U.S. patent application number 11/463532 was filed with the patent office on 2008-02-14 for low phosphorus lubricating oil composition having lead corrosion control.
This patent application is currently assigned to Chevron Oronite Company LLC. Invention is credited to Alexander B. Boffa.
Application Number | 20080039348 11/463532 |
Document ID | / |
Family ID | 39051541 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080039348 |
Kind Code |
A1 |
Boffa; Alexander B. |
February 14, 2008 |
LOW PHOSPHORUS LUBRICATING OIL COMPOSITION HAVING LEAD CORROSION
CONTROL
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.
Inventors: |
Boffa; Alexander B.; (San
Francisco, CA) |
Correspondence
Address: |
CHEVRON CORPORATION
P.O. BOX 6006
SAN RAMON
CA
94583-0806
US
|
Assignee: |
Chevron Oronite Company LLC
|
Family ID: |
39051541 |
Appl. No.: |
11/463532 |
Filed: |
August 9, 2006 |
Current U.S.
Class: |
508/371 |
Current CPC
Class: |
C10N 2030/42 20200501;
C10M 2207/026 20130101; C10M 169/04 20130101; C10N 2020/04
20130101; C10M 2215/064 20130101; C10N 2030/45 20200501; C10N
2040/25 20130101; C10M 2223/045 20130101; C10M 2215/28 20130101;
C10M 137/10 20130101; C10M 2207/028 20130101; C10N 2030/12
20130101; C10N 2030/43 20200501; C10N 2010/04 20130101; C10M
2219/044 20130101; C10M 2223/045 20130101; C10N 2010/04 20130101;
C10M 2207/028 20130101; C10N 2010/04 20130101; C10M 2223/045
20130101; C10N 2010/04 20130101; C10M 2207/028 20130101; C10N
2010/04 20130101 |
Class at
Publication: |
508/371 |
International
Class: |
C10M 137/10 20060101
C10M137/10 |
Claims
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 compression.
3. The lubricating oil composition according to claim 1, wherein
the minor amount of them 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 about C.sub.1 to about C.sub.13 carbon atoms.
9. The lubricating oil composition according to claim 8, wherein
the primary alkyl group of the zinc primary dialkyl dithiophosphate
has from about C.sub.3 to about C.sub.10 carbon atoms.
10. The lubricating oil composition according to claim 9, wherein
the primary alkyl group of the zinc primary dialkyl dithiophosphate
has from about C.sub.6 to about C.sub.8 carbon atoms.
11. The lubricating oil composition according to claim 1, wherein
the secondary alkyl group of the zinc secondary dialkyl
dithiophosphate has from about C.sub.3 to about C.sub.13 carbon
atoms.
12. The lubricating oil composition according to claim 11, wherein
the secondary alkyl group of the zinc secondary dialkyl
dithiophosphate has from about C.sub.3 to about C.sub.8 carbon
atoms.
13. The lubricating oil composition according to claim 12, wherein
the secondary alkyl group of the zinc secondary dialkyl
dithiophosphate has from about C.sub.3 to about C.sub.6 carbon
atoms.
14. The lubricating oil composition according to claim 1, wherein
the aryl group of the zinc diaryl dithiophosphate has from about
C.sub.6 to about C.sub.30 carbon atoms.
15. The lubricating oil composition according to claim 14, wherein
the aryl group of the zinc diaryl dithiophosphate has from about
C.sub.8 to about C.sub.24 carbon atoms.
16. The lubricating oil composition according to claim 15, wherein
the aryl group of the zinc diaryl dithiophosphate has from about
C.sub.6 to about C.sub.20 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 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 a about 2:1 based on the phosphorus
content.
21. The lubricating oil composition according to claim 1, wherein
the respective ratio of the mixture of zinc primary dialkyl
dithiophosphate 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 in
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 in 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 in 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
in 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
in 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
in 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.
Description
[0001] 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 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
[0002] Emissions arising from automotive exhaust 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 arising from leaded fuels), oxygenated fuel (to reduce
hydrocarbon emissions), the use of catalytic converters (also to
reduce hydrocarbon emissions), etc.
[0003] 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 unburnt or partially 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.
[0004] 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 gasoline in
order to avoid lead poisoning of the catalyst as well as lead
discharge into the environment. See, for example, Buckley, III,
"Long Chain Aliphatic Hydrocarbyl Amine Additive Having an
Oxyalkylene Hydroxy Connecting Group", U.S. Pat. No. 4,975,096,
issued Dec. 4, 1990.
[0005] As to the lubricants, one additive family currently being
addressed by industry standards is 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 converter as a result of, for example, exhaust gas
recirculation and/or oil blow-by processes as well as other methods
known in the are. 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 from TWC-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
GF-4 specifications for lubricant compositions have proposed
significantly lower phosphorus contents than heretofore
employed.
[0006] 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 the
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
antiwear additive. For instance, as exemplified in U.S. Pat. No.
6,696,393, issued Feb. 24, 2004, lowering the level of phosphorus
glue 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 in engine wear.
[0007] Zinc dithiophosphates have either dialkyl or diaryl groups.
Zinc dialkyl dithiophosphates are further subdivided into primary
alkyl and secondary alkyl zinc dithiophosphates. 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).
TABLE-US-00001 Primary Alkyl Secondary Alkyl Aryl Thermal Stability
Medium Low High Antiwear Protection Medium High Low Hydrolytic
Stability Medium High Low
[0008] Each type has important applications in modern additive
packages. It is therefore important to have the right mix of zinc
dithiophosphates in any given lubricating oil composition to
provide adequate anti-wear performance and at 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
[0009] As previously mentioned, 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 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 lubricating oil
composition in internal combustion engines.
[0010] Accordingly, in its broadest aspect, the present invention
is related to a lubricating oil composition comprising a major
amount of bases 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 phosphorous 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 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.
[0011] The minor amount of the mixture of a zinc primary dialkyl
dithiophosphate, a zinc secondary dialkyl dithiophosphate and a
zinc diaryl dithiophosphate employed in the lubricating oil
composition of the present invention is from about 0.1 wt % to
about 1.5 wt % to about 1.0 wt %, based on the total weight of the
lubricating oil composition.
[0012] The lubricating oil composition of the present invention
will contain from about 0.05 wt % to about 1.2 wt % of a 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 % of 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 a zinc primary
dialkyl dithiophosphate, from about 0.1 wt % to about 0.7 wt % of a
zinc secondary 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 % of a zinc primary dialkyl
dithiophosphate, from about 0.2 wt % to about 0.5 wt % 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.
[0013] The primary alkyl group of the zinc primary dialkyl
dithiophosphate has from about C.sub.1 to about C.sub.13 carbon
atoms, preferably from about C.sub.3 to about C.sub.10 carbon atoms
and more preferably, from about C.sub.6 to about C.sub.8 carbon
atoms.
[0014] The secondary alkyl group of the zinc secondary dialkyl
dithiophosphate has from about C.sub.3 to about C.sub.13 carbon
atoms, preferably from about C.sub.3 to about C.sub.8 carbon atoms
and more preferably, from about C.sub.3 to about C.sub.6 carbon
atoms.
[0015] The aryl group of the zinc diaryl dithiophosphate has from
about C.sub.6 to about C.sub.30 carbon atoms, preferably from about
C.sub.6 to about C.sub.24 carbon atoms and more preferably, from
about C.sub.6 to about C.sub.20 carbon atoms.
[0016] In a preferred embodiment, the respective ratio, based on
the phosphorus content, of zinc primary dialkyl dithiophosphate to
zinc secondary dialkyl dithiophosphate is from about 3:2 to about
2:3. More preferably, the ratio is about 1:1.
[0017] In a preferred embodiment, 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 from about 4:1 to about 1:1. More
preferably, the ratio is about 2:1.
[0018] In an especially preferred embodiment, the respective ratio,
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.
[0019] In another embodiment, the total phosphorus content 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.
[0020] 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 %, 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 oil composition.
[0021] 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 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 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.
[0022] Among other factors, 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 mixture of zinc dithiophosphates contains a
zinc primary dialkyl dithiophosphate, a zinc secondary dialkyl
dithiophosphate and a zinc diaryl 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 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, greatly reduces lead corrosion when
used to lubricate internal combustion engines.
DETAILED DESCRIPTION OF THE INVENTION
[0023] 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 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 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. The low phosphorus lubricating oil composition of
the present invention is effective in lead corrosion control when
used as a lubricating oil in internal combustion engines.
[0024] 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.
[0025] The term "alkyl" refers to both straight- and branched-chain
alkyl groups.
[0026] The term "aryl" refers to a substituted or unsubstituted
aromatic group, such as the phenyl, tolyl, xylyl, ethylphenyl and
cumenyl groups.
[0027] 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 weight percent to
about 0.06 weight percent based on the total weight of the
lubricating oil composition.
[0028] The term "total phosphorus" refers to the total amount of
phosphorus in the lubricant composition regardless of whether such
phosphorus is present as part of an oil-soluble,
phosphorus-containing, anti-wear compound or in the form of a
contaminant in the lubricant composition such as residual
phosphorus remaining due to the presence of P.sub.2S.sub.5 used to
prepare metal dihydrocarbyl dithiophosphates. In either event, the
amount of phosphorus permitted in the lubricant composition is
independent of source. Preferably, however, the phosphorus is part
of a lubricant additive.
[0029] Unless otherwise specified, all percentages are in weight
percent.
The Zinc Dithiophosphate Compound
[0030] 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:
##STR00001##
wherein each R is independently a group containing from about 1 to
about 30 carbon atoms.
[0031] The R groups in the dithiophosphate can independently be
about C.sub.1 to about C.sub.13 primary alkyl, about C.sub.3 to
about C.sub.13 secondary alkyl, and about C.sub.6 to about C.sub.30
aryl group. Preferably, the R groups in the dithiophosphate can
independently be about C.sub.3 to about C.sub.10 primary alkyl,
about C.sub.3 to about C.sub.8 secondary alkyl, and about C.sub.6
to about C.sub.24 aryl group. More preferably, the R groups in the
dithiophosphate can independently be about C.sub.6 to about C.sub.8
primary alkyl, about C.sub.3 to about C.sub.6 secondary alkyl, and
about C.sub.6 to about C.sub.20 aryl group. The R groups may be a
substantially hydrocarbon group. By "substantially hydrocarbon" is
meant hydrocarbons that contain substituent groups such as ether,
ester, nitro, or halogen which do not materially affect the
hydrocarbon character of the group.
[0032] The R group of the zinc dithiophosphate may be derived, for
example, from a primary alcohol such as methanol, ethanol,
propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol,
decanol, dodecanol, octadecanol, propenol, butenol, 2-ethylhexanol:
a secondary alcohol such as isopropyl alcohol, secondary butyl
alcohol, isobutanol, 3-methylbutan-2-ol, 2-pentanol,
4-methyl-2-pentanol, 2-hexanol, 3-hexanol, amyl alcohol, an aryl
alcohol such as phenol, substituted phenol (particularly
alkylphenol such as butylphenol, octylphenol, nonylphenol,
dodecylphenol), disubstituted phenol.
[0033] Preferably the R group will be independently a primary
alkyl, a secondary alkyl or an aryl group.
[0034] For the present invention it is contemplated that the
mixture of a zinc primary dialkyl dithiophosphate, a zinc secondary
dialkyl dithiophosphate and a zinc diaryl dithiophosphate will be
in a respective ratio, based 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 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. Preferably, the respective ratio,
based on the phosphorus content, of zinc primary dialkyl
dithiophosphate to zinc secondary dialkyl dithiophosphate is a
range from about 3:2 to about 2:3, more preferably about 1:1.
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 the mixture of zinc primary dialkyl dithiophosphate to
zinc secondary dialkyl dithiophosphate to zinc diaryl
dithiophosphate is 1:1:1.
[0035] Many of the zinc dithiophosphates useful in the present
invention are available commercially. However, zinc
dithiophosphates are widely known in the art and a skilled artisan
can readily synthesize such compounds for the purposes of the
present invention. Typically, zinc dithiophosphates 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.degree. C. to about 200.degree. C. Thus, the preparation of
O,O-di-n-hexyl phosphorodithioic acid, for example, involves the
reaction of phosphorous pentasulfide with four moles of n-hexyl
alcohol at about 100.degree. 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 affected 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.
[0036] Patents describing the synthesis of such zinc
dithiophosphates include U.S. Pat. Nos. 2,680,123; 3,000,822;
3,151,075; 3,385,791; 4,377,527; 4,495,075 and 4,778,906. Each of
these patents is incorporated herein by reference in their
entirety.
The Lubricating Oil Composition
[0037] 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
[0038] 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.
[0039] Refined stock shall be substantially free from materials
introduced through manufacturing, contamination, or previous use.
The base oil of this invention may be any natural or synthetic
lubricating base oil fraction particularly those having a kinematic
viscosity at 100.degree. Centigrade (.degree. C.) and about 4
centistokes (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 comprised
little, if any, heavy fraction; e.g., little, if any, tube oil
fraction of viscosity about 20 cSt or higher at about 100.degree.
C. Oils used as the base oil will be selected or blended depending
on the desired end use and the additives in the finished oil to
give the desired of engine oil, e.g. a lubricating oil composition
having an SAE Viscosity Grade of 0W, 0W-20, 0W-30, 0W-40, 0W-50,
0W-60, 5W, 5W-20, 5W-30, 5W-40, 5W-50, 5W-60, 10W, 10W-20, 10W-20,
10W-30, 10W-40, 10W-50, 15W, 15W-20, 15W-30, 15W-40.
[0040] The base oil may be derived from natural lubricating oils,
synthetic lubricating oils or mixtures thereof. Suitable base oil
includes base stocks obtained by isomerization of synthetic wax and
slack wax, as well as hydrocrackate base stocks produced by
hydrocracking (rather than solvent extracting) the aromatic and
polar components of the crude. Suitable base oils include those in
all API categories, I, II, III, IV and V as defined in API
Publication 1509, 14th Edition, Addendum I, December 1998.
Saturates levels and viscosity indices for Group I, II and III base
oils are listed in Table I. Group IV base oils are polyalphaolefins
(PAO). Group V base oils include all other base oils not included
in Group I, II, III, or IV. Group III base oils are preferred.
TABLE-US-00002 TABLE I SATURATES, SULFUR AND VISCOSITY INDEX OF
GROUP I, II, III, IV AND V BASE STOCKS Saturates (As determined
Viscosity Index by ASTM D2007) (As determined by ASTM Sulfur (As
determined D4294, ASTM D4297 Group by ASTM D2270) or ASTM D3120) I
Less than 90% saturates and/or Greater than or equal to 80 Greater
than to 0.03% sulfur and less than 120 II Greater than or equal to
90% Greater than or equal to 80 saturates and less than or equal
and less than 120 to 0.03% sulfur III Greater than or equal to 90%
Greater than or equal to 120 saturates and less than or equal to
0.03% sulfur IV All Polyalphaolefins (PAOs) V All others not
included in Groups I, II, III, or IV
[0041] Natural lubricating oils may include animal oils, vegetable
oils (e.g., rapeseed oils, castor oils and lard oil), petroleum
oils, mineral oils, and oils derived from coal or shale.
[0042] Synthetic oils may include hydrocarbon oils and
halo-substituted hydrocarbon oils such as polymerized and
inter-polymerized olefins, alkylbenzenes, polyphenyls, alkylated
diphenyl ethers, alkylated diphenyl sulfides, as well as their
derivatives, analogues and homologues thereof, interpolymers,
copolymers and derivatives thereof wherein the terminal hydroxyl
groups have been modified by esterification, etherification, etc.
Another suitable class of synthetic lubricating oils comprises the
esters of dicarboxylic acids with a variety of alcohols. Esters
useful as synthetic oils also include those made from about C.sub.5
to about C.sub.12 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 as base oils.
[0043] Silicon-based oils (such as the polyalkyl-, polyaryl-,
polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils)
comprise another useful class of synthetic lubricating oils. Other
synthetic lubricating oils include esters of phosphorus-containing
acids, polymeric tetrahydrofurans, polyalphaolefins, and the
like.
[0044] The base oil may be derived from unrefined, refined,
rerefined oils, or mixtures thereof. Unrefined oils are obtained
directly from a natural source or synthetic source (e.g., 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 an ester oil obtained directly from
an esterification process, each of which may then be used without
further treatment. Refined oils are similar to the unrefined oils
except that refined oils have been treated in one or more
purification steps to improve one or more properties. Suitable
purification techniques include distillation, hydrocracking,
hydrotreating, dewaxing, solvent extraction, acid or base
extraction, filtration, and percolation, all of which are known to
those skilled in the art. Rerefined oils are obtained by treating
used oils in processes similar to those used to obtain the refined
oils. These rerefined oils are also known as reclaimed or
reprocessed oils and often are additionally processed by techniques
for removal of spent additives and oil breakdown products.
[0045] Base oil derived from the hydroisomerization of wax may also
be used, either alone or in combination with the aforesaid natural
and/or synthetic base oil.
[0046] Such wax isomerate oil is produced by the hydroisomerization
of natural or synthetic waxes or mixtures thereof over a
hydroisomerization catalyst.
[0047] It is preferred to 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 %,
more preferably about 60 wt % to about 97 wt % and 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 the lubricating oil unless otherwise specified.
[0048] The amount of the mixture of zinc dithiophosphates 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 %
to about 1.5 wt %, preferably from about 0.3 wt % to about 1.2 wt %
and more preferably from about 0.5 wt % to about 1.0 wt %, based on
the total weight of the lubricating oil composition.
[0049] The lubricating oil composition of the present invention
will contain from about 0.05 wt % to about 1.2 wt %, preferably
from about 0.1 wt % to about 0.7 wt %, and more preferably from
about 0.2 wt % to about 0.5 wt % of a zinc primary dialkyl
dithiophosphate, based on the total weight of the lubricating oil
composition.
[0050] The lubricating oil composition of the present invention
will contain from about 0.05 wt % to about 1.2 wt %, preferably
from about 0.1 wt % to about 0.7 wt %, and more preferably from
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.
[0051] The lubricating oil composition of the present invention
will contain from about 0.02 wt % to about 0.7 wt %, preferably
from about 0.05 wt % to about 0.5 wt %, and more preferably from
about 0.1 wt % to about 0.3 wt % of a zinc primary diaryl
dithiophosphate, based on the total weight of the lubricating oil
composition.
[0052] 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.
[0053] In another embodiment, the lubricating oil composition of
the present invention will further have a sulfur content less than
about 0.5 wt % and, preferably less than about 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 oil composition.
Other Additive Components
[0054] 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. [0055] (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 form during the combustion of the 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 or alkenyl
aromatic compounds, alkyl or alkenyl hydroxy aromatic sulfonates,
sulfurized or unsulfurized alkyl or alkenyl naphthenates, metal
salts of alkanoic acids, metal salts of an alkyl or alkenyl
multiacids and chemical and physical mixtures thereof. [0056] (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 lacquer. Typically, the ashless dispersants are
nitrogen-containing dispersants formed by reacting alkenyl succinic
acid anhydride with an amine. Examples are alkenyl succinimides,
alkenyl succinimides modified with other organic compounds, e.g.,
ethylene carbonating post-treatment and alkenyl succinimides
modified with boric acid, polysuccinimides, alkenyl succinic ester.
[0057] (C) Oxidation Inhibitors: [0058] 1) Phenol type (phenolic)
oxidation inhibitors: 4,4'-methylenebis (2,6-di-tert-butylphenol),
4,4'-bis(2,6-di-tert-butylphenol),
4,4'-bis(2-methyl-6-tert-butylphenol),
2,2'-methylenebis(4-methyl-6tert-butyl-phenol,
4,4'-butyldienebis(3-methyl-6-tert-butylphenol),
4,4'-isopropylidenebis(2,6-di-tert-butylphenol),
2,2'-methylenebis(4-methyl-6-nonylphenol),
2,2'isobutyldiene-bis(4,6-dimethylphenol),
2,2'-methylenebis(4-methyl-6-cyclohexylphenol),
2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol,
2,4-dimethyl-6-tert-butyl-phenol,
2,6-di-tert-.alpha.-dimethylamino-p-cresol, 2,6-di-tert-4(N,N'
dimethylaminomethylphenol),
4,4'-thiobis(2-methyl-6-tert-butylphenol),
2,2'-thiobis(4-methyl-6-tert-butylphenol),
bis(3-methyl-4hydroxy-5-tert-butylbenzyl)-sulfide and bis
(3,5-di-tert-butyl-4-hydroxybenzyl). [0059] 2) Diphenylamine type
oxidation inhibitor: alkylated diphenylamine,
phenyl-.alpha.-naphthylamine and alkylated .alpha.-naphthylamine.
[0060] 3) Other types: metal dithiocarbamate (e.g., zinc
dithiocarbamate) and methylenebis(dibutyldithiocarbamate). [0061]
(D) Rust inhibitors (Anti-rust agents) [0062] 1) Nonionic
polyoxyethylene surface active agents: polyoxyethylene lauryl
ether, polyoxyethylene higher alcohol ether, polyoxyethylene
nonylphenyl ether, polyoxyethylene octylphenyl ether,
polyoxyethylene octyl stearyl ether, polyoxyethylene oleyl ether,
polyoxyethylene sorbitol monostearate, polyoxyethylene sorbitol
mono-oleate and polyethylene glycol monooleate. [0063] 2) Other
compounds: stearic acid and 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. [0064] (E) Demulsifiers: addition product of
alkylphenol and ethyleneoxide, polyoxyethylene alkyl ether and
polyoxyethylene sorbitane ester. [0065] (F) extreme pressure agents
(EP agents): sulfurized oils, diphenyl sulfide, methyl
trichlorostearate, chlorinated naphthalene, benzyl iodide,
fluoroalkylpolysiloxane and lead naphthenate. [0066] (G) Friction
modifiers: fatty alcohol, fatty acid, amine, borated ester and
other esters. [0067] (H) Multifunctional additives: sulfurized
oxymolybdenum dithiocarbamate, sulfurized oxymolybdenum organo
phosphorodithioate, oxymolybdenum monoglyceride, oxymolybdenum
diethylate amide, amine-molybdenum complex compound and
sulfur-containing molybdenum complex compound. [0068] (I) Viscosity
Index Improvers (VII): polymethacrylate type polymers,
ethylene-propylene copolymers, styrene-isoprene copolymers,
hydrogenated styrene-isoprene copolymers, hydrogenated
star-branched polyisoprene, polyisobutylene, hydrogenated
star-branched styrene-isoprene copolymer and dispersant type
viscosity index improvers. [0069] (J) Pour point depressants:
polymethyl methacrylates, alkylmethacrylates and dialkyl
fumarate-vinyl acetate copolymers. [0070] (K) Foam Inhibitors:
alkyl methacrylate polymers and dimethyl silicone polymers.
EXAMPLES
[0071] 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
[0072] The low phosphorus lubricating oil composition of the
present invention was prepared by blending a 0.78 wt % mixture of
zinc bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate (0.24 wt %,
primary), zinc bis(O,O'-di-(2-butyl/4-methyl-2-pentyl)
dithiophosphate (0.15 wt %, secondary) and zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate (0.39 wt %, aryl) with
a Group II base oil of lubricating viscosity. The ratio of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate to zinc
bis(O,O'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate was about
1:1, based on the phosphorus content. The ratio of the mixture of
zinc bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate and zinc
bis(O,O'-di-(2-butyl/4-methyl-2-pentyl)dithiophosphate to zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate was about 2:1, based on
the phosphorus content. The resulting ratio of the three-way
mixture of zinc bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate to
zinc bis(O,O'-di-(2-butyl/4-methyl-2phenyl) dithiophosphate to zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate was 1:1:1, based on the
phosphorus content. The wt % of phosphorus in the prepared
lubricating oil composition was less than about 0.06 wt % based on
the total weight of the lubricating oil composition. Further, the
sulfur content and sulfated ash content 0.2 wt % and 0.8 wt %
balance of the lubricating oil composition containing a 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
[0073] Comparative Example A was prepared according to Example 1
except only about 1.16 wt % aryl zinc bis(O,O'-di-(dodecylphenyl)
dithiophosphate was added, instead of the mixture of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc
bis(O,O'-di-(2-butyl/4-methyl-2pentyl) dithiophosphate and zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate.
Comparative Example B
[0074] Comparative Example B was prepared according to Example 1
except only about 0.46 wt % zinc
bis(O,O'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate was added,
instead of the mixture of zinc bis(O,O'-di-(2-ethyl-1-hexyl)
dithiophosphate, zinc bis(O,O'-di-(2-butyl/4-methyl-2-pentyl)
dithiophosphate and zinc bis(O,O'-di-(dodecylphenyl)
dithiophosphate.
Comparative Example C
[0075] Comparative Example C was prepared according to Example 1
except only about 0.71 wt % zinc bis(O,O'-di-(2-ethyl-1-hexyl)
dithiophosphate, zinc bis(O,O'-di-(2-butyl/4-methyl-2-pentyl)
dithiophosphate and zinc bis(O,O'-di-(dodecylphenyl)
dithiophosphate.
Comparative Example D
[0076] Comparative Example D was prepared according Example 1
except about 0.81 wt % of a mixture of zinc bis
(O,O'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate and zinc bis
(O,O'-di-(dodecylphenyl) dithiophosphate in about a 1:1 ratio were
added, instead of the mixture of zinc bis(O,O'-di-(2-ethyl1-hexyl)
dithiophosphate, zinc bis(O,O'-di-(2-butyl/4-methyl-2pentyl)
dithiophosphate and zinc bis(O,O'-di-(dodecylphenyl)
dithiophosphate.
Comparative Example E
[0077] Comparative Example E was prepared according to Example 1
except about 0.94 wt % of a mixture of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate and zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate in about a 1:1 ratio
were added, instead of the mixture of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc
bis(O,O'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate and zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate.
Comparative Example F
[0078] Comparative Example F was prepared according to Example 1
except about 0.59 wt % of a mixture of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate and zinc
bis(O,O'-di-(2-butyl/4-methyl-2-pentyl) dithiophosphate in about a
1:1 ratio were added, instead of the mixture of zinc
bis(O,O'-di-(2-ethyl-1-hexyl) dithiophosphate, zinc
bis(O,O'-di-(2-butyl/4-methyl-2pentyl) dithiophosphate and zinc
bis(O,O'-di-(dodecylphenyl) dithiophosphate.
[0079] Each formulation according to Example 1 and Comparative
Example A-F were tested for lead corrosion 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, at an 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.
[0080] The test results are summarized in Table II.
TABLE-US-00003 TABLE II HTCBT Results Comparative Examples Example
1 A B C D E F Lead, 48.4 113.4 93.4 305 64.6 87.3 99.4 ppm
[0081] 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 lubricating oil composition of the present
invention.
* * * * *