Electrostatic atomization device and method for characterizing atomization of indirectly charged atomizer

Abstract

The present invention provides an electrostatic atomization device comprising the following parts: (A) an indirect charging atomizer comprising a rotating bell cup for atomizing and dispensing an electrically non-insulating coating composition, (B) an indirect charging part having an input port for connection with a high voltage power source, (C) an input port secured to the bell cup for electrostatically charging the atomized and dispensed coating composition, and (C) a device for quantitatively characterizing the atomization of the indirectly charged atomizer, the device comprising an optical measurement part for optically capturing droplets of a spray of the electrostatically charged atomized coating composition, wherein the optical measurement part is grounded and remains substantially equipotential with the bell cup of the indirectly charged atomizer. The invention further provides a method for characterizing atomization of the electrostatic atomization equipment.

Description

Technical Field

[0001] This invention relates to an electrostatic atomization device and a method for characterizing the atomization of an indirect charging atomizer. Background Technology

[0002] Today, the automotive industry employs a variety of coating compositions, such as base coats, which are often applied to substrates via atomization (e.g., using electrostatic atomization equipment). Automotive OEM (Original Equipment Manufacturer) production lines always use high voltage to atomize coating materials via electrostatic charging to improve application efficiency (i.e., increase the amount of coating droplets ultimately deposited on the substrate) and reduce overspraying, which can lead to contamination and surface defects such as pinholes after the coating composition has cured or been baked.

[0003] Characteristic parameters of atomization (such as the size and quantity of atomized paint droplets, and the droplet size distribution and uniformity of the spray formed by atomization) are used to characterize and evaluate the atomization of paint compositions. For example, smaller droplet size and a larger number of droplets indicate a higher degree of atomization and spray uniformity.

[0004] In automotive OEM production lines or paint shops, atomization is achieved using electrostatic atomization equipment, particularly indirect charging atomizers with rotating bell cups. This atomization is influenced by numerous factors, such as the bell cup's rotation speed, the forming air volume, the flow rate of the liquid paint, and the high voltage applied to the atomizer. Therefore, atomization in electrostatic atomization equipment can be managed by adjusting these influencing factors.

[0005] However, the correlation between the high voltage applied to the atomizer via electrostatic charging and atomization characteristic parameters (e.g., droplet size distribution of the spray) has not been thoroughly explored. Therefore, the quality of the coating after curing or baking can only be controlled empirically, and repeated experiments are required to select the optimal conditions.

[0006] Therefore, there is still a need to provide a method for characterizing atomization and an electrostatic atomization device thereof, through which paint spraying can be accurately controlled. Summary of the Invention

[0007] In one aspect, the present invention provides an electrostatic atomizing device comprising the following components:

[0008] (A) An indirect charging atomizer comprising a rotating bell cup for atomizing and dispensing an electrically non-insulating coating composition.

[0009] (B) An indirect charging component having an input port for connection to a high-voltage power supply, the input port being fixed to the indirect charging atomizer for electrostatic charging of the atomized and dispensed coating composition, and

[0010] (C) An apparatus for quantitatively characterizing the atomization of the indirect-charge atomizer, the apparatus comprising an optical measuring element for optically capturing droplets of a spray of an electrostatically charged atomized coating composition, wherein the optical measuring element is grounded and maintained substantially at the same potential as the bell cup of the indirect-charge atomizer.

[0011] In another aspect, the present invention provides a method for characterizing the atomization of the electrostatic atomization device of the present invention, the method comprising the following steps:

[0012] (i) Applying a coating composition atomized by the electrostatic atomization device by spraying a rotating bell-shaped cup.

[0013] (ii) The atomized coating composition was detected by optical measuring components, and

[0014] (iii) Determine the characteristic parameters of atomization based on the data obtained through the optical measurement component. Detailed Implementation

[0015] The undefined articles “a”, “an”, and “the” refer to one or more kinds specified by the term following the article.

[0016] In the context of this disclosure, any specific value mentioned for a feature (including specific values ​​mentioned as endpoints in a range) may be recombinated to form a new range.

[0017] In the context of this disclosure, each aspect so defined may be combined with any one or more other aspects unless expressly indicated to the contrary. In particular, any feature indicated as preferred or advantageous may be combined with any one or more other features indicated as preferred or advantageous.

[0018] In the context of this disclosure, “coating” and “paint” can be used interchangeably to mean the same thing, namely, a substance consisting of a solid material suspended in a liquid medium and applied as a protective or decorative coating to the surface of various substrates.

[0019] In the automotive OEM industry, liquid coating materials (including primers, base coats, and clear coats) are sprayed onto the vehicle body surface via atomizers. To maximize transfer efficiency and minimize overspray, atomizers that operate electrostatically by applying high voltage (i.e., electrostatic atomizers) are the most common in paint shops of automotive production plants. Among electrostatic atomizers, indirect / externally charged atomizers (such as the Duerr ecobell EXT and ABB RB1000 EXT) are widely used globally in automotive OEM production lines involving high voltages up to 100,000 volts for electrically non-insulated coating materials, such as water-based coatings or water-based liquid paints.

[0020] This invention provides an electrostatic atomization device, which includes the following components:

[0021] (A) An indirect charging atomizer comprising a rotating bell cup for atomizing and dispensing an electrically non-insulating coating composition.

[0022] (B) An indirect charging component having an input port for connection to a high-voltage power supply, the input port being fixed to the indirect charging atomizer for electrostatic charging of the atomized and dispensed coating composition, and

[0023] (C) An apparatus for quantitatively characterizing the atomization of the indirect-charge atomizer, the apparatus comprising an optical measuring element for optically capturing droplets of a spray of an electrostatically charged atomized coating composition, wherein the optical measuring element is grounded and maintained substantially at the same potential as the bell cup of the indirect-charge atomizer.

[0024] The present invention also provides a method for characterizing the atomization of the electrostatic atomization device of the present invention, the method comprising the following steps:

[0025] (i) Applying a coating composition atomized by the electrostatic atomization device by spraying a rotating bell-shaped cup.

[0026] (ii) The atomized coating composition was detected by optical measuring components, and

[0027] (iii) Determine the characteristic parameters of atomization based on the data obtained through the optical measurement component.

[0028] By implementing the method of the present invention, the properties of coatings can be improved through electrostatic charging atomization, particularly overcoming surface defects such as pinholes and clouding. Furthermore, determining the uniformity of the coating composition helps avoid surface defects such as streaks. In summary, the method of the present invention provides a simple, efficient, and cost-effective approach for screening coating formulations. Example

[0029] The following examples further illustrate how the invention can be carried out.

[0030] Example 1

[0031] An electrostatic atomizing device includes the following components:

[0032] (A) An indirect charging atomizer comprising a rotating bell cup for atomizing and dispensing an electrically non-insulating coating composition.

[0033] (B) An indirect charging component having an input port for connection to a high-voltage power supply, the input port being fixed to the indirect charging atomizer for electrostatic charging of the atomized and dispensed coating composition, and

[0034] (C) An apparatus for quantitatively characterizing the atomization of the indirect-charge atomizer, the apparatus comprising an optical measuring element for optically capturing droplets of a spray of an electrostatically charged atomized coating composition, wherein the optical measuring element is grounded and maintained substantially at the same potential as the bell cup of the indirect-charge atomizer.

[0035] Example 2

[0036] According to the electrostatic atomization device of Embodiment 1, the device for quantitatively characterizing the atomization of the indirect charging atomizer includes a data collection and processing unit that collects optical data from the optical measurement component and determines characteristic parameters of atomization based on the collected data.

[0037] Example 3

[0038] According to the electrostatic atomization device of Example 2, these characteristic parameters include the average size and size distribution of droplets of the atomized coating composition after spraying, as well as the uniformity of spraying.

[0039] Example 4

[0040] According to any one of Embodiments 1 to 3, the electrostatic atomizing device includes a grounded metal mesh placed in a plane substantially parallel to the mouth plane of the rotating bell cup.

[0041] Example 5

[0042] According to the electrostatic atomizing device of Embodiment 4, the shortest path between the plane of the metal mesh and the bottom plane of the rotating bell cup is in the range of 15 cm to 50 cm, and preferably in the range of 20 cm to 30 cm.

[0043] Example 6

[0044] According to any one of embodiments 1 to 5, the electrostatic atomizing device has a metal mask at its head portion, the metal mask including a through hole for allowing light emitted by the head portion of the optical measuring component to pass through.

[0045] Example 7

[0046] According to any one of Embodiments 1 to 6, the electrostatic atomization device wherein the light source of the optical measuring component is a laser.

[0047] Example 8

[0048] According to any one of embodiments 1 to 7, in the electrostatic atomizing device, the indirect charging component is fixed to the atomizer head, and the indirect charging component has an input port connected to a high-voltage power supply.

[0049] Example 9

[0050] A method for characterizing the atomization of an electrostatic atomizing device according to any one of Examples 1 to 8, the method comprising the following steps:

[0051] (i) Applying a coating composition atomized by the electrostatic atomization device by spraying a rotating bell-shaped cup.

[0052] (ii) The atomized coating composition was detected by optical measuring components, and

[0053] (iii) Determine the characteristic parameters of atomization based on the data obtained through the optical measurement component.

[0054] Example 10

[0055] According to the method described in Embodiment 9, in step (i), the grounded metal mesh is placed in a plane substantially parallel to the plane of the mouth of the rotating bell-shaped cup.

[0056] Example 11

[0057] According to the method described in Example 10, the shortest path between the plane of the metal mesh and the bottom plane of the rotating bell cup is in the range of 15 cm to 50 cm, and preferably in the range of 20 cm to 30 cm.

[0058] Example 12

[0059] According to any one of Embodiments 9 to 11, in step (i), the indirect charging component is fixed to the atomizer head, the indirect charging component having an input port connected to a high-voltage power supply.

[0060] Example 13

[0061] According to any one of Embodiments 9 to 12, in step (ii), the optical measuring component has a metal mask at its head portion, the metal mask including a through hole for allowing light emitted by the head portion of the optical measuring component to pass through.

[0062] Example 14

[0063] According to any one of embodiments 9 to 13, the light source of the optical measuring component is a laser.

[0064] Example 15

[0065] According to any one of Examples 9 to 14, in step (iii), these characteristic parameters include the average size and size distribution of droplets of the atomized coating composition after spraying, as well as the uniformity of spraying. Attached Figure Description

[0066] Figure 1 A schematic diagram of an electrostatic atomization device according to the present invention is shown.

[0067] Figure 2 A schematic structural diagram of the indirect charging atomizer of the electrostatic atomizing device according to the present invention is shown.

[0068] Figure 3 A comparison of characteristic parameters of sprays formed by atomization under different voltages and rotational speeds is shown. Example

[0069] The invention will be better understood from the following non-limiting examples. These examples do not limit the scope of the invention as described and claimed.

[0070] Figure 1 An electrostatic atomization device 10 according to the invention is shown, wherein the electrostatic atomizer, implemented in the form of an indirect / external charging atomizer 101, is used to atomize and dispense paint droplets toward a target (such as a substrate or workpiece) and to electrostatically charge the dispensed atomized paint droplets as they fly away from the atomizer.

[0071] Specifically, refer to Figure 2An indirect / externally charged atomizer 101, comprising an atomizer nozzle 1011 and a grounded rotating bell cup 1012 (e.g., rotating at a speed of 10-70 kRPM), is supplied with liquid paint P (e.g., a water-based or aqueous paint composition) by a paint supply system. The atomizer atomizes the liquid paint by applying centrifugal force, forming filaments to produce a spray in the form of droplets. The indirect / externally charged atomizer 101 further includes an indirect charging component 1013 having an input port connected to a high-voltage power supply HV and operatively mounted relative to the bell cup 1012.

[0072] exist Figure 2 In the atomizer shown, liquid paint P is dispensed by being broken into numerous droplets by centrifugal force at the edge of bell cup 1012, and then indirectly charged by corona discharge from indirect charging component 1013. The indirect charging component is implemented in the form of a transmitting electrode needle. The charging of the droplets occurs due to ionization of ions generated by corona discharge at the electrode needle. During propagation through an electric field E, the droplets are charged by contacting the ion stream generated between the normally grounded substrate W and the charging droplets. Since there is no continuous path between the indirect charging component 1013 and the paint supply system, a shunt from the high-voltage power supply to ground is avoided.

[0073] Therefore, the atomizer can be called an indirect charging atomizer or an external charging atomizer, where the external electrode is used to generate free ions that interact with and charge the already formed paint droplets after they leave the rotating bell cup.

[0074] For the indirect charging atomizer 101, the liquid paint is typically selected from electrically non-insulating (e.g., water-based) liquid paints with high conductivity, such as base coats or primers. By doing so, insulation measures for the entire liquid supply system can be eliminated.

[0075] Figure 1 The electrostatic atomizing device 10 further includes a means 102 for characterizing the atomization of the atomizer. The means 102 includes an optical measuring component 1021 configured to optically capture spray droplets generated by the atomizer. In the illustrated embodiment, the optical measuring component 1021 is grounded via a grounding cable and thus maintains substantially the same potential as the bell cup 1012 of the indirectly charged atomizer. Charge carried by oversprayed droplets attached to the optical measuring component can be directly released therefrom. By spacing the optical measuring component and the atomizer at an appropriate distance (e.g., greater than 150 mm), the optical measuring component can be protected from severe contamination by splashed paint droplets, while avoiding high-energy discharges between the optical measuring component and the atomizer. Therefore, it can be ensured that the optical measuring component can operate safely and reliably.

[0076] In this context, the term "substantially equipotential" means that the optical measuring components and the bell cup of the indirect charging atomizer are at essentially the same zero potential, and the potential difference between them (if any) is kept so small that it can be directly ignored.

[0077] In the context in which this term is used, "high voltage" refers to a voltage with an amplitude above zero and, in most cases, below 100 kV. This can vary depending on the specific application of the electrostatic atomizer.

[0078] The optical measurement component 1021 is a laser measurement device, such as an AOM SpraySpy sensor unit. The optical measurement component includes a head portion from which light is emitted and propagates into the spray. A detector lens is disposed in a region of the head portion to allow light to pass through it. Preferably, the optical measurement component has a metal mask 10211 disposed at or near the head portion. The head portion (particularly including the detector lens) is covered by the metal mask and protected from contamination by splashed paint droplets. The metal mask 10211 includes through-holes for allowing light emitted from the head portion to enter the spray. Therefore, the metal mask acts as a Faraday cage shield, helping to capture splashed paint droplets that would otherwise accumulate on and contaminate the detector lens, and thus helping to keep the detector lens clean, thereby protecting laser transmission from obstruction and preventing optical measurement failure.

[0079] The electrostatic atomizing device 10 includes a grounded metal mesh M placed in a plane intersecting the spray direction. The grounded metal mesh M allows the electric field to be captured and the spray pattern (particularly the spray pattern between the plane containing the metal mesh and the bell cup) to be shaped, thus significantly reducing overall overspray. With the bell cup 1012 oriented downwards, the metal mesh M is placed vertically below the bell cup, and its dimensions are set to have sufficient length and width so that the entire spray is shaped in the desired manner. In a preferred embodiment, the metal mesh is spaced 15 cm to 50 cm, and preferably 20 cm to 30 cm, from the edge of the bell cup of the indirect-charge atomizer at a distance h.

[0080] The apparatus 102 for characterizing paint atomization of an atomizer includes a data collection and processing unit 1022 for collecting optical data obtained from an optical measurement component 1021 and determining characteristic parameters of atomization (e.g., at least one characteristic parameter of droplet size distribution and / or uniformity of spraying) based on the collected optical data.

[0081] The indirect charging component 1013 of the indirect charging atomizer 101 is spaced at a predetermined distance, for example, at least 20 cm, from surrounding grounded objects (grounded objects placed near the atomizer, such as optical measurement components, support brackets for supporting optical measurement components, panels or walls or substrates to be coated, etc.). By maintaining this distance between the indirect charging component and the optical measurement component, the risk of high voltage (such as electrical sparks caused by extremely high potential differences between the indirect charging component and the optical measurement component) can be reduced to an acceptable level.

[0082] Using the electrostatic atomization device 10 of the present invention, a method for characterizing atomization can be implemented by taking the following steps:

[0083] Step S01: A spray of electrostatically charged atomized coating composition is generated by means of an indirect charging atomizer 101.

[0084] Step S02: Optically capture the spray droplets using an optical measuring component 1021, wherein the optical measuring component is grounded and maintains substantially the same potential as the bell cup of the indirectly charged atomizer, and

[0085] Step S03: The data collection and processing unit 1022 determines the characteristic parameters of atomization (e.g., at least one characteristic parameter of droplet size distribution and / or uniformity of spraying) based on the optical data obtained from the optical measurement component.

[0086] It should be noted that "characteristic parameters of atomization" here refers to all characteristic parameters that can indicate atomization behavior, including but not limited to characteristic parameters of droplet size distribution and / or the uniformity of spray produced by atomization.

[0087] In step S01, the spray droplets formed by atomization are optically captured by an optical measurement L that traverses the entire spray. This traversing optical measurement L can extend from the outside to the inside of the entire spray in an imaginary plane parallel to the substrate to be applied. If the spray is imagined as a cone, it can travel radially or chordally relative to the projected area of ​​the spray on the imaginary plane. Performing this traversing measurement allows the entire spray and thus the entire droplet spectrum forming the spray to be captured completely. Therefore, all droplet sizes forming the spray can be captured. The entire spray can be measured holistically, not just in individual areas of the spray. The traversing measurement allows for point-specific optical measurements of droplets at many locations in the atomized spray, and thus achieves the determination in step S03 with greater accuracy. Optical capture is performed by fixed optical measurements at fixed locations within the spray.

[0088] In step S02 of the method, optical capture is accomplished through optical measurement based on the study of scattered light from liquid paint droplets during spraying. Preferably, at least one laser is used as the light source in this measurement.

[0089] The optical capture in step S02 is preferably performed using a PDA (phase Doppler velocimetry) and / or time-shifting (TS) technique. Based on the optical data obtained when performing step S02 via the PDA, at least one characteristic parameter of the droplet size distribution can be determined in step S03. Based on the optical data obtained via TS in step S02, both the droplet size distribution and the uniformity of the spray can be determined in step S03.

[0090] The droplet size distribution in step S03 is determined using methods known to those skilled in the art, such as dN,50% (median based on quantity) and dV,50% (median based on volume). The uniformity of the spray coating refers to the ratio between the two quotients, i.e., T1 / T. Total1 With T2 / T Total2 The ratio between them, where T1 refers to the number of transparent droplets at the first position P1, T2 refers to the number of transparent droplets at the second position P2, and T... Total1 This refers to the total number of droplets in the spray, including both transparent and opaque droplets at the first position P1, and T Total2 This refers to the total number of all droplets in the spray, including both transparent and opaque droplets at the second position P2, where position P1 is closer to the center of the spray than position P2. Figure 1 As shown. And preferably, both positions are located on the measurement axis passing through the spraying.

[0091] The method for characterizing atomization of the present invention allows for the study of differences in atomization between waterborne coating compositions under electrostatic charging and uncharged conditions. For example... Figure 3 As shown, the higher the voltage applied to the atomizer, the finer the droplets obtained.

[0092] The method for characterizing atomization in this invention allows for the study of how the rotational speed of the bell cup affects the atomization effect. Figure 3 As can be seen, for water-based coating compositions, a higher bell cup rotation speed results in a smaller droplet dN,50%. Furthermore, when the bell cup rotation speed is approximately 25,000 rpm, applying a voltage of approximately 45 kV significantly reduces the droplet dN,50%.

[0093] The method for characterizing atomization according to the present invention further includes the step of placing a grounded metal mesh in a plane substantially parallel to the mouth plane of the rotating bell cup. Using the grounded metal mesh, an electric field can be formed between the metal mesh and the charged paint droplets, thus shaping the spray pattern to avoid overspraying. For safety, the metal mesh is placed at a distance of 15 cm to 50 cm, preferably 20 cm to 30 cm, from the edge of the bell cup of the atomizer.

[0094] The method for characterizing atomization according to the present invention includes the step of covering a head portion of an optical measurement component with a metal mask comprising through-holes for allowing light emitted from the head portion of the optical measurement component to pass through. The metal mask can trap splashed paint droplets that might otherwise deposit on the head portion (i.e., the lens) of the optical measurement component and keep the head portion clean.

[0095] The indirect charging component of the atomizer should be kept at a distance of at least 20 cm from surrounding grounded objects to ensure successful and safe measurement of the atomization of the external / indirect charging atomizer.

[0096] The method of this invention allows for direct measurement of electrostatic atomization of indirect / externally charged atomizers under high voltage. The resulting suitable conditions can be used in industrial applications, such as in the base coat painting workshops of automotive OEM production lines.

[0097] The method of this invention allows for the prediction of optical and / or surface defects in coatings based on droplet size distribution and spray uniformity. Sufficient atomization reduces the humidity of the resulting coating, which can easily cause defects such as pinholes, poor color tone, discoloration at angles, and moiré patterns.

[0098] Based on these characteristic parameters (such as droplet size distribution and spray uniformity), the properties of the coating can be predicted and defects such as pinholes, clouding, and streaks can be avoided.

[0099] The method of the present invention provides a simple and efficient approach for developing coating compositions without the need for curing or baking steps and subsequent performance testing.

[0100] Various modifications and variations that may be conceived by those skilled in the art may be made without departing from the scope or spirit of this disclosure. This specification and the examples disclosed herein should be considered illustrative only, and the scope of protection of this disclosure should be specified by the appended claims and their equivalents.

Claims

1. An electrostatic atomizing device, comprising the following components: (A) An indirect charging atomizer comprising a rotating bell cup for atomizing and dispensing an electrically non-insulating coating composition. (B) An indirect charging component having an input port for connection to a high-voltage power supply, the input port being fixed to the indirect charging atomizer for electrostatic charging of the atomized and dispensed coating composition, and (C) An apparatus for quantitatively characterizing the atomization of the indirect-charge atomizer, the apparatus comprising an optical measuring component for optically capturing droplets of a spray of an electrostatically charged atomized coating composition, wherein... The optical measuring component is grounded and remains substantially at the same potential as the bell cup of the indirect charging atomizer.

2. The electrostatic atomizing device according to claim 1, wherein, The apparatus for quantitatively characterizing the atomization of the indirect charging atomizer includes a data collection and processing unit that collects optical data from the optical measurement component and determines characteristic parameters of the atomization based on the collected data.

3. The electrostatic atomizing device according to claim 2, wherein, The characteristic parameters include the average size and size distribution of droplets of the atomized coating composition after spraying, as well as the uniformity of the spraying.

4. The electrostatic atomizing device according to any one of claims 1 to 3, wherein, The electrostatic atomizing device includes a grounded metal mesh placed in a plane substantially parallel to the mouth plane of the rotating bell-shaped cup.

5. The electrostatic atomizing device according to claim 4, wherein, The shortest path between the plane of the metal mesh and the bottom plane of the rotating bell cup is in the range of 15 cm to 50 cm, and preferably in the range of 20 cm to 30 cm.

6. The electrostatic atomizing device according to any one of claims 1 to 5, wherein, The optical measuring component has a metal mask at its head portion, the metal mask including a through hole for allowing light emitted by the head portion of the optical measuring component to pass through.

7. The electrostatic atomizing device according to any one of claims 1 to 6, wherein, The light source for this optical measuring component is a laser.

8. The electrostatic atomizing device according to any one of claims 1 to 7, wherein, The indirect charging component is fixed to the atomizer head and has an input port for connecting to a high-voltage power supply.

9. A method for characterizing the atomization of an electrostatic atomizing device according to any one of claims 1 to 8, the method comprising the following steps: (i) Applying a coating composition atomized by the electrostatic atomization device by spraying a rotating bell-shaped cup. (ii) The atomized coating composition was detected by optical measuring components, and (iii) Determine the characteristic parameters of atomization based on the data obtained through the optical measurement component.

10. The method according to claim 9, wherein, In step (i), the grounded metal mesh is placed in a plane that is substantially parallel to the plane of the spout of the rotating bell-shaped cup.

11. The method according to claim 10, wherein, The shortest path between the plane of the metal mesh and the bottom plane of the rotating bell cup is in the range of 15 cm to 50 cm, and preferably in the range of 20 cm to 30 cm.

12. The method according to any one of claims 9 to 11, wherein, In step (i), the indirect charging component is fixed to the atomizer head, the indirect charging component having an input port connected to a high-voltage power supply.

13. The method according to any one of claims 9 to 12, wherein, In step (ii), the optical measuring component has a metal mask at its head portion, the metal mask including a through hole for allowing light emitted by the head portion of the optical measuring component to pass through.

14. The method according to any one of claims 9 to 13, wherein, The light source for this optical measuring component is a laser.

15. The method according to any one of claims 9 to 14, wherein, In step (iii), the characteristic parameters include the average size and size distribution of the atomized coating composition droplets after spraying, as well as the uniformity of the spraying.

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