LASER COATING PROCESS AND DEVICE THEREFOR

Abstract

The invention relates to a process for applying a coating material to a surface, comprising the steps of:providing a stream of gas mixture (8) comprising a carrier gas and a coating material (2),feeding the stream of gas mixture (8) onto the surface (3a), wherein the stream of gas 12 s mixture (8) impinges on the surface (3a) and the coating material (2) applied there forms an area of impingement (11) on the surface (3a)coupling at least one laser beam (7) into the stream of gas mixture (8),wherein the coupled-in energy of the at least one laser beam (7) is determined in such a way that the solid coating material (2) at least partially melts andwherein each laser beam (7) is directed onto the stream of gas mixture (8) in such a way that the laser beam (7) does not fall on the area of impingement (11) on the surface. The invention also relates to a device for carrying out the process.

Claims

1-27. (canceled)

28. A process for applying a coating material to a surface comprising the steps of: providing a stream of gas mixture comprising a carrier gas and a solid, powdered coating material; feeding the stream of gas mixture to the surface, the stream of gas mixture impinging on the surface and the coating material applied to the surface forming an area of impingement on the surface, moving the surface and the stream of gas mixture relative to one another during the feeding of the stream of gas mixture to the surface; coupling at least one laser beam into the stream of gas mixture, the coupling in of the at least one laser beam being interrupted for a time during the feeding of the stream of gas mixture, wherein an amount of the coupled-in energy of the at least one laser beam is set such that the coating material is at least partially melted by the at least one laser beam, each of said at least one laser beam being directed onto the stream of gas mixture such that the laser beam does not impinge on the area of impingement on the surface,

29. The process as claimed in claim 28, wherein the coating material is partially melted only by the coupled-in energy of the at least one laser beam.

30. The process as claimed in claim 29, wherein at least a surface of the powder particles melts.

31. The process as claimed in claim 28, wherein the at least one laser beam is coupled in continuously by a continuous wave laser or discontinuously by a pulsed laser.

32. The process as claimed in claim 31, wherein the at least one laser beam is coupled in as focused or defocused by a laser optical unit.

33. The process as claimed in claim 28, wherein, during the coupling of the at least one laser beam into the stream of gas mixture, the alignment of each of the at least one laser beam is kept unchanged.

34. The process as claimed in claim 28, wherein, during the coupling of the at least one laser beam into the stream of gas mixture, the alignment of each of the at least one laser beam is changed.

35. The process as claimed in claim 28, wherein the stream of gas mixture is provided with a volumetric flow of the carrier gas in the range from 1-50 l/min

36. The process as claimed in claim 28, wherein the stream of gas mixture is provided with a volumetric flow of the carrier gas in the range from 1-20 l/min.

37. The process as claimed in claim 28, the stream of gas mixture is provided with a mass flow of the coating material in the range from 0.1 g/min-100 g/min.

38. The process as claimed in claim 28, wherein the stream of gas mixture is provided with a volumetric flow of the carrier gas in the range from 2 g/min-20 g/min.

39. The process as claimed in claim 28, wherein the carrier gas is an inert gas, nitrogen or ambient air.

40. The process as claimed in claim 28, wherein the coating material has a grain size distribution of 100 nm to 120 m.

41. The process as claimed in claim 28, wherein the feeding of the stream of gas mixture is performed using a feeding element with an outlet for the stream of gas mixture, the outlet being kept at a vertical distance from the area of impingement in the range from 1 mm-100 mm.

42. The process as claimed in claim 28, wherein the feeding of the stream of gas mixture is performed using a hollow needle with an inside diameter in the range from 0.1-10 mm.

43. The process as claimed in claim 28, wherein the feeding of the stream of gas mixture is performed using a diffuser, which widens the flow cross section of the stream of gas mixture.

44. The process as claimed in claim 28, wherein the surface with the area of impingement is a component part of a substrate,

45. The process as claimed in claim 28, wherein a plurality of layers of the coating material are deposited one on top of the other,

46. The process as claimed in claim 28, wherein the surface with the area of impingement has undercuts.

47. The process as claimed in claim 28, further comprising, before the feeding of the stream of gas mixture, at least partially providing the surface with a top layer with anti-adhesive properties with respect to the coating material that is subsequently fed with the stream of gas mixture.

48. The process as claimed in claim 28, wherein the surface or an article that has the surface includes at least in certain portions a sacrificial material, the sacrificial material having anti-adhesive properties with respect to the coating material that is fed with the stream of gas mixture.

49. The process as claimed in claim 48, wherein the sacrificial material comprises at least one acrylic group (CH.sub.2CHCOR), the proportion of the acrylic group preferably being at least 1 percent by weight of the sacrificial material.

50. A device for applying a coating material to a surface for carrying out the process as claimed in claim 1, the device comprising: a powder conveyor configured to provide a stream of gas mixture comprising a carrier gas and a coating material, a feeding element for feeding the stream of gas mixture to the surface, the feeding element being configured so that the stream of gas mixture impinges on the surface and the coating material applied on the surface forms an area of impingement on the surface, a laser producing a laser beam, the lase configured to couple the laser beam into the stream of gas mixture, the laser beam being aligned in relation to the stream of gas mixture such that the laser beam does not impinge on the area of impingement on the surface, a handling system configured to produce a relative movement between the feeding element and the surface to be coated, and means for interrupting the coupling of the laser beam into the stream of gas mixture for a time, by one of shutting off the laser beam with a shutter or deflecting the laser beam with a laser optical unit such that for a time the laser beam is not directed onto the stream of gas mixture.

51. The device as claimed in claim 50, wherein the handling system includes: a turntable,. which is rotatable about an axis of rotation and is configured to receive at least one object having the surface to be coated; and a linear system configured to pruduce a linear movement of the feeding element in the direction of an axis of displacement, wherein the axis of displacement is parallel to the axis of rotation.

52. The device as claimed in claim 51, wherein at least one of: the laser includes a laser optical unit set up for aligning the laser beam and the laser is arranged on a handling device configured to align the laser beam.

Description

[0040] The invention is explained in more detail below on the basis of the figures, in which:

[0041] FIG. 1A shows a first exemplary embodiment of a device for applying a powdered coating material to a surface of a substrate,

[0042] FIG. 1B shows a second exemplary embodiment of a device for applying a powdered coating material to a surface of a substrate,

[0043] FIG. 2 shows a device corresponding to FIG. 1A with a feeding element configured as a hollow needle,

[0044] FIGS. 3 A-E show a schematic representation to illustrate a process for applying a powdered coating material to a surface of a substrate that is partially provided with a top layer,

[0045] FIGS. 4 A-C show a schematic representation to illustrate a process for applying a powdered coating material to a surface with different material properties,

[0046] FIGS. 5 A-C show a schematic representation to illustrate a process for producing a three-dimensional article,

[0047] FIG. 6 shows a schematic representation to illustrate a process for the structured application of coating materials to the surface of a substrate,

[0048] FIG. 7 shows a preferred device for applying a powder coating material to a number of substrates and

[0049] FIG. 8 shows a representation to illustrate a surface of a substrate that has undercuts.

[0050] The device (1) schematically represented in Figure la for applying a powdered coating material (2) to a surface (3a) of a substrate (3) consists essentially of a powder conveyor (4) that is just partially represented, a feeding element (5) that is configured as a powder nozzle (5b) and also a laser (6) for producing a laser beam (7) parallel to the surface (3a) of the substrate (3).

[0051] The powder conveyor (4) comprises a powder pump (not represented), which introduces the powdered coating material (2) from a container into a stream of carrier gas. The stream of gas mixture (8) is fed to the powder nozzle (5b) via a feed line (9). The outlet (5a) of the powder nozzle (5b) is directed onto the surface (3a) of the substrate (3) and is at a vertical distance of approximately 50 mm. The powder nozzle (5b) is movable with the aid of a handling system (not represented) in and counter to the direction of the arrow (12) parallel to the surface (3a) of the substrate. The laser (6) is preferably mechanically coupled to the powder nozzle (5b), and therefore likewise moves in the direction of the arrow (12) with respect to the substrate (3), which in the exemplary embodiment as shown in FIG. 1 is kept fixed in place. The coupling-in area (10), in which the laser beam (7) is coupled into the stream of gas mixture (8), is located directly above the surface (3a) of the substrate (3).

[0052] It is ensured by the parallel beam guidance of the laser beam (7) that the laser beam (7) does not impinge on the area of impingement (11) of the stream of gas mixture (8) on the surface (3a). As a consequence, in the coupling-in area (10) the energy of the laser beam (7) is only transferred to the powdered coating material (2) in the stream of gas mixture (8). The powdered coating material (2) that has already been at least partially melted in the stream of gas mixture (8) by the effect of the laser beam (7) is applied under pressure to the surface (3a).

[0053] The device as shown in FIG. 1B) differs from the device shown in FIG. 1A) essentially in that the laser (6) has a laser optical unit (not represented), which widens the laser beam in the direction of the coupling-in area (10) into the stream of gas mixture (8). This has the effect that the coupling-in area (10) extends over a greater length of the stream of gas mixture (8) between the outlet (5a) of the powder nozzle (5b) and the surface (3a). As a result of the widening, a higher level of energy can be coupled into the powdered coating material (2) by corresponding raising of the laser power of the defocused laser beam (7), in order for example to be able to deposit higher-melting metallic coating materials.

[0054] The device (1) as shown in FIG. 2 differs from the device as shown in FIG. 1A) just with regard to the design of the feeding element (5). To avoid repetition, reference is therefore made to the statements made in relation to FIG. 1A) in their entirety. The feeding element (5) is designed as a hollow needle (5c), which has an inside diameter that is small in relation to the length, of less than 10 mm. Forming the feeding element (5) as a hollow needle (5c) has the effect of establishing a quasi laminar flow of the stream of gas mixture (8) between the outlet (5a) and the surface (3a) of the substrate (3).

[0055] The application of the powdered coating material (2) to the surface (3a) of a substrate (3) partially provided with a top layer (13) is explained in more detail on the basis of FIG. 3: the surface (3a) of the substrate (3) is provided at each periphery with a top layer (13) (compare FIG. 3b). Between the peripheral portions with the top layer (13), the surface (3a) of the substrate (3a) is exposed in a central area (14). The top layer (13) has anti-adhesive properties with respect to the powdered coating material (2). If therefore the powder nozzle (5b) is moved in the direction of the arrow (12) parallel to the surface (3a) of the substrate (3) that is partially provided with the top layer (13), as is indicated in FIG. 3C), the powdered coating material (2) does not adhere on the top layer (13) on account of the anti-adhesive properties. As can be seen from FIG. 3D), in the central area (14) however the powdered coating material (2) forms a firmly adhering layer (15) on the surface (3a) of the substrate (3). After ending the application of the coating material (2), the surface is cleaned. FIG. 3E) finally shows the cleaned substrate (3), selectively coated just in the central area (14).

[0056] FIG. 4 shows an inhomogeneous substrate (3) with portions (3b), which consist of an anti-adhesive material with respect to the powdered coating material (2), and a portion (3c) arranged inbetween, which consists of an adhesion-promoting material with respect to the powdered coating material (2). As a consequence of the adhesion-promoting or anti-adhesive properties of the portions (3c, 3b), on the surface (3a) of the substrate (3) no firmly adhering bond between the coating material (2) and the surface is created in the portions (3b). On the central portion (3c) however there forms a firmly adhering layer (15) of the coating material (2). After ending the application of the coating material (2), the surface of the portions (3b) is freed of the applied coating material (2). FIG. 4 C) finally shows the cleaned substrate (3), which is just selectively coated in portion (3c).

[0057] FIG. 5 schematically illustrates a process for applying different coating materials (2a, 2b), which are deposited one after the other in a number of layers one on top of the other. The device (1) for applying the coating material largely corresponds to the device as shown in FIG. 1A). However, the powder conveyor (4) (not represented) has two powder containers, from which the powder pump alternately introduces the first or second coating material (2a, 2b) into the stream of carrier gas. The stream of gas mixture (8) therefore optionally comprises the first or second coating material (2a, 2b).

[0058] FIG. 5A) shows how the surface (3a) of the substrate (3) is first coated with the first coating material (2a) in the area of impingement (11) by relative movement of the powder nozzle (5b) in the direction of the arrow (12). Subsequently, as represented in FIG. 5B), a second layer (17) with the second coating material (2b) is applied to the surface of the first layer (16) of the first coating material (2a). Finally, as shown in FIG. 5C), four third layers (18) with the first coating material (2a) are applied to the surface of the second layer (17) by repeatedly moving the powder nozzle (5b) back and forth in a smaller area of impingement (11b).

[0059] The first and second coating materials (2a, 2b), which are melted by the laser beam (7) during the application, enter into a firmly adhering bond with one another, so that the article (19) that can be seen in FIG. 5C) can be created with the aid of the process according to the invention.

[0060] Depending on the nature of the surface of the substrate (3), the first layer (16) bonds with the surface (3a) or does not enter into a firmly adhering bond with it. In the latter case, the surface (3a) just serves as a temporary support for the production of the article (19). If, however, a permanent adhesive attachment of the coating material (2) to the surface is desired, it is recommendable to roughen the surface in a way corresponding to FIG. 8, causing the formation of undercuts (20), in which the coating material (2) can become enmeshed, as can be seen from the enlargement A.

[0061] Usually, articles that are created by means of molding, extruding or compression-molding processes have smooth surfaces with low roughness and no undercuts. If adhesive attachment of the coating material to the surface of the article is desired, the mechanical interlocking of the at least partially melted coating material in the undercuts of the surface represents an essential adhering mechanism. It is therefore meaningful to fashion the surface in such a way that undercuts of an order of magnitude of 0.1 m-100 m occur repeatedly and distributed over the surface. For this purpose, a roughening of the surface, and simultaneous formation of micro undercuts, can be created in the areas of the surface with adhesion-promoting properties, for example by means of a laser.

[0062] Alternatively, for example in a first process step, an adhesion-promoting, ceramic coating with undercuts may be deposited on the smooth surface of the article. For this purpose, powdered ceramic coating material is incipiently melted and deposited on the surface by means of a plasma coating process. The choice of suitable powder particle sizes (1-50 m) and coating parameters allows undercuts to be selectively created on the surface, by the particles not melting completely but remaining intact in the core. The accumulation on the surface of partially round, irregular or undefined powder particles leads to an open-pore formation with numerous undercuts. Such ceramic, adhesion-promoting layers are preferably applied to the surface in thicknesses of 1-500 m. The coating material that is then applied to the ceramic, adhesion-promoting layer by the process according to the invention becomes mechanically enmeshed in the undercuts.

[0063] The application of the powdered coating material (2) that is structured in certain portions by a device as shown in FIG. 1A) is explained on the basis of FIG. 6: During the continuous feeding of the stream of gas mixture (8), the laser beam (7) is interrupted for a time, which takes place for example by switching the laser power on and off. While the laser (6) is switched on and the laser beam (7) is being coupled into the stream of gas mixture (8), the coating material (2) is deposited in a firmly adhering manner on the surface (3a) of the substrate (3).

[0064] In the phases of interruption of the laser (6), coating material (2) is still applied to the surface (3a). Since, however, no laser energy is being coupled into the coating material (2), this material is not melted, and therefore does not bond to the surface (3a) in a firmly adhering manner. Periodic switching on and off produces the sequence of firmly adhering layers (15) that can be seen from FIG. 6 after the removal of the not firmly adhering coating material (2).

[0065] A preferred device (1) for carrying out the process according to the invention is described below on the basis of FIG. 7. The device (1) has a turntable (24), which is rotatable about an axis of rotation (23). In order to set the turntable (24) in rotation about the axis of rotation (23), in the direction and counter to the direction of the arrow (25), the turntable (24) has a drive (26). Detachably fastened to the outer circumference of the turntable (24) are substrates (3) with an outwardly facing surface (3a).

[0066] The device (1) also has a linear system (27), for example a driven linear slide, which can move the feeding element (5) in the direction of a linear axis of displacement (28). The outlet (5a) of the feeding element (5) is directed onto the surface (3a) of one substrate (3) after the other, in order that the stream of gas mixture (8) can be fed to the substrate surface (3a). The feeding element (5) is arranged on the linear system (27) in such a way that the stream of gas mixture (8) impinges on the surface (3a) of each substrate (3) perpendicularly. The axis of displacement (28) runs parallel to the axis of rotation (23) of the turntable (24). Displacing the feeding element (5) in and/or counter to the axis of displacement (28) therefore allows the coating material (2) to be applied in the form of strips to the substrate (3) that is positioned in each case with respect to the outlet (5a) of the feeding element (5) with the aid of the turntable. If the coating cannot be applied to the substrate (3) with one trace, a number of vertical traces can be applied next to one another by the turntable (24) being turned slightly after the application of each trace.

[0067] The laser (6) may be arranged fixed in place, as represented in FIG. 7, or on a handling device. The laser optical unit is aligned in such a way that the laser beam (7) impinges on the stream of gas mixture (8) perpendicularly in the coupling-in area (10).

[0068] The device (22) is finally surrounded by an enclosure (29) to form a working space. The drive both of the turntable (24) and of the linear system (27) and also the laser (6) are program-controlled, in order to ensure a fully automatic coating of substrates (3).

[0069] A number of cases of how the process according to the invention is used are given below by way of example: [0070] 1. In the electronics industry, the process can be used for depositing structured conductor tracks on three-dimensional bodies, in particular of plastic and ceramic. In addition, the process is used for depositing structured conductor tracks on planar printed circuit boards. [0071] 2. In the semiconductor industry, the process can be used for depositing porous metal layers on wafers, for example for producing IGBT modules. In addition, with the process according to the invention, contacts between semiconductors and supporting bodies can be established as a substitute for bonding connections. [0072] 3. In particular in medical technology, the process can also be carried out in evacuated working spaces, in order for example to produce medically effective coatings for implants with the exclusion of the atmosphere. [0073] 4. In the area of photovoltaics, electrically conductive contact structures and/or semiconductor materials can be deposited on the solar cells by the process according to the invention. [0074] 5. In the area of display production, for example conductive structures can be deposited by the process according to the invention on the surface of glasses for producing displays. [0075] 6. In industrial reel-to-reel coating processes, for example film webs and sheets can be provided with porous metal layers, which are applied by means of a preferably widening stream of gas mixture.

TABLE-US-00001 No. Designation 1. Device 2. Coating material 2a. First coating material 2b. Second coating material 3 Substrate 3a. Surface 3b. Substrate portion 3c. Substrate portion 4. Powder conveyor 5. Feeding element 5a. Outlet 5b. Powder nozzle 5c. Hollow needle 6. Laser 7. Laser beam 8. Stream of gas mixture 9. Feed line 10. Coupling-in area 11/11b. Area of impingement 12. Arrow 13. Top layer 14. Central area 15. Firmly adhering layer 16. First layer 17. Second layer 18. Third layer 19. Article 20. Undercuts 21. 22. Device 23. Axis of rotation 24. Turntable 25. Arrow 26. Drive 27. Linear system 28. Axis of displacement 29. Enclosure