EP0706592B1 - Process and device for producing paper webs coated on both sides - Google Patents

Abstract

PCT No. PCT/EP95/01627 Sec. 371 Date Mar. 21, 1996 Sec. 102(e) Date Mar. 21, 1996 PCT Filed Apr. 28, 1995 PCT Pub. No. WO95/30049 PCT Pub. Date Nov. 9, 1995Disclosed are a process of and an apparatus for producing paper webs coated on both sides, in particular so-called LWC-papers, in a paper making machine. Firstly, one side of the paper web (1) is coated in a first coating station (8) and then dried. Subsequently, the other side of the paper web (1) is coated in a second coating station (25) and then dried. Each coating station (8, 25) includes an application role (10), an opposing roll (11) and an application unit (13) arranged on the application roll for indirectly coating the paper web. The metering of the coating mass on the application roll (10) takes place by means of a smooth roll doctor. The coated paper web (1) is calendered by means of an on-line calendering unit (60).

Description

The invention relates to a method for manufacturing on both sides coated paper webs, in particular so-called LWC papers, within a paper making machine according to the preamble of claim 1. Die The invention also relates to a device for performing of such a method, according to the preamble of claim 15.

A method with the in the preamble of claim 1 specified features is known from DE-A-43 02 437 A1. A freshly made in a paper making machine Paper web coming out of a spout in a Press section is dewatered, i.e. is still raw and moist, is first in a dryer section Papermaking machine dried itself. According to FIG. 1 this publication is the one in the dryer section of the Paper machine dried paper web then first one downstream smoothing system supplied, which is a so-called soft nip calender with two double rolls. The smoothing in the smoothing unit takes place before you Coating the paper web instead. Coming from the calender, the paper web is then a first coating unit fed. In it one side of the paper web becomes indirect by means of a first application roller, which with a first Counter roll forms a first application gap, with a Coated coating. This is done in that on the Coat the applicator roller by means of a nozzle applicator Spreading film is formed, which the application roller then transfers to the paper web. The first coating of the Ergo paper web is only found after the previously mentioned soft nip calender instead of. The coating unit has a metering element a squeegee with a grooved outer surface. Then the Paper web dried and a second coating unit fed, wherein the other side of the paper is also indirect is coated. After another drying process the finished, double-sided coated paper web is rolled up.

A similar procedure is described in the after Priority date of the present invention published EP-A-0 596 365 A1.

There are some problems in the already cited DE-A-43 02 437 A1 portrayed that when manufacturing waste paper and Relatively thin paper webs to be coated on both sides occur. The same problems lie here present invention. The known method solves however only a part of the problems described. In particular with the known method it is not yet possible to to produce paper web coated on both sides, the upmarket Requirements are sufficient, especially with regard to uniform and as smooth as possible and with regard to high gloss.

An application device is known from EP-A-0 454 643 A1 for indirect two-sided or direct one-sided Apply a coating slip to a running paper web. For indirect two-sided application, this has Device two opposing application rollers, which form a nip between them through which the paper web to be coated runs through. Everyone Applicator roller is assigned to a chamber applicator that First spread on the rotating surface of the applies the respective application roller. Then the Coating slip in the nip of the respective Transfer the outer surface to the paper web. For direct one-sided application, this device has a single Roller over which the paper web to be coated runs, and a chamber applicator assigned to this roller and the paper web, with which the coating slip directly onto the Paper web is applied. The chamber commissioned works of these have two device variants on the in Direction of rotation of the (application) roller downstream side a "smooth" doctor rod with "big" Diameter against the running surface of the roller or the paper web is pressed to add a coating amount or set a profile of the applied coating medium.

The invention has for its object the known To further develop methods so that both sides coated paper webs with compared to previously essential higher smoothness and gloss values can be produced. The task also includes one for implementation specify suitable device for this method.

This task will solved by a method with the features of claim 1 and by a device having the features of claim 15.

The invention led to the realization that the use a known smooth doctor element for forming the Coating films on each of the applicator rollers with a smoothing of the paper web coated on both sides by means of at least one smoothing unit to much higher ones Smoothness and / or gloss values lead than before. presumably this surprisingly good result is achieved in that the use of a smooth doctor element compared to the conventional grooved squeegee, on the coating color exerts a higher shear effect, and that platelet-shaped pigment particles are aligned in such a way that they lie flat on the paper surface from the start. As a result, there is far less than after smoothing So far the tendency that the surface of the finished paper has a matt character.

The process steps of the process according to the invention are preferably controlled so that the surfaces of the finished, coated and smoothed paper at least is predominantly free of orange peel-like bumps.

It is possible to use a doctor blade as Doctor element. However, the use of a is preferred smooth squeegee because this creates the cross profile of the Coating is more controllable; in other words: it succeeds easily, permanently improved, in particular to get a uniform cross profile.

A favorable side effect of the method and the corresponding device according to the invention in that roller doctor blades with a smooth outer surface are essential wear out more slowly than those with a grooved outer surface.

Other features that the result of the invention can further improve are in the subclaims specified. Among these features, it is particularly important that smoothing after coating at higher temperature than so far takes place (claim 10) and that it does not heatable "relatively soft rollers" (according to claim 31) harder are compared to conventional "soft nip" smoothing machines. One can therefore the inventive (after the coating units arranged) smoothing units, e.g. as "Super Compact Calendar" describe.

In the subject of DE-A-43 02 437 A1, the rollers are each Coating unit arranged one above the other so that the Paper web essentially in the horizontal direction through the Order gap runs through. This requires a relative complex device for pivoting the movable Counter roll. It also makes removing the overhead Counter roller required if the application roller below must be expanded. An important part of the The present invention is therefore the rollers at least one of the two coating units in this way to arrange that the web is essentially bottom-up, preferably diagonally from bottom to top through the Order gap runs through. Among other things, through this the device according to the invention also differs from Subject of EP-A-0 596 365 A1, in which the web is inclined from runs down through the order gap.

Otherwise, the device according to the invention makes of the known possibility of use on each coating unit following drying device above the coating unit to arrange. This facilitates heat dissipation; because the predominantly upward heat-air flow will not hindered by the coating unit. It also avoids that dirty when cleaning the coating unit Cleaning waste water drips onto the drying device.

Finally, another advantage is that in one possible paper tear that towards the coating unit current committee paper before reaching the Coating unit falls down under the force of gravity cannot accumulate before the order split.

Fig. 1

eine schematische Seitenansicht auf einen Teil einer Papiermaschine mit einer On-line-Streichanlage;

Fig. 2 - 4

je eine schematische Querschnittsansicht unterschiedlicher Auftragswerke, und

Fig. 5 - 7

Varianten mit unterschiedlichen Glätteinrichtungen.

The invention is explained in more detail below using an exemplary embodiment with reference to the accompanying drawings. Show it:

Fig. 1

a schematic side view of part of a paper machine with an on-line coating system;

Figs. 2-4

each a schematic cross-sectional view of different commissioned works, and

5 - 7

Variants with different smoothing devices.

As illustrated in FIG. 1, the material web 1 runs on leaving a dryer section T by a smoothing unit G and thence via web guide rollers 2 to 6 in the area of first coating station 8 a. Instead of the dryer section T downstream smoothing unit G could also within the Dryer section a smoothing device (e.g. a large smoothing drying cylinder or "Yankee" cylinder) can be provided. The The first coating station 8 is a spreader roller 7 upstream, which the material web 1 from a in essential horizontal direction in an oblique direction redirects upward direction, after which the material web then by one trained in the coating station 8 Order gap runs through. The coating station 8 includes one Applicator roller 10, one opposite and with it the backing roller 11 forming the application gap and a Applicator 13. As shown in Fig. 1 is the applicator roller 10 preferably arranged obliquely below the counter roller 11, so that the material web 1 obliquely from bottom to top through the Order gap is running. The arrangement may differ also be taken such that the web 1 essentially runs vertically from bottom to top through the application gap.

The position of the spreader roller 7 is variable, so that the Web before entering the application nip of the counter roller 11 wraps around something; i.e. the web 1 covers on the counter roller 11 a variable inlet angle e, which is between 0 and 15 ° can be. In another, shown in broken lines Variant wraps around part of the application roller 10; this allows the penetration time of the coating medium in the Web can be increased.

The first coating station 8 is a web guide roller 12 downstream, the one running out of the order gap Material web from its diagonally upward direction deflects upward in a substantially vertical direction. The web guide roller 12 touches the material web 1 on the not provided with a liquid medium (coating slip) Hinge side. The position of the web guide roller 12 is also variable, so that the web 1 on the counter roll 1 variable outlet angle a that covers between 0 and 20 ° can be (see under half of Fig. 1).

After leaving the web guide roller 12, the material web passes an infrared dryer 15 and then over two more Web guide rolls 16 and 17 through a hot air dryer 18 guided. Then the material web is over a Web guide roller 19 and a spreader roller 20 of a first Contact drying cylinder assembly 21 of known type supplied. This arrangement has a number of e.g. four Drying cylinders to which the material web 1 in itself known manner by means of a so-called upper felt 22 and a bottom felt 23 is pressed. With dashed lines is indicated a variant in which instead of two above felted cylinders only a single cylinder felted above is provided.

After leaving the first contact drying cylinder arrangement 21 the material web 1 runs over further web guide rollers 14, 14a, and an (again adjustable) spreader roller 24 in the Area of a second coating station 25.

This second piercing station 25 is in the present Embodiment compared to the first coating station 8 executed essentially in mirror image. The second Coating station 25 comprises an application roller 10 ', a Counter roll 11 'and an applicator 13'. Again it directs the spreading roller 24 upstream of the coating station Material web from an essentially horizontal Inflow direction in an obliquely upward running direction um, in which the material web through the two rollers 10 ' and 11 'formed order gap. Analogous to the first Coating station 8 is the second coating station 25 one Web guide roller 26 connected downstream from the press nip material web 1 running out of it obliquely upwards directed in a substantially vertical direction Direction of travel deflected upwards.

After leaving the web guide roller 26, the material web passes 1 an infrared dryer 28. Then the Material web over a web guide roller 27, one without contact working deflection device 29 and a web guide roller 30 in introduced a hot air dryer 31. After passing the Hot air dryer 31 runs the material web 1 over a Spreader roller 32 into a second Contact drying cylinder assembly 33 which is similar Can be structured like the first Contact drying cylinder arrangement 21. However, is shown a space-saving arrangement with only two, approximately superimposed cylinders 34, with only one Felt 35 in front of the first cylinder via a suction guide roller 35a runs, there the felt 35 comes in for the first time with the web 1 Contact. Between the two cylinders 34, the web 1 temporarily without the felt 35 via a paper guide roller 1a to run. It is important that on the drying cylinders 34 - directly or indirectly - a smoothing unit, preferably a directly following on-line calender 60 follows. An on-line calender has compared to an off-line calender (75, Fig. 7) et al. the advantage that in the smoothing The effort for the heat supply to the paper web is lower because the paper web before it enters the smoothing unit has relatively high temperature.

Preferably two two-roll calenders are provided, by which each have a relative heatable to at least 130 ° C hard metal roller 61 and a non-heatable counter roller 62 has a "relatively soft" coating. After that the finished paper web wound up in a conventional manner (in Fig. 1 not shown).

As can be seen in FIG. 1, the application unit 13 or 13 ' the coating station 8 or 25 in the lower downward Quadrants of the application roller 10 arranged, that is approximately compared to the order gap. The order work 13 can also approximately at the lower vertex of the roll surface to be ordered. As can be seen clearly in FIG two coating stations 8 and 25 to the respective Application roller 10 applied liquid film between the Application unit 13 or 13 'and the material web 1 from below visible and can be checked.

In Fig. 2, an applicator 13 is relative in one position to the applicator roller 10 shown the arrangement of Commissioned work 13 in the first coating station 8 in FIG. 1 equivalent. The embodiment of the shown in Fig. 2 Commissioned work 13 works with a smooth roller doctor 36, the is mounted in an angled doctor bed 45. The liquid medium is from a distribution channel 51 and through a feed gap 39 supplied under pressure to an application chamber 38 by the Roller doctor bed 45, the application roller 10 and a baffle bar 37 is limited. The liquid from the application chamber 38 Medium over the roller doctor 36 on the applicator roller 10 in one desired line width applied. Excess liquid Medium flows over the damming bar 37 (or through openings in the storage rail) and over the front wall 50 carrying it under Effect of gravity along a drain surface 40 in a drainage channel 41. Thanks to the angled doctor bed 45 can feed gap 39 and discharge surface 40 approximately radially to The lateral surface of the roller 10 run. This enables the Arrangement of the order work in the lower downward running Quadrants of the roller 10.

The application work 13 shown in Fig. 2 is with a known deflection compensation system provided the one Deflection of the beam 43 carrying the coating unit by means of a measuring system 52 detects and then a Deflection compensation using pressure pads 42 makes that between the bar 43 and an articulated in this received yoke 44 are arranged.

Finally, the application unit has a pressure hose 58 which extends over the entire width of the application work 13 extends and in contact with the bent doctor bed 45 stands. The pressure hose 18 is supported by a pressure bar 59 acted on, which also runs continuously. About the Spindle shafts 49 are distributed across the width of the application unit 13 arranged at one end with a handwheel 48 are provided and with their other end with the Pressure bar 59 are in operative connection. The pressure hose 58, the pressure bar 59 and the adjusting spindle 49, which as flexible shafts or designed as cardan shafts a system with which the pressure of the doctor blade 36 against the Roller 10 variably adjusted over the length of the applicator can be to the cross profile of the on the roll surface to regulate the coating slip film formed.

3 is another embodiment of a Commissioned work 13A shown that for a position in the lower upward running quadrant of the applicator roller 10 suitable is. The application unit 13A also works with a smooth one Roller doctor blade 36. The liquid medium now becomes approximately tangential to the roll jacket through the feed gap 39 'of the application chamber 38 'supplied by a conventional (essentially level) roller doctor bed 45 ', the applicator roller 10 and the Storage bar 37 'is limited. Excess liquid medium in turn flows over the baffle bar 37 'under the influence of Gravity along the drainage surface 40 into a drainage channel 41 from.

A deflection compensation system is also provided here, this is a deflection of the beam bearing the commissioned work 43 determines by means of a measuring system and then one Deflection compensation using pressure pads 42 makes that between the bar 43 and an articulated in this received yoke 44 are arranged.

4 is another embodiment of a Commissioned work 13B shown that for a position in the lower upward quadrant of the applicator roll 10 'of the figure 1 is suitable. This commissioned work comes with a Provide doctor blade 36a (instead of a doctor blade). The Scraper blade 36a bounded together with a baffle 37 ' and with the application roller 10 'an application chamber 38'. Liquid coating slip is in turn under pressure Order chamber fed, taking excess coating slip over the damming bar 37 'along a drain surface 40 into a Collecting channel 41 runs. The commissioning work 13B shown in FIG. 4 is designed without a deflection compensation device.

Of course, the 8 and 25 of the coating system shown in FIG. 1 Commissioned works 13 and 13 'from both in Fig. 2 and in Fig. 3 shown type and need only in their spatial positioning corresponding to the first and the second coating station can be adjusted. In addition, you can the applied works 13 and 13 'also compared to examples shown in FIGS. 2 and 3 further be modified.

5 differs from FIG. 1 in the following points:
The paper web 1 runs essentially vertically from bottom to top through the nips of the coating stations 8 and 25. After each coating station 8, 25, any drying station 68, 69, only shown symbolically, is provided. The on-line calender comprises a total of four two-roll calenders, each with a hard and heatable roll 61 and each with a non-heatable "relatively soft" roll 62. Each roll type 61 or 62 is arranged alternately below and above , so that a symmetrical smoothing of the web 1 takes place.

FIG. 6 shows a variant in which the on-line calender 60 two three-roll calenders, each with a central heatable hard roller 61 and two “relatively soft” counter rollers 62 having. A smoothing station 70 follows the smoothing unit 60.

7 is a reeling station 70 immediately behind the Drying station 64 provided. Here the smoothing of the ready-coated paper web 1 in a regardless of the Paper machine operated off-line calender 75 instead. Also here it is ensured that each paper page at least once with a hard heatable roller 61 and with a "relative soft "non-heatable counter roller 62 comes into contact.

Claims (28)

1. Process for producing paper webs with lightweight coating on both sides, within a paper-manufacturing machine, having the following process steps:

   a) Initially the one side of the paper web (1) dried in the paper machine is coated with a coating composition indirectly by means of a first application roller (10), which forms a first application gap with a first counter-element (11), and then dried;

   b) then the other side of the paper web (1) is coated with a coating composition indirectly by means of a second application roller (10'), which forms a second application gap with a second counter-element (11'), and then dried;
   characterised by the following process steps:

   c) metering of the coating composition onto the shell of at least one of the application rollers (10, 10') takes place by means of a smooth doctor-blade element (36 or 36a);

   d) the process is carried out at an operating speed of at least 900 m/minute;

   e) the paper web (1) is at least partly dried;

   f) after at least partial drying of the paper web (1) coated on both sides, calendering of the paper web (1) takes place by means of at least one heatable calendering machine (60, 75);

   g) calendering (60, 75) takes place at elevated temperature between 130°C and 400°C.
2. Process according to claim 1, characterised in that metering of the coating composition onto the application rollers (10, 10') takes place by means of a smooth roller doctor blade (36) or a coating blade (36a).
3. Process according to claim 1 or 2, characterised in that calendering takes place on-line, that is within the paper machine (60, Figures 1, 5, 6).
4. Process according to one of claims 1 to 3, characterised in that calendering takes place off-line, that is outside the paper machine (75, Figure 7).
5. Process according to one of claims 1 to 4, characterised in that during calendering, each paper web side comes into contact with at least one hard heatable roller (61) and with at least one relatively soft roller (62).
6. Process according to one of claims 1 to 5, characterised in that a linear force between 0 and 60 kN/m is set in at least one of the two application gaps.
7. Process according to one of claims 1 to 6, characterised in that a linear force between 5 and 20 kN/m is set in at least one of the two application gaps.
8. Process according to one of claims 1 to 7, characterised in that it takes place at an operating speed of at least 1,100 m/minute.
9. Process according to one of the preceding claims, characterised in that the paper web (1) is calendered by means of a calendering device (G) before coating.
10. Process according to one of the preceding claims, characterised in that an application weight (M) of 2 to 20 g/m² (based on dry substance) is applied to each web side.
11. Process according to claim 10, characterised in that an application weight (M) of 5 to 12 g/m² (based on dry substance) is applied to each web side.
12. Process according to one of the preceding claims, characterised in that a coating composition having a consistency of 25 to 75 %, preferably 45 to 65 %, is applied.
13. Process according to claim 9, characterised in that the consistency of the coating composition is selected such that misting is avoided during coating.
14. Process according to one of the preceding claims, characterised in that the finished paper web (1) has a quality value (Qw) of 0.3 to 2.4, preferably 0.6 to 1.8, wherein the quality value (Qw) is determined according to the following formula: Qw = M [g/m2 ] • smoothness after PPS 10S [µm] / gloss [%], (wherein M is the application weight for each web side, based on dry substance and wherein for the gloss, a measuring value according to Hunter, for example at 75 degrees, or Lehmann is used).
15. Device for carrying out the process according to one of claims 1 to 14,

    having a first coating unit (8) arranged within the paper-manufacturing machine, having a first application roller (10), which forms a first application gap with a first counter-element (11), for indirect coating of the one paper side, and having a drying device (21) belonging to the first coating unit (8), and

    having a second coating unit (25), having a second application roller (10'), which forms a second application gap with a second counter-element (11'), for indirect coating of the other paper side, and having a drying device (33) belonging to the second coating unit (25),

    characterised in that

    each of the coating units (8, 25) has as metering element a smooth doctor-blade element (36 or 36a), which forms a coating composition film on the shell of the assigned application roller (10, 10'),

    the device is designed to operate at an operating speed of at least 900 m/minute,

    and in that at least one on-line calendering machine (60) or off-line calendering machine (75) which can be heated to a temperature between 130°C and 400°C is provided after the second coating unit (25) and the associated drying device (33) for calendering the paper web (1).
16. Device according to claim 15, characterised in that a smooth roller doctor blade (36) is provided as doctor-blade element.
17. Device according to claim 15, characterised in that a coating blade (36a) is provided as smooth doctor-blade element.
18. Device according to one of the preceding claims, characterised in that each of the application rollers (10, 10') has a relatively soft roller covering, the hardness of which has 20 to 200 P & J, preferably 30 to 100 P & J.
19. Device according to one of the preceding claims, characterised in that the counter-element (11, 11') is designed as a hard, preferably chrome-plated counter-roller.
20. Device according to one of the preceding claims, having a web-guiding roller (12, 26) arranged behind the application gap in the running direction of the web, characterised in that the position of the web-guiding roller is variable such that the discharge angle (a) provided on the counter-roller (11, 11') can be varied between 0 and 20 degrees, preferably between 5 and 15 degrees.
21. Device according to one of the preceding claims, characterised in that a broad stretching roller (7, 24) is arranged before the application gap in the running direction of the web.
22. Device according to claim 21, characterised in that the position of the broad stretching roller (7, 24) is variable such that the entry angle (e) provided on the counter-roller (11, 11') can be varied between 0 and 15 degrees, preferably between 4 and 8 degrees.
23. Device according to one of the preceding claims, characterised in that the application mechanism is designed as a nozzle application mechanism (13), which

    has a retaining strip (37) arranged counter to the direction of rotation of the roller (10) at a distance from the roller doctor blade 36, which defines an application chamber (38) with the shell of the application roller (10, 10'),

    and has a discharge surface (40), by means of which excess liquid medium emerging from the application chamber (38) flows away under the influence of gravity.
24. Device according to one of the preceding claims, characterised in that the application mechanism (13) is arranged in the region of the roller shell (10) running downwards.
25. Device according to claim 24, characterised in that the application mechanism (13) is arranged in that quadrant of the roller shell of the application roller (10) which runs downwards and lies below the horizontal plane running through the roller axis.
26. Device according to one of the preceding claims, characterised in that the application roller (10, 10') and the counter-element (11, 11') are arranged in at least one of the coating units (8, 25) such that the web (1) passes through the application gap essentially from the bottom to the top, preferably at an angle from the bottom to the top.
27. Device according to one of the preceding claims, characterised in that the calendering machine (60, 75) has at least two roller gaps, formed by in each case a hard heatable roller (61) and a relatively soft roller (62), wherein the one web side comes into contact with the hard heatable roller (61) in the one roller gap and the other web side in the other roller gap.
28. Device according to claim 27, characterised in that the "relatively soft" rollers (62) have a Shore D hardness of at least 80.

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