Refrigeration Lubricant Based on Polyolester for Use With HFCs and Prospect of its Application With R-22 (Part 2) Hydrolytic Stability and Compressor Endurance Test Results

Application ofHFC refrigerants for air conditioners and refrigerators has been studied. Development of a common oil, based on a combination ofpolyolester and additive packages, is aimed for R-22 and HFCs refrigerants, and the evaluation tests of reliability in compressor and refrigeration system brought about good results. This refrigeration lubricant is already partly commercialized in HFC refrigerants and the application for R-22 is now under development. INTRODUCTION Recently protection of the earth circumstance against the ozone layer destruction and global warming has become a challenge for the world. As the measures for this point, the total abolition of CFC refrigerants in 1995 and start of regulation on HCFC refrigerants from 1996 with aim of abolition in principle in the year of2020 has been agreed upon. Therefore, HFC refrigerants have been noted as the alternative refrigerants. R-134a is expected to substitute for R-12, meanwhile R-404A and R-407C for R-22. Polyolester(POE) has been developed as the refrigeration lubricant applicable for both commercial refrigerants ofR-22 and the expected HFC refrigerants. Part 1 report is mainly dealing with the testing result oftribology, and Part 2 with stability of base oil, effect of additives and testing result of hydrolytic stability by use of moisture absorbent as element test, and endurance test result of compressor, reliability test result in refrigeration system and the related practical situation as reliable test. ELEMENT TESTS Hydrolytic stability Principal physical properties as a refrigeration lubricant are miscibility with refrigerant, high electrical insulating property, high lubricity and thermal and chemical stability. POE is the most suitable in HFC refrigerants though having a fear of oil deterioration and material corrosion by the unique hydrolytic reaction of POE (eq. (1)). RCOOR' + H20 ~ RCOOH + R'OH -----(1) First, a stability test was made by using an autoclave testing device for the purpose of grasping the hydrolytic properties due to the difference in molecular structure ofPOE. Study on a: -branched acid rich POE (A32) as the base oil showed that the increase in total acid number(T AN) was lower and more stable than that of a: -branched acid free POE (N32) in Fig. 1. From this result, a: -branched acid rich POE(A32) was selected as the base oil and thereafter various tests were made by using POE(A32) unless it is specified. As one of the methods to further improve the hydrolytic stability, the epoxy type additive was added. Two types of additives, L-A and L-B, were evaluated under the same condition as shown in Fig. 2. Figure 2 shows that thermal stability and hydrolytic stability as refrigeration lubricant could be enhanced by the addition of epoxide L-B to POE (A32). From above results, the optimal composition of epoxy type additive (L-B), antiwear additives (Part 1: AP and S-P) and other additives has been studied in the case of base oil POE(A32). (Refer to table 1) Thermal stability Thermal stability testing was made to study the possibility of application of the selected POE-C to both HFC refrigerants and R-22. As a thermal stability evaluation method, the sealed glass tube test including a very small amount