AT508815A2 - METHOD FOR TREATING A FIBER TRAIN IN A METAL BELT CALENDAR AND DEVICE FOR CARRYING OUT THE METHOD - Google Patents

Description

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The present invention relates to a method for treating a fibrous web in a metal belt calender, wherein in the method an endless metal belt is arranged to rotate about a guide means and to form a process zone with a mating member provided outside the metal belt, and wherein the fibrous web is moistened on at least one side before passing through the process zone.

The present invention further relates to an apparatus for handling a fibrous web in a metal belt calender, wherein in the apparatus an endless metal belt is arranged to rotate about a guide means and to form a process zone with a mating member provided outside the metal belt and wherein the apparatus comprises means for wetting the fibrous web at least on one side before passing through the process zone.

The above-explained method and apparatus for carrying out the same have heretofore been known, for example, from Finnish Patent Application No. 2002 0159 (FI 2002 0159) by the applicant of the present invention. It is disclosed in this document that the moisture control of the web to be treated can be carried out by methods known per se, such as by steaming the surface (s) of the web before the web enters the press zone. By means of moistening and / or temperature regulation, the transverse direction profile of the web can be effected in the desired manner, and this method allows a considerable variation of the web moisture. 2

There are a variety of different types of paper and paperboard and these can be divided into two categories based on basis weight: papers that have a single ply and a grammage of 25-300 g / m2, and boxes made by a multi-ply technique manufactured and have a basis weight of 150-600 g / m2. As can be seen from the above, the borderline between paper and paperboard is slippery, since cartons with the lightest basis weight are lighter than the heaviest papers. Paper is generally used for printing and cartonboard is generally used for packaging.

In the description set forth below, examples of values currently used for fibrous webs are listed, and these may vary considerably from the values disclosed. The descriptions are mainly based on the reference publication Papermaking Science and Technology, Section: Papermaking Part 3, edited by Jokio, M., published by Fapet Oy, Jyväskylä 1999, 361 pages.

Printing papers based on mechanical pulp, i. Wood-containing printing papers include newsprint, uncoated magazine paper, and coated magazine paper.

Newsprint consists either entirely of mechanical pulp or may contain a little bleached softwood pulp (0-15%) and recycled fiber as a replacement for some mechanical pulp. As general values for newsprint, the following values can be considered: basis weight 40-48.8 g / m2, ash content (SCAN-P 5:63) 0-20%, PPS-sl0 roughness (SCAN-P 76-95) 3.0-4.5 pm, Bendtsen roughness (SCAN-P21: 67) 100-200 ml / min, density 600- * · ···

···························································································································································································································· ) 57-63% and opacity (ISO 2470: 1998) 90-96%.

Uncoated magazine paper (SC = supercalendered - supercalendered) typically uses 50-70% mechanical pulp, 10-25% bleached softwood pulp and 15-30% filler. Typical values for calendered SC paper (including, for example, SC-C, SC-B and SC-A / A +) are: basis weight 40-60 g / m2, ash content (SCAN-P 5:63) 0-35%,

Gloss according to Hunter (ISO / DIS 8254/1) < 20-50%, PPS-s10 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%.

Coated magazine paper (LWC = light weight coated) contains 40-60% of mechanical pulp, 25-40% of bleached softwood pulp and 20-35% of fillers and spreads. As general values for LWC paper, the following values can be considered: basis weight 40-70 g / m2, Hunter gloss 50-65%, PPS-sl0 roughness 0.8-1.5 μm (offset) and 0, 6-1.0 pm (roto), density 1100-1250 kg / m3, brightness 70-75% and opacity 89-94%.

As general values for MFC (machine finished coated) paper, the following values can be considered: basis weight 50-70 g / m2, Hunter gloss 25-70%, PPS-s10 roughness 2.2-2, 8 pm, density 900-950 kg / m3, brightness 70-75% and opacity 91-95%.

As general values for film coated offset (FCO) paper, the following values can be considered: basis weight 40-70 g / m2, Hunter gloss 45-55%, PPS-s10 roughness 1.5-2, 0 pm, density 1000-1050 kg / m3 brightness 70-75% and opacity 91-95%.

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As general values for medium weight coated (MWC) paper, the following values can be considered: basis weight 70-90 g / m2, Hunter gloss 65-75%, PPS-sl0 roughness 0.6-1, 0 μπι, density 1150-1250 kg / m3, brightness 70-75% and opacity 89-94%. HWC (heavy weight coated) has a basis weight of 100-135 g / m2 and can be even more than double coated.

Wood-free printing papers made of chemical pulp or fine papers include uncoated and painted chemical pulp based printing papers in which the mechanical pulp content is less than 10%.

Uncoated chemical pulp (WFU) based papers contain 55-80% bleached birch pulp, 0-30% bleached softwood pulp and 10-30% fillers. For WFU the values vary considerably: basis weight 50-90 g / m2 (up to 240 g / m2), Bendtsen roughness 250-400 ml / min,

Brightness 86-92% and opacity 83-98%.

For chemical pulp (WFC) coated printing papers, the amount of coating varies greatly according to the requirements and the intended use. The following values are typical values for once and twice coated printing papers based on chemical pulp: once coated printing paper: basis weight 90 g / m2, Hunter gloss 65-80%, PPS-SLO roughness 0.75-2.2 μπι , Brightness 80-88% and opacity 91-94%, and twice coated printing paper: basis weight 130 g / m2, gloss according to Hunter 70-80%, PPS-SLO roughness 0.65-0.95 μm, brightness 83- 90% and opacity 95-97%. 5

Release papers have a basis weight ranging from 25-150 g / m2.

Other papers include kraft paper, tissue and wallpaper base paper.

Cartons form a rather heterogeneous group comprising such varieties having a high basis weight of up to 500 g / m 2 and those having a low basis weight of approximately 120 g / m 2, the varieties of varieties being on the Base of primary fiber up to 100%, grades based on recycled fiber and ranging from uncoated to multi-coated. In the following, the types of cardboard are divided into coated and uncoated grades, since the coating (coating) has the greatest effect on the calendering process. In coated grades both pre-calendering before the coating station (coating machine) and the end calender after the coating station (coating machine) are used. Uncoated varieties are only exposed to end calendering. These two groups include several types of cardboard as follows:

Coated board: - based on virgin fiber (folding carton box (FBB), bleached pulp board (SBS = solid bleached board), liquid packaging board (LPB), coated white top liner, carrier board) - on base recycled fiber (so-called White-Lined Chipboard (WLC), coated recycled cardboard). ·· • · · · · · · · • · '· · · · · · ♦ ♦ • t ······ • "t · · · · · · · · · · · · ♦♦ ♦ · · · · - 6 -

Uncoated carton: - on the basis of primary fiber (kraft liner, white top liner, liquid packaging board) - on the basis of recycled fiber (so-called test liner).

The following describes calendering concepts for various types of coated paperboard such as cartonboard, white-lined chipboard, solid bleached board and liquid packaging board. Coated carton types vary from one box to one layer to a five-layer carton. The most important properties are a high specific volume, a high rigidity and a high smoothness. The carton is often one-sided but can also be two-sided (SBB cartons).

Pre-calendering is used before the coating station (coating machine) to reduce the roughness and porosity to a desired level characteristic of the coating station. The pre-calendering process is dependent on many variables, the most important variables being: - the construction of the board machine (Yankee cylinder or Yankee cylinder) - raw materials (primary fiber versus recycled fiber, European fiber versus southern US fiber).

The pre-calendering mainly serves the purpose of a calibration control in the CD direction when a Yankee cylinder is present in the board machine (typically a carton box machine). The Yankee cylinder produces an extraordinarily smooth surface with a high specific volume. Pre-calendering is usually done with a hard-nip- ····································································································· ····································································· calander based on either a thermal or hydraulic calibration control. The line loads are typically quite low, 10-30 kN / m, and the thermo roll temperatures are 70-100 ° C.

Typical paperboard grades produced without a plain cylinder are solid bleached paperboard, white-lined chipboard, coated recycled paperboard and liquid packaging board.

Conventionally, pre-calendering was carried out by using a calender with a plurality of rolls and a hard nip, and the calendering effect was enhanced by adding water by means of water boxes (wet pile calender). The number of rolls varies from 4 to 11 depending on the type of cardboard; the even lighter calendered European fibers do not require as many fissures as the fibers originating from the southern United States. Recycled fibers are more easily calendered than primary fibers in a similar fashion.

The ability to raise the temperature of the thermo roll has shifted from pre-calendering to hot calendering. Currently, the goal is to apply a hot hard-edge calendering or soft-calendering. Increased thermocouple temperatures (even exceeding 200 ° C) lead to savings in specific volume due to the temperature gradient. The runnability of a hot hard-nip calender or soft calender is better than that of a multi-roll, hard-nip calender. Similarly, the use of water in wet stack calenders is not easy to control.

Uncoated board grades often have only one layer or two layers. Multilayer uncoated cartons such as

For example, liquid packaging cartons can also be produced, as in the case of coated cartons, the calendering of uncoated cartons should also save specific volume and rigidity.

For some varieties, such as so-called fluting and certain untreated testliner varieties, calendering is not required. Traditionally, calendering has almost always been performed on hard-calender calenders. The presentation and advertising function of wave packaging (fluting) has become increasingly important in the recent past. This has led to increasing demands for a higher quality bleached surface layer. Soft calenders are therefore also used for uncoated board grades where good printability is required. Steam jet sprayers may be used before the calender to improve the calendering result when the board is cooled.

The future trend, as far as the coated grades are concerned, is a long-gap calendering.

It is the object of the present invention to optimally calender a fiberboard, which preferably consists of at least one of the abovementioned paper and board grades, to a higher roughness and to a higher specific volume in the formation step at a lower micron level roughness (PPS) and improved printing properties.

To achieve this object, the method according to the present invention is characterized in that, in order to moisten the fibrous web, the moistening agent is applied to the surface of the fibrous web in a time of 0.2 to 4 seconds before its 9th

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Is delivered to the process zone and that 0.01 to 10 grams of humectant is delivered per square meter, whereby, following passage through the process zone, the specific volume of the fibrous web is greater than 1.40 cm 3 / g and the PPS roughness is 2 to 6 pm.

Moreover, it is characteristic of the apparatus embodying the method of the present invention that the means for wetting the fibrous web at such a point in front of the process zone is arranged in the direction of travel of the fibrous web to which the wetting agent is applied to the surface of the fibrous web Fibrous web can be delivered in a time of 0.2 to 4 seconds before being conveyed to the process zone and that the device for wetting the fibrous web is arranged to deliver 0.01 to 10 grams of the wetting agent per square meter, whereby, subsequent to passing through the process zone, the specific volume of the fibrous web is more than 1.40 cm 3 / g and the PPS roughness is 2 to 6 μτα.

By the method mentioned above, the following objects for improving the properties are achieved. The advantage of these methods is, for example, a significant improvement of the final product.

Preferred embodiments of the present invention are disclosed in the dependent claims.

The present invention will be described below in more detail with reference to the accompanying drawings.

Fig. 1 shows the apparatus for carrying out the method according to the present invention in an exemplary manner. - 10

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Figure 2 is a graph of changes in surface roughness and specific volume of unfoamed and moistened carton in conjunction with calendering.

Fig. 1 shows an apparatus according to the present invention embodied as a belt calender comprising a calendering belt 2 made of metal and rotating about guide rollers 3, of which guide rollers at least one guide roller is movable to control the tension of the belt 2 as desired. The calendering belt 2 passes around a roller 5 arranged outside of it, whereby a calendering zone is formed between the belt 2 and the roller 5. The web W to be calendered passes through the calendering zone, being exposed to the desired pressure pulse and the desired thermal effect as a function of time. Fig. 1 shows by means of a dashed line 9 the shape of the pressure pulse, when a nip roll 4, which acts as a pressing means, is disposed inside the calendering belt 2, said roller presses the belt against the roller 5 and thus a splitting zone with higher pressure within the calendering zone forms. The dashed line 8 in turn shows the shape of the pressure pulse when the contact pressure acting in the calendering zone is generated only by the tension of the belt 2 when the nip roll 4 is not in pressure contact with the belt 2 (or if no nip roll 4 in FIG Inside of the belt 2 is mounted). It is understood from the above explained that this arrangement forms a so-called extended nip. The roll 5, like the nip roll 4, may be a deflection roll, but it need not be such a roll, and it is selected from a group having a flexible surface roll such as one with a polymer 11 11 · · ···

1 1 coated roller, a rubber coated roller or | a roller having an elastomer surface, a shoe roll, a thermo roll and a fiber roll. In the embodiment shown in Fig. 1, the nip roll is a shoe roll. Reference numeral 6 indicates a heater such as an induction heater;

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Infrared radiator, a gas burner or a capacitive heater. In the solution according to the invention, especially when a metal belt is used, elevated temperatures may be applied, for example from more than about 100 ° C to more than about 200 ° C and even up to about 400 ° C, depending on the application. Increased temperature, along with a long operating time and extended pressure regulating range, provides a good calendering result at both high and low speeds, for example at speeds ranging from 100 m / min to 4000 m / min.

To enhance calendering according to the present invention, the web is moistened in the direction of travel of the web at a point preceding the process zone (treatment zone). For this purpose, a moistening device 7 is provided in the vicinity of the fibrous web for distributing a moistening agent onto the surface of the fibrous web. The humectant is usually water (water vapor or mist). Depending on the nature of the web, 0.01-10 grams of humectant per square meter is distributed on the surface of the web. In addition, the humectant is spread on the surface of the web in terms of time 0.2-4 seconds before that point reaches the process zone. This time is also partly dependent on the type of fiber web. It is also obvious that the moistening device 7 is not used 12 φφ ·· ·· ·· ····

In this case, no moistening agent should be spread on the surface of the fibrous web.

The length and / or the total pressure of the process zone can be adjusted with regard to the feed time and / or the volume of the humectant.

As an example, a test measurement carried out by the assignee of the present invention on uncoated carton box, the arrangement corresponding to the arrangement of Figure 1, wherein the roll 5 was a thermo roll and a nip roll 4 was not used to form a to generate increased pressure. The temperature of the surface of the thermo roll was about 170 ° C and the temperature of the back surface of the metal belt was about 80 ° C. The moistening agent was spread on the surface of the web W on the side of the thermo roll where the measurements were made.

With no moistening, a PPS roughness of about 5.7-8.1 μm was typically achieved (the nip pressures were 3-9 MPa), but with moisture levels of 2-6 g / m 2 (with a constant pressure of 5 MPa) PPS roughness about 5.5-6.5 pm. This is shown in FIG. 2. Fig. 2 shows a diagram in which a curve 10 shows the measurement results without moistening. The point 10a corresponds to a press nip pressure of 3 MPa, the point 10b corresponds to a pressure of 6 MPa, and the point 10c corresponds to a pressure of 9 MPa. The curve 11 shows a calendering performed at a constant pressure of 5 MPa of the nip without wetting. Point 11a corresponds to a humidification value of 0 g / m2, point 11b corresponds to a humidification value of 2 g / m2, point 11c corresponds to a humidification value of 3 g / m2, point Ild corresponds to a humidification value of 4 g / m2, and Point Ile corresponds to a humidification value of 6 g / m2. The graph clearly shows an advantageous reduction in roughness when the surface of the web is moistened according to this method. It should be noted here that the square shown in the thick solid line diagram is a target zone (target zone) within which the specific volume and value of the PPS roughness should be desired after calendering. It can be seen that by means of moistening both the PPS roughness and the specific volume will fall into this zone. The setpoint for the specific volume is greater than 1.40 cm2 / g and the setpoint for the PPS roughness is 2-6 μτα.

The experiments carried out by the assignee of the present invention also show a marked improvement in the Bendtsen roughness of the carton in question on the side of the thermo roll.

It is conceivable to use humidification instead of pressure adjustment (metal belt tension adjustment), gap length adjustment, or temperature regulation to obtain PPS roughness. The test was also carried out without a counter roll, which makes it conceivable that the method of improving the smoothness (but so as to maintain the high specific volume) without a counter roll is applicable at least to some types of fiber web. It is also conceivable to reduce the gap load and the temperature while maintaining the quality. This in turn reduces the voltage on the system, increasing its life or replacement interval or maintenance interval.

The present invention is not limited to the above-described embodiment, but may be applied to various ways within the scope limited by the claims. For example, the moistening may be performed on both sides of the web w, and the temperatures applied to the surfaces of the thermo roll and the metal belt may vary considerably depending on the nature of the material.

Claims (4)

·· ····················· Claims 1. A method of treating a fibrous web (W) in a metal belt calender (1), wherein in said method an endless metal belt (2) is arranged to extend around a guide means (Fig. 3) rotates and forms a process zone with a counter element (5) provided outside the metal belt (2), and wherein the fiber web (W) is moistened on at least one side before passing through the process zone, characterized in that to wet the fibrous web (W), the wetting agent is delivered to the surface of the fibrous web (W) in a time of 0.2 to 4 seconds prior to its transport into the process zone, and 0.01 to 10 grams of wetting agent per square meter supplied is, whereby subsequent to passing through the process zone, the specifi volume of the fibrous web (W) is more than 1.40 cm3 / g and the PPS roughness is 2 to 6 pm. 2. The method according to claim 1, characterized in that the wetting agent is distributed at least on that side of the fibrous web (W) whose surface facing the counter element (5) in the process zone. 3. The method according to claim 1 or 2, characterized in that the length and / or the total pressure of the process zone with respect to the feed time and / or the volume of the humectant is adjusted. 4. A device for handling a fiber web (W) in a metal belt calender (1), wherein in the device an endless metal belt (2) is arranged so that it rotates about a guide device (3) and a process zone with a counter element (5) provided outside the metal belt, and wherein the apparatus comprises means (7) for wetting the fibrous web (W) at least on one side before passing through the process zone characterized in that the means (7) for moistening the fibrous web (W) is located at such a point in front of the process zone in the direction of travel of the fibrous web at which the moistening agent is applied to the surface of the fibrous web (W) at a time of 0.2 to 4 seconds before being conveyed to the process zone, and that the device for wetting the fibrous web (W) is arranged so that 0.01 to 10 grams of the wetting agent per square meter dr meter are supplied, whereby the specific volume of the fiber web is more than 1.40 cm3 / g and the PPS roughness is 2 to 6 μιη subsequent to passing through the process zone. Vienna, December 2, 2010 Metso Paper, Inc. by: Haffner and Keschmann Patentanwälte OG