Method and device for coating workpieces

Abstract

The invention relates to a method for coating workpieces, which preferably consist at least sectionally of wood, wood-based materials, plastics material or the like, with a coating material, wherein the method includes the steps of: providing a functional layer, which can be rendered adhesive by energy input, supplying a coating material to the workpiece to be coated, at least partially activating the functional layer by treating the functional layer with a heated gas, wherein the heated gas is emitted onto the functional layer via at least one outlet opening and is at a positive pressure of at least 1.5 bar in a region of the at least one outlet opening, and joining the coating material to the workpiece by means of the activated functional layer.

Claims

1. A method for coating a workpiece made at least sectionally of wood, wood-based materials, or plastics, with a coating material, wherein the method comprises the steps: providing a functional layer which can be made adhesive by energy input, supplying the coating material from a thermally insulated supply device to the workpiece to be coated, at least partially activating the functional layer by treating the functional layer with a heated air, wherein the heated air is a fluid consisting of air and is emitted to the functional layer via at least one outlet opening and, in a region of the at least one outlet opening, the heated air has a positive pressure of at least 3 bar, and joining of the coating material to the workpiece by use of the activated functional layer, wherein the functional layer prior to activation is an integral part of the coating material, and wherein the functional layer and the coating material are coextruded.

2. The method according to claim 1, characterised in that in the region of the at least one outlet opening, the air has a temperature of at least 300 C.

3. The method according to claim 1, characterised in that the at least one outlet opening has a distance of a maximum of 10 mm from the functional layer.

4. The method according to claim 1, characterised in that plural outlet openings are provided, wherein the air has a different temperature in a region of at least two of the plural outlet openings, which temperature rises in a direction of a relative movement between the plural outlet openings and the functional layer to be activated.

5. The method according to claim 1, characterised in that the functional layer comprises an element for increasing thermal conductivity through the functional layer selected from the group consisting of polyolefins and metal particles.

6. The method according to claim 1, characterised in that the functional layer is substantially free from absorbers for laser light or other radiation sources.

7. The method according to claim 1, characterised in that the air supplied to the functional layer is partly recovered and can be used at least indirectly via a heat exchanger for heating the supplied air flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows diagrammatically a top view of an embodiment of the device according to the invention;

(2) FIG. 2 shows diagrammatically a detail from FIG. 1;

(3) FIG. 3 shows diagrammatically a further detail from FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) Preferred embodiments of the invention are described below in detail with reference to the accompanying drawings.

(5) A device 10 for coating workpieces 2 according to a preferred embodiment of the present invention is depicted diagrammatically in top view in FIG. 1. Although the device 10 according to the invention may be used for coating widely varying workpieces, it is preferably used for coating workpieces which consist at least in sections of wood, wood-based materials, plastics or the like, as are widely used in the kitchen, furniture and construction element industries. Any surfaces such as narrow or broad surfaces can be coated.

(6) The coating material 4 may also be selected from widely varying materials, preferably a coating material provided with a functional layer 4 being used. The functional layer 4 may also be an integral part of the coating material 4, for example in the sense of a coextruded or fully monolithic coating material. Alternatively or additionally, it is also possible that the functional layer 4 is already provided on the surface of the workpiece to be coated and/or is supplied separately to the area between the coating material 4 and the surface of the workpiece 2 to be coated.

(7) The functional layer 4 in the present embodiment deploys its adhesive properties by the input of energy (such as for example heating) so that the coating material can be joined to the workpiece. The joining effect may be based fully or partly on other mechanisms. Furthermore in the present embodiment, the functional layer may comprise means for increasing the thermal conductivity, such as for example low-melt polyolefins and/or metal particles. Furthermore it is particularly preferred if the functional layer 4 is substantially free from absorbers for laser light or other radiation sources.

(8) Furthermore the device 10 comprises a contact pressure device 14 for pressing the coating material 4 onto a surface of the workpiece 2, for example in the form of one or more contact pressure rollers. In the present embodiment, the supply device 12 for supplying the coating material 4 is thermally insulated at least in sections.

(9) As shown in FIG. 1, the device 10 furthermore comprises a transport device 16 for generating a relative movement between the contact pressure device 14 and the respective workpiece 2, wherein the transport device 16 in the embodiment shown in FIG. 1 being configured as a continuous passage transport device (for example in the form of a conveyor chain). It must, however, be noted that the device according to the invention may also be configured as a stationary machine, in which the workpieces remain substantially stationary during the coating process and the transport device 16 serves for relative movement of the contact pressure device 14 and other components relevant for the coating process. Combinations of the two concepts are also possible. The decisive factor is the possibility of a relative movement between the contact pressure device 14 (or further components) and the respective workpiece 2, where applicable in several spatial directions or about one or more rotational axes. For this, various devices may be used such as conveyor belts, portals, but also robots and many others.

(10) Immediately upstream of the contact pressure device 14, in the region between the coating material 4 and the surface of the workpiece 2 to be coated, an activation unit 20 is provided which in the present embodiment has plural outlet openings 20 for the supply of a heated pressurised gas 6 (or gas mixture such as air) to the respective functional layer 4. Depending on the position of the respective functional layer 4, either on the coating material 4 or on the workpiece 2, the outlet openings 20 are oriented to the functional layer 4 accordingly. The outlet openings 20 have a distance from the respective functional layer 4 of maximum 10 mm, preferably maximum 4 mm, for example around 2 mm. It is, however, also possible that the activation unit 20, as indicated in FIG. 1, has corresponding outlet openings 20 in several directions, the respective outlet openings each being able to be switched on or off as required.

(11) The outlet openings 20 of the activation unit 20 are connected to a pressurised gas source 22. The pressurised gas source 22 provides heated pressurised gas 6 to the respective outlet openings 20 such that a positive pressure is present in the region of at least one outlet opening 20. Advantageous values for the positive pressure present in the region of at least one (preferably all) outlet openings 20 are at least 1.5 bar, particularly preferably 3 bar.

(12) One possible configuration of the activation unit 20 is depicted diagrammatically in side view in FIG. 2. FIG. 2 shows the side face of the activation unit 20 which is turned towards the functional layer 4 to be activated.

(13) As shown in FIG. 2, in the present embodiment the activation unit 20 has plural outlet openings 20, where the gas may have different temperatures in the region of at least two outlet openings 20. Thus, for example, it is preferred that the temperature of the emerging pressurised gas rises in the direction of a relative movement between the outlet openings 20 and the functional layer 4 to be activated, i.e. in the present case in the passage direction (from left to right in FIG. 2). Irrespective of this, at least individual nozzles may have means for adaptation to the geometry of the functional layer to be activated. Furthermore, irrespective of the above embodiments, widely varying nozzle geometries may be used such as round, polygonal, elliptical etc.

(14) Furthermore, in the region of one or plural outlet openings 20, means may be provided for forming a turbulent flow on emergence of the heated pressurised gas 6. Although not shown in FIG. 2, this may be achieved, for example, in that the respective outlet opening 20 is configured as a nozzle with an at least partially variable cross-section in the flow direction.

(15) Furthermore, although also not shown in FIG. 2, in the region of the outlet opening(s) 20 a material with low thermal conductivity and/or low heat storage capacity may be provided.

(16) A preferred exemplary embodiment of the pressurised gas source 22 is shown diagrammatically in FIG. 3. In the present embodiment, the pressurised gas source 22 has a heat exchanger section 24 which is configured to heat the supplied pressurised gas to a temperature of at least 450 C., preferably at least 600 C. The system as a whole is designed such that in the region of the at least one outlet opening 20, the gas has a temperature of at least 300 C., preferably at least 350 C.

(17) The heat exchanger section 24 may, for example, have at least one heat exchanger element which is provided with voids, is in particular porous and/or bulk-porous, and/or is provided with continuous openings, and which is connected to the heat source shown in FIG. 3. In the present embodiment, the heat exchanger element may at least in sections consist of a material which is selected from stainless sinter material, porous ceramics, metal foam, in particular aluminium foam, and combinations thereof. Evidently other suitable materials may also be used, in particular if they have a high thermal conductivity and/or high heat storage capacity.

(18) In the present embodiment, the heat source 28 comprises heating elements, not shown in more detail, which may be selected, for example, from heating cartridges, ceramic heating elements, high current heaters, lasers, infrared sources, ultrasound sources, magnetic field sources, microwave sources, plasma sources and gas-treatment sources.

(19) Furthermore, the pressurised gas source 22 in the present embodiment comprises a pressurised gas generating unit 26, for example in the form of a compressor. This may draw in gas to be compressed from the environment or from a gas supply, and transfer it to the heat exchanger section 24. Alternatively or additionally, the heat exchanger section 24 may also be supplied by an external, where applicable central, pressurised gas source, as shown in FIG. 3.

(20) As is evident from FIG. 3, the device 10 according to the invention may furthermore comprise a second pressurised gas source which is configured to feed-in pressurised gas upstream of the at least one outlet opening (far right in FIG. 3), in order to increase the pressure of the gas emerging at the at least one outlet opening.

(21) As most clearly visible on FIG. 1, the device 10 according to the invention furthermore comprises a discharge device 32, such as for example a capture hopper. In this way the gas supplied to the functional layer 4 may at least partially be discharged and preferably also recovered. To this end, as shown in FIG. 1, a heat exchanger 30 may be provided downstream of the discharge device 32, by means of which the waste heat from the gas supplied to the functional layer 4 may be captured and, for example, returned to the pressurised gas source 22 as thermal energy.

(22) The operation of the device 10 according to the invention is performed, for example, as follows. A workpiece 2 to be coated is transported by means of the transport device 16 in a transport direction (from left to right in FIG. 1). In synchrony with this, a coating material 4 is supplied by means of the supply device. The functional layer provided on the coating material and/or workpiece (or separately) is activated by means of the heated pressurised gas 6 emerging from the outlet openings 20, immediately before the coating material is pressed by means of the contact pressure device 14 onto the surface of the workpiece 2 to be coated. Here the coating material 4 is joined to the workpiece 2 by means of the activated functional layer 4.