Method for deposition of film from wet powder

Abstract

To provide a method for deposition of a film from wet powder, the method enabling the wet powder to be properly transferred onto a sheet-shaped substrate by using a pressure roll, thereby enabling the wet powder to be deposited .SOLUTION: A coating apparatus CE including a first roll 1, a second roll 2, and a third roll 3 is used. The first roll 1 and the second roll 2 are rotated in such a manner that a peripheral speed of the second roll 2 becomes faster than a peripheral speed of the first roll 1, thereby transferring wet powder 6 onto the second roll 2. At an initial stage of supplying the wet powder 6 into a supply gap 4, the second roll 2 and the third roll 3 are rotated in such a manner that a peripheral speed of the second roll 2 becomes equal to a peripheral speed of the third roll 3. After a predetermined time elapses from a time when the wet powder 6 first enters into a film-formation gap 5, the second roll 2 and the third roll 3 are rotated in such a manner that a peripheral speed of the third roll 3 becomes faster than a peripheral speed of the second roll 2, thereby transferring the wet powder 6 onto a substrate 7 on the third roll 3.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for forming a film from wet powder, in which wet powder is transferred by a pressure roll to form a film. [Background technology]

[0002] Patent Document 1 describes an electrode manufacturing apparatus that produces an electrode in which a metal foil and an active material layer are laminated by transferring an active material, which is the material for the electrode, onto a metal foil. The electrode manufacturing apparatus described in Patent Document 1 includes three rolling rolls, namely, roll A, roll B, and roll C, which rotate by receiving a driving force. Roll B is disposed parallel to roll A with a supply gap therebetween. Roll B rotates in the opposite rotational direction to roll A. Roll C is disposed parallel to roll B with a film-forming gap therebetween. Roll C rotates in the opposite rotational direction to roll B. The electrode manufacturing apparatus described in Patent Document 1 supplies active material to the supply gap, and the active material transported by roll B through the supply gap is transferred to metal foil transported by roll C in the film-forming gap, thereby forming a layer of active material on the surface of the metal foil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-10822 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional electrode manufacturing process (electrode material coating process), electrodes are manufactured by coating a metal foil with a slurry or paste of active material. In contrast, the electrode manufacturing apparatus described in Patent Document 1 uses a manufacturing apparatus (coating apparatus) consisting of three rolling rolls to form a film of a wet powder or wet granulated active material, which contains less solvent than a slurry or paste active material. The wet powder is formed on the surface of a sheet-shaped metal foil (substrate). For example, the wet powder is a powder containing a material such as the electrode active material, a binder, a thickener, etc., and a small amount of solvent (e.g., water), which is then stirred and granulated into spherical particles. Using such a wet powder as a coating material can shorten the time required to dry the solvent, thereby reducing the cost of the product (battery). This also reduces the amount of energy consumed for drying the solvent, thereby contributing to a reduction in environmental impact.

[0005] Furthermore, in the electrode manufacturing apparatus described in the above-mentioned Patent Document 1, three rolling rolls are arranged parallel to one another, and the rotation speed and roll diameter of each rolling roll are set so that there is a difference in the circumferential speed when each rolling roll rotates. The difference in circumferential speed is such that the circumferential speed of roll B is faster than that of roll A, and the circumferential speed of roll C is faster than that of roll B. As a result, when the wet powder coating material (electrode active material) introduced between roll A and roll B enters the gap between roll A and roll B, a press reaction force (or crushing force) F as shown in Figure 1(a) acts on the coating material. Furthermore, when the circumferential speed V of roll A A The peripheral speed of B roll V is B Since the shear force τ is faster than the press reaction force F, a shear force (coating interface shear force, stretching force, or transfer force) τ is generated as shown in Figure 1(a). The combined force of the press reaction force F and the shear force τ becomes the transfer force Ft, which acts on the coating material and the surface of each roll. Therefore, the coating material is transferred by the transfer force Ft on the A roll side. A Transfer force Ft BThe image is transferred to the B roll side where the B roll acts, and is transported by the B roll, and enters the gap between the B roll and the C roll. In the gap between the B roll and the C roll, the B roll's peripheral speed V B The peripheral speed of the roll C is V C is faster, so the press reaction force F and shear force τ B ,τ C The transfer force Ft occurs on the surface of the coating material and each roll. B ,Ft c Therefore, the coating material is transferred by the transfer force Ft B Transfer force Ft C Therefore, the coating material is transferred to the metal foil that is wound around the C roll and transported as a web. In other words, a layer of the active material that will become the electrode is formed on the surface of the metal foil. As shown in Figure 1(b), the peripheral speed of the B roll is V B and the peripheral speed of the C roll V C When and are equal, the shear force τ B ,τ C does not occur, and only the press reaction force F acts on the coating material that has entered the gap between rolls B and C.

[0006] On the other hand, when the electrode manufacturing apparatus (rolling mill) described in Patent Document 1 is used to form a film using the electrode active material in the wet powder state described above as a coating material, the film thickness of the portion where the coating material is first transferred is thicker than the normal thickness. Specifically, as shown in Figure 2(a), when the coating material is introduced into the apparatus and enters the gap between roll A and roll B, the high viscosity and compressive strength of the wet powder coating material causes the gap between roll A and roll B to elastically bend and expand. As a result, the portion that first passes through the gap between roll A and roll B and is transferred to roll B becomes a "thick coating portion" with a thickness greater than the normal thickness. When such a "thick coating portion" is transported by roll B and enters the gap between roll B and roll C as shown in Figure 2(b), the "thick coating portion" of the coating material is subjected to greater than normal press reaction and shear forces. Therefore, the metal foil on roll C is subjected to a greater than normal load as a reaction force to these large forces. If such a large load exceeds the strength of the metal foil, the metal foil may be damaged.

[0007] The present invention has been devised with a focus on the above-mentioned technical problems, and aims to provide a method for forming a film from a wet powder, which can appropriately transfer the wet powder to a sheet-like substrate using a rolling roll to form a film. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a method for forming a film from a wet powder by transferring the wet powder to a substrate using a coating device comprising a first roll, a second roll, and a third roll arranged parallel to one another, the coating device transferring a coating material introduced into a supply gap between the first roll and the second roll to the second roll and transporting the coating material by the second roll, and transferring the coating material transported by the second roll and entering a film-forming gap between the second roll and the third roll to a substrate transported by the third roll, the method comprising: and the second roll are rotated so that the peripheral speed of the second roll is equal to the peripheral speed of the third roll at the beginning of feeding the wet powder into the supply gap, and after a predetermined time has elapsed from the time when the tip of the wet powder first enters the deposition gap, the second roll and the third roll are rotated so that the peripheral speed of the third roll is faster than the peripheral speed of the second roll, thereby transferring the wet powder to the surface of the substrate on the third roll.

[0009] The predetermined time in the present invention may be at least the time required for the tip of the wet powder that first enters the coating gap to pass completely through the coating gap, or a time longer than this.

[0010] The wet powder in the present invention is a granulated product formed by adding a solvent whose content is smaller than that of a slurry or paste fluid to a powder of an active material that is to be used as a material for a battery electrode, and the substrate in the present invention may be a foil-shaped current collector (electrode foil) that is to be used as a material for the electrode. [Effects of the Invention]

[0011] This invention uses a coating device consisting of three parallel-positioned rolls to apply a coating material in a wet powder state to a substrate. Specifically, the wet powder is transferred to the surface of a sheet-like substrate to form a film. By creating a difference in peripheral speed between two opposing rolls, a press reaction force (crushing force) and a shear force (stretching force) are applied to the wet powder entering between the two rolls, and the wet powder is transferred to the roll with the faster peripheral speed. On the other hand, the wet powder targeted in this invention is, for example, a granulated material with a lower solvent content than a slurry or paste-like fluid, resulting in a coating material with high viscosity and compressive strength (in other words, low fluidity). This invention envisions transferring such a high-viscosity and high-strength wet powder to the surface of a web-transported sheet-like substrate. Therefore, in the wet powder film formation targeted in this invention, the press reaction force and shear force are larger than those in conventional film formation using slurry or paste-like materials, and these press reaction force and shear force act simultaneously. Therefore, the transfer force, which is the combined force of the press reaction force and the shear force, exceeds the strength of the substrate, which may result in damage to the substrate. Therefore, in the wet powder film-forming method of the present invention, when transferring the wet powder to the substrate, the wet powder is first introduced between two rolling rolls without creating a difference in peripheral speed between the two rolling rolls. That is, when the wet powder is first introduced between the second roll and the third roll, the second roll and the third roll are rotated so that the peripheral speed of the second roll and the peripheral speed of the third roll are equal. Then, after a predetermined time has elapsed, a difference in peripheral speed is created between the second roll and the third roll, thereby generating a shear force and a transfer force, and the wet powder is transferred to the substrate on the third roll.

[0012] Thus, in the wet powder film-forming method of the present invention, when the transfer of the wet powder begins, the peripheral speeds of the second roll and the third roll are initially set equal, so that only the press reaction force acts on the wet powder passing between the second roll and the third roll. Then, after a predetermined time has elapsed, a difference in peripheral speed is created between the second roll and the third roll, so that a shear force acts on the wet powder in addition to the press reaction force. In other words, in the wet powder film-forming method of the present invention, the press reaction force and shear force are distributed and acted upon. Therefore, the force applied to the substrate can also be distributed, preventing damage to the substrate due to excessive transfer force and enabling the wet powder to be properly transferred to the substrate.

[0013] Therefore, according to the method for forming a film from a wet powder of the present invention, a coating device consisting of at least three rolling rolls can be used to appropriately transfer the wet powder onto a sheet-like substrate to form a film. [Brief explanation of the drawings]

[0014] [Figure 1] Figure 1 is a diagram illustrating the press reaction force, shear force, and transfer force that act on a coating material that has entered between the rolls when the coating material (wet powder) is transferred by the rolls. Figure 1(a) shows a state in which a difference in peripheral speed is created between the two rolls, generating a press reaction force and a shear force, while Figure 1(b) shows a state in which the peripheral speeds of the two rolls are equal, and only a press reaction force acts (no shear force or transfer force is generated). [Figure 2] Figure 2 is a diagram for explaining the problems with the conventional technology, and shows an image of the "thick coating area" that occurs when coating begins. Figure 2(a) shows the state in which the "thick coating area" is generated where the coating material (wet powder) first passes between roll A and roll B, and Figure 2(b) shows the state in which the "thick coating area" generated after passing between roll A and roll B enters between roll B and roll C. [Figure 3]Figure 3 is a diagram illustrating the effect of transferring a coating material (wet powder) using the wet powder film-forming method of this invention, showing the transition of a "thick coating" that occurs at the start of coating. Figure 3(a) shows the state in which a "thick coating" is generated where the coating material (wet powder) first passes between the first and second rolls. Figure 3(b) shows the state in which the "thick coating" generated after passing between the first and second rolls enters between the second and third rolls, which are rotating at the same peripheral speed. Figure 3(c) shows the state in which the "thick coating" that passed between the second and third rolls and was initially subjected only to a press reaction force enters between the second and third rolls, which are rotating at a different peripheral speed due to a reduction in the rotation speed of the second roll. [Figure 4] FIG. 4 is a process diagram (flowchart) showing typical steps when applying the wet powder film-forming method of the present invention to transfer a coating material (wet powder), as well as an overview of the operation of the coating device and the coating material. [Figure 5] FIG. 5 is a diagram for explaining the press reaction force, shear force, and transfer force acting on a coating material (wet powder) that has entered between the rolling rolls when the coating material (wet powder) is transferred using the wet powder film-forming method of this invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of specific embodiments of the present invention and are not intended to limit the scope of the present invention.

[0016] A wet powder film-forming method according to an embodiment of the present invention is directed to a process of applying a coating material to a substrate to form a film using a coating device equipped with three rolling rolls. Specifically, as shown in FIG. 3 , the coating device CE according to this embodiment of the present invention includes a first roll 1, a second roll 2, and a third roll 3 arranged parallel to one another. The second roll 2 is arranged parallel to the first roll 1, with a supply gap 4 between the first roll 1 and the second roll 2. The second roll 2 rotates in the opposite direction to the first roll 1. The third roll 3 is arranged parallel to the second roll 2, with a film-forming gap 5 between the second roll 2 and the second roll 2. The third roll 3 rotates in the opposite direction to the second roll 2.

[0017] The coating device CE causes the coating material 6 supplied to the supply gap 4 to enter the supply gap 4 and transfer it onto the surface of the second roll 2. Then, the coating material 6 transferred to the second roll 2 and transported by the second roll 2 enters the deposition gap 5 and is transferred onto the surface of the substrate 7 transported by the third roll 3. As a result, a layer of the coating material 6 is formed on the surface of the substrate 7.

[0018] Furthermore, in a wet powder film-forming method according to an embodiment of the present invention, a coating material 6 in a "wet powder" state is formed into a film on a sheet-like substrate 7 that is conveyed by a web. The "wet powder" is a "granule" that contains a lower content of a solvent (not shown), such as water, compared to, for example, a slurry or paste-like fluid. As an example, in the wet powder film-forming method according to an embodiment of the present invention, a granule formed by impregnating a powder of an active material (not shown) that will be used as a material for a battery electrode (not shown) with a solvent, i.e., a "wet powder" coating material 6, is assumed to be applied to a substrate 7 that will become a foil-shaped "current collector" or "electrode foil," which is the material for the electrode.

[0019] 3 indicates, for example, a negative electrode active material 8 (e.g., carbon) for a lithium ion battery, and therefore, in the example shown in Fig. 3, the coating material 6 is a "wet powder" formed by impregnating a positive electrode active material for a lithium ion battery (e.g., lithium cobalt oxide) with a solvent and forming it into granules. That is, Fig. 3 shows an example of manufacturing an "electrode (bipolar electrode)" for a so-called "bipolar battery" in which a positive electrode and a negative electrode are formed on both sides of a foil-shaped current collector (electrode foil; substrate 7).

[0020] In the wet powder film forming method according to the present invention, the coating device CE described above is used to transfer the "wet powder" (coating material 6) onto the surface of the "electrode foil" (substrate 7). As described above, the "wet powder" (coating material 6) has a higher viscosity and compressive strength than, for example, a slurry or paste-like fluid. Therefore, as shown in FIG. 3(a), when the "wet powder" (coating material 6) is introduced into the coating device CE and enters the supply gap 4 between the first roll 1 and the second roll 2, the high viscosity and compressive strength of the "wet powder" (coating material 6) causes the rolls 1 and 2 forming the supply gap 4 to elastically deflect, temporarily widening the gap 4. As a result, the leading edge 6a of the "wet powder" (coating material 6) that first passes through the supply gap 4 and is transferred to the second roll 2 becomes a "thick coating portion" with a thickness greater than the normal film thickness. When the thick coating portion of the leading edge 6a is conveyed by the second roll 2 and enters the film-forming gap 5 between the second roll 2 and the third roll 3 as shown in FIG. 3(b), a larger-than-normal press reaction force acts on the thick coating portion of the leading edge 6a. If a shear force acts simultaneously with the press reaction force, as in the prior art, the electrode foil (substrate 7) on the third roll 3 is subjected to a larger-than-normal load as a result of the combined force (i.e., transfer force) of the large press reaction force and shear force. If this load exceeds the strength of the electrode foil (substrate 7), the electrode foil (substrate 7) may be damaged. Therefore, in the wet powder film-forming method according to an embodiment of the present invention, the above-described press reaction force and shear force are generated in a dispersed manner, thereby preventing damage to the electrode foil (substrate 7) and appropriately transferring the wet powder (coating material 6) to the electrode foil (substrate 7) on the third roll 3. Each step is defined to ensure this.

[0021] FIG. 4 shows an example of a film-forming process of "wet powder" (coating material 6) to which the method for forming a film from wet powder according to an embodiment of the present invention is applied.

[0022] First, in step P1 (initial peripheral speed adjustment step), the rotational speed or rotational speed of each of the rolls 1, 2, and 3 is controlled to adjust the peripheral speed of each of the rolls 1, 2, and 3. The adjustment of the peripheral speed of each of the rolls 1, 2, and 3 in step P1 determines the initial peripheral speed in the film-forming process of this coating material 6, and sets the peripheral speed of each of the rolls 1, 2, and 3 at the "initial stage" of feeding, from the start of feeding the next coating material 6 until a "predetermined time" (described later) has elapsed. In adjusting the peripheral speed at the "initial stage" of this film-forming process, for example, as shown in FIG. 3(a), when the peripheral speed of the third roll 3 is 100%, the rotational speed or rotational speed of each of the rolls 1, 2, and 3 is controlled so that the peripheral speed of the second roll 2 is 100%, equal to the peripheral speed of the third roll 3, and the peripheral speed of the first roll 1 is 40% of the peripheral speed of the third roll 3 (i.e., 40% of the peripheral speed of the second roll 2).

[0023] In process P2 (coating material introduction process / supply gap entry process), coating material 6, granulated in a "wet powder" state, is introduced into the supply gap 4 between the first roll 1 and the second roll 2. At the same time, as shown in Figure 3(a), the coating material 6 first enters the supply gap 4, and the aforementioned "thick coating portion" is inevitably formed at the tip 6a of the coating material 6.

[0024] In process P3 (second roll transfer process), the coating material 6 that entered the supply gap 4 in process P2 is transferred to the surface of the second roll 2. In this process P3, the peripheral speed of the second roll 2 (100% of the peripheral speed of the third roll 3) is faster than the peripheral speed of the first roll 1 (40% of the peripheral speed of the third roll 3), and the press reaction force and shear force described above act on the "wet powder" coating material 6 that entered the supply gap 4. Therefore, as shown in Figure 3(a) and Figure 3(b), the coating material 6 is transferred to the second roll 2 side.

[0025] In process P4 (first entry into the film formation gap process), as shown in FIG. 3(b), the leading edge 6a (i.e., the "thick coating portion") of the coating material 6 transferred to the surface of the second roll 2 in process P3 and transported by the second roll 2 first enters the film formation gap 5 between the second roll 2 and the third roll 3. In this process P3, the peripheral speeds of the second roll 2 and the third roll 3 are equal, and there is no difference in peripheral speed. Therefore, the shear force and transfer force described above do not occur, and only the press reaction force acts on the coating material 6 that has entered the film formation gap 5. Therefore, the coating material 6 transported by the second roll 2 is not transferred to the third roll 3, and the leading edge 6a of the coating material 6 that first entered the film formation gap 5 is crushed by the press reaction force. If the "thick coating portion" of the tip portion 6a is crushed when it first enters the film-forming gap 5, the press reaction force acting on the tip portion 6a will decrease when the tip portion 6a passes through the film-forming gap 5 the next time after the second roll 2 has rotated once.

[0026] In step P5 (a predetermined time waiting step), after the tip 6a of the coating material 6 first enters the deposition gap 5 in step P4, the process waits without changing the peripheral speed of either the second roll 2 or the third roll 3 for a period from the time the tip 6a of the coating material 6 first enters the deposition gap 5 until a "predetermined time" (or waiting time) has elapsed. In other words, after the tip 6a of the coating material 6 first enters the deposition gap 5, the peripheral speeds of the second roll 2 and the third roll 3 are maintained equal for the "predetermined time." Therefore, no shear force or transfer force is generated until the "predetermined time" has elapsed, and the coating material 6 is not transferred to the third roll 3, and remains attached to the surface of the second roll 2. In this case, the "predetermined time" is at least the time required for the tip 6a of the coating material 6 that first enters the coating gap 5 to completely pass through the coating gap 5, or a longer "waiting time," which is set in advance based on the results of experiments, simulations, etc.

[0027] In step P6 (peripheral speed adjustment step), after waiting until the "predetermined time" has elapsed in step P5, the number of rotations or rotation speed of each of the rolls 1, 2, and 3 is again controlled to adjust the peripheral speed of each of the rolls 1, 2, and 3. In this step P6, the peripheral speeds of each of the rolls 1, 2, and 3 after the "predetermined time" has elapsed are set. In adjusting the peripheral speeds in this step P6, for example, as shown in FIG. 3(c), when the peripheral speed of the third roll 3 is 100%, the number of rotations or rotation speed of each of the rolls 1, 2, and 3 is controlled so that the peripheral speed of the second roll 2 is 70% of the peripheral speed of the third roll 3 and the peripheral speed of the first roll 1 is 28% of the peripheral speed of the third roll 3 (i.e., 40% of the peripheral speed of the second roll 2). Specifically, from the state in which the rotation of each of the rolls 1, 2, and 3 is controlled between the above-mentioned steps P1 and P5, the rotation speed of the second roll 2 is reduced, thereby reducing the peripheral speed of the second roll 2 to approximately 70% of the peripheral speed of the third roll 3. In addition, as the peripheral speed of the second roll 2 is reduced, the peripheral speed of the first roll 1 is also reduced to approximately 40% of the peripheral speed of the second roll 2. Therefore, a new peripheral speed difference is generated between the second roll 2 and the third roll 3. By providing a peripheral speed difference between the second roll 2 and the third roll 3, a shear force and a transfer force are applied to the coating material 6 when it enters the film-forming gap 5 between the second roll 2 and the third roll 3.

[0028] In process P7 (deposition gap entry process), the coating material 6, which was transferred to the surface of the second roll 2 in the aforementioned process P3 and then passed through the deposition gap 5 for the first time in the aforementioned process P4, with the "thick coating portion" of the leading edge 6a crushed, enters the deposition gap 5 in the aforementioned process P6, where a peripheral speed difference has been established between the second roll 2 and the third roll 3. In this process P7, as shown in Figure 3(c) , the peripheral speed difference between the second roll 2 and the third roll 3 generates the shear force described above. Therefore, a transfer force, which is a combined force of the press reaction force and the shear force, acts on the surfaces of the second roll 2 and the third roll 3.

[0029] Specifically, as shown in Figure 5, if the press reaction force is F, the shear force (coating interface shear force) is τ, and the transfer force is Ft, the film formation gap (G 2·3 When the coating material 6 enters the coating film interface 5, press reaction forces F2 and F3, shear forces τ2 and τ3, and transfer forces Ft2 and Ft3, which are the combined forces of press reaction forces F2 and F3 and shear forces τ2 and τ3, act on the interface between the surfaces of the second roll 2 and the third roll 3 and the coating material 6 (i.e., the coating film interface). In this case, because the peripheral speed V3 of the third roll 3 is faster than the peripheral speed V2 of the second roll 2, the shear force τ3 acting on the coating film interface on the third roll 3 is greater than the shear force τ2 acting on the coating film interface on the second roll 2. The press reaction force F2 acting on the coating film interface on the second roll 2 and the press reaction force F3 acting on the coating film interface on the third roll 3 are equal regardless of the difference in peripheral speed. Therefore, the transfer force Ft3 acting on the coating film interface on the third roll 3 is greater than the transfer force Ft2 acting on the coating film interface on the second roll 2. Therefore, the coating material 6 that has entered the film-forming gap 5 is peeled off from the coating interface of the second roll 2 and transferred to the third roll 3 side (specifically, to the surface of the substrate 7 on the third roll 3).

[0030] Then, in process P8 (third roll transfer process), the coating material 6 that entered the deposition gap 5 in process P7, where a peripheral speed difference was established between the second roll 2 and the third roll 3, is transferred to the third roll 3. Specifically, the coating material 6 is transferred to the substrate 7 that is wrapped around the third roll 3 and transported like a web. In other words, a layer of the "wet powder" (coating material 6) is deposited on the substrate 7.

[0031] As described above, in the wet powder coating method according to an embodiment of the present invention, when starting to transfer the "wet powder" (coating material 6), the rotation of the second roll 2 and the third roll 3 is initially controlled so that the peripheral speed of the second roll 2 and the peripheral speed of the third roll 3 are equal. Therefore, only a press reaction force (squeezing force) acts on the "wet powder" (coating material 6) that passes through the coating gap 5 between the second roll 2 and the third roll 3 for the first time. Then, after a "predetermined time" has elapsed, the rotation of the second roll 2 is controlled so that the peripheral speed of the second roll 2 is decelerated, creating a peripheral speed difference between the second roll 2 and the third roll 3, so that a shear force (stretching force) acts on the "wet powder" (coating material 6) in addition to the press reaction force. In this way, in the wet powder film-forming method according to an embodiment of the present invention, the rotation of the second roll 2 and the third roll 3 is controlled when starting to transfer the "wet powder" (coating material 6), thereby dispersing and applying the above-mentioned press reaction force and shear force. This also disperses the force acting on the substrate 7 being transported as a web on the third roll 3, preventing damage to the foil-like substrate 7 due to the combined force of the press reaction force and shear force acting as an excessive transfer force on the substrate 7.

[0032] Therefore, according to the wet powder film forming method of this embodiment of the present invention, a coating device CE consisting of at least three rolling rolls (first roll 1, second roll 2, and third roll 3) can be used to appropriately transfer the coating material 6 in a "wet powder" state to a foil-like substrate 7 to form a film. [Explanation of symbols]

[0033] 1 Roll 1 2. Roll 2 3 Third Roll 4. Supply Gap 5. Deposition gap 6 Coating material (wet powder; positive electrode active material) 6a (Coating material) tip 7. Substrate (current collector, electrode foil) 8 Negative electrode active material CE Coating Device

Claims

[Claim 1] A method for forming a film from a wet powder using a coating device that includes a first roll, a second roll, and a third roll arranged parallel to one another, the coating device transferring a coating material introduced into a supply gap between the first roll and the second roll to the second roll and transporting the coating material by the second roll, and transferring the coating material that has entered a film-forming gap between the second roll and the third roll to a substrate transported by the third roll, the method comprising: rotating the first roll and the second roll so that the peripheral speed of the second roll is faster than the peripheral speed of the first roll, transferring the wet powder to the second roll; At the beginning of feeding the wet powder into the supply gap, the second roll and the third roll are rotated so that the peripheral speed of the second roll and the peripheral speed of the third roll are equal to each other; After a predetermined time has elapsed since the tip of the wet powder first entered the film formation gap, the second roll and the third roll are rotated so that the peripheral speed of the third roll is faster than the peripheral speed of the second roll, thereby transferring the wet powder to the substrate on the third roll. A method for forming a film from wet powder.

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