JP4823231B2 - Fiber web processing method and apparatus - Google Patents

Abstract

An Arrangement for processing a paper or board web (1) or a similar fibre web is shown, by means of which arrangement a processing mixture is applied to the surface of the web (1). The arrangement comprises a nip formed by two moving surfaces, elements for taking the web (1) to said nip, and spray nozzles (11) arranged between a dryer-cylinder group (2) and said nip for feeding the processing mixture to at least one surface of the web (1) in such a way that wet processing mixture comes at least between one of the two moving surfaces and the web (1) to said nip, wherein at least one of the moving surfaces forming said nip is provided by a soft roll (8) or a belt.

Description

  The invention relates to a method for treating a fibrous web according to the beginning of claim 1, which method comprises the diffusion of a size mixture, a coating agent or a corresponding treatment mixture, in particular on a paperboard web. The present invention is also applicable to paper webs and other types of fiber webs.

  The invention also relates to an apparatus for applying the method.

  This application relates to processing webs by sizing, pigmenting and coating and calendering. Hereinafter, the present invention will be described using the sizing as an example, which is the most preferable application of the present invention. Of course, the present invention is also applicable to the other objects described above.

The term size usually refers to a water-starch mixture, which is diffused onto the paperboard or paper surface and pushed into the web, for example in the nip between rolls. Size also improves paper printability and surface properties. In addition to starch, the size mixture can also contain a number of additives, and in some cases latex can be used as a binder in size. In principle, the invention is applicable to different types of fiber webs and all size mixtures. Product strength is one of the most important properties of some paperboard grades, such as liners and corrugations used in the manufacture of corrugated paper. The use of size, among other things, significantly increases bending and surface strength, so the objective is to use large amounts of size in these paperboard grades. Currently, larger application rates are achieved using pound-application devices, but their highest running speed is too low for modern demands. Therefore, in modern paperboard machines, film transfer coating is used to spread the size. In film transfer coating, the size is first diffused onto the surface of the film transfer roll, thereby transferring the size to the web. In paperboard machines, simultaneous double sided coating is often used, where the web travels through a nip formed by two film transfer rolls. With these devices, a reasonably high coating amount on the surface of one web, as expressed as a 30-35 g / m ² wet film, is achieved.

  The embodiment using the coating mixture differs from sizing in that the purpose is to keep solid particles of the coating agent on the surface of the web.

  However, film transfer coaters have limitations that reduce their efficiency and economy. The nip pressure obtained at the nip of the film transfer roll provides good size penetration into the fiber structure of the web, but the nip length is very short, so the actual absorption of the size into the web is It only happens later. In practice, the overall absorption time remains short because size drying must be initiated immediately after the nip so that the web can be contact dried and controlled. Even when large amounts of processing agent can be spread on the web using film transfer spreader (s), pounds can be generated between the surface of the web and the surface of the film transfer roll. While the generation of pounds causes splashing damage at high web speeds, pooling can easily occur at low speeds. This so-called mini-pound production limits the highest application amount. This is because the pound causes splashing, web vibration, and also causes the passage of air through the nip when rotating rapidly. In the film transfer nip, the web is wet with a large amount of size, which causes runnability problems. When the web gets wet, the web becomes weaker and breaks more easily. In addition, wetting and drying changes the dimensions of the web, which must be taken into account by adjusting the web tension and, if possible, using a spreader roll. The coating chamber of the film transfer coater is designed with extremely high precision to ensure uniform diffusion of size. However, the material continuously detaches from the surface of the fibrous web and moves directly on the surface of the film transfer roll or moves with the machine circulation into the coating chamber. This can cause disturbances and shield the application chamber, especially when it reaches below the doctor rod. Also, the cradle that bounds the doctor rod and application chamber wears out prematurely, as does the roll surface, which results in a short service interval. This causes a reduction in productivity and direct maintenance costs due to maintenance interruptions. These problems are significant in a paper machine using recycled fibers. This is because foreign substances that cause abrasion are always present in the fibers, the most important of which are sand and especially abrasive pigment-coated particles. Since recycled fiber is an important raw material in the production of paperboard, these problems are particularly pronounced in paper machines used during the production of paperboard. During application, air and impurities can easily enter the coater's machine circulation and must be removed with efficient air removal and filter equipment. These devices are expensive and require a longer machine circulation, increasing their capacity.

  The problems and limitations that appear in filter transfer application have different emphasis when manufacturing different products. Obviously, the risk of web tearing is not as great at paperboard grade as thinner paper that can be made from recycled fibers. On the other hand, when making printed paper or paperboard, the apparatus is less worn and contaminated.

  The present invention diffuses a treatment, effectively a surface size or pigment coating agent, onto a moving fibrous web in an amount that can be varied over a wide range to produce a conventional film transfer or pound press sizer. It is an object to produce a method and a device that makes it possible to eliminate the limitations that exist during application by means of.

  The present invention aims to produce a method and apparatus that can eliminate separate drying after application and subsequent pressing in the nip.

  The present invention is that the treatment agent mixture is diffused onto at least one surface of the web using a spray applicator, after which the web is directed to a nip between two moving surfaces at a location away from the diffusion point. Based. Further, according to one embodiment of the present invention, after application, the web is directed to a nip where at least one surface in contact with the web is heated.

  More specifically, the method according to the invention is characterized by reference to the features of claim 1.

  The device according to the invention is characterized by reference to the features of claim 17.

  A considerable effect is obtained by the present invention.

  The most important effect of the present invention is the variable application amount over a very large area. In particular, a large coating amount makes the method according to the invention more effective than conventional methods. Thanks to the long delay time, even large size mixtures have time to cure on and in the web surface and are not squeezed out in the roll nip. In principle, it is possible with this method to use as many sizes as desired, at least within the limits of existing known sized products. If necessary, a large application amount allows the production of new types of products. The amount and profile of the size can be adjusted by the nozzle feed rate or by changing the nozzle size. The delay is adjusted simply by changing the distance between the coating unit and the press roll. Final adjustment of size penetration is made by changing the nip pressure of the nip of the press roll.

  Preferably, the application is performed simultaneously on both sides of the web, in which case only one application station and dryer are required. The method also allows double application (double application) on a wet surface. This is performed by a roll nip formed in the form of a normal film transfer unit, such as the form in which the press roll has a conventional coating beam, so that a second layer of size is transferred to the web in the roll nip. The treating agent mixture diffuses at a high temperature on the surface of the web, where it is more fluid than usual and drying and curing occurs more quickly on the surface of the web. The evaporation of water is also facilitated by the fact that the web can be brought to high temperatures in a coating device that forms the dryer directly.

  The calendar nip can also be used as, for example, a roll nip in a mode where one of the rolls is a soft roll and the other is a heated roll. Thus, one or both of the rolls can be replaced with a belt, or the nip can be formed from a shoe calendar. Thanks to a heated roll or belt and a long, preferably adjustable delay, drying after pressing can be eliminated if the drying action transferred to the web in the nip is sufficient. In this case, it is possible according to the present invention to replace the application, the nip press process of the application, the calendering and the drying with the application and hot calender nip. In particular, expensive floating or infrared dryers are eliminated, system purchase costs can be reduced, and small spaces can be accommodated, which is particularly effective when rebuilding production lines. This solution is most suitable for pigment application. This is because, in the case of a size with starch, the size adherence to the hot roll or belt surface precludes the use of the method. With regard to sizing, particular attention needs to be paid to the selection of hot surface material so that adhesion is prevented.

  In addition to the effects described above, the disadvantages of sizing by the film transfer press are prevented, which is due to insufficient penetration of the size into the web, i.e. limited strength of the product, the amount of size passing through the film transfer nip Increasingly, avoiding the formation of too large pounds in the roll nip, and premature wear of the application rod and rod cradle and roll surface, especially in recycled fiber machines. Since there is no coating chamber, the chamber is prevented from being shielded by material that detaches from the web. Material that detaches from the web does not enter the machine circulation, and therefore the treating agent mixture does not need to be filtered to remove impurities. Return circulation is also usually not required because all of the coating mixture can be directed to the web. If excess processing agent has to be collected from the roll or spray chamber, excess processing agent can be directed back to the supply tank in a simple manner. The amount is small at this time, and the required transfer device is inexpensive. In addition to these, the pound press has the speed limitation disadvantage imposed by splashing from the pound, which limits the possibility of using them at the web speeds required today.

  The invention will now be described by way of example with reference to the accompanying drawings.

  A sizing station according to the invention is shown in FIG. 1 and is adapted to the production line. In the traveling direction of the web 1, first, the drying cylinder assembly 2 comes, and from there, the web 1 is directly guided to the coating device 3. The application device 3 is followed by a press roll 4 and an air dryer 5 from which the web 1 is guided to finish. Between the drying cylinder assembly 2 and the coating device 3 there is a measuring device 6 that is used to monitor the web 1.

  The coating device 3 includes a press roll 8 mounted in a bearing in the frame 7, and the press roll 8 forms a nip through which the web 1 being processed travels. The roll 8 and the frame 7 may be parts of a conventional film transfer coater, so that in this respect the coating device corresponds to a film transfer coater from which the roll 8 coating device has been removed. The web 1 is guided through the guide roll 9 so as to travel directly downward to the roll 8. The area between the web guide roll 9 and the press roll 8 is surrounded by casings 9 on both sides of the web. Accordingly, the web 1 travels in a space surrounded by the web guide roll 9, the press roll 8 and the casing 10. The edges of the web 1 and possible gaps can be sealed using rubber or sheet metal sealing strips. A necessary number of spray nozzles 11 for diffusing the size mist on the surface of the web are arranged in the casing 10. The pressure dispersion nozzle is preferably used as the spray nozzle 11, which provides a uniform coverage but no drying effect of the dispersion gas. The nozzle pressure is very low, usually less than 1 Mpa and usually about 1-10 bar. However, the moisture in the sizing mixture is so high that, for example, dispersed air cannot detrimentally dry the size mixture in a casing with high internal humidity. If necessary, water vapor can be used as the dispersed gas in the nozzle, in which case no drying occurs, but the size mixture can be heated simultaneously. In this embodiment, no size collection system is required. This is because the size mixture condenses in the chamber on the casing wall, or the mist in the chamber falls or flows onto the press roll 8 and from there onto the web 1. The wall of the casing 10 can be heated, in which case the size mist adhering to the wall will not dry. If the size mixture flowing on the press roll 8 causes defects in the web 1, the excess size mixture is collected and returned to the pulper or machine circulation, for example using a groove in the lower part of the casing 10.

  When the web is treated with a pigment coating agent, drying of the coating mixture can be a greater problem when using an air dispersing nozzle. Therefore, it is more effective to use a pressure distribution nozzle with the coating mixture. At this time, in order to prevent the pigment coating agent from drying, it is desirable that the surface of the coating chamber be cooled without being heated. While the flowability of starch size mixtures increases with increasing temperature, the drying of pigment coatings containing large amounts of mineral-based solids is very rapid when water can evaporate from the mixture into the environment.

  If necessary, several rows of spray nozzles can be used. In this case, for example, when one nozzle row fails during cleaning, the operation can be continued using another nozzle. The device according to the invention is most effective when used in double-sided coating, but of course application on only one side can be used if desired. While the web is torn and other production is interrupted, the nozzle beam is rotated 180E or 90E away from the casing to the cleaning trough, if needed, and the nozzle is checked, cleaned or replaced. Be able to The wall of the casing can preferably be opened for cleaning.

  In the above-described embodiment, the delay time can be adjusted by changing the position of the nozzle row in the casing 10. In this case, however, the casing is large and the adjustment distance is usually short.

  In the solution according to FIGS. 2 and 3, the entire nozzle casing 10 is moved relative to the press roll 8. In this embodiment, the web 1 is guided by the guide roll 10 directly into the nip of the press roll 8 in such a manner that both sides of the web are in contact with the press roll 8 simultaneously. This makes the distance and the amount of delay between coating and pressing the same on both sides of the web 1. The nozzle casing 10 is arranged on a base 13 in a guide 12 that runs parallel to the web 1 and is moved along the guide in order to change the distance between the size mixture diffusion point and the nip between the press rolls 8. Can. The length of the guide 12 can be very large. In practice, the length of guide 12 and the maximum amount of delay are limited by the available space and the length of the section where the web can be moved with a free draw while remaining under control.

  According to the present invention, the amount of delay is adjusted to form the desired amount of processing agent on the web after nip. This adjustment can occur by changing the amount of processing agent or other manufacturing or quality factors of the product, such as web speed, base web material, or the like at a time. Alternatively, the adjustment can be based on a measure of the amount of processing agent after nip, the profile, or surface quality, or it can be based on an adjustment caused by web speed.

  In the nozzle casing 10, nozzle beams 14 exist on both sides of the web 1. The teaching presented in the above example applies to the operation, position and maintenance of the nozzle 10. However, the configuration of the nozzle casing 10 is different. This is because the rolls 8 and 10 do not seal the inside of the casing 10 from the environment. The air conveyed by the web 1 creates a high pressure in the narrow gap and prevents size mist from entering the casing through the gap. Air does not enter the casing through a substantially narrow gap 15 and does not impede nozzle operation. In this case, the nozzle 11 is oriented in the same direction as the web 1, so the nozzle jet 16 will be drawn with the air carried by the web 1 and will be on the web 1. A narrow exit gap 19 is also present in the trailing direction of the web 1 in the traveling direction. The gap 19 is bounded on both sides by the heating chamber 17. The task of these chambers is to prevent the size mixture from drying in the region of the tail of the web. Instead of a chamber, a heated plate or even an unheated surface can be used. Excess treating agent mist is removed through outlet grooves 18 located on both sides of the heating chamber. If necessary, a vacuum can be used to remove the mist, or a small overpressure can be created in the casing with the aid of air provided by the web. Air can be blown into the exit gap on the tail side of the web using a device such as an air doctor to prevent mist from leaking. According to this embodiment, another size spreading device can be arranged to operate at any position on the web, so that the web 1 feed has sufficient straight sections before the press roll. As far as you can, you are extremely free.

  Within the scope of the present invention, the mixture diffused on the web 1 should be wet (wet) when it reaches the press roll nip. In this case, the term wet is the fact that thanks to the nip pressure it will still be possible to achieve penetration of the size into the web, i.e. the fact that the size mixture can be pushed inside the fiber layer. Point to. Otherwise there will be no benefit from the nip. Thanks to the distance between the size mixture diffusion and the press nip, the penetration into the web 1 is adjusted as desired. The size mixture can of course be spread over the web at a fixed distance from the nip, but in this case a substantial part of the adjustment capability will be lost. When the size mixture is made, the size mixture is typically at an elevated temperature of about 50-80 ° C., and the size can be obtained using a heat exchanger before the size is supplied to the nozzle or in the nozzle. In addition, or by air of the circulating heating medium in the nozzle beam, it can be heated to be maintained at that temperature. Size heating reduces its viscosity, improves liquid formation in the nozzle, and promotes evaporation of water on the surface of the web. Since the web comes from the final roll of the dry roll assembly, it is usually very hot, so water will be efficiently evaporated from the hot size mixture that hits the hot web surface. When using a pigment coating agent, it is also possible to use a heated mixture and it is often preferred that water is efficiently evaporated from the coating mixture as it is transferred to the hot web. However, the use of a hot coating mixture causes undesired drying of the coating mixture onto the walls of the application chamber, and therefore, when using a high temperature coating mixture, special considerations prevent drying and prevent the application chamber from drying. Must be done to keep it clean.

  Instead of the roll of the film transfer press used in the present method, for example, it is possible to use a calender nip having one roll having a soft surface and the other roll being heated. Both rolls may also be soft or hard and one or more rolls may be heated. If the rolls are different from each other, two roll nips may be required. In this case, however, the effect of the latter roll nip on treatment penetration will be small. This is because the surface of the web can become dry after the first roll nip. Instead of a roll nip, it is possible to use a shoe calendar or belt comprising one or two consecutive nips. If a metal belt is used in the calendar, the belt can be easily heated or cooled to change the surface properties of the web.

  The present invention is well suited for use in reconstructing or replacing existing pound size presses or film transfer presses. In this case, the technique required to form the pounds, or the coating chamber and the coating or size circulation are removed accordingly. These coating methods are replaced by the present invention by placing a spray coating beam before the roll nip. This type of reconstruction is relatively inexpensive, which can substantially increase the running speed and the amount of processing agent used. Thanks to the higher amount of processing agent, the device can be used to produce a wider product range than before.

1 is a schematic diagram of an embodiment of the present invention. Schematic of 2nd Example of this invention. Detailed view of FIG.

Claims (31)

A method for treating a fiber web (1) of paper or paperboard comprising the application of a treatment mixture to the surface of said web,
Said web (1) to be treated is led from the last cylinder of the drying cylinder assembly (2) to run from a press nip (8) between two moving surfaces,
The treatment mixture is pushed into the web (1) in the press nip (8),
Before the web enters the nip, an amount of the treatment mixture is diffused on at least one side of the web (1) such that the treatment mixture is still wet when the web enters the nip. ,
The treatment mixture is diffused onto the surface of the web (1) in the region between the last cylinder of the drying cylinder assembly (2) and the press nip (8) using a pressure diffusion nozzle (11),
A process, characterized in that excess mist of the processing mixture is removed from the nozzle casing through outlet grooves located on both sides of the heating chamber .   The method according to claim 1, characterized in that the treatment mixture is diffused from a spray nozzle (11) on both sides of the web (1) before the web enters the nip.   At least the amount of treatment agent remaining in the web (1) is reduced by a spray nozzle to change the degree of cure of the treatment agent diffused on the web and the delay time between the spray nozzle (11) and the nip. 3. A method according to claim 1 or 2, characterized in that it is changed by changing the distance to the nip.   4. A method according to any one of the preceding claims, characterized in that the treatment mixture is heated before being fed from a nozzle (11) onto the surface of the web.   The size mixture of claim 1 wherein the size mixture is diffused from at least one surface of the roll forming the press nip to direct additional sizing on the surface of the web and to the press nip. The method of any one of them.   6. A method according to any one of the preceding claims, characterized in that the treatment mixture is diffused onto the surface of the web using a gas dispersion nozzle.   7. A method according to any one of the preceding claims, characterized in that the web (1) is guided to travel from a nip between two rolls (8).   7. A method according to any one of the preceding claims, characterized in that the web (1) is guided to travel from a nip between one roll and a belt.   9. A method according to claim 7 or 8, characterized in that the surface of at least one roll or belt is soft.   10. A method according to any one of claims 7 to 9, characterized in that the surface of at least one roll or belt is hard.   11. A method according to any one of claims 8 to 10, characterized in that at least one roll or belt can be heated.   12. A method according to any one of claims 7 to 11, characterized in that at least one roll or belt can be cooled.   11. A method according to claim 10, characterized in that a heated roll or belt transfers so much heat to the web (1) that no drying is required after the press nip (8).   14. A method according to any one of the preceding claims, characterized in that the web is calendered in the press nip (8) after the application.   15. A method according to any one of claims 1 to 14, characterized in that a shoe nip is used as the press nip (8). An apparatus for treating a fiber web (1) of paper or paperboard , wherein a treatment mixture is applied to the surface of said web;
At least one press nip (8);
A member for guiding the web (1) to the press nip (8);
A member that diffuses the treatment mixture in such a way that the wet treatment mixture reaches the nip between the member and the web (1),
The member for diffusing the processing mixture is a pressure diffusion nozzle (11), and the last cylinder of the drying cylinder assembly (2) and the said cylinder for supplying the processing mixture on at least one side of the web (1) Arranged at an adjustable distance in the direction of arrival of the web from the press nip (8) in the region between the press nips (8),
An apparatus, characterized in that excess mist of the processing mixture is removed from the nozzle casing through outlet grooves arranged on both sides of the heating chamber .   17. The device according to claim 16, characterized in that the spray nozzle (11) is arranged on either side of the web (1).   18. An apparatus according to claim 16 or 17, characterized in that the element for heating the processing mixture is heated before the web is fed. At least one of the elements forming the nip is a roll (8);
19. Apparatus according to any one of claims 16 to 18, characterized by an element that diffuses the treatment mixture onto at least one of the at least one roll (8) forming the press nip.   The apparatus according to claim 16, wherein the spray nozzle is a pressure dispersion nozzle.   The apparatus according to claim 16, wherein the spray nozzle is a gas dispersion nozzle.   Device according to any one of claims 16 to 21, characterized in that the spray nozzle is arranged in the casing (10).   23. Apparatus according to any one of claims 16 to 22, characterized in that the spray nozzle is arranged in a casing which is movable relative to the press nip of the roll (8).   The element forming the nip is two rolls (8), characterized in that the web (1) is guided to travel from the nip between the two rolls (8). The apparatus of any one of 16-23.   The at least one of the elements forming the nip is a belt and the web (1) is guided to travel from the nip between at least one roll and the belt. 25. The apparatus according to any one of 24.   26. Device according to claim 24 or 25, characterized in that the surface of at least one roll or belt is soft.   27. Apparatus according to any one of claims 24 to 26, characterized in that the surface of at least one roll or belt is hard.   28. Device according to any one of claims 24 to 27, characterized in that at least one roll or belt can be heated.   29. Apparatus according to any one of claims 24 to 28, characterized in that at least one roll or belt can be cooled.   30. Apparatus according to any one of claims 16 to 29, characterized in that the press nip (8) is a calendar nip.   30. Apparatus according to any one of claims 16 to 29, characterized in that the press nip (8) is a shoe nip.

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