Patent Grant
8722600
The present application relates to lubricant oil formulations which comprise copolymers or graft copolymers which are formed from free-radically polymerizable monomers and which, in addition to ethylenically unsaturated compounds substituted by long alkyl chains, especially acrylates or methacrylates, additionally also comprise monomers with hydrogen bond donor functions. According to the invention, the monomer with the hydrogen bond donor property is present either in the polymer backbone or in the grafted side branches. In addition to polymers which contain monomers with hydrogen bond donor function, also disclosed are those which contain monomers which simultaneously bear hydrogen bond donor and hydrogen bond acceptor functions. The polymers are suitable as additives for lubricant oil formulations, for example for motor oils or for hydraulic fluids with improved wear performance. It has been found that the hydrogen bond donor functions in the polymer, but in particular the simultaneous presence of hydrogen bond donor and acceptor functions, have positive effects on wear protection, detergency and dispersancy.
Polyalkyl acrylates are common polymeric additives for lubricant oil formulations. Long alkyl chains (typical chain length: C8-C18) in the ester functionalities of the acrylate monomers impart a good solubility in a polar solvents, for example mineral oil, to polyalkyl acrylates. Common fields of use of the additives are hydraulic, gearbox or motor oils. A viscosity index (VI)-optimizing action is attributed to the polymers, from where the name VI improvers originates. A high viscosity index means that an oil possesses a relatively high viscosity at high temperatures (for example in a typical range of 70-140° C.) and a relatively low viscosity at low temperatures (for example in a typical range of −60-20° C.). The improved lubricity of an oil at high temperatures compared to a non-polyacrylate-containing oil which has an otherwise identical kinematic viscosity at, for example, 40° C. is caused by a higher viscosity in the increased temperature range. At the same time, in the case of utilization of a VI improver at relatively low temperature, as is present, for example, during the cold-start phase of an engine, a lower viscosity is recorded in comparison to an oil which otherwise has an identical kinematic viscosity at 100° C. As a result of the lower viscosity of the oil during the start-up phase of an engine, a cold start is thus eased substantially.
In recent times, polyacrylate systems which, as well as VI optimization, provide additional properties, for example dispersancy, have become established in the lubricants industry. Either alone or together with dispersant-inhibitor (DI) additives used specifically for dispersion purposes, such polymers have the effect, inter alia, that the oxidation products occurring as a result of stress on the oil contribute less to a disadvantageous viscosity rise. By means of improved dispersibility, the lifetime of a lubricant oil can be extended. By virtue of their detergent action, such additives likewise have the effect that the engine cleanliness, for example expressed by the piston cleanliness or ring sticking, is influenced positively. Oxidation products are, for example, soot or sludge. In order to impart dispersancy to polyacrylates, nitrogen-containing functionalities may be incorporated into the side chains of the polymers. Common systems are polymers which bear partly amine-functionalized ester side chains. Often, dialkylamine-substituted methacrylates, their methacrylamide analogs or N-hetero-cyclic vinyl compounds are used as comonomers for improving the dispersion capacity. A further class of monomer types which should be mentioned owing to their dispersancy in lubricants is that of acrylates with ethoxylate- or propoxylate-containing functions in the ester substituents. The dispersible monomers may be present either randomly in the polymer, i.e. are incorporated into the polymer in a classical copolymerization, or else grafted onto a polyacrylate, which results in systems with a non-random structure. There has to date been no targeted research for polyacrylates which, as well as the known advantages in relation to dispersancy detergency, also offer advantages in relation to wear reduction.
EP 164 807 (Agip Petroli S.p.A) describes a multi-functional VI improver with dispersancy, detergency and low-temperature action. The composition of the VI improvers corresponds to NVP-grafted polyacrylates which additionally contain difficult-to-prepare acrylates with amine-containing ethoxylate radicals.
DE-A 1 594 612 (Shell Int. Research Maatschappij N.V.) discloses lubricant oil mixtures which comprise oil-soluble polymers with carboxyl groups, hydroxyl groups and/or nitrogen-containing groups and a dispersed salt or hydroxide of an alkaline earth metal. As a result of the synergistic mode of action of these components, wear-reducing action is observed.
U.S. Pat. No. 3,153,640 (Shell Oil Comp.) includes copolymers consisting of long-chain esters of (meth)acrylic acid and N-vinyllactams, which exhibit an advantageous influence on wear in lubricant applications. The polymers described are random copolymers. Monomers having hydrogen bond donor function and graft copolymers are not mentioned.
In ASLE Transactions (1961, 4, 97-108), E. H. Okrent states that polyisobutylenes or polyacrylates used as VI improvers have influence on the wear behavior in the engine. No inferences are made on the chemistry used and the specific composition of the polymers. Wear-reducing action is accounted for merely with visco-elastic effects of polymer-containing oils. For example, no differences are detected between polyacrylate and PIB-containing oils in influence on wear.
Literature publications by Neudörfl and Schödel (Schmierungstechnik 1976, 7, 240-243; SAE Paper 760269; SAE Paper 700054; Die Angewandte Makromolekulare Chemie 1970, 2, 175-188) emphasize in particular the influence of the polymer concentration on the engine wear. Reference is made to the aforementioned article by E. H. Okrent and, in analogy to Okrent, no connection of a wear-improving action with the chemistry of the polymer is made. Generally, it is concluded that viscosity index improvers of low molecular weight bring improved wear results.
Like Neudörfl and Schödel, K. Yoshida (Tribology Transactions 1990, 33, 229-237) attributes effects of polymers on the wear behavior merely to viscometric aspects. Advantageous effects are explained with the preferred tendency to elastohydrodynamic film formation.
Almost without exception, the polymers known in the prior art are formed from monomers whose dispersing functionalities bear groups which are hydrogen bond acceptors (referred to hereinafter as H-bond acceptors), or, like dimethylaminopropylmethacrylamide, have both a functionality with exclusive hydrogen bond acceptor function (amine function in dimethylamino-propylmethacrylamide) and a functionality with hydrogen bond donor (referred to hereinafter as H-bond donor). It is a further feature of such polymers useful for motor oil applications that the monomers bearing N-heterocycle have preferably been grafted onto the polymer backbone. Polymers containing dimethylamino-propylmethacrylamide are, in contrast, random copolymers and not graft copolymers.
The inventive lubricant oil formulations which will be discussed in even more detail later may base be based either on motor or on gearbox oils, but it is also possible for improved hydraulic oils to result therefrom. In addition to viscometric properties, the influence on the tribological wear constitutes one of the most important quality demands on a hydraulic fluid. For this reason, so-called anti-wear components, which are usually sulfur- and phosphorus-containing and have a wear-reducing action on metals owing to their surface activity, are added to common hydraulic oils. Increasing wear tendencies in hydraulic pumps are observed especially during the overheating of hydraulic fluids under difficult operating conditions. Friction of individual components of the hydraulic system, volume flows with high pressure drop and the flow resistances in the line system lead to a temperature increase in the fluid and also to enhanced wear behavior.
The rheological properties of a modern hydraulic formulation are generally optimized by adding a polymeric viscosity index improver (VI improver). In most cases, polyalkyl methacrylates are used for this purpose. They are usually polymethacrylates which partly bear long-chain (C8-C18) alkyl substituents in their methacrylic ester groups. The thickening action of the polymer dissolved in the oil allows a maximum kinematic viscosity of the fluid to be enabled at high temperatures (usually measured at 100° C.). This reduces wear tendencies and a decline in the volumetric efficiency of a hydraulic pump. The viscosity-increasing action of the polymer is not as marked at relatively low temperatures (measured at 40° C.) as, for example, at 100° C. Too high a rise in the kinematic viscosity at relatively low temperatures, at which wear and efficiency losses as a result of increasing internal leakage rates in any case play a minor role, is thus prevented. A lowered viscosity at relatively low temperatures brings the advantage of operating a hydraulic plant with small hydromechanical losses. The optimized viscosity behavior, expressed by a maximum kinematic viscosity at 100° C. and a minimum viscosity at 40° C., is expressed by the viscosity index (VI index).
An additional wear-reducing effect independent of viscometric effects, which arises, for example, as a result of interaction with metal- or metal oxide-like surfaces (as described for anti-wear additives), has to date not been found for polyalkyl methacrylates. Were it possible by means of a polymer not just to optimize the rheology but also to improve the viscosity-independent wear behavior, this would be an elegant method of either reducing or entirely eliminating the content of common anti-wear components in hydraulic fluids.
It was therefore an object of the present invention
A hydraulic fluid of ISO grade 46, which, according to DIN 51524, has a kinematic viscosity, measured at 40° C., of 46 mm2/s+/−10%, should accordingly also lead to lower wear compared to a higher-viscosity fluid, for example in comparison with a hydraulic oil of ISO grade 68 (kinematic viscosity measured at 40° C.: 68 mm2/s+/−10%).
In such a comparison, the ISO 68 fluid should have a kinematic viscosity increased compared to the ISO 46 fluid not just at 40° C., but also at elevated temperatures, for example at 100° C.
These objects, and also further objects which are not stated explicitly but which can be derived or discerned directly from the connections discussed by way of introduction herein are achieved by a lubricant oil composition containing from 0.2 to 30% by weight, based on the overall mixture, of a copolymer formed from free-radically polymerized units of
Appropriate modifications of the inventive lubricant oil formulations are protected in the subclaims dependent upon claim 1. With regard to the process for preparing graft copolymers, claims 11 to 14 provide solutions to the underlying problems, while claims 15 to 20 protect particularly suitable polymers. In the context of claims 21 to 24 relate to advantageous embodiments in connection with hydraulic applications.
The inventive polymers with hydrogen bond donor functions in the polymer, especially the polymers with simultaneous presence of hydrogen bond donor and acceptor functions, have positive effects on wear protection, detergency and dispersancy of the lubricant oil formulations produced with them. The polymers therefore constitute a wear-reducing alternative or supplement to the phosphorus and sulfur additives customary in industry, and help to avoid their known disadvantages.
In relation to motor oils, the advantages achieved in wear behavior have a positive effect on the energy consumption, for example of a diesel or gasoline engine.
The inventive formulations lead to distinctly better wear results compared to conventional oils.
In the particular case of use in hydraulic oils, the copolymers may be used as VI improvers and, irrespective of the kinematic viscosity of the hydraulic oil, contribute to wear reduction in hydraulic units.
The wear protection is achieved either solely by the copolymer or together with common wear-reducing additives, for example friction modifiers.
As well as VI action and wear protection, the copolymers also exhibit pour point-depressing action.
The formulations produced using the inventive graft copolymers feature good corrosion behavior and also good oxidation resistance.
The kinematic viscosity of polymer solutions which comprise methacrylic acid grafted in accordance with the invention has been lowered substantially compared to the comparable polymer which contains exclusively methacrylic acid in the polymer backbone.
At the same time, the process according to the invention allows a series of further advantages to be achieved. These include:
The polymers which have VI and dispersing action and have been used to date in motor oils, as discussed above, comprise preferably monomer types with H-bond acceptor functionalities, which are especially N-heterocycles. It was therefore not directly foreseeable that the use of monomers with H-bond donor properties leads to polymers which possess the improved properties described.
The lubricant oils contain from 0.2 to 30% by weight, preferably from 0.5 to 20% by weight and more preferably from 1 to 10% by weight, based on the overall mixture, of a copolymer formed from free-radically polymerized units of
from 0 to 40% by weight of one or more (meth)acrylates of the formula (I)
Examples of components of the formula I include (meth)acrylates which derive from saturated alcohols, such as
The content of (meth)acrylates of the formula (I) is from 0 to 40% by weight, from 0.1 to 30% by weight or from 1 to 20% by weight, based on the total weight of the ethylenically unsaturated monomers of the main chain of the graft copolymers.
As a further component, the polymers contain from 35 to 99.99% by weight of one or more ethylenically unsaturated ester compounds of the formula (II)
These compounds of the formula (II) include (meth)acrylates, maleates and fumarates, each of which have at least one alcohol radical having from 6 to 40 carbon atoms.
Preference is given here to (meth)acrylates of the formula (IIa)
in which
R is hydrogen or methyl and R1 is a linear or branched alkyl radical having from 6 to 40 carbon atoms.
When the term (meth)acrylates is utilized in the context of the present application, this term in each case encompasses methacrylates or acrylates alone or else mixtures of the two. These monomers are widely known. They include
The ester compounds with long-chain alcohol radical can be obtained, for example, by reacting (meth)acrylates, fumarates, maleates and/or the corresponding acids with long-chain fatty alcohols to obtain generally a mixture of esters, for example (meth)acrylates with various long-chain alcohol radicals. These fatty alcohols include Oxo Alcohol® 7911 and Oxo Alcohol® 7900, Oxo Alcohol® 1100 from Monsanto; Alphanol® 79 from ICI; Nafol® 1620, Alfol® 610 and Alfol® 810 from Sasol; Epal® 610 and Epal® 810 from Ethyl Corporation; Linevol® 79, Linevol® 911 and Dobanol® 25L from Shell AG; Lial 125® from Sasol; Dehydad® and Lorol® from Henkel KGaA and Linopol® 7-11 and Acropol® 91.
The long-chain alkyl radical of the (meth)acrylates of the formula (II) has generally from 6 to 40 carbon atoms, preferably from 6 to 24 carbon atoms, more preferably from 8 to 18 carbon atoms, and may be linear, branched, mixed linear/branched or have cyclic parts. The preferred embodiment consists in using, as the methacrylates, a mixture of methyl methacrylate and C8-C18-alkyl methacrylates.
The alcohols with long-chain alkyl radicals, which are used to prepare the (meth)acrylic esters, are commercially available and consist generally of more or less broad mixtures of various chain lengths. In these cases, the specification of the number of carbon atoms relates generally to the mean carbon number. When an alcohol or a long-chain (meth)acrylic ester prepared using this alcohol is referred to in the context of the present application as “C-12” alcohol or “C-12” ester, the alkyl radical of these compounds will generally contain not only alkyl radicals having 12 carbon atoms but possibly also those having 8, 10, 14 or 16 carbon atoms in smaller fractions, the mean carbon number being 12. When, in the context of the present application, for example, a compound is referred to as C12-C18-alkyl acrylate, this means a mixture of esters of acrylic acid which is characterized in that linear and/or branched alkyl substituents are present and that the alkyl substituents contain between 12 and 18 carbon atoms.
The content of the (meth)acrylates of the formula (II) or (IIa) is from 35 to 99.99% by weight, from 40 to 99% by weight or from 50 to 80% by weight, based on the total weight of the ethylenically unsaturated monomers of the main chain of the graft copolymer.
To form the polymer, it is also possible for from 0 to 40% by weight, in particular from 0.5 to 20% by weight, based on the total weight, of one or more free-radically polymerizable further monomers to be involved. Examples thereof are
Examples of representatives include:
Also suitable are alkenes-1 having from 10 to 32 carbon atoms, which are obtained in the polymerization of ethylene, propylene or mixtures thereof, these materials in turn being obtained from hydrocracked materials.
An essential constituent of the inventive polymers is from 0.01 to 20% by weight of a compound of the formula (III)
Likewise conceivable is a grafting process with monomer d of the formula (III) or a grafting process both with monomer d of the formula (III) and with monomer e of the formula (IV) onto polymer consisting almost exclusively or exclusively of carbon and hydrogen. Processes for grafting heteroatom-containing monomers onto such purely hydrocarbon-containing polymers are known to those skilled in the art. Useful hydrocarbon-based polymers include, for example, copolymers of ethylene and propylene or hydrogenated styrene/diene copolymers. The grafted products of these polymers, just like the polyacrylates underlying the present invention, can be used as additives to lubricant oil formulations to improve the wear behavior and for the purpose of raising the viscosity index.
The definition of a functionality as a group with hydrogen bond acceptor or hydrogen bond donor action can be taken from the current literature or known chemical reference works, for example “Römpp Lexikon Chemie, 10th edition, 1999, Verlag Thieme Stuttgart New York”.
According to this, a hydrogen bond (H-bond) is an important form of secondary valence bond which forms between a hydrogen atom bonded covalently to an atom of an electronegative element (hydrogen bond donor, proton donor, X) and the solitary electron pair of another electronegative atom (proton acceptor, Y). In general, such a system is formulated as RX—H . . . YR′, where the dotted line symbolizes the hydrogen bond. Possible X and Y are mainly O, N, S and halogens. In some cases (e.g. HCN), C can also function as a proton donor. The polarity of the covalent bond of the donor causes a positive partial charge, δ+, of the hydrogen (proton), while the acceptor atom bears a corresponding negative partial charge, δ−.
Characteristic, structural and spectroscopic properties of a complex bonded via a hydrogen bond are:
For hydrogen atoms of structural units which are capable of forming H-bonds and are an H-donor, it is characteristic that they are bonded to relatively electronegative atoms, for example oxygen, nitrogen, phosphorus or sulfur. The terms “electronegative” or “electropositive” are familiar to those skilled in the art as a designation for the tendency of an atom in a covalent bond to pull the valence electron pair or pairs toward it in the sense of an asymmetric distribution of the electrons, which forms a dipole moment. A more detailed discussion of the terms “electronegativity” and “hydrogen bonds” can be found, for example, in “Advanced Organic Chemistry”, J. March, 4th edition, J. Wiley & Sons, 1992.
In some dimers, more than one hydrogen bond is formed, for example in dimers of carboxylic acids which form cyclic structures. Cyclic structures are frequently also favored energetically in higher oligomers, for example in oligomers of methanol above the trimers. The dissociation energy of the trimer into 3 monomers at 52 kJ·mol−1 is nearly four times as large as that of the dimer. Non-additivity in the dissociation energies per monomer is a typical property of complexes bonded via hydrogen bonds.
In the case of H-bond-forming functionalities, the present invention relates in particular to heteroatom-containing groups, where the heteroatom is preferably O, N, P or S. Even though a carbon-hydrogen bond can theoretically also function as an H-bond donor, such functions shall not fall within the scope of the claims made herein for functionalities with H-bond donor function.
Monomers with H-bond donor functions are, for example, the ethylenically unsaturated carboxylic acids and all of their derivatives which still have at least one free carboxyl group. Examples thereof are:
Further suitable monomers with H-bond donor function are acetoacetate-functionalized ethylenically unsaturated compounds, for example 2-acetoacetoxymethyl methacrylate or 2-acetoacetoxyethyl acrylate. These compounds may be present at least partly in the tautomeric enol form.
Also suitable as monomers with H-bond donor function are all ethylenically unsaturated monomers having at least one sulfonic acid group and/or at least one phosphonic acid group. These are all organic compounds which have both at least one ethylenic double bond and at least one sulfonic acid group and/or at least one phosphonic acid group. They include, for example:
Particular preference is given to 10-undecenoic acid.
Equally suitable as monomers are acid amides, which are known, just like the carboxylic acids, to be able to act simultaneously both as H-bond donors and as H-bond acceptors. The unsaturated carboxamides may either bear an unsubstituted amide moiety or an optionally mono-substituted carboxamide group. Suitable compounds are, for example:
Carboxylic esters likewise suitable as H-bond donors are:
The content of compounds which have one or more structural units capable of forming H-bonds and are H-donors is from 0.01 to 20% by weight, preferably from 0.1 to 15% by weight and more preferably from 0.5 to 10% by weight, based on the total weight of ethylenically unsaturated monomers used.
The polymers may optionally additionally contain with from 0 to 20% by weight or with from 0 to 10% by weight, based on the total weight of the copolymer, of one or more compounds of the formula (IV)
in which R10, R11 and R12 and R13 are each as already defined.
Examples of compounds of the formula (IV) include N,N-dimethylacrylamide and N,N-dimethylmethacrylamide, N,N-diethylacrylamide and N,N-diethylmethacylamide, aminoalkyl methacrylates such as tris(2-methacryloyloxyethyl)amine, N-methylformamidoethyl methacrylate, 2-ureidoethyl methacrylate; heterocyclic (meth)acrylates such as 2-(1-imidazolyl)-ethyl (meth)acrylate, 2-(4-morpholinyl)ethyl (meth)acrylate and 1-(2-methacryloylethyl)-2-pyrrolidone,
According to the invention, the compound d) of the formula (III) may be present either only in the backbone or only in the grafted-on side chains of the polymer formed.
If present, the compound e) of the formula (IV) is likewise present either only in the backbone or only in the grafted-on side chains of the polymer formed.
The percentage by weight of the different components is based generally on the total weight of the monomers used.
The lubricant oil composition also comprises, as a further component, from 25 to 90% by weight of mineral and/or synthetic base oil and altogether from 0.2 to 20% by weight, preferably from 0.5 to 10% by weight, of further customary additives, for example pour point depressants, VI improvers, aging protectants, detergents, dispersing assistants or wear-reducing components.
Typically, a plurality of these components have already been combined into so-called DI packages which are commercially available. Examples of such multipurpose additives which, in most cases, comprise P- and S-containing components as anti-wear additives are, for example,
The aforementioned ethylenically unsaturated monomers may be used individually or as mixtures. It is additionally possible to vary the monomer composition during the polymerization.
The preparation of the polymers from the above-described compositions is known per se. For instance, these polymers can be effected especially by free-radical polymerization, and also related processes, for example ATRP (=atom transfer radical polymerization) or RAFT (=reversible addition fragmentation chain transfer).
The customary free-radical polymerization is explained, inter alia, in Ullmanns's Encylopedia of Industrial Chemistry, Sixth Edition. In general, a polymerization initiator is used for this purpose.
These include the azo initiators well known in the technical field, such as AIBN and 1,1-azo-biscyclohexanecarbonitrile, and also peroxy compounds such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, tert-butyl peroctoate, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyisopropylcarbonate, 2,5-bis-(2-ethylhexanoylperoxy)-2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, dicumyl peroxide, 1,1-bis(tert-butylperoxy)cyclohexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis(4-tert-butylcyclohexyl) peroxydicarbonate, mixtures of two or more of the aforementioned compounds with one another, and also mixtures of the aforementioned compounds with compounds which have not been mentioned and can likewise form free radicals.
The ATRP process is known per se. It is assumed that it is a “living” free-radical polymerization, without any intention that this should restrict the description of the mechanism. In these processes, a transition metal compound is reacted with a compound which has a transferable atom group. This transfers the transferable atom group to the transition metal compound, which oxidizes the metal. This reaction forms a radical which adds onto ethylenic groups. However, the transfer of the atom group to the transition metal compound is reversible, so that the atom group is transferred back to the growing polymer chain, which forms a controlled polymerization system. The structure of the polymer, the molecular weight and the molecular weight distribution can be controlled correspondingly. This reaction is described, for example, by J-S. Wang, et al., J. Am. Chem. Soc., vol. 117, p. 5614-5615 (1995), by Matyjaszewski, Macromolecules, vol. 28, p. 7901-7910 (1995). In addition, the patent applications WO 96/30421, WO 97/47661, WO 97/18247, WO 98/40415 and WO 99/10387, disclose variants of the ATRP explained above.
In addition, the inventive polymers may be obtained, for example, also via RAFT methods. This process is presented in detail, for example, in WO 98/01478, to which reference is made explicitly for the purposes of disclosure.
The polymerization may be carried out at standard pressure, reduced pressure or elevated pressure. The polymerization temperature too is uncritical. However, it is generally in the range of −20°-200° C., preferably 0°-130° C. and more preferably 60°-120° C.
The polymerization may be carried out with or without solvent. The term solvent is to be understood here in a broad sense.
The polymerization is preferably carried out in a nonpolar solvent. These include hydrocarbon solvents, for example aromatic solvents such as toluene, benzene and xylene, saturated hydrocarbons, for example cyclohexane, heptane, octane, nonane, decane, dodecane, which may also be present in branched form. These solvents may be used individually and as a mixture. Particularly preferred solvents are mineral oils, natural oils and synthetic oils, and also mixtures thereof. Among these, very particular preference is given to mineral oils.
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. Mineral oils are also produced in a smaller proportion from raw materials of vegetable (for example from jojoba, rapeseed) or animal (for example neatsfoot oil) origin. Accordingly, mineral oils have, depending on their origin, different proportions of aromatic, cyclic, branched and linear hydrocarbons.
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. The fraction of n-alkanes in preferred mineral oils is less than 3% by weight, the proportion of O—, N— and/or S-containing compounds less than 6% by weight. The proportion of the aromatics and of the mono-methyl-branched paraffins is generally in each case in the range from 0 to 30% 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. 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 from approx. 18 to 31 carbon atoms:
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 Ullmanns's Encyclopedia of Industrial Chemistry, 5th Edition on CD-ROM, 1997, under “lubricants and related products”.
Synthetic oils include organic esters, organic ethers such as silicone oils, and synthetic hydrocarbons, especially polyolefins. They are usually somewhat more expensive than the mineral oils, but have advantages with regard to their performance.
Natural oils are animal or vegetable oils, for example neatsfoot oils or jojoba oils.
These oils may also be used as mixtures and are in many cases commercially available.
These solvents are used preferably in an amount of from 1 to 99% by weight, more preferably from 5 to 95% by weight and most preferably from 10 to 60% by weight, based on the total weight of the mixture. The composition may also have polar solvents, although their amount is restricted by the fact that these solvents must not exert any unacceptably disadvantageous action on the solubility of the polymers.
The molecular weights Mw of the polymers are from 1500 to 4 000 000 g/mol, in particular 5000-2 000 000 g/mol and more preferably 20 000-500 000 g/mol. The polydispersities (Mw/Mn) are preferably in a range of 1.2-7.0. The molecular weights may be determined by known methods. For example, gel permeation chromatography, also known as “size exclusion chromatography” (SEC), may be used. Equally useful for determining the molecular weights is an osmometric process, for example vapor phase osmometry. The processes mentioned are described, for example, in: P. J. Flory, “Principles of Polymer Chemistry” Cornell University Press (1953), Chapter VII, 266-316 and “Macromolecules, an Introduction to Polymer Science”, F. A. Bovey and F. H. Winslow, Editors, Academic Press (1979), 296-312 and W. W. Yau, J. J. Kirkland and D. D. Bly, “Modern Size Exclusion Liquid Chromatography”, John Wiley and Sons, New York, 1979. To determine the molecular weights of the polymers presented herein, preference is given to using gel permeation chromatography. It should preferably be measured against polymethyl acrylate or polyacrylate standards.
The residual monomer contents (for example C8-C18-alkyl acrylate, MMA, methacrylic acid, NVP) were determined by customary HPLC analysis processes. They are stated either in ppm or % by weight in relation to the total weight of the polymer solutions prepared. It should be mentioned by way of example for acrylates having long-chain alkyl substitution that the residual monomer content stated for C8-C18-alkyl acrylates for example includes all acrylate monomers used which bear alkyl substitutions in the ester side chains, which are characterized in that they contain between 8 and 18 carbon atoms.
The syntheses described in the present invention comprise the preparation of polymer solutions, by prescribing that the syntheses described cannot be undertaken without solvent. The kinematic viscosities specified relate accordingly to the polymer solutions and not the pure, isolated polymers. The term “thickening action” relates to the kinematic viscosity of a polymer solution, which is measured by diluting a certain amount of the polymer solution with a further solvent at a certain temperature. Typically, 10-15% by weight of the polymer solution prepared in each case are diluted in a 150N oil and the kinematic viscosities of the resulting solution are determined at 40° C. and 100° C. The kinematic viscosities are determined by customary processes, for example in an Ubbelohde viscometer or in automatic test apparatus from Herzog. The kinematic viscosity is always specified in mm2/s.
The process for preparing the graft copolymers of the present invention is characterized in that the polymers are prepared either by copolymerization of all individual components, or in that, in another embodiment, the backbone is prepared in a first step by free-radical polymerization of the monomers a), b) and c), and in that one or more of the monomers d) and, if appropriate, e) are then grafted onto the backbone in the second step.
In an advantageous embodiment of the process for preparing graft copolymers, after the grafting of one or more monomers of the formula (III), a further grafting process is carried out with one or more monomers of the formula (IV) which do not have structural units capable of forming H-bonds.
It is likewise possible to reverse the above-described sequence of the grafting steps. In this embodiment of the process for preparing graft copolymers, after the polymerization of the backbone, a grafting process is first carried out with one or more monomers of the formula (IV), followed by a further grafting process with one or more monomers of the formula (III).
The present process for preparing the graft copolymers can also be carried out advantageously by carrying out a grafting process using a mixture of in each case one or more monomers of the formulae (III) and (IV).
In a further advantageous embodiment of the present process for preparing graft copolymers, the grafting process is carried out up to 5 times in succession. In this case, a plurality of graftings with in each case a small amount of monomer, for example in each case 1% by weight of a monomer which can act as an H-bond donor, are carried out successively. When, for example, a total of 2% by weight of such a monomer is used for grafting, preference is given to carrying out two successive grafting steps with, for example, in each case 1% by weight of the monomer in question. It is clear to those skilled in the art that, depending on the individual case, it is also possible here to use a number of other values for the amounts of monomer used and for the number of grafting steps, so that they do not have to be listed individually here. It is self-evident that the multiple, up to 5-fold repetition of the grafting step can also be effected with mixtures of the monomers of the formulae (III) and (IV).
The N-functionalized monomer e) may be an N-vinyl-substituted monomer, for example N-vinylpyrrolidone, N-vinylcaprolactam, N-vinyltriazole, N-vinylbenzotriazole or N-vinylimidazole. In another embodiment, it may also be a vinylpyridine, for example 2-vinylpyridine. It may equally be a methacrylate or acrylate which contains an N-heterocycle in its ester function. In addition, the N-containing monomer may be an N,N-dialkylamino acrylate or its methacrylate analog, where the aminoalkyl groups contain 1-8 carbon atoms. With regard to the further possible compounds, reference is made at this point to the comprehensive list in the definition of the monomers of the formula (IV).
In practice, acid-functionalized polymers are often neutralized in polymer-like reactions with amines, polyamines or alcohols; methods for this purpose are disclosed, for example, by DE-A 2519197 (ExxonMobil) and U.S. Pat. No. 3,994,958 (Rohm & Haas Company). Just as in these two applications, the inventive polymers of the present application may subsequently be neutralized or esterified in a polymer-like reaction with primary or secondary amine compounds or alcohols. In this case, a partial or full neutralization of the polymers can be carried out.
In addition to VI, dispersancy and properties not discussed herein, for example oxidation stability, the influence of a lubricant oil on the wear behavior of a machine element is also of particular interest. Wear-reducing additives intended specifically for this purpose are generally added to lubricant oils. Such additives are usually phosphorus- and/or sulfur-containing. In the lubricants industry, there is a drive to reduce the phosphorus and sulfur input into modern lubricant oil formulations. This has both technical (prevention of exhaust gas catalytic converter poisoning) and environmental politics reasons. The search for phosphorus- and sulfur-free lubricant additives has thus become, specifically in the recent past, an intensive research activity of many additives manufacturers.
Advantages in the wear behavior can have a positive effect on the energy consumption, for example of a diesel or gasoline engine. The polymers of the present invention have to date not yet been connected with a positive effect on wear behavior.
The polymers of the present invention are superior to known, commercial polymers with N-functionalities in relation to wear protection.
According to the current state of the art, crankshaft drive, piston group, cylinder bore and the valve control system of an internal combustion engine are lubricated with a motor oil. This is done by conveying the motor oil which collects in the oil sump of the engine to the individual lubrication points by means of conveying pump through an oil filter (pressure circulation lubrication in conjunction with injection and oil-mist lubrication).
In this system, the motor oil has the functions of: transferring forces, reducing friction, reducing wear, cooling components, and gas sealing of the piston.
The oil is fed under pressure to the bearing points (crankshaft, connection rod and camshaft bearings). The lubrication points of the valve drive, the piston group, gearwheels and chains are supplied with injected oil, spin-off oil or oil mist.
At the individual lubrication points, forces to be transferred, contact geometry, lubrication rate and temperature vary within wide ranges in operation.
The increase in the power density of the engines (kW/capacity; torque/capacity) lead to higher component temperatures and surface pressures of the lubrication points.
To ensure the motor oil functions under these conditions, the performance of a motor oil is tested in standardized test methods and engine tests (for example API classification in the USA or ACEA test sequences in Europe). In addition, test methods self-defined by individual manufacturers are used before a motor oil is approved for use.
Among the abovementioned lubricant oil properties, the wear protection of the motor oil is of particular significance. As an example, the requirement list of the ACEA Test Sequences 2002 shows that, in each category (A for passenger vehicle gasoline engines, B for passenger vehicle diesel engines and E for heavy goods vehicle engines) with a separate engine test, the confirmation of sufficient wear protection for the valve drive is to be conducted.
The oil is exposed to the following stresses in operation:
The listed stresses of evaporation, oxidation, nitration, dilution with fuel and input of particles, owing to the engine operation, change the motor oil itself and components of the engine which are wetted with motor oil in operation. As a consequence, the following undesired effects for the trouble-free operation of the engine arise:
The reduction in the deposit formation and the provision of high detergency and dispersancy and also anti-wear action over a long utilization time are of central significance in current clearance procedures, as can be seen by the following example of ACEA test sequences from 1998:
For the present invention, the influence of the lubricant used on wear was measured by test method CEC-L-51-A-98. This test method is suitable both for the investigation of the wear behavior in a passenger vehicle diesel engine (ACEA category B) and in a heavy goods vehicle diesel engine (ACEA category E). In these test methods, the circumference profile of each cam is determined in 1° steps on a 2- or 3-D test machine before and after test, and compared. The profile deviation formed in the test corresponds to the cam wear. To assess the tested motor oil, the wear results of the individual cams are averaged and compared with the limiting value of the corresponding ACEA categories.
In a departure from the CEC test method, the test time was shortened from 200 h to 100 h. The investigations performed showed that clear differentiations can be made between the oils used even after 100 h, since significant differences in the wear were detected already after this time.
Oil A (see tables 1 and 2) of the present invention served as the first comparative example for the wear experiment. It was a heavy-duty diesel motor oil formulation of the category SAE 5W-30. As usual in practice, this oil was mixed up from a commercial base oil, in the present case Nexbase 3043 from Fortum, and also further typical additives. The first of these additives is Oloa 4549 from Oronite. The latter component is a typical DI additive for motor oils. In addition to ashless dispersants, the product also comprises components for improving the wear behavior. The latter components in Oloa 4549 are zinc and phosphorus compounds. Zinc and phosphorus compounds can be regarded as the currently most commonly used additives for improving the wear behavior. As a further additive, for the purpose of thickener or VI improver action, an ethylene-propylene copolymer (Paratone 8002 from Oronite) was used. As usual in practice, Paratone 8002 was used as a solution in a mineral oil. Even though their VI action is limited, ethylene-propylene copolymers are currently the most common VI improvers in passenger vehicle and heavy goods vehicle motor oils owing to their good thickening action. A noticeable wear-improving action has not been described to date for such systems. A polyacrylate was not used as an additive component for oil A. In summary, oil A was composed of 75.3% by weight of Nexbase 3043, 13.2% by weight of Oloa 4594 and 11.5% by weight of a solution of Paratone 8002.
The second comparative example used for the wear experiments was oil B (see tables 1 and 2). Oil B differs from oil A in that some of the Paratone 8002 was replaced by a polyacrylate, in the specific case the polyacrylate from comparative example 1. The polymer from comparative example 1 is an NVP-containing polyacrylate which has already been described as advantageous in relation to wear protection. The polyacrylate used for oil C (third comparative example for the wear study) stems from comparative example 2 and, unlike the polymer from comparative example 1, is a polymer with dispersing functionalities consisting of oxygen instead of nitrogen. In addition, the polymer solution from comparative example 2 comprises, as a further solvent component, a small amount of an alkyl alkoxylate to which a detergent action in the engine is attributed. As is evident from table 2, oils A and B, and also all further formulations used for the wear experiments, essentially do not differ with regard to their kinematic viscosity data. This can be seen with reference to the kinematic viscosities measured at 40 and 100° C. (denoted in table 2 as KV40° C. and KV100° C. respectively). Table 2 likewise shows that the formulations used do not differ markedly with regard to viscosity index (VI), total base number (TBN), cold-start behavior expressed by crank case simulator data (CCS), and temporary shear losses at high temperatures expressed by high-temperature high-shear data (HTHS). The KV40° C., KV100° C., VI, TBN, CCS and HTHS data were determined by the ASTM methods known to those skilled in the art.
Also with regard to corrosion behavior and oxidation resistance, no noticeable differences of the inventive formulations compared to the comparative examples were recognizable. By way of example, the inventive formulations D and E were examined with regard to their corrosion behavior in direct comparison with oils A, B and C (see table 3). These examinations were carried out to ASTM D 5968 for lead, copper and tin, and to ASTM D 130 for copper.
The oxidation behavior was determined using the PDSC method known to those skilled in the art (CEC L-85-T-99).
It was common to oils B, C, D and E that 3% by weight of the Paratone 8002 solution in each case was replaced by 3% by weight of the particular polyacrylate solution. Oils D and E are inventive formulations with regard to wear behavior.
The polymer from example 1 was found to be particularly advantageous (mean cam wear: 5.7 μm). The copolymer from example 3 which is simple to prepare was found to be improved over the prior art, indicated by a comparison in the cam wear of oil E compared to oil A.
Suitable base oils for the preparation of an inventive lubricant oil formulation are in principle any compound which ensures a sufficient lubricant film which does not break even at elevated temperatures. To determine this property, it is possible, for example, to use the viscosities, as laid down, for example, in the SAE specifications.
Particularly suitable compounds include those which have a viscosity which is in the range from 15 Saybolt seconds (SUS, Saybolt Universal Seconds) to 250 SUS, preferably in the range from 15 to 100 SUS, in each case determined at 100° C.
The compounds suitable for this purpose include natural oils, mineral oils and synthetic oils, and also mixtures thereof.
Natural oils are animal or vegetable oils, for example neatsfoot oils or jojoba oils. Mineral oils are obtained mainly by distillation of crude oil. They are advantageous especially with regard to their favorable cost. Synthetic oils include organic esters, synthetic hydrocarbons, especially polyolefins, which satisfy the abovementioned requirements. They are usually somewhat more expensive than the mineral oils, but have advantages with regard to their performance.
These base oils may also be used in the form of mixtures and are in many cases commercially available.
In addition to the base oil and the polymers mentioned herein, which already make contributions to the dispersion behavior and to the wear protection, lubricant oils generally comprise further additives. This is the case especially for motor oils, gearbox oils and hydraulic oils. The additives suspend solids (detergent-dispersant behavior), neutralize acidic reaction products and form a protective film on the cylinder surface (EP additive, “extreme pressure”). In addition, friction-reducing additives such as friction modifiers, aging protectants, pour point depressants, corrosion protectants, dyes, demulsifiers and odorants are used. Further valuable information can be found by those skilled in the art in Ullmanns's Encyclopedia of Industrial Chemistry, Fifth Edition on CD-ROM, 1998 edition. The inventive polymers of the present invention may, owing to their contribution to wear protection, ensure sufficient wear protection even in the absence of a friction modifier or of an EP additive. The wear-improving action is then contributed by the inventive polymer, to which friction modifier action could therefore be attributed.
The amounts in which abovementioned additives are used are dependent upon the field of use of the lubricant. In general, the proportion of the base oil is between 25 to 90% by weight, preferably from 50 to 75% by weight. The additives may also be used in the form of DI packages (detergent-inhibitor) which are widely known and can be obtained commercially.
Particularly preferred motor oils comprise, in addition to the base oil, for example,
The inventive lubricant oil may additionally, preferably in a concentration of 0.05-10.0 percent by weight, comprise an alkyl alkoxylate of the formula (V). The alkyl alkoxylate may be added to the lubricant oil composition directly, as a constituent of the VI improver, as a constituent of the DI package, as a constituent of a lubricant concentrate or subsequently to the oil. The oil used here may also be processed used oils.
R1-(CR2R3)n
z-L-A-R4 (V),
in which
Hydrocarbon radicals having up to 40 carbon atoms shall be understood to mean, for example, saturated and unsaturated alkyl radicals which may be linear, branched or cyclic, and also aryl radicals which may also comprise heteroatoms and alkyl substituents, which may optionally be provided with substituents, for example halogens.
Among these radicals, preference is given to (C1-C20)-alkyl, in particular (C1-C8)-alkyl and very particularly (C1-C4) -alkyl radicals.
The term “(C1-C4)-alkyl” is understood to mean an unbranched or branched hydrocarbon radical having from 1 to 4 carbon atoms, for example the methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, 2-methylpropyl or tert-butyl radical;
In addition, (C3-C8)-cycloalkyl radicals are preferred as the hydrocarbon radical. These include the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl group.
In addition, the radical may also be unsaturated. Among these radicals, preference is given to “(C2-C20)-alkenyl”, “(C2-C20)-alkynyl” and in particular to “(C2-C4) -alkenyl” and “(C2-C4) -alkynyl”. The term “(C2-C4)-alkenyl” is understood to mean, for example, the vinyl, allyl, 2-methyl-2-propenyl or 2-butenyl group;
In addition, preference is given to aromatic radicals such as “aryl” or “heteroaromatic ring systems”. The term “aryl” is understood to mean an isocyclic aromatic radical having preferably from 6 to 14, in particular from 6 to 12 carbon atoms, for example phenyl, naphthyl or biphenylyl, preferably phenyl;
The R2 or R3 radicals which may occur repeatedly in the hydrophobic moiety of the molecule may each be the same or different.
The linking L group serves to join the polar alkoxide moiety to the nonpolar alkyl radical. Suitable groups include, for example, aromatic radicals such as phenoxy (L=—C6H4—O—), radicals derived from acids, for example ester groups (L=—CO—O—), carbamate groups (L=—NH—CO—O—) and amide groups (L=—CO—NH—), ether groups (L=—O—) and keto groups (L=—CO—). Preference is given here to particularly stable groups, for example the ether, keto and aromatic groups.
As mentioned above, n is an integer in the range from 4 to 40, in particular in the range from 10 to 30. If n is greater than 40, the viscosity which is generated by the inventive additive generally becomes too great. If n is less than 4, the lipophilicity of the molecular moiety is generally insufficient to keep the compound of the formula (V) in solution. Accordingly, the nonpolar moiety of the compound (V) of the formula (VI) contains preferably a total of from 10 to 100 carbon atoms and most preferably a total of from 10 to 35 carbon atoms.
The polar moiety of the alkyl alkoxylate is illustrated by A in formula (V). It is assumed that this moiety of the alkyl alkoxylate can be illustrated by the formula (VII)
in which the R5 radical is hydrogen, a methyl radical and/or ethyl radical, and m is an integer in the range form 2 to 40, preferably from 2 to 25, in particular 2 and 15, and most preferably from 2 to 5. In the context of the present invention, the aforementioned numerical values are to be understood as mean values, since this moiety of the alkyl alkoxylate is generally obtained by polymerization. If m is greater than 40, the solubility of the compound in the hydrophobic environment is too low, so that there is opacity in the oil, in some cases precipitation. When the number is less than 2, the desired effect cannot be ensured.
The polar moiety may have units which are derived from ethylene oxide, from propylene oxide and/or from butylene oxide, preference being given to ethylene oxide. In this context, the polar moiety may have only one of these units. These units may also occur together randomly in the polar radical.
The number z results from the selection of the connecting group, and from the starting compounds used. It is 1 or 2.
The number of carbon atoms of a nonpolar moiety of the alkyl alkoxylate of the formula (VI) is preferably greater than the number of carbon atoms of the polar moiety A, probably of the formula (VII), of this molecule. The nonpolar moiety preferably comprises at least twice as many carbon atoms as the polar moiety, more preferably three times the number or more.
Alkyl alkoxylates are commercially available. These include, for example, the ®Marlipal and ®Marlophen types from Sasol and the ®Lutensol types from BASF.
These include, for example, ®Marlophen NP 3 (nonylphenol polyethylene glycol ether (3EO)), ®Marlophen NP 4 (nonylphenol polyethylene glycol ether (4EO)), ®Marlophen NP 5 (nonylphenol polyethylene glycol ether (5EO)), ®Marlophen NP 6 (nonylphenol polyethylene glycol ether (6EO));
Products and Starting Materials Used:
The starting materials such as initiators or chain transferrers used for the polymer syntheses described herein were entirely commercial products, as obtainable, for example, from Aldrich or Akzo Nobel. Monomers, for example MMA (Degussa), NVP (BASF), DMAPMAM (Degussa), 10-undecenoic acid (Atofina) or methacrylic acid (Degussa) were likewise obtained from commercial sources. Plex 6844-0 was a methacrylate containing urea in the ester radical from Degussa.
For other monomers used herein, for example C8-C18-alkyl methacrylates or ethoxylated methacrylates, reference is made to the description of the present application. This is equally true for the more precise description of the solvents used, for example oils or alkyl alkoxylates.
Explanations of Terms, Test Methods
When an acrylate or, for example, an acrylate polymer or polyacrylate is discussed in the present invention, this is understood to mean not only acrylates, i.e. derivatives of acrylic acid, but also methacrylates, i.e. derivatives of methacrylic acid, or else mixtures of systems based on acrylate and methacrylate.
When a polymer is referred to as a random polymer in the present application, this means a copolymer in which the monomer types used are distributed randomly in the polymer chain. Graft copolymers, block copolymers or systems with a concentration gradient of the monomer types used along the polymer chain are referred to in this context as non-random polymers or non-randomly structured polymers.
Motor Oil Formulations
Wear tests were carried out to the method CEC-L-51-A-98.
Hydraulic Formulations
The wear protection capacity was determined by the Vickers pump test (DIN 51389 part 2). For this test, as prescribed, a V 105-C vane pump was used. This was operated at a speed of 1440 min−1. The size of the full-flow filter used was 10 μm, the difference between liquid level and pump inlet 500 mm. Under these conditions, delivery flow rates of 38.7 1/min at 0 bar and of 35.6 1/min at 70 bar were established. As laid down in DIN 51389 part 2, the fluid temperature to be established was adjusted to the kinematic viscosity of the particular hydraulic fluid, i.e. a liquid with a relatively high kinematic viscosity at 40° C. was heated to a higher temperature for the wear test than a lower-viscosity fluid. The fluids used for the wear tests, including data on composition, viscosity and viscosity index, can be taken from table 4. The pump operating conditions during the wear tests and the particular results for wear on ring and vane can be found in table 5.
The formulations were prepared according to DIN 51524. The kinematic viscosities of the oils of IOS grade 46 (F, G and H in Tab. 4) were accordingly in the viscosity region of 46 mm2/s +/−10%, and the viscosity of the oil with ISO grade 68 (oil I) in a region of 68 mm2/s +/−10%. Oils F and G were polyalkyl methacrylate-containing liquids. G contained a polymer which is used in a standard manner as a VI improver for hydraulic oils.
In contrast, the polymer from example 6 present in oil F had a composition as is typically not used for hydraulic applications. Oils H and I did not contain any polyalkyl methacrylates. Owing to their content of VI improver, the viscosity indices of F and G had been raised. Owing to its higher ISO grade, oil I had an increased base viscosity over F, G and H. The selection of the above oils thus ensured that any wear-reducing effects occurring could not be investigated with regard to purely viscometric effects, but rather with regard to polymer-based effects. In other words: should a high base viscosity contribute to reduced wear, the best results should be expected with the ISO 68 oil I. Should a maximum viscosity index be required, no great differences should be expected between F and G. The DI package used for all formulations shown in Tab. 4 was the commercial product Oloa 4992 from Oronite. The concentration of Oloa 4992 was kept constant at 0.6% by weight for all formulations investigated.
It can be seen that the inventive formulation F leads to distinctly better wear results compared to all other hydraulic oils used (see Tab. 5). This became noticeable by a reduced loss of mass both on the ring and on the vane of the pumps used in comparison to all experiments. It can be stated that the improved results are attributable to the use of the inventive formulation F comprising the polymer from example 6.
For hydraulic oil formulations, the lubricant oil compositions preferably contain a polymer in which monomers a) and b) are preferably selected from the monomers methyl methacrylate, n-butyl methacrylate, 2-ethyhexyl methacrylate, isononyl methacrylate, isodecyl methacrylate, dodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate and octadecyl methacrylate.
The inventive lubricant oil compositions are characterized in that the copolymer is used as a VI improver and contributes to wear reduction in hydraulic units irrespective of the kinematic viscosity of the hydraulic oil.
The inventive lubricant oil compositions are also characterized in that the wear protection is provided either solely by the copolymer or together with common wear-reducing additives, for example friction modifiers.
In the inventive hydraulic formulations, the copolymer is present in the solution in 1-30% by weight, in particular 2-20% by weight and particularly advantageously in 3-15% by weight.
The inventive hydraulic formulations are characterized in that the copolymer provides, in addition to VI action and wear protection, also pour point-depressing action.
In the inventive hydraulic formulations, other common lubricant oil additives may be present in addition to the copolymers, for example antioxidants, corrosion inhibitors, antifoams, dyes, dye stabilizers, detergents, pour point depressants or DI additives.
The inventive hydraulic formulations may be used in a vane pump, a gear pump, radial piston pump or an axial piston pump.
Polymer Syntheses
(Polyacrylate with 3% by weight of NVP in the grafted part)
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 430 g of a 150N oil and 47.8 g of a monomer mixture consisting of C12-C18-alkyl methacrylates and methyl methacrylate (MMA) in a weight ratio of 99/1. The temperature is adjusted to 100° C. Thereafter, 0.71 g of tert-butyl peroctoate is added and, at the same time, a monomer feed consisting of 522.2 g of a mixture of C12-C18-alkyl methacrylates and methyl methacrylate in a weight ratio of 99/1 and 3.92 g of tert-butyl peroctoate is started. The feed time is 3.5 hours and the feed rate is uniform. Two hours after the feeding has ended, another 1.14 g of tert-butyl peroctoate are added. The total reaction time is 8 hours. The mixture is then heated to 130° C. After 130° C. has been attained, 13.16 g of a 150N oil, 17.45 g of N-vinylpyrrolidone and 1.46 g of tert-butyl perbenzoate are added. One hour, 2 hours and 3 hours therafter, another 0.73 g of tert-butyl perbenzoate is added in each case. The total reaction time is 8 hours. The polymer solution of a pour point improver which makes up 7 percent by weight of the overall solution is then added.
(Polyalkyl Acrylate Dissolved in a Mixture of Oil and an Ethoxylate)
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 400 g of a 150N oil and 44.4 g of a monomer mixture consisting of C12-C18-alkyl methacrylates, methyl methacrylate (MMA) and of a methacrylate ester of an iso-C13 alcohol with 20 ethoxylate units in a weight ratio of 87.0/0.5/12.5. The temperature is adjusted to 90° C. After 90° C. has been attained, 1.75 g of tert-butyl peroctoate are added and, at the same time, a feed of 555.6 g of a mixture consisting of C12-C18-alkyl methacrylates, methyl methacrylate and of a methacrylate ester of an iso-C13 alcohol with 20 ethoxylate units in a weight ratio of 87.0/0.5/12.5, and also 2.78 g of tert-butyl peroctoate is started. The feed time is 3.5 hours. The feed rate is uniform. Two hours after the feeding has ended, another 1.20 g of tert-butyl peroctoate are added. The total reaction time is 8 hours. The polymer solution of a pour point improver is then added, which is present thereafter to an extent of 5 percent by weight. The solution is then diluted with an ethoxylated iso-C13 alcohol which contains 3 ethoxylate units in a ratio of 79/21.
Random Polyacrylate with 3% by Weight of Methacrylic Acid in the Polymer Backbone
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser was initially charged with 430 g of a 150N oil and 47.8 g of a monomer mixture consisting of C12-C18-alkyl methacrylates, methyl methacrylate and methacrylic acid in a weight ratio of 82.0/15.0/3.0. The temperature is adjusted to 100° C. After the 100° C. has been attained, 0.38 g of tert-butyl peroctoate is added and, at the same time, a feed of 522.2 g of a mixture consisting of C12-C18-alkyl methacrylate, methyl methacrylate and methacrylic acid in a weight ratio of 82.0/15.0/3.0 together with 2.09 g of tert-butyl peroctoate (dissolved in the monomer mixture) is started. The feed time is 3.5 hours and the feed rate is uniform. Two hours after the feeding has ended, another 1.14 g of tert-butyl peroctoate are added. The total reaction time is 8 hours. The mixture is then diluted with 150N oil down to an overall polymer content of 45% by weight. A clear reaction product with a homogeneous appearance is obtained.
Polyacrylate with 3% by Weight of Methacrylic Acid in the Polymer Backbone and 3% by Weight of NVP in the Grafted Part
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 430 g of a 150N oil and 47.8 g of a monomer mixture of C12-C18-alkyl methacrylate and methacrylic acid in a weight ratio of 87.0/3.0. The temperature is adjusted to 100° C. After the 100° C. has been attained, 0.66 g of tert-butyl peroctoate is added and, at the same time, a feed of 522.2 g of a monomer mixture of C12-C18-alkyl methacrylate and methacrylic acid in a weight ratio of 87/3 together with 3.66 g of tert-butyl peroctoate is started. The feed time is 3.5 hours and the feed rate is uniform. Two hours after the feeding has ended, another 1.14 g of tert-butyl peroctoate are added. The total reaction time is 8 hours. The mixture is then heated to 130° C., and then 13.16 g of 150N oil, 17.45 g of N-vinylpyrrolidone (NVP) and 1.46 g of tert-butyl perbenzoate are added. One hour and 2 hours thereafter, another 0.73 g of tert-butyl perbenzoate is added in each case. The total reaction time is 8 hours. A reaction product with homogeneous appearance is obtained.
Random Polyacrylate with 3% by Weight of the Urea-Derivatized Methacrylates Plex 6844-0 in the Polymer Backbone
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 430 g of 150N oil and 47.8 g of a monomer mixture of C12-C18-alkyl methacrylate, methyl methacrylate and Plex 6844-0 in a weight ratio of 82.0/15.0/3.0. The temperature is adjusted to 100° C. After the 100° C. has been attained, 0.56 g of tert-butyl peroctoate is added and, at the same time, a feed of 522.2 g of a mixture of C12-C18-alkyl methacrylate, methyl methacrylate and Plex 6844-0 in a weight ratio of 82.0/15.0/3.0 together with 3.13 g of tert-butyl peroctoate is started. The feed time is 3.5 hours and the feed rate is uniform. Two hours after the feeding has ended, another 1.14 g of tert-butyl peroctoate are added. The total reaction time is 8 hours. A slightly opaque reaction product which nevertheless has a homogeneous appearance is obtained.
Random Polyalkyl Acrylate with 10% by Weight of Methacrylic Acid in the Polymer Backbone
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 300 g of 150N oil and 33.3 g of a monomer mixture of C12-C15-alkyl methacrylate and methacrylic acid in a weight ratio of 90.0/10.0. The temperature is adjusted to 100° C. After the 100° C. had been attained, 0.36 g of tert-butyl peroctoate, 0.63 g of dodecyl mercaptan and 0.63 g of tert-dodecyl mercaptan are added and, at the same time, a feed of 666.7 g of a mixture of C12-C15-alkyl methacrylate and methacrylic acid in a weight ratio of 90.0/10.0, together with 2.00 g of tert-butyl peroctoate, 12.67 g of dodecyl mercaptan and 12.67 g of tert-dodecyl mercaptan is started. The feed time is 3.5 hours and the feed rate is uniform. The total reaction time is 8 hours. 30 minutes after the feeding has ended, the mixture is diluted with 150N oil in relation to a total polymer content of 50% by weight. One and two hours after the feeding has ended, another 1.40 g of tert-butyl peroctoate are added in each case. A clear reaction product with a homogeneous appearance is obtained.
Random 10-Undecenoic Acid-Containing Polyalkyl Acrylate
A 2 liter four-neck flask equipped with saber stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 240 g of 10-undecenoic acid. The temperature is adjusted to 140° C. After the 140° C. has been attained, a mixture of C9-C13-alkyl methacrylate with a 20-tuply ethoxylated methacrylate (prepared by, for example, a transesterification of MMA with Lutensol TO20 from BASF) in a weight ratio of 71.43/28.57 is added, and 6.14 g of 2,2-bis(t-butylperoxy)butane (50% in white oil) are added dropwise separately. The feed time is 7 hours for the monomer mixture and 11 hours for the initiator solution. After the initiator feed has ended, the mixture is allowed to react for a further hour. A clear reaction product with a homogeneous appearance is obtained.
Kinematic viscosity at 100° C.: 153 mm2/s
Synthesis of the Polymers for Hydraulic Formulations
The polymers were synthesized as described below in example 6 and comparative example 3 by means of solution polymerization in a mineral oil. The resulting polymer solutions in oil were, as specified in table 4, used to prepare the hydraulic oils F and G.
A 20 liter polymerization reactor equipped with stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 4125 g of a 100 N oil, 2.07 g of dodecyl mercaptan, 2.9 g of tert-butyl-peroctoate and 460.4 g of a monomer mixture consisting of C12-C18-alkyl methacrylates, methyl methacrylate and methacrylic acid in a weight ratio of 86.0/11.0/3.0. The temperature is adjusted to 104° C. After the 104° C. has been attained, a mixture consisting of 26 g of tert-butyl peroctoate, 46.86 g of dodecyl mercaptan and 10 414.6 g of a mixture of C12-C18-alkyl methacrylate, methyl methacrylate and methacrylic acid (weight ratio as above: 86.0/11.0/3.0) is metered in. The feed time is 214 min and the feed rate is uniform. Two hours after the feeding has ended, another 21.8 g of tert-butyl peroctoate are added. The total reaction time is 10 hours. 7.5 g of a demulsifier (Synperonic PE/L 101 from Uniqema) are then added. A clear reaction product with a homogeneous appearance is obtained.
A 20 liter polymerization reactor equipped with stirrer (operated at 150 revolutions per minute), thermometer and reflux condenser is initially charged with 4125 g of a 100 N oil, 3.45 g of dodecyl mercaptan, 2.9 g of tert-butyl peroctoate and 460.4 g of a monomer mixture consisting of C12-C18-alkyl methacrylates, methyl methacrylate and methacrylic acid in a weight ratio of 86.0/14.0. The temperature is adjusted to 100° C. After the 100° C. had been attained, a mixture consisting of 26 g of tert-butyl peroctoate, 78.11 g of dodecyl mercaptan and 10 414.6 g of a mixture of C12-C18-alkyl methacrylate and methyl methacrylate (weight ratio as above: 86.0/14.0) is metered in. The feed time is 214 min and the feed rate is uniform. Two hours after the feeding has ended, another 21.8 g of tert-butyl peroctoate are added. The total reaction time is 10 hours. 7.5 g of a demulsifier (Synperonic PE/L 101 from Uniqema) are then added. A clear reaction product with a homogeneous appearance is obtained.
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