JP2014111795A - Refrigeration oil for cooling medium r32 - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration oil in which excellent compatibility and dissolubility to a cooling medium R32 are possessed, a viscosity in which lubricity is not damaged can be retained, and stability, lubricity, and electrical insulation properties or the like are excellent.SOLUTION: A refrigeration oil for a cooling medium R32 is such that an ester in which an ester intermediate in which trimethylol propane and/or neopentyl glycol is reacted with a 2-12C dibasic acid and esterification is performed by a 1-12C monohydric alcohol or a 2-12C monovalent fatty acid, and an acid number is at most 0.1 mgKOH/g is made a base oil, and a kinematic viscosity at 100°C is 2-30 mm/s.

Description

The present invention relates to a refrigerating machine oil that uses R32 (difluoromethane, CH ₂ F ₂ ) having a low global warming potential as a refrigerant.

Conventionally, in refrigerators, air conditioners, refrigerators, etc., chlorofluorocarbons (CFCs) such as R-11 (trichloromonofluoromethane) and R-12 (dichlorodifluoromethane) containing fluorine and chlorine as refrigerants are used as refrigerants. ), Hydrochlorofluorocarbon (
HCFC) such as R-22 (monochlorodifluoromethane) has been used, but related to the recent ozone depletion problem, its production and use has been regulated internationally, and now it does not contain chlorine For example, tetrafluoroethane (R-134 or R-134a)
And new hydrogen-containing chlorofluorocarbon refrigerants such as R410A and R407C, which are mixed refrigerants. However, although these HFCs do not destroy the ozone layer, they have a large greenhouse effect.
From the viewpoint of global warming, which has become a problem in recent years, it is not necessarily an excellent refrigerant.

Thus, R32 has recently been attracting attention because it does not destroy the ozone layer and has a much lower impact on global warming than the above-mentioned chlorinated or non-chlorinated fluorinated hydrocarbons. It is considered to use this compound as a refrigerant in refrigeration systems with high cooling efficiency such as room air conditioners and industrial refrigerators composed of compressors, condensers, throttle devices, evaporators, etc., cultivated with the above-mentioned fluorocarbon refrigerants. Compared with R410A, which is a mixed refrigerant of hydrofluorocarbon (HFC), which is currently widely used as a refrigerant for room air conditioners, the global warming potential is about 1/3, high efficiency, and large-scale design of air conditioners There is a possibility that the impact on global warming can be greatly reduced without any changes. However, since there is slight combustibility, technical development for safe use and selection of refrigerating machine oil compatible with this refrigerant as a lubricant are problems.

In Patent Documents 1 and 2, a refrigeration apparatus using R32 (difluoromethane, CH ₂ F ₂ ) as a refrigerant, a refrigeration cycle, or an air conditioner is presented. As refrigeration oil, polyvinyl ether, polyol ester, carbonate ester, Examples include alkylbenzene, mineral oil, ester oil, ether oil or PAG oil having a kinematic viscosity at 40 ° C. of 32 cSt or more.
However, the compatibility, solubility, lubricity in the refrigerant mixed state, etc., which are essential performances for refrigeration oil, vary depending on the type of refrigerant. It cannot be generally said that even a freezer oil can be used satisfactorily as it is. In particular, compatibility with the refrigerant is important, and incompatible refrigerating machine oil cannot be used from the viewpoint of oil return in the refrigeration system. In the case of the refrigeration cycle, if the oil taken out from the compressor is not compatible with the refrigerant and stays in the cycle and does not return to the compressor, the lubricating oil (refrigerant oil) supplied to the sliding part decreases and wear occurs. In addition, seizure occurs, causing the system to break. That is, the lubricant suitable for the refrigerant R32 has compatibility with the refrigerant,
Although it can be understood by evaluating the performance as described above, it has not been done yet, and no suitable refrigerating machine oil has been proposed.

JP 2006-153439 A JP 2005-83704 A

The present invention solves the above problems, has moderate compatibility and solubility with respect to the refrigerant R32, can maintain a viscosity that does not impair the lubricity, and can reduce the amount of refrigerant charged, An object of the present invention is to provide a refrigerating machine oil having excellent stability and lubricity.

As a result of intensive studies to solve the above problems, the present inventor has a specific ester having moderate compatibility and solubility with respect to the refrigerant R32, high stability, low hygroscopicity, and good lubrication. Therefore, the present invention has been found out that it is excellent as a refrigerating machine oil for the refrigerant R32.

The present invention as means for solving the above problems is as follows.
(1) An ester intermediate obtained by reacting trimethylolpropane and / or neopentyl glycol with a dibasic acid having 2 to 12 carbon atoms is further converted to a monohydric alcohol having 1 to 12 carbon atoms or one having 2 to 12 carbon atoms. A refrigerating machine oil for refrigerant R32 having a kinematic viscosity at 100 ° C. of ² to 30 mm ² / s based on an ester esterified with a hydric fatty acid and having an acid value of 0.1 mg KOH / g or less.

(2) The dibasic acid is any one or more selected from adipic acid, pimelic acid, suberic acid, azelaic acid or sebacic acid, the monohydric alcohol is a branched alcohol, and the monovalent fatty acid is a branched fatty acid. ) Refrigerating machine oil for refrigerant R32.
(3) The above (1), wherein the monohydric alcohol is 2-ethylhexanol and / or 3,5,5-trimethylhexanol, and the monohydric fatty acid is 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid Or the refrigerating machine oil for refrigerant | coolant R32 as described in (2).

(4) An ester intermediate obtained by reacting a dibasic acid with more than 1.5 mol and less than 3 mol with respect to 1 mol of trimethylolpropane is further converted into 2-ethylhexanol and / or 3,5,5-trimethyl. The refrigerating machine oil for R32 according to any one of the above (1) to (3), wherein an ester esterified with hexanol is used as a base oil.
(5) A combination of any one or more of hindered phenol compounds, aromatic amine compounds, epoxy compounds, carbodiimides or phosphate esters, and 0.05 to 0.05 based on the total amount of refrigerating machine oil.
Refrigerating machine oil for refrigerant | coolant R32 in any one of said (1)-(4) consisting of having added 5.0 weight%.
(6) The refrigerating machine oil for refrigerant R32 according to any one of (1) to (5), wherein the volume resistivity is 10 ¹¹ Ω · cm or more.

The refrigerating machine oil of the present invention has moderate compatibility and solubility with respect to the refrigerant R32, and also has high electrical insulation, low moisture absorption, good lubricity, and high thermal oxidation stability. The filling amount can be reduced, and the refrigerating machine oil for the refrigerant R32 is excellent in overall performance.

In the present invention, an ester intermediate obtained by reacting neopentyl polyol trimethylolpropane and / or neopentyl glycol with a dibasic acid having 2 to 12 carbon atoms is synthesized,
Further, an ester esterified with a monohydric alcohol or a monohydric fatty acid is used as a base oil.
Since the refrigerant R32 has a large polarity, the polyol ester synthesized with neopentyl glycol and monohydric fatty acid, which has been used for conventional HFC refrigerants, is compatible with a low molecular weight, that is, having a low viscosity. At the required proper viscosity, refrigerant R32
Refrigerating machine oil compatible with can not be selected.

In the present invention, the esterification with two steps of esterification has a higher polarity and is easily compatible with R32, and has a viscosity necessary for a refrigeration compressor. That is, the first stage trimethylolpropane and / or neopentyl glycol and dibasic acid are esterified, and the molar ratio of these is adjusted to arbitrarily obtain a carboxyl group or hydroxyl group as an intermediate. When the group remains, it is esterified with a monohydric alcohol, and when the hydroxyl group remains, it is further esterified with a monovalent fatty acid to obtain an ester having a desired performance. In this case, the neopentyl polyol having more than 7 carbon atoms has a too large hydrocarbon portion, and the ester synthesized therefrom has low compatibility and solubility with the refrigerant R32. Refrigerant R3
Trimethylolpropane is particularly preferred because it is compatible with 2 and can synthesize high-viscosity esters.

In short, when trimethylolpropane is used, first, trimethylolpropane 1
More or less than 1.5 moles of equimolar dibasic acid with respect to moles, preferably 0.1.
The esterification reaction is carried out using at least 5 mol and less than 1.5 mol, or more than 1.5 mol and 5 mol or less. Next, when the dibasic acid is less than 1.5 mol, the remaining hydroxyl group is esterified using a monovalent fatty acid, and the remaining monovalent fatty acid is removed by distillation under normal pressure or reduced pressure. Also,
When the dibasic acid exceeds 1.5 mol, the remaining carboxyl group is esterified with a monohydric alcohol, and the remaining monohydric alcohol is removed by distillation under normal pressure or reduced pressure.
In addition, with respect to 1 mol of trimethylolpropane in the first stage, more than 1.5 mol of dibasic acid,
When less than 3 moles are used and the carboxyl group remaining in the second stage is esterified with 2-ethylhexanol and / or 3,5,5-trimethylhexanol, an ester having excellent compatibility with the refrigerant R32 and lubricity is obtained. Therefore, it is more preferable.

On the other hand, when neopentyl glycol is used, the dibasic acid is excessive or less than 1 mol which is equimolar to 1 mol of neopentyl glycol, preferably 0.1 mol or more.
The esterification reaction is carried out using less than 1 mol, or more than 1 mol and 5 mol or less. Next, when the dibasic acid is less than 1 mol, the remaining hydroxyl group is esterified using a monovalent fatty acid, and the remaining monovalent fatty acid is removed by distillation . When the dibasic acid exceeds 1 mol, the remaining carboxyl group is esterified with a monohydric alcohol, and the remaining monohydric alcohol is removed by distillation.
The obtained ester has an acid value of 0.1 mg KOH / g or less by a method such as adsorption of clay.

Specific examples of the dibasic acid having 2 to 12 carbon atoms include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, subvalic acid, azelaic acid, sebacic acid, dodecadic acid, and methylmalon. Acid, ethylmalonic acid, dimethylmalonic acid, methylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, 2-ethyl-2-methylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid, Saturated aliphatic dicarboxylic acids such as 3,3-dimethylglutaric acid and 3-methyladipic acid, unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid and mesaconic acid, phthalic acid, isophthalic acid, Aromatic dicarboxylic acids such as terephthalic acid can be used.
In particular, it has the following structure:
HOOC (CH ₂₎ nCOOH (n is a positive number of 1 to 10)
C3-C12 linear saturated aliphatic dicarboxylic acid is preferred, n is 4-8 adipic acid,
Pimelic acid, suberic acid, azelaic acid, and sebacic acid are particularly preferred because they can synthesize esters having relatively large polarity and excellent compatibility with R32.

As the monohydric alcohol having 1 to 12 carbon atoms, linear and branched saturated alcohols are preferable, and methanol, ethanol, n-propanol, n-butanol, n-pentanol, n
Any of linear alcohols such as -heptanol, n-octanol and n-nonanol or branched alcohols which are structural isomers of the linear alcohols can be used.
In order to synthesize an ester that is more compatible with R32, a branched alcohol is preferred,
Of these, 2-ethylhexanol and 3,5,5-trimethylhexanol are more preferable.

As the linear monovalent fatty acid having 2 to 12 carbon atoms, linear and branched saturated fatty acids are suitable,
Branched chain 1 which is a straight chain fatty acid such as acetic acid, n-propanoic acid, n-butanoic acid, n-pentanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid or the structural isomer of the straight chain fatty acid Any monovalent fatty acid can be used. In order to obtain compatibility, solubility and optimum lubricity, branched fatty acids are preferred, and among them, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid or a mixture thereof is more preferred.

The ester of the present invention comprises the above-mentioned specific neopentyl polyol and dibasic acid, further esterification reaction by dehydration reaction with a specific monohydric alcohol or monohydric fatty acid, or an acid anhydride or acid chloride which is a derivative of fatty acid. It can be obtained by a general esterification reaction via or a transesterification reaction of each derivative.

Further, the ester obtained by the above method does not particularly limit the unreacted remaining acid and hydroxyl group, but preferably no carboxyl group remains. If there is a large amount of residual carboxyl groups, it will generate metal soap and other substances by reaction with the metal used in the refrigerator.
Since undesired phenomena such as precipitation also occur, an ester having an acid value of 0.1 mgKOH / g or less is used as a base oil, and the acid value as a refrigerating machine oil is also 0.1 mgKOH / g or less. In addition, if the residual amount of hydroxyl groups is too large, undesired phenomena occur, such as refrigeration oil becoming cloudy at low temperatures and blocking the capillary device of the refrigeration cycle.
It is preferable to set it as 00 mgKOH / g or less, and 30 mgKOH / g or less is more preferable.

Furthermore, the refrigerating machine oil of the present invention has a kinematic viscosity at 100 ° C. of ² to 30 mm ² / s in order to properly operate the refrigerating machine and ensure high efficiency. This kinematic viscosity is preferably 5 to 15 mm ² / s, and 8 to 12 mm ² / s is more preferable as an appropriate viscosity for improving the reliability of the wear resistance of the compressor.

The refrigerating machine oil of the present invention having the above ester as a main component is a refrigerating machine oil for refrigerant R32, and exhibits appropriate compatibility and solubility in a wide range from low temperature to high temperature, and its lubricity and thermal stability. Can be greatly improved. Furthermore, compared with polyalkylene glycol (PAG) etc. which are used as refrigerating machine oil for alternative CFCs, the electrical insulation is much higher and the hygroscopicity is also smaller.

In the refrigerating machine oil according to the present invention, other types of esters, ethers such as PAG and polyvinyl ether (PVE), or hydrocarbon-based alkylbenzenes and mineral oils, etc., can be used as long as the functions of the refrigerating machine oil are satisfied. Oil can be mixed as appropriate.
In order to further improve the stability of the mixture fluid of the refrigerant and the refrigerating machine oil, a stability improving additive may be added to the refrigerating machine oil of the present invention. As the stability improving additive, one or more of hindered phenol compounds, aromatic amine compounds, epoxy compounds, and carbodiimides may be added, and it is more preferable to add the epoxy compound and carbodiimide together. It is also effective to add phosphate esters as antiwear agents, and it is sufficient to add these additives in a total amount of 0.05 to 5.0% by weight based on the total amount of the refrigerating machine oil.

As the hindered phenol compound, 2,6-ditertiary butylphenol,
2,6-Di-tert-butyl-P-cresol, 4,4-methylene-bis- (2,6-
Di-tert-butyl-P-cresol), α-naphthylamine, p, p'-di-octyl-diphenylamine, etc. as aromatic amine compounds, glycidyl ether group-containing compounds, epoxidized fatty acids Monoesters, epoxidized oils and fats, epoxycycloalkyl group-containing compounds and the like are suitable. Further, as the phosphate ester, triphenyl phosphate, tricresyl phosphate and the like are suitable.

Conventionally, anti-wear agents such as organic sulfur compounds used in refrigerator oil, alcohol,
Additives such as oily agents such as higher fatty acids, metal deactivators such as benzotriazole derivatives, and antifoaming agents such as silicone oil can be added as appropriate.

Since the refrigerant R32 is used in a room air conditioner or the like, it is also necessary to have characteristics of refrigeration oil suitable for a motor built-in type (sealed type) compressor, that is, high electrical insulation. Therefore, the refrigerating machine oil of the present invention preferably has a volume resistivity of 10 ¹¹ Ω · cm or more after the additive is blended.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
(Test oil of Example)
The following esters were provided as base oils for the examples (both are mixtures of esters)
.
Base oil A: An ester intermediate obtained by reacting 1 mol of neopentyl glycol (NPG) and 1.5 mol of adipic acid (AA) is further added with an excess of 2-ethylhexanol (1.5 mol).
In addition, ester obtained by esterification and removing residual alcohol by distillation.
Base oil B: To ester ester obtained by reacting 1 mol of neopentyl glycol with 0.5 mol of adipic acid, 1.1 mol of 3,5,5-trimethylhexanoic acid was further added for esterification.
An ester obtained by removing residual fatty acid by distillation.
Base oil C: ester intermediate obtained by reacting 1 mol of trimethylolpropane (TMP) with 2 mol of adipic acid and adding tert.-butanol in excess (1.5 mol) to esterify the remaining alcohol Ester obtained by distillation.
Base oil D: 1.1 mol of 2-ethylhexanoic acid was added to the ester intermediate reacted with 1 mol of trimethylolpropane and 1 mol of suberic acid (SA), and the remaining fatty acid was removed by distillation. The ester obtained.
In addition, about these test ester, the adsorption process (white clay process) was performed in the last process, and the trace amount impurity was removed. The total acid values of these test esters were all 0.01 mgKOH / g or less.

(Additive)
The following were used as additives.
Hindered phenol compounds: di-tert.-butyl-p-cresol (DBPC)
Aromatic amine compound: Dioctyl-diphenylamine (DODA)
Epoxy compound: 2-ethylhexyl glycidyl ether (2-EHGE)
Carbodiimide: Diphenylcarbodiimide (DPCI)
Phosphate ester: tricresyl phosphate (TCP)

(Test oil of comparative example)
The following oil was used as the base oil for the comparative example.
Base oil E: ester of pentaerythritol (PE) and 3,5,5-trimethylhexanoic acid.
Base oil F: An ester obtained by adding 1.1 mol of 2-ethylhexanoic acid to an ester intermediate obtained by reacting 1 mol of pentaerythritol and 1.5 mol of adipic acid to remove the remaining fatty acid.
Base oil G: ester of trimethylolpropane and oleic acid.
Base oil H: polyalkylene glycol (PAG, terminal is butyl group and hydroxyl group, skeleton is oxypropylene, average molecular weight is 1200), total acid value: 0.01 mgKOH / g.
Base oil I: polyalphaolefin (PAO, polymer of decene), total acid value: 0.01 mgKOH / g
.
Of these, esters were subjected to adsorption treatment (white clay treatment) in the final step to remove a small amount of impurities. The total acid values of these esters were all 0.01 mg KOH / g or less.

Table 1 shows the additive content and properties of each test oil.
The kinematic viscosity was measured according to JIS K2283, and the total acid value and hydroxyl value were measured according to JIS K2501.

About the said test oil, each following performance as refrigerating machine oil was measured and evaluated on the conditions shown next, and the result was shown in Table 2.
(Compatibility)
According to JIS K2211, “Testing method for compatibility with refrigerant”, the two-layer separation temperature at an oil content of 10% by mass with refrigerant R32 was measured.
(Thermal stability)
In accordance with ANSI / ASHRAE 97-1983, test oil (20 g), refrigerant R32 (20 g) and catalyst (iron, copper, and aluminum wires) are sealed in a stainless steel cylinder (100 ml), heated to 175 ° C., and 14 After holding for one day, the hue (ASTM display) and acid value of the test oil were measured.
(Lubricity)
In accordance with ASTM D-3233-73, the Falex seizure load was measured in a controlled atmosphere (70 ml / min) of refrigerant R32.
(Electrical insulation)
Based on JIS C2101, the volume resistivity at 80 ° C. was determined.

As can be seen from Tables 1 and 2, the ester according to the present invention is compatible with the refrigerant R32 in a wide temperature range, and has good characteristics as a refrigerating machine oil including thermal stability. In particular, Examples 4 to 8 in which additives were added had little increase in the total acid value after the thermal stability test, and in particular, in Example 8 in which both the epoxy compound and carbodiimide were added, there was no increase in the total acid value. In the case of the esters of Comparative Examples 1 to 3, they are not compatible with the refrigerant R32 and do not satisfy the characteristics as refrigerating machine oil. Comparative Example 4
This ether is not compatible with the refrigerant, and the electrical properties shown by volume resistivity are about 1000 times worse than the ester of the present invention, indicating that it is not suitable as a refrigerating machine oil. PAO, which is the synthetic hydrocarbon oil of Comparative Example 5, has no polarity and is therefore completely incompatible with R32 and cannot be used.

The refrigerating machine oil of the present invention is used as a lubricating oil for a refrigerating machine using R32 as a refrigerant. In particular, a compressor, a condenser, a throttle device (a refrigerant flow control unit such as an expansion valve or a capillary tube), an evaporator, etc. It is a refrigeration system with high cooling efficiency that circulates refrigerant between them, and can be used as lubricating oil in refrigerators having compressors such as rotary type, swing type, scroll type compressor, room air conditioner, packaged air conditioner, It can be suitably used for industrial refrigerators and the like.

Claims (6)

An ester intermediate obtained by reacting trimethylolpropane and / or neopentyl glycol with a dibasic acid having 2 to 12 carbon atoms is further converted to a monohydric alcohol having 1 to 12 carbon atoms or a monovalent fatty acid having 2 to 12 carbon atoms. A refrigerating machine oil for refrigerant R32 having a kinematic viscosity at 100 ° C. of ² to 30 mm ² / s based on an ester having an esterified acid value of 0.1 mg KOH / g or less. The refrigerant R32 according to claim 1, wherein the dibasic acid is at least one selected from adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid, the monohydric alcohol is a branched alcohol, and the monovalent fatty acid is a branched fatty acid. Refrigeration machine oil. 3. The monohydric alcohol is 2-ethylhexanol and / or 3,5,5-trimethylhexanol, and the monohydric fatty acid is 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid. Refrigerating machine oil for refrigerant R32. An ester intermediate obtained by reacting a dibasic acid with more than 1.5 moles and less than 3 moles per mole of trimethylolpropane is further esterified with 2-ethylhexanol and / or 3,5,5-trimethylhexanol. The R32 refrigerating machine oil according to any one of claims 1 to 3, wherein the esterified ester is a base oil. A combination of one or more of a hindered phenol compound, an aromatic amine compound, an epoxy compound, a carbodiimide, and a phosphate ester, and 0.05 to 5.0% by weight based on the total amount of refrigerating machine oil. The refrigerating machine oil for refrigerant | coolant R32 in any one of -4. Refrigerating machine oil for refrigerant | coolant R32 in any one of Claims 1-5 whose volume resistivity is 10 < ¹¹ > ohm * cm or more.