Title of Invention	HIGH PERFORMANCE PHOSPHATE ESTER HYDRAULIC FLUID
Abstract	This application discloses a high performance hydraulic fluid suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl) phosphate, a minor amount of a triaryl phosphate and optionally a minor amount of tri(isobutyl)phosphate. The compositions of this invention provide superior performance with respect to flash and fire points as well as extended usefiil fluid life in service. Such properties are highly valuable as hydraulic fluids modem jet aircrafts.

Title of Invention

HIGH PERFORMANCE PHOSPHATE ESTER HYDRAULIC FLUID

Abstract

This application discloses a high performance hydraulic fluid suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl) phosphate, a minor amount of a triaryl phosphate and optionally a minor amount of tri(isobutyl)phosphate. The compositions of this invention provide superior performance with respect to flash and fire points as well as extended usefiil fluid life in service. Such properties are highly valuable as hydraulic fluids modem jet aircrafts.

Full Text	HIGH PERFORMANCE PHOSPHATE ESTER HYDRAULIC FLUID This invention relates to phosphate ester functional fluid compositions and more particularly to such compositions that provide superior perfonnaace with respect to flash and fire points as well as extended useful fluid life in service. BACKGROUND OF THE INVENTION Most aircraft hydraulic fluids used in civilian aircraft contain some combination of phosphate esters including trialkyl phosphates, dialkyl aryl phosphate esters, allcyl diaryl phosphate esters aad tri aryl phosphate esters. Such formulations are disclosed in RE 37,101 to Deetman and are said to provide superior thermal, oxidative and hydxolytic stability. A hydraulic fluid useful in aircraft is available from applicants' assignee under the trademark Skydrol RTM LD4. This composition typically contains 18 to 25% by weight dibutyl phenyl phosphate, 50 to 60% by weight tributyl phosphate, 4 to 8% of butyl diphenyl phosphate, 5 to 10% of viscosity index improvers, 0.13 to 1% of a diphenyldithioethane copper corrosion inhibitor, 0.005% to about 1% by weight, but preferably 0.0075% to 0.075% of a perfluoroalkylsulfonic acid salt antierosion agent, 4% to 8% by weight of an acid scavenger of the type described in U.S. Pat. No. 3,723,320 and about 1% by weight of 2,6-di-tertiary-butyl-p-cresol as an antioxidant. This composition has proved highly satisfactory in high performance aircraft application. Since the publication of the Deetman patent, various formulations varying from the base stock disclosed by Deetman have been published to provide hydraulic fluids of varying properties. U.S. Patents 6,319,423 and 6,649,080 to Okazald et al. disclose variations. These base stocks contain a major amount of trialkyl phosphates wherein the alkyl portion is preferably isobutyl or isopentyl and a minor amount of triaryl phosphate. Typical base stock fomiulations are those containing from 30% to 45% triisobutyl phosphate, 30% to 45% tri-n-butyl phosphate and 10 % to 15% triaryl phosphate. Other base stock formulation disclosed in these patents include those having 35% to 45% triisobutyl phosphate, 40% to 50% tri-n-butyl phosphate and 12% to 16% triaryl phosphate. Because of the concern for attack by hydraulic fluid degradation products on the elastomers employed in hydraulic systems seals, the Okazalki et al base stocks provide a mixture of triisobutyl phosphate and tri-n-butyl phosphate together with an amount of triaryl phosphates such that the fluid will produce no more than 25% elastomer seal swell under standard test procedures wherein the amount of triisobutyl phosphate ranges from about 35% to about 50% based on the total weight of the base stock. It is stated that such fluids have a combination of properties useful as aircraft hydraulic fluid compositions including acceptable hydrolytic stability, high flash point, good antiwear properties, acceptable erosion protection, acceptable low temperature flow properties and elastomer compatibility. While the above noted patents indicate a high degree of effort to provide fluids usefal in hydraulic aircraft fluid systems with optimum properties, the aircraft industry continually increases demands for higher requirements. Demand for overall improved properties of the hydraulic fluids is caused by ever higher performance aircraft being flown. Therefore, there is a need for even greater level of performance with regard to fluid life, (thermal stability and low temperature viscosity, while maintaining acceptable fire/flash points, auto ignition temperature as well as compatibility with materials used in aircraft hydraulic systems), SUMMARY OF THE INVENTION This invention is directed to phosphate ester base stock compositions and aircraft hydraulic fluid cornpositions containing a base stock having a novel combination of phosphate ester components. There is provided in accordance with this invention, compositions containing a mixture of a major amount of tri(n-butyl)pho8phate ester and a minor amount of a triaryl phosphate and optionally a minor amount of tri(iso-butyl)phosphate. Suck compositions demonstrate improved thermal stability and low temperature viscosity. As employed in this specification and claims the term "major amount" is an amount at least 50% but not greater than about 80%, As employed in the specification and claims the term "minor amount* is an amount less than about 25%, of the total weight of the base stock. As is well known in the art, many additives are employed in hydraulic fluids, particularly in those fluids employed in aircraft hydraulic systems. Such additives further enhance the properties of the fluid as compared with fluids previously available in the art fox use in aircraft hydraulic systems. Typically such additives comprise about 15%, by weight, of the total weight of the fluid. Accordingly, the amount of phosphate ester components provided in the specification and claims is expressed in the percent by weight of the total amount of the final composition, including the additives commonly employed in aircraft hydraulic fluids. Briefly, the present invention is directed to a fluid composition suitable for use as an aircraft hydraulic fluid. The composition comprises a fire resistant phosphate ester base stock, the base stock comprising between about 50% to about 80%, preferably 55% to about 65% of tri(n-butyl)phosphflte, between about 5% to about 15%, preferably between about 8% to about 12% of tri(iso-propylphenyl) phosphate, and up to about 20%, preferably between about 8% to about 12% of tri(iso-butyl)phosphate with the proviso that the sum of proportionate amounts of each base stock component and additives must equal 100%. The high performance fluids of this invention are those that meet the stringent standards of the modem passenger jets. In order to meet the needs of the latest high performance jet aircraft fluids employed in the hydraulic systems of such airplanes must have a fluid life of greater than 1000 hours in standard laboratory testing at 0.5% water and 25ppm chlorine content at 125°C, and also a fluid life greater than 10,000 hours at 60*C. The fluid life is defined as the tune required for the fluid sample to reach a Neutralization No. of 1.5mg KOH/g sample under the procedure of ASTM D 974. DETAILED DESCRIPTION OF THE INVENTION A particularly preferred phosphate ester base stock of this invention is one containing about 60% tri(n-butyl)phosphate, about 10% tri(iso-propylated) aryl phosphate and about 10% tri(n-butyl) phosphate with the proviso that the sum of proportionate amounts of each base stodc component together with additives must equal 100%. As noted above, the phosphate ester base stocks of this invention contain many additives as is well known in the art to provide various beneficial properties to the fluid or aid in preventing degradation or the effects of degradation during use. Such additives are described in RE. 37,101 to Deetman, the entire disclosure of which is incorporated herein by reference. isopxopylphenyl, isobutylphenyl, tert-bntylphenyl, and the like. Preferred triaryl phosphate esters are tri(isopropylphenyl)phosphate and tri(tert-butylpheiiyl)phosphate. It is also preferred that the majority of the aryl groups are substituted by only one allcyl group. All percentages expressed in this specification and claims are percent by weight unless otherwise specified. The following examples illustrate the invention. EXAMPLE Hydraulic fluids having compositions set forth in Table 1 were prepared by mixing at ambient temperature in a suitable container agitated to provide adequate mixing. The phosphate ester components were introduced into the tank last. The other additives were added first in the sequence indicated in Table 1. In Table 1 "TBP" and "TIBP" refers to tri-n-butyl phosphate ester and tri-isobutyl phosphate ester, respectively. "IPTPP" refers to iso-propyltriphenyl phosphate ester. "Van Lube" refers to a commercial rust inhibitor, available from Vanderbilt as Van Lub RIG. "FC-98" refers to an antierosion agent comprising a potassixmi salt of perfluoroethylcyclohexy sulfonic acid, also known as perfluoroethylcyclohexylsulfonic acid. "lONOL" refers to 2,6-di-tert-butyl-p-cresol, an antioxidant, commercially available firom Shell Chemical Company. "E-330" refers to l,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butylhydroxyphenyl)benzene, an antioxidant, commercially available under the trade designation Ethanox.RTM. 330 firom Ethyl Corporation. "DODPA" refers to dioctyl diphenyl amine available firom Vanderbilt, "FH-132" refers to l,2-di(phenylthio)ethane, a copper corrosion inhibitor, "MCS-1562" refers to 2-ethylhexyl epoxy cyclohexyl carboxylate, available fiom Dixie Chemicals, "HF4H" refers to poly(butytaiethacrylate) and "HF460" refers to polyallcylmethacrylate polymer in TBP, both are viscosity index improvers, "Antifoam" refers to silicone fluid available firom Dow Coming Co. Tests were conducted to determine the &e safety, low temperature viscosity, pour point and specific gravity of the fluids described in Table 1. The flash aad fire points were determined by means of the procedure of ASTM D-92. The compositions 5 were then tested to determine their properties with regard to autoignition temperature (ATT) under the procedure of ASTM D-2155, viscosity, pour point and specific gravity. In Table 1, all examples are based upon 100 gram samples. The results of the tests appear below in Table 2. TABLE2 WHAT IS CLAIMED IS: 1. A hydraulic fluid composition suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl)phosphate, a minor amount of a triaryl phosphate and optionally a minor amount of tri(isobutyl)phosphate. 2. A composition of claim 1 comprising from about 50% to about 80% tri(n-butyl)phosphate, from about 5% to about 15% triaryl phosphate and up to about 20% tri(isobutyl)phosphate. 3. A composition of claim 1 wherein the triaryl phosphate is triphenyl phosphate. 4. A composition of claim 1 wherein the aryl is an allcyl substituted aryl. 5. A composition of claim 4 wherein the aryl group is substituted by one allcyl group. 6. A composition of claim 5 wherem the allcyl subustituent is selected from C1 to C9 alkyl groups. 7. The composition of claim 6 wherein the allcyl substituents are selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert.-butyl, pentyl, isopentyl, hexyl, heptyl, octyl and nonyl. 8. A composition suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl)phosphate, a minor amount of an allcyl substituted arylphosphate and optionally a minor amount of tri(isobutyl)phosphate. 9. A composition of claim 8 wherein the alkyl substituted aryl phosphate is a mono-substituted aryl phosphate. 10. A composition of claim 9 comprising from about 50% to about 80% of tri(n-butyl)phosphate, from about 5% to about 15% of an alkyl substituted triaryl phosphate, and up to about 20% of tri(isobutyl)phosphate. 11. A composition of claim 10 compriskig from about 55% to about 65% of tri(n-butyl)phosphate, from about 8% to about 12% of an allcyl substituted triaryl phosphate, and up to about 20% of tri(isobutyl)phosphate. 12. A composition of claim 11 wherein the alkyl substituted triaryl phosphate is tri(iso-propylphenyl)phosphate. 13. A composition of claim 10 comprising about 65% tri(n- butyl)phosphate, about 10% of tri(iso-propylphenyl)phosphate and about 10% of tri(iso-butyl)phosphate. 14. The composition of claim 1 further including about 15% additives by weight of llie final composition.

Full Text

HIGH PERFORMANCE PHOSPHATE ESTER HYDRAULIC FLUID
This invention relates to phosphate ester functional fluid compositions and more particularly to such compositions that provide superior perfonnaace with respect to flash and fire points as well as extended useful fluid life in service.
BACKGROUND OF THE INVENTION
Most aircraft hydraulic fluids used in civilian aircraft contain some combination of phosphate esters including trialkyl phosphates, dialkyl aryl phosphate esters, allcyl diaryl phosphate esters aad tri aryl phosphate esters. Such formulations are disclosed in RE 37,101 to Deetman and are said to provide superior thermal, oxidative and hydxolytic stability. A hydraulic fluid useful in aircraft is available from applicants' assignee under the trademark Skydrol RTM LD4. This composition typically contains 18 to 25% by weight dibutyl phenyl phosphate, 50 to 60% by weight tributyl phosphate, 4 to 8% of butyl diphenyl phosphate, 5 to 10% of viscosity index improvers, 0.13 to 1% of a diphenyldithioethane copper corrosion inhibitor, 0.005% to about 1% by weight, but preferably 0.0075% to 0.075% of a perfluoroalkylsulfonic acid salt antierosion agent, 4% to 8% by weight of an acid scavenger of the type described in U.S. Pat. No. 3,723,320 and about 1% by weight of 2,6-di-tertiary-butyl-p-cresol as an antioxidant. This composition has proved highly satisfactory in high performance aircraft application.
Since the publication of the Deetman patent, various formulations varying from the base stock disclosed by Deetman have been published to provide hydraulic fluids of varying properties. U.S. Patents 6,319,423 and 6,649,080 to Okazald et al. disclose variations. These base stocks contain a major amount of trialkyl phosphates wherein the alkyl portion is preferably isobutyl or isopentyl and a minor amount of triaryl phosphate. Typical base stock fomiulations are those containing from 30% to 45% triisobutyl phosphate, 30% to 45% tri-n-butyl phosphate and 10 % to 15% triaryl phosphate. Other base stock formulation disclosed in these patents include those having 35% to 45% triisobutyl phosphate, 40% to 50% tri-n-butyl phosphate and 12%

to 16% triaryl phosphate. Because of the concern for attack by hydraulic fluid degradation products on the elastomers employed in hydraulic systems seals, the Okazalki et al base stocks provide a mixture of triisobutyl phosphate and tri-n-butyl phosphate together with an amount of triaryl phosphates such that the fluid will produce no more than 25% elastomer seal swell under standard test procedures wherein the amount of triisobutyl phosphate ranges from about 35% to about 50% based on the total weight of the base stock. It is stated that such fluids have a combination of properties useful as aircraft hydraulic fluid compositions including acceptable hydrolytic stability, high flash point, good antiwear properties, acceptable erosion protection, acceptable low temperature flow properties and elastomer compatibility.
While the above noted patents indicate a high degree of effort to provide fluids usefal in hydraulic aircraft fluid systems with optimum properties, the aircraft industry continually increases demands for higher requirements. Demand for overall improved properties of the hydraulic fluids is caused by ever higher performance aircraft being flown. Therefore, there is a need for even greater level of performance with regard to fluid life, (thermal stability and low temperature viscosity, while maintaining acceptable fire/flash points, auto ignition temperature as well as compatibility with materials used in aircraft hydraulic systems),
SUMMARY OF THE INVENTION
This invention is directed to phosphate ester base stock compositions and aircraft hydraulic fluid cornpositions containing a base stock having a novel combination of phosphate ester components.
There is provided in accordance with this invention, compositions containing a mixture of a major amount of tri(n-butyl)pho8phate ester and a minor amount of a triaryl phosphate and optionally a minor amount of tri(iso-butyl)phosphate. Suck compositions demonstrate improved thermal stability and low temperature viscosity.
As employed in this specification and claims the term "major amount" is an amount at least 50% but not greater than about 80%,
As employed in the specification and claims the term "minor amount* is an amount less than about 25%, of the total weight of the base stock.

As is well known in the art, many additives are employed in hydraulic fluids, particularly in those fluids employed in aircraft hydraulic systems. Such additives further enhance the properties of the fluid as compared with fluids previously available in the art fox use in aircraft hydraulic systems. Typically such additives comprise about 15%, by weight, of the total weight of the fluid. Accordingly, the amount of phosphate ester components provided in the specification and claims is expressed in the percent by weight of the total amount of the final composition, including the additives commonly employed in aircraft hydraulic fluids.
Briefly, the present invention is directed to a fluid composition suitable for use as an aircraft hydraulic fluid. The composition comprises a fire resistant phosphate ester base stock, the base stock comprising between about 50% to about 80%, preferably 55% to about 65% of tri(n-butyl)phosphflte, between about 5% to about 15%, preferably between about 8% to about 12% of tri(iso-propylphenyl) phosphate, and up to about 20%, preferably between about 8% to about 12% of tri(iso-butyl)phosphate with the proviso that the sum of proportionate amounts of each base stock component and additives must equal 100%.
The high performance fluids of this invention are those that meet the stringent standards of the modem passenger jets. In order to meet the needs of the latest high performance jet aircraft fluids employed in the hydraulic systems of such airplanes must have a fluid life of greater than 1000 hours in standard laboratory testing at 0.5% water and 25ppm chlorine content at 125°C, and also a fluid life greater than 10,000 hours at 60**C. The fluid life is defined as the tune required for the fluid sample to reach a Neutralization No. of 1.5mg KOH/g sample under the procedure of ASTM D 974.
DETAILED DESCRIPTION OF THE INVENTION
A particularly preferred phosphate ester base stock of this invention is one containing about 60% tri(n-butyl)phosphate, about 10% tri(iso-propylated) aryl phosphate and about 10% tri(n-butyl) phosphate with the proviso that the sum of proportionate amounts of each base stodc component together with additives must equal 100%.

As noted above, the phosphate ester base stocks of this invention contain many additives as is well known in the art to provide various beneficial properties to the fluid or aid in preventing degradation or the effects of degradation during use. Such additives are described in RE. 37,101 to Deetman, the entire disclosure of which is incorporated herein by reference.

isopxopylphenyl, isobutylphenyl, tert-bntylphenyl, and the like. Preferred triaryl phosphate esters are tri(isopropylphenyl)phosphate and tri(tert-butylpheiiyl)phosphate. It is also preferred that the majority of the aryl groups are substituted by only one allcyl group.
All percentages expressed in this specification and claims are percent by weight unless otherwise specified.
The following examples illustrate the invention.
EXAMPLE
Hydraulic fluids having compositions set forth in Table 1 were prepared by mixing at ambient temperature in a suitable container agitated to provide adequate mixing. The phosphate ester components were introduced into the tank last. The other additives were added first in the sequence indicated in Table 1. In Table 1 "TBP" and "TIBP" refers to tri-n-butyl phosphate ester and tri-isobutyl phosphate ester, respectively. "IPTPP" refers to iso-propyltriphenyl phosphate ester. "Van Lube" refers to a commercial rust inhibitor, available from Vanderbilt as Van Lub RIG. "FC-98" refers to an antierosion agent comprising a potassixmi salt of perfluoroethylcyclohexy sulfonic acid, also known as
perfluoroethylcyclohexylsulfonic acid. "lONOL" refers to 2,6-di-tert-butyl-p-cresol, an antioxidant, commercially available firom Shell Chemical Company. "E-330" refers to l,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butylhydroxyphenyl)benzene, an antioxidant, commercially available under the trade designation Ethanox.RTM. 330 firom Ethyl Corporation. "DODPA" refers to dioctyl diphenyl amine available firom Vanderbilt, "FH-132" refers to l,2-di(phenylthio)ethane, a copper corrosion inhibitor, "MCS-1562" refers to 2-ethylhexyl epoxy cyclohexyl carboxylate, available fi*om Dixie Chemicals, "HF4H" refers to poly(butytaiethacrylate) and "HF460" refers to polyallcylmethacrylate polymer in TBP, both are viscosity index improvers, "Antifoam" refers to silicone fluid available firom Dow Coming Co.

Tests were conducted to determine the &e safety, low temperature viscosity, pour point and specific gravity of the fluids described in Table 1. The flash aad fire points were determined by means of the procedure of ASTM D-92. The compositions 5 were then tested to determine their properties with regard to autoignition temperature (ATT) under the procedure of ASTM D-2155, viscosity, pour point and specific gravity. In Table 1, all examples are based upon 100 gram samples. The results of the tests appear below in Table 2. TABLE2

WHAT IS CLAIMED IS:
1. A hydraulic fluid composition suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl)phosphate, a minor amount of a triaryl phosphate and optionally a minor amount of tri(isobutyl)phosphate.
2. A composition of claim 1 comprising from about 50% to about 80% tri(n-butyl)phosphate, from about 5% to about 15% triaryl phosphate and up to about 20% tri(isobutyl)phosphate.
3. A composition of claim 1 wherein the triaryl phosphate is triphenyl phosphate.
4. A composition of claim 1 wherein the aryl is an allcyl substituted aryl.
5. A composition of claim 4 wherein the aryl group is substituted by one allcyl group.
6. A composition of claim 5 wherem the allcyl subustituent is selected from C1 to C9 alkyl groups.
7. The composition of claim 6 wherein the allcyl substituents are selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert.-butyl, pentyl, isopentyl, hexyl, heptyl, octyl and nonyl.
8. A composition suitable for use as an aircraft hydraulic fluid comprising a major amount of tri(n-butyl)phosphate, a minor amount of an allcyl substituted arylphosphate and optionally a minor amount of tri(isobutyl)phosphate.
9. A composition of claim 8 wherein the alkyl substituted aryl phosphate is a mono-substituted aryl phosphate.
10. A composition of claim 9 comprising from about 50% to about 80% of tri(n-butyl)phosphate, from about 5% to about 15% of an alkyl substituted triaryl phosphate, and up to about 20% of tri(isobutyl)phosphate.
11. A composition of claim 10 compriskig from about 55% to about 65% of tri(n-butyl)phosphate, from about 8% to about 12% of an allcyl substituted triaryl phosphate, and up to about 20% of tri(isobutyl)phosphate.
12. A composition of claim 11 wherein the alkyl substituted triaryl phosphate is tri(iso-propylphenyl)phosphate.

13. A composition of claim 10 comprising about 65% tri(n-
butyl)phosphate, about 10% of tri(iso-propylphenyl)phosphate and about 10% of
tri(iso-butyl)phosphate.
14. The composition of claim 1 further including about 15% additives by
weight of llie final composition.

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Patent Number

269265

Indian Patent Application Number

5759/CHENP/2007

PG Journal Number

42/2015

Publication Date

16-Oct-2015

Grant Date

13-Oct-2015

Date of Filing

14-Dec-2007

Name of Patentee

SOLUTIA INC.

Applicant Address

575 MARYVILLE COURT DRIVE, ST. LOUIS, MISSOURI 63141, USA

Inventors:

#	Inventor's Name	Inventor's Address
1	WOLFE, TERRY, CALVIN	2 BLACKPOOL LANE, OLIVETTE, MO 63132, USA

PCT International Classification Number

C09K 5/00

PCT International Application Number

PCT/US06/21407

PCT International Filing date

2006-06-02

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/152,361	2005-06-14	U.S.A.