least one of the group consisting of branched butyric acid, branched valeric acid, and linear valeric acid, and either branched octanoic acid or branched nonanoic acid.

[0014] [2] The ester for refrigerating machine oil according to [1], wherein the content of the first ester is 30% by mass or more and 90% by mass or less, the content of the second ester is 5% by mass or more and 50% by mass or less, and the content of the third ester is 2% by mass or more and 40% by mass or less, based on the total amount of the ester for refrigerating machine oil.

[0015] [3] A base oil for refrigeration oil, comprising a first ester which is an ester of a polyol and a fatty acid having 6 to 9 carbon atoms, a second ester which is an ester of pentaerythritol and a fatty acid, and a third ester which is an ester of pentaerythritol, a dicarboxylic acid, and a fatty acid, wherein the fatty acid constituting the second ester and the fatty acid constituting the third ester are both mixed fatty acids selected from at least one of the group consisting of branched butyric acid, branched valeric acid, and straight-chain valeric acid, and either branched octanoic acid or branched nonanoic acid.

[0016] [4] The refrigeration oil base oil according to [3], wherein the content of the first ester is 30% by mass or more and 90% by mass or less, the content of the second ester is 5% by mass or more and 50% by mass or less, and the content of the third ester is 2% by mass or more and 40% by mass or less, based on the total amount of the refrigeration oil base oil.

[0017] [5] A refrigeration oil comprising the refrigeration oil base oil according to [3] or [4].

[0018] [6] The refrigeration oil according to [5], which is used together with a refrigerant containing difluoromethane.

[0019] [7] A working fluid composition comprising the refrigeration oil according to [5] or [6] and a refrigerant.

[0020] [8] The working fluid composition according to [7], wherein the refrigerant contains difluoromethane.

[0021] Effects of the Invention

[0022] According to one aspect of the present invention, a refrigeration oil ester, a refrigeration oil base oil, and a refrigeration oil can be provided. The refrigeration oil ester can increase the refrigerant viscosity when difluoromethane is dissolved in the refrigeration oil without excessively increasing the kinematic viscosity of the refrigeration oil itself. According to another aspect of the present invention, a refrigeration oil ester, a refrigeration oil base oil, and a refrigeration oil having excellent compatibility with difluoromethane can be provided. DETAILED DESCRIPTION

[0023] One embodiment of the present invention is a refrigeration oil ester comprising a first ester of a polyol and a fatty acid having 6 to 9 carbon atoms, a second ester of an ester of pentaerythritol and a fatty acid, and a third ester of an ester of pentaerythritol, a dicarboxylic acid, and a fatty acid.

[0024] The first ester is represented by the following formula (1).

[0025]

[0026] In the formula, PO represents the residue after removing H atoms from m -OH groups in the polyol, R 1 represents a residue obtained by removing the -OH group from the -COOH group of a fatty acid having 6 to 9 carbon atoms, and m represents an integer greater than 2. 1 They can be the same as or different from each other.

[0027] The polyol constituting the first ester may be, for example, a polyol having 2 to 6 hydroxyl groups. That is, m in formula (1) may be an integer from 2 to 6. The number of carbon atoms in the polyol may be, for example, 4 or more, or 5 or more, or 12 or less, or 10 or less.

[0028] The polyol may be, for example, a hindered alcohol such as neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, di-(trimethylolpropane), tri-(trimethylolpropane), pentaerythritol, or dipentaerythritol. Neopentyl glycol or pentaerythritol is preferred, and pentaerythritol is more preferred, because they have particularly excellent compatibility with difluoromethane.

[0029] The ester for refrigerating machine oil may contain one first ester, two first esters, or three or more first esters. When the ester for refrigerating machine oil contains one first ester, the polyol constituting the first ester is preferably pentaerythritol. When the ester for refrigerating machine oil contains two first esters, the polyol constituting one first ester is preferably neopentyl glycol, and the polyol constituting the other first ester is preferably pentaerythritol.

[0030] The fatty acid having 6 to 9 carbon atoms constituting the first ester may be a saturated fatty acid. The fatty acid may have 7 to 9 or 8 to 9 carbon atoms. Examples of such fatty acids include hexanoic acid, heptanoic acid, octanoic acid, and nonanoic acid. These fatty acids may be linear or branched, preferably branched, and more preferably having branches at the α and / or β positions. The fatty acid is preferably at least one selected from the group consisting of 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid, more preferably at least one selected from the group consisting of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.

[0031] The second ester is an ester of pentaerythritol and a fatty acid, wherein the fatty acid is a mixed fatty acid of at least one selected from the group consisting of branched butyric acid, branched valeric acid, and linear valeric acid, and either branched octanoic acid or branched nonanoic acid. The second ester is represented by the following formula (2).

[0032]

[0033] Wherein, PE represents the residue after removing H atoms from the four -OH groups in pentaerythritol, R 2 represents a residue after removing the -OH group from the -COOH group in branched butyric acid (also referred to as an iC4 acid residue), a residue after removing the -OH group from the -COOH group in branched valeric acid (also referred to as an iC5 acid residue), a residue after removing the -OH group from the -COOH group in straight-chain valeric acid (also referred to as an nC5 acid residue), a residue after removing the -OH group from the -COOH group in branched octanoic acid (also referred to as an iC8 acid residue), or a residue after removing the -OH group from the -COOH group in branched nonanoic acid (also referred to as an iC9 acid residue). 2 At least one of R is an iC4 acid residue, an iC5 acid residue or an nC5 acid residue, and R 2 At least one of them is an iC8 acid residue or an iC9 acid residue.

[0034] The branched butyric acid constituting the second ester is preferably 2-methylpropionic acid. The branched valeric acid constituting the second ester is preferably 2-methylbutyric acid. The branched octanoic acid constituting the second ester is preferably 2-ethylhexanoic acid. The branched nonanoic acid constituting the second ester is preferably 3,5,5-trimethylhexanoic acid.

[0035] Preferred R 2 At least one of them is an iC4 acid residue, R 2 At least one of them is a C8 acid residue, more preferably R 2 are all iC4 acid residues or iC8 acid residues (wherein, R 2 At least one of them is an iC4 acid residue, R 2At least one of the residues is an iC8 acid residue. In this case, the molar ratio of the iC4 acid residue / iC8 acid residue may be 50 / 50 or more, 60 / 40 or more, 70 / 30 or more, or 75 / 25 or more, and may be 95 / 5 or less, 90 / 10 or less, or 85 / 15 or less.

[0036] The third ester is an ester of pentaerythritol, a dicarboxylic acid, and a fatty acid, wherein the fatty acid is an ester (complex ester) of a mixed fatty acid of at least one selected from the group consisting of branched butyric acid, branched valeric acid, and linear valeric acid, and either branched octanoic acid or branched nonanoic acid. The third ester is represented by the following formula (3).

[0037]

[0038] In the formula, PE represents the residue after removing H atoms from the four -OH groups in pentaerythritol, DCA represents the residue after removing -OH groups from the two -COOH groups in dicarboxylic acid, and R 3 represents the residue after removing the -OH group from the -COOH group in branched butyric acid (iC4 acid residue), the residue after removing the -OH group from the -COOH group in branched valeric acid (also referred to as iC5 acid residue), the residue after removing the -OH group from the -COOH group in linear valeric acid (also referred to as nC5 acid residue), the residue after removing the -OH group from the -COOH group in branched octanoic acid (iC8 acid residue), or the residue after removing the -OH group from the -COOH group in branched nonanoic acid (iC9 acid residue). 3 At least one of R is an iC4 acid residue, an iC5 acid residue or an nC5 acid residue, 2 At least one of them is an iC8 acid residue or an iC9 acid residue.

[0039] Preferred R 3 At least one of them is an iC4 acid residue, R 3 At least one of R 3 are all iC4 acid residues, iC8 acid residues or iC9 acid residues (wherein, R 3 At least one of them is an iC4 acid residue, R 3 At least one of which is an iC8 acid residue or an iC9 acid residue), and more preferably R 3 are all iC4 acid residues or iC8 acid residues (wherein, R 3 At least one of them is an iC4 acid residue, R 3In this case, the molar ratio of iC4 acid residues / iC8 acid residues, or the molar ratio of iC4 acid residues / iC9 acid residues may be 50 / 50 or more, 60 / 40 or more, 70 / 30 or more, 75 / 25 or more, 84 / 16 or more, or 86 / 14 or more, and may be 95 / 5 or less, 90 / 10 or less, or 85 / 15 or less.

[0040] The dicarboxylic acid constituting the third ester may be a dibasic aliphatic carboxylic acid. The dicarboxylic acid may be linear or branched. The dicarboxylic acid may have 4 or more carbon atoms, or 6 or more carbon atoms, or 12 or less carbon atoms, or 10 or less carbon atoms. Examples of the dicarboxylic acid include adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and phthalic acid. The dicarboxylic acid is preferably adipic acid.

[0041] The branched butyric acid constituting the third ester is preferably 2-methylpropionic acid. The branched octanoic acid constituting the third ester is preferably 2-ethylhexanoic acid. The branched nonanoic acid constituting the third ester is preferably 3,5,5-trimethylhexanoic acid.

[0042] In one embodiment, the fatty acid having 6 to 9 carbon atoms constituting the first ester may be a mixture of two or more fatty acids, for example, a mixture of a fatty acid having 5 to 8 carbon atoms and a fatty acid having 9 carbon atoms, preferably a mixture of a fatty acid having 8 carbon atoms and a fatty acid having 9 carbon atoms. The molar ratio of the content of the fatty acid having 5 to 8 carbon atoms (preferably a fatty acid having 8 carbon atoms) to the content of the fatty acid having 9 carbon atoms (the content of the fatty acid having 5 to 8 carbon atoms (preferably a fatty acid having 8 carbon atoms) / the content of the fatty acid having 9 carbon atoms) may be 10 / 90 or more, 40 / 60 or more, 55 / 45 or more, 60 / 40 or more, or 75 / 25 or more, and may be 95 / 5 or less, 90 / 10 or less, 85 / 15 or less, or 80 / 20 or less.

[0043] In one embodiment, the molar ratio (iC4 acid / iC8 acid ratio) of the branched butyric acid (preferably 2-methylpropionic acid) / branched octanoic acid (preferably 2-ethylhexanoic acid) in the fatty acid having 6 to 9 carbon atoms constituting the first ester and the fatty acid constituting the second ester may be 5 / 95 or more, 10 / 90 or more, or 20 / 80 or more, and may be 95 / 5 or less, 60 / 40 or less, 50 / 50 or less, 40 / 60 or less, or 35 / 65 or less.

[0044] In the mixture of the first ester and the second ester, the molar ratio of branched butyric acid (preferably 2-methylpropionic acid) / branched octanoic acid (preferably 2-ethylhexanoic acid) in the fatty acids constituting the pentaerythritol tetraester (the iC4 acid / iC8 acid ratio in the fatty acids constituting the pentaerythritol tetraester) may be 5 / 95 or more, 10 / 90 or more, or 20 / 80 or more, and may be 95 / 5 or less, 60 / 40 or less, 50 / 50 or less, 40 / 60 or less, 35 / 65 or less, or 34 / 66 or less.

[0045] In one embodiment, the molar ratio of the branched butyric acid (preferably 2-methylpropionic acid) / branched nonanoic acid (preferably 3,5,5-trimethylhexanoic acid) in the fatty acid having 6 to 9 carbon atoms constituting the first ester and the fatty acid constituting the second ester (iC4 acid / iC9 acid ratio) can be 20 / 80 or more, 50 / 50 or more, 80 / 20 or more, or 90 / 10 or more, and can be 100 / 0 or less, 99 / 1 or less, or 95 / 5 or less.

[0046] In the mixture of the first ester and the second ester, the molar ratio of branched butyric acid (preferably 2-methylpropionic acid) / branched nonanoic acid (preferably 3,5,5-trimethylhexanoic acid) in the fatty acids constituting the pentaerythritol tetraester (the iC4 acid / iC9 acid ratio in the fatty acids constituting the pentaerythritol tetraester) may be 20 / 80 or more, 50 / 50 or more, 80 / 20 or more, 86 / 14 or more, or 90 / 10 or more, and may be 100 / 0 or less, 99 / 1 or less, or 95 / 5 or less.

[0047] In one embodiment, the kinematic viscosity of the first ester at 40°C can be lower than that of the second ester at 40°C. Furthermore, the first ester's refrigerant compatibility region on the low-temperature side can be narrower than that of the second ester. For example, the maximum temperature of the two-layer separation on the low-temperature side when the first ester is mixed with difluoromethane can be higher than that of the second ester. Selecting such a first ester tends to facilitate maintaining a balance between the refrigerant's melt viscosity and the two-layer separation temperature without significantly thickening the refrigeration oil.

[0048] The iC4 acid / iC8 acid ratio and the iC4 acid / iC9 acid ratio were measured by the methods described in the Examples. Furthermore, the molar ratio of iC4 acid residues / iC8 acid residues and the molar ratio of iC4 acid residues / iC9 acid residues in the third ester (the complex ester (octaester) represented by formula (3)) can also be measured similarly using the calibration curves described in the Examples.

[0049] The content of the first ester, based on the total amount of esters for the refrigerating machine oil, may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more, and may be 93% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less. The content of the second ester, based on the total amount of esters for the refrigerating machine oil, may be 5% by mass or more, 10% by mass or more, or 20% by mass or less, and may be 68% by mass or less, 50% by mass or less, 40% by mass or less, or 30% by mass or less. The content of the third ester, based on the total amount of esters for the refrigerating machine oil, may be 2% by mass or more, 5% by mass or more, or 10% by mass or more, and may be 65% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less. Furthermore, the total content of the second ester and the third ester may be 7% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total amount of the esters for refrigeration oil.

[0050] The kinematic viscosity of the first ester at 40° C. may be, for example, 5 mm 2 / s or above, can be 100mm 2 / s or less, can be 20mm 2 / s or more, 30mm 2 / s or above, or 40mm 2 / s or above, can be 80mm 2 / s or less, 60mm 2 / s or less, or 50mm 2 The kinematic viscosity of the first ester at 100°C may be 1 mm 2 / s or more, 3mm 2 / s or above, or 5mm 2 / s or above, can be 20mm 2 / s or less, 10mm 2 / s or less, or 8mm 2 The viscosity index of the first ester may be 50 or more, 60 or more, or 70 or more, or 120 or less, 110 or less, or 100 or less. The kinematic viscosity and viscosity index in this specification refer to those measured in accordance with JIS K2283:2000.

[0051] The acid value of the first ester may be 0.1 mgKOH / g or less, or 0.05 mgKOH / g or less. The hydroxyl value of the first ester may be 15 mgKOH / g or less, 10 mgKOH / g or less, or 5 mgKOH / g or less. The pour point of the first ester may be -20°C or less, or -40°C or less. The acid value in this specification refers to the acid value measured in accordance with JIS K2501:2003. The hydroxyl value in this specification refers to the hydroxyl value measured in accordance with JIS K0070:1992. The pour point in this specification refers to the pour point measured in accordance with JIS K2269:1987.

[0052] The kinematic viscosity of ester for refrigerator oil at 40°C can be 20 mm 2 / s or more, 30mm 2 / s or above, or 40mm 2 / s or above, can be 200mm 2 / s or less, 100mm 2 / s or less, or 80mm 2 The kinematic viscosity of the ester for refrigeration oil at 100°C can be 1 mm 2 / s or more, 3mm 2 / s or above, or 5mm 2 / s or above, can be 30mm 2 / s or less, 20mm 2 / s or less, or 10mm 2 The viscosity index of the ester for refrigerating machine oil may be 50 or more, 60 or more, or 70 or more, and may be 120 or less, 110 or less, or 100 or less.

[0053] The refrigeration oil esters described above are suitable for use as refrigeration oil base oils. Therefore, the term "refrigeration oil ester" in the above description can be replaced with "refrigeration oil base oil." That is, another embodiment of the present invention is a refrigeration oil base oil comprising the first ester, the second ester, and the third ester described above.

[0054] Another embodiment of the present invention is a refrigeration oil containing the above-mentioned refrigeration oil base oil (refrigeration oil ester). The content of the refrigeration oil base oil (refrigeration oil ester) can be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of the refrigeration oil.

[0055] Refrigerator oils may also contain other base oils. Examples of other base oils include mineral oils and synthetic oils. Mineral oils may include paraffinic mineral oils, cycloparaffinic mineral oils, and the like. Synthetic oils include synthetic hydrocarbon oils such as polyalphaolefins and alkylbenzenes, and oxygenated oils such as esters other than the above-mentioned refrigeration oil esters, polyvinyl ethers, and polyalkylene glycols.

[0056] The refrigeration oil may further contain additives. Examples of additives include acid scavengers, oxygen scavengers, antioxidants, extreme pressure agents, oiliness agents, defoamers, metal deactivators, antiwear agents, viscosity index improvers, pour point depressants, and detergent dispersants. The content of the additives may be 0.1% or more by mass, or 1% or more by mass, and may be 10% or less by mass, or 5% or less by mass, based on the total amount of the refrigeration oil.

[0057] The kinematic viscosity of refrigeration oil at 40°C can be 20 mm 2 / s or more, 30mm 2 / s or above, or 40mm 2 / s or above, can be 200mm 2 / s or less, 100mm 2 / s or less, or 80mm 2 The kinematic viscosity of the refrigeration oil at 100°C can be 1 mm 2 / s or more, 3mm 2 / s or above, or 5mm 2 / s or above, can be 30mm 2 / s or less, 20mm 2 / s or less, or 10mm 2 The viscosity index of the refrigeration oil may be 50 or more, 60 or more, or 70 or more, and may be 120 or less, 110 or less, or 100 or less.

[0058] Refrigerator oil can exist in the form of a refrigerator working fluid composition mixed with a refrigerant in a refrigerator. That is, in one embodiment, refrigerator oil is used together with a refrigerant. In addition, another embodiment of the present invention is a working fluid composition containing the above-mentioned refrigerator oil and a refrigerant.

[0059] The refrigerator oil of this embodiment contains the above-mentioned refrigerator base oil (refrigerator ester), which has excellent compatibility with difluoromethane and refrigerant solubility viscosity characteristics. Therefore, the refrigerant is preferably a refrigerant containing difluoromethane (R32). The difluoromethane content can be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, based on the total amount of the refrigerant.

[0060] The refrigerant may consist solely of difluoromethane, or may contain other refrigerants in addition to difluoromethane. Examples of other refrigerants include saturated fluorinated hydrocarbons (also known as HFCs) other than difluoromethane, unsaturated fluorinated hydrocarbons (also known as HFOs), hydrocarbons, fluorinated ethers, bis(trifluoromethyl)sulfide, trifluoroiodomethane, ammonia (R717), and carbon dioxide (R744).

[0061] The content of the refrigeration oil in the working fluid composition may be 1 part by mass or more or 2 parts by mass or more, and may be 500 parts by mass or less or 400 parts by mass or less, relative to 100 parts by mass of the refrigerant.

[0062] Example

[0063] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

[0064] Using the following first ester, second ester, and third ester, refrigerating machine oil esters (refrigerating machine oil base oils) having the compositions shown in Table 1 were prepared.

[0065] (First Ester)

[0066] 1A: Diester of neopentyl glycol and 2-ethylhexanoic acid (40°C kinematic viscosity: 7.4 mm 2 / s, 100℃ kinematic viscosity: 2.0mm 2 / s, viscosity index: 52, acid value: less than 0.01mgKOH / g, hydroxyl value: less than 2mgKOH / g, pour point: less than -45℃)

[0067] 1B: Tetraester of pentaerythritol and 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid (molar ratio: 70 / 30) (40°C kinematic viscosity: 56.5 mm 2 / s, 100℃ kinematic viscosity: 7.43mm 2 / s, viscosity index: 90, acid value: less than 0.01mgKOH / g, hydroxyl value: less than 2mgKOH / g, pour point: less than -45℃)

[0068] 1C: Tetraester of pentaerythritol and 2-ethylhexanoic acid / 3,5,5-trimethylhexanoic acid (molar ratio: 85 / 15) (40°C kinematic viscosity: 48.5 mm 2 / s, kinematic viscosity at 100℃ 6.67mm 2 / s, viscosity index: 86, acid value less than 0.01mgKOH / g, pour point: less than -45℃)

[0069] (Second ester)

[0070] 2A: Tetraester of pentaerythritol and 2-methylpropionic acid / 2-ethylhexanoic acid (molar ratio: 76 / 24)

[0071] 2B: Tetraester of pentaerythritol and 2-methylpropionic acid / 2-ethylhexanoic acid (molar ratio: 87 / 13)

[0072] 2C: Tetraester of pentaerythritol and 2-methylpropionic acid / 2-ethylhexanoic acid (molar ratio: 82 / 18)

[0073] 2D: Tetraester of pentaerythritol and 2-methylpropionic acid / 2-ethylhexanoic acid (molar ratio: 88 / 12)

[0074] (Third ester)

[0075] 3A: complex ester represented by the following formula (3a) (R 3a The molar ratio of iC4 acid residue / iC8 acid residue in the group represented by: 76 / 24)

[0076]

[0077] PE represents the residue after removing H atoms from the four -OH groups in pentaerythritol, AA represents the residue after removing -OH groups from the two -COOH groups in adipic acid, R 3a It represents a residue obtained by removing the -OH group from the -COOH group in 2-methylpropionic acid (iC4 acid residue), or a residue obtained by removing the -OH group from the -COOH group in 2-ethylhexanoic acid (iC8 acid residue).

[0078] 3B: Complex ester represented by the above formula (3a) (R 3a The molar ratio of iC4 acid residue / iC8 acid residue in the group represented by: 87 / 13)

[0079] 3C: Complex ester represented by the above formula (3a) (R 3a The molar ratio of iC4 acid residue / iC8 acid residue in the group represented by: 82 / 18)

[0080] 3D: complex ester represented by the above formula (3a) (R 3a The molar ratio of iC4 acid residue / iC8 acid residue in the group represented by: 88 / 12)

[0081] (Measurement of the iC4 Acid / iC8 Acid Ratio and the iC4 Acid / iC9 Acid Ratio in Fatty Acids Constituting Pentaerythritol Tetraester)

[0082] Use has utilized the gas chromatography of general nonpolar column, in above-mentioned first ester, second ester, 3rd ester and their mixed ester sample, measure the iC4 acid / iC8 acid ratio and iC4 acid / iC9 acid ratio (mol ratio) in the fatty acid that constitutes pentaerythritol tetraester.During this mensuration, as standard sample, use the iC4 acid tetraester of pentaerythritol, the iC8 acid tetraester of pentaerythritol and the iC9 acid tetraester of pentaerythritol, use the area of ​​each fatty acid that is obtained by its typical curve, mass and the relative sensitivity of mole basis, correction coefficient and other necessary parameters.In table 1, with " iC4 acid / iC8 acid ratio " and " iC4 acid / iC9 acid ratio " respectively represent result.

[0083] (Determination of kinematic viscosity and viscosity index)

[0084] The kinematic viscosity at 40° C., the kinematic viscosity at 80° C., the kinematic viscosity at 100° C., and the viscosity index of each ester for refrigerating machine oil (base oil for refrigerating machine oil) were measured in accordance with JIS K2283: 2000. The results are shown in Table 1.

[0085] (Determination of refrigerant melt viscosity, refrigerant melt viscosity / kinematic viscosity ratio, and viscosity maintenance rate)

[0086] 100 g of each refrigeration oil ester (refrigeration oil base oil) was added to a 400 ml pressure-resistant container equipped with a vibration viscometer. After vacuum degassing the container, R32 was added as a refrigerant to prepare a working fluid composition. The refrigerant pressure and the temperature of the pressure-resistant container were adjusted to achieve a temperature of 80°C and an absolute pressure of 3.4 MPa. The absolute viscosity and volume of the working fluid composition at this time were measured. The refrigerant solution viscosity (mm) was calculated from parameters such as the refrigerant gas density, the amount of oil and refrigerant filled, and the mass of the working fluid. 2 The results are shown in Table 1.

[0087] The refrigerant dissolution viscosity when the first ester 1C was used alone as the base oil was also evaluated in the same manner and the result was 2.7 mm 2 / s.

[0088] In addition, the refrigerant solution viscosity (mm) of each ester for refrigerator oil (refrigerator oil base oil) was calculated. 2 / s) relative to the kinematic viscosity at 40°C (mm 2 / s) ratio (refrigerant solution viscosity / kinematic viscosity at 40°C), and refrigerant solution viscosity (mm 2 / s) relative to the kinematic viscosity at 100°C (mm 2 The results are shown in Table 1. A larger ratio means that the ester for refrigerator oil (refrigerator oil base oil) can increase the refrigerant solution viscosity without increasing the kinematic viscosity of the refrigerator oil itself too much.

[0089] In addition, the viscosity maintenance rate at 80°C of each ester for refrigerator oil (refrigerator oil base oil) before and after the refrigerant dissolution (= the refrigerant dissolution viscosity (mm) at 80°C and 3.4 MPa of the working fluid after the refrigerant dissolves) was calculated. 2 / s) / Kinematic viscosity of each ester for refrigeration oil at 80°C and 1 atm (mm 2 / s)×100). The results are shown in Table 1. A larger viscosity maintenance rate means that the kinematic viscosity is easily maintained at a higher level even when the refrigerant is dissolved.

[0090] (Evaluation of refrigerant compatibility)

[0091] In accordance with the "Compatibility Test Method with Refrigerants" of JIS K2211:2009 "Refrigerator Oils," a mixture of refrigerant (R32) and various refrigeration oil esters (refrigeration oil base oils) (the proportion of refrigeration oil esters (refrigeration oil base oils) in the mixture (oil ratio): 5 to 40% by mass) was slowly cooled from 20°C to -60°C, and the temperature at which the mixture separated into layers or became cloudy was evaluated as the two-layer separation temperature (°C). The maximum value of the two-layer separation temperature within this oil ratio range is shown in Table 1. In addition, the oil ratio at which the two-layer separation temperature reached its maximum value is shown in the parentheses of "Maximum value of the two-layer separation temperature (°C)" in Table 1.

[0092] The refrigerant compatibility when the first ester 1B and the first ester 1C were used alone as base oils was similarly evaluated. As a result, both separated into two layers at 20° C. or lower.

[0093] [Table 1]

[0094]

Claims

1. An ester for refrigeration oil, comprising: As a first ester of an ester of a polyol and a fatty acid having 6 to 9 carbon atoms, as a second ester of an ester of pentaerythritol and a fatty acid, and As a tertiary ester of an ester of pentaerythritol with a dicarboxylic acid and a fatty acid, The fatty acid constituting the second ester and the fatty acid constituting the third ester are both mixed fatty acids of at least one selected from the group consisting of branched butyric acid, branched valeric acid, and linear valeric acid, and either branched octanoic acid or branched nonanoic acid.

2. The ester for refrigeration oil according to claim 1, wherein Based on the total amount of the ester for refrigeration oil, the content of the first ester is 30% by mass or more and 90% by mass or less, the content of the second ester is 5% by mass or more and 50% by mass or less, and the content of the third ester is 2% by mass or more and 40% by mass or less.

3. A base oil for refrigeration oil, comprising: As a first ester of an ester of a polyol and a fatty acid having 6 to 9 carbon atoms, as a second ester of an ester of pentaerythritol and a fatty acid, and As a tertiary ester of an ester of pentaerythritol with a dicarboxylic acid and a fatty acid, The fatty acid constituting the second ester and the fatty acid constituting the third ester are both mixed fatty acids of at least one selected from the group consisting of branched butyric acid, branched valeric acid, and linear valeric acid, and either branched octanoic acid or branched nonanoic acid.

4. The refrigeration oil base oil according to claim 3, wherein Based on the total amount of the refrigeration oil base oil, the content of the first ester is 30% by mass or more and 90% by mass or less, the content of the second ester is 5% by mass or more and 50% by mass or less, and the content of the third ester is 2% by mass or more and 40% by mass or less. 5 . A refrigerating machine oil comprising the refrigerating machine oil base oil according to claim 3 . The refrigerating machine oil according to claim 5 , which is used together with a refrigerant containing difluoromethane.

7. A working fluid composition comprising the refrigeration oil according to claim 5 and a refrigerant.

8. The working fluid composition according to claim 7, wherein: The refrigerant includes difluoromethane.

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