Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
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
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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
28 P
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
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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.
12 EXAMPLE I
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.
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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.
EXAMPLE 2
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.
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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.
