US3793207A

US3793207A - Fire-resistant hydraulic fluid

Info

Publication number: US3793207A
Application number: US00196209A
Authority: US
Inventors: M Burrous
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1971-11-05
Filing date: 1971-11-05
Publication date: 1974-02-19
Anticipated expiration: 1991-02-19

Abstract

Fire-resistant hydraulic fluids having improved low temperature characteristics, e.g., viscosity, pour point, and cloud point, consist mainly of a mixture of a synthetic hydrocarbon, a dialkyl carboxylate ester and an orthosilicate.

Description

United States Patent [1 1 Burrous Feb. 19, 1974 FIRE-RESISTANT HYDRAULIC FLUID [75] Inventor: Merwyn L. Burrous, El Cerrito,

Calif.

[22] Filed: Nov. 5, 1971 [21] Appl. No.: 196,209

[52] US. Cl. 252/78, 252/49.6 [51] Int. Cl C09k 3/02 [58] Field of Search 252/78, 75, 49.6, 73

[56] References Cited UNITED STATES PATENTS 2,550,760 5/1951 Bishop 252/79 2,691,633 10/1954 Benoit 252/49.6 2,960,474 11/1960 Furby et al. 252/78 3,296,138 1/1967 Cupper et al... 252/78 X 3,478,113 11/1969 Bray et a1. 252/73 X 3,513,097 5/1970 Langenfeld 252/78 3,538,001 11/1970 Gothel et al. 252/78 X 3,637,507 1/1972 Gentit 252/78 2,509,620 5/1950 Watson et a1 252/78 2,746,926 5/1956 Barry 252/78 3,074,889 1/1963 252/78 3,657,128 4/1972 Street 252/78 X OTHER PUBLICATIONS Synthetic Lubricant Fluids from Branched Chain Diesters, Industrial Engineering Chemistry, Vol. 39 (1947) pp. 484, 489.

Primary Examiner-Richard D. Lovering Attorney, Agent, or FirmJ. A. Buchanan, Jr.

[5 7 ABSTRACT Fire-resistant hydraulic fluids having improved low temperature characteristics, e.g., viscosity, pour point, and cloud point, consist mainly of a mixture of a synthetic hydrocarbon, a dialkyl carboxylate ester and an orthosilicate.

7 Claims, No Drawings FIRE-RESISTANT HYDRAULIC FLUID BACKGROUND OF THE INVENTION 1. Field of the Invention A hydraulic fluid should be fire-resistant; it should not adversely affect the materials of construction of the system in which it is used; it must possess adequate lubricity and mechanical stability; it must be chemically stable; it must possess good low temperature properties such as viscosity, pour point and cloud point; and, finally, it must be low foaming. These characteristics have been summarized in specification MIL-I-I-83282.

2. Description of the Prior Art Aryl and alkyl phosphates are widely used in fireresistant hydraulic fluids to provide both flame resistance and lubricity. Petroleum-base oils, though good lubricants and economically desirable, are not often used in high proportions in fire-resistant hydraulic fluids because of their flammability. Chlorinated hydrocarbons are often used as good flame retardants for petroleum-base oils. A typical fire-resistant hydraulic fluid would be a phosphate ester, a chlorinated hydrocarbon or a mixture of these with or without a minor amount of mineral oil.

SUMMARY OF THE INVENTION We have discovered that a fire-resistant functional fluid can be prepared from a synthetic hydrocarbon oil, 20-30 percent by weight of an ester of a dicarboxylic acid and -1 5 percent of an alkyl silicate, with small percentages of other functional additives. Such functional additives include antiwear agents, such as tricresyl phosphate, antioxidants such as dialkyl paracresol, hydrolysis suppressants such as cycloaliphatic epoxides, and antifoamants.

The synthetic hydrocarbon oil of the present invention comprises substantially a dialkyl aromatic hydrocarbon oil having a viscosity of from 8,500 to 10,000 cs at 40F., 25-35 cs at 100F., and 4-8 cs at 210F. The preferred ester of a dicarboxylic acid is a dialkyl adipate ester of a C C alcohol. This fluid is hydrolytically stable, has excellent low temperature properties such as viscosity, pour point and cloud point, and has a high flash point, fire point, and autogenous ignition temperature.

DESCRIPTION OF THE INVENTION The hydrocarbon oils suitable for purposes of the present invention comprises hydrocarbons and mixtures of hydrocarbons which are alkyl, alkenyl, aryl and aralkyl hydrocarbons. Individual hydrocarbons will contain from about 8 to about 50 carbon atoms and be chosen from the classes of aromatic, alkyl aromatic, alkane, alkene, paraffinic and naphthenic molecules. The hydrocarbon oil is present in the hydraulic fluid composition to the extent of 30-80 percent by weight of the total composition. An important characteristic of the hydrocarbon oil is its viscosity, especially at low temperatures. The viscosity should range from 8,000 to 10,000 cs at 40F., to 40 cs at 100F., and 2-10 cs at 212F. A preferred oil is substantially a dialkyl aromatic hydrocarbon such as di(tridecyl)benzene, tridecyl-(tetradecyl)benzne, di(tetradecyl)benzene, or mixtures of same. The hydrocarbon oil may be a dewaxed mineral oil, or preferably a synthetic hydrocarbon oil. A synthetic hydrocarbon oil is preferred over a mineral oil because of its lower pour point. The most stable mineral oils are parafi'mic in nature and characterized by their high pour points. The pour point is the lowest temperature at which the oil is observed to flow when cooled and examined under prescribed conditions, ASTM D 97-66. However, in choosing a synthetic hydrocarbon oil for its pour point, the viscosity of the oil, its flammability, and other properties, must be balanced by the discovery of additional components to form the base fluid meeting the severe specifications of the present invention.

The second important component of the hydraulic fluid is an ester of a C -C dicarboxylic acid, i.e., a dialkyl carboxylate. Such acids include oxalic, succinic, malonic, glutaric, adipic, pimelic, suberic, azeleic acid, and substituted acids of the same names. The alcoholic portion of the ester is derived from a C C, aliphatic alcohol such as methyl, ethyl, propyl, butyl, amyl, hexyl, hectyl, octyl, nonyl, decyl, and undecyl alcohol. These terms include all geometrical isomers, e.g., the term butyl alcohol includes isobutyl alcohol. For best over-all performance in low temperature viscosity, rubber swell, cost, stability and flash point, a dialkyl ester of adipic acid is preferred. The ester will usually be present in 10-40 percent by weight and preferably 15-35 percent by weight.

The third important component of the hydraulic fluid is an alkyl silicate ester of the general formulae SIOR O R R R x R wherein R (where i l-8) is an alkyl group of from 3-12 carbon atoms and preferably from 6-10 carbon atoms, and x has the value of 0 or 1. Examples of the alkylsilicates include isopropyl orthosilicate, butyl orthosilicate, hexyl orthosilicate, 2-ethyl hexyl orthosilicate, 2-ethylbutoxy disiloxane, 3-propyl heptyl orthosilicate, and Z-methyl hexyl orthosilicate. The alkylsilicate esters will usually be present in 2-25 percent by weight and preferably 5-20 percent by weight.

The hydrocarbon oil, dicarboxylate ester and alkylsilicate ester form the fire-resistant base stock of the present hydraulic fluid. Specific additives are combined with this base stock to impart particular proper ties. For example, antiwear agents, antioxidants, hydrolysis suppressants, rust inhibitors, antifoamants, and additional viscosity index improvers may be added in small percentages. Specifically, a triaryl phosphate, and preferably tricresyl phosphate is present in the amount of 0.5-3 percent by weight, as is a dialkyl paracresol, such as dipropyl paracresol, dibutyl paracresol, or dihexyl paracresol. A very small amount (0.05-0.5 weight percent) of a diepoxide as described in US application Ser. No. 865,471, filed Oct. 10, 1969 and now abandoned, is usually present as a hydrolysis suppressant. Usually an antifoamant will be present in percentages below 0.01 percent by weight.

The hydrolytic stability of the composition is excellent. It undergoes little change in acid number, viscosity, or flash point when subjected to 275F. for one week even in the presence of added water.

The following are typical examples of base fluid formulations which are in accord with this invention. They are given by way of illustration and not by limitation. The ingredients are known and commercially available chemicals. The fluids are prepared by simply mixing together the components of Table I with small amounts (0.5 percent or less) of specific additives discussed hereinbefore, such as antifoamant and hydrolysis suppressant, at l40l 50F.

The properties of the fire-resistant hydraulic fluid of Table l are summarized in Table 11. This fluid meets or exceeds MlL-H-83282 specifications in these categories; oxidation-corrosion inhibition, low temperature stability, lack of rubber swelling, low foaming tendency, water content below 100 ppm, lack of solid contamination, lubricity, resistance to flame propagation, and compatibility with other fluids TABLE II Property MlL-H-83282 Fluid Viscosity, cs

100F 16.5 minimum 17.0

210F 3.5 minimum 3.74

Flash point, "F ASTM D 92 400 minimum 420 Fire Point, F ASTM D 92, 475 minimum 475 Acid No., mg KOH/g ASTM D 974 0.10 maximum 0.01

Pour Point, F 65 maximum 80 Lubricity, 4-Ball Wear Test 40 kg, Scar diameter, mm 0.65 maximum 0.52, 0.53

This specification describes a hydraulic fluid which is fire-resistant and has a synthetic hydrocarbon base. Hydraulic Fluid B of Table I.

In addition, this fluid has been subjected to additional tests which are not within the scope of MIL-H-83282 specifications. These results are summarized in Table 111.

Shear Stability TABLE Ill-Continued Property Fluid Percent viscosity loss after 2 hours in sonic oscillator Oxidation Hours to absorb 1 liter of 0 ml of fluid at 340F 14.4

Hydrolytic Stability Percent change in viscosity 2.0 Final acid number 0.10

Metal weight change, mg/em Copper 0.02 Magnesium +0.06 Aluminum +0.00 Iron +0.08 Cadmium -0.01

Hydraulic Fluid 8 of Table 1. In this test, ml offluid, 0.15 percent by weight of H 0 and 5 metal specimens are sealed in a 250 ml jar under air. The jar is rotated end over end at 5 rpm for 1 week at 275F.

The fire resistance of the fluids of the present invention is demonstrated by the flash point and fire point of Table II and by the following test comparisons with a petroleum-base hydraulic fluid meeting Specification MIL-H-5606B (see Table IV).

TABLE IV Fluid B in Table l M1L-H-5606B Hydraulic Fluid,

Petroleum Base number of passes Flame Propagation No propagation after Propagation after 36 MlL-H-83282, Sec. 2 hours seconds 4.4.3.1.1

High Ignites with lgnites when any portion Temperature-High Pressure Spray Ignition, Fed. Std. 791-6052 difficulty. Does not of flame touches any continue to burn portion of stream. after source of Continues to burn ignition is removed. vigorously when ignition source is removed.

As will be evident to those skilled in the art, numerous modifications and variations of the invention illustrated above may be made without departing from the spirit of the invention, or the scope of the following claims.

I claim:

1. A fire-resistant hydraulic fluid comprising a base stock consisting essentially of;

30-80 percent by weight of a hydrocarbon oil having a maximum viscosity of 10,000 cs at 40F. and a minimum viscosity of 4 cs at 210F.,

15-35 percent by weight of a dialkyl carboxylate ester of a C -C alkanol and a C -C dicarboxylic acid, and

5-20 percent by weight of an alkyl silicate ester of the general formulae:

0 0 O O R 0SiOR or R OSi-O Si-O- SiOR a a Ra x R:

wherein the R, i being an integer of from 1-8, are alkyl groups of from 3 to 12 carbon atoms and x has the value of or I.

2. The fire-resistant hydraulic fluid of claim 1, in which the hydrocarbon oil is a dialkyl aromatic hydrocarbon oil, wherein the alkyl contains 12-14 carbon atoms.

3. The fire-resistant hydraulic fluid of claim 1, in which the alkyl of the alkyl silicate contains from 6-! 0 carbon atoms.

4. The fire-resistant hydraulic fluid of claim 1, in which the carboxylic acid is of the form HOOC(CH drolysis suppressant.

Claims

2. The fire-resistant hydraulic fluid of claim 1, in which the hydrocarbon oil is a dialkyl aromatic hydrocarbon oil, wherein the alkyl contains 12-14 carbon atoms.
3. The fire-resistant hydraulic fluid of claim 1, in which the alkyl of the alkyl silicate contains from 6-10 carbon atoms.
4. The fire-resistant hydraulic fluid of claim 1, in which the carboxylic acid is of the form HOOC(CH2)xCOOH, where x 2 to 10.
5. The fire-resistant hydraulic fluid of claim 1, in which the dialkyl carboxylate ester is diisooctyl adipate.
6. The fire-resistant hydraulic fluid of claim 4, in which the alkyl silicate is 2-ethylhexyl orthosilicate.
7. The fire-resistant hydraulic fluid of claim 1, additionally containing 1-3 percent by weight of tricresyl phosphate, 0.5-2 percent by weight of dialkyl paracresol, and 0.05-0.5 percent by weight of a diepoxide hydrolysis suppressant.