NO131462B - - Google Patents

Description

Hydraulic fluid.

A number of functional fluids are known and used in the hydraulic systems in aircraft. Such hydraulic systems require a lot of the hydraulic fluid. Not only must these hydraulic fluids meet stringent application requirements, but they must also be sufficiently non-flammable to meet FAA fire resistance requirements. In to-

moreover, the hydraulic fluid must be able to work in the hydraulic system for a long period of time without causing significant damage to

the various lines, valves, pumps, etc. that the fluid must

flow in during use.

In the past, damage has been reported to valves and other metal parts that came into contact with phosphate ester liquids. The damage can be seen by metal particles being worn loose. Many explanations have been proposed in an attempt to characterize the phenomenon causing the damage and to suggest solutions. The state of the art refers to hollowing, erosion, corrosion and other phenomena as causes of metal particles being detached from the metal surroundings in a hydraulic system. A solution that has been proposed to overcome the problem of damage is to have a small percentage of water in the liquid. Fos fat ester fluids containing small amounts of water are known from US-PS 2,470,792 to be effective in aircraft hydraulic systems. While the presence of small amounts of water reduces certain types of damage when added to some phosphate ester containing hydraulic fluids, worse the presence of water can have an undesirable effect on corrosion as well as on the stability of the fluid. For these reasons, the main purpose of this invention is to provide a satisfactory non-aqueous additive which will reduce all types of damage caused by the fluid in the hydraulic system.

It has now been discovered that the addition of a small amount of certain quaternary phosphonium compounds to the hydraulic fluid prevents damage to the metal surroundings containing the hydraulic fluid.

The invention thus relates to a hydraulic fluid comprising a main quantity of a base material selected from among the esters of a phosphoric acid; and possibly the following additives:

a rust inhibitor, a dye and an antifoam agent, a corrosion inhibitor, which corrosion inhibitor is preferably benzotriazole, and an acid acceptor, and it is characterized in that it also contains 0.1-10% by weight of a wear-inhibiting phosphonium compound of the general formula:

where R, R' and R" represent alkyl, aryl, alkaryl and aralkyl groups containing from 1 to 10 carbon atoms and R"' represents alkyl or aralkyl containing from 1 to 10 carbon atoms, X represents an oxygen or sulfur atom, and Y' and Y" represent lower alkoxy, lower alkyl, phenyl, lower alkylphenyl, phenyl-lower alkyl, phenoxy and lower alkylphenoxy, and Z represents oxygen.

Typical connections are illustrated as follows:

(1) methyltrioctylphosphonium dimethyl phosphate

(2) ethyltrioctylphosphonium diethylphosphonate

(3) ethyl trioctylphosphonium dimethyl phosphate

(4) - butyltrioctylphosphonium dibutyl phosphate

(5) isobutyltrioctylphosphonium dimethyl phosphate

(6) benzyltriphenylphosphonium dibenzyl phosphate

(7) methylphenyldioctylphosphonium dimethyl phosphate

(8) phenyltriethylphosphonium ethylphenylphosphonate

(9) methyldiphenyloctylphosphonium dimethyl phosphate

(10) tetraethylphosphonium diethyl phosphate

(11) methyltriphenylphosphonium dimethyl phosphate

(12) methyltributylphosphonium dimethyl phosphate

(13) methyltributylphosphonium diethyl phosphate

(14) methyltrioctylphosphonium methyl methylphosphonate

(15) methyltrioctylphosphonium dimethylphosphonate

(16) methyltrioctylphosphonium dimethyl phosphate.

Preparation of such quaternary phosphonium compounds

which are useful in the liquid preparations according to the invention, are known in the art and need no further explanation here. Such salts have proved useful as polymerization catalysts, antistatic agents, stabilizers, surfactants and in dye baths for textile materials.

Lubricant preparations to which the phosphonium compounds may be added are referred to as "base materials". They include, as mentioned above, esters of a phosphoric acid.

The concentration of the phosphonium compound required to prevent damage depends on the particular base material or mixture of base materials used. According to the invention, between 0.1 and 10% by weight of the phosphonium compound is used. More preferably used between approx. 0.5 and approx. 2.0% by weight. The hydraulic fluid according to the invention can be prepared in any manner known to the person skilled in the art for introducing an additive into a base material with stirring until a homogeneous liquid preparation is obtained.

The active liquid preparations used as basic materials in the invention can be esters of a phosphoric acid with the following structure:

where Y is selected from the group consisting of oxygen, sulfur and Y^ is selected from the group consisting of oxygen, sulfur and and Y2 is selected from the group consisting of oxygen, sulfur and

R, R-^, R£, R-j» R^ and R,, are each selected from the group consisting of

alkyl, aryl, substituted aryl and substituted alkyl where R, R^, R^,

R^, R^ and R^ may each be identical or different to

account for any other radical, and a, b and c are whole numbers with a value of from 0 to 1 and the sum of a+b+c is from 1 to 3.

Typical examples of alkyl radicals are as follows:

methyl-, ethyl-, normal-propyl-, isopropyl-, normal-butyl-, isobutyl-, secondary-butyl-, tertiary-butyl-, normal-amyl-, isoamyl-, 2-methyl-butyl-, 2,2-dimethyl -propyl-, 1-methyl-butyl-, diethylmethyl-, 1,2-dimethyl-propyl-, tertiary amyl-, normal—hexyl-, 1-methylamyl-, 1-ethyl-butyl-, 1,2,2- trimethyl-propyl-, 3,3-dimethyl-butyl-, 1,1,2-trimethyl-propyl-, 2-methyl-amyl-, 1,1-dimethyl-butyl-, l-ethyl-2-methyl-propyl -, 1,3-dimethyl-butyl-, isohexyl-, 3-methylamyl-, 1,2-dimethyl-butyl-, 1-methyl-1-ethyl-propyl-, 2-ethyl-butyl-, normal-heptyl- , 1,1,2,3-tetra-methyl-propyl-, 1,2-dimethyl-1-ethyl-propyl-, 1,1,2-trimethyl-butyl-, 1-cispropyl-2-methyl-propyl- , l-methyl-2-ethyl-butyl-, 1,1-diethyl-propyl-, 2-methyl-hexyl-, 1,1-dimethyl-amyl-, 1-isopropyl-butyl-, l-ethyl-3- methyl-butyl-, 1,4-dimethyl-amyl-, isoheptyl-, 1-methyl-1-ethyl-butyl-, l-ethyl-2-methyl-butyl-, 1-methyl-hexyl-, 1-propyl- butyl-, normal octyl-, 1-methyl-heptyl-, 1,1-diethyl-2-methyl-propyl-, 1,1,3,3-tetramethyl-butyl-, 1,1-diethyl-butyl-, 1 ,1-dimethyl-hexyl-, 1-methyl-1 -ethyl-amyl-, 1-methyl-1-propyl-butyl-, 2-ethyl-hexyl-, 6-methyl-heptyl-(iso-octyl), normal-nonyl-, 1-methyl-octyl, 1-ethyl -heptyl-, 1,1-dimethyl-heptyl-, 1-ethyl-1-propyl-butyl-, 1,1-diethyl-3-methyl-butyl-, diisobutyl-methyl-, 3,5,5-trimethyl- hexyl-, 3,5-dimethyl-heptyl, normal-decyl-, 1-propyl-heptyl-, 1,1-diethyl-hexyl, 1,1-dipropyl-butyl-, 2-isopropyl-5-methyl-hexyl- and C^^_^galkyl groups . Also included are aralkyl groups, e.g. benzyl, α- or β-phenylethyl, α-α-dimethyl-benzyl and the like. Also included are cyclohexyl,

cycloheptyl and the like.

Typical examples of substituted alkyl radicals are the halogen-alkyl radicals which can be represented by the structure:

where Hal refers to a halogen, m is less than or equal to 2n+1> and n can have any value from 0 to 18, and R 1 and R 2 can be hydrogen, halogen or alkyl radicals. Preferred radicals are those where Hal is fluorine and include those represented by the following formulas:

where Rg and R? have their previously described meanings.

The halogenated alkyl radicals can be primary, secondary or tertiary.

Other suitable fluorine-containing radicals include fluorinated alkoxyalkyl radicals and in particular those represented by the following formulas:

where Rg and R^ have the previously described meaning.

It is also considered to be within the scope of the invention that the hydrogen and fluorine in the previously described haloalkyl radicals can be replaced by other halogens, such as e.g. chlorine or bromine.

Typical examples of aryl and substituted aryl radicals are phenyl, cresyl, xylyl, halogenated phenyl, alkoxylated phenyl, cresyl and xylyl in which the available hydrogen on the aryl or substituted aryl is partially or completely replaced by a halogen, c--, m- and p_- trifluoromethylphenyl, o-, m- and p_-2, 2, 2-trifluoroethylphenyl, o-, m- and p_-3,3,3-trifluoropropylphenyl and _o-, m- and p_-4, 4, 4 -trifluorobutylphenyl. Also included are isopropylphenyl, butylphenyl, α-alkylbenzylphenyl and α,α-dialkylbenzylphenyl, e.g. α-methylbenzylphenyl, α,α-dimethyl-benzylphenyl.

Hydraulic fluids according to the invention can also contain pour point depressants, antioxidants, viscosity index improvers such as e.g. polyalkyl acrylates, polyalkyl methacrylates, polycyclic polymers, polyurethanes, polyalkylene oxides and polyesters, lubricants, water and the like. Particularly desirable combinations of basic materials as well as additives are proposed in BE-PS 728 309, to which reference is hereby made.

It is assumed that the basic materials as mentioned above can be used separately or as a liquid preparation containing two or more basic materials in varying proportions. The base materials can also contain other liquids which include, in addition to the active liquids, desirable liquids obtained from coal products, artificial products and synthetic oils, e.g. alkylene polymers (such as polymers of propylene, butylene, etc. and mixtures thereof), alkylene oxide type polymers (eg propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing the alkylene oxide in the presence of water or alcohol, e.g. ethyl alcohol, alkylbenzenes (eg monoalkylbenzene such as dodecylbenzene, tetradecylbenzene, etc.) and dialkylbenzene (eg n-nonyl-2-ethylhexylbenzene), halogenated lower alkylbenzene and mono-halogenated diphenyl ethers.

In the preferred form of the present invention, however, the phosphonium compound is combined with a phosphate-functional liquid base material. The base material will primarily consist of trialkyl phosphates which are present in amounts from 50 to 90% by weight and preferably from 65 to 75% by weight. The trialkyl phosphates which give optimum results are those in which each of the alkyl groups contains from 3 to 12 carbon atoms, preferably from 4 to 9 carbon atoms. The alkyl groups should be straight chain. A single trialkyl phosphate may contain the alkyl group in all three positions or may have a mixture of different alkyl groups. Mixtures of different trialkyl phosphates can be used. Suitable types of trialkyl phosphates that can be used as base material preparations include tripropyl phosphates, tributyl phosphates, trihexyl phosphates, trioctyl phosphates, dipropyloctyl phosphates, dibutyloctyl phosphates, dipropylhexyl phosphates, dihexyloctyl phosphate, dihexylpropyl phosphate and propyl-butyloctyl phosphate.

The trialkyl phosphates can be combined with at least one triaryl phosphate comprising tricresyl phosphate, trixylene phosphate, ethylphenyldicresyl phosphate or isopropylphenyldiphenylphosphate, phenyl-bis(4-a-methylbenzylphenyl)phosphate. In one preferred embodiment, tricresyl phosphate and trixylenyl phosphate are used. In this case, the triaryl phosphates act as thickeners for the trialkyl phosphates. The amount of tricresyl phosphate can thus vary between 0 and 25% by weight, while the trixylenyl phosphate can vary between 0 and 25% by weight. The preferred range for the triaryl phosphates is from 5 to 15% tricresyl phosphate and from 5 to 15% trixylenyl phosphate. The combined mixture of tricresyl phosphate and trixylenyl phosphate is mixed together

to give a viscosity of between 145 to 230 Saybolt Universal seconds measured at 37.8°C. This mixture of materials can then be combined with a trialkyl phosphate in a known manner.

A conventional polymeric material is then mixed with a mixture of trialkyl phosphate and triaryl phosphate which acts as a viscosity index improver. The polymeric material suitable for the invention can be a mixture of from 10 to 55% by weight of polymethacrylates, polyacrylates, each containing from 1 to 20 carbon atoms. The polymeric materials can be in a solvent carrier such as e.g. di-2-ethylhexyl sebacate, dioctyl adipate, di-2-ethylhexyl adipate or similar conventional carriers. The polymeric materials can be any combination of these materials. This material is thoroughly mixed with a combination of ingredients so that a uniform material is formed. The amount of material introduced into the mixture can vary between 5 and 20% by weight.

A rust inhibitor is then mixed in a solvent such as an alkyl succinic acid or its derivatives, with the material. This latter material may be present in amounts between 0.01 and 0.5% by weight. A corrosion inhibitor such as e.g. benzotriazole, quinizarin or the like in an amount varying between 0.001 and 0.5% by weight to the mixture and thoroughly mixed with it. A dye is then added, which can vary between 5 and 20 parts per million and mixed in conventionally. As usual, a silicone antifoam agent is added^ and this may be present in an amount varying between 5 and 50 ppm.

The invention will be better understood with the help of the following examples.

EXAMPLE 1.

A basic material consisting of tricresyl phosphate in a quantity

of 10.45% by weight is mixed well with 8.55% by weight of trixylenyl phosphate so that a viscosity of 155 Saybolt Universal seconds measured at 37.8°C is obtained. This mixture of materials is mixed with 68.96

wt% tributyl phosphate until the materials are completely mixed together. Then 12% by weight of a mixture of approx. 40% of a polyalkyl methacrylate and approx. 60% di-2-ethylhexyl sebacate solvent carrier thoroughly with the mixture. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate is mixed with the mixture at an addition level of 1.0% by weight. A common rust inhibitor of the acrylic succinic acid type in an amount of 0.02% by weight in a solvent carrier is then mixed in. Then 0.02% by weight of benzotriazole is thoroughly mixed together with a common dye and antifoam agent in an amount of 10 and 15 ppm respectively. Next, trioctylmethylphosphonium dimethylphosphate is mixed into the mixture in different addition amounts comprising 5, 3, 1 and 0.5% by weight.

The preparations described in example 1 as well as other preparations

bel.tested in the apparatus to be described below.

The device is a modified Boeing wear device designed to simulate the constricting current in the servo valve in eVfly's hydraulic system. The device consists of an air-driven hydraulic pump of the piston type, accumulator, filter, flow meter, heat exchanger, reservoir and wear device. The wear device is layer 3 of 52100 steel hardened to R c62. The fluid enters the device through a 0.21 cm I.D. nozzle at 175.8 kg/cm^ and 0.15

gpm and hits a flat plate 0.025 cm from the nozzle. The wear device is taken apart after 24 test hours and the amount worn off is estimated with the naked eye and with the help of a microscope. The results are as follows:

The above results illustrate the ability of methyltri-octyl phosphonium dimethyl phosphate to reduce the wear characteristics of a phosphate ester hydraulic fluid and thereby prevent damage to hydraulic systems.

EXAMPLES 2-16

Typical phosphonium compounds 2 to 16 described above also reduce the wear characteristics of the fluid when added to the phosphate ester base material.

In addition to use in aircraft hydraulic systems, the phosphonium compounds described here are useful in a wide range of lubricants. The term "lubricant" as used herein is intended to include liquids used primarily for their lubricity as well as

those used as pressure transfer agents. The phosphonium compounds are useful as extreme pressure additives in fluids including aircraft gas turbine lubricants, as additives in fire resistant industrial lubricants including gear and cutting oils and in brake fluids.

Claims (2)

1. Hydraulic fluid which includes a major amount of a base material selected from the esters of a phosphoric acid; and optionally the following additives: a rust inhibitor, a dye and an antifoam agent, a corrosion inhibitor, which corrosion inhibitor is preferably benzotriazole, and an acid acceptor, characterized in that it also contains 0.1-10% by weight of a wear-inhibiting phosphonium compound of the general formula : where R, R' and R" represent alkyl, aryl, alkaryl and aralkyl groups containing from 1 to 10 carbon atoms and R"1 represents alkyl or aralkyl containing from 1 to 10 carbon atoms, X represents an oxygen or sulfur atom, and Y' and Y" represent lower alkoxy, lower alkyl, phenyl, lower alkylphenyl, phenyl-lower alkyl, phenoxy and lower alkylphenoxy, and Z represents oxygen. 2. Hydraulic fluid according to claim 1, characterized in that said phosphonium compound is present in an amount between 0.5 and 2.0% by weight.