EP1760195B1 - Apparatus and process for coating a fibrous web - Google Patents

Description

The invention relates to a method for manufacturing and in particular the present invention relates to a method in which the paper or board web is first produced and then coated online.

The on-line coating of paper, cardboard or other fibrous webs is known. Whereas until a few years ago the production of the fibrous web took place separately from the coating, it has recently been proposed to carry out the coating on-line, that is to say the production and coating of the fibrous web takes place in a single apparatus or machine without intermediate storage and intermediate storage. and -brollung the fibrous web. The conventional separately carried out production and coating of the fibrous web on various devices with an intermediate storage of the fibrous web after its production is referred to by the person skilled in the art as an off-line method.

In the off-line method, the fibrous web, in particular the paper or board web, is first produced by means of a first device. At the end of the device, the fibrous web is wound into a web roll and thus stored temporarily. This web roll is fed to a coater, in which the web roll is unwound again to a moving fibrous web, which is then painted in the coater.

In the on-line method, the coating device - in the context of the present invention generally called coating device -, in the direction of movement of the Fibrous web disposed behind the web forming device, and the fibrous web is fed continuously without caching from the web forming apparatus of the coating apparatus. The present invention relates exclusively to such an on-line coating device or such an on-line coating method. An intermediate storage, for example in the form of fibrous web rolls, therefore does not take place.

While in offline applications for some years contactless coating devices are used, ie coating devices in which the liquid or pasty application medium is applied without a Druckpenetration on the web, for example by a free coating curtain (curtain coating) or by a free Auftragmediumsprühschleier (Spray Coating), such an order process for online applications did not seem to be possible for a long time. Only recently has it been proposed to use such a contactless applicator in an on-line coating device, see, for example, the publications DE 102 28 134 A1 or DE 102 28 117 A1 ,

The online coating or the online coating of the fibrous web offers the advantage of a significantly higher throughput compared to the offline applications, that is to say an improved quantity efficiency. It is initially irrelevant in terms of throughput, whether the coating takes place without contact or by Druckpenetration in a so-called contacting application device. However, it combines with the non-contact coating further advantages compared to the contact coating, see in particular the introduction to the description of the two abovementioned publications DE 102 28 134 A1 and DE 102 28 117 A1 ,

In practice, however, in the case of on-line coating, in particular in contactless on-line coating, problems have repeatedly arisen with regard to coating quality, the reason of which could not be established. So Irregular defects and separation phenomena occurred in the coating, the cause of which was unknown.

Reference is still made to DE A1. It discloses a curtain application method for applying liquid to pasty application medium to a material web of paper or cardboard. The application medium used has a temperature between 20 ° C and 60 ° C.

In addition, on the WO A1 97/29238 referring to feeding starch to a suspension of paper fibers. The resulting suspension is degassed and then heated to 150 ° F = 66 ° C, to be subsequently cast on a screen such as a free-falling curtain to form the web.

The invention is therefore based on the object to represent a method for simultaneous coating of a paper, cardboard or other fibrous web, that is with a coating in the so-called on-line method, which avoids the problems mentioned above or at least mitigates.

The object of the invention is achieved by a method having the features of claim 1. The subclaims describe advantageous and particularly expedient embodiments of the invention.

In the known coating devices or coating methods, in particular in the so-called non-contact coating of fibrous webs has been taken with additional measures to ensure that the temperature of the application medium at least at the point of his immediate job on the fibrous web, especially when applying a coating color to a paper or Board web, at or below 25 degrees Celsius (° C). For example, the so-called curtain coater installations, that is to say coating devices which apply the application medium in a free application medium curtain directly or indirectly to the fibrous web, are always arranged in an air-conditioned space in order to reliably keep the application medium temperature below 25 ° C. (The climate chamber should also protect the coating medium curtain from unwanted air boundary layer influences.)

Background of these measures, even in the known contacting coating devices, is the necessary degassing of the coating medium before coating.

The degassing of the application medium, in particular the coating color, is usually carried out by vacuum degasser, which are upstream of the coating device in the conveying direction of the application medium. The process conditions in the vacuum degassers are chosen so that the application medium, in particular the coating color, does not boil in the degasser or in the vicinity of the boiling range. The coating color temperatures used are 18 ° C to a maximum of 25 ° C. The pressures in such vacuum degassers conventionally range from 30 to 80 millibar (mbar). The boiling temperature is determined by the vapor pressure curve of the solvent, in the case of coating colors water. A boiling of the coating color should therefore be avoided because it has been assumed that the water vapor emerging from the coating color reduces the vacuum in the degasser and thus leads to a poorer deaeration result.

However, the inventors of the present invention have recognized that the hitherto predetermined low coating temperature of 25 ° C. or below in on-line coating is the cause of the above-mentioned problems. Thus, at the time of its coating, the fibrous web, due to previous treatments, has a temperature of at least 30 ° C, e.g. B. after predrying usually in the range of 60 ° C to 100 ° C, in exceptional cases, on. The application of the comparatively cold application medium, in particular the maximum of 25 ° C warm coating color, led to the said defects.

The invention therefore proposes applying the application medium to the fibrous web at a temperature of at least 30 ° C.

If the fibrous web in the region of the direct application of the application medium, that is in the direction of movement of the fibrous web at the point at which the order is carried out, a temperature of at least 40 ° C, in particular from 60 ° C to 100 ° C or more adjust the temperature of the application medium at the point of its immediate application and / or at the point of exit from the dispensing nozzle such that the application medium, the temperature of which is generally below the temperature of the fibrous web, has a temperature which deviates a maximum of 40 Kelvin (K) from the temperature of the fibrous web. Particularly advantageously, the temperature difference is limited to 30 K, 20 K or 10 K. For example, the application medium at the point of its immediate application to the fibrous web have a temperature in the range of 40 ° C to 70 ° C, in particular in the range of 50 ° C to 70 ° C.

bestimmt werden.According to the invention, the temperature of the fibrous web according to the following formula: $${\mathrm{T}}_{\mathrm{train}}\mathrm{-}{\mathrm{T}}_{\mathrm{application\; medium}}=<{\mathrm{T}}_{\mathrm{train}}\mathrm{/}\mathrm{1}\mathrm{.}\mathrm{5}$$

be determined.

In particular, in the manufacture and on-line coating of a paper or board web, the application medium is an aqueous pigment suspension, starch or a coating color.

The coating device has, for example, at least one delivery nozzle for the application medium, by means of which the application medium is applied either indirectly via the surface of a transfer element, in particular a transfer roller, or directly on at least one side of the moving fibrous web "online". The application nozzle is part of a non-contact coating device, that is designed and arranged at a distance from the surface of the transmission element or the at least one side of the moving fibrous web to be coated, that it applies the application medium in at least one free coating medium curtain. The application is advantageously carried out by gravity or alternatively or additionally by applied to the application medium jet forces, for example by pressurization or acceleration of the application medium in the dispensing nozzle. In terms of gravity in the context of the present invention means in particular that the application medium between the nozzle (or the nozzles) and the current background, that is either the fibrous web or the Transmission element is guided or guided over at least a partial route by no mechanical components, but moves freely. In a purely gravity-related non-contact coating, the application medium thus moves at least on a partial section in "free fall". However, additional forces can be applied by force fields, for example by electrostatics, hydrostatics or hydrodynamics, on the application medium, which overlap with gravity.

An example of a non-contact coating device is the so-called curtain coater, that is to say a curtain coating plant, in which the application medium forms a closed curtain over at least part of its length.
In particular, the application medium overcomes the entire distance between the at least one dispensing nozzle and the surface of either the transfer member or the traveling fibrous web in a free form through said free application media curtain.

The application medium advantageously has a comparatively high solids content, for example in the range of 60-80%, in particular in the range of 65-72%, preferably more than 68%. As a result, the energy required for the subsequent drying of the coating can be reduced. In the conventional contacting coating applications, the maximum solids content has been regularly limited to below 50 to 65%, otherwise problems with the coating process could occur, for example, a so-called stick-spitting in the film press, overcooking on a blade in a blade coater, or too high a bar-coating. / Rakelanpressdruck resulted. However, the low solids content resulted in an increased energy expenditure in the subsequent drying of the coating.

According to the invention advantageously provided a degasser of the application medium for the on-line coating of the fibrous web, which is carried out in particular with a vacuum degasser. To the optimum Venting or degassing of the application medium, in particular the coating color, a stream of gas bubbles is advantageously generated in the degasser, which moves against the conveying direction of the application medium. This is for example possible because the application medium in the degasser has a temperature of 40 ° C to 60 ° C and in particular an absolute pressure of 0.02 to 0.1 bar, that is, the application medium is advantageously in the vicinity of the boiling range or in boiling range. A decrease in the vacuum can be prevented by a planned correspondingly powerful pump or by multiple vacuum pumps.
In the degasser also the solids content of the application medium is increased, whereby a better coverage of the substrate to be coated or the current fibrous web and a reduction of the later required effort for drying the applied layer is achieved.

The coating medium may, for example, at its entry into the degasser, in particular vacuum degasser, have a temperature of at least 30 ° C., advantageously from 40 ° C. to 60 ° C., in particular a temperature which does not exceed +/- 20 ° C. advantageously +/- 10 K, deviates from the temperature of the application medium immediately in its place of the order on the fibrous web. When the application medium is cooled in the region behind the degasser, for example by free cooling, the temperature of the application medium in the degasser can also be above the stated value or the specified tolerance.

Advantageously, the temperature of the application medium in an integrated into the apparatus for manufacturing and on-line coating of the fibrous web application medium forming device, and in particular in the degasser and the coating device is tuned such that the entire distance between the application medium forming device and the coating device, in particular up to the point of immediate job on the fibrous web, free from forced cooling. Under forced cooling is in the context of the present invention in contrast to a free cooling Such a cooling understood in which with a forced supplied cooling medium flow heat is dissipated from the application medium. By "free cooling" is meant a "natural" cooling, in particular by natural or free convection.

Insofar as the temperature of the application medium in the application medium-forming device or optionally the degasser is lower than the desired coating temperature, a suitable heating device for the application medium, in particular in the conveying direction of the application medium between the application medium forming device and the coating device and / or in the coating device can be provided.
The arrangement of the heating device in front of the degasser is preferred.

In addition to avoiding the problems described above, the invention offers further advantages. Thus, a cooling of the coating color, or generally the application medium, omitted after its production.
The comparatively high temperature of the application medium leads, in particular in combination with the vacuum degasser described, to a high venting efficiency because, during the boiling of the application medium, the vapor formed entrains the gas or air bubbles contained in the medium and is thus discharged. As a result, the total number of degasser can be kept low, which leads to cost savings.

A further cost saving results from an energy saving and by structural savings in the drying section for the drying of the coating layer behind the coating device, because now comparatively high solids contents of the application medium, in particular the coating color are possible.

The high coating color temperature (coating medium temperature) combined with the high fibrous web temperature, in particular paper or board web temperature, also leads to savings in drying both on the energy side and in terms of structural complexity.

Finally, the refrigerated climate chamber, as it has been provided in non-contact coating devices omitted.

Another advantage of the hot coating medium is its better penetration into the fibrous web, whereby the application layer adheres to the fibrous web better than before and thus the quality of the order is improved.

The invention will be explained below with reference to exemplary embodiments.

Figur 1

eine schematische Darstellung einer erfindungsgemäß ausgeführten Vorrichtung zum Herstellen und gleichzeitigen Beschichten einer Faserstoffbahn;

Figur 2

eine alternative Ausführung einer Beschichtungsvorrichtung, wie sie beispielsweise alternativ in der in der Figur 1 gezeigten Vorrichtung verwendet werden kann.

Show it:

FIG. 1

a schematic representation of an inventively executed device for producing and simultaneously coating a fibrous web;

FIG. 2

an alternative embodiment of a coating device, as for example, alternatively in the in the FIG. 1 shown device can be used.

In the FIG. 1 For example, a web forming apparatus 1 for producing a fibrous web 10 can be seen. The web forming apparatus 1 can be, for example, a paper machine which produces a paper web or a board web.

The produced fibrous web 10 runs continuously along a predetermined path, in which case a horizontally rectilinear path is shown for the sake of simplicity. Of course, other tracks, for example, by additional units not shown here, such as a press section and / or a dryer section for the fibrous web and optionally a fibrous web smoothing device possible. Other units are conceivable.

In the coating apparatus 2, the fibrous web 10 is coated with a coating medium 11. According to the FIG. 1 is the coating device 2 in the form of a contactless acting coating device, a so-called curtain coater (curtain applicator) formed. As can be seen, occurs in the coating device 2, the application medium 11 from a discharge nozzle 3 and sets in free fall, ie in a coating medium curtain 11a, the distance between the dispensing nozzle 3 and the fibrous web 10 back before it in a uniform layer 11 b on the Fiber web 10 is applied. Of course, other coating devices can be used, for example, an indirect contacting coating device 2, as shown in the FIG. 2 is shown. The in the FIG. 2 illustrated coating apparatus 2 has two transfer rollers 4, on which the application medium 11 is applied in each case, for example, by one or more dispensing nozzles 3 (not shown). From the transfer rollers 4, the application medium 11 is then applied to the fibrous web 10 by a pressure effect. For the application of the application medium 11 initially on a (single-sided order) or on both transmission elements (with intended double-sided order) again contactless coating devices can be used, for example, the here for direct order on the fibrous web devices mentioned.

The coating medium 2 applied to the fibrous web 10 application medium 11, in particular a coating color, for example, may have a temperature of 50 ° C and a solids content of 70%. The fibrous web 10, in particular the paper or board web, may, for example, have a temperature of 60 ° C. to 100 ° C. at the location of the job. One of the advantages of the stated selected temperatures is that the drying distance for the application layer 11 b behind the coating device 2, which is not shown here, can be smaller and / or a lower energy consumption is required.

How to get in the FIG. 1 can recognize the application medium 11, in particular a coating color produced in a Auftragmediumbildungsvorrichtung 6 or put together from different components, mixed and then fed to a degasser 5, in which the application medium 11 brought by a suitably selected combination of pressure and temperature to boiling becomes. As a result, gas bubbles rise in the application medium 11 upwards against the conveying direction of the application medium 11, which leads to an optimized degassing of the application medium 11. Subsequently, the application medium 11 is fed to the coating device 2.

From the production in the application medium forming device 6 to the application to the fibrous web 10, the temperature of the application medium 11 can be kept constant or substantially constant. For example, the temperature of a coating by its production in the application medium forming device 6 in the range of 50 ° C (especially 40 ° C to 60 ° C) or is exactly 50 ° C and is then introduced into the degasser 5 at this temperature. By suitable insulation or heating of the degasifier 5 can be avoided that the application medium 11 cools in this, so that the temperature of the application medium 11 at the exit from the degasser 5 still in the range of 50 ° C (for example, a range of 40 ° C to 60 ° C) or to exactly 50 ° C. Subsequently, the application medium 11 is passed without cooling in the coating device 2 and applied to the fibrous web 10 at the same temperature.

Insofar as an unwanted cooling occurs between the application medium forming device 6 and the degasser 5 or the degasser 5 and the coating device 2 or in the coating device 2, an additional heating device 7 may be provided.
In the FIG. 1 For example, such a heater 7 is provided between the application medium forming device 6 and the degasser 5. In addition or in alternation, a device 7 between the degasser 5 and the coating device 2 is shown with dashed lines.

It should be added that in the FIG. 1 for clarity, existing inlet and discharge pumps, as filters and pulsation dampers are not shown.

Claims (7)

1. Method for producing and simultaneously coating a paper, board or other fibrous web (10), comprising the following steps:

   in a web forming apparatus (1), a continuous paper, board or other fibrous web (10) moving along a predefined web path is produced,

   the fibrous web (10) is fed to a coating apparatus (2) arranged downstream in the direction of movement of the said web and arranged along the predefined web path, a liquid or pasty application medium (11) being applied on-line to the fibrous web (10) by the coating apparatus (2), at least to one side of the moving fibrous web (10),

   - the application medium (11) being applied to the at least one side of the moving fibrous web (10) by means of a discharge nozzle (3) of the coating apparatus (2) indirectly via the surface of a transfer element, in particular at least one transfer roll (4), or directly,

   - the application medium (11) being an aqueous pigment suspension, starch or coating colour,

   - the application medium (11) being applied to the moving fibrous web (10) by means of discharge nozzle (3) with a single-layer or multilayer application medium curtain (11a), in particular under the force of gravity and/or by means of forces applied to the application medium (11) or the curtain (11a),

   characterized in that

   - at the point of the direct application and/or at the point of the emergence from the discharge nozzle (3), the application medium has a temperature of at least 30°C, or the application medium (11) is applied to the fibrous web (10) at a temperature in the range from 40°C to 70°C, in particular in the range from 50°C to 70°C, and the fibrous web (10) is produced in a web forming apparatus (1) or is treated along the web path in such a way that, in the area of the direct application of the application medium (11), it reaches a temperature of at least 40°C, in particular 60°C to 100°C or more,

   - the application medium (11), in particular the coating colour, before it is supplied to the coating apparatus (2), is de-aerated in a de-aerator, in particular a vacuum de-aerator (5), the application medium (11) in the de-aerator having a temperature, in particular being led into the de-aerator at a temperature, which corresponds to the temperature of the application medium (11) at the point of its direct application to the fibrous web (10) with a tolerance of +/- 20 K, in particular of +/- 10 K, or which lies above it.
2. Method according to Claim 1,
   characterized in that
   the application medium (11) is applied to the fibrous web (10) at a temperature which is at most or exactly 40 K below the temperature of the fibrous web (10) in the area of the application, in particular at most or exactly 30 K, 20 K or 10 K below.
3. Method according to Claim 1 or 2,
   characterized in that
   the temperature of the fibrous web can be determined in accordance with the following formula: $${\mathrm{T}}_{\mathrm{web}}\mathrm{-}{\mathrm{T}}_{\mathrm{application\; medium}}\le {\mathrm{T}}_{\mathrm{web}}\mathrm{/}\mathrm{1.5.}$$

   
4. Method according to one of Claims 1 to 3,
   characterized in that
   the application medium (11), in particular the coating colour, has a solids content of 60 to 80%, in particular of 65 to 72%.
5. Method according to Claim 1,
   characterized in that
   the solids content of the application medium (11) is increased in the de-aerator (5).
6. Method according to one of Claims 1 to 5,
   characterized in that
   the application medium (11) is produced or mixed together in an application medium forming apparatus (6) and supplied to the coating apparatus (2) in a manner free of forced cooling and is conveyed as far as the fibrous web (10).
7. Method according to Claim 6,
   characterized in that
   after its emergence from the application medium forming apparatus (6) and/or in the coating apparatus (2), the application medium (11) is heated by an additional heating device (7).

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