Lubricant composition

Abstract

The present invention provides a non-aqueous lubricant composition comprising a base stock and 5 at least 0.02 wt % of a friction reducing additive which comprises a block co-polymer of at least one block A which is an oligo- or polyester residue of a hydroxycarboxylic acid and at least one block B which is a residue of a polyalkylene glycol. The invention also provides the use of a block co-polymer of at least one block A which is an oligo- or polyester residue of a hydroxycarboxylic acid and at least one block B which is a residue of a polyalkylene glycol to reduce the kinetic co-efficient 10 of friction in a non-aqueous lubricant composition when compared to an equivalent lubricant composition comprising no block co-polymer.

Claims

1. A non-aqueous lubricant composition comprising: a base stock; and at least 0.5 wt % of a friction reducing additive which comprises a mixture of a first and second block co-polymer, wherein the first and second block co-polymer each comprise at least one block A with a molecular weight in a range of 1000 to 2500 which is an oligo- or polyester residue of a saturated and an aliphatic hydroxycarboxylic acid that is a hydroxystearic acid, the first block co-polymer comprises at least one block B having a molecular weight in a range of 400 to 4600 which is a residue of a polyethylene glycol, and the second block co-polymer comprises at least one block B having a molecular weight in a range of 3000 to 5000 which is a residue of a polyethylene glycol; wherein the first and second block co-polymer have an ABA structure and the mixture of the first and second block co-polymers has an HUB value of at least 6.5, and wherein the lubricant composition at 40° C. to 150° C. reduces kinetic coefficient of friction by at least 20% when measured by a mini-traction machine at 0.01 m/s and 0.02 m/s when compared with an equivalent lubricant composition which does not comprise the friction reducing additive.

2. A non-aqueous lubricant composition as claimed in claim 1 wherein the number average molecular weight of the mixture of the first and second block co-polymer is in the range 3000 to 5000.

3. A non-aqueous lubricant composition as claimed in claim 1 wherein the base stock is selected from the group consisting; of an API Group I, II, IV, V base oil or mixtures thereof.

4. A non-aqueous lubricant composition as claimed in claim 1 wherein the kinetic coefficient of friction is reduced by at least 40%.

5. A non-aqueous lubricant composition as claimed in claim 1 wherein the lubricant composition is an engine oil, the friction reducing additive is present in the range from 0.5 to 10 wt % and the HLB value of the mixture of the first and second block co-polymer is at least 7.

6. A non-aqueous lubricant composition as claimed in claim 1 wherein the lubricant composition is a hydraulic oil or fluid, the friction reducing additive is present in the range from 0.5 to 10 wt % and the HLB value of the mixture of the first and second block co-polymer is at least 7.

7. A non-aqueous lubricant composition as claimed in claim 1 wherein the lubricant composition is a gear oil, the friction reducing additive is present in the range from 0.5 to 10 wt % and the HLB value of the mixture of the first and second block co-polymer is at least 7.

8. A non-aqueous lubricant composition as claimed in claim 1 wherein the lubricant composition is a metal working fluid and the friction reducing additive is present in the range from 1 to 20 wt %.

9. A non-aqueous lubricant composition consisting essentially of: a base stock; at least 0.5% of a friction reducing additive which comprises a mixture of a first and second block co-polymer, wherein the first block co-polymer comprises at least one block A with a molecular weight in a range of 1000 to 2500 which is an oligo- or polyester residue of a saturated and an aliphatic hydroxycarboxylic acid that is a hydroxystearic acid, the first block co-polymer comprises at least one block B having a molecular weight in a range of 400 to 4600 which is a residue of a polyethylene glycol, the second block co-polymer comprises at least one block 13 having a molecular weight in a range of 3000 and 5000 which is a residue of a polyethylene glycol; and wherein the first and second block co-polymer have an ABA structure and the mixture of the first and second block co-polymers has an MB value of at least 6.5, and wherein the lubricant composition at 40° C. to 150° C. reduces kinetic coefficient of friction by at least 20% when measured by a mini-traction machine at 0.01 m/s and 0.02 m/s when compared with an equivalent lubricant composition which does not comprise the friction reducing additive.

10. A method of reducing the kinetic co-efficient of friction in a non-aqueous lubricant composition, the method comprising: blending a base stock with at least 0.5 wt % of a mixture of a first and second block co-polymer to form a lubricant composition, wherein the first and second block co-polymer each comprise at least one block A with a molecular weight in a range of 1000 to 2500 which is an oligo- or polyester residue of a saturated and an aliphatic hydroxycarboxylic acid that is a hydroxystearic acid, the second block co-polymer comprises at least one block B having a molecular weight in a range of 400 to 4600 which is a residue of a polyethylene glycol, and the second block co-polymer comprises at least one block B having a bolecular weight in a range of 3000 to 5000 which is a residue of a polyethylene glycol; wherein the first and second block co-polymer have an ABA structure and the mixture of the first and second block co-polymer have an HLB value of at least 6.5, and wherein the lubricant composition at 40° C. to 150° C. reduces kinetic coefficient of friction by at least 20% when measured by a mini-traction machine at 0.01 m/s and 0.02 m/s when compared with an equivalent lubricant composition which does not comprise the mixture of the first and second block co-polymer.

11. The method as claimed in claim 10 wherein the non-aqueous lubricant composition is an engine oil.

12. The method as claimed in claim 10 wherein the non-aqueous lubricant composition is a hydraulic oil or fluid.

13. The method as claimed in claim 10 wherein the non-aqueous lubricant composition is a gear oil.

14. The method as claimed in claim 10 wherein the non-aqueous lubricant composition is a metal working fluid.

15. The method as claimed in claim 14 wherein the amount of torque required to cut a thread in a pre-drilled hole in a metal bar as measured using a Microtap II thread tapping machine with the non-aqueous lubricant composition is reduced by at least 10% when compared to an equivalent lubricant composition which does not comprise the mixture of the first and second block co-polymer.

16. A method of reducing friction in a system comprising adding a non-aqueous lubricant composition as claimed in claim 1 to the system.

Description

EXAMPLES

(1) The present invention will now be described further by way of example only with reference to the following Examples. All parts and percentages are given by weight unless otherwise stated.

(2) It will be understood that all tests and physical properties listed have been determined at atmospheric pressure and room temperature (i.e. about 20° C.), unless otherwise stated herein, or unless otherwise stated in the referenced test methods and procedures.

Example 1

Preparation of Block Co-Polymer I

(3) A flask fitted with a distillation condenser and an overhead stirrer was charged with 73 g of polyethylene glycol with a molecular weight of about 1500 (PEG 1500) and 146 g of PEG 4000. The flask was heated to 85-90° C. with stirring and a nitrogen sparge to keep the reaction mixture under a flow of nitrogen. Next, 450 g of 12-hydroxystearic acid was charged to the flask. Once the 12-hydroxystearic acid had been charged 1.4 g of tetrabutyl titanate (TBT) catalyst was added. The temperature of the reaction mixture was increased to 222° C. and the acid value of the mixture was monitored every hour. Once the acid value reached 10 mgKOH/g or below, the reaction was stopped. The reaction product was a block co-polymer of polyhydroxystearate (A)—polyethylene glycol (B)—polyhydroxystearate (A). The block co-polymer had an HLB value of about 8 as measured experimentally by comparison of its solubility in water against compositions of known HLB.

(4) The block co-polymer produced by this Example will be referred to as Block Co-polymer I. The number average molecular weight of Block Co-polymer I was determined using Gel Permeation Chromatography (GPC) as follows.

(5) Samples of Block Co-polymer I were prepared at a concentration of approximately 10 mg/ml using THF as a solvent. Approximately 100 mg of sample was dissolved in 10 ml eluent. The solution was left for 24 hours at room temperature to fully dissolve and then filtered through a 0.2 μm PTFE filter prior to injection into the GPC column. The samples were analysed using the conditions listed below. The samples were injected using automatic sample injection. Data capture and subsequent data analysis was carried out using Viscotek's ‘Omnisec’ software. Each sample was injected in duplicate.

(6) TABLE-US-00002 Instrument Viscotek GPC Max Columns 3*30 cm Plgel 100A, 1000A & 10,000 GPC columns Eluent THF + 1% TEA Flow rate 0.8 ml/min Detection RI (refractive index) Temperature 40° C.

(7) The GPC system was calibrated using a conventional method of calibration against a series of linear polystyrene standards. These standards covered the range from approximately 150 to 450,000 daltons. The GPC columns selected for this analysis have a linear response up to approximately 600,000 daltons.

(8) The number average molecular weight measured as above for Block Co-polymer I was in the range 3,500 to 4,100, with an average value of about 3825.

Example 2

Preparation of Block Co-Polymer II

(9) A flask fitted with a distillation condenser and an overhead stirrer was charged with 219 g of PEG 1500 and heated to 85-90° C. with stirring and a nitrogen sparge. Next, 450 g of 12-hydroxystearic acid was charged to the flask. Once the 12-hydroxystearic acid had been charged, 1.4 g of TBT (tetrabutyl titanate) catalyst was added. The temperature of the reaction mixture was increased to 222° C. and the acid value of the mixture was monitored every hour. Once the acid value reached 10 mgKOH/g or below, the reaction was stopped. The reaction product was a block co-polymer of polyhydroxystearate (A)—polyethylene glycol (B)—polyhydroxystearate (A). The polyhydroxystearate residues each contain about 6 acid residues, corresponding to a molecular weight for each A block of about 1800. The block co-polymer had an HLB value of about 6 as measured experimentally by comparison of its solubility in water against compositions of known HLB.

(10) The block co-polymer produced by this Example will be referred to as Block Co-polymer II. The number average molecular weight of Block Co-polymer II was determined using Gel Permeation Chromatography (GPC) as described above for Example 1.

(11) The number average molecular weight measured for Block Co-polymer II was in the range 3,700 to 3900, with an average value of about 3775.

Example 3

Assessment of the Reduction of the Co-Efficient of Friction in an Engine Oil by Block Co-Polymer I

(12) The coefficient of friction of an automotive engine oil lubricant composition (with no friction reducing additive) comprising 92 wt % of a Group IV base stock (Durasyn 166 polyalphaolefin ex INEOS) and 8 wt % of a Group V base stock (Priolube 3970 ester ex Croda) was determined at 100° C. and 150° C. using a Mini Traction Machine (MTM) with a ¾ inch ball on a smooth disc.

(13) The MTM was supplied by PCS Instruments of London, UK. The disc was AISI 52100 hardened bearing steel with a mirror finish (Ra<0.01 μm) and the ball was AISI 52100 hardened bearing steel. The load applied was 36N (1 GPa contact pressure) and the speed of rotation was from 0.01 to 0.05 m/s. The MTM provides a method of defining the Stribeck curve of a given lubricant. The Stribeck curve is a plot of friction in relation to viscosity, speed and load. The MTM is a computer controlled precision traction measurement system. The test specimens and configuration have been designed such that realistic pressures, temperatures and speeds can be attained without requiring very large loads, motors or structures. In the configuration used in this Example, the test specimens are a 19.05 mm (¾ inch) steel ball and a 46 mm diameter steel disc. Approximately 60 ml of the lubricant composition is then added. The ball is loaded against the face of the disc and the ball and disc are driven independently to create a mixed rolling/sliding contact. The frictional force between the ball and disc is measured by a force transducer. Additional sensors measure the applied load, the lubricant temperature and (optionally) the electrical contact resistance between the specimens and the relative wear between them.

(14) The lubricant composition was heated to 40° C. and then run in for 15 minutes at 0.03 m/s once the temperature is reached. A Stribeck curve plot is achieved by measuring the coefficient of friction with speed (reducing the speed from 2.0 m/s to 0.01 m/s), the Stribeck curve plot is repeated 2 more times. The lubricant composition was then heated to 100° C. and then 150° C. and 3 Stribeck curve plots were completed at each temperature.

(15) The above method was then repeated with the addition of 0.5 wt % of Block Co-polymer I from Example 1 to the lubricant composition. Results at 0.01 m/s and 0.02 m/s from these tests are given in Table 2 below.

(16) For comparison, the results of the addition 0.5 wt % of the known friction reducing additives Glycerol Mono-oleate and Oleylamide to the lubricant composition are also provided. It can be seen that Block Co-polymer I performs better (provides a lower co-efficient of friction) than Glycerol Mono-oleate and Oleylamide.

(17) TABLE-US-00003 TABLE 2 Effect of addition of friction reducing additives on co-efficient of friction of Engine Oil 0.5 wt % of 0.5 wt % of Block Block 0.5 wt % of 0.5 wt Copolymer Copolymer Glycerol % of Friction Not I from II from Monooleate Oleylamide Reducing present Example 1 Example 2 (comparative) (comparative) Additive Co-efficient Co-efficient Co-efficient Co-efficient Co-efficient Speed Temperature of of of of of (m/s) (° C.) friction friction friction friction friction 0.01 40 0.088 0.062 0.052 0.079 0.076 0.02 40 0.072 0.053 0.047 0.067 0.071 0.01 100 0.088 0.035 0.045 0.070 0.063 0.02 100 0.077 0.044 0.045 0.059 0.065 0.01 150 0.097 0.035 0.052 0.043 0.069 0.02 150 0.089 0.031 0.054 0.036 0.063

(18) It can be seen from Table 2 that at 40° C., the addition of 0.5 wt % of Block Co-polymer I reduces the co-efficient of friction by about 30% (0.062 compared to 0.088) at 0.01 m/s and by about 26% at 0.02 m/s when compared to a lubricant composition without Block Co-polymer I. At 100° C., the addition of 0.5 wt % of Block Co-polymer I reduces the co-efficient of friction by about 50% at 0.01 m/s and by about 55% at 0.02 m/s. At 150° C., the addition of 0.5 wt % of Block Co-polymer I reduces the co-efficient of friction by about 64% at 0.01 m/s and by about 65% at 0.02 m/s.

(19) The addition of 0.5 wt % of Block Co-polymer II also shows a reduction in the co-efficient of friction when compared to the lubricant composition with no friction reducing additive present. It also reduces the co-efficient of friction when compared with Oleylamide at 40° C., 100° C. and 150° C. When Block Co-polymer II is compared with Block Co-polymer I, it can be seen that the friction reduction provided by Block Co-polymer II is greater at 40° C. but that the friction reduction provided by Block Co-polymer I is greater at 100° C. and 150° C. Without being bound by theory, it is believed that the HLB value of Block Co-polymer I (about 8) may be related to its improved performance at 100° C. and 150° C. when compared with the HLB value of Block Co-polymer II (HLB of about 6).

Example 4

Assessment of the Reduction of the Co-Efficient of Friction in a Hydraulic Fluid by Block Co-Polymer I

(20) The experimental procedure for Example 3 was repeated for a hydraulic fluid lubricant composition. Hydraulic Fluid Compositions A and B were tested and the results compared.

(21) Hydraulic fluid Composition A comprises 99.15 wt % of a Group II base stock (Catenex T129) and 0.85 wt % of the commercially available additive package Additin RC 9207 ex. Rhein Chemie Rheinau GmbH, Germany.

(22) Composition B comprises an amount of Composition A with 1 wt % of Block Co-polymer I added.

(23) The results of these tests are given in Table 3 below.

(24) TABLE-US-00004 TABLE 3 Effect of addition of Block Co-polymer I on co-efficient of friction of Hydraulic Fluid Co-efficient of friction of Relative reduction Co-efficient of Hydraulic Fluid in co-efficient of friction of Hydraulic composition B friction in Fluid composition A (including 1 wt % of composition B Temperature (without Block Co- Block Co-polymer I compared to Speed (m/s) (° C.) polymer I) from Example 1) composition A 0.01 100 0.099 0.040 60% 0.02 100 0.085 0.035 59% 0.01 150 0.100 0.017 83% 0.02 150 0.093 0.013 86%

(25) It can be seen from Table 3 that Block Co-polymer I reduces the co-efficient of friction in composition B under all conditions tested.

Example 5

Assessment of the Reduction of Wear Scar in a Four-Ball Wear Test by the Addition of Block Co-Polymer I

(26) The Four-Ball Wear test is a standardised test and is described in ASTM D4172. A Seta-Shell 4 Ball Lubricant Tester available from Stanhope-Seta of Surrey, UK was used to perform the Four-Ball Wear test in accordance with ASTM D4172. In the Four-Ball Wear test, a steel ball is rotated under load against three stationary steel balls in a pot containing the sample lubricant. The diameters of the wear scars that occur on the stationary balls are measured after completion of the test. For a given load, the smaller the wear scar diameter, the better the load-carrying properties of the fluid.

(27) Compositions C and D were tested and the results compared. Composition C was Catenex S321, a Group I base stock available from Shell. Composition D was 5 wt % of Block Co-polymer I added to Composition C and then diluted with Durasyn 162 polyalphaolefin ex IN EOS to have the same viscosity as Composition C so that both C and D comply with ISO 22.

(28) The results are given in Table 4 below

(29) TABLE-US-00005 TABLE 4 reduction in wear scar by Four-Ball test Wear Scar for Wear Scar for Relative reduction in Wear Composition Composition Scar for Composition D C (mm) D (mm) compared with Composition C 0.72 0.52 28%

(30) It can be seen from Table 4 that Block Co-polymer I reduces the wear in composition D.

Example 6

Microtap Test of Block Co-Polymer I with Regard to Metal Working Fluids

(31) A Microtap II thread tapping machine supplied by Microtap USA, Inc. is used to measure the tapping torque of metal working fluids. The Microtap II machine cuts threads in pre-drilled holes at a selected set of operating parameters. Tests were performed on 50 mm×200 mm×8 mm metal bars containing 3.7 mm diameter holes. They were supplied by the company Robert Speck Ltd. Two materials of metal bars were tested: mild steel and Aluminium 6061.

(32) For this Example, the following parameters were used:

(33) 1 ml of metal working fluid (lubricant composition) is added to the Microtap II machine using a micro pipette

(34) Ambient temperature

(35) 6.0 mm depth of hole

(36) 4 mm forming tap

(37) Maximum torque set at 200 Ncm

(38) Cutting speed 1000 rpm

(39) After applying the metal working fluid, the holes were threaded and the amount of torque required was recorded.

(40) If a lubricant composition isn't adequate to allow the thread to be formed within the set maximum torque of 200 Ncm then multiple attempts are made by the machine and then declared as a fail.

(41) The results are given in Table 5 below.

(42) TABLE-US-00006 TABLE 5 Micro Tap Test Results Catenex S321 + 5 wt % Catenex S321 + 10 wt % Catenex S321 Block Co-polymer I Block Co-polymer I (Composition C) (Composition D) (Composition E) Mild Steel- Fail 198 180 Torque required (Ncm) (more than 200 Ncm of torque required) Aluminium 6061- 62 39 48 Torque required (Ncm)

(43) Using mild steel the reference test of 100 wt % Catenex S321 (Gpl) failed. With the addition of 5 wt % of Block Co-polymer I (viscosity controlled to ISO 22) the torque was 198 Ncm. With the addition of 10 wt % of Block Co-polymer I the torque was 180 Ncm.

(44) Using aluminium 6061 the reference test of 100 wt % Catenex S321 (Gpl) had a torque of 62 Ncm. With the addition of 5 wt % of Block Co-polymer I (viscosity controlled to ISO 22) the torque was 39 Ncm. With the addition of 10 wt % of Block Co-polymer I the torque was 48 Ncm.

Example 7

Reichert Testing of Wear Prevention of Block Co-Polymer I

(45) A Reichert testing machine provided by Anton Parr of Dahlewitz, Germany was used to test wear prevention. In the Reichart testing machine, a rigidly clamped cylinder is pressed against a rotating sliding ring. This involves rotating a roller bearing over a known distance (100 m) with a load of 1.5 kg at ambient temperature. It has to be insured that the fluid flowing into the contact point (friction wear point) between test cylinder and test ring is always sufficient. After testing, abrasive areas (elliptic wear scars) appear on the test cylinder. The dimensions of these wear scars depend on the load-carrying capacity of the test fluid and A/W performance. The higher the load carrying capacity (A/W performance) the smaller the wear scar is after a certain running time or precise distance.

(46) For this example, the following parameters were used:

(47) A hardened steel ring and roll were placed in the Reichert testing machine

(48) The ring was rotated at 1000 rpm

(49) The applied load was 294 N

(50) The ring and roll are cleaned and secured in place. Approximately 25 ml of the lubricant composition is added to the test reservoir. The load is applied and the test is started and run for 100 m sliding distance. The average wear scar area is then calculated.

(51) The wear scar area of the reference Composition C comprising Catenex S321 (Group I) was 35 mm.sup.2. Composition E comprising Composition C with the addition of 10 wt % of Block Co-polymer I produced a wear scar area was 25 mm.sup.2. Therefore the wear scar area produced by Composition E was reduced by 29% when compared with Composition C.

(52) It is to be understood that the invention is not to be limited to the details of the above embodiments, which are described by way of example only. Many variations are possible.