Method for painting a surface of a polymer component

Abstract

The invention relates to a method for painting the surface of a polymer component (10), in particular an exterior add-on part for motor vehicles, wherein the component surface has at least one area to be painted and at least one masking area (12) not to be painted. The masking is carried out using a polymer material (14), wherein the component (10) is first prepared and fixed. Then the masking area (12) of the component (10) is coated with the polymer material (14), preferably in the form of a liquid mass, and the polymer material (14) solidifies into a polymer film. The area to be painted is then painted, and subsequently the polymer film is peeled off, preferably in one piece.

Description

[0001] The invention relates to a method for painting the surface of a polymeric component, in particular an exterior attachment for motor vehicles, wherein the component surface has at least one coating area to be painted and at least one masking area not to be painted, wherein the masking is carried out using a polymeric material. The polymeric exterior attachments can be, for example, bumpers, rear spoilers, wheel arch trims, or sills.

[0002] For various applications, painted components must be protected from overspray in certain surface areas that are to remain unpainted. These unpainted areas are intended, for example, for the later assembly of other components or on another component. Therefore, masking must secure the areas to be protected so that the areas to be protected are not exposed to paint and remain fully available for subsequent assembly operations, for example. Masking with masking tapes is generally known. However, these are limited in terms of their geometry and also disadvantageous in terms of application. A method with the features described above is known, for example, from DE 10 2009 020 264 B4 and DE 10 2021 132 337 A1.While the methods known in the prior art are generally functional, they also have disadvantages, particularly when the polymer material is applied to the component surface at a certain distance. Document DE 197 37 065 A1 is also cited as prior art. The component can generally be coated with a single layer or multiple layers, with the individual coating layers being applied directly one after the other or separately at a time interval.

[0003] The invention is based on the object of specifying a method with the features described above, which avoids the disadvantages of the methods known in the prior art and enables a mask that is easy to apply and also easy to remove.

[0004] According to the invention, the object is achieved by a method for painting a surface of a polymer component, in particular an exterior attachment for motor vehicles, wherein the component surface has at least one painting area to be painted and at least one masking area not to be painted, wherein the masking is carried out using a polymer material, a. wherein the component is first provided and fixed, b. wherein the masking area of ​​the component is then coated with the polymer material, preferably in the form of a liquid mass, c. wherein the polymer material then solidifies to form a polymer film, d. wherein the painting area is then painted, and e. wherein the polymer film is then peeled off, preferably in one piece.

[0005] As an alternative to applying the polymer material in the form of a liquid mass, it is also possible to apply the polymer material in the form of solid particles. The term "liquid" also includes a viscous, for example, gel-like consistency of the polymer material.

[0006] It is within the scope of the invention that the cohesive and / or adhesive properties of the solidified polymer film are modified by applying energy (e.g., through the associated crosslinking and / or curing processes), so that the cohesive forces are smaller than the adhesive forces. This allows the polymer film to be removed in one piece.

[0007] The invention is particularly characterized in that the application of the polymer material to the masking area does not produce splashes or other defects on the component surface. The masking can be applied individually to the required locations, optionally three-dimensionally, for example in a ring-like manner, by swirling, spraying, doctoring, or even stamping. The liquid polymer material can harden through physical processes, e.g., by simple cooling, by circulating air, or by active curing through the application of energy. The polymer material expediently cures without chemical reactions or without any thixotropy of the polymer material playing a role. Preferably, no chemical reactions are required to develop the desired cohesive and adhesive properties of the polymer film.

[0008] Nevertheless, the component in the masking area can already have a pre-coating or contrasting coating before the masking is applied, so that the masking protects a previously painted surface, for example, against overpainting or against the thermal stress of a paint drying oven. While in the prior art, the polymer material is applied at a very close distance to the masking area, e.g., less than 5 mm, in particular less than 1 mm, within the scope of the invention, the application distance—that is, the distance between a device for ejecting the polymer material and the masking area—can be more than 10 mm, e.g., even more than 20 mm.

[0009] The masking area can have virtually any geometry. If a polymer material with thixotropic properties is used, the masking area can also be positioned "upside down," as the polymer material's thixotropic properties prevent it from dripping. The masking area can, for example, be band-shaped to provide unpainted surfaces for bonding or welding the component to other components.

[0010] The painting area is expediently cleaned and electrostatically activated or deactivated before painting. The polymer material can be designed as a one-component (1K) system or alternatively as a two-component (2K) system. The polymer material preferably has thixotropic properties. The term thixotropy describes the property of a non-Newtonian fluid that its viscosity gradually decreases over time when subjected to shear, or the viscosity increases again when there is little or no shear. The polymer material can thus be adjusted accordingly to solidify due to its thixotropic properties and through cooling after application to the masking area. This enables the polymer material to be applied contour-accurately without it flowing after application.

[0011] It is within the scope of the invention that the polymer material is applied to the masking area in spray form. In particular, application can be carried out in foamed spray form. Application as a spray or foamed spray allows for particularly close-to-contour application in hard-to-reach, curved masking areas. The polymer material is preferably sprayed onto the masking area using an automated spraying device. Such a spraying device is preferably attached to an industrial robot, cobot, or handling device and preferably has an automated dosing device.

[0012] The polymer material is expediently applied to the masking area in a layer thickness of 50 to 700 µm, preferably 100 to 500 µm, particularly preferably 150 to 450 µm. At this thickness, the polymer material or the polymer film formed therefrom can withstand the stresses encountered during the painting process. Furthermore, the internal strength of the polymer film is sufficiently high that the polymer film can be removed or peeled off without leaving residue, particularly after absorbing overspray in the painting system. The required thickness of the polymer film can vary depending on the selected polymer material and process requirements. The layer thickness is expediently applied as required, based on the specific process requirements.

[0013] The polymer material can have polar properties and be formed, for example, as a polyvinyl acetate copolymer (e.g. EVATANE ®< 18-500 or PLANATOL ®< HSP). Alternatively, polymer materials based on polyamide or polyactone are also within the scope of the invention. Suitable materials here include the substances C41404 from Bühnen, Bremen, or Hotbond AH 780L from BASF ®<. However, it is also within the scope of the invention to provide an alternative non-polar polymer material for the masking. It can be advantageous if the polymer material is adhesive to plastic. For the application of the polymer material to non-polar component plastics, it is advantageous if the polymer material has non-polar properties. For polar component plastics, non-polar polymer materials, e.g. based on polypropylene, optionally filled, or blends thereof, are particularly suitable for masking. Examples of these include, but are not limited to, polyolefins, such asSiKA ®< Hotmelt 050 or Jowat ®< 253.70 or PP Hot Melt Adhesive 3731-B from 3M ®< . The polymer material is preferably designed as a hot melt adhesive with a dynamic viscosity of no more than 2000 mPas at 150 °C.

[0014] It is within the scope of the invention that the polymer material is applied to the masking area using circular movements. In principle, the polymer material can be applied to the area of ​​the component to be masked in various ways, e.g. by doctoring, brushing, spraying, curling, foaming, or by stamping / pad printing. The application can, if necessary, be carried out with the simultaneous (or even without) supply of warm or hot air. The polymer material can, in principle, be applied to the masking area using an automated application device. According to a preferred embodiment of the invention, the polymer material can be applied to the masking area in a state foamed with air. The mixing ratio of air to polymer material by volume is expediently in the range from 95 / 5 to 85 / 15, in particular 92 / 8 to 88 / 12.The application speeds at which the polymer material emerges from a corresponding application device, e.g. a nozzle, for application to the masking area depend on the geometry of the surface to be protected and the requirements. Without being limited to these, suitable application speeds are, for example, 0.05 to 0.5 m / sec, in particular 0.1 to 0.35 m / sec. The application quantities of the polymer material also depend on the geometry of the surface to be protected and the requirements. These quantities can be 10 to 100 g per component, in particular 20 to 90 g per component. Likewise, when polymer material is applied together with air, e.g. as a foam, the volume flows depend on the geometry of the surface to be protected and the requirements.For example, but not limited to, suitable total volume flows are 0.1 to 100 liters / sec, in particular 0.2 to 10 liters / sec (see above for preferred volume fractions of the mixture of air and polymer material). The mass flows also depend on the geometry of the surface to be protected and the requirements. The mass flows can be 0.1 to 100 g / sec, in particular 0.2 to 10 g / sec. The application device for the air / polymer material mixture, which can in particular be designed as a nozzle, can have a nozzle opening for the air in the center and nozzle openings for the polymer material arranged in a ring around the outside. Alternatively, a nozzle opening for the polymer material can also be provided in the center with nozzle openings for the polymer material arranged in a ring around the outside.

[0015] The invention is explained in detail below with reference to a drawing that represents only one exemplary embodiment. The drawings schematically show: Fig. 1 shows a method according to the invention for painting a polymeric component surface, and Fig. 2-4 shows various nozzle geometries for masking an area of ​​the component surface.

[0016] The Fig. 1shows a method for painting a surface of a polymer component 10 in the form of an exterior add-on part for motor vehicles, wherein the component surface has at least one painting area to be painted and at least one masking area 12 not to be painted, and wherein the masking is carried out using a polymer material 14. First, the component 10 is prepared and fixed. The masking area 12 of the component 10 is then coated with the polymer material 14 in the form of a liquid mass. The polymer material 14 then solidifies after being coated on the masking area 12 to form a polymer film. The painting area is then painted, during which process the masking area 12 is protected by the polymer film from overspray. After the paint has cured, the polymer film is peeled off in one piece. Before painting, the painting area is usually cleaned and, if necessary,electrostatically activated or deactivated. The polymer material 14 can be designed as a 1-component system or as a 2-component system, wherein in the exemplary embodiment the polymer material 14 has thixotropic properties. The polymer material 14 is applied in spray form to the masking area 12 with a layer thickness of 150 to 450 µm. In the exemplary embodiment, the polymer material 14 is designed as a polyvinyl acetate copolymer or as SIKA ®< Hotmelt 050, although this does not exclude other materials. The polymer material 14 can in principle be designed as a hot-melt adhesive and has a dynamic viscosity of at most 2000 mPas at 150 °C.

[0017] The polymer material 14 is applied to the masking area 12, preferably using circular movements. Furthermore, the polymer material 14 is applied to the masking area 12 in a foamed state with air 50. The application device 16 for the polymer material 14 is attached to an industrial robot 18 and has a nozzle 100 (see FIG. 1) that enables the spray application of the mixture of air 50 and polymer material 14. Fig. 2 to 4). The industrial robot 18 is guided in a straight line along the longitudinal extent of the component 10, wherein the component 10 can be located on a movable product carrier (not shown in detail). The automated application device 16 for the polymer material 14 has an automatic or automated dosing device with a heating element. With the aid of the application device 16, the masking area 12 is sprayed with the polymer material 14 in order to cover the masking area 12 with the polymer material 14 and thus protect it from overspray during the painting process. The application device 16 comprises the nozzle 100 with the appropriate geometry in order to be able to apply the polymer material 12 in the desired thickness.In order to be able to cover any desired area of ​​the surface of the component 10 with the polymer material 14, the application device 16 has a control device (not shown in detail) that is configured to flexibly control the application device 16 via the industrial robot 18. By means of this method, a very high degree of accuracy can be achieved with regard to the application of the polymer material 16 to the masking area 12. The masking area 12 provided by the method according to the invention and remaining unpainted is, for example, a functional surface that can advantageously be connected, e.g., glued or welded, to surfaces of other components.

[0018] The Fig. 2 to 4 show different embodiments of the nozzle 100 for applying the mixture of air 50 and polymer material 14 to the masking area 12. In the embodiment according to Fig. 2the exit of air 50 and liquid polymer material 14 from the same block 60 takes place. In the embodiment according to Fig. 3 whereas the air 50 and the liquid polymer material 14 exit from different blocks 61 and 62. Fig. 4 shows a further embodiment of a nozzle 100 in a view from below. A central opening 101 can be seen, around which several openings 102 are arranged in a ring. Such a nozzle 100 is particularly suitable for applying the mixture of liquid polymer material 14 and air 50 to the masking area 12 using circular movements. For example, the polymer material 14 can be applied through the central opening 101 and the air 50 through the openings 102. Alternatively, the air 50 can also be applied through the central opening 101 and the polymer material 14 through the openings 102.

[0019] The peel strength of the polymer film can be determined as follows: Analogous to the ASTM posiTest, the tensile shear strength can be determined at a preload of 5 N and a test speed of 1.2 MPa / s. SKs that cannot be peeled by hand or are extremely difficult to peel (B119) result in a tensile shear strength of 1.67 MPa. SKs based on EVA (A44004) or PA (C41404) applied using the curling technique achieve tensile shear strengths of 0.27 to 0.78 MPa.

Claims

1. A method for painting a surface of a polymeric component (10), in particular an exterior add-on part for motor vehicles, wherein the component surface has at least one painting area to be painted and at least one masking area (12) not to be painted, wherein the masking is carried out using a polymer material (14), a. wherein the component (10) is first provided and fixed, b. wherein the masking area (12) of the component (10) is then coated with the polymer material (14), preferably in the form of a liquid mass, c. wherein the polymer material (14) then solidifies to form a polymer film, d. wherein the painting area is then painted, and e. wherein the polymer film is then peeled off, preferably in one piece.

2. Method according to claim 1, characterized in that the painting area is cleaned and electrostatically activated or deactivated before painting.

3. Method according to one of claims 1 or 2, characterized in that the polymer material (14) is designed as a 1K system or as a 2K system.

4. Method according to one of claims 1 to 3, characterized in that the polymer material (14) has thixotropic properties.

5. Method according to one of claims 1 to 4, characterized in that the polymer material (14) is applied in spray form to the masking area (12).

6. Method according to one of claims 1 to 5, characterized in that the polymer material (14) is applied to the masking area (12) with a layer thickness of 50 to 700 µm, preferably 100 to 500 µm, particularly preferably 150 to 450 µm.

7. Method according to one of claims 1 to 6, characterized in that the polymer material (14) is formed as a polyvinyl acetate copolymer.

8. Method according to one of claims 1 to 7, characterized in thatthe polymer material (14) is designed as a hot melt adhesive with a dynamic viscosity of at most 2000 mPas at 150 °C.

9. Method according to one of claims 1 to 8, characterized in that the polymer material (14) is applied to the masking area (12) using circular movements.

10. Method according to one of claims 1 to 9, characterized in that the polymer material (14) is applied to the masking area (12) in a state foamed with air (50).

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