Patent Description:
The present invention relates to the field of lubrication. Lubricants are compositions that reduce friction between surfaces. In addition to allowing freedom of motion between two surfaces and reducing mechanical wear of the surfaces, a lubricant also may inhibit corrosion of the surfaces and/or may inhibit damage to the surfaces due to heat or oxidation. Examples of lubricant compositions include, but are not limited to, engine oils, transmission fluids, gear oils, hydraulic fluids, industrial lubricating oils, greases and metalworking oils.

Lubricants typically contain a base fluid and variable amounts of additives. Conventional base fluids are hydrocarbons, such as mineral oils. The terminology base oil or base fluid is commonly used interchangeably. Here, base fluid is used as a general term.

A wide variety of additives may be combined with the base fluid, depending on the intended use of the lubricant. Examples of lubricant additives include, but are not limited to, viscosity index improvers, thickeners, pour point depressants, oxidation inhibitors, corrosion inhibitors, dispersing agents, high pressure additives, anti-foaming agents and metal deactivators.

Typical non-polymeric base fluids are less effective as lubricants, because of their low viscosity and further decreased viscosity at higher operating temperatures. Therefore, polymeric additives are used to thicken the base oil and reduce the change in viscosity with change in temperature. The term Viscosity Index (VI) is used to describe this change in viscosity with temperature. The lower the VI, the greater the change in viscosity with temperature, and vice versa. Thus, a high VI is desired for lubricant formulations. In order to improve the VI, polymeric additives or Viscosity Index Improvers (VII) may be added to a lubricant formulation.

It is well-known in the art that alkyl acrylates are not recommended in VI improver applications, and commercial VI improvers are usually based on methacrylates. While literature (<NPL>; <NPL>) and patents (<CIT>) exist, it is generally known that the performance of polyacrylates as VI improver is inferior to the ones of polymethacrylates. Especially in <CIT>, it is mentioned that it was unexpectedly found that poly(alkyl acrylate) esters typically fail to adequately reduce the effect of temperature on viscosity when used in the hydraulic fluids.

The drawback of adding polymeric additives to a lubricant formulation is that they will undergo shear stress and will mechanically degrade over time. Higher molecular weight polymers are better thickeners but will be more prone to shear stress leading to polymer degradation. In order to decrease the amount of polymer degradation, the molecular weight of a polymer can be decreased, thereby obtaining a more shear stable polymer. However, these shear stable low molecular weight polymers are no longer very effective thickeners and must be used in larger concentrations in the lubricant in order to reach a desired viscosity. These low molecular weight polymers typically have molecular weights below <NUM>,<NUM>/mol and are also called synthetic high viscosity base fluids. High viscosity base fluids are used to lift the VI and to thicken lubricant formulations with demanding shear stability requirements. A typical application are gear oils which have very demanding requirements due high mechanical stress and a broad temperature range in operation.

Typical products in this market are high viscosity polyalphaolefins (PAOs) and metallocene polyalphaolefins (mPAOs), typically sold in viscosity ranges from <NUM> to <NUM> cSt at <NUM> (<NPL>), whose key feature is good handling properties in term of viscosity since these base fluids are polymeric in nature and provide for an improved viscosity index. However, the apolar nature of the PAO base oils is a disadvantage as can lead to poor solubility of DI packages and ageing products in oil, which can cause subsequent problems.

It has been already described that higher polarity is provided by copolymers of alpha-olefins with maleates (<CIT>), copolymers of alpha-olefins and acrylates (<CIT>), copolymers of alpha-olefins and methacrylates (<CIT>) or terpolymers based on the aforementioned monomers (<CIT>). Another example is <CIT>, which describes acrylate-olefin copolymers for use as high viscosity base stocks or lubricant additives in a lubricating oil composition. The resulting lubricating oil compositions show good low temperature properties and good viscosity index level, when compared with methacrylate-olefin copolymers and pure polyacrylates. The document is silent on the problem of dispersancy and sludge sedimentation.

<CIT> relates to copolymers prepared by a reaction of (<NUM>) an unactivated olefin, (<NUM>) an activated olefin, and (<NUM>) a hydroxyl functional activated olefin and/or a hydroxyl functional unactivated olefin. It is described that these copolymers are well suited for optically clear, pressure sensitive, polyurethane and/or barrier adhesives.

Dispersant additives can prevent sedimentation of sludge and contribute to better ratings in the test and finally longer lifetimes of the finished lubricants. The disadvantage of dispersing sludge is a viscosity increase of the lubricant. Keeping this viscosity increase as low as possible is a major performance parameter for a dispersant. Typical dispersants are for example end-functionalized polyisobutylene (PIB) oligomers. PAMAs with nitrogen functionality are also well-known as dispersants additives (see for example <CIT>).

There is still the need to provide highly shear stable synthetic base fluids or lubricating oil additives, which, in lubricant oil compositions, have a positive influence on oil solubility and component solubility, as well as on low temperature performance. Furthermore, the new products should not only be able to thicken an oil to a desired viscosity, but should also improve the sludge sedimentation and dispersancy performance of the resulting lubricating oil composition.

The inventors of the present invention have surprisingly found that hydroxy-functionalized acrylate-olefin copolymers comprising a certain amount of hydroxy-functional (meth)acrylate ester, as defined in claim <NUM>, are able to thicken very efficiently an oil to a desired viscosity, and simultaneously also improve the sludge sedimentation and dispersancy performance of the resulting lubricating oil composition. As exemplified in the experimental part of the present invention, it has unexpectedly been found that the specific weight ratio combination of acrylate monomers, with C<NUM>-C<NUM> alpha-olefins and hydroxy-functional (meth)acrylate ester monomers, as defined in claim <NUM>, are crucial to achieve a combination of good thickening properties and excellent sludge sedimentation reduction, while still maintaining good low temperature properties. Furthermore, these copolymers are highly shear stable and have a high viscosity index to reduce the effect of changes in viscosity with temperature.

Accordingly, a first aspect of the invention is a lubricant formulation comprising a base oil and a hydroxy-functionalized acrylate-olefin copolymer comprising hydroxy-functional (meth)acrylate ester monomer units as defined in claim <NUM> and its dependent claims.

A second aspect of the invention is a method for preparing the lubricant formulation according to the invention.

A third aspect of the invention is a method of thickening lubricant formulation and improving the dispersancy and/or reducing the sludge sedimentation of a lubricant formulation, by adding a hydroxy-functionalized acrylate-olefin copolymer according to the present invention, as a lubricant additive or a synthetic base fluid, to said lubricant formulation.

The present invention relates to a lubricant formulation comprising a base oil and a hydroxy-functionalized acrylate-olefin copolymer,
wherein the copolymer has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol according to DIN <NUM>-<NUM> and comprises:.

The terms "polymer" and "copolymer" are used interchangeably to define the copolymer according to the present invention.

The terms "lubricant formulation" and "lubricating oil composition" are used interchangeably to define the lubricant formulation according to the present invention.

In the present invention, the term "alkyl methacrylate" refers to esters of methacrylic acid and the term "alkyl acrylate" refers to esters of acrylic acid. The term "(meth)acrylate" refers to esters of acrylic acid, esters of methacrylic acid or a mixture of esters of acrylic acid and methacrylic acid.

In formula (III) above, the polymer treat rate (TR) corresponds to the total amount in weight percent of polymer in the lubricant formulation, based on the total weight of the lubricant formulation.

The base oils correspond to lubricant base oils, mineral, synthetic or natural, animal or vegetable oils suited to their use/chosen depending on the intended use.

The base oils used in formulating the lubricating oil compositions according to the present invention include, for example, conventional base stocks selected from API (American Petroleum Institute) base stock categories known as Group I, Group II, Group III, Group IV and Group V. The Group I and II base stocks are mineral oil materials (such as paraffinic and naphthenic oils) having a viscosity index (or VI) of less than <NUM>. Group I is further differentiated from Group II in that the latter contains greater than <NUM>% saturated materials and the former contains less than <NUM>% saturated material (that is more than <NUM>% unsaturated material). Group III is considered the highest level of mineral base oil with a VI of greater than or equal to <NUM> and a saturates level greater than or equal to <NUM>%. Group IV base oils are polyalphaolefins (PAO). Group V base oils are esters and any other base oils not included in Group I to IV base oils. These base oils can be used individually or as a mixture.

Preferably, the base oil included in the lubricating oil composition of the present invention is selected from the group consisting of an API Group II base oil, an API Group III base oil, API Group IV base oil, or a mixture thereof. Most preferably, the lubricant composition comprises an API Group III base oil or a mixture thereof.

Preferably, the lubricant formulation comprises from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, of the hydroxy-functionalized acrylate-olefin copolymer according to the invention, based on the total weight of the lubricant formulation.

In a preferred embodiment of the invention, the lubricant formulation comprises from <NUM> to <NUM>% by weight, preferably from <NUM> to <NUM>% by weight, of at least one base oil and from <NUM> to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight, of at least one copolymer according to the present invention, based on the total weight of the lubricating composition.

All preferred aspects of the polymer, base oil and amounts as listed above apply for this lubricating oil composition.

The lubricating oil compositions according to the present invention may also comprise any other additional additives suitable for use in the formulations. These additives include additional viscosity index improvers, pour point depressants, dispersants, demulsifiers, defoamers, lubricity additives, friction modifiers, antioxidants, detergents, dyes, corrosion inhibitors and/or odorants.

According to a preferred aspect of the invention, the total content of the copolymer according to the invention and base oil in the lubricant composition sums up from <NUM>% by weight or more, more preferably sums up from <NUM>% by weight or more, based on the total weight of the lubricant composition.

Within the meaning of the present invention, the monomer composition corresponds to the monomers used to prepare the polymer according to the present invention (not including other reactants such as initiators, stabilizers).

According to the present invention, the copolymer of the invention comprises <NUM> to <NUM>% by weight, based on the total weight of the copolymer, of monomer units a) derived from acrylate monomer of formula (I). Preferably, the copolymer comprises from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, of monomer units a) derived from acrylate monomer of formula (I), based on the total weight of the copolymer.

The acrylates a) of formula (I) refer to esters of acrylic acid with straight chain or branched alcohols having <NUM> to <NUM> carbon atoms. The term encompasses individual acrylic esters with an alcohol of a particular length, and likewise mixtures of acrylic esters with alcohols of different lengths.

Particularly preferred acrylates a) of formula (I) are selected from the group consisting of n-octyl acrylate, <NUM>-ethylhexyl acrylate, <NUM>-propylheptyl acrylate, isononyl acrylate, isodecyl acrylate, isotridecylacrylate, n-decyl acrylate, lauryl acrylate, or a mixture thereof.

According to the present invention, the copolymer of the invention comprises <NUM> to <NUM> % by weight, based on the total weight of the copolymer, of monomer units b) derived from at least one non-functionalized alpha-olefin of formula (II), wherein R<NUM> means a linear alkyl group having from <NUM> to <NUM> carbon atoms. According to one aspect of the invention, it is preferred that the copolymer comprises from <NUM> to <NUM>% by weight, preferably from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight, of monomer units b) derived from at least one non-functionalized alpha-olefin of formula (II), based on the total weight of the copolymer.

Most preferred non-functionalized alpha-olefins b) of formula (II) are selected from the group consisting of decene, dodecene, tetradecene, hexadecene, or a mixture thereof.

According to the present invention, the copolymer of the invention also comprises <NUM> to <NUM>% by weight, based on the total weight of the copolymer, of monomer units c) derived from at least one hydroxy-functional (meth)acrylate ester of formula (III). Preferably, the copolymer comprises from <NUM> to <NUM>% by weight, preferably from <NUM> to <NUM>% by weight, of monomer units c) derived from at least one non-functionalized alpha-olefin of formula (II), based on the total weight of the copolymer.

Preferred hydroxy-functional (meth)acrylate ester c) of formula (III) are selected from the group consisting of <NUM>-hydroxyethyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, <NUM>,<NUM>-dihydroxypropyl (meth)acrylate, <NUM>-hydroxybutyl (meth)acrylate, <NUM>-hydroxybutyl (meth)acrylate, <NUM>-hydroxybutyl (meth)acrylate, trimethylolpropane mono(meth)acrylate, <NUM>-ethoxy ethyl (meth)acrylate, <NUM>-(<NUM>-ethoxyethoxy)ethyl (meth)acrylate, <NUM>-hydroxy-<NUM>-methylpropyl (meth)acrylate, or a mixture thereof. Most preferred hydroxy-functional (meth)acrylate esters c) of formula (III) are selected from the group consisting of <NUM>-hydroxyethyl (meth)acrylate, <NUM>-hydroxypropyl (meth)acrylate, <NUM>,<NUM>-dihydroxypropyl (meth)acrylate, or a mixture thereof.

According to another aspect of the invention, it is preferred that the copolymer has a kinematic viscosity from <NUM> to <NUM>,<NUM><NUM>/s at <NUM> according to ASTM D <NUM>, more preferably from <NUM> to <NUM><NUM>/s at <NUM> according to ASTM D <NUM>, even more preferably from <NUM> to <NUM><NUM>/s at <NUM> according to ASTM D <NUM>.

According to another preferred aspect of the invention, the total content of monomer units derived from monomers a), b) and c) in the copolymer of the invention sums up to <NUM> % by weight or more, more preferably sums up to <NUM>% by weight or more, even more preferably sums up to <NUM> % by weight or more, most preferably sums up to <NUM> % by weight, based on the total weight of the copolymer.

According to the present invention, the copolymer has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol, preferably from <NUM>,<NUM> to <NUM>,<NUM>/mol, more preferably from <NUM>,<NUM> to <NUM>,<NUM>/mol, even more preferably from <NUM>,<NUM> to <NUM>,<NUM>/mol, according to DIN <NUM>-<NUM>.

According to the present invention, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) of the polymers is determined by gel permeation chromatography (GPC) according to DIN <NUM>-<NUM> using polymethylmethacrylate (PMMA) calibration standard using the following measurement conditions:.

Preferably, the copolymers of the invention have a very low degree of cross-linking and a narrow molecular weight distribution, which further contributes to the shear resistance. The low degree of crosslinking and the narrow molecular weight are reflected in the polydispersity index of the copolymers. Preferably, the polydispersity index (PDI) of the copolymers according to the invention is in the range of <NUM> to <NUM>, more preferably of <NUM> to <NUM>, even more preferably of <NUM> to <NUM>, most preferably in the range of <NUM> to <NUM>. A polydispersity index in the range of <NUM> to <NUM> is considered optimal for most industrial applications with regard to the shear resistance of the copolymers. The polydispersity index is defined as the ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn).

According to a preferred aspect of the present invention, the polymer of the invention has a COC flashpoint above <NUM> according to ASTM D92.

According to an aspect of the present invention, the monomer composition may also comprise further monomers d), other than the monomers a), b) and c), as long as the properties of the hydroxy-functionalized acrylate-olefin copolymer are not negatively affected.

According to the invention, the copolymer is a statistical copolymer, wherein the monomer units a), b) and c), and optionally any other monomer units d), are distributed randomly, and sometimes unevenly, in the copolymer.

Surprisingly, it has been observed that the combination of monomer units a) of formula (I) with alpha olefin monomer units b) of formula (II) and hydroxy-functional (meth)acrylate ester c) of formula (III), allows to prepare copolymers with great properties when used as an additive or a base fluid in thickening a lubricant oil formulation. As shown in the experimental part of the present invention, the lubricant formulations of the present invention, shows great thickening properties and improved dispersancy and/or reduction in the sludge sedimentation of a lubricant formulation.

According to the present invention, the above-mentioned polymers are prepared following the method comprising the steps of:.

Standard free-radical polymerization is detailed, inter alia, in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition. In general, a polymerization initiator and optionally a chain transfer agent are used for this purpose.

The polymerization step ii) can be conducted under standard pressure, reduced pressure or elevated pressure. In the context of the present invention, the term "standard pressure" means no added pressure, but ambient or atmospheric pressure.

For the radical copolymerization of olefins with acrylates, the polymerization temperature is critical. In general, the copolymerization temperature is in the range from <NUM> to <NUM>, preferably from <NUM> to <NUM>.

The polymerization step ii) may be performed with or without dilution in oil or any solvent. Preferably, the polymerization step ii) is made without dilution in oil or any solvent.

Preferably, step ii) comprises the addition of a radical initiator. Preferably, the radical initiator is selected from di-tert-amyl-peroxide, <NUM>,<NUM>-di-(tert-butylperoxy) butane, <NUM>,<NUM>-di-tert-butylperoxy-<NUM>,<NUM>,<NUM>-trimethylcyclohexane, dicumyl peroxide or di-tert-butyl-peroxide. Preferably, the total amount of radical initiator relative to the total weight of the monomer mixture is <NUM> to <NUM> % by weight, more preferably <NUM> to <NUM> % by weight. Preferably, the total amount of radical initiator is added continuously over the course of the copolymerization reaction ii).

Preferably, the copolymerization step ii) is made by feeding the acrylate monomers a), and the monomers c) and optionally any other comonomers, together with the initiator to the non-functionalized alpha-olefin monomers b). Preferably, the total reaction time of the radical polymerization is <NUM> to <NUM> hours, more preferably <NUM> to <NUM> hours, most preferably <NUM> hours.

In another preferred aspect of the invention, a further step after step ii) is optionally performed, corresponding to a distillation step to remove the unreacted alpha-olefin monomer b). Preferably, residual unreacted alpha-olefin monomer b) is removed by distillation at a temperature from <NUM> to <NUM> and pressures as low as <NUM> mbar using a rotary evaporator.

According to the present invention, the above-mentioned lubricant formulations are prepared following the method the steps of:.

All preferred aspects of the copolymer, preparation of the copolymer, base oil and amounts as listed above apply to the lubricant formulation according to the invention and to the preparation thereof.

The invention also relates to the use of a lubricant formulation according to the present invention as a lubricant formulation by adding the hydroxy-functionalized acrylate-olefin copolymer as defined herein to said lubricant formulation.

The invention also relates to a method of thickening a lubricant formulation and improving the dispersancy and/or reducing the sludge sedimentation of a lubricant formulation, by adding a hydroxy-functionalized acrylate-olefin copolymer as defined in the present invention, as a lubricant additive or a synthetic base fluid, to said lubricant formulation.

Preferably, the lubricating oil composition is a gear oil composition, a transmission oil composition, a hydraulic oil composition, an engine oil composition, a marine oil composition, an industrial lubricating oil composition or in grease.

The invention is further illustrated in detail hereinafter with reference to examples and comparative examples, without any intention to limit the scope of the present invention. All percentages in relation to monomers or base fluids given in the tables below are weight percentages (wt%).

In the present invention, the bulk viscosity (BV) of the polymer (product obtained from polymerization reaction) corresponds to the kinematic viscosity (KV) of the resulting product of the polymerization measured in accordance with ASTM D445. Thus, the bulk viscosity of the polymers (BV100) as shown in Table <NUM> below, were measured as kinematic viscosity at <NUM> in accordance with ASTM D445.

The oxidative performance of the inventive and comparative examples in the present invention were evaluated using an oxidation test (CEC SG-L-<NUM> Oxidation Stability of Lubricating Oils used in Automotive Transmissions by Artificial Ageing). The performance of a lubricating oil composition in the oxidation test according to CEC SG-L-<NUM> is an important criteria for automotive gear oils. Parts of this test are a visual inspection of residues in the glass tube and a chromatographic test which both indicate how well the lubricant can prevent the sedimentation of insoluble oxidation products. The method is conducted at <NUM> for <NUM> hours. The kinematic viscosity at <NUM> and <NUM> as well as the acid number (TAN, ASTM D <NUM>) of the fresh formulation is measured before the oxidation test (fresh oil) and compared to the corresponding values after oxidation (oxidized oil). The difference of the KV100 and TAN values between the fresh oil and the oxidized oil are termed as "delta KV100" and "delta TAN", respectively. Additionally, a blotterspot test is performed to evaluate the dispersancy performance by placing a single drop of the formulation after oxidation (<NUM>) on a patch of blotter paper and evaluating size of the spot. A higher value for the blotterspot area corresponds to a better dispersant.

<NUM> of DBPO (<NUM> wt% relative to the monomers in the feed) dissolved in <NUM> EHA and <NUM> HEMA (<NUM> wt% relative to all monomers) was slowly fed to <NUM> of <NUM>-decene (<NUM> wt% relative to all monomers) under nitrogen at <NUM> for <NUM> hours. After stirring for another <NUM> hours, the resulting clear polymer was cooled down. Subsequently, the residual decene was removed by distillation at <NUM> and pressures as low as <NUM> mbar using a rotary evaporator. The amount of decene incorporated in the polymer is determined gravimetrically assuming that no residual (meth)acrylate monomer is present.

All examples were prepared in the same way as inventive example Ex. <NUM>, except that the amounts of reactants and other reaction conditions were changed as listed in Table <NUM>. <NUM> to Ex. <NUM> and Ex. <NUM>, <NUM> wt% of stabilizer (<NUM>-methyl-<NUM>,<NUM>-di-tert-butylphenol) relative to the reaction mixture was added before the distillation step.

Further details regarding the synthetic procedures of the individual examples are provided in Table <NUM> together with basic properties of the polymers. The alpha-olefin monomers are always first charged to the reactor. The acrylate and dispersant monomers and the initiator are then fed over a set period of time. For acrylate-olefin copolymers with acrylate (mixtures) and dispersant monomer, all of them were mixed with the initiator before feeding to the olefin. For all examples, <NUM> wt% of DBPO as initiator relative to the monomers in the feed was used. The temperatures given in Table <NUM> correspond to the reaction temperature during the feed.

It is observed that all inventive polymers Ex. <NUM> to Ex. <NUM> are colorless, which is a further advantage looked for in the industry in comparison to comparative N-dispersant polymers Ex. <NUM>* to Ex. <NUM>*, which are yellowish-colored.

Furthermore, the total base number (TBN) according to ASTM D2896 was evaluated. The TBN of the inventive polymers Ex. <NUM> to Ex. <NUM> is always below <NUM>, whereas the comparative Ex. <NUM>* containing DMAEMA exhibits a significantly higher TBN of <NUM>. A lower TBN of the thickener offers more flexibility in the lubrication formulation and is beneficial for the long-term performance as a lower impact of acidic oxidation products on dispersancy performance is expected.

Formulations comprising the inventive and comparative polymers of Table <NUM> were prepared. The ratio of the different components is provided in Tables <NUM> to <NUM>. The properties of the different formulations using inventive examples such as viscosity index, kinematic viscosity, Brookfield viscosity and shear loss are shown along with the results from the oxidation test.

Tables <NUM> to <NUM> also list the content of hydroxy-functional monomer c) (OH-functional monomer c) content) in formulation which corresponds to the weight content (wt%) of monomer c) in the polymer multiplied by the treat rate (TR). For example, formulation example F-<NUM> contains <NUM> wt% polymer Ex. <NUM> with <NUM> wt% HEMA. Thus, wt% of monomer c) is <NUM> and TR is <NUM>, resulting in a OH-functional monomer c) content in formulation of <NUM> x <NUM> = <NUM>. As shown in Tables <NUM> and <NUM>, all inventive formulations according to the invention have a OH-functional monomer c) content in formulation of less than <NUM>.

The target was to obtain formulations fulfilling SAE 75W-<NUM> (Table <NUM>) or 75W-<NUM> (Table <NUM>) standard (SAE is the organization Society of Automotive Engineers). Table <NUM> gives comparative examples of 75W-<NUM> and 75W-<NUM> formulations and their oxidative performance.

Comparative Ex. <NUM>* of the present patent application is similar to example <NUM> of EP401604 comprising EHA and <NUM>-decene. These copolymers comprising EHA, which are consequently rather polar due to the short side-chain, show poor performance in the dispersancy rating of the oxidation test according to CEC SG-L-<NUM> as shown in formulation example F-<NUM>* in Table <NUM>. Better performance in sludge handling is achieved with lubricant formulations comprising the inventive hydroxy-functionalized acrylate-olefin copolymers according to the invention. Indeed, as shown in Table <NUM> above, the oxidation tests of the 75W-<NUM> formulations comprising the hydroxy-functionalized acrylate-olefin copolymers according to the invention (F-<NUM> to F-<NUM>) deliver good oxidative performance with <NUM>% dispersancy rating in the blotterspot test (blotterspot area). Even at lower treat rates as in the 75W-<NUM> formulations shown in Table <NUM> (F-<NUM> to F-<NUM>), the dispersancy is surprisingly still above <NUM>%.

Furthermore, comparative formulation examples F-<NUM>* and F-<NUM>* demonstrate that high amounts of OH-functional groups in the formulation result in a high viscosity increase in the oxidation test. For these cases, it was not even possible to clearly determine the values for the increase of the KV100 between fresh and oxidized oil but only a range for the increase can be given. For both formulations F-<NUM>* and F-<NUM>*, an increase of the KV100 higher than <NUM><NUM>/s was found. The polymer composition of comparative example Ex. <NUM>* used in F-<NUM>* comprises > <NUM> wt% of the OH-functional monomer HEMA. The polymer Ex. <NUM> used for F-<NUM>* comprises <NUM> wt% HEMA and therefore the concentration of OH-functional monomer in the final formulation is also higher than allowed by the restriction of [wt% of monomer c)] x TR < <NUM>. However, the same polymer (Ex. <NUM>) used in a 75W-<NUM> formulation (F-<NUM>) which only requires <NUM> wt% of polymer treat rate shows good oxidative performance. Here, the restriction [wt% of monomer c)] x TR < <NUM> is fulfilled.

The hydroxy-functionalized polymers perform on the level of the nitrogen-containing ones regarding dispersancy, which is quite unexpected because nitrogen functionality is more typical in dispersants (<CIT>, <CIT>). Even more surprising is the lower acid number after oxidation of the formulations containing the hydroxy-functional monomers and especially the lower acid number increase. The basic nitrogen functionalities were expected to perform better in both tests. Polymers containing N-dispersant functions such as comparative examples Ex. <NUM>* and Ex. <NUM>* exhibit this higher increase of the acid number after the oxidation test. These comparative examples in 75W-<NUM> formulations show an increase in acid number (delta TAN) of <NUM> KOH/g (F-<NUM>*) up to <NUM> KOH/g (F-<NUM>*), while the increase of the inventive examples in the 75W-<NUM> formulation are at <NUM> KOH/g or below (F-<NUM> to F-<NUM>).

Claim 1:
A lubricant formulation comprising a base oil and a hydroxy-functionalized acrylate-olefin copolymer,
wherein the copolymer has a weight-average molecular weight from <NUM>,<NUM> to <NUM>,<NUM>/mol according to DIN <NUM>-<NUM> and comprises:
a) <NUM> to <NUM>% by weight, based on the total weight of the copolymer, of monomer units derived from at least one acrylate of formula (I),
<CHM>
wherein R<NUM> means a linear or branched alkyl group having from <NUM> to <NUM> carbon atoms,
b) <NUM> to <NUM>% by weight, based on the total weight of the copolymer, of monomer units derived from at least one non-functionalized alpha-olefin of formula (II),
<CHM>
wherein R<NUM> means a linear alkyl group having from <NUM> to <NUM> carbon atoms, and
c) <NUM> to <NUM>% by weight, based on the total weight of the copolymer, of monomer units derived from at least one hydroxy-functional (meth)acrylate monomer c),
and
wherein the lubricant formulation has a content of hydroxy-functional (meth)acrylate monomer c) in formulation of less than <NUM>, calculated with the formula (III) <MAT>
wherein [wt% of monomer c)] is the total weight content of monomers c) in the polymer and wherein TR is the polymer treat rate in weight percent in the lubricant formulation.