USE OF A LUBRICANT FOR IMPROVING THE LOW TEMPERATURE VISCOSITY OF LUBRICANT COMPOSITIONS

Description

[0001] The invention relates to lubricant compositions for use in industrial applications having improved low temperature viscosity characteristics.

[0002] Lubricants for use in industrial applications typically comprise a base oil, such as a mineral oil or synthetic oil, and one or more additives. Additives deliver, for example, reduced friction and wear, increased viscosity, improved viscosity index, and resistance to corrosion, oxidation, aging or contamination.

[0003] The ability of a lubricant to reduce friction is dependent on its viscosity. Generally, the least viscous fluid, which still forces two moving surfaces apart, is desired. Many lubricant applications require good lubricant properties over a broad temperature range, for example, when the engine is cold as well as when it has reached its operating temperature. Therefore, a lubricant's viscosity should change as little as possible with temperature to provide constant lubricant properties over a broad temperature range.

[0004] The temperature-dependence of a lubricant's viscosity is measured by the viscosity index (VI). The higher the viscosity index, the smaller is the relative change in viscosity with temperature. The viscosity index is determined from the kinematic viscosity at 40°C (KV₄₀) and the kinematic viscosity at 100°C (KV₁₀₀), which is a good reflection of most engines' operating conditions. Additives that increase the viscosity index are referred to as viscosity index improvers (VIIs).

[0005] Polymers of alkyl (meth)acrylates are known in the art to act as good viscosity index improvers in lubricants oils. For example, US 2008/0194443 A1 demonstrates the use of alkyl (meth)acrylate containing comb polymers as viscosity index improvers in mineral oils.

[0006] Another option to obtain the desired viscosity characteristics is to use synthetic base oils having an inherently high viscosity index. Polyalphaolefines (PAOs) such as 1-decene oligomers have been successfully used as synthetic base oils for this purpose. US Patent Nos. 4,827,064 and 4,827,073 disclose base oils having a high viscosity index based on low-branch-ratio PAOs.

[0007] Another class of synthetic base oils is polysiloxanes. For example, WO 2014/028632 A1 describes lubricant compositions having a high viscosity index comprising PAOs and organomodified polysiloxanes, e.g. polymethyloctylsiloxane. WO 2015/117804 A1 describes cross-linked organomodified siloxanes, e.g. crosslinked polymethyldodecylsiloxane, having an inherently high viscosity index.

[0008] The viscosity index, however, does not properly reflect the lubricant's properties at temperatures lower than 40°C, for instance at a low temperature range of -20°C to +20°C. A lubricant having good lubricant properties at the operating temperature of a machine or an engine, therefore, does not necessarily have equally good properties during the engine's cold-start phase. The cold-start properties of a lubricant are, however, an important factor contributing to an improved fuel efficiency of engines.

[0009] The low-temperature properties of lubricants can be measured by the R-factor, which is defined as the ratio of the kinematic viscosity at -20°C to the kinematic viscosity at +20°C. Since the kinematic viscosity at -20°C is generally higher than at +20°C, the R-factor is generally greater than 1. Thus, a narrow viscosity difference between -20°C and +20°C is reflected by a low R-factor (an R-factor close to 1).

[0010] The problem of providing lubricant compositions having good viscosity properties at low operating temperatures has not been sufficiently addressed in the prior art. Mostly, the prior art reports the VI measured between 40°C and 100°C, but gives no indication of the viscosity characteristics at, for examples -20°C to +20°C.

[0011] Therefore, the aim of the present invention is to provide lubricant compositions with good low temperature viscosity properties. In particular, the difference of the kinematic viscosity of the lubricant composition at -20°C and +20°C should be small.

[0012] It has been surprisingly found that the use of special polyorganosiloxanes as a lubricant or part of lubricant compositions significantly improves the low temperature properties of the lubricant. In particular, the use of the polyorganosiloxanes reduces the R-factor of the lubricant.

[0013] Therefore, the invention relates to the use of a polyorganosiloxane to produce a lubricant composition having an R-factor of less than or equal to 8,
wherein the R-factor is defined as the ratio of the kinematic viscosity of the lubricant composition at -20°C to the kinematic viscosity at +20°C measured according to ASTM D445,
wherein the polyorganosiloxane is obtainable by hydrosilylation of

a) at least one siloxane A of general formula (I)

         M_a'M^H_b'D_d'D^H_e'T_g'T^H_h'Q_i'     (I),

wherein

a'

is 0 to 80, preferably 0 to 50, more preferably 0 to 25, most preferably 0 to 5;

b'

is 0 to 80, preferably 0 to 30, more preferably 0 to 15, most preferably 0 to 5;

d'

is 10 to 1200, preferably 20 to 900, more preferably 25 to 500, most preferably 30 to 200;

e'

is 0 to 100, preferably 0 to 80, more preferably 0 to 60, most preferably 0 to 25;

g'

is 0 to 30, preferably 0 to 20, more preferably 1 to 15, most preferably 1 to 5;

h'

is 0 to 20, preferably 0 to 10, most preferably 0;

l'

is 0 to 20, preferably 0 to 15, most preferably 0;

with the proviso that the following conditions are satisfied

a' + b'

is not more than 8, preferably not more than 4, more preferably not more than 3, most preferably equal to 2;

g' + h' + l'

is not more than 20, preferably less than 15, more preferably less than 5, most preferably equal to 0;

b' + e' + h'

is at least 1 and not more than 30, preferably at least 1 and less than 20, more preferably at least 1 and less than 15, even more preferably at least 1 and less than 10, and most preferably at least 1 and less than 5;

b) at least one compound of general formula (II)

         CH₂=CHX     (II)

wherein

X

is selected from hydrogen or an alkyl, aryl, alkaryl group having 1 to 30 carbon atoms, preferably 6 to 14 carbon atoms, which is optionally substituted with one or more hydroxyl or methoxy groups;

and optionally

c) at least one siloxane B of general formula (III)

         M_aM^H_bM^v_cD_dD^H_eD^V_fTgT^H_hQ_i     (III),

wherein

a

is 0 to 80, preferably 0 to 50, more preferably 0 to 25, most preferably 0 to 5;

b

is 0 to 80, preferably 0 to 30, more preferably 0 to 15, most preferably 0 to 5;

c

is 0 to 80, preferably 0 to 30, more preferably 0 to 15, most preferably 0 to 5;

d

is 10 to 1200, preferably 20 to 900, more preferably 25 to 500, most preferably 30 to 200;

e

is 0 to 100, preferably 0 to 80, more preferably 0 to 60, most preferably 0 to 25;

f

is 0 to 100, preferably 0 to 80, more preferably 0 to 60, most preferably 0 to 25;

g

is 0 to 30, preferably 0 to 20, more preferably 1 to 15, most preferably 1 to 5;

h

is 0 to 20, preferably 0 to 10, most preferably 0;

i

is 0 to 20, preferably 0 to 15, most preferably 0;

with the proviso that the following conditions are satisfied

a + b + c

is not more than 8, preferably not more than 4, more preferably not more than 3, most preferably equal to 2;

g + h + i

is not more than 20, preferably less than 15, more preferably less than 5, most preferably equal to 0;

b + e + h

is at least 1 and not more than 30, preferably at least 1 and less than 20, more preferably at least 1 and less than 15, even more preferably at least 1 and less than 10, and most preferably at least 1 and less than 5;

c + f

is at least 1 and not more than 20, preferably at least 1 and less than 15, more preferably at least 1 and less than 10, most preferably equal to 2;

wherein

M

is a building block [R¹₃SiO_1/2],

M^H

is a building block [R¹₂R²SiO_1/2],

M^V

is a building block [R¹₂R³SiO_1/2],

D

is a building block [R¹₂SiO_2/2],

D^H

is a building block [R¹R²SiO_2/2],

D^V

is a building block [R¹R³SiO_2/2],

T

is a building block [R¹SiO_3/2],

T^H

is a building block [R²SiO_3/2],

Q

is a building block [SiO_4/2],

each R¹ is independently selected from the group consisting of C₁ to C₁₈ alkyl and phenyl,
each R² is hydrogen, and
each R³ is independently selected from the group consisting of C₂ to C₁₈ alkenyl, or C₂ to C₁₈ alkynyl.

[0014] In the context of the invention, the siloxanes A and B are characterized by the so-called "MDTQ" nomenclature, which describes the siloxane polymer according to the presence of various siloxane monomer units that make up the polymer. Briefly, the symbol M denotes the mono-functional siloxane units, for example (CH₃)₃Si-O_1/2; D denotes the bifunctional units, for example (CH₃)₂SiO_2/2; T denotes the trifunctional units, for example (CH₃)SiO_3/2; and Q denotes the tetrafunctional unit SiO_4/2.

[0015] The nomenclature for the M, M^V, M^H, D, D^V, D^H, T, T^H, Q as defined above is applicable to both siloxanes A and B.

[0016] The siloxanes of the invention may in particular be linear (containing exactly two M units and no T or Q units), circular (containing only D and no M units), or branched (containing one or more T and/or Q units).

[0017] The sequence of the MDTQ monomer units of the polyorganosiloxanes is not limited by the formulae given herein. In particular the MDTQ monomer units may be in random and/or blockwise distribution. They may also have an alternating sequence in the polymer or else form a gradient.

[0018] The siloxanes of the invention usually have a molecular weight distribution. Consequently, the indices associated with the individual MDTQ monomer units represent the average number of the respective monomer unit in a given polymer.

[0019] The siloxanes of the invention may be produced by the platinum-catalyzed reaction of siloxanes carrying SiH groups with unsaturated organic compounds, such as alkenes and alkynes. This process is also referred to as hydrosilylation. Hydrosilylation can be carried out in the presence or absence of a solvent, as described in EP 2 628 771 A1, or in the presence of water, as described in EP 1 754 740 A1.

[0020] The polyorganosiloxane obtainable by hydrosilylation may be a crosslinked or non-crosslinked siloxane.

[0021] Hydrosilylation of the siloxanes A and B and the unsaturated compound according to formula (II) results in a crosslinked polyorganosiloxanes by the reaction of the unsaturated groups in M^V and D^V of B with the SiH groups in M^H, D^H, and T^H of A and B. Further, the siloxanes A and B are modified by addition of the unsaturated compounds according to formula (II) to the SiH groups present in A and B.

[0022] Hydrosilylation of the siloxane A and the unsaturated compound according to formula (II) yields a non-crosslinked polyorganosiloxane that is modified by addition of the unsaturated compounds according to formula (II) to the SiH groups present in A.

[0023] In one embodiment, the invention relates to the use of a composition of crosslinked and non-crosslinked polyorganosiloxanes. The polyorganosiloxane may, therefore, be a composition comprising a first polyorganosiloxane obtainable by hydrosilylation of a), b) and c), and a second polyorganosiloxane obtainable by hydrosilylation of a) and b).

[0024] In a preferred embodiment, the siloxane A is linear. Hence, the following conditions are preferably satisfied for the siloxane A of general formula (I):

a'+b'

is 2,

g' + h' + l'

is 0, and

b' + e'

is at least 10.

[0025] In a preferred embodiment, the siloxane B is linear. Hence, the following conditions are preferably satisfied for the siloxane B of general formula (III):

a + b + c

is 2,

g + h + i

is 0, and

b + e

is at least 10.

[0026] In a preferred embodiment, each R¹ is independently selected from methyl or phenyl group. Preferably R¹ is methyl.

[0027] In a preferred embodiment, each R³ is independently selected from the group consisting of C₂ to C₁₈ alkenyl, or C₂ to C₁₈ alkynyl, wherein the alkenyl contains at least one terminal C-C-double bond and alkynyl contains an internal or terminal C-C-triple bond. Preferably, each R³ independently represents a C₂ to C₁₈ alkenyl having a terminal C=C-double bond.

[0028] In a preferred embodiment, each R³ is independently selected from vinyl (ethenyl) or allyl (2-propenyl) group.

[0029] In a preferred embodiment, the siloxane A is a linear siloxane of general formula (IV)

         M₂D_d'D^H_e'     (IV),

wherein

d'

is 10 to 80,

e'

is 10 to 30, and

each R¹ is a methyl group.

[0030] In a preferred embodiment, the siloxane B is a linear siloxane of general formula (V)

         M^V₂D_dD^H_e     (V),

wherein

d

is 10 to 80,

e

is 10 to 30,

each R¹ is a methyl group, and
each R³ is a vinyl group.

[0031] The compound according to formula (II) is preferably an alkene having 2 to 32 carbon atoms and a terminal carbon-carbon double bond. Hence, X is preferably hydrogen or an alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, more preferably 6 to 12 carbon atoms, most preferably 6 to 8 carbon atoms.

[0032] In a preferred embodiment, X is an alkyl group having 6 to 8 carbon atoms.

[0033] In a preferred embodiment, the compound according to formula (II) is 1-octene.

[0034] In one embodiment, the polyorganosiloxane is obtainable by hydrosilylation of a composition comprising

a) 30 to 85% by weight, preferably 40 to 70% by weight of siloxane A,

b) 5 to 69.8% by weight, preferably 30 to 55% by weight of at least one compound according to formula (II),

c) 0.2 to 10% by weight, preferably 0.5 to 5% by weight of siloxane B, and

d) 1 to 50 ppm by weight, preferably 2 to 10 ppm by weight of a catalyst,

wherein the amounts of a), b) and c) are based on the total weight of siloxane A, compound according to formula (II) and siloxane B, and wherein the amount of d) is based on the total weight of the composition.

[0035] Alternatively, the polyorganosiloxane is obtainable by hydrosilylation of a composition comprising

a) 30 to 85% by weight, preferably 40 to 70% by weight of siloxane A,

b) 5 to 69.8% by weight, preferably 30 to 55% by weight of at least one compound according to formula (II), and

d) 1 to 50 ppm by weight, preferably 2 to 10 ppm by weight of a catalyst,

wherein the amounts of a) and b) are based on the total weight of compound according to formula (II) and siloxane A, and wherein the amount of d) is based on the total weight of the composition.

[0036] The amount of polyorganosiloxane according to the invention used to produce the lubricant composition is preferably 50 to 100% by weight, more preferably 70 to 95% by weight, most preferably 80 to 90% by weight, based on the total weight of the lubricant composition.

[0037] The lubricant composition produced by the use of the polyorganosiloxane according to the invention may comprise additional base oils, such as mineral oils, synthetic oils and/or oils of natural origins.

[0038] Base oils for lubricant oil formulations are divided into groups according to API (American Petroleum Institute). Mineral oils are divided into group I (non-hydrogen- treated; sulfur content > 0.03% by weight and/or 90% by weight saturates, viscosity index 80-120) and, depending on the degree of saturation, sulfur content and viscosity index, into groups II (hydrogen-treated; sulfur content < 0.03% by weight, and > 90% by weight saturates, viscosity index 80-120) and III (hydrogen-treated; sulfur content < 0.03% by weight, and > 90% by weight saturates, viscosity index > 120). Polyalphaolefins (PAOs) correspond to group IV. All other base oils are encompassed in group V.

[0039] Mineral oils are known per se and commercially available. They are generally obtained from mineral oil or crude oil by distillation and/or refining and optionally further purification and finishing processes, the term "mineral oil" including in particular the higher-boiling fractions of crude or mineral oil. In general, the boiling point of mineral oil is higher than 200°C, preferably higher than 300°C, at 5000 Pa. The production by low-temperature carbonization of shale oil, coking of bituminous coal, distillation of brown coal with exclusion of air, and also hydrogenation of bituminous or brown coal is likewise possible. Accordingly, mineral oils have, depending on their origin, different proportions of aromatic, cyclic, branched and linear hydrocarbons.

[0040] In general, a distinction is drawn between paraffin-base, naphthenic and aromatic fractions in crude oils or mineral oils, in which the term "paraffin-base fraction" represents longer-chain or highly branched isoalkanes, and "naphthenic fraction" represents cycloalkanes. In addition, mineral oils, depending on their origin and finishing, have different fractions of n-alkanes, isoalkanes having a low degree of branching, known as mono-methyl-branched paraffins, and compounds having heteroatoms, in particular O, N and/or S, to which a degree of polar properties are attributed. However, the assignment is difficult, since individual alkane molecules may have both long-chain branched groups and cycloalkane radicals, and aromatic parts. For the purposes of the present invention, the assignment can be effected to DIN 51 378, for example. Polar fractions can also be determined to ASTM D 2007.

[0041] The proportion of n-alkanes in preferred mineral oils is less than 3% by weight, the fraction of O-, N- and/or S-containing compounds less than 6% by weight. The fraction of the aromatics and of the mono-methyl-branched paraffins is generally in each case in the range from 0 to 40% by weight. In one interesting aspect, mineral oil comprises mainly naphthenic and paraffin-base alkanes which have generally more than 13, preferably more than 18 and most preferably more than 20 carbon atoms. The fraction of these compounds is generally 60% by weight, preferably 80% by weight, without any intention that this should impose a restriction. A preferred mineral oil contains 0.5 to 30% by weight of aromatic fractions, 15 to 40% by weight of naphthenic fractions, 35 to 80% by weight of paraffin-base fractions, up to 3% by weight of n-alkanes and 0.05 to 5% by weight of polar compounds, based in each case on the total weight of the mineral oil.

[0042] An analysis of particularly preferred mineral oils, which was effected by means of conventional processes such as urea separation and liquid chromatography on silica gel, shows, for example, the following constituents, the percentages relating to the total weight of the particular mineral oil used:

n-alkanes having approx. 18 to 31 carbon atoms: 0.7 to 1.0%,

slightly branched alkanes having 18 to 31 carbon atoms: 1.0 to 8.0%,

aromatics having 14 to 32 carbon atoms: 0.4 to 10.7%,

iso- and cycloalkanes having 20 to 32 carbon atoms: 60.7 to 82.4%,

polar compounds: 0.1 to 0.8%,

loss: 6.9 to 19.4%.

[0043] An improved class of mineral oils (reduced sulfur content, reduced nitrogen content, higher viscosity index, lower pour point) results from hydrogen treatment of the mineral oils (hydroisomerization, hydrocracking, hydrotreatment, hydrofinishing). In the presence of hydrogen, this essentially reduces aromatic components and builds up naphthenic components.

[0044] Valuable information with regard to the analysis of mineral oils and a list of mineral oils which have a different composition can be found, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition on CD-ROM, 1997, under "lubricants and related products".

[0045] Synthetic oils include organic esters, for example diesters and polyesters, polyalkylene glycols, polyethers, synthetic hydrocarbons, especially polyolefins, among which preference is given to polyalphaolefins (PAOs), silicone oils and perfluoroalkyl ethers. In addition, it is possible to use synthetic base oils originating from gas to liquid (GTL), coal to liquid (CTL) or biomass to liquid (BTL) processes. They are usually somewhat more expensive than the mineral oils, but have advantages with regard to their performance.

[0046] GTL oils may be oils from Fischer-Tropsch-synthesized hydrocarbons made from synthesis gas containing hydrogen and carbon monoxide using a Fischer-Tropsch catalyst. These hydrocarbons typically require further processing in order to be useful as base oil. For example, they may, by methods known in the art be hydroisomerized, dewaxed, or hydroisomerized and dewaxed. Natural oils are animal or vegetable oils. Examples of vegetable oils which can be used in accordance with the invention are palm oil, rapeseed oil, coriander oil, soya oil, cottonseed oil, sunflower oil, castor oil, olive oil, groundnut oil, corn oil, almond oil, palm kernel oil, coconut oil, mustard seed oil, jojoba oil, jatropa oil, olive oil etc. Examples of animal fats which can be used in accordance with the invention are oils which are derived from animal tallow, especially beef tallow, bone oil, fish oils, lard, chicken oil, whale sperm, etc. and used cooking oils. Further examples include oils which derive from cereal, wheat, jute, sesame, rice husks, jatropha, arachis oil and linseed oil.

[0047] In a preferred example, the lubricant composition comprises an additional synthetic base oil, such as organic esters, synthetic hydrocarbons, polyalkylene glycols, polyethers, silicone oils (other than the polyorganosiloxane described above) and perfluoro-alkyl ethers. Particularly preferred examples for synthetic hydrocarbons are polyolefins, among which preference is given to polyalphaolefins.

[0048] The additional base oils are typically characterized by their kinematic viscosity, i.e. the kinematic viscosity of the pure base oil without any additives. Preferably, the additional base oils have a kinematic viscosity at 100°C according to ASTM D445 of 1 mm²/s to 20 mm²/s, more preferably 1 to 10 mm²/s, most preferably 1 to 5 mm²/s and especially preferred 2 to 3 mm²/s.

[0049] In a preferred embodiment, the lubricant compositions comprises 1 to 50% by weight, more preferably 5 to 30% by weight, most preferably 10 to 20% by weight, based on the total weight of the lubricant composition, of an additional base oil.

[0050] In one embodiment, the lubricant composition comprises a polyalphaolefin, preferably a polyalphaolefin having a kinematic viscosity at 100°C according to ASTM D445 of 1 mm²/s to 20 mm²/s, more preferably 1 to 10 mm²/s, most preferably 1 to 5 mm²/s and especially preferred 2 to 3 mm²/s. Preferably, the lubricant composition comprises 1 to 50% by weight, more preferably 5 to 30% by weight, most preferably 10 to 20% by weight, based on the total weight of the lubricant composition, of the polyalphaolefin.

[0051] The lubricant composition in accordance with the present invention may further comprise auxiliary additives selected from the group consisting of pour point depressants, antiwear agents, antioxidants, dispersants, detergents, friction modifiers, antifoam agents, extreme pressure additives, and corrosion inhibitors. The auxiliary additives are preferably added in an amount of 0.1 to 25% by weight, based on the total weight of the lubricant composition.

[0052] Suitable pour-point depressants include ethylene-vinyl acetate copolymers, chlorinated paraffin-naphthalene condensates, chlorinated paraffin-phenol condensates, polymethacrylates, polyalkylstyrenes, etc. Preferred are polymethacrylates having a mass-average molecular weight of from 5.000 to 50.000 g/mol.

[0053] The preferred antiwear and extreme pressure additives include sulfur-containing compounds such as zinc dithiophosphate, zinc di-C3-12-alkyldithiophosphates (ZnDTPs), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, polysulfides, etc.; phosphorus-containing compounds such as phosphites, phosphates, for example trialkyl phosphates, triaryl phosphates, e.g. tricresyl phosphate, amine-neutralized mono-and dialkyl phosphates, ethoxylated mono- and dialkyl phosphates,phosphonates, phosphines, amine salts or metal salts of those compounds, etc.; sulfur and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, amine salts or metal salts of those compounds, etc..

[0054] The suitable antioxidants include, for example, phenol-based antioxidants and amine-based antioxidants.

[0055] Phenol-based antioxidants include, for example, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; 4,4'-methylenebis(2,6-di-tert-butylphenol); 4,4' -bis(2,6-di-t-butylphenol); 4,4'-b is(2-methyl-6-t-butylphenol); 2,2' -methylenebis(4-ethyl-6-t-butylphenol); 2,2' - methylenebis(4-methyl-6-t-butyl phenol); 4,4'-butyl idenebis(3-methyl-6-t-butylphenol); 4,4'-isopropylidenebis(2,6-di-t-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-t-butyl-4-methylphenol; 2,6-di-t-butyl-4-ethyl-phenol; 2,4-dimethyl-6-t-butylphenol; 2,6-di-t-amyl-p-cresol; 2,6-di-t-butyi-4-(N,N'-dimethylaminomethylphenol); 4,4'thiobis(2-methyl-6-t-butylphenol); 4,4'-thiobis(3-methyl-6-t-butylphenol); 2,2'-thiobis(4-methyl-6-t-butylphenol); bis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide; bis(3,5-di-t-butyl-4-hydroxybenzyl) sulfide; n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; 2,2'-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], etc. Of those, especially preferred are bis-phenol-based antioxidants and ester group containing phenol-based antioxidants.

[0056] The amine-based antioxidants include, for example, monoalkyldiphenylamines such as monooctyldiphenylamine, monononyldiphenylamine, etc.; dialkyldiphenylamines such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphe nylamine, 4,4'- dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, etc.; polyalkyldiphenylamines such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, etc.; naphthylamines, concretely alpha-naphthylamine, phenyl-alpha-naphthylamine and further alkyl-substituted phenyl-alpha-naphthylamines such as butylphenyl-alpha-naphthylamine, pentylphenyl-alpha-naphthylamine, hexylphenyl-alpha-naphthylamine, heptylphenyl-alpha-naphthylamine, octylphenyl-alpha-naphthylamine, nonylphenyl-alpha-naphthylamine, etc. Of those, diphenylamines are preferred to naphthylamines, from the viewpoint of the antioxidation effect thereof.

[0057] Suitable antioxidants may further be selected from the group consisting of compounds containing sulfur and phosphorus, for example metal dithiophosphates, for example zinc dithiophosphates (ZnDTPs), "OOS triesters" = reaction products of dithiophosphoric acid with activated double bonds from olefins, cyclopentadiene, norbornadiene, α-pinene, polybutene, acrylic esters, maleic esters (ashless on combustion); organosulfur compounds, for example dialkyl sulfides, diaryl sulfides, polysulfides, modified thiols, thiophene derivatives, xanthates, thioglycols, thioaldehydes, sulfur-containing carboxylic acids; heterocyclic sulfur/nitrogen compounds, especially dialkyldimercaptothiadiazoles, 2-mercaptobenzimidazoles; zinc bis(dialkyldithiocarbamate) and methylene bis(dialkyldithiocarbamate); organophosphorus compounds, for example triaryl and trialkyl phosphites; organocopper compounds and overbased calcium- and magnesium-based phenoxides and salicylates.

[0058] Appropriate dispersants include poly(isobutylene) derivatives, for example poly(isobutylene)succinimides (PIBSIs), including borated PIBSIs; and ethylene-propylene oligomers having N/O functionalities.

[0059] The preferred detergents include metal-containing compounds, for example phenoxides; salicylates; thiophosphonates, especially thiopyrophosphonates, thiophosphonates and phosphonates; sulfonates and carbonates. As metal, these compounds may contain especially calcium, magnesium and barium. These compounds may preferably be used in neutral or overbased form.

[0060] Friction modifiers used may include mechanically active compounds, for example molybdenum disulfide, graphite (including fluorinated graphite), poly(trifluoroethylene), polyamide, polyimide; compounds that form adsorption layers, for example long-chain carboxylic acids, fatty acid esters, ethers, alcohols, amines, amides, imides; compounds which form layers through tribochemical reactions, for example saturated fatty acids, phosphoric acid and thiophosphoric esters, xanthogenates, sulfurized fatty acids; compounds that form polymer-like layers, for example ethoxylated dicarboxylic partial esters, dialkyl phthalates, methacrylates, unsaturated fatty acids, sulfurized olefins or organometallic compounds, for example molybdenum compounds (molybdenum dithiophosphates and molybdenum dithiocarbamates MoDTCs) and combinations thereof with ZnDTPs, copper-containing organic compounds.

[0061] Suitable antifoam agents are silicone oils, fluorosilicone oils, fluoroalkyl ethers, etc..

[0062] The above-detailed additives are described in detail, inter alia, in T. Mang, W. Dresel (eds.): "Lubricants and Lubrication", Wiley-VCH, Weinheim 2001; R. M. Mortier, S. T. Orszulik (eds.): "Chemistry and Technology of Lubricants".

[0063] The lubricant composition according to the invention can be useful for various applications including industrial gear oil, lubricant for wind turbine, compressor oil, hydraulic fluid, paper machine lubricant, engine or motor oil, transmission and/or drive-trains fluid, machine tools lubricant, metalworking fluids, and transformer oils to name a few.

[0064] The lubricant composition is preferably formulated to yield a certain kinematic viscosity at 40°C according to ASTM D445. This can be achieved by adjusting the relative amounts of polyorganosiloxane according to the invention, base oils and optional additives. Preferably, the lubricant composition has a kinematic viscosity at 40°C according to ASTM D445 of 10 to 120 mm²/s, more preferably 40 to 100 mm²/s, most preferably 70 to 80 mm²/s.

[0065] The lubricant composition produced by the use of the polyorganosiloxane according to the invention preferably has an R-factor of 1 to 8, more preferably 1 to 6.

[0066] In a further aspect the invention relates to a method of producing a lubricant composition having an R-factor of 1 to 8, preferably 1 to 6, wherein the R-factor is defined as the ratio of the kinematic viscosity of the lubricant composition at -20°C to the kinematic viscosity at +20°C measured according to ASTM D445, the method comprising the step of adding a polyorganosiloxane according to the present invention to a synthetic base oil, the synthetic base oil being preferably a polyalphaolefin base oil having a kinematic viscosity at 100°C according to ASTM D445 of 1 mm²/s to 20 mm²/s, more preferably 1 to 10 mm²/s, most preferably 1 to 5 mm²/s and especially preferred 2 to 3 mm²/s.

[0067] The method is preferably characterized by adding the polyorganosiloxane in an amount to get a lubricant composition with a kinematic viscosity at 40°C according to ASTM D445 of 10 to 120 mm²/s, more preferably 40 to 100 mm²/s, most preferably 70 to 80 mm²/s.

[0068] Another advantageous effect of using the polyorganosiloxane according to the invention is that it decreases flammability of the lubricant composition and, therefore, improves the lubricant composition's fire resistance. This effect may be quantified using the autoignition temperature determined according to ASTM D 2155 or the spray ignition characteristic according to ISO 15029-1.

[0069] In one embodiment, the lubricant composition produced by the use of the polyorganosiloxane according to the invention has an autoignition temperature determined according to ASTM D 2155 of at least 350°C, preferably at least 380°C, most preferably at least 400°C.

[0070] In one embodiment, the lubricant composition produced by the use of the polyorganosiloxane according to the invention has a spray ignition characteristic determined according to ISO 15029-1 of maximum 30 seconds, preferably not more than 25 seconds.

[0071] The spray ignition characteristic is defined as "Flame Persistence", which means the maximum time between the removal of igniting flame and extinction of combustion of the spray. The faster the spray combustion disappears, the better it is.

[0072] The lubricant composition produced by the use of the polyorganosiloxane according to the invention can be useful for various applications including industrial gear oil, lubricant for wind turbine, compressor oil, hydraulic fluid, paper machine lubricant, engine or motor oil, transmission and/or drive-trains fluid, machine tools lubricant, metalworking fluids, and transformer oils to name a few.

Experimental Part

Synthesis of polymers

[0073] The following polyorganosiloxanes are examples of the invention.

[0074] Polymer 1 is a cross-linked polyorganosiloxane obtained by hydrosilylation of a linear siloxane A having the formula [(CH₃)₃SiO_1/2]₂[(CH₃)₂SiO_2/2]₃₆[(CH₃)HSiO_2/2]₁₄, 1-octene, and a linear siloxane B having the formula [(CH₃)₂R³SiO_1/2]₂[(CH₃)₂SiO_2/2]₃₆[(CH₃)HSiO_2/2]₁₄, wherein R³ is vinyl. Specifically, 325 g siloxane A were placed together with 12 g siloxane B, 263 g 1-octene and 600 g toluene in a 2-L-three-necked flask with stirrer and Dimroth condenser. The mixture was heated to 100°C and 8 ppm of Pt in the form of the Karstedt catalyst were added. An exothermic reaction was observed. The mixture was stirred for additional 2 h at 100°C. Afterwards the volatile components were removed under reduced pressure (< 10 mbar) at 100°C. A colourless liquid was obtained without any formation of gel.

[0075] Polymer 2 is a non-crosslinked polyorganosiloxane obtained by hydrosilylation of a linear siloxane A having the formula [(CH₃)₃SiO_1/2]₂[(CH₃)₂SiO_2/2]₃₆[(CH₃)HSiO_2/2]₁₄ and 1-octene. Specifically, 336 g siloxane A were placed together with 264 g 1-octene and 600 g toluene in a 2-L-three-necked flask with stirrer and Dimroth condenser. The mixture was heated to 100°C and 8 ppm of Pt in the form of the Karstedt catalyst were added. An exothermic reaction was observed. The mixture was stirred for additional 2 h at 100°C. Afterwards the volatile components were removed under reduced pressure (< 10 mbar) at 100°C. A colourless liquid was obtained without any formation of gel.

[0076] Comparative copolymer 3 is a polyalkylmethacrylate prepared from 89.97% by weight dodecyl pentadecyl methacrylate and 10.03% by weight methyl methacrylate. Dodecyl pentadecyl methacrylate is a mixture of branched and linear C₁₂ to C₁₅ alkyl methacrylates with an average composition of 16 to 26% by weight C₁₂ alkyl methacrylate, 24 to 34% by weight C₁₃ alkyl methacrylate, 24 to 34% by weight C₁₄ alkyl methacrylate, and 16 to 26% by weight C₁₅ alkyl methacrylate, and approximately 80% linear alkyl methacrylates.

[0077] Comparative copolymer 4 is a polyalkylmethacrylate is prepared from 99.80% by weight C₁₂ to C₁₅ alkyl methacrylate (comprising 20% C₁₂ alkyl methacrylate, 34% C₁₃ alkyl methacrylate, 29% C₁₄ alkyl methacrylate, and 17% C₁₅ alkyl methacrylate, with approximately 40% linear alkyl methacrylates) and 0.20% by weight methyl methacrylate.

[0078] The polyalkylmethacrylates in comparative compositions 3 and 4 are known viscosity index improvers.

[0079] The following Table 1 shows the lubricant compositions which were prepared by mixing a poly-alpha-olefin base oil (PAO2) having a kinematic viscosity at 100°C of 2 mm²/s according to ASTM D445 and the indicated amount of polymers as viscosity index improvers targeting a KV₄₀ of 76 mm²/s.

Table 1: lubricant compositions comprising polysiloxanes, comparative copolymers and base oil

CompositionN o.	Base oil	polymer	Amount of copolymer [% by weight]**)
1	PAO2	siloxane 1	87.1
2	PAO2	siloxane 2	84.5
3	PAO2	copolymer 3	41.1	CE
4	PAO2	copolymer 4	48.5	CE

CE: comparative example

[0080] The lubricant compositions 1 to 4 were tested by determining the kinematic viscosity at different temperatures, the viscosity index and the R-factor. The kinematic viscosity was determined according to ASTM D445, the viscosity index was determined according to ASTM D2270, and the R-factor was calculated as the ratio of the kinematic viscosity at -20°C to the kinematic viscosity at +20°C. The results are given in the following Table 2.

Table 2: viscosity data of lubricant compositions

No.	Kinematic viscosity [mm2/s]							VI	R-factor
	100°C	40°C	20°C	10°C	0°C	-10°C	-20°C
1	24.36	77.30	137.7	194.6	289.8	456.8	778.4	341	5.65
2	24.10	76.61	136.6	193.1	286.9	453.6	769.7	339	5.63
3	17.55	76.08	165.0	264.3	450.8	825.2	1686	251	10.22	CE
4	14.83	76.39	180.2	304.5	550.5	1491	2375	205	13.18	CE

CE: comparative example

[0081] These results show that by using polyorganosiloxanes of the present invention, lubricant compositions having a good VI and an R-factor of less than 8 can be prepared. In contrast, the use of conventional viscosity index improvers are not as effective in improving low-temperature properties, albeit they are effective viscosity index improvers at a high temperature range of 40°C to 100°C. The invention, therefore, provides a surprising way of preparing lubricant compositions having superior low-temperature properties.

[0082] Further, the fire resistance properties of lubricant composition 1 were tested by determining the autoignition temperature and the spray ignition characteristic. The results are given in the following Table 3.

Table 3: fire resistance data

	Composition 1
Autoignition temperature according to ASTM D 2155	405°C
Spray ignition characteristic according to ISO 15029-1	25.1 seconds

[0083] These results show that the present invention provides a way of preparing lubricant compositions having improved fire resistance.

Claims

1. Use of a polyorganosiloxane to produce a lubricant composition having an R-factor of less than or equal to 8,
wherein the R-factor is defined as the ratio of the kinematic viscosity of the lubricant composition at -20°C to the kinematic viscosity at +20°C measured according to ASTM D445,
wherein the polyorganosiloxane is obtainable by hydrosilylation of

a) at least one siloxane A of general formula (I)

         M_a'M^H_b'D_d'D^H_e'T_g'T^H_h'Q_i,     (I),

wherein

a' is 0 to 80;

b' is 0 to 80;

d' is 10 to 1200;

e' is 0 to 100;

g' is 0 to 30;

h' is 0 to 20;

i' is 0 to 20;

with the proviso that the following conditions are satisfied

a' + b' is not more than 8;

g' + h' + i' is not more than 20;

b' + e' + h' is at least 1 and not more than 30;

b) at least one compound of general formula (II)

         CH₂=CHX     (II)

wherein

X is selected from hydrogen or an alkyl, aryl, alkaryl group having 1 to 30 carbon atoms, which is optionally substituted with one or more hydroxyl or methoxy groups;

and optionally

c) at least one siloxane B of general formula (III)

         M_aM^H_bM^V_cD_dD^H_eD^V_fT_gT^H_hQ_i     (III),

wherein

a is 0 to 80;

b is 0 to 80;

c is 0 to 80;

d is 10 to 1200;

e is 0 to 100;

f is 0 to 100;

g is 0 to 30;

h is 0 to 20;

i is 0 to 20;

with the proviso that the following conditions are satisfied

a + b + c is not more than 8;

g + h + i is not more than 20;

b + e + h is at least 1 and not more than 30;

c + f is at least 1 and not more than 20;

wherein

M is a building block [R¹₃SiO_1/2],

M^H is a building block [R¹₂R²SiO_1/2],

M^V is a building block [R¹₂R³SiO_1/2],

D is a building block [R¹₂SiO_2/2],

D^H is a building block [R¹R²SiO_2/2],

D^V is a building block [R¹R³SiO_2/2],

T is a building block [R¹SiO_3/2],

T^H is a building block [R²SiO_3/2],

Q is a building block [SiO_4/2],

each R¹ is independently selected from the group consisting of C₁ to C₁₈ alkyl and phenyl,
each R² is hydrogen, and
each R³ is independently selected from the group consisting of C₂ to C₁₈ alkenyl, or C₂ to C₁₈ alkynyl.

2. The use according to claim 1,
wherein for the siloxane A of general formula (I) the following conditions are satisfied:

a' + b' is 2,

g' + h' + i' is 0, and

b' + e' is at least 10.

3. The use according to any one of claims 1 to 2,
wherein for the siloxane B of general formula (III) the following conditions are satisfied:

a + b + c is 2,

g + h + i is 0, and

b + e is at least 10.

4. The use according to any one of claims 1 to 3,
wherein each R¹ is independently selected from methyl or phenyl group.

5. The use according to any one of claims 1 to 4,
wherein each R³ is independently selected from vinyl or allyl group.

6. The use according to any one of claims 1 to 5,
wherein the siloxane A is a compound of general formula (IV) M₂D_d'D^H_e' (IV),
wherein

d' is 10 to 80,

e' is 10 to 30, and

each R¹ is a methyl group.

7. The use according to any one of claims 1 to 6,
wherein the siloxane B is a compound of general formula (V)

         M^V₂D_dD^H_e     (V),

wherein

d is 10 to 80,

e is 10 to 30,

each R¹ is a methyl group, and
each R³ is a vinyl group.

8. The use according to any one of claims 1 to 7, wherein X is an alkyl group having 6 to 8 carbon atoms.

9. The use according to any one of claims 1 to 8,
wherein the compound according to formula (II) is 1-octene.

10. The use according to any one of claims 1 to 9,
wherein the lubricant comprises a polyalphaolefin base oil.

11. The use according to any one of claims 1 to 10,
wherein the lubricant comprises a polyalphaolefin base oil having a kinematic viscosity at 100°C according to ASTM D445 of 1 mm²/s to 20 mm²/s.

12. The use according to any one of claims 1 to 11,
wherein the lubricant has an R-factor of 1 to 6.