Device for coating and drying the front and back of a web, particularly one consisting of paper or cardboard

The invention relates to a coating / drying apparatus with a first application device for applying liquid or pasty application medium to a first side of a material web moving in the direction of movement, in particular of paper or cardboard, with a second application device for applying liquid or pasty application medium to one The second side of the material web opposite the first side, and a drying device.

Such coating / drying devices are well known in the art. Usually, in these devices, a layer of application medium is first applied to one side of the material web and then dried in a drying device. Only then is an application medium layer applied to the other side of the material web and dried. A disadvantage of these coating / drying devices is, on the one hand, that two drying devices must be provided, which is not only expensive in terms of purchase and maintenance of these drying devices, but also requires a great deal of space. On the other hand, the energy efficiency of one-sided drying, ie the drying effect per spent energy unit, leaves much to be desired.

A coating / drying apparatus according to the preamble of claim 1 is known from US-A-2 299 026.

DE-A-19 53 878 discloses a device for the production of a paper laminate in which a cellulose web is sprayed at least from one side by means of a syringe device with a binder dispersion and the pretreated side of the cellulose web is connected to a further web of water-resistant silk crease paper , Wherein the at least one syringe device is arranged in a housing.

US Pat. No. 4,577,585 discloses a spray applicator with a plurality of spray nozzles arranged in a common housing, by means of which a differently colored pattern can be applied to a wallpaper web in a vertical direction from above.

DE 43 18 273 A1 discloses a device for the color coating of profile bars which comprises at least two color spraying heads arranged in a common housing in order to coat a horizontally arranged profile bar with color from the top.

It is an object of the invention to provide a coating / drying apparatus of the type mentioned at the outset, which enables the coating and drying of both sides of the material web in a space-saving and energy-saving manner.

This object is achieved by a coating / drying apparatus having the features of claim 1.

In the coating / drying device, the second application device is a non-contact application device and the drying device is arranged downstream of the two application devices in the direction of travel of the material web. There is therefore no intermediate drying, ie there is no intermediate between the position of the first application device and the position of the second application device. Drying device. This saves on the one hand the installation space otherwise required for the second drying apparatus and, on the other hand, the costs required for the acquisition and maintenance of the second drying apparatus. Moreover, the heat provided by the drying apparatus can be absorbed not only by a wet application medium layer, but by two moist application medium layers. The higher heat absorption thereby improves the energy efficiency of the coating / drying apparatus according to the invention compared to prior art coating / drying apparatus.

The second application device is arranged downstream of the first application device in the direction of travel of the material web by a predetermined distance, the two application devices being arranged in essentially horizontally extending sections of the course of the material web in order to enable application of the application medium from above. This is particularly advantageous when using curtain application devices. Since this application "from above" is still possible, even in the case of deviations of up to 45 ° from an exactly horizontal course of the material web, the wording "substantially horizontally extending" is to be correspondingly extended.

An overlapping arrangement of the application devices, which utilizes the available structural height and thus saves the overall length, results in that the material web is deflected by essentially at least one web deflecting unit by substantially 180 ° between the essentially horizontally extending sections. It goes without saying that the wording "to be substantially 180 ° deflected" is to be broadly interpreted as described above and can include deflections of about 140 ° to about 210 °.

The mentioned non-contacting application device carries the application medium essentially without excess onto the material web ( "1: 1 order"). Therefore, there is no need to scrape excess medium and thus no physical contact with the material web. As a result, the contactlessly acting application device stresses the material web only to a small extent, namely only by means of the softening of the material web by the liquid contained in the application medium. For example, a spray application device or a curtain application device can be used as a non-contact application device.

According to the invention, the first application device is a non-contact application device, for example a curtain application device. The associated low stress on the material web is important in connection with the present invention in particular because the material web does not undergo any intermediate consolidation between the two application devices by moisture removal in an intermediate drying device.

In order to prevent influencing the surface properties of the application medium layer which has just been applied and thus still moist, by means of the web deflection units responsible for curved path courses, it is provided that the web deflection units are arranged on the uncoated second side of the material web between the first application device and the second application device. In the case of the use of so-called "airturns", ie, deflection units, in which the material web is guided without contact on a compressed air cushion ejected from these "airturns", the web deflection units can be arranged on the coated first side of the material web between the first application device and the second application device be.

Finally, it is also possible for a web reversing device to be arranged between the first application device and the second application device. The axes or shafts of the deflecting units of this path reversing device extend parallel to a web section of the material web entering the respective deflecting unit and at a predetermined angle to the transverse direction of this incoming web section. In this context, preferred "airtums" can also be used as web-deflecting units. These can, for example, be embodied as perforated tubes, the perforations for the impingement of compressed gas being used to form a compressed gas cushion.

Irrespective of the arrangement of the two application devices, however, it is advantageous if both application devices are accommodated in a common housing and this is not least to prevent contamination of the entire coating installation by application medium droplets or the like.

In a further development of the invention, it is also proposed that curved sections of the web path of the material web between the first application device and the drying device have a radius of curvature of at least 300 mm. Only when this minimum radius of curvature is observed is it ensured that the centrifugal forces acting on the still moist application layers in the region of the curved sections of the course of the web are so small that a centrifugal force of the application medium droplets is prevented. This is particularly true at web speeds of more than 1,000 m / min.

The coating / drying device according to the invention can advantageously have at least one non-contact device for stabilizing the running material web and / or preventing or reducing ripples, in particular transverse ripples, of the running material web. For example, advantageously at least one coil-effect nozzle arrangement can be provided. It is also expedient to use at least one nozzle arrangement for generating a counter-ripple, in particular longitudinal ripple, which counteracts a ripple, in particular a transverse ripple, which is to be avoided or reduced.

Furthermore, the coating / drying apparatus according to the invention can advantageously have at least one device for the disturbance and preferably for the elimination or reduction of an air boundary layer entrained by the running material web which should ideally be arranged shortly before or directly in front of a respective application device so that the application of the application medium can not be prevented The air boundary layer is disturbed, so that a string of high quality requirements is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail below with reference to the appended drawing in some embodiments. It shows:<dl id="dl0001"><dt>1 to 3</dt><dd>Schematical representations of arrangements and path sequences in embodiments of coating / drying devices according to the invention.</dd><dt>FIG</dt><dd>Shows a further example of a coating device according to the invention which is arranged downstream of a drying section in a paper machine.</dd><dt>FIG</dt><dd>Also shows an example of a coating / drying apparatus in a paper machine.</dd><dt>FIGS. 6 to 8</dt><dd>Are further schematic representations of arrangements and path sequences in embodiments of coating / drying devices according to the invention.</dd></dl>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a coating / drying apparatus according to the invention is generally designated 10. It comprises a first application device 14 for applying a first layer of application medium to a first side 12a of a material web 12 moving in the direction of travel L, a second application device 16 for applying a second layer of application medium to the side 12b of the material web 12 opposite the side 12a, And a drying device 18 which is arranged downstream of the two application devices 14 and 16 in the running direction L of the material web 12. According to the invention, the course of the web between the two application devices 14 and 16 is free of further drying devices. In other words, the material web 12 does not undergo intermediate drying between the application unit 14 and the application unit 16.

As indicated in FIG. 1, in the present exemplary embodiment, both application devices 14 and 16 are designed as curtain application devices, ie as application devices in which the application medium leaves a nozzle of the application device as a closed application medium curtain and, under the influence of external forces, In particular the gravity, through the free space to the material web 12. This non-contact type of application of the application medium onto the material web 12 ensures that the material web 12 is stressed only to a small extent. In particular, there is no risk of damage by physical interaction of the material web with elements of the application devices, such as, for example, doctor blades, roller blades or the like. In principle, however, the application devices 14, 16 could also be designed as spray application devices.

It should also be pointed out that the two application devices 14, 16 are arranged in essentially horizontally extending sections 12 'and 12 "of the course of the material web 12 and apply the application medium essentially from above onto the material web 12. To enable this arrangement, According to FIG. 1, deflection rollers 20 are provided which deflect the material web 12 between the two application devices 14 and 16. These deflection rollers 20 are both arranged on the still uncoated side 12b of the material web 12 in the exemplary embodiment according to FIG The two deflection rollers 20 have a relatively large diameter, so that the layer applied by the application device 14 to the material web 12 has only low centrifugal forces during the deflection of the material web 12 .

Between the applicator device 16 and the drying device 18, a non-contact deflecting device 22 is finally arranged. This deflecting device 22 can, for example, be formed by a so-called "airturn", which guides the material web 12 without contact on a compressed air cushion.

FIG. 2 shows a further embodiment of a coating / drying apparatus according to the invention, which essentially corresponds to the embodiment according to FIG. Therefore, analogous parts are provided with the same reference symbols in FIG. 1, but are increased by the number 100 in FIG. 2. Furthermore, the embodiment according to FIG. 2 is described in the following only in so far as it differs from the embodiment according to FIG , The description of which is hereby expressly incorporated herein by reference.

2 differs from the coating / drying apparatus 10 according to FIG. 1 only with regard to the formation of the deflecting units 120 which cover the material web 112 between the first curtain applicator 114 and the second curtain applicator 116. Namely, the deflecting units 120 according to FIG. 2 are arranged on the first coated side 112 a of the material web 112. They are therefore designed as non-contact deflection devices, for example so-called "airturns", as explained with reference to the embodiment according to FIG. 1 using the example of the deflection device 22. 2, a non-contact deflecting device 122 is provided between the application device 116 for spreading the second side 112b of the material web 112 and the drying device 118. In the embodiment shown in FIG.

FIG. 3 shows a further embodiment of a coating / drying apparatus according to the invention, which essentially corresponds to the embodiment according to FIG. Therefore, analogous parts are provided with the same reference numerals as in FIG. 1, but by the number 300, in FIG. 3. Furthermore, the embodiment according to FIG. 3 will be described in the following only in so far as it differs from the embodiment according to FIG , The description of which is hereby expressly incorporated herein by reference.

3 differs from the embodiments according to FIGS. 1 and 2 only by the manner of the deflection of the material web 312 between the first curtain applicator 314 and the second curtain applicator 316, namely according to FIG 3, a web reversing device 326 is used. The axes or shafts 328a of the deflecting units 328 of this path reversing device 326 run parallel to a web section of the material web 312 entering the respective deflecting unit 328 and at a predetermined angle to the transverse direction Q of this incoming web section.

These axles and shafts are designed as a tube and have a plurality of openings which, in conjunction with a compressed air source, lead to the formation of a web-bearing air cushion.

FIG. 4 shows a coating device 410 according to the invention downstream of a drying section 440 in a paper machine. The running material web 412 is guided from above into the coating device (the coater), with the web being deflected by a guide roller 442. The further course of the web guide under a first curtain applicator 414 and a second curtain applicator 416 substantially corresponds to the exemplary embodiment of FIG. 1. Two deflection rollers 420 are used. However, an element for removing or at least reducing an air boundary layer entrained by the running material web, for example a suction box 444 or 446, is preferably provided in front of the respective application device.

As indicated by double arrows, the applicator devices 414 and 416 are preferably height-adjustable. The material web runs between the respective application device 414 or 416 and a trough 448 or 450, respectively, which collects excess application medium.

After passing under the second application device, the material web 412 is guided via an airtum 422 to a non-contacting drying device (not shown). For example, a hot-air dryer can be provided. Alternatively, or in addition to the airturn 422, guidance by air nozzles 452 can also be provided. An exemplary course of the material web through the air nozzles is shown by dashed lines (412 '). The air nozzles can be arranged in such a way that a slight ripple is produced in the running material web with corrugation valleys and wave crests following one another in the running or longitudinal direction of the material web, which counteracts an undesired cross-ripple of the material web with transversely successive corrugation crests and corrugation valleys.

Regarding the deflection rollers 420, it is primarily intended to have these with a comparatively large diameter, for example greater than 600 mm, in order to prevent the application medium (the coating color) from being thrown off.

As can be clearly seen from the FIGURE, according to the invention, there is no intermediate drying of the material web between the application by the first application device 414 and by the second application device 416. An important aspect of the web guide realized according to FIG. 4 is that the respectively coated web side does not touch a web guide roller or the like until a sufficient drying has been completed.

In the arrangement according to FIG. 5, the coating / drying device is likewise arranged downstream of a paper machine of a drying section 540. The material web 512 is guided from below into the coating device, and the web is deflected against the machine direction by means of a plurality of guide rollers. The first application device 514 is preferably preceded by an element for the removal of an air boundary layer, for example a suction box 544. Similar to the arrangement according to FIG. 2, a deflection of the material web 512 takes place by means of two airtums 520 so that the material web is deflected again in the machine direction. The second application device 516 bears on the material web section that is running again in the machine travel direction. Preferably, an element 546 for discharging / avoiding the air boundary layer is also connected to the second application device 516.

The two airtums 520 act with their guide air on the (coated) web side coated by the first application device 514. The other material web sides, which have not yet been coated, may be assigned one or more support rollers in order to ensure a defined and stable material web guide. After passing through the material web under the second application device 516, which is likewise designed as a curtain application device, as is the first application device 514, the material web runs through air nozzles 552 serving for stabilization and is then deflected by means of a further airturn 522 into a contactless dryer 518, Which can be followed by a further drying device 560 acting in the manner of a touch, in the manner of a conventional drying section.

4 and 5 according to FIG. 5, the underside and then the upper side are first coated. It is also possible to provide for a reversal, namely to first coat the upper side and then the lower side. Both solutions according to FIGS. 4 and 5 as well as the solutions of the preceding exemplary embodiments are very compact and can therefore also be considered as conversion measures for existing systems. Conversely, conventional solutions (for example, bladders and film strips, instead of the curtain coating which is preferably to be provided) can be significantly reduced in investment costs, which is achieved, in particular, by dispensing with intermediate drying and the associated compactness.

The coating / drying device 610 according to FIG. 6 largely corresponds to the arrangement according to FIG. 4. As in the preceding exemplary embodiments, the same reference symbols are used for analogous or corresponding components, each increased by 100. The first curtain application 614 for the lower side of the material web, with a preceding element 644 for air layer removal (instead of a suction box, a kind of scraper blade is also contemplated), the deflection rollers again effecting the deflection in the machine travel direction 620, the second curtain applicator 616, also typically with an upstream element 646 for air-layer removal, and the further guidance of the material web 612 via an airtum 622 into the contactless dryer 618. In the area X identified by a dashed circle, a coanda- Arrangement or stabilizing nozzle arrangement, for example, can be provided corresponding to the arrangement 452 or 552.

A further suitable arrangement is shown in FIG. A suction box 744 or 746 or another element for air-boundary layer removal or reduction is preferably arranged upstream of the curtain application units 714 and 716, respectively. An anasturn arrangement 720 and an airtum 722, which are designed with segments, accomplish the non-contact path deflection toward the second curtain applicator 716 or toward the drying device (not shown).

An arrangement very similar to the arrangement of FIG. 5 is schematically shown in FIG. The nature and mode of operation of the components shown results directly from the correspondence of the reference symbols with the reference symbols used in FIG. The airtum 722 deflects the material web 712 obliquely upwards, not obliquely downwards as in FIG. 4.

Referring once again to the elements or elements 452, 552 and the region X as well as to the elements 444, 446, 544, 546, 644, 646, 744 and 746, it should be pointed out that for high-quality streak results the avoidance of ripples and attainment A high stability of the web guide, as well as the avoidance or at least the reduction of the interfering air boundary layers which are interfering with the order is of great importance in practice. For the web stabilization and avoiding disturbing ripples, the already mentioned coanda effect air nozzle arrangements are advantageously considered, which force the controlled web guidance and leveling of possible material web ripples due to the generation of negative pressure, as well as the aforementioned application nozzle arrangements having a plurality of nozzles arranged in succession on different web sides and defining the web of material Ripple in the direction of travel, which counteracts a harmful ripple in the transverse direction.