High temperature shear stable nanographite dispersion lubricants

US 20100022422Al

(12) Patent Application Publication (10) Pub. No.: US 2010/0022422 A1 (19) United States

Wu et al. (43) Pub. Date: Jan. 28, 2010

(54) HIGH TEMPERATURE SHEAR STABLE NANOGRAPHITE DISPERSION LUBRICANTS WITH ENHANCED THERMAL CONDUCTIVITY AND METHOD FOR MAKING

(76) Inventors: Gefei Wu, Lexington, KY (US); Zhiqiang Zhang, Lexington, KY (US); Frances E. Lockwood, Georgetown, KY (U S); Stephanie M. McCoy, Lexington, KY (U S); Thomas R. Smith, Lexington, KY (Us)

Correspondence Address: WOOD, HERRON & EVANS, LLP 2700 CAREW TOWER, 441 VINE STREET CINCINNATI, OH 45202 (US)

(21) App1.No.: 11/803,715

(22) Filed: May 15, 2007

Related U.S. Application Data

(63) Continuation-in-part of application No. 11/796,708, ?led on Apr. 27, 2007, Continuation-in-part of appli cation No. 10/730,762, ?led on Dec. 8, 2003, noW Pat. No. 7,348,298, Which is a continuation-in-part of application No. PCT/US02/ 16888, ?led on May 30, 2002.

(60) Provisional application No. 60/795,814, ?led on Apr. 27, 2006.

Publication Classi?cation

(51) Int. Cl. C10M 125/02 (2006.01) C10M 129/26 (2006.01) C10M 133/00 (2006.01) C10M 129/00 (2006.01) C10M 145/14 (2006.01)

(52) U.S. Cl. ....... .. 508/118; 508/113; 508/122; 508/128; 508/130; 508/131; 977/775

(57) ABSTRACT

A process for producing a nanographite dispersion in a ?uid Wherein the thermal conductivity of the dispersion is enhanced from the base ?uid by more than 10% for a 1% graphite dispersion. A high purity graphite With high crystal linity and reduced surface damage and oxidation is selected as the starting material. The starting material is subjected to a process of Wet media milling in the presence of dispersant and solvent ?uid. The mill temperature is controlled to control and reduce surface damage to yield a nanographite With ?ake shape and controlled aspect ratio until a particle siZe average of 300 nm diameter and 50 nm is obtained. The process recycles a portion of the milled material to increase the ratio of small particle distribution to large particles in an interme diate product With small and large particle bi-modal distribu tion. The large particle distribution is removed by a separation process such as centrifugation or ?ltration.

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US 2010/0022422 A1

HIGH TEMPERATURE SHEAR STABLE NANOGRAPHITE DISPERSION

LUBRICANTS WITH ENHANCED THERMAL CONDUCTIVITY AND METHOD FOR

MAKING

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US. Provi sional Application Ser. No. 60/ 800,557 ?led on May 15, 2006 and US. application Ser. No. 11/796,708 ?led on Apr. 27, 2007 claiming priority from Provisional Application Ser. No. 60/795,814 ?led on Apr. 27, 2006 and claims priority from 1 1/370,1 18 ?led on Mar. 7, 2006 claiming priority from PCT/ US06/001675 ?led on Jan. 17, 2006 claiming priority from Provisional Application Ser. No. 60/644,042 ?led on Jan. 14, 2005 all of Which are incorporated by reference herein in their entirety. Reference to documents made in the speci?cation is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited Within such docu ments as if fully set forth in this speci?cation.

TECHNICAL FIELD

[0002] The technical ?eld of this invention is a process for making nanographite dispersions.

BACKGROUND OF THE INVENTION

[0003] Thermally conductive nano-siZed graphite particles can only be produced under speci?c processing conditions. Heretofore the common processing for making graphite par ticles (larger than the particles disclosed herein, typically With average particle siZe 0.8 microns and above) has included dry milling and other milling processes that render the ?nal particles loW in thermal conductivity. For example, the commercially available samples from Acheson, Inc. have a thermal conductivity for 1% graphite in oil dispersions insigni?cantly greater than the oils Without graphite (typi cally 0.13 to 0.14 W/mK) By the methods of this invention, ?ake, or more speci?cally, plate shaped nanographites are produced that have signi?cantly higher thermal conductivity, and When dispersed in oil at 1 percent by Weight, have an increased thermal conductivity of up to 10 to 15 percent as measured in W/mK, resulting in experimental values of typi cally from 0.165 to 0.17 WmK or more as compared to the 0.13 to 0.14 values for oil Without the graphite particles control sample of the instant invention.

DESCRIPTION OF THE PRIOR ART

[0004] The starting material for making nanographites can be any high thermal conductivity graphite either in ?bers. Previously, naturally formed “nano-graphites” have not been available in the marketplace at all. Recently, Hyperion Catalysis International, Inc. commercialized carbon nano tubes or so-called carbon ?brils, Which have a graphitic con tent as set forth in US. Pat. No. 5,165,909 by Tennent et al. Which issued in Nov. 24, 1992 and is hereby incorporated by reference. Carbon nanotubes are typically holloW graphite like tubules having a diameter of generally several to several tens nanometers. They exist in the form either as discrete ?bers or aggregate particles of nano?bers. The thermal con ductivity of the Hyperion Catalysis International, Inc. mate rial is not stated in their product literature; hoWever, the

Jan. 28, 2010

potential of carbon nanotubes to convey thermal conductivity in a material is discussed in US. Pat. No. 5,165,909. Actual measurement of the thermal conductivity of the carbon ?brils they produced Was not given in the patent, so the inference of thermal conductivity is general and someWhat speculative, based on graphitic structure.

[0005] Bulk graphite With high thermal conductivity is available from Poco Graphite as a graphite foam, With ther mal conductivity higher than 100 W/mK, and is also available from the Carbide/ Graphite Group, Inc. Graphite poWders can be obtained from UCAR Carbon Company Inc., With thermal conductivity 10-500 W/mK, and typically >80 W/mK, and from Cytec Carbon Fibers LLC, With thermal conductivity 400-700 W/mK. [0006] For many applications carbon nanotubes Would be a preferable substitute, hoWever, for stability in a high shear ?uid ?oW, the nano graphites are stable Whereas carbon nano tubes break up. The present invention provides a process to mill graphite into plate shape and the subsequently disper sions have a higher thermal conductivity and are shear stable at a high temperature of as much as 4300 C. Typically, engine lubricant applications are subjected to temperatures in the 200 to 3000 F. range.

SUMMARY OF THE INVENTION

[0007] The compositions, methods, or embodiments dis cussed are intended to be only illustrative of the invention disclosed by this speci?cation. Variation on these particle nanomaterial, compositions, methods, or embodiments are readily apparent to a person of skill in the art based upon the teachings of this speci?cation and are therefore intended to be included as part of the inventions disclosed herein. [0008] Graphite materials having a controlled aspect ratio and high thermal conductivity are produced by the milling process of the present invention. The aspect ration must not be too high so as to be brittle in shear ?elds, but high enough to have enhanced thermal conductivity. [0009] The bulk graphite from Poco Graphite is a graphite foam With a high thermal conductivity and can be obtained in bulk quantities and reduced to a nanometer-sized poWder by the methods of this invention. [0010] The use of bulk graphite foam or graphite poWders as an inexpensive sources of nanomaterials for further pro cessing into controlled aspect ratio and high thermal conduc tivity products has not been used before. The instant invention provides a method of reducing the graphite to produce an inexpensive nanomaterial having a particle siZe suitable for long term dispersion in various ?uids, polymers, composites, gels, greases, plastics etc. and the method of dispersing same. [0011] HoWever, only certain processes Will produce these nanographites With high thermal conductivity and the thermal conductivity can either be drastically reduced (to impart no bene?t) or increased by the subsequent processing. Dry mill ing imparts too much change in surface characteristics and reduces thermal conductivity. It is critical to have the graphite poWder further milled in a horiZontal mill With liquid media (eg base oil or solvent) and to use dispersants during Wet milling in order to prevent paste formation. [0012] It is an object of the present invention to provide a process for producing a nanographite dispersion in a ?uid Wherein the thermal conductivity of the dispersion is enhanced from the base ?uid by more than 10% for a 1% graphite dispersion.

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[0013] It is an object of the present invention to provide a process Wherein a high purity graphite With high crystallinity and reduced surface damage and oxidation is selected as the starting material. [0014] It is an object of the present invention to provide a process of Wet media milling the starting material in the presence of dispersant and solvent (?uid). [0015] It is an object of the present invention to provide a process of controlling mill temperature to adjust the viscosity of the milling mixture to achieve high milling e?iciency. [0016] It is an object of the present invention to provide a process of milling until a nanographite With ?ake shape and controlled aspect ratio is achieved. [0017] It is an object of the present invention to provide a process of milling until a particle siZe average of 300 nm diameter and 50 nm thick is reached or smaller.

[0018] It is an object of the present invention to provide a process of recycling the milled material throughly to increase the ration of small particle distribution to large particle in an intermediate product With small and large particle bi-modal distribution. [0019] It is an object of the present invention to provide a process of removing the large particle distribution from the ?nished product by centrifugation or ?ltration. [0020] It is an object of the present invention to provide a method of preparing a stable dispersion of the carbon nano materials in a liquid medium With the combined use of dis persants/ surfactants and physical agitation for use in a lubri cant.

[0021] It is an object of the present invention to provide a method in Which the carbon nanomaterials are made from cost-effective high-thermal-conductivity graphite (With ther mal conductivity higher than 80 W/mK). [0022] It is an object of the present invention to provide a method of developing a method of forming carbon nanoma terials from inexpensive bulk graphite. [0023] It is an object of the present invention to provide a method of utiliZing carbon nanotube, graphite ?akes, carbon ?brils, carbon particles and combinations thereof. [0024] It is an object of the present invention to provide a method of using carbon nanotubes Which are either single Walled, or multi-Walled, With typical aspect ratio of 500 5000.

[0025] It is an object of the present invention Whereby the carbon nanomaterial can optionally be surface treated to be hydrophilic at surface for ease of dispersing into the aqueous medium. [0026] It is an object of the present invention to provide a method Wherein the said dispersants/ surfactants are soluble or highly dispersible in the said liquid medium. [0027] Other objects, features, and advantages of the inven tion Will be apparent With the folloWing detailed description taken in conjunction With the accompanying draWings shoW ing a preferred embodiment of the invention and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] A better understanding of the present invention Will be had upon reference to the folloWing description in con junction With the accompanying draWings in Which like numerals refer to like parts throughout the several vieWs and Wherein:

Jan. 28, 2010

[0029] FIG. 1 is a scanning electron microscope micropho tograph of the graphitic raW material obtained from UCAR GS4-E shoWing the material shaped as chunks; [0030] FIG. 2 is a scanning electron microscope micropho tograph shoWing the graphitic material of FIG. 1 after solvent milling illustrating the graphite nanoparticles shoWn as plate like structure. [0031] FIG. 3 is a graph shoWing rheological measurement of graphite dispersion; [0032] FIG. 4 is a graph shoWing rheological measurement of graphite dispersion; [0033] FIG. 5 is an enlarged section taken from the micro photograph of FIG. 1; [0034] FIG. 6 is an enlarged section taken from a micro photo graph after further processing of the nano graphite mate rial of FIG. 1; [0035] FIG. 7 is an enlarged section taken from the micro photograph of FIG. 2 resulting from additional processing of the nanographite material shoWn in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] The folloWing examples of the process is illustrated With nanographites dispersed in lubricant formulations. [0037] The term dispersant in the instant invention refers to a surfactant added to a medium to promote uniform suspen sion of extremely ?ne solid particles, often of colloidal siZe. In the examples provided the dispersant is generally a long chain oil soluble or dispersible compound that attaches to the particles and disperses them. The term surfactant in the instant invention refers to any chemical compound that reduces surface tension of a liquid When dissolved into it, or reduces interfacial tension betWeen tWo liquids or betWeen a liquid and a solid. It is usually, but not exclusively, a long chain molecule comprised of tWo moieties; a hydrophilic moiety and a lipophilic moiety. The hydrophilic and lipo philic moieties refer to the segment in the molecule With a?inity for Water, and that With a?inity for oil, respectively. These tWo terms, dispersant and surfactant, are mostly used interchangeably in the instant invention for often a surfactant has dispersing characteristics and many dispersants have the ability to reduce interfacial tensions. [0038] The ashless dispersants used in the examples con tain a lipophilic hydrocarbon group and a polar functional hydrophilic group. The polar functional group can be of the class of carboxylate, ester, amine, amide, imine, imide, hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhy dride, or nitrile. The lipophilic group can be oligomeric or polymeric in nature, usually from 70 to 200 carbon atoms to ensure oil solubility. Hydrocarbon polymers treated With various reagents to introduce polar functions include prod ucts prepared by treating polyole?ns such as polyisobutene ?rst With maleic anhydride, or phosphorus sul?de or chloride, or by thermal treatment, and then With reagents such as polyamine, amine, and ethylene oxide. [0039] Of these ashless dispersants the ones typically used include N-substituted polyisobutenyl succinimides and suc cinates, alkyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylaminoethyl methacrylate copoly mers, alkyl methacrylate-polyethylene glycol methacrylate copolymers, and polystearamides. Preferred oil-based dis persants include dispersants from the chemical classes of alkylsuccinimide, succinate esters, high molecular Weight amines, MANNICH base and phosphoric acid derivatives.

US 2010/0022422 A1

Some speci?c examples are polyisobutenyl succinimide polyethylenepolyamine, polyisobutenyl succinic ester, poly isobutenyl hydroxybenZyl-polyethylenepolyamine, bis-hy droxypropyl phosphorate. Commercial dispersants suitable include LUBRIZOL 890 (an ashless PIB succinimide), LUBRIZOL 6420 (a high molecular Weight PIB succinim ide), and ETHYL HITEC 646 (a non-boronated PIB succin imide), and ORONITE OLOA 12002 (succinimide). Pre ferred dispersants include PIB Succinimide and a dispersant VI improver ole?n copolymer such as ORONITE OLOA 1 9075. [0040] Furthermore, the carbon nanomaterial dispersion can be pre-sheared in a turbulent ?oW such as a noZZle, a high pressure fuel injector, an ultrasonic device, or a mill in order to achieve a stable viscosity. This may be especially desirable in the case Where carbon nanotubes With high aspect ratio are used as the graphite source, since they, even more than spheri cal particles, Will thicken the ?uid but loose viscosity When exposed in turbulent ?oWs. Pre-shearing, for example by milling, sonicating, orpassing through a small ori?ce, such as in a fuel injector, is a particularly effective Way to disperse the particles and to bring them to a stable siZe so that their vis cosity increasing effect Will not change upon further use. [0041] The milling process itself, or other pre-shearing pro cess, can have a rather dramatic effect on the long term dispersion stability. [0042] A novel method has been developed Whereby graph ite particles are milled to form a thick pasty liquid of particles With mean siZe less than 500 nanometers in diameter and typically 300 nm plus or minus 200 nm in diameter and 50 nm plus or minus 30 nm in thickness. It is expected that there are many Ways of process that Would produce similar particle siZes but destroy the thermal conductivity of the particles because the energy input causes surface damage such that the particle structure becomes less crystalline, more amorphous and also has a chunk-like shape instead of a platelet shape. For example, if one takes high thermal conductivity poWders produced in a jet mill and further dry mills these poWders, a material of loW thermal conductivity Would be expected to result due to high surface temperatures produced in the dry milling process.

Oil Base Stocks

[0043] The petroleum liquid medium can be any petroleum distillates or synthetic petroleum oils, greases, gels, or oil soluble polymer composition. More typically, it is the mineral base stocks or synthetic base stocks used in the lube industry, e.g., Group I (solvent re?ned mineral oils), Group II (hydro cracked mineral oils), Group III (severely hydrocracked oils, sometimes described as synthetic or semi-synthetic oils), Group IV (polyalphaole?ns), and Group VI (esters, naph thenes, and others). One preferred group includes the polyal phaole?ns, synthetic esters, and polyalkylglycols. [0044] Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymeriZed ole?ns (e.g., polybutylenes, polypro pylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-octenes), poly(1-decenes), etc., and mixtures thereof; alkylbenZenes (e.g., dodecylbenZenes, tet radecylbenZenes, dinonylbenZenes, di-(2-ethylhexyl)ben Zenes, etc.); polyphenyls (e.g., biphenyls, terphenyls, alky lated polyphenyls, etc.), alkylated diphenyl, ethers and alkylated diphenyl sul?des and the derivatives, analogs and homologs thereof and the like.

Jan. 28, 2010

[0045] Alkylene oxide polymers and interpolymers and derivatives thereof Where the terminal hydroxyl groups have been modi?ed by esteri?cation, etheri?cation, etc. constitute another class of knoWn synthetic oils. [0046] Another suitable class of synthetic oils comprises the esters of dicarboxylic acids (e.g., phtalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, aZelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, alkenyl malonic acids, etc.) With a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol diethylene glycol monoether, propylene glycol, etc.). Speci?c examples of these esters include dibutyl adipate, di(2-ethylhexyl) seba cate, di-hexyl fumarate, dioctyl sebacate, diisooctyl aZelate, diisodecyl aZealate, dioctyl phthalate, didecyl phthalate, dici cosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, the complex ester formed by reacting one mole of sebacic acid With tWo moles of tetraethylene glycol and tWo moles of 2-ethylhexanoic acid, and the like. [0047] Esters useful as synthetic oils also include those made from C (5) to C (12) monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpro pane, pentaerythritol, dipentaerythritol, tripentaerythritol, etc. Other synthetic oils include liquid esters of phosphorus containing acids (e. g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid, etc.), polymeric tet rahydrofurans and the like. [0048] Polyalphaole?ns (PAO), useful in the present inven tion include those sold by BP Amoco Corporation as DURA SYN ?uids, those sold by Exxon-Mobil Chemical Company, (formerly Mobil Chemical Company) as SHF ?uids, and those sold by Ethyl Corporation under the name ETHYL FLO, orALBERMARLE. PAO’s include the ETHYL-FLOW series by Ethyl Corporation, Albermarle Corporation, includ ing ETHYL-FLOW 162, 164, 166, 168, and 174, having varying viscosity from about 2 to about 460 centistokes. [0049] MOBIL SHE-42 from Exxon-Mobil Chemical Company, EMERY 3004 and 3006, and Quantum Chemical Company provide additional polyalphaole?ns base stocks. For instance, EMERY 3004 polyalphaole?n has a viscosity of 3.86 centistokes (cSt) at 212° F. (1000 C.) and 16.75 cSt at 104° F. (40° C.). It has a viscosity index of 125 and a pour point of—98° F. and it also has a ?ash point of about 432° F. and a ?re point of about 478[deg] F. Moreover, EMERY 3006 polyalphaole?n has a viscosity of 5.88 cSt at +212° F. and 31.22 cSt at +104° F. It has a viscosity index of 135 and a pour point of —87° F. [0050] Additional satisfactory polyalphaole?ns are those sold by Uniroyal Inc. under the brand SYNTON PAO-40, Which is a 40 centistoke polyalphaole?n. [0051] It is contemplated that Gulf Syn?uid 4 cSt PAO, commercially available from Gulf Oil Chemicals Company, a subsidiary of Chevron-Texaco Corporation, Which is similar in many respects to EMERY 3004 may also be utiliZed herein. MOBIL SHE-41 PAO, commercially available from Mobil Chemical Corporation, is also similar in many respects to EMERY 3004.

[0052] Especially useful are the polyalphaole?ns Will have a viscosity in the range of up to 100 centistoke at 100[deg] C., With viscosity of 2 and 10 centistoke being more preferred. [0053] The most preferred synthetic based oil ester addi tives are polyolesters and diesters such as di-aliphatic diesters of alkyl carboxylic acids such as di-2-ethylhexylaZelate, di isodecyladipate, and di-tridecyladipate, commercially avail

US 2010/0022422 A1

able under the brand name EMERY 2960 by Emery Chemi cals, described in US. Pat. No. 4,859,352 to Waynick. Other suitable polyolesters are manufactured by Mobil Oil. MOBIL polyolester P-43, NP343 containing tWo alcohols, and Hatco Corp. 2939 are particularly preferred. [0054] Diesters and other synthetic oils have been used as replacements of mineral oil in ?uid lubricants. Diesters have outstanding extreme loW temperature ?oW properties and good residence to oxidative breakdown.

[0055] The diester oil may include an aliphatic diester of a dicarboxylic acid, or the diester oil can comprise a dialkyl aliphatic diester of an alkyl dicarboxylic acid, such as di-2 ethyl hexyl aZelate, di-isodecyl aZelate, di-tridecyl aZelate, di-isodecyl adipate, di-tridecyl adipate. For instance, Di-2 ethylhexyl aZelate is commercially available under the brand name of EMERY 2958 by Emery Chemicals.

[0056] Also useful are polyol esters such as EMERY 2935, 2936, and 2939 from Emery Group of Henkel Corporation and HATCO 2352, 2962, 2925, 2938, 2939, 2970, 3178, and 4322 polyol esters from Hatco Corporation, described in US. Pat. No. 5,344,579 to Ohtani et al. and MOBIL ESTER P 24 from Exxon-Mobil Chemical Company. Esters made by reacting dicarboxylic acids, glycols, and either monobasic acids or monohydric alcohols like EMERY 2936 synthetic lubricant base stocks from Quantum Chemical Corporation and MOBIL P 24 from Exxon-Mobil Chemical Company can be used. Polyol esters have good oxidation and hydrolytic stability. The polyol ester for use herein preferably has a pour point of about —100° C. or loWer to 400 C. and a viscosity of about 2 to 100 centistoke at 1000 C.

[0057] A hydrogenated oil is a mineral oil subjected to hydrogennation or hydrocracking under special conditions to remove undesirable chemical compositions and impurities resulting in a base oil having synthetic oil component and properties. Typically the hydrogenated oil is de?ned by the American Petroleum Institute as a Group III base oil With a sulfur level less than 0.03 With saturates greater than or equal to 90 and a viscosity index of greater than or equal to 120. Most useful are hydrogenated oils having a viscosity of from 2 to 60 CST at 100 degrees centigrade. The hydrogenated oil typically provides superior performance to conventional motor oils With no other synthetic oil base. The hydrogenated oil may be used as the sole base oil component of the instant invention providing superior performance to conventional mineral oil bases oils or used as a blend With mineral oil and/ or synthetic oil. An example of such an oil isYUBASE-4.

[0058] When used in combination With another conven tional synthetic oil such as those containing polyalphaole?ns or esters, or When used in combination With a mineral oil, the hydrogenated oil may be utiliZed as the oil base stock in an amount of up to 100 percent by volume, more preferably from about 10 to 80 percent by volume, more preferably from 20 to 60 percent by volume and most preferably from 10 to 30 percent by volume of the base oil composition. [0059] A Group I or II mineral oil basestock may be incor porated in the present invention as a portion of the concentrate or a basestock to Which the concentrate may be added. Pre ferred as mineral oil base stocks are the ASHLAND 325 Neutral de?ned as a solvent re?ned neutral having a SABOLT UNIVERSAL viscosity of 325 SUS @ 1000 F. and ASH LAND 100 Neutral de?ned as a solvent re?ned neutral having a SABOLT UNIVERSAL viscosity of 100 SUS @ 1000 F., manufactured by the Marathon Petroleum corporation.

Jan. 28, 2010

[0060] Other acceptable petroleum-base ?uid composi tions include White mineral, paraf?nic and MVI naphthenic oils having the viscosity range of about 20-400 centistokes. Preferred White mineral oils include those available from Witco Corporation, Arco Chemical Company, PSI and Pen reco. Preferred paraf?nic oils include API Group I and II oils available from Exxon-Mobil Chemical Company, HVI neu tral oils available from Shell Chemical Company, and Group II oils available from Arco Chemical Company. Preferred MVI naphthenic oils include solvent extracted oils available from Equilon Enterprises and San Joaquin Re?ning, hydrotreated oils available from Equilon Enterprises and Ergon Re?ning, and naphthenic oils sold under the names HYDROCAL and CALSOL by Calumet, and described in US. Pat. No. 5,348,668 to Oldiges.

Dispersants

[0061] The ashless dispersants commonly used in the auto motive industry contain an lipophilic hydrocarbon group and a polar functional hydrophilic group. The polar functional group can be of the class of carboxylate, ester, amine, amide, imine, imide, hydroxyl, ether, epoxide, phosphorus, ester car boxyl, anhydride, or nitrile. The lipophilic group can be oli gomeric or polymeric in nature, usually from 70 to 200 car bon atoms to ensure oil solubility. Hydrocarbon polymers treated With various reagents to introduce polar functions include products prepared by treating polyole?ns such as polyisobutene ?rst With maleic anhydride, or phosphorus sul ?de or chloride, or by thermal treatment, and then With reagents such as polyamine, amine, ethylene oxide, etc. [0062] Of these ashless dispersants the ones typically used in the petroleum industry include N-substituted polyisobute nyl succinimides and succinates, allyl methacrylate-vinyl pyrrolidinone copolymers, alkyl methacrylate-dialkylamino ethyl methacrylate copolymers, alkylmethacrylate-polyeth ylene glycol methacrylate copolymers, and polystearamides. Preferred oil-based dispersants that are mo st important in the instant application include dispersants from the chemical classes of alkylsuccinimide, succinate esters, high molecular Weight amines, Mannich base and phosphoric acid deriva tives. Some speci?c examples are polyisobutenyl succinim ide-polyethylenepolyamine, polyisobutenyl succinic ester, polyisobutenyl hydroxybenZyl-polyethylenepolyamine, bis hydroxypropyl phosphorate. For instance, bis-succinimide is a dispersant based on polybutene and an amine Which is suitable for oil based dispersions and is commercially avail able under the tradenames of INFINEUM C9231, INFINEUM C9232, and INFINEUM C9235 Which is sold by In?neum, USA, LP. The C9231 is borated While the C9232 and C9235 are not; hoWever, all are bis-succinimides Which differ due to their amine to polymer ratio.

[0063] The dispersant may be combined With other addi tives used in the lubricant industry to form a dispersant detergent (DD additive package, e.g., LUBRIZOL[R] 9802A and/or the concentrated package (LUBRIZOL[R] 9802AC), Which are mixed Dispersants having a high molecular Weight succinimide and ester-type dispersant as the active ingredi ent, and Which also contains from about to 9.9 percent by Weight of Zinc alkyldithiophosphate, from 1 to 4.9 percent by Weight of a substituted phenol, from 1 to 4.9 percent of a calcium sulfonate, and from 0.1 to 0.9 percent by Weight of a diphenylamine; Wherein the Whole DI package can be used as dispersing agent for the carbon nanomaterial dispersion.

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[0064] Another preferred dispersant package is LUBRI ZOL OS#154250 Which contains from about 20 to 29.9 per cent by Weight of a polyole?n amide alkeneamine, from 0.5 to 1.5 percent by Weight of an alkylphosphite, about 1.1 percent by Weight of a phosphoric acid, and from 0.1 to 0.9 percent by Weight of a diphenylamine, With primary active ingredient believed to be polyisobutenyl succinimides and succinates. Another preferred dispersant package is a high molecular Weight succinimide DI package for diesel engines LUBRI ZOL[R] 4999 Which also contains from about 5 to 9.9 percent Zinc alkyldithiophosphate by Weight.

Other Types of Dispersants

[0065] Alternatively a surfactant or a mixture of surfactants With loW HLB value (typically less than or equal to 8), pref erably nonionic, or a mixture of nonionics and ionics, may be used in the instant invention.

[0066] The dispersant for the Water based carbon nanoma terial dispersion, more speci?cally carbon nanotube disper sion, should be of high HLB value (typically less than or equal to 10), preferable nonylphenoxypoly(ethyleneoxy)ethanol type surfactants are utiliZed.

[0067] The dispersant can be in a range of up from 0.001 to 30 percent, more preferably in a range of from betWeen 0.5 percent to 20 percent, more preferably in a range of from betWeen 1.0 to 8.0 percent, and most preferably in a range of from betWeen 2 to 6 Weight percent.

[0068] The carbon nanotube or graphite nanoparticles can be of any desired Weight percentage in a range of from 0.0001 up to 50 percent by Weight providing for an effective amount to obtain the desired thermal enhancement of the selected ?uid media. For practical application an effective amount of carbon nanomaterials is usually in a range of from betWeen 0.01 percent to 20 percent, and more preferably in a range of from 0.02 to 10 percent, and most preferably in a range of from betWeen 0.05 percent to 5 percent. The remainder of the formula is the selected medium comprising oil, Water, or combinations thereof together With any chemical additives deemed necessary to provide lubricity, corrosion protection, viscosity, or the like.

[0069] It is believed that in the instant invention the dispers ant functions by adsorbing onto the surface of the nanopar ticle material.

Other Chemical Compounds

[0070] This dispersion may also contain a large amount of one or more other chemical compounds, preferably polymers, not for the purpose of dispersing, but to achieve thickening or other desired ?uid characteristics.

[0071] The viscosity improvers used in the lubricant indus try can be used in the instant invention for the oil medium, Which include ole?n copolymers (OCP), polymethacrylates (PMA), hydrogenated styrene-diene (STD), and styrene polyester (STPE) polymers. Ole?n copolymers are rubber like materials prepared from ethylene and propylene mixtures through vanadium-based Ziegler-Natta catalysis. Styrene-di ene polymers are produced by anionic polymeriZation of styrene and butadiene or isoprene. Polymethacrylates are pro duced by free radical polymerization of alkyl methacrylates. Styrene-polyesterpolymers are prepared by ?rst co-polymer iZing styrene and maleic anhydride and then esterifying the intermediate using a mixture of alcohols.

Jan. 28, 2010

[0072] Other compounds Which can be used in the instant invention in either the aqueous medium or the oil medium include: acrylic polymers such as polyacrylic acid and sodium polyacrylate, high-molecular-Weight polymers of ethylene oxide such as Polyox[R] WSR from Union Carbide, cellulose compounds such as carboxymethylcellulose, poly vinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), xanthan gums and guar gums, polysaccharides, alkanolamides, amine salts of polyamide such as DISPARLONAQ series from King Industries, hydrophobically modi?ed ethylene oxide ure thane (e.g., ACRYSOL series from Rohmax), silicates, and ?llers such as mica, silicas, cellulose, Wood ?our, clays (in cluding organoclays) and nanoclays, and resin polymers such as polyvinyl butyral resins, polyurethane resins, acrylic resins and epoxy resins. [0073] Other chemical additives used in lubricants such as pour point depressant can also be used in the instant inven tion. Most pour point depressants are organic polymers, although some nonpolymeric substances have been shoWn to be effective. Commercial pour point depressants include alkylnaphthalenes, polymethacrylates, polyfumarates, sty rene esters, oligomeriZed alkylphenols, phthalic acid esters, ethylenevinyl acetate copolymers, and other mixed hydrocar bon polymers. The treatment level of these additives is usu ally loW. In nearly all cases, there is an optimum concentra tion above and beloW Which pour point depressants become less effective. [0074] Acrylic copolymers such as manufactured by Supe leo Inc. in Bellefonte, Pa. as ACRYLOID 3008 is a pour point depressant useful in the present invention. [0075] Still other chemical additives used in lubricants, such as rust and oxidation inhibitors, demulsi?ers, foam inhibitors, and seal-sWelling agents can also be used in the instant invention. Physical Agitation. [0076] The folloWing trade names correspond to the chemi cal de?nition as folloWs:

Additive Description

Yubase 4 Group III base oil Yubase 6 Group III base oil PAO 4 Group IV base oil LZ 21303 Passenger car detergent-inhibitor package LZ 8676 Antioxidant mixture LZ 8650 Organic friction modi?er Afton 5777 dispersant viscosity modi?er LZ 7749B PMA pour point depressant T503-209-2 Nano graphite concentrate Star 4 Group II base oil Star 8 Group II base oil LZ 20010 Passenger car detergent-inhibitor package LZ 6473 Calcium sulfonate detergent LZ 7075F OCP viscosity modi?er A- 11 Nano graphite concentrate

[0077] Milling Procedure: [0078] Graphite particles Were obtained by pulveriZing big graphite chunks from the Carbide/Graphite Group, and siZe selected through a mesh ?lter to be less than 75 um. Thirty (30) grams of the above graphite particles and 270 grams of DURASYN 162 (a commercial 2 centistokes polyalphaole ?n, abbreviated hereafter as 2 cSt PAO or preferably 4 csT PAO), Were added into the EIGER Mini Mill (Model: M250 VSE-EXP). The milling speed Was gradually increased to 4000 rpm. In about 4 hours the above mixture turned into

US 2010/0022422 A1

thick paste. Sixty grams of this paste Was discharged and labeled as Paste A. For the rest of the mixture in the mill, 48 grams of a dispersant Was added and an additional dispersant inhibitor package (DI package) from LubriZol, LUBRIZOL 9677MX Was added into the mill and the paste became very thin, and successful recirculation Was restored. The mill Was stopped after another 4 hours of milling and the discharged paste Was labeled as Paste B. Paste C Was obtained by milling a mixture of 30 grams of graphite With diameter less than 75 um, 60 grams of LUBRIZOL 9677MX, and 270 grams of DRASYN 162 at 4000 rpm for 8 hours. Note here the dis persing agent LUBRIZOL 9677MX Was added into the mill at the very beginning. Three ?uids A through C Were formu lated using the above three pastes as concentrates Whereby

Jan. 28, 2010

[0081] To illustrate the importance of the milling process, and in minimiZing the heating that occurs in dry milling We compared the thermal conductivity increase achieved using tWo dry processes and the Wet process described in this inven tion. Sample “V 174-01” is obtained by milling “UCAR GS4-E” in PAO 2 With a polyisobutenylsuccinimide dispers ant for 1 1 hours at 1200 F. The UCAR GS4-E starting material has high bulk thermal conductivity, but due to its shape and siZe does not give the desired bene?t in increasing ?uid ther mal conductivity. Thus the Wet milling creates the particle shape that improves thermal conductivity and also avoids surface damage that can decrease thermal conductivity. The thermal conductivity (k) percent increase reported is com pared to the base ?uid (PAO) alone. The data are shoWn in Table 2 beloW:

TABLE 2

Thermal Conductivi? Percent Increase Compared to Base Fluid Alone

Graphite Source Way of Milling peak 1 peak 2 k increase @2%(%)

Acheson SLA1275 dry(ba11) 124 nm(33%) 497 nm(67%) 8.59 V 174-01 Wet(horiZontal) 117 nm(69%) 2413 nm(31% 29.27 UCAR GS4-E dry(jet) 3304 nm(100% 3.4

their ?nal composition Were exactly the same: 2% graphite, [0082] It is evident that both the particle siZe and the Way of 4% LUBRIZOL 9677 MX, 18% DURASYN 162, 76% DURASYN 166 (a commercial 6 centistokes polyalphaole ?n, abbreviated hereafter as 6 cSt PAO) (all percentage by Weight). Example 3 illustrates the 1000 C. viscosity and ther mal conductivity increase of the ?uids.

[0079] It Was also found that the graphite particle siZe before milling Was very critical on the viscosity modi?cation effect as Well. For example, starting With graphite smaller than 10 (obtained as graphite poWder from UCAR Carbon Company Inc.) and folloWing the same procedure as Paste B, a thin Paste D Was obtained. A ?uid D Was formulated With

the same composition as ?uid A and the result is listed in Example 3 as Well. The particle siZe is measured by atomic force microscopy (AFM), and FIG. 2 illustrates an AFM picture of Fluid B. The graphite nanoparticles are plate-like structure, With average diameter is around 50 nm and thick ness around 5 nm (as described earlier, nanodisks or nano

plates).

TABLE 1

Fluids and viscosig data from Example 1

Fluid A B C D

From Concentrate Paste A Paste B Paste C Paste D Kinematic viscosity at 1000 C., cSt 7.55 19.68 10.83 7.48 Kinematic viscosity at 400 C., cSt 28.44 29.32 28.77 27.85 Thermal Conductivity W/mK 0.18 0.19

[0080] It is important to note that Without added dispersant the mixture of graphite and base oil turns into paste in hours and thus su?icient milling can not be accomplished. With good dispersant the milling can be extended to as long as desirable Without paste formation. It is also important to adjust the temperature to maintain the right viscosity during the milling process so that the e?icient milling is achieved.

milling are important to thermal conductivity increase.

[0083] Results from the table shoW that the commercial Acheson sample generally has smaller particles than the sample V174-01 of graphitic material obtained from the instant process, hoWever, the V174-01 sample has a much higher thermal conductivity boost. This surprising result is contrary to the expected relationship of increasing thermal conductivity With decreasing particle siZe, but it indicates the importance of the invention milling process in increasing thermal conductivity. [0084] It is believed that in the dry ball milling process, local high temperature exists Which could cause graphite surface fracture or surface defects, including oxidation Which reduces thermal conductivity. For example, in Us. Pat. No. 4,434,064 Which issued in February of 1984 by Chao et al., a graphite dispersion Was made (With larger graphite particles as compared to the instant invention) and surface oxidation caused by dry grinding in oxygen atmosphere is preferred because it aids in dispersion. In the instant invention, the Wet milling process this effect is very much controlled and mini miZed. It is also important to begin With graphites developed in a process that preserves purity and crystalline structure.

[0085] One preferred starting material is jet-milled graph ite. Jet mills have higher e?iciency in producing ultra ?ne grade particles and they are claimed to be contamination free. The basic premise of the jet mill is to utiliZe the energy of compressed gas to perform the grinding. The gas accelerates the material, causing high-speed particle-on-particle colli sions. As a result, the material grinds against itself, ensuring product quality. With the expansion of the compressed gas, a cooling effect takes place alloWing heat-sensitive materials to be processed Without degradation. HoWever, Without further milling in the solvents, the thermal conductivity boost is still very limited due to siZe and shape. For example, a 2% dis persion of j et-milled graphite has only 3.4% increase in ther mal conductivity.

US 2010/0022422 A1

[0086] Scanning electron microscope pictures demonstrate this important shape change Which occurs to the graphite particle shape With solvent milling. The raW material, UCAR GS4-E, is composed in the shape of chunks as best illustrated in FIG. 1. After the solvent milling, the chunks are processed and appear as a plate-like shape as shoWn in FIG. 2.

[0087] Carbon nanotubes, double Wall, multi-Wall or single Wall having a controlled aspect ratio, are another preferred type of nanomaterial or particles. The nanotubes have a typi cal nanoscale diameter of 1-200 nanometers. More typically the diameter is around 10-30 nanometers. The length of the tube can be in submicron and micron scale, usually from 50 nanometers to 100 microns. More typical length is 500 nanometers to 50 microns. The aspect ratio of the tube (Which is de?ned by the average length of the tubes divided by the average diameter) can be from hundreds to thousands, more typical 100 to 2000. The surface of the nanotube can be treated chemically to achieve certain level of hydrophilicity, or left as is from the production.

[0088] The nanoplates and nanotubes can be mixed to obtain desired viscosity/shear and thermal conductivity behavior. Other high thermal conductivity carbon materials are also acceptable as long as they meet the thermal conduc tivity and siZe criteria set forth heretofore.

[0089] To confer long-term stability, an effective amount of one or more chemical dispersants or surfactants is preferred,

although the special milling procedure in base oil described heretofore Will also confer long term stability. The thermal conductivity enhancement, compared to the ?uid Without graphite, is proportional to the amount of nanomaterials added, their thermal conductivity, and their siZe and method of dispersion. The particles of the instant invention Will impart a thermal conductivity in ?uid higher than the neat ?uid, Wherein the term ‘neat’ is de?ned as the ?uid before the particles are added.

[0090] The concentration, siZe and shape of the graphite nanoparticles or nanotubes, along With the dispersant/surfac tant type and concentration, is adjusted to provide the desired contribution to the overall ?uid characteristics as for example the .viscosity and shear stability. Similar adjustments can be envisioned for producing composite resins or polymer melts to produce plastics. [0091] It is observed that a bimodal distribution of particles is found in the ?nished sample. To reduce the large particle distribution recycling of the dispersion in the mill is neces sary. A selected recycle ratio of to is desirable. Furthermore the large particles in the ?nal material can be removed by a ?ltration or centrifugation step.

[0092] High-Temperature Shear Stable Graphite Disper sion.

[0093] According to the Albert Einstein equation regarding the viscosity of dispersions, a good dispersion just has slight viscosity increase While a bad dispersion has a big viscosity increase. The viscosity ranges of many ?uids are very critical. So it is very important to not cause viscosity change While integrating nano particles into many ?uids. The particles can be dispersed in oil by choosing the right dispersants, typically

Jan. 28, 2010

fairly loW molecular Weight materials (<2500 m. W.) such as polysuccinimides, and someWhat higher molecular Weight viscosity index improvers, With dispersant functionality. To determine good or bad dispersions rheometer are used instead

of viscosity tubes. The rheometer measures viscosities under

varying shear stress. For a NeWtonian ?uid the viscosity is a

constant regardless of shear rate. Many ?uids are non-NeW

tonian ?uids, but at loW shear rates the viscosity is also a

constant. For bad dispersions the viscosity shoWs shear-thin ning With a increase in shear rate and builds up at high tem

perature as time pass by. As set forth in FIG. 3, repeatable almost ?at lines in the rheometer plots of viscosity are com

parable against the shear rate for Well dispersed graphite oils shoWn in FIG. 4.

[0094] The viscosity ranges of many ?uids are very critical. So it can be very important to not cause viscosity change While integrating nano particles into many ?uids. By choos ing the right viscosity improver, “VI”, (polymers knoWn to the lubricants industry as viscosity index improvers), disper sions can be improved. The V1 improvers We used are dis

persant VI improvers. [0095] To determine good or bad dispersions a rheometer is used instead of viscosity tubes. Rheometer measures viscosi ties under shear stress Which is variable. For a NeWtonian

?uid the viscosity is a constant regardless of shear rate. Motor oils are non-Newtonian ?uids, but at loW shear rates the viscosity is also a constant. For bad dispersions the viscosity shoWs shear-thinning With a increase in shear rate and builds

up at high temperature as time passes by as exhibited in FIG. 3. Repeatable, almost ?at lines in the rheometer plots of viscosity against the shear rate for Well dispersed graphite oils as shoWn in FIG. 4.

[0096] Table 3 shoWs hoW increasing the percentage of carbon nanotubes in oil results in a much greater increase in

viscosity as compared With increasing the percentage of car bon nanographite particles of the instant invention due to the particle shape Which is changed during the milling process.

TABLE 3

Viscosity Increase With Weight Percentage of nanotube and Nanographite

% Carbon Viscosity 100O % Milled Viscosity 100O Nanotube C./cST Nanographite C./cST

0 3.92 0 3.92 0.005 4 0.01 5.36 0.05 8.59 0.1 16.75 0.1 4.04 0 2 65 0.2 4 19

[0097] The folloWing examples provide formulations of compositions in accordance With the present invention and provide examples of the range of ingredient percentages by Weight providing an effective amount of the particular ingre dients deemed necessary to obtain the desired results in single application.

US 2010/0022422 A1

Synthetic Lubricant Composition Containing Nan ographite Particles

[0098]

Example 1

Jan. 28, 2010

Synthetic SAE 5W-30

Yubase 4 Yubase 6 FAQ 4 LZ 21303C LZ 8676 LZ 8650 Afton 5777 LZ 7749B

T503-209-2 (Cut 2) V100 Before V100 After DeltaV

CCS@—30 C. NOACK, % Loss MRV @ —35 C. YS Viscosity HTHS

Conventional Lubricant Composition Containing

[0099]

Example 2

Nanographite Particles

Conventional SAE 5W-30

Yubase 4 Star 4 Star 8 LZ 20010 LZ 8650 LZ 8676

-continued

Conventional SAE 5W-30

LZ 6473 0.50 Afton 5777 1.00 LZ 7075F 4.60 LZ 7749B 0.40 A-l 1 2.96

100.00

KV (100 C.)bfr KV (100 c.) aftr

39.43 ccs (-30 c.) 25.00 NOACK 10.00 After Bosch 11.00 1.00 3.40 360 Example 3 0.40

9-17 Semi Synthetic Lubricant Composition Containing 9 88 Nanographite Particles

[0100] 5361

12.08 <35

17022 Ingredients Percentage range

Graphite 0.1-2 Group III and IV base oils 80.0-85.0 LZ DI package 7.0—15.0 LZ additives 0.1-2.0 Viscosity improver l.0—7.5 Viscosity at 1000 C. 7.5—15.0

[0101] Table 4 shoWs that adding nanomaterials into a lubricant can signi?cantly increase the thermal conductivity of the formulation, Which implies better thermal management for the system. [0102] For example in Table 4, a semi-synthetic blended motor oil such as DURABLEND Which is sold by Valvoline

50 00 Inc., a division of ASHLAND INC. is compared as DB (a 8:59 conventional 5W-30 motor oil), NF-l (a 5W-30 motor oil 2050 containing graphite nanoplates), and NF-2 (a 5W-30 motor 18% oil containing graphite nanoplates and carbon nanotubes) 0_30 shoWing the effect on viscosity index and thermal conductiv

ity K(W/m~K).

Code DB NF-l NF-2

Product Conventional DuraBlend DuraBlend 5W-30 With DuraBlend 5W-30 With graphite

description 5W-30 graphite nanoplate nanoplate and carbon nanotubes

Percent by Wt. 0 1.0, graphite nanoplate* 1.0, graphite nanoplate*

Nanomaterial 0.1, carbon nanotubes**

Vis100O C. 10.66 10.9 10.9

Vis at 40 C. 61.14 57.1 54.34

Viscosity Index 166 186 197

k (W/m - K) 0.1423 0.1591 0.1768

*Graphite is obtained as carbon ?bers from Union Carbide and fulther processed through in-house method into graphite nanoplate. **MultiWalled carbon nanotubes are obtained from University of Kentucky.

Documents

High temperature shear stable nanographite dispersion lubricants