Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Compound of indeterminate structure – prepared by reacting a...
Reexamination Certificate
1999-07-22
2001-01-30
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Compound of indeterminate structure, prepared by reacting a...
C508S231000
Reexamination Certificate
active
06180575
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lubricating oils and more particularly to lubricating oils of synthetic or mineral oil origin which may be used for the lubrication of bearings, gears and in other industrial applications where wide temperature range characteristics are desired. The oils of the present invention are characterized by an excellent balance of performance properties including improved anti-wear characteristics coupled with ant-rust performance. They may find utility as gear oils, circulating oils, compressor oils as well as in other applications, for example, in wet clutch systems, blower bearings, coal pulverizer drives, cooling tower gearboxes, kiln drives, paper machine drives and rotary screw compressors.
BACKGROUND OF THE INVENTION
Gear oils and industrial oils are required to meet certain exacting performance specifications. They must exhibit long term stability, implying good resistance to oxidation over a wide range of temperatures coupled with other performance properties including good anti-wear performance. Depending upon the specific application, other performance characteristics may be required. For example, in high temperature circulating oils, high temperature stability must be the main requirement while minimum anti-rust performance is necessary since little water is present at high temperatures. However, in other applications, anti-rust performance becomes important, for example, in wet applications such as use in paper-making machinery.
The properties of oils may be differentiated on the basis of whether they are bulk properties which are not affected significantly by contact with the surface of other materials, for example, the components of a machine or surface-related properties which affect and are affected by the surfaces with which the oil is in contact Oxidation resistance, for instance, belongs largely in the fromer category although the rate at which an oil undergoes oxidation in use is affected by the character of the metal surfaces in contact with the oil. Extreme pressure resistance may also be included in this category. Other properties such as anti-corrosion, anti-rust, anti-wear are directly dependent on the nature of the surfaces—usually metal—with which the oil is in contact during use. The properties which are surface dependent impart another consideration into the formulation of a finished lubricant since the additives which are used to improve the properties of the lubricant base stock and provide the desired balance of properties may be in competition for available sites on the metal surface. For this reason, it is often difficult to obtain a good balance between the performance properties which are surface dependent. One instance of this is with anti-wear and anti-rust properties: it is difficult to produce an oil which possesses both properties in good measure at the same time.
Different types of base stocks have different performance characteristics. Ester base stocks, for example, the neopentyl polyol esters such as the pentaerythritol esters of monobasic carboxylic acids, have excellent high performance properties as indicated by their common use in gas turbine lubricants. They also provide excellent anti-wear characteristics when conventional anti-wear additives are present and they do not have any adverse effect on the performance of rust inhibitors. On the other hand, esters have relatively poor hydrolytic stability, undergoing hydrolysis readily in the presence of water at even moderate temperatures. They are, therefore, less well suited for use in wet applications such as paper-making machinery.
Hydrolytic stability can be improved by the use of hydrocarbon base stocks. The use of alkyl aromatics in combination with the other hydrocarbon base stocks such as hydrogenated polyalphaolefin (PAO) synthetic hydrocarbons and the improved hydrolytic stability of these combinations is described, for example, in U.S. Pat. No. 5,602,086, corresponding to EP 496 486. Traditional formulations containing PAO's, however, present other performance problems. Although the hydrolytic stability of hydrocarbon base stocks including PAOs is superior to that of the esters, it is frequently difficult to obtain a good balance of the surface-related properties such as anti-wear and anti-rust because, as noted above, these surface-related properties are dependent upon the extent to which the additives present in the base stock compete for sites on the metal surfaces which they are intended to protect and high quality hydrocarbon base stocks such as PAOs do not favorably interact with the additives used for this purpose. It is therefore continuing problem to produce a good combination of surface-related properties including anti-wear performance and anti-rust performance in synthetic oils based on hydrocarbon base stocks such as PAO's.
SUMMARY OF THE INVENTION
We have now developed lubricating oils based on hydrocarbon base stocks of synthetic or mineral oil origin which have an excellent combination of performance characteristics. These lubricants are characterized by an excellent balance of anti-wear and anti-rust characteristics. The anti-wear performance is indicated by a 4-Ball (ASTM D 4172) wear test value of not more than 0.35 mm maximum scar diameter (steel on steel) with values of not more than 0.30 mm being attainable, as well as by other excellent performance indicia, as described below. ASTM 4-Ball steel-on-bronze values of 0.07 mm wear scar diameter may be achieved. The rust inhibition performance is indicated by a Pass in ASTM D 665B with synthetic sea water. Excellent hydrolytic stability, high temperature performance, rust inhibition, corrosion inhibition, oxidation resistance and long oil life are all characteristics of the present oils, as described below.
Compositionally, the present synthetic oils comprise a major portion of a primary base stock component which is a saturated hydrocarbon component with which other lubricant base stock components may be blended. Base stock components which would generally be considered suitable for this purpose include the hydrocarbons such as those which are primarily saturated and which generally have viscosity indices about 110 or greater, a sulfur content generally below 0.3 weight percent and a total aromatics and olefinic content of below 10 weight percent each. Hydrocarbon base stock components of this type include the API Group III base stocks (as well as some oils in Group II), the Group IV base stocks (PAOs) as well as other synthetic hydrocarbon base stocks in API Group V. These components can optionally be combined with other blend components by the addition of hydrocarbyl substituted aromatics, such as the longer chain substituted aromatics. Preferred secondary base stock component are the oils of lubricating viscosity which are hydrocarbon substituted aromatic compounds, such as the long chain alkyl substituted aromatics, including the alkylated naphthalenes, alkylated benzenes, alkylated diphenyl compounds and alkylated diphenyl methanes. Typically, this secondary base stock component will comprise less than 50% of the total base stock with amounts up to no more than 25% being preferred.
A characteristic feature of the present compositions is that the excellent combination of anti-wear and anti-rust performance is achieved in the absence of an ester in the base stock although esters may optionally be included in order to improve certain properties, for example, haze. If this is done, the amount of ester will normally not exceed 10% of the base stock and usually no more than 5% is required in order to deal with any haze problems which may arise. Minor amounts of other materials may be present, either as intentional liquid components or as solvents or carrier fluids for additives.
A synergistic combination of additives confers the desired balance of anti-wear and anti-rust properties in the present compositions. This combination is a unique blend of an adduct of a substituted triazole such as benzotriazole or a substituted benzotriazole e.g. tolyltriazo
Brumlik Charles J.
Howard Jacqueline V.
Keen Malcom D.
Mobil Oil Corporation
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