WATER-GLYCOL HYDRAULIC FLUID

Abstract

This invention provides a water-glycol hydraulic fluid comprises from 0.2 to 0.6% by mass of a dimer acid as a fatty acid lubricant, and more than 0.10% by mass and 0.20% by mass or less of a phosphoric acid ester of Formula (1), wherein the sum of the dimer acid and the phosphoric acid ester is more than 0.35% by mass wherein R.sub.1 and R.sub.2 may be the same or different, each representing a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, R.sub.3 represents a hydrocarbon group having from 1 to 20 carbon atoms, R.sub.4 represents a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, and X.sub.1, X.sub.2, X.sub.3 and X.sub.4 may be the same or different, each representing an oxygen atom or a sulfur atom.

##STR00001##

Claims

1. A water-glycol hydraulic fluid comprising: from 20 to 60% by mass of water; 0.2% by mass or more and 0.6% by mass or less of a dimer acid as a fatty acid lubricant; and more than 0.10% by mass and 0.20% by mass or less of a phosphoric acid ester represented by general formula (1) below, ##STR00005## wherein R.sub.1 and R.sub.2 may be the same or different, each representing a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, R.sub.3 represents a hydrocarbon group having from 1 to 20 carbon atoms, R.sub.4 represents a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms, and X.sub.1, X.sub.2, X.sub.3 and X.sub.4 may be the same or different, each representing an oxygen atom or a sulfur atom, and wherein the sum of the dimer acid and the phosphoric acid ester is more than 0.35% by mass.

2. A water-glycol hydraulic fluid according to claim 1, wherein X.sub.1 and X.sub.2 in the phosphoric acid ester are oxygen atoms, X.sub.3 and X.sub.4 are sulfur atoms, and R.sub.3 is —CH(CH.sub.3)— or —CH.sub.2—CH.sub.2—.

3. A water-glycol hydraulic fluid according to claim 1, wherein the amount of phosphoric acid ester is from 0.15 mass % to 0.20 mass %.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention provides a water-glycol hydraulic fluid containing from 20 to 60% by mass water and from 20 to 60% by mass glycol, along with, for example, a fatty acid-based lubricant, an alkaline hydroxide compound, a thickener, a rust inhibitor, an anticorrosive, and an antifoaming agent to bring the total to 100% by mass. As a result of extensive research and development conducted to solve this problem, the present inventor discovered that use of a dimer acid as a fatty acid-based lubricant and a phosphoric acid ester with a specific structure could significantly improve the wear resistance of a water-glycol hydraulic fluid. The present invention is based on this discovery.

[0009] By using this configuration, the present invention is able to readily obtain an easy-to-use water-glycol hydraulic fluid with significantly improved wear resistance without impairing any other type of performance provided by the water-glycol hydraulic fluid.

[0010] A fatty acid lubricant is used in a water-glycol hydraulic fluid of the present invention, and a dimer acid is used as this fatty acid lubricant. This dimer acid is a dimer of an unsaturated fatty acid having 18 carbon atoms, and is mainly composed of a dibasic acid of a dicarboxylic acid having 36 carbon atoms produced by dimerization of an unsaturated fatty acid having 18 carbon atoms derived from plant-based fats and oils. It is a liquid fatty acid containing a monobasic acid and a tribasic acid.

[0011] This dimer acid is included in an amount of 0.2% by mass or more and 0.6% by mass or less relative to the total mass of the water-glycol hydraulic fluid composition. When less than 0.2% by mass is used, sufficient wear resistance cannot be obtained. When more than 0.6% by mass is used, sludge is more likely to be produced.

[0012] This water-glycol hydraulic fluid also contains a phosphoric acid ester. This phosphoric acid ester is represented by the Formula (1) below:

##STR00003##

[0013] In this general formula, R.sub.1 and R.sub.2 each represent a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms. Here, R.sub.1 and R.sub.2 may be the same or different. R.sub.3 represents a hydrocarbon group having from 1 to 20 carbon atoms, and R.sub.4 represents a hydrogen atom or a hydrocarbon group having from 1 to 30 carbon atoms. X.sub.1, X.sub.2, X.sub.3 and X.sub.4 may be the same or different and each represents an oxygen atom or a sulfur atom.

[0014] This phosphoric acid ester is included in an amount of more than 0.10% by mass and 0.20% by mass or less relative to the total mass of the water-glycol hydraulic fluid composition, and the sum of the dimer acid and the phosphoric acid ester is more than 0.35% by mass. The phosphoric acid ester is preferably used in an amount of 0.12% by mass or more, and more preferably in an amount of 0.15% by mass or more.

[0015] The glycols in this water-glycol hydraulic fluid composition can be, for example, ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, dibutylene glycol, dihexylene glycol, trimethylene glycol, triethylene glycol, and tripropylene glycol. One type of glycol can be used alone, or a mixture of two or more types of glycol can be used. Use of propylene glycol or dipropylene glycol is preferred. These glycols are included in an amount from 20 to 60% by mass, and preferably from 30 to 50% by mass, relative to the total mass of the water-glycol hydraulic fluid composition.

[0016] An alkanolamine can be used as a rust inhibitor. Examples of alkanolamines include methanolamine, ethanolamine, propanolamine, diethanolamine, triethanolamine, dimethylethanolamine, N-methylethanolamine, N-methyldiethanolamine, N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,N-dipropylaminoethanol, N,N-dibutylaminoethanol, N,N-dipentylaminoethanol, N,N-dihexylaminoethanol, N,N-diheptylaminoethanol, and N,N-dioctylaminoethanol. The alkanolamine is included in an amount of 1.0 to 5.0% by mass based on the total mass of the composition.

[0017] The alkaline hydroxide compounds mentioned above are potassium hydroxide and sodium hydroxide, and these may be used alone or together. The alkaline hydroxide compound is included in an amount from 0.01 to 0.12% by mass, and preferably from 0.04 to 0.06% by mass, relative to the total mass of the composition.

[0018] Well-known additives can be included in the water-glycol hydraulic fluid if necessary. Examples include thickeners, lubricants, metal deactivators, anti-wear agents, extreme pressure agents, dispersants, metal detergents, friction modifiers, corrosion inhibitors, anti-emulsifiers, and defoamers. These additives may be used alone or in combinations of more than one. An additive package for a water-glycol hydraulic fluid may also be used.

EXAMPLES

[0019] Water-glycol hydraulic fluids of the present invention will now be described in detail with reference to examples and comparative examples. The present invention is not limited to these examples. The components were thoroughly mixed together in the amounts shown in Table 1 and Table 2 to obtain the water-glycol hydraulic fluids in Examples 1 to 7.

Example 1

[0020] A water-glycol hydraulic fluid was obtained by thoroughly mixing together 0.20% by mass dimer acid, 0.20% by mass 3-(di-isobutoxy-thiophosphorylsulfanyl)-2-methyl-propionic acid serving as the phosphoric acid ester, 38.628% by mass propylene glycol serving as the glycol, 16.10% by mass of water-soluble polymer serving as a thickener, a total of 2.565% by mass of other additives such as sodium hydroxide, a corrosion inhibitor, and a defoamer, etc., and 42.307% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, the 40° C. kinematic viscosity was 46 mm.sup.2/s, and the pH was 10.6.

[0021] The phosphoric acid ester used in Example 1 is represented by the following structural formula:

##STR00004##

Example 2

[0022] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.30% by mass dimer acid, 0.15% by mass of the phosphoric acid ester described above, and 42.257% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Example 3

[0023] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.30% by mass dimer acid, 0.20% by mass of the phosphoric acid ester described above, and 42.207% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Example 4

[0024] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.40% by mass dimer acid, 0.15% by mass of the phosphoric acid ester described above, and 42.157% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Example 5

[0025] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.40% by mass dimer acid, 0.20% by mass of the phosphoric acid ester described above, and 42.107% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Example 6

[0026] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.60% by mass dimer acid, 0.15% by mass of the phosphoric acid ester described above, and 41.957% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Example 7

[0027] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.60% by mass dimer acid, 0.20% by mass of the phosphoric acid ester described above, and 41.907% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Comparative Example 1

[0028] A water-glycol hydraulic fluid was obtained in the same manner as Example 1 using 0.20% by mass dimer acid, 0.05% by mass of the phosphoric acid ester described above, and 42.457% by mass water. The alkali reserve of the water-glycol hydraulic fluid obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

Comparative Examples 3 to 5

[0029] The components were thoroughly mixed together in the amounts shown in Table 3 to obtain the water-glycol hydraulic fluids in the same manner as Example 1. The alkali reserve of the water-glycol hydraulic fluids in Comparative Examples 2 to 5 obtained in accordance with JIS K2234-1994 was 20, and the 40° C. kinematic viscosity was 46 mm.sup.2/s.

[0030] The following test was performed on the examples and comparative examples to evaluate the wear resistance and lubricity performance.

Shell Four Ball Lubricant Test

[0031] The operations were performed at room temperature for 30 minutes in accordance with ASTM D4172, in which the spindle rotation speed was 1,500 rpm and the load was 40 kgf. Afterwards, the diameter (mm) of the wear marks on the steel balls was measured. The test results are shown in Table 1 to Table 3.

Evaluation Standards:

[0032] Wear mark diameter≤0.65 mm . . . Passed (○) [0033] Wear mark diameter>0.65 mm . . . Failed (x)

Observations

[0034] As shown in Table 1 and Table 2, in Examples 1 to 7, which contained 0.20% by mass or more and 0.60% by mass or less of a dimer acid and more than 0.15% by mass and 0.20% by mass or less of a phosphoric acid ester, with the sum of the dimer acid and the phosphoric acid ester being more than 0.35% by mass, the wear mark diameter in the Shell four ball lubricant test was 0.65 mm or less, which indicates superior wear resistance and lubricity.

[0035] As shown in Table 3, in Comparative Examples 1, 2, 4 and 5, which contained 0.2% by mass or more and 0.6% by mass or less of a dimer acid but less than 0.10% by mass of a phosphoric acid ester, and in Comparative Example 3, which contained more than 0.10% by mass of a phosphoric acid ester but with the sum of the dimer acid and the phosphoric acid ester being less than 0.35% by mass, the wear mark diameter in the Shell four ball lubricant test was 0.681 mm or more, which indicates poor results. In the case of Comparative Example, 1, scorching occurred.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Dimer Acid 0.20 0.30 0.30 Phosphoric Acid 0.20 0.15 0.20 Ester Glycol 38.628 38.628 38.628 Thickener 16.100 16.100 16.100 Other Additives 2.565 2.565 2.565 Water 42.307 42.257 42.207 Diameter of Wear Marks (mm) 0.643 0.621 0.618 Evaluation ◯ ◯ ◯

TABLE-US-00002 TABLE 2 Example 4 Example 5 Example 6 Example 7 Dimer Acid 0.40 0.40 0.60 0.60 Phosphoric Acid 0.15 0.20 0.15 0.20 Ester Glycol 38.628 38.628 38.628 38.628 Thickener 16.100 16.100 16.100 16.100 Other Additives 2.565 2.565 2.565 2.565 Water 42.157 42.107 41.957 41.907 Diameter of Wear 0.535 0.547 0.526 0.484 Marks (mm) Evaluation ◯ ◯ ◯ ◯

TABLE-US-00003 TABLE 3 C. C. C. C. C. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Dimer Acid 0.20 0.20 0.20 0.40 0.60 Phosphoric 0.05 0.10 0.15 0.10 0.10 Acid Ester Glycol 38.628 38.628 38.628 38.628 38.628 Thickener 16.100 16.100 16.100 16.100 16.100 Other 2.565 2.565 2.565 2.565 2.565 Additives Water 42.457 42.407 42.357 42.207 42.007 Diameter Scorched 0.837 0.681 0.725 0.685 of Wear Marks (mm) Evaluation x x x x x