JP5248959B2 - Refrigerator oil, working fluid for refrigerator, and refrigerator - Google Patents

Description

  The present invention relates to a low-viscosity refrigerating machine oil excellent in energy saving, a working fluid for a refrigerating machine using the same, and a refrigerator.

  Conventionally, a refrigerant compression refrigeration cycle apparatus used in a refrigerator, an air conditioner, a refrigerator, or the like has a fluorocarbon having fluorine and chlorine as refrigerants, for example, R-11 (trichloromono) which is chlorofluorocarbon (CFC). Fluoromethane), R-12 (dichlorodifluoromethane), hydrochlorofluorocarbon (HCFC) R-22 (monochlorodifluoromethane), etc. have been used. At present, hydrogen-containing chlorofluorocarbon refrigerants that do not contain chlorine, such as difluoromethane (R-32), tetrafluoroethane (R-134 or R-134a), and halogen atoms with a lower greenhouse effect are used. Does not contain hydrocarbon refrigerants such as ethane, propane, butane, isobutane, etc. It has been.

The inventors have proposed a refrigerant refrigerating machine oil based on an ester using a polyhydric alcohol such as a polyol as a refrigerant refrigerating machine oil used for these refrigerants (Patent Document 1). Thereby, when a lower hydrocarbon refrigerant | coolant etc. were used for the working fluid, the effect of preventing generation | occurrence | production of an oligomer (polymer substance) was able to be acquired. Recently, however, further energy savings have been demanded for refrigerators, air conditioners, refrigerators, etc., and energy saving type refrigerating machine oils with reduced viscosity have been demanded for refrigerating machine oils.
Patent Document 2 discloses that certain fatty acid polyol esters have low viscosity and excellent lubricity, but in order to reduce the viscosity with fatty acid polyol esters, the number of carbon atoms of the fatty acid must be 5 or less. The hydrolysis stability is significantly reduced.
Patent Document 3 proposes a refrigerating machine oil containing at least one aliphatic saturated branched carboxylic acid monoalkyl ester as a refrigerating machine oil having low viscosity and excellent hydrolysis stability. Mixtures with fatty acid polyol esters are disclosed. However, there are countless combinations of aliphatic saturated branched carboxylic acid monoalkyl esters and fatty acid polyol esters, low viscosity, excellent lubricity, high flash point, excellent safety, and hydrolytic stability. It was extremely difficult to find something that could satisfy the requirements.
JP 2007-254713 A JP 2007-248020 A Re-published patent WO00 / 68345

As described above, in refrigerators that use hydrogen-containing chlorofluorocarbon refrigerants that do not contain chlorine and hydrocarbon refrigerants that do not contain halogen atoms that have a small greenhouse effect, a low-viscosity lubricating oil must be refrigerated to improve energy savings. Although it is effective to use as machine oil, in the case of so-called mineral oil-based refrigerating machine oil based on paraffin mineral oil or naphthene mineral oil, there is a problem that the flash point becomes low and the danger increases in handling. On the other hand, when an ester using a polyhydric alcohol such as a polyol is used as a base oil, a fatty acid having a small number of carbon atoms must be used. However, this structure significantly reduces the stability and corrodes the fatty acid generated during decomposition. Is also a concern.
The present invention solves the above-mentioned problems, and is used with a hydrogen-containing chlorofluorocarbon refrigerant that does not contain chlorine and a hydrocarbon refrigerant that does not contain a halogen atom that has a small greenhouse effect. The present invention provides an excellent refrigerant refrigerating machine oil.

  As a result of earnest research to achieve the above object, the inventor of the present invention is a refrigeration oil in which a polyol ester is blended with a specific monoester as a base oil in a hydrogen-containing fluorocarbon refrigerant or hydrocarbon refrigerant that does not contain chlorine. The present invention has been found to be excellent as a lubricating oil for refrigerant compression refrigeration cycle equipment, that is, a refrigerating machine oil, having a low viscosity and good lubricity and high hydrolytic stability. I came up with it.

That is, this invention is the following refrigerator oil, the working fluid for refrigerators, and a refrigerator.
(1) 75 to 95% by mass of a monoester of an aliphatic monoalcohol having 8 carbon atoms and a monovalent fatty acid having 8 carbon atoms, 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid and carbon A refrigerating machine oil comprising 5 to 25% by mass of at least one kind of polyol ester with neopentyl polyol of several 5 to 10.
(2) The kinematic viscosity at 40 ° C. is 2 to 4 mm ² / s, the flash point is 130 ° C. or more, the acid value is 0.1 mg KOH / g or less, and the volume resistivity at 25 ° C. is 10 GΩm or more. Refrigeration oil.
(3) The refrigerating machine oil according to (1) or (2), wherein the monoester is an ester of n-octyl alcohol and 2-ethylhexanoic acid.
(4) The refrigerating machine oil according to any one of (1) to (3), wherein the polyol ester is neopentylglycol-di-2-ethylhexanoate and / or pentaerythritol-tetra-2-ethylhexanoate. .

(5) The refrigerating machine oil according to any one of (1) to (4), wherein 0.01 to 1% by mass of an acid scavenger comprising a compound having an epoxy ring or a carbodiimide compound is added.
(6) The refrigerating machine oil according to any one of (1) to (5), wherein 1 to 100 mass ppm of a metal deactivator having a benzotriazole structure is added.
(7) The refrigerating machine oil according to any one of (1) to (6), wherein 0.01 to 1% by mass of an oily agent having two or more hydroxyl groups in the molecule is added.
(8) The above (1) to (7), wherein 1 to 100 mass ppm of at least one antifoaming agent selected from silicone oil, silicone oil modified with polyalkylene glycol or ester, or fluorinated silicone oil is added. Refrigerating machine oil according to any one of the above.

(9) A working fluid for a refrigerating machine comprising the refrigerating machine oil according to any one of the above (1) to (8) and at least one hydrocarbon refrigerant selected from ethane, propane, butane, or isobutane.

(10) The working fluid for a refrigerator according to (9), a hermetic compressor that compresses the fluid, a condenser that condenses the refrigerant, an expansion mechanism that expands the refrigerant, and an evaporator that evaporates the refrigerant. The hermetic compressor includes a motor having a rotor and a stator, and the motor includes any one of polyethylene terephthalate, polybutylene terephthalate, polyamideimide-coated polyester, polyphenylene sulfide, and polyetheretherketone. And a stator having a winding wire covered with an enamel material having a glass transition temperature of 120 ° C. or higher.
(11) The refrigerator according to (10), wherein the hermetic compressor is a reciprocating type.

    The refrigerating machine oil of the present invention has an effect of low viscosity, excellent energy saving, excellent lubricity, high flash point, excellent safety, and satisfactory hydrolytic stability and oxidation stability. Play. Moreover, the working fluid for refrigerators of the present invention using such refrigerator oil has an effect that the refrigeration system can be stably operated over a long period of time without damaging each device and part of the refrigeration system. Furthermore, in the freezer using this refrigerating machine oil, there exists an effect that it can be operated stably for a long time with energy saving.

  In the present invention, a monoester of an aliphatic monoalcohol having 8 carbon atoms and a monovalent fatty acid having 8 carbon atoms is used. When the alcohol and acid have 8 carbon atoms, low viscosity can be achieved, the flash point can be increased, and hydrolysis stability is excellent.

  Examples of the aliphatic monoalcohol having 8 carbon atoms include n-octyl alcohol, isooctyl alcohol, 2-ethylhexanol, 1-methylheptanol, 2-methylheptanol, 2-propylpentanol, and dimethylcyclohexanol. . Among these, it is preferable to use n-octyl alcohol which is easily available.

  Examples of the monovalent fatty acid having 8 carbon atoms include n-octanoic acid, isooctanoic acid, 2-ethylhexanoic acid, 1-methylheptanoic acid, 2-methylheptanoic acid, 2-propylpentanoic acid and dimethylcyclohexane acid. It is preferable to use 2-ethylhexanoic acid which is easily available.

  In the present invention, a polyol ester of 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid and neopentyl polyol having 5 to 10 carbon atoms is used. By blending a predetermined amount of this polyol ester with a predetermined amount of the monoester, it is possible to match the desired kinematic viscosity and to improve the hydrolysis stability.

  Neopentyl polyol is a divalent or higher valent alcohol having a neopentane structure, and in the present invention, one having 5 to 10 carbon atoms is used. Those having more than 10 carbon atoms are difficult to adjust the kinematic viscosity, and the compatibility with the refrigerant deteriorates. As this neopentyl polyol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol can be used, and in particular, neopentyl glycol and pentaerythritol are preferably used.

    The ester used in the present invention is an esterification reaction by dehydration reaction between the specific alcohol or polyol and a specific fatty acid, or a general esterification reaction via an acid anhydride or acid chloride which is a derivative of a fatty acid. Or by transesterification of each derivative.

  The refrigerating machine oil of the present invention contains a monoester and a polyol ester. In this preparation, the monoester and the polyol ester are first synthesized separately by the above means, and then mixed in a predetermined ratio. First, monoalcohol, monohydric fatty acid, 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid, and neopentyl polyol, or a derivative thereof may be mixed in the required amount. You may synthesize | combine by the said means. In this case, the polyol ester may be one type or two or more types may be mixed.

  The ester obtained by the above method does not particularly limit the unreacted remaining acid and alcohol, but it is preferable that the carboxyl group does not remain as much as possible. If the residual amount of carboxyl groups is large, an undesirable phenomenon such as generation and precipitation of metal soap due to reaction with the metal used in the refrigerator occurs, so that the acid value of the refrigerator oil of the present invention is 0. Less than 0.1 mgKOH / g is preferable. This acid value is based on the method prescribed in JIS K2501 “Petroleum products and lubricants—neutralization number test method, indicator titration method”.

  The refrigerating machine oil of the present invention contains 75 to 95% by mass of the monoester and 5 to 25% by mass of a polyol ester. By using this blending ratio, a refrigerating machine oil having a low viscosity, that is, a VG3 grade viscosity can be obtained, and it has excellent lubricity, high flash point and volume resistivity, safety, and hydrolysis stability. , Excellent compatibility can be obtained.

In addition, the refrigerating machine oil of the present invention preferably has a kinematic viscosity of 2 to 4 mm ² / s at 40 ° C. in order to obtain a refrigerating machine oil having a viscosity of VG3 grade, and ensures safety in handling. For this reason, it is preferable that the flash point is 130 ° C. or higher and the volume resistivity at 25 ° C. is 10 GΩm or higher from the viewpoint of safety such as prevention of electric shock.
The kinematic viscosity at 40 ° C. is measured by the method specified in JIS K2283 “Crude oil and petroleum products—Kinematic viscosity test method and viscosity index calculation method”. The flash point is JIS K2265-4 “How to determine the flash point—Part 4: Measured by the method prescribed in “Cleveland Opening Method”, volume resistivity at 25 ° C. is measured at a sample temperature of 25 ° C. in accordance with the method prescribed in JIS C 2101 “Electrical insulating oil test method, 24. Volume resistivity test”. Is.

As the monoester, it is preferable to use an ester of n-octyl alcohol and 2-ethylhexanoic acid, that is, 2-ethylhexanoic acid-n-octyl, because the viscosity of VG3 grade can be easily adjusted.
Similarly, as the polyol ester, neopentyl glycol-di-2-ethylhexanoate which is an ester of 2-ethylhexanoic acid and neopentyl glycol or pentaerythritol which is an ester of 2-ethylhexanoic acid and pentaerythritol- It is preferable to use tetra-2-ethylhexanoic acid ester.

In the refrigerating machine oil of the present invention, in order to improve hydrolysis stability, it is preferable to add an acid scavenger such as a compound having an epoxy ring or a carbodiimide compound to the above-mentioned ester. Examples of the compound having an epoxy ring include glycidyl ether group-containing compounds, glycidyl ester group-containing compounds, epoxidized fatty acid monoesters, epoxidized oils and fats, and epoxycycloalkyl group-containing compounds. Of these, glycidyl ether group-containing compounds, glycidyl ester group-containing compounds, epoxidized fatty acid monoesters, epoxidized fats and oils, and epoxycycloalkyl group-containing compounds are particularly preferred.
The addition amount of the acid scavenger is preferably from 0.01 to 1% by mass, more preferably from 0.2 to 0.7% by mass, based on the whole refrigerating machine oil.

（式中、Ｒ¹は、水素原子又はメチル基を示し、Ｒ²は、水素原子、又は窒素原子及び／又は酸素原子を含有する炭素数０〜２０の基を示す）、
冷凍機油全体を基準として１〜１００質量ppm、さらには１０〜８０質量ppm程度含有されるよう添加することが好ましい。 Similarly, in order to improve hydrolysis stability, it is preferable to add a compound having a benzotriazole structure as a metal deactivator. The compound having a benzotriazole structure is a compound represented by the following general formula 1,

(Wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a hydrogen atom or a group having 0 to 20 carbon atoms containing a nitrogen atom and / or an oxygen atom),
It is preferable to add so that it may contain about 1-100 mass ppm with reference to the whole refrigerating machine oil, Furthermore, about 10-80 mass ppm.

    Furthermore, in order to improve lubricity, it is preferable to add an oily agent having two or more hydroxyl groups in the molecule. Examples of the oily agent having two or more hydroxyl groups in the molecule include glycerol monooleate, glycerol monooleyl ether, glycerol monolauryl ether and the like, and glycerol monooleate or glycerol monooleyl ether is particularly preferable. The addition amount is preferably 0.01 to 1% by mass, more preferably 0.1 to 0.5% by mass, based on the entire refrigerating machine oil.

  Further, in order to prevent the refrigerating machine oil from foaming in the refrigeration system, at least one antifoaming agent selected from silicone oil, silicone oil modified with polyalkylene glycol or ester at the end, or fluorinated silicone oil is added. It is preferable. The addition amount is preferably 1 to 100 ppm, particularly preferably 10 to 80 ppm, based on the whole refrigerating machine oil.

  In the refrigerating machine oil of the present invention, additives other than those described above may be further appropriately blended as necessary. Such additives include, for example, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 4,4-methylene-bis- (2,6-di-tertiary Butyl-p-cresol), p, p'-di-octyl-di-phenylamine and other phenolic or amine-based antioxidants, other well-known detergents, viscosity index improvers, rust inhibitors, corrosion Additives such as an inhibitor and a pour point depressant can be appropriately blended as necessary. These additives are usually added so that the refrigerating machine oil of the present invention contains about 1 mass ppm to 2 mass%. In particular, the stability and durability of the lubricant can be greatly improved by adding about 0.01 to 0.5% by mass of a phenol-based or amine-based antioxidant.

  The refrigerating machine oil of the present invention can be suitably used together with a refrigerant that does not contain chlorine and also a refrigerant that does not contain halogen. That is, the refrigerating machine oil of the present invention contains a hydrogen-containing Freon refrigerant that does not contain chlorine and has a low ozone depletion coefficient, such as difluoromethane (R-32), tetrafluoroethane (R-134 or R-134a), and particularly Hydrocarbon refrigerant that does not contain halogen and has a low ozone depletion potential and a low global warming potential, such as ethane (R170), propane (R290), butane (R600), isobutane (R600a), or two or more of these It is suitably used for a refrigerator that uses a mixed refrigerant or the like.

  The refrigerating machine oil of the present invention becomes a working fluid when mixed with these refrigerants, and controls lubrication of the refrigerating apparatus. It can be used as a working fluid by mixing the refrigerating machine oil of the present invention and the refrigerant in a ratio of 5:95 to 80:20. If this range is exceeded and the amount of oil is small, there is a risk of poor lubrication. If the amount of oil is too large, the efficiency decreases, which is not preferable.

  The working fluid for a refrigerator of the present invention is used as a working fluid for a refrigerant compression refrigeration apparatus having at least a compressor, a condenser, an expansion mechanism, and an evaporator, for example, a refrigerator, an air conditioner, a refrigerator, In particular, it is preferably used for a refrigerator in which mainly hydrocarbon refrigerant is used.

  In a refrigerator in which the working fluid of the present invention is used, a sealed rotary type or reciprocating type compressor is generally used. As an insulating film which is an electrical insulation system material of a motor part of these refrigerant compressors, , A crystalline plastic film having a glass transition temperature of 50 ° C. or higher, such as polyethylene terephthalate, polybutylene terephthalate, polyamideimide-coated polyester, polyphenylene sulfide, polyetheretherketone, or a film having a low glass transition temperature. A composite film that covers the resin layer is used.

  Similarly, the magnet wire used in the motor part is also enameled with a glass transition temperature of 120 ° C. or higher, for example, a single layer of polyester imide, polyamide, polyamide imide or the like, or a lower layer of glass transition temperature. Enamel films, etc., in which a high layer is combined with the upper layer, are used.

  In addition, since the working fluid for refrigerators of this invention is low-viscosity, it is used suitably for a reciprocating hermetic type compressor with high sealing performance.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to an Example.
In order to evaluate the present invention, refrigerant refrigerant oils (sample oils) for Examples and Comparative Examples were prepared. The base oils and additives used in the test oil are as follows.
(Base oil)
ME-1: n-hexanoic acid-n-hexyl ME-2: 2-ethylhexanoic acid-n-octyl ME-3: n-decanoic acid-n-decyl PE-1: neopentylglycol-di-n-hexane Acid ester PE-2: Neopentyl glycol-di-2-ethylhexanoic acid ester PE-3: Pentaerythritol-tetra-2-ethylhexanoic acid ester PE-4: 2-ethylhexanoic acid (50% by mass) and 3, Esters of mixed acid of 5,5-trimethylhexanoic acid (50% by mass) and pentaerythritol

(Additive)
Acid scavenger: 2-ethylhexyl glycidyl ether [EPO]
Dialkylphenylcarbodiimide [CDI]
Oiliness agent: Glycerol monooleate [GMO]
Metal scavenger: Benzotriazole [BTA]
Antifoaming agent: Dimethylsiloxane (1000mPa.s@25°C) [Silicone oil]

  Using the above base oil and additives, blending was performed at the ratio (mass%) shown in the upper part of Table 1 to obtain sample oils (refrigeration machine oils) of Examples and Comparative Examples.

The refrigeration oils of these examples and comparative examples were measured and evaluated for properties such as physical properties, compatibility and stability. The results are shown in Table 2.
The physical property measurement and performance evaluation tests other than the measurement methods described above were performed as follows.

Foaming:
The degree of foaming at 24 ° C. and the degree of foam stability were measured by the methods specified in JIS K2518 “Petroleum product-lubricating oil foaming test method”.
Two-layer separation temperature:
The two-layer separation temperature was measured by the method specified in Appendix 3 “Testing method for compatibility with refrigerant” of JIS K 2211. In addition, isobutane (R600a) was used as the refrigerant, and the sample oil / refrigerant ratio (weight) was measured under the condition of 2/8.

Hydrolytic stability:
A mixture of 7 ml of the test oil and 3 ml of isobutane refrigerant (R600a) was added to an oil content of 500 ppm at a temperature of 175 according to the method specified in Annex 2 “Test method for chemical stability with refrigerant (shield tube test)” of JIS K2211. The total acid value was measured every 14 days in an environment of ° C.
Lubricity (FALEX seizure):
A Falex test (290 rpm, room temperature) in accordance with ASTM D3233 was performed, and the load when the test piece was seized was measured.
Lubricity (SRV wear marks):
Using a ball (SUJ-2) / disk (SUJ-2) SRV friction tester, wear marks after a test time of 25 minutes under the conditions of load 100N, amplitude 50Hz, amplitude 1mm, temperature 60 ° C It was measured.

Compressor test:
An endurance test was conducted under the following conditions using 220 ml of test oil in a refrigerator compressor and 30 g of isobutane as a refrigerant.
<Conditions> Discharge pressure: 10 kg / cm ² G, suction pressure: 0 kg / cm ² G, compressor surface temperature (top): 100 ° C., operation time: 1000 hours Disassemble compressor after endurance test The wear of moving parts was evaluated.

  ME-2: 2-ethylhexanoic acid (n-octyl) which is an ester of n-octanol which is an aliphatic monoalcohol having 8 carbon atoms and 2-ethylhexanoic acid which is a monovalent fatty acid having 8 carbon atoms; -A mixture of ethylhexanoic acid or 3,5,5-trimethylhexanoic acid and neopentyl glycol or pentaerythritol, which is a neopentyl alcohol having 5 to 10 carbon atoms, is used as a base oil. Examples 1 to 7, which are low-viscosity oils, have a high flash point, excellent compatibility with refrigerants, hydrolysis stability, volume resistivity, and good lubricity.

  On the other hand, Comparative Examples 1-4 using monoester ME-1 to ME-3 and neopentyl polyol ester PE-1 alone as a base oil have poor hydrolysis stability. In Comparative Examples 1-4, Also, the lubricating SRV wear marks are poor. In particular, Comparative Example 1 has poor flash point, volume resistivity, and lubricating FALEX seizure. In addition, the comparative example 5 which used PE-2 independently has a high viscosity, and cannot fully achieve energy saving. Moreover, what used the ester of C6 or C10 alcohol and acid, even if it mixes with the ester of neopentyl polyol (Comparative Examples 6-8), hydrolysis stability is bad, and a comparative example 6-7 have a low volume resistivity. Those using these base oils could not be improved even when additives were added (Comparative Examples 9 to 11).

  According to the present invention, it is possible to provide a refrigerant refrigerating machine oil having a low viscosity and excellent stability, which is used for a hydrogen-containing fluorocarbon refrigerant not containing chlorine or a hydrocarbon refrigerant not containing a halogen atom having a small greenhouse effect. It was. Therefore, since it has a small impact on the environment such as global warming and is expected to save energy with low viscosity, it is effectively suitable for refrigerators, air conditioners, refrigerators, etc. that use refrigerant compression refrigeration cycles. Can be used.

Claims (10)

75-95% by mass of a monoester of n-octyl alcohol and 2-ethylhexanoic acid , 2-ethylhexanoic acid and / or 3,5,5-trimethylhexanoic acid, neopentyl glycol and / or pentaerythritol It is used for a hydrocarbon refrigerant containing 5 to 25% by mass of at least one polyol ester and is ethane, propane, butane, isobutane, or a mixture thereof, and a two-layer separation temperature with the hydrocarbon refrigerant is −50 ° C. The following der Ru refrigerating machine oil. The refrigerating machine oil according to claim 1, wherein the kinematic viscosity at 40 ° C is 2 to 4 mm ² / s, the flash point is 130 ° C or more, the acid value is 0.1 mgKOH / g or less, and the volume resistivity at 25 ° C is 10 GΩm or more. The refrigerating machine oil according to claim 1 or 2 , wherein the polyol ester is neopentyl glycol-di-2-ethylhexanoate or pentaerythritol-tetra-2-ethylhexanoate. The refrigerating machine oil according to any one of claims 1 to 3 , wherein 0.01 to 1% by mass of an acid scavenger composed of a compound having an epoxy ring or a carbodiimide compound is added. The refrigerating machine oil according to any one of claims 1 to 4 , wherein 1 to 100 ppm by mass of a metal deactivator having a benzotriazole structure is added. The refrigerating machine oil according to any one of claims 1 to 5 , wherein 0.01 to 1% by mass of an oily agent having two or more hydroxyl groups in the molecule is added. Silicone oil, terminated according to any one of claims 1 to 6 modified silicone oil with a polyalkylene glycol or ester, or fluorinated At least one anti-foaming agent selected from silicone oil is added to 1 to 100 ppm by weight Refrigerator oil. Claim 1 refrigerating machine oil and ethane according to any one of 7, propane, butane, or at least one hydrocarbon refrigerant and refrigerant working fluids containing selected from isobutane. A working fluid for a refrigerator according to claim 8 , a hermetic compressor that compresses the fluid, a condenser that condenses the refrigerant, an expansion mechanism that expands the refrigerant, and an evaporator that evaporates the refrigerant, The hermetic compressor includes a motor having a rotor and a stator, and the motor includes an insulating film of any one of polyethylene terephthalate, polybutylene terephthalate, polyamideimide-coated polyester, polyphenylene sulfide, and polyetheretherketone. And a refrigerator provided with a winding covered with an enamel material having a glass transition temperature of 120 ° C. or higher. The refrigerator according to claim 9 , wherein the hermetic compressor is a reciprocating type.