Patent Application
20060142419
1. Field of the Invention
The present invention relates to compositions containing fine magnetic particles and a process for preparing them. It also relates to methods for the use of the compositions for detecting the occurrence of fraud in transactions involving marked articles. More particularly, the present invention relates to methods for marking articles and packaging with magnetically encoded information, and specifically methods that significantly increase the density of the encoded information therein.
2. Description of the Prior Art
In order to prevent fraud during the conduct of commerce, it has become conventional to mark articles of commerce in some manner, in order to identify the article and/or verify that the article is authentic and has been made and/or sold legally. Legitimate businesses such as manufacturers, suppliers, distributors, and/or vendors are concerned with the growth of various fraudulent practices in commercial transactions. Examples of fraudulent practices that are of concern to legitimate businesses include diversion, dilution, and counterfeiting. Perpetrators of fraud (hereinafter, perpetrators) use illicit tactics to divert profits from legitimate business concerns, and these tactics can also include theft of the authentic goods.
For example, diversion is a practice whereby authentic product is diverted from being sold in a market in which the product was intended to be sold at a low market value, but is rerouted by a perpetrator to another market where the product can be sold at a higher market value. Often the market of lower value is a market that is one that is needy but unable to pay the higher market value. Dilution is a fraudulent practice whereby an authentic product is mixed with an inactive ingredient and the product is represented as being identical to an unmixed product. Counterfeiting is producing a copy of an original article and passing it off as an authentic original article, that is, the article that was copied.
Marking is one method that is used to prevent these fraudulent practices. Methods of marking include overt methods, whereby the marked item is identified in such a manner as to make it apparent to an observer (customer, merchant, perpetrator, or the like) that the item is in fact marked. Overt markings can include, for example, bar codes on the external surface of the marked article, fluorescent ink or pigments easily visible to the naked eye; holograms; trademarks; logos; labels; and unique color schemes. Overt marking has the advantage of being readily apparent to a possible perpetrator and/or merchant that the item is identifiable, and thus can discourage fraud. Dovgodco, et al., in U.S. Pat. No. 6,351,537 B1 describes an article having an overt verifiable holographic image.
Covert marking is a marking practice wherein an article is marked using an identifier that is not easily seen by a consumer. A covert method for detection of fraud is described Doljack, in U.S. Pat. No. 6,442,276 B1, wherein is described a method whereby random codes are provided for marked goods and a database of the random codes is kept to confirm or deny authenticity. Cyr, et al., in U.S. Pat. No. 6,138,913, describes covert encoded information detected by fluorescence at wavelengths of about 650 nm when exposed to near infrared radiation, while Kaiser et al., in U.S. Pat. No. 6,477,277, describes taggants in or on an article that are detected by x-ray fluorescence analysis.
Hardwick, et al., in U.S. Pat. No. 6,403,169, describe a magnetic watermark as method to produce a security document with sheet-like plastic substrates wherein the coating layers contain magnetic particles that are oriented by a magnetic field.
Snelling, et al., in WO 03/091953 A2, describe substrates with magnetic and visual security features comprising ferromagnetic particles that have a magnetic remenence in the absence of an applied magnetic field and the coercivity of greater than 100 Oe.
Dean et al., in U.S. Pat. No. 6,741,770 describe polymer compositions complexed with rare earth ions, said ions being the magnetic component.
It can be desirable to provide compositions useful as improved formulations for curable magnetic films, comprising fine paramagnetic and preferably superparamagnetic nanoparticles, having a particle size (diameter) of less than 1 micrometer, maximum achievable magnetic mass susceptibilities, and dispersed in a curable mixture of monomers.
In one aspect, the present invention is a composition, which is a dispersion comprising:
In another aspect, the present invention is a film having dispersed therein superparamagnetic particles having a diameter of less than about 1 micrometer.
In still another aspect, the present invention is an article comprising a polymeric film obtained from a curable dispersion comprising superparamagnetic particles, wherein the film comprises superparamagnetic particles having a diameter of less than about 1 micrometer.
In still another aspect, the present invention is a method of preparing a substrate comprising a superparamagnetic film comprising the steps of: (1) applying a superparamagnetic dispersion to a substrate; and (2) curing the dispersion on the surface of the substrate to form the superparamagnetic film, wherein the film comprises superparamagnetic particles having a diameter of less than about 1 micrometer.
In still another aspect, the present invention is a method of preparing a substrate comprising a superparamagnetic film comprising the steps of: (1) curing a curable dispersion comprising (a) either of (i) a mixture of monomers, (ii) a mixture of oligomers, or (iii) a mixture of monomers and a mixture of oligomers, wherein the mixture is cured using a curing agent; (b) superparamagnetic particles dispersed in the mixture of part (a), wherein the superparamagnetic particles have a diameter of less than 1 micrometer; (c) optionally at least one curing agent or polymerization agent selected from photoinitiators, radiation initiators, chemical initiators, thermally activated initiators; and (d) optionally one or more viscosity modifiers, other taggants, and solvents; and (2) applying the film to the substrate.
In still another aspect, the present invention is a method for preparing nanoparticles that comprises treating a carbon-containing compound or compounds and a metal-containing compound or compounds with a direct current (DC) electric arc plasma. The carbon-containing compounds include C1 to C5 hydrocarbons, including but not limited to methane, ethane, propane, butane, and pentane. The metal-containing compounds include one or more of the volatile carbonyls of iron [iron pentacarbonyl, Fe(CO)5] and nickel [nickel tetracarbonyl, Ni(CO)4], fed as a vapor, and crystalline cobalt [dicobalt octacarbonyl, CO2(CO)8] fed as a powder.
The plasma torch reactor is shown schematically in
Trademarks are shown in upper case.
The term “(meth)acrylate” means either methacrylate or acrylate; the term “(meth)acrylic” means either methacrylic or acrylic.
The terms “superparamagnetic” and “paramagnetic” are used herein. Ferromagnetism is characterized by a long-range ordering of the atomic moments of the material, even in the absence of an external applied magnetic field. The direction of the magnetization with respect to the crystalline axes is determined by forces that are a result of the individual particle shape or crystalline magnetic anisotropy. Below a certain particle size, the magnetization is no longer fixed in a particular direction dictated by particle shape or crystal anisotropy, but ambient thermal energy is large enough to cause the magnetization to jump among different energetically equivalent orientations. Application of a modest external magnetic field will lead to nearly complete alignment of the individual magnetizations of all of the particles, and thus the material will exhibit a large magnetic response. Materials with such properties are referred to as being superparamagnetic, and their particle sizes are typically of the order of 30 nm or less.
A different type of magnetic behavior is paramagnetism, for which the atomic moments are not long-range ordered but can also be induced to align in a common direction by application of a magnetic field. This alignment is generally much less perfect than in a ferromagnet at routinely available magnetic field strengths and at ambient temperature, so the magnetization of a paramagnetic material is generally much smaller than that of a ferromagnetic material when each is measured at equivalent applied magnetic field strengths.
The compositions of the present invention comprise superparamagnetic particles having a diameter of less than 1 micrometer dispersed in a curable mixture comprising (a) monomers, or (b) oligomers, or (c) a combination thereof, wherein the mixture can be cured or polymerized using a curing or polymerizing agent. Said composition optionally further comprises at least one curing agent or polymerization agent selected from photoinitiators, radiation initiators, chemical initiators, thermally activated initiators, and optionally viscosity modifiers, taggants, and solvents.
The term “curable superparamagnetic dispersion” is hereinafter used to describe these compositions. The invention also provides the polymerized or cured dispersion (hereinafter the “cured superparamagnetic polymer”). For the purposes of the present invention, no distinction is made herein between “curing” and “polymerizing”, and either or both processes may be referred to herein simply as “curing”.
The compositions of the present invention comprise superparamagnetic particles that are smaller and easier to disperse without settling than previously described ferromagnetic particles. The small superparamagnetic particles of the present invention provide a means of incorporating more magnetic information into a smaller area, and therefore can be suitable for providing more information on marked articles of commerce.
The curable superparamagnetic dispersions of the present invention are now described in greater detail. The curable or polymerizable monomers and oligomers useful in the practice of the present invention are selected from (meth)acrylate monomers and oligomers and mixtures thereof that polymerize to form poly(meth)acrylates, and other monomers and oligomers that polymerize to form polymers. Alkoxylated multifunctional acrylate monomers (such as ethoxylated 15 trimethylolpropane triacrylate) can be used to accelerate the curing, improve the toughness, and reduce shrinkage of the cured products. Illustrative polymers include epoxy resins, phenoxy resins, cured varnishes, and polyesters, urethanes, and mixtures thereof.
The curable superparamagnetic dispersions of the present invention comprise a matrix in which are dispersed fine paramagnetic or superparamagnetic particles (about 0.01 to about 30% by weight, and preferably from about 0.2% to about 10%, based on the weight of the curable superparamagnetic dispersion. The matrix of the curable superparamagnetic dispersion include a monomer such as methyl (meth)acrylate (MMA, 0 to about 80 wt. %), an alkoxylated multifunctional acrylate monomer (such as ethoxylated 15 triethylolpropane triacrylate (ethoxylated TMPTA), 0% to about 99 wt. %) as a comonomer, a viscosity modifier such as polymethylmethacrylate, PMMA, 0 to about 40 wt. %), and an optional photoinitiator (0 to about 2 wt. %), such that the amounts of monomer and comonomer are not both 0% and that all the components add to 100%. In some cases, curing can be accomplished without incorporating a photoinitiator, and therefore the use of a photoinitiator can be optional, but is preferred.
Preferred fine paramagnetic or superparamagnetic nanoparticles are a metal or a metallic mixture comprising a plurality of metals. Suitable fine paramagnetic or superparamagnetic nanoparticles are transition metals, particularly iron, cobalt, nickel, and their alloys or mixtures. The fine paramagnetic or superparamagnetic particles are preferably superparamagnetic nanoparticles of iron or of mixed iron and cobalt. The primary particle size of the magnetic particles can be less than 1 micrometer, but is preferably 100 nm or less, preferably less than 50 nm, and more preferably less than 30 nm. A notable size range is from about 2 nm to about 30 nm. One particular benefit for using the finer superparamagnetic particles in the present invention is that they can be more easily dispersed in the UV curable composition to provide strong magnetic signals in a limited area.
The magnetic nanoparticles can be coated with carbon or iron oxide, and preferably the nanoparticles are coated with carbon. While not wanting to be bound by theory, the preferred carbon coating or matrix is believed to suppress oxidation of the metallic nanoparticle and to aid dispersion. Suitable nanoparticles for use in the practice of the present invention are described in various publications, including: “Carbon-coated Nanoparticle Formation and Plasma Torch Synthesis” (Majetich et al., ECS/America Proceedings, Fullerenes—Vol. 3 pp. 673-687, 1996); “Carbon Coated Nanoparticle Composites Synthesized in a Plasma Torch” (Scott, et al., Materials Research Society Symposium Proceedings, Vol. 457, pp. 219-224, 1997); Ruoff, et al., in U.S. Pat. No. 5,547,748; Burke et al., in “Magnetic Nanocomposites: Preparation and Characterization of Polymer-Coated Iron Nanoparticles”, (Chem. Mater. 2002, 14, 4752-4761); Geus, in WO 99/46782.
Nanoparticles suitable for use in the practice of the present invention can be made by plasma torch synthesis radio frequency techniques, and are available from the Department of Materials Science and Engineering at Carnegie Mellon University.
In a preferred embodiment, carbon-coated superparamagnetic particles of the present invention are prepared by a direct current plasma process as described in more detail below and in a U.S. Provisional Patent Application entitled “Process for Preparing Superparamagnetic Transition Metal Nanoparticles” filed Oct. 14, 2005, and assigned to E. I. DuPont de Nemours and Company.
The process of the present invention for preparing nanoparticles comprises treating carbon-containing compound(s) and metal-containing compound(s) with a direct current (DC) electric arc plasma. The carbon-containing compounds include C1 to C5 hydrocarbons, including but not limited to methane, ethane, propane, butane, and pentane. The metal-containing compounds may be fed as a vapor stream in a hydrocarbon such as methane, as a liquid, or as a powder. Preferred metal compound feeds include one or more of the volatile carbonyls of iron [iron pentacarbonyl, Fe(CO)5] and nickel [nickel tetracarbonyl, Ni(CO)4], which may be fed as vapor mixtures in methane or as liquids, and crystalline cobalt [dicobalt octacarbonyl, CO2(CO)8], which may be fed as a powder or as a liquid above its melting point of 51° C. The DC arc source that can be used is a plasma torch reactor such as that illustrated in
A nickel tetracarbonyl vapor phase source, and/or a dicobalt octacarbonyl source can be used to prepare nanoparticles having iron mixed with nickel and/or cobalt. More preferred materials for the preparation of superparamagnetic carbon-coated iron nanoparticles comprise an iron pentacarbonyl vapor phase source and methane.
In an example of the preparation of the preferred carbon-coated superparamagnetic iron particles by the process of the present invention, a bubbler, shown schematically in
The fine paramagnetic or superparamagnetic nanoparticles are included in the curable superparamagnetic dispersion in an amount of from about 0.01% to about 30%, and preferably from about 0.2% to about 10%, based on the weight of the curable superparamagnetic dispersion.
Use of mechanical means, viscosity modifiers, and/or other technologies conventional to those of ordinary skill in the coating art can reduce the potential of the curable superparamagnetic dispersions to separate on standing. High shear processes such as a three-roll mill or a Hoover muller achieve this mixing of the solids and binders and to obtain stable dispersions. An alternative is the use of ultrasonic mixing equipment (such as an Ultrasound Processor UIP 1000, available from Hielscher, Teltow, Germany).
The curable superparamagnetic dispersions of the present invention optionally further contain at least one curing agent or polymerization agent selected from photoinitiators, radiation initiators, chemical initiators, thermally activated initiators present in an amount of up to about 2 wt %; one or more components, optionally present in any effective amount, selected from the group consisting of: (i) viscosity modifiers (up to about 40 wt %), (ii) other taggants and/or (iii) solvents.
Initiators are generally chemical agents that break down or are changed upon exposure to an external influence such as heat, light, or other chemicals, and by this action initiate the curing step. Such initiators can be photo-initiators that are activated by light or, radiation-activated initiators, or chemical initiators, or initiators that are activated by heat. Suitable curing agents or initiators useful in practice of the present invention are those that are commonly used for the polymerization of (meth)acrylates, epoxy resins, and polyesters and are well known to those skilled in the art. For example, an initiator suitable for (meth)acrylate polymers is 1-hydroxycyclohexylphenylketone, (such as IRGACURE 184). Added or ambient moisture may be used to cure urethanes. Curing in the practice of the present invention can also be accomplished using high-energy processes such as electron beam initiation.
Modifiers are optional in the practice of the present invention, but can be preferred depending on the application for which the invention is being utilized. Suitable optional viscosity modifiers are well known to those skilled in the art and can be suitable for use herein. For example, viscosity modifiers suitable for use with curable acrylate systems are acrylate oligomers or polymers such as polymethylmethacrylate with a molecular weight of 350,000.
Luminescent taggants can be mixed with the curable superparamagnetic dispersions of the present invention to provide multiple information storage resources, both overt and covert, in the cured superparamagnetic polymer of the present invention.
Solvents are optional in the practice of the present invention, but are not desirable because they have to be removed and contribute to environmental concerns. The effectiveness of the present invention is not affected by the use of solvents.
Such curable superparamagnetic dispersion compositions are curable by various methods. For instance for a curable superparamagnetic dispersion comprising (meth)acrylates, a tri-wavelength UV lamp is suitable, (254, 302, and 365 nm), or a single wavelength UV lamp (302 nm). A low wattage UV lamp of about 10 watts can be used to effect the cure. For instance, in the Examples an 8 W UVLMS-38, 3UV EL Series UV Lamp, available from UVP, Inc. Upland, Calif. was used to cure the dispersion; similar lamps may be substituted. The curable superparamagnetic dispersions containing curable monomers, curing agents, and optional additives occasionally tend to separate on standing prior to polymerization. Minimal standing time, adjustment of the ratio of monomers such as SARTOMER SR9035 (ethoxylated 15 trimethylolpropane triacrylate, see Materials, below) to any other monomers, and the use of optional viscosity modifiers, provide adequate dispersions for curing under ambient conditions.
Superparamagnetic dispersions comprising epoxy resins can be cured using conventional resin/hardener systems. Conventional resin/hardener systems for use in epoxy resin ink compositions are described, for example, in U.S. Pat. No. 3,607,349.
An electron beam can be used to cure superparamagnetic dispersions comprising radiation-curable phenoxy resins. Conventional phenoxy resin formulations are described in U.S. Pat. No. 4,818,780, for example. Curing by electron beam does not require the inclusion of a photoinitiator.
Irradiation (UV light, electron beam radiation, etc.) can be used to cure superparamagnetic dispersions comprising varnishes, such as can be applied to printed food-packaging films, or radiation-curable varnish systems. Conventional radiation-cured varnishes are described in WO 0194451.
The curable superparamagnetic dispersion compositions of the present invention can be cured by UV light to provide UV-cured films, coatings, or inks and provide high magnetic moments, as is shown in Table 2. The viscosity and cure time of the compositions of the present invention can be adjusted by changing the ratio between MMA, PMMA, ethoxylated 15 trimethylolpropane triacrylate. A stable dispersion formation can be prepared with a high particle content and fast curing.
The cured superparamagnetic polymer of the present invention can be used in various types of carrier liquids, including inks for screen, thermal transfer, flexographic, offset, gravure, and intaglio printing; and varnishes and coatings.
The cured polymer comprising the dispersed superparamagnetic particles provides a plurality of spatially separated and magnetically readable superparamagnetic, particles that provide magnetic information when exposed to an arbitrary large magnetic field.
The invention also provides the use of cured superparamagnetic polymers for magnetic coatings, varnishes, films, and inks—including inks for inkjet devices and other marking or printing devices. The superparamagnetic polymer compositions can be applied to articles to provide information storage and product identification/authentication measures. The compositions can be used for bar codes, packaging, labels and containers. By means of the information encoded by the superparamagnetic polymer compositions, the compositions can be used to provide information in combination with magnetic reader systems to provide anti-theft devices, and devices used for product identification, authentication, and anti-counterfeiting.
Among the many applications for the cured superparamagnetic polymer are documents including passports, money, and security instruments; labeling on various substrates including cellulosic compositions and polymeric compositions such as labels made from polyolefins (polypropylene, polyethylene, etc.), polyesters, polyamides, ethylene copolymers, polyvinyl chloride, polyalkylene terephthalate, polyurethane, and copolymers; packaging including wrappings and packaging substrates; labeling on substrates that are opaque, clear, transparent, semitransparent or a combination thereof; labeling that is invisible or visible or a combination of both; directly labeled products (wherein the printing is directly on the product); carrier spatial information identification, e.g. one- and two-dimensional bar codes and logos; and the like. Such uses of the cured superparamagnetic polymer of the present invention can be detected with a reader system capable of reading magnetic information. The cured superparamagnetic polymer can be used as formulations for curable transparent or semitransparent magnetic film, coating or ink as part of the packaging and also as a marker such as a bar code for product identification and anti-counterfeiting. The cured superparamagnetic polymer may be positioned on the top or surface, under a protective layer, or in a hidden layer. For instance, the cured superparamagnetic polymer can be underneath an upper layer comprising black or other nontransparent layer, rendering the cured superparamagnetic polymer invisible but still detectable by a reader.
IRGACURE 184 is available from Ciba Specialty Chemical Corp., Tarrytown N.Y.
SARTOMER SR9035 (ethoxylated 15 trimethylolpropane triacrylate) is available from the Sartomer Company, Exton Pa.
Oleic acid, MMA, MAA, PMMA, were obtained from Sigma-Aldrich, St. Louis Mo.
Barium ferrite was obtained from Toda-Kogyo Corporation (Otake, Hiroshima, Japan) as HEX-UF70/30.
Dysprosium acetate (hydrated) was obtained from Aldrich Chemical, Milwaukee Wis. The material was dried at 130° C. and 80 kPa for 5 days prior to use. The dry material is hygroscopic and should be transferred rapidly to the monomer mixture.
Superparamagnetic samples of carbon coated Fe/Co nanoparticle sized powder and iron oxide coated Fe/Co powders were obtained from Carnegie Mellon University. A sample of each was used, made by radio frequency (RF) plasma torch synthesis and described herein as “Sample A” and “Sample B” respectively.
Iron pentacarbonyl, (195731, Batch # 01114MA) was obtained from Sigma-Aldrich, St. Louis, Mo.
Methane cylinder gas (Ultra-High Purity), helium cylinder gas (Scientific Grade), argon cylinder gas (Ultra-High Purity), and hydrogen cylinder gas (Ultra High Purity) were all obtained from MG Industries, Malvern, Pa.
Test Method 1. Magnetic Measurements
Magnetization measurements were made using a Superconducting Quantum Interference Device (“SQUID”, Model MPMS-XL, manufactured by Quantum Design, San Diego, Calif.
Polycrystalline samples were weighed on an analytical balance and placed in gel capsules that were then suspended in polyethylene tubes in the SQUID sample chamber. Typical sample weights were 10-100 mg. The magnetization measurements (hysteresis loops) were made at a temperature of 300° K. (27° C.). The applied magnetic field was stepped up in increments, starting at zero field and ending at a field well above that needed to saturate the sample magnetization. The field was then stepped down in the same increments to a negative value again sufficient to saturate the sample magnetization, and finally the field sweep was reversed and stepped back up to positive saturation. This generated a hysteresis loop for each sample, from which was determined the magnetization per gram as a function of magnetic field. The saturation magnetization, as well as the magnetization at a field of 100 Oe (7958 A/m), and the coercive fields, were then extracted from the data and are given in Table 2.
To a 50-mL round bottom flask, the required amount of superparamagnetic particles (Sample A, 0.02 g) was added. SARTOMER 9035 (2.00 g) was placed in the flask and the mixture was stirred by hand using a metal stirrer to wet the additive before the monomers were added. MMA (8.00 g) was added and the mixture was vigorously mixed using an air driven mixer with glass rod and Teflon blade until the mixture was well dispersed (about 1 hr). Lastly, IRGACURE 184 (curing agent) was added and the mixture was stirred for an additional 10 minutes. The mixture was quickly transferred to a small aluminum pan (diameter 2 inches, height 1 inch, (5.1×2.5 cm). The liquid depth in the aluminum pan was about 1/16″. The pan was placed under an UV lamp (e.g., a UVLMS-38, 3UV EL Series UV Lamp, 8 W, available from UVP, Inc. Upland, Calif., or equivalent) for a period of 6 hrs at a wavelength of 302 nm to produce an acceptable film for subsequent evaluation of the magnetic properties by Test Method 1. Although these mixtures tended to separate upon standing prior to polymerization, careful adjustment of the ratio of SARTOMER 9035 to MMA listed above provided good the best dispersion under these ambient conditions.
Examples 2 and 3 were prepared according to the method of Example 1 except that the components and quantities were varied as shown in Table 1.
Comparative Example C1 was prepared according to the method of Example 1 except that the components and quantities were varied as shown in Table 1. The high density of the barium ferrite required an increased viscosity to maintain the suspension until cured. The viscosity increase was obtained by the addition of PMMA.
Comparative Example C2 was prepared according to the procedure of Example 1 except that the components and quantities were varied as shown in Table 1. The dysprosium acetate, a hygroscopic material, was dried for 5 days at 130° C. in a vacuum oven (about 80 kPa). Moisture cannot be present as it will cause a gel to form or make the solution cloudy when added to the recipe. Oleic acid (5.88 g), methyl methacrylate (MMA, 14.50 g), and methacrylic acid (MAA, 3.57 g) were added to a 100-mL three-neck reaction flask. The stirred mixture was heated to 95° C. The dysprosium acetate was transferred directly from the vacuum oven to the flask as quickly as possible and the mixture stirred and heated to 105° C. until clear and free of bubbles. The mixture was cooled and transferred to a glass container to give a clear, light yellow liquid. Clarity was a required property, if the product was cloudy or showed a precipitate on the bottom, as can be caused by moisture, the mixture was discarded and the procedure repeated.
Comparative Example C3, a control, was prepared according to the procedure of Example 1 except the reaction mixture was MMA (8.00 g, 78.39%), SARTOMER 9035 (2.00 g, 19.60%), and IRGACURE 184 (0.2045 g, 2.00%). No magnetic material or other chemicals were present in this example. The polymerization and testing of magnetic properties was as in Example 1.
1MMA: methylmethacrylate; MAA: methacrylic acid; PMMA: polymethyl methacrylate, MW: 350,000.
2PMMA provides increased viscosity to aid the suspension of the dense barium ferrite.
3A and B are samples of superparamagnetic Fe/Co nanoparticles coated with carbon (A) and iron oxide (B).
4See Materials, above, for sources.
4See footnotes to Table 1.
5For preparation of the anhydrous salt, see Comparative Example C2.
Table 2 shows that 2 wt % carbon-coated Fe/Co nanoparticles (Sample A) showed ˜30 times higher magnetic susceptibility compared with that of 20% Dy salt sample. (1.26E-05 vs. 4.40E-07).
An iron pentacarbonyl source (bubbler) and plasma torch were used as shown schematically in
The plasma torch reactor, shown schematically in
Below the nozzle holder was a water-cooled quench chamber that had three radial input ports to provide additional quench using helium (scientific grade, MG Industries, see above) fed through each of the ports for a total helium quench of 15 L/min. Below the quench chamber was an adapter connecting the quench chamber to the water-cooled, single-filter element product collector. The collector housed a 3 micrometer sintered INCONEL 600 filter element (from GKN Sinter Metals, Auburn Hills Mich.). The carbon-coated nanometer iron particles were collected on the filter and removed for analysis.
Typically each synthesis constituted multiple shorter runs between which any plugging that occurred at the nozzle or at the methane injection tips was cleared. Specifically for Example 4, a total of 10.7 g of carbon-coated iron particles were produced in 15 h for a production rate of about 0.7 g/h. The reactor was shut down to clear plugging ten times during the synthesis. Run time between plugs was about 30 minutes and product was collected four times from the filter over the course of the 15 h run. The total amount of iron pentacarbonyl fed was 20 g (feed rate 22 mg/min). The reactor pressure at the start and end of the entire run was 812 and 991 Torr (108 and 132 kPa), respectively.
A superparamagnetic sample (Sample C) of carbon-coated Fe nanoparticle powder was prepared by direct current plasma torch synthesis as described in Example 4.
Superparamagnetic particles (Sample C, 3.0 g) were pre-dispersed in SARTOMER 9035 (UV curable monomer, 147.0 g) in a 500-ml beaker. The mixture was ground with 0.2 mm yttrium stabilized zirconia grinding beads (669 g) using an electric motor with a 1-inch (2.54 cm) high-speed disperser (HTD) polyurethane blade (made by Firestone, Indianapolis Ind.) at 3000 rpm for 4 hours. The product after grinding was a dark colored slurry.
To a 50-mL round bottom flask, the required amount of the slurry (0.25 g) was added. Additional UV curable monomer, SARTOMER 9035 (9.75 g), and IRGACURE 184 (curing agent, 0.204 g) were added to the flask and the mixture was stirred by hand using a TEFLON stirrer for 30 min. The mixture was quickly transferred to a small aluminum pan having a diameter of 2 inches and height of 1 inch (5.1×2.5 cm). The liquid depth in the aluminum pan was about 1/16 inch (1.6 mm). The pan was placed under an UV lamp (e.g., a UVLMS-38, 3UV EL Series UV Lamp, 8 W, available from UVP, Inc. Upland Calif.) for a period of 4 h at a peak wavelength of 302 nm to produce a film suitable for subsequent evaluation of the magnetic properties by Test Method 1. Details of the film composition are given in Table 3 and measurements of magnetic properties by Test Method 1 are shown in Table 4.
Example 6 was prepared according to the procedure of Example 5 except the reaction mixture in the 50 ml flask contained slurry (1.00 g), SARTOMER 9035 (UV curable monomer, 9.00 g), and IRGACURE 184 (curing agent, 0.204 g). The polymerization and testing of magnetic properties was as in Example 4. Details of the film composition are given in Table 3 and measurements of magnetic properties by Test Method 1 are shown in Table 4.
1Sample C is a sample of superparamagnetic Fe nanoparticles coated with carbon, prepared as described in Example 4.
1Sample C is a sample of superparamagnetic Fe nanoparticles coated with carbon, prepared as described in Example 4.
Table 4 indicates that the sample with 0.2 wt % carbon-coated Fe nanoparticle (Sample C) showed about the same magnetic susceptibility as that of 20% Dy salt sample described in Comparative Example C2. (5.0E-07 vs. 4.40E-07 m3/kg).
This application claims the benefit of U.S. Provisional Application No. 60/619,310, filed Oct. 14, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60619310 | Oct 2004 | US |
