US 3026262 A
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ite States Patent Oilfice 3,026,262 Patented Mar. 29, 1962 3,026,262 SYNTHETEC LUBRICANT COMPOSITTQN Lloyd P. Foster and Earl W. Wilson, Kingsport, Tenn, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Aug. 5, 1958, Ser. No. 753,210 4 Claims. (@l. 252-498) This invention relates to a new additive system for synthetic-base lubricants which imparts improved eX- treme-pressure properties coupled with anti-sludging, anticorrosive and related properties to the lubricants.
' The use of jet engines in aircraft has presented many new problems connected with lubrication. In the past, high viscosity petroleum oils or low viscosity mineral oils performed satisfactorily in the aircraft engines in use. However, with the newer turbo-prop and turbo jet engines, these oils or lubricants fell short of requirements. Low viscosity mineral oils were too volatile and were poor in load-carrying ability. High viscosity petroleum oils did not possess the low temperature fluidity required for pumpability.
As a result of these deficiencies in petroleum base oils, a new type of lubricant was developed especially for jet engines. This lubricant was composed of a synthetic diester base stock usually modified with a regenerative oxidation inhibitor such as phenothiazine, an anti-wear agent such as tricresyl phosphate, and occasionally a viscosity index improver such as poly [n-butyl methacrylate].
These synthetic lubricants possessed good low temperatur viscosities, high flash points, moderate coking and evaporation valves. However, they displayed a moderate amount of dirtiness in the engine which was often attributed to the oxidation stabilizer. Upon storage, often they would become corrosive to metals used in the engines. Without modification with extreme pressure agents, these lubricants ran from 1600 to 2500 pounds per inch load-carrying ability in the Ryder Gear Tester, exact values depending on the viscosity of the lubricant. This generally has been satisfactory for the early model turboprop and turbo-jet engines. However, the newer turboprop and turbo-jet plants require lubricant oils having load carrying ability of at least 2800 pounds per inch. Attempts were made to achieve this end through the use of an ester lubricant with a higher viscosity. However,
poor low temperature properties accompanied this change.
Some attempts were made to incorporate therein extreme pressure agents, leaving viscosity at the low value of the base stock without a viscosity index improver. extreme pressure agents generally produced sludging, corrosion and coking. Quite often the additive was too volatile for efiective use in high temperature systems.
The ideal lubricant should have the good low temperature properties or" accepted synthetic diester lubricants without viscosity index improvers. It should have the good load-carrying properties of high viscosity petroleum oils. It should have low coking and sludging tendencies. In addition, a lubricant should have low volatility, high flash point, and should not be corrosive to metals used in aircraft engines.
It is an object of this invention to provide a novel synthetic ester lubricant composition.
It is another object of this invention to provide a new synthetic ester lubricant system that displays substantially less coking and sludglng than is displayed by conventional synthetic ester lubricant systems.
It is another object of this invention to provide a new additive system which together with a synthetic ester base stock gives a lubricant having high load-carrying ability, yet retaining the good low temperature properties of the base stock.
These It is another object of the invention to provide a new additive system for synthetic ester lubricants which produces a pronounced stable life and prevents corrosion under severe oxidizing conditions through a synergistic action of the additives comprising the new additive system.
It is also an object of this invention to provide a new synthetic ester lubricant composition particularly useful in contemporary turbo-prop and turbo-jet aircraft engmes.
These and other objects of the invention are accomplished by incorporating into synthetic ester lubricant base stock a combination of a Sterically hindered phenolic compound having an alkyl group in a position ortho to the hydroxyl group and an inorganic phosphorous compound such as phosphorous acid, phosphoric acid, or phosphorous pentoxide, or mixtures thereof. While the proportions of the components of the present additive system vary largely with the type of ester base stock, the phenolic compound is generally employed in amounts of at least .l% and preferably .5% to 5%, based on the weight of the synthetic ester base stock; and the inorganic phosphorous compound is employed in amounts of .001% to 4%, and preferably .Ol% to .1%, based on the weight of the synthetic ester base stock.
The phenolic compound used in combination with the inorganic phosphorous compound is a sterically hindered phenol having at least one alkyl substituent on the benzenoid nucleus ortho to the hydroXyl group, this substituent substantially reducing the chemical activity of the hydroxyl group. While the alkyl substituent can be widely varied, usually from about 4 to 12 carbon atoms, this substituent is preferably an alkyl group having substantial steric bulkiness such as a tertiary alkyl group, typical of such groups being the tertiarybutyl group. Sterically hindered phenolic compounds that can be suitably em ployed in the invention include 2,6-ditertiarybutyl phenol, 2,6-ditertiarybutyl-p-cresol, 2,4,6-tri-tertiarybutyl phenol, 2,2-ethylene bis-(o-tertiarybutyl-p-cresol), and related well-known Sterically hindered phenols. The Sterically hindered hydroxyl groups on the phenolic compounds employed do not react with the inorganic phosphorous compounds employed in combination therewith, these two compounds retaining their original form when dispersed in synthetic ester lubricants. Hence, the subject additive combination for synthetic lubricants is to be distinguished from various additives such as organic phosphorous-containing compounds and other additives not having free hydroxyl groups on a benzenoid nucleus or not having an inorganic phosphorous compound in combination therewith.
The subject combination of a hindered phenolic, compound and an inorganic phosphorous compound can be efiectively employed to improve the properties and utility of a wide variety of synthetic organic ester lubricants. Typical of such synthetic lubricants are the esters described in Bell et al., US. Patent No. 2,798,083, and include diesters of the formula i CH3 (DH-CH wherein each R is a straight or a branched chain alkyl group, one R containing 4 to 21 carbon atoms and the other R containing 8 to 21 carbon atoms. Illustrative of such synthetic organic ester lubricants described by Bell et al. are 2,2,4-trimethyl1,3-pentanediol dicaprate, 2,2-dimethylpropanediol dipelargonate, 2,2-dimethyl-l,3- propanediol didecanoate, 2,2-dimethyl-1,3-propanediol ditridecanoate, 2,2 dimethyl 3 isopropyl 1,3 propanediol didecanoate, 2,2-dimethyl-3-isopropyl-1,3-propanediol ditridecanoate and the like. The synthetic ester lubricants described in the copending application by Brannock, U.S. Serial No. 699,530 which was filed November 29, 1957, now US. Patent No. 2,919,447, can also be improved in accordance with the invention,'and, include diesters having. the formulas ll CHzO O R r II C 020 CR and l CHzO R CH2OCR T l wherein R is an alkyl group containing 6 to 11 carbon atoms. Illustrative synthetic ester lubricants described by Brannock are l,1-cyclopentanedimethanol di-n-octanoate, 1,l-cyclopentanedimethanol dipelargonate, 1,1- cyclopentanedimethanol di-n-octanoate, and 2,2-norcamphanedimethanol di-n-octanoate. In addition, the synthetic ester lubricants described in another copending application by Brannock, U.S. Serial No. 710,851 which was filed January 24, 1958, now US. Patent No. 2,912,458, can be improved in accordance with the invention. In this latter application, Brannock described synphorous pentoxide is a system that imparts improved properties to synthetic organic ester lubricants. This new additive system displays none of the sludging evident in conventional diester base stock systems of the prior art. This effect is achieved by a synergistic action between the two additives in the system. The present invention concerns an additive system which together with a synthetic base stock gives a lubricant having a loadcarrying ability of greater than 3000 pounds per inch, yet retaining the good low temperature properties of the base stock without additives. The new system has less coking tendency than prior art synthetic ester lubricantcompositions. The present additive system actually inhibits lead corrosion in base stocks which are of such a poor quality that they are corrosive to lead when inhibited by prior art additives. The present additive system also produces in synthetic ester lubricants a pronounced stable life and prevents corrosion under severe oxidizing conditions through a synergistic action of the two additives.
The improved properties of synthetic organic ester lubricants containing the present additive system are demonstrated by the data set out in the examples below. Conditions for the tests used in these examples are set out in Federal Test Method Standard 791 and Military Specification MiL-L-7808C. Included in many of the examples for comparison purposes is a MIL-L-7808C approved synthetic ester lubricant composed of 96% by Weight of di(Z-ethylhexyl)sebacate, 3% by weight of tricresyl phosphate and 1% by weight of phenothiazine.
Example 1 Di(2-ethylhexyl)sebacate (DOS) containing 1% by weight of 2,6-ditertiarybutyl-p-cresol (BHT) and .07% by weight of phosphorous acid was subjected to various standard lubricant tests and compared with a MIL-L- 7808C approved oil composed of 96% by Weight of di(2- ethylhexyl)sebacate (DOS), 3% by weight of tricresyl phosphate (TCP) and 1% by weight of phenothiazine (PTZ) as well as with Grade 1010 jet engine oil and Grade 1100 piston engine oil. The results of the various standard tests are summarized by the data in Table 1 below.
Table 1 Load- Viscosity, cps. Percent Carrying Evapo- Ability, Pour Flash Foam ration Lubricant Ryder Point, Point, Test,
Ratin F. 210 F. 65 F. Hours lbs/in. at
(1) DOS+1% BHT+.07% Phosphoric Acid 4, 200 75 430 3. 2 8, 260 Pass 20 (2) MIL-L-7S08C Approved 011-. 2. 200 75 455 3.5 12, 200 Pass 15 (3) Grade 1010 Jet Engine Oil 3, 300 75 290 2. 5 25,000 Pass 90 (4) Grade 1100 Piston Engine Oil 500 +5 500 20. 5 solid Pass 5 I thetic ester lubricants having the formula wherein n is an integer of 5 to 10, typical esters of this group being bis-(2-methyl-2-norcamphanemethanol)azelate and bis-(2-methyl-2-norcamphanemethanol)sebacate. Other synthetic organic ester lubricants that can be improved in accordance with the invention include di(2- ethylhexyl)sebacate, di(Z-ethylhexyDazelate, di(2,2,4- trimethyl-pentyl)azelate, the S-carbon 0x0 alcohol diester of 1,1-cyclohexanediacetic acid and related synthetic organic ester lubricants. Any of the known synthetic organic ester lubricants can be improved with the additive system described herein.
The combination of a hindered phenolic compound having at least one alkyl group in a position ortho to the hydroxyl group and an inorganic phosphorous compound such as phosphorous acid, phosphoric acid and phos- As can be seen from the data in Table 1, the synthetic ester base of di(2-ethylhexyl)sebacate containing BHT and phosphorous acid in accordance with the invention has high load-carrying ability without an undesirable increase in viscosity at low temperatures. The data concerning the other tests shown indicate that the synthetic ester lubricant of the invention also has additional properties lending to its utility as a lubricant.
EXAMPLE 2 Table 2 347 F. Corrosion and Oxidation 347 F. Base Stock Addltlve Induction Period, Condition of Condition Acid No. Hours Metals of Ester Change Lubricant (1) DOS .07% Phosphorous Acid +1% 2,6- 90 Clean Clear 2.6
Ditertiarybutyl Phenol. (2) DOS 05% Phosphoric Acid +1% BET-" 115 do do 1.7 (3) DOS .OQgTP lIi OSphQrQus pentoxide +l% 70 do do 2.3 (4) TMPDDP 07% Phosphorous Acid +1% BHI 200 do do 1.1 DOA. 07% Phosphorous Acid +1% BI-ITL. 100 do ..d 3. 3 (6) TMPDDP Phosphorous Acid +1% Phe- 90 Moderate Heavy 1.2
nothinzine. Coking. Sediment (7) DOS 07% Phosphorous Acid +1% 2,2Bis 72 Some Moderate 4. 8
(4-hydroxyphenyl) Propane. Coking. Sludge.
As can be observed from the data in Table 2, synthetic (C) Table 5 organic ester lubricants containing the present additive composed of a hindered phenol and an inorganic phosphorous compound display various improved properties such as resistance to coking and sludge formation.
EXAMPLE 3 Various standard tests were effected on a di(2ethylhexy1)sebacate lubricant base stock containing varying amounts of 2,6-ditertiarybutyl-p-cresol and phosphorous acid to show the synergistic efiect of these two additives. The results of the various tests are summarized by the data set out in Tables 3 to 6 below.
(A) Table 3 CONDITION OF OXIDIZED DI(2-ETIIYLHEXYL) SEBACATE AFTER 347 F. CORROSION AND OXIDATION TEST Percent of 2,6-DitcrtiarybutyLp-Crcsol Percent Phosphorous cid 0.000 Broom, Brown, Brown, Brown,
Solid. Sludgy Sludgy Sludgy. 0.001 Brown, Brown, Sludgy Clear 0.050 do Light Deep Red,
Orange, Clear. Clear. 0.100 d0 Orange, Clear.
A sample consisting of 96% by Weight of di(2-ethylhexyl) sobacate, 3% by weight of tricresyl phosphate, and 1% by.
weight of phenothiazine was sludgy and sediment formed during the standard 347 F. corrosion and oxidation test. The data in Table 3 demonstrates the action of the present additive system in preventing the formation of sludge in oxidized ester lubricants.
(B) Table 4 ACID NUMBER RISE OF DI(2-ETHYLHEXYL) SEBACATE AFTER 317 F. CORROSION AND OXIDATION TEST Percent of 2,6-Ditertiarybutylp Cresol Percent Phosphorous Acid The data in Table 4 demonstrates the action of the present additive system in preventing acid number rise in synthetic ester lubricants subjected to the oxidizing conditions of the standard 347 F. corrosion and oxidation test.
PERCENT RISE OF F. VISCOSITY OF DI(2-ETHYL- HEXYL) SEBAGATE AFTER 317 F. CORROSION AND OXIDATION TEST Percent of 2,rDitertiarybutylp-Crcsol Percent Phosphorous Acid Solid 193 17 The data in Table 5 demonstrates the action of the present additive system in preventing viscosity rise in synthetic ester lubricants subjected to the standard 347 F. corrosion and oxidation test.
(D) Table 6 LIETAL CORROSION OBSERVED IN DI(2-EIHYLI EXYL) %I%1g%CATE AFTER 347 F. CORROSION AND OXIDATION Percent Percent 2,6-Ditertiarybutyl-p-Cresol Phosphorous 0.000 Heavy Magne- Heavy Magne- Heavy Magneslum Corrosion. siuin Corrosion. sium and Moderate Copper Corrosion. 0.050 Heavy Magne- Moderate Mngnc No Corrosion to slum and Modsium Corrosion. any crate Copper Metals. Corrosion.
The data in Table 6 demonstrates the action of the present additive system in preventing metal corrosion in synthetic ester lubricants subjected to the standard 347 F. corrosion and oxidation test. The test included standard test metal samples of copper, a mild carbon steel, an aluminum alloy, a magnesium alloy and a cadmium plated steel.
EXAMPLE4 aoeaeee weight of tricresyl phosphate (TCP) and 1% by weight of phenothiazine (PTZ).
Table 7 SOD Base Stock Additive Lead Wt. Loss, mg./i11.
(1) DOS 1% BET +0.07% +0.8
Phosphorous c1 (2) TMPD-DP do +0.4 (3) DOA do +0. 7 (4) (96% DOS+3% TCP+1% PTZ) 15 l The data in Table 7 demonstrates the anti-corrosive properties the present additive system lends to synthetic ester lubricants. The SOD lead corrosion test was designed to indicate corrosion to bearings that might be caused by lubricants and/or their additives. The superiority of the present additive system in combination with synthetic ester lubricants over the lubricant composition consisting of DOS, TCP and PTZ is pointed up by the data in Table 7. 7
EXAMPLE A sample of di(2-ethylhexyl)sebacate (DOS) containing 1% by weight of 2,6-ditertiarybutyl-p-cresol (BHT) and 0.07% by weight of phosphorous acid, and a sample consisting of 96% by weight of di(2-ethylhexyl)sebacate (DOS), 3% by weight of t'ricre'syl phosphate (TCP) and 1% by weight of phenothiazine (PTZ) were subjected to the standard Panel Coking Test at varying elevated tem The panel coking test gives an indication of the quantity of coking that would be expected to collect in aircraft feed lines, for example, at elevated temperatures. As shown by the data in Table 8, the present additive system for synthetic ester lubricants is a substantial improvement with respect to coking over the standard DOS-TCP-PTZ mixture.
The above examples illustrate some of the improved properties of synthetic ester lubricants containing the present synergistic additive system composed of a hindered phenol and an inorganic phosphorous compound. The present invention thus provides a new and useful combination in the lubrication arta particularly useful combination for use in turbo-prop and turbo-jet aircraft engines requiring lubricants having high load carrying ability.
Although the invention has been described in detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims,
1. A synthetic lubricant composition comprising a major amount of an organic carboXylic acid ester selected from the group consisting of 2,2,4-trirnethyl-1,3-pentanediol pelargonate and di(2-ethylhexyl)sebacate and .1% to 5% by weight basedon said ester of 2,6-ditertiarybutyl-pcresol and 001% to .4% by weight based on said ester of an inorganic phosphorous compound selected from the group consisting of phosphorous acid and phosphoric acid.
2. A synthetic lubricant cmposition comprising a major amount of di(2-ethylhexyl)sebacate and .5% to 5% of 2,6 ditertiarybutyl phenol and 01% to .1% of phosphorous acid based on the weight of said di(Z-cthylhexyDsebacate.
3. A synthetic lubricant composition comprising a major amount of di(2-ethylhcxyl)sebacate and 5% to 5% of 2,6-ditertiarybutyl-p-cresol and 01% to .1% of phosphoric acid based on the weight of said di(2-ethylhexyl)sebacate.
4. A synthetic lubricant composition comprising a major amount of 2,2,4-trimethyl-1,3-pentanediol dipelargonate and .5% to 5% of 2,6-ditertiarybutyl-p-cresol and 01% to .1% of phosphorous acid based on the weight of said 2,2,4-trirnethyl-1,3-pentanediol dipelargonate.
References Cited in the file of this patent UNITED STATES PATENTS 2,119,240 Lyons May 31, 1938 2,215,956 Downing et a1 Sept. 24, 1940 2,417,281 Wasson et a1 Mar. 11, 1947 2,622,066 Jehle Dec. 16, 1952 2,798,083 Bell et al July 2, 1957 FOREIGN PATENTS 743,571 Great Britain Ian. 18, 1956