Applicator for electrostatic deposition coating of continuously moving web

Abstract

An applicator for electrostatically depositing dry powder on a grounded continuously moving conductive web is provided that includes a powder feed system, at least one powder dispenser, an electrostatic deposition chamber, and at least one wire electrode in the electrostatic deposition chamber. The opening of the powder dispenser outlet is arranged along the latitude of the electrically conductive web, the ratio of the width of the outlet opening to the coating width of the web being in the range of 0.25-1.0. The powder dispenser has a defined angle with respect to the web and a vertical distance between the powder dispenser outlet and the web. The first wire electrode creates a corona discharge zone having a radius and having a vertical distance between the coils.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to co-pending, commonly assigned U.S. Provisional Patent Application No. 63 / 356,199, filed on June 28, 2022. The entire contents of the above-mentioned provisional application are incorporated herein by reference. Background Art

[0003] The application of electrostatic spray deposition (ESD) technology in solvent-free composite electrode coating for lithium-ion batteries has been discussed previously. Solvent-free electrode coating technology is attractive because it can significantly reduce the energy consumption in the manufacturing process and thus significantly reduce the manufacturing cost of the battery. In principle, ESD technology allows for simpler and more flexible electrode coating, as the composite electrode powder is directly deposited on the metal current collector through an electrostatic spray deposition process.

[0004] ESD is widely used for dry powder coating of metal parts. For ESD coating, the coating quality and transfer efficiency are directly related to the characteristics of the particles of the coating powder. A typical electrostatic deposition applicator for dry powder coating may include a powder hopper, a powder fluidization system, a powder diffusion and clouding system, a powder corona charging system, a powder deposition system, and a powder recovery system.

[0005] FIG1 shows a conventional electrostatic deposition gun or applicator 10. A conventional electrostatic deposition applicator 10 may have a gun-shaped powder spreading and clouding system. The applicator 10 may include a powder inlet 12 and an electrostatic nozzle 14 for depositing powder onto a grounded web 16 having a web moving direction 18. The fluidized powder is carried by a pressurized gas and passes through the nozzle 14 with an electrode. The powder is corona charged by the electrode and spread and cloudified through the nozzle 14, and the charged powder stream is deposited on a grounded conductive substrate (e.g., grounded web 16).

[0006] The "transfer efficiency" of an ESD system is the ratio of the mass of electrostatically charged particles deposited on the conductive substrate to the total mass of fluidized particles. Higher transfer efficiency means more particles are deposited on the conductive substrate, resulting in higher utilization of the coating material. The "uniformity" of the deposited layer includes the stoichiometric consistency between the deposited layer and the raw powder mixture, as well as the stoichiometric consistency and geometric consistency within the deposited layer.

[0007] In conventional ESD designs, the sprayed powder is spread in a cone shape, which is deposited on the substrate 16 in a general pattern based on the nozzle tip. In the system described in FIG. 1 , a circular nozzle tip / deflector is used, resulting in a circular spray pattern (e.g., a circular deposition area 20). In a continuously moving web or substrate 16 with a target coating width of L, if the diameter of the coating circle D is less than the target coating width L, the coating will not cover the width of the web 16, resulting in poor coating uniformity. If the diameter of the coating circle D is greater than the target coating width L, although uniformity can be improved, transfer efficiency will be reduced due to overspraying. In some cases, the target coating width L may be equal to or less than the width of the web 16. However, for ease of describing the technology, hereinafter, the target coating width L is considered to be equal to the width of the web 16.

[0008] Conventional ESD system designs typically use point electrodes that produce a gradient in the electric field that is related to the width of the web 16. When the electrode is a point charge at the center of the width of the web 16, the electric field strength associated with the web 16 is greatest directly beneath the electrode and smallest at the edge of the web 16 due to the separation distance. This inherent geometric non-uniformity in the electric field results in poor uniformity across the width of the web 16.

[0009] In addition, when the powder cloud density is high, the corona discharge generated by the point electrode tends to be suppressed. Since the gun nozzle and the electrode tip in the conventional ESD design are coupled together, coating at a high mass flow rate results in low transfer efficiency and uniformity due to the difference in chargeability of the powder particles. Therefore, the conventional ESD design may be limited to a relatively low powder mass flow rate. Summary of the invention

[0010] Embodiments of the present disclosure provide exemplary applicators for electrostatic deposition coating of continuously moving webs. The electrostatic deposition applicator for dry powder coating of continuously moving conductive webs provides improved coating uniformity and transfer efficiency, as well as increased powder deposition rate and coating thickness.

[0011] According to an embodiment of the present disclosure, an exemplary system applicator (e.g., system or applicator system) for electrostatic deposition of dry powder on a grounded continuously moving conductive web is provided. The applicator includes a powder supply system, at least one powder dispenser, an electrostatic deposition chamber, and at least one wire electrode in the electrostatic deposition chamber. The opening of the powder dispenser outlet of at least one dispenser is arranged along the latitude of the conductive web, and the ratio (P) of the width (W) of the opening to the coating width (L) of the conductive web is in the range of about 0.25-1.0 cm. At least one powder dispenser includes a defined angle (α) relative to the conductive web and a vertical distance (h) between the powder dispenser outlet and the conductive web. dThe first wire electrode of the at least one wire electrode generates a corona discharge zone having a radius (R) and is at a perpendicular distance (h) relative to the conductive web. e ) is set. The powder distributor outlet and the first wire electrode are at a horizontal distance (d1). The following relationship and conditions are satisfied:

[0012]

[0013] In some embodiments, the electrostatic deposition chamber includes two or more wire electrodes. In such embodiments, the two or more wire electrodes are arranged in parallel and cross the width of the continuously moving conductive web. In some embodiments, the radius (R) of the corona discharge zone generated by the first wire electrode can be in the range of about 1 cm-20 cm. In some embodiments, the vertical distance (h) between the first wire electrode and the conductive web is about 1 cm-20 cm. e ) can be in the range of about 2 cm-30 cm. In some embodiments, the vertical distance (h) between the powder dispenser outlet and the conductive coil is d ) can be in the range of about 2cm-70cm.

[0014] The powder dispenser outlet can be arranged outside the corona discharge zone generated by the first wire electrode. In some embodiments, the horizontal distance (d1) between the at least one powder dispenser and the first wire electrode can be about 2-40 cm. In some embodiments, the two or more wire electrodes (N e ) can be determined by: Wherein: d is the horizontal distance between the edge of the powder deposition on the conductive web and the powder dispenser outlet, d1 is the horizontal spacing between the first wire electrode and the powder dispenser outlet, d2 is the horizontal spacing between two adjacent wire electrodes, and d3 is the horizontal distance between the edge of the powder deposition on the conductive web and the last wire electrode of the two or more wire electrodes.

[0015] In some embodiments, the horizontal spacing (d2) between two adjacent wire electrodes may be within the range of R-2R. In some embodiments, the horizontal distance (d3) between the edge of the powder deposition on the conductive web and the last wire electrode may be within the radius (R). In some embodiments, the vertical distance between the conductive web of the second or nth wire electrode of the two or more wire electrodes is the same as or slightly smaller than the first electrode or the (n-1)th wire electrode, and the vertical distance between the last wire electrode and the conductive web is greater than 5 cm.

[0016] At least one wire electrode includes two or more wire electrodes, and the voltages of the two or more wire electrodes are different. The electrostatic deposition chamber includes a deflector, and the number of deflectors is equal to the number of wire electrodes. In some embodiments, the applicator may include a powder recovery system. The powder recovery system may include at least one powder collection port, wherein at least two turbulence elimination baffles are located between the conductive web and the powder collection port. The powder collection port may be disposed at the top of the electrostatic deposition chamber, or at the bottom of the electrostatic deposition chamber, or a combination thereof.

[0017] In some embodiments, at least one powder dispenser may include two powder dispensers. In some embodiments, the two powder dispensers may be arranged to face each other in a mirror-image orientation along the longitudinal direction of the conductive web. In some embodiments, the horizontal distance between the two powder dispensers may be twice the horizontal distance between the edge of the powder deposition on the conductive web and the powder dispenser outlet plus about 0-20 cm. In some embodiments, the two powder dispensers may be arranged on the top side of the conductive web and the back side of the conductive web in a mirror-image orientation.

[0018] Any combination and / or permutation of the embodiments may be envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. However, it should be understood that the drawings are designed only for illustration, and not for definition of the limits of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To assist those skilled in the art in making and using an applicator for electrostatic deposition coating, reference is made to the accompanying drawings, in which:

[0020] FIG1 is a schematic diagram of a conventional electrostatic spray deposition gun;

[0021] Figure 2 is a schematic diagram of an exemplary application of electrostatic deposition coating according to an embodiment of the present disclosure;

[0022] Figure 3 is a schematic diagram of the corona discharge zone;

[0023] Figure 4A is a schematic side view of an exemplary powder dispenser according to an embodiment of the present disclosure;

[0024] Figure 4B yes Figure 4A A schematic top view of an exemplary powder dispenser of ;

[0025] Figure 5 is a schematic diagram of an exemplary electrostatic deposition coating chamber according to an embodiment of the present disclosure;

[0026] Figure 6 is a schematic diagram of an exemplary electrostatic deposition coating chamber according to an embodiment of the present disclosure;

[0027] Figure 7 is a schematic diagram of an exemplary electrostatic deposition coating chamber according to an embodiment of the present disclosure;

[0028] Figure 8 is a schematic diagram of an exemplary electrostatic deposition coating chamber with powder recovery according to an embodiment of the present disclosure;

[0029] Fig. 9 is a table of experimental setup conditions for testing an exemplary electrostatic deposition coating applicator;

[0030] Fig.10 is a table of transfer efficiency results from testing of an exemplary electrostatic deposition coating applicator;

[0031] Fig.11 is a table of experimental setup conditions for testing an exemplary electrostatic deposition coating applicator including a plurality of discharge electrodes; and

[0032] Fig.12 is a table of transfer efficiency results from testing of exemplary electrostatic deposition coating applicators including a multi-wire comparison. DETAILED DESCRIPTION

[0033] Figure 2 2 is a schematic diagram of an exemplary applicator (hereinafter referred to as "applicator 200") for dry powder electrostatic deposition coating. Applicator 200 may be referred to as a "system" herein. Figure 2 As shown, the applicator 200 may include a powder metering device hopper 201, a powder metering device 202, a powder feeding device hopper 203, and a powder feeding device 204. The applicator 200 may include a powder dispenser 205, an ESD chamber 210, and one or more powder recovery system ports 220. The ESD chamber 210 includes one or more wire electrodes 211, an electrode drawer 212, and one or more electric field deflectors 213.

[0034] According to an exemplary embodiment of the disclosed ESD system, dry powder for deposition is loaded into a powder metering device hopper 201. Powder is fed from the powder metering device hopper 201 to the powder metering device 202 via gravity, although alternative feeding mechanisms may be employed, such as belt conveyors, screw conveyors, pneumatic conveyors, vibrating conveyors, tube and chain conveyors, any other dry bulk powder handling system, combinations thereof, etc. The powder metering device 202 accurately meters powder into the powder feeder hopper 201 to maintain a consistent powder head pressure for the powder feeder 204. The powder feeder 204 deagglomerates the powder and accurately feeds it into the powder dispenser 205.

[0035] The powder is sucked into the distributor 205 by gravity and the negative pressure caused by the Venturi effect of the air jet (not shown), which inserts the air to axially convey, diffuse and further deagglomerate the powder, and disperses it from the powder distributor 205 through the outlet 206 as an aerated powder cloud to the ESD chamber 210. The air jet can be oriented to control the direction of powder distribution and movement to the ESD chamber 210. The powder distributor 205 can distribute powder by injecting and diffusing air into and through the powder feed stream. In some embodiments, the powder distributor 205 can be conveyed, diffused and deagglomerated by other suitable devices. For example, an alternative or additional method can use a brush feed and diffusion system, as disclosed in U.S. Patent No. 5,769,276, the contents of which are incorporated herein by reference. The distributed charged powder particles are deposited on a grounded conductive substrate coil 230.

[0036] The powder particles are diffused into a powder cloud through the powder dispenser outlet 206. The shape of the powder dispenser outlet 206 can take various forms, such as rectangular, elliptical, etc. The powder dispenser outlet 206 is elongated along the web width, for example, the dimension at the outlet 206 is larger than the remaining width of the powder dispenser 205 (see, for example, Figure 4B ). Within the ESD chamber 210, one or more wire electrodes 211 are mounted in parallel across the width of the ESD chamber 210 and oriented perpendicular to the direction of movement of the powder cloud and web 230. When a high negative voltage is applied to the wire electrodes 211, a corona discharge is generated where free electrons and air molecular ions exist in the ESD chamber 210 (see, e.g. Figure 3 ). The voltage required to generate the corona discharge is called the "corona inception voltage". This corona discharge is most concentrated around a specific radius R perpendicular to the surface of the wire electrode 211, which is defined and referred to as the "corona discharge zone" in this article. R is defined as the radial distance from the wire electrode 211, where the measured voltage is equal to the corona inception voltage. Typically, the corona inception voltage is about 18kV in air. For example, if the applied voltage to the wire electrode 211 is 50kV, and the voltage measured at 15cm radially from the wire electrode 211 is 18kV, then the corona discharge zone is defined as a radius R of 15cm.

[0037] The process and design parameters of the wire electrode 211 that determine the size of the corona discharge zone are the applied voltage, the applied current, the size of the cross-section of the wire electrode 211, the shape of the wire electrode, and the material of the wire electrode 211. A circular cross-section of the wire electrode 211 may be preferred to assume electric field symmetry, although other cross-sectional shapes of wire electrodes 211 may be used in the system.

[0038] When the powder particles pass through the corona discharge zone, static charges accumulate on the surface of the powder particles due to the field charging and diffusion charging of the ions generated by the corona discharge. The accumulated charge changes with time q t and the particle's saturation charge q m It is described by the Pauthenier equation, as shown in Equations 1 and 2 below.

[0039]

[0040] where r is the radius of the particle, E is the electric field strength, e is the charge of the electron, k is the electron mobility, n is the electron concentration, t is the time, ε0 is the absolute permittivity, and ε r is the relative permittivity of the powder.

[0041] The ability of powder particles to effectively acquire surface charge and deposit uniformly on a grounded conductive substrate can be significantly affected by several geometric factors related to the relative position of the powder dispenser outlet, the position of one or more wire electrodes, and the placement of the grounded coil. The main forces affecting the trajectory of powder particles in this system can be divided into kinematic forces and electrostatic forces. The kinematic forces are controlled by the powder dispenser air settings and positioning, the ESD chamber design (affecting the distribution of the flow field), the size of the powder recovery system negative pressure, the geometric design, and the relative position in the ESD chamber. The electrostatic force is mainly determined by the voltage, current and positioning of the wire electrodes, as well as the positioning and size of the electric field deflector.

[0042] In order to obtain highly uniform electrostatic deposition of powder particles, it is critical to enable electrostatic forces to become the main force during deposition. In particular, when a high coating rate is required, the initial momentum of the powder particles leaving the powder dispenser outlet may be large. Whenever possible, the exit velocity of the powder particles leaving the powder dispenser outlet should be minimized. When the exit velocity has been minimized to a target range between about 100-1300 ft / min (not less than 35 ft / min and not more than 2000 ft / min), the positioning of the functional components in the ESD chamber is critical for maximizing the electrostatic force during the final deposition on the grounded coil, because it is related to the exit velocity and relative trajectory of the powder particles. In some embodiments, the exit velocity may be minimized to, for example, about 100-1300 ft / min (inclusive), 200-1300 ft / min (inclusive), 300-1300 ft / min (inclusive), 400-1300 ft / min (inclusive), 500-1300 ft / min (inclusive), 600-1300 ft / min (inclusive), 700-1300 ft / min (inclusive), 800-1300 ft / min (inclusive), 900-1300 ft / min (inclusive), 1000-1300 ft / min (inclusive), 1100-1300 ft / min (inclusive), 1200-1300 ft / min (inclusive), 100-1200 ft / min (inclusive), 100-1100 ft / min (inclusive), 1 The target range is between 100-1000ft / min (inclusive of endpoints), 100-900ft / min (inclusive of endpoints), 100-800ft / min (inclusive of endpoints), 100-700ft / min (inclusive of endpoints), 100-600ft / min (inclusive of endpoints), 100-500ft / min (inclusive of endpoints), 100-400ft / min (inclusive of endpoints), 100-300ft / min (inclusive of endpoints), 100-200ft / min (inclusive of endpoints), 100ft / min, 200ft / min, 300ft / min, 400ft / min, 500ft / min, 600ft / min, 700ft / min, 800ft / min, 900ft / min, 1000ft / min, 1100ft / min, 1200ft / min, 1300ft / min, etc.

[0043] The following discussion focuses on the relative positioning of key components that affect particle trajectory, chargeability, and ultimate deposition capability. Figure 4A is a side view of the powder dispenser 205 within the ESD chamber 210, Figure 4B is its top view, and Figure 5 is another side view of the powder dispenser 205 relative to the ESD chamber 210 . Figure 4A , 4B and Figure 5 The main positioning variables are shown, which are critical to balancing each other to achieve a high degree of deposition uniformity. The variables include the angle α, h between the dispenser 205 arrangement and the web 230 e represents the vertical distance between the coil 230 and the first wire electrode 211a, h d represents the vertical distance between the web 230 and the dispenser outlet 206, R represents the radius of the corona discharge zone generated by the first wire electrode 211a, d1 represents the horizontal distance between the powder dispenser outlet 206 and the first wire electrode 211a, and the relative size W of the powder dispenser outlet 206 related to the web width L.

[0044] The width W of the opening 206 of the powder dispenser outlet generally determines the span of the powder cloud on the web 230 after the powder cloud is ejected from the powder dispenser 205 (see, e.g., Figure 4B ). The width W and angle α of the opening of the outlet 206 of the powder dispenser 205 are selected and designed to meet the following requirements: (1) the powder particles are spread out from the outlet 206 of the dispenser 205 to allow all particles (minimum about 80%, target greater than 95%) to be easily and uniformly charged by one or more electrode wires 211 in the corona discharge zone; (2) the powder cloud exiting from the powder dispenser outlet 206 has a planar geometry, and the width W in the charging zone matches the width L of the web 230, so that there is minimal overspray between the sides of the web 230 and the adjacent walls of the coating chamber 210 (target is 5-10% of the total powder dispensed, maximum overspray is 50%); and (3) when the powder trajectory passes through the first wire electrode 211a, the powder trajectory is within the web width L to ensure that the powder particles have equivalent electrostatic potential relative to the web 230.

[0045] When the ratio P (e.g., represented by the equation P=W / L) of the width W of the opening of the powder dispenser outlet 206 to the width L of the web 230 is too large (e.g., greater than about 1), the powder cloud will be oversprayed, resulting in low transfer efficiency. When the ratio P is too small (e.g., less than about 0.25), the powder cloud will not cover the web 230 well, resulting in low uniformity. According to the present disclosure, the ratio P of the exemplary system or applicator 200 is designed to be, for example, about 0.25-1 (inclusive), 0.3-1 (inclusive), 0.35-1 (inclusive), 0.4-1 (inclusive), 0.45-1 (inclusive), 0.5-1 (inclusive), 0.55-1 (inclusive), 0.6-1 (inclusive), 0.65-1 (inclusive), 0.7-1 (inclusive), 0.75-1 (inclusive), 0.8-1 (inclusive), 0.85-1 (inclusive), 0.9-1 (inclusive), 0.95-1 (inclusive), 0.25-0.95 (inclusive), 0.25-0.95 (inclusive), 0.25- 0.85 (inclusive), 0.25-0.8 (inclusive), 0.25-0.75 (inclusive), 0.25-0.7 (inclusive), 0.25-0.65 (inclusive), 0.25-0.6 (inclusive), 0.25-0.55 (inclusive), 0.25-0.5 (inclusive), 0.25-0.45 (inclusive), 0.25-0.4 (inclusive), 0.25-0.35 (inclusive), 0.25-0.3 (inclusive), 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc.

[0046] The combination of the relative positions of the above variables needs to provide the following balance function. All particles leaving the dispenser outlet 206 should pass through one of the corona discharge zones generated by one or more wire electrodes 211 to be charged to a saturation charge as efficiently as possible. The particle trajectory should minimize the vertical motion force between the powder particles and the web 230 to reduce the impact of the powder particles with the web 230 and the associated potential deflection. The electrostatic attraction momentum between the charged powder particles and the grounded web 230 should be greater than the inherent motion momentum of the particles at their speed when in contact with the web 230. This ensures that the electrostatic force is the primary force controlling deposition and reduces the deflection of the powder from the web 230, which provides a high degree of uniformity in coating.

[0047] In order to maximize the possibility of reaching a saturation charge, the angle α must be set so that the majority of the powder trajectory points into the corona discharge zone previously defined by the radius R perpendicular to the wire electrode 211 (e.g., greater than about 80%, greater than 85%, greater than 90%, greater than 95%, etc.). According to the present disclosure, in order to effectively charge the powder particles, the radius of the corona discharge zone R is set in the range of about 1-20 cm, wherein the diameter of the wire electrode 211 is set in the range of about 0.05-2 mm; and the applied electrode voltage is set in the range of about 15 kV to about 100 kV.

[0048] In some embodiments, the radius of the corona discharge zone R can be, for example, about 1-20 cm (inclusive), 1-18 cm (inclusive), 1-15 cm (inclusive), 1-13 cm (inclusive), 1-10 cm (inclusive), 1-8 cm (inclusive), 1-5 cm (inclusive), 1-4 cm (inclusive), 1-3 cm (inclusive), 1-2 cm (inclusive), 2-20 cm (inclusive), 3-20 cm (inclusive), 4-20 cm (inclusive), 5-20 cm (inclusive), 8-20 cm (inclusive), 10-20 cm (inclusive), 13-20 cm (inclusive), 15-20 cm (inclusive), 18-20 cm (inclusive), 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm, 13 cm, 15 cm, 18 cm, 20 cm, etc. In some embodiments, the diameter of the wire electrode 211 can be in the range of approximately, for example, 0.05-2mm (inclusive), 0.25-2mm (inclusive), 0.5-2mm (inclusive), 0.75-2mm (inclusive), 1-2mm (inclusive), 1.25-2mm (inclusive), 1.5-2mm (inclusive), 1.75-2mm (inclusive), 0.05-1.75mm (inclusive), 0.05-1.5mm (inclusive), 0.05-1.25mm (inclusive), 0.05-1mm (inclusive), 0.05-0.75mm (inclusive), 0.05-0.5mm (inclusive), 0.05-0.25mm (inclusive), 0.05mm, 0.25mm, 0.5mm, 0.75mm, 1mm, 1.25mm, 1.5mm, 1.75mm, 2mm, etc. In some embodiments, the applied electrode voltage can be in the range of about, for example, 15-100 kV (inclusive), 25-100 kV (inclusive), 50-100 kV (inclusive), 75-100 kV (inclusive), 15-75 kV (inclusive), 15-50 kV (inclusive), 15-25 kV (inclusive), 15 kV, 25 kV, 50 kV, 75 kV, 100 kV, etc.

[0049] The angle α between the powder dispenser 205 and the web is ( Figure 4A) can vary. Angle α needs to be optimized for the application to allow (i) a higher degree of powder particles exiting the powder dispenser 205 to be charged by the corona discharge zone located in the ESD chamber 210, and (ii) the powder cloud to be delivered from the dispenser 205 to the grounded conductive web 230 in a continuous and uniform stream with maximum transfer efficiency and uniformity. High transfer efficiency is achieved by minimizing overspray in the area between the sides of the web 230 and the adjacent walls of the coating chamber 210, and minimizing air turbulence within the ESD chamber 210.

[0050] According to the present disclosure, in order to effectively charge the powder particles and deposit the charged powder particles on the web 230 with high uniformity, the relationship between the angle α, the position of the powder dispenser outlet 206 and the position of the first wire electrode 211a needs to satisfy the following conditions, as shown in Equation 3:

[0051]

[0052] where h e is the vertical distance between the first wire electrode 211a and the coil 230, h d is the vertical distance between the powder dispenser outlet 206 and the web 230. R is the radius of the corona discharge zone, and d1 is the horizontal distance between the powder dispenser 205 and the first wire electrode 211a.

[0053] In order to demonstrate the importance of this geometrical relationship on particle charging and therefore on the transfer efficiency, a set of experiments was performed under conditions where the above relationship was satisfied and others where it was not. The effects on the transfer efficiency were compared. Figure 5 A similar setup as described in . Three conditions were tested and compared. The applied voltage and angle α were varied. d1, h d 、h e The and powder mass flow rates were kept constant. The corona discharge radius was measured to be about 3 cm for the associated discharge electrodes and applied electric field strength. The web speed was operated continuously at about 1 m / min, and the web width was about 260 mm.

[0054] Fig. 9 The experimental setup conditions for three experiments are shown. The first experiment was operated at 0 applied voltage to demonstrate that the geometric configuration satisfies the uncharged baseline condition of the relationship. Based on the amount of powder applied, the transfer efficiency was calculated to be 13% ( Fig.10 ). The second experiment was a configuration that satisfied the geometric relationship, and the transfer efficiency increased to 27%, more than 2 times higher than the no-voltage condition. The third experiment changed the angle α from 20 degrees to 25 degrees, which resulted in an unsatisfied condition of the relationship based on the calculations and inputs. The calculated transfer efficiency dropped to 22%, nearly 20% lower than the satisfied condition. The results are summarized in Fig.10 middle.

[0055] It should be noted that in the experimental setup, the powder output from the powder dispenser is not a discrete jet, but rather expands vertically, resulting in some powder output that meets the conditions. This is why there is still some increase under no-voltage conditions. The experiments show that when the amount of powder toward the corona discharge radius decreases, the proportion of charged particles decreases, thereby reducing the transfer efficiency to the grounded web.

[0056] The vertical distance between the first wire electrode 211a and the web 230 must exceed the range of the arch and provide a sufficient electric field for electrostatic deposition. In some embodiments, the vertical distance (h) between the first wire electrode 211a and the web 230 is greater than 1. e ) can be in the range of about, for example, 2-30cm (inclusive), 3-30cm (inclusive), 4-30cm (inclusive), 5-30cm (inclusive), 10-30cm (inclusive), 15-30cm (inclusive), 20-30cm (inclusive), 25-30cm (inclusive), 2-25cm (inclusive), 2-20cm (inclusive), 2-15cm (inclusive), 2-10cm (inclusive), 2-5cm (inclusive), 2-4cm (inclusive), 2-3cm (inclusive), 5-25cm (inclusive), 5-20cm (inclusive), 5-15cm (inclusive), 5-10cm (inclusive), 2cm, 3cm, 4cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, etc.

[0057] In some embodiments, the vertical distance (h) between the powder dispenser outlet 206 and the web 230 is d，) can be set at about, for example, 2-70cm (inclusive), 3-70cm (inclusive), 4-70cm (inclusive), 5-70cm (inclusive), 10-70cm (inclusive), 15-70cm (inclusive), 20-70cm (inclusive), 25-70cm (inclusive), 30-70cm (inclusive), 35-70cm (inclusive), 40-70cm (inclusive), 45-70cm (inclusive), 50-70cm (inclusive), 55-70cm (inclusive), 60-70cm (inclusive), 65-70cm (inclusive), 2-65cm (inclusive), 2-60cm (inclusive), 2-55cm (inclusive), 2-50cm (inclusive), 2-45cm (inclusive), 2-40cm (inclusive), 2-35cm (inclusive), 2-30cm (inclusive), 2-25cm ( Including the endpoints), 2-20cm (inclusive), 2-15cm (inclusive), 2-10cm (inclusive), 2-5cm (inclusive), 2-4cm (inclusive), 2-3cm (inclusive), 5-40cm (inclusive), 10-40cm (inclusive), 15-40m (inclusive), 20-40m (inclusive), 25-40cm (inclusive), 30-40cm (inclusive), 35-40cm (inclusive), 5-35cm (inclusive), 5-30cm (inclusive), 5-25cm (inclusive), 5-20cm (inclusive), 5-15cm (inclusive), 5-10cm (inclusive), 2cm, 3cm, 4cm, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm, 55cm, 60cm, 65cm, 70cm, etc.

[0058] In some embodiments, the radius of the corona discharge zone can be set in a range of about, for example, 1-20 cm (inclusive), 1-18 cm (inclusive), 1-15 cm (inclusive), 1-13 cm (inclusive), 1-10 cm (inclusive), 1-8 cm (inclusive), 1-5 cm (inclusive), 1-4 cm (inclusive), 1-3 cm (inclusive), 1-2 cm (inclusive), 2-20 cm (inclusive), 3-20 cm (inclusive), 4-20 cm (inclusive), 5-20 cm (inclusive), 8-20 cm (inclusive), 10-20 cm (inclusive), 13-20 cm (inclusive), 15-20 cm (inclusive), 18-20 cm (inclusive), 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 8 cm, 10 cm, 13 cm, 15 cm, 18 cm, 20 cm, etc.

[0059] In some embodiments, the horizontal distance (d1) between the powder dispenser 205 and the first wire electrode 211a can be set in a range of about, for example, 2-40 cm (inclusive), 3-40 cm (inclusive), 4-40 cm (inclusive), 5-40 cm (inclusive), 10-40 cm (inclusive), 15-40 cm (inclusive), 20-40 cm (inclusive), 25-40 cm (inclusive), 30-40 cm (inclusive), 35-40 cm (inclusive), 2-35 cm (inclusive), 2-30 cm (inclusive), 2-25 cm (inclusive), 2-20 cm (inclusive), 2-15 cm (inclusive), 2-10 cm (inclusive), 2-5 cm (inclusive), 2-4 cm (inclusive), 2-3 cm (inclusive), 2 cm, 3 cm, 4 cm, 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, and the like. The powder dispenser outlet 206 needs to be positioned outside the corona discharge zone.

[0060] When angle α is relatively small or relatively large, it is an important consideration to maximize transfer efficiency and coating uniformity by achieving saturation charge, minimizing corona suppression, and minimizing the effects of incident particle coating deflection on web 230 by reducing the normal velocity vector of the incident powder particles.

[0061] When the angle α is relatively small, such as between 0° and 10°, it is most effective to direct the powder flow trajectory to the lower half of R, thereby reducing the possibility of corona discharge suppression. This usually results in h d Less than h e .

[0062] When the angle α is relatively large, such as between about 55°-85°, the exit velocity of the powder particles from the dispenser 205 should be relatively low. The velocity should be low because the vertical vector of the velocity increases as the angle α increases. If the vertical velocity vector is too high compared to the electrostatic force, the incoming powder particles will have a larger "pulse" that can overcome the electrostatic attraction when the particles collide with the web 230, resulting in deflection and low uniformity and transfer efficiency.

[0063] In order to expand and enhance the corona discharge area, such as Figure 5 As shown, a plurality of wire electrodes 211a, 211b (e.g., first and second wire electrodes) may be installed in the ESD chamber 210. Although two wire electrodes 211a, 211b are shown, it should be understood that two or more wire electrodes may be included in the system. The wire electrodes 211a, 211b are typically arranged parallel to the first wire electrode 211a (i.e., the wire electrode closest to the dispenser outlet 206) to provide an extended corona discharge zone to charge powder particles that are not effectively charged by the previous one or more wire electrodes and to provide an additional electrostatic field to direct the charged particles toward the web 230. The voltages of these wire electrodes 211a, 211b may be the same or different to optimize the effectiveness of particle charging. For example, the first wire electrode 211a may have a higher voltage than the second wire electrode 211b, and vice versa. The vertical distances between the individual wire electrodes 211a, 211b measured relative to the web 230 may be the same or different. Typically, the second or nth wire electrode (e.g., the last wire electrode) is located at the same or slightly smaller vertical distance between the web 230 than the first or (n-1)th electrode (e.g., the second to last wire electrode, etc.). The last electrode is preferably located at a vertical distance greater than 5 cm from the web 230. The distance and position of the wire electrodes 211a, 211b should be selected in such a way that the powder particles are deposited on the continuous web 230 in as uniform a manner as possible, thereby minimizing the amount of overspray and particle deposition on the inner walls of the ESD chamber 210.

[0064] For example, the spacing distance (d2) between two adjacent wire electrodes 211a, 211b should be larger than the interference region R of the two corresponding electrodes 211a and 211b. The spacing distance d2 between two adjacent wire electrodes 211a, 211b may be between about R-2R (e.g., between about 2-40 cm (inclusive), 3-40 cm (inclusive), 4-40 cm (inclusive), 5-40 cm (inclusive), 10-40 cm (inclusive), 15-40 cm (inclusive), 20-40 cm (inclusive), 25-40 cm (inclusive), 30-40 cm (inclusive), 35-40 cm (inclusive) The position of the last wire electrode 211b (i.e., the wire electrode 211b farthest from the powder dispenser outlet 206) is determined by the powder trajectory and the position of the powder deposition. Figure 5 As shown, the distance d3 between the farthest edge of the powder deposition on the web 230 and the last electrode 211b should be no greater than R, for example, no greater than about 20 cm. The edge of the powder deposition on the web 230 is the farthest powder particle deposited on the web 230. The maximum number of wire electrodes (Ne) in the ESD chamber 210 can be determined by Equation 4:

[0065]

[0066] Wherein d is the horizontal distance between the farthest edge of the powder deposition on the web 230 and the powder dispenser outlet 206, d1 is the horizontal distance between the first wire electrode 211a and the powder dispenser outlet 206, d2 is the spacing distance between two adjacent wire electrodes 211a, 211b, and d3 is the horizontal distance between the farthest edge of the powder deposition on the web 230 and the last electrode 211b.

[0067] To demonstrate the effect of utilizing multiple discharge electrodes to improve particle charging and therefore transfer efficiency, experiments were completed using two wire electrodes with applied voltage and compared to the results of no voltage condition and a condition where voltage was applied only to electrode one. The geometric configuration remained constant throughout all experiments. The height of electrode two was set to be the same as the height of electrode one, approximately 12.7 cm. Electrode two was placed 25 cm downstream of electrode one, denoted as d2. The web speed was kept constant at approximately 1 m / min and the web width was approximately 260 mm. The powder mass flow rate was kept constant throughout all experiments. The transfer efficiency was calculated for each experimental condition. Experiment four was completed with both electrode one and electrode two reaching a potential of approximately 25 kV. The experimental setup results are summarized in Fig.11 The transfer efficiency was calculated to be 31%. This is an increase of 15% compared to when electrode 2 was at 0 potential and electrode 1 was at 25 kV potential. The transfer efficiency was increased by about 2.25 times compared to the case where no voltage was applied. The transfer efficiency results are summarized in Fig.12 middle.

[0068] The electrode drawer 212 is designed to support the wire electrodes 211a, 211b and can be made of a non-conductive material (e.g., polycarbonate, etc.). Parallel (or substantially parallel) to each corresponding wire electrode 211a, 211b, one or more non-conductive angled shields (one or more deflectors 213a, 213b) are mounted within the electrode drawer 212. Each shield has two purposes: (a) during the charging process, the deflector 213a, 213b is charged with the same polarity as the corona wire (i.e., the electrode 211a, 211b), thereby enhancing the flow of ionized air toward the powder cloud, thereby improving the charging process, and (b) the deflector 213a, 213b provides a physical barrier and directs the aerodynamic flow from the ejector / diffuser arrangement to the outlet of the powder coating chamber 210, thereby promoting laminar air flow and preventing uncontrollable turbulence within the electrostatic coating chamber 210. The distance between the wire electrodes 211a, 211b and the corresponding deflectors 213a, 213b can be, for example, between about 1-10cm (inclusive), 2-10cm (inclusive), 3-10cm (inclusive), 4-10cm (inclusive), 5-10cm (inclusive), 6-10cm (inclusive), 7-10cm (inclusive), 8-10cm (inclusive), 9-10cm (inclusive), 1-9cm (inclusive), 1-8cm (inclusive), 1-7cm (inclusive), 1-6cm (inclusive), 1-5cm (inclusive), 1-4cm (inclusive), 1-3cm (inclusive), 1-2cm (inclusive), 1cm, 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm, 10cm, etc.

[0069] Reference Figure 6 In some embodiments, the applicator 500 (e.g., system) can include two powder dispensers 503a, 503b. The two dispensers 503a, 503b can be oriented on opposite sides of the ESD chamber 510 in a mirror-image orientation facing each other along the longitudinal direction of the web 230. The dispensers 503a, 503b are located at the same vertical height relative to the web 230 and at the same (but mirror-image / opposite) position relative to the chamber 510. Figure 6In the arrangement of the dispensers 503a, 503b are configured to simultaneously (or selectively) coat the same surface of the web 230. In such an arrangement, the positions of the wire electrodes 511 and the deflectors 513 in the ESD chamber 510 can also be arranged in a mirror image relative to each other. For example, two wire electrodes 511 can be positioned on one side of the chamber 510 and associated with the dispensers 503a, and two wire electrodes 511 can be positioned on the opposite side of the chamber 510 and associated with the dispensers 503b. The deflectors 513 are placed adjacent to the corresponding wire electrodes 511, and the paired deflectors 513 are angled in opposite directions to direct the powder to the top surface of the web 230.

[0070] The horizontal distance between the two powder dispensers 503a, 503b is 2d+d4. The horizontal distance between the two powder dispensers 503a, 503b is designed to be large enough to avoid interfering with the application of powder from each powder dispenser 503a, 503b. On the other hand, the horizontal distance between the two powder dispensers 503a, 503b should not be too large, which may result in a larger footprint of the ESD chamber 510. Therefore, in some embodiments, the distance between the two powder dispensers 503a, 503b can be twice the horizontal distance between the edge of the powder deposition on the web 230 and the powder dispenser outlet, plus about 0-20 cm (for example, a range of about 2d to (2d+20) cm; such as about 50-100 cm (inclusive), 60-100 cm (inclusive), 70-100 cm (inclusive), 80-100 cm (inclusive), 9-100 cm (inclusive), 50-90 cm (inclusive), 50-80 cm (inclusive), 50-70 cm (inclusive), 50-60 cm (inclusive), 50 cm, 60 cm, 70 cm, 80 cm, 90 cm, 100 cm, etc.).

[0071] Reference Figure 7 In some embodiments, the applicator 600 may include two powder dispensers 603a, 603b that are arranged to simultaneously (or selectively) coat opposing surfaces of the web 230. The dispensers 603a, 603b may be positioned on the same side of the chamber 610, but on opposing sides of the web 230, with the web 230 passing between the dispensers 603a, 603b. Thus, the dispensers 603a, 603b are positioned on the top and back of the web 230 in a mirrored arrangement. Figure 7 In the arrangement of FIG. 6 , the wire electrodes 611 and the deflector 613 in the ESD chamber 610 are arranged on opposite sides of the web 230 and are associated with their respective dispensers 603a, 603b.

[0072] Reference Figure 8, the applicator / dispenser system discussed herein may include a powder recovery system 800. The powder recovery system 800 may be disposed below the ESD chamber 810. The powder recovery system 800 is used to capture all undeposited powders (e.g., powders that miss the coil 230) and recover them for reuse, thereby maximizing material utilization. To this end, the powder recovery position is placed in the coating chamber 810 and collects powders via any dry bulk powder handling mechanism, such as the following alone or in combination: a belt conveyor, a pneumatic conveyor (positive or negative pressure), a screw conveyor, a vibrating conveyor, a tubular and chain conveyor, etc. The collection port 801 of the powder recovery system 800 may be located at any position within the coating chamber 810. In some embodiments, the position of the port 801 may be such that they have no or little interference with the powder trajectory. The baffle 802 is utilized near the collection port 801 to diffuse any turbulent air and prevent it from entering the powder coating area. The baffle 802 helps maintain a uniform laminar flow, which is predictable under steady-state coating conditions. Baffle 802 may be most useful when a pneumatic delivery system is used directly in chamber 810 .

[0073] Ports 801 should be close enough to the coating area so that volatile uncharged particles can be collected, but far enough away so that the collection of charged particles is minimized. Typically, the collection ports 801 above the web can be located toward the far end of the coating chamber 810 away from the powder dispenser. The collection ports 801 below the web should be along the entire coating chamber 810 to properly collect any overspray. Figure 8 As shown, the diffusion baffle 802 can move parallel to the web and facilitate the powder flow direction 803. For proper collection, the effective collection speed can be slightly under pressure relative to the ESD chamber 810. In some embodiments, multiple applicators can be deployed in series along the longitudinal direction of the continuously moving web to increase the coating thickness. The applicators discussed herein are suitable for solvent-free electrode coating of batteries (such as lithium-ion batteries).

[0074] Although exemplary embodiments are described herein, it should be clearly pointed out that these embodiments should not be interpreted as limiting, but additions and modifications to the contents explicitly described herein are also included within the scope of the present invention. In addition, it should be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and arrangements without departing from the spirit and scope of the present invention, even if these combinations or arrangements are not explicitly indicated herein.

Claims

1. An applicator for electrostatically depositing a dry powder on a grounded, continuously moving conductive web, the applicator comprising: a powder feed system, at least one powder dispenser, an electrostatic deposition chamber, and at least one wire electrode in said electrostatic deposition chamber; wherein the opening of the powder dispenser outlet of the at least one dispenser is arranged along the latitude of the conductive web, and the ratio (P) of the width (W) of the opening to the coating width (L) of the conductive web is in the range of about 0.25 to 1.0 cm; wherein the at least one powder dispenser comprises a defined angle (α) relative to the conductive web and a vertical distance (h) between the powder dispenser outlet and the conductive web. d ); wherein a first wire electrode of the at least one wire electrode generates a corona discharge zone having a radius (R) and is at a perpendicular distance (h) relative to the conductive web. e ) is set; wherein the powder dispenser outlet and the first wire electrode are at a horizontal distance (d1); and The following relations and conditions are met:

2. The applicator of claim 1, wherein the electrostatic deposition chamber comprises two or more wire electrodes, wherein the two or more wire electrodes are arranged in parallel and intersect the width of the continuously moving conductive web.

3. The applicator of claim 1, wherein a radius (R) of the corona discharge zone generated by the first wire electrode is in the range of about 1 cm to 20 cm.

4. The applicator according to claim 1, wherein the vertical distance (h e ) is in the range of about 2cm to 30cm.

5. The applicator according to claim 1, wherein the vertical distance (h d ) is in the range of about 2cm to 70cm.

6. The applicator of claim 1, wherein the powder dispenser outlet is disposed outside of the corona discharge zone created by the first wire electrode.

7. The applicator of claim 1, wherein a horizontal distance (d1) between the at least one powder dispenser and the first wire electrode is about 2 to 40 cm.

8. The applicator according to claim 2, wherein the two or more wire electrodes (N e ) is determined by the following factors: in: d is the horizontal distance between the edge of the powder deposit on the conductive web and the outlet of the powder dispenser; d1 is the horizontal distance between the first wire electrode and the powder dispenser outlet; d2 is the horizontal spacing between two adjacent wire electrodes; and d3 is the horizontal distance between the edge of the powder deposition on the conductive web and the last wire electrode of the two or more wire electrodes. 9 . The applicator according to claim 8 , wherein a horizontal interval ( d2 ) between two adjacent wire electrodes is in the range of R to 2R.

10. The applicator of claim 8, wherein a horizontal distance (d3) between an edge of the powder deposition on the conductive web and the last wire electrode is within a radius (R).

11. The applicator according to claim 8, wherein the vertical distance between the conductive web and the second or nth wire electrode of the two or more wire electrodes is the same as or slightly smaller than that of the first electrode or the (n-1)th wire electrode, and the vertical distance between the last wire electrode and the conductive web is greater than 5 cm. 12 . The applicator of claim 1 , wherein the at least one wire electrode comprises two or more wire electrodes, and voltages of the two or more wire electrodes are different.

13. The applicator of claim 1, wherein the electrostatic deposition chamber comprises deflectors, wherein the number of deflectors is equal to the number of wire electrodes.

14. The applicator of claim 1, comprising a powder recovery system.

15. The applicator of claim 14, wherein the powder recovery system comprises at least one powder collection port, wherein at least two turbulence eliminating baffles are located intermediate the conductive web and the powder collection port.

16. The applicator of claim 15, wherein the powder collection port is disposed at a top of the electrostatic deposition chamber, or disposed at a bottom of the electrostatic deposition chamber, or a combination thereof.

17. The applicator of claim 1, wherein the at least one powder dispenser comprises two powder dispensers.

18. The applicator of claim 17, wherein the two powder dispensers are arranged to face each other in a mirror image orientation along the longitudinal direction of the conductive web.

19. The applicator according to claim 18, wherein the horizontal distance between the two powder dispensers is twice the horizontal distance between the edge of the powder deposition on the conductive web and the powder dispenser outlet plus about 0 to 20 cm.

20. The applicator of claim 17, wherein the two powder dispensers are arranged in mirror image orientation on the top side of the conductive web and on the back side of the conductive web.

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