CA1159437A - Lubricating oil with improved thermal stability - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A high viscosity index lubricating oil with improved thermal stability, anticorrosion and antiwear properties comprising a major amount of paraffinic mineral oil basestock and effective amounts of a combination of a basic zinc dialkyl dithiophosphate and 2,6 di-tertiary butyl phenol.

Description

L~ 7

2 This invention relates to a hydraulic lubricating

3 oil composition having particularly improved thermal stabil-

4 ity properties. More particularly this invention is di-rected to a hydraulic lubricating oil composition of 6 relatively high viscosity index (VI) with good antiwear, 7 anticorrosion and thermal stability properties comprising 8 a major amount of paraffinic mineral oil and a particular 9 combination of a basic zinc dialkyl dithiophosphate and 2,6 di-tertiary butyl phenol.
11 The field of lubricants and lubricating oils has 12 been extensively developed over the years. Because of the 13 wide variety of applications and conditions a large number 14 of different oil compositions with a plurality of additives have been developed and manufactured. However, because of 16 the complexity of the properties associated with such 17 lubricants and the relationship of the different components 18 to one another, it is oftentimes difficult to develop suit-19 able lubricant compositions for a particular application.
The use of metal dithiophosphates as antiwear 21 additives and also as antioxidants in lubricating oils has 22 long been known. Various antioxidants including phenolic 23 compounds and particularly hindered phenols are also well-24 known additives for lubricating oils as disclosed in "Lubricant Additives" by C. V. Smalheer and R. Kennedy Smith 26 1967, pp. 6-11; Kir~-Othmer "Encyclopedia of Chemical 27 Technology," Second Edition, Vol. 12, 1967, pp. 574-575 28 and U.S. Patents 2,202,877; 2,265,582; 3,032,502 and 29 3,929,654.
While the use of various compounds as antioxidants 31 and antiwear additives in lubricating oils is known as pre-32 viously indicated, nevertheless, it was difficult to 33 develop a hydraulic oil composition having a paraffinic 34 mineral oil basestock with high VI and with the requisite antiwear, anticorrosion and thermal stability properties.

I~..J

1 SUMMARY O~ THE INVENTION
2 In accordance with this invention, it was un-3 expectedly found that lubricating oil compositions com-4 prising a major amount of paraffinic mineral oil of high VI and effective amounts of selected basic zinc dialkyl 6 dithiophosphates and 2,6 di-tertiary butyl phenol had 7 particularly improved thermal stability, antiwear and 8 anticorrosion properties. This was particularly surprising, 9 since other similar lubricating oils containing the same zinc dialkyl dithiophosphates with the commonly used and 11 very similar hindered phenol, i.e., 2,6 di-tertiary-butyl-4 12 methyl phenol give inferior thermal stability and anti-13 corrosion properties.
14 This invention is particularly directed to a lubricating oil composition with improved thermal stability 16 comprising a major amount of a paraffinic mineral oil, from 17 about 0.1 to about 1.5% by weight of a basic zinc dialkyl 18 dithiophosphate having alkyl groups made from primary 19 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-21 tertiary butyl phenol, said composition havi-.lg a viscosity 22 of about 4 to about 160 centistokes (cSt) at 40~ and a 23 viscosity index (VI) of from about 80 to about 115.
24 DETAILED DESCRIPTION OF THE INVENTIO_ As previously indicated this invention involves 26 a hydraulic lubricating oil comprising a major amount of 27 paraffinic mineral oil and effective amounts of a combina-28 tion of a basic zinc dialkyl dithiophosphate and 2,6 di-29 tertiary butyl phenol.
The base oil used in the lubricating oil composi-31 tion of this invention is generally a paraffinic mineral oil 32 and is largely comprised of paraffin hydrocarbons, either 33 straight or branched chain, and cycloparaffins or naphthenes 34 While the amount of aromatics and polar constituents will be substantially lowered in processing the basestock, it is 36 likely that lesser amounts of aromatic compounds and other _ 3 ~ 7 1 components which are difficul~ to separate may remain along 2 with the paraffinics and cycloparaffins. Typically, the 3 aromatic content may be up to about 35% and more preferably 4 up to about 25% by weight of the bassstock material. It is therefore intended that the term '`paraffinic mineral oil 6 basestock" as used through this application, include such 7 lesser amounts of aromatic and other components. The 8 mineral oil basestock material is generally obtained from 9 crude oil using conventional refining techniques which in-clude one or more steps such as distillation, solvent 11 extraction, hydrofining and dewaxing.
12 The paraffinic mineral base oil will generally be 13 of such quality that the resulting lubrication composition 14 will have a viscosity index (VI) of from about 80 to about 115, preferably about 90 to about 105, and a viscosity of 16 about 4 to about 160, preferably about 20 to about 100 17 centistokes (cSt) at 40C. The pour point of the resulting 18 composition will generally be from about -20 to about 20F.
19 The dithiophosphate component used in this in-vention will be a basic zinc dialkyl dithiophosphate having21 alkyl groups made from primary alcohols containing about 4 22 to about 20 carbon atoms. Generally the basic zinc dialkyl 23 dithiophosphate will ha~e a zinc to phosphorus ratio of 24 about 1.10-1.65 to 1, preferably about 1.15-1.50 to 1.
The zinc dialkyl dithiophosphate are generally 26 made from dialkyl dithiophosphoric acid having the formula:
27 RO ~ S

29 RO / \ SH
wherein R comprises an alkyl group containing about 4 to 31 about 20, preferably about 6 to about 12 carbon atoms. The 32 alkyl groups generally originate from primary alcohols in-33 cluding normal alcohols such as n-hexyl, n-heptyl, n-octyl, 34 n-decyl, n-dodecyl and stearyl alcohol and branched chain alcohols such as methyl or ethyl branched isomers of the 36 above. Suitable branched alcohols are 2-methyl-1-pentanol, 1 2-ethyl-1-hexanol, 2,2 dimethyl-l-octanol and alçohols 2 prepared from olefin oligomers such as propylene dimer or 3 trimer by hydroboration-oxidation or by the Oxo process.
4 It may be desirable to use mixtures of alcohols because of their low cost and possible improvements in performance.
6 "Lorol B" alcohol, a mixture consisting of alcohols in the 7 C8 to C18 range is one such ex~ample.
8 The zinc dialkyl dithiophosphates are generally 9 prepared by first reacting the alcohol with phosphorus pentasulfide (P2S5). The resulting dialkyl dithiophosphoric 11 acid is then reacted with zinc oxide or zinc hydroxide to 12 form the basic zinc dialkyl dithiophosphate. By basic is 13 meant an excess of zinc oxide or hydroxide over what is 14 needed to stoichiometrically neutralize the acid. As previously noted, the basic material will have a zinc to 16 phosphorus ratio of about 1.10-1.65 to 1, preferably about 17 1.15-1.50 to 1.
18 The zinc dialkyl dithiophosphates as used in this 19 invention can be prepared by batch or continuous process.
2C Further information about such compounds and the method of 21 prepara~ion can be found in U.S. Patent 4,094,800.
22 The other essential ingredient used in this in-23 vention in combination with the basic zinc dialkyl dithio-24 phosphate is 2,6 di-tertiary butyl phenol. It is parti-cularly important that the para position remain open since 26 a similar type compound, 2,6 di-tertiary butyl para cresol, 27 which has a methyl group in the para position gave unsatis-28 factory results when used in the lubricating oil composition 29 of this invention.
The paraffinic mineral oil base oil will be used 31 in the lubricating oil composition in a major amount i.e., 32 about 80% or more preferably about 90% or more by weight 33 based on the total weight of the composition. The basic 34 zinc dialkyl dithiophosphate component will be used in amounts of from about 0.1 to about 1.5% by weight and 36 preferably about 0.2 to about 1.0% by weight. The 1 2,6 di-tertiary butyl phenol component will be used in 2 amounts of from about 0.05 to about 1.0% by weight and 3 preferably about 0.1 to about 0.5% by weight.
4 The hydraulic lubricating oil of this invention can also contain other conventional type additives such as 6 an antifoamant, pour point depressants, demulsifiers, rust 7 inhibitors, etc., which are typically used in lubricating 8 compositions. Generally, such additives are used in 9 relatively small amounts with the total amount of additives being usually less than 20% and more usually less than 10%
11 by weight.
12 One useful additive is an anti-rust compound and 13 more particularly a nonacid lubricating oil anti-rust 14 compound which is the reaction product of an alkenyl succinic anhydride and an alcohol or amine or mixtures 16 thereof. By nonacidic is meant those~anti-rust compounds 17 which do not have an appreciable number of free acid groups 18 and generally have a neutralization number of less than 19 about 100 as determined by ASTM D-974. The hydrocarbyl substituent of the succinic anhydride can be saturated or 21 unsaturated, branched or unbranched and will be of such a 22 nature that the final nonacidic anti-rust compound is oil 23 soluble. The oil soluble hydrocarbyls can be of relatively 24 low molecular weight such as those having about 6 to 60 carbon atoms. Generally, succinic acids of up to about 50 26 carbon atoms are the most effective rust inhibitors.
27 Preferably the hydrocarbyl group will contain about 8 to 28 about 50, more preferably about 10 to about 20 carbon atoms.
29 The alcohols used in préparing the nonacidic anti-rust compound commonly contain about 2 to about 30 and preferably 31 from about 4 to about 20 carbon atoms. Such alcohols may be 32 monoalcohols or polyols, e.g., ethanol, dodecanol, propylene 33 glycol, glycerol, etc. The amines which can be used in 34 preparing the nonacidic anti-rust compound commonly contain about 2 to about 30, preferably about 4 to about 20 carbon 36 atoms. These amines can be mono or polyamines, primary or - 6 - ~ L~

1 secondary, branched or unbranched and may contain un-2 saturation. Examples of some use~ul amines include ethyl 3 amine, dipropyl amine, isobutyl amine, cyclohexyl amine, q benzyl amine etc. Such anti-rust additives will generally be used in amounts of from about 0.02 to about 1.0~ by 6 weight and preferably from about 0.02 to about 0.1% by 7 weiqht. Further details about anti-rust compounds of this 8 type can be found in U.S. Patent 4,094,800.
9 The following examples are set forth to illustrate the invention and should not be construed as a limitation 11 thereof.

13 A hydraulic lubricating oil was prepared having 14 a major amount of paraffinic mineral oil solvent 330N base stock (viscosity 330 SUS at 100F), 0.45% by weight of basic 16 zinc dialkyl dithiophosphate with the alkyl groups having 17 8 carbon atoms and 0.2% by weight of 2,6 di-tertiary butyl 18 phenol. The composition also contained a wax naphthalene 19 pour depressant, a methacrylate polymer antifoamant, a naphthalene sulfonate soap demulsifier and an alkenyl 21 succinic acid derivative rust inhibitor. The resulting 22 composition had a VI of 95-100 and a pour point of 15F.
23 The composition was tested for thermal stability 24 properties using a test procedure developed by Cincinnati Milacron Company. The test procedure utilizes two clean 26 weighed rods of 0.25 inch diameter and three inches long, 27 one of 99.9 percent copper and the other one 1.0 percent 28 carbon steel. The rods are submerged in 200 cc of the 29 test oil in contact with each other and the oil is heated to 135C. After 168 hours at 135C, the rods are removed 31 from the oil and loose sludge is squeezed back into the oil.
32 At this poin~ the copper rod is visually evaluated and rated 33 as to stain and discoloration by ASTM D-130 ratins scale.
34 The copper rod is washed with acetone to remove oil before being weighed to determine the total weight of 36 the rod.

_ 7_ ~ 3~

The difference in the weight of this cleansed rod from the initial rod weight ~s the copper weiyht change.
The results obtained from this composition were copper corrosion (ASTM) 2C, and copper weight change mg. -0.2.
~ or comparison purposes, the same composition having 0.2%
by weight of 2,6 di~tertiary butyl para cresol substituted for the 2,6 d~tertiary butyl phenol was tested in the same manner and found to have copper eorrosion of 4C (black flaky corrosion), and copper weight change mg. -27.6. ~t is quite significant that the comparative composition had poor stability properties as compared to the composition of this invention which eontained 2,6 di-ter~iary butyl phenol in eombination with basie zinc dialkyl dithiophosphate.

Another sample of lubricating oil using a similar prepared eomposition as Example 1 with the basestoek material and the basie zine dialkyl dit~iophosphate eomponents being obtained from different manufaeturing batehes.
The results of the thermal stability were eopper eorrosion lA, and copper weight change mg. -1Ø
A similar composition but having 2,6 di-teritiary butyl para cresol instead of the 2,6 di-teritiary butyl phenol gave a copper corrosion of 4A ~black flaky eorrosion) and eopper weight changes mg. 4~6. The comparative sample failed the test on blaek flaky eopper corros~on deposit and the results are quite elearly poor in eomparison to the composition of this invention.

1 ~he above results show the significantly improved 2 and unexpected thermal stability results when using the 3 composition of this invention which contains basic zinc 4 dialkyl dithiophosphate and 2,6 di-tertiary butyl phenol.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A lubricating oil composition with improved thermal stability and anti corrosion properties comprising a major amount of paraffinic mineral oil, from about 0.1 to about 1.5% by weight of a basic zinc 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 cSt at 40°C and a VI of from about 80 to about 115.

2. The composition of claim 1 wherein said basic zinc dialkyl dithiophosphate has a zinc to phosphorus ratio of about 1.10-1.65 to 1.

3. The composition of claim 2 wherein said alkyl groups in said dialkyl dithiophosphates have from about 6 to about 12 alkyl groups.

4. The composition of claim 3 containing from about 0.1 to about 0.5% by weight of 2,6 di-tertiary butyl phenol.

5. The composition of claim 4 containing from about 0.2 to about 1.0% by weight of basic zinc dialkyl dithiophosphate.

6. The composition of claim 5 wherein said composition contains at least about 80% by weight of said paraffinic mineral oil and has a viscosity of about 20 to about 100 cSt and a VI of from about 90 to about 105.

7. The composition of claim 6 wherein said basic zinc dialkyl dithiophosphate has a zinc to phosphorus ratio of about 1.15-1.50 to 1.

8. The composition of claim 7 which contains from about 0.02 to about 1.0% by weight of a nonacid lubricant anti-rust compound comprising the reaction product of a succinic anhydride substituted with an alkenyl group of from about 8 to about 50 carbon atoms and an alcohol, an amine or mixtures thereof.

9. The composition of claim 8 wherein said composition contains at least 90% by weight of said paraffinic mineral oil.