Lubricant for refrigerators

Abstract: The objective of the present invention resides in providing a lubricant for refrigerators that reacts rapidly with free acids and contains a stabilizer that has good compatibility with a chlorine-free Flon-thpe coolant such as Flon 134a and the like whose molecules do not contain chlorine. The lubricant for refrigerators employing a chlorine-free Flon-type coolant in accordance with the present invention 100 parts by weight of a synthetic oil and is compounded with 0.05 to 15 parts by weight of an alicyclic epoxy compound having one or more functional groups represented by the follwing formula: (wherein R₁ and R₂ independently represent a hydrogen or methyl group, and may be the same or different).

Description: BACKGROUND OF THE INVENTION i) Field of the Invention The present invention relates to a lubricant for refrigerators. More specifically, the present invention relates to a lubricant for refrigerators employing a chlorine-free Flon-type ('Flon' signifies fluorinated hydrocarbon) coolant such as Flon 134a (1,1,1,2-tetrafluoroethane), Flon 32 (difluoromethane), Flon 125 (1,1,1,2,2-pentafluoroethane), Flon 143a (1,1,1-trifluoroethane), Flon 152a (1,1-difluoroethane), Flon 134 (1,1,2,2-tetrafluoroethane) and the like, and a composition for refrigerators using said lubricant. ii) Description of the Related Art Flon-type coolants have conventionally been excellent for use as a coolant for refrigerators as they are chemically stable and have low toxicity. However, the recent Montreal Protocol decided that the use of chlorofluorocarbons, for example Flon 12 (dichlorodifluoromethane), among these Flon-type coolants shall be totally abolished by the year 2000, because chlorofluorocarbons are a cause of damage to the ozone layer in the stratosphere and contribute to global warming. In such circumstances, Flon-type coolants not having chlorine in the molecules thereof, i.e. chlorine-free Flon-type coolants have been developed and are representatively illustrated by Flon 134a as an alternative to Flon 12. However, because of the higher polarity thereof, these chlorine-free Flon-type coolants without chlorine in molecules thereof, such as Flon 134a and the like, have poor compatibility with naphthene mineral oils, alkylbenzene and the like which have been employed as lubricants for refrigerators. In order to improve the compatibility, therefore, polyalkylene glycol lubricants for refrigerators have been proposed as used in the Specification of US Patent No. 4,755,316, Japanese Patent Laid-Open No. 3-28296 and the like, while ester lubricants for refrigerators have been proposed as disclosed in Japanese Patent Laid-Open Nos. 2-268068, 3-88892, 3-128991, 3-128992 and the like. On the other hand, trace amounts of water and oxygen are present in refrigerator compressors, and the polyalkylene glycol refrigerator oils if used as a lubricant are oxidized and deteriorate, resulting in a tendency for the acid value to increase; ester refrigerator oils if used as a lubricant are hydrolyzed to generate free acids and as such, they are not very practicable. In order to improve them, Japanese Patent Application Nos. 2-73649 and 2-164431 have proposed the use of glycidyl ether-type epoxy compounds which have good compatibility with Flon 134a and the like as a stabilizer. However, these glycidyl ether-type epoxy compounds not only have such drawbacks that the products thereof inevitably involve generation chlorine residues which is not preferable environmentally, but the compounds are also so slow in the reaction with free acids and the like that the corrosive action of the free acids is not sufficiently suppressed. Much further prior art exists:- 1) US-A-5108634 and WO-A-8907129 (D.1). D1 relates to a lubricating oil composition and teaches that a glycidyl ether type epoxy compound and an epoxidated fat (such as epoxidated soybean oil) can be added as a chlorine scavenger. However, while the glycidyl ether type epoxy compound has high compatibility with a chlorine-free fluorinated hydrocarbon coolant such as R 134a, an epoxidated fat has low compatibility with said coolant. 2) FR-A-2265851 (D.2). D2 relates to an operating fluid composition containing a base stock and an epoxy compound, for use in a hydraulic system; it does not teach the differences in properties of chlorine-containing coolant and chlorine-free coolant. 3) FR-A-2260616 (D.3). D3 relates to a working fluid composition for use in a hydraulic system. The disclosure is not directed to a lubricating oil for a chlorine-free coolant, and is characterised in the use of cycloalkyl epoxide and phenylnaphthyl amine as the essential components. 4) EP-A-0501440 (D.4, published after the present priority date). D4 relates to an operating fluid composition for a refrigerator which comprises a refrigerator oil and a hydrofluorocarbon. It discloses that an alicyclic epoxy compound can be added, and illustrates 4-epoxyethyl-1,2-epoxycyclohexane. Only certain oils are however disclosed. 5) EP-A-0496937 (D.5, published after the present priority date). D5 describes the following: "A lubricant composition miscible in hydrofluorocarbon and hydrochlorofluorocarbon refrigerants comprising as a base oil at least one member selected from the group consisting of ester oil, alkylbenzene oil and mineral oils, and a glycidyl ether compound having at least two epoxy groups". Only certain epoxy compounds are however disclosed. 6) EP-A-0475751 (D.6, published after the present priority date). D6 discloses a working fluid composition for a refrigerator comprising a hydrocluorocarbon, an epoxy compound and an ester formed from neopentyl polyol and a saturated branched aliphatic monocarboxylic acid. D6 illustrates on page 7, 4-epoxyethyl-1,2-epoxycyclohexane. Only certain oils are however disclosed. 7) EP-A-0435253 (D.7). The disclosure includes a hydrofluorocarbon coolant. However the epoxy compounds disclosed include epoxy compounds such as epoxidized vegetable oils which can not be used in combination with a hydrofluorocarbon coolant such as R 134a. 8) JP-A-57063395 and WPI/Derwent Abstract AN 82-42572E (D.8). D8 discloses a composition for a refrigerator containing a compound having a polyether type synthetic oil and an epoxycycloalkyl group. However, it neither teaches nor suggests the differences in characteristics between chlorine-containing coolants and chlorine-free coolants. Therefore, it is an object of the present invention to provide a lubricant for refrigerators, containing a stabilizer capable of reacting rapidly with free acids and having good compatibility with chlorine-free Flon-type coolants, such as Flon 134a. SUMMARY OF THE INVENTION The present inventors, as a result of having made various studies regarding lubricants for refrigerators employing chlorine-free Flon-type coolants, have found very particular compositions of value. According to the present invention, there is provided a lubricant for refrigerators employing a chlorine-free fluorinated hydrocarbon coolant particularly 1,1,1,2-tetrafluroethane, characterised in that a) said lubricant contains 100 parts by weight of a synthetic oil and 0.05 to 15 parts by weight of an alicyclic epoxy compound represented by the following formula: wherein m is the integer O or 1; R 1 , R 2 and (where m = O) R 3 each independently represent a group selected from the class consisting of hydrogen and methyl; and (where m = 1), R 3 = H and X represents a group selected from the class consisting of -CH 2 -, -CH 2 CH 2 - and -CH(CH 3 )-, and b) the synthetic oil comprises a polyoxyalkylene glycol or an ester of pentaerythritol with a mixture of 2-methylbutanoic acid and hexanoic acid. Further, according to the present invention, there is provided a refrigerant composition for refrigerators characterised by containing the above lubricant and a chlorine-free fluorinated hydrocarbon coolant, in a ratio of from 1:99 to 99:1 by weight. GENERAL DESCRIPTION OF THE INVENTION In terms of compatibility with Flon 134a and the like, specifically preferable alicylic epoxy compounds to be used in the present invention are those set out. Furthermore, in terms of the reactivity with free acids, the most preferable among these compounds are those set out. The addition amount of the alicyclic epoxy compound to be used in the present invention is satisfactory within a range of 0.05 to 15 parts, preferably 0.5 to 10 parts, and more preferably 0.5 to 5 parts by weight to 100 parts by weight of a synthetic refrigerator base oil. If the addition amount is less than the amount described above, no sufficient effect can be obtained; if the addition amount exceeds the amount described above, the effect of the addition is not very enhanced, but on the contrary, such addition amount induces polymerization, causing sludge. The oil has good compatibility with chlorine-free Flon-type coolants such as Flon 134a and the like particularly in range of -30°C to 50°C, and also has a kinematic viscosity of 2 to 50 cSt. Polyoxyalkylene glycol (which here and in the claims includes modified products thereof) can be used as such oil, and they may be used in a mixture of two or more of them. For specific explanation of these synthetic oils, a polyoxyalkylene glycol may be illustrated by such as polyoxypropylene glycol, polyoxyethylene glycol, polyoxyethylene polyoxypropylene glycol, and the like, preferably having a molecular weight of 200 to 3,000. The oxyethylene group and oxypropylene group in polyoxyethylene polyoxypropylene glycol may be in random or block form. The invention also extends to use of modified products of polyoxyalkylene glycols, still regarded as such, and there may be used for example the alkylene oxide adduct of polyoxyalkylene glycol monoalkyl ether, polyoxyalkylene glycol dialkyl ether, polyoxyalkylene glycol monester, polyoxyalkylene glycol diester alkylene diamine, and the like, specifically including the ether of a linear or branched alkyl group having 1 to 18 carbon atoms with the polyoxyalkylene glycol, the ether of an aliphatic carboxylic acid having 2 to 18 atoms with the above glycol, the propylene oxide adduct, ethylene oxide adduct, ethylene oxide propylene oxide random adduct and ethylene oxide propylene oxide block adduct of ethylene diamine, diethylene triamine adduct, and triethylene tetramine, and the like; furthermore, the modified product of the polyoxyalkylene glycol includes polyoxyalkylene glycol glycerol triether, and the halogenated product of polyoxyalkylene glycol (the chlorinated product thereof, in particular, may be satisfactory). The present invention does not prohibit the combination of the specified with other epoxy compounds. The lubricant for refrigerators in accordance with the present invention may be used with extreme pressure agents such as tricresyl phosphate and antioxidants such as α-naphthylbenzylamine, phenothiazine, BHT and the like, in customary amount. The lubricant for refrigerators of the present invention is completely compatible with chlorine-free Flon-type coolants (for example, Flon 134a and the like), at practically any ratio from 1:99 to 99:1, from -50°C to 60°C. DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be explained in detail in the following examples, but the invention is not to be limited thereby. In the embodiments, Samples 1 to 4, 7 and 8 as additives (7 and 8 are comparative) and Samples 9 and 10 as base oil were employed as shown below. Sample 1 Epoxy compound represented by the following formula: Sample 2 Epoxy compound represented by the following formula: Sample 3 Epoxy compound represented by the following formula: Sample 4 Epoxy compound represented by the following formula: Sample 7 (Comparative; there are no Samples 5 and 6) Phenylglycidyl ether Sample 8 (Comparative) Epoxylated soya bean oil Sample 9 Polypropylene glycol diacetate represented by the following formula: (Kinematic viscosity is 9.8 cSt at 100°C) Sample 10 Full ester of a mixture of 2-methylbutanoic acid and hexanoic acid (molar ratio=1:1) and pentaerythritol (kinematic viscosity is 4.2 cSt at 100°C). Example 1 and Comparative Example 1 15 parts by weight of each of the lubricants for refrigerator shown in Table 1 and 85 parts by weight of Flon 134a were charged to determine compatibility at -50 to 60°C. As shown in Table 1, the results indicate that the products of the invention show excellent compatibility with Flon 134a. Sample No. of base oil Sample No. of additives Compounded amount of additives of base oil (%) Temperature when turning opaque with Flon 134a Invention product 9 1 3 Complete dissolved 9 2 3 Complete dissolved 9 3 3 Complete dissolved 9 4 3 Complete dissolved 10 1 3 Complete dissolved 10 2 3 Complete dissolved 10 3 3 Complete dissolved 10 4 3 Complete dissolved Comparative product 9 8 3 Opaque in the entire temperature range 10 8 3 Opaque in the entire temperature range 9 7 3 Complete dissolved 10 7 3 Complete dissolved Example 2 and Comparative Example 2 With the organic acids shown in Table 2, Samples 9 and 10 were adjusted to the acid values as shown in Table 2, and were then individually divided at 200 g in 300-ml beakers, followed by addition of 2 g of additives and agitation under heating at 60°C. The samples were collected over time to measure the acid values. The results are shown in Table 2. As clearly shown in Table 2, the invention products reduced the acid values rapidly. The initial acid values of Samples 9 and 10 were individually 0.01 and 0.02. Sample No. of base oil Organic acid Sample No. of additives Acid value adjusted (mg·KOH/g) Acid value after addition of additives (mg·KOH/g) 2 hrs later 4 hrs later 8 hrs later Invention product 9 Ace. 1 0.52 0.23 0.10 0.03 9 Ace. 2 0.52 0.17 0.08 0.02 10 Hexa. 1 0.68 0.26 0.13 0.05 10 Hexa. 2 0.68 0.21 0.09 0.03 10 Hexa. 3 0.68 0.28 0.10 0.05 10 Hexa. 4 0.68 0.25 0.11 0.07 10 Hexa. 1 2.34 0.86 0.36 0.18 10 Hexa. 2 2.34 0.52 0.21 0.11 Comparative product 9 Ace. 7 0.52 0.45 0.31 0.24 10 Hexa. 7 0.68 0.55 0.42 0.35 10 Hexa. 7 2.34 2.05 1.70 1.27 Ace. = acetic acid; Hexa. = hexanoic acid Example 3 and Comparative Example 3 To the individual oil compositions for refrigerators shown in Table 3 was added 1000 ppm of water. 20 parts by weight of the individual resulting mixtures and 80 parts by weight of Flon 134a were then placed in a 100-ml stainless-steel (SUS-316) autoclave, followed by addition of pieces of steel, copper and aluminium (50 x 50 x 1.5 mm) prior to sealing. Subsequently, heating was done at 150°C for 14 days (336 hours). After the termination of the heating test, degassing to vacuum to remove Flon 134a and water was done to evaluate the kinematic viscosity, appearance and acid value of the oil compositions for refrigerator after the testing. The metal pieces were washed in toluene and methanol, to measure the increase or decrease of the weight thereof. All of the results are shown in Table 4. Oil for refrigerators Sample No. of base oil Sample No. of additives Compounded amount of additives of base oil (%) 1 9 1 2 2 9 2 2 3 9 3 2 4 9 4 2 7 10 1 1 8 10 1 3 9 10 1 5 10 10 2 0.3 11 10 2 3 12 10 2 7.5 13 9 14 10 (There were no oils 5 and 6) The advantage of the present invention resides in providing a lubricant for refrigerators, reacting rapidly with free acids and containing a stabilizer with good compatibility with a chlorine-free Flon-type coolant such as Flon 134a and the like. That is, the lubricant for refrigerators in accordance with the present invention has the following advantages: 1. No trouble in vaporizers because of the good compatibility with Flon 134a and the like in refrigerators; 2. Rapid reaction with free acids, oxides and other active groups generated in refrigerators, to prevent corrosion, and the like.

Claims: A lubricant for refrigerators employing a chlorine-free fluorinated hydrocarbon coolant particularly 1,1,1,2-tetrafluoroethane, characterised in that a) said lubricant contains 100 parts by weight of a synthetic oil and 0.05 to 15 parts by weight of an alicyclic epoxy compound represented by the following formula: wherein m is the integer O or 1; R 1 , R 2 and (where m = O) R 3 each independently represent a group selected from the class consisting of hydrogen and methyl; and (where m = 1), R 3 = H and X represents a group selected from the class consisting of -CH 2 -, -CH 2 CH 2 - and -CH(CH 3 )-, and b) the synthetic oil comprises a polyoxyalkylene glycol or an ester of pentaerythritol with a mixture of 2-methylbutanoic acid and hexanoic acid. A refrigerant composition for refrigerators characterised by containing the lubricant of claim 1 and a chlorine-free fluorinated hydrocarbon coolant, in a ratio of from 1:99 to 99:1 by weight.

Inventors: KAMAKURA TAMIJI, NAMIKI MASATO, NAMIWA KIMIYOSHI, TANAKA NORIYOSHI, TATSUMI YUKIO, KAMAKURA, TAMIJI, NAMIKI, MASATO, NAMIWA, KIMIYOSHI, TANAKA, NORIYOSHI, TATSUMI, YUKIO, Kamakura, Tamiji, c/o Asahi Denka Kogyo K. K., Namiki, Masato, c/o Asahi Denka Kogyo K. K., Namiwa, Kimiyoshi, c/o Asahi Denka Kogyo K. K., Tanaka, Noriyoshi, c/o Asahi Denka Kogyo K. K., Tatsumi, Yukio, c/o Asahi Denka Kogyo K. K.
Applicants: ASAHI DENKA KOGYO KK, ASAHI DENKA KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: C10M129
IPC codes: C10M129, C10N40, C10N30, C10M171, C10M169