Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Reexamination Certificate
1998-12-02
2004-04-27
Szekely, Peter (Department: 1714)
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
C508S261000
Reexamination Certificate
active
06726855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to the improvement in oxidation stability of lubricating oils and, more particularly, to the oxidation stability of mineral oil and polyol ester base oils by a combination of at least two antioxidants.
2. Description of Related Art
Lubricating oils, as used in the internal combustion engines of automobiles, trucks, trains, ships, and aircraft, are subjected to a demanding environment during use. This environment results in the oxidation of the oil, which oxidation is catalyzed by impurities that are present in the oil, e.g., iron compounds, and further promoted by the elevated temperatures that arise during use. This oxidation of lubricating oils during use is usually controlled, at least to some extent, by the addition of antioxidants that may extend the useful life of the oil.
Lubricant compositions containing various secondary diarylamines are widely known in the art. The use of 2,2,4-trimethyl-1,2-dihydroquinoline polymers is also known, although to a lesser extent.
JP 53051206 (May 10, 1978) discloses 2,2,4-trimethyl-1,2-dihydroquinoline polymer as a useful antioxidant for ester or mineral oil based lubricating oils that also contain disulfides.
JP 57115493 (Jul. 17, 1982) discloses 2,2,4-trimethyl-1,2-dihydroquinoline polymer as a useful antioxidant for lubricating oils.
JP 53051206 (Dec. 24, 1984) discloses 2,2,4-trimethyl-1,2-dihydroquinoline homopolymer as a useful antioxidant for polyol ester based lubricating oils in combination with thiobisphenols.
Polish PL-172885 (Dec. 31, 1997) discloses that poly (2,2,4-trimethyl-1,2-dihydroquinoline) is useful in a transmission oil to decrease copper corrosion.
U.S. Pat. No. 4,158,000 discloses antidegradants for rubber comprising a mixture consisting essentially of 2,2,4-trimethyl-1,2-dihydroquinoline monomer, dimer thereof, and more highly polymerized products than the dimer, the contents of the quinoline monomer and the quinoline dimer being less than 5 percent by weight and 25 percent by weight or more, respectively. The antidegradants for rubber are said to be useful for preventing both heat aging and flex cracking of rubber.
U.S. Pat. No. 4,326,062 discloses that 2,2,4-trimethyl-1,2-dihydroquinoline polymer containing 25 percent by weight or more of the dimer is effectively prepared by the polymerization of 2,2,4-trimethyl-1,2-dihydroquinoline monomer in the presence of hydrochloric acid, the concentration of hydrochloric acid being from 15 to 25 percent by weight, and the amount of hydrochloric acid being 0.2 to 0.5 mole per mole of the total of the monomer and impurity amines contained in the monomer. The polymer is said to be useful as an antioxidant for rubber.
U.S. Pat. No. 4,374,218 discloses that rubber compositions containing, inter alia, poly(2,2,4-trimethyl-1,2-dihydroquinoline) exhibit a combination of properties especially suited for use as fluid sealing elements, such as valve seals, piston seals, washers, and faucet seats.
Canadian Patent No. 943,962 discloses substituted 1,2-dihydroquinolines that are said to have excellent antioxidant, bactericidal, insecticidal and fungicidal properties and a process and apparatus for their preparation.
The disclosures of the foregoing are incorporated herein by reference in their entirety.
SUMMARY OF THE INVENTION
It has now been discovered that a combination of a secondary diarylamine and a 2,2,4-trialkyl-1,2-dihydroquinoline or polymer thereof is highly effective in inhibiting oxidation in lubricating oil compositions. The 2,2,4-trialkyl-1,2-dihydroquinoline polymer acts synergistically with secondary diarylamines to provide significant improvement in oxidation control.
More particularly, the present invention is directed to a composition comprising lubricating oil and at least a first antioxidant and a second antioxidant, the first antioxidant being a secondary diarylamine and the second antioxidant being a 2,2,4-trialkyl-1,2-dihydroquinoline or a polymer thereof.
In another aspect, the present invention is directed to a method of increasing the oxidation stability of a lubricating oil comprising adding thereto at least a first antioxidant and a second antioxidant, the first antioxidant being a secondary diarylamine and the second antioxidant being a 2,2,4-trialkyl-1,2-dihydroquinoline or a polymer thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The ratio of the secondary diarylamine to the 2,2,4-trialkyl-1,2-dihydroquinoline or polymer thereof in the mixture employed in the lubricating oil compositions of the present invention can be in substantially all proportions. Preferably, the ratio of secondary diarylamine to 2,2,4-trialkyl-1,2-dihydroquinoline polymer will be in the range of 1:99 to 99:1, more preferably, about 90:10 to about 10:90 parts by weight. The secondary diarylamine may be in the lubricating oil composition in a range of about 0.01 to about 10 weight percent, and preferably about 0.1 to about 5 weight percent. The 2,2,4-trialkyl-1,2-dihydroquinoline or polymer thereof also may be in the lubricating oil composition in a range of about 0.01 to about 10 weight percent, and preferably about 0.1 to about 5 weight percent.
The secondary diarylamines are well known antioxidants, and there is no particular restriction on the type of secondary diarylamine that can be used in the practice of this invention. Preferably, the secondary diarylamine antioxidant is one of the formula R
1
—NH—R
2
where R
1
and R
2
each independently represent a substituted or unsubstituted aryl group having from 6 to 46 carbon atoms. Illustrative of substituents for the aryl moieties are aliphatic hydrocarbon groups, such as alkyl of 1 to 40 carbon atoms, hydroxyl, carboxyl, amino, N-alkylated amino, N-arylated amino, N′N-dialkylated amino, nitro, or cyano. The aryl moieties are preferably substituted or unsubstituted phenyl or naphthyl, particularly where one or both of the aryl moieties are substituted with alkyl, such as one having 4 to 24 carbon atoms.
The alkyl moiety, which can be of 1 to 40 carbon atoms, can have either a straight chain or a branched chain, which may be a fully saturated or a partially unsaturated hydrocarbon chain; for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, oleyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, triacontyl, pentatriacontyl, tetracontyl, and the like, and isomers and mixtures thereof.
Examples of some of the secondary diarylamines that are useful in the practice of the present invention include: diphenylamine, monoalkylated diphenylamine, dialkylated diphenylamine, trialkylated diphenylamine, or mixtures thereof, 3-hydroxydiphenylamine, 4-hydroxydiphenylamine, mono- and/or di-butyldiphenylamine, mono- and/or di-octyldiphenylamine, mono- and/or di-nonyldiphenylamine, phenyl-&agr;-naphthylamine, phenyl-&bgr;-naphthylamine, diheptyldiphenylamine, mono- and/or di-(&agr;-methylstyryl)diphenylamine, mono- and/or distyryidiphenylamine, 4-(p-toluenesulfonamido)diphenylamine, 4-isopropoxydiphenylamine, t-octylated N-phenyl-1-naphthylamine, mixtures of mono- and dialkylated t-butyl-t-octyldiphenylamines, N-phenyl-1,2-phenylenediamine, N-phenyl-1,4-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, N,N′-di(naphthyl-2)-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine, and N-cyclohexyl-N′-phenyl-p-phenylenediamine.
In the 2,2,4-trialkyl-1,2-dihydroquinoline and polymers thereof that are employed as the second antioxidant in the present invention, the trialkyl moiety can comprise any alkyl groups that will not adversely affect the antioxidizing properties of the compound. Typically, the three alkyl groups, which may be the same or different, will be lower alkyl groups, for example those having one to four carbon atoms, i.e., methyl, ethyl, propyl, isopropyl, b
Abbott Ronald D.
Migdal Cyril A.
Dilworth Michael P.
Szekely Peter
Uniroyal Chemical Company, Inc.
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