JPS6259695A - Lubricating oil for refrigerator - Google Patents

Abstract

PURPOSE:To prepare the titled lubricating oil showing little change in viscosity with change of temperature and having excellent heat resistance and lubricating properties, by adding a specified viscosity index improver, a heat resistance improver and an extreme pressure agent to a mineral oil and/or alkylbenzene. CONSTITUTION:Less than 2.0wt% polyacrylate having a weight-average M.W. of not higher than 100,000 as viscosity index improver, less than 2.0wt% epoxy group-contg. compd. (e.g. phenyl glycidyl ether) as heat resistance improver and less than 2.0wt% phosphorus compd. (e.g. tricresyl phosphate) as extreme pressure agent are mixed into a mineral oil and/or alkylbenzene to produce a lubricating oil for a refrigerator having a kinematic viscosity of 2.0-6.0cSt. at 100 deg.C. The lubricating oil shows a minimized decrease of viscosity at a high temp., improved sealing and lubricating properties in mechanical parts of a compressor and a minimized increase of viscosity at a low temp. thus reducing resistance in mechanical parts of the compressor due to oil viscosity and improving the efficiency of the compressor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a lubricating oil for a refrigerator, which is sealed in a compressor of a refrigerator or the like.

BACKGROUND OF THE INVENTION In recent years, lubricating oils with high viscosity have been used as lubricating oils for refrigerators as compressors in refrigerators and the like have shifted from reciprocating type to rotary type.

The composition of these high viscosity lubricating oils is naphthenic mineral oil or alkylbenzene synthetic oil, which has excellent low-temperature properties, and provides lubricity and gas sealing properties for the mechanical parts of the compressor.

□ Problems to be solved by the invention However, in the above-mentioned lubricating oil, the viscosity changes significantly with temperature changes, so the viscosity increases more than necessary at low temperatures, and the resistance due to oil viscosity in the mechanical part of the compressor increases. This increases the input power and therefore reduces the efficiency of the compressor. On the other hand, at high temperatures, the viscosity decreases significantly and the gas sealing properties and lubricity of the mechanical seal portion of the compressor deteriorate, which is a problem regarding the efficiency and reliability of the compressor.

In view of the above-mentioned problems, the present invention provides a lubricating oil for refrigerating machines that exhibits small changes in viscosity with respect to temperature changes, that is, has an excellent viscosity index.

Means for Solving the Problems In order to solve the above-mentioned problems, the lubricating oil for refrigerators of the present invention is a lubricating oil for refrigerators which is mixed with polymethacrylate as a viscosity index improver.

Effects The present invention has the above-described configuration, so that the change in viscosity with respect to temperature change is small, and the increase in viscosity is small even at low temperatures, so the increase in resistance due to oil viscosity in the mechanical part of the compressor is small, and therefore the increase in input is also small. However, since the decrease in viscosity is small even at high temperatures, the efficiency and reliability of the compressor can be improved by satisfying the gas sealing properties and lubricity of the mechanical seal portion of the compressor.

Example An embodiment of the present invention will be described below.

As an example, the base oil is a mixture of naphthenic and paraffinic oils, and the kinematic viscosity at 40°C is 6. ○8cst
So, we used mineral oil with a viscosity index of 70 and polymethacrylate with a weight average molecular weight of 60,000, and by changing the additive concentration, we investigated the kinematic viscosity and temperature change of the mixed oil of both at 40°C and 100°C. The viscosity index, which is an index of viscosity change, was measured in accordance with Tl5K2283.

The results are shown in Table 1 and the figure.

Table 1 Examples of improving the viscosity index of refrigeration oil (1) Kinematic viscosity measurement method...JIS K 2283 (2) Viscosity index calculation method...Evided from JIS K 2283 Table 1 As can be seen, the conventional 100% naphthenic mineral oil has a viscosity index of 1o or less, and its viscosity changes significantly with temperature changes. On the other hand, the kinematic viscosity and viscosity index of Yumishi's developed oil improved in proportion to the amount of polymethacrylate mixed, and the viscosity change with temperature changes became smaller. Furthermore, when the amount of polymethacrylate mixed was 20 wt% or more, the effect of improving the viscosity index reached near the saturation point, so when the amount of polymethacrylate mixed was 20 wt% or less, the effect of improving the viscosity index was necessary and sufficient.

In addition, as is clear from the diagram showing the correlation between the temperature and viscosity of refrigerating machine oil, compared to the conventional example, the developed oil (q) has a high viscosity at temperatures above about 40°C, resulting in poor gas sealing and lubricity for the mechanical parts of the compressor. This improves the cooling capacity and reliability of the compressor, and at the same time, the viscosity becomes low at temperatures below about 40°C, reducing the resistance due to oil viscosity in the mechanical parts of the compressor, which reduces input to the compressor. In addition, the developed oil side (B)
The developed oil side (q) exhibits the same effect at approximately 100° C. and at approximately 150° C. or higher for developed oil example 4.

The kinematic viscosity of the developed oil at this time was 2.0 to 6.0c at 100℃.
A range of st is preferred to ensure compressor efficiency and reliability.

Further, as an example, naphthenic mineral oil and base oil of ~300,000 were used, each was mixed to give a predetermined overall viscosity, and a life test of this mixed oil was conducted using a refrigerator compressor. This result is displayed secondly.

Table 2: Life test results for refrigerating machine oil compressors.

Test conditions: high pressure conditions of the compressor,
20 K9 /c Shoulder-G0Rl Low pressure condition + ' -
OK1'/crtl G,) to
l Temperature conditions, 100°C operation period, 30 days As is clear from Table 2, when the weight average molecular weight of polymethacrylate is 100,000 or more, the shear stability is poor, resulting in a significant decrease in kinematic viscosity and viscosity index. Therefore, the weight average molecular weight is preferably 100,000 or less.

In addition, these developed oils can be used as refrigerating machine oils by incorporating 2.0% by weight or less of each of a compound having an epoxy group such as phenyl glycidyl ether as a heat resistance improver and a phosphorus compound such as tricresyl phosphate as an extreme pressure agent. Improves thermal stability and lubricity.

Effects of the Invention As described above, the present invention is a refrigerating machine lubricating oil to which polymethacrylate is added and mixed, and provides the following effects.

By adding and mixing polymethacrylate as a viscosity index improver to mineral oil, alkylbenzene, or a mixture of both,
By setting the kinematic viscosity at 100°C to 2.0 to 6.0 cst, the change in viscosity due to changes in oil temperature is reduced, and the decrease in viscosity at high temperatures is reduced, thereby improving the sealing performance and lubricity of the mechanical parts of the compressor. This improves the efficiency and reliability of the compressor by improving the viscosity of the compressor, and at the same time improves the efficiency of the compressor by reducing the resistance caused by oil viscosity in the mechanical parts of the compressor by reducing the increase in viscosity at low temperatures. It is something that makes you In addition, by setting the weight average molecular weight of the polymethacrylate used in the above to 1Q0,000 or less, the shear stability is excellent, the rate of decrease in kinematic viscosity and viscosity index after actual machine operation is small, and reliability is satisfied. The amount is 20
A necessary and sufficient effect of improving the viscosity index can be obtained at wt% or less. In addition, heat resistance and lubricity are improved by incorporating 2.0% by weight or less of a compound having an epoxy group such as phenyl glycidyl ether, and a phosphorus compound such as tricresyl phosphate.

[Brief explanation of drawings]

Claims (4)

[Claims] (1) A lubricating oil for refrigerators having a kinematic viscosity of 2.0 to 6.0 cst at 100° C., which is obtained by adding and mixing polymethacrylate as a viscosity index improver to mineral oil, alkylbenzene, or a mixture of both. (2) The weight average molecular weight of the polymethacrylate is 10
The refrigerating machine lubricating oil according to claim 1, wherein the lubricating oil is less than 10,000. (3) The mixing ratio of the polymethacrylate is 20wt%.
A lubricating oil for a refrigerator as set forth in claim 1 below. (4) 2.0% by weight each of a compound having an epoxy group such as phenyl glycidyl ether as a heat resistance improver, and a phosphorus compound such as tricresyl phosphate as an extreme pressure agent.
A lubricating oil for a refrigerator according to claim 1, which is formulated as follows.