EP1264642B1 - Drying process for lacquer coated on a component and apparatus for performing the drying - Google Patents

Description

The invention relates to a drying method for applied to components in particular on vehicle bodies or parts thereof paint materials according to the preamble of claim 1 and an apparatus for performing the drying method according to the preamble of claim 5, as disclosed in the document US-A-6,231,932.

In conventional painting processes, in particular in vehicle construction, coating materials such as KTL, fillers, basecoats, clearcoats, etc. are used, which must be dried at reaction temperatures of about 80 ° (basecoat) up to about 200 ° (KTL). The resulting enormous energy costs as well as the problems of the online coating of plastic components have led to more recent developments of paint materials, which are cured at a lower temperature of about 90 °. However, longer drying times are usually associated with this, which can lead to problems with existing paint shops that are not designed for it.

In particular, the high temperatures in the conventional drying processes, which are carried out with conventional circulating air drying, as well as the long drying times in the new planned low-temperature painting process lead to develop methods for shortening paint drying processes. For shorter paint drying processes is generally It is possible to reduce energy costs and to switch to low-temperature painting processes in existing plants without having to adapt to longer drying times due to longer dryers. In addition to the conventional conventional and generally known circulating air drying, multi-stage drying processes in connection with different heat sources are already known:

In a known drying method (DE 198 57 940 C1) a combined UV / IR curing is utilized. For this purpose, the coating material to be cured is irradiated alternately with IR and UV radiation in several successive irradiation intervals. Special UV-curable coating materials are required for this process. Applications are preferred in refinishes. A circulating air drying is not provided here.

Furthermore, a two-stage drying method is known (DE 195 03 775 C1), in which infrared emitters are used in the first drying stage, which contour matched in their arrangement to the shape of the object to be dried or by means of adjusting devices can be brought up to a small distance. In the first drying stage, the heating and drying is carried out only to a certain degree of drying and then the object to be dried is conveyed in the longitudinal direction in a second dryer for the second drying stage, where then the further drying at a given object temperature with predominantly stationary infrared radiators until for complete drying of the paint. A circulating air drying for curing is not provided Only before the first drying stage an intermediate evaporation is optionally provided using hot air at an elevated temperature as well as a blowing ring between the first dryer cubicle and the second dryer cubicle to a temperature reduction when passing through the intermediate area prevent.

Next, a drying method for paint materials is known (DE 38 14 871 A1), in which only an infrared drying is used. In a first step, cleaning water is dried from the workpiece by means of an infrared drying with a radiation frequency in the near infrared (NIR). After a spray painting zone, the spray-painted workpiece is transferred to a kiln, on both sides of which several rows of NIR radiators are arranged. The wavelength ranges are here in the near infrared at 1.0 to 4.0 microns. For drying, there is a change from low temperature to high temperature ranges. A problem with such pure NIR drying is that hidden areas to which the NIR radiation does not directly impinge are only slightly heated and cured, so that this method can only be used for objects without hidden areas, in particular not for heavily structured vehicle bodies is.

Next, a generic two-stage drying method using an infrared drying and a circulating air drying is known (DE 43 36 856 A1). It should be important for the paint drying that in a heating time only infrared emitters are used and no circulating air drying takes place. Only in the subsequent after the heating time holding time drying by air circulation alone or in combination with infrared heaters or pure infrared heating can take place. For example, should be achieved here in the heating up a drying temperature of 150 ° in a maximum of 6 min, corresponding to a heating of about 20 ° / min. Such an extremely short heating time can lead to blistering and thus an unsatisfactory Lackierergebnis. At most, such short extreme heating times are manageable only in conjunction with the specified paint materials, so that this known method is limited and not universally applicable to all painting processes. Information about the wavelengths used in the infrared heating are not made here.

The object of the invention is to propose a drying process with which relatively short drying times can be achieved and which can be used universally to achieve optimally smooth paint surfaces. Another object of the invention is to provide an apparatus for carrying out such a drying process.

The object is achieved in terms of the drying process with the features of claim 1.

After an application of the paint material and a venting, preferably at room temperature, in a first process step, a circulating air drying is carried out to a predetermined degree of cure of the paint material.

In a second process step, an infrared drying is subsequently carried out as near-infrared drying (NIR drying), with a radiation frequency in the near infrared (NIR) by means of at least one near-infrared radiator (NIR radiator) for a further increase the degree of cure in the radiation-accessible areas of the component after the circulating air drying.

This method achieves a degree of curing of the paint material that is analogous to the conventional pure air circulation drying method in all radiation-sensitive areas. Thus, a corresponding early post-processing, for example, a polishing of these radiation-sensitive areas, advantageously in the same manner as in the conventional pure air circulation drying possible. In the case of vehicle bodies, these radiation-accessible regions in the irradiation region of the NIR emitters correspond to the visible outer skin surfaces, so that the paint material for post-processing has already advantageously cured optimally with smooth paint surfaces, especially in these viewing regions. In the areas that are not accessible to the radiation, you get Although only a lower degree of curing essentially by the circulating air drying in the first process step. However, this is not critical, since the non-radiopaque areas are not visible areas and thus u. U. less optimal paint surfaces and / or a subsequent reworking in favor of reduced drying times are tolerable and not appear on the finished vehicle in the field of vision.

Overall, the process can be significantly reduced with existing drying systems investment and operating costs. The combination of the circulating air drying with the NIR drying also partial hardening of the paint materials is guaranteed at the non-radiation areas, with the use of the upstream circulating air drying in conjunction with the post-drying effect by the NIR radiation universal use with different coating materials without the risk of blistering is given.

In a further process step according to claim 2, a subsequent curing at room temperature for complete curing of hidden areas to perform that were not reached in the second step of the NIR radiation.

According to claim 3, a wavelength range of 0.76 microns to 1.2 microns has been found to be particularly suitable for gentle NIR drying.

The drying process according to the invention can be used universally after each coating step, in particular after cathodic, filler, basecoat and clearcoat. Particularly suitable lacquer systems are produced on a polyuretane basis.

In a specific example, when applying a 140 ° clearcoat in the first step, a circulating air drying at 140 ° to perform. If in a conventional single recirculating air drying a drying temperature of 30 min would be required, this time can be shortened to 1/3, so that in the first process step a circulating air drying of 10 min with an object temperature of 140 ° plus / minus 10 ° perform is.

In the second process step, the NIR drying then follows, in which temperatures on the substrate surface should occur in a range of minus 10 ° to plus 40 ° with respect to the circulating air temperature of 140 °. The NIR drying is thus carried out at temperatures of 130 ° to 180 ° with a loading time of about 0.3 to 4.0 min.

With regard to the device, the object of the invention with the features of claim 5 is achieved.

According to claim 5, the circulating-air drying according to the first method step takes place in a first drying booth. The first drying booth is followed by a second drying booth in which the NIR drying takes place. The components to be dried, in particular vehicle bodies, are transported by suitable conveying means through the drying cabins. Depending on the circumstances, a continuous or discontinuous transport is possible. Particularly good results with an effective use of energy are achieved with the features according to claim 6, by the NIR emitters are mounted for the second step on controllable adjusting devices, such that they contour adapted to the components to be dried in particular on vehicle bodies zoom down to a small distance are.

Reference to a drawing, the invention is explained in detail.

Fig. 1

ein schematisches Temperatur-Zeitdiagramm eines erfindungsgemäßen Trocknungsverfahrens,

Fig. 2

eine schematische Prinzipdarstellung einer Trocknungsvorrichtung,

Fig. 3

eine schematische Frontansicht einer NIR-Trocknungskabine, und

Fig. 4

eine schematische Seitenansicht der NIR-Trocknungskabine der Fig. 3.

Show it:

Fig. 1

a schematic temperature-time diagram of a drying method according to the invention,

Fig. 2

a schematic diagram of a drying device,

Fig. 3

a schematic front view of an NIR drying booth, and

Fig. 4

a schematic side view of the NIR drying booth of Fig. 3rd

FIG. 1 schematically shows a temperature-time diagram of a drying method according to the invention for a 140 ° clear coat which can be applied to a vehicle body.

As can be seen from this diagram, in a first process step for a time t ₁ of, for example, about 10 minutes, a circulating air drying up to a predetermined degree of curing of the clearcoat with an object temperature of 140 ° C, as shown in the diagram with the solid thick black line.

In the second method step, an NIR drying is subsequently then carried out for a time t ₂ of, for example, 0.3 to 4 minutes, at which temperatures occur on the substrate surface that lie in a range of approximately 160 ° C., as shown in FIG 1 is again visible from the solid thick line.

As shown in dashed lines in FIG. 1, the circulating-air drying can be carried out as the first method step with an object temperature of +/- 10 ° C., based on the object temperature of 140 ° C. As is further shown by dashed lines in FIG. 1, the NIR drying can also be carried out in a range from -10.degree. C. to + 40.degree. C., based on the circulating air temperature of 140.degree.

In NIR drying, e.g. Wavelength ranges of 0.76 microns to 1.2 microns used.

With such a process procedure, in the first process step, a circulating air drying with a minimum load time of about one third of the time take place, which would be required in a conventional single circulating air drying without the second process step. This is shown schematically in the diagram of FIG. 1 by the arrow 1 and only by way of example.

FIG. 2 schematically shows a construction of a device 2 according to the invention for carrying out the drying process, which has a first drying booth as circulating air drying booth 3 and a second drying booth as NIR drying booth 4. The vehicle to be painted 5 can be promoted by the two drying cabins 3, 4, for example, with a conveyor not shown here.

FIG. 3 shows a schematic cross section through the NIR drying booth, in which NIR radiators 6 are arranged, which are thus mounted on controllable adjusting devices which are not shown here in detail, so that they are contour-adapted to the vehicle bodies to be dried except for one small distance are approached.

In the illustration of FIG. 4, finally, a side view of the illustration of FIG. 3 is shown.

Claims (6)

1. Method for drying paint materials applied to components, in particular vehicle bodies, the drying method being carried out in two stages after application of the paint material and ventilation and making use of drying by circulating air and by infrared radiation, characterised by the following process steps:

   a) the circulating-air drying is carried out first up to a predetermined partial degree of hardening of the paint material, the latter being not yet suitable for after-treatment, in particular polishing, but using a treatment duration (t₁) of at least one-third of the time which would be required for conventional drying by circulating air alone without process step (b), a circulating-air drying temperature analogous to that used in conventional drying by circulating air alone being used during the circulating-air drying, and

   b) the infrared drying is then carried out as near-infrared drying (NIR drying) using a radiation frequency in the near infrared (NIR) by means of at least one near-infrared radiator (NIR radiator) to achieve a further increase in the degree of hardening in the areas of the component accessible to radiation, using a treatment duration (t₂) from 0.3 to 4 min, the surface temperature being maintained within a range from minus 10° to plus 40° in relation to the circulating-air drying temperature.
2. Drying method according to claim 1, characterised by a further process step:

   c) whereby subsequent hardening at room temperature is carried out, in particular as moisture hardening for complete hardening of concealed areas which have not been reached by the NIR radiation in process step (b).
3. Drying method according to claim 1 or 2, characterised in that wavelengths in the range from 0.76 µm to 1.2 µm are used in the NIR drying.
4. Drying method according to any one of claims 1 to 3, characterised in that the drying method is utilised after each painting step and suitable, in particular polyurethane-based, painting systems are used.
5. Apparatus for carrying out a drying method according to any one of claims 1 to 4, comprising at least two drying cubicles (3, 4), the components to be dried, in particular vehicle bodies (5), being transportable independently through the drying cubicles (3, 4) by conveyor means, characterised in that only the circulating-air drying according to process step (a) is carried out in a first drying cubicle (3) by circulating-air drying means mounted therein, and only NIR radiators (6) are arranged in a second drying cubicle (4) adjoining the first drying cubicle (3), and the NIR drying according to process step (b) is carried out in said second drying cubicle (4).
6. Apparatus according to claim 5, characterised in that the NIR radiators (6) for process step (b) are mounted on controllable positioning devices in such a way that they can be moved to within a short distance of the components to be dried, in particular to vehicle bodies (5), in a manner adapted to the contours thereof.

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