JP2624543B2 - Lubricating oil composition for refrigerator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lubricating oil for a compressor using chlorofluorocarbon as a refrigerant, and particularly to a hydrofluorocarbon (HFC) containing no chlorine among fluorocarbons. R134a (1,1,
The present invention relates to a lubricating oil suitable for use when compressing a hydrogen-containing Freon refrigerant such as (1,2-tetrafluoroethane).

(Conventional technology) Conventionally, refrigerators, air conditioners, refrigerators, and the like have been used as refrigerants in which chlorofluorocarbon (CFC) such as R11 (trichloromonofluoromethane) and R12 (dichlorodifluoromethane) are used as refrigerants. HFC-134a is used as a new type of refrigerant that has no influence on the recent ozone depletion problem due to the use of fluorocarbons such as R22 (monochlorodifluoromethane), which is a hydrochlorofluorocarbon (HCFC). Hydrogen-containing CFC refrigerants have begun to appear.

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, abrasion resistance, sealing properties, heat resistance, and sludge deposition prevention properties. These points also need to be considered. It is.

Incidentally, examples of conventionally known synthetic oils include polyether-based synthetic lubricating oils.
Vol. 9, No. 9, pages 336-343 (1980) and Petrotech, Vol. 8, No. 6, pages 562-566 (1985). JP-A-61-281199 discloses a mixture of a polyglycol represented by the following formula: R ₁ O- (R ₂ O) -R ₃ ] _n and alkylbenzene, and JP-A-57-63395 discloses a mixture thereof. Polyether, for example, an oil obtained by mixing an epoxycycloalkyl-based compound with a polyoxypropylene monobutyl ether having a high molecular weight 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 compatibility temperature range with HFC-134a is introduced as -40 ° C to + 50 ° C.

On the other hand, HFC-134a is an alternative refrigerant candidate for CFC-12 and is mainly used for car air conditioners and refrigerators. For refrigerators,
Although compatibility between oil and refrigerant is required, most motors have a motor in the refrigerant system, and the oil itself must be electrically insulated. However, PAG, which has been conventionally studied as a refrigerating machine oil for HFC-134a, including the compound disclosed in U.S. Pat. No. 4,755,316, has remarkably inferior electrical insulation properties as compared with conventional mineral oil based refrigerating machine oil.

Therefore, an object of the present invention is to provide HFC-1 which is a new refrigerant.
An object of the present invention is to provide a lubricating oil for refrigerators that has excellent compatibility over a wide temperature range with respect to 34a and has high electrical insulation.

(Means for Solving the Problems) The present inventors have intensively studied various synthetic oils for the purpose of solving the above problems, and found that a compound having a specific carboxyl group and a specific polyalkylene glycol derivative can be used. The inventors have found that esters are effective in achieving the object of the present invention, and have completed the present invention.

That is, the present invention provides the following general formula (1): (Where X is a residue of a dibasic acid, AO _{1 to} AO ₄ are oxyalkylene groups having 1 to ₄ carbon atoms, R ₁ and R ₂ are hydrocarbon groups having 1 to 17 carbon atoms, a, b, c and d is an integer of 0 to 50, and a
+ B + c + d represents an integer of 1 or more and 50 or less), and a lubricating oil composition for refrigerators mainly comprising an ester of a compound having a carboxyl group and a polyalkylene glycol derivative.

Here, in the above formula (1), as the dibasic acid whose residue is represented by X, adipic acid, azelaic acid, sebacic acid,
Examples thereof include phthalic acid and terephthalic acid, and among them, adipic acid and sebacic acid are preferred in view of the compatibility between the formed ester and HFC-134a. Examples of the oxyalkylene group represented by AO include oxymethylene, oxyethylene, oxypropylene, oxybutylene, and HFC-134.
Oxyethylene and oxypropylene are preferred in terms of compatibility with a.

In the above formula (1), both R ₁ and R ₂ are a hydrocarbon group having 1 to 17 carbon atoms.
This is because the compatibility with -134a decreases. For the same reason, the polymerization degree is specified to be 50 or less for a and b.

The compound (ester) of the general formula (1) according to the present invention
Is an esterification reaction of a polyalkylene glycol derivative and a compound having a carboxy group by a dehydration reaction, or an acid anhydride that is a derivative of a compound having a carboxyl group,
It can be obtained by a general esterification reaction via an acid chloride, a lower alcohol ester or the like. Further, the esterification ratio is preferably 70% or more, and if it is less than 70%, the electric insulation property is lowered and the hygroscopicity is increased.

The ester according to the present invention can be obtained by the above-mentioned method, but it is preferable that no carboxyl group remains.

(Operation) The lubricating oil composition for a refrigerator according to the present invention, which contains the ester of the general formula (1) as a main component, is used as a lubricating oil particularly for a refrigerator using HFC-134a as a refrigerant. 134a
And good solubility in a wide range from low temperature to high temperature, thereby greatly improving lubricity and thermal stability. Furthermore, compared with PAG, which is generally studied as a refrigerating machine oil for HFC-134a, it has much higher electric insulation and lower hygroscopicity. Therefore, the refrigerator lubricating oil of the present invention containing the above-mentioned ester as a main component can solve the problems of compatibility with HFC-134a and the problem of hygroscopicity, which are problems of the prior art, and furthermore, HFC-134a is used for refrigerators. It has become possible to improve the electrical insulation, which is a major problem when using the refrigeration compressor, and also to solve this problem.

In addition, it goes without saying that additives such as an antioxidant, an antiwear agent, an epoxy compound and the like conventionally used in refrigerator oils can be appropriately added to the refrigerator oil according to the present invention.

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

Examples 1 to 8, Comparative Examples 1 to 3 The refrigerants HF were prepared using the test oils of A1 to 8 shown in Table 1 (all of which were not commercially available and were manufactured as test oils) as esters according to the present invention.
The performance as a lubricating oil for C-134a refrigerator was evaluated. As Comparative Example 1, the general PAGs (B1 to B1) shown in Table 2 were used.
The evaluation of 3) was also performed.

The lubricating properties, compatibility, and thermal stability of the test oils shown in Tables 1 and 2 as compressor lubricating oils 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 test oil and 2.4 g of refrigerant (HFC-134a) in a glass tube, cooling and heating at 1 ° C. per minute were performed.
The temperature at which two-phase separation occurred, that is, the two-phase separation temperature was measured.

Thermal stability After filling 1 g of test oil, 1 g of refrigerant (HFC-134a) and catalyst (iron, copper, aluminum wires) in a glass tube,
After heating to 5 ° C., and 10 days later, the hue of the test oil was determined by ASTM display.

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

The evaluation results are as shown in Table 3.

As can be seen from Table 3, the seizure load and thermal stability of the test oil were good in both Examples and Comparative Examples, and there was no problem, but the two-layer separation temperature and electrical insulation were clearly different. The present invention (Example) is far superior to Comparative Example.

HFC-134a is a powerful refrigerant that replaces R12 Freon and is used in car air conditioners and refrigerators. Especially in the case of refrigerators and car air conditioners, since the compressor starts even in the summer, compatibility between oil and refrigerant at high temperatures is high. Is important. When the oil and the refrigerant cause two-layer separation in the compressor at the time of the above startup,
Since the refrigerant having a large specific gravity stays in the lower layer, it may cause seizure of the compressor.

Also, in the case of refrigerators, the motor is a built-in type in the compressor, and leakage is a problem, but the ester according to the present invention has a volume resistivity 1000 times or more higher than that of PAG, and is excellent in electrical insulation. It can be said that this is a lubricating oil for refrigerators.

(Effect of the Invention) In order to respond to the ozone depletion caused by chlorofluorocarbons, which has become a major problem on a global scale, HFC-134a, which has almost no ozone depletion, has been replaced with R12, which is widely used as a refrigerant. Although it is a close-up, it has the drawback of poor compatibility with refrigeration oil and has been a barrier to the development of alternative systems. However, the lubricating oil composition for refrigerators of the present invention maintains sufficient compatibility with Freon HFC-134a as a refrigerant, has high electrical insulation properties, and has excellent overall performance. Instead of R12 or R22 Freon
Even if HFC-134a is used, the effect that the conventional system can be used as it is can be obtained.

Claims (2)

(57) [Claims] 1. The following general formula (1): (Wherein, X is a residue of a dibasic acid, and AO _{1 to} AO ₄ are
R ₁ and R ₂ are hydrocarbons having 4 to 12 carbon atoms, a, b, c and d are each an integer of 0 to 20, and a
+ B + c + d represents an integer of 6 or more and 48 or less), and a lubricating oil composition for a refrigerator comprising, as a main component, an ester of a compound having a carboxyl group and a polyalkylene glycol derivative. 2. In the above general formula (1), the dibasic acid whose residue is represented by X is adipic acid, azelaic acid, sebacic acid, phthalic acid or terephthalic acid, and the oxylalkylene group is oxyethylene or oxypropane. The lubricating oil composition for a refrigerator according to claim 1, which is pyrene or oxybutylene.