Title of Invention
REFRIGERATING MACHINE OK, AND WOKWNG FLUID
COMPOSITION FOR REFRIGERATING MACHINES
5 Technical Field
[0001] The present invention relates to a working fluid composition for
a refrigerating machine. The "refrigerating machine" as used herein
includes air conditioners for automobiles, dehumidifiers, refrigerators,
freezing-refrigerating warehouses, vending machines, showcases,
10 cooling apparatus for chemical plants or the like, air conditioners for
housing, package air conditioners and heat pumps for supplying hot
water.
Background Art
[0002] Currently, as a refrigerant for refrigerators, car air conditioners,
15 room air conditioners, industrial refrigerating machines or the like are
widely used 1,1,1,2-tetrafluoroethane (R134a), which is one of
hydrofluorocarbons (HFC), an R410A which is a mixed rekigerant of
difluoromethane (R32) and pentafluoroethane (R125) in a mass ratio of
1/1 and the like. However, the use of these III;C re~igerants is
20 regulated by the so-called F-gas Regulation, the purpose of which is to
protect the global environment, because they havc a high global
warming potential (GWP) of 1000 or more although their
ozone-depleting potential (ODP) is zero.
[0003] As a substitute candidate for a refrigerant with a high GWP,
25 single 2,3,3,3-tetrafluoropropene (HFO-1234yf) or difluoromethane
(332) is studied because of the thermodynamic properties. In addition,
these refrigerants and a mixed refrigerant of them with other refiigerants
which have balanced properties with GWP are also studied. It is
essential for the substitute for a HFC refrigerant to have a low G\W and
HFO-1234yf has a low GWP of 4. R32 has a slightly high GWP of
5 675, however it is studied as a potential candidate because it has a high
gas pressure and is a highly efficient refrigerant.
[0004] Further, hydrocarbon refrigerants such as isobutane (R600a) and
propane (R290), which are practically used for refrigerators, have a low
GWP of 20 or less and proper physical properties, and therefore are
10 studied although their combustibility, and carbon dioxide 01744), which
has a GWP of 1 (standard), is studied as a single rekigcrant or a
refrigerant to be mixed for the purpose of fireproofing.
[0005] When these refiigerants are used, the working fluid in which a
refrigerant and a refrigerating machine oil are mixed together is required
15 to have a higher wear resistance than that of the conventional one
because of severe lubrication conditions.
[0006] In general, as a wear-resistant additive to improve the lubricity
of a lubricating oil are known oily agents such as alcohols, esters and
long-chain fatty acids, wear-resistant agents such as phosphates, metal
20 dithiophosphates, and extreme-pressure agents such as organic sulhr
compounds and organic halogen compounds. In the case of a
refrigerating machine oil, alcohol-based or ester-based oily agents or
triphenyl phosphate or tricresyl phosphate among phosphates are used
because they do not precipitate even when coexisting with a refrigerant
25 and only an additive which does not adversely affect stability can be
used.
[0007] Furthennore, Patent Literature 1 suggests a lubricating oil
including one for refrigerating machine in which a phosphorus-based
additive and a specific epoxy compound are added in combination,
Patent Literature 2 suggests a lubricating oil for a compressor in which a
5 triphenyl phosphate and a tri(alkylpheny1) phosphate are added in
combination for a HFC reeigerant, and Patent Literature 3 suggests a
refrigerating machine oil in which a tsicresyl phosphate and an epoxy
consisting of a glycidyl ether or a carbodiimide are added for a HFC
refiigerant.
10 [0008] However, oily agents among these additives form a lubricating
film by adsorption, and therefore the fiiction coefficient can be
maintained low in the case of relatively mild loading conditions such as
a mixed lubricating area, however the antiwear effect is lost in the case
of severe loading conditions. On the other hand, triphenyl phosphate
15 and tricresyl phosphate have an insufficient wear resistance under
severe lubrication conditions in which a refiigerant with a low GWP
coexists although they have a ceitain degree of a wear resistance effect.
[0009] Because of these facts, a refrigerating machine oil with a higher
wear resistance is demanded and a working fluid with a high wear
20 resistance in which a reffigerant is mixed is required in a freezinglair
conditioning system.
Citation List
Patent Literature
[OO 101 [Patent Literature 11 Japanese Patent Application Laid-Open No.
25 5-171174
[Patent Literature 21 Japanese Patent Application Laid-Open No.
8-157847
[Patent Literature 31 Japanese Patent Application Laid-Open No.
9-189453
Summarjr of Invention
5 Technical Problem
LO0 1 I] The present invention was made in view of the above problems,
and it is the object of the present invention to provide a refrigerating
machine oil and working fluid composition having a high antiwear
effect and being excellent in long-term reliability even under severe
10 lubrication conditions in which a low-GWP refrigerant coexists.
Solntion to Problem
[0012] The present inventors found that a refi-igerating machine oil in
which a sulfide compound and an orthophosphoric acid ester are
blended in a base oil and a working fluid for freezinglair-conditioning
15 comprising a low-GWP refi-igerant can significantly improve the wear
resistance of a refrigerating machine oil without any adverse effect on
other properties, and the present invention was completed.
[0013] That is, the present invention provides a working fluid
composition for a refiigerating machine according to the following [I]
20 to [8].
(11 A refiigerating machine oil comprising: a base oil; a sulfide
compound; and an orthophosphoric acid ester, wherein a content of the
sulfide compound is 0.01 to 2.0% by mass atid a content of the
orthophosphoric acid ester is 0.1 to 5.0% by mass, based on a total
25 amount of the refrigerating machine oil, and the refrigerating machine
oil having a kinematic viscosity at 40°C of 3 to 500 mm2/s.
[2] The refiigerating machine oil according to [I], wherein the
base oil is at least one selected from the group consisting of an ester
with a carboi~/oxygenm olar ratio of 2.5 or more and 5.8 or less and an
ether with a carbodoxygen molar ratio of 2.5 or more and 5.8 or less;
and the kinematic viscosity of the refrigerating machine oil at 40°C is 3
to 300 i d s .
[3] The refrigerating machine oil according to [l] or [2],
wherein the base oil is at least one selected from the group consisting of
a polyol ester obtainable by synthesis from a fatty acid with 4 or more
and 9 or less carbon atoms and a polyhydric alcohol with 4 or more and
12 or less carbon atoms, a polyalkylene glycol, a compound obtainable
by etherifying hydroxyl groups at both ends of a polyalkylene glycol,
and a polyvinyl ether.
[4] The refiigerating machine oil according to any one of [l] to
[3], wherein the sulfide compound is a thiobisphenol compound and the
o~thophosphoric acid ester is at least one selected from the group
consisting of triphenyl phosphate, tricresyl phosphate, and an
alkylphenyl phosphate having a C3-C4 alkyl group.
[5] The reeigerating machine oil according to any one of [I] to
[4] further comprising 2 to 20% by mass of pentaerythl-it01
tetra(2-ethylhexanoate) based on the total amount of the refiigerating
machine oil.
[6] A working fluid composition for a refiigerating machine
comprising: a reeigerant wit11 a global warming potential of 700 or less;
and the refiigerating machine oil according to any one of [I] to [S].
[7] The working fluid composition for a refrigerating machine
according to [6], wherein the refrigerant is a rekigerant comprising at
least one selected from the group consisting of a hydrofluorocarbon, a
hydrofluoroolefin, carbon dioxide and a hydrocarbon with 2 to 4 carbon
atoms.
[8] The working fluid composition for a refrigerating machine
according to [6] or [7], wherein the rekigerant is a rekigerant
comprising at least one selected from the group consisting of
difluoromethane and 2,3,3,3 -tetrafluoropropene.
Advantageous Effects of Envention
10 [0014] The refrigerating machine oil and working fluid composition for
a refrigerating machine accordiig to the present invention exert a
special effect that they have a significant antiwear effect even under
severe lubrication conditions in which a low-GWP rekigerant coexists
and can be used stably for a long time.
15 Description of Embodiments
[0015] The refrigerating machine oil according to the present
embodiment is a refrigerating machine oil which contains a base oil and
0.01 to 2.0% by mass of a sulfide compound and 0.1 to 5.0% by mass of
an orthophosphoric acid ester based on a total amount of the
20 refrigerating machine oil, and has a kinematic viscosity at 40°C of 3 to
500 mm2/s.
[0016] In the present embodiment, at least one selected from a mineral
oil-based base oil and a synthesized oil-based base oil can be used as the
base oil. These base oils may be used in a mixture of two or more
25 thereof.
[0017] Examples of the mineral oil-based base oil include
paraffin-based mineral oils, naphthene-based mineral oils and
mixed-base mineral oils, and any of them is a refmcd lubricating oil
fraction obtained by treating the lubricating oil fiaction obtained by
subjecting a crude oil to atmospheric distillation and firther
5 reduced-pressure distillation with means for refining a lubricating oil
such as solvent deasphalting, solvent extraction, hydrorefhing,
hydrocracking, solvent dewaxing, hydrodewaxing and clay treatment in
combination appropriately, and can be suitably used. Among them, the
solvent extraction, hydrorefining and hydrocracking are processes to
I0 control the composition, and the solvent dewaxing and hydrodewaxing
to remove the wax component are processes to control low-temperature
properties such as a pour point, and the clay treatment is a process to
remove the nitrogen component mainly to improve the stability of a
base oil. Refmed lubricating oil fractions with different characteristics
15 obtained by combining various raw materials with various refining
means may be used singly or in combination of two or more.
[0018] Examples of the synthesized oil-based base oil include
oxygen-containing compounds such as esters and ethers, hydrocarbon
oils such as poly-a-olefins (PAO), ethylene-a-ole% oligomers,
20 alkylbenzenes and alkylnaphthalenes.
[0019] Among the oxygen-containing compound base oil, esters are
compounds having vaious molecular structures, and are a base oil
characterized in they have unique viscosity properties and
low-temperature properties respectively and have a higher flash point
25 than that of hydrocarbon-based base oil with the same viscosity. Esters
can be obtained by subjecting an alcohol and a fatty acid to dehydration
condensation reaction, and in the present embodiment, examples of the
suitable base oil component include diesters of a dibasic acid and a
monol~ydric alcohol, polyol esters of a polyol (particularly, a neopentyl
polyol) and a monocarboxylic acid, and complex esters of a polyol, a
polybasic acid and a monol~ydric alcohol (or a monocarboxylic acid)
from the viewpoint of chemical stability.
[0020] In the case that an ester is used as the oxygen-containing
compound base oil, it is preferable that the ester have the carbonloxygen
molar ratio of 2.5 or more and 5.8 or less horn the viewpoint of
compatibility with low-GWIZ refrigerants (such as R32) which have a
high polarity. In addition, more preferred are polyol esters which are
synthesized from a linear or branched fatty acid with 4 to 9 carbon
atoms and a polyhydiic alcohol with 4 to 12 carbon atoms and which
are excellent in compatibility with various low-GWP reeigerants.
[0021] Specific examples of the linear fatty acid with 4 to 9 carbon
atoms include butanoic acid, pentanoic acid, hexanoic acid, heptanoic
acid, octanoic acid and nonanoic acid. Specific examples of the
branched fatty acid include branched butanoic acids, branched
pentanoic acids, branched hexanoic acids, branched heptanoic acids,
branched octanoic acids and branched nonanoic acids, More
specifically, fatty acids having a branch at the a- and/or P-position are
preferable, and isobutanoic acid, 2-methylbutanoic acid,
2-methylpentanoic acid, 2-methylhexanoic acid, 2-ethylpentanoic acid,
2-methylheptanoic acid, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic
acid and the like are preferable, and among them, 2-ethylhexanoic acid
andlor 3,5,5-trunethylhexanoic acid are the most preferable. Note that
fatty acids other than the fatty acids with 4 to 9 carbon atoms may be
contained.
[0022] Polyhydric alcohols with 2 to G hydroxy groups are preferable as
the polyhydric alcohol. Further, it is preferable that the number of
5 carbon atoms of the polyhydric alcohol be 4 to 12. Specifically
hindered alcohols such as neopentyl glycol, trimethylolethane,
trimethylolpropane, trimethylolbutane, di-(trimethylolpropane),
pentaerythritol and di-(pentaerythritol) are preferable. Pentaerythritol
or a mixture ester of pentaelythritol and di-(pentaerythritol) is the most
10 preferable because they are excellent in compatibility with refi.igerants
and hydrolytic stability.
[0023] Examples of the ether include polyalkylene glycols, compounds
in which one end or both ends of a polyalkylene glycol islare etherified
and polyvinyl ethers. Examples of the polyalkylene glycol include
15 polypropylene glycols, polyethylene glycols and copolymers of
propylene oxide and ethylene oxide. With regard to the end structure,
at least one of the ends is preferably an alkyl group, particularly
preferably a methyl group, from the viewpoint of hygroscopicity.
Further, £ram the viewpoint of easiness to manufacture and costs, it is
20 preferable that one of the ends be an alkyl group and the other be a
hydrogen atom, and especially preferable that one be a methyl group
and the other be a hydrogen atom. With regard to the main backbone,
a copolymer containing an oxyethylene (EO) group and an
oxypropylene (PO) group is preferable kom the viewpoint of lubricity,
25 the ratio of oxyethylene groups relative to the total of oxyethylene
groups and oxypropylene groups (EO / (PO + EO)) is preferably in a
range of 0.1 to 0.8, and more preferably in a range of 0.3 to 0.6.
Furthermore, fiom the viewpoint of hygroscopicity and heaVchemica1
stability, the value of EO I (PO + EO) is preferably in a range of 0 to
0.5, more preferably in a range of 0 to 0.2, and most preferably 0 (i.e., a
5 homopolymer of propylene oxide).
[0024] A polyvinyl ether has a st~uctural unit represented by the
following folmula (I). The polyvinyl ether in the present embodiment
may be a homopolymer whose structural units are identical or a
copolymer which is composed of two or more types of structural units,
10 however a copolymer is preferable because it enables to adjust the
properties in a balanced manner.
[Chemical Formula 11
[R', R2 and R~ may be identical to or different f?om each other and eaclr
15 represents a hydrogen atom or a hydrocarbon group; R~ represents a
divalent hydrocarbon group or a divalent hydrocarbon group containing
an oxygen constituting an ether bond; R' represents a hydrocarbon
group; m represents an integer of 0 or more, and it is preferable that the
average value of m be 0 to 10; R' to R~ may be identical to or different
20 from each other in each stluctural unit; and when m is 2 or more in one
structural.unit, a plurality of ~~0 may be identical to or different fiom
each other.]
[0025] Also with regard to these ethers, more p~eferablea re ethers with
a carbon/oxygen molar ratio of 2.5 or more and 5.8 or less, which is
excellent in compatibility with low-GWP refi-igerants, particularly i
refrigerants containing R32.
I
[0026] A PA0 is widely used among hydrocarbon oils. Because a i
PA0 is a polymer of an a-olefin, the properties can be modulated
5 depending on the degree of polymerization. Alkylbenzenes are used in
the field of lubricating oils for a refrigerating machine, and they are
classified into a linear type and a branched type on the basis of the
sttucturc of the alkyl group and used in a different way depending on
the object because they have different properties from each other.
10 [0027] The above mineral oil-based base oil and synthesized oil can be
blended in an appropriate fraction so that various performances required
depending on the application can be satisfied. In this case, a plurality
of mineral oil-based and synthesized oil-based base oils may be used
respectively.
15 [0028] Any of monosulfide compounds, disulfide compounds and
polysulfide compounds can bc used as the sulfide compound in the
present embodiment, however, monosulfide compounds are preferable.
Monosulfide compounds, for example, have a less activity than
disulfide compounds and arc preferable from the viewpoint of the
20 stability of a refrigerating machine oil, the suppression of the
degeneration of cupper widely used in a refiigerating machine, or the
like.
[0029] Examples of the sulfide compound include diphenyl sulfide,
dibenzyl sulfide, didecyl sulfide, didodecyl sulfide and thiobisphenol
25 compounds, and thiobisphenol compounds, which are commonly known
as antioxidants, have radical capturing ability and are also stabilizers,
are preferable for the application of the present invention. As the
thiobisphenol compound, a compound represented by the following
formula (2) is preferably used.
[Chemical Formula 21
F~ and R~ may be identical to or different from each other and each
represents a hydrocarbon group; p, q, r and s may be identical to or
different eom each other and each represents an integer of 0 to 5 such
that p+q and r+s are 0 to 5, with the proviso that at least one of q and s
10 is 1 or more; and t and u may be identical to or different from each other
and each represents an integer of 0 to 10.1
[0030] In the formula (2), R~ and R~ may be identical to or different
from each other and each represents a hydrocarbon group, and p, q, r
and s may be identical to or different from each other and each
15 represents an integer of 0 to 5 such that p+q and rts are 0 to 5.
However, at least one of q and s is 1 or more and most preferably both
of q and s are 1. Further, t and u may be identical to or different from
each other and each represents an integer of 0 to 10. t and u are
preferably 0 to 4, more preferably both oft and u are 0 or 1, and most
20 preferably both oft and u are 0. A preferred hydrocarbon goup is an
alkyl group, cycloalkyl group and alkenyl group with 1 to 10 carbon
atoms, preferably with 1 to G carbon atoms and phenyl group, and
specific examples thereof include a methyl group, an ethyl group, an
n-propyl gsoup, an i-propyl group, an n-butyl group, a sec-butyl group
and a tert-butyl group.
[003 I] Preferred examples of the compound represented by the fo~mula
(2) specifically include 4,4'-thiobis (3-methyl-6-tert-butylphenol),
4,4'-thiobis(2,6-di-tert-butylphenol), 4,4'-thiobis
5 (2-methyl-6-tert-butylphenol), 2,2'-thiobis
(4-methyl-6-tert-butylphenol), 2,2'-thiobis (4,6-di-tert-butylphenol) and
his (3,5-di-tert-butyl-4-hydroxybenzy1)sulfide.
[0032] The content of the sulfide compound is 0.01 to 2.0% by mass,
preferably 0.05 to 1.0% by mass, and more preferably 0.1 to 0.5% by
10 Inass based on the total amount of the refrigerating machine oil. If the
content is below the above lower limit value, then the wear
resistance-improving effect is insuEcient, and if the content is over the
above upper limit value, then corrosive wear may be caused on the
contrary depending on the atmosphere.
15 [0033] Triphenyl phosphate (TPP), tricresyl phosphate (TCP) and
alkylphenyl phosphates (APP) having a C3-C4 alkyl group (alkyl group
with 3 to 4 carbon atoms) are preferable as the orthophosphoric acid
ester in the present embodiment. TPP and TCP have a single structure
and an APP is a mixture of one having one alkylphenyl group
20 (mono-type), one having two akylphenyl groups (di-type) and one
having thee alkylphenyl groups (hi-type), and the mixture ratio thereof
is not particularly limited.
[0034] The content of the orthophosphoric acid ester is 0.1 to 5.0% by
mass, preferably 0.1 to 3.0% by mass, and more preferably 0.2 to 2.0%
25 by mass based on the total amount of the refrigelating machine oil. If
the content is below the above lower limit value, the wear
resistance-improving effect is insufficient, and if the content is over the
above upper limit value, then the stability may be lowered.
LO0351 In the present embodiment, the wear resistance of the working
fluid can be dramatically improved by further blending pentaerythritol
5 tetra(2-ethylhexanoate) in the refrigerating machine oil.
Pentaemitol tetxa(2-ethylhexanoate) is an ester synthesized fiom
pentae'ythitol and 2-ethylhexanoic acid. It is preferable that it be a
complete ester (also refened to as a "full ester") in which all of the
hydroxyl groups in the pentaerythritol are esterified. It is preferable
10 that the acid value of the ester be 0.1 mgKOHlg or less and the hydroxyl
value thereof be 10 mgKOHIg or less, respectively. The amount of the
above ester to be blended is preferably 2 to 20% by mass based on the
total amount of the refrigerating machine oil, and more preferably 2 to
7% by mass, although the optimum amount to be blended varies
15 depending on the type and viscosity of the base oil. A significant wear
resistance-improving effect cannot be exerted in the cases of a large
amount and a small amount to be blended, although the mechanism has
not been revealed.
[0036] In the present embodiment, in order to hther improve the
20 perfolmance, an additive conventionally used for a lubricating oil such
as an antioxidant, a friction modifier, an antiwear agent, an
extreme-pressure agent, a rust inhibitol; a metal deactivator and an
antifoaming agent can be contained in the refrigerating machine oil
within a range not impairing the object of the present invention.
25 [0037] Examples of the antioxidant include phenol compounds such as
di-tert-butyl-p-cresol, and amine compounds such as an
alkyldiphenylamine; examples of the friction modifies include aliphatic
amines, aliphatic a~nides, aliphatic hides, alcohols and esters;
examples of the antiwear agent include acidic phosphate amine salts,
phosphite amine salts and zinc dialkyldithiophosphates; examples of the
5 extreme-pressure agent include olefin sulfides and sulfurized oils and
fats; examples of the mst inhibitor include alkenyl succinates or alkenyl
succinic acid partial- esters; examples of the metal deactivator include
benzotriazole, thiadiazole and gallates; and examples of the antifoaming
agent include silicone compounds and polyester compounds,
10 respectively.
[0038] The kmematic viscosity of the refrigerating machine oil at 40°C
is 3 to 500 mm2/s, preferably 3 to 300 d s , and more preferably 5 to
150 rnm2/s. By setting the kinematic viscosity in the above range, a
sufficient wear resistance can be obtained and compatibility with a
15 refrigerant can be enhanced.
[0039] The characteristics of the refrigerating machine oil other than
the kinematic viscosity at 40°C are not particularly limited, however,
the viscosity index is preferably 10 or more. The pour point is
preferably -lO°C or lower, and more preferably -20°C or lower. The
20 flash point is preferably 120°C or higher, and more preferably 200°C or
higher.
[0040] In addition, the acid value of the refrigerating machine oil is not
particularly limited, however, in order to prevent the corrosion of metals
used in a refrigerating machine or a piping and suppress the
25 deterioration of the refitgerating machine oil itself, the acid value can be
preferably set to 0.1 mgKOWg or less, and inore preferably 0.05
mgKOWg or less. Note that the acid value in the present invention
means an acid value measured in accordance with JIS K2.501
"Petroleum products and lubricants-Determination of neutralization
number".
5 [0041] The moisture content of the refrigerating machine oil is not
particularly limited, howcver, it is preferably 200 ppm or less, more
preferably 100 ppm or less, and most preferably 50 ppm or less.
Particularly in the case that the refrigerating machine oil is used for a
sealed-type refsigerating machine, the moisture content is required to be
10 low from the viewpoint of the stability and electrical insulation
properties of the refrigerating machine oil.
[0042] With regard to refrigerating machines, there is a trend that the
current HFC refrigerant with a high GWP is replaced with a refrigerant
with a low GWP froin the viewpoint of preventing the global warming
15 as described above, and a refsigerating machine oil applied thereto has
been needed and a suitable working fluid in which a refrigerant and a
refifprating machine oil are mixed together is required.
Currently, 1,1,1,2-tetrafluoroethane (R134a) is widely used for
refrigerators and car air conditioners, and R410A which is a mixed
20 refrigerant of difluoromethane (R32) and pentafluoroethane (R125) in a
mass ratio of 111 is widely used for room air conditioners. For the
base oil of the refrigerating machine oil for these refrigerants, esters,
polyethers, particularly polyol esters, polyalkylene glycols and
polyvinyl ethers, which have a moderate mutual solubility
25 (compatibility), are suitable.
[0043] In a refrigerant circulation cycle in a refsigeratinglair
conditioning machine, the refrigerating machine oil lubricating the
compressor circulates in the cycle along with the regigerant, and
therefore the compatibility of the refsigerating machine oil with the
refrigerant is requked. If the refrigerating machine oil and thc
5 refrigerant are not compatible, the reeigerating machine oil discharged
from the compressor is likely to remain in the cycle, and as a result the
amount of the oil in the compressor is decreased to cause problems such
as wear due to defective lubrication and the blockage of an expansion
mechanism such as a capillary.
10 [0044] However, any of the above refrigerants has a high GWF' of 1000
or more and therefore the use thereof is going to be regulated by the
so-called F-gas Regulation. As an alternative therefor,
hydrofluoroolefins WO) which are unsaturated hydrocarbons with a
low GWP and difluoromethane (R32), or hydrocarbon refrigerants such
15 as isobutane (R600a) and propane (R290), carbon dioxide (R744), and
in addition mixed refrigerants containing them are studied and
considered to be leading candidates.
[0045] Examples of the unsaturated hydrocarbon include
2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,3,3,3-tetrafluoropropene
20 (HFO-1234ze) and 1,2,3,3,3-pentafluoropropene (HFO-1225ye).
These HFO refrigerants have an olefin structure subject to
decomposition in the molecule, and therefore characterized in that they
have a low stability, although having a low GWP. In particular, under
conditions of a high loading, a local heat generation occurs at a sliding
25 part of metaumetal contact to cause the decomposition of the refrigerant
to be accelerated along with wear and hydrofluoric acid is generated,
which may lead to the deterioration of the working fluid in which the
refrigerant and the refrigerating machine oil are mutually dissolved and
moreover may cause corsosive wear in relation to lubricity, and
therefore the lubricity of the refrigerating machine oil is critical
5 properties.
[0046] In the case of R32 which is a hydrofluorocarbon (I-PC)h aving a
low boiling point and a high pressure or a mixed refrigerant containing a
large amount of R32, the discl~arge temperature of the compressor is
increased to reduce the thickness of the oil film of the refiigerating
10 machine oil, resulting in severe lubrication conditions. In the case of a
hydrocarbon refrigerant, it has no fluorine in the hydrocarbon molecule,
which contributes to the improvement of lubricity, and has a high
solubility in the refrigerating machine oil, which lowers the viscosity of
the refrigerating machine oil, resulting in severe lubrication conditions.
15 As described above, any of the refrigerant candidates having a low
GWP causes severe conditiolis in view of lubricity, and therefore the
refrigerating machine oil to be used is required to have a high lubricity.
[0047] The refrigerant in the present embodiment is not pa~ficularly
limited as long as the GWP thereof is 700 or less, however, a refrigerant
20 which dissolves mutually, that is, a refrigerant which dissolves mutually
without being separated into two layers at a normal temperature is
preferable. In particular, a refi'igerant containing one or more selected
fsom a hydrofluorocarbon (HFC), a hydrofluoroolefin (HFO), carbon
dioxide (R744) and a hydrocarbon with 2 to 4 carbon atoms is more
25 preferable, and a refrigerant containing difluoromethane (R32) andlor
2,3,3,3-tetrafluoropropene( HFO-1234yf)is the most preferable.
[0048] In the working fluid composition for a refrigerating machine
according to the present embodiment, the blending ratio of the
reeigerating machine oil/ref?igerant is not particularly limited, however,
the blending ratio is usually 1 to 1000 parts by weight, and preferably 2
5 to 800 parts by weight based on 100 parts by weight of the refrigerant.
Examples
[0049] Hereinafter, the present invention will be specifically described
on the basis of Examples and Comparative Examples, however, the
present invention is never limited to the following Examples.
10 [0050] [Examples 1 to 12, Comparative Examples 1 to 121
In Examples 1 to 12 and Cotnparative Examples 1 to 12,
refrigerating machine oils having the compositions shown in Tables 1 to
3 were prepared using the base oils and additives shown in the
following. Note that the content of the base oil and the additive shown
15 in Tables 1 to 3 is a content based on the total amount of the
refrigerating machine oil.
[005 11 [Base Oil]
(A-1) Polyol ester (POE-1): an ester of pentae~ythritol and a
mixed acid of 2-methylpropanoic acid and 3,5,5-trimethylhexanoic acid
20 in a mass ratio of 35:65 (kinematic viscosity: 68.1 mm2/s at 40°C;
viscosity index: 84; pour point: -40°C; flash point: 240°C;
carbonloxygen molar ratio: 3.6)
(A-2) Polyol ester (POE-2): an ester of pentaerytl~ritol and a
mixed acid of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid in
25 a mass ratio of 5:5 (kinematic viscosity: 66.7 mn2/s at 40°C; viscosity
index: 92; pour point: -40°C; flash point: 248°C; carbonloxygen molar
ratio: 4.8)
(A-3) Polyalkylene glycol (PAG): a polyoxypropylene in which
the both ends are each blocked with a methyl group (average molecular
weight: 1000; kinematic viscosity: 46.0 m d s at 40°C; viscosity index:
5 190; pour point: -4S°C; flash point: 218°C; carbodoxygen molar ratio:
3.0)
(A-4) Polyvinyl ether (PVE): a copolymer of ethyl vinyl ether
and isobutyl vinyl ether (ethyl vinyl ether: isobutyl vinyl ether is 7:l in a
weight ratio), (average molecular weight: 910; kinenlatic viscosity: 66.4
10 mm2/s at 40°C; viscosity index: 85; pour point: -35°C; flash point:
210°C; carbodoxygen molar ratio: 4.3)
(A-5) Mineral oil-based base oil NO): paraffin-based refined
mineral oil (kinematic viscosity: 22.3 i d s at 40°C; viscosity index:
95; pour point: -lS°C; flash point: 200°C)
15 Note that the kinematic viscosity and the viscosity index were
measured in accordance with JIS K2283, the pour point was measured
in accordance with JIS K2269, and the flashing point was measured in
accordance with JIS K2265.
[0052] [Sulfide Compound]
20 (S-1) Dibenzyl sulfide
(S-2) Didodecyl sulfide
(S-3) 4,4'-thiobis (3-methyl-6-tert-butylphenol)
[0053] [Orthophosphoric acid ester]
(P-1) Tricresyl phosphate (TCP)
25 0-2) Triphenyl phosphate (TPP)
(P-3) Tridecyl phosphate (TDP)
[0054] [Other Material]
(D-1) Pentaerythritol tetra(2-ethylhexanoate) (an ester of
peniaeiythritol and 2-ethylhexanoic acid; acid value: 0.01 mgKOK/g;
hydroxyl value: 1.2 mgKOH1g)
5 [0055] Next, the refrigerating machine oils in Examples I to 12 and
Comparative Examples 1 to 12 were subjectcd to the following lubricity
test and stability test in combil~ationw ith the various refrigerants shown
in Tables 1 to 3. Note that "1234yf" in Tables 1 to 3 means
HEO-1234yf.
10 [0056] (Lubiicity Test)
The lubricity test was in accordance with ASTM D3233-73 and
the wear test was can-ied out with a Falex (pitvll-block) test machine at
a constant loading.
In the Falex wear test, a running-in was performed for 5 min at
15 an initial temperature of 50°C, a rotational frequency of 290 rpm and a
loading of 50 Lbf under an atmosphere with the blowing of the
rekigerant controlled (70 mllmin), and thereafter the final test was
performed for 1 h at the same rotational frequency and a loading of 100
Lbf to measure the total va111e (mg) of the amounts of wear for the pin
20 and the V-block after the test.
R32, HFO-1234yf and R600a (isobutane) were used as the
refrigerant to be blown.
[0057] (Stability Test)
The stability test was in accordance with JIS K2211-09
25 (autoclave test), in which 90 g of a sample oil whose moisture content
was adjusted to 100 ppm was weighed in a autoclave, and catalysts
(wires made of iron, copper, and aluminum, respectively, outer diameter
1.6 mm x 50 nun for any of them) and 10 g of each refrigerant (R32,
HFO-1234yf, R600a) were sealed in, and thereafter heated to 175'C and
the appearance and acid value (JIS C2101) of the sample oil after 100 h
5 were measured.
The acid values of sample oils before the stability test (new oil)
were all 0.01 mgKOWg.

CLAIMS
1. A refrigerating machine oil comprising:
a base oil;
a sulfide compound; and
an orthophosphoric acid ester,
wherein a content of the sulfide compound is 0.01 to 2.0% by
mass and a content of the orthophosphoric acid ester is 0.1 to 5.0% by
mass, based on a total amount of the refrigerating machine oil, and
the re£rigerating machine oil having a kinematic viscosity at
2. The refrigerating machine oil according to claim 1, wherein the
base oil is at least one selected from the group consisting of an ester
with a carbon/oxygen molar ratio of 2.5 or more and 5.8 or less and an
ether with a carbonloxygen molar ratio of 2.5 or more and 5.8 or less;
15 and the kinematic viscosity of the refrigerating machine oil at 40°C is 3
to 300 mm2/s.
3. The refrigerating machine oil according to claim 1 or 2, wherein
the base oil is at least one selected &om the group consisting of a polyol
ester obtainable by synthesis from a fatty acid with 4 or more and 9 or
20 less carbon atoms and a polyhydric alcohol with 4 or more and 12 or
lcss carbon atoms, a polyalkylene glycol, a compound obtainable by
etherifying hydroxyl groups at both ends of a polyalkylene glycol, and a
polyvinyl ether.
4. The refrigerating machine oil according to any one of claims 1
25 to 3, wherein the sulfide compound is a thiobisplienol compound and
the osthophosphoric acid ester is at least one selected ffom the group
consisting of triphenyl phosphate, tricresyl phosphate, and an
alkylphenyl phosphate having a C3-C4 alkyl group.
5. The refrigerating machine oil according to any one of- claims 1
to 4 further comprising 2 to 20% by mass of pentaerytlvtol
5 tetra(2-ethylhexanoate) based on the total amount of the refrigerating ';
machine oil.
6. A working fluid composition for a refrigerating machine
--
comprising:
a refiigerant with a global warming potential of 700 or less; and
10 the refrigerating machine oil according to any one of claims 1 to
5.
7. The working fluid composition for a refrigerating machine
according to claim 6, wherein the refri erant is a 1 refrigerant comprising
at least one selected from the group consisting of a hydrofluorocarbon, a
15 hydrofluoroolefin, carbon dioxide and a hydrocarbon with 2 to 4 carbon
- s + atoms.
8. The working fluid comi;osition for a refrigerating machine
according to claim 6 or 7, where& the refrigerant is a refrigerant
comprising at least one selected from the group consisting of
20 difluoromethane and 2,3,3,3-tetrafluoropropene.