Base oil for refrigerator oil, refrigerator oil, and working fluid composition

Abstract

A base oil for refrigerator oil, which contains: a hexaester of dipentaerythritol and a fatty acid; and at least one ester selected from the group consisting of a diester of neopentyl glycol and a fatty acid, and a tetraester of pentaerythritol and a fatty acid including a C4-6 fatty acid.

Description

Technical Field

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

[0002] Refrigerators, car air conditioners, room air conditioners, vending machines, and other refrigerators are equipped with compressors that circulate refrigerant within the refrigeration cycle. These compressors are filled with refrigeration oil to lubricate sliding components. This refrigeration oil contains a base oil as its main component. The appropriate base oil is selected based on the required properties.

[0003] As a base oil, for example, polyol esters are known. For example, Patent Document 1 discloses a refrigeration oil containing an ester of dipentaerythritol and a fatty acid, wherein the proportion of 2-methylvaleric acid in the fatty acid is 20 mol % or more.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-206059 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] When using an ester of dipentaerythritol, as disclosed in Patent Document 1, the ester is a hexaester and has a relatively large molecular weight. Therefore, while it is effective in maintaining a high kinematic viscosity and / or refrigerant dissolution viscosity of the base oil (refrigeration oil) at high temperatures (e.g., 100°C), the kinematic viscosity and / or refrigerant dissolution viscosity at low temperatures (e.g., -20°C) tend to be higher than necessary. Therefore, it is considered to adjust the viscosity of the base oil (refrigeration oil) to an appropriate level by mixing the hexaester of dipentaerythritol with a polyol ester having a lower viscosity than the hexaester.

[0009] However, studies by the present inventors have revealed that it is not always easy to maintain the high-temperature side kinematic viscosity while suppressing the low-temperature side refrigerant solution viscosity to a low level, depending on the type of polyol ester mixed with the hexaester.

[0010] Therefore, one aspect of the present invention is to provide a refrigeration oil base oil, refrigeration oil, and working fluid composition that can maintain a high-temperature side kinematic viscosity while suppressing a low-temperature side refrigerant dissolution viscosity.

[0011] Solutions for solving problems

[0012] The present inventors have conducted research and found that a mixed base oil obtained by mixing at least one selected from the group consisting of diesters of neopentyl glycol and tetraesters of pentaerythritol and specific fatty acids with a hexaester can maintain the kinematic viscosity on the high temperature side while suppressing the refrigerant solution viscosity on the low temperature side.

[0013] The present invention includes the following aspects.

[0014] [1] A base oil for refrigeration oil, comprising: a hexaester of dipentaerythritol and a fatty acid; and at least one ester selected from the group consisting of a diester of neopentyl glycol and a fatty acid, and a tetraester of pentaerythritol and a fatty acid containing a fatty acid having 4 to 6 carbon atoms.

[0015] [2] The base oil according to [1], wherein the kinematic viscosity of the base oil at 100°C is 8.5 mm 2 / s or above.

[0016] [3] The base oil according to [1] or [2], comprising the hexaester, the diester, and the tetraester.

[0017] [4] A refrigeration oil containing the base oil according to any one of [1] to [3].

[0018] [5] A working fluid composition comprising the refrigeration oil described in [4] and a refrigerant.

[0019] Effects of the Invention

[0020] According to one aspect of the present invention, a refrigeration oil base oil, refrigeration oil, and working fluid composition can be provided that can maintain a high-temperature side kinematic viscosity while suppressing a low-temperature side refrigerant dissolution viscosity. DETAILED DESCRIPTION

[0021] One embodiment of the present invention is a refrigeration oil base oil containing: a hexaester of dipentaerythritol and a fatty acid (hereinafter also referred to as "ester (A)"), and at least one ester (hereinafter also referred to as "ester (B)") selected from the group consisting of a diester of neopentyl glycol and a fatty acid (hereinafter also referred to as "ester (B-1)"), and a tetraester of pentaerythritol and a fatty acid containing a fatty acid having 4 to 6 carbon atoms (hereinafter also referred to as "ester (B-2)").

[0022] The fatty acid constituting the ester (A) is preferably a saturated fatty acid, more preferably a saturated fatty acid having 4 to 9, 5 to 9, 6 to 9, 7 to 9, or 8 to 9 carbon atoms. The fatty acid may be linear or branched. The fatty acid preferably includes a fatty acid having a branch at the α-position and / or β-position. The fatty acid more preferably includes at least one selected from the group consisting of 2-methylpropionic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, pivalic acid, 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid. From the viewpoint of easily maintaining a higher kinematic viscosity at 100°C, it is further preferred to include at least one selected from the group consisting of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.

[0023] The fatty acid may be a mixed fatty acid of branched fatty acids. Examples of the mixed fatty acid include a mixed fatty acid of 2-methylpropionic acid and 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid, a mixed fatty acid of 2-methylbutanoic acid and 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid, a mixed fatty acid of 2-methylpentanoic acid and 2-ethylhexanoic acid or 3,5,5-trimethylhexanoic acid, and a mixed fatty acid of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.

[0024] The fatty acid may be a straight-chain fatty acid or a mixed fatty acid of a straight-chain fatty acid and a branched-chain fatty acid. Examples of the straight-chain fatty acid include n-butyric acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, and n-nonanoic acid. Examples of the mixed fatty acid of a straight-chain fatty acid and a branched-chain fatty acid include a mixed fatty acid of n-pentanoic acid and 2-methylbutanoic acid, a mixed fatty acid of n-pentanoic acid and 3,5,5-trimethylhexanoic acid, a mixed fatty acid of n-heptanoic acid and 3,5,5-trimethylhexanoic acid, and a mixed fatty acid of n-pentanoic acid, n-heptanoic acid, and 3,5,5-trimethylhexanoic acid.

[0025] The fatty acid constituting the ester (B-1) is preferably a saturated fatty acid, more preferably a saturated fatty acid having 4 to 9, 5 to 9, 6 to 9, 7 to 9, or 8 to 9 carbon atoms. The fatty acid may be linear or branched. From the perspective of further ensuring the amount of refrigerant dissolved at low temperatures and suppressing the refrigerant dissolution viscosity at low temperatures to a lower level, the fatty acid is preferably branched, more preferably selected from 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid, and even more preferably 3,5,5-trimethylhexanoic acid.

[0026] The fatty acid constituting the ester (B-2) includes a fatty acid having 4 to 6 carbon atoms (hereinafter also referred to as "C4-C6 acid"). The C4-C6 acid is preferably a saturated fatty acid, more preferably a saturated fatty acid having 4 to 5 or 4 carbon atoms. The C4-C6 acid may be linear or branched. The C4-C6 acid may be at least one selected from the group consisting of linear or branched butyric acid, linear or branched valeric acid, and linear or branched hexanoic acid, preferably includes at least one selected from the group consisting of branched butyric acid, branched valeric acid, and branched hexanoic acid, more preferably includes at least one selected from the group consisting of 2-methylpropionic acid, 2-methylbutyric acid, 3-methylbutyric acid, pivalic acid, and 2-methylvaleric acid, includes at least one selected from the group consisting of 2-methylpropionic acid and 2-methylbutyric acid, and further preferably includes 2-methylpropionic acid.

[0027] The fatty acid constituting the ester (B-2) may include other fatty acids in addition to C4-C6 acids. The other fatty acids are preferably fatty acids having 7 to 9 carbon atoms (hereinafter also referred to as "C7-C9 acids"). The C7-C9 acids are preferably saturated fatty acids, more preferably saturated fatty acids having 8 to 9 carbon atoms. The C7-C9 acids may be linear or branched. The C7-C9 acids are preferably branched, more preferably selected from 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid, and further preferably 3,5,5-trimethylhexanoic acid.

[0028] The fatty acid constituting the ester (B-2) may be a mixed fatty acid of a linear fatty acid and a branched fatty acid. Examples of such a mixed fatty acid include a mixed fatty acid of one or more selected from n-pentanoic acid and n-heptanoic acid and 3,5,5-trimethylhexanoic acid.

[0029] The molar ratio of C4-C6 acid to C7-C9 acid in the fatty acid constituting ester (B-2) (C4-C6 acid / C7-C9 acid) can be 10 / 90 or more, 20 / 80 or more, or 30 / 70 or more, and can be 90 / 10 or less, 80 / 20 or less, 70 / 30 or less, 60 / 40 or less, or 50 / 50 or less.

[0030] The ester (A) may contain an ester having 40 or more or 50 or more carbon atoms, but preferably contains an ester having 54 or more carbon atoms, or 60 or more and 64 or less carbon atoms, from the viewpoint of easily maintaining a high kinematic viscosity at 100°C. For example, in the case of a hexaester of dipentaerythritol and a fatty acid having 4 to 9 carbon atoms, the ester (A) has 34 to 64 carbon atoms.

[0031] Ester (B) may contain esters having 38 or less or 35 carbon atoms. However, from the perspective of increasing the amount of refrigerant dissolved at low temperatures and easily reducing the refrigerant dissolution viscosity at low temperatures, esters having 31 or less or 25 or more, or 18 or more or 20 or more carbon atoms are preferably contained. For example, in the case of a diester of neopentyl glycol and a fatty acid having 4 to 9 carbon atoms, ester (B-1) has 13 to 23 carbon atoms. Alternatively, in the case of a tetraester of pentaerythritol and a fatty acid having 4 to 9 carbon atoms, ester (B-2) has 21 to 41 carbon atoms.

[0032] The difference between the maximum carbon number (maximum carbon number) and the minimum carbon number (minimum carbon number) of the esters in the mixture of esters (A) and (B) is preferably 28 or more, 35 or more, 37 or more, or 41 or more, and preferably 46 or less or 44 or less.

[0033] The average carbon number of ester (A) may be 40 or more or 50 or more, preferably 54 or more or 60 or more, and may be 64 or less. The average carbon number of ester (B) may be 38 or less or 35 or less, preferably 31 or less or 25 or less, and preferably 18 or more or 20 or more. The average carbon number of the mixture of ester (A) and ester (B) contained in the base oil is preferably 35 or more, 38 or more, or 40 or more, and preferably 58 or less, 55 or less, 52 or less, 48 ​​or less, or 45 or less.

[0034] The value obtained by dividing the difference between the maximum and minimum carbon numbers in the mixture of esters (A) and (B) by the average carbon number is preferably 0.70 or more, 0.80 or more, 0.85 or more, or 0.90 or more, and preferably 1.50 or less, 1.20 or less, 1.00 or less, or 0.97 or less. It should be noted that this value represents the degree of molecular weight dispersion of the esters. Even with the same average carbon number, the molecular weight of the ester is zero in a single molecule, and the molecular weight increases as the maximum and minimum values ​​of the ester are greater. However, considering the balance between refrigerant compatibility, flash point, 100°C kinematic viscosity, and the effect of reducing the refrigerant solution viscosity, the above range is preferred.

[0035] The ratio (Mw / Mn) of the number average molecular weight (Mn) of the mixture of ester (A) and ester (B) to the weight average molecular weight (Mw) may be 1.01 or more, 1.05 or more, or 1.10 or more, and may be 1.5 or less, 1.4 or less, or 1.3 or less. Mw and Mn in this specification refer to the values ​​obtained by GPC analysis (polystyrene (standard sample) conversion values). Specifically, for example, tetrahydrofuran is used as a solvent, diluted to prepare a solution with a sample concentration of 1% by mass, and a GPC apparatus (e.g., ACQUITY APC UV RI system manufactured by Waters) is used. The flow rate of the solvent is set to 0.7 ml / min, the temperature is set to 40°C, a column capable of analyzing molecular weights of 100 to 10,000 is used, and analysis is performed using a refractive index detector. It should be noted that the relationship between the column retention time and the molecular weight is obtained using a polystyrene standard with a clear molecular weight, and after separately preparing a standard curve, the molecular weight is determined by the obtained retention time.

[0036] The contents of ester (A) and ester (B) (and further, ester (B-1) and ester (B-2)) in the base oil are appropriately adjusted depending on the desired kinematic viscosity of the base oil, etc. In one embodiment, the content of ester (A) in the base 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 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 base oil.

[0037] In one embodiment, the content of the ester (B) in the base 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 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 base oil.

[0038] In one embodiment, the content of the ester (B-1) in the base oil may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 20% by mass or more, and may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less, based on the total amount of the base oil.

[0039] In one embodiment, the content of the ester (B-2) in the base oil may be 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, or 50% by mass or more, and may be 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less, based on the total amount of the base oil.

[0040] Ester (B) may contain either ester (B-1) or ester (B-2), or both. From the perspective of lowering the refrigerant's melt viscosity, ester (B) preferably contains both ester (B-1) and ester (B-2). That is, from the perspective of lowering the refrigerant's melt viscosity, the base oil preferably contains ester (A), ester (B-1), and ester (B-2).

[0041] In one embodiment, when the base oil contains both ester (B-1) and ester (B-2), the content of ester (B-1) may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, or 9% by mass or more, and may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 15% by mass or less, based on the total amount of the base oil. In this case, the content of ester (B-2) 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 less, 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 base oil.

[0042] In one embodiment, the proportion of dipentaerythritol in the total amount of alcohols constituting ester (A) and ester (B) in the base oil may be 5 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more, and may be 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, or 30 mol% or less.

[0043] In one embodiment, the proportion of neopentyl glycol in the total amount of alcohols constituting ester (A) and ester (B) in the base oil may be 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, or 20 mol% or less, and may be 0 mol%, or may be 5 mol% or more, or 10 mol% or more.

[0044] In one embodiment, the proportion of pentaerythritol in the total amount of alcohols constituting ester (A) and ester (B) in the base oil may be 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, or 30 mol% or less, may be 0 mol%, or may be 5 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more.

[0045] In one embodiment, the proportion of C7-C9 acids in the total amount of fatty acids constituting esters (A) and (B) in the base oil may be 40 mol% or greater, 50 mol% or greater, 60 mol% or greater, or 70 mol% or greater, or may be 100 mol% or less, or may be 90 mol% or less, 85 mol% or less, or 80 mol% or less. The proportion of fatty acids having 8 to 9 carbon atoms (C8-C9 acids) in the total amount of fatty acids constituting esters (A) and (B) in the base oil may be within the above ranges.

[0046] In one embodiment, the proportion of fatty acids having 9 carbon atoms (C9 acids) in the total amount of fatty acids constituting esters (A) and esters (B) in the base oil may be 10 mol% or more, 30 mol% or more, 40 mol% or more, or 50 mol% or more, and may be 90 mol% or less, 85 mol% or less, 80 mol% or less, 75 mol% or less, or 70 mol% or less.

[0047] In one embodiment, the proportion of fatty acids having 8 carbon atoms (C8 acids) in the total amount of fatty acids constituting esters (A) and esters (B) in the base oil may be 80 mol% or less, 85 mol% or less, 50 mol% or less, 30 mol% or less, 20 mol% or less, 16 mol% or less, or 14 mol% or less, and may be 5 mol% or more, 7 mol% or more, 9 mol% or more, or 10 mol% or more.

[0048] In one embodiment, the proportion of C4-C6 acids in the fatty acids constituting esters (A) and (B) in the base oil may be 50 mol% or less, 35 mol% or less, 30 mol% or less, or 26 mol% or less, or may be 5 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more. The proportion of fatty acids with a carbon number of 4 (C4 acids) in the total amount of fatty acids constituting esters (A) and (B) in the base oil, the proportion of fatty acids with a carbon number of 5 (C5 acids) in the total amount of fatty acids constituting esters (A) and (B) in the base oil, or the total proportion of C4 and C5 acids in the total amount of fatty acids constituting esters (A) and (B) in the base oil may each be within the above ranges.

[0049] In one embodiment, the ratio of C4-C6 acid in the fatty acids constituting ester (A) and ester (B) in the base oil relative to the ratio of C7-C9 acid in the fatty acids constituting ester (A) and ester (B) in the base oil (molar ratio of C4-C6 acid / C7-C9 acid) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less, or 0, or 0.1 or more, 0.15 or more, or 0.2 or more.

[0050] In one embodiment, the ratio of C4 acid in the fatty acids constituting esters (A) and (B) in the base oil relative to the ratio of C8-C9 acid in the fatty acids constituting esters (A) and (B) in the base oil (molar ratio of C4 acid / C8-C9 fatty acids) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less, or may be 0, or may be 0.1 or more, 0.15 or more, or 0.2 or more. The ratio of C5 acid in the fatty acids constituting esters (A) and (B) in the base oil relative to the ratio of C8-C9 acid in the fatty acids constituting esters (A) and (B) in the base oil (molar ratio of C5 acid / C8-C9 fatty acids), or the ratio of the total of C4 acid and C5 acid in the fatty acids constituting esters (A) and (B) in the base oil relative to the ratio of C8-C9 acid in the fatty acids constituting esters (A) and (B) in the base oil (molar ratio of C4 acid and C5 acid / C8-C9 fatty acids) can be within the above-mentioned range.

[0051] In one embodiment, the average carbon number of the fatty acids constituting ester (A) and ester (B) in the base oil may be 5 or more, 6 or more, 6.5 or more, 7 or more, or 7.5 or more, and may be 9.0 or less, 8.4 or less, 8.2 or less, or 8.0 or less.

[0052] The kinematic viscosity of the ester (A) at 40°C may be 40 mm 2 / s or more, 100mm 2 / s or more, 150mm 2 / s or above or 200mm 2 / s or above, can be 500mm 2 / s or less, 400mm 2 / s or less, 300mm 2 / s or less or 250mm 2 / s or less.

[0053] The kinematic viscosity of ester (B) at 40°C may be 3 mm 2 / s or more, 5mm 2 / s or more, 10mm 2 / s or above or 20mm 2 / s or above, can be 100mm 2 / s or less, 90mm 2 / s or less, 80mm 2 / s or less or 70mm 2 / s or less.

[0054] The kinematic viscosity of ester (B-1) at 40°C may be 3 mm 2 / s or more, 5mm 2 / s or more, 10mm 2 / s or above, can be 50mm 2 / s or less, 30mm 2 / s or less, 20mm 2 / s or less or 15mm 2 / s or less.

[0055] The kinematic viscosity of ester (B-2) at 40°C may be 20 mm 2 / s or more, 30mm 2 / s or more, 40mm 2 / s or above or 50mm 2 / s or above, can be 100mm 2 / s or less, 90mm 2 / s or less, 80mm 2 / s or less or 70mm 2 / s or less.

[0056] The kinematic viscosity of the base oil at 40°C can be 10 mm 2 / s or more, 20mm 2 / s or more, 30mm 2 / s or more, 40mm 2 / s or more, 50mm 2 / s or more, 60mm 2 / s or above or 70mm 2 / s or above, can be 500mm 2 / s or less, 400mm 2 / s or less, 300mm 2 / s or less, 200mm 2 / s or less, 150mm 2 / s or less, 100mm 2 / s or less, 90mm 2 / s or less or 80mm 2 / s or less.

[0057] The kinematic viscosity of the ester (A) at 100°C may be 5 mm 2 / s or more, 10mm 2 / s or more, 15mm 2 / s or above or 20mm 2 / s or above, can be 50mm 2 / s or less, 40mm 2 / s or less, 30mm 2 / s or less or 20mm 2 / s or less.

[0058] The kinematic viscosity of the ester (B) at 100°C may be 1 mm2 / s or more, 2mm 2 / s or more, 3mm 2 / s or above or 5mm 2 / s or above, can be 20mm 2 / s or less, 15mm 2 / s or less, 10mm 2 / s or less or 8.5mm 2 / s or less.

[0059] The kinematic viscosity of ester (B-1) at 100°C may be 1 mm 2 / s or more, 1.5mm 2 / s or more, 2mm 2 / s or above or 2.5mm 2 / s or above, can be 5mm 2 / s or less, 4mm 2 / s or less or 3.5mm 2 / s or less.

[0060] The kinematic viscosity of ester (B-2) at 100°C may be 3 mm 2 / s or more, 5mm 2 / s or more, 6mm 2 / s or above or 8mm 2 / s or above, can be 20mm 2 / s or less, 15mm 2 / s or less, 10mm 2 / s or less or 8.5mm 2 / s or less.

[0061] The kinematic viscosity of the base oil at 100°C can be 5 mm 2 / s or more, 6mm 2 / s or more, 7mm 2 / s or more, 8mm 2 / s or more, 8.5mm 2 / s or above or 9mm 2 / s or above, can be 50mm 2 / s or less, 40mm 2 / s or less, 30mm 2 / s or less, 20mm 2 / s or less, 15mm 2 / s or less, 13mm 2 / s or less, 11mm 2 / s or less or 10.5mm 2 / s or less.

[0062] The kinematic viscosity of the base oil at -20°C can be 5000 mm2 / s or more, 10000mm 2 / s or more, 12000mm 2 / s or more, 14000mm 2 / s or above or 20000mm 2 / s or above, can be 50000mm 2 / s or less, 45000mm 2 / s or less, 40000mm 2 / s or less, 35000mm 2 / s or less or 30000mm 2 / s or less.

[0063] The viscosity index of ester (A), ester (B), ester (B-1) and ester (B-2) may be 50 or more, 60 or more, 70 or more or 80 or more, or 150 or less, 130 or less, 120 or less or 100 or less, respectively.

[0064] The viscosity index of the base oil may be 70 or higher, 80 or higher, or 90 or higher, and may be 150 or lower, 130 or lower, or 110 or lower.

[0065] The kinematic viscosity and viscosity index in this specification refer to the kinematic viscosity and viscosity index measured in accordance with JIS K2283:2000, respectively.

[0066] The refrigeration oil base oil described above can maintain a high-temperature kinematic viscosity while keeping the refrigerant solution viscosity low at low temperatures. Furthermore, in one embodiment, the refrigeration oil base oil can also exhibit excellent refrigerant compatibility. Furthermore, in one embodiment, the refrigeration oil base oil can also keep the kinematic viscosity low at low temperatures.

[0067] Another embodiment of the present invention is a refrigeration oil containing the aforementioned refrigeration oil base oil. The refrigeration oil base oil is included in the refrigeration oil as a base oil constituting the refrigeration oil. The refrigeration oil may contain the base oil as a main component. The base oil content may be 50% by mass or greater, 70% by mass or greater, 90% by mass or greater, or 95% by mass or greater, based on the total amount of the refrigeration oil.

[0068] In one embodiment, the content of the ester (A) in the refrigeration oil can 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 less, based on the total amount of the refrigeration oil, and can 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.

[0069] In one embodiment, the content of the ester (B) in the refrigeration oil can 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 less, based on the total amount of the refrigeration oil, and can 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.

[0070] In one embodiment, the content of the ester (B-1) in the refrigeration oil can be 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 20% by mass or more, and can be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less, based on the total amount of the refrigeration oil.

[0071] In one embodiment, the content of the ester (B-2) in the refrigeration oil can be 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, or 50% by mass or more, and can be 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, or 70% by mass or less, based on the total amount of the refrigeration oil.

[0072] In one embodiment, when the refrigeration oil contains both ester (B-1) and ester (B-2), the content of ester (B-1) can be 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, or 9% by mass or more, based on the total amount of the refrigeration oil, and can be 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 15% by mass or less. In this case, the content of ester (B-2) can 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 less, based on the total amount of the refrigeration oil, and can 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.

[0073] The base oil constituting refrigerator oil can only contain the above-mentioned refrigerator oil base oil, and can also further contain other base oils on the basis of the above-mentioned refrigerator oil base oil.Other base oils can be hydrocarbon oils, or can be mineral oils or synthetic hydrocarbon oils.As mineral oil, can list out with crude oil or its distillation residue as raw material, suitably combine common petroleum refining treatment (solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrofining, sulfuric acid cleaning, bleaching earth treatment, distillation etc.) and carry out refined paraffinic or cycloparaffinic mineral oil obtained.As synthetic hydrocarbon oil, for example, can list out polyalphaolefin or its hydride, normal paraffin, isoparaffin, alkylbenzene, alkylnaphthalene etc.

[0074] Other base oils may be oxygen-containing oils other than esters (A) and (B). Examples of oxygen-containing oils include esters other than esters (A) and (B), ethers, carbonates, ketones, silicones, and polysiloxanes. Examples of esters include monoesters, polyol esters other than esters (A) and (B), aromatic esters, dibasic acid esters, complex esters, and carbonates. Examples of ethers include polyvinyl ethers, polyalkylene glycols, polyphenylene ethers, and perfluoroethers.

[0075] The refrigerator oil may further contain additives. Examples of additives include anti-wear agents, antioxidants, acid scavengers, oxygen scavengers, metal passivators, pour point depressants, detergent dispersants, and defoamers. Based on the total amount of refrigerator oil, the total content of the additives may be 10% by mass or less or 5% by mass or less.

[0076] The kinematic viscosity of refrigeration oil at 40°C can be 10 mm 2 / s or more, 20mm 2 / s or more, 30mm 2 / s or more, 40mm 2 / s or more, 50mm 2 / s or more, 60mm 2 / s or more, 70mm 2 / s or above or 75mm 2 / s or above, can be 500mm 2 / s or less, 400mm 2 / s or less, 300mm 2 / s or less, 200mm 2 / s or less, 150mm 2 / s or less, 100mm 2 / s or less, 90mm 2 / s or less or 87mm 2 / s or less.

[0077] The kinematic viscosity of refrigeration oil at 100°C can be 5 mm 2 / s or more, 6mm 2 / s or more, 7mm 2 / s or more, 8mm 2 / s or more, 8.5mm 2 / s or more, 9mm 2 / s or above or 9.5mm 2 / s or above, can be 50mm 2 / s or less, 30mm 2 / s or less, 20mm 2 / s or less, 15mm 2 / s or less, 13mm 2 / s or less, 12mm 2 / s or less or 11mm 2 / s or less.

[0078] The kinematic viscosity of refrigeration oil at -20°C can be 5000mm 2 / s or more, 10000mm 2 / s or more, 12000mm 2 / s or more, 14000mm 2 / s or above or 20000mm 2 / s or above, can be 50000mm 2 / s or less, 45000mm 2 / s or less, 40000mm 2 / s or less, 35000mm 2 / s or less or 30000mm 2 / s or less.

[0079] The viscosity index of the refrigeration oil may be 70 or higher, 80 or higher, or 90 or higher, and may be 150 or lower, 130 or lower, or 110 or lower.

[0080] The refrigerator oil can exist in the form of a working fluid composition mixed with a refrigerant in a refrigerator. That is, another embodiment of the present invention is a working fluid composition containing the refrigerator oil and the refrigerant. The content of the refrigerator oil in the working fluid composition can be 1 or more parts by mass or 2 or more parts by mass relative to 100 parts by mass of the refrigerant, and can be 500 or less parts by mass or 400 or less parts by mass.

[0081] Examples of the refrigerant include saturated fluorocarbons (also referred to as HFCs), unsaturated fluorocarbons (also referred to as HFOs), hydrocarbons, fluorinated ethers, bis(trifluoromethyl)sulfide, trifluoroiodomethane, ammonia, and carbon dioxide. The refrigerant may be a single refrigerant of these refrigerants or a mixture of two or more. From the perspective of further ensuring the amount of refrigerant dissolved and suppressing the refrigerant dissolution viscosity to a lower level, the refrigerant preferably contains at least one selected from the group consisting of unsaturated fluorocarbons and hydrocarbons, and more preferably contains at least one selected from the group consisting of unsaturated fluorocarbons.

[0082] Examples of unsaturated fluorinated hydrocarbons include unsaturated fluorinated hydrocarbons having one or more carbon-carbon double bonds and containing fluorine and hydrogen and having 2 to 4 carbon atoms. Unsaturated fluorinated hydrocarbons are preferably fluoropropenes, and more preferably fluoropropenes having 3 to 5 fluorine atoms. Examples of unsaturated fluorinated hydrocarbons include 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). The unsaturated fluorinated hydrocarbon is preferably at least one selected from HFO-1225ye, HFO-1234ze, and HFO-1234yf.

[0083] The unsaturated fluorinated hydrocarbon may be vinyl fluoride, preferably vinyl fluoride having 1 to 3 fluorine atoms, and more specifically, for example, may be at least one selected from monofluoroethylene (HFO-1141), 1,1-difluoroethylene (HFO-1132a), (E)-1,2-difluoroethylene (HFO-1132(E)), (Z)-1,2-difluoroethylene (HFO-1132(Z)) and 1,1,2-trifluoroethylene (R1123).

[0084] The unsaturated fluorinated hydrocarbon may be a fluorobutene, preferably a fluorobutene having 1 to 7 fluorine atoms and having 4 carbon atoms. More specifically, for example, it may be at least one selected from (E)-1,1,1,4,4,4-hexafluoro-2-butene (R1336mzz(E)) and (Z)-1,1,1,4,4,4-hexafluoro-2-butene (R1336mzz(Z)).

[0085] The unsaturated fluorinated hydrocarbon may be an unsaturated fluorinated hydrocarbon having chlorine atoms and fluorine atoms, and specifically, for example, may be at least one selected from 1-chloro-2,2-difluoroethylene (HCFO-1122), (Z)-1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd(Z)), and (E)-1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd(E)).

[0086] The refrigerant may be a mixed refrigerant containing the unsaturated fluorinated hydrocarbon having 2 to 4 carbon atoms. Specific examples of the mixed refrigerant include R444A, R444B, R445A, R446A, R447A, R447B, R448A, R448B, R449A, R449B, R449C, R450A, R451A, R451B, R452A, R452B, R452C, R454A, R454B, R454C, R455A, R455C, R455D, R456A, R457A, R457B, R457C, R457D, R459A, R459B, R460A, Refrigerants R460B, R460C, R463A, R464A, R465A, R468A, R468B, R468C, R470A, R470B, R471A, R473A, R474A, R474B, R475A, R476A, R478A, R479A, R480A, R481A, R482A, R486A, R488A, R491A, R513A, R513B, R514A, R515A, R515B, R516A, HFO-1123, and R32 and / or R1234yf.

[0087] The GWP of the unsaturated fluorocarbon refrigerant or the mixed refrigerant containing the unsaturated fluorocarbon may be, for example, 1500 or less, 1000 or less, 500 or less, 300 or less, 150 or less, 100 or less, or 10 or less.

[0088] The hydrocarbon is preferably a hydrocarbon having 1 to 5 carbon atoms, more preferably a hydrocarbon having 2 to 4 carbon atoms. Examples of the hydrocarbon include methane, ethylene, ethane, propylene (R1270), propane (R290), cyclopropane, n-butane, isobutane, cyclobutane, methylcyclopropane, 2-methylbutane, and n-pentane. The hydrocarbon is preferably a single refrigerant or a mixed refrigerant of two or more selected from the group consisting of propane, propylene, n-butane, isobutane, and 2-methylbutane.

[0089] Example

[0090] Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the Examples.

[0091] Using the esters shown below, base oils (refrigeration oils) having the compositions (mass % based on the total amount of base oil) shown in Tables 1 and 2 were prepared. 2 The blending ratio of the esters was adjusted so that the ratios were approximately the same within the range of 1:1 / s.

[0092] Ester (A)

[0093] Hexaester of dipentaerythritol (DiPE) and a fatty acid (a mixed fatty acid of 50 mol% 2-ethylhexanoic acid (iC8 acid) and 50 mol% 3,5,5-trimethylhexanoic acid (iC9 acid)) (average carbon number: 61, maximum carbon number: 64)

[0094] Ester (B-1)

[0095] Neopentyl glycol (NPG) diester with 2-ethylhexanoic acid (iC8 acid) (average carbon number: 21, minimum carbon number: 21, kinematic viscosity at 100°C: 2.0 mm 2 / s, viscosity index: 56)

[0096] Neopentyl glycol (NPG) diester with 3,5,5-trimethylhexanoic acid (iC9 acid) (average carbon number: 23, minimum carbon number: 23, kinematic viscosity at 100°C: 3.1 mm 2 / s, viscosity index: 101)

[0097] Ester (B-2)

[0098] Tetraester of pentaerythritol (PE) and fatty acid (mixed fatty acid of 60 mol% 2-methylpropionic acid (iC4 acid) and 40 mol% 3,5,5-trimethylhexanoic acid (iC9 acid)) (average carbon number: 29, minimum carbon number: 21, kinematic viscosity at 100°C: 6.3 mm) 2 / s, viscosity index: 78)

[0099] Tetraester of pentaerythritol (PE) and a fatty acid (a mixed fatty acid of 37 mol% 2-methylpropionic acid (iC4 acid) and 63 mol% 3,5,5-trimethylhexanoic acid (iC9 acid)) (average carbon number: 34, minimum carbon number: 21, kinematic viscosity at 100°C: 8.2 mm) 2 / s, viscosity index: 84)

[0100] Ester (C)

[0101] Tetraester of pentaerythritol (PE) and a fatty acid (a mixed fatty acid of 48 mol% 2-ethylhexanoic acid (iC8 acid) and 52 mol% 3,5,5-trimethylhexanoic acid (iC9 acid)) (average carbon number: 39, minimum carbon number: 37, kinematic viscosity at 100°C: 8.3 mm) 2 / s, viscosity index: 88)

[0102] The kinematic viscosity and viscosity index of each of the obtained base oils (refrigeration oils) at -20°C, 40°C, and 100°C were measured in accordance with JIS K2283:2000. Furthermore, the following measurements were performed using each of the obtained base oils (refrigeration oils). The measurement results are shown in Tables 1 and 2.

[0103] In Tables 1 and 2, the proportions (mol %) of DiPE, NPG, and PE in the total amount of alcohols constituting the esters are respectively described as "Proportion of DiPE (mol %)", "Proportion of NPG (mol %)", and "Proportion of PE (mol %)". In addition, in Tables 1 and 2, the proportions (mol %) of iC9 acids, iC8 acids, C7-C9 acids, and C4-C6 acids in the total amount of fatty acids constituting the esters are respectively described as "Proportion of iC9 acids (mol %)", "Proportion of iC8 acids (mol %)", "Proportion of C7-C9 acids (mol %)", and "Proportion of C4-C6 acids (mol %)", and the ratio (molar ratio) of C4-C6 acids to C7-C9 acids is described as "Molar ratio of C4-C6 acids / C7-C9 acids".

[0104] (Determination of the Second Layer Separation Temperature)

[0105] According to JIS K2211:2009, "Refrigerator Oils," "Compatibility Test Method with Refrigerants," working fluid compositions containing various refrigeration oils and a refrigerant (HFO-1234yf) (refrigeration oil ratio in the working fluid composition: 20 mass%) were slowly cooled from 20°C to -60°C. The temperature at which the working fluid composition experienced phase separation or clouding was evaluated as the two-layer separation temperature (°C). In Tables 1 and 2, "<-60" indicates that neither phase separation nor clouding was observed within the measured temperature range.

[0106] (Determination of Refrigerant Dissolved Amount and Refrigerant Dissolved Viscosity)

[0107] Each refrigeration oil was filled into a pressure-resistant container equipped with a vibration viscometer, a thermometer, and a pressure gauge. After vacuum degassing the pressure container, a refrigerant (HFO-1234yf) was filled in such a way that the refrigerant ratio became about 13.6%, and a working fluid composition containing refrigeration oil and refrigerant was prepared (about half the capacity of the pressure-resistant container). Under the condition that the temperature of the working fluid composition was stable at -20°C, the absolute viscosity P (mPa·s) of the working fluid composition was measured using a vibration viscometer. The density (g / cm 3 ) is used to calculate the refrigerant viscosity (mm 2 / s).

[0108] The amount of dissolved refrigerant S (mass %) is calculated by the following formula.

[0109] S=(Rf-Vv×Dv)×100 / ((Rf-Vv×Dv)+Of)

[0110] Rf: Amount of refrigerant filled into the pressure vessel (g)

[0111] Vv: Volume of refrigerant vapor in pressure container (cm3 )(=volume V of pressure vessel - volume Vmix of working fluid composition)

[0112] Dv: Refrigerant vapor density (g / cm 3 )

[0113] Of: Amount of refrigeration oil filled into the pressure container (g)

[0114] In addition, the refrigerant solution viscosity R-Vis (mm 2 / s) as the absolute viscosity P (mPa·s) divided by the density Dw (g / cm 3 The density Dw (g / cm2) of the working fluid composition is obtained by calculating P / Dw. 3 ) is calculated by the following formula.

[0115] Dw=(Rf-Vv×Dv+Of) / Vmix

[0116] Dw: density of the working fluid composition (g / cm 3 )

[0117] Rf: Amount of refrigerant filled into the pressure vessel (g)

[0118] Vv: The volume of the refrigerant vapor in the pressure container (cm 3 )(=volume V of pressure vessel - volume Vmix of working fluid composition)

[0119] Dv: Refrigerant vapor density (g / cm 3 )

[0120] Of: Amount of refrigeration oil filled into the pressure container (g)

[0121] Vmix: Volume of working fluid composition (cm 3 )

[0122] The ratio of the refrigerant melt viscosity measured as described above to the 100°C kinematic viscosity of the refrigeration oil (refrigerant melt viscosity / 100°C kinematic viscosity) was calculated. The results are shown in Tables 1 and 2. A smaller ratio indicates that the kinematic viscosity on the high-temperature side is maintained while the refrigerant melt viscosity on the low-temperature side is suppressed.

[0123] [Table 1]

[0124]

[0125] [Table 2]

[0126]

[0127] As shown in Tables 1 and 2, Examples 1 to 6 show a smaller ratio of refrigerant dissolved viscosity to 100°C kinematic viscosity compared to Comparative Example 1, maintaining the kinematic viscosity on the high-temperature side while keeping the refrigerant dissolved viscosity low on the low-temperature side. In Examples 1, 2, 5, and 6, the refrigerant dissolved viscosity at the low-temperature side (-20°C) is significantly lower than in Comparative Example 1, despite the higher -20°C kinematic viscosity of the base oil (refrigeration oil) itself. This is particularly surprising. Furthermore, in Examples 1 to 6, the amount of dissolved refrigerant is greater, resulting in a lower refrigerant dissolved viscosity than in Comparative Example 1.

Claims

1. A base oil for refrigeration oil, comprising: Hexaesters of dipentaerythritol and fatty acids; and At least one ester selected from the group consisting of diesters of neopentyl glycol and fatty acids, and tetraesters of pentaerythritol and fatty acids including fatty acids having 4 to 6 carbon atoms.

2. The base oil according to claim 1, wherein The kinematic viscosity of the base oil at 100°C is 8.5 mm 2 / s or above. 3 . The base oil according to claim 1 , comprising the hexaester, the diester, and the tetraester. 4 . A refrigeration oil comprising the base oil according to claim 1 .

5. A working fluid composition comprising the refrigeration oil according to claim 4 and a refrigerant.

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