ADDITIVE

BACKGROUND

[0001] The present invention relates to lubricating compositions comprising a base oil and a volatility reducing additive for particular use in the crankcase of an internal combustion engine, in particular an internal combustion engine used in a passenger vehicle or light duty van.

[0002] In practice, various lubricating compositions for crankcase engines are known. A disadvantage of low viscosity crankcase engine oils is that they they may have undesirably high volatility, in particular as measured by the ASTM D5800B NOACK volatility test.

[0003] Attempts have been made to overcome the above problems by formulating with low volatility base oils, such as Fischer- Tropsch derived base oils. WO2010020653 discloses the use of Fischer- Tropsch base oils in lubricating compositions. The composition of Example 1 of WO2010020653 shows a surprisingly low NOACK volatility when compared to the composition of Comparative Example 1 (using a Group III mineral base oil).

[0004] However, for future low viscosity engine oils such as OW-16 (as per SAE J300 table of engine oil viscosity grades) and lower viscosities (OW-12, 0W-8, etc), additional benefits beyond those conferred via the use of Fischer-Tropsch base oils may be desired.

[0005] It has surprisingly been found that by including certain lubricant additives in the lubricating formulation the NOACK volatility can be lowered.

SUMMARY

[0006] According to the present invention, there is provided a lubricating composition comprising:

(i) a base oil; and

(ii) a volatility reducing additive;

wherein the lubricating composition has a kinematic viscosity at 100°C (according to ASTM D445) of 16.3 mm ² /s or less, a low temperature cranking viscosity of at most 6200cP at -35°C (ASTM D5293) and a NOACK volatility of at most 15.0% according to ASTM D5800B. [0007] According to another aspect of the present invention, there is provided the use of a volatility reducing additive for reducing the NOACK volatility of a lubricating composition, in particular wherein the lubricating composition comprises a Fischer-Tropsch base oil.

DETAILED DESCRIPTION

[0008] The base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils; thus, according to the present invention, the term "base oil" may refer to a mixture containing more than one base oil. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

[0009] Suitable base oils for use in the lubricating oil composition of the present invention are Group III mineral base oils, Group IV poly-alpha olefins (PAOs), Group III Fischer-Tropsch derived base oils and mixtures thereof.

[0010] By "Group III" and "Group IV" base oils in the present invention are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) for category III and IV. These API categories are defined in API Publication 1509, 15th Edition, Appendix E, April 2002.

[0011] Fischer-Tropsch derived base oils are known in the art. By the term "Fischer- Tropsch derived" is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention are those as for example disclosed in EP 0776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

[0012] Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), alkyl naphthalenes and dewaxed waxy isomerates. Synthetic hydrocarbon base oils sold by the Shell Group under the designation "Shell XHVI" (trade mark) may be conveniently used.

[0013] 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 linear C ₂ to C32, preferably C ₆ to C½, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and 1-tetradecene.

[0014] Preferably, the base oil as used in the lubricating composition according to the present invention comprises a Fischer-Tropsch derived base oil.

[0015] There is a strong preference for using a Fischer-Tropsch derived base oil over a PAO base oil, in view of the high cost of manufacture of the PAOs. Thus, preferably, the base oil contains more than 50 wt. , preferably more than 60 wt. , more preferably more than 70 wt.%, even more preferably more than 80 wt.%, most preferably more than 90 wt.% Fischer-Tropsch derived base oil.

[0016] The total amount of base oil incorporated in the lubricating composition is preferably present in an amount in the range of from 60 to 99 wt.%, more preferably in an amount in the range of from 65 to 90 wt.%, and most preferably in an amount in the range of from 70 to 85 wt.%, with respect to the total weight of the lubricating composition.

[0017] According to the present invention, the base oil (or base oil blend) preferably has a kinematic viscosity at 100°C of at least 3.0 cSt (according to ASTM D445), preferably between 3.0 and 4.0 cSt.

[0018] The lubricating composition of the present invention further comprises a volatility reducing additive. As used herein, the term "volatility reducing additive" pertains to any compound added into a lubricating composition at low levels (typically 1% or less) that confers a reduction in NOACK volatility. Some examples of suitable volatility reducing additives include, but are not necessarily limited to, an aminic anti-oxidant, molybdenum based friction modifier, and a combination thereof.

[0019] The volatility reducing additive may be present in the lubricating composition on its own or as part of an additive package. The volatility reducing additive is preferably present in the lubricating composition in an amount in the range of from 0.5 wt.% to 5 wt.%, preferably 0.5 wt.% to 2 wt.%, with respect to the total weight of the lubricating composition.

[0020] As mentioned above, the lubricating composition according to the present invention meets certain specific requirements for the low temperature cranking viscosity at -35°C, the kinematic viscosity at 100°C and the NOACK volatility. Typically, the low temperature cranking viscosity at -35°C (according to ASTM D5293) of the lubricating composition is at most 6200cP.

[0021] Typically, the kinematic viscosity at 100°C (according to ASTM D445) of the lubricating composition is at most 16.3 cSt, preferably from 3.8 to 16.3 cSt, and more preferably from 3.8 to 9.3 cSt.

[0022] Typically, the high temperature, high shear viscosity ("HTHS") (according to ASTM D4683) of the lubricating composition is in the range of from 1.7 to 3.7 mPa.s, preferably in the range of from 1.7 to 2.6 mPa.s.

[0023] Typically, the NOACK volatility (according to ASTM D5800B) of the lubricating composition is 15.0 wt or below, preferably 12.5 wt or below, even more preferably 10.0 wt. or below.

[0024] The lubricating compositions according to the present invention may optionally further comprise one or more additives such as anti-oxidants, anti-wear additives, dispersants, detergents, overbased detergents, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, metal passivators, corrosion inhibitors, demulsifiers, anti-foam agents, seal compatibility agents and additive diluent base oils, etc.

[0025] As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail. Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

[0026] Optional anti-oxidants that may be conveniently used in lubricant formulations include phenyl-naphthylamines (such as "IRGANOX L-06" available from Ciba Specialty Chemicals) and diphenylamines (such as "IRGANOX L-57" available from Ciba Specialty Chemicals) as e.g. disclosed in WO 2007/045629 and EP 1 058 720 Bl, phenolic anti-oxidants, etc. The teaching of WO 2007/045629 and EP 1 058 720 Bl is hereby incorporated by reference.

[0027] Anti-wear additives that may be conveniently used include zinc-containing compounds such as zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl- dithiophosphates, molybdenum-containing compounds, boron-containing compounds and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof. Examples of such molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO 98/26030, sulphides of molybdenum and molybdenum dithiophosphate.

[0028] Boron-containing compounds that may be conveniently used include borate esters, borated fatty amines, borated epoxides, alkali metal (or mixed alkali metal or alkaline earth metal) borates and borated overbased metal salts.

[0029] The dispersant used is preferably an ashless dispersant. Suitable examples of ashless dispersants are polybutylene succinimide polyamines and Mannich base type dispersants.

[0030] The detergent used is preferably an overbased detergent or detergent mixture containing e.g. salicylate, sulphonate and/or phenate-type detergents.

[0031] Examples of viscosity index improvers which may conveniently be used in the lubricating composition of the present invention include the styrene -butadiene stellate copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers. Dispersant-viscosity index improvers may be used in the lubricating composition of the present invention.

[0032] Preferably, the lubricating composition contains at least 0.1 wt. of a pour point depressant. As an example, alkylated naphthalene and phenolic polymers, polymethacrylates, maleate/fumarate copolymer esters may be conveniently used as effective pour point depressants. Preferably not more than 0.5 wt.% of the pour point depressant is used.

[0033] Furthermore, compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole -based compounds may be conveniently used in the lubricating compositions as corrosion inhibitors.

[0034] Compounds which may be conveniently used in the lubricating compositions of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

[0035] The lubricating compositions of the present invention may be conveniently prepared by admixing the volatility reducing additive, and any optional additives, with the base oil(s).

[0036] The above-mentioned additives are typically present in an amount in the range of from 0.01 to 35.0 wt.%, based on the total weight of the lubricating composition, preferably in an amount in the range of from 0.05 to 25.0 wt.%, more preferably from 1.0 to 20.0 wt.%, based on the total weight of the lubricating composition.

[0037] Preferably, the lubricating composition contains from 10 wt.% to 15 wt.% of an additive package comprising a combination of additives including anti-oxidants, a zinc- based anti-wear additive, an ashless dispersant, an overbased detergent mixture, and a silicone -based anti-foaming agent.

[0038] In another aspect, the present invention provides the use of a volatility reducing additive to lower NOACK volatility of a lubricating composition, in particular wherein the lubricating composition comprises a Fischer- Tropsch derived base oil.

[0039] Also the present invention provides a method of improving NOACK volatility properties, which method comprises lubricating the crankcase of an engine, in particular a passenger car motor engine, with a lubricating composition according to the present invention.

[0040] The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES

Lubricating Oil Compositions

[0041] Various engine oils for use in a crankcase engine were formulated. Table 1 indicates the properties for the base oil used.

Table 1

According to ASTM D 445

According to ASTM D 2270

According to ASTM D 5800B [0042] Table 2 indicates the composition and properties of the fully formulated engine oil formulations that were tested; the amounts of the components are given in wt. , based on the total weight of the fully formulated formulations.

[0043] All tested formulations contained a combination of a base oil and additive, wherein the base oil in each case was GTL 4.

[0044] "Base oil 1" was a Fischer- Tropsch derived base oil ("GTL 4") having a kinematic viscosity at 100°C (ASTM D445) of approx. 4 cSt (mmV ¹ ). This base oil may be conveniently manufactured by the process described in e.g. WO-A-02/070631, the teaching of which is hereby incorporated by reference.

[0045] "Additive A" was a dispersant, Infineum C9280, which is commercially available from Infineum.

[0046] "Additive B" was an aminic antioxidant, Infineum C9452, which is commercially available from Infineum.

[0047] "Additive C" was a molybdenum based friction modifier, Infineum C9455, which is commercially available from Infineum.

[0048] The compositions of Examples 1 to 3 and Comparative Example 1 and 2 were obtained by mixing the base oils with the additive, where present, using conventional lubricant blending procedures. The results of NOACK volatility testing via ASTM D5800B are shown in Table 2.

Table 2

Discussion

[0049] As can be learned from Table 2, Examples 1-3, which contain a volatility reducing additive, have significantly lower NOACK volatility values than Comparative Examples 1 and 2, which do not contain a volatility reducing additive. These results are particularly surprising because each additive included in the formulations shown for Examples 1-3 is comprised of a concentrate wherein the additive has been diluted in a base oil with NOACK volatility of greater than 12.5% as measured by ASTM D5800B, thus the expectation is that addition of the additives in Examples 1-3 will increase NOACK volatility rather than decrease it.

[0050] An important benefit of the present invention is that for future low viscosity engine oils such as OW-16 (as per SAE J300 table of engine oil viscosity grades) and lower viscosities (OW-12, OW-8, etc), stringent NOACK volatility requirements can be met with lesser or no need to use (relatively expensive) poly-alpha olefin (PAO) base oils.

[0051] Given these findings, it is expected that many other chemistries may impart similar benefits in serving to lower NOACK volatility, such as known lubricant additive chemistries (anti-wear, anti-oxidant, viscosity index improver, friction modifier, detergent, dispersant, pour point depressant, etc) and any other chemical species that interacts strongly with the oil-air interface so as to lower the rate of evaporation including but not limited to surfactants, functionalized polymers, ionic liquids, nanoparticles, etc.