EP0425367A1 - Overbased lubricating oil additive containing a copper derivate or a copper and boron derivate, method of preparation and compositions containing said additive - Google Patents

Abstract

The oxidation-promoting effect of the overbased additives can be attenuated or even eliminated by incorporation into the overbased additive of a copper carboxylate originating from aliphatic carboxylic acids containing a linear or branched C7-C10 chain. These copper carboxylates can also be employed in the form of combination with a boron derivative.

Description

This invention relates to overbased additives for lubricating oils containing a copper derivative or a copper and boron derivative, their preparation process and lubricant compositions containing said additives.

Overbased additives are alkali or alkaline earth metal salts of organic acids, overbased by carbonation with carbon dioxide. The term overbased is used to designate the excess of alkali or alkaline earth metal relative to the stoichiometric quantity necessary to neutralize the organic acid used.

The structure of the overbased additives is that of a colloidal dispersion, the micelles of which contain the alkali or alkaline earth metal carbonate formed during carbonation. The micelles are stabilized by the alkali or alkaline earth metal salts of organic acids which have a detergent effect.

The organic acid salts used in the overbased additives are generally the sulphonates, salicylates or sulfurized phenates, described respectively in US Patents 4,606,219, EP-A 279,493 and FR 2,305,494.

These overbased additives are particularly useful in lubricants used in internal combustion engines of the "gasoline" type or of the "diesel" type.

Thanks to their detergent and dispersant effect, they prevent the formation of lacquers and varnishes and keep soot in dispersion from the incomplete combustion of the fuel.

Another important function of these additives is the neutralization of acid compounds, such as organic acids formed by oxidation of the oil and the sulfur derivatives supplied by the fuels.

This neutralization function is particularly appreciated when using fuels rich in sulfur, such as heavy fuels used in marine engines.

Certain overbased additives, in particular overbased sulfonates have the disadvantage of significantly degrading the antioxidant performance of lubricant formulations.

The use of additives according to the invention makes it possible to avoid this degradation and even to improve the resistance of lubricants to oxidation.

Multi-valent metals such as copper, molybdenum, iron and cobalt influence the oxidation of oils. Copper, for example, at concentrations below 50 ppm, catalyzes the oxidation of the lubricant. In the concentration range between 50 and 500 ppm, on the other hand it has an oxidation inhibiting effect.

Patent application EP-A-0024146 describes formulations containing such copper concentrations in the form of cupric oleate.

US Patent 4,715,974 describes the use in lubricants of copper salts of sulfurized unsaturated fatty acids. US Patent 4,770,799 relates to the copper salts of succinic esters of substituted phenols.

Copper derivatives are also used in combination with amines, which in turn promote the decomposition of peroxides.

US patents 3,093,585, 3,634,238, 4,110,234 and 4,122,033 describe such associations between copper salts and amines.

Oil-soluble copper salts, such as copper oleate cannot be used in overbased additives. The overbasing of a reaction mixture containing the copper oleate is not possible and the addition of the copper oleate to an overbased additive gives an unstable mixture.

Patent application EP-A-0225580 describes the introduction into an overbased additive of a copper carboxylate insoluble in hydrocarbons, the total number of carbons of which does not exceed six. These oil-insoluble copper carboxylates are found inside the micelles of the colloidal dispersion, in the same way as the alkali or alkaline earth metal carbonate, most often calcium carbonate.

The stability of these dispersions, the micelles of which are loaded with calcium carbonate and copper carboxylate, requires the presence of significant amounts of detergents.
We have now found that it is possible to introduce, in an overbased additive, copper carboxylates, of medium chain length, with a detergent effect. These carboxylates do not enter inside the micelle, but remain at the interface and participate themselves in its stabilization, in the same way as alkaline or alkaline earth salts of organic acids, usually used as detergents in additives overbased.

The invention relates to an overbased additive for lubricating oils, composed of an alkali or alkaline earth metal carbonate dispersed in a diluent oil using a mixture of detergents, characterized in that said mixture contains at least one copper carboxylate. , derived from straight chain or branched C₇ to C linéaire aliphatic carboxylic acids.

These C₇ to C₁₀ copper carboxylates are partially soluble in hydrocarbons, enough to pass through a dialysis membrane. On the other hand, the additive obtained, after elimination of the promoters, solvents and solid residues, does not dialyze through a membrane. This proves that the copper carboxylate is not present in the form of free molecules, but is part of a micelle.

Examination with an electron microscope confirms the presence of micelles whose diameter is between 5 and 10 nm. Copper carboxylates of medium chain length, between C₇ and C₁₀ are part of this micelle and participate in its stability thanks to their surfactant effect. At the same time, the presence of copper gives the additive an antioxidant effect.

It is also possible to incorporate the copper carboxylate in the form of an association formed with an inorganic derivative of boron. The presence of boron contributes to the antioxidant effect and improves the extreme pressure performance of the additive.

The incorporation of copper and possibly boron into the micelle, according to the invention makes it possible to obtain multifunctional additives, with antioxidant and extreme pressure effect. Such multifunctional additives are superior to mixtures of additives, since they make it possible to avoid the problems of incompatibility between additives and the instability of the mixtures.

The copper carboxylates used are derived from aliphatic carboxylic acids with a linear or branched chain from C₇ to C₁₀, such as n-heptanoic acid, ethyl-hexanoic acid or n-decanoic acid. It may be advantageous to use mixtures of acids, obtained from alpha-olefins or rather from alpha-olefin cuts, by oxo synthesis. Among these mixtures of acids, mention may be made of C₇ to C₁₀ oxo acids branched in the alpha or beta position or else VERSATIC 10 acids, sold by SHELL. VERSATIC 10 acids are obtained by oxo reaction from a mixture of branched C₉ olefins. They mainly consist of tertiary acids, with a trialkylacetic acid structure.

Copper carboxylates are generally obtained by reacting a carboxylic acid with cupric hydroxide or a mixture of cupric hydroxide and carbonate in an organic solvent. Copper carboxylates can also be prepared by displacing the sodium from a sodium carboxylate with a solution of a mineral salt of copper, such as cupric chloride.

The copper carboxylates can be prepared in the form of solids containing approximately 12 to 17% by weight of copper or in the form of a solution. In this second case, the solvent is preferably identical to that used for carbonation. These copper carboxylates dialyze through a latex membrane.

The associations of copper carboxylates with inorganic boron derivatives are prepared by reacting a solution of copper carboxylate with a solution of a mineral boron compound, such as ammonium borate, sodium tetraborate, metaborate sodium or boric anhydride. The preferred boron compound is boric anhydride, B₂O₃. The preferred solvent is a glycol ether, such as propylene glycol methyl ether. The two solutions are mixed at a temperature in the region of 100 ° C., then the mixture is brought to reflux for at least one hour. After distilling off part of the solvents, a small amount of a glycol, such as butyl glycol, is optionally added. The concentration of the latter does not exceed 5% by weight of the final mixture. The copper carboxylate / boron compound associations obtained contain between approximately 8 to 12% by weight of copper and 0.8 to 2% by weight of boron and are in the form of an intense blue solution, which very quickly crosses a membrane. latex dialysis machine. In the additives according to the invention, the copper carboxylate or the copper-boron carboxylate association is used in mixture with a usual detergent of overbased additives.

Among these detergents, mention may be made of naphthenates, sulfonates, phenates, salicylates, phosphonates and alkali or alkaline earth thiophosphonates soluble in the hydrocarbon medium.

The sulfonic acids used for the preparation of the sulfonates can be of petroleum or synthetic origin. Petroleum sulfonic acids are prepared by sulfonation of oils from the distillation of petroleum. Their structure does not correspond to a well defined formula but their average molecular weight must be at least equal to 300.

Synthetic sulfonic acids are prepared by alkylation of aromatic compounds such as benzene, toluene, xylene or naphthalene with olefinic cuts and then by sulfonation of the alkylate obtained. The structure of the alkyl chains attached to the nucleus is linear or branched depending on the olefins used for the alkylation. The number of carbon atoms per alkyl chain is greater than or equal to 8.

The preparation of the alkali or alkaline earth metal sulfonate is carried out by bringing the sulfonic acid into contact with an alkali or alkaline earth metal derivative (preferably oxide or hydroxide) in a hydrocarbon solvent optionally in the presence of an alcohol.

The alkali or alkaline earth metal phenates are prepared under analogous conditions from sulfurized alkylphenol or alkylphenol. The phenol ring can carry one or two straight or branched alkyl chains, having at least eight carbon atoms. The most common compound is dodecylphenol.

The optional sulfurization of phenol is carried out by the action of sulfur monochloride S₂Cl₂ or by the action of elemental sulfur at temperatures ranging from 150 to 200 ° C. The sulfurized product contains approximately 0.6 to 2 sulfur atoms per phenolic nucleus.

The alkylsalicylic acids are prepared by alkylation of salicylic acid or by carboxylation under pressure of alkylphenols. The alkyl chain contains a minimum of 12 carbon atoms.

The phosphonates and thiophosphonates are prepared by the action of P₂O₅ or P₂S₅ on a polyisobutene then neutralization with an alkali or alkaline earth oxide or hydroxide. The molecular weight of polyisobutene is between 300 and 2000.

All of these detergents can be used in admixture with dispersants which are soluble in a hydrocarbon medium, for example of the alkylsuccinimide type or esters of alkylsuccinic acids with a molecular weight of 300 to 2500.

Instead of detergents, the reaction medium can contain the precursors. In this case, neutralization is carried out in the reaction medium just before carbonation.

The alkali or alkaline earth metal carbonate used in the composition of the additive according to the invention is generally calcium carbonate or magnesium carbonate.

The multifunctional additive according to the invention is prepared by carbonation of a reaction medium containing a mixture of detergents, a derivative of an alkali or alkaline earth metal, a nitrogenous and / or oxygenated promoter and optionally a hydrocarbon solvent in a diluent oil, characterized in that the detergent mixture contains at least one copper carboxylate derived from aliphatic acids with a straight or branched chain C₇ to C₁₀ or a combination of this carboxylate with an inorganic boron derivative.

The detergent mixture contains in addition to copper carboxylate, a usual detergent for overbased additives, such as naphthenates, sulfonates, phenates, salicylates, phosphonates and thiophosphonates, alkali or alkaline earth.

The alkali or alkaline earth metal derivatives can be oxides, hydroxides or alcoholates. The preferred derivatives are the oxides and hydroxides and particularly the oxide or hydroxide of calcium or magnesium.

These are added to the reaction medium in stoichiometric excess relative to the detergent or its precursor. The stoichiometric excess can vary between 5: 1 and 30: 1.

In the process according to the invention, an oxygenated promoter is introduced into the reaction medium before carbonation, which is generally an aliphatic alcohol or aromatic, an alkoxyalkanol, a glycol or even an alkanolamine. Preferably used aliphatic alcohols C₁ to C₂₀ or mixtures thereof. The aliphatic alcohols can be used in admixture with glycols, alkoxyalkanols or alkanolamines.

The molar ratio of the oxygenated promoter to the detergent is generally between 1 and 30.

The use of a nitrogenous promoter is optional. This nitrogenous promoter is generally chosen from ammonia, ammonium salts, primary, secondary or tertiary amines in C₂ to C₁₀ and their salts with carboxylic acids or boric acid, polyamines or even alkanolamines.

Among the nitrogenous promoters, ammonia, carbonate and ammonium chloride, ethylenediamine, ethanolamine or diethanolamine are preferred.

The promoter to detergent molar ratio is generally between 1 and 30.

The hydrocarbon solvent allows perfect homogenization of the various reactants as well as a lowering of the viscosity which will subsequently facilitate the recovery of solid carbonation residues. The solvent represents from 10 to 70% by weight of the reaction mixture. The solvents used are the Chat to C ar aliphatic or aromatic compounds. The preferred solvents are aromatic solvents such as benzene, toluene, xylene, ethylbenzene and chlorinated aromatics. Their choice is dictated by the characteristics of the additive collected, by their boiling point and by the boiling point of the azeotropes which they can form with oxygenated promoters and water.

The handling of the overbased additive obtained according to the invention is facilitated by the addition of oil. The oil represents approximately 20 to 50% by weight of the additive obtained. This can be added to the reaction medium before carbonation or even after this, that is to say just before the removal of the solvent. The diluent oils used are of a paraffinic nature of the 100 or 150 Neutral solvent type or of a predominantly naphthenic nature such as 100 - 150 pale solvent.

The carbonation reaction can be carried out after optional addition of water to the reaction medium. The addition of water is particularly beneficial when the alkali or alkaline earth metal derivative is an oxide. Generally the amount of water added is such that the water / metal oxide molar ratio is of the order of 0.5.

The implementation of the method according to the invention consists in successively introducing into a reactor equipped with an agitator, a temperature control, a device for bubbling carbon dioxide, a heating and heating system. empty:
- 0 to 700 parts by weight of a hydrocarbon solvent - an alkali or alkaline earth metal derivative in stoichiometric excess relative to the detergent or its precursor. This stoichiometric excess is between 5: 1 and 30: 1
- an oxygenated promoter whose molar ratio to the detergent or to its precursor is between 1 and 30
- optionally a nitrogenous promoter whose molar ratio to detergent is between 1 and 30
- optionally an amount of water such that the water / metal oxide molar ratio is of the order of 0.5
- optionally diluent oil in quantity such that it represents 20 to 50% by weight of the additive recovered at the end of the operations
- 15 to 200 parts by weight of copper carboxylate in solid form or in solution or a solution of a copper-boron carboxylate association
- 100 to 400 parts by weight of a conventional detergent or a detergent precursor.

In the case where a detergent precursor is used, it is preferable to successively introduce the precursor, the excess of the alkali or alkaline earth metal derivative and the oxygenated promoter. Neutralization of the precursor is then carried out before adding the other constituents of the mixture with a view to carbonation.

The stoichiometric excess of the alkali metal derivative is carbonated or alkaline earth at a temperature between room temperature and the reflux temperature of the mixture. The molar ratio of CO₂ introduced to the stoichiometric excess of alkali or alkaline earth metal is between 0.6 and 1.2. The mixture is optionally stabilized by heating under vacuum or under a stream of nitrogen so as to eliminate the oxygenated promoters of low boiling point and the water added as well as the water produced by carbonation. Solid residues are removed by centrifugation and / or filtration using diatomaceous earth. If the diluent oil has not been added before carbonation, it is then added before possible elimination of the hydrocarbon solvent and heavy alcohols, by heating under vacuum at temperatures of the order of 100 to 200 ° C.

It should be noted that the filtration operation can be carried out after recovery of the solvent.

The incorporation rate of copper and possibly boron is close to 100%.

The overbased additives according to the invention are clear and stable liquids. Their coloring is generally blue. Phenates and salicylates are much darker than sulfonates.

Neither the copper nor the boron present in the additive does not dialyze through a latex membrane, which proves that these compounds are incorporated into the micelles.

These additives have a copper content of between 0.2 and 5% by weight, preferably 0.8 to 3%, and a boron content of between 0 and 1%, preferably 0.2 to 0.8%.

They are characterized by their copper and boron content, by their alkaline value (VA) expressed in mg KOH / g and determined according to standard ASTM D-2896 and by their stability in dilution at a VA of 70 mg KOH / g in a mixture of base oils.

These additives are incorporated into lubricating oils of natural origin in the synthetic at a concentration between 0.5 and 40% by weight and preferably 1 to 30% by weight, which corresponds to a concentration of 0.004 to 1.2%. weight of copper and 0.32% weight of boron in the final lubricating formula.

The lubricant compositions thus obtained can contain other additives with antiwear, dispersant, detergent, antioxidant, friction modifier effect, as well as polymers improving the viscosity index.

The following examples illustrate the invention without, however, limiting it.
The percentages indicated are by weight, unless otherwise indicated.

EXAMPLE A: Copper Carboxylate

In a reactor fitted with a stirring system and a heating device, 25 g of cekanoic acid Ck₉ containing 96% active material (CDF chemistry) and 316 ml of 0.5N sodium hydroxide are brought into contact. After heating at 90 ° C for 30 minutes, 53.8 g of cuClrique chloride CuCl₂, 2H₂O diluted in 100 ml of water are added over 30 minutes. The blue precipitate formed is recovered by filtration, washed and dried. 27.9 g of pulverulent solid containing 16.5% copper are recovered.

EXAMPLE B: Copper Carboxylate:

72g of xylene, 120g of a 50/50 mixture by weight of ethyl-2- acid are introduced into a reactor fitted with a stirring system, a temperature control and a Dean-Stark apparatus. hexanoic acid and Versatic 10 (SHELL chemistry) as well as 43g of basic copper carbonate CuCO₃, Cu (OH) ₂ ,. 13.2 ml of water are collected by azeotropic entrainment in one hour thirty. 214 g of a solution in xylene of neutral copper salts, the copper content of which is 10.3%, are obtained after filtration or centrifugation.

EXAMPLE C: Copper / boron carboxylate association

770 g of a solution of carboxylate obtained in Example B are used. This is maintained at 130 ° C. 32 g of boric anhydride B₂O₃ are dissolved in 288 g of methyl ether of propylene glycol (PE: 120 ° C.) at a temperature of 100 ° C. The boron solution is introduced in 20 minutes into the carboxylate solution. After one hour of reflux, a total clarification of the reaction medium is observed; then distilling all of the ether and part of the solvent so as to obtain a copper content of the order of 11.2%. We then add 30g of butylglycol to perfectly stabilize the mixture: the product obtained contains 10.7% copper and 1.38% boron.

EXAMPLE 1: (comparative)

In a 1 liter reactor equipped with a temperature control, a coolant, a stirring system and a gas bubbling device are successively introduced:
- 130ml of toluene, 32.95g of alkylarylsulfonic acid with linear alkyl chain, of molecular weight 430 and with 96% of active material, 42g of diluent oil 100 Neutral solvent, 28.31g of slaked lime at 96% of purity and 12 ml of methanol. After neutralization of the sulfonic acid with lime which can optionally be carried out by heating the reaction medium at 60 ° C. for 30 minutes, 13.5 g of carbon dioxide are introduced into the mixture maintained at a temperature of 42 ° C. After carbonation, the methanol and the water produced by the reaction are removed by heating the mixture under partial vacuum. The medium is clarified by filtration using 2% by weight of Diatomées Clarcel DICS from CECA SA.

After removing the solvent, 103 g of product containing 13% calcium are recovered. Its alkaline value is 313mg KOH / g.

The product is limpid brown and stable when diluted in mineral or synthetic oils. No clouding or settling is observed after several weeks at 60 ° C.

EXAMPLE 2: comparison

The procedure is as in Example 1, but 30 g of alkyl aryl sulfonic acid with a branched alkyl chain are introduced, the molecular weight of which is 520 and 70% of active material and 10 g of CO₂.

The amount of diluent oil is 22.5 g.
The product is in the form of a brown liquid, its alkaline value is 378mg KOH / g. It is stable when diluted in lubricating oils and its viscosity is 18,250 mPa.s at 20 ° C;

EXAMPLE 3:

The procedure is as in Example 1, but 10 g of a solution prepared in Example C are introduced into the reaction medium, before carbonating with 12 g of carbon dioxide.
112 g of overbased sulfonate containing 0.96% copper and 0.117% boron are recovered. Its alkaline value is 314 mg KOH / g and its viscosity is 3500 mPa.s at 20 ° C. It is blue in color and perfectly stable when diluted in oils.

EXAMPLE 4:

The procedure is as in Example 1, but 15g of solution described in Example C are introduced before carbonating with 12g of CO₂. 111 g of overbased sulfonate containing 1.41% copper and 0.15% boron are then collected. The alkaline value is 309 mg KOH / g and the viscosity at 20 ° C is 4950 mPa.s. The dilution stability in oils is remarkable.

EXAMPLE 5:

The procedure is as in Example 1, but 20g of solution prepared in Example C are added before carbonating with 11g of carbon dioxide.
115.5 g of an overbased sulfonate containing 1.88% copper and 0.224% boron are collected. The alkaline value is 297 mg KOH / g and the viscosity at 20 ° C is 11,650 mPa.s. It is perfectly stable in mineral and synthetic oils.

Note that, unlike solution C, none of the products of examples 3,4,5 do not pass through a dialysis membrane, which constitutes indirect proof of the incorporation of copper and boron in the colloidal dispersion calcium carbonate, the main constituent of the products 3,4,5.

EXAMPLE 6

The procedure is as in Example 2, but 4 g of copper carboxylate described in Example A are added to the reaction medium before carbonating with 8.3 g of carbon dioxide.
75 g of overbased sulfonate containing 0.85% copper are recovered and the dilution stability in oils is correct. The color is dark green, the viscosity at 20 ° C is 260,000 mPa.s and the alkaline value is 334 mg KOH / g.

EXAMPLE 7:

The procedure is as in Example 2, but 1.5 g of the copper carboxylate described in Example A are introduced before carbonating with 8.3 g of carbon dioxide.

After a treatment similar to that of Example 2, 73 g of finished product of alkaline value 323 mg KOH / g and of brown green color are recovered. The viscosity at 20 ° C is 8850 mPa.s and the copper content of 0.33%.
The product is stable when diluted in oils.
Unlike the product of Example A, the products of Examples 6 and 7 diluted with a solvent do not pass through a dialysis membrane.

EXAMPLE 8:

The procedure is as in Example 1, but 20 g of the cupric solution prepared in Example B are introduced before carbonating with 12 g of carbon dioxide. After a treatment similar to that of Example 1, 113 g of an overbased sulfonate containing 1.77% of copper and whose alkaline value is 321 mg KOH / g are recovered. Its color is blue-green and its stability in oils is remarkable.

EXAMPLE 9: (Comparative)

77.8 g of dodecylphenol and 20 g of sulfur chloride are introduced into a 250 ml reactor equipped with a condenser, a temperature control and a gas bubbling device at a temperature of 20 to 30 ° C. The mixture is heated under nitrogen sweep and with stirring for one hour at 150 ° C then 1 hour at 180 ° C and finally 1 hour at 200 ° C. The sulfurized dodecylphenol is collected, the respective chlorine and sulfur contents of which are 2200 ppm and 11.4%. In another 250ml reactor fitted with a stirring system, a temperature control and a gas bubbling device, 43g of sulfurized dodecylphenol, 30g of 100 Neutral solvent diluent oil, 90ml of xylene are successively introduced. , 11.8g of calcium oxide, 66ml of methanol and 2g of calcium nitrate Ca (NO₃) ₂, 4H₂O. The mixture is brought to reflux for 45 minutes before elimination of the water produced by neutralization. 66 ml of methanol are added to the mixture before carbonating with carbon dioxide excess stoichiometric lime, at a temperature of 50 ° C. After carbonation, the residual water and methanol are removed by heating under partial vacuum before recovering the solid residues by filtration.
After evaporation of the solvent, an overbased sulfurized dodecyl phenate of brown green color is collected, stable in oils. Its alkaline value is 245mg KOH / g.

EXAMPLE 10:

The procedure is as in Example 9, but 10 g of a cupric solution such as that prepared in Example B are introduced into the reaction medium just after the removal of the neutralized water from the sulfurized dodecylphenol. The rest of the procedure is identical to that of Example 9.
91 g of overbased sulfurized calcium dodecylphenate containing 1.1% copper and an alkaline value of 251 mg KOH / g are then recovered.
The color of the product is blackish green and it is stable when diluted in base oils.

EXAMPLE 11 (comparative)

The procedure is as in Example 1, but 78g (C₁₄, C₁₈-alkyl) salicylic acid, 9.49g of slaked lime, 37ml of methanol and 25g of diluent oil are introduced into the reactor. After neutralization and carbonation at 42 ° C with 1.9g of CO₂, 7.5g of lime is added which is carbonated with 2.5g of CO₂. A dark brown additive is collected which is stable in oils. Its calcium content is 7.6%, and its alkaline value 205mgKOH / g.

EXAMPLE 12

The procedure is as in Example 11 but 10 g of the cupric solution of Example B are introduced after neutralization of the salicylic acid. The rest of the operations are identical to those of Example 11.
120 g of an overbased calcium alkylsalicylate containing 0.85% copper are then recovered. Its alkaline value is 201 mg KOH / g and it is stable when diluted in base oils.

EXAMPLE 13

The procedure is as in Example 2, but 4 g of copper carboxylate are added to the reaction medium after carbonation. described in Example B. A slightly cloudy blue color mixture is obtained. Its alkaline value is 300mgKOH / g.

EXAMPLE 14

The performance of the additives is evaluated using an oxidation test. The 30g samples of lubricant, containing variable amounts of additives, are heated at 165 ° C for 64 hours. The oxidation is catalyzed by 40 ppm of iron in the form of acetylacetonate. At the end of the test, the temperature is brought back to 40 ° C., and the viscosity is compared to 40 ° C. before and after oxidation. The increase in viscosity (Δ V) is expressed as a percentage of the initial viscosity. The lower this percentage, the more effective the additive.
Tables 1 and 2 summarize the viscosity measurement results with two lubricant formulas A and B.
A = mineral oil with 0.6% sulfur,
1% primary Zn dithiophosphate
B = mineral oil with 0.6% sulfur
1% primary Zn dithiophosphate
3.3% dispersant.

The two tables show the pro-oxidant effect of overbased sulfonates. In fact, the overbased sulfonates prepared according to Comparative Examples 1 and 2 lead to solidification, and the viscosity can no longer be measured. The overbased phenates (comparative example 9) also increase the viscosity compared to the sample without additive, but their pro-oxidant effect is weaker. Table 1 shows that the addition of additives according to the invention makes it possible to reduce or even eliminate the pro-oxidant effect of the overbased additives (Examples 5, 7 and 10). Additive 5 also containing boron is more effective than additive 7 containing only copper.

The additives according to the invention can be used in admixture with conventional overbased additives, provided that the copper content is at least 160 ppm: in fact the presence of 40 ppm of copper does not prevent solidification. TABLE 1 LUBRICANT FORMULA = A Addendum of the ex. % Weight additive Copper ppm Boron ppm ΔV at 40 ° C% 1 (comp. 0.85 - - mass 5 0.85 160 20 137 2 (comp.) 4.23 - - mass 2 + 6 3.5 + 0.5 40 - mass 2 + 6 2.5 + 2 166 - 259 7 5 166 - 509 9 (comp.) 1.5 - - 257 10 1.45 166 - 35

Table 2 shows that the pro-oxidant effect of the overbased additive is attenuated by the addition of an additive to copper (Example 7), on the other hand the addition of a conventional amino antioxidant does not prevent solidification of the sample.

It is found that for identical copper contents, around 160 ppm, the use of a single additive (Example 7) is more effective than the use of mixtures of conventional overbased sulfonates and overbased copper additives (Example 2 +6, 1 + 3, 1 + 5).

The use of mixtures of conventional overbased sulfonates and copper carboxylates gives very poor results. TABLE 2 LUBRICANT FORMULA = B Example addendum % Weight additive copper ppm Boron ppm ΔV at 40 ° C% 2 (comp.) 4.23 - - mass 2 (comp.) 4.23 + 0.2% _L57 * - - mass 2 + 6 2.5 + 2 166 - 1300 7 5 166 - 298 1 (comp.) 4.8 - - mass 1 + 3 3.09 + 1.7 163 20 1010 1 + 5 3.96 + 0.88 165 20 1000 2 + 13 1.7 + 2.6 160 - 3450 * L₅₇: amino antioxidant.

Claims (13)

1 - Overbased additive for lubricating oils, composed of an alkali or alkaline earth metal carbonate dispersed in a diluent oil using a mixture of detergents, characterized in that said mixture contains at least one copper carboxylate, derived from aliphatic carboxylic acids with straight or branched chain from C en to C₁₀. 2 - Additive according to claim 1 characterized in that the copper carboxylate is incorporated in the form of association formed with an inorganic derivative of boron. 3 - Additive according to claim 1 or 2 characterized in that it contains 0.2 to 5% by weight and preferably 0.8 to 3% of copper and 0 to 1% by weight preferably 0.2 to 0.8% boron. 4 - Additive according to claim 2 characterized in that the inorganic boron derivative is ammonium borate, sodium tetraborate, sodium metaborate and preferably boric anhydride. 5 - Additive according to one of claims 1 to 4 characterized in that the carboxylic acid is n-heptanoic acid, ethyl-hexanoic acid, or n-decanoic acid. 6 - Additive according to one of claims 1 to 4 characterized in that the carboxylic acid is a mixture obtained from alpha-olefins or cuts of alpha-olefins by oxo synthesis. 7 - Additive according to claim 6 characterized in that the acid obtained by oxo synthesis is VERSATIC 10 acid, marketed by SHELL. 8 - Additive according to one of claims 1 to 7 characterized in that the mixture of detergents contains a naphtenate, a sulfonate, a phenate, a salicylate, a phosphonate or an alkali or alkaline earth thiophosphonate. 9 - Additive according to one of claims 1 to 8 characterized in that the alkali or alkaline earth metal carbonate is a calcium or magnesium carbonate. 10- Process for the preparation of overbased additives according to one of claims 1 to 9 by carbonation of a reaction medium containing a mixture of detergents, a derivative of an alkali or alkaline earth metal, a nitrogenous and / or oxygenated promoter and optionally a hydrocarbon solvent in a diluting oil, characterized in that the detergent mixture contains at least one copper carboxylate derived from straight chain or branched C₇ to C₁₀ aliphatic acids or a combination of this carboxylate with an inorganic boron derivative. 11- A method according to claim 10 characterized in that the derivative of an alkali or alkaline earth metal is an oxide, hydroxide or alcoholate and preferably an oxide or hydroxide of calcium or magnesium. 12- Lubricating composition characterized in that it contains 0.5 to 40% by weight and preferably 1 to 30% by weight of an additive according to one of claims 1 to 9. 13- Composition according to claim 12 characterized in that it contains additives with antiwear effect, dispersant, detergent, antioxidant, friction modifier, as well as polymers improving the viscosity index.