JPH11124590A - Lubricating oil for refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lubricating oil for refrigerators of which the degradation is not accelerated even under heating at a high temp. by adding a specific phenol deriv. as an antioxidant to a base oil. SOLUTION: A phenol deriv. having a mol.wt. of 230 or higher is added as an antioxidant to a base oil. A phenol deriv. represented by formula I (provided the number of H atoms coordinated with C is 3 or lower), formula II, or formula III is pref. In addition to the phenol deriv., a thioether deriv. and/or a phosphorus deriv. may be added. The thioether deriv. pref. has a mol.wt. of 200 or higher; and the phosphorus deriv., a mol.wt. of 380 or higher. For instance, a thioether deriv. of formula IV (wherein n is an integer of 2-18) provides an excellent performance; and so does a phosphorus deriv. of formula V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a refrigerating machine lubricating oil used for a refrigerating compressor such as an air conditioner and a refrigerator. More specifically, the present invention relates to a lubricating oil for a refrigerator that compresses a refrigerant such as a hydrogen-containing fluorinated hydrocarbon or a lower hydrocarbon.

[0002]

2. Description of the Related Art Conventionally, refrigerators, refrigerators, air conditioners and the like have been used for refrigerants containing fluorine and chlorine as refrigerants, for example, chlorofluorocarbon (CFC) such as R11 (trichloromonofluoromethane) and R12 (dichlorodifluoromethane). Hydrochlorofluorocarbon (HCF
C), such as R22 (monochlorodifluoromethane). As lubricating oils for refrigerators used together therewith, mineral oils such as paraffinic and naphthenic oils and synthetic oils such as alkylbenzene and ester oils are known. Chlorine contained in molecules such as R11 and R12 has a favorable effect of preventing abrasion by reacting with a metal on a sliding surface in a refrigerator system. When released, most are not degraded, destroy the stratospheric ozone layer, and are being regulated internationally for their adverse effects on living systems.

[0003] For this reason, studies have been made on alternative CFC materials that do not contain chlorine. As a substitute for R11 and R12, a hydrogen-containing fluorinated hydrocarbon such as R134a (1,1,1,2-tetrafluoroethane) has been proposed. R134a shows almost the same physical properties as R12 and has an ozone depletion potential of zero, but it is noted that it has sufficient properties such as compatibility, heat stability, electrical insulation, lubricity, and hydrolysis stability. Development of lubricating oils satisfying these requirements has become an important issue. In addition, although a system using a lower hydrocarbon as a refrigerant is being proposed,
In optimizing the system configuration for the use of flammable gas, it is necessary to develop various materials, and lubricating oils and lubricating oil compositions optimal for those refrigerants have been developed.

[0004]

When these new alternative chlorofluorocarbons or lower hydrocarbons are used as refrigerants for refrigeration systems, the lubricating oil used must be optimized as described above. For example, in a refrigeration system using an alternative Freon refrigerant, the use of ester oil is being studied. However, the ester oil is decomposed into an alcohol component and a fatty acid component by a reaction with residual moisture remaining in the system, and this reacts with iron such as a sliding portion to produce an iron salt insoluble in the refrigerant. Further, ether oil does not cause a hydrolysis reaction, but when exposed to a high temperature state in the refrigeration system, degradation products such as water and carbon dioxide are generated by the decomposition reaction of the oil itself.

[0005] To address these issues,
How to remove as much residual water as possible in the system,
There has been proposed a method of providing a dryer for adsorbing moisture in the middle of a coolant flow path. However, in a refrigeration system that requires piping connection after factory shipment, for example, in an air conditioner that is configured by connecting an indoor unit and an outdoor unit using a connection pipe, the amount of air mixed during It is necessary to set a management value for The reason for this is
If the refrigerator oil is kept at a high temperature in an oxygen atmosphere,
This is because the autoxidation chain reaction shown in the following reaction formula (reaction 1) occurs.

As a method for suppressing such a chain reaction, a method in which an antioxidant is added to the refrigerating machine oil is considered in addition to a method for suppressing initial oxygen as much as possible. The most common antioxidants are 2,6-di-tert-butyl.
Paracresol (DBPC) is known. This DB
PC reacts with peroxy radicals generated by oil and oxygen to generate hydroperoxide and suppress a radical generation chain reaction. Further, the compound itself becomes a radical having low activity and is stabilized by resonance (reaction 2).

[0007] In addition to the above-mentioned antioxidants using phenol derivatives such as DBPC, antioxidants using thioether derivatives and phosphorus derivatives are known. These antioxidants are added for the purpose of further decomposing the hydroperoxide in which the peroxy radical is non-radicalized into hydroxy. Further, these antioxidants synergistically exhibit an effect of suppressing a radical chain reaction in combination with an antioxidant comprising a phenolic derivative.

At present, the above-mentioned antioxidants are used in refrigerating machine oil. However, even if such an antioxidant is added in combination, in a refrigeration system that easily becomes a high-temperature atmosphere, the performance may not be sufficiently exhibited because DBPC has volatility. Such a problem may lead to deterioration of the lubricating oil or even failure of the refrigeration system.

The lubricating oil for refrigerators of the present invention has been developed to solve such problems, and provides a lubricating oil that does not deteriorate quickly even when heated to a high temperature.

[0010]

SUMMARY OF THE INVENTION In view of the above problems,
The inventors of the present invention have intensively studied to develop a lubricating oil for a refrigerator having excellent performance. As a result, they have found that a specific antioxidant achieves the above object, and have completed the present invention.

The lubricating oil for refrigerators of the present invention contains the following antioxidant, and has a molecular weight of 230
It contains the above phenolic derivative. As such a phenolic derivative, the following structural formula (Chem. 9)
To (Chemical Formula 11) give particularly excellent performance.

[0012]

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[0013]

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[0014]

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Further, the lubricating oil for refrigerator of the present invention is characterized in that the antioxidant contains an antioxidant comprising a thioether derivative and / or a phosphorus derivative in addition to the phenol derivative.

The lubricating oil for refrigerators containing an antioxidant comprising the thioether derivative and / or the phosphorus derivative may be a thioether antioxidant having a molecular weight of 200 or more and / or a phosphoric acid antioxidant having a molecular weight of 380 or more. It is characterized by containing an agent. As such thioether-based derivatives, those represented by the following structural formulas (Formula 12) or (Formula 13) give particularly excellent performance.

[0017]

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[0018]

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Further, as the phosphorus derivative, those represented by the following structural formulas (Formula 14), (Formula 15) or (Formula 16) give particularly excellent performance.

[0020]

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[0021]

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[0022]

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[0023]

Embodiments of the present invention will be described below.

Conventionally, DBPC, which has been widely used as an antioxidant for oil used in the operation of a refrigerator, has a property of being easily volatilized due to its low molecular weight. For this reason, in a portion where the reactivity of oil is likely to occur, such as a sliding portion of the refrigeration system, it may not be possible to sufficiently fulfill the role of antioxidation.

A thermogravimetric measurement (TG) of the DBPC with respect to a change in temperature was performed using a thermobalance. As a result, 40% of the initial weight at 160 ° C. was further increased by 1% under an atmosphere of nitrogen gas flow.
It was found that a weight loss of 90% occurred at 80 degrees. Therefore, as a result of various studies on phenolic antioxidants with further improved heat resistance, it was found that those having the structures shown in (Chemical Formula 1) to (Chemical Formula 3) were more optimal.

As an example, TG measurement was carried out on the antioxidant represented by the chemical formula (4) in the same manner as described above.
No weight loss was observed to any degree. That is, it has been found that when an antioxidant having a higher molecular weight than DBPC is used as the structural formula, volatility can be suppressed and the compound can be used as a more effective radical chain reaction inhibitor.

Further, a radical chain reaction inhibitor comprising these phenolic derivatives may be used as a peroxide decomposing agent.
It has been found that a chain reaction can be suppressed by adding a thioether derivative or a phosphorus derivative. The peroxy radical generated by the above-mentioned oxidation reaction reacts with a radical chain reaction inhibitor composed of a phenolic derivative to form a peroxide, which is a peroxide, and the chain reaction is temporarily stopped. It is radicalized again by the above. This is because when a thioether-based derivative or a phosphorus-based derivative is added, it reacts with hydroperoxide to form a hydroxy compound and suppress radical generation.

Further, the antioxidant composed of a thioether derivative and a phosphorus derivative used as a peroxide decomposer has a molecular weight of 200 or more for a thioether derivative and 380 or more for a phosphorus derivative. It has been found that volatility can be further suppressed by using such a material.

The lubricating oil for refrigerators of the present invention may contain, in addition to the above-mentioned antioxidants, various additives generally used (for example, a water scavenger, an acid scavenger, an extreme pressure agent, an oil agent, an antifoaming agent). )
Was added at a ratio of 0.1-5.0 wt%, the performance did not decrease.

Now, the present invention will be described in further detail with reference to Examples. However, the present invention is not limited to the embodiments.

(Example 1) Of the refrigerating machine oil composition according to this example, a polyol ester having a kinematic viscosity of 65 centistokes at 40 degrees Celsius, which is a condensate of a mixed acid of a branched acid and pentaerythritol as a base oil, was used. Using. To this base oil was added 0.5 wt% of a phenol derivative having a molecular weight of 306 represented by the chemical formula (17) as an antioxidant.

[0032]

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The following refrigeration system was prepared as an evaluation refrigeration system. An outdoor unit having a refrigerating compressor, a heat exchanger, and a capillary tube and an indoor unit having a heat exchanger installed at a site where refrigerating and air-conditioning are performed were fixed to respective installation positions. Next, the refrigerant pipes between them were connected using copper pipes to form a refrigeration system. Here, 1.5 liters of the ester-based refrigerating machine oil to which the antioxidant was added is sealed in the outdoor unit compressor, and the system capacity of the outdoor unit is 20 liters and is pre-filled with nitrogen. . The indoor unit was filled with air, and the total capacity including the piping capacity of the part excluding the outdoor unit was 30 liters.

After the evacuation process, a refrigerant is charged, and then
The vacuum pump and the refrigerant charging device were removed from the refrigerant channel.
After the operation was performed for one hour, the operation was stopped, 1 ml of refrigerant mixed gas was extracted from the sampling port, and the amount of oxygen mixed as an initial state in the system was analyzed by gas chromatography. It turned out that it contained 15 liters. This amount of oxygen is an amount corresponding to about 20% by weight of the antioxidant in the oil.

Thereafter, after 5,000 hours of continuous acceleration operation, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed, and the total acid value of the refrigerating machine oil was 0.02 mgKOH /
g and the value at the start of operation (0.01 mg KOH / g)
It was almost the same value. Analysis of the antioxidants in the oil revealed that about 70% remained,
And it was found that the oxygen in the system was zero. In other words, the oxygen initially mixed reacted with the refrigerating machine oil to generate radicals, but was immediately trapped by the antioxidant added to the oil, the radical chain reaction was suppressed, and the refrigerating machine oil and the refrigerating system Did not have any adverse effects.

(Example 2) The same base oil as used in Example 1 was added to a phenol derivative antioxidant (Formula 17: molecular weight 306) as an antioxidant in an amount of 0.5 w.
% of thioether derivative antioxidant, phenylsulfide ((C6H5) 2S: molecular weight 186).
A refrigerator oil composition was prepared by adding 3 wt%.

A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 8 liters.

Thereafter, after performing a continuous acceleration operation for 4500 hours, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, suppressing the radical chain reaction, and the hydroperoxide generated during the oxidative deterioration reaction was converted to the hydroxy form by phenylsulfide. It is believed that the conversion did not adversely affect the refrigeration oil and the refrigeration system.

(Example 3) The same base oil as that used in Example 1 was added with a phenol derivative antioxidant (Formula 17: molecular weight 306) as an antioxidant in an amount of 0.5 w.
t%, phosphorus-based derivative antioxidant, tricresyl phosphate ((CH3 (C6H4) O) 3P = O: molecular weight 3
67) was added to obtain a refrigerator oil composition.

A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 3 liters.

Thereafter, after performing the continuous acceleration operation for 4800 hours, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, the radical chain reaction was suppressed, and the hydroperoxide generated during the oxidative degradation reaction was also reduced by tricresyl phosphate to the hydroxy. It is believed that the refrigeration oil and the refrigeration system were not adversely affected because they were converted into body.

(Example 4) The same base oil as that used in Example 1 was added with a phenol derivative antioxidant (Formula 17: molecular weight 306) as an antioxidant in an amount of 0.5 w.
t% and a phosphorus-based derivative antioxidant (molecular weight: 645) represented by Chemical Formula 6 were added in an amount of 0.2 wt% to prepare a refrigerator oil composition.

[0043]

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A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 6 liters.

After 5,000 hours of continuous acceleration operation, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed, and the value of the total acid value of the refrigerating machine oil was 0.1 as in the start of operation.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, the radical chain reaction was suppressed, and the hydroperoxide generated during the oxidative degradation reaction was also reduced by the phosphorus derivative antioxidant. It is considered that the conversion to the hydroxy form did not adversely affect the refrigerating machine oil and the refrigerating system.

(Example 5) The same base oil as that used in Example 1 was added with a phenol derivative antioxidant (Formula 17: molecular weight 306) as an antioxidant in an amount of 0.5 w.
A refrigeration oil composition was prepared by adding 0.15 wt% of a thioether-based derivative antioxidant (molecular weight: 286) represented by the following chemical formula (t).

[0047]

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A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 3 liters.

After 5,000 hours of continuous acceleration operation, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed, and the value of the total acid value of the refrigerating machine oil was 0.1 as in the start of operation.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, and the radical chain reaction was suppressed. It is considered that the conversion to the hydroxy form did not adversely affect the refrigerating machine oil and the refrigerating system.

Example 6 The same base oil as that used in Example 1 was replaced with a phenol derivative antioxidant (molecular weight 522) represented by the following chemical formula (2) as an antioxidant. A refrigerator oil composition was prepared by adding 5 wt%.

[0051]

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A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 3 liters.

After 5,000 hours of continuous acceleration operation, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed, and the value of the total acid value of the refrigerating machine oil was 0.1 as in the start of operation.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, and the radical chain reaction was suppressed. It is considered that the conversion to the hydroxy form did not adversely affect the refrigerating machine oil and the refrigerating system.

(Example 7) The same base oil as that used in Example 1 was replaced with a phenol derivative antioxidant (molecular weight 774) represented by the following chemical formula (3) as an antioxidant. A refrigerator oil composition was prepared by adding 5 wt%.

[0055]

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A refrigeration system similar to that of Example 1 was prepared.
The oxidation stability was evaluated. At this time, the initial mixing amount is 0.1
It was 3 liters.

After 5,000 hours of continuous acceleration operation, the refrigerating machine oil was taken out, but no oxidative deterioration of the refrigerating machine oil was observed, and the value of the total acid value of the refrigerating machine oil was 0.1 as in the start of operation.
It was 01 mgKOH / g. When the antioxidant in the oil was analyzed, it was found that about 70% remained and oxygen in the system was zero.
In other words, the oxygen that was initially mixed reacts with the refrigerator oil,
Although radicals were generated, they were immediately trapped by the antioxidant added to the oil, and the radical chain reaction was suppressed. It is considered that the conversion to the hydroxy form did not adversely affect the refrigerating machine oil and the refrigerating system.

[0058]

As described above, according to the present embodiment, the use of a phenolic derivative having a molecular weight of 230 or more as an antioxidant in a lubricating oil for a refrigerator enables the lubricating oil for a refrigerator to have good oxidation stability. And a stable refrigeration system can be supplied.

Further, by using an antioxidant of a thioether derivative or a phosphorus derivative together with an antioxidant of a phenol derivative, a more stable lubricating oil for a refrigerator can be provided.

Further, thioether derivatives thereof,
By limiting the molecular weight of the phosphorus-based derivative antioxidant, a more stable lubricating oil for a refrigerator can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an oxidation reaction of an oil and an oxidation mechanism of an antioxidant.

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Claims (7)

[Claims] A lubricating oil for a refrigerator comprising a phenolic derivative having a molecular weight of 230 or more as an antioxidant. 2. The lubricating oil for a refrigerator according to claim 1, wherein the structural formula of the phenolic derivative is (Chemical Formula 1), (Chemical Formula 2) or (Chemical Formula 3). Embedded image Embedded image Embedded image 3. The lubricating oil for a refrigerator according to claim 1, wherein the antioxidant contains the phenol derivative and a thioether derivative and / or a phosphorus derivative. 4. The thioether derivative has a molecular weight of 2
The lubricating oil for a refrigerator according to claim 3, wherein the lubricating oil is at least 00. 5. The lubricating oil for a refrigerator according to claim 3, wherein the phosphorus derivative has a molecular weight of 380 or more. 6. The lubricating oil for a refrigerator according to claim 5, wherein the structural formula of the thioether derivative is (Chem. 4) or (Chem. 5). Embedded image Embedded image 7. The structural formula of the phosphorus-based derivative is
The lubricating oil for a refrigerator according to claim 5, which is (Chem. 7) or (Chem. 8). Embedded image Embedded image Embedded image