Method for powder coating a component

Abstract

The invention relates to a method for powder coating a component, comprising a provisioning step in which the component and a coating powder comprising polymer particles and additives are provided, an electrical charging step in which the coating powder particles are provided with electrical charges, a dispersion step in which the electrically charged polymer particles are mixed with a dispersing liquid to form a dispersion, and an application step in which the dispersion is brought into contact with the surface of the component by evaporating the dispersing liquid and depositing the polymer particles, wherein the surface is electrically oppositely and / or negatively charged and / or grounded compared to the electrically charged polymer particles, and wherein the surface has a surface temperature that is above the boiling point of the dispersing liquid.as well as a fusion step in which the component and / or the polymer particles deposited on the surface are heated by means of a heat source, so that the polymer particles fuse together and / or foam up and / or expand, forming a polymer coating arranged on the surface of the component.

Description

[0001] The invention relates to a method for powder coating a component according to claim 1.

[0002] In an exemplary process for the conventional powder coating of a component, the component and a coating powder containing polymer particles are first provided in a preparation step. Subsequently, the coating powder is electrically charged in a charging step using a charging unit. In a subsequent application step, the electrically charged coating powder is brought into contact with a surface of the component that is either electrically oppositely charged to the coating particles or grounded, so that the electrically charged polymer particles are electrostatically attracted to the surface or discharge across the component surface and are thus deposited on the surface.In a subsequent fusion step of the process, the component and / or the polymer particles deposited on its surface are heated by a heat source, causing the coating particles to fuse together to form a polymer coating on the component's surface. Particularly with components that enclose a narrow cavity or have limited access to it, it is difficult to reliably apply the polymer coating to the area of ​​the component's surface facing the cavity using conventional powder coating methods.

[0003] DE 10 2019 125 162 B3 discloses a device and a spray booth for powder coating by means of triboelectric charging. EP 3 727 703 B1 discloses a device and a system for the electrostatic powder coating of objects. DE 20 2011 051 418 U1 discloses a lance for powder coating by electrostatic tribocharging.

[0004] One object of the invention is to provide a method for powder coating a component, with which the application of a polymer coating to the entire surface of the component is possible in a process-reliable manner and with low equipment costs.

[0005] This problem is solved by the features of the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0006] The invention proposes a method for powder coating a component, comprising a provisioning step in which the component and a coating powder comprising polymer particles and additives are provided, an electrical charging step in which the coating powder particles are provided with electrical charges, a dispersion step in which the electrically charged particles of the coating powder are mixed with a dispersing liquid to form a dispersion, and an application step in which the dispersion is brought into contact with the surface of the component by evaporating the dispersing liquid and depositing the coating particles, wherein the surface is electrically oppositely charged and / or grounded compared to the electrically charged coating particles, and wherein the surface has a surface temperature.which is above the boiling point of the dispersing liquid, and a melting step in which the component and / or the coating particles deposited on its surface are heated by a heat source, causing the polymer particles to fuse together and / or foam and / or expand, forming a polymer coating on the surface of the component. The dispersing liquid, which evaporates even at low temperatures, acts as a carrier for the coating particles, so that the coating particles are, for example, evenly distributed by the dispersing liquid within a cavity enclosed by the component and subsequently deposited evenly on the inside of the difficult-to-access component cavity as the dispersing liquid evaporates. Compared to known methods for the conventional powder coating of a component, the proposed method makes it possible toThe polymer coating can be applied reliably and with minimal equipment to the entire surface of the component, including hard-to-reach areas. Because the electrically charged coating particles are mixed with the dispersing liquid, further advantages arise: For example, discharge of the coating particles before the actual powder coating process is prevented. The electrical charges of the coating particles are effectively preserved in the dispersing liquid. Furthermore, this prevents the coating particles from repelling each other as strongly due to their like charges. This makes the process suitable, for example, for powder coating hard-to-reach grooves in all types of electric motors to apply an electrically insulating layer to the grooves.

[0007] By way of example, it is provided that the polymer particles of the coating powder each comprise the same material, preferably being a thermoset or a thermoplastic or a mixture of at least one thermoset and at least one thermoplastic. Particularly preferred is that the material be polyphenylene sulfide (PPS), polyetherimide (PEI), polyetherketoneketone (PEKK), polyetheretherketone (PEEK), or an epoxy resin. Alternatively, it is of course also possible for the polymer particles to comprise different materials, wherein the materials are selected from the group comprising: thermosets or thermoplastics or a mixture of at least one thermoset and at least one thermoplastic. In addition to the polymer particles, the coating powder can also contain conventional additives, such as additives to increase thermal conductivity.

[0008] In order to heat the component to be coated particularly efficiently, it is envisaged, for example, that the heat source is formed by an induction heater or by an infrared radiator.

[0009] For example, it is further stipulated that the particles contained in the coating powder have percentiles in the range of D 10 : 1-200 µm, D 50 : 10-500 µm and D 90 : 15-1000 µm.

[0010] For the purpose of electrically charging the coating powder, it is envisaged, by way of example, that the coating powder is charged using a Gema-Optistar® system with a flat jet nozzle. The following parameters are set as examples: Powder output: 25% at a total airflow of 4.5 m³ / h. Applied high voltage of -60 KV at a maximum current of 10 µA. Electrode clearance air of 0.2 m³ / h. Fluidization airflow of 0.8 m³ / h.

[0011] To effectively mix the coating powder particles from the electrical charging unit with the dispersing liquid, it is exemplified that, during the provisioning step, a container, preferably a thermally insulated container and / or a Dewar vessel, is provided which defines an interior space, and that the interior space of the container is filled with the dispersing liquid, and that, during the dispersion step, at least the electrically charged polymer, additive or coating particles are blown into the dispersing liquid, preferably below the level of the dispersing liquid in the interior of the container.

[0012] In order to selectively influence the behavior of the dispersion and the properties of the resulting polymer coating, it is preferably provided that the dispersion has at least one additive component, wherein it is provided that the at least one additive component is either mixed with the initially electrically neutral polymer particles before the electrical charging step or mixed with the dispersing liquid and the electrically charged polymer particles before the dispersion step, preferably in the interior of the container.

[0013] For example, it is provided that additives are also added to the polymer particles. Preferably, these can be chemical blowing agents and / or thermal conductivity (TVC) additives to increase thermal conductivity. Hexagonal boron nitride and / or aluminum oxide can preferably be used as TVC additives. Physical blowing agents, especially expanding microspheres, can preferably be used as blowing agents. An electrical charging process can also be advantageous for the additives, particularly the TVC additives. Therefore, the additives can also be added to the polymer powder before the electrical charging process and then mixed with the dispersing liquid as a coating particle stream.

[0014] The expanding microspheres can be, for example, of the Expancel® type from Nouryon®, preferably Expancel® type 951 DU 120, Expancel® type 950 DU 80, Expancel® type 930 DU 120, Expancel® type 920 DU 120, or Expancel® type 093 DU 120. In particular, the WLF additive increases the thermal conductivity of the polymer particles deposited on the surface, so that the polymer particles fuse together more quickly during the fusion step and the polymer coating forms faster. The blowing agents cause a foamed and / or expanded polymer coating to form during the fusion step.

[0015] In order to be able to guide the dispersion out of the interior of the container and supply it to the component, it is provided, by way of example, that the container has a syringe- and / or nozzle-shaped application unit on its underside opposite the dispersion liquid level, which defines an application outlet to the outside, which in turn is in flow communication with the interior of the container.

[0016] In order to be able to coat the component even in the area of ​​a cavity enclosed by the component, it is provided, for example, that during the application step the dispersion is introduced into a cavity bounded to the outside by the component by means of the application unit and via the application outlet and / or is applied to an area of ​​the surface of the component which is preferably facing a cavity bounded to the outside by the component.

[0017] If the component is formed, for example, by a tube, and in order to be able to coat the component reliably even in the area of ​​the inner circumferential surface, it is preferably provided that during the application step the dispersion is introduced by means of the application unit and via the application outlet into a cavity bounded by the component to the outside in such a way that the dispersion rises in the cavity against the direction of gravity, wherein it is preferably provided that the evaporated dispersing liquid flows out of the cavity, preferably into the environment, via an opening bounded by the component to the outside.

[0018] For example, the component is provided for by a pipe open at both ends or by a pipe open at one end.

[0019] In order to coat the entire surface of the component completely and in one operation, it is provided, for example, that the component is immersed, preferably completely, in the dispersion during the application step.

[0020] Purely optionally, and in the event that the coating particles blown into the dispersing liquid do not mix sufficiently with the dispersing liquid, it is preferably provided for improved mixing that the container has an agitator which is arranged in the interior of the container and is designed and / or suitable for mixing the dispersing liquid at least with the polymer particles blown into the dispersing liquid or with the polymer particles and the at least one additive component to form the dispersion.

[0021] To enable the dispersing liquid to evaporate quickly and without residue from the dispersion, it is preferably provided that the boiling point of the dispersing liquid is equal to or less than -50 °C, preferably less than -100 °C, and / or that the dispersing liquid is liquid nitrogen or a liquid noble gas or liquid carbon dioxide, and / or that the surface temperature is in a range of 10 °C to 50 °C, preferably in a range of 15 °C to 25 °C.

[0022] To obtain a closed and seamless polymer coating, it is envisaged, for example, that during the fusion step the polymer particles deposited on the surface and the first additive component and / or the second additive component fuse together to form the polymer coating.

[0023] For illustrative purposes only, the dispersion is specified as containing 80 wt% liquid nitrogen and 20 wt% polymer particles. However, the dispersion can also contain 1 wt% to 50 wt% polymer particles in liquid nitrogen. Alternatively, the dispersion can be specified as containing 70 wt% liquid nitrogen, 20 wt% polymer particles, and 10 wt% WLF additive. However, the dispersion can also contain 1 wt% to 30 wt% polymer particles and 1 wt% to 20 wt% WLF additive in liquid nitrogen. Alternatively, the dispersion can be specified as containing 70 wt% liquid nitrogen, 20 wt% polymer particles, and 10 wt% expanding microspheres. However, the dispersion can also contain 1 wt% to 30 wt% polymer particles and 1 wt% to 20 wt% expanding microspheres in liquid nitrogen. Alternatively, the dispersion can be specified as containing 60 wt% liquid nitrogen.-% liquid nitrogen, 20 wt% polymer particles, 10 wt% WLF additive, and 10 wt% expanding microspheres. However, the dispersion can also contain 1 wt% to 30 wt% polymer particles, 1 wt% to 20 wt% WLF additive, and 1 wt% to 20 wt% expanding microspheres in liquid nitrogen.

[0024] The following are embodiments of the invention described with reference to the accompanying figure.

[0025] It shows: Figure 1 shows a side-sectional view of a container in whose interior a dispersing liquid is located; Figure 2 shows a side-sectional view of a pipe open at both ends as an example of a component in whose pipe opening a dispersion rises against the direction of gravity; Figure 3 shows a side-sectional view of a component enclosing a cavity, with the dispersion being introduced into the cavity; Figure 4 shows a side-sectional view of the component according to the Figure 3, wherein the dispersing liquid of the dispersion, which evaporates in the cavity, flows out through an opening associated with the component; Figure 5 in a side section view shows a tube closed at one end as an example of a component, wherein the dispersion is introduced into the cavity bounded to the outside by the tube through an opening associated with the tube, and Figure 6 in a side section view shows the tube closed at one end, the dispersing liquid of the dispersion, which evaporates in the cavity, flows out through the opening associated with the tube.

[0026] Based on the Figures 1 to 6 The following describes a process for powder coating a component. The process comprises a preparation step, a charging step, a dispersion step, an application step, and a fusion step.

[0027] During the provisioning step, a component, such as those found in the Figures 2 to 6The device is depicted in various embodiments and includes a coating powder comprising polymer particles, which may also contain additives. Furthermore, in the provisioning step, a thermally insulated container 1 is provided, which defines an interior space and is filled with liquid nitrogen (this is merely an example). The container 1 has a syringe- and / or nozzle-shaped application unit 2 on its underside, opposite the liquid nitrogen level, which defines an application outlet. The application outlet is in flow communication with the interior of the container.

[0028] The coating powder contains polymer particles and may also contain other additives. The material of the polymer particles can be a plastic, such as a thermoset or a thermoplastic. Specifically, the material of the polymer particles can be, for example, polyphenylene sulfide (PPS), polyetherimide (PEI), polyetherketone ketone (PEKK), polyetheretherketone (PEEK), or an epoxy resin.

[0029] The electrical charging step follows the preparation step. In this step, the coating powder is fluidized by means of a fluidization device (not shown), whereby the powder particles are mixed with air. The mixture of coating powder particles and air exits the fluidization device as a coating powder particle-air stream and is fed to a charging device (not shown). The fluidization device can be designed in different ways depending on the application of the process. During the charging step, the coating powder particle-air stream is passed through the charging device, thereby electrically charging the coating powder particles.In the charging device, the coating powder particles can be electrically charged, for example, tribologically, by means of corona discharge, by means of a strong electric field, or by means of a grid electrode of the charging device.

[0030] The dispersion step is carried out immediately following the charging step. In the dispersion step, the coating particle air stream, whose coating particles are electrically charged after the charging step, is blown into the liquid nitrogen below the level of the liquid nitrogen inside the container. The blowing in of the coating particle air stream is carried out in the Figure 1This is illustrated by arrows 3. The coating particles subsequently mix with the liquid nitrogen, forming a dispersion of the electrically charged coating particles and the liquid nitrogen. Optionally, and to ensure optimal mixing of the coating particles blown into the liquid nitrogen to form the dispersion, the container 1 has an agitator 4 located inside the container. This agitator mixes the liquid nitrogen with the coating particles blown into the dispersion liquid, forming the dispersion.

[0031] The application step is carried out immediately following the dispersion step. In the application step, the dispersion is brought into contact with at least part of the component's surface. The component's surface is electrically grounded via a grounding conductor 5, allowing the charges of the polymer particles to dissipate upon contact with the grounded surface. Furthermore, the component's surface has a temperature above the boiling point of liquid nitrogen. Depending on the component's design, the dispersion can be brought into contact with the surface in various ways.

[0032] As in the Figure 2As shown, the component can, for example, be formed by a pipe 11. The pipe 11 defines a pipe passage to the outside. The pipe passage is open on two sides: downwards, relative to the direction of gravity, via a lower opening, and upwards, relative to the direction of gravity, via an upper opening. During the application step, the dispersion can be introduced into the pipe passage by means of the application unit and via the lower opening of the application outlet. The introduction of the dispersion is described in the Figure 2 This is illustrated by arrow 13. The dispersion rises against gravity in the pipe passage, causing the nitrogen to evaporate and the coating particles to be deposited on the inner circumferential surface as part of the surface of pipe 11. The evaporated nitrogen then escapes from the pipe passage through the opening at the top. The escape of the evaporated nitrogen is shown in the Figure 2 Illustrated by arrow 15.

[0033] As in the Figures 3 and 4 The component can, for example, also be represented by an oval or ovoid-shaped hollow body 21. The hollow body 21 defines a cavity to the outside, which is open to the outside via an opening 23 defined by the hollow body 21. During the application step, the dispersion can be introduced into the cavity via the application unit and the application outlet through the opening 23 against the direction of gravity. The introduction of the dispersion is described in the Figure 3 This is illustrated by arrow 25. The nitrogen evaporates in the cavity, and the coating particles are deposited on the inner circumferential surface as part of the surface of the hollow body 21. The evaporated nitrogen then escapes from the cavity through opening 23, against the direction of gravity. The escape of the nitrogen is visible in the Figure 4Illustrated by arrow 27.

[0034] As in the Figures 5 and 6 As shown, the component can, for example, also be formed by a pipe 31 with a tube sheet 33 that defines a pipe passage to the outside, which is only open via an opening 35 located at the top with respect to the direction of gravity. The pipe passage is closed in the direction of gravity by means of the tube sheet 33. During the application step, the dispersion can be introduced into the pipe passage via the application unit and the application outlet through the opening 35. The introduction of the dispersion is described in the Figure 5 This is illustrated by arrow 37. The nitrogen evaporates in the pipe passage, and the coating particles are deposited on the inner circumferential surface as part of the surface of pipe 31. The evaporated nitrogen then exits the pipe passage through opening 35 against the direction of gravity. The escape of the nitrogen is visible in the Figure 6 Illustrated by arrow 39.

[0035] Alternatively, the component, regardless of its specific geometric shape, can also be completely immersed in the dispersion. In this process, the nitrogen evaporates and the polymer particles are deposited across the entire surface of the component.

[0036] The fusing step is carried out immediately following the application step. During the fusing step, the surface of the component is heated by a heat source, at least in the area where the coating powder particles were deposited during the application step. This causes the coating powder particles to fuse together, forming a polymer layer on the surface of the component.

[0037] The polymer particles can optionally be mixed with one or more additive components before or during the dispersion step. These additive components then become part of the dispersion and are deposited onto the component surface along with the polymer particles during the application step. The additive components can include, for example, a chemical blowing agent, hexagonal boron nitride as a thermal conductor, aluminum oxide as a thermal conductor, or a physical blowing agent such as expanding microspheres. The additive components are deposited onto the component surface along with the polymer particles and, after the fusion step is complete, form part of the polymer coating. Reference symbol list

[0038] 1 Container 2 Application unit 3 Arrow 4 Agitator 5 Grounding conductor 11 Pipe 13 Arrow 15 Arrow 21 Hollow body 23 Opening 25 Arrow 27 Arrow 31 Pipe 33 Pipe base 35 Opening 37 Arrow 39 Arrow

Claims

1. A method for powder coating a component comprising: a provisioning step in which the component and a coating powder comprising polymer particles and additive particles are provided; an electrical charging step in which the coating powder particles are provided with electrical charges; a dispersion step in which the electrically charged coating powder particles are mixed with a dispersing liquid to form a dispersion; an application step in which the dispersion is brought into contact with the surface of the component by evaporating the dispersing liquid and depositing the coating powder particles, wherein the surface is electrically oppositely charged to the electrically charged coating powder particles and / or grounded, and wherein the surface has a surface temperature that is above the boiling point of the dispersing liquid.a fusion step in which the component and / or the coating powder particles deposited on the surface are heated by means of a heat source, so that the coating powder particles fuse together and / or foam up and / or expand to form a polymer coating arranged on the surface of the component.

2. Method according to claim 1, characterized by the fact that In the provision step, a container (1), preferably a thermally insulated container and / or a Dewar vessel, is provided which defines an interior space of the container, and the interior space of the container is filled with the dispersing liquid, and in the dispersion step, at least the electrically charged polymer particles are blown into the dispersing liquid, preferably below the level of the dispersing liquid in the interior of the container.

3. Method according to claim 1 or 2, characterized by the fact thatthe dispersion comprises at least one additive component, wherein it is provided that the at least one additive component is mixed with the dispersing liquid and the electrically charged polymer particles prior to the dispersion step, or wherein it is provided that the at least one additive component is mixed with the dispersing liquid and the polymer particles during the dispersion step, specifically in the interior of the container.

4. Method according to claim 2 or 3, characterized by the fact that The container (1) has on its underside opposite the free surface of the dispersing liquid a syringe- and / or nozzle-shaped application unit (2) which defines an application outlet to the outside, which in turn is in flow communication with the interior of the container.

5. Method according to claim 4, characterized by the fact thatIn the application step, the dispersion is introduced by means of the application unit (2) and via the application outlet into a cavity bounded to the outside by the component and / or is applied to an area of ​​the surface of the component which is preferably facing a cavity bounded to the outside by the component.

6. Method according to claim 4, characterized by the fact that In the application step, the dispersion is introduced by means of the application unit (2) and via the application outlet into a cavity bounded to the outside by the component in such a way that the dispersion rises in the cavity against the direction of gravity, wherein it is preferably provided that the evaporated dispersing liquid flows out of the cavity, preferably into the environment, via an opening bounded to the outside by the component.

7. Method according to any one of the preceding claims, characterized by the fact thatDuring the application step, the component is immersed, preferably completely, in the dispersion.

8. Method according to any one of claims 2 to 7, characterized by the fact that the container (1) has a stirrer (4) which is arranged in the interior of the container and is designed and / or suitable for mixing the dispersing liquid at least with the coating powder particles blown into the dispersing liquid or with the polymer particles and the at least one additive component to form the dispersion.

9. Method according to any one of the preceding claims, characterized by the fact that the boiling point of the dispersing liquid is equal to or less than -50 °C, preferably less than -100 °C, and / or that the dispersing liquid is liquid nitrogen or a liquid noble gas or liquid carbon dioxide, and / or that the surface temperature of the surface is in a range of 10 °C to 50 °C, preferably in a range of 15 °C to 25 °C.

10. Method according to any one of claims 3 to 9, characterized by the fact that During the fusion step, the coating powder particles and / or other additive components deposited on the surface fuse together to form the polymer coating.

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