Abstract:
An improved system for applying a coating to a sheet is disclosed. The system allows precise control of the actuation of the valves and movement of the nozzle to create a plurality of coating profiles. The system includes a controller, which is used to actuate the valves to begin and terminate the flow of material onto the sheet through a nozzle. In addition, the controller may move the nozzle from its operative position to an inoperative position away from the sheet. In some embodiments, a fluid displacement mechanism is used. The controller is also able to coat the opposite side of the sheet. Registration of the coating can be programmed to be in exact alignment, or advanced or delayed by a specific amount.

Description:
[0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 61/474,985, filed Apr. 13, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    There are various applications in which is it desirable to deposit a coating onto at least a portion of a sheet of material. For example, in some embodiments, the electrodes of batteries are produced by applying a layer or coating to a sheet, and then cutting the sheet into portions of a suitable dimension. Of particular importance is that the layer be applied at a uniform thickness. In some embodiments, the layer or coating is not applied to the sheet in the region where the sheet will subsequently be cut. 
         [0003]    Based on this, it is necessary to provide a system that can apply a uniform layer or coating to a sheet, with the ability to enable and disable the application of that layer as required.  FIG. 1  shows a system which may be used to apply such a layer of coating to a sheet. 
         [0004]    The system  100  includes a sheet of material  10  to be coated, which typically proceeds through the system by passing over one of more rollers  15 . 
         [0005]    The coating is typically held in a tank or reservoir  30 . The coating is drawn from the reservoir  30 , through conduit  31  by pump  40 . The coating is then passed through conduit  32  by the action of the pump  40 . 
         [0006]    In the case where coating is not being applied to the sheet  10 , bypass valve  50  is open while supply valve  60  is closed. This allows the coating that is pumped through conduit  32  to pass through conduit  33  and back to reservoir  30 . 
         [0007]    In the case where coating is being applied to the sheet  10 , the bypass valve  50  is closed, while supply valve  60  is opened. This permits the flow of coating through conduit  62  to the nozzle  70 , and onto the sheet  10 . While the supply valve  60  is open, the coating is discharged by the nozzle  70 . However, when the supply valve  60  is closed, the pressure needed to propel the coating through the nozzle  70  is eliminated. In some cases, this causes excess coating material to remain in the cavity, or manifold  71 , and the lips  72  of the nozzle. 
         [0008]    When the supply valve is next opened, this excess material may cause an uneven application of coating to the sheet  10 .  FIG. 2  shows an example of the result of this phenomenon on the coated patch thickness. Coated patch  500  is shown as a cross-section profile of thickness “x” applied to web  10 . As the sheet moves toward the left, starting profile  520  is thicker than the rest of the coating  500 . This excess material  510  is due to the residual coating material that remained in the nozzle  70  after the supply valve was closed  60 . In this figure, the ending profile  525  is shown to be uneven, as the valves may be transitioning while the coating is still being applied. Such an uneven coating may be unacceptable. 
         [0009]    Therefore, to prevent this uneven application, a fluid suction mechanism  80 ′ may be used, as shown in  FIG. 1 . This fluid suction mechanism is used to draw the excess coating that is left in the manifold  71  or on the lips  72  away from the nozzle  70 . 
         [0010]    In operation, pump  40  draws coating material from reservoir  30 . The coating material passes through conduits  31 ,  32  and is directed toward the nozzle  70 , where it is discharged onto the sheet  10  as the sheet is drawn past roller  15 . To stop the flow of coating onto the sheet  10 , the bypass valve  50  is opened and the supply valve  60  is closed, thereby diverting the coating material through conduit  33  and back into the reservoir  30 . To remove excessive coating material that may be present in the manifold  71  or on the lips  72  of the nozzle  70 , valve  85  is opened to suction source  80  so that fluid is drawn by vacuum through conduit  86  which is in fluid communication with die manifold  71 . The suction source  80  is typically comprised of a vacuum reservoir tank in communication with a suction pump to create a draw of fluid from die cavity  71  when valve  85  is opened. Coating fluid material is collected in said reservoir tank and periodically removed for reuse or, more often, discarded as waste material. 
         [0011]    To restart the flow of coating onto the sheet  10 , valve  85  is closed to remove the vacuum drawing fluid through conduit  86 . Bypass valve  50  is closed while supply valve  60  is opened. 
         [0012]    In some embodiments, the nozzle  70  can be moved relative to the roller  15  so as to minimize the amount of coating material that may drip out onto the sheet  10 . The nozzle  70  may move in the direction of the sheet (i.e. up and down in  FIG. 1 ). In other embodiments, the nozzle  70  moves orthogonal to the sheet (i.e. in and out of the page). The movement of the nozzle  70  may be linear or rotational. 
         [0013]    It would be advantageous if there were no need for a fluid suction mechanism in the system and the associated handling and disposal of coating fluid. Furthermore, it would be beneficial if there were an enhanced system and method for creating a coating on a sheet, where the starting profile and ending profile may be controlled to create various patterns at high production rates without the use of a suction mechanism. 
       SUMMARY 
       [0014]    An improved system for applying a coating to a sheet is disclosed. The system allows precise control of the actuation of the valves and movement of the nozzle to create a plurality of coating profiles. The system includes a controller, which is used to actuate the valves to begin and terminate the flow of material onto the sheet through a nozzle. In addition, the controller may move the nozzle from its operative position to an inoperative position away from the sheet. In some embodiments, a fluid displacement mechanism is used. The controller is also able to coat the opposite side of the sheet. Registration of the coating can be programmed to be in exact alignment, or advanced or delayed by a specific amount. In addition, the present system is a position based system, thereby being capable of automatically accommodating changes in line speed. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0015]      FIG. 1  shows a representative prior art system that may be used to apply a layer of coating to a sheet; 
           [0016]      FIG. 2  shows the profile of a coating applied to the sheet using the system of  FIG. 1 ; 
           [0017]      FIG. 3  shows a representative system of the present invention; 
           [0018]      FIG. 4  shows a timing diagram used to produce the coating profile of  FIG. 2 ; 
           [0019]      FIG. 5  shows a second profile of a coating that may be applied to a sheet; 
           [0020]      FIG. 6  shows a timing diagram used to produce the coating profile of  FIG. 5 ; 
           [0021]      FIG. 7  shows a third profile of a coating that may be applied to a sheet; and 
           [0022]      FIG. 8  shows a timing diagram used to produce the coating profile of  FIG. 7 . 
           [0023]      FIG. 9  shows a representative embodiment of an optional fluid displacement mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 3  shows a representative embodiment of the present invention. In this embodiment, the system comprises a reservoir  30 , pump  40 , bypass valve  50 , supply valve  60 , nozzle  70 . Optionally, a fluid displacement mechanism  90 ′ is included to alternatingly draw and replace a small volume of fluid through conduit  96 . A controller  210  is incorporated into the system, which is able to control the actions of the bypass valve  50 , the supply valve  60 , and the nozzle  70 . In some embodiments, which utilize a fluid displacement mechanism, the controller  210  controls the actions of fluid displacement actuator drive  91 . 
         [0025]    The controller  210  includes a processing unit which executes computer readable instructions, adapted to perform the actions described below. The processing unit may be a general purpose computing device, such as a microprocessor. Alternatively, it may be a specialized processing device, such as a programmable logic controller (PLC). The controller  210  also contains a storage element, which is used to store the instructions, as well as provide temporary storage for the processor&#39;s use. The storage element may utilize any memory technology, such as RAM, ROM, EEPROM, Flash ROM, NVRAM, or any other suitable technology. The controller  210  also includes an input device, such as a touchscreen, keyboard, or other suitable device. The input device is used to allow the operator to input a set of parameters or a profile which should be used by the controller  210 . This input device may also be referred to as a human machine interface or HMI. The controller  210  also has outputs adapted to control the valves and nozzle as described above. These outputs may be analog or digital in nature, and may provide a binary output (i.e. either on or off), or may provide a range of possible outputs, such as an analog signal or a multi-bit digital output. Using these outputs, the controller  210  is able to control the opening and closing of bypass valve  50  and supply valve  60 , as well as the speed at which these operations occur. Similarly, it can control the movement of the nozzle  70 , as well as the speed of that movement. 
         [0026]    The valve actuators  51  and  61  driving valves  50  and  60 , respectively, and fluid displacement actuator  91  driving chamber  90  are preferably servomotor drives having precise positioning capability at high travel speed. Preferably, the actuators  51  and  61  are capable of driving their respective valves through the travel range from open to closed and closed to open positions in less than milliseconds. Similarly, actuator  91  is selected to expand volume chamber  90  in less than 50 milliseconds and return to the compressed position in less than 50 milliseconds. Coating nozzle  70  is positioned by actuator  73 , preferably a linear motor having positioning capability at high travel speed to allow movement from pull-back to operating position and from operating position to pull-back position in less than 50 milliseconds. 
         [0027]    To establish a profile of the thickness of one or more coated patches to be applied along a length of a sheet comprising a continuous web in the direction of web travel, the operator may enter the position on the sheet referenced to a starting position, and additional reference positions defined in terms of web travel distance for control of actuation of the various valves  50 ,  60  and nozzle  70 . These reference positions are initially determined from the desired lengths of coated and uncoated areas to be applied to the web to produce one or more coated patches of precise dimension along the direction of web movement with intervening segments of uncoated web having a second precise dimension along said web movement direction. These reference position parameters may also be adjusted depending on various criteria, such as the fluid rheology, and slot die setup. 
         [0028]    The following describes an example in which the operator sets the parameters to produce coated patches of a precise desired length. Referring to the supply valve  60 , the operator may provide the “position at which the valve opens”, “position at which the valve closes”, or an intermediate “open” and “closed” positions wherein the valve is partially open or partially closed. In some embodiments, the operator may supply a set of positions and a corresponding indication of the state of the valve, such as 20% open, 40% open, etc. In some embodiments, the opening and closing of the valve  60  may follow a custom mathematical curve. For example, the mathematical curve may be a linear ramp, an exponential function, a step function, or a parabolic function, or any combination of the previous. Similar parameters may be used for the bypass valve  50 . In one embodiment, profiles are determined through a working knowledge of the coating being applied and by generating a corresponding timing diagram. The valve timing and open/close profiles are then refined through experimentation. 
         [0029]    The movement of the nozzle  70  can also be controlled by the controller  210 . In some embodiments, the nozzle  70  is moved by an actuator  73  perpendicular to the surface of roller  15 . The operator may enter a reference position when the nozzle  70  starts moving away from the roller  15 . The operator may also enter a reference position when the nozzle  70  moves toward the roller  15 . Subsequently, the speed of movement is automatically adjusted based on the line speed and web position relative to the slot die. As above, a graph of the position of nozzle  70  vs. sheet position may be a simple linear ramp, an exponential function, or a parabolic function. This graph determines the speed of movement of the nozzle  70 . In some embodiments, the operator may supply a set of reference positions and a corresponding indication of the state of the nozzle, such as 20% away from roller, 40% away from roller, etc. 
         [0030]    Similarly, the movement of the optional fluid displacement mechanism  90 ′ may be likewise programmed and controlled. 
         [0031]    It is likely that certain combinations of parameters for the valves  50 ,  60 , nozzle  70  and fluid displacement mechanism  90 ′ will be utilized frequently. Therefore, in lieu of entering all of the parameters for each component separately, the operator may create a “recipe”, which is a predefined set of parameters which describe the operation of all of the components. At a later time, the operator can simply enter the name of the recipe, which conveys all of the associated details movement information to the processing unit. In some embodiments, the details of each recipe are stored in the storage element in the controller  210 . For example, a “recipe” may be stored that generates the coating pattern shown in  FIG. 5 , while a second “recipe” generates the coating pattern shown in  FIG. 7 . In addition, the recipe may be stored locally and control only the coated patch profiles, or it may be stored remotely as part of a larger global recipe that stores other variable conditions such as line speed, web tension, dryer settings, and settings for other equipment that is integrated to the coating line. 
         [0032]    Using this controller, the operating characteristics of the various components can be programmed to create a wide range of coating profiles. For example,  FIG. 4  shows the operation of the bypass valve  50 , the supply valve  60 , and the nozzle  70  which can be used to create the profile shown in  FIG. 2 . The horizontal axis represents distance on the sheet. This profile assumes that the coating is applied for 200 mm, and then is not applied for 30 mm. This pattern is then repeated. The embodiments disclosed herein are not limited to this pattern. Indeed, the coated and uncoated portions can be as small as 1 mm and can be arbitrarily large. 
         [0033]    The following embodiments utilize the reference position of the sheet along the direction of web travel to determine the actions of the various components. The position of the substrate materials is tracked by a high resolution encoder  220  attached to a roller shaft. In another embodiment, the encoder is coupled to a drive motor that represents web movement. Upon initial start of the coating operation, the length of web travel in relation to the location of die lips  72  is computed from encoder information and translated into terms of web reference position. The signals from encoder  220  are in communication via a data bus to the servo drive controls of servomotors  51 ,  61 ,  73  and  91  to carry out the respective positioning actions of valves  50 ,  60 , slot die  70  and fluid displacement chamber  90 , respectively. As is known to those skilled in the knowledge of application of servo drives, these positioning actions may be carried out at very high speed with excellent precision according to mathematically programmed cam action profiles defined by the user. Positioning actions of two or more actuators may be coordinated to obtain precise control of the patch location and coating thickness profile and are represented as timing diagrams. 
         [0034]      FIG. 4  shows an example timing diagram wherein at reference position 199.5 mm, the bypass valve  50  begins to open, while the supply valve  60  begins to close. This operation is completed by reference position 200 mm, therefore the transition between the coating region and the uncoated region is very abrupt. This rapid transition tends to leave excessive coating in the nozzle  70 , which is unevenly applied when the supply valve  60  next opens at time  230  (see  FIG. 2 ). While the valves  50 ,  60  are being actuated, the nozzle is moved from its operational position to an inoperative position, away from the roller  15 . This movement begins at reference position 199.5 mm and ends at reference position 200 mm. The coating is again applied at reference position 230 mm. In preparation for this application, the bypass valve  50  begins to close at reference position 229.5 mm. The bypass valve  50  is closed by reference position 230 mm. The supply valve  60  executes a similar profile going from the closed state to the open state beginning at position 229.5 mm and ending at position 230 mm. The nozzle  70  is also moved into the operational position as well. This movement begins at reference position 229.5 mm and is completed by reference position 230 mm. 
         [0035]    It should be noted that while the examples presented herein demonstrate the supply valve  60  and the bypass valve  50  operating in concert, this is not a requirement. In other words, these valves  50 ,  60  are separate and their actuation may be controlled separately. In another embodiment, a three way valve may be employed, in which case, the actuation of these valves would be dependent on each other. 
         [0036]    In some embodiments, particularly at higher coating speeds exceeding 5 meters per minute, a fluid displacement mechanism  90 ′ is preferably used as shown in  FIG. 3 . In these embodiments, the fluid displacement mechanism  90 ′ may be a chamber  90  having a changeable volume and a single fluid connection  96 , such that when the volume increases, material is drawn away from the nozzle lips  72  into cavity  71 , through conduit  96  and into the chamber. Conversely, when the volume decreases, material in the chamber  90  is forced back through conduit  96  into the nozzle cavity  71  and into nozzle lips  72  and is applied to the sheet. In the profile shown in  FIG. 4 , the fluid displacement chamber  90  of  FIG. 3  is preferably driven by a linear actuator  91  which begins to expand the volume of chamber  90  at reference position 199.5 mm and is fully expanded by reference position 200 mm. When the material is to be applied again, the fluid displacement chamber  90  is decreased in volume by actuator  91  at reference position 229.5 mm. This chamber contraction is complete at reference position 230 mm. 
         [0037]    Referring to  FIG. 9 , the fluid displacement mechanism  90 ′ may be comprised of a sealed bellows or diaphragm element to form chamber  90  which is attached to stationary frame  97  which supports both the chamber  90  and actuator  91 . Actuator  91  is mechanically connected to the diaphragm element of chamber  90  by a mechanical coupling  92  to move the position of the diaphragm inward to chamber to reduce the internal volume, or outward from chamber  90  to increase the internal volume. Fluid conduit  96  is in fluid communication with the internal volume of chamber  90  and is also in fluid communication with the fluid system of  FIG. 3 . Prior to operation, the chamber  90  and conduit  96  are filled with coating fluid, coating solvent, or other suitable fluid media to prime the fluid displacement mechanism. In operation, the actuation distance “Y” is controlled by actuator  91  in accordance with the instructions from controller  210  of  FIG. 3 . In order to allow fast actuation of the fluid displacement action, the design of the diaphragm element of chamber  90  is to be made with consideration of minimizing the actuation distance while obtaining the desired change in internal volume in the expanded state versus the volume in the contracted state. Travel distance is preferably less than 6 mm for a response speed less than 50 milliseconds. The diaphragm may be selected from commonly available elastomeric materials, optionally reinforced with fabric strands, and sealed to a rigid shell or bowl to form the variable volume chamber  90 . In a preferred embodiment, the volume chamber is constructed as a metal bellows of corrosion and solvent resistant material such as T304 stainless steel. A single bellows type is preferred for effective priming of the chamber to avoid inclusion of air bubbles during operation. The forgoing descriptions of the variable volume chamber  90  are meant to be exemplary as numerous designs of bellows and diaphragm elements are known to those skilled in the art and may be applied to meet the requirements for minimal actuation distance, fast speed, and volume displacement. 
         [0038]    It is to be appreciated that the coating fluid contained in chamber  90 , conduit  95 , cavity  71  and die lips  72  undergoes a reversal in flow direction for each actuation by actuator  91  such that fluid is temporarily displaced from the exit of die lips  72  into the die cavity  71  and into fluid displacement chamber  90  when expanded and then returned via the same path to the die lips  72  when the chamber  90  is compressed. Therefore, coating fluid is not withdrawn from the process to accommodate the control of the deposition of fluid on the web to make discrete coated patches of precise dimension. 
         [0039]    Of course, other coating profiles may be desired.  FIG. 5  shows a coating profile where the leading edge  540  is much more even than that of  FIG. 2 . Trailing edge  545  is also more even and abrupt. To create this profile, the timing and speed of the various components is modified from that explained in conjunction with  FIG. 4 . A representative timing diagram that may be used to create this coating profile is shown in  FIG. 6 . 
         [0040]    In this profile, the supply valve  60  and bypass valve  50  are controlled so as to begin closing earlier. In this profile, these valves  50 ,  60  begin transitioning by reference position 195 mm and are completely transitioned by reference position 196 mm. The nozzle  70  is not moved until reference position 199.5 mm, and is quickly moved away from the roller  15 . When the coating is to be applied again, the valves begin transitioning by reference position 228 mm and are completely transitioned by reference position 229.5 mm. The nozzle  70  is moved toward the roller  15 , starting at reference position 229 mm and is completed by reference position 230 mm. In those embodiments where a fluid displacement mechanism  90 ′ is utilized, the fluid displacement chamber  90  begins to expand at reference position 199 mm and is fully expanded by position 200 mm. Before the coating is applied again at position 230 mm, the fluid displacement chamber  90  begins to contract at reference position 229 mm. Its contraction is completed at reference position 230 mm. 
         [0041]      FIG. 7  shows another coating profile that can be created using the present invention. In this embodiment, the leading edge  562  is ramped to its maximum value. Similarly, the trailing  565  is tapered, rather than abrupt.  FIG. 8  shows a timing diagram that may be used to create this profile. In this embodiment, the valves  50 ,  60  open and close more slowly, so as to create the tapered leading edge  562  and trailing edge  565 . 
         [0042]    It should be noted that the representative timing diagrams described herein are not the only timing diagrams that can be used to create the desired coating profiles. In addition, other coating profiles are possible and can be created by varying the operation of the valves, nozzle and fluid displacement mechanism. 
         [0043]    The use of a controller to control the actuation of the valves  50 ,  60  and the movement of the nozzle  70  may allow the elimination of a fluid displacement mechanism  90 ′, particularly at coating speeds below 5 meters per minute. For example, by precisely controlling the position and the speed at which the valves turn on and off, the amount of excess coating that remains in the nozzle  70  can be reduced. 
         [0044]    In the examples above, the system is programmed by referencing all actuations to position. In another words, the system receives input wherein an absolute position and a desired action are presented together. However, other points of references may be used to indicate when an action should take place. For example, the actions of the valves  50 ,  60  and the nozzle  70  may be referenced to the turn-on and turn-off positions. For example, the user may specify that the coating should be applied for 200 mm, followed by a 30 mm uncoated region. The actuation of the valves  50 ,  60  may be input as relative offsets from these turn-on and turn-off positions. Referring to  FIG. 6 , the valves would be programmed to being transitioning at position offset −6 mm (200 mm−194 mm), and would complete this transition at position offset −4 mm. Similarly, the next transition of the valves would be referenced to the turn-on position (230 mm). This method of conveying information to the controller may be extremely valuable, as it allows the same coating profiles to be used with different length regions, by simply modifying the turn-on and turn-off locations, without modification to the other parameters. 
         [0045]    Another advantage of the position based reference system described herein is that the controller may automatically compensate for changes in coating speed. For example, if the speed of the roller  15  is changed, the controller can determine that the times associated with each actuation are different and can compensate for this change and generate the same coating profile as was done previously. 
         [0046]    The controller can also be used to apply a coating to the opposite side of a previously coated sheet as well. In some embodiments, it is imperative that the coating patches on the first side are exactly aligned with those created on the opposite side. In other embodiments, it may be desirable to advance or delay the application of coating relative to the pattern on the first side. Using the input device, the operator can program the registration of the opposite side. In some embodiments, this is achieved by programming the start and stop positions to have a certain relationship to the previously applied coatings on the first side. In other embodiments, the operator enters the desired offset (i.e. 0 indicates alignment, positive values indicate a delay and negative values indicate an advancement). In this embodiment, the system may contain a vision system  230  as shown in  FIG. 3  positioned to view the previously coated patches and capable of detecting the transition between an uncoated region and a coated region. Once this web position point is determined, the controller can use the speed of the roller  15  as computed from the signal of encoder  220  or a suitable roller drive information signal to determine the time at which coating should be applied to the second side. The vision system  230  may be comprised of a contrast sensor in data communication with controller  210  and with servo drives controlling actuators  51 ,  61 ,  71  and  91 . A number of such vision systems are available in the industrial controls and sensors market and may be selected to provide fast response speed in order to report the detected transitions from coated to uncoated locations on the moving web and from uncoated to coated locations in order to effect timely action by controller  210  and the servo drives controlling servomotors  51 ,  61 ,  71 , and  91 . Response time for the contrast sensor device is preferably less than 100 microseconds. In embodiments including the vision system for registration of patches, the controller  210  must be capable of processing all mathematical operations to initiate the actuator and drive motor actions at a frequency at least 2 times the rate at which the desired coated patch sequences (coated and uncoated lengths) are passing by the sensor  230 . 
         [0047]    Another, more preferred type of registration controller not only senses the edge of the coating patch before it arrives at the coating head for alignment of the coating patches, but also has a second set of sensors  231  and  232  that measure the alignment of the two coated patches and compares the measured value against the target value and automatically applies a correction to the registration distance of the subsequent coated patch. This type of system provides for more robust operation by providing both feed-forward and feed-back control of the coating registration process and can automatically compensate for the time lags associated with communication delays among the various control systems used in the entire coating device. Furthermore, this preferred type of registration system improves the production yield by reducing the number of defects caused during changes in the coating line speed, or tension changes due to splices, for example. 
         [0048]    Another benefit from the preferred coating registration method is that the coating patches are automatically measured and the measurement data can subsequently be recorded into a data logging system for statistical analysis and quality control. 
         [0049]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.