CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application under 35 U.S.C. 371 of co-pending PCT application number PCT/JP2018/043855 designating the United States and filed Nov. 28, 2018, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to a lubricating oil composition.

BACKGROUND ART

The agricultural machinery includes a machine for soil preparation such as a tractor, a machine for plant raising control such as a rice-planting machine, a machine for harvesting such as a binder and a combine harvester, etc., and a tractor is most widely used.

Although a tractor has many metal-to-metal contact points in a hydraulic pump unit, a transmission unit, a power take-off (PTO) clutch unit, a differential gear unit, a wet brake unit, etc., in many cases, only one type of lubricating oil for agricultural machinery is used for these contact points.

Therefore, the lubricating oil for agricultural machinery is required to have multifunctional roles, such as frictional performance, abrasion resistance, oxidation stability, an anti-corrosive property, and organic material compatibility. In order to secure these performances, and further enhance them, various additives are currently blended with a selected base oil to form a lubricating oil composition for agricultural machinery, such as the lubricating oil compositions disclosed in Japanese Patent Application Laid-Open (JP-A) No. S59-25890, or JP-A No. H03-20396. Further, as a functional fluid to be used in a method to improve the braking performance and clutch performance of a functional fluid, for example, a functional fluid is disclosed in JP-A No. 2004-59930.

Meanwhile, since the load on gears or the like is increasing along with the power increase in tractors, it is desired that such lubricating oil for agricultural machinery should have an even higher extreme-pressure performance.

Meanwhile, agricultural machinery is sometimes used in an environment where it is liable to come into contact with water, for example, in a paddy field, and contamination of a lubricating oil with water is frequently observed during use. Therefore, it is required that the function of agricultural machinery can be maintained even in a water-infesting environment.

In particular, when an agricultural machine is used in a paddy field, or when a machine is washed, water is prone to enter the oil tank, through which an emulsion is formed in the lubricating oil to cause clogging of the filter. From this point of view, for example, JP-A No. 2009-144098 and JP-A No. 2010-121063 disclose that better inhibition of emulsion formation is intended by optimizing the blending amounts of a metal-based cleaner, and an abrasion preventing agent in the lubricating oil composition.

As mentioned above, it is known that an abrasion preventing agent is blended in a lubricating oil composition for agricultural machinery, and that an acid phosphate amine salt is often blended as the abrasion preventing agent. For example, JP-A No. 2014-19735 discloses a lubricating oil composition for agricultural machinery, in which formation of an emulsion can be inhibited by blending a metal-based cleaner, and a zinc dialkyldithiophosphate with a lubricating oil base oil, and adding a specific amount of an aspartic acid ester derivative expressed by Formula (1).



(In Formula (1), each of R1, R2, R3, and R4represents an alkyl group with a carbon number of 1 to 30, and all of which may be the same alkyl group, or alkyl groups different from each other.

SUMMARY OF INVENTION

Technical Problem

Since the load on gears or the like is increasing in recent years along with the power increase of tractors, it is desired for a lubricating oil composition or a functional fluid described in JP-A No. S59-25890, JP-A No. H03-20396, or JP-A No. 2004-59930 to have even higher extreme pressure property. In particular, when an agricultural machine is used in a paddy field, or when a machine is washed, water is prone to enter the oil tank, through which an emulsion is formed in the lubricating oil to cause clogging of the filter. Consequently, it is desired that the lubricating oil is excellent at inhibiting emulsion formation.

However, when an acid phosphate amine salt is added to a lubricating oil composition in order to prevent wear and inhibit formation of an emulsion, it becomes difficult to obtain a synergistic effect with a zinc dialkyldithiophosphate in the lubricating oil composition. Consequently, further development of lubricating oil compositions is desired because strong inhibition of emulsion while maintaining extreme-pressure performance is hardly attainable in a lubricating oil composition for agricultural machinery described in JP-A No. 2009-144098, JP-A No. 2010-121063, and JP-A No. 2014-19735.

An embodiment of this disclosure was made in view of such circumstances, and provides a lubricating oil composition that inhibits formation of an emulsion after contamination with water while maintaining the extreme pressure property, and exhibits excellent filtration property.

Solution to Problem

As a result of intensive research, the inventors have found that a lubricating oil composition, in which a zinc dialkyldithiophosphate having a specific structure, and an acid phosphate amine salt having a specific structure are added in a specific ratio in terms of phosphorus concentration to a specific base oil, inhibits formation of an emulsion after contamination with water while maintaining the extreme pressure property, and exhibits excellent filtration property.

In other words, this disclosure includes the following modes of implementation.

<1> A lubricating oil composition including:

at least one base oil selected from the group consisting of a mineral oil-based lubricating oil, a synthetic oil-based lubricating oil, and a mixed oil thereof,

zinc dialkyldithiophosphate X represented by the following Formula (1), and

an acid phosphate ester amine salt Y represented by the following Formula (2), wherein:

a content PXof the X is from 0.06% by mass to 0.08% by mass in terms of phosphorus concentration with respect to a total mass of the lubricating oil composition, and a content PYof the Y is from 0.015% by mass to 0.025% by mass in terms of phosphorus concentration with respect to the total mass of the lubricating oil composition.



in Formula (1), each of R1, R2, R3, and R4independently represents a primary alkyl group having a straight chain or branched chain with a carbon number of 10 to 20.



In Formula (2), each of R, R5, and R6independently represents a hydrogen atom, or a hydrocarbon group with a carbon number of 3 to 30, and at least one of R5or R6represents a hydrocarbon group.

<2>The lubricating oil composition according to <1>, wherein each of R1, R2, R3, and R4in the above Formula (1) is independently a primary alkyl group having a straight chain with a carbon number of 10 to 12.

<3>The lubricating oil composition according to <1> or <2>, wherein the hydrocarbon group in each of R5and R6is at least one hydrocarbon group selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkylaryl group, and an arylalkyl group.

<4>The lubricating oil composition according to any one of <1> to <3>, wherein the lubricating oil composition is an agricultural machinery lubricating oil.

Advantageous Effect of Invention

According to an embodiment of this disclosure, it is possible to provide a lubricating oil composition that inhibits formation of an emulsion after contamination with water while maintaining the extreme pressure property, and exhibits excellent filtration property.

