JP5214151B2 - Refrigerating machine oil for hydrocarbon refrigerant and refrigerating machine system using the same - Google Patents

Description

  The present invention relates to a lubricating oil for a refrigerator using a hydrocarbon refrigerant, particularly propane or isobutane, which has no fear of destroying the ozone layer and has a global warming ability much lower than that of a halogen-containing hydrocarbon refrigerant, and The present invention relates to a refrigerator system using

  In general, a refrigerator system compresses a refrigerant with a compressor, dissipates heat at a high pressure / high temperature with a condenser, and then lowers the pressure with an expansion mechanism (for example, an expansion valve). When evaporating, it takes cooling heat from the surroundings and cools it down. This refrigerator system is used in refrigerators, freezers, air conditioners, showcases, vending machines such as soft drinks and ice creams, and the like. In addition, in an air conditioner, a vending machine, etc., it is utilized also for heating using the heat which arises in the case of condensation, and heating and holding a drink and foodstuffs.

  Conventionally, fluorinated hydrocarbons (CFC or HCFC) containing chlorine such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12), and chlorodifluoromethane (R22) have been used as the refrigerant. However, since these CFCs and HCFCs cause environmental problems that destroy the ozone layer, their production and use are regulated internationally, and now they do not contain chlorine, such as difluoromethane (R32), tetrafluoroethane. (R134 or R134a), non-chlorinated fluorinated hydrocarbons (HFC) such as difluoroethane (R152 or R152a), so-called alternative CFCs.

  However, although these alternative chlorofluorocarbons do not destroy the ozone layer, they are not preferred from the long-term viewpoint of protecting the global environment due to their high global warming potential, while they have a low molecular weight of about 1 to 5 carbon atoms. Lower hydrocarbons, ammonia, etc. have attracted attention as environmentally friendly refrigerants because they do not destroy the ozone layer and have a very low global warming ability compared to the above-mentioned chlorinated or non-chlorinated fluorinated hydrocarbons. (Patent Documents 1 and 2).

  In a refrigerator system, a working fluid in which a refrigerant and so-called refrigerator oil are mixed circulates in the system for lubrication in a compressor. The refrigerating machine oil used for such a working fluid is required to have compatibility with the refrigerant and lubrication performance.For example, the present inventor uses a mineral oil having specific properties as a refrigerating machine oil suitable for a lower hydrocarbon refrigerant. It has been proposed (Patent Document 3).

Japanese Patent Laid-Open No. 2003-041278 JP 2005-162883 A International Publication WO2000 / 60031

  However, it has been found that when a refrigerating machine oil mainly composed of a lower hydrocarbon refrigerant and mineral oil is used as the working fluid, an oligomer (polymer substance) made of an organic substance is generated in the working fluid. Such oligomers may cause clogging of the capillary of the expansion valve or adhere to the valve of the compressor, resulting in poor opening and closing.

  The present invention has been made to solve the above problems, and an object of the present invention is to generate an oligomer in a working fluid when a refrigerating machine oil mainly composed of a lower hydrocarbon refrigerant and mineral oil is used. It is to suppress. The present inventors have found that oligomers can be suppressed by containing a predetermined amount of a specific organic compound in refrigerating machine oil, and have completed the present invention.

The refrigerating machine oil for hydrocarbon refrigerant according to the present invention is used in a refrigerating machine system in which a working fluid containing isobutane as a refrigerant and refrigerating machine oil contacts an organic polymer material made of polyethylene terephthalate or polybutylene terephthalate inside the refrigerating machine system. Refrigerating machine oil, having a % CA of 15 or less, a nitrogen content of 50 ppm or less, and a sulfur content of 2000 ppm or less according to ndM ring analysis, 85 to 99% by weight of mineral oil, neopentyl polyol, and 4 to 12 carbon atoms. a synthetic oil 1-15 wt% consisting of a polyol ester of a monovalent fatty acid is including ones. Further, the refrigerator system according to the present invention is a refrigerator system in which a working fluid containing isobutane as a refrigerant and refrigerator oil contacts an organic polymer material made of polyethylene terephthalate or polybutylene terephthalate inside the refrigerator system, The refrigerating machine oil comprises 85 to 99% by weight of a mineral oil having a% CA of 15 or less, an nitrogen content of 50 ppm or less and a sulfur content of 2000 ppm or less, and neopentyl polyol and 1 to 4 carbon atoms. a synthetic oil 1-15 wt% consisting of a polyol ester of a valence fatty characterized including that.

  The refrigeration oil for hydrocarbon refrigerant of the present invention can suppress the generation of oligomers by containing a predetermined amount of a specific organic compound in mineral oil, effectively preventing clogging of capillaries and valve opening and closing due to oligomers. Has a special effect of being able to. Further, the refrigerator system of the present invention uses such refrigerator oil, and since the generation of oligomers is suppressed, clogging of capillaries due to oligomers and occurrence of valve opening / closing failure are effectively prevented. .

[Refrigerator oil]
Refrigerating machine oil of the present invention, n-d-M ring analysis% CA is 15 or less, the nitrogen content of 50ppm or less, 85 to 99 wt% sulfur content 2000ppm or less of mineral oil, and preferably 88 to 97 wt%, neo pentyl polyol and 1 to 15 wt% synthetic oil consisting of a polyol ester of a monovalent fatty acid having 4 to 12 carbon atoms, preferably Dressings containing and 3-12% by weight. When the content of synthetic oil composed of a polyol ester of neopentyl polyol and monovalent fatty acid having 4 to 12 carbon atoms is less than 1% by weight or more than 15% by weight (that is, the content of mineral oil exceeds 99% by weight If it is less than 85% by weight, the generation of oligomers cannot be sufficiently suppressed.

The refrigerating machine oil of the present invention preferably has a kinematic viscosity at 40 ° C. of 3 to 150 mm ² / s, particularly 5 to 100 mm ² / s, and more preferably has a pour point of −25 ° C. or less. When the pour point is higher than −25 ° C., the lubricant discharged together with the refrigerant from the compressor is lowered in fluidity by an expansion mechanism or an evaporator, and stays in a low temperature part of the refrigeration equipment, leading to a decrease in heat transfer efficiency. This is not preferable because it may cause wear and seizure of the bearing due to lack of lubricant in the compressor. In general, the pour point is −60 ° C. or higher. Further, the viscosity index is preferably 20 or more, particularly 50 or more, more preferably 80 or more, and the viscosity index is usually 120 or less. In the refrigeration cycle, the lubricant becomes high temperature at the compressor discharge section and is exposed to a low temperature at the outlet of the expansion mechanism and used in a relatively wide temperature range. Therefore, a lubricant having a high viscosity index with little change in viscosity due to temperature, that is, a mineral oil having a high viscosity index is desired. In general, a lubricant containing a large amount of long-chain hydrocarbons has a high viscosity index and tends to have a high lubricating performance.

[Mineral oil]
As the mineral oil, a mineral oil having a property of% CA of 15 or less, nitrogen content of 50 ppm or less, and sulfur content of 2,000 ppm or less by ndM ring analysis is used . The value of% CA greatly affects the viscosity index. When this value is increased, the viscosity index is lowered. Mineral oil having a% CA exceeding 15 is not preferable as a refrigerating machine oil. Mineral oil with a% CP of 40 or more, particularly 50 or more, has high lubricity and can maintain sufficient lubricity even when diluted with a hydrocarbon refrigerant having poor lubricity, such as bearing wear and seizure. Therefore, it is preferable to use a mineral oil having a% CP of 40 or more, and more preferably a mineral oil having a% CP of 50 or more. These% CA and% CP are determined by the ndM ring analysis specified in ASTM D3238.

  Moreover, the nitrogen content and sulfur content contained in the mineral oil may adversely affect the characteristics of the lubricating oil. If the nitrogen content exceeds 50 ppm, the stability tends to deteriorate, and it is preferably 50 ppm or less. Moreover, since sulfur content is corrosive, it is preferable to make it 2,000 ppm or less. In addition, nitrogen content and sulfur content are specified in mass ppm.

  Such mineral oil can be used to remove solvent, extract, hydrocrack, hydrodewax, solvent dewax, hydrorefining the lubricating oil fraction obtained by atmospheric and vacuum distillation of crude oil. In addition, it can be obtained by appropriately combining one or two or more purification means of sulfuric acid washing and clay treatment.

[Synthetic oil]
As the synthetic oil , one kind of polyol ester of neopentyl polyol and monovalent fatty acid having 4 to 12 carbon atoms or a mixture of two or more kinds is used.

[Polyol ester]
As the polyol ester, an ester of a polyol having 3 to 20 diols or hydroxyl groups and a fatty acid having 6 to 20 carbon atoms is preferably used. Here, as the diol, specifically, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2 diethyl-1,3-propanediol.

Specific examples of the polyol having 3 to 20 hydroxyl groups include trimethylolethane, trimethylolpropane, trimethylolbutane, di- (trimethylolpropane), tri- (trimethylolpropane), pentaerythritol, Examples thereof include polyhydric alcohols such as-(pentaerythritol) and tri- (pentaerythritol).

  Among these, diols and polyols include neopentyl glycol, trimethylol ethane, trimethylol propane, trimethylol butane, di- (trimethylol propane), tri- (trimethylol propane), pentaerythritol, di- (pentaerythritol). Hindered alcohols such as tri- (pentaerythritol) are preferred.

In the fatty acid used for polyol ester, the carbon number is 4-12 . Among the fatty acids having 4 to 12 carbon atoms, from the viewpoint of lubricity, preferably not less than 5 carbon atoms, particularly preferably those having 10 or more carbon atoms. Moreover, from a compatibility point with a refrigerant | coolant, a C10 or less thing is preferable and a C9 or less thing is especially preferable.

The fatty acid may be either a linear fatty acid or a branched fatty acid, but a linear fatty acid is preferable from the viewpoint of lubricity, and a branched fatty acid is preferable from the viewpoint of hydrolysis stability. preferable. As the fatty acid, specifically, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, and these fatty acids are straight-chain fatty acids, branched Any of fatty acids may be used, and furthermore, a fatty acid (neoic acid) in which the α carbon atom is a quaternary carbon atom may be used. Among these, valeric acid (n-pentanoic acid), caproic acid (n-hexanoic acid), enanthic acid (n-heptanoic acid), caprylic acid (n-octanoic acid), pelargonic acid (n-nonanoic acid), caprin Acid (n-decanoic acid) , isopentanoic acid (3-methylbutanoic acid), 2-methylhexanoic acid, 2-ethylpentanoic acid, 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid are preferably used.

For the refrigerating machine oil of the present invention, an ester of neopentyl polyol and a monovalent fatty acid having 4 to 12 carbon atoms is used. Here, as a neopentyl polyol which is a polyhydric alcohol having a neopentyl structure, neopentyl glycol, trimethylolpropane, and pentaerythritol are preferably used, and in particular, a mixture of two or more kinds of neopentyl polyols may be used. preferable. Moreover, as a monovalent fatty acid, a C5-C10 fatty acid and a branched fatty acid are particularly preferably used.

  In addition, as long as it has two or more ester groups, the polyol ester according to the present invention may be a partial ester in which some of the hydroxyl groups of the polyol remain without being esterified. May be a complete ester esterified, and may be a mixture of a partial ester and a complete ester, but is preferably a complete ester. If the residual amount of carboxyl groups is large, an undesirable phenomenon such as the formation and precipitation of metal soap due to the reaction with the metal used inside the refrigerator will occur, so that the acid value is 3 mgKOH / g or less. Those having a concentration of 0.1 mgKOH / g or less are more preferable. In addition, if the residual amount of hydroxyl group is large, the ester becomes cloudy at low temperature and undesired phenomena such as blocking of the capillary device of the refrigeration cycle occur. The following are more preferable.

[Refrigerant]
Refrigerant used in the present invention is isobutane.

[Refrigerator system]
The refrigerator system of the present invention is a refrigerator system in which a working fluid containing isobutane as a refrigerant and refrigerator oil contacts an organic polymer material made of polyethylene terephthalate or polybutylene terephthalate inside the refrigerator system, Machine oil is 85 to 99% by weight of mineral oil having % CA of 15 or less, nitrogen content of 50 ppm or less and sulfur content of 2000 ppm or less by ndM ring analysis , neopentyl polyol and monovalent fatty acid having 4 to 12 carbon atoms. a synthetic oil 1-15 wt% consisting of polyol esters of characterized including that. The refrigerator system of the present invention includes, for example, a compressor, a condenser, an expansion mechanism (for example, an expansion valve), and an evaporator, and a working fluid including a refrigerant and refrigerator oil circulates in the system. The compressor is housed in the same housing as the electric motor that drives the compressor, and is preferably used when the electric motor is lubricated and cooled by the working fluid. The working fluid is preferably a mixture of refrigerant and refrigerating machine oil in a weight ratio of 10:90 to 90:10, particularly 20:80 to 80:20.

For the electric motor, an organic polymer material is used for electrical insulation . When polyethylene terephthalate or polybutylene terephthalate is used as the organic polymer material , the effect of the present invention becomes remarkable. Note that the present invention can also be applied to the case where such an organic polymer material is used in addition to the electric motor.

[Other additives]
You may mix | blend another additive suitably with the refrigerating machine oil of this invention as needed. As the additive, 2,6-di-tertiary butylphenol, 2,6-di-tertiary butyl-p-cresol, 4,4-methylene-bis- (2,6-di-tertiary butyl-p -Cresol), p, p'-di-octyl-di-phenylamine and other phenol-based or amine-based antioxidants, phenyl glycidyl ether, alkyl glycidyl ether, phenyl glycidyl ester, stabilizer such as alkyl glycidyl ester, tri Extreme pressure agents such as cresyl phosphate and triphenyl phosphate, oily agents such as glycerol monooleate, glycerol monooleyl ether and glycerol monolauryl ether, metal deactivators such as benzotriazole, polydimethylsiloxane, polymethacrylate, etc. Antifoaming agent or antifoaming agent And the like.

  In addition, additives such as known detergent dispersants, viscosity index improvers, rust inhibitors, corrosion inhibitors, pour point depressants, and the like can be blended as necessary. These additives are usually blended in the lubricant of the present invention so as to be contained at about 10 ppm by weight to 10% by weight. In particular, the addition of about 0.01 to 0.5% by weight of a phenol-based or amine-based antioxidant greatly improves the stability and durability of the lubricant. Phosphate esters such as tricresyl phosphate and triphenyl phosphate are useful as extreme pressure agents. Lubricating properties such as seizure load and abrasion resistance can be added in small amounts (for example, 0.05 to 2.0% by weight). Effectively improve.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these specific examples.

  As the base oil, paraffinic mineral oils 1 and 2, naphthenic mineral oil and ester oil having the properties shown in Table 1 were used. The ester oil is an ester synthesized from a mixed polyol of 80% by weight of neopentyl glycol and 20% by weight of pentaerythritol and 2-methylhexanoic acid.

  These base oils were blended in the blending amounts shown in Tables 2 and 3 to prepare test oils 1 to 10 which were Examples 1 to 5 and Comparative Examples 1 to 5.

[Oligomer precipitation test]
30 g of test oil, 10 g of a hydrocarbon refrigerant (isobutane, R600a) and 1 g of a PET (polyethylene terephthalate) film were placed in a 100 mL capacity cylinder and left at 150 ° C. for 14 days using an autoclave. Thereafter, the sample oil and the hydrocarbon refrigerant were filtered through a 0.8 μm Millipore filter, and the amount of precipitation was measured by weight increase. The results are shown in Tables 2 and 3 as the amount of precipitates.

  Sample oils 6 to 10 have an oligomer precipitation amount of 10 mg or more. However, it is found that the sample oils 1 to 5 are less than 10 mg and it is difficult for the oligomer to be precipitated from PET.

[Capillary clogging test]
220 ml of refrigeration oils 2, 3, 6, and 7 shown in Tables 2 and 3 were placed in a refrigerator compressor, and 30 g of a hydrocarbon refrigerant (isobutane, R600a) was used as a refrigerant. A condenser and an evaporator were connected to the discharge side and the suction side of the refrigerator compressor, respectively, and a capillary was connected between the condenser and the evaporator to constitute a refrigeration system for evaluation. The refrigerator compressor includes a reciprocating compressor and an electric motor that drives the reciprocating compressor, and polyethylene terephthalate is used to insulate the electric motor. The working fluid consisting of refrigerating machine oil and refrigerant is in direct contact with the electric motor for cooling. The refrigerator compressors discharge pressure 5~6kg / cm ² · G, in the conditions of suction pressure 0kg / cm ² · G, were 500 hours of continuous operation. As a result, whether or not capillary clogging occurred was evaluated and is shown in Tables 2 and 3 together.

  A small amount of capillary clogging occurred in the test oils 6 and 7. However, capillary clogging did not occur in sample oils 2 and 3.

  The refrigeration oil for hydrocarbon refrigerant of the present invention can suppress the generation of oligomers by containing a predetermined amount of a specific organic compound in mineral oil, effectively preventing clogging of capillaries and valve opening and closing due to oligomers. It is very useful for long-term stable operation of the refrigeration system.

Claims (2)

A working fluid containing isobutane as a refrigerant and refrigerating machine oil is a refrigerating machine oil used in a refrigerating machine system in contact with an organic polymer material made of polyethylene terephthalate or polybutylene terephthalate inside a refrigerating machine system,
85% to 99% by weight of mineral oil having a% CA of 15 or less by nitrogen analysis and a nitrogen content of 50 ppm or less and a sulfur content of 2000 ppm or less ,
Neopentyl consisting polyol and polyol ester of a monovalent fatty acid having 4 to 12 carbon atoms synthetic oil 1-15 wt% and the including hydrocarbon refrigerant refrigeration oil. A working fluid containing isobutane as refrigerant and refrigerating machine oil is a refrigerating machine system in contact with an organic polymer material made of polyethylene terephthalate or polybutylene terephthalate inside the refrigerating machine system,
The refrigerating machine oil comprises 85 to 99% by weight of a mineral oil having a% CA of 15 or less, an nitrogen content of 50 ppm or less and a sulfur content of 2000 ppm or less, and neopentyl polyol and 1 to 4 carbon atoms. refrigeration system characterized in including that the synthetic oil 1-15 wt% consisting of polyol esters of valence fatty acids.