Hydraulic fluid composition

Patent metadata

Field	Value
Publication number	US-11261398-B2
Application number	US-201716301271-A
Country	US
Kind code	B2
Filing date	Apr 19, 2017
Priority date	May 18, 2016
Publication date	Mar 1, 2022
Grant date	Mar 1, 2022

Abstract

A hydraulic fluid includes an oil of lubricating viscosity and at least 2 wt. % of an ester of a carboxy group-containing interpolymer comprising units derived from a vinyl aromatic monomer and units derived from a carboxylic acid monomer. The interpolymer also contains nitrogen functionality. The hydraulic fluid is at least substantially free of polyacrylates and polymethacrylates.

First claim

What is claimed is:

1. A hydraulic fluid comprising:
(a) at least 60 wt. % of a Group I or Group II base oil;
(b) 3.4 to 5.2 wt. % of an ester of a carboxy group-containing interpolymer comprising units derived from a vinyl aromatic monomer, the vinyl aromatic monomer comprising styrene, and units derived from a carboxylic acid monomer, the carboxylic acid monomer comprising maleic anhydride, the interpolymer also comprising nitrogen functionality provided by a nitrogen-containing moiety which comprises at least one of aminopropylmorpholine and dimethylaminopropylamine, the ester of the carboxy group-containing interpolymer having a weight average molecular weight of 30,000 to 70,000, the ester of a carboxy group-containing interpolymer including up to 0.44 wt. % nitrogen; and
(c) at least one phosphate compound comprising zinc;
wherein the hydraulic fluid is at least substantially free of polyacrylates and polymethacrylates that contain, in total, at least 30 mol. % of at least one of acrylate and methacrylate units and have a weight-average molecular weight of at least 1500, such that said polyacrylates and polymethacrylates, in total, amount to no more than 0.3 wt. % of the hydraulic fluid; and
wherein the hydraulic fluid includes, in total, less than 0.1 wt. % of nitrogen-containing ashless dispersants, other than the esterified interpolymer, the nitrogen-containing ashless dispersants being characterized by a nitrogen-containing functional group attached to a polymeric hydrocarbon backbone.

2. The hydraulic fluid of claim 1 , wherein a mole ratio of units derived from maleic anhydride to units derived from styrene is from 0.9:1 to 1.1:1.

3. The hydraulic fluid of claim 1 , wherein:
the ester of the carboxy group-containing interpolymer includes at least 0.01 wt. % nitrogen.

4. The hydraulic fluid of claim 1 , wherein the ester of the carboxy group-containing interpolymer comprises esters of the carboxy groups formed by reaction of the carboxy groups with one or more alcohols having from 4 to 24 carbon atoms.

5. The hydraulic fluid of claim 1 , wherein esters of the carboxy groups in the interpolymer are derived from an alcohol mixture comprising at least 50 wt. % of C 8 and higher linear alcohols.

6. The hydraulic fluid of claim 1 , wherein esters of the carboxy groups in the interpolymer are derived from an alcohol mixture comprising at least 0.1 wt. % of C 18 and higher linear alcohols.

7. The hydraulic fluid of claim 1 , wherein the nitrogen functionality is provided by the nitrogen-containing moieties condensed onto at least 5% of the carboxy groups of the interpolymer.

8. The hydraulic fluid of claim 1 , wherein the ester of the carboxy group-containing interpolymer comprises at least 0.1 wt. % nitrogen.

9. The hydraulic fluid of claim 1 , wherein the ester of the carboxy group-containing interpolymer comprises up to 0.25 wt. % nitrogen.

10. The hydraulic fluid of claim 1 , wherein at least 90% of the units in the backbone of the ester of the carboxy group-containing interpolymer comprise the units derived from a vinyl aromatic monomer and the units derived from a carboxylic acid monomer.

11. The hydraulic fluid of claim 1 , wherein the ester of the carboxy group-containing interpolymer comprises a maleic anhydride/styrene alternating copolymer, esterified with a mixture of alcohols comprising at least 80 wt. % of alcohols with 8 to 18 carbon atoms.

12. The hydraulic fluid of claim 1 , wherein the ester of the carboxy group-containing interpolymer comprises less than 5 wt. % of units derived from methacrylic acid or acrylic acid.

13. The hydraulic fluid of claim 1 , further comprising at least one of a pour point depressant, an overbased detergent, an antioxidant, and a corrosion inhibitor.

14. The hydraulic fluid of claim 13 , wherein the pour point depressant comprises a polymethacrylate.

15. A method for lubricating a hydraulic system comprising pressurizing a hydraulic fluid in the hydraulic system, the hydraulic fluid comprising:
(a) at least 60 wt. % of a Group I or Group II base oil;
(b) 3.4 to 5.2 wt. % of an ester of a carboxy group-containing interpolymer comprising units derived from a vinyl aromatic monomer and units derived from a carboxylic acid monomer, the interpolymer also comprising nitrogen functionality, the ester of the carboxy group-containing interpolymer having a weight average molecular weight of 30,000 to 70,000, the ester of a carboxy group-containing interpolymer including up to 0.44 wt. % nitrogen; and
(c) 0.05-0.5 wt. % of a zinc dialkyldithiophosphate,
wherein the hydraulic fluid is at least substantially free of polyacrylates and polymethacrylates that contain, in total, at least 30 mol. % of at least one of acrylate and methacrylate units and have a weight-average molecular weight of at least 1500, such that said polyacrylates and polymethacrylates, in total, amount to no more than 0.3 wt. % of the hydraulic fluid; and
wherein the hydraulic fluid includes, in total, less than 0.1 wt. % of nitrogen-containing ashless dispersants, other than the esterified interpolymer, the nitrogen-containing ashless dispersants being characterized by a nitrogen-containing functional group attached to a polymeric hydrocarbon backbone.

16. A hydraulic system comprising a pump and a device which is supplied with the hydraulic fluid of claim 1 by the pump.

17. The hydraulic fluid of claim 1 , wherein the hydraulic fluid has a viscosity at 40° C. (KV_40), determined according to ASTM D2270-10e1, of from 30 to 80 cSt.

Assignees

• Lubrizol Corp

Inventors

• Knapton Daniel J
• Cressey David
• Visger Daniel C

Classifications

• C10N2040/08

  Hydraulic fluids, e.g. brake-fluids · CPC title

• C10M2217/06

  Macromolecular compounds obtained by functionalisation op polymers with a nitrogen containing compound · CPC title

• C10M2203/1006

  used as base material · CPC title

• C10M2209/086

  polycarboxylic, e.g. maleic acid · CPC title

• C10N2030/24

  Emulsion properties · CPC title