Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M111/00—Lubrication compositions characterised by the base-material being a mixture of two or more compounds covered by more than one of the main groups C10M101/00 - C10M109/00, each of these compounds being essential
  • C10M111/04—Lubrication compositions characterised by the base-material being a mixture of two or more compounds covered by more than one of the main groups C10M101/00 - C10M109/00, each of these compounds being essential at least one of them being a macromolecular organic compound
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
  • C10M169/04—Mixtures of base-materials and additives
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M171/00—Lubricating compositions characterised by purely physical criteria, e.g. containing as base-material, thickener or additive, ingredients which are characterised exclusively by their numerically specified physical properties, i.e. containing ingredients which are physically well-defined but for which the chemical nature is either unspecified or only very vaguely indicated

Definitions

• the present invention is related to novel lubricants characterized as stable liquid emulsions or liquid-in-liquid dispersions and methods of lubrication using the same.
• the invention is related to lubricant emulsions that are comprised of a low viscosity carrier fluid and a relatively small amount of a higher viscosity fluid, the combination imparting superior lubrication properties to the composition such as low viscosity and thick lubricating films.
• Lubrication results from the formation of a film of lubricant that is entrained into movable contacting surfaces of a mechanical assembly. The film separates the surfaces, thereby reducing friction and mechanical wear. Thicker films generally impart greater surface protection. Certain properties of lubricants are associated with lubrication performance and film thickness. In the case of liquid lubricants, viscosity of the fluid is directly correlated with the magnitude of the film (or film thickness) that builds and separates moving surfaces under contact, the greater viscosities contributing to greater film thickness.
• EHL elastohydrodynamic lubrication
• the variation of viscosity with pressure (expressed as the pressure- viscosity coefficient) contributes to lubricant film thickness.
• liquid lubricants of identical viscosity at an arbitrary operating temperature may differ in film thickness.
• the lubricant with a higher pressure- viscosity coefficient provides greater film thickness.
• lubricants with high pressure- viscosity coefficients typically show greater variation of viscosity with temperature.
• the variation of viscosity with temperature is generally expressed as viscosity index (VI), and lubricants showing greater variation (reduced film thickness at higher temperatures) are characterized as having lower VI.
• VI viscosity index
• the lower VI counterbalances any benefit derived from a high pressure- viscosity coefficient at higher temperatures.
• the present invention encompasses novel lubricant compositions comprising at least two components, a carrier fluid and a minor amount of higher viscosity fluid, which are substantially immiscible. Together the two fluids form a stable emulsion capable of producing a lubricating film thickness greater than the expected film thickness.
• preferred lubricant compositions of the present invention comprise a low viscosity, carrier fluid and a minor amount of an immiscible or semi-miscible higher viscosity fluid. More specifically, preferred lubricant compositions of the present invention comprise a relatively non-polar, hydrocarbon carrier fluid and a minor amount of an immiscible or semi-miscible polar, hydrocarbon fluid. More specifically, preferred lubricant compositions of the present invention comprise a hydrocarbon carrier fluid and from about 0.01% to about 10% by weight of a higher viscosity poly-THF ester fluid.
• the carrier fluid preferably comprises a blend of low viscosity PAO or a blend of low viscosity PAO with an alkylated aromatic fluid such as an alkylated naphthalene fluid.
• a method of lubrication which includes applying a lubricant to a mechanical assembly having movable contacting surfaces wherein the lubricant comprises a stable emulsion of (1) a carrier fluid and (2) a higher viscosity fluid which together produce a film thickness greater than the expected film thickness.
• a method of lubrication which includes the steps of providing a lubricant comprising a) hydrocarbon carrier fluid and b) poly-THF ester, and applying the lubricant to a mechanical assembly having movable contacting surfaces operating under elastohydrodynamic lubricating conditions.
• the carrier fluid preferably contains a blend of a low viscosity PAO and alkylated naphthalenes.
• the poly-THF ester fluid may be present in the lubricant in an amount of from about 0.01% to about 10% by weight.
• lubricant compositions are encompassed that are prepared by a method comprising the steps of:
• Figure 1 displays comparative data for compositions of the present invention showing enhanced film thickness, expressed as LP, as a function of temperature.
• Figure 2 displays comparative data for compositions of the present invention showing enhanced film thickness, expressed as LP, as a function of viscosity.
• Figure 3 displays reduced shear strength for compositions of the present invention with respect to shear strength of the carrier alone.
• lubricating film thickness EHL film thickness
• film thickness film thickness
• expected film thickness refers to a theoretical or calculated film thickness based on the expected contribution of the two fluid components.
• the expected film thickness may be calculated from the dynamic viscosity of the mixture.
• the expected film thickness may also be calculated from the dynamic viscosity or the dynamic viscosity and pressure-viscosity coefficient of the carrier fluid alone.
• the expected film thickness represents a film thickness based on the viscosity of at least the carrier fluid.
• substantially immiscible refers to fluids that tend to remain as separate phases when in contact with each other and do not readily form a single phase solution, even under mixing conditions such as elevated temperature and agitation.
• stable emulsion denotes a liquid composition having a continuous hydrocarbon, liquid phase and a discontinuous, hydrocarbon, liquid phase with the discontinuous phase remaining substantially evenly dispersed throughout the continuous phase for an extended time period, including reasonable storage and usage times.
• Preferred embodiments of the present invention can be characterized as novel liquid lubricants having at least two distinct liquid phases combined together as a stable emulsion.
• the components of the lubricant emulsion include a continuous phase of carrier fluid and a discontinuous phase of a fluid having a viscosity higher than the carrier fluid.
• These novel lubricants may be useful in many applications and are desirable for their superior properties related to low viscosities, improved film thickness, and better lubricating performance.
• the lubricants of the present invention comprise a carrier fluid.
• This fluid can be any mixture of hydrocarbons, but is more suitably a composition of hydrocarbons useful in lubrication applications.
• crude oil products including mineral oils, lube oils, lube oil distillates, solvent refined oils, hydrotreated oils, deasphalted oils, dewaxed oils, hydrocracked oils, oils derived from Fischer-Tropsch products, and the like may be used as the carrier fluid.
• lubricant base oils, synthetic oils, and blends thereof may also be used, including for example, polyalphaolefins (PAO), alkylated aromatic fluids, and mixtures thereof.
• PAO polyalphaolefins
• Carrier fluids comprising blends of polyalphaolefins and alkylated aromatics are particularly suitable for the present invention.
• the polyalphaolefins may be derived from alphaolefins which include, but are not limited to, from C2 to about C32 alphaolefins.
• a preferred PAO is PA06 which is characterized as a polyalphaolefin fluid having a kinematic viscosity of about 6 cSt at 100°C.
• Polyalphaolefins are well known to those skilled in the art and are well described in the literature, such as, for example, U.S. Pat. No. 4,041,098, herein incorporated by reference.
• a preferred alkylated aromatic may be alkylated naphthalene (AN).
• PAO-based carrier fluids containing from about 5% to about 95% by weight PAO and from about 5% to about 95% by weight alkylated aromatics, or more preferably from about 50% to about 90% by weight PAO and from about 10% to about 50% by weight alkylated aromatic, or even more preferably about 75% to about 85% by weight PAO and about 15% to about 25% by weight alkylated aromatic, are encompassed by the present invention.
• Other suitable PAO/alkylated aromatic blends include those disclosed in U.S. Patent No. 5,602,086, incorporated herein by reference in its entirety.
• the lubricants of the present invention also contain proportionally smaller amounts of a high viscosity fluid which contribute to lubrication performance.
• the high viscosity fluid may be characterized as having greater viscosity than the carrier fluid. Preferred viscosities range from about 10 to about 10,000 cSt at 100°C.
• the high viscosity fluid is also preferably substantially immiscible with the carrier fluid over the range of temperatures likely to be encountered under storage and lubricating conditions so as to maintain a two-phase system throughout its use.
• Suitable high viscosity fluids may include any type of viscous liquid.
• Preferable high viscosity fluids include, but are not limited to, polyethers and derivatives thereof.
• Polyethers may include any polymer or oligomer containing a plurality of ether moieties including, for example, polyalkylene glycols, such as polypropylene glycol and polyethylene glycol, and their corresponding monoethers, diethers, monoesters, and diesters.
• polyethers derived from the polymerization of cyclic ethers such as epoxides and oxiranes, including tetrahydrofuran.
• polymerized cyclic ethers suitable as high viscosity fluids are disclosed in U.S. Pat. Nos. 4,481,123; 4,568,775; 4,988,797; 5,180,856; and U.S. Ser. No. 09/192,966, incorporated herein by reference in their entireties.
• a particularly suitable high viscosity fluid may be poly- tetrahydrofuran (p-THF) ester fluids. These fluids can be made by the condensation reaction between p-THF and dibasic carboxylic acids to yield crosslinked p-THF products which are further reacted with monobasic carboxylic acids to endcap the terminal hydroxyl groups in a second condensation reaction.
• the resulting p-THF ester fluid may be described as a mixture of polymers comprising one or more each of the structural polymeric components depicted in formulas la, lb, and Ic below.
• Formula la displays the repeating THF unit and Formula lb displays the end-capped p-THF units of the ester fluid wherein R 1 is hydrogen or any substituted or unsubstituted to C 3 o alkyl, aryl, or aralkyl group, including but not limited to methyl, ethyl, n-proply, isopropyl, n-butyl, t- butyl, phenyl, and benzyl.
• formula Ic depicts the p-THF linking dicarboxylic acid repeating units of the ester fluid wherein R and R are, independently, hydrogen or any substituted or unsubstituted to C 30 alkyl, aryl, alkoxy, aryloxy, or aralkyl group.
• Variables m and p can be, independently, any integer of 1 or more.
• Other repeating units derived from, such as for example, substituted or unsubstituted ethylene glycols, propylene glycols, and cyclic ethers, may also be incorporated into the p-THF ester fluids.
• the p-THF ester fluids may be characterized as having viscosities ranging from about 150 to about 10,000 cSt at 100°C.
• the higher viscosity fluid is dispersed in the carrier fluid such that a stable emulsion or liquid-in- liquid dispersion is formed.
• the carrier fluid constitutes the continuous phase while the higher viscosity fluid constitutes the discontinuous phase of the stable emulsion.
• the higher viscosity fluid preferably remains evenly dispersed throughout the carrier for relatively long periods of time such that the emulsion is stable for its duration of use and reasonable storage time.
• Preferred lubricants of the present invention are characterized by small droplets of the high viscosity fluid dispersed in the carrier fluid. Ideally, the droplets are of a size sufficient to prevent rapid coalescence, thus contributing to emulsion stability.
• the mean number average droplet size (as determined for example by laser light scattering experiments) may range from about 0.01 microns to about 10 microns, or more preferably from about 0.1 microns to about 5 microns, or even more preferably, may be about 1 micron.
• the higher viscosity fluid is preferably present in the lubricant in an amount sufficient to promote improved lubrication performance relative to the carrier fluid.
• a sufficient amount of higher viscosity fluid is desirable to promote the formation of a two-phase lubricant.
• an amount of fluid may be required such that it surpasses the critical miscibility concentration.
• the higher viscosity fluid will be present in the carrier fluid in relatively small amounts.
• the amount of higher viscosity fluid in the lubricant ranges from about 0.1% to about 10% by weight, or more preferably from about 0.1% to about 10% by weight, or even more preferably from about 0.1% to about 3% by weight.
• the higher viscosity fluids of the present invention may comprise p-THF ester fluids in any amount.
• the presently described lubricant emulsions comprise ester fluids in amounts ranging from about 0.01% to about 10% by weight, or more preferably from about 0.01% to about 3% by weight, or even more preferably from about 0.01% to about 1.6% by weight.
• the lubricant comprises about 98.4% 4:1 PA06/AN mixture by weight and about 1.6% by weight p-THF ester fluid.
• the lubricants of the present invention may also contain additives that impart certain desirable properties to the compositions.
• the additives contemplated for use herein can be, for example, emulsifiers, rust and corrosion inhibitors, metal passivators, dispersants, antioxidants, thermal stabilizers, EP/antiwear agents and the like. These additives materials do not detract from the value of the compositions of this invention, rather they serve to impart their customary properties to the particular compositions in which they are incorporated.
• the lubricant emulsions of the present invention can be prepared by any method known in the art for making stable emulsions. More specifically, the lubricants described herein can be prepared by heating the carrier and the high viscosity fluid together to a temperature where they dissolve with agitation followed by cooling the mixture.
• a protocol for producing lubricants of the present invention may include the steps of combining carrier fluid and higher viscosity fluid, heating the resulting mixture with simultaneous agitation to a temperature at which the fluids substantially dissolve, and cooling the dissolved fluids to a temperature at which the fluids separate into a continuous phase and a discontinuous phase so that an emulsion is formed.
• lubricants Some of the most important and interesting aspects of the presently described lubricants include their unexpectedly superior lubricating performance. Generally, better lubricants form thicker films on the surfaces they coat. However, greater film thickness is a characteristic of fluids having high viscosity, itself an undesirable property that contributes to lower operating efficiencies. The lubricants described herein counter this film thickness/viscosity trend by showing unusually greater film thickness for their measured viscosities. This unusual property has been observed in a point contact optical EHL film thickness measurement device in which EHL film thickness is measured as a function of temperature and dynamic viscosity (product of kinematic viscosity and density). EHL film thickness can be expressed as LP, the lubricant parameter, which is a product of the dynamic viscosity, ⁇ 0 (cP), and the pressure-viscosity coefficient, (psi -1 ), according to equation 1 :
• LP is the lubricant contribution to film thickness in EHL contacts.
• the lubricant parameter (LP) concept is fully described in the industry publication Mobil EHL Guidebook, Fourth edition, Mobil Oil Corp., Technical Publications, Fairfax, VA, 1992, herein incorporated by reference.
• the lubricants of the present invention show only a slight increase in viscosity relative to carrier fluid alone, essentially no detectable difference in EHL film thickness (or LP) would be expected between the two.
• the dynamic viscosity and pressure- viscosity coefficient for lubricants of the present invention are approximately the same as for carrier fluid alone because the high viscosity fluid makes up such a small component of the lubricant.
• film thickness (LP) is predicted to be similar for both carrier fluid and present lubricant.
• Figures 1 and 2 display the superior film thickness, expressed as LP, of the presently described lubricants as a function of temperature and dynamic viscosity in comparison with carrier fluid alone.
• film thickness enhancement by the relatively small amounts of added high viscosity fluid can be up to 50% greater relative to the carrier fluid alone at any given viscosity. In order to achieve this result with standard liquid lubricants known in the art, approximately a 75% higher viscosity fluid at operating temperatures would be required.
• the lubricants of the present invention show reduced EHL shear strength (measured as traction coefficients) relative to carrier fluid alone as measured in a Line Contact Traction Rig described in U.S. Pat. No. 5,372,033, incorporated herein by reference.
• high viscosity fluids suitable for the present invention may have lower EHL shear strengths as compared with carrier fluid alone, and shear strength behavior can be considered, to a first approximation, as a linear additive function of the shear strength properties of the components.
• shear strength (SS) of a composition having components A (50% by weight), B (30% by weight), and C (20% by weight), with respective shear strengths a, b, and c, would be the weighted average of component shear strengths as expressed in equation 2 for this particular example:
• lubricant compositions of the present invention preferably have lower (or reduced) shear strengths as compared with the calculated shear strength based on the weighted average of the components of the lubricant composition.
• the lubricants described herein have shear strengths reduced by at least about 5%, or more preferably by at least about 15%, or even more preferably by at least about 30% as compared with the calculated shear strength for the individual components.
• Also contemplated by the present invention are methods of lubrication. Specifically, encompassed is a method of lubrication comprising the steps of providing a lubricant described herein and applying the lubricant to a mechanical assembly having movable contacting surfaces.
• the mechanical assembly may be any machine containing surfaces that repeatedly move against each other.
• the mechanical assembly can have components that operate normally under hydrodynamic, elastohydrodynamic, mixed boundary and/or boundary condition or combinations of any or all of these.
• the mechanical assembly operates under elastohydrodynmic lubricating conditions which involves the generation and maintenance of a lubricating film by the elastic deformation of non-conforming, contacting surfaces. Examples of mechanical assemblies that operate under elastohydrodynamic lubricating conditions include, but are not limited to, gears, rolling bearings, cams, and traction devices.
• the unusual properties of the lubricants of the present invention contribute to the observed superior lubricating performance. For instance, lowered shear strength and relatively low viscosities help maintain lower operating temperatures for decreased oil film breakdown and longer oil and machine component lives and improved energy efficiency. Further, reduction in shear strength contributes to reduced surface shear stress for longer machine component life involving reduced metal fatigue and higher scuffing loads. Greater film thickness benefits all aspects of lubrication, providing better protection of surfaces from reduced friction and operational wear and reducing the need for other lubricating additives to compensate for insufficient surface protection.
• Example 1 Lubricants of the present invention
• Table 1 Presented in Table 1 are four lubricant compositions (indicated by weight percent) and their corresponding carrier composition. Selected properties are included at the bottom of the table. Both PTE fluids were derived from p- THF and i-C9 mono-acid/oleic dimer diacid and differ by kinematic viscosity (specified below). As is evidenced in this Table 1, the viscosities of the carrier fluid and the lubricants of the present invention are comparable.
• Example 2 Process description for preparation of poly- r THF complex ester fluids
• Adipic acid 212 1.45 2.90

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