CA2022832A1 - Polyglycol lubricant composition for use with tetrafluoroethane refrigerant - Google Patents

Abstract

ABSTRACT
A lubricant composition for use with tetrafluoroethane refrigerant, such as R134a (1,1,1,2-tetrafluoroethane) comprises a mono-functional polyglycol oil having a single functional hydroxyl group at one end of the molecule and a n-alkyl group at the other end, and a zinc dithiophosphate additive.

Description

2~22~3~'~

POLYGLYCOL LUBRICANT COMPOSITION
FOR USE WITH TETRAFLUOROET ANE REFRIGERANT
; For many years refrigeration compressors have operated quite satisfactorily using dichloro difluoromethane, CC12F2, as a refrigerant. This refrigerant is commonly referred to as R12. In recent years, however, the scientific community as well as the community-at-large have begun to recognize certain environmental hazards associated with the continued wide-spread use of chlorofluorocarbons (CFC's) such as R12, and particularly in regard to its apparent adverse effect on the ozone layer surrounding the earth. Therefore, efforts have been made to find an environmentally acceptable substitute for R12. R134a (1,1,1,2 tetrafluoroethane) has been identified as a possible substitute for R12, and wide-spread use of R134a in the future as a refrigerant isexpected. The thermodynamic properties of R134a are close to those of Rl2, and, being free of chlorine, R134a is believed to be benign to stratospheric ozone.
With the use of R12 in refrigeration compressors, it has been common to use mineral oils to provide sufficient bcundary lubrication to the moving parts of the compressor.
Generally these mineral oils are fully miscible with R12 throughout the operating temperature range, and provide satisfactory lubrication throughout the refrigeration loop travelled by the refrigerant. These mineral oils, however, are almost completely immiscible with R134a. No matter what proportion of oil and refrigerant one employs, be it 95%
R134a or 95~ oil, the refrigerant and the oil remain as two distinct layers regardless of temperature, although the two layers are in themselves solutions, each often carrying significant dissolved amounts of the other so-called 2~2~

immiscible partner. This immiscibility has lead to a fear that the compressor would not be adequately lubricated, and that the lubricant would not return to the compressor from the evaporater in the refrigeration loop, resulting in the eventual premature failing of the compressor. As a result, it has been necessary to utilize different lubricants with R134a than the mineral oils commonly used with R12.
In 1972, the present inventor along with M.W. Larime presented a paper at an ASHRAE Symposium held in Nassau, ; 10 Bahamas, titled "A Review of Synthetic Oils for Refrigerant Use". In this paper, the authors noted that various synthetic oils for use with refrigerants have been commercially manufactured and used since 1929. It was stated in the paper that these synthetic oils had been used due to certain problems encountered with mineral oils, such as wax separation and low miscibility of the oils with certain refrigerants. At the time the paper was presented, however, the authors noted that many of the earlier drawbacks that had been associated with the use of mineral oils as lubricants had been overcome as a result of impxovements in petroleum processing and system design, which had extended the useful low temperature limit of mineral oils. As a result, actual usage of synthetic oils in refrigeration systems remained low. The synthetic oils mentioned by the authors that were commercially available at the time of the article included certain synthetic hydro-carbons such as paraffins and alkyl benzenes, dibasic acid esters, neopentyl esters, phosphate esters, polyglycols, and silicate esters and silicones.
In a research disclosure published by DuPont in 1978 (Disclosure No. 17463 - Refrigeration oil), it was disclosed 2~2~32 that certain polyalkylene glycol oils sold by Union Carbide Corporation, such as "Ucon" LB-165 and "Ucon" LB-525 can be employed as refrigeration oils in combination with R134a.
This combination of oil and refrigerant was said to be miscible in all proportions at tempexatures at least as low as -50C, and to be thermally stable in the presence of steel, copper and aluminum at 175C for at least six days.
The disclosure did not provide an upper temperature operating range for the R134a/polyalkylene glycol composition, nor did it discuss the lubricating properties of the composition or provide any data regarding long-term chemical stability of the lubricant.
U.~. Patent No. 4,755,316 discloses the use of certain polyoxyalkylene glycol lubricants for use with R134a refrigerant. According to this patent, certain members of a class of polyglycols having at least two hydroxyl groups (i.e. di-functional with respect to hydroxyl groups) have a wider range of miscibility with R134a when compared to the mono-functional glycols LB-165 and LB-525 disclosed in the DuPont research disclosure. Therefore it was stated that these di-functional polyglycols should operate without separation from R134a over much of the operating temperature range of the refrigeration system, such as an automotive air conditioning system as discussed in the patent. It was stated that the polyglycol oils suggested in the DuPont reference are not fully miscible at higher temperatures, and would be expected to form two-phase systems at some locations in the refrigeration loop. In general, the '316 patent is directed to a determination of the miscibility of the refrigerant/lubricant composition at temperatures up to about 50C, and does not deal in any substantive detail with 2 ~ 3 ~

questions regarding the chemical stability of the lubricant or the ability of the lubricant to prevent excessive wear to the compressor.
In the paper presented by the present inventor at the ASHRAE Symposium in 1972 referred to previously, it was - noted that the synthetic oils commonly referred to as "polyglycols" should properly be called ethers and esters rather than glycols, because the terminal hydroxyl groups are bound by ether or ester groups. It was stated that this substitution of the ether or ester groups makes the poly-glycols suitable for lubrication, and also renders them water insoluble. In this regard, the multi-functional polyglycols referred to in U.S. Patent No. 4,755,316 may be considered as "true" glycols, whereas those mono-functional polyglycols referred to in the DuPont reference are actually monoethers. Nevertheless, it has become conventional to refer to each of these classes of compounds as "polyglycols". For purposes of clarity in the present specification, those polyglycols having a hydroxyl functional group at one end of each molecule and an alkyl group at the other end will be referred to as mono-functional polyglycols or monoethers. Those compounds having at least two hydroxyl functional groups (i.e. diols or triols) will be referred to as di-functional or ; 25 multi-functional polyglycols.
Although di-functional polyglycols mentioned in the 4,755,316 patent have a wide range of miscibility with Rl34a over the operating temperature range of a refrigeration system, and the mono-functional glycols mentioned in the DuPont reference are said to be miscible with R134a at low temperatures, certain unanswered questions remain with 2~2~3~

regard to finding a lubricant suitable for widespread use with R134a refrigerant. For instance, the di-functional polyglycols have not been widely used in the past, and there is a lack of data and practical working experience with these compounds. Very little is known regarding the lubricity, activity and compatibility of these compounds with materials used in hermetic compressors. Many of these di-functional glycols are of very high viscosity and, therefore, may be unsuitable for lubrication in many instances, such as in refrigeration compressor applications.
Similarly, the monoethers discussed in the DuPont reference may not provide sufficient lubricity under severe operating conditions or at high temperatures. In addition, neither of the references deals with the issue of the presence of peroxide in the lubricant. Many lubricants contain peroxides which may already be present in the lubricant when purchased, or which may be introduced into the lubricant by oxidation. The presence of peroxide in the lubricant may cause premature breakdown of its lubricating properties, and also causes problems by reducing the shelf life of the lubricant. As the peroxide reacts with and breaks down the lubricant, the acid content of the lubricant is increased.
Eventually the oxidation can result in a loss of effectiveness of the lubricant, and may cause a breakdown of the compressor. The acidity of the polyglycols tends to dissolve the metal parts of the refrigeration system, and eventually hasten the destruction of the entire refrigeration apparatus. The acidity may be removed by evacuation, however, this type of removal often tends to corrode the vacuum pump. Therefore, it is preferred to avoid these problems with the use of a lubricant in the 3 :~

system that is free of peroxide, and that is chemically stable.
Table D of the 4,755,316 patent includes a very general list of typical additives that may be used to enhance the performance of the di-functional polyglycols described in that patent. For example, additives such as phosphates, thio-phosphates, zinc diorganodithiophosphates, organic sulfides and compounds containing chlorine and sulfur were said to be extreme pressure and anti-wear additives.
Sterically hindered phenols, aromatic amines, dithiophosphates and sulfides were listed as examples of oxidation and thermal stability improvers. Other additives that may be used to enhance performance and act as corrosion inhibitors, viscosity index improvers, pour and floc point depressants, detergents, anti-foaming agents and viscosity adjusters were also listed. Other than providing a very general list of possible examples of typical compounds that may be used in each of the above classifications, this patent does not otherwise provide any actual working examples or other data concerning the use of any of these additives with the di-functional polyglycols described in that patent.
It is desired to provide a lubricant composition for use in a hermetic compressor system that provides sufficient lubricity to the system to prevent wear of the working parts, that inhibits oxidation and prevents the increase in acidity in the system.
In accordance with the present invention, there is provided a polyglycol lubricant for use with Rl34a refrigerant comprising a mono-functional polyglycol with a zinc dithiophosphate ~ZDP) additive. The addition of ZDP to 2~2~3f~ , a mono-functional polyglycol improves the lubricity of the lubricant and also stabilizes the lubricant.
The invention solves the problems in the prior art associated with finding a suitable lubricant for use with R134a refrigerant. A class of materials identified as zinc dithiophosphates has been found to fulfill the dual role of a lubricity additive as well as an oxidation inhibitor. The addition of ZDP to a mono-functional polyglycol expands the lubricity of the polyglycol lubricant and enables these lubricants to be used with R134a in conditions wherein the lubrication may not otherwise be satisfactory, such as in high temperature operation and under severe operating conditions. In addition, the ZDP acts to inhibit oxidation by decomposing peroxide which may be present in the lubricant, by preventing the formation of additional peroxides. As a result, the storage life of the lubricant is greatly increased. Additionally, the acid content of the lubricant is kept at an acceptable level if the level of peroxide in the system is minimized. As a result, premature destruction of the compressor caused by the metal parts of the compressor reacting with these acids is also minimized.
The present invention, in one form thereof, provides a lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor comprising a monofunctional polyglycol oil having a single functional hydroxyl group at one end of the molecule and an n-alkyl ; group at the other end. The mono-functional polyglycol oil has a molecular weight of from about 550 to about 1000, and a viscosity of about 22 to about 68 centistokes at 100F
(38C). A zinc dithiophosphate is added to the polyglycol 2 ~ 3 ~

oil and fulfills the dual role o a lubricity additive as well as an oxidation inhibitor.
The present invention, in another form thereof, provides a refrigeration composition for use in a hermetic compressor. The refrigeration composition comprises a tetrafluoroethane refrigerant, a mono-functional polyglycol lubricant having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, and a zinc dithiophosphate to act as a lubricity additive and an oxidation inhibitor.
The present invention relates to lubricant compositions for use in hermetic compressor systems that utilize a tetrafluorethane refrigerant. In particular, this invention relates to lubricant compositions comprising a mono-functional polyglycol oil and a zinc dithiophosphate additive.
For many years, R12 (dichloro difluoromethane) has been used as a refrigerant in hermetic compressor systems. As a result of certain environmental hazards believed to be associated with the use of Rl2, an environmentally acceptable substitute for R12 has been sought. Preferably, a substitute for R12 would exhibit thermodynamic properties close to those of R12, yet would not pose the environmental threat believed to be associated with the use of R12.
Additionally, it is desired that the substitute function as near as possible as a "drop in" replacement for R12, meaning that the substitute could be employed in the system with little or no change being necessitated to the working parts and to the operation conditions of the compressor. Certain tetrafluoroethanes such as Rl34a (1,1,1,2 tetrafluoroethane) and R134 ~1,1,2,2 tetrafluoroethane) have been identified as 2~22~32 promising substitutes for R12. Widespread use of R134a in the future is expected.
Generally, mineral oils have been used as lubricants in a hermetic compressor system using R12. Unfortunately, however, mineral oils are almost completely immiscible with R134a, which results in phase separation of the refrigerant and the lubricant. This phase separation may result in insufficient lubrication of the compressor, and cause problems throughout the refrigeration loop traveled by the refrigerant. As a consequence, it is important to use a lubricant composition having sufficient miscibility to avoid significant separation of the lubricant phase from the refrigerant phase, yet also provide sufficient boundary lubrication to the compressor. Also, it is preferred that the lubricant composition be chemically stable, and act to prevent the increase of acidity into the refrigeration ~ system.
; The present inventor has found that a lubricant composition comprising a mono-functional polyglycol with a zinc dithiophosphate (ZDP) additive provides favorable results when used with tetrafluoroethane refrigerants, such as R134a. Polyglycols are actually ethers and esters, rather than true glycols, because the terminal hydroxyl groups are bound by ether or ester groups. It is this substitution that makes the polyglycols suitable for lubrication, and also renders them water insoluble.
However, it has been conventional to refer to the ethers and esters as polyglycols. Mono-functional polyglycols comprise a particular class of polyglycols having a single functional hydroxyl group at one end of the molecule and, generally, an n-alkyl group at the other end of the molecule. Zinc _g_ 2 ~ 3 ~

dithiophosphates are compounds that combine both sulfur and phosphorous in a single compound. Sulfur and phosphorous are both aids to boundary lubrication. The ZDP also acts to inhibit oxidation in the lubricant.
Preferably, the mono-functional polyglycols used in the lubricant composition described in the present invention have a preferred range of molecular weights of between about 550 and 1000. The viscosity of the lubricant should be within the range of approximately 22 to 68 centistokes at 100F (38C). Many commonly used monofunctional polyglycoïs such as polypropylene glycol, and polypropylene polyethylene glycol fall within this range and are considered to be within the scope of the invention.
The zinc dithiophosphate is a compound of the general formula (R'O)2 - P - S - Zn - S ~ P ~ (OR")2 , S S
wherein R' and R" may be identical with or different .~
from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms, and preferably at least six carbon atoms. The ZDP is generally purchased in bulk and is mixed with the base Iubricant. It is preferable to use a dilute solution of ZDP, such as 0.2% by weight ZDP in the base lubricant.
Higher concentrations of ZDP above approximately 1~ tend to increase the amount of moisture introduced into the solution to an undesirable level, due to the relatively high water content of many commercially available zinc products.
In an earlier publication by the present inventor, "Materials Compatability of R134a in Refrigerant Systems", the mono-functional polyglycols, such as polyoxypropylene , --10--9 ~ 3 ~

glycol butyl monoether in the 32 centistokes viscosity grade, have been identified as acceptable lubricants with respect to miscibility, solubility, and functionality in a hermetic compressor system employing R134a. Since that time, however, it has been determined that the lubricity of the mono-functional polyglycol in the presence of R134a is not as good as that of the traditional refrigeration working fluid, such as the mineral oil Suniso 3GS, in the presence of R12. Laboratory data have also shown that R134a is not an aid to boundary lubrication, in contrast to R12 which has been known to aid boundary lubrication.
The term "boundary lubrication" refers to lubrication of portions of the compressor wherein the metal surfaces are not separated completely by the lubricant. That is, there is some metal to metal contact notwithstanding the film of oil or lubricant between the surfaces of the metals.
It is characteristic of polyglycol oils to combine with oxygen over time to form peroxides. These peroxides are precursors to full-fledged oxidation which breaks down the polyglycol oil, and perhaps more importantly, increases the acidity of the polyglycol. An increase in acidity of the lubricant may eventually attack the metal parts of the compressor, and lessen the useful life of the compressor.
The present inventor has found that the introduction of a zinc dithiophosphate (ZDP) to the mono-functional polyglycol lubricant improves the boundary lubrication properties of the R134a/polyglycol system. Sulfur and phosphorous are known as aids to boundary lubrication, and in the ZDP, these two elements are combined in one compound.
Additionally, the ZDP acts as an oxidation inhibitor by decomposing peroxide in the lubricant, and preventing the f~ 3 ~

formation of additional peroxide otherwise likely to form during storage of the lubricant. ~ince ZDP reacts with peroxides, it will decompose peroxides formed in the lubricant during its storage and, to the extent the ZDP is not used up, it will continue to react with peroxides as they are formed. Thus, oxidation of the lubricant is inhibited and the lubricant remains acid-free.
The mono-functional polyglycol/zinc dithiophosphate lubricant composition of the present invention is intended for use in hermetic compressors of the type commonly used in refrigerators, beverage coolers, dehumidifiers, and the like. However, other types of uses are also contemplated, such as with air conditioning systems. In order to provide sufficient lubricity for the particular application desired, it is necessary to utilize a polyglycol oil having sufficient viscosity to lubricate the hermetic compressor.
The operating conditions in a hermetic reciprocating compressor of the type utilized in the typical household refrigeration/freezer typically involve an oil temperature 20 of from 150F to 175F (65C-79C), and approximately 5 psig R12 pressure. In this type of compressor a range of viscosity of about 22 centistokes to about 68 centistokes at 38C would be preferred. For other hermetic compressors, such as the rotary type, a range of viscosity of 68 to 100 25 centistokes at 100F (38C) would be preferred.
The particular advantages to be obtained by the lubricant composition of the present invention is best shown by the following examples.

Certain tests were run in order to determine whether the particular refrigerant itself acts as an aid to boundary 2 ~ 3 ~

lubrication. R12 was compared to R134a, in the presence of a mineral oil and a mono-functional polyglycol, respectively. The mineral oil used was Suniso 3GS, produced by Witco Chemical Corporation, and the polyglycol was LB-165, produced by Union Carbide Corporation. The ZDP
additive was not used in this test, because the focus of the test was to determine whether the refrigerant itself was an aid to boundary lubrication. The tests were run in a Falex tester that had been modified to create a sealed chamber in order to approximate the conditions inside a hermetic compressor. The modifications were fairly simple, and included the addition of three seals in the tester, one at the rotating shaft and the other two at the movable jaw arms. The tests were made with hardened steel pins and cast iron vee blocks. All specimens were 6-7 rms at the start.
A sufficient amount of liquid refrigerant was added to the lubricant in order to saturate the lubricant with refrigerant. The pin and vee blocks were assembled in the ; modified Falex tester. The saturated lubricant was then added and the cup of the tester was closed. The lubricant was then preheated to 150F (66C). The load was then applied and the test was started. The closed chamber was not pressurized. At the end of two hours the test was stopped and the test specimens were examined for scar width and surface finish. The increase in final temperature resulted because of friction during the testing. The -` results are shown in Table A below.
TABLE A
Load Final Finish Width of Refri~erant Oil Initial/~inal Temp. (F? (rms) Scar (in.) Remarks R12 3GS250/230 177 Smooth .03 Baseline (5-6) Good 2~22'~32 R134a 3GS 250/260 210 Very Rough .02 Unacceptable (60-70) Poor R134a 3GS 250/- Failed in one minute R12LB165 258/258 162 Smooth .01 Excellent (5-6) R134a LB165 250/220 160 Smooth .04 Excess wear (9-10) but acceptable These tests indicate that, unlike R12, R134a itself is not an aid to boundary lubrication. A second item that comes from the above tests is that the polyglycol oil LB-165 may be a better lubricant than Sun 3&S.

Both oils tested in Example 1, Sun 3GS and LB165, were tested in the presence of R134a in th~ modified Falex tester. A second mono-functional polyglycol oil, ICI30, produced by ICI Chemicals Limited was also tested. In this test, a zinc dithiophosphate additive, namely 0.2% Lubrizol 1097 made by Lubrizol Petroleum Chemicals Co., was added to the respective oils in selected samples. The 0.2% Lubrizol solution was prepared in the laboratory by adding 2 g. of the bulk Lubrizol 1097, material as purchased, per 1000 ml of polyglycol oil. The test conditions were the same as used in Example 1. The results of this test are shown in Table B below.
TABLE B
Load Final Surfaces Width of 25 OilAdditive Initial Final Temp.(~F) (rms) Remarks Scar (in.) LB165 None Z50 220 160 Smooth ~xcess Wear .04 (9-10) " 350 290 180 " " .04 (7-8) "Yes 250 250 170 " No Wear ,015 2 ~ 3 2 ; (4-5) " " 350350 195 " " .015 (5-6) IC130None 350325 155 Medium Excess Wear .060 Smooth ICI30Yes 350350 178 Smooth No Wear .01 (4-5) 3GS None 250. 260 210 Very Unacceptable .02 Rough (60-70) " Yes 250240 173 Smooth Equivalent .03 (6-7) to test in R12 As may be noted from Table ~, the lubricity of each oil has been improved with the addition of the 0.2~ Lubrizol 1097.

' 10 The peroxide resistance of the zinc dithiophosphate Lubrizol 1097 was examined in the mono-functional polyglycol oil LB-165. Testing was performed to determine if adding lS 0.2~ Lubrizol 1097 would prevent the formation of peroxide, and also whether this ZDP would decompose any peroxide already present in the polyglycol oil. The LB-165 was l removed from a five gallon can as received. The peroxide - number of this lubricant was checked and found to be 5. ~n 20 oxidation resistance test was performed with 5ml of lubricant or lubricant/additive, a valve steel strip and 800 mm Hg of oxygen. The sealed tubes were then heated at 90C
for four hours. The results, after heating, show that LB-165 with no additive, forms a peroxid~ number of 35, 25 whereas the LB-165 with 0.2g Lubrizol 1097 additive has a peroxide of zero. This test shows that the ZDP not only - 2Q2~',3~

prevents the formation of peroxides but also decomposes the existing peroxide.

The ability of Lubrizol 1097 to reduce existing peroxide within a certain period of time and at a certain temperature was examined. In this test, 5 ml samples of LB-165 (from the 5 gallon can) plus 0.2% Lubrizol 1097 were placed in screw cap test tubes and heated at 90C. Samples were removed at one hour intervals and the peroxide number was checked. One sample remained at room temperature (R.T.), no heat, and another that contained LB-165, no additive, was heated at 90C. The results are shown in Table C.
TABLE C
Oil Additive Time Temp. Peroxide No.
LB-165 no treatment 5 LB-165 0.2~ Lubrizol 1097 4 hrs R.T. 2 20 LB-165 0.2% Lubrizol 1097 2 hrs 90C
LB-165 0.2% Lubrizol 1097 3 hrs 90C 0 LB-165 no additive 3 hrs 90C 5.2 This test shows that the ZDP decomposes the existing peroxide, even at room temperature. At higher temperatures this decomposition occurs at an increased rate. The sample that had no ZDP additive and was heated to 90C for 3 hours showed no decomposition of the peroxide, and in fact, showed a slight increase in the peroxide number.

2~2~3~
.

The LB-165 which was used in the oxidation resistance test (peroxide = 35) was used to perform the previous test for peroxides of higher magnitude, in this case a peroxide number of 35. The results are shown in Table D.
TABLE D
Oil Additive Time Temp.Peroxide No.
LB-165 (initial) 35.0 LB-165 0.2~ Lubrizol 1097 1 hrs 90C 6.5 10LB-165 0.2% Lubrizol 1097 2 hrs 90C 6.5 LB-165 0.2~ Lubrizol 1097 3 hrs 90C 4.3 + R.T. overnight As shown in Table D, show that adding Lubrizol 1097 to LB-165 will decompose peroxide until the ZDP is exhausted.

The compatibility of a mono-functional polyglycol lubricant (monoether-type polyglycol) with the ground insulation used in hermetic compressors was examined, and this compatibility was compared with that of a di-functional polyglycol lubricant (diol-type polyglycol). The hermetic motors have magnet wire as the current carrying conductor, and have an auxiliary phase-to-phase and phase-to-ground insulation in the form of a plastic film, such as polyethylene teraphthalate (PET) film. One of the problems that may be encountered with the use of this film is embrittlement. Embrittlement is most often caused by hydrolysis that may occur as a result of the reaction of the PET film with the hydroxyl groups of water, or alcohols, such as methyl alcohol, which are sometimes added to 2 ~

refrigeration systems. It was suspected that the hydroxyl groups in the polyglycol molecule might also cause embrittlement of the PET film.
The mono-functional polyglycol used in this test was Union Carbide MLX-1389, and the di-functional polyglycol used was Dow P-400, both having ISO viscosity of 32. The ; PET film used was Mylar, produced by DuPont. The Mylar film was cut into strips ~0.25 in. x 3 in. x 0.01 in.) to be used as test specimens. The strips were then placed in a desiccator for an extended period of time. Both of the polyglycol oils used were free of peroxide and acidity.
Five milliliters of each of the oils was added to respective 5/8 in. O.D. glass tubes containing a Mylar ; strip, and constrictions were made in each tube. Two other tubes were also prepared and constricted in a like manner, ; one tube containing MLX-1389 plus a Mylar strip (to be used as a moisture blank) and the other tube containing a Mylar strip with no oil (Mylar blank). All of the tubes were placed in a vacuum bell jar. A heat lamp was applied and a 2~ vacuum was pulled for four days. In a repeat test, the heat and vacuum were applied for three days. After the evacuation, the bell jar was back-filled with nitrogen to cool. Each tube was then placed on a vacuum manlfoldt a vacuum was pulled; and the tubes were sealed. The tube containing the moisture blank oil was not sealed, but rather was checked for moisture. All of the other tubes were then placed in an oven and heated for seven days at 300F. After heating, the tubes were cooled and each tube was broken individually. The Mylar strips were checked for embrittlement by first wrapping the strips around a 5/8 in.
mandrel, then a 1/3 in. mandrel and finally by folding the 2~2~32 stxip in two. The results of the test are listed in Tables E and F below.

TABLE E
Test #l Vacuum and Heat 4 days Heated 7 days at 300F
5/8 in. 1/3 in.
Oil Used Mandrel Mandrel Fold in Two None Pass Pass Pass UCON MLX-1389 Pass Pass Fail lO Dow P-400 Fail Fail Fail TABLE F
Test #~2 Vacuum and Heat 3 days Heated 7 days at 300F
5/8 in. 1/3 in.
Oil Used Mandrel Mandrel Fold in Two None Pass Pass Pass UCON MLX-1389 Pass Pass Pass Dow P-400 Pass Fail Fail ; Ucon MLX-1389 Pass Pass Fail ;~ ~(Second tube; Mylar preconditioned ~20~ 1 hr. 300F in oven) The results in Table E and Table F show that the mono-functional polyglycol oil causes muah less embrittlement of the PET film than does the di-functional polyglycol.
~25 From the examples provided herein, it can be concluded *hat adding a ZDP, such as 0.2% Lubrizol 1097, to a mono-functional polyglycol oil, such as LB-165, improves the lubricity of the oil and aids in the prevention of peroxide formation. The ZDP will also reduce existing peroxide in the oil to the point where the ZDP is exhausted. It has also been demonstrated that the mono-functional oils have 2 ~ 3 ~

better compatibility in hermetic compressors than the di-functional oils.
Based upon the results shown in the examples, and the discussion provided above, a lubricant composition for use with a tetrafluoroethane refrigerant, such as R134a, has been described.

Claims (24)

1. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor, comprising: a mono-functional polyglycol oil, and a zinc dithiophosphate additive represented by the general formula:
wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

2. The lubricant composition as claimed in Claim 1, wherein the mono-functional polyglycol oil has a molecular weight of from about 550 to about 1000.

3. The lubricant composition as claimed in Claim 1, wherein the mono-functional polyglycol oil has a viscosity of about 22 to about 68 centistokes at 100°F.

4. The lubricant composition as claimed in Claim 1, wherein the mono-functional polyglycol is polypropylene glycol, polypropylene polyethylene glycol or a mixture thereof.

5. The lubricant composition as claimed in Claim 1, wherein the zinc dithiophosphate additive present in an amount not exceeding 1% by weight of the lubricant composition.

6. The lubricant composition as claimed in Claim 1, wherein the zinc dithiophosphate additive is present in an amount of about 0.2% by weight of the lubricant composition.

7. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor, comprising: a mono-functional polyglycol oil having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, and a zinc dithiophosphate additive represented by the general formula:
(R'O)2 - ? - S - Zn - S - ? - (OR")2 wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

8. The lubricant composition as claimed in Claim 7, wherein the mono-functional polyglycol oil has a molecular weight of from about 550 to about 1000.

9. The lubricant composition as claimed in Claim 7, wherein the mono-functional polyglycol oil has a viscosity of about 22 to about 68 centistokes at 100°F.

10. The lubricant composition as claimed in Claim 7, wherein the mono-functional polyglycol is polypropylene glycol, polypropylene polyethylene glycol or a mixture thereof.

11. A refrigeration composition for use in a hermetic compressor, comprising:
(a) a tetrafluoroethane, (b) a sufficient amount to provide lubrication of a mono-functional polyglycol lubricant having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, and (c) a zinc diothiophosphate additive represented by the general formula:
(R'O)2 - ? - S - Zn - S - ? - (OR")2 wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

12. The refrigeration composition as claimed in Claim 11, wherein said tetrafluoroethane is 1,1,1,2-tetrafluoroethane.

13. The refrigeration composition as claimed in Claim 11, wherein said mono-functional polyglycol lubricant has a molecular weight of from about 550 to about 1000.

14. The refrigeration composition as claimed in Claim 11, wherein said mono-functional polyglycol lubricant has a viscosity of from about 22 to about 68 centistokes at 100°F.

15. The refrigeration composition as claimed in Claim 11, wherein said mono-functional polyglycol lubricant is polypropylene glycol, polypropylene polyethylene glycol, or a mixture thereof.

16. The refrigeration composition as claimed in Claim 11, wherein the composition (c) is present in an amount not exceeding 1% by weight of composition (b).

17. The refrigeration composition as claimed in Claim 11, wherein the composition (c) is present in an amount from about 0.1% to about 1.0% by weight of composition (b).

18. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor, comprising:
a mono-functional polyglycol lubricant having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, said mono-functional polyglycol lubricant having a molecular weight of from about 550 to about 1000, and having a viscosity of from about 22 to about 68 centistokes at 100°F, and a zinc dithiophosphate additive represented by the general formula:

(R'O)2 - ? - S - Zn - S - ? - (OR")2 wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

19. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor, comprising:
a sufficient amount to provide lubrication of a mono-functional polyglycol lubricant having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, and a zinc dithiophosphate additive represented by the general formula:
(R'O)2 - ? - S - zn - S - ? - (OR")2 wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

20. The lubricant composition as claimed in Claim 19, wherein the zinc dithiophosphate additive present in an amount not exceeding l% by weight of the lubricant composition.

21. The lubricant composition as claimed in Claim 19, wherein the zinc dithiophosphate additive is present in an amount of about 0.2% by weight of the lubricant composition.

22. The lubricant composition as claimed in Claim 19, wherein said mono-functional polyglycol lubricant has a molecular weight between 550 and 1000, and a viscosity of about 22 to about 68 centistokes at 100°F.

23. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor comprising:
a polyoxypropylene glycol butyl monoether having a viscosity of about 22 centistokes at 100°F, and a zinc dithiophosphate additive represented by the general formula:
(R'O)2 - ? - S - Zn - S - ? - (OR")2 wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms.

24. A lubricant composition for use with tetrafluoroethane refrigerant in a hermetic compressor consisting essentially of:
a mono-functional polyglycol lubricant having a single functional hydroxyl group at one end of the molecule and an n-alkyl group at the other end, said mono-functional polyglycol lubricant having a molecular weight of from about 550 to about 1000, and having a viscosity of from about 22 to about 68 centistokes at 100°F, and a zinc dithiophosphate additive represented by the general formula:
wherein R' and R" may be identical with or different from each other, and represent alkyl, aryl, alkylaryl or arylalkyl radicals containing at least three carbon atoms, said zinc dithiophosphate additive being present in an amount of about 0.2% by weight relative to the lubricant composition.