Coating device and coating method

Abstract

A coating device (1A) that atomizes a coating material having a resistivity of 20 M [Omega] cm or less by the action of an electric field, the coating device (1A) being provided with: a nozzle (21) to which a voltage is applied; a flow path (23) through which the paint flows; a measurement unit (42) that measures the supplied current; and a control unit (5) that controls the voltage applied to the nozzle (21) on the basis of the measurement value of the measurement unit.

Description

Technical Field

[0001] The present invention relates to a coating apparatus and a coating method. Background Art

[0002] Electrostatic atomization coating is a coating method in which paint is made into fine droplets by the action of an electric field formed between a charged nozzle and a conductor disposed opposite to the nozzle, and the droplets are sprayed onto an object to be coated.

[0003] For example, Japanese Patent Application Laid-Open No. 2018-8253 (Patent Document 1) discloses an electrostatic spraying device used in coating by an electrostatic coating method. According to the electrostatic spraying device of Patent Document 1, regardless of the spraying direction of the liquid, the deviation of the spraying amount of the liquid from each nozzle can be reduced.

[0004] In order to achieve uniform coating in electrostatic atomization coating, it is effective to make the particle size of the paint particles uniform. For this purpose, it is necessary to control the nozzle so that the electric field formed between the nozzle and the conductor becomes a uniform electric field. Since the intensity of the electric field is a function of the distance between the positive and negative electrodes and the applied voltage, if the voltage applied to the nozzle is controlled according to the distance between the nozzle and the conductor, the intensity of the electric field can be kept constant. Typically, by moving the nozzle mounted at the tip of an industrial robot along the shape of the object to be coated along a preset path and controlling the voltage applied to the nozzle according to the distance between the nozzle and the conductor at each point on the path, the particle size of the paint can be made uniform.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-8253 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, when the object to be coated and the conductor are not in a specified position, the above control will cause deviation. For example, when the object to be coated and the conductor are located at a position farther from the nozzle path than the specified position, a lower voltage is applied relative to the distance between the nozzle and the conductor, and the intensity of the electric field is weaker than the specified value. That is, the positional deviation between the object to be coated and the conductor will hinder the uniformization of the particle size of the paint, and may further cause a decrease in the coating quality.

[0010] Therefore, there is a need to find a coating apparatus and a coating method in which the positional deviation between the object to be coated and the conductor does not easily affect the coating quality.

[0011] Solutions to the Problems

[0012] The present invention provides a coating device which atomizes a coating material having a resistivity of 20 MΩ·cm or less by the action of an electric field. The coating device is characterized in that it comprises: a nozzle to which a voltage is applied; a flow path through which the coating material flows; a measuring unit that measures the supplied current; and a control unit that controls the voltage applied to the nozzle based on the measurement value of the measuring unit.

[0013] The present invention provides a coating method which atomizes a coating material having a resistivity of 20 MΩ·cm or less by the action of an electric field. The coating method is characterized by including the following steps: measuring the supplied current; and controlling the voltage applied to a nozzle that ejects the coating material according to the measurement value of the current.

[0014] According to the above structure, by measuring the current and performing voltage control based thereon, it is possible to suppress the non-uniformity of the electric field caused by the deviation of the relative positional relationship between the nozzle and the conductor. Therefore, the positional deviation between the object to be coated and the conductor is less likely to affect the coating quality.

[0015] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a cross-sectional view of the coating device of the first embodiment.

[0017] Figure 2 is a block diagram showing the structural elements of the coating device of the first embodiment.

[0018] Figure 3 is a schematic diagram showing the usage state of the coating device of the first embodiment.

[0019] Figure 4 is a cross-sectional view of the coating device of the second embodiment.

[0020] Figure 5 is a cross-sectional view of the coating device of the third embodiment.

[0021] Figure 6 is a block diagram showing the structural elements of the coating device of the third embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Embodiments of the coating device and coating method of the present invention will be described with reference to the accompanying drawings.

[0023] 〔First Embodiment〕

[0024] Hereinafter, an example of applying the coating device of the present invention to a coating device 1A for electrostatic atomization coating and a coating method using the coating device 1A will be described.

[0025] (Structure of the coating device)

[0026] The coating device 1A of the first embodiment includes a nozzle head 2, a main body 3 connected to an operating arm of a coating robot (not shown), a power supply device 4, and a control device 5 (an example of a control unit). ( Figure 1 , Figure 2 )

[0027] The nozzle head 2 has a nozzle 21 to which a voltage is applied, a paint chamber 22 connected to the base end of the nozzle 21, and a flow path 23 (23a, 23b) communicating with a paint supply source (not shown) via the main body 3. A plurality of nozzles 21 are provided and arranged in a straight line in this embodiment. The paint chamber 22 is a member that functions to distribute the paint supplied from the paint supply source to the plurality of nozzles 21, and is provided as a space having a substantially rectangular parallelepiped shape in this embodiment. Two flow paths 23 are provided. One flow path 23a is a part of the flow path of the paint supplied from the paint supply source to the paint chamber 22 (hereinafter sometimes referred to as the "forward path"), and the other flow path 23b is a part of the flow path of the paint returning from the paint chamber 22 to the paint supply source (hereinafter sometimes referred to as the "return path"). In addition, in the nozzle head 2, in addition to these, structural elements such as an opening / closing valve device V for opening and closing each nozzle 21 may be included.

[0028] The voltage applied to the nozzle 21 depends on the output of the power supply device 4. The output of the power supply device is controlled by the control device 5. In addition, except for the path electrically connecting the nozzle 21 and the power supply device 4, each part of the coating device 1A is designed to be insulated and at least not configured to be actively conductive.

[0029] The main body 3 has a flow path 31 (31a, 31b) connecting the nozzle head 2 and a paint supply source (not shown) and a control valve 32 (32a, 32b) for controlling the flow of the paint in the flow path 31 (31a, 31b). In the flow path 31 and the control valve 32, the flow path 31a and the control valve 32a are the forward paths of the paint in the same manner as the flow path 23a of the nozzle head 2, and the flow path 31b and the control valve 32b are the return paths of the paint in the same manner as the flow path 23b of the nozzle head 2. Therefore, the control valve 32a controls the flow of the paint supplied to the paint chamber 22, and the control valve 32b controls the flow of the paint returning to the paint supply source. In addition, the operation of the control valve 32 (32a, 32b) is controlled by the control device 5.

[0030] The flow path 31 (31a, 31b) is formed in a spiral shape. Therefore, the extended distance of the length of the flow path 31 (31a, 31b) is longer compared to the case where the proximal end side and the distal end side of the main body 3 are linearly connected. In addition, the proximal end side of the main body 3 refers to the side connected to the working arm of a painting robot (not shown), and is the side located on the lower side of the paper surface in Figure 1 . Further, the distal end side of the main body 3 refers to the side connected to the nozzle head 2, and is the side located on the upper side of the paper surface in Figure 1 .

[0031] As the material constituting the flow path 23 (23a, 23b) and the flow path 31 (31a, 31b), from the viewpoint of using a material with excellent insulation properties, a resin material is preferred. Examples of such resin materials include fluororesin, nylon resin, etc., but are not limited to these. In addition, the materials constituting the flow path 23a, the flow path 23b, the flow path 31a, and the flow path 31b can be selected independently of each other.

[0032] As the power supply device 4, a known power supply device can be used. The power supply device 4 can measure a measurement value related to its operating state and input it to the control device 5. Specifically, the power supply device 4 includes: a voltmeter 41 that measures the voltage applied to the nozzle head 2 (nozzle 21); an ammeter 42 (an example of a measurement unit) that measures the current flowing through the nozzle head 2; and a power supply unit 43 that supplies voltage to the nozzle head 2 ( Figure 2 ).

[0033] As the control device 5, a known control device such as a computer can be used. The control device controls the output (voltage applied to the nozzle 21) of the power supply device 4 based on the measurement value of the ammeter 42. In addition, the control device 5 may also have other functions, such as controlling a painting robot, etc.

[0034] (Principle of painting and control of painting)

[0035] The painting device 1A is a painting device that atomizes the paint by the action of an electric field formed between the nozzle 21 that ejects the paint and the conductor C provided opposite to the nozzle 21 ( Figure 3 ). By forming an electric field between the nozzle 21 to which voltage is applied and the conductor C connected to the ground, and making the paint carry electricity with the same polarity as the nozzle 21, an action of attracting the paint by the conductor C is generated. In addition, since the droplets P of the paint leaving the nozzle 21 are charged, a repulsive force is generated between the droplets P to prevent coalescence, and thus fine droplets P are realized.

[0036] The coating material that becomes fine droplets P is attracted by the conductor C and flies under the action of an electric field, and adheres to the object to be coated W. The object to be coated W is grounded, and the charge possessed by the droplets P of the coating material flows to the ground through the grounding point of the object to be coated W. Through the above operations, an electric current flows between the nozzle 21 and the object to be coated W with the droplets P as the medium. In other words, if the coating apparatus 1A is controlled so that the magnitude of the current flowing between the nozzle 21 and the object to be coated W becomes constant, it is possible to expect that the size, ejection speed, etc. of the formed coating material droplets P will become constant. This contributes to the stabilization of the coating quality. Therefore, it is necessary to determine the magnitude of the current flowing between the nozzle 21 and the object to be coated W.

[0037] As described above, except for the path electrically connecting the nozzle 21 and the power supply device 4, each part of the coating apparatus 1A is designed to be insulated. Therefore, at least in terms of design, the current supplied to the coating apparatus 1A is consistent with the current flowing between the nozzle 21 and the object to be coated W with the droplets P as the medium. However, as an unwanted current, a current (hereinafter referred to as leakage current) flowing through the coating material flow path (flow path 23, flow path 31) to the coating material supply source may be generated. That is, the current flowing between the nozzle 21 and the object to be coated W becomes the value obtained by subtracting the leakage current from the measured value of the ammeter 42. Therefore, in order to correctly determine the current flowing between the nozzle 21 and the object to be coated W, it is necessary to determine the leakage current.

[0038] In the present embodiment, instead of determining the leakage current, the leakage current is suppressed to a negligible level so that the measured value of the ammeter 42 can be regarded as consistent with the current flowing between the nozzle 21 and the object to be coated W for processing. Specifically, by making the flow path 31 (31a, 31b) spiral to extend its extension distance, the resistance of the coating material flow path is increased, so that the grounding resistance of the nozzle 21 becomes 25 GΩ or more, and thus the leakage current is suppressed to a negligible level. Therefore, in the present embodiment, the measured value of the ammeter 42 represents the current flowing between the nozzle 21 and the object to be coated W. If the output of the power supply device 4 is controlled so that this measured value becomes constant, it is possible to make the size, ejection speed, etc. of the coating material droplets P constant.

[0039] In addition, above, the case where the object to be coated W is an insulator has been described as an example, but a conductor may also be used as the object to be coated. When the object to be coated W is a conductor, the object to be coated W itself plays a role in forming an electric field between it and the nozzle 21, so it is not necessary to provide a separate conductor C. This also applies to the subsequent embodiments.

[0040] 〔Second Embodiment〕

[0041] In the coating apparatus 1B of the second embodiment, instead of the flow paths 31 (31a, 31b) in the first embodiment, linear flow paths 33 (33a, 33b) are provided ( Figure 4 ). However, the inner diameter of the flow paths 33 (33a, 33b) is 0.8 mm or more and 1.0 mm or less, which is thinner than the piping used as the flow path for the coating material in such a coating apparatus. By narrowing the flow paths 33 (33a, 33b) to increase the resistance of the flow path for the coating material, the grounding resistance of the nozzle 21 becomes 25 GΩ or more. Therefore, as in the first embodiment, the leakage current is suppressed to a negligible level.

[0042] If the inner diameter of the flow paths 33 (33a, 33b) is 1 mm or less, the grounding resistance of the nozzle 21 is likely to become large enough, and it is easy to suppress the leakage current. On the other hand, if the inner diameter of the flow paths 33 (33a, 33b) is 1 mm or more, it is easy to supply the coating material smoothly to the nozzle 21.

[0043] In addition, other structural elements are the same as those in the first embodiment.

[0044] 〔Third Embodiment〕

[0045] In the coating apparatus 1C of the third embodiment, instead of the flow paths 31 (31a, 31b) in the first embodiment, linear flow paths 34 (34a, 34b) are provided ( Figure 5 ). As the flow paths 34 (34a, 34b), flow paths within the size range typically used as the flow path for the coating material in such a coating apparatus are used. Therefore, in the third embodiment, it is difficult to expect the effect that the leakage current is suppressed to a negligible level as seen in the first and second embodiments.

[0046] Therefore, in the third embodiment, in addition to the ammeter 42 provided in the same manner as in the first and second embodiments, a second ammeter 44 (an example of a measurement unit) for measuring the current (leakage current) flowing in the flow path 34 is provided ( Figure 6 ). That is, if the measured value of the ammeter 42 representing the total amount of current supplied to the nozzle head 2 is subtracted from the measured value of the ammeter 44 representing the leakage current, the current flowing between the nozzle 21 and the object to be coated W can be determined. Thus, if the output of the power supply device 4 is controlled so that the difference between the measured value of the ammeter 42 and the measured value of the ammeter 44 becomes constant, the size, ejection speed, etc. of the coating droplets P can be made constant.

[0047] In addition, other structural elements are the same as those in the first embodiment.

[0048] 〔Other Embodiments〕

[0049] Finally, other embodiments of the coating device of the present invention will be described. In addition, for the structures disclosed in the following respective embodiments, as long as there is no contradiction, they can also be combined and applied with the structures disclosed in other embodiments.

[0050] In particular, the above-described first embodiment, second embodiment, and third embodiment can be combined within a non-contradictory range. For example, a structure in which the flow path is spiral and the inner diameter is 1.6 mm or more and 2.0 mm or less can be adopted. This combination example is the same as the second embodiment in that a pipe thinner than the pipe used as the paint flow path in the same type of coating device is used, but a thicker pipe than the second embodiment can be used. The reason is that both using a relatively thin pipe and making the flow path spiral contribute to increasing the resistance of the paint flow path. Therefore, the contribution required for using a thinner pipe is less than that of the second embodiment. Similarly, the contribution required for the spiral shape is less than that of the first embodiment. Therefore, the number of turns of the spiral can also be less than that of the first embodiment. In addition, other than this, a structure in which a measurement unit measures the current flowing in the flow path on the basis that the flow path is spiral can also be adopted.

[0051] In the above embodiment, the structure in which the nozzles 21 are arranged linearly has been described as an example. However, in the present invention, the arrangement of the nozzles is not limited. For example, the nozzles may be arranged along the circumference.

[0052] Regarding other structures, the embodiments disclosed in this specification are illustrative in all aspects, and it should be understood that the scope of the present invention is not limited by these contents. Those skilled in the art can easily understand that appropriate changes can be made without departing from the gist of the present invention. Therefore, other embodiments obtained by making changes without departing from the gist of the present invention are of course included in the scope of the present invention.

[0053] Description of Reference Numerals

[0054] 1A, coating device (first embodiment); 2, nozzle head; 21, nozzle; 22, paint chamber; 23, flow path; 3, main body portion; 31, flow path; 32, control valve; 4, power supply device; 41, voltmeter; 42, ammeter; 43, power supply section; 5, control device; P, droplet; C, conductor; W, object to be coated; 1B, coating device (second embodiment); 33, flow path; 1C, coating device (third embodiment); 34, flow path; 44, ammeter.

Claims

1. A coating device that atomizes a coating material with a resistivity of 20 MΩ·cm or less by the action of an electric field, wherein, the coating device includes: a nozzle to which a voltage is applied; a flow path through which the coating material flows; a measurement unit that measures the supplied current; and a control unit that controls the voltage applied to the nozzle based on the measurement value of the measurement unit.

2. The coating device according to claim 1, wherein, at least a part of the flow path is spiral.

3. The coating device according to claim 1, wherein, the inner diameter of at least a part of the flow path is 0.8 mm or more and 1.0 mm or less.

4. The coating device according to claim 2 or 3, wherein, the ground resistance of the nozzle is 25 GΩ or more.

5. The coating device according to claim 1, wherein, the measurement unit also measures the current flowing in the flow path.

6. A coating method that atomizes a coating material with a resistivity of 20 MΩ·cm or less by the action of an electric field, wherein, the coating method includes the following: measuring the supplied current; and controlling the voltage applied to the nozzle that ejects the coating material based on the measurement value of the current.

Images