Patent Application
20170327760
The invention relates to high-temperature lubricants, more particularly oils and greases, based on an aromatic ester, such as a trimellitic ester and mixtures of different trimellitic esters, alkylaromatics, estolides, and a fully hydrogenated or hydrogenated polyisobutylene or a mixture thereof, a thickener. The invention further relates to the use of this high-temperature grease for long-term service temperatures of up to 250° C.
In addition to the lubricating activity, the lubricants are required to fulfil a great many other functions: they must cool, reduce friction, wear, and force transmission, protect against corrosion, and at the same time exhibit a sealing effect. Furthermore, the high-temperature greases ought to be low in noise.
Conventional lubricants are unsuitable for high-temperature applications because at high temperatures they are destroyed, through oxidation reactions and/or thermal decomposition reactions and polymerizations, for example, and their lubricating properties are severely restricted. In the case of decomposition reactions, the lubricant is split into volatile components of low molecular mass. Evaporation of these components causes unwanted changes in viscosity, loss of oil, and excessive vapor formation. The result of this is a loss in the lubricating activity. Polymerization as well causes the lubricants to lose their lubricating activity, owing to the formation of insoluble polymerization products.
Removing these contaminants increases maintenance efforts and produces chemical waste which has to be disposed of, which is costly and inconvenient. On account of the increased cleaning and maintenance efforts, downtimes are increased. Overall, the use of unsuitable lubricants in high-temperature applications results in higher costs, since the working implements are fouled and there is a greater demand for lubricants. Furthermore, product quality is lowered.
Base oils used for high-temperature applications are often synthetic esters, since these esters possess very good oxidative, hydrolytic, and thermal stability.
In order to meet the diverse requirements in high-temperature applications, the lubricants are required to exhibit qualities including high stability, low coefficients of friction, and high wear resistance. In order to be able to ensure uniform lubrication even at high temperatures, there must be a liquid lubricating film maintained between metal parts throughout the processing operation. At the maximum processing temperature, therefore, the lubricant must undergo only little evaporation, form little residue, and form cracking residues to as small an extent as possible.
High temperatures often occur in the context of use in chains, roller bearings and plain bearings, in vehicle technology, in conveying technology, in mechanical engineering, in office technology, and also in industrial plants and machines, but also in the areas of household appliances and consumer electronics.
In roller bearings and plain bearings, lubricants ensure that a separating, load-transmitting lubricating film is built up between parts which slide or roll against one another. As a result, the metallic surfaces do not come into contact and there is therefore also no wear. The lubricants, therefore, have to satisfy exacting requirements. These requirements include extreme operating conditions, such as very high or very low speeds, high temperatures as a result of high speeds or of external heating, very low temperatures, in the case of bearings which operate in a cold environment, for example, or bearings which are used in the aerospace sector. The modern lubricants ought also to be able to be used under what are called cleanroom conditions, in order to prevent contamination of the room by the abrasion and/or by the consumption of lubricants. In the application of the modern lubricants, moreover, there ought to be no vaporization and hence no “varnishing”—where after a short time of application the lubricants become solid and no longer display a lubricating activity. Lubricants are also subject to particular requirements in use to the effect that the running surfaces of the bearings are not attacked by low friction, the bearing surfaces run with low noise, and that long run times without relubrication are achieved. Lubricants are also required to withstand exposure to forces, such as centrifugal force, gravity, and vibrations.
An important parameter for long functioning of a grease-lubricated roller bearing in the high-temperature range, as well as the upper service temperature, are the noise characteristics of the lubricant. In the event of participating in the circulation (being rolled over or flexed), a lubricating grease may excite oscillations in the roller bearing, which as “lubricant noise” is located in the 300 to 1800 Hz medium frequency bands and 1800 to 10 000 Hz high frequency bands, relative to the bearing noises in the low frequency band at 50 to 300 Hz. Superimposed on the lubricant noise are the noise peaks produced when the rolling bodies roll over hard particles, in the form of impact pulses on the bearing ring. Noise characteristics are evaluated according to the SKF BeQuiet+ method. Grease noise is classed as follows:
GNX: somewhat poorer than GN1 (very poor noise characteristics)
GN1: >95% of all peaks are <=40 μm/s (poor noise characteristics)
GN2: >95% of all peaks are <=20 μm/s; >98% of all peaks are <=40 μm/s (medium noise characteristics)
GN3: >95% of all peaks are <=10 μm/s; >98% of all peaks are <=20 μm/s; >100% of all peaks are <=40 μm/s (good noise characteristics)
GN4: >95% of all peaks are <=5 μm/s; >98% of all peaks are <=10 μm/s; >100% of all peaks are <=20 μm/s (very good noise characteristics)
The better the noise characteristics of a lubricating grease, the lower the bearing oscillations imposed by the lubricant. This is synonymous with a low load on the bearing, and leads to a longer functional life of the bearing system.
The object of the present invention is to provide a high-temperature oil and a high-temperature grease that meet the requirements specified above. In particular, the lubricating oil or grease is to exhibit good lubricating activity at high temperature over a long time period. Furthermore, the cracking residues formed are not to exhibit “varnishing”, but are instead to be redissoluble by means of fresh grease. Furthermore, the high-temperature lubricant is to have good stability to hydrolysis, be resistant to corrosion and to wear, and to possess good oxidation resistance and good low-temperature behavior adapted to the requirement. This is defined in the case of lubricating oils by the pour point and in the case of lubricating greases by the flow pressure at low temperatures. Moreover, the high-temperature grease ought to exhibit good noise characteristics, long running times, and is to produce substantially no wear phenomena on the part of the apparatus.
This object is achieved in accordance with the invention by means of a high-temperature oil comprising the following components:
a) 93.9 to 45 wt % of at least one oil selected from the group consisting of alkylaromatics, preferably an aliphatically substituted naphthalene, estolides, trimellitic esters, or a mixture of different trimellitic esters wherein the alcohol group of the ester is a linear or branched alkyl group having 8 to 16 carbon atoms;
b) 6 to 45 wt % of a polymer, specifically a hydrogenated or fully hydrogenated polyisobutylene, or a mixture of hydrogenated or fully hydrogenated polyisobutylene;
c) 0.1 to 10 wt % of additives, individually or in combination, selected from the group consisting of anticorrosion additives, antioxidants, antiwear additives, UV stabilizers, inorganic or organic solid lubricants.
This object is achieved in accordance with the invention by means of a high-temperature grease comprising the following components:
a) 91.9 to 25 wt % of at least one oil selected from the group consisting of alkylaromatics, preferably an aliphatically substituted naphthalene, estolides, trimellitic esters, or a mixture of different trimellitic esters wherein the alcohol group of the ester is a linear or branched alkyl group having 8 to 16 carbon atoms;
b) 6 to 45 wt % of a polymer, specifically a hydrogenated or fully hydrogenated polyisobutylene or a mixture of hydrogenated or fully hydrogenated polyisobutylene;
c) 0.1 to 10 wt % of additives, individually or in combination, selected from the group consisting of anticorrosion additives, antioxidants, antiwear additives, UV stabilizers, inorganic or organic solid lubricants, and
d) 2 to 20 wt % of thickener.
Surprisingly it has been found that the high-temperature oil of the invention and the high-temperature grease of the invention are notable for outstanding performance. Hence the high-temperature oil or high-temperature grease of the invention exhibits high thermal stability in combination with long lifetime and good lubricating properties.
The high-temperature oil of the invention comprises as ester compound an estolide or a mixture of different estolides, or an aliphatically substituted naphthalene or a mixture of different aliphatically substituted naphthalenes.
The preferred viscosities of the estolides, measured at 40° C., are between 30 and 500 mm2/sec. Particularly preferred are viscosities from 30 to 140 mm2/sec.
By estolides are meant ester compounds which are prepared with acidic or enzymatic catalysis from fatty acids, preferably oleic acid, or dicarboxylic acids, or a mixture of both. In this reaction, the acid function attacks the double bond of an adjacent fatty acid molecule, to form an ester compound of higher molecular mass. The terminal acid group is then conventionally esterified with an alcohol, preferably 2-ethylhexanol, and the remaining double bonds are subsequently hydrogenated or esterified with carboxylic acid—acetic acid for example. Other alcohols such as isoamyl alcohol or Guerbet alcohols, for example, are likewise conceivable for the esterification of the terminal acid group.
Further estolides may also be synthesized via a condensation of hydroxycarboxylic acids or a condensation of hydroxycarboxylic acids with fatty acids, examples being derivatives of oleic acid or of stearic acid. The chain lengths of the hydroxycarboxylic acids or unsaturated acids used may range from C6 to C54. The acids may contain further functional groups, e.g. amines, ethers, sulfur-containing groups.
Also conceivable, furthermore, is esterification with alpha-olefins or β-farnesene.
The high-temperature oil of the invention may comprise a second oil which comprises an alkylaromatic. Preference is given to using an aromatic. An aromatic for the purposes of the invention is a monocyclic, bicyclic or tricyclic ring system having four to fifteen carbon atoms, the monocyclic ring system being aromatic, or at least one of the rings in a bicyclic or tricyclic ring system being aromatic. Preference is given to using a bicyclic ring system, having preferably 10 carbon atoms.
The aromatic is preferably substituted by one or more aliphatic substituents. With particular preference the aromatic is substituted by one to four aliphatic substituents and more particularly by two or three aliphatic substituents.
An alkyl group in accordance with the invention is a saturated aliphatic hydrocarbon group having 1 to 30, preferably 3 to 20, more preferably 4 to 17, and more particularly 6 to 15 carbon atoms. An alkyl group may be linear or branched and is optionally substituted by one or more of the substituents stated above.
With particular preference in accordance with the invention, the lubricating oil comprises at least one aliphatically substituted naphthalene, more particularly at least one alkyl-substituted naphthalene. The naphthalene is preferably substituted by one to four aliphatic substituents and more particularly by two or three aliphatic substituents.
Practical experiments have shown that mixtures of differently substituted naphthalenes, i.e. mixtures of naphthalenes which have a different degree of substitution and different aliphatic substituents, are particularly suitable. By varying the mixture composition it is possible in this case for the properties, such as the viscosity, for example, of the high-temperature lubricant to be adjusted in a particularly simple way. Aliphatically substituted naphthalenes, furthermore, are notable for outstanding dissolution properties and high thermooxidative stability.
The viscosity, measured at 40° C., of the aliphatically substituted naphthalene is preferably 30 to 600 mm2/s, more preferably 30 to 300 mm2/s.
The high-temperature oil of the invention further comprises a polyisobutylene. Through appropriate choice of the polyisobutylene, especially with regard to degree of hydrogenation and molecular weight, it is possible to influence the properties of the oil of the invention in a desired way—for example, its kinematic viscosity and, above all, its formation of residue. The polyisobutylene may be used in hydrogenated or fully hydrogenated form, and a mixture of hydrogenated and fully hydrogenated polyisobutylene may also be used.
Preference is given to using fully hydrogenated polyisobutylenes. The polyisobutylene is present in an amount of 6 to 45 wt % in the composition, with preferably 10 to 45 wt % and more particularly 15 to 45 wt % being used.
The high-temperature oil of the invention further comprises from 0.1 to 10 wt % of additives, which are used individually or in combination and are selected from the group consisting of anticorrosion additives, antioxidants, antiwear additives, UV stabilizers, inorganic or organic solid lubricants.
The high-temperature grease of the invention comprises, as an ester compound, a trimellitic ester or a mixture of different trimellitic esters, the alcohol group of the ester being a linear or branched alkyl group having 8 to 16 carbon atoms. Depending on the choice of the aromatic ester it is possible to adapt the properties of the lubricant—for example, the viscosity, the viscosity/temperature characteristics, the oxidation resistance, and residue characteristics.
The high-temperature grease of the invention may comprise a second oil which comprises an alkylaromatic. Preference is given to using an aromatic. An aromatic for the purposes of the invention is a monocyclic, bicyclic or tricyclic ring system having four to fifteen carbon atoms, the monocyclic ring system being aromatic, or at least one of the rings in a bicyclic or tricyclic ring system being aromatic. Preference is given to using a bicyclic ring system, having preferably 10 carbon atoms.
The aromatic is preferably substituted by one or more aliphatic substituents. With particular preference the aromatic is substituted by one to four aliphatic substituents and more particularly by two or three aliphatic substituents.
An alkyl group in accordance with the invention is a saturated aliphatic hydrocarbon group having 1 to 30, preferably 3 to 20, more preferably 4 to 17, and more particularly 6 to 15 carbon atoms. An alkyl group may be linear or branched and is optionally substituted by one or more of the substituents stated above.
With particular preference in accordance with the invention, the lubricating grease comprises at least one aliphatically substituted naphthalene, more particularly at least one alkyl-substituted naphthalene. The naphthalene is preferably substituted by one to four aliphatic substituents and more particularly by two or three aliphatic substituents.
Practical experiments have shown that mixtures of differently substituted naphthalenes, i.e. mixtures of naphthalenes which have a different degree of substitution and different aliphatic substituents, are particularly suitable. By varying the mixture composition it is possible in this case for the properties, such as the viscosity, for example, of the high-temperature lubricant to be adjusted in a particularly simple way. Aliphatically substituted naphthalenes, furthermore, are notable for outstanding dissolution properties and high thermooxidative stability.
The viscosity, measured at 40° C., of the aliphatically substituted naphthalene is preferably 30 to 600 mm2/s, more preferably 30 to 300 mm2/s.
It is also possible, furthermore, to use estolides. Preferred viscosities, measured at 40° C., are between 30 and 500 mm2/sec. Particularly preferred are viscosities of 30 to 140 mm2/sec.
The high-temperature grease of the invention further comprises a polyisobutylene. Through appropriate choice of the polyisobutylene, especially with regard to degree of hydrogenation and molecular weight, it is possible to influence the properties of the grease of the invention in a desired way—for example, its kinematic viscosity. The polyisobutylene may be used in hydrogenated or fully hydrogenated form, and a mixture of hydrogenated and fully hydrogenated polyisobutylene may also be used. Preference is given to using fully hydrogenated polyisobutylenes. The polyisobutylene is present in an amount of 6 to 45 wt % in the composition, with preferably 10 to 45 wt % and more particularly 15 to 45 wt % being used.
According to a further preferred embodiment, the polyisobutylene has a number-average molecular weight of 115 to 10 000 g/mol, preferably of 160 to 5000 g/mol.
The high-temperature grease of the invention further comprises from 0.1 to 10 wt % of additives, which are used individually or in combination and are selected from the group consisting of anticorrosion additives, antioxidants, antiwear additives, UV stabilizers, inorganic or organic solid lubricants.
The high-temperature grease of the invention further comprises a thickener. The thickener in the high-temperature grease of the invention in the lubricant composition is either a reaction product of a diisocyanate, preferably 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane, 2,4′-diisocyanatophenylmethane, 4,4′-diisocyanato-biphenyl, 4,4′-diisocyanato-3,3′-dimethylphenyl, 4,4′-diisocyanato-3,3′-dimethylphenylmethane, which may be used individually or in combination, with an amine of the general formula R′2—N—R, or with a diamine of the general formula R′2—N—R—NR′2, where R is an aryl, alkyl or alkylene radical having 2 to 22 carbon atoms and R′ identically or differently is a hydrogen or an alkyl, alkylene or aryl radical, or with mixtures of amines and diamines,
or
is selected from Al complex soaps, simple metal soaps of the elements of the first and second main groups of the Periodic Table, metal complex soaps of the elements of the first and second main groups of the Periodic Table, bentonites, sulfonates, silicates, Aerosil, polyimides or PTFE, or a mixture of the aforesaid thickeners.
As additives for high-temperature oils and greases, the additives stated below have particularly good physical and chemical properties:
The addition of antioxidants may reduce or even prevent oxidation of the oil or grease of the invention, especially in the course of its use. In the event of oxidation, unwanted free radicals may form and, consequently, decomposition reactions may occur to an increased extent to the high-temperature lubricant. The addition of antioxidants stabilizes the high-temperature grease.
Antioxidants particularly suitable in accordance with the invention are the following compounds:
Styrenized diphenylamines, diaromatic amines, phenolic resins, thiophenolic resins, phosphites, butylated hydroxytoluene, butylated hydroxyanisole, phenyl-alpha-naphthylamine, phenyl-beta-naphthylamine, octylated/butylated diphenylamine, di-alpha-tocopherol, di-tert-butylphenyl, benzenepropanoic acid, sulfur-containing phenol compounds, phenol compounds, and mixtures of these components.
The high-temperature grease may, furthermore, comprise anticorrosion additives, metal deactivators or ion complexing agents. These include 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, mixture of phosphoric acid and mono- and diisooctyl esters reacted with (C11-14)-alkylamines, mixture of phosphoric acid and mono- and diisooctyl esters reacted with tert-alkylamine and primary (C12-14)-amines, dodecanoic acid, triphenyl phosphoorthionate, and amine phosphates. Commercially available additives are the following: IRGAMET® 39, IRGACOR® DSS G, Amine O; SARKOSYL® O (Ciba), COBRATEC® 122, CUVAN® 303, VANLUBE® 9123, CI-426, CI-426EP, CI429 and CI-498.
Further antiwear additives are amines, amine phosphates, phosphates, thiophosphates, phosphoorthionates, and mixtures of these components. The 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.
The grease may further comprise solid lubricants such as PTFE, BN, pyrophosphate, Zn oxide, Mg oxide, pyrophosphates, thiosulfates, Mg carbonate, Ca carbonate, Ca stearate, Zn sulfide, Mo sulfide, W sulfide, Sn sulfide, graphites, graphene, nanotubes, SiO2 modifications, or a mixture thereof.
Practical experiments have shown that the high-temperature oil or grease of the invention exhibits no decomposition phenomena or negligible decomposition phenomena up to a temperature of 250° C. This means that less than 10% of the lubricant undergoes decomposition.
As a further base oil, the high-temperature oil or grease of the invention may comprise an oil preferably selected from the group consisting of mineral oil, aliphatic carboxylic and dicarboxylic esters, fatty acid triglycerides, pyromellitic esters, diphenyl ethers, phloroglucinol esters and/or poly-alpha-olefins, alpha-olefin copolymers.
In one particular embodiment, the high-temperature oil or grease of the invention comprises an estolide, the main constituents of the estolide preferably being obtained by chemical or enzymatic processes on the basis of natural oils from the group of sunflower oil, rapeseed oil, castor oil, linseed oil, corn oil, safflower oil, soybean oil, linseed oil, groundnut oil, “Lesqueralle” oil, palm oil, olive oil, or mixtures of the aforesaid oils.
Practical experiments have shown that the high-temperature oil or grease of the invention, on the basis of its physical and chemical properties, is outstanding in the context of use in chains, roller bearings and plain bearings, in vehicle technology, in conveying technology, in mechanical engineering, in office technology, and also in industrial plants and machines, but also in the areas of household appliances and of consumer electronics. On account of its good temperature resistance, it may be employed even at high service temperatures up to 260° C., preferably at temperatures of 150 to 250° C.
The invention further relates to a method for producing the high-temperature oil or grease described above, wherein the base oils and the additives are mixed with one another.
The invention is now elucidated in more detail with reference to the following examples.
Production of a High-Temperature Oil of the Invention
Estolides or aliphatically substituted naphthalenes are charged to a stirred vessel. At 100° C., with stirring, the polyisobutylene and optionally a further oil are added. The mixture is subsequently stirred for 1 hour in order to give a homogeneous mixture. The antiwear agents and the antioxidant are added to the vessel with stirring at 60° C. After about 1 hour, the completed oil can be dispensed into the intended containers.
The base data of the oil examples can be taken from table 3.
Furthermore, the abrasion behavior of the oils was measured in SRV in a method based on DIN 51834-2, and the loss on evaporation was measured in dynamic TGA. The results are shown in tables 4 and 5 and are reproduced graphically in
Production of a High-Temperature Grease of the Invention
The base oil is charged to a stirred vessel. At 100° C., with stirring, the polyisobutylene and optionally a further oil and the thickener are added.
The thickener is formed by in situ reaction of the reactants used in the base oil. The mixture is subsequently heated to 150° C. to 210° C., stirred for a number of hours and cooled again. In the cooling process, at approximately 60° C., the required antiwear agents, antioxidants, and anticorrosion agents are added. A homogeneous grease mixture is obtained by the concluding homogenization step via roller, colloid mill or the Gaulin.
The compositions of the high-temperature greases are shown in table 6.
The thickeners used in examples 3 to 8 are as follows:
example 3: LiOH, 12-hydroxystearic acid, azelaic acid
example 4: LiOH, 12-hydroxystearic acid, azelaic acid
example 5: LiOH, 12-hydroxystearic acid, azelaic acid
example 6: diurea; methylenediphenyl diisocyanate (MDI), octylamine, oleylamine
example 7: diurea; MDI, octylamine, oleylamine
example 8: diurea; MDI, octylamine, oleylamine
The general characteristics of grease specimens 3 to 8 are shown in table 7.
The losses on evaporation of the various grease specimens at 150° C. after 30 h are between 2% and 5%, thereby emphasizing the very good thermal stability of these grease designs.
A critical influence on the lubricating activity of a grease is possessed by the oil deposition. Here it should be ensured that first of all the oil deposition is not too high and that the oil runs from the bearing and therefore is no longer available to the tribological system, and on the other hand that no oil deposition is observed with loss of the lubricating activity of the grease. The oil deposition ought ideally to be between 0.5 and 8 wt %, to allow an optimum lubricating film to be formed in the bearing.
The greases of the examples were subjected to a DIN 51 821 FE 9 roller bearing test, which determines the lifetime of the greases under investigation and determines the upper service temperature of lubricating greases in roller bearings at moderate speeds and moderate axial loads.
The greases investigated and the results of the L10 and L50 values are shown in table 8.
Table 8 shows that the running times, as a result of the use of PIB in conjunction with various base oils, exhibit long running times and are therefore suitable for high application temperatures in long-term operation.
Furthermore, the noise characteristics of the greases were measured in accordance with SKF Be Quiet+ for examples 3 to 8. The results are reported in table 9.
The noise characteristics of the various grease formulations are influenced very positively by the use of the fully hydrogenated polyisobutylene. With the exception of example 6, good to very good noise qualities can be achieved.
The properties of the grease of example 3, for which fully hydrogenated PIB was used, were then compared with a grease (comparative example 3) containing a PIB in which double bonds were still present, in other words a non-fully hydrogenated PIB.
The rest of the composition of the grease of comparative example 3 corresponded to that of inventive example 3.
The comparison of the greases with fully hydrogenated PIB and non-fully hydrogenated PIB in table 10 shows that the grease of inventive example 3 exhibits twice the running time in the FE9 test, and has lower losses on evaporation and significantly better noise characteristics.
For verifying the advantageous properties of the oil containing fully hydrogenated PIB, it was compared with an oil containing a partially hydrogenated PIB. Table 11 shows the results.
Table 11 shows that there are distinct differences in connection with the use of fully hydrogenated and partially hydrogenated PIB. Thus the dissolution of the residue on the basis of the partially hydrogenated PIV is no longer possible, whereas the oil with the fully hydrogenated PIB exhibits very good redissolution properties.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2014 018 718.7 | Dec 2014 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/002322 | 11/19/2015 | WO | 00 |
