FI116980B - Pre-calendering procedure and processing line for paper - Google Patents

Description

Pre-calendering method and paper handling line

The invention relates to a pre-calendering method in which the paf is moistened and passed through a pre-calendering nip which intervenes between two surfaces, whereby the surface of the web to be calendered is already heat-applied and pressurized, and subsequently coated. The invention also relates to a paper processing line in a successive direction in the direction of the paper web, for performing the aforesaid operation.

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After drying the paper, the surface structure of the web is subjected to mechanical treatment on the surface, there are many calendering methods, but all of them have a common feature of passing through one or more nips formed between the normally rotating roll surfaces. The purpose of calendering is to improve the quality of the paper by squeezing it to a certain thickness and, in particular, smoothing its surface. When the fish is followed by paper coating, the surface of the paper is precalendered and the surface of the paper is processed so that it has the properties specifically for the coating process. bond ii particles to the surface and close the surface to ensure a smooth coating layer.

In pre-etching, the web can be exposed to temperature and p; Most commonly, heat is transferred to the surface of the web through contact with a hot contact surface guiding it r, e. E., E.g., a metal surface of a calender roll. By using a p s - coating on at least one roll, or by passing through this second roll or special shoe, an elastic strap is provided on both sides of the nip by the force of the elements being pressed against each other to extend the so-called. so the length of 2 1 so it matters what moisture content the web ki or rehydrates before pre-calendering.

After pre-calendering, the paper is coated, and a coating paste is applied to the surface of the calendered paper by a suitable method. The coating paste is an aqueous based pigment which is a pigment affecting the optical properties of paper and an agent for fixing the pigment. The pre-calendering methods aim to make the surface suitable for coating, smoothen, and in particular to make the base paper compact, the h coating methods being able to apply a very uniform application rate f.

The problem with coating pre-calendered paper is the roughness and absorbency of the 15 papers. The water used in the coating changes the paper through the pre-calendering, the original shape is restored, and during calendering, the compressed fibers become "tubular" again. As a result, the paper tends to roughen again during coating. There is a problem with all finishing treatments after pre-calendering where the surface of the paper comes into contact with water, such as surface sizing.

• «9 · · • ·« • ·: y. A roughening problem has been encountered, for example, on base papers containing the mechanical pulp 25, which have good coating performance in the coating process with small coatings / Other paper grades may also have the same problems. On the other hand, it is desirable to keep certain amounts, e.g. paper quality attribute * in target values.

30 tt 4: V In International Application WO 01/98585 is a C 1: a pre-calendering method in which the web is led to calendering and 3 is provided on paper surface layer fibers having a relal roughing problem and the paper in the z-center can be left open the bulk remains. Typical for the method is 5 inlet moisture for pre-calendering, between 10-20%, and would add to target moisture after pre-etching, whereby consciously increasing the roughness and restoring the fibers to their original mi partially. This prevents further surface roughening when exposed to Vail · water during the subsequent coating process. Alternatively, the 10 pre-calendering parameters may be selected so that the paper reaches the target moisture content during pre-calendering before coating.

WO 02/103109 discloses a pre-calendering machine in which, after drying, the paper web is passed through a wetting process to a pre-calender nip. A suitable residence time between the wetting I and the pre-calendering nip is between 0.05 and 0.5 s. Suitably with the action of the wetting water, both webs can be wetted and the central portion substantially unhydrated. After my foreplay, the web is passed through a coating station.

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Despite advances in pre-calendering methods, it has not been possible to reduce the coarse absorbency of the coating process: Y: as low as desired.

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• <9:. ·. It is an object of the invention to eliminate the above disadvantages and to maintain surface quality in pre-calendering with respect to the above-mentioned variables in relation to * *; .e.e, for example, film transfer coating \ .f is obtained in an ideal quality. This allows you to select, for example, a coating material • * * ··· without any restrictions on the quality of the surface to be coated.

In order to accomplish this purpose, the mi '• J method of the invention is characterized in the Dasia by its nature. which is 4 in contact is 0.6 to 6.0 s, preferably 0.8 to 1.5 s. Due to the long absorption time, the porosity of the base paper surface decreases and the coating layer becomes smoother and smoother.

5 The pre-calendering can be carried out, for example, with a soft cal shoe calender, a flexible-surface belt calender or a meti calender, all with a heated surface, and in contact with a nip load determined by the nip length and web speed. The hot 10 provides a certain surface temperature to the web. Heated in contact with the nip to at least the surface of the web that is applied after pre-calendering. If two consecutive nipples are used on top of both Rana surfaces, wherein the calendering gesture position is symmetrical with respect to the plane of the web, or 15 nipples may be used with heated elements on either side of the nip

When the previously wetted web in the annealing nip is pressurized to a contact with a hot surface in sufficient time, the absorbency and roughness of the paper surface can be reduced. Because high web speeds require a long distance wetting point to achieve the above delay and the calender nip can be arranged to run in a meandering: Y: from the wetting point to the first or only pre-calender: Y: This does not increase the machine length. By arranging one or * 1:. From the elements controlling the passage of the 25 paths in this interval, such as being movable, the distance and the residence time can be adjusted.

·· t ♦ · * YI * Note that the surface temperature of the hot roller should be <above the transition temperature to bring the surface fibers to the glass 30. With a sufficiently long residence time in the calendering nip: The surface temperature of the Y contact surface is between 100 and 300 ° (and then between 150 ° C and 250 ° C, to obtain a sufficient 5 l lower humidity in the other nip, requiring a higher overheating to occur. (roughness, absorption), whereby it may be necessary to calender s <5 to an extent "asymmetrically" to compensate for these differences.

The long nip provides low pressure and long residence time, which saves bulk and can, on the other hand, raise the fiber temperature. The calorific input moisture and calendering account 10 are variables that allow one or both of the variables to adjust the surface quality roll result to the coating. For example, it is possible to keep the variable constant and change one to obtain the desired smoothness and 1 surface. High humidity is also advantageous in that after calendering, the final humidity is not too low and high temperature is used.

The paper processing line according to the invention is characterized by pu which is set forth in the characterizing part of the appended claim 20. The path of the paper web before the coating humidifier and the hot pre-calendering nip surface νetty is arranged long enough for the aforementioned beneficial effects of coating: Y to be realized.

The invention will now be described in more detail with reference to the following drawings, wherein the effect of the amount of wetting on the PPS-s10 - roughness * »** ·· * with a soft calender 30 for calendering, M Figure 2 shows the effect of wetting amount on Cobb-Ur 6 1 figure 4 shows the effect of dwell time on Cobb-Unc oil absorption by different wetting rates in soft-ka pre-calendering, and Figure 5 shows a paper lightening line with pre-calendering according to k € is used.

Figure 5 illustrates an apparatus disposed in a continuous papermaking line in which the paper web is first muc from a fiber suspension and then dried by pressing. From the drying section D of the papermaking machine where the dry has taken place by heat, a continuous paper web W moving at the speed of the paper production speed is led by t <15 to the calender C where the precalendering is performed. The paper web is also continuously fed to the same web track coating unit S. Thereafter, the coated pa | passing through drying to winding, where; forming sequential rolls in a continuous action winding roll 20 shown).

The apparatus includes a humidifying device 1 which, in the web running direction: Y: between the drying section D and the calender C. The wetting device 1 is \ i: Y: to wet the surface of the web in a manner known per se> 9 9% w / w with a fine jet of water. The humidifier is not !!!: a water humidifier which can dispense a precise amount of water to the web ..... The humidifier 1 is arranged to moisten the other side of the web in the precalendering nip against a hot nip surface i such as a thermo roll or hot metal 30 strap). The humidifier 1 is located sufficiently far from the fish: V pre-calendering nip N in the direction of web travel so that the water reaches the surface of the web W at the precalendering nip N is 7 1 0.5 to 3 g / m 2 / side. Figure 5 shows two wetting devices on each side of the web W for performing a mutual cos, wherein preferred dispensing amounts are used on each side. Figure 5 also shows a measuring device M pap <between the humidifier 5 for measuring properties, e.g., moisture profile and / or overall humidity, so that the results can be taken into account in subsequent humidification. Other measuring devices may also be suitable for position 10 To provide a sufficient distance between the humidifier pre-calender nip N and the dwell time settings regardless of line speed, adjuster 3 is used. In the picture, the web did a succession of turns, but their number may be The turn need not be 180 degrees or more, but may be less than, for example, 130 to 180 degrees. Bends can be o other than horizontal, eg vertical. Always! Preferably, the plurality of deflection elements 2 may be displaced to substantially extend or shorten the bend provided by the spreader element, i.e.: V: in the free direction of the web.

• «# *« * * *: 25 With adjuster 3, the distance from the wetting point (wetting I; to the pre-calendering nip N) is such that the wetting of the wetting • * ..... pre-calendering is 0.6 to 6.0 s, preferably 0.8 to 1 ♦ · • * • · * ··· * Figure 5 shows a pre-calendering calender 30 duplexed with dampers 1: V pre-calendered by performing the same on both sides

In my first pre-calendering, N strip W to calend * 8 11

After the calender C, the coating process of the webW is conducted in a coating unit S, whereby at least one of the webs which has been pre-calendered against the hot nip surface 5 has consequently obtained a suitable coating surface, i.e. an aqueous coating composition. the coating paste is applied to the surface by any suitable process. The coating paste is an aqueous mixture containing a pigment affecting the optical properties of the paper and a binder for pigmentation and possibly other adjuvants.

The coating is performed in the figure as a two-sided film coating in a film transfer coating comprising two | rolls 6 between which the precalendered paper web W passes. When a thin layer of finishing agent is applied evenly to the surface of roller 15, it is transferred in a nip between rollers 6 to the surface of the web. Selling coating methods come into question.

By allowing the wetting water to be absorbed into the web for a long time prior to pre-calendering, the surface absorbency and roughness in pre-calendering prior to coating is obtained, and the coating layer is smoother and smoother. This is particularly useful for: V: Coating amounts, e.g., in the manufacture of LWC paper.

• 0 »*» · * ♦: 25 Humidification, pre-calendering and coating are carried out !!!: in the production line as an on-line process whereby the calender is placed • * ..... in the so-called "wear" machine. to dry end after dry | ..f. The humidifier or humidifiers 1 are placed after the dry '* · **, whereby the humidification is carried out on a paper web already dried by a drying section 30 to a certain residual moisture. It is possible to start wetting the paper with the drying section * · * during drying but not yet

The wetting apparatus 1 may be well known in the art for VIB water to accurately dispense the amount of water to the surface of the paper web W.

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The invention is particularly suitable for the pre-calendering of mechanical pulp-based substrates, e.g. LWC substrates, which are coated with film transfer coating (Sizer). The invention is limited to this type of paper, but can be utilized in 10 other coated woody and wood-free pa | for pre-calendering board grades. Although the advantages of the invention, especially with respect to the manufacture of relatively thin-coated (LWC and ULWC), the invention is not limited to the amount of coating it can also be used for thicker coatings. Examples of other coated paper grades are MWC WFC and board grades FBB and SBS.

The invention will now be further described by way of further examples, which are not limiting of the invention.

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The 40 g / m 2 LWC base paper was subjected to pre-blotting experiments with a 1-nip OptiSoft soft calender with a hard: Y: soft-surface polymer roll in the form of a relatively short nip roll. The inlet moisture before wetting was: V; 25 (total humidity), line pressure in pre-calender nip 148 k !!!: thermo roll temperature 200 ° C. The line speed was 1000 m / min. Calf; v> PPS roughness was 5.5 / 6 μνη (TS / WS) before treatment. PPS-ki was measured from the underside (WS, side facing the wire) with different lag * * * ·· 'amounts of wetting water. Similarly, Cobb-Unger oil was measured on 30 of the same paper starting at 19/15 g / m 2 f: The results are shown in Figures 1-4.

The amount of water going into the water is typically smaller than the nozzles; (metered) water. The amount of water shown in the figures, 1-4 g / m 2, corresponds to a past (absorbed) amount of water of about 0.5 to 2 g / m 2.

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Claims (9)

A pre-calender process, in which a paper web is moistened by a pre-calender nip (N) formed between two surface calender, a shoe calender, a strip calender with a flexible metal strip calender, heat being conducted in the nip to the surface of the web (W) to be calendered. subjected to the printing web is coated, characterized in that the delay between the interlacing and the pre-calendering of the same web is 0.6, that the dosed at wetting to the paper web (W) is 0.2-15 g / m2 / side, preferably 0.5-3 g / m2 / side of water. Method according to claim 1, characterized in that the current 15 is 0.8-1.5 seconds. 3. A method according to claim 1 or 2, characterized in that the paper web (W) is guided from the wetting to the pre-calender, a curved web, the length of which is adjustable to adjust the delay 20. 4. A method according to any of the preceding claims ..... characterized in that, after the pre-calendering, the paper web (W) has the same treatment line by passing it on bare as one web running at the same web speed [25]. «·: #V Method according to any of the preceding claims, characterized in that the paper web (W) is LWC base paper. : 30 6. A processing line for paper in which on the paper web (V. ···) which is arranged to carry the running speed arranged so long relative to the web speed that the web resides in the humidifier (1) and the relatively hot pre-calender nip surface of this web web. ka is 0.6-6.0 s, preferably 0.8-1.5 s Treatment line according to claim 7, characterized in, the moisture device (s) (1) and the calender (C) on the runway of the web are several control elements (2) for the web, which control the web along a curving path, and the position of the ether 10. preferably several control elements (2) can be changed so that the path which has run between the moisture device (s) (1) or (C) is changed. Treatment line according to claim 6 or 7, characterized in that the calender (C) comprises two pre-calendering nip (N), at which the heated calendering element, such as the surface of e is on different sides of the web, and in the run direction in the calendering nip (N) there is a or a plurality of coating means for performing the coating on both sides. 20 9. Treatment line according to some of the preceding patents! > v <characterized in that the coating unit (S) is a film machine. «« * »· * •» # · · • · «« · · * · «« «« · «f *« «•» * • · • • • ft * • · «•« · • «ft« · « «*