Drying method of the coating film of a secondary battery and the coating device thereof

Abstract

The present invention is a method for drying a coating film. A coating liquid (2) of an active material composite for a secondary battery is intermittently or continuously coated onto a metal foil current collector (1) that is conveyed in one direction to form a coating film (3) on the current collector (1). The metal foil current collector (1) is transferred to a drying process, and the metal foil current collector (1) is heated in the drying process to dry the coating film (3). Before or during the drying process of the coating film (3), a laser light (L) is irradiated onto the coating film (3) to form holes (3h) in the coating film (3).

Description

Technology Field

[0001] The present invention relates to a drying method for a coating film of a high-capacity secondary battery (including a lithium-ion capacitor) thickly coated on a current collector composed of a long and wide metal foil, and to a coating apparatus. Background Technology

[0002] Currently, secondary batteries, such as large-capacity lithium-ion batteries, are receiving great attention as an environmental measure, serving as power sources for electric vehicles, power engines, and electronic devices. Taking lithium-ion batteries as an example, the positive and negative electrodes are formed by applying a mixture of positive and negative active materials (coating solution) thickly, for example, to a thickness of 100 μm onto a strip-shaped current collector (metal foil), and then drying and curing this to create an original sheet for the secondary battery. Then, this current collector (original sheet for the secondary battery) is divided into narrow current collectors or rectangular sheets by a predetermined width.

[0003] A narrow current collector is wound into a cylindrical shape through a separator to form an electrode assembly, which is then housed in a cylindrical battery can, or the cylindrical electrode assembly is molded into a flatter shape and housed in a rectangular battery can, and an electrolyte is injected to form a secondary battery.

[0004] In the case of rectangular sheets, multiple positive and negative electrodes are stacked through a separator and stored in an envelope, and an electrolyte is injected in the same way to form a secondary battery.

[0005] The coating film of the positive / negative electrodes above is formed by applying a coating liquid (active material mixture) extruded from the die of a coating device in a rectangular shape at regular intervals on one or both sides of a long and wide current collector (metal foil), or by continuous application. The coating liquid is a viscous material in the form of a water-based or solvent-based slurry or paste.

[0006] After coating, the above coating film is transferred to a drying oven in a viscous state, where most of the solvent or moisture is removed by volatilization or evaporation. Subsequently, a roll press is performed to increase the density of the cured coating film. Additionally, further drying is performed to remove any remaining solvent or moisture within the coating film, thereby forming a hard coating film on the metal foil (one or both sides), which becomes the electrode plate of the secondary battery.

[0007] Patent Document 1 can be cited as an example of the above drying oven. The drying oven described in Patent Document 1 comprises a furnace body through which a strip-shaped collector conveyed in a horizontal direction passes, and a blower unit that blows air into the furnace body to dry a coating film. Prior art literature

[0008] Japanese Patent Publication No. Hei 10-228898 The problem to be solved

[0009] In such a drying oven that conveys the entire strip-shaped current collector in a horizontal direction, if the positive / negative coating film is applied thickly, drying takes time, so the drying oven becomes, for example, 100m long. This long drying oven requires a vast installation area.

[0010] The present invention has been made in consideration of the problems of the conventional example. The first objective of the present invention is to provide a method for drying a coating film of a large-capacity secondary battery that can shorten the length of the drying furnace by rapidly drying the coating film of the secondary battery thickly coated on a current collector composed of a long and wide metal foil, and the second objective is to provide a coating device that can shorten the drying furnace of the coating film of the secondary battery. means of solving the problem

[0011] The invention described in claim 1 is a method for drying a thickly coated coating film (3).

[0012] A coating liquid (2) of an active material composite for a secondary battery is intermittently or continuously coated onto a long strip-shaped metal foil current collector (1) that is conveyed in one direction to form a coating film (3) on the current collector (1).

[0013] In a method for drying a coating film, wherein the metal foil current collector (1) is transferred to a drying process and the metal foil current collector (1) is heated in the drying process to dry the coating film (3),

[0014] During the drying process of the coating film (3), a laser beam (L) is irradiated from the surface side of the coating film (3) to form a hole (3h) in the coating film (3) in a semi-dry state in which the surface is dried and the interior is maintained in a paste state.

[0015] The invention described in claim 2 is a drying method for a coating film (3) described in claim 1, wherein

[0016] The above hole (3h) is characterized as being a blind hole (3h1) that does not reach the metal foil current collector (1) from the surface of the coating film (3), or a through hole (3h2) that penetrates the coating film (3) and the metal foil current collector (1).

[0017] The invention described in claim 3, in a method for drying a coating film described in claim 1 or 2,

[0018] It is characterized by sucking in the atmosphere within the irradiation range of the above laser light (L) to remove fine dust generated from the coating film (3) by laser irradiation.

[0019] The invention described in claim 4 is a first coating apparatus (furnace irradiation: FIG. 1, FIG. 2) for carrying out the drying method of a coating film described in claim 1. The first apparatus (20) is,

[0020] A collector transmission unit (30) that transmits a collector (1) composed of a long metal foil in one direction, and

[0021] A die (21) for forming a coating film (3) on the surface of the current collector (1) by applying a coating liquid (2), which is an active material mixture for a secondary battery, to the surface of the current collector (1), and

[0022] A drying oven (40) for drying the coating film (3), which is installed downstream of the above die (21) and is equipped with a passageway (46) through which the above collector (1), which is conveyed in one direction, passes, and a drying heat source (H), and

[0023] A recovery unit (38) that recovers a current collector (1) coated with a dried coating film (3) that is discharged from the above drying oven (40), and

[0024] A coating device (20) comprising a laser irradiation device (50) that irradiates a laser beam (L) onto a coating film (3) that has become semi-dried in the above drying oven (40) to form a blocked hole (3h1) that does not reach the current collector (1) from the surface of the coating film (3), or to form a penetrating hole (3h2) that penetrates the coating film (3) and the current collector (1).

[0025] The laser irradiation device (50) is formed on the side of the drying oven (40), and

[0026] The side wall (40a) of the above drying oven (40) is characterized by having a transparent window (42) through which the laser light (L) passes.

[0027] The invention (suction treatment) described in claim 5 is, in the coating device (20) described in claim 4,

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[0034] It is characterized by further having a suction nozzle (70) having a suction port (71) that covers the irradiation range of the laser light (L). Effects of the invention

[0035] According to the present invention, holes (3h) are formed in the coating film (3) using laser light (L) before or during the drying process of the coating film (3). Therefore, when the drying process begins, the solvent or moisture within the coating film (3) evaporates not only from the surface of the coating film (3) but also from the inner surface of the holes (3h), thereby shortening the drying time of the coating film (3) and further shortening the drying distance, that is, the total length of the drying oven (40).

[0036] In addition, by sucking in the atmosphere within the irradiation range of the laser light (L), fine dust generated from the coating film (3) by laser irradiation can be sucked out and removed, thereby avoiding problems that occur in subsequent processes caused by fine dust adhering to the surface of the coating film (3). Brief explanation of the drawing

[0037] FIG. 1(a) is a schematic diagram of embodiment 1 of the coating device of the present invention, and FIG. 1(b) is a schematic diagram of the drying oven of the device. Figure 2 is an enlarged perspective view of the laser irradiation portion of Figure 1 on a rectangular coating film. Figure 3 is an enlarged perspective view of the laser irradiation portion of Figure 1 for a continuous coating film. FIG. 4 is a schematic diagram of embodiment 2 of the coating device of the present invention. FIGS. 5(a) and FIGS. 5(b) are schematic diagrams of embodiment 3 of the coating device of the present invention. FIGS. 6(a) and FIGS. 6(b) are enlarged perspective views of the laser irradiation part of a branched laser irradiation device. FIG. 7(a) is an enlarged cross-sectional view showing a hole formed in the coating film, and FIG. 7(b) is an enlarged cross-sectional view showing a through hole formed in the coating film and the current collector. Specific details for implementing the invention

[0038] Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an embodiment 1 according to the present invention, FIG. 4 is an embodiment 2, FIG. 5(a) and FIG. 5(b) are schematic diagrams of an embodiment 3 of a coating device (20). Any coating device (20) is a device for manufacturing a substrate (10) for a large-capacity secondary battery by coating a coating liquid (2) onto a wide and long metal foil current collector (1) that is conveyed by roll-to-roll, and drying the same. The device (20) is composed of a current collector delivery unit (30), a coating unit including a die (21), a backup roller (34), a conveying roller (36a to 36n), a drying oven (40), a recovery unit (38), a laser irradiation device (50), an image processing device (60) installed as needed, a suction nozzle (70), and a control unit (80).

[0039] The current collector (1) applied to the coating device (20) is composed of a wide and long metal foil and is wound in a roll shape. This is called a metal foil roll (1a). The current collector (1) is aluminum foil when it is the positive electrode and copper foil when it is the negative electrode.

[0040] The coating liquid (2) applied to the current collector (1) is, in the case of an anode, an anode active material composite prepared by dispersing and mixing a lithium transition metal composite oxide, such as LixCoO2, LixNiO2, LixMn2O4, LixMnO3, LixNiyCo(1-y) O2, etc., with a conductive material such as carbon black, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP).

[0041] In the case of the coating liquid (2) of the cathode, for example, a carbonaceous material such as carbon fiber, activated carbon, a conductive polymer material such as polyacetylene, polypyrrole, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP) is dispersed and mixed with a conductive material such as carbon black, a binder such as polyvinylidene fluoride (PVDF), and a cathode active material composite prepared by mixing the following: a pyrolytic carbonaceous material such as pitch coke, needle coke, petroleum coke, graphite, glassy carbonaceous material, phenolic resin, furan resin, etc., a carbonaceous material such as carbon fiber, activated carbon, etc., a binder such as polyacetylene, etc., and a solvent such as N-methyl-2-pyrrolidone (NMP).

[0042] A metal foil roll (1a) wound in a roll shape is rotatably maintained in a current collector output unit (30) and is supplied from the current collector output unit (30) and continuously conveyed in one direction.

[0043] Upon reaching the die (21), the coating liquid (2) discharged from the die (21) is coated on one or both sides. Then, when it enters the drying oven (40), the coating liquid (2) is dried and hardened, and a hardened coating film (3z) is formed on the surface of the current collector (1), becoming a plate (10) for a secondary battery and recovered in the recovery unit (38).

[0044] During this time, while the coating layer (3) is in an un-dried or semi-dried state, a laser light (L) is irradiated onto the surface of the coating film (3) to create a plurality of holes (3h) at predetermined intervals throughout the coating film (3).

[0045] The hole (3h) has a closed hole (3h1) that does not reach the current collector (1) from the surface of the coating layer (3) as in FIG. 7(a), and a through hole (3h2) that penetrates the coating layer (3) and the current collector (1) as in FIG. 7(b).

[0046] Coating of the coating liquid (2) onto the collector (1) by the coating device (20) may be performed on only one side as in FIG. 1 or FIG. 4, or on both sides as in FIG. 5(a) and FIG. 5(b). In the case where it is performed on only one side, the coating is performed by one die (21), and in the case where it is performed on both sides, the coating is performed by two dies (21a and 21b) installed facing the front and back of the collector (1), or by two dies (21a and 21b) installed at a position away from the entrance side of the drying oven (40) and close to the entrance side as in FIG. 5(b). Of course, it is not limited to these. The transport of the collector (1) is continuous transport in one direction.

[0047] In the coating process, there is a case where a rectangular coating film (3) is formed at regular intervals in the central part of the current collector (1) by intermittently extruding the coating liquid (2) from the die (21) by pump operation (Fig. 2), and a case where the coating liquid (2) is continuously extruded from the die (21) by continuous transfer of the current collector (1) to continuously coat the coating film (3) of the coating liquid (2) in the central part of the current collector (1) (Fig. 3).

[0048] In the case of a rectangular coating film (3), the area between the side edge portion (3c) of the coating film (3) and the side of the collector (1), and the area between adjacent coating films (3) at the front and rear, becomes a non-coated area (5) (Fig. 2).

[0049] In the case of continuous extrusion, the area between the side edge portion (3c) of the coating film (3) and the side edge of the collector (1) becomes a non-coated area (5) (Fig. 3).

[0050] And this entire unit (1) becomes a plate (10) for a secondary battery after undergoing a drying and curing treatment of the coating film (3), and although not shown, it can then be separated into a plurality of strips or rectangular sheets according to the shape of the product as described above, and a tab is formed in the non-coated area (5) as needed.

[0051] Products to which the original plate (10) is applied include, for example, secondary batteries or capacitors. The secondary battery is not limited to lithium-ion secondary batteries and may be other secondary batteries such as nickel-hydrogen secondary batteries or nickel-cadmium secondary batteries. The capacitor may be, for example, an electric double layer capacitor or a lithium-ion capacitor.

[0052] A coating film (3) coated on the surface of the collector (1) has a hole (3h1) or a through hole (3h2) formed by a laser beam (L). However, as shown in FIG. 1, there is a case where the laser beam (L) is irradiated inside the drying oven (40) (Embodiment 1), and as shown in FIG. 4, there is a case where the irradiation is performed before entering the drying oven (40) (Embodiment 2). Furthermore, the drying oven (40) is divided into two types based on the difference in the irradiation position of the laser beam (L) as described above. In Embodiment 1, a transparent window (42) made of heat-resistant glass (44) is formed on the side wall (40a) of the drying oven (40) ( FIG. 1(b)).

[0053] As for heat-resistant glass (44), borosilicate glass or quartz glass is used, but quartz glass is preferred to allow laser light (L) to pass through without distortion.

[0054] The collector output unit (30) supports and rotates a metal foil roll (1a) wound in a roll shape and supplies it to the collector (1) in the direction of the die (21), and the supply of the collector (1) is performed by a supply servo motor (not shown).

[0055] The coating unit including the die (21) is composed of the die (21) and a coating liquid supply unit (25) that supplies the coating liquid (2) to the die (21) without excess or deficiency by pump operation.

[0056] The die (21) has a tapered cross-section, and a liquid storage section (22) is formed inside it as a space for storing the coating liquid (2), and this liquid storage section (22) is connected to a slit-shaped nozzle opening (23).

[0057] The nozzle opening (23) is extended along the width direction of the collector (1). The opening dimension (height dimension) of the nozzle opening (23) is, for example, 0.1 to 10 mm. And, the coating liquid (2) is coated on the collector (1) with a width dimension approximately the same as the width dimension of the nozzle opening (23).

[0058] A coating liquid supply unit (25) that supplies a coating liquid (2) is connected to the liquid storage unit (22). The direction in which the coating liquid (2) stored in the liquid storage unit (22) flows from the nozzle opening (23) to the collector (1) is perpendicular to the surface of the collector (1), and the coating is applied along the conveying direction of the collector (1).

[0059] The liquid storage unit (22) can store the coating liquid (2) supplied from the coating liquid supply unit (25), and the coating liquid (2) stored in the liquid storage unit (22) is discharged onto a collector (1) that is transferred from the nozzle port (23) in a roll-to-roll manner by pump pressure, and the coating liquid (2) is coated onto the collector (1). The thickness of the film (coating film (3)) of the coating liquid (2) coated on the collector (1) is designed to be almost constant in the width direction.

[0060] When a coating operation is being performed on a die (21), the amount of coating liquid (2) in a tank (not shown) that supplies coating liquid (2) to the die (21) may decrease, or the temperature of the liquid may change due to ambient temperature, or the viscosity of the coating liquid (2) may change, and the discharge amount of the pump (not shown) that supplies coating liquid (2) to the die (21) may change.

[0061] If the discharge amount changes, basically, the pump's rotational speed is corrected to compensate, but if the change in the discharge amount is small, the gap (g) between the die (21) and the collector (1) is adjusted.

[0062] By this, in the case of continuous coating, the dimensions in the width direction of the coating film (3) and the coating thickness are maintained. In the case of intermittent coating, in addition to these, the precision of the dimensions in the width direction of the coating section is maintained.

[0063] The backup roller (34) of FIG. 1 is positioned facing the die (21) in the front. In FIG. 5(a), a pair of front and back dies (21a and 21b) face each other in the front with the collector (1) in between, and there is no backup roller (34). FIG. 5(b) is another example in which the back die (21b) is installed near the entrance of the drying oven (40) relative to the front die (21a).

[0064] The collector (1) is guided in one direction by a backup roller (34) positioned facing the die (21). The gap (gap (g)) between the collector (1) and the slit-shaped nozzle opening (23) of the die (21) is maintained constant, and coating of the coating liquid (2) is performed in this state. The width direction of the nozzle opening (23) of the die (21) and the direction of the rotation centerline of the backup roller (34) are parallel.

[0065] At the front and rear of the backup roller (34), an inlet-side return roller (36a) and an outlet-side return roller (36b) that guide the collection unit (1) are installed so as to be rotatable. The entire return roller is indicated by the symbol 36.

[0066] In order to adjust the gap (g) between the nozzle opening (23) of the die (21) and the current collector (1) running on the backup roller (34), the die (21) or the backup roller (34) is supported so that it can move in a close-range direction with an air cylinder not shown.

[0067] The collector (1) supplied from the collector output unit (30) is conveyed at a predetermined speed while maintaining a predetermined tension (tension) by the rotational drive of a plurality of conveying rollers (36a to 36n) arranged at predetermined intervals. In addition, the rotational speed of the metal foil roll (1a) in the collector output unit (30), the winding speed of the recovery unit (38), and the rotational speed of the conveying rollers (36a to 36n) are controlled by the control unit (80).

[0068] The drying oven (40) is positioned downstream of the die (21). The drying oven (40) is roughly composed of a cylindrical body surrounded by side walls (40a) and having a passage (46) through which a long metal foil collector (1) passes, a heat source (a high-temperature steam passed through a pipe or an electric heater) (H) installed as needed to heat and dry the metal foil collector (1) while it is moving in the passage (46), a dryer (48) that blows air to dry the metal foil collector (1), and a suction nozzle (70) that sucks up fumes or fine dust generated from the irradiation area.

[0069] Inside the drying oven (40), a plurality of heat sources (H) or dryers (48) are arranged along the passage (46) of the collector (1). The drying oven (40) dries the coating film (3) formed on the collector (1) by the radiant heat of the heat source (H) or the hot air of the dryer (48).

[0070] And, there are two types (Embodiments 1 and 2) of this drying oven (40) depending on the location where hole formation treatment by laser light (L) is performed.

[0071] In the drying oven (40) of embodiment 1, laser processing is performed on the coating film (3) inside the oven, so a transparent window (42) with heat-resistant glass (44) inserted is formed on the side wall (40a).

[0072] In the drying oven (40) of embodiment 2, laser processing is performed on the coating film (3) in front of the oven, so a transparent window (42) is not formed on the side wall (40a).

[0073] And, in the case of FIG. 1, since the coating film (3) is formed on only one side of the collector (1), the transparent window (42) is formed on one side wall (40a), but as in FIG. 5, when the coating film (3) is formed on both sides of the collector (1), the transparent window (42) is formed on both side walls (40a).

[0074] The suction nozzle (70) opens toward the irradiation range of the laser light (L) and has a suction port (71) that covers this irradiation range. Additionally, a blower nozzle (76) that blows air toward the suction port (71) may be installed. The discharge port (77) of the blower nozzle (76) is directed toward the suction port (71), and the space between the suction port (71) and the discharge port (77) is the irradiation range of the laser light (L).

[0075] The recovery unit (38) is installed on the opposite side of the collector discharge unit (30) and is installed at the lowest downstream end of the coating device (20) in the area where a rectangular dry coating film (3z) is formed at a predetermined interval on at least one surface of the collector (1), or where a disc (10) having a continuous dry coating film (not shown) formed thereon is wound into a roll shape.

[0076] Winding is performed by synchronizing a winding servo motor (not shown) through a dancer roller (e.g., a conveyor roller (36a or 36n)) which is one of the conveyor rollers (36), so that the tension of the current collector (1) supplied in cooperation with the current collector discharge unit (30) is always constant.

[0077] The laser irradiation device (50) is composed of a laser emission unit (51) composed of an optical system combining various lens systems, a laser generation unit (52) that outputs laser light (L), and a galvanometer driving unit (59), and the laser emission unit (51) and the laser generation unit (52) are connected by a laser transfer member (54). By this, laser light (L) is input to the laser emission unit (51).

[0078] The laser irradiation device (50) may emit a single laser beam (L) as in FIG. 2 or FIG. 3, or it may branch as in FIG. 6. The laser irradiation device (50) of FIG. 6 has a branching lens (58) installed at the exit port of the laser emission unit (51), and the laser beam (L) coming out of the exit port of the laser emission unit (51) is branched to become multiple laser beams (La~Ln).

[0079] The galvanometer drive unit (galvanometer scanner) (59) is installed in either a laser irradiation device (50) that emits a single laser beam (L) or a branched laser irradiation device (50).

[0080] This laser irradiation device (50) is a device that uses galvanometer mirrors (59a and 59b) to control the laser light (L) in any direction in XY 2D (or, not shown, XYZ 3D) by adjusting the mirror angle of a driving motor (59m and 59n) to irradiate the laser light (L) to a pinpoint (in the case of 3D, the height can be adjusted).

[0081] Additionally, as shown in FIG. 5, when the laser irradiation device (50) is on the front and back sides, to simplify the explanation, the laser irradiation device (50b) on the back side uses the description and symbol of the laser irradiation device (50a) on the front side.

[0082] In the present invention, since the current collector (1) is moving continuously in a certain direction, as shown in FIG. 1(b), the galvanometer driving unit (59) is operated in two dimensions in the XY direction by adjusting the mirror angle in accordance with the movement speed of the current collector (1), and the laser light (L) is moved in the same direction to a single point from the home position to the hole formation processing completion position to perform the hole formation processing. When the hole formation processing is finished, the laser light (L) is turned off, returns to the home position, and performs the hole formation processing of the next stage.

[0083] In the case where the laser emitter (51) has a structure in which the branched laser beams (La~Ln) branch in a direction perpendicular (or intersecting) to the conveying direction as in FIG. 6(b), it is preferable to move back and forth in accordance with the direction of movement of the collector (1). However, in the case of a branched structure dispersed in a cylindrical shape as in FIG. 6(a), or in the case where there is only one laser beam (L) as in FIG. 2, a plurality of laser emitters (not shown) are prepared at a position perpendicular (or intersecting) to the direction of movement of the collector (1), or the laser beam (L) is steered along the XY two axes by adjusting the mirror angle to perform hole formation processing.

[0084] The laser light (L) used here is a YAG laser or YVO4 laser of 1.064 μm as the fundamental wave, a green laser light of 532 nm obtained through a wavelength conversion element of the second harmonic (SHG), a UV laser light of 355 nm obtained through a wavelength conversion element of the third harmonic (THG), or a laser light of a shorter wavelength or longer.

[0085] Laser light (L) is suitable for micro-processing because its focusing ability increases as the wavelength shortens, resulting in higher energy efficiency per unit; therefore, it is used in precision parts and semiconductor-related industries.

[0086] The laser light (L) is output by methods such as continuous oscillation, pulse oscillation, Q-switched pulse oscillation, and single mode. Since the second harmonic and third harmonic have a high absorption rate with respect to the metal foil, when the second harmonic or third harmonic reaches the metal foil during the hole processing described later, it is heated instantaneously, causing the metal foil to instantly become high temperature, thereby increasing the adhesion between the coating film (3) applied to the metal foil current collector (1) and the current collector (1). In other words, the peel strength of the coating film (3) is improved.

[0087] When drilling a hole (3h) with 1.064 μm YAG laser light or YVO4 laser light, it is usually done in pulsed mode.

[0088] When using green laser light (second harmonic) or UV laser light (third harmonic), the irradiated material is sublimated and immediately becomes a gas. When using green laser light or UV laser light, thermal deterioration of the material forming the coating film (3) is suppressed, making it suitable.

[0089] When forming holes using YAG or YVO4 laser light in pulsed mode, it is preferable to blow air (assist air) onto the molten portion to remove the molten material (active material composite or metal foil) from the molten area. In this case, since the molten material becomes fine particles and scatters into the surroundings, it is necessary to remove them by suction.

[0090] In addition, when using green laser light or UV laser light, vapor from the active material mixture or metal foil rises from the irradiated area and cools and solidifies to become fine dust that scatters into the surroundings; therefore, it is similarly necessary to remove it by suction.

[0091] The image processing device (60) is composed of a CCD camera (62), a light source for illumination (not shown), an external monitor (65), an input device (68), and a control unit (80) including a CPU (81), ROM (82), and RAM (83).

[0092] A CCD camera (62) is used to interpret an image of a hole (3h) formed on the surface of a coating film (3) and convert it into a digital signal, and is connected to a CPU (81) within a control unit (80). An image of a hole (3h) of the coating film (3) captured by the CCD camera (62) is converted into a digital signal and transmitted to the CPU (81).

[0093] Typically, a He-Ne laser is used for aligning the optical axis between the image processing device (60) and the laser light (L).

[0094] A total reflection mirror (56) of the type of transmission is built into the optical system of the laser emitter (51) as described above, and the laser light (L), illumination light, and laser light for optical axis alignment input into the laser emitter (51) are total reflections.

[0095] The optical axis of the light that is totally reflected by the total reflection mirror (56) is set to coincide with the optical axis of the light input to the image processing device (60), and the laser light (L) can be concentrated at a point on this optical axis. In addition, in the coating device (20) of this embodiment, the focal position of the CCD camera (62) equipped in the image processing device (60) is set to coincide with the focal position of the laser light (L) irradiated by the laser generating unit (52).

[0096] A light source (not shown) for work lighting is directed to a laser emitter (51) through a fiber optic cable (not shown), and the directed light passes through an optical system via a transparent total reflection mirror (56) to illuminate the surface (hole (3h)) of the coating film (3).

[0097] The control unit (80) is composed of a CPU (81), ROM (82), RAM (83), an external monitor (65), and an input device (68) such as a keyboard, and the processing sequence of the coating device (20) and the galvanometer driving sequence are all programmed in the ROM (82). In addition, the image signal of the hole (3h) of the coating film (3) captured from the image processing device (60) is stored in the RAM (83).

[0098] The galvanometer driving sequence is connected to the CPU (81) for control purposes to convert the optical path of the laser light (L) into 1 to 3 dimensions, and is configured to move the optical path of the laser light (L) based on the command of the CPU (81).

[0099] The external monitor (65) is for illuminating the holes (3h) of the coating film (3) captured by the image processing device (60).

[0100] The input device (68) is for the operator to manually input the condition settings of the CPU (81).

[0101] In this embodiment, the laser irradiation device (50) and the image processing device (60) are integrated.

[0102] In the following description, Embodiment 1 is described, followed by Embodiments 2 and 3. In the description of Embodiments 2 and 3, to avoid duplication of explanation, the focus will be on the parts that differ from Embodiment 1.

[0103] Also, in FIGS. 1, FIGS. 4, FIGS. 5(a), and FIGS. 5(b), examples of rectangular coating films (3) are shown, but of course, they also apply to continuous coating films (3).

[0104] (Embodiment 1: FIG. 1)

[0105] Here, a representative example is given in which the entire house (1) is coated on one side.

[0106] In the normal operating state of the coating device (20), the collector (1) is discharged from the metal foil roll (1a) of the collector discharge unit (30) by the operation of the collector discharge unit (30).

[0107] A viscous coating liquid (2) is extruded from a die (21) onto a discharged collector (1), and the coating liquid (2) is applied to the surface of the collector (1) with the width of the nozzle opening (23) of the die (21). The applied film-shaped coating liquid (2) is formed into a coating film (3).

[0108] In the case of continuous coating, the coating liquid (2) is continuously extruded onto the surface of the collector (1) in accordance with the movement of the collector (1), and a strip-shaped coating film (3) is formed.

[0109] In the case of intermittent extrusion, the coating liquid (2) is extruded intermittently to form rectangular coating films (3) on the surface of the current collector (1) at regular intervals. The formed portions of the coating films (3) and the non-coated areas (5), which are non-formed portions, appear alternately.

[0110] The coating film (3) formed in this way is transferred to a drying oven (40) in a state where it is applied to a strip-shaped collector (1) in the form of a viscous paste.

[0111] In the drying oven (40), the coating film (3) is gradually dried from the surface by receiving radiant heat from a drying heat source (H) and also being exposed to a drying wind from a dryer (48). At the point where the coating film (3) is semi-dried, the coating film (3) is irradiated with laser light (L). Furthermore, semi-drying means that the surface of the coating film (3) is dried while the interior remains in a paste state.

[0112] The CCD camera (62) continues to observe the current collector (1) being transported. When the CCD camera (62) captures the starting end (3b) of the coating film (3) and confirms that the leading end of the coating film (3) has entered the irradiation range of the laser light (L), the laser light (L) is irradiated from the laser emitter (51), and the laser light (L) moves in accordance with the movement of the current collector (1) according to the operation of the galvanometer drive unit (59), thereby making a hole (3h) (blocked hole (3h1) or through hole (3h2)) on the surface of the coating film (3) to the required depth.

[0113] As shown in Fig. 6(a), in the case of a branched type, multiple holes (3h) are formed simultaneously at once.

[0114] As shown in FIG. 2, in the case of a non-branching type, drilling operations are performed simultaneously by the required number of laser emitters (51). At this time, as described above, the laser beam (L) may be steered in two dimensions of XY (or three dimensions of XYZ if adjustment of the depth of focus in the Z direction is also necessary) by adjusting the mirror angle while matching the movement speed of the collector (1), so that multiple drilling operations are performed by one laser emitter (51).

[0115] A hole (3h) formed by laser light (L) (in the case of multiple holes, one hole (3h) aligned with the optical axis) is observed by a CCD camera (62), and the data is stored in RAM.

[0116] When the laser light (L) is YAG or VO4, the irradiated material only melts at the irradiation point and does not sublimate. Therefore, generally, an assist gas is sprayed toward the hole (3h) to blow away the molten material (hot water). As previously described, this molten material becomes fine particles and adheres to the surface of the coating film (3), thereby impairing the quality of the product, so it is removed by suction through the suction nozzle (70). At this time, if the discharge port (77) of the blower nozzle (76) is formed toward the suction port (71) of the suction nozzle (70), the fine particles can be effectively removed.

[0117] In this regard, if the laser light (L) is a green laser light (second harmonic) or a blue laser (third harmonic), sublimation occurs in the irradiated part, and the irradiated object rises immediately from the irradiated part as a high-temperature gas. This high-temperature gas also comes into contact with the surrounding cold air directly above it and instantly becomes fine powder, but, as with the above, it is sucked out by the suction nozzle (70) and does not adhere to the surface of the coating film (3). Furthermore, if the laser light (L) is a green laser light (second harmonic) or a blue laser (third harmonic), the thermal effect on the irradiated part is small, so it does not cause damage to the coating film (3).

[0118] Since the periphery and inner surface of the hole (3h) formed in this way are maintained in a viscous state, the irradiation marks caused by the laser light (L) are erased by the surface tension of the periphery and inner surface of the hole (3h), and these surfaces become smooth surfaces without irregularities.

[0119] As described above, if a blocked hole (3h1) or a through hole (3h2) is formed in the coating film (3) during drying, the solvent or moisture remaining inside the coating film (3) then escapes through the hole (3h), thereby promoting the drying of the coating film (3). When the drying of the coating film (3) is promoted, the drying time or the distance required for drying is naturally shortened, and as a result, the overall length of the drying oven (40) can be shortened.

[0120] When drying is finished, the current collector (1) becomes a secondary battery plate (10) and is wound onto the recovery unit (38).

[0121] FIGS. 5(a) and FIGS. 5(b) show the case where the coating liquid (2) is applied to both sides of the current collector (1). FIGS. 5(a) shows the case where the dies (21a and 21b) are positioned facing each other directly on the front and back sides with the current collector (1) in between, and coating is performed simultaneously. Therefore, in the downstream portion of the dies (21a and 21b), a conveyor roller is not installed up to the exit of the drying oven (40) within the range where the coating film (3) is formed.

[0122] Likewise, FIG. 5(b) shows a case where the dies (21a and 21b) are installed at different locations, and a return roller cannot be installed in the area where the coating film (3) is formed from the lower die (21b) to the exit of the drying oven (40). However, a return roller can be installed in the non-coating area (5) on both sides of the collector (1).

[0123] In addition, to enable hole formation treatment by laser light (L) on both sides of the entire house (1), a transparent window (42) is formed on both side walls (40a) of the drying oven (40).

[0124] In addition, even when a coating film (3) is formed on both sides of the current collector (1), if the hole (3h) is a through hole (3h2), it is sufficient to form a transparent window (42) only on one side wall (40a) and process the hole formation by laser light (L) from one side.

[0125] (Embodiment 2: FIG. 4)

[0126] In this case, the hole-forming treatment is performed before entering the entrance of the drying oven (40). At this point, the coating film (3) is entirely in an un-dried state. When a laser beam (L) is irradiated onto the coating film (3) in this state, in the case of short-term irradiation, a depression (a blocked hole (3h1)) occurs because the coating film (3) is soft.

[0127] In the case of long-term irradiation, the area around the hole (3h) is dried into a thin film shape by heat, maintaining the shape of the hole (3h). Since the rest is the same as Embodiment 1, the description of Embodiment 1 is used by reference.

[0128] In the present invention, as described above, a hole-forming treatment is performed on an un-dried or semi-dried coating film (3) using a laser light (L), so that the evaporation of the solvent (moisture or solvent) from the hole (3h) is promoted in the subsequent drying process, thereby shortening the drying time and further shortening the overall length of the drying oven (40). Explanation of the symbols

[0129] g: Gap, H: Drying heat source, L: Laser light, La∼Ln: Branched laser light, 1: Metal foil current collector, 1a: Metal foil roll, 2: Coating liquid, 3: Coating film, 3b: Starting end, 3c: Side edge portion, 3h: Hole, 3h1: Blind hole, 3h2: Through hole, 3z: Cured coating film, 5: Non-coated area, 10: Disc (for secondary battery), 20: Coating device, 21(21a·21b): Die, 22: Liquid reservoir, 23: Nozzle opening, 25: Coating liquid supply section, 30: Current collector discharge section, 34: Backup roller, 36(36a∼36n): Return roller, 38: Recovery section, 40: Drying oven, 40a: Side wall, 42: Transparent window, 44: Heat-resistant glass, 46: Pass-through, 48: Dryer, 50: Laser irradiation device, 51: Laser emitter, 52: Laser generator, 56: Total reflection mirror, 54: Laser transfer element, 58: Branching lens, 59: Galvanometer drive unit, 59m·59n: Drive motor, 59a·59b: Galvanometer mirror, 60: Image processing unit, 62: CCD camera, 65: External monitor, 68: Input device, 70: Suction nozzle, 71: Suction port, 76: Blower nozzle, 77: Ejection port, 80: Control unit, 81: CPU, 82: ROM, 83: RAM

Claims

Claim 1 A method for drying a coating film, wherein a coating liquid (2) of an active material composite for a secondary battery is intermittently or continuously coated onto a long strip-shaped metal foil current collector (1) that is conveyed in one direction to form a coating film (3) on the current collector (1), and subsequently, the metal foil current collector (1) is transferred to a drying process inside a drying oven (40), and the metal foil current collector (1) is heated in the drying process to dry the coating film (3), wherein, during the drying process of the coating film (3), a laser light (L) is irradiated from the surface side of the coating film (3) from a laser irradiation device (50) disposed on the side of the drying oven (40) to pass through a transparent window (42) formed on the side wall (40a) of the drying oven (40) to form a hole (3h) in the coating film (3). Drying method of a coating film. Claim 2 A drying method for a coating film according to claim 1, wherein the hole (3h) is a closed hole (3h1) that does not reach the metal foil current collector (1) from the surface of the coating film (3), or a through hole (3h2) that penetrates the coating film (3) and the metal foil current collector (1). Claim 3 A method for drying a coating film according to claim 1 or 2, characterized by sucking in the atmosphere within the irradiation range of the laser light (L) to remove fine dust generated from the coating film (3) by laser irradiation. Claim 4 A current collector output unit (30) that transmits a current collector (1) composed of a long metal foil in one direction; a die (21) that forms a coating film (3) on the surface of the current collector (1) by applying a coating liquid (2), which is an active material composite for a secondary battery, to the surface of the transmitted current collector (1); a drying furnace (40) that dries the coating film (3) by being installed downstream of the die (21) and having a passageway (46) through which the current collector (1) being transported in one direction passes and a drying heat source (H); a recovery unit (38) that recovers the current collector (1) with the dried coating film (3) applied thereon, which is transmitted from the drying furnace (40); and a laser light (L) that irradiates the coating film (3), which has become a semi-dried state in which the surface is dried and the interior is maintained in a paste state within the drying furnace (40), so that the laser light does not reach the current collector (1) from the surface of the coating film (3). A coating device (20) comprising a laser irradiation device (50) that forms a blocked hole (3h1) or a penetrating hole (3h2) that penetrates the coating film (3) and the collector (1), wherein the laser irradiation device (50) is formed on the side of the drying oven (40), and a transparent window (42) through which the laser light (L) passes is formed on the side wall (40a) of the drying oven (40). Claim 5 A coating device according to claim 4, further characterized by having a suction nozzle (70) having a suction port (71) that covers the irradiation range of the laser light (L). Claim 6 delete

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