Lubricant composition for refrigerators

Abstract: The object of the present invention is to provide a lubricant for refrigerators having good compatibility with chlorine-free Flon-type coolants, good lubricity and resistant to hygroscopicity and a composition for refrigerators using this lubricant. This lubricant contains a monomethylether of polyoxyethyleneoxypropyleneglycol where the end group at the hydrogen terminal is an oxyethylene group, represented by the following general formula (1): CH₃O(AO) m (CH₂CH₂O) n H wherein the AO group represents oxypropylene group, or copolymeric group of oxypropylene groups and oxyethylene groups wherein the copolymeric form may be a block type and/or a random type, m is a number of 1 ≦ m ≦ 50, n is a number of 1 number of 1 ≦ n ≦ 10, and the content of the oxyethylene group in the compound ranges from 5 to 60 percent by weight. A composition for refrigerators using said lubricant is also provided.

Description: BACKGROUND OF THE INVENTION i) Field of the Invention The present invention relates to a composition for use in refrigerators. More specifically, the present invention relates to a composition for use in refrigerators employing a chlorine-free Flon-type coolant such as Flon 134a (1,1,1,2-tetrafluoroethane), Flon 32 (difluoromethane), Flon 125 (1,1,2,2-pentafluoroethane), Flon 143a (1,1,1-trifluoroethane), Flon 152a (1,1-difluoroethane), Flon 134 (1,1,2,2-tetrafluoroethane), Flon 134 (1,1,2,2-tetrafluoroethane) and the like. 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 among these Flon-type coolants the use of chlorofluorocarbons such as Flon 12 (dichlorodifluoromethane) shall be totally abolished by the year 2000, because chlorofluorocarbons are a source 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 described above as an alternative to Flon 12. However, because the polarity of chlorine-free Flon-type coolants without chlorine in molecules thereof such as Flon 134a and the like is higher than Flon 12, these chlorine-free Flon-type coolants have poor compatibility with naphthene mineral oils, alkylbenzene and the like which have been employed as lubricants for refrigerators and cause poor lubricity and frictional wear in the compressors of refrigerators. Therefore, a lubricant having good compatibility with Flon 134a and the like has been sought. As a lubricant for refrigerators using Flon 134a as a coolant, polyoxyalkylene glycol has been disclosed in U.S. Patent No.4,755,316, Japanese Patent Laid-Open Nos. 01-271491, 02-129294, 03-103496 and the like, polyoxyalkylene glycol containing an acyl group as a modified compound of polyoxyalkylene glycol has been disclosed in Japanese Patent Laid-Open Nos. 01-198694, 03-33193, 03-79696, 03-81396 and the like, and polyoxyalkylene glycol containing halogen group has been disclosed in Japanese Patent Laid-Open Nos. 02-180987 and 02-132176. However, since the above polyoxyalkylene glycols are a highly hygroscopic and have poor stability, those modified compounds of polyoxyalkylene glycol have problems with corrosiveness and also, dialkylethers of polyoxyalkylene glycol have poor lubricity, so all of these lubricants have not been practical. On the other hand, Japanese Patent Laid-Open Nos. 01-259093, 01-259095, 02-43290, 02-84491, 02-102296, 02-182780, 02-242888, 02-277097, 02-281098, 03-50297, 03-103496, 03-103497, 03-50297 and the like disclose monoalkylether of polyoxyalkylene glycol that have good stability and no corrosive properties and are expected to be practicable. However, the publicly known monoalkylethers of polyoxyalkylene glycol described above, still have insufficient lubricity and further have poor compatibility with chlorine-free Flon-type coolants such as Flon 134a and the like. Further disclosures, of polyoxyethylene oxypropylene glycol lubricants are in EP-A-0377122, 0386851, 0463773 and 0533165. It is an object of the present invention to provide a composition for use in refrigerators comprising a lubricant having superior compatability with chlorine-free Flon-type coolants, good lubricity and resistant to hygroscopicity. The present inventors, as a result of having made various studies regarding lubricants for refrigerators employing chlorine-free Flon-type coolants, have achieved the present invention. According to the present invention there is provided a composition for use in refrigerators characterised in that said composition contains a lubricant containing a monomethylether of polyoxyethylene-oxypropyleneglycol where the end group at the hydrogen terminal is an oxyethylene group (any contaminant oxypropylene-terminated monomethylether being less than 10 molar percent) represented by the general formula (1): CH 3 O(AO) m (CH 2 CH 2 O) n H wherein the AO group represents a copolymeric group of oxypropylene groups and oxyethylene groups wherein the copolymeric form may be a block type in which the oxypropylene moiety is bonded to the (CH 2 CH 2 O) n group or a random type, m is a number of 5 ≦ m ≦ 45, n is a number of 2 ≦ n ≦ 10 and the content of the oxyethylene groups in the compound ranges from 5 to 60 percent by weight, and a chlorine-free Flon-type coolant whose molecules do not contain chlorine, at a weight ratio of from 1:99 to 99:1. In a compound represented by the general formula (1) described above used in the present invention, one end group should be a methyl group and the other end group should be a hydrogen group, because if hydrocarbyl groups rather than methyl groups are used as one end group, the resulting lubricants will have poor compatibility with Flon 134a, if both end groups are methyl groups, lubricity of the resulting lubricants may be deteriorated, and if both end groups are hydrogen groups, resistance to hygroscopicity of the resulting lubricants may be deteriorated, so these end groups can not be employed. In the compound represented by the general formula (1) used in the present invention the polymerization degree i.e. m of the copolymeric group is a number of 5 ≦ m ≦ 45. If said polymerization degree, i.e. m is over the above range, the resulting lubricants have poor compatibility with Flon 134 and the like. In the compound represented by the general formula (1) used in the present invention, the end group of the hydrogen terminal should be oxyethylene groups and the polymerization degree i.e. n of said oxyethylene groups is a number of 2 ≦ n ≦ 10, preferably 2 ≦ n ≦ 5. If the end group of the hydrogen terminal is an oxypropylene group, the lubricity may be deteriorated and if the polymerization degree of the oxyethylene groups of the end group of the hydrogen terminal is greater than said upper limit, the pour point of the resulting lubricants may be increased. Further, the content of the oxyethylene groups in said compound should be from 5 to 60 percent by weight and preferably from 10 to 40 percent by weight. If the content of said oxyethylene group is less than said lower limit, the resulting lubricants can not obtain sufficient lubricity, if the content has higher molecular weight, the resulting lubricants will have poor compatibility with Flon 134a and the like, and if the content is greater than that range, the pour point of the resulting lubricants will increase. The compound represented by the general formula (1) used in the present invention can be prepared by well-known processes, for example said compound can be obtained by polymerizing methanol as a starting material with a mixture having an appropriate ratio of propyleneoxide and ethyleneoxide in the presence of a suitable catalyst and then polymerizing, the resulting material with ethyleneoxide. When in the presence of suitable cataylst, methanol as a starting material is polymerized with mixture of propyleneoxide and ethyleneoxide, the probability that the oxypropylene group will be situated at the end group of the hydrogen terminal is increased since the oxypropylene group has relatively moderate reactivity, therefore this end group will finally need to be polymerized with ethyleneoxide. Although it is of course preferable that the lubricant for refrigerators according to the present invention use only the compound having the general formula (1) that is the compound having the oxyethylene end group of the hydrogen terminal, commercially there are cases when a compound having an oxypropylene end group of the hydrogen terminal may be included as a contaminant; said contaminant is less than 10 molar percent. The ratio of oxyethylene group can be calculated by trifluoroacetylating the oxyethylene group by a conventional method employing trifluoroacetic anhydride and then analyzing said oxyetylene group by NMR (See Analytical Chemistry Vol.38 No.8, 1063 ∼ 1065, July, 1966). The lubricant for use in refrigerators according to the present invention comprises substantially the compound having the general formula (1), but said lubricant does not prohibit the combination of said compound with well-known base oils for refrigerator oil without deviating from the spirit and object of the present invention, and in this case the content of the other base oil for refrigerator oil is preferably less than 50 percent by weight. Further, the lubricant for refrigerators according to the present invention may when desired and within the scope of the object of the invention, contain extreme-pressure additives such as tricreasyl phosphate, trialkylphosphate as well as well-known additive(s) ordinarily used in lubricants for refrigerators employing Flon-type coolants, such as a stabilizing additive, for example diglycidylether, polypropyleneglycol diglycidylether, phenyl glycidylether, cycloaliphatic epoxy compound and the like, and an anti-oxidation agent for example α-naphtylbenzylamine, phenothiadine and BHT. The content of such additives, when used, should be within a range which is ordinarily adopted in lubricants for refrigerators. 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. The following Samples 2-8 and 10 were used as specimens for the tests. Further, Samples 1 to 6 were monomethylethers of polyoxyethyleneoxypropyleneglycol according to the present invention and Samples 7,8 and 10 were comparative products. Sample 2 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 14 (CH 2 CH 2 O) 2 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 15 percent by weight. Sample 3 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 14 (CH 2 CH 2 O) 4 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 22 percent by weight. Sample 4 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 14 (CH 2 CH 2 O) 8 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 34 percent by weight. Sample 5 Monomethylether of polyoxyalkyleneglycol represented by the following formula: wherein oxyalkylene groups were block form and the ratio of oxyethylene groups in the compound was 23 percent by weight. Sample 6 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 17 (CH 2 CH 2 O) 2 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 41 percent by weight. Sample 7 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 16 (CH 2 CH 2 O) 2 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 79 percent by weight. Sample 8 Monomethylether of polyoxyalkyleneglycol represented by the following formula: CH 3 O(AO) 14 (CH 2 CH 2 O) 15 H wherein AO groups represented random polymeric groups of oxypropylene groups and oxyethylene groups, and the ratio of oxyethylene groups in the compound was 49 percent by weight. Sample 10 Monomethylether of polypropyleneglycol represented by the following formula: Example and Comparative Example The Samples described above were subjected to tests which were conducted as follows for the purpose of examining solubility to Flon 134a and anti-seizure performance. Flon 134a solubility test: A mixture of 15 parts by weight of each of the samples and 85 parts by weight of Flon 134a was charged in a 1-litre glass autoclave for the purpose of examining compatibility in a temperature range of -50 to 60°C. Anti-seizure test A test was conducted on each lubricant (sample) for refrigerators in accordance with ASTM-D3233 using a Falex tester. The anti-seizure test was conducted at an initial oil temperature of 25°C and after a 5-minute running-in operation at 250 lb. As will be understood from the foregoing description, the present invention provides a composition for referigerators using a lubricant which exhibits superior compatibility with chlorine-free Flon-type coolants which do not contain chlorine in their molecules such as Flon 134a and the like, as well as excellent lubricity and resistance to hygroscopicity. Thus, the composition of the present invention for use in refrigerators offer the following advantages: (1) Eliminates troubles in the evaporator of the refrigeration cycle because it exhibits superior compatibility with Flon 134a and the like; (2) Eliminates troubles in the compressor of the refrigeration cycle because it exhibites superior lubricity.

Claims: A composition for use in refrigerators characterised in that said composition contains a lubricant containing a monomethylether of polyoxyethylene-oxypropyleneglycol where the end group at the hydrogen terminal is an oxyethylene group (any contaminant oxypropylene-terminated monomethylether being less than 10 molar percent) represented by the general formula (1): CH 3 O(AO) m (CH 2 CH 2 O) n H wherein the A0 group represents a copolymeric group of oxypropylene groups and oxyethylene groups wherein the copolymeric form may be a block type in which the oxypropylene moiety is bonded to the (CH 2 CH 2 O) n group or a random type, m is a number of 5 ≦ m ≦ 45, n is a number of 2 ≦ n ≦ 10 and the content of the oxyethylene groups in the compound ranges from 5 to 60 percent by weight, and a chlorine-free Flon-type coolant whose molecules do not contain chlorine, at a weight ratio of from 1:99 to 99:1.

Inventors: BABA YUJI, KAMAKURA TAMIJI, NAMIKI MASATO, NAMIWA KIMIYOSHI, TANAKA NORIYOSHI, TATSUMI YUKIO, BABA, YUJI, KAMAKURA, TAMIJI, NAMIKI, MASATO, NAMIWA, KIMIYOSHI, TANAKA, NORIYOSHI, TATSUMI, YUKIO, Baba, Yuji, c/o Asahi Denka Kogyo K.K., 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: C10M107
IPC codes: C10M171, C10N40, C10N30, C10M107