GB2083073A

GB2083073A - Hydraulic Lubricating Oils

Info

Publication number: GB2083073A
Application number: GB8126573A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1980-09-02
Filing date: 1981-09-02
Publication date: 1982-03-17
Also published as: FR2489361A1; CA1159437A; GB2083073B; FR2489361B1

Abstract

A hydraulic lubricating oil composition, comprises a major amount, normally at least 80wt%, of paraffinic mineral oil, (i) 0.1-1.5% by wt. of a basic zinc di-C4-20 alkyl dithiophosphate and (ii) 0.05-1.0% by wt. of 2,6 di-tertiary butyl phenol, the composition having a VI of 80- 115 and a viscosity of 4-160 cSt at 40 DEG C. Conventional additions may also be present, for example an alkenyl succinic acid derivative rust inhibitor. The hydraulic oil has improved thermal stability and anti-wear and anti-corrosion properties.

Description

SPECIFICATION Lubricating Oil with Improved Thermal Stability Background of the Invention This invention relates to a hydraulic lubricating oil composition having particularly improved thermal stability properties. More particularly this invention is directed to a hydraulic lubricating oil composition of relatively high viscosity index (VI) with good antiwear, anticorrosion and thermal stability properties comprising a major amount of paraffinic mineral oil and a particular combination of a basic zinc dialkyl dithiophosphate and 2,6 ditertiary butyl phenol.

The field of lubricants and lubricating oils has been extensively developed over the years.

Because of the wide variery of applications and conditions a large number of different oil compositions with a plurality of additives have been developed and manufactured. However, because of the complexity of the properties associated with such lubricants and the relationship of the different components to one another, it is oftentimes difficult to develop suitable lubricant compositions for a particular application.

The use of metal dithiophosphates as antiwear additives and also as antioxidants in lubricating oils has long been known. Various antioxidants including phenolic compounds and particularly hindered phenols are also wellknown additives for lubricating oils as disclosed in "Lubricant Additives" by C. V. Smalheer and R. Kennedy Smith 1967, pup.6~11; Kirk-Othmer "Encyclopedia of Chemical Technology," Second Edition, Vol 12, 1 967, pp. 574-575 and U.S.

Patents 2,202,877; 2,265,582; 3,032,502 and 3,929,654.

While the use of various compounds as antioxidants and antiwear additives in lubricating oils is known as previously indicated, nevertheless, it was difficult to develop a hydraulic oil composition having a paraffinic mineral oil basestock with high VI and with the requisite antiwear, anticorrosion and thermal stability properties.

Summary of the Invention In accordance with this invention, it was unexpectedly found that lubricating oil compositions comprising a major amount of paraffinic mineral oil of high VI and effective amounts of selected basic zinc dialkyl dithiophosphates and 2,6 di-tertiary butyl phenol had particularly improved thermal stability, antiwear and anticorrosion properties. This was particularly surprising, since other similar lubricating oils containing the same zinc dialkyl dithiophosphates with the commonly used and very similar hindered phenol, i.e., 2,6 di-tertiary-butyl4 methyl phenol give inferior thermal stability and anti-corrosion properties.

This invention is particularly directed to a lubricating oil composition with improved thermal stability comprising a major amount of a paraffinic mineral oil, from about 0.1 to about 1.5% by weight of a basic zine dialkyl dithiophosphate having alkyl groups made from primary alcohols containing from about 4 to about 20 carbon atoms and from about 0.05 to about 1.0% by weight of 2,6 di-tertiary butyl phenol, said composition having a viscosity of about 4 to about 160 centistokes (cSt) at 400C and a viscosity index (VI) of from about 80 to about 115.

Detailed Description of the Invention As previously indicated this invention involves a hydraulic lubricating oil comprising a major amount of paraffinic mineral oil and effective amounts of a combination of a basic zinc dialkyl dithiophosphate and 2,6 di-tertiary butyl phenol.

The base oil used in the lubricating oil composition of this invention is generally a paraffinic mineral oil and is largely comprised of paraffin hydrocarbons, either straight or branched chain, and cycloparaffins or naphthenes. While the amount of aromatics and polar constituents will be substantially lowered in processing the basestock, it is likely that lesser amounts of aromatic compounds and other components which are difficult to separate may remain along with the paraffinics and cycloparaffins. Typically.

the aromatic content may be up to about 35% and more preferably up to about 25% by weight of the basestock material. It is therefore intended that the term "paraffinic mineral oil basestock" as used through this application, includes such lesser amounts of aromatic and other components. The mineral oil basestock material is generally obtained from crude oil using conventional refining techniques which include one or more steps such as distillation, solvent extraction, hydrofining and dewaxing.

The paraffinic mineral base oil will generally be of such quality that the resulting lubrication composition will have a viscosity index (VI) of from about 80 to about 11 5, preferably about 90 to about 105, and a viscosity of about 4 to about 160, preferably about 20 to about 100 centistokes (cSt) at 400 C. The pour point of the resulting composition will generally be from about -20 to about 200 F.

The dithiophosphate component used in this invention will be a basic zinc dialkyl dithiophosphate having alkyl groups made from primary alcohols containing about 4 to about 20 carbon atoms. Generally the basic zinc dialkyl dithiophosphate will have a zinc to phosphorous ratio of about 1.10-1.65 to 1, preferably about 1.15- 1.50 to 1.

The zinc dialkyl dithiophosphate are generally made from dialkyl dithiophosphoric acid having the formula

wherein R comprises an alkyl group containing about 4 to about 20, preferably about 6 to about 12 carbon atoms. The alkyl groups generally originate from primary alcohols including normal alcohols such as n-hexyl, n-heptyl, n-octyl, n decyl, n-dodecyl and stearyl alcohol and branched chain alcohols such as methyl or ethyl branched isomers of the above. Suitable branched alcohols are 2-methyl-i -pentanol, 2-ethyl-i -hexanol, 2,2 dimethyl-i -octanol and alcohols prepared from olefin oligomers such as propylene dimer or trimer by hydroboration-oxidation or by the Oxo process.It may be desirable to use mixtures of alcohols because of their low cost and possible improvement in performance. "Lorol B" alcohol, a mixture consisting of alcohols in the C8 to C, range is one such example.

The zinc dialkyl dithiophosphates are generally prepared by first reacting the alcohol with phosphorous pentasulfide (P2S5). The resulting dialkyl dithiophosphoric acid is then reacted with zinc oxide or zinc hydroxide to form the basic zinc dialkyl dithiophosphate. By basic is meant an excess of zinc oxide or hydroxide over what is needed to stoichiometrically neutralize the acid.

As previously noted, the basic material will have a zinc to phosphorous ratio of about 1.10-1.65 to 1, preferably about 1.15-1.50 to 1.

The zinc dialkyl dithiophosphates as used in this invention can be prepared by batch or continuous process. Further information about such compounds and the method of preparation can be found in U.S. Patent 4,094,800.

The other essential ingredient used in this invention is combination with basic zinc dialkyl dithiophosphate is 2,6 di-tertiary butyl phenol. It is particularly important that the para position remain open since a similar type compound, 2,6 di-tertiary butyl para cresol, which has a methyl group in the para position give unsatisfactory results when used in the lubricating oil composition of this invention.

The paraffinic mineral oil base oil will be used in the lubricating oil composition in a major amount i.e., about 80% or more preferably about 90% or more by weight based on the total weight of the composition. The basic zinc dialkyl dithiophosphate component will be used in amounts of from about 0.1 to about 1.5% by weight and preferably about 0.2 to about 1.0% by weight. The 2,6 di-tertiary butyl phenol component will be used in amounts of from about 0.05 to about 1.0% by weight and preferably about 0.1 to about 0.5% by weight.

The hydraulic lubricating oil of this invention can also contain other conventional type additives such as an antifoamant, pour point depressants, demulsifiers, rust inhibitors, etc., which are typically used in lubricating compositions.

Generally, such additives are used in relatively small amounts with the total amount of additives being usually less than 20% and more usually less than 10% by weight.

One useful additive is an anti-rust compound and more particularly a nonacid lubricating oil antirust compound which is the reaction product of an alkenyl succinic anhydride and an alcohol or amine or mixtures thereof. By nonacidic is meant those anti-rust compounds which do not have an appreciable number of free acid groups and generally have a neutralization number of less than about 100 as determined by ASTM D-974.

The hydrocarbyl substituent of the succinic anhydride can be saturated or unsaturated, branched or unbranched and will be of such a nature that the final nonacidic anti-rust compound is oil soluble. The oil soluble hydrocarbyls can be of relatively low molecular weight such as those having about 6 to 60 carbon atoms. Generally, succinic acids of up to about 50 carbon atoms are the most effective rust inhibitors. Preferably the hydrocarbyl group will contain about 8 to about 50, more preferably about 10 to about 20 carbon atoms. The alcohols used in preparing the nonacidic anti-rust compound commonly contain about 2 to about 30 and preferably from about 4 to about 20 carbon atoms. Such alcohols may be monoalcohols or polyols, e.g., ethanol, dodecanol, propylene glycol, glycerol, etc.The amines which can be used in preparing the nonacidic anti-rust compound commonly contain about 2 to about 30, preferably about 4 to about 20 carbon atoms.

These amines can be mono or polyamines, primary or secondary, branched or unbranched and may contain unsaturation. Examples of some useful amines include ethyl amine, dipropyl amine, isobutyl amine, cyclohexyl amine, benzyl amine etc. Such anti-rust additives will generally be used in amounts of from about 0.02 to about 1.0% by weight and preferably from about 0.02 to about 0.1% by weight. Further details about anti-rust compounds of this type can be found in U.S. Patent 4,094,800.

The following examples are set forth to illustrate the invention and should not be construed as a lamination thereof.

Example 1 A hydraulic lubricating oil was prepared having a major amount of paraffinic mineral oil solvent 330N base stock (viscosity 330 SUS at 100%F), 0.45% by weight of basic zinc dialkyl dithiophosphate with the alkyl groups having 8 carbon atoms and 0.2% by weight of 2,6 ditertiary butyl phenol. The composition also contained a wax naphthalene pour depressant, a methyacrylate polymer antifoament, a naphthalene sulfonate soap demulsifier and an alkenyl succinic acid derivative rust inhibitor. The resulting composition had a VI of 95-100 and a pour point of 1 50F.

The composition was tested for thermal stability properties using a test procedure developed by Cincinnati Milacron Company. The test procedure utilizes two clean weighed rods of 0.25 inch diameter and three inches long, one of 99.9 percent copper and the other one 1.0 percent carbon steel. The rods are submerged in 200 cc of the test oil in contact with each other and the oil is heated to 1 350C. After 168 hours at 1 350C, the rods are removed from the oil and loose sludge is squeezed back into the oil. At this point the copper rod is visually evaluated and rated as to stain and discoloration by ASTM D130 rating scale.

The copper rod is washed with acetone to remove oil before being weighed to determine the total weight of the rod plus sludge deposit. It is then subjected to a ten percent solution of potassium cyanide for one minute to strip the sludge deposit from the rod and is then sequentially washed in distilled water and acetone before being weighed again. The difference in the weight of this cleansed rod from the initial rod weight is copper loss. The difference in weight of this cleansed rod and the weight obtained prior to cleaning is the weight of the sludge deposit.

The results obtained from this composition were copper corrosion (ASTM) 2C, copper weight change mg. -0.2 and sludge, mg. 0.1.

For comparison purposes, the same composition having 0.2% by weight of 2,6 ditertiary butyl para cresol substituted for the 2,6 di-tertiary butyl phenol was tested in the same manner and found to have copper corrosion of 4C (black flaky corrosion), copper weight change mg.

-27.6 and sludge, mg. 3.0. It is quite significant that the comparative composition had poor stability properties as compared to the composition of this invention which contained 2,6 di-tertiary butyl phenol in combination with basic zinc dialkyl dithiophosphate.

Example 2 Another sample of lubricating oil using a similar prepared composition as Example 1 with the basestock material and the basic zinc dialkyl dithiophosphate components being obtained from different manufacturing batches.

The results of the thermal stability were copper corrosion 1 A, copper weight change mg. -1.0 and sludge, mg. 0.45.

A similar composition but having 2,6 di-tertiary butyl paral cresol instead of the 2,6 di-tertiary butyl phenol gave a copper corrosion of 4A (black flaky corrosion) copper weight changes mg. 4.6 and sludge mg. 0.35. The comparative sample failed the test on black flaky copper corrosion deposit and the results are quite clearly poor in comparision to the composition of this invention.

The above results show the significantly improved and unexpected thermal stability results when using the composition of this invention which contains basic zinc dialkyl dithiophosphate and 2,6 di-tertiary butyl phenol.

Claims

1. A lubricating oil composition with improved thermal stability comprising: a major amount of paraffinic mineral oil from 0.1 to 1.5% by weight of a basic (as herein defined) zinc dialkyl dithiophosphate having alkyl groups derived from primary alcohols containing from 4 to 20 carbon atoms, and from 0.05 to 1.0% by weight of 2,6 di-tertiary butyl phenol; said composition having a viscosity of 4 to 160 cSt at 40 CandaVloffrom80to 115.

2. A composition as claimed in claim 1, wherein said basic zinc dialkyl dithiophosphate has a zinc to phosphorus ratio of from 1.10:1 to 1.65:1.

3. A composition as claimed in claim 2, wherein said basic zinc dialkyl dithiophosphate has a zinc to phosphorus ratio of from 1.15:1 to 1.50:1.

4. A composition as claimed in any preceding claim, wherein the said alkyl groups in the said dialkyl dithiophosphate have from 6 to 12 alkyl groups.

5. A composition as claimed in any preceding claim containing from 0.2 to 1.0% by weight of the basic zinc dialkyl dithiophosphate.

6. A composition as claimed in any preceding claim, containing from 0.1 to 0.5% by weight of the 2,6 di-tertiary butyl phenol.

7. A composition as claimed in any preceding claim, further containing from 0.02 to 1.0% by weight of a non-acid lubricant anti-rust compound comprising the reaction product of (i) a succinic anhydride substituted with an alkenyl group of from 8 to 50 carbon atoms and (ii) an alcohol or an amine or a mixture thereof.

8. A composition as claimed in any preceding claim, wherein said composition has a viscosity of about 20 to about 100 cSt and a VI of from about 90 to about 105.

9. A composition as claimed in any preceding claim, wherein said composition contains at least 80% by weight of said paraffinic mineral oil.

10. A composition as claimed in claim 9, wherein the composition contains at least 90% by weight of said paraffinic mineral oil.

11. A lubricating oil composition as claimed in claim 1 and substantially as herein described.

12. A lubricating oil composition as claimed in claim 1 and substantially as herein described with reference to either of the Examples.