Patent Publication Number: US-9902123-B1

Title: Method and apparatus for producing large uniform thickness nanomaterial sheets

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the fabrication of large uniform thickness sheets of nanomaterials, including micro-fibrillated cellulose, nano-crystalline cellulose, carbon fibers, nanotubes, nanofibers, and nanoparticles of other sources including but not limited to graphene, boron nitride nanotubes, quantum dots, fullerenes, and the like. 
     2. Description of the Prior Art 
     Nanomaterials can possess much greater strength, conductivity, surface area, and other attractive properties at a much lower weight than standard engineering materials such as wood, metals, plastics, and the like. 
     It is difficult to produce large, freestanding sheets of such materials with high levels of purity and nanomaterial content. Conventional manufacturing processes such as solvent casting, vapor deposition and the like require the use of additives, binders, surfactants and adhesives which reduce the purity and nanomaterial content, and thereby reduce the strength or other desirable properties of the resulting sheet. Vapor deposition is limited in scale and requires prohibitively expensive substrate preparations. 
     Alternative methods such as micro-filtration produce small sheets of high nanomaterial content. Sheet uniformity is sacrificed, however, if the micro-filtration process is scaled upwardly to produce larger sheets. 
     Thus there is a need for an apparatus and method for producing strong, uniform large sheets of high purity and high nanomaterial content. 
     Conventional microfiltration devices make sheets of nanomaterials by forcing an aqueous solution of nanomaterial particles through a filter at high pressures. 
     An alternative conventional method involves solvent casting, where the nanomaterials are mixed with solvents, additives, binders, adhesives, surfactants or combinations thereof and placed into sheet form. The solvent is dried off or evaporated, leaving a sheet of nanomaterial particles. It is not always possible to remove all of the solvents or other additives in sheets produced by solvent casting, thereby often reducing the mass or volume content of nanomaterials in the sheet. This process often does not produce sheets that retain their permeability. 
     Thus there is a need for an improved process for producing nanomaterial sheet materials that does not require the use of solvents, additives, binders, adhesives or combinations thereof. 
     Conventional microfiltration presses supply a constant pressure to the aqueous suspension of nanomaterial particles throughout the process. The deposition rate therefore decreases since the flow rate of the aqueous suspension decreases as the thickness of the nanomaterial sheet increases. 
     Thus there is a need for an improved deposition method so that the deposition rate can be controlled as the process continues. 
     Conventional microfiltration presses used for filter cake formation include a single inlet and nozzle in the feed platen which deposits the nanomaterial suspension onto the filter membrane resting on the drain platen. This commonly produces a dispersion of particles in the filter cake that is not uniform or homogeneous across the filter cake. 
     Thus there is a need for an improved apparatus that provides a more uniform or homogeneous dispersion of nanoparticles in the filter cake. 
     Conventional microfiltration presses include filter media supported by a stack of cloth that acts like a screen, which is then placed onto a support structure with holes formed therein through which the filtered effluent flows to a drain. This commonly produces sheets with a rough or uneven surface finish. The cloth is also prone to adhering to the thin sheets making them non-ideal for membrane formation applications, and the filter cake is often disrupted upon discharge. 
     There is a need, therefore, for an improved structure for supporting the filter media that produces a satisfactory surface finish on the filter cake and preserves the integrity of the filter cake upon discharge. 
     Conventional microfiltration presses have inefficient flow patterns that introduce non-homogeneous flow and non-homogeneous filter cake formation which results in papers of un-even or non-uniform thickness. Inefficient flow patterns underneath the filter stack which result from vortex formation/flow anisotropy cause uneven pressure underneath the membrane resulting in uneven membrane formation and reflux of the filtrate. 
     Thus there is a need for an improved press that includes efficient flow patterns and dispersers to reduce non-homogeneous flow and non-homogeneous filter cake formation. 
     Conventional microfiltration presses include an elastomeric O-ring gasket that is compressed between the platens to form the filter envelope. The O-ring is typically held in place by a groove or channel in one or both platens, but such O-rings have limited capabilities to withstand high pressures and the filter membrane is crushed or damaged when such high pressures are created and the filter membrane is forced into the O-ring groove or channel. 
     Thus there is a need for an improved gasket capable of withstanding the high pressures needed to obtain a uniform flow rate for the aqueous nanomaterial suspension while maintaining the integrity of the filter membrane. 
     Conventional microfiltration presses employ hydraulic cylinders which provide a constant clamping force during filtration process to hold the upper and lower platens together. At the end of the filtration process, the aqueous suspension of nanoparticles is expended and air enters into the filtration envelope. That air easily flows through the filter, causing the pressure within the filtration envelope to be reduced sharply. Since the clamping force must be supported only by the gasket, the gasket compresses, causing the upper and lower platens to crush the nanomaterial sheet. 
     Thus there is a need for an improved apparatus that does not rely upon hydraulic cylinders and which controls the offset or relative position between the upper and lower platens under various or modulating pressure so that the nanomaterial sheet is not crushed when the nanomaterial suspension is expended. 
     In view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the needed improvements could be provided. 
     SUMMARY OF THE INVENTION 
     The long-standing but heretofore unfulfilled need for a device that can produce large uniform thickness sheets of nanomaterials is now met by a new, useful, and non-obvious invention. 
     The inventive structure includes an apparatus and method for producing large uniform thickness sheets of nanomaterials of variable size, shape and thickness. 
     More particularly, the novel apparatus includes an upper platen having a fixed position and a lower platen disposed in spaced apart, parallel relation to the upper platen. The lower platen is movably mounted so that a distance between the lower platen and the upper platen is controllable. 
     The upper platen has a plurality of input nozzles mounted therein and a plurality of flow dispersers with asymmetric fluid pathways associated with each of the input nozzles. 
     A gasket is disposed in underlying relation to the upper platen and a fine filter membrane is disposed in underlying relation to the gasket. Nanoparticles are deposited on the fine filter membrane when the press is operating. 
     A membrane support is disposed in underlying relation to the fine filter membrane, a drain substrate is disposed in underlying relation to the membrane support, a substrate sealpack is disposed around the edges of the drain substrate, and the lower platen is disposed in underlying relation to the drain substrate. 
     A plurality of flow channels and a plurality of drain holes are formed in the lower platen. Each of the flow channels follows a path of travel that interconnects two of the drain holes and each path of travel is non-linear. 
     A closed-loop fluid control system maintains a predetermined rate of nanoparticle deposition onto the fine filter membrane. The system includes a fluid controller, a source of compressed air, a motorized regulator under the control of the fluid controller, an input pressure gage that sends data to the fluid controller, a flow sensor that sends data to the fluid controller, a proportional valve under the control of the fluid controller, and an output pressure gage that sends data to the fluid controller. 
     Compressed air flows from the compressed air source, through a nanomaterial suspension, and to the lower platen. The nanoparticle deposition rate is thereby maintained at controlled levels while modulating both the pressure of the fluid and the volume of aqueous suspension that is allowed to flow through said upper and lower platens. In the current embodiment, the filtered effluent is removed from the lower platen by use of gravity flow. The removal of the filtered effluent can be enhanced by use of a partial or full vacuum to the drain system on the lower platen underneath the filter media. 
     A plurality of jack screws support the lower platen and control the distance between the lower platen and the upper platen. 
     A motion control system controls the operation of the motor that controls the raising and the lowering of the jack screws. The motor has an output shaft that raises the jack screws when rotating in a first direction and which lowers the jack screws when operating in a second direction opposite to said first direction. 
     A rotary encoder produces digital data representing the rotational position of the output shaft, hence the amount of extension or retraction of the jack screws relative to a predetermined starting point, and therefore the distance between the upper and lower platens; 
     A motion controller controls the motor and receives signals from the rotary encoder. An upper limit switch prevents raising of the lower platen beyond its predetermined maximum height and a lower limit switch prevents lowering of the lower platen below its predetermined minimum height, and allows the rotary encoder to be set to its starting point. 
     The motion control system maintains a constant displacement instead of constant pressure, enabling the production of clean, undamaged sheets of nanomaterial papers. 
     An aqueous suspension of nanomaterial particles flows between the upper and lower platens through the filter membrane under high pressure. The pressure can range from 5 to 200 psi, depending on the types of nanomaterials used, the concentration of the nanomaterial suspension, the type of filter membrane used, and the desired thickness and density of the nanomaterial sheet. 
     The novel fluid and motion control means ensure a high pressure capability, uniform flow, even dispersion, and stable deposition rate of the nanomaterial particle suspension onto the filter membrane. 
     The fine filter membrane collects the nanomaterial particles, and the high pressure causes controlled de-wetting, molecular bonding and entanglement among the particles, resulting in a large sheet of uniform thickness with an extremely high content of desired nanomaterials. 
     The primary object of this invention is to create large, uniform thickness sheets with an extremely high content of nanomaterials without the use of undesirable binders, fillers or adhesives. 
     These and other important objects, advantages, and features of the invention will become clear as this disclosure proceeds. 
     The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the disclosure set forth hereinafter and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed disclosure, taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a rear perspective view of the novel structure; 
         FIG. 2  is a front perspective view thereof; 
         FIG. 3  is a front elevation view thereof; 
         FIG. 4  is an end view thereof: 
         FIG. 5  is a bottom plan view thereof; 
         FIG. 6  is a top plan view thereof; 
         FIG. 7  is an exploded front perspective view thereof; 
         FIG. 8A  is an exploded perspective view of the lower platen assembly: 
         FIG. 8B  is a top plan view of the lower platen; 
         FIG. 9A  is an exploded perspective view of the upper platen assembly; 
         FIG. 9B  is a plan view of a novel flow disperser; 
         FIG. 9C  is a perspective view of the novel flow disperser; 
         FIG. 9D  is a side elevation view of the novel flow disperser; 
         FIG. 10  is a diagram of the novel fluid control system; and 
         FIG. 11  is a diagram of the novel motion control system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Structure  10  depicted in  FIGS. 1-7  is a preferred structure. The front and rear perspective views of  FIGS. 1 and 2  disclose frame  12  to which the various parts are mounted but those parts are best seen in the exploded view of  FIG. 7 . Upper platen  14 , lower platen  16 , fine filter media  18 , nanoparticles  20 , jack screws  22 , gasket  24  and the other main elements of the invention can be connected to one another in many different ways and on differing frames and not just in the specific ways on the particular frame depicted. 
     Referring therefore to  FIG. 7 , there it will be seen that structural side frames  26 ,  26  are rectangular in this preferred embodiment and are positioned parallel to one another in respective vertical planes. They are longitudinally disposed as drawn relative to transversely disposed, equidistantly spaced apart I-beams, collectively denoted  28 , that form the foundation of novel batch-automated microfiltration press  10  and which overlie a floor, a table top, or other support surface, not depicted. Said support beams  28  underlie side frames  26 ,  26  as best depicted in  FIGS. 1-4 . 
     Central load beam  30  is longitudinally disposed and overlies each support beam  28  at the center of each support beam. I-beam hardware, collectively denoted  32  throughout  FIG. 7 , provides the preferred interconnection means for all I-beam to I-beam connections throughout the novel structure. 
     A first pair of jack screw mounting I-beams, collectively denoted  34 , is transversely disposed atop a first end of central load beam  30  and a second pair of jack screw mounting I-beams, collectively denoted  36 , is transversely disposed atop a second end of central load beam  30 . A pair of box frame motor mounting beams, collectively denoted  38 , is transversely disposed atop said central mounting beam  30  mid-length thereof, in centered and equidistantly spaced relation to said pairs  34  and  36  of jack screw mounting beams. 
     A first pair of jack screws  22  is supported by jack screw supports  22   a ,  22   a  associated with the first pair of mounting beams  34  and a second pair of said jack screws is similarly supported by a second pair of jack screw supports  22   a ,  22   a  associated with mounting beams  36 . A small extent of said second pair of jack screw supports can be seen upon careful inspection of  FIG. 7  but said partially visible supports are un-numbered to avoid cluttering of the drawing. 
     A load plate  22   b  having platen connectors  22   c  surmounts each jack screw  22 . Items  22   d  are load pad connectors/fasteners, said fasteners attaching load plate  22   b  to jackscrew load pad  22   e.    
     Motor  40  is transversely disposed between the first and second pair of jack screws and is supported by said pair of box frame mounting beams  38 . Speed reducer  40   a  forms a part of motor  40 . Item  40   b  is a two (2)-way miter block, there being one (1) of said miter blocks on each side of speed reduced  40   a  because motor  40  is between said two sets of jack screws  22 , i.e., each miter block transmits the torque of the output shaft of motor  40  ninety degrees (90°) so that one (1) motor can drive four (4) jack screws. Items  40   c ,  40   c  are miter box mounting plates, and item  40   d  is a shim for gearbox  40   a . Washers or other suitable spacers, not depicted, raise miter blocks  40   b ,  40   b  up to the elevation of gear reducer  40   a  if needed. 
     Transversely disposed first jack screw beam  42   a  overlies and engages the platen connectors  22   c  associated with the first pair of jack screws  22  and transversely disposed second jack screw beam  42   b  overlies and engages the platen connectors  22   c  associated with the second pair of jack screws  22 . 
     Each bracer of a pair of longitudinally disposed lower platen bracers, collectively denoted  44 , has a first end that overlies jack screw beam  42   a  at opposite ends of said jack screw beam as perhaps best depicted in  FIG. 4  and each bracer of said pair has a second end that overlies jack screw beam  42   b  at opposite ends of said jack screw beam  42   b.    
     Lower platen bracers  44  thus are displaced upwardly and downwardly as jack screws  22  are displaced upwardly and downwardly. 
     Lower platen  16  overlies and is secured by I-Beam hardware  32  to each lower platen bracer  44 ,  44  and a plurality of NPT sanitary plumbing adaptors, collectively denoted  46   a  and  46   b , depend from opposite sides of said lower platen as perhaps best depicted in said  FIG. 4 . Items  44   a  are platen connectors. Adaptors  46   a ,  46   b  perform the function of draining the filtered effluent from the filtration envelope. 
     First bushing block  48   a  is secured to a first end of lower platen  16  and second bushing block  48   b  is secured to a second end of said lower platen  16 , said first and second bushing blocks being disposed along the longitudinal axis of symmetry of said lower platen. 
     Lower platen  16  is re-positioned from a lower “loading” position to an upper “operating” position using jack screws  22  or other similar position controlling devices. 
     Upper platen  14  is horizontally disposed in vertically spaced apart, parallel relation to lower platen  16  and first and second alignment shaft capture blocks  52   a ,  52   b  are secured to opposite ends of said upper platen at its longitudinal axis of symmetry. Items  14   a  are input nozzles and items  14   b  are dispersion inserts that perform the function of flow dispersers, i.e., they are influent flow disrupters. 
     First vertical alignment post  50   a  interconnects first bushing blocks  48   a ,  52   a  and second vertical alignment post  50   b  interconnects second bushing blocks  48   a ,  52   b . Bushing blocks  48   a  and  48   b  are apertured to slidingly receive vertical alignment posts  50   a  and  50   b  so that lower platen  16  may be moved toward and away from fixed position upper platen  14  by jack screws  22 . 
     Novel gasket  24  is sandwiched between said lower and upper platens as best depicted in the exploded view of  FIG. 7 . The above-mentioned channels that enhance the flow of the effluent or filtrate are formed in lower platen  16  and are denoted generally by the reference numeral  16   a . In this particular example, thirty two (32) arcuate flow channels  16   a  are formed in lower platen  16 , including eight (8) groupings of four (4) flow channels each. 
     Upper platen bracers, collectively denoted  56 , are longitudinally disposed and overlie said upper platen. Platen connectors, collectively denoted  56   a , interconnect platen braces  56  to upper platen  14 . Upper beams, collectively denoted  58 , are transversely disposed and overlie said upper platen bracers. The opposite ends of said upper beams  58  are secured to the underside of the top rail of each structural side frame  26 ,  26 . That arrangement of parts prevents movement of said upper beams  58 , upper platen bracers  56 , and upper platen  14 . 
       FIGS. 8A and 8B  disclose the parts associated with lower platen  16  in greater detail. As depicted in  FIG. 8A , gasket  24  has two windows  24   a ,  24   a  formed and a fine filter membrane  18  is in registration with each of said windows. Nanoparticles  20  are deposited on said filter media  18  but due to their small size are indicated with said reference numeral  20  but are not depicted. Membrane support  18   a  underlies filter media  18  and provides support therefor. 
     The novel structure employs a novel porous sintered metallic substrate to support filter media  18 , thereby eliminating the stack of cloth of the prior art. This substrate presents a smooth surface to the filter media, thereby improving the surface finish of the paper. The substrate also incorporates micron-sized holes (1-200 μm) which are capable of passing the filtered effluent, and which also promotes cross flow of the effluent, thereby improving the dispersion of the nanomaterial suspension and uniformity of deposition of the nanoparticles onto the filter. 
     Item  18   b  is a substrate sealpack that prevents or inhibits reflux and item  18   c  is a drain substrate. Membrane support  18   a  provides support and a smooth surface for the filter media. The membrane support can be a fibrous cloth, plastic mat, or metal sheet material. 
     The smooth micro-porous substrate on which filter media  18  is supported promotes unrestricted cross flow, enables improved dispersion, uniformity and surface finish of the nanoparticle sheet. 
     The filtration envelope is defined by the bottom surface of the top platen, the top surface of the filter media and the inside edges of the cut-out in the gasket. 
     A high pressure is created within the filtration envelope in order to densely pack the nanoparticles and ensure a constant deposition rate onto fine filter membrane  18 . 
     Flat elastomeric gasket  24  has considerable surface area that is clamped along flat surfaces of the upper and lower platens. The high clamping force between the upper and lower platens adequately constrains gasket  24  to enable higher pressures within the filtration envelope. Higher pressure flows are accommodated by increasing the width of the gasket, enabling greater surface area. 
     The higher pressures during sheet fabrication improves intermolecular bonding and tangling of the nanomaterial particles, resulting in a stronger sheet of paper. Gasket  24  is depicted in a rectangular shape but it can be provided in any practical predetermined configuration that can produce an operable filtration envelope, thereby enabling creation of arbitrarily shaped nanomaterial papers. 
     As best depicted in  FIG. 8B , all flow channels  16   a  are in fluid communication with associated drain holes  16   b . The flow channels avoid the central drain hole as depicted to prevent the formation of a large vortex and resulting flow anisotropy, which would cause an uneven sheet formation. The central drain hole is fed by cross-flow in the drain material, and has sloped sides that allow effluent passage if a sufficient flow rate is present in the flow channels. Grooves or flow channels  16   a  and said drain holes  16   b  efficiently drain the filtered effluent, reducing flow anisotropy and turbulence, improving dispersion and uniformity. Said grooves and drain holes also promote homogeneous dispersion and deposition of the nanomaterials onto filter media  18  and speed filter cake formation. 
     In the current embodiment, gravity is used to drain the filtered effluent from the lower platen. To further promote homogeneous dispersion of the nanomaterials on the filter media and to increase effluent flow rate, a vacuum can be applied at the drain holes to overcome higher effluent viscosities, developing flow anistropies or less than desired effluent flow rates. 
     The depicted novel pattern of grooves  16   a  and drain holes  16   b  minimizes vortex formation and flow anisotropy of the effluent. This enables faster, more efficient flow of the nanomaterial suspension through the filter, and results in the production of nanomaterial sheets having uniform thickness. 
     More specifically, when a fluid flows through a closed geometry in a turbulent fashion, intersecting fluid flow direction/force vectors cause anistropic pressure conditions in the dynamic flow geometry of the fluid system, resulting in eddies, waves and vortices. These anistropic pressure conditions below the filter material will cause irregular flow velocities through the filter membrane, and therefore uneven or non-uniform deposition rates, across the filter media. 
     The pattern of the grooves is determined by taking into consideration the geometry of the solid pocket that the drain material resides in, the viscosity of the effluent fluid, and the expected flow rate range to which the system will be exposed. The grooves are then placed along the lines of flow vector collision where anistropic pressure conditions will take place. In the current embodiment, consideration of flow anistropy is taken to the third (3 rd ) order of calculating these flow vector collisions. For a system which would have higher effluent flow velocities it would be advantageous to calculate groove positioning beyond the third (3 rd ) order, and for a system with lower effluent flow or viscosity it would be possible to reduce the number of grooves. 
     More particularly, grooves  16   a  which are used to channel away the filtered effluent are provided in a recess on the top of lower platen  14 . Drain substrate  18   c  sits within the recess. The depth of the recess is equal to the height of drain substrate  18   c , so the surface appears to be flat. Substrate sealpack  18   b  prevents effluent from flowing out of the recess in the lower platen that goes around the substrate. Membrane support  18   a  helps provide a smooth surface to the paper, as it does not allow the pattern of the substrate to show up on the paper. It also promotes cross-flow of the effluent, enabling a more uniform thickness paper. Filter media  18  is a hydrophilic or hydrophobic microporous or nanoporous flat polymer, metal or cellulose sheet membrane containing discrete holes, or it can be a mat-like material. 
       FIG. 9A  is an exploded view of upper platen  14 . In order to ensure a homogeneous dispersion of the nanomaterial suspension, upper platen  14  having a plurality of inlets, also known as input nozzles. As depicted in  FIG. 9A , the input nozzles are collectively denoted  14   a . At least one flow disperser, a plurality of which is collectively denoted  14   b  in  FIG. 9A , is used within each inlet to disperse the flow homogeneously. This design is inherently scalable to larger nanomaterial sheet sizes, as each input nozzle  14   a  is capable of supplying and dispersing the nanomaterial suspension according to a certain desired surface area. A larger number of nozzles can therefore be used to produce a larger sheet size. 
     Flow dispersers  14   b  are depicted with enhanced detail in  FIGS. 9B-D . Each flow disperser is a rigid, flat disc as depicted with a large number of through apertures formed therein. Flow dispersers  14   b  significantly improve the dispersion of the nanomaterials onto fine filter membrane  18 . As depicted, the center of each flow disperser  14   b  is imperforate and the preselected pattern of holes that is radially outward of that imperforate center does not follow a radial symmetric pattern. The pattern maximizes turbulent flow, and thereby improves dispersion of the nanomaterial suspension. 
     During normal operation, an aqueous suspension of nanomaterial particles flows between platens  14  and  16  through fine filter membrane  18  under high pressure. The two platens, together with gasket  24 , filter media, membrane support and drain substrate create a filtration envelope within which nanoparticles  20  are deposited onto fine filter membrane  18  and the paper is formed. 
     The aqueous solution of nanomaterial particles does not require use of binders, fillers or adhesives and enables a stronger sheet of nanomaterial paper. 
     The pressure and flow characteristics of the nanoparticle suspension must be controlled with precision in order to produce high strength, large and uniform thickness papers with intentional through-thickness nanostructures. The novel structure advances the art by incorporating various novel means to provide the nanomaterial particle suspension under high pressure, constant flow and uniform deposition rate onto fine filter membrane  18 . 
     More particularly, during the filtration process, the filter media is initially devoid of nanomaterial particles and gradually collects said nanoparticles to form a paper. Since flow of the suspension is continuously restricted by the nanomaterial particles, the amount of pressure needed to ensure a constant deposition rate of the nanoparticles onto the filter media must increase. A decrease in deposition/flow rate can result in lower density, creating an inhomogeneous through-thickness nanostructure. 
     As mentioned above, conventional microfiltration presses supply a constant pressure to the aqueous suspension of nanomaterial particles throughout the process and the deposition rate therefore decreases. 
     The present invention employs a novel closed-loop fluid control system in which the nanoparticle deposition rate is maintained at controlled levels while modulating both the pressure of the fluid and the volume of aqueous suspension that is allowed to flow through the platens. 
     The closed loop fluid control system is depicted in  FIG. 10 . It controls nanomaterial suspension supply pressure and flow volume, enabling a uniform nanomaterial deposition rate, resulting in a uniform thickness sheet. 
     More particularly, as depicted in said  FIG. 10 , novel fluid control system  60  includes a source of compressed air  62 , motorized regulator  64  under the control of fluid controller  66 , input pressure gage  68  that sends data to said fluid controller  66 , flow sensor  70  that sends data to fluid controller  66 , proportional valve  72  under the control of fluid controller  66 , and output pressure gage  74  that sends data to fluid controller  66 . The compressed air flows from compressed air source  62 , through a tank or pressure vessel containing the nanomaterial suspension  76 , and from there to input nozzles on upper platen  14   a.    
     To prevent the lower platen from crushing the nanomaterial sheet when air is introduced into the filtration envelope at the end of the process, jack screws  22  provide a constant displacement (or offset) between the upper and lower platens. When the aqueous suspension is expended, the pressure within the filtration envelop may decrease without resulting in relative movement between the upper and lower platens, thereby eliminating the potential for the paper to be crushed. 
     The motion control system is diagrammatically depicted in  FIG. 11  and is denoted  80  as a whole. Motion controller  82  receives input signals from rotary encoder  84 , upper limit switch  86  and lower limit switch  88 . Rotary encoder  84  converts the physical rotational position of the output shaft of motor  40  and gear reducer  40   a  into digital signals. Lower platen  16  is raised and lowered by jack screws  22  as indicated by double-headed directional arrow  81 , each of said jack screws being raised when the output shaft rotates in a first direction and each being lowered when the output shaft rotates in an opposite direction to said first direction. The amount of up or down travel of the jack screws is known for each rotation of the output shaft so motion controller  82  knows the distance of lower platen  16  from each limit switch  84 ,  86  and the travel speed and direction of travel of said lower platen at all times. 
     Motion control system  80  thus maintains a constant displacement instead of constant pressure, enabling the production of clean, undamaged sheets of nanomaterial papers. 
     The novel nanomaterial sheet fabrication process produces stronger and lighter sheets with a higher content of nanomaterials that have uniform thickness and a larger surface area. 
     It will thus be seen that the objects set forth above, and those made apparent from the foregoing disclosure, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing disclosure or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.