JP7730966B2 - Water-glycol based hydraulic fluid composition and supplemental additive therefor - Google Patents

Description

The present invention relates to a water-glycol-based hydraulic fluid composition and its supplemental additives.

Hydraulic fluids are used as a power transmission medium in hydraulic systems. Petroleum-based hydraulic fluids are widely used, and the most commonly used general-purpose hydraulic fluids are those that use mineral oil-based base oils such as highly refined paraffin-based base oils.

However, the various hydraulic equipment, aluminum die-casting equipment, and extrusion processing machines used within steelworks and other facilities are operated under high temperatures and pressures, posing a high risk of fire. To avoid this risk, water-glycol-based hydraulic fluids are used as hydraulic fluids for such equipment instead of those using the mineral oil-based base oils mentioned above.

When using such a water-glycol-based hydraulic fluid, it is important to ensure smooth hydraulic operation and to extend the life of the hydraulic equipment, which requires rust prevention. In particular, it is necessary to add a volatile alkaline rust inhibitor to prevent rust on wall and ceiling surfaces that are not in contact with the hydraulic fluid.
Furthermore, although water-glycol based hydraulic fluids have excellent performance, their performance deteriorates due to a decrease in pH during use and oxidation. Therefore, as a technology for improving performance such as inhibiting pH decrease and improving oxidation stability, for example, a water-containing hydraulic fluid composition containing a polyoxyalkylene glycol diether compound of a specific structure, a polyoxyalkylene glycol monoether compound, a polyoxypropylene glycol monoether compound, and a fatty acid salt in water is known (Patent Document 1).

Furthermore, this water-glycol hydraulic fluid is a hydraulic fluid whose main components are water and glycol, but when hydraulic equipment uses this fluid, the water in the fluid evaporates during use. Water-glycol hydraulic fluids generally contain liquid or vapor-phase rust inhibitors as additives, but as the water evaporates during use, the additives also evaporate, causing the properties of the water-glycol hydraulic fluid to exceed the appropriate range.

In such cases, it is common to add or replenish additional additives to maintain the performance of the water-glycol hydraulic fluid, thereby managing the fluid's properties to maintain them within the appropriate range.

Patent No. 3233490

For these reasons, the present invention aims to improve the performance of water-glycol-based hydraulic fluids filled in hydraulic equipment, while also providing an effective supplemental additive for maintaining that performance, particularly vapor-phase rust prevention.

A water-glycol-based hydraulic fluid contains, out of a total of 100% by mass, 20-60% by mass of water, 20-60% by mass of glycols, a fatty acid-based lubricant, an alkali hydroxide compound, a thickener, a corrosion inhibitor, an antifoaming agent, etc. The inventors conducted extensive research to solve the above-mentioned problems and discovered that the use of a specific alkanolamine compound can significantly improve the vapor-phase rust prevention properties of water-glycol-based hydraulic fluids, and that this alkanolamine compound can also be effectively used as a supplementary additive. Based on these findings, the present invention was completed.

That is, the present invention provides a compound represented by the following general formula:
(In the above general formula, _R1 and _R2 are hydrocarbon groups having 1 to 8 carbon atoms, and _R3 is a hydrocarbon group having 2 or more carbon atoms.)
The alkanolamine compound is represented by the formula (I) and has a specific gravity at 20° C. of 0.86 to 0.89 , and is blended with a water-glycol based hydraulic fluid.
The alkanolamine compound is also used as a supplementary additive in a water-glycol based hydraulic fluid composition.

According to the present invention, a water-glycol-based hydraulic fluid with excellent rust prevention properties can be obtained by blending a specific alkanolamine compound. Furthermore, if the water in a water-glycol-based hydraulic fluid used in hydraulic equipment evaporates, using this alkanolamine compound as a supplemental additive can improve the vapor-phase rust prevention properties of the water-glycol-based hydraulic fluid, which decrease as the water evaporates, to their initial performance.

1 is an explanatory diagram showing an outline of an apparatus for vapor phase rust prevention testing according to the present invention.

The alkanolamine compound of the present invention is
It is a compound represented by the general formula:
_R1 and _R2 above represent hydrocarbon groups having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms. The most preferred carbon number is 3 or 4. _R1 and _R2 may have the same or different carbon atoms, but it is generally preferred that they are the same. _R3 above is a hydrocarbon having 2 or more carbon atoms, and since the water solubility of the compound tends to decrease as the carbon number increases, those having about 2 to 4 carbon atoms are preferred.

Examples of such alkanolamine compounds include N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,N-dipropylaminoethanol, N,N-dibutylaminoethanol, N,N-dipentylaminoethanol, N,N-dihexylaminoethanol, N,N-diheptylaminoethanol, N,N-dioctylaminoethanol, N,N-dimethylaminopropanol, N,N-diethylaminopropanol, N,N-dipropylaminopropanol, N,N-dibutylaminopropanol, N,N-dipentylaminopropanol, N,N-dihexylaminopropanol, N,N-diheptylaminopropanol, N, Examples thereof include N-dioctylaminopropanol, N,N-dimethylaminobutanol, N,N-diethylaminobutanol, N,N-dipropylaminobutanol, N,N-dibutylaminobutanol, N,N-dipentylaminobutanol, N,N-dihexylaminobutanol, N,N-diheptylaminobutanol, N,N-dioctylaminobutanol, N-butyl(N-pentyl)aminoethanol, N-butyl(N-hexyl)aminoethanol, N-butyl(N-heptyl)aminoethanol, N-butyl(N-pentyl)aminopropanol, N-butyl(N-hexyl)aminopropanol, and N-butyl(N-heptyl)aminopropanol.
Such alkanolamine compounds are blended so that the reserve alkalinity of the water-glycol-based working fluid as specified in JIS K 2234-1994 is 10 to 25, more preferably 15 to 23, and even more preferably 18 to 21. The specific gravity of such alkanolamine compounds at 20°C is preferably 0.86 to 0.89. Those with a specific gravity exceeding 0.89 are not preferred because they have reduced volatility and reduced vapor-phase rust prevention properties relative to the reserve alkalinity.

Such alkanolamine compounds are used by being blended with a water-glycol based hydraulic fluid. There are no particular limitations on the type of water-glycol based hydraulic fluid, but it is preferable that the fluid have the following composition, for example.
Of the total 100% by mass, the lubricant contains 20 to 60% by mass, more preferably 30 to 50% by mass, water, 0.6 to 1.2% by mass of a fatty acid-based lubricant, 0.01 to 0.12% by mass of an alkali hydroxide compound, and 20 to 60% by mass of glycols.

Examples of the glycols include ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, dipropylene glycol, dibutylene glycol, dihexylene glycol, trimethylene glycol, triethylene glycol, and tripropylene glycol.
The glycols may be used alone or in combination of two or more of the above. Propylene glycol or dipropylene glycol is preferably used. The glycol is used in an amount of 20 to 60 mass %, more preferably 30 to 50 mass %, based on the total amount of the water-glycol-based hydraulic fluid composition.

Examples of the fatty acid-based lubricants include saturated fatty acids such as capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, and stearic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid.
Sodium salts of these fatty acids can also be used, such as sodium caprate, sodium undecylate, sodium laurate, sodium tridecylate, sodium myristate, sodium pentadecylate, sodium palmitate, sodium margarate, sodium stearate, sodium oleate, sodium linoleate, and sodium linolenate.

Other examples include aromatic fatty acids and dimer acids. Dimer acids are liquid fatty acids that contain monobasic and tribasic acids and are primarily composed of dibasic C36 dicarboxylic acids produced by dimerization of C18 unsaturated fatty acids derived from vegetable oils and fats.
These fatty acid-based lubricants, such as fatty acids, sodium salts of fatty acids, and dimer acids, may be used singly or in appropriate mixtures of two or more of the above-mentioned types.

The alkali hydroxide compound mentioned above includes potassium hydroxide or sodium hydroxide, which may be used alone or in combination as appropriate. The alkali hydroxide compound is contained in an amount of 0.01 to 0.12% by mass, and more preferably 0.04 to 0.06% by mass, based on the total amount of the composition.

Additionally, specific phosphate ester compounds may be used as anti-wear agents, and these phosphate esters have the following structure:
(In the formula, _R1 and _R2 may be the same or different and each represent a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms; _R3 represents a hydrocarbon group having 1 to 20 carbon atoms; _R4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms; and _X1 , _X2 , _X3 , and _X4 may be the same or different and each represent an oxygen atom or a sulfur atom.)

In addition, these water-glycol-based hydraulic fluids may contain known additives, such as thickeners, lubricants, metal deactivators, anti-wear agents, extreme pressure agents, dispersants, metal-based detergents, friction modifiers, corrosion inhibitors, demulsifiers, anti-foaming agents, and various other additives, either alone or in combination. In this case, an additive package for water-glycol-based hydraulic fluids may be used.

The above-mentioned alkanolamine compounds can be used as supplemental additives when water-glycol-based working fluids are being used. For example, when new water-glycol-based working fluid is being used, water evaporates, and as a result, additives evaporate as well, resulting in a decrease in vapor-phase rust prevention. One indicator of vapor-phase rust prevention is the measurement of reserve alkalinity as specified in JIS K 2234-1994, which decreases with evaporation. In such cases, adding the above-mentioned alkanolamine compounds as supplemental additives to the water-glycol-based working fluid restores the initial reserve alkalinity, maintaining vapor-phase rust prevention and enabling stable, long-term use.

Among the above alkanolamine compounds, both dimethylethanolamine and diethylethanolamine are designated as hazardous substances and therefore require strict handling control. Therefore, when used as a supplemental additive, _R1 and _R2 preferably have 3 or 4 carbon atoms. Such compounds are easy to handle as supplemental additives and can be safely replenished by on-site workers into hydraulic fluids for hydraulic equipment.

The following provides a detailed explanation of water-glycol-based hydraulic fluids containing the alkanolamine compounds of the present invention, using examples and comparative examples, but the present invention is not limited to these in any way.

The "reserve alkalinity" mentioned above is measured using the reserve alkalinity measurement method specified in JIS K 2234-1994 to measure the basic components in a water-glycol-based working fluid. This reserve alkalinity is expressed in ml as the amount of 0.1 N hydrochloric acid required to neutralize the basic components contained in 10 ml of sample oil to a pH of 5.5.

Example 1
A water-glycol-based hydraulic fluid was prepared by thoroughly mixing 1.90% by mass of N,N-dibutylaminoethanol as an alkanolamine compound, 37.73% by mass of propylene glycol as a glycol, 16.10% by mass of a water-soluble polymer as a thickener, equal amounts of dimer acid and lauric acid as a fatty acid lubricant (0.80% by mass in total), 0.06% by mass of sodium hydroxide as an alkali hydroxide compound, 1.57% by mass of other additives including corrosion inhibitors and antifoaming agents, and 41.84% by mass of water. The reserve alkalinity measured according to JIS K 2234-1994 was 20. The kinematic viscosity at 40°C was 46 mm ² /s, and the pH was 11.
The molecular weight of the N,N-dibutylaminoethanol used is 173, its specific gravity at 20°C is 0.860, its flash point is 90°C, and its boiling point is 226°C.

Example 2
A water-glycol based working fluid was obtained by thoroughly mixing 1.00 mass% of N,N-dimethylaminoethanol as an alkanolamine compound, 38.63 mass% of glycol, 16.10 mass% of a thickener, 0.80 mass% of a fatty acid lubricant, 0.06 mass% of an alkali hydroxide compound, 1.57 mass% of other additives, and 41.84 mass% of water. The reserve alkalinity according to JIS K 2234-1994 was 20, and the kinematic viscosity at 40°C was 46 ^mm2 /s.
The N,N-dimethylaminoethanol used has a molecular weight of 89, a specific gravity at 20°C of 0.888, a flash point of 40°C, and a boiling point of 134°C.

(Comparative Example 1)
A water-glycol based hydraulic fluid was obtained by thoroughly mixing 1.40% by mass of N-ethyldiethanolamine as an alkanolamine compound, 38.23% by mass of glycol, 16.10% by mass of a thickener, 0.80% by mass of a fatty acid lubricant, 0.06% by mass of an alkali hydroxide compound, 1.57% by mass of other additives, and 41.84% by mass of water. The reserve alkalinity according to JIS K 2234-1994 was 20, and the kinematic viscosity at 40°C was 46 mm ² /s.
The molecular weight of the compounded N-ethyldiethanolamine is 133, its specific gravity at 20°C is 1.07, its flash point is 124°C, and its boiling point is 251°C.

(Comparative Example 2)
A water-glycol based hydraulic fluid was obtained by thoroughly mixing 1.00 mass% of N-methylethanolamine as an alkanolamine compound, 38.63 mass% of glycol, 16.10 mass% of a thickener, 0.80 mass% of a fatty acid lubricant, 0.06 mass% of an alkali hydroxide compound, 1.57 mass% of other additives, and 41.84 mass% of water. The reserve alkalinity according to JIS K 2234-1994 was 20, and the kinematic viscosity at 40°C was 46 mm ² /s.
The molecular weight of the N-ethyldiethanolamine used is 75, its specific gravity at 20°C is 0.940, its flash point is 73°C, and its boiling point is 156°C.

(Comparative Example 3)
A water-glycol based hydraulic fluid was obtained by thoroughly mixing 1.00 mass% of 2-ethylaminoethanol as an alkanolamine compound, 38.63 mass% of glycol, 16.10 mass% of a thickener, 0.80 mass% of a fatty acid lubricant, 0.06 mass% of an alkali hydroxide compound, 1.57 mass% of other additives, and 41.84 mass% of water. The reserve alkalinity according to JIS K 2234-1994 was 20, and the kinematic viscosity at 40°C was 46 mm ² /s.
The molecular weight of the compounded 2-ethyldiaminoethanol is 117, its specific gravity at 20°C is 0.918, its flash point is 77°C, and its boiling point is 199°C.

(Comparative Example 4)
A water-glycol based hydraulic fluid was obtained by thoroughly mixing 1.23% by mass of mono-n-butylethanolamine as an alkanolamine compound, 38.40% by mass of glycol, 16.10% by mass of a thickener, 0.80% by mass of a fatty acid lubricant, 0.06% by mass of an alkali hydroxide compound, 1.57% by mass of other additives, and 41.84% by mass of water. The reserve alkalinity according to JIS K 2234-1994 was 20, and the kinematic viscosity at 40°C was 46 mm ² /s.
The N-mono-n-butylethanolamine used has a molecular weight of 117, a specific gravity at 20°C of 0.893, a flash point of 77°C, and a boiling point of 199°C.

(Comparative Example 5)
A water-glycol-based hydraulic fluid was obtained by thoroughly mixing 39.63% by mass of glycol, 16.10% by mass of thickener, 0.80% by mass of fatty acid lubricant, 0.06% by mass of alkali hydroxide compound, 1.57% by mass of other additives, and 41.84% by mass of water. Because no alkanolamine compound was blended, the reserve alkalinity obtained according to JIS K 2234-1994 was 9, and the kinematic viscosity at 40°C was 46 mm ² /s.

〔test〕
The following tests were carried out to evaluate the vapor phase rust prevention properties of the above-mentioned Examples and Comparative Examples.
(Gas-phase corrosion prevention test)
As shown in FIG. 1 , 100 g of the water-glycol-based working fluid of the Examples or Comparative Examples was placed in a hard glass test tube having a height of 600 mm and an outer diameter of 50 mm, which is used in the turbine oil oxidation stability test of JIS K2514-2, and two test pieces of general structural rolled steel (SS-400) measuring 80 × 30 × 2 mm were hung so as to be positioned at the top and bottom of the test tube.
The top opening of the test tube was covered with a cooler, and the bottom of the test tube was placed in a thermostatic bath at 50°C. After leaving the test tube standing for 200 hours, the test piece was visually inspected for rust.
Evaluation criteria: No rust on either side of the test piece - Pass
Rust is found on either or both test pieces: Fail

(Test results)
The test results are shown in Table 1.

(Consideration)
As shown in Table 1, in Examples 1 and 2, an alkanolamine compound was blended so that the reserve alkalinity was 20.0, and in both cases, no rust was observed in the vapor phase rust prevention test, resulting in a passing result.
Comparative Example 5 shown in Table 2 does not contain any alkanolamine compound, has a low reserve alkalinity of 9.0, and failed the vapor phase rust prevention test due to the presence of rust, indicating that it is not preferable.
In Comparative Examples 2 to 4, an alkanolamine compound was blended so that the reserve alkalinity was 20.0. However, since this alkanolamine compound was not a dialkylaminoalkanol as defined in the present invention, rust was observed in the vapor phase rust prevention test, resulting in failure, and it is clear that this is not preferable.

Claims (1)

A water-glycol-based hydraulic fluid composition comprising an alkanolamine compound represented by the following general formula, the alkanolamine compound having a specific gravity at 20°C of 0.86 to 0.89; 20 to 60 mass% of water, 20 to 60 mass% of glycols, 0.6 to 1.2 mass% of a fatty acid lubricant, and 0.01 to 0.06 mass% of an alkali hydroxide compound selected from potassium hydroxide and/or sodium hydroxide; and a reserve alkalinity of 10 to 25 as measured by the method specified in JIS K 2234-1994:
(In the above general formula, R1 _and R2 _are hydrocarbon groups having 1 to 8 carbon atoms, and R3 _is a hydrocarbon group having 2 or more carbon atoms.)