FI121185B - Method for Processing a Fiber Conveyor Imported into a Metal Belt Calender Prior to Export to a Metal Belt Calender and a Metal Belt Calender - Google Patents

Description

Method for Processing a Fiber Conveyor Imported into a Metal Belt Calender Prior to Export to a Metal Belt Calender and a Metal Belt Calender

The present invention relates to a method of treating a fiber web to a metal belt calender prior to exporting it to a metal belt calender to prevent an excessive increase in vapor pressure of the fiber web in a metal belt calender comprising a heated metal belt rotation having at least one a counter roll around which the metal belt is rotated so as to form an extended calendering area between the belt and the counter roll. The present invention further relates to a metal belt calender with which the method can be implemented.

There are a number of different types of paper and board, and they can be divided into two classes by basis weight: single-ply papers with a basis weight of 25-300 g / m2 and cartons made with a multilayer technology and 100-600 g / m2. As noted, the boundary between paper and board is sliding, since the lightest board is lighter than the heaviest paper. Usually paper is used for printing and cardboard for packaging.

The following descriptions are examples of currently used fiber web values and may exhibit considerable variations in the given values. The descriptions are mainly based on the source paper Paperma-25 king Science and Technology, part Papermaking Part 3, Finishing, ed. Jokio, M., published by Fapet Oy, Jyväskylä 1999, 361 pages.

Mechanical pulp or wood-containing printing papers are newsprint, uncoated magazine paper and coated magazine paper.

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Newsprint can either consist entirely of mechanical pulp or may contain low levels of bleached softwood pulp (0-15%) and / or recycled fiber may be used to replace mechanical pulp. Common values for newsprint are: 40-48.8 g / m 2, ash content (SCAN-P 5:63) 0-20%, PPS 50 (SCAN-P 76-95) 3.0-4.5 pm, Bendtsen roughness (SCAN-P21: 67) 100-200 ml / min, density 600-750 kg / m3, lightness (ISO 2470: 1999) 57-63% and opacity (ISO 2470: 1998) 90-96%.

Uncoated magazine paper (SC = supercalendered) generally has a mechanical pulp of 50-70%, bleached softwood pulp 10-25% and fillers 15-30%. Typical values for calendered SC paper (including, inter alia, SC-C, SC-B and SC-A / A +) are 40-60 g / m 2 basis weight, ash content (SCAN-P 5:63) 0-35%, Hunter gloss ( ISO / DIS 8254/1) <20 - 50%, 15 PPS slO roughness (SCAN-P 76:95) 1.0 - 2.5 pm, density 700 - 1250 kg / m3, brightness (ISO 2470: 1999) 62 - 70% and opacity (ISO 2470: 1998) 90 -95%.

Lightweight coated magazine paper (LWC) contains 40-60% mechanical pulp, 25-40% bleached softwood pulp and 20-35% fillers and coatings. The general values for LWC paper are as follows: basis weight 40-70 g / m2, Hunter gloss 50-65%, PPS S10 roughness 0.8-1.5 pm (offset) and 0.6-1.0 pm (roto), density 1100-1250 kg / m3, brightness 70-75% and opacity 89-94%.

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The general values for machine finished coated MFC paper are: 50-70 g / m2 basis weight, Hunter gloss 25-70%, PPS S10 roughness 2.2-2.8 pm, density 900-950 kg / m3, lightness 70- 75% and opacity 91-95%.

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The general values for FCO (film coated offset) paper are: non-specific weight 40-70 g / m2, Hunter gloss 45-55%, PPS S10 roughness 1.5-2.0 pm, density 1000-1050 kg / m3, lightness 70-75% and opacity 91-95%.

General values for MWC (medium weight coated) paper are: 70-90 g / m2 basis weight, Hunter gloss 65-75%, PPS S10 roughness 0.6-1.0 pm, density 1150-1250 kg / m3, lightness 70 - 75% and opacity 89-94%.

10 HWCs (heavy weight coated) have a basis weight of 100-135 g / m2 and can be coated more than twice.

Pulp wood-free printing papers, ie fine papers, are uncoated - and coated pulp-based papers with a mechanical pulp content of less than 10%.

Uncoated pulp base in printing papers (WFU) is bleached birch pulp 55-80%, bleached softwood pulp 0-30% and fillers 10-30%. The values for WFU range widely: 50-90 g / m 2 (up to 20,240 g / m 2), Bendtsen roughness 250-400 ml / min, brightness 86-92% and opacity 83-98%.

For coated cell-based printing papers (WFCs), the coating amounts vary widely depending on the requirements and the application. The following are typical values for single and double coated pulp based paper: 90 g / m2 coated once, Hunter gloss 65-80%, PPS slO roughness 0.75-2.2 pm, brightness 80-88% and opacity 91-94 % and double coated 130 g / m2, Hunter gloss 70-80%, PPS S10 roughness 0.65-0.95 pm, brightness 83-90% and opacity 95-97%.

For release papers, the basis weight ranges from 25 to 150 g / m2.

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Other papers include e.g. packaging papers (Sackkraft), tissue papers (Tissue) and wallpaper (Wallpaper).

Pulp, mechanical pulp and / or recycled pulp is used for the production of paperboard. The cartons can be divided into e.g. to the following main categories according to their intended use.

Corrugated cardboard with a liner and fluting.

10 Cartons for making cartons, boxes. The cartons are e.g. liquid packaging board (FBB = folding boxboard, LPB = liquid packaging board, WLC = white-lined chipboard, SBS = solid bleached sulfite, SUS = solid unbleached sulfite).

15 Graphic paperboard, of which cards, folders, folders, covers, covers, etc.

He deceived the cardboard (Wallpaper base).

20 The surface properties and thickness profile of the various papers and board are adapted to the requirements of printing and finishing by calendering. Typically, coated species are pre-calendered before coating and final calendered after coating.

25 Calendars are divided into machine calendars, soft calendars and multi-roll calendars. The machine calender typically has 1-2 nips and both rolls of the nip are hard rolls. The soft calender generally has 1-4 nips and at least one of the nip rolls is covered with a soft coating. The multi roll calender typically has 5-11 nips. The multi roll calender roller has both heated roller-30 and soft-surface rollers.

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Special calendars include: wet stack, breaker stack, and long nip calendars.

The Wet stack calender is approximately identical to the multi-roll machine calender 5, but the calendering process is completely different. The Wet Stack Calender effectively utilizes a moisture gradient so that the humidity of the web entering the calender is only about 1-2%. The Wet stack calender has water boxes to form a film of water on the surface of the web before the nip, which film is pressed onto the web surface in the nip. In this case, the web is only wetted from the surface by calendering 10 more from the surface than from the overdried interior. The Wet stack calender is used as a pre-calender for a variety of board grades.

An intermediate calender is a machine calender located in the drying section of a paper machine.

15 Long nip calendars include a shoe calender with a soft jacket around the shoe roll and typically having a nip length of 50 ^ 400 mm, and belt calendars. A conventional belt calender consists of a soft roll calender thermo roll, a belt roll and an inside roll roll counter roll, which can be a hard or soft roll. The belt rotates through the counter roll and the guide / tension rolls.

A special application of the belt calender is a metal belt calender, wherein the calendering belt is a metal belt that rotates around the guide rolls and together with a counter member, typically a roll, forms a long nip band of up to 5000 mm in length. In addition, a compression member, e.g. a deflection compensated roll, can be tracked inside the belt passage, by means of which a nip point of a higher compression pressure can be tracked in the middle of the long nip zone.

The high temperature of the belt is used with the metal belt calender, whereby the web typically dries by about 2%, which means that the moisture of the web when entering the calender must be reasonably high. When the web becomes wet and hot, the metal belt calender runs the risk that the pressure of the steam in the web exceeds the pressure exerted by the belt against a counter roll, e.g., a thermal roll (about 0.2 MPa). When the vapor pressure exceeds the belt pressure, a certain type of sound "vibration" is heard from the vapor discharge. This phenomenon may cause quality problems for the final product. Poor hall air conditioning and a nearby hot cylinder group can exacerbate this problem.

Because of this problem, the metal belt calender may not be able to run under the desired process conditions, such as certain belt temperatures and the incoming track humidity, which will reduce the drive belt calender window.

It is an object of the present invention to provide a method by which the above problem can be significantly overcome. To achieve this object, the method according to the invention is characterized by the features set forth in the characterizing part of independent claims 1 and 3. For cooling, a separate cooling apparatus may be used, located at a position ahead of the metal belt calender, or alternatively, cooling may be accomplished using an imaging device integrated with the metal belt calender, including a metal via the metal belt calender to the calendering area located between the heated metal belt and the counter roll.

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A separate cooling device may be, for example, a cooling float in which cool dry air mixes with water vapor from the web and lowers the humidity and temperature of the boundary layer air and further reduces the risk of said "buzzing problem". In addition, such a fluid blower removes damp boundary air.

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In the method according to the invention, a metal belt calender comprising a metal belt arranged to rotate around at least one guide member is provided as a separate cooling device, and at least one cooled roll forming a contact surface with the belt is provided on the outside of the belt. A cooling zone is formed between the belt 5 and the roll through which the web to be processed can be passed. The roll is preferably arranged to be internally cooled, e.g. by liquid air or nitrogen, cooled particles, ice cubes, low temperature vaporizing agent and / or various combinations thereof.

10 For example, with the single wire drainage dryer used for runnability, the moisture of the paper is gradually drained to the non-heated side. Then, immediately after the drying section, strong evaporation occurs on the upper surface of the paper, whereby the paper is typically curved upwards. Curvature is currently controlled by a separate water humidifier installed at the end of the drying section, or by drying unit processes (such as coating) that follow it. A particular disadvantage of water humidification is often the line drying limitation resulting from the wetting, which prevents the running speed from being increased. In addition, investing in a humidifier entails relatively high costs, the amount of which depends on the width and speed of the machine. The metal belt calender makes it possible to heat both sides of the web 20 with a long lag time, whereby the web's moisture profile in the direction of the web may seek equilibrium. By driving the moisture profile symmetrically or possibly slightly compensating for the stresses generated by the drying section, the curvature of the fiber web due to unilateral drying stress can be controlled. This means that the drying section does not require a separate humidifier with its relatively high investment costs and, on the other hand, the entire drying section can be realized from the beginning to the end with the best single wire delivery. This curl management solution is particularly suitable for newsprint, enhanced newsprint and copy paper where the metal belt calender provides sufficient paper quality properties 30 and, on the other hand, calendering no longer follows other unit processes. Solution 8 can also be applied to other grades of paper or board if the long-nip fishter serves as a final calender.

The invention further relates to an improved metal belt calender which provides a relatively simple solution for cooling a fiber web to be introduced into the calender area of the metal belt calender before being exported to said calender region. To achieve this object, the metal belt calender according to the invention is characterized in that a drying device is integrated with the metal belt calender prior to the metal belt calendering region 10, which includes a through the cooling zone between the heated metal belt to the calender area of the metal belt calender.

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The invention will now be further described with reference to the accompanying drawings, in which:

Figure 1 is a schematic schematic view of a metal belt calender arrangement of the invention,

Figure 2 shows a prior art arrangement for polishing cardboard with a polishing cylinder; Figure 3 shows a modification of the apparatus of Figure 2 with a metal belt cycle,

Figure 4 illustrates the use of a metal belt calender for applying a chemical to a fiber web surface;

Figure 5 illustrates the use of a metal belt calender as a replacement for a cooled winding cylinder,

Figure 6 illustrates a metal belt calender arrangement in which the fiber web to be processed is arranged to rotate around a metal belt cycle,

Figure 7 illustrates an arrangement for preheating a fiber web,

Figure 8 shows an arrangement for heating a roll of a metal belt calender, and

Fig. 9 shows an arrangement for heating a belt of a metal belt calender.

The improved metal belt calender 1 according to the invention shown in Fig. 1 includes a heated metal belt 2 arranged to rotate around the guide rollers 3 arranged to rotate around the heatable roll 4 so that a long calendering zone is formed between the roll 4 and the metal belt 2. Optionally, an additional loading roll 5 may be provided inside the metal belt loop 2 to form a higher pressure nip with the hot roll 4. The improved metal belt calender according to the invention further comprises a cooling device integrated therein, which includes a cooled cylinder 6 disposed at a position preceding the zone, around which the wire or felt 8 is wound through a guide roll 7. The fiber web W is arranged to pass through a cooling area between the wire or felt and the heated metal belt to the calendering area of the metal belt calender. The fiber web is then supported by a cooled wire / felt and the other side of the fiber web is pressed with a lightly heated metal belt, whereby the water in the web is condensed on the cold surface of the wire.

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In the integrated cooling device and metal belt calender solution of the invention, the fiber path is supported in the first step of the process by a cooled wire / felt, which in turn is cooled. On one side, the fiber web is pressed with a lightly heated metal belt, whereby the water of the web stays on a cold surface in a wire. For example, the cooling cylinder can be made from a used Yankee cylinder by converting it into a large cooling cylinder. In the second step of the process, the fiber web is calendered with a metal belt calender to achieve final smoothness. In particular, since the drying process carried out by means of a cooling core cylinder and a metal belt produces an asymmetric product (wire pattern on the backside), the calendering is adjusted as best as possible to correct this bias. If necessary, other drying techniques (over-blowing, cylinder drying, etc.) can further enhance the drying efficiency. Metal belt calendering also provides part of the drying power. The integrated structure according to the invention is advantageous over the solution implemented as a separate cooling device and as a metal belt calender because the metal belt rotation is combined, whereby the structure is simpler and can be achieved with the same belt heating devices.

Metal belt rotation can also be utilized in board polishing, for example. Currently, cardboard polishing is typically performed as illustrated in Figure 2 by a polishing apparatus 20 equipped with a polishing cylinder 21 (Yankee cylinder). The web W is pressed onto the polishing cylinder 21 by a press n felt 25. Outside the board web, the wire 22 orbiting the guide rollers 23 holds the web against the polishing cylinder. The web is detached from the cylinder surface when the wire contact ends and is passed through guide rollers 24 for further processing. In order to remove the web without damage, the web must have a dry solids content of about 72%. The drying capacity is proportional to the circumference of the cylinder, the practical maximum age would be and when the cylinder is 6.7 m, this condition limits the machine speed.

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Figure 3 illustrates an improved belt polishing device solution 30 utilizing a metal belt. In it, the metal belt 33 runs around the polishing cylinder 21 and is provided with a cam-like extension that rotates through the guide rollers 31 and 32. The cylinder heats upon contact with the metal belt, which in turn 5 heats the board web W. The press felt 25 presses the web onto the metal belt 33. The wire 22 outside the carton track holds the web against the metal belt 33. The web is removed from the surface of the cylinder when the wire stops contacting the web. The metal belt 33 may be significantly longer than the diameter of the cylinder 21. Once the metal belt is released from the cylinder contact, it still has a thermal capacity of 10 that can be used to dry the web. The belt may also be heated from the opposite side of the web. By this method, the drying capacity of the polishing cylinder and the production speed of the machine can be increased to a greater extent than is possible with the cylinder alone.

The metal belt calender can also be utilized for the application of small or very small amounts of functional chemicals, for example, in connection with wetting the calender. The application arrangement can be accomplished by introducing the paper into the nip of the metal belt calender through a vapor chamber containing the chemical in the vapor phase, whereby the paper receives a "steam bath" before going to the metal belt calender. In this way, it is attempted to fill the paper with the desired chemical prior to pressure treatment in the metal belt calender. Figure 4 illustrates one such arrangement. This arrangement includes steam chambers 46A, 46B, between which the fibrous web is introduced before being introduced into an extended treatment zone between the heated roller 44 and the metal belt loop 42. A metal belt is arranged to rotate around the guide rollers 43 and a press roll 45 is provided inside the metal belt cycle to provide an elevated pressure nip point with the heated roller 44. The fiber web W passing through the steam chamber receives steam treatment before going into the metal belt calender, whereby the desired chemical can be applied to the fiber web prior to pressure treatment in the metal belt calender. Applying the chemical in the vapor phase to the paper prior to entering the pressurized metal belt calender compression zone provides the most favorable conditions for the reaction of various chemicals with the cellulosic fibers of the paper. When dispensing the appropriate amount of steam before the nip, the steam discharge after the nip contains almost 5 steam only water. This allows 100% retention of the chemical. In addition, keeping all metal surfaces in contact with the steam hot prevents the condensation of water-containing water vapor on the fibers and calender surfaces.

It is also an essential part of this solution that the chemical reacting directly from the vapor phase with the OH groups of the cellulosic fibers in the paper avoids the disadvantage of the prior art in which almost all chemicals to be dispensed are introduced into the paper in liquid phase or liquid (water). Wetting the paper in this way requires the re-drying of the 15 webs and causes various adhesion problems to the surfaces of the paper machine components.

This solution offers significant advantages: - providing a practical embodiment for dispensing many wet-applied chemicals, such as hydrophobic adhesive, into dry paper without wetting it - many (or even all) chemicals can be applied to dry paper and fabricated from fiber, filler only. and water. The mere removal of hydrophobic sizing from the wet end results in significant savings through wet end cleanliness and simplification of equipment.

- Allows dosing of extremely small and at the same time absolutely uniform amounts of chemicals - this allows for untreated chemical treatment with a calender calender using small quantities of chemicals 13 - "Calender dosing" can be accomplished without roller sticking risks, applicator sticking, etc.

5 The application of a surface chemical can be utilized to control the moisture content of the fiber web by changing the dry matter content of the surface chemical. The penetration of the chemical into the fiber web can be controlled by nip pressure. The wetting of the fiber web can also utilize the belt of the metal belt calender, e.g. by spraying water to the surface of the belt, from where it is transferred to the fiber web.

10 A metal belt with cooling elements may also be used as a replacement for a cooled winding cylinder. Figure 5 illustrates an example of such an embodiment in which the winding cylinder is replaced by a metal belt twist 52. The metal belt rotates around the guide rollers 53 and cooling members 55 are provided in connection with the metal belt cycle to cool the metal belt. The fiber web W from the multi-roll calender 56 is rolled up by the apparatus 50 to 54.

The path of the web in the metal belt calender can be arranged such that the web rotates along the metal belt rotation to form a hood, thereby providing both web preheating and a substantial reduction in heat loss. Figure 6 illustrates an example of such a web export in a metal belt calender. The fiber web W is arranged to rotate around the metal belt 62 passing around the guide rollers 63 before being introduced into the calendering zone between the metal belt 62 and the counter roll 64. In this arrangement, the 60 fiber web W forms a hood that prevents heat loss while providing preheating of the web prior to its introduction into the calendering area.

For example, a steam blasting device may be used to preheat the web before the nip of the metal belt calender. Figure 7 illustrates one such arrangement for preheating the fiber web W before the nip of the metal belt calender. This device 70 includes a steam shoe consisting of a plurality of steam chambers 71, which slide over a vapor film directed against the web, whereby the steam is pressurized and a higher temperature is achieved. The device is used to heat / humidify the web and to perform a star addition. The steam box box 5 can also be used to heat a roll or belt.

Fig. 8 shows an arrangement in which the heated roller 81 of the metal belt calender 80 is heated by a steam chamber 82 and Fig. 9 shows an arrangement 90 in which the steam chamber 10 with sliding seals 94 is used to heat the metal belt 92.

The integrated cooling device and metal belt calender solution described above can also be considered as a non-cooling solution in which the cooling cylinder is replaced by a thermal roller, whereby two elongated nips are formed in the metal belt calender. Figure 10 illustrates one embodiment of such an alternative metal belt calender as a schematic example. Arrangement 100 includes a metal belt 102 rotating about guide rollers 103, as well as two thermal rollers 104 outside the belt. Optional press rolls 105, which may be e.g. deflection compensated rolls, are disposed on each of the rolls. The guide rollers 103 may further be provided with support rollers 107, which may be one or more per guide roller. In the case of a plurality of support rollers, they may be disposed axially successively along the length of the guide roll and / or at different positions viewed in the circumferential direction. The path W passes from the long nip 25 between the first thermal roller 104a and the metal belt 102 to the second extended nip between the second thermal roller 104b and the metal belt 102. This arrangement can also be used so that, if necessary, one of the extended nips is bypassed, thus providing greater access to the calender.

Claims (4)

A method of treating a fibrous web (W) to be measured in a metal strip calender prior to the web is fed to the metal strip calender to prevent the meadow pressure in the moisture of the fibrous web from rising too much in the metal strip calender, the metal strip calender having a heatable metal strip run (2). ), within which is provided at least one guide roll (3) and above which is provided at least one heated support roll (4), around which the metal strip runs, so that an extended calender zone is formed between the belt and the support roll, in which the method web (W ) is cooled at least from one side and the moisture content of the web is lowered before it is brought into the calender zone of the metal band calender by using a separate cooling device arranged at a location before the calender zone of the metal band calender, characterized in that in the method used as the separate cooling device, a metal band cage is used. an at least one control means running the metal strips above which the strip is arranged at least one contact surface formed with the strip forming a cooled roll, such that a cooling zone is formed between the strip and the roll through which the web to be treated is passed. 20 2. A process according to claim 1, characterized in that in the process the cooling roll is cooled internally with liquid or nitrogen air, cooled particles, ice cubes, low temperature extensible substances and / or their various combinations. 25 3. A method of treating a fibrous web (W) to be measured in a metal strip calender before the web is fed to the metal strip calender to prevent the meadow pressure in the moisture of the fibrous web from rising too much in the metal strip calender, the metal strip calender exhibiting a heatable metal strip run (2) , inside which is provided at least one guide roller (3) and above which is provided at least one heated support roller (4), around which the metal belt runs, so that an extended calender zone is formed between the belt and the support calender, in which the method web (W ) is cooled at least from one side and the moisture content of the web is lowered before it is brought to the metal band calender zone by using a separate cooling device arranged at a position before the metal band calender zone, characterized in that in the method an dryer integrated into the metal band calender is used. to which one belongs to the band run of metal band scandals p (2) provided cooling cylinder (6) around which a wire or blanket (8) runs, the web being passed through the cooling zone between the wire or felt (8) running around the cooling cylinder and the heated metal band to the metal band calender zone, arranged between it heated metal strip (2) and support roll (4). 4. Metal band calender (1) for treating the coated or uncoated fiber web, to which calender includes a heated metal strip (2) running around a food element (3), outside of which a band surface at least one with the band forming a contact surface forming means (4) ) is arranged so that a calender zone is formed between the belt and the support member through which the web to be treated can be passed, the length of the calender zone defined by the position of the belt guide member and / or the design of the support member, characterized in that in connection with the metal belt calender a drying device has been integrated into a position before the calender zone of the metal band calender, which device has a cooling cylinder (6) arranged against the metal band calender running around which a wire or a blanket (8) runs, the web being arranged to pass through the cooling zone between the cooling cylinder running the wire or felt (8) and the heated metal band (2) to metal band alander's calender zone.