JP3933872B2 - Lubricant for compression refrigerator using hydrocarbon refrigerant - Google Patents

Description

性能評価試験
潤滑剤として鉱物油１〜４及びＨＡＢ１〜２の基油と、冷媒としてｉ−ブタン（Ｒ６００ａ）を使用して、実用性能、潤滑性（Ｆａｌｅｘ焼付荷重）及び冷媒との相溶性などの性能評価試験を行った。
潤滑剤の実用性能の性能評価試験は、冷蔵庫用の圧縮機を用いた冷凍サイクルによる耐久試験によって実施した。すなわち、前記基油でなる潤滑剤を２００ｇ及びＲ６００ａ冷媒を１５ｇ圧縮機に装入し、圧縮機吐出圧を１２ｋｇｆ／ｃｍ^２、圧縮機表面温度を８０℃に保ち１０００時間の運転を実施した。該耐久試験終了後、圧縮機を開放し、試験後の潤滑剤、いわゆる使用油を採取して色及び全酸価を測定し、さらに圧縮機を分解してピストン、シリンダ、コンロッド及び軸受の磨耗量を測定した。
さらに、潤滑性としてＦａｌｅｘ焼付荷重及び冷媒との相溶性（二層分離温度）についても評価した。これらの測定結果を表３に示す。

表３によると、本発明の潤滑剤（鉱物油１〜３）は、色が全てＬ１．０と低く、全酸価は全て０．０１ｍｇＫＯＨ／ｇと新油の時の値と変わりがなく、さらに圧縮機の部材（ピストン、シリンダ、コンロッド及び軸受）の磨耗量が全て１．０μｍ以下であった。これに対して比較例に相当する鉱物油４及びＨＡＢ１〜２は、これらの値の殆どが実施例の値より大きく、潤滑剤の劣化及び圧縮機部材の磨耗が認められる。
安定性試験（ボンベテスト）
また、鉱物油１〜８について安定性試験（ボンベテスト）を次のようにして行った。鉱物油１〜８のそれぞれについて、３００ｍｌのボンベに鉱物油１００ｇとイソブタン（Ｒ６００ａ冷媒）２０ｇを入れ、さらに触媒として鉄（Ｆｅ）、銅（Ｃｕ）、アルミニウム（Ａｌ）の針金（１．６ｍｍφ×２０ｃｍ）を入れて密封し、１７５℃で３０日間保持した。放置冷却後、ボンベから鉱物油１〜８及び触媒を取り出し、劣化後の鉱物油の色、スラッジ析出の度合い、及び各触媒表面の変化を目視で観察した。触媒の変色量は「大」、「中」、「小」及び「なし」の４段階で評価し、スラッジ析出の度合いは「多」、「中」、「少」及び「なし」の４段階で評価した。その結果を表４に示す。

表４によると、本発明の潤滑剤（鉱物油１〜３及び６）は、全ての項目について満足できる安定性を示したが、粘度指数、％Ｃ_Ｐ、窒素分、硫黄分％及びヨウ素価に関する規定値の何れか１つ又は複数を満足していない潤滑剤（鉱物油４〜５及び７〜８）は、色もＬ２．０以上と悪く、触媒の変色、スラッジの析出も認められた。
添加剤添加効果の評価
さらに、添加剤の添加効果を評価するために、鉱物油１に極圧剤としてトリクレジルホスフェート（ＴＣＰ）及び酸化防止剤として２，６−ジ−ターシャリーブチル−ｐ−クレゾール（ＤＢＰＣ）を表５に示す割合で添加して試験油１〜３を調製し、前記と同様の安定性試験（ボンベテスト）を行い、さらにＦａｌｅｘ焼付荷重を測定した。その結果を表５に示す。

なお、上記基油、使用油及び圧縮機部材に関する各種測定試験方法は次の方法に従って実施した。色はＪＩＳ Ｋ ２５８０のＡＳＴＭ色試験方法に、動粘度及び粘度指数はＪＩＳ Ｋ ２２８３に、％Ｃ_Ｐ及び％Ｃ_ＡはＡＳＴＭ Ｄ３２３８に規定されるｎ−ｄ−Ｍ環分析に、流動点はＪＩＳ Ｋ ２２６９に、全酸価はＪＩＳ Ｋ ２５０１に、窒素分はＪＩＳ Ｋ ２６０９に、硫黄分はＪＩＳ Ｋ ２５４１に、Ｆａｌｅｘ焼付荷重はＡＳＴＭ Ｄ ３２３３に、及び冷媒との相溶性（二層分離温度）はＪＩＳ Ｋ ２２１１（附属書３、ただし、Ｒ１２をＲ６００ａと読み替えた。）にそれぞれ準拠して求めた。
本発明の冷凍機用潤滑剤は、特定の物性及び成分組成を有する鉱物油を主成分とする潤滑剤であるので、炭化水素冷媒との相溶性に優れ、炭化水素冷媒の存在下における安定性、潤滑性に優れている。したがって、地球環境にやさしい炭化水素冷媒を用いる冷凍機の潤滑剤として非常に有用である。 TECHNICAL FIELD The present invention relates to a compression refrigeration using a hydrocarbon refrigerant composed of lower hydrocarbons that does not cause destruction of the ozone layer and has a much lower global warming ability than halogen-containing hydrocarbon refrigerants. It relates to a machine lubricant. The present invention also relates to a working fluid composition comprising the hydrocarbon refrigerant and the lubricant, and a refrigeration apparatus filled with the working fluid composition.
Background of the invention A compression refrigerator includes a compressor, a condenser, an expansion mechanism (e.g., an expansion valve), an evaporator, and the like, and takes away heat of evaporation from the surroundings when a highly volatile refrigerant evaporates. It cools using its properties and is used in vending machines such as refrigerators, freezers, air conditioners, showcases, soft drinks and ice creams. Note that air conditioning, vending machines, and the like are also used for heating using heat generated during condensation, and for heating and holding beverages and foods.
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), and have been converted to non-chlorinated fluorinated hydrocarbons (HFC) such as difluoroethane (R152 or R152a). However, although these HFCs do not destroy the ozone layer, they are concerned that they have problems from the long-term viewpoint of protecting the global environment due to their high global warming potential.
Therefore, low molecular weight lower hydrocarbons having about 1 to 5 carbon atoms, ammonia, etc. do not destroy the ozone layer, and the global warming ability is very low compared to the above-mentioned chlorinated or non-chlorinated fluorinated hydrocarbons. Therefore, it has been attracting attention as an environmentally friendly refrigerant. These compounds have been used for a long time, although they have not been mainstream as refrigerants. Further, as the lubricant for the refrigerant composed of the hydrocarbon, for example, according to Japanese Patent Laid-Open No. 10-130585, synthesis of naphthenic or paraffinic mineral oil, alkylbenzene oil, ether oil, ester oil, fluorine oil, etc. Oil is presented. Among these lubricants, synthetic oils are generally expensive, so mineral oils that are inexpensive and easily available are expected from a practical viewpoint.
However, there are various problems even in the combination of a low molecular weight hydrocarbon refrigerant (lower hydrocarbon refrigerant) and a mineral oil-based lubricant. In particular, a refrigerating machine lubricant that uses a hydrocarbon refrigerant is desired to have excellent lubrication characteristics for the following reasons.
Low molecular weight hydrocarbons as refrigerants and mineral oils as lubricants are compatible, but due to the large difference in specific gravity, there are cases where they are difficult to mix by natural diffusion alone. It is often the case that the refrigerator is placed in such a state that it is difficult to mix. For example, when the refrigerant is charged into the compressor, the refrigerant having a low density is stacked on the lubricant having a high density previously charged. Such a state also occurs when the refrigerant is in a so-called stagnation state when the refrigerant returns to the compressor in a liquid state while the compressor is stopped. When the compressor is started in such a state, the lubricant gathers outside the rotation due to the centrifugal force, and the lubricant is not sufficiently dispersed in the sliding portion such as an internal bearing that requires lubrication. There is a problem that wear occurs and seizure is likely to occur. For this reason, what has the outstanding lubrication characteristic is desired for the lubricant for refrigerators using a low molecular weight hydrocarbon refrigerant. Further, unlike a chlorinated fluorinated hydrocarbon refrigerant, which can be expected to have an extreme pressure effect due to chlorine in the molecule, the hydrocarbon refrigerant itself has a small molecular weight, and therefore, no lubricating performance can be expected. This also helps to demand excellent lubricating properties for lubricants for refrigerators using hydrocarbon refrigerants.
Moreover, although the lubricant for refrigerators is generally used in a closed system, it is always exposed to a refrigeration cycle that repeats high and low temperatures, and therefore, a lubricant that is not easily deteriorated and has good stability is required. .
DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a lubricant for a refrigerator that uses a low molecular weight hydrocarbon refrigerant, Another object of the present invention is to provide a lubricant that is excellent in compatibility and excellent in lubricity and stability.
The present inventor has eagerly searched and examined a mineral oil-based lubricant that is compatible with a hydrocarbon refrigerant, and a lubricant mainly composed of a mineral oil having a specific physical property and component composition is a hydrocarbon refrigerant. The present inventors have found that it has excellent compatibility and is excellent in stability and lubricity in the presence of a hydrocarbon refrigerant, and has completed the present invention.
That is, the present invention provides a kinematic viscosity at 40 ° C. is 5~150mm ² / s (cSt), a pour point of -25 ° C. or less, a viscosity index of 50 or more and n-d-M ring analysis% _{C P} is 50 or more and% _{C a} of 12 or less, the nitrogen content of 20ppm or less, compression using a hydrocarbon refrigerant sulfur content 0.02 to 0.3% and iodine value is predominant mineral oil is less 10gI ₂ / 100g It is a lubricant for a refrigerating machine.
The present invention is also a working fluid composition used for a compression refrigerator comprising at least one hydrocarbon refrigerant comprising a hydrocarbon compound having 1 to 5 carbon atoms and the lubricant, and further comprising the working fluid A refrigeration apparatus filled with the composition.
The lubricant preferably further contains an extreme pressure agent composed of a phosphate ester and / or a phenol-based or amine-based antioxidant.
Such a lubricant mainly composed of mineral oil is excellent in compatibility with a hydrocarbon refrigerant, has high wear resistance with respect to a compressor sliding member, and further exhibits excellent stability.
BEST MODE FOR CARRYING OUT THE INVENTION The mineral oil used in the present invention has a kinematic viscosity at 40C of ³ to 150 mm < ² > / s. If the kinematic viscosity is low, the sealing performance and lubricity of the compressor will be low, and if it is high, the pour point will be too high or the energy efficiency will be reduced. Preferably it is 5-100 mm < ² > / s.
Mineral oil has a pour point of -25 ° C or lower. When the pour point is high, the lubricant discharged together with the refrigerant from the compressor is lowered in fluidity by an expansion mechanism or an evaporator, etc., and stays in the low temperature part of the refrigeration equipment, leading to a decrease in heat transfer efficiency, There is a risk of bearing wear and seizure due to lack of lubricant.
Mineral oil has a viscosity index of 50 or more. In the refrigeration cycle, the lubricant becomes hot when discharged from the compressor, 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 lot of long-chain hydrocarbons has a high viscosity index and a high lubricating performance. The viscosity index of mineral oil is more preferably 80 or more.
Further, the mineral oil,% _{C P} by n-d-M ring analysis of 50 or more, and% _{C A} of 12 or less. Lubricants, as is rich chain hydrocarbon, in other words,% since higher lubricity value of C _P is used a large mineral oil is higher, diluted by a hydrocarbon refrigerant lubricity poor low molecular weight However, sufficient lubricity can be maintained and bearing wear and seizure are less likely to occur. % _{C P} is more preferably 80 or more. Moreover,% C value of _A greatly affects the viscosity index, which is not preferable because the larger the viscosity index is low. % _{C A} is more preferably 10 or less. Incidentally,% _{C P} and% _{C A} can be determined by n-d-M ring analysis defined in ASTM D3238.
Moreover, the nitrogen content and sulfur content contained in the mineral oil affect the characteristics of the lubricating oil. If the nitrogen content exceeds 20 ppm by weight, the hue stability deteriorates. The sulfur content is 0.02 to 0.3% by weight, preferably 0.02 to 0.1%. When the sulfur content is large, the corrosivity increases, and when the sulfur content is small, the lubricity decreases. Therefore, it is important to contain the sulfur content within the above range.
Further, iodine value of the mineral oil used in the refrigerator lubricants of this invention is less 10gI 2 _/ 100g in order to ensure the stability against deterioration. Stability when the iodine value exceeds 10gI ₂ / 100g is deteriorated.
The hydrocarbon refrigerant used in the present invention is a low molecular weight hydrocarbon compound having 1 to 5 carbon atoms. Specific examples include alkane compounds such as methane, ethane, propane, n-butane, i-butane, n-pentane, i-pentane, and neopentane, and cycloparaffin compounds such as cyclopropane, cyclobutane, and cyclopentane. Furthermore, a derivative of the compound in which some of the carbon bonds are double bonds (olefin corresponding to the compound) can also be used. Moreover, as a hydrocarbon refrigerant | coolant, these compounds can be used individually or can be used in combination of 2 or more types as appropriate.
The effect of the present invention is exhibited by using a combination of the mineral oil having the above physical properties in a compression refrigerator using a low molecular weight hydrocarbon refrigerant. That is, the mineral oil not only exhibits the above-described good lubricity and stability in the presence of a hydrocarbon refrigerant, but the mineral oil has a molecular structure much greater than that of an ester oil or an ether oil. It is similar and shows good compatibility. Further, since the mineral oil is less expensive than ester oil or ether oil, it is very useful in practical terms.
The lubricant of the present invention may contain other components as necessary. For example, known lubricant base oils for refrigerators such as mineral oils other than the above-described mineral oils used in the present invention (for example, naphthenic mineral oils), synthetic oils such as alkylbenzene oils, ether oils, ester oils, fluorine oils, etc. Well-known additives may be appropriately blended. Examples of the additive include 2,6-di-tertiary butylphenol, 2,6-di-tertiary butyl-p-cresol, 4,4-methylene-bis- (2,6-di-tertiary butyl-p -Cresol), phenol-based or amine-based antioxidants such as p, p'-di-octyl-di-phenylamine, stabilizers such as phenyl glycidyl ether and alkyl glycidyl ether, tricresyl phosphate, triphenyl phosphate, etc. Extreme pressure agent, glycerin monooleate, glycerin monooleyl ether, glycerin monolauryl ether and other oily agents, benzotriazole and other metal deactivators, polydimethylsiloxane, polymethacrylate and other antifoaming or antifoaming agents, etc. Is mentioned. 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 wear resistance can be added in small amounts (for example, 0.05 to 1.0% by weight). Effectively improve.
Examples 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.
Oil used for evaluation In order to evaluate the refrigerating machine lubricant of the present invention, mineral oils 1 to 8 and hard alkylbenzene (HAB) having physical properties and compositions shown in Tables 1 and 2 respectively. 1-2 were prepared and used for the below-mentioned evaluation test. Of these, mineral oils 1 to 3 and 6 correspond to the base oil of the lubricant of the present invention.

Performance evaluation test Using mineral oils 1 to 4 and HAB 1 to 2 base oils as a lubricant and i-butane (R600a) as a refrigerant, practical performance, lubricity (Falex seizure load) and refrigerant Performance evaluation tests such as compatibility were conducted.
The performance evaluation test of the practical performance of the lubricant was carried out by an endurance test using a refrigeration cycle using a refrigerator compressor. That is, 200 g of the lubricant composed of the base oil and 15 g of R600a refrigerant were charged into a compressor, and the operation was performed for 1000 hours while maintaining the compressor discharge pressure at 12 kgf / cm ² and the compressor surface temperature at 80 ° C. After the endurance test, the compressor is opened, the lubricant after the test, so-called used oil, is collected to measure the color and total acid value, and the compressor is disassembled to wear the piston, cylinder, connecting rod and bearing. The amount was measured.
Furthermore, the Falex stoving load and the compatibility with the refrigerant (two-layer separation temperature) were also evaluated as lubricity. These measurement results are shown in Table 3.

According to Table 3, the lubricants (mineral oils 1 to 3) of the present invention are all low in color as L1.0, and the total acid value is all 0.01 mg KOH / g, which is the same as the value of the new oil, Furthermore, the amount of wear of the compressor members (piston, cylinder, connecting rod and bearing) was all 1.0 μm or less. On the other hand, most of these values of the mineral oil 4 and the HAB 1 and 2 corresponding to the comparative example are larger than those of the examples, and deterioration of the lubricant and wear of the compressor member are recognized.
Stability test (bomb test)
Moreover, the stability test (cylinder test) was performed for mineral oils 1 to 8 as follows. For each of the mineral oils 1 to 8, 100 g of mineral oil and 20 g of isobutane (R600a refrigerant) are placed in a 300 ml bomb, and iron (Fe), copper (Cu), and aluminum (Al) wires (1.6 mmφ × 20 cm) and sealed, and kept at 175 ° C. for 30 days. After leaving to cool, the mineral oils 1 to 8 and the catalyst were taken out from the cylinder, and the color of the deteriorated mineral oil, the degree of sludge precipitation, and the change in the surface of each catalyst were visually observed. The amount of discoloration of the catalyst is evaluated in 4 levels of “Large”, “Medium”, “Small” and “None”, and the degree of sludge deposition is 4 levels of “High”, “Medium”, “Low” and “None” It was evaluated with. The results are shown in Table 4.

According to Table 4, the lubricants of the present invention (mineral oils 1 to 3 and 6) showed satisfactory stability for all items, but viscosity index,% C _P , nitrogen content, sulfur content% and iodine value. The lubricants (mineral oils 4 to 5 and 7 to 8) that do not satisfy any one or more of the specified values regarding the color were poor in color as L2.0 or more, and discoloration of the catalyst and sludge precipitation were also observed. .
Evaluation of additive addition effect Further, in order to evaluate the additive addition effect, mineral oil 1 was subjected to tricresyl phosphate (TCP) as an extreme pressure agent and 2,6-di-tertiary as an antioxidant. Test oils 1 to 3 were prepared by adding Libutyl-p-cresol (DBPC) in the proportions shown in Table 5. A stability test (cylinder test) similar to the above was performed, and the Falex seizure load was measured. The results are shown in Table 5.

In addition, the various measurement test methods regarding the said base oil, use oil, and a compressor member were implemented in accordance with the following method. The ASTM color test method color JIS K 2580, the kinematic viscosity and viscosity index JIS K 2283,% on _{C P} and% _{C A} is n-d-M ring analysis defined in ASTM D3238, pour point JIS K 2269, total acid number in JIS K 2501, nitrogen content in JIS K 2609, sulfur content in JIS K 2541, Falex stoving load in ASTM D 3233, and refrigerant compatibility (two-layer separation temperature) Was determined in accordance with JIS K 2211 (Appendix 3, where R12 was replaced with R600a).
Since the lubricant for refrigerators of the present invention is a lubricant mainly composed of mineral oil having specific physical properties and composition, it is excellent in compatibility with hydrocarbon refrigerants and stable in the presence of hydrocarbon refrigerants. Excellent lubricity. Therefore, it is very useful as a lubricant for a refrigerator using a hydrocarbon refrigerant that is friendly to the global environment.

Claims (4)

In a lubricant for a compression type refrigerator using a hydrocarbon refrigerant, the kinematic viscosity at 40 ° C. is 3 to 150 mm ² / s, the pour point is −25 ° C. or less, the viscosity index is 50 or more, and the ndM ring analysis 50 or more, and% _{C a} of 12 or less by% _{C P} in the nitrogen content of 20ppm or less, sulfur content from 0.02 to 0.3% and iodine value is predominant mineral oil is less 10gI ₂ / 100g A lubricant characterized by that. The lubricant according to claim 1, further comprising an extreme pressure agent comprising a phosphate ester and / or a phenol-based or amine-based antioxidant. At least one hydrocarbon refrigerant comprising a hydrocarbon compound having 1 to 5 carbon atoms, a kinematic viscosity at 40 ° C. of 5 to 150 mm ² / s, a pour point of −25 ° C. or less, a viscosity index of 50 or more and ^nd -M% by ring analysis _{C P} is 50 or more, and% _{C a} of 12 or less, the nitrogen content of 20ppm or less, sulfur content is from 0.02 to 0.3% and an iodine value of mineral oil is 10gI ₂ / 100g or less A working fluid composition for use in a compression refrigerator comprising a lubricant as a main component. In a refrigeration apparatus including a compressor, a condenser, a dryer, an expansion mechanism, and an evaporator, at least one hydrocarbon refrigerant composed of a hydrocarbon compound having 1 to 5 carbon atoms, and a kinematic viscosity at 40 ° C. of 5 to 5. 150 mm ² / s, a pour point of -25 ° C. or less, more than 50 viscosity index and n-d-M ring analysis% _{C P} is more than 50 and% _{C A} of 12 or less, the nitrogen content of 20ppm or less, sulfur content 0.02 to 0.3% and a refrigerating apparatus working fluid composition comprising a lubricant iodine value as a main component a mineral oil or less 10gI ₂ / 100g is characterized in that it is filled.