DE29723289U1 - Application device for the wet area of a machine for producing a material web, in particular from paper or cardboard - Google Patents

Description

PATENT ATTORNEYS

European Patent Attorneys
European Trade Mark Attorneys ^- TC JVEJCKMANN "..no. F.'Ä. WEICKMANN DIPL-CHEM. B. HUBER DR-mo H. LISKA

DlPL-PHYS DR J. PRECHTEL DlPL.-CHEM. DR. B. BÖHM

DIPL.<HEM. DR. W. WEISS

DIPL-PHYS. DR. J. TIESMEYER DIPL PHYS DR M. HERZOG

PO BOX 860

81635 MUNICH

KOPERNIKUSSTRASSE 81679 MUNICH

TELEPHONE (089) 4 SS 63-0 TELEX S 22 FAX (089) 4 70 50 eMail weickmann@compuserve.com

Our sign:

17292G DE/HGff

Applicant:

Voith Sulzer Paper Technology Patent GmbH
St. Pöltener Street 43

D 89522 HEIDENHEIM

Application device

for the wet area of a machine

for producing a material web,

especially made of paper or cardboard

Application device

for the wet area of a machine

for producing a material web,

especially made of paper or cardboard

Description

&iacgr;&ogr; The invention relates to a device for the direct or indirect application of a liquid or pasty medium to a fully formed but still wet material web, in particular made of paper or cardboard.

For example, an application device is known from DE-OS 19 42 348, in which the application medium is applied to a material web held between two long sieves. Suction devices are also provided which remove moisture from the still wet material web. Due to the relatively loose guidance of the material web in a direction orthogonal to the plane of the material web inherent in the long sieves, the material web has a relatively loose structure in the area of the application device. The application medium applied to the material web therefore tends to be absorbed into the volume of the material web and does not remain in the area of the surface of the material web, as is actually desired. The application device known from DE-OS 19 42 348 therefore cannot achieve the coating quality required by modern machines for producing paper or cardboard.

US-PS 5,152,872 describes an application device arranged in the wet area, in which a material web supported on one side by a screen is guided around a roller. The screen is arranged between the material web and the roller surface, with a roller application device being provided on the side of the material web facing away from the screen. Due to the fact that the material web is only supported on one side by a screen

the material web has a relatively loose structure, at least in the area of the side facing away from the screen, i.e. precisely on the side of the material web on which the roller application device is also located. The application device known from US Pat. No. 5,152,872 therefore has the same problems with the coating quality as were discussed above with reference to DE-OS 19 42 348.

Another application device arranged in the wet area is known from US-PS 4,793,899. In this application device, a material web supported on one side is guided around a roller, whereby the screen in this case runs on the side of the material web facing away from the roller, so that the material web is in direct contact with the roller. An application device applies liquid or pasty medium to the surface of the roller, which is then pressed under pressure into the material web in the area of an application gap formed between the roller and another roller. Although the application device known from US-PS 4,793,899 does not have the problems with the coating quality resulting from a loose structure of the material web, the application medium is pressed so intensively into the material web in the application gap formed by the two rollers that the aim explicitly stated in US-PS 4,793,899 of keeping the application medium as close as possible to the surface of the material web is not achieved to the desired extent. In addition, the application device known from US-PS 4,793,899 has a large number of guide and press rollers for the material web as well as screens that guide it and is therefore structurally complex.

In contrast, it is the object of the invention to provide an application device for the wet area of a machine for producing a material web, in particular from paper or cardboard, which makes it possible to keep the application medium applied to the material web close to its surface, and this with a simple construction of the application device.

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This object is achieved according to the invention by a device for the direct or indirect application of a liquid or pasty medium to a fully formed but still wet material web, in particular made of paper or cardboard, which device comprises a roller, wherein the roller guides the material web along part of its circumference in a wrapping area, further comprises an application unit for applying the liquid or pasty medium to the surface of the material web or the surface of the roller, and comprises at least one screen belt carrying the material web, wherein the screen belt is arranged between the application unit and the material web and wherein the application medium comes into contact with the material web in the wrapping area of the roller.

The mode of operation of the application device according to the invention is based primarily on the combination of two features, namely, firstly, that the application medium comes into contact with the material web in the wrapping area of the roller, and secondly, that the application medium is always applied to the material web through a screen, regardless of whether the application medium is applied to the material web from the inside or the outside. The terms "inside" and "outside" refer to the curved course of the material web in the wrapping area, i.e. the "inside" is understood to mean the side of the material web facing the roller, while the "outside" is understood to mean the side of the material web facing away from the roller.

If the application unit is arranged on the outside of the material web, the screen belt arranged between the material web and the application unit leads to a compression of the fiber structure of the material web. This means that the applied application medium cannot penetrate into the volume of the material web and remains in the area of its outer surface. If, however, the application unit and thus also the screen belt are arranged on the inside of the material web, the material web is wrapped around the material web.

area is compacted due to the existing cohesion of its fiber structure, which in turn makes it more difficult for the application medium to be absorbed into the volume of the material web. At the same time, the screen belt acts as a pressure buffer for the hydrodynamic pressure that builds up at the entrance to the wrapping area. The pressure cannot therefore assume values that could cause the application medium to be absorbed through the compacted area into the volume of the material web. In addition, there is no counter roller on the outside of the material web. The material web can therefore avoid pressure peaks of the application medium in question and thus prevent it from being absorbed into the volume of the material web. In addition, the application device according to the invention has a simple structure, since its basic equipment only requires a wrapping roller, a screen belt and an application unit.

Whether the application unit is arranged on the outside of the material web or on the inside of the material web, it is advantageous to hold the material web between two screen belts. In the first case, the second screen belt provided on the inside of the material web prevents direct contact between the material web and the roller surface, which prevents damage to the material web due to unwanted adhesion to the roller surface, particularly at the end of the wrapping area. In the second case, the second screen belt provided on the outside of the material web contributes to its compaction.

In the case of application from the outside of the material web, the application unit can be in sliding contact with the screen belt according to one design variant. This design variant makes it easy to ensure that the application medium comes into contact with the material web through the screen belt. The application unit can have an application chamber from which the application medium emerges under pressure and comes into contact with the material web through the screen belt.

By selecting the appropriate value of the pressure in the application chamber, the application medium can be pressed into the material web to a desired depth.

According to an alternative design variant, the application unit can also be arranged at a distance from the screen belt and be formed, for example, by a free-jet nozzle application unit. The application medium only "gradually" passes through the screen belt and comes into contact with the material web.

In both variants, a removal device can be arranged downstream of the application unit to remove excess application medium from the material web. In particular in connection with the first variant discussed above, the removal device can be arranged directly downstream of the application unit. To ensure that the coating is as even as possible, a leveling device can additionally or alternatively be arranged downstream of the application unit to level the application medium and, if desired, to remove excess application medium from the material web. This leveling device can, for example, comprise a scraper arrangement or another known doctor unit.

Even in the case of application from the inside of the material web, i.e. application via the surface of the roller, the application device can be in sliding contact with the surface of the roller according to a first embodiment variant or can be arranged at a distance from the surface of the roller according to a second embodiment variant.

In each of the cases discussed above, it is advantageous if the roller has a negative pressure zone extending over at least part of the wrapping area. In the case of application from the outside of the material web, the pressure present in the still wet material web is

Moisture is sucked away towards the roller, which makes it easier to anchor the application medium in the area of the outer surface of the material web. In the case of application from the inside of the material web, excess application medium can be removed from the surface of the material web using the vacuum zone.

As already indicated above for one application, the applicator can have an application chamber from which the application medium emerges under pressure. For example, the pressure in the application chamber can be between 300 Pa and 10 kPa, preferably between 500 Pa and 5 kPa. The exposure time can be between 1 ms and 10 ms. In order to enable the application medium to be used as economically as possible, it is also proposed that the applicator is designed to dispense the application medium in a metered manner.

The radius of the roller can have a value of between 200 mm and 1200 mm. Finally, the solids content of the paper web can be between 5% and 50%, preferably between 8% and 17%, and the solids content of the application medium can be between 5% and 50%, preferably between 10% and 30%, wherein the application medium can contain, for example, water, mineral fillers such as kaolin, CaCO ₃ , TiO ₂ and the like, binders such as starch, latex or the like, retention agents and optical brighteners.

The invention will be explained in more detail below using the accompanying drawings and exemplary embodiments. It shows:

Fig. 1 and 2 Embodiments in which the application medium

is applied to the material web from the outside;

Fig. 3 to 5 Embodiments in which the application medium

is applied to the material web from the inside; and

Fig. 6 is a rough schematic diagram to explain the

Application principle of the embodiment according to Fig. 1.

In Figure 1, a first embodiment of the application device according to the invention is generally designated 10. The application device is arranged in the wet area of a machine for producing a material web 12, in particular made of paper or cardboard, which can be seen in Figure 1 from the fact that the still wet material web 12 is held between two screen belts 14 and 16, which ensure the cohesion of the fiber structure of the material web 12. The material web 12 is guided around a roller 18 along with the screen belts 14 and 16 and rests on the surface 18a of the material web in a wrap area U. The roller A is driven to rotate about its axis A in the direction of the arrow P, so that the material web 12 engages the surface 18a of the roller 18 in an essentially slip-free manner during its movement in the running direction L.

On the outside of the material web 12, i.e. on the side of the material web 12 facing away from the roller 18, an application unit 20 is arranged, the structure and function of which will be explained in more detail below with reference to Figure 6.

In Figure 6, the material web 12 taken up by two screen belts 14 and 16 and the application unit 20 are shown. In the roughly schematic sectional view of Figure 6, the application unit 20 comprises an upstream boundary wall 20a and a downstream boundary wall 20b, which are in sliding contact with the screen belt 14. The two boundary walls 20a and 20b as well as lateral boundary walls (not shown) enclose an application area that is open towards the screen belt 14.

chamber 22, into which application medium 24 is supplied from the outside (arrow M). The distance d between the application chamber walls 20a and 20b in the running direction L of the material web 12 is selected such that, at the usual running speeds of the material web 12, the material web 12 has a dwell time in the area of the application unit 20 of approximately 1 ms to 10 ms. In addition, the application medium 24 in the application chamber 22 is under a pressure &rgr; of between 300 Pa and 10 kPa, preferably between 500 Pa and 5 kPa, whereby the pressure value is selected such that the application medium 24 during the residence time of the material web 12 in the area of the application device 20 is, on the one hand, pressed sufficiently through the screen belt 14 into a region 12a of the material belt 12 near the surface and anchored there in its fiber structure, but on the other hand does not migrate into the volume 12b of the material web 12.

As shown in Figure 1, in the direction of travel L immediately following

A suction device 26 is provided on the application unit 20, by means of

whose application medium that has not bonded sufficiently with the material web 12 can be removed from it again. The suctioned-off quantity S of application medium can be fed back to the application unit 20 after filtering out any suctioned-off fiber material, whereby the dilution of the application medium by the moisture also removed from the material web can be compensated for if desired by feeding in application medium with a correspondingly high solids content. The boundary walls of the suction device 26 are also preferably in sliding contact with the sieve belt 14, whereby the required sealing effect towards the environment can be ensured.

The roller 18 can be equipped with a vacuum zone 28 at least over part of the wrapping area U. Such rollers with a vacuum zone are known in the art, so that at this point there is no need to describe their structure in detail. The vacuum zone 28 is mainly used to dehumidify the material web.

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12, which of course means that the moisture present in the material web 12 is sucked away from the surface area 12a and through the screen belt 16. Since the surface area 12a becomes drier as a result, the application medium 24 can penetrate it more easily and anchor itself there in the fiber structure of the material web 12.

Figure 2 shows a further embodiment of an application device according to the invention, which essentially corresponds to that according to Figure 1. Analogous parts are therefore provided with the same reference numerals in Figure 2 as in Figure 1, but increased by the number 100. The application device 110 according to Figure 2 will only be described below insofar as it differs from the application device 10 according to Figure 1, to whose description reference is otherwise made hereby.

The application device 110 according to Figure 2 differs from that according to Figure 1 only in that on the side of the material web 112 accommodated between the screen belts 114 and 116 facing away from the roller 118, a free-jet nozzle application device 120 is arranged, which is arranged at a distance from the material web 112 or the screen belt 114 and applies the application medium 124 in a pre-dosed manner to the material web 112 or the screen 114. A leveling device 130 is arranged downstream of the application device 120, which in the embodiment according to Figure 2 comprises a scraper arrangement 132, but in principle can also be formed by any other known doctor blade or leveling device. The leveling device 130 smoothes the applied medium 124 and removes any excess medium 124 that has been applied in order to add it again to the feed stream M to the nozzle applicator 120 after an intermediate cleaning step. According to the embodiment according to Figure 1, the roller 118 also has a vacuum zone 128.

Figure 3 shows a further embodiment of an application device according to the invention, which is essentially the same as that shown in Figure 1

Analogous parts are therefore provided with the same reference numerals in Figure 3 as in Figure 1, but increased by the number 200. The application device 210 according to Figure 3 will only be described below insofar as it differs from the application device 10 according to Figure 1, to whose description reference is otherwise made hereby.

The application device 210 according to Figure 3 differs from the embodiment according to Figure 1 in particular in that the application unit 220 is arranged on the side of the material web 212 taken up by the screen belts 214 and 216 facing the roller 218. The application unit 220 is basically constructed in the same way as was explained for the application unit 20 with reference to Figure 6. However, the boundary walls of the application unit 220 are in sliding contact with the surface 218a of the roller 218, so that a layer of application medium 224 is applied to this surface 218a. This application layer is conveyed as a result of the rotation of the roller 218 about the axis A in the direction of the arrow P to the wrapping area U, in which the application medium 224 is brought into contact with the material web 212. In particular, when entering the wrapping area U, the application medium 224 is pressed into the material web 212 as a result of the hydrodynamic pressure developing between the roller surface 218a and the material web 212, although the interposition of the screen belt 216 ensures that the pressure does not assume such high values that the application medium 224 is pressed into the volume 212b of the material web 212, but remains on the surface 212a of the material web 212. Furthermore, in the embodiment according to Figure 3, no counter roller is provided on the side of the material web 212 facing away from the roller 218, so that the material web 212 can also avoid the hydrodynamic pressure and thus prevent the application medium 224 from penetrating into the volume of the material web 212.

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In the embodiment according to Figure 3, the vacuum zone 228 serves primarily to suck out excess application medium 224 applied to the material web 212 and, after intermediate cleaning, to feed it to the feed stream M to the application unit 220. In Figure 3, a cleaning device 234 is also provided for cleaning the surface 218a of the roller 218. The cleaning device 234 comprises a dispensing device 236 for applying a cleaning medium 238 to the roller surface 218a and a scraper blade 240 for removing contaminants from the surface 218a.

Figure 4 shows a further embodiment of an application device according to the invention, which essentially corresponds to that according to Figure 3. Analogous parts are therefore provided with the same reference numerals in Figure 4 as in Figure 3, but increased by the number 100, i.e. increased by the number 300 compared to Figure 1. The application device 310 according to Figure 4 will only be described below insofar as it differs from the application device 210 according to Figure 3, to whose description reference is otherwise made hereby.

The application device 310 according to Figure 4 differs from the application device 210 according to Figure 3 only in that instead of the application device 220, a free-jet nozzle application device 320 is provided, which applies the application medium 324 in a metered manner to the surface 318a of the roller 318, which in turn, as a result of the rotation about the axis A in the direction of the arrow P, conveys the application medium to the material web 312 received between the screen belts 314 and 316. Otherwise, the embodiment according to Figure 4, including the provision of a vacuum zone 328 and a cleaning device 334, corresponds to the embodiment according to Figure 3.

Figure 5 shows a further embodiment of an application device according to the invention, which is essentially the same as that shown in Figure 3

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Analogous parts are therefore provided with the same reference numerals in Figure 5 as in Figure 3, but increased by the number 200, i.e. compared to Figure 1 increased by the number 400. The application device 410 according to Figure 5 will only be described below insofar as it differs from the application device 210 according to Figure 3, to whose description reference is otherwise made hereby.

The application device 410 according to Figure 5 differs from the application device 210 according to Figure 3 only in that the material web 412 is only supported by a screen belt 416 on the side facing the application roller 418. Furthermore, the roller 418 in the embodiment according to Figure 5 does not have a zone corresponding to the vacuum zone 228. The roller 418 can therefore be, for example, a simple deflection roller for the material web 412. With regard to the application of the application medium 424 by means of the application unit 420 to the roller surface 418a and the conveyance of the application medium 424 to the material web 412, the embodiment according to Figure 5 corresponds to that according to Figure 3. Finally, a cleaning device 434 is also provided.

Although only embodiments for applying a liquid or pasty medium on one side have been described above, it is understood that the application device according to the invention can also be designed for applying on both sides. Any combination of one of the "outer" application arrangements according to Figures 1 and 2 with one of the "inner" application arrangements according to Figures 3 and 4 is possible.

It should also be added that the solids content of the material web 12 in the area of the application unit 20 can be between 5% and 50%, preferably between 8% and 17%, while the solids content of the application medium 24 can be between 5% and 50%, preferably between 10% and 30%. The solids content of the material web is defined as the percentage mass fraction of solid substances, for example

Fibers, fillers and the like, based on the total mass of the material web consisting of fibers, fillers, water and the like. Furthermore, the solids content of the application medium is understood to mean the percentage mass fraction of solid substances, for example mineral pigments, binders, auxiliaries and the like, based on the total mass of the application medium additionally containing liquid components, mainly water. The application medium can be composed, for example, of water, mineral fillers such as kaolin, CaCO ₃ , TiO ₂ and the like, binders such as starch, latex or the like, retention agents and optical brighteners.

It should also be added that the increase in mass due to the application of the liquid or pasty medium per side is preferably between about 1 g/m ² and 10 g/m ² .

The application device according to the invention can be used, for example, in a twin-wire former and, due to its design, can replace a film press, which increases the effectiveness of the machine for producing the material web.

It should be pointed out again that the material web is compressed in the wrapping area so that the application medium is evenly distributed over its surface instead of completely saturating it, i.e. absorbing into the volume of the material web. Overall, the application device according to the invention can therefore achieve a uniform, smooth line with a low application weight.

Claims (20)

- 14- Claims 1. Device (10; 110; 210; 310; 410) for the direct or indirect application of a liquid or pasty medium (24; 124; 224; 324; 424) to a fully formed but still wet material web (12; 112; 212; 312; 412), in particular made of paper or cardboard, comprising: a roller (18; 118; 218; 318; 418) which guides the material web (12; 112; 212; 312; 412) along a part of its circumference in a wrapping area (U), an application unit (20; 120; 220; 320; 420) for applying the liquid or pasty medium (24; 124; 224; 324; 424) to the surface of the material web (12; 112) or the surface (218a; 318a; 418a) of the roller (218; 318; 418), and at least one screen belt (14; 114; 216; 316; 416) carrying the material web (12; 112; 212; 312; 412) which is arranged between the application unit (20; 120; 220; 320; 420) and the material web (12; 112; 212; 312; 412), wherein the application medium (24; 124; 224; 324; 424) comes into contact with the material web (12; 112; 212; 312; 412) in the wrapping area (U) of the roller (18; 118; 218; 318; 418). 2. Application device according to claim 1, characterized in that the application unit (20; 120) is arranged on the side of the material web (12; 112) facing away from the roller (18; 118). 3. Application device according to claim 1 or 2, characterized in that the application unit (20) is in sliding contact with the screen belt (14). - 15 - 4. Application device according to claim 1 or 2, characterized in that the application unit (120) is arranged at a distance from the screen belt (114). 5. Application device according to one of claims 1 to 4, characterized in that a removal device (26) is arranged downstream of the application unit (20), preferably immediately downstream, for removing, preferably sucking off, excess application medium (24) from the material web (12). 6. Application device according to one of claims 1 to 5,
characterized in that a leveling device (130) is arranged downstream of the application unit (120) for leveling the application medium (124) and, if desired, for removing excess application medium (124) from the material web (112). 7. Application device according to claim 6, characterized in that the leveling device comprises a scraper arrangement (132). 8. Application device according to claim 1, characterized in that the application unit (220; 320; 420) applies the application medium (224; 324; 424) to the surface (218a; 318a; 418a) of the roller (218; 318; 418) guiding the material web (212; 312; 412). 9. Application device according to claim 8, characterized in that the application unit (220; 420) is in sliding contact with the surface (218a; 418a) of the roller (218; 418). 10. Application device according to claim 8, characterized in that the application unit (320) is arranged at a distance from the surface (318a) of the roller (318). 11. Application device according to one of claims 1 to 10, characterized in that the roller (18; 118; 218; 318) has a negative pressure zone (28; 128; 228; 328) at least over part of the wrapping region (U). 12. Application device according to one of claims 1 to 11, characterized in that the application unit (20) has an application chamber (22) from which the application medium (24) emerges under pressure (p). 13. Application device according to claim 12, characterized in that a pressure (p) of between 300 Pa and 10 kPa, preferably between 500 Pa and 5 kPa, prevails in the application chamber (22). 14. Application device according to claim 12 or 13, characterized in that the exposure time of the application medium (24) emerging from the application chamber (22) is between 1 ms and 10 ms. 15. Application device according to one of claims 1 to 14, characterized in that the application unit (20; 120; 220; 320; 420) is designed for the metered dispensing of the application medium (24; 124; 224; 324; 424). 16. Application device according to one of claims 1 to 15, characterized in that the application unit is a free-jet nozzle application unit (120; 320). 17. Application device according to one of claims 1 to 16, characterized in that the material web (12) is received between two sieve belts (14, 16). 18. Application device according to one of claims 1 to 17, characterized in that the radius (r) of the roller (18) has a value of between 200 mm and 1200 mm. 19. Application device according to one of claims 1 to 18, characterized in that the solids content of the material web (12) is between 5% and 50%, preferably between 8% and 17%. 20. Application device according to one of claims 1 to 19, characterized in that the solids content of the application medium (24) is between 5% and 50%, preferably between 10% and 30%. 17292GDE-anm/06.05.98 15:02