Coating Method

Abstract

To reduce waste of a coating liquid, and to form a coating layer on a wire surface with good efficiency.SOLUTION: A coating device 20 comprises: an external electrode 32; an electrostatic atomization type spray nozzle 33 which has an exhaust nozzle 33A from which a coating liquid 37 is exhausted, and which is so located that the exhaust nozzle 33A faces the external electrode 32; an unwinding roll 21 and a winding roll 22 that so support a core wire 11 as to be arranged between the external electrode 32 and the exhaust nozzle 33A; a first electric power supply unit 38 which applies a voltage to the spray nozzle 33; and a second electric power supply unit 39 which applies a voltage to the external electrode 32.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a coating apparatus and a coating method. [Background technology]

[0002] For example, when coating a linear substrate such as a wire, an electrostatic coating method is sometimes used in which a charged coating liquid is sprayed and applied to the substrate by electrostatic force. In electrostatic coating, a method for atomizing the coating liquid is known, in which a voltage is applied to a spray nozzle, and the charged coating liquid is atomized by utilizing its own repulsive force (see Patent Document 1). The droplets of the coating liquid are attracted to and adhere to the grounded substrate by electrostatic force. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-60059 Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to the workpiece, there are other grounded components in the coating space, such as the nozzle, components for supporting the workpiece, and the frame of the coating booth. At a certain distance from the workpiece in the coating space, the direction of the electric field is directed toward these grounded components other than the workpiece, causing droplets of the coating liquid to be attracted to these grounded components. This results in a lot of wasted coating liquid. [Means for solving the problem]

[0005] The coating device disclosed in this specification is a coating device for applying a coating to the surface of a wire by electrostatic coating, and includes an external electrode, an electrostatic atomization spray nozzle having an outlet from which a coating liquid is sprayed, the outlet being positioned toward the external electrode, a support member that supports the wire so that it is positioned between the external electrode and the outlet, and a power supply unit that applies a voltage to the spray nozzle and the external electrode.

[0006] The coating method disclosed in this specification is a coating method for applying a coating to the surface of a wire by electrostatic coating, and includes a voltage application step of applying a voltage to an external electrode and an electrostatic atomization spray nozzle having an outlet from which a coating liquid is sprayed, with the outlet facing the external electrode, and a spray step of placing the wire between the external electrode and the outlet and spraying the coating liquid from the spray nozzle. [Effects of the Invention]

[0007] According to the technology disclosed in this specification, it is possible to reduce the waste of coating liquid and efficiently form a coating layer on the surface of a wire. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic side view showing the configuration of a coating apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic side view showing the direction of an electric field generated by applying a voltage to the spray nozzle and the external electrode, and droplets of a coating liquid moving in accordance with the direction of this electric field, in the embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the medical wire according to the embodiment. [Figure 4] FIG. 4 is an image showing the spray pattern in the test example when no voltage was applied to the external electrode. [Figure 5] FIG. 5 is an image showing the spray pattern when a voltage of 0.5 kV was applied to the external electrode in the test example. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Outline of the embodiment] (1) The coating device disclosed in this specification is a coating device for applying a coating to the surface of a wire by an electrostatic coating method, and includes an external electrode, an electrostatic atomization spray nozzle having an outlet from which a coating liquid is sprayed and arranged with the outlet facing the external electrode, a support member that supports the wire so that it is positioned between the external electrode and the outlet, and a power supply unit that applies a voltage to the spray nozzle and the external electrode.

[0010] The coating method disclosed in this specification is a coating method for applying a coating to the surface of a wire by electrostatic coating, and includes a voltage application step of applying a voltage to an external electrode and an electrostatic atomization spray nozzle having an outlet from which a coating liquid is sprayed, with the outlet facing the external electrode, and a spray step of placing the wire between the external electrode and the outlet and spraying the coating liquid from the spray nozzle.

[0011] According to the above configuration, the direction of the electric field generated around the wire by applying voltage to the spray nozzle and the external electrode converges from the spray nozzle and the external electrode toward the wire. The droplets of the coating liquid move toward the wire according to the direction of the electric field and adhere to the wire. This improves the efficiency of the coating liquid transfer to the wire compared to when the external electrode is not provided. This reduces waste of the coating liquid and enables the efficient formation of a coating layer on the surface of the wire.

[0012] (2) In the coating device or coating method described in (1) above, it is preferable that the length of the external electrode, which is expressed as the distance between both ends in the direction along the extension direction of the wire, is equal to or greater than the spray width, which is expressed as the distance between both ends in the direction along the extension direction of the wire of the spray range of the coating liquid sprayed from the spray nozzle.

[0013] In addition, in the coating device or coating method described above in (1), it is preferable that the width of the external electrode, which is expressed as the distance between both ends in a direction perpendicular to the extension direction of the wire, is equal to or greater than the width of the wire.

[0014] According to this configuration, the efficiency of the droplets of the coating liquid being applied to the wire is further improved, and the waste of the coating liquid can be further reduced.

[0015] [Details of the embodiment] Specific examples of the technology disclosed in this specification will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0016] <Embodiment> An embodiment will be described with reference to Figures 1 to 3. A medical wire 10 of this embodiment is a component used as a guide wire for medical instruments such as endoscopes, and as shown in Figure 3, includes a core wire 11 (corresponding to a wire material) and a coating layer 12 that covers the surface of this core wire 11. The core wire 11 is conductive and is, for example, a stainless steel solid wire. The coating layer 12 is formed by coating the surface of the core wire 11 with, for example, a fluorine-based coating liquid 37.

[0017] As shown in FIG. 1, the coating device 20 for applying a coating to the core wire 11 includes a winding roll 21 that unwinds the core wire 11, a winding roll 22 that winds up the core wire 11 after coating, a film-forming chamber 31 installed between the winding roll 21 and the winding roll 22, an external electrode 32 and a spray nozzle 33 provided inside the film-forming chamber 31, a liquid supply unit 34 connected to the spray nozzle 33, a first power supply unit 38 (an example of a power supply unit) that applies a voltage to the spray nozzle 33, and a second power supply unit 39 (an example of a power supply unit) that applies a voltage to the external electrode 32.

[0018] The core wire 11 fed from the unwinding roll 21 passes through the inside of the film forming chamber 31 and is taken up by the take-up roll 22. The core wire 11 is grounded and serves as an earth electrode.

[0019] The external electrode 32 is a thin, electrically conductive plate-like member, and is disposed inside the film-forming chamber 31 below the core wire 11. The external electrode 32 is made of a metal such as stainless steel.

[0020] Spray nozzle 33 is an electrostatic atomization nozzle used to spray coating liquid 37 by electrostatic coating, and has a nozzle 33A from which coating liquid 37 is sprayed. Spray nozzle 33 is installed with nozzle 33A facing external electrode 32, and core wire 11 passes between nozzle 33A and external electrode 32. An internal electrode (not shown) is provided inside spray nozzle 33.

[0021] The first power supply device 38 is connected to an internal electrode provided inside the spray nozzle 33 and applies a voltage to the spray nozzle 33 .

[0022] The liquid supply unit 34 includes a storage container 35 in which a coating liquid 37 is stored, and a liquid supply pipe 36 that connects the storage container 35 to the spray nozzle 33. The coating liquid 37 in the storage container 35 is sent to the spray nozzle 33 at a set flow rate by a liquid supply device (not shown) such as a pump.

[0023] The second power supply unit 39 is connected to the external electrode 32 and applies a voltage to the external electrode 32. The first power supply unit 38 and the second power supply unit 39 are independently controlled, and can apply different voltages to the spray nozzle 33 and the external electrode 32.

[0024] The external electrode 32 is disposed such that its length is oriented along the extension direction of the core wire 11 passing through the interior of the film formation chamber 31 (the left-right direction in FIG. 1 ). In this embodiment, the core wire 11 is disposed horizontally within the film formation chamber 31, and the external electrode 32 is disposed horizontally and parallel to the core wire 11. The length Le of the external electrode 32, which is expressed as the distance between both ends of the external electrode 32 in the direction along the extension direction of the core wire 11, is preferably equal to or longer than the spray width Ws, which is expressed as the distance between both ends of the spray range of the coating solution 37 sprayed from the spray nozzle 33 in the direction along the extension direction of the core wire 11 (see FIG. 1 ). Furthermore, the width We of the external electrode 32, which is expressed as the distance between both ends of the external electrode 32 in the direction perpendicular to the extension direction of the core wire 11, is preferably equal to or longer than the diameter D of the core wire 11 (corresponding to the width of the wire) (see FIG. 2 ).

[0025] Next, a process of coating the core wire 11 using the coating device 20 configured as above will be described.

[0026] First, a positive voltage is applied from the first power supply 38 to the internal electrode of the spray nozzle 33, thereby forming an electric field between the spray nozzle 33 and the grounded core wire 11. In addition, a positive voltage is applied from the second power supply 39 to the external electrode 32, thereby forming an electric field between the external electrode 32 and the grounded core wire 11 (voltage application step).

[0027] Next, the unwinding roll 21 and the winding roll 22 are driven so that the core wire 11 passes between the spray outlet 33 A of the spray nozzle 33 and the external electrode 32 .

[0028] In this state, the liquid delivery device is driven to supply the coating liquid 37 from the storage container 35 to the spray nozzle 33. The coating liquid 37 supplied to the spray nozzle 33 is charged inside the spray nozzle 33 by applying a voltage to the spray nozzle 33, and is then ejected from the ejection port 33A and atomized. Droplets 37D of the atomized coating liquid 37 are attracted to the core wire 11 by electrostatic force and adhere to the core wire 11 (spraying process). In this manner, the core wire 11 is coated.

[0029] Thereafter, the coated core wire 11 wound around the winding roll 22 is cut to a predetermined length, and the medical wire 10 is completed.

[0030] Here, in electrostatic coating, three forces act on the droplets 37D of the sprayed coating liquid 37: an electric field formed by applying a voltage to the spray nozzle 33, an electrostatic attractive force possessed by each droplet 37D, and gravity.

[0031] Assuming that the only objects present in the coating environment are the spray nozzle and a grounded object, the electric field created by applying voltage to the spray nozzle will all converge on the object. Therefore, if the effect of gravity is ignored, theoretically, all droplets will adhere to the object.

[0032] However, in a real coating environment, there are always grounded bodies other than the object to be coated, such as supports for the spray nozzle and the object to be coated, and the frame of the coating chamber. Therefore, in the coating environment, at positions more than a certain distance from the object to be coated, the electric field is directed toward these grounded bodies other than the object to be coated and does not converge on the object to be coated. Therefore, droplets that fly at positions more than a certain distance from the object to be coated are attracted to grounded bodies other than the object to be coated, resulting in a lot of wasted coating liquid.

[0033] In this embodiment, an external electrode 32 is disposed in a film-forming chamber 31, and a spray nozzle 33 is disposed with its outlet 33A facing the external electrode 32. Coating is performed with the core wire 11 passing between the outlet 33A and the external electrode 32. In this configuration, the direction of an electric field generated around the core wire 11 by applying a voltage to the spray nozzle 33 and the external electrode 32 converges from the spray nozzle 33 and the external electrode 32 toward the core wire 11, as shown by the arrows in FIG. 2 . Droplets 37D of the coating liquid 37 move toward the core wire 11 in accordance with the direction of the electric field and adhere to the core wire 11. This improves the efficiency of application of the coating liquid 37 to the core wire 11 and reduces waste of the coating liquid 37, compared to when the external electrode 32 is not provided.

[0034] As described above, the coating device 20 of this embodiment comprises the external electrode 32, an electrostatic atomization type spray nozzle 33 having an outlet 33A from which the coating liquid 37 is sprayed, with the outlet 33A positioned toward the external electrode 32, an unwinding roll 21 and a winding roll 22 that support the core wire 11 so that it is positioned between the external electrode 32 and the outlet 33A, a first power supply unit 38 that applies a voltage to the spray nozzle 33, and a second power supply unit 39 that applies a voltage to the external electrode 32.

[0035] The coating method of this embodiment also includes a voltage application step of applying voltage to the external electrode 32 and to an electrostatic atomization spray nozzle 33 having an outlet 33A from which the coating liquid 37 is sprayed, with the outlet 33A positioned toward the external electrode 32; and a spray step of arranging a core wire 11 between the external electrode 32 and the outlet 33A and spraying the coating liquid 37 from the spray nozzle 33.

[0036] According to the above configuration, the direction of the electric field generated around the core wire 11 by applying a voltage to the spray nozzle 33 and the external electrode 32 is a direction converging from the spray nozzle 33 and the external electrode 32 toward the core wire 11. The droplets 37D of the coating liquid 37 move toward the core wire 11 in accordance with the direction of the electric field and adhere to the core wire 11, improving the efficiency of application of the coating liquid 37 to the core wire 11 compared to a case in which the external electrode 32 is not provided. This reduces waste of the coating liquid 37 and enables the coating layer 12 to be efficiently formed on the surface of the core wire 11.

[0037] Furthermore, the length Le of the external electrode 32, which is represented by the distance between both ends in the direction along the extension direction of the core wire 11, is equal to or greater than the spray width Ws, which is represented by the distance between both ends in the direction along the extension direction of the core wire 11 of the spray range of the coating liquid 37 sprayed from the spray nozzle 33.

[0038] Furthermore, the width We of the external electrode 32, which is expressed as the distance between both ends in a direction perpendicular to the extending direction of the core wire 11, is equal to or larger than the diameter D of the core wire 11.

[0039] According to this configuration, the efficiency of the droplets 37D of the coating liquid 37 being applied to the core wire 11 is further improved, and waste of the coating liquid 37 can be further reduced.

[0040] <Test example> 1. Test Method A 0.3 mm diameter stainless steel wire was supported by a framework formed by an insulator. A stainless steel plate-shaped external electrode was placed directly below the wire. The wire was coated by spraying the coating solution vertically downward using an electrostatic atomization spray nozzle. The coating solution used was a black acrylic resin paint (Acrylist Hi Black) manufactured by Natoco Corporation diluted with acrylic resin paint thinner (Acrylist Thinner for Electrostatic Use M No. 312) at a mass ratio of 1:1. After coating, the wire was baked on a hot plate. The test conditions are shown in Table 1.

[0041] [Table 1]

[0042] When no voltage was applied to the external electrode, most of the droplets of the coating liquid adhered to the wire, but many droplets were observed to fall without adhering to the wire, as shown in Figure 4. When a voltage of 0.5 kV was applied to the external electrode, most of the droplets of the coating liquid adhered to the wire, and in particular, it was observed that the droplets that had passed through the wire turned upward and were attracted to the wire. This is thought to be because an upward electric field was formed from the external electrode to the wire when a voltage was applied to the external electrode.

[0043] <Other embodiments> (1) In the embodiment, the external electrode 32 is an elongated plate-like member, but the shape of the external electrode is arbitrary, and it may be, for example, rod-like, wire-like, disk-like, or the like. (2) In the embodiment, one external electrode 32 is used, but multiple external electrodes may also be used. (3) In the embodiment, an example was shown in which coating was performed using a continuous coating device that continuously coats the core wire 11 passing through the film-forming chamber 31 by driving the unwinding roll 21 and the winding roll 22. However, a batch coating device may also be used to coat a wire that has been cut to a predetermined length in advance. In such a case, a spray nozzle may be scanned over a stationary wire. In that case, for example, an external electrode may be connected to the spray nozzle and move in conjunction with the spray nozzle. (4) In the embodiment, the wire material is the core wire 11 for the medical wire 10, but the wire material may be a member used for purposes other than medical wire. (5) In the embodiment, the core wire 11 and the external electrode 32 were disposed below the spray nozzle 33, and the coating liquid 37 was sprayed downward. However, the arrangement of the wire and the relative positions of the wire, the external electrode, and the spray nozzle are arbitrary as long as the wire is disposed between the spray nozzle nozzle and the external electrode. For example, the wire and the external electrode may be disposed above the spray nozzle, the spray nozzle may be disposed with its nozzle facing upward, and the coating liquid may be sprayed upward. Alternatively, the wire and the external electrode may be disposed to the side of the spray nozzle, the spray nozzle may be disposed with its nozzle facing laterally, and the coating liquid may be sprayed laterally. Furthermore, in the embodiment, the core wire 11 and the external electrode 32 were disposed horizontally. However, the orientation of the wire is arbitrary. For example, the wire may be disposed vertically or obliquely. In either case, if the external electrode is a member having a length, it is preferable that the external electrode be disposed parallel to the wire. (6) In the embodiment, the first power supply unit 38 is connected to the spray nozzle 33, and the external electrode 32 is connected to the second power supply unit 39. However, the same power supply unit may be connected to both the spray nozzle and the external electrode. In this case, it is preferable that the voltage applied to the spray nozzle and the voltage applied to the external electrode can be controlled separately. [Explanation of symbols]

[0044] 11: Core wire (wire material) 20: Coating equipment 21: Unwinding roll (support member) 22: Winding roll (support member) 32: External electrode 33: Spray nozzle 33A: Spout 37: Coating liquid 38: 1st power supply device (power supply device) 39:Second power supply device (power supply device)

Claims

[Claim 1] A coating method for applying a coating to the surface of a wire by electrostatic coating using a coating device, comprising: The coating device comprises: An external electrode; an electrostatic atomization spray nozzle having a spray outlet from which the coating liquid is sprayed, the spray outlet being positioned facing the external electrode; a pair of support members that support the wire so as to be disposed between the external electrode and the jet nozzle; a power supply device that applies a voltage to the spray nozzle and the external electrode, a film formation chamber is disposed between the pair of support members, and the external electrode and the spray nozzle are provided inside the film formation chamber; the external electrode is an elongated plate-like member having electrical conductivity, and is arranged such that its length direction is along the extending direction of the wire material, and is arranged horizontally inside the film formation chamber below the wire material that is arranged horizontally; an internal electrode is provided inside the spray nozzle, and a voltage is applied to the internal electrode from the power supply device; a voltage application step of applying a voltage to each of the external electrode and the spray nozzle; a spraying step of disposing the wire between the external electrode and the spray nozzle and spraying the coating liquid from the spray nozzle, In the voltage application step, a voltage is applied from a first power supply to an internal electrode provided inside the spray nozzle, thereby forming an electric field between the spray nozzle and the grounded wire, and a voltage of the same polarity as that of the internal electrode is applied from a second power supply to the external electrode, thereby forming an electric field also between the external electrode and the grounded wire; The wire is passed between the nozzle outlet of the spray nozzle and the external electrode, In this state, the coating liquid is supplied to the spray nozzle, and by applying a voltage to the spray nozzle, the coating liquid is charged inside the spray nozzle and ejected in an atomized state from the nozzle, and the atomized droplets of the coating liquid are attracted to and adhere to the wire by electrostatic force, in a coating method.

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