CA2659854C

CA2659854C - A low phosphorus lubricating oil composition having lead corrosion control

Info

Publication number: CA2659854C
Application number: CA2659854A
Authority: CA
Inventors: Alexander B. Boffa
Original assignee: Chevron Oronite Co LLC
Current assignee: Chevron Oronite Co LLC
Priority date: 2006-08-09
Filing date: 2007-08-08
Publication date: 2016-05-10
Anticipated expiration: 2027-08-08
Also published as: WO2008021901A2; JP2010500457A; EP2049631A2; WO2008021901A3; EP2049631A4; US20130137616A1; EP2049631B1; CA2659854A1; US20080039348A1; JP5345935B2

Abstract

The present invention provides a low phosphorus lubricating oil composition containing a mixture of zinc dithiophosphates in a certain ratio surprisingly yields improved lead corrosion. The synergistic combination of mixed zinc dithiophosphates containing a zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate in a respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiphosphate to zinc secondary dialkyl dithiophosphate from about 2:1 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate from about 6:1 to about 1:1. When used in a lubricating oil composition having a total phosphorus content less than about 0.06 wt %, based on the total weight of the lubricating oil composition to lubricate internal combustion engines. The mixture of zinc dithiophosphates greatly reduces lead corrosion.

Description

A LOW PHOSPHORUS LUBRICATING OIL COMPOSITION HAVING LEAD
:CORROSION CONTROL
Thepresentinvention is related, in part, to a lubricating oil composition.
More particUlarly, the presentinvention relatesito a low phosphorus lubricating oil composition employing a Mixture of zinc dithiophosphates and wherein the lubricating oil composition has less than about 0.06 wt % total phosphorus content-based on the total weight of the lubricating oil composition. The low phosphorus lubricating oil composition of The present invention is effective in lead corrosion control when Used as a lubricating oil Composition in internal combustion engines:
BACKGROUND OF THE INVENTION
Emissions arising fromautornotiveexhaust has been a problem for several decades and approaches for addressing this problem have included the use of unleaded fuel (to deal, in part, with lead pollution ariting from leaded fuels), oxygenated fuel (to reduce hydrocarbon emissions), the use of catalytic converters (also to reduce .hydrocarbon emissions), etc.
Catalytic converters are now universally employed with gasoline powered vehicles and the efficiency of these converters is directly related to the ability of the catalyst to effect conversion of unbyrnt orliertially burnt hydrocarbons generated during .combustion to carbon dioxide and water. One problem arising with the use of such converters is poisoning of the catalyst resulting in reduced catalyst efficiency. Since catalytic converters are intended for extended use, catalyst poisoning results in higher levels of atmospheric discharges of pollutants from internal combustion engines over prolonged periods of time.
In Order to minimize such poisoning, the industry has set standards for both fuel and lubricant contents. For example, standards for fuels have included the use of unleaded gasolinein order to .avoid lead poisoning of the catalyst as well as lead discharge into'the anVironment. SpejorexaMple, Buckley, Ill; "Long Chain Aliphatic:HydrocarbytAmine AdditiVes Having an Oxyalkylene Hydroxy Connecting Group''., U.S..Patent No. 4,97,5,096, issued December 4, 1990.
As to the lubricants, one additive family currently be addressed by industry Standards1S the phoSphorus-containing additives such as zinc dithiophosphate wear inhibitors used in lubricant compositions employed to lubricate internal Combustion engines. Specifically, phosphorus-containing additives reach the catalytic:converteras a result of, for example, exhaust gas recirculation and/or oil blow-by prOCesses as well as other methods known in the art. See, for eXample, Beck, et al. "Impact of Oil-Derived Catalyst Poisons on FTP Performance of LEV
Catalyst Systems", SAE Technical Paper 972842 (1997) and Darr et al. "Effects of Oil-Derived Contaminants on Emissions fromTWC-Equipped Vehicles", SAE
2000-01-1881 (2000). In any event, the phosphoruS is known to accumulate in the catalytic converter, at active Metal sites; thus reducing catalyst efficiency and effectively over time, poisoning the catalyst. As a 'result of the above, a new focus is to lower phosphorus in the lubricating oils. For example, the draft specifications for lubricant compositions have proposed significantly lower phosphorus contents than heretofore employed.
A problem.arises when the level of phosphorus is: reduced in a lUbricant composition containing an oil-soluble, phosphorus-containing, anti-wear compound in that there is a, significant reduction in anti-wear performance arising from this diminution, in phosphorus content. One well known class of antiwear additives are metal'alkylPhoSphates, especially zinc dialkyl dithiophosphates, are generally employed. in lubricating oils at phosphorous levels above 0.1 weight percent when used for wear control. At lower levels, it is not found to be an effective antivvear additive. For instance, as exemplified. in U.S. Patent NO.

6,696,393, issued February 24 2004, 'lowering the level Of phosphorus due to the presence of a metal dithiophosphate additive in a lubricant composition by one-half from 0.095 weight percent .to 0.048 weight percent phosphorus results in about a seven-fold increase ihengine wear.
Zinc dithiophosphates have either dialkyl or diary' groups. Zinc dialkyl dithiophosphates aro further subdivided into primary allsyl and secondary alkyl

2 zinc dithiophosphatee. Pentan-1-ol and 3-methylbutan-2-ol are illustrative of the primary and secondary alcohols used to prepare primary and secondary zinc dithiophosphates. Different zinc dithioPhosphate chemical types perform differently (See below).
Performance Parameters of Zinc Dithiophasphate Types Primary Alkyl Secondary Alkyl Aryl ThermatStability.
Medium =Low High Antiwear Protection' MediuM 'High Low Hydrolytic Stability Medium High Low Each type has important applications in modern additive packages. It it therefore important to have the right rnik of zinc dithiophosphatesin any, given lubricating oil composition to provide adequate anti-wear performance anciat the same time keeping the phosphorus levels, due to the presence of a metal dithiophosphate additive, below.0:.:1 wt %-because phosphorus has a-tendency to accumulate in the catalytic converter thus reducing catalyst efficiency, poisoning the catalyst.
,SUMMARY OF THE INVENTION
As previously mentioned, the present invention is related, in part, to a lubricating oitComposition. More particularly, the present invention relates to a low phosphorus lubricating oil composition employing a mixture of zinc dithiophosphates in a certain ratio and wherein the lubricating oil composition has less than about 0.06 wt % total phosphorus content, based on the total weight of the 'lubricating oil composition. The low phosphorus lubricating oil composition of the present invention is effective in lead corrosion control when used as a ,55- lubricating oil composition in internal Combustion engines.
Accordingly, in its broadest aspect, the present invention is related to a =lubricating:oil composition comprising a major amount of base oil of lubricating

3 viScosity arida minor amount Of a mixture ofa zinc primary dialkyl dithiophosphate, a zinc,secondary dialkyl dithiophosphate and a zinc diaryl dithiophO4hate wherein 'the respective, ratio, based on the phosphorus content, Of the.zinc primary dialkyl.dithiophosphate to zinc secondary dialkyl dithiophosphate is frorn abOUt 2:1 to abbut 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diary' dithiophosphate is from about 5:1 to about 1:1 and wherein the total phosphorus content of the lubricating, oil composition is less than about 0.06 wt %, based on the total Weight of the lubricating oil composition.
The minor amount Of the mixture of a zinc primary .dialkyl dithiophosphate, a zinc secondaryclialkyl dithiophosphate:,anda zinc diary' dithiophosphate employed in.
the lubricating oil composition of the present invention is from about 0.1 wt % to about 1.5 wt %, 'preferably from about 0.3 wt A) to about 1.2 wt % and More preferably about 0.5 wt % to about 1.0 wt %, based on the total weight of the lubricating oil composition.
The lubricating oilcomposition of the present invention Will contain from about 0.05 wt % to about 1:2 wt % ofa zinc primary dialkyl dithiophosphate,.from about 0.05 wt % to about,1.2 wt % of a zinc secondary dialkyl dithiophosphate and from about 0.02 wt % to about 0.7 wt %Iof a zinc diaryl dithiophosphate, based on the total weight of the lubricating oil coMposition. Preferably, the lubricating oil Composition of the present invention=will contain from about 0.1 Wt % to about 0.7 wt % of aginc primary dialkyldithiophosphate, from about 0.1 wt % to about 9.7 WI % of a zinCsecondary dialkyl dithiophosphate and from about 0.05 wt % to about 0.5 wt % of a zinc diaryl dithiophosphate, based on the total weight of the lubricating oil composition. More preferably, the lubricating oil composition Of the present invention will contain from about 0.2 wt % to about 0.5 wt A) of a zinc primary dialkyl dithiOphosphate, from about 0.2 wt % to about 0.5 wt Y9 of a zinc secondary dialkyl dithiophosphate and from about 0.1 wt % to about 0.3 wt % of a zinc diaryl dithiophosphate, based on the total weight of the lubricating oil composition.

4 .5 The primary alkyl group of the zinc primanidialkyl clithiophosphate has from about Ct to about C13 carbon atoms., preferably froen about C3 tO about Ciocarbon atoms and more preferably, from about C6 to about C8 carbon atoms.
The teccm.dary alkyl =group of the zinc secondary dialkyl dithiophosphate has from about C3 to aboutCis carbon atotns, preferably from about C3 to about C8 carbon atotns and more preferably, from about Cs to about C6 carbon atoms.
The aryl group of the zinc diaryl dithiophosphate has from about C6 to about carbon atoms-preferably frorn'about C6 to about C24 carbon atoms and more preferably, from aboUt C6 to about C26 carbon atoms.
In a .preferred embodiment .the respective ratio, based on the phosphorus content, of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is from to about 2:3. More preferably, the ratio is about 1:1.
In a preferred embodiment, the respective ratio, based on the phosphorus content, of the mixture of zinc primarydialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate,to zinc diaryl dithiophosphate is from abOut 4:1 to about 11. More preferably,, the ratio is about 2:1.
In an especially preferred embodiment, the respective ratib, based on the phosphorus content, of the mixture of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate to.zinc diaryl dithiophosphate is 1:1:1.
.30 In 'another embodiment, the total 'Phdsphoruscontent.in-the lubricating oil composition of the present invention is preferably less than about 0.05 wt %, more preferably, based on the total weight of the lubricating oil composition.
In still another embodiment, the sulfur content in the lubricating oil composition of the.present invention is less than about 0.5 wt % and', preferably, less than about 0.2 wt /0, based on. the total weight...of the lubricating-oil composition and the total sulfated ash content in,the lubricating oil .composition of the present invention is

5 less than about 1.2 wt %, preferably, less than about 1.0 wt %, and more, preferably less than about 0.8 wt %, based on the total weight of the lubricating oil COmP,osition.
In One of its method aSPeCts, the Present invention further relates to a method for improving lead corrosion. The method involves operating an internal combustion engine with a lubricating oil composition comprising a major amount of base oil of lubricating viscosity and a minor amount of a Mixture of a zinc primary dialkyl clithibphoSphate, a zinc secondary dialkyl dithiophosphate and a zinc diaryl dithiophosphath wherein the respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is,from.aboUt.2:1 to-about1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diary' dithiophosphate is from about 6:1 to about 1:1 and wherein the total phosphorus content of the lubricating. oil composition is less than about 0.06 wt /0, based on the total vveight,of the lUbriCating.Oil composition.
Among,other factors, the Presertinvention provides a iow phosphorus lubricating Oil composition containing:a mixture of zinc dithioPhosphates in a certain ratio surprisingly yields improved lead Corrosion. The mixture of zinc dithiOphospates contains a zinc primary dialkyl dithiophosphate, a zinc secondary dialkyl dithiophosphate and a zinc diary! dithiophosphate. The synergistic combination of mixed zinc dithiophosphates wherein the respective ratio, based on the phoSphorus content, of the zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is from about 2:1 to abOut 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary 'dialkyl =dithiophosphate to Zinc diaryl dithiophosphate is from about 6:1 to about 11 when used:in a lubricating oilcomposition having a total phosphorus content less than about 0.06 wt %, based on-the total Weight Of the lubricating oil composition, greatly reduces lead corrosion when used to lubricate internal combustion engines:

6 DETAILED DESCRIPTION OF THE INVENTION
The present invention is related, in part, to a lubricating oil composition.
More particularly, the present invention relates to a low phosphorus lubricating Oil compositiOn employing, a Mixture of zinc dithiophosphates Containing a zinc primary dialkyl dithiophosphate, a zinctecondary dialkyl clithiophosphate and a zinc diary! dithiciphosphate wherein the respective :ratio, based on the phosphorus content; of the zinc primary clialkyl dithiophosphate to zinc secondary dialkyidithiophosphate is from about2:1-to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate,and zinc secondary dialkyl "clithiOphosphate to zinc diaryl dithiophosphate is from about 6:1 to about 1:1 and wherein the lubricating oil Composition hasless than about 0.06 wt % total phosphorus content, based on the total weightof the lubricating oil composition.
The low phosphorus lubricating oil composition of the present invention is .
effective in lead cOrTosion control when usedas a lubricating oil in internal combustion engines.
Each of these components in the claimed composition will be described in detail herein. However, prior to such a description, the following terms will first be defined.
The *I'M "alkyl" refers to both.straight7.and branched-chain alkyl groups.
The tprm "aryl" refers tp a subStituted or unsubstituted aromatic group, such as the phenyl, tolyl, xylyl, ethylphenyl and cymenyl groups.
The term "low phosphorus" refers to the phosphorus content of the lubricating oil coMposition of the present-invention. The phosphorus content is in the range of about 0.005 weightpercentto about,0.06 weight percent based on the total Weight of the lubricating oil composition.
The term "total phosphorus" refers td the total amount of phosphorus in the lubricant compositionregardless of whether such phosphorus is present as part of an Oil-soluble, phosphorus-containing, anti-wear compound or in the form of a

7 contaminant in the lubricant composition such as residual phosphorus remaining due to the'presence of P2S5 used to prepare metal dihydrocarbyl dithiophosphates. In either event, the amountof phosphorus permitted in the lubricant composition is independent of source. Preferably, however, the phosphorus is part of .a lubricant additive Unless otherwise specified, all percentages are in weight percent.
The Zinc Dithiophosphate Compound The lubricating oil composition of the present .invention will employ, in part, a mixture of zinc dithiophosphates. The zinc dithiophosphates are independently characterized by formula I:
/FD s ________________________________________ Zn - ?
RO
wherein each R is independently a group containing from about Ito about 30 carbon atoms, The ft groupsin thedithiophosphate can independently be about C1 to,about Ci3 primary alkyl, about C3 to about C13.secondary allsyl, and about C6Jo aboilt aryl group. Preferably, the Ft groups in the dithiophosphate can independently be about 03 to about Cio primary alkyl, about C. to about C8 secondary alkyl, and about C6 to Ob011t c:24. aryl group. More preferably, the R groups in the dithiophosphate can independently be about C6to abiput C8 primary alkyl, about C3 to about C6 secondary alkyl, and about C6 to about C20 aryl group. The R
groups may be a substantially hydrocarbon grout,. By "Substantially hydrocarbon"
is meant hydrOcarbonsthat contain substituent groups such as ether, ester, nitro, or halogen which do not materially affect the hydrocarbon character of the group.

The.IR group of thezinc dithiophosphate may be derived, for example, from a primary alcohol such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptatiol, octanol,.:nonanol, decanol, dodecanol, octadecanol, propenol, butenol, 2ethylhexanol; a,secondary alcohol such as isopropyl alcohol, secondary butyl alcOhol, isobutanol, 3-methylbutan-2-ol, 2-pentanol, 4-methy1-2-pentanol, 2-hexanol,, 3-hexanol; arnyl alcohol; an aryl alcohol such as phenol, substituted phenol (particularly alkylphenol such as butylphenol, octylphenol, nonylphenol, dodecylphenol), disubstituted phenol, Preferably the R: group will be independently a primary alkyl, a secondary alkyl or an aryl group.
Forthe,presentinvention it is contemplated that the mixture of a zinc primary dialkyl dithibphoSphate, a zinc secondary dialkyl dithiophosphate and a zinc diaryl dithiophosphate will be in a respective.ratio,:basad on the phosphorus content, in ,the lubricating oil composition of the present invention. The ratio of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate will be from about:21 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is from abOut 61 to about 1:1. Preferably, the respective ratio, based on the phosphorus content, of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiciphosphate is a range from about 3:2 to about 23, more preferably about 11 Preferably, the respective ratio, based on the phosphorus content, of the Mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is a range from about 4:1 to about 1:1, More preferably about 2:1. Most preferably, the respective ratio, based on the phosphorus content, of mixture of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is 111.
Many of the zinc dithiophosphates useful in the present invention are available commercially. However, zing clithiophosphatesare widely known in the art and a skilled artisan can readilysynthesize such compounds for the purpose of the present invention. Typically, Zinordithiophosphates can be made by initial reaction of phosphorous pentasulfide and an alcohol or phenol or mixtures of alcohols and/or phenols such as those illustrated above for the R group. The reaction involves four moles of the alcohol or phenol per mole of phosphorous pentasulfide and may be carried out within the temperature range from about 50 C to about 200 C. Thus, the preparation of 0,0-di-n-hexyl phosphorodithioic acid, for example, involves the reaction of phosphorous pentasulfide with four moles of n-hexyl alcohol at about 100 C for about two hours. Hydrogen sulfide is liberated and the residue is phosphorodithioic acid. The preparation of the metal salt of this acid may be effected by reaction with either zinc oxide or zinc hydroxide to yield the zinc dithiophosphate. Simply mixing and heating these two reactants is sufficient to cause the reaction to take place and the resulting product is sufficiently pure for the purposes of the present invention.
Patents describing the synthesis of such zinc dithiophosphates include U.S.
Patent Nos. 2,680,123; 3,000,822; 3,151,075; 3,385,791; 4,377,527; 4,495,075 and 4,778,906.
The Lubricating Oil Composition The mixture of zinc dithiophosphates of the present invention is typically added to a base oil in sufficient amounts to provide lead corrosion control in internal combustion engines. Generally, the lubricating oil composition of the present invention will contain a major amount of base oil of lubricating viscosity and a minor amount of the mixture of zinc dithiophosphates of the present invention.
Base Oil of Lubricating Viscosity Base oil as used herein is defined as a base stock or blend of base stocks which is a lubricant component that is produced by each manufacturer to the same specifications (independent of feed source or manufacturer's location); that meets the same manufacturer's specification; and that is identified by a unique formula, product identification number, or both. Base stocks may be manufactured using a variety of different processes including but not limited to distillation, solvent refining, hydrogen processing, oligomerization, esterification, and rerefining.

fierefined.stockShall be substantially free from materials introduced through manufacturing, contamination, or previous use. The base oil of this invention may be any natural orsynthetic. lubricating base oil fraction particularly those having a kinematic viscosity at.100 Centigrade ( C) and about ,4 pentistokes (cSt) to about 20 cSt: Hydrocarbon synthetic Oils may include, for example, oils prepared from the polymerization of ethylene, polyalphaolefin or PAO, or from hydrocarbon synthesis procedures using carbon monoxide and hydrogen gases such as in .a Fisher-Tropsch.process. A preferred base oil is one that comprises little, if any, heavy fractiOn, e:g., little, if any, lube oil.fraction Of viscosity about 20 cSt or higherst about 100 C. Oils used,as.the base oil will beSelected or blended depending on the desired end use and.the additives in the finished oil to give the desired grade of engine oil, e.g. a lubricating oil composition having an SAE
Viscosity Grade of OW, OW-20, OW-30, OW-40, OW-50, OW-60, 5W, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W, 10W-20, 10W-30, 10W-40, 10W-50, 15W, 15W-20; 15W-30, or.15W-4Ø
The base Oil may be derived =from.natural lubricating oils, synthetic lubricating oils or mixtures thereof: Suitable base oil includes basestocks obtained by isomerizatiOn of synthetic wax and slack-wax, as well as hydrocrackate base stocks produced by hydrocracking ftather than solvent extracting) the aromatic and polar components of the crude. Suitable base oils include those in all API
categories 1,11,111, IV and V as defined in API Publication 1509, 14th Edition, Addendum I, December 1-998. Saturates levels and viscosity indices for Group I, II and III base oils arejiSted in Table I. Group IV base oils are polyalphaolefins .(PA0). Group V base. oils includeall Other base oils not included in Group I, II, Ill, or IV. Group III base oils are preferred.

TABLE l.
SATURATES, SULFUR-.AND VlSCOSITY INDEX OF GROUP I, 11, III, IV AND
V BASE STOCKS
Saturates (As deterenined by ASTM
D007) Viscosity Index .Group `(As determined by ASTM D4294, Sulfur (As=determined by ASTM
ASTM D4297 or ASTM D3120) D2270) Less than 90 % saturates- and/or Greater than or equal to 80 and Greater than to 0.03 %,sultur less than 120 Greater than =or equal to 90 %
II saturates and less than or equal to Greater than or equal to 80 and.
tn 1 0.03 /0 sulfur less an 20 Greater than or equal to .W .0/0 III saturates and less than or equal to Greater than or equal to 120, 0.03% sulfur IV All Polyalphaolefins (PA0s) V All others not included in Groups I, II, III, or Iv Natural lubricating oils may include animal oils, vegetable oils (e.g., rapeseed oils, castor oils-arid lard oil), .petroleum oils, mineral oils, and oils derived from coal or shale.
Synthetic oils may include hydrocarbon oils-and halo-stibstituted hydrocarbon oils such as polymerized and inter-polymerized olefins, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, alkylated diphenytSulfides, as well as their derivatives, analOgues and homologue's' thereof, and the like. Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers and derivatives thereof wherein the terminal hydroxyl groups have= been modified by esterification, etherification, etc. i.tknOther suitable class of synthetic lubricating Oils comprises the ettere of dicarboxylic acids with a variety of alcohols. Esters useful as synthetic oils'also include those 'Made from about db. to about Ciz MonocarbOxylic acids and polyols and polyol ethers. Tri-alkyl phosphate ester oils such as those exemplified by tri-n-butyl 'phosphate and tri--iso-butyl phosphate are also suitable for Use base oils.
Silicon-based oils (such as the polyaryl-, polyalkoxy-, or pOlyaryloxy-siloxane oils and silicate oils) compriseanother useful Class of synthetic lubricating Oils. Othersynthetiblubri*ing Oils include liquidesters of phosphorus-containing acids, polymeric tetrahydrofUrans, polyalphaolefins, and the like.' The base Oil May be derived from unrefined, refined, rerefined oils; or mixtures thereof. Unrefined oils are obtained directly froth a natural source or synthetic .Source coal, shale, or tar sand bitumen) without further purification or treatment: Examples of unrefined oils include a shale Oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or on ester oil,obtained directly from on eSterification process, each of.which may then be =
used withoutiurther treatment. Refined oils.are.similar to the unrefined oils except:that refined oils have been' treated jn one or more purification steps to irriproVe one or more properties. Suitable purification techniques include distillation, hydrocracking, hydrOtreating, dewoXing,:solvent extraction, acid or base extraction, filtration, and percolation, all of which are known to those skilled in theart.: Rerefihed oils are obtained by treating used oils in processes similar to those used to obtain the refined oils. These rerefined gils.are also known as reclaimed or reprocessed oils and often are .additionally processed by techniques for removal .of spent additives and oil breakdown products.
Base oil derived from the hydroisornerization of wa* may also be used, either alone or in combination with the aforesaid natural and/or synthetic base oil.
Such wax isorrierate oil is produced by the hydroisomerization of natural or synthetic waxes mixtures thereof overa hydroiSomerization catalyst.
It is preferredlo use .a major amount of base oil in the lubricating oil composition of the present invention. A major amount of base oil as defined herein comprises about 40 wt % or more. Preferred amounts of base Oil comprise about 40 wt % to about 97 Wt %, preferably greater than about 50 wt % to about 97 wt A), more preferably about 60 wt % to about 97 wt % ard most preferably-about 80 wt % to about 95 wt-% of the lubricating oil composition. (When weight percent is used herein, it is referring to Weight percent of tha lubricating oil unless otherwise specified.) The amount of the mixture of zinc clithiophosphates employed in the lubricating oil composition of the present invention will be in a minor amount compared to the base oil of lubricating viscosity. Generally, it will be in an amount from about 0.1 wt % tcc,about wt %, -preferably from about 03 wt % to about 1.2 wt %
and more preferably froi-n about 0.5 M % to aboul 1.0 wt %, based on the total weight of the lubricating oil composition.
The lubricating oil composition of the present invention will contain from abOut 0.05 wt % to'about 1.2 wt %, preferably from about 01 wt % to about 0.7 wt and more preferably from about 02 wt % to about 0.5 wt % of a zinC primary dialkyl dithiophosphate, based on the total weight of the lubricating oil composition.
The lubricating oil composition-of the present invention will contain from about 0.05 wt %.to about 1.2 wt %, preferablyfrom about 0.1 wt % to about 0.7 wt A), and more preferablyfrom about 0.2 wt .% to about 0.5 wt % of a zinc secondary dialkyl dithiophosphate, based on the total weight of the lubricating oil composition.
The lubricating, oil composition of the present invention will contain from about 0.02 wt %:to about 0.7 M %, preferably from about 0.05 wt % to about 0.5 wt %, and more preferably from about al wt to about-0.3 wt 6/0 of .a zinc primary dialy1 dithiophosphate, based on the total weight of the lubricating oil composition.
In a preferred embodiment, the lubricating oil composition of the present invention will have a phosphorus content preferably less than about 0.05 wt %, based on the total weight of the lubricating oil composition.

In another erribodiment, the lubricatingoil composition of the present invention will further have a-sulfur content less than about 0.5 wt % and, preferably less.
tharrabout 0.2 wt %, based on the total weight of the lubricating oil composition and the total. sulfated ash content in the lubricating oil composition of the present invention is less than about 1.2 wt preferably; less than about 1.0 wt %, and more-preferably less than about=0.8 wt %, based on the tOtal weight of the lubricating oilcomposition.
Other Additive Components The following additive components are examples of components that can be favorably employed in combination with the lubricating additive, of the present' invention. These examples of additives are .provided to illustrate the present invention, but they are not intended to limit it, (A) Detergents are additives designed tO'hold the acid-neutralizing_compounds in solution in the oil. They are usually alkaline and, react with the strong acids (sulfuric and nitric) which forth during the combustion.olthe fuel and which would cause corrosion :to the engine. parts if left unchecked. Examples are carboxylates, sulfurized or unsulfurized alkyl or alkenyl phenates, alkyl or alkenyl aromatic sUlfonates, sulfurized or unsulfurized metal salts of multi-hydroxy alkyl oralkenyl aromatic compounds; alkyl oralkenyl hydroxy aromatic sulfonates, sulfurized or unsulfurizeci alkyl or alkenyl naphthenates, metal ,salts of alkanoicacids, Metal salts of an alkyl or alkenyl multiecids and chemical and physical:mixtures thereof.
(B) Dispersants are additives that keep soot and combustion products in suspension in the body of the oil and therefore prevent deposition as sludge or lacOtier. Typically, the ashless dispersants are nitrogen-containing dispersants formed by reacting alkenyl:succinic acid anhydride with an amine.
Examples are alkenyl succinimideS, alkenyl siaccinirnides modified with other organic con-pounds, e.g., ethylene carbonating post-treatment and alkenyl succinimides:modified-with boric adid, polysuccinirnides, alkenyl succinic ester.
(C) QxilatiOn Iribilojtors:
1) PhenOI type (phenolic) oxidation inhibitors: 4,4'-methylenebis (2,6-di-tert-butylphenol),4,4'-bis(2,6-di4ert-butylphenol), 4,4'-bis(2-Methy1-6-tert-butylphenol), 2,2'-methyleriebis(4-methy1-6=tert-butyl-phenol), 4,4'-butyldienebis(3-methy1-6-tert-butylphenol), 4,4'-isoproPylidenebis(2,6-di-tert-butylphenol), 2,2'-rnethylenebis(4,-methyl-6-nonylphenol), 2,2'-isobutyldiene-bis(4,6-dimethylphenol), 2,2'-rnethylenebis(4-methyl-6-cyClohexylphenol), 2,6-di-tert-byty1-4-methylphenol, 2,6-di-tert-butyl-4,ethylphenol, 2,4-dimethy1-6-tert-butyl-phenol, .2,6-di-tert-a-dimethylamino-p-Cresol, 2,6-di-tert-4(N,N1 dimethylorninomethylphenol),4,41-thiobis(2-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl=6-tert-butylphenol), bis(3-methyl-4-hydroxy-5-tert-butylbenzy1)-sulfide and bis (3,5-di4ert-butyl-4-hydroxybenzyl).
2) Diphenylamine type oxidation inhibitor: alkylated diphenylamine, pheny141-naphthylamine and alkylated a-naphthylamine.
3) Other types: metal dithiocarbamate (e:g., zinc dithiocarbamate) and methylenebis(dibutyldithiocarbamate).
(D).Rust Inhibitors (Anti-rust agents):
1) Nonionic polyoxyethylene surface active agents: polyoxyethylene lauryl ether;
polyOxyethylene higher alcohol ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether., polyoxyethylene ottyl stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene sorbitol monostearate, polyoxyethylene sorbitol mono-oleate and polyethylene glycol monooleate.
2) Other compounds: stearic acictand Other fatty acids, dicarboxylic acids, metal soaps, fatty acid amine salts, metal salts of heavy:sulfonic acid; partial carboxylic acid ester of polyhydric alcohol and phosphoric ester.
(E) Demulsifiers: addition product Of alkylphenol and.ethyleneoxide, polyoxyethylene alkyl ether and polyoxyethylene sorbitane ester.

.(F) Extreme pressure agents (EP agents): sUlfurized oils, diphenyl sulfide, methyl trichlorbStearate, chlorinated naphthalene, benzyl iodide, flboroalkylpolysiloxane and lead naphthenate.
16 (G) Friction modifiers: fatty alcohol, fatty acid, amine, borated ester and other esters.
'(H) lµtflultifunctional additives:. sulfurized oxymolybdenum dithiocarbamate, sulfurized oxymolybdenurn organo phosphorodithiOate, Oxymolybdenum monoglyceride, oXymolybdenum diethylate amide, amine-molybdenum complex compound and ,sulfur-containing molybdenum complex compound (I) Viscosity Index,ImproVers (VII): polyrnethacrylate type polymers, ethylene-propylene copolymers, styrene-isoprene coPolyMers, hydrogenated styrene-isoprene Copolymers, hydrogenated Star-branched polyisoprene, poly.isobutyiene, hydrogenated star-branched styrene-isoprene copolymer and dispersant type visdosity index improvers.
(J) Pour point depressants: polymethyl methacrylates, alkylmethacrylates and dialkyl fumarate-vinyl acetate copolymer*
(K) Foam Inhibitors: alkyl methacrylate .pOlymers and dimethyl silicone polymers.
EXAMPLES
The present invention will be further illustrated by the following examples, which set forth particularly advantageous method embodiments. While the Examples are provided to-illustrate the present inVention,.they are not. intended to limit it.
Example 1 The low phosphorus lubricating oil composition of the present invention was prepared by blending a 0.78 wt % mixture .of zinC-bis(0,0'-di-(2-ethyl-i-hexyl) dithiophosphate (0.24 wt %, zinc biS(010'-di-(2-buty1/4-methy1-2-pentyl) dithiophosphate (0,15 wt %, secondary) and zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate (p.39 wt /0, aryl) with a Group II base oil of lubricating viscosity.
The ratio of zinc.bis(0,0'-di(2-ethy1-1-hexyl) dithiophosphate to zinc bis(0,01-di-(2-buty1/4-methylL2perityl) dithiophosphate was about 1:1, based on the phOsphorus.coriteht. The ratio of the mixture of zinc bis(0,0'-di(2-ethyl-1-hexyl) dithiophosphate and .zinc bis(0,01-di-(2-buty1/4-methyl-2-pentyl) dithiophosphate to zinc bis(0;0''-di-(dodecylphenyl) dithiophosphate was about 2:1, based on the phosphorus Content. The resulting ratio of the three-way mixture of zinc bis(0,0'-,cli(2-ethy14-hexyl),dithiophdsphate to zinc bis(0,0'-di-(2-buty1/4-methyl-2-pentyl) dithiophosphate to ziriobis(0,0'-di-(dodegylphenyl) dithiophosphate was 111, based on the:phosphorus content. Thewt % Of phosphorus in the prepared lubricating Oil composition was less than about Ø06 wt % based on the total weight of the lubricating oil composition. Further, the sulfur content and sulfated ash contentmere 0.2 wt % and 6.8 wt%, respectively, based on the total weight of the lubricating, oil'composition.. The wt % balance of the lubricating oil composition containinga 1200 molecular weight (MW) iSobutylene bis-succinimide dispersant, a 2300 MW iSobutylene bis-succinimide dispersant, a neutral sulfonate detergent, an overbased calcium phenate, a molybdenum oxidation inhibitor, diphenylamine oxidation inhibitor, a phenolic oxidation inhibitor, anti-foam agent, pour point depressant and a viscosity index improver to complete the 100 Wt % lubricating oil composition.
Comparative Example A
Comparatiye Example A was prepared accordinoto Example 1 except only about 1.16 wt % aryl zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate was added, instead Of the mixture of zinc bis(0,0'-dk(2-ethyl-1-hexyl) dithiophosphate, zinc bis(0,0'-di-(2-buty1/4-methyl-2-pentyl) dithiophosphate and zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate.

CoMparative Example B
Comparative Exemple.B was prepared according to Example 1 except only about 0.46 wt id zinc bis(0,0'-di-(2-buty1/4-methyl-2-pentyl) dithiophosphate Was :added, instead of the Mixture of zinc bis(0,0'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc bis(0,0'-di-(2-buty1/4-methyl-2-pentyl) dithiophOsphate and zinc bis(0.,0'-di-(dOdecylphenyl) dithiophosphate.
Comparative ExampleC
Comparative Example C was prepared according to Example 1 except only about 0.71 wt % dithiophosphate was added, instead .of the mixture of zinc bis(0,0'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc bis(0,0'-di-(2-buty1/4-Methy1-2-pentyl) dithiophosphate and zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate.
Comparative Example D
COmparative Example,D=was prepared according to Example 1 except about 0.81 wt % of a mixture Of zinc bis (0,0'-di-(2-buty1/4-methyl-2-pentyl) dithiophosphate and zinc.bis (0,0'-di-(dodecylphenyl) dithiophosphate in about a 1;1 ratio were added, instead of 'the mixture of zinc bis(p,0'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc bis(0,0'-di-(2-buty114-methyl-2-pentyl) dithiophosphate and zinc ,bis(0,0'-di-(dedecylphenyl) dithiophosphate.
Comparative Example E
Comparative Example E was prepared according to Example 1 except about 0,94 =wt % of a mixture of zinc Ois(0,0'-di-(2;=ethy1-1-hexyl) dithiophosphate and zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate in about a 1:1 ratio Were added, instead of the mixtUre of zinc bis(0,0'-dl-(2-ethy1-1-hexyl) dithiophosphate, zinc bis(0,0'-di-(2-bLity1/4-methyl-2-pentyl) dithiophosphate and zinc bis(0,0'-di-(dodecYlphenyl) dithiophosphate, 1,9 5= ComearatiVe ExaMele F
Comparative Ekarnple F was prepared a$ccording to Example 1 except about 0.59 % of a-mixture of zinc bis(0,0'-di-(2-ethyl-1-hexyl) dithiophosphate and zinc bit(0,0'-di-(2-bUty1/4-methyl-2-pentyl) dithiophosphate in about a 1:1 ratio were added, instead of the mixture of zinc bis(0,0'-di-(2-ethyl-141exyl) dithiophosphate, zinc bis(0,0'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate and zinc bis(0,0'-di-(dodecylphenyl) dithiophosphate.
Each formulation according to Example 1 and Comparative Example A-F were tested for lead corrosn using the High Temperature Corrosion Bench Test (HTCBT)(ASTM D6594) which is an industry standard bench test to measure cOrrosion.performance of a motor oiL Briefly, four metal specimens of copper, lead, tin, and phosphor bronze are immersed in a measured amount of engine oil.
The oil, atan elevated temperature, is blown with, air for a period of time.
When the test is completed, the lead specimen and the stressed oil are examined to detect corrosion and corrosion products, respectively. A reference oil is tested with each group of tests to verify test acceptability.
The_tedt results are summarized in Table II.
Table' II. HTCBT Results Example Comparative Examples Lead, 48.4 113.4 93.4 305 64.6 87.3 99.4 ppm These resUlts demonstrate that the low phosphorus lubricating oil composition of the present invention (Example 1) containing a Mixture of zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate-in a 1'1:1 ratio, and wherein the phosphorus content of the lubricating oil composition. is less than 0.06 wt%, provides excellent lead corrosion .performance when compared to the comparative examples not having 'a mixture of all three dithiophosphates. The amount of lead corrosion is significantly reduced by the luOricating OH composition Of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A lubricating oil composition comprising a major amount of base oil of lubricating viscosity and a minor amount of a mixture of a zinc primary dialkyl dithiophosphate, a zinc secondary dialkyl dithiophosphate and a zinc diaryl dithiophosphate wherein the respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is from about 2:1 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is from about 6:1 to about 1:1 and wherein the lubricating oil composition has less than about 0.06 wt %
total phosphorus content, based on the total weight of the lubricating oil composition.

2. The lubricating oil composition according to claim 1, wherein the minor amount of the mixture of zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate is from about 0.1 wt % to about 1.5 wt %, based on the total weight of the lubricating oil composition.

3. The lubricating oil composition according to claim 1, wherein the minor amount of the mixture of zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate is from about 0.3 wt % to about 1.2 wt %, based on the total weight of the lubricating oil composition.

4. The lubricating oil composition according to claim 1, wherein the minor amount of the mixture of zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate is from about 0.5 wt % to about 1.0 wt %, based on the total weight of the lubricating oil composition.

5. The lubricating oil composition according to claim 1, wherein the mixture contains from about 0.05 wt % to about 1.2 wt % zinc primary dialkyl dithiophosphate, from about 0.05 wt % to about 1.2 wt % zinc secondary dialkyl dithiophosphate and from about 0.02 wt % to about 0.7 wt % zinc diaryl dithiophosphate, based on the total weight of the lubricating oil composition.

6. The lubricating oil composition according to claim 5, wherein the mixture contains from about 0.1 wt % to about 0.7 wt % zinc primary dialkyl dithiophosphate, from about 0.1 wt % to about 0.7 wt % zinc secondary dialkyl dithiophosphate and from about 0.05 wt % to about 0.5 wt % zinc diaryl dithiophosphate, based on the total weight of the lubricating oil composition.

7. The lubricating oil composition according to claim 6, wherein the mixture contains from about 0.2 wt % to about 0.5 wt % zinc primary dialkyl dithiophosphate, from 0.2 wt % to about 0.5 wt % zinc secondary dialkyl dithiophosphate and from about 0.1 wt % to about 0.3 wt % zinc diaryl dithiophosphate, based on the total weight of the lubricating oil composition.

8. The lubricating oil composition according to claim 1, wherein the primary alkyl group of the zinc primary dialkyl dithiophosphate has from C1 to C13 carbon atoms.

9. The lubricating oil composition according to claim 8, wherein the primary alkyl group of the zinc primary dialkyl dithiophosphate has from C3 to C10 carbon atoms.

10. The lubricating oil composition according to claim 9, wherein the primary alkyl goup of the zinc primary dialkyl dithiophosphate has from C6 to C8 carbon atoms.

11. The lubricating oil composition according to claim 1, wherein the secondary alkyl group of the zinc secondary dialkyl dithiophosphate has from C3 to C13 carbon atoms.

12. The lubricating oil composition according to claim 11, wherein the secondary alkyl group of the zinc secondary dialkyl dithiophosphate has from C3 to C8 carbon atoms.

13. The lubricating oil composition according to claim 12, wherein the secondary alkyl group of the zinc secondary dialkyl dithiophosphate has from C3 to C6 carbon atoms.

14. The lubricating oil composition according to claim 1, wherein the aryl group of the zinc diaryl dithiophosphate has from C6 to C30 carbon atoms.

15. The lubricating oil composition according to claim 14, wherein the aryl group of the zinc diaryl dithiophosphate has from C6 to C24 carbon atoms.

16. The lubricating oil composition according to claim 15, wherein the aryl group of the zinc diaryl dithiophosphate has from C6 to C20 carbon atoms.

17. The lubricating oil composition according to claim 1, wherein the respective ratio of zinc primary dithiophosphate to zinc secondary dialkyl dithiophosphate is a range from -about 3:2 to about 2:3, based on the phosphorus content.

18. The lubricating oil composition according to claim 17, wherein the respective ratio of zinc primary dithiophosphate to secondary dialkyl dithiophosphate is about 1:1, based on the phosphorus content.

19. The lubricating oil composition according to claim 1, wherein the respective ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is a range from about 4:1 to about 1:1, based on the phosphorus content.

20. The lubricating oil composition according to claim 19, wherein the respective ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is about 2:1 based on the phosphorus content.

21. The lubricating oil composition according to claim 1, wherein the respective ratio of zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is 1:1:1, based on the phosphorus content.

22. The lubricating oil composition according to claim 1, wherein the total phosphorus content of the lubricating oil composition is less than 0.05 wt %, based on the total weight of the lubricating oil composition.

23. The lubricating oil composition according to claim 1, wherein the total sulfur content of the lubricating oil composition is less than 0.5 wt %, based on the total weight of the lubricating oil composition.

24. The lubricating oil composition according to claim 23, wherein the total sulfur content of the lubricating oil composition is less than 0.2 wt %, based on the total weight of the lubricating oil composition.

25. The lubricating oil composition according to claim 1, wherein the total sulfated ash content of the lubricating oil composition is less than 1.2 wt %, based on the total weight of the lubricating oil composition.

26. The lubricating oil composition according to claim 25, wherein the total sulfated ash content of the lubricating oil composition is less than 1.0 wt %, based on the total weight of the lubricating oil composition.

27. The lubricating oil composition according to claim 26, wherein the total sulfated ash content of the lubricating oil composition is less than 0.8 wt %, based on the total weight of the lubricating oil composition.

28. A
method for improving lead corrosion, said method comprising operating an internal combustion engine with a lubricating oil composition comprising a major amount of base oil of lubricating viscosity and a minor amount of a mixture of zinc primary dialkyl dithiophosphate, zinc secondary dialkyl dithiophosphate and zinc diaryl dithiophosphate wherein the respective ratio, based on the phosphorus content, of the zinc primary dialkyl dithiophosphate to zinc secondary dialkyl dithiophosphate is from -about 2:1 to about 1:2 and the ratio of the mixture of zinc primary dialkyl dithiophosphate and zinc secondary dialkyl dithiophosphate to zinc diaryl dithiophosphate is from about 6:1 to about 1:1 and wherein the lubricating oil composition has less than about 0.06 wt % total phosphorus content, based on the total weight of the lubricating oil composition.