EP0957202A2 - Process and apparatus for making SC-A-paper online - Google Patents

Abstract

An assembly for online production of supercalender paper, has a multi-nip soft calender (14) after the drying section of a papermaking machine and a number of roller pressure gaps (151-1511) where the paper web (3) passes through. An intermediate cooling station (2) is provided at the end of the drying section, to reduce the temperature of the paper web (3), followed by a steaming section (7) to increase the paper web's (3) moisture content. A steam delivery unit (19,19') is positioned directly in front of the first roller gap (151) of the supercalender (14), so that the paper web (3) is not balanced through the temperature and moisture increase of the steam action, when passing through the first roller gap (151).

Description

The invention relates to a method for producing SC-A paper with high gloss and high smoothness, which from the Paper machine coming paper online a super calender (Multinip soft calender) is fed, in which it is used Achievement of the desired gloss and smoothness properties Variety of nips passes through, as well as a device to carry out this procedure.

Gloss and smoothness are characteristics of a paper web that are not only their appearance, but also their further processability influence. For certain applications, gloss and / or Smoothness values are desired that are reproducible as evenly as possible should be.

The gloss and smoothness of the paper web are common thereby increased that the paper web following the Drying section of the paper machine consisting of a smoothing unit passes through one or more nips, the gloss and / or the smoothness of the paper web by the pressure in the Nip and the temperature of the nip forming the nip rolling is increased. This allows the gloss and However, influence the smoothness of the paper web only to a limited extent, because if the pressure in the Nip the paper web as a whole is strongly compressed and suffered a loss of volume. There is a risk here that the paper web loses stability. Also an increase There are limits to the roller temperature because of this procedure is very energy consuming. So to achieve Roll temperatures of 200 ° C continuously considerable amounts of energy are fed because the rollers pass by Paper web are constantly cooled. It was, for example Silicon papers, therefore already tried to shine and to influence the smoothness by the moisture of the paper web. However, this has the disadvantage that the supplied Moisture at least partially again after the treatment must be removed, which means further process steps which attracts the time and equipment required for the Increase paper web treatment.

There are basically two types of smoothing units. So-called. Supercalenders have a large number on top of each other arranged rollers and nips provided between them that are traversed by the paper web. Through the Many nips result in a high degree of coverage and a good distribution of the satin work between print and Temperature. Super calenders are usually provided offline, i.e. the one coming out of the paper machine Paper web first wound up on a spool and with this is transferred to the super calender, which she then with at a significantly lower speed than the paper machine speed goes through. The offline installation has the advantage that the paper web is in the Supercalender can still compensate, so that in the supercalender not with the conditions influenced by many factors must be worked from the paper machine. The installation needs however, is significantly higher. Classically points out a super calender on the one hand heated steel rolls and on the other hand paper rolls or rolls covered with cotton on. In recent times, so-called multinip soft calenders have also become available used, where instead of the paper rollers with rollers Polymer covers are used. These point to another elastic behavior on than the paper rollers, so that with smaller nip pressure can be worked.

Second, there are so-called machine or soft calenders can be connected online to a paper machine and therefore be traversed at paper machine speed. Machine calenders, however, have only a few nips, see above that worked with higher pressure and temperature and the Paper web is stressed accordingly. More essential The disadvantage of the soft calender is that not all types of paper in high quality can be refined. In particular it is not possible with a high-density online soft calender Manufacture SC-A paper. It is more recent managed the printability properties of a with 11 Nips of super calendered gravure paper too to achieve with only four nips of a soft calender, however, relatively high roller temperatures and Compressive stress in the nips required. Also are these qualities only at a speed range achievable, that of the usual satin speed for this paper in supercalender. (see Rothfuss, Ulrich: Inline and offline satinizing of wood-containing, rotogravure printing paper in: weekly paper for Papierfabrikation 1993, No. 11/12, pages 457-466). Hence Such qualities can only be achieved with offline installation of the soft calender can be reached.

In contrast, the object of the invention is the online production of SC-A paper.

This object is essentially achieved with the invention solved that the coming out of the paper machine, online one Supercalender (multinip soft calender) fed paper web immediately before the first nip of the supercalender Steam is moistened and passed through the first nip before the steam application increased surface moisture below a predetermined value has dropped in the range of 12% to 25%.

Paper is a voluminous fiber structure with different behavior in the thickness direction. To simplify this, one could imagine three areas (layers) arranged one above the other for SC-A paper with a material weight of approx. 50 g / m ² . The paper surface is understood here to mean the uppermost area of the paper, that is to say the upper third of the material web in the case of the SC-A paper mentioned. After the application of steam, the moisture tends to equalize across the cross-section of the material web, it being provided according to the invention that the paper web enters the first nip before the surface moisture (upper third of the material web) reaches a predetermined value of 12% to 25 % has dropped. The moisture gradient between the paper web surface and the central region of the paper web allows the surface to be worked more strongly in order to achieve better gloss and smoothness properties in the nip, while the central region of the paper web ensures sufficient stability.

This not only achieves moistening of the paper web, but at the same time achieves an increase in temperature. The in Heat contained in steam is transferred when condensing the paper web, so that by this measure a paper web receives the necessary temperature on the surface and has the necessary moisture. Now this paper web passed through the nip, affects the nip before all the surface area of the paper web, during the middle (and lower) area much less affected than with conventional methods. In the middle (and lower) area there is therefore no significant change in the thickness direction. The volume of the paper web remains in preserved to a greater extent, although the surface quality is clear is improved. The rollers need to be heated much less and the pressure in the nip can be lower than before to get voted. This saves considerable energy. One can determine mathematically (finite element method) or empirically, how long it takes for moisture to get into that Penetrates inside the web. Before this condition occurs the train, more precisely its surface, but already in Nip has been treated. By applying steam immediately before the paper web enters the nip the surface of the web is still relatively high Temperature and has a relatively high humidity, so that the increase in gloss and / or smoothness even at low Pressures and low temperatures are carried out in the nip becomes. On the other hand, the train takes no significant Amount of moisture, so that expensive post-treatments omitted. The energies required to reshape the surface are held in the area that is reshaped, i.e. smoothed shall be. The remaining parts of the track are not or only in slightly affected.

By applying steam immediately before the first Supercalender nip and therefore high moisture content the web surface when passing through the first Nip will be a very gentle treatment of the Paper web reached so that the previously before entering the Supercalender necessary strong drying of the paper web for Avoiding cockling is no longer necessary.

The invention makes use of the ideas that DE 43 01 023 C2 for machine calenders are known. Also there is already provision for the paper web to be in front of it to vaporize the nip and the paper web through the nip to conduct before the temperature and humidity in the Have compensated for the paper web. The online production of However, SC-A papers are not compatible with such machine calenders possible. It has now been recognized that this is for machine calenders known methods such a gentle treatment of the Paper web allows the paper web to be used without the previously The usual strong drying is fed online to a supercalender can be, making an online production of SC-A paper is made possible.

According to a preferred embodiment of the invention, the Paper web through the first nip of the supercalender performed before the one caused by the steam application Temperature increase in the middle third of the paper web 1 / e times the temperature increase at the surface reached Has. The temperature curve over the paper web can also be determine mathematically or empirically. By double Temperature and moisture gradients can be the gloss and Influencing the smoothness of the paper web surface still improve.

The paper web is expediently exposed to steam cooled on the supercalender to the temperature gradient to reinforce.

In addition, it is provided that the temperature of the calender or Steel roller in the first nip of the supercalender is greater than 125 ° C and is preferably about 150 ° C to to remove the high humidity of the web surface. At the same time the temperature gradient and thus the smoothness and Enhancement of gloss increased.

Because the paper web has the dryer section of the paper machine a relatively high temperature of, for example, 125 ° C. According to the invention, an intermediate cooling is provided with which the Web temperature is preferably reduced to about 30 ° C.

After it due to the careful handling of the paper web is possible by the method according to the invention Supercalender the paper web with higher initial moisture feed, it is provided that the paper web after leaving the dryer section of the paper machine and, if necessary, intermediate cooling moistened and before entering the supercalender (again) is intercooled. This increases the moisture content, i.e. better deformability, the paper web at the same time guaranteed sufficient temperature gradient on the first Nip of the super calender enables.

The rewetting of the paper web after the dryer section takes place in a further development of this inventive idea in one Steam generator, in which steam is first applied to the paper web and then through a heating duct with warm, saturated air. This can cause the moisture Compensate across the entire cross-section of the paper web. The saturated air is extracted again at the end of the heating duct.

Because the moisture of the paper web is Roll gap in the supercalender is reduced is according to the invention also provided that the paper web in Supercalender is moistened with steam. The essentially steam moistening influencing the surface of the paper web enables gentle handling of the paper web and additional reinforcement. the smoothness and gloss improvement in the nip.

According to the invention it is further provided that the moisture of the Paper web behind the intermediate cooling section (s) is determined, and that the steam application at Post-moistening and / or before the first nip of the Supercalender depending on the determined actual moisture values and predetermined target values is regulated.

In addition, it is provided that the gloss and / or smoothness the paper web after the supercalender and the Steam delivery depending on the determined actual values and predetermined target values is regulated.

The task is done with a device for online production solved by SC-A paper in that in a paper machine with a dryer section and one behind the dryer section supercalender arranged online (multinip soft calender) with a variety of nips by the paper web be run through, following the dryer section of the An intermediate cooling section is provided to paper machine to reduce the temperature of the paper web, that the Intermediate cooling section connects an evaporation device, to increase the moisture of the paper web, and that immediately before the first nip of the supercalender Steam delivery device is provided so that the through the Steam exposure causes temperature and humidity to increase the paper web is not yet balanced when the paper web passes through the nip.

According to the invention, the vaporization device follows a second cooling section to adjust the web temperature before Reduce supercalender again. By cooling the web before applying the steam to the first nip of the supercalender there is a sufficient amount of steam for condensation brought. The moisture and moisture generated by vaporization Temperature gradient is maintained until the first nip, because the Vaporization only immediately before the first nip of the supercalender takes place so that a compensation of the temperature and Moisture is not possible.

In a development of the invention it is provided that behind the first intermediate cooling section and / or behind the second Cooling section a measuring frame is provided with which the Moisture of the paper web is detected, the determined Measured values for controlling the vaporization device and / or the Steam delivery device can be used. This allows the Steaming always adapted to the current conditions become.

According to the invention is also behind the super calender Measuring frame provided with which the gloss and / or smoothness the paper web is detected, the measured values determined for Control of the steam delivery device can be used to undesirable changes in gloss or smoothness immediately to be able to correct. In addition, it can be provided that the Temperature of the rollers on the basis of the measured values determined is adjusted.

In a preferred embodiment of the invention there is one Steam delivery device on both sides of the paper web arranged the first nip of the supercalender, so that the improvements in gloss and smoothness properties both on the top and bottom of the paper web at the same time he follows.

Since the efficiency of the steam delivery device is limited, not all of the steam emitted from the paper web is recorded, is particularly in the previously described Sandwich construction with steam delivery devices on the top and Underside of the paper web has a suction for removing the provided supersaturated air. Otherwise there is a risk droplet formation, causing damage to the paper web would lead.

In a development of the invention are in the super calender further nips further steam delivery devices for Post-wetting of the paper web is provided in order according to the invention accordingly the surface improvements in these Support nips.

The steaming device that follows the dryer section is provided for rewetting the paper web According to the invention, a steam delivery device on the inlet side to which a heating duct connects, which is separated from the Paper web is traversed. This ensures that the moisture applied by the steam delivery device can even out over the cross section of the paper web.

This process is supported according to the invention in that warm, saturated air is provided in the heating duct is suctioned off again at the end of the heating duct.

Further training, advantages and possible applications of Invention also result from the following description of exemplary embodiments and the drawing. Thereby everyone described and / or illustrated features for himself or in any combination the subject of Invention, regardless of its summary in the Claims or their relationship.

The single figure shows schematically the structure of an inventive Device for online production of SC-A paper.

A device 1 for the online production of SC-A paper has a paper machine, of which in the Drawing only the last section of the dryer section is indicated. The detailed design of the paper machine plays no role in the invention.

This includes the dryer section of the paper machine Intermediate cooling section 2, which is from a paper web 3rd is run through in the section shown two Suction rolls 4, 4 'and two cooling rolls 5, 5' rotates, the Temperature of paper web 3 drops from 125 ° C to 32 ° C. At the end the intermediate cooling section 2 has a paper web Humidity of 3 to 7% on a moisture measuring frame 6 is detected.

Subsequent to the intermediate section 2 passes through the Paper web 3 a steaming device 7, the input side a steam delivery device 8 and an adjoining one Has heating channel 9, the warm, saturated Air is filled. At the end of the heating duct 9 there is a suction 23 provided. After passing through the vaporization device 7 the paper web 3 has a temperature of approx. 92 ° C, i.e. the temperature in the steaming device 7 was approx. 60 ° C increased. At the same time, through the steam application also the moisture of the paper web 3 increased.

Following the vaporization device 7 passes through the Paper web 3 a second cooling section 10, here two Cooling rollers 11, 11 'and a suction roller arranged between them 12 has. In the cooling section 10, the temperature of the Paper web 3 cooled down again to approx. 32 ° C, the Paper web 3 at the end of the cooling section 10 a moisture from 7 to 11.5%. The moisture content of the paper web 3 is detected via a measuring frame 13.

The paper web 3 is then online a super calender 14 fed from a plurality of nips (Nips) 15 consists of one after the other from the paper web be run through. With supercalender it becomes a multinip soft calender designated. Each nip 15 is replaced by a Polymer roller 16 and a steel roller 17 formed on at least 125 ° C, preferably heated up to 150 ° C.

To the paper web 3 through the corresponding nips lead, pulleys 18 are provided.

Immediately in front of the first nip 15 _{1 of} the supercalender 14, a steam delivery device 19 is provided, which in particular can consist of a steam blow box, as described in DE 43 01 023 C2. In the embodiment shown, steam delivery devices 19, 19 'are arranged on the top and bottom of the paper web 3. However, it is also possible to provide only one steam delivery device 19 on the top of the paper web 3. A suction 20 is assigned to the steam delivery device 19, 19 ', via which supersaturated air is extracted.

In the supercalender 14, further steam delivery devices 21 are provided in front of further nips 15 ₂ , 15 ₃ , 15 ₄ , 15 ₆ , 15 ₇ , 15 ₉ , via which the paper web 3 is rewetted in order to partially compensate for the loss of moisture in the nips 15.

Following the supercalender 14 is a measuring frame 22 provided the gloss and / or smoothness of the paper web 3rd determined.

Instead of the supercalender 14 shown in FIG a so-called double-stack supercalender can be used, where two groups of nips in a row are arranged, which successively pass through the paper web become. This increases the height of the calender decreased. Otherwise, the device 1 remains unchanged. The method according to the invention can be used in a double-stack calender perform in the same way as in Fig. 1 shown calender.

The mode of operation of the invention is described below Device 1 described:

The paper web 3 emerging in the usual way from the dryer section of the paper machine first passes through the intermediate cooling section 2, in which its temperature is reduced to 32 ° C. The paper web 3 is moistened and heated in the subsequent vapor deposition device 7. The heating channel 9 through which the paper web 3 passes ensures that the moisture is evened out over the cross section of the paper web 3. The paper web 3 leaves the vapor deposition device 7 at a temperature of approximately 92 ° C., which would, however, impair the increase in gloss and smoothness in the supercalender 14, since not enough steam would condense in front of the first nip 15 ₁ . The temperature of the paper web 3 in the second cooling section 10 is therefore reduced again to approximately 32 ° C., the paper web having a moisture content of approximately 7 to 11.5%.

With the steam delivery device 19, 19 ', hot, droplet-free steam is now applied to the paper web surface immediately in front of the first nip 15 _{1 of} the supercalender 14, the steam temperature in the steam blowing chamber of the steam delivery device 19, 19' being approximately in the range from 102 ° C. to 110 ° C is to prevent condensation of the steam. The steam delivery device 19, 19 'is brought as close as possible to the nip 15 ₁ , the distance being adjustable depending on the speed at which the paper web 3 passes through the nip 15. The steam emerging from the steam delivery device 19, 19 'spreads at a relatively uniform pressure and a uniformly high speed of, for example, 25 m / s or more. As soon as the steam comes into contact with the relatively cold paper web 3, it condenses, drastically increasing the temperature on the surface of the paper web 3. In the case of a paper web 3 which is approximately 30 ° C. cold, the surface will be approximately 90 ° C. hot after the condensation of the steam. At the same time, the condensed steam forms a moisture film, the strength of which is, for example, in the range of a thousandth of a millimeter. The condensation results in an almost sudden increase in temperature of the surface of the paper web 3, which, however, compensates for itself within a very short time via the thickness of the paper web 3, so that the paper web 3 has a uniform temperature distribution within fractions of a second. The homogenization of the moisture takes a little longer, since the moisture penetrates into the paper web 3 more slowly than the temperature. For this reason, the top layer (in the case of SC-A paper with a fabric weight of approx. 50 g / m ^2, about a third of the paper web) has a significantly higher relative humidity than the central region of the paper web 3. The further the moisture inside the Paper web 3 penetrates, the more the relative humidity decreases. Before the moisture of the surface (upper third or, in the case of vapor deposition, the lower third) of the paper web 3 has dropped below a predetermined value in the range from 12% to 25%, in particular from 16% to 25%, the paper web 3 passes through the first nip 15 _{1 of} the supercalender 14. Also the temperature of the paper web 3 is not yet balanced at this time, rather the temperature increase in the middle third of the paper web caused by the steam application should not yet have reached 1 / e times the temperature increase of the surface of the paper web 3 .

In the first nip 15 _{1 of} the supercalender, the paper web 3 is treated by smoothing the surface of the web 3, which still has the increased temperature and humidity, or is provided with an increased gloss. The areas of the paper web 3 lying further inside are not significantly changed by the roller gap 15 ₁ . The paper web 3 then runs through the further nips 15 ₂ to 15 _{11 of} the supercalender 14, the paper web 3 being moistened by the steam delivery devices 21 before individual nips in order to improve the increase in gloss and smoothness.

On the basis of the measured values of the measuring frame 22 and The setpoint is the steam delivery through the Steam delivery devices 19, 19 'and / or 21 and possibly the Heating of the calender rolls 17 controlled. In a similar way serve the moisture values determined by the measuring frame 6 and 13 together with the corresponding setpoints Control of the steam application in the steaming device 7 and the steam delivery device 19, 19 '.

With the invention it is possible to make SC-A paper online to produce, with gloss values of 48 to 50 Hunter gloss points (SC-A) and when performing rewetting and Intercooling 50 to 52 Hunter highlights (SC-A +) are reachable. This is essentially due to the gentle Treatment of the paper web with high humidity and temperature achieved in the surface areas that allow the Supercalender a paper web with high initial moisture feed.

Reference symbol list :

1

contraption

2nd

Intercooling section

3rd

Paper web

4, 4 '

Suction roll

5, 5 '

Chill roll

6

Measuring frame (humidity)

7

Steaming device

8th

Steam dispenser

9

Heating duct

10th

Cooling section

11, 11 '

Chill roll

12th

Suction roll

13

Measuring frame (humidity)

14

Super calender

15 ₁ -15 ₁₁

Nip

16

Paper roll

17th

Steel roller

18th

Pulley

19, 19 '

Steam dispenser

20th

Suction device

21

Steam dispenser

22

Measuring frame (gloss)

23

Suction

Claims (21)

Process for the production of SC-A paper with high gloss and high smoothness, the paper web (3) coming from the paper machine being fed online to a super calender (multinip soft calender) (14) in which it is used to achieve the desired gloss and Smoothness properties passes through a plurality of nips (15 ₁ -15 ₁₁ ), the paper web (3) immediately before the first nip (15 ₁ ) of the supercalender (14) moistened with steam and passed through the nip (15 ₁ ) before the increased moisture in the surface caused by the application of steam has dropped below a predetermined value in the range from 12% to 25%. A method according to claim 1, characterized in that the paper web (3) is guided through the nip (15 ₁ ) before the temperature increase in the middle third of the paper web (3) caused by the steam application is 1 / e times the temperature increase on the surface has reached. Method according to claim 1 or 2, characterized in that the paper web is cooled on the supercalender (14) before the steam is applied. Method according to one of claims 1 to 3, characterized in that the temperature of the steel roller (17) in the first nip (15 ₁ ) of the supercalender (14) is greater than 125 ° C, preferably about 150 ° C. Method according to one of claims 1 to 4, characterized in that the paper web (3) is cooled to a temperature of below 50 ° C, preferably about 30 ° C, after leaving the drying section of the paper machine. Method according to one of claims 1 to 5, characterized in that the paper web (3) is moistened after leaving the drying section of the paper machine and possibly intermediate cooling and is (again) intercooled before entering the supercalender (14). A method according to claim 6, characterized in that the rewetting takes place in an evaporator (7), in which steam is first applied to the paper web (3) and this is then passed through a heating duct (9) with warm, saturated air. Method according to claim 6 or 7, characterized in that the saturated air is suctioned off after the heating duct (9). Method according to one of claims 1 to 8, characterized in that the paper web (3) in the supercalender (14) is moistened with steam. Method according to one of claims 1 to 9, characterized in that the moisture of the paper web (3) is determined behind the intermediate cooling section (2) and / or the cooling section (10), and in that the steam is applied during the rewetting and / or before the first Roll gap (15 ₁ ) of the supercalender (14) is regulated as a function of the actual moisture values determined and predetermined target values. Method according to one of Claims 1 to 10, characterized in that the gloss and / or the smoothness of the paper web (3) is determined according to the supercalender (14) and the steam output is regulated as a function of the determined actual values and predetermined target values. Device for the online production of SC-A paper with a paper machine with a dryer section and a supercalender (multinip soft calendar) (14) arranged behind the dryer section with a multiplicity of nips (15 ₁ -15 ₁₁ ) from the paper web (3) are passed through, an intermediate cooling section (2) being provided after the dryer section of the paper machine in order to reduce the temperature of the paper web (3), with an evaporating device (7) connecting to the intermediate cooling section (2) To increase the moisture of the paper web (3), and a steam delivery device (19, 19 ') is provided directly in front of the first nip (15 ₁ ) of the supercalender (14), so that the temperature and moisture increase in the paper web caused by the steam application ( 3) is not balanced when the paper web (3) passes through the nip (15 ₁ ). Apparatus according to claim 12, characterized in that a cooling section (10) adjoins the evaporation device (7), via which the temperature of the paper web (3) can be reduced again. Apparatus according to claim 12 or 13, characterized in that a measuring frame (6, 13) is provided behind the intermediate cooling section (2) and / or the cooling section (10), with which the moisture of the paper web (3) is detected, the determined Measured values for controlling the steaming device (7) and / or the steam delivery device (19, 19 ') can be used. Device according to one of claims 12 to 14, characterized in that a measuring frame (22) is provided behind the supercalender (14) with which the gloss and / or the smoothness of the paper web (3) is detected, the measured values being determined for control purposes the steam delivery device (19, 19 ') and / or the temperature of the steel roller (17) in the first nip (15 ₁ ) can be used. Device according to one of claims 12 to 15, characterized in that a steam delivery device (19, 19 ') is arranged on both sides of the paper web (3) in front of the first nip (15 ₁ ) of the supercalender (14). Device according to one of claims 12 to 16, characterized in that the steam delivery device (19, 19 ') has a suction (20) for removing the supersaturated air. Device according to one of claims 12 to 17, characterized in that in the supercalender (14) in front of further nips (15 ₂ , 15 ₃ , 15 ₄ , 15 ₆ , 15 ₇ , 15 ₉ ) further steam delivery devices (21) for rewetting the paper web (3) are provided. Device according to one of claims 12 to 18, characterized in that the steaming device (7) has a steam delivery device (8) on the input side, to which is connected a heating duct (9) through which the paper web (3) passes. Apparatus according to claim 19, characterized in that warm, saturated air is provided in the heating duct (9). Apparatus according to claim 19 or 20, characterized by a suction (23) at the end of the heating channel (9).

Images