FI105839B - Process and device for making surface-treated printing paper - Google Patents

Description

1 105839

Method and apparatus for producing surface-treated printing paper

The present invention relates to a method for producing surface-treated printing paper according to the preamble of claim 1, wherein the paper is treated after drying.

Such a method advantageously produces paper having certain desired properties.

The invention also relates to an apparatus according to the preamble of claim 13.

Prior art is known e.g. a papermaking process in which the finished calendered paper web is produced in separate processes. In this case, on a paper-15 machine, the web is typically first dried to about 2-4% moisture, i.e. "over-dried", and then the paper is typically moistened with 8-12% moisture before the web is wound. After this, when the paper is on the roll, the moisture is able to even out in the paper in the thickness direction prior to surface treatment in the calender, i.e. calendering. By over-drying herein is meant drying the paper 20 to a lower moisture than it normally should by the time it reaches the calender nip, taking into account that during calendering the moisture of the web is further reduced by more than 2%, resulting in drier paper obtained under calendering .

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Also known is a papermaking process in which the paper • 1 <

In connection with drying Tj, for example, a drying section is used for wetting the web to correct the paper: / moisture profile.

• · 1 t «• · · *:: 30 Calendered paper is also proposed to be produced by calendering the paper making process, whereby the web; calendering moisture, i.e. calendering: T: target moisture.

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However, the prior art presents considerable problems and drawbacks. Particularly in SC paper grade manufacturing processes, in addition to wetting the paper, it is important to control the moisture before calendering to the target moisture for calendering.

Thus, it is an object of the present invention to eliminate the disadvantages of the prior art and to provide a completely novel solution in which the paper-making process takes place in an optimal manner.

The invention is mainly based on the idea that while the paper web is produced by a papermaking process, the paper web is first dried by a drying section or the like to a certain first moisture content, then the web moisture is added to a second, web treating moisture content, after which the web is rolled onto the paper rolls thus formed.

More specifically, the method according to the invention is essentially characterized in what is stated in the characterizing part of claim 1.

In the context of the present invention, the moisture content of a web is defined as the ratio of its water content to its total mass.

According to a first preferred embodiment of the invention, papermaking is performed as a continuous process in the following manner. The webing and mechanical dewatering of the paper .v, 25 are performed in a preselected manner. Thus

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the formed web is further dried so that the moisture content j of the web decreases as desired to a certain first moisture content, after which the moisture of the web is added to a second, # 30, moisture content of the web, which is then higher than the first moisture content; paper handling where its surface properties are affected. The paper is then rolled: V: in a roller reel.

• f · • · · · · ·. In this case, essentially direct web guiding means '*'! 35 wetting locations to achieve the desired dwell time from wetting to paper handling. Preferably, this is determined such that the residence time ·: ·: from wetting to paper handling is 0.2 to 2.0 seconds. The lower limit is determined by • · · i 3 105839 mainly to ensure a uniform wetting distribution in the paper and an upper limit for moisture penetration into the paper. Machine construction is also a determining factor in the upper limit, since the distance traveled by the web from wetting to processing will be long.

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Influencing surface properties is, within the scope of this application, preferably calendering or providing a similar effect. After drying the paper, the surface structure of the web is made desirable by mechanical treatment on the surface, calendering. There are many methods of calendering-10, but they all have in common the passing of a web through one or more nips formed between two surfaces, normally rotating roll surfaces. The purpose of calendering is to improve the quality of the paper by squeezing it to a certain constant final thickness and, in particular, smoothing its surface. Moisture is known to improve the ductility of the fibers contained in the paper during calendering. As a result, calendering is performed at a specific moisture content, the "target calendering moisture".

Preferably, the increase in moisture from the first moisture to the second moisture 20 prior to affecting the surface properties of the paper, such as calendering, is up to 10%, preferably 2 to 10%.

According to another preferred embodiment of the invention, the papermaking is carried out in a continuous process so that the formed web. Drying so that the desired moisture content of the web decreases to a desired first moisture content, preferably <6%, typically T: 2-6% depending on the case, followed by the moisture of the web *; added to the second, to a treatment moisture content of the web, preferably> 8%, more preferably 8% to 12%, i.e. higher than the first: **; 30, after which the web is introduced substantially immediately into the paper treatment where its surface properties are affected.

The invention provides considerable advantages. First of all paper. . ·! ; the dimensional stability is improved when the fibers undergo the first pass.

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'35 This'' over-drying '' is justified by the fact that the moisture expansion potential of the paper decreases as its lowest moisture content in papermaking decreases. This translates into a quieter-acting 4 105839 web, for example in printing. On the other hand, drying to the first moisture content of the paper will equalize any moisture in the paper. In particular, smoothing of small-scale (1-3 cm) old age is important in the method of the invention.

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It is also essential in the process according to the invention that the moisture profile of the resulting paper web is sufficiently straight. Thus, one feature of the solution according to the invention is a method for controlling the moisture profile in the papermaking process. It is conventionally known to use an actuator for controlling the humidity profile 10 with a so-called press section. a profiling steam box and, later on, a profiling water humidifier. However, it has now surprisingly been found that there is a certain stage in the overall process where the use of wetting is not advantageous. Namely, there has been observed in the drying of the web a phase in which the web shrinks sharply, mainly in the transverse direction, and it has been found that the use of wetting in this region can have adverse effects. Typically, the web shrinks strongly in the cross-section in the dry solids content range of 65 to 85%. This range may vary e.g. process conditions and the type of paper being manufactured.

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The invention will now be explained in more detail with reference to the accompanying drawings, in which Figure 1 schematically shows the evolution of the dry solids content of the paper; Figure 2 schematically shows the method according to the invention. development of the moisture content of the web, P · · p m * · FIG. 30: schematically illustrates the process control: T: principle of the process according to the invention, "P f ': 35 FIG. 5 illustrates a preferred arrangement according to the invention for increasing the final test level and calendering, and *"' Fig. 6 shows a possible wetting device with a drying section.

Figure 1 shows how the dry matter content typically develops in evaporative drying of a papermaking machine, such as a multi-cylinder dryer.

5 In the figure, the x-axis numbering corresponds to the number of drying cylinders. Drying cylinders refer to heated cylinders. The drying member may also have non-heated cylinders, such as vacuum rollers, which guide the web. The figure shows a certain area where the aforementioned web shrinkage occurs. On the basis of this observation, the management of the moisture profile 10 according to the invention can be arranged as follows, as shown in Fig. 3.

Figure 2 shows the evolution of the moisture content of the web obtained by the process of the invention. It is seen how the formed web 15 is dried so that the moisture content of the web is desirably lowered to a certain first Moisture content I, after which the web moisture is added to a second Moisture content II, which is higher than the first moisture content, the web is guided substantially immediately into the treatment of the paper where its surface properties are affected. The dashed line and two arrows illustrate the ability to select the Moisture content I of the web. According to the invention, influencing surface properties comprises multi-page calendering or a similar process.

As can be seen in the figure, the first moisture level can be selected for any desired result or other reason. Typically, the first moisture level is 2-6%. This kind of method has I r i t e ... ____ T: There are mainly two purposes. First, the dimensional stability of the paper is improved when the fibers undergo a drying step where it is dried to a first moisture content. In practice, this means more calmly: · :; 30 conductive webs, for example in printing. On the other hand, this procedure smoothes out the moisture in the paper. In particular, smoothing of small-scale (1-3 cm) elders is important with the method of the invention.

Conventional moisture profiling devices have a range of about 50. X. mm and beyond. χΊ 35

According to Figure 3, the apparatus implementing the method can preferably be provided with three actuator positions. The letter A is represented by a press section

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6 105839 steam profile, letter B in the initial drying section, and letter C at the end of the drying section.

The process principle according to one embodiment of the process according to the invention operates in that the paper is dried to the extent or to a high dry matter content that the drying capacity of the drying section is sufficient. In practice, this means a 5-6% moisture level, which means a slight overdrying, but the paper is clearly below the calendering ta 10 moisture level. The paper is rewetted with the post-humidifier in position C. This device may be, for example, a 2 or 4-nozzle row humidifier extending across a 50 mm nozzle spacing. It is preferably mounted above the paper since this way the natural one-sidedness of the paper is best considered. The wetting device may also be provided on both sides of the web to provide mutual wetting.

The moisture profiling of the paper is thus accomplished at positions A and B of Figure 3. The aim is to make the moisture profile of the paper as straight as possible prior to the onset of shrinkage. Preferably, position A has a steam box profiling the press section. By doing this, you will achieve a higher paper dry content and good profile control.

; **; In section B is the water profiling of the paper. A water humidifier is preferably used for this. The profiling in A and B aims to ensure that the moisture profile is as flat as possible before the transverse shrinkage • f r T | Beginning of (CD shrink). According to the invention, the system can also be equipped / also with a moisture profile measurement immediately after point B, whereby the control of the steam box and the water profiler would be based on the signal measured here: 30. This can also be done, if necessary, with a measuring device fitted before the calender and / or roller.

•: •: T: At C, there is a re-humidifier, mainly for the moisture level of the paper. ; is raised from the overdried state to the level required for calendering, i.e. I% r ': 35 to the target calendering moisture. The position of the humidifier is selected according to the principles set out below to ensure an appropriate water absorption time before the first nip of the calender. Humidifier insert-

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Preferably, the I Ϊ 7 105839 is positioned over the paper, which is considerably coarser on the underside. The final roughness of the paper is then minimized. The wetting can also be carried out mutually.

Figure 4 shows a preferred profile management method of the method according to the invention. In the figure, the x-axis shows the number of drying cylinders of the drying section and the y-axis the dry matter content of the paper. The apparatus preferably comprises two measuring devices which are scanner beams having a transverse measuring sensor. The first measuring device is after 10 drying sections before the calender and the second after the calender before the roller. The adjustment method is preferably implemented as follows: Adjustment of the CD moisture profile by means of a vaporizer and / or water moistening prior to the shrinkage area (CD shrinkage area) is based on the humidity measurement of the first measuring device (scanner I). The adjustment is preferably 15 degrees of compromise control, where, for example, 70% of possible moisture profile errors are corrected by steam box A and water profiler B and the remaining 30% by humidifier C. The final humidity adjustment is performed based on the latter humidity measurement (scanner II).

20 A more favorable method of such a solution is shown below. After the water profiler B located before the shrinkage area (in this example, the cylinder 10), a moisture profile measurement is installed which controls both the press box steam box A and the water profile B. Preferably, the measurement is a one-sided 2525 reflective IR humidity meter. The goal is, of course, a straight · *., Moisture profile. Prior to the T: re-humidifier C (located on cylinder 39 in this example), there is preferably a spot humidity measurement (e.g., a reflective / IR meter). This measures the average humidity level before the • · · humidifier C. The actual feedback control humidifier receives: · *: 30 from both the pre-calendar humidity measurement (scanner I) and the pre-roller humidity measurement (scanner II). Pre-calender measurement · · is preferably used for fine-tuning the profile and pre-roller: T: for the correct final moisture level.

• * «♦« J 35 As mentioned above, the rehumidifier is at the end of the drying section. It may then be located within the last drying cylinder group such that the web no longer substantially dries from the moisture level obtained from the rehydration.

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The rehumidification device can then also be located on both sides of the web. Particularly in machine rebuilds, where the distance between the dryer section and the calender cannot be increased or additional devices are placed between them, a sufficiently long distance 5 is obtained between the wetting point and the first calender nip due to the meandering path provided by the last drying cylinders of the dryer section.

Figure 5 shows a preferred apparatus for carrying out the method of the invention. In it, the web W from the drying section is guided through the first 10 measuring devices for measuring the moisture profile, after which the wetting level of the web is raised. Two humidifying devices 1 are shown here, but in certain cases, for example, only one can be used, which is arranged on the desired side of the paper. This is influenced by e.g. the moisture content of the web and the desired paper end properties. The humidifying device 15 is arranged sufficiently far in the direction of web travel before the calender 2 to allow water to be absorbed into the surface layer of the web. The wetting device 1 is preferably a water wetting device which dispenses a suitable amount of wetting water to the surface of the web. A humidifier is, for example, a roller humidifier or a spray humidifier or another humidifier that brings water to the surface of the paper, which may also be in the form of a vapor or a mixture of steam and liquid water. Moisturizing water, as used herein, refers to any aqueous substance, either pure water or water containing or dissolved therein. Calender 2 is a multi-nip calender in which successive nipples are formed between the overlapping rolls of the calender roll stack. The calender can be of any structure used in on- • 25 line multi-nip calendars. It preferably has more than 4 nips, and Figure 1 shows a 6-roll 5-nip calender. It is possible to use; also 8-, 10- or 12-roll calendars and 7-, 9- or 11-nip calendars respectively.

ly The calender comprises rolls with metal and polymer surfaces in a known manner.

After the calender, the paper web W is rolled into a machine roll in the rewinder 3.

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The positioning of the humidifier (s) 1 in position C to achieve a sufficient residence time • · v: is determined by the water absorption time required.

O: Absorption time refers to the time after the application of water to the paper to achieve an optimal calendering result.

e 35 The absorption time is 0.2 to 2.0 s. Relative to the web speeds used on printing papers such as SC papers, the wetting device 1 is located at "... 105 939, usually 5 to 40 m, preferably 5 to 35 m before the calender passes the web. along the track.

Figure 6 shows one way to perform profiling at point B before the start of the transverse shrinkage region. Connected to the lower cylinder of the drying cylinder group is a belt-roll assembly in which the belt loop is guided by a guide roll into contact with the top of the cylinder passing through the cylinder. At the same time, it comes into contact with the roll around which the belt loop passes and which can also be used to influence the pressure of the belt 10 against the web. The belt is in contact with a certain distance to the web, after which it moves to another guide roll which guides the belt to the roll. The wrapping angle of the belt around the cylinder can be adjusted by moving one or both of the guide rollers. By moving the guide rollers, the belt tension can also be adjusted. The water is metered into the belt in a profiling manner before the belt enters the paper web, for example in the area between the roll and the first guide roll. A spray bar or a blade or rod scraper can be used for dispensing water. Due to the good contact between the belt and the web, wetting occurs evenly in forced contact with the web. The strap should be of such a surface that it is well absorbed by water, so that it can be provided with a suitable coating. However, the strap must be able to release the water applied to it into the web.

In addition to profiling wetting, the belt provides a pre-calendering effect on the web. The surface of the web is so moist at this point that the .y of the webbing. The calendering effect is effective even with a slight compression. The belt will then flatten the surface of the web only on a small scale, and • <\\\ | the thickness is not substantially changed. The belt tension and roller generated / pressure also allows water to penetrate well into the paper structure to smooth out the moisture profile. The roller may not be needed: 30 but only the belt tension can be used.

· · V .: The present method preferably also provides so-called.

: T: "gradient paper" in which the bulk of the central portion of the paper is retained in the calendering process using the method of the invention. The calendering process after wetting * · <'\ 35 is characterized in that the process is a gradient calendering process. • "1 dip it to 2-4% moisture and re-moisten it to target II * 10 105839 humidity 8-12% (total moisture) .This type of moistening is that it is done just before calender 2, as opposed to earlier where re-moistening is done. The placement of the humidifier (s) 1 is determined by the water absorption time required by the water 5 as described above.

The wetting device 1 is characterized in that it provides a sufficiently uniform film or layer of water on the surface of the paper. With a spray humidifier, it is known that the average droplet size should be proportional to the amount of water sprayed. Typically, for amounts of water of 0.1 to 10 g / m 2, an average droplet size of about 10 to 100 µm is preferred.

The effect of the moisture gradient on the quality of the paper depends essentially on the steepness of the gradient. When dry, the central parts of the paper behave more resiliently than wet surfaces when pressed. In this case, most of the calendering paper-shaping effect is limited to moist surfaces. After compression, the central portion resumes almost to its original state. As a result, the surfaces are relatively more compacted in calendering than the center of the paper.

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Claims (21)

1. A process for producing surface-treated printing paper, in the folded paper web, is first dried under the surface moisture of the surface treatment and it is again wetted to the surface moisture before the surface treatment, characterized in that dewetting to the surface moisture is carried out on the web applied directly to the surface of the web. treatment of the web surface design device. 2. A method according to claim 1, characterized in that wetting is carried out on the web running from the drying section to treat the web surface. 3. A method according to claim 2, characterized in that the wetting is carried out within the drying portion, preferably in the last drying cylinder group. 15 Method according to claim 2, characterized in that the wetting is carried out after the drying portion. 5. A method according to any one of claims 2 to 4, characterized in that, prior to wetting, the moisture profile of the web is adjusted at the drying portion by wetting the web in a location which is in the running direction of the web before the area of strong shrinkage. Method according to claim 5, characterized in that the moisture profile is adjusted by wetting the web before the paper has reached the dry matter content of 65% in the drying. »C 7. A method according to claim 5 or 6, characterized in that the moisture profile is adjusted before the drying cylinder of the drying portion, preferably before the drying cylinder in the drying cylinder of the portion 21. V ·! 30: V: 8. A method according to claim 7, characterized in that the moisture profile is adjusted prior to the drying portion 15-19. cylinder. 9. A method according to any of the preceding claims 5 to 8, characterized in that the moisture profile of the web is measured according to the moisture wetting carried out at the drying section, and on the basis of this the profiling wetting is adjusted. i t i <»M (•« <<4 4 ((I • • · • · · «« · «« «· * ·« • «· •» - I 16 105839 Method according to any of claims 5 to 9, characterized in that water is spread in a profiled way on the web with a band in contact with the web. 5 11. A method according to any of the preceding claims, characterized in that, in order to achieve the surface moisture of the surface treatment, the wetting water is spread on the moving web 0.2 - 2 s prior to the treatment of the web surface. Method according to any of the preceding claims, characterized in that the surface treatment is multi-nipple calendering. 13. Apparatus for the manufacture of surface-treated printing paper, comprising a device for treating the web surface and means for controlling the web of said device, characterized in that the device comprises a wetting device on the course of the paper web before said device, which humidifier is arranged to moisten the web which has been dried to a moisture lower than the surface moisture of the surface treatment to the surface moisture of the surface treatment. Device according to claim 13, characterized in that the wetting device is in the running direction of the paper web 0.2 - 2.0 seconds before a surface finishing machine, calculated as the absorption time of the wetting water. Device according to claim 13 or 14, characterized in that the wetting device is 5-40 m, preferably 5 to 35 m before said device, measured along the course of the paper web. • · · j Device according to any one of the preceding claims 13-15, characterized in: / ·! In that it comprises a profiling wetting device at the dryer portion. • · • · ♦ • · ♦ • · Device according to claim 16, characterized in that the profiling wetting device is at the drying portion before the 25th drying cylinder,, ··, preferably before the 21st drying cylinder. '' 35 18. Device according to claim 17, characterized in that the profiling wetting device is located before 15-19. drying cylinder. * l «f« «t I <(f I I · c i» · $ «t f (<·« M «w 16 105839 19. Device according to any of the preceding claims 16-18, characterized in that it comprises a humidity profile measuring apparatus after the profiling wetting device in the running direction of the web, which measuring device is reconnected to the profiling wetting device. Apparatus according to any of the preceding claims 16-19, characterized in that the profiling wetting device comprises a band or a corresponding means forming an endless loop and which is arranged in contact with the web, and a profiling dosing device which is arranged to dispense water to the surface of the tape or the like. Apparatus according to any of the preceding claims 13-20, characterized in that the device which performs the treatment of the surface is a multi-nip calender. • · • c • <II • «I • <f • f •« • · · · · · · · · · · · ♦ · • ·· • · · · · · · * · · • · · • # · • • f «· · • • • • f · • · · • * C r> l * tfrir II« »« «I (I t I •« · • ·