EP0349534B1

EP0349534B1 - Hydraulic fluids

Info

Publication number: EP0349534B1
Application number: EP88901051A
Authority: EP
Inventors: Gert Stenmark; Kari Jokinen; Heikki Kerkkonen; Eero LEPPÄMÄKI; Eino PIIRILÄ
Original assignee: Raision Tehtaat Oy AB
Current assignee: Raisio Oyj
Priority date: 1987-01-28
Filing date: 1988-01-27
Publication date: 1992-12-02
Anticipated expiration: 2008-01-27
Also published as: DE3876432T2; DK536188D0; DE3876432D1; EP0349534A1; NO884237D0; DK536188A; ATE83003T1; WO1988005808A1; AU1227388A; NO174060B; NO884237L

Abstract

Hydraulic fluids based on natural triglycerides. The base composition for these hydraulic fluids consists of at least one natural triglyceride and one anti-oxidant additive. The triglyceride suitable for the composition can be defined as an ester of a straight-chain C10 to C22 fatty acid and glycerol which has an iodine number of between 50 and 128. The fraction of the anti-oxidant additives is selected preferably among hindered phenolics and aromatic amines, but can be completed by compounds selected from metal salts of dithioacids, phosphites, sulfides, amides, non-aromatic amines, hydrazides and triazols. Preferred amount of the anti-oxidant(s) in the fluid is 1.5 to 4.5 percent by weight.

Description

The present invention is concerned with hydraulic fluids based on oily triglycerides of fatty acids.
The hydraulic fluids commonly used are petroleum-based, chemically saturated or unsaturated, straight-chained, branched or ring-type hydrocarbons.
The petroleum-based hydraulic fluids involve, however, a number of environmental and health risks. Hydrocarbons may constitute a cancer risk when in prolonged contact with the skin, as well as a risk of damage to the lungs when inhaled with the air. Moreover, oil allowed to escape into the environment causes spoiling of the soil and the ground water, even in small quantities. They are also toxic to the aquatic life in rivers, lakes, etc.
In addition to the above, hydrocarbon oils as such have in fact a rather limited applicability for hydraulic purposes, wherefor the hydraulic fluids based on such oils contain a variety of additives in considerable amounts. Petroleum is also a non-renewable, and consequently limited, natural resource.
Thus there is an obvious need for fluids for hydraulic purposes which are based on renewable natural resources, and which are, at the same time, environmentally acceptable. One such a natural base component for hydraulic fluids is the oily triglycerides, as suggested in the patent specification GB 2 134 923.
The triglycerides described in the said specification GB 2 134 923 are glycerol esters of fatty acids, and the chemical structure of the said esters can be defined by means of the following formula:

wherein R₁, R₂ and R₃ can be the same or different and are selected from the group consisting of saturated and unsaturated straight-chained alkyl, alkenyl, and alkadienyl chains of ordinarily 9 to 22 carbon atoms.
The triglyceride may also, according to the teaching of the specification GB 2 134 923, contain a small quantity of an alkatrienylic acid residue, but a larger quantity is detrimental, because it promotes oxidation of the triglyceride oil. Certain triglyceride oils, so-called drying oils, contain considerable quantities of alkatrienyl and alkadienyl groups, and they form solid films, under the effect of the oxygen in the air. Such oils, the iodine number of which is usually higher than 130 and which are used i.a. as components of special coatings, cannot be considered for use in the hydraulic fluids.

As is stated in the specification GB 2 134 923, any other oily triglyceride with an iodine number of at least 50 and no more than 128 is suitable for the purpose. Particularly suitable are the triglycerides of the oleic acid-linoleic acid type which contain no more than 20 per cent by weight of esterified saturated fatty acids calculated on the quantity of esterified fatty acids. These oils are liquids at 15 to 20°C, and their most important fatty acid residues are derived from the following unsaturated acids: oleic acid, 9-octadecenoic acid, linoleic acid, 9,12-octa-decadienoic acid. The most preferred among these triglycerides of vegetable origin, under normal temperatures of use, are described to be those that contain esterified oleic acid in a quantity in excess of 50 per cent by weight of the total quantity of fatty acids (Table 1).

It is characteristic of all of these oily triglycerides that their viscosities change on change in temperature to a lesser extent than the viscosities of hydrocarbon basic oils. The viscosity-to-temperature ratio characteristic of each oil can be characterized by means of the empiric viscosity index (VI), the numerical value of which is the higher the less the viscosity of the oil concerned changes with a change in temperature. The viscosity indexes of triglycerides are clearly higher than those of hydrocarbon oils with no additives, so that triglycerides are to their nature so-called multi-grade oils. This is of considerable importance under conditions in which the operating temperature may vary within rather wide limits. The viscosities and viscosity indexes of certain triglycerides are given in Table 2.

Table 2

Viscosity properties of oils
	Viscosity mm²/s		Viscosity index
	38°C	99°C
	1)		2)
Olive oil	46.68	9.09	194
Rape seed oil (eruca)	50.64	10.32	210
Rape seed oil	36.04	8.03	217
Mustard oil	45.13	9.46	215
Cottonseed oil	35.88	8.39	214
Soybean oil	28.49	7.60	271
Linseed oil	29.60	7.33	242
Sunflower oil	33.31	7.68	227
Hydrocarbon-based basic oils			0 - 120
1) Method ASTM D 445 2) Method ASTM D 2270

The fume point of triglycerides is above 200°C and the flash point above 300°C (both determinations as per AOCS Ce 9a-48 or ASTM D 1310). The flash points of hydrocarbon basic oils are, as a rule, clearly lower.
The triglyceride oils differ from the non-polar hydrocarbons completely in the respect that they are of a polar nature. This accounts for the superb ability of triglycerides to be adsorbed on metal faces as very thin adhering films. A study of the operation of glide faces placed in close relationship to each other, and considering pressure and temperature to be the fundamental factors affecting lubrication, shows that the film-formation properties of triglycerides are particularly advantageous in hydraulic systems.
In addition, water cannot force a triglyceride oil film off a metal face as easily as a hydrocarbon film.
Rape seed oil has been considered as an example of the monomeric triglyceride oils used in the hydraulic fluids in accordance with the specification GB 2 134 923, which rape seed oil is also obtained from the sub-species Brassica campestris and which oil, in its present-day commercial form, contains little or no erucic acid, 13-docosenoic acid. However, it is to be kept in mind that applicable triglyceride oils differ from rape seed oil only in respect of the composition of the fatty acids esterified with glycerol, which difference comes out as different pour points and viscosities of the oils. Even oils obtained from different sub-species of rape and from their related sub-species display differences in pour points and viscosities, owing to differences in the compositions of fatty acids, as appears from Table 3. Of the rape seed oils mentioned in the table, the first one (eruca) has been obtained from a sub-species that has a high content of erucic acid (C 22:1).

The characterizing data of rape seed oil are compared in Table 4 with certain commercial basic mineral oils.

Table 4

Characteristic data of rape seed oil and certain basic mineral oils
		Rape seed oil	Gulf 300 paramid	Gulf 300 Texas oil	Nynäs S 100	Nynäs H 22
Density g/cm³ 1)	15°C	0.9205	0.878	0.914	0.910	0.926
Viscosity mm²/s	-20°C	660
	40°C	34.2	60.7	57.9	99	26
	100°C	8	8.1	6.6	8.6	3.9
Viscosity index		217	101	26	31	-
Pour point °C		-27	-12	-34	-18	-33
Flash point °C 2)		> 300	238	188	215	180
Acid value mg KOH/g 3)		0.06	0.04	0.09	0.01	0.01

1) Method ASTM D 1298
2) Method ASTM D 93
3) Method ASTM D 974

The above data indicate that the said triglycerides have many properties which are of advantage especially in hydraulic fluids. As mentioned already before, the viscosity index (VI) of triglycerides, as compared with mineral oil products, is superior. The viscosity index of the triclyceride oils is apparently also more stable against mechanical and heat stresses existing in the hydraulic systems than the viscosity index of the hydraulic fluids based on formulated mineral oils and containing polymeric viscosity index improves. In addition it can be expected that the ability of the polar triglyceride molecule to adhere onto metallic surfaces improves the lubricating properties of these triglycerides.
The only property of the natural triglycerides which has shown to impede their intended use for hydraulic purposes is their tendency to be easily oxidized.
The oxidation has many negative effects to the properties of a natural triglyceride based hydraulic fluid, wherefore the fluid has to be replaced by fresh fluid more frequently than fluids based on hydrocarbon oils.
For instance the viscosity of the natural triglyceride hydraulic fluid is increased due to the oxidation. The oxidation causes also foaming of the fluid, the filtration properties of the fluid are decreased, and the higher water solubility causes problems in the hydraulic system. The oxidation products are also corrosive. In order to avoid these problems caused by oxidation the working temperature of the hydraulic system is to be kept lower than when hydrocarbon based oils are used.
It has, however, been noted that the tendency of the said natural triglycerides to be oxidized can be decreased essentially to the same level as that of the common hydrocarbon based hydraulic oils, by using additives in very moderate amounts, which additives have been selected according to the invention. This fact is evident from the results of the following example 1.

Example 1

In this example the stability of the hydraulic fluids against oxidative degradation was tested. The fluids were tested with an apparatus according to the test method ASTM D 525 by introducing into a pressure vessel 100 ml of the fluid to be tested. The vessel was closed and placed into boiling water. During the test the oxygen pressure in the vessel was determined.
The additives used were: Irgalube 349, amino phosphate derivative, Ciba-Geigy; Irganox L 130, mixture of tertiary-butyl phenol derivatives, Ciba-Geigy; Reomet 39, triazole derivative, Ciba-Geigy; Anglamol 75, zinc dialkyldithio-phosphate, Lubrizol; EN 1235, kortacid T derivative, Akzo Chemie; Hitec 4735, mixture of tertiary-butyl phenol derivatives, Ethyl Pertoleum Additives Ltd; Irganox PS 800, dilauryl thio di propionate, Ciba-Geigy; Irganox L 180, triaryl phosphite, Ciba-Geigy; Irganox L 57, mixed alkyl diphenyl amine, Ciba-Geigy; Irganlube TPPT, triphenylphosphorothionate, Ciba-Geigy; Tinuvin 770, bis (2,2,6,6-tetrametyl-4-piperidyl) sebacate, Ciba-Geigy; Vanlube AZ, zinc diamyldithiocarbamate, R.T. Vanderbilt; Additin 10, 2,6-di-tertiary-butyl-4-mathylphenol, Rhein-Chemie.
The results of this test are given in Table 5.
As can bee seen from the results of Table 5, the compositions 3, 4, 5, 6, 8, 10, 11, 12, 13 and 14 are clearly comparable with the common mineral-oil based hydraulic oils 15 and 16 used for comparison in this example. The compositions 2 and 9 contain the anti-oxidant additives selected according to the invention, but the amounts used have not been sufficient. From the data in Table 5 it can be derived that a triglyceride complying with the definitions presented at the beginning of this description and containing a certain amount of carefully selected anti-oxidant additives can form a base for a fluid composition usable for hydraulic purposes.
According to the invention the anti-oxidant fraction in the composition forms 2.0 to 4.5 percent by weight of the composition, and the anti-oxidants are selected so that at least one compound is from the group (1) of hindered phenolics and aromatic amines, and the remaining compound(s) forming the balance in the composition, is from the group (2) of metal salts of dithioacids, phosphites and sulphides, or from the group (3) of amides, non-aromatic amines, hydrazides and triazols.
Examples of compounds which belong to the abovementioned groups can be named as follows:

1) 2,6-di-tert-butyl-4-methyl phenol; 2'2-methylenebis-(4-methyl-6-tert-butylphenol); N,N'-disecbutyl-p-phenylene-diamine; alkylated diphenyl amine; alkylated phenyl-alfa-naphtyl amine
2) zinc dialkyldithiophosphates; tris (nonylphenyl) phosphite; dilauryl thiodipropionate
3) N,N'-diethyl-N,N'-diphenyloxamide;
N,N'-disalicylidene-1,2-propenylenediamine;
N,N'-bis (beta-3,5-ditertbutyl-4-hydroxyphenylpropiono) hydrazide

Example 2

In the tests a Cameron Plint tester (High Frequency Friction Machine TE. 77) was used. In this tester the friction between a moving and a stationary element is determined at increasing temperatures. As the moving element is used a steel ball having a diameter of 6 mm, whereas the stationary element consists of a steel plate. The lubricant to be tested is spread on the plate, and it is exposed to the ambient air oxygen during the tests. In the tests conducted the ball was pressed towards the plate by a force of 40 N during its reciprocating movement having an amplitude of 5 mm and a frequency of 20 Hz. The temperature at the beginning of each test was adjusted to 40 °C, whereafter it was increased by 2 °C per minute. The temperature in which the friction began to increase sharply was registered, and it was used as an indication of the failure of the lubricative film between the ball and the plate. The film failure temperature is a measure of the oxidation resistance of the oil.
The results of this test are given in the following table 6.
From the results of table 6 (tests 2 and 3) it can be seen, that if the oil contains an anti-oxidant which can be classified to hindered phenolics (Hitec 4735) or to aromatic amines (Irganox L 57) the film failure temperature is higher than that of pure rape seed oil. The test 3, however, shows that the percentage of the anti-oxidant has not been high enough. The result is clearly better if the oil contains also a small amount of other anti-oxidant (Irgalube 349, amino phosphate derivative, test 5). Higher percentages of the anti-oxidants give results which are superior to the results of commercial hydrocarbon based hydraulic oils.
The ability of the hydraulic fluids according to the invention was also tested in a full scale test, which is described in the following example 3.

Example 3

A vegetable oil based hydraulic fluid was tested using as a reference a commercial mineral oil based hydraulic fluid. In the test two new identical hydraulic driven mining loaders were used. During the test the pressures in the hydraulic circuits varied from 0 to 165 bar and the hydraulic fluid temperature from 60 to 80°C. Hydraulic pressure was generated by gear pumps and the power was taken out by means of cylinder-piston devices.
The hydraulic fluids tested were:

The following Table 7 gives the viscosity of the oils after a prolonged time in operation. Table 7

Time, hours Viscosity, mm²/s / 40 °C

Fluid

1 2 3

0 34 33.2 44.6

300 36.8 33.2 38.1

600 39.5 33.5 35.2

900 44.3 33.9 34.3

1200 51.8 34.1 34.2

1500 55.6 34.3 34.2

In the same test also the volumetric efficiency of the hydraulic systems 2 and 3 was recorded during the test period and the results are given in the following table 8.

Table 8

Time, hours	µ v / µ ref
	Fluid
	2	3
0	1	1
300	0.960	0.94
600	0.945	0.88
900	0.940	0.84
1200	0.935	0.79
1500	0.93	0.76
µ v means efficiency recorded µ ref means efficiency at the beginning of the test

The efficiency tests were conducted using a fluid pressure of 165 bar, and a temperature of 65°C.
The test results of Table 7 indicate that the durability against shear stress of the vegetable oil based fluid was better than that of the mineral oil based fluid.
The test results of Table 8 indicate that the efficiency of the system containing the vegetable oil based fluid decreased slower than that of the mineral oil based fluid.
The lubricative properties of a hydraulic fluid based on the triglyceride composition of the invention were tested by using the testing method described in the following example 4.

Example 4

The suitability of rape seed oil as a hydraulic fluid was tested in a four ball tester according to the test method IP 239, in which the test period is one hour and the load 1 kg, as well as according to the standard Test Method STD No 791/6503,1, in which the load is increased stepwise during the test period of 10 seconds. The oils tested are given in the Table 9.
All the oils tested belong to the viscosity cathegory ISO VG 32 according to the test method ASTM D 2422.
The results of the said tests are given in the Table 10. Table 10

IP 239, 1 h / 50 kg wear, mm STD No 791/6503,1 load to welding of the balls

1. 0.46 over 300

2. 0.71 200

3. 1,52 140

4. 1.49 200

5. 0.81 260

6. 0.57 200
The lubricating properties were compared also by using a gear system, which test is described in the following Example 5.

Example 5

The protective action of three hydraulic fluids on gear systems against wear was tested by using the FZG-method according to the standard DIN 51354 E (FZG gear rig test machine).
The oils used were:
The results of this test are given in the following table 11. Table 11

Oil Load degree to damage Specific wear, mg/horsepower/hour

1 above 12 0.05

2 above 12 0.033

3 11 0.10
In addition to the basic composition the hydraulic fluid according to the invention may also comprise other constituents such as:

Boundary lubrication additives, such as
metal dialkyl dithiophosphates;
metal diaryl dithiophosphates;
metal dialkyl dithiocarbamates;
alkyl phosphates;
phosphorized fats and olefins; sulphurized fats and fat derivatives; chlorinated fats and fat derivatives
Corrosion inhibitors, such as metal sulfonates;
acid phosphate esters; amines; alkyl succinic acids
VI (Viscosity Index) improvers, such as polymethacrylates; styrene butadiene copolymers; polyisobutylenes
Pour point depressants, such as chlorinated polymers; alkylated phenol polymers; polymethacrylates
Foam decomposers, such as polysiloxanes; polyacrylates
Demulsifiers, such as heavy metal soaps; Ca and Mg sulphonates

From the base composition according to the invention can be made hydraulic fluids for different purposes by adjusting its viscosity. The following table 12 gives one example of adjusting possibilities.

Table 12

From a base composition according to the invention was made hydraulic fluids for different viscosity classes (ASTM D 2422)
	Oil	comp. % by weight	visc. mm²/s	class
1.	Refined rape seed oil	62.5	20.6	ISO VG 22
	Rilanit EHO	35
	Hitec 4735	2.0
	Anglamol 75	1.5
2.	Refined rape seed oil	96.5	34.3	ISO VG 32
	Hitec 4735	2.0
	Anglamol 75	1.5
3.	Refined rape seed oil	73.5	45.2	ISO VG 46
	Priolube 3987	23
	Hitec 4735	2.0
	Anglamol 75	1.5
4.	Refined rape seed oil	76.5	73.0	ISO VG 68
	Priolube 3987	14
	Priolube 3986	6
	Hitec 4735	2.0
	Anglamol 75	1.5
Rilanit EHO, 2-ethylhexyl oleate, Henkel Priolube 3987, pentaerythritol ester, Unichema Priolube 3986, complex ester, Unichema

Claims

A base composition for hydraulic fluids consisting of:
- one or several natural triglycerides which are esters of a straight-chain C₁₀ to C₂₂ fatty acid and glycerol, which triglyceride has an iodine number of at least 50 and not more than 128, and

- one or several anti-oxidant additives,

- characterized in

- that the anti-oxidant additive fraction forms at least 1.5 percent by weight of the composition,

- that the anti-oxidant additive fraction contains one or several compounds selected from the group:

- (I) hindered phenolics and aromatic amines,

- and in that at least in anti-oxidant percentages of 1.5 to 2.0 the anti-oxidant fraction contains one or several additional anti-oxidants selected from one or both of the following groups:

- (II) metal salts of dithioacids, phosphites and sulfides.

- (III) amides, non aromatic amines, hydrazides and triazols.
A base composition for hydraulic fluids according to the claim 1, characterized in that the anti-oxidant fraction forms 1.5 to 4.5 percentage by weight of the composition.
A base composition for hydraulic fluids according to the claims 1 or 2, characterized in that the anti-oxidants selected from the group I form 1.0 to 3.0 percentage by weight of the composition.
A base composition for hydraulic fluids according to the claims 1 to 3, characterized in that the triglyceride is of oleic-acid-linoleic-acid type and contains saturated fatty acids of not more than 20 percent by weight calculated on the quantity of fatty acids esterified with glycerol.
A base composition for hydraulic fluids according to the claim 4, characterized in that the triglyceride consists of rape seed oil.
A hydraulic fluid made of a base composition according to any of the preceeding claims 1 to 5, characterized in that the fluid in addition contains at least one component selected from: boundary lubrication additives, corrosion inhibitors, VI-improvers, pour point depressants, foam decomposers, demulsifiers.