Patent Application
20120180435
Not Applicable
Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to packaging of powdered materials and, more specifically, to a process and system for packaging and increasing the packaged density of micro-metric powders.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Paper bags are usually utilized for storage and transport of micrometric powders (e.g., graphite, silicon dioxide, titanium dioxide, calcium fluoride, powdered concrete or drywall joint compound mixes, or other suitably pulverized substances). For example, almost any home improvement retail outlet will have pallets of stacked bags of powdered concrete or mortar mix for commercial purchase. Such bags almost always utilize multiple independent layers of heavyweight paper material to minimize the chance for rupture and spillage, and sometimes utilize an inner polymeric liner, such as PE, to prevent moisture from entering. However, such bags are not hermetically sealed because trapped air within the bag would cause it to rupture from the weight of other bags (and/or pallets of bags) stacked on top. To prevent rupture, some means for allowing air to escape is always provided. One such means is to partially close and seal the PE liner opening. The remaining small opening then vents the trapped air into the subsequent layer of paper bag material where the air may pass through yet another small opening in the partially-closed paper bag. However, if any small opening happens to plug the bag may yet rupture and spill its contents. Moreover, the small opening will always leak some amount of the contained powder and cause area contamination as well as powder contamination. Entry of moisture into packaged concrete or mortar mix (hygroscopic materials) will ruin the contained powder and render the package worthless—resulting in increased waste and expense.
Another attempt at dealing with trapped air is through the use of microperforations. The inner layers of the bag are perforated using microperforations to allow air to escape. Nonetheless, the microperforations—even when purposely designed to be smaller than the average contained powder particle size—tend to leak a certain amount of powder and inevitably allow entry of moisture. Attempts have been made to stagger the perforations between layers such that the perforations of one layer fall somewhere between those of the next layer. This effectively creates a labyrinth through which air may pass while, in theory, retaining the powder within the bag. However, this inevitably results in powder becoming trapped between the layers and eventually leaking from the package. Also, if air can escape then moisture and other contaminants may enter.
Micrometric powders tend to be greatly influenced by air currents and static forces because of their extremely small particle size. The powders become airborne easily and are difficult to control in the presence of such forces, which can occur during filling and storage of product containers. For example, pouring measured quantities of these powders into flexible bags made of polymeric materials creates significant air currents and static energy due to friction of the particles against the bag wall. The air currents tend to force more of the powder into the air and onto all exposed surfaces. Also, depending on processing conditions, the static electricity that is generated can cause the deposited powder to cling to the interior surfaces of the bag—including the opening area of the bag that is used to form the bag closure. The presence of powder contamination on this closure area prevents the formation of a sufficient seal, resulting in continued leakage of powder and further contamination of the powder with moisture and other atmospheric contaminants. Although the area may be wiped clean before forming the closure, such a cleaning process is impractical for use with automated packaging given the added time and expense.
Storage and transport of large quantities of such powders—as is often necessary in industry—highlights the aforementioned problems. For example, it is common to see pallets of stacked bags of concrete, mortar, and/or drywall joint compound at typical home improvement centers. To keep these powders dry, the bags often contain polymeric linings. With the contamination that occurs during the sealing process, these bags often leak and pollute the entire storage area with airborne powder, reducing the healthfulness, attractiveness and overall consumer appeal of such displays. Further, as the bags leak significant amounts of air enter the container and allow the bulk powders to shift in form. Such movement makes it difficult to maintain an organized stack of bags, limiting the height of such displays and, consequently, the amount of product available for sale. Moreover, the entry of significant amounts of air into a container can cause pressure spikes to occur within the bag when the bag is manipulated or compressed during stacking, which, as mentioned previously, tends to rupture the bag and cause leakage of the contents.
Graphite in micrometric powder form (typically fine to ultrafine grade) is utilized in the formation of lithium oxide battery electrodes using powder metallurgy techniques. Impurities are present even in relatively “pure” graphite because of the aforementioned powder storage problems and also because of material processing and cost limitations. Consequently, the graphite powder must be sintered to remove these impurities and to form a solid mass of graphite for subsequent use. However, sintering takes place at temperatures of approximately 2,500 C and higher. Pores and voids within the graphite powder microstructure act as insulators and prevent the efficient transfer of heat through the graphite powder mass, which increases the energy required to achieve the desired sintering temperature and increases the resultant costs of the sintering process.
Both natural and synthetic graphite powders (as with other micrometric powders) have a relatively high porosity at room temperature and standard atmospheric pressure. The density of the powder can be improved somewhat through use of vibration and traditional compaction methods, but any such gains in density and reduction in porosity are relatively minimal, reducing the overall effectiveness. Vibration of such powders tends to force more of the product airborne, which increases waste and pollution of the atmosphere and surrounding surfaces. In addition, friction of the particles within the vibrating graphite powder prevents significant compaction and densification. The remaining porosity serves as a thermal insulating barrier between graphite particles, which increases the amount of energy required to achieve the sintering temperatures. Moreover, depending on the thickness of the graphite being sintered, surface temperatures of the graphite might readily reach the desired temperatures while the core graphite material fails to reach the same temperature, resulting in uneven temperature distribution and the addition of internal mechanical stresses on the end product. High porosity also increases the space between graphite particles effectively limiting the current handling capabilities of the graphite because of the relatively large distance that electrons must cover when flowing through the graphite microstructure.
Accordingly, what is needed is a micrometric powder storage bag and method for densitization of contained micrometric powders that allows for hermetic sealing even in the presence of contamination, and high-densitization of the contained powder without rupturing the bag under the strains of the densitization process. Further, it is necessary that this bag and method be affordable and capable of producing quantities of packaged and densitized powders on a commercial or industrial production rate scale.
The present invention provides a method for packaging micrometric powders, the method steps comprise: filling a flexible container with a predetermined quantity of a micrometric powder, the flexible container wall comprised of a polymeric material, the flexible container further comprising a first opening through which the powder enters, wherein the first opening is capable of mechanical closure to form a substantially airtight seal even in the presence of a detectable amount of the micrometric powder contamination; deaerating the flexible container and contained micrometric powder to remove substantially all air from within the powder and the container; sealing the deaerated flexible container to create a hermetic seal; and densitizing the micrometric powder by compressing the flexible container and contained micrometric powder within a mold with at least one force-concentrating device to achieve a desired micrometric powder density.
In a second method, the method steps comprise: filling a flexible container with a predetermined quantity of a micrometric powder, the flexible container having a wall comprised of a single layer of co-extruded polymeric material; deaerating the flexible container and contained micrometric powder to achieve a desired level of vacuum within the powder; densitizing the micrometric powder utilizing at least one force concentrating device; and sintering the resulting densitized micrometric powder to remove substantially all impurities.
The present invention will be more fully understood by reference to the following detailed description of the preferred embodiments of the present invention when read in conjunction with the accompanying drawings, wherein:
The above figures are provided for the purpose of illustration and description only, and are not intended to define the limits of the disclosed invention. Use of the same reference number in multiple figures is intended to designate the same or similar parts. Furthermore, when the terms “top,” “bottom,” “first,” “second,” “upper,” “lower,” “height,” “width,” “length,” “end,” “side,” “horizontal,” “vertical,” and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawing and are utilized only to facilitate describing the particular embodiment. The extension of the figures with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the following teachings of the present invention have been read and understood.
In the present embodiment, the single-walled flexible container incorporates one or more co-extruded layers of polymeric material as the container walls. As depicted in
Although multiple layers are generally recommended to provide additional barriers of protection from abrasion and exposure to elements, one of ordinary skill will appreciate that it is possible to utilize a monolayer film. Use of a monolayer film (single layer of polymeric material) of approximately 5.0 mil may be sufficient for commodity or industrial applications wherein the elongation properties are not as critical. Still other embodiments may utilize containers created from the same or similar polymeric materials applied in a different order than the preferred embodiment discussed above, and may even include multiple layers of the same polymeric material.
In yet another embodiment the flexible container utilizes a layer of aluminum as the base material layer (204) with a LDPE outer layer (202) and metallocene inner layer (206) superimposed thereon. The aluminum core layer provides additional protection for the contained hygroscopic micrometric powder to prevent the introduction of moisture, air and light. Such a bag acts like a metal container, but is more economical and provides an equivalent shelf life for the stored product. To further increase the shelf of a micrometric powder, the container may be gas-flushed with dry nitrogen to displace any moisture bearing air that might be present, and to prevent oxidation of the contents of the bag.
Referring once again to
Once the appropriate quantity of powder (by weight) is dosed, it is then dispensed into a container (112). A flexible container (112) is positioned beneath a filling spout (108) through which the weighed powder is poured. Because micrometric powders have a tendency to go airborne when pouring, the present embodiment utilizes an arrangement wherein a bag hanger suspends the flexible container (112), completely enclosing the filling spout so as to capture any airborne product. In this embodiment gravity moves the product into the container (112). However, another embodiment may use a mechanical or pressure differential means to achieve the same ends. To aid in subsequent closure of the first opening, a void space is retained above the powder and below the sealing surface (108).
As the measured powder is pouring into the flexible container (112), the container is simultaneously deaerated to remove air being displaced by the entering powder. By removing the displaced air as the powder enters, the air currents within the flexible container are minimized and less powder will become airborne. Also, the simultaneous performance of filling the container as it is deaerated saves on overall processing cycle time. The vacuum probe continues even after the bag is fined in order to remove as much trapped air from the powder as desired. However, in another embodiment the pre-deaeration step is performed independently of the dosing step.
In the pre-deaeration stage the present embodiment utilizes one or more porous metal probes (110) attached to a controllable vacuum pump (128). An intermediate vacuum probe chamber (122) is utilized to minimize fouling of the vacuum pump filter (130) due to powder that passes through the vacuum probe (110). The intermediate chamber (122) utilizes additional porous metal probes (124) to further limit or prevent passage of micrometric powders. Powders that make it past the first probe (110) tend to settle out in the intermediate chamber (124), accumulating in the chamber bottom (126). The bottom (126) may be periodically removed to empty the settled powder.
The metal probes in this embodiment (110 and/or 124) are covered with an additional micro-porous material sufficient to minimize passage of quantities of the micrometric powder. The micro-porous material includes, for example, material sold under the trademark GORETEX or the like. Such micro-porous material is helpful because it is readily replaceable when it becomes clogged. Further, the metal probes in this embodiment are cylindrical. In other embodiments the probe cross section differs depending, inter alia, on the material being deaerated. For example, a probe having a sword shape allows the probe to penetrate the powder material relatively easily and quickly, which helps to speed up the processing cycle time. Also, a sword shape with an incremental width provides the ability to maintain a differential pressure when used within a highly-aerated product that is prone to quickly clog the probe pores.
In yet another embodiment the probes (110 and/or 124) are made of ceramic or plastic and feature micro-porous openings such that no additional micro-porous covering material is necessary. Such material is capable of being micro-perforated to achieve sufficiently small pore size to minimize passage of quantities of the micrometric powder being deaerated. One skilled in the art will appreciate that the type of probe material and shape may be chosen based on the density of powder through which it is intended to penetrate, the speed of the penetration operation, the particle size of the powder, the pore forming ability of the material, cost, etc.
In operation, the probes (110) are enclosed by the first container opening (108) and located within the micrometric powder. A vacuum (128) is applied to the probes (110), drawing trapped air from the powder. Air is also drawn from the void space above the powder but within the bag (112), causing the flexible container (112) to compress around the contents. In yet another embodiment, the porous metal probes (110) are utilized without an additional layer of micro-porous material.
During pre-deaeration, a substantial amount of the air is removed from the powder and from within the container (112). In the present embodiment this step can take approximately 8 seconds to complete. However, more or less time may be taken depending on factors including desired production rate, amount of powder, amount of aeration of the powder, size of the flexible container, etc. Removal of air from the powder results in a first level of densitization of the micrometric powder.
Following pre-deaeration, the filled flexible container is further deaerated within a post-deaeration vacuum chamber (114). In the chamber (114), the air external to the flexible container (120) is removed to draw any of the remaining air from the container and to further compress the powder. With approximately 1% of air remaining in the bag, the bag is essentially airless and the maximum amount of air has been removed from the powder. The combination of the two deaeration stages eliminates essentially all of the air from within the microstructure of the powder, achieving the highest density of the powder without mechanical means. However, pores (i.e., space between particles) still exist within the microstructure, allowing the density to be further increased with subsequent mechanical compression stages.
With the container still in the vacuum chamber and the air removed, a clamp (134) is placed on the top of the bag but below the first opening in order to seal the vacuum within the bag. The vacuum chamber is opened (118) and the bag, which is now essentially devoid of air, (132) is removed. The filled flexible container (132) is sealed by forming a seam or joint at the first opening area above the top surface of the powder and by welding the seam. Powder contamination present at the seam is initially blown clear with compressed gas (136) (such as but not limited to air, nitrogen, etc.) to substantially clear the seam for subsequent mechanical closure by welding. Use of metallocene is beneficial in this regard because of its ability to accept a suitable weld even in the presence of a minor amount of contamination. One of ordinary skill will appreciate that the type of welding technology utilized is dependent upon the polymeric materials used in container construction. In the present embodiment an impulse sealing unit is employed. Once welded, the vacuum is retained in the substantially airtight hermetically sealed container and the contained powder (132) may be further shaped.
As an alternative to merely welding the seam and leaving an extended flap of material, the embodiment may also utilize a gluing device to retain the loose flap. The top portion of the bag (dead space or top flap) and roll it over in a winding motion to compress the flap against the portion of the bag containing the compressed micrometric powder. Hot glue melt is applied beneath the edge of the rolled top portion and the bag wall. The rolled top portion is then held on the hot glue as the glue solidifies.
If shaping of the bag is necessary, the bag may be then be processed by a “bag flattener.” The bag flattener is a bottom belt conveyor and a top metal roller which squeezes the malleable bag into a perfect rectangle. When the bag's top flap is first rolled over and glued before being flattening, the product inside the bag has little room to travel. The bag flattener “forms” the bag or shapes it into a very small and compact rectangle which is much smaller than its former bag size. Finally an adhesive tape is applied to assist in holding the top flap in place. Over time the glue may stretch, but the addition of a small amount of adhesive tape helps to maintain the integrity of the package.
In certain circumstances, such as with powders that are highly reactive to air, it is desirable to perform a gas-flush of the container and micrometric powder using an inert gas such as nitrogen. This may be performed by placing the filled container in the vacuum chamber, removing the air from the vacuum chamber, filling the chamber with nitrogen, removing the nitrogen with the vacuum pump, filling the chamber again with nitrogen, and repeating the process until all possible oxygen is eliminated from the container and contained powder.
In yet another embodiment, the pre-deaeration and post-deaeration (114) steps are combined and occur simultaneously. The filled flexible container is placed within the vacuum chamber and the porous probes are inserted within the powder. The air is then removed from the chamber and from the powder, simultaneously. Other embodiments use only a single deaeration means, as described above, for removing air from the bag (112/120). If the single means is a vacuum chamber, the processing cycle time is rather slow since a longer amount of time is required to draw entrapped air from the powder. If the single means is a vacuum probe, then processing cycle times are faster but a hermetically seated bag is not possible because air will quickly reenter the contained powder since it is an open system. However, by using the combination of vacuum probe and vacuum chamber the ultimate benefits of fast cycle time and hermetic sealing of a single-walled flexible container as described above may be realized.
The next stage of processing in the present embodiment is the molding stage (138). In this stage, the filled flexible container (140) is placed within a metal mold (142) of the desired shape. For example, a cylindrical mold is provided to force the contained micrometric powder to assume a cylindrical shape. One of ordinary skill in the art will appreciate that other container shapes may be obtained through use of the proper shaped mold, and such other container shapes are within the scope of the present invention.
The filled flexible container (146) within the cylindrical mold may then be densitized (148). During densitization (148), dynamic hydraulic piston compression means (148) are utilized to place compressive forces on the top and bottom surfaces of the container within the mold. As the top (148) and bottom (150) surfaces of the powder are compressed by this force concentration device, radial expansion of the powder is statically resisted by the strength of the walls of the mold (142). In another embodiment, a single dynamic hydraulic piston means (148) is utilized to provide dynamic compressive forces on the top surface of the cylindrical powder form, and static resistance to expansion is also generated by the strength of the bottom surface of the mold. Once the powder is adequately compressed, the cylindrical form is removed and the molded container—resembling a “hockey puck” or a cylindrical disc—remains.
The amount of air removed from the flexible container influences the hardness and density of the deaerated micrometric powder. For example, the present embodiment can create a “soft brick” of micrometric powder by leaving a small amount of air inside the filled flexible container. This air allows the powder particles to move relative to one another, making the bag malleable, which allows the container to be shaped accordingly for transport or storage. For example, the bags can be formed into brick-like rectangular shapes for stacking on pallets. The heavy weight to which the bottom layer of palletized bags is subjected due to the top layer bags will not cause the bags to rupture because the remaining amount of air is insufficient to cause pressure spikes on the bag seals.
If substantially all of the air is removed from the flexible container during the deaeration stage, then the micrometric powder forms into a “hard brick” that is extremely rigid and resistant to deformation. This rigidity is caused by the friction that occurs between particles of the micrometric powder in the absence of air trapped within the void spaces within the powder microstructure. Because of the resistance to deformation of the resulting “hard brick,” the filled flexible container is initially placed within a form so that it assumes its initial shape. For example, if a rectangular brick shape is desired, the filled flexible container is first placed within a rectangular form prior to deaeration.
When compressing the flexible container within a mold, outward pressures caused by the densitized powder may be felt by the inside walls of the mold (142). This outward pressure can cause substantial friction between the molded container and the mold walls, hampering removal of the molded container. In one embodiment depicted in
When graphite powder is densitized using the present embodiment, the resulting powder density can measure 55 lbs/ft3 or more. This density is ideal for creating pure graphite for use in anodes for Li-ion batteries, primarily because of the energy savings during the sintering process. For example, a certain manufacturing process for creating pure graphite requires removal of all impurities from packaged graphite powder. The present embodiment may be employed to create 25 lb puck-shaped containers of graphite powder having a material density of 55 lbs/ft3. Four of the 25 lb puck-shaped containers are inserted into a graphite form which is then heated to approximately 2,000 to 2,500 C or higher (but less than the melting point) to sinter the graphite powder. During this sintering process, the flexible container and any impurities within the graphite are completely vaporized leaving behind a single 100 lb cylinder of pure graphite for subsequent processing into battery electrode materials. Because the air was removed from the densitized graphite powder and the powder density was increased substantially, less energy is required for the heat flux to penetrate to the center of the powder material, resulting in a beneficial cost savings. In yet another embodiment a 100 lb quantity of micrometric powder is packaged in a single bag. One of ordinary skill will appreciate that the desired quantity of powder may be selected based upon the needs of the end consumer.
In another embodiment, such as that depicted in
The compression means (144) in this embodiment is a hydraulic piston arrangement having a top piston (148) and a bottom piston (150). The top piston (148) enters the top opening of the mold (802) while the bottom piston (150) enters the lower opening. Hydraulic forces applied to the top and bottom pistons compress the powder (132) to achieve maximum desired densitization. In yet another embodiment a bottom piston (150) is provided merely to support the mold solid bottom such that the pressures applied to the powder by the top piston (148) are countered.
Once the desired densitization is achieved, the densitized powder is removed from the mold (802). If the mold is solid, friction between the bag material and the mold inner walls necessitates use of a force means (146 or 148) for removal of the densitized powder. In another embodiment, the hydraulic pistons (146 or 148) remain steady and the mold walls are moved to remove the densitized powder container from the mold (802). If a hinged or multi-pieced mold is utilized, the mold is opened or disassembled and the densitized powder and bag are removed and conveyed for further processing.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive. Accordingly, the scope of the invention is established by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Further, the recitation of method steps does not denote a particular sequence for execution of the steps. Such method steps may therefore be performed in a sequence other than that recited unless the particular claim expressly states otherwise.
