CA2255656A1

CA2255656A1 - Method and device for coating a continuous strip of material, specially paper or cardboard, with a liquid or paste-like application medium, method for the production of a coated strip

Info

Publication number: CA2255656A1
Application number: CA 2255656
Authority: CA
Inventors: Wilhelm Gansberger; Ingo Gottwald; Harald Hess; Friedrich Kunz; Martin Kustermann
Original assignee: Individual
Current assignee: Voith Sulzer Papiermaschinen GmbH
Priority date: 1997-03-27
Filing date: 1998-03-26
Publication date: 1998-10-08
Also published as: EP0909356A1; JP2000511604A; WO1998044201A1

Abstract

The invention relates to a method and a device for coating a continuous strip of material (B), specially paper or cardboard, with a liquid or paste-like application medium. Said pre-dosed application medium is applied (at 240) directly or indirectly to the material strip (B), whereupon final dosing according to the desired weight of application and/or equalization (at 255) is carried out. Final dosing and/or equalization occurs only after a minimum time period (tmin) starting from pre-dosing in order to guarantee the formation of a coating of immobilized solids on the material surface in the application medium. Additionally or alternately, the immobilization of solids can be actively accelerated (by 278, 280, 282, 284). Another aspect of the invention provides for final dosing only after a maximum time period (tmax).

Description

CA 022~6~6 1998-11-20 Method and device for coating a moving web of material, in particular made of paper or cardboard, with a liquid or pasty coating medium, Method for producing a coated web of material Descri,.tion This invention relates to a method for the coating of a moving web of material, in particular made of paper or cardboard, with liquid or pasty coating medium, said coating medium being directly or indirectly applied on the web of material in a previously metered manner and subsequently finally metered to the desired coating weight or/and levelled.

The terms "paper" and "cardboard" refer to all webs of material with orwithout a portion of used paper containing wood-containing or wood-free, bleached or unbleached fibers or any other fibers. Apart from their application these webs of paper primarily differ in their mass per unit area. It can be dealt, for instance, with writing paper, drawing paper, printing paper or fine paper or the like, with packaging paper or even with cardboard.

In many applications at least the front side, but partly also the back side is to be provided with characteristic overprints or design patterns. The web of material has to provide a high-quality ground. In practice, however, every now and then the coating medium gives rise to problems regarding the quality of covering the surface of the web of material.

To obtain good coverage of the web of material it is necessary that thecoating medium, when it is applied, is not only deposited on the peaks of the "mountain and valley" structure of the rough construction of the fibrous material, but also penetrates into the "valleys", thus following the contour of the web of material substantially over its entire surface.

Hitherto is has been supposed that such a nature of the contour coat of the CA 022~6~6 1998-11-20 coating and thus the desired good coverage of the web of material can only be obtained by finally metering the coating medium by means of an air knife or an air brush, i.e. a doctor device which blows away the excessive coating medium from the web of material by means of compressed air. However, the following drawbacks had to be accepted:
- maximum speed of the web of material 400 m/min;
- maximum working width approximately 7.0 m;
- the solids content of the coating medium must not exceed 40 %, which results in an increased expense during the drying process;
- high tendency to contaminations, in particular due to the formation of aerosol or/and foam;
- high noise level;
- high investment and operating costs.

From the W0 96/28609 there is known a coated cardboard which is used for the production of shaped pieces made of cardboard, such as milk cardboard boxes. The cardboard is made of one or several layers of fibrous material and is coated with respect to the printing of its surface. After the coating and optionally even before the coating the cardboard is additionally smoothed, by means of a heatable or non-heatable calander which can comprise a hard as well as a soft nip. Details on coating the cardboard are not disclosed.

It is an object of the invention to indicate a method according to the above manner which allows to obtain good coverage of the web of material even at a high speed of the web, large working width and high solids content of the coating medium.

According to a first aspect of the invention the object is solved by means of a generic method in which the coating medium is finally metered or/and levelled at the earliest after a time tmjn which is formularized as follows:
tmin = ko x (k, x CW + k2) x CW2, wherein CA 022~6~6 l998-ll-20 CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, ko denotes a first constant the value of which amounts to at least 1, preferably at least 1.5, k, denotes a second constant the value of which amounts to -O . 03603 x 1 o-5 m6min/g3, and k2 denotes a third constant the value of which amounts to 206 x 1 O-5 m4min/92 In accordance with the invention the coating medium is given a predetermined minimum time to react with the web of material. During this time a part of the solids contained in the coating medium is immobilized on the surface of the web of material. On the one hand, a part of the moisture contained in the coating medium is absorbed by the web of material. Furthermore the capillary forces exerted on the coating medium by the web of material have the effect that the coating medium is also sucked into the valleys of the structure of the fibrous material. Both effects, when taken together, result in a uniform and good coverage of the surface of the web of material. The subsequent final metering preferably does not engage with the portion of the contour coat formed by the immobilized coating medium but meters and levels that part of the coating medium Iying above said contour and which is still liquid and/or pasty and thus not yet immobilized.

The immobilization of a part of the coating medium can thus be further intensified in that the value of said first constant ko amounts to at least 2, preferably at least 3, even more preferred at least 4.

To obtain a coating result as good as possible and in particular a covering degree as good as possible it is furthermore proposed in accordance with the invention that said time t between previous metering and final metering is adjustable. The location of the previous metering or/and the location of the final metering can be alterable in the running direction of the web of material.

CA 022~6~6 1998-11-20 Favourably at least one property of the finally metered coating medium layer, e.g. the above-mentioned covering degree, can be detected by means of a sensor device and the time between previous metering and final metering is adjusted in dependence of the detected result. It goes without saying that in adjusting other parameters of the finally metered coating medium layer, such as smoothness, gloss, withness and the like, can additionally or alternatively be taken into account.

The covering degree or/and the other parameters mentioned above can be detected at the still damp coating medium layer or/and during the drying process or/and the dried coating medium layer. Furthermore detection can also take place at the bobbin carriage.

When sufficiently dimensioning the diameter of a supporting roller, which is wrapped by the web of material at least at a part of its circumference, previous metering as well as final metering can take place in a circumferential section of the supporting member, which is wrapped by the web of material.
The time when the diameter of the supporting roller is "sufficiently"
dimensioned, obviously depends on the speed of the web and other similar operating parameters. In order to prepare the minimum dwell time in accordance with the invention the web of material can be led around a supporting member, preferably a supporting roller, in the previous metering portion and led around a further supporting member, preferably a further supporting roller, in the final metering portion.

In both alternatives discussed above the web of material can be deviated between previous metering and final metering by at least an intermediate guide member, preferably at least one guide roll. In the case of the first alternativethe web of material is thus, after previous metering, led away by the supporting roller, runs around the intermediate guide member and then back to the supporting roller, where final metering takes place. Thus, even in the case of supporting rollers with a relative small diameter previous metering and ... .. .... . .

CA 022~6~6 1998-11-20 final metering can be carried out on one and the same supporting roller.

According to a further aspect the above-referenced object is solved in that the immobilization of the medium applied on the web of material during the movement thereof from the previous metering to the final metering is actively accelerated. It can be attended to the fact that an immobilized layer of solids contained in the coating medium is formed on the surface of the web of material, which covers the surface of web of material evenly and well.

The formation of the immobilized layer can for instance be actively influenced in that the applied layer is heated or/and dried. But the web of material can also be heated which, in turn, indirectly heats the coated layer.

For heating purposes the applied layer or/and the web of material can be irradiated for example with infrared light or/and microwaves. Additionally or alternatively heated air or/and vapour can be supplied to the applied layer or/and the web of material. Eventually it is also possible to heat the web of material with z convective heating device or bring it into contact with at leasta heatable member, preferably a heatable roller or a heatable belt.

This latter possibility of heating the web of material or/and the coating mediumlayer can be realized in that a supporting member, preferably a supporting roller, around which the web of material is led in the previous metering portion, is heated. Additionally or alternatively a web guide or/and treatment member, preferably a roller, which is provided between previous metering and final metering, can be heated.

A further possibility to actively accelerate the immobilization process is to apply a partial vacuum on the web of material from the side opposite to the coating side. In this case, for instance a supporting member, preferably a supporting roller, around which the web of material is led in the portion of theposition, can be equipped with a suction device. It is also possible that CA 022~6~6 1998-11-20 between previous metering and final metering there is provided a web guide or/and treatment member equipped with at least a suction device, preferably a guide roll having a suction box.

Additionally or alternatively to the above-discussed solution of applying a partial vacuum, it can also be possible that excess pressure is applied on the web of maerial from the coating side.

To accelerate the immobilization of the coating medium the web of material and/or the applied layer can be exposed to vibrations, for instance in irradiating the web of material or/and the applied layer with ultrasound or/and in that the web of material or/and the applied layer is brought into contact with an oscillating device, preferably operable in a high-frequency manner.

To obtain the desired quality of the coating medium layer the intensity of actively influencing the immobilization of the applied layer can be adjustable at the web of material, for instance in dependence of the detected result of at least one parameter of the finally metered coating medium layer. Again, the covering quality of the coating medium layer, its smoothness, its gloss, its whiteness and the like can be used to determine the respectively necessary influencing intensity.

The coating medium can be finally metered by means of a smooth doctor bar as well as by means of a profiled doctor bar as well as by means of a doctor blade. A "profiled" doctor bar is understood to be a perforated, etched, engraved, grooved or wire-framed doctor bar. In tests it has turned out that a contour coat effect can primarily be attained by volumetric metering with a profiled doctor bar as a doctor member.

In order to avoid profiled grooves when using a grooved doctor bar on the coated web of material, it can be advantageous to reduce the solids content of the coating medium with respect to the usual value (coating with roll coater CA 022~6~6 l998-ll-20 and subsequently with a doctor blade), so that the coating medium can creep again after wiping off. In other words the coating medium should be so liquid that the groove generated can creep again after metering and levelling.

When using a smooth doctor bar the above-described contour coat effect is present only to a small extent when metering. But due to the scoop effect of the smooth bar satisfying results, however, are achievable in particular in the valleys of the web. In this case the coating medium can be more viscous and does not have to be as liquid as in the case of a profiled doctor bar since there is no danger of groove formation.

According to a further aspect the above-identified object is solved in that the the coating medium is finally metered or/and levelled at the latest after a timetmaX which is formularized as follows:
tmaX = A (CW/K)2 - A' wherein CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, K denotes the solids content of the coating medium in %, A denotes a first constant the value of which, in the case of the profiled doctor bar amounts to 9.28 m4%2sg~2 and in the case of the smooth doctor bar as well as the doctor blade amounts to 1 8 . 86 m4%2sg~2, A' denotes a second constant the value of which, in the case of the profiled doctor bar amounts to 21.4 x 1 O-3 S and in the case of the smooth doctor bar as well as the doctor blade amounts to 24.0 x 1O-3 S, and wherein the formula only applies to CW/K 2~/~7~.
This particularly guarantees that the doctor member exclusively moves in the still liquid and/or pasty part of the coating medium layer and does not engage with the already immobilized solids. Thus, defects of the coat can be avoided .. . . . .

CA 022~6~6 1998-11-20 and a good coverage of the surface of the web of material is guaranteed.
Another advantage is that in the portion of the doctor member there is an enhanced rinsing effect. Particles or deposits dissolving from the paper or the cardboard can thus be withdrawn.

Preferably final metering or/and levelling is carried out after a time t, said time t being 0.1 tmaX ~ t ~ 0.8 tmaX, preferably 0.1 tmaX S t ~ 0.5 tmaX.

To further improve the quality of the coated web of material it is proposed to apply a plurality of coating layers onto the web of material. For instance, the upper side, often also called covering side, can be coated a second time after the drying process and, if necessary, a previous smoothing process. In most cases, however, a precoat, a mid coat and a finishing coat are applied on the web of material to obtain good coverage.

The individual coats can for example be applied by means of a roll coater. Roll coaters belong to the group of LDTAs and comprise a scoop roller, which scoops out the coating medium from a storage bin. In accordance with the invention also other types of applicators can be used, which will be more explicitly described in the following.

After the respective coating the excessive coating medium is wiped off the web of material. In the case of the precoat a doctor blade or a smooth doctor bar is used. The wiping off serves the purpose of planing the surface in the micro as well as the fiber flock range.

For the second coat, the mid coat, usually a higher coating weight is applied than for the precoat. According to prior art the excessive coating medium was wiped off by means of an air knife or an air brush to obtain good coverage of the surface of the web of material. Now, in the method in accordance with the invention, a doctor blade, a smooth or a profiled doctor bar can be used.

..

CA 022~6~6 1998-11-20 Finally, the finishing coat can be applied with a somewhat lower coating weight than the mid coat, approximately corresponding to the upper limit of the coating weight of the precoat. The excessive medium is removed by means of a doctor blade as it provides for a better smoothness of the coated layer.

In accordance with the invention it is also possible, for example, to wipe off and/or meter the precoat and the mid coat by means of a smooth or profiled doctor bar and the remaining coat(s) by means of a doctor blade. However, it is also possible to wipe off and/or meter all applied coats by means of a doctorbar.

It is particularly favourable when the previous metering, i.e. the excessive coat, is carried out in at least one of the coats with a jetflow applicator (i.e.
a jet applicator having a fountain and/or jetflow acting on the web). In jetflowapplication the pressure penetration is smaller - almost negligible - than for example in roll coating. Thus, in jetflow application the coat is deposited closer to the surface of the web of material whereas in roll coating, which exhibits a considerable higher penetration pressure in the nip between applicator and counter roller, the coating medium penetration and absorption varies due to the given base paper formation in the paper plane. Therefore the nature of the contour coat of the portion of the coat, which is immobilized up to the doctor member, is weaker than in the jetflow applicator.

In jetflow application the liquid portion of the medium applied to the surface of the web of material, which contributes to the coating weight, is higher than in roll coating, which facilitates the use of the doctor bars for metering. Thusdoctor streaks are largely avoided. Furthermore due the a low extent of fiber swelling and re-roughening in the paper or cardboard better smoothness values can be obtained.

Moreover the thickness of the coating medium is lower so that higher solids .... . ..

CA 022~6~6 1998-11-20 contents of the coating medium can be used for operation which is advantageous for a good coverage of the surface of the web of material. This results in a more compact coat having higher gloss and smoothness. A further advantage can be seen in the fact that the drying device requires less drying power.

SDTA-applicators can also be used as applicators. In these kind of applicators the coating medium can act on the web of material only a relative short period of time until it is metered by means of a doctor member. Eventually the coating medium can be applied on the surface of the web of material by means of the film coating process.

The method in accordance with the invention shows the above discussed advantages independently of the respective structure of the base paper supplied to the coating station, i.e. independently of the way it was manufactured in the wet portion of the paper machine. The paper and/or cardboard can be produced in a single-ply or multi-ply or even in a single-layered or multi-layered manner, i.e. it can be worked with one or a plurality of headboxes and sieves or even with a primary headbox and optionally several secondary headboxes or even corresponding combinations thereof. The base paper can at least be bulk-glued in one of the layers and/or plies, or starch was already contained in the raw material.

Depending on the requirements set for the covering quality of the coated web of material there can be provided in accordance with the invention that at any desired location within the paper machine impregnating agent or/and solidifying agent such as starch, synthetic glue with or without pigments is applied on the surface of one or both sides of the web of material in addition to the coating process. This impregnating and/or sealing agent coat can serve to prepare the applied layer for the coating process or/and the subsequent treatment process.

CA 022~6~6 1998-11-20 The treatment with impregnating and/or solidifying agent can for instance take place in the sieve portion or/and between sieve portion and press portion or/and in the press portion or/and between press portion and dry portion or/and after the dry portion with or without subsequent drying or/and in front of the bobbin carriage. In the case of multiple coating the treatment can also be carried out between successive partial coatings.

In a further embodiment of the invention the web of material can also be smoothed before or after the coating and/or between successive partial coatings. A previous smoothing even before applying the coating and/or the first partial coating, i.e. the precoat, is of advantage. Subsequent smoothing is particularly advantageous when very high smoothness and gloss values are to be obtained. To further improve the quality smoothing can also be carried out between the individual partial coatings.

Smoothing can be carried out with hard nips, soft nips or with an extended nip. It is advantageous for high smoothness and gloss values when at least one of the two smoothing surfaces forming the respective nip is heatable.

Smoothing devices as such are known. For instance, they comprise at least two counteracting smoothing surfaces, for example roller surfaces, between which the web of material is subjected to a smoothing treatment. Extended nip smoothing devices, for example shoe smoothing devices or roll smoothing devices having a large roller diameter, which have a longer nip, are also known. This increases the dwell time of the web in the nip resulting in an enhanced smoothness. Extended nip smoothing devices can be used with advantage in previous smoothing as well as in subsequent smoothing process.

Nip combinations made of hard rollers, soft rollers or hard and soft rollers canbe used. Further such nip combinations can be arranged in series. For example, a device having two separate nips with a heatable hard and a soft roller each is also possible. The above mentioned combinations shall not limit .. .. . .

CA 022~6~6 1998-11-20 the scope of protection. It is rather that even more combinations are conceivable, in particular devices having three or more rollers per unit.

A water scraper smoothing device may also be used as a previous smoothing device. Finally it is possible to smooth the coating medium layer by means of a blowing device.

In particular in the case of previous smoothing it can be of advantage when the web of material is damped with water or vapour before it is smoothed to obtain even better smoothing results, for example planing of the surface and at the same time protecting the volume.

The coating medium can have a viscosity of c 500 mPas, preferably 30 mPas to 250 mPas, when using a profiled doctor bar, a viscosity of ' 2500 mPas, preferably 300 mPas to 1000 mPas, when using a smooth doctor bar, and a viscosity of < 4000 mPas, preferably 300 mPas to 1500 mPas, when using a doctor blade, wherein each of said viscosity values are to be determined according to Brookfield 100. Furthermore the coating medium can contain 4 to 20 (or 25) parts of binding agents per 100 parts of pigments, wherein at least partly plastics binding agent or/and starch are present. Often the coatingmedium - partly also the finishing coat- contains titanium dioxide (TiO2), as this pigment has a positive effect on the obtainable coverage and the obtainable whiteness.

In multiple coating at least two of the coating layers can be formed of a coating medium having a different composition. However, it is also possible that at least two of the coating layers are formed of coating medium having the same composition.

At least one of the coating layers can be formed of a coating medium having a solids content which is at least 2 % to 5 % lower than that of at least one other coating layer, said solids content of said at least one other coating layer . , ., . ~ . , CA 022~6~6 1998-11-20 amounts to approximately 50 % to 73 %.

To obtain a covering quality as high as possible or/and a coating result as good as possible it is proposed that the composition or/and the temperature of the coating medium or/and the temperature of the web of material is adjusted, for example in detecting at least one property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like and in adjusting the composition or/and the temperature of the coating medium or/and the temperature of the web of material in dependence of the detected result.

According to further aspects the invention relates to various devices for coating a moving web of material, in particular made of paper or cardboard, with a liquid or pasty coating medium. Details and advantages of these devices were already explained in the above discussion of the methods in accordance with the invention. At this point particular reference is made to thebefore-mentioned discussion.

The advantages of the method and/or methods in accordance with the invention, as well as the device and/or devices in accordance with the invention can be seen in the following: Depending on the case lower coating weights can be obtained. The operation can be carried out with higher solids contents of the coating medium. Depending on the case the TiO2-content in the coating medium can be reduced. The webs of material can be coated at higher running speeds of the webs of above 600 m/min over larger working widths.

Tests have shown that the method in accordance with the invention leads to a satisfying covering quality already with an applied coat of 9 g/m2. When applying a coat of 15 g/m2 a covering quality could be obtained which even exceeded the covering quality of a coating which, with a comparable coating weight, had been finally metered by means of an air knife according to a ....

CA 022~6~6 l998-ll-20 method of the art.

According to a further aspect the invention relates to a method for producing a coated web of material, in particular made of paper or cardboard according to the preamble of the claims 82 and 85.

The terms "paper" and "cardboard" refer to all grades containing wood-containing and wood-free, bleached or unbleached fibers, and any other fibers, also to all grades containing used paper and those not containing used paper.
It can be dealt, for instance, with paper in general, packaging paper or, as hasalready been mentioned, with cardboard, wherein these grades not only differ in their application but particularly also in their mass per unit area.

In all these grades problems arise concerning the covering quality on at least one side lin most cases on the upper side, partly also on the back side), when they are coated.

As a rule the coated side is to be provided with distinguishing overprints or design patterns. In this case the coated side has to offer a good basis.

However, there are no satisfying solutions yet.

From the W0 96/28609 there is known a coated cardboard for shaped articles such as milk boxes.

From said laid-open print it can be seen that the cardboard has one or several layers of fibrous material and the surface of the cardboard, in order to be suitable for printing, is coated and subsequently smoothed, alternatively even before the coating process.

The surface is smoothed with a heatable or non-heatable calander having a hard or a soft nip.

,, . ., . . ... , ~

CA 022~6~6 1998-11-20 Details on the coating of the cardboard are not disclosed.

Hitherto in practice the upper side, often also called covering side, of cardboard has been coated at least twice after a drying and, if necessary, a previous smoothing process. In most cases, however, it has been coated three times, i.e. with a precoat, a mid coat and a finishing coat, in order to obtain a good coverage.

Primarily roll coaters and air knife units, belonging to the group of LDTAs, were used for the individual coats.

In roll coaters one scoop roller was used respectively, which scoops out the coating medium from a storage bin. After the respective coating process excessive medium was wiped off the web. In the case of the precoat it was wiped off by means of a blade or a smooth doctor bar. It serves the purpose of planing the surface in the micro as well as in the fiber flock range.

In the case of the second coat (mid coat), which was usually applied with a higher coating weight than the first precoat, the excess medium was blown away with an air knife or an air brush. In this case good coverage of the web of fibrous material was obtained (which is an advantage of the air knife coating process), but the following disadvantages also had to be put up with:

- speed limit of the web approx. 400 m/min - limit of the working width up to approx. 7.0 m dependent on the production, limit of the solids contents of the coating medium of approx. 40 %
dependent on the production, which required higher expense of the drying of the coat.

In the case of the third coat, i.e. the finishing coat, in most cases a somewhatlower coating weight than in the case of the mid coat was applied (almost CA 022~6~6 1998-11-20 corresponding to the upper limit of the first coat). The excessive medium was wiped off by means of a doctor blade because a better smoothness can be obtained. In some cases the last coat was also effected as an air knife coat.

Hitherto is has been supposed that only a coat levelled by means of an air knife shows the best results with respect to coverage, and therefore the above-mentioned disadvantages were accepted.

The corresponding coat (i.e. the coating medium) - partly also the finishing coat - often contains titanium dioxide (TiO2) in order to further contribute to coverage and whiteness by this pigment.

It is an object of the invention to develop a method which enables the production of coated papers. In this process higher web speeds, larger web widths and higher solids contents of the coating medium are possible and nevertheless coverage, gloss and smoothness are the same or even better as has hitherto been the case.

In accordance with the invention the object is solved by means of the characterizing features of claim 82 and the subordinated claim 85.

Appropriate embodiments of the method in accordance with the invention arise from the dependent claims 83, 84 and 86 to 102.

It was found that the desired properties of the paper or the cardboard may be obtained with a first method when the coat, i.e. the coat guaranteeing the coverage e.g. pre- and/or mid coat, is not metered, as is the case in prior art,with an air knife or air brush coating unit having inevitably a lower speed, butrather by means of a smooth or profiled (e.g. perforated, etched, engraved, grooved or wire-framed) doctor bar. In this case lower coating weights are sufficient and nevertheless higher web speeds, higher solids contents of the coating colour and even lower portions of TiO2 are obtainable.

CA 022~6~6 1998-11-20 It has shown that a contour coat effect can primarily be obtained by volumetric metering with the profiled doctor bar as a doctor member.

Contour coat means that the coating medium follows the contours, i.e. the mountains and valleys of the web of fibrous material, so that the contour of the paper or cardboard web is covered completely and uniformely.

Until it reaches the doctor member only so much of the offered coating medium is immobilized that on the portion of the immobilized coat as much liquid coating colour contributing to the desired coating weight is present as is necessary to enable the above-mentioned effect.

In order to prevent profile grooves from forming on the coated web whenusing the grooved doctor bar, it can be of advantage to reduce the solids content of the coating medium with respect to the usual value (coating with roll coater and subsequent doctor blade) so that the coating medium can creep again after wiping off (metering).

In other words the portion of liquid colour is correspondingly high and the coating medium (coating colour) is still so liquid that the generated grooves can creep smoothly after levelling (metering, wiping off).

When using a smooth doctor bar the above-described contour effect is only present to a lower extent when metering. However, satisfying results can be attained in particular in the valleys of the web due to the scoop effect of the smooth bar.

In this case the coating medium can be somewhat more viscous and does not have to be so liquid as in the case of the profiled doctor bar since there is nodanger of forming grooves.

In the portion of the smooth or profiled doctor bar sufficient liquid medium is CA 022~6~6 l998-ll-20 present. Therefore the doctor bar does not wipe off in the range of solid coats.
A further advantage can be seen in the fact that a better rinsing effect is present in this portion. By means of said rinsing effect particles or deposits dissolving from the paper or cardboard can be withdrawn.

In accordance with the invention it is possible to wipe off and/or meter for example the pre- and mid coat by means of a smooth or profiled doctor bar and the remaining coat/s by means of a doctor blade.

It is also possible to wipe off and/or meter all applied coats by means of the doctor bar.

It was found that the good covering quality is obtainable when wiping off and/or metering is carried out within a time t since the medium has been transferred to the web. Said time equals to or is smaller than a time to.
~mpirically to is formularized as follows:
to = A (CW/K)2- A' Wherein A = 9.28 m4%2sg~2 and A' = 21 .4 x 1 O-3 S in the case of a profiled doctor bar and A = 18.86 m4%2sg~2 and A' = 24.0 x 1 O-3 S in the case of a smooth doctor bar, and/or a doctor blade, wherein CW = coating weight and/or applied coat indicated in g/m2 K = solids content of the coating medium in %.

The equation is to be applied for (CW/K) 2 ~/Z~

It turned out favourable when t amounts to < 0.1 to 0.8 to~ in particular, however, < 0.1 to 0.5 to.

CA 022~6~6 1998-11-20 This guarantees that a sufficient amount of applied liquid coating colour remains on the surface of the immobilized layer to obtain another good contour coat effect when metering with a profiled or a smooth doctor bar. Altogether, this results in a good coverage without the danger of forming doctor streaks.
As already mentioned above, this prevents that the doctor members have to engage in the portion of the coating colour layer where the coat has already been immobilized so that coating defects are prevented.

The invention can be formed particularly advantageously when previous metering (excess coating) at least one of the coats by means of a jetflow applicator (jet applicator having a fountain and/or jetflow acting on the web) can cause a first immobilized coat portion having the nature of a contour. In this case the immobilized portion of the coating medium follows the contours of the paper or cardboard web.

In the case of jetflow applicators a lower and almost negligible pressure penetration is present as e.g. in the case of a roll coater, so that the corresponding coat is deposited closer to the surface of the web whereas in the case of roll coaters - due to the considerable higher penetration pressure in the nip between applicator and counter roller - the coating medium penetration and absorption varies due to the given base paper formation of the paper plane. Therefore the nature of the contour coat of the coat portion immobilized up to the doctor member is expressed to a weaker extent than in the case of a jetflow applicator.

In the jetflow applicator the liquid portion of the applied coating medium, contributing to the coating weight, is higher that in roll coaters. Thus the above-described doctor bars can be used advantageously for metering. Doctor streaks are largely prevented. Due to lower fiber swelling and re-roughening in the paper or cardboard better smoothing values are obtainable.

Further a lower thickening of the coating medium can be measured. Thus CA 022~6~6 1998-11-20 higher solids contents of the medium (i.e. coating colour) can be used, resulting in a more compact coat as well as higher gloss and smoothness. A
further advantage is that a lower drying capacity is required.

In an alternative method (acc. to claim 85) there is provided to previously meter at least one coat by means of a jetflow applicator instead of a roll coater, and meter (as a rule final meter) by means of a doctor blade.

When metering by means of a doctor blade the first contour coat effect is provided by the coating medium immobilization; however, the second contour effect is not produced as is provided in the first method acc. to claim 82.
However, a very good levelling effect is obtained. The use of the jetflow applicator considerably favours the nature of the contour coat by uniform immobilization .

In accordance with the invention the methods according to claim 82 and claim 85 distinguish themselves in that metering (wiping off excessive amount of the applied medium to the desired coating weight) can be done without the air knife or air brush known in the art. Thus, all limits of applications connected therewith and described above can be overcome, in particular as units as such cannot keep up with the precision requirements with respect to the widths of the web which are to be produced ever larger.

An additional advantage is that higher solids contents of the coating medium (for an improved coverage of the web) can be used. If air knifes were used the impulse of the escaping air would be too low to be effectively able to wipe off the corresponding amount with high solids content.

In the method of claim 82 and claim 85 the composition of the base paper is irrelevant, i.e. how it was produced in the wet portion of the paper machine.

The paper and/or cardboard can have been produced in a single-ply or multi-CA 022~6~6 1998-11-20 ply (several headboxes and sieves or with one or several secondary headboxes or corresponding combinations thereof) or in a single-layered or multi-layered manner.

The base paper can be bulk-glued in at least one of the layers or plies or contain starch in the material.

Depending on the requirements to be met by the covering quality of the coated web of material, there can be provided in accordance with the invention that at any eligible place within the paper machine impregnating agent and/or solidifying agent (such as starch, synthetic glue with or without pigments) is applied on the surface of one or even both sides of the web in addition to the pigment-containing coat.

This can take place - in the sieve portion and/or between sieve portion and press portion - in the press portion and/or between press portion and dry portion and/or after it with or without subsequent drying and/or before a bobbin carriage as well as before the first pigment-containing applied coat and/or between several pigment-containing coats.

The pigment-containing coat in accordance with the invention is understood to be a coating in which 4 to 20 (or 25) parts per 100 parts pigments of the medium are binding agents and at least portions of plastic binding agents and/or starch are contained. The pigment-containing coat is applied with a relative high coating weight and solids contents. Glueing and/or impregnating is regarded as glueing and/or impregnating with starch and/or synthetic glue.

It is particularly favourable when the web is additionally smoothed.

CA 022~6~6 1998-11-20 As a rule previous smoothing will be carried out even before applying the first pigment-containing coat (precoat).

Subsequent smoothing after applying the finishing coat is especially advantageous when very high smoothness and gloss values are to be obtained.

The smoothing process itself can be carried out by means of hard nips, soft nips or an extended nip.

To obtain high smoothness and gloss values it is advantageous when at least one of the two smoothing surfaces forming the nip is heatable.

To further influence the quality a smoothing process can also be carried out between the individual coating steps.

Smoothing devices as such are known and consist of at least two counteracting smoothing surfaces, e.g. rollers, wherein the web is treated in the nip between the two respective smoothing surfaces.

Nip combinations consisting of hard rollers, hard and soft rollers, or only consisting of soft rollers can be used.

Furthermore such nip combinations can also be arranged in series. For instance, it is conceivable to provide a device having two separate nips with a heatable hard and a soft roller.

The above-mentioned combinations are not intended to limit the scope ofprotection, other combinations, in particular devices having three or more rollers per unit are conceivable. A water scraper smoothing device may also be used as a smoothing device.

CA 022~6~6 1998-11-20 In particular in the case of previous smoothing it can be of advantage when the web surface is damped with water or vapour before it is smoothed to generate better smoothing effects, e.g. planing of the surface and protection of the volume.

It is appropriate to use extended nip smoothing devices, which are known as such, e.g. shoe smoothing devices or large rollers, as smoothing devices, to guarantee a longer nip. This increases the dwell time of the web in the nip, thus providing for a higher smoothing potential. Extended nip smoothing devices may be used for previous as well as for subsequent smoothing processes.

Concludingly the advantages of the inventions (according to claim 82 and 85) can be seen in - depending on the case, lower coating weights - higher solids contents of the coating medium - depending on the case, lower content of TiO2 in the coating medium - speeds of above 600 m/min and larger treatable web widths.

Tests have shown that the method in accordance with the invention leads to satisfying covering qualities already with a coat of 9 g/m2.

In a coat of 15 g/m2 the coverage was even better than in the case of an air knife coat according to prior art, which was applied with a similar coating weight.

In the following, the invention will be illustrated in more detail with reference to the accompanying drawings, in which Figs. 1 to 5 show various embodiments of units for coating a web of material with a precoat, a mid coat and a finishing coat;
and Figs. 6 to 10 show illustrations of various embodiments of individual CA 022~6~6 1998-11-20 devices for coating a web of material, in which the coating medium forms an immobilized layer between previous metering and final metering.

In the following, the invention according to claim 82 will be illustrated by wayof example (fig. 1 and 2):

In a method for producing coated folding box boards the web B is previously smoothed in a calander 5 contiguous to a dry portion not shown in fig. 1.
Then the web B is supplied to a first coating station 30 via guide rollers 20 for applying a precoat (pigment-containing coat) on the side 2, e.g. the lower side of the web B.

The coating station 30 comprises a counter roller 35 supporting the web B. An applicator in the form of a jetflow applicator 40 for directly (directly on the web B) applying the precoat is allocated to the counter roller 35. The excessively applied precoat is then wiped off with a doctor bar 45, in particular a profiled doctor bar which is also allocated to the counter roller 35.

Afterwards the web B is supplied to a second coating station 30' via further guide rollers 20 for applying the mid coat (pigment-containing coat) on the lower side of the web (in a direct manner).

The coating station 35' is constructed analogously to the coating station 30 and comprises a counter roller 35', a jetflow applicator 40' and a doctor bar 45'. The finishing coat (also a pigment-containing coat) is applied in a subsequent third coating station 30'' having a counter roller 35'', a jetflow applicator 40" and a doctor bar 45". The finishing coat is also directly appliedto the web. Then the web B is finally smoothed in a further calander 50. The doctor bars 45' and 45'' are advantageously profiled for volumetric metering.

The doctor bar 45 could also be smooth. A blade could also be CA 022~6~6 1998-11-20 advantageously used instead of the doctor bar 45, as it provides for high gloss and smoothness.

The other web side 3 e.g. the upper side of the web, is coated (also with pigment-containing coat), as is illustrated in fig. 2, in the same order, in a direct manner and with coating stations constructed in the same manner, therefore the same reference numerals are used.

A further possiblility for coating the web 3, apart from the one shown in fig.

2, is to use a device called duocoater 60, 60' and 60''.

Such a duocoater, which is indicated in fig. 1 with a dashed line, is already known from the DE G 9409820.4. The duocoater is an applicator device for indirectly applying the medium onto the other web side (here web side 3). The medium is applied on the exterior surface of the roller 35, 35' and/or 35''. Therotation of the roller transports the applied film to a delivery station where the web to be coated withdraws the film (i.e. the coating medium).

The following example (fig. 3 and 4) illustrates a possible embodiment of the invention according to claim 85.

The web 1, i.e. the web side 2 is treated in the same order as indicated in the first example.

A coating blade 55, 55' and 55" is used instead of the doctor bar 45, 45' and 45''. The rest of the components are the same as shown in fig. 1 and 2 and were thus left out in fig. 4 (treatment of the web side 3) for reasons of clarity.

Even in this example it is possible to also coat the other paper side 3 by means of a duocoater, as is described in fig. 1. In fig. 3 the duocoater is designated with the reference numeral 65, 65', 65''.

CA 022~6~6 1998-11-20 In fig. 1 to 4 the coating processes are illustrated without an intermediate drying. However, this is no limitation. If necessary, there can be provided intermediate drying processes, for example with contact-free drying devices and/or these processes are interconnected in practice.

Fig. 5 shows a further embodiment of a coating unit for coating a web of material with a precoat, a mid coat and a finishing coat. The embodiment of fig. 5 substantially corresponds to the embodiments of fig. 1 and 3. Therefore in fig. 5 the same reference numerals as in fig. 1 and 3, are used for analogous parts, however supplemented by 100. Further the embodiment of fig. 5 is described only in so far as it differs from the embodiment of fig. 1 and 3. Reference is made to the description of these components.

The coating unit 100 according to fig. 5 comprises three coating stations and/or coating devices, i.e. a coating station 130 for applying a precoat, a coating station 130' for applying a mid coat and a coating station 130" for applying a finishing coat.

The incoming web of material B coming from the left side in the illustration according to fig. 5 first of all passes through a smoothing device 105, which in the present embodiment, is formed by two smoothing rollers. However, other kinds of smoothing devices can be used, for instance shoe smoothing devices, having a particularly long nip and/or dwell gap for smoothing the surface ot the web of material. To obtain an improved smoothing effect water or vapour D can be sprayed onto the web of material B before it is smoothed, preferably on its surface 102 to be coated.

In the portion of the first coating station 130 the web of material is led around a counter roller 135 by means of web guide rollers 120. The counter roller 135 is supported rotationally around its axis A in the direction of arrow P. A roll coater 140 is arranged in the portion of the counter roller 135 which scoops out coating medium from a stock of coating medium 142 by means of a scoop .... . . . . ..

CA 022~6~6 1998-11-20 and/or transfer roller 141 and transports it to the surface of the web of material 102. The coating medium is previously metered in the coating gap S
formed between the transfer roller 141 and the counter roller 135. In accordance with the invention a doctor bar 145 is provided in the first coating station 130 for finally metering the coating medium. The doctor bar can be of the smooth type as well as of the profiled type.

The construction of the second coating station 130' for applying the mid coat substantially corresponds to the construction of the first coating station 130 for applying the precoat. In contrast to the first one, however, instead of a roll coater 140 there is provided a jetflow applicator 140' for applying the coating medium in a previously metered manner onto the surface 102 of the web of material B which is led around the counter roller 135'. The applied coating medium is again finally metered by means of a doctor bar 145'.

Even in the third coating station 130" for applying the finishing coat the coating medium is applied onto the web of material B by means of a jetflow applicator 140''. The web of material B is led around the counter roller 135".
Contrary to the pre- and mid coat stations 130 and/or 130', final metering in the finishing coat station is carried out by means of a doctor blade 155'', as the blade provides for a particularly high smoothness of the coating medium layer.

After leaving the third coating station 130'' the web of material B can again pass through a smoothing device 150. Although it is not shown in fig. 5, the web of material can be sprayed with water or vapour in front of the smoothing device 150. Moreover it is possible to heat the smoothing device 150, just like the smoothing device 105, to obtain a better smoothing result.

In the three coating stations 130,130' and 130" the coating medium can be used in different compositions and applied on the web of material with different coating weights. However, it is also possible to use coating medium CA 022~6~6 1998-11-20 having the same composition in at least two of the coating stations.

It has to be added that also the back side 103 of the web of material B can be coated in the coating stations 130, 130' and 130''. In this case, for instance, applicators 160, 160' and 160'' for indirectly applying the coating medium can be used. Such applicators are, for instance, sold by Voith Sulzer Papiermaschinen GmbH under the name "DuoCoater".

It has to be added that the web of material B can be prepared for the coating of coating medium by applying impregnating agent and/or solidifying agent, such as starch, synthetic glue with or without pigments and/or can be subsequently treated after applying the coating medium. This is only schematically shown for the mid coat 130' by 138 and 139 in fig. 5.

In fig. 6 to 10 embodiments of coating stations are illustrated by means of which various possibilities are to be shown which guarantee that a layer of immobilized solids forms in the coating medium applied on the surface of the web of material between previous metering and final metering. The layer guarantees the high-quality coverage of the web of material. It has to be mentioned that the various possibilities subsequently shown in fig. 6 to 10, can also be used in combination.

According to fig. 6 the distance L, for instance, which has to be covered by the web of material B between previous metering by means of the jetflow applicator 240 around the counter roller 235 to the final metering by means of the doctor blade 255, has to be dimensioned to such an extent that the solids of the coating medium have enough time for forming the immobilized layer. The distance L has to have a value of at least Lmjn, which is formularized as follows:

Lmjn = ko x (k, x CW + k2) x CW2 x v, wherein .

CA 022~6~6 l998-ll-20 CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, v denotes the running speed of said web of material indicated in m/min, ko denotes a first constant the value of which amounts to at least 1, preferably at least 1.5, k1 denotes a second constant the value of which amounts of -0.03603 x 10-5 m6min/g3, and k2 denotes a third constant the value of which amounts to 1.206 x 1O-5 m4mjn/92 According to fig. 6 the coating result can be optimized by varying the running distance L between previous metering and final metering, i.e. by variation of the position of the applicator 240 or/and the position of the doctor blade 255 on the circumference of the counter roller 235, which is indicated in fig. 6 with the small arrows V. The applicator 240 and/or the doctor blade 255 can be adjusted by controlling with a control unit, which is not shown, on the basis of detected signals of various sensors. These sensors can be designed for detecting coat quality parameters, such as covering degree, smoothness, gloss, whiteness and the like. These parameters can optionally be determined before, during or after the drying of the coating layer by means of a drying device 270 or even not before it reaches the portion of the bobbin carriage 272 at the finally coated and dried web of material. Accordingly in fig. 6 sensors 274 are provided at four different places.

To further increase the distance L, according to fig. 7 a web guide member 320 can be adjustably arranged in the direction of double arrow V so that the looping angle of the web of material B around the counter roller 335 increases due to the adjustment. In the present case, when adjusting the web guide roll 320, the looping of the counter roller 335 changes in the portion of the final metering by means of the doctor blade 355. Thus the position of the doctor blade 355 can be adjusted over a correspondingly large angle at CA 022~6~6 1998-11-20 circumference .

In the embodiment according to fig. 8 the web of material B wraps around the counter roller 435 in the portion of the final metering 440 in a first circumferential section, then it runs around a guide roll 476 and finally returns to the counter roller 435 to again wrap it in the portion of the final metering 455 in a second circumferential section. In arranging the guide roll 476 at a corresponding distance from the counter roller 435 sufficient running distance between previous metering 440 and final metering 455 can be provided to guarantee the formation of a layer of immobilized solids on the surface of the web of material. By adjusting the distance of the guide roll 476 from the counter roller 435 the running distance L can be varied, for instance in dependence of the detected signals of the above-mentioned sensors 274.

In the embodiment according to fig. 9 sufficient running distance between previous metering 540 and final metering 555 can be attained in that previous metering takes place at a first counter roller 5351 and final metering 555 takesplace at a second counter roller 5352. In varying the distance of the two rollers 5351 and 5352, the running distance L can be varied. Additionally or alternatively it is possible according to fig.10 to provide a web guide member 676 between the two counter rollers 6351 and 6352 where previous metering 640 and/or final metering 655 takes place. The relative position of the web guide member 676 is variable with respect to the two counter rollers.

To avoid that too large an amount of the solids of the coating medium is immobilized on the surface of the web of material, to be precise to avoid that the smooth or profiled doctor bar or the doctor blade engages with the immobilized layer when finally metering, which would give rise to coating defects, there is provided in accordance with the invention that the running distance L between previous metering and final metering is smaller than a predetermined maximum distance LmaX, the value of which is formularized as follows:

.. . ..... . . ... . . . . ..

CA 022~6~6 l998-ll-20 LmaX = v x [A (CW/K)2- A']
wherein v denotes the running speed of the web of material indicated in m/min, CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, K denotes the solids content of the coating medium in %, A denotes a first constant the value of which, in the case of the profiled doctor bar amounts to 9.28 m4%2sg~2 and in the case of the smooth doctor bar as well as the doctor blade amounts to 1 8 . 86 m4%2S9-2 A' denotes a second constant the value of which, in the case of the profiled doctor bar amounts to 21.4 x 1O-3s and in the case of the smooth doctor bar as well as the doctor blade amounts to 24.0 x 1 O-3s, and wherein the formula only applies to CW/K 2 ~/~7~

Fig. 6 to 10 further illustrate various possibilities to actively accelerate theimmobilization of the solids on the surface of the web of material. A first possibility is to heat or/and dry the coating medium applied to the web of material and/or the web of material itself. Therefore the counter roller can forinstance be heatable. This is schematically indicated by the heating coil 278 at the counter roller 235 of fig. 6. In prior art heatable rollers are known in various em~odiments. A detailed discussion of heatable rollers is therefore omitted .

Furthermore heating and/or drying can be carried out by irradiating with infrared light and/or with microwaves. These two types of heating are concludingly indicated in fig. 6 by means of the wavy arrows 280. In addition the web of material can be blown with hot air by means of a blowing device 282 and/or it can be treated with superheated steam by means of a device . . . .

CA 022~6~6 1998-11-20 284.

In fig. 9 there are also shown various possibilities of immobilization-acceleration between previous metering 540 and final metering 555, i.e. a device 586 which treats the web of material and/or the coating layer with ultrasound, a device 588 which brings the web of material B into contact with a high-frequency oscillator, and a device 590 which can correspond to one of the above mentioned devices 280, 282 and 284. A peculiarity of the devices 586, 588 and 590 can be seen in that they are able to treat the web of material B on both surfaces at the same time.

A further group of immobilization-accelerating devices aims at driving the solids contained in the coating medium toward the surface of the web of material by applying pressure. Therefore according to fig. 7 the counter roller 335 is formed as a suction roller having a suction box 392. The effect of the suction box is based on the fact that moisture is withdrawn from the side of the web of material facing away from the coating layer, so that the capillary suction effect is intensified on the coating side of the web of material. The effect of the suction box 392 can be further intensified by providing an excess pressure box 394 on the coating side of the web of material B. According to fig. 10 the guide roll 676 can be equipped with a suction box 692, and a suction box corresponding to the suction box 394 can also be provided.

It has to be added that also the operation of the above explained immobilization accelerating devices can be controlled by the control unit, which is not shown, on the basis of the detected signals of the sensors 274 according to fig. 6.

Further it has to be added that when using a profiled doctor bar for finally metering the danger of marks of the profile remaining in the finally metered coating layer can be reduced when using a blowing device which smooths the surface of the web of material. In this case, for instance, an "air-turn" 494 can .. . .. .. . . . . .....

CA 022~6~6 1998-11-20 be used, i.e. a guide device which deviates the web of material B on a pad of compressed air without touching it. However, it is also conceivable to use an air brush and/or an air knife, which only serves the purpose of smoothing the surface of the web of material. In any case the blowing device is to be arranged as close to the final metering as possible.

Apart from the above-mentioned possibilities of controlling the runningdistance L or/and the operation of one of the immobilization-accelerating devices 278, 280, 282, 284, 392, 394, 586, 588, 590, 692 in dependence of the detected results of the sensors 274, the temperature or/and the composition of the coating medium can also be influenced in dependence of these detected results.

.. ..

Claims

1. A method for the coating of a moving web of material (B), in particular made of paper or cardboard, with liquid or pasty coating medium, said coating medium being directly or indirectly applied on the web of material(B) in a previously metered manner and subsequently finally metered to the desired coating weight or/and levelled, characterized in that the coating medium is finally metered or/and levelled at the earliest after a time t min which is formularized as follows:
t min = k0 x (k1 X CW + k2) x CW2, wherein CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, k0 denotes a first constant the value of which amounts to at least 1, preferably at least 1.5, k1 denotes a second constant the value of which amounts to -0.03603 x 10-5 m6min/g3, and k2 denotes a third constant the value of which amounts to 1.206 x 10-5 m4min/g2

2. A method according to claim 1, characterized in that said value of said first constant k0 amounts to at least 2, preferably at least 3, even more preferred at least 4.

3. A method according to claim 1 or 2, characterized in that said time t between previous metering and final metering is adjustable.

4. A method according to claim 3, characterized in that at least on property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like, is detected (by 274) and the time t between previous metering and final metering is adjusted in dependence of the detected result.

5. A method according to claim 4, characterized in that the at least one property of the finally metered coating medium layer is detected at the still damp coating medium layer.

6. A method according to claim 4, characterized in that the at least one property of the finally metered coating medium layer is detected during the drying process.

7. A method according to claim 4, characterized in that the at least one property of the finally metered coating medium layer is detected at the dried coating medium layer.

8. A method according to claim 4, characterized in that the at least one property of the finally metered coating medium layer is detected at the bobbin carriage (272).

9. A method according to one of the claims 1 to 8, characterized in that the web of material (B) wraps a supporting member, preferably a supporting roller (235; 435), at least on a part of its circumference, and that both previous metering (240; 440) and the final metering (255; 455) are carried out in a circumferential section of the supporting member (235; 435) which is wrapped by said web of material (B).

10. A method according to one of the claims 1 to 8, characterized in that said web of material is led around a supporting member, preferably a supporting roller (535 1; 635 1) in the previous metering portion (540; 640) and led around a further supporting member, preferably a further supporting roller (535 2; 635 2) in the final metering portion (555; 655).

11. A method according to claim 9 or 10, characterized in that said web of material (B) is deviated between the previous metering (440; 640) and the final metering (455; 655) by at least an intermediate guide member, preferably at least one guide roll (476; 676).

12. A method according to the generic part of claim 1 and optionally the characterizing part of one of the claims 1 to 11, characterized in that the immobilization of the medium applied on the web of material (B) during the movement thereof from the previous metering to the final metering is actively accelerated.

13. A method according to claim 12, characterized in that the applied layer is heated or/and dried (by 280, 282, 284).

14. A method according to claim 12 or 13, characterized in that the web of material is heated (by 278).

15. A method according to claim 13 or 14, characterized in that the applied layer or/and the web of material is irradiated with infrared light (280).

16. A method according to one of the claims 13 to 15, characterized in that the applied layer or/and the web of material is irradiated with microwaves (280).

17. A method according to one of the claims 13 to 16, characterized in that heated air (282) is supplied to the applied layer or/and the web of material.

18. A method according to one of the claims 13 to 17, characterized in that vapour (284) is supplied to the applied layer or/and the web of material.

19. A method according to one of the claims 13 to 18, characterized in that said web of material or/and the applied layer is brought into contact with at least a heated member, preferably a heatable roller (235/278) or a heatable belt.

20. A method according to claim 19, characterized in that a supporting member, preferably a supporting roller (235), around which the web of material (B) is led in the previous metering portion (240), is heated (278).

21. A method according to claim 19 or 20, characterized in that a web guide or/and treatment member (676), preferably a roller, which is provided between previous metering (670) and final metering (655), is heated (678).

22. A method according to one of the claims 12 to 21, characterized in that a partial vacuum is applied (392) on the web of material (B) from the side opposite to the coating side.

23. A method according to claim 22, characterized in that a supporting member (335), preferably a supporting roller, around which the web of material (B) is led in the previous metering portion (340), is equipped with a suction device (392).

24. A method according to claim 22 or 23, characterized in that between previous metering (640) and final metering (655) there is provided a web guide or/and treatment member (676) equipped with at least a suction device (692), preferably a guide roll having a suction box.

25. A method according to one of the claims 12 to 24, characterized in that excess pressure (394) is applied on the web of material (B) from the coating side.

26. A method according to one of the claims 12 to 25, characterized in that said web of material or/and the applied layer are exposed to vibrations (586, 588).

27. A method according to claim 26, characterized in that said web of material or/and the applied layer is irradiated with ultrasound (586).

28. A method according to claim 26 or 27, characterized in that said web of material or/and the applied layer is brought into contact with an oscillating device (588), preferably operable in a high-frequency manner.

29. A method according to one of the claims 12 to 28, characterized in that the intensity of actively influencing the immobilization of the applied layer is adjustable at the web of material (B).

30. A method according to claim 29, characterized in that at least one property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like, is detected (274) and the intensity of influence is adjusted in dependence of the detected result.

31. A method according to one of the claims 1 to 30, characterized in that the coating medium is finally metered by means of a smooth or profiled doctor bar (145, 145') or a doctor blade (155'').

32. A method according to the generic part of claim 1, the characterizing part of claim 31 and optionally the characterizing part of one of the claims 1 to 30, characterized in that the coating medium is finally metered or/and levelled at the latest after a time t max which is formularized as follows:
t max = A (CW/K)2 - A' wherein CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, K denotes the solids content of the coating medium in %, A denotes a first constant the value of which, in the case of the profiled doctor bar amounts to 9.28 m4%2sg-2 and in the case of the smooth doctor bar as well as the doctor blade amounts to 18.86 m4%2sg-2, A' denotes a second constant the value of which, in the case of the profiled doctor bar amounts to 21.4 x 10-3 S and in the case of the smooth doctor bar as well as the doctor blade amounts to 24.0 x 10-3 s, and wherein the formula only applies to CW/K ~~

33. A method according to claim 32, characterized in that final metering or/and levelling is carried out after a time t, said time t being 0.1 t max ~ t ~ 0.8 t max, preferably 0.1 t max ~
t ~ 0.5 t max.

34. A method according to one of the claims 1 to 33, characterized in that a plurality of coating layers are applied onto the web of material (B), for example in the form of a precoat (130), a mid coat (130') and a finishing coat (130").

35. A method according to claim 34, characterized in that at least two of the coating layers are formed of coating medium having a different composition.

36. A method according to claim 34 or 35, characterized in that at least two of the coating layers are formed of coating medium having the same compositions.

37. A method according to one of the claims 34 to 36, characterized in that at least one of the coating layers is formed of a coating medium having a solids content which is at least 2 % to 5 %
lower than that of at least one other coating layer, said solids content of said at least one other coating layer amounts to approximately 50 %
to 73 %.

38. A method according to one of the claims 1 to 37, characterized in that said coating medium layer and/or at least one coating layer is formed of a coating medium having a viscosity of ~
500 mPas, preferably 30 mPas to 250 mPas, when using a profiled doctor bar, a viscosity of ~ 2500 mPas, preferably 300 mPas to 1000 mPas, when using a smooth doctor bar, and having a viscosity of ~
4000 mPas, preferably 300 mPas to 1500 mPas, when using a doctor blade, wherein said given viscosities are determined according to Brookfield 100.

39. A method according to one of the claims 1 to 38, characterized in that said coating medium layer and/or at least one coating layer is applied by means of a roll coater (140), a SDTA-applicator, a jetflow applicator (140') or according to the film coating process.

40. A method according to one of the claims 1 to 39, characterized in that said coating medium layer and/or the last coating medium layer (by 130") is finally metered by means of a doctor blade (155'').

41. A method according to one of the claims 1 to 40, characterized in that the web of material is prepared (138) for the coating of coating medium by supplying impregnating agent or/and solidifying agent, such as starch, synthetic glue with or without pigments.

42. A method according to one of the claims 1 to 41, characterized in that after the coating medium has been applied the web of material is subsequently treated (139) by supplying impregnating agent or/and solidifying agent, such as starch, synthetic glue with or without pigments.

43. A method according to one of the claims 1 to 42, characterized in that said web of material is smoothed (105) before coating medium is applied.

44. A method according to one of the claims 1 to 43, characterized in that said web of material is smoothed (150) after coating medium has been applied.

45. A method according to claim 43 or 44, characterized in that the smoothing process is carried out by means of hard nips and/or soft nips and/or an extended nip.

46. A method according to one of the claims 43 to 45, characterized in that at least one of the two smoothing surfaces forming the respective nip is heatable.

47. A method according to claim 43 or 44, characterized in that said coating medium layer is smoothed by means of a blower (494).

48. A method according to one of the claims 43 to 47, characterized in that said web of material is damped with water or vapour (D) before it is smoothed.

49. A method according to one of the claims 1 to 48, characterized in that the composition or/and the temperature of the coating medium or/and the temperature of the web of material is adjusted.

50. A method according to claim 49, characterized in that at least one property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like, are detected (274) and the composition or/and the temperature of the coating medium or/and the temperature of the web of material is adjusted in dependence of the detected result.

51. A device for coating a moving web (B), in particular made of paper or cardboard, with a liquid or pasty medium, comprising - an applicator (240) for directly or indirectly applying a previously metered layer of said liquid or pasty medium on the web of material, wherein said applicator (240) is arranged at a first position when viewed along the running direction of said web of material, and - a device (255) for finally metering or/and levelling the applied layer at a second position, arranged behind first position with respect to the running direction of the web of material, said second position has a distance L from said first position, characterized in that said second position has a minimum distance L min which is formularized as follows:
L min = k0 x (k1 x CW + k2) x CW2 x v, wherein CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, v denotes the running speed of said web of material indicated in m/min, k0 denotes a first constant the value of which amounts to at least 1, preferably at least 1.5, k1 denotes a second constant the value of which amounts of -0.03603 x 10 -5 m5min/g3, and k2 denotes a third constant the value of which amounts to 1.206 x 10 -5 m4min/g2.

52. A device according to claim 51, characterized in that said value of said first constant k0 amounts to at least 2, preferably at least 3, even more preferred at least 4.

53. A device according to claim 51 or 52, characterized in that the distance of said second position from said first position is adjustable (V).

54. A device according to claim 53, characterized in that for adjusting said distance of said second position from said first position the location of said first position or/and the location of said second position is adjustable (V).

55. A device according to claim 53 or 54, characterized in that there are provided a sensor device (274) for detecting at least one property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like, as well as a control unit which adjusts the distance of said second position from said first position in dependence of the detected result.

56. A device according to claim 55, characterized in that said sensor device (274) is arranged in front of the drying device (270) or in the portion of the drying device (270) or behind the drying device (270) or at the bobbin carriage (272) when viewed along the running direction of the web of material (B).

57. A device according to one of the claims 51 to 56, characterized in that said web of material (B) wraps a supporting member (235; 435), preferably a supporting roller, at least on a part of its circumference, and that both the first position and the second position are arranged within a circumferential section of said supporting member wrapped by said web of material.

58. A device according to one of the claims 51 to 56, characterized in that in the portion of said first postion said web of material (B) is led around a supporting member (535 1; 635 1), preferably a supporting roller, and in the portion of said second position it is led around a further supporting member (535 2; 635 2), preferably a further supporting roller.

59. A device according to claim 57 or 58, characterized in that between said first position and said second position there is provided at least an intermediate guide member (476;
676), preferably at least a guide roll, for deviating said web of material.

60. A device according to the generic part of claim 51 and optionally according to the characterizing part of one of the claims 51 to 59, characterized in that between said first position and said second position there is provided a device for accelerating the immobilization of the applied medium at the web of material.

61. A device according to claim 60, characterized in that the immobilization accelerating device comprises a device for heating or/and drying the applied layer or/and heating said web of material.

62. A device according to claim 61, characterized in that there is provided a infrared irradiation device (280) .

63. A device according to claim 61 or 62, characterized in that there is provided a microwave heating device (280).

64. A device according to one of the claims 61 to 63, characterized in that there is provided a convective heating device (282).

65. A device according to one of the claims 61 to 64, characterized in that there is provided a device (284) for heating or/and drying said applied layer or/and said web of material by means of vapour.

66. A device according to one of the claims 61 to 65, characterized in that there is provided at least a heatable member (235/278), preferably a heatable roller or a heatable belt, which may be brought into contact with said web of material or/and the applied layer.

67. A device according to claim 66, characterized in that in the portion of the first position said web of material is led around a supporting member (235), preferably a supporting roller, which is heatable (278).

68. A device according to claim 66 or 67, characterized in that between the first position and the second position there is provided a web guide or/and treatment member (676), preferably a roller, which is heatable (678).

69. A device according to one of the claims 60 to 68, characterized in that said immobilization accelerating device comprises a suction device (392; 692).

70. A device according to claim 69, characterized in that in the portion of the first position the web of material is led around a supporting member (335), preferably a supporting roller, which is equipped with a suction device (392).

71. A device according to claim 69 or 70, characterized in that between said first position and said second position there is provided at least a web guide or/and treatment member (676) equipped with a suction device (692), preferably a guide roll having a suction box.

72. A device according to one of the claims 60 to 71, characterized in that said immobilization accelerating device comprises an excess-pressure device (394).

73. A device according to one of the claims 60 to 72, characterized in that said immobilization accelerating device comprises a vibration device (586, 588).

74. A device according to claim 73, characterized in that said vibration device comprises an ultrasound radiating device (586).

75. A device according to claim 73 or 74, characterized in that said vibration device is an oscillating device (588) which may be brought into contact with the web of material or/and the applied layer, and is preferably operable in a high-frequency manner.

76. A device according to one of the claims 60 to 75, characterized in that the power of said immobilization accelerating device is adjustable.

77. A device according to claim 76, characterized in that there are provided a sensor device (274) for detecting at least one property of the finally metered coating medium layer, such as covering quality, smoothness, gloss, whiteness and the like, as well as a control unit which adjusts the power of the immobilization accelerating device in dependence of the detected result.

78. A device according to one of the claims 51 to 77, characterized in that there is provided a roll coater (140), a SDTA-applicator, a jetflow-applicator (140') or a film coater for applying said coating medium onto the web of material.

79. A device according to one of the claims 51 to 78, characterized in that there is provided a smooth or profiled doctor bar (145) or a doctor blade (155') for finally metering the coating medium layer.

80. A method according to the generic part of claim 1, the characterizing part of claim 79 and optionally the characterizing part of one of the claims 51 to 78, characterized in that said second position has a maximum distance L max from said first position which is formularized as follows:
L max = v x [A (CW/K)2 - A']
wherein v denotes the running speed of the web of material indicated in m/min, CW denotes the coating weight to be obtained of the applied coating medium layer, indicated in g/m2, K denotes the solids content of the coating medium in %, A denotes a first constant the value of which, in the case of the profiled doctor bar amounts to 9.28 m4%2sg -2 and in the case of the smooth doctor bar as well as the doctor blade amounts to 18.86 m4%2sg -2 A' denotes a second constant the value of which, in the case of the profiled doctor bar amounts to 21.4 x 10 -3 and in the case of the smooth doctor bar as well as the doctor blade amounts to 24.0 x 10 -3, and wherein the formula only applies to CW/K ~

81. A method according to claim 80, characterized in that the second postion is spaced at a distance L from the first position, said distance L being 0.1 L max ~ L ~ 0.8 L max, preferably 0.1 L max ~ L ~ 0.5 L max.

82. A method for producing a coated web of material, in particular made of paper or cardboard, comprising the steps:
- producing a web of fibrous material (in the following termed web) having a headbox and a contiguous sieve portion in a paper machine - dehydrating by means of mechanical pressing and thermal drying of the web - applying liquid or pasty medium on at least one side of the web for gluing and/or impregnating and/or coating - winding the web by means of a bobbin carriage characterized in that at least a pigment-containing layer (coat) is applied on the at least one side of the web, said layer being metered with a smooth or profiled doctor bar after a time t since the medium has been transferred, which is formularized as follows:
t ~ t0 with t0 = A (CW/K)2 - A' and with A = 9.28 m4%2sg -2 and A' = 21.4 x 10 -3 s valid for the profiled doctor bar and A = 18.86 m4%2sg -2 and A' = 24.0 x 10 -3 s valid for the smooth doctor bar, CW = coating weight indicated in g/m2 K = solids content of the coating medium in %
being valid for (CW/K) ~

83. A method according to claim 82, characterized in that the at least one or all (excessively) applied coats are applied by means of a jetflow applicator.

84. A method according to claim 82, characterized in that when several coats are applied the last one is metered by means of a doctor blade.

85. A method for producing a coated web of material, in particular made of paper or cardboard, comprising the steps:
- producing web of fibrous material having a headbox and a contiguous sieve portion in a paper machine - dehydrating by means of mechanical pressing and thermal drying of the web - applying liquid or pasty medium on at least one side of the web for impregnating and/or gluing and/or pigmentation and/or coating - winding the web by means of a bobbin carriage characterized in that at least a pigment-containing coat is applied on at least one side of the web, said layer being applied by means of a jetflow applicator and being metered with a doctor blade after a time t after transferring said medium, which is formularized as follows:
t ~ t0 with t0 = A (CW/K)2 -A' and with A = 18.86 m4%2sg -2 and A' = 24.0 x 10 -3 s CW = coating weight indicated in g/m2 K = solids contend of the coating medium in %
being valid for (CW/K) ~ A/A'.

86. A method according to claim 82 or 85, characterized in that said pigment-containing coat is applied in the form of a precoat and/or mid coat and/or finishing coat.

87. A method according to claim 86, characterized in that one of the coats is realized in a multiple manner, wherein the coating medium has a different or the same composition.

88. A method according to claim 82, characterized in that at least one pigment-containing coat is applied by means of a roll coater.

89. A method according to claim 82 and 85, characterized in that at least one pigment-containing coat is applied on the web with an applicator having a short dwell time of the coating medium until it is metered by means of the doctor member (doctor bar, doctor blade) (SDTA).

90. A method according to one or several of the claims 82 - 89, characterized in that at least one of the coats is applied with such a coating medium having a solids content which is at least 2 - 5 % lower than that of the other or the others (usually common) coats, said other coats having a solids content of approximately 50 - 73 %.

91. A method according to one or several of the claims 82 - 90, characterized in that at least one of the coats is applied with such a coating medium having a coating dye viscosity according to Brookfield 100 of < 500 mPas, preferably 30 - 250 mPas, when using a profiled bar, or having a coating dye viscosity of < 2500 mPas, preferably 300 - 1000 mPas when using a smooth doctor bar and < 4000 mPas, preferably 300 - 1500 mPas when using a doctor blade.

92. A method according to one of the claims 82 or 85, characterized in that before the pigment-containing layer is applied impregnating agent or/and solidifying agent (such as starch, synthetic glue with or without pigments) is supplied to the material.

93. A method according to one of the claims 82 or 85, characterized in that in addition to applying the pigment-containing coat the surface is treated in the sieve portion and/or between the sieve portion and press portion with impregnating agent and/or solidifying agent on at least one of the two sides of the web.

94. A method according to one of the claims 82 or 85, characterized in that in addition to applying the pigment-containing coat the surface is treated in the press portion and/or between press portion and dry portion with impregnating agent and/or solidifying agent on at least one of the two sides of the web.

95. A method according to one of the claims 82 or 85, characterized in that in addition to applying the pigment-containing coat the surface is treated with impregnating agent and/or solidifying agent in the dry portion and/or behind said dry portion with or without subsequent drying in at least one of the two sides of the web.

96. A method according to one of the claims 82 or 85, characterized in that in addition of applying the pigment-containing coat the surface is treated with impregnating agent and/or solidifying agent even before a bobbin carriage with or without subsequent drying on at least one of the two sides of the web.

97. A method according to one of the claims 82 or 85, characterized in that a surface treatment is carried out by means of impregnating agent and/or solidifying agent even before the first pigment-containing coat is applied and/or between the individually applied multiple pigment-containing coats.

98. A method according to one of the claims 82 or 85, characterized in that the first and/or second and/or any further pigment-containing coat is applied onto the web in the portion of the headbox and/or in the sieve portion and/or between sieve portion and press portion and/or in the press portion and/or between press portion and dry portion and/or within or behind the dry portion.

99. A method according to one or several of the claims 82 - 98, characterized in that said web is smoothed even before the pigment-containing layer is applied, wherein said smoothing process is carried out with hard nips and/or soft nips and/or an extended nip and wherein at least one of the two smooth surfaces, which form the respective nip, is heatable.

100. A method according to one or several of the claims 82 - 99, characterized in that said web of material is smoothed between each coating of pigment-containing coat and/or after said pigment-containing coat.

101. A method according to claim 97 or 98, characterized in that the web is damped with water or vapour before it is smoothed.

102. A method according to one of the claims 82 or 85, characterized in that t amounts to < 0.1 to 0.8 t0, in particular, however, < 0.1 to 0.5 t0.