U.S. patent application number 10/291902 was filed with the patent office on 2004-05-13 for alkyl (meth) acrylate copolymers.
Invention is credited to Liesen, Gregory Peter.
Application Number | 20040092409 10/291902 |
Document ID | / |
Family ID | 32107665 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040092409 |
Kind Code |
A1 |
Liesen, Gregory Peter |
May 13, 2004 |
Alkyl (meth) acrylate copolymers
Abstract
Alkyl (meth) acrylate copolymers comprising from about 10 to
about 23 weight percent C.sub.3-C.sub.7 alkyl (meth) acrylate; from
about 77 to about 90 weight percent C.sub.12-C.sub.14 alkyl (meth)
acrylate(s); and from 0 to about 6 weight percent of at least one
C.sub.6-C.sub.20 alkyl (meth) acrylate, which provide excellent low
temperature properties and shear stability to lubricating oils. The
preferred embodiment comprises butyl (meth) acrylate as the
C.sub.3-C.sub.7 alkyl (meth) acrylate, and is essentially free from
methyl (meth) acrylate.
Inventors: |
Liesen, Gregory Peter;
(Mechanicsville, VA) |
Correspondence
Address: |
Ethyl Corporation
330 South Fourth Street
Richmond
VA
23219
US
|
Family ID: |
32107665 |
Appl. No.: |
10/291902 |
Filed: |
November 11, 2002 |
Current U.S.
Class: |
508/469 ;
526/329.7 |
Current CPC
Class: |
C08F 220/1804
20200201 |
Class at
Publication: |
508/469 ;
526/329.7 |
International
Class: |
C10M 145/14 |
Claims
I claim:
1. An alkyl (meth) acrylate copolymer comprising: (A) about 10 to
about 23 weight percent of at least one C.sub.3-C.sub.7 alkyl
(meth) acrylate; (B) about 77 to about 90 weight percent of at
least one C.sub.12-C.sub.14 alkyl (meth) acrylate; and (C) 0 to
about 6 weight percent of at least one C.sub.16-C.sub.20 alkyl
(meth) acrylate.
2. An alkyl (meth) acrylate copolymer product obtained by combining
components comprising: (A) from about 10 to about 23 weight percent
of at least one C.sub.3-C.sub.7 alkyl (meth) acrylate; (B) from
about 77 to about 90 weight percent of at least one
C.sub.12-C.sub.14 alkyl (meth) acrylate; and (C) 0 to about 6
weight percent of at least one C.sub.16-C.sub.20 alkyl (meth)
acrylate.
3. The copolymer of claim 1 or claim 2, wherein the copolymer is
essentially free from methyl (meth) acrylate units.
4. The copolymer of claim 1 or claim 2, wherein the C.sub.3-C.sub.7
alkyl (meth) acrylate is butyl (meth) acrylate.
5. The copolymer of claim 1 or claim 2, wherein the copolymer has
an average molecular weight number from about 5,000 to about
50,000.
6. A method for making a lubricating oil, comprising adding to an
oil of lubricating viscosity a copolymer according to claim 1 or
claim 2.
7. A lubricating oil composition comprising: (A) an oil of
lubricating viscosity; and (B) a copolymer according to claim 1 or
claim 2.
8. The lubricating oil composition of claim 7, wherein the
C.sub.3-C.sub.7 alkyl (meth) acrylate is butyl (meth) acrylate.
9. The lubricating oil composition of claim 7, wherein the
composition is essentially free from methyl (meth) acrylate
units.
10. The lubricating oil composition of claim 7, wherein component
(B) is present in an amount of from 1 to about 30 parts by weight
of active copolymer per 100 parts by weight of oil in a final
composition.
11. The lubricating oil composition of claim 7 further comprising
at least one additive selected from the group consisting of
oxidation inhibitors, corrosion inhibitors, friction modifiers,
antiwear agents, extreme pressure agents, detergents, dispersants,
antifoamants, additional viscosity index improvers, and pour point
depressants.
12. A method for improving the low temperature properties of an
oil, said method comprising adding to an oil of lubricating
viscosity a copolymer according to claim 1 or claim 2.
13. A method for improving the compatibility of a lubricating oil
containing additive components, said method comprising adding to an
oil of lubricating viscosity at least one additive component, and a
copolymer according to claim 1 or claim 2.
14. A method for improving the viscosity index of a lubricating
oil, said method comprising adding to an oil of lubricating
viscosity a copolymer according to claim 1 or claim 2.
15. A gear lubricant composition comprising: (A) an oil of
lubricating viscosity; and (B) a copolymer according to claim 1 or
claim 2.
16. The gear lubricant composition of claim 15, wherein the
C.sub.3-C.sub.7 alkyl (meth) acrylate is butyl (meth) acrylate.
17. The gear lubricant composition of claim 15, wherein the
copolymer is essentially free from methyl (meth) acrylate.
18. The gear lubricant composition of claim 15, wherein component
(B) is present in an amount of 1 to about 30 by weight of active
copolymer by weight in said gear lubricant composition.
19. A composition for an automatic transmission fluid comprising:
(A) an oil of lubricating viscosity; (B) a copolymer according to
claim 1 or claim 2; and (C) at least one additive selected from the
group consisting of oxidation inhibitors, corrosion inhibitors,
friction modifiers, antiwear agents, extreme pressure agents,
detergents, dispersants, antifoamants, viscosity index improvers,
and pour point depressants.
20. A method for lubricating a continuously variable transmission,
comprising applying thereto the composition of claim 19.
21. The composition of claim 19, wherein the automatic transmission
fluid has a percent shear stability index, as determined by the 20
hour Tapered Bearing Shear Test, in the range of 1% to about
80%.
22. The composition of claim 19, wherein said automatic
transmission fluid has a percent shear stability index, as
determined by the 20 hour Tapered Bearing Shear Test, in the range
of 1% to 20%.
23. The composition of claim 19, wherein the transmission fluid is
a continuously variable transmission fluid.
25. A vehicle comprising an automatic transmission lubricated with
the composition of claim 19.
25. An automatic transmission lubricated with the composition of
claim 19.
26. The automatic transmission of claim 25, wherein the
transmission is a continuously variable transmission.
27. The copolymer of claim 1, wherein component (A) is present in
an amount of about 11 to about 18 weight percent.
28. The copolymer of claim 1, wherein component (A) is present in
an amount of about 12 to about 13 weight percent.
Description
TECHNICAL FIELD
[0001] This invention relates to novel alkyl (meth) acrylate
copolymers having excellent low temperature properties and shear
stability in a wide variety of base oils. The present invention
also relates to the use of these copolymers as viscosity index
improvers for lubricating oils. In addition, this invention
demonstrates a benefit with respect to compatibility of said VIIs
with additive packages.
BACKGROUND OF THE INVENTION
[0002] Polymethacrylate (PMA) viscosity index improvers (VIIs) are
well known in the lubricating industry. Many attempts have been
made to produce PMA VIIs that have the desired balance of high
temperature and low temperature viscometrics, as well as the
required shear stability for a given application. Refiners who
blend with different base oils desire a single product that
performs effectively in all of these different base oils.
[0003] The present invention is directed to novel alkyl (meth)
acrylate copolymers which exhibit excellent low temperature
performance and superior shear stability in a wide variety of base
oils. The copolymers of the present invention also demonstrate
superior compatibility with other additives. While combinations of
various alkyl (meth) acrylates may be found in viscosity index
improver formulations, specific reliance on copolymers of
C.sub.3-C.sub.7 alkyl (meth) acrylates, with the exclusion of
methyl (meth) acrylate, leads to the novelty of the present
invention.
[0004] U.S. Pat. No. 6,103,673 discloses a composition that
includes a variety of poly (meth) acrylates as viscosity modifiers.
The broad objective of the '673 patent is to prepare a viscosity
modifier incorporating poly (meth) acrylates having alkyl groups
containing from 1 to 18 carbon atoms. (Column 5, lines 29-33)
Specifically, the '673 patent discloses a viscosity modifier
prepared using butyl (meth) acrylate as one component in a mix of
poly (meth) acrylates. (Column 7, line 12) However, the '673 patent
does not teach the contribution of the present invention, which is
the primary use of C.sub.3-C.sub.7 alkyl (meth) acrylate copolymers
and the benefit resulting from the exclusion of methyl (meth)
acrylate, ultimately yielding a superior viscosity index
improver.
[0005] The present invention is directed to butyl (meth) acrylate
copolymers in a viscosity index improver (VII) formulation, whereas
the preferred nitrogen-containing dispersant-type viscosity
modifiers of the '673 patent are notably different. For example,
the '673 patent's specification discloses as its preferred
embodiment a composition consisting essentially of C.sub.2-C.sub.24
(meth) acrylates (Column 6, lines 44-46), with the remaining active
monomers being nitrogen-containing. The scope of the '673 patent
also differs from that of the present invention, which additionally
eliminates methyl (meth) acrylate materials from its product to
achieve superior low temperature properties.
[0006] U.S. Pat. No. 6,271,184 discloses an optional component of
methacrylic acid esters containing from 2 to about 8 carbon atoms
in the ester group. The '184 patent presents embodiments that do
not utilize a methacrylic acid component, and it is stipulated in
the '184 patent that methyl (meth) acrylate is especially
preferred. The teaching of the '184 patent additionally provides
that the optional component may be a nitrogen-containing monomer,
styrene, or substituted styrene. While various alkyl (meth)
acrylate monomers are discussed in the '184 patent, the preferred
use of methyl (meth) acrylate as a constituent in the composition
does not articulate the novelty of the present invention.
[0007] Specifically, in an embodiment, the composition of the
present invention is essentially free from methyl (meth) acrylate,
in favor Of C.sub.3-C.sub.7 alkyl (meth) acrylate copolymers in a
viscosity improver formulation.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a novel formulation of
alkyl (meth) acrylate copolymers and their use as viscosity index
improvers for lubricating oils.
[0009] The alkyl (meth) acrylate copolymers of the present
invention comprise material derived from the combining of:
[0010] (A) about 10 to about 23 weight percent C.sub.3-C.sub.7
alkyl (meth) acrylate copolymers;
[0011] (B) about 77 to about 90 weight percent of C.sub.12-C.sub.14
alkyl (meth) acrylates; and
[0012] (C) 0 to about 6 weight percent of C.sub.16-C.sub.20 alkyl
(meth) acrylates.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention is directed, in an embodiment, to
alkyl (meth) acryl ate copolymers comprising material derived from
the combining of:
[0014] (A) about 10 to about 23 weight percent C.sub.3-C.sub.7
alkyl (meth) acrylate copolymers;
[0015] (B) about 77 to about 90 weight percent Of C.sub.12-C.sub.14
alkyl (meth) acrylates; and
[0016] (C) 0 to about 6 weight percent Of C.sub.16-C.sub.20 alkyl
(meth) acrylates.
[0017] Alkyl (meth) acryl ate copolymers of the present invention
can comprise the product, reaction product or products resulting
from the process of combining:
[0018] (A) about 10 to about 23 weight percent C.sub.3-C.sub.7
alkyl (meth) acrylate copolymers;
[0019] (B) about 77 to about 90 weight percent Of C.sub.12-C.sub.14
alkyl (meth) acrylates; and
[0020] (C) 0 to about 6 weight percent of C.sub.16-C.sub.20 alkyl
(meth) acrylates.
[0021] As used herein, "combining" may be used to mean the mixing,
blending, contacting, free-radical polymerization, sequential
polymerization, or anionic polymerization of elements in a
composition.
[0022] Also, as used herein, a "C.sub.3-C.sub.7 alkyl (meth)
acrylate" means an alkyl ester of acrylic or methacrylic acid
having a straight or branched alkyl group of 3 to 7 carbon atoms
per group, including but not limited to, n-propyl, isopropyl,
n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, and
n-heptyl monomers.
[0023] In one embodiment of the present invention, n-propyl (meth)
acrylate is used as component (A). In another embodiment of the
present invention, isopropyl (meth) acrylate is used as component
(A). In another embodiment of the present invention, n-butyl (meth)
acrylate is used as component (A). In another embodiment of the
present invention, isobutyl (meth) acrylate is used as component
(A). In another embodiment, tert-butyl (meth) acrylate is used as
component (A). In another embodiment of the present invention,
n-pentyl (meth) acrylate is used as component (A). In another
embodiment, isopentyl (meth) acrylate is used as component (A). In
another embodiment of the present invention, n-hexyl (meth)
acrylate is used as component (A). In another embodiment, n-heptyl
(meth) acrylate is used as component (A).
[0024] As used herein, "at least one C.sub.12-C.sub.14 alkyl (meth)
acrylate" means an alkyl ester of acrylic or methacrylic acid
having a straight or branched alkyl group of 12 to 14 carbon atoms
per group, including, but not limited to, n-dodecyl, t-dodecyl, and
n-tetradecyl monomers.
[0025] As used herein, "at least one C.sub.16-C.sub.20 alkyl (meth)
acrylate" means an alkyl ester of acrylic or methacrylic acid
having a straight or branched alkyl group of 16 to 20 carbon atoms
per group, including, but not limited to, n-hexadecyl, n-octadecyl,
and n-eicosyl monomers.
[0026] It is an object in an embodiment of this invention to
optimize the C.sub.3-C.sub.7 alkyl (meth) acrylate concentrations
in the composition, and reduce or preferably eliminate methyl
(meth) acrylate components. This enhances compatibility with
additive packages while preserving desirable low temperature and
shear stability properties. Therefore, it is a further object of
this invention is to improve the composition's compatibility with
components in additive packages.
[0027] The comonomers in the alkyl groups useful in one embodiment
of the present invention are generally prepared by standard
esterification procedures using technical grades of long chain
aliphatic alcohols. These commercially available alcohols are
mixtures of alcohols of varying chain lengths in the alkyl groups.
Consequently, for the purposes of this invention, an alkyl (meth)
acrylate is intended to include not only the individual alkyl
(meth) acrylate product named, but also to include mixtures of the
alkyl (meth) acrylates with a predominant amount of the particular
alkyl (meth) acrylate named. However, it is an objective of the
present invention to reduce or eliminate methyl (meth) acrylate
constituents from the composition.
[0028] In a preferred embodiment, the C.sub.3-C.sub.7 alkyl (meth)
acrylate copolymers of the present invention comprise the
polymerization reaction products of (A), (B), and (C). However,
those skilled in the art will appreciate that minor levels of other
monomers, polymerizable with monomers (A), (B), and (C), disclosed
herein, may be present as long as they do not adversely affect the
low temperature properties of the fully formulated fluids.
Typically, additional nonspecific monomers are present in an amount
of less than about 5 weight percent, preferably in an amount of
less than 3 weight percent, most preferably in an amount of less
than 1 weight percent. In a preferred embodiment, the sum of the
weight percent of (A), (B), and (C) equals 100%. Thus, as an
objective of the present invention is to eliminate methyl (meth)
acrylate from the product, a composition that is "essentially free"
of methyl (meth) acrylate will encompass those containing trace
amounts of methyl (meth) acrylate as described above.
[0029] The copolymers of the present invention may be prepared
using various polymerization techniques including free-radical and
anionic polymerization.
[0030] Conventional methods of free-radical polymerization can be
used to prepare the copolymers of the present invention.
Polymerization of the acrylic and/or methacrylic monomers can take
place under a variety of conditions, including bulk polymerization,
solution polymerization, usually in an organic solvent, preferably
mineral oil, emulsion polymerization, suspension polymerization and
non-aqueous dispersion techniques.
[0031] "Reaction product," as used herein, is intended to mean the
material resulting from the mixing, blending, contacting, reacting,
polymerizing, anionic polymerizing, and/or copolymerizing of two or
more materials.
[0032] Solution polymerization is preferred. In solution
polymerization, a reaction mixture is prepared comprising a
diluent, the alkyl (meth) acrylate monomers, a polymerization
initiator, and a chain transfer agent.
[0033] In an embodiment, the diluent may be any inert hydrocarbon
and is preferably a hydrocarbon lubricating oil that is compatible
with or identical to the lubricating oil in which the copolymer is
to be subsequently used. The mixture includes, e.g., from about 15
to about 400 parts by weight (pbw) diluent per 100 pbw total
monomers and, more preferably, from about 50 to about 200 pbw
diluent per 100 pbw total monomers. As used herein, "total monomer
charge" means the combined amount of all monomers in the initial,
i.e., unreacted, reaction mixture.
[0034] In preparing the copolymers of the present invention by
free-radical polymerization, the acrylic monomers may be
polymerized simultaneously or sequentially, in any order. In at
least one preferred embodiment, the total monomer charge includes
from 10 to 23, preferably 12 to 18, weight percent of at least one
C.sub.3-C.sub.7 alkyl (meth) acrylate; 77 to 90, preferably 82 to
88, weight percent of at least one C.sub.12-C.sub.14 alkyl (meth)
acrylate; and 0 to 6, preferably 0 to 3, weight percent of at least
one C.sub.16-C.sub.20 alkyl (meth) acrylate. The most preferred
embodiment, presented herein, is one in which the total monomer
charge comprises 12 to 14 weight percent butyl (meth) acrylate, 86
to 88 weight percent of at least one C.sub.12-C.sub.14 alkyl (meth)
acrylate, and 0 to 3 weight percent of at least one
C.sub.16-C.sub.20 alkyl (meth) acrylate.
[0035] Suitable polymerization initiators include initiators which
disassociate upon heating to yield a free radical, e.g., peroxide
compounds such as benzoyl peroxide, t-butyl perbenzoate, t-butyl
peroctoate and cumene hydroperoxide; and azo compounds such as
azoisobutyronitrile and 2,2'-azobis (2-methylbutanenitrile). The
reaction mixture typically includes from about 0.01 wt % to about
1.0 wt % initiator relative to the total monomer mixture.
[0036] Suitable chain transfer agents include those conventional in
the art, e.g., dodecyl mercaptan and ethyl mercaptan. The selection
of the amount of chain transfer agent to be used is based on the
desired molecular weight of the polymer being synthesized as well
as the desired level of shear stability for the polymer, i.e., if a
more shear stable polymer is desired, more chain transfer agent can
be added to the reaction mixture. Preferably, the chain transfer
agent is added to the reaction mixture in an amount of 0.01 to 5
weight percent, preferably 0.02 to 3 weight percent, relative to
the monomer mixture.
[0037] By way of example and without limitation, the reaction
mixture is charged to a reaction vessel that is equipped with a
stirrer, a thermometer and a reflux condenser and heated with
stirring under a nitrogen blanket to a temperature from about
50.degree. C. to about 125.degree. C., for a period of about 0.5
hours to about 8 hours to carry out the copolymerization reaction.
In another embodiment, the copolymers may be prepared by initially
charging a portion, e.g., about 25 to 60% of the reaction mixture
to the reaction vessel and heating. The remaining portion of the
reaction mixture is then metered into the reaction vessel, with
stirring and while maintaining the temperature of the batch within
the above describe range, over a period of about 0.5 hours to about
8 hours. A viscous solution of the copolymer of the present
invention in the diluent is obtained as the product of the
above-described process.
[0038] To form the lubricating oil compositions of the present
invention, a base oil is treated with at least one of the alkyl
(meth) acrylate copolymers of the present invention in a
conventional manner, i.e., by adding the alkyl (meth) acrylate
copolymer to the base oil to provide a lubricating oil composition
having the desired low temperature properties. In an embodiment of
the present invention, the lubricating oil contains from about 10
to about 23 parts by weight (pbw), preferably 11 to 18 pbw, most
preferably 12 to 13 pbw, of at least one of the C.sub.3-C.sub.7
alkyl (meth) acrylates (i.e., excluding diluent oil) per 100 of the
monomer mixture. In a particularly preferred embodiment, the alkyl
(meth) acrylate copolymer is added to the base oil in the form of a
relatively concentrated solution of the copolymer in a diluent. The
relative amount of the (meth) acrylate copolymer(s) in the
concentrated VII solution of the preferred embodiment can be, for
example, 80 weight %, and can be ultimately diluted to
approximately 60 weight % polymer for improved compatibility. The
diluent includes any of the oils referred to below that are
suitable for use as base oils.
[0039] FIG. 1, shown below, demonstrates that the low temperature
properties of the present invention are best achieved using a
specific range of concentrations of C.sub.3-C.sub.7 (meth) acrylate
in the neat copolymer. The preferred embodiment, butyl (meth)
acrylate, was tested at concentrations ranging from 7.5 weight % to
23 weight %. As shown in FIG. 1, butyl (meth) acrylate at
concentrations less than 10 weight % demonstrated -40.degree. C.
Brookfield Viscosities that were in excess of 10,000 (not
acceptable). At concentrations greater than 18 weight %, butyl
(meth) acrylate again exceeded acceptable -40.degree. C. Brookfield
Viscosity levels. In order to achieve desirable low temperature
properties, the optimal range of concentrations for butyl (meth)
acrylate fell within the range of approximately 10 weight % and 18
weight %.
[0040] A final formulation containing additives and alkyl (meth)
acrylate copolymers must be evaluated for compatibility of
components, as well as performance as a viscosity index improver.
The preferred embodiment of the present invention was further
evaluated, utilizing butyl (meth) acrylate in a concentrate of
approximately 80 weight % copolymer. Ultimately a final product was
diluted to a ratio in which the copolymer component in the VII is
generally 58 weight %. The optimal weight % range for butyl (meth)
acrylate in a formulation is thus evaluated based upon at least two
criteria: effectiveness as a VII at low temperatures, and degree of
haziness or separation of components when combined with other
additives-an indicator of compatibility. Using the effective
low-temperature range of butyl (meth) acrylate concentrations
provided by FIG. 1 (above), compatibility with additive packages
was evaluated and the results are shown in Table 1.
1TABLE 1 Compatibility of Copolymers of Butyl (meth) Acrylate (BMA)
at Varying Concentrations of BMA with an Additive Package Number of
Days Before Sample Wt % BMA Indication of Dropout (A) 7.5 Clear
after 1 month (B) 10 Hazy near bottom after 1 month (C) 12.3 5 (D)
15 3 (E) 17.5 2 (F) 23.1 2
[0041] The butyl (meth) acrylate containing copolymer:additive
package compatibility differed based upon the level of butyl (meth)
acrylate in the prepared copolymer. For example, Samples (A) and
(B) were clear for long periods of time, demonstrating successful
compatibility with the additive package. Sample (C) demonstrated
acceptable compatibility, followed by a separation after five days.
Samples (D), (E), and (F) were not as compatible as preferred,
having separation of the copolymer from the formulation in three
days or less.
[0042] A comparison analysis using methyl (meth) acrylate
copolymers was performed. Methyl (meth) acrylate is a preferred
component in many conventional poly (meth) acrylate viscosity index
improvers. It is noted that the present invention is essentially
free of methyl (meth) acrylate. The comparison analysis utilized
butyl (meth) acrylate at two concentrations, 17.5 wt % and 23.0 wt
%, and methyl (meth) acrylate at 17.5 wt %. Even at the higher
concentration of butyl (meth) acrylate (BMA) of 23.0 wt %, less
haziness and separation was shown in comparison to the sample of
methyl (meth) acrylate (MMA). Table 2 demonstrates increased
haziness and separation when the formulation incorporates MMA
instead of BMA at a cold temperature (-1.degree. C.), room
temperature, and at 60.degree. C.
2TABLE 2 Compatability Comparison of Copolymers with an additive
package:Representative levels of Butyl (Meth) Acrylate to Methyl
(Meth) Acrylate STORAGE DURATION AND TEMPERATURE -1.degree. C. Room
Temperature 60.degree. C. 3 Days 10 Days 3 Days 10 Days 3 Days 10
Days BMA clear slight haze clear clear clear clear (17.5 wt. %) BMA
slight haze slight haze very slight very slight clear very slight
(23.0 wt. %) haze haze haze MMA hazy hazy hazy hazy hazy hazy,
(17.5 wt. %) 1 mm separation
[0043] Furthermore, samples of VII formulations incorporating butyl
(meth) acrylate and methyl (meth) acrylate were compared for
performance at equivalent molar concentrations. The sample of
methyl (meth) acrylate achieved a Brookfield viscosity at
-40.degree. C. of >153,000 cP, exceeding the 14,000 cP maximum
allowed. The sample using butyl (meth) acrylate achieved a
Brookfield viscosity at -40.degree. C. of 8,480 cP, a superior and
successful performance. Thus, riot only is butyl (meth) acrylate
demonstrated to be more compatible with additive components, but it
is also superior in performance to methyl (meth) acrylate
formulations.
[0044] The copolymers of the present invention include the
preferred embodiment, butyl (meth) acrylate, as well as
C.sub.3-C.sub.7 alkyl (meth) acrylates as described herein. As may
be understood from Table 2, it is particularly important in
achieving the present invention's compatibility with additive
packages to reduce or eliminate methyl (meth) acrylate from the
concentrate and lubricating oil compositions.
[0045] The copolymers of the present invention typically have a
relative number average molecular weight, as determined by gel
permeation chromatography using polymethyl methacrylate standards,
between 5,000 and 50,000, preferably 7,500 to 25,000.
[0046] The molecular weight of the alkyl (meth) acrylate copolymer
additive of the present invention must be sufficient to impart the
desired thickening properties to the lubricating oil. As the
molecular weight of the polymers increase, the copolymers become
more efficient thickeners; however, the polymers can undergo
mechanical degradation in particular applications and for this
reason, polymer additives with number-average molecular weights
(Mw) above about 50,000 are generally not suitable for certain
applications because they tend to undergo "thinning" due to
molecular weight degradation resulting in loss of effectiveness as
thickeners at the higher use temperatures (for example, at
100.degree. C.). Thus, the molecular weight is ultimately governed
by thickening efficiency, required shear stability, cost, and the
type of end-use application.
[0047] Those skilled in the art will recognize that the molecular
weights set forth throughout this specification are relative to the
methods by which they are determined. For example, molecular
weights determined by GPC, and molecular weights calculated by
other methods, may have different values. It is not molecular
weight per se, but the handling characteristics and performance of
a polymeric additive (shear stability, low temperature performance
and thickening power under use conditions) that are important.
Generally, shear stability is inversely proportional to molecular
weight. A VII additive with good shear stability (low SSI value) is
typically used at higher initial concentrations relative to another
additive having reduced shear stability (high SSI value) to obtain
the same target thickening effect in a treated fluid at high
temperatures; the additive having good shear stability may,
however, produce unacceptable thickening at low temperatures due to
the higher use concentrations.
[0048] Conversely, although lubricating oils containing lower
concentrations of reduced shear stability VI-improving additives
may initially satisfy the higher temperature viscosity target,
fluid viscosity will decrease significantly with use causing a loss
of effectiveness of the lubricating oil. Thus, the reduced shear
stability of specific VI-improving additives may be satisfactory at
low temperatures (due to its lower concentration) but it may prove
unsatisfactory under high temperature conditions. Thus, polymer
composition, molecular weight and shear stability of VI improvers
must be selected to achieve a balance of properties that satisfy
both high and low temperature performance requirements.
[0049] The finished lubricating oil composition may include other
additives in addition to the copolymer of the present invention,
e.g., oxidation inhibitors, corrosion inhibitors, friction
modifiers, antiwear agents, extreme pressure agents, detergents,
dispersants, antifoamants, additional viscosity index improvers,
and pour point depressants.
[0050] Base oils contemplated for use in this invention include
natural oils, synthetic oils and mixtures thereof. Suitable base
oils also include basestocks obtained by isomerization of synthetic
wax and slack wax, as well as basestocks produced by hydrocracking
(rather than solvent extracting) the aromatic and polar components
of the crude. In general, both the natural and synthetic base oils
will each have a kinematic viscosity ranging from about 1 to about
40 cSt at 100.degree. C., although typical applications will
require each oil to have a viscosity ranging from about 2 to about
20 cSt at 100.degree. C.
[0051] Natural base oils can include, but are not limited to,
animal oils, vegetable oils (e.g., castor oil and lard oil),
petroleum oils, mineral oils, and oils derived from coal or shale.
The preferred natural base oil is mineral oil.
[0052] The mineral oils useful in this invention include all common
mineral oil base stocks. This would include oils that are
naphthenic or paraffinic in chemical structure. Oils that are
refined by conventional methodology using acid, alkali, and clay or
other agents such as aluminum chloride, or they may be extracted
oils produced, for example, by solvent extraction with solvents
such as phenol, sulfur dioxide, furfural, dichlordiethyl ether,
etc. They may be hydrotreated or hydrorefined, dewaxed by chilling
or catalytic dewaxing processes, or hydrocracked. The mineral oil
may be produced from natural crude sources or be composed of
isomerized wax materials or residues of other refining
processes.
[0053] Typically the base oils will have kinematic viscosities of
from 2 cSt to 40 cSt at 100.degree. C. The preferred base oils have
kinematic viscosities of from 2 to 20 cSt at 100.degree. C.
[0054] The American Petroleum Institute has categorized these
different basestock types as follows: Group I, >0.03 wt. %
sulfur, and/or <90 vol % saturates, viscosity index between 80
and 120; Group II, .ltoreq.0.03 wt. % sulfur, and .gtoreq.90 vol %
saturates, viscosity index between 80 and 120; Group III,
.ltoreq.0.03 wt. % sulfur, and .gtoreq.90 vol % saturates,
viscosity index >120; Group IV, all polyalphaolefins.
[0055] Group II and Group III basestocks are typically prepared
from conventional feedstocks using a severe hydrogenation step to
reduce the aromatic, sulfur and nitrogen content, followed by
dewaxing, hydrofinishing, extraction and/or distillation steps to
produce the finished base oil. Group II and III basestocks differ
from conventional solvent refined Group I basestocks in that their
sulfur, nitrogen and aromatic contents are very low. As a result,
these base oils are compositionally very different from
conventional solvent refined basestocks. Hydrotreated basestocks
and catalytically dewaxed basestocks, because of their low sulfur
and aromatics content, generally fall into the Group II and Group
III categories. Polyalphaolefins (Group IV basestocks) are
synthetic base oils prepared from various alpha olefins and are
substantially free of sulfur and aromatics.
[0056] Synthetic base oils include hydrocarbon oils and
halo-substituted hydrocarbon oils such as oligomerized,
polymerized, and interpolymerized olefins (such as polybutylenes,
polypropylenes, propylene, isobutylene copolymers, chlorinated
polylactenes, poly(1-hexenes), poly(1-octenes) and mixtures
thereof); alkylbenzenes (including dodecyl-benzenes,
tetradecylbenzenes, dinonyl-benzenes and di(2-ethylhexyl)benzene);
polyphenyls (such as biphenyls, terphenyls and alkylated
polyphenyls); and alkylated diphenyl ethers, alkylated diphenyl
sulfides, as well as their derivatives, analogs, and homologs
thereof, and the like. The preferred synthetic oils are oligomers
of alpha-olefins, particularly oligomers of 1-decene, also known as
polyalpha olefins or PAO's.
[0057] Synthetic base oils also include alkylene oxide polymers,
interpolymers, copolymers, and derivatives thereof where the
terminal hydroxyl groups have been modified by esterification,
etherification, etc. This class of synthetic oils is exemplified
by: polyoxyalkylene polymers prepared by polymerization of ethylene
oxide or propylene oxide; the alkyl and aryl ethers of these
polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol
ether having an average molecular weight of 1000, diphenyl ether of
polypropylene glycol having a molecular weight of 100-1500); and
mono- and poly-carboxylic esters thereof (e.g., the acetic acid
esters, mixed C.sub.3-C.sub.8 fatty acid esters, and C.sub.12 oxo
acid diester of tetraethylene glycol).
[0058] Another suitable class of synthetic lubricating oils
comprises the esters of dicarboxylic acids (e.g., phthalic acid,
succinic acid, alkyl succinic acids and alkenyl succinic acids,
maleic acid, azelaic acid, subric acid, sebasic acid, fumaric acid,
adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids,
alkenyl malonic acids, etc.) with a variety of alcohols (e.g.,
butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl
alcohol, ethylene glycol, diethylene glycol monoethers, propylene
glycol, etc.). Specific examples of these esters include dibutyl
adipate, diisobutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl
fumarate, dioctyl sebacate, diisooctyl phthalate, diisooctyl
azelate, diisooctyl adipate, diisodecyl azelate, didecyl phthalate,
diisodecyl adipate, dieicosyl sebacate, the 2-ethylhexyl diester of
linoleic acid dimer, and the complex ester formed by reacting one
mole of sebasic acid with two moles of tetraethylene glycol and two
moles of 2-ethyl-hexanoic acid, and the like. A preferred type of
oil from this class of synthetic oils are adipates of C.sub.4 to
C.sub.12 alcohols.
[0059] Esters useful as synthetic base oils also include those made
from C.sub.5 to C.sub.12 monocarboxylic acids and polyols and
polyol ethers such as neopentyl glycol, trimethylolpropane
pentaerythritol, dipentaerythritol, tripentaerythritol, and the
like.
[0060] Silicon-based oils (such as the polyalkyl-, polyaryl-,
polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils)
comprise another useful class of synthetic lubricating oils. These
oils include tetra-ethyl silicate, tetraisopropyl silicate,
tetra-(2-ethylhexyl) silicate, tetra-(4-methyl-2-ethylhexyl)
silicate, tetra-(p-tert-butylphenyl) silicate,
hexa-(4-methyl-2-pentoxy)-disiloxane, poly(methyl)-siloxanes and
poly (methylphenyl) siloxanes, and the like. Other synthetic
lubricating oils include liquid esters of phosphorus containing
acids (e.g., tricresyl phosphate, trioctylphosphate, and diethyl
ester of decylphosphonic acid), polymeric tetra-hydrofurans,
poly--olefins, and the like.
[0061] Lubricating oil compositions of the present invention
comprising the alkyl (meth) acrylate copolymers of the present
invention may be used in numerous applications including gear
lubrication, automatic transmission fluids, continuously variable
transmission fluids, manual transmission fluids, hydraulic fluids,
crankcase applications and shock absorber fluids.
[0062] Depending upon the intended end use of the lubricating oil
formulations and the compositions of the present invention, the
shear stability of the inventive acrylate copolymer can be adjusted
by controlling the amount of initiator and/or chain transfer agent
present in the polymerization reaction mixture.
[0063] For example, in automatic transmission fluid applications it
may be desired to have a highly shear stable lubricating fluid. In
an embodiment of the present invention, automatic transmission
fluids are prepared by adding to a base oil a copolymer of the
present invention and a detergent/inhibitor package such that the
fluids have a percent shear stability index (SSI) as determined by
the 20 hour Tapered Bearing Shear Test in the range of 1% to about
80%, preferably 1 to 20%. The 20 hour Tapered Bearing Shear Test is
a published standard test entitled "Viscosity Shear Stability of
Transmission Lubricants" and is described in CEC L-45-T-93 (Taper
Roller Bearing) and is also published as DIN 51 350, part 6, said
publication being incorporated by reference herein in its
entirety.
[0064] The general procedure used to prepare the butyl (meth)
acrylate polymer, the preferred embodiment of the present
invention, was as follows: To a 2 liter resin kettle fitted with an
overhead stirrer, a thermocouple, a sparge tube, and a condenser
was charged the monomer and the reaction oil. The stirrer was set
at 300 rpm and the temperature was increased to 40.degree. C. The
sparge tube was replaced with a nitrogen blanket and the
temperature was increased to about 78.degree. C. Then, lauryl
(dodecyl) mercaptan as a chain transfer agent was then added,
followed by AIBN (azobisisobutyronitrile). The mixture was heated
and stirred for 4 hours at 78.degree. C. The temperature was then
increased to about 104.degree. C. for 1.5 hours to decompose any
residual catalyst. Diluent oil was added to arrive at 58% polymer
solution by weight and stirring and heating continued at about
70-80.degree. C. for 1 hour. The reactor was cooled and the diluted
polymer was then stored at room temperature until testing.
[0065] After preparing the copolymers and fluids in embodiments of
the present invention, a final formulation may be produced that
exceeds the capabilities known or expected in the art. As shown
below in Table 3, a commercially available VII product,
Viscoplex.TM. 0-030, was compared an embodiment of the present
invention prepared as described herein. The preferred embodiment of
the present invention, butyl (meth) acrylate (BMA) copolymers,
demonstrated compatibility with a standard additive package as well
as improved performance. Table 3 demonstrates the superior low
temperature properties of the BMA copolymers of the present
invention, wherein the two lubricant compositions were tested using
the identical type and amount of additive package. No pour point
depressant was added. The low temperature properties of these
fluids were tested according to ASTM D 2983, which is incorporated
herein by reference.
3TABLE 3 Test Performance of Butyl (Meth) Acrylate Compared to a
Competitive Product Viscoplex .TM. BMA 0-030 TESTING LIMITS
Kinematic Viscosity, 100 C 7.17 7.06 7.0 cSt min (cSt) Kinematic
Viscosity, 40 C 33.53 33.21 40 cSt max (cSt) Pour Point (C) -45 -48
-45 C max Brookfield @ -40C (cP) 8480 15720 14000 cP max Brookfield
@ -30C (cP) 2660 4120 3300 cP max 20 hour KRL, % viscosity 2.95
5.53 minimize loss
[0066] It is clear that lubricant formulation comprising the
viscosity index improver of the present invention exhibits superior
low temperature properties compared to polymethacrylate viscosity
index improver outside the scope of the present invention, as
evidenced by the superior results in Table 3. Specifically, the
inventive sample exhibited a Brookfield viscosity at -40C of 8480
cps (a "pass") versus the 15,720 cps (a "fail") for the
commercially available Viscoplex 0-030.TM., which was selected for
comparison. Similarly, the inventive example exhibited a Brookfield
viscosity at -30C of 2660 cps (a "pass") versus the 4120 cps (a
"fail") of the Viscoplex 0-030.TM..
[0067] This invention is susceptible to considerable variation in
its practice. Accordingly, this invention is not limited to the
specific exemplifications set forth hereinabove. Rather, this
invention is within the spirit and scope of the appended claims,
including the equivalents thereof available as a matter of law.
[0068] The patentees do not intend to dedicate any disclosed
embodiments to the public, and to the extent any disclosed
modifications or alterations may not literally fall within the
scope of the claims, they are considered to be part of the
invention under the doctrine of equivalents.
* * * * *