JP2850983B2 - Lubricant - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lubricating oil for a compressor using chlorofluorocarbon as a refrigerant, and in particular, a hydrofluorocarbon containing no chlorine among fluorocarbons, HFC-134a. (1,1,
Used to compress hydrogen-containing Freon refrigerants such as 1,2-tetrafluoroethane), HFC-134 (1,1,2,2-tetrafluoroethane) and HFC-152a (1,1-difluoroethane) It relates to a suitable lubricating oil.

(Prior Art) Conventionally, refrigerators, air conditioners, refrigerators, and the like have a refrigerant containing fluorine and chlorine as constituent elements, such as chlorofluorocarbon (CFC) R-11 (trichloromonofluoromethane) and R-12. (Dichlorodifluoromethane),
R-22 which is hydrochlorofluorocarbon (HCFC)
The use of fluorocarbons such as (monochlorodifluoromethane) has started to emerge as a new type of refrigerant containing hydrogen, such as HFC-134a, as a new type of refrigerant that has no effect on the recent ozone depletion problem. I have.

On the other hand, as for lubricating oils for refrigerators, many mineral oil-based and synthetic oil-based lubricating oils have hitherto been known.
It was found that compatibility with HFC-134a was so poor that it could not be used. Therefore, this measure has become an important issue today. In addition, other properties required for refrigerating machine oil include lubricity, electrical insulation, energy saving, friction resistance,
Sealing properties, heat resistance and sludge deposition prevention properties are mentioned, and these points also need to be considered.

Incidentally, examples of conventionally known synthetic oils include polyether-based synthetic lubricating oils.
29, No. 9, pp. 336-343 (1980) and Petrotech, Vol. 8, No. 6, 562-566 (1985). Additionally, the following equation in JP 61-281199, R _{[O- (R 2 O) m -R} 3 ] a mixture of polyglycols and alkylbenzene represented by _n, in JP-A-57-63395 Are oils obtained by mixing an epoxycycloalkyl compound with a polyether, for example, a high molecular weight polyoxypropylene monobutyl ether such that the number of moles added is 53 per functional group, and JP-A-59-117590.
In the publication, high viscosity mixed oils of a polyether compound and a paraffinic or naphthenic mineral oil are respectively introduced.

(Problems to be Solved by the Invention) However, none of the above-mentioned known synthetic oil-based lubricating oils could be lubricating oils for refrigerators using HFC-134a as a refrigerant due to problems such as compatibility.

Under such circumstances, US Patent No. 4,755,316 discloses HFC-
Polyoxyalkylene glycol (hereinafter abbreviated as PAG) whose both ends are hydroxyl groups (-OH) is introduced as a refrigerating machine oil for 134a, and this PAG is compared with a general PAG having a hydroxyl group and an alkyl group at the end. The compatibility with HFC-134a melts over a wider temperature range, improves oil return to the compressor in the refrigeration system, and prevents seizure when the compressor starts at high temperatures.
The range of the compatible temperature with HFC-134a is stated to be −40 ° C. to + 50 ° C.

On the other hand, hydrogen-containing Freon refrigerants such as HFC-134a
It is a candidate for an alternative to FC, and is expected to be a new refrigerant mainly for car air conditioners and refrigerators. In the case of refrigerators, compatibility between oil and refrigerant is required, but most types have a motor in a refrigerant system, and the oil itself requires high electrical insulation. However, conventionally, HFC-134a
PAG being considered as a refrigerating machine oil is U.S. Pat.
The electrical insulation properties, including the compounds disclosed in Japanese Patent No. 5,316, are remarkably inferior to conventional mineral oil-based refrigerating machine oils, and have high hygroscopicity.

Therefore, an object of the present invention is to provide HFC-1 which is a new refrigerant.
Lubricating oil for refrigerators with excellent compatibility in a wide temperature range, high electrical insulation, and low hygroscopicity for chlorine-free hydrogen-containing chlorofluorocarbon refrigerants such as 34a, HFC-134, and HFC-152a. To provide.

(Means for Solving the Problems) Commercially available esters are a very small part, but although they are currently used in systems such as refrigerants R-12 and R-22, these esters are different from HFC-134a, a new refrigerant. It is not compatible at all or its compatibility range is extremely narrow. The present inventors have focused on high electrical insulation, low hygroscopicity, good lubricity, and high thermal oxidation stability of esters as compared with PAG, and when designing molecules, how to design hydrogen-containing fluorocarbons such as HFC-134a After extensive studies on compatibility with the refrigerant in a wide range, the present inventors have found that only an ester having an extremely limited structure can be used in a refrigerant system such as HFC-134a, and have completed the present invention.

The present invention provides at least one or more kinds of trihydric alcohols having 15 or less carbon atoms (excluding glycerin), linear monovalent fatty acids having 2 to 18 carbon atoms (excluding acetic acid and acetic anhydride) and 4 to 4 carbon atoms. The main component is an ester obtained from one or more monovalent fatty acids selected from the group consisting of 18 branched monovalent fatty acids (excluding neoheptanoic acid), and the acid value of the ester is 3 mgKOH / g or less. The present invention relates to a chlorine-free lubricating oil for a hydrofluorocarbon refrigerant, which has a hydroxyl value of 50 mgKOH / g or less.

Polyhydric alcohol used as a raw material in the present invention,
Use those having 15 or less carbon atoms. Polyhydric alcohols having 16 or more carbon atoms have too large a hydrocarbon portion of the alcohol itself, and the synthesized esters also have poor compatibility with HFC-134a and the like, which is not preferable as lubricating oil for refrigerators.

Examples of such trihydric alcohols include trimethylolpropane, trimethylolethane, 3-methyl-1,3,
5-pentanetriol, 1,2,3-butanetriol, 1,
2,3-pentanetriol, 2-methyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 5-ethyl-4,5,6-nonanetriol , 1,2,4-butanetriol and the like.

Also, limiting the carbon number of monovalent fatty acids to 2-18 is
If the number of carbon atoms is 19 or more, the compatibility between HFC-134a and the synthesized ester is extremely deteriorated, and preferred as monovalent fatty acids are linear or branched ones having 3 to 10 carbon atoms. is there. For example, as a monovalent fatty acid, propionic acid, isopropionic acid, butanoic acid, isobutanoic acid, pentanoic acid, isopentanoic acid, hexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3,5 , 5-trimethylhexanoic acid, decanoic acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, palmitooleic acid, stearic acid, isostearic acid, oleic acid, linoleic acid and linolenic acid.

In the present invention, one or more of these monohydric fatty acids are appropriately mixed to cause an ester reaction with a specific polyhydric alcohol to obtain an ester which satisfies desired physical properties required by various refrigerators. It is.

In order to further improve the compatibility with the hydrofluorocarbon, a monovalent fatty acid is preferably a mixed system having a straight chain having 3 to 11 carbon atoms and a branched chain having 4 to 14 carbon atoms, and more preferably a mixed system having 5 to 14 carbon atoms. A mixed system of a straight-chained one having 10 to 10 and a branched one having 7 to 9 carbon atoms can be used. The blending ratio of the branched monovalent fatty acid to the total monovalent fatty acid used as a raw material
It is preferred to be at least 50 mol%.

With respect to polybasic acids, polybasic acids having 3 or less carbon atoms are special products, are difficult to obtain at low cost, and are inferior in stability of esters after synthesis. In addition, since polybasic acids having 15 or more carbon atoms have significantly reduced compatibility with HFC-134a and the like, the number of carbon atoms is preferably 4 to 14, and HFC is particularly preferable in a wide range.
Those having 4 to 10 carbon atoms are preferable to ensure compatibility with -134a and the like. As polybasic acids, succinic acid, glutaric acid,
Adipic acid, pimelic acid, suberic acid, azelaic acid,
Sebacic acid, phthalic acid, maleic acid, trimellitic acid, and the like. Particularly preferably, the monovalent fatty acid is 2-ethylhexanoic acid, and the polybasic acid is adipic acid.

The ratio of one or more polybasic acids having 4 to 14 carbon atoms is preferably 80 mol% or less based on the total amount of the acid used as the raw material. The reason for this is that if it exceeds 80 mol%, gelation may occur in some cases, making it difficult to obtain desirable physical properties. It is more preferably at most 25 mol%.

The compound according to the present invention is an esterification reaction by a dehydration reaction between the above-mentioned specific polyhydric alcohol and a specific fatty acid, or a general esterification reaction via an acid anhydride that is a derivative of a fatty acid, an acid chloride or the like. It can be obtained by transesterification of each or a derivative.

The ester according to the invention can be obtained by the method described above. When the acid value is 3 mgKOH / g or more, metal soap or the like is generated by the reaction with the metal used in the refrigerator, and may precipitate. Therefore, the acid value is 3 mgKOH / g or less. When the hydroxyl value exceeds 50 mgKOH / g, undesired phenomena such as clouding of the ester at low temperatures may occur. Therefore, the hydroxyl value is set to 50 mgKOH / g or less.

(Operation) The lubricating oil for a refrigerator of the present invention containing the above-described ester as a main component is, for example, a lubricating oil used for a refrigerator using HFC-134a as a refrigerant, and has a wide range from a low temperature to a high temperature with the refrigerant HFC-134a. The regions exhibit good solubility in one another and their lubricity and thermal stability can be greatly improved. further,
Compared to PAG, which is generally considered as a refrigerating machine oil for HFC-134a, it has much higher electric insulation and lower hygroscopicity. Therefore, the lubricating oil for a refrigerator of the present invention containing the above-mentioned ester as a main component can solve the problems of the compatibility and the hygroscopicity with respect to a hydrogen-containing Freon refrigerant such as HFC-134a, which are problems of the prior art. The use of the refrigerant in a refrigeration compressor for refrigeration has improved electrical insulation, which is a major problem, and has solved this problem.

In the refrigerating machine oil according to the present invention, it goes without saying that lubricating oils such as PAG and mineral oil can be appropriately mixed within a range that satisfies the function as the refrigerating machine oil. Needless to say, additives such as an antioxidant, an antiwear agent, and an epoxy compound can be appropriately added.

(Examples) Hereinafter, the present invention will be described specifically with reference to examples.

Examples 1 to 8, Comparative Examples 1 to 5 A-1 to 8 shown in Table 1 as esters according to the present invention.
The test oils (no commercial products, no trial oils, trimethylol ethane and trimethylol propane as polyhydric alcohols) were used to evaluate the performance as a lubricant for refrigerant HFC-134a refrigerator. As comparative examples, general PAGs (B-1 to 3) shown in Table 2 and commercially available esters (C
-1 and 2) were also evaluated. As the PAG, a commercially available product of Asahi Denka Co., Ltd., and as the ester, Nippon Oil & Fats Co., Ltd., whose use as a lubricating oil was known.

The ester was synthesized as follows. In the case of the trial oil of Example 1, a mixture of a monovalent fatty acid and a polybasic acid mixed in the ratio of mol% shown in Table 1 (in the case of Example 1, the polybasic acid was not contained and 2-ethylhexane was used. The acid separator) and trimethylolethane were mixed with a stir bar, a nitrogen gas blowing tube, a thermometer, and a water separator with a cooler in such a ratio that the amounts of carboxyl groups and hydroxyl groups of alcohols in the mixture became equal. The mixture was charged into a four-necked flask equipped with the flask, and subjected to an esterification reaction at 230 ° C. for 8 hours under a nitrogen stream while removing distilled water outside the system.
g), and the reaction was carried out at the same temperature for 2 hours to obtain a trial oil A-1 of Example 1. In the other Examples 2 to 8, and Examples 9 to 17 and 18 to 25 described later, the esterification reaction was performed in the same manner, and trial oils A-2 to A-8, A-9 to A-17, and A-18 to
A-25 was obtained.

The lubricating properties, compatibility and thermal stability of the test oils shown in Tables 1 and 2 as lubricating oils for refrigerators were evaluated under the following conditions.

Lubricity According to ASTM D-3233-73, Falex
The seizure load is controlled under an atmosphere controlled by HFC-134a (70ml / mi
n).

Compatibility After filling 0.6 g of the test oil and 2.4 g of refrigerant (HFC-134a) in a glass tube, cool and raise the temperature at 1 ° C per minute, and the temperature at which two layers separate at low and high temperatures, The phase separation temperature was measured.

Thermal stability According to ANSI / ASHRAE 97-1983, 1 g of test oil and refrigerant (HFC
After enclosing 1 g of -134a and R-12) and a catalyst (each wire of iron, copper and aluminum) in a glass tube, the mixture was heated to 175 ° C, and 10 days later, the hue of the test oil was judged by ASTM.

Electrical insulation A volume resistivity test at 80 ° C. according to JIS C2101 was performed.

Hygroscopicity 60 g of the sample oil was placed in a 100 ml beaker in an atmosphere at a temperature of 25 ° C. and a humidity of 70%, and compared and evaluated based on the moisture concentration 3 hours after opening.

The evaluation results are as shown in Table 3.

As can be seen in Table 3, the esters according to the invention are PA
Compared with G (B-1 to 3), the electrical insulation indicated by volume resistance is 100,000 times or more, and no two-layer separation at high temperature is observed. Also, the seizure load is excellent and the hygroscopicity is low. The thermal stability is similar in the HFC-134a system, but is overwhelmingly superior in the R-12 system. This indicates that the HFC at the stage where the refrigerant transitions from R-12 to HFC-134a
Since mixing of R-12 with -134a is unavoidable, it is extremely advantageous in practice.

Further, the ester according to the present invention is converted to a commercially available ester (C-1).
As compared with the above (2), there is a marked difference in the two-layer separation temperature, and the commercial oil hardly dissolves with R-134a. This point is a great feature of the molecularly designed ester according to the present invention.

From these facts, it can be said that the present invention is far superior to that of the comparative example.

HFC-134a is expected to replace R-12 and is used in car air conditioners and refrigerators. In particular, car air conditioners are mainly used in summer, and the compressor is started at a high temperature. Therefore, compatibility between oil and a refrigerant at a high temperature is important. If the oil and the refrigerant are separated into two layers in the compressor at the time of the start-up, the refrigerant having a large specific gravity stays in the lower layer, and only the refrigerant is supplied to the compressor.

In the case of refrigerators, there are many built-in types in which a motor and a compressor are integrated, and leakage is a problem,
Since the ester according to the present invention has a volume resistivity 100,000 times or more higher than that of PAG, it can be said that it is a lubricating oil for refrigerators having excellent electrical insulation properties.

Examples 9 and 10 Test oils using trihydric alcohols as esters according to the present invention are shown in Table 4 as A-9 and A-10. Table 5 shows the performance evaluation results of the respective esters as lubricating oils for HFC-134a refrigerators. Note that the evaluation method described above was used.

As a result of the evaluation, when the ester according to the present invention was used,
As in Example 1-8, for refrigeration oil suitable for refrigerant HFC-134a, having compatibility with HFC-134a, excellent electrical insulation, lubricating properties, excellent heat stability, and much lower hygroscopicity than PAG It can be said that it is a lubricating oil.

(Effects of the Invention) In order to respond to the ozone depletion caused by chlorofluorocarbon, which has recently become a major problem on a global scale, HFC with almost no ozone depletion has been used as an alternative to R-12, which is widely used as a refrigerant. Although 134a has been highlighted, it has the drawback of poor compatibility with refrigeration oil, which has been a barrier to the development of alternative systems. However, the lubricating oil for a refrigerator according to the present invention uses Freon HFC-134a, HFC-134 and HFC-15 as refrigerants.
Since it maintains sufficient compatibility with hydrogen-containing chlorofluorocarbon refrigerants such as 2a, has high electrical insulation properties, and is also excellent in overall performance, it is particularly suitable for HF instead of conventional R-12 and R-22 fluorocarbons.
Even if C-134a is used, the effect that the conventional system can be used as it is can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C10M 105 / 38,109 / 02 C10N 40:30

Claims (12)

(57) [Claims] At least one kind of trihydric alcohol having 15 or less carbon atoms (excluding glycerin), a linear monovalent fatty acid having 2 to 18 carbon atoms (excluding acetic acid and acetic anhydride) and 4 carbon atoms. The main component is an ester obtained from one or more kinds of monovalent fatty acids selected from the group consisting of branched monovalent fatty acids (excluding neoheptanoic acid) of ~ 18, and the acid value of the ester is 3 mgKOH / g A lubricating oil for a chlorine-free hydrofluorocarbon refrigerant, wherein the lubricating oil has a hydroxyl value of 50 mgKOH / g or less. 2. One or more trihydric alcohols having 15 or less carbon atoms, linear monovalent fatty acids having 2 to 18 carbon atoms and 4 to 4 carbon atoms.
2. The lubricating oil according to claim 1, wherein the main component is an ester obtained from one or more monovalent fatty acids selected from the group consisting of 18 branched monovalent fatty acids. 3. The lubricating oil according to claim 1, wherein at least one kind of polybasic acid having 4 to 36 carbon atoms is used as a raw material of said ester. 4. The lubricating oil according to claim 3, wherein the ratio of the polybasic acid is 80 mol% or less based on the whole acid used as a raw material. 5. The method according to claim 1, wherein an ester obtained by mixing at least 50 mol% of the branched monovalent fatty acid with respect to the entire monovalent fatty acid is used as a main component. A lubricating oil according to one claim. 6. The lubricating oil according to claim 5, wherein the entirety of the monovalent fatty acid comprises only a branched monovalent fatty acid. 7. The lubricating system according to claim 5, wherein the monovalent fatty acid comprises at least 50 mol% of a branched monovalent fatty acid and at most 50 mol% of a linear monovalent fatty acid. oil. 8. The lubricating oil according to claim 1, wherein the linear monovalent fatty acid has 5 to 10 carbon atoms. 9. The lubricating oil according to claim 1, wherein the branched monovalent fatty acid has 4 to 14 carbon atoms. 10. The branched monovalent fatty acid having 7 to 9 carbon atoms.
The lubricating oil according to claim 9, wherein: 11. The lubricating oil according to claim 3, wherein the polybasic acid has 4 to 10 carbon atoms. 12. The ester having a volume resistivity at 80 ° C. of 1
2. The lubricating oil according to claim 1, wherein the lubricating oil has a density of not less than × 10 ¹² Ω · cm.