FI101488B - Method for drying a surface-treated paper web or the like in a post-drying section of a special paper machine and a post-drying section of a paper machine applying the method - Google Patents

Abstract

The invention concerns a method for drying a surface-treated paper web or equivalent in an after-dryer of a paper machine, in which method the paper web (W) is first finished in a finishing section, in which finishing section the paper web (W) is surface-sized or coated by means of a finishing device (10), after which the paper web (W) is dried. In the after-dryer the paper web (W) is dried in a dryer group/groups making use of a normal single-wire draw, and, in connection with or after the drying, the paper web (W) is treated by means of a device/devices (192, 191, 201, 202) in order to compensate for a tendency of curling of the paper web (W). Further, the invention concerns an after-dryer for a paper machine for applying the method to the drying of a surface-treated paper web or equivalent, which after-dryer is placed after the finishing device (10), by means of which finishing device (10) the paper web (W) is surface-sized or coated. The after-dryer comprises at least one dryer group that applies a normal single-wire draw so as to dry the paper web (W) and a device/devices (191, 192, 201, 202) for compensating for a tendency of curling of the paper web (W).

Description

101488

Method for drying a surface-treated paper web or the like in a post-drying section of a paper machine and a post-drying section of a paper machine applying the method A method for drying a paper machine or a similar paper in a paper machine or a paper machine

The invention relates to a method for drying a surface-treated paper web or the like in a post-drying section of a paper machine, in which method the paper web is first post-treated in a post-treatment section in which the paper web is surface glued or coated on both sides with a post-treatment device.

The invention also relates to a post-drying section of a paper machine for applying the method according to the invention for drying a surface-treated paper web or the like, which post-drying section is located downstream of the post-treatment device.

• · '20 It is known that paper machine multi-cylinder dryers use a two-wire outlet • · «: ·' and / or a single wire outlet. In the two-wire outlet, the drying cylinder groups have two wires, • · \ which press the web one against the upper and the other against the heated cylinder surfaces. Between the rows of drying cylinders, usually horizontal rows, the web has free and unsupported stretches that are prone to flutter, which can cause web breaks, • · · 25 especially when the web is still relatively moist and therefore weak. Because of this :·. whereas the use of such single - wire exports has recently begun to take place,. ·: ·. wherein each drying cylinder group has only one drying wire supported. the web passes through the entire array so that the drying wire presses the web against the heated cylinder surfaces with the drying cylinders • · • · · and with the turning cylinders _ · 30 or rolls between the drying cylinders the web remains on the outer curve side. Thus, for single-wire exports, the drying cylinders *; '; are outside the wire loop and the pivot cylinders or rollers are inside it.

I «I • · 101488 2

In the already known so-called in normal single-wire export groups, the heated drying cylinders are in the top row and the pivot cylinders are in the bottom row, which rows are generally horizontal and parallel to each other. In inverted single-wire export groups, on the other hand, the inverting cylinders are in the top row and the drying cylinders in the bottom row. When the terms "normal (drying) group H and" inverted (drying) group "are used in the following 5, single wire export groups of multi-cylinder dryers such as those mentioned above are specifically meant.

When the paper is dried with normal single wire export groups on its lower surface side and if such asymmetrical drying is extended over the entire length of the front drying section, drying takes place by first drying the lower surface side of the paper web and spreading the drying effect to the upper surface side of the paper web. Thus, the dried paper is generally curved when viewed from above.

15 The tendency of the paper to warp is already known in connection with the quotation, especially in the sheet-forming phase by the choice of the speed difference between the lip jet and the wire, as well as by other driving parameters. As is already known, e.g. with copy paper, the drying one-sidedness in the post-drying section adjusts the initial curvature suitable for the sheet so that the curvature of the paper after one- and two-sided copying can be optimized. On copy paper, the reactivity of the curl, i.e., how much curvature occurs per unit of moisture change, is more affected by the i * .. layered structure of the paper, which is formed during webbing at the wet end.

• «I t» • · • ·

The most recent state of the art related to the invention in high speed paper machines, especially in fine paper machines, has been based on drying sections with a single wire length for most of its length and in practice a inverted group has always been used to control the tendency to curl. sufficiently symmetrical in the z-direction.

In conventional post-drying sections of a paper machine in which the web is dried after coating or surface sizing, the problem has been the swelling of the web due to the moisture introduced into the web by the coating, which causes "wrinkles" and other similar runnability problems. In the two-wire export traditionally used with the post-drying section, the web flakes between the top and bottom rows, whereby web breaks are easily caused, and in addition, the bottom row drying cylinders easily damage the bottom row drying wire 5 due to the wrinkles.

In addition, as is known in the art, problems have also been caused by the deterioration of the web caused by the coating, whereby long free web exports have been quite problematic.

Solutions are known in the art for the post-drying section of paper to be coated, in particular fine paper or the like, having first an upper and a lower cylinder and then one group applying a normal single-wire export and then a drying group applying a two-wire fifth. The problem with these applications is that the ratio of the upper and lower cylinders is incorrect in terms of the tendency of the paper to warp, if it is desired to effectively adjust the warp. As is known in the art, the temperature of the first cylinders in the post-drying section has had to be kept low due to the adhesion of the web and the adhesive / paste to the cylinder.

! ' 20: ’: Groups of finishing paper, especially fine paper, such as those described above, are shown in e.g. in the applicant's FI patent application 950434. The main object of the invention is to further develop the solutions presented in this application so that the tendency of the paper to curl can be controlled even more effectively with the post-drying section.

♦ · ·: 25

It is a further object of the invention to provide a solution for the post-drying section which is particularly suitable for use with drying sections in which the front drying section has not been able or desired to control the curvature of the paper web.

It is a further object of the invention to provide an arrangement in which there are no long free: * * ': exports while the web is still moist after coating.

♦ · · 101488 4

It is also an object of the present invention to provide a post-drying section of a paper machine in which the runnability is brought to a particularly high level.

In addition, it is a further object of the invention to provide such a post-drying section of a paper machine 5 in which the so-called so-called rope-free headrest, which contributes to simpler structures and shorter downtimes.

In order to achieve the above and later objects, the method according to the invention 10 is mainly characterized in that in the post-drying section the paper web is dried only in a normal single-wire drying group (s) and that the paper web is treated with a paper web.

15

Furthermore, the post-drying section applying the method according to the invention is mainly characterized in that the post-drying section comprises only the drying group (s) applying the normal single-wire export for drying the paper web. ; and device (s) to control the tendency of the paper web to warp.

• · ·: ./ ’20 L. In the arrangement according to the invention, in which the entire post-drying section is formed in a single line. as a nutrient group or a single-wire export group, the web is supported along the entire drying section, • · · • · · where the runnability is very good. Possible web curvatures are compensated for by, for example, steam boxes and / or soft calendering. It is also possible to apply the web to the 25 upper cylinders immediately after coating, in which case the export is closed from the beginning of the post-drying section «: *:’: along the entire post-drying section.

• · • · • · ·

In the following, the invention will be described in more detail with reference to the figures of the accompanying drawing, the details of which, however, are not intended to be limited in any way.

101488 5 y

Fig. 1 schematically shows an application example of a post-drying section formed of a drying group applying normal single-wire export, and Fig. 2 schematically shows an arrangement in which, after coating, the upper cylinder of the single-wire export group is moved directly to the upper cylinder via a rotary blow box or turntable or the like.

In Fig. 1, the coating device is denoted by reference numeral 10 and the coating device 10 is e.g. a coating device marketed by the applicant under the name SYM-SIZER ™, comprising two 10 opposite coating rollers 11 and 12, both of which have glue feeders. In the coating nip between 11 and 12. The direction of travel of the paper web W is indicated by the reference arrow S.

After the coating apparatus 10, the web W is passed through a drying cylinder 171 to a drying group applying a normal single wire export, where

on the swivel rollers 175 in the bottom row RA so that the web W is dried on the drying cylinders 174

comes against the heated surface of the drying cylinder 174 and with the pivot rolls 175 in the bottom row RA, the web W remains on the outer curve side of the wire 176. Drying group; *]: then the paper web W is passed through a guide roll 195 to a soft calender 191 which: * comprises two calender nips N1 and N2. ♦ · • two steam boxes 192 are also placed in connection with the soft calender, and soft calendering and steam boxes compensate for the »curvature of the paper web W. Through the guide roller 197, the paper web is fed through a nip device ·· «: 25 198 for further processing. Between the calendering nips N1, N2, the web is passed through the guide roll 196.

t • · · ··· ·· «*« · · * In Fig. 1, after the coating device 10, a pre-drying

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The heating unit 15, which may be an infrared dryer or a fluidized bed dryer known per se or a combination thereof. At the end of the post-drying section, a blowing unit 201 is placed, the aim of which is to promote evaporation through the wire, i.e. to smooth the moisture distribution in the thickness direction of the paper leaving the post-drying section. In addition, the arrangement may have a steam box 202 known per se, such as disclosed in e.g. FI patent application No. 906216 or a humidifying device 202, which is also known per se, by means of which devices 202 smooth the Z-direction moisture distribution of the web and / or reduce curvature. Of course, these accessories may not all be used in the same construction.

Regarding the curvature of the paper web, the applicant has performed experiments on a newsprint machine, the drying section of which has been a completely single-wire export and which has been followed by a 10-nip soft calender and a steam box in front of it. Under these control test conditions, the web was found to curve in the direction of the top surface - the edges of a 100 mm diameter sample increased by 3 cm in the direction of the top surface. When the running conditions were otherwise kept the same, but before the latter soft calender nip the lower surface of the track was steamed, the curvature was significantly reduced to 1.2 cm. In the second experiment, the drying section was run normally, with the curvature being measured to be 1.5 to 2 cm, and when the lower surface of the web was steamed as mentioned above, the web no longer curled at all.

The application example shown in Fig. 2 essentially corresponds to the application example shown in Fig. 1, but in this embodiment a turning device 14 is arranged after the coating device, by means of which a web device 14 is turned so that it is led directly to the top row drying system. · For the liner 174. This is followed by two drying groups applying normal single-wire export, · · • · · '· * groups, with closed export between the groups. The parts of the first drying group applying the normal single-wire line are denoted by reference numerals corresponding to Fig. 1, and the drying cylinders of the second drying group are denoted by reference numeral 182 and the pivot roller. 25 and / the cylinders by reference numeral 181. 186 travels under the guidance of guide rollers 187. After the drying groups, the dried paper web W after the guide roll 184 is fed to a soft calender 191 as shown in Fig. 1, which

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•; ·; steam boxes 192 are also preferably arranged in connection with it, whereby the curvature of the web W can be controlled by appropriately adjusting the calendering nips 30 N1, N2 of the steam boxes 192 and the soft calender 191.

«· • · · • · · • 101488 7

In the arrangement according to the invention, the swivel rollers / cylinders used are particularly preferably suction cylinders marketed by the applicant under the trademark "VAC-ROLL", without an internal suction box, the details of which are referred to in the applicant's FI patent No. 83,680 (cf. U.S. Pat. Nos. 5,022,163 and 5,172,491). .

5

The invention has been described above only with reference to some of its preferred application examples, the details of which, however, are not intended to be limited in any way.

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Claims (23)

101488 A method for drying a surface-treated paper web or the like in a post-drying section of a paper machine, wherein the paper web (W) is first post-treated in a post-treatment section, in which a paper web (W) is surface-glued or coated that in the post-drying section the paper web (W) is dried only in the drying group (s) applying normal single-wire export and that the paper web (W) is treated during or after drying by device (s) (192,191,201,202) to compensate for the curvature of the paper web (W). Method according to claim 1, characterized in that in the post-drying section the paper web (W) is dried in a drying group (s) applying normal single-wire export and that after drying the paper web (W) is passed past at least one steam box (192) and / or at least one soft calender nip ( N1; N2) to compensate for the tendency of the paper web (W) to warp. Method according to Claim 1 or 2, characterized in that the ; in the drying section, the paper web (W) is dried using a normal single - wire export; 1 20 in the drying group (s) and that the paper web after drying *. . passing at least one blowing unit (201) to promote evaporation through the wire • «^ to smooth the thickness distribution of the web (W) leaving the post-drying section (T«). Method according to one of Claims 1 to 3, characterized in that in the post-drying section the paper web is dried in a normal single-wire drying group (s) and the paper web (W) is passed past a steam box and / or wetting device (202) to smooth the Z-direction moisture distribution and / or to reduce the curvature of the web (W). 30 I «1 · 101488 Method according to one of the preceding claims 1 to 4, characterized in that in the post-drying section, the paper web is dried in the initial part of the post-drying section before contacting the drying group (s) without contact with the pre-drying section (15). 5 Method according to claims 1-5, characterized in that after finishing the paper web (W) after the device (10) the paper web (W) is passed through a drying cylinder (171) to a single wire export drying group (s) and after said drying group the paper web (W) is passed to a steam box. (192) past, 10 to compensate for the curvature of the paper web (W), to a soft calender (191), where the paper web (W) is calendered in two successive calendering nips (N1, N2), between which the curvature of the paper web (W) is compensated by a steam box (192). Method according to one of Claims 1 to 6, characterized in that the paper web (W) is dried in one drying group (FIG. 1) which applies a single wire export. Method according to one of Claims 1 to 6, characterized in that in the '20 method, the paper web (W) is dried in two single-wire applications. in the drying group (FIG. 2). 4 · · • · Method according to one of Claims 1 to 8, characterized in that, after the finishing device (10), the paper web (W) is fed via a rotary blowing device (14) to a drying group which applies a single-wire export. • «· Method according to one of Claims 1 to 8, characterized in that the paper web (W) is guided in the bottom row (RA) after the finishing device (10). via a drying cylinder (171) to a drying group applying single wire export. 30 101488 Method according to one of Claims 1 to 9, characterized in that in the method, after the post-processing device (10), the paper web (W) is fed to the first drying cylinder (174) in the top row (RY) of the drying group as a single export. 5 Method according to one of the preceding claims, characterized in that in the method, the paper web (W) is passed from one drying group to another as a closed export. A paper machine post-drying section for applying a method 10 according to any one of claims 1 to 12 for drying a surface-treated paper web or the like, which post-drying section is located downstream of the post-treatment device (10), the paper web (W) comprises surface gluing or coating on both sides; a drying group (s) applying only a single single wire export to dry the paper web (W) and an apparatus (s) (191,192,201,202) for controlling the tendency of the paper web (W) to warp. Post-drying section according to Claim 13, characterized in that there is a drying group (s) after the single-wire export. : * placed a soft calender (191) and / or steam boxes (192) to compensate for the curvature of the paper web (W) or I * · '·' 20. •: i Post-drying section according to Claim 13 or 14, characterized in that a blowing unit (201) is arranged on the rest of the post-drying section to promote evaporation through the wire and to even out the moisture distribution in the thickness-25 direction of the paper web (W) leaving the post-drying section. • · · • * · • · · Post-drying section according to one of Claims 13 to 15, characterized in that. that a steam box and / or a wetting device (202) is arranged in the post-drying section to smooth the Z-direction moisture distribution of the paper web i '! "(W) and / or to reduce the curvature« I «·« "· 30 of the paper web (W). «« T <· «« «•« 101488 J Post-drying section according to one of Claims 13 to 16, characterized in that a pre-dryer (15) for pre-drying the paper web in a non-contact manner is arranged at the beginning of the post-drying section before the single-wire drying group (s). 5 Post-drying section according to one of Claims 13 to 17, characterized in that the post-drying section comprises a single-wire drying group arranged downstream of the post-treatment device (10). Post-drying section according to one of Claims 13 to 17, characterized in that the post-drying section comprises two single-wire drying groups arranged downstream of the post-processing device (10). Post-drying section according to one of Claims 13 to 19, characterized in that two steam boxes (192) are arranged downstream of the drying group (s). Post-drying section according to Claim 20, characterized in that the steam box (192) is arranged before the calendering nip (N1; N2) of the soft calender (191). • «« M I I • · «•« «*. '20 Post-drying section according to one of Claims 13 to 21, characterized in that. that a reversing blowing device (14) is placed downstream of the after-treatment device (10) before • 4 l, a drying group applying single wire export. t · 1 »· · • · · • · ·« Post-drying section according to one of Claims 13 to 22, characterized in that the export of the paper web (W) is closed between the drying groups of the post-drying section. · ♦ · «· 1 • · · ·· • · • ··« • 4 · i: • I «· f · ·« «« $ I · 4 »4 • 44 • · 101488