US2203102A - Lubricant - Google Patents

Description

Patented June 4, 1940 LUBRICANT I Kenneth P. Powers, Pittsburgh, Pa., assignor to Gulf Research 8; Development Companm'littsburgh, Pa., a corporation of Delaware No Drawing. Application January 18, 1938, Serial No. 185,625

9 Claims.

This invention relates to lubricants and it comprises as an improved lubricant a hydrocarbon oil containing an oiliness agent and an organic ester or thioester of a phosphorous acid, the

oiliness agent and ester being. present in such amounts and such relative proportions as to impart to the lubricant a greater degree of lubricity than is imparted by either the oiliness agent or the ester alone in the same amount; all as more fully hereinafter set forth and as claimed.

The purpose of lubrication is, of course, to-reduce friction between metallic bearing surfaces in. motion relative to each other. As is well known by specialists in this art, a lubricant employed for thepurpose of reducing friction between relatively moving metallic bearing sur faces may function in two ways. The two ways are commonly referred to as thick-film" lubrication and thin-film lubrication.

faces-are completely separated by a relatively thick continuous film of lubricant and when friction between the moving parts is measured, the results obtained are independent of all factors except pressure, speed, and viscosity of the lubricant. I

Thin-film lubrication refers to a border line condition wherein the bearing surfaces are so close together that there may be momentary contact between them. In thin-film lubrication, friction depends on the composition of the lubricant as well as its viscosity. Under thinfllm" conditions the coefficient of friction increases rapidly with each slight further increase in pressure or decrease in viscosity or speed.

v'I'he most common lubricants presently employed are petroleum oils and these are satisfactory for most purposes, particularly under conditions 'of thick-film" lubrication. Petroleum lubricating oils are, however, susceptible of improvement as lubricants under thin-film" conditions, both with respect to maintaining a relatively low coeflicient of friction under thiniilm" conditions and also with respect :to increasing the maximum bearing load which can be safely carried by the oils without complete breakdown resulting in seizure or scoring of the bearing surfaces.

Thus, in the past, certain agents have been 5 added to petroleum oils for the purpose of in-' creasing the oilines's" of the oil, 1. e., reducing the coeflicient of friction under thin-film conditions, and certain agents have-been added for the purpose of increasing the maximum bearing 55 load which can" be carried by the lubricant. 4 There are, for example, certainagents, commonly known .as oiliness. agents" which have the effect, when incorporated in small amounts in petroleum lubricating oils, of reducing the coeilicient 'of friction under thin film conditions.

In "thick-film" lubrication the bearing sur- Among these known oiliness agents, there may becited high molecular weight fattyacids, fatty acid esters, alcohols, ketones, oxidized paraflin waxes, other oil-soluble, polar compounds of carbon, hydrogen, and oxygen, certain halogenated hydrocarbons, halogenated fatty acid esters, chlorinated fatty acids and certain sulfur containing organic compounds such as sulfurized mineral oil.

While such oiliness agents have been used for the purpose of increasing the oiliness or lubricity of petroleum oils, such use is always of necessity a compromise. The beneficial effect upon the lubricity of the lubricant of course increases within certain limits as the amount of oiliness agent added is increased, but there are definite limitations upon the amount of such agents which can be added to individual lubricating oils. For one thing,. many of these agents are relatively expensive and the increase in beneficial effect obtained may not justify the addition of more than a limited amount of the oiliness agent to a given oil for a given purpose. Again, some of these agents, such as stearic acid, are of very limited solubilityin petroleum lubricating oils and the amount added to the oil may have to be very small in proportion to the oil in orderto prevent the oil from assuming a cloudy or hazy appearance. Any excess of such an agent over and beyond that amount which will be soluble in the oil under ordinary operating and storage conditions represents an inefficient and undesirable condition. Moreover, increasing amounts of such addition agents often render the lubricating compositions thereby obtained more susceptible to oxidation and sludging, and many of these oiliness agents if present in more than very limited amounts may exhibit an undesirable tendency to attack bearing surfaces or other metal parts in contact with the lubricating composition.

The various oiliness agents mentioned above differ among themselves with regard to their effect upon the load carrying capacity of the oils to which they are added. Some improve the load carryingcapacity of petroleum oils when added .thereto and others do not. They are primarily characterized by their beneficial effect in lowering the coeiiicient of friction under thin-film conditions. v

By the term oiliness agen as hereinafter employed in the description and claims I mean an oil-soluble organic polar compound which,-

when incorporated in small amounts in petroleum lubricating oils effects a reduction in the coefllcient of friction under "thin-film condi- 'tions.

' There is, another class of additionagents,

which has been usedto some extent in petroleum ing capacity of the oil without regard to oiliness or ability to maintain a low coemcient of frlcscoring is increased. Usually, added mildEP compounds effect little or no reduction in the coefficient of friction underthin-film conditions, while in most instances they actually increase it.

I have discovered that a much lower coeflicient of friction is secured when a lubricating oil contains not only a minute quantity of an oiliness agent, as defined, but also certain oil-soluble esters and thioesters of phosphorus coming under the general category of mild EP additions. In the presence of both the oiliness agent and the mild EP agent, the lubricating properties of the oil are much improved; the improvement being much more than the sum of the two several efiects.

For example, the oil-soluble esters and thioesters of the acids of phosphorus, such as tricresyl phosphate, improve lubricating oil by imparting mild EP characteristics, increasing the load carrying power and inhibiting corrosion of sensitive bearing alloys. But an oil containing only a phosphorous ester exhibits a higher coeflicient of friction and to this extent is less adapted for thin film work as it is less oily.

In the present invention I utilize the stated discovery in adding to a hydrocarbon oil both an oiliness agent such as stearic acid, and an ester or thioester of phosphorus such as tricresyl phosphate. In the new oil, the friction between bearing surfaces is lower instead of being in creased as is the case when tricresyl phosphate amyl-phenyl-phosphite, mono-butyl-di-phenyb;

phosphite, mono-cresyl-di-propy1-phosphite, diphenyl-phosphite, and other alkyl, aryl, alkaryl, and mixed alkyl-aryl esters of phosphorous acid and phosphoric acid. Thio esters of these acids, such as tri cresyl mono thio phosphate, tri-cresyl-di-thio-phosphate, tri-cresyl-tri-thiophosphate, tri butyl tri thio phosphate, and other alkyl-aryl, alkaryl and mixed alkyl-aryl thio esters prepared from thio alcohols and thio phenols by reaction with PClalor POCld are also within this category.

As examples of specific oiliness agents within the purview of the present invention I may cite stearic acid, oleic acid, tallow oil, oxidation products of parafiin waxes, alcohols or ketones of high molecular weight, sperm oil, sulfurized mineral oils, fatty acid esters such as methyl stearate,

The maximum load under which Advantageously, the hydrocarbon lubricating 4' oil is chosen with a view toward the ultimate application of the lubricant. For instance, where a gear lubricant is contemplated, the lubricating oil used may advantageously be a cylinder stock having an S. A; E. rating of 70. Where lubrica tion of aircraft engines is contemplated, the oil chosen is advantageously a cylinder stock having an S. A. E. rating of 60, while for lubrication of other internal combustion engines, the oil chosen may be any one of the lubricating oil distillates or blends at present in common use.

In general, I find it unnecessary and usually undesirable to add more than 2 per cent of oiliness agent by weight of the oil. With most of the known oiliness agents 1 per cent by weight or less is suilicient, while with certain compounds the effect desired is produced by as little as 0.05 per cent. Using 95 per cent pure stearic acid, I find that an advantageous amount to use is 0.06 per cent by weight of the lubricating oil. Other oiliness agents such as oleic acid, lard oil, high molecular weight ketones. less pure stearic acid, ete., generally require addition to the oil in larger amounts in order to achieve an eifect commensurate with stearic acid. For instance, 0.2 per cent of oxidized and neutralized paraflin wax does not reduce the coeiilcient of friction as much as 0.1 per cent double pressed stearic acid, while, in turn, 0.1 per cent of 95 per cent stearic acid reduces the coemcient of friction more than either of the agents abovein the given concentrations.

As before stated, the amount of oiliness agent to be added varies with its effectiveness in increasing the lubricity, with cost, solubility, and

tendency to sludge, etc.

I add the phosphorous ester to the lubricating oil in amounts of not more than 2 or 3 per cent by weight of the oil. The amount added varies to some extent with the oil employed, the particular phosphorous compound employed and the amount and character of the oiliness agent-used. No exact rule can be given, but in actual embodiments of the invention I-have employedto advantage phosphorous esters in percentages between 0.05 per cent and 3 per cent by weight of the oil in combination with Pennsylvania cylinder stocks and distillates containing stearic acid, oleic acid, oxidized and neutralized paraflin waxes, phenoxyphenyl alkyl ketone, chlorinated naphthalene or acidless tallow oil as the oiliness agent. Upto 3 per cent by weight of phosphorous ester usually effects an improvement in the lubricity of the oil when containing oiliness agents, but in the higher ranges of concentration the effect is usually less marked. The most effective range of concentrations for the phosphorous ester I have found to be between 0.05 and .5 per cent by weight of the petroleum oil, particularly when used with stearic acid as the oiliness agent.

The lowering of friction produced by the addi tion of phosphorous esters to oils containing oiliness agents was hitherto unexpected. It'would' be expected that the effect on lubricity would be ,the arithmetical sum of the efiect produced by the individual addition agents. However, I have made the unexpected discovery that when combined with oiliness agents in accordance with the principles of this invention, phosphorous esters exert a peculiar effect. The net efiect of the phosphorous ester and the oiliness agent is not the sum of the two individual effects. It is something better. Thus, for example, the addition of 0.06 per cent by weight of 95 per cent pure stearic acid to a Pennsylvania lubricating oil of good grade lowered the coeflicient of friction 2 per cent below the coeflicient of friction of the oil without addition. 0.1 per cent by weight of tri-phenylphosphite when added to the same oil alone increased thecoeilicient of friction 12.1 per cent. However, when 0.06 per cent of stearic acid and 0.10 per cent tri-phenyl-phosbhite were-together incorporated in the same oil the coeflicient of friction of the lubricant was reduced 9.2 per cent. I am unable to explain the effect produced by the addition of phosphorous esters to lubricating oils containing oiliness agents. However, the fact remains that the efiect is markedly consistent and beneficial. While no mathematical rule can be given as to the amounts of diflerent oiliness agents and phosphorous esters to be employed, certain rough generalizations can be made and the most eflective concentrations may be readily determined empirically.

According to the results of my investigations, using 0.06 per cent by weight 95 per cent stearic agent in the same concentration the addition of 0.10 per cent tri-cresyl-phosphate appears to be the'most advantageous concentration. Also 0.10 per cent is most eflective with respect to tri-paraamyl-phenyl-phosphite. Using 0.1 per cent acidless tallow oil as an oiliness agent the most eifec tive concentration of tri-cresyl-phosphate in combination therewith proved to be 3.0 per cent and this concentration was also most effective when the concentration of tallow oil was increased-to 2 per cent.

In the tables below there are shown the results of numerous tests made to compare the effect of combinations of difl'erent oiliness agents with different phosphorous esters and to determine the relative lowering in the coefllcient of friction produced by varying the concentrations of each, the variations in coeflicients of friction being referred back to the coemcient of friction obtained with the base oil alone. r

The tests are divided into three groups; those in'which the base oils employed are residual oils having an S. A. E. rating of 60 such as the oils commonly employed for lubrication .of aircraft engines; those in which the base oils employed are residual oils having an S. 'A. E. rating of '70 such as those commonly employed for lubrication of gear mechanisms; and those in which the base oils employed are distillate oils having an S. A. E. rating of such as oils commonly employed as winter crankcase lubricants for automobiles.

refined with aluminum chloride.

Table 1 Static coefficient of friction Oilincu agent and amt. added in percent by weight a g Per cent of base d] on) 7 Welsh 3888' Base increase on oil or decrease I I add. produced byaddition sauce BM acid (06% pur 00 0. 108 0. 104 2. 0 Y Ta... h... 2-1:: as a:

I p p I Steal-lurid (06% pure) 0.00 -do 0.06 0.204 0. 174 -14. 7 0n 00 0. l0 0. 204 0. 157 -2a 0 D 0.20 0. 204 0. 168 17. 0 no 0. 60 0. 204 0. 111 -10, 1 1): 1.00 0. 204 0. 17.3 15. 2 no Tri wron I 1 31 53 3' 4 3' it 1 -pars- -am phenyl phosp to. y Madd 0.10 do 0.10 0.204 0.160 --i7.l Mixtnrcol- I hthalcncandakatone..- 0.10 0.177 0. 166 -6.2 Mixtum M diamonds: in ii Trla'esyl 1100 hate 0 10 i i e no.-. p p Husdilctmphtlnknc 0.10 do 0.10 0. 177 0.145 --18. 1 0. 10 0. 108 0. 222 +12. 1 0. 06 0. 00 0.207 0. 102 -7. 2 0.00 0.10 0.201 0.188 -0.2 0. 00 0. 20 0. 2m 0. 184 11. 1 0.00 0.40 0.207 0.177 -14.5 0. 00 110 0. 207 0. 101 -7. 7 0.10 0.181 0.170 -2.8 0.10 'lricresylphosphaie.-- 0.80 0. 1131 0. 107 0.s 'lriphenyl phosphate. 0. a 0. ate 0. 207 +11. 0 ns' 02 T11 11 1 11' hite 05 8'3? 137 p ,eny osp Steal-1c add (double plus) 0. 1 p 0. 206 0. 212 -20. 3 D 0. 1 Triphenyl phosphite-- 0 5 0. m0 0. 180 20. 0

s.A.E.20 oxuham memu mmnw a2 0.203 0.100 '-1.0.

D 7 y 0.2 Triuesylphosphatc... 0.1 0. 203 0.101 6.8

acid the most advantageous concentration of triphenyl-phosphite to be added appears to be about 18 with the same oil alone. with the same oiliness In the above tests, the coefllcients of friction were determined by the'method of Herschel at; room temperature and with a, bearing combination of steel to steel.

The following examples show various specific embodiments illustrative of'compositions within the purview of my invention.

Example 1 Oils prepared according to the following formulae are particularly adapted for lubrication of gear mechanisms:

" Per cent by weight Penna. cylinder stock (S. A. E. 70) 99.5 Double pressed stearic acid 0.1 Tri-phenyl phosphite 0.4 Penna. cylinder stock (S. A. E. '70) 99.5 Double pressed stearic acid 0.1 Di-phenyl phosphite 0.1 Pe a.- cylinder stock (S. A. E. 70) 99.4 Do le pressed stearic acid 0.l. Tri-cresyl-mono-thio-phosphite 0.5 Penna. cylinder stock (S. A. E. 70) 99.84 per cent stearic acid 0.06 Tri-cresyl phosphate 0.1

Penna. cylinder stock (S. A. E. '10) 99.8 Double pressed stearic acid"--. 0.1 "I'ri-butyl-tri-thio-phosphate 0.1

Penna. cylinder stock (S. A. E. '10) 99.4 Acldless tallow oil 0.2 iIri-phenyl-phosphate 0.4

Example I! Lubricating compositions effective for crankcase lubrication of air-craft engines may be compounded according to the following formulae:

Per cent by weight Penna. cylinder stockis. A. E. 60) 99.54 95 per cent stearic acid 0.06 Tri-phenyl-phosphitm. 0.4 Penna. cylinder stock (S. A. E. 60) 99.82 95 per cent stearic acid 0.06 Tri-cresyl phosphate r 0.12

Penna. cylinder stock (S. A. E. 60) 99.8 95 per cent stearic acid 0.1 Tri-para-tertiary-amyi-phenyl phosphite 0.1

Penna. cylinder stock (S. A. E. 60) 99.7 Hexachlornaphthalene 02 Tri-cresyl phosphate 0.1

Example III Lubricating compositions prepared according to the following formulae are effective for lubrication of automotive engines: I a

Per cent by weight Penna. distillate (S. A. E. 20) 99.82 95 per cent stearic acid 0.06

Tri-para-tertiary-amyl-phenyl phosphite... 0.12

In the preparation of the above lubricants, Mid-Continent or coastal oils may be substituted in placeof Pennsylvania oils, other oiliness agents may be substituted for those disclosed and other phosphorous esters may be substituted for the compounds specifically described, without departing from the scope of the invention. The determination of the amounts of such equivalent amazon agents to be added will be facilitated by reference to Table 1 above. I

I find it advantageous to use stearic acid as the oiliness agent where possible because only very small concentrations are required to produce the desired effect. Whenit is desired to impart mild extreme pressure properties to the lubricating composition I ordinarily employ esters of phosphoric acid, but when the compositions are used to lubricate sensitive bearing alloys I flnd it advantageous to employ the'esters of phosphorous acid as they are beneficial in inhibiting corrosion of sensitive metals. The phosphite esters also stabilize the lubricating composition and inhibit deterioration due to'oxidation under accelerated conditions.

What I claim is:

1. An improved lubricant comprising a petroleum lubricating oil containing in admixture therewith between 0.05"and 0.1 per cent stearic acid and between 0.05 and 0.5 per cent by weight of a mild extreme pressure agent selected from the class consisting of esters and thioesters or.

by the addition thereto of approximately 0.06 per cent by weight of stearic acid and 0.1 per cent tricresyl-phosph'ate.

5. An improved lubricant comprising a petroleum lubricating oil containing' 0.05 to 0.5 per cent by weight of a high molecular weight fatty acid and 0.05 to 0.5 per cent by weight of an aryl ester of a phosphorous acid; said improved lubricant having a lower coefilcient of friction between metallic bearing surfaces under thin-film conditions than obtainable with a lubricant consisting of said lubricating oil and said fatty acid alone in like amount. g

' 6. The improved lubricant of claim 5 wherein said ester is a phosphateemfl '1. The improved lubricant of claim 5 wherein said ester is a phosphite.

8. An improved lubricant comprising a petroleum lubricating oil containing in admixture therewith 0.05 to 2.00 per cent by weight of a high molecular weight fatty acid and 0.05 to 3 per cent by weight of a mild extreme pressure agent selected from the class consisting of esters and thin-esters of phosphorous acids, said improved lubricant having a lower coeflicient of friction .be-

tween metallic bearing surfaces under thin-film conditions than obtainable with a lubricant consisting of said lubricating oil and said fatty acid alone in like amount.

9. An improved lubricant comprising a petroleum lubricating oil containing in admixture therewith 0.05 to 0.5 per cent by weight of a high molecular weight fatty acid and 0.05 to 0.5 per cent by weight of a mild extreme pressure agent selected from theclass consisting of esters and thio-esters of phosphorous acids and capable of lowering the coeflicient of friction of the mixture of said lubricating oil and fatty acid alone as measured between metallic bearing surfaces under thin-film conditions. K

KENNETH P.

CERTIFICATE OF CORRECTION. Patent No. 2,205,102; 1 Jun- 1;, 19km KENNETH P. POWERS.

It is hereby certified that error appears in the printed specification of. the above numbered patent requiring correction asiollows: Page 1, first column, line 14., page 2, first column, lines 5515\nd. 50, same-page, second column, lines 11, 14.9, 55, 57, 6h, 69 -and 71+, page 5,":tirst column, lines 6, 8, 23 and-28, same page, second column, line 15, page 14., first column,

line 2,andsame page, secondcolumfi, lines 21+, 11.1, 57 and 69, claims 1,

5, 8 and 9 respectively, for "phosphorous" read --phosphorus-} and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 25rd day of Ju1y,-A. 'D. 1914.0.

Henry Van Arsdele (Seal) Acting dominis ioner of Patents.