Device and method for induction heating of a coated web substrate during process operation

Abstract

An apparatus, system, and method for simultaneously drying a coating on a substrate using at least two different drying phenomena, e.g., induction heating and convection heating, or a combination of induction heating, convection heating, and infrared heating. The coating on the substrate is dried by generating heat within the substrate while simultaneously applying convection heat and / or radiant heat to the coating. Simultaneous drying means drying the same area of ​​the substrate simultaneously, and in certain embodiments, means applying induction heating and convection simultaneously to the same area of ​​the substrate. Preferably, the substrate is at least partially conductive.

Description

Technology Field

[0001] This application claims priority to U.S. Patent Application No. 18 / 415,868 filed on January 18, 2024, the entire disclosure of which is incorporated by reference into this specification.

[0002] The present invention relates to an apparatus and method for inductive heating of a coated web substrate during a process operation. Background Technology

[0003] A roll of substrate material is often coated with a liquid-suspended mixture, such as ink, adhesive resin, varnish, or other material, to form a wet film to be dried. In special cases, the material to be applied to the surface of the substrate may be a mixture of a binder, such as in powder form, and a drying compound. In the finished form, the dried film adhered to the substrate constitutes a web-based product with useful applicability depending on the characteristics of the material components. In some cases, the substrate material may be paper or cardboard printed with ink to produce books, magazines, or packaging materials. In other cases, the substrate may be a polymer film, such as polyethylene, polyethylene terephthalate, polyimide, etc., and may be coated with another polymer dissolved in a liquid solvent or a wet adhesive film to form a second functional layer on the first layer, which is the polymer substrate. In certain cases, the substrate web may comprise aluminum or copper, such as in the production of metal foil (foil web), metallized or conductive treated, finished, or coated webs, and battery electrodes also known as current collectors. In the manufacture of electrodes for lithium-ion battery cells, the coating material applied to the substrate is a liquid suspension slurry or paste composed of fine powder mixed with a binder material, which is generally a polymer that may be water-soluble. In other cases, the binder is dissolved in an organic solvent, such as NMP, NEP (1-ethyl-2-pyrrolidone), TEP, EAA (ethyl acetoacetate), DMAc, GBL (gamma-butyrolactone), xylene, acetone, alcohol, or a similar industrial solvent selected to dissolve the organic binder, to form a coating liquid. As a special sub-application, the coating material may consist of a dry fine powder mixed with a binder without an aqueous or liquid solvent suspension.

[0004] For the purposes of this description, the term "solvent" may apply to water in aqueous coatings where the solvent is water, to coatings having one or more of the aforementioned organic solvents, or to a mixture of water and one or more organic solvents. In dry coating applications, there is little to no solvent supporting the dry powder, and no aqueous suspensions exist. In all cases except for dry powder forms, the term solvent refers to a vehicle that dissolves a binder or binder-like substance introduced to make the coating fluid so that it can be applied to a substrate in liquid form by a coating device. Dry powder applications require special treatment to ensure the coating adheres to electrode support surfaces.

[0005] In the manufacture of battery electrodes, a strip-shaped metal / metallized / conductive treated web / foil roll is unwound and transported through a coating line, where it is coated in lanes along the width direction of the foil web or continuously or semi-continuously over the entire width. The coating may be applied to one side or both sides of the web. FIG. 1a illustrates an example of single-sided coating, and FIG. 1b illustrates an example of simultaneous double-sided coating. In full-width continuous coating, the edges of the foil web are mostly uncoated, leaving exposed (conductive) web at the edges. The coating on each side may be applied by a suitable coating device, preferably a slot die (12) (nozzle). Alternative coating devices include a roll applicator, a comma coater, or a gravure cylinder, depending on the required coating thickness and the rheological properties of the wet slurry. In a dry coating process, the dry powder can be applied via electrostatic, deposition, or mechanical methods. Additionally, the dry coating process for electrode fabrication can basically consist of a two-stage process, wherein in at least one first manufacturing stage, a powder mixture containing an active material and an activated binder is prepared by a roller press or extrusion to produce a dry, self-supporting or self-supporting film of the active material, and in the second manufacturing stage, the pre-prepared film is laminated onto a current collector web. In certain cases, the coating is generally applied in the form of discontinuous patches along the length of the foil web in the direction of travel using a slot die coater, leaving bare current collectors between the patches. It can also be coated in the form of lanes, in which case bare current collectors remain between the lanes.These exposed bare regions provide uncoated foil regions for connecting tabs that will be connected between individual electrodes when assembling battery cells into a battery (see Fig. x).

[0006] In certain cases, the aforementioned web-based products are coated on one side (side) of a substrate via a roll-to-roll process as illustrated in FIG. 1a (wherein reference numeral 10 indicates a web, 12 indicates a slot die coater, 11, 13, and 14 indicate rollers, and 15 indicates a dryer). In such cases, a wet coating is applied to a moving web and dried in an oven to remove the solvent, thereby solidifying the applied coating. In certain cases, the aforementioned web-based products are coated on both sides (sides) of a substrate. In the general case where both sides of the substrate are coated, a first wet coating is applied to a moving web substrate and dried in an oven, after which a second wet coating is applied and dried in a second dryer. In a preferred embodiment for manufacturing battery electrodes, a wet slurry is applied to both sides of a foil web and then dried in an oven. This method is referred to as "simultaneous double-sided coating and drying" and is illustrated in FIG. 1b (wherein the same reference numerals refer to the same features in other drawings, and element (16) is a roller). In the case of manufacturing lithium-ion electrodes, this method is particularly advantageous for improving productivity because it requires only one drying step after applying a wet coating slurry to both sides.

[0007] The first drying step removes almost all solvent from the wet coating applied to the foil web to manufacture battery electrode materials, and this is referred to as primary drying. A second drying step is generally included to reduce residual solvent and, in particular, moisture content to very low levels before the cell assembly step. In this secondary drying step, the residual solvent entering the dryer is already at a low level, generally less than 1% by weight in the coating layer, but must be further reduced to less than 400 ppm, and in some cases less than 100 ppm, to meet the specifications required for cell assembly.

[0008] As is known to those skilled in the art of coating and drying, certain coatings exhibit defects during the drying process when heat and mass transfer are too aggressive or when drying impairs the quality of the wet substrate. These defects include loss of adhesion to the substrate, bubble formation, surface roughness resembling an orange peel, a mottled appearance, surface cracks, or cracks penetrating the dried coating thickness. In the drying of lithium-ion electrodes, the occurrence of so-called "mud cracks" and / or loss of adhesion can be problematic, particularly with conventional drying methods, especially when the coating thickness is thick or heavy. When applied, the coating slurry generally contains 30 to 80% solvent by weight. As the wet surface of the coating dries and begins to solidify, the coating volume on the surface also decreases due to the removal of the solvent by evaporation. In some cases, particularly for thick coatings of 50 microns or more, the coating slurry near the interface of the foil substrate experiences less solvent removal as drying progresses compared to the free surface exposed to convective air. Consequently, a portion of the coating thickness near the coating surface undergoes volumetric strain due to volume shrinkage, which can lead to stress cracks in the dried or nearly dried coating material, most notably on the exposed surface. These cracks result in electrode materials unsuitable for battery cell manufacturing. To prevent these defects, in most cases, the drying rate must be kept gradual while removing water or solvent from the coating, and the line speed of the coating process must be reduced to reach an acceptable residual solvent level (typically less than 1%, often less than 0.1% of the coating mass).

[0009] During drying, the coated area is heated, and the wet coating and foil substrate receive a thermal load in terms of sensible heating of the coating and web substrate and the latent heat of vaporization of the solvent. In contrast, the previously mentioned bare substrate areas do not have a wet coating and therefore do not receive the same thermal load during drying as the coated area. Consequently, these bare substrate areas generally reach higher temperatures than adjacent coated areas during drying. In the case of convection drying, the bare substrate quickly reaches the temperature of the convective air in contact with the substrate. On the other hand, the coated area tends to rise more slowly and maintain a temperature lower than that of the convective air due to the greater sensible heat load of the wet coating and the wet-bulb temperature drop (evaporative cooling) effect during drying. This creates a local temperature gradient within the substrate between the coated area and the bare area, causing differential thermal growth of the substrate between the two areas, as shown in Fig. 2b. If the temperature difference becomes too large, the resulting thermal strain causes the substrate to buckle, rendering the product electrode unusable. To prevent excessive thermal strain and buckling, the applied convective heat transfer coefficient and air temperature are often limited, which limits production throughput to maintain acceptable product quality. Additionally, when drying energy is applied to the substrate via non-convective methods, such as infrared emitters or dielectric fields, the temperature of the exposed substrate may rise further while simultaneously supplying drying heat to the coated areas of the substrate. For example, US 9,310,130 by (Nissan) Kazama et al. discloses a process for heating electrode materials by an induction field.To prevent overheating of the exposed substrate area, they propose a method to block the inductive field when it passes through the uncoated area. However, this method is not compatible with the line speed capabilities of current battery electrode coating operations. In particular, under practical constraints regarding blocking time and distance within commercial drying devices, it is very difficult to block and restore the inductive field at high speeds.

[0010] In conventional drying ovens for web-based products, heat and mass transfer to facilitate drying are achieved through high-temperature convective air and, in some cases, controlled humidity and / or solvent concentration. In convection drying ovens, air is heated to a desired temperature and then ejected from nozzles in the form of impact jets to contact the web, creating controlled levels of heat and mass transfer conditions based on the selection of air velocity, temperature, and nozzle array / configuration. To apply milder drying conditions, the air velocity, air temperature, and the size or number of air jets from the array of nozzles applied within the drying oven are reduced, or the magnitude of heat and mass transfer is reduced by some combination thereof. Such milder drying reduces the solvent removal rate, requiring more time to reach the target moisture. Considering the fixed length of the oven or realistic constraints on the oven length available for a given facility, the production line speed of the coating operation must also be reduced accordingly.

[0011] In certain cases, an infrared emitter may be placed on one or both sides of the substrate web to apply additional heat flux to the wet coating. The infrared emitter may be positioned between air jets emanating from convection nozzles. In this way, the heat flux to the substrate web can be increased by raising the temperature of the emitter, while the convection provided by the air jets can be maintained or, if applicable, reduced to prevent disturbance of the wet coating. In some cases, particularly when the wet film thickness is thicker, the combination of infrared radiation flux and convective heating reduces the tendency to form mud cracks by limiting the drying rate of the coating surface by convection while heating the wet coating slurry layer to a higher temperature. Experiments have confirmed that by balancing the magnitude of convective heat and mass transfer with the heat flux from the infrared emitter, the overall solvent removal rate can be increased compared to using convection alone, while preventing mud cracks.

[0012] Nevertheless, as previously described, adding infrared heat flux to a drying device is primarily limited to applying heat to the exposed surface of the coating. Heat is transferred from the coating surface into the interior of the material, creating both a thermal gradient and a solvent concentration gradient. In some cases, the heat flux added from the infrared emitter is dissipated relatively quickly through the wet coating thickness by the thermal conduction of the coating material, making the thermal gradient negligibly small. This is especially true when the solvent fraction of the coating surface is still high and the solid content is low, or when the magnitude of the applied IR heat flux is moderate (on the web surface, <3000 watts / m²). However, even such limited energy flux from the IR source must first heat the surface and then be conducted into the interior.

[0013] When a heat flux is applied from heated convective air, infrared heat flux, or a combination thereof, the coating is heated from the outside in. Before significant drying occurs, the thermal conductivity of the slurry coating is relatively high, approaching that of the liquid solvent itself. Subsequently, as the surface dries, the thermal conductivity of the partially dried coating decreases. As the coating dries, the thermal conductivity decreases because the outer dried layers block the inner wet layers from heat and mass transfer to moisture. If the local solid content on the coating surface increases further due to drying, the decrease in thermal conductivity causes the coating surface temperature to rise relative to the average temperature of the entire coating and the substrate temperature. A temperature profile is formed in which the temperature decreases in the thickness direction of the coating from the coating surface to the coating interface with the substrate. Given sufficient time under conditions where heated convective air and / or infrared heat flux is continuously applied, the coating and the substrate eventually reach a more uniform temperature consistent with the surface temperature, and the substrate also approaches this temperature. However, if the coating thickness is relatively thick, a significant portion of the coating layer may dry out before the substrate temperature reaches the coating surface temperature. When this occurs, the substrate temperature rises after the coating solidifies, causing thermal expansion of the substrate. Consequently, the expansion of the substrate causes deformation in the dried coating, resulting in elongation in a plane parallel to the interface between the coating and the substrate. This resulting strain can lead to several defects. First, cracks may develop as the dried coating stretches due to the substrate adhering to it. Second, the adhesion between the substrate and the coating weakens, potentially causing the coating to peel off or detach from the substrate. Third, as drying progresses, the simultaneous decrease in coating volume and thermal expansion of the substrate can lead to a combination of cracking, buckling, and loss of adhesion. Consequently, if these defect patterns appear on the dried electrode, it cannot be used as an electrode material.These defects include crazing (initial cracking), localized variations in coating thickness, cracks extending from the coating surface to the substrate interface (substrate exposure), separation of the dried coating from the substrate in fragments or linear patterns, and the occurrence of wrinkle patterns due to deformation of the substrate's flatness. Among these various defects, so-called mud cracking is generally the most critical as the required coating thickness increases. Various methods have been applied to mitigate these problems, but they often result in other undesirable side effects.

[0014] It has long been known that metallic objects, particularly those made of iron and its alloys, can be heated by exposure to a vibrating electromagnetic field in a method known as induction heating. While induction heating for non-ferrous metals is not as effective as for ferrous metals, it can be utilized in certain situations.

[0015] Common examples of induction heating include heating to relieve or induce stress in metal castings, and zone refining of material billets to obtain desired metallurgical properties. In these applications, the metal is heated to a temperature sufficient to alter at least a portion of the material's metallic phase structure (e.g., crystalline or amorphous metal structure). In some cases, objects are induction heated to expand metal objects; for instance, a hub is heated to expand it, then fitted into a shaft and subsequently cooled to a lower temperature to create a rigid bond. In most cases, the objective is to heat the workpiece to a high temperature while minimizing heat loss due to radiation and convection. Therefore, most induction processing units are configured and operated to maximize the temperature of the workpiece. This is typically achieved by including thermal radiation shielding and insulation to eliminate the effects of convective cooling.

[0016] As previously mentioned, while research has been conducted on the heating of metals in the form of thin strips, commercial applications in the field of battery electrode processing have been limited. Kazama et al.'s US 9,310,130 presents a method in which a wet-coated electrode foil is first induction-heated and then optionally heated by a convection dryer. The foil and coating are heated to a temperature sufficient to increase the vapor pressure of the solvent, causing the solvent to evaporate in the subsequent convection zone. Gaugler et al.'s EP 3439079A1 presents a method in which an induction coil element is placed to heat the coated web and vaporize the solvent, after which the solvent vapor is condensed onto the coil element. In both of these prior art examples, virtually all heat supplied for the drying heat load is transferred by an induction field.

[0017] In these prior art embodiments, the temperature of the exposed substrate regions becomes excessively high compared to the uncoated regions, leading to thermal deformation and buckling. Accordingly, Kazama further proposes a method to block the inductive field when the exposed foil regions pass through field coils in an attempt to mitigate the excessive temperature. These uncoated regions are essential for the manufacture of current collectors to provide conductive tabs at the edges of electrode cell elements required for the assembly of cylindrical, flat, prismatic, and pouch-type batteries. The uncoated regions, or "mass-free zones," may exist in the form of uncoated lanes at the edges of a single-width continuous coating applied within the substrate width, and in some cases, may also exist between lanes when two or more lanes are applied within the substrate width. In some battery types, cell tabs are formed during cell assembly, which requires uncoated regions between coated patches of active electrode material along the direction of movement of the current collector foil substrate. This electrode manufacturing method is often referred to as intermittent, patch, or skip coating. As mentioned, Kazama proposes a method to prevent overheating of regularly spaced mass-free zones during induction heating by actively controlling and blocking the induction field to reduce energy absorbed by intermittently uncoated areas as the web passes through each field element. In this method, the induction field elements must be sized and positioned to precisely match the spacing and patch dimensions required for the specific battery cell to be produced. In many cases, since a given electrode production line must supply multiple current collector formats with varying spacing dimensions between coated patches, the hardware must be changed for each production run.In addition, this method does not provide a solution to the problem of overheating in the uncoated areas between lanes and at the edges of the substrate web in the continuous lane coating described above.

[0018] All conventional methods inherently face specific limitations in the drying process, requiring a reduction in the solvent drying rate, the temperature of the exposed foil substrate, or both. In all cases, the impact of these limitations leads to reduced process line speeds and shortened turnaround times, resulting in decreased production throughput or increased investment costs due to longer dryer lengths. This is a common dilemma in current practice.

[0019] Considering that the aforementioned problems are issues arising from external heating of thickly coated metal foil substrates—namely, cracks / gap and surface defects, and foil substrate buckling—and that conventional solutions fail to resolve these problems without undesirable consequences including reduced production speed and / or extended dryer length, a preferred solution would be to generate heat internally within the thickness of the coated substrate while applying balanced drying heat and mass transfer conditions at the surface of the coating.

[0020] The present solution relates to a coated substrate as a common structure for current collectors, for example, for lithium-ion battery electrodes. Accordingly, it would be advantageous to gradually raise the temperature of the substrate by applying thermal energy to the base substrate through inductive coupling in conjunction with convective heating, and to promote heat flow into the coating by thermal conduction at the interface with the coating layer. Inductive heating, combined with the convective heating, provides an independent but additional thermal contribution to the substrate. This heating combination is performed simultaneously, that is, simultaneously within the same web region of the coated substrate, on the surface of the coating and within the base substrate in interface contact with the coating. In some cases, infrared radiation may be added.

[0021] Throughout this specification, the terms foil, metal foil, at least partially conductive substrate, web, current collector, web substrate, and various combinations thereof are used synonyms and all refer to current collector materials in the form of sheets, foils, or webs used in the manufacture of electrodes, for example, in batteries, secondary batteries, capacitors, fuel cells, etc.

[0022] The purpose of the embodiments disclosed herein is to disclose means for improving the drying rate by raising the temperature of the substrate by an inductive field and promoting mass transport of solvent components within the coating thickness to the free surface. A coating applied to the surface of a web substrate can be conceived of being subdivided into a plurality of layers within the total coating thickness to represent a profile of temperature and solvent components according to location in the thickness direction. These layers are often defined in a finite element numerical model to provide the form of solution equations and computational algorithms for predicting and visualizing key physical parameters, such as temperature and solvent concentration according to location within the coating thickness. For illustrative purposes, three such layers may be described, wherein the first layer is closest to and in contact with the substrate foil, the second layer is located midway between the foil interface and the exposed free surface of the coating, and the third layer is closest to and exposed to the free surface of air (or other gas) in the drying environment. By supplying heating energy directly to the metal foil substrate by an induction field, the foil heats the first layer at the foil interface by conduction. This heats the interior of the coating at the substrate interface to a certain level, thereby promoting the mass transfer of liquid carrier solvent(s) within the coating to the free surface (air interface) of the coating. Specifically, by heating the coating layer in close contact with the substrate (e.g., metal foil) to promote the movement of the liquid solvent within the coating layer, an enhanced mass transfer scenario is created, in which the liquid solvent undergoes mass transfer by diffusion, capillary action, phase change to vapor, or other internal transfer mechanisms, moving from the interior layers to the exterior layers toward the free surface.This is essentially the reverse of the process that initially occurs when heating from the outside inward by thermal convection. Experimental results showed that internal heating of the coating can reduce or eliminate surface defects that commonly occur when heating only the free surface; these surface defects occur because the outermost coating layers solidify first, resulting in a disproportionate reduction in volume compared to the subsequent inner layers closer to the substrate.

[0023] Additionally, the objective of the embodiments disclosed herein is to mitigate excessive temperature applied to exposed substrate areas by selecting and controlling the convective air temperature and heat transfer coefficient in relation to the applied induction heating intensity. The temperature and heat transfer coefficient provided by the convective air applied for drying the wet coating can be selected and controlled to provide a cooling effect to the substrate (e.g., exposed foil), which prevents the substrate from being heated to a higher temperature by induction field coupling alone, thereby offsetting the tendency of the substrate to buckle due to the thermal gradient between the coated area and the uncoated area.

[0024] In addition, heating the metal foil substrate from the inside alleviates the thermal expansion deformation that occurs when heating the coated metal foil composite from the outer coating surface inward. The metal foil substrate is heated simultaneously with the wet coating, and the foil undergoes thermal expansion growth while the attached coating layers remain in a liquid or plastic state. Consequently, the deformation that would have been exacerbated if the coating had dried and densified before foil growth is alleviated, thereby preventing the aforementioned thermal deformation defects. In other words, if the metal foil substrate undergoes thermal expansion growth before the coating solidifies, the coating can be reshaped fluidly or plastically in compliance with the expansion of the substrate without generating harmful internal deformation energy within the coating layer and / or at the foil-coating interface, thereby reducing the generation of a stress field and preventing the formation of coating cracks and / or the separation (drying) of the coating from the foil.

[0025] This method, which simultaneously heats metal foil substrates using internal heating by induction in conjunction with conventional convection heating or convection and IR energy transfer heating methods, can further accelerate the energy-mass transfer process required to dry the coating. By combining the internal heating method with conventional external heating methods, defects can be reduced or eliminated without the need to slow down production speeds or provide longer drying systems. Therefore, combining the internal heating method with conventional external heating methods such as convection allows for increased production speeds without capital investment for drying system extensions. The elimination of coating defects or the effective minimization of quality defects in coated electrode foils offers the advantage of significantly increasing the effective yield during electrode production. Since electrodes exist in various grades, products with fewer defects lead to battery packs with superior performance and value.

[0026] Accordingly, in certain embodiments, an apparatus and method for simultaneously drying a coating on a substrate using at least two different drying phenomena, e.g., induction heating and convection heating, or a combination of induction heating, convection heating, and infrared heating are disclosed. In certain embodiments, the coating on the substrate is dried by generating heat within the substrate while simultaneously applying convection heat and / or radiant heat to the coating. Simultaneous drying means drying the same area of ​​the substrate simultaneously, and in certain embodiments, means applying induction heating and convection simultaneously to the same area of ​​the substrate. Accordingly, the embodiments relate to a synergistic combination of outside-in / top-down drying and inside-out / bottom-up heating (e.g., induction heating). In the case of radiant heat, one suitable approach is to use an infrared float bar, such as the FLOATIR® bar commercially sold by Durr Systems, Inc. This includes the apparatus and method disclosed in US Patent No. 9,228,779, the disclosure of which is incorporated herein by reference. In certain embodiments, infrared emitters may be arranged as described above.

[0027] In certain embodiments, a method and apparatus for induction heating a substrate (e.g., foil web) having a wet coating are disclosed, wherein the induction heating is performed simultaneously at the same location on the substrate in combination with convection of dry air or a gas jet to control the volumetric strain profile within the coating during drying.

[0028] In certain embodiments, a method and apparatus for applying an induction field to control the thermal expansion of a metal substrate, e.g., a foil, on one or more coating layers on the substrate during drying are disclosed.

[0029] In certain embodiments, a method and apparatus are disclosed for applying a combination of thermal energy by electric induction and convection simultaneously and at the same location on a coated at least partially electrically conductive substrate to control the drying rate profile of a wet coating according to exposure time. The substrate may be coated on one or two sides, wherein, preferably, the two sides are opposing sides.

[0030] In certain embodiments, a method and apparatus are disclosed for applying a combination of thermal energy by electric induction and convection simultaneously and at the same location on a coated at least partially electrically conductive substrate to control the drying rate profile of a wet coating according to the percentage of solid content in the coating. The substrate may be coated on one or two surfaces, wherein preferably the two surfaces are opposite surfaces.

[0031] In certain embodiments, a method and apparatus are disclosed for simultaneously and simultaneously applying a combination of thermal energy by electric induction and convection and infrared heat flux (e.g., FLOATIR® bar) to at least partially electrically conductive substrates to control the drying rate profile of a wet coating according to exposure time. The substrate may be coated on one side or two opposing sides.

[0032] In certain embodiments, a method and apparatus are disclosed for simultaneously and simultaneously applying a combination of thermal energy by electric induction and convection and infrared heat flux on a coated at least partially electrically conductive substrate to control the drying rate profile of a wet coating according to the percentage of solid content in the coating. The substrate may be coated on one or two surfaces, wherein preferably the two surfaces are opposite surfaces.

[0033] Accordingly, in certain embodiments, an apparatus for drying a web coating on a region of a moving web is disclosed, wherein the web is at least partially electrically conductive, and the apparatus comprises: a web entry opening and a web exit opening spaced apart from the web entry opening; at least one drying chamber having at least one nozzle for convectively heating the web; and a dryer enclosure having at least one inductive heater for inductively heating the web; wherein the at least one nozzle and the at least one inductive heater are disposed within the apparatus to simultaneously heat the web coating on the region of the web.

[0034] In certain embodiments, the dryer enclosure has a first drying chamber and a second drying chamber downstream of the first drying chamber in the direction of movement of the web. In certain embodiments, the at least one induction heater is disposed within the first drying chamber, at least one nozzle for convectively heating the web is disposed within the first drying chamber, and at least one nozzle for convectively heating the web is disposed within the second drying chamber.

[0035] In certain embodiments, at least one induction heater is disposed outside the dryer enclosure, upstream of the web entry opening.

[0036] In certain embodiments, the at least one induction heater comprises one or more electromagnetic coils disposed within the dryer enclosure, and a convective air jet from the at least one nozzle passes through the space between the one or more electromagnetic coils and the surface of the web, so that an oscillating magnetic field penetrating the web and a convective jet field from the at least one nozzle act simultaneously at the same location on the web.

[0037] In certain embodiments, the induction heating zone within the dryer enclosure extends from the web entry opening to a location within the dryer enclosure where the constant rate period drying ends and the falling rate period of drying begins.

[0038] In certain embodiments, the location of the induction heater and the accompanying oscillating power supply are configured to deliver the inductive energy flux absorbed by the web to a range of 1 to 75% of the total drying heat flux within the dryer enclosure. In certain embodiments, the inductive energy flux absorbed by the web is within a range of 10 to 50% of the total drying heat flux within the dryer enclosure.

[0039] In certain embodiments, a method for drying a conductive substrate partially covered with at least one layer to be dried is disclosed, the method comprising the step of heating the substrate by applying convective heat, radiant heat, or both convective heat and radiant heat to the layer while simultaneously generating heat within the substrate by induction heating.

[0040] In certain embodiments, the substrate is only partially electrically conductive, and the heating of the substrate is performed at least partially by induction heating.

[0041] In certain embodiments, the temperature and heat transfer coefficient provided by the convective air applied for drying the at least one layer are selected and controlled to provide a cooling effect to the substrate, which can be heated to a higher temperature by the induction heat.

[0042] In certain embodiments, the substrate is electrically conductive, and when the coating weight of the layer is up to 300g per square meter, the range of induction heating of the substrate is 10% to 30%.

[0043] In certain embodiments, the substrate is electrically conductive, and when the coating weight of the layer is heavier than 300g per square meter, the induction heating range of the substrate is 20% to 40%.

[0044] In specific embodiments, a method for coating a first surface and a second surface of a substrate in a single pass is disclosed, said method comprising:

[0045] a. A step of applying a first coating layer to a first surface of the substrate using a first coater;

[0046] b. A step of applying a second coating layer to a second surface of the substrate using a second coating machine;

[0047] c. A step of non-contact drying the first and second coating layers in a flotation dryer located downstream of the first and second coating machines, so as to maintain a predetermined level of residual moisture when the first and second coating layers exit the dryer;

[0048] d. a step of inductively heating the substrate in the floating dryer while simultaneously convectively heating the first and second coating layers; and

[0049] e. A step of calendering the coated substrate downstream of the dryer; is included.

[0050] In specific embodiments, a method for applying and drying a coating on a web is disclosed using a system comprising a supply valve, a bypass valve, a nozzle, a web lifter, and a controller for controlling the supply valve, the bypass valve, and the nozzle, wherein the method comprises:

[0051] A step of inputting reference positions on the web to the controller for opening and closing the supply valve;

[0052] A step of inputting reference positions on the web to the controller for opening and closing the bypass valve;

[0053] A step of inputting reference positions on the web to which the web lifter is to be operated in order to move the web toward the nozzle and away from the nozzle to the controller;

[0054] A step of moving the above web to pass through the above nozzle;

[0055] Step of tracking the location of the above web;

[0056] A step of applying the coating to the web by controlling the supply valve, the bypass valve, the nozzle, and the web lifter using the controller based on the input reference positions; and

[0057] The method includes the step of heating the substrate by applying convective heat, radiant heat, or both convective and radiant heat to the coating while simultaneously generating heat within the substrate by induction heating.

[0058] In specific embodiments, a system for applying a coating to a material moving along a path and drying said coating is disclosed, said system:

[0059] A coater nozzle for applying the above coating;

[0060] A supply valve communicating with the nozzle to allow the flow of coating to the nozzle;

[0061] A bypass valve for diverting the flow of the coating from the nozzle;

[0062] A fluid displacement mechanism for withdrawing a coating from the nozzle after the supply valve is closed, wherein the fluid displacement mechanism comprises a chamber having a changeable volume:

[0063] An actuator, wherein the movement of the actuator is arranged to change the volume;

[0064] A movable web lifter to deflect the above material;

[0065] A controller communicating with the supply valve, the bypass valve, the actuator, the nozzle, and the web lifter to control the application of the coating; and

[0066] A dryer enclosure comprising a web entry opening and a web discharge opening spaced apart from the web entry opening, at least one drying chamber having at least one nozzle for convectively heating the web, and at least one inductive heater for inductively heating the web;

[0067] The above at least one nozzle and the above at least one induction heater are arranged within the device to simultaneously heat the web coating on the above area of ​​the web.

[0068] In certain embodiments, the dryer enclosure of the system has a first drying chamber and a second drying chamber downstream of the first drying chamber in the direction of movement of the web.

[0069] In certain embodiments, the at least one induction heater of the system is disposed within the first drying chamber, at least one nozzle for convectively heating the web is disposed within the first drying chamber, and at least one nozzle for convectively heating the web is disposed within the second drying chamber.

[0070] In certain embodiments, at least one induction heater is disposed outside the dryer enclosure of the system, upstream of the whip entry opening.

[0071] In certain embodiments, the at least one induction heater of the system comprises one or more electromagnetic coils disposed within a dryer enclosure, the dryer enclosure comprising a web entry opening and a web discharge opening spaced apart from the web entry opening, at least one drying chamber having at least one nozzle for convectively heating the web, and at least one inductive heater for inductively heating the web, wherein the at least one nozzle and the at least one inductive heater are disposed within the device to simultaneously heat the web coating on the said area of ​​the web, and a convective air jet from the at least one nozzle passes through the space between the one or more electromagnetic coils and the surface of the web so that an oscillating magnetic field penetrating the web and a convective jet field from the at least one nozzle act simultaneously on the same location of the web.

[0072] In certain embodiments, the inductive heating zone within the dryer enclosure of the system extends from the web entry opening to a location within the dryer enclosure where the constant rate period drying ends and the falling rate period of drying begins. In certain embodiments, the location of the inductive heater and the accompanying oscillating power supply are configured to deliver the inductive energy flux absorbed by the web to a range of 10 to 50% of the total drying heat flux within the dryer enclosure. Brief explanation of the drawing

[0073] The embodiments disclosed herein may take the form of various components and arrangements of components, and various process operations and arrangements of process operations. The drawings are for the purpose of illustrating preferred embodiments only and should not be interpreted as being limited thereto. FIG. 1a is a schematic diagram of a single-pass coating layout; FIG. 1b is a schematic diagram of a double coating layout; FIG. 2a is a drawing showing a conductive substrate having exposed bare metal regions that provide uncoated foil regions for connection tabs to be connected between individual electrodes within an assembly of battery cells according to specific embodiments; FIG. 2b is a graph of foil temperature versus heating time according to the prior art; FIG. 3a is a plan view of a device applying transverse electrically conductive electromagnetic induction coils to heat moving webs; FIG. 3b is a schematic diagram of a device for applying transverse electrically conductive electromagnetic induction coils to heat moving webs; FIG. 4a is a schematic diagram of a single-sided dryer slot nozzle arrangement having electromagnetic coil elements disposed between slot nozzles according to specific embodiments; FIG. 4b is a schematic diagram of a double-sided dryer air bar array having electrically conductive electromagnetic coils arranged opposite air bar nozzles according to specific embodiments; FIG. 4c is a schematic diagram of a double-sided dryer air bar arrangement having electrically conductive electromagnetic coils disposed opposite the air bar nozzles and electrically conductive electromagnetic coils disposed within the air bar nozzles, according to specific embodiments; FIG. 4d is a perspective view of a single-sided dryer air foil array having electromagnetic coil elements disposed between air foil nozzles according to specific embodiments; FIG. 5 is a schematic diagram of induction coils applied to a conventional coating line process according to specific embodiments; FIG. 6a is a graph showing foil temperature modeling during single convection drying according to the prior art; Figure 6b is a graph showing foil temperature modeling during convection and induced drying; FIG. 7 is a schematic diagram illustrating the application of induction field coils for calendar temperature control in inline process calendering according to specific embodiments; FIG. 8 is a schematic diagram illustrating the application of induction field coils in a process including secondary drying according to specific embodiments; FIG. 9a is a schematic diagram illustrating the application of induction coils to a coating line process including inline processing according to specific embodiments; FIG. 9b is a schematic diagram illustrating the application of induction coils to a coating line process including inline processing and immediate processing according to specific embodiments; FIG. 9c is a schematic diagram illustrating the application of induction coils to a coating line process including secondary lamination according to specific embodiments; FIG. 10a is a schematic diagram showing the application of induction coils to a dry battery electrode coating (dry powder coating) line process, which is a single-sided coating process, according to specific embodiments; FIG. 10b is a schematic diagram showing the application of induction coils to a dry battery electrode coating (dry powder coating) line process, which is a simultaneous double-sided coating process according to specific embodiments; FIG. 10c is a perspective view showing the application of induction coils to a dry battery electrode coating (dry powder coating) line process according to specific embodiments; Figures 11a and 11b are graphs showing the drying profile and volumetric strain according to Example 2. Specific details for implementing the invention

[0074] A more complete understanding of the components, processes, systems, and devices disclosed herein can be obtained by referring to the accompanying drawings. The drawings are merely schematic representations based on convenience and ease of describing the invention and are not intended to indicate the relative sizes and dimensions of the devices or their components, or to define or limit the scope of exemplary embodiments.

[0075] For clarity, specific terms are used in the following description, but these terms are intended to refer only to specific structures of the embodiments selected to be illustrated in the drawings. In the drawings and the following description, the same reference numbers should be understood to refer to components of the same function.

[0076] The singular forms "a," "an," and "the" include plural references unless otherwise specified in the context.

[0077] Various devices and parts used herein may be described as "comprising" other components. The terms used herein, such as "comprising," "having," "having," "may," "containing," and variations thereof, are intended to be open connectors, terms, or words that do not exclude the possibility of additional components.

[0078] All ranges disclosed in this specification include the described endpoints and can be independently combined (e.g., the range “2 inches to 10 inches” includes the endpoints 2 inches and 10 inches and includes all intermediate values).

[0079] The approximate language used in this specification may be applied to modify any quantitative expressions that may vary without causing a change in the underlying function. Accordingly, terms such as "approximately" and "substantially," or values ​​modified by such terms, may not, in some cases, be limited only to the specified exact values. The modifier "approximately" should be considered to indicate a range defined by the absolute values ​​of two endpoints. For example, the expression "approximately 2 to approximately 4" includes the range "2 to 4".

[0080] It should be noted that many of the terms used in this specification are relative. For example, the terms "upper" and "lower" are relative to each other in terms of position; that is, the upper component is located at a higher elevation than the lower component, and should not be interpreted as requiring a specific orientation or position of the structure. As an additional example, "inside," "outside," "inward," and "outward" are relative to the center and should not be interpreted as requiring a specific orientation or position of the structure.

[0081] The terms "top" and "bottom" are relative to an absolute standard, namely the Earth's surface. In other words, the top position is always located at a higher altitude than the bottom position closer to the surface.

[0082] The terms "horizontal" and "vertical" are used to indicate direction relative to an absolute standard, namely ground level. However, these terms should not be interpreted as requiring structures to be absolutely parallel to each other or absolutely perpendicular.

[0083] The solution of the present invention to the problems caused by conventional methods of heating and drying thick coatings (e.g., 300 to 1000 μm) on a metal foil substrate is to add internal direct heating of the metal foil independently and preferably simultaneously with the external heating method. Induction heating provides a suitable and unique means to achieve internal selective heating of the metal foil. In the manufacture of lithium-ion battery electrodes, metal foil substrates are typically aluminum and copper in the form of crystal lattice metal ions with very high electrical conductivity. Consequently, the foil structure responds to electromagnetic induction through an electromagnetic field, and this process is known as induction heating. In certain embodiments, the appropriate format for the application of induction heating is an induction heater system and an electrically conductive "component" or object or substrate to be heated, preferably a metal foil web substrate. The web substrate must be at least partially electrically conductive, and in some embodiments, preferably a metal or graphite foil, a metallized and / or graphite / carbon-added web substrate (e.g., a porous, nonwoven, or woven substrate or foil), or a web treated, finished, or coated with other conductivity. In some embodiments, the web substrate has a coating or a coating precursor that becomes a coating upon drying according to the embodiments disclosed herein, or is covered with a coating or a coating precursor. The coating itself does not need to be electrically conductive, but preferably is electrically conductive. The coating or coating precursor is present on at least one major surface of the web substrate, and in some embodiments, may be present on both major surfaces of the web substrate.In some embodiments, the coating or coating precursor is a slurry for electrodes of a lithium-ion battery and may include conductive black carbon, graphite, etc., or may include any suitable amount of nickel, manganese and / or cobalt known to those skilled in the art that has magnetic properties.

[0084] As is known in the art, the inductive heater may include an electromagnet composed of a conductive element of a suitable shape and an electronic oscillator that passes alternating current (AC) through the electromagnet. An alternating magnetic field penetrates the object and generates a current called an eddy current inside the conductive component. The eddy current flowing through the material of the “component” or object overcomes the resistive impedance of the material and heats the material by Joule heating. When heating a web of moving material, the web may be a metal foil substrate that is thickly coated (e.g., 300 to 10000 μm) in at least specific areas, and the coating may be applied to both sides of the foil or to only one side. One or more electrically conductive electromagnetic coils may be placed in close contact with one or both sides of the web in a non-contact manner (e.g., between 5 and 50 mm, preferably 25 mm), and these coils serve as sources of alternating magnetic fields. As illustrated in FIGS. 3a and 3b (where the same reference numerals refer to the same features in other drawings), the electromagnetic coil elements (20) or coil elements are generally positioned in a plane parallel to the center plane of the web substrate (10) (e.g., in a floating dryer, the web is generally floated in a sinusoidal waveform, so in this embodiment, the zero-line of the sinusoidal waveform becomes the center plane) and spaced apart by a certain distance (e.g., 5 to 50 mm) to avoid mechanical contact, and the electromagnetic field surrounding each coil element extends into the plane of the web. In the illustrated embodiment, the web is moved from a feed roller (16) through an induction field and wound by a roller (11).Then, the heat generated within the metal foil substrate tends to raise the foil temperature, which causes the heat within the foil mass to flow to the coating by thermal conduction.

[0085] In a preferred embodiment, the electromagnetic coils are placed inside an oven / dryer enclosure having an oscillating power supply that is electrically connected to or communicates with the coils. A controller may be used to regulate the power supply. The dryer enclosure is configured to have passage openings, such as web entry and exit openings or slots, to provide a web entry path moving into the enclosure and a web exit path moving out of the enclosure. In some embodiments, the dryer enclosure also includes at least one chamber or zone, preferably a plurality of chambers or zones fluidly communicating with one another. For example, the dryer enclosure may have two, three, four, five, etc. drying zones arranged in series in the direction of web movement through the drying enclosure. In some embodiments, the dryer enclosure also includes an air or gas supply or circulation device and one or more air or gas nozzles for heating the web substrate by convection as the web substrate moves within and through zones or sections of the dryer enclosure. Accordingly, in certain embodiments, controlled convection is provided within the enclosure through nozzles or blow boxes (22), which discharge air or gas (e.g., air, oxygen-deficient air, nitrogen) in the form of jets supplied by circulation fans that transport dry air or other gases to promote heat and mass transfer on the surface of the coated web. The air jets from the nozzles (22) may be discharged from one or more consecutive slots or from a plurality of apertures, such as round holes, squares, or other shapes, suitable for uniformly distributing air over the entire surface of the web.Drying air may be heated to a temperature controlled by a resistance coil heater, hot water, steam or thermal oil, or other suitable heating methods known in the field of oven design. Air may be exhausted from the dryer enclosure to ventilate the atmosphere within the dryer to maintain moisture and solvent content at controlled levels and to prevent exfiltration from the dryer enclosure openings, particularly from web entry and exit slots. Additionally, makeup air may be supplied or drawn into the dryer to replace the amount of continuously exhausted air (or other gas). The makeup air may be regulated to control humidity and / or solvent content, which is generally done by controlling the makeup air and exhaust flow rates, and in a preferred case for battery electrode manufacturing, includes drying to a humidity level lower than the dew point of minus 40°C.

[0086] In some cases, the web can withstand mechanical contact with internal oven elements such as rollers.

[0087] IR and conductive heating may also utilize a single-side flotation method using step foils to further optimize the drying process.

[0088] As shown in FIG. 4a, the electromagnetic coil elements (20) may be positioned between the supply air nozzles (22) on one side, with spaced rollers (21) located on the opposite side. It is most preferable that the coil elements (20) be positioned to overlap at least a portion of the convection field generated by the air jets discharged from the nozzles (22) and to generate an electromagnetic field vibrating within it. It should be noted that the air jets discharged from the nozzles (22) are deflected by the web surface when they collide with the web surface (10) and flow along the surface of the web (10) over a certain distance from the point of impact or line, as indicated by the dotted arrow in FIG. 4a. This air flow parallel to the web surface generates the desired simultaneous convective heat and mass transfer in the air / web boundary layer within the space between the electromagnetic coil elements (20) and the web (10).

[0089] In some cases, the web (10) is coated on both sides as in FIG. 1b, so that mechanical contact with the wet coating on both sides of the web (10) needs to be avoided. FIG. 4b shows a preferred embodiment in which one or more coil elements (20) are placed between flotation air bars (23), the flotation air bars (23) provide convective heat and a mass transfer field within the air / web boundary layer in the space between each electromagnetic coil element (20) and the web (10), and position the web (10) without mechanical contact by means of an air cushion support. The floating air bars (23) may be of the Coanda type, each having two slots that form a nozzle for discharging a jet of air that generates a heat and mass transfer field, and forming an air cushion between the two slots for non-contact support of the web, for example, commercially available HI-FLOAT® air bars from Durr Systems, Inc. exhibit high heat transfer and excellent floating characteristics. A standard 1X HI-FLOAT® air bar features a 2.5-inch slot spacing; a slot width of 0.070 to 0.075 inches, typically 0.0725 inches; a 10-inch installation pitch; and a 1 / 8-inch web-to-air bar gap. The air bar size may be larger or smaller. For example, air bars 1 / 2, 1.5, 2, or 4 times the size of the standard size may be used. Generally, as the distance between the slots increases, a larger air pressure pad is formed between the air bar and the web, which allows the air bar spacing to be increased. In a typical dryer configuration with such Coanda floating nozzles, upper and lower opposing nozzle arrays are provided, and each nozzle of the lower array (excluding the nozzle at the end) is located between two nozzles of the upper array.That is, the upper and lower nozzles are arranged staggered relative to each other. In certain embodiments, one or more nozzles are elongated members having one or more outlets for discharging air or gas, such as elongated slots or multiple openings. Each nozzle may include an air or gas receiving compartment, which is in communication with a header to receive air or gas, and the header receives air or gas from a suitable source.

[0090] In the embodiment of FIG. 4b, the Coanda air bars (23) are positioned on both sides of the web (10) in the direction of web movement and are arranged staggered relative to each other. The floating air bars may also be air foil or Bernoulli type (24) as shown in FIG. 4d, which non-contactually support the web (10) on only one side, and each air foil bar (24) forms a flotation pressure field between the surface (25) of the air foil bar and the web (10). The pressure field represents both a positive cushion area and a negative suction area, and these two areas push the web (10) away from the air foil bar surface (25) and pull the web (10) toward the surface by negative pressure, thereby maintaining the web (10) in a stable position without mechanical contact.

[0091] Any number of air bar configurations and arrangements may be used. In each case, the key feature is that one or more air bars generate an air convective field, and one or more electromagnetic coils (20) are arranged so that the nozzle air jet moves within the space between the electromagnetic coils (20) and the surface of the web (10), so that an oscillating magnetic field and a convective jet field acting simultaneously at the same location on the web (10) where the web (10) moves are oscillating. For example, the air bar device may include air floating nozzles for floating the web substrate and direct air impact nozzles to enhance the drying of the web substrate (and / or coating thereon). Thus, a plurality of air floating nozzles or air bars may be mounted in one or more sections of a dryer enclosure, preferably both above and below the web substrate, so as to communicate with headers and air receiving for non-contact convective drying of the web substrate. Along with these air-floating nozzles, one or more sections of the dryer may also include direct impingement nozzles, such as hole-array bars or slot bars. Thus, the drying surface of the web is heated by air ejected from both the air-floating nozzles and the direct impingement nozzles. Consequently, the dryer has a high drying rate within a small, enclosed space while maintaining a pleasant working environment. The nozzle array may include pairs of direct impingement nozzles and pairs of directly opposing air-floating nozzles.

[0092] In some cases, it may be advantageous to fabricate the supply air nozzles or other internal dryer components from electrically nonconductive materials to prevent excitation and induced heating within the material of the supply air nozzles or blow boxes themselves, as they are adjacent to the vibrating magnetic field generated by the induction heating source. In many cases, the heat generated in this way contributes only to the energy required to heat the supply air, and thus these components are effectively cooled by the air. In a very compact array of components, the materials of the structure may expand due to the local temperature of the supply air nozzles, and thermal deformation may occur to an unacceptable level. In such cases, the supply air nozzles, air bars, blow boxes, etc., may be fabricated wholly or partially from nonconductive materials such as high-temperature polymers (e.g., polytetrafluoroethylene (TEFLON®), polyphenylene sulfide (PPS), and other polymers that are heat-stable above 150°C), and, in some cases, may be fabricated in the form of extruded parts reinforced with carbon fiber or glass fiber, or other composites suitable for strength and temperature during dryer oven operation.

[0093] An example of a more compact arrangement is illustrated in FIG. 4c. In this embodiment, the electromagnetic coil elements (20) are integrated within a floating air bar body (24) and act simultaneously with the air jet convection field. In this configuration, it is preferable that at least some of the constituent materials of the air bar body (24) be electrically non-conductive materials so that the electromagnetic field can be generated without interference with the conductive materials within the air bar body. In certain embodiments, in addition to the electromagnetic coil elements (20) integrated within the air bar body (24), additional electromagnetic coil elements (20) may be placed on the opposite side of the air bar body (24), i.e., on the opposite side of the web (10), as illustrated in FIG. 4c. In certain embodiments, the spacing of the additional electromagnetic coil elements (20) may be selected to optimize drying, for example, the center-to-center distance may be selected to be 10 inches, 15 inches, or 20 inches.

[0094] FIG. 5 shows an exemplary embodiment in which a plurality of arrays of the nozzle array of FIG. 4b are mounted within a dryer enclosure (15) configured to process a wet coating applied to both main sides of a web (10). In the embodiment of FIG. 5, the web (10) is conveyed via a roller (11) and supplied to a first slot die coater (12) located opposite the roller (13) so that the first main side of the web (10) is coated, and then the second main side of the web (10) is coated via a second free-span slot die coater (12') located downstream of the roller (14). The double-sided coated web (10) enters the dryer (15) through a web entry opening or slot downstream of the slot die coater. According to certain embodiments, a web lifter or stabilizer (not shown) may be used to move the web to a slot die coater (12) (and / or slot die coater (12')) used for skip coating or intermittent coating operations, as disclosed in US Patent No. 9,908,142, the disclosure of which is incorporated herein by reference. In some embodiments, the web lifter / stabilizer may be operated to move the web away from the die lips of the slot die coater (12 and / or 12') and to stop the application of a coating (e.g., slurry) to the web, thereby creating uncoated areas on the surface of the web. Then, the web lifter / stabilizer device can be operated to move the web to contact the slot die coater again to start applying a coating to the web, thereby creating coated areas on the web surface.In certain embodiments, web lifting is achieved by rotating the device in a first direction to lift the web from the slot die coater, and by rotating the device in the opposite direction to return the web to contact the slot die coater again. A controller may be used to operate the device. Accordingly, in certain embodiments, a coater is provided for intermittently applying a coating to the web, and a web lifter and / or stabilizer may be provided at a first position upstream of the coater in the opposite direction of web movement. When it is desired to form a gap or skip within the coating on the surface of the web, a coating gap (e.g., an area of ​​the web without coating) can be formed on the web by rotating the web lifter body from the first position toward the web to deflect the web away from the coater (e.g., away from the coater lip). The body may be rotated back to the first position once the desired gap is formed, and negative pressure is maintained during the bidirectional rotation.

[0095] In some embodiments, a computer-controlled fluid delivery system may be used to precisely control the operation of valves and the movement of the web lifter / stabilizer to generate multiple coating profiles. This system may include a controller, which is used to operate the valves to start and end the flow of material onto the web through the slot die coater (12 and / or 12'). Additionally, the controller may move the web from an on-coat position to an off-coat position away from the coater by the movement of the web lifter / stabilizer. In some embodiments, a fluid displacement mechanism may be used to temporarily recover coating fluid from the slot die lip during the off-coat cycle and supply coating fluid back to the lip during the next on-coat cycle. In double-sided coating embodiments, the controller may be configured to control the start and end positions of coated patches on opposite sides of the sheet. The registration of the above coating can be programmed to match exactly, or to be ahead or behind by a specific amount. Additionally, the system may be a position-based system and can therefore automatically respond to changes in line speed.Accordingly, such a coating system for coating a material moving along a path may comprise: a nozzle for applying a coating; a supply valve communicating with the nozzle to allow the flow of the coating to the nozzle; a bypass valve for diverting the flow of the coating from the nozzle; a fluid displacement mechanism for withdrawing the coating from the nozzle after the supply valve is closed, wherein the fluid displacement mechanism comprises a chamber having a changeable volume; an actuator, wherein the movement of the actuator is positioned to change the volume; a web lifter movable to deflect a moving material web; and a controller communicating with the supply valve, bypass valve, actuator, nozzle, and web lifter to control the application of the coating to the material web.

[0096] In the embodiment illustrated in FIG. 5, there are two drying zones, the first zone (Zone 1) contains induction heating coil elements (20), and the second zone (Zone 2), located downstream of Zone 1 in the direction of web movement, does not contain induction heating coil elements. Generally, the electromagnetic induction coil elements (20) may be included in a single dryer zone, a portion of the dryer zone, or multiple zones that partially or completely occupy the spaces between the convective air bars. In some cases, the electromagnetic coil elements (20) may be included in all zones along the entire length of the dryer. The coil elements (20) may be located on one side or both sides of the web (10). The web exits the dryer (15) through a web discharge opening or slot and may be wound, for example, by a roller (16).

[0097] Selecting the most advantageous drying method among the various drying methods described above depends at least in part on the data and characteristics of the slurry coating to be applied. These characteristics include the wet thickness of the coating, the number of sides (1 or 2 sides) of the web (10) to be coated, the percentage of solid content of the wet slurry, the type of solvent, the coating line speed, and the behavior of the wet coating film during drying when solidifying. These design data can be determined through pilot or production tests, laboratory tests, and / or computational drying models. When proceeding with drying conditions applied within a drying oven, determining the optimal drying rate based on the percentage of solid content of the coating or residual solvent can be obtained through experimental and / or computational methods, preferably both. For induction heating for drying electrode materials for lithium-ion batteries, as already described, a combination of convection drying and induction heating performed simultaneously is most advantageous.

[0098] An important design point is determining the portion of the dryer length where the induction coil elements (20) will be placed. In practice, when drying an electrode material slurry coated on a foil web, it is often most advantageous to incorporate the induction heating coils at the beginning of the drying process, that is, within the first zone or zones of a multi-zone dryer, and in some cases, in the web path just before the web enters the convection field of the supply air nozzle (Fig. 7). In some cases, as illustrated in Fig. 7 (the same reference numerals indicate the same features in other drawings), one or more electromagnetic coil elements (20') may be mounted outside the dryer just before entering the dryer enclosure (i.e., upstream of the dryer inlet). This promotes early heating of the base foil and initiates heat conduction from the inside to the wet coating, thereby raising the coating temperature to some extent. Optionally, as shown in FIG. 7, induction heating coils (20) can be placed downstream of the dryer (5), for example, upstream of the calendar assembly (200) as shown in the figure, in connection with a calendaring operation.

[0099] As the web enters the convection field generated by the supply air nozzles, the solvent evaporates due to convective mass transfer from the surface. In some cases, as the web moves within the dryer, the temperature of the wet coating remains constant due to the latent heat of vaporization of the solvent, similar to the case of a wet-bulb thermometer, even though convective heat flux is applied and induced heat may be included. In some cases, as the web continues to pass through the dryer, the web temperature may decrease slightly or show only a gradual increase. In most cases, the temperature of the wet coating tends to approach the wet-bulb temperature property of the air supplied to the drying nozzles in the initial zones. This wet-bulb temperature property can be determined from a psychrometric chart or thermodynamic calculations for a water-air or solvent-air mixture. While the coating surface is in a relatively wet state (often even visually), the temperature decreases due to convective drying, which is called the wet bulb depression. When other heat sources, such as induction heating, are added in addition to the nozzle supply air convection, the magnitude of the wet bulb depression decreases. Consequently, the coating tends to have a higher temperature during convective drying with added induction heating. This is not the case when only convective drying is performed, because as long as sufficient moisture (or solvent concentration) is present on the coating surface, the magnitude of the wet bulb depression remains constant regardless of the magnitude of convection. During this drying phase, often referred to as the "constant rate period" of drying, the surface of the electrode slurry coating appears wet and / or dark in color because the surface is rich in solvent (water or organic solvent).As the web (10) moves through the dryer (15) and drying proceeds, the solvent continues to evaporate, and at some point, the liquid solvent on the surface decreases, causing the coating surface to dry out or begin to take on a bright color. As the web continues to move past this drying time and location, the temperature of the coating surface begins to rise more rapidly, indicating that the drying speed is decreasing. The surface is now partially or significantly solidified, but the coating beneath the surface still contains a significant amount of solvent. If the drying speed becomes excessively fast at this critical point and location within the dryer—that is, if drying proceeds too quickly due to the size of the convection field generated by the drying air speed and temperature that occurred before that point—defects such as mud cracks tend to begin to occur. It is most desirable to add induction heating coil elements between the convection air nozzles in the section from the web inlet to the web travel distance (or the same residence time determined by the distance and web speed) along the length of the dryer. In other words, the induction heating zone is preferably from the inlet of the dryer to the location where the constant-speed drying period ends and the deceleration drying period begins. When there are multiple electrode coating products to be processed in a given coating line dryer, this distance is determined based on the wet coating weight thickness, desired line speed, and coating sensitivity to the formation of such bonds for each product, and the longest value among the set of all products is selected. Additionally, considering future demand, it may be desirable to extend the length of the induction heating coil filament by, for example, 25%, or possibly up to 50%, to accommodate new electrode manufacturing specifications and slurry compositions. Accordingly, the induction heating elements may be extended beyond the induction heating zone within the dryer by 25%, 30%, 35%, 40%, 45%, or 50%, or by any percentage between these values.

[0100] FIG. 8 illustrates the application of inductive field coils in a process involving secondary drying. In the illustrated embodiment, the inductive coils are provided within the drying oven. Air discharged from the oven can be circulated to a desiccant dehumidification system as illustrated and then sent back to the drying oven. The path of the web proceeds in the order of unwound, coating, heating, drying, cooling, and rewound. When the web enters the dryer, the inductive coils begin to heat the metal web. The temperature of the web rises until the slurry reaches steady-state evaporation. As the web dries and passes through the air bars, the temperature of the web will drop as the evaporation of the solvent increases. After passing through the inductive heaters, the product remains in the oven for a certain period of time. The product undergoes final drying in this section, leaving only a trace amount of solvent. Drying air is supplied to the dryer. The air containing the solvent exits the dryer and enters the dehumidification unit. This air is heated again and supplied back to the dryer.

[0101] FIG. 9a illustrates the use of induction heating elements (20) in a coating line process in which inline processing takes place. In this embodiment, the dryer (15) contains induction heating elements (20) only in zone 1, and Coanda air bar nozzles (230) are positioned in both zone 1 and zone 2 of the dryer (15) as illustrated. Coating heads (12 and 12') apply a coating to both sides of the web (10) upstream of the dryer (15). The web (10) exits the dryer (15) and moves to a calendering station (27), then undergoes further drying in a secondary dryer (28), after which the web (10) is wound onto a roller (16). As illustrated, induction heating elements (26) may be positioned upstream of the dryer.

[0102] FIG. 9b illustrates an embodiment similar to FIG. 9a, except that the web (10) is sent to a slitting station (29) downstream of a secondary dryer (28) and then undergoes direct post-processing operations.

[0103] FIG. 9c illustrates an embodiment similar to FIG. 9a, including a secondary lamination operation and a slitting station (29) after secondary drying.

[0104] FIGS. 10a, 10b, and 10c illustrate an example of dry powder coating that does not use a dryer enclosure. Induction heating elements (20) are arranged alternately on both upstream and downstream of a fluidized bed dry powder application station (50), preferably on both sides of the web (10).

[0105] When induction heating is applied simultaneously with convection heating, improvements are made in terms of reducing volumetric deformation of the coating layer; however, if induction heating is applied excessively, thermal deformation and buckling may occur in the foil between the coated and uncoated areas, so it is necessary to set a desirable range for induction heating. According to laboratory experiments and numerical simulation results, the contribution of the desirable heating capacity provided to the web from the added induction heating coil elements and their respective vibration power supplies was found to be in the range of 10 to 50% of the total drying energy flux in the constant-speed drying zones. That is, in certain embodiments, the induction heating coil elements and associated vibration power supplies to be installed in the portion of the dryer length described above (induction heating zone) are selected so that the induction energy flux absorbed by the foil web is delivered in the range of 10 to 50% of the total drying heat flux. A controller may be used to control the power supply.

[0106] The determination of the actual limit of the induction heat flux can be based on the estimation of the thermal strain between the coated and uncoated areas of the web, as shown in FIG. 2b. This calculation is based on the material properties of the coated base foil and the design drying rate calculation for convection only performed in the prior art. FIG. 6a shows a drying process performed in a prior art convection dryer. FIG. 6b shows drying with simultaneous induction heating added to the base foil according to specific embodiments. In the case of convection only in FIG. 6a, the magnitude of the thermal strain can be determined by assuming that the exposed bare foil is close to the temperature of the convective air supplied to the air nozzle jet, while the wet coating at the same location along the web movement direction in the oven and the foil in contact with the coating at that location are close to the wet-bulb temperature characteristics of the supply air and the characteristics of the solvent in the wet electrode coating (slurry). The difference between these two temperature values ​​is referred to as the wet bulb depression (wbd) in psychrometric calculations in engineering and meteorology. Since this wet bulb depression value is expressed as a temperature difference, it is appropriate to represent it in units of temperature degrees rather than simple degrees. For example, the wet bulb depression value should be expressed in Celsius (C degrees) or Fahrenheit (F degrees), not °C or °F. Conversions of these temperature difference values ​​must be performed accordingly.

[0107] The described wet-bulb temperature difference value represents, at least as shown in FIG. 2a, the relative magnitude of the thermal deformation occurring between the coated and uncoated areas of the foil along the coating edge or the line created by the edges. The design limit of said thermal deformation can be estimated as follows:

[0108] ΔT strain< (f D x Buckling yield strength) / (Elastic modulus x Coefficient of thermal expansion)

[0109] Here, f D is a deflection force.

[0110] If this temperature difference, estimated from the wet-bulb temperature difference, is reduced, the relative thermal deformation within the foil is also reduced proportionally. For example, if the wet-bulb temperature difference with added induced heat flux is reduced to half the value when only convection is considered, the resulting thermal stress is reduced by substantially half.

[0111] In the case of convection alone, the known wet-bulb temperature difference in the field of humid air is commonly expressed as follows:

[0112] ΔT wbd = Ta - Tw = (Hvap (Yw - Ya)) / (hc / kx)

[0113] Here:

[0114] * Ta is the temperature of the dry air supplied to the nozzle jet

[0115] Tw is the local web temperature Humid air wet-bulb temperature of the supplied air during constant-speed drying

[0116] Hvap is the heat of vaporization of the solvent

[0117] Yw is the solvent humidity at Tw determined from the psychrometric chart or the thermodynamic equation of state.

[0118] * Ya is the humidity of the dry air supplied to the nozzle jet

[0119] (hc / kx) is the ratio of the heat transfer coefficient to the mass transfer coefficient, determined by the Chilton-Colburn equation known in engineering mass transfer literature from generally known solvent properties.

[0120] According to the aforementioned Chilton-Colburn analogy, if the magnitude of the convective heat transfer coefficient increases or decreases, the magnitude of the mass transfer coefficient also increases or decreases proportionally and correspondingly. Therefore, even if the convective heat transfer field in contact with the web is changed by increasing or decreasing the air pressure supplied to the nozzle jet to increase or decrease the impact velocity, or by increasing or decreasing the mass of the nozzle jet to change the flow rate of air supplied from the nozzle jet, the magnitude of the wet-bulb temperature difference remains essentially constant.

[0121] Unlike heating by convection alone, the wet-bulb temperature difference can be altered by adding a non-convective heat flux source. Induction heating provides this thermal mechanism. In a simple but useful approach to estimating this effect, the contribution of induction heating can be expressed as a factor representing the amount of heat flux replacing a portion of the heat flux in the basic case of convection alone; thus, the above equation is modified as follows:

[0122] Reduced ΔTwbd = Ta - Tw = ((1-fi) Hvap (Yw - Ya)) / (hc / kx)

[0123] Here:

[0124] fi is the proportionality factor of the induction flux replacing the heat flux in the basic case.

[0125] For example, if induced heat is applied at a level one-third the magnitude of the basic convective heat flux due to convection alone, fi = 0.33 and the magnitude of the wet-bulb temperature difference decreases to 0.67 times. Comparing Figures 6b and 6a, a decrease in the magnitude of the wet-bulb temperature difference can be confirmed, which corresponds to thermal deformation (ΔT strain It leads to a decrease in ).

[0126] The various operations described herein may include a controller or a control system. Any such control system may use a suitable controller, such as a controller having a processing unit and a storage element. The processing unit may be a general-purpose computing device, such as a microprocessor. Alternatively, the processing unit may be a specialized processing unit, such as a programmable logic controller (PLC) or a proportional-integral-derivative controller (PID). The storage element may use any memory technology, such as RAM, DRAM, ROM, flash ROM, EEROM, NVRAM, magnetic media, or any other medium suitable for storing computer-readable data and instructions. The controller unit may communicate electrically (e.g., wired or wireless communication) with one or more operating units within the system, including one or more valves, actuators, sensors, conveyors, etc. Additionally, the controller may be associated with a human-machine interface (HMI) that displays or informs an operator of one or more parameters related to the operation of the system and / or the execution of the methods described herein. The above storage element may include commands, which enable the system to perform the functions described herein when executed by a processing unit. In some embodiments, more than one controller may be used.

[0127] Example 1

[0128] The drying energy flux due to convection alone in the constant velocity zone is determined through test data from a double-sided air bar nozzle array having a heat transfer coefficient of 85 W / m²-C degree per side, 80°C feed air, and an average zone web temperature of 65°C, basic drying calculations (e.g., the wet-bulb temperature method above), or computational modeling. The basic convective flux derived from the target design drying rate can be calculated as follows:

[0129] q convectio n = 2 hc (Ta-Tw)

[0130] q convection = 2 sides x 85W / ㎡-Cdegree x (80℃-65℃) = 2550W / ㎡

[0131] Note that the wet-bulb temperature difference ΔTwbd = Ta-Tw ​​= 15 C degrees implied in the basic case of convection alone.

[0132] In this example, if the target value of the induction flux is selected as 33% to replace a portion of the convective heat, fi = 0.33. The wet-bulb temperature difference is corrected as follows:

[0133] ΔTwbd = (1 - 0.33) x 15 C degree = 10 C degree

[0134] As illustrated in Fig. 6b, due to the addition of induced heat flux, the temperature of the exposed bare foil tends to rise to a temperature exceeding the temperature of the convective air. Under these conditions, the convective air serves to cool the exposed foil by counteracting the heating caused by the induced flux. An equilibrium point and maximum exposed foil temperature are reached when the induced flux becomes equal to the cooling heat flux of the simultaneous convection field, and for a double-sided convective nozzle array, this is as follows:

[0135] ΔT a-w2 = qi / 2hc = (fi q convection ) / 2hc

[0136] Here, the nomenclature is as described above and is as follows:

[0137] * ΔT a-w2 is the temperature difference between the temperature of the dry air supplied to the nozzle jet and the temperature of the foil web exposed at the end of the simultaneous induction and convection field.

[0138] * qi is the effective induced heat flux that is electromagnetically coupled to the metal foil and generates heat within the foil.

[0139] * hc is the convective heat transfer coefficient transferred to the web by the nozzle jet in the entire convective field generated by the airflow of the nozzle jet per face of the web.

[0140] In this example,

[0141] ΔT a-w2 = 0.33 x 2550 watts / m² / (2 x 85 watts / m² - C degree) = 5 C degree

[0142] As shown in FIG. 6b, the combined thermal deformation is reduced ΔTwbd and ΔT a-w2 It is the sum of.

[0143] ΔT strain = 10 C degree + 5 C degree = 15 C degree

[0144] In this example, the yield strength against buckling is 69 MPa, the elastic modulus is 117,000 MPa, and the coefficient of thermal expansion is 17x10 -3 When a design factor fD of 0.7 is applied to a copper foil with mm / mm per C degree, the design limits are calculated as follows:

[0145] ΔT strain limit = 0.7 x 69 MPa / (117 MPa x 17 x 10 -3 mm / mm-C degree)

[0146] = 24 C degree

[0147] The design induction flux corresponding to 33% of the basic convection case produces thermal deformation smaller than the limit deformation above, so this design is acceptable. If the estimated thermal deformation exceeds the limit, a lower design level for the induction flux is selected and re-evaluated as above until a satisfactory result is obtained.

[0148] When operating, it is preferable that the delivered flux be controlled and regulated to be delivered within the range of 10 to 33% of the convective flux, i.e., within the range of 255 to 842 W / m² which is electromagnetically coupled to the base foil and heats it. In some cases, to provide reverse capacity according to the desired drying speed and drying coating quality considerations, the design specifications of the induction heating elements and the vibration power source may be selected to deliver a larger induction flux exceeding the values ​​calculated above.

[0149] The example described above provides a simplified method for determining the design dimensions of induction heating components. Alternative methods, including the numerical finite element method, analytical mathematics, laboratory or pilot test operations, or other suitable development tools known to those skilled in the art, may also be applied. The calculation of the drying profile in terms of the percentage of solvent within the wet coating and the corresponding volume fraction of the solvent can be determined by finite element calculations. The shrinkage and volume reduction of the wet slurry coating during the drying process can be quantified. A drying case in which induction heating and convection drying are applied simultaneously can be compared with a case in which convection drying is applied only. The application of induction heating can result in a desirable reduction of volume stress occurring within the coating depending on the time or location (drying profile) within the dryer.

[0150] Example 2

[0151] Here, the drying profile and volumetric strain graph shown in Fig. 11a are illustrated as examples, where each web temperature has a given steady-state evaporation rate. Induction heating can heat the web to a higher temperature than when convection heating is used alone. As the product dries, the strain applied to the product increases due to differences in residual solvent layers within the product. Fig. 11b is a graph showing the thermal strain of the foil passing through the dryer. This illustrates the different strains induced in the web under various induction fluxes.

[0152] The following table summarizes the results of numerical finite element modeling for anode battery slurry coating by comparing the case where only convection is used with the case where convection and induction heating at an increasing rate are added simultaneously.

[0153] Numerical calculation of maximum coating volumetric strain 200gms dry coating weight anode coating Design goal induction heat Calculated maximum volumetric strain Calculated thermal strain within the foil (limit = 0.04%) 0% 11.3% 0.04% 10% 5.4% 0.04% 20% 1.2% 0.04% 50% 1.0% 0.10% 90% <1% 0.34%

[0154] As can be seen in the table, most of the beneficial effect of reducing the volumetric strain of the coating during the drying and solidification process is achieved by a small portion of the drying heat flux from the induction flux. In fact, the 10% to 20% range provides a significant improvement compared to when only heating is used (0%). Even when the proportion of induction flux is increased to 90%, the beneficial effect on volumetric strain is negligible or almost non-existent.

[0155] On the other hand, if a dry heat flux contribution of approximately 50% or more is generated from induction heating, significant thermal deformation occurs between the coated and uncoated areas of the foil. Accordingly, when the typical dry coating weight is up to 300g per square meter, the desirable range for induction heating of the anode electrode material is 10% to 30%. For heavier dry coating weights, an analysis similar to the table above indicates that the desirable range for heat flux from induction is 20% to 40%. Although cathode coatings on aluminum foil substrates exhibit similar results in volumetric strain behavior, the thermal strain limit of aluminum foil is approximately twice as large as that of copper, so the cathode material can be dried using an induction heating contribution of up to 50%. To configure the oven system to handle various electrode compositions and dry coating weights, it is preferable that the induction heating coil elements and oscillating power supply be selected and installed to provide an electromagnetically coupled inductive field capacity for heating the foil in the range of 10% to 50% of the total dry heat flux. This indicates a transfer heat flux in a desirable range of 200 to 1500 watts / m² when designing the installation capacity, when the lithium-ion battery electrode materials of the current configuration have a convective heat transfer field of 25 to 125 watts / (m²·degree) per side. This range can be extended to other materials according to the present invention in relation to the desirable limits of volumetric deformation of the coating and the thermal deformation limits of each of the conductive base web materials to be processed and dried.

[0156] Induction heating may be used to raise the temperature of the coated and substantially dried web after calendering (to minimize the size and cost of the secondary dryer and / or maximize the processing speed of the production line), and simultaneous convection may be applied to limit the temperature variation between the coated area and the uncoated area. Likewise, as in the application of secondary drying after the calendering operation on the coated electrodes, for example, at the part indicated by the arrow in the drying / heating curve, when heating the substantially dried coated foil, the induction flux range and variation limit can be determined.

[0157]

[0158] Although various aspects and embodiments are disclosed in this specification, other aspects, embodiments, modifications, and changes will become apparent to those skilled in the art by reading and understanding the foregoing detailed description. The various aspects and embodiments disclosed in this specification are presented for illustrative purposes only and are not intended to be limiting. The invention should be interpreted to include all such aspects, embodiments, modifications, and changes insofar as they fall within the scope of the appended claims or their equivalents.

Claims

Claim 1 A device for drying a web coating on a region of a moving web, wherein the web is at least partially electrically conductive, and the device comprises: a web entry opening and a web discharge opening spaced apart from the web entry opening, at least one drying chamber having at least one nozzle for convectively heating the web, and a dryer enclosure having at least one inductive heater for inductively heating the web; wherein the at least one nozzle and the at least one inductive heater are disposed within the device to simultaneously heat the web coating on the region of the web. Claim 2 The apparatus according to claim 1, wherein the dryer enclosure has a first drying chamber and a second drying chamber downstream of the first drying chamber in the direction of movement of the web. Claim 3 A device according to paragraph 2, wherein at least one induction heater is disposed within the first drying chamber, at least one nozzle for convectively heating the web is disposed within the first drying chamber, and at least one nozzle for convectively heating the web is disposed within the second drying chamber. Claim 4 The device according to claim 1, further comprising at least one induction heater disposed upstream of the web entry opening outside the dryer enclosure. Claim 5 A device according to claim 1, wherein the at least one induction heater comprises one or more electromagnetic coils disposed within the dryer enclosure, and a convective air jet from the at least one nozzle passes through the space between the one or more electromagnetic coils and the surface of the web, so that an oscillating magnetic field penetrating the web and a convective jet field from the at least one nozzle act simultaneously at the same location on the web. Claim 6 A device according to claim 1, wherein the induction heating zone within the dryer enclosure extends from the web entry opening to a location within the dryer enclosure where the constant rate period drying ends and the falling rate period of drying begins. Claim 7 A device according to claim 1, wherein the oscillating power supply accompanying the location of the induction heater is configured to transfer the inductive energy flux absorbed by the web to a range of 1 to 75% of the total drying heat flux within the dryer enclosure. Claim 8 A device according to claim 7, wherein the induced energy flux absorbed by the web is within the range of 10 to 50% of the total drying heat flux within the dryer enclosure. Claim 9 A method for drying a conductive substrate partially covered with at least one layer to be dried, the method comprising the step of heating the substrate by applying convective heat, radiant heat, or both convective heat and radiant heat to the layer while simultaneously generating heat within the substrate by induction heating. Claim 10 In claim 9, the substrate is only partially electrically conductive, and the heating of the substrate is performed at least partially by induction heating. Claim 11 A method according to claim 9, wherein the temperature and heat transfer coefficient provided by the convective air applied for drying the at least one layer are selected and controlled to impart a cooling effect to the substrate which can be heated to a higher temperature by the induction heat. Claim 12 A method according to claim 9, wherein the substrate is electrically conductive, and when the coating weight of the layer is up to 300g per square meter, the range of induction heating of the substrate is 10% to 30%. Claim 13 A method according to claim 9, wherein the substrate is electrically conductive, and when the coating weight of the layer is heavier than 300g per square meter, the induction heating range of the substrate is 20% to 40%. Claim 14 A method for coating a first surface and a second surface of a substrate in a single pass, the method comprising: a. applying a first coating layer to the first surface of the substrate using a first coater; b. applying a second coating layer to the second surface of the substrate using a second coater; c. drying the first and second coating layers non-contactually in a flotation dryer located downstream of the first and second coaters so as to maintain a predetermined level of residual moisture when the first and second coating layers exit the dryer; d. inductively heating the substrate in the flotation dryer while simultaneously convectively heating the first and second coating layers; and e. calendering the coated substrate downstream of the dryer. Claim 15 A method for applying and drying a coating on a web using a system comprising a supply valve, a bypass valve, a nozzle, a web lifter, and a controller for controlling the supply valve, the bypass valve, and the nozzle, wherein the method comprises: inputting reference positions on the web to which the supply valve is to be opened and closed into the controller; inputting reference positions on the web to which the bypass valve is to be opened and closed into the controller; inputting reference positions on the web to which the web lifter is to be operated to move the web toward the nozzle and away from the nozzle into the controller; moving the web past the nozzle; tracking the position of the web; applying the coating to the web by controlling the supply valve, the bypass valve, the nozzle, and the web lifter using the controller based on the input reference positions; and heating the substrate by applying convective heat, radiant heat, or both convective and radiant heat to the coating while simultaneously generating heat within the substrate by induction heating. Claim 16 A system for applying a coating to a material moving along a path and drying said coating, the system comprising: a coater nozzle for applying said coating; a supply valve communicating with said nozzle to allow flow of said coating to said nozzle; a bypass valve for diverting flow of said coating from said nozzle; a fluid displacement mechanism for withdrawing the coating from said nozzle after said supply valve is closed, said fluid displacement mechanism comprising a chamber having a changeable volume; an actuator, said actuator positioned such that movement of said actuator changes said volume; a web lifter movable to deflect said material; a controller communicating with said supply valve, said bypass valve, said actuator, said nozzle, and said web lifter to control the application of said coating; and an apparatus according to claim 1. Claim 17 In paragraph 16, the dryer enclosure comprises a first drying chamber and a second drying chamber downstream of the first drying chamber in the direction of movement of the web, a system. Claim 18 A system according to claim 17, wherein at least one induction heater is disposed within the first drying chamber, at least one nozzle for convectively heating the web is disposed within the first drying chamber, and at least one nozzle for convectively heating the web is disposed within the second drying chamber. Claim 19 In paragraph 16, the system further comprises at least one induction heater disposed outside the dryer enclosure, upstream of the web entry opening. Claim 20 A system according to claim 16, wherein the at least one induction heater comprises one or more electromagnetic coils disposed within the dryer enclosure, and a convective air jet from the at least one nozzle passes through the space between the one or more electromagnetic coils and the surface of the web, such that an oscillating magnetic field penetrating the web and a convective jet field from the at least one nozzle act simultaneously at the same location on the web. Claim 21 A system according to claim 16, wherein the induction heating zone within the dryer enclosure extends from the web entry opening to a location within the dryer enclosure where the constant rate period drying ends and the falling rate period of drying begins. Claim 22 A system according to claim 16, wherein the location of the induction heater and the accompanying oscillating power supply are configured to transfer the inductive energy flux absorbed by the web to a range of 10 to 50% of the total drying heat flux within the dryer enclosure.

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