JP4961666B2 - Lubricating oil composition for refrigerator - Google Patents

Description

  The present invention uses a lubricating oil composition for a refrigerator, in particular, a lubricating oil composition for a refrigerator for a non-chlorine fluorocarbon refrigerant, a refrigerator working fluid containing the lubricating oil composition, and the refrigerator working fluid. The present invention relates to a refrigeration apparatus.

  CFC-containing refrigerants have been used in refrigerators, air conditioners, and the like. However, in recent years, due to problems such as destruction of the ozone layer, 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), difluoromethane can be used instead of a chlorofluorocarbon refrigerant. (R-32) Furthermore, conversion to non-chlorine-based Freon refrigerants such as these mixed solvents is being promoted. Accordingly, various lubricating oil compositions for refrigerating machines (hereinafter sometimes referred to as refrigerating machine oils) based on polyol esters having good compatibility with non-chlorine fluorocarbons have been proposed.

  In order to ensure the stability of refrigeration oil, such as refrigerators and air conditioning equipment, in addition to compatibility with the above-mentioned non-chlorine fluorocarbon refrigerant, lubricity, thermal stability, hydrolysis resistance, low-temperature fluidity, electrical insulation Various performances such as performance are required. Among these, from the viewpoint of hydrolysis resistance and compatibility with non-chlorinated chlorofluorocarbons, a hindered ester having excellent heat resistance composed of a branched carboxylic acid and pentaerythritol has been put into practical use. For example, Patent Document 1 discloses a refrigerating machine oil mainly composed of an ester composed of pentaerythritol and a mixed fatty acid of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid, and has stability at high temperatures. It is described that it is improved. Patent Document 2 discloses a refrigerating machine oil mainly composed of an ester composed of pentaerythritol, a linear or branched fatty acid having 6 to 8 carbon atoms, and a mixed fatty acid of 3,5,5-trimethylhexanoic acid, It is described that this improves compatibility with the refrigerant and electrical insulation.

  On the other hand, due to the recent increase in environmental awareness, refrigerators and air conditioners are required to save energy. In refrigerating machine oil, in order to contribute to energy saving properties such as a refrigerator, lowering the viscosity is the most effective means, and lowering the viscosity of refrigerating machine oil is aimed at.

  In order to achieve low viscosity of refrigerating machine oil, use an ester made of dihydric alcohol such as neopentyl glycol, which has lower viscosity than pentaerythritol ester and is superior in hydrolysis resistance, thermal stability, viscosity, etc. It is effective to do. However, since these esters have low volume resistivity, there is a problem that they are inferior in electrical insulation. Thus, reducing the viscosity in order to contribute to energy saving produces an effect contrary to the original purpose, ie, lowering the electrical insulation, and obtaining a refrigerating machine oil excellent in the reduction in viscosity and electrical insulation. It is very difficult.

  In addition, since refrigeration oil is used in devices intended for cooling, stability at low temperatures is important, and in particular, the ability to prevent crystals from depositing even in such a low temperature range is required. It has been. However, none of the mixed esters obtained by combining the polyhydric alcohol and the specific carboxylic acid described in Patent Documents 1 and 2 have been sufficiently studied for long-term stability at low temperatures. .

As described above, a refrigerating machine oil having excellent low-temperature stability, low viscosity, and high electrical insulation (high volume resistivity) is desired, but its production is difficult as described above.
Japanese Patent Laid-Open No. 10-8084 JP-A-6-330061

  An object of the present invention is to provide a lubricating oil composition for a refrigerator that has a low viscosity, a high volume resistivity, and an excellent long-term stability in a low temperature region, and in particular, lubrication for a refrigerator that uses a non-chlorine fluorocarbon refrigerant. It is to provide an oil composition. Another object of the present invention is to provide a refrigerator working fluid using the above lubricating oil composition for a refrigerator and a refrigerant compression refrigeration apparatus using the above refrigerator working fluid.

  The present inventors diligently investigated the volume resistivity and low-temperature stability of a low-viscosity lubricating oil composition used in a freezer using a non-chlorinated fluorocarbon refrigerant, and combined various alcohols and carboxylic acids to design a molecular design. Went. As a result, by combining a mixed alcohol consisting of neopentyl glycol, pentaerythritol, and dipentaerythritol and satisfying a certain quantitative relationship with a saturated monocarboxylic acid having 5 to 10 carbon atoms, volume resistivity is obtained. The present invention was completed by finding that a low-viscosity ester having a high viscosity and a long-term low-temperature stability was obtained.

  The present invention is a lubricating oil composition for a refrigerator mainly comprising a mixed ester obtained from a mixed alcohol and a saturated monocarboxylic acid having 5 to 10 carbon atoms, wherein the mixed alcohol is 1 to 90 mol%. It consists of neopentyl glycol, 10 to 80 mol% pentaerythritol, and 0.01 to 20 mol% dipentaerythritol, and the following relational formula:

Meet, and kinematic viscosity at 40 ° C. of the composition is 6~28mm ² / s, a hydroxyl value of Ri der following 2.0 mg KOH / g, 85 mol% of a saturated monocarboxylic acid constituting the mixed ester These procedures provide a Ru saturated monocarboxylic acids der refrigeration lubricant composition having α- branched chain.

In a preferred embodiment, the saturated monocarboxylic acid constituting the mixed ester is a saturated monocarboxylic acid having an α-branched chain.

  In a preferred embodiment, 10 to 65 mol% of an ester having a molecular weight of 370 to 1000 is contained in the mixed ester.

  Moreover, this invention provides the refrigerator working fluid which consists of the said lubricating oil composition for refrigerators, and a chlorine-free CFC refrigerant.

  Furthermore, the present invention provides a refrigerant compression refrigeration apparatus including a compressor, a condenser, an expansion mechanism, and an evaporator, and a refrigeration apparatus that uses the chiller working fluid.

  The lubricating oil composition for refrigerators of the present invention has a low viscosity, a high volume resistivity, and excellent long-term low-temperature stability. Furthermore, it is excellent in compatibility with non-chlorine fluorocarbon refrigerants required as a lubricating oil composition for refrigerators, heat resistance, and lubricity. Therefore, the composition of the present invention is a lubricating oil for a refrigerator using a non-chlorine-based chlorofluorocarbon refrigerant, in particular, a non-chlorine-based chlorofluorocarbon refrigerant containing at least one of 1,1,1,2-tetrafluoroethane and difluoromethane, Alternatively, it is useful as a refrigerator working fluid mixed with a non-chlorine-based chlorofluorocarbon refrigerant, and contributes to fuel saving of various refrigeration apparatuses.

  Hereinafter, mixed ester contained in the composition of the present invention, a lubricating oil composition for a refrigerator containing the mixed ester, a refrigerator working fluid containing the composition, and a refrigerant compression type using the refrigerator working fluid The refrigeration apparatus will be described.

(Mixed ester)
The mixed ester contained in the lubricating oil composition for a refrigerator of the present invention is obtained from a mixed alcohol and a saturated monocarboxylic acid having 5 to 10 carbon atoms, and the mixed alcohol is 1 to 90 mol% neopentyl glycol, It consists of 10 to 80 mol% pentaerythritol and 0.01 to 20 mol% dipentaerythritol, and has the following relational formula:

Meet. The inventors of the present invention have found that an ester composed of a dihydric alcohol such as neopentyl glycol reduces the volume resistivity by designing the ester molecule so as to satisfy the above relational expression. It was possible to provide a low-viscosity ester excellent in long-term low-temperature stability without lowering. That is, neopentyl glycol, pentaerythritol and dipentaerythritol are mixed so as to satisfy the above relational expression, and by combining this mixed alcohol with a saturated monocarboxylic acid having 5 to 10 carbon atoms, the viscosity is low, and the volume It was found that a mixed ester having high specific resistance (without lowering) and excellent long-term low-temperature stability can be obtained.

  In the mixed ester contained in the lubricating oil composition for a refrigerator of the present invention, 85 mol% or more of the saturated monocarboxylic acid constituting the mixed ester has an α-branched chain from the viewpoint of hydrolysis stability and the like. A saturated monocarboxylic acid is preferred.

  The mixed ester contained in the lubricating oil composition for a refrigerator of the present invention contains 10 to 65% by mass of an ester having a molecular weight of 370 to 1000 from the viewpoint of long-term low-temperature stability, volume resistivity, and heat resistance. It is preferable.

  Hereinafter, the manufacturing method of the said mixed ester is demonstrated.

  The mixed alcohol used as the raw material of the mixed ester is composed of 1 to 90 mol% neopentyl glycol, 10 to 80 mol% pentaerythritol, and 0.01 to 20 mol% dipentaerythritol as described above. When an ester is obtained using the above three types of mixed alcohol, the mixed ester prepared outside the above composition range is inferior in any of fuel saving, lubricity, and heat resistance, and has a volume resistivity and long-term low-temperature stability. A satisfactory product cannot be obtained.

  The C5-C10 saturated monocarboxylic acid used as the raw material for the mixed ester is not particularly limited. Either a linear saturated monocarboxylic acid or a saturated monocarboxylic acid having a branched chain may be used. From the viewpoint of long-term low-temperature stability, compatibility with non-chlorine fluorocarbon refrigerants, and corrosion resistance, linear saturated monocarboxylic acids having 5 to 7 carbon atoms or branched saturated monocarboxylic acids having 7 to 10 carbon atoms are used. preferable. When the saturated monocarboxylic acid has 5 or more carbon atoms, an ester having good lubricity can be obtained. When the number of carbon atoms is 10 or less, a mixed ester excellent in low-temperature stability and compatibility with a non-chlorine fluorocarbon refrigerant can be obtained.

  Examples of the saturated monocarboxylic acid having 5 to 10 carbon atoms include pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, 2-methylpentanoic acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylbutanoic acid, 3-ethylbutanoic acid, heptanoic acid, 2-methylhexanoic acid, 3-methylhexanoic acid, 4-methylhexanoic acid, 5-methylhexanoic acid, 2,2-dimethylpentanoic acid, 2-ethylpentanoic acid 3-ethylpentanoic acid, 2-ethylhexanoic acid, 2-methylheptanoic acid, 3-methylheptanoic acid, 4-methylheptanoic acid, 5-methylheptanoic acid, 6-methylheptanoic acid, 2,2-dimethylhexanoic acid 3,5-dimethylhexanoic acid, nonanoic acid, isononanoic acid, decanoic acid, neodecanoic acid and the like. From the viewpoint of good lubricity and hydrolysis stability of the resulting mixed ester, and corrosiveness to metals, α-branched saturated monocarboxylic acid, more preferably 2-ethylhexanoic acid, is preferably used. The above-mentioned saturated monocarboxylic acid having 5 to 10 carbon atoms may be used alone, considering hydrolysis resistance, lubricity, compatibility with non-chlorine fluorocarbons, heat resistance, low temperature stability, viscosity and the like. Two or more kinds may be used in combination.

  Despite the use of neopentyl glycol by combining the mixed alcohol and the saturated monocarboxylic acid having 5 to 10 carbon atoms, the volume resistivity is maintained high without lowering and long-term low-temperature stability. An excellent mixed ester is obtained. For example, depending on the target viscosity, a mixed alcohol obtained by blending neopentyl glycol, pentaerythritol, and dipentaerythritol so as to satisfy the range of the above formula (1), and saturation of 5 to 10 carbon atoms A monocarboxylic acid, preferably a saturated monocarboxylic acid containing 85% by mass or more of a saturated monocarboxylic acid having an α-branched chain, or 10 to 65% by mass of an ester having a molecular weight of 370 to 1000 in the resulting mixed ester. The saturated monocarboxylic acid set as described above is reacted.

  The reaction is carried out by a usual esterification reaction or transesterification reaction. The ratio of the mixed alcohol to the saturated monocarboxylic acid having 5 to 10 carbon atoms is such that the resulting mixed ester has a hydroxyl value of 5.0 mgKOH / g or less and an acid value of 0.05 mgKOH / g or less. It can be adjusted appropriately.

  Specifically, the manufacturing method of the mixed ester used for this invention is obtained as follows. First, with respect to 1 equivalent of the hydroxyl group of the mixed alcohol, the carboxyl group of the mixed carboxylic acid is preferably 1.0 to 1.5 equivalent, and preferably 1.05 to 1.3 equivalent in terms of production efficiency and economy. Mix and add catalyst as needed. The mixture is reacted at 220 to 260 ° C. for 3 to 15 hours under a nitrogen stream, and when the hydroxyl value becomes 2.0 mgKOH / g or less, excess carboxylic acid is removed under reduced pressure. Thereafter, after deoxidation with alkali, operations such as adsorption treatment using activated clay, acid clay, and synthetic adsorbent, and steaming are performed alone or in combination.

(Refrigerator lubricating oil composition)
The lubricating oil composition for a refrigerator of the present invention contains the above mixed ester as a main component, and may contain other esters and additives other than the mixed ester as necessary. The specific amount of the “main component” is 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, based on the whole lubricating oil composition for refrigerators. It may be 100% by mass.

  Examples of the ester other than the mixed ester that can be contained in the lubricating oil composition for a refrigerator of the present invention include, for example, divalent to octavalent and carbon number other than neopentyl glycol, pentaerythritol, and dipentaerythritol as an alcohol moiety. 5-15 neopentyl polyols (2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, trimethylolethane, triethylolethane, trimethylolpropane, And esters obtained from a monocarboxylic acid or a polyvalent carboxylic acid. The ester may be appropriately contained within a range that does not impair the characteristics of the refrigerator lubricating oil composition of the present invention.

  Examples of additives that can be contained in the lubricating oil composition for refrigerators of the present invention include phenolic antioxidants, metal deactivators such as benzotriazole, thiadiazole, and dithiocarbamate, and acids such as epoxy compounds and carbodiimides. Examples include scavengers and phosphorus-based extreme pressure agents. The ratio contained is arbitrary.

The lubricating oil composition for a refrigerator of the present invention has a kinematic viscosity at 40 ° C. of 6 to 28 mm ² / s. Further, from the viewpoint of obtaining excellent lubricity and compatibility with a non-chlorine-based chlorofluorocarbon refrigerant, and from the viewpoint of good startability and energy saving of a refrigerator by using the lubricating oil composition, preferably 6.5 to 27. 0.5 mm ² / s, more preferably 7 to 27 mm ² / s.

  The acid value of the lubricating oil composition for a refrigerator of the present invention is not particularly limited. Preferably it is 0.05 mgKOH / g or less, More preferably, it is 0.03 mgKOH / g or less, More preferably, it is 0.01 mgKOH / g. When an acid value is 0.05 mgKOH / g or less, there is little possibility of corroding a metal and hydrolysis resistance is favorable.

  The hydroxyl value of the lubricating oil composition for a refrigerator of the present invention is not particularly limited. Preferably it is 5.0 mgKOH / g or less, More preferably, it is 3.0 mgKOH / g or less, More preferably, it is 2.0 mgKOH / g, Most preferably, it is 1.0 mgKOH / g or less. When the hydroxyl value is 5.0 mgKOH / g or less, it is difficult to reduce the volume resistivity of the composition, and sufficient electrical insulation can be maintained. Therefore, there is no possibility of adversely affecting the sealing agent used as an organic material in an apparatus in which the composition is used. Furthermore, there is no possibility of adversely affecting the additive contained.

(Refrigerator working fluid)
The refrigerating machine working fluid of the present invention is composed of the above lubricating oil composition for a refrigerating machine and a non-chlorine fluorocarbon refrigerant. Although there is no restriction | limiting in particular in the compounding ratio of the lubricating oil composition for refrigerators, and a non-chlorine-type Freon refrigerant, Preferably, the lubricating oil composition for refrigerators: Non-chlorine-type Freon refrigerant is 10: 90-90: by mass ratio. The ratio is 10. When the blending ratio of the non-chlorine-based chlorofluorocarbon refrigerant is higher than the above range, the viscosity of the obtained refrigerator working fluid is lowered, and there is a risk of causing poor lubrication. When it is lower than the above range, there is a risk that the refrigeration efficiency may be lowered when the obtained refrigerator working fluid is used in equipment.

  Specific examples of the non-chlorofluorocarbon refrigerant include 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), difluoroethane (R-32), and trifluoroethane ( R-23), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a) and the like. It is done. These may be used alone or as a mixed refrigerant of two or more.

  The above mixed refrigerant is commercially available, for example, R-407C (R-134a / R-125 / R-32 = 52/25/23 wt%), R-410A (R-125 / R-32 = 50). / 50wt%), R-404A (R-125 / R-143a / R-134a = 44/52 / 4wt%), R-407E (R-134a / R-125 / R-32 = 60/15 / 25wt) %), R-410B (R-32 / R-125 = 45/55 wt%), and the like. Among these, a mixed refrigerant containing at least one of R-134a and R-32 is particularly preferable.

(Refrigerant compression refrigeration system)
The refrigerant compression refrigeration apparatus of the present invention includes a compressor, a condenser, an expansion mechanism, and an evaporator, and is configured such that the above-described refrigerator working fluid that is a refrigerant in the refrigeration apparatus circulates these. The refrigeration apparatus can further include a dryer. Examples of such a refrigeration apparatus include air conditioners such as room air conditioners and packaged air conditioners; low temperature apparatuses such as refrigerators and freezers; industrial refrigerators; and car air conditioners such as hybrid cars and electric cars.

  Hereinafter, the present invention will be described more specifically with reference to examples.

The following describes the test methods for the esters produced in the examples and comparative examples:
<Kinematic Viscosity and Viscosity Index> Based on JIS K-2283, the kinematic viscosity at 40 ° C. and 100 ° C. is measured using a Canon-Fenske viscometer, and the viscosity index is calculated.
<Acid Value> Measured according to JIS C-2101.
<Hydroxyl value> Measured according to JIS K-0070.
<Hue> Measured according to JOCS 2.2.1.4-1996.
<Volume Resistivity> Volume resistivity (TΩ · m) at 25 ° C. is measured according to JIS C-2101.
<Pour point> Measured according to JIS K-2269.
<Long-term low temperature test> 400 g of a sample whose water content is adjusted to 100 ppm or less is put in a steel square can and left in a low temperature storage at −28 ° C. for 1000 hours to visually check whether crystals are precipitated.
<Two-Phase Separation Temperature> A thick Pyrex (registered trademark) tube (total length 300 mm, outer) in which 0.6 g of sample (ester) and 2.4 g of refrigerant R-134a were cooled in an ethanol bath containing dry ice. The temperature was increased or cooled at a rate of 1 ° C./min, and the two-phase separation temperature at high and low temperatures was visually measured in the range of −70 ° C. to + 80 ° C.
<Shield tube test> A glass tube was filled with 10 g of a sample whose water content was adjusted to 200 ppm or less in advance, 5 g of Freon R-410A, and 10 mm long pieces of iron, copper, and aluminum. , Seal. After heating this at 175 ° C. for 14 days, the acid value and hue (APHA) of the fluorocarbon-containing sample excluding the metal pieces are measured.
<Falex Friction Test> In accordance with ASTM D-2670, a Falex friction test was performed while blowing R-134a into the sample at a rate of 150 mL / min. A sample temperature is set to 100 ° C., a test run is performed for 1 minute at a load of 150 pounds, and then run for 2 hours under a load of 250 pounds.

(Synthesis Example 1: Preparation of ester)
In a 1 liter four-necked flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and a condenser tube, the mixed alcohol and saturated monocarboxylic acid shown in Table 1 were mixed with the hydroxyl group of the mixed alcohol and the carboxyl group of the saturated monocarboxylic acid. In an equivalent ratio of 1: 1.1, and the reaction was carried out at atmospheric pressure while distilling off the reaction water at 220 ° C. in a nitrogen stream. During the reaction, the hydroxyl value was monitored, and the reaction was stopped when it was below 2.0 mgKOH / g. Thereafter, stripping was performed under a reduced pressure of 1 to 5 kPa to remove unreacted carboxylic acid over 1 hour. An aqueous potassium hydroxide solution was added to the obtained reaction mixture and washed with water. Washing with water was repeated 5 times so that the pH of the wastewater was neutral. Next, the obtained ester layer was dehydrated under reduced pressure at 100 ° C. and 1 kPa, and acid clay and silica-alumina-based adsorbent were respectively added so as to be 1.0 mass% of the theoretically obtained ester amount. And adsorption treatment. The adsorption treatment temperature, pressure, and adsorption treatment time were 100 ° C., lkPa, and 3 hours, respectively. Thereafter, filtration was performed using a 1-micron filter to obtain an ester (ester A). About obtained ester A, kinematic viscosity in 40 degreeC and 100 degreeC was measured by said method. The results are shown in Table 1.

(Synthesis Examples 2 to 7)
Esters (esters B to G) were obtained in the same manner as in Example 1 except that the mixed alcohols and saturated monocarboxylic acids shown in Table 1 were used. About each ester, kinematic viscosity in 40 degreeC and 100 degreeC was measured by said method. The results are also shown in Table 1.

(Comparative Synthesis Examples 1 to 5)
An ester (esters H to L) was obtained in the same manner as in Example 1 except that the mixed alcohol and the saturated monocarboxylic acid shown in Table 1 were used. About each ester, kinematic viscosity in 40 degreeC and 100 degreeC was measured by said method. The results are also shown in Table 1.

As can be seen from Table 1, the esters (Esters A to G) in Synthesis Examples 1 to 7 satisfy the conditions for the esters used in the present invention, but the esters (Esters H to L) in Comparative Synthesis Examples 1 to 5 are not filled. That is, the esters H to J of Comparative Synthesis Examples 1 to 3 do not use three types of alcohols. The value of the relational expression of the ester K of Comparative Synthesis Example 4 is 10.30 and does not satisfy the range of 0.2 to 7.0. Since the ester L of Comparative Synthesis Example 5 has a high viscosity at 40 ° C. of 30.20 mm ² / s, it cannot satisfy the viscosity range (6 to 28 mm ² / s) of the lubricating oil composition of the present invention alone.

(Example 1: Performance evaluation of lubricating oil)
A lubricating oil was prepared using the ester A obtained in Synthesis Example 1 (referred to as lubricating oil 1). For Lubricant 1, kinematic viscosity at 40 ° C. and 100 ° C., viscosity index, hue, acid value, hydroxyl value, volume resistivity, pour point, two-phase separation temperature measurement, long-term stability test, shield A tube test and a Falex test were performed. The results are shown in Table 2.

(Examples 2 to 7: Performance evaluation of lubricating oil)
Lubricating oils were prepared using the esters (esters B to G) obtained in Synthesis Examples 2 to 7 (referred to as lubricating oils 2 to 7). For each lubricating oil, kinematic viscosity at 40 ° C. and 100 ° C., viscosity index, hue, acid value, hydroxyl value, volume resistivity, pour point, two-phase separation temperature measurement, long-term stability test, shield A tube test and a Falex test were performed. The results are also shown in Table 2.

(Comparative Examples 1-5)
Lubricating oils were prepared using the esters (esters H to L) obtained in Comparative Synthesis Examples 1 to 5 (referred to as lubricating oils 8 to 12). For each lubricating oil, kinematic viscosity at 40 ° C. and 100 ° C., viscosity index, hue, acid value, hydroxyl value, volume resistivity, pour point, two-phase separation temperature measurement, long-term stability test, shield A tube test and a Falex test were performed. The results are also shown in Table 2.

  As is apparent from the results in Table 2, the lubricating oils (lubricating oils 1 to 7) satisfying the conditions of the present invention in Examples 1 to 7 have a low viscosity, a high volume resistivity, and a long-term low temperature test. It turns out that it has the outstanding stability which a precipitate does not generate | occur | produce. These lubricating oils 1 to 7 further have a low pour point, excellent compatibility with the chlorofluorocarbon refrigerant from the two-phase separation temperature, and little thermal oxidative deterioration from the shield tube test, and as other lubricating oils for refrigerators It is clear that it is an excellent lubricant to meet the required performance. On the other hand, the lubricating oils 8 to 10 made of esters (esters H to J) prepared without including any of the three types of alcohols used in the present invention have a low volume resistivity or a long term. Precipitates were generated in the low temperature test. Although the above three types of mixed alcohols are used, the lubricating oil 11 made of ester K that does not satisfy the relational expression produced precipitates in the long-term low-temperature test. Although the lubricating oil 12 used the above three types of mixed alcohols and satisfied the above relational expression, the kinematic viscosity at 40 ° C. was high and the low temperature stability was poor.

  The lubricating oil composition for a refrigerator of the present invention has a low viscosity, a high volume resistivity, and excellent low-temperature stability. In addition, since it has good compatibility with chlorofluorocarbons, especially non-chlorofluorocarbons, it can be used as a lubricating oil for refrigerators that use non-chlorofluorocarbon solvents, or as a refrigerator working fluid that is mixed with non-chlorofluorocarbon refrigerants. Preferably used. The refrigerator working fluid of the present invention and the refrigerator working fluid containing the lubricating oil composition and the non-chlorine fluorocarbon refrigerant are specifically air conditioners such as room air conditioners and packaged air conditioners; refrigerators, freezers, etc. Low temperature equipment; industrial refrigerators; and compressors for car air conditioners such as hybrid cars and electric cars.

Claims (5)

A lubricating oil composition for a refrigerating machine mainly comprising a mixed ester obtained from a mixed alcohol and a saturated monocarboxylic acid having 5 to 10 carbon atoms,
The mixed alcohol consists of 1 to 90 mol% neopentyl glycol, 10 to 80 mol% pentaerythritol, and 0.01 to 20 mol% dipentaerythritol, and the following relational formula:
0.2 ≦ (mol% of pentaerythritol) / {(mol% of neopentyl glycol) × (mol% of dipentaerythritol)} ≦ 7.0
The filled, and a kinematic viscosity of 6~28mm ² / s at 40 ° C. of the composition state, and are a hydroxyl value of 2.0 mg KOH / g or less,
Wherein more than 85 mole% of the saturated monocarboxylic acid constituting the mixed ester is a saturated monocarboxylic acid der Ru composition having α- branched chain. The lubricating oil composition for a refrigerator according to claim 1, wherein the saturated monocarboxylic acid constituting the mixed ester is a saturated monocarboxylic acid having an α-branched chain.   The lubricating oil composition for a refrigerator according to claim 1 or 2, wherein an ester having a molecular weight of 370 to 1000 is contained in the mixed ester in an amount of 10 to 65 mol%.   A refrigerator working fluid comprising the lubricating oil composition for a refrigerator according to any one of claims 1 to 3 and a non-chlorine-based chlorofluorocarbon refrigerant. A refrigerant compression refrigeration apparatus comprising a compressor, a condenser, an expansion mechanism, and an evaporator,
A refrigeration apparatus using the refrigerator working fluid according to claim 4.