FI101489B - Method and device for coating moving web - Google Patents

Abstract

A belt (2) arranged in a continuous loop, is moved at the same speed as a web (1), to guide the web to a nip (12) between a film transfer roll (3) and backing roll (4). Then, the rolls are rotated so that a coating mix on the roll (3) is partly transferred to the web surface. The contact length between rolls is controlled by altering incoming and departure angles (alpha ,beta ) of the web and belt in relation to the transfer roll. The belt supports the web against the film transfer roll before the nip and separates from the web after the nip. Alternately the belt is arranged around the backing roll such that the belt contacts the roll at two points. The film transfer roll is arranged at one contact point and a coater is arranged at the other contact point. The web applied with a primary coating by the transfer roll is guided to the coater by the belt. And then the secondary coating is applied on the primary coated surface. The primary coated surface is dried by a dryer, before the application of the secondary coating. The backing roll serves as a pressing roll to control the nip pressure between film transfer backing rolls. Alternately, the cleaning of the belt with a doctor knife is performed after the web separates from the belt and the web is cleaned using a cleanser apparatus operating with liquid, and air or steam jet is performed once the web has been separated from the belt. Alternately, the web before being separated from the belt is dried using an IR radiating dryer, microwave or some other electromagnetic radiating dryer, an overhead blast dryer, a coanda dryer, or some other dryer where the web is supported by flow. Alternately, an auxiliary backing roll presses the web and the belt against the film transfer roll in order to form a precise contact line. An independent claim is also included for the arrangement of the film transfer coater in which a pair of primary guide rolls (7,18) are configured such that the web guided on the belt surface by the roll (18) is transferred to the nip between the transfer film roll and the backing roll by both rolls. Both the primary guide rolls, a secondary guide roll (8), belt, and rollers (13-17) takes the web through the nip and turns the transfer film roll and backing roll so as to apply a coating mix in the web surface. The secondary guide roll separates the belt from the web after nip. The position of the primary guide roll (7) is controlled to alter the incoming angle alpha and departure angle beta of the web and belt film transfer roll so as to control the contact length of the web and the film transfer roll. The position of the secondary guide roll (8) is controlled to alter the departure angle beta of the web and belt from the film transfer roll so as to control the contact length of the web and the film transfer roll.

Description

101489

The present invention relates to a method according to the preamble of claim 1 for coating a moving paperboard or paper web by a film transfer method.

The invention also relates to a method for coating a web twice using a film transfer coating according to the invention in a first or second coating step.

The invention also relates to devices for carrying out the method.

15

To improve the printability of the paper and board, they can be coated with one or more coating layers. The more coating layers are used, the better the paper quality can be achieved and at the same time coating materials with different properties can be used. The use of two coating layers greatly increases the manufacturing cost, as the coating is usually done in different stages and the coating layer is dried before the next layer is applied.

The coating can be applied either directly to the surface of the paper, e.g. with blade or rod coaters, or with a film transfer coater, in which the film pre-applied to the film roll is transferred to the surface of the paper in a roll nip. It is characteristic of blade and rod coatings that the scraper fills the roughness volume of the coating substrate and smoothes the surface, whereby the thickness of the coating layer varies according to the roughness volume variations of the coating substrate. The result is a smooth coating with an uneven brightness coverage and difficult control of the uniform ab-35 sorption properties of the coating.

In film transfer coating, a substantially uniform ♦ N is obtained.

2 101489 a narrower coating layer, which makes it easy to control the absorption properties, but adequate smoothness properties are a problem, especially with thicker papers and paperboards. The coating also has a fairly even coverage, whereby, for example, the brightness of a low-brightness coating substrate can be significantly improved by this coating method. Also, since there is no scraper dragging the coating substrate in the film transfer coating, the runnability of the method is excellent with respect to coating breaks. However, the problem with the film transfer-10 coating is the fogging of the coating and the so-called cracking of the film formed on the surface of the web detaching from the film transfer roll and the coating on the surface of the roll. an orange peel pattern that appears as small craters on the coating. The nebulization and the orange peel pattern somewhat limit the maximum possible coating speed of the film transfer coaters.

The special features of the blade and film transfer coating methods have been exploited in two different ways.

Film coating is widely used in pre-coating as well as surface coating. As a pre-coating, it already improves. even through the total amount of coating from the coating result, and the presence of as many as 25 blade coatings ensures sufficient smoothness. Usually, the precoat is dried before the next surface coating, which is usually performed with a blade coater. It is also known from U.S. Pat. No. 2,937,955 to make a blade coating directly on a semi-wet film coating. A prerequisite for this method is that the precoat is set or solidified to such an extent that it can withstand the surface coating with a blade. Solidification can be promoted, for example, by partial drying of the precoat, if the coating has not been sufficiently dehydrated by the effects of pressure penetration in the coating nip and the absorption of 3,101,489 water between the precoaters and the surface coats in the free space.

The delay and settling time between the film pre-coating and the blade surface coating can be extended, for example, by increasing the web travel between the coating devices, whereby the pre-coating is made sufficiently settled and dry for the next blade coating as the impregnation time on the web is extended. U.S. Patent No. 5,340,611 discloses a method in which the amount of film coating is kept so small that the scraper blade of the blade coating device does not scrape off the pre-layer. In this way, however, the large amount of application made possible by the film transfer coater cannot be utilized and the thickness of the first coating layer remains very small. Instead of a blade, a rod scraper can also be used to coat the second stage.

In the pilot carton coating test runs performed, the method did not add enough time to the 10 g / m2 precoat to increase the delay time between coating operations, so that the next blade coating event would not have partially dissipated the precoat already made. Another problem was that as the film coating nip determined the speed of the web and the subsequent blade coating slowed down, the speed of the web tended to form a bag or loose in front of the blade which caused track breaks. Therefore, in this case, the method did not work. The probability of track breaks is further increased by the fact that the blade coating 30, which is much more stressful on the web than the film transfer coating, is made on a damp web, the strength of which is naturally inferior to that of a dry web.

Another way to take advantage of the special features of film and blade coatings is disclosed in Applicant's patent application F1 35 941803, in which the coating unit is constructed so that based on end product requirements and / or runnability considerations 4101489 This device cannot take advantage of the advantages of 5 double-layer coating, so it mainly increases the flexibility of production, but does not improve the quality of the final product compared to similar single-layer coating methods.

10 Especially for thick papers and paperboards, it is necessary to combine the advantages of film coating and blade coating. However, based on space requirements and investment costs, intermediate drying of the pre-coating is not always possible. In this case, the only option is a wet-on-wet coating as described above, but current methods do not achieve sufficiently high total coatings to make the best use of the good coverage of the film transfer coating and the good smoothness provided by the blade coating.

20

The film transfer method can also be used to make a surface coating, in which case the layer produced by the film transfer method applied on top of the first layer smoothed with a blade or a rod becomes smooth. The solution according to the invention 25 is particularly well suited for wet-on-wet coating, in which case the second coating layer is applied at least partially on top of the wet first coating layer.

It is an object of the present invention to provide a film transfer coating method which allows the coating process to be better controlled than before and thus to improve the runnability and increase the coating speed of the film transfer coating.

The invention is based on the fact that the web to be coated is conveyed through a film transfer nip supported by a belt and the angle of the belt 5 101489 over the applicator roll is adjusted so that the contact distance between the web and the roll can be changed.

Furthermore, in the double coating method 5 according to the invention, the web is conveyed through two successive coating stages supported by a belt and one of the coatings is made with a film transfer coater and the other with, for example, a short residence coater.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The device according to the invention, in turn, is characterized by what is set forth in the characterizing part of claim 12.

The invention provides considerable advantages.

By means of the belt, the adjustability of the roll application station can be substantially improved, because by changing the inlet and outlet angles of the belt, the entry of the web to be coated into the nip, its release from the surface of the brush roll and the wetting time and pressure can be influenced. By increasing the wetting time, i.e. the delay time of the film transfer 25, the coating is better absorbed into the web, whereby a thicker first coating layer is left on the surface of the web. In double coating in particular, this has a great effect because due to the better absorption, sufficient coating is left on the surface of the web even after the coating of the blade coating. On the other hand, if the blade coating is performed before the film transfer coating, the belt improves the smoothness of the coating because it allows the angle of detachment of the web from the brush roll to be adjusted so as to minimize the formation of an orange pattern. Using the belt and adjusting the belt angle 35 before the web enters and leaves the nip. on the road from there further improve the runnability of the film transfer coating and the controlled removal of the web reduces the orange pattern. Naturally, a rod can be used instead of a blade.

5 In the brush roller application, the belt replaces the soft roller. The belt is easier to change after the roller and is considerably cheaper than the roller. The belt change intervals can thus be kept short. The runnability is also good in double coating, because in the first coating step the wetted web 10 is supported by a belt, whereby the stress on the web itself is lower. The belt-supported web is not bagged as easily as the unsupported web. In the pre-coating step, a preferred coating can be used to smooth the surface of the paper and the blade coating is made with a more expensive fine-grained coating which provides good printability and coverage properties.

The invention is explained in more detail below with the aid of the accompanying drawings.

20

Figure 1 shows diagrammatically one film transfer coater according to the invention.

. Figure 2 shows diagrammatically a double coating method according to the invention.

Fig. 1 shows a belt-supported film transfer coater in which the incidence angle α of the web 1 to be coated on the film transfer roll 3 and the exit angle β from the roll 3 can be adjusted by changing the web of the belt 2 supporting the web 1. The coating comprises an applicator roll 3, a counter roll 4 forming a nip therewith and a belt 2. The coating is applied to the surface of the film transfer roll 3 by a blade or rod applicator, a jet applicator or possibly even a pool applicator 35 and transferred from the roll surface to the web. The belt 2 is adapted to pass through a plurality of guide rollers and its speed is set to be the same as the speed of the web to be coated. The guide rollers 7, 8 are arranged on both sides of the roller nip. The web 1 inlet side guide roller 7 can be moved by means of the threaded rod 10 and thus changes the input of the web 5 the angle o. The angle of incidence is the sector of the applicator roll by the web support belt 1 and the cover 2 in each of the inlet side guide roller 7, the control position before the center of the nip 12. Similarly, the downstream guide roller 8 can be moved along guide rails 11 and thus to change the departure angle β, which is the nip October 12 and the center of one of the web separation point assigned sector that roller 3. These angles may also be referred esipeitto-area and the second coverage area. Figure 1 does not show actuators for changing the position of the guide rollers 7 and 8 by means of remote control or automation, for example during operation of the device 15, but such adjustment can be implemented simply by means of threaded rods and controlled electric motors, for example. The force with which the web 1 is pressed against the application roll is adjusted by changing the tension of the belt and by means of both the guide rollers 7, 8 and the counter roll 4.

The counter roll 4 can act as a pressure roller by means of which the nip pressure is adjusted, in which case an adjustment by means of the belt tension is not required or it can be used as another adjustment method. Using both the belt tension adjustment and ·. the adjustment of the nip pressure by means of the counter roll gives a variable pressure for the contact distance of the applicator roll 3 and the web.

Since the distance traveled by the belt 2 changes when the guide rollers 7, 8 are moved, the change must be compensated by always moving at least one other guide roller. In this case, the compensation is made by a control roller 13 adapted to be moved by guides. The track tension of the belt 2 is kept correct by a tensioning roller 14 provided with beams 15. In addition to the above-mentioned rollers, the belt 2 is guided by folding rollers 16 and 17, 35, which can also be movable. In Fig. 1, the web to be coated enters the belt 2 from the left and the web 1 is applied to the surface of the belt 2 via a folding roll 18 so that the web 1 passes between the roll 18 and the belt 2 which folds over it.

8 101489

By changing the incidence angle of the belt 2, the web 1 is made to face the film transfer roll 3 as smoothly as possible, and by adjusting the output angle, the formation of the surface pattern can be controlled. However, these adjustments have the greatest effect on the contact time between the web 1 and the film transfer roll 3. By changing the contact time and distance, the transfer of the coating 10 from the roll 3 to the web can be controlled. The belt also reduces possible vibrations due to cracking of the coating film, which contributes to higher track speeds. The inlet and outlet angles can still be retrieved so that under certain driving conditions as little coating mist as possible is generated when the web detaches from the press nip.

By means of the invention, a double coating method can be implemented with the aid of existing coating devices. In the embodiment of Fig. 2, the blade coater is a short-stay coater and the film transfer coater is a device in which the coating is applied to the film transfer roll 3 by an applicator rod 5. The web 1 to be coated is introduced into the film transfer roll 3 by 8 and the belt 2. The belt guide rollers 7, 8 are arranged on both sides of the counter roll 4 on the inlet side and the outlet side of the web 1. The diameter of the guide rollers 7, 8 is smaller than the diameter of the counter roll 4, whereby the belt 2, guided by the rollers, passes through the triangular web and contacts the counter roll 4 at two points on opposite sides of its axis. The first contact point 30 has a nip formed by a counter roll 4 and a film transfer roll 3, where the counter roll 4 presses the belt 2 against the film transfer roll. On the opposite side of this nip there is a short residence coater 6 with which a second coating layer is applied to the surface of the web 1 against the belt 2 and the counter roll 4. From the short stay device 6, the web leaves the guide roller 9 of the web 1.

9 101489

As can be seen from Figure 2, the belt guide rollers 7, 8 are movable. In the first extreme position of the guide rollers 7, 8, their outer surfaces are flush with the outer surface of the counter roll 4, whereby the belt 2 and the web 1 5 passing through it come from the direction A along a straight line to the nip of the film transfer roll 3 and the counter roll 4. Each belt guide roll 7, 8 can be moved in the direction of the film transfer roll 3 independently or simultaneously with the other roll. Upstream roll 7 transferring the web influencing the angle of incidence, and the application 10 travel date and time before the nip. Inlet second extreme position of the angle of incidence of the web is illustrated by dashed lines, and in this extreme position, the web 1 comes from the direction 8 in extreme position B. The second output side OH jaintelan is also shown in dashed lines. Output-side angle can be influenced by Applikon 15 in time of addition to the coating layer in breakage of the web 1 leaves the coat transfer roll 3. The initial angle is selected so that the applied coating layer should be as smooth as possible.

In addition to the inlet and outlet angle of the web and the application time, the application pressure between the film transfer roll 3 and the belt 2 can also be adjusted. This is only possible when using a belt, since in the nip between the two rollers the pressure is applied only to a short area in the nip, and even if the contact angle of the web 25 with the brush roll is longer, the web can be pressed against the brush roll with little force. In the solution according to the invention, a long-lasting pressure effect is provided on the film transfer roll, by means of which the water contained in the coating is efficiently absorbed into the web and the coating dries, whereby the first coating layer is very resistant to scraper coating.

In addition to the above, the present invention has other embodiments.

10 101489

The double coating can also be made by first applying a first coating layer to the web by a blade coating method, for example a short-stay coating, followed by a second coating layer by a film-5 transfer roll. In this way, a smooth surface is obtained, even if a film transfer roll is used to apply the second layer, because the blade coating smoothes the surface of the web, whereby the next layer also becomes smooth. The quality of the surface is further enhanced by the fact that the belt allows the adjustment of the brush roll appli-10 to be adjusted very well and to provide a better quality coating than before. In addition to the film transfer coating, the application method used may be any known coating method, but methods based on blade or rod scraping are most preferred because they can combine the contour-type coating of the film transfer coating and the flat surface obtained by scraping. The blade coating can be performed with short-stay type devices as described above or in some other way, for example, using roll application, nozzle application or a similar method and subsequent scraping with a rod or blade.

It is clear that the belt passage and the guide and counter rollers. the amount can be freely selected as needed, but if, for example, a separate counter roll is used for each applicator, the structure of the device becomes more expensive. There may be one or more guide rollers and they may be moved independently or synchronously connected to each other. As the scraper member of the film transfer coater, another scraper device can be used instead of the rod. Intermediate drying can be used between the blade coating and the film transfer coating, whereby the amounts of coating used can be increased and the pre-layer can be better utilized.

Claims (20)

A method of coating a paper or paperboard web, wherein the coating (1) web is guided into a film transfer coating device and fed to the notch (12) between the coating surface of the coating device (3) and its counter roll (4), 10 - the coating smear is spread on the surface of the film transfer roller (3), and the web (1) is conveyed through the nip 15 (12) of the rollers (3, 4) and the rollers (3, 4) are rotated, spreading on the applicator roll (3) at least partially transmitted to the surface of the web (1), characterized in that the web (1) is supported by the nip (12) by means of a belt (2) running at the same speed as the web. The web (1) is guided to the surface of the strip (2) before the nip (12) and separated from the strip (2) after the nip, and - the web (1) is pressed by the strip (2). against the film transfer roll (3) and by changing the position of the web (1) and the strip (2), contact sections are controlled. between the web (1) and the film transistor (3). Method according to claim 1, characterized in that the web (1) is pressed against the film transfer roll by the counter roll (4). 3. A method according to claim 1 or 2, characterized in that the contact section between the web (1) and the film transfer roller (3) is controlled by changing the angle of incidence (a) of the web (1) and the band (2). ) to the film transfer roller (3). 5 Method according to claim 1, 2 or 3, characterized in that the contact section between the web (1) and the film transfer roller (3) is controlled by changing the output angle (β) of the web (1) and the strip (2) from the film transfer roller 10. (3). Method according to any of the preceding claims, characterized in that the contact section between the web (1) and the film transfer roller (3) is controlled by changing the incident angle (a) of the web (1) and the strip (2) of the film transfer roller. (3) and their exit angle (β) from the film transfer roller (3). Method according to any of the preceding claims for double-coating a paper or cardboard web, wherein: - a first coating layer is spread on the web including a first coating device, and - a second coating layer is then applied to the coated surface of the web by means of a second coating device, characterized in that the 30: ) is supported by the band (2) at both coating steps. 101489 Process according to claim 6, characterized in that the coating smear is spread at the second stage of the dry first coating layer. 5 Method according to claim 6, characterized in that the coating layer spread at the first stage is dried before the spreading of the second layer. Method according to any of the preceding claims, characterized in that the first coating layer is spread by a film transfer coating device. Method according to claim 9, characterized in that the second coating layer is leveled by means of a blade or a blade. Method according to any of the preceding claims 6-10, characterized in that the first and second coating layers are spread on the web (1) against the band supported by the same counter roll (4). An apparatus for coating a paper or cardboard web, comprising: 25. guide rollers (7, 8) for guiding the web (1) for coating a film transfer coating device and for conveying it to the nip (12) between the film transfer roller (3) of the coating device and its counter roll (4), 30. - a device (5) for spreading the coating on the surface of the film transfer roller (3), and - devices (2, 7, 8, 13) - 18) for transporting the web (1) through the nip (12) of the rollers (3, 4) and for rotating the rolls (3, 4), whereby it is mounted on film. the widening roll (3) widespread coating method is at least partially transferred to the surface of the web (1), characterized by 5. a band (2) for supporting the web (1) through the nip (12), which band is arranged to run around the counter - a first guide roller (18) for guiding the web (1) to the surface of the strip (2) of the nip (12), and of a second guide roller (8) for separating the web (1) from the strip (2) after the nip, and - means (4, 7, 8) for printing the web (1) by the strip (2) against the film transfer roller (3) and for changing the position of the web (1) and the strip ( 2) for controlling the contact section between the web (1) and the film transfer roller (3). Device according to claim 12, characterized in that the position of the first articulated roller (7) can be adjusted to control the contact section between the web (1) and the film transfer roller (3) by changing the inlet angle (a) of the web (1) and the belt (2). ) to the film transfer roller (3). 25 Device according to claim 12 or 13, characterized in that the position of the second articulated roller (8) can be adjusted for controlling the contact section between the web (1) and the film transfer roller (3) by changing the output angle (β) of the web (1). ) and the tape (2) from the film transfer roller (3). Device according to any of the preceding claims 12-14, characterized in that the contact section between the web (1) and the film transfer roll (3) can be controlled by changing the inlet angle (a) of the web (1) and the strip (2) of the film transfer roll ( 3) and their exit angle (β) from the film transfer roller (3). Apparatus according to any of the preceding claims 12-15 for double coating a paper or cardboard web, comprising: - a first coating device for propagating a first coating layer on the surface of the web, and 10. a second coating device for spreading a second coating layer on the coated surface of the web, characterized by - at least one film transfer coating device (3, 5) for spreading a coating layer, and - a band (2) arranged to support the coating web (1) and running from the first coating device (3, 5) to the second coating device (6) and supporting the web (1) during the bite coating steps. Device according to claim 16, characterized by a wiper for drying the coating layer which is widened at the first stage before spreading the second layer. Apparatus as claimed in claim 16 or 17, characterized in that the belt (2) is arranged to run around a counter roll (4) in a manner that it contacts two counter points (4), and that the first application device (3, 5) is arranged in the first point of contact and the second in the second point of contact. . Apparatus according to any of claims 16-18, characterized in that the first application device is a film transfer coating device (3, 5) and the second a coating device (6) comprising a cutting device. 5 Device according to any of claims 12-19, characterized in that it comprises means for controlling the nip pressure between the film transfer roll (3) and the counter roll (4) - 10.