Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic sulfur compound – wherein the sulfur is single bonded...
Reexamination Certificate
1999-03-29
2001-06-26
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic sulfur compound, wherein the sulfur is single bonded...
C508S413000, C508S500000, C508S530000, C508S551000
Reexamination Certificate
active
06251841
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a grease composition. Particularly, the present invention relates to a grease composition having improved rust-proofing properties. More particularly, the present invention relates to a grease composition for use in lubricated parts such as rolling bearing liable to rusting due to invasion of water, saline or brine from the road as occurring with automobile electric parts during running or invasion of cooling water in the iron industry.
BACKGROUND OF THE INVENTION
A rolling bearing or other parts which are liable to rusting are provided with a proper seal or other mechanical countermeasures to prevent the entrance of rusting substances. In automobiles, for example, bearings are disposed at positions which are not directly exposed to muddy water or mudguards are provided to prevent the entrance of rusting substances. Further, a dust-proofing seal plate is used to prevent the entrance of rusting substances into the interior of bearings.
However, a rolling bearing cannot be completely sealed because of its mechanism and thus normally is lubricated with a wetting grease provided with rust-proofing properties.
The provision of a grease with rust-proofing properties is normally accomplished by adding a material called rust preventive to the grease. As such a rust preventive there is widely used a chromate, nitrite, molybdate, tungstate or the like, particularly an inorganic passivator made of sodium salt thereof from the standpoint of its high performance. In particular, sodium nitrite is most effective and thus is most widely used. However, such an inorganic passivator is water-soluble and thus can hardly be dispersed in an oil-based material such as grease. Thus, a grease comprising a surface active agent in combination with such an inorganic passivator is commercially available as well.
Further, an organic rust preventive is used as well. Such an organic rust preventive is also called lipophilic organic inhibitor. Representative examples of such an organic rust preventive include sulfonate and carboxylate. However, this lipophilic organic inhibitor cannot itself exhibit rust-proofing properties so strong as the foregoing inorganic passivator and leaves something to be desired in rust-proofing properties particularly when exposed to saline. Thus, there is provided a grease comprising such a lipophilic organic inhibitor in combination with an inorganic passivator and optionally a surface active agent. This grease comprising an oil-soluble organic inhibitor in combination with an organic passivator and optionally a surface active agent exhibits better rust-proofing properties than a grease comprising an inorganic passivator alone.
However, sodium nitrite, which is a representative example of inorganic passivator, exhibits excellent rust-proofing properties but can affect animals and plants under some working conditions. It is thus said that the use of sodium nitrite should be avoided if possible.
On the other hand, stricter rust-proofing properties have been required of greases in recent years.
In the automobile industry, for example, as the use of automobiles diversifies as in running by the sea shore and running on the road sprinkled with salt for prevention of freezing, stricter rust-proofing properties have been required of greases. In the iron industry, too, improved rust-proofing properties have been required of greases, because the molding powder, which is used in continuous casting facilities, was changed to that which causes a part thereof to be dissolved in the cooling water, thereby accelerating rusting on bearings mounted in rolling mill.
In recent years, not only rust-proofing properties but also safety have been required of greases. However, there are no greases satisfying both the two requirements.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a grease which exhibits excellent rust-proofing properties and safety.
The foregoing object of the present invention will become more apparent from the following detailed description and examples.
The present invention has been worked out as a result of extensive studies of solution to the foregoing problems. The present invention concerns a grease composition comprising a lubricating base oil and a thickener, characterized in that there are incorporated a lipophilic organic inhibitor, a nonionic surface active agent and a hydrophilic organic inhibitor selected from the group consisting of lanolin fatty acid derivative and alkanolamine derivative modified with a hydrophilic group each in an amount of from 0.1 to 10% by weight based on the total weight of said grease composition.
In accordance with the present invention, the use of a specific hydrophilic organic inhibitor in combination with a lipophilic organic inhibitor and a nonionic surface active agent makes it possible to obtain a grease composition having rust-proofing properties equivalent to or higher than that of a grease composition comprising sodium nitrite, which has heretofore been said to have excellent rust-proofing properties.
The combination of a lipophilic organic inhibitor, a hydrophilic organic inhibitor and a surface active agent in the grease composition according to the present invention brings forth a higher rust-proofing effect than that of each of these inhibitors. This is a so-called synergistic effect. In this mechanism, each of these inhibitors acts to help the other ingredients to act effectively in addition to its own rust-proofing properties. The surface active agent used herein allows water, which causes rusting, to be taken into the grease base oil as an emulsion to inhibit the exchange between the lipophilic inhibitor and corrosive materials contained in water on the surface of metal. Further, the hydrophilic organic inhibitor can be taken into the emulsion, making it possible to further inhibit rusting.
Accordingly, the combination of a lipophilic organic inhibitor, a hydrophilic organic inhibitor and a surface active agent according to the present invention makes it possible to provide a grease having rust-proofing properties far better than that expected with the single use of these inhibitors and equivalent to or better than that of inorganic passivator.
DETAILED DESCRIPTION OF THE INVENTION
The grease composition according to the present invention will be further described hereinafter.
The grease composition according to the present invention comprises as rust preventives a lipophilic organic inhibitor and a hydrophilic organic inhibitor in combination.
The lipophilic organic inhibitor to be used herein is not specifically limited. Any lipophilic organic inhibitor which has heretofore been incorporated in greases may be used. Examples of such a lipophilic organic inhibitor include compounds having a polar group such as carboxylic acid, carboxylate, sulfonate and amine. Such a lipophilic organic inhibitor is said to be adsorbed by the surface. of metal (e.g., inner ring, outer ring and rolling elements of bearing) with its polar group arranged toward the surface of metal to form a rust-proofing film.
Particularly preferred among these lipophilic organic inhibitors is an organic sulfonate. This organic sulfonate is represented by the general formula RSO
3
.M. Examples of RSO
3
, which is the acid moiety of the salt, include petroleum sulfonic acid, and dinonylnaphthalenesulfonic acid. Examples of M, which is the alkali moiety of the salt, include metal such as Ba, Ca, Zn, Pb, Na and Li, and amine such as NH
4
and H
2
N(CH
2
)
2
NH
2
.
These lipophilic organic inhibitors may be used singly or in proper combination.
The hydrophilic organic inhibitor is taken into an emulsion. The hydrophilic organic inhibitor employable herein may be selected from the group consisting of lanolin fatty acid derivative and alkanolamine derivative modified with a hydrophilic group. Specific examples of the hydrophilic organic inhibitor will be given below.
Examples of lanolin fatty acid derivative modified with a hydrophilic group include lanolin fatty acid polyethy
Endo Toshiaki
Iso Kenichi
Koizumi Hideki
Naka Michiharu
Shibayama Atsushi
Medley Margaret
NSK Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Toomer Cephia D.
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