Lubricant oil composition for compression refrigerator

Abstract

The present invention is able to provide a lubricating oil composition having excellent thermal/chemical stability even when used for a compression refrigerating machine using a saturated fluorinated hydrocarbon refrigerant having a low carbon number and a low global warming potential, by using a refrigerant containing a saturated fluorinated hydrocarbon having from 1 to 3 carbon atoms, which uses, as a base oil, an oxygen-containing organic compound composed of at least one member selected from a polyoxyalkylene glycol, a polyvinyl ether, a copolymer of a poly(oxy)alkylene glycol and a polyvinyl ether, a copolymer of a poly(oxy)alkylene glycol monoether and a polyvinyl ether, and a polyol ester, each having a water content of not more than 500 ppm by mass.

Claims

1. A composition comprising: (i) a refrigerant consisting of difluoromethane (R32); and (ii) a lubricating oil composition consisting of: (a) a base oil consisting of at least one member selected from the group consisting of a polyvinyl ether, a copolymer of a poly(oxy)alkylene glycol and a polyvinyl ether, and a copolymer of a poly(oxy)alkylene glycol monoether and a polyvinyl ether, each having a water content of not more than 500 ppm by mass, (b) optionally from 0.01 to 5 mass % of an antioxidant, based on a total mass of the lubricating oil composition, (c) optionally from 0.005 to 10 mass % of an acid scavenger, based on the total mass of the lubricating oil composition, and (d) optionally at least one additive selected from the group consisting of an extreme pressure agent, an oiliness agent, a metal deactivator, and a defoaming agent.

2. The composition according to claim 1, wherein the base oil comprises a polyvinyl-based compound having a constituent unit represented by a formula (II): ##STR00017## wherein each of R.sup.4, R.sup.5, and R.sup.6 represents a hydrogen atom or a hydrocarbon group having from 1 to 8 carbon atoms, and they may be the same as or different from each other; R.sup.7 represents a divalent hydrocarbon group having from 2 to 10 carbon atoms; R.sup.8 represents a hydrocarbon group having from 1 to 10 carbon atoms; p represents a number of from 0 to 10 in terms of an average value thereof; R.sup.4 to R.sup.8 may be the same as or different from each other for every constituent unit; and when plural R.sup.7Os are present, the plural R.sup.7Os may be the same as or different from each other.

3. The composition according to claim 1, wherein the antioxidant is present in an amount of 0.05 to 3 mass %, based on the total mass of the lubricating oil composition, and wherein the acid scavenger is present in an amount of 0.005 to 3 mass %, based on the total mass of the lubricating oil composition.

4. The composition according to claim 1, wherein the base oil has a number average molecular weight of 300 or more and not more than 3,000.

5. The composition according to claim 1, wherein the base oil has a viscosity index of 60 or more.

6. The composition according to claim 1, wherein at least one of the extreme pressure agent, the oiliness agent, the metal deactivator, and the defoaming agent is present.

7. The composition according to claim 1, which is suitable for use in a compression refrigerating machine, wherein a sliding portion of which comprises an engineering plastic, an organic coating film or an inorganic coating film.

8. The composition according to claim 7, wherein the organic coating film is selected from the group consisting of a polytetrafluoroethylene coating film, a polyimide coating film, a polyamide-imide coating film, and a thermosetting insulating film formed using a resin coating material comprising a resin base material comprising a polyhydroxy ether resin and a polysulfone-based resin and a crosslinking agent.

9. The composition according to claim 7, wherein the inorganic coating film is selected from the group consisting of a graphite film, a diamond-like carbon film, a tin film, a chromium film, a nickel film, and a molybdenum film.

10. The composition according to claim 1, which is suitable for use in a car air conditioner, an electric car air conditioner, a gas heat pump, an air conditioner, a refrigerator, an automatic vending machine, a showcase, a hot water supply system, or a refrigerating/heating system.

11. The composition according to claim 10, wherein the system has a water content of not more than 300 ppm by mass and a residual air partial pressure of not more than 10 kPa.

12. The composition according to claim 1, wherein the base oil comprises the polyvinyl ether.

13. The composition according to claim 1, wherein the base oil comprises the copolymer of a poly(oxy)alkylene glycol and a polyvinyl ether.

14. The composition according to claim 1, wherein the base oil comprises the copolymer of a poly(oxy)alkylene glycol monoether and a polyvinyl ether.

15. The composition according to claim 12, wherein said polyvinyl ether has a water content of not more than 200 ppm by mass.

16. The composition according to claim 1, wherein the antioxidant is a phenol antioxidant, and wherein the acid scavenger a glycidyl ether acid scavenger.

Description

EXAMPLES

(1) Next, the present invention is described in more detail by reference to the following Examples, but it should be construed that the present invention is not limited to these Examples at all.

(2) Incidentally, properties of a base oil and various properties of a lubricating oil composition for refrigerating machine were determined according to the following manners.

(3) <Properties of Base Oil>

(4) (1) Kinematic Viscosity at 100 C.:

(5) The kinematic viscosity at 100 C. was measured using a glass-made capillary viscometer according to JIS K2283-1983. (2) Number Average Molecular Weight:

(6) The number average molecular weight was measured by means of gel permeation chromatography (GPC). For the GPC, HLC-8120GPC and SC-8020 (manufactured by Tosoh Corporation) were used, and the measurement was conducted with THF (tetrahydrofuran) as an eluent by using an IR detector. The number average molecular weight was determined from a calibration curve according to a polystyrene standard sample on the basis of the measurement results. (3) Flash Point:

(7) The flash point was measured according to JIS K2265 (COC method).

(8) <Thermal Stability Test of Lubricating Oil Composition for Refrigerating Machine>

(9) An autoclave having an internal capacity of 200 mL was filled with an oil/refrigerant mixture (ratio: 30 g/30 g, water content in oil: 500 ppm by mass) and a metal catalyst composed of iron, copper, and aluminum and then sealed, and the autoclave was held under a condition at an air pressure of 0.7 kPa and a temperature of 200 C. for 720 hours. Thereafter, appearance of the oil, a deposit, and change in properties of the catalyst were visually observed, and an acid value was also measured. Incidentally, the acid value was measured by an indicator method according to the lubricating oil neutralization test method defined in JIS K2501.

(10) <Measurement of Two-layer Separation Temperature>

(11) A prescribed amount of a sample was added in a pressure-resistant glass ampule such that its amount was 10% by mass relative to Freon 32 difluoromethane (Freon 32), and this was connected to a vacuum pipe and a Freon 32 gas pipe. The ampule was subjected to vacuum deaeration at room temperature and then cooled with liquid nitrogen, thereby collecting a prescribed amount of the Freon 32. Subsequently, the ampule was sealed and gradually cooled from room temperature in a thermostat, thereby measuring a low-temperature separation temperature at which phase separation commenced. On the other hand, the ampule was gradually heated from room temperature to +40 C., thereby measuring a high-temperature separation temperature at which phase separation commenced.

(12) <Volume Resistivity>

(13) A sample oil at room temperature, which had been prepared by drying under reduced pressure (0.3 to 0.8 mmHg) at 100 C. for one hour, was sealed in a liquid cell for measurement of specific volume resistivity. The volume resistivity was measured at an applied voltage of 250 V by using a digital ultrahigh resistance/micro ammeter R8340, manufactured by Advantest Corporation.

(14) <Formulation Components>

(15) The kind of each of components used for the preparation of each of lubricating oil compositions for refrigerating machine is shown below. (1) Base Oil: PVE-A1 to PVE-A7: Polyethyl vinyl ether PVE-B1 to PVE-B2: Polyethyl vinyl ether (PEVE)/[polyisobutyl vinyl ether copolymer (PIBVE/PIBVE (molar ratio) 9/1)] PVE-C1 to PVE-C2: Polyethyl vinyl ether (PEVE)/[polyisobutyl vinyl ether copolymer (PIBVE/PIBVE (molar ratio) 8/2)] PAG-1 to PAG-2: Polyoxypropylene glycol ECP-1 to ECP-2: Polypropylene glycol (PPG)/polyethyl vinyl ether (PEV) copolymer (PPG/PEV molar ratio: 5/5) POE-1 to POE-2: Pentaerythritol octanoate (C8 acid) nonanoate (C9 acid) ester (C8 acid/C9 acid molar ratio: 1/1.1)

(16) The properties of these base oils are shown in Table 1. (2) Antioxidant:

(17) 2,6-Di-t-butyl-4-methylphenol (0.3% by mass) (3) Acid Scavenger:

(18) 2-Ethylhexyl glycidyl ether (0.3% by mass) (4) Other Additives:

(19) The following respective components were used and added in such a manner that the adding amounts of the components with respect to a total amount of the composition were the amounts (% by mass) shown in the parentheses, thereby making the total content of the components of 1.1% by mass. Extreme pressure agent: Tricresyl phosphate (1.0% by mass) Defoaming agent: Silicone-based defoaming agent (0.1% by mass)

Examples 1 to 8 and Comparative Examples 1 to 9

(20) Refrigerating oil compositions each having a formulation shown in Table 2 were prepared by using the base oil described in Table 2, and the thermal stability of each of the above-described compositions was evaluated by using, as a refrigerant, R32 (difluoromethane) or R410A [50/50 (mass ratio) mixture of R32 and R125 (pentafluoroethane)]. The results are shown in Table 2.

(21) TABLE-US-00001 TABLE 1 Kinematic Number Water viscosity average Flash Kind of content at 100 C. molecular point base oil (ppm) (mm.sup.2/s) weight ( C.) PVE-A1 50 9.5 865 204 PVE-A2 150 24.8 1200 228 PVE-A3 500 7.5 660 201 PVE-A4 1100 8.4 640 200 PVE-A5 1900 20.5 1020 219 PVE-A6 4000 9.1 560 205 PVE-A7 6000 8.3 665 208 PVE-B1 150 7.8 645 201 PVE-B2 2600 19.8 1000 225 PVE-C1 200 10.9 660 199 PVE-C2 5000 19.5 965 219 PAG-1 250 9.8 970 218 PAG-2 3000 19.9 1400 225 ECP-1 180 11.2 840 206 ECP-2 2200 10.6 860 216 POE-1 60 8.6 675 268 POE-2 3200 11.3 680 264

(22) TABLE-US-00002 TABLE 2 Water content Example (ppm) 1 2 3 4 5 6 7 8 Formulation Base PVE-A1 50 98.30 (% by oil PVE-A2 150 98.30 mass) PVE-A3 500 98.30 PVE-B1 150 98.30 PVE-C1 200 98.30 PAG-1 250 98.30 ECP-1 180 98.30 POE-1 60 98.30 Antioxidant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Acid scavenger 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Other additives 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Thermal stability Refrigerant R32 test Acid value (mgKOH/g) 0.01> 0.01> 0.01> 0.01> 0.01> 0.01 0.01 0.02 Appearance of oil Good Good Good Good Good Good Good Good Deposit Not Not Not Not Not Not Not formed Not formed formed formed formed formed formed formed Appearance of catalyst No/no/no No/no/no No/no/no No/no/no No/no/no No/no/no No/no/no No/no/no Fe/Cu/Al Two-layer Separation temperature on 50 50 50 50 30 Separated Separated Separated separation low-temperature side ( C.) temperature Separation temperature on 5 5 5 5 20 Separated Separated Separated high-temperature side ( C.) Volume resistivity ( .Math. m) 1.8 10.sup.11 1.7 10.sup.11 1.6 10.sup.11 1.0 10.sup.11 1.0 10.sup.11 2.0 10.sup.7 1.0 10.sup.10 6.0 10.sup.11 Water content of base oil (ppm by Comparative Example mass) 1 2 3 4 5 6 7 8 9 Formula- Base PVE-A4 1100 98.30 tion oil PVE-A5 1900 98.30 (% by PVE-A6 4000 98.30 mass) PVE-A7 6000 98.30 PVE-B2 2600 98.30 PVE-C2 5000 98.30 PAG 3000 98.30 ECP 2200 98.30 POE 3200 98.30 Antioxidant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Acid scavenger 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Other additives 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Thermal stability Refrigerant R32 test Acid value 0.15 0.15 0.17 0.22 0.19 0.18 0.25 0.18 1.32 (mgKOH/g) Appearance of oil Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellowish brown Deposit Not Not Not Not Not Not Not Not Formed formed formed formed formed formed formed formed formed Appearance of catalyst No/no/yes No/no/yes No/no/yes No/no/yes No/no/yes No/no/yes No/no/yes No/no/yes No/no/yes Fe/Cu/Al Two-layer Separation 50 50 50 50 30 Separated Separated Separated Separated separation temperature on temperature low-temperature side ( C.) Separation 5 5 5 5 20 Separated Separated Separated Separated temperature on high-temperature side ( C.) Volume resistivity ( .Math. m) 1.6 10.sup.11 1.6 10.sup.11 1.5 10.sup.11 1.3 10.sup.11 5.0 10.sup.10 4.0 10.sup.10 8.0 10.sup.6 7.0 10.sup.9 8.0 10.sup.10

(23) In all of Examples 1 to 8 using the lubricating oil composition for compression refrigerating machine of the present invention for the system using R32 (difluoromethane) as a refrigerant, in the heat/oxidation stability test, the appearance of the oil is good, no deposit is formed, no discoloration of the catalyst is found, and the acid value is low. In addition, the volume resistivity is high.

(24) On the other hand, in Comparative Examples 1 to 9, since a base oil having a large water amount is used, not only the acid value is high, but the appearance of the oil assumes a yellow color, a pale yellow color, or a brown color, a deposit is formed, and the change in properties of the catalyst is conspicuous. In addition, the volume resistivity is unfavorably low.

INDUSTRIAL APPLICABILITY

(25) The lubricating oil composition for compression refrigerating machine of the present invention is useful for a compression refrigerating machine using a refrigerant which uses a saturated fluorinated hydrocarbon having from 1 to 3 carbon atoms and a low global warming potential, in particular, a refrigerant capable of being used for an air conditioner, a car air conditioner, and the like, and exhibits excellent heat/oxidation stability.