EP4685214A1

EP4685214A1 - Base oil for refrigerator oil, refrigerator oil, and working fluid composition

Info

Publication number: EP4685214A1
Application number: EP24811117.1A
Authority: EP
Inventors: Satoshi Goto; Tsukasa Sakuraba; Hidetoshi Ogata
Original assignee: Eneos Corp
Current assignee: Eneos Corp
Priority date: 2023-05-25
Filing date: 2024-05-21
Publication date: 2026-01-28
Also published as: JPWO2024242110A1; WO2024242110A1; CN120641541A; KR20250144457A

Abstract

A base oil for refrigerating machine 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.

Description

Technical Field

The present invention relates to a base oil for refrigerating machine oil, a refrigerating machine oil, and a working fluid composition.

Background Art

Refrigerating machines such as refrigerators, car air conditioners, room air conditioners, and vending machines are equipped with compressors for circulating a refrigerant within a refrigeration cycle. The compressor is filled with a refrigerating machine oil for lubricating sliding members. The refrigerating machine oil contains a base oil as a main component. As the base oil, a suitable base oil is selected according to required properties.
As the base oil, for example, polyol esters are known. For example, Patent Literature 1 discloses a refrigerating machine oil containing an ester of dipentaerythritol and a fatty acid, wherein the proportion of 2-methylpentanoic acid in the fatty acid is 20 mol% or more.

Citation List

Patent Literature

[Patent Literature 1] Japanese Unexamined Patent Publication No. 2015-206059

Summary of Invention

Technical Problem

When using an ester of dipentaerythritol as disclosed in Patent Literature 1, since the ester is a hexaester having a relatively large molecular weight, it is effective in maintaining high kinematic viscosity and refrigerant dissolution viscosity of the base oil (refrigerating machine oil) at high temperature side (for example, 100°C), but the kinematic viscosity and refrigerant dissolution viscosity at low temperature side (for example, -20°C) become higher than necessary. Therefore, it is conceivable to mix a polyol ester having a lower viscosity than the hexaester with the hexaester of dipentaerythritol to adjust the viscosity of the base oil (refrigerating machine oil) to an appropriate viscosity.
However, according to the studies by the present inventors, it has been found that depending on the type of polyol ester mixed with the hexaester, it is not necessarily easy to suppress the refrigerant dissolution viscosity at low temperature side while maintaining the kinematic viscosity at high temperature side.
Accordingly, one aspect of the present invention aims to provide a base oil for refrigerating machine oil, a refrigerating machine oil, and a working fluid composition that can suppress the refrigerant dissolution viscosity at low temperature side while maintaining the kinematic viscosity at high temperature side.

Solution to Problem

As a result of studies by the present inventors, it has been found that a mixed base oil obtained by mixing at least one selected from a diester of neopentyl glycol and a tetraester of pentaerythritol and a specific fatty acid with a hexaester can suppress the refrigerant dissolution viscosity at low temperature side while maintaining the kinematic viscosity at high temperature side.
The present invention includes the following aspects.

[1] A base oil for refrigerating machine 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.
[2] The base oil according to [1], wherein the kinematic viscosity of the base oil at 100°C is 8.5 mm²/s or more.
[3] The base oil according to [1] or [2], comprising the hexaester, the diester, and the tetraester.
[4] A refrigerating machine oil comprising the base oil according to any one of [1] to [3].
[5] A working fluid composition comprising the refrigerating machine oil according to [4] and a refrigerant.

Advantageous Effects of Invention

According to one aspect of the present invention, it is possible to provide a base oil for refrigerating machine oil, a refrigerating machine oil, and a working fluid composition that can maintain kinematic viscosity on the high temperature side while suppressing refrigerant dissolution viscosity on the low temperature side to a low level.

Description of Embodiments

One embodiment of the present invention is a base oil for refrigerating machine oil comprising: a hexaester of dipentaerythritol and a fatty acid (hereinafter also referred to as "ester (A)"); and at least one ester 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)") (hereinafter also referred to as "ester (B)").
The fatty acid constituting ester (A) is preferably a saturated fatty acid, and 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-methylpropanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, neopentanoic acid, 2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-methylheptanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid, and from the viewpoint of more easily maintaining higher kinematic viscosity at 100°C, further preferably includes at least one selected from the group consisting of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid.
The fatty acid may be a mixed fatty acid of branched fatty acids. Examples of such mixed fatty acids include a mixed fatty acid of 2-methylpropanoic 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.
The fatty acid may be a linear fatty acid, or may be a mixed fatty acid of linear fatty acids and branched fatty acids. Examples of linear fatty acids include n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, and n-nonanoic acid. Examples of mixed fatty acids of linear fatty acids and branched fatty acids 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.
The fatty acid constituting ester (B-1) is preferably a saturated fatty acid, and 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 viewpoint of further securing the amount of refrigerant dissolved at low temperatures and further suppressing refrigerant dissolution viscosity at low temperatures to a low level, the fatty acid is preferably branched, more preferably selected from 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid, and further preferably 3,5,5-trimethylhexanoic acid.
The fatty acid constituting ester (B-2) contains 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, and 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 butanoic acid, linear or branched pentanoic acid, and linear or branched hexanoic acid, preferably includes at least one selected from the group consisting of branched butanoic acid, branched pentanoic acid, and branched hexanoic acid, more preferably includes at least one selected from the group consisting of 2-methylpropanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, neopentanoic acid, and 2-methylpentanoic acid, includes at least one selected from the group consisting of 2-methylpropanoic acid and 2-methylbutanoic acid, and further preferably includes 2-methylpropanoic acid.
The fatty acid constituting ester (B-2) may further contain other fatty acids in addition to the C4-C6 acid. The other fatty acids are preferably fatty acids having 7 to 9 carbon atoms (hereinafter also referred to as "C7-C9 acid"). The C7-C9 acid is preferably a saturated fatty acid, and more preferably a saturated fatty acid having 8 to 9 carbon atoms. The C7-C9 acid may be linear or branched. The C7-C9 acid is preferably branched, more preferably selected from 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid, and further preferably 3,5,5-trimethylhexanoic acid.
The fatty acid constituting ester (B-2) may be a mixed fatty acid of linear fatty acids and branched fatty acids. Examples of such mixed fatty acids include a mixed fatty acid of one or more selected from n-pentanoic acid and n-heptanoic acid, and 3,5,5-trimethylhexanoic acid.
The molar ratio of C4-C6 acid to C7-C9 acid (C4-C6 acid/C7-C9 acid) in the fatty acid constituting ester (B-2) may be 10/90 or more, 20/80 or more, or 30/70 or more, and may be 90/10 or less, 80/20 or less, 70/30 or less, 60/40 or less, or 50/50 or less.
Ester (A) may include an ester having 40 or more or 50 or more carbon atoms, and from the viewpoint of easily maintaining high kinematic viscosity at 100°C, preferably includes an ester having 54 or more or 60 or more, and 64 or less carbon atoms. For example, in the case of a hexaester of dipentaerythritol and a fatty acid having 4 to 9 carbon atoms, ester (A) has 34 to 64 carbon atoms.
Ester (B) may include an ester having 38 or less or 35 or less carbon atoms, and from the viewpoint of increasing the amount of refrigerant dissolved at low temperatures and easily reducing refrigerant dissolution viscosity at low temperatures, preferably includes an ester having 31 or less or 25 or less, and 18 or more or 20 or more carbon atoms. 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. Also, for example, 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.
The difference between the maximum value of the number of carbon atoms of the ester (maximum carbon number) and the minimum value of the number of carbon atoms of the ester (minimum carbon number) in the mixture of ester (A) and ester (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.
The average carbon number of ester (A) may be 40 or more or 50 or more, is 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, is preferably 31 or less or 25 or less, and may preferably be 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.
The value obtained by dividing the difference between the maximum carbon number and the minimum carbon number in the mixture of ester (A) and ester (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. This value indicates the degree of dispersion of the molecular weight of the ester, and even with the same average carbon number, it becomes 0 for a single molecule and becomes a larger value as the maximum and minimum values of the molecular weight of the ester become larger. From the viewpoint of the balance with refrigerant compatibility, flash point, 100°C kinematic viscosity, and the effect of reducing refrigerant dissolution viscosity, the above range is preferable.
The ratio (Mw/Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) in the mixture of ester (A) and ester (B) 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 mean values obtained by GPC analysis (polystyrene-equivalent values (standard sample)). Specifically, for example, a solution is prepared by using tetrahydrofuran as a solvent and diluting to a sample concentration of 1% by mass, and analysis is performed using a GPC apparatus (for example, ACQUITY APC UV RI system manufactured by Waters Corporation) with the solvent flow rate set to 0.7 ml/min, the temperature set to 40°C, using a column with an analyzable molecular weight of 100 to 10000, and using a refractive index detector. The relationship between column retention time and molecular weight is determined using polystyrene standards with known molecular weights, a calibration curve is separately prepared, and the molecular weight is determined from the obtained retention time.
The content of ester (A) and ester (B) (and further ester (B-1) and ester (B-2)) in the base oil is appropriately adjusted according to the desired kinematic viscosity of the base oil and other factors. 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.
In one embodiment, the content of 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.
In one embodiment, the content of 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.
In one embodiment, the content of 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.
Ester (B) may contain either one of ester (B-1) and ester (B-2), or may contain both ester (B-1) and ester (B-2). From the viewpoint of further suppressing refrigerant dissolution viscosity to a low level, ester (B) preferably contains both ester (B-1) and ester (B-2). That is, from the viewpoint of further suppressing refrigerant dissolution viscosity to a low level, the base oil preferably contains ester (A), ester (B-1), and ester (B-2).
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 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.
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.
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, may be 0 mol%, and may be 5 mol% or more, or 10 mol% or more.
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%, and may be 5 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more.
In one embodiment, the proportion of C7-C9 acid in the total amount of fatty acids constituting ester (A) and ester (B) in the base oil may be 40 mol% or more, 50 mol% or more, 60 mol% or more, or 70 mol% or more, may be 100 mol%, and 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 acid) in the total amount of fatty acids constituting ester (A) and ester (B) in the base oil may be in the above range.
In one embodiment, the proportion of fatty acids having 9 carbon atoms (C9 acid) in the total amount of fatty acids constituting ester (A) and ester (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.
In one embodiment, the proportion of fatty acids having 8 carbon atoms (C8 acid) in the total amount of fatty acids constituting ester (A) and ester (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.
In one embodiment, the proportion of C4-C6 acid in the fatty acids constituting ester (A) and ester (B) in the base oil may be 50 mol% or less, 35 mol% or less, 30 mol% or less, or 26 mol% or less, and may be 5 mol% or more, 10 mol% or more, 15 mol% or more, or 20 mol% or more. The proportion of fatty acids having 4 carbon atoms (C4 acid), the proportion of fatty acids having 5 carbon atoms (C5 acid), or the proportion of the total of C4 acid and C5 acid in the total amount of fatty acids constituting ester (A) and ester (B) in the base oil may each be in the above range.
In one embodiment, the ratio of C4-C6 acid to C7-C9 acid (molar ratio of C4-C6 acid/C7-C9 acid) in the fatty acids constituting ester (A) and ester (B) in the base oil 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, may be 0, and may be 0.1 or more, 0.15 or more, or 0.2 or more.
In one embodiment, the ratio of C4 acid to C8-C9 acid (molar ratio of C4 acid/C8-C9 fatty acid) in the fatty acids constituting ester (A) and ester (B) in the base oil 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, may be 0, and may be 0.1 or more, 0.15 or more, or 0.2 or more. The ratio of C5 acid to C8-C9 acid (molar ratio of C5 acid/C8-C9 fatty acid) or the ratio of the total of C4 acid and C5 acid to C8-C9 acid (molar ratio of C4 acid and C5 acid/C8-C9 fatty acid) in the fatty acids constituting ester (A) and ester (B) in the base oil may be in the above range.
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.
The kinematic viscosity of ester (A) at 40°C may be 40 mm²/s or more, 100 mm²/s or more, 150 mm²/s or more, or 200 mm²/s or more, and may be 500 mm²/s or less, 400 mm²/s or less, 300 mm²/s or less, or 250 mm²/s or less.
The kinematic viscosity of ester (B) at 40°C may be 3 mm²/s or more, 5 mm²/s or more, 10 mm²/s or more, or 20 mm²/s or more, and may be 100 mm²/s or less, 90 mm²/s or less, 80 mm²/s or less, or 70 mm²/s or less.
The kinematic viscosity of ester (B-1) at 40°C may be 3 mm²/s or more, 5 mm²/s or more, or 10 mm²/s or more, and may be 50 mm²/s or less, 30 mm²/s or less, 20 mm²/s or less, or 15 mm²/s or less.
The kinematic viscosity of ester (B-2) at 40°C may be 20 mm²/s or more, 30 mm²/s or more, 40 mm²/s or more, or 50 mm²/s or more, and may be 100 mm²/s or less, 90 mm²/s or less, 80 mm²/s or less, or 70 mm²/s or less.
The kinematic viscosity of the base oil at 40°C may be 10 mm² /s or more, 20 mm²/s or more, 30 mm²/s or more, 40 mm²/s or more, 50 mm²/s or more, 60 mm²/s or more, or 70 mm²/s or more, and may be 500 mm²/s or less, 400 mm²/s or less, 300 mm²/s or less, 200 mm²/s or less, 150 mm²/s or less, 100 mm²/s or less, 90 mm²/s or less, or 80 mm ²/s or less.
The kinematic viscosity of ester (A) at 100°C may be 5 mm²/s or more, 10 mm²/s or more, 15 mm²/s or more, or 20 mm²/s or more, and may be 50 mm²/s or less, 40 mm²/s or less, 30 mm²/s or less, or 20 mm ²/s or less.
The kinematic viscosity of ester (B) at 100°C may be 1 mm²/s or more, 2 mm²/s or more, 3 mm²/s or more, or 5 mm²/s or more, and may be 20 mm²/s or less, 15 mm²/s or less, 10 mm²/s or less, or 8.5 mm²/s or less.
The kinematic viscosity of ester (B-1) at 100°C may be 1 mm²/s or more, 1.5 mm²/s or more, 2 mm²/s or more, or 2.5 mm²/s or more, and may be 5 mm²/s or less, 4 mm²/s or less, or 3.5 mm²/s or less.
The kinematic viscosity of ester (B-2) at 100°C may be 3 mm²/s or more, 5 mm²/s or more, 6 mm²/s or more, or 8 mm²/s or more, and may be 20 mm²/s or less, 15 mm²/s or less, 10 mm²/s or less, or 8.5 mm ²/s or less.
The kinematic viscosity of the base oil at 100°C may be 5 mm² /s or more, 6 mm²/s or more, 7 mm²/s or more, 8 mm²/s or more, 8.5 mm²/s or more, or 9 mm²/s or more, and may be 50 mm²/s or less, 40 mm²/s or less, 30 mm²/s or less, 20 mm²/s or less, 15 mm²/s or less, 13 mm²/s or less, 11 mm²/s or less, or 10.5 mm²/s or less.
The kinematic viscosity of the base oil at -20°C may be 5000 mm ²/s or more, 10000 mm²/s or more, 12000 mm²/s or more, 14000 mm² /s or more, or 20000 mm²/s or more, and may be 50000 mm²/s or less, 45000 mm²/s or less, 40000 mm²/s or less, 35000 mm²/s or less, or 30000 mm²/s or less.
The viscosity index of ester (A), ester (B), ester (B-1), and ester (B-2) may each be 50 or more, 60 or more, 70 or more, or 80 or more, and may be 150 or less, 130 or less, 120 or less, or 100 or less.
The viscosity index of the base oil may be 70 or more, 80 or more, or 90 or more, and may be 150 or less, 130 or less, or 110 or less.
The kinematic viscosity and viscosity index in this specification mean the kinematic viscosity and viscosity index measured in accordance with JIS K 2283:2000, respectively.
The base oil for refrigerating machine oil described above can maintain kinematic viscosity on the high temperature side while suppressing refrigerant dissolution viscosity on the low temperature side to a low level. In one embodiment, the base oil for refrigerating machine oil may also have excellent refrigerant compatibility. In one embodiment, the base oil for refrigerating machine oil can also suppress kinematic viscosity on the low temperature side to a low level.
Another embodiment of the present invention is a refrigerating machine oil containing the above-described base oil for refrigerating machine oil. The above-described base oil for refrigerating machine oil is contained in the refrigerating machine oil as a base oil constituting the refrigerating machine oil. The refrigerating machine oil may contain the base oil as a main component. The content of the base oil may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the refrigerating machine oil.
In one embodiment, the content of ester (A) in 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 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 refrigerating machine oil.
In one embodiment, the content of ester (B) in 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 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 refrigerating machine oil.
In one embodiment, the content of ester (B-1) in the refrigerating machine 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 refrigerating machine oil.
In one embodiment, the content of ester (B-2) in the refrigerating machine 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 refrigerating machine oil.
In one embodiment, when the refrigerating machine 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 refrigerating machine 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 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 refrigerating machine oil.
The base oil constituting the refrigerating machine oil may contain only the above-described base oil for refrigerating machine oil, or may further contain other base oils in addition to the above-described base oil for refrigerating machine oil. The other base oils may be hydrocarbon oils, and may be mineral oils or synthetic hydrocarbon oils. Examples of mineral oils include paraffinic or naphthenic mineral oils refined by appropriately combining ordinary petroleum refining processes (solvent deasphaltening, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, clay treatment, distillation, etc.) using crude oil or its distillation residue oil as a raw material. Examples of synthetic hydrocarbon oils include poly- α -olefins or their hydrides, normal paraffins, isoparaffins, alkylbenzenes, alkylnaphthalenes, and the like.
The other base oils may be oxygen-containing oils other than ester (A) and ester (B). Examples of oxygen-containing oils include esters other than ester (A) and ester (B), ethers, carbonates, ketones, silicones, polysiloxanes, and the like. Examples of esters include monoesters, polyol esters other than ester (A) and ester (B), aromatic esters, dibasic acid esters, complex esters, and carbonate esters. Examples of ethers include polyvinyl ethers, polyalkylene glycols, polyphenyl ethers, and perfluoroethers.
The refrigerating machine oil may further contain additives. Examples of additives include antiwear agents, antioxidants, acid scavengers, oxygen scavengers, metal deactivators, pour point depressants, detergent/dispersants, defoamers, and the like. The total content of additives may be 10% by mass or less or 5% by mass or less, based on the total amount of the refrigerating machine oil.
The kinematic viscosity of the refrigerating machine oil at 40°C may be 10 mm²/s or more, 20 mm²/s or more, 30 mm²/s or more, 40 mm²/s or more, 50 mm²/s or more, 60 mm²/s or more, 70 mm²/s or more, or 75 mm²/s or more, and may be 500 mm²/s or less, 400 mm²/s or less, 300 mm²/s or less, 200 mm²/s or less, 150 mm²/s or less, 100 mm²/s or less, 90 mm²/s or less, or 87 mm²/s or less.
The kinematic viscosity of the refrigerating machine oil at 100°C may be 5 mm²/s or more, 6 mm²/s or more, 7 mm²/s or more, 8 mm²/s or more, 8.5 mm²/s or more, 9 mm²/s or more, or 9.5 mm²/s or more, and may be 50 mm²/s or less, 30 mm²/s or less, 20 mm²/s or less, 15 mm²/s or less, 13 mm²/s or less, 12 mm²/s or less, or 11 mm²/s or less.
The kinematic viscosity of the refrigerating machine oil at -20°C may be 5000 mm²/s or more, 10000 mm²/s or more, 12000 mm²/s or more, 14000 mm²/s or more, or 20000 mm²/s or more, and may be 50000 mm²/s or less, 45000 mm²/s or less, 40000 mm²/s or less, 35000 mm²/s or less, or 30000 mm²/s or less.
The viscosity index of the refrigerating machine oil may be 70 or more, 80 or more, or 90 or more, and may be 150 or less, 130 or less, or 110 or less.
The refrigerating machine oil can exist in a refrigerating machine in the state of a working fluid composition mixed with a refrigerant. That is, another embodiment of the present invention is a working fluid composition comprising the above refrigerating machine oil and a refrigerant. The content of the refrigerating machine 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.
Examples of the refrigerant include saturated fluorocarbon (also called HFC), unsaturated fluorocarbon (also called HFO), hydrocarbon, fluorinated ether, bis(trifluoromethyl) sulfide, trifluoroiodomethane, ammonia, and carbon dioxide. The refrigerant may be a single refrigerant of one of these refrigerants, or may be a mixed refrigerant of two or more. From the viewpoint of further securing the amount of refrigerant dissolved and further suppressing refrigerant dissolution viscosity to a low level, the refrigerant preferably includes at least one selected from the group consisting of unsaturated fluorocarbon and hydrocarbon, and more preferably includes at least one selected from the group consisting of unsaturated fluorocarbon.
Examples of unsaturated fluorocarbon include unsaturated fluorocarbon having 2 to 4 carbon atoms that has one or more carbon-carbon double bonds and has fluorine and hydrogen. The unsaturated fluorocarbon is preferably fluoropropene, and more preferably fluoropropene having 3 to 5 fluorine atoms. Examples of unsaturated fluorocarbon 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 fluorocarbon is preferably at least one selected from HFO-1225ye, HFO-1234ze, and HFO-1234yf.
The unsaturated fluorocarbon may be fluoroethylene, preferably fluoroethylene having 1 to 3 fluorine atoms, and more specifically, may be at least one selected from, for example, 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).
The unsaturated fluorocarbon may be fluorobutene, preferably fluorobutene having 4 carbon atoms and 1 to 7 fluorine atoms, and more specifically, may be at least one selected from, for example, (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)).
The unsaturated fluorocarbon may be an unsaturated fluorocarbon having chlorine atoms and fluorine atoms, and specifically, may be at least one selected from, for example, 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)).
The refrigerant may be a mixed refrigerant containing the above unsaturated fluorocarbon having 2 to 4 carbon atoms. Specific examples of such mixed refrigerants 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, 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, and refrigerants containing HFO-1123 and R32 and/or R1234yf.
The GWP of the above unsaturated fluorocarbon refrigerant or mixed refrigerant containing 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.
The hydrocarbon is preferably a hydrocarbon having 1 to 5 carbon atoms, and more preferably a hydrocarbon having 2 to 4 carbon atoms. Examples of hydrocarbons include methane, ethylene, ethane, propylene (R1270), propane (R290), cyclopropane, normal butane, isobutane, cyclobutane, methylcyclopropane, 2-methylbutane, and normal pentane. The hydrocarbon is preferably a single refrigerant or a mixed refrigerant of two or more selected from the group consisting of propane, propylene, normal butane, isobutane, and 2-methylbutane.

Examples

Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to the examples.
Using the esters shown below, base oils (refrigerating machine oils) having the compositions shown in Tables 1 and 2 (mass% based on the total amount of base oil) were prepared. The blending ratios of the esters were adjusted so that the kinematic viscosity at 100°C of each base oil (refrigerating machine oil) was approximately the same in the range of 8.5 to 10.5 mm²/s.

Ester (A)

· Hexaester of dipentaerythritol (DiPE) and fatty acid (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)

Ester (B-1)

· Diester of neopentyl glycol (NPG) and 2-ethylhexanoic acid (iC8 acid) (average carbon number: 21, minimum carbon number: 21, kinematic viscosity at 100°C: 2.0 mm²/s, viscosity index: 56) · Diester of neopentyl glycol (NPG) and 3,5,5-trimethylhexanoic acid (iC9 acid) (average carbon number: 23, minimum carbon number: 23, kinematic viscosity at 100°C: 3.1 mm²/s, viscosity index: 101)

Ester (B-2)

· Tetraester of pentaerythritol (PE) and fatty acid (mixed fatty acid of 60 mol% 2-methylpropanoic 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 mm²/s, viscosity index: 78)
. Tetraester of pentaerythritol (PE) and fatty acid (mixed fatty acid of 37 mol% 2-methylpropanoic 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 mm²/s, viscosity index: 84)

Ester (C)

. Tetraester of pentaerythritol (PE) and fatty acid (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 mm²/s, viscosity index: 88)
For each of the obtained base oils (refrigerating machine oils), kinematic viscosity and viscosity index at -20°C, 40°C, and 100°C were measured in accordance with JIS K 2283:2000. In addition, the following measurements were performed using each of the obtained base oils (refrigerating machine oils). The measurement results are shown in Tables 1 and 2.
Tables 1 and 2 show the proportions (mol%) of DiPE, NPG, and PE in the total amount of alcohols constituting the esters as "DiPE proportion (mol%)", "NPG proportion (mol%)", and "PE proportion (mol%)", respectively. Tables 1 and 2 also show the proportions (mol%) of iC9 acid, iC8 acid, C7-C9 acid, and C4-C6 acid in the total amount of fatty acids constituting the esters as "iC9 acid proportion (mol%)", "iC8 acid proportion (mol%)", "C7-C9 acid proportion (mol%)", and "C4-C6 acid proportion (mol%)", respectively, and the ratio (molar ratio) of C4-C6 acid to C7-C9 acid is shown as "C4-C6 acid/C7-C9 acid molar ratio".

(Measurement of Two Layer Separation Temperature)

In accordance with the "Compatibility Test Method with Refrigerant" in JIS K 2211:2009 "Refrigerating machine Oil", a working fluid composition consisting of each refrigerating machine oil and refrigerant (HFO-1234yf) (proportion of refrigerating machine oil in the working fluid composition: 20% by mass) was gradually cooled from 20°C to - 60°C, and the temperature at which the working fluid composition underwent layer separation or cloudiness was evaluated as the two layer separation temperature (°C). In Tables 1 and 2, "<-60" indicates that no phase separation or cloudiness was observed in the measured temperature range.

(Measurement of Refrigerant Dissolution Amount and Refrigerant dissolution viscosity)

Each refrigerating machine oil was filled into a pressure-resistant vessel equipped with a vibrational viscometer, thermometer, and pressure gauge. After vacuum degassing the inside of the pressure-resistant vessel, refrigerant (HFO-1234yf) was filled so that the refrigerant ratio was approximately 13.6%, and a working fluid composition consisting of the refrigerating machine oil and refrigerant was prepared (approximately half the capacity of the pressure-resistant vessel). Under conditions where the temperature of this working fluid composition was stable at - 20°C, the absolute viscosity P (mPa· s) of the working fluid composition was measured using a vibrational viscometer, and the refrigerant dissolution viscosity (mm²/s) was calculated from the measurement results of the density (g/cm³) of the working fluid composition.
The refrigerant dissolution amount S (mass%) was calculated by the following formula: $S = (Rf - Vv \times Dv) \times 100 / ((Rf - Vv \times Dv) + Of)$

Rf: Amount of refrigerant filled into the pressure-resistant vessel (g)
Vv: Volume of refrigerant vapor portion in the pressure-resistant vessel (cm³) (= vessel volume V - working fluid composition volume Vmix)
Dv: Refrigerant vapor density (g/cm³)
Of: Amount of refrigerating machine oil filled into the pressure-resistant vessel (g)

The refrigerant dissolution viscosity R-Vis (mm²/s) was determined as P/Dw, where the absolute viscosity P (mPa· s) was divided by the density Dw (g/cm³) of the working fluid composition. The density Dw (g/cm³) of the working fluid composition was calculated by the following formula: $Dw = (Rf - Vv \times Dv + Of) / Vmix$

Dw: Density of working fluid composition (g/cm³)
Rf: Amount of refrigerant filled into the pressure-resistant vessel (g)
Vv: Volume of refrigerant vapor portion in the pressure-resistant vessel (cm³) (= vessel volume V - working fluid composition volume Vmix)
Dv: Refrigerant vapor density (g/cm³)
Of: Amount of refrigerating machine oil filled into the pressure-resistant vessel (g)
Vmix: Volume of working fluid composition (cm³)

The value of the ratio of refrigerant dissolution viscosity to the kinematic viscosity at 100°C of the refrigerating machine oil measured as described above (refrigerant dissolution viscosity/kinematic viscosity at 100°C) was calculated. The results are shown in Tables 1 and 2. The smaller this ratio, the more it means that the refrigerant dissolution viscosity on the low temperature side can be suppressed to a low level while maintaining the kinematic viscosity on the high temperature side.

[Table 1]

			Example 1	Example 2	Example 3	Example 4
Base Oil Composition (mass%)	Ester (A)	DiPE/ iC8:50%+iC9:50%	46	25	80	72
	Ester (B-1)	NPG/iC8	-	-	20	-
	Ester (B-1)	NPG/iC9	-	-	-	28
	Ester (B-2)	PE/ iC4:60%+iC9:40%	54	-	-	-
	Ester (B-2)	PE/ iC4:37%+iC9:63%	-	75	-	-
	Ester (C)	PE/ iC8:48%+iC9:52%		-	-	-
DiPE Ratio (mol%)			28.9	15.0	56.8	46.7
NPG Ratio (mol%)			0.0	0.0	43.2	53.3
PE Ratio (mol%)			71.1	85.0	0.0	0.0
iC9 Acid Ratio (mol%)			42.9	61.0	28.4	76.6
iC8 Acid Ratio (mol%)			14.4	7.5	71.6	23.4
C7-C9 Acid Ratio (mol%)			57.3	68.6	100	100
C4-C6 Acid Ratio (mol%)			42.7	31.4	0.0	0.0
C4-6 Acid/C7-C9 Acid Molar Ratio			0.74	0.46	0.0	0.0
Average Carbon Number of Ester (X)			43.7	40.8	53.0	50.4
Difference Between Maximum and Minimum Carbon Numbers of Ester (Y)			43	43	43	41
(Y)/(X)			0.98	1.06	0.81	0.81
Molecular Weight Distribution (Mw/Mn)			1.21	1.11	1.03	1.29
Measurement Results	-20°C Kinematic Viscosity (mm²/s)		30,580	33,560	14,980	15,050
	40°C Kinematic Viscosity (mm²/s)		91.1	89.1	83.6	78.9
	100°C Kinematic Viscosity (mm²/s)		10.1	9.9	10.2	9.9
	Viscosity Index		89	87	103	104
	Two Layer Separation Temperature (°C)		<-60	<-60	<-60	<-60
	Refrigerant Dissolution Amount (mass%)		32.6	32.9	30.8	35.6
	Refrigerant Dissolution Viscosity (mm²/s)		32	34	51	34
Refrigerant Dissolution Viscosity/ 100°C Kinematic Viscosity			3.2	3.4	5.0	3.4

[Table 2]

			Example 5	Example 6	Comparative Example 1
Base Oil Composition (mass%)	Ester (A)	DiPE/ iC8:50%+iC9:50%	40	35	16
	Ester (B-1)	NPG/iC8	-	-	-
	Ester (B-1)	NPG/iC9	10	7	-
	Ester (B-2)	PE/ iC4:60%+iC9:40%	-	-	-
	Ester (B-2)	PE/ iC4:37%+iC9:63%	50	58	-
	Ester (C)	PE/ iC8:48%+iC9:52%	-	-	84
DiPE Ratio (mol%)			24.5	21.2	11.6
NPG Ratio (mol%)			17.9	12.4	0.0
PE Ratio (mol%)			57.6	66.3	88.4
iC9 Acid Ratio (mol%)			66.4	64.8	51.8
iC8 Acid Ratio (mol%)			12.2	10.6	48.2
C7-C9 Acid Ratio (mol%)			78.7	75.5	100
C4-C6 Acid Ratio (mol%)			21.3	24.5	0.0
C4-6 Acid/C7-C9 Acid Molar Ratio			0.27	0.33	0.0
Average Carbon Number of Ester (X)			43.7	42.7	42.5
Difference Between Maximum and Minimum Carbon Numbers of Ester (Y)			41	41	27
(Y)/(X)			0.94	0.96	0.63
Molecular Weight Distribution (Mw/Mn)			1.18	1.16	1.06
Measurement Results	-20°C Kinematic Viscosity (mm²/s)		23,780	26,200	18,000
	40°C Kinematic Viscosity (mm²/s)		83.5	84.8	76.7
	100°C Kinematic Viscosity (mm²/s)		9.7	9.8	9.1
	Viscosity Index		94	92	91
	Two layer Separation Temperature (°C)		<-60	<-60	<-60
	Refrigerant Dissolution Amount (mass%)		33.6	33.1	28.3
	Refrigerant Dissolution Viscosity (mm²/s)		25	26	54
Refrigerant Dissolution Viscosity/ 100°C Kinematic Viscosity			2.6	2.7	5.9

As shown in Tables 1 and 2, in Examples 1 to 6, the ratio of refrigerant dissolution viscosity/100°C kinematic viscosity was smaller compared to Comparative Example 1, indicating that refrigerant dissolution viscosity on the low temperature side could be suppressed to a low level while maintaining kinematic viscosity on the high temperature side. In Examples 1, 2, 5, and 6, it is particularly surprising that the refrigerant dissolution viscosity on the low temperature side (-20°C) was remarkably suppressed to a low level, despite the fact that the -20°C kinematic viscosity of the base oil (refrigerating machine oil) itself was higher compared to Comparative Example 1. Moreover, in Examples 1 to 6, the amount of refrigerant dissolved was larger and the refrigerant dissolution viscosity was lower compared to Comparative Example 1.

Claims

A base oil for refrigerating machine 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.
The base oil according to claim 1, wherein the kinematic viscosity of the base oil at 100°C is 8.5 mm²/s or more.
The base oil according to claim 1, comprising the hexaester, the diester, and the tetraester.
A refrigerating machine oil comprising the base oil according to any one of claims 1 to 3.
A working fluid composition comprising the refrigerating machine oil according to claim 4 and a refrigerant.