Lubricating oil composition

Abstract

This invention provides a lubricating oil composition comprising: a) one or more additives, including in the range of from greater than 0.5 mass% to no more than 5 mass%, based on the overall mass of the lubricating oil composition, of at least one viscosity index improver; and b) a base oil composition having an aniline point in the range of from 114 to 120˚C, said base oil composition comprising: - in the range of from 20 to 60 mass%, based on the overall mass of the lubricating oil composition, of a group II base oil with a kinematic viscosity at 100˚C in the range of from 2.5 to 3.5 mm2 / s; and - in the range of from 30 to 70 mass%, based on the overall mass of the lubricating oil composition, of a further base oil selected from the group consisting of group III base oils, group IV base oils and mixtures thereof with a kinematic viscosity at 100˚C in the range of from 3.6 to 5.0 mm2 / s, wherein the lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 6.1 to 9.3 mm2 / s. The present invention also provides a method of improving NOACK volatility properties, which method comprises lubricating the crankcase of an engine with said lubricating oil composition in order to suppress volatility loss as measured in a NOACK test at 150˚C.

Description

[0001]SP3086 - 1 - LUBRICATING OIL COMPOSITION Field of the Invention This invention relates to a lubricating oil composition and a method of improving NOACK volatility properties. 5 Background of the invention It is highly desirable to maximise the fuel economy benefits provided by engine oils for use in passenger cars and other vehicles. In order to achieve increasingly stringent global fuel economy and carbon emissions 10 targets, use of low viscosity engine oil compositions has become more common. A major challenge in use of low viscosity engine oil lubricant composition is simultaneously increasing fuel efficiency while also maintaining engine wear protection 15 and low oil consumption. The use of low viscosity base oils provides a fuel efficiency benefit but can result in increased volatility and oil consumption. There is an increase in hybrid vehicles, in which at least a portion of the power is provided by a battery. 20 These vehicles reduce the operating frequency of the engine and, thus, generally result in longer periods of time in which a lower running temperature is present. JP2023004932 describes the use of a lubricating oil composition comprising a (co)polymer in a GTL base oil in 25 order to provide suitable viscometric properties without increasing NOACK volatility at 250˚C. US20230105922 discloses a polyalphaolefin based engine oil lubricant composition with a NOACK volatility of about 20wt% or less measured according to ASTM D5800. 30 There remains a need for a lubricating oil composition suitable for use in passenger car engine oils that effectively improves fuel economy while also providing desirable levels for Noack volatility. It is particularly important that the volatility levels are reduced at the temperatures at which hybrid-type engines 5 are regularly operated, for instance at 150˚C. Summary of the Invention The present invention provides a lubricating oil composition comprising: a) one or more additives, including in the range of from 10 greater than 0.5 mass% to no more than 5 mass%, based on the overall mass of the lubricating oil composition, of at least one viscosity index improver; and b) a base oil composition having an aniline point in the range of from 114 to 120˚C, said base oil composition 15 comprising: - in the range of from 20 to 60 mass% , based on the overall mass of the lubricating oil composition, of a group II base oil with a kinematic viscosity at 100˚C in the range of from 2.5 to 3.5 mm2 / s; and 20 - in the range of from 30 to 70 mass%, based on the overall mass of the lubricating oil composition, of a further base oil selected from the group consisting of group III base oils, group IV base oils and mixtures thereof with a kinematic viscosity 25 at 100˚C in the range of from 3.6 to 5.0 mm2 / s, wherein the lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 6.1 to 9.3 mm2 / s. The present invention also provides a method of improving NOACK volatility properties, which method 30 comprises lubricating the crankcase of an engine, in particular a passenger car motor engine, with a lubricating oil composition comprising: a) one or more additives, including in the range of from greater than 0.5 mass% to no more than 5 mass%, based on the overall mass of the lubricating oil composition, of at least one viscosity index improver; and b) a base oil composition having an aniline point in the range of from 114 to 120˚C, said base oil composition 5 comprising: - in the range of from 20 to 60 mass% , based on the overall mass of the lubricating oil composition, of a group II base oil with a kinematic viscosity at 100˚C in the range of from 2.5 to 3.5 mm2 / s; and 10 - in the range of from 30 to 70 mass%, based on the overall mass of the lubricating oil composition, of a further base oil selected from the group consisting of group III base oils, group IV base oils and mixtures thereof with a kinematic viscosity 15 at 100˚C in the range of from 3.6 to 5.0 mm2 / s, wherein the lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 6.1 to 9.3 mm2 / s, in order to suppress volatility loss as measured in a NOACK test at 150˚C. 20 Detailed Description of the Invention One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a 25 concise description of these embodiments, not all features of an actual implementation may be described in the specification. When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” 30 are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 5 In the context of the present invention, in a case where a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100 mass%. The present inventors have found that an improved 10 lubricating oil composition can be provided by the combination of base oils and additive described herein. Said lubricating oil composition provides excellent viscometric properties for fuel economy performance while reducing volatility loss according to the NOACK test, in 15 particular when that test is carried out at 150˚C. The lubricating oil composition comprises one or more additives, including in the range of from greater than 0.5 mass% to no more than 5 mass%, based on the overall mass of the lubricating oil composition, of at 20 least one viscosity index improver. Viscosity index improvers are known in the art. Suitable viscosity index improvers may be or may include one or more linear or star-shaped polymers and / or copolymers of methacrylate, butadiene, olefins, isoprene 25 or alkylated styrenes, polyisobutylene, polymethacrylate, ethylene-propylene, hydrogenated block copolymer of styrene and isoprene, polyacrylates, styrene-isoprene block copolymer, styrene-butadiene copolymer, ethylene- propylene copolymer, hydrogenated star polyisoprene, and 30 combinations thereof. The term “polymer” refers to any two or more of the same or different repeating units. The term “homopolymer” refers to a polymer having units that are the same. The term “copolymer” refers to a polymer having two or more units that are different from each other and includes terpolymers and the like. The term “terpolymer” refers to a polymer having three units that are different from each other. The term “different” refers to units indicates that 5 the units differ from each other by at least one atom or are different isomerically. Likewise, the definition of polymer, as used herein, includes homopolymers, copolymers, and the like. Furthermore, the term “styrenic block copolymer” refers to any copolymer that includes 10 units of styrene and a mid-block. One particularly suitable viscosity index improver is polymethacrylate. More preferably, the viscosity index improver is a comb type polymethacrylate. The viscosity index improver is present in an amount 15 of at least 0.5 mass%, more preferably at least 1 mass%, based on the overall mass of the lubricating oil composition. Preferably, the viscosity index improver is present in an amount of at most 5 mass%, more preferably at most 4 mass%, based on the overall mass of the 20 lubricating oil composition. The viscosity index improver concentrations are based on active composition present in the lubricating oil composition and do not include any diluent oil included in the commercially available VII preparation. 25 The lubricating oil composition may also include one or more other additives typical for engine oils. These other additives may include any one or more friction modifiers, dispersants, anti-wear additives, detergents, antioxidants, pour point depressant, corrosion inhibitors, 30 anti-rust additives, metal deactivators, seal compatibility additives, and anti-foam agents. These other additives may be provided to the lubricant composition individually or in the form of an additive package. The one or more other additives suitably may be incorporated into the lubricating oil composition at treat rate of at least 7 mass% to at most 12 mass% based on the total mass of the lubricating oil composition. The lubricating oil composition also comprises a 5 base oil composition, which has an aniline point in the range of from 114 to 120˚C. Preferably, the base oil composition has an aniline point in the range of from 115 to 119˚C, more preferably in the range of from 116 to 118.5˚C. Aniline point is an indicator for a polarity of 10 oils and it affects an interaction between base oils and additives including VII, FM and addpack. By controlling aniline point of base oils in the lubricating composition to suitable range, the interaction is improved to provide preferable viscosity property and volatility loss in NOACK 15 test at 150ºC. The aniline point is measured in accordance with JIS K2256:2013. The base oil composition comprises a mixture of two base oil in different API groups. The API groups are broad categories of base oil stocks developed and defined by the 20 American Petroleum Institute (API Publication 1509; www.API.org) to create guidelines for lubricant base oils. The table below summarizes properties of each of the five groups. Table 1 Viscosity Saturates Sulfur index Group I <90% and / or >0.03% and ≥ 80 &<120 Group II ≥90% and≤0.03%and ≥ 80 &<120 Group III ≥90% and≤0.03%and ≥120 Group IV Includes polyalphaolefins (PAO) Group V All other base oil stocks not in Groups I - IV Firstly, the base oil composition comprises in the range of from 20 to 60 mass%, preferably in the range of from 25 to 50 mass%, based on the overall mass of the lubricating oil composition, of a group II base oil with a 5 kinematic viscosity at 100˚C in the range of from 2.5 to 3.5 mm2 / s. The group II base oil may be a natural or mineral oil or may be a synthetic or partially synthetic base oil such as a Fischer-Tropsch derived base oil. Secondly, the base oil composition comprises in the 10 range of from 30 to 70 mass%, based on the overall mass of the lubricating oil composition, of a further base oil selected from the group consisting of group III base oils, group IV base oils and mixtures thereof with a kinematic viscosity at 100˚C in the range of from 3.6 to 5.0 mm2 / s. 15 The group III base oil may be a natural or mineral oil or may be a synthetic or partially synthetic base oil, such as a Fischer-Tropsch derived base oil. Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” is meant that a 20 base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. Fischer-Tropsch derived base oils are often classified by the starting material in the Fischer-Tropsch process, i.e. ‘X-to-liquids’ or ‘XTL’, with X standing for said starting material. Biomass-to- 25 liquid (BTL), coal to liquids (CTL), gas-to-liquid (GTL) and power-to-liquid (PTL) processes are some examples of Fischer-Tropsch processes producing base oils. Preferably, the Fischer-Tropsch derived base oil is a GTL (Gas-To- Liquids) base oil. 30 Suitable Fischer-Tropsch derived base oils are those as for example disclosed in EP0776959, EP0668342, WO97021788, WO0015736, WO0014188, WO0014187, WO0014183, WO0014179, WO0008115, WO9941332, EP1029029, WO0118156 and WO 0157166. Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Suitable poly-alpha olefin base oils that may be used in the lubricating compositions of the present invention may be derived from 5 linear C2 to C32, preferably C6 to C16, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and 1- tetradecene. There is a strong preference for using a Fischer-Tropsch derived base oil over a PAO base oil, in 10 view of the high cost of manufacture of the PAOs. Therefore, if a PAO base oil is present, it is suitably present in an amount of less than 50 mass % of the lubricating oil composition. Preferably, the lubricating oil composition has a 15 volatility loss of less than 2% as measured in the NOACK test at 150˚C for 4 hours. More preferably, the volatility loss is less than 1.8% as measured in the NOACK test at 150˚C for 4 hours. The lubricating oil composition also preferably has 20 a volatility loss less than 5%, more preferably less than 4.6% as measured in the NOACK test at 150˚C for 12 hours. The NOACK test at 150˚C is carried out as same manner as ASTM D5800 for 250˚C test only changing test temperature setting. The NOACK test for 12 hours is 25 carried out by repeating 4 hours test for 3 times without changing a test sample. The lubricating oil composition has a kinematic viscosity at 100˚C in the range of from 6.1 to 9.3 mm2 / s covering viscosity grade 16 and 20 by SAE J300, preferably 30 in the range of from 6.1 to 8.2 mm2 / s covering viscosity grade 16 by SAE J300. Kinematic viscosities noted herein are measured according to ASTM D445. The invention will now be further illustrated by reference to the following non-limiting examples. Examples The following components were used to formulate a range of lubricating oil compositions as set out in Tables 2 and 3. 5 Base oil 1 – 4cSt Group III, GTL base oil Base oil 2 – Yubase 4; 4cSt, Group III mineral oil Base oil 3 – Spectrasyn 4; 4cSt, group IV PAO Base oil 4 – 3cSt Group II, GTL base oil Base oil 5 – Yubase 3; a 3cSt, Group II mineral oil 10 Base oil 6 – Durasyn 162; 2cSt, Group IV base oil Viscosity index improver (VII) – 20% of comb type polymethacrylate dissolved in dilute oil, Mw of polymethacrylate is 530,000 as measured by gel permeation chromatography. 15 Friction modifier (FM) – MoDTC type friction modifier, Mo atom content 10% Addpack –passenger car motor engine oil addpack, containing ZnDTP, Ca detergent, Mg detergent, succinimide type dispersant, anti-oxidants and other inhibitors. 20 The lubricating oil compositions were then tested according to the following methods and the results ae reported in Tables 2 and 3. Kinematic viscosity－ JIS K 2283 Viscosity index－ JIS K 2283 25 Aniline point－ JIS K 2256 Density(15˚C)－ JIS K 2249 NOACK (250˚C)－ ATTM D5800 NOAK (150˚C) – ASTM D5800 Modified. Only changing test temperature setting from 250˚C to 150˚C. 12 hours test is 30 carried out by repeating 4 hours test for 3 times without changing a test sample. Table 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Base oil 1 43.95 35.45 - - 54.15 41.65 Base oil 2 - - 36.85 - - - Base oil 3 - - - 33.25 - - Base oil 4 36 44 44 46 Base oil 5 - - - - 28 40 Base oil 6 - - - - - - VII 10.7 11.2 9.8 11.4 8.5 9 FM 0.75 0.75 0.75 0.75 0.75 0.75 Add pack 8.6 8.6 8.6 8.6 8.6 8.6 Total 100 100 100 100 100 100 Base oil properties VI 121 118 116 116 120 116 KV40 (mm2 / s) 13.83 12.94 13.25 12.70 16.23 15.26 KV100 (mm2 / s) 3.398 3.238 3.275 3.188 3.741 3.569 Aniline point 118.1 117.4 114.1 116.7 117.2 115.0 (˚C) Lubricating oil composition properties VI 269 284 281 285 232 251 KV40 (mm2 / s) 21.82 20.85 20.74 20.48 23.92 23.19 KV100 (mm2 / s)6.224 6.240 6.189 6.169 6.242 6.358 Aniline point 117.4 116.6 113.7 115.8 116.7 114.6 (˚C) Density 0.8318 0.831 0.8373 0.8322 0.8391 0.8415 NOACK 250˚C (%) 22.1 25.3 25.4 25.3 18.4 21.8 NOACK Volatility 1.6 1.8 1.8 1.8 1.6 1.8 150˚C loss 4h(%) KV40, 4h 21.95 21.09 (mm2 / s) KV40 increase 0.6 1.2 4h (%) Volatility loss 12h 3.9 4.3 4.3 4.5 3.6 4.4 (%) Table 3 – Comparative Experiments Ex 7 Ex 8 Ex 9 Ex 10 Ex 11 Ex 12 Base oil 1 82.85 - 29.25 21.45 - 65.15 Base oil 2 - - - - 30.25 - Base oil 3 - - - - - - Base oil 4 - 77.75 - - - - Base oil 5 - - 52 60 52 - Base oil 6 - - - - - 15 VII 7.8 12.9 9.4 9.2 8.4 10.5 FM 0.75 0.75 0.75 0.75 0.75 0.75 Add pack 8.6 8.6 8.6 8.6 8.6 8.6 Total 100 100 100 100 100 100 Base oil properties VI 126 111 112 110 111 122 KV40 (mm2 / s) 18.51 9.864 14.46 13.91 14.74 14.48 KV100 (mm2 / s) 4.126 2.690 3.428 3.330 3.460 3.502 Aniline point(˚C) 122.1 113.3 112.8 111.2 110.2 118.9 Lubricating oil composition properties VI 204 362 270 267 256 255 KV40 (mm2 / s) 26.04 17.35 22.48 22.32 23.14 22.3 KV100 (mm2 / s) 6.235 6.184 6.470 6.390 6.422 6.221 Aniline point(˚C) 121.5 112.8 112.5 111.0 110.0 118.1 Density 0.843 0.834 0.8287 0.8452 0.8491 0.8324 8 NOACK 250˚C (%) 11.0 35.9 25.0 27.9 25.5 21.9 NOACK Volatility 2.5 2.0 2.2 2.0 3.2 150˚C loss 4h(%) KV40, 4h 2 17.82 23.6 (mm / s) KV40 increase, 2.7 5.8 4h (%) Volatility loss, 12h 6.1 4.9 5.3 4.9 7.4 (%) The lubricating oil compositions of Examples 1 and 2 are composed of 4cSt Group III GTL base oil and 3 cSt 5 Group II GTL base oil. These Examples demonstrate suitable viscosity properties such as a viscosity index (VI) of more than 230 and kinematic viscosity at 100˚C (KV100) of around 6.2 mm2 / s. The volatility loss in NOACK test at 150º C is less than 2% for 4hours and less than 5% for 12 10 hours. Examples 3 and 4 show similar results when Group III mineral oil or PAO are used as 4cSt base oils instead of the Group III GTL base oil. Examples 5 and 6 demonstrate that a Group II mineral oil is also applicable as 3cSt Group II base oil instead of Group II GTL base oil 15 used in Examples 1 and 2. When using a single (only 4cSt or 3cSt) base oil in Examples 7 or 8, suitable viscosity properties and low volatility loss in NOACK test at 150ºC are not demonstrated. The lubricating oil composition of Example 7 20 has a low viscosity index. The lubricating oil composition of Example 8 shows high volatility loss in NOACK test at 150ºC. The Examples also demonstrate that, when using 4cSt base oil and 3cSt Group II base oil, the desired range of aniline point of the base oil mixture is necessary to 25 achieve both preferable viscosity property and low volatility loss in NOACK test at 150ºC. Examples 9, 10 and 11 use base oil mixtures having aniline points of less than 114˚C and show high volatility loss in NOACK test at 150˚C of more than 2% for 4 hours. When using a base oil 30 composition comprising 4cSt base oil and 2cSt base oil such as in Example 12, even though the base oil composition has an aniline point in the desirable range, the volatility loss in the NOACK test at 150˚C is high. Further, there are examples which have similar volatility loss in NOACK test at 250˚C such as Examples 2 (of the invention) and 9 (comparative) or Examples 6 (of the invention) and 12 (comparative). It can be seen, by 5 comparing these Examples, both the base oil selection and range of the aniline point of the base oil mixture are required in order to achieve the desired low volatility loss in NOACK test at 150ºC.

Claims

SP3086 - 14 - C L A I M S 1. A lubricating oil composition comprising: a) one or more additives, including in the range of from greater than 0.5 mass% to no more than 5 mass%, based on the overall mass of the lubricating oil composition, of 5 at least one viscosity index improver; and b) a base oil composition having an aniline point in the range of from 114 to 120˚C, said base oil composition comprising: - in the range of from 20 to 60 mass% , based on the 10 overall mass of the lubricating oil composition, of a group II base oil with a kinematic viscosity at 100˚C in the range of from 2.5 to 3.5 mm2 / s; and - in the range of from 30 to 70 mass%, based on the overall mass of the lubricating oil composition, of 15 a further base oil selected from the group consisting of group III base oils, group IV base oils and mixtures thereof with a kinematic viscosity at 100˚C in the range of from 3.6 to 5.0 mm2 / s, wherein the lubricating oil composition has a kinematic 20 viscosity at 100˚C in the range of from 6.1 to 9.3 mm2 / s.

2. A lubricating oil composition as claimed in Claim 1, wherein the group II base oil is present in an amount in the range of from 25 to 50 mass%, based on the overall mass of the lubricating oil composition. 25 3. A lubricating oil composition as claimed in Claim 1 or Claim 2, wherein the viscosity index improver comprises a comb polymethacrylate.

4. A lubricating oil composition as claimed in any one of Claims 11 to 3, wherein the volatility loss of said 30 lubricating oil composition is less than 2% as measured using the NOACK test at 150ºC for 4 hours.

5. A lubricating oil composition as claimed in any one of Claims 1 to 4, wherein the volatility loss of said lubricating oil composition is less than 5% as measured using the NOACK test at 150ºC for 12 hours. 5 6. A method of improving NOACK volatility properties, which method comprises lubricating the crankcase of an engine, with a lubricating oil composition according to any one of claims 1 to 5, in order to suppress volatility loss as measured in a NOACK test at 150˚C. 10 7. A method as claimed in Claim 6, wherein the engine is a passenger car motor engine.