EP0666370B1 - Method of coating at least one side of a fibrous web with a coating medium and device for carrying out the method - Google Patents

Abstract

To apply a coating to a fibre web, and esp. paper, the coating is applied as an initial dosing directly to an applicator roller through at least one free spray stream. Pref. the free jet stream (13) is applied directly at the mantle surface (11, 12) of the applicator roller (1, 2), or at the surface of a transfer roller which carries the coating to the applicators (1, 2). The free jet stream (13) and/or its application angle can be adjusted.

Description

The invention relates to a method for at least one-sided coating of a fibrous web with a Order medium, specifically with the characteristics from the The preamble of claim 1, further a device for Execution of the procedure.

In the field of paper finishing are for coating different from fibrous webs with an application medium Methods and devices known. The Coating the fibrous web with an application medium either directly by application to the fibrous web, the a rotationally symmetrical body on part of it Wraps around the circumference or is on the outer surface of a predisposed rotationally symmetrical body. In both cases the order takes place in two successive steps - the application of coating or glue in excess by means of an application nozzle and the subsequent doctoring the excess application mass with a leveling system, mostly in the form of subordinate doctor blades and Blade devices. The implementation of the device in the latter case occurs, for example, in a Film press. With conventional film presses, this is done Application of the application medium on the lateral surfaces of the Application rollers, the dosage being usually through downstream doctor blade devices is realized. At the Applicator rollers are the pre-metering devices arranged and are over cylinders or similar aids can be pressed against the lateral surfaces of the application rollers. The Predosing device comprises a nozzle applicator, in which Glue or coating color via a special distribution system is passed into the pressure chamber of the application nozzle and one Squeegee device. The application medium passes through a Slot nozzle from the pressure chamber into the order area. The The amount of glue or coating slip is applied using a doctor blade or a pressable blade controlled.

Disadvantages of such designs are above all a complicated structure of the application or metering system and the use of a wearing part as a metering element, which is why keeping the amount of film constant over time is very problematic and cannot be influenced directly. Even the cross profile of the applied medium can only be kept constant by lengthy profile adjustment work, ie the application across the machine width is not necessarily even. With high solids contents or with extremely absorbent paper there is also the risk of forming profile grooves, which leads to a limitation of the minimum possible application quantity.
The use of a wearing part as a metering element leads to short downtimes of the metering element and thus to undesirable downtimes of the machine which are caused by the change of the metering element. Furthermore, it is hardly possible to control the order quantity without changing the dosing elements or lengthy adjustment work.

DE-A-2 310 526 describes a method for coating both sides of a Paper web in a device comprising an application roller and a Counter element, which together form a gap through which the paper web is passed through, and in which the application medium on the roller pre-dosed an order media free jet and in the gap on the web is transmitted. However, further rollers are connected upstream. Further is a sump of the application medium is provided. Such a swamp is absolute harmful, because it moistens the paper web much too much and therefore its Strength reduced. Evenness is on both sides of the Paper web no longer exist. At today's high Such a swamp would affect the web and the web Spray off the rollers, causing further irregularities in the application on the Would lead.

DE-A-3 526 257 describes a two-roll applicator. Here an order medium is pre-dosed by a direct one Application on the rollers.

As a means of application, however, are nozzles with elastic lips provided that are pressed onto the jacket of the applicator roller. A such an embodiment does not produce a free jet. The pressure of the lips against the surface of each roller guarantees none even, controlled order.

The invention is therefore based on the object of a method and also a method Device for performing the method of the type mentioned to develop in such a way that the disadvantages mentioned are avoided. The amount of film to be transferred to the fibrous web is over time and over the machine working width, i.e. transverse to the direction of the fibrous web to keep constant. The amount of film to be applied should also be certain Bandwidths can be controlled. There are also essential ones Requirements for the process or device to be further developed especially in minimizing the wear of the dosing element and thus a longer service life between the required change of the Realize dosing elements. Low operating costs and suitability for the use for the application of coating color and starch are further essential Requirements.

The dosing element should be robust with regard to its handling and one have low susceptibility to damage, for use at high Order speeds are suitable and easy to use as well have a very small number of wearing parts.

The achievement of the object is characterized by the characterizing features of claim 1.
The implementation of the device takes place according to claim 3.
Furthermore, there is the possibility of solving the problem with a device according to claim 13. Advantageous design options are given in the subclaims.

According to the invention, the pre-metering takes place in one Two-element application device on the outer surface of an application roller at least indirectly, i.e. both directly and indirectly through the order of order medium by means of at least one free jet. The use of a Free blasting offers the advantage of direct control of the order quantity and thus the thickness of the application film on the outer surface by change certain parameters such as the exit cross section, the Exit speed and the application angle of the free jet in Connection with the speed of the application roller.

The free jet can be directed directly onto the outer surface of the application roller be or on the outer surface of a transfer roller, which in turn the Application medium at least indirectly, i.e. directly or through another Transfer roller on the outer surface of the application roller transmits. The latter variant (indirect order) also offers the advantage a further metering effect, in particular the stretching of the application film by the appropriate adjustment of the diameter ratio of Application roller and transfer roller achieved speed difference of Shell surfaces of application and transfer roller.

The implementation of the device according to the invention is determined by the characterizing features of claim 3. In the case of a two-element application device
At least one application element, preferably an application roller, is assigned an application unit comprising a device for generating a free jet which at least indirectly applies the application medium to the surface of the application element. The device for generating a free jet can be directly assigned to the order element (free jet is directed directly onto the surface of the order element) or, if at least one transmission element is connected in series, can be directly assigned to it.

1) der Auftrag erfolgt unmittelbar, d.h. direkt auf die Mantelfläche einer Auftragswalze;

2) der Auftrag erfolgt hier mittelbar bzw. indirekt, d.h. auf die Mantelfläche einer der Auftragswalze zugeordneten Übertragungswalze.

The two-element application device is preferably designed in the form of a two-roller application device, ie two application rollers which are axially parallel to one another are driven in opposite directions to one another and together form a press nip through which the fibrous web is passed. The application of application medium to the fibrous web takes place when it is passed through the press nip, in which the quantity of application predosed on the surface of the application roller is transferred to the fibrous web. This device is suitable both for one-sided coating and for two-sided coating of fibrous webs with application mass, the same or different application media can be provided for both fibrous web sides.
According to the invention, two possibilities are conceivable:

1) the application takes place immediately, ie directly on the outer surface of an application roller;

2) the application takes place indirectly or indirectly, ie on the outer surface of a transfer roller assigned to the application roller.

The second option offers the advantage of being more suitable Design of the diameter ratio between order and Transfer roller an additional metering effect, in usually in the form of a film stretching through the Achieve transfer roller. It is special advantageous if a particularly thin application film on the Fibrous web is desired.

1) eine Freistrahldüseneinrichtung

2) ein geschlossener Stoffauflauf mit einem druckbeaufschlagten zentralen Behälter und veränderlich einstellbarer Auslaßöffnung.

There are two preferred variants for the design of the device for generating a free jet:

1) a free jet nozzle device

2) a closed headbox with a pressurized central container and variably adjustable outlet opening.

The free jet nozzle device can be as in the US-A-3,418,970, US-A-3,521,602 and US-A-4,231,318 be designed. Acting with the free jet nozzle device it is usually a pure order setup with own supporting body, for example a distributor and a slot nozzle extending across the machine width includes. The application takes place without contact of the nozzle with the Lateral surface of the application element. The Free jet nozzle device is in the radial direction displaceable relative to the outer surface of the application roller and rotatable about a certain axis so that the Application angle with respect to the outer surface of the application roller is variably adjustable. Preferably, the Nozzle device according to US-A-3,418,970 such arranged opposite the lateral surface of the application roller, that in the order direction, i.e. in the direction of the Roll a converging gap between the outer surface the application or transfer roller and the Free jet nozzle device results.

Furthermore, the nozzle channel of the nozzle device, i.e. the connecting line between the distributor and the nozzle outlet be curved. The curvature runs in the essentially converging to the order or Transfer roller. With this procedure lies then low-air layer on the roller and the air-rich layer Outside.

1) der Strömungs- bzw. Austrittsquerschnitt aus der Freistrahldüse oder dem Behälter des Stoffauflaufes;

2) die Austrittsgeschwindigkeit des Auftragsmediums;

2) der Druck im Verteiler oder Behälter;

3) die Drehzahl der Auftragswalze.

The dosing effect of both systems when applying is determined by various factors. This includes:

1) the flow or outlet cross-section from the free jet nozzle or the headbox container;

2) the exit speed of the application medium;

2) the pressure in the manifold or container;

3) the speed of the application roller.

A change in the outlet cross-section and the speed the application or transfer rollers are constructive easy to implement while changing the Exit velocity as a function of Outlet cross section and the design of the nozzle or Container (specifically the changes in cross section between Distributor or container and outlet cross section) look at is.

In another aspect, the Two-element application device an application roller include an extended with a circulating belt Press nip for passing the fibrous web forms. The The free jet is then preferably applied to the Lateral surface of the application roller, but also the order the tape may be conceivable. Such Device is also suitable for one-sided and double-sided coating of fibrous webs.

Preferably, the devices for generating the Free jet in the part of the lateral surface of the order or Transfer roller arranged in the direction of rotation Rolls in the area before the nip inlet. A Arrangement in areas away from the press nip inlet is also conceivable. In this case, be preferred additional leveling devices, for example in form of air brushes applied to even out the Film used on the outer surface.

The order according to the invention by means of a free jet on the The surface of an application element offers the advantage of a direct controllability of the pre-dosing of the application medium on the surface of an order element and thus the Predosing for the one to be transferred in the press nip Order quantity. The system according to the invention offers further the advantage that the amount of film to be applied kept constant over time and across the working width can be. The order or. Dosing system stands out due to a small number of wearing parts and thus longer downtimes between the necessary changes the dosing elements. The adjustability of the size of the Outlet openings and changes in position with respect to the Order elements are easy to construct. The inventive method is suitable for Coating slip as well as starch.

For the application by means of an open headbox Take additional precautions to get the one you want to influence the dosage directly. Additional throttling or other disruptive elements in the drain the open container are conceivable.

Fig. 1

eine Zweiwalzenauftragsvorrichtung mit zugeordneter Freistrahldüseneinrichtung an einer Auftragswalze und SDTA mit Rakel an der anderen Auftragswalze;

Fig. 2

eine Zweiwalzenauftragsvorrichtung mit zugeordneter Freistrahldüseneinrichtung und zusätzlichem Egalisiersystem;

Fig. 3

eine Zweiwalzenauftragsvorrichtung mit Übertragungswalze;

Fig. 4

eine Zweiwalzenauftragsvorrichtung mit geschlossenem Stoffauflauf an einer Auftragswalze und offenem Stoffauflauf an der anderen Auftragswalze;

Fig. 5

eine Zweielementenauftragsvorrichtung bestehend aus Walze und Band mit Freistrahldüseneinrichtung.

The achievement of the object according to the invention is explained below with reference to figures. Show it:

Fig. 1

a two-roller application device with associated free jet nozzle device on one application roller and SDTA with doctor blade on the other application roller;

Fig. 2

a two-roller application device with associated free jet nozzle device and additional leveling system;

Fig. 3

a two-roll applicator with transfer roll;

Fig. 4

a two-roll applicator with closed headbox on one applicator roll and open headbox on the other applicator roll;

Fig. 5

a two-element application device consisting of roller and belt with free jet nozzle device.

FIG. 1 shows a two-roller application device. A Applicator roller 1 and an applicator roller 2, the axially parallel arranged to each other and rotatably formed with each other a nip 3 for passing one Fibrous web, in particular paper web 4. The two Application rollers 1 and 2 are opposite to each other driven. Essentially below that from below above running part of the roll circumference of each roll 1, 2 an application unit 5, 6 for a flowable medium arranged. The fibrous web 4 is from bottom to top passed through the nip 3. It is in the Areas 7, 8, the nip 3 with the Fibrous web 4 forms a film of a flowable Medium over the roller surfaces on both sides of the Fibrous web 4 applied. By leading the Fibrous web 4 from bottom to top through the nip 3, the application medium, for example coating slip in the desired thickness according to the distances of the Rolling circles of both rollers 1 and 2 onto the fibrous web 4 applied.

The application devices 5 is as Free jet nozzle device executed. The nozzle channel of the Free jet nozzle device 5 is preferably curved executed. The free jet 13 is corresponding represented schematically. The application device 6 is as an STDA with a squeegee, for example as in the on 17.03.1994 published DE-A-42 30 276. The The coating slip is applied to the outer surface 11 and 12 respectively the rollers 1 and 2 applied.

FIG. 2 illustrates an embodiment analogous to FIG. 1 with additional leveling devices. For the same elements therefore became the same reference numerals chosen. However, the fibrous web 4 is here from above passed down through the press nip 3. In the area of lower part of the part of the Roll circumference or the lateral surfaces 11, 12 of each roll 1, 2 is an order unit 5a or 5b for each Application medium, for example coating color, arranged. The fibrous web 4 is from top to bottom through the Roll nip 3 out. In the areas 7, 8, which the nip forms with the fibrous web, a film a flowable medium over the roller surface 11 or 12 applied to the fibrous web 4. In addition are in the order devices 5a and 5b in Part of the roll shells downstream of the roll rotation direction 11 or 12 additional leveling devices 14 or 15 in Form of air brushes provided. The generated with it Air jets equalize the applied coating slip before transfer to the Fibrous web 4 in the nip 3.

FIG. 3 illustrates a two-roller application device with additional transfer rollers that run counter to the Rotate application rollers and form a gap with them. The basic structure corresponds to that in Figure 2, which is why for same elements same reference numbers have been used. Each applicator roller 1 or 2 is a transfer roller 16 or 17 with an application device 5a or 5b in the form assigned to at least one free jet nozzle. Application rollers 1 and 2 and transfer rollers 16 and 17 respectively form a gap 30 or 31 with each other. The transfer rollers 16 and 17 preferably have a smaller diameter than the application rollers 1 and 2 respectively, whereby each between application roller 1 or 2 and transfer roller 16 or 17 a speed difference between them Shell surfaces 11 and 18 or 12 and 19 results. This Speed difference contributes to a stretching of the Coating film and thus for an additional metering effect at.

Figure 4 illustrates a possibility of pre-metering Coating paint directly on an applicator roller Two-roller application device by means of a closed Headbox 19. The basic structure of the Two-roller application device corresponds to that in the figures 1 to 3, which is why the same reference numerals for the same elements were used. The coating slip is fed directly on the lateral surface 12 of the application roller 2. The headbox includes a pressurizable one Container 20 with one, essentially over the outlet line 21 that extends across the entire width of the machine The flow cross section of the outlet line 21 is in the Cross section changeable - however over the width of the Order constant.

The application on the application roller 1 takes place by means of a open headbox 25, for example a central open container 26 with overflow weir and a Has drain element 27, via which the coating slip is passed onto the lateral surface 11 of the application roller 1.

To adjust the metering effect are additional, here in individual means, not shown, on the headbox required, for example one, the drain element 27 assigned aperture that acts like a choke.

In Figure 5 is a two-element applicator shown that an applicator roller 1 with a circumferential band 22 forms an extended press nip 23, includes. The application roller 1 is one Free jet nozzle device 5a assigned. The circulating Band 22 is made by passing the band through a Glue suspension filled container 28, the quantity of glue carried along by the tape 22 by an in Blade 24 downstream direction is equalized.

The embodiment shown in Figure 5 is preferably for coating on both sides with different application media can be used, while the in 1 to 4 preferably shown for the double-sided coating with the same Application medium are suitable. However, here is one too different or only one-sided coating conceivable. In those shown in Figures 1 and 4 There is also the option of both Order elements the same order units assign.

Claims (13)

1. Method of coating at least one side of a fibrous web with an application medium in a two-element application device, comprises two applicator elements (1,2;1,22) which are driven in opposite directions and together form a gap (3,23) through which the fibrous web (4) is led, in which method the application medium is pre-metered onto at least one applicator roll (1,2) and is transferred to the fibrous web in the gap (3,23), characterized in that the pre-metering is carried out by means of at least one free jet of application medium, and in that the free jet (13) is aimed directly at the surface (11,12) of an applicator element (1,2).
2. Method according to Claim 1, characterized in that the free jet (13) and/or its application angle can be varied.
3. Device for coating at least one side of a fibrous web (4) with an application medium, having the following features:

   two applicator elements (1,2;22) are provided, which are driven in opposite directions and together form a gap (3,23) for the fibrous web (4) to be led through;

   at least one applicator element (1,2,22) is assigned an applicator unit;

   characterized by the following feature:
   the applicator unit includes at least one device for producing a free jet (5a,5b) which pre-meters the application medium, at least indirectly, on to the surface (11,12) of the applicator element.
4. Device according to Claim 3, characterized in that the device (5a,5b) for producing a free jet is assigned directly to the applicator element.
5. Device according to Claim 3, having the following features:

   the applicator element is an applicator roll (1,2);

   the applicator unit further includes a transfer roll (16,17), which is assigned to the applicator roll (1,2) in such a way that the two together form a press nip (30,31); characterised in that

   the device (5a,5b) for producing the free jet (13) is assigned to the transfer roll (16,17).
6. Device according to one of Claims 3 to 5, characterized in that the device (5a,5b) for producing a free jet (13) is at least one nozzle-like element (free-jet nozzle device).
7. Device according to Claim 6, characterized in that the position of the outlet opening of the free-jet nozzle can be set variably with respect to the circumferential surface (11,12,18,19) of the applicator roll (1,2) or transfer roll (16,17).
8. Device according to either of Claims 6 and 7, characterized in that the free-jet nozzle device (5a,5b) is arranged opposite the circumferential surface (11,12,18,19) of the applicator roll (1,2) or transfer roll (16,17) in such a way that these two together form a converging gap in the direction of rotation of the applicator roll or transfer roll.
9. Device according to one of Claims 3 to 5, characterized in that the device (5a,5b) for producing a free jet (13) is a closed head box (19) with pressurised containers (20).
10. Device according to one of Claims 3 to 9, characterized in that the cross section of the outlet openings for the free jet can be set variably.
11. Device according to one of Claims 3 to 10, characterized in that additional equalising devices (14,15) are connected downstream of the device for producing a free jet (5a,5b).
12. Device according to Claim 11, characterized in that the equalising devices are designed in the form of air knives.
13. Device for coating at least one side of a fibrous web with an application medium, having the following features:

    two applicator elements (1,2,22) are provided, which are driven in opposite directions and together form a gap (3,23) for the fibrous web (4) to be led through;

    at least one applicator element (1,2,22) is assigned an applicator unit;

    characterized by the following features:

    the applicator unit is implemented as an open head box (25), which supplies the application medium, at least indirectly, on to the surface (11,12) of the applicator element (1,2);

    means for metering the quantity applied are provided on the head box.

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