CA1090774A - Low water-sensitive hydraulic fluids containing borate esters and formals - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to a low water-sensitive hydraulic fluid composition which contains from about 20 to about 96% by weight of at least one borate ester as the base fluid and additionally, from about 2 to about 40% of a bis (glycol ether) formal. Such low water-sensitive hydraulic fluids are high boiling compositions which also have desirable properties at low temperatures, particularly viscosity, and thus are useful under a wide variety of climatic and operational conditions.

Description

lU~ 7''1 This application relates to Canadian Patent No. 929,925 dated July 10, 1973.
This invention relates to new and improved, low water-sensitive hydraulic pressure transmission fluids for use in fluid pressure operating devices such as hydraulic brake systems, hydraulic steering mechanisms, hydraulic transmissions, hydraulic jacks, hydraulic lifts, etc. More particularly, this invention relates to hydraulic fluids having a low sensitivity to water which employ as the base fluid one or more borate esters of glycol monoethers and additionally a bis (glycol ether) formal. The term "base fluid" as used throughout the specification and claims means the major active ingredient (not necessarily present in the major or largest proportion) of the hydraulic fluid, i.e. that ingredient which is most active in maintaining the desired properties of the hydraulic fluid especially in the face of aqueous contamination.
A great number of hydraulic fluid compositions have been suggested in the art. Commonly, the hydraulic pressure transmission fluids, such as brake fluids are made up of three principal units. The first is a base stock or lubricant for the system which may include heavy bodied fluids such as polyglycols, castor oil, mixtures of these materials, etc.
Diluents, which are employed for the purpose of controlling -;
the viscosity of the fluid as represented by glycol ethers, glycols, alcohols, etc., form the second basic unit. Finally, the third basic unit is represented by an additive or inhibitor package comprising small quantities of materials which are added to control or modify various chemical and physical properties of the fluid, e.g. to reduce oxidation, to improve ~ $

lO~V~ 7~

C_5718 wetting and flow and to malntain the pH of the hydraulic system above 7 ln order to minimize corrosion. By varying the composition, particularly desired properties can generally be attained. However, hydraulic fluids have been sub~ect to increasingly stringent reguirements with regard to properties, particularly boiling point and viscosity-temperature relation-ship. This had made it extremely difficult to produce a desirable fluid since very often a change in composition which improves one or more of the properties will detrimentally a~fect some other propertyO ~hus, it has been pos~ible to -~ obtain hydraulic fluids having high boiling points by using ; higher molecular weight organic compounds, such as the polyoxyalkylene glycol ethers, as the ma~or component, however, the viscosity of these fluids is generally unsatisfactory, particularly at low temperaturesO This problem is magnified when water gets into the hydraulic fluid since many of the properties are af~ected, some to a substantial extent.
Hydraulic fluids, as exemplified by the commercial motor vehicle brake fluids, are hygroscopic by nature and therefore, absorb molsture from ambient atmospheres with resulting degradation o~ their boiling point. mis ef~ect that water has on the boiling polnt of hydraulic fluids has been studied extensively and a great deal of public interest has been generated concerning the safety qualities of hydraullc fluids especially brake fluids as is pointed out, for example by C. F. Pickett in an article entitled "Automotive Hydraulic Brake Fluids" published as part of the 51st Mid-Year Meeting Proceedings of the Chemical Specialties Manufacturing Association, Inc.,N.Y. (1965). As indicated in the above-noted artlcle, when small amounts of water, e.g. ~.5~ by welght was added to various commercial brake fluids, some having C-571~ inltlal bolling points o~ 500~., the resulting ~luid compositions exhibited boiling polnts below 300F. In contrast, the hydraulic ~luid composltions o~ this invention generally malntain boiling points o~ greater than 300F. and more o~ten greater than 320F. and 350Fo when pre~erred embodiments are used, after the addition o~ 7.5% water.
The importance o~ having a hydraulic fluid which has a low æensitivity to water and thus can maintain the boiling point at levels above those previously found in available commercial ~luids is more readily understood when the follow-lng ~acts are considered. First o~ all, it is known that hydraulic brake ~luid temperatures can reach rather high levels and o~ten approach and even exceed the 300F. level.
This is substantiated by the results o~ field studies in 1966 by the Society of Automotive Engineers (See SP-338, "Automotive Brake Evaluation Under Customer Usage Condit~ons", pp. 1 and 2, ~1968))wherein it was shown that brake ~luid temperatures approached 270~. under typical driving conditions o~ vehicles `
which were loaded only to their manu~acturer's recommended limit. It could reasonably be assumed ~rom these results, that when abnormal conditions are encountered temperatures would exceed 270F. and approach and even pass 300F.
It ls also known that so-called conventional type motor ~ehicles often accumulate small amounts o~ moisture in their hydraulic fluids during usage. This is substantiated by results disclosed in a meeting of the SAE Hydraulic Brake Systems Actuating Committee in 1966 (See minutes o~ meeting o~ October 26_27, 1966) and further by the report o~ Charles B. Jordan, '~ffect of Water on Hydraulic Brake Fluid", U.S~
Army Coating and Chemical Laboratory, May, 1966. These articles clearly show that amounts o~ water have been accumulated in hydraulic brake ~luids under use conditions ~ 7~

C-5718 ln varying proportlons and have o~ten reached levels o~ up to 3.5~ and even have been as high as 5~ by weight. The fact that hydraulic ~luids do accumulate ~ome water durlng usage i8 further supported by the SAE Standard J-1703, Motor Vehicle ~rake Fluld, which requires certain water tolerance tests to be passed a~ter the addition of 3.5~ water and also, requires a corro~ion test to be passed a~ter the addition o~ 5% water to the brake fluid.
From the above discusslon, it can readlly be under~tood that hydraulic fluids under certain conditions can approach temperatureæ o~ the magnitude o~ 300F. and higher and ~urther-more such ~luids can accumulate small amounts o~ moisture durlng usage. Thus, hydraulic ~luids which have low dry boillng polnts and are ~ensitive to water to a large degree can encounter problems such as vapor lock which can result in the ~ailure of a hydraulic brake system and consequently cause an accident. This clearly illustrates the advantage of the hydraulic fluids o~ this inventlon which possess a high degree o~ water tolerance and are able to maintain their boiling points at higher and sa~er levels.
The seriousness o~ the problem o~ water accumulation and its e~ects on the hydraulic ~luid system is ~urther signified by the fact that the U.S. Department of Transporta-tion presently is considering acceptance o~ standards for motor vehicle brake ~luids which would ~or the first time include a minimum wet re~lux boiling point (equivalent to approximately 3.5~ by weight o~ water addedj. The proposed standards include one for a ~luid having a minimum dry reflux bolling point o~ ~01F. and a minimum wet reflux boiling polnt of 284F. and another for a ~luid having a minimum dry re~lux boiling point of ~46F. and a minimum wet re~lux boiling point o~ 320F. The term "dry reflux boillng point" as used herein 10~3U"~7~

C_5718 ls de~ined as the bolling point o~ the hydraulic ~luid as delivered to the consumer or distributors (i.e. ~luid ready for use). Wet reflux boiling point i5 the boiling point o~
the hydraulic fluid a~ter a discrete amount o~ water has been added thereto.
The above considerations clearly point out the need ; for a hydraulic ~luid which has a low sensit~ vity to water and thus is able to maintain certain properties and characteristics when amounts o~ water commonly encountered during use are present. In addition, a hydraulic ~luid which will be used under various climatic and operational conditions must maintain adequate viscosity (~luidity) over the temperature range o~ anticipated operating conditions ; so as to assure proper ~unctionality o~ the system.
` There are various hydraulic ~luids known in the art as shown for example in Introduction to Hydraulic ~luids by Roger E. Hatton, Reinhold Publishing Corp<, (1962); U.S. ~ -Patent 2,998,~89 issued to Chester M. White on August 29, 1961 and U.S. Patent 3,~77,288 issued to Arthur W. Sawyer on April 9, 1968~ Generally, these fluids do not have the low water sensitivity that is required to maintain their orlginal properties after there is an accumulation o~
moisture and additionally such ~luids generally do not have the ability to operate under a wide variation o~ conditions.
One o~ the basic ob~ects of this invention is to provide hydraulic pressure transmission ~luids ~or use in hydraulic systems which retain to a high degree their original properties when water is added, l.e. they have a low sensitivity to water.
Another ob~ect is to provide hydraulic pressure transmission ~luids whlch are high boiling compositions and ..~
~ -6-l~J(~ 7~

_5718 which malntain relatively high boiling points even when water is added to the ~nitial fluid composltion.
Another ob~ect o~ this invention is to provide hydraulic pressure transmission ~luids having a high degree o~ lubricity while maintaining desired viscosities within a predetermined range under wide var~ations of temperature conditions, especially subrreezing temperaturesO
The hydraulic fluids of this invention generally comprise from about 20 to about 96 percent by weight, based on the total hydraulic fluid weight, of at least one borate ester of a glycol monoether as the base ~luid and from about

2 to about 40 percent by weight o~ a ~ormal o~ the glycol ethers. Generally the remainder o~ the ~luid is made up of diluent and one or more additives.
The hydraulic fluids of this invention are especially desirable because they have a low water-sensitiv~ty and also have a desired viscosity-temperature relationship over a wide range of temperature conditions. These properties make such ~luids particularly attractive because they can satis~actorily per~orm at low winter temperatures where the viscosity requirements are stringent and also can be used in warm weather climates and under heavy duty conditions particularly because of their high boiling points and low sensitivity to water. Additionally, the hydraulic ~luids of thls invention are o~ low cost, are essentially odorless and colorless, possess a high degree of compatibility with other ~luids and exhibit a very low rate of corrosivity.
Another ~eature o~ the hydraulic ~luids o~ this invention is that they have a satis~actory rubber compatibilityO
m e significance o~ rubber compatibility and the ru~ber swell-ing properties of the fluids cannot be overlooked since too ` 1111~ 7~

little swelling will result in lea]~age of the fluid past the rubber cup sealing means and past the piston and hydraulic cylinders with corresponding loss of power. On the other hand, fluids which cause too much rubber swelling are not desirable since they destroy the structural properties of the rubber sealing cups and rubber cylinders which, in turn, results in malfunction or inoperativeness of the unit.
The hydraulic fluids of this invention generally comprise four principal units: 1) base fluid, 2) formal,

3) diluent and 4) additives.
Base Fluid The base fluid employed in the novel hydraulic fluids of this invention generally comprises at least one borate ~ -ester of a glycol monoether. More particularly, the hydraulic fluids of this invention will comprise from about 20 to about 96 percent by weight, based on the total hydraulic fluid weight, of at least one borate ester of a glycol monoether.
Preferably, the amount of borate ester will vary from about 30 to about 92 percent and more preferably from about 54.5 to about 92 percent by weight based on the total hydraulic fluid weight. When using hydraulic fluids which can safely operate under somewhat lower temperature conditions, the range of borate ester used may vary from about 20 to about 54.4 percent and preferably from about 30 to about 54.4 percent by weight, based on the total weight of the hydraulic fluid.
Although a wide variety of borate esters can be employed as the base fluid in the novel hydraulic fluids of this invention, an especially useful class of borate esters are the so-called tri-borate esters of glycol monoethers having the general formula:
[Rl(~Ra)y~]3-B ' (I) 15)~ J7~

C-5718 wherein Rl ls a lower alkyl radical containing from 1 to 4 carbon atoms prererably 1 to 2, Ra ls alkylene o~ from 2 to

4 carbon atoms, pre~erably 2 to 3, ~nd y 18 an lnteger ~rom 2 to 4 lncluslve. The Rl and Ra gr~ups may be elther stralght or branched chaln structures. Borates o~ the a~ove-mentloned type include, ~or example: r H3(0CH2CH2)2~ 3-B, Hs(OCH2CH2)3 ~3-B, r 3H7(0CH2CH2)g ~3-B, H3(OCH2CHCH3)2 ~3-B, ~ H3(OCH2CHCH3)3 ~3-B, H3(0CH2CHCH3)g~3_B, ~ 2H5(0CH2CHCH3)2 ~3-B, ~2H5(OCH2CHCH3)3 ~3-B, ~ 2H5(0CH2CHCH3)4~3-B, r3H7(0CH2CHCH3)2-g ~3-B, ~ gH9(0CH2CHCH3)2-4~ 3-B, ~H30(oCHCH9CH2)2-4~73-B, ~2H5(ocHcH3cH2)2-g~73-B~
~ H3(W HCH3CHCH3)2_g ~3-B, ~ 2H5(0CHCH3CHCH3)2-g~3-B, H3(0CH2CHCH2CH3)2-g~3-B, ~ 2H5(0CH2CHCH2CH3)2-g~3-B, ~ r H3(0CH - CH2)2-g~3-B, ~ 2H5(0CH - CH2)2-4~3-B-: While any o~ khe borate esters de~ined by formula (I) may be u~ed, the ~ollowing borate esters are part~cularly use~ul: ~ H3(0CH2CH2)3 ~3-B, ~ 2H5(0CH2CH2)2 ~3-BJ
~zH5(0CH2CH2)3 ~3_B, ~ 2H5(OCH2CH2j~ ~3-B, r3H7(0CH2CH2)3 ~3-B, ~ gH9(0CH2CH2)2~ 3-B and ~ gHg(OCH2CH2)3 ~3-B.
, ' _g_ ., ll)~3V'-~ 7~

C-5718 Borate~ o~ the above-mentloned type can be conveniently prepared by reacting orthoboric acid and the glycol monoether while in the presence Or a water-azeotrope ~orming solvent.
Water ~ormed ln the esteri~ication reaction is continuously removed as the azeotrope. At rirst, the temperature Or the reaction mixture is maintained between about 0C. and about l90~C. and desirably at the distillation temperature o~ the water-solvent azeotrope. Arter essentially complete removal o~ the water formed durlng esteri~ication, the excess solvent is conveniently removed from the reaction mixture by distillatlon. The borate ester product, which is left in a residue, may then be recovered by distilling under reduced pressure or by extraction with a suitable solvent ~ollowed by evaporatlon o~ the solvent. For example, the compound H5(OCH2CH2)2~-B can be prepared by reacting two moles o~ C2H5(0CH2CH2)20H, 0.67 mole o~ orthoboric acid and 700 ml.
Or ethylbenzene with heating and mixing to yield 198 grams o~
the ester, a water-white liquid boiling at 222~_223C. (5 mm.
Hg). It i~ noted that in the preparation o~ these esters, a small proportion Or concomitant reaction products may be formed and other minor impurities may al~o be present.
Generally, the predominant portion Or ~uch other reaction products ~ormed will be a boroxine type compound havlng the following general structure:
/0\
Rz - B B Rz \ B
Rz whereln Rzis derived from the particular glycol ether belng used, e.g. CH3(OCH2CH2)20-, C2H5(OCH2CH2)20-, etc. The amount of such concomltant reaction products rormed and other lmpuritles present may be up to about 10~ by welght lr the . -~ V'7 7~
C-5718 reacted mixture is not dlstilled. Dlstillatlon will reduce the amount o~ other reaction product~ and impurities to about 1% or less, however, either the distllled or undistilled - product can be used provided the reaction medium or solvent 18 stripped off. me term "borate ester" as used in the speoi~ication and claims is intended to include relatively pure borate ester as well as crude borate ester which contains impurltles and other by-products ~ormed during preparation as described above. The preparation o~ the tri-borate esters per se is more completely described in U. S. Patent 3,080,412 issued to D. M. Young on March 5, 1963. It i8 0~ lnterest to note that this patent (U.S. 3,080,412) dlscloses the use of trl-borate esters, such as tris ~ -(2-ethoxyethoxy)ethy~
borate, as stabllizer and corroslon inhibltors ~or lubricants and non-aqueous hydraulic ~luids. However, use o~ these esters ~or such purposes, i.e. as a stabilizer or corrosion inhlbitor, would not impart satisfactory low water sensitivity to the ~ -hydraulic ~luid since such usage would generally be in very small or mlnor proportions (e.g. ~rom 0.5 to 2%) in accordance with the generally accepted practice in the art (e.g. see U.S. Patent ~403J104 issued to P. B. Sullivan on September 24J 1968). Additionally ~luids containing such amounts of esters would not have desired temperature-viscosity relatlon-ship over the wide range of operating conditions as provlded ~y the hydraulic fluids o~ thi~ invention.
A second highly use~ul class of borate esters includes compounds of the general ~ormula:
~ l-(ocH2cHR2)m-(ocH2cHR3)n~3-B (II) wherein R2 and R3 are independently selected from the group con~isting of hydrogen and methylJ m and n are positive integers whose sum is ~rom 2 to 20 and Rl is alkyl o~ ~rom 1 , -11--J~J()'~ 7~}

C-5718 to 4 carbon atom~ and with provi~o that one o~ R2 and R3 is methyl and one of R2 and R9 1~ hydrogen. Rl may be a straight chain or branched alkyl. Borate esters of Type II
can be prepared in the general way as those esters previously described (Type I) above, utllizing the so-called block type glycol monoethers. The preparation of esters of Type II
18 described in detail in U.S. Patent 3,316,287 issued to L. G. Nunn, Jr. et al on Aprll 25, 1967.
Type II borate esters use~ul in preparlng the novel ~luids o~ thl~ invention include, ~or example:
~H3(0CHzCH2)-(OCH2CHCH3) ~3-B
Hs(OCHzCHCH3)~(0CH2CH2) ~3-B
~3H7(0CH2CHCH3)2-(OCHzCH2) ~3-B
4Hg(OCH2CH2)5-(OCH2CHCH3) ~3-B
~H3(0CHzCH2)a-(OCH2CHCH3)5~3-B
~ 2H5(OCH2CHCH3) 12- ( OCHzCH2)8~3-B
r3~7(OCH2CHCH3) lo-(OCH2CH2)3-B
Another class o~ borate ester~ useful in the fluid composltions o~ this invention include esters having heteric oxyalkylene chalns, that is, oxyalkylene chalns in which oxyethylene and oxypropylene units are distr~buted randomly throughout the chain. These Type III esters have the general ~ormula:
(Rlr ~ 0)3-B , (III) Rg represents a heteric oxyalkylene chain havlng the ~ormula:
~ (OCHzCH2)r , (OCH2CHCH3)8 ~7 where the sum o~ r and 8 is not more than 20 and whereln the welght percent of oxyethylene units in the said chain is not less than 20 based on the total weight of all the oxyalkylene Imits in the chain and Rl is alkyl o~ ~rom 1 to 4 carbon atoms and may be straight or branched chain.
The preparation of Type III esters can be aocompllshed ln the same general manner as the preparatlon o~ Types I and II

_12-. -~ )'7 7~
C-5718 described above by reaoting orthobor~c acid ln the presence o~ toluene with a heteric glycol monoether o~ the ~ormula:
R ~ ~ OH
where Rl and Rg have the same meaning as previously set ~orth.
Glycol monoethers o~ this class can be conveniently prepared by methods well known in the art such as the process described ln U.S. Patent 2,425,845 issued to W. J. Toussaint et al on August 19, 1947.
A ~ourth type o~ borate ester suitable for use in the ~luid compositions o~ this inventlon have the general formula:
T2(0CH2CHR7)m-(OCH2CHR~)nO O(R4CHCH20)n (R5CHCH20)mT

( CV) O(R8cHcH2o)n-(R9cHcH2o)mT3 wherein Tl, T2 and T3 are each an independently ~elected alkyl group having ~rom 1 to 4 carbon atoms, R4, R5, R~, R7, R8 and R~ are lndependently selected ~rom the group cons~st-lng o~ hydrogen and methyl, n and m are poslt~ve ~ntegers ~ndependently selected ln each chaln and whose sum ln each chain is from 2 to 20J and with the proviso that ln no more than two o~ the chains i8 the sum o~ n and m the same. It is also noted that Tl, T2, and T3 may be a straight or branched chaln alkyl group.
Borate e ters o~ this type can be prepared ~n the same way as the proces~ described ~or Type I esters previously mentioned.
Type IV borate esters su~table for use in the ~luids of this ~nvention ~nclude, for example: -,,,., :, . . .. . . . .

tU~()'7 7~

`~ C-5718 O(CH3CHCH20)-(CH2CH20)CH3 C2H5(OCH2CHCH3) 3 - ( OCH2CH2)2-O-B\
O(CH3CHCH20)-(CH2CH20)2CH3 .O(CH3CHCH20)-(CH2CH20) loC4H~, .. .
CH3(OCH2CH2) 6 - ( OCH2CHCH9)5-O-B
O(CH2CH20)6-(CH2CHCH20)l0C4H9 O(CH3CHCH20)15C3H7 j C2H5(OCH2CH2)2-(OCH2CHCH3)0-B\
,;; O(CH2CH20)-(CH3CHCH20)CH3 It is ~urther noted that borate esters of Types II, III and IV will include concomitant reactlon products and other impurities o~ the type as described above ~or Type I
~ esters. Re~eren¢e to these types o~ borate esters in the ,:"'! speci~icatlon and claims is intended to include relatively pure borate ester as well as crude borate ester whlch contalns impurities and other by-products formed durlng preparation ~ as described above ~or Type I.
;~ Formal Comonent The formal portion of the hydrauli¢ ~luid composition l 20 o~ this invention will generally comprise ~rom about 2 to about ;
40 percent by weight, based on the total weight of the hydraulic ~luld, of one or more bis(glycol ether) formals having the ~ormula:
~ . . .
~bQ(Ra)x ~ 2CH2 (V) -~
wherein Rbis alkyl of 1 to 6 carbon atoms, preferably 1 to 4, ~ Ra is alkylene o~ 2 to 4 carbon atoms, pre~erably 2 to 3 -; and x is an integer of 1 to 5, preferably 1 to 3. The ~ and Ra groups may be straight or branched chained and it is also intended that the alkylene oxide group (RaO) in the above formula (V) include mixtures o~ said alkylene oxides.
Illustrative of the above type formals (V) are the v Jj -14_ .

.".' '' .

1~90~717 C-5718 ~ollowing compounds:
~H3(CZH4,~2CH2 rH3O(C2H40)~72CH2 rH3O(C2H40),~72CH2 ~2H50(C2H40)272CH2 ~4H90(C2H40~2CH2 ~4H90(C2H40)~72CH2 ~H30(CH2CHCH30~72CH2 ~H30(CH2CHCH30)~72CH2 r2H50(CH2CHCH30)272CH2 ~H3(C2H4)(CH2CHCH3~72CH2 While any of the above ~ormals defined by ~ormula (V) may be used, the ~ollowing bls(glycol ether) ~ormals are partlcularly use~ul:
~H3(C2H4~72CH2 ~H30(C2H40)~72CH2 ~H30(C2H40)~72CH2 ~2H50(C2H40);z72CH2 ~4H90(C2H40.~72CH2 ~4H90(C2H40)~72CH2 ::
The above ~ormals may be prep`ared by reactlng the appropriate glycol with paraformaldehyde and removing the water o~ condehsation which forms. Preparative technigues are commonly known in the art, e.g. British patent 506,613 (June 1, 1939); Chemical Abstracts, 33, 9325 (1939) discloses a proce~s ~or the preparation o~ condensation products o~
aldehydes with polyhydric alcohols or partial ethers thereo~.
Other known methods of preparation are disclosed in Canadian patent 390,733 (August 13, 1940); Chemical Abstracts, ~4, 6948 (1940), and in J.Am.Chem.Soc., "Formaldehyde bis(~ -ethoxy-ethyl) and bis(~ -ethoxyethoxyethyl) acetal by M. Sulzbacher, I~, 2795_6, (1950).

.

0'~'7~

C-571~ While the hydraullc fluld composition of this invention may contain from about 2 to about 40 percent by weight, based on the total weight o~ the hydraulic fluid, of the above rormals (V), preferred embodiments include about 2 to about 15 and more preferably ~rom about 2 to about 10 percent by weight.
The use of these formals enable the hydraulic ~luids of this invention to function over a wide range of climatlc and operational conditions particularly because o~ desirable temperature_viscosity relationships which such hydraulic fluids possess.
Dlluents The diluent portion of the hydraulic fluid composition of this invention generally will comprise one or more compounds selected ~rom the group consisting of a) glycol monoethers or diethers b) glycols and polyglycols and c) aliphatic saturated alcohols.
More particularly, the glycol monoethers or diethers s have the formula:
R~ -R~ yORI (VI) wherein R is alkyl of from 1 to 4 carbon atoms,preferably 1 to 2, R~ is hydrogen or alkyl of from 1 to ~ carbon atoms,pr~ably 1 to 2, R" is alkylene of 2 to 4 carbon atoms, preferably 2 to 3, and y is 2 to 40 The R, R' and R" groups may be straight chained or branched and it is also intended that the alkylene oxide groups (O-R") in the above formula (VI) include mixtures of said alkylene oxides.
Illustrative of the diluents o~ this type (VI) are the following compounds: diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-isopropyl ether, diethylene glycol monoisobutyl ether, 1~ ~0'7~7~
-5718 triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol mono-n-butyl ether, tetra-ethylene glycol monomethyl ether, tetraethylene glycol mono-ethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, trlpropylene glycol monoethyl ether, trlpropylene glycol mono-n-butyl ethèr, tetrapropylene glycol monomethyl ether, tetrapropylene glycol monoethyl ether, dibutylene glycol monomethyl ether, dibutylene glycol monoethyl ether, tri-butylene glycol monomethyl ether, tributylene glycol monoethyl ether, tributylene glycol mono-n-propyl ether, tetrabutylene glycol monomethyl ether, tetrabutylene glycol monoethyl ether, tetrabutylene glycol mono-n-butyl ether and the corresponding diethers thereo~. It is ~urther noted that the above diluents include the various isomer3 o~ the respective compounds and mixtures thereo~.
While any o~ the above glycol ethers de~ined by formula (VI) may be used, the ~ollowing glycol ethers are partlcuIarly use~ul: dlethylene glycol monomethyl ether, dlethylene glycol monoethyl ether~ diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, trlethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetra-i ethylene glycol monomethyl ether and tetraethylene glycol -monobutyl ether.
The glycol ether~ are the most pre~erred diluent ~ince their use will result in a ~luid having a de~irably high boiling point with good vi~c~osity and water solubility properties. Most pre~erred df the glycol ethers are the ethylene glycols.
The second group o~ use~ul diluents are the glycols and polyglycol3, including alkylene, polyalkylene and poly-oxyalkylene glycols, having a molecular weight o~ ~rom about '74 C_~718 60 to about 450 and pre~erably ~rom about 100 to about 300~
Illustratlve Or such type diluents are the following compounds:
ethylene glycol, propylene glycol, ~lexylene glycol, diethylene glycol, dlpropylene glycol, triethylene glycol, tripropylene glycol, polyethylene glycol and polypropylene glycolO
The use o~ the glycols and polyglycols as diluents is not as desirable as the glycol ethers since their use may result in some loss o* fluidit~ at ~ery low temperatures, however, they may be used in condi~ion~ ~here the reguirements - are not as demanding.
The third type o~ use~ul diluents are aliphatic, saturated monohydric alcohols containir~ ~rom 6 to 1~ carbon atoms, preferably ~rom 8 to 10. Illustrative o~ such diluents are the following alcohols: hexanol, octanol, isooctanol, decanol, isodecanol, dodecanol, and tridecanol Since the use o~ the allphatlc alcohols in a high boiling hydraulic fluid may result in some loss of water solubility, they are not as desirable as the glycol ethers.
However, they may be used in conditions where the requirements are not as stringent.
The diluent portion of the hydraulic fluids o~ this lt~3~ ' 7'~

- invention generally will comprise from 0 to about 78 percent by weight, preferably from about 2 to about 70 and more preferably from about 6 to about 45 percent by weight, based on the total weight of the hydraulic fluid composition.
While the above diluents, especially the glycol ethers, are particularly preferred, other diluents may be used if the desired properties and characteristics of the hydraulic fluid can be attained. For example, certain diesters derived from organic aliphatic acids and aliphatic alcohols might be usefully employed. Examples of diesters which might be used include dibutyl adipate, bis(methoxyethyl) azelate, diisopropyl succinate, dipropylene glycol dipropionate and triethylene glycol dibutyrate.
Additives When desired, various additives may be added to the hydraulic fluids of this invention to control or modify various chemical and physical properties of the fluids. Among the various types of additives which can be added to the hydaulic fluids of this invention are included: inhibitors -for pH and corrosion control, antioxidants, rust inhibitors, - viscosity index improvers, pour point depressants, lubricating additives, antifoamants, stabilizers, demulsifiers, dyes and odor suppressants. Generally, the total amount of additives which may be incorporated into the fluid composition will vary depending on the particular composition and the desired properties. More particularly, the total amount of additives will comprise from 0 to about 10 percent and preferably from about 0.1 to about 8.0 percent by weight based on the total weight of the hydraulic fluid composition.
For example, inhibitors for pH and corrosion control, such as alkaline inhibitors as exemplified by the alkali metal borates, can be employed in an amount sufficient to .

. .

maintain alkaline conditions in the fluid compositions, e.g. a pH value of from about 7.0 to about 11.5. These inhibitors are generally added in an amount of from 0 to about 8.0 per-cent by weight based on the total weight of the hydraulic fluid composition and preferably from about 0.2 to about 6.0 percent by weight on the same basis. Useful inhibitors in-clude alkali metal borates, such as sodium borate, potassium tetraborate, etc.; sodium meta arsenite; alkali metal salts of fatty acids, such as potassium oleate, the potassium soap of rosin or tall oil; alkylene glycol condensates with alkali metal borates, such as the ethylene glycol condensate of pot-assium tetraborate; amines, for example, ethanolamine, methyl diethanolamine, diethanolamine, isopropanolamines (mono, di and tri), di(2-ethylhexyl) amine, di-N-butyl amine, monoamyl amine, diamylamine, dioctylamine, salicylal monoethanolamine, di-~-naphthyl-p-phenylene diamine, N,N'-disalicylidene-1,2-propanediamine, N,N'-disalicylal ethylene diamine, dicyclohexyl-amine, and amine salts such as mono or dibutyl ammonium borate;
phosphites, such as triphenyl phosphite, tri(tertamylphenyl) phosphite, diisopropyl phosphite, etc.; mercaptobenzotriazole;
morpholine compounds including alkyl morpholines having from 1 to 4 carbon atoms in the alkyl group such as N-ethyl morpho-line, N-isopropyl morpholine, N-butyl morpholine; N-phenyl mor-pholine, N-(2-aminoethyl) morpholine, N-(2-hydroxyethyl) mor-pholine, etc.; phosphates, including the alkali metal phos-phates, dibutyl amine phosphates, the dialkyl acid o-phos-phates and amine salts thereof; triazoles including benzotri-azole, 1,2-naphthotriazole, 4-nitrobenzotriazole, tolutriazole, aminobenzotriazoles such as 5-acylaminobenzotriazole, and alkyl triazoles having 1 to 10 carbon atoms in the alkyl group as ex-emplified by methyl triazole, ethyl triazole, n-propyl triazole, tertiary butyl triazole, hexyl triazole, isodecyl triazole, etc. Other useful corrosion inhibitors include adenine, 4-methylimidazole, 3,5-dimethyl pyrazole, 6-nitroimidazole, imidazole, benzimidazole, quinine, indazole, ammonium dinonylnaphthalene sulfonate, dioleyl thiodipropionate, -ethylbenzoate, ethyl-p-aminobenzoate, cyclohexyl ammonium nitrite, diisopropyl ammonium nitrite, butynediol, glycerin, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert. butyl-4-hydroxybenzoyl), 4,4'-methylene bis(2,6-di-tert. butylphenol), 4-hydroxymethyl-2,6-di-tert. butylphenol, 4,4'-methylene bis(4-methyl-6-tert.
butylphenol), salicylal-o-aminophenol, 2,6-di-tert. butyl-2-dimethylamino-p-cresol, 4,4'-thio bis(6-tert. butyl-o-cresol).
Mixtures of the above-mentioned inhibitors can be employed if desired.
While any of the above-mentioned inhibitors may be used for pH and corrosion control, the following inhibitors are particularly useful: glycerin, butynediol, diethanolamine, methyl diethanolamine, mixed isopropanolamines, diisopropanol-amine and triisopropanolamine.
An antioxidant may be used as an additive in the hydraulic fluid compositions of this invention if desired.
Generally the amount of antioxidant used will vary from 0 to about 2 percent and preferably will be from about 0.001 to about 1.0 percent by weight based on the total weight of the fluid composition. Typical antioxidants include phenolic compounds, such as 2,2-di-(4-hydroxyphenol) propane, 7~

C-5718 phenothiazlne, phenothiazlne carboxylic acid esters, N-alkyl or N-arylphenothiazines, such as N-ethyl phenothiazlne, N-phenyl phenothiazine, etc.; polymerlzed trimethyldihydro-guinoline, amines, such as phenyl-alpha-naphthylamine, phenyl-beta_naphthylamine, dioctyl diphenylamine, N~N-di-~ -naphthyl-p-phenylene diamine, p-isopropoxy diphenylamine, N,N-dibutyl-p_phenylene diamine, diphenyl-p-phenylene diamine, N,N'-b1s(1,4_dimethylpentyl)_p-phenylene diamine, N,N'-diiso-propyl-p-phenylene diamine, p-hydroxydiphenylamine, etc O;
~ 10 hindered phenols such as dibutyl cresol, 2,6_dimethyl-p-cresol, ;; butylated 2,2_di-(4-hydroxyphenyl) propane, n-butylated aminophenol, butylated hydroxyanisole~, such as 2,6-dibutyl-p-hydroxyaniqole; anthraquinone, dihydroxyanthraquinone, hydroquinone, 2,5_di_tertiarybutylhydroguinone, 2_tertiary butylhydroquinone, quinoline, p-hydroxydiphenylamine, phenyl benzoate, 2,6-dimethyl p-cresol, p-hydroxyanisole, nordihydro-quaiaretic acid, pyrocatechol, styrenated phenol, polyalkyl polyphenols, sodium nitrite, etc, Mixtures o~ the above-mentioned antioxidants can be emplo~ed, i~ desired. It should be emphasized that wlth a variety o~ the ~luids of this lnvention, which are suitable ~or a wide range o~ industrial - application, a separate antioxidant is not required.
While any of the above_mentioned antioxidants may be used, the ~ollowing antioxidants are particularly pre~erred:
sodium nitrite and dioctyl diphenylamine.
The above-noted inhibitors and additives are merely exemplary and are not intended a~ an exclusive listing o~ the many well-known materials which can be added to fluid ., ; compositlons to obtain various desired properties. Numerou~
~-dditives u~e~ul in hydraulic ~luids are disclosed in Introduction to EYdraulic Fluids by Roger E. Hatton, Reinhold Publishing Corp., (1962).

_22_ , . . . .

r~ 7~

C-5718 Formulation o~ the novel hydraulic fluids of this invention 18 accomplished by blending the components to a homogeneous stage in a mixing vessel~ The pre~erable blend-ing temperature is ~rom about 50-125F. It ls preferable to warm the solution during preparation to ~acilitate dis-solution. The blending o~ the compounds is conveniently conducted at atmospheric pressure in the absence o~ moi~tureO
In general, any suitable method can be used in pre-paring the liguid compositions o~ this invention. The components can be added together or one at a time, in any desired sequence. It is pre~erable, however, to add the antioxidant and alkaline inhibitor as a solution in the glycol ether component. All components are mixed until a single phase composition is obtainedO
The ~ollowing examples which illustrate varlous embodiments of this invention are to be considered not limitative.

_2~_ ~ 4 C-571~ EXAMPLE 1 A hydraulic rluid was prepared having the ~ollowing composition: .
Percent by Wel~ht Borate Ester r2Hs ( OC2H4) 3~3 -B . 51.80 ~ 2H5(0C2X4)4~ 3-B 18.20 Triethylene glycol monoethyl ether 14.35 .
rH3O(c2H~o)~72cH2 10. 00 l~xed isopropanolamine . (10~15~ mono, 40-50% di, 40-50% trl) 3.00 Glycerin 2.00 ~utynedlol 0.50 .P Dioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.~ 0.10 Sod-lum nitrlte 0.05 .~ , .
- 100. 00 This ~luid compositlon was tested accord~ng to the ~: 20 : procedures set forth in Society o~ Automotive En6ineers - Standard J1703. The data relating to these tests, which illustrate the outstanding properties Or this fluid is i shown in Table 1.
~ he re~lux boiling point (dry) o~ the above fluid was measured and ~ound to be 532F. at atmospheric pressure.
To test the water insensitivity of the fluid composition, a - sample of 100 parts by volume o~ the fluid plus 3.5 parts . by volume o~ water was prepared and it was found to have a re~lux boiling point (wet) at atmosp~eric pressure o~ 367CF. .
indicating the high degree o~ water insensitivity.
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C_5718 EXAMPLE 2 A hydraulic ~luid was prepared havlng the ~ollowing compositlon:
Percent by Welght Borate Ester H5(OC2H4)3 ~3-B 51~80 2Hs(CC2H4)4~ 3-B 18.20 Hs(OC2H4)2~3-B 14.35 ~H30(C2H40)~72CH2 lOo 00 Mixed isopropanolamines (10-15~ mono, ~0-50%.di, 40-50~ tri) 3.00 Glycerin - 2.00 Butynediol 0.50 ~ioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.) 0.10 Sodium nitrite : 0-05 ~0. 00 Properties:
Reflux boiling point (dry) 515F
Re~lux boiling point (wet) -:
(3.5 ml~ water ~ 100 ml. ~luid) 365F.
Viscosity at -40Fo 1852 csO

_28-~; ... . . .

~ ~.C~ t 7 C_5718 EXAMPLE 3 A hydraulic ~luid was prepared having the ~ollowlng compositlon:
Percent by Weight Borate Ester Hs(OC2H4)3 ~3.B 51.80 ~ 2H5(0C2Hg) ~ 3-B 18.20 Triethylene glycol monoethyl ether 19.35 ~ H30(C2H40~ 2CH2 5~00 Mixed isopropanolamines (10-15% mono, 40~50~ dl, 40~50% tri) 3~00 Glycerin 2.00 Butynediol o. 50 Dioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.) 0.10 Sodium nitrite o.o5 ., 100. 00 Properties:
Reflux boiling point (dry) 481Fo Reflux boiling point (wet) ; (3~5 ml. water + 100 ml. ~luid) 339F.
V1soos1ty at -40F. 1515 8-.

_29-, . , ~ ()7 7~

A hydraulic ~luid was prepared having the following compo~ition:
Peraent by . Weight Borate Ester H5(0C2H4)3 ~9-B 51.80 H5(0C2H4)~ ~3-B 18.20 Triethylene glycol monoethyl ether 4-35 ~ H30(C2H40~ 2CH2 20.00 Mlxed i~opropanolamines (10-15~ mono, 40-50~ di, 40-50% tri)3.00 ` Glycerin 2.00 Butynediol -5 :
Dioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.) 0.10 Sodlum nltrite . 0-05 100. 00 ~:
Properties:
Re~lux boiling point (dry) 453F.
Re~lux boillng point (wet) (3.5 ml. water + 100 ml. ~luid)333F-Vl~co~ity at -40F. 720 c~

.
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~ 7 C-5713 E~MP.IE 5 A hydraulic ~luid was preparecl having the ~ollowing composition:
Percent by Weight Borate Ester H5(oc2H4)3o73-B 51.80 ~ 2H5(oC2H4)4o73_B 18020 Triethylene glycol monoethyl ether 19.35 r H30(C2HgO) ~ 2CH2 5 Mixed isopropanolamines (10-15~ mono, 40-50~0 di, 40-50~0 tri) 3.00 Glycerin 2.00 Butynediol 0050 Dio¢tyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.) 0.10 Sodium nitrite 0.05 Properties: -Reflux boiling point (dry) 505Fo Re~lux boiling point (wet) (3.5 ml. water ~ lOQ ml. fluid)345 F~
Viscosity at -40Fo 1865 CS.

, `7 C-5718 EXAMPL$ 6 A hydraulic ~luid was prepared having the ~ollowlng composition:
Percent by ~; Weight Borate Ester H5(0C2H4)3 ~3-B 51.80 ~H5(OC2H4)4 ~3-B 18.20 Triethylene glycol monoethyl ether 4.35 ~ H30(C2H40) ~2CH2 20~00 Mlxed isopropanolamines (10-15% mono, 40-50% di, 40-50% tri)3.00 Glycerln ~ 2.00 Butynediol 0.50 Dioctyl diphenylamine (Van Lube 81 produced by R. T. ~anderbilt Co.3 0~10 Sodium nitrite 0.05 rOO. OO ~ ~
Properties:
Reflux boiling point (dry) 523F.
Re~lux boiling point (wet) :
(3.5 ml. water + 100 ml. fluid) 354~. :
Vlcoo~lty at -40~. 1415 o~.

.

:

, _32_ .

` ~U ~)''37 C-5718 EXAMPLE ~
` A hydraulic fluid was prepared having the ~ollowing ¢omposition:
Percent by Wei~ht Borate Ester r 2Hs(oc2H4)3 ~3-B 51.80 ~ 2H5(0C2H4) 4~3 -B 18020 Triethylene glycol monoethyl ether 19.35 ~ 4H90(C2H40~ 2CHz 5 : Mixed isopropanolamines (10-15% mono, 40-50~0 di, 40-50% tri)3.00 Glycerin 2.00 Butynediol 0050 Dioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.) 0.10 Sodium nitrite 0.05 100. 00 Propertle~: -; 20 Reflux boiling point (dry) 502F
Re~lux boiling point (wet) (3.5 ml. water ~ 100 ml. ~luid)~4~ F.
ViDoo~1ty at -40~F. 1771 oa.

' ' -3~-. '' .: .

~ ) 7 C_5718 EXAMPLE 8 A hydraulic ~luid was prepared having the ~ollowing composition:
Percent by Wei~ht Borate Ester zH5(0C2H4)3 ~3-B 51 ~ 80 ~ zH5(0C2H4) ~ 3-B 18 ~ 20 Triethylene glycol monoethyl ether 19. 35 r H30(CzH40)~ zCHz 5000 Mixed isopropanolamines (10-15% mono, 40~50% di, 40~50% tri) 3~00 Glycerin 2~ 00 Butynediol -5 ~:
Dioctyl diphenylamine (Van Lube 81 produced by R. T. Vanderbilt Co.)0.10 Sodlum nitrite 0.05 lOOo 00 Propertie~:
Re~lux boiling point (dry) 504Fo Re~lux boiling point (wet) (3.5 ml. water ~ 100 ml. ~luid) 343 Viscosity at _40F~ 2083 c~
.' A hydraulic ~luid was prepared having the ~ollowlng compo~ition:
Peraent by Wei~ht ~H3 (OC2H4)35~73-13 20. 00 Triethylene glycol monomethyl ether 58.00 ~Z2H50(C2H40)~72CH2 15.00 Polyethylene glycol (M.W. 300) 5000 Dlethanolamine 2.00 100. 00 Properties:
Reflux boiling point (dry) 490F.
Re~lux bo~ling point (wet) (3.5 ml. water ~ 100 ml. ~luid)308 F.
Viscosity at -~0Fo 522.3 cs.

A hydraulic ~luid was prepared having the ~ollowing composition: -Weight ~2H5 ( OC2H4 ) 2S~73-B 25.00 Tetraethylene glycol monoethyl ether 15.00 Triethylene glycol monoethyl ether 39.00 ~4Hgo(C2H40)972CH2 20.00 Monoethanolamlne 1.00 100. 00 Properties:
Reflux boiling point (dry3 436F.
Reflux boiling point (wet) (3.5 ml. water ~ 100 ml. ~luid)30~ F.
Visco~ity at -~0F. 607.1 c~.

~ `7 C-5718 EX~MPLE 11 A hydraulic fluid ~Jas prepared having the ~ollowing composition: ~
Percent by Weight _ ~ H3(0C2H~) 9 (OCH2CHCH3)(OC2Hg )~3 -B 30.00 Triethylene glycol monomethyl ether 57.00 H30(CzH40) ~2CH2 10.00 Triisopropanolamine 3.00 Propertie~:
Reflux boiling poin~ (dry) 504F.
Re~lux boiling point (wet) (3.5 ml. water + 100 ml. flu~d) 308F
Viscosity at -40F. 516.3 cs.

A hydraulic ~luid was prepared having the ~ollowing composition:
- Percent by ~20 - Wei~h~
4Hg0(50% C2H40 + 50% CH2CHCH30) ~3B 35.00 (Prepared using Union Carbide glycols -*UCON 50-B55) Triethylene glycol monoethyl ether 22.00 Polyethylene glycol (M.W. ~00) 10.00 H30(C2X40) ~2CH2 3 Diisopropanolamine 2.5 Dioc~yl diphenylamine tVan Lube 81 produced by R. T. Vanderbilt Co.) 0.5 '' ' '100.00 , Properties:
- Reflux boiling point (dry~ 542F.
; Re~lux boiling point (~et) (~.5 ml. water + 100 ml. fluid) ~15F.
Viscosity at -40F. 848.8 cs.

" .
* Trade Mark , ~ .
_~6-~ C~ 7 A hydraulic ~luid was prepared having the ~ollowing composition:
Percent by Wel~ht Borate Ester ~ H3(OC2H4)3 ~ 3-B 3 ~
Tetraethylene glycol monomethyl ether 22.0 Triethylene glycol monoethyl ether 4200 ~ H30(C2H40)~ 2CH2 5 Monoethanolamine 1.0 100. 0 Properties:
Reflux boiling polnt (dry) 467F~
Re~lux boiling point (wet) 321F~
(3~5 ml. water + 100 ml. ~luid) Viscoslty at -40F. . 660 c8 A hydraullc ~luid was prepared havlng the ~ollowlng composltlon:
Percent by Wei~ht Borate Ester H3(OC2H4)3 J3_B 20.0 ~ 2Hs(OC2H4)2 ~3-B 15 ~ 0 Trlethylene glycol monomethyl ether 20.0 Trlethylene glycol monobutyl ether 17~0 Polyethylene glycol (M.W. 300) 15~0 H50(C2H40)2J 2CH2 10.0 Monolsopropanolamine 3~ 0 Propertles:
Reflux bolllng polnt (dry) 445Fo Re~lux boiling point (wet) 321F~
(3~5 ml. water + 100 ml. ~luid) Viscosity at -40F. 2437 cs ~37~

)f~ 7~

A hydraulic ~luid was prepared having the ~ollowlng - :
composition:
Percent by Wei~ht Borate ester H5(0CzH4)3 ~3-B 2906 ~ ~ 2H5(0C2H4)4~3-B 1004 : Tetraethylene glycol monoethyl ether 10.0 Triethylene glycol monoethyl ether 41.0 : ~ gHgO(C2H40) ~ 2CH2 50 M~thyl diethanolamine 4.0 Propertie~:
~' Reflux boiling point (dry) 487F.
Reflux boiling point (wet) 319Fo .5 ml. water + lOQ ml. ~luld) Viscosity at -40F. 901 c~ -., .
,. . . .

, . . . ..

- .

~8

Claims (30)

WHAT IS CLAIMED IS:

1. A hydraulic fluid composition comprising (A) from about 20 to about 96 percent by weight, based on the total weight of the hydraulic fluid composition, of at least one base fluid selected from the group consisting of (a) a borate ester of the formula:
[R1(O-Ra)y-O]3-B , wherein R1 is alkyl of from 1 to 4 carbon atoms, Ra is alkylene of from 2 to 4 carbon atoms and y is an integer of from 2 to 4; (b) a borate ester of the formula:
[R1-(OCH2CHR2)m-(OCH2CHR3)nO]3-B , wherein R1 is alkyl of from 1 to 4 carbon atoms, R2 and R3 are independently selected from the group consisting of hydrogen and methyl, m and n are positive integers whose sum is from 2 to 20, and with the proviso that one of R2 and R3 is methyl and one of R2 and R3 is hydrogen; (c) a borate ester of the formula:
(R1[Rg]O)3-B , wherein R1 is alkyl of from 1 to 4 carbon atoms, Rg is a heteric oxyalkylene chain of the formula:
[- (OCH2CH2)r , (OCH2CHCH3)S -] , wherein the sum of r and s is not more than 20 and wherein the weight percent of the oxyethylene units is not less than 20 based on the total weight of all the oxyalkylene units;
and (d) a borate ester of the formula:

wherein T1, T2 and T3 are each an independently selected alkyl group having from 1 to 4 carbon atoms; R4, R5, R6, R7, R8 and R9 are independently selected from the group consisting of hydrogen and methyl, n and m are positive integers independently selected in each chain and whose sum in each chain is from 2 to 20, and with the proviso that in no more than two of the chains is the sum of n and m the same;(B) from about 2 to about 40 percent by weight, based on the total weight of the hydraulic fluid composition, of at least one bis(glycol ether) formal having the formula:
[RbO(RaO)X]2CH2 , wherein Rb is alkyl of 1 to 6 carbon atoms, Ra is alkylene of 2 to 4 carbon atoms and x is an integer of 1 to 5 and (C) from 0 to about 78 percent by weight, based on the total weight of the fluid composition, of at least one diluent selected from the group consisting of: (aa) glycol ethers having the formula:
R[O-R']yOR' , wherein R is alkyl of from 1 to 4 carbon atoms, R1 is selected from the group consisting of hydrogen and alkyl of from 1 to 4 carbon atoms, R" is alkylene of from 2 to 4 carbon atoms and y is an integer of from 2 to 4; (bb) glycols and poly-glycols having a molecular weight of from about 60 to about 450 and (cc) aliphatic saturated monohydric alcohols having from 6 to 13 carbon atoms.

2. The hydraulic fluid composition of claim 1 wherein said formal has an alkyl Rb group of 1 to 4 carbon atoms, an alkylene Ra group of 2 to 3 carbon atoms and x is 1 to 3.

3. The hydraulic fluid composition of claim 2 wherein from about 2 to about 15 percent by weight, based on the total weight of the hydraulic fluid, of said formal is present.

4. The hydraulic fluid composition of claim 3 wherein said formal is selected from the group consisting of:

[CH3O(C2H4O)]2CH2, [CH3O(C2H4O)3]2CH2, [C2H5O(C2H4O)2]2CH2, [C4H9O(C2H4O)]2CH2, and [C4H9O(C2H4O)3]2CH2.

5. The hydraulic fluid composition of claim 2 wherein said base fluid is a borate ester of type (a).

6. The hydraulic fluid composition of claim 5 wherein said base fluid comprises from about 20 to about 54.4 percent by weight, based on the total weight of the hydraulic fluid composition.

7. The hydraulic fluid composition of claim 5 wherein said base fluid comprises from about 54.5 to about 92 percent by weight, based on the total weight of the hydraulic fluid composition.

8. The hydraulic fluid composition of claim 7 wherein said borate ester of type (a) has an alkyl R1 group of 1 to 2 carbon atoms and an Ra alkylene group of 2 to carbon atoms.

9. The hydraulic fluid composition of claim 7 wherein said base fluid is a borate ester selected from the group consisting of: [CH3(OCH2CH2)3O]3-B, [C2H5(OCH2CH2)2O]3-B, [C2H5(OCH2CH2)3O]3-B, [C2H5(OCH2CH2)4O]3-B, [C3H7(OCH2CH2)3O]3-B, [C4H9(OCH2CH2)2O]3-B and [C4H9(OCH2CH2)3O]3-B.

10. The hydraulic fluid composition of claim 9 wherein prom about 2 to about 15 percent by weight, based on the total weight of the hydraulic fluid composition, of said formal is used.

11. The hydraulic fluid composition of claim 10 wherein said formal is selected from the group consisting of:
[CH3O(C2H4O)]2CH2, [CH3O(C2H4O)2]2CH2, [CH3O(C2H4O)3]2CH2, [C2H5O(C2H4O)2]2CH2, [C4H9O(C2H4O)]2CH2 and [C4H9O(C2H4O)3]2CH2.

12. The hydraulic fluid composition of claim 11 wherein said diluent comprises from about 2 to about 70 percent by weight, based on the total weight of the hydraulic fluid composition.

13. The hydraulic fluid composition of claim 12 wherein said diluent is selected from the group consisting of diethylene glycol monomethyl ether, diethylene glycol mono-ethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether and tetraethylene glycol monobutyl ether.

14. The hydraulic fluid composition of claim 13 wherein from about 0.2 to about 6.0 percent by weight of an inhibitor for pH and corrosion control is used.

15. The hydraulic fluid composition of claim 14 wherein said inhibitor is selected from the group consisting of glycerin, butynediol, diethanolamine, methyl diethanolamine, mixed isopropanolamines, diisopropanolamine and triisopro-panolamine.

16. The hydraulic fluid composition of claim 15 wherein from about 0.001 to about 1.0 percent by weight, based on the total weight of the hydraulic fluid composition, of an antioxidant is used.

17. The hydraulic fluid composition of claim 16 wherein said antioxidant is selected from the group consisting of sodium nitrite and dioctyl diphenylamine.

18. The hydraulic fluid composition of claim 5 wherein said diluent is a glycol ether of type (aa).

19. The hydraulic fluid composition of claim 18 wherein said diluent comprises from about 2 to about 70 percent by weight, based on the total weight of the hydraulic fluid composition.

20. The hydraulic fluid composition of claim 19 wherein said diluent is selected from the group consisting of:
diethylene glycol monomethyl ether, diethylene glycol mono-ethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether and tetraethylene glycol monobutyl ether,

21. The hydraulic fluid composition of claim 20 wherein said formal is selected from the group consisting of:
[CH3O(C2H4O)]2CH2. [CH3O(C2H4O)2]2CH2, [CH3O(C2H4O)3]2CH2, [C2H5O(C2H4O)2]2CH2, [C4H9O(C2H4O)]2CH2, and [C4H9O(C2H4O)3]2CH2.

22. The hydraulic fluid composition of claim 18 having incorporated therein from 0 to about 8.0 percent by weight, based on the total weight of the hydraulic fluid composition, of an inhibitor additive for pH and corrosion control.

23. The hydraulic fluid composition of claim 22 wherein from about 0.2 to 6.0 percent by weight of said inhibitor is used.

24. The hydraulic fluid composition of claim 23, wherein said inhibitor is selected from the group consisting of: glycerin, butynediol, diethanolamine, methyl diethanol-amine, mixed isopropanolamines, diisopropanolamine and triisopropanolamine.

25. The hydraulic fluid composition of claim 22 wherein from 0 to about 2 percent by weight, based on the total weight of the hydraulic fluid composition, of an antioxidant additive is incorporated therein.

26. The hydraulic fluid composition of claim 25 wherein from about 0.001 to about 1.0 percent by weight of said antioxidant is used.

27. The hydraulic fluid composition of claim 26 wherein said antioxidant is selected from the group consisting of sodium nitrite and dioctyl diphenylamine.

28. The hydraulic fluid composition of claim 27 wherein said inhibitor is selected from the group consisting of glycerin, butynediol, diethanolamine, methyl diethanolamine, mixed isopropanolamines, diisopropanolamines and triisopropanol-amine.

29. The hydraulic fluid composition of claim 28 wherein said formal is selected from the group consisting of [CH3O(2H4O)]2CH2, [CH3O(C2H4O)2]2CH2, [CH3O(C2H4O)3]2CH2, [C2H5O(C2H4O)2]2CH2, [C4H9O(C2H4O)]2CH2 and [C4H9O(C2H4O)3]2CH2.

30. A nonaqueous hydraulic fluid composition comprising A. from 18 to 28% by volume of an orthoborate ester of a glycol monoether selected from the group consisting of triethylene glycol monomethyl ether, diethylene glycol mono-(lower alkyl) ether, tetraethylene glycol monomethyl ether or mixtures thereof;
B. from about 15 to 40% by volume of at least one bis (glycol ether) formal having the formula CH3O(CH2CH2O)1-2 -CH2-(OCH2CH2)1-2OCH3;

C. from about 35 to 55% by volume of triethylene glycol monomethyl ether;

D. from 0 to 31.5% by volume of at least one diluent selected from the glycol ethers other than triethylene glycol monomethyl ether having the formula R[O-R"]y OR', wherein R is alkyl from 1 to 4 carbon atoms, R' is selected from the group consisting of hydrogen and alkyl of from 1 to 4 carbon atoms, R" is alkylene of from 2 to 4 carbon atoms and y is an integer of from 2 to 4;

E. from 0.5 to 4% by volume of compatible antioxidants and corrosion inhibitors;

the total of components B and D not exceeding 40% by volume and the total of components A to E being 80 to 100% by volume of the hydraulic fluid composition.