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  Hydraulic fluidUSPTO Application #: 20070191237Title: Hydraulic fluid Abstract: A method for reducing total wear-induced weight loss during wear-inducing operation of equipment, the method comprises a) providing a hydraulic fluid comprising a combination of an amount of zinc dithiophosphate and a quantity of magnesium salicylate, wherein said quantity of magnesium salicylate is from 0.001 to at most 1% wt and said amount of zinc dithiophosphate is from 0.01 to 1% wt. and b) operating the equipment using the hydraulic fluid under wear-inducing conditions that reduce the weight of the equipment. The hydraulic fluid is effective to produce a first total weight loss that is less than a second total weight loss that would be observed using a second hydraulic fluid comprising a quantity of calcium salicylate in place of said quantity of magnesium salicylate. (end of abstract)
Agent: Shell Oil Company - Houston, TX, US Inventors: Andrew John Holmes, Cameron William Watson USPTO Applicaton #: 20070191237 - Class: 508245000 (USPTO) Related Patent Categories: Solid Anti-friction Devices, Materials Therefor, Lubricant Or Separant Compositions For Moving Solid Surfaces, And Miscellaneous Mineral Oil Compositions, Lubricants Or Separants For Moving Solid Surfaces And Miscellaneous Mineral Oil Compositions (e.g., Water Containing, Etc.), Heterocyclic Ring Compound; A Heterocyclic Ring Is One Having As Ring Members Only Carbon And At Least One Hetero Atom Selected From Nitrogen And Chalcogen (i.e., Oxygen, Sulfur, Selenium, Or Tellurium), The Hetero Ring Contains Six Members Including Nitrogen And Carbon (e.g., Pyridine, Picoline Salts, Etc.), Chalcogen In The Hetero Ring The Patent Description & Claims data below is from USPTO Patent Application 20070191237. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED CASES [0001] The present application is a divisional of U.S. application Ser. No. 09/648,325, filed Aug. 25, 2000, which is incorporated herein by reference. FIELD OF THE INVENTION [0002] The present invention relates to a hydraulic fluid. BACKGROUND OF THE INVENTION [0003] WO 93/03121 relates to hydraulic fluids having improved wet filterability and having increased resistance to loss of zinc when the oil is exposed to water. These compositions comprise (A) a combination of a metal salt selected from the group consisting of sulfonates, phenates, carboxylates and mixtures thereof, (B) an aliphatic carboxylic acid or anhydride, or carboxylic acid group containing derivative thereof, wherein the aliphatic group contains at least 20 carbon atoms, and optionally (C) a metal salt of (C)(I) at least one organic phosphorus acid or mixture of (C)(I) at least one organic phosphorus acid and (C)(II) at least one carboxylic acid group, and optionally (D) triazole. In one embodiment, the carboxylic acids of (A) are aromatic carboxylic acids. Zinc, calcium and magnesium salts of these aromatic carboxylic acids, and especially salicylic acids, are preferred. Although magnesium salicylate and zinc dithiophosphate are both mentioned per se, there is no teaching to use the combination of these compounds. [0004] WO 89/04358 relates to compositions comprising (A) a neutral or basic metal salt of an acidic organic compound, (B) a metal deactivator, preferably an optionally substituted benzotriazole, and (C) a sulfur and/or phosphorus-containing compound selected from the group consisting of (C-1) phosphorus-containing amide, (C-2) phosphorus-containing ester, (C-3) sulfur-coupled dithiocarbamate, (C-4) sulfur-containing compound according to formula (I). Particularly preferred metals for the salts (A) are sodium, magnesium, calcium or mixtures of two or more thereof. In the extensive list of additional compounds which can be present, zinc dialkyl dithiophosphate is mentioned. Although magnesium salicylate and zinc dithiophosphate are both mentioned per se, there is no teaching to use the combination of these compounds. [0005] EP-A-604 218 describes functional fluids comprising a major amount of an oil of lubricating viscosity, at least one metal salt of thiophosphoric acid, a zinc salt of salicylic acid, and a rust inhibitor, which fluid contains less than about 1% wt of dispersant and less than about 1% wt of basic sulfonate salt. The thiophosphoric acid is most commonly a dihydrocarbyl dithiophosphoric acid; the metal is most preferably zinc. The teaching of the document is restricted to the use of zinc salicylate. [0006] In U.S. Pat. No. 4,627,928, a process has been described for preparing basic magnesium salicylates which can be characterised as having a magnesium content of at least 150% up to 500%, of the stoichiometrically equivalent amount of magnesium based on the amount of total acid present. The magnesium salts obtained are described to be suitable for use as additives in general, more specifically as additives for a variety of lubricating oils and fuels, e.g. gasoline and diesel fuels. It is mentioned that these specific magnesium salicylates can be used in combination with a wide range of other compounds. There is no disclosure or teaching to apply a combination of zinc dithiophosphate and magnesium salicylate in a hydraulic fluid. [0007] Hydraulic fluids need to meet special requirements as they both lubricate and transmit pressure. In order to meet these requirements, hydraulic fluids contain additives. Generally, hydraulic fluids contain antiwear/extreme pressure additives. The conditions for a hydraulic fluid are especially difficult in vane pumps where the vane tips slide against the casing at high speed under heavy load and at high temperature. Further, the increasingly high operating temperatures of modern hydraulic equipment requires the fluid to be thermally stable to avoid the formation of deposits and sludge and to resist the corrosion of both ferrous and non-ferrous metals. The requirement of good thermal stability in hydraulic fluids containing an anti-wear additive, means that these additives are often used in combination with detergents. However, the calcium salts of alkylbenzene sulphonates, alkyl-naphthalene sulphonates, petroleum sulphonates, alkylphenates, alkyl sulphurized phenates or alkylsalicylates which are usually applied, give increased wear. The increased wear is especially marked in vane pumps, more specifically under low load conditions. Low load conditions occur in practice when the pump is idle. SUMMARY OF THE INVENTION [0008] It has now surprisingly been found that hydraulic fluid containing a combination of magnesium salicylate and zinc dithiophosphate, gives improved performance at low load compared with a combination containing calcium salicylate. Additionally, it was found that this combination also provides greater thermal stability. Less sludge and deposits are formed when subjecting the hydraulic fluid of the present invention to the Cincinnati Milacron Thermal Stability Test. [0009] The present invention provides a hydraulic fluid comprising a lubricant base oil in combination with (a) from 0.001 to 5% wt of magnesium salicylate, (b) from 0.01 to 8% wt of zinc dithiophosphate, which amounts are based on total weight of hydraulic fluid. DETAILED DESCRIPTION OF THE INVENTION [0010] The magnesium salicylate for use in the present invention can be either neutral or overbased. The expression "overbased" is equivalent to "basic", "superbased", "hyperbased" and "high-metal containing salts". These magnesium salicylates contain an excess metal content compared to the amount of metal which would be present according to the stoichiometry of the metal and the salicylic acid reacted with the metal. Processes for making such neutral and basic metal salts are well known in the art. Neutral salts can be made by heating a mineral oil solution of an acidic organic compound with a stoichiometric equivalent amount of a metal neutralizing agent such as the metal oxide, hydroxide, carbonate, bicarbonate, or sulfide at a temperature above 50.degree. C. and filtering the resulting mass. Basic salts are made similarly with the exception that a stoichiometric excess of the metal is used. [0011] Preferably, overbased magnesium salicylate is used. These compositions can be characterized by their total base number (TBN). The total base number is preferably at least 100 mg KOH/g, more preferably at least 200 mg KOH/g, most preferably at least 300 mg KOH/g. The total base number is preferably at most 600 mg KOH/g. Another method of characterising overbased magnesium salicylates is by the magnesium content relative to the stoichiometrically equivalent amount of magnesium based on the amount of total acid present. Overbased magnesium salicyclates for use in the present invention preferably have a magnesium content of more than 500% of the stoichiometrically equivalent amount of magnesium based on the amount of total acid present, more preferably at least 550%. [0012] The salicylate can be either substituted or unsubstituted. Suitable substituents include aliphatic groups containing from 1 to 40 carbon atoms and optionally containing one or more oxygen and/or nitrogen atoms, and hydroxy groups. Preferred substituents are alkyl groups containing from 6 to 30 carbon atoms, preferably from 12 to 20 carbon atoms. Preferably, the substituents are linear. The salicylate can contain from 1 to 4 substituents, preferably from 1 to 3, most preferably 1 or 2 substituents. Most preferably, the salicylate is substituted by 1 linear alkyl group containing from 14 to 18 carbon atoms. [0013] Generally, mono-alkyl salycylic acids are prepared by alkylation of phenol and subsequent carboxylation. Therefore, a small amount (generally at most 20% mol) of dialkyl salicylate and unsubstituted salicylate can be present in the mono-alkyl salicylate. [0014] Magnesium salicylate which can be used in the present invention, is commercially available. A suitable commercial product is SAP 007 (ex Infineum). The magnesium salicylate will usually be supplied in combination with mineral oil. The amounts referred to in this document, relate to the compound per se without mineral oil. [0015] A process by which suitable magnesium salicylate can be prepared, has been described in U.S. Pat. No. 4,627,928. [0016] Zinc dithiophosphate is well known in the art. Preferred dithiophosphate for use in the present invention are represented by the following formula in which R8 and R9 can be either hydrogen or an aliphatic group. The aliphatic group is preferably a hydrocarbyl group. The hydrocarbyl group optionally contains an acid, a hydroxy and/or an ester group. The hydrocarbyl group is preferably an alkyl containing up to 12 carbon atoms optionally further containing an acid, a hydroxy and/or an ester group. The hydrocarbyl substituted dithiophosphate can contain 1 or 2 aliphatic groups, or it can be a mixture of dithiophosphates having 1 aliphatic group and dithiophosphates having 2 aliphatic groups. Preferably, the zinc dithiophosphate is a zinc dialkyl dithiophosphate. [0017] Substituted dithiophosphates can contain primary, secondary and/or tertiary aliphatic substituents, i.e. substituents which are attached to the oxygen atom via a carbon atom attached to one, two or three further carbon atoms, respectively. In the present invention, it is preferred that at least 60% wt of the aliphatic, preferably alkyl, substituents of the zinc dithiophosphate, are primary aliphatic substituents. More preferably at least 80% wt of the aliphatic substituents are primary aliphatic substituents. [0018] Suitable zinc dithiophosphates which are commercially available include Elco 108 (ex Elco Corporation), Lz 1375 (ex Lubrizol), OLOA 4269Q (ex Oronite) and HITEC 680 (ex Ethyl). [0019] The amount of magnesium salicylate which is present is preferably at most 1% wt, based on total composition, more preferably at most 0.5% wt, most preferably at most 0.3% wt. The amount of magnesium salicylate which is present is preferably at least 0.001% wt, more preferably at least 0.005 % wt more preferably at least 0.01% wt, most preferably at least 0.015% wt. The amount of zinc dithiophosphate which is present is preferably at most 5% wt, based on total composition, more preferably at most 3% wt, most preferably at most 1% wt. The amount of zinc dithiophosphate which is present is preferably at least 0.05% wt, more preferably at least 0.7% wt, most preferably at least 0.1% wt. Continue reading... Full patent description for Hydraulic fluid Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Hydraulic fluid patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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