Title of Invention

" A PROCESS AND APPARATUS FOR PYROLYSIS OF THIN COATINGS OF POLYMER MIXTURES ON CONDUCTING WEBS"

Abstract

The invention relates to a process and apparatus for applying thin coatings to a conducting metallic web, that may, by way of example, be advantageously employed for anodes and cathodes of rechargeable batteries. Such a coating reduces the inter-facial resistance between the metallic eeb and its adjacent non-conductive active electrode. The apparatus comprises a coating rotatable roller adapted to be in contact with a coating solution for coating of the metallic web. A pivotable wiper blade coacts with the roller for removal of excess quantities of the coating solution. A swing arm is provided in the proximity of the roller for adjusting the angle of wrap.

Full Text

FIELD OF INVENTION The invention relates to a process and apparatus for applying ultra thin coatings to a conducting metallic web, and which advantageously be used for manufacture of anodes and cathodes for ultra-high density, both volumetric and weight, rechargeable batteries. By way of example, but without implying any limitation thereto, the coatings can comprise polymer and/or copolymer mixtures and conducting carbon. BACKGROUND OF INVENTION In such batteries, anode and cathode elements comprise of an active electrode layers are carried on a conductive grid, which acts as the current collector. Different ingredients comprise the active electrode layers in different constructions of batteries. Collector grids of high-conductivity material, generally copper or aluminium, are in foil, expanded metal or woven form. The active electrode layer is applied as a thin layer to the collector grid, on one or both sides, in the form of tape, gel or paste. It is recognized in the art known that there is a substantial discontinuity at the inter-face of the active electrode layer and current collector due to the basic dissimilarity of materials. This discontinuity creates resistance to current flow and consequent loss battery-efficiency. Since different battery-applications invariably involve multi-layer, multi-cell configurations, cumulative efficiency loss is substantial. Extensive effort has therefore been directed in recent years to reduction of inter-facial resistance. An effective route for reduction of inter-facial resistance has been found in the application of thin coatings of a mixture of die active ingredients of the electrodes (which are non-conductors) and a conductive material like graphite, on the current collector grid which has been previously chemically pre-cleaned for removal of n on -conductive oxides, oils and greases and dirt. Coating layers are extremely thin and weights of the order of 0.1-0.5 gms/sq. ft. are not uncommon. Coating mixture is applied as a solution in appropriate solvents, which are subsequently removed by evaporation. The active bond created by the conductive ingredient of the coating between the non-conductive electrode layer and the conductive collector, reduces the resistance. Fineness, close-tolerance and uniformity of the coating layer are important parameters to battery performance. Because of today's large requirements, such close-tolerance coatings are applied in continuous processes on high-speed moving webs. Another technical demand arising from subsequent manufacturing operations, is the application of coatings in a defined band(s) with sharp definition of edge-boundaries. To meet such stringent demands, processes such as extrusion and electronically-controlled spraying are commonly deployed. These processes are complex, capital intensive and wasteful in material use. US Patent No.6306215 also describes a photogravure process wherein the web picks up the coating during a controlled nip as it moves between a rotating etched roller which has picked up the coating solution from a tray during its rotation, and, a counter-rotating soft-surfaced roller. This process is however unsuitable when volatile solvents, such as acetone, are employed. Quick viscosity rise due to fast solvent evaporation makes fine control of coating thickness impracticable. Clogging of the soft surface of the nip roller by the solid constituents of the solution as solvent evaporates is another problem. Discontinuities and irregularities in boundary-definition of the band because of solid-constituent dry-up is yet another. OBJECTS OF THE INVENTION An object of this invention is to propose a process and apparatus for applying ultra thin coatings to a conducting metallic web. Another object of this invention is to propose a process and apparatus for applying ultra thin coatings to a conducting metallic web which reduces the inter-facial resistance between the conducting web and the adjacent non-conductive active electrode layer. Still another object of this invention is to propose a process and apparatus for applying ultra thin coatings to a conducting metallic web which is economical. Yet another object of this invention is to propose a process and apparatus for applying ultra thin coatings to a conducting metallic web which is efficient. DESCRIPTION OF INVENTION According to this invention, there is provided a process for applying ultra thin coatings to a conducting metallic web comprising in providing a movement to the web so as to contact a rotatable roller having the coating solution, the angle of wrap subtended by the web on toe roller being adjustable, the excess coating solution on the roller being removed by the step of shearing by a pivoted blade. Further, according to this invention, there is provided an apparatus for applying ultra thin coatings to conducting metallic webs comprising : i. a coating solution tray; it. a rotatable coating roller adapted to be in contact with the coating solution contained in said tray; iii. said roller being a coating roller for providing a coating on a moveable conducting web; iv. a wiper blade coacting with said roller for removal of excess quantity of coating solution; v. a swing arm in the proximity of said roller for adjusting the angle of wrap. DESCRIPTION WITH REFERENCE TO DRAWINGS Further objects and advantages of this invention will be more apparent from die ensuing description when read in conjunction with the accompanying drawings and wherein Fig.l shows the roller; Figs.2a and 2b show the wiper blade; Fig.3 shows the roller with the coating solution tray. Referring to the drawings, continuous web 1 passes over a rotating uniform diameter finely-ground cylindrical roller 2 etched in desired zone 3 with uniform pits by photogravure or any other process, said roller dipping in the coating solution carried in a tray 4 to a controllable constant depth 5. The said solution is kept in constant circulation through make-up reservoir 6 with arrangement 7 for compensation for deposit, and arrangement 8 for loss of solvent by evaporation to ensure uniform solution viscosity. Dependence of pick-up of coating film thickness on roller diameter, surface speed, etching pattern and dipping depth, and coating ingredients, viscosity and evaporation rate is known in the art. Further control on thickness on coating film picked up by the roller is provided by pivoted blade 9 pressed against the roller at constant pressure by counter-weight 10. Since external diameter of etched and unetched zones of roller is ground in the same pass and is consequently equal, the blade shears-off excess material along the entire length of the roller as shown in 11. While removal in non-etched zone is complete, that in the etched zone is of excess beyond the etched surface. Result is precise confinement of coating within desired boundary-lines and accurate control of film-thickness to engraving depth in the etched zone. Shear angle 12 of the blade is adjusted to ensure complete shearing-off of excess film and could lie anywhere between 15 and 60 degrees. Final and super-fine control of the quantity of coating solution picked up by the web from the roller is provided by angle contact 13 subtended by the web on and the roller, commonly called angle of wrap. Angularly adjustable swing arm 14 carrying roller 15 provides adjustability to the angle of wrap. In case coating is required on both sides of the web, a similar arrangement may be provided a second time in continuation, after reversing the web face. Similarly, arrangements may also be incorporated in the same continuous traverse of the web for solvent removal and drying in one or multiple stages. Subsequent finishing treatment(s) may also follow the coating process as may be required in different constructions of batteries. CLAIM; 1. A process for applying ultra thin coatings to a conducting metallic web comprising in providing a movement to the web so as to contact a rotatable roller having the coating solution, the angle of wrap subtended by the web on the roller being adjustable, the excess coating solution on the roller being removed by the step of shearing by a pivoted blade. 2. An apparatus for applying ultra thin coatings to conducting metallic webs comprising: i. a coating solution tray; ii. a rotatable coating roller adapted to be in contact with the coating solution contained in said tray; iii. said roller being a coating roller for providing a coating on a moveable conducting web; iv. a wiper blade coacting with said roller for rem oval of excess quantity of coating solution; v. a swing arm in the proximity of said roller for adjusting the angle of wrap. 3. An apparatus as claimed in claim 2 wherein said roller has an etched and non-etched zone. 4. An apparatus as claimed in claim 2 wherein said wiper blade is a pivoted blade. 5. An apparatus as claimed in claim 2 wherein the wiper blade has an adjustable shear angle. 6. An apparatus as claimed in claim 2 wherein said swing arm carries a roller and adapted to be in contact with the moveable web. 7. An apparatus as claimed in claim 6 wherein the swing arm is provided at the discharge side of said coating roller. 8. An apparatus for applying thin coatings on a conducting web substantially as herein described and illustrated.

Documents:

695-DEL-2002-Abstract-31-03-2008.pdf

695-del-2002-abstract.pdf

695-DEL-2002-Claims-31-03-2008.pdf

695-del-2002-claims.pdf

695-DEL-2002-Correspondence-Others-(27-02-2009).pdf

695-DEL-2002-Correspondence-Others-31-03-2008.pdf

695-del-2002-correspondence-others.pdf

695-del-2002-correspondence-po.pdf

695-del-2002-description (complete).pdf

695-DEL-2002-Description (Complete)31-03-2008.pdf

695-del-2002-drawings.pdf

695-del-2002-form-1.pdf

695-del-2002-form-18.pdf

695-DEL-2002-Form-2-(27-02-2009).pdf

695-del-2002-form-2.pdf

695-DEL-2002-GPA-(20-02-2009).pdf

695-DEL-2002-GPA-(27-02-2009).pdf

695-del-2002-gpa.pdf