Patent Publication Number: US-2023140800-A1

Title: Slot Die Coater

Description:
TECHNICAL FIELD 
     The present disclosure relates to a slot die coater, and more particularly to a slot die coater capable of uniformly forming a coating boundary formed in a machine direction (MD). The present application claims priority to Korean Patent Application No. 10-2020-0141477 filed on Oct. 28, 2020 in the Republic of Korea, the disclosures of which are incorporated herein by reference. 
     BACKGROUND ART 
     As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and such secondary batteries essentially include an electrode assembly which is a power generation element. The electrode assembly has a form in which a positive electrode, a separator, and a negative electrode are stacked at least once, and the positive electrode and the negative electrode are prepared by applying and drying a positive electrode active material slurry and a negative electrode active material slurry on a current collector made of aluminum foil and copper foil, respectively. In order to equalize charging/discharging features of secondary batteries, the positive electrode active material slurry and the negative electrode active material slurry should be uniformly coated on the current collector, and a slot die coater is conventionally used. 
       FIG.  1    shows an example of a coating method using a conventional slot die coater.  FIG.  2    is a cross-sectional view of the slot die coater taken along II-II′ of  FIG.  1    along a machine direction (MD) (a traveling direction of a current collector). 
     Referring to  FIGS.  1  and  2   , in an electrode manufacturing method using a slot die coater  30 , an electrode active material slurry discharged from the slot die coater  30  is applied on an current collector  20  transferred by a coating roll  10 . The electrode active material slurry discharged from the slot die coater  30  is widely applied on one surface of the current collector  20  to form an electrode active material layer. The slot die coater  30  includes two die blocks  32  and  34  and forms a slot  36  between the two die blocks  32  and  34 . The electrode active material slurry supplied from a feed portion (not shown) is accommodated in a manifold  38 , and discharged through a discharge port  40  communicatively connected to the slot  36 , thereby forming the electrode active material layer. Reference numerals  42  and  44  denote die lips which are front ends of the die blocks  32  and  34 , respectively. 
     A coating width of the electrode active material layer coated on the current collector  20  is determined according to a width of the slot  36 . When it is necessary to change the coating width, various coating widths may be implemented by changing a shim plate  50  that determines an inner space of the manifold  38  and the width of the slot  36 . In this regard,  FIGS.  3 A to  3 C  schematically show examples of adjusting the coating width by varying the size and shape of the shim plate  50  inserted between the die blocks  32  and  34 . 
     Referring to  FIG.  3 A , the shim plate  50  includes an open portion  50   a  by cutting one region thereof and is interposed in the remaining parts except for one side of an edge region of an opposite surface of each of the die blocks  32  and  34 . A width of the open portion  50   a  of the shim plate  50  is designed such that an electrode active material layer  60  having a coating width a is formed on the current collector  20 , and uncoated portions  62  are formed on both sides of the electrode active material layer  60 . 
     Referring to  FIG.  3 B , in order to form the electrode active material layer  60  having a coating width b smaller than a on the current collector  20 , the width of the open portion  50   a  of the shim plate  50  is designed as b. 
     If necessary, the electrode active material layer  60  having a stripe pattern shape may be formed on the current collector  20 . In such a case, the shim plate  50  as shown in  FIG.  3 C  is used. Referring to  FIG.  3 C , a region of the shim plate  50  is intermittently cut so that the shim plate  50  includes a plurality of open portions  50   a,  and the width of the open portion  50   a  is c smaller than a or b. When such a shim plate  50  is used, the electrode active material layer  60  having the coating width c is formed on the current collector  20  in a plurality of stripe pattern shapes as many as the number of the open portions  50   a,  and the uncoated portions  62  are formed on both sides of the electrode active material layer  60 . 
     It should be noted that, in  FIGS.  3 A to  3 C , a die lip  42  and the end of the shim plate  50  are aligned. For various reasons, when a coating gap, that is, a distance between the discharge port  40  of the slot die coater  30  and the current collector  20  (or a distance between the die lips  42  and  44  and the current collector  20 ) is small, in particular, when the coating gap is smaller than a coating thickness, a large pressure is applied to the discharged electrode active material slurry due to the small coating gap. For this reason, the following problems frequently occur when the electrode active material layer  60  having the stripe pattern shape as shown in  FIG.  3 C  is formed. 
       FIG.  4    is a diagram showing a problem when a conventional shim plate is used. Referring to  FIG.  4   , as a result of applying a large pressure to a discharged electrode active material slurry, a defect caused by intermittently scattering the electrode active material slurry to a region outside a boundary, rather than stably forming the boundary between the electrode active material layer  60  and the uncoated portion  62 , is illustrated. As the electrode active material slurry scatters and is coated on the uncoated portion  62 , contamination of a boundary portion occurs, or non-uniformity of a boundary such as a wave pattern occurs on the boundary. A coating boundary formed in an MD needs to be uniformly formed in order to avoid a slitting defect when slitting along the uncoated portion  62  later to form an electrode with each electrode active material layer  60 , and to prevent possible occurrence of an electrode disconnection after a secondary battery is manufactured due to the contamination remaining in the uncoated portion  62 . 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a slot die coater capable of uniformly forming a coating boundary formed in a machine direction (MD). 
     These and other objects and advantages of the present disclosure may be understood from the following detailed description and will become more fully apparent from the exemplary embodiments of the present disclosure. Also, it will be easily understood that the objects and advantages of the present disclosure may be realized by the means shown in the appended claims and combinations thereof. 
     Technical Solution 
     In one aspect of the present disclosure, there is provided a slot die coater including at least two die blocks; a shim plate provided between the two die blocks to form a slot; and a manifold provided in the die block and configured to accommodate a coating solution, wherein the coating solution is discharged and applied to a substrate through a discharge port communicatively connected with the slot, and wherein an end of the shim plate is moved backward relative to a die lip which is a front end of the die block such that the end of the shim plate is offset with respect to the die lip which is a front end of the die block. 
     A size of the offset may be 50 μm to 2000 μm. 
     The shim plate may include an open portion by cutting one region thereof so that a coating width of a coating layer applied on the substrate is determined. 
     The shim plate may include a plurality of open portions by intermittently cutting one region thereof so that a coating width of a coating layer applied on the substrate is determined, and the coating layer of a stripe pattern shape may be formed on the substrate. 
     In another aspect of the present disclosure, there is provided a dual slot die coater including a lower die block; an intermediate die block disposed on an upper portion of the lower die block to form a lower slot therebetween; an upper die block disposed on an upper portion of the intermediate die block to form an upper slot therebetween; a lower shim plate configured to define the lower slot; and an upper shim plate configured to define the upper slot, wherein the lower die block, the intermediate die block, and the upper die block respectively comprise a lower die lip, an intermediate die lip and an upper die lip forming front ends thereof, a lower discharge port communicatively connected with the lower slot is formed between the lower die lip and the intermediate die lip, and an upper discharge port communicatively connected with the upper slot is formed between the intermediate die lip and the upper die lip, the dual slot die coater is configured to discharge and apply an electrode active material slurry to a surface of a continuously traveling substrate through at least one of the lower slot and the upper slot and form an electrode active material layer, and ends of the lower shim plate and the upper shim plate are moved backward relative to the lower die lip, the intermediate die lip and the upper die lip so as to be offset relative to the lower die lip, the intermediate die lip and the upper die lip. 
     Each of the lower shim plate and the upper shim plate may include an open portion by cutting one region thereof so that a coating width of an electrode active material layer formed on the substrate is determined. 
     Each of the lower shim plate and the upper shim plate may include a plurality of open portions by intermittently cutting one region thereof so that a coating width of an electrode active material layer formed on the substrate is determined, and the electrode active material layer of a stripe pattern shape is formed on the substrate. 
     The lower shim plate and the upper shim plate may be aligned with each other in an up and down direction. 
     The lower die block may include a first manifold accommodating a first electrode active material slurry and communicatively connected with the lower slot and the intermediate die block may include a second manifold accommodating a second electrode active material slurry and communicatively connected with the upper slot. 
     The lower shim plate is interposed between the lower die block and the intermediate die block to adjust a width of the lower slot, and the upper shim plate is interposed between the intermediate die block and the upper die block to adjust a width of the upper slot. 
     An offset size A of the upper shim plate and an offset size B of the lower shim plate may be the same. 
     An offset size A of the upper shim plate may be different from an offset size B of the lower shim plate. 
     The dual slot die coater may be configured to simultaneously discharge two types of electrode active material slurries through the upper slot and the lower slot to form an electrode active material layer of a double layer on the substrate, and when a coating gap G to a coating solution thickness D of the electrode active material slurries formed on the substrate is equal to or greater than 1.06, with respect to an offset size A of the upper shim plate and an offset size B of the lower shim plate, A:B may be set to 7:1 to 1:7. 
     Advantageous Effects 
     According to an aspect of the present disclosure, the end of the shim plate is moved backward relative to the die lip so as to be offset relative to the die lip. According to this configuration, even if a large pressure is applied to the coating solution discharged from the discharge port when the coating gap is small, after the coating solution is sufficiently expanded from the end of the shim plate in an offset section, that is, after a certain part of the discharge pressure is relieved, the coating solution may leave the die lip and reach the substrate so that the coating solution does not scatter. Accordingly, the boundary may be stably formed between the coating portion and the uncoated portion. 
     According to another aspect of the present disclosure, the dual slot die coater optimized for application of the electrode active material slurry is provided. The end of the shim plate is also moved backward relative to the die lip so as to be offset relative to the die lip. According to this configuration, even if a large pressure is applied to the electrode active material slurry when the coating gap is small, the coating solution does not scatter. Accordingly, the boundary may be stably formed between the coating portion and the uncoated portion. In particular, when the electrode active material layer having a stripe pattern shape is formed, it is possible to stably form the electrode active material layer without contamination of the boundary or non-uniformity of the boundary such as a wave pattern on the boundary. 
     According to another aspect of the present disclosure, the dual slot die coater capable of simultaneously discharging two types of electrode active material slurries through the upper slot and the lower slot and forming the electrode active material layer of a double layer on the substrate is provided. It is possible to stably form a boundary between the electrode active material layer of a double layer and the uncoated portion. Accordingly, it is possible to obtain a coating product of uniform quality, particularly an electrode for a secondary battery. 
     According to another aspect of the present disclosure, when the coating gap relative to the thickness of the coating solution is equal to or greater than a predetermined value, with respect to the offset size A of the upper shim plate and the offset size B of the lower shim plate, even A:B is adjusted, and thus a pattern defect may be completely prevented. 
     When the slot die coater of the present disclosure is used, it is possible to uniformly form the coating layer, particularly the electrode active material layer, with a desired thickness and shape, and preferably, it is possible to simultaneously coat two types of electrode active material slurries, and thus both performance and productivity are excellent. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The accompanying drawings illustrate a preferred embodiment of the present disclosure and together with the foregoing disclosure, serve to provide further understanding of the technical features of the present disclosure, and thus, the present disclosure is not construed as being limited to the drawing. 
         FIG.  1    is a schematic diagram showing an example of using a slot die coater according to the conventional art. 
         FIG.  2    is a cross-sectional view taken along II-II′ of  FIG.  1   . 
         FIGS.  3 A to  3 C  show various examples of using a conventional slot die coater. 
         FIG.  4    is a diagram showing a problem when a conventional shim plate is used. 
         FIG.  5    is a cross-sectional view of a slot die coater according to an embodiment of the present disclosure. 
         FIG.  6    is a schematic exploded perspective view of a slot die coater according to an embodiment of the present disclosure. 
         FIG.  7    shows an example of use of a shim plate in a slot die coater according to an embodiment of the present disclosure. 
         FIG.  8    is a schematic cross-sectional view of a dual slot die coater according to another embodiment of the present disclosure. 
         FIG.  9    is a schematic exploded perspective view of a dual slot die coater according to another embodiment of the present disclosure. 
         FIG.  10    shows an example of use of a lower shim plate in a dual slot die coater according to another embodiment of the present disclosure. 
         FIG.  11    is a side view of the dual slot die coater shown in  FIG.  8   . 
     
    
    
     MODE FOR DISCLOSURE 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the disclosure, so it should be understood that other equivalents and modifications could be made thereto without departing from the scope of the disclosure. 
     The slot die coater or the dual slot die coater of the present disclosure is an apparatus including a slot and coating a coating solution on a substrate through the slot. Since the dual slot die coater includes a lower slot and an upper slot, the dual slot die coater is an apparatus capable of coating a coating solution in a double layer. The ‘substrate’ described below is a current collector and the coating solution is an ‘electrode active material slurry’. Both a first coating solution and a second coating solution are electrode active material slurries, and may mean electrode active material slurries that have the same or different composition (types of an active material, a conductive material, and a binder), content (an amount of each of the active material, the conductive material, and the binder), or physical properties. In particular, the dual slot die coater of the present disclosure is optimized for electrodes manufactured by applying at least two types of electrode active material slurries at the same time or by forming pattern coating while applying at least two types of electrode active material slurries in an alternating manner to form pattern coating. However, the scope of the present disclosure is not necessarily limited thereto. For example, the substrate may be a porous scaffold constituting a separation membrane, and the first coating solution and the second coating solution may be organic matters having different compositions or physical properties. That is, when thin film coating is required, any substrate and any coating solution or any first coating solution and any second coating solution may be good. 
       FIG.  5    is a cross-sectional view of a slot die coater according to an embodiment of the present disclosure.  FIG.  6    is a schematic exploded perspective view of the slot die coater according to an embodiment of the present disclosure.  FIG.  7    shows an example of use of a shim plate in the slot die coater according to an embodiment of the present disclosure. 
     Referring to  FIGS.  5  to  7   , the slot die coater  100  includes two die blocks  110  and  130 . A shim plate  113  for forming a slot  101  is provided between the die blocks  110  and  130 . The die blocks may be two or more. 
     In  FIG.  5   , the slot die coater  100  is installed in a substantially horizontal direction (X direction) in which an electrode active material slurry which is a coating solution is discharged (approximately: ±5 degrees). However, the slot die coater  100  is not limited to the example form here. For example, the slot die coater  100  may be configured as a vertical die in which a direction in which the coating solution is discharged upward (Y direction). The Z direction is a width direction of the slot die coater  100 . 
     The slot  101  is formed between where the die blocks  110  and  130  face each other. The shim plate  113  is provided between the die blocks  110  and  130  to provide a gap between the die blocks  110  and  130  so that the slot  101  corresponding to a passage through which the coating solution  150  may flow is formed. A thickness of the shim plate  113  determines a vertical width (Y direction and a slot gap) of the slot  10 . 
     As shown in  FIG.  6   , the shim plate  113  may include a plurality of open portions  113   a  by intermittently cutting one region thereof and may be interposed in the remaining parts except for one side of an edge region of an opposite surface of each of the die blocks  110  and  130 . Accordingly, a discharge port  101   a  through which the coating solution 150  may be discharged to the outside is formed between a die lips  111  and  131 , which are fore ends of the die blocks  110  and  130 , respectively. The discharge port  101   a  may be formed when the die lips  111  and  131  are spaced apart from each other. 
     For reference, the shim plate  113  functions as a gasket to prevent the coating solution  150  from leaking into the gap between the die blocks  110  and  130 , except for a region where the discharge port  101   a  is formed, and thus the shim plate  113  is preferably made of a material having a sealing property. 
     Any one of the die blocks  110  and  130  includes a manifold  112  having a predetermined depth and communicatively connected with the slot  101 . Although not shown, the manifold  112  is connected to a coating solution supply chamber (not shown) installed outside through a supply pipe to receive the coating solution  150 . When the coating solution  150  is fully filled in the manifold  112 , the flow of the coating solution  150  is induced along the slot  101  and discharged to the outside through the discharge port  101   a.    
     According to the slot die coater  100  having such a configuration, a rotatably provided coating roll  180  is disposed in front of the slot die coater  100 , the substrate  190  to be coated by rotating a coating roll  180  is driven, the coating solution  150  may be applied on the substrate  190  by discharging and continuously contacting the coating solution  150  with the surface of the substrate  190 . Alternatively, supply and interruption of the coating solution  150  may be alternately performed so that pattern-coating may be intermittently performed on the substrate  190 . 
     Here, the shim plate  113  determines a coating width of a coating layer applied on the substrate  190 , and has a state of use as in  FIG.  7   . 
     Referring to  FIG.  7   , the slot die coater  100  of  FIG.  5    viewed in a down direction after the die block  130  thereon is removed is illustrated. The end  113   b  of the shim plate  113  is moved backward relative to the die lip  111  so as to be offset relative to the die lip  111 . Since the die lips  111  and  131  are usually aligned in a straight line, the end  113   b  of the shim plate  113  is moved backward even relative to the die lip  131  which is not shown here. 
     In particular, the shim plate  113  shown in  FIG.  7    may include a plurality of open portions  113   a  by intermittently cutting one region thereof and form a coating layer  170  of a stripe pattern shape on the substrate  190 . Reference numeral  172  denotes an uncoated portion on which a coating layer is not formed. If there is one open portion  113   a,  one coating layer  170  may be formed on the substrate  190 . 
     Preferably, the size of an offset O of the shim plate may be 50 μm to 2000 μm. When the size of the offset O is smaller than 50 μm, the effect of having the offset is insignificant. When the size of the offset O is greater than 2000 μm, since it may cause non-uniformity of the boundary, the size needs not to exceed 2000 μm. The size of the offset O may be determined in consideration of the coating speed, the viscosity of the coating solution, the thickness of the coating solution, the coating gap, etc. When the other conditions are the same and the coating speed is high, the size of the offset O needs to be increased. When the other conditions are the same, and the viscosity of the coating solution increases, the size of the offset O needs to be increased. When the other conditions are the same and the thickness of the coating solution is large, the size of the offset O needs to be increased. When the other conditions are the same, and the coating gap is decreased, the size of the offset O needs to be increased. 
     As such, in the slot die coater  100  of the present disclosure, the end  113   b  of the shim plate  113  is moved backward relative to the die lips  111  and  131  so as to be offset relative to the die lip  111 . According to this configuration, even if a large pressure is applied to the coating solution  150  when the coating gap is small, after the coating solution  150  is sufficiently expanded from the end  113   b  of the shim plate  113  in a section of the offset O, that is, the coating solution  150  may leave the die lips  111  and  131  and reach the substrate  190  so that the coating solution  150  does not scatter to other parts. Accordingly, the boundary may be stably formed between the coating portion and the uncoated portion. 
       FIG.  8    is a schematic cross-sectional view of a dual slot die coater according to another embodiment of the present disclosure.  FIG.  9    is a schematic exploded perspective view of a dual slot die coater according to another embodiment of the present disclosure.  FIG.  10    shows an example of use of a lower shim plate in a dual slot die coater according to another embodiment of the present disclosure.  FIG.  11    is a side view of the dual slot die coater shown in  FIG.  8   . 
     A dual slot die coater  200  according to the present disclosure is an apparatus including a lower slot  201  and an upper slot  202 , and capable of simultaneously or alternately applying the same or different two kinds of coating solutions on a substrate  290  through the lower slot  201  and the upper slot  202 . 
     Referring to  FIGS.  8  and  9   , the dual slot die coater  200  includes a lower die block  210 , an intermediate die block  220  disposed on an upper portion of the lower die block  210 , and an upper die block  230  disposed on an upper portion of the intermediate die block  220 . 
     In  FIG.  8   , the dual slot die coater  200  is installed in a substantially horizontal direction (X direction) in which an electrode active material slurry which is a coating solution is discharged (approximately: ±5 degrees). 
     The intermediate die block  220  is a block located in the middle of blocks constituting the dual slot die coater  200 , and is a block disposed between the lower die block  210  and the upper die block  230  to form a dual slot. A cross section of the intermediate die block  220  of the present embodiment is a right triangle, but is not necessarily limited to such as shape. For example, the cross section may be provided as an isosceles triangle. 
     A first surface  220   a  of the intermediate die block  220  facing the upper die block  230  lies almost horizontally, and a surface  230   d  (that is, a surface forming an upper surface of an outer circumferential surface of the dual slot die coater  200 ) opposite to a surface  230   b  of the upper die block  230  facing the first surface  220   a  also lies almost horizontally. In this way, the first surface  220   a  and the opposite surface  230   d  are almost parallel to each other. And a surface  210   d  (that is, a surface forming a lower surface of the outer circumferential surface of the dual slot die coater  200 ) opposite to a surface  210   b  of the lower die block  210  facing the intermediate die block  220  also lies almost horizontally, and this surface is a bottom surface  210   d  (X-Z plane). 
     Surfaces of the lower die block  210 , the intermediate die block  220 , and the upper die block  230  which are opposite to a direction in which the electrode active material slurry is discharged, that is, rear surfaces  210   c,    220   c,  and  230   c,  lie almost vertically (Y direction). 
     In a surface forming the outer circumferential surface of the dual slot die coater  200  in the lower die block  210  and the upper die block  230  which are the outermost die blocks, the bottom surface  210   d  of the lower die block  210  and the upper surface  230   d  of the upper die block  230  manufactured to be almost vertical to the rear surfaces  210   c  and  230   c  may be used. And, the first surface  220   a  of the intermediate die block  220  manufactured to be almost vertical to the rear surface  220   c  may be used. In such die blocks  210 ,  220 , and  230 , since edges formed by surfaces are formed at right angles, there is a right angle portion in the cross section, and since a vertical or horizontal surface may be used as a reference surface, manufacturing or handling of the die blocks  210 ,  220 , and  230  are easy and the precision thereof is guaranteed. In addition, a state in which the lower die block  210 , the intermediate die block  220 , and the upper die block  230  are combined has an approximately rectangular parallelepiped shape as a whole, and only a front portion from which the coating solution is discharged is inclined toward the substrate  290 . This is advantageous in that a shape after assembly is approximately similar to that of a slot die coater including a single slot (e.g.,  100  in  FIG.  5   ) so that a slot die coater stand, etc. may be shared. 
     The dual slot die coater  200  may further include two or more fixing units  240  provided on the rear surfaces  210   c,    220   c,  and  230   c  thereof. The fixing units  240  are provided for fastening between the lower die block  210  and the intermediate die block  220  and for fastening between the intermediate die block  220  and the upper die block  230 . A plurality of fixing units  240  may be provided in the width direction of the dual slot die coater  200 . Bolts are fastened to the fixing units  240 , through which the lower die block  210 , the intermediate die block  220 , and the upper die block  230  are assembled with each other. 
     The lower die block  210 , the intermediate die block  220 , and the upper die block  230  are not necessarily limited to shapes of the above examples, and may be configured, for example, as vertical dies with the direction in which the coating solution is discharged as an upper direction and the rear surfaces  210   c,    220   c,  and  230   c  as bottom surfaces. 
     The lower die block  210  is a lowermost block among the blocks constituting the dual slot die coater  200 , and the surface  210   b  facing the intermediate die block  220  has an inclined shape to form an angle of approximately 20 degrees to 60 degrees with respect to the bottom surface  210   d.    
     The lower slot  201  may be formed where the lower die block  210  and the intermediate die block  220  face each other. For example, a lower shim plate  213  is interposed between the lower die block  210  and the intermediate die block  220  to provide a gap therebetween, so that the lower slot  201  corresponding to a passage through which the first coating solution  250  may flow may be formed. That is, the lower shim plate  213  defines the lower slot  201 , and in this case, the thickness of the lower shim plate  213  determines the vertical width (Y-axis direction and a slot gap) of the lower slot  201 . 
     The lower shim plate  213  includes a plurality of open portions  213  a by intermittently cutting one region thereof so that a coating width of the electrode active material layer formed on the substrate  290  is determined and may be interposed in the remaining portion except for one side in an edge region of an opposite surface of each of the lower die block  210  and the intermediate die block  220  as shown in  FIGS.  9  and  10   . Accordingly, a lower discharge port  201   a  through which the first coating solution  250  may be discharged to the outside is formed only between a lower die lip  211  which is a front end portion of the lower die block  210  and the intermediate die lip  221  which is a front end portion of the intermediate die block  220 . The lower discharge port  201   a  may be formed by making the lower die lip  211  and the intermediate die lip  221  spaced apart from each other. 
     For reference, the lower shim plate  213  functions as a gasket to prevent the first coating solution  250  from leaking into a gap between the lower die block  210  and the intermediate die block  220  except for the region where the lower discharge port  201   a  is formed, and thus the lower shim plate  213  is preferably made of a material having sealing property. 
     The lower die block  210  includes a first manifold  212  having a predetermined depth on the surface  210   b  facing the intermediate die block  220  and communicatively connected to the lower slot  201 . Although not shown in the drawings, the first manifold  212  is connected to a supply chamber (not shown) of the first coating solution  250  installed outside through a supply pipe to receive the first coating solution  250 . When the first coating solution  250  is fully filled in the first manifold  212 , the flow of the first coating solution  250  is induced along the lower slot  201  and discharged to the outside through the lower discharge port  201   a.    
     As another example, the first manifold  212  may be provided on a surface  220   b  of the intermediate die block  220  facing the lower die block  210 . 
     The upper die block  230  is disposed to face the first surface  220   a  which is an upper surface of the intermediate die block  220  that is horizontal with respect to a bottom surface. The upper slot  202  is thus formed where the intermediate die block  220  and the upper die block  230  face to each other. 
     Like the lower slot  201  described above, a second shim plate  233  may be interposed between the intermediate die block  220  and the upper die block  230  to provide a gap therebetween. Accordingly, the upper slot  202  corresponding to a passage through which a second coating solution  260  may flow is formed. In this case, a vertical width (Y-axis direction and a slot gap) of the upper slot  202  is determined by the second shim plate  233 . 
     In addition, the second shim plate  233 , which also has a structure similar to that of the above-described first shim plate  213 , includes a plurality of open portions  233   a  by intermittently cutting one region thereof, and may be interposed in the remaining portion except for one side in an edge region of an opposite surface of each of the intermediate die block  220  and the upper die block  230 . Similarly, a circumferential direction of the second shim plate  233  except for the front of the upper slot  202  is blocked, and the upper discharge port  202   a  is formed only between the front end portion of the intermediate die block  220  and a front end portion of the upper die block  230 . The front end portion of the upper die block  230  is defined as the upper die lip  231 . In other words, the upper discharge port  202   a  may be formed by making the intermediate die lip  221  and the upper die lip  231  spaced apart from each other. As such, the upper shim plate  233  defines the upper slot  202 . 
     In addition, the intermediate die block  220  includes a second manifold  232  having a predetermined depth on the surface  220   a  facing the upper die block  230  and communicatively connected to the upper slot  202 . Although not shown in the drawings, the second manifold  232  is connected to a supply chamber of the second coating solution  260  installed outside through a supply pipe to receive the second coating solution  260 . When the second coating solution  260  is supplied from the outside along the supply pipe in the shape of a pipe and fully filled in the second manifold  232 , the flow of the second coating solution  260  is induced along the upper slot  202  communicatively connected to the second manifold  232  and discharged to the outside through the upper discharge port  202   a.    
     As another example, the second manifold  232  may be provided on the surface  230   b  of the upper die block  230  facing the middle die block  220 . 
     The upper slot  202  and the lower slot  201  form a certain angle, and the angle may be approximately 20 degrees to 70 degrees. The upper slot  202  and the lower slot  201  may intersect each other at one point, and the upper discharge port  202   a  and the lower discharge port  201   a  may be provided near the intersection point. Accordingly, discharge points of the first coating solution  250  and the second coating solution  260  may be concentrated approximately at one point. 
     In the dual slot die coater  200 , a rotatably provided coating roll  280  is disposed in front of the dual slot die coater  200 , the substrate  290  to be coated by rotating the coating roll  280  is driven, a coating solution such as the electrode active material slurry is extruded through at least one of the upper slot  202  and the lower slot  201  to form the electrode active material layer on the substrate  290 . 
     Here, the lower shim plate  213  and the upper shim plate  233  determine the coating width of the electrode active material layer applied on the substrate  290 , and have the same state of use as in  FIG.  10   . 
     Referring to  FIG.  10   , the slot die coater  200  of  FIG.  8    viewed in a down direction after the upper die block  230  and the intermediate die block  220  thereon are removed is illustrated. The end  213   b  of the lower shim plate  213  is moved backward relative to the lower die lip  211  so as to be offset relative to the lower die lip  211 . The first coating solution  250  may be discharged from the first manifold  212  toward the substrate  290  through the open portion  213   a  of the lower shim plate  213 . Since the lower die lip  211  and the intermediate die lip  221  are usually aligned in a straight line, the end  213   b  of the lower shim plate  213  is also moved backward relative to the intermediate die lip  221  which is not shown here. 
     The size of the offset O may be 50 μm to 2000 μm. 
     The example of use of the upper shim plate  233  is the same as that of the lower shim plate  213 , and the end  233   b  of the upper shim plate  233  is also offset relative to the upper die lip  221  and the intermediate die lip  221 . The size of the offset O of the upper shim plate  233  may also be 50 μm to 2000 μm. 
     The lower shim plate  213  and the upper shim plate  233  are aligned with each other in the up and down direction (X direction) and left and right direction (Z direction), and thus may be used as shown in  FIG.  11   . According to the dual slot die coater  200  having the configuration described above with further reference to  FIG.  11   , the rotatably provided coating roll  280  is disposed in front of the dual slot die coater  200 , the substrate  290  to be coated by rotating the coating roll  280  is driven, and the first coating solution  250  and the second coating solution  260  are continuously contacted with the surface of the substrate  290  so that the substrate  290  may be coated in a double layer. Alternatively, supply and interruption of the first coating solution  250  and supply and interruption of the second coating solution  260  are alternately performed so that pattern-coating may be intermittently performed on the substrate  290 . 
     Here, the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213  may be the same or different. For example, A&gt;B, A&lt;B, or A=B. 
     When the first coating solution  250  and the second coating solution  260  are continuously contacted with the surface of the substrate  290  so that the substrate  290  is coated in the double layer as shown, in the relationship between the total coating solution thickness D which is the sum of the first coating solution thickness d 1  and the second coating solution thickness d 2  formed on the substrate  290  and the coating gap G , which is a distance between the discharge ports  201   a  and  202   a  of the slot die coater  200  and the substrate  290  or a distance between the die lips  211 ,  221 , and  231  and the substrate  290 , the coating gap G is preferably adjusted between a value 20% greater than and a value 20% smaller than the coating solution thickness D. In other words, the coating gap G relative to the coating solution thickness D is preferably set to have a value between 0.8 and 1.2. When the coating gap G is much greater than the coating solution thickness D, fat-edge occurs in which the edge of the coating layer is thickly formed. When the coating gap G is much smaller than the coating solution thickness D, since a large pressure is applied, a pattern defect occurs due to scattering of the coating solution, etc. The standard of 20% is determined in consideration of this point. 
     In particular, when the coating gap G is equal to or greater than a predetermined value compared to the coating solution thickness D, the coating width is beyond a range adjustable by the coating gap G. The present inventors have found that with respect to the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213 , A:B is preferably in the range of 7:1 to 1:7 when the coating gap G relative to the coating solution thickness D is equal to or greater than 1.06. When the coating gap G relative to the coating solution thickness D is equal to or greater than 1.06, if A:B is beyond the above range, a pattern defect occurs. 
     In the present disclosure, the pattern defect is prevented by basically setting each of the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213  within the range of 50 μm to 2000 μm. Furthermore, it is proposed that the ratio of the offset size A of the upper shim plate  233  to the offset size B of the lower shim plate  213  also needs to be considered when the coating gap G relative to the coating solution thickness D is greater than 1.06. 
     When the coating gap G relative to the coating solution thickness D is smaller than a predetermined value, it is sufficient to set each of the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213  within the range of 50 μm to 2000 μm as a solution to relieve the pressure applied to the coating solution, but it should be noted that when the coating gap G relative to the coating solution thickness D is equal to or greater than a predetermined value, with respect to the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213 , even A:B is adjusted, and thus a pattern defect may be completely prevented. 
     The dual slot die coater  200  is optimized for application of the electrode active material slurry for manufacturing a secondary battery. In order to manufacture a secondary battery of high energy density, the thickness of the electrode active material layer which was about 130 μm gradually increased to reach 300 μm. When the thick electrode active material layer is formed with the conventional slot die coater, since migration of a binder and a conductive material in the active material slurry deepens during drying, a final electrode is manufactured non-uniformly. In order to solve this problem, when coating is performed two times such as applying thinly and drying the electrode active material layer and then applying and drying the electrode active material layer, a disadvantage is that it takes a long time. In order to simultaneously improve electrode performance and productivity, when the dual slot die coater  200  is used, two types of electrode active material slurries may be simultaneously applied. 
     And, according to the offset configuration of the lower shim plate  213  and the upper shim plate  233  as proposed in the present disclosure, even if a large pressure is applied to the electrode active material slurry when the coating gap is small, the coating solution does not scatter. Accordingly, the boundary may be stably formed between the coating portion and the uncoated portion. In particular, when the electrode active material layer having a stripe pattern shape is formed, it is possible to stably form the electrode active material layer without contamination of the boundary or non-uniformity of the boundary such as a wave pattern on the boundary. This leads to no defect in the slitting along the uncoated portion. It is possible to reduce a discarded electrode plate, and thus the cost reduction effect is excellent. In addition, in the case where the coating gap is relatively large, under the condition that it is difficult to adjust the coating width, with respect to the offset size A of the upper shim plate  233  and the offset size B of the lower shim plate  213 , even A:B is adjusted, and thus a double layer is stably formed without scattering the electrode active material slurry. 
     According to the present disclosure, when the electrode active material layer of a double layer is formed on the substrate  290  by simultaneously discharging two types of electrode active material slurries through the upper slot  202  and the lower slot  201 , it is possible to stably form a boundary between the electrode active material layer of a double layer and the uncoated portion in both cases where different types of electrode active material slurries are used or the electrode active material layer is thickly coated by using the same electrode active material slurry. Accordingly, it is possible to obtain a coating product of uniform quality, particularly an electrode for a secondary battery. 
     When the dual slot die coater  200  of the present disclosure is used, it is possible to uniformly form the coating layer, particularly the electrode active material layer, with a desired thickness and shape, and preferably, it is possible to simultaneously coat two types of electrode active material slurries, and thus both performance and productivity are excellent. 
     Meanwhile, in the present embodiment, the case of applying the coating solution in two layers or the case of performing pattern-coating by alternately supplying the coating solution has been described as an example, but it will be understood without separate explanation that it is also applied to the case where three or more layers are simultaneously applied by providing three or more slots. 
     As described above, according to the present disclosure, even if the discharge pressure of the electrode active material slurry increases, the effect of preventing the electrode active material slurry from scattering by relieving the pressure of the electrode active material slurry by the shim plate offset structure is excellent. This has the effect of forming a stable boundary, securing coating processability, and securing reproducibility. 
     Hereinafter, comparative examples and embodiments will be described in order to explain the effect of the shim plate offset as proposed in the present disclosure. First, with respect to Comparative Examples 1 to 5 and Embodiments 1 to 5 in the slot die coater including one slot as described with reference to  FIG.  5   , etc., the experimental conditions and results are summarized in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Coating 
                   
                 Shim 
                   
                   
                   
               
               
                   
                 Coating 
                   
                 solution 
                 Coating 
                 plate 
                 Contamination 
                 Non- 
               
               
                   
                 speed 
                 Viscosity 
                 thickness 
                 gap 
                 offset 
                 of boundary 
                 uniformity 
                 Other 
               
               
                   
                 (m/min) 
                 (cps) 
                 (μm) 
                 (μm) 
                 (μm) 
                 portion 
                 of boundary 
                 defects 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Comparative example 1 
                 50 
                 4000 
                 100 
                 105 
                 0 
                 ◯ 
                 X 
                 Fat-Edge 
               
               
                 Comparative example 2 
                 50 
                 4000 
                 100 
                 115 
                 0 
                 X 
                 X 
                 Fat-Edge 
               
               
                 Comparative example 3 
                 50 
                 4000 
                 100 
                 125 
                 0 
                 X 
                 X 
                 Fat-Edge 
               
               
                 Comparative example 4 
                 50 
                 4000 
                 100 
                 90 
                 0 
                 ◯ 
                 X 
                 X 
               
               
                 Embodiment 1 
                 50 
                 4000 
                 100 
                 90 
                 50 
                 X 
                 X 
                 X 
               
               
                 Embodiment 2 
                 50 
                 4000 
                 100 
                 90 
                 200 
                 X 
                 X 
                 X 
               
               
                 Embodiment 3 
                 50 
                 4000 
                 100 
                 105 
                 500 
                 X 
                 X 
                 X 
               
               
                 Embodiment 4 
                 50 
                 4000 
                 100 
                 105 
                 1000 
                 X 
                 X 
                 X 
               
               
                 Embodiment 5 
                 50 
                 4000 
                 100 
                 105 
                 2000 
                 X 
                 X 
                 X 
               
               
                 Comparative example 5 
                 50 
                 4000 
                 100 
                 105 
                 2500 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     Comparative Examples 1 to 4 are cases where the offset is 0 when the end of the shim plate is aligned with the die lip. Embodiments 1 to 5 are cases where the end of the shim plate is moved backward from the die lip so that the shim plate has the offset of 50 μm to 2000 μm. Comparative Example 5 is case where the offset is 2500 μm which exceeds the preferred offset range proposed in the present disclosure. 
     The coating speed was all set to 50 m/min. The viscosity of the electrode active material slurry which is the coating solution was all 4000 cps. The thickness of the coating solution was 100 μm as a target. Cases where the coating gap is 90 μm, 105 μm, 115 μm, and 125 μm were experimented. 
     As a result of the experiment, in all the embodiments of the present disclosure in which the shim plate offset is present, contamination of the boundary portion has not occurred. When the coating gap is 115 μm and 125 μm as in Comparative Examples 2 and 3 in which the shim plate offset is 0, contamination of the boundary portion has not occurred, but other defects such as fat-edge has occurred. In Comparative Example 1 in which the coating gap is reduced to 105 μm, not only other defects but also contamination of the boundary portion has occurred. In particular, in Comparative Example 4, in which more pressure is applied to the electrode active material slurry because the coating gap is 90 μm which is smaller than 100 μm which is the coating solution thickness, the contamination of the boundary portion was severe. Therefore, when there is no shim plate offset as in Comparative Examples 1 to 3, other defects occur, and when the coating gap is reduced as in Comparative Examples 1 and 4, contamination of the boundary portion occurs. 
     The non-uniformity of the boundary has occurred in Comparative Example 5 in which the shim plate offset is 2500 μm. Therefore, the offset should not be too large. 
     As described above, according to an embodiment of the present disclosure, the shim plate offset is 50 μm to 2000 μm, thereby forming the electrode active material layer having no contamination of the boundary portion, a uniform boundary and no other defects. In particular, as in Embodiments 1 and 2, since the coating gap is 90 μm which is smaller than 100 μm which is the coating solution thickness, it should be paid to the remarkable effect of forming a stable boundary even when more pressure is applied to the electrode active material slurry. 
     Next, Comparative Examples 6 to 13 and Embodiments 6 to 15 in the dual slot die coater including two slots as described with reference to  FIG.  8   , etc. will be described. 
     The experimental conditions and results are summarized in Table 2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Coating gap 
                 Shim plate offset 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Coating solution 
                   
                 relative 
                 (μm) 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 thickness (μm) 
                 Coating 
                 to coating 
                 upper 
                 lower 
                   
                 Contamination 
                 Non- 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 upper 
                 lower 
                 gap 
                 solution 
                 layer 
                 layer 
                   
                 of boundary 
                 uniformity 
                 Other 
               
               
                   
                 layer 
                 layer 
                 (μm) 
                 thickness 
                 (A) 
                 (B) 
                 A:B 
                 portion 
                 of boundary 
                 defects 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Comparative example 6 
                 80 
                 80 
                 170 
                 1.06 
                 0 
                 0 
                   
                 ◯ 
                 X 
                 Fat-Edge 
               
               
                 Comparative example 7 
                 80 
                 80 
                 180 
                 1.13 
                 0 
                 0 
                   
                 X 
                 X 
                 Fat-Edge 
               
               
                 Comparative example 8 
                 80 
                 80 
                 190 
                 1.19 
                 0 
                 0 
                   
                 X 
                 X 
                 Fat-Edge 
               
               
                 Embodiment 6 
                 80 
                 80 
                 170 
                 1.06 
                 50 
                 50 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 7 
                 80 
                 80 
                 170 
                 1.06 
                 500 
                 500 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 8 
                 80 
                 80 
                 170 
                 1.06 
                 1000 
                 1000 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 9 
                 80 
                 80 
                 170 
                 1.06 
                 2000 
                 2000 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Comparative example 9 
                 80 
                 80 
                 170 
                 1.06 
                 2500 
                 2500 
                 1:1 
                 X 
                 ◯ 
                 ◯ 
               
               
                 Embodiment 10 
                 80 
                 80 
                 170 
                 1.06 
                 300 
                 100 
                 3:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 11 
                 80 
                 80 
                 170 
                 1.06 
                 650 
                 100 
                 6.5:1     
                 X 
                 X 
                 X 
               
               
                 Comparative example 10 
                 80 
                 80 
                 170 
                 1.06 
                 800 
                 100 
                 8:1 
                 X 
                 ◯ 
                 X 
               
               
                 Embodiment 12 
                 80 
                 80 
                 170 
                 1.06 
                 100 
                 650 
                     1:6.5 
                 X 
                 X 
                 X 
               
               
                 Comparative example 11 
                 80 
                 80 
                 170 
                 1.06 
                 100 
                 800 
                 1:8 
                 X 
                 ◯ 
                 X 
               
               
                 Comparative example 12 
                 80 
                 80 
                 150 
                 0.94 
                 0 
                 0 
                   
                 ◯ 
                 X 
                 X 
               
               
                 Embodiment 13 
                 80 
                 80 
                 150 
                 0.94 
                 50 
                 50 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 14 
                 80 
                 80 
                 150 
                 0.94 
                 200 
                 200 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Embodiment 15 
                 80 
                 80 
                 150 
                 0.94 
                 2000 
                 2000 
                 1:1 
                 X 
                 X 
                 X 
               
               
                 Comparative example 13 
                 80 
                 80 
                 150 
                 0.94 
                 2500 
                 2500 
                 1:1 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     The total thickness of the coating solution which is the sum of the coating solution thickness of the upper layer by the second coating solution  260  and the coating solution thickness of the lower layer by the first coating solution  250 , is 160 μm as a target. Cases where the coating gap is 150 μm, 170 μm, 180 μm, and 190 μm were experimented. 
     Comparative Examples 6 to 8 and 12 are cases where the offset is all 0 when the ends of the upper shim plate and the lower shim plate are aligned with the die lip. Comparative Examples 9 and 13 are cases where the offset is 2500 μm which exceeds the preferred offset range proposed by the present disclosure. Embodiments 6 to 15 are cases where the ends of the upper shim plate and the lower shim plate are moved backward from the die lip so that the upper shim plate and the lower shim plate have the offset of 50 μm to 2000 μm. 
     As a result of the experiment, in all the embodiments of the present disclosure in which the shim plate offset is present, contamination of the boundary portion has not occurred. There was no non-uniformity of the boundary. In Comparative Examples 6 to 8 and 12 in which the shim plate offset is 0, contamination of the boundary portion or fat-edge has occurred. In Comparative Examples 9 and 13 in which the shim plate offset is 2500 μm, non-uniformity of the boundary and other defects have occurred. 
     In particular, it is noticeable that Comparative Examples 10 and 11 are cases where the offset size A of the upper shim plate and the offset size B of the lower shim plate are within the range proposed in the present disclosure, but the coating gap to the coating solution thickness is 1.06 and A:B is beyond the range proposed in the present disclosure. At this time, the non-uniformity of the boundary has been observed. 
     As described above, according to an embodiment of the present disclosure, the offset size A of the upper shim plate and the offset size B of the lower shim plate are adjusted within 50 μm to 2000 μm, thereby forming the electrode active material layer having no contamination of the boundary portion, a uniform boundary and no other defects. In particular, as in Embodiments 6 to 12, when the coating gap is greater than the coating solution thickness, and the coating gap to the coating solution thickness is equal to or greater than 1.06, A:B is set to 7:1 to 1:7, thereby forming the electrode active material layer having no contamination of the boundary portion, a uniform boundary and no other defects. 
     The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description. 
     Meanwhile, although terms indicating directions such as up, down, left, and right are used in the present specification, these terms are only for convenience of description, and it is apparent to those skilled in the art that these terms may vary depending on a position of a target object or a position of an observer. 
     
       
         
           
               
             
               
                   
               
               
                 [Explanation of Reference Numerals] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 100: slot die coater 
                 101: slot 
               
               
                   
                 101a: discharge port 
                 110, 130: die block 
               
               
                   
                 111, 131: die lip 
                 112: manifold 
               
               
                   
                 113: shim plate 
                 113a: open portion 
               
               
                   
                 113b: end 
                 O: offset 
               
               
                   
                 150: coating solution 
                 170: coating layer 
               
               
                   
                 172: uncoated portion 
                 180, 280: coating roll 
               
               
                   
                 190, 290: substrate 
                 200: dual slot die coater 
               
               
                   
                 201: lower slot 
                 201a: lower discharge port 
               
               
                   
                 202: upper slot 
                 202a: upper discharge port 
               
               
                   
                 210: lower die block 
                 211: lower die lip 
               
               
                   
                 212: first manifold 
                 213: lower shim plate 
               
               
                   
                 220: intermediate die block 
                 221: intermediate die lip 
               
               
                   
                 230: upper die block 
                 231: upper die lip 
               
               
                   
                 232: second manifold 
                 233: upper shim plate 
               
               
                   
                 240: fixing unit 
                 250: first coating solution 
               
               
                   
                 260: second coating solution