DE102015218673B4 - Method for operating a commissioned work - Google Patents

Abstract

The invention relates to a roll cover for an applicator roll for coating a fibrous web with a coating medium, comprising a functional layer which can be exposed to the application medium, a functional material which can be displaced from a hydrophilic to a hydrophobic state by external energy input, or vice versa, wherein the functional material the functional layer is assigned.

Description

The invention relates to a method for operating a commissioned work for coating a running paper, cardboard or other fibrous web with application medium, such as glue, starch or coating color.

Such rolls are commonly found in commissioned work, such as coating units, which are part of paper, board or tissue machines. In commissioned work, at least two rollers form a nip with each other through which the fibrous web to be coated, e.g. in a free move, without support from below. At least one of these rollers is then an applicator roll. That is, it transfers a coating medium on the fibrous web in the area of the nip. When commissioned, the commissioned work generates a uniform film layer of application medium over its entire width on the fibrous web.

In today's job shops, the surfaces of the applicator rolls are designed to have good wettability for the application medium, in other words to be hydrophilic throughout their circumference. As a result, after passing through the nip, that is, in the nip spout, a relatively large amount of application medium continues to adhere to the surface of the roll cover of such applicator rolls. On the one hand, this has the disadvantage that the transfer rate of the application medium to the fibrous web per revolution of the applicator roll is relatively low. On the other hand, the application medium is accelerated and swirled outwards due to the centrifugal forces due to the rotating application roller. As a result, droplets of application medium dissolve in the nip spout from the applicator roll and are whirled up there. He occurs an unwanted fogging of the application medium. The fluidized droplets sometimes settle on the fibrous web and lead to unwanted effects on it. The result is e.g. a coated paper whose surface quality appears uneven.

The present invention relates to the aforementioned generic objects.

Commissioned works have become known inter alia from:
DE 603 12 709 T2
EP 2 511 418 A1
DE 34 17 487 A1 ,

It is therefore an object of the invention to provide a method which avoids the disadvantages of the prior art. In particular, the object is, on the one hand, to ensure a comparatively high transfer rate of the application medium to the fibrous web during operation of the applicator roll and, on the other hand, to avoid said mist formation.

The object is achieved by the method according to the independent claim. Particularly preferred and advantageous embodiments of the invention are given in the subclaims.

A roll according to the invention, such as applicator roll, in the sense of the invention comprises a roll body, which is designed in sections or over its entire length as a cylinder or hollow cylinder and the roll cover according to the invention. In general, such applicator rolls have a roll body of a metal, such as steel or a fiber composite material, which is provided with a single or multi-layer roll cover. Such an application roller is set up in such a way that it serves to coat a fibrous web with a coating medium. This means that their peripheral surface can absorb coating medium in the normal operation of the applicator and deliver it to the fibrous web. In other words, during normal operation, the roll cover or the functional layer comes in direct contact with the application medium, but never in contact with the fibrous web itself, either directly or indirectly.

Coating medium according to the invention may be a liquid to pasty medium, such as glue, starch, coating color or the like. The application medium is set up in such a way that it adheres permanently to the fibrous web, at least after the coating, ie after leaving the nip or the applicator unit. After a subsequent drying, the application medium forms a permanent layer or a film on the fibrous web. The application medium may be a water-based mixture.

A roll cover according to the invention has at least one radially outermost layer, which is also referred to as a functional layer. The connection of the roll cover to the roll body can be produced by a so-called base layer or adhesion-promoting layer. Such a base layer is then part of the roll cover and is preferably applied directly to the radially outermost surface of the roll body. Seen in the radial direction can then be applied then the actual functional layer. Between the base layer and the functional layer, further intermediate layers can be provided. The base layer and / or the functional layer itself can also consist of several, one above the other in the radial direction be arranged arranged individual layers. In other words, the roll cover can be multi-layered. As a finished roll cover applies a roll cover, which is ready for normal operation, so fully cured and possibly machined to provide on the lateral surface any surface structures.

For the purposes of the present invention, functional layer is understood to mean that section of the roll cover which indirectly (directly) or directly (indirectly, eg via further means such as the fibrous web or in the form of unwanted spatters of the application medium) comes into contact with the application medium during normal operation of the roll cover comes, so this is exposable. In general, this is the radially outermost surface (lateral surface) of the functional layer, which comes into temporary or permanent contact with the application medium during normal operation. The roll cover, the functional layer or its lateral surface is consequently designed such that it forms a surface receiving the application medium, from which the application medium can be transferred to the fibrous web to be coated. The functional layer may be made of a polymer, preferably an elastomeric polymer.

The roll cover can, as is known to those skilled in the art, be produced for example by a rotational casting process. The polymer is applied from a relatively movable along the longitudinal axis of the roller body to be coated nozzle with uniform rotation of the roller body. The roll cover can therefore be primitive, so be made by Geissen. It can extend over the circumference of the roller body as a closed functional layer.

For the purposes of the invention, a fibrous web is to be understood as a scrim of fibers, such as wood fibers, synthetic fibers, glass fibers, carbon fibers, additives, additives or the like. Thus, the fibrous web may be formed, for example, as a paper, board or tissue web, which essentially comprise wood fibers, wherein small amounts of other fibers or additives and additives may be present.

By functional material within the meaning of the invention is meant a material which is selectively displaceable by energy input from the outside of a hydrophilic to a hydrophobic state, or vice versa. The change between these two states is reversibly changeable. It can be set up in the intended operation of the applicator roll or the commissioned work such that there is a hydrophilic state without energy input. Upon application of energy, the functional material could change from a hydrophilic to a hydrophobic state. In principle, it would be conceivable that the functional material could be embodied in such a way that, conversely, it also has a hydrophobic state when there is no supply of energy, whereas it changes into a hydrophilic state when energy is supplied. In both cases, the functional material would be designed in such a way that it automatically returns to its corresponding initial state upon removal of the energy or in the event of non-supply, that is to say it would be unidirectionally switchable. Of course, it would also be conceivable that the functional material is set up in such a way that it could be switched bidirectionally. The latter means that the functional material, upon a first energy input, indicates its state of e.g. changes from hydrophobic to hydrophilic and, in response to a second energy input, its state is opposite thereto, e.g. hydrophilic to hydrophobic changes.

The functional material may be a responsive to an energy input material. Thus, it may react to electromagnetic energy such as light or magnetic energy due to induction or thermal energy to change its wettability with application medium. The functional material can basically be a polymer. It may be selected from poly (N-isopropylacrylamides) (PNIPA or PNIPAAM), photo-responsive compounds comprising azobenzene (azobenzene, AZO) or mixtures thereof. However, it can also comprise titanium dioxide (TiO ₂ ), so that it can be excited, for example by light, to change its wettability.

If, in the context of the invention, wettability is mentioned, then this means the wettability of the roll cover for the application medium. The wettability depends on the surface tension (or surface energy) of the application medium. The surface tension can on the one hand be understood as a pulling force, which is localized on the surface of a liquid and has its direction of action parallel to the surface of the liquid. On the other hand, this can be described as the energy needed to increase the liquid surface area of the coating medium by one unit area. The wettability can be measured by the contact angle (Young's equation) resulting from the interaction of application medium and roll cover. The smaller the contact angle, the greater the wettability. To assess whether a drop of application medium is spreading on a surface such as the roll cover, one compares the cohesive forces within the drop with the adhesion forces against the surface. If the adhesion forces far outweigh the cohesive forces, the droplet will spread completely on the surface, completely moistening it. In practice it is however, so that the cohesive forces of the application medium can not be changed arbitrarily. Rather, they are predetermined by the use of eg a special coating color.

According to the invention, the roll cover or applicator roll is designed in such a way that, when the roll is operated as intended, part of the peripheral surface of the roll cover is predominantly hydrophilic and at the same time a part predominantly hydrophobic. In this case, the hydrophobic part can make up only a fraction of the entire peripheral surface of the functional layer.

Hydrophilic in the sense of the present invention means the property of the functional material to exert an attraction on the application medium. If the application medium is based on water, hydrophilic means that it attracts the water in it. Hydrophobic, on the other hand, means that the functional material is repellent to the application medium, e.g. for water is. Hydrophilic can e.g. meant that the functional material produces a greater resultant attractive force on the same volume of application medium as compared to its hydrophobic state.

If, for the purposes of the invention, the term "predominantly hydrophilic" or "predominantly hydrophobic" is used, then the corresponding property of the circumferential surface of the roll cover is always meant, which in this part - ie locally - emerges clearly measurable. This means that, for example, a predominantly hydrophilic roll cover may, in terms of its circumference, for example, be particularly highly hydrophilic locally, but less hydrophilic elsewhere.

The terms hydrophobic, predominantly hydrophobic, hydrophilic and predominantly hydrophilic, describe a relative property of the roll cover. They are thus a description of the term wettability or surface tension. In the case of a hydrophobic state of the roll cover, the cohesion forces of the application medium outweigh the adhesion forces of the roll cover, so that the application medium is more or less repelled by the roll cover. The roll cover has in this case, at least locally, a lower wettability for the application medium.

If, according to the invention, it is mentioned that the functional material or the roll cover can be displaced from a hydrophobic to a hydrophilic state (reversibly), or vice versa, it is tantamount to mean that its adhesion forces (at least locally) for given cohesion forces of the application medium ) are increased or decreased.

If, for the purposes of the present invention, the term "functional material is assigned to the functional layer" is understood to mean that the functional material is provided on the one hand separately from the functional layer, but is connected to the latter. This can e.g. be achieved by coating the functional layer with the functional material. On the other hand, it may be understood that the functional material is formed integrally with the functional layer, that is, it is produced in original form together with it or embedded in it.

If in the context of the present invention, "in the area of the nip" is mentioned, then the extent of the nip in the direction of the fibrous web (nip length), as well as an extent in the direction immediately before the nip (Nipeinlauf) and in the direction immediately after the Nip (Nipauslauf) meant. The nip run and nip run may in turn be multiples (e.g., one, two, three, four, five, ten, twenty, fifty, one hundred, etc.) of the nip length. With Nipeinlauf and Nipauslauf each of the radially outer surfaces of the at least two nip forming rollers spanned space can be understood. The spanned space can be seen in plan view of the longitudinal axes of said rollers each from the nip on both sides (in the direction of Nipeinlauf and Nipauslauf) along the arcuate line of the surfaces of the rollers and seen in the selected plan view measured from the center of the nip in extension of passed fiber web extending on both sides of the nip.

In the context of the invention, the term transfer rate is understood to mean the ratio of the quantity picked up by the applicator roll and discharged by it to the fibrous web, based on a full revolution of the applicator roll about its longitudinal axis during normal operation of the applicator. Basically, the amount taken up by the applicator roll depends on the quantity delivered by the respective application unit to the applicator roll. In general, the latter amount in the normal operation of the commissioned work, so for example during the rotation of the applicator roll is constant. The invention thus does not aim at adjusting the amount delivered by the application unit, but rather at the amount of application medium actually absorbed or absorbable by the applicator roll due to its wettability. The transfer rate can be measured in terms of a uniform area such as a part of the peripheral surface of the applicator roll. This can be done, for example, by measuring the amount of coating medium adhering to the surface before the nip (eg in the nip inlet) and remaining after the nip (eg in the nip outlet) on this surface. The remaining amount may be in terms of volume, Mass or a measured variable derived therefrom.

Furthermore, the invention also relates to an applicator mentioned above, such as coating unit comprising at least one applicator roll according to the invention. However, such is not covered by the scope of the claims.

The invention also relates to the use of an applicator roll according to the invention in a commissioned work according to the invention. However, such is not covered by the scope of the claims.

Furthermore, the invention relates to a method for operating a commissioned work according to the invention. The latter can be set up in such a way that it can carry out the individual method steps.

Finally, the present invention relates to a paper, board or tissue machine comprising a commissioned work according to the invention. However, such is not covered by the scope of the claims.

The invention will be explained in more detail below with reference to the drawings without limiting the generality. In the drawings show:

1 a highly schematic representation of a commissioned work with two applicator rollers in a side view;

2a . 2 B in each case a highly schematized, not to scale and partially cut representation by a further embodiment of an applicator roll of 1 ,

In the 1 is a commissioned work 1 as a coating unit, which may be part of a paper, board or Tissuemaschine not shown, shown schematically in a side view. The commissioned work 1 is here for the indirect coating of a running fibrous web 2 with application medium 3 executed. Indirect means that the order medium 3 not directly on the fibrous web to be coated 2 , but first - so indirectly - on rollers such as applicator rolls 5 . 6 is applied. The commissioned work 1 in the present case comprises two mutually parallel with respect to their longitudinal axes, together with a nip 4 forming, in the arrow direction (in each case in opposite directions) about their longitudinal axis rotating rollers, in the present case both as application rollers 5 and 6 are executed. In the nip 4 Both applicator rollers roll 5 . 6 indirectly via the fibrous web 2 from each other, so are not in direct contact with each other, but by the fibrous web 2 separated from each other. The fibrous web 2 becomes in the free train - thus without support this by means of eg a covering - by the commissioned work 1 , more precisely through the nip 4 guided. In the nip 4 it lies directly on the peripheral surfaces of the applicator rolls 5 . 6 at.

In the present case, the two applicator rolls shown 5 and 6 in each case a roll cover according to the invention 5a . 6a on. The roll cover 5a . 6a is on a respective roll body 5b . 6b applied and comprises at least one functional layer 10 (please refer 2a and 2 B ).

For coating the fibrous web 2 with application medium 3 (eg glue, starch or a coating color) here is each applicator roll 5 . 6 a job aggregate 7 . 8th assigned. The application aggregate 7 . 8th is directly the corresponding application roller 5 . 6 arranged opposite, so that the application medium 3 on the radially outermost surface (lateral surface or peripheral surface) of the roll cover 5a and 6a the respective applicator roll 5 and 6 can be applied. The application takes place in the direction L of the fibrous web to be coated 2 (or in the direction of rotation of the applicator roll 5 . 6 seen) in front of the nip 4 , So on the part of the peripheral surface of the roll cover 5a . 6a that is between the respective job aggregate 7 . 8th and the nip 4 runs.

That of the peripheral surface of the roll cover 5a . 6a recorded application medium 3 will be in the nip afterwards 4 to the respective web page by the nip 4 in the direction L moving fibrous web 2 transfer. For double-sided application on the web pages 2a and 2 B - as in 1 shown - so are both order aggregates 7 and 8th against the applicator rolls 5 and 6 hired. With only one-sided order on one of the two web sides 2a or 2 B is a job aggregate of the applicator roll pivoted, which is not shown here.

The in the direction of the fibrous web 2 or the rotation of the applicator rolls 5 . 6 the nip 4 Immediately upstream dotted area represents the Nipeinlauf 4.1 On the other hand, the name of the corresponding nip 4 immediately downstream dotted area the Nipauslauf 4.2 , In the chosen representation are nipeinlauf 4.1 and nip run 4.2 from between the opposed peripheral surfaces of the applicator rollers 5 . 6 formed limited space. ingoing nip 4.1 and nip run 4.2 set the area around the nip 4 represents.

This area thus extends in the illustration shown on both sides of the nip 4 along the boundary of the applicator rolls 5 . 6 , ie along their dotted circular arc line. The length of the dotted circular arc of nipeinlauf 4.1 and nip run 4.2 can each be a multiple of the nip length of the nip 4 (indicated by the bold lines).

To the wettability of applicator rolls 5 . 6 during normal operation of the commissioned work 1 on the one hand, the applicator rollers 5 . 6 and on the other hand, the commissioned work 1 specially coordinated.

So show the 2a and 2 B each in a partially sectioned and highly schematic and not to scale representation perpendicular to the longitudinal axis through the applicator roll 5 . 6 from 1 the structure of the roll cover 5a . 6a each in an embodiment of the invention. The roll cover 5a . 6a in the present case comprises a radially inner base layer 9 and a radially outer functional layer applied thereto 10 , Although not shown, baselayer could 9 and / or functional layer 10 each be composed of several individual layers.

As in 2a indicated by the punctuation, indicates the functional layer 10 a functional material. The latter is completely over the entire functional layer 10 distributed and embedded in this. According to the embodiment of the 2 B is the functional material separate to the functional layer 10 intended. It also forms a layer, which in the present case in the radial direction on the functional layer 10 is arranged and at the same time the radially outermost surface of the roll cover 5a . 6a forms. This is the surface that is in the intended operation of the commissioned work 1 directly with the application medium 3 comes into contact. The layer is on the radially outer surface of the functional layer 10 permanently applied. Permanently means that these are solid with the functional layer seen over their lifetime 10 connected is.

Regardless of the embodiment in the 2a and 2 B is the functional material chosen such that its wettability with application medium 3 optionally adjustable between a comparatively low wettability (hydrophobic) and a comparatively high wettability (hydrophilic). This optional setting may be in normal operation of the commissioned work 1 take place, so while the at least one applicator roll 5 . 6 rotates about its longitudinal axis. In other words, the applicator roll 5 . 6 executed such that a part of the peripheral surface of the roll cover 5a . 6a predominantly hydrophilic and at the same time a part may be predominantly hydrophobic. It is preferred if the lateral surface of the applicator roll 5 . 6 at least in the area between the order aggregate 7 . 8th and the nip 4 in the direction of the fibrous web 2 seen in front of the nip 4 is hydrophilic. In this case, a relatively large amount of order medium 3 from the part of the lateral surface of the applicator roll 5 . 6 get picked up. On the other hand, a relatively large transfer rate of the application medium 3 on the fibrous web 2 should be achieved in the area of the nip 4 or within the nip 4 itself the wettability of the roll cover 5 . 6 in terms of the order medium be lower than before. These two requirements are achieved by the wettability of the roll cover 5a . 6a from the commissioned work 1 is set. This is the commissioned work 1 an energy source 11 assigned to the part of the commissioned work 1 can be.

By means of the energy source 11 can the functional material of the roll cover 5a . 6a Energy are supplied, so that its wettability before the nip 4 and its wettability after the nip 4 is selectively and mutually adjustable. This is an alternate switching of a hydrophilic state of the functional material in the direction of the fibrous web 2 in front of the nip 4 in a hydrophobic state in or after the nip 4 possible. Due to the fact that the functional material in the nip 4 becomes hydrophobic, the application medium from the lateral surface of the roll cover 5a . 6a repelled and therefore easier on the fibrous web 2 be transferred.

The energy source 11 is adapted to the functional material. This means that it emits such an energy form, which stimulates the functional material to a corresponding change in the wettability. Thus, the functional material may be designed such that it is due to one of the energy source 11 emitted magnetic, electrical, electromagnetic or thermal energy whose wettability changes.

The energy source 11 is right here above the nip 4 arranged. In this case, the applicator roll 5 . 6 be designed as a hollow cylinder, so that the energy source 11 stationary - not with the applicator roller 5 . 6 co-rotated - within the applicator roll 5 . 6 , more precisely within the radial boundary could be arranged. It could be designed such that it through the jacket of the hollow cylinder a corresponding energy in the nip 4 sending out. However, the energy source could also be in the nipeinlauf 4.1 be arranged. The energy source 11 may be designed such that it extends over the entire length of the applicator roll 5 . 6 extends or only a fraction of this amount and then relative to the applicator roll 5 . 6 along the nip 4 be executed displaceable.

Present is exactly one source of energy 11 intended. The functional material is therefore arranged to be after irradiation by the energy source 11 - or after passing through the nip 4 - automatically returns to the state it receives from the radiation - so then as this no energy from the energy source 11 was fed - had. In this case, this is the hydrophilic state. In other words, the applicator roll 5 . 6 becomes hydrophilic without an energy input and is only made hydrophobic by such a process.

Preference could also be multiple, over the circumference of the at least one applicator roll 5 . 6 arranged energy sources 11 be provided. Preferably can then in the region of the Nipauslaufs 4.2 or in the direction of rotation of the corresponding applicator roll 5 . 6 even further behind, such an additional source of energy 11 (shown here by dashed lines) may be provided. This is particularly advantageous when the functional material is designed such that, after the energy supply through the first, in or before the nip 4 arranged energy source 11 does not automatically return to the hydrophobic state. Then such a second energy source 11 necessary to transfer the functional material after passing through the nip 4 to spend again in its hydrophilic state. According to a preferred embodiment of the invention (not shown) are exactly two such energy sources 11 intended.

Regardless of whether the functional material is now designed so that it automatically returns to its initial state in terms of its wettability or not, is in the normal operation of the commissioned work 1 always a part of the lateral surface of the applicator roll 5 . 6 at the same time hydrophilic and hydrophobic. The part of the lateral surface which is (predominantly) hydrophilic may be a multiple of the part of the lateral surface that is (predominantly) hydrophobic at the same time.

LIST OF REFERENCE NUMBERS

1

commissioned

2

Fibrous web

2a

Top of the fibrous web

2 B

Bottom of the fibrous web

3

application medium

4

nip

5

applicator roll

5a

roll cover

5b

 roller body

5.1, 5.2

roll edge

6

applicator roll

6a

roll cover

6b

roller body

7, 8

application unit

9

 Base layer

10

 functional layer

11

 energy

L

 direction

Claims (2)

Method for operating a commissioned work ( 1 ) for coating a fibrous web ( 2 ) with a job medium ( 3 ) comprising at least one applicator roll comprising a roll body ( 5b . 6b ) and a roll cover arranged thereon ( 5a . 6a ), wherein the roll cover ( 5a . 6a ) a functional layer ( 10 ) which is assigned to the order medium ( 3 ), a functional material which can be displaced from a hydrophilic to a hydrophobic state by external energy input, or vice versa, wherein the functional material of the functional layer ( 10 ), the method comprising the following steps: a) application of application medium ( 3 ) on the at least one roller in the running direction of the fibrous web ( 2 ) seen in front of the nip ( 4 ), wherein the functional layer ( 10 ) is set in a hydrophilic state associated functional material; b) passing the fibrous web ( 2 ) through the nip ( 4 ); c) input of energy from outside into the roll cover ( 5a . 6a ) in the area of the nip ( 4 ), so that the roll cover ( 5a . 6a ) in the area of the nip ( 4 ) changes from the hydrophilic to the hydrophobic state. A method according to claim 1, characterized in that in the running direction of the fibrous web ( 2 ) seen behind the nip ( 4 ), the roll cover ( 5a . 6a ) is adjusted so that it changes from hydrophobic back to the hydrophilic state.

Images