ORDERED PARTICLE STRUCTURES AND METHODS OF MAKING SAME
Technical Field The present invention relates to techniques and processes for forming ordered mixtures of particles.
Background Art The terms "ordered mixing" and "ordered mixtures" formed by such mixing processes were coined to describe the mixing of cohesive, interactive particulate systems, in differentiation to the traditional randomization mixing process of comparatively coarse, free- flowing, non-interacting particulate systems. Ordered Powder Mixing, Nature, Volume 262, July 15, 1976, Pages 262-263, Chee Wai Yip, John A. Hersey; Ordered mixing: A new concept in powder mixing practice, Powder Technology, Volume 11, Issue 1, January- February 1975, Pages 41-44 J. A. Hersey. The basic principle of ordered mixing is that fine particles will adhere, especially to larger particles. The adhesion forces involved may be electrostatic, van der Waals, or surface tensional. Coarser components assist in the mixing process by breaking down agglomerates of the fine powder, thus allowing the adhesion of single cohesive particles to the surfaces of the coarser constituents. Ideally, ordered mixtures in the form of clusters may be formed due to complete adhesion of an identical number of equal sized fine particles to each coarse, homo-sized carrier, resulting in perfect mixtures with zero standard deviation. It is not adhesion per se which allows the improved degree of homogeneity to be achieved, but only ordered adhesion. To produce ordered powder mixtures, it is the basic requirement that ordered, not random, adhesion must be achieved during mixing. To date, no prior art mechanism has been established that yields ordered adhesion. Most work in ordered mixing is carried out in pharmaceutical industry for production of solid dosage forms, where the small drug particles adhere on coarser excipient carrier particles to achieve content uniformity. In practice, ideal ordered mixtures with zero standard deviation have not been achievable since the amount or number of particles interacting with carrier units is not constant but varies in such a way that is generally random. In the pharmaceutical industry, any addition of binder/glue in the ordered mixing process to enhance the adhesion between small drug particles and coarser carrier particles may reduce the dissolution rate and thus the bioavailability of the final dosage form. As a result, the relatively weak interactive forces between the guest (drug) and host (carrier excipient) particles tend to segregate by frictional attrition during subsequent solids handling and processing steps. Ordered mixtures formed by adhesion of particles will segregate into the two constituents if the forces applied to the mixture are sufficient to break the adhering bond between particles. Constituent segregation takes place due to the frictional attrition, which causes fine particle dislodgement from the ordered mixture of clusters, between adjacent particles and the containing wall. Segregation can be as much as problem in an ordered mixture with weakly formed interaction as in a random mixture. An ordered system has a greater stability than a random system due to the particle interaction; but once this interaction is disturbed, the segregation pattern of an ordered mixture may be more unpredictable than a random mixture. Although content uniformity is very important especially for very low content high potent drugs, stoichiometry is not necessarily required. For some mixtures, stoichiometry is very important, however, currently there is no process or method available for creating ordered, stoichiometric mixtures. It is also believed that there is currently no process available for simultaneously coating fine as well as coarser particles and clustering particles to form an ordered mixture.
Disclosure of Invention In a preferred embodiment the present invention comprises formation of ordered mixtures of particles by "clustering". Clustering according to the present invention comprises local "structuring" consisting of a large "host" and smaller "guest" particles. Small amounts of polymer can be coated onto solid particles by various means. In one embodiment, an ordered mixture is created wherein the material that is of lesser quantity is of small particle size (the "B" particles) and the "A" particles are of larger size. The "B" particles are then coated onto a single A particle. By creating this ordered structure, each composite particle has the proper amount of all ingredients; i.e., each composite particle is stoichiometric. This dry composite material can then be further processed for use in various applications such as but not limited to pharmaceutical formulations in the form of tablets, capsules, oral suspensions, inhalant, parenteral formulations and the like; energetics manufacture such as but not limited to explosives, propellants and pyrotechnics, especially those made by net shape manufacturing techniques; agricultural products including but not limited to fertilizers, herbicides and pesticides; nutritional supplements and the like. Clustering techniques for processing particles contemplated by the present invention include but are not limited to triboelectric clustering, magnetic clustering, and Sequential Particle Addition (SPA), each of which techniques can be employed to achieve stoichiometric clustering. Such clustering techniques may be employed to provide various combinations of clusters, including but not limited to all large clusters, large and small coated particles, large coated particles with small granulated or agglomerated particles, and large and small clusters. Various coating methods, such as but not limited to ultraviolet particle coating, Rotating Fluidized Bed Coating (RFBC) and magnetically fluidized bed coating are disclosed for achieving the novel coating and clustering approaches described herein. Dry and wet coating methods and devices are also contemplated by the present invention to coat B particles onto A particles. Regardless of the coating method employed, the process will create a freely flowing powder. It is an object of the present invention to provide novel clustering techniques for achieving stoichiometric clusters of materials. It is a further object of the present invention to permit higher solids loading where desirable. It is another object of the present invention to provide a process for producing products possessing exceptional microscopic homogeneous composition uniformity. It is a further object of the present invention to provide novel, versatile and cost effective processes for coating components with curable polymeric materials in order to enhance their flow properties.
Brief Description of Drawings FIGs. 1 and IA are depictions of starting materials according to one embodiment of the present invention. FIG. 2 is a side cross-sectional view of a device employed in connection with one embodiment of the present invention. FIGs. 3 and 3 A are depictions of clustered materials made in accordance with one embodiment of the present invention FIG. 4 is a graphical representation of one embodiment of clustering according to the present invention. FIG. 5 is a scanning electron micrograph of a coated particle produced according to a prior art coating technique. FIG. 6 is a graphical representation of clustering in accordance with one embodiment of the present invention. FIG. 7 is an alternative embodiment of a clustering approach in accordance with the present invention. FIG. 8 is a cross-sectional side view of a coating and granulating apparatus that may be employed in connection with the present invention. FIGS. 9A and 9B are scanning electron micrographs of pre and post coating processes. FIG. 9C is a graphical representation of a dissolution profile. FIG. 9D is a scanning electron micrograph of a cornstarch particle prior to coating in a rotating fluidized bed apparatus. FIGS. 9E - 91 are scanning electron micrographs of cornstarch particles at various stages of the granulation process. FIGS. 1OA and 1OB are scanning electron micrographs of uncoated Dechlorane Plus 515 particles. FIGS 1OC and 1OD are scanning electron micrographs of coated Dechlorane Plus 515 particles. FIGS. 1OE and 1OF are scanning electron micrographs of Dechlorane Plus 515 particles after granulation. FIG. 11 is schematic representation of a magnetically assisted fluidization system in accordance with one embodiment of the present invention. FIG. 1 IA is a schematic of a magnetically assisted fluidization device according to one embodiment of the present invention. FIG. 1 IB is a schematic of a tumbling magnetically assisted fluidized bed in accordance with one embodiment of the present invention. FIG. 11C is a cross-sectional view of a preferred embodiment of a shaft of a tumbling magnetically assisted fluidized bed according to one embodiment of the present invention. FIGS. 1 ID - 1 IF are cross-sectional views of preferred embodiments of the shaft according to FIG. 11C taken at various cross-sections A - A', B - B', and C - C, respectively. FIG. 12 is a preferred embodiment of a coater according to the present invention. FIG. 13 is a preferred embodiment of a coater according to the present invention. FIGS. 14A and 14B are scanning electron micrographs of material prior to coating in accordance with one embodiment of the present invention. FIGS. 14C and 14D are scanning electron micrographs of uncoated material in accordance with one embodiment of the present invention. FIGS. 14E and 14F are graphical representations of particle size distribution of the materials according to FIGS. 14A - 14B and 14C - 14D, respectively. FIG. 14G is a graphical representation of viscosity change over time for a preferred coating material according to the present invention. FIGS. 15A and 15B are scanning electron micrograms of particles coated according to one embodiment of the present invention. FIGS. 15C and 15D are scanning electron micrographs of materials subjected to coating according to one embodiment of the present invention. FIGS. 16A - 16D are scanning electron micrographs of materials prepared according to one embodiment of the present invention. FIG. 17A is a scanning electron micrograph of a material prepared according to one embodiment of the present invention. FIG. 17B is a graphical representation of mean particle size increase for materials prepared according to one embodiment of the present invention. FIGS. 18A and 18B are scanning electron micrographs of materials prepared according to one embodiment of the present invention. FIGS. 19 and 19B are scanning electron micrographs of materials prepared according to one embodiment of the present invention. FIG. 19C is a graphical representation of mean particle size increase of materials prepared according to one embodiment of the present invention. FIGS. 2OA - 2OD are scanning electron micrographs of materials prepared according to one embodiment of the present invention. FIG. 2OE is a graphical representation of a particle before being processed according to one embodiment of the present invention. FIG. 2OF is a graphical representation of the mean particle size of clusters prepared according to one embodiment of the present invention. FIGS. 21 A - 2 ID are scanning electron micrographs of materials clustered according to one embodiment of the present invention. FIGS. 22 A - 22D are scanning electron micrographs of materials clustered according to one embodiment of the present invention. FIGS. 23 A - 23D are scanning electron micrographs of materials clustered according to one embodiment of the present invention.
Best Mode For Carrying Out The Invention In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one having ordinary skill in the art that the invention may be practiced without these specific details. In some instances, well-known features may be omitted or simplified so as not to obscure the present invention. Furthermore, reference in the specification to phrases such as "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of phrases such as "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment. According to the present invention, a series of coating and particulate handling processes are employed to achieve stoichiometric clusters of materials with compositional uniformity at the cluster level. Suitably sized materials are selected and clustered according to at least one of the methods disclosed herein. Exemplary steps for preparing two types of formulations in accordance with the present invention comprise: For formulations requiring only a single substance such as but not limited to an active energetic pharmaceutical ingredient, pesticide, herbicide or the like in particulate form, exemplary unit steps are: i. Coating the particulates of the needed size distribution with thin coats of monomer(s) or oligomer(s) (different coat thicknesses may be used for different size ranges and for product specific formulations). ii. Polymerizing to form a solid coating. iii. Tumble-mixing different sizes of particulates to achieve specific bulk densities. iv. Optionally employing steps i-iii is to achieve large and small clusters and granules to achieve desired bulk densities. This series of unit steps assure local and global composition uniformity and desired packing densities for single component formulations. b. For formulations requiring two components in particulate form of similar or different sizes, the specific process unit steps comprise: i. Coating particulates A with the appropriate thickness coat of polymer a. ii. Polymerizing or evaporating solvent to form a polymer coat which is solid at subsequent handling temperatures. iii. Coating particulates B with the appropriate thickness polymer a or b. iv. Polymerizing or evaporating solvent to form a polymer coat which is solid at handling temperatures. Before continuing with the subsequent unit steps it must be noted that, in this example, coating of both particulate components not only achieves passivation and moisture resistance for both but, additionally and most importantly, when using the proper "chemistry" polymer coat formulations, it allows for the local composition uniformity of such two-component systems, that is, it enables local "structuring" of the two different types of particulates in the form of A-B pairs, "nuclear" single large A-multiple small B clusters, or, for that matter, any needed and achievable local structuring, as follows: v. If polymers or polymer formulations a and b are chosen and designed to be well separated in the triboelectric series, one becoming more negative and the other more positive when tumbled in a vessel of the appropriate wall material, enough smaller (ca tens of microns in size) particulates are attracted to the surface of the larger (ca hundreds of microns in size) particulates to approach surface charge neutralization. The chemistry of the two polymer coats are preferably adjusted to achieve "stoichiometric" local composition required by the energetic product requirements. vi. Together with van der Waals forces, the clusters form rather stable structures. vii. If the local structures are not mechanically stable and stability is required, an appropriate cluster "stabilization" unit step is carried out. viii. If required, A-B pairs or clusters of different overall sizes are tumbled together to increase bulk density. Similar to the utilization of the electrostatic forces to form stoichiometric local "structuring," the present invention also contemplates creating a polymer coat formulation a which contains magnetic particles and polymer formulation b containing super paramagnetic particles (SPM). They will attract each other when brought together. A novel clustering technique of SPA is also contemplated by the present invention. These clustering techniques are discussed in detail herein below.
Clustering Clustering according to the present invention may be achieved according to various techniques such as but not limited to triboelectric clustering, magnetostatic clustering, chemical reaction or fusion clustering, dry, wet or wet-coated based clustering by using rotating fluidized bed coaters or the like, and SPA, each of which may be employed to achieve stoichiometric clustering. Other techniques may be employed according to techniques known to those having skill in the art. Now referring to FIGs. 1-3 A, one embodiment of a clustering approach in accordance with the present invention is shown. A first component A coated with a polymer a (FIG. 1) and a second component B coated with polymer b (FIG. IA) are charged into a coater (FIG. 2), in this case a rotary cluster blender (RCB), to achieve clusters such as but not limited to energetic clusters E (FIGs. 3 and 3A). Stabilization or anchoring of clusters is achieved, if necessary, employing the same equipment used in the clustering step. For example, in the event a rotary cluster blender is employed for clustering, stabilization may be achieved by heating above the glass transition temperature of the coated polymer to form fusion points. If a liquid-solids spray coater is employed, stabilization may be achieved by spraying a binder polymer C. Optionally, an appropriate polymer may be introduced to induce a chemical reaction between pre-polymers. In a preferred embodiment clustering comprises local "structuring" consisting of a large "host" and smaller coated or uncoated "guest" particles or granulates. Small amounts of polymer can be coated onto solid particles by various means. In this embodiment, instead of simply mixing coated "A" particles with coated "B" particles, an ordered mixture is created wherein the material that is of lesser quantity is of small particle size (the "B" particles) and the "A" particles are of larger size. The "B" particles are then coated onto a single A particle. By creating this ordered structure, each composite particle has the proper amount of all ingredients. In accordance with this embodiment, it is generally desirable for the particle size of the ingredients to be approximately proportional to some function of their amounts in total. For example, an ingredient that is only 5% of total is of much smaller size than the ingredient that is 80% of the total, and the smaller particles are coated onto the larger ones to make an ordered mixture - what is referred to herein as "clustered" particles. Various coating methods, such as but not limited to ultraviolet particle coating, rotating fluidized bed coating and magnetically fluidized bed coating are disclosed for achieving the novel coating and clustering approaches described herein. Dry coating devices, such as but not limited to RFBC, magnetically assisted fluidization, Hybridizer, Mechanofusion, Theta-Composer, or the like may be employed to coat B particles onto A particles. Wet coating devices such as but not limited to wet-RFBC can also be employed when necessary. In either event, the process will create a freely flowing powder. Nano-fluidization and supercritical fluid based coating techniques can be employed for intermediate steps where certain co-polymers or polymers must be coated onto constituents "A", "B", etc. in order to create a proper sub-structure. The present invention contemplates various approaches to clustering such as but not limited to employing 1) a mixture of separately coated large and small particles for achieving desired packing density; 2) coated clusters for achieving good pouring properties, with a downside of possible diminished packing density, 3) a mixture of large coated and small granulated particles that is a compromise of 1) and 2) in that problems of pouring and segregation are reduced, the loss of packing is quite small, and, in the case of munitions applications, insensitivity for handling purposes is good; and 4) big and small clusters. These approaches are discussed in more detail hereinbelow. In general, in category 1) hereinabove, large and small coated particles will typically have a size disparity ranging from a factor of about 5 to about 10, with large particles ranging in size from about 100 microns to about 400 microns. The coating thickness for the larger particles ranges from about 0.5 to about 5 microns, and for the smaller particles, about 0.1 to about 2 microns. In category 2) above, all large clusters, particles are in the range of from about 100 microns to about lmm, and smaller particles are about one or two orders of magnitude smaller. The coatings vary in thickness from less than one micron to about 5 microns, and preferably in the range of about 0.2 to about 1 micron. In category 3) above, particle sizes are similar to that for category 1) but the granulated size is in terms of enlargement of small particles by a factor in the range of from about 2 to 5. That is, if the small particles are 10 microns, then granule size will be in the range of from about 20 to about 50 microns. Coating thicknesses are similar to those for category 1). In category 4) above, big and small clusters, the range of possibilities is vast. Preferably sizes of clusters are selected so as to maximize packing density. The number of cluster sizes is preferably two but may vary depend on the requirements of the mixture. For example, a first, largest cluster might range from about 200 micros to about 1 mm, an intermediate sized cluster would be about five times smaller than the largest cluster size, and the smallest cluster would be in the range of about 10 to about 20 times smaller than the largest cluster. In addition, any "fine" particles coated on each large particle would be in the range of about 5 to about 20 times smaller than the smallest of the clusters. Coating thicknesses are similar to those for category 1). Polymer/monomer systems are discussed in more detail herein below. Preferably, clusters are selected in ratios that are stoichiometric so that the interaction between host and guest particles are optimized to the extent necessary for the desired reaction in a given product.
Triboelectric Clustering The present invention relates in one aspect to creation of a mixture of particles A and B to form a particulate assembly. In one embodiment, the present invention discloses a collection of numerous small particles of B clinging to larger particles of A. One method of holding small particles together is by means of electrostatic attraction. It is well known that oppositely charged particles attract one another. This attraction can be promoted by coating particles with selected polymers which electrostatically "charge" either positively or negatively. These can be selected from the triboelectric series which ranks materials on their tendency to develop positive or negative charge. Table 1 Triboelectric Series Positive Glass Human hair Nylon Wool Fur Aluminum Polyester Paper Cotton Steel Copper Nickel Rubber Acrylic Polyurethane PVC Negative Teflon
The phenomena of static electrification are widely encountered. For example, in dry weather, walking across a nylon carpet in rubber-soled shoes may create a buildup of charge which is readily sensed when contact is made with a grounded metal object such as a doorknob. The same triboelectric phenomenon is the basis for xerography in which small particles of pigmented plastic toner are attracted to larger "carrier" beads for transfer to a photoreceptor where they "transfer" and "develop" the electrostatic pattern into an image. See, "Electrophotography and Development Physics" by L.B. Schein, Springer Verlag, Berlin and New York, Second Edition, 1992, incorporated herein by reference. In the process of xerography, small particles are manipulated by means of electrostatic forces. Typically, toner particles (5 to 20 μm in diameter) made of a polymer are transported to the image by carrier particles (50 to 200 μm in diameter.) These carrier-toner pairs are held together by electrostatic forces alone. The carrier particles are typically a magnetic material such as a ferrite with a coating to control its electrostatic charging characteristics. The toner is a spray-dried or ground particle, typically of an acrylic copolymer heavily loaded with carbon black (CB). The attraction between carrier and toner is engineered by choice of the carrier coating, the kind and dispersion of CB, and "charge control agents" which can be incorporated in the polymers. For example, a chlorinated or fluorinated oligomer or small molecule will cause the particle to develop a negative charge. Amides favor a positive charge. These relative charging effects can be ordered in a triboelectric series. Toner and earner are attracted to the electrostatic image on a xerographic photoreceptor. Together they "develop" the latent image. The heavy carrier particles are then separated by application of a magnetic field, leaving the toner clinging to the image areas where it can be transferred to paper and fused. The phenomenon of triboelectricity may be utilized quite generally to cause association of one particle (type A) with another (type B). Now referring to FIG. 4, a schematic of clustering according to a triboelectric technique is shown. The requirement is that the particles charge with opposite polarity with respect to one another. Various materials have been ranked with regard to their triboelectric charging propensity in the foregoing triboelectric series. If spontaneous triboelectric charging does not occur between A and B, this can be affected and adjusted by coating one or both particles with materials such as various polymers of the triboelectric series, such as but not limited to by coating the particles with polymers which have opposite polarities in the triboelectric series. Employing these principles in one embodiment the present invention comprises coating large particles (e.g. 100-200 μm) with a polymer a and smaller particles (10-30 μm) with a different polymer b which develops an opposite charge. For example, an oxidizer particle such as but not limited to ammonium perchlorate is coated with polyacrylate and the metal "fuel" is coated with a polyamide. When stirred together dry with aluminum particles, the coated aluminum particles tend to cluster around the oxidizer particles. An example is shown in the book "Physics" by Tipler, 3rd Edition at p. 684, incorporated herein by reference and reproduced as FIG. 5 herein. Due to the attraction of opposite charges, B particles tend to agglomerate on the surface of A particles. The usual case is that B particles are smaller in particle size than A particles. However, depending on the desired formulation, the proportions of A and B can be varied. The nature and percent coverage of the polymer coatings and the relative sizes of A and B results can be varied to adjust the clustering effect. In some cases it may be necessary to coat only one of particle A or B. In the case of energetic materials (propellants, explosives, etc.) A can comprise material such as but not limited to ammonium perchlorate crystals of 200 micrometers average diameter and B can comprise aluminum or magnesium powder with average diameter of 10 to 20 micrometers. Under appropriate circumstances (ignition or detonation) B is oxidized by A with the liberation of significant energy. In other systems, the particles A and B can comprise other materials such as but not limited to freeze-dried enzyme and its substrate, a drug and its carrier, and other kinds of reactants known to those of skill in the art, and can be brought into close proximity by clustering for subsequent chemical reaction. Moreover, particle flow characteristics of the A-B pairs can be modulated by the addition of various agents to improve flow. In a most preferred embodiment the relative amounts-the stoichiometry-of A and B are controlled.
Example 1 In one embodiment particle A is a particle of ammonium perchlorate averaging 200 μm in diameter and the B particles are aluminum powder averaging 10 μm (micrometers) in diameter. Electrostatic attraction in the maximum case coats B around A to create a composite particle of 220 μm diameter. The volume of A would be 4.19 X 106 μm3 and the volume of the surrounding B would be a maximum of 1.39 X 106 μm3 . However, realistic covering of A would be only 60 volume percent because of voids and non-ideal packing of B. Given that the density of ammonium perchlorate (AP) is 1.95 and that of aluminum is 2.70 grams/cubic centimeter, these volume proportions of 4.19 to 1.39 would give a composite particle of 69:31 by mass. With 60% coverage, the ratio is 78:22. By controlling the particle sizes, especially the average diameter of A, the proportions of B to A can be adjusted. Ideally, aluminum powder charges positive with respect to AP. When such is not the case, in a preferred embodiment the AP is coated with an acrylic, urethane, or vinyl polymer to create the relative charge needed. Tumbling the A and B particles together in an aluminum cylinder or a glass jar charges them by the phenomenon of "contact electrification."
Example 2 Particle A is acetaminophen and B is powdered polyvinyl acetate). The oppositely charged polymer particles surround and agglomerate on the drug. The formulation is employed to modulate the pharmacological release of the active drug. The advantages of triboelectric clustering according to the present invention are that no viscous liquid binder is required, A and B are in close proximity, the combined powders A and B are flowable and there is a degree of control of the proportions of B to A ("stoichiometry"). Magnetic Clustering As is well known, a collection of iron particles can be magnetized and will adhere to one another. This is an unstructured array of one type of particle. Typically, the powder becomes an agglomerate and does not flow. This is undesirable for the present invention in which a flowable powder is preferred. Magnetic particles with permanent magnetic moments (ferrites, iron powder, etc.) attract one another mdiscriminantly. To overcome this, what is needed is a large particle with a permanent moment and small particles which only develop a magnetic moment in the presence of a field. Paramagnetic materials such as copper do this very weakly.. If however, the particle size of iron or ferrites is reduced below 5 nm (50 A) they exhibit a phenomenon called superparamagnetism (SPM). See, "Introduction to Magnetic Materials" by B. D. Cullity, Addison- Wesley Publ. Co., 1972, pages 410-422; United Kingdom Patent No. 1,573,166 to Davidson; Canada Patent No. 1,105,759 to Davidson, all of which are incorporated in full herein by reference. In SPM, all the unpaired spins on the atoms align collectively and generate a super-paramagnetic state. Therefore, if particles of B are initially paramagnetic or diamagnetic, they can still be attracted to a magnetic particle of A if the B particles are coated with a dispersion of superparamagnetic (SPM) nanoparticles. Alone, these coated B particles would have no attraction for one another. Only in the presence of an attractive "permanent" magnet do they develop an induced magnetization attracting B to A. Now referring to FIG. 6, a schematic of ordered clustering in accordance with the present invention according to magnetic attraction is shown. SPM ferrites can be prepared by chemical reaction and by attrition. In one embodiment ferrites 2 are suspended in a polymer solution such as polystyrene in toluene and coated onto larger B particles to confer SPM properties onto B. These coated B particles have a negligible tendency to self-associate. In a preferred embodiment a permanent magnetic material 4 such as but not limited to Fe3O4 is suspended in a polymer and coated onto particles A. The SPM material is then coated onto particles B. When mixed together, there is a tendency for SPM B particles to cluster around the magnetic A particles. Similar stoichiometric considerations apply as in the case of electrostatically bound B and A.
Example 1 "A" is a 100 μm diameter particle of barium ferrite. "B" is an organic polymer containing or coated with numerous nanoparticles of SPM ferrous ferrite, Fe3O4.. The barium ferrite is premagnetized, and thus retains a remanent magnetism. This is the attractor for particles of B which cluster around the A particle, held by magnetostatic forces. IfA is not an intrinsically magnetic material, it can be coated with a layer of attached material containing a ferrimagnet such as barium ferrite. Magnetic clustering in accordance with the foregoing method can be used to combine A and B into a dry flowable composite suitable for the manufacture of many materials including energetics and explosives.
Chemical Reaction or Fusion Now referring to FIG. 7, clustering may be achieved by heating a charge of different sized particles A and B and polymer D above the glass transition temperature of the coated polymer to form fusion points 10 between particles. Alternatively, permanent anchoring among the large and small particles A and B can be achieved via chemical reaction between the selected chemical moieties imparted in the polymeric coating materials. The chemical moiety can be, but is not limited to, carboxyl, hydroxyl or ionic living teraiinals, amine, silane, epoxy or isocyanate functionalities. The reaction can be induced thermally with or without the use of catalyst, or induced by irradiation such as E-beam or UV.
Sequential Particle Addition (SPA) Sequential Particle Addition (SPA) is a novel method of forming clustered particles involving the simultaneous coating of small "guest" particles with large "host" particles with thin polymerizable liquids and the concurrent formation of clusters, formed by a core of individual host particle and a shell of many small guest particles. Coating small guest particles, especially those in the range of 20 microns or less, has always been a tedious and difficult task. Dry blending of big and small particles before particle-filling presents high probability for particle segregation. Infusion of large and small particle composite in a long tube, such as those employed in energetics applications, has also encountered some technical difficulties connected to long infusion times. In one embodiment the present invention includes a method of simultaneous coating (both large and small particles) and clustering (of large host and small guest particles) that solves all above-mentioned issues. In this process, the method of cluster formation between large and small particles is simplified to a single step of coating the large particles with sequential addition of the small particles, which are coated with the same liquid coat of the large particles. Thus, there is no need for pre-coating small guest particles. Additionally, no dry blending is needed since the clustered host and guest particles are held together strongly by a single polymerizable liquid which coats the surfaces of both particles. The end result of practicing this process is the creation of stoichiometric clusters and spatially unifonn product, consisting of small and large single or multicomponent particles. In one embodiment, large host particles are first preblended and coated with polymerizable prepolymer liquids. The coated host particles are then tumble-blended with small guest particles, added sequentially after the coating of the large particles. The tumbling action in the coating equipment further homogenizes the polymerizable liquid coat on the host particles and coats the small guest particles at the same time. The polymerizable liquid acts as the "glue" between the large and the small particles and also as a liquid coat on both. The polymerizable liquid is subsequently cross-linked in the same or a different vessel so that the clusters formed by the SPA method are mechanically strong enough to maintain their integrity during the subsequent particle handling and processing steps of processes employing the clusters. In this novel process, particle coating and clustering are carried out concurrently, eliminating the need for separate coating of large and small particles, simplifying processing steps, and reducing the large difficulties of handling small guest particles. The clusters of host and guest particles formed are held together strongly, eliminating the need for mechanical stabilization of the clusters, which may be necessary for clusters formed via electrostatic and/or magnetic interparticle attraction forces. Finally and importantly, stoichiometry between host and guest particles is easily achieved by varying material parameters, such as the amount of the polymerizable liquids, their composition and the particle sizes. The amount of polymerizable liquid blended on the large host particles and the amount of small particles can be varied, and result in different number of attached small particles found in the clusters formed by the SPA process. The host particles are preferably in the range of 50 μ to several millimeters and tumble- blended with different levels of liquid binder. The guest particles( are preferably about one or two orders of magnitude smaller than the host particles. The polymerizable liquid system is preferably selected from a polymer solution, suspension, or preferably reactive monomeric/oligomeric combination, all of which react later, after the cluster formation, forming a solid continuous polymer film on the particle cluster surface. The polymerizable liquid serves the dual purpose of both coating the host and guest particles and causing adhering of small guest particles on the big host particles. The particle clusters of host and guest particles may comprise various materials, such as but not limited to oxidizers and fuels in solid rocket propellant systems, big and small RDX particles in plastic bond explosive (PBX) formulations, active pharmaceutical ingredients (API) and recipient particles in pharmaceutical formulations and the like. A wide range of stoichiometric ratios between host and guest particles is obtainable by controlling the amount of guest particles being added as well as the amount of the polymerizable liquid preblended with the large particles. In a most preferred embodiment composite particle clusters with multiple, layers of guest particles with different properties are obtained by sequentially coating different guest particle systems. Under appropriate processing conditions, individual clusters of host and guest particles have been produced according to the present invention without any significant cluster agglomeration.
Coating Coating of powders by polymer films is of great interest in many diverse fields, and may be accomplished by a number of different processes. Processing of fine particles, typically smaller than 40 microns, poses formidable challenges due to the presence of strong cohesive forces that are significantly larger than the weight of each particle. When such particles have to be coated or granulated, it is necessary to suspend or fluidize them. Specifically, the coating or granulation processes essentially consist of two generally independent tasks that must work in conjunction: fluidization of fine powders so that the particles are suspended and circulate within the apparatus so that they are all exposed to the spray; and spraying of monomers or polymer solutions in such a way that the aerosol is fine and can allow for coating of the suspended particles without excessive agglomeration. Problems typically arise when the liquid is sprayed onto the fluidized powder bed, and the powder tends to stick and agglomerate, resulting in a loss of fluidization and creation of large agglomerates. Nonetheless, there are many techniques and procedures that can be found commercially or in literature where use of specific agitations or other "tricks" help alleviate such problems. However, when particles are fine, particularly less than 50 microns, most of the fluidized bed techniques fail, as now these particles are fall into class "C" of Geldart's classification (see, Geldart's Fluidization Map, Powder Technology, 7, 285 (1973), incorporated herein by reference) and are considered too cohesive for successful fluidization. Moreover, even if they are fluidized (for example, 50-60 micron size), then the problem of sticking and agglomeration is more pronounced. Hence fluidization becomes the most important part of such processes. However, according to Geldart's theory, these fine particles are class "C" particles and cannot be fluidized through use of a conventional fluidized bed.
Continuous Rotating Fluidized Bed (RFB) Coating and Granulating Processes As best seen in FIG. 8, a rotating (or centrifugal) fluidized bed, such as but not limited to commercially available equipment like the Omnitex, commercially available from Nara Machinery of Japan, provides a unique advantage, because the high speed of rotation creates a large centrifugal force field, and it has been found by the present inventors that under such field, the fine cohesive group C particles can act as fluidizable group A particles. In other words, in a rotating fluidized bed, the centrifugal field effectively shifts the boundary between class "A" and class "C" powders. Thus, employing a RFB for processing can make fine powders such as but not limited to fine RDX powders readily fluidizable. Experiments show that fine particles can be coated in a controlled manner using this approach. The RFB can also be used to granulate cohesive fine powders. Through "microgranulation", the flowability of cohesive fine powders with narrow size distribution is improved while inhibiting the granule size increase as much as possible due to high agitation in the RFB. Moreover, the same technique allows for creating ordered particulate structures, useful for the process of net shape manufacturing of the present invention.
Experiment - Coating of Cornstarch 0.3 kg of cornstarch, having a median diameter of about 15 microns, was charged in a rotating fluidized bed and sprayed with a 10% aqueous solution of hydroxypropylcellulose (HPC-L). The liquid feed rate of the HPC-L was 0.75 g/min, the spray air pressure was 0.55 MPa, the air temperature 333K, the airflow rate 0.805 m/s (u/umf=2.5) and the rotational speed of the rotating fluidized bed was 7.88 rps (5OG i.e., 50 times the gravitational force). Now referring to FIGs. 9A and 9B scanning electron micrographs (SEMs) of cornstarch before coating and after coating are shown. FIG. 9B shows a particle having a 9% HPC-L solution coating. Coating appeared uniform, and very little agglomeration was observed. A drug-release study was performed comparing uncoated cornstarch and the 9% HPC- L coated cornstarch. Aqueous pigment food blue No. 1 was used as a model drug, which was precoated (0.05 wt. %) onto the cornstarch powder. The coated product was placed in a standard dissolution vessel. Now referring to FIG. 9C, for the uncoated cornstarch, 80% release of the "drug" occurred in less than one minute. For the 9% coated cornstarch, 80% release took over ten minutes.
Experiment - Granulation of Cornstarch 0.15 kg of cornstarch, having a median diameter of about 11 microns (see FIG. 9D) was charged in a rotating fluidized bed and sprayed with a 3% aqueous solution of HPC-L. FIGs. 9E-9I, SEMs of the cornstarch particles at various stages of the granulation process, clearly show an increase of particle agglomeration/granulation with time. FIG. 91, the SEM taken at t=1200 s, shows granulates having a diameter of about 30 microns and no unagglomerated particles.
Experiments - Coating and Granulating in a RFB for RDX Simulants Experiments were conducted using an Omnitex RFB to test the feasibility of coating and granulating RDX-5 simulants using an RFB. The simulant materials used were Dechlorane Plus 515 powder having an average particle size of 10 microns and hydroxypropyl cellulose (HPC-L), a common water-soluble polymer used in binding applications. The description of materials and parameters are set forth in Table 2.
Coating of Dechlorane Plus Now referring to FIGS. 10A- 10D, SEMs of uncoated Dechlorane Plus 515 particles (FIGs. 1OA and 10B) are compared to SEMs of coated Dechlorane Plus 515 particles (FIGs. 1OC and 10D) prepared according to the parameters set forth in Table 2. FIGs. 1OC and 1OD show little agglomeration and uniform coating of the particles. The uncoated particles have a different surface morphology than the coated particles. Thus, RFB can be used for wet coating of small cohesive particles, including RDX-5 powders, without significant agglomeration. As compared to a conventional fluidized bed, high shear due to high gas velocities prevents the product from forming excessive agglomerates. The RFB can also be used to create controlled or sustained-release products for pharmaceuticals, fertilizers, supplements and nutritional additives. The RFB is particularly well suited for use in preparations of materials for use in munitions in accordance with the teachings of United States Patent Application Serial No. 10/819,898, entitled "Manufacturing Net Shape Processes and Compositions," filed April 7, 2004 and incorporated herein by reference.
Granulation of Dechlorane Plus In granulation of RDX material in a RFB, the spray rate that is employed is preferably higher than that used for RDX coating. Now referring to FIGs. 1OE andlOF, SEMs of Dechlorane Plus 515 particles after granulation show granules are formed of Dechlorane Plus fines, along with some individually coated particles. Therefore, wet granulation in a RFB can be employed to enhance the flowability of cohesive fine powder to produce a narrower size distribution while inhibiting granule size increase.
Coating/Granulation of Fine Particles through Magnetically Assisted Fluidization Magnetically assisted fluidization techniques may be applied for coating or granulating particles, such as according to the methods and processes disclosed in United States Patent No. 5,962,082 to Hendrickson et al., the teachings of which are incorporated fully herein by reference. In one embodiment magnetically assisted fluidization can be utilized for smaller, 10-20 micron sized particles. Now referring to FIG. 11, a general schematic of a magnetically assisted fluidization system 20 is disclosed. A mixing chamber 22 is disposed within an electromagnetic field coil 24 connected to a power source such as an AC power supply 26. Large host particles A are charged and tumbled in the chamber 22 with smaller guest particles B and magnetic particles M. A number of experiments indicate that the use of magnetic agitation combined with either aeration or tumbling may be used to achieve a well-fluidized bed of fine powders, and due to the action of spinning magnets, agglomeration of the sticky/coated particles may be avoided or greatly controlled. Two systems are disclosed in which in each system, the powder to be coated is placed in a vessel along with permanent magnets that are 50 to 100 times larger in diameter than the powder to be coated, indicating that the surface area of the magnets is well over an order of magnitude smaller than the powder to be coated. The vessel is subjected to an oscillating magnetic field causing the magnetic particles to spin vigorously and undergo collisions with the walls and the other particles. As a result, the whole system is intensely fluidized, and is able to handle fine, cohesive particles for subsequent processing such as coating or granulation. The proposed devices can be employed for granulation of fine powders and coating of larger particles by polymer and smaller particles.
Aerated Magnetically Assisted Fluidized Bed (AMA-FB) FIG. 1 IA refers to a first embodiment of a magnetically assisted fluidization device 30. A cylindrical chamber 32 is disposed within an electro-magnetic field coil 34, which is supplied with an alternating current (A/C) from a power supply (not shown). The chamber 32 further comprises at least one filter 36 such as but not limited to a fine non-metallic mesh or sintered ceramic distributor at the bottom through which air is supplied. The chamber 32 is filled with a powder to be coated, mixed with magnets M (preferably about 2 mm in size), and barium ferrite, coated with polystyrene or polyurethane. The weight ratio of magnets to powder is adjustable depending on the performance of the system, but typically ranges from 1:1 to 3:1. Air or other acceptable gas such as argon, nitrogen or CO2, supply system 38 keeps the powder well mixed and prevents it from forming a cake at the bottom of the vessel. Where a solvent- based polymer spray is employed (not a necessity for this process), the air also helps in drying of the coated product. The coil 34 is preferably a stator coil, and can be custom-made or extracted from an A/C motor. The size of the coil 34 is dictated the geometry of the chamber 32 and the required magnetic field strength. In one embodiment a 3-phase A/C coil with a variac is employed. The chamber 32 is typically conductive plastic or glass. A commercially obtainable vial may also be used. The size of the chamber 32 is dictated by the loading amount of powders. Preferably the bottom 40 of the chamber comprises a sintered ceramics plate, as a distributor for air. The pore size of the distributor is restricted by the size of loading powders. The lid 42 of the container can be made of simple mesh, and the exhaust (not shown) preferably is sent to a hood. Capillary tubes 44 are incorporated into the lid 42 for monomer injection from tanks 46 and 48. A spray system for monomer injection (not shown) comprises appropriate commercially available nozzles and syringe pumps. Preferably a dedicated spray system is employed for each monomer in a multi-monomer system. The monomers may be added in an alternating mode to build polymer layers to a desired thickness, such as sequential injection of di-isocyanate and polyol to form polyurethane. An alternative for syringe system injection is an airflow atomizer. Lab compressed air can be served as an air supply system 38 with a flow meter. Other suitable gases that may be employed include but are not limited to N2, CO2, or argon. In a preferred embodiment this fluidization device is suitable for polymer solution coating if heated air is used for drying.
Tumbling Magnetically Assisted Fluidized Bed (TMA-FB) Now referring to FIG. 1 IB, in A TMA-FB system 50, a drum 52 is placed within an electro-magnetic field coil 54, which is supplied with an alternating current (A/C) from motor 56, in such a way that it can be rotated in a manner like a tumbling ball mill. The coil 54 is preferably a stator coil, and can be custom-made or extracted from an A/C motor. The size of the coil is dictated by the geometry of the drum and the required magnetic field strength. In an alternate embodiment, the coil need not fully cover the drum 52, but can be of a rectangular shape and be placed below the drum unit. The drum 52 is preferably made of a plastic material. The geometry is preferably cylindrical and the ratio of length to diameter is preferably approximately 1 :2. The size of the drum 52 is determined by the amount of material to be added. One end of the drum 52 is operably connected to a motor output shaft 58 to move the drum 52. In an alternate embodiment, drum 52 rests on rollers (not shown) one of which is a driver and another an idler as in a typical ball mill. In one embodiment one end of the drum 52 is wrapped with abrasive tape 60 to connect with the motor 56 to drive the drum 52. An opening 62 is formed, preferably in the middle of the drum 52 for feeding and discharging materials. Bearings 64, preferably plastic, are connected on the center of the side of drum 52 to connect the moving drum 52 and the shaft 58. The rotational speed of the motor 56 is preferably variable such as from tens of rpm to hundreds of rpm. Optimal rotational speed can be varied. Now referring to FIG. HC a preferred embodiment is shown of a configuration of a shaft 58 that is used for spray of monomers or liquids. Now referring to FIGS. 1 ID-I IF, the shaft 58 preferably comprises at least one bore 59 and is used to support the drum 52 and inject monomers from vessels 66 and 68 (FIG. HB) into the chamber. Syringes (not shown) are used to inject monomers into the drum 52. In a preferred embodiment at least one capillary tube 70 is employed to achieve improved atomization of injected monomers. The capillary tube 70 is disposed in the bore 59. Preferably the inject position 72 is adjusted manually by moving the tube 70 inside the shaft. In use, the vessel is filled with the powder to be coated, mixed with magnets (about 2 mm in size), barium ferrite, coated with polystyrene or polyurethane. The weight ratio of magnets to powder is adjusted depending on the performance of the system, but typically ranges from 1:1 to 3:1. The tumbling is needed to keep the powder well mixed and to prevent it from forming a cake at the bottom. In a preferred embodiment a fixed arm (not shown) is positioned near the wall of the drum to scrape the powder off of the wall of the drum. The ball mill type of TMA-FB is suitable for in-situ reaction of two monomers. Both AMA-FB and TMA-FB are designed to coat, cluster or granulate materials.
Ultraviolet Particle Coating Conventional liquid spray particle coating processes are commonly known to be prone to agglomeration due to the prolonged period of time needed to convert coated liquid to tack free solid, even when the un-coated particles can be well separated in the suspension stage. The common use of solvent/non-solvent in conventional particle coating processes also pose environmental, health and cost concerns. A new solvent-less process of coating particles comprises introducing UV curable liquid onto a suspended particle, followed by curing when exposed to UV irradiation. The particle suspension can be achieved by conventional dry particle coating devices such as fluidized coaters, drum coaters, or tumbling coaters with some modifications, which are equipped with liquid spray capabilities. The suspension media, depending on specific application, can be air, nitrogen, carbon dioxide or any other gases, where non oxygen containing media is preferred due to its potential to inhibit the UV polymerization reaction as well as improved safety. Vacuum can also be applied in closed system coaters such as drum or tumbling coaters. After a selected amount of UV-curable liquid is coated on the particle surfaces, the coated UV liquid is rapidly converted to a cured coating when exposed to a UV source. This novel particle coating process takes advantages of UV curable material's ability to form almost instantaneously tack-free surfaces. Essentially, the novel UV particle coating technology comprises the steps of fluidization and UV curing.
Fluidization A variety of coaters may be employed for fluidization including but not limited to batch operating coaters such as a Glatt Mini fluidized bed with liquid spray (top or bottom) nozzle, rotating fluidized bed, AMA-FB, TMA-FB, drum coater with or without mixing baffles and deflectors; and continuous coaters such as free fall coaters with or without the use of deflectors and spin coaters. Preferably, any coater employed is modified for UV delivery by providing quartz windows where applicable. Now referring to FIG. 12, a fluidized bed coater 80 is equipped with a UV lamp 82, swirl accelerator 84 and a UV curable liquid port 86. Now referring to FIG. 13, a magnetically assisted fluidized coating device 90 comprising drum 92, coil 94, and shaft 96 in accordance with the previous discussion is adapted to include a UV light source 98. UV curable liquid is injected in port 100 and injected into coater 90 through injectors/atomizers 102. Magnets 104 are tumbled with particles to be coated 106 such as but not limited to RDX.
UV curing The UV curing step may employ free radical systems or ionic systems. In free radical systems the curable materials polymerize and cure only when exposed to UV radiation. Suitable UV curable monomers include aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, epoxy acrylate, ether acrylate and amine modified ether acrylate. Reactive diluents include mono or multi-functional acrylates. Photo initiators include α-hydroxylketone, α-aminoketone, mono acyl phosphine and bis acyl phosphine. The UV range is in the range of 200-400 nm. Preferably, the surface tack-free time in free radical systems ranges from a fraction of a second to minutes, most preferably less than about 10 seconds. Complete through cure time can range from a fraction of a second to minutes, most preferably less than 30 seconds. The coating thickness ranges from 1 to 100 microns, preferably less than 5 microns. Optimum curing temperature ranges from about 2O0C to about 800C, preferably about 2O0C. Appropriate acceptable gas media include air, argon, CO2, and N2, preferably CO2. Coatings made in accordance with the present invention employing free radical systems exhibit good adhesion, cost-effectiveness, and a wide range of attainable properties. In ionic systems, once initiated, polymerization and curing will advance even without exposure to UV radiation. Suitable cationic curable materials include monocycloaliphatic epoxides and biscycloaliphatic epoxides. Examples of suitable co-monomers are vinyl ethers. Suitable photo initiators include diaryliodonium salts and triarylsulfonium salts. The UV range is in the range of 200~400 nm Preferably, the surface tack-free time in ionic systems ranges from a fraction of a second to minutes, most preferably less than about 10 seconds; in general, however, the time is somewhat slower than in free radical systems. The complete through cure time can range from a fraction of a second to minutes, most preferably less than about 30 seconds. The coating thickness ranges from 1 to 100 microns, preferably less than 5 microns. Optimum curing temperature ranges from about 2O0C to about 8O0C, preferably about 2O0C to about 500C. Appropriate acceptable gas media include air, CO2 and nitrogen, preferably CO2. Coatings made in accordance with the present invention employing ionic systems exhibit low shrinkage, excellent mechanical properties and good adhesion. The UV particle coating methods of the present invention permit at least one thin layer of crosslinked polymeric materials to be evenly coated onto selected particles, while the particle agglomeration is kept at a minimum or entirely eliminated. The methods allow the tailoring the coating structure and thickness, which can be achieved by controlling numbers of spray/curing cycles of the same or different UV curable liquids.
Particle Coating and Clustering Various known powder mixing/blending equipment such as those described hereinabove, including some continuous equipment, can be employed to practice the SPA technique to form clustered structures. Experiments were conducted in accordance with the present invention in which particles were coated and clustered using a drum coater. The drum coater employed four baffles and a variable speed drum. The basic steps in the experiments comprised preblending particles with reactive binder having a pot life of about 20 minutes; charging binder-coated particles into the drum coater (these first two steps are preferably combined when using drum coaters having binder injection capability); further homogenizing the binder coat by tumbling; and after being lifted by the baffles suspended particles in free-fall become tack-free via cross-linking of the reactive binder coat. In the series of Experiments 1-7, the materials employed were RDX simulant particles. In these experiments potassium chloride (KCl) having a size of about 200 μm (REHEIS: PHARMA-K)(40-200 mesh: 70 ~ 400 μm); and Dechlorane Plus (Ci8H12CIi2) 515: ~ 10 μm (Occidental Chemical Corporation: Dechlorane Plus-515) were employed.
Experiment 1 Now referring to FIGs.14A and 14B SEMs of uncoated KCl (about 200 μm) show cubic crystals with surface defects. Now referring to FIGs. 14C and 14D SEM photographs of uncoated dechlorane (about 10 μm) show particles of irregular shape and size. Now referring to FIGs. 14E and 14F, particle size distributions for dechlorane and pure KCl are shown. The pure KCl has a mean of 284 μm. The binder employed in these experiments was Smooth-Cast 327™, a two component system with an A:B mixed ratio of 1:1 pbv. The shrinkage of Smooth-Cast 327™ is 0.35% with a specific gravity of equal volume mixture A:B of 1.60 g/cc. The viscosity of the Smooth-Cast 327™ mixture increases with time. Now referring to FIG. 14G a graphical representation of the changes of viscosity with time for Smooth-Cast 327™ is disclosed. Employing the SPA method of the present invention, a particle mixture of KCl and Dechlorane Plus was coated. 240 g of KCl was preblended with 3 ml of equal volume of A and B Smooth-Cast 327™ in a Ziploc™ bag for a few minutes. After a uniform binder coat was formed on the KCl particle surface, 60 g of Dechlorane Plus was added and tumbling in the bag was continued for another few minutes. The preblended particle mixture with binder was charged into the drum coater. The coater was rotated at 40 rpm for about 1 hour. The SPA technique resulted in good coating with only a few weak agglomerates which were easily deagglomerated. Now referring to FIGs. 15A and 15B SEMs show the large KCl particles having a continuous film coating. The particle mixture exhibited enhanced flow properties because the large KCl particles enhanced the flow and small dechlorane particles absorbed the extra binder as a result of greater surface area. Now referring to FIGs. 15C and 15 D, SEMs show the small dechlorane particles resulting from the foregoing coating procedure. The small dechlorane particles were also coated. This technique provides a method of simultaneous coating of big and small particles thus eliminating the difficulties encountered in coating small particles alone, such as about 10 μm Dechlorane Plus particles.
Experiment 2 240 g of KCl was preblended with 6 ml of equal volume of A and B of Smooth-Cast 327™ in a Ziploc™ bag for a few minutes. After a uniform binder coat was formed on the KCl particle surface, 60 g of Dechlorane Plus was added and tumbling was continued in the bag for another few minutes. The preblended particle mixture with the binder was charged into the drum coater. The coater was rotated at 40 rpm for 50 minutes. No free flowing curtain of particles formed inside the drum coater and occasional beating of the drum coater was required to energize or loosen the caked bed. Now referring to FIGS. 16A and 16B, SEMs for small dechlorane particles are shown. Fewer unbound small dechlorane particles were observed due to increased binder level (FIG. 16A), and the small dechlorane particles were coated as well (FIG. 16B). Now referring to FIGs.lόC and 16D, SEMs for big KCl particles prepared according to this experiment are shown. The FIGS. indicate a continuous film coating of big KCl particles was achieved (FIG. 16C) but bound small dechlorane particles on a KCl surface were not clearly identifiable in FIG.16D. Experiment 3 240 g of KCl was preblended with 12 ml of equal volume of A and B of Smooth Cast 327™ in a Ziploc™ bag for a few minutes. After a uniform binder coat was formed on the KCl particle surface, 60 g of Dechlorane Plus was added and tumbling was continued in the bag for another few minutes. The preblended particle mixture was charged into the drum coater and the drum coater was rotated at 35 rpm for 50 minutes. Wet particles tended to take up and rest on the sidewall of the drum coater, requiring constant beating of the drum coater to energize or loosen the caked bed. Now referring to FIG. 17A, a SEM of a coated particle prepared according to the foregoing experiment, very few or no unbound small dechlorane particles were observed. The small dechlorane particles were bound to big KCl particles forming clusters. Deagglomeration was required for a smooth operation according to this experiment. Now referring to FIG. 17B, the mean particle size of the uncoated KCl increased from 284μ to 380μ as a result of this experiment. The foregoing experiments show clustering is possible via coating small particles together with large particles, eliminating difficulties encountered in coating small particles alone. In addition, the large particles act as a flow and fluidization enhancer for the small particles. Employing the SPA technique, clusters of large host particles and small guest particles are formed with particles in both size ranges coated, depending on the binder levels. In a preferred embodiment, the process includes steps to loosen the particle bed in a drum coater to make the particles flowable when wetted with liquid binder. Such methods, include, but are not limited to, large amplitude, low frequency vibrations and the use of deagglomeration media such as but not limited to glass or metal spheres in the coating apparatus. Experiment 4 - Drum Coating With Mechanical Deagglomeration Using Glass Spheres 300 g of approximately 200 μm KCl was preblended with 3 ml of well-mixed Smooth Cast 327™ (equal volume of components A and B) in a Ziploc™ bag. The binder coated particles together with 1 Ib of 3 mm glass spheres were charged into the drum coater. The coater was rotated at 40 rpm for 50 minutes. The coated products were separated from the glass beads by passing through a 1 mm opening sieve. The addition of 3 mm glass spheres improved fluidity of the 1% binder coated KCl particles. No beating of the drum coater was required. Now referring to FIGs. 18A and 18B, SEMs show no agglomeration of the coated particles. Experiment 5 300 g of about μm KCl was preblended with 6 ml of well-mixed Smooth Cast 327™ (equal volume of components A and B) in a Ziploc™ bag. The binder-coated particles together with 1 Ib of 3 mm glass spheres were charged into the drum coater. The drum coater was rotated at 40 rpm for 1 hour. The coated products were separated from the glass beads by passing the mixture through a 1 mm opening sieve. The addition of 3 mm glass spheres improved fluidity of the 2% binder coated/wetted KCl particles. No beating of the drum coater was required to reduce caking. Now referring to FIGS. 19A and 19B, SEMs show a free-flowing product was achieved. This experiment was repeated to determine the effect of the process on mean particle size. Now referring to FIG. 19C, the mean particle size of the KCl increased from 280 μm for the uncoated KCl to 323 μm, a 14% increase.
Experiment 6 24O g of KCl with 6 ml of equal volume of A and B of Smooth Cast 327™ were preblended in a Ziploc™ bag for a few minutes. After a uniform binder coat was formed on the KCl particle surface, 60 g of Dechlorane Plus was added and tumbling was continued in the bag for another few minutes. The preblended particle mixture with the binder was charged into the drum coater with 1 Ib of 3 mm glass beads. The drum coater was rotated at 40 rpm for 50 minutes. The coated products were then separated from the glass beads by passing the mixture through a 1 mm opening sieve. Free-flowing particle mixture was obtained even after incorporation of 2% (6 ml) of liquid binder. Now referring to FIGs. 2OA and 2OB, SEMs of the product resulting from the foregoing experiment show that small particles were coated simultaneously with big particles. These FIGs. show small particles bound on individual KCl particles forming clusters with stoichiometric balance down to the individual particle/cluster level. Now referring to FIGS. 2OC and 2OD, SEMs of the big host particles obtained according to this experiment show that clusters of individual KCl host particles and guest Dechlorane Plus particles were formed. No obvious agglomeration between the host KCl particles or clusters was observed and very few unbound small particles were observed. Now referring to FIG. 2OE, the mean particle size of pure KCl before mixing was recorded as 284 μm. Now referring to FIG. 2OF, the mean particle size of the clusters of KCl and Dechlorane Plus after mixing was shown to be 296 μm. Experiment 7 240 g of KCl was preblended with 12 ml of equal volume of A and B of Smooth Cast 327™ in a Ziploc™ bag for a few minutes. After a uniform binder coat was formed on a KCl particle surface, 60 g of Dechlorane Plus was added and tumbling was continued in the bag for another few minutes. The preblended particle mixture with the binder was charged into the drum coater with 1 Ib of 3 mm glass beads. The drum coater was rotated at 40 ipm for 50 minutes. The coated products were separated from the glass beads using a sieve with diameter openings of 1 mm. The particle mixture was caked upon the drum sidewall. However the weak cake crumbled manually. Mechanical deagglomeration using 3 mm glass beads improved the fluidity of binder/wetted particles greatly, but excessive binder concentrations caused the formation of a weak cake of the particles. Now referring to FIG. 2 IA, a SEM shows the bound small particles achieved according to this experiment. Now referring to FIGs. 2 IB and 21C, SEMs of the big host particles show clusters formed by the individual KCl host particles and the guest Dechlorane Plus particles. No obvious agglomeration was observed between the host KCl particles or clusters and very few unbound small particles were found. FIG. 2 ID is a SEM of a cluster of KCl and bound dechlorane showing good coverage of the dechlorane on the host KCl and very few if any unbound small dechlorane particles. In addition to a drum coater, TMA-FB was utilized in Experiments 8 and 9 for making clustered particles. The TMA-FB employed an external magnetic field to excite the magnetic particles that act as self-energized media, mixed in with the other powders, and a variable speed drive for the drum or a cylindrical vessel. The basic steps in the experiments comprised adding larger host particles, magnetic particles and reactive binder having a pot life of about 20 minutes; into the drum (the binder could also be sprayed into the drum for systems having binder injection capability); coating and homogenizing the binder by the action of tumbling as well as agitation due to the magnetic particles that are spinning and translating; and then adding the smaller guest particles that subsequently disperse onto the surface of large particles by tumbling and agitation by magnets, eventually forming clusters that become tack-free via cross-linking of the reactive binder coat.
Experiment 8 This experiment was carried out using a simplified embodiment for TMA-FB. 24 g of KCl and 30 g of barium ferrite magnets (size 1.4-1.7 mm) were premixed with 0.75 ml of equal volume of A and B of Smooth Cast 327™ in a cylindrical vessel of TMA-FB for two minutes, so that a uniform binder layer was formed on KCl particles surface. After that, 6 g of Dechlorane Plus was added and the TMA-FB process was continued. The vessel was rotated at about 30 rpm for 10 minutes. The coated products were separated from the magnets using a sieve with diameter opening of 850 microns. There was no observed sticking or caking of powders on the sidewall of the cylindrical vessel. The final coated material was found to be free flowing. The tapped density of the formed clusters was 1.21 g/cc. Now referring to FIG. 22A, a SEM image shows the cluster of an individual KCl and a number of small Dechlorane Plus particles formed as a result of this experiment. Now referring to FIG. 22B and FIG. 22C, the lower magnification SEMs show there are no observed agglomerates between the host KCl particles or clusters, while a few unattached small particles are found. FIG. 22D is a higher magnification SEM showing a small, partial area of a cluster of KCl and attached Dechlorane Plus particles showing good coating and bonding of Dechlorane Plus particles onto the host KCl particle.
Experiment 9 16 g of KCl and 20 g of barium ferrite magnets (size 1.4-1.7 mm), were premixed with 0.5 ml of equal volume of A and B of Smooth Cast 327™ in a cylindrical vessel of TMA-FB for two minutes, so that a uniform binder layer was formed on KCl particles surface. After that, 4 g of Dechlorane Plus was added and the TMA-FB process was continued. The vessel was rotated at about 30 rpm for 20 minutes. The coated products were separated from the magnets using a sieve with diameter openings of 850 microns. There was no observed sticldng or caking of powders on the sidewall of the cylinder vessel. There was no observed sticking or caking of powders on the sidewall of the cylindrical vessel. The final coated material was found to be free flowing. The tapped density of the formed clusters was 1.28 g/cc, indicating that longer processing time improved packing density. Now referring to FIG. 23A, a SEM image shows the cluster of an individual KCl and a number of small Dechlorane Plus particles formed as a result of this experiment. Now referring to FIG. 23B and FIG. 23 C, the lower magnification SEMs show there are no observed agglomerates between the host KCl particles or clusters, while no unattached small particles are found. FIG. 23D is a higher magnification SEM showing a small, partial area of a cluster of KCl and attached Dechlorane Plus particles showing good coating and bonding of Dechlorane Plus particles onto the host KCl particle. Mechanical deagglomeration in the SPA technique, such as by using 3 mm glass spheres, improves the fluidity of binder wetted particles greatly within certain binder levels. The SPA technique of the present invention formed clusters with enhanced levels of control in terms of both composition and stoichiometry. The small guest particles were found to bind strongly to the individual host particles, enabling composition homogeneity down to the individual particle/cluster level, about 200 μm in the foregoing experiments. Similarly, the action of tumbling and the magnets in TMA-FB method of the present invention improves fluidity of binder wetted particles, and allows a very uniform dispersion of the small particles, resulting in enhanced levels of control both in terms of composition and stoichiometry. In addition, it improves- the packing density of the formed clusters. The small guest particles were found to bind very strongly to the individual host particles, enabling composition homogeneity down to the individual particle/cluster level, about 200 μm in the foregoing experiments, with a possibility of going down in size of the host particle. Other coating devices such as, but not limited to, the UV coating method described herein, can be employed in the techniques of cluster formation such as SPA and TMA-FB. While the preferred embodiments have been described and illustrated it will be understood that changes in details and obvious undisclosed variations might be made without departing from the spirit and principle of the invention and therefore the scope of the invention is not. to be construed as limited to the preferred embodiment.