USE OF POLYCLYCERIN ESTERS AS FRICTION MODIFIERS IN LUBRICANT FORMULATIONS

Abstract

The present invention relates to a lubricating oil composition comprising polyglycerol partial esters of polyfunctional carboxylic acids and saturated or unsaturated, linear or branched fatty acids and/or poly(hydroxystearic acid) and the use thereof to lubricate an engine and reduce friction.

Claims

1. A lubricating oil composition comprising (a) 0.2 to 5% by weight of one or more polyglycerol partial esters, based on a total weight of the lubricating oil composition, wherein the polyglycerol partial esters are obtained by esterification of a polyglycerol mixture with (i) one or more polyfunctional carboxylic acids and (ii) one or more saturated or unsaturated, linear or branched fatty acids and/or (ii) poly(hydroxystearic acid), wherein a degree of esterification of the poly-glycerol mixture is between 30 and 75% of the OH goups; (b) 85 to 99.8% by weight of an apolar base stock selected from the group consisting of API Group II, III and IV and mixtures thereof, based on the total weight of the lubricating oil composition; and (c) 0 to 10% by weight of a polar ester oil of API Group V, based on the total weight of the lubricating oil composition.

2. The lubricating oil composition according to claim 1, wherein the polyglycerol has a mean degree of condensation of from 3 to 6.

3. The lubricating oil composition according to claim 1, wherein the fatty acids are saturated or unsaturated, linear or branched having 8 to 22 carbon atoms.

4. The lubricating oil composition according to claim 1, wherein the saturated fatty acids are one or more selected from the group consisting of caprylic acid, capric acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, margaric acid, stearic acid, isostearic acid, arachidic acid, behenic acid, and 12-hydroxy stearic acid.

5. The lubricating oil composition according to claim 1, wherein the unsaturated fatty acids are one or more selected from the group consisting of hexadecenoic acids, octadecenoic acids, eicosenoic docosenoic acids, octadecadienoic acids, octadecatrienoic acids, and ricinoleic acid.

6. The lubricating oil composition according to claim 1, wherein the polyfunctional carboxylic: acids have 4 to 54 carbon atoms, and a mean functionality of from 2 to 2.5.

7. The lubricating oil composition according to claim 1, wherein the polyfunctional carboxylic acids are aliphatic dicarboxylic acids which are selected from the group consisting of malonic acid, succinic acid, furmaric acid, maleic acid, dimethylgiutaric acid, adipic acid, trimethyladipic acid, azelaic acid, sebacic acid, dodecanedioic acid and their anhydrides.

8. The lubricating oil composition according to claim 1, wherein the polyglycerol partial esters have HLB values of from 3 to 7.

9. The lubricating oil composition according to claim 1, wherein the polyglycerol partial esters have an OH-number in the range of 50 to 180 mg KOH/g.

10. The lubricating oil composition according to claim 1, further comprising an additive.

11. The lubricating oil composition according to claim 10, wherein the additive is at least one selected from the group consisting of viscosity index (VI) improvers, pour point depressants, dispersants, detergents, defoamers, corrosion inhibitors, antioxidants, antiwear and extreme pressure additives and fiction modifiers.

12. The lubricating oil composition according to claim 1, wherein the polyglycerol partial esters have a weight-average molecular weight of 2,000 to 15,000 g/mol.

13. A method of lubricating an engine, comprising adding the lubricating oil composition according to claim 1 to the engine.

14. A method of reducing friction in an engine, comprising applying the lubricating oil composition according to claim 1 to the engine.

Description

EXAMPLE 1

Polycarboxylic Acid Ester Prepared from polyglycerol, isostearic acid, sebacic acid and poly(hydroxystearic acid) according to synthesis example 2 of EP 1 500 427 B1

[0067] A mixture of isostearic acid (91.1 g, 0.320 mol) and poly(hydroxystearic acid) (141.7 g, 0.120 mol, acid number of 47 mg KOH/g) was esterified with polyglycerol (61.9 g, 0.121 mol, hydroxyl value of 950 mg KOH/g) at 240 C. while nitrogen flowing through. After 2 h at this temperature, the acid number of the reaction mixture was <10. Then, the mixture was cooled to 130 C., sebacic acid (20.2 g, 0.100 mol) was added and the mixture was heated again to 240 C. After 3 h at this temperature, a viscous product having an acid number of <5 was obtained.

COMPARATIVE EXAMPLE 1

Polycarboxylic Acid Ester Prepared from Ethoxylated Soybean Oil, Oleic Acid and Dimer Acid

[0068] A mixture of epoxidized soybean oil (300 g, 0.302 mol) with an oxirane-[O] content of 6.3%, oleic acid (331 g, 1.18 mol) and dimer acid (57.5 g; 0.101 mol, comprising about 2% monobasic acids, about 96% dimer acids and about 2% trimer acids and higher polyacids) was heated to 240 C. until the acid value was <10 mg KOH/g.

[0069] The structure of this polymer is different to polyglycerol partial ester according to the present invention and therefore not encompassed by the present invention.

COMPARATIVE EXAMPLE 2

Polycarboxylic Acid Ester Prepared from Polyglycerol, Isostearic Acid and Sebacic Acid

[0070] A mixture of 72 g isostearic acid and 11 g sebacic acid was esterified with 17 g polyglycerol (average degree of polymerization=3) at 240 C. while nitrogen flowing through. Reaction was cooled down when an acid number of 12 was reached.

[0071] The OH-value of this polymer is much lower than the favorable range according to the present invention.

COMPARATIVE EXAMPLE 3

[0072] Polymeric friction modifier Perfad 3006, which is commercially available by Croda Inc. (see US 2013/0079536, WO 2011/107739 A1 for structure and Lube Magazine No. 120, April 2014, page 27 for physical properties).

[0073] The structure of this polymer is different to polyglycerol partial ester according to the present invention and therefore not encompassed by the present invention.

COMPARATIVE EXAMPLE 4

[0074] Polymeric friction modifier Perfad 3057, diluted form of Perfad 3050, which is commercially available by Croda Sucursal Colombia (see US 2013/0079536, WO 2011/107739 A1 for structure and Lube Magazine No. 120, April 2014, page 27 for physical properties).

[0075] The structure of this polymer is different to polyglycerol partial ester according to the present invention and therefore not encompassed by the present invention.

TABLE-US-00002 TABLE 1 physical data of examples and comparative examples HLB acid number OH-number M.sub.n M.sub.w value [mg KOH/g] [mg KOH/g] [g/mol] [g/mol] Ex 1 ~5 5 125-145 2600 6100 Comp. Ex 1 9 24 4600 16000 Comp. Ex. 2 12 10-20 3200 10600 Comp. Ex. 3 1.2 Comp. Ex. 4 4*.sup.) M.sub.n and M.sub.w are measured via GPC using PMMA (polymethyl methacrylate) as standard *.sup.)value given for Perfad 3050; Perfad 3057 is a diluted form of Perfad 3050

[0076] All polymers were diluted in Nexbase 3043 which is a Group III oil according to the American Petroleum Institute (API). The final blends have a similar kinematic viscosity at 100 C. (KV.sub.100) of about 4.45 cSt.

[0077] For Comparative Examples 3 and 4 treat rates of 0.5% are recommended by the manufacturer.

TABLE-US-00003 TABLE 1 Viscosity values of the tested blends Comparative Example 1 [% wt] 1 Comparative Example 2 [% wt] 1 Comparative Example 3 [% wt] 0.5 Comparative Example 4 [% wt] 0.5 Example 1 [% wt] 1 Reference Nexbase 3043 [% wt] 99 99 99.5 99.5 99 KV.sub.100 mm.sup.2/s 4.49 4.45 4.48 4.43 4.48 (KV.sub.100 = Kinematic Viscosity @ 100 C.)

[0078] Determination of Friction-Reducing Action:

[0079] The measurements of the coefficient of friction at 100 C. were performed on a Mini Traction Machine (MTM) from PCS Instruments. The test consist of evaluating the friction level occurring in a lubricated contact formed by a steel ball and a steel disc. The speeds of the ball and the disc are driven independently. The ball is loaded and rubbed in rolling sliding conditions against the steel disc, the contact being fully immersed in oil.

[0080] For each sample, the test was performed in two steps:

[0081] 1) Run In phase

[0082] For this phase, the conditions described in Table 2 below have been applied, SRR referring to Sliding Roll Ratio. This parameter was maintained constant during the 2 hours testing and is defined as:

[00002]$\frac{.Math.U.Math..Math.\mathrm{Ball}-U.Math..Math.\mathrm{Disc}.Math.}{U}$

where U BallU Disc represents the sliding speed and U the entrainment speed, given by U=(U Ball+U Disc)/2

TABLE-US-00004 TABLE 2 test parameters for run in phase Test Rig MTM 2 von PCS Instruments Disc Highly polished stainless Steel AISI 52100 Disc diameter 46 mm Ball Highly polished stainless Steel AISI 52100 Ball diameter 19.05 mm Mean Speed 100 mm/s Temperature 100 C. Duration 2 hours Load 30 N SRR 50%

[0083] 2) Stribeck Curve Evaluation

[0084] A Stribeck was then obtained by measuring the friction coefficient under the conditions shown in Table 3.

TABLE-US-00005 TABLE 3 conditions for Stribeck curve evaluation Test Rig MTM 2 von PCS Instruments Disc Highly polished stainless Steel AISI 52100 Disc diameter 46 mm Ball Highly polished stainless Steel AISI 52100 Ball diameter 19.05 mm Mean Speed from 5 to 2500 mm/s Temperature 100 C. Load 30 N SRR 50%

[0085] The Stribeck curves are plotted in FIG. 1. The curve NB3043-Ref refers to the formulation containing 100% of Group III oil named Nexbase 3043.

[0086] FIG. 1: Stribeck curve measurements after two hours of run in phase

[0087] To express in % the friction reduction obtained by working Example 1, a quantifiable result can be expressed as a number is obtained as follows:

[0088] Integration of the friction value curves in the range of sliding speed 0.005-2.5 m/s using the trapezoidal rule. The area corresponds to the total friction over the entire speed range examined. The smaller the area, the greater the friction-reducing effect of the polymer examined.

[0089] The percentage friction reductions calculated therefrom in relation to the reference oil are compiled in Table 4 below.

TABLE-US-00006 TABLE 4 Quantitative evaluation of the reduction in friction Comp. Comp. Comp. Comp. Reference Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Area in 99.239 51.079 62.675 71.354 65.109 86.581 mm/s reduction in 0 48.53 36.84 28.10 34.39 12.75 friction relative to reference [%]

[0090] The data in Table 4 and FIG. 1 show clearly that the inventive polymers have a much better effect with regard to the reduction in friction than the corresponding comparative polymers of the prior art using different chemistry. The effect is even more pronounced in the low speed regime as revealed in Table 5 below.

[0091] Since the low speeds are of particular economic interest for the use of the lubricant compositions in accordance with the, Table 5 shows the integration data of the friction value curves within the sliding speed range from 0.005 to 0.090 m/s.

[0092] The areas determined and the percentage reductions in friction calculated therefrom in relation to the reference oil are compiled in Table 5 in an analogous manner to Table 4.

TABLE-US-00007 TABLE 5 Quantitative evaluation of the reduction in friction at low frequency (from 0.005 to 0.090 m/s) Comp. Comp. Comp. Comp. Reference Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Area 7.863 1.855 4.429 5.464 3.405 4.025 [mm/s] reduction in 0 76.41 43.67 30.51 56.70 48.81 friction relative to reference in low speed regime [%]

[0093] The data in Table 5 show clearly that the inventive polymers have a much better effect once again with regard to the reduction in friction than the corresponding comparative polymers of the prior art.

[0094] Compared to the results as shown in Table 4, it is found that the friction-increasing action of lubricant composition for use in accordance with the invention is very clearly marked specifically within the range of low sliding speeds.