Lubricating grease

Abstract

A lubricating grease comprising - between 30 wt.% and 60 wt.% silicone oil, - between 10 wt.% and 35 wt.% mineral oil, - between 10 wt.% and 45 wt.% overbased calcium sulfonate thickener, the quantity specifications each referring to the total weight of the lubricating grease.

Description

[0001] LUBRICANT GREASE

[0002] The invention relates to a lubricating grease containing silicone oil and mineral oil as base oils. The invention further relates to its use for the lubrication of tribological systems, in particular tribological systems with high energy efficiency requirements, even at low or high temperatures. The lubricating grease can achieve good energy efficiency, even at low or high temperatures, and good friction values ​​even without containing PTFE.

[0003] For the lubrication of tribological systems with high requirements in terms of energy efficiency even at low or high temperatures, e.g. in the automotive sector, PTFE micropowder is often used in practice, as it can achieve very low friction levels.

[0004] Because PTFE micropowders also exhibit very high temperature resistance, they are often used as thickeners or additives in the lubrication of tribological systems with a high upper operating temperature, for example, at operating temperatures above 160°C and where continuous relubrication is not possible. The use of per- or polyfluorinated products, such as polyfluorinated polyethers or fluorinated silicone oils, as base oils is also common.

[0005] The PTFE powder can be used both as a thickener and as an additive in consistent lubricants. PTFE is known for its excellent lubricating properties, thanks to very low and consistent friction coefficients even under high loads. It can effectively prevent stick-slip and demonstrates good stability even when used under high shear stress. Furthermore, it is highly chemically inert to oxygen. This prevents the oxidation-related deposits frequently found in lubricating greases caused by the reaction of the thickener with atmospheric oxygen, thus achieving a consistent and long-lasting lubricating effect.

[0006] The disadvantage of using per- or polyfluorinated products is that they are problematic from an environmental perspective.

[0007] The object of the present invention is to provide a lubricating grease that exhibits low friction coefficients, particularly good antiwear (AW) and extreme pressure (EP) properties, and can be used for the lubrication of tribological systems with high energy efficiency requirements over a wide temperature range, e.g., in the automotive sector. Furthermore, the lubricating grease should be able to dispense with the use of PTFE as a thickener or additive.

[0008] This task is solved by a lubricating grease comprising

[0009] - from 30 wt% to 60 wt% silicone oil,

[0010] - from 10 wt% to 35 wt% mineral oil,

[0011] - from 10 wt% to 45 wt% overbased calcium sulfonate thickener, the amounts being based on the total weight of the lubricating grease.

[0012] Surprisingly, it was found that the inventive lubricating grease eliminates the need for PTFE as a thickener or additive, yet still exhibits very low friction coefficients combined with good antiwear (AW) and extreme pressure (EP) properties. Thus, the lubricating grease can also be used for the lubrication of tribological systems with high energy efficiency requirements, for example, in the automotive sector, and over a wide temperature range.

[0013] It was also surprising that the lubricating grease according to the invention, despite its relatively high silicone oil content, exhibits very good anti-wear (AW) and extreme pressure (EP) properties, as silicone oils are known to lack these properties. For this reason, silicone oil is usually additived or thickened with special solid lubricants, such as PTFE, in practice to improve its friction properties. The lubricating grease according to the invention, on the other hand, does not require the use of PTFE as a thickener or additive.

[0014] It is also known and has been confirmed in practical tests that typical liquid antiwear (AW) and extreme pressure (EP) additives, such as sulfur carriers, amine phosphates, neutral phosphoric acid esters, (organic) carbamates, thiophosphates cannot replace PTFE.

[0015] Furthermore, it was found that even typical solid lubricants such as calcium carbonate do not sufficiently improve the antiwear (AW) and extreme pressure (EP) properties of silicone oil.

[0016] Surprisingly, however, the antiwear (AW) and extreme pressure (EP) properties have been improved by using an overbased calcium sulfonate thickener. Without committing to a specific mechanism, it is suspected that the calcium carbonate contained in the overbased calcium sulfonate thickener, unlike conventional calcium carbonate, can perform the function of separating the friction partners—possibly because it has a micellar structure and is thus very finely distributed.

[0017] Practical tests have shown that the use of the overbased calcium sulfonate thickener in the lubricating grease according to the invention enables the inherently non-homogeneous base oils silicone oil and mineral oil to be permanently and homogeneously mixed. In particular, practical tests have shown that the overbased calcium sulfonate thickener in the lubricating grease according to the invention exhibits performance almost equivalent to that of PTFE.

[0018] In a preferred embodiment of the invention, the lubricating grease therefore contains no polytetrafluoroethylene and / or polytetrafluoroethylene in a proportion of less than 4 wt.%, more preferably less than 2 wt.%, more preferably less than 1 wt.%, more preferably less than 0.5 wt.%, and more preferably less than 0.1 wt.%, in each case based on the total weight of the lubricating grease. However, in a particularly preferred embodiment of the invention, the lubricating grease contains no polytetrafluoroethylene.

[0019] The polytetrafluoroethylene content in the lubricating grease is preferably determined based on the fusion enthalpy of PTFE using the standard DIN EN ISO 11357-1, edition 2008.04. The measurement is conveniently carried out as follows: The oil phase of the lubricating grease, including the soluble additive components, is separated from solid, insoluble components (e.g., thickeners, insoluble additives, and / or solid lubricants) by extraction with a suitable solvent, as this increases measurement accuracy. The polytetrafluoroethylene is part of the insoluble components. Depending on the base oil used, suitable solvents include special gasoline 80 / 110, ethanol, and / or methyl perfluorobutyl ether. Special gasoline 80 / 110 is particularly suitable for lubricating greases whose base oil contains mineral oils, PAO, alkylated aromatics, phenyl ethers, esters, silicone oils and polyglycols with no or low content of ethylene oxide and their mixtures.Ethanol is particularly suitable for lubricating greases containing polyglycol base oils with a high ethylene oxide content. Methyl perfluorobutyl ether is particularly suitable for lubricating greases containing perfluoropolyethers as base oils. Greases containing two immiscible oils are preferably subjected to two extractions. Such greases are commonly referred to as hybrid greases. For example, such hybrid greases can contain both perfluoropolyethers and, preferably, esters. Such a hybrid grease is therefore preferably extracted with both 80 / 110 special gasoline and methyl perfluorobutyl ether to separate both oils and the additives soluble therein. The solvent residues are stripped off from the resulting residue. The dried residue is then related to the amount of lubricating grease used. This gives the residue content in wt.%.20 mg of the dry residue is weighed into a 25 μl aluminum DSC crucible and heated to 600°C at a heating rate of 10 K / min. The endothermic signal between 300 and 450°C is integrated; the area of ​​the peak (enthalpy sample) is proportional to the amount of PTFE in the residue. For calibration, a pure PTFE micropowder (particle size D50 according to ASTM D4894 = 5 μm, melt flow index at 372°C / 2.16 kg / 2095 mm according to ASTM D1238 = 0.5 g / 10 min) is measured analogously (enthalpy reference). The PTFE content in the lubricating grease is determined using the following equation:

[0020] (Enthalpy sample) / (Enthalpy reference) * Residue content in wt.% = PTFE content in wt.%

[0021] For the purposes of this invention, the term "lubricating grease" is understood in the conventional sense. Lubricating greases are defined as solid to semi-liquid substances that can be produced by dispersing a thickener in a liquid lubricant. In addition to the thickener, lubricating greases can also contain other additives that impart special properties to the grease. Lubricating greases are defined in the standard ASTM D217-21, edition 2021.07.

[0022] Mineral oils are base oils that can be produced by distilling crude oil. Mineral oils contain paraffinic (saturated chain-shaped hydrocarbons), naphthenic (saturated cyclic hydrocarbons), and / or aromatic (cyclic hydrocarbons with an aromatic double bond system) components. They usually contain mixtures of the aforementioned components. In addition, mineral oils can also contain alkenes (olefins) and, depending on their origin, small amounts of sulfur-containing and nitrogen-containing organic compounds. Mineral oils are assigned to groups I, II, II+, and III according to the classification of the American Petroleum Institute (API) [NLGI Spokesman, N. Samman, Volume 70, Number 11, p. 14ff]. The mineral oil is preferably a solvent-refined paraffinic mineral oil. More preferably, the mineral oil contains a combination of hydrocarbons obtained as a raffinate from the solvent extraction process.More preferably, the mineral oil contains at least 50% by weight, based on the total weight of the mineral oil, of saturated C20 to C50 hydrocarbons.

[0023] Preferably, the mineral oil has a kinematic viscosity at 40°C of 12 mm 2 / s up to 400 mm 2 / s, more preferably 16 mm 2 / s up to 100 mm 2 / s, especially 18 mm 2 / s up to 65 mm 2 / s, measured according to DIN EN 16896 - 2017-02.

[0024] In a further preferred embodiment of the invention, the lubricating grease contains no boric acid and no boric acid compounds selected from metal borates and boric acid esters and / or boric acid and boric acid compounds selected from boric acid, metal borates and boric acid esters only in a proportion of less than 2 wt.%, more preferably less than 1 wt.%, based on the total weight of the lubricating grease. "Proportion of boric acid and boric acid compounds" refers to the combined amounts of boric acid and boric acid compounds present in the lubricating grease, if any. This embodiment is advantageous because these compounds are toxicologically undesirable. In a particularly preferred embodiment of the invention, the lubricating grease therefore contains no boric acid and no boric acid compounds selected from boric acid, metal borates and boric acid esters.

[0025] Metal borates are boron compounds obtained by chemically reacting boric acid with inorganic bases. Boric acid esters are boron compounds obtained by chemically reacting boric acid with organic alcohols.

[0026] According to the invention, the lubricating grease contains from 30 wt.% to 60 wt.%, preferably from 33 wt.% to 57 wt.%, even more preferably from 35 wt.% to 55 wt.%, in particular from 40 wt.% to 50 wt.% silicone oil, in each case based on the total weight of the lubricating grease. The silicone oil acts as a base oil. The silicone oil is preferably a fluorine-free silicone oil, i.e. it has no fluorine atoms in its structural formula. The silicone oil preferably contains alkylated silicone oil, arylated silicone oil and / or alkylaryl silicone oil. The silicone oil particularly preferably contains alkylated silicone oil, preferably C1-5 alkylated silicone oil, for example methylated silicone oil, in particular dimethyl silicone oil and / or phenylmethyl silicone oil. The lubricating grease particularly preferably contains from 30 wt.% to 60 wt.%, preferably from 33 wt.% to 57 wt.%, even more preferably from 35 wt.% to 55 wt.%, in particular from 40 wt.% to 50 wt.% of dimethyl silicone oil, in each case based on the total weight of the lubricating grease.

[0027] The silicone oil may also be a mixture of silicone oils with different chemical compositions and / or different kinematic viscosities.

[0028] The silicone oil, preferably the dimethyl silicone oil and / or phenylmethyl silicone oil, preferably has a kinematic viscosity at 25°C of 550 mm 2 / s up to 15,000 mm 2 / s, more preferably 700 mm 2 / s up to 10,000 mm 2 / s, more preferably 800 mm 2 / s up to 8 000 mm 2 / s, measured according to DIN EN 16896 - 2017-02. The silicone oil preferably also has a kinematic viscosity at 40°C of 500 mm 2 / s up to 10,000 mm 2 / s, more preferably 1000 mm 2 / s up to 6000 mm 2 / s, measured according to DIN EN 16896 - 2017-02.

[0029] In a further preferred embodiment, the silicone oil has a kinematic viscosity at 25°C of 10 mm 2 / s up to 1,000,000 mm2 / s, more preferably 50 mm 2 / s up to 100,000 mm 2 / s, more preferably 100 mm 2 / s up to 25,000 mm 2 / s, measured according to DIN EN 16896 - 2017-02. The silicone oil preferably also has a kinematic viscosity at 40°C of 500 mm 2 / s up to 10,000 mm 2 / s, more preferably 1000 mm 2 / s up to 6000 mm 2 / s, measured according to DIN EN 16896 - 2017-02. These viscosities are particularly suitable for lubricating joints and actuators in automobiles.

[0030] In a preferred embodiment, the lubricating grease contains mineral oil in a proportion of 12 wt.% to 32 wt.%, in particular 15 wt.% to 30 wt.%, based on the total weight of the lubricating grease. In addition to the mineral oil and the silicone oil, the lubricant composition may contain other base oils. A base oil is understood to mean the base fluids commonly used for the production of lubricants, in particular oils that can be assigned to groups I, II, II+, III, IV, or V according to the classification of the American Petroleum Institute (API) [NLGI Spokesman, N. Samman, Volume 70, Number 11, p. 14ff]. Particularly preferred other base oils are selected from groups IV or V.Particularly preferred further base oils are selected from the group consisting of esters, ethers, in particular polyethers, phenyl ethers, perfluoropolyethers, synthetic hydrocarbons, in particular polyalphaolefins, synthetic hydrocarbons which do not belong to the class of polyalphaolefins, in particular alkylated naphthalenes, copolymers of unsaturated hydrocarbons, for example polymers of ethylene and alphaolefins (for example Lucant HC-600®), natural hydrocarbons, native oils and derivatives of native oils and mixtures thereof.

[0031] Particularly preferred further base oils according to the invention are esters, ethers, preferably polyethers, diphenyl ethers, polyphenyl ethers, synthetic hydrocarbons, especially polyalphaolefins, alkylated naphthalenes, copolymers of unsaturated hydrocarbons, and / or mixtures thereof. Very particular preference is given to ethers, preferably polyalkylene glycols, especially polypropylene glycol homopolymers and / or copolymers with ethyl groups and 1-methylethyl groups as carbon groups in the repeating unit.

[0032] In a particularly preferred embodiment of the invention, the further base oil is selected from the group consisting of esters, ethers, preferably polyethers, synthetic hydrocarbons, in particular polyalphaolefins, perfluoropolyethers, alkylated naphthalenes and mixtures thereof.

[0033] Other preferred base oils are polyethers. Polyethers are polymers whose organic repeating units are formed from ether functionalities (COC). In the subgroup of polyphenyl ethers, the carbon portion of the repeating unit consists of phenyl groups. In the subgroup of polyalkylene glycols, the carbon portion of the repeating unit consists of substituted or unsubstituted ethyl groups (OCCO), such as ethyl groups, 1-methylethyl groups, or 1-ethylethyl groups. Such polyalkylene glycol homopolymers are typically also referred to as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Polyalkylene glycols also refer to polymers that contain mixtures of variously substituted ethyl groups, such as ethyl groups, 1-methylethyl groups, or 1-ethylethyl groups, as carbon portions of the repeating unit.These polyalkylene glycols can be present both as block polymers and as polymers with a random distribution of carbon groups. Other preferred polyethers are polytetrahydrofurans and oxetane polymers, which have four (OCCCCO) or three carbon atoms (OCCCO) in the carbon portion of the repeat unit, respectively.

[0034] Preferred polyethers are polyalkylene glycols. Particularly preferred polyalkylene glycols are polypropylene glycol homopolymers and / or copolymers with ethyl groups and 1-methylethyl groups as carbon groups in the repeating unit.

[0035] The end groups of the polyalkylene glycols, polytetrahydrofurans and oxetane polymers are, independently of one another, preferably hydroxide groups and / or alkoxide groups, where the alkyl portion of the alkoxide groups can be formed from C1 to C20 alkyl groups. The end groups of the polyalkylene groups can additionally be substituted. The end group can be introduced during the preparation of the polyalkylene glycols, polytetrahydrofurans and oxetane polymers by reacting the monomeric ethylene oxides, tetrahydrofurans or oxetanes with a monofunctional starter. Monofunctional starters are preferably alcohols, in particular butanol. Two or more chains of polyalkylene glycols, polytetrahydrofurans and oxetane polymers can also be linked via an end group. Alkyl groups are preferred as the linking end group. This can occur during the preparation of the polyalkylene glycols, polytetrahydrofurans and oxetane polymers from ethylene oxides, tetrahydrofurans orOxetanes can be prepared with a nucleophilic di- or higher-functional starter. Examples of difunctional starters are diols, especially 1,2-ethanediol.

[0036] Very particularly preferred polyethers are polyalkylene glycols, even more preferably polypropylene glycol homopolymers and / or copolymers with ethyl groups and 1-methylethyl groups as carbon groups in the repeating unit. The aforementioned polyalkylene glycols are also particularly preferred when butanol or 1,2-ethanediol are used as starters. The aforementioned polyalkylene glycols are also particularly preferred when they have a butyl group as the end group and / or are linked via an ethylene group.

[0037] Preferred esters are carboxylic acid esters, preferably monoesters, diesters, triesters, tetraesters, pentaesters, polyesters, estolides, and mixtures thereof. Diesters, triesters, tetraesters, pentaesters, polyesters, estolides, and mixtures thereof are particularly preferred. Estolides are especially preferred, as they can be particularly suitable for food-grade lubricants.

[0038] Likewise preferred esters are aromatic esters, preferably of aromatic di-, tri-, or tetracarboxylic acids with one or a mixture of C7- to C22-alcohols, and aliphatic esters, preferably of monocarboxylic acids and / or dicarboxylic acids with a mono-, di-, tri-, tetra-, penta-, or hexa-alcohol having a carbon number of 3 to 22, present individually or in mixtures, polyol esters, such as preferably complex esters, estolides, and mixtures thereof, these esters preferably being suitable for NSF / H1. The acid and / or alcohol component of the carboxylic acid esters, independently of one another, preferably has a number of carbon atoms from C3 to C54.

[0039] Estolides are oligomers of aliphatic hydroxycarboxylic acids, preferably of 12-hydroxystearic acid or oligomers of unsaturated carboxylic acids, preferably of oleic acid, in which the terminal carboxylic acid group is esterified with a mono-alcohol, dialcohol, trialcohol and / or tetraalcohol, preferably branched monoalcohols, very particularly preferably Guerbet alcohols, and in which any free hydroxide groups may be esterified by reaction with monocarboxylic acids or dicarboxylic acids.

[0040] Particularly preferred are aliphatic esters of monocarboxylic acids and / or dicarboxylic acids having a carbon number of C3 to C40 with a mono-, di-, tri-, tetra, penta, hexa-alcohol having a carbon number of 3 to 22, present individually or in mixtures.

[0041] Even more preferred are aliphatic esters of monocarboxylic acids and / or dicarboxylic acids having a carbon number of C3 to C40 with a mono-, tri-, tetra, hexa-alcohol having a carbon number of 3 to 22, present individually or in mixtures.

[0042] Even more preferred are aliphatic esters of monocarboxylic acids having a carbon number of C5 to C22 with a tri, tetra, hexa-alcohol having a carbon number of C3 to C10, in particular trimethylolpropane, pentaerythritol and / or dipentaerythritol, present individually or in mixtures, and / or of dicarboxylic acids having a carbon number of C6 to C40, in particular C18 dimer acids, with a mono- and / or dialcohol having a carbon number of 6 to 22, present individually or in mixtures.

[0043] Particularly preferred are esters of trimethylolpropane, pentaerythritol, and / or dipentaerythritol with aliphatic C7- to C22-carboxylic acids and / or esters of C18 dimer acids with C7- to C22-alcohols. Particularly preferred are esters for which approval for incidental contact with food is possible, particularly in accordance with EN ISO 21469 (February 2006), Annex B. Approval should preferably be granted by the National Sanitation Foundation (NSF), USA.

[0044] The proportion of the additional base oil in the lubricant composition, if present, is preferably from 5 to 35 wt.%, more preferably from 10 to 25 wt.%, in particular from 12 to 20 wt.%, in each case based on the total weight of the lubricating grease. In a preferred embodiment of the invention, the lubricating grease contains from 10 wt.% to 35 wt.%, preferably from 12 wt.% to 32 wt.%, in particular from 15 wt.% to 30 wt.%, of polyalphaolefin (PAO), in each case based on the total weight of the lubricating grease. The PAO can function as an additional base oil. An advantage of polyalphaolefin (PAO) is its good low-temperature behavior.

[0045] The polyalphaolefin preferably further has a kinematic viscosity at 40°C of 14 mm 2 / s up to 6000 mm 2 / s, more preferably 18 mm 2 / s up to 1500 mm 2 / s, especially 27 mm 2 / s up to 400 mm 2 / s, measured according to DIN EN 16896 - 2017- 02.

[0046] The polyalphaolefin may also comprise a mixture of polyalphaolefins of different chemical structure and / or different kinematic viscosity.

[0047] The polyalphaolefin can be an acid-catalyzed polyalphaolefin or a metallocene-catalyzed polyalphaolefin. The polyalphaolefin is preferably an acid-catalyzed polyalphaolefin.

[0048] According to the invention, the lubricating grease contains from 10 wt.% to 45 wt.%, preferably from 15 wt.% to 43 wt.%, more preferably from 15 wt.% to 41 wt.%, even more preferably from 15 wt.% to 36 wt.%, in particular from 16 wt.% to 33 wt.% of overbased calcium sulfonate thickener based on the total weight of the lubricating grease.

[0049] Overbased calcium sulfonate thickeners are well-known thickeners. They are described, for example, in Lubricants and Lubrication, 2005, Wiley-VCH Verlage GmbH Co. KGaA, Weinheim, p. 141, and, for example, in US Pat. No. 3,242,079;

[0050] 3,372,115 ; 3,376,222 , 3,377,283 ; and 3,492,231.

[0051] Overbased calcium sulfonate thickeners are assumed to form a micellar structure when combined with base oils such as silicone oil and / or mineral oil. The core of the micelle is formed by calcium carbonate with a proportion of crystalline calcium carbonate. Sulfonate and carboxylate anions accumulate on the surface of the calcium carbonate core.

[0052] According to the invention, the overbased calcium sulfonate thickener in the lubricating grease is therefore preferably present in a micellar structure.

[0053] The overbased calcium sulfonate thickener therefore preferably contains calcium sulfonate, calcium carbonate with a proportion of crystalline calcium carbonate, and calcium carboxylate. In addition to the crystalline calcium carbonate, the calcium carbonate may also contain amorphous calcium carbonate.

[0054] To calculate the proportion of overbased calcium sulfonate thickener in the lubricating grease, the sum of the proportions of calcium sulfonate, calcium carbonate with a proportion of crystalline calcium carbonate, and calcium carboxylate is determined according to the invention and based on the total weight of the lubricating grease. Preferably, the proportion of crystalline calcium carbonate based on the total amount of calcium carbonate is more than 90 wt.%, particularly preferably more than 95 wt.%.

[0055] More preferably, the proportion of crystalline calcium carbonate based on the total amount of overbased calcium sulfonate thickener is 25 wt.% to 50 wt.%.

[0056] A preferred process according to the invention for producing calcium sulfonate thickeners is a two-stage process comprising the steps of "promotion" and "conversion." Typically, the first step ("promotion") involves reacting a stoichiometric excess of calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) as the base source with an alkylbenzenesulfonic acid, carbon dioxide (CO2), and other acids, yielding an oil-soluble overbased calcium sulfonate with amorphous calcium carbonate dispersed therein. This reaction can be carried out in a suitable base oil, for example, silicone oil and / or mineral oil. This overbased calcium sulfonate is not (yet) considered a calcium sulfonate thickener, but is a liquid, usually a Newtonian liquid. The overbased calcium sulfonate can be introduced into a suitable base oil, for example, silicone oil and / or mineral oil.

[0057] The second step ("conversion") typically involves adding one or more conversion agents, such as propylene glycol, isopropyl alcohol, water, fatty acid, formic acid, and / or acetic acid, to the product of the promotion step, as well as a suitable base oil, such as silicone oil and / or mineral oil if necessary to prevent the reaction mixture from becoming too hard, to convert the amorphous calcium carbonate contained in the overbased calcium sulfonate into a very finely divided dispersion of crystalline calcium carbonate (calcite). When acetic acid or other acids are used as conversion agents, water and another non-aqueous conversion agent (a third conversion agent, e.g., an alcohol) are typically also used; alternatively, only water (without the third conversion agent) is added, but the conversion is then usually carried out in a pressure vessel.Since an excess of calcium hydroxide or calcium oxide is used to achieve overbasing, a small amount of residual calcium oxide or calcium hydroxide may also be present as part of the oil-soluble superfatted calcium sulfonate and becomes dispersed in the original fatty structure. The extremely finely divided calcium carbonate formed by the conversion, also called a colloidal dispersion, interacts with the calcium sulfonate to form a fat-like consistency, thereby forming the overbased calcium sulfonate thickener. Neutral conversion agents such as water and alcohols can act as swelling agents in the micelle core. Such overbased calcium sulfonate thickeners prepared by the two-step process are disclosed, for example, in U.S. Pat. Nos. 3,242,079; 3,372,115; 3,376,222; 3,377,283; and 3,492,231.

[0058] It is also possible to combine these two steps into a single step. In this one-step process, the overbased calcium sulfonate thickener is produced by reacting a suitable sulfonic acid with either calcium hydroxide or calcium oxide in the presence of carbon dioxide and a system of reagents that simultaneously act as both a promoter (generating the amorphous calcium carbonate overbased product by reacting carbon dioxide with an excess amount of calcium oxide or calcium hydroxide) and a converting agent (converting the amorphous calcium carbonate into very finely divided crystalline calcium carbonate). In this way, the fat-like consistency is formed in a single step, with the overbased, oil-soluble calcium sulfonate (the product of the first step of the two-step process, not yet a thickener) never actually being formed and being isolated as a separate product.This one-step process is disclosed, for example, in U.S. Patent Nos. 3,661,622, 3,671,012, 3,746,643 and 3,816,310.

[0059] In a preferred embodiment of the invention, the overbased calcium sulfonate thickener is prepared by a process comprising adding to an overbased calcium sulfonate one or more converting agents, preferably propylene glycol, isopropyl alcohol, water, fatty acid, formic acid and / or acetic acid, thereby obtaining the overbased calcium sulfonate thickener.

[0060] Overbased calcium sulfonate contains an excess of calcium carbonate and / or calcium hydroxide. Preferred embodiments of the process include those described above and below.

[0061] The calcium sulfonate thickener preferably has a primary particle size, measured according to DIN Spec 52407: 2015 DE, of 100 nm to 250 nm, more preferably of 120 nm to 200 nm.

[0062] The overbased calcium sulfonate thickener preferably contains calcium sulfonate. It is assumed that in the lubricating grease, the calcium sulfonate of the overbased calcium sulfonate thickener is oriented with respect to the base oil such that the polar part is oriented toward calcium carbonate particles and the non-polar part is oriented toward the oil phase. The term calcium sulfonate is intended to encompass a single calcium sulfonate compound or mixtures of different calcium sulfonate compounds. The calcium sulfonate preferably comprises mixtures of different calcium sulfonate compounds. For the sake of simplicity, the term calcium sulfonate is used below in the description of preferred embodiments; however, as explained above, it is also intended to encompass mixtures of different calcium sulfonate compounds.

[0063] The calcium sulfonate can contain a natural sulfonate derived from petroleum fractions, a synthetic sulfonate derived from the alkylation of aromatic compounds, or mixtures of natural or synthetic sulfonates. Synthetic sulfonates include alkylsulfonates and alkylarylsulfonates. The calcium sulfonate preferably contains alkylarylsulfonates, more preferably alkylbenzylsulfonates, and especially dialkylbenzylsulfonates, preferably dialkylbenzylsulfonates in combination with monoalkylbenzylsulfonates. In the alkylbenzylsulfonates, the alkyl is preferably formed as one or more side chains attached as substituents to the benzyl position of the benzyl ring. More preferably, each side chain independently has 1 to 25 carbon atoms, preferably 1 to 19 carbon atoms. The side chains can be straight-chain or branched-chain. Straight-chain side chains are preferred.More preferably, the calcium sulfonate comprises at least two structurally different alkylbenzylsulfonates.

[0064] In a particularly preferred embodiment, the calcium sulfonate contains a calcium salt of an alkylbenzylsulfonic acid of the following formula

[0065] where the radicals R1 and R2 are independently selected from hydrogen, C1-C25, preferably C1-C19 alkyl, with the proviso that R1 and R2 are not simultaneously hydrogen. R1 is preferably selected from hydrogen, C1-C4 alkyl, and R2 is selected from C7-C19 alkyl. Very particularly preferably, R1 is selected from hydrogen, C1-C4 alkyl, and R2 is selected from C10-C19 alkyl. The radicals R1 and R2 are preferably unbranched. The radical C(R1 R2) is preferably in the para-position to the sulfonic acid radical. The alkylbenzylsulfonic acid preferably contains a mixture of structurally different alkylbenzenesulfonic acids. The alkylbenzylsulfonic acid preferably contains a mixture of alkylbenzenesulfonic acids that differ in the chain length of their alkyl substituents.

[0066] In a particularly preferred embodiment, the calcium sulfonate contains a calcium salt of an alkylbenzylsulfonic acid of the following formula

[0067] where R1 is selected from C1-C4 alkyl, preferably C2-C4 alkyl and especially C3 alkyl, and R2 is selected from C4-C19 alkyl, preferably C5-C19 alkyl, more preferably C5-C19 alkyl and especially C9-C19 alkyl. Preferably, the C(R1 R2) radical is in the para-position to the sulfonic acid radical. Further preferably, the R1 and R2 radicals are unbranched.

[0068] More preferably, the calcium sulfonate contains a calcium salt of an alkylbenzylsulfonic acid of the formula where R1 is selected from hydrogen and R2 is selected from C3-C25 alkyl, preferably C5-C19 alkyl, more preferably C7-C19 alkyl, and especially C10-C19 alkyl. The radicals R1 and R2 are preferably unbranched. The calcium salt is preferably a mixture that can be obtained from structurally different alkylbenzenesulfonic acids. Likewise, the radical C(R1 R2) is preferably in the para-position to the sulfonic acid radical. Further preferably, the radicals R1 and R2 are unbranched.

[0069] In a particularly preferred embodiment, the calcium sulfonate contains a calcium salt of an alkylbenzylsulfonic acid of the following formula wherein R1 is selected from C1-C4 alkyl, preferably C2-C4 alkyl and in particular C3 alkyl and R2 is selected from C4-C19 alkyl, preferably C5-C19 alkyl, more preferably C8-C19 alkyl and in particular C9-C19 alkyl in combination with a calcium salt of an alkylbenzylsulfonic acid of the formula

[0070] where R1 is selected from hydrogen and R2 is selected from C3-C25 alkyl, preferably C5-C19 alkyl, more preferably C7-C19 alkyl, and especially C10-C19 alkyl. Preferably, the C(R1 R2) radical is in the para-position to the sulfonic acid radical. Likewise, the R1 and R2 radicals are unbranched. The calcium salt preferably represents a mixture that can be obtained from structurally different alkylbenzenesulfonic acids. Likewise, the alkyl substituent is in the para-position to the sulfonic acid radical.

[0071] In a particularly preferred embodiment of the invention, the overbased calcium sulfonate thickener contains calcium dodecylsulfonate. More preferably, the overbased calcium sulfonate thickener contains calcium octadecylsulfonate. Most preferably, the overbased calcium sulfonate thickener contains calcium dodecylsulfonate in combination with calcium octadecylsulfonate.

[0072] The calcium sulfonate thickener preferably further contains calcium carboxylate. The term calcium carboxylate is intended to encompass a single calcium carboxylate compound or mixtures of different calcium carboxylate compounds. For the sake of simplicity, the term calcium carboxylate is used below in the description of preferred embodiments, although, as explained above, it is also intended to encompass mixtures of different calcium carboxylate compounds. In a preferred embodiment of the invention, the calcium carboxylate comprises C1-C20 alkyl carboxylate. Preferably, the calcium carboxylate comprises a combination of calcium acetate and / or calcium propionate with calcium stearate. More preferably, the calcium carboxylate comprises calcium acetate in combination with calcium stearate, preferably calcium acetate in combination with

[0073] Calcium hydroxystearate, especially calcium acetate in combination with calcium 12-hydroxystearate.

[0074] The calcium sulfonate thickener preferably also contains calcium carbonate with a proportion of crystalline calcium carbonate.

[0075] In a preferred embodiment, the crystalline calcium carbonate contains calcium carbonate with a calcite crystal structure. The crystalline calcium carbonate may further contain calcium carbonate with a vaterite and / or calcium carbonate with an aragonite structure.

[0076] In a preferred embodiment, the overbased calcium sulfonate thickener is present at least partially in the form of micelles. Micelles are aggregated molecular complexes (aggregates) of amphiphilic molecules. This is advantageous because the thickener components are very finely distributed and can therefore particularly effectively perform the function of separating the friction partners.

[0077] In a preferred embodiment of the invention, the lubricating grease contains 1 wt.% to 20 wt.%, preferably from 3 wt.% to 15 wt.%, even more preferably from 4 wt.% to 11 wt.%, each based on the total weight of the lubricating grease, of co-thickener. The co-thickener is preferably selected from bentonite, lithium soap, in particular Li-12-hydroxystearate, boron nitride, talc, graphite, metal phosphate, polyetheretherketone (PEEK), polyphenylene sulfide, in particular calcium phosphate, molybdenum disulfide, polyimide, melamine cyanurate, tin sulfide, sodium pyrophosphate, sodium thiosulfate, zinc sulfide, and / or fumed silicon dioxide. More preferably, the lubricating grease contains from 1 wt.% to 20 wt.%, preferably from 3 wt.% to 15 wt.%, even more preferably from 4 wt.% to 11 wt.%, in each case based on the total weight of the lubricating grease, of bentonite and / or pyrogenic silicon dioxide as co-thickener.The co-thickener preferably contains bentonite and fumed silica, particularly preferably in a ratio of bentonite to fumed silica of 30 wt.% : 70 wt.% to 70 wt.% : 30 wt.%. Preferred fumed silica is fumed silica functionalized with organic groups. The bentonite preferably has a particle size, measured by laser diffraction, evaluated using Mie theory (ISO 13320:2020-1), of 2 to 15 pm.

[0078] Suitable fumed silica is described, for example, in the technical journal "Technical Overview: Aerosil-Pyrogenic Silica" by Evonic Industries 03-2017. This journal also describes suitable fumed silica functionalized with organic groups.

[0079] In a particularly preferred embodiment, the fumed silica is fumed silica functionalized with organic groups.

[0080] Particularly preferably, the functionalized pyrogenic silicon dioxide has a BET surface area, measured according to ISO 9277 2014 01, of 10 to 500 m 2 / g, more preferably from 50 to 400 m 2 / g, especially from 50 to 200 m 2 / g. More preferably, the functionalized pyrogenic silicon dioxide has a primary particle size, measured by transmission electron microscopy, of 5 to 50 nm. More preferably, the functionalized pyrogenic silicon dioxide has a tapped density measured according to ISO787 / 11 1995 of 50 g / l to 280 g / l, even more preferably of 50 g / l to 200 g / l. More preferably, the functionalized pyrogenic silicon dioxide has a carbon content, measured according to ISO-3262-20 2021, of 0.5 wt.% to 8.8 wt.%, preferably of 0.5 wt.% to 6 wt.%, in particular of 0.5 wt.% to 2 wt.%.

[0081] Preferred organic groups are branched or unbranched aliphatic and / or aromatic groups, preferably with 1 to 20 carbon atoms. Preferred aromatic groups have 6 to 10 carbon atoms. Preferred aliphatic groups have 1 to 10 carbon atoms. Particularly preferred organic groups are methyl, ethyl, propyl, vinyl, butyl, pentyl, hexyl, heptyl, octyl, and / or phenyl. Methyl groups are particularly preferred organic groups. Another advantage of using these materials is their friction level, which is comparable to PTFE even under high tribological loads, and the fact that they enable lubrication concepts with significantly lower shear viscosities compared to PTFE products.

[0082] More preferably, the lubricating grease contains 0.1 to 8 wt.% additives selected from the group consisting of corrosion protection additives, antioxidants, wear protection additives, metal deactivators, ion complexing agents and / or UV stabilizers.

[0083] Antioxidants particularly suitable according to the invention are the following compounds: styrenated diphenylamines, diaromatic amines, phenolic resins, thiophenol resins, phosphites, butylated hydroxytoluene, butylated hydroxyanisole, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, octylated / butylated diphenylamine, di-alpha-tocopherol, di-tert-butyl-phenyl, benzenepropanoic acid, sulfur-containing phenolic compounds and mixtures of these components.

[0084] Also suitable antioxidants are compounds containing sulfur, nitrogen, and / or phosphorus in the molecule. Preferred compounds containing sulfur, nitrogen, and / or phosphorus in the molecule are selected from the group consisting of aromatic amine antioxidants, such as alkylated phenyl-alpha-naphthylamine, dialkyldiphenylamine, sterically hindered phenols such as butylhydroxytoluene (BHT), phenolic antioxidants with thioether groups, Zn-, Mo-, or W-dialkyldithiophosphates, and phosphites.

[0085] Preferred corrosion inhibitors, metal deactivators, and / or ion complexing agents are triazoles, imidazolines, N-methylglycine (sarcosine), benzotriazole derivatives, N,N-bis(2-ethylhexyl)-ar-methyl-1H-benzotriazole-1-methanamine; n-methyl-N(1-oxo-9-octadecenyl)glycine, mixtures of phosphoric acid and mono- and diisooctyl esters reacted with (C11-14)-alkylamines, mixtures of phosphoric acid and mono- and diisooctyl esters reacted with tert-alkylamine and primary (C12-14)-amines, dodecanoic acid, triphenyl phosphorothionate, and amine phosphates, and mixtures thereof. Commercially available additives are the following: IRGAMET® 39, IRGACOR® DSS G, Amin 0; SARKOSYL® 0 (Ciba), COBRATEC® 122, CUVAN® 303, VANLUBE® 9123, CI-426, CI-426EP, CI-429 and CI-498.

[0086] Preferred antiwear additives according to the invention are amines, amine phosphates, phosphates, thiophosphates, phosphothionates, and mixtures of these components. Preferred antiwear additives are selected from the group consisting of antiwear additives based on diphenyl cresyl phosphate, amine-neutralized phosphates, alkylated and non-alkylated triaryl phosphates, alkylated and non-alkylated triaryl thiophosphates, zinc or Mo or W dialkyl dithiophosphates, carbamates, thiocarbamates, zinc or Mo or W dithiocarbamates, dimercaptothiadiazole, neutral calcium sulfonates, and benzotriazole derivatives. Commercially available antiwear additives include IRGALUBE® TPPT, IRGALUBE® 232, IRGALUBE® 349, IRGALUBE® 211 and ADDITIN® RC3760 Liq 3960, FIRC-SHUN® FG 1505 and FG 1506, NA-LUBE® KR-015FG, LUBEBOND®, FLUORO® FG, SYNALOX® 40-D, ACHESON® FGA 1820 and ACHESON® FGA 1810.

[0087] In a preferred embodiment of the invention, the lubricating grease is used for lubricating joints and actuators in automobiles. The lubricating grease is particularly suitable for lubricating ball joints, especially for commercial vehicles and / or for PA-overmolded joints, for sunroofs, spindle drives, especially spindle drives with nuts, for example, for rear-axle steering and / or the parking brake, for actuators, especially with sintered components, for belt starters and / or planetary gears.

[0088] In a particularly preferred embodiment of the invention, the lubricating grease is used to lubricate ceramic friction partners. The lubricating grease is particularly suitable for lubricating tribosystems consisting of ceramic friction partners. It was surprisingly found that the lubricating grease exhibits performance almost equivalent to PTFE in these applications, thus eliminating the need for PTFE. In the following non-inventive example, an attempt is made to improve the performance of silicone oil using conventional liquid additives.

[0089]

[0090] It turns out that the performance of silicone oil cannot be improved with the selected liquid additives.

Claims

Patent claims 1. A lubricating grease comprising from 30% to 60% by weight of silicone oil, from 10% to 35% by weight of mineral oil, from 10% to 45% by weight of overbased calcium sulfonate thickener, the amounts being based on the total weight of the lubricating grease.

2. Lubricating grease according to claim 1, characterized in that the lubricating grease contains no polytetrafluoroethylene and / or contains polytetrafluoroethylene in a proportion of less than less than 1 wt.%, more preferably less than 0.5 wt.%, more preferably less than 0.1 wt.%, in each case based on the total weight of the lubricating grease.

3. Lubricating grease according to claim 1 or 2, characterized in that the lubricating grease contains no boric acid and no boric acid compounds selected from boric acid, metal borates and boric acid esters and / or contains boric acid and boric acid compounds selected from metal borates and boric acid esters only in a proportion of less than 1 wt.%, based on the total weight of the lubricating grease.

4. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains the silicone oil in a proportion of 33 wt.% to 57 wt.%, more preferably 35 wt.% to 55 wt.%, in particular 40 wt.% to 50 wt.%, based on the total weight of the lubricating grease.

5. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains 30 wt.% to 60 wt.% dimethyl silicone oil, based on the total weight of the lubricating grease.

6. Lubricating grease according to one or more of the preceding claims, characterized in that the silicone oil has a kinematic viscosity at 25°C of 10 mm 2 / s up to 1,000,000 mm 2 / s, more preferably 50 mm 2 / s up to 100,000 mm 2 / s, more preferably 100 mm 2 / s up to 25,000 mm 2 / s, measured according to DIN EN 16896 - 2017-02.

7. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains polyalphaolefin (PAO) in a proportion of 10 wt.% to 35 wt.%, preferably 12 wt.% to 32 wt.%, in particular 15 wt.% to 30 wt.%, based on the total weight of the lubricating grease.

8. Lubricating grease according to claim 7, characterized in that the polyalphaolefin has a kinematic viscosity at 40°C of 14 mm 2 / s up to 6000 mm 2 / s, more preferably 18 mm 2 / s up to 1500 mm 2 / s, especially 27 mm 2 / s up to 400 mm 2 / s, measured according to DIN EN 16896 - 2017-02.

9. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains mineral oil in a proportion of 12 wt.% to 32 wt.%, in particular of 15 wt.% to 30 wt.%, based on the total weight of the lubricating grease.

10. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains overbased calcium sulfonate thickener in a proportion of 15 wt.% to 41 wt.%, more preferably 15 wt.% to 36 wt.%, in particular 16 wt.% to 33 wt.%, based on the total weight of the lubricating grease.

11. Lubricating grease according to one or more of the preceding claims, characterized in that the overbased calcium sulfonate thickener contains calcium sulfonate, calcium carbonate with a proportion of crystalline calcium carbonate and calcium carboxylate.

2. Lubricating grease according to one or more of the preceding claims, characterized in that the calcium sulfonate contains a calcium salt of an alkylbenzylsulfonic acid of the following formula wherein R1 is selected from C1-C4 alkyl, preferably C2-C4 alkyl and in particular C3 alkyl and R2 is selected from C4-C19 alkyl, preferably Cs-C19 alkyl, more preferably C8-C19 alkyl and in particular C9-C19 alkyl in combination with a calcium salt of an alkylbenzylsulfonic acid of the formula wherein R1 is selected from hydrogen and R2 is selected from C3-C25 alkyl, preferably C5-C19 alkyl, more preferably C7-C19 alkyl and especially C10-C19 alkyl.

13. Lubricating grease according to one or more of the preceding claims, characterized in that the overbased calcium sulfonate thickener contains calcium dodecylsulfonate in combination with calcium octadecylsulfonate.

14. Lubricating grease according to one or more of the preceding claims, characterized in that the lubricating grease contains 1 wt.% to 20 wt.%, preferably from 3 wt.% to 15 wt.%, more preferably from 4 wt.% to 11 wt.%, in each case based on the total weight of the lubricating grease, of bentonite and / or pyrogenic silicon dioxide as co-thickener.

15. Use of a lubricating grease according to one or more of the preceding claims for lubricating joints and actuators in automobiles.

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